This application claims priority under 35 U.S.C. Section 119 of Japanese Patent Application No. 2010-208525 filed Sep. 16, 2010, entitled “BEAM IRRADIATION DEVICE AND LASER RADAR SYSTEM”. The disclosure of the above application is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a beam irradiation device for irradiating a targeted area with laser light, and a laser radar system for detecting a condition of a targeted area based on reflected light of laser light with respect to the targeted area.
2. Disclosure of Related Art
In recent years, a laser radar system has been loaded in a family automobile or a like vehicle to enhance security in driving. Generally, the laser radar system is so configured as to scan a targeted area with laser light to detect presence or absence of an obstacle at each of scanning positions, based on presence or absence of reflected light at each of the scanning positions. The laser radar system is also configured to detect a distance to the obstacle at each of the scanning positions, based on a required time from an irradiation timing of laser light to a light receiving timing of reflected light at each of the scanning positions.
A beam irradiation device is loaded in a laser radar system to scan a targeted area with laser light. In the above arrangement, it is possible to use an actuator which drives a mirror into which laser light is entered about two axes, or an actuator which drives a lens for transmitting laser light, as an arrangement for scanning a targeted area with laser light. Alternatively, laser light may be scanned using a polygonal mirror.
Laser light is irradiated onto a targeted area, with a predetermined shape. The beam irradiation device is provided with a lens for shaping laser light into an intended shape. It is desirable to irradiate laser light onto the targeted area in a state that a boundary of laser light is clearly recognized, in other words, in a state that the light intensity is sharply decreased at a boundary portion of laser light. The lens for shaping laser light is so designed as to make optical characteristics (beam profile) of laser light satisfactory in the targeted area.
Normally, the beam irradiation device is housed in a housing to be shielded from the outside. A transparent emission window for transmitting laser light of a use wavelength is formed in the housing, and laser light is projected onto a targeted area through the emission window. Accordingly, characteristics of laser light in the targeted area are affected by the characteristics of the emission window to some extent. If the characteristics of the emission window are poor, optical characteristics (beam profile) of laser light in the targeted area may be degraded, even if the characteristics of the beam shaping lens are enhanced.
A first aspect of the invention relates to a beam irradiation device. The beam irradiation device according to the first aspect includes a laser light source which emits laser light; an actuator which causes the laser light to scan a targeted area; and an emission window through which the laser light via the actuator is transmitted. The emission window is formed with reflection suppressing means for suppressing surface reflection.
A second aspect of the invention relates to a laser radar system. The laser radar system according to the second aspect includes the beam irradiation device according to the first aspect, and a light receiving portion which receives laser light reflected on the targeted area.
In the following, an embodiment of the invention is described referring to the drawings.
Referring to
The housing 10 has a cubic shape, and houses therein the projection optical system 20, the light receiving optical system 30, and the circuit unit 40. As shown in
The projection optical system 20 is provided with a laser light source 21, a beam shaping lens 22, and a mirror actuator 23.
The laser light source 21 emits laser light of a wavelength of or about 900 nm.
The beam shaping lens 22 converges laser light in such a manner that laser light emitted from the laser light source 21 has a predetermined shape in a targeted area. For instance, the beam shaping lens 22 is designed in such a manner that the beam shape in a targeted area (which is located at a position ahead of a beam output port of the beam irradiation device by about 100 m in this embodiment) has an elliptical shape of about 2 m in longitudinal direction and about 0.2 m in transverse direction.
The mirror actuator 23 is provided with a mirror 150 into which laser light transmitted through the beam shaping lens 22 is entered, and a mechanism for rotating the mirror 150 about two axes. Laser light is scanned in a targeted area by rotating the mirror 150. The details of the mirror actuator 23 will be described later referring to
The light receiving optical system 30 is provided with a filter 31, a light receiving lens 32, and a photodetector 33. The filter 31 is a band-pass filter which transmits only light of a wavelength region of laser light to be emitted from the laser light source 21. The light receiving lens 32 collects light reflected on a targeted area. The photodetector 33 is constituted of an avalanche photodiode (APD) or a PIN photodiode, and outputs an electrical signal of a magnitude corresponding to the received light amount, to the circuit unit 40.
The circuit unit 40 is provided with e.g. a CPU and a memory, and controls the laser light source 21 and the mirror actuator 23. Further, the circuit unit 40 determines presence or absence of an obstacle in a targeted area, and measures a distance to the obstacle, based on a signal from the photodetector 33. Specifically, laser light is emitted from the laser light source 21 at a predetermined scanning position in a targeted area. In response to output of a signal from the photodetector 33, the photodetector 33 detects presence of an obstacle at the scanning position. Further, a distance to the obstacle is measured based on a time difference between a timing at which laser light is emitted and a timing at which a signal is outputted from the photodetector 33 at the scanning position.
The emission window 50 is constituted of a transparent flat plate having a uniform thickness. The emission window 50 is configured to suppress degradation of optical characteristics of laser light when the laser light transmitted from the side of the mirror actuator 23 is transmitted through the emission window 50. Specifically, the emission window 50 is made of a material having a high transparency, and the surface roughness and the haze value of the emission window 50 are set to small values to prevent light scattering on the incident surface and the output surface of the emission window 50. Further, an anti-reflection film (AR coat) is formed on each of the incident surface and the output surface of the emission window 50 to prevent internal reflection of the emission window 50.
Examples of the material composing the emission window 50 are cycloolefin polymer and polycycloolefin polymer. For instance, polymers under the trade names of “ZEONEX 480R”, “ZEONEX E48R”, “ZEONEX 330R”, “ZEONOR 1430R” of ZEON CORPORATION may be used as the material for the emission window 50.
As described above, the emission window 50 is configured in such a manner that the surface roughness and the haze value of the laser light incident surface and the laser light output surface thereof are set to small values in order to prevent laser light scattering. Laser light scattering on the incident surface or the output surface is maximized when the height of a projection or a recess on the incident surface or the output surface is set to one-half of the wavelength of laser light, and is sharply decreased, as the height of a projection or a recess is smaller than one-half of the wavelength. In view of the above, in this embodiment, the surface roughness (Rmax) of the incident surface and the output surface is set to a value smaller than 900 nm/2=450 nm, and is set to e.g. 300 nm or less. Further, the haze value is set to 2% or less.
Configuring the emission window 50 as described above enables to suppress degradation of optical characteristics of laser light when the laser light is transmitted through the emission window 50.
Further, in this embodiment, an anti-reflection film (AR coat) is formed on each of the incident surface and the output surface of the emission window 50. With this arrangement, it is possible to more effectively suppress degradation of optical characteristics of laser light. The characteristics and the effects of the anti-reflection film (AR coat) will be described later referring to
In this embodiment, the light receiving window 60 is configured in the same manner as the emission window 50. With this arrangement, it is possible to more efficiently guide weak laser light reflected on a targeted area to the photodetector 33.
The mirror actuator 23 is provided with a tilt unit 110, a pan unit 120, a magnet unit 130, a yoke unit 140, a mirror 150, and a transparent plate 160.
The tilt unit 110 is provided with a support shaft 111, a tilt frame 112, and two tilt coils 113. The support shaft 111 is formed with grooves 111a near both ends of the support shaft 111. E-rings 117a and 117b are mounted in the respective grooves 111a.
The tilt frame 112 is formed with coil mounting portions 112a at left and right ends thereof for mounting the tilt coils 113. The tilt frame 112 is further formed with a groove 112b for engaging the support shaft 111, and vertically aligned two holes 112c.
The support shaft 111 is engaged in the groove 112b formed in the tilt frame 112, and adhesively fixed to the tilt frame 112 in a state that bearings 116a and 116b, the E-rings 117a and 117b, and polyslider washers 118 are mounted on both side of the support shaft 111. Further, bearings 112d are mounted in the two holes 112c in the tilt frame 112 from an upper direction and a lower direction. With this operation, as shown in
The pan unit 120 is mounted on the assembled tilt unit 110 in the manner as described below. Thereafter, the tilt unit 110 is attached to a yoke 141 in the manner as described below, using the bearings 116a and 116b, the E-rings 117a and 117b, the polyslider washers 118, and a shaft fixing member 142.
Referring back to
Further, a downwardly extending leg portion 121f is formed on the lower plate portion 121c, and a recess portion 121g for receiving a transparent plate 160 is formed in the leg portion 121f. The transparent plate 160 is mounted in the recess portion 121g from beneath the recess portion 121g, and the transparent plate 160 is fixed to the leg portion 121f of the pan frame 121 by a transparent plate fixing bracket 161. A balancer 122d is attached to an upper end of the support shaft 122.
The magnet unit 130 is provided with a frame 131, two pan magnets 133, and eight tilt magnets 132. The frame 131 has such a shape that a recess portion 131a is formed on the front side thereof. An upper plate portion 131b of the frame 131 is formed with horizontally extending two cutaways 131c, and is further formed with a screw hole 131d in the middle thereof. The eight tilt magnets 132 are mounted in upper and lower two rows on the left and right inner surfaces of the frame 131. Further, as shown in
The yoke unit 140 is provided with the yoke 141 and the shaft fixing member 142. The yoke 141 is constituted of a magnetic member. The yoke 141 is formed with wall portions 141a at left and right sides thereof, and recess portions 141b for mounting the support shaft 111 of the tilt unit 110 are formed in respective lower ends of the wall portions 141a. The yoke 141 is formed with vertically extending two screw through-holes 141c in an upper portion thereof, and is further formed with a screw hole 141d at a position corresponding to the screw hole 131d of the magnet unit 130. The distance between the inner side surfaces of the two wall portions 141a is set larger than the distance between the two grooves 111d of the support shaft 111.
The shaft fixing member 142 is a thin plate metal member having flexibility. Plate spring portions 142a and 142b are formed on a front portion of the shaft fixing member 142. Receiving portions 142c and 142d for restricting falling of the bearings 116a and 116b of the tilt unit 110 are formed on respective lower ends of the plate spring portions 142a and 142b. Further, an upper plate portion of the shaft fixing member 142 is formed with holes 142e at positions corresponding to the two screw holes 141c of the yoke 141, and is further formed with a hole 142f at a position corresponding to the screw hole 141d of the yoke 141.
In assembling the mirror actuator 23, the tilt unit 110 shown in
After the pan unit 120 is mounted as described above, the mirror 150 is placed in the step portions 121e of the pan frame 121, and fixed thereat. Thereafter, the bearings 116a and 116b mounted on both ends of the support shaft 111 of the tilt unit 110 are placed in the recess portions 141b of the yoke 141 shown in
In this way, a structure member shown in
The assembled structure member shown in
In the assembled state shown in
The balancer 122d is adapted to adjust pivotal movement of the structure member shown in
In the assembled state shown in
Further, in the assembled state shown in
Referring to
The laser light source 21 and the beam shaping lens 22 are disposed on a top surface of the base plate 500. The laser light source 21 is mounted on a laser light source circuit board 400 disposed on the top surface of the base plate 500.
Laser light emitted from the laser light source 21 is converged in horizontal direction and in vertical direction by the beam shaping lens 22, and is shaped into a predetermined form in a targeted area. Laser light transmitted through the beam shaping lens 22 is entered into the mirror 150 of the mirror actuator 23, and is reflected on the mirror 150 toward the targeted area. Laser light is scanned in the targeted area by driving the mirror 150 by the mirror actuator 23.
The mirror actuator 23 is disposed at such a position that scanning laser light from the beam shaping lens 22 is entered into the mirror surface of the mirror 150 at an incident angle of 45 degrees with respect to the horizontal direction, when the mirror 150 is set to a neutral position. The term “neutral position” indicates a position of the mirror 150, wherein the mirror surface is aligned in parallel to the vertical direction, and scanning laser light is entered into the mirror surface at an incident angle of 45 degrees with respect to the horizontal direction.
A circuit board (not shown) for supplying a drive signal to the coils 113 and 123 of the mirror actuator 23 is disposed behind the mirror actuator 23, on the top surface of the base plate 500, in addition to a circuit board 400 and other members. Further, a circuit board 300 is disposed underneath the base plate 500, and circuit boards 301 and 302 are disposed on a side surface and a back surface of the base plate 500.
These circuit boards are included in the circuit unit 40 shown in
As shown in
A light collecting lens 304, an aperture 305, and a ND (neutral density) filter 306 are mounted on the flat surface 503 on the back surface of the base plate 500 by an attachment member 307. The flat surface 503 is formed with an opening 503a, and the transparent plate 160 mounted on the mirror actuator 23 is projected from the back surface of the base plate 500 through the opening 503a. In this example, when the mirror 150 of the mirror actuator 23 is set to the neutral position, the transparent plate 160 is set to such a position that the two flat surfaces of the transparent member 200 are aligned in parallel to the vertical direction, and are inclined with respect to an optical axis of emission light from the semiconductor laser 303 by 45 degrees.
Laser light (hereinafter, called as “servo light”) emitted from the semiconductor laser 303 transmitted through the light collecting lens 304 has the beam diameter thereof reduced by the aperture 305, and has the light intensity thereof reduced by the ND filter 301. Thereafter, the servo light is entered into the transparent plate 160, and subjected to refraction by the transparent plate 160. Thereafter, the servo light transmitted through the transparent plate 160 is received by the PSD 308, which, in turn, outputs a position detection signal depending on a light receiving position of servo light.
Servo light is refracted by the transparent plate 160 disposed with an inclination with respect to an optical axis of laser light. In this arrangement, when the transparent plate 160 is pivotally moved from the broken-line position in the arrow direction, the optical path of servo light is changed from the dotted-line position to the solid-line position in
When a targeted area is scanned with laser light, the circuit unit 40 shown in
Further, the circuit unit 40 controls the laser light source 21 to emit laser light at a timing at which the scanning position of laser light has reached a predetermined position.
Then, as described above, presence or absence of an obstacle at the scanning position is detected, based on a signal from the photodetector 33 at the emission timing, and a distance to the obstacle is measured.
In this embodiment, the swing angle of laser light for scanning a targeted area is set to ±20 degrees in horizontal direction, and ±5 degrees in vertical direction. With this arrangement, the incident angle of laser light to be entered into the emission window 50 is set to about 20 degrees as a maximum value. In this embodiment, an anti-reflection film is formed on each of the incident surface and the output surface of the emission window 50 to suppress a reflectance in the incident angle range up to 20 degrees.
As shown in
In the characteristics shown in
As described above, it is possible to suppress internal reflection of the emission window 50 in the swing angle range (0°±20°) of laser light, and to keep the beam profile of laser light in a targeted area satisfactory by forming the anti-reflection film 51 having the characteristics shown in FIG. 8 on each of the incident surface and the output surface of the emission window 50.
In each of the drawings of
Beam profile measurement was carried out using the arrangement shown in
The measurement result shown in
As shown by the broken line in
Transmittance measurement was carried out using the arrangement shown in
Referring to
Further, in the case where “ZEONEX 480R” is used, although optical characteristics (beam profile) of laser light are not significantly improved as compared with the case where “ZEONOR 1430R” is used, the transmittance of the emission window 50 is remarkably improved, as is clearly shown in
In the measurement, improvement on optical characteristics (beam profile) of laser light was hardly observed, in the case where “ZEONEX E48R” was used. In the above case, however, as is clearly shown in
As described above, in this embodiment, it is possible to make optical characteristics (beam profile) of laser light to be irradiated onto a targeted area satisfactory by using a material having a high transparency as a material for the emission window 50, setting the surface roughness and the haze value of the emission window 50 to small values, and forming the anti-reflection film 51 on each of the incident surface and the output surface of the emission window 50.
In particular, it is possible to make optical characteristics (beam profile) of laser light satisfactory, and to enhance the detection precision of an obstacle in the targeted area, while enhancing the intensity of laser light to be irradiated onto a targeted area, by forming the anti-reflection film 51 on each of the incident surface and the output surface of the emission window 50. Use of “ZEONOR 1430R” as a material for the emission window 50 enables to realize optical characteristics (beam profile) substantially the same as the case devoid of the emission window 50.
Further, in this embodiment, the anti-reflection film 51 is so configured as to keep the lower limit of the reflectance in the incident angle range of laser light at least corresponding to the laser light scanning range (0°±20°). With this arrangement, it is possible to suppress degradation of optical characteristics of laser light resulting from internal reflection of the emission window 50 at any scanning position.
In the embodiment, internal reflection of the emission window 50 is suppressed by forming the anti-reflection film 51 on each of the incident surface and the output surface of the emission window 50. In the modification, internal reflection of the emission window 50 is suppressed by forming a fine periodic structure on each of the incident surface and the output surface of the emission window 50. The arrangement of the light receiving window 60 is substantially the same as the arrangement of the emission window 50.
As shown in
Accordingly, establishing the expression: P≦λ/n, where P is the pitch of the projections 52a on the periodic structure 52, n is the refractive index of a material, and λ is the wavelength of laser light, enables to suppress reflection of laser light on the incident surface and the output surface of the emission window 50. In the modification, the pitch P of the periodic structure 52 formed on each of the incident surface and the output surface of the emission window 50 is determined to satisfy the expression: P≦λ/n, in view of the above aspect.
In the modification, since the reflection suppressing function of the periodic structure 52 is substantially kept unchanged without depending on the incident angle of laser light, it is possible to suppress degradation of optical characteristics of laser light resulting from inner reflection of the emission window 50 at any laser light scanning position, as well as the embodiment.
The embodiment of the invention has been described as above. The invention is not limited to the foregoing embodiment, and the embodiment of the invention may be modified in various ways other than the above.
For instance, in the embodiment, there has been described an arrangement example of a mirror actuator configured such that a mirror is rotated about two axes. Alternatively, the invention may be applicable to a mirror actuator having an arrangement other than the above arrangement, an actuator of a type such that laser light is scanned by driving a lens, or an actuator incorporated with a polygonal mirror.
In the embodiment and the modification, the light receiving window 60 has substantially the same arrangement as the arrangement of the emission window 50. Alternatively, the light receiving window 60 may be devoid of the anti-reflection film 51. Further alternatively, the light receiving window 60 may be made of a material other than the above. Further alternatively, the surface roughness and the haze value of the light receiving window 60 may be the ones other than the above.
Further alternatively, a filter may be disposed on the back surface side of the emission window 50 to prevent intrusion of external light into the housing 10 through the emission window 50 and the opening 11. The above filter is a band-pass filter for transmitting only light of a wavelength region of laser light to be emitted from the laser light source 21, as well as the light-receiving-side filter 31. With this arrangement, it is possible to prevent external light of a wavelength near the wavelength of servo light from reaching the PSD 308, which may adversely affect control of the mirror actuator 23. In the above arrangement, the emission window 50 itself may have filter characteristics substantially the same as the characteristics of the filter 31.
Furthermore, the wavelength region of laser light may be changed to a range other than the range described in the embodiment, as necessary. In the case where the wavelength region of laser light is changed from the one described in the embodiment, the characteristics of the anti-reflection film 51 may also be modified to be in conformity with the changed wavelength region.
The embodiment of the invention may be changed or modified in various ways as necessary, as far as such changes and modifications do not depart from the scope of the present invention hereinafter defined.
Number | Date | Country | Kind |
---|---|---|---|
2010-208525 | Sep 2010 | JP | national |