JPS63292016A - Distance-measuring type photoelectric switch - Google Patents

Abstract

PURPOSE:To simplify a construction and to improve the precision of an arithmetic operation, by a method wherein the sum of a pair of output currents of an optical position sensor (PSD) or one output current thereof is inputted alternatively to one preliminary circuit element by a switching element. CONSTITUTION:First a preset switch (SW) 8a is set so that the sum I1+I2 of two output currents of PSD 1 is inputted to a preliminary circuit element 2. On the occasion, a preset switch (SW) 8b in linkage to SW 8a is so set as to input an output of an A/D conversion element 4 to a memory element 5. Accordingly, a value corresponding to the quantity of a received light reflected from an object of detection is written as a reference value in the memory element 5. Next, SW 8a is switched so that only the output current I1 of PSD 1 is inputted to the circuit element 2. At this time, the gain of the circuit element 2 takes an optimum value, since an impedance variable element 6 is adjusted to have an optimum value corresponding to the quantity of received light, on the basis of the reference value. Besides, SW 8b is switched and an output of the conversion element 4 is inputted to an arithmetic circuit element 3. Thus, a distance to the object of detection can be determined by a prescribed calculation formula together with the reference value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to a distance-measuring photoelectric switch that detects the distance to a detection target by triangulation using an optical position sensor.

[Background Art] In general, a photoelectric switch that determines whether or not a detection target exists within a predetermined set distance and outputs an output detects the detection target based on the intensity of the reflected light of the light beam irradiated from the light emitting part to the detection target. Provided by a reflective photoelectric switch that detects '! −
However, since reflective photoelectric switches detect signals based on the amount of light received by the light receiving section, they are susceptible to light rays from the background surrounding the detection target, resulting in low reliability. be. On the other hand, as a charging switch to eliminate such problems, a light position sensor (hereinafter abbreviated as PSD) is installed in the light receiving section.
etCctor) to detect countermeasure objects by triangulation. As shown in Fig. 2, PSDI is a photovoltaic element having a structure in which the p layer of a pin7 photodiode is a high resistance layer, electrodes 11a and llb are provided at both ends, and a common electrode 12 is provided on the n layer side. It is. PSDI p l? When the spot light is irradiated on the surface on the Ij side, p/lij is equal to the minute at the irradiation position of the spot light! l
I, and a current inversely proportional to the distance between each electrode 11a, 11b and the dividing position is output from each type 4!1lla, 11b. That is, the direction connecting both electrodes 11a and 116 is the X direction, and the center position between both electrodes 11a+11b is the origin, α
, the distance between both electrodes 11a and Ilb! (that is, the length of the light receiving part) is 21, a spot light is irradiated on the surface of pJl at a distance X from the origin to the electrode 11a side, and the electromotive current at that time is . Assuming that, the currents I, , r2 taken out from each electrode 11a and 11b and the electromotive force. The relationship is as shown in the following equation.

1, /I. =(1-X)/21 ・・・・・・■r2
/Io=(t'+X)/21--■Here, l0=I,
It was set as +12. If we take the logarithm of the ratio of both formulas, we get: If we assume that the spot light is irradiated near the origin (the center of the light receiving part), then (X#)<<1.
Equation 0 can be transformed as follows.

In this manner, the irradiation position of the spot light on the light receiving surface of the PSDI can be detected as the ratio of the currents output from both electrodes 11a and 11b, and the electromotive current I corresponding to the light intensity of the spot light. It does not depend on. In other words, a spot light is irradiated onto the detection target from a light emitting unit set so that the irradiation direction is a constant direction, and the reflected light is passed through a lens system to the PS.
If the light is focused on the light-receiving surface of the DI, the focal position of the spot light on the PSD-I becomes a function of the distance between the light-emitting part or the light-receiving part and the detection target, so it is independent of the intensity of the reflected light. It is possible to detect the distance to the detection target.

Based on the above principle, it has been considered to configure a charging switch using PSDI as shown in FIG. 3. In order to remove disturbance noise, a light emitting section (not shown) is configured to emit a spot light modulated with a high frequency, and the optical axis direction of the light emitting section is set in a constant direction. The currents taken out from both electrodes 11a and Ilb of the PSDl that receive the reflected light from the detection target are transferred to the front circuit parts 2a and 2, respectively.
b, and an output corresponding to the current ratio is calculated in the arithmetic circuit section 3', which is a division circuit. Therefore, the output voltage of the arithmetic circuit g3' corresponds to the irradiation position of the spotlight on the light-receiving surface of the PSDl, and as mentioned above, the irradiation position of the spotlight on the light-receiving surface of the PSDI corresponds to the distance to the detection target. Since it is a function, the output value of the arithmetic circuit section 3' corresponds to the distance to the detection target. Therefore, if a comparison circuit is provided at the subsequent stage and the preset threshold value is compared with the output value of the arithmetic circuit section 3°, then
Based on the magnitude relationship, it can be determined whether or not a detection target exists within a predetermined set distance, and it can be configured to obtain a contact and α output from the output circuit based on this determination output.

By the way, the above-mentioned photoelectric switch can, in principle, detect the detection target without depending on the intensity of the reflected light, but in reality, the intensity of the reflected light changes as the distance from the detection target increases, and the intensity of the reflected light changes. Since the electromotive current of PSDI changes depending on the wavelength,
It is believed that the magnitude of the output current of PSD 1 varies over a fairly wide range.

Therefore, a wide dynamic range is required for the T1 circuit sections 2a and 2b, but since the upper limit of the dynamic range depends on the power supply voltage, it is difficult to use a relatively low voltage power supply such as a battery power supply. It is not possible to obtain a wide dynamic range. In other words, in order to prevent the circuit from saturating with large input signals, it is necessary to set the transfer impedance small, and with small input signals, it is necessary to prevent the increase in current thermal noise due to the feedback resistor and to obtain sufficient gain. In order to improve ranging accuracy, it is necessary to increase the transfer impedance.

The circuit in Figure 3 takes this point into consideration, and once the detection target and detection conditions (position of the detection target, etc.) are determined, the PSD
Since the intensity of the reflected light received by I is determined, if the transfer impedance of the front circuit parts 2a and 2b is set so that the circuit operates under optimal conditions when the detection target is located at a predetermined position, The circuit is designed with the focus on the point that even if the circuit is relatively narrow, the input current will not deviate from the operating range of the circuit and stable operation can be achieved.

That is, the total current of PSDI ■. 7 analog-to-digital converter 4 that converts the signal into a digital signal, a storage unit 5 that stores the output value of the analog-digital converter 4, and a pre-circuit g.
Impedance variable sections 6m and 6b that adjust the transfer impedances of impedances 2a and 2b, and a control circuit section 7 that controls the impedance variable sections 6a and 6b based on the values stored in the storage section 5 are provided. Therefore, before distance measurement, the amount of light received from the detection target to be actually measured is detected, and the amount of received light corresponding to the detection target is stored as a reference value in the storage unit 5 by operating the preset switch 8°. , in distance measurement, the pre-circuit unit 2
Since the transfer impedances of a and 2 b are adjusted, the transfer impedances are set to optimal values that suit the detection target.

Here, the input value to the arithmetic circuit section 3' is a current (2) corresponding to the electromotive current. Since it corresponds to the ratio of the current I outputted from one electrode 11a, if we take the logarithm of both sides of the above equation 0, and furthermore, if we introduce the relationship (X#)<<1, we get Based on this current ratio, the position of the spot light, that is, the distance to the detection target is calculated.

In the circuit configuration shown in FIG. 3, the Guinami accuracy of the pre-circuit sections 2a and 2b can be reduced, but the pair of pre-circuit sections 2a and 2b each amplify the pair of output currents of the PSD 1.
2b, the number of pre-circuit sections 2a' and 2b is large, and since the input signal to the arithmetic circuit section 3.degree. is an analog signal, there are problems with arithmetic accuracy, especially temperature characteristics.

[Objective of the Invention 1 The present invention has been made in view of the above-mentioned points, and its purpose is to simplify the configuration by integrating the front circuit section into one, and to improve the calculation accuracy. The object of the present invention is to provide a distance-measuring photoelectric switch.

[Disclosure of the Invention] (Structure) In the distance-measuring photoelectric switch according to the present invention, the position of the receiving spot of the reflected light on the detection target of the spot light irradiated from the light emitting part to the detection target corresponds to the distance to the detection target. In a distance-measuring photoelectric switch that detects the distance to the detection target by triangulation based on the position of the light-receiving spot, a pair of switches move in opposite directions depending on the position of the light-receiving spot. An optical position sensor that can obtain a current output, a front circuit section that transmits the output current of the optical position sensor to a subsequent stage, a 7-analog-to-digital conversion section that converts the output of the front circuit section into a digital signal, and an optical position sensor. A switch that allows selection between a first setting in which the sum of a pair of output currents is input to the front circuit section and a second setting in which one output current of one of the optical position sensors is input to the front circuit section. a storage section that stores the output value of the analog-to-digital conversion section as a reference value when the switching section is in the first setting; and a reference value stored in the storage section when the switching section is in the second setting. an impedance variable section that sets the transfer impedance of the pre-circuit section to an optimum value in response to a reference value stored in a storage section and an output value of the analog-to-digital conversion section when the switching section is in the second setting; It is equipped with an arithmetic circuit section that calculates the distance to the detection target based on the ratio of The calculation accuracy is improved by satisfying the configuration and digitizing the calculations in the calculation circuit section.

(Example) As shown in FIG. 1, the output current of PSDI is input to a pre-circuit section 2 that performs amplification. As the output current of PSDl, both electrodes 11a and ll explained in the background technology section are used.
The output current from b is adopted, and the preset switch 8a as a switching section changes the output current of both output currents to +r2 (=
ro) to the pre-circuit section 2, and only one output current 11 is input to the pre-circuit section 2? and the second setting to be input to is alternatively selected. Is the output of front circuit section 2 an analog-to-digital conversion? The output terminal of the analog-to-digital converter 4 is connected to the preset switch 8a.
When the preset switch 8b is connected, and the preset switch 8a is in the first setting, the output of the analog-to-digital converter 4 is input to the storage part 5, and when the preset switch 8a is in the second setting, The output of the analog-digital converter 4 is sent to the arithmetic circuit ff1s3.
It is now entered into The storage unit 5 is usually a ROM such as an EEPROM so that the stored values are retained even after the power is turned off, and the preset switch 8
Writing is performed by operations a and 8 b, and the subsequent data is stored. If the stored value can be erased after the power is turned off, RAM is used as the storage unit 5.
You can also use Based on the stored value in the storage section 5, the control circuit section 7 controls the variable impedance section 6 to set the transfer impedance of the front circuit section 2 to the optimal value. Further, the arithmetic circuit unit 3 calculates the distance to the detection target from the stored value in the storage unit 5 and the output value of the 7-nalog-de-phthal conversion unit 4.

(Operation) The operation will be explained below. Before measuring the insect distance, the preset switch 8a is set to the first setting, and the sum 1 + +I 2 (=ro) of both output currents of the PSD1 is input to the front circuit section 2. At this time, the output of the analog-to-digital converter 4 is input to the storage unit 5 by the preset switch 8b, so if the detection target for which distance measurement is actually performed is placed near the detection distance, the storage unit 5 stores the detection target. A value corresponding to the amount of reflected light received is written as a reference value. In distance measurement, if the preset switch 8a is set to the second setting, only one output current (2) from the PSD1 is input to the front circuit section 2. At this time,
Based on the reference value stored in the recording section 5, the variable impedance section 6 sets i1'll! to the optimum value corresponding to the amount of received light. ! Therefore, the transfer impedance, that is, the gain of the front circuit section 2 has an optimum value. The output of the analog-to-digital converter 4 is input to the arithmetic circuit section 3, and together with the reference value stored in the storage section 5 (i.e., the digital value corresponding to the total current of PSD I), the output is input to the background art section. The distance to the detection target can be determined using the calculation formula explained above.

[Effect of the Invention 1] As described above, the present invention is configured such that the position of the receiving spot of the reflected light on the detection target of the spot irradiated from the light emitting unit to the detection target moves in accordance with the distance to the detection target. In a distance-measuring photoelectric switch that uses triangulation to detect the distance to a detection target based on the position of the light-receiving spot, it is a light that produces a pair of current outputs that change in opposite directions depending on the position of the light-receiving spot. a position sensor, a pre-circuit section that transmits the output current of the optical position sensor to the subsequent stage, an analog-to-digital converter section that converts the output of the pre-circuit section into digital conversion, and a pair of output currents of the optical position sensor. a switching section capable of selectively selecting a first setting for inputting the sum of the sum into the front circuit section and a second setting for inputting one output current of the optical position sensor to the front circuit section; A storage section that stores the output value of the analog-to-digital converter as a reference value when the first setting is set; When the impedance variable section sets the transfer impedance of the section to the optimum value and the switching section is in the second setting, the following is described in 1! The reference value stored in the section and 7
It is equipped with an arithmetic circuit section that calculates the distance to the detection target based on the ratio of the output value of the analog-to-digital conversion section, and since there is only one pre-circuit section, the circuit configuration is simplified. The analog-to-digital conversion section used to optimize the transfer impedance of the front circuit section is also used for distance measurement to digitize the arithmetic circuit section, so linearity is good. In particular, it has the advantage of improved temperature characteristics. This device can perform accurate measuring forceps when there is little variation in the distance to the detection target during distance measurement, and is effective in detecting parts on a manufacturing line.

[Brief explanation of drawings]

FIG. 1 is a block diagram of main parts showing one embodiment of the present invention, and FIG.
The figure is a cross-sectional view showing an optical position sensor used in a chisel type photoelectric switch according to the present invention, and FIG. 3 is a block diagram of main parts showing a conventional example. 1 is an optical position sensor, 2 is a front circuit section, 3 is an arithmetic circuit section,
4 is a 7-analog-to-digital converter, 5 is a storage section, 6 is an impedance variable section, 7 is a control circuit section, and 8a and 8b are preset switches. Agent Patent Attorney Ishi 1) Ai 7 Figure 2 Figure 3

Claims (1)

[Claims] (1) The light-receiving spot position of the reflected light on the detection target of the spot light irradiated from the light emitting unit to the detection target moves in accordance with the distance to the detection target, and the light-receiving spot position of the reflected light on the detection target moves according to the distance to the detection target. A distance-measuring photoelectric switch that detects the distance to a detection target using a distance-measuring method uses an optical position sensor that provides a pair of current outputs that change in opposite directions depending on the position of the light-receiving spot, and an output current from the optical position sensor. an analog-to-digital converter that converts the output of the front circuit to a digital signal; and a first circuit that inputs the sum of the output currents of the pair of optical position sensors to the front circuit. and a second setting for inputting one output current of the optical position sensor to the front circuit section, and a switching section that allows analog-to-digital conversion when the switching section is in the first setting. a storage section that stores the output value of the section as a reference value; and an impedance that sets the transfer impedance of the front circuit section to an optimal value in response to the reference value stored in the storage section when the switching section is in the second setting. a variable section; and an arithmetic circuit section that calculates the distance to the detection target based on the ratio between the reference value stored in the storage section and the output value of the analog-to-digital conversion section when the switching section is in the second setting. A distance-measuring photoelectric switch characterized by comprising: