Control system for tandem rolling mill

Details Control system for tandem rolling mill Control system for tandem rolling mill

2002-03-07

2003-09-16

Tolan, Ed (Department: 3725)

Metal deforming

With use of control means energized in response to activator...

Metal deforming by use of roller or roller-like tool element

C072S011400, C700S152000

Reexamination Certificate

active

06619086

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a control system for a tandem rolling mill for rolling a steel strip or the like.
BACKGROUND ART
A tandem rolling equipment comprises a tandem rolling mill in which rolls are rotated at each of a plurality of mill stands disposed successively to feed and roll a strip (rolling material). In the tandem rolling mill for performing such rolling, a feeding shape restricting mechanism called looper is disposed between the mill stands, for such a control that the strip maintains a loop (curve) with a predetermined length between the stands and maintains a desired tension, whereby quality of thickness of strip and width of strip is secured and stable operation is provided.
FIG. 1
is a general constitutional view of a major part of a tandem rolling mill, and
FIG. 2
is a block diagram of a control system for a tandem rolling mill using a first prior art described in “Application of H∞ Control to Actual Plant” (The Society of Instrument and Control Engineers) pp. 70-73. In
FIG. 1
, numeral
1
denotes a tandem rolling mill,
21
denotes a strip which is a rolling material,
22
denotes a former-stage mill stand,
23
denotes a latter-stage mill stand,
24
denotes a mill motor,
25
denotes a looper,
26
denotes a looper motor,
27
denotes a tension detector for detecting the tension of the strip
21
, and numeral
28
denotes a looper angle detector for detecting the rotating angle and rotating speed of the looper
25
. The control system in
FIG. 1
is in a general representation without any symbol, because its constitution differs according to the contents of the applied technique, namely, whether the prior art or an embodiment of the present invention. In addition, the tension detector
27
and the looper angle detector
28
are shown within the box of dotted line indicating the tandem rolling mill
1
for easy recognition, but in actual classification, they belong to the components of the control system. In
FIG. 2
, numeral
20
denotes a control system according to the prior art,
2
denotes a mill speed controller,
3
denotes a looper torque controller,
5
denotes a tension setting torque arithmetic unit, and
6
denotes a looper angle controller.
Next, action or operation will be described.
In the tandem rolling mill
1
, rolls are driven to rotate by the mill motor
24
while making a draft at each of the mill stands
22
,
23
, here the former-stage mill stand
22
, and the strip
21
is rolled by feeding out the strip
21
. The looper
25
driven by the looper motor
26
as well as attendant mechanisms is disposed between the mill stands
22
and
23
, and the looper
25
is brought into contact with the strip
21
drivingly fed by the mill motor
24
, whereby the feeding shape of the strip
21
is restricted. On the other hand, in the control system
20
, the mill speed controller
2
controls so as to make the speed of the mill motor
24
coincide with a mill speed command vr, and the looper torque controller
3
controls so as to make the torque of the looper motor
26
coincide with a torque command qr. Namely, the control system
20
appropriately calculates the mill speed command vr and the looper torque command qr, and controls so that the strip
21
forms a predetermined loop (curve) between the mill stands, namely, the angle of the looper
25
has a predetermined value, while giving a predetermined tension to the strip
21
.
While a constitution in which the mill speed of the former-stage mill stand
22
is controlled in order to control the tension &sgr; of the strip
21
between the mill stands
22
and
23
and the angle &thgr; of the looper
25
has been presented as an example in the above description, the object of control of the mill speed is not limited to the former-stage mill stand
22
, and may be the latter-stage mill stand
23
.
The first prior art applied to the control system
20
is a system which has been used most generally for a long time, and, although it has not a specially excellent tension control performance, it promises a simple and easily usable control system. The control system
20
is externally supplied with a tension command &sgr;r and a looper angle command &thgr;r, and is supplied with a looper angle &thgr; detected by the looper angle detector
28
. The tension setting torque arithmetic unit
5
, in the condition where the tension &sgr; of the strip
21
is steadily conformed to the tension command &sgr;r, based on the tension command &sgr;r, calculates in a feed-forward manner a torque of the looper motor
26
for the looper
25
to support the strip
21
, and outputs the calculated result as a tension setting torque qs. The tension setting torque qs is inputted as a torque command qr to the looper torque controller
3
, which performs such a control as to make the torque of the looper motor
26
coincide with the torque command qr. The looper angle controller
6
is supplied with an angle deviation &thgr;e which is the difference between the looper angle command &thgr;r and the looper angle &thgr;, and calculates the sum of a signal obtained by multiplying the angle deviation &thgr;e by an angle proportional gain Cp and a signal obtained by integrating the angle deviation &thgr;e and multiplying the integrated value by an angle integral gain Ci. Namely, a PI (proportional integral) arithmetic operation is conducted so that the looper angle &thgr; does not have a steady deviation, and outputs the result of the arithmetic operation as a mill speed command vr. The mill speed controller
2
performs such a control as to make the mill speed coincide with the mill speed command vr.
Thus, the control system
20
generates a tension setting torque qs such that the strip
21
with a tension &sgr; conforming to the tension command &sgr;e is steadily supported by the looper
25
in a balanced manner; in addition, under variations in the speed of the strip
21
generated by variations in the draft at the former-stage mill stand
22
and the latter-stage mill stand
23
or the like, the control system
20
corrects the mill speed command vr so that the looper angle &thgr; coincides with the looper angle command &thgr;r, namely, the length of the loop between the former-stage mill stand
22
and the latter-stage mill stand
23
becomes constant. In this manner, the looper angle &thgr; and the tension &sgr; are controlled with the looper angle command &thgr;r and the tension command &sgr;r as target values. Furthermore, the control system
20
in this type does not necessarily need the tension detector
27
, and feed-back control is conducted by only the looper angle controller
6
, so that operation can be continued by only applying easy adjustments to a one-loop control system based on the looper angle controller
6
.
However, the simplicity of a control system and the quality of control performance are opposed to each other in many cases. The characteristics of the tandem rolling mill
1
are basically governed by resonance characteristics of a spring inertia system consisting of the elasticity of the strip
21
and the inertia of the looper
25
; therefore, the prior art control system
20
in which the tension &sgr; is not feedback controlled has the problem that the control system becomes instable when the gain of the looper angle controller
6
is raised, and it is difficult to control the tension &sgr; and the angle &thgr; with high accuracy.
Next,
FIG. 3
shows the constitution of a control system for a tandem rolling mill according to a second prior art described in “Application of H∞ Control to Actual Plant” (The Society of Instrument and Control Engineers) pp. 77-79. The constitution of the tandem rolling mill
1
which is the object of control is as shown in FIG.
1
. Numeral
30
denotes a control system according to the second prior art,
201
denotes a looper angle controller,
202
denotes a tension controller,
203
denotes a noninterference controller having coefficient units H
12
and H
21
, and
204
denotes a looper speed controller. The second prior art

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