JP2002278629A - Servo control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent vibration which is likely to be generated at the time of stopping the rotation of a servo motor. SOLUTION: This system is provided with an arithmetic part 8 for calculating torque command fluctuation from a speed command and speed feedback, a torque command fluctuation gain multiplying part 10 for multiplying the torque command fluctuation calculated from the arithmetic part by a gain, and an integrating part 12 for integrating the value outputted from the multiplying part. Also, this system is provided with a control loop for defining the value stored in the integrating part as the toque command, a counter 18 for measuring the lapse of a time since the change value of the position command is turned into zero until a count limit value, a count limit value setting unit 19 for deciding the count limit value of the counter by using the change value of the position command just before the change value of the position command is turned into zero and the torque command, and a toque command variation gain switching unit 22 for setting and switching the gain by which the torque command variation should be multiplied by using the count value and the count limit set value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for a servomotor, and more particularly, to a control method for preventing vibration of a controlled object at the time of stopping axis feed.

[0002]

2. Description of the Related Art In a mechanical control system in which a servomotor moves a table via a ball screw to perform positioning control, when a servomotor is stopped, rotational vibration occurs on a rotating shaft. I have. Therefore, two conventional control methods for preventing the vibration will be described. First, the first conventional method will be described with reference to the block diagram of FIG. In the figure, 4 is a position control unit, 205, 206, 208 are coefficient units, 6 is a differentiator, 2
01 is a counter, 203 is a speed deviation / speed feedback gain switch, 16 is a servo motor, 17 is an encoder built in the servo motor 16, 23 is a ball screw connected to the servo motor 16, and 24 is driven by a ball screw 23. It is a machine table. The encoder 17 outputs a position feedback b according to the rotation amount of the servo motor 16. The machine table 24 is connected to the motor 16 by a ball screw 23 and moves according to the amount of rotation of the servomotor 16. Under such a configuration, the difference between the position command a and the position feedback b becomes the position deviation c, and the position control unit 4 receiving the position deviation c multiplies the position loop gain to output the speed command d. The differentiator 6 to which the position feedback b has been input differentiates and outputs a speed feedback e, and a difference between the speed command d and the speed feedback e is set as a speed deviation f. The coefficient unit 205 to which the speed deviation f is input is multiplied by the gain α, and the output signal is multiplied by the coefficient unit 206 by the speed loop integration constant Ti. The difference between the signal obtained by integrating the output signal by the integrator 207 and the signal obtained by multiplying the speed feedback e by α is multiplied by the speed loop proportional gain Kv by the coefficient unit 208 to obtain the torque command g.

[0003] The current amplifier 14 which has received the torque command g outputs a current command h to the servomotor 16, and the servomotor 16 outputs a torque corresponding to the torque command g. The counter 201 monitors the change amount of the position command a, initializes the count value i when the change amount becomes 0, and continues counting up to the counter limit. The speed deviation / speed feedback gain switch 203 compares the count value i with a predetermined counter limit which is a fixed value.
The gain α of 1 is set to 1, and if they are the same, the value is switched to a value smaller than 1.

Next, a second conventional method will be described with reference to the block diagram of FIG. The speed loop gain switch 301 compares the count value i counted by the counter 201 with the counter limit, and if they are different, the speed loop integral gain Ki
And the speed loop proportional gain Kv is switched to a normal gain in which parameters are set, and if they are the same, the gain is switched to a smaller gain than the normal gain.

[0005]

However, in the above-mentioned conventional method, for example, when the count limit value is set to be longer, the gain α or the speed loop integral gain Ki starts when the amount of change of the position command a becomes zero. In some cases, shaft vibration may occur within a period until the speed loop proportional gain Kv switches. Conversely, if the count limit value is set to a short value, the gain will change during the cutting feed in the case of fine feed in which the period during which the position command change amount is 0 is longer than the counter limit value. There has been a problem that the apparatus is easily affected by disturbance such as force and the precision of the cut surface is reduced.

Further, in the first conventional method, the gain α is multiplied by both the speed deviation f and the speed feedback e.
The calculation of the speed loop is complicated, and the processing time is increased. Further, in the second conventional method, when there is an accumulation in the speed loop integrator 207, in order to maintain the continuity of the torque command g, the speed loop proportional gain Ki and the speed feedback e are used to calculate the speed from the torque command g. There is also a problem that the integration pool of the loop integrator 207 needs to be back calculated, which significantly increases the processing time. Therefore, the present invention has been made to solve these problems, and it is intended to prevent vibration which tends to occur when the rotation of a servomotor is stopped, and to enable accurate positioning. Aim.

[0007]

According to the present invention, there is provided a control method for generating a torque command using a position command and a speed command, position feedback, and speed feedback. A calculating unit for calculating the command variation, a torque command variation gain multiplying unit for multiplying the gain by the torque command variation calculated from the calculating unit, and an integrating unit for integrating the value output from the multiplying unit. A control loop that uses the value stored in the accumulator as a torque command, a counter that measures the elapsed time from the point at which the amount of change in the position command becomes zero to a count limit value, and a change in the position command becomes zero A count limit value setting device that determines the count limit value of the counter using the change amount of the immediately preceding position command and the torque command; Using the count limit set value, to set the gain applied to the torque command variation is characterized in that it comprises a torque command varies the gain switcher for switching. Due to such a configuration, vibration which tends to occur when the rotation of the servomotor is stopped is prevented, and accurate positioning can be performed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a servomotor control device for implementing the control method of the present invention. Since the same components as those described in the related art perform the same operation, different components will be described. In the figure, reference numeral 8 denotes a torque command variation generator, 10 is a torque command variation gain, 12 is an integrator, 18 is a counter, 19
Denotes a count limit value setting device, and 22 denotes a torque command fluctuation gain switching device. Under such a configuration, the torque command fluctuation creator 8 generates the speed command m and the speed feedback e.
To calculate and output the torque command fluctuation j. The count limit value setting unit 19 uses the change amount of the position command a immediately before the change amount of the position command a becomes zero and the torque command g,
The count limit value k of the counter 18 is determined. The counter 18 measures the elapsed time from the time when the change amount of the position command a becomes zero to the count limit value k. Using the count value i and the count limit value k, the torque command variation gain switch 22 sets and switches the torque command variation gain 10 to be applied to the torque command variation j. The integrator 12 adds the torque command fluctuation gain 10 to the torque command fluctuation j.
Are multiplied, and the value is used as a torque command g.

Next, the operation of the torque command variation generator 8 will be described with reference to FIG. In the torque command variation generator 8, a value obtained by subtracting the speed feedback e from the speed command m is set as a speed deviation n, and a value obtained by subtracting the previous speed feedback p from the speed feedback e is set as a speed feedback change q. The value obtained by subtracting the speed feedback fluctuation q from the value obtained by multiplying the speed deviation n by the speed loop integration gain 206 is calculated by the coefficient unit 2.
The value multiplied by the speed loop proportional gain Kv at 08 is output as the torque command fluctuation j.

Next, the processing procedure of the counter 18 will be described with reference to the flowchart of FIG. First (S51)
The amount of change in the position command a is monitored to determine whether or not the amount of change in the position command a is 0. If it is 0 (S52), the count is incremented by 1. If the amount of change is not 0 (S53).
The count value is set to 0. Then, when performing the clamp processing of the count when the count is increased, (S54)
It is compared whether the count is larger than the count limit value. If the count is larger (S55), the count is set as the count limit value, and if not larger, the process is terminated.

Next, the processing procedure of the count limit value setting unit 19 will be described with reference to the flowchart of FIG. First, (S61) the change amount of the position command a is monitored, and the position command a
It is determined whether or not the change amount is 0, and if not, (S6
7) Set the count limit value to 0. If it is 0 (S6
2) The amount of change in the previous position command a is monitored to determine whether or not the amount of change in the position command a is 0. If it is 0 (S67), the count limit value is set to 0. If not 0, then (S
63) It is determined whether or not the torque command is 0. If it is 0 (S66), the count limit value is set to the limit value B. Otherwise (S64), the sign of the previous position command change amount and the sign of the torque command are set. By comparison, it is determined whether the signs are the same. If they are the same (S65), the count limit value is set to the count value A, and if they are different (S66), the count limit value is set to the limit value B. The limit value A and the limit value B are values set by parameters.

Next, the processing procedure of the torque command fluctuation gain switch 22 will be described with reference to the flowchart of FIG. First, (S71) the count value i is compared with the count limit value k to determine whether they are the same.
2) The torque command fluctuation gain is set to 1, and if the same (S73), the torque command fluctuation gain is set to a value set in advance as a parameter.

[0013]

As described above, according to the control method of the present invention, the optimum switching timing of the torque command fluctuation gain s is set according to the amount of change of the position command a, that is, the feed speed command. Because there is no shaft vibration at the time of stop,
In addition, there is an effect that the surface accuracy at the time of extremely low-speed cutting feed can be improved. In addition, there is only one torque command variation gain s, and there is an effect that the calculation time is reduced as compared with the case of using two gains α in the first conventional method. Further, since the torque command variation is multiplied by the torque command variation gain s, the torque command variation gain is multiplied. Therefore, when the torque command variation gain is switched, the integrator 207 of the integrator 207 is reduced from the torque command g as compared with the gain switching method of the second conventional method. Since there is no need to calculate the accumulation back, the torque command fluctuation gain s can be switched very efficiently.

[Brief description of the drawings]

FIG. 1 is a block diagram of a servomotor control device illustrating a method of the present invention.

FIG. 2 is a block diagram of a servo motor control device illustrating a conventional method.

FIG. 3 is a block diagram illustrating a second conventional method for switching a speed loop gain.

FIG. 4 is a block diagram of a calculation unit for calculating a torque variation;

FIG. 5 is a flowchart showing a processing procedure of a counter unit 18;

FIG. 6 is a flowchart showing a processing procedure of a count limit value setting device 19;

FIG. 7 is a flowchart showing a processing procedure of a torque command fluctuation gain switch 22;

[Explanation of symbols]

 4 Position Control Unit 6 Differentiator 8 Torque Command Fluctuation Creator 10 Torque Command Fluctuation Gain 12 Integrator 14 Current Amplifier 16 Servo Motor 17 Encoder 18, 201 Counter 19 Count Limit Value Setter 22 Torque Command Fluctuation Gain Switch 23 Ball Screw 24 Table 205, 2051, 206, 208 Coefficient unit 207 Integrator 301 Speed loop gain switch

Claims (1)

[Claims] 1. A control method for generating a torque command using a position command and a speed command, a position feedback, and a speed feedback, comprising: a calculating unit for calculating a torque command variation from the speed command and the speed feedback; A torque command variation gain multiplying unit for multiplying the gain by the torque command variation to be performed, an integration unit for integrating values output from the multiplication unit, and a control loop that uses the value stored in the integration unit as a torque command. Using a counter that measures the elapsed time from the point in time when the amount of change in the position command becomes zero to a count limit value, and the amount of change in the position command and the torque command immediately before the amount of change in the position command becomes zero, A count limit value setting device for determining a count limit value of the counter; and a torque command change using the count value and the count limit value. Servo control method to set the gain to be applied to minute, characterized in that and a torque command varies the gain switcher for switching.