Cross-Reference to Related Applications
Field of the Invention
[0002] The invention generally relates to wrapping loads with packaging material through
relative rotation of loads and a packaging material dispenser, and in particular,
to the control of the rate in which packaging material is dispensed during wrapping.
Background of the Invention
[0003] Various packaging techniques have been used to build a load of unit products and
subsequently wrap them for transportation, storage, containment and stabilization,
protection and waterproofing. One system uses wrapping machines to stretch, dispense,
and wrap packaging material around a load. The packaging material may be pre-stretched
before it is applied to the load. Wrapping can be performed as an inline, automated
packaging technique that dispenses and wraps packaging material in a stretch condition
around a load on a pallet to cover and contain the load. Stretch wrapping, whether
accomplished by a turntable, rotating arm, vertical rotating ring, or horizontal rotating
ring, typically covers the four vertical sides of the load with a stretchable packaging
material such as polyethylene packaging material. In each of these arrangements, relative
rotation is provided between the load and the packaging material dispenser to wrap
packaging material about the sides of the load.
[0004] A primary metric used in the shipping industry for gauging overall wrapping effectiveness
is containment force, which is generally the cumulative force exerted on the load
by the packaging material wrapped around the load. Containment force depends on a
number of factors, including the number of layers of packaging material, the thickness,
strength and other properties of the packaging material, the amount of pre-stretch
applied to the packaging material, and the wrap force applied to the load while wrapping
the load. The wrap force, however, is a force that fluctuates as packaging material
is dispensed to the load due primarily to the irregular geometry of the load.
US 2011/0131927 A1 discloses a control system for a wrapping apparatus according to the preamble of
independent claim 1, including a packaging material dispenser configured to dispense
packaging material for wrapping a load.
[0005] In particular, wrappers have historically suffered from packaging material breaks
and limitations on the amount of wrap force applied to the load (as determined in
part by the amount of pre-stretch used) due to erratic speed changes required to wrap
loads. Were all loads perfectly cylindrical in shape and centered precisely at the
center of rotation for the relative rotation, the rate at which packaging material
would need to be dispensed would be constant throughout the rotation. Typical loads,
however, are generally box-shaped, and have a square or rectangular cross-section
in the plane of rotation, such that even in the case of square loads, the rate at
which packaging material is dispensed varies throughout the rotation. In some instances,
loosely wrapped loads result due to the supply of excess packaging material during
portions of the wrapping cycle where the demand rate for packaging material by the
load is exceeded by the rate at which the packaging material is supplied by the packaging
material dispenser. In other instances, when the demand rate for packaging material
by the load is greater than the supply rate of the packaging material by the packaging
material dispenser, breakage of the packaging material may occur.
[0006] When wrapping a typical rectangular load, the demand for packaging material typically
decreases as the packaging material approaches contact with a corner of the load and
increases after contact with the corner of the load. When wrapping a tall, narrow
load or a short load, the variation in the demand rate is typically even greater than
in a typical rectangular load. In vertical rotating rings, high speed rotating arms,
and turntable apparatuses, the variation is caused by a difference between the length
and the width of the load, while in a horizontal rotating ring apparatus, the variation
is caused by a difference between the height of the load (distance above the conveyor)
and the width of the load. Variations in demand may make it difficult to properly
wrap the load, and the problem with variations may be exacerbated when wrapping a
load having one or more dimensions that may differ from one or more corresponding
dimensions of a preceding load. The problem may also be exacerbated when wrapping
a load having one or more dimensions that vary at one or more locations of the load
itself. Furthermore, whenever a load is not centered precisely at the center of rotation
of the relative rotation, the variation in the demand rate is also typically greater,
as the corners and sides of even a perfectly symmetric load will be different distances
away from the packaging material dispenser as they rotate past the dispenser.
[0007] The amount of force, or pull, that the packaging material exhibits on the load determines
in part how tightly and securely the load is wrapped. Conventionally, this wrap force
is controlled by controlling the feed or supply rate of the packaging material dispensed
by the packaging material dispenser. For example, the wrap force of many conventional
stretch wrapping machines is controlled by attempting to alter the supply of packaging
material such that a relatively constant packaging material wrap force is maintained.
With powered pre-stretching devices, changes in the force or tension of the dispensed
packaging material are monitored, e.g., by using feedback mechanisms typically linked
to spring loaded dancer bars, electronic load cells, or torque control devices. The
changing force or tension of the packaging material caused by rotating a rectangular
shaped load is transmitted back through the packaging material to some type of sensing
device, which attempts to vary the speed of the motor driven dispenser to minimize
the change. The passage of the corner causes the force or tension of the packaging
material to increase, and the increase is typically transmitted back to an electronic
load cell, spring-loaded dancer interconnected with a sensor, or to a torque control
device. As the corner approaches, the force or tension of the packaging material decreases,
and the reduction is transmitted back to some device that in turn reduces the packaging
material supply to attempt to maintain a relatively constant wrap force or tension.
[0008] With the ever faster wrapping rates demanded by the industry, however, rotation speeds
have increased significantly to a point where the concept of sensing changes in force
and altering supply speed in response often loses effectiveness. The delay of response
has been observed to begin to move out of phase with rotation at approximately 20
RPM. Given that a packaging dispenser is required to shift between accelerating and
decelerating eight times per revolution in order to accommodate the four corners of
the load, at 20 RPM the shift between acceleration and deceleration occurs at a rate
of more than every once every half of a second. Given also that the rotating mass
of a packaging material roll and rollers in a packaging material dispenser may be
100 pounds or more, maintaining an ideal dispense rate throughout the relative rotation
can be a challenge.
[0009] Also significant is the need in many applications to minimize acceleration and deceleration
times for faster cycles. Initial acceleration must pull against clamped packaging
material, which typically cannot stand a high force, and especially the high force
of rapid acceleration, which typically cannot be maintained by the feedback mechanisms
described above. As a result of these challenges, the use of high speed wrapping has
often been limited to relatively lower wrap forces and pre-stretch levels where the
loss of control at high speeds does not produce undesirable packaging material breaks.
[0010] In addition, due to environmental, cost and weight concerns, an ongoing desire exists
to reduce the amount of packaging material used to wrap loads, typically through the
use of thinner, and thus relatively weaker packaging materials and/or through the
application of fewer layers of packaging material. As such, maintaining adequate containment
forces in the presence of such concerns, particularly in high speed applications,
can be a challenge.
[0011] Therefore, a significant need continues to exist in the art for an improved manner
of controlling the rate at which packaging material is dispensed during wrapping of
a load, particularly to provide greater wrap force, and ultimately greater containment
force to the load.
Summary of the Invention
[0012] The invention addresses these and other problems associated with the prior art by
providing in one aspect an effective circumference-based wrap speed model that dynamically
controls the rate at which packaging material is dispensed based on an effective circumference
of the load during relative rotation established between the load and a packaging
material dispenser. The effective circumference of a load, in this regard, is indicative
of an effective consumption rate of the load, and refers to a dimension or size of
a tangent circle that is substantially centered at the center of rotation of the load
and substantially tangent to a line substantially extending between a first point
proximate to where the packaging material exits the dispenser and a second point proximate
to where the packaging material engages the load. The effective circumference of the
load dynamically changes throughout the relative rotation of the load, and by controlling
the dispense rate based at least in part on this dimension, fluctuations in tension
in the packaging material may be reduced, often enabling containment force to be increased
while reducing the risk of breakage in the packaging material.
[0013] Therefore, consistent with one disclosed aspect, a wrapping apparatus includes a
packaging material dispenser for dispensing packaging material to the load, a load
support for supporting the load during wrapping, where the packaging material dispenser
and the load support are adapted for rotation relative to one other about a center
of rotation, and a controller configured to control a dispense rate of the packaging
material dispenser during the relative rotation based at least in part on an effective
circumference of the load that varies during the relative rotation.
[0014] In some disclosed embodiments, an effective circumference of a load may be determined
based upon a film angle calculated for a portion of packaging material that extends
between an exit point for a packaging material dispenser and a point of engagement
with the load. Based upon the determined film angle and a determined rotational position
of the load relative to the packaging material dispenser, the effective circumference
of the load, and thus the effective consumption rate of the load at any given rotational
position can typically be determined and utilized to control the dispense rate of
the packaging material dispenser.
[0015] Therefore, consistent with another disclosed aspect, an apparatus for wrapping a
load with packaging material may include a packaging material dispenser for dispensing
packaging material to the load, a load support for supporting the load during wrapping,
where the packaging material dispenser and the load support are adapted for rotation
relative to one other about a center of rotation, an angle sensor configured to sense
an angular relationship between the load and the packaging material dispenser about
the center of rotation, and a controller coupled to the packaging material dispenser
and the angle sensor. The controller is configured to determine, at each of a plurality
of angles about the center of rotation, a film angle for a portion of the packaging
material extending between a first point proximate to where the packaging material
exits the packaging material dispenser and a second point proximate to where the packaging
material engages the load, determine, at each of the plurality of angles, an effective
circumference of the load from the determined film angle, and control a dispense rate
of the packaging material dispenser during the relative rotation based at least in
part on the determined effective circumference and the sensed angular relationship.
[0016] In other disclosed embodiments, the film angle used to determine an effective circumference
of the load may be determined using a film angle sensor that is configured to sense
the actual film angle of the packaging material during a wrapping operation. As such,
the effective circumference may be based on a characteristic of the packaging material
as determined during the dispensing operation.
[0017] Therefore, consistent with another disclosed aspect, an apparatus for wrapping a
load with packaging material may include a packaging material dispenser for dispensing
packaging material to the load, a load support for supporting the load during wrapping,
where the packaging material dispenser and the load support are adapted for rotation
relative to one other about a center of rotation, a film angle sensor configured to
sense an angle of a portion of the packaging material extending between a first point
proximate to where the packaging material exits the packaging material dispenser and
a second point proximate to where the packaging material engages the load, an angle
sensor configured to sense an angular relationship between the load and the packaging
material dispenser about the center of rotation, and a controller coupled to the packaging
material dispenser, the film angle sensor and the angle sensor. The controller is
configured to determine, at each of a plurality of angles about the center of rotation,
an effective circumference of the load from the sensed angle of the portion of the
packaging material, and control a dispense rate of the packaging material dispenser
during the relative rotation based at least in part on the determined effective circumference
and the sensed angular relationship.
[0018] In still other disclosed embodiments, an effective circumference of a load may be
determined based upon a film speed determined from a speed sensor that measures the
speed of the packaging material as it exits a packaging material dispenser. Based
upon the determined film speed and a determined rotational position of the load relative
to the packaging material dispenser, the effective circumference of the load, and
thus the effective consumption rate of the load at any given rotational position can
typically be determined and utilized to control the dispense rate of the packaging
material dispenser.
[0019] Therefore, consistent with yet another disclosed aspect, an apparatus for wrapping
a load with packaging material may include a packaging material dispenser for dispensing
packaging material to the load, a load support for supporting the load during wrapping,
where the packaging material dispenser and the load support are adapted for rotation
relative to one other about a center of rotation, an angle sensor configured to sense
an angular relationship between the load and the packaging material dispenser about
the center of rotation, a speed sensor configured to sense a speed at which the packaging
material exits the packaging material dispenser, and a controller coupled to the packaging
material dispenser, the angle sensor and the speed sensor. The controller is configured
to determine, at each of a plurality of angles about the center of rotation, an effective
circumference of the load from the sensed speed, and control a dispense rate of the
packaging material dispenser during the relative rotation based at least in part on
the determined effective circumference and the sensed angular relationship.
[0020] In further disclosed embodiments, an effective circumference of a load may be determined
based upon a distance between a reference point and a surface of the load along a
radius of the center of rotation as determined from a load distance sensor. Based
upon the determined distance speed and a determined rotational position of the load
relative to the packaging material dispenser, the effective circumference of the load,
and thus the effective consumption rate of the load at any given rotational position
can typically be determined and utilized to control the dispense rate of the packaging
material dispenser.
[0021] Therefore, consistent with another disclosed aspect, an apparatus for wrapping a
load with packaging material may include a packaging material dispenser for dispensing
packaging material to the load, a load support for supporting the load during wrapping,
where the packaging material dispenser and the load support are adapted for rotation
relative to one other about a center of rotation, an angle sensor configured to sense
an angular relationship between the load and the packaging material dispenser about
the center of rotation, a load distance sensor configured to sense a distance between
a reference point and a surface of the load along a radius of the center of rotation,
and a controller coupled to the packaging material dispenser, the angle sensor and
the load distance sensor. The controller is configured to determine, at each of a
plurality of angles about the center of rotation, an effective circumference of the
load from the sensed distance, and control a dispense rate of the packaging material
dispenser during the relative rotation based at least in part on the determined effective
circumference and the sensed angular relationship.
[0022] In accordance with the invention, control over the dispense rate of a packaging material
dispenser may utilize controlled interventions to effectively apply modifications
to a wrap speed model to account for inherent physical, mechanical limitations of
wrapping apparatus components and other inherent system lags. The controlled interventions
may be performed proximate points at which a controller anticipates the packaging
material engages with the corners of the load to effectively modify the dispense rate
relative to a predicted demand for the packaging material as calculated using a wrap
speed model.
[0023] Therefore, consistent with another aspect of the invention, an apparatus for wrapping
a load with packaging material includes a packaging material dispenser for dispensing
packaging material to the load, a load support for supporting the load during wrapping,
where the packaging material dispenser and the load support are adapted for rotation
relative to one other about a center of rotation, and a controller configured to control
a dispense rate of the packaging material dispenser during the relative rotation.
The controller is further configured to anticipate a contact between the packaging
material and a corner of the load and in response thereto perform a controlled intervention
that varies the dispense rate relative to a predicted demand for packaging material.
[0024] In accordance with the invention, control over the dispense rate of a packaging material
dispenser may utilize a rotational data shift to effectively advance a wrap speed
model to an earlier point in time or rotational position to offset system lags in
a wrapping apparatus. The rotational shift is applied, for example, to the sensed
data used by the wrap speed model or to the calculated dimensions or position of the
load so that the actual dispense rate at the load will more closely line up with that
calculated by the wrap speed model, and so that the phase of the profile of the actual
dispense rate will be more aligned with that of the desired dispense rate calculated
by the wrap speed model.
[0025] Therefore, consistent with another aspect of the invention, an apparatus for wrapping
a load with packaging material may include a packaging material dispenser for dispensing
packaging material to the load, a load support for supporting the load during wrapping,
where the packaging material dispenser and the load support are adapted for rotation
relative to one other about a center of rotation, and a controller configured to control
a dispense rate of the packaging material dispenser during the relative rotation based
upon a wrap speed model, where the controller is further configured to offset system
lag by applying a rotational data shift to the wrap speed model.
[0026] These and other advantages and features, which characterize the invention, are set
forth in the claims annexed hereto and forming a further part hereof. However, for
a better understanding of the invention, and of the advantages and objectives attained
through its use, reference should be made to the Drawings, and to the accompanying
descriptive matter, in which there is described exemplary embodiments of the invention.
Brief Description of the Drawings
[0027]
FIGURE 1 shows a top view of a rotating arm-type wrapping apparatus consistent with
the invention.
FIGURE 2 is a schematic view of an exemplary control system for use in the apparatus
of Fig. 1.
FIGURE 3 shows a top view of a rotating ring-type wrapping apparatus consistent with
the invention.
FIGURE 4 shows a top view of a turntable-type wrapping apparatus consistent with the
invention.
FIGURE 5 is a top view of a packaging material dispenser and a load, illustrating
a tangent circle defined for the load throughout relative rotation between the packaging
material dispenser and the load.
FIGURE 6 is a block diagram of various inputs to a wrap speed model consistent with
the invention.
FIGURE 7 is a top view of a mechanical film angle sensor consistent with the invention.
FIGURE 8 is a top view of a force-based film angle sensor consistent with the invention.
FIGURE 9A is a top view of a light curtain film angle sensor consistent with the invention.
FIGURE 9B is a cross-sectional view of the light curtain film angle sensor of Fig.
9A, taken along lines 9B-9B.
FIGURE 10 is a plot of film lengths at a plurality of angles around a rotating load.
FIGURE 11 is a graph of the film lengths plotted in Fig. 10.
FIGURES 12A, 12B and 12C are respective graphs of effective circumference, film angle
and idle roller speed for an example offset load at a plurality of angles of a relative
rotation between the load and a packaging material dispenser.
FIGURES 13-14 are block diagrams illustrating various dimensions and angles defined
on an example load.
FIGURES 15-17 are block diagrams illustrating various dimensions and angles defined
on another example load during a wrapping operation.
FIGURE 18 is a graph of dispense rates for four corners of a load.
FIGURES 19A-19E are block diagrams illustrating various dimensions and angles defined
on another example load during a wrapping operation and used to determine a contact
angle for a corner.
FIGURE 20 is a flowchart illustrating an example sequence of steps performed by an
effective consumption rate-based wrapping operation consistent with the invention.
FIGURE 21 is a flowchart illustrating an example sequence of steps performed by a
corner location angle-based wrapping operation consistent with the invention.
FIGURE 22 is a flowchart illustrating an example sequence of steps performed by a
wrapping operation implementing controlled interventions in a manner consistent with
the invention.
FIGURES 23A-23C are graphs of example controlled interventions capable of being implemented
by the wrapping operation of Fig. 22.
FIGURES 24A and 24B are graphs illustrating an example rotational data shift consistent
with the invention.
FIGURE 25 is a flowchart illustrating an example sequence of steps performed by a
wrapping operation implementing a rotational data shift consistent with the invention.
Detailed Description
[0028] Embodiments consistent with the invention utilize in one aspect the effective circumference
of a load to dynamically control the rate at which packaging material is dispensed
to a load when wrapping the load with packaging material during relative rotation
established between the load and a packaging material dispenser. Prior to a discussion
of the aforementioned concepts, however, a brief discussion of various types of wrapping
apparatus within which the various techniques disclosed herein may be implemented
is provided.
[0029] In addition, reference is made to the disclosures of each of
U.S. Pat. No. 4,418,510, entitled "STRETCH WRAPPING APPARATUS AND PROCESS," and filed Apr. 17, 1981;
U.S. Pat. No. 4,953,336, entitled "HIGH TENSILE WRAPPING APPARATUS," and filed Aug. 17, 1989;
U.S. Pat. No. 4,503,658, entitled "FEEDBACK CONTROLLED STRETCH WRAPPING APPARATUS AND PROCESS," and filed
Mar. 28, 1983;
U.S. Pat. No. 4,676,048, entitled "SUPPLY CONTROL ROTATING STRETCH WRAPPING APPARATUS AND PROCESS," and filed
May 20, 1986;
U.S. Pat. No. 4,514,955, entitled "FEEDBACK CONTROLLED STRETCH WRAPPING APPARATUS AND PROCESS," and filed
Apr. 6, 1981;
U.S. Pat. No. 6,748,718, entitled "METHOD AND APPARATUS FOR WRAPPING A LOAD," and filed Oct. 31, 2002;
U.S. Pat. No. 7,707,801, entitled "METHOD AND APPARATUS FOR DISPENSING A PREDETERMINED FIXED AMOUNT OF PRE-STRETCHED
FILM RELATIVE TO LOAD GIRTH," filed Apr. 6, 2006;
U.S. Pat. No. 8,037,660, entitled "METHOD AND APPARATUS FOR SECURING A LOAD TO A PALLET WITH A ROPED FILM
WEB," and filed Feb. 23, 2007;
U.S. Patent Application Publication No. 2007/0204565, entitled "METHOD AND APPARATUS FOR METERED PRE-STRETCH FILM DELIVERY," and filed
Sep. 6, 2007;
U.S. Pat. No. 7,779,607, entitled "WRAPPING APPARATUS INCLUDING METERED PRE-STRETCH FILM DELIVERY ASSEMBLY
AND METHOD OF USING," and filed Feb. 23, 2007;
U.S. Patent Application Publication No. 2009/0178374, entitled "ELECTRONIC CONTROL OF METERED FILM DISPENSING IN A WRAPPING APPARATUS,"
and filed Jan. 7, 2009; and
U.S. Patent Application Publication No. 2011/0131927, entitled "DEMAND BASED WRAPPING," and filed Nov. 6, 2010.
Wrapping Apparatus Configurations
[0030] Fig. 1, for example, illustrates a rotating arm-type wrapping apparatus 100, which
includes a roll carriage 102 mounted on a rotating arm 104. Roll carriage 102 may
include a packaging material dispenser 106. Packaging material dispenser 106 may be
configured to dispense packaging material 108 as rotating arm 104 rotates relative
to a load 110 to be wrapped. In an exemplary embodiment, packaging material dispenser
106 may be configured to dispense stretch wrap packaging material. As used herein,
stretch wrap packaging material is defined as material having a high yield coefficient
to allow the material a large amount of stretch during wrapping. However, it is possible
that the apparatuses and methods disclosed herein may be practiced with packaging
material that will not be pre-stretched prior to application to the load. Examples
of such packaging material include netting, strapping, banding, tape, etc. The invention
is therefore not limited to use with stretch wrap packaging material.
[0031] Packaging material dispenser 106 may include a pre-stretch assembly 112 configured
to pre-stretch packaging material before it is applied to load 110 if pre-stretching
is desired, or to dispense packaging material to load 110 without pre-stretching.
Pre-stretch assembly 112 may include at least one packaging material dispensing roller,
including, for example, an upstream dispensing roller 114 and a downstream dispensing
roller 116. It is contemplated that pre-stretch assembly 112 may include various configurations
and numbers of pre-stretch rollers, drive or driven roller and idle rollers without
departing from the spirit and scope of the invention.
[0032] The terms "upstream" and "downstream," as used in this application, are intended
to define positions and movement relative to the direction of flow of packaging material
108 as it moves from packaging material dispenser 106 to load 110. Movement of an
object toward packaging material dispenser 106, away from load 110, and thus, against
the direction of flow of packaging material 108, may be defined as "upstream." Similarly,
movement of an object away from packaging material dispenser 106, toward load 110,
and thus, with the flow of packaging material 108, may be defined as "downstream."
Also, positions relative to load 110 (or a load support surface 118) and packaging
material dispenser 106 may be described relative to the direction of packaging material
flow. For example, when two pre-stretch rollers are present, the pre-stretch roller
closer to packaging material dispenser 106 may be characterized as the "upstream"
roller and the pre-stretch roller closer to load 110 (or load support 118) and further
from packaging material dispenser 106 may be characterized as the "downstream" roller.
[0033] A packaging material drive system 120, including, for example, an electric motor
122, may be used to drive dispensing rollers 114 and 116. For example, electric motor
122 may rotate downstream dispensing roller 116. Downstream dispensing roller 116
may be operatively coupled to upstream dispensing roller 114 by a chain and sprocket
assembly, such that upstream dispensing roller 114 may be driven in rotation by downstream
dispensing roller 116. Other connections may be used to drive upstream roller 114
or, alternatively, a separate drive (not shown) may be provided to drive upstream
roller 114.
[0034] Downstream of downstream dispensing roller 116 may be provided one or more idle rollers
124, 126that redirect the web of packaging material, with the most downstream idle
roller 126 effectively providing an exit point 128 from packaging material dispenser
102, such that a portion 130 of packaging material 108 extends between exit point
128 and a contact point 132 where the packaging material engages load 110 (or alternatively
contact point 132' if load 110 is rotated in a counter-clockwise direction).
[0035] Wrapping apparatus 100 also includes a relative rotation assembly 134 configured
to rotate rotating arm 104, and thus, packaging material dispenser 106 mounted thereon,
relative to load 110 as load 110 is supported on load support surface 118. Relative
rotation assembly 134 may include a rotational drive system 136, including, for example,
an electric motor 138. It is contemplated that rotational drive system 136 and packaging
material drive system 120 may run independently of one another. Thus, rotation of
dispensing rollers 114 and 116 may be independent of the relative rotation of packaging
material dispenser 106 relative to load 110. This independence allows a length of
packaging material 108 to be dispensed per a portion of relative revolution that is
neither predetermined or constant. Rather, the length may be adjusted periodically
or continuously based on changing conditions.
[0036] Wrapping apparatus 100 may further include a lift assembly 140. Lift assembly 140
may be powered by a lift drive system 142, including, for example, an electric motor
144, that may be configured to move roll carriage 102 vertically relative to load
110. Lift drive system 142 may drive roll carriage 102, and thus packaging material
dispenser 106, upwards and downwards vertically on rotating arm 104 while roll carriage
102 and packaging material dispenser 106 are rotated about load 110 by rotational
drive system 136, to wrap packaging material spirally about load 110.
[0037] One or more of downstream dispensing roller 116, idle roller 124 and idle roller
126 may include a corresponding sensor 146, 148, 150 to monitor rotation of the respective
roller. In particular, rollers 116, 124 and/or 126, and/or packaging material 108
dispensed thereby, may be used to monitor a dispense rate of packaging material dispenser
106, e.g., by monitoring the rotational speed of rollers 116, 124 and/or 126, the
number of rotations undergone by such rollers, the amount and/or speed of packaging
material dispensed by such rollers, and/or one or more performance parameters indicative
of the operating state of packaging material drive system 120, including, for example,
a speed of packaging material drive system 120. The monitored characteristics may
also provide an indication of the amount of packaging material 108 being dispensed
and wrapped onto load 110. In addition, in some embodiments a sensor, e.g., sensor
148 or 150, may be used to detect a break in the packaging material.
[0038] Wrapping apparatus also includes an angle sensor 152 for determining an angular relationship
between load 110 and packaging material dispenser 106 about a center of rotation 154.
Angle sensor 152 may be implemented, for example, as a rotary encoder, or alternatively,
using any number of alternate sensors or sensor arrays capable of providing an indication
of the angular relationship and distinguishing from among multiple angles throughout
the relative rotation, e.g., an array of proximity switches, optical encoders, magnetic
encoders, electrical sensors, mechanical sensors, photodetectors, motion sensors,
etc. The angular relationship may be represented in some embodiments in terms of degrees
or fractions of degrees, while in other embodiments a lower resolution may be adequate.
It will also be appreciated that an angle sensor consistent with the invention may
also be disposed in other locations on wrapping apparatus 100, e.g., about the periphery
or mounted on arm 104 or roll carriage 102. In addition, in some embodiments angular
relationship may be represented and/or measured in units of time, based upon a known
rotational speed of the load relative to the packaging material dispenser, from which
a time to complete a full revolution may be derived such that segments of the revolution
time would correspond to particular angular relationships.
[0039] Additional sensors, such as a load distance sensor 156 and/or a film angle sensor
158, may also be provided on wrapping apparatus 100. Load distance sensor 156 may
be used to measure a distance from a reference point to a surface of load 110 as the
load rotates relative to packaging material dispenser 106 and thereby determine a
cross-sectional dimension of the load at a predetermined angular position relative
to the packaging material dispenser. In one embodiment, load distance sensor 156 measures
distance along a radial from center of rotation 154, and based on the known, fixed
distance between the sensor and the center of rotation, the dimension of the load
may be determined by subtracting the sensed distance from this fixed distance. Sensor
156 may be implemented using various types of distance sensors, e.g., a photoeye,
proximity detector, laser distance measurer, ultrasonic distance measurer, electronic
rangefinder, and/or any other suitable distance measuring device. Exemplary distance
measuring devices may include, for example, an IFM Effector 01D100 and a Sick UM30-213118
(6036923).
[0040] Film angle sensor 158 may be used to determine a film angle for portion 130 of packaging
material 108, which may be relative, for example, to a radial (not shown in Fig. 1)
extending from center of rotation 154 to exit point 128 (although other reference
lines may be used in the alternative).
[0041] In one embodiment, film angle sensor 158 may be implemented using a distance sensor,
e.g., a photoeye, proximity detector, laser distance measurer, ultrasonic distance
measurer, electronic rangefinder, and/or any other suitable distance measuring device.
In one embodiment, an IFM Effector 01D100 and a Sick UM30-213118 (6036923) may be
used for film angle sensor 158. In other embodiments, film angle sensor 158 may be
implemented mechanically, e.g., using a cantilevered or rockered follower arm having
a free end that rides along the surface of portion 130 of packaging material 108 such
that movement of the follower arm tracks movement of the packaging material. In still
other embodiments, a film angle sensor may be implemented by a force sensor that senses
force changes resulting from movement of portion 130 through a range of film angles,
or a sensor array (e.g., an image sensor) that is positioned above or below the plane
of portion 130 to sense an edge of the packaging material. Additional details regarding
these alternate film angle sensor implementations are discussed in greater detail
below in connection with Figs. 7, 8 and 9A-9B.
[0042] Wrapping apparatus 100 may also include additional components used in connection
with other aspects of a wrapping operation. For example, a clamping device 159 may
be used to grip the leading end of packaging material 108 between cycles. In addition,
a conveyor (not shown) may be used to convey loads to and from wrapping apparatus
100. Other components commonly used on a wrapping apparatus will be appreciated by
one of ordinary skill in the art having the benefit of the instant disclosure.
[0043] An exemplary schematic of a control system 160 for wrapping apparatus 100 is shown
in Fig. 2. Motor 122 of packaging material drive system 120, motor 138 of rotational
drive system 136, and motor 144 of lift drive system 142 may communicate through one
or more data links 162 with a rotational drive variable frequency drive ("VFD") 164,
a packaging material drive VFD 166, and a lift drive VFD 168, respectively. Rotational
drive VFD 164, packaging material drive VFD 166, and lift drive VFD 168 may communicate
with controller 170 through a data link 172. It should be understood that rotational
drive VFD 164, packaging material drive VFD 166, and lift drive VFD 168 may produce
outputs to controller 170 that controller 170 may use as indicators of rotational
movement. For example, packaging material drive VFD 166 may provide controller 170
with signals similar to signals provided by sensor 146, and thus, sensor 146 may be
omitted to cut down on manufacturing costs.
[0044] Controller 170 may include hardware components and/or software program code that
allow it to receive, process, and transmit data. It is contemplated that controller
170 may be implemented as a programmable logic controller (PLC), or may otherwise
operate similar to a processor in a computer system. Controller 170 may communicate
with an operator interface 174 via a data link 176. Operator interface 174 may include
a screen and controls that provide an operator with a way to monitor, program, and
operate wrapping apparatus 100. For example, an operator may use operator interface
174 to enter or change predetermined and/or desired settings and values, or to start,
stop, or pause the wrapping cycle. Controller 170 may also communicate with one or
more sensors, e.g., sensors 146, 148, 150, 152, 154 and 156, as well as others not
illustrated in Fig.2, through a data link 178, thus allowing controller 170 to receive
performance related data during wrapping. It is contemplated that data links 162,
172, 176, and 178 may include any suitable wired and/or wireless communications media
known in the art.
[0045] As noted above, sensors 146, 148, 150, 152 may be configured in a number of manners
consistent with the invention. In one embodiment, for example, sensor 146 may be configured
to sense rotation of downstream dispensing roller 116, and may include one or more
magnetic transducers 180 mounted on downstream dispensing roller 116, and a sensing
device 182 configured to generate a pulse when the one or more magnetic transducers
180 are brought into proximity of sensing device 182. Alternatively, sensor assembly
146 may include an encoder configured to monitor rotational movement, and capable
of producing, for example, 360 or 720 signals per revolution of downstream dispensing
roller 116 to provide an indication of the speed or other characteristic of rotation
of downstream dispensing roller 116. The encoder may be mounted on a shaft of downstream
dispensing roller 116, on electric motor 122, and/or any other suitable area. One
example of a sensor assembly that may be used is an Encoder Products Company model
15H optical encoder. Other suitable sensors and/or encoders may be used for monitoring,
such as, for example, optical encoders, magnetic encoders, electrical sensors, mechanical
sensors, photodetectors, and/or motion sensors.
[0046] Likewise, for sensors 148 and 150, magnetic transducers 184, 186 and sensing devices
188, 190 may be used to monitor rotational movement, while for sensor 152, a rotary
encoder may be used to determine the angular relationship between the load and packaging
material dispenser. Any of the aforementioned alternative sensor configurations may
be used for any of sensors 146, 148, 150, 152, 154 and 156 in other embodiments, and
as noted above, one or more of such sensors may be omitted in some embodiments. Additional
sensors capable of monitoring other aspects of the wrapping operation may also be
coupled to controller 170 in other embodiments.
[0047] For the purposes of the invention, controller 170 may represent practically any type
of computer, computer system, controller, logic controller, or other programmable
electronic device, and may in some embodiments be implemented using one or more networked
computers or other electronic devices, whether located locally or remotely with respect
to wrapping apparatus 100. Controller 170 typically includes a central processing
unit including at least one microprocessor coupled to a memory, which may represent
the random access memory (RAM) devices comprising the main storage of controller 170,
as well as any supplemental levels of memory, e.g., cache memories, non-volatile or
backup memories (e.g., programmable or flash memories), read-only memories, etc. In
addition, the memory may be considered to include memory storage physically located
elsewhere in controller 170, e.g., any cache memory in a processor in CPU 52, as well
as any storage capacity used as a virtual memory, e.g., as stored on a mass storage
device or on another computer or electronic device coupled to controller 170. Controller
170 may also include one or more mass storage devices, e.g., a floppy or other removable
disk drive, a hard disk drive, a direct access storage device (DASD), an optical drive
(e.g., a CD drive, a DVD drive, etc.), and/or a tape drive, among others. Furthermore,
controller 170 may include an interface with one or more networks (e.g., a LAN, a
WAN, a wireless network, and/or the Internet, among others) to permit the communication
of information to the components in wrapping apparatus 100 as well as with other computers
and electronic devices. Controller 170 operates under the control of an operating
system, kernel and/or firmware and executes or otherwise relies upon various computer
software applications, components, programs, objects, modules, data structures, etc.
Moreover, various applications, components, programs, objects, modules, etc. may also
execute on one or more processors in another computer coupled to controller 170, e.g.,
in a distributed or client-server computing environment, whereby the processing required
to implement the functions of a computer program may be allocated to multiple computers
over a network.
[0048] In general, the routines executed to implement the embodiments of the invention,
whether implemented as part of an operating system or a specific application, component,
program, object, module or sequence of instructions, or even a subset thereof, will
be referred to herein as "computer program code," or simply "program code." Program
code typically comprises one or more instructions that are resident at various times
in various memory and storage devices in a computer, and that, when read and executed
by one or more processors in a computer, cause that computer to perform the steps
necessary to execute steps or elements embodying the various aspects of the invention.
Moreover, while the invention has and hereinafter will be described in the context
of fully functioning controllers, computers and computer systems, those skilled in
the art will appreciate that the various embodiments of the invention are capable
of being distributed as a program product in a variety of forms, and that the invention
applies equally regardless of the particular type of computer readable media used
to actually carry out the distribution.
[0049] Such computer readable media may include computer readable storage media and communication
media. Computer readable storage media is non-transitory in nature, and may include
volatile and non-volatile, and removable and non-removable media implemented in any
method or technology for storage of information, such as computer-readable instructions,
data structures, program modules or other data. Computer readable storage media may
further include RAM, ROM, erasable programmable read-only memory (EPROM), electrically
erasable programmable read-only memory (EEPROM), flash memory or other solid state
memory technology, CD-ROM, digital versatile disks (DVD), or other optical storage,
magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage
devices, or any other medium that can be used to store the desired information and
which can be accessed by controller 170. Communication media may embody computer readable
instructions, data structures or other program modules. By way of example, and not
limitation, communication media may include wired media such as a wired network or
direct-wired connection, and wireless media such as acoustic, RF, infrared and other
wireless media. Combinations of any of the above may also be included within the scope
of computer readable media.
[0050] Various program code described hereinafter may be identified based upon the application
within which it is implemented in a specific embodiment of the invention. However,
it should be appreciated that any particular program nomenclature that follows is
used merely for convenience, and thus the invention should not be limited to use solely
in any specific application identified and/or implied by such nomenclature. Furthermore,
given the typically endless number of manners in which computer programs may be organized
into routines, procedures, methods, modules, objects, and the like, as well as the
various manners in which program functionality may be allocated among various software
layers that are resident within a typical computer (e.g., operating systems, libraries,
API's, applications, applets, etc.), it should be appreciated that the invention is
not limited to the specific organization and allocation of program functionality described
herein.
[0051] Now turning to Fig. 3, a rotating ring-type wrapping apparatus 200 is illustrated.
Wrapping apparatus 200 may include elements similar to those shown in relation to
wrapping apparatus 100 of Fig. 1, including, for example, a roll carriage 202 including
a packaging material dispenser 206 configured to dispense packaging material 208 during
relative rotation between roll carriage 202 and a load 210 disposed on a load support
218. However, a rotating ring 204 is used in wrapping apparatus 200 in place of rotating
arm 104 of wrapping apparatus 100. In many other respects, however, wrapping apparatus
200 may operate in a manner similar to that described above with respect to wrapping
apparatus 100.
[0052] Packaging material dispenser 206 may include a pre-stretch assembly 212 including
an upstream dispensing roller 214 and a downstream dispensing roller 216, and a packaging
material drive system 220, including, for example, an electric motor 222, may be used
to drive dispensing rollers 214 and 216.Downstream of downstream dispensing roller
216 may be provided one or more idle rollers 224, 226, with the most downstream idle
roller 226 effectively providing an exit point 228 from packaging material dispenser
206, such that a portion 230 of packaging material 208 extends between exit point
228 and a contact point 232 where the packaging material engages load 210.
[0053] Wrapping apparatus 200 also includes a relative rotation assembly 234 configured
to rotate rotating ring 204, and thus, packaging material dispenser 206 mounted thereon,
relative to load 210 as load 210 is supported on load support surface 218. Relative
rotation assembly 234 may include a rotational drive system 236, including, for example,
an electric motor 238. Wrapping apparatus 200 may further include a lift assembly
240, which may be powered by a lift drive system 242, including, for example, an electric
motor 244, that may be configured to move rotating ring 204 and roll carriage 202
vertically relative to load 210.
[0054] In addition, similar to wrapping apparatus 100, wrapping apparatus 200 may include
sensors 246, 248, 250 on one or more of downstream dispensing roller 216, idle roller
224 and idle roller 226. Furthermore, an angle sensor 252 may be provided for determining
an angular relationship between load 210 and packaging material dispenser 206 about
a center of rotation 254, and in some embodiments, one or both of a load distance
sensor 256 and a film angle sensor 258 may also be provided. Sensor 252 may be positioned
proximate center of rotation 254, or alternatively, may be positioned at other locations,
such as proximate rotating ring 204. Wrapping apparatus 200 may also include additional
components used in connection with other aspects of a wrapping operation, e.g., a
clamping device 259 may be used to grip the leading end of packaging material 208
between cycles.
[0055] Fig. 4 likewise shows a turntable-type wrapping apparatus 300, which may also include
elements similar to those shown in relation to wrapping apparatus 100 of Fig. 1. However,
instead of a roll carriage 102 that rotates around a fixed load 110 using a rotating
arm 104, as in Fig. 1, wrapping apparatus 300 includes a rotating turntable 304 functioning
as a load support 318 and configured to rotate load 310 about a center of rotation
354 while a packaging material dispenser 306 disposed on a dispenser support 302 remains
in a fixed location about center of rotation 354 while dispensing packaging material
308. In many other respects, however, wrapping apparatus 300 may operate in a manner
similar to that described above with respect to wrapping apparatus 100.
[0056] Packaging material dispenser 306 may include a pre-stretch assembly 312 including
an upstream dispensing roller 314 and a downstream dispensing roller 316, and a packaging
material drive system 320, including, for example, an electric motor 322, may be used
to drive dispensing rollers 314 and 316, and downstream of downstream dispensing roller
316 may be provided one or more idle rollers 324, 326, with the most downstream idle
roller 326 effectively providing an exit point 328 from packaging material dispenser
306, such that a portion 330 of packaging material 308 extends between exit point
328 and a contact point 332 (or alternatively contact point 332' if load 310 is rotated
in a counter-clockwise direction) where the packaging material engages load 310.
[0057] Wrapping apparatus 300 also includes a relative rotation assembly 334 configured
to rotate turntable 304, and thus, load 310 supported thereon, relative to packaging
material dispenser 306. Relative rotation assembly 334 may include a rotational drive
system 336, including, for example, an electric motor 338. Wrapping apparatus 300
may further include a lift assembly 340, which may be powered by a lift drive system
342, including, for example, an electric motor 344, that may be configured to move
dispenser support 302 and packaging material dispenser 306 vertically relative to
load 310.
[0058] In addition, similar to wrapping apparatus 100, wrapping apparatus 300 may include
sensors 346, 348, 350 on one or more of downstream dispensing roller 316, idle roller
324 and idle roller 326. Furthermore, an angle sensor 352 may be provided for determining
an angular relationship between load 310 and packaging material dispenser 306 about
a center of rotation 354, and in some embodiments, one or both of a load distance
sensor 356 and a film angle sensor 358 may also be provided. Sensor 352 may be positioned
proximate center of rotation 354, or alternatively, may be positioned at other locations,
such as proximate the edge of turntable 304. Wrapping apparatus 300 may also include
additional components used in connection with other aspects of a wrapping operation,
e.g., a clamping device 359 may be used to grip the leading end of packaging material
308 between cycles.
[0059] Each of wrapping apparatus 200 of Fig. 3 and wrapping apparatus 300 of Fig. 4 may
also include a controller (not shown) similar to controller 170 of Fig. 2, and receive
signals from one or more of the aforementioned sensors and control packaging material
drive system 220, 320 during relative rotation between load 210, 310 and packaging
material dispenser 206, 306.
[0060] Those skilled in the art will recognize that the exemplary environments illustrated
in Figs. 1-4 are not intended to limit the present invention. Indeed, those skilled
in the art will recognize that other alternative environments may be used without
departing from the scope of the invention.
Effective Circumference-Based Wrapping
[0061] As noted above, embodiments consistent with the invention utilize in one aspect the
effective circumference of a load to dynamically control the rate at which packaging
material is dispensed to a load when wrapping the load with packaging material during
relative rotation established between the load and a packaging material dispenser.
[0062] It will be appreciated that in many wrapping applications, the rate at which packaging
material is dispensed is also controlled based on a desired payout percentage, which
in general relates to the amount of wrap force applied to the load by the packaging
material during wrapping. Further details regarding the concept of payout percentage
may be found, for example, in the aforementioned
U.S. Pat. No. 7,707,801.
[0063] In many embodiments, for example, a payout percentage may have a range of about 80%
to about 120% Decreasing the payout percentage slows the rate at which packaging material
exits the packaging material dispenser compared to the relative rotation of the load
such that the packaging material is pulled tighter around the load, thereby increasing
containment force. In contrast, increasing the payout percentage decreases the wrap
force. For the purposes of simplifying the discussion hereinafter, however, a payout
percentage of 100% is initially assumed. It will be appreciated also that other metrics
may be used as an alternative to payout percentage to reflect the relative amount
of wrap force to be applied during wrapping, so the invention is not so limited.
[0064] Fig. 5, for example, functionally illustrates a wrapping apparatus 400 in which a
load support 402 and packaging material dispenser 404 are adapted for relative rotation
with one another to rotate a load 406 about a center of rotation 408 and thereby dispense
a packaging material 410 for wrapping around the load. In this illustration, the relative
rotation is in a clockwise direction relative to the load (i.e., the load rotates
clockwise relative to the packaging material dispenser, while the packaging material
dispenser may be considered to rotate in a counter-clockwise direction around the
load).
[0065] In embodiments consistent with the invention, the effective circumference of a load
throughout relative rotation is indicative of an effective consumption rate of the
load, which is in turn indicative of the amount of packaging material being "consumed"
by the load as the load rotates relative to the packaging dispenser. In particular,
effective consumption rate, as used herein, generally refers to a rate at which packaging
material would need to be dispensed by the packaging material dispenser in order to
substantially match the tangential velocity of a tangent circle that is substantially
centered at the center of rotation of the load and substantially tangent to a line
substantially extending between a first point proximate to where the packaging material
exits the dispenser and a second point proximate to where the packaging material engages
the load. This line is generally coincident with the web of packaging material between
where the packaging material exits the dispenser and where the packaging material
engages the load.
[0066] As shown in Fig. 5, for example, an idle roller 412 defines an exit point 414 for
packaging material dispenser 404, such that a portion of web 416 of packaging material
410 extends between this exit point 414 and an engagement point 418 at which the packaging
material 410 engages load 406. In this arrangement, a tangent circle 420 is tangent
to portion 416 and is centered at center of rotation 408.
[0067] The tangent circle has a circumference C
TC, which for the purposes of this invention, is referred to as the "effective circumference"
of the load. Likewise, other dimensions of the tangent circle, e.g., the radius R
TC and diameter D
TC, may be respectively referred to as the "effective radius" and "effective diameter"
of the load.
[0068] It has been found that for a load having a non-circular cross-section, as the load
rotates relative to the dispenser about center of rotation 408, the size (i.e., the
circumference, radius and diameter) of tangent circle 420 dynamically varies, and
that the size of tangent circle 420 throughout the rotation effectively models, at
any given angular position of the load relative to the dispenser, a rate at which
packaging material should be dispensed in order to match the consumption rate of the
load, i.e., where the dispense rate in terms of linear velocity (represented by arrow
V
D) is substantially equal to the tangential velocity of the tangent circle (represented
by arrow Vc). Thus, in situations where a payout percentage of 100% is desired, the
desired dispense rate of the packaging material may be set to substantially track
the dynamically changing tangential velocity of the tangent circle.
[0069] Of note, the tangent circle is dependent not only on the dimensions of the load (i.e.,
the length L and width W), but also the offset of the geometric center 422 of the
load from the center of rotation 408, illustrated in Fig. 5 as O
L and O
W. Given that in many applications, a load will not be perfectly centered when it is
placed or conveyed onto the load support, the dimensions of the load, by themselves,
typically do not present a complete picture of the effective consumption rate of the
load. Nonetheless, as will become more apparent below, the calculation of the dimensions
of the tangent circle, and thus the effective consumption rate, may be determined
without determining the actual dimensions and/or offset of the load in many embodiments.
[0070] It has been found that this tangent circle, when coupled with the web of packaging
material and the drive roller (e.g., drive roller 424), functions in much the same
manner as a belt drive system, with tangent circle 420 functioning as the driver pulley,
dispenser drive roller 424functioning as the follower pulley, and web 416 of packaging
material functioning as the belt. For example, let N
d be the rotational velocity of a driver pulley in RPM, N
f be the rotational velocity of a follower pulley in RPM, R
d be the radius of the driver pulley and R
f be the radius of the follower pulley. Consider the length of belt that passes over
each of the driver pulley and the follower pulley in one minute, which is equal to
the circumference of the respective pulley (diameter
∗ π, or radius
∗ 2π) multiplied by the rotational velocity:
where L
d is the length of belt that passes over the driver pulley in one minute, and L
f is the length of belt that passes over the follower pulley in one minute.
[0071] In this theoretical system, the point at which neither pulley applied a tensile or
compressive force to the belt (which generally corresponds to a payout percentage
of 100%) would be achieved when the tangential velocities, i.e., the linear velocities
at the surfaces or rims of the pulleys, were equal. Put another way, when the length
of belt that passes over each pulley over the same time period is equal, i.e., L
d = L
f. Therefore:
[0072] Consequently, the velocity ratio VR of the rotational velocities of the driver and
follower pulleys is:
[0073] Alternatively, the velocity ratio may be expressed in terms of the ratio of diameters
or of circumferences:
where D
f, D
d are the respective diameters of the follower and driver pulleys, and C
f, C
d are the respective circumferences of the follower and driver pulleys.
[0074] Returning to equations (1) and (2) above, the values L
d and L
f represent the length of belt that passes the driver and follower pulleys in one minute.
Thus, when the tangent circle for the load is considered a driver pulley, the effective
consumption rate (ECR) may be considered to be equal to the length of packaging material
that passes the tangent circle in a fixed amount of time, e.g., per minute:
where C
TC is the circumference of the tangent circle, N
TC is the rotational velocity of the tangent circle (e.g., in revolutions per minute
(RPM)), and R
TC is the radius of the tangent circle.
[0075] Therefore, given a known rotational velocity for the load, a known circumference
of the tangent circle at a given instant and a known circumference for the drive roller,
the rotational velocity of the drive roller necessary to provide a dispense rate that
substantially matches the effective consumption rate is:
where N
DR is the rotational rate of the drive roller, C
TC is the circumference of the tangent circle and the effective circumference of the
load, CDR is the circumference of the drive roller and NL is the rotational rate of
the load relative to the dispenser.
[0076] In addition, should it be desirable to scale the rotational rate of the drive roller
to provide a controlled payout percentage (PP), and thereby provide a desired containment
force and/or a desired packaging material use efficiency, equation (8) may be modified
as follows:
[0077] The manner in which the dimensions (i.e., circumference, diameter and/or radius)
of the tangent circle may be calculated or otherwise determined may vary in different
embodiments. For example, as illustrated in Fig. 6, a wrap speed model 500, representing
the control algorithm by which to drive a packaging material dispenser to dispense
packaging material at a desired dispense rate during relative rotation with a load,
may be responsive to a number of different control inputs.
[0078] In some embodiments, for example, a sensed film angle (block 502) may be used to
determine various dimensions of a tangent circle, e.g., effective radius (block 504)
and/or effective circumference (block 506). As shown in Fig. 5, for example, a film
angle FA may be defined as the angle at exit point 414 between portion 416 of packaging
material 410 (to which tangent circle 420 is tangent) and a radial or radius 426 extending
from center of rotation 408 to exit point 414.
[0079] Returning to Fig. 6, the film angle sensed in block 502, e.g., using an encoder and
follower arm or other electronic sensor, is used to determine one or more dimensions
of the tangent circle (e.g., effective radius, effective circumference and/or effective
diameter), and from these determined dimensions, a wrap speed control algorithm 508
determines a dispense rate. In many embodiments, wrap speed control algorithm 508
also utilizes the angular relationship between the load and the packaging material
dispenser, i.e., the sensed rotational position of the load, as an input such that,
for any given rotational position or angle of the load (e.g., at any of a plurality
of angles defined in a full revolution), a desired dispense rate for the determined
tangent circle may be determined.
[0080] Alternatively or in addition to the use of sensed film angle, various additional
inputs may be used to determine dimensions of a tangent circle. As shown in block
512, for example, a film speed sensor, such as an optical or magnetic encoder on an
idle roller, may be used to determine the speed of the packaging material as the packaging
material exits the packaging material dispenser. In addition, as shown in block 514,
a laser or other distance sensor may be used to determine a load distance (i.e., the
distance between the surface of the load at a particular rotational position and a
reference point about the periphery of the load). Furthermore, as shown in block 516,
the dimensions of the load, e.g., length, width and/or offset, may either be input
manually by a user, may be received from a database or other electronic data source,
or may be sensed or measured.
[0081] From any or all of these inputs, one or more dimensions of the load, such as corner
contact angles (block 518), corner contact radials (block 520), and/or corner radials
(block 522) may be used to determine a calculated film angle, such that this calculated
film angle may be used in lieu of or in addition to any sensed film angle to determine
one or more dimensions of the tangent circle. Thus, the calculated film angle may
be used by the wrap speed control algorithm in a similar manner to the sensed film
angle described above.
[0082] Moreover, as will be discussed in greater detail below, in some embodiments additional
modifications may be applied to wrap speed control algorithm 508 to provide more accurate
control over the dispense rate. As shown in block 526, for example, a compensation
may be performed to address system lag. In some embodiments, for example, a controlled
intervention may be performed to effectively anticipate contact of a corner of the
load with the packaging material. In addition, in some embodiments, a rotational shift
may be performed to better align collected data with the control algorithm and thereby
account for various lags in the system.
Effective Circumference Based on Sensed Film Angle
[0083] Returning to Fig. 5, when sensed film angle is used in a wrap speed model consistent
with the invention, the effective circumference may be determined based upon the right
triangle 428 defined by center of rotation 408, exit point 414, and a tangent point
430 where web 416 of packaging material 410 intersects with tangent circle 420. Given
that an effective radius R
TC extending between center of rotation 408 and point 430 forms a right angle with web
416, and further given that the length of the rotation radial (RR), i.e., the radius
426 from center of rotation 408 to exit point 414, is known, the effective radius
R
TC may be calculated using the film angle (FA) and length RR as follows:
[0084] Furthermore, the effective circumference C
TC may be calculated from the effective radius as follows:
[0085] Thereafter, equation (9) may be used to control the dispense rate in the manner disclosed
above.
[0086] In some embodiments, exit point 414 is defined at a fixed point proximate idle roller
412, e.g., proximate a tangent point at which web 416 disengages from idle roller
412 when web 416 is about half-way between the maximum and minimum film angles through
which the web passes for a particular load, or alternatively, for all expected loads
that may be wrapped by wrapping apparatus 400. Alternatively, exit point 414 may be
defined at practically any other point along the surface of idle roller 412, or even
at the center of rotation thereof. In other embodiments, however, it may be desirable
to dynamically determine the exit point based on the angle at which web 416 exits
the dispenser. Other dynamically or statically-defined exit points proximate the packaging
material dispenser may be used in other embodiments consistent with the invention.
[0087] As previously noted, film angle may be sensed in a number of manners consistent with
the invention. For example, as illustrated in Figs. 1-3, a film angle sensor 158,
258, 358 may be implemented using a distance sensor that measures distance between
the plane of the web of packaging material and the fixed location of the sensor.
[0088] Alternatively, as illustrated in Fig. 7, a film angle sensor 550 may be mechanical
in nature, and utilize a cantilevered or rockered follower arm 552 that rotates about
an axis 554 and includes a foot 556 that rides along the surface of a web 558 of packaging
material extending between an exit roller 560 on the packaging material dispenser
and the point of engagement with a load 562. Thus, for example, as the web deflects
to a position 558' as a result of rotation of load 562, arm 552 rotates to a position
552'. Sensor 550 may include, for example, a rotary encoder or other angle sensor
to determine the angle of arm 552, and thus, the corresponding film angle. It will
be appreciated that arm 552 may be spring loaded or otherwise tensioned against web
558 such that foot 556 rides along the web throughout the rotation of the load. Furthermore,
foot 556 may include rollers or a low friction surface to minimize drag on the web
of packaging material. In addition, other manners of detecting the relative position
of arm 552 and/or foot 556, e.g., a distance sensor directed at the arm, foot or other
portion of the assembly, may also be used.
[0089] As another alternative, as illustrated in Fig. 8, a film angle sensor 570 may be
implemented as a force sensor that senses force changes resulting from movement of
the web through a range of film angles. In particular, a pair of roller 572, 574 may
be provided as an exit point for a packaging material dispenser, such that a web 576
projects through the rollers 572, 574 and engages a load 578. Each roller 572, 574
may be coupled to a force sensor that measures the force applied perpendicular to
the rotational axis of each roller by web 576. Furthermore, in some embodiments, the
axle of each roller 572, 574 may be configured to move perpendicular relative to the
axis of rotation. Thus, for example, as web 576 deflects to a position 576' as a result
of rotation of load 578, a force is applied to roller 572, displacing the roller to
the position shown at 572'. It will be appreciated that the amount of force applied
is proportional to the film angle, and thus the film angle may be derived from the
force measurement.
[0090] In some embodiments, rollers 572, 574 may be mounted for linear displacement or displacement
along an arc. In other embodiments, rollers 572, 574 may not be displaced through
the application of force. In still other embodiments, only one roller may be used,
while in other embodiments, rollers 572, 574 may be replaced with low friction surfaces
over which the web passes during wrapping.
[0091] As another alternative, as illustrated in Figs. 9A-9B, an array of sensors, e.g.,
in the form of a light curtain 580, may be positioned above and/or below a web 582
of packaging material between an exit roller 584 of a packaging material dispenser
and a point of engagement with a load 586 to effective sense the position of an edge
of the packaging material. As shown in Fig. 9B, light curtain 580 may include an array
of transmitters 588 opposing an array of receivers 590, with each transmitter 588
emitting a beam such as an infrared light beam or a laser beam that is sensed by a
corresponding receiver 590. Whenever web 582 passes between a corresponding pair of
transmitter 588 and receiver 590, the beam is interrupted and thus the position of
the web may be determined. Thus, for example, when the web is positioned as shown
at 582, a receiver 590a does not detect a beam, while when the web is positioned as
shown at 582', a receiver 590b does not detect a beam.
[0092] It will be appreciated that the positions of transmitters 588 and receivers 590 may
be swapped relative to one another, and that in some embodiments, a reflective surface
may be used along one edge of the web such that the transmitters and receivers may
both be positioned along the same edge of the web. In other embodiments, a sensor
array may be implemented using an image sensor, such as in a digital camera, with
image processing techniques used to detect the position of the web in a digital image.
In still other embodiments, a laser or infrared scanner, e.g., as used in bar code
readers, may be used.
[0093] It will also be appreciated that in any of the aforementioned film angle sensor implementations,
various lighting or illumination techniques may be used to improve sensing of the
packaging material, and in some embodiments, the packaging material may be tinted
or colored to improve recognition. Other modifications will be apparent to one of
ordinary skill in the art having the benefit of the instant disclosure.
Effective Circumference Determined Based on Calculated Film Angle
[0094] As noted above, in other embodiments of the invention, the film angle, and thus the
effective radius and effective circumference used in a wrap speed model consistent
with the invention, may be calculated or derived from other measurements and/or input
data.
[0095] Fig. 10, for example, illustrates a representative plot of the length of a web of
packaging material from an exit point of a packaging material dispenser to a point
of engagement with an example load throughout a full relative rotation between the
packaging material dispenser and the load. Put another way, consider a fixed load
600 and a packaging material dispenser that rotates about load 600 with an exit point
that traverses a circular path 602 having a center of rotation 604. Each line represents
the length of the web of packaging material at a particular angular relationship between
the packaging material dispenser and the load, and for the purposes of this example,
the load is assumed to be 40 x 40 inches and offset from the center of rotation.
[0096] Fig. 11, in turn, illustrates a graph of the distances of the lines at a plurality
of angles in a full relative rotation of 360 degrees, and it has been found that the
graph accurately depicts the effective consumption rate of the load throughout the
relative rotation. Moreover, as has been discussed above in connection with equations
(1)-(11), the dimensions of the tangent circle (e.g., the effective circumference
and the effective radius), the film angle and the film speed are all geometrically
related to this effective consumption speed.
[0097] As shown in Figs. 12A-12C, for example, effective circumference, film angle, and
idle roller speed (which is proportional to film speed) are respectively graphed over
a plurality of angles for an example load with a 48 inch length, a 40 inch width,
and an offset of 4 inches in length and 0 inches in width. It can be seen that all
three parameters follow the same general profile (though film speed is both dampened
and delayed), and thus, each may be used to control dispense rate to match an effective
consumption rate of the load.
[0098] In some embodiments, the effective consumption rate may be determined in part based
on the dimensions and offset of the load, which may be determined using the locations
of the corners of the load. For example, as shown in Fig. 13, an example load 610
of length L and width W, and having four corners denoted C1, C2, C3 and C4, may be
considered to have four corner radials Rc1, Rc2, Rc3 and Rc4 extending from a center
of rotation 612 to each respective corner. The load has a geometric center 614 that
is offset along the length and width as represented by Lo and Wo.
[0099] The location of each corner may be defined, for example, using polar coordinates
for each of the corner radials, defining both a length (RcX, where X = 1, 2, 3, or
4) and an angle (referred to as a corner location angle, LAcX) relative to a base
angular position, such as defined at 616. Alternatively, Cartesian coordinates may
be used.
[0100] The length and the width of the load may be determined using the corner radial locations,
for example, by applying the law of cosines to the triangles formed by the corner
radials and the outer dimensions of the load. For example, with the corner radials
for corners 1 and 4 known, the length may be determined as follows:
where Ac4c1 = 360 - LAc4 + LAc1.
[0101] Alternatively, the length may be determined using the corner radials for corners
2 and 3, as follows:
where Ac2c3 = LAc3 - LAc2.
[0102] Similarly, the width of the load may be determined using either the corner radials
for corners 3 and 4, or the corner radials for corners 1 and 2:
where Ac3c4 = LAc4 - LAc3 and Ac1c2 = LAc2 - LAc1.
[0104] Furthermore, to determine the corner location angle for the corner radials, the orthogonal
distances from the center of rotation to the sides of the rectangle may be used to
define a right triangle with the corner radial as the hypotenuse. As shown in Fig.
13, for example, for corner radial Rc1, a right triangle is defined between the corner
radial and line segments 618, 620. Taking the arcsine of the ratio of segment 620
and the corner radial Rc1 gives the corner location angle LAc1:
[0105] To determine the corner location angle LAc2 for corner radial Rc2, this angle may
be considered to include LAc1 summed with the angle defined between corner radials
Rc1 and Rc2, which in turn may be considered to be defined by two sub-angles LAc2a
and LAc2b, as shown in Fig. 14, or:
[0106] LAc2a may be determined using a right triangle defined by corner radial Rc1 and line
segments 622 and 624, e.g., by taking the arcsine of the ratio of segment 622 and
corner radial Rc1:
[0107] LAc2b may be determined using a right triangle defined by corner radial Rc2 and line
segments 624 and 626, e.g., by taking the arcsine of the ratio of segment 626 and
corner radial Rc2:
[0108] For corner location angles LAc3 and LAc4, a similar summation of angles may be performed.
Thus, LAc3 = LAc2 + LAc3a + LAc3b, where:
[0109] In addition, LAc4 = LAc3 + LAc4a + LAc4b, where:
[0110] It should be noted that instead of arcsines, arccosines may be used to determine
the corner location angles. Alternatively, the corner location angles may be determined
without having to first calculate the lengths of the corner radials and/or without
having to sum together the angles from preceding corners. As shown in Fig. 13, for
example, for corner radial Rc1, a right triangle is defined between the corner radial
and line segments 618, 620, which respectively have lengths of W/2-Wo and L/2-Lo.
Taking the arctangent of the ratio of these two distances gives the corner location
angle LAc1:
[0112] Based on the locations of the corner radials, the film angle at any rotational position
of the load may be determined. For example, in one embodiment, the film angle FA may
be determined by first determining the length of a web of packaging material, e.g.,
web 630 of Fig. 15, which extends between an exit point 632 of a packaging material
dispenser and corner c1 of a load 634. Of note, in Fig. 15, the load rotates counterclockwise
relative to the dispenser.
[0113] For the first corner c1, for example, the corner film length FLc1 may be determined
using the law of cosines based upon the known rotation angle RA of the load, the corner
location angle LAc1 of corner c1, and the lengths Rr and Rc1 of the rotation radial
and the corner radial for corner c1, as follows:
where Ac1 = RA - LAc1.
[0114] Likewise, for corners c2, c3 and c4, the respective corner film lengths FLc2, FLc3
and FLc4 may be calculated as follows:
where Ac2 = RA - LAc2, Ac3 = RA - LAc4, and Ac4 = RA - LAc4.
[0115] Upon calculation of the corner film length, the law of cosines may then be used to
determine the film angle as follows:
[0117] Once the film angle is known for a given corner, the dimensions of the tangent circle,
and thus the effective consumption rate, may be determined, and equation (9) as discussed
above may be used to control the dispense rate.
[0118] It will be appreciated that in some embodiments of the invention, the dimensions
of the tangent circle may be determined without one or more of the intermediate calculations
discussed above. For example, in some embodiments, film angle does not need to be
separately calculated. As shown in Fig. 16, for example, for a given corner, a triangle
636 is defined by the rotation radial, web 630 and the corner radial, each respectively
having a length Rr, FLc1 and Rc1. The altitude of this triangle is the effective radius
of tangent circle 638. This altitude may be calculated by applying Heron's formula
to obtain the area of the triangle, and then deriving the altitude from the area formula
for a triangle (area=1/2
∗base
∗altitude), where the base in the area formula corresponds to the film length FLc1:
where s, the semiperimeter, is one half the sum of the sides, or (FLc1+Rr+Rc1)/2.
[0119] It will be appreciated that other trigonometric formulas and rules may be utilized
to derive various dimensions and angles utilized herein to determine effective consumption
rate without departing from the spirit and scope of the invention.
Load Distance
[0120] As noted above, a load distance sensor may be used to determine film angle, and thus,
effective circumference and/or effective consumption rate. In one embodiment, for
example, a load distance sensor 432, as illustrated in Fig. 5, may be oriented along
a radius from the center of rotation 408 and at a known and fixed distance from and
angular position about the center of rotation. By orienting this sensor such that
a corner passes the sensor prior to engaging the packaging material, both the length
and the contact angle of the corner radial may be determined prior to contact with
the packaging material, and used to control dispense rate through the phase of the
rotation in which the web of packaging material extends between the corner and the
exit point of the dispenser. For example, a corner typically may be identified at
a local minimum in the output of load distance sensor 432, which occurs when the corner
passes the sensor.
[0121] Alternatively, the load distance sensor may be used to determine the complete geometric
profile of the load, e.g., through an initial full revolution in which the distance
to the surface of the load is stored and used to derive the length, width and offset
of the load and/or the locations of each of the corners. In addition, given that some
loads may have varying dimensions from top to bottom, it may be desirable in some
embodiments to record the output of the load distance sensor during each revolution
for use in determining the dimensions of the load to be used for the subsequent revolution
(or for multiple subsequent revolutions).
[0122] Derivation of the corner locations (e.g., corner radials and corner location angles)
from the determined dimensions and offset of the load may then be performed in the
manner discussed above, such that an effective consumption rate and/or effective circumference/radius-based
wrap speed model may be employed to control the dispense rate during a wrapping operation.
Film Speed
[0123] Another input that may be used to determine film angle, and thus, effective circumference
and/or effective consumption rate, is film speed, e.g., the speed of idle roller 126
as sensed by sensor 150 of Fig. 1 and converted from rotational velocity to linear
velocity based on the known radius of the idle roller.
[0124] To correlate the film speed to the dimensions of the load, the amplitudes of the
local minimums and maximums of the film speed, or alternatively, the local minimums
and maximums of the rotational velocity of the idle roller, may be used. In general,
the amplitude of the peak, or maximum, speed after a corner passes approximates the
length of its corner radial, while the amplitude of the minimum speed where a corner
passes approximates the length of its contact radial, which is typically the effective
radius of the load at corner contact. The angle where the peak or maximum speed occurs
after a corner passes approximates the corner location angle where the length of the
corner radial and the effective radius are approximately equal, and the angle where
the minimum speed occurs after a corner passes approximates the contact angle for
that corner. Fig. 12C, for example, illustrates the points matching the approximate
amplitudes and angles corresponding to the corner radials Rc1, Rc2, Rc3 and Rc4 for
corners c1, c2, c3 and c4, and to the contact radials CRc1, CRc2, CRc3 and CRc4.
[0125] With reference to Fig. 17, for example, the corner radial length (Rc1) and the contact
radial length (CRc1) for corner c1 for may be determined as follows:
where FS
max is the local maximum film speed after a corner passes, FS
min is the local minimum film speed after the corner passes, and K is a constant used
to convert film speed units into length/revolution (e.g., if film speed units are
in inches/sec, K may be rotation speed in second/revolution).. It will be appreciated
that K may be determined empirically or may be calculated based upon the dimensions
and configuration of the wrapping apparatus and the sensor used to determine the film
speed.
[0127] Calculation of the corresponding values for corners c2, c3 and c4 are performed in
a similar manner. Derivation of the dimensions and offset of the load from these values
may be performed in the manner discussed above, and an effective consumption rate
and/or effective circumference/radius-based wrap speed model may be employed to control
the dispense rate during a wrapping operation based upon these values.
Load Dimensions
[0128] Yet another input that may be used to determine film angle, and thus, effective circumference
and/or effective consumption rate, is the measured or input dimensions of the load.
In some embodiments, for example, the dimensions and/or offset may be manually input
by an operator through a user interface with a wrapping apparatus. In an alternate
embodiment, the dimensions and/or offset may be stored in a database and retrieved
by the controller of the wrapping apparatus. In some embodiments, for example, where
a conveyor is used to convey loads to and from the wrapping apparatus, upstream machinery
may provide dimensions of the load to the wrapping apparatus prior to arrival, or
a bar code or other identification may be provided on the load to be read by the wrapping
apparatus and thereby enable retrieval of the dimensions based on the identification.
[0129] In still other embodiments, a light curtain or other dimensional sensor or sensor
array may be used to visually determine the dimensions and/or offset of the load.
The dimensions and offset may be determined, for example, before the load is conveyed
to the wrapping apparatus, or alternatively, after the load has been conveyed to the
wrapping apparatus, and prior to or during initiation of a wrapping operation for
the load.
[0130] Derivation of the corner locations (e.g., corner radials and corner location angles)
from the determined dimensions and offset of the load may then be performed in the
manner discussed above, such that an effective consumption rate and/or effective circumference/radius-based
wrap speed model may be employed to control the dispense rate during a wrapping operation.
Corner Rotation Angle-Based Wrapping
[0131] In some embodiments of the invention, a wrap speed model and wrap speed control utilizing
such a wrap speed model may be based at least in part on rotation angles associated
with one or more corners of a load. In this regard, a corner rotation angle may be
considered to include an angle or rotational position about a center of rotation that
is relative to or otherwise associated with a particular corner of a load. In some
embodiments, for example, a corner rotation angle may be based on a corner location
angle for a corner, and represent the angular position of a corner radial relative
to a particular base or home position. Alternatively, a corner rotation angle may
be based on a corner contact angle for an angle, representing an angle at which packaging
material first comes into contact with a corner during relative rotation between the
load and a packaging material dispenser. Given that these and other angles are geometrically
related to one another based on the geometry of the load, it will be appreciated that
a corner rotation angle consistent with the invention is not limited to only a corner
location angle or a corner contact angle, and that other angles relative to or otherwise
associated with a corner may be used in the alternative.
[0132] As will become more apparent below, corner rotation angles may be used in connection
with wrap speed control in a number of manners consistent with the invention. For
example, in some embodiments corner rotation angles may be used to determine to what
corner the packaging material is currently engaging, and thus, what corner is driving
the effective consumption rate of the load. In this regard, in some embodiments, multiple
corners may be tracked to enable a determination to be made as to when to switch from
a current corner to a next corner when controlling dispense rate. In other embodiments,
corner rotation angles may be used to anticipate corner contacts and perform controlled
interventions, and in still other embodiments, corner rotation angles may be used
in the performance of rotational data shifts.
[0133] In some embodiments of the invention, for example, it may be desirable to determine
and/or predict or anticipate a rotation angle such as a contact angle of each corner
of a load during the relative rotation. In some embodiments, a contact angle, representing
the rotational position of the load when the packaging material first contacts a particular
corner, may be determined for each corner.
[0134] The contact angles may be sensed using various sensors discussed above, or determined
via calculation based on the dimensions/offset of the load and/or corner locations.
In addition, the contact angles may be used to effectively determine what corner is
driving the wrap speed model, and thus, what corner profile should be used to control
dispense rate.
[0135] Fig. 18, for example, illustrates a graph of the ideal dispense rates for corner
profiles 650a, 650b, 650c and 650d for the four corners of the same load depicted
in Figs. 12A-12C. It should be noted that the intersections of these profiles, at
652a, 652b and 652c, represent the contact angles when the packaging material, which
is being driven by one corner, contacts the next corner such that the next corner
begins to drive the desired dispense rate of the packaging material. Comparing Fig.
18 to Figs. 12A-12B it may be seen that the effective circumference and film angle
track these profiles and contact angles, and as such, in some embodiments, the contact
angles may be sensed using a number of the aforementioned sensors.
[0136] For example, each of a film angle sensor and a load distance sensor will reach a
local minimum proximate each contact angle. Thus, a wrap speed control may be configured
to switch from one corner to a next corner based on the anticipated rotational position
of each corner as sensed in either of these manners. As another example, an effective
radius or effective circumference may be calculated based upon a current corner and
a next corner, such that the contact angle is determined at the angle where the effective
radius/effective circumference of the next corner becomes larger than that of the
current corner.
[0137] Alternatively, the contact angles may be calculated based on the dimensions of the
load. As shown in Fig. 19A, for example, the contact angle (CAc1) for corner c1 represents
the angle where corner c1 intersects the plane between the previous corner c4 and
exit point 632. The contact angle may be calculated, for example, using the length
and location angles of the corner radials for the corner at issue and the immediately
preceding corner in the rotation (here, Rc1, Rc4, LAc1 and LAc4) and the length of
the rotation radial (Rr), which are illustrated in Fig. 19B.
[0138] Fig. 19C illustrates two values, Ac4c1 and Lc4c1, that may be calculated from the
aforementioned values. Ac4c1 is the angle between the corner location angles for corners
c1 and c4:
[0139] Lc4c1 is the distance between the corners, which in this instance is equal to the
length of the load:
[0141] Next, as shown in Fig. 19E, the contact angle CAc1 for corner c1 may be isolated
from the known and calculated angles:
[0142] For corners c2, c3 and c4, a similar analysis may be performed, except that since
the location angle preceding corner will be smaller than the current corner (unlike
the case with corner c1, where corner c4 has a larger location angle), the determination
of the angle between the current and preceding corners in equation (41), and the determination
of the contact angle in equation (47), do not need to take into account negative angles.
Thus, for example, for corner c2:
[0143] The other calculations discussed above for equations (42)-(46), however, are essentially
the same.
[0144] The contact angle of each corner may therefore be determined and used to select which
corner is currently "driving" the dispensing process, based upon the known angular
relationship of the load to the packaging material dispenser at any given time. In
addition, the contact angle may be used to anticipate a contact of the packaging material
with a corner so that, for example, a controlled intervention may be performed.
Wrapping Operation
[0145] Returning briefly to Fig. 6, implementation of a wrap speed model 500 using any of
the aforementioned techniques may be used to wrap packaging material around a load
during relative rotation between the load and a packaging material dispenser. During
a typical wrapping operation, a clamping device, e.g., as known in the art, is used
to position a leading edge of the packaging material on the load such that when relative
rotation between the load and the packaging material dispenser is initiated, the packaging
material will be dispensed from the packaging material dispenser and wrapped around
the load. In addition, where prestretching is used, the packaging material is stretched
prior to being conveyed to the load. Thereafter, wrapping continues while a lift assembly
controls the height of the packaging material so that the packaging material is wrapped
in a spiral manner around the load from the base of the load to the top. Multiple
layers of packaging material may be wrapped around the load over multiple passes to
increase containment force, and once the desired amount of packaging material is dispensed,
the packaging material is severed to complete the wrap.
[0146] Based upon the various techniques discussed above, the manner in which the dispense
rate is controlled during this operation may vary in different embodiments. For example,
in some embodiments, an initial revolution may be performed to determine the dimensions
of the load, such that corner locations may be determined prior to wrapping and then
wrapping may commence using these predetermine corner locations to drive the dispenser
rate based on a calculated effective consumption rate. In other embodiments, no initial
revolution may be performed, and either dimensions of the load as input or retrieved
from a database may be used to drive the dispenser rate based on the effective consumption
rate. In still other embodiments, sensed film angle, sensed film speed, sensed load
distance, etc. may be used to calculate effective consumption rate as soon as wrapping
is commenced.
[0147] Furthermore, as noted above, some loads may not have a consistent length and width
from top to bottom. Loads may include different layers of objects or containers having
different lengths and/or widths, and some layers may be offset relative to other layers.
As such, it may be desirable in some embodiments to recalculate load dimensions and/or
corner locations for different elevations on a load. For example, in some embodiments,
as each corner approaches and/or passes the packaging material dispenser, the location
of the corner may be recalculated and used for the next pass of the same corner. In
some embodiments, load dimensions calculated during one full revolution may be used
for the next full revolution, such that as the lift assembly changes the elevation
of the packaging material dispenser, the load dimensions are dynamically updated based
on the dimensions sensed at a particular elevation of the packaging material dispenser.
[0148] One example wrap speed control process 660, which is based on concurrent tracking
of multiple corner locations, is shown in Fig. 20. In this process, two corners are
effectively tracked at all times. The first is referred to herein as the "current
corner," which is the corner that is currently driving the dispensing process, in
terms of being the corner at which the packaging material is engaging the load. The
second is referred to herein as the "next corner," which is the immediately subsequent
corner that will engage the load after further revolution of the load relative to
the packaging material dispenser. These corners are concurrently tracked such that
each contact between the packaging material and a new corner can be anticipated or
detected, thereby allowing the dispense rate to be controlled appropriately based
upon the location of the new corner.
[0149] One manner of anticipating or detecting a corner contact is based on applying a wrap
speed model based on the locations of two corners, and comparing the results. Thus,
in blocks 662 and 664, the effective consumption rate is determined based on the location
of the current corner and based on the location of the next corner. A corner contact
occurs when the effective consumption rate based on the next corner exceeds that of
the current corner, as discussed above in connection with Fig. 18, and as such, block
666 compares these two effective consumption rates. So long as the corner contact
has not yet occurred, and the effective consumption rate of the current corner is
used to control the dispense rate, block 666 passes control to block 668 to control
the dispense rate based on the effective consumption rate for the current corner.
Control then returns to block 662 to continue tracking the current and next corners.
[0150] If, however, the effective consumption rate based on the next corner exceeds that
of the current corner, a corner contact has occurred, and block 666 passes control
to block 670 to update the current corner to what was previously the next corner.
Thus, for example, if the current corner is corner c1 and the next corner is c2, and
the effective consumption rate based on corner c2 exceeds that calculated based on
corner c1, c2 becomes the new current corner, and consequently, corner c3 becomes
the new next corner. Control then passes to block 668 to control the dispense rate
based on the new current corner.
[0151] As noted above in connection with Fig. 18, the effective circumference, effective
radius, film angle, and film speed all track the effective consumption rate. As such,
blocks 662, 664 and 666 may alternatively track the corners based on calculating any
of these values and compare the results to determine a corner contact.
[0152] Alternatively, as illustrated by process680 of Fig. 21, a wrap speed control process
may be performed by tracking the corner contact angle for a next corner in block 682,
determining the current rotational position of the load in block 684 (e.g., using
an angle sensor such as angle sensor 152 of Fig. 1), and then determining in block
686 whether the corner contact angle for the next corner has been reached (i.e., where
the rotational position of the load matches the corner contact angle). So long as
the corner contact has not yet occurred, block 686 passes control to block 688 to
control the dispense rate based on the effective consumption rate calculated from
the location of the current corner, and control returns to block 682. Otherwise, if
contact has occurred, block 686 passes control to block 690 to set the current corner
to the next corner, such that when control is passed to block 688, the next corner,
now the new current corner, is used to determine the dispense rate.
Controlled Interventions
[0153] It will be appreciated that, even when a desired wrap speed model may be determined
for a load, various system lags typically exist in any wrapping apparatus that can
make it difficult to match the desired wrap speed. From an electronic standpoint,
delays due to the response times of sensors and drive motors, communication delays,
and computational delays in a controller will necessarily introduce some amount of
lag. Moreover, from a physical or mechanical standpoint, sensors may have delays in
determining a sensed value and drive motors, such as the motor(s) used to drive a
packaging dispenser, as well as the other rotating components in the packaging material,
typically have rotational inertia to overcome whenever the dispense rate is changed.
Furthermore, packaging material typically has some degree of elasticity even after
prestretching, so some lag will exist before changes in dispense rate propagate through
the web of packaging material. In addition, mechanical sources of fluctuation, such
as film slippage on idle rollers, out of round rollers and bearings, imperfect mechanical
linkages, flywheel effects of downstream non-driven rollers, also exist.
[0154] As a result of many of these issues, it may be desirable to implement controlled
interventions in some embodiments. Within the context of the invention, an intervention
is an operation that controls the dispense rate in a predetermined manner based on
a predetermined intervention criteria. In some embodiments, an intervention is an
operation that modifies the dispense rate relative to a predicted demand or a dispense
rate that has been calculated by a particular wrap model, e.g., a wrap speed model
based on effective circumference or effective consumption rate. An intervention may
also be an operation that modifies the dispense rate relative to another type of wrap
model and/or a wrap model based on another type of control input, e.g., a wrap force
model based on wrap force or packaging material tension as monitored by a load cell.
[0155] For example, Fig. 22 illustrates an example process 700 that selectively applies
one or more controlled interventions at predetermined times or rotational positions
relative to a corner contact. In this process, a corner contact angle for a next corner
is determined, e.g., predicted or anticipated (block 702) and one or more intervention
criteria are determined (block 704). An intervention criteria may include, for example,
an absolute rotational position (e.g., at 75 degrees) or a relative rotational position
(e.g., 10 degrees before or after corner contact), and may be relative to a corner
contact angle, a corner location angle, or another calculated angle. Alternatively,
an intervention criteria may be based on absolute or relative times or distances (e.g.,
100 ms before or after corner contact). In some embodiments, separate start and end
criteria may be specified (e.g., start 10 degrees before corner contact and stop at
contact), while in other embodiments, a start criteria may be coupled with a duration
such that an intervention is applied for a fixed duration of angles, times or distances
after being initiated.
[0156] Next, in block 706, the rotational position of the load is determined, e.g., in terms
of an angle, a time or distance within a revolution of the load relative to the packaging
material dispenser. Block 708 then determines whether an intervention criteria has
been met. If not, block 708 passes control to block 710 to control the dispense rate
without the use of an intervention, e.g., in any of the manners discussed above based
on effective circumference or effective consumption rate. If the criteria for an intervention
is met, however, block 708 passes control to block 712 to instead control dispense
rate based on the intervention.
[0157] It will be appreciated that in different embodiments, a number of interventions may
be performed. For example, it may be desirable to reduce the dispense rate below a
predicted demand as calculated by a wrap speed model a few degrees prior to a corner
contact to build wrap force as the corner approaches, e.g., as shown in Fig. 23A.
In some embodiments, for example, the dispense rate may be advanced a few degrees
so that the wrap speed model is time shifted to decrease the dispense rate sooner
than would otherwise be performed. In other embodiments, the dispense rate may be
set to the dispense rate to be used at the corner contact, only a few degrees early.
In still other embodiments, the wrap speed model may be scaled such that the dispense
rate is decreased by a certain percentage from that of the wrap speed model as the
corner approaches, e.g., as shown in Fig. 23B.
[0158] Likewise, it may also be desirable to increase the dispense rate above a predicted
demand as calculated by a wrap speed model a few degrees after a corner contact to
allow the peak force after the corner to be reduced. Similar to prior to the corner
contact, the wrap speed model may be delayed a few degrees or scaled to otherwise
increase the dispense rate above that calculated from the wrap speed model. In other
embodiments, the dispense rate may be set to hold the dispense rate used at the corner
contact for a few extra degrees. It may also be desirable in some embodiments to contact
a corner at dispense rate that is a factor less than the dispense rate calculated
from the wrap speed model to create a force spike at the corner contact.
[0159] As another alternative, as shown in Fig. 23C, it may be desirable to step between
minimum and maximum dispense rates calculated based on a wrap speed model at predetermined
times relative to the corners. The dispense rate calculated from an example wrap speed
model is illustrated at 720, and as shown at 722, interventions may be applied to
essentially switch between the maximum calculated dispense rate for a corner at or
a few degrees after the contact with that corner, and then switch to the minimum calculated
dispense rate for that corner a few degrees after the peak has passed.
[0160] In general an intervention may be used to effectively modify a wrap speed model to
improve performance, e.g., by improving containment force and/or reducing the risk
of breakage. In many instances, some interventions may be selected to increase force
immediately prior to a corner and increase containment force, while other interventions
may be selected to relieve force immediately after a corner contact to reduce breakage
risk and otherwise ensure that wrap forces built up in the corner are not wasted after
the corner contact has occurred. It will be appreciated that multiple interventions
may be applied or combined, and that different interventions may be applied to different
corners or at different times in the wrapping operation, and that interventions may
be tailored for particular corners based on the dimensions of the load. In addition,
it will be appreciated that interventions may be applied to wrap models other than
effective circumference-based wrap speed models, e.g., wrap force models.
Rotational Data Shift
[0161] In addition to or in lieu of a controlled intervention, it may also be desired to
account for system lags through the use of a rotational shift of the data utilized
by a wrap speed model. As discussed above, electrical and physical delays in sensors,
drive motors, control circuitry and even the packaging material necessarily introduce
a system lag, such that a desired dispense rate at a particular rotational position
of the load, as calculated by a wrap speed model, will not occur at the load until
after some duration of time or further angular rotation.
[0162] To address this issue, a rotational shift typically may be applied to the sensed
data used by the wrap speed model or to the calculated dimensions or position of the
load, which in either case has the net effect of advancing the wrap speed model to
an earlier point in time or rotational position such that the actual dispense rate
at the load will more closely line up with that calculated by the wrap speed model,
thereby aligning the phase of the profile of the actual dispense rate with that of
the desired dispense rate calculated by the wrap speed model.
[0163] In some embodiments, the system lag from which the rotational shift may be calculated
may be a fixed value determined empirically for a particular wrapping apparatus. In
other embodiments, the system lag may have both fixed and variable components, and
as such, may be derived based upon one or more operating conditions of the wrapping
apparatus. For example, a controller will typically have a fairly repeatable electronic
delay associated with computational and communication costs, which may be assumed
in many instances to be a fixed delay. In contrast, the rotational inertia of packaging
material dispenser components, different packaging material thicknesses and compositions,
and the wrapping speed (e.g., in terms of revolutions per minute of the load) may
contribute variable delays depending upon the current operating condition of a wrapping
apparatus. As such, in some embodiments, the system lag may be empirically determined
or may be calculated as a function of one or more operating characteristics.
[0164] As shown in Fig. 24A, for example, a calculated wrap speed model may calculate a
desired dispense rate having a profile 714, yet due to system lag, if that profile
is applied to control the dispense rate of a packaging material dispenser, the actual
profile 716a may be delayed relative to the desired profile 714. By accounting for
system lag and providing a rotational shift such that the dispense rate is applied
based on a dispense rate control signal having a rotationally shifted profile 718
as shown in Fig. 24B, the resulting actual profile 716b more closely approximates
the desired profile 714.
[0165] A rotational shift may be performed, for example, in the manner illustrated by process
720 of Fig. 25, which is similar to process 680 of Fig. 21. Process 720 may begin
in block 722 by determining the geometry of the load, e.g., the dimensions, offset
and/or corner locations. In one embodiment, for example, an initial revolution of
the load may be performed, while in another embodiment, the dimensions of the load
may be input or retrieved from a database. Alternatively, the geometry may be determined
during wrapping via any of the sensed inputs discussed above.
[0166] Next, in block 724, the system lag is determined. In some embodiments, the system
lag may be a fixed value, and in other embodiments, the system lag may be a variable
value that may be calculated, for example, based on wrapping speed. In still other
embodiments, system lag may be determined dynamically during wrapping, e.g., so that
a system lag determined during one revolution is used to perform a rotational shift
in one or more subsequent revolutions.
[0167] Next, process 720 proceeds by tracking the corner contact angle for a next corner
in block 726, determining the current rotational position of the load in block 728
(e.g., using an angle sensor such as angle sensor 152 of Fig. 1), and then performing
a rotational shift of either the corner contact angle (by subtracting from the calculated
corner contact angle) or the current rotational position of the load (by adding to
the sensed rotational position) to offset the system lag in block 730. Thereafter,
block 732 determines whether the corner contact angle for the next corner has been
reached, but in this case, the comparison incorporates the rotational shift such that
the corner contact is detected earlier than would otherwise occur based on the wrap
speed model.
[0168] So long as the corner contact has not yet been detected, block 732 passes control
to block 734 to control the dispense rate based on the effective consumption rate
calculated from the location of the current corner, and control returns to block 726.
In addition, based upon the rotational shift applied in block 730, the wrap speed
model is effectively advanced to offset the system lag.
[0169] Returning to block 732, if corner contact has been detected, control is passed to
block 736 to set the current corner to the next corner, such that when control is
passed to block 734, the next corner, now the new current corner, is used to determine
the dispense rate, again with the rotational shift accounted for in the wrap speed
model.
[0170] Rotational shifts may also be applied in other manners consistent with the invention.
For example, through positioning of a sensor such as a load distance sensor at an
earlier rotational position, e.g., shifted a few degrees in advance of a base or home
position, the sensor data may be treated as if it were collected at the base or home
position to apply a rotational shift to the model.
Conclusion
[0171] Embodiments of the invention may be used, for example, to increase containment force
applied to a load by packaging material, and moreover, reduce fluctuations in wrap
force that may occur during a wrapping operation, particularly at higher wrapping
speeds. By reducing force fluctuations, the difference between the maximum applied
wrap forces, which might otherwise cause packaging material breakages, and the minimum
applied wrap forces, which affect the overall containment force that may be achieved,
may be reduced, enabling improved containment forces to be achieved with reduced risk
of breakages. In many instances, reducing the force fluctuations will permit higher
containment forces to be obtained with thinner packaging material, with increased
prestretch and/or with less packaging material (e.g., through the use of fewer layers).
In many instances, containment forces are more consistent across all corners and sides
of the load.
[0172] It is also contemplated that any sequence or combination of the above-described methods
may be performed during the wrapping of one or more loads. For example, while wrapping
a load, one method may be performed, whereas while wrapping another load, another
method may be performed. Additionally or alternatively, while wrapping a single load,
two or more of the three methods may be performed. One method may be performed during
one portion of the wrapping cycle, and another method may be performed during another
portion of the wrapping cycle. Additionally or alternatively, one load may be wrapped
using a first combination of methods, while another load may be wrapped using a second
combination of methods (e.g., a different combination of methods, and/or a different
sequence of methods).
[0173] Other embodiments will be apparent to those skilled in the art from consideration
of the specification and practice of the present invention. It is intended that the
specification and examples be considered as exemplary only, with a true scope being
defined by the following claims.