JPH0330119B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an area reflection type photoelectric switch used for industrial equipment, consumer detection, etc.

[Background technology]

Conventionally, area reflection type photoelectric switches have been constructed as shown in FIG. In Fig. 1, reference numeral 1 denotes a position detection element, which is arranged side by side at a predetermined distance from a light projecting means (not shown), and detects reflected light from a detected object (not shown). Output current after receiving light
Ip ₁ and Ip ₂ are output and amplified and converted into signal voltages by two light receiving circuits 2 and 3. Reference numeral 4 denotes a first logarithmic amplification circuit, which obtains logarithmic amplification characteristics using the voltage-current characteristics of the feedback diode _D1 , and logarithmically amplifies the output of the light receiving circuit 2. Reference numeral 5 denotes a second logarithmic amplification circuit, which obtains logarithmic amplification characteristics based on the characteristics of the feedback diode D ₂ and logarithmically amplifies the output of the light receiving circuit 3. 6 is a differential amplification circuit which differentially amplifies the outputs of the first and second logarithmic amplification circuits 4 and 5, and inputs the output thereof to the first comparator 8 together with the output of the distance setting circuit 7. ,
When there is an object to be detected within the set distance, an output circuit (not shown) is operated by the output of the first comparator.
Reference numeral 9 denotes an operation level setting circuit, which generates a reference voltage V ₃ by logarithmically amplifying it in a third logarithmic amplifying circuit 10 and converting the reference voltage V ₃ and the output of the second logarithmic amplifying circuit 5 into a second logarithmic amplifying circuit 10 .
and a third comparator 12. The output of the second comparator 11 is used to prevent malfunctions due to noise, and depends on whether a signal higher than the reference voltage V ₃ is obtained from the output V ₂ of the second logarithmic amplification circuit 5. Then, it is determined whether a light receiving signal that does not malfunction due to external noise or internal noise generated in the light receiving circuit 3 is obtained. The output of the third comparator 12 indicates a margin, and when the output V ₂ of the second logarithmic amplification circuit 5 is larger than the reference voltage V ₃ , it indicates that there is a margin with respect to the normal operating range. Regarding this one,
To obtain the reference voltage _V3 , the third logarithmic amplification circuit 1
0 is used, the drift due to ambient temperature is the output V ₁ , V ₂ , V ₃ of each logarithmic amplifier circuit 4, 5, 10.
In other words, the relative drift of V ₁ , V ₂ , and V ₃ with respect to a change in ambient temperature is compensated for by the same amount, but the absolute drift is not compensated for.

Normally, when the forward current of a diode is kept constant, the diode generates heat due to the current flowing in the forward direction, thereby reducing the forward voltage. The current flowing through the feedback diodes D ₁ and D ₂ has a pulse waveform and its duty is 1%, so the feedback diodes
Self-heating due to the current flowing through D ₁ and D ₂ can be ignored. In other words, the drift due to self-heating of V ₁ and V ₂ can be ignored. However, since DC current flows through the feedback diode _D3 , self-heating cannot be ignored.
The drift of V ₃ is larger than that of V ₁ and V ₂ . As is clear from FIG. 1, V ₂ and V ₃ are directly input to the second comparator 11 and the third comparator 12, and if the temperature drift due to self-heating is different between V ₂ and V ₃ , The apparent performance level has decreased. When the operating level decreases, there is a problem in that disturbance noise or internally generated noise in the circuit may lead to malfunction.

[Purpose of the invention]

It is an object of the present invention to prevent malfunctions caused by a drop in the reference voltage due to heat generated by the feedback diode of the third logarithmic amplification circuit, and to prevent V ₁ , V ₂ ,
The purpose is to prevent saturation of the logarithmic amplifier circuit due to voltage fluctuations in _V3 .

[Disclosure of the invention]

In FIG. 2, 13 is an automatic gain adjustment circuit;
The output V 2 of the second logarithmic amplification circuit ₅ and the reference voltage V ₃ obtained from the third logarithmic amplification circuit 10 are input, and the third logarithmic amplification circuit 10 is adjusted so that the difference becomes 0. Controls the DC amplification rate. In other words, at the moment when V ₃ is adjusted by the operating level setting circuit 9 so that the absolute potential is the same as the absolute potential of V ₂ when the circuit is irradiated with the lowest level of light that will not cause malfunction, there is no self-heating of the feedback diode D ₃ . In this state, the difference between V ₂ and V ₃ is 0, and the automatic gain adjustment circuit 1 is adjusted to maintain this state.
Controlled by 3. The rest is the same as the conventional example shown in FIG. The voltage drop due to the heat generated by the feedback diode D ₃ only needs to be controlled by the third logarithmic amplifier circuit 10;
There is a limit to the dynamic range of each logarithmic amplifier circuit 4, 5, 10, and the potentials of V ₁ , V ₂ , V ₃ fluctuate due to temperature drift of V ₁ , V ₂ , V ₃ due to ambient temperature. There is a possibility that each logarithmic amplification circuit 4, 5, 10 becomes saturated. Therefore, the automatic gain adjustment circuit 13 sets the difference between V ₂ and V ₃ to 0 as described above, and at the same time,
The absolute potentials of V ₂ and V ₃ are detected, and the gains of all logarithmic amplifier circuits 4, 5, 10 are controlled so that each logarithmic amplifier circuit 4, 5, 10 does not become saturated.

〔Effect of the invention〕

As described above, the present invention provides an automatic gain adjustment circuit that receives the output of the second logarithmic amplification circuit and the output of the third logarithmic amplification circuit; Since the logarithmic amplifier circuit is controlled so that the output of the circuit and the output of the third logarithmic amplifier circuit become 0, malfunctions caused by a drop in the reference voltage due to heat generation of the feedback diode of the third logarithmic amplifier circuit are prevented. In addition, it is possible to prevent saturation of the logarithmic amplifier circuit caused by voltage fluctuations of V ₁ , V ₂ , and V ₃ due to ambient temperature and heat generation of the feedback diode.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of a conventional area reflection type photoelectric switch, and FIG. 2 is a block circuit diagram of an embodiment of the present invention. 2... Light receiving circuit, 3... Light receiving circuit, 4... First
a logarithmic amplification circuit, 5... a second logarithmic amplification circuit, 6
... Differential amplification circuit, 7 ... Distance setting circuit, 8 ...
First comparator, 9... Operation level setting circuit, 10
... third logarithmic amplification circuit, 11 ... second comparator, 12 ... third comparator, 13 ... automatic gain adjustment circuit.

Claims (1)

[Claims] 1. Two light receiving circuits that detect a change in the amount of light received by an object to be detected, first and second logarithmic amplification circuits that logarithmically amplify the output of the light receiving circuit, and the first and second logarithmically amplifying circuits. a first comparator that differentially amplifies the output of the width circuit and the output of the distance setting circuit; and a third logarithm amplifier that logarithmically amplifies the output of the operation level setting circuit and generates a reference voltage. In the area reflection type photoelectric switch, the area reflection type photoelectric switch is equipped with a width circuit, and second and third comparators for comparing and determining the output of the third logarithmic amplifier circuit and the output of the second logarithmic amplifier circuit. An automatic gain adjustment circuit is provided which receives the output of the logarithmic amplification circuit and the output of the third logarithm amplification circuit, and the automatic gain adjustment circuit adjusts the output of the second logarithm amplification circuit and the output of the third logarithmiamplification circuit. 1. An area reflection type photoelectric switch characterized by controlling a logarithmic amplification circuit so that the output of the switch becomes zero.