JPH055618A - Optical type displacement meter - Google Patents

Abstract

PURPOSE:To obtain an optical type displacement meter with better S/N ratio and measuring accuracy. CONSTITUTION:This apparatus has a timing pulse generation circuit 8, amplifiers 9 and 10 and an addition circuit 12 S/H circuits 13 and 14 into which outputs of the addition circuit 12 and the amplification circuit 9 81-8 taken separately synchronizing a sampling pulse PS and a molecule signal switching circuit 15 which receives outputs of the S/H circuit 13 and the amplification circuit 9 to switch and output any one of the two signals according to the level of a molecule switching pulse PD. Moreover a division circuit 16 is provided to divide an output of the molecule signal switching circuit 15 by an output of the S/H circuit 14, an offset signal removal circuit 16 to remove an offset signal from an output of the division circuit 16 and an S/H circuit 18 to take in an output of the offset signal removal circuit 16 synchronizing a sampling pulse PS2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention applies an intermittently projected laser beam to an object to be measured, forms an optical image on a position detecting element (PSD), and uses two outputs of the position detecting element. The present invention relates to an optical displacement meter that measures a displacement of a measurement target and outputs the displacement amount as an analog signal.

[0002]

2. Description of the Related Art As a conventional optical displacement meter, for example, FIG.
There is the circuit of FIG. Describing from the circuit of FIG. 6, this device is configured such that the light projecting element 4 for irradiating the measuring object 40 with the inspection light is used.
1 and a light projecting control section 4 for making the light projecting element 41 emit light intermittently.
2 and a light projecting lens 4 for converging the inspection light from the light projecting element
3 and a light-receiving lens 4 that converges the reflected light from the measurement target
4, a light receiving element 45, and a measuring unit 46 that measures the position of the measuring object 40 based on the output current of the light receiving element 45. Then, the light projecting controller 42 controls the light projecting element 4
1 is composed of a light projecting element drive circuit 47 that intermittently emits light and a timing pulse generating circuit 48 that generates a pulse that controls the light emitting timing of the light projecting element 41. _A signal amplification circuit 49, 50 that outputs a voltage proportional to the output currents I _A , I _B and a subtraction circuit 51 that obtains the difference between the output voltages of the signal amplification circuits 49, 50.
And an adder circuit 52 that obtains the sum of the output voltages of the signal amplifier circuits 49 and 50, and a sample hold circuit that captures each output voltage of the subtractor circuit 51 and the adder circuit 52 by the sampling pulse P _S from the timing pulse generation circuit 48 (hereinafter S / H circuit) 53, 54 and S / H
A division circuit 55 that divides the output voltage of the circuit 53 by the output voltage of the S / H circuit 54.

The operation of the apparatus of FIG. 6 configured as above is as follows. The light projecting element drive circuit 47 causes the light projecting element 41 to output a pulsed beam in accordance with the light projecting pulse P _L from the timing pulse generating circuit 48.
Then, this beam is imaged on the measuring object 40 by the action of the light projecting lens 43, and the reflected light is imaged on the light receiving element 45 by the action of the light receiving lens 44. Then, the light receiving element 45 outputs the light receiving signals I _A and I _B according to the image forming position, which are processed by the signal amplifying circuits 49 and 50, the subtracting circuit 51, and the adding circuit 52, and thus to the S / H circuit 53. the input signal is a value proportional to I _a -I _B, also the input signal to the S / H circuit 54 becomes a value proportional to I _a + I _B. Both of these signals are synchronized with the sampling pulse P _S from the timing pulse generating circuit 48, and the S / H circuit 5
The value is held until the next sampling pulse P _S is input by the signals 3 and 54. Division circuit 55
The output of the divider circuit 55 so dividing the output of the S / H circuit 53 at the output of the S / H circuit 54 _{(I A -I B) / (} I
It becomes proportional to the value of _A + I _B). As we all know,
The displacement amount L of the measuring object 40 from the reference position is (I
Is proportional to the value of _{A -I B) / (I A} + I B), after all,
The displacement amount of the measuring object can be measured by the output value of the division circuit 55.

Next, another conventional apparatus shown in FIG. 7 will be described. This device is also almost the same as the device of FIG. 6, and the same parts are denoted by the same numbers. The difference from the device of FIG. 6 is that the timing pulse generation circuit 48 outputs the sampling pulse B in addition to the sampling pulse A, and the S / H circuit 5
3 does not exist, and the high pass filter 56 and the S / H circuit 57 are provided in the subsequent stage of the division circuit 55. The waveform of the main part of this device is shown in FIG. That is, (a) to (g) are (a) light projection pulse P, respectively.
_L , (b) sampling pulse A, (c) subtraction circuit 51
Output, (d) output of addition circuit 52, (e) division circuit 5
5 output, (f) sampling pulse B, (g) S / H
The output of the circuit 57 is shown. The rising edge of the sampling pulse B is later than that of the sampling pulse A,
The falling edge is the same pulse as A or a little earlier.

The circuit of FIG. 7 will be described below with reference to the waveform of FIG.
The operation of will be described. Light emitting pulse P _L(Sampling parameters
The same operation as the circuit of FIG. 6 is output.
To the subtraction circuit 51 and the addition circuit 52 respectively.
_A-I_B) And (I_A＋ I_B) Is output in proportion to
(See c and d in FIG. 8). The output of the adder circuit 52 is S / H
Since it is added to the circuit 54, this voltage is
In the S / H circuit 54 in synchronization with the pulse A
Is held until the sampling pulse A of
(Refer to the broken line of d of FIG. 8). The output of the subtraction circuit 51 (see FIG.
c) is divided by the output of the S / H circuit 54 (dashed line of d in FIG. 8).
The output of the division circuit 55 is as shown in FIG.
I want it. Then, this voltage is applied to the high-pass filter 56.
DC component including offset voltage is removed when passing through
In synchronization with the sampling pulse B (see f in FIG. 8)
It is taken in and held in the S / H circuit 57 (see g in FIG. 8).
See). As a result of the above operation, the S / H circuit 57_A-I
_B) / (I_A＋ I_BOutput a voltage proportional to the value of
Therefore, the device of FIG. 7 also has the same displacement as the device of FIG.
The amount can be measured. The features of the device in FIG. 7 are
The bypass circuit 56 is used to offset the division circuit 55.
The point is to remove the voltage.

[0006]

First, considering the circuit of FIG. 6, since the sampled and held DC signal is input to both inputs of the division circuit in this circuit, the influence of the offset of the division circuit and the temperature drift. Is greatly affected by
Therefore, there is a problem that the accuracy of displacement measurement is poor. This adverse effect is especially caused by the denominator input, that is, the S / H circuit 5
This is remarkable when the output value of 4 (the output value of the adding circuit 52) is small.

On the other hand, the circuit of FIG. 7 also has the following problems.
That is, in the circuit of FIG. 7, the output of the subtraction circuit 51 is directly input to the division circuit 55 without being sampled and held, and the output of the division circuit 55 is sampled and held through the high-pass filter 56. Is difficult to remove before the division circuit 55. Therefore, this noise is amplified by the division circuit 55, and eventually the S / N ratio of the displacement measurement signal is deteriorated. This adverse effect is also remarkable when the output value of the S / H circuit 54 is small.

Further, when the output of the division circuit 55 is sample-held while the noise component is included as in the device of FIG. 7, the high frequency noise contained in the signal is converted into the low frequency noise. Becomes difficult to remove. That is, a low-pass filter having a large-capacity capacitor is required to remove low-frequency noise, but if such a filter is adopted, the response frequency becomes low and the mounting area becomes large. Because it occurs in.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an optical displacement type which has good S / N ratio of displacement measurement output, measurement accuracy and resolution with respect to displacement, and has a high response frequency. To aim.

[0010]

To achieve the above object, the present invention intermittently irradiates a measuring object with inspection light,
An optical displacement meter that forms an image of the reflected light on the position detection element and outputs the displacement amount of the measurement object as an analog signal based on the two output signals of the position detection element, and indicates the irradiation timing of the inspection light. Light emission pulse, a first sampling pulse output later than the light emission pulse, a molecule switching pulse output in synchronization with the light emission pulse and having a wider pulse width than the light emission pulse, and a light emission pulse Timing pulse generation circuit for outputting each of the offset removal pulse that is output in advance and the second sampling pulse that is output without the output periods overlapping after the output of the first sampling pulse, and the output of the position detection element A first and a second amplifier circuit for converting the current into a voltage value proportional to each of them, an adder circuit for adding the output voltages of the first and second amplifier circuits, and First and second sample and hold circuits that take in the output voltages of the first amplifier circuit and the adder circuit in synchronization with the first sampling pulse, respectively, and the first sample and hold circuit and the first amplifier circuit. A molecular signal switching circuit that receives an output and switches and outputs one of the two signals in accordance with a change in the level of the molecular switching pulse, and an output of the molecular signal switching circuit as the second sample hold. A division circuit for dividing by the output of the circuit, an offset signal removal circuit for removing the offset signal from the output of the division circuit by using the offset removal signal, and an output of the offset signal removal circuit for the second sampling pulse. It is composed of a third sample-and-hold circuit which takes in in synchronization.

[0011]

When the dimming pulse generating circuit outputs the light projecting pulse, the reflected light from the object to be measured forms an image on the position detecting element, and the position detecting element outputs two kinds of signal currents. Then, the signal current of this position detecting element is
After being processed by the amplifier circuit and the adder circuit, the signals are added to the first and second sample hold circuits as the first signal and the second signal, respectively. Then, these two signals are stored in the first and second sample hold circuits, respectively, in synchronization with the first sampling pulse. The output of the first sample and hold circuit is applied to the molecular signal switching circuit, and the molecular signal switching circuit is also applied with the offset voltage of the circuit when the position detecting element is not operating.

This 2 which joins the molecular signal switching circuit
The two signals are switched and output according to the level of the offset removal pulse, and one of the two signals is added to the division circuit. Then, the division circuit divides the output of the molecule switching circuit by the output of the second sample hold circuit. Since the output (offset) of the division circuit when the position detection element is not operating is stored in the offset signal removal circuit in synchronization with the offset removal pulse, when the original signal from the position detection element is applied. This offset is subtracted and output. That is, the offset signal removing circuit outputs a signal from which the offset signal included in the original signal is removed. Then, the signal from which the offset signal has been removed is stored in the third sample hold circuit in synchronization with the second sampling pulse, and is output from the third sample hold circuit as a displacement measurement signal.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention. This apparatus includes a light projecting element 2 that irradiates a measurement target 1 with inspection light, a light projecting element drive circuit 3 that intermittently emits light from the light projecting element 2, a light projecting lens 4, a light receiving lens 5, and a light receiving element. 6 and a measurement control unit 7 that measures the position of the measuring object 1 based on the output current of the light receiving element 6. Then, the measurement control unit 7 causes the light projecting pulse P _L , the first sampling pulse P _S1 , the molecule switching pulse P _D , and the offset removal pulse P.
Timing pulse generation circuit 8 for generating _OFF and second sampling pulse P _S2 , and signal amplification circuits 9 and 10
, The subtraction circuit 11, the addition circuit 12, and the subtraction circuit 11 and the addition circuit 12 in synchronization with the first sampling pulse P _S1.
S / H circuits 13 and 14 that take in each output voltage of
The output voltage of the molecule signal switching circuit 15 and the molecule signal switching circuit 15 which receives the output voltage of the H circuit 13 and the subtraction circuit 11 and outputs one of the voltages according to the level of the molecule switching pulse P _D is S / H. A division circuit 16 that divides by the output voltage of the circuit 14, an offset signal removal circuit 17 that removes an offset signal from the output voltage of the division circuit 16, and an output voltage of the offset signal removal circuit 17 are synchronized with the second sampling pulse P _S2 . And S / H circuit 18 which is taken in. Further, the molecular signal switching circuit 15 switches the switching elements S ₁ and S ₂ that are turned on when an H level signal is applied, and NO for inverting the molecular switching pulse P _D.
It is composed of a T gate 19.

FIG. 2 shows an internal circuit of the S / H circuits 13, 14, and 18. This S / H circuit forms a resistor 20 and a capacitor 21 which form an integrating circuit, and a voltage follower. And an analog switch 23 that controls whether or not the input signal is applied to the integrating circuit by the level of the GATE pulse. Further, FIG. 3 shows an internal circuit of the offset signal removing circuit 17, and this offset signal removing circuit 17
Is a capacitor 24 charged by an input signal, an amplifier 25 forming a voltage follower, and an amplifier 25.
The analog switch 26 controls the connection between the + terminal and the ground according to the level of the GATE pulse.

Regarding the circuit of FIG. 1 having the above configuration,
The operating waveforms of the main parts of the circuit are shown in FIG. That is, (a) to (k) of FIG. 4 are (a) light projecting pulse P _L , (b) first sampling pulse P _S1 , and
(C) Output of subtraction circuit 11, (d) Output of addition circuit 12, (e) Output of molecular switching pulse P _D , (f) Output of molecular signal switching circuit 15, (g) Output of division circuit 16, (h)
Offset removal pulse P _OFF , (I) output of the offset signal removal circuit 17, (j) second sampling pulse P
The output (displacement measurement output) of the _S2 , (k) S / H circuit 18 is shown.

The operation of the circuit shown in FIG. 1 will be described below with reference to FIG. When the light emitting pulse P _L (see a in FIG. 4) is output from the tamming pulse generating circuit 8, the light emitting element drive circuit 3 operates to irradiate the measuring object 1 with the inspection light and receive the reflected light. An image is formed on the element 6. Then, the output signals I _A and I _{B of} the light receiving element 6 are converted into signal amplification circuits 9 and 10 and a subtraction circuit 1
1, is treated by the addition circuit 12, I _A value proportional to the -I _B is applied to the S / H circuit 13, a value proportional to I _A + I _B is applied to the S / H circuit 14 (c in Fig. 4, d reference). Both signals are S / H synchronized with the first sampling pulse P _S1.
It is taken into the circuits 13 and 14 and held in the section S / H circuit of T ₁ (see the broken lines c and d in FIG. 4). That is, FIG.
Then, the output voltages of the S / H circuits 13 and 14 are set to (c) and (d).
Is indicated by a broken line. Incidentally, the molecular signal switching circuit 15, and applied molecular switching pulse P _D rises in synchronization with the light projection pulse P _L (see e in Fig. 4). Therefore, the switch element S ₁ is in the ON state while the molecule switching pulse P _D is at the H level, and the output voltage of the S / H circuit 13 is output from the molecule signal switching circuit 15 at the same level. The divider circuit 16, the output voltage of the output voltage and the S / H circuit 14 of this molecule signal switching circuit 15 is applied, the division circuit 16 for a period of T ₂ of the FIG. 4 (I _A -
_A value E ₋ / E ₊ proportional to I _B ) / (I _A + I _B ) is output. The output voltage of the S / H circuit 13 is set to E _−, and S
The output voltage of the / H circuit 14 is E ₊ . At this time, the offset removal pulse P _OFF is at the L level (h in FIG. 4).
(See FIG. 3), the analog switch 26 is in the OFF state (see FIG. 3). Therefore, the output voltage of the dividing circuit 16 is superimposed on the voltage across the capacitor 24 and added to the amplifier 25, and is output from the offset signal removing circuit 17. The output of the offset signal removing circuit 17 is taken into the S / H circuit 18 in synchronism with the timing when the second sampling pulse P _S2 becomes H level, and the value is held for the period of T ₃ (FIG. 4). J, k).

Next, the operation of the offset signal removing circuit will be described in further detail, focusing on the period (T _{0 in} FIG. 4) in which the light projection pulse P _L is at the L level and the molecular input switching pulse P _D is at the L level. .. At this time, since the projection pulse P _L is at the L level, the inspection light is not imaged on the light receiving element 6,
Therefore, the output of the subtraction circuit 11 is only the offset voltage of the circuit. Further, since the pulse P _D applied to the molecular signal switching circuit 15 is at L level, the switch element S ₂ is turned on, and the offset voltage output from the subtraction circuit 11 is applied to the division circuit 16 as it is. As a result of the above operation, the value of E _OFF / E ₊ is output from the division circuit 16 (assuming the offset voltage of the entire circuit including the division circuit is E _OFF ). The output voltage of the S / H circuit 14
That is, the output voltage of the adder circuit 12 is E ₊ . This voltage E _OFF / E ₊ is added to the capacitor 24 shown in FIG. 3, but since the analog switch 26 is turned on at the timing when the offset signal removal pulse P _OFF becomes the H level, as a result, the capacitor 24 becomes E _OFF. It is charged to the level of / E ₊ . The charging voltage of the capacitor 24 is maintained as it is after the offset signal removal pulse P _OFF changes to the L level. Then, the next light projection pulse is output, and the division circuit 1 for this light projection pulse is output.
When the output voltage E ₋ / E _{+ of 6} (the original division signal with the offset voltage superimposed) is applied to the capacitor 24,
The voltage (E _OFF / E ₊ ) of the capacitor is subtracted from the output voltage E ₋ / E _{+ of the} division circuit 16 and is output from the amplifier 25. That is, the offset signal removing circuit 17 stores the offset voltage (E _OFF / E ₊ ) of the circuit in the capacitor 24 while the light projecting pulse P _L is at the L level, and the next light projecting pulse P _L is stored. The offset voltage is removed by subtracting this offset voltage from the output value (E ₋ / E ₊ ) for

Next, the description of the circuit operation of FIG. 2 will be supplemented. FIG. 2 shows an internal circuit of the S / H circuits 13, 14, and 18. Since this S / H circuit forms an integrating circuit by the resistor 20 and the capacitor 21, it operates as a low-pass filter for the input signal. That is, the S / H circuit 1
3, 14, 18 store the input signal in the capacitor 21 when the analog switch 23 is in the ON state, but at this time, the noise component is reduced by the action of the integrating circuit. When the analog switch 23 is turned off, the voltage of the capacitor 21 holds its value until the analog switch is turned on again, and performs a sample hold operation.

FIG. 5 is a circuit diagram showing another embodiment of the present invention. The configuration is almost the same as the circuit of FIG. 1, except that the subtraction circuit 11 of FIG. 1 does not exist in FIG. That is,
In the circuit of FIG. 5, the output of the signal amplification circuit 9 is directly applied to the S / H circuit 13 and the molecule switching circuit 15. The circuit operation is the same as in the case of FIG. 1, and the S / H circuits 13, 14, 1
8, the noise component is reduced, and the offset signal removing circuit 1
At 7, the circuit offset is removed.

[0020]

As described above, according to the present invention, since the S / H circuit having a constant integration time constant is provided in the preceding stage of the dividing circuit, the noise signal included in the light receiving signal is converted into the S / H circuit.
It can be reduced by the H circuit. Further, since the offset removing circuit is provided in the next stage of the dividing circuit, the offset voltage of the circuit can be removed. Further, since the S / H circuit having a constant integration time constant is provided at the next stage of the division circuit, the S of the displacement measurement output can be obtained.
The / N ratio is improved.

As a result, the S / N ratio of the displacement measurement output and the measurement accuracy are improved, and the resolution with respect to the displacement can be improved. It is also possible to increase the response frequency.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an S / H circuit of the circuit shown in FIG.

FIG. 3 is a circuit diagram showing an offset signal removal circuit of the circuit of FIG.

FIG. 4 is a waveform diagram showing waveforms at various parts of the circuit of FIG.

FIG. 5 is a circuit block diagram showing another embodiment of the present invention.

FIG. 6 is a circuit block diagram showing a conventional example.

FIG. 7 is a circuit block diagram showing another conventional example.

FIG. 8 is a waveform diagram showing waveforms at various parts of the circuit of FIG.

[Explanation of symbols]

1 Object to be Measured 6 Position Detection Element 8 Timing Pulse Generation Circuit 9 First Amplification Circuit 10 Second Amplification Circuit 12 Addition Circuit 13 First S / H Circuit 14 Second S / H Circuit 15 Molecular Signal Switching Circuit 16 Division circuit 17 Offset signal removal circuit 18 Third S / H circuit P _L Light emitting pulse P _S1 First sampling pulse P _D Molecule switching pulse P _OFF Offset removal pulse P _S2 Second sampling pulse

Claims (1)

Claim: What is claimed is: 1. An object to be measured is intermittently irradiated with inspection light, the reflected light is imaged on a position detection element, and measurement is performed based on two output signals of the position detection element. In an optical displacement meter that outputs the displacement amount of an object as an analog signal, a light projecting pulse that indicates the irradiation timing of inspection light, a first sampling pulse that is output after the light projecting pulse, and a light projecting pulse Without the overlap of the output period after the output of the numerator switching pulse, which is output in synchronization with the pulse width, wider than the light emission pulse, the offset removal pulse output prior to the light emission pulse, and the first sampling pulse. Timing pulse generation circuit for outputting each of the second sampling pulses to be output, and first and second amplification for converting the output current of the position detection element into a voltage value proportional to each of them. A circuit, an adder circuit for adding the output voltages of the first and second amplifier circuits, and a first circuit for taking in the output voltages of the first amplifier circuit and the adder circuit in synchronization with the first sampling pulse, respectively. The second sample and hold circuit and the first
Of the sample and hold circuit and the first amplifier circuit, and outputs one of the two signals by switching between the two signals in accordance with the change in the level of the molecule switching pulse, and the molecule signal switching circuit. A division circuit that divides the output of the signal switching circuit by the output of the second sample hold circuit, an offset signal removal circuit that removes the offset signal from the output of the division circuit using the offset removal signal, and this offset signal An optical displacement meter, comprising: a third sample and hold circuit that captures the output of the removal circuit in synchronization with the second sampling pulse.