JPS5950938B2 - speed measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a speed measuring device that utilizes the original spotting phenomenon that occurs in reflected light when laser light is projected onto a target surface.

This type of speed measurement device that uses laser light has the advantage of being able to measure the relative speed to an object without contact, and can be used to measure the ground speed of moving objects such as aircraft and vehicles, but it is especially It is effective in various industrial processes, and is extremely useful in, for example, measuring the speed of rolled material extruded from a rolling mill, measuring the running speed of wire rod in the wire manufacturing process, etc., because it has no effect on the object to be measured and improves measurement accuracy. It is.

The original speckle phenomenon of reflected light that occurs when a laser beam is projected onto a target surface is particularly noticeable due to the single wavelength and uniform phase characteristics of the laser beam, but also when the target surface is not a mirror or a uniform surface. The reason for this is that each of the elements constituting the object surface has a certain phase relationship with respect to the reflected light, and when observing the reflected light of the laser beam, the origin of the irregular brightness and darkness can be seen.

That is, even if the laser beam to be projected is one beam, a beam divided into many parts is obtained as reflected light, and by using this, it is possible to measure the relative velocity. FIG. 1 is a diagram showing the configuration of a typical conventional speed measuring device that utilizes this phenomenon, and is used to measure the ground speed of a moving object.

In the figure, a laser oscillator 2 is fixed to a moving object 1, and a laser beam 3 is projected onto the ground 4 as a target surface, and the reflected light is scattered and reflected as a large number of beams on the surface of the ground 4 as described above. 5 reaches the surface of the grid-like slit 6 provided in the moving body 1. However, the lattice-like slits 6 are formed perpendicularly to the moving direction of the moving body 1, and the slit widths and shading areas are equal to each other, and the slit spacing g
are all uniform. A part of the reflected light 5 that reaches the lattice slit 6 is composed of many beams due to the original spotting phenomenon, and these beams cause the reflected light 5 to reach the lattice slit 6.
A mottled pattern is formed on the surface of the lattice-shaped slit 6, but since the projection surface of the laser beam 3 moves as the movable body 1 moves, the slits in the pattern also cross the lattice slits 6 in sequence. It cuts, moves, and finally disappears.

However, as the projection surface of the laser beam 3 advances one by one, a new origin is generated and this is repeated. The original moving speed VB on the surface of the grid slit 6 is the moving body 1 and the ground 4.
relative velocity V. is proportional to , and is given by the following equation.
Here, a is the distance between the surface of the ground 4 that reflects the laser beam 3 and the grid-like slit 6, and b is the distance between the virtual projection point 7 of the laser beam 3 and the surface of the ground 4.

There is a photoelectric conversion element 8 behind the lattice-shaped slit 6, which generates an electrical output by a part of the reflected light 5 that has passed through the slit, but as mentioned above, the light spots generated by a part of the reflected light 5 are transmitted through the lattice-shaped slit. 6, the light spot is repeatedly blocked and transmitted, resulting in a signal with a frequency fo proportional to the moving speed of the light spot 8, and this frequency f.

is expressed by the following equation. However, as mentioned above, g is
There are 5 slit intervals.

Therefore, the output signal frequency fo of the photoelectric conversion element 8 and the relative speed V of the moving body 1.

Since there is a certain relationship with the output signal frequency f. If detected by the electronic frequency measuring device 9, the relative velocity V is obtained. You can do it by asking for. Note that the relative speed V can be calculated by providing a predetermined calculation circuit. It is also possible to read directly. The above description has been made using the earth 4 as the target surface, but if the target surface is not a plane but a rotating body and its rotational speed is to be measured, the photoelectric conversion element for the linear velocity of the rotating body. The output signal frequency of the child 8 increases compared to the case where the target surface is a plane, and is expressed by the following equation. That is, the output signal frequency at the rotating body is f. '', where r is the radius of the rotating body.

In this way, when the target surface is both a plane and a rotating body,
Furthermore, when the relative velocity range with the target surface is large, the response frequency band required of the photoelectric conversion element 8 increases, and accordingly, the measurement range of the frequency measuring device 9 must also be widened. However, in order to widen the response frequency band of both, expensive components must be used.

Note that in order to avoid the above-mentioned drawbacks, it is possible to change the slit interval g of the lattice-like slits 6, but in order to realize this, a large number of lattice-like slits 6 with different slit intervals g are prepared, and the slit interval g of the lattice-like slits 6 is changed depending on the object to be measured. Therefore, it has to be replaced each time, which is extremely inconvenient in practical terms. In addition, in addition to a part of the reflected light 5 that should be captured, unnecessary light rays also enter the photoelectric conversion element 8, and the light spots consist of irregular bright and dark spots, so the output signal of the photoelectric conversion element 8 is not necessary. A noise component is included as well as a frequency component, and in order to maximize the ratio of the two, that is, the signal-to-noise ratio, there is a restriction that the slit interval g must be twice the average diameter of the light spot. This is because the slit width and the light shielding width are the same, so when the slit interval g becomes twice the average diameter of the light spots, the slit width and the average diameter of the light spots become equal, and the light spots come onto the slit. This is clear from the fact that all the light energy of the light spot can pass through the slit when Now, if the diameter of the laser beam 3 projected from the laser oscillator 2 is d, and the average diameter of the light spot is defined as the half width of the luminous intensity distribution, then the average diameter L is expressed by the following equation.

However, this is the case when the target surface is an ideal diffusion surface,
In reality, there are cases where the surface has regular irregularities or irregularly large and small irregularities, and there are many conditions in which equation (4) cannot be directly applied. As mentioned above, it is necessary to prepare and replace a large number of lattice-like slits 6, and from this point of view, the conventional method also has the drawbacks of complicating the handling of the device and making the device expensive. had.

The present invention solves all of the above drawbacks of the conventional art at once, by projecting a laser beam onto a target surface, receiving the reflected light from the target surface by a photoelectric conversion element through a lattice-like slit, and converting the photoelectric conversion element into A device for measuring the relative velocity with a target surface based on the electrical output of the target surface, in which reflected light from the target surface is projected onto the front surface of a grid-like slit having a constant slit interval so as to be enlarged or contracted, The feature is that a lens is provided that continuously changes the equivalent slit interval of the lattice-shaped slits, and the size of the light spot on the lattice-shaped slit surface can be freely adjusted according to the measurement speed or the situation of the target surface. By setting the slit interval arbitrarily,
The present invention provides a speed measuring device that narrows the response frequency band for a photoelectric conversion element and a frequency measuring device. Hereinafter, details will be explained with reference to FIG. 2 and subsequent figures showing embodiments of the present invention. FIG. 2 is a diagram showing the configuration of the present invention corresponding to FIG. 1, and shows the front lens 1 of the grid-like slit 6.
0 is provided, and a lattice-like slit 6 is provided by a mechanism described later.
The lens 10 is configured to move in the direction of the arrow along the optical axis 11 of the reflected light. Note that the lattice-like slit 6 may be fixed and only the lens 10 may be moved, or the same can be done even if both are fixed and a variable focus type lens is used as the lens 10. FIG. 3 is a diagram showing only the above-mentioned part for receiving part of the reflected light 5,
A part of the reflected light 5 from the ground 4 as the target surface is reflected by the lens 1
0 and is projected onto the surface of the lattice-like slits 6 with a constant slit spacing g. However, since the laser beam 3 is used, the reflected light is reflected depending on the distance between the lens 10 and the lattice-like slits 6. A part of the projected image 5 is projected as it is without being diffused, and can be enlarged or reduced.

In the figure, the distance between the ground 4 as the object plane and the lens 1O is assumed to be a, the focal length of the lens 10 is F, the distance between the lens 10 and the grid-like slit 6 is y, and the magnification of the lens 10 is assumed to be m.

If there is an image of the earth 4 at point p, the magnification m = (distance between lens 10. and point p)/a, so the distance between lens 10 and point p is am, and furthermore, (1/ F)=(1/a
)+(1/am), m=F/(a-F). Here, the lattice-like slit 6 is distant from point p, and if this distance is defined as "degree defocus amount", then Iam
−y1. Also, the light spot velocity VB and the relative velocity (■) on the surface of the lens 10.

The ratio is (1+a/b) as shown in equation (1), but
Velocity magnification on the surface of the lattice slit 6 in FIG. 3, that is, the light spot velocity and the relative velocity (2). The ratio mv is given by the following equation. Here, yo is the distance between the lens 10 and the virtual projection point 7 of the laser beam 3, and is expressed by the following formula:
As is clear from equation 5), by varying the distance y between the lens 10 and the lattice slit 6, that is, the amount of defocus, the velocity magnification mv on the surface of the lattice slit 6 changes, and accordingly, Output signal frequency f from the photoelectric conversion element 8.

will be the following. Note that 〆 is an equivalent slit interval of the lattice-like slits 6, and is expressed by the following equation.

As described above, by varying the amount of defocus, it is possible to continuously change the slit interval g of the lattice slit 6 equivalently as g, so that it can be changed continuously depending on the measurement speed and the situation of the target surface. Any equalizing slit spacing g'' can be obtained, allowing speed measurements to be made under the most favorable circumstances.

Note that, as is clear from FIG.
The distance y between the lattice slits 6 changes, and as a result, the projected image of the light spot on the surface of the lattice slit 6 is enlarged or reduced, and even if the slit width is constant, the effective slit width changes relatively. it is conceivable that. In addition, when the target surface is a rotating body and its linear velocity Vo is to be measured, the velocity magnification mVR of the light spot on the surface of the lattice-shaped slit 6 is given by the following equation. Fifth, the output signal frequency f of the photoelectric conversion element 8 in this case.

will be the following. g'' is an equivalent slit interval, similar to the term in equation (7), and is given as.

Note that the relative velocity V with respect to the target surface.

When the frequency is low and it is desired to obtain a high frequency as the output signal of the photoelectric conversion element 8, a concave diverging lens may be used as the lens 10 instead of a convex focusing lens. In addition, when the average diameter of the light spots on the surface of the lens 10 is set to L, the average diameter of the light spots on the surface of the lattice slit 6 is expressed as follows, and as is clear from this, the average diameter of the light spots is 1L.
It is directly proportional to the amount of defocus, and it is easy to make the average light spot diameter L to 1/2 of the slit spacing g by changing the spacing y between the lens 10 and the grid-like slits 6. , thereby making it possible to maximize the signal-to-noise ratio at the output of the photoelectric conversion element 8.

FIG. 4 is a perspective view of an embodiment that realizes a lens mechanism for freely expanding or contracting the reflected light onto the surface of the grid-like slit 6 and for continuously changing the size of the projected image. It is shown broken away.

A lens barrel 12 housing a lens 10 is fixed to a lens barrel mount 13, and is optically connected by a bellows 14 to a detector mount 15 on which a lattice-shaped slit 6 and a photoelectric conversion element 8 are mounted. . The lens barrel mount 13 and the detector mount 15 are mated to a guide pedestal 17 which is cut from the rack z16.
When the internal pinions 18 and 19 are rotated by knobs 20 and 21, they can freely slide along the guide table 17.

Note that in some cases, the detector mount 15 may be fixed and only the lens barrel mount 13 may be movable, and the same result can of course be obtained in the opposite relationship. If a focusing lens is used, the relationship between the two may be fixed.

In addition, in Figures 2 and 3, the target plane is earth 4,
Although the explanation has been made assuming that the measuring device is attached to the moving body 1,
When the target surface is a moving body, the measuring device may be fixed, and the velocity of the moving body target surface can be determined in exactly the same way as the relative velocity Vo.

As is clear from the above description, according to the present invention, the lattice-like slits 6 are continuously formed on the assumption that the laser beam 3 is used.
Since the slit spacing can be changed equally, it is possible to obtain an output signal at any frequency depending on the measurement speed and the situation of the target surface, and also to maximize the signal-to-noise ratio at the same output. Accordingly, speed measurement with sufficient accuracy has been realized using a photoelectric conversion element with a narrow response frequency band and a frequency measuring device, and for these reasons, it has become easy to provide speed measuring devices at low cost. Great effects can be achieved in various non-contact speed measurements.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a typical conventional speed measuring device, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 shows a part for receiving part of the reflected light from Fig. 2. The extracted figure, FIG. 4, is a longitudinal side view of an embodiment of the mechanism for supporting the lattice-like slits and lenses, and a cross-sectional view taken along line A--A. 2...Loser oscillator, 3...Loser light, 4
... Earth (object surface), 5 ... Reflected light,
6... Lattice slit, 8... Photoelectric conversion element, 9... Frequency measuring device, 10...
Luns, 12... Lens barrel, 13... Lens barrel mount, 15... Detector mount, 16...
...Rack, 18, 19...Pinion, 20
, 21...Pick.

Claims (1)

[Claims] 1 In a device that projects a laser beam onto a target surface, receives reflected light from the target surface via a lattice-shaped slit by a photoelectric conversion element, and measures the relative velocity with the target surface based on the electrical output of the photoelectric conversion element. A lens is provided in front of a grid-like slit having a constant slit interval to project the reflected light from the target surface onto the grid-like slit surface in a manner that can be enlarged or reduced, thereby continuously changing the equivalent slit interval of the grid-like slit. A speed measurement device characterized by: