JPH06165556A - Rotational fluctuation suppressing circuit for servo motor - Google Patents

Abstract

PURPOSE:To provide a rotational fluctuation suppressing circuit for servo motor in which rotational fluctuation can be suppressed by additionally providing a simple circuit. CONSTITUTION:A mode switch 6 is turned to rotational command clock side to write an encoder feedback pulse from a rotary encoder 4 into a digital memory 5 and then the mode switch 6 is turned to the digital memory 5 side to read out the pulse from the digital memory 5 and deliver the pulse to a phase comparison circuit 1. The phase comparison circuit 1 compares the pulse with the encoder feedback pulse and delivers a difference command to a driver 2 which then feeds a corresponding drive current to a motor 3. Rotation of the motor is then detected by the rotary encoder 4 in order to suppress rotational fluctuation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation unevenness reducing circuit for a servomotor, and more particularly to a PLL (Phase locked loop).
) Is used to servo-control the motor, the invention relates to a rotation unevenness reduction circuit for a servo motor, which reduces rotation unevenness.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a conventional servomotor. In FIG. 2, the phase comparison circuit 1 is supplied with a rotation command clock signal from the outside and an encoder feedback pulse from the rotary encoder 4 which detects the rotation speed of the motor 3. The phase comparison circuit 1 compares the phases of the rotation command clock signal and the encoder feedback pulse, and gives the driver 2 a deviation command signal corresponding to the phase difference. The driver 2 supplies a drive current to the motor 3 according to the deviation command signal.

The servo motor using the PLL shown in FIG. 2 can control even the phase difference between the rotation command clock signal and the feedback pulse from the rotary encoder 4 as compared with the drooping pulse type servo motor, so that the rotation unevenness is considerable. It has the characteristic of being reduced.

[0004]

However, even in the servo motor using the PLL as shown in FIG.
If there is unevenness in the feedback pulse from the rotary encoder 4, in principle, it causes uneven rotation of the motor 3, and uneven rotation comes from the performance of the rotary encoder 4. The performance of the rotary encoder 4 is determined by the accuracy of the slit of the encoder itself and the mounting accuracy when the rotary encoder 4 is mounted on the motor 3. At present, the accuracy is usually about 0.1% in total.

The rotation unevenness of the servo motor as a whole is often better than the accuracy of the rotary encoder 4 alone due to the inertia of the rotating portion. However, in that case, the unevenness of the encoder feedback pulse adds a noise component to the deviation command. Therefore,
Further, if the servo gain is increased to improve the servo characteristics in order to reduce the rotation unevenness, the rotation unevenness increases.

Therefore, a main object of the present invention is to provide a rotation unevenness reducing circuit for a servo motor which can reduce the rotation unevenness only by adding a simple circuit.

[0007]

SUMMARY OF THE INVENTION The present invention is a servo for detecting the number of revolutions of a motor by an encoder, comparing the phases of the detection output signal and the rotation command clock signal, and servo-controlling the motor by the phase comparison output signal. The motor includes a clock signal generation circuit that generates a clock signal including unevenness similar to the rotation unevenness of the encoder, and is configured to compare the clock signal with the detection signal of the encoder instead of the rotation command clock signal.

[0008]

The circuit for reducing uneven rotation of the servomotor according to the present invention is provided with a clock signal generating circuit for generating a clock signal including unevenness similar to that of the encoder while maintaining the accuracy of the encoder as it is in the prior art. By comparing the phase with the detection signal of the encoder instead of the signal, the phase difference of the clock signals to be compared is eliminated, and the deviation command does not include a noise component, thereby reducing rotational unevenness.

[0009]

1 is a block diagram of an embodiment of the present invention. The embodiment shown in FIG. 1 has a rotary encoder 4
From the digital memory 5 for writing the encoder feedback pulse output from the digital memory 5, and the mode changeover switch 6 for switching the clock read from the digital memory 5 and the rotation command clock to the phase comparison circuit 1.
2 are provided, and other configurations are the same as those in FIG.

When the mode selector switch 6 is switched to the rotation command clock side, the digital memory 5 enters the "writing mode". In the "writing mode", the motor 3 rotates based on the rotation command clock. Then, the encoder feedback pulse output from the rotary encoder 4 is input to the digital memory 5 and written.

Next, when the mode selector switch 6 is switched to the digital memory 5 side, the digital memory 5 is in the "reading mode". At this time, the previously written pulse is read from the digital memory 5 and given to the phase comparison circuit 1 via the mode changeover switch 6. The phase comparison circuit 1 compares the pulse signal with the encoder feedback pulse, gives a deviation command to the driver 2, and the driver 2 supplies a drive current to the motor 3. As a result, the motor 3 rotates. In this case, since the noise component included in the deviation command output from the phase comparison circuit 1 is reduced, the rotation unevenness is reduced.

Further, in order to reduce the rotation unevenness,
This is realized by alternately repeating the above two modes and writing a more appropriate encoder feedback pulse in the digital memory 5. However, in that case, in the “write mode”, the encoder selector feedback pulse is transferred to the digital memory 5 while the mode selector switch 6 is switched to the digital memory 5 side and the motor 3 is rotated based on the written pulse. Written.

The rotation speed of the motor 3 can be changed by changing the speed at which pulses are output from the digital memory 5 in the "reading mode".

A ROM is prepared in place of the digital memory 5 shown in FIG. 1, and an encoder feedback pulse is written in the ROM in advance. In actual use, the ROM is stored at a speed proportional to the rotation command clock. The contents may be read and given to the phase comparison circuit 1 as an actual rotation command clock.

[0015]

As described above, according to the present invention, a clock signal generating circuit for generating a clock signal including unevenness similar to the rotation unevenness of the encoder is separately provided, and the clock signal of this clock signal generating circuit is commanded to rotate. By comparing with the detection signal of the encoder instead of the clock signal,
The rotation unevenness of the motor can be reduced, and it can be applied to a drive circuit such as a precise spindle motor. Further, it is possible to reduce rotation unevenness by adding a simple circuit without using an expensive high-precision rotary encoder, and further, it is not necessary to adjust the rotary encoder for mounting, thereby reducing the cost.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional servo motor.

[Explanation of symbols]

 1 phase comparison circuit 2 driver 3 motor 4 rotary encoder 5 digital memory 6 mode selector switch

Claims (1)

[Claims] 1. A servomotor that detects the number of rotations of a motor by an encoder, compares the phases of the detection output signal and a rotation command clock signal, and servo-controls the motor by the phase comparison output signal. A clock signal generation circuit for generating a clock signal including unevenness similar to rotation unevenness is provided, and rotation unevenness is reduced by replacing the clock signal of the clock signal generation circuit with the rotation command clock signal and comparing with the detection signal of the encoder. A circuit for reducing unevenness in rotation of a servo motor, which is characterized in that