JPH0277604A - Hologram distance measuring device - Google Patents

Abstract

PURPOSE:To measure the displacement of an object to be measured with the accuracy of the wavelength order of light by providing the first beam splitting means, a non-parallel beam converting means and the first beam synthesizing means. CONSTITUTION:When an object 15 to be measured is present at a reference position Z=Zo, the object to be measured is irradiated with beam from the first laser 10 and the emitted beam from said object being almost parallel beam is split into transmitted beam and reflected beam by the first beam splitting means 11a. The reflected beam is allowed to be incident to a non-parallel beam converting means 12 while the beam path of said reflected beam is converted to an almost right angle by a beam path converting means 11b and, for example, the focus position of the lens behind said means 12 is adjusted to convert the emitted beam to diverging beam. This diverging beam is split into reflected beam and transmitted beam by the second beam splitting means 14 and the transmitted beam is applied to the object 15 to be measured and the reflected beam thereof is again reflected by the means 14 to be incident to the first beam synthesizing means 16 to transmit therethrough. Then, the pattern image of the interference fringe with reference beam at the measuring position of the object 15 to be measured is compared with that when the object 15 is present at the reference position to make it possible to measure the displacement of the object 15.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical distance measuring device that uses light to measure the displacement of an object in a non-contact manner, and particularly to a hologram distance measuring device that uses a hologram to measure distance from an interference fringe pattern. It is related to the device.

2. Description of the Related Art The configuration of a conventional optical distance measuring device will be described below with reference to the drawings. FIG. 8 is a block diagram of a conventional optical distance measuring device. 1 is a laser, 2 is a first deflection mirror that scans the beam in the X direction in the figure, 3 is a second deflection mirror that scans the beam in the Y direction in the figure, 4 is the object to be measured, and 5 is the object to be measured. A condensing lens condenses the reflected light from the measurement object 4, and 6 is a line sensor placed behind the condensing lens.

Next, the principle of this conventional optical distance measuring device will be explained with reference to FIG. In FIG. 9, S is the center of the condenser lens 5,
Let L be the center of the emitted beam from laser 1, 0 be the point on the object to be measured 4, θ and φ be the reflected beams from each of the four points 0, and the angle that the emitted beam from laser l makes with the base line LS. ,D
If we set the length of the base line LS as the length of the base line LS, the distance to point 0 can be calculated using the formula (1)
It is expressed as

h-Rotanetan・(tane+tan・)・・・
Formula (1) Here, the angle θ is the direction of the optical axis of the condenser lens 5, and is given by formula (2) tanθ=f/d---Formula (2) f=focal length d of the condenser lens 5: According to the distance between the center point of the condenser lens 5 and the beam detection point on the line sensor 6, the laser beam is scanned in the X direction and the Y direction by the first and second deflection mirrors 2.3, and the laser beam is scanned onto the line sensor 6. Between the beam detection point S on the condensed line sensor 6 and the center of the output beam and the point O on the object to be measured 4, formula (1) is used.
, the distance of the object to be measured 4 can be measured by solving equation (2).

Problems to be Solved by the Invention However, in the above configuration, equations (1) and (2)
Therefore, the distance measurement accuracy is determined by d, that is, the detection accuracy of the distance between the center point of the condenser lens 5 and the beam detection point on the line sensor 6. However, the detection resolution of the beam detection point on the line sensor 6 is determined by the size of the constituent cells of the line sensor 6, and the distance measurement accuracy is on the order of several tens of μm. The accuracy was insufficient.

An object of the present invention is to solve the problems of the conventional optical distance measuring devices described above.

Means for Solving the Problems The hologram ranging device of the present invention includes a first beam splitting unit that splits a beam emitted from a light source into two optical paths;
This two-divided optical path has a non-parallel light converting means placed on one side, and a beam made non-parallel by the non-parallel light converting means is transmitted and reflected, and one beam is irradiated onto the object to be measured. a second beam splitting means for combining the reflected light from the object to be measured and the other beam split into two by the first beam splitting means; a third beam splitting means for splitting the combined light into two; and an optical spatial modulation element for recording interference fringes formed by the combined light disposed in one of the optical paths split by the third beam splitting means. , a second beam combining means for combining the recording pattern reading light from the optical spatial modulation element and one of the beams split by the third beam splitting means; The invention is characterized by comprising a beam blocking means for blocking the incident light.

According to the above-described configuration, the present invention irradiates the object to be measured with non-collimated light at a certain reference position, and generates interference fringes between the reflected light from the object to be measured and the reference light on the optical spatial modulation element. The reference interference fringe pattern obtained by recording and irradiating readout light onto this optical spatial modulation element, and the reflection obtained from the object to be measured by irradiating the non-parallel light when the object to be measured is at an arbitrary position. By forming interference fringes between the light and the reference light, and measuring the displacement of the object to be measured from this interference fringe pattern and the reference interference fringes, it is possible to measure the displacement of the object to be measured with an accuracy on the order of the wavelength of the light. That is.

EXAMPLES The present invention will be explained below based on drawings showing examples thereof.

FIG. 1 is a plan view of a first embodiment of the holographic distance measuring device of the present invention. 10 is a first laser whose emitted light is substantially parallel light; lla is a first beam splitting means for splitting the beam emitted from the first laser 10 into two optical paths; llb is an optical path converting means; Reference numeral 12 denotes a non-parallel light converting means disposed on one side of this two-divided optical path, and is a confocal optical system consisting of two lenses. This converts the beam into diverging or converging light, ie, non-parallel light. 13 is a beam expander disposed in the other optical path divided into two by the first beam splitting means 11; 14 transmits and reflects the beam that has been made non-collimated by the beam parallel light intensity adjusting means 12; a second beam splitting means 16 for irradiating the transmitted light onto the object to be measured 15;
17 is a first beam combining means for combining the reflected light from the object to be measured 15 and the other beam divided into two by the first beam splitting means 11, and 17 is a first beam combining means for dividing the combined light into two. 3 is a beam splitting means, 18 is an optical spatial modulation element, which is arranged in the transmission optical path of the third beam splitting means 17, and 19 and 20 are each the remaining beam split into two by the third beam splitting means 17. This is an optical path converting means for one optical path. 21 is a second laser for reading out the optical spatial modulator 18; 22 is a second laser for combining the recording pattern reading light from the optical spatial modulating element 18 and one beam split by the third beam splitting means 17; The TV left camera 24 is the optical spatial modulation element 1.
This is a beam blocking means for blocking recording light from entering the recording beam 8.

The operation of the first embodiment of the present invention constructed as described above will be explained using FIGS. 1 to 5.

First, when the object to be measured 15 is at the reference position 2=20 shown in FIG. 1, a beam is irradiated from the first laser 10. This emitted light is substantially parallel light, and is split into two by the first beam splitting means 11a into transmitted light and reflected light. The optical path of this reflected light is converted to a substantially right angle by the optical path conversion means 11b, and the optical path is made to enter the non-parallel light conversion means 12. By adjusting the focal position of, for example, a rear lens of the non-parallel light conversion means 12, The substantially parallel emitted light from the laser 10 is converted into diverging light as shown in FIG. This diverging light is split into two by the second beam splitting means 14 into reflected light and transmitted light. This transmitted light is irradiated onto the object to be measured 15 located at the reference position, and the reflected light is again sent to the second beam splitting means 14.
The beam is reflected by the beam, enters the first beam combining means 16, and is transmitted therethrough.

On the other hand, the other beam divided into two by the first beam splitting means 11a is expanded by the beam expander 13 and reflected by the first beam combining means 16.

Therefore, the object to be measured 1 is
The reflected light from 5 becomes the object light, and the beam expander
The light transmitted through 13 corresponds to the reference target, and concentric interference fringes as shown in FIG. 3 are formed. This interference fringe is a type of Newton's ring caused by the difference in curvature between the wavefronts of diffused light and parallel light, that is, a spherical wave and a plane wave, and the pitch of the interference fringe is wavelength/2. This interference fringe pattern is separated into reflected light and transmitted light by the third beam splitter 17,
The transmitted light is incident on the beam blocking means 24, but at this time the beam blocking means 24 is in an on state and is transmitted, so that the light is incident on the spatial light modulation element 18.

The configuration of this spatial light modulator 18 is shown in FIG. 30 is a nematic liquid crystal layer, 31 is a reflective layer, 32 is a cover glass, 33 is a transparent electrode, 34 is a photoconductor, 35 is a light shielding layer, 3
6 is a liquid crystal alignment film, and a voltage is applied between transparent electrodes 33. When the interference fringe pattern enters from the photoconductor 34 side, the irradiation of the photoconductor 34 decreases in the portions irradiated with light, and a higher voltage is applied to the portions irradiated with light than in the portions not irradiated with light. As a result, a voltage pattern corresponding to the interference fringe pattern is applied to the nematic liquid crystal layer 30, and the alignment state of the liquid crystal molecules in the nematic liquid crystal layer 30 is spatially modulated, so that the measured object 15 at the reference position 2=20 The interference fringe pattern formed by the reference light is recorded on the spatial light modulation element 18.

Next, the object to be measured 15 is moved to an arbitrary measurement position Z using FIG.
The case of displacement to the position =Zl will be explained. All numbers 10 to 24 in the figure indicate the same things as in FIG. 1. At this time, similarly to when the object to be measured 15 was at the reference position 2=20, the first beam combining means 16 receives the beam that has passed through the non-parallel light converting means 12 and was converted into divergent light. The reflected light from the measurement object 15 becomes object light, and the light transmitted through the beam expander 13 corresponds to the reference target, forming concentric interference fringes.

However, the curvature of the wavefront of the diverging light at this arbitrary measurement position Z=Z+ is different from the curvature at the reference position Z=Zo, that is, the curvature of the wavefront at the position Z=Zl is smaller due to the longer optical path length. . Therefore, as shown in FIG. 5, the interference fringe pitch becomes wider.

When the object to be measured 15 is located at this arbitrary measurement position Z=ZI, the beam blocking means 24 is in the OFF state, so the interference fringe pattern shown in FIG. 5 is not written on the spatial light modulation element 18. The optical path of the beam is changed by the optical path converting means 19 and 20, and the beam enters the second beam combining means 22.

On the other hand, when the spatial light modulator 18 is irradiated with the second laser 21, the alignment state of the liquid crystal molecules of the nematic liquid crystal layer 30 is spatially modulated, and the spatial light modulator 18 moves to the reference position 2=20 as described above. Since the interference fringe pattern formed by the object to be measured 15 and the reference beam is recorded, the second
The polarization state of the incident light from the laser 21 is spatially modulated.

Therefore, by making the reflected light from the spatial light modulation element 18 incident on the second beam combining means 22 via a polarizing beam splitter (not shown), or by By using that as a polarizing beam splitter, the intensity pattern of this incident light can be adjusted to the reference position 2 =
It can be an interference fringe pattern formed by the object to be measured 15 at 20 and the reference light.

Therefore, the image captured by the TV camera 23 is a superposition of the interference fringe pattern when the object to be measured 15 is at the reference position 2 = 20 and the interference fringe pattern when the object 15 is at the measurement position Z = Zl. Therefore, from the comparison of these two interference fringes, we can determine the curvature change of the diverging light with a resolution of wavelength/2, that is, 20 and Zl
Can measure distance.

That is, according to this embodiment, interference fringes with divergent light as object light and parallel light as reference light are first recorded on the spatial light modulator when the object to be measured is at a reference position, and this interference fringe pattern and m constant are recorded. By superimposing and comparing the interference fringe patterns when the object is at an arbitrary measurement position, the displacement of the object to be measured can be accurately measured with a resolution of wavelength/2.

Next, a second embodiment of the present invention will be described using FIG. 6. FIG. 6 is a block diagram of a variable non-parallel light converting means 40 according to a second embodiment of the present invention. 40a is the first convex lens, 40b is the second convex lens, and 40c is the second convex lens 4.
0b, and is composed of, for example, a motor and a gear train. If the variable non-parallel light converting means 40 configured as described above is used in the hologram ranging device shown in FIGS. 1 and 2, the non-parallel luminous intensity of the object light, that is, the curvature of the wavefront can be set arbitrarily. , the pitch and number of interference fringes formed between the position of the measured object and the reference light at the reference position and the measurement position are determined to be optimal for the desired measurement distance range, in other words, the range of change in the curvature of the object light. For example, when used as a visual device for an assembly robot, the dynamic range and accuracy can be selected depending on the work content.

Next, a third embodiment of the present invention will be described using FIG. 7. 50 is a confocal optical system consisting of two lenses with different focal lengths, and 50a is a first lens with a focal length fl.
, and 50b is a second convex lens having a focal length of f2. These two lenses constitute a confocal optical system.

This confocal optical system 50 is disposed between the first beam combining means 16 and the third beam splitting means 17 of the hologram ranging device shown in FIGS. 1 and 2. By passing through this confocal optical system 50, the rate of change of the curvature of the wavefront of the object light depending on the distance position of the object to be measured 15 is determined by the ratio of the focal lengths of the first and second convex lenses, that is, 2 of (f2/fl). Multiplyed.

Therefore, by setting fl=10-■ and f2=1001, for example, the rate of change in the curvature of the wavefront of the object light depending on the distance position of the object to be measured 15 can be reduced to 1/100. That is, by using the confocal optical system 50, it is possible to increase or decrease the pitch of interference fringes and the number of documents depending on the distance to the object to be measured, so it is possible to obtain the same effect as the second embodiment of the present invention.

Effects of the Invention The hologram ranging device of the present invention includes a first beam splitting means that splits a beam emitted from a light source into two optical paths;
This two-divided optical path has a non-parallel light conversion means placed on one side, an optical spatial modulation element that records interference fringes when the object to be measured is at the reference position, and 5 recording pattern readout light and a combining means for combining the interference fringes when the object to be measured is at an arbitrary measurement position, the wavefront of the object light, which is non-parallel light, is Since the curvature changes, by comparing the pattern image of interference fringes with the reference light at the measuring position of the non-measuring object and the interference fringe pattern when the measured object is at the reference position, accuracy on the order of the wavelength of light can be obtained. This is a hologram ranging device that can measure the displacement of an object to be measured.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a first embodiment of a hologram distance measuring device according to the present invention, and FIGS. 2, 3, 4, and 5 each illustrate the operation of the first embodiment of the present invention. Diagram for explanation,
FIG. 6 is a plan view of the variable non-parallel light conversion means of the second embodiment of the holographic distance measuring device according to the present invention, and FIG. 7 is a plan view of the confocal optical system of the third embodiment of the present invention. FIG. 8 is a block diagram of a conventional optical distance measuring device, and FIG. 9 is a diagram explaining the principle of the device. DESCRIPTION OF SYMBOLS 10... First laser, 12... Non-parallel light conversion means, 15... Measured object, 18... Spatial light modulation element,
21...Second laser, 23...TV left camera 24
... Beam blocking means, 40... Variable non-parallel light conversion means, 50...° Confocal optical system. Name of agent: Patent attorney Shigetaka Awano and one other person Figure 2 Figure 3 Figure 4 30 years old Matsutik LCD layer Figure 6 Figure 8 Figure 9

Claims (4)

[Claims] (1) An interference fringe pattern reproduced from a hologram in which non-parallel light is irradiated onto an object to be measured at a certain reference position and interference fringes formed by the reflected light from the object to be measured and a reference beam are recorded; The displacement of the object to be measured is measured by irradiating the object to be measured with the non-parallel light at an arbitrary position and superimposing interference fringes formed by the reflected light from the object to be measured and the reference light. A hologram ranging device that is characterized by the following: (2) a light source, a first beam splitting means for splitting the beam emitted from the light source into two optical paths, a beam parallel luminous intensity adjusting means disposed on at least one of the two split optical paths, and a second beam splitting means that transmits and reflects the beam that has been made into a non-collimated beam by the parallel light conversion means and irradiates one of the beams onto the object to be measured, the reflected light from the object to be measured, and the first beam; A first beam multiplexer that combines the other beam split into two by the splitter, a third beam splitter that splits the combined light into two, and a beam split by the third beam splitter. an optical spatial modulation element for recording interference fringes formed by the combined light in one optical path; and one beam split by the recording pattern readout light from the optical spatial modulation element and the third beam splitting means. 2. The hologram distance measuring device according to claim 1, further comprising a second beam combining means for combining the two beams, and a beam blocking means for blocking the recording light from entering the optical spatial modulation element. (3) The non-parallel light converting means is constituted by a confocal optical system consisting of two lenses, and at least one lens is provided with a movable means to make the parallel light intensity of the beam variable. Hologram ranging device. (4) A confocal optical system consisting of two lenses with different focal lengths is arranged between the first beam combining means and the third beam splitting means for dividing the combined light into two. The hologram distance measuring device according to claim 2 or 3.