JPH0634758A - On-vehicle distance measuring device - Google Patents

Abstract

PURPOSE:To provide an on-vehicle distance measuring device in which distortion of a receiving pulse signal is suppressed and high speed distance measuring can be attained. CONSTITUTION:A pulse beam Lt is transmitted from a beam transmission part 1, and a pulse beam Lr reflected by a reflecting body and returned is received by a beam receiving part 2. The received pulse signal is amplified by an amplifying part 5 wherein a signal pass band width is limited in order to avoid interference of the received pulse signal on a next received pulse signal, and based on the transmitted pulse and received pulse a distance to the reflecting body is detected by a distance detecting part 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle-mounted distance measuring device for transmitting pulsed light and receiving pulsed light returned from a reflector to detect the distance to the reflector.

[0002]

2. Description of the Related Art Showa 48 is an example of a conventional distance measuring device.
11.4 of "Laser Handbook" published by Asakura Shoten
Some are listed in the item of laser radar. FIG. 4 is a block diagram showing a schematic configuration of a conventional device. Figure 4
In the figure, 1 is a light-transmitting unit formed of a laser diode for transmitting pulsed light Lt, 2 is a light-receiving unit that receives the reflected pulsed light Lr from a reflector, 3 is an amplifying unit that amplifies the received pulse signal, 4 Is a distance detection unit that detects the distance to the reflector from the timing of light transmission from the light transmission unit 1 and the timing of reception pulses from the amplification unit 3.

Next, the operation will be described with reference to FIG.
The light sending unit 1 generates and sends a light sending pulse Lt for distance measurement. The emitted pulsed light Lt strikes a reflector (not shown), becomes reflected pulsed light Lr, and is received by the light receiving unit 2. The received light pulse signal is amplified by the amplifier 3. The light-transmitting timing signal from the light-transmitting unit 1 and the light-receiving timing signal from the amplifying unit 3 are input to the distance detecting unit 4, and the distance data Da is output.

[0004]

The conventional distance measuring device is constructed as described above. In an in-vehicle range finder that mounts such a device on a vehicle to measure a distance, in order to prevent detection of a constant background noise from sunlight or the like other than the signal light, the amplification unit 3 Has a configuration of an AC amplifier that blocks DC.

Therefore, repulsion due to sag occurs in the pulse waveform after amplification. Also, since the pass band is wide,
Undershoot due to the parasitic impedance of the circuit occurs at the trailing edge of the received pulse waveform. When the received signal level is high, the distortion of the received waveform interferes with the rising portion of the leading edge of the next received pulse signal. If the repetition cycle of distance measurement is lengthened to avoid this, there is a problem in that the movement of an obstacle such as a vehicle moving at high speed cannot be measured in real time.

The present invention has been made in order to solve the above-mentioned problems, and suppresses the distortion of the waveform of the received pulse signal, speeds the repeatability of distance measurement, and makes it possible to detect the movement of obstacles in real time for in-vehicle use. It is an object of the present invention to obtain a vehicle-mounted distance measuring device capable of measuring a distance.

[0007]

A vehicle-mounted distance measuring apparatus according to the present invention receives light from a light-transmitting means for sending pulsed light, light-receiving means for receiving pulsed light reflected by a reflector and returned. Amplifying means for amplifying the pulse signal and distance detecting means for detecting the distance to the reflector based on the light transmitting pulse and the light receiving pulse are provided, and the amplifying means is provided so that the received pulse signal does not interfere with the next light receiving pulse signal. The signal pass band width of is limited.

[0008]

In the on-vehicle range finder according to the present invention, the signal pass bandwidth of the amplifying means is limited so that the received pulse signals do not interfere with each other. The distance repeating cycle can be shortened.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numerals 1, 2 and 4 are the same as those in FIG. Reference numeral 5 denotes an amplification unit whose band is limited so that received pulse signals do not interfere with each other, and is connected between the light receiving unit 2 and the distance detection unit 4.

Next, the operation will be described. The light sending unit 1 generates and sends a light sending pulse Lt for distance measurement. The emitted pulsed light Lt strikes the reflector and becomes reflected pulsed light Lr, which is received by the light receiving unit 2. The received pulse signal is amplified by the band-limited amplifier 5. The light-transmitting timing signal from the light-transmitting unit 1 and the timing signal from the band-limited amplifier 5 are input to the distance detecting unit 4, and the distance from the time interval between the light-transmitting pulse and the light-receiving pulse to the reflector is detected. Then, the distance data Da is output. The above distance measuring operation is repeated.

The operation of the band-limited amplifier 5 will be described with reference to FIGS. 2 and 3. FIG. 2 is an explanatory diagram of the signal pass bandwidth of the amplifier 5, and FIG. 3 is a signal waveform diagram showing the relationship between the received pulse signals.

In FIG. 2, the signal pass bandwidth of the amplification section of the conventional distance measuring apparatus is a relatively wide bandwidth of f _{LO to} f _H as shown by the dotted line, while in the embodiment, the solid line is used. the low cutoff frequency limit to higher frequencies as shown in, is obtained by the relatively narrow bandwidth of f _L ~f _H. Here, f _LO is a low cutoff frequency for the purpose of only conventional DC blocking, f _L is a low cutoff frequency set so as not to interfere between received pulse signals according to the present invention, and f _H
Is the high cutoff frequency.

Next, the effect will be described with reference to the waveform diagram of FIG. In FIG. 3, the trailing edge of the received pulse signal has a distorted waveform in which sag rebound and undershoot overlap.
Threshold detection is normally used for signal detection of the received pulse, so the distortion level at the trailing edge of this received pulse exceeds the threshold level for the threshold level for the next received pulse detection. Need not to.

If the rebound level due to the sag is Vs, the level due to undershoot is Va, and the threshold level for detecting the received pulse is Vth, Vs + Va <Vth is satisfied at the time of the next received pulse detection. If so, there will be no interference between the received pulse signals.

The level Vs of the rebound caused by the sag is t = the rising edge of the received pulse waveform with the received pulse width being Tw.
If it is set to 0, it is expressed by the following formula 1 in the range of t> Tw. Here, τ is the time constant of the circuit that defines the low cutoff frequency f _L, and there is a relation of τ = 1 / (2πf _L ). Also, E: received pulse amplitude.

[0016]

[Equation 1]

On the other hand, the undershoot level Va is
Similarly, under the condition of t> Tw, it is expressed by the following formula 2. Here, α and β are values defined by the circuit element and the parasitic impedance.

[0018]

[Equation 2]

Since the above equation 2 is a vibration waveform, considering the worst condition, paying attention to the envelope curve of the amplitude of the undershoot,
A condition that satisfies the above expression Vs + Va <Vth may be obtained from this and the above expression 1. If Tr is the pulse repetition period that enables real-time distance measurement, then t = Tr
The above condition of Vs + Va <Vth can be replaced by the following expression (3).

[0020]

[Equation 3]

In this equation, the value on the left side becomes smaller as τ becomes smaller, that is, as f _L becomes higher. Therefore, the lower limit of f _L can be obtained from the above equation (3).

On the other hand, increasing the low cutoff frequency f _L causes the pulse amplitude to be attenuated. If the allowable attenuation ratio with respect to the original amplitude is A, and the rising time (time until the peak) of the leading edge of the received pulse signal is Tp,
The upper limit of the low cutoff frequency f _L can be obtained by the following equation (4).

[0023]

[Equation 4]

After all, by defining the low cutoff frequency f _L from τ satisfying the conditions of the equations 3 and 4, it is possible to prevent the distortion of the received pulse waveform from affecting the detection of the next received pulse. it can.

[0025]

As described above, according to the present invention, the signal pass bandwidth of the amplifying section is limited so that there is no interference between the received pulse signals, so that the distortion of the waveform of the received pulse signal is suppressed and the high speed is achieved. This has the effect of enabling real-time distance measurement for in-vehicle use.

[Brief description of drawings]

FIG. 1 is a block diagram of an in-vehicle distance measuring device showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a signal pass bandwidth of an amplification section of a vehicle-mounted distance measuring device showing an embodiment of the present invention.

FIG. 3 is a waveform diagram showing a relationship between received pulse signals of the vehicle-mounted distance measuring apparatus showing the embodiment of the invention.

FIG. 4 is a block diagram of a conventional distance measuring device.

[Explanation of symbols]

 1 Light Transmitter 2 Light Receiver 4 Distance Detector 5 Band-Limited Amplifier

Claims (1)

[Claims] 1. A light sending means for sending pulsed light, a light receiving means for receiving the pulsed light reflected by the reflector and returned from the reflector, an amplifying means for amplifying the received pulse signal, and this sending means. In a vehicle-mounted distance measuring device having a distance detecting means for detecting a distance to the reflector based on an optical pulse and a light receiving pulse, the pulse signal received does not interfere with the next light receiving pulse signal. Thus, the on-vehicle distance measuring device is characterized in that the signal pass bandwidth of the amplifying means is limited.