JPH07191143A - Distance measuring device - Google Patents

Abstract

PURPOSE:To eliminate a measurement error caused in accordance with an intensity change and a saturation degree of a light receiving pulse signal due to dispersion of radiated laser beams by providing a time correcting part for applying specified correction to a required time measured by a time measuring part. CONSTITUTION:A start pulse is outputted from a pulse generating part 21 of a time measuring unit 20 to an LD drive circuit 9 of a laser radar head 1. Then, the circuit 9 drives an LD being a light emitting element 2 by means of a trigger of the start pulse, and the laser pulse is received by either or both of light receiving elements 3, 4 to generate a specified output current which is amplified by a light receiving circuit 10 and outputs a stop pulse to a time measuring part 22. The measuring part 22 measures a time interval between a start pulse from the pulse generating part 21 and a stop pulse from the light receiving circuit 10 and outputs it as a time data to a distance measuring part 31, which calculates a distance to a preceding vehicle based on the time data to output it as a distance data to a control unit ASC 34.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical distance measuring device mounted on a vehicle and useful for measuring the distance to a preceding vehicle or an obstacle existing in the traveling direction of the vehicle.

[0002]

2. Description of the Related Art Recently, as a distance measuring device for detecting a preceding vehicle or an obstacle existing in the traveling direction of the vehicle and measuring a distance to the preceding vehicle or the obstacle, an optical distance using a laser beam is used. Many measuring devices are used.

Generally, this type of laser distance measuring apparatus irradiates a distance measuring object with a laser beam of a single short pulse, detects the reflected light thereof, and transmits the laser light and receives the reflected light. Since the time interval between is the round trip time of light, distance measurement is performed by measuring it.

However, the reflected light reflected from the object to be measured and captured by the distance measuring device is inevitably attenuated and contains noise. Therefore, in order to avoid erroneous distance measurement due to the noise, the receiving circuit should be provided. It is necessary to accurately extract only the signal component by using a wave height discriminator having a predetermined threshold value.

Therefore, a conventional general laser distance measuring device has such a signal processing circuit as a transmitting and receiving circuit,
The time intervals of the rising points discriminated by the respective wave heights are measured (see, for example, Japanese Patent Laid-Open No. 62-134584).

[0006]

However, like the conventional laser distance measuring device, when the received signal is timed at the time intervals of the rising points at which the wave height is discriminated at a certain reference level, the wave height discriminator. Since the reference value of is constant, if the intensity of the received light with a Gaussian time waveform changes, the rising point of the pulse height discrimination changes with time.
(I'll be late). Normally, the intensity of the transmitted light can be made constant, but the received light greatly changes depending on the degree of diffusion of light corresponding to the distance to the object to be measured and the passage rate of air in the middle, so that as shown in FIG. The rising point changes in an inclined shape from the weakest rising part that can be separated from the noise of the received light to the peak part of the maximum intensity.

Therefore, the distance measuring accuracy of the conventional laser type distance measuring device is determined by the rising time according to the light receiving intensity of the pulsed laser light used for the distance measuring, and there is a problem that the distance measuring cannot be performed with high accuracy.

[0008]

The invention described in each of claims 1 to 4 of the present application has been made for the purpose of solving the above-mentioned conventional problems, and is configured as follows. ing.

(1) Structure of the Invention According to Claim 1 The distance measuring device of the present invention includes: a light emitting section which emits a pulse laser beam toward an object; and a pulse laser beam which is emitted from the light emitting section. The light receiving section that receives the pulsed laser light reflected through the object and outputs the light receiving pulse signal, and the reflection laser when the level of the light receiving pulse signal output from the light receiving section exceeds a predetermined reference level. A time measuring unit that determines the arrival time of light and measures the required time from the laser light emission time of the light emitting unit to the arrival time, and the light emitting unit based on the required time measured by the time measuring unit or A distance measuring device comprising a distance measuring unit for measuring a distance from a light receiving unit to an object, characterized in that a time correction unit for adding a predetermined correction to the required time measured by the time measuring unit is provided. There is.

(2) Configuration of the Invention According to Claim 2 The distance measuring device according to the invention is based on the configuration of the invention according to claim 1, in which the time correction section is output from the light emitting section. It is characterized in that the level of the received light pulse signal is compared with a predetermined reference level, and the correction time is reduced as the pulse width of the received light pulse signal is larger than the reference level.

(3) Structure of the Invention According to Claim 3 The distance measuring device according to the invention is based on the structure of the invention according to claim 1 or 2, and in the same structure, a light receiving pulse signal output from the light receiving section. The saturation determining unit for determining the saturation state is provided, and when the saturation state of the light receiving pulse signal is determined, the correction operation for the required time by the time correction unit is canceled.

(4) Structure of the Invention of Claim 4 The distance measuring device of the invention is based on the structure of the invention of claim 1 or 2, and in the same structure, the required time measured by the time measuring unit. When is large, the correction time of the time correction unit is made longer than when it is small.

[0013]

The invention described in each of the above-mentioned claims 1 to 4 of the present application operates as follows corresponding to each of the constitutions.

(1) Operation of the Invention According to Claim 1 In the configuration of the distance measuring device of the invention, as described above, the light emitting section for emitting the pulsed laser beam toward the object and the light emitting section for emitting the pulsed laser beam. Of the pulsed laser light, which receives the pulsed laser light reflected through the object and outputs a received light pulse signal, and the level of the received light pulse signal output from the light receiver exceeds a predetermined reference level. A time measuring unit that determines the time point as the arrival time of the reflected laser light and measures the required time from the laser light emission time of the light emitting unit to the arrival time, and based on the necessary time measured by the time measuring unit. And a distance measuring device including a distance measuring unit that measures a distance from the light emitting unit or the light receiving unit to an object, and a time correcting unit that adds a predetermined correction to the required time measured by the time measuring unit is provided. And The time required for the laser light to reach the light receiving unit from the light emitting unit measured by the time measuring unit is appropriately corrected.

Therefore, it is possible to measure the distance accurately regardless of the difference in the received light intensity due to the difference in the diffusion degree of the laser light due to the distance or the distance.

(2) Action of the invention described in claim 2 In the configuration of the distance measuring device of the invention, when the action similar to that of the invention described in claim 1 is realized by the basic configuration, more specifically, the time is concerned. The correction unit is configured to compare the level of the light receiving pulse signal output from the light emitting unit with a predetermined reference level, and to reduce the correction time when the pulse width of the light receiving pulse signal is larger than the reference level. Therefore, when the received light intensity is high and the measurement error is small, the correction is small, and when the received light intensity is low and the measurement error is large, the correction is large, and more accurate correction is possible.

(3) Operation of the invention according to claim 3 In the structure of the distance measuring device of the invention, when the same operation as the invention according to claim 1 or 2 is realized by the basic structure, the distance measuring device further includes A saturation determination unit that determines the saturation state of the received light receiving pulse signal is provided, and when the saturation state of the received light receiving pulse signal is determined, the correction operation of the required time by the time correction unit is canceled, so it is too close. The measurement operation of the measurement system is simplified when the received light pulse signal is saturated and there is no time delay when the received light intensity is very strong such as at a distance.

(4) Action of the invention of claim 4 In the configuration of the distance measuring device of the invention, when the action similar to that of the invention of claim 1 or 2 is realized by the basic configuration, the time measuring unit concerned Since the correction time of the time correction unit is set to be longer when the required time measured at is longer than when it is small, it is possible to perform appropriate correction according to the diffusion degree of the laser light that increases as the distance increases. , The measurement error at long distance is as small as possible.

[0019]

As a result of the above, according to the distance measuring device of the present invention, it is possible to always measure an appropriate distance, and the accuracy and reliability of the measuring device are improved.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in FIGS.

First, FIG. 1 shows a system configuration of an optical distance measuring apparatus according to the embodiment. In the case of the present embodiment, this distance measuring device is configured to be mounted on a vehicle, for example.

The distance measuring device shown in FIG. 1 is roughly divided into three parts: a laser radar head 1, a time measuring unit 20, and a signal processing unit 30.

The laser radar head 1 has one light emitting element 2 composed of an LD (laser diode) and two first and second light receiving elements 3 and 4 composed of a PD (pin photodiode). A light-emitting lens (condensing lens) 5 is arranged on the front side of 2, and a light-receiving lens (condensing lens) having a lattice-shaped mechanical filter 8 on the front sides of the first and second light-receiving elements 3 and 4, respectively. ) 6, 7 are arranged.
Reference numeral 9 is an LD drive circuit, and 10 is a light receiving circuit.

The one light emitting element 2 and the first and second light receiving elements 3 and 4 are mounted on the turntable 14 as shown in FIG. 2, and the lenses 5, 6, and 7 and the mechanical filter 8 belonging to them are placed. Is also mounted on the turntable 14. As can be seen from FIG. 2, the light emitting element 2 and the lens 5 thereof are drawn on one side of the laser radar head 1 in FIG. 1, but in reality, as shown in FIG. 2, the first and second light receiving elements 3, 4 and the lenses 6 and 7 thereof.

The time measuring unit 20 includes a pulse generator 21 for generating a start pulse for the LD drive circuit.
And the light-receiving circuit 10 starts timing by the start pulse.
Time measuring unit 22 that finishes time measurement with a start pulse from
And a power supply unit 23. The signal processing unit 30 also includes a distance measuring unit 31 that calculates a distance based on the time data obtained by the time measuring unit 22 and a display unit 32 that displays the result.

Further, the laser radar head 1 rotates the turntable 14 so that the light receiving areas 43 and 44 of the first and second light receiving elements 3 and 4 and the light emitting area of the light emitting element 2 (not shown). 2 to FIG. 4, a servo mechanism 11 for deflecting it and a drive motor 12 therefor are provided. The current rotation angle of the servo mechanism 11 is the drive motor 1
It is adapted to be detected by a potentiometer 13 which works in conjunction with 2.

Further, the signal processing unit 30 always captures the reflector 40 of the preceding vehicle in the overlapping area of the light receiving areas 43 and 44 of the first and second two light receiving elements 3 and 4 as shown in FIG. Further, as a control means for rotating the turntable 14, a servo operating section 33 for giving an appropriate command to the drive motor 12 of the servo mechanism 11 is provided. More specifically, the servo operation unit 33 is configured to measure the servo mechanism 11 from the combination of the magnitude relationships of the measured values of the first and second light receiving elements 3 and 4 measured by the distance measuring unit 31. A command regarding whether or not the drive motor 12 is rotating and a rotation direction is given.

Next, the operation of the above configuration will be described.

Now, referring to FIG. 1, for example, the pulse generator 21 of the time measuring unit 20 to the laser radar head 1
A start pulse is output to the LD drive circuit 9 of FIG. Then, the LD drive circuit 9 drives the LD which is the light emitting element 2 by the trigger of the start pulse, and the laser pulse is received by one or both of the first and second light receiving elements 3 and 4, and a predetermined output current is obtained. After being generated and amplified by the light receiving circuit 10, a stop pulse is output to the time measuring unit 22. The time measuring unit 22 measures the time interval between the start pulse from the pulse generating unit 21 and the stop pulse from the light receiving circuit 10, and outputs it as time data to the distance measuring unit 31. The distance measuring unit 31 calculates (converts) the distance to the preceding vehicle from the time data and outputs it as distance data to the vehicle control unit (ASC) 34.

Here, when the first and second light receiving elements 3 and 4 do not receive the reflected light, the distance measurement value at the corresponding light receiving element coefficient in the distance measuring section 31 becomes "maximum", and the distance data is It is treated as a signal that there is no preceding vehicle.
However, if there is some distance measurement value, it is determined that there is a preceding vehicle, and is treated as a signal to that effect.

Next, the relationship with the operation of the optical system will be described.

FIG. 2 shows a case where the reflector 40 of the preceding vehicle is located only within the light receiving area 44 of the second light receiving element 4 on the left side.
Further, FIG. 4 shows a case where the reflector 40 is located in the light receiving areas 43 and 44 of the left and right first and second light receiving elements 3 and 4, respectively.

For convenience of explanation, the reflector 40 of the preceding vehicle is first shown.
However, as shown in FIG. 2, it is assumed that it is located only within the light receiving area 44 of the second light receiving element 4. In this case, the reflector 4 of the preceding vehicle
The reflected light from 0 is received only by the second light receiving element 4, and the output states of the first and second light receiving elements 3 and 4 are as shown in FIG. At this time, the distance measurement value in the distance measuring unit 31 has a relationship of “maximum distance” for the first light receiving element 3 and “small distance” for the second light receiving element 4. Then, the servo control unit 33 of the signal processing unit 30 estimates that the preceding vehicle is in the left direction based on the magnitude relationship of the signals of the distance measurement values, and causes the servo mechanism 11 to rotate the turntable 14 counterclockwise. Give "left move command". As a result, the drive motor 12 rotates forward, the turntable 14 rotates in the direction of the arrow in FIG. 2, and the light receiving areas 43 and 44 move to the left. When the reflector 40 of the preceding vehicle enters the overlapping area of the light receiving areas 43 and 44 as shown in FIG.
The output state of each of the second light receiving elements 3 and 4 is as shown in FIG. 5, and the distance measurement value has a "small distance" relationship for both the first and second light receiving elements 3 and 4. Here, the servo control unit 33 stops the "left movement command".

Contrary to the above, the reflected light is reflected by the first light receiving element 3
When the light is received by only the distance measurement value, the first light receiving element 3 has a “small distance” and the second light receiving element 4 has a “maximum distance” relationship. When it is judged to be in the right direction, the servo mechanism 11 is given a "right movement command" for moving the turntable 14 in the clockwise direction. As a result, the drive motor 12 rotates in the reverse direction, the turntable 14 rotates clockwise from FIG. 2, and the light receiving areas 43 and 44 move to the right. When the reflector 40 of the preceding vehicle enters the overlapping area of the light receiving areas 43 and 44, the distance measurement values of both the first and second light receiving elements 3 and 4 have a "small distance" relationship at that time. The servo control unit 33 stops the "right movement command". When the distance measurement value is “maximum distance” for both the first and second light receiving elements 3 and 4, the servo control unit 33 gives no instruction to the servo mechanism 11.

As described above, the turntable 14 is held until the distance measurement value of some value is obtained in both the first and second light receiving elements 3 and 4, that is, the above "small distance" is obtained. By rotationally displacing, the preceding vehicle can always be captured directly in front of the optical system of the laser radar head 1. Therefore, without unnecessarily expanding the light emission field,
In addition, it is possible to widen the distance measurement area without performing unnecessary data processing by performing wide-range scanning.

However, in the optical distance measuring device as described above, the attenuation of the signal level of the received light pulse signal is considerably different depending on the distance of the measurement distance, as shown in FIG. The peak level and pulse width also change due to the change.

As a result, there is a problem that the arrival time at the rising edge of the received light pulse signal, which is determined by the predetermined reference level Vs, changes and causes a measurement error.

Further, in an extreme case, the received light pulse signal becomes oversaturated and the pulse width becomes extremely large as shown in the figure.

Therefore, the content of the distance measurement control by the signal processing unit 30 for solving the problem will be described in detail next with reference to the flowchart of FIG.

That is, first, in step S ₁ , the arrival time t of the laser light from the light emission time of the light emitting element 2 to the arrival time of the laser light to the light receiving element 3 and the pulse width W of the light receiving pulse signal are calculated and detected. Enter.

Then, in step S ₂ , the saturation pulse width Wmax of the light receiving pulse signal corresponding to the arrival time t of the laser light is calculated using the characteristic map of FIG.

Next, the process proceeds to step S ₃ thereon, the pulse width W of the light receiving pulse signal detected input at step S ₁ is, than the saturation pulse width Wmax calculated in the step S ₃ and the large (supersaturated) Is determined.

As a result, when NO is not oversaturated, a pulse width W of the light receiving signal proportional to the measured distance (for example, Wa, in FIG. 9) is used by using a map having different characteristics for short distance and long distance in FIG. According to (Wb, Wc, Wd), the correction time Δt is calculated for each required arrival time t.

Then, in step S ₅ , the time (t-Δt) obtained by correcting the arrival required time t with Δt is finally converted into the distance D.

On the other hand, when the pulse width W determined to be NO in the above step S ₃ is oversaturated like Wd in FIG. 9, the process proceeds to step S ₆ without performing the correction by the map in FIG. The time t required for arrival of the laser light input in step S ₁ is converted into the distance D as it is.

As a result, according to the measurement control system of the present embodiment, it is possible to prevent the erroneous measurement at the time of the light receiving pulse signal oversaturation due to the change of the light receiving signal intensity due to the size of the distance and the light diffusion, and the measurement accuracy is improved. .

Further, since unnecessary correction is not performed when the light receiving pulse signal is saturated, the control sequence at the time of the same oversaturation is simplified.

[Brief description of drawings]

FIG. 1 is a control circuit showing a system configuration of a distance measuring device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a relationship between a first rotation position of a laser head of the same apparatus and a direction of a light receiving area.

FIG. 3 is a time chart showing light emission and light reception timing between the light emitting element and the light receiving element of the laser head in the state of FIG.

FIG. 4 is a schematic diagram showing a relationship between a second rotation position of a laser head of the same apparatus and a direction of a light receiving area.

FIG. 5 is a time chart showing light emission and light reception timing between the light emitting element and the light receiving element of the laser head in the state of FIG.

FIG. 6 is a flowchart showing the content of distance measurement control of the device.

7 is a characteristic diagram of a saturation pulse width calculation map of a light reception signal used in the control of FIG.

8 is a characteristic diagram of a correction time calculation map which is also used in the control of FIG.

FIG. 9 is a time chart of a light receiving pulse signal showing a problem of the conventional distance measuring device.

[Explanation of symbols]

1 is a laser radar head, 2 is a light emitting element, 3 is a first light receiving element, 4 is a second light receiving element, 10 is a light receiving circuit, 20
Is a time measuring unit, 21 is a pulse generating unit, 22 is a time measuring unit, 30 is a signal processing unit, and 40 is a reflector.

Claims (4)

[Claims] 1. A light emitting section for emitting pulsed laser light toward an object, and pulsed laser light reflected through the object out of the pulsed laser light emitted from the light emitting section is received to receive pulses. A light receiving unit that outputs a signal, and a time when the level of the light receiving pulse signal output from the light receiving unit exceeds a predetermined reference level is determined as the arrival time of the reflected laser light, and from the laser light emission time of the light emitting unit. A time measuring unit that measures a time required to reach the arrival time and a distance measuring unit that measures a distance from the light emitting unit or the light receiving unit to the object based on the time required measured by the time measuring unit. In the distance measuring device, the distance measuring device is provided with a time correction unit that adds a predetermined correction to the required time measured by the time measuring unit. 2. The time correction unit compares the level of the light receiving pulse signal output from the light emitting unit with a predetermined reference level, and decreases the correction time as the pulse width of the light receiving pulse signal is larger than the reference level. The distance measuring device according to claim 1, wherein the distance measuring device is configured as described above. 3. A saturation determination unit that determines the saturation state of the received light pulse signal output from the light receiving unit is provided, and when the saturation state of the received light pulse signal is determined, the correction operation for the required time by the time correction unit is canceled. The distance measuring device according to claim 1 or 2, characterized in that. 4. The distance measuring device according to claim 1, wherein when the required time measured by the time measuring unit is long, the correction time of the time correcting unit is set longer than when the required time is small.