JPH0672777B2 - Copy measuring method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a scanning measuring method and an apparatus therefor, and more specifically, to a surface of a measuring object that moves in one direction at a constant speed by optical heterodyne interferometry. The present invention relates to a novel method and a device for measuring a shape.

<Prior Art and Problems to be Solved by the Invention> Conventionally, various devices having various configurations have been provided as devices for measuring a distance to an object to be measured. Specifically, there are those that apply the principle of triangulation, those that apply the principle that interference of light, ultrasonic waves, etc. changes based on the difference in distance, but applications that require higher measurement accuracy. In the above, it is preferable to use laser light that is less likely to be affected by external conditions as the measurement light.

2. Description of the Related Art As a distance measuring device that uses the above laser light as a measurement light, conventionally, a laser light whose frequency is linearly modulated is divided into two, and one is irradiated to a measurement object, and the other has a known distance. It is possible to obtain a beat signal by irradiating the reference reflector with the reflected light from the measurement target and the reflected light from the reference reflection, and calculate the distance to the measurement target based on the frequency of the beat signal. It is known (see JP-A-61-223576).

Specifically, the optical path length on the measurement object side is L, the optical path length on the reference reflector side is L0, the speed of light is C, the modulation frequency of the semiconductor laser (hereinafter abbreviated as LD) is fm, and the frequency of the beat signal is fb. ,
If the maximum oscillation frequency deviation due to the LD modulation is δ, then there is a relationship of L−L0 = C · fb / 4 · fm · δ, and L0, C, fm, fb, and δ are known. Can be calculated, and by extension, the distance to the measurement object can be calculated.

However, the method of measuring the distance to the object to be measured based on the beat signal obtained as described above can only perform highly accurate distance measurement only when the object to be measured is stationary. However, when performing the scanning measurement, there is a problem that the distance measurement cannot be performed with very high accuracy, that is, the scanning measurement.

More specifically, since the measurement object to be subjected to the scanning measurement is moved at a constant speed in a preset direction, a frequency shift caused by the Doppler effect occurs, and the measurement object is sequentially changed. Only the interference signal frequency in which the above frequency shift is superimposed on the beat frequency determined according to the distance to the measured point is obtained. Therefore, if the distance is calculated by regarding the interference signal frequency as the beat frequency, the distance data will be considerably different from the actual distance.

Furthermore, if the LD is frequency-modulated in a triangular wave shape with the same rising and falling slopes, the amount of change in the frequency deviation of the laser light at the rising and falling portions of the triangular wave has the same absolute value, and the sign is the same. Since it is reversed, the interference signal frequency largely deviates from the true beat frequency due to the influence of the change amount of the Doppler shift frequency and the frequency shift of the laser light.

That is, in consideration of such a problem, when performing the scanning measurement of the measuring object moving at a constant speed in a predetermined direction,
Only a so-called contact-type scanning measuring method and device is provided which measures the amount of movement of the movement axis by providing the movement axis that moves back and forth following the surface shape of the measurement object, and uses the optical heterodyne interferometry method. The so-called non-contact type scanning measuring method and device have not been provided at all.

<Objects of the Invention> The present invention has been made in view of the above problems,
It is an object of the present invention to provide a scanning measurement method and an apparatus therefor, which employs the optical heterodyne interferometry and eliminates the influence of the Doppler shift and can perform accurate scanning measurement without contact.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the scanning measuring method of the present invention makes the reflected light from the measuring object moving at a constant speed interfere with the reflected light from the reference reflector. , Turn on the laser light,
Based on the interference signal corresponding to the rising edge and the interference signal corresponding to the falling edge of the modulated wave that frequency-modulates the triangular wave shape with the same falling slope, mutually different interference signal frequencies are calculated, and based on both interference signal frequencies This is a method of removing the Doppler shift frequency component by performing addition and subtraction, and calculating the distance to the measurement position of the measurement object that changes sequentially based on the frequency from which the Doppler shift frequency component has been removed.

In order to achieve the above-mentioned object, the scanning measuring apparatus of the present invention is such that the measuring object moves at a constant speed, and the semiconductor laser rises, and a modulating means for modulating the falling slope into a triangular wave shape. An interference signal extracting means for extracting an interference signal corresponding to the rising edge of the modulated wave and an interference signal corresponding to the falling edge, a frequency calculating means for calculating the frequency of each extracted interference signal, and based on the calculated both frequencies. And a distance calculating means for calculating the distance to the measurement position of the measuring object that changes sequentially based on the frequency from which the Doppler shift frequency component has been removed. is doing.

However, as the calculation means, the frequency of the interference signal corresponding to the fall of the modulated wave is subtracted from the frequency of the interference signal corresponding to the rise of the modulated wave on the condition that the Doppler shift frequency is higher than the beat frequency, and the frequency is multiplied by 1/2. However, on the condition that the Doppler shift frequency is smaller than the beat signal, the frequency of the interference signal corresponding to the falling edge of the modulated wave is added to the frequency of the interference signal corresponding to the rising edge, and the frequency is multiplied by 1/2. Preferably, in this case, the calculation means is
It may have a condition determination means for holding condition determination data determined based on the moving speed and moving direction of the measurement object, and an addition / subtraction means for selecting a subtraction operation and an addition operation based on the result of the condition determination. More preferable.

<Operation> According to the above-described scanning measurement method, the laser light output from the semiconductor laser that is frequency-modulated in a triangular wave shape with the same rising and falling inclinations is divided into two, and one is moved at a constant speed in a predetermined direction. While irradiating the measurement object, irradiating the other to the reference reflector, by causing the reflected light from the measurement object and the reflected light from the reference reflector to interfere, the distance to the measurement object, the measurement object It is possible to obtain an interference signal having a frequency corresponding to the moving speed and the moving direction of the.

The frequency of this interference signal is the beat frequency fb and the Doppler shift frequency fd at the rising edge of the triangular wave modulation wave.
And fb + fd, and the absolute value of the difference between both frequencies becomes | fb−fd | at the trailing edge of the modulated wave.

Therefore, the influence of the Doppler shift frequency can be eliminated by performing addition and subtraction based on the frequencies corresponding to the respective parts, and the measurement object that changes in sequence based on the frequency from which the influence of the Doppler shift frequency is eliminated. The distance to the target point can be accurately measured. Then, if the influence of the Doppler shift frequency is eliminated as described above, it is possible to eliminate the influence of the change amount of the frequency shift in which the signs are opposite between the rising portion and the falling portion, and the distance measurement The accuracy can be further improved.

As a result, the distance to each point on the entire surface of the measuring object can be measured, and by performing necessary processing thereafter, the uneven shape of the entire surface of the measuring object can be measured by scanning.

In the scanning measuring apparatus having the above-described configuration, the laser light output from the semiconductor laser frequency-modulated into a triangular wave having the same rising and falling slopes by the modulation means is divided into two, and one is moved at a constant speed in a predetermined direction. While irradiating the moving measurement object, irradiating the other with the reference reflector, the reflected light from the measurement object and the reflected light from the reference reflector are caused to interfere with each other, thereby measuring the distance to the measurement object. An interference signal having a frequency corresponding to the moving speed and moving direction of the object can be obtained.

The frequency of this interference signal is the beat frequency fb and the Doppler shift frequency fd at the rising edge of the triangular wave modulation wave.
And fb + fd, and the absolute value of the difference between both frequencies becomes | fb−fd | at the trailing edge of the modulated wave.

Therefore, the interference signal extraction means extracts the interference signal corresponding to each part of the modulated signal, and the extracted interference signals are supplied to the frequency calculation means, whereby the frequencies f1 = fb + fd and f2 = fb of the interference signals are obtained. -Fd or fd-fd can be calculated. Then, by supplying both the frequencies f1 and f2 to the calculating means, it is possible to obtain the frequency fb or 2fb from which the Doppler shift frequency component fd is removed, and thus the obtained frequency fd or 2fb is supplied to the distance calculating means. By doing so, the distance to the measurement object can be accurately calculated.

The above is the distance measuring operation for any one point of the measuring object, but since the measuring object is moving in a predetermined direction at a constant speed, the above operation is performed over the entire range of the measuring object. By repeating the measurement, it is possible to measure the uneven shape of the surface of the measuring object, that is, the scanning measurement.

Then, the calculating means subtracts the frequency of the interference signal corresponding to the falling from the frequency of the interference signal corresponding to the rising of the modulated wave by multiplying by 1/2 under the condition that the Doppler shift frequency is higher than the beat frequency. , If the Doppler shift frequency is smaller than the beat signal, and the frequency of the interference signal corresponding to the falling edge of the modulated wave is added to the frequency of the interference signal corresponding to the rising edge, , The beat frequency fb can be obtained by selectively performing the calculation of (f1 + f2) / 2 or (f1−f2) / 2 based on the magnitude relationship between the Doppler shift frequency and the beat frequency. The manual operation for doing so can be omitted.

Further, the calculating means includes condition determining means that holds condition determining data that is determined based on the moving speed and moving direction of the measurement target, and an adding and subtracting means that selects a subtracting operation and an adding operation based on the result of the condition determining. If you have
The influence of Doppler shift can be eliminated by setting the moving speed and moving direction of the measuring object before performing the scanning measurement, and then performing the above series of operations while moving the measuring object. Accurate scanning measurement can be performed.

<Example> Hereinafter, detailed description will be given with reference to the accompanying drawings illustrating an example.

FIG. 8 is a schematic view showing an example of an optical system applied to the distance measuring method and device of the present invention.

The LD (1) that outputs laser light for measurement is mounted at a predetermined position of a Peltier element (not shown) that is a kind of electro-thermal conversion element, and the injection current is controlled by the drive current controller (2). Is being supplied. The Peltier element is controlled so as to keep the temperature of the LD (1) constant, and the injection current supplied by the drive current control unit (2) rises to form a triangular wave with the same slope. By changing it, the laser light whose frequency changes in accordance with the change of the injection current (see FIG. 2A) is output.

Then, the laser light is split into two by a beam splitter (3), and one of them is a reference reflector (4) having a known optical path length.
And irradiate the measurement target (5) with the other. Interference light can be obtained by guiding the reflected light from the reference reflector (4) and the reflected light from the measurement object (5) to the beam splitter (3).
This interference light is converted into an electric signal by being guided to the light receiving element (6), and the interference signal output from the light receiving element (6) is supplied to the processor (7), and up to the measurement object (5). The distance is calculated.

The LD (1) is mounted on a constant temperature block (8) covered with a heat insulation layer (8 ') such as cork on the outside as shown in FIG. The temperature detecting element (9) is mounted at a position close to the mounting position of the, and the drive signal supplied to the Peltier element (10) is controlled based on the temperature detecting signal output from the temperature detecting element (9). Thus, the influence of the ambient temperature is largely blocked so that the LD (1) can be operated stably.

FIG. 1 is a flow chart for explaining the scanning measurement process in the processor (7).
The interference signals output from the light receiving element (6) are written in different memory areas corresponding to the rising and falling portions of the modulated wave of the LD (1), and the interference signal corresponding to one cycle of the modulated wave is stored in the memory. If written in the area, in steps, the frequencies f1 and f2 of the interference signal corresponding to each part of the modulated wave
To calculate. Then, in step, it is determined whether or not the Doppler shift frequency fd is larger than the beat frequency fb, and when it is determined that fd> fb,
The beat frequency fb is calculated by performing the calculation of (f1-f2) / 2 in the step, and conversely, when it is determined that fd <fb, the calculation of (f1 + f2) / 2 is performed in the step. The beat frequency fb is calculated by

After the above step or steps are performed, the distance to the measurement object (5) can be calculated based on the beat frequency fb in the step, and the calculated distance data is written in the memory in the step. After that, the discrimination and processing below the steps are performed again.

Therefore, by performing the series of operations while moving the measurement object (5) in a predetermined direction at a constant speed, the distance to each point on the surface of the measurement object (5) is influenced by the Doppler shift frequency. It can be accurately calculated in the excluded state, and as a result, the uneven state of the surface of the measurement object (5) can be accurately measured.

More specifically, the frequency of the laser light emitted from the LD (1) changes in a triangular wave shape having the same rising and falling slopes as shown in FIG. 2A. Therefore, the change amounts of the frequency deviation of the laser light at the rising portion and the falling portion of the triangular wave have the same absolute value and opposite signs.

Then, if the laser light shown in FIG. 2A is divided into two parts, one of which is reflected by the reference reflector (4) and the other of which is reflected by the measurement object (5) that moves at a constant speed, and interferes with each other.
The intensity of the interference light, as shown in FIG. 2 B, and corresponding to the rising portion of the triangular wave ^{E 2 0 + E 2 0cos {} 2π (fb + fd) t}, corresponding to the falling portion of the triangular wave E ² 0 + E ² 0cos {2π | fb−fd | t} (where E0 is the electric field amplitude of the laser light, fb is the beat frequency,
Since fd is the Doppler shift frequency), it is possible to obtain an interference signal having a high frequency f1 corresponding to the rising portion of the triangular wave and a low frequency f2 corresponding to the falling portion of the triangular wave.

Therefore, by performing an operation based on both the frequencies f1 and f2, it is possible to eliminate the influence of the Doppler shift frequency and the change amount of the frequency shift of the laser light to obtain an accurate beat frequency fb. An accurate distance to the measurement object (5) can be calculated based on the frequency fb.

Then, by performing this operation on the entire surface of the measurement object (5), it is possible to accurately perform the scanning measurement.

FIG. 3 is a block diagram showing an embodiment of the scanning measuring apparatus, which includes a waveform shaper (11) for inputting an output signal from the light receiving element (6) and a waveform shaper (11). A pair of clock counters that take the output signal as input (12)
(13), a clock generator (14) for supplying a clock signal to both clock counters (12, 13), and a time setter (for supplying a count operation time setting signal to each clock counter (12) (13) ( 15) and both clock counters (12)
An arithmetic circuit (16) for calculating the beat frequency fb by performing an arithmetic operation with the count signal output from (13) as an input,
And a display (17) for displaying the calculated beat frequency fb.

The operation of the scanning measuring apparatus having the above configuration will be described with reference to the waveform chart of FIG.

By supplying the LD (1) with a triangular-wave-shaped modulation signal having the same rising and falling slopes as shown in FIG. 4A, laser light whose frequency changes in a triangular-wave shape is emitted, and the laser light is divided into two parts and each becomes a reference. The reflected light reflected by the reflector (4) and the object to be measured (5) and interfered by the beam splitter (3) to obtain interference light whose intensity changes periodically is obtained from the light receiving element (6) as shown in FIG. As shown in B, signals having different frequencies are output corresponding to the rising portion and the falling portion of the modulated signal.

The signal output from the light receiving element (6) is supplied to both clock counters (12) and (13), and the reference clock signal output from the clock generator (14) is also supplied to both clock counters (12) (13). ), The time setter (15) selectively operates the gate signal (corresponding to the rising and falling portions of the modulation signal) of the gate counter (Fig. 4, C, (See D), it is possible to alternately obtain the interference signal frequencies f1 and f2 by each clock counter. That is, one clock counter (12) outputs the interference signal frequency f1 corresponding to the rising portion of the modulation signal, and the other clock counter (13) outputs the interference signal frequency f2 corresponding to the falling portion of the modulation signal. Is output.

Therefore, by supplying both the interference signal frequencies f1 and f2 to the arithmetic circuit (16), the Doppler shift frequency fd
Beat frequency by performing a predetermined calculation to eliminate
The distance to the measurement object (5) can be calculated by obtaining fb and performing a predetermined calculation based on the obtained beat frequency fb and the known optical path length on the reference reflector side. After that, the calculated distance to the measurement object (5) is displayed on the display (17), and if necessary, written in a memory (not shown).

Since the above operation is performed on the entire surface of the measuring object (5), the uneven shape of the surface of the measuring object (5) can be grasped based on a large number of distance data.

FIG. 5 is a block diagram showing another configuration of the arithmetic circuit (16), including a memory (18) in which reference data for determining the magnitude relationship between the beat frequency fb and the Doppler shift frequency fd is set. , The moving speed v (cm / min) of the measuring object (5) set for performing the scanning measurement and the moving direction θ (deg) of the measuring object (5) with reference to a plane orthogonal to the laser light are The above memory by being supplied (18)
A read control unit (19) for reading the corresponding data from (f1 +
The first arithmetic circuit (20) for performing the operation of f2) / 2 and (f1−f
2) / 2 The second arithmetic circuit (21) for performing the arithmetic operation, and the third arithmetic circuit (22) for calculating the distance to the measurement object (5) by inputting the beat frequency obtained by either arithmetic circuit.
And have. Then, the read data from the memory (18) is used as an operation control signal for both arithmetic circuits (20) (21).
Is being supplied to.

More specifically, if the laser light with which the measurement object (5) is irradiated is in the state shown in FIG. 6, the moving direction θ is the intersection angle of the moving direction with respect to the plane orthogonal to the laser light. Then, by the moving speed v and the moving direction θ,
A curve (see B in FIG. 7) at which the beat frequency fb becomes equal to the Doppler shift frequency fd is determined. With this curve as a boundary, a region of fb> fd (see region A in FIG. 7) and fb <
It will be divided into the area of fd (see area C in FIG. 7). Although the position of the curve changes depending on the heterodyne interference system, the curve is uniquely defined because the heterodyne interference system for scanning measurement is already set.

Therefore, if the memory (18) is allocated so as to correspond to FIG. 7 and the moving speed v and the moving direction θ are supplied as read address data by the read control unit (19), the areas are respectively allocated. Different operation control data which are different from each other are read out.

The operation of the scanning measuring device having the above configuration is as follows.

Similar to the embodiment of FIG. 3, a pair of clock counters (1
2) The interference signal frequency f1 corresponding to the rising portion of the triangular wave and the interference signal frequency f2 corresponding to the falling portion of the triangular wave are alternately obtained by (13) and supplied to the arithmetic circuit (16).

In the arithmetic circuit (16), a curve is set in advance, and a memory (18) that stores mutually different calculation restriction data for each area partitioned by the curve is provided, and the read control unit is provided. (19) The moving speed v and moving direction θ are stored in the memory (1
Since it is supplied to 8), the operation control data assigned to any area is read. Then, by supplying the arithmetic control data to both arithmetic circuits (20) (21), only one of the arithmetic circuits is operated and the influence of the Doppler shift frequency fd is eliminated,
The beat signal fb is calculated.

Therefore, thereafter, the distance to the measurement object (5) can be calculated by the third arithmetic circuit (22).

The present invention is not limited to the above-described embodiment, and for example, the calculation of (f1 + f2) / 2 and the calculation of (f1−f2) / 2 can be selected by manual operation.
It is possible to calculate (f1 + f2) or (f1−f2) to obtain a frequency 2fb that is twice the beat frequency, and calculate the distance to the measurement object (5) based on 2fb.
In addition, various design changes can be made within the scope of the present invention.

<Effect of the Invention> As described above, the first invention is that Doppler is performed by performing addition and subtraction based on the interference signal frequencies corresponding to the rising portion and the falling portion of a triangular wave-shaped modulated wave having the same rising and falling slopes. The unique effect that the influence of the shift frequency can be eliminated and the distance of the measurement object to the measurement point that changes sequentially can be accurately measured based on the frequency from which the influence of the Doppler shift frequency is eliminated. Play.

According to a second aspect of the present invention, the influence of the Doppler shift frequency can be eliminated by performing addition and subtraction based on the interference signal frequencies corresponding to the rising portion and the falling portion of the triangular wave-shaped modulated wave having the same rising and falling slopes. Therefore, it is possible to accurately measure the distance of the measurement object to the measurement object point that sequentially changes based on the frequency from which the influence of the Doppler shift frequency is eliminated.

The third aspect of the invention has a unique effect that the type of calculation can be selected based on the magnitude relationship between the beat frequency and the Doppler shift frequency, and the manual operation for selecting the calculation can be omitted.

A fourth aspect of the invention is to set the moving speed and moving direction of the measuring object before performing the scanning measurement, and thereafter perform a series of operations while moving the measuring object, thereby performing the Doppler shift. There is a unique effect that accurate scanning measurement can be performed by eliminating the influence of.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining an example of the scanning measuring method of the present invention, FIG. 2 is a waveform diagram for explaining the relationship between the modulation signal and the interference signal, and FIG. 3 is an embodiment of the scanning measuring apparatus of the present invention. FIG. 4 is a block diagram showing the operation of the scanning measuring apparatus of FIG. 3, and FIG. 5 is a block diagram showing the essential portions of another embodiment of the scanning measuring apparatus. FIG. 7 is a schematic diagram showing the relationship between the light and the moving direction of the object to be measured, FIG. 7 is a view for explaining the magnitude relationship between the beat frequency and the Doppler shift frequency, and FIG. 8 is applied to the distance measuring method and device of the present invention. FIG. 9 is a schematic view showing an example of an optical system according to the present invention, and FIG. 9 is a longitudinal sectional view showing a mounted state of a semiconductor laser. (1) ... LD, (2) ... driving current control unit, (3) ... beam splitter, (4) ... reference reflector, (5) ... measurement object, (6) ... light receiving element , (12) (13) …… Clock counter, (16) …… Arithmetic circuit, (18) …… Memory, (20) …… First arithmetic circuit, (21) …… Second arithmetic circuit, (22) ... Third arithmetic circuit

Claims (4)

[Claims] 1. A laser beam is divided into two parts, one of which is applied to a measuring object (5) and the other of which is applied to a reference reflector (4) to reflect light from the measuring object (5), and In an interferometer that measures reflected light from a reference reflector (4) to obtain an interference signal and measures the distance to the measurement object (5) based on the interference signal, the measurement object (5) has a constant speed. The laser beam rises and the slope of the trailing edge is equal to the triangular wave, but the interference signal corresponding to the rising edge and the interference signal corresponding to the falling edge of the modulated wave cause different interference. Calculate the signal frequency,
The Doppler shift frequency component is removed by performing addition and subtraction based on both interference signal frequencies, and the distance to the measurement position of the measurement object that changes sequentially is calculated based on the frequency from which the Doppler shift frequency component is removed. A characteristic scanning measurement method. 2. A laser beam emitted from a semiconductor laser (1) is divided into two parts, one of which is applied to a measurement object (5) and the other of which is applied to a reference reflector (4) to obtain a measurement object. In an interference measuring device for interfering the reflected light from (5) and the reflected light from the reference reflector (4) to obtain an interference signal, and measuring the distance to the measurement object (5) based on the interference signal, The object to be measured (5) moves at a constant speed, and the modulation means (2) that modulates the semiconductor laser (1) into a triangular wave shape with rising and falling slopes is equivalent to rising of the modulated wave. Interference signal extraction means (15) for extracting the interference signal and the interference signal corresponding to the falling edge, and frequency calculation means (1) for calculating the frequency of each extracted interference signal.
2) (13), calculation means (16) (20) (21) for calculating the frequency from which the Doppler shift frequency component has been removed based on both calculated frequencies, and the frequency from which the Doppler shift frequency component has been removed Distance calculation means (16) (2) for calculating the distance to the measurement position of the measuring object that changes in sequence.
2) A scanning measuring device having: 3. An arithmetic means (16) subtracts the frequency of the interference signal corresponding to the falling edge from the frequency of the interference signal corresponding to the rising edge of the modulated wave on the condition that the Doppler shift frequency is higher than the beat frequency. 1/2 times and adding 1/2 the frequency of the interference signal corresponding to the rising edge to the frequency of the interference signal corresponding to the falling edge of the modulated wave, provided that the Doppler shift frequency is smaller than the beat frequency The scanning measuring apparatus according to claim 2, wherein 4. A condition discriminating means (18) for holding a condition discriminating data determined by a moving speed and a moving direction of an object to be measured, and a subtracting operation and an adding operation based on the result of the condition discriminating. Addition and subtraction means (20) (2
1) The copying measuring device according to claim 2 having the above.