JPH10105247A - Overshoot preventing method for servomotor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of overshoot when the servomotor moves and stops and to prevent the degradation of positioning precision at the time of positioning. SOLUTION: While there is a move command, a flat F is set to '0' to perform speed loop processes as ordinary proportional integral processes, and a torque command Tc is found and outputted (S1 to S3, S9, S10, S7, and S8). When the move command becomes '0' and position deviation becomes less than set threshold width ε, an integral value Σn-1 up to a last cycle is multiplied by a coefficient K3 which is less than 1 to obtain a small integral value, and a torque command Tc is found (S5, S6, and S7). Further, the flag F is set to '1'. In subsequent cycles, the ordinary speed loop processes (S10 and S7) are performed. When the move command becomes '0' and the position deviation becomes less than the threshold width ε, the integral value is switched to the small value only once. Consequently, an overshoot is prevented, the position precision is improved, and vibration generation at a stop time can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a servomotor for positioning a movable portion of various industrial machines such as machine tools and robots, and more particularly to a method for preventing occurrence of overshoot.

[0002]

2. Description of the Related Art In controlling movable parts of various industrial machines, such as a feed shaft of a machine tool or a robot arm, which is driven using a servomotor, an overshoot occurs immediately before the movable part is stopped at a target position. Occurs. As a method of preventing the occurrence of the overshoot, at the moment when the actual position of the servomotor or the movable portion reaches the command target position, that is, the position deviation which is the difference between the target command position and the actual position is set to the set threshold width. When it is within the range, the contents of the integrator in the speed control loop are cleared to reduce the torque command to the servomotor, and the output torque of the servomotor is reduced to the dynamic friction level or less to prevent overshoot. Have been.

[0003]

In order to improve the response, a method of controlling the position of the servomotor by applying a feedforward to a position loop has been adopted. In the method of controlling the motor, in order to prevent the occurrence of overshoot at the time of positioning, when the above-described method of setting the value of the integrator of the speed loop to “0” when the position deviation is within the threshold width is adopted, the movement is reduced. In some cases, the value of the integrator is set to “0” on the way. That is, when driving the servo motor at a very slow speed, the feed forward control works effectively, and the servo motor is driven with a small position deviation,
This is because the position deviation falls within the set threshold width and the value of the integrator of the speed loop is set to “0”.

When the actual position reaches the vicinity of the target position after the end of the movement command, the position deviation falls within the set threshold width and the integrator is set to "0", the output torque of the servomotor decreases. On the other hand, the motor may be pushed back by the machine due to the spring element of the machine driven by the servo motor, and the positional deviation may again be out of the threshold width. When the position deviation is out of the threshold width, the torque command is increased so as to reduce the position deviation, and the motor output torque is also increased, so that the position deviation again falls within the threshold width, and the integrated value is cleared to "0" again. . This was repeated, and as a result, the position of the machine sometimes oscillated around the threshold value. Also, depending on which side (+ side, − side) of the threshold width, the center of vibration is located on the + side or the − side of the threshold width, and the location thereof is different. The phenomenon that was damaged was occurring.

Accordingly, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, to prevent the occurrence of overshoot when the movement of the servomotor is stopped, and to prevent the positioning accuracy from being deteriorated during positioning. Things.

[0006]

According to the present invention, when the position deviation falls within a set threshold value width after the movement command becomes zero, the value of the integrator of the speed loop is switched to a small value to thereby reduce the value. Shooting was prevented, and the integrator was switched to a small value during the movement to prevent the movement from stopping. Further, the value of the integrator in the above speed loop is switched to a small value only when the position deviation first becomes within the set threshold width after the movement command becomes zero, thereby generating vibration during positioning. Was prevented.

[0007]

FIG. 2 is a schematic block diagram of an embodiment of a servomotor control system in a machine tool or the like to which the present invention is applied. Since it is the same as a conventional configuration, only an outline is shown. I have. Numeral 1 denotes a numerical controller (CNC) with a built-in computer for controlling a machine tool or the like, and numeral 2 transfers movement commands and various signals output from the numerical controller 1 to a processor of a digital servo circuit 3, and Is a shared memory used to transfer the various control signals and status signals to the numerical controller 1.
The digital servo circuit 3 includes a processor, ROM, and R
It consists of a memory such as AM, etc.,
The speed feedback control is performed by software control. Reference numeral 4 denotes a servo amplifier which is constituted by a transistor inverter or the like and drives the servo motor 5, and 6 denotes a position and speed detector such as a pulse coder which detects the position and speed of the servo motor 5 and feeds it back to the digital servo circuit 3.

[0008] The processor of the digital servo circuit 3
The process shown in FIG. 1 is executed for each position / speed loop processing cycle, and the servo motor 5 is controlled. The processor of the digital servo circuit 3 reads the movement command for each distribution cycle sent from the numerical controller 1 via the shared memory 2 and converts it into the movement command for each position / speed loop processing cycle, as in the related art. The position deviation is obtained by adding the movement command to a register for storing the position deviation and subtracting and inputting the movement amount of the servo motor 5 fed back from the position / speed detector 6 into the register. A position loop process for obtaining a speed command Vc by multiplying by a loop gain is performed (steps S1 and S2).

Next, it is determined whether or not the movement command input to the register is "0". If not, the flag F is set to "0" (step S9), and the position loop processing in step S2 is performed. From the obtained speed command Vc,
The speed deviation obtained by subtracting the actual speed Vfb of the servo motor 5 fed back from the speed detector 6 is multiplied by the integral gain k1, and the obtained value is integrated by the integral value Σn- Then, the integral value に お け る n in the cycle is obtained by adding the value to 1 (step S10). That is, the integration process in the speed loop control is performed in step S10.

Thereafter, a value obtained by multiplying the speed deviation (Vc-Vfb) by the proportional gain K2 is added to the integral value .DELTA.n of the cycle to obtain a torque command Tc. This step S10
And the processing in step S7 correspond to the speed loop processing. In this embodiment, the speed loop processing of the proportional integration (PI) processing is performed. The torque command Tc obtained in this way is transferred to the current loop (step S8), and the processing of the position / speed loop processing cycle ends. In the current loop processing, the servo motor 5 is driven by controlling the current flowing through each phase of the servo motor based on the torque command Tc.

In the following, steps S1 to S3, S9, S10,
The processes of S7 and S8 are repeatedly executed, and the position and speed of the servo motor 5 are feedback-controlled. On the other hand, if there is no movement command and it is determined in step S3 that the movement command is "0", it is determined whether the flag F is "1" (step S3).
4) Since the flag F is initially set to "0" in step S9, the process proceeds from step S4 to step S5, where the position deviation stored in the register is read by the position loop processing in step S2, and the position deviation is read. It is determined whether the position deviation is equal to or smaller than the set threshold width ε. If the positional deviation is larger than the threshold width ε, the above-described step S1
The normal integration process of 0 is performed, and the torque command T
Deliver c to the current loop. That is, normal speed loop processing is performed.

As long as the position deviation is larger than the threshold width ε, the processing of steps S1 to S5, S10, S7 and S8 is performed for each position / speed loop processing cycle, and the actual position of the servo motor 5 is near the target position where the command is issued. Is reached and the position deviation falls within the threshold width ε, the process proceeds from step S5 to step S6, where the integral value Σn-1 up to the previous cycle is multiplied by the set coefficient k3 to obtain the integral value Σn of the cycle. The coefficient 3 is set to a value larger than 0 and smaller than 1 (0 <K3 <1), and as a result, the integral value becomes a small value. Further, the flag F is set to “1”. Then, a value obtained by multiplying the speed deviation (Vc-Vf) by the proportional gain K2 and the integral value .DELTA.n are added to obtain a torque command Tc of the cycle (step S7) and output to the current loop (step S8). Since the integral value can be switched to a smaller value,
The torque command Tc becomes small, the output torque of the servo motor 5 becomes small, and the occurrence of overshoot is prevented.

From the next cycle, since the flag F is set to "1", after performing the processing of steps S1 to S4, the processing shifts to step S10 to perform the normal integration processing.
Since the integration value has already been switched to a small value, the integration value does not become large even if the integration process of step S10 is executed. Then, the process proceeds to step S7, and a value obtained by multiplying the integral value by the speed gain by the proportional gain K2 is added to obtain a torque command Tc, which is transferred to the current loop (step S8). This prevents overshoot from occurring when the servomotor stops moving. Thereafter, the above steps S1 to S4, S10, S
7 and S8 are executed for each cycle. As a result, even if the integral value is switched to a small value and the torque command Tc becomes small, the output torque of the servomotor 5 decreases, and even if the servomotor is pushed back in the opposite direction by the spring element of the machine, the position deviation increases. , The flag F is set to “1”, and steps S4 to S10
Then, the processing of steps S5 and S6 is not performed, and the integrated value is not switched to a small value again, so that the occurrence of vibration can be prevented.

Next, a movement command is output again and step S is executed.
If it is detected in step 3 that the movement command is not "0", the process proceeds to step S9, where the flag F is set to "0" and the normal speed loop processing (steps S10 and S7) is performed to obtain the torque command Tc. Become. When the position feedforward control is performed, the position feedforward control process is executed together with the position loop process in step S2 to obtain the speed command Vc. However, since the position feedforward process is conventionally known, it will be described. Is omitted.

FIG. 3 is a diagram for explaining the operation of the above processing.
When the movement command as shown in FIG. 3A is output, the servo motor 5 is driven, and the speed of the servo motor 5 is stable, the position deviation and the position deviation as shown in FIGS. The integrated value of the integrator keeps a substantially constant value. When there is no movement command (step S3), the position deviation decreases. When the position deviation falls below one of the set threshold widths (step S5), the integral value of the integrator is reduced to a small value. Switching and setting the flag F to "1" (see step S6 and FIGS. 3 (c) and 3 (d)). When the position deviation is within the threshold width ε, the speed is low, so the speed deviation is not large and the increase in the integral value of the integrator is small. Then, when the next movement command is output, the flag F is set to "0", the integrated value gradually increases, and the ordinary position / velocity loop processing is performed.

FIGS. 4 to 6 show the results of experiments performed to see the effects of the present embodiment. For positioning at a position of 0.1 mm, when moving from a position smaller than the position and when moving from a position larger than the position (positioning by moving in the positive direction and positioning by moving in the negative direction) It is an experimental result of two examples. FIG. 4 shows an experimental result when the overshoot prevention for reducing the integral value when the movement is stopped is not performed. As shown in FIG. 4, overshoot occurs at the time of stopping.

FIG. 5 shows the result of an experiment performed when the integrated value is reduced to a small value when the position deviation, which has been performed conventionally, falls below the threshold value. Although the occurrence of overshoot is prevented, a step is generated in the positioning position depending on the positioning direction, which deteriorates the positioning accuracy. In addition, the vibration at the time of stopping is increased. FIG. 6 shows an experimental result when the present invention is implemented. As shown in FIG. 6, it can be seen that no overshoot occurs, no step occurs depending on the positioning direction, and the vibration at the time of stop is smaller than that in FIG.

In the above embodiment, step S6
In order to reduce the integral value in the above, the integral value was reduced by multiplying the integral value Σn-1 up to the previous cycle by a coefficient K3 smaller than 1, but instead of this processing, the integral value was switched to a preset small value. It may be.

[0019]

According to the present invention, the positioning accuracy is improved without generating an overshoot when the movement of the servomotor is stopped, and no step relative to the positioning position is generated depending on the positioning direction, and the vibration at the time of stopping is reduced. Can be.

[Brief description of the drawings]

FIG. 1 is a flowchart of processing in a position / velocity loop processing cycle according to an embodiment of the present invention.

FIG. 2 is a block diagram of a control system of the embodiment.

FIG. 3 is an operation explanatory diagram in the embodiment.

FIG. 4 is a diagram showing an experimental result when a servomotor is positioned by a conventional control method without taking measures to prevent the occurrence of overshoot.

FIG. 5 is an experimental result when a servomotor is positioned by applying a conventional overshoot prevention method for reducing an integral value when a position deviation becomes equal to or less than a threshold value.

FIG. 6 is an experimental result when a servomotor is positioned by applying the present invention.

[Explanation of symbols]

 Reference Signs List 1 Numerical controller (CNC) 2 Shared memory 3 Digital servo circuit 4 Servo amplifier 5 Servoter 6 Position / speed detector

Claims (2)

[Claims] In a control method of a servomotor having a speed loop in a position loop, when a position deviation falls within a set threshold width after a movement command becomes zero, a value of an integrator of the speed loop is changed. An overshoot prevention method for a servo motor, characterized in that overshoot is prevented by switching to a small value. 2. A method for controlling a servomotor having a speed loop in a position loop, wherein the integrator of the speed loop is provided only when the position deviation first becomes within a set threshold width after the movement command becomes zero. A method for preventing overshoot of a servo motor, characterized in that overshoot is prevented by switching the value of (1) to a small value.