JPH0244278A - Optical proximity sensor - Google Patents

Abstract

PURPOSE:To provide the title sensor having detection sensitivity only with respect to the light from a specific light source and made hard to be affected by the light from other sensor and disturbance light by controlling the change of the quantity of the light from a light source in a sine wave like form and providing frequency selectivity to a detection circuit part. CONSTITUTION:A sine wave of predetermined constant frequency is generated by a sine wave generator 1 and a light emitting element 3 is controlled by a control circuit 2 so that quantity of emitting light is modulated by said sine wave to become a sine wave shape. The sine wave modulated light being the output of the light emitting element 3 is applied to a reflecting surface and the reflected light from the reflecting surface is received by a phototransistor to be photoelectrically converted. The photoelectric conversion output of the phototransistor is obtained by photoelectrically converting all of the light incident to the phototransistor. Therefore, a light source is selected by a filter 5 set so as to permit only the same frequency as the sine wave generated by the sine wave generator 1 to pass. By this method, the effect of the light from other sensor or disturbance light is made hard to receive and a distance can be accurately measured.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an optical proximity sensor.

[Conventional technology]

Conventional optical proximity sensors use a light receiving element that detects light from a light source, and determine distance based on the amount of light incident on the light receiving element.

[Problems to be solved by the invention]

However, in the case of the above-mentioned conventional optical proximity sensor, since it detects the magnitude of the amount of light, it has a drawback that it is easily influenced by ambient light. Furthermore, if an optical proximity sensor is used as a reflective sensor by opposing the same type of sensor, the opposing sensor will detect light from the other side's light source, making it inoperable. This invention has been made in view of the above-mentioned problems of the conventional example, and aims to provide an optical proximity sensor that is not affected by light from other sensors' light sources or ambient light. There is.

[Means to solve the problem]

That is, the optical proximity sensor of the present invention controls the change in the light amount of the light source in a sinusoidal manner, and has frequency v1 selectivity in its detection circuit, so that it has detection sensitivity only for light from a specific light source. This is a characteristic feature. Furthermore, in addition to the light source of the sensor itself, another light source is installed at a position opposite to it, so that even if the light intensity of the light source of the sensor itself decreases, detection performance can be maintained by the other light source located at the opposite position. It is also characterized by the fact that Therefore, since the light source can be identified based on the light intensity change frequency of the light source which is controlled in a sine wave manner, the distance can be reliably detected without being affected by light from other sensors or ambient light. Furthermore, when used as a reflective sensor, the detection performance decreases as the light intensity of the sensor's own light source decreases, but when the same type of sensor is installed and used in opposing positions, In order to perform distance detection using the light source of the sensor facing the sensor, the detection circuit is adjusted to have frequency selectivity, and even if one of the sensors is abnormal, the overall function can not be degraded.

【Example】

An embodiment of the optical proximity sensor of the present invention will be described below with reference to the drawings. In FIG. 1, a sine wave generator 1 is provided which generates a predetermined frequency (on the order of 1 to several kHz), which is comprised of a sine wave power source, such as an RLC circuit. A light emitting element control circuit 2 for modulating the emitted light is connected to the sine wave generator l output, and a light emitting element 3, for example a light emitting diode, is connected to the output of the light emitting element control circuit 2. On the other hand, a light receiving element 4, for example a photodiode, is provided at a position to receive the reflected light of the light emitted from the light emitting diode, and a filter 5, for example a band pass filter, is connected to the output of this diode. A comparator 6 is connected to the output. That is, a sine wave generator 1 generates a sine wave with a predetermined constant frequency, and the light emitting element 3 is controlled by the control circuit 2 so that the amount of emitted light is modulated by this sine wave and has a sine waveform.
control. The light emitting element 3 outputs sinusoidally modulated light, and the reflected light from the 1 reflecting surface is received by the light receiving element 4, for example, a phototransistor, and is photoelectrically converted. This photoelectric conversion output is obtained by photoelectrically converting all the light incident on the phototransistor. Therefore, the light source is selected by using the filter 5, which is set to pass only the same frequency as the sine wave generated by the sine wave generator l. The comparison is made to determine whether the reflective surface has approached. In this way, only light with a specific frequency (light intensity change frequency) is sensed, so distance can be measured accurately regardless of the influence of light from other sensors or ambient light. . FIG. 2 shows a case where the optical proximity sensors having the configuration shown in FIG. 1 are used as reflective sensors by facing each other. In FIG. 2 sensors, 10 a first moving stage, and 11 a second moving stage. The sensor 78 and reflector 8 are installed on the moving stage 10, and the sensor 9 and the reflector 8 are installed on the moving stage 11. For example, the first sensor 7 controls the light source at a frequency of l k Hz, and the filter 5
The center frequency of is also set to l kHz. In addition, the second sensor 9 controls a light source, for example, at a frequency of 2 kHz,
The center frequency of the filter 5 is also set to 2kHz. In this example, even if the detection performance of the first sensor 7 decreases due to a decrease in the amount of light from its own light source, the sensor 9 of the same type is also installed at the opposite position, so the opposite sensor Distance detection can be performed using 9 light sources. That is, if the detection circuit is adjusted to have frequency selectivity depending on the amount of light from each sensor, the overall function will not deteriorate even if one sensor itself is abnormal. FIG. 3 shows the frequency characteristics of a general bandpass filter. The frequency mR near the center frequency (fo) also passes through the filter at a certain level. Using this characteristic, the distance is determined by detecting the light intensity level from the light source of the opposing sensor. FIG. 4 shows a case where the sensor is used as a reflective sensor, and shows the level of the amount of light incident on the sensor 7 and the signal level after passing through the filter. Comparator Lake 6's proximity detection level ■
When it is set to 1, the comparator 6 operates when the reflected light level of the light source of the sensor 7 reaches 1. Also, sensor 7
When the light source fails and the amount of light emitted decreases, the comparator 6 operates when the light source enters the sensor 9 and reaches the discrimination level Vl. Due to these features, even if there is an abnormality in the sensor's own light source, it can reliably operate as a proximity switch, making it very effective as a collision prevention sensor for moving stages and the like.

【Effect of the invention】

Since the optical proximity sensor of the present invention can identify the light source based on the light intensity change frequency of the light source, it is less susceptible to the effects of light from other sensors and ambient light. Furthermore, when used as a reflective sensor, if the amount of light from the sensor's own light source is insufficient, the detection performance will deteriorate. However, when sensors of the same type are installed and used in opposite positions as in this invention, the detection circuit is adjusted so that distance detection can be performed using the light source of the opposite sensor. It is possible to prevent the function from deteriorating by 4 degrees even when the device itself is abnormal.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the reflective optical proximity sensor of the present invention, FIG. 2 is a schematic diagram of the reflective type sensor used oppositely, and FIG. 3 is a schematic diagram showing an embodiment of the optical proximity sensor of the present invention. FIG. 4 is a graph showing the frequency characteristics of a general bandpass filter, and is a graph showing the level of the amount of light incident on the sensor and the signal level after passing through the filter. l...Sine wave generator 2...Control circuit 3...
Light emitting element 4... Light receiving element 5... Filter 6... Comparator 7... First sensor 8... Reflection plate 9... Second sensor 10.
...First moving stage 11...Second moving stage

Claims (1)

[Claims] 1. By controlling the change in the light amount of the light source in a sinusoidal manner and giving the detection circuit section frequency selectivity, it is characterized by having detection sensitivity only for light from a specific light source. Optical proximity sensor. 2.In addition to the light source of the sensor itself, another light source is installed at the opposite position, so that even if the light intensity of the sensor's own light source decreases, the detection performance can be maintained by the other light source located at the opposite position. The reflective optical proximity sensor according to claim 1, characterized in that: