JPH084750Y2 - Reflective photoelectric switch - Google Patents

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention irradiates light from a light projecting portion onto a regressive reflection plate, receives the reflected light from a light receiving portion to form a light path, and the light path is blocked by a detection object. The present invention relates to a retroreflective photoelectric switch that detects an object when it is turned on.

[Conventional technology]

Conventionally, there is known a regressive reflection type photoelectric switch in which a light projecting / receiving unit is housed in one case, light is projected from a light projecting unit to a retroreflector and reflected light is received, and a detection signal is obtained by shielding a detection object. ing. Such a retro-reflection type photoelectric switch has a feature that when the surface of a detection object has a mirror surface such as metallic luster, the light from the light projecting unit is reflected by the mirror surface and given to the light receiving unit. Nevertheless, there was a problem that this could not be detected.

Therefore, as disclosed in, for example, Japanese Patent Laid-Open No. 63-166118, a retroreflective plate is irradiated with the light by using a light projecting unit that emits light of the first and second wavelengths. A recursive reflection type photoelectric switch has been proposed in which only the light of a wavelength is reflected so that the recursive reflection plate and the detection object are distinguished by the level of the reflected light.

[Problems to be solved by the device]

However, according to the conventional retroreflective photoelectric switch, the presence or absence of an object is detected based on the output ratio of the light receiving section having sensitivity to two wavelengths, but the ratio varies depending on the temperature. For example, in the reflection type photoelectric switch shown in FIG. 7, the input ratio of the color sensor with respect to the ambient temperature changes as shown by a curve A in a state where there is no object and all the incident light is reflected by the regressive reflection plate. When a specular body is detected, it changes as shown by a curve B, for example.
As indicated by hatching due to changes in the ambient temperature, there is an overlapping portion where the ratios of the curves A and B are the same, so there is a drawback that the detection signal may be erroneously output.

The present invention has been made in view of the problems of the conventional reflection type photoelectric switch, and an object thereof is to make it possible to detect an object stably even with a temperature change.

[Means for solving the problem]

The present invention provides a light projecting portion having a light projecting element for emitting light of the first and second wavelengths provided in a photoelectric switch, and a first light sensitive portion of the light projecting portion for the light of the first and second wavelengths, respectively. A photoelectric switch body having a light receiving element having a second color sensor and a discrimination circuit section for discriminating an object based on the output of each color sensor of the light receiving element; A regressive reflection plate that reflects one of the first and second wavelengths and absorbs the other wavelength of light,
A reflection type photoelectric switch that detects an object by causing light from a light projecting portion of the photoelectric switch body to reciprocate through a regressive reflection plate and blocking the optical path of the detection object, which is a second color sensor of a light receiving element. The temperature compensation is provided on the output side of the so that the output ratio of the first and second color sensors will be constant regardless of the temperature change in the state where the object does not block the light between the photoelectric switch body and the return reflection plate. And a light receiving ratio adjusting circuit that is provided at the output end of the first color sensor and that amplifies the output of the first color sensor by a predetermined amplification factor.

[Operation] According to the present invention having such a feature, light of different first and second wavelengths is emitted from one light projecting element and is applied to the return reflector with the same optical axis. The regressive reflection plate reflects only one of the wavelengths of light, and the reflected light is given to a light receiving element provided in the photoelectric switch body and sensitive to both wavelengths of light. Then, the object passing through the optical path between the regressive reflection plate and the photoelectric switch is detected by comparing the levels of the reflected light obtained by the first and second color sensors of the light receiving element. That is, when an object without a mirror surface blocks the optical axis, it cannot receive any wavelength, and when an object with a mirror surface blocks the optical axis, light of both wavelengths is reflected and the light receiving unit Therefore, the object is identified based on the comparison of the reflected light levels. Then, the output of the second color sensor is input to the temperature compensating circuit, and the ratio of the output of the first and second color sensors changes due to the temperature change in the state where the object does not pass between the photoelectric switch body and the return reflection plate. The temperature is compensated so that it is constant regardless. The output of the first color sensor is given to the light receiving ratio adjusting circuit. The light receiving ratio adjusting circuit amplifies the output of the first color sensor whose output ratio is kept constant with respect to the output of the temperature compensating circuit by a predetermined amplification factor, and outputs the output ratio of the light receiving ratio adjusting circuit and the temperature compensating circuit. Is set arbitrarily. The pair of outputs thus obtained is input to the determination circuit unit to determine the presence or absence of a passing object.

[Effect of device]

As described above, according to the present invention, since light of different wavelengths is emitted by one light projecting element, the configuration of the optical system becomes extremely simple and the entire photoelectric switch can be downsized. Further, even when the ambient temperature changes, the output ratio of the pair of color sensors is kept constant in the absence of an object, so that malfunction can be eliminated and the degree of freedom in setting the threshold value can be increased. .

[Explanation of Example]

FIG. 2 is a schematic diagram showing the overall structure of a reflective photoelectric switch according to an embodiment of the present invention. In this figure, a light projecting element 3 and a light receiving element 4 are mounted on a printed circuit board 2 of a photoelectric switch body 1. The light projecting element 3 is, for example, a light emitting diode having a GaAlAs heterojunction structure, and simultaneously emits different wavelengths, for example, strong red light having a wavelength of 660 nm and weak infrared light having a wavelength of 880 nm as shown by curves C and D in FIG. Light emitting diode. Condensing lenses 5 and 6 are provided at opposing positions on the light emitting and receiving elements 3 and 4, respectively. The condenser lens 5 irradiates the return reflection plate 7 distant from the photoelectric switch main body with light emitted from the light projecting element 3. The retroreflective plate 7 absorbs light of either wavelength, for example, red light and reflects only infrared light. The retroreflective plate 7 is mixed with a dye that absorbs red light and transmits infrared light. It is constructed by integrally molding a group of corner cubes made of acrylic resin. A curve E in FIG. 3 shows an example of the spectral characteristic of the retroreflector 7, and has a characteristic that it hardly reflects red light of 700 nm or less and reflects 90% or more of infrared light of 800 nm or more. ing.

The condenser lens 6 provided on the front surface of the photoelectric switch focuses the reflected light on the light receiving element 4. The light receiving element 4 is a color sensor that obtains a signal by separating light of different wavelengths. For example, as shown in FIG. 4 (a), two photodiodes having different junction depths are formed in one chip. It is assumed that the color is determined by utilizing the difference in the spectral characteristics of each. This photodiode is equivalently composed of two photodiodes PD-a and PD- as shown in FIG. 4 (b).
It is displayed as b. These photodiodes PD-a, P
Each of Db has characteristics with respect to the wavelength as shown in FIG. 4 (c), for example. Here, the photodiode PD-a
To the first color sensor and the photodiode PD-b to the second
Color sensor.

Next, the structure of the detection circuit unit of this embodiment will be described with reference to FIG. First, the output of the photodiode PD-a is given to the light receiving ratio adjusting circuit including the amplifier 11. The variable resistor VR1 is connected to the input and output ends of the amplifier 11. The amplifier 11 is the photodiode PD which is the first color sensor.
It has an I / V conversion function of converting the current input of −a into a voltage, and the amplification factor thereof can be arbitrarily set. The output of the photodiode PD-b is given to the amplifier 12. The amplifier 12 has a resistor R connected in series at the input and output ends.
The temperature compensating circuit is configured with the thermistor R4 which is connected in parallel with the R2 and the resistor R3. This amplifier 12 also has an I / V conversion function of converting the current output of the photodiode PD-b, which is the second color sensor, into a voltage. The outputs of the amplifiers 11 and 12 are given to logarithmic amplifiers 13 and 14, respectively. Logarithmic amplifier 1
The outputs of 3, 14 are given to the adder 15 and the subtractor 16. The outputs of the adder 15 and the subtractor 16 are given to the first and second comparators 17 and 18, respectively. The comparators 17 and 18 use the input voltages as thresholds Vth1 and Vth2, respectively.
And the output is given to the AND circuit 19. The output of the AND circuit 19 is output to the outside via the output circuit 20. Here, the logarithmic amplifier 13 to the AND circuit 19 constitute a discrimination circuit section for discriminating an object based on the output of the color sensor of the light receiving element. The light projecting element 3 described above is intermittently driven by the oscillation circuit 21.

Now, the amplifiers 11 and 12 of the light receiving ratio adjusting circuit and the temperature compensating circuit
Of the amplifiers 11 and 12 at room temperature.
Let Va ₀ and Vb _0, and let the outputs of the amplifiers 11 and 12 at a certain temperature t be Vat,
Vbt. At this time, even if the temperature changes by selecting resistors R2, R3 and thermistor R4, Is set so that In this way, the ratio of I / V conversion output is always constant. At this time, α has the same tendency as the temperature characteristic of the thermistor R4, and the value becomes smaller as the temperature rises. Thus the resistance R4 ₀ at room temperature thermistor R4, When R4t the resistance value at a predetermined temperature, the resistance value of the resistors R2, R3 is the formula Shall be set so that This way the fifth
As shown in the figure, the output ratio of the amplifiers 11 and 12 with respect to the ambient temperature is almost constant as shown by the curve F when there is no object that shields the light from the retroreflector 7, and when detecting a blank sheet or a specular object, the curve As shown in G, an output having a slight temperature characteristic is obtained. Further, the light reception ratio of visible light and infrared light is determined by the variable resistor VR1 which is a feedback resistor of the amplifier 11. At this time, even if the value of VR1 is changed and multiplied by k, only the output ratio of the outputs of the amplifiers 11 and 12 changes, and the temperature characteristics are not affected. Therefore, temperature compensation and adjustment of the light receiving ratio can be set independently.

Further, in this embodiment, the temperature compensating circuit and the light receiving ratio adjusting circuit are respectively constituted by using amplifiers, but as shown in FIG. 6, the photodiodes PD-a and PD-b are variable between one end and the grounding end. The resistance VR5 and the combined resistance of the resistances R6 to R8 may be connected to each other, and the temperature compensation and the light receiving ratio may be adjusted by these resistance values. Other configurations are the same as those in the above-described embodiment. When Va / Vb monotonously increases with increasing temperature, the circuit shown in Fig. 1 or 6 is used, and when monotonically decreasing, the temperature compensating circuit and the light receiving ratio adjusting circuit are reversed to similarly perform temperature compensation. And the light receiving ratio can be set independently.

[Brief description of drawings]

FIG. 1 is a block diagram showing the structure of a reflective photoelectric switch according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing the structure of an optical system of this embodiment, and FIG. 3 is a multicolor light emitting diode. And a graph showing the sensitivity characteristics of the retroreflector, FIG. 4 (a)
Is a diagram showing the structure of a color sensor used as a light receiving element,
FIG. 4 (b) is a diagram showing an equivalent circuit of the color sensor,
FIG. 4 (c) is a graph showing the sensitivity characteristic, FIG. 5 is a diagram showing the temperature characteristic of this embodiment, FIG. 6 is a block diagram showing another embodiment of the present invention, and FIG. It is a graph which shows the change of the output voltage with respect to the temperature of a photoelectric switch. 3 ... Emitting element, 4 ... Light receiving element, 7 ... Return reflector,
11 …… Amplifier (light receiving ratio adjustment circuit), 12 …… Amplifier (temperature compensation circuit), 13 …… Adder, 14,15 …… Comparator, 16 ……
Subtractor, 19 ... AND circuit, R4 ... Thermistor

Claims (1)

[Scope of utility model registration request] 1. A light projecting portion having a light projecting element for emitting light of first and second wavelengths provided in a photoelectric switch, and sensitivity of the light projecting portion to light of first and second wavelengths, respectively. A photoelectric switch body having a light receiving element having the first and second color sensors and a discrimination circuit section for discriminating an object based on the output of each color sensor of the light receiving element, and a photoelectric switch body at a position distant from the photoelectric switch body. A return reflection plate that reflects and absorbs light of one of the first and second wavelengths that are arranged and emitted, and that absorbs light of the other wavelength. A reflection-type photoelectric switch that detects an object by reciprocating through the regression reflection plate and blocking a light path of the detection object, the photoelectric switch body being provided on an output side of a second color sensor of the light-receiving element. And the retroreflective plate A temperature compensating circuit for compensating the temperature so that the output ratios of the first and second color sensors are constant regardless of temperature changes in a state where light is not shielded; and a temperature compensating circuit provided at the output end of the first color sensor, 1
And a light-reception ratio adjusting circuit for amplifying the output of the color sensor at a predetermined amplification factor.