LASER RADAR DEVICE

A laser radar device includes: a light source; a mirror rotatable about a rotation shaft to reflect laser light emitted by the light source; a window; and a detector to detect laser light. The mirror has a low reflection area having a lower reflectance than the other region of the mirror, in a state where a mirror surface faces toward the light source, at position adjacent to the light source than the detector in an axial direction of the rotation shaft and adjacent to the window than a region where the laser light emitted by the light source hits for a first time in a radial direction of the rotation shaft. The window has an inclined posture in which a distance from the rotation shaft is shorter at position adjacent to the detector than at position adjacent to the light source.

TECHNICAL FIELD

The present disclosure relates to a laser radar device, and more particularly to technology for suppressing detection of stray light.

BACKGROUND

A device suppresses detection of stray light by a detector. The device includes a light blocking section that partitions a light projecting space and a light receiving space in order to suppress stray light from entering the light receiving space from the light projecting space.

SUMMARY

According to one aspect of the disclosure, a laser radar device includes: a light source configured to emit laser light; a mirror rotatable about a rotation shaft to reflect the laser light emitted by the light source; a window through which the laser light reflected by the mirror passes; and a detector configured to detect the laser light passing through the window to be reflected by the mirror. The mirror has a low reflection area having a lower reflectance than the other region of the mirror, in a state where a mirror surface of the mirror faces toward the light source, at position adjacent to the light source than the detector in an axial direction of the rotation shaft and adjacent to the window than a region where the laser light emitted by the light source hits for a first time in a radial direction of the rotation shaft. The window has an inclined posture in which a distance from the rotation shaft is shorter at position adjacent to the detector than at position adjacent to the light source.

DETAILED DESCRIPTION

A device suppresses detection of stray light by a detector. The device includes a light blocking section that partitions a light projecting space and a light receiving space in order to suppress stray light from entering the light receiving space from the light projecting space.

By providing the light blocking section, it is possible to prevent the projected light from entering the light receiving space directly from the light projecting space. However, the light blocking section cannot prevent stray light that is reflected by a window, reflected again by a mirror, and then detected by the detector on the path of going out of the device and entering the detector.

An example of stray light that will be described with reference toFIG.20, which is reflected by a window, reflected again by a mirror, and then detected by the detector on the path of going out of the device and entering the detector. A light projected from a light source101is reflected by a mirror102in the device and strikes a window103of the device. Then, the light reflected by the window103is reflected again by the mirror102, and exits the device by passing through the window103. When the light emitted from the device hits a retroreflector104, the light travels toward the light source101by hitting the mirror102in the device in the reverse path, being reflected by the window103, and being reflected again by the mirror102. If the light source101and the detector105are close to each other, the light traveling toward the light source101through the above-described path may be detected by the detector105. When the light is detected by the detector105along such a path, it is erroneously determined that a direction in which the retroreflector104exists is a direction in which the ghost106exists.

The present disclosure has been made based on this situation, and provides a laser radar device capable of suppressing a detection of stray light that goes out of the device and enters the device.

The laser radar device is achieved by a combination of features described in independent claims and sub-claims define further advantageous examples of the disclosure. Note that a reference numeral in parentheses in claims indicate a correspondence relationship with specific means described in embodiments to be described later as one aspect, and does not limit the technical scope of the present disclosure.

According to one aspect of the disclosure, a laser radar device includes: a light source configured to emit laser light; a mirror rotatable about a rotation shaft to reflect the laser light emitted by the light source; a window through which the laser light reflected by the mirror passes; and a detector configured to detect the laser light passing through the window to be reflected by the mirror. The mirror has a low reflection area having a lower reflectance than the other region of the mirror, in a state where a mirror surface of the mirror faces toward the light source, at position adjacent to the light source than the detector in an axial direction of the rotation shaft and adjacent to the window than a region where the laser light emitted by the light source hits for a first time in a radial direction of the rotation shaft. The window has an inclined posture in which a distance from the rotation shaft is shorter at position adjacent to the detector than at position adjacent to the light source.

According to another aspect of the disclosure, a laser radar device includes: a light source configured to emit laser light; a mirror rotatable about a rotation shaft to reflect the laser light emitted by the light source; a window through which the laser light reflected by the mirror passes; and a detector configured to detect the laser light passing through the window to be reflected by the mirror. The mirror has a low reflection area having a lower reflectance than the other region of the mirror, in at least a part of an area where a stray light to be detected by the detector hits the mirror, after the laser light emitted by the light source is reflected by the mirror, the window, and the mirror in this order and exiting through the window to be reflected by an external object and passing through the window to be reflected in order of the mirror, the window, and the mirror, within a rotation angle range in which the laser light emitted by the light source is reflected by the window and hits the mirror again. The window has an inclined posture in which a distance from the rotation shaft is shorter at position adjacent to the detector than at position adjacent to the light source.

The laser radar device has the low reflection area formed in at least a part of the area where the stray light hits the mirror. Therefore, the intensity of the stray light entering the detector is reduced. Thus, detection of this stray light can be suppressed.

In addition, the window has the inclined posture in which the distance from the rotation shaft is shorter at position adjacent to the detector than at position adjacent to the light source. As a result, the travelling direction of the laser light reflected by the window is shifted away from the mirror, compared to a case where the distance from the window to the rotation shaft is the same between the position adjacent to the light source and the position adjacent to the detector. Therefore, compared to the case where the distance from the window to the rotation shaft is the same, the low reflection area can be made smaller. By making the low reflection area small, normal laser light, which is not stray light, is less likely to be weakened in the low reflection area, so the SN ratio can be improved.

An embodiment will be described below with reference to the drawings.FIG.1is a schematic diagram illustrating a laser radar device1according to the embodiment. The laser radar device1includes a housing10and a window20. The housing10is provided with an opening into which the window20is fitted. The window20is fitted into the opening of the housing10in an inclined posture with respect to a flat back plate portion11of the housing10opposite to the window20.

The window20is light transmissive, flat and rectangular in shape. The laser radar device1irradiates a laser light L from the window20to the outside of the device. Glass can be used as the base material of the window20. The base material of the window20may be a transparent resin.

The laser radar device1irradiates the laser light L outward of the device while scanning. A direction perpendicular to the window20from the back plate portion11is defined as a front direction of the laser radar device1. Let the front direction be a Z direction. A plane perpendicular to the Z axis is an XY plane. When the laser light L is reflected at position outside the device, a part of the reflected laser light L enters the laser radar device1through the window20.

The laser radar device1is attached to a vehicle and detects an object around the vehicle. One or more laser radar devices1are attached to a vehicle in order to detect objects around the vehicle. The laser radar device1can be attached to the vehicle in any orientation. In the description of the embodiment, for convenience, a positive direction in the Y axis is defined as an upward direction of the vehicle. Hereinafter, the upward direction of the vehicle will simply be referred to as the upward direction.

FIGS.2and3explain component positions of an optical system provided inside the housing10and the window20. In the following diagrams, configurations other than those necessary for explanation are omitted as appropriate.FIG.2is a diagram viewed from a direction II inFIG.1.FIG.3is a diagram viewed from a direction III inFIG.1.FIG.4is a diagram viewed from a direction IV inFIG.1, and shows the relative positions of the components of the optical system. The internal surface of the window20inside the device is coated with an antireflection film21. The external surface of the window20may also be coated with an antireflection film. The optical system includes a light source30, a projection lens32, a mirror40, a motor50, a detector60and a light-receiving lens62.

The light source30emits laser light L, and a laser diode can be used as the light source30. The laser light L emitted by the light source30is directed toward the mirror40. The projection lens32is provided between the light source30and the mirror40and suppresses the diffusion of the laser light L.

The mirror40has a plate portion42with one surface being a mirror surface41. The mirror surface41has a rectangular shape, in which the short sides are parallel to the Z axis and the long sides are parallel to the rotation shaft44. The long sides may be parallel to the Z axis, and the short sides may be parallel to the rotation shaft44. The shape of the mirror surface41may be square.

A low reflection area43is formed on a part of the mirror surface41. The upper portion of the mirror40, in other words, adjacent to the light source30is a first mirror portion40athat reflects the laser light L emitted by the light source30. The lower portion of the mirror40, in other words, adjacent to the detector60is a second mirror portion40bthat reflects the laser light L entering the device through the window20toward the detector60. The mirror40is an integral light emitting and receiving type having the first mirror portion40aand the second mirror portion40b.

The rotation shaft44is attached to the plate portion42. The rotation shaft44is parallel to the Y-axis and arranged at position passing through the center of the plate portion42between the short sides opposing to each other. The rotation shaft44is integrated with a rotation shaft of the motor50. Therefore, the mirror40is driven by the motor50and rotates around the rotation shaft44. Rotation is not limited to 360 degrees, but includes, for example, 120 degrees and 150 degrees in an angle range narrower than 360 degrees. Rotation of the mirror40in the angle range narrower than 360 degrees means that the mirror40reciprocates. When the mirror40rotates while the light source30is continuously emitting the laser light L, the laser light L is emitted outward of the device through the window20while being scanned in the XZ plane.

A part of the laser light L reflected by an external object outside the device enters the device through the window20, and is reflected by the mirror40to travel toward the detector60. The detector60is arranged below the light source30in the Y-axis direction. The light source30and the detector60are arranged on the same plane parallel to the XY plane. A photodiode can be used for the detector60.

The light-receiving lens62is arranged between the mirror40and the detector60in the travelling direction of the laser light L that enters the device from the outside to be reflected by the mirror40. The light-receiving lens62condenses the laser light directed from the mirror40toward the detector60.

As shown inFIG.2, the window20is in an inclined posture such that the distance from the rotation shaft44is shorter at position adjacent to the detector60than at position adjacent to the light source30. The distance is defined along the Z axis.

FIG.5shows the detailed configuration of the mirror40of this embodiment. The plate portion42of the mirror40has a structure in which a sheet glass42a, an adhesion film42b, a silver thin film42c, and a protective film42dare stacked in this order. The upper side surface of the protective film42dinFIG.5is the mirror surface41. A part of the mirror surface41is formed with the low reflection area43described above.

The low reflection area43has a lower reflectance than the mirror surface41. The low reflection area43can be formed, for example, by applying matte paint to the area by screen printing or the like. The paint color is black, for example. The low reflection area43can also be said to be an area in which the reflection of light is suppressed more than the mirror surface41by absorbing or attenuating the irradiated light.

[Position of Low Reflection Area43]

As shown inFIG.2, when the mirror surface41of the mirror40faces the light source30, the low reflection area43is formed on the rectangular mirror surface41at position where the Y-axis side faces the light source30and the Z-axis side is biased toward one of the long sides of the mirror surface41. In other words, when the mirror surface41of the mirror40faces the light source30, the low reflection area43is positioned closer to the light source30than the detector60in the Y-axis direction and closer to the window20than an area where the laser light L emitted by the light source30hits for the first time in the Z-axis direction. The reason why the low reflection area43is formed at this position and having this size will be described below. A state in which the mirror surface41of the mirror40faces the light source30is a state in which the laser light L emitted by the light source30directly hits the mirror40.

FIG.6shows a path of the laser light L when a stray light to be suppressed by the low reflection area43occurs. The laser light L emitted by the light source30hits the mirror40after passing through the projection lens32. The laser light L emitted by the light source30and irradiated outward of the device is called a projection beam.

The projection beam reflected by the mirror40is reflected by the window20, re-reflected by the mirror40, and exits the device from the window20. Then, the projection beam is reflected by an external object outside the device, and is received by the detector60as stray light. When simply describing stray light, the stray light means the laser light L detected by the detector60along this path.

As can be seen fromFIG.6, when the projection beam reflected by the mirror40is reflected by the window20, re-reflected by the mirror40, and exits the device from the window20, an area where the projection beam hits the mirror40at the re-reflection time is closer to the window20than an area where the projection beam strikes the mirror40for the first time.

FIG.7conceptually shows a projection region45where the projection beam hits the mirror40and a light receiving region46where the reception beam hits the mirror40. The reception beam means a laser light L that is reflected by an external object outside the device and enters the device again.

The reason why the projection region45is trapezoidal inFIG.7is as follows. The projection beam is adjusted to spread in the Y-axis direction as traveling, and the mirror40inFIG.7is tilted with respect to the optical axis of the projection beam. The left side of the mirror40shown inFIG.7is closer to the light source30than the right side of the mirror40shown inFIG.7is. Therefore, the projection region45is trapezoidal. The light receiving region46is also trapezoidal because the mirror40shown inFIG.7is closer to the detector60on the left side than on the right side.

FIG.8shows the travelling direction of the projection beam traveling in various directions when the projection beam is reflected by the window20. It should be noted thatFIG.8omits the low reflection area43. The projection beam shown inFIG.8is a part of the projection beam projected by the laser radar device1. As can be seen fromFIG.8, in the vicinity of the mirror40, the range of the projection beam reflected by the window20in the Y-axis direction partially overlaps the range of the projection beam directed toward the window20. As described above, as shown inFIG.7, the low reflection area43is located adjacent to the light source30in the Y-axis direction, in the mirror40. The position of the low reflection area43in the radial direction of the rotation shaft44is closer to the window20than the region where the projection beam hits the mirror40for the first time in the state where the mirror surface41faces the light source30.

[Size of Low Reflection Area43]

Next, the size of the low reflection area43will be explained.FIG.9is a diagram in which the incident angle of the laser light L from the light source30entering the mirror40is minimized when stray light occurs.FIG.10is a diagram showing the maximum incident angle when stray light occurs.FIGS.9and10are diagrams for explaining the rotation angle range of the mirror40in which stray light occurs. For easy understanding, the window20is not slanted, differently from the laser radar device1of the embodiment.

InFIG.9, the projection beam reflected by the window20and re-reflected by the mirror40passes through the end of the window20and exits the device. If the incident angle of the laser light L is made smaller than this, the projection beam re-reflected by the mirror40hits the frame of the window20and does not exit the device.

InFIG.10, the projection beam reflected by the window20hits the region of the mirror40closest to the window20. If the incident angle of the laser light L is increased any further, the projection beam reflected by the window20will not strike the mirror40.

FIG.11shows the positional relationship between the mirror40and the stray light region47aproduced in the state ofFIG.9and the stray light region47bproduced in the state ofFIG.10. In the stray light region47a,47b, the projection beam is reflected by the window20and hits the mirror40or passes near the mirror40. The two stray light regions47aand47bshown inFIG.11and the region between the two stray light regions47aand47bare the stray light region47shown inFIG.7. In the stray light region47, the stray light strikes the mirror40or passes near the mirror40in the rotation angle range of the mirror40in which the stray light occurs. The size of the low reflection area43is determined so as to include an area where the stray light region47and the mirror surface41of the mirror40overlap with each other.

The stray light region47shown inFIG.7includes an area outside the mirror surface41. The area outside the mirror surface41in the stray light region47is larger, when the window20is tilted as in the present embodiment, compared with a case where the window20is not tilted.

FIG.12shows a comparison case where the window20is not tilted, in which the travelling direction of the projection beam reflected by the window20is indicated. As can be seen by a comparison betweenFIG.12andFIG.8, the travelling direction of the projection beam reflected by the window20is upward in the Y-axis when the window20is tilted than when the window20is not tilted.

FIG.13shows changes in position of the stray light region47a,47bwith respect to the mirror40when the tilt of the window20is changed. InFIG.13, the angle in parentheses is the tilt angle of the window20with respect to the XY plane.

As can be seen inFIG.13, when the window20is tilted, the stray light region47moves upward relative to mirror40, compared with a case where the window20is not tilted. The stray light region47moves toward the window20relative to the mirror40when the window20is tilted compared with a case where the window20is not tilted.

Referring back toFIG.7. InFIG.7, the stray light region47partially overlaps the projection region45and the light receiving region46. Accordingly, the low reflection area43formed to include the stray light region47also partially overlaps the projection region45and the light receiving region46. As the stray light region47moves upward and rightward inFIG.7, the low reflection area43becomes smaller. As the low reflection area43becomes smaller, the overlap area between the low reflection area43and the projection region45and the light receiving region46becomes smaller. When the overlap area between the low reflection area43and the projection region45and the light receiving region46is reduced, the regular laser light L is restricted from being weakened in the low reflection area43. As a result, the SN ratio is improved.

Overview of Embodiment

In the laser radar device1of the embodiment, the low reflection area43is formed in the first mirror portion40aof the mirror40. The low reflection area43is formed in the area where stray light strikes the mirror40. Therefore, the laser radar device1can suppress detection of stray light.

In addition, the window20is in an inclined posture such that the distance from the rotation shaft44is shorter at position adjacent to the detector60than at position adjacent to the light source30. As a result, the low reflection area43can be made smaller, compared with a case where the window20is not tilted, that is, when the distance from the window20to the rotation shaft44is the same between the position adjacent to the light source30and the position adjacent to the detector60. The regular laser light L, which is not stray light, is less likely to be weakened in the low reflection area43which is made small, so that the SN ratio can be improved.

In addition, since the antireflection film21is provided on the internal surface of the window20, the laser light L is restricted from being reflected by the internal surface of the window20so as to suppress the stray light.

Second Embodiment

Next, a second embodiment will be described. In the following description of the second embodiment, elements having the same reference symbols as those used so far are the same as the elements having the same reference symbols in the previous embodiment, except when specifically mentioned. When only a part of the configuration is described, the embodiment described above can be applied to other parts of the configuration.

FIG.14shows a laser radar device200of the second embodiment, in which the shape of the mirror240differs from the mirror40of the first embodiment in. The mirror240includes a first mirror portion240aand a second mirror portion240b. The first mirror portion240ahas the same shape as the first mirror portion40aof the first embodiment. The shape of the second mirror portion240bis different from that of the second mirror portion40bof the first embodiment.

The length of the second mirror portion240bin the radial direction of the rotation shaft44becomes shorter toward the lower side inFIG.14, that is, toward the side opposite to the first mirror portion240a. Therefore, in the second mirror portion240b, both outer sides of the second mirror portion240bin the radial direction of the rotation shaft44form an inclined side portion244that approaches the rotation shaft44toward the end of the mirror240adjacent to the detector60.

The inclined side portion244is parallel to the window20, in other words, along the window20. The state in which the inclined side portion244is along the window20includes not only the state in which the inclined side portion244is completely parallel to the window20but also the state in which the inclined side portion244is nearly parallel to the window20.

The first mirror portion240ahas a parallel side portion245parallel to the rotation shaft44at the outer side in the radial direction of the rotation shaft44. The mirror surface241of the mirror240having such a shape has a line-symmetrical shape as a whole with the rotation shaft44as an axis of symmetry.

The mirror240has the inclined side portion244, and the distance between the window20and the optical system component such as the mirror240in the second embodiment is shorter than the distance between the window20and the optical system component such as the mirror40in the first embodiment. The distance between the window20and the mirror240is so short that the mirror240would hit the window20if the parallel side portion245extends to the end of the mirror240adjacent to the detector60.

The closer the distance between the window20and the optical system component such as the mirror240is, the smaller the area where the stray light hits the mirror240. Therefore, the low reflection area243included in the mirror240of the second embodiment can be made smaller than the low reflection area43included in the mirror40of the first embodiment. Since the low reflection area243can be made smaller, the SN ratio can be improved.

Also, the mirror surface241of the mirror240has a line-symmetrical shape with the rotation shaft44as the axis of symmetry. As a result, the center of gravity of the mirror240is on the rotation shaft44, so vibrations can be suppressed when the mirror240rotates.

Third Embodiment

In the third embodiment, a laser radar device that prevents clutter will be described. Unlike the stray light described above, the clutter in this third embodiment is not the laser light L that has once exited the device, but the projection beam that is reflected by the window20and then reflected by the mirror40toward the detector60, which is the laser light L to be detected by the detector60.

Therefore, clutter can occur when the mirror40reflects the projection beam in the 0° direction of the Z coordinate. Detection of clutter can be suppressed by inclining the window20. In the third embodiment, the window20is inclined to prevent clutter from being detected.

The inclination angle of the window20for suppressing detection of clutter will be described with reference toFIG.15. InFIG.15, the optical path between the light source30and the window20and the optical path between the detector60and the window20are set straight for the sake of clarity of explanation.

In other words,FIG.15illustrates the light source30at the position indicated by the double chain line shown inFIG.16. The position of the light source30indicated by the double chain line is on a straight line including the travelling direction of the laser light L reflected by the mirror40. As previously mentioned, clutter can occur when the mirror40reflects the projection beam in the 0° direction of the Z coordinate. Therefore, in the description of clutter, the light source30, which is actually located at the position indicated by the solid line, may be considered to be located at the position indicated by the double chain line.

InFIG.15, the window20indicated by the double chain line is the window20that is not tilted. The laser light L indicated by the double chain line indicates the traveling direction of the laser light L reflected by the non-inclined window20when the projection beam from the light source30is directed most downward in the Y-axis direction.

The laser light L indicated by the solid line is also the laser light L that is most directed downward in the Y-axis direction, among the projection beam from the light source30. However, the solid line represents the traveling direction of the laser light L reflected by the inclined window20indicated by the solid line. The angle α is defined between the travelling direction of the laser light L indicated by the double chain line and the travelling direction of the laser light L indicated by the solid line. At this time, the inclination of the window20is α/2.

Therefore, the inclination of the window20is made larger than α/2. In this way, the laser light L emitted from the light source30, which is most directed toward the detector60, passes closer to the light source30than the detector60, and is not incident on the detector60. Therefore, clutter is not detected by the detector60.

Although the embodiments have been described above, the disclosed technology is not limited to the above-described embodiment, and the following modifications are included in the present disclosure, and various modifications can be made without departing from the spirit of the present disclosure.

First Modification

FIGS.17to19show modifications in the configuration of the mirror. A mirror340shown inFIG.17includes an aluminum thin film42einstead of the adhesion film42band the silver thin film42cincluded in the mirror40.

A mirror440shown inFIG.18includes a sheet glass42a, an aluminum thin film42e, a protective film42d, and a low reflection area43, similar to the mirror340. However, the low reflection area43is directly laminated on the sheet glass42a, differently from the mirror340.

Second Modification

The mirror40has an axisymmetric shape with two inclined side portions244having the same length and inclination. However, the two inclined side portions244may have different lengths and inclinations. The parallel side portion245may be shorter and the inclined side portion244may be longer, compared with the embodiment. Further, the parallel side portion245may not be provided, and the inclined side portion244may extend from the end of the mirror adjacent to the light source30to the end of the mirror adjacent to the detector60.