JPH0266484A - Pulse laser range finding device - Google Patents

Abstract

PURPOSE:To furthermore improve range finding accuracy determined by the rise time of a pulse laser waveform by receiving reflected beams from an object to be measured at its distance by plural different intensity level sand selecting the most appropriate signal. CONSTITUTION:A short pulse laser beam generated by a laser device 1 is projected to the object 3 to be measured at its distance by a beam splitter 2 and simultaneously inputted to a transmitting optoelectric converter 5 through an optical attenuator 4 and the input signal is converted into a light transmitting signal. A counter circuit 19 receives a clock pulse from a clock circuit 20 and counts up time between the trailing timing of a pulse inputted to a start input and the trailing timing of a pulse inputted to a stop input. Since the counted time data correspond to the light reciprocating time of a distance up to the object 3, the data are set up as distance data up to the object 3. When the quantity of reflected light is extremely small, received light is attenuated by optical attenuators 10, 11, the received light is not detected by receiving photoelectric converters 12, 13 and received by a receiving photoelectric converter 7.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a distance measuring device using a pulsed laser, and particularly to a pulsed laser distance measuring device that measures distance by measuring the round trip time of a pulsed laser beam. It is related to.

[Conventional technology]

This type of pulse laser distance measuring device irradiates a distance measuring object with a single short pulse laser beam and detects the reflected light. Since the time interval between when the laser beam is transmitted and when the reflected beam is received is the round trip time of the light, the distance is measured by this timing.

The reflected light reflected from the distance measuring object and captured by the distance measuring device is attenuated and contains noise, so in order to avoid erroneous distance measurement due to noise, a pulse height discriminator with a threshold value set in the receiving circuit is installed. It is necessary to extract only the signal whose waveform has been shaped using

A conventional pulse laser distance measuring device of this type has such processing circuits in the transmitting and receiving circuits, and measures the time interval between rising points whose respective wave heights are discriminated.

An example of this conventional pulse laser distance measuring device is shown in FIG. 3 and will be described.

In the figure, 31 is a laser device that generates a short pulse laser beam, 32 is a beam sinter, 33 is an object to be measured, and 3
4 is an optical attenuator, 35 is a transmitting photoelectric converter, 36 is a receiving optical system, 3T is a receiving photoelectric converter, 38.39 is a wave height discrimination waveform shaping circuit, 40 is a counter circuit, and 41 is a clock circuit.

Next, the operation will be explained.

First, a short pulse laser beam generated by a laser device 31 is projected by a beam splitter 32 toward a distance measuring object 33, and at the same time passes through an optical attenuator 34, inputs into a transmitting photoelectric converter 35, and is transmitted. becomes an optical signal. This light transmission signal is shaped by a wave height discrimination waveform shaping circuit 38 and supplied to a counter circuit 40.

On the other hand, the reflected light from the distance measuring object 33 is collected by the receiving optical system 36. The collected reflected light is input to the reception photoelectric converter 37 and becomes a light reception signal.

This received light signal is shaped by a wave height discrimination waveform shaping circuit 39,
The signal is supplied to the counter circuit 40.

Next, the counter circuit 40 is supplied with cyclic pulses from the clock circuit 41, and each pulse height discrimination waveform shaping circuit 38.
39 is counted, and the time interval between the rising points υ whose pulse heights are discriminated is measured.

This counted time data corresponds to the round trip time of the light to the distance to the object 33, so it can be used as distance data to the object 33.

[Problem to be solved by the invention]

The above-mentioned conventional pulse laser distance measuring device measures the time interval between the rising points of the light transmission signal and the light reception signal, which are subjected to pulse height discrimination. Since the time waveform of a pulsed laser normally has a Gaussian type, the point at which the shaped waveform rises is determined by the intensity level at which the threshold value of the pulse height discriminator discriminates the pulse height.

Here, the threshold of the wave height discriminator is set to a constant value that can be separated from noise, and the intensity of the transmitted light is also set to a constant value accordingly. It varies greatly depending on the laser beam reflectance of the object to be measured. When the received light intensity is large, the 9 rising points after pulse height discrimination reach the threshold of the pulse height discriminator even at a low intensity level in the laser light time waveform.
It rises at an early point in the laser beam time waveform. However, when the received intensity is small, the threshold value is reached at the maximum intensity level of the laser beam time waveform, so the signal rises approximately at the center of the time waveform. This aspect is shown in the time chart of FIG.

In FIG. 4, (a) shows a light transmission signal, and (,) shows a light reception signal. and,
VTh indicates a discrimination threshold.

In other words, the reception strength varies depending on the conditions of the object to be measured and the state of the atmosphere, and as a result, the time measurement changes due to these fluctuations. It is determined by the time from the rise of the laser beam until it reaches the maximum level, that is, the rise time. Therefore, there was a problem that the distance measurement accuracy was low.

[Means to solve the problem]

The pulsed laser distance measuring device of the present invention is a laser ranging device that measures distance by counting the round trip time of pulsed laser light, and includes a plurality of optical attenuators each having a different amount of optical attenuation, and a plurality of optical attenuators each having a different amount of optical attenuation. A plurality of photoelectric converters that are paired with an attenuator and receive reflected light passing through the optical attenuator, and an appropriate translation circuit that selects the most appropriate signal from among the signals output from the plurality of photoelectric converters. It has the following.

[Effect]

In the present invention, reflected light from a distance measuring object is received at a plurality of different intensities, and the most appropriate signal is selected.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing an embodiment of a pulse laser distance measuring device according to the present invention.

In the figure, 1 is a laser device that generates a short pulse laser beam, 2 is a beam splitter, 3 is a distance measurement target, 4 is an optical attenuator, 5 is a transmitting photoelectric converter, 6 is a receiving optical system, and 7 is a receiving photoelectric converter, 8 and 9 are beam sinter, 10.1
1 is an optical attenuator each having a different amount of optical attenuation; 12
．． 13 is a receiving photoelectric converter that is paired with the optical attenuator 10.11 and receives the reflected light passing through the optical attenuator 10.11; 14.15 and 16.17 are pulse height discrimination waveform shaping circuits; 18 is a selection circuit that selects the most appropriate signal from among the signals output from the receiving photoelectric converters 7, 12, and 13; 19 is a counter circuit; and 20 is a clock circuit.

Figure 2 is a time chart used to explain the operation of Figure 1.
(,) shows the light transmission signal, (b) is the light reception signal with the least amount of optical attenuation, (C) is the light reception signal with the medium amount of optical attenuation, and (d) is the light reception signal with the least amount of optical attenuation. This shows the largest received light signal. Further, VTh indicates a discrimination threshold.

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to FIG. 2.

First, a short pulse laser beam generated by a laser device 1 is projected by a beam sinter 2 toward a distance measurement object 3, and at the same time passes through an optical attenuator 4 and enters a transmitting photoelectric converter 5. υ Becomes a light transmission signal. The waveform in (,) in FIG. 2 is this light transmission signal.

On the other hand, the reflected light from the distance measuring object 3 is collected by the receiving optical system 6. The collected reflected light enters the receiving photoelectric converter 7, but part of it is separated by beam splitters 8 and 9 on the way, passes through optical attenuators 10 and 11, and enters the receiving photoelectric converter 12. and 13.

Among these, the optical attenuator 10 has a very large amount of attenuation, and if the optical attenuation amount of the optical attenuator 11 is medium, the received light entering the receiving photoelectric converters 7, 12 and 13 is relatively very large. When I say "dog", "medium", "very small", it becomes "K".

ζHere, since the time waveform of the short pulse laser beam is a Gaussian shape as shown in 6) of FIG. 2, the reflected light from the distance measurement object 3 also has a similar waveform. Therefore, when receiving reflected light, the receiving photoelectric converter receives the reflected light when the amount of received light is large and the case where the amount of received light is small, and the waveforms are shaped by a wave height discrimination waveform shaping circuit having a certain discrimination threshold value v'rh and then compared. When the amount of received light is large, the time width of the shaped waveform is wide;
When the amount of received light is small, the time width of the shaped waveform is narrow. This is shown in FIGS. 2(b), (e), and (d).

Next, the light transmission signal obtained from the transmission photoelectric converter 5 is shaped by a wave height discrimination waveform drum-shaped circuit 14, and input to the start input of the counter circuit 19 at the falling edge of the shaped waveform.

On the other hand, the received light signals obtained from the receiving photoelectric converters T, 12 and 13 are transmitted to the respective wave height discrimination waveform shaping circuits 15 and 16.
and formatted with 1T. Then, of each waveform shaping, the timing at which the shaped waveform falls at the earliest timing is selected by the selection circuit 18, and inputted to the stop input of the counter circuit 19.

In this case, since the time width of the shaped waveform of the smallest of the detected received lights is narrow, the fall of the shaped waveform enters the stop input of the counter circuit 19 whose timing υ is early.

The counter circuit 19 receives a cyclic pulse from the clock circuit 20 and counts the time between the falling edge of the pulse input to the start input and the falling edge of the pulse input to the stop input. and,
The counted time data corresponds to the round trip time of the light at the distance measuring object 3t, so it can be used as distance data to the distance measuring object 3. In FIG. 2, a distance corresponding to time t is measured.

In the case of a pulse laser distance meter, the amount of reflected light varies greatly depending on the distance to the object to be measured, the reflectance of the object to be measured, and the transmittance of the atmosphere.

In the embodiment shown in FIG. 1, when the amount of reflected light is very large, it is received by the receiving photoelectric converters 7, 12, and 13, but the received light passes through the optical attenuator 10, which has a very large amount of optical attenuation. The receiving photoelectric converter 12 that detects light outputs the smallest received signal, which is input to the stop input of the counter circuit 19.

When the amount of reflected light is very small, the receiving photoelectric converters 12 and 13 include optical attenuators 10 and 11, respectively, to attenuate the received light, so the received light is not detected and the receiving photoelectric converters 12 and 13 are not detected. is received by device 7. At this time, since the amount of reflected light is originally small, the received light signal is also small.

Further, if the amount of reflected light is neither very large nor very small, it is not detected by the receiving photoelectric converter 12,
A receiving photoelectric converter 13 receives received light received by the receiving photoelectric converters 7 and 13 but attenuated by the optical attenuator 11.
outputs the smallest light reception signal and inputs it to the stop input of the counter circuit 19.

FIG. 2 shows the received light intensity and the timing of the rangefinder.

In other words, in the embodiment shown in FIG. 1, it is possible to select received light signals of almost the same level even if there is a large variation in the amount of reflected light, thereby reducing the distance measurement error caused by the rise time of the laser pulse. It's coming.

〔Effect of the invention〕

As explained above, the present invention receives reflected light from a distance measurement object at a plurality of different intensities and selects the most appropriate signal, thereby achieving distance measurement accuracy determined by the rise time of the pulsed laser waveform. This has the effect of making it very accurate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a pulse laser distance measuring device according to the present invention, FIG. 2 is a time chart for explaining the operation of FIG. 1, and FIG. 3 is an example of a conventional pulse laser distance measuring device. The block diagram shown in FIG. 4 is a time chart for explaining the operation of the third factor. 1e...Laser device, 2.φ...Beam sinter,
3... Distance measurement target, 6... Receiving optical system, 7...
. . . Photoelectric converter for reception, 8, 9 . . . φ beam splitter, l, 11 . . . Optical attenuator, 12.13- . .

Claims (1)

[Claims] A laser distance measuring device that measures distance by measuring the round trip time of a pulsed laser beam includes a plurality of optical attenuators each having a different amount of optical attenuation, and an optical attenuator that is paired with the plurality of optical attenuators. A pulsed laser ranging device characterized by having a plurality of photoelectric converters that receive reflected light passing through the plurality of photoelectric converters, and a selection circuit that selects the most appropriate signal from among the signals output from the plurality of photoelectric converters. Device.