JP3151066B2 - 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 by the regions 1 to 4 in FIG. 1, the intensity of the light beam has a distribution, and the pulse shape of the reflected light depends on which region of the reflector in FIG. fluctuate.

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.

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. Therefore, as shown in FIG.
In the case of 1 and the case of 13, a difference of 20 to 30 nanoseconds occurs, which appears as an error of 3 to 4.5 m 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 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 propose a distance measuring apparatus which eliminates a measurement error caused by a difference in the intensity of a received pulse. .

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems and achieve the object, a distance detecting device according to the present invention transmits a light beam and receives reflected light from an object.
In a distance detection device including a calculation unit that calculates a distance to the object based on a time until the reflected light is received, an intensity detection unit that detects an intensity of the reflected light,
Peak detection means for detecting the peak of the intensity of the reflected light;
The distance to the object, after sending the light beam,
Based on the time to peak detected by the peak detection means
Distance calculating means for calculating based on the
Depending on the intensity of the reflected light at the peak detected
Correction means for correcting the distance to the object calculated by the calculation means . With such a configuration
And the distance without being affected by the difference in the intensity of the received light
The measurement can be made personally. In addition, the reflected light intensity
Accurate to the object, regardless of whether or not a sum has occurred
Distance is required.

[0008]

[0009]

[0010]

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Four preferred embodiments of the present invention will be described below with reference to the accompanying drawings. <First Embodiment> FIG. 3 is a block diagram of a distance measuring system according to a first embodiment of the present invention. In FIG.
The light beam pulse emitted from 02 is irradiated on the forward object (target) 104 via the optical system 103. The time of irradiation is controlled by the computer 100. That is, when the computer 100 sends a transmission command to the transmission circuit 101, the transmission circuit 101
To excite. The transmission circuit 101 sends a time measurement start command to the counter 105.

A reflected wave of light applied to the object 104 is received by a photoelectric converter such as a photo sensor 109 via a light receiving optical system 107. The electric signal is a logarithmic compression amplifier 11
The range is widened by logarithmic conversion by 0. This wider range expands the dynamic range and prevents signal saturation in subsequent stages. Low level cutter 113
Removes noise by removing low level signals. The level to be cut is controlled by the timing control circuit 106 according to the distance.

The signal from which the low-level component has been cut is sent to a differentiating circuit 111. This differentiating circuit 111 detects a peak as shown in FIG. 4B by differentiating the signal. The detected peak signal is sent to a hysteresis comparator 112, where only sufficiently large peaks are selected. FIG. 5 shows a hysteresis characteristic of the comparator 112. When the peak is detected in this manner, a stop command is issued to the counter 05, whereby the time measurement for distance measurement ends.

Thus, after the peak is detected by the differentiating circuit, only those having only a peak of a predetermined size or more are recognized as reflected light by the hysteresis comparator, so that the measuring accuracy is improved. <Second Embodiment> The second embodiment shown in FIG. 6 is different from the first embodiment of FIG.
14 and an A / D converter 115 are added.

FIG. 7 shows the measurement principle of the second embodiment.
According to the method of the first embodiment, if already generated saturation the input signal to the differentiating circuit 111, erroneously detected as a peak at t ₁ in FIG. However, the actual peak should the t ₂ time in FIG. The second embodiment focuses on the point that the time between times t ₁ and t ₂ is related to the magnitude p of the peak level of the saturation signal. In other words, the computer 100 previously stores the correlation between the magnitude p of the saturation level and the delay time (= t ₁ −t ₂ ) in a predetermined memory.

Therefore, in the system shown in FIG. 6, the comparator 112 of the first embodiment detects a peak having a predetermined magnitude and immediately sends a stop command to the counter 105.
A hold command is sent to the sample and hold circuit 114, and the sample and hold is performed for A / D conversion of the input signal. The held signal is A / D-converted by the converter 115, and digital data as shown in FIG. Computer 100, based on the digital data from the peak level p and peak time t ₁ Tokyo, read the time t ₂ from the memory. At time t ₂ , the computer 100 determines the timing at which the stop command should be issued to the counter 105 by the comparator 11.
Inform 2

Thus, according to the second embodiment, even when saturation occurs, the saturation level is estimated based on the magnitude of the peak level, thereby correcting the time t ₁ calculated based on the saturation signal. As a result, an accurate time t ₂ can be obtained, and the distance measurement accuracy can be improved. <Third Embodiment> The system of the third embodiment is characterized in that the intensity of outgoing light is controlled so that the level of a received signal becomes appropriate. Therefore, as compared with the first embodiment, the system of FIG. 8 is provided with a sample-and-hold circuit 114 and an A / D converter 115 so that the level of the received signal can be grasped digitally.

That is, in FIG.
Always converts the value of the received signal into a digital value for the sample and hold circuit 114 and the A / D converter 115, and monitors the level. If an excessively low signal level or an excessively saturated signal level is detected, the computer 100 sends a transmission light level control signal to the laser 02 via the transmission circuit 201. For example, when the received signal level is low, the transmitted light intensity is increased, and when the received signal level is opposite, it is decreased.

Accordingly, the intensity of the transmitted light is controlled so that the received signal does not become saturated and does not become excessively low, so that accurate distance measurement can be performed. <Fourth Embodiment> In the fourth embodiment, the amount of received light is controlled before the photoelectric conversion is performed so that the received signal becomes appropriate. To this end, the system according to the fourth embodiment includes an electro-optic modulator 108 capable of controlling the amount of transmitted light by an electric signal, as shown in FIG.

The modulator 108 controls the time for transmitting light and the time for transmitting light.
Controls the ratio (duty ratio) of the cutoff time. FIG.
0 indicates a change characteristic of the duty ratio. This change characteristic is
Basically, it has a characteristic that increases in proportion to the fourth power of time t.
I do. Theoretically, the amount of received light is inverse to the fourth power of the distance to the object.
Proportional. Since distance and time are proportional, the above characteristic is t ^Four
To be proportional to Incidentally, the laser 102 is excited.
Time (t₀The duty ratio in) is
Duty ratio to make the time width for transmitting
Is initialized to be zero.

[0021]

As described above, according to the present invention,
The distance measurement can be accurately performed without being affected by the difference in the intensity of the received light. Also, the reflected light intensity is saturated.
The exact distance to the object, whether or not
Separation is required.

[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 a configuration of a first example of the present invention.

FIG. 4 is a view for explaining the operation of the differentiating circuit in the first embodiment.

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

FIG. 6 is a diagram illustrating a configuration of a second example of the present invention.

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

FIG. 8 is a view for explaining the configuration of a third embodiment of the present invention.

FIG. 9 is a diagram for explaining the configuration of a fourth embodiment of the present invention. .

FIG. 10 is a diagram for explaining duty characteristics of the fourth embodiment.

Continuation of front page (56) References JP-A-63-81289 (JP, A) JP-A-3-160389 (JP, A) JP-A-1-197684 (JP, A) JP-A-3-4190 (JP) JP-A-4-339289 (JP, A) JP-A-3-73880 (JP, A) JP-A-4-49890 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB G01S 7/48-7/51 G01S 17/00-17/95

Claims (1)

(57) [Claims] 1. A distance detecting device comprising a calculating means for transmitting a light beam, receiving reflected light from an object, and calculating a distance to the object based on a time required to receive the reflected light. Intensity detecting means for detecting the intensity of the reflected light, and peak detecting means for detecting the peak of the intensity of the reflected light
And the distance to the object , before sending the light beam.
Time to the peak detected by the peak detection means
Distance calculating means for calculating based on the peak value,
A correction unit configured to correct a distance to the object calculated by the calculation unit in accordance with an intensity of the reflected light .