JP3304564B2 - Optical position detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical position detecting apparatus for measuring the position of a point light source which emits light directly or indirectly by using an image pickup device. More specifically, the present invention relates to a technique for improving the accuracy of such an optical position detecting device.

[0002]

2. Description of the Related Art Conventionally, when monitoring the behavior of landslides, for example, targets composed of point light sources are installed at equal intervals on a slope (slope) of a mountain, and light beams emitted directly or indirectly from each point light source. Was captured by a television camera from a distance, and the video signal was analyzed to detect the position of each target. In particular, when three-dimensional displacement information of each target is required, a stereo method using two television cameras is often used.

[0003]

In order to increase the measurement accuracy in such a monitoring system, it is necessary to improve the resolution of the television camera. However, for that purpose, the number of elements of an imaging device such as a CCD incorporated in a television camera must be greatly increased, but this is difficult in terms of manufacturing technology.

A technique for improving the apparent resolution without increasing the number of elements of the image pickup device has been proposed, for example, disclosed in Japanese Patent Application Laid-Open No. Sho 60-218002. According to this, a cross filter is attached to a lens of a television camera, a light beam from each target is converted into a streak cross-shaped image by the cross filter, and is projected on a light receiving surface of an imaging device. This projection image is subjected to image processing, the intersection of the cross image is calculated, and the position of the point light source constituting each target is determined. However, in this conventional method, a streak-shaped cross-shaped image does not occur unless the light from the point light source is strong to some extent. Therefore, there is a disadvantage that the sensitivity is poor.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, the present invention provides an optical position detecting apparatus having improved resolution without increasing the number of elements of an image pickup device and without sacrificing sensitivity. The purpose is to provide. The following measures were taken to achieve this purpose. That is, the optical position detection device according to the present invention has, as a basic configuration, an imaging unit, a scale plate, and an imaging unit which are sequentially arranged along the optical axis, and an arithmetic unit connected to the imaging unit.
In such a configuration, the scale plate has a plurality of pattern elements regularly arranged along a forward coordinate plane orthogonal to the optical axis. Further, the imaging means condenses a light beam emitted from a target measurement point and converts it into reference light converged on a corresponding imaging point, and spot-illuminates a part of the scale plate with the reference light. Enlarge and project a specific pattern element.
Further, the image pickup means has a light receiving surface arranged along a rear coordinate plane orthogonal to the optical axis, and picks up an enlarged and projected pattern shadow and outputs corresponding image data. Finally, the calculating means detects the rear coordinate value of the pattern shadow by processing the image data, and detects the position of the imaging point based on this and the forward coordinate value of the original pattern element, The position of the measurement point is calculated based on the position of the imaging point.

The scale plate has a plurality of pattern elements (for example, lattice pattern elements) which are two-dimensionally regularly arranged along the front coordinate plane. On the other hand, the imaging means images the enlarged and projected pattern shadow in a plane and outputs corresponding two-dimensional image data. The calculating means processes the two-dimensional image data to detect a two-dimensional backward coordinate value of the pattern shadow, and calculates a two-dimensional position of the imaging point based on the two-dimensional backward coordinate value of the original pattern element. Is calculated, and the two-dimensional position of the measurement point is calculated based on the two-dimensional position. In this case, the calculating means integrates the two-dimensional image data to generate one-dimensional cross-section data orthogonal to each other, and analyzes the one-dimensional cross-section data to detect the two-dimensional rear coordinate value. When handling three-dimensional information instead of two-dimensional information, the imaging means captures at least a pair of enlarged and projected pattern shadows and outputs corresponding image data. The computing means processes the image data to detect a two-dimensional backward coordinate value of the pair of pattern shadows, and based on this and the two-dimensional forward coordinate value of the original pair of pattern shadows, calculates a cubic value of the image point. An original position is calculated, and a three-dimensional position of the measurement point is calculated based on the three-dimensional position.

Such an optical position detecting device can handle not only a single measuring point but also a plurality of measuring points. In this case, the imaging means captures a plurality of pattern shadows separately enlarged and projected by light beams emitted from a plurality of measurement points and outputs corresponding image data. The arithmetic means processes the image data to detect backward coordinate values for each pattern shadow, and thereby independently and simultaneously calculates the positions of the plurality of measurement points. In this case, the amount of light of the point light source forming each measurement point is relatively small. For this purpose, the imaging means has an image intensifier having a photomultiplier effect for amplifying a weak reference light. Further, it includes a computer or the like which analyzes the position information output from the arithmetic means with time and comprehensively monitors the moving state or the displacement state of the plurality of measurement points, so that a measurement monitoring system can be constructed.

[0008]

According to the present invention, a target measurement point is formed by interposing a scale plate between an imaging means and an imaging means and projecting a pattern element formed thereon on a light receiving surface of the imaging means in an enlarged manner. The displacement of the point light source to be enlarged can be detected. Therefore, the resolution of the measurement point position detection can be improved without increasing the number of elements of the image sensor incorporated in the imaging means. In particular, in the case of a two-dimensional image sensor, it is difficult to increase the number of elements in terms of manufacturing technology. Therefore, it is practical to improve the resolution by optical spatial modulation according to the present invention. You can open up fields. Further, by combining the image intensifier with the image pickup means, it is possible to perform high-accuracy measurement utilizing its high sensitivity. If the measurement points are spaced apart to some extent, the positions of a plurality of point light sources can be detected at the same time, so that behavior monitoring such as landslide can be performed at high speed. By connecting such an optical position detecting device to a computer, an applied system such as a moving object measurement monitoring system can be easily constructed. Such a system allows for accurate and fast real-time measurements.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of an optical position detecting device according to the present invention. As shown in the drawing, the optical position detecting device includes an imaging unit 1, a scale plate 2, and an imaging unit 3 arranged in order along the optical axis. A target measurement point 4 is arranged in the optical axis direction. In this example, a plurality of measurement points 4 are arranged along the slope 5 of the mountain, and are used for monitoring behavior such as landslide. Each measurement point 4 is composed of a point light source, and can be constituted by a light emitting element such as an LED. Alternatively, a reflective light source such as a corner cube may be used instead of the light emitting element. When a light emitting element is used, an LED that emits infrared light is preferable. On the other hand, the imaging means 1 includes a bandpass filter 6 and an objective lens 7. The band-pass filter 6 is made of, for example, a multilayer filter and selectively passes only infrared wavelengths contained in a light beam emitted from a point light source. The imaging means 3 is composed of a combination of an image intensifier 8 and a CCD image sensor 9. A position calculation unit 10 is connected to the CCD image sensor 9. Further, a computer 11 is connected to the position calculation unit 10.

The scale plate 2, which is a characteristic component of the present invention, has a plurality of pattern elements regularly arranged along a forward coordinate plane orthogonal to the optical axis. In this example, a plurality of pattern elements (lattice-like pattern elements) arranged two-dimensionally and regularly are formed. Note that the two-dimensional scale pattern is not limited to a lattice shape, and may be, for example, a pattern in which dot patterns are arranged in a matrix. Furthermore, it is conceivable to calculate the one-dimensional position of the target measurement point using a one-dimensional stripe pattern or the like instead of the two-dimensional scale pattern. The scale plate 2 is disposed at a position separated from the image plane 12 of the objective lens 7 on the rear side in the optical axis direction. This is for illuminating the scale plate 2 in a state where the objective lens 7 is defocused. Therefore, in some cases, the scale plate 2 may be arranged away from the image forming plane 12 on the front side in the optical axis direction.

The objective lens 7 is used for measuring individual target measuring points 4.
The light flux emitted from the light source is condensed and converted into reference light that converges to a corresponding imaging point, and a part of the scale plate 2 is spot-illuminated with the reference light to enlarge and project a specific pattern element.
The CCD image sensor 9 has a light receiving surface arranged along a rear coordinate plane orthogonal to the optical axis, and captures an enlarged and projected pattern shadow and outputs corresponding image data. The position calculation unit 10 processes the image data to detect the backward coordinate value of the pattern shadow, calculates the position of the image forming point based on this and the forward coordinate value of the original pattern element, and further calculates the image forming point. The position of each measurement point 4 is calculated based on the position. In this example, the CCD image sensor 9 captures a plurality of pattern shadows separately enlarged and projected by light beams emitted from a plurality of measurement points and outputs corresponding image data. The position calculation unit 10 processes the image data, detects the backward coordinate value for each pattern shadow, and calculates the positions of the plurality of measurement points 4 independently and simultaneously. The position information output from the position calculation unit 10 is analyzed over time by the computer 11, and the movement state or the displacement state of each measurement point 4 is comprehensively monitored. Thus, the behavior of the slope 5 of the mountain can be monitored, and an accident such as a landslide can be predicted in advance. In such a monitoring system, the optical position detecting device main body is disposed at a long distance from the slope 5 of the mountain. Therefore, the amount of light reaching the main body of the detection device from each measurement point 4 is extremely small, and the reference light is weak. Therefore, it may be difficult to illuminate the scale plate 2 with practical light intensity as it is. Therefore, in this embodiment, the image intensifier 8 is combined with the CCD image sensor 9 to amplify a weak reference light. However, while the image intensifier 8 increases the sensitivity, it has a lower resolution than the CCD image sensor 9,
There is a concern that the resolution of the entire device may be impaired. In this regard, in the present invention, since the resolution is substantially improved by optical spatial modulation using the scale plate 2, the performance degradation due to the incorporation of the image intensifier 8 is prevented.

FIG. 2 shows a light receiving surface 1 of the CCD image sensor.
3 shows an example of the enlarged projection image shown in FIG. The enlarged projection image includes spot images 14 corresponding to individual measurement points. A pattern shadow 15 is provided inside each spot image 14.
Is projected. As described above, in this example, the scale plate has the lattice-shaped pattern elements regularly arranged two-dimensionally along the front coordinate plane. Therefore, on the light receiving surface 13, a lattice-shaped pattern shadow 15 that is spot-illuminated by the defocused reference light and projected in an enlarged manner is projected.
In response, the CCD image sensor outputs two-dimensional image data. Further, the position calculation unit 10 processes the two-dimensional image data to detect the two-dimensional rear coordinate value of the pattern shadow 15, and based on this and the two-dimensional front coordinate value of the original pattern element, determines the two-dimensional position of the imaging point. Is calculated, and the two-dimensional position of the corresponding measurement point is calculated based on the two-dimensional position.

FIG. 3 is a geometrical optical diagram of the optical position detecting device according to the present invention. In this example, a pair of light emitting elements a and b are arranged as measurement points for easy understanding. A light beam 16a emitted from the light emitting element a is condensed by the objective lens 7 and forms a corresponding image point A on the image plane 12. In other words, the incident light beam 16a is converted by the objective lens 7 into the reference light beam 17a that converges on the image point A. The scale plate 2 is arranged along a front coordinate plane that is separated from the imaging plane 12 and is orthogonal to the optical axis. The specific pattern element 18a provided on the scale plate 2 is spot-illuminated by the reference light 17a, and the corresponding pattern element 15a is enlarged and projected on the light receiving surface 13. As described above, this pattern shadow 15a is the spot image 1
4a. The light receiving surface 13 is arranged along the rear coordinate plane orthogonal to the optical axis as described above.
Similarly, the incident light beam 16b emitted from the light emitting element b is converted into reference light 17b by the objective lens 7 and forms an image point B on the image plane 12. The reference light 17b enlarges and projects a specific pattern element 18b to form a corresponding pattern pattern 15b on the spot image 14.
Appears with b.

As is apparent from the illustrated geometric relationship,
The pattern elements 18a and 18b are spot-illuminated with the corresponding imaging points A and B as apparent point light sources, and are enlarged and projected on the light receiving surface 13. Therefore, the magnification of the pattern shadows 15a and 15b depends on the ratio of the distance from the image plane 12 to the scale plate 2 and the distance from the image plane 12 to the light receiving surface 13. For example, the distance between the imaging plane 12 and the scale plate 2 is set to 0.
Set to about 5 mm and set the distance between the scale plate 2 and the light receiving surface 13 to 3
When set to about 4 mm, a magnification of 6 to 8 times is obtained,
This means that the resolution has been improved. In this case, the arrangement pitch of the pattern elements provided on the scale plate 2 is set to, for example, about 80 μm. However, the above-mentioned calculation of the magnification is performed with the imaging plane 12 fixed.
Depending on the optical configuration of the objective lens 7, the imaging surface 12 may move depending on the distance to the light emitting element, and the magnification may slightly change. If it is desired to fix the imaging plane 12, a short focus lens may be used or an autofocus mechanism may be incorporated.

As described above, the CCD having the light receiving surface 13
The image sensor 9 captures the enlarged and projected pattern shadow and outputs corresponding image data. On the other hand, the position calculation unit 1
0 processes the image data to detect, for example, the backward coordinate position of the pattern shadow 15a. The position of the imaging point A is calculated based on this and the forward coordinate value of the original pattern element 18a. As is apparent from the geometrical optical relationship shown in the figure, the image forming point A is a straight line connecting the pattern shadow 15a and the pattern element 18a and the image forming surface 12a.
Located at the intersection of. Further, based on the detected position of the imaging point A, the position of the corresponding light emitting element a can be calculated according to a known lens formula. In this example, the two-dimensional position of the imaging point A along the imaging plane 12 is obtained. Therefore, the two-dimensional position of the light emitting element a is obtained.

However, when the imaging plane 12 fluctuates, the position of the imaging point A cannot be determined by one straight line connecting the pattern shadow 15a and the pattern element 18a. At this time, the position of the imaging point A is determined by calculating at least two straight lines connecting the pair of pattern shadows and the corresponding pair of original pattern elements, and calculating the intersection. In this case, the three-dimensional position of the imaging point A is inevitably determined. Therefore, the three-dimensional position of the corresponding light emitting element can be calculated.

FIG. 4 is a geometrical optical diagram showing the movement of a spot image and the projection range of a pattern element when one light emitting element (not shown) moves in a direction crossing the optical axis. The illustrated example shows a state in which the image forming point changes from A to D along the image forming plane 12 as the light emitting element moves. At this time, the spot image projected on the light receiving surface 13 corresponds to the movement of each of the imaging points A, B, C, and D, and corresponds to 14A,
It moves like 14B, 14C, 14D. On the other hand, a plurality of pattern elements P, Q, and R are provided on the scale plate 2. At this time, the pattern element P is placed inside the spot image 14A.
Is projected. Next, when moving to the spot image 14B, the pattern shadow 15P moves upward, and the pattern shadow 15Q corresponding to the next pattern element Q enters the lower end side of the spot image 14B. Therefore, the spot image 14B includes two pattern features 15P and 15Q. Subsequently, when the pattern pattern shifts to the spot image 14C, the pattern pattern 15Q advances to the center, and the pattern pattern 15P at the destination deviates from the spot image 14C. Further spot image 1
When the pattern pattern moves to 4D, the pattern pattern 15Q moves to the upper end side, and the pattern pattern 15R corresponding to another pattern element R enters. Therefore, the spot pattern 14D has two pattern features 15Q, 1
5R will be included. When a plurality of pattern shadows are included in one spot image, it is necessary to specify one pattern shadow. At this time, the center position of the spot image may be calculated by image processing, and the pattern shadow closest to the center position may be selected. In other words, this is equivalent to reducing the lens aperture of the objective lens 7 and reducing the area of the spot image.

On the other hand, with the movement of the spot images 14A to 14D, the projection range of each of the pattern elements P, Q, and R is changed to the light receiving surface 13 as well.
And has a certain width. However, since the projection ranges of the pattern elements P, Q, and R do not overlap on the light receiving surface 13, it is possible to specify individual pattern elements by image processing. That is, if the projection ranges of all the pattern elements are stored in advance as table data, the corresponding original pattern elements can be specified based on the coordinate values of the individual pattern shadows by referring to the table data. In order to identify individual pattern elements, the dimensions and shapes of each pattern element may be changed.

Next, the position calculation processing will be described in detail with reference to the flowchart of FIG. First, step S1
Captures image data output from the CCD image sensor. Here, the captured image data is
It is represented by [I, J]. Note that I and J represent row numbers and column numbers assigned to all pixels. BUF
FIG. 2 schematically shows [I, J].
As apparent from FIG. 2, the image data includes a plurality of circular spot images 14.

Next, in step S2, the center position BUF [I ₀ , J ₀ ] of each spot image is determined. FIG. 6 schematically shows this calculation. However, FIG. 6 shows only one spot image 14 for easy understanding. As a specific method of obtaining the center position of each spot image, for example, a peak may be extracted by performing a product-sum operation of BUF using a circular two-dimensional operator.

Next, the process proceeds to step S3, in which the X-section component and the Y-section component are obtained within the range of each spot image. FIG. 7 schematically shows this calculation. That is, two-dimensional image data BUF is subjected to integration processing for each row and each column, and one-dimensional cross-sectional data (X cross-sectional component, Y cross-sectional component) orthogonal to each other.
Is generated, and the one-dimensional cross-sectional data is analyzed to detect the two-dimensional rear coordinate position of the pattern shadow 15. In particular, by performing the integration process, it is possible to compensate for the weakened reference light due to defocus. In the example of FIG. 7, the spot image 14 includes two column-direction pattern shadows.
Two peaks appear in the X-section component XBUF. Similarly, since the spot image 14 includes two row direction pattern shadows, the Y section component YBUF also includes two peaks.

Next, in step S4, two-dimensional backward coordinate values X ₀ and Y ₀ of the pattern shadow close to the center position (I ₀ , J ₀ ) of each spot image 14 are obtained. This calculation process is also schematically shown in FIG.

In step S5, two-dimensional forward coordinate values X _p and Y _p of the original pattern element corresponding to the projection pattern shadow are obtained from X ₀ and Y ₀ from the projection range table described above. For reference, FIG. 8 shows an example of a scale pattern assigned to the front coordinate plane (X, Y).

Finally, in step S6, the two-dimensional forward coordinates (X _p , Y _p ) on the scale plate and the two-dimensional backward coordinates (X ₀ , Y ₀ ) on the CCD light receiving surface are used to determine the image point. Find two-dimensional position. Further, the two-dimensional position of the corresponding measurement point is obtained. When the three-dimensional position is obtained, the intersection of two straight lines connecting at least one pair of pattern elements and a corresponding pair of pattern elements included in each spot image may be calculated.

Finally, an example of a high-sensitivity video camera combining the CCD image sensor 9 and the image intensifier 8 will be described with reference to FIG. This camera can capture very weak images even with very high sensitivity.
As illustrated, when an enlarged projection image is formed on an input surface through an optical system (not shown) such as a lens, an amount of electrons corresponding to incident light is emitted from the semiconductor thin film 21 formed on the input surface. You. The electronic image created in this way is stored in the electronic lens 22.
Is projected on the microchannel plate 23 by
The microchannel plate 23 is a thin plate-like device in which a number of extremely thin channels whose inner walls are made of a material having a secondary electron emission property are bundled and independent secondary electron multipliers are two-dimensionally arranged. The electrons incident on each channel of the microchannel plate 23 generate on average about two secondary electrons by one channel wall collision per electron. Therefore, the incident electrons repeat the wall collision a plurality of times in the process of passing through the channel, and are doubled several thousand times. Further, the electrons output from the microchannel plate 23 are accelerated by a high voltage, collide with the phosphor film 24 formed on the output surface, and are converted into light. Thus, a bright image that is about 10,000 times as large as the input light is generated on the output surface. After that, the bright and enhanced output image is captured by the CCD image sensor 9. At this time, bundle many optical fibers,
A sufficiently bright screen can be obtained by interposing the fiber optic plate 25 that can transmit the two-dimensional information of the image from one screen to another.

[0026]

As described above, according to the present invention, a scale plate is arranged in the vicinity of an image plane, and its pattern element is enlarged and projected on a light receiving surface, thereby forming a point light source constituting a measuring point. Since the displacement can be detected in an enlarged manner, the position detection resolution can be improved without increasing the number of elements of the imaging device. In particular, in a two-dimensional image sensor, it is difficult to increase the number of elements in terms of manufacturing technology, so the practical value of the present invention is extremely large, and it is possible to open up application fields that were not possible before. There is. Further, by combining the image pickup device and the image intensifier, there is an effect that high-accuracy measurement utilizing its high sensitivity becomes possible. In addition, if the point light sources are spaced apart to some extent, a plurality of measurement point positions can be detected simultaneously, so that there is an effect that behavior monitoring such as landslide can be performed at high speed. In addition, by connecting such an optical detection device to a computer, an applied system such as a moving object measurement monitoring system can be easily constructed. Such a system allows for accurate and fast real-time measurements.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an optical position detecting device according to the present invention.

FIG. 2 is a plan view showing an enlarged projection image.

FIG. 3 is a geometrical optical diagram of the optical position detecting device according to the present invention.

FIG. 4 is also a geometrical optical diagram.

FIG. 5 is a flowchart for explaining the operation of the optical position detecting device according to the present invention.

FIG. 6 is a schematic diagram similarly illustrating the operation.

FIG. 7 is a schematic view similarly used for explaining the operation.

FIG. 8 is a schematic view similarly illustrating the operation.

FIG. 9 is a sectional view showing an example of an image intensifier incorporated in the optical position detecting device according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 imaging means 2 scale plate 3 imaging means 4 measurement point 6 bandpass filter 7 objective lens 8 image intensifier 9 CCD image sensor 10 position calculation unit 11 computer 12 imaging surface 13 light receiving surface 14 spot image 15 pattern shadow

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01B 11/00-11/30 G01D 21/00

Claims (7)

(57) [Claims] 1. An optical position detecting device comprising: an imaging unit, a scale plate, and an imaging unit arranged in order along an optical axis; and an arithmetic unit connected to the imaging unit. A plurality of pattern elements regularly arranged along a forward coordinate plane orthogonal to the axis, wherein the imaging means condenses a light beam emitted from a target measurement point and converges the light flux on a corresponding imaging point. And a specific pattern element is enlarged and projected by spot illuminating a part of the scale plate with the reference light, and the imaging unit is arranged along a rear coordinate plane orthogonal to the optical axis. An image of the projected pattern shadow having an enlarged light-receiving surface and outputting corresponding image data; andthe arithmetic means processes the image data to detect a backward coordinate value of the pattern shadow. And the forward coordinate value of the original pattern element. Calculates the position of the point, the optical position detecting device, characterized in that to calculate the position of the surveying fixed point further based on the position of the focal point. 2. The scale plate has a plurality of pattern elements arranged two-dimensionally regularly along a forward coordinate plane, and the imaging means images the enlarged and projected pattern shadow in a plane. Outputting the corresponding two-dimensional image data, the arithmetic means processes the two-dimensional image data to detect a two-dimensional rear coordinate value of the pattern shadow, and a two-dimensional forward coordinate value of the original pattern element; 2. The optical position detecting device according to claim 1, wherein a two-dimensional position of the imaging point is calculated based on the two-dimensional position, and a two-dimensional position of the measurement point is calculated based on the two-dimensional position. 3. The arithmetic means performs integral processing on the two-dimensional image data to generate one-dimensional cross-sectional data orthogonal to each other, and analyzes the one-dimensional cross-sectional data to detect the two-dimensional rear coordinate value. 3. The optical position detecting device according to claim 2, wherein: 4. The image capturing means captures at least one pair of pattern shadows projected and enlarged and outputs corresponding image data, and the arithmetic processing means processes the image data to obtain a two-dimensional image of the pair of pattern shadows. A backward coordinate value is detected, a three-dimensional position of the imaging point is calculated based on the backward coordinate value and a two-dimensional forward coordinate value of the original pair of pattern elements, and a third order of the measurement point is further determined based on the three-dimensional position. 3. The optical position detecting device according to claim 2, wherein the original position is calculated. 5. The image capturing means captures a plurality of pattern shadows which are separately enlarged and projected by luminous fluxes emitted from a plurality of measurement points, and outputs corresponding image data. 2. The optical position detecting apparatus according to claim 1, wherein the processing is performed to detect the backward coordinate value for each pattern shadow, and to independently and simultaneously calculate the positions of the plurality of measurement points. 6. The optical position detecting device according to claim 1, wherein said image pickup means includes an image intensifier having a photomultiplier effect for amplifying a weak reference light. 7. A computer according to claim 1, further comprising a computer which analyzes the information on the position of the measurement point output from said arithmetic means with time and monitors the moving state or the displacement state of said measurement point. Optical position detector.