JPH05172517A - Optical displacement measuring method and multiple-head type optical displacement gage using this method - Google Patents

Abstract

PURPOSE:To decrease measuring errors by preventing the interference of mutual optical beams even when the measurements are performed with optical heads, which are arranged in close proximity in an optical displacement gage. CONSTITUTION:A plurality of optical heads H1 and H1' are modulated and driven by mutually different natural frequencies F1 and f2. Thus, the modulated lights are cast on an object, and the reflected lights returned from the object are received and detected by the respective optical heads H1 and H1'. Detected position signals I1 and I2 corresponding to the natural frequencies f1 and f2 are taken out. Displacement amounts (a) and (b) with respect to the specified reference position are computed for every optical heads H1 and H1' by operating the obtained detected position signals I1 and I2. The computed displacement amounts (a) and (b) are further operated, and the distance is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement measuring method using a plurality of optical heads and a multi-head type optical displacement meter using this method.

[0002]

2. Description of the Related Art A sharp light beam such as a laser beam output from an optical head is applied to an object, and reflected light from the object is received by a position detecting element to obtain a displacement amount from a reference position. Optical displacement meters have been developed and are in use.

FIG. 6 shows an example of the essential configuration of a displacement gauge 100 in which two such optical displacement gauges are incorporated to measure the level difference of an object. , The same as the conventional optical displacement meter. That is, in the optical head H1, the laser beam emitted from the light projecting lens L1 and reflected at a point apart from the reference distance Rc by a is received by the position detection element PSD through the light receiving lens L2 and the reference distance Rc. If the displacement from the point reflected by the point and received by the position detection element PSD is ΔX, then ΔX
Is given by the following equation. ΔX = A × a / (B + a) (1) where A = f × tan θ B = Rc / (cos θ) 2 f is the distance θ between the light receiving lens L2 and the position detection element PSD It is the inclination of L2 with respect to the projection lens L1. On the other hand, the output current value across the position detection element PSD is I
Assuming 1 and I2, ΔX is expressed by the following equation. ΔX = ((I1−I2) / (I1 + I2)) × (L / 2) (2) Therefore, the signal processing unit 101a executes the arithmetic processing in which the expression (2) is substituted into the expression (1). Then, the reference distance R of the measuring object
The displacement amount a from c can be calculated. Incidentally, 101
Reference numeral b is an oscillating circuit for modulating the laser beam, which is adapted to demodulate the modulated signal received and output from the position detecting element PSD to remove the influence of interference light from the outside. In addition, the above (1), (2)
In the following equation derived from the equation, (I1-I2) / (I1 + I2) = (2A × a / (L × (B + a))), the distance measurement signal value (I1-I2) / on the left side with respect to the displacement amount a on the right side Since (I1 + I2) has a non-linear relationship, in actual displacement measurement, as shown in the following formula (2) ′, by performing arithmetic processing by a correction formula including the correction constant k, the triangular distance measurement is performed. The non-linearity-based signal is compensated for. ΔX = ((I1−I2) / (I1 + kI2)) × (L / 2) ... (2) ′

By the way, the displacement meter 10 as shown in FIG.
According to 0, the displacement measuring units 101 and 101 ′ individually obtain the displacement amounts a and b from the reference distance Rc, and the difference (ab) between the obtained displacement amounts a and b is calculated by the arithmetic circuit 1.
It is also possible to obtain the step D or the like of the target object by calculating 02.

However, in such a displacement meter 100,
When the displacement measurement is performed by bringing the optical heads H1 and H1 ′ close to each other, the laser beam output from the optical head H1 is reflected by the object and the position detection element PS on the optical head H1 ′ side is detected.
D may be erroneously incident on D (see the broken line in FIG. 6), or conversely, the laser beam output from the optical head H1 ′ side may be reflected by the object and erroneously incident on the position detection element PSD on the optical head H1 side. Therefore (see the broken line in FIG. 6), the position detection element P
The position detection signal output from the SD deviates from the value corresponding to the displacement amount of the object, and accurate measurement cannot be performed.

When measuring the thickness of an object,
As shown in FIG. 7, the optical heads H1 and H1 ′ of the displacement meter 100 are arranged so as to face each other so as to sandwich the target object so that the reference positions (in the figure, they are in the center of the target object) are aligned. The displacement measurement units 101 and 101 ′ of the displacement measurement units a and b are subjected to addition processing in the arithmetic circuit 102 to obtain the thickness (a + b), but the object is thin and the laser beam is transmitted. When the object is transmissive, the laser beam output from the optical head H1 causes the position detection element P of the other optical head H1 '.
Since it erroneously enters the SD, a position detection signal corresponding to the amount of displacement cannot be obtained, which is a factor that hinders accurate measurement.

[0007]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above circumstances. Even when a plurality of optical heads are placed close to each other for measurement, mutual interference of light beams is prevented and measurement error is reduced. An object of the present invention is to provide an optical displacement measuring method that can reduce displacement and perform highly accurate displacement measurement. In addition, the present invention proposed at the same time provides a multi-head type optical displacement meter capable of performing high-accuracy displacement measurement by preventing interference between a plurality of optical heads using this measuring method. Has a purpose.

[0008]

An optical displacement measuring method according to the present invention, which is proposed to achieve the above object, comprises a plurality of optical heads which are modulated and driven at different natural frequencies. The modulated light is emitted to the target object, the reflected light returning from the target object is received and detected by each optical head, the position detection signal corresponding to the natural frequency is extracted, and the extracted position detection signal is calculated. The amount of displacement with respect to a predetermined reference position is calculated for each optical head by processing, and the calculated amount of displacement is further calculated to perform distance measurement.

An optical displacement gauge according to a second aspect of the present invention is a plurality of optical displacement gauges which irradiate an object with a modulated light beam, detect reflected light by a position detection element, and output a position detection signal. An oscillation circuit unit that has a head and an oscillation circuit corresponding to each of the optical heads, and that generates and outputs a modulation signal of a different natural frequency assigned to each optical head,
A position detection signal corresponding to the natural frequency assigned to each optical head is extracted from the position detection signal provided from each optical head side provided corresponding to each optical head, and the extracted position detection signal Is calculated to calculate a displacement amount from a predetermined reference position for each of the optical heads, and the calculated displacement amount is further processed to perform a distance measurement. There is.

The optical displacement gauge of the present invention according to claim 3 irradiates a modulated light beam on an object, detects the reflected light by a position detection element, and outputs a position detection signal. Optical head and an oscillation circuit corresponding to each of the optical heads, and an oscillation circuit section for generating and outputting modulation signals of different natural frequencies assigned to each optical head, and the optical heads are sequentially selected. Corresponding to the natural frequency assigned to each optical head from the switching control section that sequentially outputs the designated and modulated position detection signals and the position detection signals that are sequentially output from the optical head side selected by the switching control section. The extracted position detection signals are sequentially taken out, and the taken-out position detection signals are arithmetically processed to calculate the displacement amount from the predetermined reference position for each of the optical heads. Processing to have a configuration in which a common signal processing unit for performing distance measurement.

[0011]

According to the method of the present invention as set forth in claim 1, the plurality of optical heads are modulated and driven at different natural frequencies to irradiate the object with modulated light and the reflected light returning from the object. Is detected by each optical head to detect the position detection signal corresponding to the natural frequency, and the displacement amount with respect to a predetermined reference position is calculated for each optical head by performing arithmetic processing on the extracted position detection signal,
The calculated displacement amounts are further processed to perform distance measurement. Therefore, even if a light beam or ambient light output from another optical head is accidentally incident, signals other than the natural frequency assigned to each optical head are removed to prevent interference of light between the optical heads. Therefore, even if a plurality of optical heads are arranged close to each other and measurement is performed at the same time, accurate displacement measurement with reduced error due to interference can be performed.

According to the second aspect of the present invention, when the position detection signal output from each optical head is input to the signal processing unit, the signal processing unit responds to the natural frequency assigned to the optical head. The detected position detection signal is extracted, the extracted position detection signal is arithmetically processed to calculate the displacement amount from the predetermined reference position for each optical head, and the distance measurement is performed based on the obtained displacement amount. Therefore, modulated light can be simultaneously emitted from a plurality of optical heads toward the object, and the position detection signal can be captured and the arithmetic processing can be performed at the same time, so that the measurement processing can be speeded up.

According to the third aspect of the present invention, when the position detection signals are sequentially taken out from the optical head side selected by the switching control section, the common signal processing section sets the natural frequency assigned to the optical head. Corresponding position detection signals are sequentially taken out, the extracted position detection signals are arithmetically processed to calculate the displacement amount from the predetermined reference position for each optical head, and distance measurement is performed based on the obtained displacement amounts. .. Therefore, since the position detection signals sequentially taken out from the respective optical heads are processed by the common signal processing unit, it is possible to perform high-accuracy distance measurement in which errors due to temperature changes and temporal changes are offset.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the basic configuration of an optical displacement meter 1 of the present invention. In the figure, 10A and 10B are provided corresponding to the optical heads H1 and H1 ′, and each optical head H
1, H1 'output from the position detection signals I1, I2 or I1', I2 '(voltage signal corresponding to the photocurrent output from the position detection element PSD) to calculate displacements from the reference position. It is a signal processing unit that does. Also, 11
Is an oscillation circuit unit that oscillates a modulation signal for modulating the natural frequency of the laser beam output from the laser light emitting element LA of the optical heads H1 and H1 ′. The modulation signal of the natural frequency f1 with respect to the optical head H1. A natural frequency f2 with respect to the oscillation circuit 11a for outputting
And an oscillation circuit 11b that outputs the modulated signal of.
The details of the signal processing units 10A and 10B will be described later.

The optical displacement gauge 1 of the present invention having such a configuration
The optical displacement measuring method according to the first aspect of the present invention will be described with reference to the configuration example. When the modulation signal of the natural frequency f1 generated by the oscillation circuit 11a of the oscillation circuit unit 11 is sent to the optical head H1 side, the laser light emitting element LA irradiates the object with the modulated laser beam of the natural frequency f1. On the other hand, when the modulation signal of the natural frequency f2 generated by the oscillation circuit 11b is sent to the optical head H1 ′ side, the laser light emitting element LA irradiates the object with the modulated laser beam of the natural frequency f2. To be done. When the light reflected by the object is incident on the position detection element PSD of the optical head H1, the position detection element PSD outputs a position detection signal (I1, I2) modulated according to the incident light to the signal processing unit 10A. When the light reflected by the object is incident on the position detecting element PSD of the optical head H1 ′, the position detecting element PSD outputs modulated position detection signals (I1, I1) according to the incident light.
2) is output to the signal processing unit 10B. The signal processing unit 10A receives the modulated position detection signal transmitted from the optical head H1 and receives the optical head H1.
The position detection signal is obtained by demodulating only the component of the natural frequency f1 assigned to 1, and the obtained position detection signal is subjected to the arithmetic processing of the above equations (1) and (2) to obtain the position detection signal from the reference position of the object. The displacement amount a is calculated. In addition, the signal processing unit 10B receives the modulated position detection signal transmitted from the optical head H1 ′, demodulates only the component of the natural frequency f2 assigned to the optical head H1 ′, and detects the position detection signal. Is calculated, and the displacement amount b from the reference position of the object is calculated by performing the arithmetic processing of the above equations (1) and (2) on the obtained position detection signal. In the signal processing unit 10A, the step D is obtained by calculating the difference (ab) between the calculated displacement amounts a and b.

As described above, according to the optical displacement measuring method of the present invention, the signal processing section selectively demodulates only the natural frequency component assigned to the optical head to obtain the position detection signal. It is possible to effectively eliminate the interference caused by the light beam or the disturbance light that is erroneously incident from the optical head, and therefore, even if the optical heads are placed adjacent to each other and the displacement measurement is performed at the same time, the error caused by the interference does not occur. It is possible to perform a highly accurate measurement that is prevented.

Next, the detailed configuration of the signal processing units 10A and 10B of the optical displacement meter 1 shown in FIG. 1 will be described. The signal processing unit 10A is a modulated position detection signal output from the optical head H1. Of the (voltage signal corresponding to the photocurrent), only the component of the natural frequency f1 (natural frequency f2 in the signal processing unit 10B) is passed to remove the disturbance noise, and the filter circuit 10b outputs the modulation. A synchronous detection circuit 10c that detects and demodulates the generated position detection signal in synchronization with the modulation signal of the oscillation circuit 11, an A / D conversion circuit 10d that converts the demodulated position detection signals I1 and I2 into digital data, and digital data. The position detection signals I1 and I2 converted into are stored in the memory unit 10f, and the displacement amount a and the difference between the displacement amounts are calculated from the stored data. The PU 10a and the D / A conversion circuit 10e that converts and outputs the analog data corresponding to the calculated difference are provided. The other signal processing unit 10B has a D / A configuration different from that of the signal processing unit 10A. The configuration is such that the conversion circuit 10e is omitted.

FIG. 2A shows the frequency characteristic of the filter circuit. The filter circuit 1 of the signal processing unit 10A is shown in FIG.
0b matches the natural frequency f1 of the optical head H1,
The filter circuit 10b of the signal processing unit 10B has a bandpass filter characteristic that allows only a signal having a predetermined bandwidth above and below the center frequency f1 to pass therethrough.
It has a band-pass filter characteristic that allows only a signal having a predetermined bandwidth above and below the center frequency f2 to pass according to the natural frequency f2 of 1 '.

According to such a filter circuit, as shown in FIG. 2B, the light beam or the disturbance light radiated from the optical head H1 'is incident on the optical head H1 to cause the optical head H1 to move. Even if a modulated signal of frequency f2 or noise of other frequency is output from the position detection element PSD, the filter circuit 10b allows only the component of frequency f1 to pass therethrough for detection, so that the occurrence of measurement error due to interference light is eliminated. You can

FIG. 3 schematically shows the position detecting element PSD. As shown in the figure, the frequency f1 to be received is f1.
When the modulated light of is incident on the position P1 and the interfering light of the frequency f2 is incident on the position P2, the output current signals I1 and I2 of the position detection element PSD have the values shown by the following expressions. I1 = I1 (f1) + I1 (f2) (3) I2 = I2 (f1) + I2 (f2) (4) Output current represented by the formulas (3) and (4) A voltage signal proportional to the filter circuit 10b and the synchronous detection circuit 10c.
And the component of frequency f2 is removed, so that I
1 = I1 (f1), I2 = I2 (f1), and by substituting these equations into the above equation (2), an accurate displacement amount with the interference wave component removed as shown in the following equation (5). A measurement can be made. ΔX = ((I1 (f1) −I2 (f2)) ÷ (I1 (f1) + I2 (f2))) × (L / 2) ... (5)

Next, the optical displacement gauge 1 of the present invention as described above.
The operation of is centered on the detailed operation of the signal processing unit 10,
This will be described with reference to the time charts shown in (a) to (h) of FIG. When the modulated position detection signals I1o and I2o output from the optical head H1 are transmitted to the signal processing unit 10A,
The noise components other than the natural frequency f1 are removed by the filter circuit 10b and transmitted to the synchronous detection circuit 10c.
0c, the natural frequency f output from the oscillation circuit 11a
The position detection signal is demodulated by the detection synchronized with 1, and then transmitted to the A / D conversion circuit 10d. ((A) of FIG. 4
(See (c)). In the A / D conversion circuit 10d, the demodulated analog position detection signal is converted into corresponding digital data I1o and I2o and stored in the memory unit 10f through the CPU 10a. (See (c) and (e) of FIG. 4). When the modulated position detection signals I1o ′ and I2o ′ output from the optical head H1 ′ are transmitted to the signal processing unit 10B, noise components other than the natural frequency f2 are filtered by the filter circuit 1.
It is removed by 0b and transmitted to the synchronous detection circuit 10c. In the synchronous detection circuit 10c, the position detection signal is demodulated by the detection synchronized with the natural frequency f2 output from the oscillation circuit 11b, and then to the A / D conversion circuit 10d. To transmit. (See (b) and (d) of FIG. 4). In the A / D conversion circuit 10d, digital data I1o ', I2 corresponding to the demodulated analog position detection signal
It is converted into o ′ and stored in the memory unit 10f through the CPU 10a. (See (d) and (f) in FIG. 4). The signal processing unit 10A calculates the displacement amount a from the data I1o and I2o stored in the memory unit 10f, and
The data I1o ′, I2o ′ stored in the memory unit 10f of the signal processing unit 10B is read to calculate the displacement amount b, and the displacement amount difference D0 = (ab) is calculated to calculate the D / A conversion circuit 10e. Output to. (See (g) of FIG. 4). In the D / A conversion circuit 10e, the displacement amount D0 = (ab)
The analog data corresponding to is output to an external circuit. (See FIG. 4 (h)).

As described above, according to the optical displacement sensor of the present invention, the signal processing unit side selectively demodulates only the natural frequency component of the optical head to obtain the position detection signal. Even if a light beam is accidentally incident, a measurement error due to interference does not occur, so it is possible to perform measurements with adjacent optical heads. Also, since the modulated light is continuously output from the optical head, the optical head High-speed displacement measurement can be stably performed as compared with a configuration in which the switch is driven.

By the way, in the above-mentioned optical displacement meter 1,
Although the signal processing units 10A and 10B corresponding to the respective optical heads H1 and H1 'are provided, it is possible to share one signal processing unit. Figure 5
A configuration example (corresponding to claim 3) of the optical displacement meter 2 having such a configuration is shown, and the same parts as those of the displacement meter 1 described above are denoted by the same reference numerals and the description thereof will be omitted.

In this optical displacement meter 2, the optical head H
1, H1 ′ are sequentially selected, the switching control unit 12 having the switching contacts SWa and SWb that are interlocked with each other is provided, and the switching contact SWa is a modulation signal of the natural frequency assigned to the selected optical head. Is added to the synchronous detection circuit 10c of the signal processing unit 10 from the oscillation circuit unit 11, and the other switching contact SWb outputs the modulated position detection signal output from the selected optical head to the signal processing unit. It is adapted to be transmitted to the 10 side. The switching control signal output from the switching control unit 12 is transmitted to the frequency variable filter circuit 10b so that only the natural frequency of the selected optical head is passed.

With such a structure, it is not necessary to provide a plurality of signal processing units in the signal processing unit, so that the circuit structure can be simplified and each of the optical heads H1, H1 '.
Since the signal processing unit 10 is shared with each other, the offset error included in each calculated displacement amount has the same value due to the factors of the temperature change and the temporal change, and the inclination increases or decreases around a specific point. Such an error can be reduced as the difference between the displacement amounts is reduced, so that it is possible to perform displacement measurement with high accuracy.

In the above description, the figure for measuring the step of the object is described as an example, but the thickness of the object can be measured by disposing the optical heads on both sides of the object. Alternatively, it is possible to measure the curved state of an object by arranging a number of optical heads close to each other, and even in such a measurement, it is possible to perform highly accurate measurement while preventing interference between the optical heads. You can

Although the above description does not refer to a specific shape of the optical displacement meter, a plurality of connectors are provided in the controller in which circuits such as a signal processing unit and an oscillation circuit unit are integrally incorporated. It is also possible to have a structure in which a required number of optical heads are detachably attached.

[0028]

As can be understood from the above description, according to the method of the present invention as set forth in claim 1, a plurality of optical heads are modulated and driven at different natural frequencies, and the modulation output from each optical head is performed. Since the signal is demodulated for the natural frequency assigned to each optical head to obtain the position detection signal, interference by other optical heads is eliminated. Therefore, even if a plurality of optical heads are arranged close to each other and displacement measurement is performed at the same time, a measurement error due to interference does not occur, so that highly accurate measurement can be performed. According to the present invention as set forth in claim 2, even if the optical beams are simultaneously emitted from the respective optical heads, interference between the optical heads can be prevented. Therefore, the position detection signals obtained from the respective optical heads can be prevented. Can be simultaneously processed in parallel to perform displacement measurement at high speed and with high accuracy. Further, according to the present invention described in claim 3,
Even if light beams are emitted from each optical head at the same time, it is possible to prevent interference between the optical heads, and by sequentially switching the position detection signals obtained from each optical head to perform arithmetic processing, the temperature change Since an error generated in the signal processing unit due to a change with time or can be effectively removed, highly accurate displacement measurement can be performed.

[Brief description of drawings]

FIG. 1 is a structural example diagram of an optical displacement meter of the present invention according to claim 2.

2A and 2B are characteristic examples of the filter circuit of the optical displacement meter shown in FIG.

FIG. 3 is a schematic diagram illustrating the structure of a position detection element.

4A to 4H are time charts for explaining the operation of the displacement meter shown in FIG.

FIG. 5 is a structural example diagram of an optical displacement meter of the present invention according to claim 3;

FIG. 6 is an explanatory diagram of interference that occurs between optical heads when measuring a step.

FIG. 7 is an explanatory diagram of interference that occurs between the optical heads when measuring the thickness.

[Explanation of symbols]

 10 ... Signal processing unit 11 ... Oscillation circuit unit 12 ... Switching control unit a, b ... Displacement amount f1, f2 ... Natural frequency H1, H1 '... Optical head

Front Page Continuation (72) Inventor Yoshihiko Sugimoto 1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works, Ltd.

Claims (3)

[Claims] 1. A plurality of optical heads are modulated and driven at different natural frequencies to irradiate an object with modulated light, and reflected light returning from the object is detected by each optical head. The position detection signal corresponding to the natural frequency is taken out, and the taken-out position detection signal is arithmetically processed to calculate the displacement amount with respect to a predetermined reference position for each optical head. An optical displacement measuring method characterized in that the distance is calculated by performing arithmetic processing. 2. A plurality of optical heads for irradiating an object with a modulated light beam, detecting the reflected light by a position detecting element and outputting a position detection signal, and an oscillation corresponding to each of the optical heads. An oscillation circuit section that has a circuit and generates and outputs modulated signals of different natural frequencies assigned to each optical head, and a position provided corresponding to each optical head and output from each optical head side A position detection signal corresponding to the natural frequency assigned to each optical head is extracted from the detection signal, and the extracted position detection signal is arithmetically processed to calculate the displacement amount from the predetermined reference position for each optical head. Thus, the multi-head type optical displacement meter is characterized by further comprising a signal processing unit for performing a distance measurement by further processing the calculated displacement amounts. 3. A plurality of optical heads for irradiating an object with a modulated light beam, detecting the reflected light by a position detection element and outputting a position detection signal, and an oscillation corresponding to each optical head. An oscillation circuit section having a circuit for generating and outputting modulation signals of different natural frequencies assigned to each optical head, and a switch for sequentially selecting and designing each of the optical heads and sequentially extracting modulated position detection signals. The position detection signal corresponding to the natural frequency assigned to each optical head is sequentially extracted from the position detection signals sequentially output from the control unit and the optical head selected by the switching control unit, and the extracted position detection signal is output. Is calculated to calculate the displacement amount from the predetermined reference position for each of the optical heads, and thus the calculated displacement amount is further processed to measure the distance. Multi-head type optical displacement meter is characterized in that a signal processing unit.