JPH0480658A - Method and apparatus for measuring velocity - Google Patents

Abstract

PURPOSE:To enable immediate measurement of velocity of a moving object by a method wherein the moving object is irradiated with a pulse light to form a two-dimensional multiple image of the moving object on a spatial light modulation means and the image is read out optically to undergo a Fourier transform optically. CONSTITUTION:A pulse light source 2 emits light at a time interval (t) to light a road surface 1. An image of the road surface 1 is formed on an input surface 71 of a spatial light modulator 7 and a position thereof shifts with the passage of time. The modulator 7 forms a phase difference image of the multiple image on an output surface 72. Reading light from a reading light source 12 is emitted to the output surface 72 as coherent linearly polarized light passing through a polarization beam splitter 9. The reflected light thus obtained is turned to an oval polarized light and impinged into a Fourier transform lens 13 being reflected with the splitter 9 according to a degree of modulation. A Fourier spectrum is formed on the output surface 72 of a camera 14 corresponding to the multiple image. Intervals between fringes of the spectrum correspond to a velocity of the road surface 1 and a direction of an array of the fringes corresponds to the direction of motion of the road surface 1. Thus, by performing a computation processing 15 of the intervals and the direction, the velocity of the road surface 1 can be measured.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a speed measuring method and device.

[Conventional technology]

A method using a spatial filter is known as a method for measuring the speed of a moving object. This is, for example, JP-A-53-52
No. 473, No. 52-15377, etc. In this method, a sensor having a light-receiving surface having a grating structure is used, and an image of a moving object is formed on the light-receiving surface. As a result, the above-mentioned lattice structure acts as a spatial filter for information on the surface of the moving object, and a signal whose repetition frequency of the sensor output is proportional to the speed of the moving object is obtained.

[Problem to be solved by the invention]

However, according to the above-mentioned prior art, when the orientation of the lattice structure of the sensor has a certain relationship with the moving direction of the moving object, it is not possible to determine whether measurement is possible or the relationship cannot be determined. Further, movement in a direction perpendicular to the direction in which the gratings are arranged generally cannot be measured. In order to detect movement in all directions, it is necessary to add special measures to the grid structure, etc.

The present invention has been made to solve the drawbacks of the prior art, and aims to provide a new method and device for speed measurement whose principle is different from the spatial filter method.

[Means to solve the problem]

The speed measuring method according to the present invention intermittently irradiates a moving object whose moving speed is to be measured with pulsed light, and generates a two-dimensional image of the moving object by irradiating the pulsed light at least twice with a spatial light modulator. A Fourier spectrum image is formed by optically reading out this multiple image and Fourier transforming the readout light image, and based on the interval and direction of this Fourier spectrum image and the irradiation time interval of the pulsed light. It is characterized by measuring moving speed.

The speed measuring device according to the present invention also includes a pulsed light source that intermittently irradiates a moving object whose moving speed is to be measured with pulsed light, and an optical image from the moving object irradiated with the pulsed light into a predetermined two-dimensional image. an imaging optical system that forms an image on an imaging surface; a spatial light modulation means that is disposed on a predetermined two-dimensional imaging surface and that superimposes and accumulates an image of a moving object for irradiation of at least two pulsed lights; It includes a Fourier transform optical system that forms a Fourier spectrum image from the output light image of the spatial light modulation means, and a detection means that detects the moving speed from the interval and direction of the Fourier spectrum image and the irradiation time interval of the pulsed light.

[Effect]

According to the method of the present invention, two-dimensional multiple images of a moving object are formed on the spatial light modulation means, but since the irradiation time interval of the pulsed light is a predetermined width, the positional relationship of the convex images of the multiple images is , has a certain relationship with the speed of a moving object. Since this multiple image is equivalently processed as a two-dimensional lattice structure by the irradiated pulsed light, it can be read out optically and optically Fourier transformed to determine the velocity and direction of the moving object. A Fourier spectral image with a certain relationship is obtained.

According to the speed measuring device of the present invention, multiple images of a moving object are formed by the pulsed light and the imaging optical system, which are read out as an output optical image by the reading means, and are converted into the velocity of the moving object by the Fourier transform optical system. A Fourier spectral image with a certain relationship is obtained.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view of a speed measuring device according to an embodiment, showing a conceptual configuration when measuring ground speed with a vehicle-mounted speed measuring device. Moreover, FIG. 2 shows its optical configuration. As shown in the figure, it is assumed that a road surface 1, which is a moving object, is moving in the direction of arrow A at a predetermined speed. Pulsed light source 2
A pulse voltage that is repeated at equal intervals as shown in waveform B is supplied from the driver 3, and therefore the pulse light source 2 emits light intermittently at time intervals t to illuminate the road surface 1.

Above the illumination position of the road surface 1, a telecentric imaging lens 4 and a diaphragm 6 are sequentially arranged to form an imaging optical system. The spatial light modulator 7 is provided so that the input surface 71 is the imaging position of the road surface 1 by the telecentric imaging lens 4, and a polarizing beam splitter 9 is provided above the output surface 72 of the spatial light modulator 7. ing. A reading light source 12 consisting of a laser diode 10 and a collimator lens 11 is provided above the polarizing beam splitter 9, and a Fourier transform lens 13 is provided on the side of the polarizing beam splitter 9.
and an imaging device 14 are arranged in this order. The output of the imaging device 14 is given to an arithmetic processing device 15.

According to the above configuration, an image of the road surface 1 is formed on the input surface 71 of the spatial light modulator 7, but since the speed measuring device is moving, the formed image is an image whose position shifts over time. Become. Since the pulsed light emission is intermittent and the time interval t is constant, the interval and alignment direction of each aircraft in this multiple image have a certain relationship with the speed and direction of movement of the road surface 1. have. Here, the spatial light modulator 7 includes a photocathode and an electro-optic crystal such as lithium niobate, which has an optical anisotropy due to the charge generated in response to light by the photocathode, for example, a polarized light with an electro-optic crystal. Since it changes the refractive index in the direction, it has a function of accumulating optical images from the road surface 1 and forming a phase difference image of multiple images on the output surface 72. This speckle multiple image functions equivalently as equally spaced multiple slits (diffraction grating) for the coherent readout light. Note that the specific configuration and operation of the spatial light modulator 7 are known, for example, from Japanese Patent Laid-Open No. 58-64742.

The readout light from the readout light source 12 passes through the polarization beam splitter 9 and becomes coherent linearly polarized light, which is incident on the output surface 72 of the spatial light modulator 7 .

Here, since the spatial light modulator 7 has refractive index information or phase difference information as multiple images, the output light generated as reflected light of the readout light becomes elliptically polarized light corresponding to the refractive index information.

Therefore, this elliptically polarized light is partially reflected by the polarizing beam splitter 9 and enters the Fourier transform lens 13. That is, the reflected light that has been modulated with a phase difference of less than half a wavelength on the output surface 72 of the spatial light modulator 7 generally becomes elliptically polarized light, is reflected by the polarizing beam splitter 9 according to the degree of modulation, and the rest is elliptically polarized light. To Penetrate. In this way, the light beam reflected by the polarizing beam splitter 9 becomes coherent light in which two-dimensional refractive index information or phase difference information on the output surface 72 is converted into two-dimensional amplitude information.

The front focal point of the Fourier transform lens 13 is the output surface 72 of the spatial light modulator 7, and the rear focal point is the imaging device 14, so a Fourier spectrum corresponding to the multiple images on the output surface 72 is formed on the imaging device 14. be done. The interval between each section of this Fourier spectrum corresponds to the speed of the road surface 1, and the direction in which each section is arranged corresponds to the movement direction of the road surface 1. The speed of can be measured.

The above situation will be explained in more detail with reference to FIGS. 3 and 4.

Now, suppose that the road surface 1 is intermittently irradiated with pulsed lights P1 to P4 at time intervals t, as shown in FIG. 3(a).
As shown in FIG. 3(b), an image of a point on the road surface 1 is formed on the spatial light modulator 7. That is, pulsed light P −P4
Corresponding to this, a point image ■ a −a is formed. Here, images a1 to a
The inclination angle θ between the line connecting 4 and the reference line corresponds to the inclination of the road surface 1 in the traveling direction, and the distance between images a-a4 corresponds to the speed of movement.

The output optical image of this image a-84 is Fourier transformed and the lens 1
3, a Fourier spectrum image is formed on the imaging device 14. That is, as shown in FIG. 4, the images a1 to a4 on the output surface 72 of the spatial light modulator 7 form linear equally spaced stripes in the imaging device 14. This Fourier spectrum image is read as an electrical signal by photoelectric conversion and is input to the arithmetic processing unit 15. The arithmetic processing unit 15 recognizes the direction and spacing of the stripes at regular time intervals,
Find the speed and direction of movement.

Here, the moving speed of the road surface 1, which is a moving object, is inversely proportional to the interval between stripes, and is also inversely proportional to the time interval t between pulsed light emissions. Therefore, the speed of the road surface 1 can be calculated by calculation. Also, if the direction of movement is relative to the reference line,
The present invention, in which the degree of inclination can also be determined from the inclination of the stripes, is not limited to the above embodiments and can be modified in various ways.

For example, the imaging optical system is not limited to one using a telecentric imaging lens, and may have any configuration as long as it can form an image of a moving object on the input surface of the spatial light modulator. Further, the reading of multiple images may be performed, for example, by using a screen such as ground glass on which a polar coordinate scale is carved in place of the imaging device 14. The distance and direction can be read from the Fourier spectrum image formed on the screen. Therefore, various configurations can be used as long as the Fourier spectrum of the image formed on the output surface of the spatial light modulator can be generated. There are various types of spatial light modulation means that can be used.
Specific examples are shown on pages 19 to 27 of ``Month''.

〔Effect of the invention〕

As explained above in detail, according to the configuration of the present invention, a two-dimensional multiple image of a moving object is formed on the spatial light modulation means, but the irradiation of pulsed light is intermittent and the intervals are a predetermined width. Therefore, the positional relationship of the multiple images has a certain relationship with the speed of the moving object. Since this multiple image is recorded in the spatial light modulation means, by optically reading it out and Fourier transforming it, a Fourier spectrum image having a certain relationship with the velocity of the moving object can be obtained. Therefore, regardless of the direction in which the moving object moves, it can be accurately measured.

Further, according to the speed measuring device of the present invention, multiple images of a moving object are formed by pulsed light and an imaging optical system, and this is read out by the reading means. Therefore, the Fourier transform optical system can obtain a Fourier spectrum image that has a certain relationship with the speed of the moving object, so by calculating the direction and interval of this Fourier spectrum image, the speed of the moving object can be measured in real time. .

[Brief explanation of drawings]

FIG. 1 is a perspective view conceptually showing the structure of a speed measuring device according to the present invention, FIG. 2 is a side view showing the structure, and FIGS. 3 and 4 are diagrams showing its operation. DESCRIPTION OF SYMBOLS 1... Road surface, 2... Pulse light source, 3... Driver, 4... Telecentric imaging lens, 6... Aperture, 7... Spatial light modulator, 9... Polarizing beam splitter , 12... Reading light source, 13... Fourier transform lens, 14... Imaging device, 15... Arithmetic processing device. Representative Patent Attorney Yoshiki Hase Figure 2 → ÷ Figure 3

Claims (1)

[Claims] 1. A spatial light modulator that intermittently irradiates a moving object whose moving speed is to be measured with pulsed light and generates a two-dimensional image of the moving object by irradiating the pulsed light at least twice. A Fourier spectrum image is formed by reading out the multiple image and optically Fourier transforming the readout light image, and the interval and direction of the Fourier spectrum image and the irradiation time interval of the pulsed light are A speed measuring method characterized in that the moving speed is measured based on the movement speed. 2. A pulsed light source that intermittently irradiates pulsed light onto a moving object whose moving speed is to be measured, and imaging optics that images the light from the moving object irradiated with this pulsed light onto a predetermined two-dimensional imaging plane. a spatial light modulation means disposed on the predetermined two-dimensional imaging plane and two-dimensionally accumulates an image of the moving object for at least two pulsed light irradiations; and an output of the spatial light modulation means. A speed measuring device comprising: a Fourier transform optical system that forms a Fourier spectrum image from a light image; and a detection means that detects a moving speed from the interval and direction of the Fourier spectrum image and the irradiation time interval of the pulsed light. . 3. Arranged on the predetermined two-dimensional imaging plane, accumulates an image of the moving object two-dimensionally on the input plane at least for irradiation with the pulsed light, and converts the two-dimensional intensity distribution information into two-dimensional transmittance. spatial light modulation means for converting the distribution into a two-dimensional reflectance distribution or a two-dimensional phase difference distribution and outputting it to the output side; and irradiating the output side of the spatial light modulation means with coherent light, It further comprises: reading means for reading out the two-dimensional reflectance distribution or the two-dimensional phase difference distribution as coherent two-dimensional amplitude information, and the Fourier transform optical system converts the output optical image having the two-dimensional amplitude information into a Fourier spectrum image. 3. The speed measuring device according to claim 2, wherein the speed measuring device comprises: