JP6032416B2 - Laser radar - Google Patents

Description

  The present invention relates to a laser radar that detects an object by irradiating a laser beam or the like.

  As a device for measuring the distance to the object, a light projecting optical system including a laser light source that emits laser light toward the object and a light receiving optical system that receives the reflected light of the laser light that hits the object are used. Laser radar is known.

  In such a laser radar, if the laser light source emits light in a pulse shape for a very short time, for example, about 10 ns, and the laser light is emitted toward the object through the light projecting optical system, the emitted laser light is instantly emitted. And is received by the light receiving element via the light receiving optical system. Here, the time difference between the emission and reception of the laser beam is the time for the laser beam to reciprocate the distance to the object, so that the distance to the object can be obtained by multiplying this time difference by the speed of light and dividing by 2. It becomes.

  In a general laser radar, a light projecting system is composed of a laser diode and a collimator, and a light receiving system is composed of a light receiving lens (or mirror) and a light detecting element such as a photodiode. A polygon mirror is disposed between the light projecting system and the light receiving system. By rotating the polygon mirror, the light beam emitted from the light projecting system is scanned on the rotating reflecting surface, and the object is irradiated and reflected. Light can be reflected by the reflecting surface and received by the light receiving system. In this way, by using the same reflecting surface of the polygon mirror at the time of light projection and light reception, it is possible to adopt a configuration that is resistant to disturbance light (see Patent Document 1). Patent Document 2 discloses a technology that can suppress distortion by making light incident with the rotation axis of the polygon mirror and the optical axis of the light projecting system at an angle close to parallel.

  In particular, an in-vehicle laser radar is used for an application in which an obstacle is detected in advance and optimal braking of the vehicle is performed. Therefore, it is required to detect the obstacle with a wide-angle visual field in the horizontal direction. However, having a wide field of view in the light receiving optical system is not preferable because it is easily affected by ambient light and the SN ratio is lowered.

On the other hand, in patent document 3, from two light projection systems which orient | assigned the output optical path to the different direction,
Two light beams are emitted toward the rotating polygon mirror, scanned on the substantially left side with one light beam reflected on one reflecting surface, and substantially on the front side with the other light beam reflected on another reflecting surface. A laser radar that can obtain a wide scanning range by scanning the right side is disclosed.

JP 2010-197341 A JP 09-274076 A JP 2010-71725 A

  However, the laser radar of Patent Document 3 requires two light projection systems to be installed, so that the configuration cannot be made compact and the cost increases. However, this is a problem particularly in an in-vehicle laser radar.

  The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a laser radar that can detect an object in a wide range with a simple configuration.

The laser radar according to claim 1,
A rotating polygon mirror having a plurality of reflecting surfaces inclined with respect to the rotation axis;
A light projecting system that emits a light beam toward an object through the reflection surface of the polygon mirror;
A light receiving system for receiving the reflected light from the object through the reflecting surface of the polygon mirror;
The optical axes of the light projecting system and the light receiving system are arranged so as to be parallel to each other after intersecting the reflecting surface,
The light receiving system includes a first light receiving unit and a second light receiving unit across the center of an angular range to be scanned ,
When the polygon mirror is in the second angle range, the light beam emitted from the light projecting system and reflected from the object is reflected by one reflecting surface of the polygon mirror, and is reflected by the first light receiving unit. A light beam that is detectable and is emitted from the light projecting system and reflected from an object different from the object is reflected by another reflecting surface of the polygon mirror and detected by the second light receiving unit. It is possible.

  For example, in a conventional laser radar having a light receiving system having a single light receiving unit, when the reflected light from an object is received by the light receiving unit through the reflecting surface of the polygon mirror, the boundary between the reflecting surfaces of the polygon mirror When the reflected light is received across the (ridgeline), it cannot be distinguished from which reflecting surface the received light. Therefore, since the reflected light from the object cannot be measured at a position across the boundary between the reflecting surfaces of the polygon mirror, there is a problem that the detection range is inherently narrowed.

  Therefore, in the light receiving system of the present invention, a plurality of light receiving portions are arranged side by side on both sides of the center of the scanning angle range. In other words, by arranging the light receiving optical path on the reflecting surface of the polygon mirror in a plurality of paths across the light projecting optical path, the laser beam can be emitted in two directions with the ridge line between the reflecting surfaces of the polygon mirror as a boundary. Even if it is divided, the reflected light from the obstacle can be appropriately separated on the light receiving system side.

  The principle of the present invention will be explained by giving an example. As a comparative example, consider a laser radar having a polygon mirror PM having four reflecting surfaces as shown in FIG. 1 and one light projecting system LP and light receiving system LR. The light projecting optical path is indicated by a solid line, and the light receiving optical path is indicated by a dotted line. Since the polygon mirror PM rotates about the rotation axis RO, as shown in FIG. 1, when one reflection surface MR1 is at an angular position facing the front (light reception system LR side), the light reception system LR is not shown. Receives reflected light from the object.

  On the other hand, when the polygon mirror PM rotates 45 degrees from the state of FIG. 1, as shown in FIG. 2, the laser light emitted from the light projecting system LP crosses the ridge line BD between the reflection surfaces MR1 and MR2 of the polygon mirror PM. It will hit two sides, and will be divided into left and right light. After that, since the two laser beams strike different objects and are reflected, the two reflected beams are reflected by the two reflecting surfaces MR1 and MR2 to which the laser beams strike, and are received by the same light receiving unit PD of the light receiving system LR. Will do. However, since the signal output from the light receiving unit PD corresponds to the sum of two reflected lights reflected from different objects, it cannot be determined which obstacle has been detected.

  Therefore, in the present invention, distance measurement in two directions is possible by using a plurality of light receiving units. As an example, as shown in FIG. 3, a polygon mirror PM whose four side surfaces are reflecting surfaces, a light projecting system LP, and a light receiving system RP having two light receiving parts PD1 and PD2 are provided. When the two light receiving parts PD are arranged at a wider distance than the spot size of the laser beam on the reflection surface of the polygon mirror PM, as shown in FIG. 3, the polygon mirror PM is positioned 45 from the position facing the front. The first light receiving part PD1 on the left side is reflected by the reflecting surface MR2 and is reflected by the reflecting surface MR1 without receiving the reflected light from the object returning from the right direction. Only the reflected light of the object returning from the direction can be received. Similarly, the second light receiving unit PD2 on the right side reflects from the object reflected from the reflection surface MR1 and returns from the left direction, and reflects from the reflection surface MR2 and returns from the right direction. Only the reflected light of the incoming object can be received. Accordingly, since it is possible to detect when the polygon mirror PM is rotated to the vicinity of the reflection surface ridge line, which could not be realized by a single light receiving unit, it is possible to measure the object regardless of the angular position of the polygon mirror PM. Thus, the object can be scanned and detected in a wide scanning range.

  Furthermore, the present invention is effective even when the laser beam is not reflected in two directions. For example, as shown in FIG. 4, when the polygon mirror PM is rotated about 30 degrees from the position facing the front, the emitted light from the light projecting system LP is reflected only on the reflecting surface MR1 and travels in one direction. If there is only one light receiving portion, there is a risk of receiving background light such as sunlight or a car headlight from the reflecting surface MR2 adjacent to the reflecting surface MR1 on which the laser beam has hit, which increases noise. However, according to the present invention, by using the two light receiving portions, in the angle range of the polygon mirror PM in which the light emitted from the light projecting system LP is incident only on the single reflecting surface MR1, one of the light receiving portions is used. By enabling only the light receiving unit and disabling the rest, the influence of noise can be suppressed.

  If there are at least two sets of light receiving parts, it is effective. As the number of light receiving parts increases, the number of parts increases, and there is a problem that the signal management becomes complicated and the cost increases due to the position adjustment of each light receiving part, but the resolution increases by increasing the number of light receiving parts. In particular, even when three or more light receiving portions are provided, similarly, the effect of the present invention can be exhibited by arranging the light receiving portions side by side on both sides of the center of the angle range for scanning the light receiving portions. Since the resolution is increased by increasing the number of light receiving sections, it is possible to finely determine which light receiving section output is used for each angle. Here, the “light receiving part” refers to a unit that can independently output a signal corresponding to the amount of received light. Even with the same photodetector, it has a plurality of optical systems and is independently at a light receiving position through different optical systems. What can output a signal shall have a some light-receiving part. Further, “the optical axes of the light projecting system and the light receiving system are arranged so as to be parallel to each other after intersecting the reflecting surface” means, for example, that the light projecting system and the light receiving system are In addition to the case where the optical axis is tilted with respect to the rotation axis or is originally parallel to the rotation axis, the projection is shifted in the rotation axis direction of the polygon mirror with respect to the reflection surface. Even if the optical axis of the optical system and the light receiving system is bent by a mirror or the like and is parallel to the rotation axis when intersecting the reflective surface, as long as they are parallel to each other after intersecting the reflective surface, The arrangement is arbitrary. In addition, in the range where the light projected through the reflecting surface of the polygon mirror can be received through the reflecting surface of the same polygon mirror, the optical axes of the light projecting system and the light receiving system are not parallel, and an angle difference is generated. You may have it. However, since the light receiving area is expanded and the light is received, the background light is received in a larger range, the S / N may be deteriorated, and the efficiency may be deteriorated. The axes are preferably close to parallel. Furthermore, “the center of the scanning angle range” means that the optical axis of the light projecting system intersects the reflecting surface of the polygon mirror and the light axis of the light projecting system on the rotation axis of the polygon mirror. The horizontal angle between two points at the same height as the intersecting point on the reflection surface of the polygon mirror.

  As the second angle range, for example, a range of −47 degrees to −40 degrees or +40 degrees to +47 degrees is determined from a position where the center of the reflection surface of the polygon mirror PM overlaps the center plane of the scanning angle range. As shown in FIG. 3, when the polygon mirror PM rotates to the second angle range, the first light receiving unit PD1 on the left side reflects from the object reflected from the reflecting surface MR2 and returns from the right direction. Without receiving the reflected light, it is possible to receive only the reflected light of the object reflected from the reflecting surface MR1 and returning from the left direction. Similarly, the second light receiving unit PD2 on the right side reflects from the object reflected from the reflection surface MR1 and returns from the left direction, and reflects from the reflection surface MR2 and returns from the right direction. Only the reflected light of the incoming object can be received. It should be noted that “detectable” does not necessarily mean that it is detected, and it is sufficient if it is arranged at a position where it can be detected.

Laser radar according to claim 2 is the invention according to claim 1, when the polygon mirror is in a different first angular range and the second angle range is emitted from the light projecting system, the The light beam reflected from the object is reflected by the same reflecting surface of the polygon mirror, and is detected by the first light receiving unit and the second light receiving unit.

As shown in FIG. 6 to be described later, as the first angle range, a range of, for example, −40 degrees to +40 degrees is determined from the position where the center of the reflection surface of the polygon mirror PM overlaps the center plane of the angle range to be scanned. When the polygon mirror PM rotates in the first angle range, the light receiving parts PD1 and PD2 can receive the reflected light from the same reflecting surface. When the polygon mirror PM is facing the front, the two light receiving parts PD1 and PD2 both receive the reflected light of the object in the same direction, so it is necessary to separate the output results from the light receiving parts PD1 and PD2. There is no. By adding the outputs of the two light receiving portions PD1 and PD2, the amount of received light is increased and the measurement distance can be increased. The first angle range and the second angle range are not limited to the above examples.
According to a third aspect of the present invention, in the laser radar according to the first or second aspect of the invention, the light emitted from the light projecting system is incident only on a single reflecting surface of the polygon mirror and is reflected from the object. When the light beam reflected by the single reflecting surface is within the angle range of the polygon mirror where only the first light receiving part can be detected, only the first light receiving part is enabled and the remaining light receiving parts are disabled. It is characterized by.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the light projecting system and the light receiving system are arranged so as to be shifted in the rotational axis direction with respect to the polygon mirror. It is characterized by being.

  As a result, the arrangement of parts around the rotation axis of the laser radar can be made efficient and compact.

  The laser radar according to claim 5 is the invention according to any one of claims 1 to 4, wherein the plurality of reflecting surfaces of the polygon mirror are inclined at different angles with respect to the rotation axis. Features.

  When the surface angles of the plurality of reflecting surfaces of the polygon mirror are different, the scanning angle for each reflecting surface is changed. Therefore, in the case of a polygon mirror having four reflecting surfaces, four scanning lines can be obtained because all surface angles are different. As a result, the measurement range also extends in the vertical direction. However, by increasing the number of reflecting surfaces, the measurement range can be increased in the vertical direction, but by increasing the number of reflecting surfaces, the angle between the boundaries of the surface becomes smaller, and accordingly, the horizontal scanning angle becomes smaller. However, by arranging the light receiving system as in the present invention, it is possible to widen the scanning angle of each surface.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the laser radar is for vehicle use. The laser radar of the present invention is suitable for in-vehicle use.

  According to the present invention, it is possible to provide a laser radar capable of detecting an object in a wide range with a simple configuration.

It is a figure which shows the laser radar of a comparative example. It is a figure which shows the laser radar of a comparative example. It is a figure which shows the laser radar concerning an example of this invention. It is a figure which shows the laser radar of a comparative example. It is the schematic which shows the state which mounted the laser radar concerning this Embodiment in the vehicle. It is a schematic block diagram of the laser radar concerning this Embodiment. It is a schematic block diagram of the laser radar concerning this Embodiment. It is a figure which shows the screen corresponding to the object area | region scanned with the laser radar LR. It is a schematic block diagram of the laser radar concerning a modification. It is a schematic block diagram of the laser radar concerning another modification.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 5 is a schematic diagram showing a state in which the laser radar according to the present embodiment is mounted on a vehicle. The laser radar LR of the present embodiment is provided behind the front window 1a of the vehicle 1 or behind the front grill 1b.

  FIG. 6 is a schematic configuration diagram of the laser radar LR according to the present embodiment, which is viewed along the horizontal direction, and FIG. 7 is a diagram when the laser radar LR is viewed from below along the vertical direction. . The shape and length of the components may differ from the actual ones. Here, it is assumed that the vertical direction of the polygon mirror of the laser radar LR is the Z direction, and the directions orthogonal to the Z direction are the Y direction and the X direction. The laser radar LR, for example, a semiconductor laser LD that emits a laser beam, a collimator lens CL that converts divergent light from the semiconductor laser LD into parallel light, and a laser beam that is collimated by the collimator lens CL is rotated and reflected. From the polygon mirror PM that reflects the reflected light from the scanned and projected object OBJ and the object OBJ that is reflected by the polygon mirror PM while scanning and projecting toward the object OBJ side (FIG. 5) by the surface. The first lens LS1 that collects the reflected light of the first, the first photodiode PD1 as the first light receiving unit that receives the light collected by the first lens LS1, and the reflected light from the object OBJ And a second photodiode PD2 as a second light receiving unit that receives the light collected by the second lens LS2.

  Here, a light projecting system LP is configured by the semiconductor laser LD and the collimating lens CL, and the light receiving system RP is configured by the first lens LS1, the first photodiode PD1, the second lens LS2, and the second photodiode PD2. Configure. These are arranged on the front side (vehicle forward direction) with respect to the rotation axis RO of the polygon mirror PM, and are shifted in the rotation axis direction with respect to the reflection surface, that is, arranged vertically downward (or upward). Has been.

  Referring to FIG. 7, the optical axis of the light projecting system LP is arranged so that the outgoing light beam is directed parallel to the rotational axis RO of the polygon mirror PM, that is, the normal line of the outgoing surface of the semiconductor laser LD is the rotational axis. Parallel to RO. The two optical axes of the light receiving system RP are also arranged in parallel with the rotation axis RO, that is, the normal lines of the light receiving surfaces of the first photodiode PD1 and the second photodiode PD2 are respectively the rotation axis RO and the rotation axis RO. Parallel. The first photodiode PD1 and the second photodiode PD2 are equidistant from the center plane PL on both sides of the center plane PL (here, the plane including the rotation axis RO and facing the front of the vehicle) in the scanning angle range. However, as shown in FIG. 7, the distances to the rotation axis RO are preferably different from each other. Thereby, the 1st lens LS and the 2nd lens LS2 can be brought close as much as possible. However, the first photodiode PD1 and the second photodiode PD2 may be arranged at an equal distance from the rotation axis RO. However, the optical axes of the light projecting system LP and the light receiving system RP are arranged so as to be parallel to each other after intersecting the reflecting surface.

  The polygon mirror PM has a plurality of reflecting surfaces MR1 to MR4 on its side surface, and each reflecting surface MR1 to MR4 is slightly inclined at a different angle with respect to the rotation axis RO along the vertical direction.

  Note that a polygon mirror is particularly effective as a reflection surface for performing scanning projection, but other scanning devices may be used.

  Next, the distance measuring operation of the laser radar LR will be described with reference to FIGS. The divergent light intermittently emitted from the semiconductor laser LD in a pulse shape is converted into a parallel light beam by the collimator lens CL, and scanned and projected to the object OBJ side through the rotating polygon mirror PM.

  FIG. 8 is a diagram showing a state where the laser beam radiated (indicated by hatching) is scanned on the screen G, which is the detection range of the laser radar LR, according to the rotation of the polygon mirror PM. The reflecting surfaces MR1 to MR4 of the polygon mirror PM are inclined at different angles with respect to the rotation axis RO, and the laser light is sequentially reflected by the facing reflecting surfaces MR1 to MR4. First, the laser beam reflected by the reflecting surface MR1 is scanned from left to right in the horizontal direction in the uppermost region LN1 of the screen G in accordance with the rotation of the polygon mirror PM. Next, the laser beam reflected by the reflecting surface MR2 is scanned in the second region LN2 from the top of the screen G from the left to the right in the horizontal direction in accordance with the rotation of the polygon mirror PM. Next, the laser beam reflected by the reflection surface MR3 is scanned from the left to the right in the horizontal direction in the third region LN3 from the top of the screen G according to the rotation of the polygon mirror PM. Next, the laser beam reflected by the reflecting surface MR4 is scanned from left to right in the horizontal direction in the lowermost region LN4 of the screen G in accordance with the rotation of the polygon mirror PM. Thereby, the scanning of one screen is completed. Then, after the polygon mirror PM makes one rotation, if the reflecting surface MR1 returns, scanning from the top of the screen G is repeated again.

  In FIGS. 6 and 7, the laser light reflected by the object OBJ out of the projected light beam is incident on the polygon mirror PM and reflected again, and is condensed by the first lens LS1 and the second lens LS2, respectively. The light is detected by the light receiving surfaces of the first photodiode PD1 and the second photodiode PD2.

  Here, as shown in FIGS. 6 and 7, when one reflecting surface MR1 of the rotating polygon mirror PM is substantially directed to the front (a position where the center of the reflecting surface overlaps the center plane PL as the second angle range). +/− 40 degrees), the laser beam reflected upon the object OBJ is reflected again by the same reflecting surface MR1 of the polygon mirror PM, and is condensed by the first lens LS1 and the second lens LS2, respectively. Since the light enters the light receiving surfaces of PD1 and the second photodiode PD2, the distance to the object OBJ is calculated using the sum of the outputs of the first photodiode PD1 and the second photodiode PD2.

  On the other hand, as shown in FIG. 3, an angular position where the light emitted from the semiconductor laser LD hits the vicinity of the boundary BD between the two reflecting surfaces MR1 and MR2 of the polygon mirror PM (first angle range as the central plane PL). On the other hand, when the polygon mirror PM is rotated by −47 degrees to −40 degrees, or +40 degrees to +47 degrees from the position where the centers of the reflecting surfaces overlap, the laser beam reflected by the object OBJ to be measured is polygon mirror PM. Therefore, the distance to the object OBJ is calculated using only the output of the first photodiode PD1 collected on the light receiving surface via the first lens LS1. In this case, the light condensed on the light receiving surface of the second photodiode PD2 via the second lens LS2 becomes noise, and high-precision measurement is performed by ignoring the output of the second photodiode PD2. be able to.

  Note that the optical axes of the light projecting system LP and the light receiving system RP may be inclined with respect to the rotation axis RO of the polygon mirror PM as shown in FIG. In the example of FIG. 9A, the optical axis LPX of the light projecting system LP and the optical axis RPX of the light receiving system RP (only one is shown) are such that their extension lines approach the rotational axis RO above the polygon mirror PM. It is an arrangement. On the other hand, in the example of FIG. 9B, the optical axis LPX of the light projecting system LP and the optical axis RPX of the light receiving system RP (only one is shown) are separated from the rotation axis RO above the polygon mirror PM. It is arranged like this.

  Further, in the example shown in FIG. 10, the mirror M1 is provided between the semiconductor laser LD and the collimating lens CL, and the optical axis is bent by 90 degrees, and the first lens LS1 (second lens LS2 overlapping in the direction perpendicular to the paper surface). And the first photodiode PD1 (second photodiode PD2 overlapping in the direction perpendicular to the paper surface) is provided with a mirror M2 to bend the optical axis by 90 degrees. Also in this example, the optical axes of the light projecting system LP and the light receiving system RP intersecting the reflecting surface MR1 are parallel to the rotation axis RO. Other configurations are the same as those of the above-described embodiment.

  The present invention is not limited to the embodiments described in the specification, and other embodiments and modifications are apparent to those skilled in the art from the embodiments and ideas described in the present specification. It is. The description and examples are for illustrative purposes only, and the scope of the invention is indicated by the following claims. For example, the polygon mirror may be a hexagonal column or an octagonal column instead of a quadrangular column. Further, the laser radar LR may be arranged at four corners without being limited to the center of the vehicle so as to scan a range in which the center of the scanning range is inclined 45 degrees with respect to the traveling direction. Thereby, a wider range of objects can be scanned. Further, the rotation axis of the polygon mirror does not necessarily have to be perpendicular to the ground, and may be inclined in the direction of the center plane PL as shown in FIG. The light may be condensed using a mirror.

DESCRIPTION OF SYMBOLS 1 Vehicle 1a Front window 1b Front grille BD Boundary CL Collimating lens G Screen LD Semiconductor laser LN1-LN4 Screen area LP Projection system LPX Projection system optical axis LR Laser radar LS1 First lens LS2 Second lens MR1-MR4 Reflection Surface M1, M2 Mirror OBJ Object PD1 First photodiode PD2 Second photodiode PL Center plane PM Polygon mirror RO Rotating axis RP Light receiving system RPX Light receiving system optical axis

Claims (6)

A rotating polygon mirror having a plurality of reflecting surfaces inclined with respect to the rotation axis;
A light projecting system that emits a light beam toward an object through the reflection surface of the polygon mirror;
A light receiving system for receiving the reflected light from the object through the reflecting surface of the polygon mirror;
The optical axes of the light projecting system and the light receiving system are arranged so as to be parallel to each other after intersecting the reflecting surface,
The light receiving system includes a first light receiving unit and a second light receiving unit across the center of an angular range to be scanned ,
When the polygon mirror is in the second angle range, the light beam emitted from the light projecting system and reflected from the object is reflected by one reflecting surface of the polygon mirror, and is reflected by the first light receiving unit. A light beam that is detectable and is emitted from the light projecting system and reflected from an object different from the object is reflected by another reflecting surface of the polygon mirror and detected by the second light receiving unit. Laser radar characterized by being capable . When the polygon mirror is in a first angle range different from the second angle range, the light beam emitted from the light projecting system and reflected from the object is reflected by the same reflecting surface of the polygon mirror. The laser laser according to claim 1 , wherein detection is performed by the first light receiving unit and the second light receiving unit.   The light emitted from the light projecting system is incident only on the single reflecting surface of the polygon mirror, and only the first light receiving unit detects the light beam reflected from the object and reflected by the single reflecting surface. 3. The laser laser according to claim 1, wherein when the angle range of the polygon mirror is within a range, only the first light receiving unit is enabled and the remaining light receiving units are disabled.   The laser radar according to any one of claims 1 to 3, wherein the light projecting system and the light receiving system are arranged so as to be shifted in a rotation axis direction with respect to the polygon mirror.   5. The laser laser according to claim 1, wherein the plurality of reflecting surfaces of the polygon mirror are inclined at different angles with respect to the rotation axis.   The laser radar according to any one of claims 1 to 5, wherein the laser radar is for in-vehicle use.

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