TECHNICAL FIELD
[0001] The present invention relates to a method of guiding a web at a substantially constant
speed. In particular the present invention relates to operations in the manufacturing
of absorbent articles such as unwinding web rolls that are wound, in particular spirally
wound web rolls, and removing web from said rolls. The invention also relates to an
apparatus for the execution of said method.
BACKGROUND
[0002] Webs for the production of hygiene products like diapers or incontinence pants usually
consist of flexible materials and are transported loosely in containers or as web
rolls wound around an axis. A special technical problem lies with unwinding the web
rolls in regard to removing the web material from the container for further processing.
[0003] Indeed, because of the soft nature of the web material used to manufacture absorbent
article, it is common for a web roll to become out-of-round. Not only the soft nature
of the web material, but also the physical size of the web rolls, the length of time
during which the web rolls are stored, and the fact that roll grabbers used to transport
web rolls grab them about their circumference can contribute to this problem. As a
result, by the time many web rolls are placed on an unwinding station they have changed
from the desired cylindrical shape to an out-of-round, or deformed shape.
[0004] In extreme cases, the web rolls can become oblong or generally egg-shaped. But, even
when the web roll is are only slightly out-of-round, there are considerable problems.
With a perfectly round web roll, the feed rate of a web material coming off of the
rotating web roll can be equal to the driving speed of a surface driven web roll and
thus can remain constant.
[0005] However, with a deformed web roll the feed rate varies from the driving speed of
a surface drive web roll depending upon the radius at the web take-off point at any
moment in time. It will be appreciated that for obtaining the best production yield,
it is desirable that the rotational speed of the web roll remains substantially constant.
[0006] A common approach to manage these issues is to implement a tension control systems
at the end of the unwinding station. However, this solution corresponds to a system
which is reacting to a change of tension and then adapts the rotational speed of the
web roll but it is not adapted for as deformed web roll where the take-off point radius
is constantly changing. To some extent, this change is unaccounted for by typical
tension control systems.
[0007] The invention thereto aims to provide a method and apparatus which ensures an efficient
and reliable bonding of the film material onto the absorbent material.
SUMMARY OF THE INVENTION
[0008] The present invention provides an apparatus for unwinding a web material comprising
:
- a. an output shaft for unwinding a web roll of web material;
- b. a driving system for actuating said output shaft and unwinding the web roll, said
driving system comprising an actuator and optionally a transmission mechanism;
- c. a measuring device configured to measure the radius of the web roll;
- d. a controller unit configured to receive signals from the measuring device, process
said data and emit at least one signal to the driving system for maintaining or modifying
the unwinding speed of said web roll.
[0009] According to the invention, the measuring device is arranged at a distance from a
web-take off point where the web material leaves the web roll.
[0010] According to the invention, by arranging the measuring device at a distance from
the point where the web material leaves the web roll ensures that the system has enough
calculation time so that the control unit can take into account other factors such
as an operator's inputs, a motor speed feedback, or additional control feedbacks.
[0011] According to an embodiment, the angular distance between the measuring device and
the web take-off point in reference to the web roll and its centre and following the
unwinding direction, is greater than about 10°, preferably greater than about 45°,
more preferably greater than about 90°. Said angular distance can be greater than
about 180°.
[0012] According to an embodiment, the measuring device is arranged on the diametrical opposite
side of the web take off point in reference to the web roll.
[0013] According to an embodiment, the measuring device is configured to measure the radius
of the web roll with a rate of 1 measurement point per every 3 to 30 ms.
[0014] According to an embodiment, the apparatus comprises a stationary secondary guiding
roll that is configured to rotate around an axis, said web material being conveyed
from the web take-off point to the secondary guiding roll.
[0015] According to an embodiment, the apparatus further comprises a velocity sensor configured
to measure the velocity of the web material and emit this measurement an output signal
to the control unit.
[0016] According to an embodiment, the velocity sensor is arranged downstream, relative
to the conveying of the web material, of the web take-off point, preferably downstream
of the secondary guiding roll.
[0017] According to an embodiment, the apparatus further comprises a rotational position
and speed determining device configured to measure the rotational speed and position
at the web roll and emit this measurement as an output signal to the control unit.
[0018] According to an embodiment, the apparatus further comprises an image detection device
configured to determine if a print mark is well positioned on the web roll and emit
this measurement as an output signal to the control unit.
[0019] According to an embodiment, wherein the control unit is configured to receive signals
from the measuring device, and at least one of the signal emitted by the velocity
sensor and/or image detection device and/or rotational position and speed determining
device, process said data and emit at least one signal to the driving system for maintaining
or modifying the unwinding speed of said web roll.
[0020] All of these embodiments mentioned above can be taken individually or in combination.
[0021] The invention also pertains to a method for unwinding a web material preferably using
an apparatus as described above, said method comprises the following steps:
- a) measuring radius R of the web roll using the measurement device and emitting this
measurement as an output signal to the control unit;
- b) processing this measurement in combination with other input signals such as an
operator's input and/or the current actuating speed of the actuator;
- c) calculating the rotational speed required based on said measurements;
- d) emitting a signal to the driving system such as an ideal speed reference signal
and/or a corrected speed reference signal;
- e) adjusting the speed of the drive system to either accelerate, decelerate or stop
the web roll depending on the situation.
[0022] According to an embodiment, in the processing step b, the control unit further processes
at least one signal emitted by the velocity sensor and/or image detection device and/or
rotational position and speed determining device.
[0023] All of these embodiments mentioned above can be taken individually or in combination.
[0024] Further embodiments are described below and in the claims.
DESCRIPTION OF FIGURES
[0025] The drawings and figures are illustrative in nature and not intended to limit the
subject matter defined by the claims. The following detailed description can be understood
when read in conjunction with the following drawings, where like structure is indicated
with like reference numerals in which:
FIG. 1 illustrates a schematic representation of the apparatus according to the invention;
FIG. 2 illustrates a profile or side view of a portion of FIG. 1;
FIG. 3A to 3C illustrates different embodiments of the web roll; and
FIG. 4 illustrates a profile or side view of a portion of FIG. 1;
FIG. 5 and 6 illustrates a profile or side view of a portion of FIG. 1 according to another embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The present invention concerns an improved apparatus and method for unwinding a web
material.
[0027] Unless otherwise defined, all terms used in disclosing the invention, including technical
and scientific terms, have the meaning as commonly understood by one of ordinary skill
in the art to which this invention belongs. By means of further guidance, term definitions
are included to better appreciate the teaching of the present invention.
[0028] As used herein, the following terms have the following meanings:
"A", "an", and "the" as used herein refers to both singular and plural referents unless
the context clearly dictates otherwise. By way of example, "a compartment" refers
to one or more than one compartment.
"About" as used herein referring to a measurable value such as a parameter, an amount,
a temporal duration, and the like, is meant to encompass variations of +/-20% or less,
preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/-1%
or less, and still more preferably +/-0.1% or less of and from the specified value,
in so far such variations are appropriate to perform in the disclosed invention. However,
it is to be understood that the value to which the modifier "about" refers is itself
also specifically disclosed.
"Angular distance" refers herein as the angle between two points in reference to the
centre of the web roll.
"Comprise," "comprising," and "comprises" and "comprised of" as used herein are synonymous
with "include", "including", "includes" or "contain", "containing", "contains" and
are inclusive or open-ended terms that specifies the presence of what follows e.g.
component and do not exclude or preclude the presence of additional, non-recited components,
features, element, members, steps, known in the art or disclosed therein.
[0029] The term "nonwoven web material" means a sheet material having a structure of individual
fibers or threads which are interlaid, but not in a regular manner such as occurs
with knitting or weaving processes. Nonwoven fabrics or webs have been formed from
many processes such as for example, meltblowing processes, spunbonding processes,
and bonded carded web processes.
[0030] The recitation of numerical ranges by endpoints includes all numbers and fractions
subsumed within that range, as well as the recited endpoints.
[0031] In the following detailed description of the preferred embodiments, reference is
made to the accompanying drawings that form a part hereof, and in which are shown
by way of illustration only of specific embodiments in which the invention may be
practiced. It is to be understood that other embodiments may be utilised and structural
or logical changes may be made without departing from the scope of the present invention.
The following detailed description, therefore, is not to be taken in a limiting sense,
and the scope of the present invention is defined by the appended claims.
[0032] In the manufacture of web material products including paper products such as paper
towels, bath tissue, facial tissue, and the like, the web material which is to be
converted into such products is initially manufactured on large web roll and placed
on unwind stands. The embodiments described in detail below provide non-limiting examples
of an apparatus for reducing feed rate variations in a web material when unwinding
a web roll to transport the web material from the web roll at a web take-off point.
In particular, the embodiments described below provide an apparatus which takes into
account any out-of-round characteristics of the web roll and makes appropriate adjustments
to reduce web feed rate variations.
[0033] With regard to these non-limiting examples, the described apparatus makes it possible
to operate effectively and efficiently an unwind stand as part of a paper converting
operation at maximum operating speed without encountering any significant and/or damaging
deviations in the tension of the web material as it leaves an out-of-round web roll
at the web take-off point.
[0034] FIG. 1 illustrates an apparatus 10 according to one embodiment, for reducing feed
rate variations in a web material 12 when unwinding a web roll 14 of said web material
12 around a central, longitudinal or rotational axis A. The web roll 14 can be carried
by a support 16 or it can be carried by an output shaft 26 exclusively. The apparatus
10 is configured to enable that the web material 12 unwinds from the web roll 14 at
a fixed web take-off point 18 at constant speed. The web material 12 can for example
be a nonwoven web material.
[0035] The apparatus 10 includes a driving system comprising an actuator 22, or motor, optionally
coupled with a transmission mechanism 24, such as a gearbox 24 and an output shaft
26, or any other adequate transmission mechanism, for imparting a rotational movement
to the web roll 14. The driving system, through the actuator 22 and the transmission
mechanism 24, rotates the web roll 14 in a counter-clockwise direction B as illustrated
in Fig.1. Alternatively, the driving system can be configured to rotate the web roll
14 in a clockwise direction.
[0036] The apparatus 10 further comprises a measuring device 28 for measuring the radius
of the web roll 14. The measuring device 28 is adapted to measure the radius of the
web roll 14 in a recuring sequence and send this data as output signals 30 to a control
unit 32 which can process this information and generate and emit both an ideal speed
reference signal 34 and/or a corrected speed reference signal 36 for the drive system,
more specifically for the actuator 22 so that it can modify and adjust, if needed,
the rotational speed,
i.e. unwinding, speed, of the web roll 14. The measuring device 28 is configured to measure
the radius of the parent 14 at a high rate preferably such as 300 measurement points
per second, or a measurement point every 30 ms to 3 ms. In particular, the ideal speed
reference signal 34 can be based upon an operator's input 35 and the corrected speed
reference signal 36 is generated for adjusting the driving speed of the drive system
to a corrected driving speed. The operator's input 35 can be entered on and recorded
by the actuator 22 or directly by the control unit 32.
[0037] To adjust the driving speed of the driving mechanism 22,24, the control unit 32 is
associated with: i) the measuring device 28 for receiving the measured radius for
the web roll 14 (output signal 30) and ii) the driving mechanism for receiving any
operator's input and/or the current actuating speed (output signal 35) for controlling
the speed of the driving mechanism based upon the ideal speed reference signal 34
and the corrected speed reference signal 36.
[0038] Fig. 2 schematically illustrates the web roll 14 from a profile view. The web material
12 is spirally wound around a central axis A forming the web roll 14 and leaves the
web roll 14,
i.e. unwinds, at a web take-off point 18 and is conveyed here toward a secondary guiding
roll 38 that is arranged at a fixed distance from the web roll 14. The secondary guiding
roll 38 may be stationary and can also optionally be configured to rotate around an
axis C, also the centre of said roll 38. In this case, the secondary guiding roll
38 rotates preferably in a free-wheel manner or it can be rotatably actuated at a
constant speed.
[0039] The web material 12 can be conveyed after the secondary guiding roll 38 toward different
elements depending on the manufacturing process line. For example, the web material
12 can be conveyed to a third guiding roll 41 as illustrated in Fig.2, or the web
material can be guided toward a cutting station comprising a roller with a knife and
a roller acting as an anvil, or toward an embossing station comprising a roller with
protrusions and a roller acting as an anvil.
[0040] The difference in shape between each web roll 14, i.e. if a web roll does not have
a perfectly circular profile, the effect of the out-of-round of the web roll 14, causes
the web take-off point 18 to fluctuate in time and the angle
α, corresponding to the angle between the lowest point of the roll 14 at any given
time and the take-off point 18 (see Fig. 2), also varies depending on time. Fig. 3A,
3B and 3C illustrate a web roll 14 with an oval, or egg-shaped, profile or with a
deformation caused by a mishandle. We can see that the angle
α" is greater than the angle
α which is itself greater than the angle
α'. The angle
α‴ can be greater or lesser than the other
α angles depending on the degree of deformation. It also makes sense that with such
elliptic profile, the angular speed for different points of the web roll 14 is not
homogenous as opposed to a perfectly circular web roll 14.
[0041] The object of the invention is to pro-actively anticipate these differences in angular
speeds and exploit the apparatus 10 as described above to calculate the value of the
angle
α for each point of the web roll 14 to deduce the web-take-off point 18 to accelerate,
decelerate or stop (in case of emergencies) the web roll 14 to ensure that the web
material 12 effectively leaves the roll 14 at the same web take-off point 18. In other
terms, the apparatus 10 ensures that the web take-off point 18 is more or less stationary
and that the angle
α stays substantially constant (up to a more or less difference of 10°), or in other
words that the web material 12 always departs from the roll at the same location (same
radial configuration). By leaving the roll 14 at the same point, the tension in the
web material 12 is constant for the rest of the process line and it possible to use
more fragile material that are prone to rupture when using a conventional system (with
tension detector). Indeed if the web material 12 is conveyed and maintained at a constant
tension, between 5 and 20 N, without having any fluctuation in the tension (more or
less 5 N), a fragile web material can go through the process line without having a
risk of rupturing.
[0042] To effectively calculate the effective web take-off point 18, the apparatus 10 exploits
the following equations (1) and (2) :

with D corresponding to the distance between the centres of the web roll 14 and the
secondary guiding roller 38 (e.g. the distance AC in Fig. 2); R representing the radius
of the web roll 14 at the web take-off point 18, r representing the radius of the
secondary guiding roller 38 and M representing the distance between the web take-off
point 18 and the point where the web material 12 first contacts the secondary guiding
roller 38.
[0043] Therefore by exploiting these equations, it is possible to anticipate the web take-off
point 18 and adjust the speed of the web roll 14 so that the web material 12 always
leaves the web roll at the same point in space to ensure a constant tension of the
web material 12. In other terms, r and
D are constants (the secondary guiding roll is arranged stationary at a fixed location
in the process line and has a given radius), the system by measuring R at a given
time can determine the angle
α and the web take-off point 18. By repeating the measurements (for example 300 measurements
points per second), it is possible to have a complete assessment of the values of
R for every points of the roll 14 and thereby have a complete prediction and control
of the web material unwinding.
[0044] The measuring device 28 is arranged at a distance from the take-off point 18. In
other words, in reference to the centre of the web roll 14, the measuring device 28
is arranged at an angular distance from the web take-off point 18.
[0045] The angle defined by the measuring device 28, the centre of the roll 14 and the web
take-off point 18 is different than 0°. As illustrated in Fig. 1, in relation to the
centre of the web roll 14 and following the unwinding direction, the angle, or the
angular distance, between the measuring device 28 and the web take-off point 18 is
greater than about 10°, preferably greater than about 45°, more preferably greater
than about 90° (π/2), even more preferably greater than about 180° (π). As illustrated
in figure 2, said angular distance is equal to 180°+
α. In reference to the web roll 14, the measuring device is preferably arranged on
the diametrical opposite side of the web take-off point 18. This ensures that the
system has enough calculation time so that the control unit can take into account
other factors such as operator's inputs 35, motor speed feedback 36, additional control
feedbacks 40 that will be explained hereunder.
[0046] The apparatus 10 can also comprise a velocity sensor 42 configured to measure the
velocity of the web material 12. The velocity sensor 42 acts as a control system to
ensure that the web material is conveyed at a constant speed and thus is maintained
at a constant tension. The velocity sensor 42 is preferably placed downstream, relative
to the conveying of the web material 12, of the secondary conveying roller 38 to measure
the speed of the web material 12 once it has passed the secondary conveying roller
38. The velocity sensor 42 can also be placed between the web roll 14 and the secondary
conveying roller 38 to measure the speed of the web material between these two elements.
The velocity sensor 42 is configured to emit an output signal 46 to the control unit
32 so that it can maintain or adjust the speed of the drive system 22,24 to either
accelerate, decelerate or stop the web roll 14 depending on the situation.
[0047] The apparatus 10 may further comprise a rotational position and speed determining
device 48, called rotational speed sensor 48 henceforth, such as a rotary or shaft
optical encoder, resolver, a synchro, a rotary variable differential transformer (RVTD),
any similar device capable of determining rotational speed and position, can be used
to determine the rotational speed and position at the web roll 14. This device can
also be associated to the control unit 32 by sending an output signal 50 to indicate
the rotational speed of the web roll 14 at a given point. The output signal 50 emitted
by the rotational speed sensor 48 can be considered as an additional control feedback
40 so that the control unit 32 can adjust the speed of the drive system 22,24 to either
accelerate, decelerate or stop the web roll 14 depending on the situation.
[0048] The rotational speed sensor 48 can be arranged at a distance from the measuring device
28 as illustrated in Fig. 1. Preferably, the rotational speed sensor 48 is arranged
to measure the rotational speed of the web roll 14 at an angular position of the roll
14 located between the point of measurement of the measuring device 28 and the web
take-off point 18. In Fig. 1, the rotational speed sensor 48 is arranged at a 90°
(or π/2) angle in reference to the centre of the web roll 14 from the measuring device
28. The rotational speed sensor 48 can be arranged at other angular position, such
as to define an angle between 5° to 180° in reference to the centre of the web roll
14 and the measuring device 28.
[0049] According to an alternative the rotational speed sensor 48 is arranged between the
web-take-off point 18 and the measuring device 28 in reference to the unwinding direction
of the web material.
[0050] According to an embodiment, the measuring device 28 and the rotation speed sensor
48 are combined, or associated, or juxtaposed, to have only one point of measurement
where the radius and the speed of the web roll are determined simultaneously.
[0051] For sake of clarity, the previous content is schematically illustrated and summarized
hereunder. Considering Fig. 4, the web roll 14 once supported by the stand 16 rotates
here in a counter-clockwise direction B around an axis A that also corresponds to
the centre of the web roll 14 (as illustrated in Fig. 4), in other words, the point
A represents the centre of the web roll 14. The web roll 14, being as substantially
circular cylindric element, extends angularly over an angle E having a value of 360°
or 2π, or in other words, the web roll 14 extends in a full revolution and has a substantially
circular profile.
[0052] As illustrated in the drawings and defined herein, the angular position Y is the
point of measurement carried out by the measuring device 28 and is the point of reference
0° (or 2π), or the start of the revolution. The web roll 14 rotates and the web material
12 at the point Y rotates to reach the angular position Z. The angular position Z
is the point of measurement carried out by the rotation speed sensor 48. As illustrated
here, the angle defined by the angular positions Z and Y in relation to the centre
A is 90° (or π /2), or

is equal to 90°. As seen previously, this angle

is comprised in a range between 0° (if the two sensors are combined) and 180° for
example. The web roll 14 further rotates and the web material 12 at the point Z rotates
to reach the angular position X. The angular position X is the web take-off point
18. Given that the secondary guiding roll 38 is at the right end side of the web roll
14, as illustrated in Fig. 1, the angular position X is located on a bottom-right
end side of the web roll 14, once the web roll 14 is placed on the support 16. In
other words the angle

is greater than 180° (or π). The angle
α is the difference between the angle

and 180°, or in other words,

or α (in radians) =

.
[0053] By assessing the radius R of the web roll at position Y, the control unit 32, taking
into consideration additional factors or inputs such as the velocity of the web material
12, the current speed of the web roll at position Z, the operator's inputs for example
setting a production pace, is able to properly adjust the speed of the web roll 14
so that the web material 12 at position Y reaches the position Z at the desired time
and maintain angle α constant. In other words, the control unit 32 has sufficient
time to take into consideration other factors and adapt the speed of the roll 14 to
have a constant angle α and thus to maintain a constant tension and velocity of the
web material 12.
[0054] According to an embodiment, the apparatus can further comprise an image detection
device 52, such as an ultrasound laser that, can be used to determine if print marks
such as drawings, logos or any ornamental elements, are well positioned on the web
material 12 and web roll 14. This device can also be associated to the control unit
32 by sending an output signal 54 to indicate the correct positioning of the print
marks of the web roll 14 at a given point. The output signal 50 emitted by the rotational
speed sensor 48 can be considered as an additional control feedback 40 so that the
control unit 32 can adjust the speed of the drive system 22,24 to either accelerate,
decelerate or stop the web roll 14 depending on the situation.
[0055] The image detection device 52 can be arranged at a distance from the measuring device
28 as illustrated in Fig. 1. In Fig. 1, the image detection device 52 is arranged
between the measuring device 28 and the rotational speed sensor 48 in reference to
the unwinding of the web material 12. The image detection device 52 can be arranged
at other angular positions such as between the rotational speed sensor 48 and the
web take-off point 18 or between the web-take-off point 18 and the measuring device
28 in reference to the unwinding direction of the web material.
[0056] The apparatus 10 can also comprise a tension control system such as a tension sensor
43 configured to measure the tension of the web material 12. The tension sensor 43
acts as a control system to ensure that the web material is conveyed at a constant
tension. The tension sensor 43 is preferably placed downstream, relative to the conveying
of the web material 12, of the secondary conveying roller 38 to measure the tension
of the web material 12 once it has passed the secondary conveying roller 38. The tension
sensor 43 can also be placed between the web roll 14 and the secondary conveying roller
38 to measure the tension of the web material between these two elements. The tension
sensor 43 is configured to emit an output signal 47 to the control unit 32 so that
it can maintain or adjust the speed of the drive system 22,24 to either accelerate,
decelerate or stop the web roll 14 depending on the situation. The tension sensor
43 can separate or combined to the velocity sensor 42.
[0057] To sum up, the additional control feedbacks 40 can comprise an operator's input 35
and/or the motor speed feedback 36 and/or the output signal 50 emitted by the rotational
speed sensor 48 and/or the output signal 46 emitted by the velocity sensor 42 and/or
the output signal 54 emitted by the image detection device 52 and/or the output signal
47 emitted by the tension sensor 43.
[0058] The control unit 32 preferably comprises a proportional-integral controller, or more
preferably a proportional-integral-derivative controller, as a control loop mechanism
employing where the additional control feedbacks 40 listed above are the process variables.
For example, if the signal emitted by the tension sensor 43 is the process variable
then the tension is the parameter variable that will be used to define if the error
between the measured value Tension (t) and the desired set point (5 N) needs a correction
or not and adapting the speed of the roll taking into account the measured radius
R. Of course other additional control feedbacks 40 can be used as the process variable
and there can be more than one additional control feedback 40 used as the process
variable.
[0059] According to an embodiment, the measuring device 28 and the image detection device
52 are combined, or associated, or juxtaposed, to have only one point of measurement
where the radius and the positioning of the print marks are determined simultaneously.
[0060] The invention also pertains to a method for unwinding a web material using such an
apparatus comprising the following steps:
- a) measuring radius R of the web roll 14 at a given time (t) using the measurement
device 28 and emitting this measurement as an output signal 30 to the control unit
32;
- b) processing this measurement in combination with other input signals 35 such as
an operator's input and/or the current actuating speed of the actuator 22;
- c) calculating the rotational speed required based on said measurements for the roll
to reach the desired the web-take point 18 at the desired time;
- d) emitting a signal 34,36 to the driving system 22,24 such as an ideal speed reference
signal 34 and/or a corrected speed reference signal 36;
- e) adjusting the speed of the drive system 22,24 to either accelerate, decelerate
or stop the web roll 14 depending on the situation.
[0061] This method can be carried out in a loop based on a fixed or variable time cycle,
for example one measurement every 500 microseconds, or one measurement every 300 microseconds
for three minutes then one measurement every second.
[0062] According to an embodiment, in the processing step b, the control unit 32 further
processes at least one signal 40, 46, 50, 54 emitted by the velocity sensor 42 and/or
image detection device 52 and/or rotational position and speed determining device
48.
[0063] In this method, the additional control feedbacks 40 can comprise an operator's input
35 and/or the motor speed feedback 36 and/or the output signal 50 emitted by the rotational
speed sensor 48 and/or the output signal 46 emitted by the velocity sensor 42 and/or
the output signal 54 emitted by the image detection device 52.
[0064] In some unfortunate cases, the roll can be too deformed and the apparatus and method
mentioned hereabove may put too much strain on the motor device when accelerating
too fast or decelerating too slow to ensure that the roll reaches the proper web-take
off point. In such cases, it is preferable to add a web-take off device 56 as illustrated
in Fig.5 and Fig.6. Said device comprises a mobile component 58 comprising a reciprocating
mechanism such as a piston, spring, pneumatic cylinder or similar reversible mechanism,
the mobile component can also comprise shock absorbing means. The device 56 also comprises
an arm 60, or rod or cantilever, linked at one end to the mobile component 58. The
device 56 comprises a roller 62 arranged at the second end of the arm 60,
i.e. at the end that is opposite to where the arm 60 is linked to the mobile component
58. The roller 62 ensures that the web material 12 always passes on its outer surface
thereby forcing the web material 12 to pass by a substantially stationary point which
can be considered as the web take off point 18 in these unfortunate cases. The measure
device 28 is at an angular distance from the roller 64 and thus the web take off point.
The roller 62 can be displaced when the web roll 14 comes into contact with said roller
62, the roller 62 thereby displaces the arm and the mobile component can absorb the
choc or displacement and move the arm and roller 62 back to its original position
once the web roll 14 doesn't abut against the roller 62. This mobile component can
also be associated to the control unit 32 by sending an output signal to indicate
the displacement of the roller 62 at a given point. The output signal emitted by the
mobile component 58 can be considered as an additional control feedback 40 and can
be taken into consideration in the method described above.
[0065] The embodiments described above can be taken alone or in combination. The apparatus
can comprise a measuring device 28 in combination or not with a rotational speed sensor
48 and/or with an image detection device 52 and/or with a velocity sensor 42 and/or
a tension sensor 43.
1. Apparatus (10) for unwinding a web material (12) comprising :
a. an output shaft (26) for unwinding a web roll (14) of web material (12);
b. a driving system (22,24) for actuating said output shaft (26) and unwinding the
web roll (14), said driving system (22) comprising an actuator (22) and optionally
a transmission mechanism (24);
c. a measuring device (28) configured to measure the radius of the web roll (14);
d. a controller unit (32) configured to receive signals (30) from the measuring device
(28), process said data and emit at least one signal (34,36) to the driving system
(22,24) for maintaining or modifying the unwinding speed of said web roll (14);
characterized in that the measuring device (28) is arranged at a distance from a web-take off point (18)
where the web material (12) leaves the web roll (14).
2. Apparatus according to claim 1, wherein the angular distance between the measuring
device (28) and the web take-off point (18) in reference to the web roll (14) and
its center and following the unwinding direction, is greater than about 10°, preferably
greater than about 45°, more preferably greater than about 90°.
3. Apparatus according to claim 2, wherein the measuring device (28) is arranged on the
diametrical opposite side of the web take off point (18) in reference to the web roll
(14).
4. Apparatus according to any of the claims 1 to 3, wherein the measuring device (28)
is configured to measure the radius of the web roll (14) with a rate of 1 measurement
point per every 3 to 30 ms.
5. Apparatus according to any of the claims 1 to 4, wherein the apparatus comprises a
stationary secondary guiding roll (38) that is configured to rotate around an axis
(C), said web material (12) being conveyed from the web take-off point (18) to the
secondary guiding roll (38).
6. Apparatus according to any of the claims 1 to 5, wherein the apparatus further comprises
a velocity sensor (42) configured to measure the velocity of the web material (12)
and emit this measurement an output signal (46) to the control unit (32).
7. Apparatus according to claim 6, wherein the velocity sensor (42) is arranged downstream,
relative to the conveying of the web material (12), of the web take-off point (18),
preferably downstream of the secondary guiding roll (38).
8. Apparatus according to any of the claims 1 to 7, wherein the apparatus further comprises
a rotational position and speed determining device (48) configured to measure the
rotational speed and position at the web roll (14) and emit this measurement as an
output signal (50) to the control unit (32).
9. Apparatus according to any of the claims 1 to 8, wherein the apparatus further comprises
an image detection device (52) configured to determine if a print mark is well positioned
on the web roll (14) and emit this measurement as an output signal (54) to the control
unit (32).
10. Apparatus according to any of the claims 1 to 9, wherein the apparatus further comprises
a tension sensor (43) configured to measure the tension of the web material (12) and
emit this measurement as an output signal (47) to the control unit (32).
11. Apparatus according to any of the claims 6 to 10, wherein the control unit (32) is
configured to receive signals (30) from the measuring device (28), and at least one
of the signal (40, 46, 47, 50, 54) emitted by the velocity sensor (42) and/or tension
sensor (43) and/or image detection device (52) and/or rotational position and speed
determining device (48), process said data and emit at least one signal (34,36) to
the driving system (22,24) for maintaining or modifying the unwinding speed of said
web roll (14).
12. Method for unwinding a web material preferably using an apparatus according to any
of the claims 1 to 11,
characterized in that said method comprises the following steps:
a. measuring radius R of the web roll (14) at a given time (t) using the measurement
device (28) and emitting this measurement as an output signal (30) to the control
unit (32);
b. processing this measurement in combination with other input signals (35) such as
an operator's input and/or the current actuating speed of the actuator (22);
c. calculating the rotational speed required based on said measurements;
d. emitting a signal (34,36) to the driving system (22,24) such as an ideal speed
reference signal (34) and/or a corrected speed reference signal (36);
e. adjusting the speed of the drive system (22,24) to either accelerate, decelerate
or stop the web roll (14) depending on the situation.
13. Method according to claim 12, wherein in the processing step b, the control unit (32)
further processes at least one signal (40, 46, 50, 54) emitted by the velocity sensor
(42) and/or image detection device (52) and/or rotational position and speed determining
device (48) and/or tension sensor (43).