JP3199769B2 - Servo control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called digital servo (software servo) in which a servo control of a servo motor is performed by a processor, and more particularly, to a servo requiring a high-precision smooth locus in a machine tool or a robot. The present invention relates to a servo control device suitable for controlling a motor.

[0002]

2. Description of the Related Art When a servomotor is used to control a feed axis of a machine tool, a robot arm, or the like, feedforward control is performed to reduce the amount of positional deviation.
In particular, when high-speed cutting is performed by a machine tool, a shape error occurs due to a delay in following the servo system. Therefore, in order to reduce this shape error, feedforward may be applied to the position loop.

FIG. 4 is a block diagram of a servo system for performing conventionally known position and speed feedforward control. In FIG. 4, Kp of the transfer function 1 is the position gain in the position loop, transfer function 2 is the transfer function of the speed loop, k1 is the integral gain in the speed loop, and k2 is the proportional gain in the speed loop. Reference numeral 3 denotes a mechanical part of the servomotor, Kt denotes a torque constant, Jm denotes inertia, and 4 denotes a transfer function for calculating the position by integrating the rotational speed of the servomotor. Also, 5 and 6 are position feedforward terms, 5 is a term of a transfer function for differentiating the movement command a, and 6 is a term multiplied by the position feedforward coefficient α1.

[0004] Reference numerals 7 and 8 denote transfer functions of the speed feedforward control, and 7 denotes a term for differentiating the output of the transfer function 5.
8 is a term multiplied by the velocity feedforward coefficient α2.

A movement command Mc for each distribution cycle (hereinafter referred to as ITP cycle) is output from a host processor such as a numerical controller, and a processor that performs servo control based on the movement command Mc obtains a movement command a in the position / speed loop processing. And performs a position / velocity loop process to control the servomotor. First, the operation when the feedforward control of the position and the speed is not performed will be described. The position deviation is calculated by subtracting the feedback amount af of the actual movement amount of the servo motor from the obtained movement command a of the position / speed loop cycle. The position deviation is multiplied by a position gain Kp to obtain a speed command Vc1, and a feedback amount Vf of the actual speed of the servo motor is subtracted from the speed command to obtain a speed deviation.
The value obtained by multiplying the integral value of the speed deviation by the integral gain K1 is
A value obtained by multiplying the speed deviation by a proportional gain K2 is added to perform a speed loop process for obtaining a torque command (current command to the servo motor) Tc1, and the servo motor is driven by the obtained torque command Tc1.

When the position and velocity feedforward control is also performed, the movement command a is differentiated (section 5).
The value obtained by multiplying the differential value by the position feedforward coefficient α1 is converted from the unit of the movement command to the unit of the speed command to obtain the feedforward amount Vc2 of the position, and the feedforward amount Vc2 of this position is obtained by ordinary position loop processing. The speed command Vc1 is added to the obtained speed command to obtain a speed command for the speed loop process. The speed command (Vc = Vc1 + Vc2)
Therefore, the above-described speed loop processing is performed to execute the torque command Tc.
Find 1 Further, the differential value of the movement command output from the term 5 is further differentiated (acceleration), and a value obtained by multiplying the differentiated value by the speed feedforward coefficient α2 is converted from the unit of the movement command to the unit of the torque command (current command). To obtain the speed feedforward amount Tc2, add the speed feedforward amount Tc2 to the previously obtained torque command Tc1, and drive the servomotor as a torque command (current command) to the servomotor.

[0007]

In the case of a digital servo in which the above-described servo control is performed by a processor, a movement command, a speed command, and a torque command are digitized, and these commands are at least digitized. It changes in the minimum unit, and an error occurs due to this quantization. Table (work) for machine tools
When the servomotor that drives the tool or tool is controlled by the above digital servo, smoothness is required for the tool trajectory, and when high-precision machining is required, an error due to quantization occurs, and the required tool trajectory is smoothed. There is a problem that does not matter. Further, when the feedforward control is performed, the derivative of the movement command and the differentiation thereof are performed. Therefore, when the value of the movement command changes, the values of the feedforward amounts Vc2 and Tc2 greatly change, Since this will be added to the speed command and torque command,
The motor speed changes instantaneously, causing a shock or a vibration.

It is an object of the present invention to reduce errors due to quantization in a digital servo, to suppress shock and vibration even when feedforward control is performed, and to obtain a highly accurate and smooth movement trajectory. It is an object of the present invention to provide a servo control device that can perform the control.

[0009]

SUMMARY OF THE INVENTION The present invention provides a command program.
Calculating means for calculating the movement command amount based on the
Position loop processing based on the movement command amount received from the
Position loop processing means for performing position control of the control target
In the servo control device having
The minimum unit of movement command to be executed is
Unit of position feedback signal detection from the position detection means
Position feedback in the position loop processing.
The amount of data is converted to the movement command unit and
The position of the target is controlled .

[0010]

The movement command output from the calculation means is
Position feedback from position detection means for detecting position
The output is performed in smaller units than the signal detection unit , and the processing of the position / velocity loop is processed in this unit. Therefore, the variation of the speed command and torque command in each position / speed loop processing cycle is also The change is caused by the small unit, and the amount of change can be reduced based on the small unit. The quantization error becomes an error in the small unit, and a smooth trajectory can be obtained. Also, when the feedforward control is performed, if the movement command is performed in the above-described small unit and the amount of change of the movement command in each cycle is reduced, the movement command is differentiated and the feedforward amount Vc2 obtained by differentiating the movement command. , it is possible to prevent the Tc2 also does not change significantly, shock or vibration motor generates.

[0011]

FIG. 3 is a block diagram of a digital servo control device for carrying out an embodiment of the present invention. Since the configuration is the same as that of a conventional device for performing digital servo control, it is schematically shown. .

In FIG. 3, reference numeral 20 denotes a numerical controller (hereinafter, referred to as NC) as a host processor, 21 denotes a shared RAM, 22 denotes a processor (CPU), ROM, and RAM.
A servo amplifier such as a transistor inverter; 24, a servomotor;
Is a pulse coder that generates a pulse with the rotation of the servomotor 24 and detects the position.

The NC 20 writes a movement command Mc into the shared RAM 21 at every IPT cycle (distribution cycle), and the CPU of the digital servo circuit 22 writes the movement command Mc into the shared RAM 21.
And the position / velocity loop processing is performed in a cycle T obtained by dividing the above ITP cycle into N pieces. That is, a movement command a for the position / velocity loop processing is determined so that the movement command Mc output from the NC 20 every ITP cycle is evenly distributed during the ITP cycle, and the current value of the servo motor 24 obtained by the feedback pulse from the pulse coder 25 is obtained. Position loop processing is performed based on the difference from the position. Further, a position feed-forward control process is performed to obtain a speed command. Next, a speed loop process is performed based on the speed command and the actual speed of the servo motor 24 obtained by a feedback pulse from the pulse coder 25. Processing is performed to obtain a torque command (current command). Then, a current loop process is performed to generate a PWM command, and the servo motor 24 is driven via the servo amplifier 23.

FIGS. 1 and 2 are flowcharts of the processing performed by the processor of the digital servo circuit 22 and the processor of the NC unit according to the present embodiment.

The processor of the NC unit 20 executes the processing of FIG. 2 for each ITP cycle, reads the NC program, and creates a movement command for each axis (steps S201 and S20).
2). In this case, conventionally, the minimum unit of the movement command is set to be substantially the same as the unit for detecting the position feedback pulse from the pulse coder 25 attached to the servomotor 24. However, in the present invention, the unit for detecting the position feedback pulse is It is calculated in a unit that is sufficiently smaller than that. Then, the calculated movement command Mc is written into the shared RAM 21, and the processing of the cycle ends. Hereinafter, this processing is referred to as NC
The processor of the device 20 repeatedly executes every IPT cycle.

On the other hand, the processor of the digital servo circuit 22 reads the movement command MC from the shared RAM 21 for each IPT cycle, and executes the processing shown in FIG. 1 for each position / speed loop processing cycle obtained by equally dividing the IPT cycle. First, a movement command a for each position / speed loop processing cycle is obtained (step S10).
1) The movement command a is stored in a register R for storing the position deviation ε.
(Ε), and a value obtained by multiplying the position feedback amount af detected by the pulse coder 25 by a conversion coefficient β for converting into the unit of the movement command a is stored in the register R.
(Ε) to obtain the position deviation (step S10)
2). Here, β = (minimum unit of position feedback pulse detection) / (minimum unit of movement command a)> 1.

Next, it is determined whether the obtained position deviation ε is within the range of the conversion coefficient β, ie, whether −β <ε <β (step S103). The speed command Vc1 is obtained by multiplying the position deviation ε by the position gain Kp in the position loop processing (step S10).
4). If the position deviation ε is within the range of the coefficient β,
The speed command Vc1 is set to “0” (step S105).
This processing (step S105 is performed when the position deviation ε
Is within the range of the conversion coefficient β, and in the position detection unit, when the position deviation is “0”, the speed command Vc1 is obtained as in step S104 and the servomotor is driven. Each time one pulse is output, the position deviation ε fluctuates by + β and −β, and becomes unstable due to generation of vibration, and so the speed command Vc1 is set to “0”.

Next, from the movement command a, the register R1 (a)
The differential of the move command is performed by subtracting the move command in the previous position / velocity loop stored in the unit. The position is multiplied to obtain a feedforward amount Vc2 at the position (step S106). That is, the processing of the transfer functions 5 and 6 in FIG. 4 is performed to determine the feedforward amount Vc2 at the position. Then, the speed command V obtained in step S104 or step S105.
The speed command Vc for the speed loop process is obtained by adding the position feedforward amount Vc2 to c1 (step S
107), the speed command Vc is added to the accumulator A, and the speed feedback amount Vf detected by the pulse coder 25 is subtracted from the accumulator A (Step S).
108), a value obtained by multiplying the value stored in the accumulator A by the integral gain K1 and a value obtained by multiplying a value obtained by subtracting the speed feedback amount Vf from the speed command Vc by a proportional gain K2 are added to obtain a torque command Tc1 (step) S109).
That is, the processing in steps S108 and S109 corresponds to the speed loop processing in FIG.

Next, the speed feedforward amount Tc2 is obtained (processing of the transfer functions 7 and 8 in FIG. 4). Assuming that the movement command in the position / speed loop processing cycle n is a (n), the movement command one cycle before is a (n−1), and the movement command two cycles before is a (n−2), The differential value by the transfer function 5 in 4 is a (n) -a (n-1). The differential value one cycle before the cycle is a (n-1) -a (n-2). Then, since the differentiation by the transfer function 7 is obtained as the difference between the above-mentioned differential values, [a (n) −a (n−1)] − [a (n−1) −a (n−2)] = a ( n) -2a (n-1) + a (n-2) (1) Therefore, the movement command a (n
-1) is stored in the register R1 (a).
(N-2) is stored in the register R2 (a), and the calculation of the above equation (1) is performed, and the obtained value is converted into a torque command (current command) from the speed feedforward coefficient α2 and the unit of the movement command. ) Is multiplied by a coefficient P2 to be converted into a unit of the speed feedforward amount Tc2 (step S1).
10).

The register R2 (a) stores the register R
The value of 1 (a) is stored in the register R1 (a) with the movement command a obtained in the cycle, and is used immediately before the next cycle.
And the movement command of the previous two cycles is stored (step S
111, S112). Next, steps S109 and S11
The torque command Tc1 and the speed feedforward amount Tc2 obtained at 0 are added to obtain a torque command Tc to the motor, and the torque command Tc is passed to the current loop processing (steps S113 and S114), and the position / speed loop processing is performed. finish. Then, the current loop processing is executed in the same manner as in the related art, a PWM command is created, and the servo amplifier 23
, The servo motor 24 is driven to control the position and speed of the motor.

5 and 6 show a radius of 150 mm and a cutting speed of 6
000 mm / min, position and velocity feedforward coefficients α1 = 1.0, α2 = 1.0, showing simulation results of tool trajectory when arc cutting is performed. FIG. 5 shows the minimum unit of the movement command as 5 μm. In FIG. 6, the tool trajectory when the minimum unit of the movement command is 0.5 μm is shown. As is clear from FIGS. 5 and 6, if the minimum unit of the movement command is reduced, the tool trajectory becomes smaller. It turns out that it becomes smooth.

[0022]

According to the present invention, in a digital servo system in which servo control is performed by processing of a processor, the minimum unit of a movement command output to the processor of the digital servo is simply reduced, and the position / velocity loop is reduced by the small unit. By performing the processing, it is possible to reduce shocks and vibrations due to errors due to quantization and to have an effect that a moving trajectory can be smoothed.

[Brief description of the drawings]

FIG. 1 is a flowchart of a position / velocity loop process executed by a processor of a digital servo circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart of a process for each distribution cycle performed by the host processor of the embodiment.

FIG. 3 is a block diagram of a digital servo device that implements the embodiment.

FIG. 4 is a block diagram of a servo system that performs feedforward control.

FIG. 5 is a diagram showing a simulation state of an arc cutting locus when a movement command is set to 5 μm.

FIG. 6 is a diagram showing a simulation state of an arc cutting locus when a movement command is set to 0.5 μm.

[Explanation of symbols]

 Reference Signs List 1 transfer function of position loop 2 transfer function of speed loop 3 transfer function of motor 4 transfer function converting speed to position 5 transfer function of differential of position feed forward 6 transfer function of position feed forward coefficient 7 differential transfer of speed feed forward Function 8 Transfer function of speed feedforward coefficient 20 Numerical controller 21 Shared RAM 22 Digital servo circuit 23 Servo amplifier 24 Servo motor 25 Pulse coder

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G05B 19/18-19/46 G05D 3/00-3/20 B23Q 15/00-15/28

Claims (3)

(57) [Claims] A movement command amount is determined based on a command program.
Calculating means for calculating, and a movement command amount received from the calculating means
Position loop processing based on the
Servo control device having position loop processing means for performing
Control the minimum unit of movement command calculated by the above calculation means.
Position feed from position detection means that detects the position of the target
Make it smaller than the back signal detection unit and
In the step, the position feedback amount is used as the unit of the movement command.
Conversion and data processing to control the position of the control target
Robot control device . 2. The servo control device according to claim 1, wherein feedforward control is added to the position loop processing. 3. The servo control device according to claim 1, wherein in the position loop processing, when a position deviation falls within a unit of detection of the position feedback signal, a speed command obtained by the position loop processing is set to zero.