Field of the Invention
[0001] The present invention relates to a strip tension control apparatus for controlling
the tension of a strip by threading the strip between a transportation roll and a
movable transportation roll and moving the movable transportation roll. The apparatus
is adapted for maintaining a given strip tension in a process line for rolling or
the like.
Description of the Related Art
[0002] In order to secure reliable quality of a strip in a process line for metal or nonmetal
rolling or the like, it is necessary, in general, to perform a continuous operation
in the central section of the line while transporting the strip at a fixed speed and
applying a tension to the strip.
[0003] In the supply- or delivery-side section of the process line, limited-length strips
are wound off or up in the form of coils. At breaks in the coil jointing or at the
time of recoiler change, each strip is accelerated, decelerated or stopped supply-
or delivery-side section.
[0004] In order to secure continuous operation in the central section despite such transitory
acceleration, deceleration or stopping in the supply- or delivery-side section, the
process line is provided with a looper.
[0005] When the looper operates as the strips are decelerated, stopped, or accelerated in
the supply- or delivery-side section, however, a variation in tension may be transmitted
from the supply- or delivery-side section to the strips in the continuously running
central section. This transmission of the variation in tension adversely effects the
quality of the strip in the central section and causes the strips to meander, thus
possibly breaking the strips.
[0006] To cope with this, a tension control apparatus has been proposed in Japanese Patent
Laid-Open No. 1-308347. The prior art apparatus includes a dancer roll disposed in
the central section, whereby the transmission of the variation in tension is deterred
to apply a fixed tension to the strips.
[0007] The prior art tension control apparatus having the dancer roll is constructed in
the manner shown in Fig. 4. In Fig. 4, a strip 1 is passed from one transportation
roll 2 to the other transportation roll 2 via a dancer roll 3. The dancer roll 3 is
linked to a wind-up drum 4 and a counterweight 6 by means of a wire 5, and the drum
4 is connected to a motor 8 through a speed reducer 7. The motor 8 causes the speed
reducer 7 to rotate the wind-up drum 4, thereby moving the dancer roll 3 up and down.
The tension of the strip 1 is controlled by regulating the torque of the motor. Guide
means 9 is used to fix the direction of action of the dancer roll 3.
[0008] However, the conventional prior art tension control apparatus having the dancer roll
is helpless against a drastic external variation in tension of the strip in the central
section. In operation, high mechanical resistances are produced between the dancer
roll 3 and the guide means 9 and between the wind-up drum 4 and the wire 5.
[0009] The dancer roll 3 is subject to a high moment of inertia during the operation caused
by the action of the wind-up roll 4, the motor means 8, and the speed reducer 7, as
shown in Fig. 4.
[0010] A backlash of the speed reducer results in a delay in operation or a new variation
in tension attributable to the action of the dancer roll.
[0011] Furthermore, the conventional tension control apparatus having the dancer roll is
quite helpless against a fine variation in tension due to its great structural mechanical
loss, backlash in its mechanical system, and high mechanical resistance. Thus, the
prior art does not permit high- accuracy tension control in response to variations
in tension in a continuous operation of the type described above.
[0012] From EP-A-161223, there is known a device for regulating the draught of the strip
in a hot rolling mill. Said device includes an arm pivotable about an axis parallel
to the strip and perpendicular to the direction of strip movement. One end of the
arm is held in contact with the strip and carries a sensor which outputs electrical
couple signals indicative of the couple applied by the strip to the arm about the
pivot axis of said arm. A processing and control unit is connected to the couple sensor
and to sensors for sensing the angular position of the arm to generate an error signal
in dependence on the difference between said couple signal and a reference couple
signal. Furthermore, drive means are arranged for changing the position of said arm
in dependence on the error signal generated by the control and processing unit.
[0013] Modern steel sheets for use in automobiles and the like are expected to respond quickly
to a fine variation in tension, since they are made of very-low-carbon steel, have
a small sectional area, and are transported at a super-high speed, as high as 1,000
m/min, as they are processed. There is, therefore, a demonstrated need for advancement
in the art of continuous operation strip tension control.
[0014] The present invention has been contrived to solve the problems not addressed by the
prior art. A first object of the invention is to provide a strip tension control apparatus
capable of controlling the tension of a strip with high responsiveness and high accuracy
despite its drastic external variation.
[0015] A second object of the present invention is to provide a strip tension control apparatus
capable of controlling the tension of a strip with good responsiveness and satisfactory
accuracy by means of a small-capacity motor, despite a fine variation in the strip
tension.
[0016] The above objects of the present invention are achieved by the subject matter of
claim 1.
[0017] Preferred embodiments and further improvements of the inventive apparatus for controlling
the tension of a strip are defined in the depending subclaims.
[0018] The torque of the arm is thus controlled by means of the arm driving motor, and the
tension control is effected by turning the movable transportation roll through the
medium of the arm. In contrast with the case of the conventional prior art dancer
roll, neither the wind-up drum nor the wire is required, so that the mechanical resistance
in the present invention is very small. Moreover, the absence of the wind-up drum
and the like in the present invention minimizes the moment of inertia of the machine
axis system. Furthermore, since the arm driving motor is connected directly to the
supporting shaft there is no possibility of undergoing a delay in operation or a new
variation in tension, which may be caused by backlash when a speed reducer is used.
[0019] Despite its drastic variation externally introduced into the central section of a
process line or the like, the tension of the strip can be controlled with high responsiveness
and high accuracy. Thus, very effective tension control which is beyond the capability
of the conventional prior art dancer roll can be enjoyed.
[0020] According to the present invention, the torque is generated in the arm by the following
method, as well as by connecting the arm driving motor directly to the supporting
shaft.
[0021] The supporting shaft is provided with a counterweight which is adjustable in position
with respect to a direction perpendicular to the supporting shaft, and the torque
around the supporting shaft is generated in the arm by means of the counterweight.
The torque to be generated in the arm can be controlled through the control of the
motor torque and the adjustment of the counterweight position.
[0022] The angle of swing motion of the arm is detected by means of the angle sensor, and
the tension of the strip is detected by means of the tension sensor. Based on the
detected angle and the detected tension, the output of the arm driving motor and the
position of the counterweight are controlled to control the torque to be generated
in the arm, whereby the tension of the strip is controlled at the target tension.
[0023] Accordingly, the torque control by means of the arm driving motor and the torque
control through the counterweight position control can be effected in combination
with each other.
[0024] Thus, the tension of the strip can be controlled with good responsiveness and satisfactory
accuracy. In consequence, very effective tension control which is beyond the capability
of the conventional prior art dancer roll can be enjoyed such that a fine variation
of the strip tension can be eliminated with high accuracy.
[0025] Since the torque control by means of the arm driving motor and the torque control
through the counterweight position control is effected in combination with each other,
the torque required of the motor can be reduced.
[0026] For example, an arm torque to be somewhat fixedly applied depending on the target
tension can be obtained through the adjustment of the counterweight position, while
an arm torque which rises quickly in response to the variation in tension can be obtained
through the torque control by means of the arm driving motor. Accordingly, the motor
must only bear the torque corresponding to the variation in tension, so that the motor
requires only a small capacity.
[0027] Thus, the arm driving motor and a drive unit may be kept to a minimum resulting in
an economical advantage. For the initialization of a torque which makes up for the
torque of the motor, moreover, reasonable tension control can be ensured such that
the torque control is effected through the counterweight position control and the
motor can be used for dynamic torque control. In consequence, high- accuracy tension
control can be enjoyed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028]
Fig. 1 is a block diagram showing an outline of a first embodiment of the present
invention, with parts in a layout diagram;
Fig. 2 is a block diagram showing an outline of a second embodiment of the present
invention, with parts in a layout diagram;
Fig. 3 is a perspective view illustrating the principal part of the present invention
shown in Fig. 2; and
Fig. 4 is a layout diagram showing an arrangement of a conventional prior art tension
control apparatus using a dancer roll.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Preferred embodiments of the present invention will now be described in detail with
reference to the drawings.
[0030] A first embodiment of the present invention is a strip tension control apparatus
constructed in the manner shown in Fig. 1.
[0031] In the strip tension control apparatus of the present invention, as shown in Fig.
1, a strip 1 is threaded between transportation rolls 2 and a movable transportation
roll 10. The apparatus generally comprises a movable transportation roll 10, an arm
11, the supporting shaft 12, an arm driving motor 14, a tension sensor 15, an arm
angle sensor 16, a tension control section 30, bridle rolls 20, a bridle roll driving
motor 21, and a strip speed control section 40. The tension of the strip 1 is controlled
through a pivoting movement of the roll 10 about the shaft 12.
[0032] The arm 11, one end of which is supported by the supporting shaft 12, is adapted
to swing around the shaft 12, and the movable transportation roll 10 is connected
to the other end. The supporting shaft 12 is pivotally supported by bearing means
13. Both axial ends of the roll 10 are supported by the arm 11.
[0033] The arm driving motor 14, which is coaxially connected to the supporting shaft 12,
is used to generate a torque around the supporting shaft 12, thereby applying a tension
to the strip 1.
[0034] The arm angle sensor 16 is used to detect the angle of swing motion of the arm 11
or the rotational angle of the arm driving motor 14. A detected angle θ is entered
in the tension control section 30 and the strip speed control section 40.
[0035] The tension sensor 15, which detects the tension of the strip 1, is located very
close to the transportation rolls 2. The tension control section 30 includes a tension
controller 31, a dead load compensating arithmetic unit 32, and a tension angle compensating
arithmetic unit 33. The tension controller 31 feeds back and comparatively calculates
the detected tension T from the tension sensor 15 with respect to the target tension
Tr, and delivers the torque control command T1. The dead load compensating arithmetic
unit 32 is used to compensate the moment of inertia for the dead load of the movable
transportation roll 10 and the arm 11 in accordance with the detected angle θ from
the angle sensor 16. The tension angle compensating arithmetic unit 33 is used to
compensate (output torque compensation) a change of the relationship between the strip
tension and the output torque of the arm driving motor 14 in accordance with the angle
of the arm 11.
[0036] The torque control command T1 is compensated by the respective outputs of the arithmetic
units 32 and 33 to become a compensatory torque command T1', which is entered in a
current controller 34.
[0037] A current sensor 17 is provided for detecting the current of the motor 14 and feeding
it back to the compensatory torque command T1'. The torque command T1' or current
command fed back in this manner is entered in the current controller 34. The current
controller 34 is used to enter a command for controlling the input current (torque)
of the motor 14 in a motor driver 18 in response to the input current command.
[0038] As an example, the dead load compensating arithmetic unit 32 may carry out dead load
compensation in the following.
If the dead load of the movable transportation roll 10, the arm 11, the distance between
its center of gravity and a supporting point, and the angle of displacement of the
arm 11 from its horizontal position (at angle of 0°) are W, Lo, and θ, respectively,
a torque compensation value Tqs for the dead load is given by
![](https://data.epo.org/publication-server/image?imagePath=2001/44/DOC/EPNWB2/EP92112605NWB2/imgb0001)
[0039] The torque for the dead load is compensated by adding the torque compensation value
Tqs to the tension command T1.
[0040] As an example, the tension angle compensating arithmetic unit 33 may carry out output
torque compensation in the following manner.
[0041] If the strip tension and the distance between the arm 11 and the supporting shaft
12 are To and Lr, respectively, an output torque compensation value Tqt for the compensation
of the output torque based on the angle θ is given by
![](https://data.epo.org/publication-server/image?imagePath=2001/44/DOC/EPNWB2/EP92112605NWB2/imgb0002)
[0042] The output torque is compensated by adding the output torque compensation value Tqt
to the tension command.
[0043] The strip speed control section 40 controls the transportation speed of the strip
1 so that it is adjusted to a target speed Vr, and controls the angle θ of the arm
11 for a target angle Ar.
[0044] The speed control section 40 includes an angle controller 41, a dead band generator
42, and a speed controller 43. The angle controller 41 compares the target angle Ar
and the detected angle θ, and delivers speed modification commands for correcting
the angle of the arm 11. The dead band generator 42 supplies the speed controller
43 with a speed modification command, among others, of which a fine transient variation
of angle is cut off. The speed controller 43 controls the speed of the bridle roll
driving motor 21, and hence, the rotational speed of the bridle rolls 20 in response
to the corrected speed modification command thereby adjusting the transportation speed
of the strip so that the angle of the arm is fixed.
[0045] The dead band generator 42 serves to remove a fine transient variation of angle in
a speed modification signal for angle correction, since any transient signal variation
is harmful.
[0046] The following is a description of the operation of the apparatus of the first embodiment.
In the tension control apparatus shown in Fig. 1, the strip 1 is windingly fed through
the bridle rolls 20, threaded between the one transportation roll 2, the movable transportation
roll 10, the other transportation roll 2, and then delivered to a subsequent stage
of flow. During this process, the tension sensor 15 detects the tension T of the strip
1, and the angle sensor 16 detects the angle θ of the arm 11 fitted with the roll
10, to its horizontal position. The detected tension T and the detected angle θ are
entered in the tension control section 30, and at the same time the target tension
Tr is set in the control section 30. The detected tension T is fed back to the target
tension Tr, whereupon the torque control command T1 is obtained.
[0047] Meanwhile, the detected angle θ is entered in the dead load compensating arithmetic
unit 32 and the tension angle compensating arithmetic unit 33, whereupon the units
32 and 33 calculate the torque compensation value Tqs for the dead load and the output
torque compensation value Tqt of the tension according to equations (1) and (2). These
compensation values are added to the tension command T1 so that the command T1 is
compensated to become the compensatory torque command T1'.
[0048] The compensatory torque command T1' is entered as a torque command value, that is,
a current command value, in the current controller 34. In response to this torque
command T1', the current controller 34 controls the motor driver 18 thereby regulating
the torque of the arm driving motor 14, and hence, the tension of the strip 1. In
this case, the motor current detected by means of the current sensor 17 is fed back
to the compensatory torque command T1', and entered in the current controller 34.
In response to this torque command T1', the current controller 34 controls the current
supply from the motor driver 18 to the arm driving motor 14, thereby regulating the
motor current so that the torque of the motor 14 is adjusted to the command value
T1'.
[0049] In order to correct the angle by comparing the angle θ with the predetermined target
angle Ar, the speed controller 43 delivers the speed modification command for the
line speed Vr. In this case, the fine transient angle variation is removed by means
of the dead band generator 42 to prevent a hindrance.
[0050] Thereafter, the speed correction signal is added to the target line speed Vr and
is entered as a speed command in the speed controller 43. In response to the input
speed command, the speed controller 43 controls the bridle roll driving motor 21,
thereby adjusting the transportation speed of the strip and the angle θ of the arm
11 to the target speed Vr and the target angle Ar, respectively.
[0051] Table 1 shows results of comparison between the strip tension control apparatus of
the present embodiment and the conventional prior art tension control apparatus using
the dancer roll.
Table 1
No. |
Items |
Prior Art |
First Embodiment |
Remarks |
1 |
GD2 (Machine axis) |
Great |
Small |
Approx. 1/2 of prior art |
2 |
Mechanical loss |
Great |
Small |
Prior art level: about 50 kg*1 Embodiment: about 2 kg*2 |
3 |
Backlash |
Some |
None |
Due to direct connection of motor |
*1: In strip tension equivalent |
*2: Frictional torque of bearing means only |
[0052] In this case, compared factors include moment of inertia GD
2, mechanical loss, and backlash. The moment of inertia of the apparatus of the present
embodiment is about half that of the conventional apparatus. The mechanical loss of
the apparatus of the first embodiment is about 2 kg in terms of strip tension, as
compared with about 50 kg for the conventional apparatus. This is because the apparatus
of the present embodiment involves only the frictional torque of the bearing means
of the supporting shaft whereas the conventional apparatus is subject to a mechanical
loss of the up-and-down motion mechanism for the dancer roll.
[0053] Although the conventional apparatus is subject to backlash, the apparatus of the
first embodiment is not. This is because the motor is connected directly to the arm
supporting shaft.
[0054] A second embodiment of the present invention will now be described.
[0055] The second embodiment is a strip tension control apparatus constructed in the manner
shown in Fig. 3. As shown in Fig. 3, this strip tension control apparatus, which is
constructed substantially in the same manner as the apparatus of the first embodiment,
further comprises a counterweight 50, a counterweight position shifting motor 51,
and a counterweight position sensor 52.
[0056] The counterweight 50 is arranged on an arm 11 for movement in the longitudinal direction
of the arm (or at right angles to a supporting shaft 12). A torque generated in the
arm 11 is controlled by adjusting the longitudinal position of the counterweight 50.
The counterweight 50 is moved by driving the counterweight shifting motor 51. The
position of the counterweight 50 is detected by means of the counterweight position
sensor 52, and is entered in a tension control section 30 (dead load compensating
arithmetic unit 32 in the section 30).
[0057] More specifically, the tension control section 30 includes a tension controller 31,
the dead load compensating arithmetic unit 32, a tension angle compensating arithmetic
unit 33, and a counterweight position setter 54. The tension controller 31 feeds back
and comparatively calculates a detected tension T with respect to a target tension
Tr, and delivers a torque control command T1. The dead load compensating arithmetic
unit 32 is used to compensate the moment of inertia for the dead load of a movable
transportation roll 10 and the arm 11 in accordance with a detected angle θ from an
angle sensor 16. The tension angle compensating arithmetic unit 33 is used to compensate
(output torque compensation) a change of the relationship between the strip tension
and the output torque of an arm driving motor 14 in accordance with the angle of the
arm 11. The counterweight position setter 54 is used to set the position of the counterweight
50 in accordance with the target tension Tr.
[0058] In response to the set target tension Tr, the counterweight position setter 54 calculates
the position St of the counterweight 50 and applies a signal indicative of this position
St to a counterweight drive section 53. The calculation of the counterweight position
St will be described in detail later.
[0059] In response to the input position signal, the counterweight drive section 53 drives
the counterweight position shifting motor 51 to move the counterweight 50 so that
the counterweight 50 is located in the position set by means of the setter 54.
[0060] The speed control section 40 includes an angle controller 41 and a speed controller
43. The angle controller 41 compares a target angle Ar and the detected angle 0, and
delivers a speed modification command for correcting the angle of the arm 11. The
speed controller 43 controls the speed of the bridle roll driving motor 21, and hence,
the rotational speed of the bridle rolls 20 in response to the delivered speed modification
command thereby adjusting the transportation speed of the strip so that the angle
of the arm is fixed.
[0061] For other parts, the second embodiment is arranged in the same manner as the first
embodiment, so that like reference numerals are used to designate the same parts throughout
the drawings.
[0062] The following is a description of some processes of operation which differentiate
the second embodiment from the first embodiment. The target tension Tr is entered
in the counterweight position setter 54, whereupon the setter 54 calculates the position
St of the counterweight 50 in accordance with the input target tension Tr, and sets
it in the counterweight drive section 53. When the target tension is set, or when
the set target tension is changed, the counterweight position is set in the following
manner.
[0063] If the strip tension is T, a torque Tq required for the counterweight shifting motor
51 is given by
![](https://data.epo.org/publication-server/image?imagePath=2001/44/DOC/EPNWB2/EP92112605NWB2/imgb0003)
where Lr is the distance between the central axis of the movable transportation roll
10 and the supporting shaft 12, Lf is the distance between the center of gravity of
the arm 11 and the shaft 12, Lm is the distance between the center of gravity of the
counterweight shifting motor 51 (including the sensor and the like) and the shaft
12, Wr is the weight of the roll 10, Ww is the weight of the counterweight 50, Wf
is the weight of the arm 11, and Wm is the weight of the counterweight shifting motor
51 (including the sensor).
[0064] In the second embodiment, as shown in Figs. 2 and 3, the counterweight shifting motor
51 is located on the opposite side of the supporting shaft 12 with respect to the
movable transportation roll 10, so that a torque Wm · St on the arm 11, which is based
on the weight Wm of the motor 51, acts in the same direction as the tension of the
strip on the arm 11 as indicated by the first term of equation (3).
[0065] If the torque of the arm driving motor 14 and the target tension are Ctq and Tref,
respectively, the counterweight position St, based on equation (3), is given by
![](https://data.epo.org/publication-server/image?imagePath=2001/44/DOC/EPNWB2/EP92112605NWB2/imgb0004)
[0066] The movable range (between the maximum and minimum values of the position St) for
the counterweight 50 should be established by setting the maximum and minimum values
of the necessary target tension Tref for operation at economical values which ensure
minimized moment of inertia and required performance in consideration of the torque
Ctq of the motor 14 and other constants in equation (4).
[0067] After the movable range for the counterweight 50 is established in this manner, the
counterweight position St is determined so that the counterweight 50 is situated as
close to the supporting shaft 12 of the arm 11 as possible within a range permitted
by the torque CTq of the motor 14. Accordingly, the moment of inertia is lowered so
that tension control can be effected with high sensitivity.
[0068] After the counterweight position St is determined in this manner, the counterweight
50 is moved to the determined position St to obtain the target tension Tref when the
time comes for the tension setting or set tension change.
[0069] In doing this, the counterweight 50 is moved from its stop position to the position
St with a certain speed pattern. Thus, the target value Tref of the strip tension
cannot be attained immediately when the time comes for the tension setting or set
tension change, so that the tension control is subject to delay.
[0070] In order to eliminate this control delay, the position of the counterweight 50 is
first detected by means of the sensor 52 and fed back to the tension control section
30 whereby the torque Tq of the motor 14 for the target tension value Tref of equation
(3) is dynamically calculated. Then, the calculated torque Tq is entered in the current
controller 34 so that the torque Tq is applied to the arm 11 by means of the arm driving
motor 14.
[0071] Thus, the delay of the tension control of the counterweight 50 is compensated so
that the tension of the strip 1 can be controlled for the target tension Tref without
a delay in the timing for tension setting or set tension change.
[0072] In the second embodiment, the counterweight 50 is arranged for movement on the arm
11 so that it is adjustable in position with respect to a direction perpendicular
to the supporting shaft 12. According to this embodiment, however, the counterweight
may be arranged on any suitable means other than the arm which is movable at right
angles to the supporting shaft.
[0073] According to the present invention, as described herein, the tension of the strip
can be controlled with high responsiveness and high accuracy despite its drastic variation
externally introduced into the central section or the like. Since the counterweight
is provided on the supporting shaft, moreover, the strip tension can be controlled
with good responsiveness and satisfactory accuracy by means of the small-capacity
motor, despite a fine variation in the strip tension. In setting the strip tension
or changing the set tension, furthermore, the tension can be adjusted to the desired
target value. Thus, very effective tension control which is beyond the capability
of the conventional dancer roll can be enjoyed. An investigation made by the inventor
hereof indicated that the apparatus of the present invention can effect high-accuracy
tension control such that the variation in the strip tension can be reduced to about
1/3 as compared with the conventional case.