JPS6234009A - Optical displacement meter - Google Patents

Abstract

PURPOSE:To measure the distance from a measuring object or the displacement quantity thereof without providing a divider, by constituting the titled displacement meter of a timing signal generation circuit, a first amplifying circuit, an integrating circuit, a second amplifying circuit and a comparing circuit. CONSTITUTION:Laser beam is projected to a measuring object and the reflected beam is formed into an image on a beam receiving element 5 by an image forming means. One of the output of the beam receiving element 5 is amplified by a first amplifying circuit A1 and integrated by the integrating circuit 6 discharged by a timing generation circuit 7. The output of the circuit 6 and the output obtained by amplifying the other output of the element 5 by a second amplifying circuit A2 are inputted to a comparing circuit 8. The circuit 8 compares the inputs to output a HIGH('H') or LOW('L') output signal. If the time constant of the circuit 6 is made constant, the pulse width of the 'H' output signal is proportional to the value obtained by subtracting a definite value from the ratio of two output currents of the element 5. Therefore, this pulse width is measured to make it possible to calculate the distance from a measuring object or the displacement quantity thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical displacement meter that projects a light beam onto an object to be measured and uses the reflected light to measure the distance to the object or the amount of displacement thereof.

[Conventional technology]

The following types of optical displacement meters have been used in the past. As shown in FIG. 8, a light spot is formed on the measurement object 3 by the light projecting element 1 and the light projecting lens 2, and this light spot is imaged as a light receiving point on the light receiving element 5 using the light receiving lens 4. . When the measuring object 3 changes its position in the figure and moves as s-4t-+u, this light-receiving point moves on the light-receiving element 5 as s'-<t'-hu' accordingly. That is, the distance to the measurement object 3 is determined not by a change in the amount of light received, but by knowing the position of the light receiving point on the light receiving element 5.

This light receiving element 5 includes P which is a -dimensional position detecting element.
S D (Position 5 sensitive D
evice) is commonly used. Then, two types of output currents 11 and 12 are output from this light receiving element 5,
These are input to a subtracter 14 and an adder 15, respectively,
(v.

−1/, ), (v, +v2) output. After this, the divider 16 calculates (■l V2) /
By being converted to ('/I +V2) output,
A voltage value corresponding to the distance to the measurement target 3 can be obtained regardless of the amount of received light.

The relationship between the output voltage of the divider 16 and the distance to the object to be measured 3 is proportional as shown in FIG.

The distances s, t, and u to the measurement object 3 are determined corresponding to the outputs S", t", and U" of the divider 16. Therefore,
By providing a comparator 17 (see FIG. 8) after the divider 16, it is possible to determine whether the object to be measured 3 is closer or farther than a certain set distance X. That is,
In the figure, if the threshold value y is set by the threshold value setting circuit 18 (see FIG. 8), it is possible to determine whether the object to be measured 3 is near or far based on the set distance X.

[Problem that the invention seeks to solve]

However, the conventional optical displacement meter using the divider 16 has the following problems. The divider 16 has various drawbacks such as poor temperature characteristics, narrow range, slow response speed, and poor linearity. Therefore, the use of the divider 16 has a great effect on the distance measurement accuracy, and there is a problem in that the optical displacement meter as a whole cannot obtain a measurement accuracy higher than that obtained by the divider 16.

This invention has been made in view of the above-mentioned problems, and an object thereof is to provide an optical displacement meter that can measure the distance to an object to be measured or the amount of displacement of the object to be measured without using a divider. do.

[Means for solving problems]

A specific means for solving the above problem is to project a light beam onto the object to be measured, use an imaging means to form an image of this reflected light onto a light receiving element, and use the output of the light receiving element to create a connection between the object and the object to be measured. An optical displacement meter that measures distance or displacement includes a timing signal generation circuit that outputs a timing signal, a first amplifier circuit that amplifies the output of one of the light receiving elements, and an output of the first amplifier circuit. an integrating circuit that integrates and discharges according to the timing signal of the timing signal generating circuit; a second amplifier circuit that amplifies the other output of the light receiving element; and inputs both outputs of the integrating circuit and the second amplifier circuit. and a comparison circuit, and the measurement is performed based on the output of the comparison circuit.

[For production]

Since this invention employs the above-mentioned means, one of the two currents generated in the light receiving element is converted into a voltage by the first amplifier circuit and amplified, and then integrated by the integrating circuit. Ru. In this case, a timing signal, which is a discharge signal, is input from the timing signal generating circuit to the integrating circuit, and the integrating capacitor repeats charging and discharging based on this signal. Further, the other current is converted into a voltage by the second amplifier circuit and then amplified. This amplified voltage value and the integral value are compared, and IIIG) I (hereinafter "H'
The comparator circuit outputs a LOW (hereinafter referred to as "L") output signal.

The pulse width T of the “H” output signal from this comparison circuit is:
The time constant of the integrator circuit is the two currents generated from the CR1 photodetector, il+it, the gain of the first amplifier circuit is A, and the second
If the gain of the amplifier circuit is KA (K>1), then T=CR(KA iz /A i 1)=CRK (
iz /it 1/K), and if the time constant CR of the integrating circuit is kept constant, the two currents of the light receiving element will be 41. izO
It is proportional to the ratio minus a constant value. therefore,
By measuring the pulse width T of the "H" output signal from this comparison circuit, the distance to the object to be measured or the amount of displacement of the object to be measured can be determined. However, in this case, it is necessary to select the light receiving range and gain K of the light receiving element so that the pulse width T of the "H" output signal from the comparator circuit does not become negative.

〔Example〕

The optical displacement meter according to the present invention will be described in detail based on two embodiments below. Note that the same parts as those in the prior art are given the same symbols. First, a first example will be described.

As shown in FIG. 2, a light beam emitted from a light projecting element 1 is projected onto a measuring object 3 by a light projecting lens 2 to form a light spot. This light spot is imaged as a light-receiving spot on the light-receiving element 5 using the light-receiving lens 4. This light receiving point is
When the measurement object 3 moves from S → t → U in the same figure,
Accordingly, it moves as S''-t''-U''. This light receiving element 5 uses a PSD.

As shown in Fig. 1, when the measurement object 3 is at position S (see Fig. 2), its light receiving point S° is at PS in the figure.
Located in the upper part of D5. As described above, when the measurement object 3 approaches this optical displacement meter from the above-mentioned position, the light receiving point moves downward on the PSDS in the figure accordingly.

In this case, when the measurement object 3 is at the position S, the currents i,, i2 (11 is P
In the diagram of SD5, the current output from the upper end and 12 is the current output from the lower end), the distance from the lower end to the light receiving point S' is 18, and the distance from the upper end to the light receiving point S° is If the distance is 12, then t, :12==1. :l□. Therefore, as described above, if the ratio of these two currents can be determined, the distance to the object to be measured and the amount of displacement thereof can be measured.

The output current i of the PSD 5 is amplified and converted into a voltage by the first amplifier circuit A1, and becomes an output signal a. On the other hand, the output current 12 of the PSD 5 is amplified by the second amplifier circuit A2 and converted into a voltage, which becomes an output signal S.

Note that, assuming that the gain of the first amplifier circuit A+ is A, the gain of the second amplifier circuit A2 is KA (K>1). The signal a is input to an integrating circuit 6. This integrating circuit 6 is the third
It has a circuit configuration as shown in the figure. Signal a is input to the positive terminal of OP amplifier 61, and the negative terminal is grounded via resistor R3. This OP amplifier 61 is a capacitor CI
has been given negative feedback by. A switch 62 that opens and closes in response to a second timing signal T2 from the timing signal generation circuit 7 is connected to both ends of the capacitor CI. That is, the switch 62 receives the second timing signal T2.
conducts and discharges the capacitor C1.

The output signal C (see FIG. 1) of the integrating circuit 6 is input to the negative terminal of the comparing circuit 8. The above-mentioned signal is inputted to the positive terminal. Comparison circuit 8 compares the input again and outputs an "H" or "L" signal. The output signal d of this comparison circuit 8 is AN
It is input to D gate 9. Since the other input of the AND gate 9 is the first timing signal T1 from the timing signal generation circuit 7, when the output signal d of the comparator circuit 8 is "H", the AND gate 9 receives the "H" signal e (the "H" first signal T1). 1 timing signal T
, ) is output.

The output signal e of this AND gate 9 is the CK of the counting circuit 10.
(clock) terminal. RE of counting circuit 10
A timing signal generation circuit 7 is connected to the S (reset) terminal.
A second timing signal T2 is inputted from.

This second timing signal T2 is the same as the discharge signal to the integrating circuit 6. The counting signal of the counting circuit 10 is D
- It is input to the A converter 11 and converted into an analog signal. This analog signal is input to the sample and hold circuit 12. The sample and hold circuit 12 performs sampling using the third timing signal T3 of the timing signal generation circuit 7, and holds the value of the analog signal.

Next, the operation of the optical displacement meter having such a circuit configuration will be explained based on waveform diagrams. The alphabets used in the waveform diagrams correspond to the alphabets of the signals in each part of FIG. 1. As shown in Figure 4,
The output signal a of the first amplifier A, which has a gain A, is Ai,V
It is. Further, the output signal of the second amplifier A2 having a gain KA is KAi,V. On the other hand, the first timing signal T of the timing signal generation circuit 7 is a continuous pulse signal, and a pulse of the second timing signal T2 is output every seven pulses of the first timing signal T1. The third timing signal T3 has the same period as the second timing signal T2 and is output two pulses earlier.

When the integrating circuit 6 receives the output signal a, the integrating capacitor CI (see FIG. 3) charges. Then, as shown in FIG. 4(C), the output signal C of the integrating circuit 6 causes the integrating capacitor C8 to be discharged by the second timing signal T2 of the timing signal generating circuit 7. As shown in the figure (dl), the output signal d of the comparator circuit 8 rises when the output signal C of the integrating circuit 6 falls below KAi2V due to discharge.Then, the charging of the integrating capacitor C1 progresses, and the output signal of the integrating circuit 6 increases. When signal C exceeds KAizV, output signal d
falls down. AND gate 9 detects that this output signal d is “H”.
”, the first timing signal T of the timing signal generation circuit 7 is inputted and output as is.Counter circuit 1
0 counts the pulses of this first timing signal T1, and D
- Input to A converter 11. D-A converter 11
converts this input into an analog signal and inputs it to the sample and hold circuit 12.

The sample and hold circuit 12 samples and holds the voltage value when the timing signal generation circuit 7 outputs a pulse of the third timing signal T3.

This voltage value is proportional to the value obtained by subtracting a constant value from the ratio of the two currents of the PSD 5, 1+/12. Therefore, i, /i2 can be determined from this voltage value, and the distance to the object to be measured or the amount of displacement of the object to be measured can be determined.

That is, in FIG. 1, when the light receiving point is near the upper end of the PSD 5 (when the distance to the object to be measured is long), the current i from the upper end of the PSD 5 increases, while the current 12 becomes smaller. Therefore, as shown in FIG. 5, the integrating capacitor C, (see FIG. 3) of the integrating circuit 6 is charged in a short time. As a result, the pulse width of the output signal d of the comparison circuit 8 becomes shorter. Therefore, to ND gate 9
The output signal e outputs only a few pulses. Due to this small number of output pulses, the output of the sample-and-hold circuit 12 has a very large 11/iz, thus indicating that the object to be measured is far away.

On the other hand, in Fig. 1, when the light receiving point is near the lower end of the PSD 5 (when the distance to the measurement target is short)
, the current 11 from the top of the PSD 5 becomes smaller,
On the other hand, the current 12 increases.

Then, as shown in FIG. 6, the integrating capacitor C+ (see FIG. 3) of the integrating circuit 6 is charged over a long period of time. As a result, the pulse width of the output signal d of the comparator circuit 8 becomes longer. Therefore, the output signal e of the AND gate 9 outputs many pulses. Due to this large number of output pulses, the output of the sample and hold circuit 12 is very small (11/12).
This indicates that the measurement target is located nearby.

Next, a second example will be described. This example is
In the first embodiment described above, since the correlation between the distance or displacement with respect to the measurement object 3 (see FIG. 2) and the position of the light receiving point of the light receiving element 5 is not linear, the output signal d of the comparator circuit 8 The purpose of this invention is to solve the difficulty of determining the distance or displacement from the obtained measurement value since the pulse width of the measurement object 3 does not have a linear relationship with the distance or displacement.

As shown in FIG. 7, the difference from the block diagram of the first embodiment is that the input side of the third amplifier circuit A3 is connected between the photodetector (PSD) 5 and the second amplifier circuit A2, and , an adder 13 is added between the first amplifier circuit A and the integrating circuit 6, and the output side of the third amplifier circuit A3 is connected to the adder 1.
This is the point connected to 3. With this configuration, the third
The amplification factor of the amplifier circuit A is determined by the measurement target 3 and the light receiving element 5.
The above objective can be achieved by selecting such that the correlation between the upper light receiving points is linear.

In these embodiments, a PSD is used as the light receiving element 5, but the present invention is not limited to this. For example, the same effect can be obtained even if a two-split photodiode is used instead.

Further, in these embodiments, the D-A converter 1
After step 1, a sample bold circuit 12 was installed to measure the distance to the measurement object 3, but the sample hold circuit 12
Instead, the same effect can be obtained by installing a latch circuit that stores digital values between the counting circuit 10 and the DA converter 11.

〔Effect of the invention〕

As is clear from the above description, the optical displacement meter of the present invention is configured without using a divider, so that the distance to the object to be measured or the amount of displacement of the object to be measured can be measured.
It can detect a wide dynamic range and fast response speed without compromising the temperature characteristics and linearity of the optical displacement meter.

Moreover, since the circuit configuration is simple, the number of parts is small, and therefore the manufacturing process can be simplified and the cost can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the optical displacement meter according to the present invention, FIG. 2 is a diagram explaining the principle of this optical displacement meter, and FIG. The circuit diagram of the embodiment, Figure 4 is an operation waveform diagram of each part of this optical displacement meter,
5 and 6 are operational waveform diagrams of each part of this optical displacement meter when the object to be measured is at a far or near position, and FIG. 7 is a diagram of a second embodiment of the optical displacement meter according to the present invention. FIG. 8 is a block diagram of a conventional optical displacement meter, and FIG. 9 is a correlation diagram between the distance of this optical displacement meter to an object to be measured and the output of a divider. 1... Light projecting element 2... Light projecting lens 3... Measurement object 4... Light receiving lens 5... Light receiving element 6.
・・Integrator circuit 7・・Timing signal generation circuit 8・
...Comparison circuit AI...First amplifier circuit A2...Second amplifier circuit Tr, Tz, Tz...Timing signal Patent applicant Reed Electric Co., Ltd. Figure 8 Figure 9 Calculator

Claims (2)

[Claims] (1) Optical displacement method in which a light beam is projected onto the object to be measured, the reflected light is imaged onto a light-receiving element by an imaging means, and the distance or amount of displacement from the object to be measured is measured based on the output of the light-receiving element. a timing signal generation circuit that outputs a timing signal; a first amplification circuit that amplifies the output of one of the light receiving elements; and a timing signal of the timing signal generation circuit that integrates the output of the first amplification circuit. a second amplifier circuit that amplifies the other output of the light-receiving element; and a comparison circuit that inputs both outputs of the integration circuit and the second amplifier circuit; An optical displacement meter characterized in that the measurement is performed based on the output of a comparison circuit. (2) The distance setting photoelectric switch according to claim 1, wherein the light receiving element is a one-dimensional position detecting element.