JPH07286862A - Displacement detector - Google Patents

Abstract

PURPOSE:To provide an excellent abnormality detecting function with a simple constitution by adding first and second sine wave signals to each other and generating third sine wave signals which are used as criteria for judgment of the levels of and phase relation between the first and second sine wave signals. CONSTITUTION:A signal conversion circuit 21 is constituted of comparators 211 and 212 which respectively convert first and second sine wave signals A and B into square waves at a prescribed comparing level. A signal adding circuit 22 is constituted of resistors R1 and R2 which synthesize the signals A and B and generate third sine wave signals. Another signal conversion circuit 23 is constituted of a reference voltage generating circuit composed of a serial circuit of resistors R3, R4, and R5, comparators 231 and 232, and an OR gate 233. The comparators 231 and 232 convert the parts above or below a prescribed threshold of the positive or negative half waves of the signals C into positive or negative square waves. When the OR of both outputs is found, therefore, third square wave signals CD which are converted into positive square waves can be obtained on both the positive and negative sides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement detecting device having an abnormality detecting function, which is constructed by using an encoder which outputs 90 ° out of phase with each other.

[0002]

2. Description of the Related Art An encoder having a scale and an index that move relative to each other and outputting two sinusoidal signals whose phases are shifted from each other by 90 ° according to the relative movement is used to process these sinusoidal signals. A displacement detection device that performs displacement measurement is known. In this type of displacement detection device,
Various types have been proposed that have an abnormality detection function for detecting and notifying an output value abnormality or a phase difference abnormality.

The basic principle of abnormality detection is to set a certain reference level range by utilizing the fact that two sinusoidal signals from the encoder are 90 ° out of phase with each other. It is detected whether there is a relation such as a wavy signal level (for example, Japanese Patent Publication No. 3-26771).
JP-A-61-66113, etc.).

[0004]

The anomaly detection methods that have been proposed so far cannot reliably detect anomalies unless the output value anomaly or the phase difference anomaly is significant, and depending on the setting of the reference level range, the accuracy of measurement may be reduced. There was a problem that even abnormalities that did not affect that much would be detected.

It is an object of the present invention to provide a displacement detecting device which realizes an excellent abnormality detecting function with a simple structure.

[0006]

The present invention provides a first sinusoidal signal and a second sinusoidal signal which have a scale and an index that move relative to each other and whose phases are deviated from each other by 90 ° according to the relative movement. An encoder for outputting, a signal processing means for processing the first sinusoidal signal and the second sinusoidal signal obtained from this encoder to obtain a displacement, a first sinusoidal signal and a second sinusoidal signal obtained from the encoder. An abnormality detecting means for detecting an abnormality using a sinusoidal signal, wherein the abnormality detecting means converts the first sinusoidal signal and the second sinusoidal signal into rectangular waves at predetermined comparator levels. And a first signal conversion means for obtaining a first rectangular wave signal and a second rectangular wave signal, and the first sinusoidal signal and the second sinusoidal signal are added to obtain a third sinusoidal signal. Signal adding means for obtaining, The third rectangular wave obtained by judging the third sinusoidal signal obtained from the signal adding means of (1) with predetermined positive and negative threshold values and converting the portion outside the range sandwiched by these threshold values into a rectangular wave. A second signal converting means for obtaining a signal and an exclusive OR of the first rectangular wave signal and the second rectangular wave signal are obtained, and the output thereof and the logical NOT of the third rectangular wave signal are taken. And a logic circuit means for outputting an abnormality detection signal.

[0007]

In the abnormality detecting means according to the present invention, the first sinusoidal signal and the second sinusoidal signal are added to obtain the first sinusoidal signal.
The third sinusoidal signal used as a reference for determining the level and phase relationship between the sinusoidal signal and the second sinusoidal signal is generated. Furthermore, the third sinusoidal signal is judged by the positive and negative predetermined threshold values, and the portion outside the range sandwiched by these threshold values is converted into a rectangular wave.
Is getting a square wave signal. Then, the abnormality detection output is output by the logic of the first and second rectangular wave signals and the third rectangular wave signal obtained by converting the first and second sine wave signals into rectangular waves, respectively, which is excellent. An abnormality detection function can be realized.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a displacement detecting device using a photoelectric encoder according to an embodiment of the present invention. The scale 11 and the index 12 are each provided with a graduation made of an optical grating and are arranged so as to be relatively movable as indicated by an arrow. The light source 13 has, for example, a semiconductor laser and means for collimating its output light, and the scale 11 is irradiated with the collimated light.

The light transmitted through the scale 11 and the index 12 is detected by the light receiving elements 14 and 15. A first sinusoidal signal A and a second sinusoidal signal B whose phases are deviated from each other by 90 ° are obtained from the two light receiving elements 14 and 15. This is realized by shifting the phase of the optical grating formed in the portion where the two light receiving elements 14 and 15 of the index 12 face each other by 90 ° in relation to the scale 11.

The first and second sinusoidal signals A and B from the two light receiving elements 14 and 15 are sent to the signal processing circuit 16 where they are subjected to predetermined signal processing and the displacement is arithmetically output.
The signal processing circuit 16 is usually a conversion circuit that converts the two sinusoidal signals A and B into a rectangular wave at a predetermined comparison level, a circuit that discriminates the displacement direction from the relationship between the obtained two rectangular wave signals, and It is composed of a counter or the like that detects the rising or falling of one rectangular wave signal to generate a pulse and counts the pulse.

The first and second sinusoidal signals A and B obtained from the two light receiving elements 14 and 15 are also used in the abnormality detection circuit 1.
Sent to 7. The abnormality detection circuit 17 detects an output abnormality or a phase difference abnormality that leads to a measurement error, and outputs an alarm output when there is an abnormality.

FIG. 2 shows a specific circuit configuration of the abnormality detection circuit 17. The abnormality detection circuit 17 includes a first signal conversion circuit 21 that converts the first and second sinusoidal signals A and B into rectangular wave signals, and a signal that adds the first and second sinusoidal signals A and B. Adder circuit 22, second signal conversion circuit 2 for converting the output of the signal adder circuit 22 into a predetermined rectangular wave signal
3, and a logic circuit 24 for generating an alarm signal by taking a predetermined logic for the output of the first signal conversion circuit 21 and the output of the second signal conversion circuit 23.

The first signal conversion circuit 21 is composed of comparators 211 and 212 which convert the first and second sinusoidal signals A and B into rectangular waves at a predetermined comparison level. In the case of this embodiment, the comparison level is the center of vibration, and as shown in FIG. 3, the positive half waves of the first and second sinusoidal signals A and B are made into rectangular waves, respectively. The rectangular wave signals AD and BD are obtained.

The first in the abnormality detection circuit 17
The signal conversion circuit 21 of FIG.
Since it is also used for, it can be shared with the signal processing circuit 16. Further, the comparator levels of the comparators 211 and 212 can be set to different values according to the respective input signal amplitudes and the like.

The signal adder circuit 22 includes resistors R1 and R2 (R1 = R2) for synthesizing the first and second sinusoidal signals A and B.
And, as shown in FIG.
A sinusoidal signal C of is obtained.

The second signal conversion circuit 23 includes resistors R3 and R3.
The reference voltage generating circuit is composed of a series circuit of R4 and R5, comparators 231, 232 and an OR gate 233. One of the comparators 231 receives an input of a predetermined reference voltage at its inverting input terminal and a third reference voltage at its non-inverting input terminal.
The sinusoidal signal C of is input. As a result, the portion of the positive half-wave of the sinusoidal signal C that is equal to or greater than the predetermined threshold is converted into a positive rectangular wave. The other comparator 232 has a non-inverting input terminal to which a predetermined reference voltage is input, and an inverting input terminal to which the third sinusoidal signal C is input. As a result, the portion of the negative half wave of the sine wave signal C that is equal to or smaller than the predetermined threshold value is converted into a positive rectangular wave.

Therefore, these two comparators 231,
By taking the OR of the output of 232, as shown in FIG. 3, except for the portion sandwiched between the positive side threshold value V1 and the negative side threshold value V2 set with the center of vibration interposed therebetween, A third rectangular wave signal CD converted into a positive rectangular wave on both the side and the negative side is obtained.

The logic circuit 24 includes an exclusive OR gate 241 to which the first and second rectangular wave signals AD and BD are input,
It is configured by a logical sum negation gate 242 to which the output and the third rectangular wave signal CD are input, and outputs an alarm output.

FIG. 3 shows waveforms of the first and second sinusoidal signals A and B obtained from the two light receiving elements 14 and 15 in a normal state where there is no phase shift or offset from the 90 ° phase difference. There is. As shown in the figure, in this case, neither the exclusive OR output of the first and second rectangular wave signals AD and BD nor the third rectangular wave signal CD becomes L level, and the alarm signal is not output.

FIG. 4 and FIG. 5 show the states of alarm output when an abnormality is detected by simulation results. In FIG. 4A, when the offset is large, that is, the offset of the second sinusoidal signal (B-phase signal) is zero, but the offset of the first sinusoidal signal (A-phase signal) is 0.3V. This is the case. FIG. 4B shows a case where there is a phase shift, that is, when the first and second sinusoidal signals A and B should have a phase difference of 90 °, but a phase difference of about 120 °. In either case, the exclusive OR output of the first and second rectangular wave signals AD and BD and the third rectangular wave signal CD are both at the L level in a time zone, and the H level alarm signal is output. To be done.

FIG. 5A shows an example in which the B-phase signal amplitude is small, specifically, the B-phase signal amplitude is 0.5V and the comparator level is 0.5V. Also in this case, the H-level alarm signal is intermittently output as shown in the figure. Figure 5
(B) shows a case where the B-phase signal amplitude is as small as 0.5 V, and correspondingly, the B-phase side comparator level is set as small as 0.2 V so that no alarm signal is output. . Even if the signal level is low as described above, if the comparator level is adjusted according to this, a normal operation without an alarm signal can be performed.

[0022]

As described above, according to the present invention, it is possible to provide a displacement detecting device which realizes an excellent abnormality detecting function with a simple structure.

[Brief description of drawings]

FIG. 1 shows a displacement detection device according to an embodiment of the present invention.

FIG. 2 shows a configuration of an abnormality detection circuit of the same embodiment.

FIG. 3 shows operation waveforms of the abnormality detection circuit during normal operation.

FIG. 4 shows how an alarm signal is output from the abnormality detection circuit.

FIG. 5 shows how an alarm signal is output from the abnormality detection circuit.

[Explanation of symbols]

11 ... Scale, 12 ... Index, 13 ... Light source, 1
4, 15 ... Light receiving element, 16 ... Signal processing circuit, 17 ... Abnormality detection circuit, 21 ... First signal conversion circuit, 22 ... Signal addition circuit, 23 ... Second signal conversion circuit, 24 ... Logic circuit.

Claims (1)

[Claims] 1. An encoder that has a scale and an index that move relative to each other, and outputs a first sinusoidal signal and a second sinusoidal signal whose phases are deviated from each other by 90 ° according to the relative movement; Abnormality detection using the signal processing means for processing the obtained first sinusoidal signal and the second sinusoidal signal to obtain the displacement, and the first sinusoidal signal and the second sinusoidal signal obtained from the encoder. And an abnormality detecting unit for converting the first sinusoidal signal and the second sinusoidal signal into rectangular waves at predetermined comparator levels to convert the first rectangular wave signal into a rectangular wave signal. And first signal converting means for obtaining a second rectangular wave signal, and signal adding means for adding the first sinusoidal signal and the second sinusoidal signal to obtain a third sinusoidal signal, Obtained from the addition means A third rectangular wave signal obtained by determining a third sinusoidal signal with a predetermined positive and negative threshold value and converting a portion outside the range sandwiched by these threshold values into a rectangular wave. A signal converting means, which takes an exclusive OR of the first rectangular wave signal and the second rectangular wave signal, and outputs an abnormality detection signal by taking the logical NOT of its output and the third rectangular wave signal. A displacement detecting device comprising: a logic circuit means.