JP3161879B2 - Angle measuring method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an angle detection system and an angle / direction detection device utilizing an interference effect by coherent light, and is used in various fields such as light control, light transmission, and light information processing.

[0002]

2. Description of the Related Art Conventionally, an angle detection method using two coherent beams has been known as a method for accurately detecting the inclination of an object without contact (for example, Japanese Patent Application Laid-Open No. Sho 59-21181).
0). Here, two coherent light beams with different frequencies are obtained using an acousto-optic element, the coherent light beam is irradiated on the object to be measured, the reflected light interferes, the phase difference coming from the path length difference is detected, and the angle is detected. are doing.

[0003]

However, in the above-mentioned conventional method, when the path difference exceeds ± λ / 4, the phase difference cannot be determined and the measurement cannot be performed. There was a problem that can not be done.

Further, there is another problem that it is necessary to scan the light beam and average it for measuring the inclination angle of a wide surface.

Also, the use of acousto-optical elements increases the size of the apparatus, necessitates an optical system for providing a phase reference because of the need for phase detection, resulting in an optically and electrically complicated structure. there were.

An object of the present invention is to solve the above problems.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to receive two coherent light beams having different light beam angles by a light receiving element and to cover the entire surface of the light receiving element.
Based on the photocurrent intensity corresponding to the total light amount of the generated interference fringes,
This is based on an angle measurement method characterized by measuring the angle of a measurement object.

[0008] The present invention also provides a coherent light source,
The light emitted from the light source is divided into two light beams, and of the two light beams,
And means for irradiating the one of the light beam on the measurement object, means for multiplexing the two light beams, and a light receiving element for receiving the interference fringes of the two light beams at least, occurs on the entire surface of the light receiving element interference
The angle measuring device is characterized in that the angle of the object to be measured is measured based on the photocurrent intensity corresponding to the total light amount of the stripes .

Further, the present invention provides a coherent light source,
The light of wavelength λ emitted from the light source is divided into two light beams, and the two light beams
Means for irradiating one of the light beams to the object to be measured, and
Means for combining the two light beams, and receiving the interference fringes of the two light beams
At least a light receiving element with a size of λ / sin δ or less.
The angle measurement device is characterized in that the angle is measured in the range from -δ to + δ . In addition to the above configuration
The coherent light is divided into two light beams, and the two light beams
A means for irradiating one of them to the object to be measured, and a light beam for the other
Means for multiplexing and receiving interference fringes caused by multiplexing
And another angle measuring system having
The intensity of each photocurrent corresponding to the total amount of interference fringes generated on the entire surface of the element
The angle of the object to be measured is measured by subtracting degrees.
You may .

Further, according to the present invention, the phase of the two light beams or
The angle measuring device of the above, wherein Rukoto such comprises means for modulating the frequency directly.

The present invention also provides the angle measuring device as described above, wherein the light receiving elements are arranged in an array in at least three directions.

[0012]

According to the present invention, when two light beams are received by a light receiving element (for example, any device that converts photodiode light into current), the current excited there is changed by the occurrence of interference fringes. Use Hereinafter, the measurement principle will be described.

As shown in FIG. 8, when two coherent lights 1 and 2 each of which is a plane wave are incident with a shift of an angle δ, interference fringes having an interval λ / sin δ appear at the irradiation part. When the entire interference fringe is detected by one light receiving element, a bright portion and a dark portion of the fringe cancel each other, and a current corresponding to the light amount is output. For example, frequency modulation of the injection current of the semiconductor laser is performed, and the beat signal current excited by the light receiving element rapidly decreases with the inclination of the wavefront,
It becomes 0 at a certain angle. This angle is determined by the size of the light receiving element and the wavelength. FIG. 9 shows the angle dependence of the intensity of the beat signal when the wavelength is 830 nm and the size of the light receiving element is 500 μm. From this figure, the angle is 0.0
If it is shifted by 89 °, the beat signal cannot be detected. By using this principle, the inclination angle can be detected. However, in order to measure a wider angle range, the size of the light receiving element must be reduced. For example, in order to enable angle detection in a range up to ± 0.25 °, the size of the light receiving element is 200 μm or less. Must. At this time, the signal strength is reduced. However, the present invention provides a method and an apparatus for detecting an angle which solves such a problem.

That is, since the measurement angle is determined from the interval between the interference fringes, a beat signal current is generated in accordance with the amount of light and dark of the fringes, and the angle is measured by measuring a point where the beat current becomes 0 or an inflection point. Can be measured. Here, the measurement is performed using the current, but the current value may be converted into a voltage, a capacity, or the like and detected.

In the semiconductor laser, a more stable oscillation wavelength is obtained by frequency modulation or phase modulation, and the noise resistance is improved.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

First Embodiment A first embodiment of the present invention will be described with reference to FIG. Here, reference numeral 8 denotes an object to be measured. The coherent light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and then enters the translucent mirror 13. Here, about の of the incident light is reflected by the surface 131 and enters the light receiving element 11. The remaining light passes through the translucent mirror 13 and is reflected by the measuring object 8 to enter the light receiving element 11 and overlaps with the previously reflected light (projected portion 14) to form interference fringes. Here, an oscillation wavelength of 830 nm, GaAlA is used as a semiconductor laser.
An s-based semiconductor laser was used. The size of the light receiving element 11 is set to be substantially equal to the width of the beam. In addition, as shown in the figure, the reflected light from the surface 132 does not overlap with the reflected light from the object 8 to be measured. When the semiconductor laser 1 is driven by a triangular wave, a beat signal current is excited in a portion 14 of the light receiving element 11 where the beams overlap, and a direct current corresponding to the intensity of the laser is excited in other portions. As described above, the amplitude of the beat signal current sharply decreases when the object to be measured is tilted, and the angle of the object to be measured can be detected from the change. In the present embodiment, the beam width is 2.5 mm, the distance between the laser 1 and the light receiving element 11 and the surface 131 is 10 mm,
The distance between 31 and the reflection surface of the measuring object 8 was 50 μm. The light receiving elements 11 are arrayed as shown in FIG. As described above, when the size of the light receiving unit is small, the angle range in which the beat signal can be detected becomes large. However, if the size of the light receiving element is reduced, sufficient signal intensity cannot be obtained. In the present embodiment, as shown in FIG. 2, light receiving elements having a width of 200 μm are arranged in three directions, and the length thereof is increased to secure light intensity. Thus, the angle detection range in the three-dimensional direction is about ± 0.25 °, and the detection of the absolute angle of 0 ° can be easily performed by processing the signals of the light receiving elements in the three directions. That is, when interference fringes appear on the light receiving elements in one direction and no interference fringes occur on the other light receiving elements, it can be understood that the measuring object 8 is tilted in one direction. When the stripes appear, it is understood that the measuring object 8 is not inclined at all.
In the present embodiment, the projection portion 14 exists in a range up to the inclination angle 6 ° of the measuring object 8 and is sufficient for angle detection up to ± 0.25 °.

Second Embodiment A second embodiment of the present invention will be described with reference to FIG. The coherent light emitted from the semiconductor laser 1 enters an optical multiplexer 4 collimated by a collimator lens 2. About の of the incident light is reflected by the half mirror, reflected by the mirror 5, and enters the condenser lens 9 (shown by a solid line). The remaining light is transmitted, reflected by the object 8 to be measured, returned to the optical multiplexer 4, and enters the condenser lens 9 (shown by a broken line). At this time, by installing the condenser lens 9 so that its focal point is at the center of the optical multiplexer 4, the two light beams are
Is focused on a surface that is separated by a focal length from Further, the light is condensed at one point by a lens 10 (same as the lens 9) provided at a position away from the light condensing surface by the focal distance. The shift angle of the wavefront of the two light beams (the solid line and the dotted line) at this converging point is twice as large as the shift angle of the object 8 to be measured.

Here, by modulating the frequency of the semiconductor laser 1, the light receiving element 11 at the above-mentioned condensing point can detect a beat signal corresponding to the difference in the path length of the two light beams. However, when many interference fringes appear on the light receiving element surface, the beat signal intensity decreases and becomes zero at a certain angle.

In this embodiment, the condenser lenses 9 and 10 having a numerical aperture of 0.13 are used. At this time, the beam waist on the light receiving element is about 5 μm. At this time, the beat signal intensity can be measured up to the inclination of the measuring object 8 of 2.5 °. The size of the light receiving element 11 was φ200 μm, and the size was such that the interference fringes could be sufficiently received. In the present embodiment, even if the distance between the measuring object 8 and the optical multiplexer 4 is not precisely adjusted, the angle can be detected, and the object can be freely set within a range of about 2 cm.

Third Embodiment A third embodiment of the present invention will be described with reference to FIG. After the coherent light emitted from the semiconductor laser 1 is condensed by the collimating lens 2, the diffraction grating 3 having a lattice spacing of 200 μm is formed.
And is split into a first-order diffracted light 6 and a -1st-order diffracted light 7. At this time, the ± 1st-order diffracted light is ±
It has a slope of 0.25 °. The split ± 1st-order diffracted light enters the optical multiplexer 4. Hereinafter, the + 1st-order diffracted light will be described. A part of the + 1st-order diffracted light is reflected in the optical multiplexer 4, then reflected by the mirror 5, and condensed on the light receiving element 11 by the condensing lenses 9 and 10 having the same structure as in the second embodiment. You. The light transmitted through the optical multiplexer 4 is reflected by the measurement target 8 at the same distance from the laser as the mirror 5 and is combined with the light reflected by the mirror 5. This light is similarly condensed on the surface of the light receiving element 11 by the condensing lenses 9 and 10. On the other hand, similarly, the -1st-order diffracted light is similarly demultiplexed by the optical multiplexer 4 and reflected by the mirror 5 and the object 8 to be measured, and then condensed on the light receiving element similarly to the + 1st-order diffracted light (not shown). .

At this time, as shown, the ± 1st-order diffracted light is reflected by different surfaces of the mirror 5. The inclination of this plane is set to ± 0.25 ° with respect to the original incident light. Therefore, the AC signal intensity generated by the ± first-order diffracted light by phase-modulating the semiconductor laser 1 changes as shown in FIG. By subtracting this output, a signal having good linearity was obtained as shown in FIG. 6, and it was possible to easily detect absolute 0 °.

As described above, the first, second, and third embodiments use the semiconductor laser. When a gas laser or the like having a small phase noise is used, the direct current excited in the light receiving element changes due to interference fringes corresponding to the inclination of the measurement object. This enables angle detection. In this case, a circuit for modulating the laser is not required.

Fourth Embodiment A fourth embodiment of the present invention will be described with reference to FIG. Here, FIG. 7 shows a direction measuring device for measuring the direction of arrival of light, in which incident light (shown by a solid line) and light emitted from the semiconductor laser 1 are optically combined on the surface of the light receiving element 11 via the collimating lens 2. It is assumed that they are multiplexed by the device 4 and interfere. At this time, the direction of the incident light can be determined by forming the light receiving element 11 in an array of three directions as shown in FIG.

[0025]

As is apparent from the above description, according to the present invention, it is possible to realize a small and simple angle measuring system utilizing interference of coherent light. As a result, high-precision surface angle measurement over a wide angle range including absolute 0 ° without scanning is possible with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a diagram showing an angle measuring device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an array arrangement of light receiving elements according to an embodiment of the present invention.

FIG. 3 is a view showing an angle measuring device according to a second embodiment of the present invention.

FIG. 4 is a view showing an angle measuring device according to a third embodiment of the present invention.

FIG. 5 is a diagram illustrating a beat signal intensity in a light receiving element according to a third embodiment of the present invention.

FIG. 6 is a diagram illustrating a result of subtraction of a beat signal intensity according to the third example of the present invention.

FIG. 7 is a diagram showing a direction measuring device according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a state where two coherent lights are incident at different angles δ.

FIG. 9 is a diagram illustrating the angle dependence of the beat signal intensity of the interference fringes due to two coherent lights.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor laser 2 collimating lens 3 diffraction grating 4 optical multiplexer 5 mirror 6 + 1st-order diffracted light 7 -1st-order diffracted light 8 measurement object 9, 10 condensing lens 11 light receiving element 13 semi-transparent mirror 14 projected part (interfering part)

Continued on the front page (72) Inventor Mototaka Tanaya 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Haruhisa Takiguchi 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation ( 56) References JP-A-64-75905 (JP, A) JP-A-63-191008 (JP, A) JP-A-3-48706 (JP, U) (58) Fields studied (Int. Cl. ⁷ , (DB name) G01B 9/00-11/30 102

Claims (6)

(57) [Claims] 1. A light receiving element receives two coherent light beams having different light beam angles, and corresponds to the total light amount of interference fringes generated on the entire surface of the light receiving element .
An angle measuring method, wherein an angle of an object to be measured is measured based on a photocurrent intensity. 2. A coherent light source, means for distributing light emitted from the light source into two light beams, and irradiating one of the two light beams to an object to be measured, and means for multiplexing the two light beams A light-receiving element for receiving the interference fringes of the two light beams, and a photoelectric element corresponding to the total amount of interference fringes generated on the entire surface of the light-receiving element
An angle measuring device for measuring an angle of an object to be measured based on a flow intensity. 3. A coherent light source and light emitted from the light source.
Light having the wavelength λ is divided into two light beams, and one of the two light beams is
Means for irradiating the object with the light beam, means for multiplexing the two light beams, and a device for receiving interference fringes of the two light beams having a size of λ / sinδ or less.
At least a light receiving element, in a range of -δ to + δ.
An angle measuring device for performing angle measurement. 4. The coherent light is split into two light beams,
A means for irradiating one of the two light beams to the object to be measured;
Means for multiplexing with the other beam and interference caused by multiplexing
Further comprising another angle measuring system having a fringe and a light receiving element,
Each corresponding to the total amount of interference fringes generated on the entire surface of each light receiving element
The angle of the object to be measured was measured by subtracting the photocurrent intensity
The angle measuring device according to claim 2 or 3, wherein: 5. The angle measuring device according to claim 2, further comprising a unit that directly modulates a phase or a frequency of the two light beams. 6. The angle measuring device according to claim 2, wherein the light receiving elements are arranged in an array in at least three directions.