JPH06109842A - Distance detection apparatus - Google Patents

Abstract

PURPOSE:To measure the accurate photodetection timing of various photodetection signals by a method wherein a detection means which detects the photodetection state of a beam of reflected light and a judgment means which judges whether a photodetection signal is suitable for finding a distance up to an object are provided. CONSTITUTION:A signal processing unit 20 sends a signal to a light-transmitting part 24 from a timing control part 23, it emits light and a distance counter 22 starts a time measurement. A laser beam which has been reflected by, and returned from, a target object is converted into an electric signal by a photodetection part 25. The electric signal is amplified by an amplification part 26, and a detection part 27 detects the rise and the fall of the amplified electric signal. When the detection part 27 detects the rise of the received signal, the counter 22 is stopped and a counter 28 starts a time measurement. When the fall time is detected, the counter 28 is stopped. The counter 22 measures the time from transmission of a laser beam to reception of reflected light, and the counter 28 measures the pulse of a received pulse.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance detecting device for detecting a distance to an object ahead of a vehicle, for example.

[0002]

2. Description of the Related Art Conventionally, as a distance detecting device, for example, as disclosed in Japanese Unexamined Patent Publication No. 59-60271, the distance to a front object is determined based on the time until the pulsed light is sent forward and the reflected wave is received. It is general to detect the distance by obtaining In this case, in the time measurement, the time from the peak detection time of the transmitted pulse to the peak detection time of the reflected pulsed light is measured.

[0003]

However, in an actual vehicle, the reflected light does not have an ideal property for detecting a peak, so that the following problems occur. As shown in the areas 1 to 4 in FIG. 1, the intensity of the light beam has a distribution, and as shown in FIG. 2, depending on which area in FIG. 1 the reflector on the vehicle that reflects the light reflects the light. The pulse waveform shape of the reflected light changes.

In FIG. 2, reference numeral 10 is the time variation of the pulse intensity of the transmitted light, and 11, 12 and 13 are the variation in the intensity of the reflected light when there are reflectors in the regions 5, 6 and 7 of FIG. 1, respectively. Indicates. Reference numeral 11 in FIG. 2 shows a case where the intensity of the received pulsed light is too strong and saturation occurs in the photoelectric conversion signal, and 13 indicates that the intensity is too weak and the level of the photoelectric conversion signal is considerably lowered. Indicates. The distance R to the target object is R = T · C / 2, where T is the time from transmission to reception and C is the speed of light.

Normally, in detecting the distance to a front object, the time between the peaks of the transmission pulse and the reception pulse is detected as described above, and this peak has a predetermined slice level as a signal level as shown in FIG. Judgment is made based on whether or not it exceeds. In the example of FIG. 2, the slice levels are shown as 14, 15. Here, since the intensity of the transmission pulse 10 is constant, no error occurs in the measurement of the peak time. However, as described above, the intensity of the received light differs depending on which region the reflector on the vehicle reflects the light, or when the target is an object having a different reflection intensity from the vehicle reflector. As shown in, a difference of 20 to 30 nanoseconds occurs between the case where the photoelectric conversion signal of the received beam is 11 and the case where the photoelectric conversion signal is 13, and this difference appears as an error in the measurement distance. In order to eliminate such an error, it is possible to detect the peak position itself of the received signal, but it is meaningless to detect the peak position of the saturated signal.

Although it is necessary to control the input to the photoelectric converter in order to prevent the signal from being saturated,
The control is not suitable for high-speed measurement because it needs to control the mechanical system. Therefore, the present invention has been proposed in order to solve the above-mentioned drawbacks of the prior art, and the purpose thereof is to easily measure an accurate light reception timing even if there are various levels of received signals of reflected light. We propose a distance detector that can do this.

[0007]

According to the present invention for achieving the above object, a light beam is transmitted, reflected light from an object is received, and the reflected light from the object is received. In a distance detecting device for obtaining a distance, a detecting means for detecting a light receiving mode of a light receiving signal of the reflected light, and based on this mode, it is judged whether or not the light receiving signal is appropriate for obtaining a distance to the object. And a determining means.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. 3 and 4 are diagrams showing the principle of distance measurement according to the embodiment of the present invention. In the measurement principle of this embodiment, among the received signals obtained by receiving the reflected wave and photoelectrically converting it, only the signal of the proper level is selected, and the light receiving timing is calculated from the selected signal. The distance to the object to be measured is measured. Whether or not it is appropriate is determined by whether or not the received signal has a pulse width corresponding to the distance to the object. This is because the pulse width of the received signal is proportional to the approximate distance to the object.

The coarse distance to the object can be estimated from the time when the received signal reaches a certain level, as shown in FIG. In the example of FIG. 3, the pulse width varies depending on the intensity of the signal pulse, and therefore the distance to the object is T′C / 2, T ″.
It differs from C / 2 and T '"C / 2, but there is no problem because absolute accuracy is not required for rough judgments such as whether an object is in a short distance. Then, if the time until the rising of the received signal is T (where T represents a coarse distance to the object), there should be a pulse width of the received signal having an appropriate intensity at that distance. Since the width and the intensity level of the signal are relatively well proportional, since such an expected pulse width W _P is a function of time T, it should be expressed as W _P = W _P (T). _{If 1} ≈ T ₂ , then W _P (T ₁ )
= W _P (T ₂ ). Such a function is stored in advance, the rough distance to the object is calculated at the time when the received signal is detected, and the expected pulse width W _P (T) is estimated from the rough distance. Further, by accurately measuring the actual pulse width W _A of the received signal and comparing this W _A with W _P (T), it is determined whether or not the received signal is appropriate.

As shown in FIG. 4, the intensity signal of the transmitted light is set to 3
When it is set to 0, it is assumed that the intensity of the received reflected light is observed in the waveforms 31 to 37. Signals 31 to 33 indicate types of waveforms of received signals when an object is present at a relatively short distance. According to the method described with reference to FIG. 3, of these three signals, the signal 33 is judged to be inappropriate because the intensity level is too low for an object located at a short distance. Further, since the pulse width of the signal 31 is too large, it is determined that the signal is saturated and is inappropriate. Therefore, the signal 32 is determined to be appropriate.

On the other hand, when the signals 36 and 37 are received when the object is estimated to be at a relatively long distance, it is determined that the signal 36 is too strong because the pulse width of the signal 36 is too large for a long distance. Then, the signal 37 is adopted. The configuration of the distance measuring system according to the embodiment will be described with reference to FIG. In the figure, the light transmitting system includes a distance counter 22, a timing control unit 23, and a light transmitting unit 24. The light receiving system includes a light receiving unit 25, an amplification unit 26, a detection unit 27, and a distance counter 28. The clock unit 21 is the distance counter 2
Generate 2, 28 counting pulses. Signal processing unit 2
Reference numeral 0 includes a CPU and the like, and performs timing control and signal processing.

The signal processing unit 20 causes the timing control section 23 to cause the light transmitting section 24 to emit laser light and causes the distance counter 22 to start time measurement. The laser light reflected and returned to the target object is received by the light receiving unit 25 and converted into an electric signal. This electric signal is amplified by the amplification unit 26, and the detection unit 27 detects rising and falling of the amplified electric signal. This detection is performed by detecting the time point when the slice level is exceeded, as shown in FIG.

When the detection unit 27 detects the rising edge of the received signal, the detection unit 27 stops the counter 22 and also stops the counter 28.
Start the time measurement by. Furthermore, the detection unit 27
Stops the counter 28 when it detects the falling time. With these operations, as shown in FIG. 6, the counter 22 can measure the time from transmitting the laser light to receiving the reflected light, and the counter 28 can measure the pulse width of the received pulse.

The signal processing unit 20 takes in the rise time of the pulse, the pulse width, etc., distinguishes an inappropriate pulse from an appropriate pulse by the method described with reference to FIG. 3, and based on the appropriate pulse. Calculate the distance to an exact object. The above-mentioned expected pulse width W _P data is RAM2
9 are stored. As described above, according to this embodiment: Since only signals of the appropriate level are selected, accurate measurement can be performed. : Objects other than vehicle reflectors (eg road signs,
An effect that an improper signal from a signboard, etc.) can be removed is obtained.

The present invention can be variously modified without departing from the spirit thereof. First Modification : In the above embodiment, the present invention was applied to a fixed laser. The present invention can be applied to a scan type laser. However, in the scan type laser system, when the laser beam is scanned, the position of the beam with respect to the target object changes, and it is not stable that the object is captured at a portion having a high beam intensity or captured at a portion having a low beam intensity. That is, the scan type has a problem that the level changes more frequently than the fixed type. Therefore, the scan cycle and 1
The number of pulses emitted within the scan cycle is adjusted so that a plurality of reflected lights are received from the reflector. If such adjustment is performed, as shown in FIG. 7, a plurality of reflected light pulses can be received from one reflector within one period, and the optimum pulse can be selected from them by the above-mentioned method. To Second Modification : In the above-mentioned embodiment, the received signal determined to be inappropriate is ignored. In this variation,
It is intended to correct improper received signals and use them for distance measurement.

FIG. 8 shows the principle. That is, when it is determined that the pulse width is too small and inappropriate, the correction is performed so as to subtract the predetermined distance α, and when it is determined that the pulse width is too large and inappropriate, alpha is added. To correct. However, there is a high possibility that an error will always occur if always corrected, and therefore, what is apparently not reflected light from the vehicle reflector (for example, when the reflected light level from an object estimated to be a long distance is too strong) Remove from correction target.

[0017]

As described above, according to the distance detecting apparatus of the present invention, only an appropriate signal is used for distance detection based on the light reception mode of the vehicle height at half an hour, so that highly accurate distance measurement can be performed. It will be possible. Here, the light receiving mode is an approximate distance to an object and a width of a received pulse.

[Brief description of drawings]

FIG. 1 is a diagram showing an intensity distribution of a light beam used in Examples and conventional devices.

FIG. 2 is a diagram illustrating a defect of the conventional technique.

FIG. 3 is a diagram illustrating the principle of an embodiment of the present invention.

FIG. 4 is a diagram illustrating the principle of this embodiment.

FIG. 5 is a diagram illustrating the configuration of this embodiment.

FIG. 6 is a diagram for explaining the operation of the embodiment.

FIG. 7 is a diagram for explaining the operation of the first modified example.

FIG. 8 is a view for explaining the operation of the second modified example.

Claims (4)

[Claims] 1. A distance detection device that transmits a light beam, receives reflected light from an object, and obtains the distance to the object based on the time until the reflected light is received. A distance detection device comprising: a detection unit that detects a light reception mode; and a determination unit that determines whether or not a light reception signal is appropriate for obtaining the distance to the object based on this mode. 2. The distance detecting device according to claim 1, further comprising means for converting the received reflected light into an electric signal,
The said aspect is the time which detected the said electric signal, and the pulse width of the electric signal, The distance detection apparatus characterized by the above-mentioned. 3. The distance detecting device according to claim 2, wherein the determining means estimates the approximate distance to the object based on a time from a light beam transmission time to a time when the electric signal is received. And a storage means for storing in advance the relationship between the distance to the object and the expected pulse width of the electric signal, and determines whether or not it is appropriate based on the actual pulse width of the electric signal and the expected pulse width. A distance detection device characterized by: 4. The distance detecting device according to claim 1, wherein the laser beam is emitted while being scanned on a horizontal plane, and a plurality of reflected light pulses are received from one target object within one scan cycle. Distance detection device.