JP3193148B2 - Distance detection device - Google Patents

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, for example, a distance to an object ahead of a vehicle.

[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, a distance to a forward object is determined based on a time until a pulse light is transmitted forward and a reflected wave is received. In general, distance detection is performed by calculating In this case, in the time measurement, the time from the peak detection time of the transmission pulse to the peak detection time of the reflected pulse light is measured.

[0003]

However, in an actual vehicle, since the reflected light does not have an ideal property for detecting a peak, the following problem occurs. As shown in the regions 1 to 4 in FIG. 1, the intensity of the light beam has a distribution, and depending on which region in FIG. 1 the reflector on the vehicle that reflects the light reflects light, as shown in FIG. The pulse waveform shape of the reflected light fluctuates.

In FIG. 2, reference numeral 10 denotes a temporal change in the pulse intensity of the transmitted light, and reference numerals 11, 12, and 13 denote a change in the intensity of the reflected light when the reflectors are located in regions 5, 6, and 7 in FIG. Is shown. 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. On the contrary, 13 shows that the intensity is too weak and the level of the photoelectric conversion signal drops considerably. Is shown. The distance R to the target object is expressed as R = TC / 2, where T represents the time from transmission to reception and C represents the speed of light.

Normally, the distance to the front object is detected by detecting the time between the peak of the transmission pulse and the peak of the reception pulse as described above. This peak, as shown in FIG. It is determined based on whether or not it has been exceeded. In the example of FIG. 2, the slice levels are indicated as 14 and 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 the area of the light reflected by the reflector on the vehicle or the case where the target is an object having a different reflection intensity from the vehicle reflector. As shown in (1), a difference of 20 to 30 nanoseconds occurs between the case where the photoelectric conversion signal of the received light beam is 11 and the case where the photoelectric conversion signal is 13 and this appears as an error in the measurement distance. To eliminate such errors, it is conceivable to detect the peak position itself of the received signal, but it is meaningless to detect the peak position of a 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 was not suitable for high-speed measurement because it needed to control a mechanical system. Therefore, the present invention has been proposed in order to solve the above-mentioned drawbacks of the prior art, and an object of the present invention is to easily measure an accurate light receiving timing even when there are various kinds of reflected light reception signals. We propose a distance detection device that can be used.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for transmitting a light beam, receiving reflected light from an object, and determining the distance to the object based on the time required to receive the reflected light. In a distance detecting device for obtaining a distance, a detecting means for detecting a reception time and a pulse width of the electric signal representing the reflected light, and receiving the electric signal from a transmission time of the light beam.
Estimated distance to the object based on the time to the time
Estimating means for estimating the distance to the object and the electricity
A memory that stores in advance the relationship with the expected pulse width of the signal
Step and the expected pulse width corresponding to the estimated distance is stored.
Means to estimate the actual electrical signal pulse width and the expected
Based on the pulse width and the estimated distance to the object
Determining means for determining whether the distance is appropriate.

[0008]

Preferred embodiments 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. The measurement principle of this embodiment is that, from among the received signals obtained by receiving the reflected wave and photoelectrically converting it, only those of an appropriate level are selected, and the light receiving timing is calculated from the selected signal. , And measures the distance to the object to be measured. Whether it is appropriate or not is determined based on 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 ''
Although it differs from C / 2, T '"C / 2, there is no problem because absolute accuracy is not required for rough judgments such as whether or not an object is at a short distance. Assuming that the time until the rise of the received signal is T (where T represents a coarse distance to the object), there must be a pulse width of the received signal having an appropriate intensity at that distance. Because the width and the signal strength level are relatively well proportional, such an expected pulse width W _P will be a function of time T and should be expressed as W _P = W _P (T). if the _{1 ≒ T 2, W P (} T 1)
= W _P (T ₂ ). Such a function is stored in advance, and when a received signal is detected, a rough distance to the object is calculated, and an estimated 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.

[0010] As shown in FIG.
When it is set to 0, it is assumed that the intensity of the received reflected light is observed in a waveform of 31 to 37. Signals 31 to 33 indicate the types of waveforms of the received signal when an object is located at a relatively short distance. According to the method described with reference to FIG. 3, out of these three signals, the signal 33 is determined to be inappropriate because the intensity level is too low for an object at a short distance. In addition, since the pulse width of the signal 31 is too large, it is determined that the signal is saturated, and it is determined that the signal is inappropriate. Therefore, it is determined that the signal 32 is appropriate.

On the other hand, when the signals 36 and 37 are received when it is estimated that an object is located 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. The signal 37 is ignored. The configuration of the distance measuring system according to the embodiment will be described with reference to FIG. In the figure, the light transmission system includes a distance counter 22, a timing control unit 23, and a light transmission unit 24. The light receiving system includes a light receiving unit 25, an amplifier 26, a detector 27, and a distance counter 28. The clock unit 21 is a distance counter 2
Generate 2,28 counting pulses. Signal processing unit 2
0 includes a CPU and the like, and performs timing control, signal processing, and the like.

The signal processing unit 20 causes the timing control unit 23 to emit a laser beam to the light transmitting unit 24 and causes the distance counter 22 to start time measurement. The laser light reflected back from the target object is received by the light receiving unit 25 and converted into an electric signal. This electric signal is amplified by the amplifier 26, and the detector 27 detects the rise and fall of the amplified electric signal. This detection is performed by detecting a time point when the slice level is exceeded, as shown in FIG.

When detecting the rising edge of the received signal, the detector 27 stops the counter 22 and sets the counter 28
To start time measurement. Further, the detection unit 27
Stops the counter 28 when the falling time is detected. By these operations, as shown in FIG. 6, the counter 22 measures 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 captures the rising time of the pulse, the pulse width, and the like, and distinguishes an inappropriate pulse from an appropriate pulse by the method described with reference to FIG. Calculate the distance to the exact object. The predicted pulse width W _P data described above is stored in RAM2.
9. As described above, according to the present embodiment,: Only signals at an appropriate level are selected, so that accurate measurement can be performed. : Objects other than vehicle reflectors (eg, road signs,
An effect that an inappropriate signal from a signboard or the like can be removed is obtained.

The present invention can be variously modified without departing from the gist thereof. First Modification : In the above embodiment, the present invention is applied to a fixed laser. The present invention is also applicable to a scanning laser. However, in the scanning laser system, when the laser beam is scanned, the position of the beam with respect to the target object changes, and the object is not captured or stabilized at a portion where the beam intensity is high or at a portion where the beam intensity is low. That is, the scan type has a problem that the frequency of the level change is higher than that of the fixed type. Therefore, the scan cycle and 1
The number of pulses emitted during the scan period is adjusted to receive a plurality of reflected lights from the reflector. By performing such adjustment, as shown in FIG. 7, a plurality of reflected light pulses can be received within one period from one reflector, and an optimum pulse is selected from them by the above-described method. To Second Modification : In the above-described embodiment, a received signal determined to be inappropriate is ignored. In this variation,
Incorrect reception signals are corrected and used 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 made so that the predetermined distance α is subtracted, and when it is determined that the pulse width is too inappropriate and alpha is added. Correction as follows. However, since there is a high possibility that an error will occur if the correction is always made, it is apparent that the reflected light is not reflected 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 the correction target.

[0017]

As described above, according to the distance detecting device of the present invention, the reception time of the electric signal representing the reflected light and the pulse
Signal width, and receives an electrical signal from the light beam transmission time.
The estimated distance to the object based on the time
The expected pulse width corresponding to the estimated distance and the actual electrical signal
The estimated distance to the object based on the pulse width of the signal
By determining whether or not the distance is appropriate , highly accurate distance measurement can be performed.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining a drawback of the related art.

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

FIG. 4 is a view for explaining the principle of this embodiment.

FIG. 5 is a view for explaining the configuration of this embodiment.

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

FIG. 7 is a diagram illustrating an operation of a first modified example.

FIG. 8 is a diagram illustrating an operation of a second modification.

Claims (2)

(57) [Claims] 1. A distance detecting device for transmitting a light beam, receiving reflected light from an object, and determining a distance to the object based on a time required to receive the reflected light, wherein an electric signal representing the reflected light is provided. Detecting means for detecting the reception time and pulse width of the electric signal, and the time from the transmission time of the light beam to the time at which the electric signal is received.
The estimated distance to the object based on the time at
Estimating means for calculating a distance between the object and the expected pulse width of the electric signal.
A storage unit for storing the relationship in advance, and an expected pulse width corresponding to the estimated distance is stored in the storage unit.
From the actual pulse width of the electrical signal and the expected pulse
The estimated distance is based on the width and the distance to the object.
And a determination unit for determining whether the distance is appropriate. 2. The distance detecting apparatus according to claim 1, wherein the laser beam is irradiated while being scanned on a horizontal plane, and a plurality of reflected light pulses are received within one scan cycle from one target object. Distance detection device.