JPH0552956A - Optical distance-measuring device - Google Patents

Abstract

PURPOSE:To enable a distance-measuring accuracy to be improved by automatically setting a reference value for comparison based on a signal level when there is no signal. CONSTITUTION:A distance is measured based on a propagation delay time between a light-transmission timing of a light transmitter 2 and an output timing of a comparator which is equivalent to a light-reception timing of a light receiver 3. Transmission of light is temporarily paused by a light-transmission controller 9 and a reference value of the comparator 7 is set variably by a threshold voltage generator 10 based on a signal level which is detected by an A/D converter 6 during thus time, thus improving the distance-measuring accuracy by a single structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention sends light in a predetermined direction, receives reflected light of the sent light by a reflector, and reflects the light based on the propagation delay time from the sending of the light to the receiving of the light. The present invention relates to an optical distance measuring device for measuring the distance to the.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration of a conventional optical distance measuring device disclosed in, for example, Japanese Patent Laid-Open No. 2-228579, in which 1 is a pulse generator and 2 is an electric signal from a pulse generator 1. Is a light-transmitting device including a light-emitting element (laser diode or the like) for converting light into an optical signal, its drive circuit, and a lens system.

Reference numeral 3 designates a light receiver comprising a lens system for receiving the light reflected by the reflector and a light receiving element (photodiode or the like) for modulating an optical signal into an electric signal, and 4 a pulse signal from the light receiver 3. A broadband amplifier 5 that amplifies the signal is a sampling processor composed of a sweeper that receives a sweep start signal from the pulse generator 1, a sample pulse generator, a sample hold device, and a low frequency amplifier. The pulse signal is converted into a low frequency reception pulse signal.

An A / D converter 6 detects the DC level of the low-frequency reception pulse signal from the sampling processor 5 in synchronization with the sampling pulse generator of the sampling processor 5.
Reference numeral 7 denotes a comparator for comparing the output of the A / D converter 6 with a reference value set to a predetermined value in advance, and 8 denotes the propagation delay time of light from the signal of the pulse generator 1 and the output signal of the comparator 7. ,
It is a signal processor that calculates the distance to the reflector.

Next, the operation will be described. The pulse generator 1 generates a clock pulse whose pulse interval is equal to or longer than the time corresponding to the maximum measurement distance. The light transmitter 2 which has received this pulse signal as a drive pulse transmits a light transmission pulse L _t . This light-transmitting pulse L _t is reflected by a reflector as a distance measurement target to become reflected light L _r , which is received by the light receiver 3 and converted into an electric signal by photoelectric conversion.

Then, this electric signal is supplied to the broadband amplifier 4
After being amplified to a predetermined level by, the shape of the low frequency signal having the same frequency as the sweep frequency, that is, the original received pulse signal is converted by the sampling processor 5, and the shape is preserved only by converting the time axis. It is converted into a pulse signal and amplified to a required level to become a low frequency reception pulse signal.

Next, the A / D converter 6 reads the DC level of the low frequency reception pulse signal from the sampling processor 5 at a timing synchronized with the sampling pulse of the sampling pulse generator of the sampling processor 5, and digitally reads it. Convert to a value. The comparator 7 compares the digital value with the reference value and outputs a signal when the value is equal to or larger than the reference value.

The signal processor 8 counts the propagation delay time based on the timing of the sweep start, that is, the light transmission timing obtained from the pulse generator 1 and the timing of the output signal of the comparator 7, and determines the distance to the reflector. calculate. The reference value of the comparator 7 is a level at which a malfunction due to noise does not occur by adding a fluctuation amount due to noise to the DC level of the output signal of the sampling processor 5 when there is no signal (a normal noise level is increased by 10 dB. Set to a fixed value.

This optical distance measuring device is mounted on a moving object such as an automobile to detect the presence or absence of a reflector around the front, rear, or side of the vehicle and to detect distance, speed, etc. Therefore, it can be effectively used for collision prevention, inter-vehicle distance control, road surface condition detection, condition detection of adjacent lanes when changing lanes, and the like.

[0010]

Since the conventional optical distance measuring device is constructed as described above, the reference value of the comparator 7 is fixed, and the fluctuation of the power supply voltage, the change of the ambient temperature and the secular change. If the DC level of the output signal of the sampling processor 5 drifts due to factors such as deterioration of measurement accuracy and erroneous detection, a high-precision constant voltage circuit or temperature compensation circuit is required. There was a problem that it was difficult to make adjustments to make strict settings.

The present invention has been made to solve the above-mentioned problems, and a threshold for comparison is automatically set and measured according to the signal level in a time zone other than the distance measurement period (distance measurement period). An object is to obtain an optical distance measuring device that can improve accuracy.

[0012]

An optical distance measuring device according to the present invention is a device for measuring a distance to a reflector based on a propagation delay time between a light sending timing and an output timing of a comparing means. Light transmission control means for temporarily suspending light transmission during the period and threshold voltage generation means for variably setting the reference value of the comparison means based on the signal level when there is no signal during the light transmission suspension period are provided. ..

[0013]

The optical distance measuring apparatus of the present invention suspends the light transmission by the light transmission control means immediately before each distance measuring period, detects the direct current level at the time of no signal at this time, and detects noise based on this detection level. The reference value of the comparison means is variably set by the threshold voltage generation means in consideration of the fluctuation due to the light source, and compared with the level of the pulse signal obtained by transmitting and receiving light to the reflector, and the result is used as the light reception timing. The distance to the reflector is measured based on the propagation delay time.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an optical distance measuring apparatus according to an embodiment of the present invention. In FIG. 1, the same or corresponding parts as those in the conventional example are designated by the same reference numerals 1 to 8 as those in FIG.
Reference numeral 9 is a light transmission controller that generates a signal for temporarily stopping the light transmission to the light transmitter 2 in a time zone other than the distance measurement period immediately before the distance measurement period of the next distance measurement cycle. A threshold voltage generator for generating the threshold voltage of the comparator 7 by adding fluctuations due to noise to the DC level of the output signal of the sampling processor 5 detected by the A / D converter 6 while the light transmission of the band is stopped. Is.

FIG. 2 is a diagram for explaining the distance measurement timing of one embodiment of the present invention, showing one distance measurement cycle. In FIG. 2, the distance measurement is started at time t ₀ , the distance measurement is ended at time t ₁ after 90 ms and the data transfer is started, and the data transfer is ended at time t ₂ 10 ms after the time t ₁ . 90 ms from time t _{0 to} t ₁
It is a distance measurement period, a light transmission period, and a reception level detection period. 10 ms from time t _{1 to} t ₂ is the distance data transfer period, the light transmission pause period, and the no-signal level detection period. Therefore, the distance measurement cycle is 100 ms from time t _{0 to} t ₂ .

Next, the operation of this embodiment will be described with reference to FIGS. During the distance measurement period from time t _{0 to} t ₁ , the reference value of the comparator 7 is not a fixed value, and is set automatically by the threshold voltage generator 10 in advance for each distance measurement cycle. Do the same. This behavior is
Since it has been described in the section of the related art, its description is omitted.

Next, the operation at times t _{1 to} t ₂ will be described. Upon receiving the distance measurement end signal from the signal processor 8, the light transmission controller 9 generates a signal for stopping the light transmission from the light transmitter 2 during the distance data transfer period, and outputs the signal to the light transmitter 2. Then
Pause light transmission. On the other hand, the background light is received by the light receiver 3 and photoelectrically converted, and then subjected to sampling processing by the sampling processor 5 via the broadband amplifier 4.

The signal output from the sampling processor 5 is a low frequency reception pulse signal by light transmission, that is, a signal when there is no distance measuring signal, and a DC level is detected by the A / D converter 6. To be done. The threshold voltage generator 10 is A /
In addition to this DC level detected by the D converter 6, fluctuations due to noise are added to set a threshold voltage at a level at which malfunction due to noise does not occur, and the threshold voltage is supplied to the comparator 7 as a reference value. Prepare for the distance measurement period of the distance cycle.

In addition to this, in order to have an STC (sensitive timing control) characteristic, the fluctuation due to noise added to the DC level when there is no signal during the light transmission suspension period is changed according to the distance to be measured. Even in such a case, the same effect as that of the above-described embodiment can be obtained by updating the DC level when there is no signal to the value detected immediately before each ranging cycle.

[0020]

As described above, according to the present invention, the light transmission is temporarily stopped during the time period other than the distance measurement period, and the signal level when there is no signal is detected during the light transmission suspension period. Since the reference value for comparison is variably set based on the detection level, distance measurement accuracy can be improved without using a highly accurate constant voltage circuit or a complicated temperature compensation circuit, and a simple configuration is possible. There is an effect that it is easy to manufacture.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing an operation period for one distance measurement cycle according to the embodiment.

FIG. 3 is a block diagram showing a configuration of a conventional optical distance measuring device.

[Explanation of symbols]

 1 pulse generator 2 light transmitter (light transmitting means) 3 light receiver 4 broadband amplifier 5 sampling processor 6 A / D converter (detecting means) 7 comparator (comparing means) 8 signal processor 9 light transmitting controller ( Light transmission control means) 10 Threshold voltage generator (threshold voltage generation means)

[Procedure amendment]

[Submission date] May 15, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

An A / D converter 6 detects the DC level of the low-frequency reception pulse signal from the sampling processor 5 in synchronization with the sampling pulse generator of the sampling processor 5.
Reference numeral 7 is a comparator for comparing the output of the A / D converter 6 with a reference value set in advance to a predetermined value, and 8 is the propagation delay time of light from the signal of the pulse generator 1 and the output signal of the comparator 7. A signal processor for calculating the distance to the reflector.

Claims (1)

[Claims] 1. A light transmitting means for transmitting a light transmitting pulse, a detecting means for detecting a level of a pulse signal obtained by receiving reflected light of the light transmitting pulse by a reflector, and a detecting means for detecting the level of the pulse signal. In the optical distance measuring device, which is provided with a comparison means for comparing the signal level and the reference value, the distance to the reflector is measured based on the propagation delay time between the light transmission timing and the output change timing of the comparison means. Light transmission control means for temporarily suspending light transmission in a time zone other than the distance period, and a reference value of the comparison means based on the signal level when there is no signal detected by the detection means during the light transmission suspension period. An optical distance measuring device comprising: a threshold voltage generating means for variably setting for the next distance measuring cycle.