JPH07261845A - Positioning control unit for servomotor - Google Patents

Abstract

PURPOSE:To provide the positioning control unit for the servomotor which can shorten a stop control time, specially, in stop control. CONSTITUTION:A speed command is found from the difference between the value of a position command part 11 and the actual position of an actual position detector 14, and this command speed command or a speed command '0' set by a speed setting part 17 is selected with a 1st switch 16. A state measurement part 18 decides a current position does not reach a final position yet and the speed command from a position control part 12 is smaller than a set value. A to decide that the actual speed is larger than the set value, and the switching to the speed command is performed with the 1st switch 16, thereby obtaining a torque command corresponding to the speed command selected under PI control. This torque command and the fixed torque command of a torque command part 21 are selected with a 2nd changeover switch 20 and when it is decided that the speed command from the position control part 12 is larger than the set value A, the fixed torque command is selected, preventing undershooting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo motor positioning control device improved so that only an undershoot at the time of stop can be suppressed even when a control loop gain is increased to shorten a positioning time.

[0002]

2. Description of the Related Art In a servomotor used for machining / assembling machine tools, work robots, etc., in order to shorten the positioning time for controlling the final stop position, a control loop gain (position loop gain, Speed loop gain, current loop gain, etc.) are increased to improve the quick response. It is scientifically considered that it is desirable to set the damping coefficient ξ to 0.6 to 0.8 in the follow-up control of the servo motor control.

However, even if the damping coefficient ξ is adjusted to increase the gain in a desired range, undershoot occurs in the process from the deceleration region to complete stop, and as a result, the positioning time cannot be shortened. . That is, if the position gain is adjusted to a high value, undershoot occurs during the period (4) of the speed command as shown in Fig. 4, and therefore undershoot also occurs at the actual speed of the servo motor, resulting in a short positioning time. I won't. In this case, the deceleration torque command is controlled to decrease as the speed command decreases in the deceleration period (2). Then, the torque deceleration command is gradually approached to zero toward the stop control period (3), and is made zero during the period (4).

Also, in the technique disclosed in Japanese Patent Laid-Open No. 62-77606, S-shaped acceleration / deceleration control and exponential acceleration / deceleration control are performed by I-PD control. Is extremely difficult to set, and this time constant results in an adverse effect of shortening the positioning time.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and in the state where the overshoot is maximized within a desired damping coefficient range by increasing the quick response of the positioning operation, the damping stop is achieved. It is an object of the present invention to provide a positioning control device for a servo motor in which undershoot is effectively suppressed and the positioning time is effectively shortened.

[0006]

In a servo motor positioning control device according to the present invention, a position control means generates a first speed command based on a difference between a control command position and an actual position, and at the same time, the first speed command is generated. The deceleration judgment is made based on the speed command of the above. The stop period is judged by judging that the first speed command from the position control means becomes smaller than a preset value. The second speed control means performs the actual speed determination by comparing the actual speed at this time with a constant based on the mechanical time constant of the controlled object in a state where it is determined to be in the stop period. When it is determined that the actual speed is smaller than the constant based on the target time constant, the speed command is set to the stop speed. Then, the control command is stopped at the stop position without undershooting.

[0007]

In the servo motor positioning control device having such a structure, in the deceleration range, the actual current is obtained from the actual position and the actual speed obtained from the position detecting means, and the actual speed becomes negative. The timing at which to be reached and the timing to reach final positioning are estimated. Then, the speed command is specified by disconnecting the speed command from the position command and further disconnecting the torque command from the first speed command before the actual speed is not opposite to the command and before the final positioning is reached. By switching to the speed command and the torque command, the actual speed is always made to have the same polarity as the command, and the occurrence of undershoot is suppressed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration, for example, a position command unit based on an operation command program set by the user.
A position command to move is output from 11 every fixed sampling time. The position command from this position command unit 11 is input to the position control unit 12, and this position control unit 12 is supplied with the actual position from the position detector 14 set corresponding to the motor and the load 13, and The difference between the command and the actual position is required. Then, the velocity signal of the difference between the position command and the actual position is multiplied by the position gain Kp and output as the first velocity command.

The first speed command from the position control unit 12 is supplied to the terminal a of the first changeover switch 16 of the speed control unit 15, and the other terminal b of the first changeover switch 16 receives the speed. The speed command from the command unit 17 is input. The speed command section 17 is supplied with a command from the state measuring section 18 to which data is supplied from the position detector 14, and outputs a preset speed command irrespective of the position control section 12.

The speed command obtained from the first changeover switch 16 is an actual value obtained by differentiating the data obtained from the position detector 14 at a constant sampling time by a differentiating circuit (differential operator s) 19. This is compared with the speed, the deviation is obtained, and PI control is performed based on the speed proportional gain Kvp and the speed integral gain Kvi. The torque command is obtained by this PI control. Then, this torque command is connected to the terminal a of the second changeover switch 20. Here, this torque command is calculated based on the following formula.

[0011]

[Equation 1]

A torque command unit 21 to which a command is given from the state measuring unit 18 is applied to the other terminal b of the second changeover switch 20.
The torque command output from the second switch 20 is input to the current loop 23 constituting the current control unit 22. Then, a current command required to generate the torque obtained from the switch 20 in the motor is created. This current command is, for example, when the load is A
In the case of the C servo motor, it is calculated based on the following equation. Here, the torque command unit 21 outputs a preset torque command regardless of the speed control unit 15. Further, the state measuring unit 18 is a portion for judging switching of the first and second switches 16 and 20, and switches from the actual position obtained from the position detector 14 and the actual speed which is a differential value thereof according to a predetermined program. Output a command.

[0013]

[Equation 2]

In the current loop 23, the deviation between the current command thus obtained and the actual current of the motor is PI controlled, and the actual current flowing to the motor is controlled by this PI control. . The output current from the current loop 23 is supplied to the motor and the load 13. "1 / (Js + d)" [where J is (rotor inertia of motor) + (load etc. coupled to shaft of motor) By the motor shaft equivalent load inertia), d is a viscous damping constant, and s is a differential operator].

FIG. 2 shows the flow of the processing operation of the device constructed as described above. First, at step 101, it is judged whether or not it is a deceleration process. That is, it is recognized whether or not the speed command generated by the position control unit 12 is in the process of being uniformly reduced, and it is recognized that the speed command is in the deceleration process. This is the process in which the speed command decreases after the decrease.

If it is determined in step 101 that the vehicle is in the deceleration process, in step 102, the current position (obtained by the position detector 14) is finally reached by the position to be finally moved (total movement amount). Value) is reached. Specifically, when the final positioning position is P _F and the actual position is P _{R (n)} , the actual position P up to the front P _A of the final position P _F (the area determined to have reached the final positioning position)
It is determined whether _{R (n)} has arrived.

If it is determined in step 102 that the actual position P _{R (n)} has not reached the front position P _A of the final position P _F , in step 103 the speed command V _CMD from the position controller 12
Is larger than a preset value A. This process corresponds to the deceleration process (2) in the timing chart shown in FIG. 3, and the value A is the value determined by the following formula based on the mechanical time constant determined by the motor and load 13. is there.

[0018]

[Equation 3]

If it is judged that the speed command V _CMD is larger than the set value A, the routine proceeds to step 104, where the torque command value T
_The current position P with respect to the constant Vy obtained corresponding to _rCMD
The value P _{R (n-1)} obtained from the previous sampling from _{R (n)}
By dividing the difference by the sampling time, the actual rate _{"P R (n) -P R} (n-1) / t s" up to this sampling is determined based on whether Vy is less than the following equation.

[0020]

[Equation 4]

When it is determined in step 104 that the actual speed is lower than the set value Vy, when it is determined in step 101 that the deceleration process is not in progress, and when it is determined in step 102 that the final positioning position is reached. Step with
In step 105, both the first changeover switch 16 and the second changeover switch 20 are set to the contact a side. Again step
When it is judged in 103 that the speed command V _CMD is larger than the set value A, the routine proceeds to step 106, where the second changeover switch
Insert 20 into the terminal b side. When it is determined in step 104 that the actual speed is higher than the set value Vy, the process proceeds to step 107, the first changeover switch 16 is changed over and connected to the b side, and the second changeover switch 20 is changed to the terminal a side. And the speed command is set to the speed command unit 17, for example, "0".

Then, in step 108, position control, speed control, and current control are performed based on the speed command and torque command obtained corresponding to the set states of the first and second changeover switches 16 and 20. To do so.

That is, when the position gain Kp is maximized in the prior art, an undershoot occurs during the period of the speed command (4) shown in FIG.

On the other hand, in the decay period (4), as shown in FIG.
In the case of, the torque command becomes smaller as the speed command becomes smaller, but in the device of the embodiment, the torque command (torque command for stopping) is changed to the second as shown in FIG.
The maximum value T _LMT of the torque command allowable value is set by switching the changeover switch 20 of b to the side b, so that the rotation of the motor _tends to be stopped. Then, in the state measuring unit 18, the actual speed of the motor is set. Is less than or equal to the set value A, it is switched to the terminal a side by the second changeover switch 20 for switching the torque command, and the speed command obtained by the speed control unit 15 is a command on the side opposite to the current rotation direction ( At the moment when the negative rotation command) is reached, the first changeover switch 16 for changing over the speed command is immediately changed over to the b side (period (4) in FIG. 3). And
The speed command is fixed to, for example, "0" set by the speed command unit 17.

When the state measuring unit 18 determines that the actual speed of the motor is equal to or less than the constant Vy,
By returning the first changeover switch 16 to the terminal a side at that moment, even if the position loop gain Kp is maximized within the range of the deceleration coefficient desirable for enhancing the quick response, the undershoot as shown in FIG. As a result, the positioning time can be shortened as shown in FIG.

[0026]

As described above, according to the servo motor positioning control device of the present invention, the timing at which the speed command from the position controller becomes negative and the speed command at the negative speed after the command speed becomes negative. By estimating the timing of turning and the timing of reaching the final positioning position, the speed command is separated from the position control unit and the torque command from the speed control unit before reaching the final positioning position, and the set speed command is set. And the torque command can be sequentially switched. Then, when the actual speed is always the same polarity as the command and the allowable value specified up to the final positioning is reached, the original position control is resumed, eliminating the undershoot at the time of stop and shortening the stop time. It will be possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining a positioning control device for a servo motor according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a flow of operations of the above embodiment.

FIG. 3 is a timing chart illustrating a control state of the above embodiment.

FIG. 4 is a timing chart illustrating a conventional control device of this type.

[Explanation of symbols]

11 ... Position command unit, 12 ... Position control unit, 13 ... Motor and load, 14 ... Position detector, 15 ... Speed control unit, 16, 20 ... First and second changeover switch, 17 ... Speed command unit, 18 ... State measuring section, 19 ... Differentiating circuit, 21 ... Torque command section, 22 ... Current control section, 23 ... Current loop.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display H02P 3/06 C

Claims (2)

[Claims] 1. A position control means for generating a first speed command based on a difference between a control command position and an actual position, and a deceleration period is determined based on the first speed command from the position control means. Deceleration determination means, stop period determination means for determining that the first speed command from the position control means has become smaller than a preset value, and in the state determined to be the stop period, When the actual speed is determined to be smaller than the constant based on the mechanical time constant by the actual speed determination means for comparing the actual speed and the constant based on the mechanical time constant of the controlled object, A positioning control device for a servo motor, comprising: a second speed control means for setting a speed command to a stop speed, so that the position is stopped without undershooting at a stop position of the control command. 2. A first position detection means for detecting a real position of a position-controlled servo motor, and a first position detection means based on a difference between an input control position command and a real position detected by the real position detection means. Position control means for outputting a speed command, first switch means for selecting one of the second speed commands specified as the first speed command, and speed command output from the first switch means. A speed control means for outputting a first torque command on the basis of the first torque command; a second switch for selecting one of the first torque command output from the speed control means and a fixed second torque command that has been set. Means and current control means for controlling the drive current of the servomotor based on the output torque command from the second switch means, and it is determined that the actual speed of the servomotor is smaller than a specified value. In the state where the first switch means selects the second speed command, and the output speed command from the first switch means is made smaller than the value specified corresponding to the stop region. 2. A servo motor positioning control device, wherein switching control is performed so as to select the second torque command corresponding to the maximum value by means of two switch means.