JPH0338775B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a photoelectric switch capable of detecting even relatively transparent objects.

[Prior art and problems] Conventionally, in this type of photoelectric switch, changes in the amount of light due to the temperature characteristics of the light emitting element and the light receiving element have a large effect on the detection of the object to be detected. Changes in the amount of light due to dirt or the like also have a large effect on the detection of the object to be detected, and this effect particularly increases as the transparency of the object to be detected increases.

[Purpose of the Invention] The present invention aims to eliminate these conventional drawbacks, and aims to provide a photoelectric switch that can detect not only opaque objects but also highly transparent objects. [Embodiment] FIG. 1 shows a block diagram of a photoelectric switch according to the present invention, and a projector 1 is designed to emit modulated light of several KHz like the projector of a well-known photoelectric switch. The light receiver 2 receives the modulated light from the light projector 1 via the object to be detected, and is composed of an element such as a photodiode, which is proportional to the amount of light, that is, has linearity in its output characteristic. The output of the photoreceiver 2 is connected to the input of an amplifier 3 which generates an output proportional to this output. This amplifier is constituted by an amplifier having a high input impedance, such as an operational amplifier. The output end of this amplifier is connected to the input end of a high pass filter 4, and the output end of this high pass filter is connected to the input end of a detection circuit 5. The output terminal of this detection circuit is connected to one input terminal of the comparator 6, and at the same time, the output terminal of the detection circuit 5 is connected to the input terminal of the peak hold circuit 7. The output end of this peak hold circuit is connected to the input end of the multiplication circuit 8, and the output end of this multiplication circuit is connected to the other input end of the comparator 6. The output end of this comparator is connected to the input end of the output circuit 9. Further, the output terminal of the comparator 6 is connected to the input terminal of an edge detection circuit 10 that detects the fall of the output signal, and the output terminal of this edge detection circuit is connected to a peak hold initialization switch constituted by, for example, an analog switch or a transistor switch. It is connected to the peak hold circuit 7 via 11. On the other hand, the output end of the peak hold circuit 7 is connected to the input end of a low pass filter 12, and the output end of this low pass filter is connected to one input end of the comparator 13. A constant voltage circuit 14 is connected to the other input terminal of the comparator 13, and the output terminal of the comparator 13 is connected to the setting display circuit 1.
It is connected to the input terminal of 5.

In the above configuration, the modulated light projected from the projector 1 passes through a highly transparent object to be detected and enters the receiver 2, where the modulated light is converted into an electrical signal and further amplified by the amplifier 3, and the amount of light is An electrical output proportional to is obtained. The output of this amplifier passes through a high-pass filter 4 to remove components of disturbance light, and is further subjected to envelope detection by a detection circuit 5. Thereafter, one of the outputs of the detection circuit 5 is inputted to one input terminal of the comparator 6, and the output of the comparator 6 is further inputted to the input terminal of the output circuit 9. The signal is also inputted to the other input terminal of the comparator 6 through the output peak hold circuit 7 and the magnification circuit 8 of the detection circuit 5 .

Also, the output of comparator 6 is output to edge detection circuit 1.
0 is detected, and the peak hold initialization switch 11 is turned on to initialize the peak hold circuit 7.

Furthermore, the output of the peak hold circuit 7 passes through a low-pass filter 12 and is input to one input terminal of a comparator 13, where it is compared with the voltage of a constant voltage circuit 14, and the comparison output is input to the input terminal of a setting display circuit 15. be done. Then, by turning on or off a light emitting diode or the like in the setting display circuit 15, a deviation of the optical axis, dirt on the lens, etc. is detected.

FIG. 2 shows the signal flow in the block diagram of FIG. Now, referring to this figure, the transmittance
The operation will be explained using a 90% detected object as an example.
That is, waveform A represents the output of the detection circuit 5. If the electrical output level when there is no object to be detected is I ₀ , the electrical output level when there is an object to be detected is
0.9xI ₀ . The peak hold circuit 7 detects and holds the peak value _I0 , and this output passes through the magnification circuit 8, so that the other input terminal of the comparator 6 becomes
If the magnification is α, then αxI is set to ₀ . This is represented by waveform B. In this embodiment, as is clear from FIG. 2, when the magnification α is set to 0.95, the comparator 6
The output of is inverted, and the presence or absence of the object to be detected can be detected.

The falling edge of the output of this comparator is detected by the edge detection circuit 10, and the peak hold initialization switch 11 is momentarily turned on to initialize the peak hold circuit 7, so that the output I ₀ of the light amount state is determined every time it is detected. detection and stability of detection can be achieved. Specifically, initializing the peak hold means charging or discharging the capacitor of the peak hold circuit to bring it into an initial state that does not depend on the input state.

As is clear from the above explanation, even if the electrical output _I0 , which is proportional to the amount of light, changes, the level when there is an object to be detected is _0.9xI0 , and the judgment level is _αxI0 , all of which are proportional to the detection output _I0 . It is understood that the presence or absence of the object to be detected can be detected without being affected by changes in the output _I0 .

In the above description, when there is an object to be detected, the output of the comparator 6 is set to a high level, but when the output is set to a low level, the edge detection circuit 10 may detect a rising edge.

[Effects of the Invention] As described above, the present invention receives modulated light from a light projector through a detected object by a light receiver, and inputs the output of the light receiver to an amplifier that generates an output proportional to this output. Then, the output of this amplifier is passed through a high-pass filter to a detection circuit, and the output of this detection circuit is passed to one input terminal of a comparator, and the output of the detection circuit is passed through a peak hold circuit and a multiplier circuit to the comparator. and the output of the comparator is input to the output circuit, while the edge detection circuit
Since input is made to the peak hold circuit via the peak hold initialization switch, both the level and the judgment level when there is an object to be detected change in proportion to the electrical output, which is proportional to the amount of light. The presence or absence of an object to be detected can be detected without being affected by changes in output, and in particular, a transparent object with high transmittance can be detected in a stable state. Moreover, it can be detected without being affected by changes in light intensity due to the temperature characteristics of the light receiving element, and in the long term, it is also unaffected by changes in light intensity due to secular changes in light intensity or dirt on the lens, etc. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a photoelectric switch according to the present invention, and FIG. 2 is a flow chart showing the signal flow in FIG. 1... Emitter, 2... Light receiver, 3... Amplifier, 4... High pass filter, 5... Detection circuit, 6... Comparator, 7... Peak hold circuit, 8... Magnification circuit, 9
...Output circuit, 10...Edge detection circuit, 11...Peak hold initialization switch, 12...Low pass filter, 13...Comparator, 14...Constant voltage source, 1
5...Setting display circuit.

Claims (1)

[Claims] 1. The modulated light from the emitter is received by the receiver via the object to be detected, the output of this receiver is input to an amplifier that generates an output proportional to this output, and the output of this amplifier is passed through a high-pass filter. The output of this detection circuit is inputted to one input terminal of a comparator, and the output of the detection circuit is inputted to the other input terminal of the comparator via a peak hold circuit and a multiplier circuit. A photoelectric switch in which the output of the comparator is input to the output circuit, and the output is input to the peak hold circuit via an edge detection circuit and a peak hold initialization switch.