JPS6038170Y2 - Abnormality detection circuit of photoelectric encoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an abnormality detection circuit for a photoelectric encoder, and particularly to an abnormality detection circuit that can quickly detect an abnormality in a signal detection section.

Photoelectric encoders are suitable for detecting changes in length or physical quantities as accurate electrical signals in length measuring instruments, coordinate measuring machines, positioning devices for machine tools, etc., and are used in various fields as linear or rotary encoders. It has been put into practical use.

Figure 1 shows the main parts of a typical photoelectric encoder.
Main scale 10 and two index scales 12.1
3 form a linear encoder.

Each scale 10, 12, 13 has a shape in which hatched light-shielding parts and light-transmitting parts are arranged alternately, and the main scale 10, index scale 12, and main scale 10 and index scale 13, respectively. As a pair, the amount of light transmission is changed when the main scale 10 in the embodiment moves.

Therefore, if the main scale 10 is moved in response to a change in length or other physical quantity, the amount of movement can be detected as a periodic change in light amount.

A light source 14 is provided on one side of the pair of optical gratings, and photoelectric converters 16 and 18 are provided on the other side in correspondence with the index scales 12 and 13, respectively.

Accordingly, the transmitted light in the embodiment from light source 14 is converted into electrical signals by photoelectric converters 16 and 18, respectively.

The index scale 12.13 is the main scale 10.
In the embodiment, the sine wave signal 101 shown in FIG. 2 is detected from the photoelectric converter 16, and at this time the photoelectric A cosine wave signal 102 shown in FIG. 2 is detected from the converter 18.

Therefore, according to this type of photoelectric encoder, it is possible to obtain a highly accurate measurement signal by performing a combination of the signals 101 and 102 having different phases.

As described above, according to the photoelectric encoder, it is possible to obtain electrical detection signals with relatively high accuracy, and in particular, it is possible to detect two types of signals with different phases, such as the aforementioned sine wave signal and cosine wave signal. According to the encoder, it is possible to provide a device with high resolution and easy direction discrimination.

However, such an encoder has a problem in that measurement accuracy is significantly reduced when the detected waveforms of the sine wave and cosine wave are disturbed.

Disturbances in the waveform include, for example, lifting of the detection head, insufficient light emitted by the light source 14 due to a drop in battery voltage in the case of a battery-powered encoder, loss of the slit shape of each scale 10, 12, 13, and intrusion of dust between optical grids. , the occurrence of moiré, or deviations in mechanically fixed positions between scales.

If the waveform is disturbed due to these various causes, the signal voltage necessary for the processing circuit to function may not be obtained, or the phase between the sine wave and cosine wave may shift, making it difficult to make accurate measurements in practice. It becomes difficult to output long signals and the like.

The conventional apparatus has no means for confirming such an abnormal situation, and for this reason, the conventional apparatus has the disadvantage that a measurement signal containing a large error is processed as is.

The present invention was developed in view of the above-mentioned conventional problems, and its purpose is to provide an improved abnormality detection circuit that can accurately detect abnormalities in the signal detection section of a photoelectric encoder and perform rapid signal processing. Our goal is to provide the following.

In order to achieve the above object, the present invention includes a main scale having aligned optical gratings, and an index scale having two optical gratings aligned with different phases, and both scales have an index scale having two optical gratings arranged in different phases. In a photoelectric encoder that detects a sine wave signal and a cosine wave signal from the brightness of light transmitted or reflected by both pairs of optical gratings by relatively moving the pair of optical gratings, the sine wave signal and the cosine wave signal are full-wave rectified at the center level, respectively. a rectifier circuit that adds the output signals of both boards; and a comparison circuit that compares the output of the addition circuit with a predetermined reference value. It is characterized by output.

Preferred embodiments of the present invention will be described below based on the drawings.

FIG. 3 shows an embodiment of the present invention, in which a sine wave signal 10
1 and the cosine wave signal 102 are respectively supplied to the rectifier circuit 30.
32, and its voltage value is full-wave rectified at the center level of each signal.

These rectified outputs are then supplied to an adder circuit 40, where both signal values, which change from time to time, are added one after another.

As is well known, sine waves and cosine waves are 90' apart from each other.
When normal sine wave signals 101 and cosine wave signals 102 having different phases are output from the detection section of the photoelectric encoder, their relative phases are maintained almost accurately.

When the detection section is normal, the detected voltage values of both signals 101 and 102 are held at a constant value.

Therefore, the addition output of the addition circuit 40 has a substantially constant value when the detection section of the encoder is normal.

That is, both signals 101 and 1 are converted by the rectifier circuits 30 and 32.
02 is full-wave rectified, its rectified output can be approximately approximated as cos''θ and 5in2θ, respectively,
From the following formula of trigonometric functions, it can be understood that CO32θ+5in2θ=1 The addition output 40 is a nearly constant value.
Therefore, the output of the adder circuit 40 is supplied to the comparator circuit 50,
Reference voltage V.

Compared to this, it can be used as an extremely accurate detection section for abnormal signals.

In other words, as mentioned above, when the encoder's detection section is normal, the addition output will be a nearly constant value, but if an abnormality occurs in the detection signal, for example, the voltage value decreases due to the floating of the detection head, etc. Or sine wave detection signal 10
1 and the cosine wave detection signal 102, the above-mentioned addition output will fluctuate, resulting in an addition output that is significantly lower or higher than normal.
This allows the comparison circuit 50 to output the abnormality detection signal without delay.

In the embodiment, the abnormality detection signal from the comparator circuit 50 is supplied to a flip-flop 60, and the flip-flop 60 is set immediately upon detection of an abnormality to invalidate subsequent detection signals or generate an error signal to the length measuring device or the like. let

As described above, according to the present invention, it is possible to accurately detect an abnormality in a photoelectric encoder with a simple circuit configuration.
The above-mentioned embodiment circuit can also be miniaturized by integrating the signal processing circuit into an IC, and can be easily incorporated into a compact or portable length measuring device, etc., and can be used in a wide range of various devices. can.

In the above-mentioned embodiment, a normal rectifier circuit is used for full-wave rectification, but it is also possible to incorporate a multiplier into this rectifier circuit, which allows more accurate abnormality detection. It is also possible.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of a general photoelectric encoder, FIG. 2 is a detection signal waveform diagram of FIG. 1, and FIG. 3 is a circuit diagram showing a preferred embodiment of the abnormality detection circuit according to the present invention. 10...Main scale, 12, 13...
Index scale, 30, 32... Rectifier circuit, 40... Addition circuit, 50... Comparison circuit, 101... Sine wave detection signal, 102...
...Cosine wave detection signal.

Claims (1)

[Scope of utility model registration request] It includes a main scale having optical gratings arranged in alignment, and an index scale having two optical gratings arranged in alignment with mutually different phases, and both scales are relatively moved to transmit or transmit light through both pairs of optical gratings. A photoelectric encoder that detects a sine wave signal and a cosine wave signal from the brightness and darkness of reflected light includes a rectifier circuit that performs full-wave rectification of the sine wave signal and the cosine wave signal at a center level, and adds both types of output signals. Abnormality detection for a photoelectric encoder, comprising: an adding circuit that compares the output of the adding circuit with a predetermined reference value; and a comparing circuit that compares the output of the adding circuit with a predetermined reference value, and outputs an abnormality detection signal from the comparing circuit when an abnormality occurs in a signal detection section. circuit.