JPH01232201A - Laser interference length measuring instrument - Google Patents

Abstract

PURPOSE:To select the installation place of a laser device optionally and to reduce the influence of return light, external vibration, etc., on the device almost to zero by detecting the relative distance between a collimator lens and an optical lens. CONSTITUTION:The laser light from the laser device 1 is made incident on the collimator lens 8 which has a half-mirror on its projection end surface through an optical fiber 7 and the laser light which is projected from the lens 11 is made incident or a distributed index lens 11. Consequently, part of the light beam is reflected by the half-mirror 12 of the lens 11 to return to the projection end of the lens 8 and reflected again to make incident on the lens 11, and consequently this reflected light interferes with the direct incident light from the lens 8 to form interference fringes 25 on the projection side of the lens 11. Then the light-shade pattern of the interference fringes 25 is converted by a photoelectric converting means 13 into an electric signal, which is supplied to a relative position detecting device to measure the movement direction of the light-shade pattern of the interference fringes 25 and the number of passed fringes, thereby measuring the relative distance between the laser device 1 and lens 11 while deciding its increase or decrease.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a laser interferometric length measuring machine that accurately measures the distance or length of a moving object, and particularly relates to a laser interferometer that measures the distance or length of a moving object with a simple configuration. This enables accurate and stable measurement.

[Conventional technology]

For example, as a conventional laser interferometric length measuring machine,
There is one described in the -201301 publication.

This conventional example includes a laser device whose multi-sided semi-transparent mirror emits substantially parallel light beams, and a laser device whose optical axis is aligned with the optical axis of the light beam of the laser device and which serves as a focal point for the light beam incident on one end. An optical lens having a semi-transparent mirror formed at the end thereof is disposed so as to be relatively movable, and a photoelectric conversion means for photoelectrically converting interference fringes generated at the output end of the optical lens; It has a configuration that includes relative distance detection means that detects the number of passing laser beams and the direction of movement to detect the relative distance between the laser device and the optical lens.

[Problem to be solved by the invention]

However, in the above-mentioned conventional laser length measuring machine, it is necessary to arrange the laser device and an optical lens that moves relative to the laser device to face each other, and the laser device is made of He-N
When using a gas laser such as an e-laser, a large installation area is required, and the laser must be placed in a straight line with the moving object to align the optical axis. When performing micro-movement measurements such as a micro-movement stage used for There were unresolved issues such as interference fringes fluctuating due to the influence of air currents, making measurement difficult.

In addition, since reflection is repeated between the semi-transparent mirror of the laser device and the half mirror of the gradient index lens, a portion of the reflected light from the gradient index lens returns from the semi-transparent mirror of the laser device to the optical resonator as light. This returned light affects the oscillation frequency and intensity of the laser device 1, causing fluctuations in interference fringes, and there is also an unresolved problem that clear interference fringes cannot be obtained.

Therefore, the present invention was made by focusing on the unresolved problems of the conventional example, and it is possible to arbitrarily select the installation location of the laser device, and also eliminates the influence of returned light and external vibrations on the laser device. The purpose of the present invention is to provide a laser length measuring machine that is almost unaffected by ambient temperature, airflow, etc.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a system in which a laser beam from a laser device that emits substantially parallel laser beams is incident through an optical fiber, and the output end face is a semi-transparent mirror. It is possible to relatively move a certain collimator lens and an optical lens in which the optical axis of the laser beam emitted from the collimator lens substantially coincides with the optical axis and a half mirror is formed at the other end, which becomes the focal point of the light beam incident on one end. a photoelectric conversion means for photoelectrically converting interference fringes generated at the output end of the optical lens; and a photoelectric conversion means for photoelectrically converting interference fringes generated at the output end of the optical lens, and detecting the number of passing interference fringes and the direction of movement based on the detection signal of the photoelectric conversion means, and connecting the collimator lens and the optical It is characterized by comprising relative distance detection means for detecting the relative distance to the lens.

Further, the half mirror formed on the optical lens may be formed around the incident end of the light beam.

Furthermore, it is preferable to use a single mode optical fiber as the optical fiber.

Furthermore, interference fringes parallel to the output end surface of the optical lens are formed with the output end surface of the collimator lens being a flat surface.

In order to efficiently detect parallel interference fringes that occur on the output end face of an optical lens, the photoelectric conversion means is arranged in multiple layers of flat optical fibers in which optical fibers are arranged in a plane layer in the direction of the interference fringes, and each flat optical fiber is The output ends of the two are bundled together to face the photoelectric detector.

Furthermore, in order to miniaturize the photoelectric conversion means, the parallel interference fringes generated on the output end face of the optical lens are compressed in the extension direction of the interference fringes using a cylindrical lens, and the compressed optical image is input into a two-layer flat optical fiber. let

[Function] In this invention, the laser beam from the laser device is made incident on the collimator lens having a semi-transparent mirror formed on the output end surface via the optical fiber, and the laser beam emitted from the collimator lens is directed to the output end side or the input end side. By entering the optical lens which has a half mirror formed on the side and the focal point of the incident light beam becomes the output end, a part of the light beam is reflected by the half mirror of the optical lens and reaches the output end of the collimator lens. Here, the reflected light is reflected again and incident on the optical lens, causing interference between this reflected light and the directly incident light from the collimator lens, thereby generating interference fringes on the output side of the optical lens. At this time, when the output end surface of the collimator lens is a convex surface, the interference fringes generated at the output end of the optical lens become concentric circles, and when the output end surface of the collimator lens is flat, a Fabry-Perot interferometer configuration is formed, and the optical lens The interference fringes generated at the output end of the beam become parallel fringes. By converting the brightness and darkness of this interference fringe into an electrical signal using a photoelectric conversion means and supplying this converted signal to a relative distance detection means, the direction of movement of the brightness and darkness of this interference fringe and the number of passing lines are measured, and the optical signal is connected to a laser device. The relative movement distance is measured, including determining whether the relative distance between the lens and the lens is increasing or decreasing.

In addition, of the reflected light reflected by the half mirror of the optical lens, the return light that enters the collimator lens is about 50%, and of this, the return light that enters the single mode optical fiber with a diameter of about 4 μm is at its critical angle. Due to the existence of
There is almost no return light that enters the laser device, and the laser device can be prevented from being affected by the return light.

Furthermore, by inserting a cylindrical lens between the optical lens and the photoelectric conversion means, the parallel interference fringes generated on the output end face of the optical lens can be compressed in the extending direction, and the parallel interference fringes of the photoelectric conversion means can be compressed. The length in the extension direction can be shortened.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In the figure, reference numeral 1 denotes a laser device placed at an arbitrary fixed part, and is composed of, for example, a He-Ne laser.
The e-laser has an external bell-shaped configuration, and a total reflection mirror 4a forming an optical resonator and a semi-transmission mirror 4b with a reflectance of 99% are disposed facing the Brewster windows 3a and 3b of the laser tube 2. ,
A parallel laser beam of a single wavelength is emitted from the semi-transparent mirror 4b.

Laser light emitted from this laser device 1 is incident on a single mode optical fiber 7 via an input lens 6, and propagates within this optical fiber 7 toward the output end side. The output end face of the optical fiber 7 is connected to the input end of a collimator lens 8 such as a plano-convex lens.

The collimator lens 8 is fixed to a fixed part so that its optical axis is in the horizontal direction, and its output end face is flat.
A semi-transparent mirror 8a is formed on this output end face by vapor depositing gold, for example.

On the other hand, a distance measuring moving body 10 that is movable along the laser beam 9 is disposed at a position facing the laser beam 9 emitted from the collimator lens 8. A gradient index lens 11 is attached so as to be substantially coincident with the above. This gradient index lens 11 has a second
As shown in Figures fa) and (b), the refractive index of the optical glass rond is made smaller as the distance from the central axis increases due to ion diffusion, and the refractive index is determined by the radius of the rond. When the direction is the X axis and the refractive index distribution constant is A, it can be expressed by the following equation.

n(x) =il, (1'AAx”) +・＊+
+++++++・++(1) And gradient index lens 1
A half mirror 12 is formed by depositing gold, for example, on an exit end 11b on the side opposite to the entrance end 11a on the collimator lens 8 side. Here, the length of the gradient index lens 11 is selected so that the focal point of the laser beam incident on the input end 11a is the output end.

Further, a photoelectric conversion means 13 is disposed at a position facing the half mirror 12 of the gradient index lens 11 of the moving body 10. As shown in FIG. 3, one example of this photoelectric conversion means 13 is to form a flat optical fiber 15 by arranging a large number of optical fibers 14 horizontally in a planar layer, and by stacking a large number of these flat optical fibers 15. A rectangular light-receiving surface R is formed on the incident end side, and the output end side of each flat optical fiber 15 is bundled to face the incident ends of a plurality of photoelectric conversion elements 16 such as photodiodes. A plane signal in the form of parallel stripes of the light rays irradiated onto the light receiving surface R by the conversion element 16 is made into a point signal, and this is output as an interference fringe detection signal.

The interference fringe detection signal output from the photoelectric conversion means 13 is A
The signal is supplied to a processing device 18 via a /D converter 17. This processing device I8 supplies the detection signal of each photoelectric conversion element 16 to a pulse signal forming circuit 19, converts it into a pulse signal by scanning it at a predetermined period in this pulse signal forming circuit 19, and converts it into a pulse signal, A two-cycle pulse signal having a phase difference (A pitch) of 2
It is multiplied by 4 by 1 and then supplied to the asop down counter 22. Therefore, the relative distance between the collimator lens 8 and the moving body 10 can be detected based on the count value of the counter 22.

Next, the operation of the above embodiment will be explained. Laser light output from the laser device 1 is input into a single mode optical fiber 7 via an input lens 6, propagates within this optical fiber 7, and is input into a collimator lens 8. Then, from the output end face of the collimator lens 8, the collimated laser beam 9 enters the input end 11a of the gradient index lens 11 mounted on the moving body 10. As shown in FIG. 4, the laser light incident on this gradient index lens 11 is
It converges at the position of the output end 11b, about 50% of which is reflected by the half mirror 12 and returns to the collimator lens 8 side, and about 50% is reflected at the output end face and enters the gradient index lens 11 again. Therefore, the direct light from the collimator lens 8 that is directly incident on the gradient index lens 11 and the reflected light are 2 times the optical distance between the output end of the collimator lens 8 and the half mirror 12 of the gradient index lens 11. A double optical path difference will occur, and the two will interfere. This interference produces parallel interference fringes 25 that are clear and have constant intervals, as shown in FIG. 4, on the exit side of the gradient index lens 7 (in FIG. 4, dark areas are indicated by hatching) ). In this way, parallel interference fringes 2
5 is because the output end of the collimator lens 8 and the half mirror 12 at the output end of the gradient index lens 11 are both flat, forming a Fabry-Bello interferometer.

Since this interference fringe 9 is projected onto the light receiving surface R of the photoelectric conversion means 13, it is transmitted as point information to the photoelectric conversion element 16 through the flat optical fiber 15, and from this photoelectric conversion element 16 in the vertical direction of the light receiving surface R. An interference fringe detection signal corresponding to the brightness of each point is inputted to the processing device 18 via the A/D converter 17.

Therefore, by scanning at a predetermined period with the pulse signal forming circuit 19 of the processing device 18, a waveform signal representing the light intensity distribution in the vertical direction of the light receiving surface R is obtained, and a waveform for two periods having a phase difference of 90 degrees is obtained. By shaping the signals as necessary and supplying them to the direction discrimination circuits 20, interference fringes 2
5 is determined. In this case, the determination is 1000 pieces stripes 2
5 moves from the lower side to the upper side of the light-receiving surface R, the distance between the collimator lens 8 and the moving object 10 decreases, and a subtraction pulse signal is output in accordance with the movement of the interference fringes 25. On the other hand, when the movement direction of the interference fringes 25 moves from the upper side to the lower side of the light-receiving surface R, the distance between the collimator lens 8 and the moving body 10 increases, and the movement of the interference fringes 25 increases. Outputs an addition pulse signal according to.

Further, when the interference fringes 25 do not move and there is no change in the waveform signal, it is assumed that the moving distance between the collimator lens 8 and the moving body 10 does not change, and neither the subtraction pulse signal nor the addition pulse signal is output.

Then, the subtraction pulse signal and addition pulse signal outputted from the direction discrimination circuit 20 are supplied to the multiplier circuit 21 and multiplied by 4, and these multiplied signals are supplied to the up/down counter 22, so that the count value is changed to the collimator lens 8.
This corresponds to the relative distance between the moving body 6 and the moving body 6, and can be digitally displayed by outputting this to a suitable display device.

At this time, the brightness of the interference fringes 25 is determined by the distance between the collimator lens 8 and the moving body 10 when the He-Ne laser beam (wavelength 0
．． Since it is inverted every time it changes by two wavelengths (6328 μm), that is, 0°3164 μm, by multiplying this by 4 in the multiplier circuit 21, a resolution of 1/8 wavelength, or 0.0791 μm, can be obtained.

Furthermore, when the reflected light reflected by the half mirror 12 of the gradient index lens 11 reaches the collimator lens 8,
50% is re-reflected by the semi-transparent mirror 8a, and the remaining 50%
enters the collimator lens 8 as return light, but
Of this return light, the return light that enters into the single mode optical fiber 7 has a small diameter of about 4 μm, and the critical angle is small, so it can be ignored. The light is attenuated during the process of propagating within the fiber, and 99% of the light is reflected by the semi-transparent mirror 4b of the laser device 1, so almost no return light actually enters the laser resonator of the laser device 1, and the laser device Clear interference fringes can be obtained without affecting the oscillation frequency or intensity of 1 and without causing fluctuations in interference fringes.

Furthermore, when the vibration is transmitted to the fixed part, the vibration with almost no phase delay is transmitted to the collimator lens 8 and the movable stage 10, so that the collimator lens 8 and the gradient index lens 11 on the movable stage 10 are The two vibrate in synchronization, and the optical axes of the two do not shift. Therefore, the output of the photoelectric conversion element 16 does not fluctuate due to the influence of vibration, and accurate measurement data can be obtained. Incidentally, in the conventional example, the laser beam of the laser device is made to directly enter the gradient index lens, and the laser device itself is large, and the phase of vibration is different between the gradient index lens side of the laser device and the opposite side. and amplitude are different, the laser device vibrates in a complicated manner in response to the external vibration input, and the laser device and the gradient index lens vibrate asynchronously, causing the optical axis of the laser device and the gradient index lens to The optical axis of the lens is misaligned, and the output of the photoelectric conversion element fluctuates in response to external vibrations, making it impossible to perform accurate length measurement.

As in the above embodiment, since the gradient index lens 11 is used as an optical lens, there may be some positional deviation or Even if an angular shift occurs, the gradient index lens 11 has convergence, so it does not have a large effect on the generation of interference fringes 25, and there is no need to increase the mounting accuracy of the gradient index lens 11. .

Further, as in the above embodiment, as the photoelectric conversion means 13,
A rectangular light-receiving surface R is formed by stacking a large number of flat optical fibers 15 in which optical fibers I4 are arranged in a plane layer, and the other ends of each flat optical fiber 15 are bundled to form a photoelectric conversion element 1, respectively.
6, surface information of the parallel interference fringes 25 generated on the light-receiving surface R can be obtained as point information, and the amount of light incident on the photoelectric conversion element 6 increases, making processing by the processing device 18 easier. In addition, there is an advantage that the optical axes of the laser beam 9 and the gradient index lens 11 can be easily aligned. That is, one of the multilayer flat optical fibers 15 and a row of optical fibers 14 in a direction perpendicular to this are respectively connected to a photoelectric conversion element, the distribution of their light intensities is measured, and the distribution is symmetrical with respect to the center. By centering the gradient index lens 11 in such a manner, optical axis alignment can be performed more easily than in a normal laser interferometer.

Note that in the above embodiment, the gradient index lens 11
Direct photoelectric conversion means 1 converts parallel interference fringes formed at the output end of
Although we have explained the case of projecting onto the light-receiving surface R of No. 3, the present invention is not limited to this. A cylindrical lens is placed between the two, and an optical image is formed by compressing the length of the parallel interference fringes in the extending direction. Two-layer flat optical cable 15
In this case, the length of the photoelectric conversion means in the width direction can be shortened.

Further, in the above embodiment, the laser device 1, the single mode optical fiber 7, and the collimator lens 8 are fixed to the fixed part.
Gradient index lens 11. The photoelectric conversion means 13 is connected to the moving body 1
Although we have explained the case where they are placed at The relative movement distance of a moving object can be measured.

Further, in the above embodiment, the case where the refractive index gradient lens 11 is applied as the optical lens has been described, but the invention is not limited to this, and two ball lenses are combined and the incident light is applied to one ball lens. Alternatively, a half mirror may be formed at the exit end of the other ball lens by converging the laser beam on the exit end of the other ball lens. It is also possible to form a half mirror, as long as the focal point of the laser beam is at the output end.In addition to forming a half mirror on the output end face, it is also possible to form a half mirror on the input end face. The same effects can be obtained.

Furthermore, in the above embodiment, the parallel interference fringes 25 are formed on the output end face of the gradient index lens 11, but the invention is not limited to this, and the output end face of the collimator lens 8 is slightly convex. By forming it into a spherical shape, it is possible to form concentric interference fringes on the output end face of the gradient refractive index lens 11. In this case, the optical fibers 14 in the photoelectric conversion means 13 are bundled concentrically to create a circular shape. By forming a bundle of fibers having a light-receiving surface and bundling the output ends of the optical fibers on concentric circles to face the photoelectric conversion element, surface information of the concentric circles can be replaced with point information.

In addition, the photoelectric conversion means 13 is not limited to the case where the flat optical fiber 15 and the photoelectric conversion element 16 are used.
Photoelectric conversion means such as photoelectric cells and image sensors can be applied, and especially when image sensors are applied,
By pattern recognition of the output, there is an advantage that it is also possible to detect the degree of meandering or inclination of the moving body.

Furthermore, the laser device 1 is not limited to a He-Ne laser, but may be any laser that has frequency stability or is configured to compensate for frequency fluctuations even if it does not have frequency stability. Other gas lasers, solid state lasers, semiconductor lasers can be used, and the overall configuration can be made more compact, especially if a semiconductor laser is used.

〔Effect of the invention〕

As explained above, according to the present invention, the collimator lens is connected to the laser device via an optical fiber and has a semi-transparent mirror formed on the output end face, and the collimator lens is connected to the laser device through the optical fiber and has a semi-transparent mirror formed on the output end face, and An optical lens forming a half mirror, a photoelectric conversion means arranged opposite to the output end of the optical lens, and an interference fringe detection signal from the photoelectric conversion means are processed to calculate the relative movement distance between the laser device and the optical lens. A highly accurate length measurement function can be obtained with an extremely simple configuration that only requires a means for detecting relative movement distance, and in addition, only the collimator lens is fixedly placed in the length measurement section facing the optical lens. Since only a small amount of light is required, it can be installed even in a small installation place, and the effects of vibration and return light on the laser device can be eliminated.

Further, when a single mode optical fiber is used as the optical fiber, mode conversion does not occur due to vibration, and accurate length measurement can be performed without being affected by temperature changes.

Furthermore, by making the output end of the collimator lens a flat surface, parallel interference fringes with constant intervals can be clearly formed at the output end of the optical lens.

Furthermore, the photoelectric conversion means can be formed by laminating a large number of flat optical fibers to form a light-receiving surface, and by bundling the output ends of each flat optical fiber and facing the photoelectric converter, parallel interference fringes can be detected as point information. This makes it possible to easily perform distance measurement processing.

Furthermore, the parallel interference fringes formed at the output end of the optical lens are compressed in the extending direction by a cylindrical lens to form an optical image,
By inputting this into a two-layer flat optical cable, the length of the photoelectric conversion means in the width direction can be shortened.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2 fa
) and (b) are respectively a perspective view of a gradient index lens applicable to the present invention and a diagram showing its refractive index distribution state;
The figure is a block diagram showing an example of a processing device applicable to the present invention, and FIG. 4 is an explanatory diagram for explaining the present invention in detail. In the figure, 1 is a laser device, 4b is a semi-transparent mirror, 6 is an input lens, 7 is a single mode optical fiber, 8 is a collimator lens, 9 is a laser beam, 10 is a moving object to be measured, and 11 is a gradient index type 12 is a half mirror, 113 is a photoelectric conversion means, 14 is an optical fiber, 15 is a flat optical fiber,
16 is a photoelectric conversion element, 18 is a processing device, 19 is a pulse signal forming circuit, 20 is a direction discrimination circuit, 2I is a multiplication circuit, 2
2 is an up/down counter, and 25 is an interference fringe.

Claims (6)

[Claims] (1) A collimator lens into which a laser beam from a laser device that emits substantially parallel laser beams is input via an optical fiber and whose output end face is a semi-transparent mirror, and an optical axis of the laser beam emitted from the collimator lens. An optical lens whose optical axes substantially coincide with each other and a semi-transparent mirror formed at the other end, which serves as the focus of the light beam incident on one end, is arranged so as to be relatively movable, and the interference fringes generated at the output end of the optical lens are photoelectrically converted. and a relative distance detection means that detects the relative distance between the collimator lens and the optical lens by detecting the number of passing interference fringes and the moving direction based on the detection signal of the photoelectric conversion means. A laser interferometric length measuring machine featuring: (2) A collimator lens into which a laser beam from a laser device that emits substantially parallel laser beams is input via an optical fiber and whose output end face is a semi-transparent mirror, and an optical axis of the laser beam emitted from the collimator lens. An optical lens whose optical axes are substantially coincident with each other, a semi-transparent mirror is formed on the incident end surface of the light beam, and the other end is a focal point is arranged so as to be relatively movable, and interference fringes generated at the output end of the optical lens are photoelectrically converted. A photoelectric conversion means, and a relative distance detection means for detecting the number of passing interference fringes and the moving direction based on the detection signal of the photoelectric conversion means to detect the relative distance between the collimator lens and the optical lens. Features of laser interferometric length measuring machine. (3) The laser interferometric length measuring device according to claim 1 or 2, wherein the optical fiber is a single mode optical fiber. (4) The laser interferometric length measuring device according to any one of claims (1) to (3), wherein the output end face of the collimator lens is flat. (5) The output end face of the collimator lens is a flat surface,
Interference fringes parallel to the output end of the optical lens are formed, and the photoelectric conversion means arranges flat optical fibers in multiple layers in which a large number of optical fibers are arranged in a plane layer, and the output end of each flat optical fiber in each layer is A laser interferometric length measuring device according to any one of claims 1 to 4, wherein the laser interferometric length measuring device is configured to be bundled and faced to a photoelectric detector. (6) A cylindrical lens is inserted between the output end of the optical lens and the photoelectric conversion means, and an optical image obtained by compressing parallel interference fringes in the length direction of the fringes is made to enter the two-layer flat optical fiber. A laser interferometric length measuring machine according to claim (5).