JPH0238985A - Device for measuring distance by light wave - Google Patents

Abstract

PURPOSE:To improve accuracy and data rate by adding a laser interference device to a device for measuring a distance by a light wave. CONSTITUTION:The laser interference device is constituted of a laser diode 3b, a semi-transmissive mirror 5c, a photodide 9b, a collimator lens 23 and a semi-transmissive reference plate 31. The reflected light of a laser beam from the semi-transmissive reference plate 31 and the reflected light of a laser beam from a conrer cube prism 6 are superposed on the incident surface of the photodiode 9b and interfere each other, so that light detecting output from the photodiode 9b gets larger every time a distance to the corner cube prism 6 changes by the half of the wavelength of the laser beam. Therefore, the counted value of subtraction counter 25 gets smaller every time the distance to the corner cube prism 6 changes by the half of the wavelength of the laser beam. A reference distance signal from an average circuit 27 is initially set in the subtraction counter 25.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a light wave ranging device used to measure the distance to a target aircraft with high precision, for example, during rendezvous dotting in space. be.

[Conventional technology]

FIG. 2 is a diagram showing an example of a conventional optical e-range finder. In FIG. 2, (1) is a reference oscillator, and (2) is a drive circuit.

(3) is a laser diode that is driven by intensity modulation by drive port #1 (23), (4) is a transmitting lens 2, (5) is a semi-transparent mirror, and (6) is a corner cube prism that is a target.

(7) is the mirror 2, (8) is the receiving lens, and (9) is the photodiode 20 placed at the focal position of the receiving lens (8).
■(Yo increase III device, C month) phase comparator, (12)
is the distance signal, (J3) is the bandpass filter, (1
41 is a reference signal input to the phase comparator (11), (
15) is a phase measurement input signal. FIG. 3 is a diagram showing an example of the configuration of the phase comparator (11), (16a), (I
fib) is the binarization circuit, (17) is the set signal applied to the flip-flop (19), (1g) is the reset signal, (20) is the oscillator, (21) is the output of the flip-flop (]9) Be controlled gate, (2
2) is game) Oscillation 1 (20) output from (21)
This is a counter that counts the output pulses.

A conventional light wave distance measuring device is configured as described above and operates as follows. The laser diode (3) has a reference oscillation M (1
The laser light is outputted from 1 and is intensity modulated at a frequency. The laser beam whose irradiation angle is narrowed down by the transmission lens (4) and passes through the semi-transparent mirror (5) is irradiated toward the corner cube prism (6) at a distance aRgi. Since the corner cube prism (6) has the property that the incident angle and the exit angle of the light are equal, the reflected laser beam returns again along the same optical path in the opposite direction, is changed direction by the semi-transparent mirror (5), and is redirected by the semi-transparent mirror (5). 7) and then passes through a bandpass filter (13) that matches the wavelength of the laser beam. The function of this bandpass filter (13) is to prevent interference light (such as sunlight) other than the p-laser light from entering the photodetection system. The laser beam incident on the receiving lens (8) is transmitted to the photodiode (9).
) is collected at the light receiving part and photoelectrically converted. The photoelectrically converted signal is amplified in amplitude by an amplifier and passed through a two-phase comparator (
11). Phase comparison! The reference signal (14) applied to i (111) and the two-phase measurement input signal (I5) are binarized by the binarization circuit (16a), (+6bl, and the gate (21) is used only for the phase difference time of the two signals. By counting the output pulses of the passed oscillator (20) by the counter (22), it is possible to know the time required for the waveform output from the reference oscillator (1) to pass through the system explained above. If this time is Tt, then the following equation holds.

Tt = 2 CR+To −−−−−−−−(1, C: Speed of light TO: Circuit system delay time To, C can be known in advance, so from (1), corner cube prism (6) Therefore, the distance signal (12) can be used to determine the distance to the destination.

[Problem to be solved by the invention]

In the conventional light wave distance measuring device as described above, the measurement error is mainly caused by the amount of noise contained in the phase measurement input signal (15) and cannot be ignored. The above noise is caused by the photodiode (91
Since this is random noise generated from the amplifier 01, a common method is to measure the distance signal (12) over a long period of time and average it to reduce the measurement error, but at the cost of reducing the data rate. However, in rendezvous docking, distance measurement in a short range requires high accuracy and high data rate, and conventional light wave distance measuring devices are not sufficient.

The present invention was made to solve this problem, and an object of the present invention is to obtain a light wave ranging device with high accuracy and high data rate.

[Means to solve the problem]

A light wave ranging device according to the present invention is a conventional light wave ranging device with a laser interferometer added thereto.

[For production]

In this invention, the distance resolution of the laser interferometer is half the wavelength of the laser beam, so the distance resolution is much higher than that of the conventional example. Furthermore, by using a laser interferometer, the processing circuit becomes simple, so the data rate can be increased.

〔Example〕

Fig. 1 is a diagram showing an embodiment of the present invention.
21, +41, (61, (81, Qα~(12) are exactly the same as the above conventional device, (3a)
(3b) , (5a) (5b) (5el p (
7al(7b), (9m) (9b), (J8
c) is each of the above conventional mounting examples (3).

(51, (7), (91, (16m)) This is the part corresponding to (18b).

(23) is a collimator lens for collimating the output light of the laser diode (3b), which also has the function of condensing the received light onto the photodiode (9b).

(24) is an amplifier that increases the output amplitude of the laser diode (9b), (25) is a subtraction counter, (26)
is a laser power supply that supplies power to the laser diode (3b).

(27) is an averaging circuit that calculates the average of distance signals (I2) of a predetermined number of data based on the calibration instruction signal (29);
8) is the reference distance signal, (30) is the precision distance signal, (
31) is a semi-transparent plane reference plate.

In the optical distance measuring device configured as described above, a laser diode (3bl) and a semi-transparent mirror (5e) are used.

Photodiode (9b), collimator lens (23)
.

A semi-transparent reference plane plate (31) constitutes a laser interferometer.

On the incident surface of the photodiode (9b), the reflected light of the laser beam from the semi-transparent flat reference plate (31) and the reflected light of the laser beam from the corner cube prism (6) overlap and interfere, and the corner cube prism Every time the distance to (6) changes by half the laser wavelength, the photodiode (9
b) The photodetection output increases. Therefore, each time the distance to the corner cube prism (6) changes by half the wavelength of the laser beam, the count value of the subtraction counter (25) becomes smaller.

During rendezvous docking, the distance to the corner cube prism (6) is monotonically decreasing, and the subtraction counter (2
The change in the count value in 5) corresponds to the change in the distance. On the other hand, in a laser interferometer, since the absolute distance is not known, it is necessary to set the initial value of the subtraction counter (25) at least once. This is done by setting the reference distance signal (28), which is the output of the averaging circuit (27) operated by the calibration instruction signal (29), in the subtraction counter (25).
It is necessary to select different oscillation wavelengths (3b) so that they do not interfere with each other.

〔Effect of the invention〕

As described above in Inventions 1 and 2, the addition of a laser interferometer has the effect of realizing a high-precision, high-data-rate optical distance measuring device.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a conventional optical distance measuring device, and FIG. 3 is a diagram showing a configuration example of the phase comparison fit (11) in FIG. 2. It is. In the figure, (1) is the reference oscillation power, (2+ is the drive circuit. (31, (3a), (3bl is the laser!
, (411f feed (g lens, (51, (5m),
(5b), (5e) are semi-transparent mirrors, (6) are corner cube prisms, (71, (7 breath), (7bl mirrors, (8) are receiving lenses, +91, (9ml)
, (9b) is a photodiode. aOl is an amplifier, (11) l is a phase comparator, (12
) is a distance signal. (13), (13m), (13b) are band pass filters, (14) are reference signals, (15) are phase measurement signal inputs, (lea), (18bl), (16c) are binarization circuits, (17) ) set signal,
(18) is a reset signal, (191 is a flip-flop, (20) is an oscillator, (21) is a gate,
(22) is a counter, (23) is a collimator lens, (24) is an amplifier, (25) is a subtraction counter,
(261 is the laser power supply, (27) l is the average circuit,
(28) is a reference distance signal, (29) is a calibration instruction signal, (30) is a precision distance signal, and (31) is a semi-transparent plane reference plate. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] In a light wave distance measuring device for measuring a distance to a corner cube prism or a plane reflecting mirror, means for irradiating parallel laser light to the corner cube prism or the plane reflecting mirror; means for detecting reflected light from a prism or a plane reflecting mirror;
A light wave ranging device characterized by comprising a semi-transparent plane reference plate disposed in a common part of the optical paths of the parallel laser beam and the reflected light.