Optical scanning object detection device detecting object that invades detection area

The entire disclosures of Japanese Patent Application No. 2016-018723 filed on Feb. 3, 2016 and No. 2016-178440 filed on Sep. 13, 2016 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety.

The present invention relates to an optical scanning type object detection device capable of detecting an object or the like which invades a detection area.

In recent years, as crime prevention awareness rises, there is an increasing demand for a monitoring system capable of accurately detecting an object that has entered the detection area. As a method of detecting such an object, a radio wave radar which transmits radio waves to detect reflected waves has been proposed. However, it is difficult to accurately identify a position of a distant object from the viewpoint of resolution.

In contrast, WO 2011/021103 A discloses a TOF (time of flight) type measurement technique of emitting a laser beam while scanning with the laser beam, receiving a reflected beam reflected from a measurement object point, and acquiring distance information to the measurement object point on the basis of a time difference between an emitting time point and a receiving time point. The scanning with such a laser beam can be performed by reflecting a beam flux emitted from a laser light source by using a rotating mirror. An object detection device employing the TOF method has already been developed. However, in the object detection device employing the TOF method, in order to detect a weak reflected beam generated at the time of irradiating an object in a distance with a laser beam, generally, a light receiving element having a high amplification ratio such as an avalanche photodiode (APD) is used. In addition, in order to increase resolution of the object to be detected, in some cases, a plurality of light receiving elements which receive the reflected beam are arranged to ensure high resolution.

JP 2015-180956 A discloses a radar device including a rotating mirror unit including first and second mirror planes which are slanted with respect to a rotation axis and a projection system including at least one light source emitting a beam flux toward an object through the mirror unit, wherein the beam flux emitted from the light source is reflected on the first mirror plane of the mirror unit, after that, is propagated toward the second mirror plane, is further reflected on the second mirror plane, and is scan-projected on the object according to rotation of the mirror unit. In the case of using such a mirror unit, the beam flux emitted from the projection system is reflected on the rotating first and second mirror planes, after that, is irradiated toward the object, is reflected on the object, is reflected again on the first and second mirror planes, and after that, is incident on a light receiving system. Therefore, in principle, only the reflected beam of the projected beam is incident on the light receiving system, and thus, there is an advantage in that the device has resistance to disturbance light, has high resolution, and has a wider field of view.

In JP 2015-180956 A, it is disclosed that a plurality of light sources are used, and thus, the number of scan lines can be increased without deterioration in longitudinal distortion. However, with a configuration disclosed in JP 2015-180956 A, detection range around the rotation axis of the mirror unit is limited.

In contrast, the specification of U.S. Pat. No. 7,969,558 discloses an optical measurement device which rotates a unit where a plurality of light sources and light receiving elements are two-dimensionally arranged to be capable of receiving reflected beams from an object with respect to a laser beam emitted from a light source one by one by using light receiving elements. According to the optical measurement device, object detection can be performed over a range of 360°.

However, in the optical measurement device in the specification of U.S. Pat. No. 7,969,558, due to providing a plurality of light sources and light receiving elements, cost becomes very large, and how the light sources and light receiving elements can be power-supplied and controlled from the outside. For example, if a plurality of the light sources and the light receiving elements are attempted to be power-supplied or communication-controlled from the outside by using a contact type rotary connector or the like, the configuration becomes large, and also noise generation or treatment difficulty occurs. In contrast, in recent years, non-contact type connectors capable of performing wireless power supply by using electromagnetic induction by coils or performing wireless communication by using infrared rays, light, or the like have also been developed. Although it may be considered that these connectors are applied to the technique disclosed in the specification of U.S. Pat. No. 7,969,558, cost may increase, or the configuration may be complicated.

One or more embodiments of the invention provide an optical scanning type object detection device having a wide detection area exceeding, for example, 180° and being capable of effectively detecting an object invading the detection area with a relatively simple configuration and low cost.

According to an aspect, an optical scanning type object detection device reflecting one aspect of the present invention comprises:

first and second light emitting/receiving units, each of which includes a light source and a light receiving portion; and

a mirror unit which rotates around a rotation axis,

wherein a beam flux emitted from the light source of the first light emitting/receiving unit is reflected on the mirror unit and is scanned according to rotation of the mirror unit, and a portion of a beam flux scattered by an object in the beam flux emitted from the light source of the first light emitting/receiving unit is reflected on the mirror unit and, after that, is received by the light receiving portion of the first light emitting/receiving unit, and

a beam flux emitted from the light source of the second light emitting/receiving unit is reflected on the mirror unit and is scanned according to the rotation of the mirror unit, and a portion of abeam flux scattered by the object in the beam flux emitted from the light source of the second light emitting/receiving unit is reflected on the mirror unit and, after that, is received by the light receiving portion of the second light emitting/receiving unit.

Advantages and features of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein:

FIG. 1 is a cross-sectional diagram illustrating a laser radar as an optical scanning type object detection device in accordance with one or more embodiments;

FIG. 2 is a perspective diagram illustrating main components of the laser radar in accordance with one or more embodiments;

FIG. 3A is a schematic diagram illustrating a second reflecting member constituting a mirror unit as viewed in a direction along a rotation axis, and FIG. 3B is a diagram illustrating a first reflecting member constituting the mirror unit as viewed in the direction along the rotation axis;

FIG. 4 is a diagram illustrating a scan range as viewed in a direction of a rotation axis of a laser radar;

FIG. 5 is a schematic perspective diagram illustrating an object detection range which can be detected by the laser radar;

FIG. 6 is a developed view illustrating a scan range of a spot beam emitted from the laser radar;

FIGS. 7A and 7B are diagrams according to a modified example in accordance with one or more embodiments which are similar to FIGS. 3A and 3B .

FIG. 8 is a diagram according to a modified example in accordance with one or more embodiments which is similar to FIG. 4 ;

FIG. 9 is a side view of Example 1 illustrating only a mirror unit, a semiconductor laser, and a collimation lens corresponding to the examples shown in FIGS. 1 to 6 ;

FIG. 10 is a diagram illustrating a configuration of FIG. 9 cut along line X-X as viewed in an arrow direction;

FIG. 11 is a side view of Example 2 illustrating only a mirror unit, a semiconductor laser, and a collimation lens corresponding to examples shown in FIGS. 7A, 7B, and 8 ;

FIG. 12 is a diagram illustrating a configuration of FIG. 11 cut along line XII-XII as viewed in an arrow direction;

FIGS. 13A to 13C are perspective diagrams illustrating various examples of the semiconductor laser and the collimation lens which can be used in one or more embodiments;

FIG. 14 is a perspective diagram illustrating a laser radar as an optical scanning type object detection device in accordance with one or more embodiments;

FIG. 15 is a perspective diagram illustrating a state that a cover is detached from the laser radar;

FIG. 16 is a schematic diagram illustrating a cross section of the laser radar in accordance with one or more embodiments;

FIG. 17 is a perspective diagram illustrating main components of a scan unit in accordance with one or more embodiments excluding a case;

FIG. 18 is a diagram illustrating the scan unit as viewed in a direction of a rotation axis;

FIG. 19 is a diagram illustrating a unit rotation scan range which can be scanned with emitted beam fluxes from two light emitting/receiving units during one rotation of a mirror unit;

FIG. 20 is a diagram illustrating the unit rotation scan range which is displaced to be partially overlapped according to rotation displacement of the scan unit around a rotation axis in an equator direction (α direction) of a celestial sphere as viewed in a horizontal direction;

FIG. 21 is an enlarged diagram illustrating a portion XXI in FIG. 20 ;

FIG. 22 is a schematic diagram illustrating an entire celestial sphere CSP of 360° where object detection can be performed by the laser radar;

FIG. 23 is a diagram illustrating main components of a scan unit in accordance with one or more embodiments;

FIG. 24 is a perspective diagram illustrating a laser radar in accordance with one or more embodiments;

FIG. 25 is a diagram illustrating a scan unit in accordance with one or more embodiments as viewed in a direction of a rotation axis;

FIG. 26 is a diagram illustrating a unit rotation scan range which can be scanned with emitted beam fluxes from two light emitting/receiving units during one rotation of a mirror unit in accordance with one or more embodiments; and

FIG. 27 is a schematic diagram illustrating an entire celestial sphere CSP of 360° where object detection can be performed by a laser radar in accordance with one or more embodiments.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

(First Example)

FIG. 1 is a cross-sectional diagram illustrating a laser radar LR as an optical scanning type object detection device in accordance with one or more embodiments. FIG. 2 is a perspective diagram illustrating main components of the laser radar LR in accordance with one or more embodiments. Herein, laser beams (solid lines) being directed to an object and reflected beams (one-dot dashed lines) from the object are illustrated by only respective optical axes. FIG. 3A is a schematic diagram illustrating a second reflecting member constituting a mirror unit as viewed in a direction along a rotation axis, and FIG. 3B is a diagram illustrating a first reflecting member constituting the mirror unit as viewed in the direction along the rotation axis. Slant angles of the reflection plane with respect to the rotation axis are attached to the respective reflection planes.

In FIG. 1 , the laser radar LR is configured to include a first light emitting/receiving unit OPD 1 , also referred to as an optical transceiver, a second light emitting/receiving unit OPD 2 , and a rotating mirror unit MU, and these units are retained in a case CS (refer to FIG. 4 ). The first light emitting/receiving unit OPD 1 is configured to include a semiconductor laser (light source) LD 1 which emits a pulsed laser beam flux LB 1 , a collimation lens CL 1 which collimates the laser beam flux LB 1 emitted from the semiconductor laser LD 1 , a lens LS 1 which condenses the reflected beam RB 1 from the object, and a photodiode (light receiving portion) PD 1 which receives the condensed reflected beam RB 1 . The second light emitting/receiving unit OPD 2 is configured to include a semiconductor laser (light source) LD 2 which emits a pulsed laser beam flux LB 2 , a collimation lens CL 2 which collimates the laser beam flux LB 2 emitted from the semiconductor laser LD 2 , a lens LS 2 which condenses the reflected beam RB 2 from the object, and a photodiode (light receiving portion) PD 2 which receives the condensed reflected beam RB 2 .

The mirror unit MU has a function of reflecting the laser beam flux LB 1 emitted from the collimation lens CL 1 of the first light emitting/receiving unit OPD 1 , scanning the object with the laser beam flux through a transparent plate (not illustrated) of the case CS according to rotation, reflecting the reflected beam RB 1 returned from the object through the transparent plate, and allowing the reflected beam to be incident on the lens LS 1 of the first light emitting/receiving unit OPD 1 and a function of reflecting the laser beam flux LB 2 emitted from the collimation lens CL 2 of the second light emitting/receiving unit OPD 2 , scanning the object with the laser beam flux through a transparent plate (not illustrated) of the case CS according to the rotation, reflecting the reflected beam RB 2 returned from the object through the transparent plate, and allowing the reflected beam to be incident on the lens LS 2 of the second light emitting/receiving unit OPD 2 . Although not illustrated, in one or more embodiments the transparent plate is attached to a window of the case CS and is slanted with respect to the emitted light. As described in detail later, the beam fluxes emitted from the semiconductor lasers LD 1 and LD 2 in a sub-scan direction (direction perpendicular to a scan direction) are longer than those in the scan direction when the beam fluxes are emitted to the object. In addition, in one or more embodiments the photodiodes PD 1 and PD 2 include a plurality of light receiving regions arranged in the sub-scan direction. However, the light receiving regions may be two-dimensionally arranged.

The optical axes (herein, centers of cross sections of the laser beam fluxes LB 1 and LB 2 ) of the first and second light emitting/receiving units OPD 1 and OPD 2 are perpendicular to the rotation axis RX of the mirror unit MU. Herein, the optical axes of the first and second light emitting/receiving units OPD 1 and OPD 2 may be slightly slanted from the perpendicular direction of the rotation axis according to factors such as a device size, shape, and arrangement of optical elements. In addition, in one or more embodiments the optical axes of the first and second light emitting/receiving units OPD 1 and OPD 2 are arranged with spacing of about 180° around the rotation axis RX. Herein, “about 180°” denotes 180°±5°.

The mirror unit MU is retained in the case CS (refer to FIG. 4 ) so as to be rotatable around the rotation axis RX which is a shaft and is formed by combining first and second reflecting members RF 1 and RF 2 as illustrated in FIGS. 2 and 3 . Referring to FIG. 3B , the first reflecting member RF 1 which is made of a resin and has a shape of a cup with an equal thickness includes, in the outer surface, an equilateral triangular bonding surface RF 1 a centered at the rotation axis RX, three substantially-fan shaped reflection planes (first mirror planes) RF 1 c , RF 1 d , and RF 1 e intersecting respective sides of the bonding surface RF 1 a , and a cylindrical outer circumferential surface RF 1 f (refer to FIG. 2 ) being in contact with the reflection planes. A central opening RF 1 g is formed at the center of the bonding surface RF 1 a.

Referring to FIG. 3A , similarly to the first reflecting member RF 1 , the second reflecting member RF 2 which is made of a resin and has a shape of a cup with an equal thickness includes, in the outer surface, an equilateral triangular bonding surface RF 2 a centered at the rotation axis RX, three substantially-fan shaped reflection planes (second mirror planes) RF 2 c , RF 2 d , and RF 2 e intersecting respective sides of the bonding surface RF 2 a , and a cylindrical outer circumferential surface RF 2 f (refer to FIGS. 3A and 3B ) being in contact with the reflection planes. A central opening RF 2 g is formed at the center of the bonding surface RF 2 a.

Herein, the slant angle of the reflection plane RF 1 c with respect to the rotation axis RX is set to 44°, the slant angle of the reflection plane RF 1 d with respect to the rotation axis RX is set to 45°, and the slant angle of the reflection plane RF 1 e with respect to the rotation axis RX is set to 46°. On the other hand, the slant angle of the reflection plane RF 2 c with respect to the rotation axis RX is set to 44°, the slant angle of the reflection plane RF 2 d with respect to the rotation axis RX is set to 45°, and the slant angle of the reflection plane RF 2 e with respect to the rotation axis RX is set to 46°.

The first and second reflecting members RF 1 and RF 2 are formed by injection molding, and a film is formed on the surface by vapor deposition of aluminum, gold, silver, or the like, so that the reflection planes can be obtained. In this manner, in the case where the slant angles of the reflection planes with respect to the rotation axis RX are individually changed, if the reflecting members are formed by injection molding, there is an advantage in that it is easy to obtain the accuracy of each reflection plane.

As illustrated in FIG. 1 , the first and second reflecting members RF 1 and RF 2 can be assembled by facing the bonding surfaces RF 1 a and RF 2 a , allowing a triangular-plate-shaped holed spacer SP to be interposed therebetween, inserting and fitting a cylindrical stepped shaft CY into the central openings RF 1 g and RF 2 g , and fastening the reflecting members by using a bolt BT. A motor MT which rotationally drives the shaft CY is fixed to the case CS.

As described above, since the first and second reflecting members RF 1 and RF 2 can be formed by molding with a good accuracy, assembling is performed so that the shafts are coincident with each other by a guide of the shaft CY being inserted into the central openings RF 1 g and RF 2 g . In assembling, the reflection plane RF 1 c and the reflection plane RF 2 c are allowed to face each other to form a pair, the reflection plane RF 1 d and the reflection plane RF 2 d are allowed to face each other to form a pair, and the reflection plane RF 1 e and the reflection plane RF 2 e are allowed to face each other to form a pair, so that a phase in the rotation direction is set. Irrespective of the manufacturing method described above, the first and second reflecting members RF 1 and RF 2 may be formed integrally.

Next, a distance measurement operation of the laser radar LR will be described. FIG. 4 is a diagram illustrating a scan range as viewed in the direction of the rotation axis of the laser radar LR. A lower half portion of the mirror unit MU is illustrated, and the light emitting/receiving units OPD 1 and OPD 2 are illustrated in brief. Object detection ranges (G 1 and G 2 ) are schematically indicated by hatching. Actual detection limit with respect to the size of the case CS of the laser radar LR is larger than the illustrated limit. FIG. 5 is a schematic perspective diagram illustrating the object detection range which can be detected by the laser radar LR. FIG. 6 is a developed view illustrating a scan range of the spot beam SB emitted from the laser radar LR and illustrating objects such as buildings. In FIG. 2 , in the state where the mirror unit MU is rotated at a constant speed by driving from a driving source (not illustrated), a pulsed laser beam flux intermittently emitted from the semiconductor laser LD 1 of the first light emitting/receiving unit OPD 1 is incident on a point P 1 of the reflection plane RF 1 c of the first reflecting member RF 1 , is reflected on the point, is propagated along the rotation axis RX or with a predetermined angle slanted from the rotation axis RX, is reflected on a point P 2 of the reflection plane RF 2 c of the second reflecting member RF 2 , and is scan-projected on the object side. At this time, the reflection planes at the points P 1 and P 2 are moved in the circumferential direction according to the rotation of the mirror unit MU. According to the rotation of the mirror unit MU, the reflection planes are moved relative to the reflection planes RF 1 d and RF 2 d , and according to the rotation of the mirror unit MU, the reflection planes are moved relative to the reflection planes RF 1 e and RF 2 e.

Similarly, a pulsed laser beam flux intermittently emitted from the semiconductor laser LD 2 of the second light emitting/receiving unit OPD 2 is incident on the directly-facing reflection plane of the first reflecting member RF 1 according to the rotation of the mirror unit MU, is reflected on the reflection plane, is propagated along the rotation axis RX or with a predetermined angle slanted from the rotation axis RX, is reflected on a reflection plane of the second reflecting member RF 2 , and is scan-projected on the object side.

In FIG. 6 , a spot beam from the laser beam flux LB 1 with which the object is irradiated is denoted by SB 1 , and a spot beam from the laser beam flux LB 2 with which the object is irradiated is denoted by SB 2 . The detection range G of the laser radar LR is scanned in the horizontal direction with the spot beams SB 1 and SB 2 according to the rotation of the mirror unit MU. A first range G 1 from 0° to 180° in the detection range G is scanned with the spot beam SB 1 , and a second range G 2 from 180° to 360° in the detection range G is scanned with the spot beam SB 2 .

Herein, as described above, the reflection planes of the mirror unit MU are different in slant angle with respect to the rotation axis RX. The top region Ln 11 of the first range G 1 is scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beam SB 1 , that is, a laser beam which is emitted from the first light emitting/receiving unit OPD 1 and is reflected on a pair of the reflection planes RF 1 c and RF 2 c . Next, the second region Lnl 2 from the top of the first range G 1 is scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beam SB 1 , that is, a laser beam which is reflected on a pair of the reflection planes RF 1 d and RF 2 d . Next, the third region Ln 13 from the top of the first range G 1 is scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beam SB 1 , that is, a laser beam which is reflected on a pair of the reflection planes RF 1 e and RF 2 e.

With scan timing shifted from the above scan timing, the top region Ln 21 of the second range G 2 is scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beam SB 2 , that is, a laser beam which is emitted from the second light emitting/receiving unit OPD 2 and is reflected on a pair of the reflection planes RF 1 c and RF 2 c . Next, the second region Ln 22 from the second range G 2 is scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beam SB 2 , that is, a laser beam which is reflected on a pair of the reflection planes RF 1 d and RF 2 d . Next, the third region Ln 23 from the top of the second range G 2 is scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beam SB 2 , that is, a laser beam which is reflected on a pair of the reflection planes RF 1 e and RF 2 e.

Namely, by one rotation of the mirror unit MU, scanning of the entire detection range G is completed. After that, when a pair of the reflection planes RF 1 c and RF 2 c is returned, scanning from the top of the detection range G is repeated again. When one of the semiconductor lasers LD 1 and LD 2 which emit pulsed light is allowed to emit light, if the other semiconductor laser is allowed to stop emitting light, influence of stray light can be avoided.

As apparent from arrangement relationships illustrated in FIGS. 3A, 3B, and 4 , in the case where the laser beam flux LB 1 emitted from the first light emitting/receiving unit OPD 1 is incident on the center of the reflection plane RF 1 c , the laser beam flux LB 2 emitted from the second light emitting/receiving unit OPD 2 starts to be incident on the reflection plane RF 1 e . Namely, the laser beam fluxes LB 1 and LB 2 are emitted from the mirror unit MU while being shifted from each other by 90° as viewed in the direction of the rotation axis (refer to FIG. 5 ).

In FIG. 2 , a portion of a scattered beam reflected on the object which is irradiated with the spot beam SB 1 becomes a reflected beam RB 1 and, again, is incident on the reflection plane RF 2 c and the like of the second reflecting member RF 2 , is reflected on the reflection plane and the like, is propagated along the rotation axis RX or with a predetermined angle slanted from the rotation axis RX, is reflected on the reflection plane RF 1 c and the like of the first reflecting member RF 1 , is condensed by the lens LS 1 , and is detected on the light receiving plane of the photodiode PD 1 . On the other hand, a portion of a scattered beam reflected on the object which is irradiated with the spot beam SB 2 becomes a reflected beam RB 2 and, again, is incident on the reflection plane RF 2 c and the like of the second reflecting member RF 2 , is reflected on the reflection plane and the like, is propagated along the rotation axis RX or with a predetermined angle slanted from the rotation axis RX, is reflected on the reflection plane RF 1 c and the like of the first reflecting member RF 1 , is condensed by the lens LS 2 , and is detected on the light receiving plane of the photodiode PD 2 . Accordingly, as illustrated in FIGS. 4 to 6 , the object detection over the range of 360° around the laser radar LR can be performed. At this time, the angle of the rotation of the mirror unit MU can be obtained on the basis of the emitting time points of the laser beam fluxes LB 1 and LB 2 , and the distance to the object can be obtained from a difference between the emitting time points of the laser beam fluxes LB 1 and LB 2 and the receiving time points of the reflected beams RB 1 and RB 2 which are reflected from the object. Therefore, the position of the object from the laser radar LR as a reference can be calculated at a good accuracy.

When the laser beam flux is incident on the three rotating reflection planes, theoretically, the scan angle of the laser beam flux scanned from one reflection plane becomes 240°. Although the laser beam fluxes LB 1 and LB 2 incident on the reflection planes of the mirror unit MU need to have some degrees of widths in order to increase detection efficiency, the scan angle of 240° cannot be fully secured for the reason. More specifically, for example, as indicated by dotted lines in FIGS. 3A and 3B , if the edge in the circumferential direction of the reflection plane RF 1 c is irradiated with the laser beam flux LB 1 , a portion of the laser beam flux LB 1 is reflected on the reflection plane RF 1 c , but the other portion of the laser beam flux LB 1 is reflected on the reflection plane RF 1 d or RF 1 e adjacent to the reflection plane.

In this case, the reflected beam from the object by the laser beam flux LB 1 reflected on the reflection plane RF 1 c is appropriately received by the photodiode PD 1 . However, the reflected beam from the object by the laser beam flux LB 1 reflected on the portion other than the reflection plane RF 1 c is not received by the photodiode PD 1 , and in some case, the reflected beam is detected by the photodiode PD 2 of the second light emitting/receiving unit OPD 2 , so that error may be detected due the reflected beam. The same error may occur in other reflection planes.

In order to avoid such error detection, a control unit (not illustrated) controlling the semiconductor laser LD 1 detects the rotation angle of the mirror unit MU and allows the semiconductor laser LD 1 to stop emitting light before the laser beam flux LB 1 is applied to the edge in the circumferential direction of each reflection plane. The same control is performed on the semiconductor laser LD 2 . However, if such control of light emitting of the semiconductor laser is performed, the scan angle of the laser beam flux cannot be fully used. According to the studies performed by the inventors or the like, it can be understood that, when the laser beam flux is incident on the three rotating reflection planes, the scan angle of the laser beam flux scanned from one reflection plane becomes at least 180°. Therefore, if the two light emitting/receiving units are used for the mirror unit MU including the three reflection planes aligned in the circumferential direction, the object detection can be performed over the entire circumference of 360°. The example will be described later.

FIGS. 7A and 7B are diagrams in accordance with one or more embodiments which are similar to FIGS. 3A and 3B , and FIG. 8 is a diagram illustrating an example in accordance with one or more embodiments which is similar to FIG. 4 . Points different from those of the above-described embodiments will be mainly described. A laser radar LR according to the modified example is configured to include three light emitting/receiving units OPD 1 , OPD 2 , and OPD 3 and one mirror unit MU. Each of the light emitting/receiving units OPD 1 , OPD 2 , and OPD 3 has the configuration similar to that of the above-described embodiments, but as illustrated in FIG. 8 , the light emitting/receiving units are arranged with spacing of about 120° around the rotation axis RX. Herein, “about 120°” denotes 120°±5°.

On the other hand, the mirror unit MU according to the modified example is configured to include four pairs of reflection planes. Specifically, referring to FIG. 7B , the first reflecting member RF 1 is configured to include four reflection planes (first mirror planes) RF 1 c , RF 1 d , RF 1 e , and RF 1 h arranged in the circumferential direction. Referring to FIG. 7A , the second reflecting member RF 2 is configured to include four reflection planes (second mirror planes) RF 2 c , RF 2 d , RF 2 e , and RF 2 h arranged in the circumferential direction to face the above-described reflection planes.

Herein, the slant angle of the reflection plane RF 1 c with respect to the rotation axis RX is set to 44°, the slant angle of the reflection plane RF 1 d with respect to the rotation axis RX is set to 45°, the slant angle of the reflection plane RF 1 e with respect to the rotation axis RX is set to 46°, and the slant angle of the reflection plane RF 1 h with respect to the rotation axis RX is set to 47°. On the other hand, the slant angle of the reflection plane RF 2 c with respect to the rotation axis RX is set to 44°, the slant angle of the reflection plane RF 2 d with respect to the rotation axis RX is set to 45°, the slant angle of the reflection plane RF 2 e with respect to the rotation axis RX is set to 46°, and the slant angle of the reflection plane RF 2 h with respect to the rotation axis RX is set to 47°.

In the modified example, the reflection planes of the mirror unit MU are different in slant angle with respect to the rotation axis RX. Therefore, the top regions of the ranges G 1 to G 3 in the vertical direction thereof (direction perpendicular to the paper surface in FIG. 8 ) are scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beams (not illustrated), that is, laser beams which are emitted from the light emitting/receiving units OPD 1 to OPD 3 and are reflected on a pair of the reflection planes RF 1 c and RF 2 c . Next, the second regions from the tops of the ranges G 1 to G 3 in the vertical direction are scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beams, that is, laser beams which are reflected on a pair of the reflection planes RF 1 d and RF 2 d . Next, the third regions from the tops of the ranges G 1 to G 3 in the vertical direction are scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beams SB 1 , that is, laser beams which are reflected on a pair of the reflection planes RF 1 e and RF 2 e . Next, the fourth regions from the tops of the ranges G 1 to G 3 in the vertical direction are scanned from the left to the right in the horizontal direction according to the rotation of the mirror unit MU with the spot beams, that is, laser beams which are reflected on a pair of the reflection planes RF 1 h and RF 2 h . Accordingly, the object detection can be performed over the range of 360° around the laser radar LR.

Herein, when the laser beam flux is incident on the four rotating reflection planes, theoretically, the scan angle of the laser beam flux scanned from the one reflection plane becomes 180°, but the scan angle of 180° cannot be fully secured for the above-described reason. According to the studies performed by the inventors or the like, it can be understood that, when the laser beam flux is incident on the four rotating reflection planes, the scan angle of the laser beam flux scanned from one reflection plane becomes at least 90°. Therefore, if the three light emitting/receiving units are used for the mirror unit MU including the four reflection planes aligned in the circumferential direction, the object detection can be performed over the entire circumference of 360°. The example will be described later.