JP5459604B2 - Control method for suppressing torsional vibration of rolling mill - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for controlling torsional vibration of a rolling mill suitable for a cold rolling mill of a steel strip.

  There are two methods for controlling the thickness of the steel strip: a method of controlling the roll reduction amount of the rolling mill and a method of controlling the tension between the stands. Unlike cold rolling, the steel strip is hardened in cold rolling. Therefore, the reduction control is not effective, and tension control is mainly performed. In order to perform this tension control accurately, it is necessary to accurately control the speed of the motor driving the rolls of each rolling stand. In particular, since the plate thickness tolerance required by users has become stricter recently, it is required to improve the plate thickness accuracy by greatly improving the motor speed response than before.

  As shown in FIG. 1, the steel strip rolling machine has a structure in which many power transmission means such as a coupling 3, a speed reducer 4, and a spindle 5 are arranged between a motor 1 and a roll 2. For this reason, even if the speed response of the motor 1 is simply improved to ideally control the motor speed, the speed of the roll 2 that actually performs rolling is not ideally controlled. That is, when the speed of the motor 1 changes, the shaft speed is slightly delayed because the shaft is not a perfect rigid body but has a spring property. That is, the shaft is twisted, and the shaft torsional vibration is generated even after the speed of the motor 1 reaches the set value. When the shaft torsional vibration occurs, the speed at the roll end or the motor end becomes oscillating, and the speed response must be lowered. Furthermore, the rotation speed of the roll 2 may slightly vary from the set value, causing a variation in the tension of the steel strip, which may cause a reduction in sheet thickness accuracy.

  In order to suppress such shaft torsional vibration, a shaft torsional vibration suppression control method as described in Patent Document 1 has been conventionally employed. The control method of Patent Document 1 is a feedback control method that detects the rotational speed of the motor driving the roll and gives a torque command to the motor so as to cancel the fluctuation of the rotational speed of the motor due to shaft torsional vibration. In a rolling mill, it is difficult to install a speed detector at the end of the roll. Therefore, it is a general method to estimate the shaft vibration component from the feedback signal at the end of the motor.

  Since the control method of Patent Document 1 is a feedback control method, it is effective against disturbance. Further, when the moment of inertia of the roll is larger than the moment of inertia of the motor, it is particularly effective because it is easy to detect the fluctuation of the rotation speed of the roll due to the torsional vibration of the roll as the fluctuation of the rotation speed of the motor. In actual equipment, however, the moment of inertia of the roll may be smaller than the moment of inertia of the motor, so it is not possible to detect fluctuations in the rotation speed of the roll caused by shaft torsional vibration as fluctuations in the rotation speed of the motor. There are cases where it is not easy. In such a case, there is a problem that the shaft torsional vibration cannot be sufficiently suppressed.

  In addition to this, a mechanical system driven by a motor (the power transmission means and the roll described above) is approximated as a rigid body with one inertia, and a corresponding one inertia model is provided in the motor control drive to rotate the roll. A control method is also used in which a torque command to be given to the motor is calculated in order to set the speed to the set speed, and the calculated torque command is given to the actual motor. This control method is called model reference control. Since the fluctuation of the rotation speed of the roll accompanying the fluctuation of the rotation speed of the motor is numerically calculated by one inertia model in the motor control drive, even when the moment of inertia of the roll is small The problem as in Patent Document 1 does not occur.

  However, as described above, an actual rolling mill has a structure in which many power transmission means such as a coupling, a speed reducer, and a spindle are arranged between a motor and a roll. It is impossible to assume that it is regarded as one inertia, especially when the motor speed response is increased from the conventional 10 to 20 rad / sec to 50 rad / sec because shaft torsional vibration that does not appear in the one inertia model becomes obvious. The actual situation is that the torsional vibration of the shaft cannot be sufficiently suppressed, and the roll end response cannot be increased.

JP-A-8-206718

  Therefore, the object of the present invention is to solve the above-mentioned conventional problems and effectively suppress the shaft torsional vibration that occurs when the motor is subjected to a speed change even when the moment of inertia of the roll is smaller than the moment of inertia of the motor. Another object of the present invention is to provide a novel rolling mill shaft torsional vibration suppression control method capable of enhancing the motor speed response.

  In order to solve the above problems, the present inventor has repeatedly studied the problems of the prior art. As a result, the cold rolling mill has no problem in actual operation even if the disturbance response is low, and the model reference control is effective. However, since the actual machine is multi-inertia, it is not appropriate to control it as one inertia. However, using a multi-inertia model complicates the arithmetic unit and requires a long calculation time, and is applicable to control of the real machine. It became clear that things could not be done. As a result of further investigations, it has been found that even if an actual rolling mill, which is actually about 10 inertia, is simplified to 2 inertia and modeled, a sufficiently effective control is possible.

The present invention has been completed on the basis of the above knowledge, and the motor and roll of the rolling mill and the power transmission means between them are two inertias in which the two inertias of the motor and the roll are connected by a spring. The transfer function of an ideal motor speed model using a quadratic expression in which the numerator taking into account these two inertias is a quadratic or cubic expression and the denominator being a third or higher order, and the numerator taking into account these two inertias are 2 Roll when a speed change command is given to a motor by a motor speed compensator of a drive device having a transfer function of an ideal torque model using a second or third order denominator whose denominator is a third or higher order denominator The ideal motor speed and ideal torque command in which the speed becomes an ideal response waveform without torsional vibration are calculated backward, and the motor speed is controlled based on these values.

  According to the present invention, an ideal motor in which the roll speed has an ideal response waveform free of torsional vibrations by a drive device including an ideal motor speed model considering two inertias and an ideal torque model considering these two inertias. Since the motor speed is controlled based on these values after reversely calculating the speed and the ideal torque command, the roll speed when a speed change is applied to the motor can be brought close to the ideal response waveform. In addition, since the actual rolling mill, which is actually about 10 inertia, has been simplified to 2 inertia, the arithmetic device is not complicated and does not require long calculation time, and can be easily mounted on the drive device. It becomes possible. According to the present invention, even when the motor speed response is increased from the conventional 10 to 20 rad / sec to a level of 50 rad / sec, it is possible to suppress fluctuations in the rotation speed of the roll due to shaft torsional vibration. In addition, as the transfer function of the ideal motor speed model that takes into account the two inertias and the transfer function of the ideal torque model that takes into account the two inertias, the response is obtained by using a fractional expression with a quadratic equation for the numerator and a cubic equation for the denominator. It is possible to stabilize.

It is a conceptual diagram which shows the structure of a rolling mill. It is explanatory drawing of a 2 inertia model and its block diagram expression. It is explanatory drawing of a 2 inertia speed control block. It is a block diagram which shows the whole control method of this invention. It is a more preferable block diagram of the control method of the present invention. It is a conventional speed response waveform diagram. It is a speed response waveform diagram of the present invention.

The present invention is described in further detail below.
In the present invention, a two-inertia model in which the two inertias of the motor and the roll and the two inertias of the motor and the roll are connected by a spring is used for the motor and the roll of the rolling mill. FIG. 2 is an explanatory diagram showing a state in which the motor 1 and the roll 2 are connected by a spring 6 representing a shaft. FIG. 2 is a simplified diagram of many power transmission means such as the coupling 3, the speed reducer 4, and the spindle 5 shown in FIG. Here, the motor 1 and the roll 2 has a moment of inertia J ₁ and J ₂ respectively, and shall have a rotational speed of the omega ₁ and omega _2. The spring constant of Matabane 6 and _{k 1.} This two-inertia model is represented by a block diagram as shown in the lower part of FIG.

Further, when the speed control of the two inertia model is expressed in a block diagram, it is as shown in the upper diagram of FIG. Here, 7 is a speed control device (ASR) having a transfer function of G ₁ (s), and T ₁ is a torque command output from the speed control device 7. The current control system is omitted for simplicity. When this block diagram is equivalently converted, the lower part of FIG. 3 is obtained. Here, the output of H ₂ (s) represents the speed of the motor 1, and the output of H ₃ (s) represents the speed of the roll 2. In FIG. 3, simultaneous equations of Formula 1 are established, and when these are solved, H ₂ (s) and H ₃ (s) are as shown in Formula 2.

FIG. 4 is a block diagram showing the entire control method of the present invention. The contents of G ₁ (s), H ₂ (s), and H ₃ (s) in FIG. 4 are as described above. It goes without saying that this block diagram can be further simplified so that H4 (s) is placed in the part entering the torque part with respect to REF, and H5 (s) is placed in front of the speed controller. .

The block having the transfer function of H ₁ (s) shown in the upper part of FIG. 4 is an ideal response waveform model 8 when the mechanical system portion driven by the motor 1 is assumed to be an ideal rigid body without axial torsion. When a torque command is given to the ideal rigid model 8 from the speed controller (ASR) 7 having a transfer function of G ₁ (s), an ideal speed ω ₀ is output. This ideal speed ω ₀ is input to the addition point 9 and the speed controller (ASR) 7 controls the motor speed by changing the torque command so that the deviation from the command motor speed (REF) becomes zero. Yes.

  However, the torque command output from the speed control device (ASR) 7 is a value when the mechanical system portion is assumed to be an ideal rigid body (one inertia). The shaft torsional vibration cannot be suppressed. Therefore, in the present invention, an ideal torque model considering two inertias is provided in the drive device. This is the torque compensator 10 in FIG. 4, and the torque command output from the speed controller (ASR) 7 is input to the torque compensator 10.

This is the torque command output from the torque compensator 10 becomes the H _{2 (s)} of the transfer function of which is input to the block omega ₁ with motor rotational speed, the transfer function of the motor rotation speed omega ₁ is H _{3 (s)} Is input to a block having a roll speed ω ₂ . Since H ₂ (s) and H ₃ (s) are as shown in Equation ₂ , the roll speed ω ₂ can be uniquely calculated by determining the torque command output from the torque compensator 10. This means that if a roll speed ω ₂ is given, the corresponding torque command can be calculated backward. Therefore, the torque compensator 10 according to the present invention reversely calculates a torque command such that the roll speed ω ₂ when the speed change command is given to the motor has an ideal response waveform without torsional vibration. This is the ideal torque described in FIG. By performing motor control with this ideal torque, the roll speed ω ₂ can be set to an ideal response waveform without torsional vibration.

In the present invention, an ideal speed model considering two inertias is provided in the drive device. This is the motor speed compensator 11 in FIG. The ideal speed ω ₀ output from the ideal rigid body model 8 is converted by the motor speed compensator 11 into an ideal motor speed considering two inertias. This motor speed compensator 11 calculates the ideal motor speed suitable for the two inertia model from the ideal speed ω ₀ in order to correct the model error between the ideal rigid body (one inertia) model 8 and the two inertia model. Then, a deviation from the actually measured motor rotational speed ω ₁ is added and calculated at the combination point 12, and the value is input to the speed control device (ASR) 13 and returned to the torque. As a result, it can be seen that even when the motor speed fluctuates due to disturbance or the like, the speed control device (ASR) can control it according to the command value. Since the ideal torque command and motor speed command are uniquely determined from the mechanical configuration of the motor, roll, and shaft, each transfer function can be expressed by one transfer function. That is, the block diagram of FIG. 4 can be equivalently expressed as shown in FIG. Since the soft volume can be reduced in the block diagram of FIG. 5 than in the block diagram of FIG. 4, FIG.

If the transfer function of the torque compensator 10 (ideal torque model considering two inertias) is H ₄ and the transfer function of the motor speed compensator 11 (ideal speed model considering two inertias) is H ₅ , these are several. It becomes 3 streets.

As shown in Equation 3, the transfer function of the model that takes into account the two inertias has a numerator of the second or third order. Therefore, it is necessary to stabilize the response by setting the denominator to the third order. For this purpose, as shown in the equation, the denominator can be a cubic expression, and a cubic Bessel filter can be used. The transfer function of the third-order Bessel filter is H (s) = 15 / (S ³ + 6S ² + 15s + 15). In order to ensure the stability of the response of the model that takes into account two inertias, the denominator should be 3rd order or higher, but there is no special advantage by increasing the order to 4th order or higher, and the computation is only complicated. Therefore, the third order is sufficient.

  As described above, according to the present invention, the roll speed when a speed change command is given to the motor of the rolling mill can be made an ideal response waveform, and the occurrence of shaft torsional vibration can be prevented. FIG. 6 is a conventional speed response waveform diagram when a step-like speed change command is given to the motor, and shows how the roll speed vibrates due to the influence of shaft torsional vibration. On the other hand, according to the present invention, the speed response waveform diagram when the step-like speed change command is given to the motor is as shown in FIG. I can confirm that. Both are simulation results with a motor speed response of 50 rad / sec.

DESCRIPTION OF SYMBOLS 1 Motor 2 Roll 3 Coupling 4 Reduction gear 5 Spindle 6 Spring 7 Speed control device 8 Ideal rigid body model 9 Adding point 10 Torque compensator 11 Motor speed compensator 12 Adding point

Claims (1)

The power transmission means between them and the rolling mill motor and roll, two inertia of the motor and the roll are virtually as a two-inertia linked by a spring, molecules considering this 2 inertia secondary or 3 The transfer function of an ideal motor speed model that uses a determinant with a denominator of the third or higher order in the following equation, and a denominator of a second or third-order numerator taking into account these two inertias and a denominator of the third or higher order The motor speed compensator of the drive device with the transfer function of the ideal torque model that uses the ideal motor speed and ideal where the roll speed becomes an ideal response waveform without torsional vibration when a speed change command is given to the motor A rolling torsional vibration suppression control method for a rolling mill, wherein a torque command is calculated backward and a motor speed is controlled based on these values.

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