JPH0326792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a reflective photoelectric switch that determines whether or not a detected object exists within a preset detection area and controls an output circuit.

[Background technology] Conventionally, the first reflective photoelectric switch of this type
As shown in the figure, the light receiving means 2' receives the reflected light R' of the diffused light P' projected from the light projecting means 1' by the detected object X. The received light output level V ₂ is the preset operating level
There was a diffuse reflection type that set the detection area DE by activating the output circuit when the voltage was higher than Vth. However, in such a conventional example, as shown in FIG. 3, for example, in order to detect the detected object When the setting is made in accordance with the width of the conveyor BC, if there is an object Z having a higher light reflectance than the detected object X behind the detection area DE, a malfunction may occur. That is,
The light receiving output level _V2 of the light receiving means 2' is the detected object X.
It is directly proportional to the light reflectance of , and inversely proportional to the square of the distance l between the light emitting and receiving means 1', 2' and the detected object X. Therefore, to set the detection area DE, the light reflectance and distance l are It is sufficient to set the operation level Vth of the discrimination control means in consideration of
If there is an object Z with a higher light reflectance than the detected object X behind the detection area DE set in this way, the received light output level V ₂ when the reflected light R' from this object Z is received. is the detection area DE
The received light output level V ₂ is the same as that when the reflected light R from the detected object I had a problem with putting it away. In the figure, 12 is a light emitting element such as a light emitting diode, 13 is a light emitting optical system, 20 is a light receiving element made of a phototransistor, photodiode, solar cell, CdS, etc., and 3 is a light receiving optical system.

Therefore, as shown in FIGS. 4 and 5, a light projecting means 1 for projecting a light beam P onto a detected object A light-receiving optical system 2 that collects the reflected light R of the light beam P caused by X, and a position detection device that outputs a position signal corresponding to the position of a light-converging spot S provided on the light-converging surface of the light-receiving optical system 2. and a distance measuring control means 5 for determining whether or not the detected object X exists within a predetermined detection area DE based on the output of the position detecting means 4 and controlling the output circuit 6. A method is considered in which the distance l to the detected object There is. The light projecting means 1 that projects a light beam P made of pulse modulated light onto the object to be detected X includes an oscillation circuit 10 that generates a synchronization signal for setting the light projection timing, a drive circuit 11, and a light emitting diode or It is formed by a light projecting element 12 such as a laser diode, and a light projecting optical system 13 consisting of a condenser lens that forms a light beam P. Light receiving means 2 arranged side by side with a predetermined distance ΔL from the light projecting means 1
are arranged in a triangular manner with respect to the light projecting means 1 and the object to be detected and a position detecting means 4 which is disposed on the condensing surface of the light receiving optical system 3 and outputs a position signal corresponding to the position of the condensing spot S. This position detecting means 4 includes two light receiving elements 20a and 20b arranged in the light collecting plane of the light receiving optical system 3 and arranged in series in the moving direction of the light collecting spot S.
It is formed in These light receiving elements 20a, 20
b is a phototransistor, a photodiode,
Solar cells, CdS, etc. are used. Further, as the position detecting means 4, a position detecting element (hereinafter abbreviated as PSD) 30 shown in FIG. 8a may be used.
The PSD 30 has a P layer 3 on the surface of the flat silicon 31.
1a, an N layer 31b on the back surface, and an I layer 31c in the middle, so that output currents I _A and I _B corresponding to the position of the condensing spot S are output. Figure 8b shows the equivalent circuit of PSD30, where Pi is a current source, Do is an ideal diode,
Co is the junction capacitance, Rt is the parallel resistance, and Ro is the interelectrode resistance. The distance measurement control means 5 includes light receiving elements 20a, 2
The light receiving circuits 21a and 21b amplify and convert the output currents I _A and I _B from 0b into signal voltages V _A and V _B , the logarithmic amplification circuits 22 a and 22 b, and the logarithmic amplification circuits 22 a and 22 b that amplify the output currents I A and I B from the logarithmic amplification circuit 22 a and convert them into signal voltages V _{A and V B} , respectively. A subtraction circuit 23 that subtracts the width circuit 22b output lnV _B , and a subtraction circuit 23 output lnV _A /
The subtraction circuit 23 outputs by comparing V _B and the reference voltage Vs set by the detection area setting volume VR.
A comparator circuit 24 outputs an H level when lnV _A /V _B is lower than the reference voltage Vs, and a comparator circuit 24 synchronizes with the projection timing of the light beam P from the light projection element 12 (synchronization signal output from the oscillation circuit 10). A signal processing circuit 25 that reliably determines whether the detected object X exists within the detection area DE by sampling (synchronous detection) the output of the comparison circuit 24.
and an integrating circuit 26 that outputs a control signal for the output circuit 6 only when a signal is continuously output from the signal processing circuit 25 for a predetermined period or longer or when the signal is not output.
It is configured to control an output circuit 6 consisting of a relay for load control, a semiconductor switch element for load control, etc. Note that the light receiving circuit 21
a and 21b include bandpass filter circuits that pass only pulsed optical signals and cut out DC optical signals, or pass only specific frequencies. In the figure, 27 is an operation display section of the output circuit 6, 28 is an overcurrent protection circuit that cuts off overcurrent due to incorrect wiring of the output circuit 6,
Reference numeral 29 denotes a malfunction prevention circuit that prevents the output circuit 6 from malfunctioning when the power supply voltage at power-on or power-off is lower than a preset voltage.

Now, when the detected object X is present at positions a, b, and c at distances la, lb, and lc from the reflective photoelectric switch Y as shown in FIG. The position of the condensing spot S with respect to the elements 20a and 20b is as shown in FIG. 6b, and when the detected object X moves in the projection direction of the light beam P,
The ratio of the amounts of light incident on the light receiving elements 20a and 20b changes, and the output currents I _A and I _B of the light receiving elements 20 a and 20 b become position signals corresponding to the position of the light collecting spot S. In the distance measurement control means 5, voltages V A and V _B proportional to the output currents I _A and I _B are formed in the light receiving circuits 21 _a and 21 b, and the logarithmic amplification circuits 22 a and 21 b
By subtracting the voltages lnV _A and lnV _B logarithmically amplified in step 22b in a subtracting circuit 23, the subtracting circuit 23 outputs a logarithm value lnV _A /V _B of the ratio of the amount of light incident on the light receiving elements 20a and 20b. It turns out. The subtraction circuit 23 output lnV _A /V _B changes according to the movement of the detected object X, and the subtraction circuit 23 for the distance l from the reflective photoelectric switch Y to the detected object
The output lnV _A /V _B becomes as shown in FIG. Therefore, the detection area setting volume of the comparison circuit 24
By appropriately setting the reference voltage Vs in VR, an accurate detection area DE can be easily set, and when the subtraction circuit 23 output lnV _A /V _B exceeds the reference voltage Vs, the comparator circuit 24 output goes to H level. Therefore, the output circuit 6 is activated via the signal processing circuit 25. In this case, the distance measurement control means 5 controls the light receiving element 20
a, 20b output level ratio is calculated, and when the level ratio is a preset reference voltage Vs, the output circuit 6
The detection area DE is activated regardless of the level of the reflected light R from the detected object X.
is now set, so the detection area
It is possible to prevent malfunctions due to objects with high light reflectance existing behind DE, and the detection area DE can be set regardless of the light reflectance of the detected object X.
Furthermore, the light emitting and receiving optical systems 13 and 3 are not affected by dirt.

By the way, in such a conventional example, when the detected object X is a specular object, there is a problem that the distance l to the detected object X does not correspond to the position of the condensing spot S, resulting in malfunction. That is, when the detected object X made of a mirror surface is directly facing the photoelectric switch Y as shown in FIG _. The position of the condensing spot S corresponds to when the detected object X is at a distance of 2l. Therefore, the position of the detected object X is incorrectly determined,
There was a problem in that the output circuit 6 did not operate even though the detected object X existed within the detection area DE.

[Object of the Invention] The present invention has been made in view of the above points, and can prevent malfunctions caused by objects with high light reflectance existing behind the detection area. To provide a reflective photoelectric switch which can set a detection area without any problem and does not malfunction even if the object to be detected is a specular object.

[Disclosure of the Invention] Example 1 Figure 10 shows one example of the present invention.
In the conventional example having the triangulation type distance measurement control means 5 shown in FIGS. It is provided with a light amount control means 7 that discriminates and controls the output circuit 6. In the figure, 8 is a malfunction prevention means, and 9 is a margin display means. Here, the light receiving circuit 21 of the distance measurement control means 5
a and 21b are an inverting amplifier _G1 and a non-inverting amplifier _G2
, resistors _R1 to _R3 , and capacitors _C1 to _C3 , and the light receiving elements 20a and 20b of the position detection means 4
The output current from the resistor is the converted impedance
It is converted into voltages V _A ′ and V _B ′ by R ₁ and amplified by non-inverting amplifier G ₂ to obtain V _A and V _B , respectively. In addition, a low pass filter is formed by resistor R ₁ and capacitor C ₁ ,
A bypass filter is formed by capacitor C ₂ and resistor R ₂ and capacitor C ₃ and resistor R ₃ .
It is designed to remove noise caused by ambient light. Logarithmic amplifier circuits 22a and 22b are inverting amplifiers.
_G3 and diode _D1 , the light receiving circuit 21
a, 21b output V _A , V _B is logarithmically compressed to lnV _A ,
Output lnV _B. The subtraction circuit 23 is a differential amplifier _G4
The logarithmic amplification circuits 22a and 22b output
Calculates the difference between lnV _A and lnV _B and outputs lnV _A /V _B. A comparison circuit 24 consisting of a comparator G ₄ compares the output lnV _A /V _B of the subtraction circuit 23 with a reference voltage _VS obtained by dividing the power supply voltage V _CC using a resistor R ₄ and a detection area setting volume VR ₁ . As in the conventional example, it is determined whether the detected object X is within the detection area DE based on the ranging signal output from the subtraction circuit 23, and an object detection signal _VX is output. The light amount control means 7 is formed by a comparator _G6 , and the power supply voltage is determined by the non-inverting amplifier _G2 output _VA of the light receiving circuit 21a, a resistor _R5 , and a detection area setting volume _VR2.
Compare it with the reference voltage V _S ′ obtained by dividing V _CC ,
When the non-inverting amplifier _G2 output V _A is higher than the reference voltage V _S ', an object detection signal V _X ' determined based on the light intensity level of the reflected light R is output. The malfunction prevention means 8 is formed of an operation level setting section using a logarithmic amplifier _G7 , a comparison circuit section consisting of a comparator _G8 , and a gate section consisting of an AND circuit (AND), and the operation level _V8 is set from the logarithmic amplification circuit 22b. Depending on whether the above signals are obtained, it is determined whether a light reception signal V _B that allows normal operation is obtained or not, and the object detection signals V _X , V are inputted to the signal processing circuit 25 via the OR circuit OR. _X ' can be freely blocked using an AND circuit (AND). The margin display means 9 is formed by a margin level setting section using a logarithmic amplifier _G9 , a comparison circuit section consisting of a comparator _G10 , and a margin display section 9a, and the margin level _V9 is set slightly higher than the operating level _V8 . and logarithmic amplification circuit 23b output V _B
When is greater than the margin level _V9 , the margin display section 9a lights up and the level of the output VB of the logarithmic amplification circuit _23b is within the normal operating range (if dirt on the lens surface or optical axis change of the optical system is present). The display indicates that the device will operate normally even if there is a problem. This margin display means 9 is useful when performing installation adjustment and pre-maintenance of the photoelectric switch Y.

The specific operation of the embodiment will be explained below.
Now, the relationship between the light amount level of the reflected light R and the distance l is shown in FIG. 11 when the detected object X is a specular surface object and when it is a diffuse surface object. Note that the specular body has a specular reflection component that allows the distance measurement control means 5 to detect the object X within a predetermined error, and since the specular reflection component of the specular body is larger than that of the specular body, distance measurement The control means 5 cannot detect the object X within a predetermined error. Here, the light amount level of the reflected light R of the detected object If the detection area setting volume VR ₂ of the control means 7 is appropriately set and the operation level is set to the level shown by the dotted line in the figure (hereinafter referred to as the priority light intensity level), it is possible to detect whether the object X to be detected is a specular object or not. This means that it is possible to accurately determine whether or not the object exists within the detection area DE. That is, even if the detected object _X made of a specular object is within the detection area DE, the object detection signal _V Reference voltage set with the detection area setting volume VR ₂
When the value exceeds V _S ′, the object detection signal _V
Photoelectric switch Y operates normally. By the way, the volume VR ₂ for setting the priority light intensity level and the detection area DE can be set by both the control means 5 and 7 by linking with the volume VR ₁ for setting the detection area DE of the ranging control means 7. The detection area DE is matched with the detected area DE, and a double volume is used as both volume VR ₁ and VR ₂ .

Embodiment 2 FIG. 12 shows another embodiment, in which the reference voltage setting section is formed using an operational amplifier Gn, and a resistor R ₈
By appropriately setting the value of ~ _R11 and changing the DANP constant, the reference voltage Vs' can be changed as shown in FIG.
It is designed to set the reference voltage
The way V _S ′ changes depends on the specular object to be detected,
The optimum change is set in consideration of the change in the light amount level of the reflected light R depending on the distance l.

Embodiment 3 FIG. 14 shows still another embodiment, in which a level detection unit is formed by a comparison circuit consisting of comparators G ₁₂ a to G ₁₂ n, and control is performed by the output of each comparison circuit of the level detection unit. The reference voltage setting section is constituted by a switch circuit consisting of a switch section SW, and resistors 14a, 15a,
14b, 15b...14n, 15n's divided voltages Vsa', Vsb',...Vsn' are output as the reference voltage Vs', and the switch section SW is formed by a switch element such as a transistor or a relay. be done. In the figure, R ₁₂ a, R ₁₃ a, R ₁₂ b, R ₁₃ b... are reference voltage generation resistors.

Embodiment 4 FIG. 15 shows still another embodiment, in which a volume VR 3 is connected in series with a light projecting element 12 consisting of an LED inserted into the collector of a transistor Q constituting a drive circuit 11 of a light projecting means ₁ . This volume VR ₃ is inserted and linked with the detection area setting volume VR ₁ of the ranging control means 5 to control the light intensity of the projected beam P, and is suitable when the detection area DE is changed. However, the light intensity level of the reflected light R from the detected object The level can be kept approximately constant. In the diagram
R ₁₆ and R ₁₇ are resistances.

Embodiment 5 FIG. 17 shows still another embodiment, in which the light intensity of the projected beam P is controlled using a differential amplifier _G13 , and the terminals of the differential amplifier _G13 are The reference voltage set by level setting volume R ₂₃ is applied, and the reference voltage Vs is applied to the terminal.
is applied. In the figure, R ₁₈ to R ₂₁ are resistances.

Embodiment 6 FIG. 18 shows yet another embodiment, in which the drive circuit 11 of the light projection means 1 is controlled using a switch circuit similar to the embodiment in FIG. 14.

Embodiment 7 FIG. 19 shows still another embodiment, which is provided with a control selection means 40 consisting of switches SWa and SWb. By turning on switch SWa and turning off switch SWb, distance measurement can be performed. The output circuit 6 is controlled by the object detection signal V _X outputted from the control means 5, and by turning off the switch SWa and turning on the switch SWb, the object detection signal _V By turning on both switches SWa and SWb, the output circuit 6 is controlled based on the object detection signals V _X and V _X ' output from both control means 5 and 7. It's becoming like that. Therefore, the operation mode can be changed with a single touch depending on the situation at the site, and a highly versatile photoelectric switch Y can be obtained.

[Effects of the Invention] As described above, the present invention includes a light projection means for projecting a light beam onto an object to be detected, and a light projection means disposed at a predetermined distance from the light projection means to reflect the light beam by the object to be detected. A light-receiving optical system that collects light; a position detecting means that is disposed on the light-converging surface of the light-receiving optical system and outputs a position signal corresponding to the position of the light-converging spot; A reflective photoelectric switch is equipped with distance measurement control means that determines whether an object exists within a predetermined detection area and controls an output circuit. This device is equipped with a light amount control means that controls the output circuit by determining whether or not the sensor exists based on the light amount level of the reflected light, and can prevent malfunctions caused by objects with high light reflectance that exist behind the detection area. Further, it is possible to provide a reflection type photoelectric switch that can set a detection area regardless of the light reflectance of the object to be detected, and does not malfunction even if the object to be detected is a specular object.

[Brief explanation of drawings]

Figure 1 is a diagram showing the configuration of a conventional example, Figures 2 and 3 are explanatory diagrams of the same operation as above, Figure 4 is a diagram showing the configuration of another conventional example, and Figure 5 is the main block circuit of the same as above. Figures 6 and 7 are explanatory diagrams of the same operation as above;
Fig. 8a is a sectional view of the PSD, Fig. 8b is an equivalent circuit diagram of the PSD, Fig. 9 is a diagram showing problems in the conventional example shown in Fig. 4, and Fig. 10 is a circuit diagram of the main part of an embodiment of the present invention. , FIG. 11 is an explanatory diagram of the same operation as above, FIG. 12 is a main circuit diagram of another embodiment, FIG. 13 is an explanatory diagram of the same as above,
14 and 15 are circuit diagrams of main parts of still other embodiments, FIG. 16 is an explanatory diagram of the operation of the embodiment of FIG. 15, and FIGS. 17 to 19 are main parts of still other embodiments. FIG. 1 is a light projecting means, 3 is a light receiving optical system, 4 is a position detection means, 5 is a ranging control means, 6 is an output circuit, and 7 is a light amount control means.

Claims (1)

[Scope of Claims] 1. Light projecting means for projecting a light beam onto a detected object; and a light receiving device disposed at a predetermined distance from the light projecting means to collect light reflected from the light beam by the detected object. an optical system for detecting light, a position detecting means disposed on the condensing surface of the optical system for receiving light and outputting a position signal corresponding to the position of the condensing spot, and a position detecting means for detecting a detected object in a predetermined detection area based on the output of the position detecting means. A reflective photoelectric switch is equipped with a distance measuring control means that determines whether an object is present within the detection area and controls an output circuit based on the distance measurement control means. A reflective photoelectric switch characterized by being provided with a light amount control means for controlling an output circuit by determining the amount of light based on the light amount level. 2. A reflective photoelectric switch according to claim 1, characterized in that the light intensity of the light beam projected from the light projecting means is controlled in conjunction with the area setting means for setting the detection area. . 3. A reflective photoelectric switch according to claim 1, wherein the detection area setting means of the distance measurement control means and the light amount control means are linked. 4. Claim 1, characterized in that a control selection means is provided for selecting whether the output circuit is controlled by the distance measurement control means, the light amount control means, or both control means. Reflective photoelectric switch described in Section 1.