Optical detector

Abstract

The optical detector is configured to project a projection beam (PB) towards a measurement area (MA) and to detect a return beam (RB) from the measurement area. The optical detector includes: a projection optical system (26) that forms a projection optical axis (POA) for projecting the projection beam; a receiving optical system (49) that forms a receiving optical axis (ROA) for receiving the return beam; and a housing (11) that has a receiving chamber (13) for accommodating the projection optical system and the receiving optical system and an optical window (14) for the projection beam and the return beam to travel between the receiving chamber and the measurement area. The projection optical axis and the receiving optical axis are offset from each other to define an overlapping area (OL) inside the receiving chamber, in which the coverage areas (PF, RF) of the projection beam and the return beam overlap each other.

Description

Technical Field

[0001] The present disclosure relates to an optical detector. Background Art

[0002] USP 9,470,520 describes an optical detector in which a projection optical axis of a projection beam and a reception optical axis of a reflected beam are aligned with each other. Summary of the Invention

[0003] However, in order to achieve a configuration in which the projection optical axis matches the reception optical axis, additional optical components such as mirrors are required. Therefore, the size of the optical detector becomes large.

[0004] An object of the present disclosure is to provide an optical detector having a configuration that can be easily reduced in size.

[0005] According to an aspect of the present disclosure, an optical detector is configured to project a projection beam toward a measurement area and detect a return beam from the measurement area. The optical detector includes: a projection optical system that forms a projection optical axis to project the projection beam; a reception optical system that forms a reception optical axis to receive the return beam; and a housing that has an accommodation chamber for accommodating the projection optical system and the reception optical system and an optical window for the projection beam and the return beam to travel between the accommodation chamber and the measurement area. The projection optical axis and the reception optical axis are offset from each other to define an overlapping area inside the accommodation chamber, in which the coverage areas of the projection beam and the return beam overlap each other.

[0006] Therefore, the overlapping area is provided inside the accommodation chamber, in which the coverage area is shared between the projection beam and the return beam. Therefore, the accommodation chamber can be reduced by the volume of the overlapping area. In addition, since the projection optical axis and the reception optical axis are offset from each other, there is no need for a space for arranging additional optical components for aligning the optical axes, so that the accommodation chamber is reduced. Therefore, an optical detector having a configuration that can be easily reduced in size can be provided.

[0007] It should be noted that the reference numerals are only illustrative of the corresponding relationships in the embodiments described below, and are not intended to limit the technical scope. Brief Description of the Drawings

[0008] Figure 1 is a diagram showing an overall configuration of an optical detector.

[0009] Figure 2 is a diagram showing a light emission part.

[0010] Figure 3 is a diagram for explaining a spot shape of a projection beam.

[0011] Figure 4This is a diagram for explaining the scanning performed by a scanning mirror.

[0012] Figure 5 This is a diagram showing the positional relationship between the light projection unit and the light reception unit.

[0013] Figure 6 This is a diagram showing the configuration of the detection unit.

[0014] Figure 7 This is a diagram showing the outer peripheral contour of the optical lens of the light reception optical system.

[0015] Figure 8 This is a block diagram showing the controller.

[0016] Figure 9 This is a flowchart executed by the decoder and the scan controller. Detailed implementation mode

[0017] The implementation mode will be described with reference to the accompanying drawings.

[0018] (First implementation mode)

[0019] As Figure 1 shown, the optical detector 10 according to the first implementation mode is a LiDAR (Light Detection and Ranging / Laser Imaging Detection and Ranging) to be installed on a vehicle as a movable unit. For example, the optical detector 10 is arranged at the front, left / right side, rear, or roof of the vehicle WC. The optical detector 10 scans the projection beam PB towards a predetermined measurement area MA around the vehicle WC in an area outside the optical detector. The optical detector 10 detects the return beam (hereinafter referred to as the reflected beam RB), which is the projection beam PB reflected by the measurement target. For the projection beam PB, light in the near-infrared region that is difficult for humans to visually recognize is usually selected.

[0020] The optical detector 10 can measure the measurement target by detecting the reflected beam RB. The measurement of the measurement target is, for example, the measurement of the distance from the optical detector 10 to the measurement target, the direction in which the measurement target exists, etc. In the optical detector 10 applied to a vehicle, typical measurement targets are pedestrians, cyclists, animals other than humans, movable objects such as other vehicles, and stationary objects such as guardrails, road signs, roadside structures, and objects on the road.

[0021] In the present implementation mode, unless otherwise specified, the front, rear, upper, lower, left, and right directions are defined with reference to the vehicle on the horizontal plane. In addition, the horizontal direction indicates the tangential direction with respect to the horizontal plane, and the vertical direction indicates the vertical direction with respect to the horizontal plane.

[0022] The optical detector 10 includes a housing 11, a light projection unit 21, a scanning unit 31, a light receiving unit 41, and a controller 61. The housing 11 has a light-shielding container 12 and a cover plate 15.

[0023] The light-shielding container 12 is made of, for example, synthetic resin or metal, and is formed in a box shape having an outer wall 12a with light-shielding properties. The light-shielding container 12 can be configured by one component, or can be configured by combining a plurality of components. The light-shielding container 12 includes a housing chamber 13 surrounded by the outer wall 12a to house the light projection unit 21, the scanning unit 31, the light receiving unit 41, and the controller 61. The housing chamber 13 is generally provided for the light projection unit 21 and the light receiving unit 41, and one housing chamber is provided in this embodiment. Since the housing chamber 13 is shared by the light projection unit 21 and the light receiving unit 41, a partition wall between the light projection unit 21 and the light receiving unit 41 can be eliminated. Therefore, an increase in the size of the optical detector 10 can be suppressed.

[0024] The light-shielding container 12 has an optical window 14 that is opened, through which both the projection beam PB and the reflected beam RB reciprocate linearly between the housing chamber 13 and the measurement area MA. The optical window 14 is provided in common for both the light projection unit 21 and the light receiving unit 41, and one optical window is provided in this embodiment.

[0025] The cover plate 15 is a member formed in a plate shape (e.g., a flat plate shape) that can transmit both the beam PB and the RB, and is made of a base material such as synthetic resin or glass. The cover plate 15 is arranged to cover the entire optical window 14 and block foreign matter from entering the housing chamber 13 from the outside.

[0026] The cover plate 15 transmits light in the near-infrared region by coloring the base material, forming an optical film, or attaching a film to the surface of the base material. In addition, it preferably has a wavelength dependence of transmittance that shields visible light to prevent the inside of the housing chamber 13 from being seen from the outside. A mirror-like surface of the base material can be exposed from the surface of the cover plate 15 facing the housing chamber 13 and / or the surface of the cover plate 15 facing the measurement area MA. An antireflection film or a moth-eye structure can be provided on the surface of the cover plate 15 facing the housing chamber 13 and / or the surface of the cover plate 15 facing the measurement area MA.

[0027] For example, the cover plate 15 can have a flat plate shape. In this case, the accuracy of detecting the position of the measurement target can be improved by suppressing the angular change caused by the refraction of the projection beam PB passing through the cover plate 15 and the angular change caused by the refraction of the reflected beam RB.

[0028] The light projection unit 21 includes a light emission unit 22, a projection optical system 26, and a projection holding member 28. As Figure 2As shown, the light emitting unit 22 has a plurality of laser oscillation elements 24 arranged in an array along the extension direction ED0 so as to form a light emission window 23 elongated along the extension direction ED0. The light emitting unit 22 uses the plurality of laser oscillation elements 24 to increase the total output of the laser. The light emitting unit 22 projects a projection beam PB from the light emission window 23 at the light emission timing in response to an electrical signal from the controller 61.

[0029] Each of the laser oscillation elements 24 may be, for example, a laser diode (LD). Each of the laser oscillation elements 24 has a structure in which a P-type semiconductor and an N-type semiconductor are joined to each other via a PN junction layer, and a resonator structure that resonates the light generated in the PN junction layer. In the resonator structure, the PN junction layer is disposed between the mirrors, and one of the mirrors forms a half mirror small window 25. Each of the laser oscillation elements 24 can emit laser light as coherent light in a beam state through the small window 25. This laser is a small beam that forms part of the projection beam PB. In the present embodiment, a group of sub-beams (beamlets) oscillated from each of the windows 25 is defined as the projection beam PB. The PN junction layer of each laser oscillation element 24 is disposed along a direction perpendicular to the arrangement direction of the small window 25 (i.e., the extension direction ED0). The axis along the perpendicular direction is the fast axis FA of the laser diode.

[0030] The plurality of small windows 25 are arranged as close to each other as possible to form the light emission window 23 as a macroscopic opening formed by an aggregate of the small windows 25. The light emission window 23 of the present embodiment has a substantially rectangular shape. The size of the light emission window 23 in the extension direction ED0 is set to be, for example, 100 times or more the size in the direction perpendicular to the extension direction ED0 (the direction along the fast axis FA).

[0031] When the optical detector is generally mounted on a vehicle, the extension direction ED0 of the light emission window 23 is along the vertical direction. When the optical detector is mounted on a vehicle, the fast axis FA is along the horizontal direction.

[0032] Each of the laser oscillation elements 24 oscillates linearly polarized light in the TE mode such that the polarization direction of the laser beam is common and along the extension direction ED0. Then, since the polarization direction of the projection beam PB is along the vertical direction in the in-vehicle state, the projection beam PB can be incident on the road surface with the vertical polarization direction substantially along the horizontal direction. Therefore, the conventional reflectivity is reduced and the diffuse reflectivity is increased. Therefore, when it is raining or freezing, the reflected beam RB can easily return from the road surface to the optical window 14.

[0033] The projection beam PB oscillates in short pulses. The respective small beams emitted from each of the laser oscillation elements 24 can oscillate substantially simultaneously, or can oscillate successively with a minute time difference. The projection beam PB travels to the measurement area MA via the projection optical system 26 and the scanning mirror 34 of the scanning unit 31.

[0034] The projection optical system 26 collects and projects the projection beam PB emitted from the light emission unit 22. The projection optical system 26 is arranged between the light emission unit 22 and the scanning mirror 34. The projection optical system 26 includes at least one optical lens 27. The projection optical system 26 forms a projection optical axis POA. The projection optical axis POA is defined as, for example, the axis along a hypothetical light ray that passes through the center of curvature of the respective refractive surfaces of the optical lens 27. The hypothetical light ray along the projection optical axis POA can pass through the projection optical system 26 by traveling straight through each lens vertex 27a without deflection. In the present embodiment, the principal ray of the projection beam PB emitted from the center point of the light emission window 23 is along the projection optical axis POA. When the center point of the light emission window 23 is located in the gap between the small windows 25, the principal ray of the projection beam PB is a hypothetical light ray in the optical design. When the beam along the projection optical axis POA is deflected by the scanning unit 31, the projection optical axis POA is also defined to include an extension portion along the deflection direction.

[0035] The focal length of the projection optical system 26 is substantially equal to the distance from the principal point of the projection optical system 26 to the light emission window 23 along the projection optical axis POA. As Figure 3 shown, the projection optical system 26 collimates the projection beam PB emitted from the light emission window 23. The distance Dp from the light emission window 23 along the projection optical axis POA is infinite (Dp = ∞) at the following position: at a point conjugate to the light emission window 23 outside the accommodation chamber 13 on the opposite side of the light emission window 23 on the optical path through the projection optical system 26. The spot shape of the projection beam PB at infinity is the far-field pattern FFP. An image corresponding to the light emission window 23 is formed at infinity, but this image is more affected by diffraction in the extension direction ED0 than the near-field pattern NFP. Therefore, the spot shape of the projection beam PB at infinity has a line shape in which each small beam is elongated, for example, along the extension direction ED0, while leaving a gap between the small windows in the light emission window 23. Alternatively, since the gap between the small windows 25 in the light emission window 23 is substantially eliminated, the spot shape of the projection beam PB at infinity has a line shape in which the small beams are integrated and elongated along the extension direction ED0.

[0036] In the accommodation chamber 13 where the distance Dp from the light emission window 23 is small, the spot shape of the projection beam PB is a near-field pattern NFP. This spot shape is less affected by diffraction in the extending direction of the fast axis FA compared to the far-field pattern FFP. In this spot shape, small spots SS corresponding to respective small beams can be respectively identified. Each small spot SS has an elliptical pattern in which the fast axis FA corresponds to the major axis. The small spots SS can be completely separated from each other or can partially overlap each other.

[0037] The range of the footprint PF of the projection beam PB can be defined by the light emission window 23 serving as a substantial diaphragm, while the image formation mode is adjusted by the projection optical system 26. The projection optical axis POA penetrates the center point of the light emission window 23. Alternatively, the range of the footprint PF can be defined by providing a diaphragm in the projection optical system 26 - the projection optical axis POA penetrates the center point of this diaphragm. In the present embodiment, the footprint means the space that can be covered by the beam trajectories contributing to measurement.

[0038] Figure 4 and Figure 5 The projection holding member 28 shown in

[0039] is formed in a tubular shape for holding one or more optical lenses 27 of the projection optical system 26. The projection holding member 28 is formed of, for example, synthetic resin or metal as the barrel of the projection optical system 26 to have light shielding properties. The projection holding member 28 can be formed to also hold the light emission unit 22. Figure 1 and Figure 4 As shown in

[0040] The scanning mirror 34 can reflect and scan the projection beam PB. The scanning mirror 34 has a main body 35 and a reflection surface 36. The scanning mirror 34 is mechanically coupled to the rotation axis 33 and is formed of a flat plate made of, for example, synthetic resin. The reflection surface 36 is formed as a mirror surface by depositing a metal film such as aluminum on one surface of the main body 35. The reflection surface 36 is, for example, flat and extends in a direction parallel to the rotation axis 33 so as to include the extended corresponding direction ED1.

[0041] The reflection surface 36 is provided in common for both the beam PB and the beam RB. The reflection surface 36 is formed in a rectangular shape, and the longitudinal direction of the rectangular shape is substantially aligned with the extended corresponding direction ED1. As Figure 3 shown, the reflection surface 36 is located at a position on the projection optical axis POA, between the conjugate point of the light emission window 23 and the projection optical system 26, where the image of the light emission window 23 is in a non-image state. The reflection surface 36 is arranged such that the projection beam PB is incident on the reflection surface 36 outside the range of the depth of focus through the image of the light emission window 23 imaged at infinity. That is, the reflection surface 36 is located at a position farther from the projection optical system 26 than the end of the depth of focus facing the projection optical system 26. Therefore, the projection beam PB is incident on the reflection surface 36 in a state where the circle of confusion in the image of the light emission window 23 is greater than or equal to the allowable circle of confusion. The diameter of the allowable circle of confusion in the image of the light emission window 23 can be, for example, the size of the small window 25 in the extending direction ED.

[0042] In addition, the reflection surface 36 is arranged at a position where the spot shape of the projection beam PB forms a near-field pattern NFP (Dp = Ds). That is, each small spot SS of the projection beam PB on the reflection surface 36 has an elliptical shape with the extended corresponding direction ED1 corresponding to the short axis. Therefore, compared with the aspect ratio of the light emission window 23 having an elongated shape and the spot having a line shape at infinity, the aspect ratio of the projection beam PB on the reflection surface 36 is compressed in the extended corresponding direction ED1. Since the coverage area PF of the projection beam PB is also compressed in the extended corresponding direction ED1, the size of the scanning mirror 34 in the extended corresponding direction ED1 is shortened.

[0043] As Figure 4 shown, the scanning mirror 34 can swing within a limited angular range AR with respect to the rotation axis 33 parallel to the extended corresponding direction ED1. The reflection angle of the projection beam PB reflected by the reflection surface 36 also changes according to the orientation change of the reflection surface 36 due to the swinging motion. The projection beam PB is scanned in time and space toward the measurement area MA.

[0044] Scanning in the present embodiment means one-dimensional scanning, in which scanning in the extending corresponding direction ED1 is omitted. The spot shape of the projection beam PB reflected by the reflecting surface 36 at infinity substantially corresponds to the illumination range of the projection beam PB in the swinging motion phase. In the vehicle-mounted state, this illumination range elongates in the vertical direction. Therefore, even if the scanning mirror 34 does not perform scanning corresponding to the vertical direction, the vertical viewing angle in the measurement area MA can be enlarged.

[0045] The illumination range of the projection beam PB that elongates in the vertical direction is moved by a swinging motion along a direction perpendicular to the extending corresponding direction ED1, that is, along the horizontal direction. The finite angular range AR in the swinging motion defines the horizontal viewing angle in the measurement area MA. A part of the projection optical axis POA between the scanning mirror 34 and the measurement area MA swings in the horizontal direction according to the swinging motion of the scanning mirror 34. However, the direction and position of this part of the projection optical axis POA between the scanning mirror 34 and the measurement area MA are uniquely determined with respect to a predetermined phase of the swinging motion (in other words, a predetermined orientation of the reflecting surface 36).

[0046] The finite angular range AR is limited by a mechanical stopper, an electromagnetic stopper, or by controlling a drive mechanism. The reflection angle of the projection beam PB is maximum at the end AR1 within the maximum finite angular range AR. The end AR1 is set such that the projection beam PB reflected by the scanning mirror 34 avoids deviating from the optical window 14 and avoids interference with the light shielding container 12.

[0047] The reflection angle of the projection beam PB is minimum at the end AR2 within the maximum finite angular range AR. The end AR2 is set such that the projection beam PB reflected by the scanning mirror 34 is prevented from interfering with the light projection unit 21. The angle of the projection holding member 28 facing the optical window 14, at which the projection beam PB is emitted, has a concave portion 29 that is recessed toward the projection optical system 26. The coverage area PF of the projection beam PB reflected by the scanning mirror 34 enters the space formed by the concave portion 29. Therefore, when the reflection angle of the projection beam PB is minimum within the finite angular range AR, the settable range of the end AR2 can be extended.

[0048] The projection beam PB scanned within the finite angular range AR passes through the optical window 14. As Figure 3As shown, the optical window 14 is arranged at a position on the projection optical axis POA, between the conjugate point of the light emission window 23 and the projection optical system 26, where the image of the light emission window 23 is in a non-image state. The optical window 14 is arranged such that the projection beam PB is incident on the optical window 14 outside the depth of focus range through the image of the light emission window 23 formed at infinity. That is, the optical window 14 is located farther from the projection optical system 26 than the end of the depth of focus facing the projection optical system 26. Therefore, the projection beam PB is incident on the optical window 14 in a state where the circle of confusion in the image of the light emission window 23 is greater than or equal to the allowable circle of confusion.

[0049] In addition, the optical window 14 is arranged at a position where the spot shape of the projection beam PB forms a near-field pattern NFP (Dp = Dw). That is, each small spot SS of the projection beam PB on the reflection surface 36 has an ellipticity smaller than that of each small spot (i.e., close to a circle) on the reflection surface 36, and the elliptical shape has a short axis along the extended corresponding direction ED1. Therefore, compared with the aspect ratio of the elongated emission window 23 and the line-shaped spot at infinity, the aspect ratio of the coverage area PF of the projection beam PB on the optical window 14 is compressed in the extended corresponding direction ED1. Therefore, the size of the optical window 14 in the extended corresponding direction ED1 can be shortened.

[0050] The projection beam PB passes through the optical window 14 and is then reflected by the measurement target object present in the measurement area MA. The reflected beam RB - which is the projection beam PB reflected by the measurement target object - passes through the optical window 14 again and enters the scanning mirror 34. The speeds of the projection beam PB and the reflected beam RB are sufficiently higher than the swinging speed of the scanning mirror 34. Therefore, the difference in the phase of the swinging motion when the projection beam PB is reflected by the scanning mirror 34 and the phase of the swinging motion when the reflected beam RB is incident on the scanning mirror 34 is slight and negligible. Therefore, the reflected beam RB is reflected at substantially the same reflection angle as the projection beam PB and is guided to the light receiving unit 41 to travel in the direction opposite to that of the projection beam PB.

[0051] As Figure 1 and Figure 5 shown, the light receiving unit 41 includes a detection unit 42, a receiving optical system 49, and a light receiving holding member 51. As Figure 6 shown, the detection unit 42 in the present embodiment has a light receiving element array 43 and a decoder 46. The light receiving element array 43 has a plurality of light receiving elements 44 arranged in an array. A single photon avalanche photodiode (SPAD) light receiving element is used as the light receiving element 44. The light receiving elements 44 are two-dimensionally arranged in a highly integrated state on a rectangular detection surface 45. Note that Figure 6 only some of the light receiving elements 44 shown in

[0052] The length direction of the detection surface 45 is aligned with the extension direction ED0 of the light emission window 23. The reflected beam RB corresponding to the projection beam PB that is straight at an infinite distance can also be a straight beam. The detection surface 45 has a shape that matches the spread of the reflected beam RB. Therefore, the detection unit 42 can effectively receive the reflected beam RB, and the detection accuracy is improved.

[0053] When one or more photons are incident, each SPAD light receiving element 44 generates an electrical pulse through an electron multiplication operation of avalanche multiplication (so-called Geiger mode). That is, each light receiving element 44 can directly generate an electrical pulse as a digital signal without using an AD conversion circuit from an analog signal to a digital signal. Therefore, the detection result of the reflected beam RB focused on the detection surface 45 via the receiving optical system 49 can be read at high speed.

[0054] The decoder 46 is arranged to output the electrical pulses generated by the light receiving elements 44, and includes a selection circuit 47 and a clock oscillator 48. The selection circuit 47 is mounted in the form of, for example, an integrated circuit, and sequentially selects the light receiving elements 44 that output electrical pulses among the light receiving element array 43. The selected light receiving element 44 outputs the electrical pulse to the controller 61. In this way, when the selection circuit 47 finishes selecting the light receiving element 44 to output once each time, one sampling is completed. The selection circuit 47 periodically repeats sampling starting from the time when the projection beam PB is emitted at a predetermined emission timing. This sampling period corresponds to the clock frequency output from the clock oscillator 48. The clock oscillator 48 is provided inside or outside the integrated circuit of the selection circuit 47.

[0055] As Figure 1 and Figure 5As shown in the figure, the receiving optical system 49 receives the reflected beam RB and focuses the reflected beam RB on the detection surface 45. The receiving optical system 49 is arranged between the detection unit 42 and the scanning mirror 34. The receiving optical system 49 includes one or more optical lenses 50. The diameter of the optical lens 50 of the receiving optical system 49 is made larger than the diameter of the optical lens 27 of the projection optical system 26. In this way, the efficiency of collecting the reflected beam RB by the receiving optical system 49 can be improved. The receiving optical system 49 forms a receiving optical axis ROA. The receiving optical axis ROA is defined, for example, along a hypothetical ray that passes through the center of curvature of each refracting surface of the one or more optical lenses 50. The hypothetical ray along the receiving optical axis ROA can pass through the receiving optical system 49 by traveling straight through each lens vertex 50a without deflection. In the present embodiment, the chief ray of the reflected light RB incident on the center point of the detection surface 45 is along the receiving optical axis ROA. The chief ray of the reflected beam RB can be a virtual ray depending on the reflection pattern of the measurement target object with respect to the projection beam PB. When the beam along the receiving optical axis ROA is deflected by the scanning unit 31, the receiving optical axis ROA is also defined to include an extension portion along the deflection direction.

[0056] A portion of the receiving optical axis ROA between the measurement area MA and the scanning mirror 34 swings horizontally in a vehicle-mounted state according to the swinging motion of the scanning mirror 34. However, the direction and position of this portion of the receiving optical axis ROA between the measurement area MA and the scanning mirror 34 are uniquely determined with respect to a predetermined phase of the swinging motion.

[0057] When the receiving optical axis ROA penetrates the center point, the range of the coverage area RF of the reflected beam RB received by the receiving optical system 49 can be defined by the detection surface 45 serving as a substantial aperture. Alternatively, when the receiving optical axis ROA penetrates the center point, the range of the coverage area RF can be defined by providing an aperture in the receiving optical system 49.

[0058] Figure 5 The light-receiving holding member 51 shown in the figure is formed as a barrel of the receiving optical system 49. The light-receiving holding member 51 is formed in a tubular shape to hold the one or more optical lenses 50 of the receiving optical system 49 and is made of, for example, synthetic resin or metal to have a light-shielding property. The light-receiving holding member 51 can be formed to also hold the detection unit 42.

[0059] As Figure 1 and Figure 5As shown, the projection optical axis POA and the reception optical axis ROA are offset from each other in the entire region outside and inside the accommodation chamber 13. Specifically, the projection optical axis POA and the reception optical axis ROA are arranged to be substantially parallel to each other, with a gap therebetween and along a common direction. The utilization efficiency of the projection beam PB and the reflected beam RB can be improved by arranging the projection optical axis POA and the reception optical axis ROA in a direction perpendicular to the rotation axis 33.

[0060] The positional relationship between the projection optical axis POA and the reception optical axis ROA in the region between the measurement area MA and the scanning mirror 34 is also uniquely determined according to the orientation of the reflection surface 36 shared by the beams PB and RB. Regardless of the phase of the swinging motion, the mutually offset form (specifically, the parallel arrangement form) is maintained.

[0061] The projection optical system 26 and the reception optical system 49 are arranged side by side in the direction along the rotation axis 33 for the swinging motion - that is, along the extension direction ED0 of the light emission window 23. Then, the reception optical system 49 can effectively receive the reflected beam RB reflected by the common reflection surface 36 at substantially the same reflection angle as the projection beam PB.

[0062] Due to the arrangement of the projection optical system 26 and the reception optical system 49, interference between the projection beam PB and the light reception holding member 51 can be suppressed, and interference between the reflected beam RB and the projection holding member 28 can be suppressed. In addition, as a result of adjusting the distance from the scanning mirror 34 to the projection optical system 26 and the distance from the scanning mirror 34 to the reception optical system 49, the size of the accommodation chamber 13 can be reduced in the common direction along the optical axes POA and ROA.

[0063] As Figure 5 and Figure 7 As shown, in the light reception optical system 49, peripheral cutting processing such as so-called D-cutting and I-cutting is performed on the optical lens 50 including the reception optical axis ROA. More specifically, the outer peripheral contour of the optical lens 50 is formed by a combination of an arc contour portion 50b formed in an arc shape and a line contour portion 50c formed in a line shape at a portion facing the projection optical system 26. The light reception holding member 51 formed in a tubular shape around the outer peripheral contour has a flat portion 52 formed in a flat shape at a position facing the light projection optical system 26. Due to the shape of the light reception unit 41, the distance between the projection optical axis POA and the reception optical axis ROA can be reduced.

[0064] The optical lens 27 including the projection optical axis POA in the light projection optical system 26 is formed in a spherical shape without undergoing peripheral cutting processes such as D-cutting and I-cutting. That is, the outer peripheral profile of the optical lens 27 is formed in a circular shape everywhere. The lens diameter in the optical lens 27 of the light projection optical system 26 is smaller than the lens diameter in the optical lens 50 of the light receiving optical system 49. Therefore, the effect of reducing the distance between the projection optical axis POA and the reception optical axis ROA by cutting the outer periphery is small.

[0065] In the vehicle-mounted state, the light receiving optical system 49 is arranged below the light projection optical system 26. Since the diameter of the optical lens 50 is larger than the diameter of the optical lens 27 of the light projection optical system 26, the weight of the light receiving optical system 49 or the light receiving unit 41 is greater than the weight of the light projection optical system 26 or the light projection unit 21. Therefore, the center of gravity of the optical detector 10 can be lowered downward, and the mounting stability of the optical detector 10 in the vehicle can be improved.

[0066] As Figure 1 shown, the coverage area PF of the projection beam PB increases the cross-sectional area perpendicular to the projection optical axis POA as it travels from the light projection optical system 26 toward the measurement area MA on the projection optical axis POA. Due to the scanning by the scanning mirror 34, the horizontal expansion width of the cross-sectional area of the coverage area PF increases in the area between the measurement area MA and the scanning mirror 34 with respect to the area between the light projection optical system 26 and the scanning mirror 34.

[0067] Similarly, the coverage area RF of the reflected beam RB increases the cross-sectional area perpendicular to the reception optical axis ROA as it travels from the light receiving optical system 49 toward the measurement area MA on the reception optical axis ROA. Due to the scanning by the scanning mirror 34, the horizontal expansion width of the cross-sectional area of the coverage area RF increases in the area between the measurement area MA and the scanning mirror 34 with respect to the horizontal expansion width of the cross-sectional area of the coverage area RF in the area between the light receiving optical system 49 and the scanning mirror 34. The horizontal expansion width means the increase in the cross-sectional area of the coverage area per unit length along the optical axis in the horizontal direction.

[0068] An overlap OL where the coverage area PF of the projection beam PB and the coverage area RF of the reflected beam RB overlap each other is formed inside the accommodation chamber 13. Compared with a comparative structure in which the coverage areas PF and RF are completely separated from each other, the size of the accommodation chamber 13 can be reduced by the volume of the overlap OL in the present embodiment provided with the overlap OL.

[0069] In the present embodiment, the coverage area PF of the projection beam PB and the coverage area RF of the reflection beam RB partially overlap each other on the reflection surface 36 of the scanning mirror 34. Specifically, the coverage areas PF and RF overlap each other in a cross-section of the reflection surface 36 including the direction along the rotation axis 33. Therefore, the size of the reflection surface 36 along the corresponding extension direction ED1 can be reduced. Accordingly, the size of the scanning mirror 34 or the accommodation chamber 13 can be reduced.

[0070] The controller 61 controls the measurement in the measurement area MA and controls the swinging movement of the scanning mirror 34. As Figure 1 shown, the controller 61 has a computer that includes a processing unit 62, a RAM 63, a storage unit 64, an input / output interface 65, and a bus connecting them. The processing unit 62 is hardware for arithmetic processing and is combined with the RAM 63. The processing unit 62 includes at least one arithmetic core, such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), and a RISC (Reduced Instruction Set Computer). The processing unit 62 may include at least one arithmetic core, such as an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit). The processing unit 62 executes various processes for implementing the functions of each functional unit described later by accessing the RAM 63. The storage unit 64 includes at least one non-volatile storage medium. The program executed by the processing unit 62 is stored in the storage unit 64.

[0071] The controller 61 is electrically connected to the light emission unit 22, the drive motor 32, and the detection unit 42 or can communicate wirelessly with the light emission unit 22, the drive motor 32, and the detection unit 42. As Figure 8 shown, the controller 61 has functional units such as a light emission control unit 66, a scanning control unit 67, and a measurement calculator 68.

[0072] The light emission control unit 66 outputs an electrical signal to the light emission unit 22 so that each laser oscillation element 24 emits the projection beam PB at a light emission timing associated with the scanning performed by the scanning mirror 34.

[0073] The scanning control unit 67 outputs an electrical signal to the drive motor 32 so that scanning associated with the light emission timing of the projection beam PB is achieved.

[0074] The measurement calculator 68 performs arithmetic processing on the electrical pulses input from the detection unit 42 to detect the presence / absence of the measurement target object in the measurement area MA and measure the distance to the measurement target object. The measurement calculator 68 counts the number of electrical pulses output from each of the light receiving elements 44 in each sampling after the emission of the projection beam PB. The measurement calculator 68 generates a histogram in which the number of electrical pulses for each sampling is recorded. The categories of this histogram show the time of flight of the light from the emission of the projection beam PB to the incidence of the reflected beam RB on the light receiving element 44, that is, TOF (time of flight). The sampling period of the decoder 46 corresponds to the time resolution in the TOF measurement.

[0075] In the present embodiment, the coverage area PF of the projection beam PB and the coverage area RF of the reflected beam RB overlap each other. The optical path of the reflected beam RB returning from the measurement area MA is geometrically inseparable from the optical path of the noise light, which is the projection beam PB reflected by the cover plate 15 for the optical window 14. Therefore, the decoder 46 of the present embodiment sets the sampling period so that the reflected beam RB can be separated from the noise light in time. The sampling period is set in a range of, for example, 100 ns or less, such as a few ns.

[0076] Then, the measurement calculator 68 of the present embodiment excludes the categories corresponding to the TOF of the noise light from the histogram generated based on the data for calculating the distance. The TOF of the noise light can be estimated by multiplying the sum of the distance from the light emitting unit 22 to the cover plate 15 and the distance from the cover plate 15 to the detection unit 42 by the speed of light.

[0077] The measurement calculator 68 specifies the distance to the object to be measured based on the histogram after excluding the TOF of the noise light. For example, the measurement calculator 68 can convert the TOF corresponding to the category with the highest frequency in the histogram into a distance to specify the distance to the object.

[0078] Next, a measurement method for the measurement object performed by the decoder 46 and the controller 61 will be described with reference to Figure 9 the flowchart. For example, for each emission of the projection beam PB, the processing according to the flowchart including steps is executed.

[0079] In S11, the decoder 46 performs sampling on each light receiving element 44 at the sampling cycle mentioned above. Electrical pulses are sequentially output from the detection unit 42 to the controller 61. After the processing in S11, the processing transfers to S12.

[0080] In S12, the measurement calculator 68 counts the number of electrical pulses for each sampling and generates a histogram. After the processing in S12, the processing transfers to S13.

[0081] In S13, the measurement calculator 68 excludes from the histogram the category corresponding to the TOF of the noise light caused by the projection beam PB reflected by the cover plate 15 of the optical window 14 when calculating the distance. After the processing in S13, the processing proceeds to S14.

[0082] In S14, the measurement calculator 68 specifies the distance to the measurement object based on the histogram. A series of processing is completed by S14.

[0083] In the first embodiment, the decoder 46 of the detection unit 42 and the processing unit 62 of the controller 61 correspond to the "at least one processor". Further, the cover plate 15 corresponds to the "cover member".

[0084] The operation and effects of the first embodiment will be described below.

[0085] According to the first embodiment, an overlapping region OL where the coverage area PF of the projection beam PB and the coverage area RF of the reflected beam RB overlap with each other is provided inside the accommodation chamber 13. Therefore, the accommodation chamber 13 can be reduced in size according to the volume of the overlapping region OL. In addition, since the projection optical axis POA and the reception optical axis ROA are offset from each other, an increase in the space for arranging additional optical components for matching the two optical axes POA and ROA is suppressed. Therefore, the size of the accommodation chamber 13 can be reduced. Thus, an optical detector 10 having a configuration capable of easily reducing the size can be provided. Further, as the horizontal viewing angle becomes larger due to the swing of the scanning mirror 34 for emitting the projection beam PB, the effect of contributing to the reduction in size becomes greater.

[0086] In addition, according to the first embodiment, the sampling period in the SPAD light receiving element 44 is set to a time at which the reflected beam RB can be separated from the noise light of the projection beam PB reflected by the cover plate 15. Therefore, the reflected beam RB can be detected while reducing the influence of the noise light while the coverage area PF of the projection beam PB and the coverage area RF of the reflected beam RB overlap with each other. Therefore, the size can be reduced while maintaining the detection accuracy.

[0087] In addition, according to the first embodiment, the scanning mirror 34 is accommodated in the accommodation chamber 13 and has a reflection surface 36 shared by both the beams PB and RB. The reflection surface 36 scans the projection beam PB from the projection optical system 26 toward the measurement region MA and guides the reflected beam RB toward the reception optical system 49. The accommodation chamber 13 can be reduced in size by the reflection surface 36 shared by both the beams PB and RB.

[0088] In addition, according to the first embodiment, the coverage area PF of the projection beam PB and the coverage area RF of the reflected beam RB partially overlap each other on the common reflection surface 36. Since the area of the reflection surface 36 can be reduced by the overlap between the coverage areas on the reflection surface 36, the size can be reduced.

[0089] In addition, according to the first embodiment, the projection optical system 26 has a focal length for imaging the light emission window 23 outside the accommodation chamber 13. Relative to the projection optical system 26, the scanning mirror 34 is arranged at a position where the light emission window 23 is in a non-image state. More preferably, the scanning mirror 34 is positioned such that the projection beam PB is incident in the near-field pattern NFP. Compared with the elongated shape of the light emission window 23 and the image of the light emission window 23 outside the accommodation chamber 13, the coverage area PF of the projection beam PB on the reflection surface 36 is relatively compressed in the extension corresponding direction ED1. Therefore, since the size of the reflection surface 36 can be reduced in the extension corresponding direction ED1, the size can be reduced.

[0090] In addition, according to the first embodiment, relative to the projection optical system 26 having a focal length for imaging the light emission window 23 outside the accommodation chamber 13, the optical window 14 is arranged at a position where the light emission window 23 is not imaged. More preferably, the optical window 14 is arranged at a position where the projection beam PB is incident in the near-field pattern NFP. Therefore, since the area of the optical window 14 can be reduced, the size can be reduced.

[0091] In addition, according to the first embodiment, the projection optical axis POA and the reception optical axis ROA are arranged at a distance from each other and extend in a common direction with respect to each other. By offsetting the optical axes POA and ROA and arranging the optical systems 26 and 49 in the common direction, the beam can efficiently travel to a distant object to be measured while forming the overlapping region OL of the coverage areas PF and RF. Therefore, the size can be reduced while improving the detection accuracy.

[0092] In addition, according to the first embodiment, the outer peripheral profile of the optical lens 50 provided in the reception optical system 49 has an arc profile portion 50b formed in an arc shape and a line profile portion 50c formed in a chord shape in a region excluding the range formed by the arc profile portion 50b at a portion facing the projection optical system 26. Therefore, the portion of the reception optical system 49 facing the projection optical system 26 can be prevented from extending to the projection optical system 26. The reception optical axis ROA can be made closer to the projection optical axis POA. Therefore, while offsetting the optical axes POA and ROA from each other, the overlapping region OL of the coverage areas PF and RF can be increased. Therefore, the size can be further reduced.

[0093] (Other embodiments)

[0094] Although one embodiment has been described, the present disclosure should not be limited to the above embodiment and can be applied to various other embodiments within the scope of the present disclosure.

[0095] Specifically, as a first modification example, the number of laser oscillation elements 24 in the light emitting unit 22 can be appropriately changed. That is, the number of small windows 25 in the light emitting window 23 can be appropriately changed and can be one or more.

[0096] As a second modification example, the light emitting unit 22 can be provided at multiple positions. For example, multiple light emitting units 22 can be arranged such that the light emitting window 23 is arranged in the horizontal direction in the vehicle-mounted state. One projection optical system 26 can be provided for the multiple light emitting units 22, or the same number of projection optical systems 26 as the number of light emitting units 22 can be provided.

[0097] When one projection optical system 26 is provided for the multiple light emitting units 22, the projection optical axis POA can be defined by a virtual principal ray emitted from the average position of the center points of the light emitting window 23.

[0098] When the same number of projection optical systems 26 are provided for the multiple light emitting units 22, the projection optical axes POA can be arranged in a mutually common direction or can be arranged in different directions. When multiple projection optical systems 26 are provided to present multiple projection beams PB, at least one coverage area PF in the coverage areas PF of the multiple projection beams PB has an overlapping area OL with the coverage area RF of the reflected beam RB.

[0099] As a third modification example, the light emitting window 23 can have various shapes, such as an elliptical shape, a circular shape, a square shape, and a polygonal shape. Therefore, the projection beam PB is not limited to forming an image in a line shape outside the accommodation chamber 13, but can form images of various shapes.

[0100] As a fourth modification example, the focal length of the projection optical system 26 is set such that the light emitting window 23 is imaged outside the accommodation chamber 13, and is not limited to the focal length for imaging the light emitting window 23 at infinity.

[0101] As a fifth modification example, the optical lens 27 of the projection optical system 26 can be subjected to peripheral cutting processes such as so-called D-cutting and I-cutting.

[0102] As a sixth modification example, the optical lens 50 of the receiving optical system 49 can be formed in a spherical shape without being subjected to peripheral cutting processes.

[0103] As a seventh modification example, the scanning mirror 34 may not swing within the limited angle range AR, but may rotate 360 degrees in one direction. In this case, the reflecting surface 36 may be formed on two surfaces of the main body 35. In addition, the scanning mirror 34 may perform two-dimensional scanning such as a polygon mirror.

[0104] As an eighth modification example, the projection optical axis POA and the reception optical axis ROA may not be arranged in parallel. For example, the distance between the projection optical axis POA and the reception optical axis ROA may be set to gradually decrease as it extends from the projection optical system 26 and the reception optical system 49 toward the measurement area MA.

[0105] As a ninth modification example, the coverage area PF of the projection beam PB and the coverage area RF of the reflected beam RB may have an overlapping area OL only in the space inside the accommodation chamber 13 after the reflection by the scanning mirror 34. In this case, the reflecting surface 36 of the scanning mirror 34 may be provided separately for both the beams PB and RB, or the scanning mirror 34 itself may be provided separately for both the beams PB and RB.

[0106] As a tenth modification example, the light projection unit 21 and the light reception unit 41 may not be arranged side by side, but may be arranged at separate positions from each other while setting the overlapping area OL.

[0107] As an eleventh modification example, the light receiving element 44 employed in the detection unit 42 may be another light receiving element such as an APD light receiving element instead of the SPAD light receiving element.

[0108] As a twelfth modification example, the controller 61 may be provided outside the accommodation chamber 13. In addition, the controller 61 may be configured as an electronic control device independent of the optical detector 10.

[0109] As a thirteenth modification example, a measurement calculation circuit may be provided in the detection unit 42. The calculation of the measurement calculator 68 of the controller 61 may be processed by the measurement calculation circuit of the detection unit 42. In this case, the histogram may be temporarily or permanently stored in the RAM 63 or the storage unit 64 of the controller 61. The detection unit 42 may also have a RAM or a non-volatile storage medium in addition to the measurement calculation circuit. In this case, the histogram may be temporarily or permanently stored in the RAM 63 or the storage medium of the detection unit 42. In addition, the measurement calculation circuit may be separate from the selection circuit 47 of the decoder 46, or may be installed as an integrated circuit shared with the selection circuit 47.

[0110] The processors and methods described in this disclosure can be implemented by a processing unit of a special-purpose computer, which is programmed to perform one or more functions implemented by a computer program. Alternatively, the processors and methods described in this disclosure can be implemented by special-purpose hardware logic circuits. In addition, the processors and their methods described in this disclosure can be implemented by discrete circuits. Alternatively, the processors and methods described in this disclosure can be any one selected from one or more processing units of a computer that executes a computer program, one or more hardware logic circuits, and one or more discrete circuits. It can be implemented by combination. The computer program can be stored as instructions to be executed by a computer in a tangible non-transitory computer-readable medium.

Claims

1. An optical detector configured to project a projection beam (PB) towards a measurement area (MA) and detect a return beam (RB) from the measurement area, the optical detector comprising: a projection optical system (26) that forms a projection optical axis (POA) to project the projection beam; a receiving optical system (49) that forms a receiving optical axis (ROA) to receive the return beam, and a housing (11) having a receiving chamber (13) for housing the projection optical system and the receiving optical system and an optical window (14) for the projection beam and the return beam to travel between the receiving chamber and the measurement area, wherein, the projection optical axis and the receiving optical axis are offset from each other to define an overlapping area (OL) inside the receiving chamber, in which the coverage areas (PF, RF) of the projection beam and the return beam overlap with each other, the optical detector further comprises: a light emitting unit (22) housed in the receiving chamber, the light emitting unit having a light emitting window (23) elongated in an extending direction (ED0) to emit the projection beam from the light emitting window towards the projection optical system by laser; and a scanning mirror (34) housed in the receiving chamber and having a reflecting surface (36) that scans the projection beam from the projection optical system towards the measurement area, wherein, the projection optical system has a focal length such that an image of the light emitting window is formed outside the receiving chamber, and the scanning mirror is positioned such that the aspect ratio of the coverage area of the projection beam on the reflecting surface of the scanning mirror is compressed in a direction corresponding to the extending direction with respect to the linear-shaped light spot of the projection beam at infinity and the aspect ratio of the light emitting window.

2. The optical detector according to claim 1, wherein, The scanning mirror is arranged at a position where the projection beam is incident in a near-field pattern (NFP).

3. An optical detector configured to project a projection beam (PB) towards a measurement area (MA) and detect a return beam (RB) from the measurement area, the optical detector comprising: a projection optical system (26) that forms a projection optical axis (POA) to project the projection beam; a receiving optical system (49) that forms a receiving optical axis (ROA) to receive the return beam, and a housing (11) having a receiving chamber (13) for housing the projection optical system and the receiving optical system and an optical window (14) for the projection beam and the return beam to travel between the receiving chamber and the measurement area, wherein, the projection optical axis and the receiving optical axis are offset from each other to define an overlapping area (OL) inside the receiving chamber, in which the coverage areas (PF, RF) of the projection beam and the return beam overlap with each other, the optical detector further comprises: A light emitting unit (22) accommodated in the accommodation chamber, the light emitting unit having a light emitting window (23) elongated in an extending direction (ED0) to emit the projection beam from the light emitting window toward the projection optical system by laser, wherein, the projection optical system has a focal length that forms an image of the light emitting window outside the accommodation chamber, and the optical window is positioned such that the aspect ratio of the coverage area of the projection beam on the optical window is compressed in a direction corresponding to the extending direction with respect to the line-shaped light spot of the projection beam at infinity and the aspect ratio of the light emitting window.

4. The optical detector according to claim 3, wherein, The optical window is arranged at a position where the projection beam is incident in a near-field pattern (NFP).

5. The optical detector according to claim 3 further comprises: A scanning mirror (34) accommodated in the accommodation chamber for both the projection beam and the return beam, wherein, the scanning mirror has a reflective surface (36) to scan the projection beam from the projection optical system toward the measurement area and guide the return beam toward the receiving optical system.

6. The optical detector according to claim 5, wherein, The coverage area of the projection beam and the coverage area of the return beam partially overlap each other on the reflective surface.

7. The optical detector according to any one of claims 1 to 6, further comprising: a cover member (15) that closes the optical window capable of transmitting both the projection beam and the return beam; a single-photon avalanche photodiode light receiving element (44) accommodated in the accommodation chamber to generate an electrical pulse in response to receiving photons by the return beam passing through the receiving optical system; and at least one processor (46, 62) that sets a sampling period of the single-photon avalanche photodiode light receiving element such that the return beam is separated from noise light caused by the projection beam reflected by the cover member.

8. The optical detector according to any one of claims 1 to 6, wherein, The projection optical axis and the receiving optical axis are arranged at a certain distance from each other and extend along a common direction shared by each other.

9. The optical detector according to claim 8, wherein, the projection optical system and the receiving optical system are arranged adjacent to each other in a direction perpendicular to the common direction, the receiving optical system has an optical lens (50), the optical lens being arranged to include the receiving optical axis, and an outer peripheral contour of the optical lens has an arc contour portion (50b) formed in an arc shape and a line contour portion (50c) formed in a line shape facing the projection optical system at a position excluding a range formed by the arc contour portion.

10. An optical detector configured to project a projection beam (PB) toward a measurement area (MA) and detect a return beam (RB) from the measurement area, the optical detector comprising: a projection optical system (26) that forms a projection optical axis (POA) to project the projection beam; a receiving optical system (49) that forms a receiving optical axis (ROA) to receive the return beam, and A housing (11) having a receiving chamber (13) for receiving the projection optical system and the receiving optical system and an optical window (14) for the projection beam and the return beam to travel between the receiving chamber and the measurement area, wherein, the projection optical axis and the receiving optical axis are offset from each other to define an overlapping area (OL) inside the receiving chamber, in which the coverage areas (PF, RF) of the projection beam and the return beam overlap with each other, the projection optical axis and the receiving optical axis are arranged at a distance from each other and extend along a common direction shared by each other, the projection optical system and the receiving optical system are arranged adjacent to each other in a direction perpendicular to the common direction, the receiving optical system has an optical lens (50), the optical lens being arranged to include the receiving optical axis, and the outer peripheral contour of the optical lens has an arc contour portion (50b) formed in an arc shape and a line contour portion (50c) formed in a line shape facing the projection optical system at a position excluding the range formed by the arc contour portion.

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