JPS5918472A - Distance measuring apparatus - Google Patents

Abstract

PURPOSE:To achieve a higher stability in the short range measurement of distance and a higher capacity of max. distance measurement by always measuring the target at a fixed error alarming probability with a gate arranged in front of a range gate for capturing a target to detect noise such as back scattered light so that the threshold level for detecting the target is set measuring noise frequency. CONSTITUTION:A range gate 29 is set at the position containing a target reflected light as shown by the drawings (a) and (b) and a range gate generator 28 always generates a range gate 30 at the positon earier by the time tp than the range gate 29 as shown by the drawing (c). The time ranges of the range gates 29 and 30 are equal, tw. The range gate 30 moves in linkage with the range gate 29 for capturing targets and thus, the target can be detected at a fixed error alarming probability as always captured with the range gate 29 to measure the distance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distance measuring device that can always measure a target distance with a constant false alarm probability.

Send a pulsed laser beam and determine the target R from the propagation delay time.
When performing distance measurement, the following methods have conventionally been used to reduce backscattering from the atmosphere and erroneous distance measurements caused by other objects.

FIG. 1 is a diagram showing an example of the configuration of a conventional device of this type,
(1) is a pulsed laser device, (2+ is a pulsed laser beam, (3) is a receiving optical system, (4) is a photoelectric conversion element, (5)
is an amplifier, (6) is a pulse signal, (7) is a voltage comparator,
(8) is a fixed direct voltage generation circuit, (9) is a fixed threshold voltage, (11 is a stop signal, (Io is a start signal,
(12 is a counter.

03 is distance data.

Pulsed laser light (
2; is transmitted toward the target, and the reflected light from the target is received by the receiving optical system (3) and photoelectrically converted by the photoelectric conversion element (4). The photoelectrically converted weak signal is sent to an amplifier (5)
The pulse signal (6) with sufficient amplitude is amplified by 3, and is applied to one input of the voltage comparator (7). A fixed threshold voltage (9) is applied from the voltage generation circuit (8), and when the amplitude of the pulse signal (6) exceeds the fixed threshold voltage (9), a stop signal θ is output from the voltage comparator (7). Ru.

The stop signal 01 far, is input to the counter 021 along with the start signal α0 output from the pulse laser device fl) when transmitting the pulsed laser beam, and the Meyanagi distance is calculated from the time interval between the two. will be output.

FIG. 2 is a diagram showing the relationship 4 between the pulse signal (6) caused by the backscattered light and the target reflected light and the fixed amount (direct voltage (9), where the horizontal axis II1+ indicates the distance and the vertical axis indicates the amplitude t1). The fixed threshold voltage (9) is such that under normal weather conditions, if the pulse signal due to backscattered light within the ranging range is smaller than the fixed threshold voltage,
ru. The threshold voltage is set to 111 (as low as possible), so that 11-point reflected light that exceeds this fixed threshold voltage by Jjν is detected.

However, when the visibility of the atmosphere deteriorates and the backscattered light increases abnormally, the pulse signal due to the backscattered light at a short (3) distance increases between fixed distances, as shown by the broken line in Figure 9.
The voltage (9) will be exceeded, and erroneous distance measurement will occur due to backscattering. Or to make it less likely that erroneous distance measurements will occur even in such cases.

If you set the fixed threshold voltage (9) a little higher.

Pulse signals from distant targets will no longer be detected, resulting in a reduced maximum range.

As described above, conventional devices of this type have the disadvantage that the probability of erroneous distance measurement, that is, the probability of false alarm, changes depending on the state of the outside world, making it impossible to obtain stable distance measurement.

The present invention provides means for eliminating this drawback, and will be explained in detail below using FIG. 1.

FIG. 3 is a diagram showing one embodiment according to the present invention.

The process of transmitting a pulsed laser beam and receiving, photoelectrically converting, and amplifying the reflected light (7) to obtain a pulsed signal (6) is the same as that of the conventional device, so a description thereof will be omitted. In Figure 3,
(14+, ae is a voltage comparator, Ql19.αη is a gate circuit, 0 is a counter, (li is a reference pulse number setting circuit.

(4) (1) is a judgment circuit, 011 is an adder circuit, Q general digital/analog (D/A) converter, (to), Q4) is a resistor, f! 9 is a switch, (2! is a manual gate position generator,
@, (c) is the range game 1 generator, 翰, (to) is the range game), (31) and (62) are the reference voltages.

In the initial stage, the switch (c) is connected to the contact point 1, and by manually operating the 9 manual range gate/position generator (to), the range gate generator outputs the range gate 1-(2). is set at a position that includes the target reflected light, as shown in FIGS. 4(a) and (1)l. The range gate generator (c) is always as shown in FIG. 4(c).

It is configured to generate the range gate clf)Y at a position earlier than the range gate Chi by a time tp, and the time widths of the range gates Ill and CI are equal tow.

At the beginning, the adder circuit 011 is configured such that the output of the adder circuit 00 is set to a low initial value.

This direct signal is converted into a low-value analog signal by the D/A converter Q3, divided by the resistor e (, ■, and input to the reference voltage input of the voltage comparator Q field, and the reference voltage (62) Become.

A pulse signal (6) is input to the signal input of the voltage comparator α, and since the reference voltage (32) is initially at a low value, there are many pulse signals that exceed this value. Voltage comparator 09 detects a pulse signal (
6) 'k, pulse shaped and output.

This is input to the gate circuit α power, so the reference voltage (3
Exceed 2). The number of pulses due to backscatter 9 etc. within the range gate (to) is counted by the counter ttn. Pulse count number m which is the output of counter α barrel
is input to one input of the 4 judgment circuit.

The reference pulse number M, which is the output of the reference pulse number setting circuit α→, is input to the other input, and according to the 9th-order determination algorithm, the determination circuit (to) outputs calmness as a KY natural number.

This [D is added to the previous value in the adder circuit Qυ. As a result, if the number m of pulse counts due to backscatter 9, etc. is greater than the reference amount M, the 9th reference voltage (32) becomes higher; if it is less, the 9th reference voltage (32) becomes higher. Since the reference voltage (62) becomes low, a pulse signal due to backscatter # within the range gate (to) will always be detected with a constant probability.

On the other hand, voltage comparator a4 for detecting stop pulse χ
The reference voltage input is the direct output of the D/A converter (6
1) is input as the reference voltage, which is greater than the reference voltage (32) mentioned above, so resistor (c).

By appropriately setting the resistance ratio of Q4 and the reference pulse number M''l, only the pulse signal due to the target reflected light is always detected within the range gate end.

The false alarm probability due to backscattered light 1, etc. within the same range gate can be maintained at an acceptable constant σ+H.

Note that when the range gate (to) captures the target and the distance data α range can be obtained continuously, the switch (c) is connected to the contact aK, and the range gate IJ1. <31 is automatically set, so the target is always captured by the range gate (c) and detected with a constant false alarm probability as described above.

The distance will be measured.

(T) In the above explanation, the range gate (to) is designed to move in conjunction with the range gate to capture the target Y, but in order to simplify the configuration of the device, the range gate (to) It is also possible to use a configuration in which the target is fixedly set at a fixed position at a short distance.

As described above, according to the present invention, a gate for detecting noise caused by backscattered light 1, etc. is provided before the range gate for capturing a target, and while measuring the frequency of noise within this gate, the range gate for target detection is Since the threshold level is set, it is possible to always measure the target with a constant false alarm probability, which significantly contributes to the stability of distance measurement at short distances and the improvement of the maximum distance.Figure 1 shows the conventional distance measurement method. The figure which shows one example of the structure of a device.

Figure 2 is a diagram showing the relationship between the pulse signal and the fixed open chain voltage.
FIG. 3 is a diagram showing one embodiment of the device according to the present invention, and FIG.
The figure shows the relationship between the target and the range gate according to the present invention, in which (1) is a pulse laser device, (2) is a pulse laser beam, (3) is a receiving optical system, and (4) and (8) are photoelectronic devices. Conversion element, (6) is a pulse signal, (1 (I is a start signal, 0υ is a stop signal, a old counter, α
row is distance data, α→, 01 is voltage comparator, as,
(lη is a gate circuit, 08 is a counter, and Ql is a reference pulse number setting circuit.

(1) is the judgment circuit, 0υ is the adder circuit, @, (c) is the range gate generator, 翰, (to) is the range gate I (3
1) and (32) are reference voltages.

In FIG. 9, the same or corresponding parts are designated by the same reference numerals.

Agent Nobu Kuzuno - Figure 1

Claims (1)

[Claims] In a distance measuring device that transmits a Hals laser beam and determines the distance to the target from the propagation delay time of the pulsed laser beam, there is a means for photoelectrically converting one reflected beam to generate a pulse signal, and a means for generating a pulse signal at a time position corresponding to the target distance. means for setting a first range gate; and means for setting a second range gate at an earlier time position than the first range gate.
means for detecting a pulse signal exceeding a first threshold voltage within the first range gate; and means for detecting a pulse signal exceeding a first threshold voltage within the first range gate;
means for detecting a pulse signal exceeding fY and counting the number of pulses; voltage generating means for increasing an output voltage when the number of pulses exceeds a predetermined number of pulses; and decreasing the output voltage when the number of pulses is less than a predetermined number; A distance measuring device comprising: means for setting the output voltage of the generating means as a first threshold voltage; and means for dividing the first threshold voltage and setting it as a second threshold @1 voltage.