JPH0769189B2 - Encoder disconnection detection device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disconnection detection device for an encoder used for detecting the position of a motor.

2. Description of the Related Art This kind of wire breakage detection device prevents runaway at the time of encoder wire breakage when positioning is performed by a servomotor, and a first conventional example is disclosed in, for example, JP-A-60-117305. As described above, the absolute value of the deviation value obtained by comparing the current value and the previous value of the pulse of the pulse signal is compared with the reference value, and if it is small, it is determined that the wire is broken.

As a second conventional example, there is an exclusive OR circuit as disclosed in Japanese Patent Laid-Open No. 62-84303. As shown in FIG. 4 and FIG. 5, this is the exclusive OR of the two-phase pulse signal No. A output from the encoder and inverted from each other, and the hazard (beard) of the output signal x is calculated by the integrating circuit. ) Is removed.

However, in the first conventional example, since the absolute value of the deviation value becomes smaller than the reference value at the time of stop, it is not possible to distinguish between the stop and the disconnection, and the disconnection detection at the stop is performed. There is a problem that you cannot do it.

On the other hand, in the second conventional example, when both pulse signals A are not input, that is, when two input lines are disconnected, both are "HIGH" even when stopped and the disconnection is detected. However, the pulse signal of one input line is "HI
If the wire is disconnected in the "GH" state, the other pulse signal is "LOW".
Since the state is maintained, there is a problem that it is not possible to detect the disconnection.

The second conventional example is electrically connected to the signal line and is susceptible to noise from the signal line. Therefore, an additional circuit such as the integrating circuit is required, and the circuit configuration becomes complicated accordingly. There is also.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to provide a disconnection detecting device for an encoder, which can detect disconnection in both cases of operation and stop and has a simple circuit configuration.

Means for Solving the Problems To achieve the above object, the present invention includes two light emitting elements that alternately emit light by inverted two-phase pulse signals, and a light receiving element that receives light from these light emitting elements. It is characterized by that.

In the above structure, it is preferable that the light emitting element is configured to have a relatively long delay time.

Operation In the above configuration, when the wire is not broken, the two light emitting elements alternately emit light during operation and one of the light emitting elements emits light during stop, so that the light receiving element receives the light.
Since the two light emitting elements do not emit light when at least one of the two input lines is broken, the light receiving element does not receive the light of the light emitting element, and the disconnection can be detected during the operation and the stop. it can.

Further, since the light receiving element is electrically isolated from the main body circuit and does not receive noise from the signal line, the integrating circuit as in the second conventional example is unnecessary and the circuit configuration can be simplified accordingly. .

Practical Example An encoder disconnection detecting device according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 3 shows a control system of a motor to which the disconnection detecting device D is attached. 1 is a servo motor, 2 is a differential transmission type encoder, 3 is a counter circuit, 4 is an arithmetic and control unit, and 5 is a motor driver circuit. Is. As shown in FIG. 1, the encoder 2 outputs phase-inverted A and two-phase pulse signals. In this embodiment, an interface circuit 6 using an optical coupling circuit is provided between the encoder 2 and the counter circuit 3 for isolation.

In the disconnection detection device D shown in FIG. 1, 7 is a first LE.
D and 8 are the second LEDs 2, which are connected in parallel to the input side. The first LED 7 emits light when the pulse signal of phase A is "HIGH". The second LED 8 has a phase pulse signal of "HIGH"
Lights when. Therefore, both LEDs 7 and 8 emit light alternately. In this embodiment, the LEDs 7 and 8 use elements having a relatively long delay time. 9 is the first and second LEDs 7,
8 is a phototransistor that receives the light of 8 and is connected to the output side. When the phototransistor 9 does not receive the light, the disconnection signal Xa output to the emergency stop circuit 10 shown in FIG. 3 becomes "HIGH".

In the above configuration, when there is no disconnection in the signal line from the encoder 2, the first and second LEDs 7, 8 alternately emit light without interruption by the A and two-phase pulse signals sent from the encoder 2. The transistor 9 receives the light. In this case, the disconnection signal Xa is "LOW".
At this time, the output signal a from the interface circuit 6
The waveform of is in agreement with the pulse signal of phase A.

When a disconnection occurs in the signal line, both the A and two-phase pulse signals become “LOW” at the disconnection occurrence time T ₁ . Along with this, the LEDs 7 and 8 do not emit light, and the disconnection signal Xa of the phototransistor 9 becomes "HIGH" with a slight time lag ΔT, which notifies the emergency stop circuit 10 that disconnection has occurred.

The present invention can be constructed in various modes other than shown in the above embodiments, and the light emitting element and the light receiving element can be constructed by appropriately combining known ones.

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a disconnection detection device for an encoder, which can detect disconnection during both operation and stop, and which does not receive noise from a signal line with a simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an encoder disconnection detecting device according to an embodiment of the present invention, FIG. 2 is a waveform diagram of an input side and an output side of the same device, and FIG. 3 is an overall configuration of an actuator control system according to the present embodiment. FIG. 4 is a circuit diagram of an encoder disconnection device in the second conventional example, and FIG. 5 is an input side and output side waveform diagram in the conventional example. 7 ... First LED, 8 ... Second LED, 9 ... Phototransistor.

Claims (2)

[Claims] 1. A disconnection detecting device for an encoder, comprising: two light emitting elements that alternately emit light by inverted two-phase pulse signals; and a light receiving element that receives light from these light emitting elements. 2. The disconnection detection device for an encoder according to claim 1, wherein the light emitting element has a relatively long delay time.