JPH02228701A - Digital servo control system - Google Patents

Abstract

PURPOSE:To suppress vibration generation, to improve system response, and to stabilize the system as a whole by reducing an integration gain as the difference between a motor speed and a machine speed increases at the time of stopping and acceleration/deceleration, and increasing the integration gain at the time of a normal operation. CONSTITUTION:An integration gain K1 of a speed controller 10 is changed according to the magnitude of a difference (omegam-omegaL) between a motor speed omegam and a machine speed omegaL. That is, when the motor speed omegam and the machine speed omegaL is the same, the integration gain K1 is set at a maximum value K10, and as the difference (omegam-omegaL) between the motor speed omegam and the machine speed omegaL increases, the integration gain K1 is decreased. Consequently at the time of the stopping and acceleration/deceleration, the integration gain K1 is decreased, the effect of an integrating operation is decreased, when a control system synchronizes to a machine system, the integration gain K1 is increased, and the responsibility is improved. Thus the whole system is stabilized, and a servo system at the high responsibility can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital servo (software servo) in which a servo motor is controlled by a processor. In particular, when the weight of a movable object driven by a servo motor becomes heavy, such as in a large machine, a spring system or torsion system is required between the motor and the table of the machine, making it difficult to obtain rigidity. The present invention relates to a fully closed loop servo control system in such a system.

Conventional technologyAs machines driven and controlled by servo motors become larger,
The connection between the servo motor and the machine will have a spring system or torsion system. Normally, a servo motor drives a machine table, etc. via a ball screw, etc., but when the machine becomes large and the table has a very long ball screw,
When the size of a movable part of a machine becomes large, twisting occurs in the ball screw, and a spring system becomes necessary.

Figure 5 is a block diagram of a conventional servo system model that uses a proportional/integral speed controller to control the speed of a controlled object in which a spring system is interposed between the motor and the mechanical system. . In FIG. 5, 10 means a speed controller, K1 is an integral gain, and K2 is a proportional gain. 12 means the motor and mechanical system, Kt is the torque constant, Jm is the motor inertia, JL is the load inertia, Km is the spring constant of the spring system between the motor and the machine (table), and VC is the speed The command, TC, is the torque command, ωm is the motor speed, and ω[ is the machine (table) speed. In the case of a fully closed loop, the machine itself enters the positioning servo loop, so the resonance frequency of the machine itself directly affects the servo characteristics.

The above mechanical system has a mechanical resonance frequency ωn expressed by the following equation (1).

ωn=Km((1/Jm)+(1/JL)) =(
1) This mechanical resonance frequency ωn means that the smaller the spring constant Km and the larger the load inertia J [, the lower the frequency becomes.

Therefore, when the load, that is, the weight of the movable parts of the machine becomes heavy and the load inertia becomes large, and the machine resonance frequency ωn approaches the response frequency band of the speed control system (usually about 20 Hz), the entire system becomes unstable and stops. Later vibrations and hunting during acceleration and deceleration will occur.

Problem to be Solved by the Invention The instability of the above system is amplified by having an integral element in the speed controller. In other words, the instability of the system is amplified due to the phase delay caused by the integral element.

In addition, the integral element is necessary to eliminate the steady value of the difference between the speed command VC and the motor speed ωm, that is, the steady deviation, and also to suppress the speed fluctuation due to disturbance, the integral gain of the integral element is Characteristics will improve if 1 is made as large as possible. Therefore, an integral element is necessary, and its gain requires a certain value of 1.

Therefore, when there is no difference between the motor speed ωm and the machine speed ωL, that is, when the machine speed ω follows the motor speed ωm and the control system and mechanical system are synchronized and act in the same phase. There is no particular problem, but if there is a difference between the motor speed ωm and the machine speed ωL during acceleration or deceleration, that is,
If the control system and mechanical system move independently and become out of phase, the instability of the entire system will be amplified by the action of the integral element.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a digital servo control system that suppresses vibrations that occur during acceleration and deceleration, and improves steady state characteristics.

Means for Solving the Problems The present invention provides a fully closed loop servo system having an integral element in the speed control loop and detection means for detecting the motor speed and the moving speed of the machine driven by the motor. The above problem was solved by controlling the gain of the integral element to become smaller as the difference between the motor speed and the machine speed increases.

Operation FIG. 1 is a block diagram of the servo control system according to the present invention. The difference from the conventional servo control method shown in FIG. 5 is that the integral gain of the speed controller 10 is set to 1, and a This is a point to be changed as shown in 2.

That is, when the motor speed ωm and the machine speed ω[ are the same, the integral gain is set to the maximum value KIO of 1, and the motor speed ωm
As the difference (ωm - ω[) between and the machine speed ω[) increases, the integral gain is decreased by 1. As a result, motor speed ωm and machine speed ω[
do not match, the difference (ωm - ωL) is large, the control system and mechanical system move independently, and the entire system is unstable.In this case, set the integral gain to 1 to reduce the influence of the integral action. (As a result, the phase delay becomes smaller and acts to stabilize the entire system.

On the other hand, the difference between motor speed ωm and machine speed ω (ωm−ω
When [) becomes small, the 11 machine follows the motor, and the control system and mechanical system are in synchronization, increase the integral gain by 1 to improve responsiveness and reduce the steady-state deviation. In addition, it acts to suppress speed fluctuations due to disturbances.

The above-mentioned effects make the entire system stable and provide a servo control system with good responsiveness.

Embodiment FIG. 3 is a schematic diagram of a digital servo system according to an embodiment of the present invention, and 14 is a digital servo circuit composed of a processor such as a digital signal processor. In the digital servo circuit 14, a movement command value ΔRn outputted at a predetermined period from a numerical control device or the like is written in addition to the processor, and a shared RAM from which the processor of the digital servo circuit 14 reads out the movement command value ΔRn; The digital servo circuit 14 has a ROM 1 storing a control program to be executed, and a memory 14a such as a RAM used for data and calculations calculated by the processing of the processor, and the configuration of these digital servo circuits 14 is conventionally known. So,
Details are omitted.

16 is a servo amplifier such as a transistor inverter, and the output of the servo amplifier 16 drives the servo motor 18.

The servo motor 18 moves a table 22 of the machine by means of a ball screw 20. The table 22 is provided with a linear scale 24, and in accordance with the movement of the table 22, a feedback pulse ΔPf is outputted from the linear scale 24 and inputted to the digital servo circuit 14. Further, 26 is a pulse coder that generates pulses in accordance with the rotation of the servo motor 18, and this feedback pulse ΔVf is also input to the digital servo circuit 14. The digital servo circuit 14 receives a feedback pulse ΔPf from the linear scale 24 and a feedback pulse ΔVf from the pulse coder 26.
It is the same as the conventional method in that the machine speed ωL and the motor speed ωm are calculated by counting at every predetermined circular period.

In addition, the movement command value ΔRn output at a predetermined period (distribution period) from a control device etc. is calculated using the linear scale 24.
Similarly to the conventional method, the position deviation is determined from the feedback pulse ΔPf from the feedback pulse ΔPf, and the speed command value VC is calculated.
The processing of the speed control section (10) which receives C and calculates the torque command value ■C to the current control section will be explained with reference to the flowchart shown in FIG.

The processor of the digital servo circuit 14 performs the processing shown in FIG. 4 every speed control processing cycle.
Motor speed ωm0 in the previous cycle stored in a
Read the machine speed ω[(step S1),
) is calculated, and the integral gain is determined to be 1 (step 82).

10(1-α1ωm-ωLl)...(2
) Note that K10 is the motor speed ωm as shown in Figure 2.
and the machine speed ωF are equal (ωm=ωL), and α is the motor speed ω, as shown in Figure 2.
It represents the slope for reducing the integral gain by 1 according to the magnitude of the difference (ωm−ωL) between m and the machine speed ω[.

Next, the value obtained by subtracting the motor speed ωm read in step S1 from the speed command value VC output by the position control section, that is, the speed deviation (Vc - ωm), is multiplied by 1 by the integral gain obtained in step S2. Add the value to the value of register Ti, which acts as an integrator. That is, the following equation (3) is calculated (step 83).

1 for Ti4-Ti+ (Vc-ωm) −・−・−・
(3) Next, as shown in equation (4), speed command value VC
The speed deviation (Vc - ωm) obtained by subtracting the motor speed ωm from the constant of the proportional term of the speed controller is multiplied by 2 to obtain the value of the proportional term TP.
(Step 84).

TP = 2 (Vc-ωm) −...(
4) Next, the integral term value T1 obtained in step S3 and the proportional term value TP obtained in step S4 are added to obtain a torque command value Tc (step 85).

TC-Ti+■P ・・・・・・(
5) Based on the determined torque command value Tc, the current 1
IIJIII processing is performed, but this current control processing is the same as before, and is performed in the same manner as before, and the servo amplifier 1
6, the servo motor 18 is driven.

The above processing is performed every speed control cycle, and when the difference (ωm - ωL) between the motor speed ωm and the machine speed ωL is large and the control system and mechanical system are not synchronized, the integral gain is set to 1.
By reducing the influence of the integral function and stabilizing the system, the difference between the motor speed ωm and the machine speed ω[((ωm−
When ωL) is small, the integral gain is increased by 1 to improve responsiveness and suppress speed fluctuations with respect to disturbance torque.

Effects of the Invention In the present invention, when there is a torsion system or a spring system between the motor and the mechanical system, and when there is a difference between the motor speed and the machine speed when stopping or accelerating/decelerating, the integral gain is reduced to generate vibration. At the same time, when the motor speed and machine speed are equal to each other, the integral gain is increased to improve the responsiveness of the system and suppress speed fluctuations due to disturbances.
Overall system stability can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the servo control system according to the present invention.
FIG. 2 is an explanatory diagram of a method for adjusting the integral gain of speed control m'a according to the present invention, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. 4 is a flowchart of operation processing in the embodiment.
FIG. 5 is a block diagram of the conventional servo III control system. 10... Speed 111111B, 12... Motor and mechanical system, 14... Digital servo circuit, 16... Servo amplifier, 18... Servo motor, 20... Ball screw, 22... Table, 24... Linear scale, 26... Valve coder, VC... Speed command (value), TC... Torque command (value), ωm... Motor speed, ω[... Machine speed, K1. ...integral gain, K2
...Proportional gain, Kt...Torque constant, Km...
Spring constant, Jm...Motor inertia, JL...Load inertia. 1st mouth 4th mouth

Claims (1)

[Claims] In a fully closed loop servo system having an integral element in the speed control loop and detection means for detecting the motor speed and the moving speed of the machine driven by the motor, the difference between the motor speed and the machine speed increases. A digital servo control method that reduces the gain of the integral element as the load increases.