JPH0954155A - Distance-measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely measure distance to a front object over a wide range of distances with uniform accuracy, by controlling an emission output so that a peak value is normally within a predetermined range, reducing the emission output to the lowest level in a short time when an object is suddenly detected within a point-blank range, and gradually increasing the emission output afterwards. SOLUTION: A peak detection circuit 22 outputs a control signal C' of an H level to a filter circuit 23 when a peak of a receiving signal (b) from an amplifier circuit 17 exceeds a reference voltage V0 , V0 +α (α is a minute voltage), thereby to control an output voltage a' of an LD-switching driver 12' so that the peak of the signal (b) is not saturated and always a predetermined size. If a vehicle interrupts immediately in front of one's own vehicle and an operation circuit 41' suddenly operates a point-blank distance, a control signal (e) of a single pulse is sent to the circuit 23 to reduce the output of a light- emitting element 13 to the lowest level. The emission output is gradually increased afterwards by a filter function of the circuit 23. The signal C' to the circuit 23 is subsequently turned to H and L levels alternately repeatedly, thereby, the emission output is maintained constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, for example, emits a laser beam to the front of the vehicle to measure the distance between the vehicle and the front vehicle and issues an alarm when the vehicle approaches the front vehicle.
The present invention relates to a distance measuring device used for a collision prevention device or the like for preventing a collision with a vehicle in front of it.

[0002]

2. Description of the Related Art A conventional distance measuring device will be described by taking an obstacle detecting device shown in FIG. 4 as an example. In the figure, reference numeral 1 is a distance detection unit that detects a distance between a vehicle and an obstacle by using a laser beam emitted from a laser diode (hereinafter referred to as LD), and 2 is a vehicle speed such as a vehicle speed. It is a running state detection unit that detects a running state of the vehicle.

Reference numeral 3 designates a vehicle based on the distance information sent back to the distance detection unit 1 in response to the distance detection command and the own vehicle speed information detected by the traveling state detection unit 2; It calculates the relative speed with the obstacle such as the vehicle in front and judges whether the obstacle is a stationary object or a moving object, and also the individual vehicle speed, relative speed, and the free running time until the driver brakes. It is a signal processing unit that determines the possibility of collision between the host vehicle and an obstacle according to the distance setting or the like set according to the difference.

4 is based on the information from the signal processing unit 3,
This is an alarm notification unit that displays the distance between the host vehicle and the obstacle and issues an alarm when the signal processing unit 3 determines that there is a possibility of collision with the obstacle.

Next, the operation of the above configuration will be described. The traveling state detection unit 2 includes a vehicle speed sensor 31, and the signal processing unit 3 includes an arithmetic circuit (distance calculation means) 41 and a distance setting switch 42.
It has. The vehicle speed signal of the own vehicle detected by the vehicle speed sensor 31 is sent to the arithmetic circuit 41, and the arithmetic circuit 41 detects the distance to the distance detecting unit 1 when the vehicle speed calculated based on the vehicle speed signal is 35 Km / h or more. Send a command signal.

In the distance detecting section 1, the drive signal generating circuit 11 receives the distance detection command signal, and the drive signal generating circuit 11 sends an LD light emission signal having a constant frequency shown in FIG. Based on the received LD light emission signal (a), the LD switching driver 12 performs the operation shown in FIG.
The signals shown in (c) and (d) are transmitted, and LD-L, LD-C, and L of the LD array (light emitting element) 13 as a light emitting means.
D-R are made to sequentially emit light with the same intensity at all times.

The laser beam from the LD-L of the LD array 13 is directed to the front left of the vehicle, the laser beam from the LD-C is directed to the front, and the laser beam from the LD-R is directed to the front right by the light projecting lens 14. Is emitted through LD-
The laser beam of C is used to detect an obstacle ahead, the laser beam of LD-L is used to detect an interrupting vehicle from the left lane, and the laser beam of LD-R is used to detect an interrupting vehicle from the right lane.

The reflected light from the obstacle is condensed by the light receiving lens 15 and received by the photodiode (light receiving element) 16. This received light signal is sent to the amplifier circuit 17, and the amplifier circuit 1
7 amplifies it and outputs the signal B of FIG.

The reference value generation circuit 18 outputs the reference voltage V0 shown in FIG. 5 (e) to the comparison circuit 19. Comparison circuit 19
Is the output signal (e) of the amplifier circuit 17 and this reference voltage V0
The reflected signal from the obstacle is extracted by performing a level comparison with and the obstacle detection pulse signal shown in FIG. 5 (f) is output.

The counter 20 has an L level as shown in FIG.
At the rise of the D light emission signal (a), the reference pulse generation circuit 21
Starts counting the clock pulse signal supplied from the obstacle, stops counting at the rising edge of the obstacle detection pulse signal (f) based on the reflection signal from the obstacle, and counts from the count-up time and the speed of light to the obstacle. Seeking distance information,
It is sent to the arithmetic circuit 41 of the signal processing unit 3.

Next, a method of determining the possibility of collision in the arithmetic circuit 41 of the signal processing unit 3 will be described with reference to the flowchart shown in FIG. First, when the power is turned on, S
Proceeding to the TART step, the CP forming the arithmetic circuit 41
U, RAM, etc. are initialized. Next, step S
At T11, a distance signal indicating information on the distance R to the obstacle from the counter 20 of the distance detecting unit 1 and a vehicle speed signal indicating information on the own vehicle speed V _f from the vehicle speed sensor 31 of the traveling state detecting unit 2 at predetermined intervals. Are taken into the arithmetic circuit 41.

Then, in step ST12, the distance signal R is converted into a display signal, which is sent to the distance display 51 and displayed.
Next, in step ST13, the inter-vehicle distance R is differentiated to calculate the relative velocity (d / dt) R between the obstacle such as the preceding vehicle and the host vehicle using a calculation method such as the least square method, and The vehicle speed V _a is calculated by the sum of the vehicle speed V _f and the relative speed (d / dt) R.

In this calculation, (d / dt) R <0
In the case of (d / dt) R> 0, the distance is decreasing, and the distance is decreasing, and (d / dt) R = 0. In the case of, it shows that there is no change in the distance.

In determining the possibility of collision with an obstacle, the initial speed of the vehicle is V _f (m / s) and the initial speed of the obstacle (preceding vehicle) is V _a (m / s). Deceleration performance is α (m /
s ² ), the difference between the stop distance V _f ² / 2α of the host vehicle and the stop distance V _a ² / 2α of the preceding vehicle is set to the time T until the host vehicle sets the brake by the distance setting switch 42. _The distance R shown in the equation 1, which is the _sum of the free running distance V _f · T _{d due} to _d , becomes the reference for collision judgment.

[0015]

[Equation 1]

Therefore, first, in step ST14, the relative speed (d / dt) R and the vehicle speed _Vf are compared, and-(d /
dt) In the case of R≈V _f , that is, when the obstacle is regarded as a road stop, the process proceeds to step ST15, and since V _a = 0 in Formula 1, the collision law is calculated according to the following formula 2 Determine the risk.

[0017]

[Equation 2]

When the equation 2 is satisfied, there is a risk of collision with an obstacle, and the process proceeds to step ST18 to generate an alarm signal and send it to the alarm notifying unit 4, and the alarm device 52 causes a danger. A warning for avoidance is issued.

On the other hand, as a result of the judgment in step ST14,
When − (d / dt) R≈V _f is not satisfied, the obstacle is a preceding vehicle traveling on the road ahead, and the danger judgment should be originally made according to Equation 1. However, the relative velocity (d /
Since the calculation accuracy of dt) R may not be strict, the calculation error may give an erroneous alarm. Therefore, in the case of a preceding vehicle in which an obstacle moves, the relative speed (d / d) is calculated in step ST16.
t) First, it is determined whether R is equal to or higher than a predetermined speed C (m / sec).

As a result, when (d / dt) R ≧ C, the relative speed is fast and the vehicle is approaching rapidly. Therefore, the preceding vehicle is regarded as infinitely close to the stopped object, and the process proceeds to step ST15. With the same logic as that of the stop obstacle, the warning output judgment is performed by the discriminant of the equation (2).

Further, the determination result of step ST16 is (d
/ Dt) R <In the case of C, the slow relative speed, regarded as being the normal follow-up running at a constant inter-vehicle distance, vehicle speed V _f
Since the preceding vehicle speed V _a is almost equal, the equation 1 becomes the equation 3 shown below. In step ST17, the danger of a collision is determined by the equation 3, and if the equation 3 is satisfied similarly, in step ST18. Give an alarm.

[0022]

(Equation 3)

[0023]

However, in the distance measuring device used for such a collision preventing device, when the distance to the front object is short, the reflection of the light beam is strong and the amplitude of the light beam is large. A large received light waveform can be obtained, but when it is far, only a received light waveform with a small amplitude can be obtained due to weak reflection of the light beam, so a measurement error occurs because the timing at which the received light waveform exceeds the reference value is different. It is possible. Therefore, when the light beam is set to be strong, and when an interrupting vehicle appears at a close range in front of the own vehicle, the reflection of the light beam becomes extremely strong and the received light waveform is saturated, which further causes the above problem. That is, there is a problem that a measurement error becomes noticeable and the distance is measured as a distance closer to the actual distance, so that an alarm is unnecessarily issued even to an interrupting vehicle whose traveling speed is faster than the own vehicle.

The present invention has been made in view of the above points, and provides an apparatus capable of surely measuring a distance to a front object while ensuring uniform measurement accuracy over a wide range for short distance measurement and long distance measurement. The purpose is to do.

[0025]

A distance measuring device according to the present invention includes a light emitting element, drive signal generating means for supplying a trigger signal to the light emitting element to drive the light emitting element, and a front object emitted from the light emitting element. Distance calculating means for calculating the distance to the front object based on the time difference between the light receiving element that receives the reflected light reflected by the light receiving element, the generation timing of the trigger signal from the drive signal generating means, and the light receiving timing of the light receiving element. In the distance measuring device comprising, detecting the peak value of the received light waveform input from the light receiving means, if the peak value is larger than a predetermined value, gradually decrease the output power of the drive signal generating means, Further, when the crest value is smaller than a predetermined value, it is provided with a first control means for outputting a signal for gradually increasing the output power of the drive signal generation means, and the distance calculation is provided. When the distance calculated by the means indicates a shortest distance compared to the distance calculated last time, the output power of the drive signal generating means is immediately decreased to the minimum voltage, and then gradually increased to the second control. And means.

[0026]

The distance measuring device according to the present invention normally controls the light emission output of the light emitting element so that the peak value of the received light waveform does not saturate to a predetermined value or falls within a predetermined range, and suddenly. When a front object is detected at a close range, the emission output is 0 level or the minimum level (within the set range)
To a short time, then gradually increase the light emission output,
Make it possible to obtain the distance to the front object in a short time.

[0027]

【Example】

[First Embodiment] The structure of this embodiment will be described below with reference to FIG. In FIG. 1, the same components as those described with reference to FIG. 4 or equivalent components are designated by the same reference numerals, and the description thereof will be omitted. Only different components will be described below.

That is, in FIG. 1, the LD switching driver 12 'has a function of the LD switching driver 12 in FIG.
A control function for receiving a control signal from the control circuit 2 and changing the output voltage is added.

Reference numeral 22 is a peak detection circuit for detecting the voltage value (for example, peak value) at the center of the received light waveform.
The light receiving signal (FIG. 3 (b)) from 7 is input, and the waveform of the light receiving signal (waveforms A and B in FIG. 3 (b)) and the output voltage of the reference value generating circuit 18, that is, the reference value V0 Compare (Figure 2
Then, when the waveform of the received light signal, for example, the waveform A exceeds the output voltage V0 of the reference value generating circuit 18, a high level (FIG. 3C) is output. Further, similarly, V0 + α obtained by adding a small voltage α to the output voltage V0 is also compared to obtain V0
When it exceeds 0 + α, a high level (Fig. 3 (c ')) is output.

The high level state output in FIGS. 3 (c) and 3 (c ') is held until the next light emission, but the LD switching driver 12' includes the drive signal generating circuit 1
When the LD generation signal from 1 is received, it emits light, and at the same time, it is reset to the low level state. In addition, amplifying circuit 1
7 shows the waveform of the received light signal (waveform A in FIG. 3B,
If B) does not exceed V0 and V0 + α, then FIG.
The high level signals shown in (c) and (c ') are not output. The output obtained by comparing the received light waveform A and V0 + α (Fig. 3
(C ′)) is a filter circuit 23 having a low-pass function
Signal supplied to the filter circuit 23 (see FIG. 3).
When (c ′)) is at a high level, the drive voltage of the light emitting element 13 is lowered so that the light emission output of the light emitting element 13 sharply drops. Further, the peak detection circuit 2 is added to the filter circuit 23.
When the signal supplied from 2 (FIG. 3 (c ')) is at a low level, the drive voltage of the light emitting element 13 is gradually increased so that the light emission output of the light emitting element 13 is gradually increased ((f in FIG. 2). )
T2).

The filter circuit 23 has a reset function and receives the output signal (c ') from the peak detection circuit 22 so that the light reception signal (b) from the amplification circuit 17 always becomes a predetermined magnitude. Thus, the output voltage of the LD switching driver 12 'is controlled. Further, the filter circuit 2
3 receives the control signal (e) of a single pulse from the arithmetic circuit 41 ', lowers the output voltage to 0 volt (or to the set minimum voltage), and then raises the output voltage with a predetermined time constant. It also has functions.

That is, for example, when the vehicle is in front of the host vehicle and the shortest distance is suddenly calculated by the arithmetic circuit 41 ′, the arithmetic circuit 41 ′ sends the single-pulse control signal to the filter circuit 19. 2 (e) is sent out, and a kind of filter function forming the switching regulator is stopped until the next light emission pulse is output. In other words, when the state of the signal c ′ from the peak detection circuit 22 to the filter circuit 23 is inverted to the high level, the output power supply voltage of the LD switching driver 12 ′ immediately drops to 0 volt (or the minimum voltage). To be made. As a result, the light emission output of the light emitting element 13 becomes the lowest level. The stop of the filter function is one distance measurement, that is, the arithmetic circuit 4
Since 1'is only the time required for one distance calculation, after that, the light emission output is gradually increased by the predetermined specific number to the required level by the filter function.

Next, the operation of the above configuration will be described with reference to FIG. First, in a state where there is no vehicle in front (T1 section of FIG. 2), the LD switching driver 12 ′ drives the light emitting element 13 with the maximum output (see (a ′) of FIG. 2), but amplifies the light reception signal. There is no output signal from the amplifier circuit 17 (see FIG. 2B). Therefore, the reference voltage V0 +
Since α is not exceeded, the peak detection circuit 22 outputs a low level signal (see (c ′) in FIG. 2) to the filter circuit 23. Since the filter circuit 23 inverts and outputs the low level signal, it maintains the output of the high level signal (see (f) of FIG. 2) to the LD switching driver 12 ′. Therefore, the power supply voltage supplied to the LD switching driver 12 'has the maximum output.

Next, when another vehicle is traveling in front of the host vehicle, the counter (distance calculating means) 20 triggers the rise of the light emission drive pulse (FIG. 3 (a)) as shown in FIG. While counting the clock pulses (FIG. 3D) from the reference pulse generating circuit 21 as a signal, the light receiving element 16
When the light receiving signal from the light receiving device (FIG. 3B) is received, when the light receiving signal exceeds the reference value V0 (reference value for determining the light receiving signal) from the reference value generating circuit 18, the counter 20 is counted. The counter 20 outputs a signal (FIG. 3 (c)) to stop the counting, and the counter 20 calculates the count value in the section T.
Supply 1 '.

Next, when the received light signal exceeds a reference value V0 + α for judging the saturation state of the received light signal, a signal for gradually decreasing the supply voltage to the LD switching driver 12 'for the filter circuit 23 (see FIG. 3 ( c ')) is supplied.

Further, at this time, if an interrupting vehicle occurs within a close range in front of the host vehicle, a drive signal for driving the light emitting element 13 until immediately before that (see (a ') in FIG. 2).
Has a maximum output, the received light signal output from the amplifier circuit 17 (see (b) of FIG. 2) becomes an excessively saturated signal. Therefore, since the voltage exceeds the reference voltage V0 + α, the output signal of the peak detection circuit 22 (see (c) of FIG. 2) is output at that time, and the arithmetic circuit 41 'calculates that it is the shortest distance. Therefore, the arithmetic circuit 41 'filters the single pulse of the signal (see (e) of FIG. 2).
Output to 3. As a result, the filter circuit 23
Is immediately lowered to 0 volt (or the lowest power supply voltage), and as a result, the output of the signal a ′ for driving the light emitting element 13 is also lowered to the lowest level.

As a result, since the light emission output is lowered, the light receiving signal (FIG. 2 (b)) at the light receiving element 16 also becomes small, the reference voltage V0 + α is not exceeded again, and the peak detection circuit 22 to the filter circuit 23 is not reached. Output (Fig. 2
(C ')) becomes low level. The low level causes the output voltage of the filter circuit 23 to gradually increase, and accordingly, the output voltage of the LD switching driver 12 ′ (FIG. 2 (a ′)) also gradually increases. Then, again when the peak voltage of the output voltage of the received light signal b from the amplifier circuit 17 exceeds the reference value V0 + α, the peak detection circuit 22
The signal from the filter circuit 23 to the filter circuit 23 (FIG. 2 (c ')) is controlled to a constant value by alternately repeating high level and low level.

[0038]

As described above, according to the present invention, it is possible to reliably detect a wide-range distance measurement from a short distance to a long distance with a predetermined accuracy, and to detect another vehicle in a short distance immediately before the own vehicle. Even if the vehicle interrupts at a faster speed than the own vehicle, the vehicle that interrupted the vehicle can be instantly detected, so that an unnecessary alarm is not issued and the reliability of the product can be improved.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment according to the present invention.

FIG. 2 is an explanatory diagram with waveforms for explaining the operation of FIG.

FIG. 3 is a waveform explanatory view for explaining the operation of the peak detection circuit and its peripheral circuits in FIG.

FIG. 4 is a circuit block diagram of a conventional device.

5 is a waveform diagram for explaining the circuit of FIG.

FIG. 6 is a flowchart for calculating a distance by the arithmetic circuit in FIG.

[Explanation of symbols]

 11 Drive Signal Generation Circuit 12 LD Switching Driver 13 Light-Emitting Element 16 Light-Receiving Element 18 Reference Value Generation Circuit 20 Counter (Distance Calculator) 22 Peak Detection Circuit 23 Filter Circuit 41 Arithmetic Circuit (Distance Calculator) 41 'Arithmetic Circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G08B 21/00 G02B 7/11 B // G01C 3/06 G03B 3/00 A

Claims (1)

[Claims] 1. A light emitting element (13), drive signal generating means for supplying a trigger signal to the light emitting element to drive the light emitting element, and reflected light emitted from the light emitting element (13) and reflected by a front object. Distance calculating means for calculating the distance to the front object based on the time difference between the light receiving element (16) to be operated, the generation timing of the trigger signal from the drive signal generating means, and the light receiving timing of the light receiving element (16) ( Two
0, 41), the peak value of the received light waveform input from the light receiving element (16) is detected, and when the peak value is larger than a predetermined value, the output of the drive signal generating means is detected. The distance calculating means (20) is provided with first control means for gradually decreasing the power and for outputting a signal for gradually increasing the output power of the drive signal generating means when the peak value is smaller than a predetermined value. 41), the output power of the drive signal generating means is immediately lowered to the minimum voltage and then gradually increased. A distance measuring device comprising two control means.