JPH0476584B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light wave distance meter that measures distance based on the phase relationship between transmitted light and reflected light that reciprocate over a measurement distance.

[Summary of the invention]

This is a light wave distance meter that uses a slit in conjunction with a variable density filter to ensure reliable distance measurement by keeping the photometric amount, which attenuates as the square of the distance, constant.
Particularly at short distances, the slit allows the measurement light flux to be confined to the center of the image space of the objective lens, reducing distance measurement errors.

[Prior Art] In the light wave distance meter described at the beginning, when the reflected light from the object to be measured is received through the objective lens, the amount of transmitted and received light is adjusted so that the amount of received light is constant regardless of the distance. Automatically adjust. For example, when measuring 5 meters with a rangefinder whose maximum measurable distance is 500 meters, the amount of light measured needs to be 1/10 ⁴ of that when fully open, based on the law that the amount of light attenuates as the square of the distance.
At this time, the output of the light receiving element is kept constant at, for example, 4V.

Mechanical iris tightening is suitable as a means for adjusting the amount of photometry, but it is large and expensive, and the tightening servo system may cause hunting due to mechanical response delay.

Therefore, a method is generally adopted in which a disc-shaped variable density filter is inserted into the light transmitting optical path and/or the light receiving optical path and the filter is rotated around its central axis to attenuate the amount of light.

The light transmission path is also provided with a calibration optical path for eliminating distance measurement errors based on the optical path length within the device and the phase change of the electric circuit. This calibration optical path is an optical path directly from the light emitting element to the light receiving element, and is formed by bending the optical transmission path using a prism or the like only during calibration.

[Problem that the invention seeks to solve]

The above-mentioned variable density filter for adjusting the amount of light is optimally placed on the focal plane of the objective lens, and in this case, the change in the amount of light is controlled for the point luminous flux of the transmitted light. However, it is mechanically difficult to achieve such an arrangement, so the measurement light beam passing through the variable density filter has a certain spread (area).
I have no choice but to insert it in the position where I held it.

However, it was found that when controlling the amount of attenuation for a spread measurement light beam, measurement errors become large when measuring short distances. In other words, when measuring short distances, the part of the variable density filter with the largest amount of attenuation is used, but the surface of the filter that corresponds to the image space of the objective lens does not allow almost any light to pass through, and only a small amount of light passes through it at one end. light passes through as measurement light. On the other hand, when measuring the farthest distance,
All of the luminous flux from the light emitting element is guided out as transmitted light without being attenuated by the filter. The calibration optical system is closest to the physical conditions when measuring this farthest distance, and performs internal calibration by averaging phase errors that have variations distributed on a plane perpendicular to the optical path within the device. Therefore, the distance measurement error for long distances is extremely reduced by averaging calibration. However, when measuring short distances, as mentioned above, only a small part of the objective lens image space and the edge are used, so the phase error factors are not averaged and the difference (phase difference) with the calibration light is It appears in the measured quantity.

Errors at short distances become more noticeable when the density error of the variable density filter is reduced. That is, since a variable density filter is very expensive, it is conceivable to take a photograph using this filter as a master to make a positive filter and use this as a substitute for the filter. In this case, the shading difference in the photographic filter is reduced to about 40 dB compared to the 80 dB in the original. This increases the tendency for only a very small portion of locally unevenly distributed light to pass through the darkest portion of the filter, as described above.

Furthermore, it is conceivable to take a photograph of the filter master to create a printing master and print it on a transparent film.
In this case, the cost of the filter can be further reduced by mass duplexing, but a contrast difference of only about 30 dB can be obtained. In other words, the darkest part of the filter is almost completely black with no difference in shading, and the linearity of the density curve is no longer compensated for.

In view of the above-mentioned problems, the first object of the present invention is to make distance measurement errors uniform and small regardless of distance. Another object of the present invention is to prevent errors from increasing even when using an inexpensive variable density filter that prints with a small difference in shading.

[Means for solving problems]

FIG. 1 shows the main parts of a light wave distance meter that measures distances based on the phase relationship between transmitted light and reflected light that travel back and forth between measurement distances.

In FIG. 1, a variable density filter 9 is inserted into the imaging space of the objective lens system 1, and the amount of light passing therethrough can be changed by rotating the optical axis of the objective lens system 1 in a perpendicular plane.

As shown in FIG. 3, this variable density filter 9
A slit aperture (slit diaphragm 14) is added whose aperture extends in the direction of concentration change and whose aperture width in a radial direction centered on the optical axis decreases as the concentration increases.

The variable density filter 9 and the slit diaphragm 1
4 are integrated in the optical axis direction, and the amount of photometry is adjusted by the product of the density of the variable density filter 9 and the opening area of the slit opening.

[Effect]

Particularly during close-range measurements, the measurement light beam is restricted to the center of the imaging space of the objective lens. Moreover, the light beam spreads out in a band-like manner along the slit opening. Therefore, the difference from the physical conditions during internal calibration becomes smaller when measuring short distances, and measurement errors are reduced.

By using the slit, the difference in density of the variable density filter can be small. This makes it possible to use, for example, an inexpensive variable density filter based on a printing method with a density difference of about 30 dB.

〔Example〕

FIG. 1 shows an optical system of a light wave distance meter which is an embodiment of the present invention. This optical distance meter includes an objective lens system 1, a light emitting element 2 such as an LED, and a light receiving element 3 such as a photodiode. The image space of the objective lens system 1 is divided into two by a plane along the optical axis 4, and one side (bottom side of the figure) has a light emitting element 2 and a triangular prism 5.
(or a triangular mirror), a diagonal mirror 6, and an objective lens system 1 to form a light transmission optical path 8 in which the transmitted light is guided. The other side (upper side in the figure) is a light receiving optical path 7 that guides reflected light from the object to be measured (such as a corner prism) to the light receiving element 3 through the objective lens system 1 and the oblique mirror 6. A variable density filter 9 as shown in FIG. 2 is inserted into the light transmitting optical path 8 and the light receiving optical path 7 between the triangular prism 5 and the oblique mirror 6 to adjust the amount of measurement light.

The variable density filter 9 can be rotated around the axis S, and its transmittance changes continuously in the circumferential direction depending on the rotation angle, as shown in FIG. When the measurement distance changes, the filter 9 is rotated by the servo circuit so that the output voltage of the light receiving element 3 is constant.

A parallel prism 10 is arranged between the light emitting element 2 and the triangular prism 5 so as to be freely inserted and removed by a motor or the like. When the parallel prism 10 is inserted, the emitted light from the light emitting element 2 is reflected twice within the parallel prism 10, further reflected by the triangular prism 5, and guided directly to the light receiving element 3, so that the internal calibration optical path 11 is It is formed. In addition, the parallel prism 1 is
0 is moved in the direction of the arrow in the figure, the emitted light from the light receiving element 2 is guided to the objective lens system 1 via the triangular prism 5 and the oblique mirror 6.

A slit tightening 14 shown in FIG. 3 is added to the front surface of the variable density filter 9. As shown in FIG. The slit tightening 14 is formed, for example, by etching a thin metal plate so that the radial width of the slit 14a changes continuously depending on the rotation angle.
As shown in FIG. 4, the variable density filter 9 and the slit diaphragm 14 may be bonded together. By adding this slit diaphragm 14, the amount of passing light is attenuated in proportion to the product of the density of the variable density filter 9 and the opening degree of the slit 14a.

The small circle in FIG. 3 indicates the image space 1a of the objective lens system 1 which is connected onto the slit diaphragm 14 and the filter 9.
The opening width of the slit 14a gradually changes within this image space 1a. Furthermore, as the concentration of the filter 9 increases, the slit width decreases. Furthermore, slit 14
At the maximum opening position of a, hole 1 corresponding to image space 1a
4b should be opened to maximize the amount of transmitted light.

The image of the slit diaphragm 14 seen from the objective lens system 1 corresponding to the image space 1a moves as shown in FIGS. 5a to 5g. That is, at a, the slit 14a is fully open, and as the measurement distance becomes shorter at b, c, . . ., the width of the slit 14a becomes narrower as the variable density filter 9 rotates (density increases). slit 1
The moving direction of the shadow (image) 4a is the arrangement direction of the light receiving optical path 7 and the light transmitting optical path 8 which bisect the image space of the objective lens system 1. FIG. 5g shows the case of the closest distance, in which the slit 14a passes through the light transmitting side and is located on the light receiving side.

Conversely, as the distance increases from the closest distance, the light transmission optical path 8
The slit 14a gradually widens from the center of the image space corresponding to the image space toward the edge from g to f.
Therefore, since the light transmission system starts to be used from approximately the center of the image space, it is less susceptible to error factors at the edges of the image space at short distances. In other words, at the shortest distance, the transmitted light beam is focused almost to a point.

Furthermore, since the measurement light amount is determined by the slit width and the density of the variable density filter 9 inside the slit,
Compared to the conventional method, the density of the filter may be relatively thin when measuring the closest distance. Therefore, as shown in Figures 5e and 5f, measurements can be made using all the light from one end of the image space 1a to the other, the phase error factors can be averaged, and the effect of error correction by internal calibration can be approximated. You will be able to get more reliable results even at a distance.

In addition, by adding the slit aperture 14,
Since the difference in shading of the variable density filter 9 can be reduced, it becomes possible to use an inexpensive filter with a shading difference of about 30 dB obtained by printing a shading pattern on a transparent filter using photolithography.

The slit 14a may have a shape whose width changes according to a linear function as the angle changes, as shown in the developed view of FIG. Furthermore, in order to correct the linearity corresponding to the angular change in filter density, a curve convex inward (or convex outward) may be provided as shown by the dotted line in FIG.

Although FIG. 1 shows an example in which the axis S of the variable density filter 9 is on the front side with respect to the plane of the drawing, the axis S may be shifted by 90 degrees as shown in FIG.
In this case, as shown in FIGS. 8a to 8g, the shadow of the slit 14a moves approximately along the dividing line between the light transmitting side and the light receiving side of the image space 1a of the objective lens system 1. Therefore, the shadow of the slit 14a enters from the edge of the image space of the light transmission optical path 8 and moves from g to f.

Note that a photographic positive film or a printing film may be prepared so that the variable density filter 9 itself has a shading pattern in the shape of the slit 14a shown in FIG. In this case, a light and shade pattern is created inside the slit pattern shown in FIG. 3, and the outside is set to the blackest level.

〔Effect of the invention〕

Since the present invention is configured as described above, during short-distance measurement, the measurement light beam is not unevenly distributed in one area on the periphery of the image space, and the physical conditions with the calibration optical system that uses almost the entire image space can be improved. The smaller the difference, the smaller the measurement error. Furthermore, the measurement error becomes uniform between long distance and short distance.

Further, by using a slit, the difference in density of the variable density filter can be reduced, and an inexpensive filter can be used. It is also possible to correct the linearity of the filter's density using the slit shape, allowing for more accurate distance measurement.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the optical system of a light wave distance meter showing an embodiment of the present invention, Fig. 2 is a plan view of a variable density filter, Fig. 3 is a plan view of a slit diaphragm, and Fig. 4 is a diagram of the filter and slit. A cross-sectional view showing the bonded structure, Figures 5a to 5g are views showing images of the slits seen from the objective lens system, Figure 6 is a developed view showing the characteristics of the shape of the slit pattern, and Figure 7 is a variable density diagram. FIG. 8 is a diagram of the optical system showing a modified example of the insertion position of the filter.
Figures a to g are views of slit images similar to those in Figure 5 in the case of a modification of Figure 7. In addition, in the symbols used in the drawings, 1...objective lens system, 2...light emitting element, 3...light receiving element, 4
...Optical axis, 5...Triangular prism, 6...Oblique mirror, 7
. . . light reception optical path, 8 . . . light transmission optical path, 9 . . . variable density filter, 10 .

Claims (1)

[Scope of Claims] 1. In a light wave distance meter that measures distance based on the phase relationship between transmitted light and reflected light that reciprocate between measurement distances, a distance meter that is inserted into the imaging space of the objective lens and perpendicular to the optical axis is used. A variable density filter that can change the amount of light passing through it by rotating within a plane, and an aperture of the variable density filter that extends in the direction of density change and whose aperture width in a radial direction centered on the optical axis changes as the density increases. The variable density filter and the slit opening are integrated in the optical axis direction, and the amount of photometry is adjusted by the product of the density of the variable density filter and the opening area of the slit opening. A light wave distance meter designed to do this.