JPH0728541B2 - Failure detection device for motor control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a motor control device for pulse-width-modulating and transmitting a current command value of a motor, and in particular, prevents runaway of the motor due to element destruction or the like, and improves safety. The present invention relates to a failure detection device suitable for improvement in a motor control device.

[Conventional technology]

As a conventional method for detecting an abnormality in a motor control device, as described in JP-A-62-24305 used in an industrial robot, a reference value of a deviation between a position command value for a motor and a current position is provided. At the same time, a time reference value is provided and an abnormality is judged when the position deviation exceeds both the deviation reference value and the time reference value.

[Problems to be solved by the invention]

The above-mentioned conventional technique, when the industrial robot moves, the deviation between the position command value and the current position becomes the reference value or more, and when the deviation is continued for the reference time or longer, it is determined abnormally. If a runaway occurs due to element destruction, an abnormality cannot be detected unless the robot moves to some extent, which poses a safety issue.

An object of the present invention is to detect an abnormality before a runaway of an object such as an electric motor or a robot or to perform safe protection even if a signal transmission circuit element between certain control means is broken or malfunction occurs. It is in.

[Means for solving problems]

The purpose of the above is to modulate the pulse width of the signal to be transmitted, and to apply a limiter to the pulse width modulated signal (may be applied in the previous stage) so that the pulse width signal with a cycle within a certain range is always transmitted and received during normal operation Has a monitoring time longer than the period of the pulse width modulated signal, and monitors the pulse width of the received pulse width modulated signal within the monitoring period or the presence or absence of a pulse edge for each period of the pulse width modulated signal. ,
Means to determine the failure of the motor control device when it is determined that there is no edge of the pulse of the pulse width modulation signal within the monitoring period or that the pulse width of the pulse width modulation signal has become longer than the monitoring period. By providing such a device, early failure detection can be achieved.

[Action]

The pulse discrimination means pulse-width modulates the electric command value and discriminates the waveform of the pulse width signal for each cycle. In other words, if an abnormality occurs due to element destruction or malfunction in the circuit that generates the pulse width modulation signal or its transmission / reception circuit, the abnormality occurs because the level change that occurs in each cycle of the pulse width modulation signal during normal times disappears. To detect.
Generally, when converting a command value input to a control circuit into a pulse width modulation signal for transmission, a pulse modulation signal having a frequency several times higher than the response frequency of the control system is required.
Therefore, the pulse discriminating means can detect an abnormality in each cycle of the pulse width modulation signal, so that the electric motor or the robot to be controlled can be protected before it goes out of control.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This drawing is an example in which the present invention is applied to the transmission of a current command signal in a speed control device for a DC motor. The microcomputer 1 has a speed command value Nr at every constant cycle output by the timer 9.
And a speed feed back signal Pe from the electric motor 10 is used to perform speed control calculation and output a current command value Ir. The pulse width modulation circuit 2 converts the digital amount current command value Ir into a pulse width modulation signal PS, and the transmission circuit transmits this signal. The transmitted pulse width modulation signal is received by the receiving circuit 4 and given to the analog type current control circuit 5. The current control circuit 5 converts this pulse width modulation signal into a DC component signal by the filter effect and a current detector.
A current control calculation is performed using the current feedback signal If obtained by 12 and a control signal for the power conversion circuit 6 is output. The power conversion circuit 6 supplies power to the DC motor 10 by the switching operation of the power transistor to change the rotation speed. The incremental encoder 11 is mechanically directly connected to the DC motor 10, and
A pulse Pe having a frequency proportional to the rotation speed of is output. The counter 8 counts this pulse Pe, and the microcomputer 1 calculates the rotation speed of the electric motor 10 based on the count value of the counter 8 and uses it as a feed back signal to control the speed of the electric motor 10 according to the command value. . The pulse discriminating circuit 7 discriminates the pulse of the pulse width modulation signal received by the receiving circuit 4 and discriminates whether the pulse width modulation signal given to the current control circuit 5 is normal or abnormal. A signal for stopping the control circuit 5 is output, and an abnormality is also notified to the microcomputer 1 to detect a failure of the pulse width modulation signal transmission circuit.

Next, a method of giving a command to the analog current control circuit 5 by the pulse width modulation signal PS will be described with reference to FIG. The current command value Ir of the digital amount output by the microcomputer 1
Has a value corresponding to the duty (Ts / Tp) of the pulse width modulation signal PS, and the pulse width modulation circuit 3 uses this current command value Ir.
The pulse width modulation signal PS corresponding to is output. This pulse width modulation signal PS is converted into a direct current component command value Irdc having pulsation as shown in FIG. 2 by the effect of a filter having a first-order lag characteristic provided at the input of the current control circuit 5, and the electric motor Controls the current flowing through 10.

Next, details of the signal transmission and the failure detection method will be described. Third
FIG. 4 shows a configuration example of a pulse width modulation signal transmission circuit and its failure detection circuit, and FIG. 4 shows a time chart for explaining the operation of FIG. Note that FIG. 4 also includes the operation when the transmitter circuit 3 or the receiver circuit 4 fails. The pulse width modulation circuit 2 holds the current command value Ir of the digital amount limited by the limiter 20 provided in the microcomputer 1 in the latch circuit 21, and outputs the output signal LD of the timer 23 which determines the cycle of the pulse width modulation signal. It is taken into the counter 22 every time. The counter 22 counts down each time the clock CLK is input, and sets the output PS to low level when the count value becomes zero. This output is the enable signal EN for the counter 22.
Then, the output PS is held at the low level while the count value of the counter 22 remains zero during the low level period. After that, the count value of the counter 22 is set by the output signal LD of the timer 23 and the output PS becomes high level, and thereafter the above operation is repeated to generate the pulse width modulated signal PS. The transmission method of the pulse width modulated signal PS is, for example, a line driver 24 as a transmission means and a photo coupler 25 as a reception means.
To transmit. The pulse width modulation signal RS received by the photo coupler 25 becomes the signal LS converted into the positive voltage PV and the negative voltage NV by the level conversion circuit 27, and the current control circuit 5
To the one-shot circuit 26 of the pulse discriminating circuit 7 together with the direct current signal Irdc due to the effect of the filter. The one-shot circuit has a function of detecting a rising edge of the pulse-modulated signal RS and holding the output at a high level for a fixed time To determined by an externally connected resistor R1 and capacitor C1. This constant time To is set to the period Tp of the pulse width modulation signal RS,
By providing the relationship of To> Tp, the one-shot circuit 26 is reset every cycle Tp and the output signal EMG is always at the high level. This means that the current command value Ir output from the microcomputer 1 is a limited signal, so a signal with a duty of 0% or 100% is not output under normal conditions, and a rising edge is generated at each cycle Tp. The fact that it is a pulse width modulation signal that it has is utilized. On the contrary, when an abnormality such as disconnection or element destruction occurs in the signal transmission path, the signal RS has a constant level as shown in FIG. 4, so that the one-shot circuit 26 is not retriggered and after a certain time To. By detecting an abnormality and setting the output signal EMG to a low level, the current control circuit 5 can be stopped to increase the power supply to the electric motor 10 and prevent the electric motor 10 from running out of control. The abnormality detection signal EM
G is input to the clear terminal of the one-shot circuit 26 to hold this signal. According to the present embodiment, the current command value Ir output from the microcomputer 1 becomes a signal limited by the software processing of the microcomputer, so that there is a hardware abnormality in the transmission path of the pulse width modulation signal. In addition to the detection of, there is an effect that abnormalities such as runaway of software of the microcomputer can be detected.

Next, another embodiment of the present invention is shown in FIG. 5, and a time chart for explaining the operation thereof is shown in FIG. The difference from FIG. 3 is that two photo couplers 30, 3 are used without using a level exchanger.
According to 1, the signal RU which becomes the positive voltage PV and the signal RL which becomes the negative voltage NV are directly added to obtain the current command value for the current control circuit 5. Therefore, the pulse discrimination circuit for detecting an abnormality requires two series. First, the signal RU received by the photocoupler 30 is compared with the reference voltage + Vs by the comparator 32, and the signal UC having the same pulse width as the pulse width modulation signal RS is output. Using this signal UC as an input, a failure of the photocoupler 30 is detected by the one-shot circuit 34 by the same method as in the above-described embodiment. Similarly, the failure of the photocoupler 31 can be detected by the comparator 33 of the signal RL outputting the negative voltage NV and the reference voltage -Vs and the one-shot circuit 35. Fault detection signal EM for each photocoupler 30 and 31
Due to the AND circuit 36, the U and EML can generate the abnormal signal EMG and stop the current control circuit 5 even if one of the photo couplers fails. FIG. 6 shows a state in which the photocoupler 31 has failed, and the failure is detected after a predetermined time To from the edge immediately before the failure. When the pulse width modulation signal generating circuit 2 or the driver 24 that transmits the signal PS has a failure or a disconnection, the output signals RU and RL of the photocouplers 30 and 31 are both at a constant level, so that an abnormality is detected. be able to. In the present embodiment, since two photo couplers are used as the receiving means, it is possible to improve the detection of the failure of the common portion such as the pulse width modulating means and the transmitting means, and it is possible to obtain the effect of improving the safety of the electric motor device. .

In this embodiment, the one-shot circuit is used as the pulse discriminating means, but the same function can be obtained by using a function of measuring a certain fixed time, such as a counter. The pulse width modulation circuit also uses a method such as making the time of the timer that determines the period of the modulation signal longer than the maximum time of the counter that counts the current command value, so that the pulse width modulation signal that is limited by hardware can be obtained. It can be generated, and the load on the software of the microcomputer can be reduced.

As for how to take the duty, in the case of a control system that issues both forward and reverse point commands, the duty 50% is set to no signal state, 0 to 50% is forward rotation, and 50 to 100% is It suffices to use a reverse rotation command. The forward rotation and reverse rotation commands may have a reverse duty relationship.

Further, although the present invention is applied to the transmission of the current command signal between the speed control circuit and the current control circuit in the present embodiment, the transmission of the speed command signal between the position control circuit and the speed control circuit or the position control circuit is performed. It is also possible to obtain the same effect by applying the present invention to the transmission of the given position command signal.

〔The invention's effect〕

According to the present invention, the current command value in the motor control device is pulse-width modulated and transmitted, so that it is possible to determine whether the transmission signal is normal or abnormal for each cycle of the pulse-width modulation signal. When an abnormality such as a malfunction of a signal generating circuit or a transmission path or a breakage of an element occurs, the abnormality can be detected before the electric motor, which is an object to be controlled, runs away, and the device can be protected safely.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an electric motor control device showing an embodiment of the present invention, FIG. 2 is a time chart for explaining the operation of FIG. 1, and FIG. 3 is a detailed configuration diagram showing an essential part of FIG. , FIG. 4 is a time chart for explaining the operation of FIG. 3, and FIG.
FIG. 6 is a detailed configuration diagram of another embodiment showing a main part of the drawing, and FIG.
6 is a time chart for explaining the operation of the figure. 1 ... Microcomputer, 2 ... Pulse width modulation circuit, 3 ... Transmission circuit, 4 ... Reception circuit, 5 ... Current control circuit, 6 ... Power conversion circuit, 7 ... Pulse discrimination circuit, 8
...... Counter, 9 ...... Timer, 10 ...... DC motor, 11 ...
… Encoder.

Claims (3)

[Claims] 1. A means for generating a pulse width modulation signal having a constant cycle having a duty corresponding to the difference between a motor speed command signal and a feedback speed signal of the motor, and the pulse width modulation signal sent via a transmission line. And a means for controlling the speed of the motor by controlling the current according to the duty of the pulse width modulated signal, and having a monitoring time longer than the cycle of the pulse width modulated signal, and transmitting the signal. The pulse width modulation signal sent through the line is taken in, and the pulse width of the pulse width modulation signal within the above monitoring period or the presence or absence of the edge of the pulse is monitored for each period of the pulse width modulation signal, and within the above monitoring period. Motor control when it is determined that there is no edge of the pulse of the pulse width modulation signal, or the pulse width of the pulse width modulation signal has become longer than the above monitoring period. Failure detection device of a motor control apparatus comprising a malfunction determining means location. 2. A failure detecting device for a motor control device according to claim 1, wherein an upper limit value of the difference between the speed command signal and the feedback signal is limited. 3. The failure detection device for a motor control device according to claim 1, wherein the monitoring period is a value that can be set arbitrarily.