JPH02297006A - Method and device for measuring displacement of object - Google Patents

Abstract

PURPOSE:To execute the measurement with high accuracy even if the displacement quantity is large by collating successively a measured image signal obtained at the time of measurement and plural scanning image signals stored in a memory and outputting a signal for showing a mutual correlation function. CONSTITUTION:The surface of a moving object 2 is irradiated by a laser beam, and a one-dimensional image sensor (that which is formed by arranging a CCD along the moving direction X of the object 2) 3 is placed so as to be opposed to the irradiated surface 21. As a result, the observation surface of a speckle pattern is formed. An image signal brought to photoelectric conversion by the sensor 3 is brought to A/D conversion 42, and stored successively to a memory 6. A correlator 7 calculates immediately a mutual correlation function of a digital signal for showing a speckle pattern of one scanning point read out of the memory 6, and a digital signal for showing a speckle pattern in one measuring point sent from the A/D converter 42. A result of this calculation is sent to an arithmetic processing circuit 8, and the circuit 8 outputs a signal corresponding to a moving amount of the object 2, based on address data sent from an address switching circuit 61.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention utilizes speckle patterns generated by diffused light from the rough surface of a target object irradiated with laser light to determine the amount of displacement of a moving object or a predetermined displacement. The present invention relates to a method and apparatus for measuring the time point of occurrence.

(Prior Art) Conventionally, a method has been proposed for measuring minute deformations of objects by applying speckle patterns (Japanese Patent Publication No. 59-52
No. 963, J. Phys, E: Sci.
Instrum, 19°1986).

This measurement method irradiates the surface of the object to be measured with a laser beam, places an image sensor in the diffusely reflected light, and calculates the cross-correlation function of the output signals before and after deforming the object based on the sensor output. The amount of movement of the speckle pattern is obtained as the position of the peak value of the cross-correlation function.

(Problem to be solved) However, in the conventional method, measurement is performed only based on the cross-correlation of two speckle patterns before and after deformation, so the deformation range where measurement accuracy is guaranteed is limited to both speckle patterns. limited to a range in which a certain degree of correlation is maintained in the pattern.

Therefore, when measuring the amount of displacement of a moving object by applying the conventional deformation measurement method, if the amount of displacement becomes larger than the diameter of the laser beam, there will be no correlation between the two speckle patterns before and after the movement. , measurement becomes impossible. Further, even when the amount of displacement is smaller than the beam diameter, a problem arises in that the measurement accuracy decreases as the amount of displacement increases.

An object of the present invention is to provide a method and apparatus for measuring the displacement of a moving object, which enables highly accurate measurement regardless of the magnitude of displacement.

(Means for Solving the Problems) A method for measuring displacement of a moving object according to the present invention includes a scanning step of irradiating the moving object with a laser beam before actual measurement;
After that, it consists of two steps: an actual measurement step in which a moving object is irradiated with a laser beam during actual measurement.

In the scanning step, a laser beam is irradiated onto the surface of the moving object (2) to form a speckle pattern on an observation surface facing the moving object (2), and the speckle pattern is converted into an image signal. Then, image signals that change with the displacement of the moving object (2) are sequentially stored in a plurality of storage sections of the memory (6) in association with the amount of displacement of the moving object (2).

In the actual measurement step, the cross-correlation function between the image signal of the speckle pattern appearing on the observation surface and the plurality of image signals stored in each storage section of the memory (6) is calculated in sequence, and the largest correlation peak is calculated. The displacement of the moving object (2) is measured based on the storage position in the memory (6) of the image signal whose value is obtained.

Further, the object displacement measuring device according to the present invention includes a laser source that irradiates a laser beam toward the surface of the object to be measured, and a laser source that is placed at a position where it can receive the diffusely reflected light from the object surface. an image sensor (3) that detects a speckle pattern of reflected light; and an image sensor (3) that detects a speckle pattern of reflected light.
A memory having a plurality of storage sections that stores the image signals obtained from the image signals in association with the laser beam irradiation position on the object at a pitch that maintains the correlation of the speckle pattern (
6), and a correlator (7) that successively collates the actually measured image signal obtained during object displacement measurement with the plurality of scanned image signals stored in the memory (6) and outputs a signal representing a cross-correlation function. and a changeover switch (5) that selectively connects the image sensor (3) to the correlator (7) or the memory (6), and performs arithmetic processing on the output signal of the correlator (7) to determine the displacement of the object. It is composed of an arithmetic processing circuit (8) that outputs a corresponding signal.

(Function) In the measurement method according to the present invention, when measuring displacement, the speckle pattern appearing on the observation surface changes as the object (2) moves, and the image signal of the speckle pattern at a certain point in time during the change, A cross-correlation function between the image signals of a plurality of speckle patterns already stored in the memory (6) is sequentially calculated.

At this time, if there is a large difference between the amount of displacement of the object corresponding to the storage position of the image signal for which the cross-correlation function is calculated and the actual amount of displacement of the object at the time of measurement, the cross-correlation function The peak value of the cross-correlation function is small, and when the difference is small, the peak value of the cross-correlation function becomes large.

Therefore, the amount of object displacement corresponding to the storage position of the image signal where the largest correlation peak value is obtained represents the actual amount of displacement of the object at the time of measurement.

In addition, when carrying out the above measurement method using the measuring device according to the present invention, first, the surface of the target object is scanned with a laser beam while the switch (5) is switched to the memory (6) side. The scanning image signals of the speckle pattern that change with the measurement are sequentially stored in the memory (6), and the scanning step in the measurement method of the present invention is executed.

After that, when measuring displacement, switch (5) is connected to correlator (7).
) side and irradiates the surface of the target object with a laser beam, the correlator (7) calculates a cross-correlation function, the arithmetic processing circuit (8) creates a signal according to the object displacement, The actual measurement step in the measurement method of the present invention is performed.

(Effects of the Invention) According to the method and apparatus for measuring the displacement of a moving object according to the present invention, even when the amount of movement of the object exceeds the beam spot diameter, measurement can be performed according to the scanning range of the laser beam in the scanning step. The range can be expanded, in this case,
It is possible to improve measurement accuracy by reducing the interval between speckle patterns to be stored as image signals in memory as small as possible.

(Example) Embodiments of the present invention will be described below along with the drawings.

It should be noted that the examples are for illustrating the present invention, and should not be construed as limiting the invention described in the claims or reducing its scope.

FIG. 1 shows the configuration of an apparatus for measuring the amount of parallel movement of a moving object (2) using the measuring method of the present invention.

A semiconductor laser (1) driven by a laser drive circuit (11) is arranged opposite the moving object (2). The laser light emitted from the semiconductor laser (1) passes through a beam expanding lens (12) and is irradiated onto the surface of the moving object (2) as a laser beam with a predetermined beam diameter (for example, 1 ++ on).

Further, a one-dimensional image sensor (
3) is placed. The image sensor (3) connects, for example, 1024 CCDs (charge coupled devices) to a moving object (2).
are arranged one-dimensionally at a pitch of 14 μm along the moving direction X, thereby forming the observation surface of the speckle pattern.

Note that as the -dimensional image sensor (3), it is also possible to use an array of photodiodes.

- The image signal photoelectrically converted by the dimensional image sensor (3) is sent to the A/D converter (42) via the amplifier (41) equipped in the measurement circuit (4) and converted into an 8-bit digital signal. be done.

The digital signal is connected to an input terminal of a changeover switch (5), and one output terminal a of the switch is connected to a memory (6).
connected to the data input port of the Further, the data output port of the memory (6) and the other output end of the changeover switch (5) are connected to a correlator (7).

The memory (6) stores a 1024-byte storage section for storing the digital signal at the -scanning point of the moving object (2) sent from the A/D converter (42), from the 1st address to the Nth address. (N = 600). Writing and reading of signals into the memory (6) is controlled by an address switching circuit (6I) as described below.

The correlator (7) also receives a digital signal representing the speckle pattern of the scanning point read out from the memory (6) and sent from the A/D converter (42) via the changeover switch (5). The cross-correlation function with a digital signal representing a speckle pattern at one measurement point is calculated in real time.

The A/D converter (42) and address switching circuit (6)
The operation timing of step 1) is controlled by the control circuit (43) as described below.

The calculation result of the cross-correlation function obtained from the correlator (7) is sent to an arithmetic processing circuit (8) consisting of a microcomputer or the like. The arithmetic processing circuit (8) outputs a signal corresponding to the amount of movement of the moving object (2) based on the calculation result and address data, which will be described later, sent from the address switching circuit (61). be.

Hereinafter, a measurement method using the above displacement measuring device and the operation of each of the above circuits will be explained.

First, before actual displacement measurement, while moving the moving object (2) at a constant speed over its entire movement range,
2) a scanning step of irradiating the laser beam from the semiconductor laser (1) and sequentially storing the speckle pattern formed by the diffusely reflected light from the laser irradiation surface (21) as an image signal in the memory (6); is executed.

At this time, the changeover switch (5) is switched to the a side.

In this process, the A/D converter (42)
The image signal from the amplifier (41) is converted into a digital signal at regular intervals under the control of the converter (41), and the digital signal is supplied to the memory (6) via the changeover switch (5).

Further, the address switching circuit (61) is a control circuit (43).
, the data storage address of the memory (6) is sequentially switched from the first address to the Nth address in synchronization with the operation cycle of the A/D converter (42).

As a result, the digital signal supplied to the memory (6) at regular intervals via the changeover switch (5) is transmitted to the storage section (M
1, Ml, . . . Mi, . . . Mn).

The plurality of digital signals (Fl, F2, -Fi, ++Fn) stored in the memory (6) in this way are as follows:
As shown in FIG. 3, N scanning spot areas (A, , A8, . . . Ail . . .
Each exhibits a unique speckle pattern corresponding to the rough surface condition of An).

Note that the above-described scanning step can also be performed by moving the measurement system consisting of a light source and an image sensor along the object movement direction while the object (2) remains stationary.

In addition, the scanning spot area (At, A2, . . .
・As a method of setting Ail...An) to a predetermined interval smaller than the spot diameter, if the relative speed between the object to be measured and the measurement system is constant, write to the memory at a constant cycle as described above. For example, when the relative velocity is not constant, as in the case of manually moving the measuring system, the following method can be adopted. In this case, a switching control circuit (51) for controlling switching of the switch (5) is provided as shown in FIG.

First, switch the changeover switch (5) in Figure 1 to side a,
In this state, the first spot area A1 is irradiated with a laser beam. As a result, the speckle pattern of the area is stored at the first address of the memory (6).

After that, the switch (5) is controlled by the switching control circuit (51).
) is switched to side b, and in this state the laser irradiation position is gradually moved. As a result, the correlation function between the measured speckle pattern and the scanning speckle pattern at the first address in the memory is repeatedly calculated, and the correlation peak value obtained as a result of the correlation function is lower than a predetermined value, that is, the correlation between both speckle patterns. The point in time before it becomes difficult to remove is detected.

Further, the amount of displacement of the laser irradiation position is calculated from the correlation peak position at this time.

At the same time, the switch (5) is switched to the a side by the switching control circuit (51), and the image data obtained from the A/D converter (42) is transferred to the second scanning spot area A in FIG. Memory as a speckle pattern (
6), and also stores the calculation result of the amount of displacement of the laser irradiation position.

Thereafter, in the same way, the position that should become the next scanning spot area is detected based on the decrease in the correlation peak value using the speckle pattern most recently stored in the memory as a reference, and the position that should become the next scanning spot area is detected, and the position that should become the next scanning spot area is detected. The operation of memorizing the interval is repeated.

As a result, each scanning spot area (AI, A3,
.

In addition, in the above scanning step, by repeating the operation of detecting the point immediately before the correlation becomes difficult to maintain and simply storing the speckle pattern at that point, the scanning spot shown in FIG. 3 can be obtained at a substantially constant pitch. Area (A i, A x
, . . . AI5 . . . An) are set, it is not necessarily necessary to calculate the amount of displacement of the scanning spot area. That is, the interval (pitch) between scanning spot areas is calculated as an approximate value from the total scanning length in the scanning step and the number of speckle patterns stored in the memory.

Next, the process moves to the step of actually measuring the amount of movement of the moving object (2). At this time, the changeover switch (5) is switched to the b side as shown in FIG. 1, and the correlator (7) and the arithmetic processing circuit (8) are further set to the operating state.

For example, when the moving object (2) moves by a certain amount of displacement and the amount of displacement is measured when the laser beam irradiates the spot area Ai' on the irradiation surface (21) as shown in FIG.
From the one-dimensional image sensor (3) in Fig. 1 to the amplifier (41
), the image signal obtained in real time is A/
After being converted into a digital signal by a D converter (42), it is sent to a correlator (7) via a changeover switch (5).

On the other hand, due to the operation of the address switching circuit (61), data is transferred from the memory (6) to the storage section M1 at the first address as shown in FIG.
The digital signals (F, , F2, . . . , Fil . . . Fn) stored in the storage unit Mn at the Nth address are sequentially read out and sent to the correlator (7) at regular intervals.

The correlator (7) sequentially calculates a cross-correlation function between the digital signal G supplied via the changeover switch (5) and the digital signal sent from the memory (6), and outputs the calculation results one after another. It is sent to the arithmetic processing circuit (8) in FIG.

The arithmetic processing circuit (8) selects the correlation function for which the maximum correlation peak value has been obtained from among the N correlation functions sent from the correlator (7), and selects the correlation function for which the maximum correlation peak value has been obtained. The storage address of the digital signal Fi in the memory (6) is detected based on the address data from the address switching circuit (61).

The speckle pattern that served as the basis for calculating the correlation function for which the maximum correlation peak value was obtained is the scanning spot area that overlaps with the measurement spot area Ai′ that is actually irradiated with the laser beam and has the largest overlap area. This is a speckle pattern for Ai. Therefore, as the position of the scanning spot area corresponding to the storage address of the digital signal Fi, the position of the measurement spot area Ai' can be determined within a certain error range from the scanning spot pitch (0.5 mm).

In addition, if the spacing between each scanning sbot area is measured and stored in the scanning step as described above, or if an approximate value of the spacing is known, the spot area spacing after the start of the actual measurement is read out. By integrating, it is possible to calculate the position of the measurement spot area Ai'.

Further, the arithmetic processing circuit (8) calculates the peak position δ shown in FIG. 5 from the distribution of the cross-correlation function from which the maximum correlation peak value was obtained, and based on the peak position δ, calculates the peak position δ shown in FIG. A positional deviation ΔX between the scanning spot area Ai and the measuring spot area Ai' is calculated.

Furthermore, the arithmetic processing circuit (8)
The position of the measurement spot area Ai', that is, the movement amount of the moving object (2), is accurately calculated by applying correction based on the positional deviation ΔX to the calculation result of the movement amount determined as the position of . Output the result.

The output signal can be supplied to, for example, a display (not shown) to digitally display the amount of movement.

In addition, when the above measuring device is applied to an automatic positioning device such as a robot arm, the arithmetic processing circuit (8)
By detecting the point in time when the positional deviation δ shown in the figure becomes zero and supplying the detection signal to a motor drive circuit or the like to be controlled, highly accurate positioning becomes possible.

In this case, by setting a scanning spot area at each position that is a positioning target in the scanning step, the arithmetic processing circuit (8) determines when the maximum correlation peak value exceeds a predetermined value. For example, when the normalized correlation peak value becomes approximately 1, it is sufficient to generate an output signal corresponding to the storage position in the memory (6) of the image signal that is the basis for calculating the correlation peak value. The calculation of the amount of movement based on the deviation of the peak position shown in FIG. 5 can be omitted.

According to the displacement measuring method according to the present invention, once the scanning step is executed, only the actual measurement step is executed after that, thereby eliminating the need to attach a special scale or the like to the moving object (2). A moving object (
2) Displacement can be measured in real time. At this time, the third
By making the pitch of the scanning spot areas shown in the figure as small as possible, measurement accuracy can be increased.

Note that the drawings and the description of the above-mentioned embodiments are for explaining the present invention, and should not be interpreted to limit the invention described in the claims or to reduce its scope.

Further, it goes without saying that the configuration of each part of the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the technical scope of the claims.

For example, if the one-dimensional image sensor (3) in FIG. 1 is replaced with a two-dimensional image sensor, it is possible to measure the amount of displacement of the object (2) in the two-dimensional direction.

Furthermore, as shown in Fig. 2, by irradiating the outer peripheral surface (24) of a drum-shaped rotating object (23) with a laser beam, the rotation angle of the rotating object (23) can be measured. It is also possible to configure an encoder.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a displacement measuring device according to the present invention,
Fig. 2 is a diagram showing another configuration example of the displacement measuring device, Fig. 3 is a diagram explaining the operation of the device in the actual measurement step, Fig. 4 is a diagram showing the positional deviation of the beam spot, and Fig. 5 is a correlator. It is a graph showing a cross-correlation function obtained from .

Claims (1)

[Claims] [1] The surface of the object (2) to be measured is scanned with a laser beam in the direction of object movement, and the surface of the object (2) to be measured is scanned on the observation surface opposite to the laser irradiation surface (21). The appearing speckle pattern is converted into an image signal, and the image signal that changes with the scanning is stored in a plurality of storage sections of the memory (6) in association with the irradiation position of the laser beam on the laser irradiation surface (21). After sequential storage, when measuring the displacement of object (2),
An image signal from which a maximum correlation peak value is obtained by calculating a cross-correlation function between an image signal of a speckle pattern appearing on the observation surface and a plurality of image signals stored in each storage section of the memory (6). A method for measuring the displacement of an object, characterized in that the displacement of the object (2) is detected based on the storage position in the memory (6) of the object (2). [2] In the process of scanning the surface of the object to be measured (2) with a laser beam, the speckle pattern that appears on the observation surface at one point in time is stored in the memory (6), and then the speckle pattern and subsequent scanning are stored in the memory (6). The cross-correlation function with the speckle pattern, which changes with the 2. The displacement measuring method according to claim 1, wherein the speckle pattern is sequentially stored in the memory (6) by repeating the operation of storing the speckle pattern in the storage position. [3] When measuring the displacement of the moving object (2), the amount of movement of the moving object (2) is determined within a certain error range based on the storage position in the memory (6) of the image signal where the maximum correlation peak value is obtained. Furthermore, the peak position of the cross-correlation function between the image signal and the image signal of the speckle pattern appearing on the observation surface is detected, and based on both detections, the amount of displacement of the moving object (2) is determined with high precision. First claim to be calculated
Displacement measurement method described in Section. [4] When measuring the displacement of the moving object (2), at the point when the maximum correlation peak value exceeds a predetermined value, according to the storage position in the memory (6) of the image signal that was the basis for calculating the correlation peak value the object (2);
The displacement measuring method according to claim 1, wherein the displacement measuring method is used as a control signal for automatic positioning. [5] An image of a laser source that irradiates a laser beam toward the surface of an object to be measured, and a laser source that is placed at a position where it can receive the diffusely reflected light from the object's surface and detects the speckle pattern of the diffusely reflected light. It has a sensor (3) and a plurality of storage units that store image signals obtained from the image sensor (3) in association with the laser beam irradiation position of the object at a pitch that maintains the correlation of the speckle pattern. a memory (6), and a correlator (for outputting a signal representing a cross-correlation function) by sequentially collating the actually measured image signal obtained during object displacement measurement with the plurality of scanned image signals stored in the memory (6); 7), and the image sensor (3) is selectively connected to a correlator (7) or a memory (6).
An object displacement measuring device consisting of a changeover switch (5) connected to the correlator (7), and an arithmetic processing circuit (8) that performs arithmetic processing on the output signal of the correlator (7) and outputs a signal according to the displacement of the object. .