JPH10253759A - Range finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a range finder which prevents a situation that an object existing at a long distance is hidden so as to be incapable of being recognized because the image of an object which exists at a short distance and whose quantity of reflected light is large is spread transversely so as to be recognized. SOLUTION: A delay-time measuring part 32 measures a delay time-up to a light-receiving signal (c) from a light-emitting signal (a), and a distance comporting part 33 computes a distance up to an object on the basis of the delay time. A light-receiving-level level detection part 30 extracts a signal at a light-receiving level designated by a light-receiving-level-designation changeover part 31, and the signal is sent to the delay-time measuring part 32. Since the light-receiving level of the light-receiving signal designated by the light-receiving- level-designation changeover part 31 is changed over at a constant cycle, a light-receiving signal which is different at every contact cycle is extracted as a signal for delay-time measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a distance measuring device. In particular, the present invention relates to a distance measuring device that measures a distance to an object by scanning a detection area with a laser pulse.

[0002]

2. Description of the Related Art A laser distance measuring device is used as an on-vehicle distance measuring device for detecting a distance and a direction of an object and measuring, for example, an inter-vehicle distance with a preceding vehicle.

FIG. 1 is a schematic block diagram showing the configuration of a conventional laser distance measuring device 1. This laser ranging device 1
Is a semiconductor laser element (LD) 2, a semiconductor laser element driving circuit (LD driving circuit) 3 for driving the semiconductor laser element 2, and optical scanning for scanning a laser pulse P emitted from the semiconductor laser element 2 toward a detection area. A light projection unit including a unit (scanner) 4 and a signal processing unit 5 are provided. The semiconductor laser element driving circuit 3 causes the semiconductor laser element 2 to emit pulses in synchronization with the light emission signal a output from the signal processing unit 5 at regular intervals. The optical scanning unit 4 is composed of, for example, a polygon mirror that is rotated by a servomotor, a diaphragm with a mirror that is rotated and vibrated by a piezoelectric vibrator, and the like. The laser pulse P emitted from the semiconductor laser element 2 is The light is reflected by the unit 4 and scans a predetermined detection area.

Here, the light projecting operation of the laser distance measuring device 1 will be specifically described with reference to FIG. The semiconductor laser element 2 has a 25 μs
Pulse emission is performed every c. On the other hand, the optical scanning unit 4
Scans the laser pulse P unidirectionally in one direction at a period of 50 msec over a measurement range of 200 mrad. The laser pulse P emits light every 25 μsec.
During 50 msec of scanning, the semiconductor laser element 2
Light emission is performed twice, and a distance measurement of 2000 pulses is performed. Of the 2000 pulses in one scan, 201 to 1
1600 pulses up to 800 are used for distance measurement,
End point area (pulses 1 to 200 and 1801 to 20
In the case of the (00th pulse), distance measurement is not performed. The 1600 pulses (201st to 1800th pulses) used for distance measurement are divided into 80 regions every 20 pulses.

The scanning direction detecting section 6 detects the scanning direction (light emitting direction) of the laser pulse P by the optical scanning section 4 with reference to the laser pulse P in the end point area. The scanning direction of the laser pulse P is transmitted to the signal processing unit 5 as scanning direction information b.

The laser distance measuring device 1 further includes a light receiving section including a light receiving element 7 such as a photodiode (PD) and a light receiving circuit 8. Laser pulse P emitted from semiconductor laser element 2 and scanned by optical scanning section 4
Is projected forward, reflected by the object, returned toward the laser range finder 1, and received by the light receiving element 7. The light receiving signal c output from the light receiving element 7 is amplified by the light receiving circuit 8 and output.

The signal processing unit 5 compares the light receiving signal c output from the light receiving circuit 8 with a predetermined threshold Vth, and when the light receiving signal c is equal to or larger than the threshold Vth, the light receiving unit emits a laser pulse P. It is determined that light has been received, and the distance to the object is calculated based on the delay time τ from the light projection timing to the light reception timing. That is, the distance to the object is L, and the speed of light is c.
Then, since the delay time is τ = 2L / c, the distance L to the object is obtained from the delay time τ. Next, the signal processing unit 5 averages the distance measurement results for 20 pulses (for one area), obtains distance measurement data, and outputs the data together with direction data (scanning direction information b).

[0008]

[Problems to be solved by the invention]

(Problem) However, in the conventional laser distance measuring device, if an object with a large amount of reflected light exists at a short distance,
The object at the short distance is recognized as an image that spreads out more than the actual size, and there is a problem that the size of the object having a large amount of reflected light existing at a short distance is erroneously determined. When an image of an object with a large amount of reflected light that is present at a short distance spreads horizontally and is recognized as larger than it actually is, a long-distance object that exists opposite the image of the object is recognized. And the distance cannot be measured.

For example, as shown in FIG. 3, a description will be given of an in-vehicle laser distance measuring apparatus 1 attached to a lower portion of a bumper of a vehicle 9, for example, with a reflector 11 of a forward vehicle 10 running in front of the vehicle 9. The distance to the vehicle 10 ahead is measured by receiving the reflected laser pulse P, and based on the measured data, when the vehicle is traveling following a constant distance, a roadside reflector, a delineator, a metallic signboard or the like on the side of the road 12 is used. An object 13 having a large amount of reflected light may enter the field of view at a short distance. In this case, if it is an ideal laser distance measuring device, as shown in FIG. 4A, the reflector 11 of the front vehicle 10 is recognized at a long distance in front and the roadside reflector is positioned at a short distance on the side of the road 12. Is recognized.

However, in practice, as shown in FIG. 4B, an object 13 such as a roadside reflector which exists at a short distance.
Image spreads inside the road 12 to block the road 12, and it becomes impossible to recognize the preceding vehicle 10 that is supposed to be present at a long distance therefrom. For this reason, until the vehicle 9 passes through the object 13 such as the roadside reflector, it is impossible to follow the fixed distance between vehicles, or the curve of the road 12 cannot be estimated from the arrangement of the object 13 such as the roadside reflector. Was dangerous.

(Clarification of Phenomenon) The inventors of the present invention have searched for the reason why such a phenomenon occurs, and as a result, have reached the following knowledge. In the laser distance measuring apparatus 1 using the laser pulse P, the laser pulse P emitted from the light projecting unit is optically collimated in the horizontal direction (light scanning direction) as shown in FIG. In the horizontal direction, the divergence angle is usually 1 mrad or less, and in the vertical direction, the divergence angle is usually 50 mrad. However, this small divergence angle θ is the same as in FIG.
As shown in the figure, the emission intensity is 1 / e of the peak value.
Or, it is an angle at a point where 1 / e ² (e is the base of the natural logarithm), and the laser pulse P spreads out in a region outside the angle, although the emission intensity is small.

For this reason, as shown in FIG. 6, considering the moment when the laser pulse P is projected toward the center of the object 14 located at the distance L ₂ , the object 14 is located away from the center. An area where the emission intensity of the laser pulse P is small is also projected on the object 15. At this time, the area of the laser pulse P projected on the object 14 located in the center direction of the laser pulse P is a hatched area A1 in FIG.
Assuming that the area of the laser pulse P projected on the object 15 located in the direction away from the center is the hatched area A2 in FIG. 7, the laser pulse projected on the object 14 located in the center direction The light irradiation amount of P and the light irradiation amount of the laser pulse P projected on the object 15 located in the direction deviated from the center correspond to the respective shaded areas A1,
The amount of light projected onto the object 15 in the direction away from the center is proportional to the area of A2,
Is smaller than the light irradiation amount projected on

However, the object 15 irradiated with the minute laser pulse P at a position deviating from the center direction of the laser pulse P has a shorter distance L than the object 14 existing in the center direction of the laser pulse P. ₁ (<L ₂ ), and the reflectance of the object 15 is high.
If the amount of reflected light from is large, the object 1 near field L ₁
May 5 receiving signals c ₁ by laser pulses P reflected by exceeding the threshold value Vth, in this case, the distance L
Only the object 15 at ₁ is recognized and the object 1 at the distance L ₂
4 is not recognized.

FIGS. 8 and 9 are diagrams for explaining the reason why the object 14 at the distance L ₂ is no longer recognized. FIG. 8 is a diagram showing a main part of the conventional signal processing unit 5, and FIG. 6 is a time chart for explaining the operation. Signal processing unit 5
Is a D-FF (D-flip-flop) with RS input
16 and a counter 17. D-FF
The 16 set inputs S ₁ are fixed at L level, the D input D ₁ is fixed at H level, and the light emission signal a is input to the reset input R ₁ . The clock input CK ₁ of the D-FF 16 is connected to the output of the light receiving circuit 8 so that the light receiving signal c is input, and the light receiving signal c having a certain level (threshold Vth) or more is input to the clock input CK _1. Output, the output Q ₁ goes high.
Change to a level. The output Q ₁ of the D-FF 16 is used as a stop input STOP (carry-in C) of the counter 17.
I). Clock input C of D-FF16
K ₂ has a constant frequency clock pulse signal CP (FIG. 9).
(A)) is input, a reset input R ₂ emission signal a is input.

[0015] Thus, the light emitting signal a is input to the reset input R ₂ of the counter 17 (FIG. 9 (b)) counter 17 is reset to "0". When the light emission signal a is D
Is input to the reset input R ₁ of -FF16, D-F
Output to Q ₁ F16 is changed to L level, because the stop input STOP ₂ counter 17 becomes L level (Fig. 9
(D)), the counter 17 starts counting the number of pulses of the clock pulse signal CP (FIG. 9E). Thereafter, when receiving the signal c from the light receiving circuit 8 to the clock input CK ₁ in D-FF16 is input (FIG. 9 (b)), D input D ₁ is H
From being fixed to the level output to Q ₁ D-FF16 is changed to H level (Fig. 9 (d)), a stop input STOP of the counter 17 stops counting at the H level (Fig. 9 (e) ). Then, the distance to the target is calculated based on the delay time τ from the light emission to the light reception measured by the counter 17 (the number of pulses of the clock pulse signal CP).

Short distance L₁Signal from object 15 at
c₁Is 2L from the emission timing of the laser pulse P.₁/
c is received with a delay of c
2L from mining_TwoLong distance L received with a delay of / c_Two
Reception signal c by the object 14 In the receiving circuit 8 before 2
Since it is received, it is irradiated with a weak laser pulse P
Short distance L₁Light receiving signal c from the object 15₁Is the threshold
When Vth is exceeded, as shown in FIGS.
Release L₁Light receiving signal c from the object 15₁Is received when
The counter 17 stops. As a result, delay time τ = 2L₁
Since the distance to the object is calculated based on / c
The center direction of the user pulse P is distance L_TwoObject 14 in
Despite being oriented, the signal processing unit 5 has a delay time τ = 2
L₁/ C based on the distance L₁That the object exists
Refuse.

As a result, as shown in FIG.
Considering the case where the laser pulses P of the scanning component is projected, a large object 15 in the amount of reflected light at a short distance L ₁ is present, an image of the object 15 corresponds to a region hatched shown in FIG. 10 (c) Despite the width Wr, the reflected light from a region deviated from the center direction of the laser pulse P is recognized as having a width Wp as shown in FIG.
The object 15 is recognized as if it has expanded in width. On the other hand, the object 14 at a long distance L ₂ is shown in FIG.
As shown in (b), a phenomenon occurs that the image is hidden behind the image of the spread object 15 and is not recognized.

In order to prevent the above phenomenon,
Even if the light in the area deviated from the center of the laser pulse P is reflected by a highly reflective object 15 located at a short distance, the laser pulse P is set so that the received light intensity does not exceed the threshold value Vth.
However, if the light emission intensity of the light projecting unit is reduced, the reflected laser pulse P from the object 14 at a long distance also has a light reception intensity equal to or less than the threshold value Vth, and the distance measurement distance of the laser distance measuring device is reduced. Becomes shorter.

The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and has as its object to provide a method for detecting an object having a large amount of reflected light at a short distance. An object of the present invention is to enable the size of an existing object to be accurately recognized.

[0020]

The distance measuring device according to the first aspect projects and scans a light beam from a light projecting section toward a detection area, receives a light beam reflected by an object by a light receiving section, and projects the light beam. A measuring means such as a distance measuring counter or a timer is started by a light emission signal for projecting a light beam from the section, and the measuring means is stopped by a light receiving signal from the light receiving section, and the target is measured based on the measurement value of the measuring means. In a distance measuring device for obtaining a distance to an object, the number of received light signals corresponding to one emitted light signal to stop the measuring means is switched according to the order of the received light signal.

In the distance measuring device according to the first aspect, the order of stopping the measuring means such as the distance measuring counter and the timer is switched according to the order of the received light signal.
It is possible to know a measured value such as a delay time from one light emission signal to a different light reception signal. Therefore, even when light receiving signals reflected by a plurality of objects are obtained for one light beam projection, measured values such as a delay time until the light beams reflected by each object are received are individually obtained. be able to.

According to a second aspect of the present invention, the distance measuring device emits and scans a light beam from the light projecting unit toward the detection area, receives the light beam reflected by the object by the light receiving unit, and receives the light beam from the light projecting unit. A measuring means such as a distance measuring counter or a timer is started by a light emission signal for projecting a light beam, and the measuring means is stopped by a light receiving signal from a light receiving section. In the distance measuring device for determining the distance, the light receiving signal of one of the plurality of light receiving signals corresponding to one light emitting signal is used to switch the measuring unit to stop.

According to the distance measuring device of the present invention, the light receiving signal of which light receiving level switches the measuring means such as the distance measuring counter and the timer is switched. Thus, it is possible to know a measured value such as a delay time until a different light receiving signal. Therefore, even when light receiving signals reflected by a plurality of objects are obtained for one light beam projection, measured values such as a delay time until the light beams reflected by each object are received are individually obtained. be able to.

Therefore, in the distance measuring apparatus according to the first and second aspects, an image of an object having a large amount of reflected light at a short distance becomes wide, and another object behind the object cannot be recognized. Therefore, it is possible to reliably recognize and measure an object at a short distance and an object at a long distance.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 11 is a block diagram showing a configuration of a laser distance measuring apparatus 21 according to an embodiment of the present invention.
This laser distance measuring device 21 drives a semiconductor laser element 22 by a semiconductor laser element driving circuit 23 to emit a pulse, and scans a laser pulse P emitted from the semiconductor laser element 22 toward a detection area by an optical scanning unit 24. Light emitting section. The semiconductor laser element driving circuit 23 causes the semiconductor laser element 22 to emit pulses in synchronization with the light emission signal a output from the signal processing unit 25 at regular intervals. The method of projecting the laser pulse P projected from the light projecting unit to the detection area is as described with reference to FIG.

The scanning direction detecting section 26 detects the scanning direction of the laser pulse P by the optical scanning section 24 based on the laser pulse P in the end point area, and detects the scanning direction of the laser pulse P detected by the scanning direction detecting section 26. The scanning direction is transmitted to the signal processing unit 25 as scanning direction information b.

The laser range finder 21 further includes a light receiving element 27 such as a photodiode (PD) and a light receiving circuit 2.
8 is provided. Semiconductor laser element 2
The laser pulse P emitted from the light source 2 and scanned by the optical scanning unit 24 is projected forward, reflected by the object, returned to the laser distance measuring device 21 and received by the light receiving element 27. . The light receiving signal c output from the light receiving element 27 is amplified by the light receiving circuit 28 and output.

The signal processing unit 25 includes a light emission signal generation unit 29,
It comprises a light reception level detection unit 30, a light reception level designation switching unit 31, a delay time measurement unit 32, a distance calculation unit 33, and a memory. The light emission signal generation unit 29 outputs a light emission signal a to the semiconductor laser element drive circuit 23 and the delay time measurement unit 32 to cause the semiconductor laser element 22 to emit light at a constant light emission cycle, and causes the delay time measurement unit 32 to output the light emission unit. Tells the light emission timing.

Upon receiving the light receiving signal c sent from the light receiving circuit 28, the light receiving level detector 30 compares the received light signal c with a predetermined threshold value Vth to determine whether the received light signal c is due to the laser pulse P reflected by the object. If the light receiving signal c is equal to or more than the threshold value Vth, it is determined that the light receiving signal c is due to the laser pulse P reflected by the object, and the light receiving timing information is transmitted to the delay time measuring unit 32.

The light receiving level designation switching section 31 changes the light receiving signal level by switching the light receiving amplification factor at predetermined time intervals, for example, for each scanning of the laser pulse P. Alternatively, the threshold value Vth of the light receiving level detection unit 30 may be switched.

The delay time measuring section 32 includes a light emitting signal generating section 2
9, the light-receiving signal c having a threshold value Vth or more is detected by the light-receiving level detector 30.
The delay time τ from light emission to light reception is measured.

The distance calculation section 33 calculates the distance L = cτ / 2 to the object based on the delay time τ measured by the delay time measurement section 32. At this time, the distance calculation unit 33
Since the scanning direction information b is received from the scanning direction detection unit 26, the distance and direction of the target object are obtained. The distance calculation unit 33 stores the distance data and the direction data in the memory 34 for each case where the light reception signal level or the threshold value Vth is changed by the light reception level designation switching unit 31, and comprehensively judges both data. To determine the distance and direction,
The result is output as distance measurement data.

FIG. 12 is a diagram showing a specific configuration of the signal processing unit 25, and FIG. 13 is a time chart specifically showing the operation of the signal processing unit 25 in FIG. This signal processing unit 25
Is a light emission signal generation unit 29, an oscillator 39 for generating a clock pulse signal CP having a constant frequency, two D-FFs 35 and 36 with RS inputs, and an amplifier 3 for amplifying a light reception signal c.
7, a signal switch 38, a counter 40, a distance calculation unit 33, and a memory 34.

In each of the two D-FFs 35 and 36, the set inputs S ₃ and S ₄ are fixed at L level, and the outputs of the light emission signal generator 29 are connected to the reset inputs R ₃ and R ₄ . The light emission signal a is output from the light emission signal generation unit 29 at the timing shown in FIG. 13B, and the light emission signal a is output from the light emission signal generation unit 29 and the reset inputs R ₃ and R ₄ are set to H. When the level becomes the level, the outputs Q ₃ and Q ₄ of the D-FFs 35 and 36 are reset to the L level. Also, both D
Since the D inputs D ₃ and D ₄ of the FFs 35 and 36 are fixed at the H level, when the light receiving signal c having a threshold value Vth or more is input to the clock inputs CK ₃ and CK ₄ , the light receiving signal c
The outputs Q _{3 of} the D-FFs 35 and 36 in synchronization with the rise of
Q ₄ is changed to the H level. Here, the light receiving signal c amplified by the amplifier 37 is input to the clock input CK ₄ of the D-FF 36.

FIG. 13C shows a light receiving signal c input to the clock input CK ₃ of the D-FF 35.
(D) shows a change in output Q ₃ of the D-FF 35,
The received light signal by the light in the weak area of the laser pulse P reflected by the object 15 having a large reflectance at a short distance is c ₁ , and the received signal by the light at the center of the laser pulse P reflected by the object 14 at a long distance is represented by c ₁ It is set to c _2. This D-FF
Threshold Vth 35 is set to be larger than the light receiving quantity c ₁ when weak areas of the laser pulses P strikes the large object 15 in reflectivity located at a short distance.

FIG. 13 (e) shows that the signal
Clock input CK of the D-FF 36 Light input to 4
FIG. 13F shows the output Q of the D-FF 36._Four
Shows the change. The amplification factor of the amplifier 37 is
A laser pulse P is applied to the object 15 having a large reflectance.
Received light amount c when a weak area hits₁Is due to the amplifier 37
After amplification, the threshold voltage Vth of the D-FF 36 is
It is determined to be larger.

The signal switch 38 is alternately toggles in synchronization with the rising operation of the signal input to the selection input SEL, a signal output from the output Q ₅ to the first input STOP_0 a second input STOP_1 Switch.
The first input STOP_0 and the second input ST of the signal switch 38
OP_1 includes the output Q of each of the D-FFs 35 and 36, respectively.
₃ and Q ₄ are connected, and the output of the light emission signal generation unit 29 is connected to the selection input SEL. Therefore, from the output Q ₅ of the signal switch 38, the outputs Q ₃ and D of the D-FF 35 are output. -F
An output Q ₄ of F36 are switched alternately in synchronization with the light emission signal a.

FIG. 13 (g) shows the output Q of the signal switch 38.
₅ , the D-FF 35 on the first input STOP_0 side and the second input S in synchronization with the light emission signal a input to the selection input SEL.
A state in which the D-FF 36 on the TOP_1 side can be alternately switched is shown.

Since the output of the light emission signal generator 29 is connected to the reset input R ₆ of the counter 40, when the light emission signal a is output from the light emission signal generator 29, the counter output Q ₆ becomes “0”. Is reset to The oscillator 39 generates a clock pulse signal CP having a constant frequency as shown in FIG. This clock pulse signal CP
Is input to the clock input CK ₆ of the counter 40, and while the count enable terminal CE (or carry-in CI) is at the L level, the count value of the counter 40 becomes 1 in synchronization with the rising of the clock pulse signal CP. The count value of the counter 40 is held when the count enable terminal CE goes high. The count value of the counter 40 is output from the counter output Q _6.

Therefore, as shown in FIGS. 13H and 13I, the counter 40 starts counting at the same time as resetting the count value to “0” in synchronization with the light emission timing. DF on the connected side
When the F35 or F36 receives the light receiving signal c equal to or more than the threshold value Vth and the count enable terminal CE goes to the H level, the counting stops, and the counter 40 counts the number of clock pulses from the light emission timing to the light reception timing, that is, the delay time τ Is measured.

When the output Q ₅ of the signal switch 38 changes to the H level and the counting of the counter 40 stops, the distance calculating unit 33 calculates the number of clock pulses or the delay time τ measured by the delay time measuring unit 32. Then, the distance to the target object is calculated, and the distance and the direction to the target object are determined together with the scanning direction information b and stored in the memory 34. As a result, the memory 3
4 shows information on the distance and direction obtained based on the received light signal c as shown in FIG. 13C, and information on the distance and direction obtained based on the amplified received light signal c as shown in FIG. Direction information is stored.

The distance calculator 33 recognizes the position of the object based on the two types of information stored in the memory 34 and outputs the data as distance measurement data. More specifically, from the information when the counter 40 detects the target based on the light reception signal c having a low light reception level, it is possible to detect the object 14 at a long distance without being hidden by the object 15 at a short distance. it can. Also,
From the information when the counter 40 detects the target based on the light reception signal c whose light reception level is amplified, the object 14 behind the spread image of the object 15 at a short distance is not visible, but the light reception level is reduced. It is possible to detect an object at a long distance that was not visible when the user was in the middle. Therefore, by comprehensively judging both data, it is possible to reliably recognize a short-distance object and a long-distance object and measure the distance.

In this embodiment, by changing the light receiving level (amplification factor) of the light receiving signal, it is possible to switch which light receiving level of the light receiving signal causes the counter 40 to stop. However, the signal processing unit 25 shown in FIG. Amplifier 3 in
7 can be considered as changing the threshold value Vth of the D-FF 36.
It is apparent that the light receiving signal of which light receiving level stops the counter 40 may be switched by changing th.

In the above embodiment, two D-FFs having the same threshold value and the amplifier 37 are used.
The same operation can be performed by using two D-FFs having different threshold values.

(Second Embodiment) FIG. 14 is a block diagram showing a configuration of a laser distance measuring apparatus 41 according to another embodiment of the present invention. Signal processing unit 25 in the first embodiment
Then, a plurality of light receiving signals c received in association with one light emitting signal a are distinguished by focusing on the difference in the light receiving signal level of each light receiving signal, and the light receiving signal of which light receiving signal level corresponds to the counter 4.
0 is stopped or switched, but in this embodiment,
Multiple light-receiving signals c received with one light-emitting signal a
Are distinguished by the number (light receiving order) of each light receiving signal c,
The counter 40 is stopped by the light receiving signal c of the designated number, and the designated number is switched.

That is, in the laser distance measuring device 41, the light receiving signal number designation switching unit 42 specifies which light receiving signal of the light receiving signals equal to or higher than the threshold value Vth should stop the counter 40. At the same time, the designated number is sequentially changed. Therefore, the delay time until the second light receiving signal c can be measured, and the distance
The delay time to the distant object 14 hidden by
In turn, the distance can be determined.

FIG. 15 shows this signal processing unit 25.
FIG. 16 shows a specific configuration of the signal processing unit 2 shown in FIG.
6 is a time chart specifically showing the operation of FIG. FIG.
12 is compared with the configuration of the signal processing unit 25 in FIG. 12, the signal processing unit 25 in FIG. 15 shows that the clock inputs CK ₃ , The same light receiving signal c is input to CK ₄ (that is, the amplifier 37 is not present), and the D-FF 3
The output Q ₃ of 5 is different in that it is input to the D input D ₄ of D-FF 36.

FIG. 16 is a time chart showing the operation of the signal processing section 25. FIG. 16A shows a clock pulse signal CP output from the oscillator 39.
(B) is a light emission signal a output from the light emission signal generation unit 29.
Is shown. FIGS. 16C and 16D show two light receiving signals c ₁ and c ₂ inputted to the clock input CK ₃ of the D-FF 35 and an output Q ₃ of the D-FF 35 for one light emitting signal.
FIG. 16E shows the D input D ₄ of the D-FF 36. FIG.
6 (f) (g) shows the D-FF 36 for one light emission signal.
The two light-receiving signal c ₁ is input to the clock input CK _4,
and c _2, indicating the output Q ₄ of D-FF 36. FIG. 16 (h)
The signal switch 38 is output Q ₅ of the first input STOP_0 side of D-FF 35 in synchronization with the light emission signal a inputted to the select input SEL second input STOP_1 side of D-FF3
6 shows a state in which the switching can be alternately performed. FIG. 16 (i)
Shows a signal sent from the signal switch 38 to the count enable terminal CE of the counter 40, and FIG. 16 (j) shows the counting operation of the counter 40.

In this embodiment, after the light emission signal a is output, the light receiving circuit 28 sends two D-FFs 35 and 36 to the two D-FFs 35 and 36.
When the two light receiving signals c ₁ and c ₂ are input, the D input of the D-FF 35 is at the H level, so that the output Q _{3 of the} D-FF 35 is output.
Changes to the H level by the rising operation of the _first light receiving signal c1 (FIGS. 16C and 16D). However, at the rising edge of the first light receiving signal c ₁ is, D input D ₄ of D-FF 36 is because it is L level, the output Q ₄ of D-FF 36 does not change from the first light receiving signal c ₁ in L level .
Further, since the output Q ₃ of the D-FF 35 has changed already H level in the first light receiving signal c _1, 2 th light reception signal c
₂ does not change. In contrast, when the rise of the second light receiving signal c ₂ is, D input D ₄ of D-FF 36 is H
Since changes in the level, the output Q ₄ of D-FF 36 changes to H level at the second light receiving signal c _2. Therefore,
The signal switch 38 causes the counter 40 to perform DF for each scan.
When the counter 40 is alternately switched to the F-35 and the D-FF 36, during the period when the counter 40 is connected to the D-FF 35,
The delay time τ = 2L ₁ / c of the _first light receiving signal c ₁ is measured, and the distance calculation unit 33 obtains the distance L ₁ to the object 15 at a short distance. Also, if the counter 40 is a D-FF3
In the period connected to 6, the delay time τ = 2L ₂ / c of the second light reception signal c ₂ is measured, and the distance calculation unit 33 obtains the distance L ₂ to the long-distance object.

Therefore, even with the laser distance measuring device 41, it is possible to eliminate the inconvenience that the long distance object 14 cannot be recognized due to the spread of the image of the short distance object 15 having a large reflectivity. Objects and distant objects can be reliably recognized and the distance can be measured.

In the above embodiment, two light receiving signals having different amplification factors are switched by the signal switch 38. For example, the amplification factor of the light receiving circuit 28 is changed by the laser pulse P.
May be changed for each scan. However, in the method of changing the amplification factor, it may take time for the amplification factor to stabilize immediately after changing the amplification factor. Therefore, the two light receiving signals having different amplification factors are switched by the signal switch 38. As a result, the detection accuracy can be stabilized.

In the above-described embodiment, the method of changing the amplification factor of the received light signal or changing the threshold value of the received light level detecting unit has been described. You may make it switch for every period.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing a configuration of a conventional laser distance measuring device.

FIG. 2 is a diagram illustrating an operation of projecting a laser pulse from a light projecting unit.

FIG. 3 is a diagram showing a vehicle that is traveling following a preceding vehicle at a constant distance;

FIG. 4A is a diagram showing an image of a reflector and a roadside delineator of a front vehicle recognized by an ideal laser ranging device, and FIG. 4B is a diagram showing a front vehicle recognized by a conventional laser ranging device. FIG. 3 is a diagram showing an image of a reflector and a roadside delineator of FIG.

FIG. 5 is a diagram illustrating a beam cross section of a laser pulse projected from a light projecting unit and a distribution of light emission intensity.

FIG. 6 is a diagram illustrating a state in which a part of a laser pulse is applied to an object at a short distance when a laser pulse is projected at an object at a long distance.

FIG. 7 is a diagram showing, among laser pulses, a region irradiated to a long-distance object and a region irradiated to a short-distance object.

FIG. 8 is a diagram illustrating a part of a configuration of a signal processing unit.

FIG. 9 is a time chart for explaining the operation of the signal processing unit of the above.

10A is a diagram illustrating a laser pulse for one scan, FIG. 10B is a diagram illustrating a light receiving signal by a laser pulse reflected by a distant object and an image of the object, and FIG. FIG. 3 is a diagram showing a light receiving signal by a laser pulse reflected by an object and an image of the object.

FIG. 11 is a block diagram illustrating a configuration of a laser distance measuring apparatus according to an embodiment of the present invention.

FIG. 12 is a diagram showing a specific configuration of a signal processing unit of the laser distance measuring device of the above.

FIG. 13 is a time chart for explaining the operation of the signal processing unit of the above.

FIG. 14 is a block diagram showing a configuration of a laser distance measuring apparatus according to another embodiment of the present invention.

FIG. 15 is a diagram showing a specific configuration of a signal processing unit of the laser distance measuring device of the above.

FIG. 16 is a time chart for explaining an operation of the above signal processing unit.

[Explanation of symbols]

 Reference Signs List 22 semiconductor laser element 24 optical scanning section 25 signal processing section 26 scanning direction detecting section 27 light receiving element 29 light emitting signal generating section 30 light receiving level detecting section 31 light receiving level designation switching section 32 delay time measuring section 35, 36 D-FF 37 amplifier 38 Signal switch 40 Counter 42 Light reception signal number designation switch

Claims (2)

[Claims] 1. A light emitting device for projecting and scanning a light beam from a light projecting unit toward a detection area, receiving a light beam reflected by an object by a light receiving unit, and projecting the light beam from the light projecting unit. In a distance measuring device that starts a measuring means such as a distance measuring counter or a timer by a signal, stops the measuring means by a light receiving signal in a light receiving unit, and obtains a distance to an object based on a measurement value of the measuring means, A distance measuring device characterized in that the number of received light signals for one light emitting signal, which light receiving signal stops the measuring means, is switched. 2. A light emitting device for projecting and scanning a light beam from a light projecting unit toward a detection area, receiving a light beam reflected by an object by a light receiving unit, and projecting the light beam from the light projecting unit. In a distance measuring device that starts a measuring means such as a distance measuring counter or a timer by a signal, stops the measuring means by a light receiving signal in a light receiving unit, and obtains a distance to an object based on a measurement value of the measuring means, A distance measuring device, wherein a light receiving signal of a light receiving level among a plurality of light receiving signals corresponding to one light emitting signal stops the measuring means.