JP5135131B2 - Light projecting unit and object detection device - Google Patents

Description

  The present invention relates to a light projecting unit that projects light emitted from a light emitting element such as a laser diode (LD), and an object detection device to which the light projecting unit is applied.

  2. Description of the Related Art Conventionally, a light projecting unit that uses a light emitting element such as a laser diode (LD) to project linearly formed light has been proposed (see Patent Document 1). In this patent document 1, the proposal which improves the utilization efficiency of the light radiate | emitted from the light emitting element is made | formed. Specifically, the light emitted from the LD, which is a light emitting element, is converted into parallel light whose divergence angle is suppressed by a collimating optical system, and this parallel light is expanded in one direction by a cylindrical lens. In addition, by using a light shielding plate provided with a rectangular opening, an unnecessary portion of light spread in one direction is shielded by a cylindrical lens. In this rectangular shape, the direction in which the cylindrical lens spreads light is longer than the direction perpendicular to this direction. And the light which shielded the unnecessary part with the light-shielding plate is projected ahead through a focusing lens. This makes it possible to project linear light extending in the direction expanded by the cylindrical lens.

  By the way, when linear light is projected through a lens, it is affected by the aberration of the lens, and the light intensity distribution in the length direction (the direction expanded by the cylindrical lens in the configuration of Patent Document 1) varies. Arise. That is, it was not possible to project linear light having a substantially uniform light intensity distribution in the length direction.

Also, a laser radar device has been put to practical use by detecting the reflected light of the laser beam irradiated in front and detecting the object existing in the direction irradiated with the laser beam and measuring the distance to the detected object. . This laser radar device is mounted on a vehicle, for example, and is used as a device that detects a preceding vehicle traveling ahead, an obstacle existing ahead, and the like.
JP-A-6-186493

  An object of the present invention is to provide a light projecting unit capable of projecting linear light with suppressed variation in light intensity distribution in the length direction.

  In addition, the present invention provides an object detection device that can accurately detect an object existing in a light projection area where linear light is projected and the position of the object by applying the light projecting unit. The purpose is to provide.

  In order to achieve the above object, the light projecting unit of the present invention is configured as follows.

  The light projecting lens projects the light emitted from the light emitting element as the light source. As the light source, a small laser diode that emits laser light with good directivity is suitable. A light guide disposed between the light emitting element and the light projecting lens forms an optical waveguide that guides light emitted from the light emitting element to the light projecting lens. That is, the light emitted from the light emitting element enters the light projecting lens through the optical waveguide formed by the light guide.

  Further, the outer shape of the light guide exit surface facing the light projecting lens is a rectangle whose horizontal width is longer than the vertical width. The shape of the light emitted from the exit surface of the light guide is the same as the outer shape of the exit surface of the light guide. Further, since the light incident on the light guide is repeatedly refracted in the light guide and propagates to the exit surface, the intensity distribution of the light exiting from the exit surface of the light guide is substantially uniform.

  In addition, since the light guide exit surface has a concave shape in which the curved surface having the radius of the focal length of the light projecting lens is formed in the lateral width direction, the light emitted from the light guide exit surface has a curved surface on the exit surface. It expands in the formed width direction. Further, since the distance between the optical center of the light projecting lens and the center of the light guide exit surface is the focal length of the light projecting lens, the optical center of the light projecting lens and the light in the lateral width direction of the light guide. The distance from the exit surface of the guide is equal.

  For this reason, the influence of the aberration of this light projection lens is suppressed with respect to the light emitted from the light guide emission surface and projected forward through the light projection lens. The light guide exit surface is a rectangle whose width is longer than the height, and the light projected forward through the light projecting lens is wider in the width direction of the light guide than in the length direction. Because it is large, it becomes linear light. Therefore, it is possible to project linear light in which variation in light intensity distribution in the length direction is suppressed.

  The object detection device of the present invention employs the light projecting unit. The light receiving unit reflects the light projected by the light projecting unit for each of a plurality of object detection directions divided in the width direction of the light guide exit surface (that is, the length direction of the projected linear light). Is detected. The measurement unit detects whether an object is present depending on whether the reflected light is detected for each object detection direction. Further, the distance to the detected object is measured based on the elapsed time from when the light projecting unit projects light to when the light receiving unit receives reflected light.

  As described above, the light projecting unit can project linear light with suppressed variation in light intensity distribution in the length direction. For this reason, the threshold of the light reception level for determining the presence or absence of reflected light (that is, the presence or absence of an object) can be set to the same level for each object detection direction. Therefore, it is possible to accurately detect the object existing in the light projection area where the linear light is projected by the light projecting unit and the position of the object.

  Further, by mounting this object detection device on a vehicle, an obstacle such as a preceding vehicle located in front of the vehicle can be detected.

  According to the present invention, it is possible to project linear light in which variation in light intensity distribution in the length direction is suppressed.

  In addition, it is possible to accurately detect an object existing in the light projection area where linear light is projected and the position of the object.

  Embodiments of the present invention will be described below.

  FIG. 1 is a diagram showing a schematic configuration of a light projecting unit according to an embodiment of the present invention. The light projecting unit 1 is a unit that projects linear light. A top view of the light projecting unit 1 is shown in FIG. In FIG. 1A, the vertical direction in the figure is called the length direction of the projected linear light. A side view of the light projecting unit 1 is shown in FIG. In FIG. 1B, the vertical direction in the figure is referred to as the thickness direction of the projected linear light. The light projecting unit 1 includes a drive control circuit 10, a laser diode 11 (hereinafter referred to as “LD 11”), a light guide 12, and a light projecting lens 13. The drive control circuit 10 controls light emission of the LD 11 that is a light emitting element. The laser light emitted from the LD 11 passes through the light guide 12 and the light projecting lens 13 in this order, and is projected in front of the light projecting lens 13.

  The light emitting surface of the LD 11 faces the incident surface of the light guide 12. Further, the exit surface of the light guide 12 faces the light projecting lens 13. The light guide 12 aligns the center of the incident surface with the optical axis of the laser beam emitted from the LD 11. Further, the optical center of the light projecting lens 13 is aligned with the optical axis of the laser light emitted from the emission surface of the light guide 12 (the center of the emission surface of the light guide 12). The laser light incident on the light guide 12 is repeatedly refracted inside the light guide 12 and propagates to the emission surface, and is emitted from the emission surface of the light guide 12. The shape of the laser light emitted from the emission surface of the light guide 12 is the outer shape of the emission surface of the light guide 12. Further, the light intensity distribution of the laser light emitted from the emission surface of the light guide 12 is substantially uniform. As described above, the light guide 12 forms an optical waveguide that guides the laser light emitted from the LD 11 to the light projecting lens 13. Here, the following description will be made with the focal length of the light projecting lens 13 as f.

  Next, the light guide 12 will be described in detail. FIG. 2A is a perspective view seen from the incident surface side of the light guide. FIG. 2B is a perspective view as seen from the light exit surface side of the light guide. FIG. 2C is a top view of the light guide. FIG. 2D is a side view of the light guide. As shown in FIG. 2, the outer shape of the light guide 12 has a substantially rectangular parallelepiped shape. The light guide 12 has a longer width (w shown in the figure) than a vertical width (h shown in the figure). The vertical width h is several mm (for example, 1-2 mm), and the horizontal width w is several tens mm (for example, 20-30 mm).

  The exit surface of the light guide 12 has a concave shape in which a curved surface having a radius of the focal length f of the light projecting lens 13 is formed in the lateral width direction. The distance between the center of the exit surface of the light guide 12 and the optical center of the light projecting lens 13 is the focal length f of the light projecting lens 13. That is, the distance from the optical center of the light projecting lens 13 to the exit surface of the light guide 12 is equal in the lateral width direction of the light guide 12. In addition, the incident surface of the light guide 12 has a planar shape here.

  1A is the horizontal width direction of the light guide 12, and the vertical direction in FIG. 1B is the vertical width direction of the light guide 12.

  The laser beam projected by the light projecting unit 1 will be described. The drive control circuit 10 controls the light emission of the LD 11. The laser beam emitted from the LD 11 has an elliptical shape. The laser beam emitted from the LD 11 is incident on the light guide 12. The laser light incident on the light guide 12 is repeatedly refracted in the light guide 12 and propagates to the exit surface. The shape of the laser beam emitted from the emission surface of the light guide 12 is the same as the outer shape of the emission surface. That is, the shape of the laser beam emitted from the emission surface of the light guide 12 is a rectangular shape having a width w × length h. Further, the horizontal width is preferably several tens of times the vertical width.

  Further, as described above, since the exit surface of the light guide 12 forms a curved surface having the radius of the focal length f of the light projecting lens 13 in the horizontal width direction, the light guide 12 is formed from the optical center of the light projecting lens 13. Is equal in the lateral direction of the light guide 12. For this reason, the influence of the aberration of the light projection lens 13 is suppressed in the lateral width direction of the laser light projected forward through the light projection lens 13.

  Further, the exit surface of the light guide 12 has a longer width than the longitudinal width, and due to the curved surface formed on the exit surface, the laser light emitted from the exit surface is expanded in the lateral direction in the longitudinal direction. Bigger than that. Therefore, a linear laser beam that is long in the width direction of the light guide 12 can be projected forward of the light projecting lens 13 through the light projecting lens 13. Further, as described above, since the influence of the aberration of the light projection lens 13 is suppressed in the lateral width direction, the light intensity distribution in the length direction of the projected linear laser light (the lateral width direction of the light guide 12). Variation of the is suppressed. That is, a linear laser beam having a substantially uniform light intensity distribution in the length direction can be projected in front of the projection lens 13.

  Since the laser light projected forward through the light projecting lens 13 has a larger spread in the horizontal width direction than the spread in the vertical width direction, the projected laser light is transmitted from the light projecting lens 13. As the distance increases, the ratio of the vertical width direction to the horizontal width direction decreases.

  FIG. 3 shows the linear laser light projected by the light projecting unit of this embodiment, the light intensity distribution in the length direction of the linear laser light (light intensity distribution with respect to the horizontal angle), and the linear shape. 2 shows the light intensity distribution (light intensity distribution with respect to the vertical angle) in the width direction of the laser beam (vertical width direction of the light guide 12). For comparison, FIG. 4 and FIG. 5 show the light intensity distribution of linear laser light emitted by a light projecting unit using a light guide having a flat exit surface.

  4B, as shown in FIG. 4A, when the distance between the center of the exit surface of the light guide and the optical center of the light projecting lens is the focal length f of the light projecting lens, The projected linear laser light, the light intensity distribution in the length direction of the linear laser light (light intensity distribution with respect to the horizontal angle), and the width direction of the linear laser light (vertical width of the light guide) The light intensity distribution in the direction (light intensity distribution with respect to the vertical angle) is shown. In this case, the optical system is designed so that the focal point coincides with the center of the optical axis. For this reason, aberration occurs at the end of the image corresponding to the exit surface of the light guide. That is, at the horizontal angle, the light amount distribution becomes gentle, and the laser beam is blurred at a position where the absolute value of the horizontal angle is large.

  In FIG. 5B, as shown in FIG. 5A, the distance between the end of the light guide exit surface and the center of the light projecting lens in the lateral width direction is the focal length f of the light projecting lens. In this case, the projected linear laser light, the light intensity distribution in the length direction of the linear laser light (light intensity distribution with respect to the horizontal angle), and the width direction of the linear laser light (light guide) 2 shows the light intensity distribution (light intensity distribution with respect to the vertical angle) in the vertical width direction). In this case, the optical system is designed so that the focal point coincides with the end of the image corresponding to the exit surface of the light guide. For this reason, aberration occurs near the center of the optical axis. Further, the laser beam spreads at the vertical angle. For this reason, the laser beam is blurred at the optical axis center of the laser beam.

On the other hand, in the light projecting unit 1 of this embodiment in which the exit surface of the light guide 12 is a curved surface, as shown in FIG. 3, the intensity distribution of the projected linear laser light is a vertical angle light quantity distribution. The both ends of the distribution of light quantity are substantially perpendicular to the horizontal axis indicating the vertical angle. Further, in the horizontal angle light quantity distribution, both ends of the light quantity distribution stand substantially perpendicular to the horizontal axis indicating the horizontal angle. Further, the laser beam does not spread more than necessary at the vertical angle and the horizontal angle. For this reason, no aberration occurs at either the optical axis center or end of the laser beam. Each intensity distribution of the laser light has a rectangular shape centered on the optical axis and is substantially similar to the main slope of the light guide. This indicates that a laser beam with little aberration is obtained.

  In the above embodiment, the light guide 12 has a rectangular parallelepiped shape, but may have a shape as shown in FIGS. 6 (A) and 6 (B). 6A and 6B are top views of the light guide. FIG. 6A shows the light guide 12 in which the entrance surface and the exit surface are orthogonal to each other, and the laser light incident on the light guide 12 is 90 ° when propagating through the light guide 12. Bend. FIG. 6B shows the light guide 12 having a larger exit surface than the entrance surface. Furthermore, in the above description, the incident surface of the light guide 12 is a flat surface, but a curved surface similar to the exit surface may be formed.

  Next, an object detection apparatus to which the light projecting unit 1 shown in FIG. 1 is applied will be described. FIG. 7 is a diagram illustrating a configuration of a main part of the object detection apparatus. The object detection device 5 is mounted on a vehicle and detects an object existing in front of the vehicle. The object detection device 5 includes the light projecting unit 1, the light receiving unit 2, and the measurement unit 3 described above. The light projecting unit 1 projects linear laser light in front of the mounted vehicle. The light receiving unit 2 detects the reflected light of the laser light projected by the light projecting unit 1. Based on the detection result of the reflected light in the light receiving unit 2, the measurement unit 3 detects an object located in front of the vehicle and measures the position of the detected object.

  The light projecting unit 1 has the above-described configuration, and is attached in a direction in which laser light is projected to the front of the vehicle. As shown in FIG. 8, the light projecting unit 1 is attached so that the horizontal width direction of the light guide 12 is aligned with the vehicle width direction. Therefore, the light projecting unit 1 projects linear laser light extending in the vehicle width direction forward of the vehicle.

  FIG. 8 is a diagram for explaining the orientation of the light guide 12 with respect to the vehicle. The light projecting unit 1 is attached to the front grille, front bumper, or the like of the vehicle. Moreover, it is the figure which showed the magnitude | size of the light guide 12 with respect to a vehicle larger than actual.

  The light receiving unit 2 includes an A / D conversion circuit 20, a light receiving unit 21, and a light receiving lens 23. As shown in FIG. 9, the light receiving lens 23 of the light receiving unit 2 and the light projecting lens 13 of the light projecting unit 1 are mounted side by side in the vehicle width direction. The light receiving unit 21 is a line sensor in which a plurality of light receiving elements 21a are arranged in a line. Each light receiving element 21 a has a light receiving surface facing the light receiving lens 23. The plurality of light receiving elements 21a are arranged in the vehicle width direction. The light incident on the light receiving lens 23 is received by the light receiving element 21a corresponding to the incident angle in the vehicle width direction. That is, the light receiving unit 21 includes a light receiving element 21a that detects incident light for each of a plurality of directions (the object detection direction referred to in the present invention) divided in the width direction of the vehicle. The A / D conversion circuit 20 has an A / D converter for A / D converting the output of the light receiving element 21a for each light receiving element 21a.

  The measurement unit 3 instructs the drive control circuit 10 of the light projecting unit 1 to emit light of the LD 11, and based on the amount of light received by each light receiving element 21a input from the A / D conversion circuit 20, Detects an existing object and measures the position of the detected object.

  The operation of the object detection device 5 will be described. The measurement unit 3 instructs the drive control circuit 10 of the light projecting unit 1 to emit light of the LD 11 at a predetermined time interval. The drive control circuit 10 causes the LD 11 to emit light according to this instruction, and projects laser light in front of the mounted vehicle. As described above, the light projecting unit 1 projects linear laser light extending in the width direction of the vehicle. The linear laser light has a substantially uniform light intensity distribution in the vehicle width direction.

  Laser light (reflected light) reflected by an object existing in front of the vehicle enters the light receiving lens 23. The reflected light enters the light receiving lens 23 at an incident angle corresponding to the position of the object in the width direction of the vehicle, and is received by the light receiving element 21a corresponding to the incident angle. The A / D conversion circuit 20 performs A / D conversion on the output of each light receiving element 21 a and inputs it to the measurement unit 3.

  The measurement unit 3 determines whether or not the reflected light is received for each light receiving element 21a. As described above, the light projecting unit 1 can project linear laser light having a substantially uniform light intensity distribution in the vehicle width direction. Therefore, the threshold of the light receiving level for determining the presence or absence of reflected light can be set to the same level for each light receiving element 21a. Therefore, it is possible to accurately determine whether or not the reflected light is received for each light receiving element 21a.

  The measurement unit 3 determines that an object exists in the direction corresponding to the light receiving element 21a that has determined that the reflected light has been received. That is, the measurement unit 3 detects the azimuth in which an object exists based on the light receiving element 21a determined to have received the reflected light. Further, the distance to the object is measured from the time from when the light projecting unit 1 projects the laser light until the light receiving element 21a receives the reflected light. For each detected object, the measurement unit 3 notifies the direction and distance of the detected object to a control device (not shown) on the vehicle side.

  Based on the notification from the measurement unit 3, the vehicle-side control device performs vehicle travel control related to follow-up traveling with respect to the preceding vehicle.

  Thus, the object detection device 5 can project linear laser light extending in the vehicle width direction, and therefore can detect an object in the vehicle width direction without scanning the laser light. That is, since no mechanism for scanning the laser beam is required, the object detection device 5 can be reduced in size and cost can be reduced.

  Further, as described above, the light projecting unit 1 can project linear laser light having a substantially uniform light intensity distribution in the length direction (vehicle width direction). Reflected light from an object existing in a light projection area where linear laser light is projected can be detected with high accuracy.

  Further, in the configuration shown in FIG. 9, the possibility of detecting the direction of the object is limited by the size of the light receiving element 21a, but as shown in FIG. 10, between the light receiving lens 23 and each light receiving element 21a. If the light guide 22 is provided, the limitation due to the size of the light receiving element 21a can be suppressed, and the possibility of detecting the direction of the object can be improved.

It is a figure which shows the structure of the outline of a light projection unit. It is a figure which shows the external appearance of a light guide. It is a figure which shows the light intensity distribution of the linear laser beam projected by this light projection unit. It is a figure which shows the light intensity distribution of the linear laser beam projected by the conventional light projection unit. It is a figure which shows the light intensity distribution of the linear laser beam projected by the conventional light projection unit. It is a figure which shows the light guide of another shape. It is a figure which shows the structure of the principal part of an object detection apparatus. It is a figure which shows the direction of the light guide with respect to a vehicle. It is a figure which shows the arrangement | positioning relationship between a light projection unit and a light reception unit. It is a figure which shows the arrangement | positioning relationship between a light projection unit and a light reception unit.

Explanation of symbols

1-light emitting unit 2-light receiving unit 3-measurement unit 5-object detection device 11-laser diode (LD)
12-light guide 13-projection lens 20-A / D conversion circuit 21-light receiving part 21a-light receiving element 23-light receiving lens

Claims (3)

A light projecting lens that projects light emitted from a light emitting element as a light source;
A light guide that is disposed between the light emitting element and the light projecting lens and forms an optical waveguide that guides the light emitted from the light emitting element to the light projecting lens;
The outer shape of the exit surface of the light guide facing the light projecting lens is a rectangle whose horizontal width is longer than the vertical width,
The exit surface of the light guide has a concave shape in which a curved surface with a focal length of the light projecting lens as a radius is formed in a lateral width direction,
Further, the light projecting unit, wherein the distance between the optical center of the light projecting lens and the center of the light guide exit surface is the focal length of the light projecting lens. The light projecting unit according to claim 1,
A light receiving unit for detecting reflected light of the light projected by the light projecting unit for each of a plurality of object detection directions divided in a width direction of an exit surface of the light guide;
An object detection comprising: a measurement unit that detects the presence or absence of an object located in the direction based on the reflected light detected by the light receiving unit for each object detection direction and measures the distance to the detected object apparatus. The width direction of the exit surface of the light guide is aligned with the vehicle width direction of the vehicle on which the object detection device main body is mounted,
The object detection device according to claim 2, wherein the light projecting unit projects light in front of the vehicle.

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