JPS61155759A - Speckle speed measuring apparatus - Google Patents

Abstract

PURPOSE:To measure the speed of an object at a high accuracy, by arranging two measuring systems each including a light source, an optical system, a light receiving section and a signal processing section to receiving light at a boiling state with a circular beam irradiating a moving object in one measuring system while an oval beam irradiates it in the other measuring system. CONSTITUTION:When a laser light is emitted, it is converted into a light beam having a convergence area, a waste area and a diffusion area by an optical system to irradiate a moving object 14. The moving object 14 is positioned at the waste area boiling on a light receiving surface and the resulting variation signal is converted into an electrical signal with a light receiving element 17 to be inputted into a signal processing section 19. Moreover, from the speckle signal inputted, DC component is cut with a DC component removing circuit 41 to detect the number of zero crossings to create a pulse train adapted to invert from high to low level with a Schmitt triggering circuit 42. The counts of zero crossings per unit time in the pulse train is counted with a counter 44. The counts of the counter 44 is free from effect of the speckle size DELTAx, opening area (a), distance R between the object and a photoelectric conversion element and wave surface curvature rho of beam and this will result in no effect on the measurement of speed, thus meaning no need for correction.

Description

[Detailed description of the invention] (a) Industrial application field This invention irradiates a moving object with coherent light such as laser light and utilizes the resulting random interference pattern (speckle pattern). , relates to a speckle speed measuring device that measures the moving speed and direction of an object.

(b) Prior Art Generally, as shown in FIG. 6, when a moving object 4 is irradiated with coherent light 3 from a laser light source 1 through a projection optical system 2, the light transmitted or reflected by the moving object 4 is When received at the light receiving point 5, the speckle pattern undergoes two movements: translation (translation) movement and boiling (the speckle does not move, the intensity of light changes and oscillates on the spot). It is known that the light pattern moves and displaces (9i magazine "Laser Research" Vol. 8, No. 2, Vol. 8, No. 3). The removed normalized autocorrelation function r(τ.

σ snow 1+□・・・・・・(2) ρ becomes.

Equation +1) above shows that the autocorrelation function attenuates as the object velocity V increases, and for example, the correlation becomes 1/
The time at which e is reached is τC (autocorrelation length), and a: the radius of the socket opening. From this τC, the speed ■ can be measured. We have already applied for a speedometer (Japanese Patent Application No. 59-54043).

Also, the number of zero crossings per unit time of light fluctuation is NO.

The speed ■ can also be measured by counting this zero-crossing number No. The inventors of this application have also already applied for a spare wheel speed hand that adopts this principle (
Utility Application No. 1983-106376, Patent Application No. 59-5404
No. 1).

All of the above-mentioned speckle velocimeters that have already been filed employ illumination methods using converging beams or expanding beams.

(c) Problems to be solved by the invention The conventional speckle velocimeter described above uses a converging beam or an expanded beam for illumination and measures the speed based on equation (3) or (4) 2 above. Therefore, if the roughness correlation length of the rough object is relatively long compared to the illumination area, the speckles will be non-Gaussian, and for paper etc., the speckles will become smaller due to the bleeding phenomenon, and the speckles will be normal. This method has the drawback that speckles with no size are formed, which changes the autocorrelation function of light fluctuations, making it impossible to perform accurate measurements. Further, when the object to be measured changes, for example from copper to paper to cloth, ΔX changes depending on the object to be measured, and therefore the signal processing section has to make corrections for each change in object. Furthermore, if the illumination beam is not a perfect spherical wave but contains wavefront aberration, the translation of speckles is strongly related to the wavefront curvature, making the translation unstable, which also has the disadvantage of reducing measurement accuracy. there were.

Therefore, in order to eliminate this drawback, the inventor of the present application placed a moving object in the waist region of the beam, which has a convergence region, a fJl region, and a diffused region, and received the speckle pattern in the boiling state in the diffused region. He created a method for measuring speed and has already filed a separate application. However, even if this method is applied to simply realize a speckle velocimeter with one light source and one light receiving part, if the direction of movement of the object is not certain, it is not possible to know the direction.

In view of the above, the present invention makes it possible to measure the velocity of an object with high accuracy even when the speckle becomes non-Gaussian, when the measurement object is changed, or when the illumination beam contains wavefront aberration. It is an object of the present invention to provide a speckle speed measuring device that can also measure the direction of movement.

(d) Means and operation for solving the problems In order to solve the above problems, the present invention is provided with two measurement systems each including a light source, an optical system, a light receiving section, and a signal processing section. The light receiving section also receives light in a boiling state, and one measurement system irradiates the moving object with a circular beam and the other measurement system irradiates the moving object with an elliptical beam.

That is, the speckle velocity measuring device of the present invention includes a first light source that emits coherent light, a first light source that converts the coherent light from the first light source into a light beam having a convergence region, a waist region, and a diffusion region. an optical system, a first light-receiving section including a photoelectric conversion element arranged so that speckles generated on the light-receiving surface are in a boiling state due to the positional relationship between the light beam and the moving object; a first measurement system that includes a first signal processing unit that outputs a signal according to the object velocity; and a second measurement system that emits coherent light.
a light source, a second optical system that converts the coherent light from the second light source into a light beam having a convergence region, a waist region, and a diffusion region and having an elliptical cross section; A second light receiving unit including a photoelectric conversion element arranged so that speckles generated on the light receiving surface due to the positional relationship with the light beam and the moving object are in a boiling state; Consisting of a second measurement system including a second signal processing section that outputs a signal according to the signal, and a direction calculation means that calculates the moving direction of the object based on the outputs of the first and second measurement systems. has been done.

In this speckle velocity measuring device, since light is received in a boiling state, the right terms of equations (3) and (4) can be ignored, so the cross-correlation length re and the zero-crossing number N.

(1) π, and the velocity V is calculated by determining the autocorrelation length τC1 or the zero crossing number NO in the first signal processing section. In addition, ΔX, ρ, etc. are no longer included in any of τc SN o, and even if these change, the measurement results are not affected.Furthermore, the second signal processing section generates different signals depending on the moving direction of the object. Therefore, by calculating the output ratio of the first signal processing section and the second signal processing section using the velocity direction calculating means, the moving direction of the object can be determined from the ratio.

(E) Examples The present invention will be explained in more detail with reference to Examples below.

FIG. 1 is a schematic diagram of a speckle velocity measuring device in which the present invention is implemented. This speckle speedometer includes a first measurement system 1O, a second measurement system 20, and a movement direction calculation means 3.
It is composed of 0. Further, the first measurement system 10 includes a light projecting section 11 including a laser light source 12 and an optical system 13, a light receiving section 15 including an interference filter 16, a light receiving element 17, and an amplifier 18, and a signal processing section 19, The second measurement system 20 includes a laser light source 21 , a light receiving section 25 including an interference filter 26 , a light receiving element 27 and an amplifier 28 , and a signal processing section 29 .

The laser light sources 12 and 22 have different wavelengths (λ
1. The optical system 13.23 is provided to convert the coherent light from the laser light source 12.22 into a light beam having a convergent region, a SN region, and a diffused region. It is being However, the optical system 12 emits a light beam with a circular cross-section, whereas the optical system 23 emits a light beam with an elliptical cross-section.

The light beams emitted from the optical shapes 13 and 23 are irradiated onto the object to be measured I4 moving at a speed V, and the reflected light beams are received by the light receiving sections 15 and 25, respectively. The interference filter 16 is used to transmit only the light (wavelength λI) from the optical system 13, and the interference filter 2
6 are provided in order to transmit only the light (wavelength λt) from the optical system 23.

In addition, the positional relationship between the optical system 13, the object 14, and the light receiving element 17, and the positional relationship between the optical system 23, the object 14, and the light receiving element 27 cause speckle boiling on the light receiving surface of the light receiving element 17.27. It is arranged like this. In order to create a boiling state on the light receiving surface, the object should be irradiated with light in the waist region of the beam light, and the light receiving surface should be placed at a distance of 2w, 2/π or more from the object position, that is, in a diffusion region, or the object should be placed in a diffusion region. The light receiving surface may be located in the convergence region and the light receiving surface may be provided in the waist 8N region, and any of these may be adopted.

The boiling speckles generated on the light-receiving surface are converted into electrical signals (speckle signals) by the light-receiving element 17.27, amplified by amplifiers 18.28, and input to the signal processing section 19.29. It has become.

The signal processing section 19 is a functional circuit that receives the speckle signal from the light receiving section 15 and calculates the zero crossing number No. or a functional circuit that calculates the autocorrelation length τC.
The signal processing unit 19 is also the same type of circuit.

When the signal processing unit 19 is a functional circuit that calculates the zero crossing number No., as shown in FIG.
It is composed of a Schmitt circuit 42, a monostable multivibrator 43, and a counter 44.

Next, the object 14 is placed in the waist region of the light beam, the light receiving element 17.27 is provided in the diffusion region (R is 2w0279 or more), and the signal processing section 19.29 is made into a circuit for detecting the number of zero crossings. The operation in this case will be explained.

When a laser beam is emitted from the laser light source 12, the optical system 1
3, the light beam is converted into a light beam having a convergence region, a waist region, and a divergence region, and is irradiated onto the moving object 14. The moving object 14 is located in the waist region, the light receiving surface is in a boiling state, and the intensity of light fluctuates over time. This fluctuation signal is converted into an electrical signal by the light receiving element 17, amplified by the amplifier 18, and input to the signal processing section 19. Signal processing section 19
Then, the DC component of the input speckle signal is further removed by a DC component removal circuit 41 to detect the number of zero crossings, and a pulse train whose high and low levels are inverted at the time of zero crossing is created by a Schmitt trigger circuit 42.

This pulse train is shaped into a predetermined pulse width by a one-shot multi-by-break 43, and a counter 44 counts the number of zero crossings per unit time N o /2.

This zero crossing number No is as shown in equation (4) as a general theoretical equation, but in this example, since the light is received in a boiling state, the burial mound in equation (4) can be ignored, and it becomes π W . Therefore, the count value of the counter 44 is not affected by the speckle size ΔX, the aperture area a, the distance between the object and the photoelectric conversion element R1, and the wavefront curvature ρ of the beam. Even if the material of the object 14 is changed, ΔX Even if the wavefront curvature ρ changes or is distorted, it does not affect the velocity measurement and no correction is necessary. Furthermore, since the light beam of the measurement system 10 has a circular cross-sectional shape, the zero crossing number NO is the same no matter which direction the object moves.

In this way, a signal corresponding to the speed can be derived from the output terminal 31.

On the other hand, the measurement system 20 is also installed in parallel with the measurement system 10 and operates in the same manner as the measurement system 10. However, since the light beam of the measurement system 20 has an elliptical cross-sectional shape, the zero crossing number No. differs depending on the moving direction of the object.

Now, assuming that the shape of the irradiation beam is shown in FIG. 4, the speed at which the speckle changes varies depending on the moving direction of the object, and increases in the order of A>B>C>.

There are also many pigeon-zero crossing points where the speckle changes quickly.

Therefore, when the moving direction is A, the number of zero crossings is the largest, and when the moving direction is C, the number of zero crossings is the smallest.

In the measurement type 10, since the cross-sectional shape of the light beam is circular, the zero crossing number does not change no matter which direction the object moves. Therefore, the zero crossing number from the signal processing section 19 and the zero crossing number from the signal processing section 29 By determining the ratio of the intersection numbers by the moving direction calculating means 30, a signal indicating the ratio' value, that is, the direction, is derived at the output terminal 32.

Further, when the signal processing sections 19 and 29 are functional circuits for detecting the autocorrelation length τC, the signal processing section 19 includes the DC component removal circuit 51, the autocorrelation function calculation means 52, and the autocorrelation length calculation means shown in FIG. It consists of 53. Even when using this type of signal processing unit, the moving speed of the object
is obtained, and the autocorrelation length τ calculated by the signal processing unit 29
The moving direction of the object is determined by calculating the ratio between cz and τC1 by the moving direction calculating means 30.

In the above embodiment, in order to create an elliptical beam using the optical system 23, a well-known technique may be used; for example, the fifth
As shown in the figure, two cylindrical lenses 23a,
23b or a prism may be used.

(f) Effects of the Invention According to this invention, speed measurement is performed by processing signals received in the boiling state of speckles.
Since speckle size and wavefront curvature do not affect measurement results, highly accurate measurements can be performed.

In addition, since two measurement systems are used, and one measurement system emits a light beam with an elliptical cross-section, it is possible to measure not only the speed of movement of an object but also the direction of movement. .

[Brief explanation of drawings]

FIG. 1 is a block diagram of a speckle speed measuring device showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a signal processing section of the speckle speed measuring device, and FIG.
A block diagram showing another example of the signal processing section of the speckle speed measuring device, FIG. 4 is a diagram for explaining the elliptical beam of the optical system of the speckle speed measuring device, and FIG. FIG. 6, which is a diagram showing an example of a beam generation mechanism, is a diagram showing an optical arrangement for explaining speed measurement using conventional laser speckles. 10: First measurement system, 12.22: Laser light source, 13.
23: Optical system, 14: Moving object, 15.25: Light receiving section,
17 and 27: light receiving element, 19 and 29: signal processing section, 20: second measurement system, 3o: movement direction calculation means.

Claims (1)

[Claims] (1) A first light source that emits coherent light; the coherent light from this first light source is converged into a convergence region, a waist region,
a first optical system that converts the light beam into a light beam having a diffused region; a first optical system that includes a photoelectric conversion element arranged so that speckles generated on the light receiving surface due to the positional relationship between the light beam and the moving object become boiling; a first measurement system comprising a light receiving section, a first signal processing section that receives a photoelectrically converted speckle signal and outputs a signal according to the object speed; a second light source that emits coherent light; a second optical system that converts coherent light from a light source into a light beam having a convergence region, a waist region, and a diffusion region and having an elliptical cross section; and a light beam from the second optical system and a moving object. a second light receiving section including a photoelectric conversion element arranged so that speckles generated on the light receiving surface due to the positional relationship are in a boiling state;
a second measurement system including a second signal processing section that outputs a signal corresponding to the speckle signal; and a direction calculation means that calculates the moving direction of the object based on the outputs of the first and second measurement systems. A speckle velocity measurement device consisting of.