JPS63228987A - Safeguard for dc motor with encoder - Google Patents

Abstract

PURPOSE:To prevent malfunction and runaway of a motor by taking out the pulsating component of current(voltage), and by discriminating the abnormal state of the breaking of the wires of an encoder through the zero rotation output of the encoder and the information of the existence of the pulsating component of the motor. CONSTITUTION:By a controlling circuit 1 and a driving circuit 2, a motor 3 is driving-controlled. To the controlling circuit 1, the input of detecting signal via a waveform shaping circuit 6 from an encoder 4 and a current detector 5 is provided, and the input of speed command from an external section is provided. Then, the waveform shaping circuit 6 is composed of a capacitor 7, resistors 8-9, and a comparator 10, and from the output of the comparator 10, rectangular-waveform output is obtained. When the output of the current detector 5 includes no pulsating component, then the output of the comparator 10 is turned into direct current determined by the voltage dividing resistors 8-9, and so by providing the input of the direct current to the controlling circuit 1 and processing the input, the existence of the pulsating component of motor current can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a safety protection device for a DC motor with an encoder, and particularly to a safety protection device suitable for detecting an abnormality when an encoder is disconnected.

[Conventional technology]

FIG. 4 shows the conventional technique described in Japanese Patent Application No. 57-7567. In FIG. 4, 1 is a control circuit, 2 is a drive circuit,
3 is a DC motor (hereinafter simply referred to as a motor), and 4 is an encoder.

When a speed command is input to the control circuit 1 from the outside, a drive signal is given from the control circuit 1 to the drive circuit 2 in the form of digital data, and the electric motor 3 starts rotating. Here, the drive circuit 2 is a D/A converting the drive signal, which is digital data, into an analog signal.
It consists of a converting section and a transistor section that applies a required voltage to the motor 3 based on this analog signal.

When the electric motor 3 rotates, the encoder 4 provides an output signal to the control circuit 1 in accordance with the rotation. Control circuit 1 is the fifth
Take in the speed command from the outside by following the steps shown in the figure.
Next, measure the speed of the electric motor. The control circuit includes a circuit that converts the number of pulses of the encoder signal into an RI number, and the counted value can be reset at regular intervals. Speed measurement is performed by reading out the 41 numerical value immediately before reset.

After measuring the speed d1, the commanded speed and the measured speed are compared, and the commanded speed is measured 'dl! If the command speed is greater than the measured speed, a drive signal is output to increase the applied voltage to the motor. If the command speed is smaller than the measured speed, a drive signal is output to decrease the applied voltage, and if the command speed and H1 measured speed are equal. Control is performed so that the applied voltage does not change.

In such a control device, if no safety protection measures are taken, if the encoder is disconnected, the encoder output (hereinafter referred to as zero circuit output) indicating that the motor is not rotating even if the motor is rotating. The result given to the control circuit 1 is that the command speed is always greater than the measured speed,
Therefore, the above-mentioned control function causes the motor to rotate more and more, which is dangerous.

In order to avoid this danger, the prior art adopts a safety protection system according to the procedure shown in FIG. In other words, as shown in the same figure, by measuring the speed of the electric motor, if the encoder's zero rotation output continues for a predetermined time (hereinafter referred to as a fixed time), it is treated as an abnormality, and in other cases, it is treated as an abnormality. is the command speed and fltill! The I speed is compared in magnitude, and the above operation according to FIG. 5 is then performed.

This procedure-based determination method could lead to malfunctions or runaway motors as described below.

[Problem that the invention seeks to solve]

As mentioned above, encoder disconnection detection in the conventional technology was performed by determining that the encoder's zero rotation output continued for a certain period of time or more, so if this certain period of time was shortened, the startup delay, especially under heavy loads, could be reduced. With a DK prisoner, the encoder will malfunction in such a way that an abnormal signal is output even though it is normal, and if you take a longer period of time to avoid this, the motor will rotate out of control after a certain period of time when the load is light. For example, robots that operate using the rotation of an electric motor,
Even if there was a limit to the distance a machine could travel, there was a possibility that the machine would be moved beyond that limit. This problem can occur not only at startup but also when the encoder is disconnected while the motor is rotating.

SUMMARY OF THE INVENTION An object of the present invention is to provide a safety protection system that immediately detects an abnormality due to a disconnection of an encoder, and does not cause malfunctions or runaway rotation of the motor as in the prior art.

[Means for solving problems]

In order to achieve the above two objects, the present invention includes a means for detecting the current of the motor and extracting the pulsation of the current or voltage caused by the rotation of the motor, such as rectification ripple, and a means for detecting the pulsation of the motor and the zero rotation output of the encoder. The apparatus is equipped with a means for determining a disconnection abnormality in the encoder based on the information on the encoder.

[Effect]

Detecting the motor current and extracting the pulsating current provides direct information as to whether the motor is actually rotating. That is, if there is a pulsation component, this indicates that the motor is rotating due to the applied voltage, and if there is no pulsation component, it indicates that the motor is not rotating. For example, in the case of a DC motor with a commutator, the pulsating component here means the pulsating component of the current due to a decrease in coil resistance due to constraints such as when the brush straddles both commutators, that is, commutation ripple. It is something that occurs.

The zero circuit output of the encoder is the encoder output when the rotational speed of the motor is zero, so this indicates that the motor is not actually rotating, but even if one electric motor is rotating, the encoder If the wire is disconnected, the output will be zero and the output will be the same as when it is not rotating.

Therefore, the presence of the encoder's zero-rotation output and the presence of pulsation information at the same time indicates that the encoder is in a disconnection abnormal state.

〔Example〕

An embodiment of the invention is shown in FIG. In FIG. 1, 1 is a control circuit, 2 is a drive circuit, 3 is an electric motor, 4 is an encoder, 5 is a current detector, and 6 is a waveform shaping circuit.

Similar to the prior art, when a speed command is input from the outside to the control circuit 1, a drive signal is applied from the control circuit to the drive circuit 2, and the drive circuit 2 applies a voltage to the motor 3, causing the motor to rotate. As the electric motor rotates, the encoder 4 outputs an output signal (ij) corresponding to the rotation, and is given to the control circuit 1, and the electric motor rotates at a commanded speed under the same arithmetic control as in the prior art.

The present invention will be specifically described below.

A current detector 5 is provided in series with the electric motor 3 to detect the current flowing through the electric motor. Due to the rectification effect, this current waveform has a pulsating component with a DC component Vo, as shown in FIG. 3, for example. This waveform output is input to the waveform shaping circuit 6. This circuit 6 includes a capacitor 7, resistors 8 and 9,
It is composed of a comparator 10. If the output of the current detector 5 includes a pulsating component, when this output is applied to the waveform shaping circuit 6, it is AC-coupled to the resistor 8 by the capacitor 7 at its input, and as a result, the +( of the comparator 10) Plus) A waveform voltage with a pulsating component added to a constant direct current is applied to the input. On the other hand, a voltage divided by resistors 8 and 9 is applied to the − (minus) input of comparator 1o, and the values of resistors 8 and 9 are adjusted so that this voltage becomes the DC voltage at the center of the input waveform on the input side. is selected, a rectangular waveform output is obtained as the output of the comparator 10.

In addition, if the output of the current detector 5 does not include a pulsating component, the output of the comparator becomes a direct current determined by the voltage dividing resistance of the waveform shaping circuit. , the presence or absence of ripples in the motor current can be detected.

FIG. 2 shows a procedure for controlling the electric motor and a procedure for detecting a disconnection abnormality in the encoder.

Similar to the conventional technology, a speed command is captured, the motor speed is measured, a command measurement is compared with the measured speed, and an increase or decrease in the applied voltage is calculated. If the encoder outputs zero rotation despite the presence information, abnormality processing is performed. In addition, if there is no pulsation, the motor is not rotating, so it is determined whether the zero-circuit state continues for a certain period of time or more, and if it is longer than a certain period of time, an abnormality processing is performed as the motor is in a stopped state, and if it is within a certain period of time, a command is issued. Compare the speed with the measured speed,
If the commanded speed is greater than the measured speed, the same control procedure as in the prior art is performed, such as increasing the voltage applied to the motor.

In the above procedure, it is a feature of the present invention that a disconnection abnormality of the encoder is detected based on the zero rotation output of the encoder and the presence information of the pulsation of the motor current, without waiting for the elapse of a certain period of time.

Although we have described the case of a DC motor with a commutator that causes commutator ripple, safety protection can be achieved in the same way in the case of a brushless DC motor by using the induced voltage of one phase instead of the current waveform. It can be carried out.

In addition, in this embodiment, the electric motor was controlled by changing the applied voltage, but there is a method in which the rotation speed is controlled by changing the energization time to the electric motor within a certain period, that is, PWM.
(pulse width modulation) method, the current waveform is input to the waveform shaping circuit through a low-pass filter.
Similar safety protection can be achieved by removing the effects of pulsation caused by the WM method.

〔Effect of the invention〕

According to the present invention, an abnormality is detected based on information on the presence of pulsation in the motor current as well as the zero-rotation output of the encoder, so that when an encoder disconnection abnormality occurs, the abnormality can be immediately detected and safety protection can be performed. Also, if the motor does not start rotating due to the vehicle load at startup, there is no pulsation in the motor current, so it can be distinguished from an encoder disconnection error.
Does not cause malfunction. Furthermore, even if the encoder is disconnected during operation, the present invention detects the pulsation of the current, so the abnormality can be immediately detected, and there is no problem such as the machine moving beyond the permissible range.

Through the above steps, the object of the present invention can be achieved.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram of the procedure of an embodiment of the present invention, Fig. 3 is a current waveform diagram of a DC motor, and Fig. 4 is a block diagram of a conventional technology. 5 and 6 are explanatory diagrams of the procedure of the prior art, 1... control circuit, 2...
l drive circuit, 3... DC motor, 4... encoder,
5... Current detector, 6... Waveform shaping circuit.

Claims (1)

[Claims] 1. To avoid abnormal rotation of the motor that may occur when the encoder is disconnected in a control device that is equipped with an encoder that outputs a signal corresponding to the rotation of the DC motor and uses the output to control the DC motor to the desired rotation. A safety protection device includes means for detecting the current of a DC motor and extracting the pulsation of the current or voltage generated by the rotation of the motor, an encoder output indicating that the motor is not rotating, and a means for detecting the pulsation. A safety protection device for a DC motor with an encoder, comprising: a means for determining a disconnection abnormality from information on