JPH0444761B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for preventing abnormal operation of a servo motor when a feedback pulse is abnormal.

An object of the present invention is to instantaneously stop a servo motor when a feedback pulse is abnormal, thereby realizing work safety and equipment protection.

Generally, as shown in Figure 1, a servo motor drive circuit consists of a command pulse 1 that provides the amount and speed of movement of the servo motor, a feedback pulse 2 that is proportional to the actual amount and speed of movement of the servo motor, and a feedback pulse and feedback pulse that is proportional to the actual amount and speed of movement of the servo motor. a counter 3 that integrates the difference between pulses; a DA conversion circuit 4 that converts the contents of the counter into an analog value; an amplifier circuit 5 that amplifies the power of the analog value;
The main components are a servo motor 6 and a pulse encoder 7 that generates the feedback pulse, and the servo motor 6 is driven in accordance with the movement amount and movement speed commanded by the command pulse 1. In this servo motor drive circuit, if the feedback pulse 2 is no longer fed back due to some reason such as failure of the pulse encoder 7 or disconnection of wiring, the counter 3 will not be decremented, causing an abnormal operation in which the servo motor 6 continues to be driven.

Conventionally, in order to prevent this abnormal operation, as shown in FIG. The servo motor 6 was stopped by disconnecting it with a relay 9 or the like. However, the conventional method requires (1) feedback pulse 2
(2) When an abnormality occurs in feedback pulse 2, it takes time for an overflow to occur in counter 2 even if command pulse 1 continues to be input. (2) When an abnormality occurs in feedback pulse 2, command pulse 1 is input. However, if the integrated pulse remains in the counter 3, overflow will not occur and the servo motor 6 will continue to operate abnormally.

Therefore, the present invention attempts to solve such problems, and its purpose is to instantly stop the servo motor when the feedback pulse is abnormal, thereby realizing work safety and equipment protection. The purpose is to provide an operation prevention circuit.

The gist of the servo motor abnormal operation prevention circuit of the present invention is as follows: 1. In the servo motor abnormal operation prevention circuit driven by the difference between a command pulse and a feedback pulse from a pulse encoder, a current flowing through the servo motor is detected. a current detecting means for detecting the current, and a voltage converting means for generating a voltage according to the current value detected by the current detecting means;
A retriggerable resistor comprising a voltage-controlled variable resistance element whose resistance value is changed by being controlled by the voltage conversion means, and the voltage-controlled variable resistance element as a time constant.
The servo motor is characterized by being comprised of a detection circuit that uses a monostable multivibrator to detect the presence or absence of the feedback pulse, and a stop circuit that stops the operation of the servo motor based on the output of the detection circuit. .

2. In an abnormal operation prevention circuit for a servo motor driven by the difference between a command pulse and a feedback pulse from a pulse encoder, a frequency-voltage conversion means converts the speed of the command pulse into a voltage, and a frequency-voltage conversion means a detection circuit that detects the presence or absence of the feedback pulse using a voltage-controlled variable resistance element whose resistance value is controlled to change; and a retriggerable monostable multivibrator having the voltage-controlled variable resistance element as a time constant; The servo motor is characterized by comprising a stop circuit that stops the operation of the servo motor based on the output of the detection circuit.

The present invention includes a zero detection circuit 10 for detecting that the contents of a counter become zero, a pulse detection circuit 11 for detecting the presence or absence of a feedback pulse, and an amplification circuit using the pulse detection circuit 11 in the servo motor drive circuit shown in FIG. Relay 9 that disconnects 5 and servo motor 6
A gate circuit 12 for inhibiting the output of the pulse detection circuit 11 by the zero detection circuit 10 is added. If there is an abnormality in the feedback pulse 2, the feedback pulse 2 will no longer be input to the pulse detection circuit 11, so the pulse detection circuit 11 will disconnect the relay 9 and stop the servo motor 6 instantly. Further, when the command pulse 1 is not input and there is no integrated pulse remaining in the counter 3, the servo motor 6 is not driven.
Therefore, since there is no need for the feedback pulse 2, the output of the pulse detection circuit 11 is prohibited by the zero detection circuit 10 and the gate circuit 12.

In general, the pulse encoder 7 outputs a feedback pulse 2 as shown in FIG. The example used will be explained with reference to FIG. By calculating the exclusive OR of the feedback pulse 2 and the feedback pulse 2 delayed by the buffer 16, the rising and falling edges 14 of the feedback pulse can be detected as shown in FIG. By using this edge 14, as shown in FIG.
TTL 74123-like functionality). By setting the time constant T3 of the monomulti 20 using the resistor 18 and capacitor 19 to be longer than the maximum value of the edge interval T1 and T2 of the feedback pulse 2 detected under normal conditions, the feedback pulse 2
When is normal, the output 15 of the monomulti 20 remains “H”, but an abnormality occurs and the feedback pulse 2
When it disappears, the output 15 of the monomulti 20 becomes "L" after T3 as shown in FIG. 4, and an abnormality can be detected.

Next, set the time constant of the monomulti 20 to the servo motor 6.
An embodiment of the pulse detection circuit 11 that changes depending on the drive current will be described with reference to FIG.
The voltage of the servo motor is detected by the voltage drop of a low resistance 21 for current detection connected in series with the servo motor 6, and the output from the current detection circuit 22 is amplified by an amplifier 23 which is a voltage conversion means that converts and amplifies the voltage. The drive current value changes the resistance value of the voltage-controlled variable resistance element 24 that sets the time constant of the monomulti 20, and changes the value of T3 shown in FIG. 4. When the servo motor 6 is driven with a large current, it moves at high speed and the edge interval T1, T2 of the feedback pulse 2 becomes small. If the resistance value of the voltage-controlled variable resistance element 24 is reduced based on the drive current value of the servo motor 6 detected at this time, T3 can be reduced in accordance with the reduction of T1 and T2. Similarly, when the servo motor 6 is driven with a small current, the voltage controlled variable resistance element 24 increases as T1 and T2 increase.
T3 can be increased by increasing the resistance value of .

As yet another method, an embodiment of the pulse detection circuit 11 in which the time constant of the monomulti 20 is changed depending on the speed of the command pulse 1 will be described with reference to FIG. The speed of the command pulse 1 is converted into voltage by the frequency-voltage conversion circuit 25, and the resistance value of the voltage control variable resistance element 24 that sets the time constant of the monomulti 20 is changed, thereby changing the value of T3 shown in FIG. let When the speed of command pulse 1 is high, servo motor 6 moves at high speed, and the edge interval of feedback pulse 2
T1 and T2 become smaller. At this time, depending on the frequency-voltage conversion value of command pulse 1, voltage control variable resistor 24
By decreasing the resistance value of T1 and T2, T3 can also be decreased. Furthermore, when the command pulse 1 is at a low speed, T3 can be similarly increased as T1 and T2 become larger.

As described in the above embodiments, using the pulse detection circuit 11 that optimally adjusts the time constant T3 of the monomulti 20 according to the speed of the feedback pulse 2,
By configuring the servo motor abnormal operation prevention circuit of the present invention as shown in FIG. 3, if an abnormality occurs in the feedback pulse 2, the servo motor 6 can be stopped instantly, and abnormal operation can be reliably prevented. can do. If the present invention is applied to, for example, driving an XY table or a robot arm, the servo motor 6
It can be expected to be extremely effective in stopping the operation of the equipment instantly and reliably, ensuring work safety and protecting the equipment.

As described above, according to the present invention, the abnormal operation prevention circuit of the servo motor driven by the difference between the command pulse and the feedback pulse from the pulse encoder includes a current detection means for detecting the current flowing in the servo motor. , a voltage conversion means that generates a voltage according to the current value detected by the current detection means, a voltage control variable resistance element whose resistance value is changed by being controlled by the voltage conversion means, and this voltage control variable resistance element. Since we configured a detection circuit that detects the presence or absence of the feedback pulse using a retriggerable monostable multivibrator (hereinafter referred to as mono-multi) provided as a time constant, we used a retriggerable monostable multivibrator (hereinafter referred to as mono-multi) to detect the presence or absence of the feedback pulse. Since it can be changed in response to
Since the time constant of the monomulti can be changed in response to changes in the rotation speed of the servo motor,
For example, if the time constant is set according to the low speed rotation of the servo motor, it will take a long time to detect an abnormality, and if the time constant is set according to the high speed rotation, it will be difficult to detect an abnormal condition when the rotation speed becomes low. The problem of conventional technology, where identification becomes impossible and malfunction occurs, has been resolved, and the servo motor's abnormal operation can be prevented regardless of whether the servo motor rotates at low or high speeds and can detect abnormalities without any time delay. This has the effect that a circuit can be provided.

In addition, the abnormal operation prevention circuit of the servo motor includes a frequency-voltage converting means for converting the speed of command pulses into voltage, a voltage-controlled variable resistance element whose resistance value is changed by being controlled by the frequency-voltage converting means, and a voltage-controlled variable resistance element whose resistance value is changed by being controlled by the frequency-voltage converting means. Since we configured a detection circuit that detects the presence or absence of a feedback pulse using a monomulti equipped with a variable resistance element as a time constant, the time constant of the monomulti can be changed in response to changes in the speed of the command pulse. It is possible to optimally adjust the time constant of the monomulti according to the speed of the feedback pulse, and it has the effect of providing a servo motor abnormality prevention circuit that does not malfunction and can detect abnormalities without time delay. .

[Brief explanation of the drawing]

Figure 1 shows a general servo motor drive circuit, Figure 2 shows a conventional abnormal operation prevention circuit using overflow detection, Figure 3 shows an abnormal operation prevention circuit using feedback pulse detection according to the present invention, and Figure 4 shows the operation of the pulse detection circuit. Timing diagram. Figure 5 shows a pulse detection circuit using a monomulti. Figure 6 shows a pulse detection circuit that controls a specific number of monomultis using the servo motor drive current. Figure 7 shows the time constant of a monomulti by controlling the speed of the command pulse. This is a pulse detection circuit that controls the 1...Command pulse, 2...Feedback pulse, 3...
Counter, 4...DA conversion circuit, 5...Power amplifier circuit, 6...Servo motor, 7...Pulse encoder, 8...Overflow detection circuit, 9...Relay, 10...Zero detection circuit, 11... Pulse detection circuit, 12... Gate circuit, 13... Delayed feedback pulse, 14... Edge of feedback pulse, 15
...Mono multi output, 16...Delay buffer, 17...Exclusive OR gate, 18...Time constant setting resistor, 19...Time constant setting capacitor, 20...Mono multi, 21... Current detection resistor, 22... current detection circuit, 23... amplifier circuit,
24... Voltage control variable resistance element, 25... Frequency voltage conversion circuit.

Claims (1)

[Scope of Claims] 1. An abnormal operation prevention circuit for a servo motor driven by a difference between a command pulse and a feedback pulse from a pulse encoder, comprising: current detection means for detecting a current flowing through the servo motor; Voltage conversion means that generates a voltage according to the current value detected by the detection means;
A retriggerable resistor comprising a voltage-controlled variable resistance element whose resistance value is changed by being controlled by the voltage conversion means, and the voltage-controlled variable resistance element as a time constant.
The servo motor is characterized by being comprised of a detection circuit that uses a monostable multivibrator to detect the presence or absence of the feedback pulse, and a stop circuit that stops the operation of the servo motor based on the output of the detection circuit. Servo motor abnormal operation prevention circuit. 2. In an abnormal operation prevention circuit for a servo motor driven by the difference between a command pulse and a feedback pulse from a pulse encoder, a frequency-voltage conversion means converts the speed of the command pulse into a voltage, and a frequency-voltage conversion means a detection circuit that detects the presence or absence of the feedback pulse using a voltage-controlled variable resistance element whose resistance value is controlled to change; and a retriggerable monostable multivibrator having the voltage-controlled variable resistance element as a time constant; 1. A circuit for preventing abnormal operation of a servo motor, comprising a stop circuit that stops the operation of the servo motor based on an output from a detection circuit.