JP3415405B2 - Hydraulic rolling down control of rolling mill - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic reduction control device for a rolling mill which is used when controlling the plate thickness of a material to be rolled such as a continuous hot rolling system.

[0002]

2. Description of the Related Art A conventional general hydraulic reduction control system for a rolling mill is provided with a host computer having a work roll interval reference output circuit and a control calculation system, and a target value output from the work roll interval reference output circuit. And a position detection signal from a position detector directly connected to the hydraulic cylinder are guided to a control calculation system, where PI (P: proportional, I) is calculated based on the deviation between the position reference signal and the position detection signal. : Integral) or P
After performing the ID (D: derivative) adjustment calculation and converting the position correction reference signal, which is the obtained calculation output, into the current reference, the opening of the servo valve is operated via the servo amplifier to adjust the flow rate of the pressure oil. As a result, the hydraulic reduction control of the work roll interval of the rolling mill is performed.

[0003]

By the way, in the hydraulic reduction control device for adjusting the work roll interval of the rolling mill, the two position points of the work roll or the support roll supporting this work roll are individually acted by the hydraulic cylinders. The position control is performed by performing the position control, but when a deviation occurs between the cylinder positions of two different position points, the speed correction is performed to perform the drive speed equalization control.

On the other hand, before the start of rolling, gap zero adjustment is carried out in order to eliminate the effects of play in the contact parts of the rolling-down system parts and radial gaps inside the bearing. Intentionally OP / considering the balance of the detection load of the drive DR side cylinder
Since the position of the DR cylinder is corrected, the hydraulic pressure reduction control needs to be performed in consideration of the positional deviation during rolling. If the hydraulic pressure reduction control is performed without considering the position deviation of the OP / DR cylinder at the time of zero gap adjustment,
Even though the position deviation is not originally abnormal, it is judged to be abnormal, and the operation shifts to so-called containment protection operation, such as stopping the opening of the servo valve, and the rolling cannot be continued.

Further, when the OP / DR cylinder stops on one side of the servo valve due to an abnormality such as a stick of the servo valve during the quick opening operation as a recovery operation at the time of containment, the work roll interval is biased and skew occurs. There is a risk of damage to the rolls and damage to the rolling machine.

Further, when the detected load at the time of zero gap adjustment varies due to the eccentricity of the work roll or the support roll,
There is a problem that an error occurs in the load judgment reference value as the reference. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a hydraulic reduction control device for a rolling mill, which performs plate thickness control of a material to be rolled by appropriate hydraulic reduction control.

[0007]

In order to solve the above problems, the present invention provides two positions of a work roll for adjusting a work roll (including a support roll; hereinafter the same) distance of a rolling mill from a host computer. A position deviation between a position reference signal of a different hydraulic cylinder acting on a point and a position detection signal from a position detector directly connected to each of the hydraulic cylinders is P.
I (P: Proportional, I: Integral) or PID (D: Derivative) adjustment calculation is executed, and after each adjustment calculation output is converted into a current reference, the valve opening of the servo valve is controlled via the servo amplifier. In a hydraulic pressure reduction controller for a rolling mill that controls the position of each hydraulic cylinder, the position of a position reference signal for each hydraulic cylinder acting on two position points of the work roll and a position detection signal from the corresponding hydraulic cylinder side. When there is a difference between the deviations, a driving speed equalizing means for extracting a signal for equalizing the driving speeds of the hydraulic cylinders, and a direct connection to each hydraulic cylinder based on a gap zero adjustment timing signal. Speed equalization correction means for obtaining a deviation between both position detection signals from each position detector, a difference signal between position deviations obtained by the drive speed equalization means, and the two positions. When the output value obtained is compared with the deviation of the detection signal and exceeds the predetermined allowable range, only the excess is output and the position deviation is corrected to equalize the drive speed of the hydraulic cylinder. The band means is provided.

By taking such means, a position detector directly connected to different hydraulic cylinders acting on two points of the work roll and the position reference signals of the operator side and drive side control arithmetic systems by the drive speed equalizing means. The difference signal between the position deviation and the position deviation of the position detection signal is taken out, and the position equalization correction means outputs the position detection signals from the position detectors directly connected to the hydraulic cylinders based on the gap zero adjustment timing signal. When the deviation is taken out and the output value of the difference between the taken out difference signal and the deviation signal exceeds a predetermined allowable range, only the excess is output and the position deviation is corrected to equalize the driving speed of the hydraulic cylinders. Therefore, the deviation between the cylinder positions of the two different position points can be reliably removed.

Another aspect of the present invention is to detect the position reference signals of different hydraulic cylinders acting on the two position points of the work rolls for adjusting the work roll interval of the rolling mill from the host computer and the position detection signals directly connected to the respective hydraulic cylinders. PI (P: Proportional, I: Integral) or PID (D: Derivative) adjustment calculation is executed for the position deviation from the position detection signal from the device, and the adjustment calculation output is converted into a current reference by the current conversion means. After that, in the hydraulic reduction control device of the rolling mill that controls the valve opening of the servo valve via the servo amplifier to control the position of each hydraulic cylinder, the rolling condition monitoring means for monitoring the rolling condition and the monitoring means Confinement control means for judging the state of containment in the servo valve as a protective operation based on the monitoring result, the current reference to the servo amplifier and the servo amplifier concerned. A deviation of the current feedback input,
When this deviation exceeds a predetermined permissible range, means for executing the containment operation of the servo valve in accordance with the judgment of the containment control means, and a quick opening control means for controlling the return operation after the containment of the servo valve are provided. It is a thing.

By taking such a measure, the condition for containing the servo valve as a protective operation is determined based on the result of monitoring by the rolling condition monitoring means for monitoring the rolling condition, and the current reference to the servo amplifier is set. When the deviation from the current feedback input by the control of the hydraulic cylinder based on this current reference exceeds a predetermined allowable range, the servo valve's containment operation is executed according to the conditions of the containment control means. On the other hand, it is possible to reliably shift to the containment protection operation, and it is possible to perform the opening at a predetermined opening speed by the quick opening control means.

Still another aspect of the present invention is a load detecting means for detecting a load between each hydraulic cylinder and a work roll, which is generated by a pressure driving of each hydraulic cylinder, and a mill based on a load detected value by the load detecting means. Correction means for correcting the rolling position of each hydraulic cylinder by adding extension to each position reference signal is provided.

By taking such means, even if the detected load fluctuates due to the eccentricity of the work roll or the support roll, it is possible to absorb it and execute reliable position control of each hydraulic cylinder.

[0013]

1 and 2 are block diagrams showing an embodiment of a hydraulic pressure control device for a rolling mill according to the present invention. This control device is a technique for controlling the position of the hydraulic cylinder 3 that individually acts on two position points of the support roll 2 that supports the work roll 1 of the rolling mill as shown in FIG. Control system 1
0 op, 10 dr, a dead band correction system 30, a monitoring and protection operation system 40, and a load correction system 50.

The basic control systems 10op and 10dr are divided into an operator OP side and a drive DR side. The operator OP side will be described.
A position deviation calculation unit 14 for obtaining a position deviation between the set position reference 12op input via 1op and the position detection signal of the position detector 13op directly connected to the operator side hydraulic cylinder 3op.
op, a position control circuit 15op that executes PI or PID control calculation based on this position deviation to obtain a position operation value that makes the position deviation zero, a leak that outputs a predetermined leak amount when the position deviation exceeds a certain value An addition calculation unit 17op for adding and compensating the leak amount to the position operation value (position reference) which is the calculation output of the correction circuit 16op and the position control circuit 15op is provided.

The reason for providing the leak correction circuit 16op is that the servo valve normally follows in response to the current reference output from the servo amplifier, but the viscous characteristic of hydraulic pressure deteriorates due to the environment during rolling, especially in cold conditions. Since there is a risk that the servo valve's tracking ability will decrease due to freezing and sticking of the pilot mechanism of the servo valve itself, and control will become impossible, it is necessary to output a predetermined leak amount in advance to improve the servo valve's tracking ability. is there.

Further, the basic control system 10op is provided with a current conversion circuit 18op for converting the position manipulated value in which the leak amount is compensated into a current reference, a servo amplifier 19op, a servo valve 20op, etc., and controls the position of the hydraulic cylinder 3op. It is configured to do.

A similar structure is provided on the drive DR side as well, and the same numeral symbols are appended with "dr" for distinction. Therefore, in FIG. 2, the hydraulic cylinders 3op and 3dr, the position detectors 13op and 13dr, and the load detectors 51op and 5 to be described later are included.
Except for 1dr, similar components are provided on the drive side.

The dead band correction system 30 constantly monitors the position deviation of the operator side control system and the position deviation of the drive side control system, outputs a signal of the difference between these two position deviations, and controls the flow rate of the pressure oil by the operator. Side hydraulic cylinder 3op
And a drive speed equalizing circuit 31 that can realize equalization of drive speeds of the drive side hydraulic cylinders 3dr, and a position detector 1 directly connected to the operator side and the drive side hydraulic cylinders 3 based on a timing signal for zero gap adjustment.
A speed equalization correction circuit 3 which instantaneously stores both position detection signals of 3 op and 13 dr and extracts the deviation between the operator side and the drive side from these both position detection signals and outputs it as a correction value.
2 is further provided, and a comparison unit 33 that performs subtraction correction on the output of the drive speed equalization circuit 31 using the output of the speed equalization correction circuit 32, and a tolerance that is determined in advance by considering the operating characteristics of the hydraulic cylinders The range is set, and the comparison unit 33
When the output exceeds the predetermined permissible range, only the excess is output, and the position deviation is added and corrected via the addition operation units 34op and 34dr on the input side of the position control circuits 15op and 15dr to correct the hydraulic cylinder 3op on the operator side. Also, a dead band circuit 35 for equalizing the cylinder driving speed of the drive side hydraulic cylinder 3dr is provided.

The reason why the drive speed equalizing circuit 31 is provided is not particularly problematic if the rolling mechanism has an ideal form. However, as described above, there are factors such as the hydraulic pressure, the environment of the servo valve, and secular change. This is also because the work roll interval is intentionally operated depending on the material of the material to be rolled, the plate thickness, the rolling conditions, etc., and it is necessary to make a correction in accordance with the position operation. The reason for providing the speed equalization correction circuit 32 is as follows.
If the hydraulic pressure reduction control is performed without considering the OP / DR cylinder position deviation at the time of zero gap adjustment, it is judged as abnormal even though it is not originally abnormal, and it moves to the containment protection operation and it becomes impossible to continue rolling. This is because it is necessary to take out the deviation between both position detection signals in advance by the adjustment timing signal and subtract it from the output of the drive speed equalizing circuit 31 to correct it.

As the monitoring and protection operation system 40, a rolling condition monitoring control circuit 41, a containment control circuit 42, a rapid opening control circuit 43, and a protection operation control processing unit 44 are provided, and the addition operation units 17op and 17dr are used. When the position operation value of is converted into a current reference by the current conversion circuits 18op and 18dr and sent to the servo amplifiers 19op and 19dr, the pressure condition monitoring result,
Containment judgment as a protective action based on this monitoring result,
This is to involve the return operation or the quick opening operation after the containment, and the operation flow is as shown in FIGS. 3 and 4.

The rolling condition monitoring control circuit 41 has a function of taking in alarms and various other operating conditions and monitoring the rolling condition to judge whether or not there is an abnormality. The containment control circuit 42 has a function of deciding conditions such as how much containment is performed when a result of monitoring of the rolling condition monitoring control circuit 41 is determined to be abnormal, or containment after a lapse of a certain time using a timer. The quick opening control circuit 43 has a function of determining conditions such as how fast the opening is performed as a return operation after containment.

The current conversion circuits 18op and 18dr are
Servo amplifier 19 from the current conversion circuit 18op, 18dr
The deviation between the current reference to op, 19dr and the current feedback input obtained by the control based on this current reference is obtained, and when the deviation exceeds a predetermined allowable range, the containment control means 4
According to the condition of No. 2, the operation of containing the servo valves 20op and 20dr is executed.

The load compensating system 50 is a cylinder 3o generated by driving the hydraulic cylinders 3op and 3dr down.
Load detector 5 that detects the load between p and 3dr and the roll
1op, 51dr, input circuits 52op, 52dr provided for each of the load detectors 51op, 51dr, for loading the load detection signals of the load detectors 51op, 51dr, and both load detection signals fetched by these input circuits 52op, 52dr Is added, a correction circuit 54 for storing and correcting a variation in the detected load due to eccentricity of the work roll 1 in advance when the gap zero is adjusted, and a correction circuit 54 for correcting the output of the addition calculation circuit 53. And a mill module circuit 55 that corrects the pressure reduction positions of the hydraulic cylinders 3op and 3dr by using the fluctuation amount of the detected load stored in the comparator module 5 on the operator side and the drive side.
Added to 6op and 56dr.

Next, the operation of the hydraulic pressure reduction control device configured as described above will be described. The position reference signal 12op set by the host computer is introduced into the position deviation calculator 14op through the rate circuit 11op. At this time, a position detection signal is introduced from the position detector 13op into the position deviation calculation unit 14op. Therefore, in this position deviation calculation unit 14op,
After the position deviation between the position reference signal and the corresponding position detection signal of the position detector 13op is obtained, it is sent to the position control circuit 15op. The position control circuit 15op executes PI or PID adjustment calculation based on the position deviation, and obtains a position operation value that serves as a position reference output.

Then, the position operation value is converted into the current conversion circuit 1
The position of the hydraulic cylinder 3op is controlled by converting to a current reference at 8op and operating the valve opening of the servo valve 20op via the servo amplifier 19op to adjust the flow rate of the pressure oil.

The position of the hydraulic cylinder 3dr is similarly controlled on the driver side. By the way, normally, the servo valves 20op and 20dr follow in response to the current reference output from the servo amplifiers 19op and 19dr, but as described above, the viscosity characteristics of the pressure oil deteriorate due to various environmental conditions during rolling. If the pilot mechanism of the servo valve itself freezes or sticks, drift or stick of the spool position detection value of the servo valve may occur, and the tracking capability of the servo valve may deteriorate.

Therefore, the leak correction circuits 16op and 16dr are provided, the leak amount is added to the position deviation on the operator side and the drive side, and the operation output value obtained from the position control circuits 15op and 15dr is added and corrected to thereby make the servo valve. 20
The followability of op and 20dr is improved, and the situation at the time of rolling is also introduced to the rolling situation monitoring control circuit 41 of the monitoring and protection operation system 40.

On the other hand, in the dead band correction system 30, the drive speed equalizing circuit 31 is directly connected to the position reference signals of the operator side and drive side control arithmetic systems and the different hydraulic cylinders 3op and 3dr acting on two points of the work roll 1. While the difference signal between the position deviations of the position detectors 13op and 13dr and the position deviations of the position detectors 13dr and 13dr is taken out, the speed equalization correction circuit 32 directly connects to the hydraulic cylinders 3op and 3dr based on the timing signal of the gap zero adjustment. When the deviations of the position detection signals from the position detectors 13op and 13dr are taken out and the output value of the difference between the taken out difference signal and the deviation signal exceeds a predetermined allowable range, only the excess is output and the position is detected. By correcting the deviation and equalizing the drive speed of the hydraulic cylinder, the operator side and the drive during gap zero adjustment Side, the influence of intentional position deviation on the side is eliminated, and when the difference of position deviation for different hydraulic cylinders 3op and 3dr acting on two position points of the work roll exceeds a predetermined allowable range, the hydraulic pressure is increased by the exceeded amount. By correcting the position deviation for the cylinders 3op and 3dr, it is possible to prevent a position deviation that is not abnormal from being judged as abnormal.

Furthermore, in the monitoring and protection operation system 40,
It operates according to FIGS. 3 and 4. That is, normally, for the position control servo output a from the servo amplifier 19op,
The position detection signal from the corresponding position detector 13op is fed back to the servo amplifier input side, for example, the current conversion circuit 18op as a control amount. In this state, the protection operation control processing unit 44 determines whether or not the quick opening control operation is performed by a manual arbitrary operation from the man-machine interface device, an automatic determination control from the rolling condition monitoring control circuit 41, or the like ( Step b).

Here, when the rapid opening control operation is not executed, but when the rolling condition control circuit 41 determines that there is an abnormality during rolling, the mechanism protection function shifts to the containment control and immediately shifts to the containment operation d. Servo amplifier 19
Servo valve 2 that opens and closes the hydraulic system by turning off the output of op
By closing the locking valve (not shown) on the 0op input side, the condition of shoulder drop skew caused by the position deviation generated between the OP / DR hydraulic cylinders is eliminated,
Prevents damage to the rolling mechanism. Then, after the error factor is restored, the reset operation is performed as shown in step e, and when the quick opening is turned on, the process proceeds to step f.

When it is determined in step b that the quick opening control operation is being executed, the normal position control output is released and the current conversion circuit 18op is caused to function as the quick opening control. As a result, the servo output MAX rise f is output from the servo amplifier 19op. Here, the rising limit with respect to the servo amplifier output is detected (step g), but in the normal state, as shown in FIG. 4B, the fall limit is detected at the rising limit detection and the output is reduced to a low-speed holdable output and remains at the upper limit position ( Step q). Then, after the reset is turned on, the condition is established r to rapidly open and return to the normal position control a again,
It is output from the servo amplifier 19op.

However, during the ascending operation before reaching the ascending limit detection in step g, the OP / DR hydraulic cylinder 3 is operated during the position control due to the environment / disturbance and rolling condition described above.
When the position deviation of op, 3dr exceeds the allowable range (step h), the operation immediately shifts to the containment operation i and the servo amplifier 1
The output of 9op is turned off, and the locking valve (not shown) on the input side of the servo valve 20op that opens and closes the hydraulic system is closed. As a result, the condition of shoulder drop skew caused by the positional deviation generated between the OP / DR hydraulic cylinders is eliminated, and damage to the rolling mechanism can be prevented in advance.

However, the conditions of steps h and i are in the middle of the transition to the rapid opening operation, and are normally of the nature that they can be executed up to the rising limit without any constraint or condition. In other words, it is an emergency avoidance when a sudden event occurs. Therefore, the MAX rise is output to the servo valve 20op. Although it is such a rapid opening circuit, if problems are raised, it cannot be denied that there are, for example, inadequate measures against the cold of the servo valve and mechanical inadequacy. Even in this situation, it is often used in many plants in recent years due to sensitivity of hydraulic response, simplification of equipment sizing, price, and the like. As a result of considering the above situation from the viewpoint of price and safety, the dead band correction system 30 in consideration of the position deviation was introduced.

On the other hand, there is a need for a method of avoiding the state of the containment operation and shifting to the position control again. This is the rapid opening containment reset j shown in FIG.
After the containment reset ON condition is established, the single stand emergency open control is executed (step k). This is to unconditionally raise all stands by using an emergency stop button that is usually hard, and opens the discharge valve that is connected to the hydraulic cylinder in parallel with the hydraulic cylinder without going through the servo valve. Although it is a mechanism for raising the MAX, this device can perform the same operation 1 with a single stand, and enhances the integration with other operations as operations from the man-machine interface device.

After the rising limit is detected m, the single stand emergency release control reset ON (step n) and all the regular stand emergency release control OFF (step o) can be used as a condition to shift to the normal position control a. Is.

Even when the rolling mechanism is stopped and held in the drop prevention low speed holding p state after the normal rising limit detection m described above, the containment operation i is performed even when the skew occurs due to an abnormality of the servo valve or the like. Transition, servo valve output OF
By setting to F, it becomes possible to optimize the hydraulic pressure reduction control of the rolling mill.

The load correction system 50 is provided for the following reason. When the detected load at the time of zero gap adjustment varies due to the eccentricity of the work roll 1 or the like, an error occurs in the reference load judgment reference value. This varies depending on the rotation speed of the work roll 1 and the read timing, and is not constant, and there is a problem in accuracy.

Therefore, by correcting the correction value from the load detectors 51op and 51dr by the correction circuit 54tok correction value by the mill module circuit 55, and applying the correction value to the position operation value on the operator side and the drive side, an appropriate load is obtained. The judgment standard value is taken in.

[0039]

According to the first aspect of the present invention, even when the position deviations on the operator side and the drive side are different due to different hydraulic cylinders acting on the two position points of the work roll, the two positions of the hydraulic cylinder can be changed. The drive speed of the position points can be surely equalized.

According to the second aspect of the present invention, even when the conditions and environment such as the material and plate thickness of the material to be rolled are changed, or when the shortage occurs due to the abnormal state of the servo valve, It is possible to easily avoid the situation of shortage and prevent the reduction of the plate thickness accuracy of the rolled material.

According to the third aspect of the present invention, even if the detected load at the time of zero gap adjustment varies due to eccentricity of the work roll or the like, the mill module is corrected to obtain an appropriate load judgment reference value. You can

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a hydraulic reduction control device for a rolling mill according to the present invention.

FIG. 2 is a configuration diagram showing a hydraulic control portion using a servo mechanism.

FIG. 3 is a flowchart illustrating the relationship between the containment operation and the quick opening operation at the time of abnormality.

FIG. 4 is a flowchart for explaining a part of the series of operations shown in FIG. 3, regarding the relationship between the containment operation and the quick opening operation at the time of abnormality.

[Explanation of symbols]

1 ... Work roll 2 ... Support role 3op, 3dr ... hydraulic cylinder 10op, 10dr ... Basic control system 13op, 13dr ... Position detector 18 op ... current conversion circuit 19op ... Servo amplifier 20op ... servo valve 30 ... Dead band correction system 31 ... Driving speed equalizing circuit 32 ... Speed equalization correction circuit 35 ... Dead band circuit 40 ... Monitoring protection operation system 41 ... Rolling condition monitoring control circuit, 42 ... Containment control circuit 43 ... Rapid opening control circuit 44 ... Protection operation control processing unit 50 ... Load correction system 51op, 51dr ... Load detector 54 ... Correction circuit 55 ... Mill module circuit

Claims (3)

(57) [Claims] 1. Position reference signals of different hydraulic cylinders acting on two position points of the work roll for adjusting the work roll distance (including support rolls for supporting the work roll, the same applies hereinafter) of the rolling mill from a host computer. And the position deviation of the position detection signal from the position detector directly connected to each of the hydraulic cylinders, PI (P: proportional, I: integral) or PID (D: derivative) adjustment calculation is executed, and this adjustment calculation output In the hydraulic pressure reduction control device of the rolling mill, which controls the valve opening of the servo valve through the servo amplifier to control the position of each of the hydraulic cylinders, the two positions of the work rolls are When there is a difference between the position reference signal for each hydraulic cylinder that operates and the position deviation of the position detection signal from the corresponding hydraulic cylinder,
Driving speed equalizing means for extracting a signal for equalizing the driving speed of the hydraulic cylinders, and both position detection signals from each position detector directly connected to each hydraulic cylinder based on the gap zero adjustment timing signal. The speed equalization correction means for obtaining the deviation is compared with the difference signal between the position deviations obtained by the drive speed equalization means and the deviation of both position detection signals by the speed equalization correction means, and the obtained output value is set in advance. When a specified allowable range is exceeded, dead band means for outputting only the excess and correcting the position deviation to equalize the driving speed of the hydraulic cylinders is provided. Control device. 2. A position reference signal of different hydraulic cylinders acting on two position points of the work roll for adjusting a work roll distance of the rolling mill from a host computer and a position from a position detector directly connected to each of the hydraulic cylinders. The position deviation from the detection signal is PI (P: proportional, I: integral) or P, respectively.
After performing the ID (D: differential) adjustment calculation and converting the adjustment calculation output to the current reference by the current conversion means, the valve opening of the servo valve is controlled via the servo amplifier to determine the position of each hydraulic cylinder. In a hydraulic pressure reduction control device for a rolling mill that performs control, rolling condition monitoring means for monitoring the rolling condition, and containment control means for determining the condition of containment in a servo valve as a protective operation based on the monitoring result by this monitoring means, The deviation between the current reference to the servo amplifier and the current feedback input obtained by the position control of the hydraulic cylinder based on this current reference is determined, and when this deviation exceeds a predetermined allowable range, the servo is controlled according to the conditions of the containment control means. It is characterized by including means for executing the valve containment operation and quick opening control means for controlling the return operation of the servo valve after containment. Hydraulic rolling reduction control device for rolling mills. 3. A position reference signal of different hydraulic cylinders acting on two position points of the work roll for adjusting a work roll interval of the rolling mill from a host computer and a position from a position detector directly connected to each of the hydraulic cylinders. The position deviation from the detection signal is PI (P: proportional, I: integral) or P, respectively.
ID (D: Derivative) adjustment calculation is executed, and each adjustment calculation output is converted into a current reference, and then the valve opening of the servo valve is controlled via a servo amplifier to control the position of each hydraulic cylinder. In a hydraulic pressure reduction control device for a machine, load detection means for detecting a load between each hydraulic cylinder and a work roll generated by the pressure driving of each hydraulic cylinder, and a mill elongation based on a load detection value by these load detection means. And a correction means for correcting the predetermined rolling position of the hydraulic cylinder.