JPH0358474B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a photoelectric switch circuit that detects the presence of an object using light.

[Background technology]

FIG. 1 is a circuit diagram of a conventional general photoelectric switch. The photoelectric switch shown in the figure has an oscillation circuit 1
A light emitting circuit 2 that sends an optical signal pulse-modulated with an oscillation clock having a predetermined cycle, a light receiving circuit 3 that receives this optical signal, an amplifying circuit 4 that amplifies the output signal of the light receiving circuit 3, and a level discrimination circuit 5 that discriminates the output of the width circuit 4 at a predetermined level; a signal processing circuit 6 that stretches the waveform according to the output signal;
It is comprised of an output circuit 7 that guides this expanded output signal to the outside, and determines the presence or absence of an object based on the magnitude of the absolute value of the amount of received light signal. The method shown in FIG. 1 is generally called a diffuse reflection method, and the presence or absence of an object is determined based on the amount of light reflected from the surface of the object to be detected. In addition, a method generally called a facing type has been proposed, in which the light emitting system and the light receiving system are configured in separate cases, and the presence or absence of an object is determined by blocking the light beam between the light emitting and receiving systems. It is something to do. Furthermore, as a third method, there is a method (area reflection method) proposed by our company that detects the presence or absence of an object using a position detection means such as a semiconductor position detection element. FIGS. 2 and 3 show a conventional example using this area reflection type. In FIG. 2, reference numeral 8 denotes a light projecting means for projecting a light beam P made of pulse modulated light onto the object X to be detected. The light projecting means 8 includes an oscillation circuit 1 that generates a synchronizing signal for setting the light projecting timing, a light projecting circuit 9, a light projecting element 10 such as a light emitting diode or a laser diode, and a half mirror 11.
and a light projection optical system consisting of a condenser lens 12. 13 is a condensing means, which includes a first condenser lens 12 that condenses the reflected light R of the light beam P by the object to be detected X, and a condensing point of the reflected light R by the first condensing lens 12 The second condenser lens 14 converts the displacement in the axial direction into the displacement in the direction (arrow M) orthogonal to the optical axis. It is arranged to be shifted by a predetermined distance ΔL with respect to the optical axis. Reference numeral 15 denotes a position detection means for detecting the position of the condensing spot S condensed by the condensing means 13, and the condensing lens 1
4, and outputs a position signal corresponding to the position of the light condensing spot S. In the block diagram of FIG. 3, reference numeral 16 denotes a discrimination control means, which discriminates whether or not the detected object X exists within a predetermined detection area based on the output of the position detection means 15, and controls the output circuit 7. It's becoming like that.

The discrimination control means 16 includes light receiving circuits 17 and 18 that amplify and convert the output currents I _A and I _B from the position detecting means 15 into signal voltages V _A and V _B , and a logarithmic amplification circuit 1.
9, 20, a subtraction circuit 21 that subtracts the output lnV _B of the logarithmic amplification circuit 20 from the output lnV _A of the logarithmic amplification circuit 19, and the output lnV _A /V _B of the subtraction circuit 21 at the detection area setting volume VR. Comparison circuit 2 that outputs H level when within a preset range
2, and by sampling the output of the comparison circuit 22 in synchronization with the projection timing of the light beam P from the light projection element 10 (synchronization signal output from the oscillation circuit 1), it is possible to detect that the object X to be detected is within the detection area. The output of the signal processing circuit 6 controls an output circuit 7 consisting of a load control relay, a load control semiconductor switch element, etc. It's becoming like that. In this conventional example, when the distance l from the first condensing lens 12 to the detected object X changes, the focal point of the first condensing lens 12 is displaced in the optical axis direction, and the second The condensing point by the condensing lens 14 is displaced in the direction (arrow M) orthogonal to the optical axis, and the position of the condensing spot S on the position detection means 15 is displaced according to the distance l. Now, the logarithm value ln of the ratio I _A /I _B of the output currents I _A and I _B of the position detection means 15 according to the position of the light condensing spot S is
Based on (I _A /I _B ), it is determined whether or not the detected object X exists within a predetermined detection area, and the output circuit 7
In other words, it controls. However, in this case, object detection is performed regardless of the level of the reflected light R from the detected object X, so if the level of the reflected light R is extremely low, the reliability of the object detection output decreases. It was hot.

[Purpose of the invention]

The present invention has been made in view of the above points, and generates an object detection output by logical product of a detection signal based on the amount of received light signal and a detection signal based on distance information between the detected object. It is an object of the present invention to provide a photoelectric switch circuit that can perform object detection with higher reliability in this manner.

[Disclosure of the invention]

Hereinafter, the configuration of the present invention will be described with reference to illustrated embodiments. FIG. 4 is a block diagram of a photoelectric switch circuit according to an embodiment of the present invention. In this figure, blocks having the same functions as those in the conventional example shown in FIG. 3 are given the same reference numerals, and their explanation will be omitted. Further, the optical system including the light projecting element 10 and the position detecting means 15 is the same as that in the conventional example shown in FIG. The portion surrounded by a dotted line T is a characteristic feature of the present invention. That is, the present invention includes a comparison circuit 23 that compares the output of the logarithmic amplification circuit 20 with a predetermined reference level, and compares the output of the comparison circuit 23 and the output of the subtraction circuit 21 with the predetermined reference level. The output of an AND circuit 24 which inputs the output of the comparator circuit 22 for comparison is provided before the signal processing circuit 6. 25 is a reference level generating means, which supplies a reference level voltage to be compared with the output of the logarithmic amplification circuit 20 to the comparator circuit 23. However, this reference level is set slightly higher than the minimum level required for the signal level output from the logarithmic amplification circuit 20 to perform a correct detection operation. Therefore, when the amount of received light signal is very small, the output of the comparator circuit 23 goes to L level, so even if the output of the comparator circuit 22 goes to H level, no object detection output is generated, and the detection output is not reliable. Sexuality is something that increases.

Hereinafter, the operation of this embodiment will be explained step by step. Detection currents I ₁ and I 2 from a position detection means 15 such as a semiconductor position detection element PSD are connected to the light receiving circuit ₁ .
The currents are converted into voltages at 7 and 18, amplified, and converted into voltages V ₁ and V ₂ , respectively. Light receiving circuit 17,1
8 passes only pulsed light and cuts out DC light,
It also includes a bandpass filter circuit that passes only specific frequencies. Furthermore, the logarithmic amplification circuit 19,
20 is a circuit that logarithmically compresses and amplifies the voltages V ₁ and V ₂ , and by passing it through the next subtraction circuit 21,
lnV ₁ /V ₂ is obtained. This becomes an input to the comparator circuit 22 and is compared with a reference voltage. The reference voltage is made variable using means such as a variable volume VR for setting the detection area, and the detection distance of the photoelectric switch is thereby set. If a detected object exists within the set distance, the output of the comparison circuit 22 changes from L level to H level. FIG. 5 shows the relationship between the received light signal amounts I ₁ and I ₂ and the distance to the object to be detected. This relationship can always satisfy the relationship I ₁ >I ₂ depending on the arrangement of the optical system (the arrangement of the light projecting system and the light receiving system). In other words, the detection current I ₁ of the position detection means 15 can always be made larger than the other detection current I ₂ . The voltage lnV ₂ becomes an input to the comparator circuit 23 and is compared with a reference voltage. This reference voltage is the minimum operating level. The minimum operating level is the lowest discrimination level determined by the conversion impedance, amplification rate, internal noise, external noise, etc. of the light receiving circuits 17 and 18 and the logarithmic amplification circuits 19 and 20. Obtaining a signal amount means a level at which the operation of the photoelectric switch circuit system is guaranteed. In this embodiment, even at this lowest operating level, the smaller detection current _I2 is monitored and compared by the comparison circuit 23. However, when a signal higher than this minimum operating level is input, the output of the comparison circuit 23 changes from L level to H level. The output of the comparison circuit 23 is sent to the AND circuit 24
is led to the signal processing circuit 6 via which the above-mentioned input is read at a timing synchronized with a predetermined clock of the oscillation circuit 1, and its output is led to the output circuit 7 and is connected to an external relay, etc. It controls the

FIG. 6 is a block diagram showing the main structure of another embodiment of the present invention. In this embodiment, the arrangement of the optical system makes it possible to always satisfy the relationship I ₂ > I ₁ , and FIG. 7 shows the amount of received light signal I ₁ ,
It shows the relationship between I ₂ and the distance to the detected object. The subtraction circuit 21 is the output of the logarithmic amplification circuit 20.
From lnV ₂ , the output lnV ₁ of the other logarithmic amplifier circuit 20
The comparator circuit 2 calculates the signal lnV ₂ /V ₁ by subtracting
2. This comparison circuit 22 produces an H level output if the signal lnV ₂ /V ₁ is higher than a predetermined level set by the volume VR. Also, the comparison circuit 23 is the logarithmic amplification circuit 1
The output lnV ₁ of 9 is compared with a predetermined reference level, and if it is higher than the reference level, an H level output is generated. Therefore, even in this embodiment, when the detection current _I1 with the smaller level is below a predetermined level, the object detection signal is not output, thereby improving the reliability of the detection output. It is something that is increasing.

FIG. 8 is a block diagram of yet another embodiment of the present invention. In this embodiment, an OR circuit 26 is interposed between the output of the comparison circuit 22 of the embodiment in FIG. 4 and the input of the AND circuit 24.
A switching circuit 27 is provided for selectively applying an H level or L level voltage signal to one input of the switch.
When the output of the switching circuit 27 is set to the L level, the operation is exactly the same as that of the embodiment of FIG. 4. Furthermore, when the output of the switching circuit 27 is set to H level,
Regardless of the output of the comparison circuit 22, the object detection output is generated only by the output of the comparison circuit 23 that determines the received light level. Therefore, in this case, the ninth
By making the connections as shown in the figure, it can be used as a diffuse reflection type photoelectric switch circuit that detects the presence or absence of an object based on the magnitude of the amount of received light, similar to the conventional example shown in FIG. That is, in the photoelectric switch circuit shown in FIG. 9, the optical signal from the light projecting element 10 is diffusely reflected by the object, and
However, the two detection currents I ₁ and I ₂ of the position detection means 15 are both input to the light receiving circuit 18 and become a voltage signal (V ₁ +V ₂ ), and the output of this light receiving circuit 18 is sent to the logarithmic amplification circuit. The voltage signal ln (V ₁ +V ₂ ) is logarithmically converted at 20 and compared with a predetermined reference level by a comparison circuit 23 . Therefore, the circuit shown in FIG. 9 performs the same operation as the conventional photoelectric switch circuit shown in FIG. If the switching circuit 27 is provided as in this embodiment and its output is switched between H level and L level, one IC can be used for each of the above-mentioned area reflection type, diffuse reflection type, and opposing type. This is convenient because it can be done.

〔Effect of the invention〕

As described above, the specific invention of the present invention obtains two signals from the position detecting means, and transmits the light emitting means and the position detecting means so that the amount of received light signal of one signal is larger than the amount of received light signal of the other signal. a subtraction circuit that logarithmically amplifies the two signals and subtracts them;
Compare this subtraction circuit output with a preset reference level, and if there is a detected object within the set distance,
A first comparison circuit that outputs a level signal compares the one of the two signals with a lower received light signal level with a preset reference value, and determines that the received light signal level is below the lowest operating level of the discrimination control means. L in case
Since it is equipped with a second comparison circuit that outputs a level signal, and an AND circuit that ANDs the outputs of both comparison circuits and outputs a signal to the output circuit,
Even if the first comparison circuit determines that a detected object exists within the predetermined detection area, the second comparison circuit outputs an output if the received light signal level is below the minimum operating level to the discrimination control means. By setting the output circuit to L level, the AND circuit output is set to L level and the output circuit is not driven. Therefore,
By not outputting the object detection output signal, it is possible to maintain high reliability of the object detection signal. Moreover, since only the second comparison circuit and the AND circuit are provided to improve the reliability of the object detection output, the circuit configuration can be simplified.

Further, in the combined invention, two signals are obtained from the position detecting means, and the light emitting means and the position detecting means are arranged so that the amount of received light of one signal is larger than the amount of received light of the other signal, A subtraction circuit that logarithmically amplifies and then subtracts the signal from 2 above, and a first circuit that compares the output of this subtraction circuit with a preset reference level and outputs an H level signal if a detected object exists within a set distance. A comparison circuit compares the one of the two signals with a lower received light signal level with a preset reference value, and outputs an L level signal when the received light signal level is below the minimum operating level of the discrimination control means. a second comparison circuit that ANDs the outputs of both comparison circuits and outputs a signal to the output circuit; Since the present invention is equipped with a switching circuit that switches between a high-level signal and a high-level signal, the above specified invention can be achieved by setting the signal input to the AND circuit by operating the switching circuit as the first comparison circuit output. It has a similar effect, and furthermore,
By operating the switching circuit to make the signal input to the AND circuit an H level signal, the output of the AND circuit is the output of the second comparison circuit.
The object to be detected will be determined based only on the received light signal level, so by adding a switching circuit,
It is possible to configure a photoelectric switch of the light intensity determination type, such as a diffuse reflection type and a facing type.Moreover, when the circuit of the present invention is configured with an IC, a single IC can be used to switch between an area reflection type and a diffuse reflection type. Compatible with various photoelectric switches such as type and opposite type,
This has the effect of reducing the cost of ICs.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional example, Fig. 2 is a schematic configuration diagram of an optical system of another conventional example, Fig. 3 is a block diagram of an electronic circuit used in the same example, and Fig. 4 is an example of an embodiment of the present invention. Block diagram, Figure 5 is an explanatory diagram of the same operation as above,
FIG. 6 is a block diagram of another embodiment of the present invention;
FIG. 8 is a block diagram of still another embodiment of the present invention, and FIG. 9 is a block diagram showing one state of use of the same. 7 is an output circuit, 8 is a light projection means, 13 is a condensing means, 15 is a position detection means, 16 is a discrimination control circuit,
22 is a first comparison circuit, 23 is a second comparison circuit,
24 is an AND circuit, and 27 is a switching circuit.

Claims (1)

[Scope of Claims] 1. A light projecting means for projecting an optical signal onto an object to be detected; and a light projecting means for projecting an optical signal onto an object to be detected; and a light projecting means that collects reflected light of the optical signal from the object to be detected, and directs a light converging spot on a converging surface to the object to be detected. a position detection means disposed on the light collection surface of the light collection means and generates a position detection signal according to the position of the light collection spot; In the photoelectric switch circuit, the photoelectric switch circuit includes a discrimination control means for controlling an output circuit by discriminating whether or not a detected object exists within a predetermined detection area based on the detection area.
a subtraction circuit that logarithmically amplifies and then subtracts the above-mentioned 2 signal, the light projecting means and the position detecting means being arranged so that the amount of received light signal of one signal is larger than the amount of received light signal of the other signal; A first comparison circuit compares the output of this subtraction circuit with a preset reference level and outputs an H level signal if a detected object exists within a set distance; A second comparison circuit compares one signal with a preset reference value and outputs an L level signal when the received light signal level is below the minimum operating level of the discrimination control means, and a second comparison circuit outputs an L level signal when the received light signal level is lower than the minimum operating level of the discrimination control means. 1. A photoelectric switch circuit comprising: an AND circuit that multiplies the signals and outputs a signal to an output circuit. 2. A light projecting means that projects an optical signal onto the object to be detected, and a light projecting means that collects the reflected light of the optical signal from the object to be detected, and adjusts the focusing spot on the focusing surface according to the distance from the object to be detected. a position detection means that is disposed on the light collection surface of the light collection means and generates a position detection signal according to the position of the light collection spot; In a photoelectric switch circuit, the photoelectric switch circuit includes a discrimination control means for controlling an output circuit by discriminating whether or not the detection area exists within a predetermined detection area.
a subtraction circuit that logarithmically amplifies and then subtracts the above-mentioned 2 signal, the light projecting means and the position detecting means being arranged so that the amount of received light signal of one signal is larger than the amount of received light signal of the other signal; A first comparison circuit compares the output of this subtraction circuit with a preset reference level and outputs an H level signal if a detected object exists within a set distance; A second comparison circuit compares one signal with a preset reference value and outputs an L level signal when the received light signal level is below the minimum operating level of the discrimination control means, and a second comparison circuit outputs an L level signal when the received light signal level is lower than the minimum operating level of the discrimination control means. an AND circuit that multiplies and outputs a signal to an output circuit;
A photoelectric switch circuit comprising: a switching circuit for switching a signal input to one of the AND circuits between an output signal of the first comparison circuit and an H level signal.