JPH04251587A - Failure detecting method for motor control circuit - Google Patents

Abstract

PURPOSE:To discriminate abnormal increase of motor current due to increase of motor load from that due to failure in a motor control circuit. CONSTITUTION:When the value of motor current detected through a resistor 18 exceeds a predetermined level, a pulse signal for reducing the motor current is superposed on a control output from a CPU 11a. If the detected current does not decrease in accordance with the pulse signal, it means failue in a motor control circuit.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a failure in a motor control circuit by which the cause of an abnormal increase in motor current can be identified and a failure in the motor control circuit can be discovered.

0002

2. Description of the Related Art A conventionally known motor control circuit generates a drive signal by applying a control signal from a microcomputer 1 to a drive section 2, as shown in FIG. The rotation of the motor 4 is made variable by applying it to the connected inverter circuit 3. A position detector 5, a tachometer, etc. are attached to the output section of the motor 4, and these detection signals are fed back to the microcomputer 1. The microcomputer 1 adjusts the control signal given to the drive unit 2 so that the detected value successively matches the command value C given from outside the system, and the whole system constitutes a so-called servo loop system. .

[0003] In such a control circuit, even when the motor 4 is in a locked state due to an overload applied to the motor rotating shaft, an excessive current is further supplied to the motor 4 to force it to rotate. Therefore, normally a resistor 6, a Hall element, etc. for current detection is provided in the DC part of the inverter circuit 3, and this detected current is also connected to the microcomputer 1.
monitors and limits current during overload.

Furthermore, even if the control output of the microcomputer 1 is limited by the method described above, for example, the AD converter, DA converter, or ROM in the microcomputer 1 may be limited.
If memory such as RAM or the next stage drive section 2 fails, there is a risk that overcurrent will be supplied, so a hardware limiting circuit 7 such as a circuit breaker is added to prevent this. It is often done.

Normally, the cutoff value by the control circuit 7 can be set to a much higher value than the control value of the motor current when the motor is locked, so in this case, it is easy to conclude that the current increase due to the failure is due to the load. , and problems such as malfunction of the limiting circuit 7 hardly occur.

[0006]

[Problem to be Solved by the Invention] However, when an upper limit is imposed on the power consumption of the entire system, the cutoff value by the limiting circuit 7 must be set to a low value, and the control circuit It is difficult to distinguish between an increase in current due to a failure and an increase in current due to an increase in motor load, and even an increase in motor load causes problems such as the limiting circuit 7 operating.

SUMMARY OF THE INVENTION An object of the present invention is to provide a failure detection method for a motor control circuit that can determine whether the cause of an increase in motor current is an increase in motor load or a failure in the control circuit.

[0008]

[Means for Solving the Problems] The gist of the present invention for achieving the above object is to output a control signal based on the difference between a detected value of the rotation amount or rotation speed of the motor and an external command value. In the motor control circuit that adjusts or reduces the motor current to be applied, the motor current is detected, and if the detected current value exceeds a predetermined value, the control circuit controls the pulse signal in the direction of reducing the motor current to be applied. Failure detection of the motor control circuit, characterized in that failure detection of the motor control circuit is performed by outputting the current value superimposed on a signal, and detecting a failure of the motor control circuit depending on whether or not a current reduction occurs in the current value in accordance with the pulse signal. It's a method.

[0009]

According to the motor control circuit failure detection method having the above-described structure, if the increase in motor current is due to a failure in the control circuit, the current detection value does not decrease in response to the pulse signal.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail based on the embodiments shown in FIGS. 1 and 2.

FIG. 1 shows an example of the configuration of a motor control circuit for carrying out the method of the present invention, and 11 is a microcomputer, and this microcomputer 11 has a CPU 1
1a, an AD converter 11b, a DA converter 11c, a ROM 11d, a RAM 11e, and an interface circuit 11f connected thereto. The motor control signal from the DA converter 11c is applied to the drive section 12, which includes a pulse width modulator 12a and a predriver 12b, and becomes a drive signal. This drive signal is input to an inverter circuit 14 connected to a DC power source 13, and the rotation of the motor 15 is made variable. Further, in response to a command from the CPU 11a, the driving section 12 can be turned on and off and the direction of rotation by the predriver 12b can be switched via the interface circuit 11f. The rotation of the motor 15 is transmitted via a reduction gear 16 or the like to output parts such as a ball screw in a linear type or a link in a rotary type, and these output parts are equipped with a position detector 1.
Sensors such as 7 and a tachometer are attached, and their detection signals are fed back to the microcomputer 11.

The microcomputer 11 adjusts the control signal given to the drive section 12 so that the detected value successively matches the command value given from the outside of the system, and the entire system constitutes a so-called servo loop system. ing. Furthermore,
In this embodiment, in order to measure the current applied to the motor 15, a resistor 18 or a Hall element is provided in the DC portion of the inverter circuit 14, and this detected current value is input to the microcomputer 11. There is.

[0013] When the detected current value is within a predetermined value or less, the above system operates as a normal servo loop system and drives the output section in accordance with the command value.
When the detected current value exceeds a predetermined value, the CPU 11a superimposes a reduction pulse with a width of about 2 milliseconds on the control signal at appropriate intervals as shown in FIG. 2, and outputs it from the DA converter 11c.

If the control circuit is normal and the current increase is simply due to an increase in the load on the motor 15, the reduced pulse is normally output from the DA converter 11c, and the pulse width modulator 12a and predriver Since the motor 12b also operates normally, the motor current generated by the inverter circuit 14 also decreases in a pulsed manner. On the other hand, if the current increase is due to a failure in the control circuit, the reduction pulse will not be reflected in the motor current. Therefore, it is possible to determine whether the control circuit is normal or abnormal by detecting that the current detection value obtained through the resistor 18 etc. decreases in a pulse-like manner.

[0015] In this manner, it is possible to output a control signal on which a reduced pulse is superimposed, and to determine whether or not the control circuit is malfunctioning depending on whether or not the motor current actually changes in accordance with the control signal. Therefore, for example, if the control circuit is normal, it is possible to continue operation while maintaining the current at a safe constant value, and on the other hand, if it is abnormal, it is possible to take appropriate measures such as issuing a warning and stopping the operation. This prevents accidents such as the circuit being cut off due to an increase in load or the motor 15 being burnt out without a failure in the control circuit being discovered.

Note that the present invention does not require the control circuit having the above-mentioned configuration, but can also be applied to a method of determining a control signal from the difference between the detected value of motor rotation and the command value, or the difference between the detected position value of the output section and the command value. It can be applied to any control circuit.

[0017]

As explained above, according to the failure detection device for a motor control circuit according to the present invention, it is possible to distinguish between an increase in current due to a failure in the control circuit and an increase in current due to an increase in motor load. Appropriate measures can be taken depending on the cause.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a motor control circuit for implementing the method of the present invention.

FIG. 2 is an explanatory diagram of a reduced pulse.

FIG. 3 is a configuration diagram of a conventional motor control circuit.

[Explanation of symbols]

11 Microcomputer 11a CPU 12 Drive section 12a Pulse width modulator 12b Pre-driver 13 DC power supply 14 Inverter circuit 15 Motor 16 Reduction gear 17 Position detector 18 Resistor

Claims (1)

[Claims] Claim 1: A motor control circuit that outputs a control signal based on the difference between a detected value of the rotational amount or rotational speed of the motor and a command value from the outside to adjust the motor current to be input. detecting the current value, and superimposing and outputting a pulse signal in the direction of reducing the motor current to be applied when the detected current value exceeds a predetermined value, on the control signal;
A failure detection method for a motor control circuit, characterized in that failure of the motor control circuit is detected based on whether or not a current reduction occurs in the current value in accordance with the pulse signal.