JPH11153664A - Object detector utilizing repetitively pulsed light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an object detector the service life of which can be prolonged and which can realize high-speed scanning. SOLUTION: A scanning section 11 which two-dimensionally scans laser light incorporates two acoustooptical elements 21 and 22 which are positioned so that ultrasonic waves may advance in the horizontal and vertical directions and piezoelectric elements 23 and 24 which are respectively stuck to the elements 21 and 22 and upon which AC voltages are respectively impressed from a laser driving section. When the scanning section 11 scans the laser light, the frequencies of the AC voltages impressed upon the elements 23 and 24 are changed in stages.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting an object such as a vehicle mounted on a vehicle and traveling in front of the host vehicle using repetitive pulse light such as pulsed laser light. The present invention relates to an object detection device installed on a road side of a road for detecting an object on a road such as an accident vehicle using repeated pulsed light.

[0002]

2. Description of the Related Art In order to prevent a collision accident or the like, the relative positional relationship between a host vehicle and a vehicle running ahead of the host vehicle or a front object such as a guardrail is important. As a technique for detecting the relative positional relationship, for example, a technique using a laser radar is known.

[0003] Techniques for detecting a positional relationship with a forward object using a laser radar are described, for example, in "Murao, Sasaki, Kajiki" Laser radar for automobiles "OPTRONICS (1994) No. 3
In the technique disclosed in this document, a pulsed laser beam is scanned at a predetermined scanning angle along a horizontal direction by reciprocating a mirror, and the mirror scans from a forward object. Is detected based on the propagation time of the reflected light.

[0004]

However, in the above-mentioned laser radar, a mechanical scanning mechanism for rotating a mirror is used, and the above-mentioned laser radar is used for a vehicle which is frequently exposed to a bad environment. Since it was installed, it was easily affected by the surrounding environment, and its performance was likely to deteriorate due to aging and the like. Therefore, there is a problem that the life is short. In addition, there is a limit to the improvement of the scanning speed of the mechanical scanning mechanism, and therefore, particularly when detecting a preceding vehicle traveling at a high speed, the preceding vehicle may not be detected quickly and accurately. there were.

In the above-mentioned laser radar, since the scanning direction of the laser beam is only the horizontal direction, it is not possible to acquire information on the height (vertical) direction of the object. Therefore, it was not possible to determine the type of the preceding vehicle such as a passenger car or a truck. In order to cope with this, for example, a configuration in which a plurality of mirrors are combined to scan laser light two-dimensionally can be considered. However, in this case, another problem arises that the size of the apparatus cannot be avoided.

Further, in the above-mentioned laser radar, the scan angle of the laser beam is fixed, so that, for example, when traveling on a curve, a range in which no forward object exists is also scanned. Therefore, there is a problem that an efficient scan cannot be performed because an unnecessary range is scanned. Moreover, since the scan angle of the laser beam is fixed, the angular resolution of the spot irradiated with the laser beam differs depending on the distance from the host vehicle. Specifically, the angular resolution becomes coarser as the position is farther from the host vehicle. Therefore, since only coarser position information can be obtained for a forward object located farther from the host vehicle, the forward object located farther from the host vehicle cannot be detected satisfactorily.

Therefore, a first object of the present invention is to provide an object detection device which can solve the above-mentioned technical problems, can prolong the service life, and can realize high-speed scanning. . A second object of the present invention is to
It is an object of the present invention to provide an object detection device capable of obtaining information in the height direction of an object without complicating the configuration.

Further, a third object of the present invention is to provide an object detecting device capable of prohibiting scanning of an unnecessary range. Still another object of the present invention is to provide an object detection device capable of eliminating a difference in resolution depending on distance.

[0009]

According to the first aspect of the present invention, there is provided an object detecting apparatus for detecting an object on a road using repetitive pulsed light. Pulse light irradiating means for irradiating repeated pulse light, scanning means for scanning the repeated pulse light radiated by the pulse light irradiating means, light receiving means for receiving reflected light, and the pulse light Detecting means for detecting an object based on the irradiation timing of the repetitive pulse light in the irradiation means and the light reception timing of the reflected light in the light receiving means, wherein the scanning means is irradiated by the pulse light irradiation means An acousto-optic device that changes the irradiation direction of repetitive pulsed light by ultrasonic waves, and the frequency of ultrasonic waves generated by this acousto-optical device An object detecting device, characterized in that those comprising a frequency changing means for changing the.

According to the present invention, since the frequency of the ultrasonic wave generated in the acousto-optic device can be changed,
The diffraction angle of the repetitive pulse light, that is, the irradiation direction can be changed. Therefore, the pulsed light can be repeatedly scanned. As described above, since the pulse light is repeatedly scanned using the acousto-optic element, compared to a conventional device having a mechanical scanning mechanism, the device has higher resistance to the surrounding environment and can have a longer life. it can.

Further, unlike the conventional device having a mechanical scanning mechanism, the speed at which the ultrasonic frequency is changed can be easily changed. Therefore, even an object requiring high-speed scanning, such as a vehicle running at high speed, can be reliably detected. According to a second aspect of the present invention, the acousto-optic device includes a horizontal-scan acousto-optic device and a vertical-scan acousto-optic device arranged in a cascade on an optical path of the repetitive pulse light irradiated by the pulse light irradiation unit. The object detection device according to claim 1, wherein:

According to the present invention, the repetitive pulse light is irradiated after passing through the horizontal-scan acousto-optic element and the vertical-scan acousto-optical element. Scanning can be realized. Therefore, it is possible to acquire not only the horizontal information of the object but also the vertical information. Therefore, for example, the type of the vehicle can be identified.

Moreover, even if two acousto-optical elements are combined, the size can be reduced as compared with a conventional device including a mirror and a mirror driving device, so that the device does not increase in size. The invention according to claim 3 is the object detection device according to claim 1 or 2, wherein the frequency changing means includes a range setting means for setting a change range of the ultrasonic frequency. .

According to the present invention, since the range of change of the ultrasonic frequency can be set, the range of the irradiation direction of the repetitive pulse light can be changed. Therefore, it is possible to realize an efficient scan excluding a range in which it is not necessary to scan the pulsed light repeatedly. According to a fourth aspect of the present invention, when the change range of the ultrasonic frequency set by the range setting unit is wide, the frequency changing unit sets the resolution to be coarse, and the ultrasonic set by the range setting unit. 4. The object detecting apparatus according to claim 3, further comprising: resolution setting means for setting the resolution finely when the frequency change range is narrow.

Note that the resolution refers to the horizontal and vertical angular resolution of a spot to be repeatedly irradiated with pulsed light. According to the present invention, when the change range of the ultrasonic frequency is wide, that is, when the scan angle of the repetitive pulse light is wide, the resolution is set roughly, and when the change range of the ultrasonic frequency is narrow, that is, the scan angle of the repetitive pulse light Is smaller, the resolution is set finer. Therefore, even in the case of an object located at a distant position, when scanning a narrow range limited to the object, the resolution is set finely, so that the object can be detected well.

According to a fifth aspect of the present invention, there is provided an image pickup means for picking up an image on a road, and an image picked up by the image pickup means is processed to extract an object existence range in which an object is likely to exist. And a scan control unit for controlling the range setting unit such that only the object existence range extracted by the range extraction unit is repeatedly scanned with the pulsed light. An object detection device according to any one of claims 1 to 4.

According to the present invention, for example, the change range of the ultrasonic frequency can be set so that only the object existence range extracted from the image on the road is repeatedly scanned with the pulse light. Therefore, when the object existence range is not extracted, the change range of the ultrasonic frequency is set to be wide, so that the pulsed light is repeatedly scanned at a predetermined scan angle, and when the object existence range is extracted, The range of change of the ultrasonic frequency can be narrowed, and only the object existing range can be repeatedly scanned with the pulsed light. in this case,
For example, when the object existence range is extracted only in a part of the screen, so-called skip scanning excluding other areas can be performed.

Further, the resolution can be set roughly when the range of change of the ultrasonic frequency is set wide, and the resolution can be set finely when the range of change of the ultrasonic frequency is set narrow. For example, when the object existence range is not extracted, a wide range can be roughly scanned, and when the object existence range is extracted, only the object existence range can be finely scanned. Therefore, efficient scanning can be realized.

[0019]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration of the object detection device according to the first embodiment of the present invention. This object detection device is mounted on a vehicle and detects an object in front of the host vehicle including an obstacle and a road structure existing in front of the host vehicle. The detection result of the object detection device is provided to an automatic driving control unit (not shown) including a brake control unit and a steering control unit, for example.
It is used as data necessary for automatically driving a vehicle.

The obstacle ahead is a vehicle running ahead of the host vehicle, a vehicle stopping in front of the host vehicle due to a breakdown, an accident, a traffic jam, or the like, or a falling object such as cardboard or wood. Road structures include guardrails, median strips,
Such as telephone poles. This object detection device is composed of a CCD (Charge Coupled Device) or the like, and has an on-vehicle camera 1 for capturing an image in front of the vehicle, and a radar head 2 for irradiating laser light or receiving reflected light. , Image processing device 3 for processing an image captured by vehicle-mounted camera 1
And a control device 4 functioning as a control center of the object detection device.

The radar head 2 is mounted, for example, at the front of a vehicle. The radar head 2 includes a light emitting unit 10 for emitting a pulsed laser light repeatedly, a scanning unit 11 for two-dimensionally scanning the laser light emitted from the light emitting unit 10, and control by the control device 4. A driving signal is given to the light emitting unit 10 based on the
A laser driving unit 12 for driving the scanning unit 11 while driving the scanning unit 11 and a light receiving unit 13 for receiving reflected light from a forward object are provided. The light emitting unit 10 is formed of, for example, a laser diode, and includes a light receiving unit 13.
Is composed of, for example, a photodiode.

The light emitting section 10 is not limited to the one that emits laser light, but may be a light emitting element such as an LED. However, it is most desirable to use one that irradiates a laser beam from which a minute spot can be obtained. Fig. 2 (a)
FIG. 2 is a plan view conceptually showing the configuration of the scanning unit 11, and FIG. 2B is a side view of the configuration shown in FIG. The scanning unit 11 performs a two-dimensional scan of the laser light L using an acousto-optic effect, and scans the laser light L in a horizontal direction H, which is cascaded on the optical path of the laser light L. The horizontal scanning acousto-optic element 21 and the vertical scanning acousto-optic element 22 for scanning the laser beam L in the vertical direction V perpendicular to the horizontal direction H, and the piezoelectric elements 23 bonded to the acousto-optic elements 21 and 22, respectively. , 24.

The piezoelectric element 23 is disposed on the side surface of the horizontal scanning acousto-optic element 21 so that the ultrasonic wave travels in the horizontal direction H. The piezoelectric element 24 transmits the ultrasonic wave in the vertical direction V. Acousto-optic device 2 for vertical scanning
2 is disposed on the upper surface. Since an AC voltage is applied from the laser drive unit 12 to each of the piezoelectric elements 23 and 24, each of the acousto-optical elements 21 and 22 travels along the horizontal direction H and the vertical direction V, respectively. Ultrasonic waves are generated. The generated ultrasonic wave functions as a diffraction grating, and the laser light L incident on each of the acousto-optic elements 21 and 22 is diffracted in the horizontal direction H and the vertical direction V, respectively.

The diffraction angle of the laser beam L is
This is a function of the wavelength of the ultrasonic wave propagating in the piezoelectric elements 1 and 22, and this wavelength is inversely proportional to the frequency of the AC voltage applied to each of the piezoelectric elements 23 and 24. Therefore, in the first embodiment, in the laser driving unit 12, the frequency (hereinafter, referred to as “horizontal frequency”) Ff of the AC voltage applied to the piezoelectric element 23 and the frequency (hereinafter, “vertical”) of the AC voltage applied to the piezoelectric element 24 are determined. The frequency is changed within a frequency change range set by the control device 4 to realize a two-dimensional scan of the laser light L.

More specifically, the laser driving unit 12
After changing the horizontal frequency Ff once within the set frequency change range, the vertical frequency Fv is changed by one step, and the change of the horizontal frequency Ff is restarted in this state. Then, the above processing is repeatedly executed. As a result, the diffraction angle of the laser light L changes stepwise along two directions, the horizontal direction H and the vertical direction V. Thus, the laser light scans a two-dimensional area defined by the horizontal scan angle θ1 and the vertical scan angle θ2 according to each frequency change range.

As the acousto-optic element, for example, an acousto-optic element having a model number "EFL-D200Y01" manufactured by Matsushita Electric Industrial Co., Ltd. can be applied. This acousto-optic device has an ultrasonic frequency of 59.5 to 94.5 (MHz).
Within the range (center frequency 77 (MHz), bandwidth 35 (MHz))
When the frequency of the applied AC voltage is changed so as to change the diffraction angle, the diffraction angle of the laser beam changes in a width of about 3.8 degrees.

The laser light emitted from the radar head 2 is reflected by a forward object. The reflected light from the forward object is received by the light receiving unit 13 (see FIG. 1) of the radar head 2 and is converted into an electric signal, which is then provided to the position detecting unit 31 of the control device 4. The position detection unit 31 is provided with data on the emission timing of the laser light and the irradiation direction of the laser light from the laser drive unit 12. The position detection unit 31 obtains a distance between the laser light reflected object and the object on which the laser light is reflected, based on a time difference between the emission timing of the laser light in the light emitting unit 10 and the signal reception timing in the light receiving unit 13. Further, the position detection unit 31
The direction of the object from which the laser light has been reflected is acquired based on the emission direction of the laser light. Therefore, the position detection unit 31 can detect the position of the forward object based on the electric signal provided from the light receiving unit 13. Position data consisting of the acquired distance data and direction data, as described above, is given to the automatic driving control unit not shown,
It is provided to the scan control unit 32.

The scan control unit 32 is also provided with image recognition data from the image processing device 3. The image processing device 3 performs image recognition processing that combines, for example, background subtraction processing, time difference processing, and spatial difference processing on image data given from the on-vehicle camera 1, so that there is a possibility that a forward object exists. (Hereinafter, referred to as “object existence range”) E0.

The image recognition process is performed, for example, by using "
Aoki, Tanaka, Nishiyama, Tokudome, Toba "Development of Vehicle Detector Using Image Processing" Sumitomo Electric No. 144, pp. 115-118
1994 ". Scan control unit 32
Determines whether or not the object existence range E0 has been extracted based on image recognition data provided from the image processing apparatus 3, and according to the determination result, determines the horizontal scan angle θ1 and the vertical scan angle θ2 of the laser beam. , The pulse rate of the drive signal for driving the light emitting unit 10 (corresponding to the number of irradiation pulses per unit time) Vp, and the frequency change rate (per unit time). Vf is set. The set frequency change range, pulse rate Vp, and frequency change speed Vf are provided to the laser drive unit 12.

The laser driving section 12 gives a driving signal to the light emitting section 10 at a set pulse rate Vp. Further, the horizontal frequency Ff is changed at a speed corresponding to the set frequency change speed Vf within the set horizontal frequency change range. Further, the vertical frequency Fv is changed according to the change timing of the horizontal frequency Ff. Hereinafter, the scanning of the laser beam will be described in detail on the assumption that the time required for the two-dimensional scan, that is, the time for scanning one frame (hereinafter, referred to as “scan time”) Δt is constant.

The scan control unit 32 determines whether the object existence region E0 has not been extracted, for example, when it is raining and the contrast between the object and the background image is not clearly separated, Object existence range E0
Exists, and if the object existence range E0 cannot be specified as one, the laser light is applied to a range (hereinafter, referred to as a "maximum field range") E1 corresponding to the range of the field of view normally seen by the driver, and the angle resolution is relatively coarse. The frequency change speed Vf is set so as to scan at Δθ.

More specifically, the scan control unit 32
As shown in (a), the horizontal first range ΔFh1 corresponding to the horizontal scan angle θ1 that defines the maximum visual field range E1 is set as the horizontal frequency change range. Further, as shown in FIG. 3B, the vertical scan angle θ2
Is set for the vertical first range ΔFv1. further,
The frequency change speed Vf is set to the first frequency change speed Vf1.

In this case, the laser drive unit 12 supplies a drive signal to the light emitting unit 10 and changes the horizontal frequency Ff at the first frequency change speed Vf1. Then, the timing at which the scanning for one line ends (t1, t2,...,
At tn), the vertical frequency Fv is changed, and in this state, the change of the horizontal frequency Ff is restarted. As a result of repeating the above processing, the laser light is sequentially irradiated in spots within the maximum visual field range E1, as shown in FIG. In this case, the angular resolution Δθ1 of the spot 40 is relatively large, so that the laser light is scanned within the maximum visual field range E1 with a coarse angular resolution.

On the other hand, if the object existence range E0 has been extracted, the scan control unit 32 sets the frequency change speed Vf so that the laser beam is scanned only in the object existence range E0 with a relatively fine angular resolution Δθ. I do. More specifically, as shown in FIGS. 4A and 4B, the scan control unit 32 controls the horizontal second range corresponding to the horizontal scan angle θ1 and the vertical scan angle θ2 that define the object existence range E0. ΔFh2,
And the second vertical range Δ corresponding to the vertical scan angle θ2
Fv2 is set as a horizontal frequency change range and a vertical frequency change range, respectively. In this case, the object existence range E0
Is usually a part of the maximum visual field range E1, so that each of the second ranges ΔFh2 and ΔFv2 are respectively equal to the first ranges ΔFh1 and ΔFh1.
Set to a range smaller than Fv1.

Further, the frequency changing speed Vf is set to a value lower than the first frequency changing speed Vf1. The reason why the frequency change speed Vf is reduced is to keep the horizontal scanning time and the vertical scanning time constant in the processing of the control device 4. Laser light is
As shown in FIG. 5, spots are sequentially radiated within the object existence range E0. In this case, the angular resolution Δθ2 of the spot 41 is finer than the angular resolution Δθ1 of the spot 40, and therefore, the laser light is scanned within the object existence range E0 with a fine angular resolution.

As described above, according to the first embodiment,
Since the laser light is scanned using the acousto-optic elements 21 and 22, the life can be extended as compared with a conventional apparatus that scans the laser light using a mirror, and high-speed scanning is realized. be able to. In addition, two acousto-optic elements 2 are used for two-dimensional scanning with laser light.
Since only 1 and 22 are combined, the size of the radar head can be smaller than when combining mirrors. Therefore, the radar head can be reduced in size and weight.

Further, when the object existence range E0 has not been extracted, a wide range is roughly scanned to obtain the object existence range E0.
When E0 is extracted, the laser beam is finely scanned by narrowing down the object existence range E0, so that very efficient scanning can be realized. When a plurality of object existence ranges E0 are extracted on the entire screen, for example, a so-called skip scan for scanning only each object existence region E0 in the entire image may be performed. According to this configuration, even when two or more object existence ranges E0 exist,
Position information of each object can be reliably obtained.

In the first embodiment, the scan time Δ
Since scanning is performed under the condition that t is constant, the angular resolution Δθ can be made coarser as the visual field range is wider, and finer as the visual field range is narrower. However, for example, there is a case where a scan in which the angular resolution Δθ is constant regardless of the size of the visual field range is desired. In this case, as the field of view becomes narrower, the frequency change speed Vf is made relatively faster, as shown in FIG. As a result, the time required for scanning one line is reduced, and the scan time Δt is also reduced. As a result, the angular resolution Δθ can be made coarser than when the scan time Δt is constant.

In some cases, a scan in which the scan time Δt is constant and the angular resolution Δθ is constant is desired. In this case, in the scan shown in FIG.
It is preferable to perform control so that the pulse rate Vp becomes slower as the first horizontal range ΔFh1 and the first vertical range ΔFv1 become narrower. FIG. 7 is a conceptual diagram illustrating an installation mode of the object detection device according to the second embodiment of the present invention.

In the first embodiment, the object detection device is mounted on the vehicle, whereas in the second embodiment, the object detection device is installed on the road side of the road. More specifically, in the second embodiment, a pole 51 having a height of L1 (L1 ≦ 10 (m); for example, L1 = 5 (m)) from the road surface is installed on the road side of the road 50. , An object detection device 52 is provided.

The object detecting device 52 is attached to the pole 51 so that the laser beam is emitted toward the road 50. In this case, the object detection device 52 has a length in the width direction of at least n lanes (for example, n = 3) and a predetermined length R (for example, R = 100) along the road 50.
(m)) The object monitoring range 53 (shaded area) having the length can be scanned.

FIG. 8 is a diagram showing the configuration of the scanning unit 11 in the radar head 2 provided in the object detection device 52. 8, the same reference numerals are used for the same functional parts as in FIG. The object detection device 52 is provided with the first
The configuration is substantially the same as the configuration of the object detection device according to the embodiment, except that a concave lens 55 is provided downstream of the vertical scanning acousto-optic element 22 provided in the radar head 2 in the laser light traveling direction.
Is different. The concave lens 55 is for widening the vertical scan angle θ2 of the laser light emitted from the vertical scanning acousto-optic element 22. By providing the concave lens 55, a point 20 to 30 (m) away from the installation point of the object detection device 52 can be set as a boundary of the object monitoring range 53.

When the object detection device 52 is provided at the tip of the pole 51, the current acousto-optic device emits laser light to a location closer to a location 200 (m) away from the installation location of the object detection device 52 in terms of performance. Since the light cannot be diffracted, no object could be detected in the vicinity of the object detection device 52. On the other hand, as described above, if the vertical scanning angle θ2 of the laser beam can be increased by using the concave lens 55, the laser beam can be irradiated also in the vicinity of the object detection device 52. An object can also be detected in the vicinity of the detection device 52.

Note that a convex mirror may be used in place of the concave lens 55 to widen the vertical scan angle θ2 of the laser beam. The detection result of the object detection device 52 is given to a system main device (not shown). The system main unit is
Based on the detection result, information about the object is given to the vehicle through a roadside beacon or a radio as needed.
Thus, for example, a secondary accident can be prevented.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described two embodiments, and various design changes can be made within the scope described in the claims. Can be applied.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an object detection device according to a first embodiment of the present invention.

FIG. 2A is a plan view conceptually showing a configuration of a scanning unit, and FIG. 2B is a side view of the configuration shown in FIG.

FIG. 3 is a diagram illustrating changes in horizontal frequency and vertical frequency when scanning the maximum visual field range under the condition that the scan time is constant.

FIG. 4 is a diagram illustrating changes in horizontal frequency and vertical frequency when scanning the object existence range under the condition that the scan time is constant.

FIG. 5 is a diagram for explaining each angular resolution when scanning a maximum visual field range and when scanning an object existence range.

FIG. 6 is a diagram showing changes in the horizontal frequency and the vertical frequency when performing a scan for keeping the angular resolution constant irrespective of the width of the visual field range.

FIG. 7 is a conceptual diagram for explaining an installation mode of an object detection device according to a second embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of a scanning unit in a radar head provided in an object detection device according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF REFERENCE NUMERALS 1 vehicle-mounted camera (imaging means) 3 image processing device (range extracting means) 10 light emitting section (pulse light irradiating means) 11 scanning section (scanning means) 12 laser driving section (scanning means, frequency changing means,
Range setting means, resolution setting means, scan control means 13 light receiving section (light receiving means) 21 acousto-optic element for horizontal scanning (acousto-optic element, acousto-optic element for horizontal scanning) 22 acousto-optic element for vertical scanning (acousto-optic element, Acousto-optic device for vertical scanning 23 Piezoelectric device (acousto-optic device, acousto-optic device for horizontal scanning) 24 Piezoelectric device (acousto-optic device, acousto-optic device for vertical scanning) 31 Position detection unit (detection unit) 32 Scan control unit ( (Scanning means, frequency changing means, range setting means, resolution setting means, scan control means) 52 Object detection device

Claims (5)

[Claims] 1. An object detecting device for detecting an object on a road using repetitive pulse light, comprising: pulse light irradiating means for irradiating repetitive pulse light; Scanning means for scanning the repetitive pulse light, light receiving means for receiving the reflected light, based on the irradiation timing of the repetitive pulse light in the pulse light irradiation means and the light receiving timing of the reflected light in the light receiving means, Detecting means for detecting an object, wherein the scanning means changes an irradiation direction of the repetitive pulse light irradiated by the pulse light irradiation means by ultrasonic waves, and an acousto-optic element generated in the acousto-optical element. And a frequency changing means for changing a frequency of the ultrasonic wave to be detected. 2. The acousto-optic device according to claim 1, wherein the acousto-optic device includes a horizontal-scan acousto-optic device and a vertical-scan acousto-optic device arranged in a cascade on an optical path of the repetitive pulse light irradiated by the pulse light irradiation means. The object detection device according to claim 1, wherein 3. An object detecting apparatus according to claim 1, wherein said frequency changing means includes a range setting means for setting a change range of the ultrasonic frequency. 4. The method according to claim 1, wherein when the change range of the ultrasonic frequency set by the range setting means is wide, the frequency setting means sets the resolution to a coarse value, and changes the ultrasonic frequency set by the range setting means. 4. The object detecting apparatus according to claim 3, further comprising: resolution setting means for setting the resolution finely when the range is narrow. 5. An image capturing means for capturing an image on a road, and a range extracting means for processing an image captured by the image capturing means to extract an object existence range in which an object is likely to exist. 5. The apparatus according to claim 1, further comprising: scan control means for controlling said range setting means so as to repeatedly scan only the object existence range extracted by said range extraction means with pulsed light. An object detection device according to any one of the above.