JPS5923196B2 - Digital servo system - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a digital servo system that can detect speed with sufficient accuracy and a high repetition rate even in a region where the rotational speed of an electric motor is low, and that can apply negative speed feedback very stably. be.

Generally, in order to reduce the steady-state deviation of the servo system and rotate the motor at a target speed, it is common to change the overall gain of 10 or the gain of the speed control loop.

In the pulse width modulation method, changing the overall gain can be achieved by changing the pulse width or pulse height value. As a speed control method, a 15-pole system using a DC speedometer generator is well known, but in the region where the motor rotation speed is low, the generated voltage is low and the signal/noise ratio becomes poor, etc. It was hot. In addition, there are known methods of calculating speed by counting feedback pulses for position detection from a position detector for a certain period of time, but in order to calculate speed with high precision, the counting time must be lengthened. Otherwise, it is necessary to generate a large number of feedback pulses for position detection. The former requires a long time to calculate the speed, and the latter requires increasing the resolution of the position detector and increasing the response speed25, making it difficult to calculate the speed at high speed and with high accuracy in practice. . The present invention solves this drawback and detects the rotational position of the motor in proportion to the rotational speed so that the speed can be measured with any precision repetition frequency even during low-speed rotation, and sufficiently stable negative speed feedback can be applied. A high-frequency signal corresponding to the rotational speed of the motor is generated by a circuit that counts the output pulse period of a detector that outputs a pulse signal with a certain frequency, and a circuit that divides a constant clock frequency into one part of this output frequency. The system is designed to enable speed detection with high accuracy of 35 degrees in a short period of time.The drawings will be explained in detail below.

In FIG. 1, 1 is an error register and is a reversible counter with a sign bit.

+F of the input signal is a pulse train in the positive rotation direction, and -F is a pulse train in the negative rotation direction. +FB and -FB are feedback signals from the position detector 2 corresponding to positive rotation and negative rotation, and are pulse trains with a frequency proportional to the rotation speed.
However, F and ±FB do not arrive at the same time.
Error register 1 counts up when +F and -FB, and counts down when -F and +FB. Therefore, the error register 1 counts and stores the deviation between the input signal F and the feedback signal FB, so that the contents of the error register 1 always correspond to the positional deviation. Next, this position deviation value is transferred to the speed negative feedback register 3 at a constant period T1, and the pulse train φ(v) of the frequency corresponding to the rotational speed of the motor 5 produced by the period-frequency conversion circuit 4 is gated. 6 for a certain period of time T2 (T1) and at the same time is controlled to count down when the rotation direction is positive and count up when the rotation direction is negative, a value obtained by multiplying the position deviation value by speed negative feedback is calculated. Therefore, this calculation result is input into the drive register 7, and according to the value, pulses controlled by the pulse width modulation circuit 8 are passed through the amplifier 9 to the motor 5.
It is used as a control signal. Next, FIG. 2 showing a specific example of the period-to-frequency conversion circuit 4 will be described.

First, when a pulse from the position detection feedback signalman FB comes from the position detector 2, the contents of the period counter 102 are transferred to the period register 103, and then the period counter 102 is reset and the period counter clock 104 is counted. start. Next, when the pulse of the position detection feedback signal ±FB comes, the contents of the period counter 102 at that moment are transferred to the period register 103, and then the period counter 102 is reset and the period counter clock 104 starts counting again. In addition, if the contents of the period counter 102 reach the maximum value before the pulse of the position detection feedback signal operator FB arrives, the contents are transferred to the period register 103, and then the position detection feedback signal ±FB is input. The period counter 103 stops counting until a pulse arrives. Therefore, the period between the feedback pulses from the position detector 101 is always held in the period register 103. This held period register 1
The contents of 03 are input to one input of the digital comparator 105, and the contents of the frequency division counter 106 are input to the other input. When the contents of the two are equal, the digital comparator 1
The output signal from 05 resets the frequency division counters 1 and 06. Frequency division counter 106 with such a function
When a clock φ with a suitable high frequency is input to the , the frequency-divided output pulse train φ(v) corresponds to the rotational speed of the motor 5 because the frequency is divided by one of the counted periods of the clock φ. Become something. Therefore, in the present invention, the position detection signal operator FB from the position detector 2 is
The period of the pulse can be counted with any precision, and the clock φ
Since the frequency can be converted to any desired frequency by changing the frequency, by adding the period-to-frequency conversion circuit 4 having such a function, it is possible to always apply stable and optimal speed feedback at the target motor rotation speed. has been realized.

As described above, in the digital servo device, the instantaneous speed can be calculated by counting the period of the feedback signalman FB pulse from the position detector 2 with arbitrary accuracy, so it is possible to calculate the instantaneous speed with high precision and high speed. It has the advantage of being able to apply velocity feedback in response, which helps stabilize the entire digital servo device, and enables operation with less steady-state deviation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a set of embodiments of the present invention, and FIG.
3 is a detailed block diagram of the period-to-frequency conversion circuit 4 shown in the figure. FIG. 1...Error register, 2...Position detector, 3...Velocity negative feedback register, 4...
・Period-frequency conversion circuit, 5...Motor, 6.
...Gate, 7...Drive register, 8.
...Pulse width modulation circuit, 9...Amplifier,
102... Period counting counter, 103...
... Period register, 104 ... Period counting clock, 105 ... Digital comparator, 10
6...Divide counter.

Claims (1)

[Claims] 1. An error register consisting of a DC motor, a detector that detects the rotational position of the motor using a digital signal, and a reversible counter that counts the difference between the output pulses of the detector, and the contents of this error register are stored every fixed period T_1. An arithmetic circuit that has the dual functions of a reversible counter and a shift register that can add or subtract a pulse train of a frequency corresponding to the rotational speed of the motor for a fixed time T_2 (T_1>T_2) to this stored value, and hold this arithmetic result. In a servo device equipped with a circuit that controls the input of the DC motor by sending out a pulse with a width corresponding to the content of the pulse, the output period of a detector that detects the rotational position of the motor and outputs a digital signal is determined. A digital servo system characterized in that a pulse train of a frequency corresponding to the rotational speed of the electric motor is created by a counting circuit and a circuit that divides a constant clock frequency by a fraction of the output cycle count value of the detector. .