JPH01118714A - Optical position detection sensor - Google Patents

Abstract

PURPOSE:To quicken response, to enable use in an environment of large temperature variation, and to improve linearity by using a couple of photodiodes which are halved along a diagonal and have mutually symmetrical photodetection areas. CONSTITUTION:The couple of photodiodes PD 11 (11a and 11b) are constituted by dividing a linearly symmetrical photodetection area in a specific shape into two along the diagonal and have the mutually symmetrical photodetection areas. Then when a shield plate 13 which is arranged between a light source 12 and the PDs 11 and has a slit 13a is displaced X, the photodetection quantities of the PDs 11 vary symmetrically. The photodetection outputs of the photodetection quantities are summed up by an adding circuit 16, and the light source 12 is driven through a driving means 21 so that the sum output is an invariably constant value. Consequently, the displacement signal of the shield plate 13 is obtained from the photodetection output of one PD 11 and even if the output of the light source 12 decreases or even if photodetection levels vary owing to temperature variation, the photodetection quantities are invariably constant, so the variation like this is compensated automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an optical position detection sensor that obtains an output corresponding to a change in the position of a shielding plate.

[Prior art and its problems]

(Prior Art) Conventionally, as shown in Japanese Patent Publication No. 39-21006, etc., as an element for detecting the displacement of an object using light,
A circuit using CdS having a symmetrical light receiving area is known. As shown schematically in FIG. 5, the photoconductive material (CdS) in the rectangular light-receiving area is configured as a pair of triangular light-receiving parts 1a and 1b symmetrical with respect to the diagonal, and the X-axis in the figure A slit plate 2 having a slit 2a that moves in the direction
There is a known device in which the light receiving area of each light receiving portion is changed by projecting light from a light source (not shown). As shown in FIG. 6, this displacement detecting element is connected to a bridge circuit having each light receiving part as one side, and by applying a constant voltage to the bridge circuit from the electric current R3, the voltage at both ends of the bridge is adjusted to Position of,
That is, it changes in response to a change in the light receiving area of the two light receiving sections la and lb. Therefore, the displacement of the slit plate 2 can be determined by the voltage across the bridge circuit.

(Problems to be Solved by the Invention) However, according to such a conventional photoelectric displacement detection element, the response speed is extremely slow because CdS is used in the light receiving part, and when the slit plate changes at high speed, It was not possible to obtain a position signal that followed this. Furthermore, CdS has poor temperature resistance and cannot be used in an environment where the temperature changes significantly. Furthermore, since the CdS has a linear light-receiving portion as shown in FIG. 5, there is a problem in that the output may change discontinuously in response to minute displacements of the slit plate.

[Purpose of the invention]

The present invention has been made in view of the problems of conventional optical displacement detection elements, and is a photoelectric sensor that has a fast response, can be used even in environments with severe temperature changes, and has improved linearity. The technical challenge is to obtain a type position detection sensor.

[Structure and effects of the invention]

(Means for Solving the Problems) The present invention is an optical position detection sensor that obtains an output corresponding to a change in the position of a shielding plate, and as shown in FIG. a pair of photodiodes having mutually symmetrical light-receiving areas configured by dividing the light-receiving area into two along a diagonal; a light source that irradiates light to all the light-receiving areas of the pair of photodiodes; and a space between the light source and the pair of photodiodes. A shielding plate that is movable in a fixed direction and has a slit that allows light to pass through, an adder circuit that adds the received light outputs obtained from a pair of photodiodes, and a light source that drives the light source so that the output of the adder circuit is a constant value. The present invention is characterized in that the displacement of the shielding plate is detected by the output of the one photodiode.

(Function) According to the present invention having such characteristics, a pair of photodiodes having mutually symmetrical light-receiving areas are used as light-receiving elements, and the light-receiving area changes depending on the displacement between the light source and the photodiode. A shielding plate is installed. Therefore, the amount of light received by the pair of photodiodes changes symmetrically with respect to the displacement of the shielding plate. However, the light receiving outputs of the amounts of light received by these photodiodes are added together by an adding circuit, and the light source is driven via a driving means so that the added output is always a constant value. In this way, a displacement signal of the shielding plate can be obtained from the light reception output of either one of the photodiodes. Even if the received light level changes due to a drop in the output of the light source or changes in temperature, etc., the amount of received light is always driven to a constant value, so such changes are automatically compensated for. .

(Effects of the Invention) As described above, according to the present invention, since the response speed of the photodiode is extremely fast compared to CdS, it is possible to obtain a position detection sensor having extremely fast response compared to conventional displacement detection elements. can. Further, since the light receiving output is controlled to be always constant, the position detection sensor can have excellent environmental resistance. Furthermore, unlike CdS, the light-receiving areas of the pair of photodiodes are uniformly structured, so the output can accurately follow even minute displacements of the shielding plate, which has the effect of improving linearity. can get.

[Explanation of Examples]

FIG. 1 is a circuit diagram showing the overall configuration of an optical position detection sensor according to an embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of a photodiode thereof. In this embodiment, as shown in FIG. 2, the photodiode is constructed in a rectangular shape and consists of a pair of photodiodes 11a and 11b having mutually symmetrical light receiving areas separated by diagonal lines. As shown in FIG. 1, these photodiodes 11a and 11b
A light source, for example, a light emitting diode 12, which can irradiate light onto the front surface of the two photodiodes at a position facing each other.
0 light emitting diode 12 is a photodiode l
It is fixed at a fixed position along with la and llb, and may be composed of a plurality of light receiving diodes in order to irradiate all light receiving areas with light. A shielding plate 13 is placed between the light emitting diode 12 and the photodiodes lla and llb.
will be established. As shown in FIG. 2, the shielding plate 13 is configured to be movable in the X-axis direction, and is provided with a slit 13a parallel to an axis perpendicular to the moving direction, that is, the Y-axis.

The displacement of this shielding plate 13 in the X direction causes two photodiodes 11a.

The light-receiving area irradiated to 11b changes, and the light-receiving output changes. Here, it is assumed that the photodiode 11 has a symmetrical shape along a center line parallel to the Y-axis. These photodiodes 11a.

11b is an operational amplifier 14.1 for converting its output.
5. The output Va of the operational amplifier 14 and the output Vb of the operational amplifier 15 are provided to an adder circuit 16. Here, in order to configure the adder circuit using a single power supply, the adder circuit is realized using two operational amplifiers 17 and 18. That is, the output terminals of the operational amplifiers 14 and 15 are connected to resistors R1 and R2 having the same resistance value, respectively, and the other ends of these resistors are commonly connected and connected to the inverting input terminal of the operational amplifier 17. A voltage divided from a reference voltage source Vr by resistors R3 and R4 is applied to the non-inverting input terminal of the operational amplifier 17. A feedback resistor R5 is connected between the output of the operational amplifier 17 and the inverting input terminal. Here resistance R1
, R2, R4, and R5 have the same resistance value Ra, and the resistor R3 has the resistance value Ra/2 of A.

In this way, the output of the operational amplifier 17 will have 2Vr-(Va+
Vb) is obtained, and this voltage is applied to the inverting input of the operational amplifier 18 via the resistor R6. Operational amplifier 1
A reference voltage source of voltage Vr is connected to the non-inverting input terminal of 8, and a resistor R7 is connected between its output and the inverting input terminal.

Here, it is assumed that the resistance values of resistors R6 and R7 are the same. Then, from the output of the operational amplifier 18, the operational amplifier 14.1
A voltage output Va+Vb is obtained by adding the outputs of 5. This voltage output is applied to the operational amplifier 1 via the resistor R8.
It is applied to the inverting input terminal of 9. A voltage Vr is applied to the non-inverting input terminal of the operational amplifier 19 from a reference voltage source,
A capacitor C to prevent oscillation is connected between the output and the inverting input terminal.
1 is connected.

This output is then applied to the non-inverting input terminal of operational amplifier 20. The output of operational amplifier 20 is applied to the base of transistor Tri. The transistor Tr1 has a light emitting diode 12 and a resistor R9 connected in series, and one end of the resistor R9 is connected to the inverting input terminal of the operational amplifier 20. The operational amplifier 20 controls the current value of the light emitting diode 12 to a given voltage level via the transistor Tri. Here, the operational amplifiers 19 and 20 and the transistor Tri constitute a driving means 21 that controls the light emission intensity of the light emitting diode 12 so that the output of the adder circuit 16 becomes equal to the reference voltage Vr (Vr = Va + Vb).

Next, the principle of position detection in this embodiment will be explained. Third
In the figure, the outputs of the two photodiodes 11a and llb can be considered to be proportional to the light receiving area. Therefore, as shown in FIG.
The center position of a is X.

If the lengths of the two photodiodes in the vertical and horizontal directions are A and B, respectively, the two photodiodes lla and l
The light receiving area al+t)I of lb is given by the following equations.

(k+ is a constant) And the output Va of the operational amplifier 14.15 which converted the light reception signals of the two photodiodes lla and llb into voltage,
Vb is given by the following equations.

Va = Ma, Vb = Mb.

(M is a constant) Here, if we calculate the ratio of voltage Va+Vb and vb, Vb
b, x Va +Vb a++blB Therefore, the sum of the output voltages of operational amplifiers 14.15 Va+vb
By keeping the voltage constant, the output vb of one operational amplifier, for example, the operational amplifier 15, is proportional to the displacement X of the shield vi13, and the position of the shield plate 13 can be detected based on this voltage.

In the first embodiment described above, the diagonal of the rectangular photodiode is divided to form a photodiode having two light-receiving areas. However, when the shielding plate rotates, the light-receiving area of the photodiode is separated from the center line. It can also be configured in a fan shape that is symmetrical with respect to the line. FIG. 4 is a diagram showing the configuration of such a photodiode, in which a sector-shaped photodiode 31 is divided into photodiodes 31a and 31b having two light-receiving areas. At this time, the shielding plate 32 has the same center as the photodiode 31, is rotatable, and has a rectangular slit 32a in the radial direction. Now, the distance f(θ) to the center of the division curve Ld of the photodiode 31 is determined by using the radius of the inner and outer circles as rl+rt, respectively, and the light receiving area for each of the photodiodes 31a and 31b when the shielding plate 32 rotates. Assuming that a Z + b2 respectively, if the slit is sufficiently thin, a! + b2 is expressed by the following formula.

Set a2=ka(f(θ)-r,) bg=to 3(rz-f(θ)) arimeni. Here, by substituting r(θ) = rt and f(δ) = r2, f(θ) is given by the following equation, where k4 is 1/δ.

θ f(θ) ” (rt r+) +rtδ The other configurations are the same as those in the previous embodiment. In this way, the two light receiving portions of the photodiode 31 are divided by the division curve Ld expressed by the polar coordinate equation f(θ). By dividing the area, a voltage output proportional to the rotation angle can be obtained.

In the first embodiment described above, the adder circuit 16 is constructed using two operational amplifiers, but when using symmetrical positive and negative power supplies, the outputs of the operational amplifiers 14 and 15 are directly added to the driving means 21. Needless to say, it is possible to make it so that it is given to

Further, the photodiode according to the present invention is not limited to rectangular or sector-shaped photodiodes, but can be applied to photodiodes of various shapes that are symmetrical about a center line.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an optical position detection sensor according to an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of the photodiode, FIG. 3 is a diagram showing the light-receiving area of the photodiode, and FIG. FIG. 4 is a diagram showing the light-receiving area of the photodiode according to the second embodiment, FIG. 5 is a schematic diagram showing the configuration of a conventional photoelectric displacement sensor, and FIG. 6 is a diagram showing its driving circuit. 11a, Ilb, 31a, 31b --- Photodiode 12--Light emitting diode 13.32--
-・Shielding plate 14, 15.1? ,,18,19゜20
・−・−Operation amplifier 16−・−Adder circuit 2
i ---------One drive means patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (and one other person) X Figure 3 Figure 5 Figure 6

Claims (1)

[Claims] (1) a pair of photodiodes each having a mutually symmetrical light-receiving area formed by dividing a line-symmetric predetermined shape light-receiving area into two along a diagonal line; and a light source that irradiates light to all the light-receiving areas of the pair of photodiodes. , a shielding plate that is movably arranged in a fixed direction between the light source and the pair of photodiodes and has a slit that transmits light; an adding circuit that adds the received light outputs obtained from the pair of photodiodes; and the adding circuit. An optical position detection device comprising: driving means for driving the light source so that the output of the circuit becomes a constant value, and displacement of the shielding plate is detected by the output of the one photodiode. sensor.