JPH11202942A - Control circuit for servo motor using encoder feedback - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce rounding errors in the control of a servo motor by providing a dither circuit on the following stage of an integration circuit in the middle circuit starting from a control circuit for servo motor using encoder feedback. SOLUTION: On the following stage of an integration amplifier in the middle circuit starting from the control circuit for a servo motor M, which is provided with a terminal for inputting a position command signal θi and an encoder E for outputting the position of the rotor of the servo motor M, using encoder feedback for digital control for the rotation of an analog motor by using these position command signal θi and output of encoder E, the contents of a low-order memory are delayed for one cycle and added to the next input signal by a dither circuit Dither and the contents of a high-order memory are outputted as a divided value. Thus, the rounding errors in the control of the servo motor M are reduced and the responsiveness of the servo motor M can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a servo motor control circuit using encoder feedback.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a control circuit for a servomotor of this type according to the prior art.

The difference (θ) between the output θ0 of the encoder E attached to the rotor of the servomotor M and the position command signal θi
i−θ0) is multiplied by kp with a position loop proportional amplifier,
It becomes the speed command signal kp (θi−θ0).

[0004] The output θ0 of the encoder E is calculated as the difference kp (θi-θ0) between the differentiator ω0 and the speed command signal kp (θi-θ0)
θ0) -ω0 is the displacement signal s. The displacement signal s is multiplied by Kvp in a proportional amplifier and integrated by an integrating amplifier, and their outputs are added by an adder. Sent to Motor controller C
The ONT controls the rotation of the servo motor M according to the output of the torque command filter.

[0005]

Since the resolution of the encoder E is finite, a dead zone occurs in a minute section. In some cases, forward or reverse rotation motor torque is generated by the quantized control state variables, and vibration may occur in a region slightly beyond the dead zone.

[0006] These processes are performed by digital signals. For example, in the integrating amplifier, the deviation signal s is integrated by adding a value every moment by digital signal processing. However, since the number of bits that can be processed in digital signal processing is constant, only the upper digit of the integrated value Σ is sent to the subsequent circuit.

For example, in a digital processing system using 10 bits, when the integral value 積分 is 16 bits,
Only the 0 bit is sent to the subsequent stage. This is because the integral Σ is 6
Divide by bits, ie 64. That is, the lower 6 bits are rounded and sent to the subsequent stage. At this time, the lower 6 bits become a dead zone, and sufficient servo characteristics cannot be obtained.

It is an object of the present invention to improve the responsiveness of a servomotor by reducing a rounding error in servomotor control using such encoder feedback.

[0009]

This problem has been solved by starting from a servomotor control circuit using encoder feedback according to the prior art and providing a dither circuit after the integration circuit therein.

FIG. 2 is a block diagram of a dither circuit.

The upper digit of the input signal is stored in the upper digit memory MH.
The lower order is stored in the lower order memory ML. Then, division is performed by outputting the contents of the upper digit memory MH. On the other hand, the contents of the lower memory ML are added to the next input data one cycle later. As a result, the lower-order data which has conventionally been truncated accumulates, and in the long term, the carry signal is sent to the upper-order memory MH by exceeding the upper limit of the lower-order memory, thereby affecting its contents. As a result, an apparent precision can be improved over a simple truncation processing in which a rounding error occurs.

[0012]

FIG. 1 is a block diagram of a servo motor control circuit using encoder feedback according to a preferred embodiment of the present invention.

This circuit differs from the circuit of FIG. 4 only in the contents of the integrating amplifier, and is otherwise the same. Therefore, corresponding members are denoted by the same reference numerals and reference symbols, and description thereof will be omitted.

At the first stage of the integrating amplifier, the deviation s, which is a speed error, is accumulated to become an integrated value Σ. In this embodiment, the lower memory ML has 6 bits, and in principle, the upper bits excluding the lower 6 bits are output as a division value. That is, Σ / 64 is output.

However, this integrating amplifier is a dither circuit Dit
Since her is used, the data in the lower memory is added to the next input signal one cycle later.

FIG. 3 shows an example of a change in the contents of the lower memory ML of the dither circuit. The value obtained by dividing the data of the lower memory by the upper limit value of the lower memory is shown. As an ideal model, it is assumed that the lower data L of the input signal Σ happens to be constant at about 0.3 as shown in the figure. At this time, ML until n = 3
And the carry signal C is transferred to the upper memory M when n = 4.
H, the contents of the lower memory ML become smaller. Then, the number increases to n = 6, and when n = 7, the carry signal C is sent to the upper memory MH again. Thus, carry signal C is n = 4,
7, 10, 14, 17, 20. . . At the upper memory MH. In this way, the data of the lower bits of the input signal is also reflected in the output in the long term.

[0017]

According to the prior art, the truncation at the time of division may cause a dead zone with respect to the position command signal θi, or the response to the speed command signal may be stepped even if it is continuous. However, the dither circuit eliminates the dead zone and the speed also changes continuously.

[Brief description of the drawings]

FIG. 1 is a block diagram of a servomotor control circuit using encoder feedback according to a preferred embodiment of the present invention.

FIG. 2 is a block diagram of a dither circuit.

FIG. 3 shows a change 1 in the contents of the lower memory ML of the dither circuit.
Here is an example.

FIG. 4 is a block diagram of a control circuit for such a servomotor according to the prior art.

[Explanation of symbols]

 CONT Motor controller DIF Differentiator Dither Dither circuit E Encoder M Servo motor MH Upper memory ML Lower memory s Deviation θi Position command signal θo Rotor position ωo Rotor rotation speed 積分 Integral value

Claims (2)

[Claims] 1. A servo motor comprising: a terminal for inputting a position command signal; and an encoder for outputting the position of a rotor of the motor. The servo motor uses an encoder feedback for digitally controlling the rotation of an analog motor based on the position command signal and the output of the encoder. In the control circuit, a division circuit included in the control circuit includes an upper memory MH for storing an upper bit signal of an input signal, and a lower memory ML for storing a lower bit signal of the input signal. A servo motor control circuit using encoder feedback, wherein the control signal is added to the next input signal with a period delay and the content of the upper memory MH is output as a divided value. 2. A terminal for inputting a position command signal, an encoder for outputting the position of the rotor of the motor, a differentiating circuit DIF for differentiating the output of the encoder, and a position for generating a speed command signal from the position command signal and the position of the rotor. A loop proportional amplifier, an integrating amplifier for integrating a deviation signal s which is a difference between an output of the position loop proportional amplifier and an output of the differentiating circuit, and a deviation signal s
And a motor controller for controlling the servomotor based on the output of the integrating amplifier, wherein the integrating amplifier includes a dividing circuit, and the dividing circuit includes a higher-order bit of the input signal. An upper memory MH for storing signals,
A lower memory ML for storing a lower bit signal of the input signal, wherein the content of the lower memory is added to the next input signal one cycle later, and the content of the upper memory MH is output as a divided value. Control circuit of servo motor using encoder feedback.