JPH05256608A - Position detecting device - Google Patents

Abstract

PURPOSE:To measure a position with precision even though a dark current fluctuates with temperature change or an output varies corresponding to standard voltage variation by deducting the output of a semiconductor position detecting element when an luminous element is turned off from the output when the luminous element is turned on so as to compute a position signal. CONSTITUTION:When measuring is performed, the digital values of the respective terminal outputs of a semiconductor position detecting element 1, under conditions that a luminous element 2 is not turned on, are read and stored in a memory 9. Almost simultaneously the digital values of the respective terminal outputs of the semiconductor position detecting element 1, under the conditions that the luminous element 2 is turned on, are read and stored in the memory 9. An arithmetic means 8 deducts the terminal output obtained when the luminous element is not turned on from the terminal output obtained when the luminous element is turned on so as to compute a position signal after an arithmetic process such as a normalizing computing. The terminal output, when the luminous element is not turned on, is an output equivalent to a dark current, and the dark current is eliminated by this processing and the variable component of a measured value caused by the variation of a standard voltage is also eliminated. The variation of the measured value, caused by the shift of a luminous center, is not allowed to occur either, since the luminous amount of the luminous element 2 is not controlled so as to increase or decrease.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device using a semiconductor position detecting element (PSD).

[0002]

2. Description of the Related Art As a conventional position detecting device using a semiconductor position detecting element, there is one shown in FIGS.

In the conventional device shown in FIG. 5, a semiconductor position detecting element 21 and a light emitting element 22 such as a light emitting diode are arranged to face each other. Usually, the semiconductor position detecting element 21 is attached to a fixed member, and the light emitting element 22 is attached to a movable member that is displaced by a load or the like. The light emitted from the light emitting element 22 is focused in a pinpoint shape by a lens 23 or a slit provided in front of the light emitting element 22 and applied to the light receiving surface of the semiconductor position detecting element 21.

In the semiconductor position detecting element 21, when the light receiving surface is irradiated with pinpoint light with a bias voltage applied to its common electrode, the distance from each end electrode to the irradiation spot is increased. Inversely proportional amount of current (photocurrent)
I ₁ and I ₂ flow. Photocurrent I ₁ , I from each end electrode
₂ is converted into voltage signals V ₁ and V ₂ by current / voltage converters 24 and 25, respectively. These voltage signals V ₁ , V
₂ is introduced into the subtractor 26 to generate a difference signal (V ₁ −V ₂ ), and this difference signal is taken out as a position signal of the irradiation spot.

Both voltage signals V ₁ and V ₂ are added to the adder 27.
Are added to each other, and the sum signal (V ₁ + V ₂ ) is input to the light emission driver 28 as a control signal, and the light emission amount of the light emitting element 22 is controlled so that the sum signal becomes constant.

In the example of FIG. 5, the difference signal (V ₁ -V ₂ ) which is the output of the subtractor 26 is taken out as a position signal, but the output V of one current / voltage converter 24 (25) is output.
₁ (V ₂ ) may be taken out as a position signal as it is.

In the conventional device shown in FIG. 6, a constant current circuit 29 is provided on the common electrode side of the semiconductor position detecting element 21. Although the total amount (I ₁ + I ₂ ) of the photocurrents I ₁ and I ₂ , which are the end output of the semiconductor position detecting element 21, flows through the common electrode,
When the total amount of photocurrent changes, the constant current circuit 29 outputs a detection signal according to the changed amount. This detection signal is input to the light emission driver 28 as a control signal, and the light emission amount of the light emitting element 22 is controlled so that the total amount of photocurrent in the semiconductor position detection element 21 becomes constant. In this example, the output V _{1 of} one of the current / voltage converters 24 is directly extracted as a position signal.

[0008]

By the way, the current extracted from each end electrode of the semiconductor position detecting element 21 is
A dark current that does not depend on light irradiation is included, and the dark current increases or decreases mainly in accordance with temperature changes.

In the case of the conventional device shown in FIG. 5, the dark current components contained in the end output of the semiconductor position detecting element 21 are canceled by subtraction in the subtractor 26, and are almost not contained in the position signal. In the adder 27, the dark current components are added together. The light emission amount of the light emitting element 22 is
Since the signal is controlled by the signal including the dark current, it is increased or decreased more than necessary, which causes a change in the output of the semiconductor position detecting element 21 that is unrelated to the position change of the irradiation spot, resulting in a measurement error. Generate.

Next, in the conventional device of FIG. 6, since the light emission amount of the light emitting element 22 is controlled by the total amount of current flowing through the semiconductor position detecting element 21, the influence of the dark current described above can be eliminated. When the reference voltage applied to the circuit 29 changes, the bias voltage applied to the semiconductor position detecting element 21 also changes, and accordingly, the semiconductor position detecting element 2 changes.
The output of 1 fluctuates, causing a measurement error.

Further, in the light emitting diode which is the light emitting element 22 used in any of the conventional devices, the emission center thereof tends to move as the amount of emitted light increases or decreases. Here, as in each conventional example, in the case where the feedback loop is formed so that the light emission amount of the light emitting diode is controlled by the output of the semiconductor position detection element 21, the light emission amount of the light emitting diode increases or decreases. Along with this, the emission center of the light emitting diode moves, which causes a measurement error.

In view of the above conventional problems, it is an object of the present invention to eliminate the measurement error caused by the dark current, the fluctuation of the reference voltage, and the increase / decrease of the light emission amount of the light emitting element, and improve the measurement accuracy. ..

[0013]

In order to achieve the above-mentioned object, the present invention is directed to a semiconductor position detecting element and a semiconductor position detecting element facing each other, as shown in FIG. In the position detecting device having the light emitting element, an A / D converter for converting each end output of the semiconductor position detecting element into a digital amount, and each end of the semiconductor position detecting element when the light emitting element is not lit and when it is lit. Reading means for reading the partial output through the A / D converter, lighting switching means for switching lighting / lighting off of the light emitting element in association with the reading operation of the reading means, and non-lighting and lighting times read by the reading means. A memory that stores the output of each end of the semiconductor position detecting element in the above, and a calculation that calculates the position signal by subtracting the output of each end when the lamp is not lit from the output of each end when the lamp is lit It is that a stage.

[0014]

In the above structure, the digital value of the output of each end of the semiconductor position detecting element is read by the reading means and stored in the memory while the light emitting element is not lit at the time of measurement. In the state where is turned on, the digital value of each end output of the semiconductor position detecting element is read and stored in the memory. The calculating means subtracts the edge output when the light emitting element is turned off from the edge output when the light emitting element is turned on, and performs an arithmetic process such as a normalization operation,
Calculate the position signal. The end output when the light emitting element is not lit is
The output corresponds to the dark current, and the dark current component is removed by the above-described processing, and the variation of the measured value due to the variation of the reference voltage is also removed. Further, since the light emission amount of the light emitting element is not controlled to increase or decrease, there is no movement of the light emission center, and the measurement value does not change due to the movement of the light emission center.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on the embodiments shown in FIGS. 2 and 3 show the first embodiment of the present invention.
2 is a circuit block diagram showing the configuration of the apparatus, and FIG. 3 is a flow chart showing the operation thereof.

As shown in FIG. 2, the position detecting device according to this embodiment includes a semiconductor position detecting element 1 and a light emitting diode 2 for irradiating the light receiving surface of the semiconductor position detecting element 1 as in the conventional example described above. And a lens 3 for narrowing the light emission of the light emitting diode 2 in a pinpoint manner. Further, the semiconductor position detecting element 1 is usually attached to a member on the fixed side,
The point that the light emitting diode 2 is attached to a movable member that is displaced by a load or the like is the same as in the conventional example.

A reference voltage is applied as a bias voltage to the common electrode of the semiconductor position detecting element 1, and two analog switches 4 and 5 and a single current / voltage converter are provided on the photocurrent output side. 6, a single A / D converter 7, C
A PU 8 and a memory 9 are provided.

Both analog switches 4 and 5 are for selectively inputting the respective end outputs I ₁ and I ₂ of the semiconductor position detecting element 1 to the current / voltage converter 6, and both analog switches 4 and 5 are provided. By this switching operation, one end electrode of the semiconductor position detecting element 1 is connected to the current / voltage converter 6, and the output of the other end electrode is grounded. The current / voltage converter 6 has one analog switch 4
The photocurrent I ₁ (I ₂ ) from any one of the end electrodes input through (5) is converted into a voltage signal V ₁ (V ₂ ). A
The / D converter 7 is composed of a voltage / frequency converter in this example, and its output V _{1 is} provided at the subsequent stage of the current / voltage converter 6.
Convert (V ₂ ) into a digital quantity. The CPU 8 reads the output of the A / D converter 7 in connection with the switching control of the analog switches 4 and 5, and sequentially stores the digital value in the memory 9 as well as the memory 9 in the memory 9 as described in the flowchart described later. The stored digital value is arithmetically processed to calculate the position signal, and functionally operates as the reading unit and the arithmetic unit shown in the corresponding diagram of the claims of FIG.

On the other hand, the light emitting diode 2 is connected to a trimmer 10 for adjusting the amount of emitted light and a switching transistor 11. The switching transistor 11 is a lighting switching means for switching between lighting and extinguishing of the light emitting diode 2, and is switching-controlled by the CPU 8 in connection with the reading operation.

Next, the operation of the above configuration will be described with reference to the flowchart of FIG. A series of operations includes (A) a routine when the light emitting diode 2 is not lit, (B) a routine when it is lit, and (C) a subsequent calculation / output routine.

After setting the load on the movable member of the apparatus,
When it is started, first, the routine (A) for non-lighting is started, and the output of each end of the semiconductor position detecting element 1 is read with the light emitting diode 2 turned off. That is, under the condition that the switching transistor 11 is off, in step S1, both analog switches 4 and 5 are set to be switched so that one end electrode in the illustrated example, which is the upper end electrode, is connected to the current / voltage converter 6. Then, in step S2, the voltage signal Va ₁ corresponding to the output of the upper end electrode is read as a digital amount through the A / D converter 7 and stored in the memory 9. Next, in step S3, both analog switches 4 and 5 are switched to the other, and the output of the lower end electrode is input to the current / voltage converter 6, and step S4
Then, the voltage signal Va ₂ indicating the end output is read as a digital amount and stored in the memory 9. In this way
The end output of the semiconductor position detecting element 1 is read one after another. At this time, the semiconductor position detecting element 1 is read.
Since the light emitting diode 2 is not lit on the front surface of, the read digital value corresponds to the current value of the dark current flowing through the semiconductor position detecting element 1.

The routine from step S5 is a routine for lighting (B). In step S5, first, the switching transistor 11 is turned on to light the light emitting diode 2. In the next step S6, both analog switches 4 and 5 are switched to one so that the output of the upper end electrode is input to the current / voltage converter 6, and in step S7,
The voltage signal V ₁ indicating the output of the upper end electrode is read as a digital amount through the A / D converter 7 and stored in the memory 9. Next, in step S8, both analog switches 4 and 5 are switched to the other, and the output of the lower end electrode is input to the current / voltage converter 6, and step S9
Then, the voltage signal V ₂ indicating the output is read as a digital amount and stored in the memory 9. In step S10,
The light emitting diode 2 is turned off. In the routine so far,
Acquisition of the non-lighted output and the lighted output required for calculation is completed.

Steps S11 and thereafter are routines for the calculation based on the fetched digital values and the output of the calculation results. In step S11, each end output V at the time of lighting is calculated.
₁ (V ₂ ) to the output V when the corresponding end is not lit
The position signal is calculated by subtracting a ₁ (Va ₂ ) and performing a normalization operation on the output difference. Position signal is P,
Expressing the processing as an expression, P = {(V ₁ −Va ₁ ) − (V ₂ −Va ₂ )} / {(V ₁ −Va ₁ ) + (V ₂ −Va ₂ )} ... (1 ) Becomes. Here, the outputs Va ₁ and Va ₂ at the time of non-lighting correspond to the dark current, and therefore, by subtracting this output, only the output (photocurrent amount) generated by the light irradiation is extracted. Further, when the reference voltage fluctuates, the fluctuation occurs in a cycle longer than the measurement cycle, and the output V
Since both a ₁ and Va _{2 and} the outputs V ₁ and V ₂ at the time of lighting change in level, the fluctuations are almost canceled by the subtraction between both outputs. In step S12, this calculation result is displayed on a display, or in some cases, converted into an analog signal and output to another device, and one measurement cycle ends. The time required for this is about 10 ms.

The calculation in step S11 is not limited to the above, and as shown in the following equation (2), each end output V ₁ (V ₂ ) at the time of lighting is changed to the corresponding end output. The output Va ₁ (Va ₂ ) during lighting may be subtracted, and the position signal may be calculated as a logarithmic function of the ratio of the output differences.
That is, the position signal P becomes _{P = log {(V 1 -Va} 1) / (V 2 -Va 2)} ............... (2).

FIG. 4 is a circuit block diagram showing the configuration of the position detecting device according to the second embodiment of the present invention. In this embodiment, a pair of current / voltage converters 61 and 62 for converting the respective outputs I ₁ and I ₂ into voltage signals V ₁ and V ₂ are provided to the respective end electrodes of the semiconductor position detecting element 1 and the respective currents. / Voltage converter 61,
A pair of A / s for converting the outputs V ₁ and V ₂ of 62 into digital quantities
D converters 71 and 72 are provided, and both A / D converters 7 are provided.
The outputs of 1, 72 are introduced into the CPU 8. The other parts are the same as those of the first embodiment, and corresponding parts are designated by the same reference numerals, and detailed description thereof will be omitted.

Further, the CPU 8 operates in substantially the same manner as that of the first embodiment, and the A on the side corresponding to each end output of the semiconductor position detecting element 1 in the state where the light emitting diode 2 is turned off. The data is read via the / D converter 71 (72) and stored in the memory 9, and then the output of each end of the semiconductor position detecting element 1 is read and stored in the memory 9 while the light emitting diode 2 is turned on. The output value stored in the memory 9 is arithmetically processed by the above-described equation (1) or (2) to calculate the position signal.

In the embodiment, the output of the semiconductor position detecting element 1 is measured when the light emitting element is not lit, and then the light emitting element is lit and the output of the semiconductor position detecting element 1 is measured. The measurement may be performed first, or if the measurement is repeated, reduce the number of times of measurement during non-lighting.
The idle time of the CPU 8, for example, when the position signal is output may be used at intervals of about a second to perform the measurement in the non-lighted state.

[0028]

According to the present invention, since the position signal is calculated by subtracting the output when the light emitting element is turned on from the output of the semiconductor position detecting element when the light emitting element is turned on, the dark current increases or decreases depending on the temperature change. Even if the output voltage fluctuates or the output fluctuates due to fluctuations in the reference voltage, the fluctuations are quantitatively removed, and high-precision measurement is possible without being affected by changes in measurement conditions. ..

Further, since the light emission amount of the light emitting element is not feedback-controlled and the light emitting element is simply turned on / off, the light emitting center of the light emitting element does not move. From this point as well, Highly accurate measurement becomes possible.

Further, the influence of the fluctuation of the reference voltage can be eliminated by the arithmetic processing of the output of the semiconductor position detecting element.
Since it is not necessary to use a highly accurate and expensive reference power supply circuit, the cost can be reduced.

In addition, since the light emitting element needs to be lighted for a short time only when necessary, it consumes less power and is advantageous in battery driving.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to the scope of the claims of the present invention.

FIG. 2 is a circuit block diagram of the position detection device according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of the above embodiment.

FIG. 4 is a circuit block diagram of a position detection device according to a second embodiment of the present invention.

FIG. 5 is a circuit block diagram of a conventional position detecting device.

FIG. 6 is a circuit block diagram of another conventional position detecting device.

[Description of Reference Signs] 1 semiconductor position detecting element 2 light emitting diode (light emitting element) 6 current / voltage converter 7 A / D converter 8 CPU (reading means, computing means) 9 memory 11 switching transistor (lighting switching means)

Claims (1)

[Claims] 1. A position detecting device having a semiconductor position detecting element and a light emitting element arranged to face the semiconductor position detecting element, wherein A / D conversion for converting each end output of the semiconductor position detecting element into a digital amount. And a reading means for reading each end output of the semiconductor position detecting element through the A / D converter when the light emitting element is not lit and when the light emitting element is lit, and turning on / off the light emitting element in association with the reading operation of the reading means. From the lighting switching means for switching between, the memory for storing each end output of the semiconductor position detecting element read by the reading means during non-lighting and during lighting, and each end output during lighting stored in the memory. A position detecting device comprising: a calculating unit that calculates a position signal by subtracting each end output when the lamp is not lit.