JPS5916234B2 - Distance measurement method using pulsed laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for easily measuring distance using a pulsed laser.

A conventionally well-known method for measuring distance using a pulsed laser is a method in which the round trip time of a laser pulse is measured using a time interval measuring device (counter) and the distance is calculated from the round trip time.

This method is particularly effective for long-distance measurement of objects such as satellites and the moon, but since it is necessary to accurately capture the point at which the reflected light returns, photoelectric conversion requires a high-speed response. It requires a container and a counter, and these must be easily susceptible to external disturbances, so various precautions and measures must be taken regarding the environmental conditions of use, which may make them difficult to use depending on the purpose of use.

SUMMARY OF THE INVENTION In view of the problems of the prior art described above, an object of the present invention is to provide a distance measuring method that enables reliable measurement using equipment that is resistant to external disturbances.

The present invention will be explained below with reference to the drawings.

First, the principle of the present invention will be explained with reference to FIG.

In FIG. 1, 1 is a rotating mirror that rotates around an axis perpendicular to the drawing, 2 is a target located at a distance H from the rotating mirror 1, and 3 is a target that can face the rotating mirror 1 while the rotating mirror 1 is rotating. A condensing lens 4 with a focal length f provided at a position as shown in FIG. route, 5 is target 2
6 is the path of the received light pulse where the reflected light pulse is further reflected by the rotating mirror 6 and enters the condensing lens; 7 is the path of the received light pulse where the received light pulse is the focal length of the condensing lens 3. It represents the position of the received light that is imaged at a distance of f.

Assume now that the rotating mirror 1 is rotating at a constant angular velocity ω, and that a laser pulse is emitted when the rotating mirror 1 is at an inclination angle θ such that the transmitted light pulse 4 reaches the target 2, as shown in the figure. do.

The distance from the center of rotating mirror 1 to target 2 is R1 The speed of light is C
Then, it takes 69 Δt = 2 for the optical pulse to be reflected by the rotating mirror 1, sent out, reflected to the target 2, and returned.
R/c time passes.

During this elapsed time, the rotating mirror 1 is Δθ=ω・Δt=2ωR
Since it rotates by an angle of /c, the path 6 of the received optical pulse, where the return optical pulse from the target 2 is reflected and enters the condenser lens 3, is 2Δθ24ωR/ with respect to the path 4 of the transmitted optical pulse.
It is tilted by c.

When this is condensed and imaged by the condenser lens 3, the image is formed at a position shifted from the original axis of the condenser lens 3 by δl2f·2Δθ=4fωR/c.

For example, the rotational angular velocity ω of the rotating mirror 1 = 200 rad/s (
(approximately 32 revolutions/second), focal length of condensing lens 3 f2 100
When mm, target distance R-500m=5X 10
In the case of 5 mm, C=3X'1011 mm/s.

However, in this case, since the distance between the light receiving position 7 and the rotating mirror is minute compared to the distance R, it is ignored in the above calculation.

FIG. 2 shows the results of calculating the relationship between the magnitude of the light receiving position deviation amount δl and the change in the distance H under the same conditions.

As is clear from Fig. 2, the magnitude of the deviation δl corresponding to the distance R from several hundred meters to several thousand meters is 100 μm.
It is on the order of ~1 mm, which is a size that can be easily detected by an image sensor.

The features of the present invention include the above-mentioned rotating mirror, condensing lens,
A laser pulse generating means and an image sensor are used to form an image of the reflected light of the laser pulse from the target on the image sensor, and by utilizing the fact that the image corresponds to the distance of the target, the distance R can be determined from the measurement of the deviation amount δl. It is characterized by seeking.

When detecting deviation, if the reflected light is strong enough, it is possible to place a screen at the focal point of the lens and read it directly with a magnifying glass, but in the present invention, a highly sensitive image sensor is used to detect the weak level of reflection. It is designed to be able to receive light and also to be able to perform electrical processing for distance display.

Next, an example of a device embodying the present invention is shown in FIG. 3 and will be described in more detail.

In FIG. 3, 8 is a drive motor that rotates the rotating mirror 1 at a constant speed, and 9 is a rotation angle detector of the rotating mirror 1.

10 is a pulse laser oscillator, 11 is a laser control circuit, 1
2 drives the laser control circuit 11 to cause the pulse laser oscillator 10 to generate a laser pulse when the rotation angle detector 9 of the rotating mirror 1 detects an angle at which the sending pulse is sent toward the target 2; This is a synchronous signal generation circuit.

A small reflecting mirror 13 is installed on the optical axis of the condensing lens 3 connecting the center of the condensing lens 3 and the center of the rotating mirror 1 at an angle with respect to the optical axis. The reflected laser pulse 14 is reflected by this reflecting mirror 13 and directed toward the center of the rotating mirror 1.

A transparent glass plate 15 reflects a part of the transmitted pulse reflected by the rotating mirror 1, and is fixed near the rotating mirror 1 and perpendicular to the path of the transmitted pulse.

The reflected pulse 16 from the glass plate 15 is reflected by the rotating mirror 1 so as to be parallel to the pulse 18 incident on the rotating mirror 1 (indicated by 17), passes near the reflecting mirror 13, and reaches the condenser lens 3. , the light is condensed by the condenser lens 3 and an image is formed at its focal position.

19 is an image sensor provided at the focal position a of the condenser lens 3, 20 is an image pickup tube, and 21 is a cathode ray tube.

In this configuration, the rotating mirror 1 is rotated at a constant speed by the motor 8, and the rotation angle detector 9 sends a rotation angle signal to the synchronization signal generator 12.

The synchronizing signal generator 12 drives the laser control circuit 11 to cause the pulsed laser oscillator 10 to emit a laser when the angle of the rotating mirror 1 reaches an angle at which the laser pulse from the pulsed laser oscillator 10 is directed toward the target 2 at the rotating mirror 1. Generate a pulse.

This laser pulse is reflected by the reflecting mirror 13, further reflected by the rotating mirror 1, a part of it is reflected by the glass plate 15, passes through the rotating mirror 1, and is condensed by the condensing lens 3, and is condensed by the image sensor 190). An image is formed at the focal position.

On the other hand, the light that has passed through the glass plate 15 reaches the target 2, is reflected there, passes through the glass plate 15 again, passes through the rotating mirror 1, is condensed by the condenser lens 3, and is condensed by the image sensor 19.
, the deviation amount δl from the focal point position of the condenser lens 3
The image is formed at a position offset by .

Among these, the light receiving point of the image sensor 19 due to the reflected pulse from the glass plate 15 is indicated by a bright spot d of the cathode ray tube 21, and the light receiving point of the image sensor 19 due to the reflected pulse from the target 2 is
The light receiving point is indicated by a bright spot e.

The distance between the bright spots d and e corresponds to the deviation amount δl.

Therefore, since L = 1 δl 2 k・4fωR/c (k is a constant), focal length f1 angular velocity ω, speed of light C
is known, and by determining the constant k in advance, the target distance R can be determined by knowing the interval between bright spots on the cathode ray tube.

Although a detector in the form of an array of semiconductor light-receiving elements may be considered as the image sensor 19, an image sensor having a channel multiplier type amplification function is used here.

In the above description, a case has been described in which the condenser lens f is 100 mm and the rotational speed ω of the rotating mirror 1 is 200 rad/s.

In this case, the size of one element of currently available image sensors is on the order of about 10 μm, and the distance resolution that can be expected when using an image sensor of such size is several tens of meters.

This resolution can be improved by increasing the density of image sensors (improving resolution), which is currently being improved.

Furthermore, as understood from the relationship δ1-4fωR/c, the resolution can be improved by increasing the focal length f of the condenser lens and/or by increasing the rotational speed ω of the rotating mirror 1. Ru.

As described above, the present invention eliminates the need to use devices that are susceptible to electrical disturbances, such as photoelectric converters and counters with fast response speeds, unlike conventional methods. The time of the reflected pulse does not matter; it is only necessary to know the incident position, so the response may be slow), so distance measurement can be performed reliably even in an environment with many electrical disturbances.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the present invention in detail, FIG. 2 is a diagram showing an example of the relationship between the target distance and the amount of light receiving position deviation in the present invention, and FIG. 3 is a diagram showing an example of the configuration of a device embodying the present invention. FIG. 1...Rotating mirror, 2...Target, 3...
... Condensing lens, 7... Imaging position, 8...
...Drive motor, 9...-Rotation angle detector, 1
0... Pulse laser oscillator, 11...
Laser control circuit, 12... Synchronization signal generation circuit,
13...Reflector, 15...Glass plate,
19... Image sensor, 20... Image pickup tube, 21... Braun tube.

Claims (1)

[Claims] 1 A rotating mirror is rotated at a constant speed, and when the laser pulse to be incident on the rotating mirror reaches a rotation angle toward the target, the laser pulse is emitted toward the rotating mirror, and the reflected pulse from the target is reflected from the rotating mirror. Measurement using a pulsed laser, characterized in that the reflected pulse is reflected by a mirror, the reflected pulse is focused by a condensing lens, and the imaging position is detected by an image sensor provided at the focal point of the condensing lens to measure the distance. Distance method.