JPH0381687A - Laser distance measuring instrument - Google Patents

Abstract

PURPOSE:To remove an error in distance measurement time due to the rounding of a signal and variation in its amplitude and to improve the measurement accuracy by providing a circuit which measures the pulse width of the output signal of a photodetector, a circuit which measures the pulse width of the output signal of a photodetection system, and an arithmetic circuit, and measuring the time interval between the centers of both the pulses. CONSTITUTION:Light with ultra short pulse width is made incident on a half- mirror 2 from a Q switch pulsed laser oscillator 1, the majority of the laser light is transmitted, and the remainder is sent to a photodetector 3. The photodetector 3 converts the pulsed laser light into an electric pulse signal and a comparator circuit converts a level above a threshold value into '1' and others into '0'. The majority of the laser light is made incident on a transmission optical system 4, narrowed down in beam divergence angle, and sent out to a distance measurement target 5. The irradiating light 6 is scattered by the surface, but part of it is converged by a reception optical system 7 and a photodetection system 8 converts only the pulsed laser light into an electric signal; and the comparator circuit generates '1' and '0' based upon the threshold value and a counter 9 measures time intervals of '1'.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a distance measuring device using pulsed laser light.

(Conventional technology) Figure 3 shows a laser distance measuring device using pulsed laser light produced using conventional technology. 1 is a Q-switched pulsed laser oscillator, and the pulse width is from several 0 seconds to several tens of nanoseconds. A semi-transparent mirror 2 transmits most of the laser light, but sends some of the light to the photodetector 3.The photodetector 3 detects the laser light. When emitted, the pulsed laser light is converted into an electrical pulse signal, and the timing at which the pulsed laser light is emitted is detected.

Most of the output light from the Q-switched pulsed laser oscillator 1 enters the transmission optical system 4 and is transmitted to the ranging target 5 after the beam divergence angle is narrowed. Laser light 6 irradiated onto distance measurement target 5 is scattered on its surface. A part of the scattered laser beam propagates through the space to be measured, and then is collected by the receiving optical system 7. In the receiving system 8, only the pulsed laser beam is selectively transmitted through an optical filter, and then converted into an electric pulse signal. ,
It is used to detect the timing at which laser light is received. In the distance measuring counter 9, the time interval between the timing of pulsed laser beam emission and light reception is measured by the electric pulse signal of the photodetector 3 and the light receiving system 8, and the pulsed laser beam is connected to the laser distance measuring device and the distance measuring target 5. Find the distance by determining the time it takes to go back and forth. The determined distance value is displayed on the display circuit 10. A control circuit 11 controls the operations of the Q-switched pulse laser oscillator 1, distance measuring counter 9, and display circuit 10 in synchronized timing.

<Problems to be Solved by the Invention> The conventional laser distance measuring device using pulsed laser light as described above does not require a retroreflector to be placed on the distance measurement target.
It has advantages such as a simple device and short measurement time, and is very convenient for measuring distances from several hundred meters to about 10k11. However, on the other hand, the pulse width of the Q-switched pulsed laser beam has a half-width value of several nanoseconds to 30 nanoseconds, which causes an error to be included in the measured distance value, as shown in FIG. That is, in FIG. 3, the light receiving system 8 receives the laser beam, converts the optical signal into an electrical signal, compares it with an appropriate light receiving threshold level, and outputs the signal as a light receiving timing signal. As shown in FIG. 4, in the case of the optical signal 12 of the light receiving system, the level is large and becomes the light reception timing signal at time 13, but even if the light signal 14 of small amplitude enters the light receiving system at the exact same time, the light reception timing signal is is time 15
Therefore, there is a delay with respect to time 13. The maximum magnitude of this delay is about the half width of the pulsed laser beam.

Assuming that the half width of the pulsed laser beam is 30 ns, the amount of error in the distance measurement value caused by this error is about 5 m, which is the largest cause of measurement error in the laser distance measuring device of this method.

A similar problem also exists when detecting the timing at which the pulsed laser beam outputted by the photodetector 3 in Fig. 3 is emitted, and due to fluctuations in the level of the output pulsed laser beam, a slight error may occur. It could have happened. Due to these factors, it has been difficult to increase the accuracy of distance measurement, and its field of use has been limited to some applications that do not require high accuracy.

In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a circuit that eliminates distance measurement errors caused by the roundness and amplitude of the output waveform of a photodetector and the output waveform of an optical signal of a light receiving system. An object of the present invention is to provide a laser distance measuring device with little distance error.

<Means for Solving the Problems> The present invention has the following means configuration to achieve the above object.

That is, the laser distance measuring device of the present invention includes: a Q-switched pulsed laser oscillator; a photodetector that detects a portion of its output laser light and converts it into an electric pulse signal; and an output laser of the Q-switched pulsed laser oscillator. a transmitting optical system for sending most of the light to the ranging target; a receiving optical system for receiving part of the laser light scattered by the ranging target; a pulsed laser focused by the receiving optical system. a light receiving system that converts light into an electrical pulse signal; a distance measuring counter that starts at the rising edge of the electrical pulse signal from the photodetector and stops at the rising edge of the electrical pulse signal from the light receiving system to measure a time interval; a first pulse width measurement circuit that measures the time width of the electric pulse signal of the output laser light outputted from the photodetector; and a first pulse width measurement circuit that measures the time width of the electric pulse signal of the received laser light outputted from the light receiving system. 2 pulse width measurement circuit; 2 of the time width of the light transmission pulse measured by the first pulse width measurement circuit from the time interval measured by the distance measuring counter;
an arithmetic circuit that calculates a time interval by subtracting 1/2 and adding 1/2 of the time width of the received light pulse measured by the second pulse width measuring circuit, and converting the calculated time interval into distance data; This is a laser distance measuring device.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.

1 is a Q-switched pulse laser oscillator, which generates a laser beam with an extremely short pulse width. 2 is a semi-transparent mirror that transmits most of the laser light but sends some of the light to the photodetector 3; When the laser beam is emitted, the photodetector 3 converts the pulsed laser beam into an electric pulse signal, and then converts the pulsed laser beam into an electric pulse signal with a comparator circuit that sets the level above the threshold as 1, and the rest as 0. Most of the laser light enters the transmission optical system 4, has its beam divergence angle narrowed, and is then sent out toward the distance measurement target 5.

Laser light 6 irradiated to distance measurement target 5 is scattered on its surface. A part of the scattered laser light propagates through space and is collected by the receiving optical system 7. In the receiving system 8, only the pulsed laser light is selectively transmitted through an optical filter, and then converted into an electric signal, which is also sent to the comparator circuit. It is converted into a signal in which levels above the threshold are set as 1'', and other levels are set as 0''.

The distance measuring counter 9 receives the electric pulse signals from the photodetector 3 and the light receiving system 8, starts counting at the rising edge of the signal from the photodetector 3, stops counting at the rising edge of the signal from the light receiving system 8, and calculates the period in between. Time intervals are measured by counting with a clock signal of an appropriate frequency.

The first pulse width measuring circuit 16 detects that the output signal of the photodetector 3 is “
The second pulse width measuring circuit 17 measures the time interval during which the output signal of the light receiving system 8 is "1".

The measured values of the distance measurement counter 9, the first pulse width measurement circuit 16, and the second pulse width measurement circuit 17 are input to the calculation circuit 18.
Errors are greatly reduced by performing calculations internally. The principle is shown in FIG. 2. In FIG. 2, 19 is a signal received by the photodetector 3 when the Q-switched pulsed laser beam is emitted, and 20 is the output signal waveform of the photodetector 3. 21 is a waveform when a portion of the laser beam scattered by the distance measurement target is received by the light receiving system 8, and 22 is an output signal waveform of the light receiving system 8. 23 indicates a period during which the distance measuring counter 9 counts the clock signal.

Reference numeral 24 indicates the time period during which the light travels back and forth between the laser distance measuring device of the present invention and the distance measuring target, when the peak of the pulse is detected and correctly measured.

From Figure 2, the accurate round trip time T of light is T = TD - ±T
1 + temple T2, and the distance is, if the speed of light is C, then D = temple CT
The above equation is calculated within the arithmetic circuit 18, and errors due to fluctuations in T1 and T2 are removed to obtain an accurate distance, which is displayed on the display circuit 10.

The operations described above are sequentially performed by the control circuit 11.

(Effects of the Invention) As explained above, the laser distance measuring device of the present invention includes a circuit for measuring the pulse width of the output signal of the photodetector, a circuit for measuring the pulse width of the output signal of the light receiving system, and an arithmetic circuit. Since the time interval between the centers of both pulses is measured, it is possible to eliminate errors in distance measurement time caused by the roundness and amplitude of the signal received by the photodetector and light receiving system, and to improve the measurement value. This has the advantage that accuracy can be significantly improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the configuration of an embodiment of the device of the present invention, Fig. 2 is a timing diagram explaining the present invention in detail, Fig. 3 is a block diagram of the configuration of a conventional pulse laser distance measuring device, and Fig. 4 is a light receiving device. FIG. 3 is an explanatory diagram showing that the timing changes when the output level fluctuates due to the slow rise of the signal received by the system. 1...Q-switched pulse laser oscillator, 2.
...Semi-transparent mirror, 3...Photodetector, 4
...Transmission optical system, 5...Distance measurement target,
6...Laser light, 7...Receiving optical system, 8...Light receiving system, 9...Distance measurement counter 10...Display circuit , 11...
...Control circuit, 16...First pulse width measurement circuit, 17...Second pulse width measurement circuit, 18
・・・・・・Arithmetic circuit.

Claims (1)

[Claims] a Q-switched pulse laser oscillator; a photodetector that detects a portion of its output laser light and converts it into an electrical pulse signal;
a transmitting optical system for transmitting most of the output laser light of the Q-switched pulse laser oscillator to the ranging target; a receiving optical system for receiving a part of the laser light scattered by the ranging target; a light receiving system that converts the pulsed laser beam focused by the optical system into an electric pulse signal; it starts at the rising edge of the electric pulse signal from the photodetector, stops at the rising edge of the electric pulse signal from the light receiving system, and then a distance measuring counter that measures the distance; a first pulse width measuring circuit that measures the time width of the electrical pulse signal of the output laser light output from the photodetector; a second pulse width measuring circuit for measuring the time width of the pulse signal; subtracting one half of the time width of the light transmission pulse measured by the first pulse width measuring circuit from the time interval measured by the distance measuring counter; A laser distance measuring device comprising: an arithmetic circuit that calculates a time interval obtained by adding one-half of the time width of the light-receiving pulse measured by the second pulse width measuring circuit and converts the calculated time interval into distance data.