JPH0425655B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of the Invention The present invention relates to a reflective photoelectric switch, in particular, a light emitting part and a light receiving part are housed in one case, and light is emitted onto a reflector plate, and the reflected light is This relates to a photoelectric switch that receives light and obtains a detection signal by blocking the light with a detection object.

(b) Prior art and its problems Conventionally, in this type of reflective photoelectric switch, when the sensing object has a mirror surface such as metal, the light from the light emitting part is reflected by the mirror surface, and the sensing object A problem arises in that it cannot be detected even though it has passed.

Therefore, as shown in Figure 1, a reflective photoelectric switch 1
A method is known in which the above-mentioned problem can be solved by setting the optical axis of the detector obliquely to the direction in which the detection object 2 passes. However, in this case, when the detection object 2 passes through the position A and when it passes through the position B, the distance l is different when the photoelectric switch 1 is activated.
This has the disadvantage that highly accurate detection cannot be performed because of the shift by the travel time of .

(c) Purpose of the Invention The present invention has been made in view of the problems of the prior art, and its purpose is to detect objects even when the sensing object has a mirror surface, and when the passing position of the sensing object is not determined. However, the object of the present invention is to provide a reflective photoelectric switch that can be detected with high precision.

(d) Structure of the Invention In order to achieve the above object, the present invention has a light projecting section that projects two lights of different wavelengths, a reflector that has a characteristic of strongly reflecting either of the lights, and the above object. The reflective plate and the detection object are discriminated by determining the magnitude relationship between the two reflected lights.

(E) Description of Embodiments Hereinafter, the present invention will be explained with reference to the accompanying drawings which are one embodiment.

In Fig. 2, 10 is the photoelectric switch body;
Inside it is a first light emitting element 11 that emits infrared light.
The spectral sensitivity of the first light emitting element 11 peaks at a wavelength of 0.94μ as shown in FIG. On the other hand, the spectral sensitivity of the second light projecting element 12 reaches its peak at a wavelength of 0.66μ, as shown in FIG. Each of the above elements 11, 12, 13
In front of the light emitting lenses 14 and 15 and the light receiving lens 1
6 are provided, and each element is located at the focal point of these lenses.

17 is a main oscillation circuit; 18 and 19 are first and second oscillation circuits that alternately oscillate pulse signals as they proceed from the main oscillation circuit; Second light projecting element 11,1
2 are connected to each other. In addition, the light receiving element 1
3 is an amplifier 20 and a comparator 21 that constitute a differentiating circuit.
It is connected to the gate circuit 22 via. This gate circuit 22 constitutes an AND gate circuit that outputs only when the signal from the comparator 21 and the signal from the second oscillation circuit 19 are input simultaneously. The signal of the gate circuit 22 is outputted to the outside via the signal processing circuit 23.

24 is a detection object, and 25 is a reflecting plate. This reflecting plate is, for example, an integrally formed collection of corner cubes, and a filter is provided in front of it to cut off visible light, as shown by the solid line in Figure 3. It has the characteristic of strongly reflecting infrared rays and hardly reflecting red rays.

The operation of the reflective photoelectric switch having the above structure will now be explained with reference to FIG.

First, to explain the case () in which the detection object 24 does not pass, the first and second oscillation circuits 18 and 19
The first light projecting element 11 and the second light projecting element 12 emit light beams a and b, respectively, in response to signals alternately output from the light emitting element 11 and the second light projecting element 12, respectively. This light passes through the projection lenses 14 and 15 and reaches the reflection plate 25, where the infrared rays a are strongly reflected and the red rays b, which are visible rays, are hardly reflected. This reflected light C is differentiated by an amplifier 20 via a light receiving element 13, and then the output d of the amplifier 20 is compared with an operating level L by a comparator 21, and only those that are equal to or higher than L are waveform-shaped into a rectangular wave and output e. get. This output e enters the gate circuit 22, and output f is obtained only during the oscillation period of the second oscillation circuit 19. This makes it possible to detect that the detection object 24 has not passed.

Fig. 4 shows the case where a detection object 24 consisting of a blank paper, a specular reflector, and a black paper passes through, respectively.In the case of a blank paper and a specular reflector, it is possible to obtain the output e of the comparator 21, but this output Since e is different from the oscillation period of the second oscillation circuit 19, the output f of the gate circuit 22 becomes zero. Furthermore, in the case of black paper, the output f is zero because it hardly reflects either the infrared rays a or the red rays b. Therefore, regardless of whether the detection object 24 has a mirror surface or not, all objects can be detected.

Note that the two lights emitted by the light projecting element are not limited to infrared rays and red rays as in the above embodiment, and the reflecting plate can also be changed as appropriate depending on the type of light.

(F) Effects of the Invention As described above, according to the present invention, the light projecting section projects two lights with different wavelengths, and the reflecting plate has a characteristic of strongly reflecting one of the lights. Since the reflector and the detection object are discriminated by determining the magnitude relationship of the reflected light of two lights, even if the detection object has a mirror surface, there is no false detection, and the light There is no need to tilt the axis, so
There is no variation in operation due to differences in the passing position of the detected object.

[Brief explanation of drawings]

Figure 1 is a layout diagram of a conventional reflective photoelectric switch.
FIG. 2 is an overall configuration diagram of a reflective photoelectric switch according to the present invention, and FIG. 3 is a diagram showing the reflection characteristics of a reflector.
FIG. 4 is an operational waveform diagram of the reflector and the detection object. 10... Photoelectric switch main body, 11, 12... Light emitting element, 13... Light receiving element, 17, 18, 19...
...Oscillation circuit, 20...Amplifier, 21...Comparator,
22...gate circuit, 24...detection object, 25...
…a reflector.

Claims (1)

[Claims] 1 Store the emitter and receiver in one case,
In a reflective photoelectric switch that detects an object by reciprocating light from a light projecting section via a reflector and causing the object to be detected to emit light along the way, the light projecting section projects two lights of different wavelengths. The reflecting plate has a characteristic of strongly reflecting one of the two lights, and the reflecting plate and the detection object are discriminated by determining the magnitude relationship between the reflected lights of the two lights. A reflective photoelectric switch characterized by: