JPH06109841A - Distance detection method - Google Patents

Abstract

PURPOSE:To accurately measure a photodetection timing by a method wherein the middle point of the pulse width of a pulse signal obtained by photoelectrically converting a beam of reflected light is used as the photodetection timing used to decide a distance up to an object. CONSTITUTION:A light-transmitting system is composed of a distance counter 22, a timing control part 23 and a light-transmitting part 24, and a photodetection system is composed of a photodetection part 25, an amplification part 26, a detection part 27 and a distance counter 28. A clock part 21 generates counting pulses for the counters 22, 28. A signal processing unit 20 instructs the light-transmitting part 24 to emit light by a signal from the control part 23 and instructs the counter 22 to start a time measurement. A laser beam which has been reflected by, and returned from, a target object is received by the photodetection part 25, and it is converted into an electric signal. The electric signal is amplified by the amplification part 26, and the detection part 27 detects the rise and the fall of the amplified electric signal. The counter 22 measures the time which elapses until the laser beam is received since it has been transmitted, and the counter 28 measures the pulse width of the 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 method for detecting a distance to a front object of a vehicle.

[0002]

2. Description of the Related Art Conventionally, as a distance detecting method, for example, as disclosed in Japanese Patent Laid-Open 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 the area of the light reflected by the reflector on the vehicle. Therefore, as shown in FIG.
A difference of α seconds occurs between the case of 1 and the case of 13, which appears as an error in the measurement distance.

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 eliminate the above-mentioned drawbacks of the prior art, and an object thereof is to propose a distance detection method capable of easily measuring an accurate light reception timing.

[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 the distance detecting method for obtaining the distance, the intermediate point of the pulse width of the pulse signal obtained by photoelectrically converting the reflected light is set as the light receiving timing for determining the distance to the object.

According to another aspect of the present invention for achieving the above object, the distance to the object is determined based on the time until the light beam is transmitted, the reflected light from the object is received, and the reflected light is received. In the method for detecting the distance, the pulse signal obtained by photoelectrically converting the reflected light is compared with a plurality of threshold values, and the time point at which the pulse signal exceeds the highest level threshold value determines the distance to the object. This is the light receiving timing for the operation.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Three preferred embodiments of the present invention will be described below with reference to the accompanying drawings. <First Embodiment> FIG. 3 is a diagram showing the principle of distance measurement according to the first embodiment of the present invention. In the measurement of the first embodiment, the measurement method is changed depending on whether the received signal obtained by receiving the reflected wave and photoelectrically converting it is saturated. Whether or not it is saturated is determined to be saturated if the width a _{1 of the} received pulse (pulse width for the slice level 15) is larger than a predetermined value, and is not saturated if the width a ₁ is smaller than a predetermined value. If it is not saturated, it is determined that there is a peak at the intermediate position of the pulse width a ₂ of the received pulse. Therefore, the time T until received from sending becomes _{T = T 2 + a 2/} 2. Here, T ₂ is the time interval from the transmission to the time when the level of the received pulse exceeds the slice level 15. On the other hand, when the pulse width is large, that is, when the pulse width is saturated, T = T ₁ + b. Here, T ₁ is the time interval from transmission to the time when the level of the received pulse exceeds the slice level 15. As is clear from the example of FIG. 2, the rising edge of the saturated pulse is steep, and thus T ₂ > T ₁ . Then, b is the average value of the distance from the rising edge of the saturated signal to the center position of the non-saturated signal pulse. Such b can be experimentally obtained in advance.

According to the method of the first embodiment, the following advantages can be obtained. : Enables highly accurate measurement independent of the level change of the received signal. : Real-time measurement is possible because there is no need to adjust the level of the received signal even if the received light intensity of the reflected light changes. The configuration of the distance measuring system according to the first embodiment will be described with reference to FIG.

In the figure, the light transmitting system is a distance counter 22.
And a timing controller 23 and a light transmitter 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 generates counting pulses for the distance counters 22 and 28. The signal processing unit 20 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. 5, the counter 22 measures the time (T ₁ ) from the transmission of the laser light to the reception of the reflected light, and the counter 28 determines the pulse width (a) of the reception pulse. ₁ and a ₂ ) can be measured.

The signal processing unit 20 takes in these T ₁ , a ₁ (a ₂ ) and the like, and detects the distance to the target object by the method described with reference to FIG. <Modification of First Embodiment> In the first embodiment, the pulse width of the photoelectric conversion signal of the received reflected light is used to determine whether the received signal is saturated. It can also be determined by the inclination of. As a method of measuring the slope, as shown in FIG. 6, two thresholds (30, 31) having different levels are set in advance, and
In this system, one more counter is added, and this counter measures the time T ₂ from the time when the signal exceeds the threshold 31 until the time when the signal exceeds the threshold 30, and when this T ₂ exceeds a predetermined value (in FIG. 6, , T ₂ > predetermined value), the inclination is small, and if the inclination is not exceeded (T ₂ <predetermined value in FIG. 6), the inclination is determined to be large. <Second Embodiment> In the first embodiment, the case where the received signal is saturated can be dealt with, but in the second embodiment, the waveform of the received signal is extremely saturated and distorted. Applies if not reached. In such a case, attention is paid to the fact that the peak position of the received signal is substantially constant regardless of the level, and the reception distance is improved by applying a reception trigger at a point as close to the peak position as possible.

7 and 8 explain the principle of the second embodiment. In the figure, it is assumed that the signal level becomes 33 or 34 depending on the intensity of the reflected light. If the received signal is not saturated, as is apparent from FIG. 7, there is little difference between the peak positions of the received signal. Therefore, the peak positions of the two signals 33 and 34 should originally be observed at the same time. However, in the prior art, the threshold level is set to be, for example, l ₁ alone, so that the peak position shift between the signals 33 and 34 is d ₁ . Therefore, a threshold value of l ₄ is applied to the signal 33.
And a threshold l ₂ for the signal 34,
As shown in, the deviation between the peak positions measured for each of the signals 33 and 34 is a small d ₂ .

FIG. 9 is a block diagram of the measuring system of the second embodiment. In the figure, the light transmission system is composed of a transmission circuit 41.
And a light transmitting section 43, and the light receiving system includes a light receiving section 44, an amplifying section 45, and a detecting section 46. When the signal processing unit 40 having a CPU inside sends a control signal to the transmission circuit 41, the transmission circuit 41 causes the light transmitting section 43 to emit a laser beam, and at the same time sends a start command to the timing control section 42 to cause a counter. The count up in 47a to 47c ... Is started. This is the time T ₁ in FIG.
The counting of T ₂ and T ₃ is started.

The laser light reflected and returned to the target object is received by the light receiving section 44 and converted into an electric signal. This electric signal is amplified by the amplification unit 45, and the detection unit 46 detects the rising edge of the amplified electric signal. The detection unit 46 is
The same number of comparators 46a to 46c as the number of counters 47
Have ... Comparator 46a, 46b, 46c ... it is _{l 1, l 2, l 3} ... have, respectively, to generate a stop command at the time of receiving the received signal exceeds the slice level of the corresponding respective counter 47a, 47b, 47c ...

If the system has finished receiving the signal 33 of FIG. 8, the counters 47a, 47b, 47c, 47 are detected.
Times T ₁ , T ₂ , T ₃ , T ₄ , and ∞ are stored in d (not shown) and 47e (not shown), respectively. Where ∞
Is a value that means a large time width. Because the threshold l
_This is because, for ₅ , the stop signal is not generated from the comparator 46e. The signal processing unit 40 is
Of T ₁ , T ₂ , T ₃ , and T ₄ , the output of the counter corresponding to the threshold with the highest slice level, that is, T ₄ is adopted.

If the system receives the signal 34, the counters 47a, 47b, 47c, 47d (not shown), 47e (not shown) will have times T ₁ , T ₂ , T respectively.
_3, ∞, ∞ is stored, the processing unit 40 as the measurement result, among _{T 1, T 2, T 3} , employing the most output of the slice level counter corresponding to the high threshold of, i.e. T _2. <Modification of Second Embodiment> In the second embodiment, the counters start counting up at the same time, but these counters may be sequentially started. That is, in FIG.
If the comparator 46a detects the threshold value l ₁ while receiving the signal 33, the counting of the counter of the counter 47a is stopped and the counting of the counter 47b is started at the same time. Next, when the comparator 46b detects the threshold value l ₂ , the counting of the counter of the counter 47b is stopped and the counting of the counter 47c is started at the same time. Next, when the comparator 46c detects the threshold value l ₃ , the counting of the counter of the counter 47c is stopped and at the same time, the counting of the counter 47d is started. Assuming that the times stored in the respective counters are t ₁ , t ₂ , t ₃ , t _4, ...
The reception time T for the signal 33 is T = t ₁ + t ₂ + t ₃ + t ₄ . Further, in order to further improve the accuracy, this modification may be further modified so that T = α ₁ · t ₁ + α ₂ · t ₂ + α ₃ · t ₃ + α ₄ · t ₄ . Here, α ₁ , α ₂ , α ₃ , and α ₄ are correction coefficients corresponding to the respective threshold levels. <Third Embodiment> The third embodiment is an improvement of the method for accurately detecting the center of the received signal (signal after photoelectric conversion).

In the third embodiment, since the intensity of the light beam is generally attenuated in proportion to the fourth power of the distance, a threshold having a downward-sloping curve whose slice level decreases with time is adopted. . The third embodiment relates to a measuring system having a curve having such a characteristic as a threshold value. FIG. 10 illustrates the principle of this third embodiment. In the figure, reference numeral 52 denotes a signal after photoelectric conversion of reflected light. The threshold function used to detect this signal has the characteristics shown at 50. Then, the peak position 53 of the signal 52 is determined by the internal point P _{c of the} straight line 1 (51) connecting the _two points P ₁ and P ₂ where the threshold 50 intersects the signal 52.
Can be approximated by. If the point Pc can be defined as an internal division point of m: n of the line segment P ₁ P ₂ , then P _c = (n · P ₁ + m · P ₂ ) / (m + n).

By the way, the waveform of the received signal is deformed according to the distance to the object, that is, its peak position changes. In other words, the peak position P _c should be modified by varying the internal division ratio according to the distance to the object. If the distance to the object is reflected in the waveform of the received signal, it is reflected in the slope of the line segment P ₁ P ₂ . In other words, if the two points are P ₁ (t ₁ , v ₁ ) and P ₂ (t ₂ , v ₂ ), the slope k of the line segment P ₁ P ₂ is k = (v ₂ −v ₁ ) / (T ₂ −t ₁ ) and m is defined as a function of k. In the third embodiment, m = 1 / 2 (1-k) n = 1-m. As an example, k = 0 → m = 1/2, n = 1/2 k = ∞ → m = 0, n = 1.

FIG. 11 is a block diagram of the measuring system of the third embodiment. The counter 70 calculates the time t _{1 of} FIG.
The counter 71 measures the time t ₂ , respectively. Also, A / D
The converter 73 A / D-converts the signal strength at times t ₁ and t ₂ in FIG. 9 and sends it to the unit 60. Unit 60
Calculates the slope k from these data. Then, the RAM 72 is searched based on the inclination k to obtain the internal division ratio data m and n.

[0023]

As described above, according to the distance detecting method of the present invention, accurate light receiving timing can be easily determined. In particular, according to the detection method of the third term, the distance can be measured even when the reflected light is too strong and the signal is saturated.

Further, in particular, according to the detection method of the fourth term, the light reception timing can be determined more strictly.

[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 for explaining the principle of the first embodiment of the present invention.

FIG. 4 is a diagram illustrating the configuration of the first embodiment.

FIG. 5 is a diagram for explaining the operation of the first embodiment.

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

FIG. 7 is a diagram for explaining the operation principle of the second embodiment.

FIG. 8 is a diagram for explaining the operation of the second embodiment.

FIG. 9 is a diagram illustrating the configuration of the second embodiment.

FIG. 10 is a diagram for explaining the principle of the third embodiment of the present invention. .

FIG. 11 is a diagram illustrating a configuration of a third embodiment.

Claims (5)

[Claims] 1. A distance detection method, wherein a reflected light from an object is sent out, a reflected light from an object is received, and a distance to the object is obtained based on a time until the reflected light is received, wherein the reflected light is photoelectrically converted. A distance detecting method in which the intermediate point of the pulse width of the pulse signal obtained as described above is used as the light receiving timing in determining the distance to the object. 2. The distance detecting method according to claim 1, wherein the pulse width of the pulse signal is a time width exceeding a predetermined threshold level. 3. The distance detecting method according to claim 1, wherein when the pulse width of the pulse signal is a predetermined value or more,
A distance detecting method, characterized in that a light reception timing is a time point obtained by adding a predetermined time from a rising time point of the pulse signal. 4. The distance detection method according to claim 2, wherein the threshold level is set so as to decrease with the lapse of measurement time, and the light reception timing is set according to the slope between the two points where the pulse signal crosses the threshold level. A method for detecting a distance, which comprises: 5. A distance detection method for detecting a distance to the object based on a time until a reflected light from an object is received by receiving a reflected light from the light beam and the reflected light is photoelectrically converted. A distance detection method in which the pulse signal obtained in this manner is compared with a plurality of threshold values, and the time when the pulse signal exceeds the highest level threshold value is used as the light reception timing for determining the distance to the object.