JPS622891A - Drift correcting method of servo system - Google Patents

Abstract

PURPOSE:To control a servo system without drift by detecting in advance the drift amount of an operational amplifier for a command voltage, and correcting it to a command voltage by considering its drift amount. CONSTITUTION:A CPU 11 first calculates a drift amount for a servo command voltage. The CPU 11 reads out a drift amount calculated value from a backup memory 13 in case of instructing a servo motor command voltage for a servo motor 21, and executes a drift correcting calculation. Thus, an operational amplifier 17 applies a servo voltage to a servo amplifier 19 in response to a servo motor command voltage after correcting the drift given from the CPU 11 to servo-control the motor 21.

Description

[Detailed description of the invention] (Technical field of invention) The present invention relates to a servo system drift correction method.

[Technical background of the invention and its problems]

Generally, a servo motor is used to control the axis of an NC device, and as shown in Figure 4, the servo motor command digital signal from the CPU of the NC device is converted to an analog voltage by the D/A converter 1, and the final stage operational amplifier 3, and is configured to be amplified and input to the servo amplifier of the servo motor.

However, in the case of such a servo system, Fig. 5<a
) If the drift voltage of the operational amplifier 3 is 0, there is no problem, but if the drift voltage VD is generated in the operational amplifier 3 as shown in (b) of the same figure, the output to the servo amplifier, i.e. There are cases where the servo motor command voltage becomes unbalanced in its positive and negative operations or becomes unable to stop.

Conventionally, therefore, a drift adjustment trimmer is provided on the positive input side of the operational amplifier 3, and the trimmer is used to adjust the output of the operational amplifier 3 to O volts when the CPU output commands O volts.

However, in the case of such a conventional configuration, an operator had to adjust the drift using a hardware trimmer, which was extremely time-consuming.

[Purpose of the invention]

The present invention was made in view of such conventional problems, and is a servo system that performs drift correction of the servo system by presetting it in CPU programming, thereby eliminating the need for adjustment by hardware trim. The purpose of this invention is to provide a drift correction method.

[Structure of the invention]

This invention applies the same positive and negative voltages to a servo amplifier to move the servo motor at the same speed in each direction, and the actual speed of the servo motor driven by this servo voltage in the positive and negative directions. Drift correction for a servo system, which detects the speed, calculates and stores the amount of drift from the actual speed in both directions, and corrects the servo motor command voltage based on this drift for the actual servo. It's a method.

[Embodiments of the invention]

FIG. 1 is a block diagram showing an embodiment of the present invention, in which a CPU 11 incorporated in the NC device is provided with a backup memory 13, and the CPU 11 has a correction function.

This CPU 11 outputs the amount of movement necessary for the servo system as a digital signal through programming.

A D/A converter 15 is connected to the cpuii, which converts the digital signal from the CPLll as an analog voltage and supplies it to the operational amplifier 17. operational amplifier 17
is for applying a servo motor command voltage to the servo amplifier 19.

In the servo system, a servo motor 21 is driven in positive and negative directions by the output voltage of a servo amplifier 19, and its rotational speed and moving distance are detected by a tacho generator 23 and an encoder 25, respectively. The tacho generator 23 then feeds back the rotation signal to the servo amplifier 19 to perform position control on the servo motor 21. Further, the pulses counted by the encoder 25 are fed back to the CPU 11 to perform speed control.

The drift correction operation by the above servo system will be explained next.

First, the cpuii gives the servo motor command voltage a+ as a digital signal, and the servo motor 21
The actual speed N+ of the encoder 25 is detected by the pulse count amount of the encoder 25. (Steps 31 and 33) Subsequently, CPtJll issues a digital signal that provides a servo motor command voltage a- to rotate the servo motor 21 in the negative direction at the same speed. Then, the speed N- at which the servo motor 21 actually rotates in the negative direction with respect to this servo motor command voltage a- is detected. (Step 35.37) Using the thus obtained actual speeds [fN+, N-, the amount of drift is calculated. (Step 39) The calculation of this drift amount is based on the following equation.

ND = (N+ -N-) / 2 Nlll - (N+ 10N-) / 2 No in the above formula is the amount of drift.

This drift mND1NIIl is the backup memory 1
3 is stored. (Step 41) The drift amount thus calculated is stored in the backup memory 13, and is used in the normal operation of the NC device.

Next, the servo operation of the servo motor will be explained based on FIG. When the CPU 11 instructs the servo motor 21 to receive the servo motor command voltage a, the backup memory 1
3, the drift amount calculation values ND and l'1Jffl are read out and a drift correction calculation is executed.

(Steps 51-55> This drift correction calculation is performed using the following equation.

x-axNo/Nm The drift correction value X thus calculated is subtracted from the servo motor command voltage a, and the CPU 11 outputs the corrected servo motor command voltage value aai=(ax). (Step 57) In response to the drift-corrected servo motor command voltage given from the CPU 11, the operational amplifier 17 gives a servo voltage to the servo amplifier 19, and the servo motor 2
Perform servo 1. (Step 59) In this way, the cpuii takes into account the amount of drift of the operational amplifier 17, performs drift correction in advance on the instruction of the servo motor command voltage aaA, and controls the servo motor using the servo motor command voltage aaL after the drift correction. It drives.

In the above embodiment, the drift correction is performed by detecting the speed by the encoder 25, but it is also possible to perform the drift correction using the position signal from the tacho generator 23, as shown by the broken line in FIG. In that case, the servo motor command voltage value a is the position command voltage value and the speed signal N
By using + and N as position signals, drift correction can be performed in the same manner as in the above embodiment.

〔Effect of the invention〕

This invention detects the drift amount of the operational amplifier in advance with respect to the servo motor command voltage value, and drives the servo motor after correcting the drift amount to the command voltage, so there is no drift in the servo system. Moreover, since this drift correction is performed by software, it is possible to perform drift correction without adjusting the hardware trimmer as in the case of conventional methods, and drift adjustment can be performed easily. It is.

[Brief explanation of drawings]

Figure 1 is a block diagram of a servo system using an embodiment of the present invention, Figure 2 is a flowchart of the above embodiment, Figure 3 is a flowchart showing the operation of the servo system, and Figure 4 is a conventional servo system. FIG. 5 is a voltage characteristic diagram showing the operation of a conventional servo system. 11... CPU 13... Backup memory 15... D/A converter 17... Operational amplifier 19... Servo amplifier 21... Servo motor 2
3...Tachogenerator 25...Encoder Fig. 1 Fig. 4 Fig. 5 Fig. 2 Fig. 3

Claims (1)

[Claims] In order to move the servo motor at the same speed in both positive and negative directions, the same positive and negative voltages are applied to the servo amplifier, and the actual speeds of the servo motor driven by this servo voltage in the positive and negative directions are detected. A servo system drift correction method characterized in that the amount of drift is calculated and stored from the actual speeds in both directions, and when the actual servo is operated, the servo motor command voltage is corrected based on this amount of drift.