Note: Descriptions are shown in the official language in which they were submitted.
2074~34
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RA~GROUND OF THE lNV ~:N'l lON
Field of the Invention
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
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.
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.
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.
When the looper operates as the strips are
decelerated, stopped, or accelerated in the supply- or
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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 i.n the central section and
causes the strips to meander, thus possibly breaking the
strips.
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.
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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.
A backlash of the speed reducer provided in the prior
art results in a delay in operation or a new variation in
tension attributable to the action of the dancer roll.
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.
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.
OBJECTS AND SUMMARY OF THE INVENTION
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.
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.
According to the present invention, there is provided
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an apparatus for controlling tension in a continuous
metallic strip in a process line in which a trailing end of
an initial strip, uncoiled from an initial coil, is
connected to a leading end of a subsequent strip, uncoiled
from a subsequent coil, to form the continuous strip, which
is threaded over bridle and transportation rolls, the
apparatus comprising:
a movable transportation roll around which the
continuous strip partially extends;
a supporting shaft rotatably supported by bearing
means;
an arm mounted pivotable about the supporting shaft
- and having one end connected to the movable transportation
roll;
an arm driving motor coupled to the supporting shaft
and generating a torque in the arm about the supporting
shaft to apply a tension to the continuous strip;
an arm angle sensor means for detecting the angular
position of the arm about the supporting shaft;
a tension sensor means for detecting tension in the
continuous strip; and
a tension control means for correcting the torque
generated in the arm based on the angular position of the
arm and the tension in the continuous strip, and
maintaining the continuous strip tension at a target
tension.
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
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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.
Despite its drastic variation externally introduced
into the central section of a process line or the Iike, 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.
lo Preferably, the tension control means includes:
a tension controller for delivering a torque control
command based on a comparison of a detected tension and the
target tension;
a dead load compensating arithmetic unit for
compensating torque for a dead load of the movable
transportation roll and the arm based on the angular
position detected by the angle sensor means;
a tension angle compensating arithmetic means for
compensating a change of the relationship between the ship
tension and the output torque of the arm driving motor
based on the angular position of the arm; and
a current controller means for controlling the arm
driving motor based on a compensated torque command
obtained as a sum of the torque control command, an output
of the dead load compensating arithmetic unit and an output
of the tension angle compensating arithmetic means.
Preferably, the apparatus further comprises:
a motor torque control means for controlling the
torque of the arm driving motor;
a counterweight disposed on the arm, the counterweight
being adjustable in a direction perpendicular the
supporting shaft to generate the torque in the arm about
the supporting shaft;
a counterweight position adjusting means for adjusting
the position of the counterweight; and
a means for controlling the torque generated in the
arm based on the angular position of the arm and the
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tension in the continuous strip.
The tension control means may include:
a tension controller for delivering a torque control
command based on a comparison of a detected tension and the
target tension;
a dead load compensating arithmetic unit for
compensating torque for a dead load of the movable
transportation roll and the arm based on the angular
position detected by the angle sensor means;
a tension angle compensating arithmetic means for
compensating a change of the relationship between the strip
tension and the output torque of the arm driving motor
based on the angular position of the arm; and
a current controller means for controlling the arm
driving motor based on a compensated torque command
obtained as a sum of the torque control command, an output
of the dead load compensating arithmetic unit and an output
of the tension angle compensating arithmetic means.
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.
Thus, the tension of the strip can be controlled with
good responsiveness and satisfactory ~ ~
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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.
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.
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,
lS the motor must only bear the torque corresponding to the
variation in tension, so that the motor requires only a
small capacity.
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
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Fig. l 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
10Fig. 4 is a layout diagram showing an arrangement of
a conventional prior art tension control apparatus using a
dancer roll.
DETATT.~n DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will
15now be described in detail with reference to the drawings.
A first embodiment of the present invention is a strip
tension control apparatus constructed in the manner shown
in Fig. 1.
In the strip tension control apparatus of the present
20invention, 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
25sensor 16, a tension control section 30, bridle rolls 20,
a bridle roll driving motor 21, and a strip speed control
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section 40. The tension of the strip 1 is controlled
through a pivoting movement of the roll 10 about the shaft
12.
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.
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.
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 ~ is entered in the
tension control section 30 and the strip speed control
section 40.
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
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torque control command T1. The dead load compensating
arithmetic unit 32 is used to compensate the.
torque for the dead load of the movable transpo~tation
roll 10 and the arm 11 in accordance with the detected
angle ~ 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
10 11.
The torque control command Tl 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.
A current sensor 17 is provided for detecting the
current of the motor 14 and feeding it back to the
compensatory torque command Tl'. 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.
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
11
~2 1
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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 ~, respectively, a torque compensation value Tqs for
the dead load is given by
Tqs = W-Lo-cos~ --- (1)
The torque for the dead load is compensated by adding
the torque compensation value Tqs to the tension command
T1.
As an example, the tension angle compensating
arithmetic unit 33 may carry out output torque compensation
in the following manner.
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 ~ is
glven by
Tqt = 2To-Lr-cos~ --- (2)
The output torque is compensated by adding the output
torque compensation value Tqt to the tension command.
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 ~ of the arm
11 for a target angle Ar.
The speed control section 40 includes an angle
controller 41, a dead band generator 42, and a speed
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controller 43. The angle controller 41 compares the target
angle Ar and the detected angle ~, 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.
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.
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 ~ of the arm 11 fitted
with the roll 10, to its horizontal position. The detected
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tension T and the detected angle ~ 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.
Meanwhile, the detected angle ~ 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 torque control command
T1 so that the command T1 is compensated to become the
compensatory torque command T1'.
The compensatory torque command Tl' is entered as a
torque command value, that is, a current command value, in
the current controller 34. In response to this torque
command Tl', the current controller 34 controls the motor
driver 18 thereby regulating the toque 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
Tl', 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
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so that the torque of the motor 14 is adjusted to the
command value T1'.
In order to correct the angle by comparing the angle
with the predetermined target angle Ar, the angle
controller 41 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.
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 ~ of the arm 11 to the
target speed Vr and the target angle Ar, respectively.
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.
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Table 1
No. Items Prior ArtFirst Embodiment Remarks
1 GD2 (Machine axis) Great Small Approx. 1/2 of
prior art
2 Mechanical lossGreat Small Prior art level:
about 50 kg
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
In this case, compared factors include moment of
inertia GD2, 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.
Although the conventional apparatus is subject to
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backlash, the apparatus of the first embodiment is not.
This is because the motor is connected directly to the arm
supporting shaft.
A second embodiment of the present invention will now
be described.
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.
The counterweight 50 is arranged on an arm ll 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).
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
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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 Tl. 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 ~ 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.
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.
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.
The speed control section 40 includes an angle
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controller 41 and a speed controller 43. The angle
controller 41 compares a target angle Ar and the detected
angle ~, 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.
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.
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.
If the strip tension is T, a torque Tq required for
the counterweight shifting motor 51 is given by
Tq = 2-T-Lr + Wm-Lm
- (Ws-St + Wr-Lr + Wf-Lf) --- (3)
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20~4434
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).
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).
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
St = (2Tref-Lr + Wm-Lm)
- (Wr-Lr + Wf-Lf + Ctq)/Ww --- (4)
The movable range (between the maximum and minimum
values of the position St) for the counterweight 50 should
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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).
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.
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.
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.
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
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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.
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.
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.
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
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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 cases.
Referring now to the prior art tension control
apparatus having a dancer roll, it 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.
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.
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.
A backlash of the speed reducer 7 results in a delay
in operation or a new variation in tension attributable to
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