JPH06342005A - Optical sensor - Google Patents

Abstract

PURPOSE:To provide an optical sensor which enables two-dimensional information detection by performing a plurality of spatial filtering processings with one unit. CONSTITUTION:A plurality of holographic patterns are projected sequentially onto an object 3 to be measured in a time-sharing manner by a projection means 10 which comprises laser light sources 11a and 11b and a holographic pattern generation optical systems 12a and 12b. The resulting reflected light is received by a detection means 13 which comprises an imaging lens system 16, a stray light stop 17, a spatial filter 18 and a photo detector and a processing thereof is performed with a signal processing section 2 which comprises an amplifier 21, a low pass passage filter 22, frequency counter 23, a counting processing section 24, a display device 25 and a synchronous control section 26 for performing a time-sharing synchronous control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor for measuring the velocity and the moving direction of an object in a non-contact manner.

[0002]

2. Description of the Related Art An optical sensor that extracts a specific signal from image information of an object to be measured by using a spatial filter and digitizes this signal for sensing is capable of handling a two-dimensional image even in a non-contact sensor. It is characterized by adapting the spatial filter to the DUT and enabling efficient sensing. Normally, this type of sensor captures the light emission pattern of the DUT itself or the reflection pattern of the uniformly illuminated DUT, and forms an image on the surface of the spatial filter installed in the measurement optical system. Filtering is performed on the surface of the object to be measured by irradiating the object to be measured with a specific spatial radiation pattern, as disclosed in the same applicant's previous application (Japanese Patent Application No. 4-361313). There is a system that realizes spatial filtering. In the latter method,
A coherent wave source such as a laser is used as the light source of the radiation pattern, and a holographic pattern utilizing the wave interference and diffraction phenomena is used as the spatial radiation pattern. In addition, by controlling the generation mechanism of this holographic pattern from the outside, the shape of the radiation pattern is changed to act as a variable spatial filter, and optimal spatial filtering is realized.

In spatial filtering, the basic processing is to superimpose two images and extract the area of the common part. However, when the two images move relatively, the area of the common part changes with time. When the state of this change is detected, a so-called cross-correlation output of two images is obtained. Generally, a change in the amplitude value of the correlation output indicates a change in the shape of the DUT,
Further, it is known that a change in frequency indicates a moving state such as speed, and an optical sensor using a spatial filter is used for a speed detector or the like by utilizing this property.

[0004]

However, the spatial filter in the conventional optical sensor has a one-dimensional lattice shape fixedly arranged on the image plane of the input optical system, or one direction generated by the interference of two coherent light beams. When using it as a sensor to detect the velocity or the movement of a moving object, the moving velocity component in the direction perpendicular to the grating or the interference fringe is most prominently detected. There was selectivity in the direction of detection such that the component parallel to was hardly detected. In addition, the direction selectivity is such that even if the shape of the grating or the interference fringe is improved two-dimensionally, the photodetector detects the light passing through the spatial filter or the entire reflected light of the spatial radiation pattern from the DUT. Therefore, it could not be omnidirectional. That is, the information of all directions is obtained at the same time, and the direction of information cannot be determined. This feature has an advantage when it is used for speed detection in one direction such as a vehicle-mounted speedometer, but it is not suitable for speed detection in all directions such as posture control of a robot arm.

An object of the present invention is to realize an optical sensor capable of non-directionally detecting a two-dimensional movement or speed of an object to be measured, which is difficult to detect by a conventional optical sensor using a one-dimensional spatial filter. It is to be.

[0006]

In order to solve the above problems, the present invention uses a mechanism for generating a plurality of holographic patterns when performing spatial filtering by irradiating a DUT with a specific spatial radiation pattern. To generate a plurality of patterns, change the grid direction of these patterns and irradiate the object to be measured to detect movement information in different directions, and perform signal processing of these signals to generate a two-dimensional object. I try to get movement and moving speed. For this reason, a coherent wave source such as a laser light source is used as the light source of the radiation pattern, and the spatial radiation pattern is a holographic pattern utilizing the interference and diffraction of waves. Further, the holographic patterns having different lattice directions are generated sequentially in time, and the light reflected or scattered by the object to be measured for each holographic pattern is detected by one optical system in a time division manner. Like
We are working to simplify the device mechanism, reduce its size, and put it into practical use.

[0007]

Function: A plurality of holographic patterns having different grid directions are sequentially irradiated on the object to be measured in a time division manner, receiving a scattering pattern from the object to be measured, and in synchronization with irradiation of the holographic pattern, for each of the grating directions. Detect movement information.
The movement information is signal-processed to obtain the two-dimensional movement and movement speed of the measured object.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a first embodiment of the present invention. The optical sensor of the present invention generates an optical pattern, radiates it to an object to be measured, receives the scattered light reflected by the object to be measured, and converts it into an electric signal, and a photoelectric conversion output of the optical sensor section 1. The signal processing unit 2 receives a signal and processes an electric signal.

In the optical sensor section 1, laser light sources 11a and 11b as coherent light sources for generating a holographic pattern for irradiating the DUT 3,
An imaging lens system incorporating a holographic pattern generator 10 for converting a laser beam emitted from the laser light source into a holographic pattern 4, and further condensing the reflected light from the DUT 3 to form an image. 16 and a photodetector 19 that photoelectrically converts the reflected light that has formed an image and outputs an electrical signal.

Here, a method of spatial filtering by irradiation of a pattern, which is the main technique of the present invention, will be described.
As a spatial filtering technique in an optical calculation system, generally, a Fourier transform lens 42 as shown in FIG. 6 is used.
Diffraction image 43 of spatial input pattern 41 obtained by
Apply a spatial filter 44 to
Further, it is well known that the image included in the spatial input pattern 41 can be sharpened or smoothed according to the characteristic (shape) of the spatial filter 44 by re-imaging with the imaging lens 45. If this optical technique is applied to not only a diffraction image but also a normal image, as shown in FIG. 7, it is possible to detect the size and change of the overlapping area of the light transmitting portions of the spatial input pattern 41 and the spatial filter 44. That is, the image correlation calculation becomes possible. When the spatial input pattern 41 is in a moving state, the overlapping area changes with time, and if the photodetector 19 detects the amount of change, the moving speed of the spatial input pattern 41 can be measured. Is effectively used by.

In the optical sensor, in order to capture an optical image of the object to be measured, illumination is necessary when the object to be measured is other than a light emitter. The present invention focuses on this illumination, and creates the light intensity distribution of the illumination in accordance with the reflection pattern characteristics of the DUT,
At the same time as illuminating the surface of the object to be measured, image correlation is performed with the two-dimensional distribution pattern of the illumination light and the reflection pattern of the surface of the object to be measured. This state is shown in FIG. 8. Compared with the image correlation method using the spatial filter 44 described above, the spatial filter 4 arranged immediately before the photodetector 19 in FIG.
In FIG. 8, it can be seen that 4 is a structure moved to the surface position of the object to be measured.

Although an illumination pattern suitable for the object to be measured, which is used in place of the spatial filter, can be realized by a simple projection optical system such as a slide projector, in such an incoherent imaging optical system, an imaging plane is formed. An accurate image formation pattern can be maintained only in a few places before and after that.

On the other hand, the characteristic of the holographic pattern created by utilizing the interference and diffraction of the wave in the holographic pattern generating optical system 12 by using coherent light whose phase is uniform is that the holographic pattern is normally illuminated by the focusing action of the lens system. This is a point that a three-dimensional lattice-like light intensity distribution orthogonal to the optical axis direction can be obtained, which is impossible with the method of generating a pattern. This state is shown in FIG. This figure shows the most basic method of using the two-wave interference fringe. FIG. 9 shows a plan view of the obtained two-wave interference fringe. When two light waves obtained by halving the same light source by the beam splitter 48 are made to intersect each other at a shallow angle using two reflecting mirrors 49a and 49b to generate an interference fringe, the interference fringe varies depending on the position in the optical axis direction. Instead, a three-dimensionally constant lattice spacing is maintained, and this lattice spacing can be accurately determined by the crossing angle of two light waves and the light wavelength.

The holographic pattern generating optical system 12 shown in FIG. 5 is an optical system for generating a diffraction pattern using the optical diffraction grating 47 and using it as an illumination pattern. FIG. 10 shows a plan view of the optical diffraction grating, and FIG. 11 shows a plan view of the diffraction pattern. As a general characteristic of the diffraction pattern, the diffraction image is a point-symmetrical figure centered on the optical axis, and the phase change (change in set position) of the diffraction grating is not reflected in the diffraction image. "It has been known. As shown in this figure,
Normally, a parallel light flux is incident on the diffraction grating to obtain a diffraction image. When the shape of the diffraction grating is a repetitive pattern, the shape of the diffraction image shows parallel lines or a grid-like bright spot distribution.The size of this image and the bright spot spacing are the grating spacing of the diffraction grating and the irradiated light. Can be accurately calculated with the wavelength of and the distance between the diffraction grating and the surface to be measured. By utilizing this, it is also possible to accurately extract the specific pattern information from the object to be measured.

The difference between the diffraction pattern and the above-mentioned interference pattern is that the bright spot spacing changes depending on the distance between the diffraction grating and the surface to be measured, and the rate of this change is the emission of the light beam incident on the diffraction grating. Since it is determined by the angle, it can be set to a desired value by diffusing or narrowing the light beam incident on the diffraction grating by the lens system.

Now, let us return to the first embodiment shown in FIG. The holographic pattern using the interference and diffraction described above is applied to the DUT 3, and reflected light, which can be called an image correlation signal with the reflection pattern on the surface of the DUT, is condensed by the imaging lens system 16 to The light is guided to the detector 19 and photoelectrically converted. At this time, the lens system is adjusted so that the image forming surface of the image forming lens system 16 is located in front of the light receiving surface of the photodetector 19 (on the side of the DUT 3), and the imaged surface of the DUT is formed. The second spatial filtering can be further performed by disposing the spatial filter 18 having a shape matching the reflection pattern of No. 2 on the image plane.

In the second spatial filtering, when a diffraction pattern is used for the holographic pattern, a similarity change (generally an expansion change proportional to the distance) of the pattern shape, which is a characteristic of the diffraction pattern, with respect to the radiation distance.
By effectively using, it is possible to maintain good filtering accuracy. That is, as described above, the bright spot spacing of the diffraction pattern changes in a similar manner in proportion to the distance to the surface to be measured depending on the focusing or diverging state of the light beam incident on the diffraction grating. The shape expansion rate with respect to the measurement distance of the diffraction pattern (the expansion rate of the diffraction pattern shape with increasing distance to the object to be measured) is the shape reduction with respect to the measurement distance when the diffraction pattern is imaged by the imaging lens system 16. If the reciprocal of the rate (the rate at which a distant image is formed is reduced compared to the closest image) is set, the optimum non-deformable diffraction pattern on the spatial filter 18 is hardly affected by the change in the measurement distance. Can be imaged. In order to always form an exact image of this optimum diffraction pattern, the imaging lens system 16 is used.
It is necessary to focus according to the change of the measurement distance of
Actually, assuming that the change of the measurement distance is about 2 to 30%, it is sufficient to make the aperture of the lens system small or to set the aperture stop and make the depth of focus deep.

The object to be measured 3 is attached to the imaging lens system 16.
In order to remove the disturbance light incident from other than the above and the stray light generated by the multiple reflection in the lens system, it is possible to further improve the detection sensitivity of the reflection pattern by appropriately disposing the stray light stop 17. .

The signal processing unit 2 receives the output signal of the photodetector 19 and outputs it to the amplifier 21 and the low pass filter 2.
The waveform is shaped by 2 and sent to the frequency counter 23 to count the frequency or the number of waveform peaks in a unit time. The signal counted here is converted into a numerical value by the counting processing unit 24 which converts it into an actual measurement unit (for example, m / s, km / h in the case of speed) and is output as a measurement output signal. Further, the light emission timing of the laser light source, that is, the light emission timing of a plurality of holographic patterns is time-division controlled, and synchronization for synchronizing the count timing of the frequency counter and the numerical conversion processing in the count processing unit 24 with the light emission timing. The control unit 26 controls the entire apparatus. The counting processing unit 24 accumulates a plurality of signals obtained for each radiation of a plurality of holographic patterns having different directions, captures all the signals, and then outputs one measurement signal by numerical analysis. For example, when this signal represents speed, analysis processing is performed so that the magnitude and direction of the speed can be obtained as a speed vector. In addition, the measurement signal output can be read by the display device 25 when necessary for adjustment or the like.

Next, a second embodiment of the present invention will be described.
FIG. 2 is a configuration diagram showing a second embodiment of the present invention. The feature of this embodiment is that the holographic pattern 4 is
A plurality of optical fibers (three in this embodiment) 33a, 33
b, 33c is a point formed by the coherent light propagated, and the holographic pattern is formed by the interference of two laser beams emitted in the air from two of the plurality of fibers. is there.

The light incident on these optical fibers may be light from any laser, but a semiconductor laser (hereinafter referred to as LD) is taken into consideration in consideration of the shape of the device and mechanical stability.
Easy and good to use the light of. In this embodiment, L
The emitted light of the D light source 31 is divided into two equal parts by the beam splitter 32, and is further distributed to the optical fibers 33a, 33b and 33c by an optical switch 37 with two inputs and three outputs. The light is distributed so that the laser light is sent to the two optical fibers at the same time, and the optical switch 37 controls the two pairs to be switched temporally. That is, first, the light emitted from the optical fibers 33a and 33b forms an interference pattern, and subsequently, the same 33b and 33c, and further 33c and 33a. In the interference of light propagating through two optical fibers, if both fiber lengths are substantially equal, interference occurs within several phases to several tens of phases, so that strong interference fringes with good visibility can be obtained. The interval of the interference fringes can be set arbitrarily by adjusting the interval between the two optical fibers and the crossing angle of the optical axes of the fibers. In addition, if two optical fibers are fixed adjacent to each other, the interference fringe spacing cannot be adjusted.
Since the relative position of each optical fiber is stable, a fine holographic pattern can be obtained extremely stably.

Further, the difference between the holographic pattern produced by directly interfering the spherical wave-like light emitted from the optical fiber in this embodiment and the holographic pattern shown in the first embodiment is the same as the first embodiment. In the embodiment described above, the radiation direction of light is almost one direction due to the interference of parallel plane waves, and the shape of the pattern does not change depending on the radiation distance.However, the holographic pattern of this embodiment is And the pattern is radially diffuse. For this reason, the energy of the emitted light decreases almost in inverse proportion to the square of the distance, and the distance between the light emitting end of the optical fiber and the object to be measured cannot be increased so much. Further, since the shape of the holographic pattern changes similarly when this distance changes, it is necessary to limit the measurement target to the object to be measured at a short distance and a fixed position in order to use it in the measuring device. Experimentally, the maximum distance to the object to be measured is about several cm by using an LD of several mW output as a light source. However, it is possible to accurately and stably create a holographic pattern having a lattice spacing of several tens of μm, which is very effective for highly accurate non-contact measurement of a minute object.

In order to avoid such a limitation on the distance and adapt the holographic pattern to the reflection pattern on the surface of the object to be measured, in the present embodiment, the vicinity A of the output end of the optical fiber is used.
And a zoom optical system 35 composed of micro optics, etc.
Are arranged. The zoom optical system 35 is an optical system that simultaneously focuses or diverges the light emitted from the three optical fibers 33a, 33b, and 33c, and has a function of zooming the holographic pattern on the surface position of the DUT 3, and A simple one is a lens system having a diameter capable of simultaneously entering the outgoing lights of two fibers.

The light emitted from two of the optical fibers 33a, 33b and 33c is used as the zoom optical system 3.
The holographic pattern 4 formed by passing through 5 is irradiated onto the DUT 3, and the reflected light thereof is provided by the light receiving optical fiber 34 which is installed in a position close to the three optical fibers and easily receiving the reflected light. Received light. Usually, the most suitable position for receiving light is the middle portion of the three optical fibers, and therefore, as shown in FIG. 3, the three optical fibers 33a, 33b, 33 are used.
The light-receiving optical fiber 34 may be installed in the central portion so as to be sandwiched by c.

The light received by the light receiving optical fiber 34 is guided to the photodetector 19 and photoelectrically converted into an electric signal. This electric signal is sent to the signal processing unit 2 and converted into a signal output in exactly the same manner as in the case of the first embodiment. In addition, in this embodiment, the light from one LD light source 31 is time-divided into three optical fibers, and the beam splitter 32 and the optical switch 37 are used together to sequentially generate a plurality of holographic patterns. The optical switch 37 is controlled by the switching control signal of the synchronization control unit 26 so as to always emit light to 2 ports out of 3 ports of output.

Although the holographic pattern is generated by using light in the first and second embodiments, the present invention is not limited to light and may be a coherent wave such as a microwave, an X-ray, an electron beam or an acoustic wave. If so, it can be used according to the measurement purpose.

[0027]

As described above, according to the present invention, the holographic pattern that matches the reflection pattern of the object to be measured is generated by the projection means for projecting the holographic pattern, and the object is irradiated with the holographic pattern. Therefore, it is possible to realize an optical sensor that can perform optimal spatial filtering, form multiple holographic patterns with different grating directions in time division, project them, and synthesize and analyze the signals obtained at each projection. Since it is decided to detect the state of the measured object, it is possible to detect the state of an object with two-dimensional movement, such as the speed and movement direction of the object can be detected by using it to detect the speed of the object. Became.

Further, by performing the time-division processing, the light source and the detecting means can be covered by one device, respectively, and it is possible to realize an optical sensor which is small and mechanically stable. The formation of the radiation pattern by the optical fiber shown in the embodiment also has a variable characteristic that the projection location of the holographic pattern can be arbitrarily changed within the reach of the optical fiber.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration in a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a configuration in a second exemplary embodiment of the present invention.

FIG. 3 is an enlarged view of part A of the second embodiment of the present invention.

FIG. 4 is a diagram showing a mechanism of generation of interference fringes due to interference of two light waves.

FIG. 5 is a diagram showing a mechanism of generating a diffraction pattern by a diffraction grating.

FIG. 6 is a diagram showing a basic configuration of spatial filtering by a Fourier transform optical system.

FIG. 7 is a diagram showing a basic configuration of image correlation calculation by spatial filtering.

FIG. 8 is a diagram showing a basic configuration of image correlation calculation using a pattern of illumination light.

FIG. 9 is a plan view of two light wave interference fringes.

FIG. 10 is a plan view of an optical diffraction grating.

FIG. 11 is a plan view of a diffraction pattern.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical sensor part 2 Signal processing part as a processing means 3 Object to be measured 4 Holographic pattern 10 Holographic pattern generation part (projection means) 11a, 11b Laser light source 12, 12a, 12b Holographic pattern generation optical system 13 Detection means 14 Optical system 15 for forming a scattering pattern 15 Extraction means 16 Imaging lens system 17 Stray light diaphragm 18 Spatial filter 19 Photodetector 21 Amplifier 22 Low-pass filter 23 Frequency counter 24 Counting processor 25 Display 26 Synchronous controller 31 LD light source 32 beam splitter 33a, 33b, 33c optical fiber 34 light receiving optical fiber 35 zoom optical system 36 detecting means 37 optical switch 41 spatial input pattern 42 Fourier transform lens 43 diffraction image 44 spatial filter 45 imaging lens 47 optical circuit Grid 48 the beam splitter 49a, 49b reflector

Claims (2)

[Claims] 1. A projection means (10) for sequentially projecting a plurality of holographic patterns with different angles on a projection target at a predetermined timing, and a scattering state for each holographic pattern projected on the projection target. An optical sensor including a detection means (13) for detecting a change in 2. A holographic pattern generator (10) that can be set so as to match a holographic pattern of a laser beam projected onto an object to be measured with the pattern of the object to be measured, and scattered light from the object to be measured. An optical system (14) for receiving a scattering pattern, an extracting means (15) for extracting desired information related to the object to be measured from the scattering pattern, and a processing of the information extracted by the extracting means. In the optical sensor including the processing means (2) for performing, the holographic pattern generation unit can generate at least two holographic patterns in spatially independent directions separately in time, and the processing means includes the holographic pattern generation section. An optical sensor including a synchronization controller (26) for processing the information in synchronization with the generation of a graphic pattern.