Optical system and distance-measuring device

Abstract

The purpose of the feature disclosed in the specification of the present invention is to achieve both a wide dynamic range and high spatial resolution.　This distance-measuring device is provided with a light-receiving sensor, a light-emitting unit, a light-projecting optical system, a deflector, and a light-receiving optical system. The light-receiving sensor has a plurality of single photon avalanche diodes arranged in a grid. The light-emitting unit emits a light projection beam. The light-projecting optical system forms a light projection spot of the light projection beam on the surface of the object. The light-receiving optical system forms a light-receiving spot on the light-receiving sensor by forming an image of the light projection spot on the light-receiving sensor. The size of the light projection spot in the secondary scanning direction is larger than the size of the light projection spot in the main scanning direction. The single photon avalanche diodes are divided into a plurality of regions arranged in the vertical direction. The horizontal resolution of the light-receiving spot is lower than the vertical resolution of the light-receiving spot.

Description

Optical system and distance measuring device

[0001] The technology disclosed in this specification relates to an optical system and a distance measuring device.

[0002] Patent Document 1 discloses an optical scanning distance measuring device. This distance measuring device employs a distance measurement principle known as TOF (Time of Flight). The distance measuring device projects a light beam onto an object. The distance measuring device receives a reflected beam from the object. The distance measuring device calculates the distance to the object based on the time difference between the light projection and the light reception. The light receiving element of this distance measuring device includes multiple highly sensitive avalanche photodiodes (APDs) arranged in an array. When the APDs are operated in Geiger mode, the output signal of the APDs is saturated even when a single photon is incident on the APD. Therefore, the light receiving element measures the received light intensity of the reflected beam based on the number of APDs that sense the photon. Because multiple APDs are arranged in an array, the dynamic range of the light receiving element is wide in a single light projection. However, a single light projection only measures the distance to a single point where the light projection beam is incident. In other words, this distance measuring device has low spatial resolution in a single light projection.

[0003] Patent No. 6519033

[0004] Therefore, the technology disclosed in this specification aims to achieve both a wide dynamic range and high spatial resolution.

[0005] To solve the above problems, this specification discloses an optical system and a distance measuring device. The optical system includes a light-projecting optical system and a light-receiving optical system. The light-projecting optical system projects a light-projecting beam emitted by a light-emitting unit toward an object and forms a light-projected spot of the light-projecting beam on the surface of the object. The light-receiving optical system guides a light-receiving beam, which is reflected when the light-projecting beam strikes the surface of the object, to a light-receiving sensor having a plurality of single-photon avalanches arranged in a grid pattern in the vertical and horizontal directions, and forms a light-receiving spot of the light-receiving beam on the light-receiving sensor by imaging the light-projected spot on the light-receiving sensor. The size of the light-projected spot in a sub-scanning direction perpendicular to the main scanning direction in which the light-projecting beam is deflected is larger than the size of the light-projected spot in the main scanning direction. The light-receiving optical system images the light-receiving spot on the light-receiving sensor with a horizontal resolution perpendicular to the vertical direction and a vertical resolution. The horizontal resolution is lower than the vertical resolution.

[0006] The distance measuring device includes a light-receiving sensor, a light-emitting unit, a light-projecting optical system, a deflector, and a light-receiving optical system. The light-receiving sensor has a plurality of single-photon avalanche diodes arranged in a grid pattern. The light-emitting unit emits a light-projecting beam. The light-projecting optical system projects the light-projecting beam emitted by the light-emitting unit toward an object to form a light-projection spot of the light-projecting beam on the surface of the object. The deflector deflects the light-projecting beam in the main scanning direction. The light-receiving optical system guides a light-receiving beam reflected by the light-projecting beam incident on the surface of the object to the light-receiving sensor, and forms a light-receiving spot of the light-receiving beam on the light-receiving sensor by imaging the light-projection spot on the light-receiving sensor. The size of the light-projection spot in a sub-scanning direction perpendicular to the main scanning direction is larger than the size of the light-projection spot in the main scanning direction. The single-photon avalanche diode is divided into a plurality of regions arranged in a vertical direction corresponding to the sub-scanning direction. The light receiving optical system forms an image of the light receiving spot on the light receiving sensor with a resolution in a horizontal direction perpendicular to the vertical direction and a resolution in the vertical direction, the resolution in the horizontal direction being lower than the resolution in the vertical direction.

[0007] The technology disclosed in this specification contributes to achieving both a wide dynamic range and high spatial resolution.

[0008] Fig. 1 is a schematic diagram showing the overall configuration of a distance measuring device according to a first embodiment, Fig. 2 is a plan view of a light receiving sensor, and Fig. 3 is a schematic diagram showing the overall configuration of a distance measuring device according to a second embodiment.

[0009] Hereinafter, embodiments will be described with reference to the drawings. Features and technical effects of the embodiments will be understood from the following detailed description and drawings. However, the scope of the present invention is not limited to the embodiments disclosed below. Because the drawings are provided for illustrative purposes only, the scope of the present invention is not limited to the examples in the drawings.

[0010] <First Embodiment> <<1. Distance Measuring Device>> FIG. 1 is a schematic diagram showing the overall configuration of a distance measuring device 1. The distance measuring device 1 is an optical sensor. The distance measuring device 1 is also called a LiDAR (Light Detection and Ranging), a range sensor, or a laser scanner. The distance measuring device 1 projects a laser beam 5 onto the surface of an object 2 and receives a laser beam 7 reflected by the surface of the object 2. The distance measuring device 1 detects the distance to the surface of the object 2 based on the time difference between the projection and reception of the laser beam. The distance measuring device 1 is a scanning distance measuring device. That is, the distance measuring device 1 deflects the laser beam 5 to trace the surface of the object 2 with a spot 6 of the laser beam 5, thereby detecting the distance and direction to each point on the surface of the object 2. Deflection of the laser beam 5 refers to a change in the emission direction of the laser beam 5.

[0011] The laser beam 5 projected from the distance measuring device 1 onto the surface of the object 2 is also called the projected beam 5. The laser beam 7 that is reflected from the surface of the object 2 when the projected beam 5 strikes the surface is also called the reflected beam 7. The spot 6 of the projected beam 5 refers to a bright area formed on the surface of the object 2 when the projected beam 5 strikes the surface. The spot 6 of the projected beam 5 is also called the projected spot 6. The direction in which the projected beam 5 is deflected, i.e., the direction in which the projected spot 6 moves, is called the main scanning direction. The direction perpendicular to the main scanning direction and parallel to the rotation axis of the deflector 90 is also called the sub-scanning direction. One cycle refers to the period from one light projection to the next. The distance is detected once per cycle by one light projection and light reception. The projected spot 6 per cycle is resolved into multiple measurement points in the sub-scanning direction. The distance measuring device 1 detects the distance to each measurement point aligned in the sub-scanning direction per cycle.

[0012] The distance measuring device 1 includes a light emitting unit 10, an optical device 50, a light receiving sensor 60, and a peripheral circuit 70. The optical device 50 has an optical system and a deflector 90, and the optical system has a light projecting optical system 20, a mirror 30, and a light receiving optical system 40. The peripheral circuit 70 has a signal processing circuit 71 and a time digitizer (TDC: Time-to-Digital Converter) 72. The light emitting unit 10, the light projecting optical system 20, the mirror 30, the light receiving optical system 40, and the light receiving sensor 60 are assembled together into a unit.

[0013] <<2. Deflector>> The deflector 90 oscillates a unit 80 having the light-emitting unit 10, the light-projecting optical system 20, the mirror 30, the light-receiving optical system 40, and the light-receiving sensor 60. In other words, the deflector 90 rotates the unit 80 reciprocally and continuously around the rotation axis. This deflects the projected beam 5 in the main scanning direction, and the projected light spot 6 is displaced in the main scanning direction along the surface of the object 2. The deflector 90 is formed, for example, by a motor.

[0014] The deflector 90 may alternately deflect the projected beam 5 in the main scanning direction by a predetermined range and deflect the projected beam 5 in the sub-scanning direction by the size of the projected spot 6 in the sub-scanning direction.

[0015] <<3. Light-Emitting Unit>> The light-emitting unit 10 is composed of, for example, a laser diode. The light-emitting unit 10 is driven by a drive circuit, causing the light-emitting unit 10 to light up periodically. Specifically, the light-emitting unit 10 lights up once per cycle and outputs the projected beam 5 once per cycle. While the deflector 90 deflects the projected beam 5 in the main scanning direction by a predetermined range, the light-emitting unit 10 outputs the projected beam 5 multiple times. The timing at which the light-emitting unit 10 lights up is the light-projection timing. The projected beam 5 is near-infrared light. The projected beam 5 may be visible light or ultraviolet light. The projected beam 5 may have a wavelength range of near-infrared light and visible light. The projected beam 5 may have a wavelength range of visible light and ultraviolet light. The projected beam 5 may have a wavelength range of near-infrared light, visible light, and ultraviolet light.

[0016] <<4. Light Projection Optical System>> The light projection optical system 20 is disposed facing the light emitting unit 10 at a distance. The light projection optical system 20 collimates the light projection beam 5 output by the light emitting unit 10 and projects the light projection beam 5 toward the object 2. In other words, the light projection optical system 20 converts the light projection beam 5 into parallel light by reducing the spread angle of the light projection beam 5. The light projection optical system 20 is, for example, a collimating lens made of a convex lens. The collimating lens is disposed facing the light emitting unit 10 at a distance, and its focal point is located at the light emitting unit 10.

[0017] <<5. Mirror and Light Projection Spot>> The mirror 30 is disposed at an angle to the optical axes of the light projecting optical system 20 and the light receiving optical system 40. The center of the mirror 30 is located at the intersection of the optical axes of the light projecting optical system 20 and the light receiving optical system 40. The mirror 30 passes the projected beam 5 collimated by the light projecting optical system 20, and reflects the reflected beam 7 from the object 2 toward the light receiving sensor 60. The mirror 30 is a prism-type beam splitter or a plate-type beam splitter. The mirror 30 may also be a mirror having a small hole through which the projected beam 5 passes.

[0018] The projected beam 5 that has passed through the mirror 30 is incident on the surface of the object 2, and a projected spot 6 is formed at the point of incidence of the projected beam 5. The size of the projected spot 6 in the sub-scanning direction is larger than the size of the projected spot 6 in the main scanning direction. This is achieved, for example, by making the size of the light-emitting unit 10 in the sub-scanning direction larger than the size of the light-emitting unit 10 in the main scanning direction. This is achieved, for example, by making the projecting optical system 20 make the spread angle of the projected beam 5 in the sub-scanning direction smaller than the spread angle of the projected beam 5 in the main scanning direction.

[0019] The projected beam 5 is reflected by the surface of the object 2. The reflection of the projected beam 5 is, for example, diffuse reflection. Of the light reflected by the surface of the object 2, the component reflected in the opposite direction to the projected beam 5 returns to the mirror 30 as a reflected beam 7. The reflected beam 7 travels the same path as the projected beam 5 in the opposite direction and reaches the mirror 30. The mirror 30 makes the optical axis of the reflected beam 7 from the object 2 to the mirror 30 coaxial with the optical axis of the projected beam 5 from the mirror 30 to the object 2. The mirror 30 reflects the reflected beam 7 toward the light-receiving optical system 40 and the light-receiving sensor 60.

[0020] <<6. Light-Receiving Optical System and Light-Receiving Spot>> The light-receiving optical system 40 is disposed between the mirror 30 and the light-receiving sensor 60. The light-receiving optical system 40 guides the reflected beam 7 reflected by the mirror 30 to the light-receiving sensor 60, thereby forming a spot 8 of the reflected beam 7 on the light-receiving sensor 60. In other words, the light-receiving optical system 40 forms an image of the light-projected spot 6 on the light-receiving sensor 60, thereby forming the spot 8 of the reflected beam 7 on the light-receiving sensor 60. The spot 8 of the reflected beam 7 is an image of the light-projected spot 6. The spot 8 of the reflected beam 7 is called a light-receiving spot 8.

[0021] Because the size of the light projected spot 6 in the sub-scanning direction is larger than the size of the light projected spot 6 in the main scanning direction, the size of the light received spot 8 in the vertical direction is larger than the size of the light received spot 8 in the horizontal direction. The vertical direction refers to the direction along the light receiving surface of the light receiving sensor 60 and parallel to the sub-scanning direction. The horizontal direction refers to the direction along the light receiving surface of the light receiving sensor 60 and perpendicular to the vertical direction. The horizontal direction on the light receiving surface of the light receiving sensor 60 corresponds to the main scanning direction on the surface of the object 2, and the vertical direction on the light receiving surface of the light receiving sensor 60 corresponds to the sub-scanning direction on the surface of the object 2.

[0022] The light receiving optical system 40 resolves the light receiving spot 8 on the light receiving sensor 60 with a vertical resolution and a horizontal resolution lower than the vertical resolution. Therefore, the blur of the light receiving spot 8 in the horizontal direction is larger than the blur of the light receiving spot 8 in the vertical direction.

[0023] The light receiving optical system 40 has a condenser lens 41 and an anisotropic optical element 42. A mirror 30, the condenser lens 41, the anisotropic optical element 42, and a light receiving sensor 60 are arranged in this order.

[0024] The condenser lens 41 condenses the reflected beam 7 reflected by the mirror 30 and forms a projected light spot 6 on the light receiving sensor 60 , thereby forming a received light spot 8 on the light receiving sensor 60 .

[0025] The anisotropic optical element 42 has different refractive powers in the horizontal and vertical directions. The anisotropic optical element 42 spreads the reflected beam 7 in the horizontal direction and blurs the light-receiving spot 8 in the horizontal direction. Therefore, the light-receiving spot 8 is blurred more in the horizontal direction than in the vertical direction. The anisotropic optical element 42 may spread the reflected beam 7 in the horizontal direction so as to make the reflected beam 7 into a top-hat shape. The top-hat reflected beam 7 has a uniform intensity distribution in the center of the reflected beam 7.

[0026] The anisotropic optical element 42 is an optical element such as a cylindrical lens, an anamorphic lens, a diffraction grating, or a beam splitter, which has optical properties that spread the reflected beam 7 laterally and blur the receiving spot 8 laterally.

[0027] <<7. Light-Receiving Sensor>> The light-receiving sensor 60 is disposed on the opposite side of the light-receiving optical system 40 from the mirror 30. The light-receiving sensor 60 is perpendicular to the optical axis of the light-receiving optical system 40.

[0028] FIG. 2 is a plan view of the light-receiving sensor 60. The light-receiving sensor 60 is a sensor array such as a multi-pixel photon counter (MPPC), a silicon photomultiplier (SiPM), or a pixelated photon detector (PPD). That is, the light-receiving sensor 60 has a plurality of photoelectric conversion elements 61 arranged in a grid pattern, i.e., vertically and horizontally. The photoelectric conversion elements 61 include single-photon avalanche diodes (SAPDs) driven in Geiger mode and quenching resistors. Because the photoelectric conversion elements 61 are driven in Geiger mode, the light-receiving sensitivity of the photoelectric conversion elements 61 is high. That is, even if the photoelectric conversion elements 61 receive only a single photon, the photoelectric conversion elements 61 sense the photon and the output signal of the photoelectric conversion elements 61 is saturated. If the photoelectric conversion element 61 does not receive a single photon, the output signal of the photoelectric conversion element 61 will not be saturated.

[0029] In the entire light receiving sensor 60, the number of photoelectric conversion elements 61 arranged in the vertical direction is greater than the number of photoelectric conversion elements 61 arranged in the horizontal direction. These photoelectric conversion elements 61 are divided into a plurality of regions 65, and these regions 65 are arranged in the vertical direction. These regions 65 are rectangular. The horizontal size of each region 65 is greater than the vertical size of each region 65. Specifically, the horizontal size of each region 65 is more than 1 time and not more than 10 times the vertical size of each region 65.

[0030] Furthermore, the number of photoelectric conversion elements 61 arranged in the horizontal direction in each region 65 is greater than the number of photoelectric conversion elements 61 arranged in the vertical direction in each region 65. Specifically, the number of photoelectric conversion elements 61 arranged in the horizontal direction in each region 65 is more than 1 time and not more than 10 times the number of photoelectric conversion elements 61 arranged in the vertical direction in each region 65. As an example, the photoelectric conversion elements 61 are divided into 600 regions 65, and the number of photoelectric conversion elements 61 arranged in the horizontal direction in each region 65 is 30, and the number of photoelectric conversion elements 61 arranged in the vertical direction in each region 65 is 3.

[0031] Regarding the field of view angle of the light receiving optical system 40 on the surface of the object 2, which corresponds to the region 65, the field of view angle in the main scanning direction is wider than the field of view angle in the sub-scanning direction. Specifically, the field of view angle in the main scanning direction is more than 1 time and not more than 10 times the field of view angle in the sub-scanning direction.

[0032] When the region 65 is divided horizontally, the region 65 has a central portion 66 and side portions 67, 68, which are arranged in the order of the side portion 67, the central portion 66, and the side portion 68 in the horizontal direction. The side portions 67, 68 are portions of the region 65 other than the central portion 66.

[0033] The light receiving spot 8 formed by the condenser lens 41 and the anisotropic optical element 42 spreads over the entire light receiving surface of the light receiving sensor 60 , so that the light receiving spot 8 covers the entire region 65 .

[0034] <<8. Signal Processing Circuit>> The light-receiving sensor 60 is connected to the signal processing circuit 71. The light-receiving sensor 60 outputs the output signal of the photoelectric conversion element 61 for each region 65 to the signal processing circuit 71. The signal processing circuit 71 counts the number of photoelectric conversion elements 61 that have sensed a photon for each region 65, for each unit time that is sufficiently shorter than one cycle period. Because the output signal of the photoelectric conversion element 61 that senses a photon becomes saturated, the signal processing circuit 71 compares the output signal of the photoelectric conversion element 61 with a saturation value for each photoelectric conversion element 61. If the output signal of the photoelectric conversion element 61 exceeds the saturation value, the signal processing circuit 71 increments a count value that represents the number of photoelectric conversion elements 61 that have sensed a photon. The count value for each region 65 represents the received light intensity of the reflected beam 7 for each region 65.

[0035] The signal processing circuit 71 outputs, in time series, signals representing the received light intensity of the reflected beam 7 for each region 65. The value of the signal output by the signal processing circuit 71 for each region 65 represents the received light intensity of the reflected beam 7 per unit time, i.e., the number of photoelectric conversion elements 61 that sense photons. The timing at which the signal output by the signal processing circuit 71 for each region 65 reaches its peak is the timing at which the reflected beam 7 is received by that region 65.

[0036] If the central portion 66 of the region 65 is blown out within a unit time, all of the photoelectric conversion elements 61 arranged in the central portion 66 of the region 65 will sense photons within the unit time, resulting in saturation of the output signals of these photoelectric conversion elements 61. In such a case, the signal processing circuit 71 ignores the output signals of the photoelectric conversion elements 61 in the central portion 66 and ignores the number of photoelectric conversion elements 61 in the central portion 66. Therefore, the value of the signal output by the signal processing circuit 71 for each region 65 represents the received light intensity of the reflected beam 7 incident on the side portions 67 and 68, i.e., the number of photoelectric conversion elements 61 in the side portions 67 and 68 that sensed photons.

[0037] <<9. Time Digitizer>> The time digitizer 73 receives the signal for each region 65 output by the signal processing circuit 71. The time digitizer 73 receives a pulse signal that rises at the lighting timing of the light-emitting unit 10, i.e., the light-projection timing. For each cycle, the time digitizer 73 calculates the time difference for each region 65 from the light-projection timing to the light-reception timing based on the signal for each region 65 and the pulse signal input from the signal processing circuit 71. The time digitizer 73 outputs a digital signal representing the calculated time difference. The time difference for each region 65 corresponds to the distance to each measurement point overlapping the light projection spot 6. The light-projection timing at which the pulse signal rises represents the emission direction, i.e., the orientation, of the light projection beam 5.

[0038] <<10. Summary>> (1) The distance measuring device 1 includes a light-emitting unit 10, a light-projecting optical system 20, a light-receiving optical system 40, a light-receiving sensor 60, and a deflector 90. The light-emitting unit 10 emits a light projecting beam 5. The light-projecting optical system 20 projects the light projecting beam 5 toward an object 2 to form a projected spot 6 of the light projecting beam 5 on the surface of the object 2. The deflector 90 deflects the light projecting beam 5 in the main scanning direction. The light-receiving optical system 40 guides a reflected beam 7, which is reflected when the light projecting beam 5 is incident on the surface of the object 2, to the light-receiving sensor 60. The light-receiving optical system 40 forms a received spot 8 of the reflected beam 7 on the light-receiving sensor 60 by forming an image of the projected spot 6 on the light-receiving sensor 60. The light-receiving optical system 40 resolves the received spot 8 on the light-receiving sensor 60 with a vertical resolution and a horizontal resolution that is lower than the vertical resolution. The size of the projected light spot 6 in the sub-scanning direction is larger than the size of the projected light spot 6 in the main scanning direction. The light-receiving sensor 60 has a plurality of photoelectric conversion elements 61 arranged in a grid pattern in the vertical and horizontal directions. The photoelectric conversion elements 61 are divided into a plurality of regions 65 arranged in the vertical direction. The light-receiving sensor 60 outputs an output signal from the photoelectric conversion element 61 for each region 65. This distance measuring device 1 contributes to improving the dynamic range when the received light intensity of the reflected beam 7 incident on each region 65 is converted into a signal. In other words, even if the output signal of the photoelectric conversion element 61 has two levels, such as detection and non-detection of a single photon, since there are multiple photoelectric conversion elements 61 in each region 65, the received light intensity of the reflected beam 7 incident on each region 65 is expressed in levels corresponding to the number of photoelectric conversion elements 61. The wide dynamic range of the signal of the received light intensity of the reflected beam 7 incident on each region 65 makes it easier to extract only the signal of the reflected beam from the object from noise due to ambient light such as sunlight, contributing to improved measurement accuracy of the light-receiving timing and further contributing to improved distance measurement accuracy. Furthermore, such a distance measuring device 1 contributes to improved spatial resolution in the sub-scanning direction. That is, the light-receiving surface of the light-receiving sensor 60 is divided into multiple regions 65, these regions 65 are arranged vertically, and the light-receiving sensor 60 outputs an output signal from the photoelectric conversion element 61 for each region 65. Therefore, the distance to each of the multiple measurement points arranged in the sub-scanning direction in the light-projected spot 6 can be detected individually for each measurement point.

[0039] (2) The light-projecting spot 6 is imaged as a light-receiving spot 8 on the light-receiving sensor 60 by the light-receiving optical system 40, and the lateral resolution of the light-receiving spot 8 is lower than the lateral resolution of the light-receiving spot 8. Therefore, the reflected light from a plurality of measurement points arranged in the sub-scanning direction in the light-projecting spot 6 spreads in the lateral direction and is incident on each of a plurality of regions 65. Therefore, the dynamic range of the signal of the received light intensity of the reflected beam 7 incident on each region 65 is wide, and the spatial resolution in the sub-scanning direction is high.

[0040] (3) The size of the light projection spot 6 in the sub-scanning direction is larger than the size of the light projection spot 6 in the main scanning direction. Such a size of the light projection spot 6 contributes to a wide dynamic range of the signal of the received light intensity of the reflected beam 7 incident on each region 65. Such a size of the light projection spot 6 contributes to high spatial resolution in the sub-scanning direction. Such a size of the light projection spot 6 contributes to an improvement in the S / N ratio when the received light intensity of the reflected beam 7 incident on each region 65 is converted into a signal.

[0041] (4) The photoelectric conversion element 61 of the light receiving sensor 60 is driven in Geiger mode, so the light receiving sensitivity of the photoelectric conversion element 61 is high. Therefore, even if the distance from the distance measuring device 1 to the object 2 is long and the intensity of the reflected beam 7 is attenuated, the distance measuring device 1 can measure the distance.

[0042] (5) The horizontal number of photoelectric conversion elements 61 arranged in each region 65 is greater than the vertical number of photoelectric conversion elements 61 arranged in each region 65. In particular, the horizontal number of photoelectric conversion elements 61 arranged in each region 65 is more than 1 time but not more than 10 times the vertical number of photoelectric conversion elements 61 arranged in each region 65. Therefore, the dynamic range of the signal of the received light intensity of the reflected beam 7 incident on each region 65 is wide, and the spatial resolution in the sub-scanning direction is high. The reason why the horizontal number of photoelectric conversion elements 61 arranged in each region 65 is not more than 10 times the vertical number of photoelectric conversion elements 61 arranged in each region 65 is to prevent a deterioration in the signal-to-noise ratio when the received light intensity of the reflected beam 7 is converted into a signal. The reason why the horizontal number of photoelectric conversion elements 61 arranged in each region 65 is more than 1 time the vertical number of photoelectric conversion elements 61 arranged in each region 65 is to ensure high vertical resolution of the projected light spot 6.

[0043] (6) The size of the region 65 in the horizontal direction is larger than the size of the region 65 in the vertical direction. In particular, the size of the region 65 in the horizontal direction is more than 1 time and not more than 10 times the size of the region 65 in the vertical direction. Therefore, the dynamic range of the signal of the received light intensity of the reflected beam 7 incident on each region 65 is wide, and the spatial resolution in the sub-scanning direction is high. The reason why the size of the region 65 in the horizontal direction is not more than 10 times the size of the region 65 in the vertical direction is to prevent a deterioration in the signal-to-noise ratio when the received light intensity of the reflected beam 7 is converted into a signal. The reason why the size of the region 65 in the horizontal direction is more than 1 time the size of the region 65 in the vertical direction is to prevent a narrowing of the dynamic range.

[0044] (7) With regard to the field of view angle of the light receiving optical system 40 on the surface of the object 2 corresponding to the region 65, the field of view angle in the main scanning direction is wider than the field of view angle in the sub-scanning direction. In particular, the field of view angle in the main scanning direction is more than 1 time and not more than 10 times the field of view angle in the sub-scanning direction. Therefore, the dynamic range of the signal of the received light intensity of the reflected beam 7 incident on each region 65 is wide, the spatial resolution in the sub-scanning direction is high, and the resolution in the scanning direction is high. The field of view angle in the scanning direction is set to be not more than 10 times the field of view angle in the sub-scanning direction in order to prevent a deterioration in the signal-to-noise ratio when the received light intensity of the reflected beam 7 is converted into a signal. The field of view angle in the main scanning direction is set to be more than 1 time the field of view angle in the sub-scanning direction in order to prevent a narrowing of the dynamic range.

[0045] (8) The mirror 30 makes the optical axis of the projected beam 5 from the mirror 30 to the object 2 coaxial with the optical axis of the reflected beam 7 from the object 2 to the mirror 30. The influence of an object between the mirror 30 and the object 2, such as air or a transparent window, on the projected beam 5 is approximately the same as the influence of that object on the reflected beam 7. This contributes to improving the measurement accuracy of the light reception timing, and further contributes to improving the distance measurement accuracy.

[0046] (9) Since the deflector 90 deflects the projected beam 5 in the main scanning direction, the area in which distances can be measured in the main scanning direction is wide.

[0047] 3 is a schematic diagram showing the overall configuration of a distance measuring device 1A. Corresponding components between the distance measuring device 1A of the second embodiment and the distance measuring device 1 of the first embodiment are denoted by the same reference numerals. The distance measuring device 1A of the second embodiment differs from the distance measuring device 1 of the first embodiment in the following points.

[0048] In the first embodiment, the deflector 90 swings the unit 80, thereby deflecting the projected beam 5 in the main scanning direction.

[0049] In contrast, in the second embodiment, the deflector 90 is of a polygon mirror type. Specifically, the deflector 90 has a polygon mirror 91 and a motor 92. The polygon mirror 91 has a plurality of mirror surfaces 91a on its outer circumferential surface, and these mirror surfaces 91a are arranged along the outer circumferential surface to form a polygonal prism surface. The polygon mirror 91 is arranged on the opposite side of the projection optical system 20 with respect to the mirror 30. The projection beam 5 is incident on the mirror surface 91a and is reflected by the mirror surface 91a toward the object 2. The motor 92 drives the polygon mirror 91 to rotate, thereby changing the orientation of the mirror surface 91a. The change in the orientation of the mirror surface 91a contributes to deflection of the projection beam 5 in the main scanning direction.

[0050] The mirror 30 makes the optical axis of the reflected beam 7 from the object 2 to the mirror 30 coaxial with the optical axis of the projected beam 5 from the mirror 30 to the object 2. Therefore, the position at which the projected beam 5 is incident on the mirror surface 91a coincides with the position at which the reflected beam 7 is incident on the mirror surface 91a. Therefore, the influence of manufacturing errors on the mirror surface 91a on the projected beam 5 is about the same as the influence of manufacturing errors on the mirror surface 91a on the reflected beam 7. This contributes to improving the measurement accuracy of the light-receiving timing, and further contributes to improving the distance measurement accuracy.

[0051] <Summary of the Disclosure> Several embodiments have been described and illustrated in detail above. The embodiments disclosed above have been created for the purpose of illustration and example only, and are not intended to limit the scope of the present invention. The scope of the present invention should be interpreted by the terms of the claims. The description of the above embodiments discloses the following optical systems (1) to (6). The description of the above embodiments discloses the following distance measuring devices (7) to (11).

[0052] (1) An optical system comprising: a projection optical system that projects a projection beam emitted by a light-emitting unit toward an object and forms a projection spot of the projection beam on the surface of the object; and a light-receiving optical system that guides a reception beam reflected by the projection beam incident on the surface of the object to a light-receiving sensor having a plurality of single-photon avalanche diodes arranged in a grid pattern in the vertical and horizontal directions, and forms a reception spot of the reception beam on the light-receiving sensor by imaging the projection spot on the light-receiving sensor, wherein the size of the projection spot in a sub-scanning direction perpendicular to the main scanning direction in which the projection beam is deflected is larger than the size of the projection spot in the main scanning direction, and the light-receiving optical system images the reception spot on the light-receiving sensor with a horizontal resolution perpendicular to the vertical direction and a vertical resolution, and the horizontal resolution is lower than the vertical resolution.

[0053] (2) The optical system of (1), wherein the single-photon avalanche diode is divided into a plurality of regions arranged in the vertical direction, and the size of the regions in the horizontal direction is more than 1 time and not more than 10 times the size of the regions in the vertical direction.

[0054] (3) An optical system according to (1) or (2), wherein the single-photon avalanche diode is divided into a plurality of regions arranged in the vertical direction, and the field of view of the light receiving optical system on the surface of the object, which corresponds to the region, is such that the field of view in the main scanning direction is more than 1 time and not more than 10 times the field of view in the sub-scanning direction.

[0055] (4) An optical system according to any one of (1) to (3), which includes a mirror that passes the projection beam projected by the projection optical system and reflects the reception beam reflected by the surface of the object toward the reception optical system and the reception sensor, and the mirror makes the optical axis of the projection beam from the mirror to the object coaxial with the optical axis of the reception beam from the object to the mirror.

[0056] (5) The optical system according to any one of (1) to (4), wherein the light receiving optical system has an anisotropic optical element that spreads the light receiving beam in the horizontal direction and blurs the light receiving spot in the horizontal direction.

[0057] (6) The optical system according to (5), wherein the anisotropic optical element is a cylindrical lens, an anamorphic lens, a diffraction grating, or a beam splitter.

[0058] (7) A light receiving sensor having a plurality of single-photon avalanche diodes arranged in a lattice pattern; a light emitting unit that emits a light projection beam; a light projection optical system that projects the light projection beam emitted by the light emitting unit toward an object and forms a light projection spot of the light projection beam on the surface of the object; a deflector that deflects the light projection beam in a main scanning direction; and a light receiving beam that is reflected by the light projection beam incident on the surface of the object and is guided to the light receiving sensor, and the light projection spot is imaged on the light receiving sensor to form a light reception spot of the light reception beam. a light-receiving optical system that forms a light-receiving spot on the light-receiving sensor, wherein the size of the light-projected spot in a sub-scanning direction perpendicular to the main scanning direction is larger than the size of the light-projected spot in the main scanning direction, the single-photon avalanche diode is divided into a plurality of regions that are arranged in a vertical direction corresponding to the sub-scanning direction, and the light-receiving optical system forms an image of the light-receiving spot on the light-receiving sensor with a resolution in a horizontal direction perpendicular to the vertical direction and a resolution in the vertical direction, and the resolution in the horizontal direction is lower than the resolution in the vertical direction.

[0059] (8) The distance measuring device according to (7), wherein the number of the single-photon avalanche diodes arranged in the horizontal direction within the region is greater than the number of the single-photon avalanche diodes arranged in the vertical direction within the region.

[0060] (9) The distance measuring device according to (8), wherein the number of the single-photon avalanche diodes arranged in the horizontal direction within the region is more than 1 time and not more than 10 times the number of the single-photon avalanche diodes arranged in the vertical direction within the region.

[0061] (10) A distance measuring device according to any one of (7) to (9), further comprising a signal processing circuit that inputs the output signal of the single-photon avalanche diode output by the light receiving sensor, and when the output signal of the single-photon avalanche diode located in the center of the region is saturated, the signal processing circuit ignores the output signal of the single-photon avalanche diode located in the center of the region.

[0062] (11) The distance measuring device according to any one of (7) to (10), wherein the light receiving sensor outputs an output signal of the single photon avalanche diode for each of the regions.

[0063] REFERENCE SIGNS LIST 1, 1A Distance measuring device 10 Light emitting unit 20 Light projecting optical system 30 Mirror 40 Light receiving optical system 41 Condenser lens 42 Anisotropic optical element 50 Optical device 60 Light receiving sensor 61 Photoelectric conversion element 65 Area

Claims

1. An optical system comprising: a light projection optical system that projects a light projection beam emitted by a light emitting unit toward an object and forms a light projection spot of the light projection beam on the surface of the object; and a light receiving optical system that guides a light reception beam that is reflected when the light projection beam strikes the surface of the object to a light receiving sensor having a plurality of single-photon avalanche diodes arranged in a grid pattern in the vertical and horizontal directions, and forms a light reception spot of the received beam on the light receiving sensor by imaging the light projection spot on the light receiving sensor, wherein the size of the light projection spot in the sub-scanning direction perpendicular to the main scanning direction in which the light projection beam is deflected is larger than the size of the light projection spot in the main scanning direction, and the light receiving optical system images the light reception spot on the light receiving sensor with a horizontal resolution perpendicular to the vertical direction and a vertical resolution, and the horizontal resolution is lower than the vertical resolution.

2. The optical system according to claim 1, wherein the single-photon avalanche diode is divided into a plurality of regions arranged in the vertical direction, and the size of the regions in the horizontal direction is more than 1 time and not more than 10 times the size of the regions in the vertical direction.

3. The optical system according to claim 1 or 2, wherein the single-photon avalanche diode is divided into a plurality of regions arranged in the vertical direction, and the viewing angle of the light-receiving optical system on the surface of the object, which corresponds to the region, is such that the viewing angle in the main scanning direction is more than 1 time and not more than 10 times the viewing angle in the sub-scanning direction.

4. An optical system as claimed in claim 1 or 2, comprising a mirror that passes the projection beam projected by the projection optical system and reflects the reception beam reflected by the surface of the object towards the reception optical system and the light receiving sensor, wherein the mirror makes the optical axis of the projection beam from the mirror to the object coaxial with the optical axis of the reception beam from the object to the mirror.

5. An optical system according to claim 1 or 2, wherein the light receiving optical system has an anisotropic optical element that spreads the received light beam in the lateral direction and blurs the received light spot in the lateral direction.

6. The optical system according to claim 5, wherein the anisotropic optical element is a cylindrical lens, an anamorphic lens, a diffraction grating, or a beam splitter.

7. A light receiving sensor having a plurality of single-photon avalanche diodes arranged in a lattice pattern; a light emitting unit that emits a light projection beam; a light projection optical system that projects the light projection beam emitted by the light emitting unit toward an object and forms a light projection spot of the light projection beam on the surface of the object; a deflector that deflects the light projection beam in a main scanning direction; and a light receiving optical system that guides a light reception beam reflected by the light projection beam incident on the surface of the object to the light receiving sensor and forms a light reception spot of the light reception beam on the light receiving sensor by imaging the light projection spot on the light receiving sensor, wherein the size of the light projection spot in a sub-scanning direction perpendicular to the main scanning direction is larger than the size of the light projection spot in the main scanning direction, the single-photon avalanche diodes are divided into a plurality of regions arranged in a vertical direction corresponding to the sub-scanning direction, and the light receiving optical system images the light reception spot on the light receiving sensor with a horizontal resolution perpendicular to the vertical direction and a vertical resolution, A distance measuring device, wherein the horizontal resolution is lower than the vertical resolution.

8. The distance measuring device according to claim 7, wherein the number of single-photon avalanche diodes arranged in the horizontal direction within said region is greater than the number of single-photon avalanche diodes arranged in the vertical direction within said region.

9. The distance measuring device according to claim 8, wherein the number of single-photon avalanche diodes arranged in the horizontal direction within said region is more than 1 time but not more than 10 times the number of single-photon avalanche diodes arranged in the vertical direction within said region.

10. A distance measuring device as claimed in any one of claims 7 to 9, further comprising a signal processing circuit that inputs the output signal of the single-photon avalanche diode output by the light receiving sensor, and when the output signal of the single-photon avalanche diode located in the centre of the region is saturated, the signal processing circuit ignores the output signal of the single-photon avalanche diode located in the centre of the region.

11. A distance measuring device according to any one of claims 7 to 9, wherein the light receiving sensor outputs an output signal of the single photon avalanche diode for each of the regions.

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