JPH0323855B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric switch, and more specifically, a light modulation signal from a light projecting means is received by a light receiving element, and the output from the light receiving element is controlled by level discrimination. The present invention relates to a photoelectric switch having a configuration capable of displaying whether or not light from a light projecting means is being received at the highest possible level.

A typical prior art is shown in FIG.
The photoelectric switch includes a light emitter 2 that derives an optical modulation signal.
5, a light receiving element 26 that receives light from the light projecting means 25, an amplifier circuit 27 that amplifies the output from the light receiving element 26, and a level valve that controls the output from the amplifier circuit 27 at a predetermined discrimination level. It also includes a control means 28 that separately controls the load. Light projecting means 2
In order to accurately align the optical axes of the light receiving element 5 and the light receiving element 26 so that the light receiving element 26 can receive the light at the highest possible level, the output from the amplifier circuit 27 is amplified. A signal level display circuit 31 consisting of one amplifier circuit 29 and a light emitting diode 30 activated by the output from this amplifier circuit 29 is provided.

According to such a configuration, the light emitting diode 30
The brightness changes depending on the amount of light received by the light receiving element 26, and therefore the optical axes of the light projecting means 25 and the light receiving element 26 can be adjusted so that the light emitting diode 30 has maximum brightness.

In such a prior art, the light emitting diode 30 is lit even when light having a level lower than the discrimination level for controlling the load in the control means 28 is led out from the amplifier circuit 27. Therefore, the operator must check only the lighting state of the light emitting diode 30 and turn on the light emitting means 25 and the light receiving element 26.
There is a risk that it may be mistakenly determined that the optical axes of the Therefore, the optical axis adjustment work ends in a state where the light receiving element 26 can only receive light at a level lower than the discrimination level of the control means 28.

An object of the present invention is to improve the ability of a photoelectric switch to adjust the optical axis without error so that the light modulation signal from the light projecting means is received by the light receiving element at the highest possible level. The purpose of the present invention is to provide a photoelectric switch that is

The present invention provides a light projecting means 1 for deriving a light modulation signal.
and a light receiving element 2 that receives light from the light projecting means 1; a first amplifying circuit 3a that amplifies the output from the light receiving element 2; and a second amplifying circuit 3b that amplifies the output from the first amplifying circuit 3a. , a control circuit 4 that performs level discrimination and control of the output from the second amplifier circuit 3b at a first discrimination level l4; and a control circuit 4 that divides the output of the first amplifier circuit 3a and applies the divided voltage to the first amplifier circuit 3a. a plurality of voltage dividing resistors R3 and R4 configured to be larger than the difference between the output of the voltage dividing resistor R3 and the first discrimination level l4; and a capacitor C1 that smoothes the voltage divided by the voltage dividing resistors R3 and R4. , the output of the first amplifier circuit 3a is given to one input 18, the smoothed output of the capacitor C1 is given to the other input 19 as the second discrimination level l3, and the first
a comparison circuit 17 that discriminates the level of the output of the amplifier circuit 3a at a second discrimination level l3; and in response to the output of the comparison circuit 17, the light is turned on only during a period when the output of the first amplifier circuit 3a is equal to or higher than the second discrimination level l3. This is a photoelectric switch characterized by including an indicator light 13.

According to the present invention, the output of the second amplifier circuit 3b is level-discriminated at the first discrimination level l4 in the control circuit 4 to control the load, etc., and the output of the second amplifier circuit 3b is saturated. Also, accurate control can be performed by the control circuit 4.

The first amplifier circuit 3a, which is a stage preceding the second amplifier circuit 3b, can prevent saturation even if the output of the light receiving element 2 increases, and the output of the first amplifier circuit 3a can be Voltage dividing resistor R
3, the voltage is divided by R4, and the divided voltage is smoothed by the capacitor C1, so that the divided voltage is larger than the difference between the output of the first amplifier circuit 3a and the first discrimination level l4. In the comparator circuit 17, the output of the first amplifier circuit 3a is at the second discrimination level l3, which is the smoothed output of the capacitor C1.
The indicator light 1 is detected for that period only.
Turn on 3.

Therefore, the operator should check the display status of this indicator light 13 and adjust the display so that its brightness becomes brighter.
The optical axes of the light projecting means 1 and the light receiving element 2 can be adjusted without error.

FIG. 1 is a block diagram showing the basic structure of the present invention. Pulse modulated light is emitted from the light projecting means 1. The optical modulation signal from the light projecting means 1 is received by the light receiving element 2, amplified by the amplifier circuit 3, and given to the control circuit 4 through the line 10. The control circuit 4 discriminates the output level from the amplifier circuit using a predetermined first discrimination level l1 (see FIG. 2, which will be described later). The signal from the level discrimination circuit is subjected to logic processing etc. in the signal processing circuit 6, and the load 8 is driven and controlled by the output circuit 7. This load 8 may be, for example, a switching circuit such as a relay. Also load 8
The operating status of is indicated by an operating indicator light 9 which receives a signal from an output circuit 7.

The output from the amplifier circuit 3 is also applied via line 10 to one input 23 of a comparison circuit 12 of a level discrimination circuit 11 for signal level indication according to the invention. The other input 14 of the comparator circuit 12 is connected to a predetermined second discrimination level l2 (see Figure 2) in which a constant DC voltage Vcc is divided by resistors R1 and R2.
A voltage is given that determines the Level discrimination circuit 1
The output from the comparison circuit 12 of No. 1 is given to a light emitting diode 13 as an indicator light for displaying the signal level. The comparison circuit 12 has one input terminal 2
It has an amplifier circuit function of energizing and driving the light emitting diode 13 when the voltage level of the input terminal 3 is lower than the voltage level of the other input terminal 14.

The second discrimination level l2 is selected to satisfy the following condition: |Va-l2|>|Va-l1|...(1), and is expressed by the second equation.

l2=Vcc·R1/R1+R2 (2) FIG. 2 is a waveform diagram for explaining the operation of the configuration shown in FIG. 1. A predetermined DC bias voltage level Va (Va is, for example, 1/2·Vcc) is applied to a line 10 from which the output from the amplifier circuit 3 is derived. The output signal from the light receiving element 2 is
It is amplified by the amplifier circuit 3, and a waveform having a large amplitude on the negative potential side of the DC bias voltage Va, for example, as shown in FIG. 2 is obtained. The amplification of the output signal from the amplifier circuit 3 is proportional to the amount of light received by the light receiving element 2.

The level discrimination circuit 5 in the control circuit 4 has a first
The level of the output signal of the amplifier circuit 3 is discriminated at the discrimination level l1.

In the level discrimination circuit 11, when the voltage of the amplifier circuit 3 exceeds the second discrimination level l2 obtained by the voltage dividing resistors R1 and R2 to the negative potential side, the anode of the light emitting diode 13 is switched off for the period W. Figure 2 2
High level as in . Therefore, the light emitting diode 13 is lit only during this period W. When the amount of light received by the light receiving element 2 is small, the amplitude of the output from the amplifier circuit 3 is relatively small as shown on the left side of FIG. Therefore, the period W during which the output from the amplifier circuit 3 exceeds the second discrimination level l2 is short. As the amount of light received by the light receiving element 2 increases, the period W during which the light emitting diode 13 emits light increases as shown on the right side of FIG. 2.
Therefore, when the frequency of the light modulation signal from the light projecting means 1 is high, even though the light emitting diode 13 is blinking, it is visible as a continuous light emitting state. Therefore, as the amount of light received by the light receiving element 2 increases, the amount of light emitted by the light emitting diode 13 increases and becomes brighter. Therefore, as the optical axes of the light projecting means 1 and the light receiving circuit 2 approach the same direction, the amount of light received by the light receiving element 2 increases. In this way, the light projecting means 1 and the light receiving element 2
When the optical axes of the light emitting diode 13 and
becomes the brightest, thus completing the adjustment of the optical axis.

Discrimination level l2 by changing voltage dividing resistors R1 and R2
By changing , it is possible to know the degree of margin in the amount of light received by the light receiving element 2 in relation to the first discrimination level l1 at which the control circuit 4 operates.

FIG. 3 is a waveform diagram for explaining the operation of another basic configuration of the present invention. In this configuration, the output of the light receiving element 2 shown in FIG.
The DC bias voltage level corresponds to the amount of light received.
The amplitude changes to the positive polarity side compared to Va (for example, 1/2·Vcc). Other structures are similar to those described above. FIG. 3 shows the signal waveform applied to the light emitting diode 13. Also in this embodiment, as the amount of light received by the light receiving element 2 increases, the brightness of the light emitting diode 13 increases.

In the above configuration, when an excessive amount of light is received by the light receiving element 2, the amplifier circuit 3 becomes saturated. As a result, a waveform in which the upper part of the pulse is flat, like the pulses p1 to p3 shown in FIG. 4, is derived on the line 10. In this case, the period W during which the light emitting diode 13 is energized by the pulses p1 to p3 when the amplifier circuit 3 is saturated depends on the amount of light received by the light receiving element 2 as shown in FIG. It remains constant regardless. Therefore, there is a problem in that it is not possible to determine whether the amount of light received by the light receiving element 2 is at the maximum level.

One embodiment of the invention shown in FIG. 5 solves these problems. Parts corresponding to the configurations described above are given the same reference numerals. A noteworthy feature is that the above-mentioned amplifier circuit 3 is a continuously connected amplifier circuit 3.
Of the amplifier circuits 3a and 3b in each stage, the output from the amplifier circuit 3a in the stage preceding the final stage amplifier circuit 3b is connected to the line 15.
The signal is applied to the level discrimination circuit 16 for signal level display through the signal level. The level discrimination circuit 16 includes the comparison circuit 1
Contains 7. One input terminal 18 of comparator circuit 17 is connected to line 15 . The voltage on line 15 is also divided by voltage dividing resistors R3 and R4, and the divided voltage is applied to the other input terminal 19 of comparator circuit 17. A capacitor C1 is connected in parallel to the resistor R4, and provides a smoothed reference level to the input terminal 19. A DC bias voltage Va is applied to the line 15.

FIG. 6 is a waveform diagram for explaining the operation of the embodiment shown in FIG. A waveform having a voltage amplitude more negative than the DC bias voltage Va corresponding to the amount of light received is obtained from the light receiving element 2. The discrimination level l3 of the level discrimination circuit 16 is expressed by the third equation.

l3=Va・R3/R3+R4...(3) The discrimination level of the level discrimination circuit 5 in the control circuit 4 is equivalently expressed as the output from the amplifier circuit 3a without passing through the amplifier circuit 3b, as shown by the reference symbol in FIG. As shown in l4. In the light emitting diode 13, as the amount of light received by the light receiving element 2 increases, the period W during which the light emitting diode 13 is driven to turn on increases, and the light emitting diode 13 becomes brighter.

In the above embodiment, a plurality of amplifier circuits 3a, 3b
is continuously connected, and the unsaturated amplified output from the amplifier circuit 3a at the stage before the amplifier circuit 3b at the final stage is level-discriminated by the level discrimination circuit 16, so that the amount of light received from the light-receiving element 2 becomes excessive. Even when the temperature is low, it is possible to detect whether the light receiving element 2 is receiving the maximum amount of light. Furthermore, it becomes possible to provide the level discrimination circuit 5 of the control circuit 4 with a signal from the light receiving element 2 at a desired amplification factor.

Further, in the embodiment shown in FIG. 5, the signal from the amplifier circuit 3a via the line 15 is divided by the resistors R3 and R4 to determine the discrimination level 13, and is smoothed by the capacitor C1 to stabilize the discrimination level. The amount of light received by line 15 is very small, so stable detection is possible even when the amplification of the signal led out from amplifier circuit 3a to line 15 is small.

Furthermore, in this embodiment, in the third equation above,
Particularly in the case of a small signal, the DC component is absorbed by the capacitor C1, and the impedance of the capacitor C1 connected in parallel to the resistor R4 becomes small.Therefore, the parallel impedance of the resistor R4 and the capacitor C1 becomes small. Therefore, the discrimination level l3 approaches the reference level Va. This state is shown in FIG. Therefore, in the case of a small signal,
The period W during which lighting can be driven becomes longer.

Instead of the light emitting diode 13, another indicator light, such as an incandescent bulb, may be used.

As described above, according to the present invention, the operator only has to adjust the optical axis between the light projecting means 1 and the light receiving element 2 so that the brightness of the indicator lamp is as bright as possible. Work can be performed reliably and without errors.

Furthermore, in the present invention, the output of the first amplifier circuit 3a is divided by voltage dividing resistors R3 and R4, and the divided voltage is further smoothed by a capacitor C1 to obtain a second discrimination level l3, In the comparison circuit 17, the output of the first amplifier circuit 3a and the second discrimination level l
3, even when the output of the light receiving element 2 is large, it is possible to prevent the output of the first amplifier circuit 3a from becoming saturated, and the indicator light 1
The optical axis can be adjusted accurately so that the brightness of No. 3 is maximized. The control circuit 4 receives and controls the output of the second amplifier circuit 3b, and the large output from the second amplifier circuit 3b may be saturated.
In this way, the operation of the control circuit 4 can be achieved reliably.

Furthermore, according to the present invention, by using the smoothing capacitor C1, it is possible to stably light the indicator lamp 13 even if the amount of light received by the light receiving element 2 is extremely small. can be,
This makes it possible to easily adjust the optical axis.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic structure of the present invention, Fig. 2 is a waveform diagram for explaining the operation of the structure shown in Fig. 1, and Fig. 3 is the operation of another basic structure of the present invention. FIG. 4 is a waveform diagram for explaining other operating states of the configuration shown in FIG. 1, FIG. 5 is a block diagram of an embodiment of the present invention, and FIG. FIG. 7 is a waveform diagram for explaining the operation of the illustrated embodiment, FIG. 7 is a waveform diagram for explaining the operation in the case of a small signal in the embodiment of FIG. 5, and FIG. 8 is a block diagram of the prior art. . 1...Light projecting means, 2...Light receiving element, 3, 3a, 3b
...Amplification circuit, 4...Control circuit, 5, 11, 16...Level discrimination circuit, 6...Signal processing circuit, 7...Output circuit, 8...Load, 9...Operation indicator, 12, 17...Comparison circuit, 13...Light emission Diode, R1 to R4...divider resistance, C1...capacitor.

Claims (1)

[Scope of Claims] 1. A light projecting means 1 for deriving an optical modulation signal; a light receiving element 2 for receiving light from the light projecting means 1; a first amplification circuit 3a for amplifying the output from the light receiving element 2; a second amplifier circuit 3b that amplifies the output from the first amplifier circuit 3a; a control circuit 4 that performs level discrimination and control of the output from the second amplifier circuit 3b at a first discrimination level l4; A plurality of voltage dividing resistors R3 and R4 configured to divide the output so that the divided voltage is larger than the difference between the output of the first amplifier circuit 3a and the first discrimination level l4; and a voltage dividing resistor. A capacitor C1 smoothing the voltage divided by R3 and R4 and the output of the first amplifier circuit 3a are applied to one input 18, and the smoothed output of the capacitor C1 is applied as a second discrimination level l3 to the other input 19. given to the first
a comparison circuit 17 that discriminates the level of the output of the amplifier circuit 3a at a second discrimination level l3; and in response to the output of the comparison circuit 17, the light is turned on only during a period when the output of the first amplifier circuit 3a is equal to or higher than the second discrimination level l3. A photoelectric switch comprising an indicator light 13.