JP2664432B2 - Servo control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial application field> The present invention relates to a servo control device, and in particular, can quickly perform backlash correction and reduce quadrant protrusions caused by friction and backlash. Related to a simple servo control device.

<Prior Art> When a servomotor is used to control a feed axis of a machine tool, in order to correct backlash of gears and the like at the time of reversing the rotation direction of the servomotor, in other words, at the time of reversing the moving direction of the machine movable part, Generates a speed command by adding the preset backlash correction data to the position deviation data,
The rotation of the servomotor is controlled based on the speed command.

However, since the backlash correction data to be applied to the speed loop through a predetermined position gain K _P, the machine does not move immediately due to the delay of the servo system, the quadrant projection is generated in the order processing direction reversal points.

Therefore, in order to reduce the influence of backlash and friction, and to reduce the projection at the quadrant switching during cutting, an appropriate acceleration amount (referred to as backlash acceleration amount) is added to the speed command for a predetermined time. . In addition, if the backlash acceleration data is performed at the same time as the NC device passes the backlash correction data to the servo side, the motor does not completely reverse direction due to the delay between the command and the servo system, and conversely cuts inward. And the like. Therefore, actually, the rotation direction of the motor is monitored, and the backlash acceleration is performed at the timing of reversal of the rotation direction. If such backlash acceleration control is performed when the rotation direction of the motor is reversed, the occurrence of quadrant protrusions due to mechanical backlash and friction can be significantly reduced.

By the way, if the amount of backlash acceleration is constant over the entire application time, there is no problem at the start of acceleration, but at the end of acceleration, since the speed command changes rapidly, the actual speed also changes rapidly. The effect of the sudden change in speed appears on the cutting surface, causing a problem of lack of smoothness.

Therefore, at the start of acceleration, the backlash acceleration amount is increased to prevent the amount of acceleration from becoming insufficient, and thereafter, it is gradually reduced with time to prevent a sudden change in speed at the end of the backlash acceleration. .

<Problems to be Solved by the Invention> However, the backlash acceleration algorithm itself is an open loop control, and it is necessary to set parameters (acceleration / deceleration time constant, various gains, etc.) for each machine accurately.

The optimum parameters vary depending on the cutting speed, the weight of the workpiece, the temperature, the condition of the cutting surface, and the like. For this reason, even if the quadrant projections can be made very small under certain conditions, there arises a problem that if they are cut under other conditions, the quadrant projections become large or cut inward.

In view of the above, an object of the present invention is to provide a servo control device capable of canceling backlash and friction in the same manner with the same parameters even when machine conditions and cutting conditions change, and eliminating quadrant protrusions. It is.

<Means for Solving the Problems> FIG. 1 is a block diagram of a servo control device of the present invention.

13 is an error counter, 15 is a speed control unit, 18 is a backlash correction timing determination unit, 19 is a torque monitoring unit, and 21 is an acceleration amount output unit.

<Operation> When the backlash correction timing determination unit 18 detects that the position error Er has become zero, the acceleration amount output unit 21
Adds a predetermined backlash acceleration amount _BACC to the speed command _VCMD to quickly and smoothly correct backlash. If the torque monitoring unit 19 detects that the torque command T _CMD output from the speed control unit 15 has become equal to the preset static maximum friction torque F _MAX , the backlash correction is completed. Assumed acceleration output unit 21
Stops the output of the backlash acceleration amount _BACC , and completes the backlash acceleration control.

<Embodiment> FIG. 1 is a block diagram of a servo control device of the present invention, and FIG.
The figure is a block diagram of the speed control unit.

11 is a NC unit, as well as generating a move command P _C every predetermined sampling time, the moving command direction outputs backlash compensation amount B _C Invert. 12 position error calculator for calculating a difference between the move command P _C and the detected amount of movement P _A, 13 is an error counter for outputting a position deviation Er by multiplying the difference, 14 a position gain K _P setting unit, 15 speed The control unit 16 receives the friction torque T _f from the torque command T _CMD output from the speed control unit 15.
Arithmetic unit for subtracting, 17 is a mechanical system including the servomotor to be controlled, the transfer function (J _m is the motor inertia) is represented by.

As shown in FIG. 2, the speed control unit 15 calculates a difference between the speed command V _CMD ′ and the actual speed (speed feedback) V _f at predetermined time intervals, and an integrator ( The transfer function is k ₁ / s) 15b, a proportional gain k ₂ setting unit (proportional unit), an arithmetic unit 15d for adding the integral output and the proportional output,
It is multiplied by a torque constant k _t to the arithmetic unit output and a torque constant setting section 15e for generating a torque command (current command) T _CMD.

Referring back to FIG. 1, reference numeral 18 denotes a backlash correction timing determining unit, 19 denotes a torque monitoring unit, 20 denotes a backlash correction amount adding unit, 21 denotes an acceleration output unit, and 22 denotes a backlash acceleration amount adding unit.

Backlash correction timing discriminating unit 18, the movement command direction is stored and held backlash correction amount B _C given from the NC unit 11 when reversed, to monitor the content (position error) E _r of the error counter 13, The reversal of the rotation direction of the servomotor is detected by _Er = 0. The outputs backlash compensation amount B _C to the adder 20 by the rotation direction reversal detection, inputs the rotational direction reversal signal RDI to the acceleration amount output unit 21.

The torque monitoring unit 19 is configured to control the torque command T _CMD output from the speed control unit 15 to a preset maximum static friction torque F
_{It is} detected whether or not the absolute value is equal to _MAX .
The static maximum friction torque F _MAX is set, for example, as follows. In other words, when the feed axis movement command is reversed, the position deviation decreases and overcomes the static maximum friction torque and moves by the last one pulse. Thereafter, the rotation direction of the motor is reversed. It is considered as the static maximum friction torque F _MAX and measured, and set in the torque monitoring unit 19.

Accelerating amount output unit 21 outputs a backlash acceleration amount B _ACC when the position deviation E _r becomes zero, stopping the output of the backlash acceleration amount when the torque command T _CMD equals the static maximum friction torque F _MAX I do.

 Next, the overall operation of FIG. 1 will be described.

Computed in the arithmetic unit 12, the difference between the movement command P _C and the detected amount of movement P _A every sampling time T _S is the error counter
Position deviation E _r next is integrated by 13, thereafter the position gain K _p is multiplied by a by the speed command V _CMD, and the rotation of the servo motor output torque command T _CMD corresponding to the speed deviation in the subsequent speed control section 15 I do.

In this state, if the command movement direction is reversed, NC
Movement command P _C to the reversing direction is generated every sampling time T _S along with backlash compensation amount B _C which is set in advance is output from the section 11.

With backlash correction timing discriminator 19 holds the backlash correction amount B _C, subsequently the contents of the error counter 13 in parallel with the servo control processing (position deviation) E _r
To monitor. When _Er = 0, it is determined that the rotation direction of the servo motor has been reversed.

The backlash correction timing determination unit 19 detects the rotation direction reversal and detects the backlash correction amount B _C
Is output to the adder 20, and the rotation direction inversion signal RDI is input to the acceleration output unit 21.

Backlash compensation amount adding section 20 is the backlash compensation amount B _C and position by adding the position deviation E _r gain setting unit 14
Fill in, the position gain setting unit 14 generates a speed command V _CMD corresponding to the backlash compensation amount by multiplying the position gain K _P.

Also, the acceleration amount output unit 21 outputs a constant backlash acceleration amount B _ACC by rotational direction reversing signal RDI. As a result, the adder 22 calculates the backlash acceleration _BACC and the speed command V
_CMD is added, and the addition result is input to the speed control unit 15 as a true speed command V _CMD ′.

The speed control unit 15 calculates a speed deviation, outputs a torque command T _CMD corresponding to the speed deviation, rotates the servomotor 17, and immediately corrects backlash.

Immediately before the completion of the backlash correction, the torque command T _CMD is set to a preset maximum static friction torque.
It becomes equal to F _MAX , the torque match signal from the torque monitor 19
TCI occurs.

As a result, the acceleration output unit 21 outputs the backlash acceleration
Stops B _ACC output and completes backlash compensation control.

According to the present invention, the backlash acceleration amount is output when the rotation direction of the servo motor is reversed, and the output of the backlash acceleration amount is stopped when the torque command becomes equal to the static maximum friction torque. With this configuration, even if the machine conditions or cutting conditions change, the backlash and friction can be canceled in the same manner with the same parameters, and the quadrant projection can be eliminated.

Further, by setting the backlash acceleration amount to a slightly larger value, the backlash can be moved faster, and the protrusion due to the backlash can be further improved.

[Brief description of the drawings]

 FIG. 1 is a block diagram of a servo control device of the present invention, and FIG. 2 is a block diagram of a speed control unit. 13… Error counter, 15… Speed control section, 18… Backlash correction timing discrimination section, 19… Torque monitoring section, 21… Acceleration amount output section,

Claims (2)

(57) [Claims] When a rotational direction of a servomotor is reversed, a backlash correction data is added to position deviation data to generate a speed command, and a backlash acceleration amount is added to the speed command for a predetermined time to perform backlash correction. In the servo control device, means for detecting the reversal of the rotation direction of the servomotor, and detection for detecting that the torque command output based on the speed deviation is equal to a preset static maximum friction torque in absolute value. Means for outputting the backlash acceleration amount when the rotation direction of the servomotor is reversed, and stopping the output of the backlash acceleration amount when the torque command becomes equal to the static maximum friction torque. Features servo control device. 2. The servo controller according to claim 1, wherein the static maximum friction torque is a torque command immediately before reversal of the rotation direction.