JP2019209370A - Servo press apparatus and control method - Google Patents

Abstract

To reduce fluctuation of a load.SOLUTION: A servo press apparatus includes a servomotor, a press mechanism operated by the servomotor, a desired output load, a current value calculation part for calculating a current value vibrating based on a center current command value by a prescribed period and by a prescribed amplitude, based on a relational expression showing a relation between the center current command value and the output load, and a control device having a current supply part for supplying a driving current having a current value calculated by the current value calculation part to the servomotor.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a servo press device and a control method.

In a device in which an electric motor is incorporated in a servomechanism, there is a method of controlling torque generated by a motor current that is a current that flows through the electric motor. Since the magnitude of the motor current is almost proportional to the magnitude of the torque generated by the motor current, the torque can be controlled by detecting the motor current. This control method is generally called current control (torque control).
As an example of a device in which an electric motor is incorporated in a servo mechanism, a servo press device using a ball screw is known (Patent Document 1).

JP 2004-167548 A

  Conventionally, in a servo press device using a ball screw, control is performed by detecting a load variation from a motor current. In the conventional control method, the influence of the load fluctuation on the motor current is reduced at low output, and the load fluctuation cannot be used for the feedback signal. The reason why the influence of the load fluctuation on the motor current is reduced at the time of low output is that the back torque from the output side to the input side is very small at the time of low output. On the input side, the value of the back torque is the reciprocal of the torque value doubled by the deceleration on the output side. As a result, at the time of low output, the back torque returning to the input side also becomes small, and the current value becomes small.

  In addition, the conventional control method is affected by the characteristics of the speed reducer. Many reducers are known to have non-linear transfer characteristics. Since the response due to the non-linear transfer characteristic can occur at any position of the speed reducer, there is a limit to the method of performing the correction. The effect of the speed reducer is particularly large due to stick motion and lost motion.

There is a jump region where the generated torque changes suddenly in response to a change in current due to stick motion or lost motion. In the jump region, a proportional relationship does not hold between the magnitude of the current and the magnitude of the generated torque.
For the above reasons, it is difficult to use a current instead of a load sensor to control torque. Therefore, in a control method that uses a current instead of a load sensor, it has been required to correct the variation in load in the jump region.

  The present invention has been made in view of the above points, and provides a servo press device and a control method capable of reducing fluctuations in load.

  The present invention has been made to solve the above-described problems. One aspect of the present invention is a servo motor, a press mechanism operated by the servo motor, a desired output load, a center current command value, and an output. Based on a relational expression indicating a relationship with a load, a current value calculation unit that calculates a current value that vibrates based on the center current command value with a predetermined period and a predetermined amplitude, and the current value calculation unit calculates And a control device that includes a current supply unit that supplies a drive current having the current value to the servo motor.

  Further, according to one aspect of the present invention, in the servo press device, the current value calculation unit has a predetermined value obtained by integrating the time difference between the current value and the center current command value with respect to time in a predetermined cycle. The current value that is equal to or less than the value of is calculated.

  One aspect of the present invention is a control method of a servo press apparatus including a servo motor, a press mechanism that is operated by the servo motor, and a control device that supplies a drive current to the servo motor. However, based on a relational expression indicating a relationship between a desired output load and a center current command value and the output load, a current value that oscillates based on the center current command value with a predetermined period and a predetermined amplitude is calculated. A control method comprising: a current value calculation process; and a current supply process in which the control device supplies a drive current having the current value calculated in the current value calculation process to the servo motor.

  According to the present invention, load fluctuations can be reduced.

It is a figure which shows an example of a structure of the servo press apparatus which concerns on embodiment of this invention. It is a figure which shows an example of a structure of the servomotor driver which concerns on embodiment of this invention. It is a figure which shows an example of the electric current value which vibrates on the basis of the center electric current command value which concerns on embodiment of this invention. It is a figure which shows an example of the process of the servomotor driver which concerns on embodiment of this invention. It is a figure which shows an example of the experimental result of the response of the load of the servo press apparatus which concerns on embodiment of this invention.

(Embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating an example of a configuration of a servo press device 1 according to the present embodiment.
The servo press device 1 includes a press mechanism 20, a servo motor 30, and a servo motor driver 40.

The press mechanism 20 will be described.
The press mechanism 20 is operated by a servo motor 30. The press mechanism 20 includes a movable jig 2, a slide 3, a stage 4, a fixing jig 5, a leaf spring 6, a load cell 7, a base plate 8, a belt 9, a driving pulley 10, and a driven pulley 11. And a ball screw 12.

  One end of the ball screw 12 is rotatably supported on the slide 3. A driven pulley 11 is attached to one end of the ball screw 12. A belt 9 is wound around the driven pulley 11 and the driving pulley 10. The ball screw 12 is rotated via the belt 9 by the rotation operation of the servo motor 30.

  A slide 3 is supported on the base plate 8 so as to be linearly movable in the axial direction. The slide 3 is screwed into the ball screw 12. When the servo motor 30 is driven to rotate, the slide 3 moves linearly up and down to generate a press load.

  A movable jig 2 is attached to the slide 3. A fixing jig 5 is attached to the stage 4. The workpiece W arranged on the fixed jig 5 is pressed by the movable jig 2 attached to the slide 3 that moves linearly.

  A load cell 7 is provided between the base plate 8 and the stage 4 via a leaf spring 6. The load cell 7 detects the press load of the servo press device 1. In the present embodiment, since the press load of the servo press device 1 is detected by the drive current ID flowing through the servo motor 30, the load cell 7 may not be provided.

  The servo motor driver 40 supplies the drive current ID to the servo motor 30 based on the output load F supplied by the computer PC.

Here, the configuration of the servo motor driver 40 will be described with reference to FIG.
FIG. 2 is a diagram illustrating an example of the configuration of the servo motor driver 40 according to the present embodiment. The servo motor driver 40 includes a current value calculation unit 41 and a current supply unit 42.

  The current value calculation unit 41 calculates a current value C that oscillates based on the center current command value I with a predetermined period and a predetermined amplitude based on the output load F supplied by the computer PC and the equation (1). .

  Expression (1) is an expression showing the relationship between the center current command value I and the output load F. Here, the derivation method of Formula (1) is demonstrated. First, when the servo press apparatus 1 is operated under predetermined conditions, the center current command value I and the output load F are measured at each time. Here, the predetermined condition is a condition in which the load is 50% in a cycle of 12 ms, for example.

  From the center current command value I measured every time, an approximate expression expressing the center current command value I as a primary expression of time is calculated by the least square method. From the output load F measured every time, an approximate expression that expresses the output load F as a linear expression of time is calculated by the least square method. The time variable is eliminated from the approximate expression expressing the central current command value I as a primary expression of time and the approximate expression expressing the output load F as a primary expression of time, and the relationship between the output load F and the central current command value I is shown. Equation (2) is obtained.

When Expression (2) is solved for the center current command value I, Expression (1) is derived.
The current value calculation unit 41 calculates a current value C that oscillates based on the center current command value I calculated by the equation (1).

Now, with reference to FIG. 3, the current value C that oscillates with the center current command value I as a reference will be described.
FIG. 3 is a diagram illustrating an example of a current value C that oscillates based on the center current command value I according to the present embodiment. In FIG. 3, the current value C is shown with respect to time. The current value C oscillates between the straight line UL and the straight line DL with reference to the center current command value I expressed by a linear expression for time in the period T1. The enlarged view G is a diagram showing the current value C in the region R with the time axis scale changed from sec to msec.

Here, the straight line UL is a straight line showing a value larger than the center current command value I expressed by a linear expression by a predetermined value. The straight line DL is a straight line showing a value smaller than the center current command value I expressed by a linear expression by a predetermined value. The straight line UL and the straight line DL define the amplitude when the current value C vibrates with the center current command value I as a reference. The amplitude when current value C vibrates with reference to center current command value I is equal to the difference between straight line UL and straight line DL.
The current value C alternately takes the value indicated by the straight line UL and the value indicated by the straight line DL at predetermined intervals. That is, the current value C oscillates by alternately taking the value indicated by the straight line UL and the value indicated by the straight line DL at predetermined intervals with the center current command value I as a reference. Here, the predetermined period is, for example, 6 msec.

  In the period T2, the center current command value I takes a constant value. In the period T2, the current value C oscillates between the straight line UL and the straight line DL with the central current command value I taking a constant value as a reference. In the period T1 and the period T2, the period and amplitude of the oscillation of the current value C are not changed.

  As described above, the current value calculation unit 41 is centered at a predetermined cycle and a predetermined amplitude based on the desired output load F and the equation (1) indicating the relationship between the center current command value I and the output load F. An oscillating current value C is calculated based on the current command value I.

Returning to FIG. 2, the description of the configuration of the servo motor driver 40 will be continued.
The current supply unit 42 supplies the drive current ID of the current value C calculated by the current value calculation unit 41 to the servo motor 30. Here, the current supply unit 42 generates a drive current ID having a current value C based on the feedback signal FB supplied from the servo motor 30. The feedback signal FB is a signal indicating the rotational position of the servo motor 30 detected by, for example, an encoder provided in the servo motor 30.

  In addition to the feedback signal FB, a press load feedback signal may be supplied from the load cell 7 to the current supply unit 42. This press load feedback signal is a signal indicating the press load of the servo press device 1 detected by the load cell 7. When a press load feedback signal is supplied from the load cell 7 to the current supply unit 42 in addition to the feedback signal FB, the current supply unit 42 receives the feedback signal FB supplied from the servo motor 30 and the press supplied from the load cell 7. A drive current ID having a current value C may be generated based on the load feedback signal.

Next, a process in which the servo motor driver 40 supplies the drive current ID to the servo motor 30 will be described with reference to FIG.
FIG. 4 is a diagram illustrating an example of processing of the servo motor driver 40 according to the present embodiment.

Step S100: The current value calculation unit 41 acquires an output load F supplied by the computer PC.
Step S110: The current value calculation unit 41 calculates a current value C that oscillates based on the center current command value I with a predetermined period and a predetermined amplitude based on the acquired output load F and Equation (1). . The current value calculation unit 41 supplies the calculated current value C to the current supply unit 42.

Step S120: The current supply unit 42 generates a drive current ID based on the current value C calculated by the current value calculation unit 41, and supplies the generated drive current ID to the servo motor 30.

With reference to FIG. 5, the experimental result of the response of the load of the servo press apparatus 1 will be described.
FIG. 5 is a diagram illustrating an example of an experimental result of load response of the servo press device 1 according to the present embodiment. The load measurement value L1 indicates the time change of the load by the servo press device 1. Here, the load measurement value L1 is a measurement value when the drive current ID of the current value C shown in FIG.
The approximate straight line LA is a straight line obtained by approximating the load measurement value L1 by a straight line in the range of 600N to 1600N.

  In order to compare with the load measurement value L1 by the servo press apparatus 1, the conventional load measurement value L0 by the conventional servo press apparatus is shown. In the conventional servo press apparatus, unlike the current value C shown in FIG. 3, a drive current having a current value that does not vibrate is supplied to the servo motor.

In the conventional load measurement value L0, a load jump point J1 occurs near 24s, and a load jump point J2 occurs near 37s. On the other hand, in the load measurement value L1, unlike the conventional load measurement value L0, the occurrence of the load jump point J1 and the load jump point J2 is suppressed.
The cause of the load jump point J1 and the load jump point J2 is considered to be mainly lost motion and stick motion.
The main cause of lost motion is elastic deformation of ball screws, nuts, and housings.

  In stick motion, due to the delay of the servo system, a torque sufficient to start the servo motor cannot be obtained, and an instantaneous stop state occurs. Stick motion occurs in a state where the speed is zero, that is, in a stationary state. The cause of stick motion is static frictional force. Unlike the lost motion, the stick motion returns to the normal trajectory when it starts to move even if an instantaneous stop state occurs.

  In the above-described embodiment, the current value calculation unit 41 vibrates by alternately taking the value indicated by the straight line UL and the value indicated by the straight line DL at predetermined intervals with the center current command value I as a reference. The case where the current value C to be calculated is described, but the present invention is not limited to this. The current value calculation unit 41 may calculate a current value in which a value obtained by integrating the time difference between the current value and the center current command value I with respect to time in a predetermined cycle is equal to or less than a predetermined value. For example, the current value calculation unit 41 may calculate the current value so that a value obtained by integrating the time difference between the current value and the center current command value I with respect to time in a predetermined period becomes zero.

As described above, the servo press device 1 according to the present embodiment includes the servo motor 30, the press mechanism 20, and the control device (servo motor driver 40).
The press mechanism 20 is operated by a servo motor 30.
The control device (servo motor driver 40) includes a current value calculation unit 41 and a current supply unit 42.
Based on a desired output load F and a relational expression (formula (1)) showing a relationship between the center current command value I and the output load F, the current value calculation unit 41 performs center current with a predetermined period and a predetermined amplitude. An oscillating current value C is calculated based on the command value I.
The current supply unit 42 supplies the drive current ID of the current value C calculated by the current value calculation unit 41 to the servo motor 30.

  With this configuration, in the servo press device 1 according to the present embodiment, the drive current ID having the oscillating current value C can be supplied to the servo motor 30, so that fluctuations in load can be reduced. Here, in the servo press device 1 according to the present embodiment, since the drive current ID having the oscillating current value C is supplied to the servo motor 30, the slide 3 does not stand still during the press working. In the servo press device 1 according to the present embodiment, since the slide 3 does not stop in the process of pressing, the occurrence of stick motion can be suppressed and the variation in load can be reduced.

Further, in the servo press device 1 according to the present embodiment, the current value calculation unit 41 has a value obtained by integrating the time difference between the current value C and the center current command value I with respect to time in a predetermined period is equal to or less than a predetermined value. A current value C is calculated.
With this configuration, in the servo press device 1 according to the present embodiment, the value obtained by integrating the time difference between the current value C and the center current command value I with respect to time in a predetermined cycle is not less than a predetermined value. Since the value obtained by integrating the current value C with respect to time in a predetermined cycle and the value obtained by integrating the center current command value I with respect to time in a predetermined cycle are close to each other, the current value C and the central current command value I are Compared to a case where the value obtained by integrating the difference with respect to time in a predetermined cycle is not less than or equal to the predetermined value, the variation in load can be reduced by the drive current ID of the current value C close to the center current command value I.

  As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to

DESCRIPTION OF SYMBOLS 1 ... Servo press apparatus, 20 ... Press mechanism, 30 ... Servo motor, 40 ... Servo motor driver, 2 ... Movable jig, 3 ... Slide, 4 ... Stage, 5 ... Fixed jig, 6 ... Leaf spring, 7 ... Load cell , 8 ... base plate, 9 ... belt, 10 ... drive pulley, 11 ... driven pulley, 12 ... ball screw, W ... work, PC ... computer, ID ... drive current, FB ... feedback signal, C ... current value, I ... center Current command value, F ... output load, 41 ... current value calculation unit 41, 42 ... current supply unit 42

Claims (3)

A servo motor,
A press mechanism operated by the servo motor;
Based on a desired output load and a relational expression indicating the relationship between the center current command value and the output load, a current value for calculating a current value that oscillates based on the center current command value with a predetermined period and a predetermined amplitude A calculation unit;
A control device comprising: a current supply unit that supplies the servo motor with a drive current of the current value calculated by the current value calculation unit;
Servo press device comprising: The current value calculation unit calculates the current value in which a value obtained by integrating a time difference between the current value and the center current command value with respect to time in a predetermined cycle is equal to or less than a predetermined value. Servo press device. A servo press apparatus control method comprising: a servo motor; a press mechanism operated by the servo motor; and a control apparatus that supplies a drive current to the servo motor.
Based on a relational expression indicating a relationship between a desired output load and a center current command value and an output load, the control device vibrates based on the center current command value with a predetermined period and a predetermined amplitude. Current value calculation process for calculating
A current supply process in which the control device supplies a drive current of the current value calculated in the current value calculation process to the servo motor;
A control method.

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