Object detection system, object detection method, and program

Abstract

To reduce influences of disturbance light using small and low cost approach when an object is scanned by a laser beam for pulse emission in a certain visual field range and detected.SOLUTION: An object detection system comprises: a scan part reciprocally scanning within a field of view using a light beam for pulse emission; a light receiving element; and a light guide part guiding to the light receiving element light entering a mirror in an optical path opposite light projection. An object detection method includes: measuring a time difference between projection of the light beam and reception of the light receiving element (S15); summing (S16) for each rank, the time difference measured for each turning on of a group set to include multiple times of turning on of the light beam of projection directions adjacent to each other, the turning on being in forward path scan, and turning on in return path scan following the forward path scan (S14); and detecting for each group set in the field of view, on the basis of projection direction of the light beam and frequency for each rank, a direction in which an object is present and a distance to the object (S17, S18).SELECTED DRAWING: Figure 24

Description

[Technical Field]

[0001] The present invention relates to an object detection system and an object detection method for detecting an object on the optical path of a projected laser beam, as well as a program for causing a computer to control the necessary hardware to execute procedures related to such object detection. [Background technology]

[0002] Conventionally, there has been known an object detection device that irradiates a pulse of laser light to the outside, detects the laser light reflected by an object and returns, and detects an object on the optical path of the laser light and the distance to the object based on the time from irradiation to detection of the reflected light (TOF: Time of flight). Such an object detection device is called a LiDAR (Light Detection and Ranging). In recent years, such lidars have come to be used in a variety of fields, including autonomous driving.

[0003] However, noise from ambient light poses a problem when detecting objects using LIDAR. This is because when the light detection unit detects incident light, it is not possible to distinguish, based solely on the presence or absence of light, whether the detected light is reflected light from the irradiated light or ambient light that is incident independently of the irradiated light. Known techniques for dealing with this problem include those using histograms, as described in Patent Documents 1 and 2. Patent Document 3 also discloses a technique using histograms. Furthermore, Patent Documents 4 to 7 are also known as publications relating to the applicant's patents or patent applications. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-91377 [Patent Document 2] Japanese Patent Publication No. 2020-112443 [Patent Document 3] Japanese Patent Application Publication No. 2020-26969 [Patent Document 4] Patent No. 6830698 [Patent Document 5] Patent Publication No. 2021-132416 [Patent Document 6] Patent No. 7097647 [Patent Document 7] Patent No. 6519033 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent documents 1 and 2 describe a technology in which the time difference between the time a pulsed light is projected and the time a pulsed light is received is measured repeatedly or using multiple SPADs (Single Photon Avalanche Diodes), a histogram of the time difference is created, and the distance to an object is calculated based on the peak position of the histogram. However, the technologies described in Patent Documents 1 and 2 relate to a type of LIDAR that does not perform optical scanning, but instead irradiates a measurement target with a wide beam of light that covers the target and receives the reflected light by forming an image on a two-dimensional array of light-receiving elements. Therefore, it was not easily applicable to a type of LIDAR that scans the field of view with laser light.

[0006] Furthermore, Patent Document 3 describes creating a histogram of the time difference between light projection and light reception by changing the light receiving position for receiving reflected light to multiple positions per one direction in which the irradiated light is irradiated, or by changing the direction in which the irradiated light is irradiated to multiple directions per one light receiving position for receiving reflected light.

[0007] However, the technology described in Patent Document 3 addresses the possibility that reflected light may not be properly received within the light receiving range due to deformation of components such as lenses and holders used in optical distance measuring devices depending on the ambient temperature, and enables distance measurement even if the light receiving position is slightly shifted. It is unclear whether this technology is also useful for reducing the effects of ambient light. In addition, the system requires a large array of light-receiving elements to receive reflected light at different positions depending on the direction of the projected light, making it difficult to apply to small devices. Furthermore, the system requires complex control of the light-receiving position and the direction of light irradiation, making it difficult to reduce costs.

[0008] The present invention aims to solve these problems and to reduce the effects of ambient light using a compact, low-cost method when scanning a predetermined field of view with pulsed laser light and detecting an object based on the timing of receiving reflected light. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the object detection system of the present invention includes an optical scanning unit that scans a predetermined field of view with a pulsed light beam by reflecting the light beam off a first reflecting material that is driven to rotate back and forth periodically around a first rotation axis by a first actuator and projecting the light beam, the scanning including a back and forth scan in a first direction that corresponds to the rotation direction of the first reflecting material, an optical detection unit that receives and detects light at a predetermined position, a light guiding unit that guides light that enters the first reflecting material to the optical detection unit along an optical path opposite to the projected light beam, and a measurement unit that measures the time difference between the projection of the light beam and its reception by the optical detection unit.

[0010] Such an object detection system may further include a counting unit that counts the time difference measured by the measurement unit for each lighting of a group of the light beam, which includes lighting during a forward scan in the first direction and lighting during a return scan following the forward scan, in units of class values ​​of the time difference, and an object detection unit that performs object detection to detect the direction in which an object exists and the distance to the object based on the lighting direction of the light beam and the frequency for each class obtained by the counting for each of the multiple groups set within the field of view.

[0011] The device may further include an adjustment unit that adjusts the frequency of the drive signal applied to the first actuator so that the frequency matches the resonant frequency of the first actuator, and a determination unit that determines whether the frequency of the drive signal matches the resonant frequency of the first actuator, and the object detection unit may use the frequency obtained by the aggregation for the object detection when the determination unit determines that the frequency of the drive signal matches the resonant frequency of the first actuator.

[0012] Furthermore, it is preferable to provide a group creation unit that pulses the light beam in the same pattern in the forward scan in the first direction and the return scan following the forward scan, and creates the multiple groups based on how many times each emission of the light beam is lit during the forward scan or the return scan.

[0013] Alternatively, the optical scanning unit may further include a second reflecting material that is driven to rotate around a second rotation axis that is not parallel to the first rotation axis, the scanning of the light beam may include a main scan in the first direction and a sub-scan corresponding to the rotation of the second reflecting material, and the lighting during the forward scan and the lighting during the return scan included in each group may be lighting whose light projection direction is adjacent to the sub-scan direction.

[0014] The device may further include an adjustment unit that adjusts the frequency of the drive signal applied to the first actuator so that the frequency of the drive signal matches the resonant frequency of the first actuator, and a determination unit that determines whether the frequency of the drive signal matches the resonant frequency of the first actuator, and the object detection unit may use the counted frequency for the detection when the determination unit determines that the frequency of the drive signal matches the resonant frequency of the first actuator.

[0015] Furthermore, it is preferable to provide a group creation unit that pulses the light beam in the same pattern in the forward scan in the main scanning direction and in the return scan at a position adjacent to the forward scan in the sub-scanning direction, and creates the multiple groups based on how many times each emission of the light beam is turned on during the forward scan or the return scan.

[0016] In addition, instead of the above-mentioned counting unit, a counting unit may be provided that counts the time difference measured by the measurement unit for each lighting of a group including multiple lightings of the light beam that are close to each other in projection directions and that are adjacent to each other in the first direction, by class of the value of the time difference. Alternatively, instead of the above-mentioned counting unit, a counting unit may be provided that counts the time difference measured by the measurement unit for each of a group of lightings of the light beam that include multiple lightings in which the projection directions are close to each other and that are included in different main scans, by class of the value of the time difference.

[0017] Furthermore, in each of the above-mentioned object detection systems, it is preferable that the light detection unit detects light for each pixel using a plurality of pixels, each of which is an avalanche photodiode operated in Geiger mode, detects incident light corresponding to each of the lighting of the light beam using the same plurality of pixels, and outputs the sum of outputs corresponding to the light detection from each of the plurality of pixels as the detection result of the incident light during the detection period.

[0018] Furthermore, each of the inventions described above can be embodied not only in the form of a system, but also in any form, such as an apparatus, a method, a program, or a recording medium on which a program is recorded. [Effects of the Invention]

[0019] According to the present invention as described above, when a predetermined field of view is scanned with pulsed laser light and an object is detected based on the timing of receiving reflected light, the influence of ambient light can be reduced using a compact and low-cost method. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a block diagram showing main components of an object detection device 10 according to an embodiment of the present invention, divided according to their functions. [Figure 2] 2 is a diagram for explaining the principle of object detection in the object detection device 10. FIG. [Figure 3] FIG. 2 is an exploded perspective view showing the structure of the main components of the object detection device 10. [Figure 4] 1 is a perspective view showing the appearance of an object detection device 10. FIG. [Figure 5] 4 is a cross-sectional view of the actuator 300 shown in FIG. 3, taken along a plane perpendicular to the rotation axis of the mirror unit 301. FIG. [Figure 6] 3 is a diagram showing an example of the waveform of a drive signal applied to a drive coil 316 of the actuator 300. FIG. [Figure 7] 10 is a diagram showing an example of the relationship between the scanning angle of a mirror 301 in an actuator 300 and the absolute value of the angular velocity. [Figure 8] FIG. 8 is a diagram corresponding to FIG. 7 and illustrating another example different from that of FIG. 7. [Figure 9] FIG. 8 is a diagram corresponding to FIG. 7 and illustrating yet another example. [Figure 10] 10 is a schematic diagram showing the relationship between the scanning range of the emitted light L2, the position where the reflecting portion 66 is provided, and the position of the effective reflecting area 66a. [Figure 11]10 is a diagram for explaining a method for detecting the timing at which the emitted light L2 is reflected by the effective reflection area 66a of the reflecting portion 66. FIG. [Figure 12] 8 is a diagram showing the time range in which reflected light from an effective reflection area 66a is detected during one main scan when the scan angle and angular velocity of the mirror 301 have the relationship shown in FIG. [Figure 13] 9 is a diagram showing the time range in which reflected light from the effective reflection area 66a is detected during one main scan when the scan angle and angular velocity of the mirror 301 have the relationship shown in FIG. 8. FIG. [Figure 14] 10 is a diagram showing the time range in which reflected light from an effective reflection area 66a is detected during one main scan when the scan angle and angular velocity of the mirror 301 have the relationship shown in FIG. [Figure 15] 2 is a schematic diagram for explaining the configuration of scanning lines formed in the field of view by the scanning unit 30. FIG. [Figure 16] 16 is a diagram for explaining an object image obtained from the scanning shown in FIG. 15 when the drive frequency of the actuator 300 matches the resonance frequency. FIG. [Figure 17] 16 is a diagram for explaining an object image obtained from the scanning shown in FIG. 15 when the drive frequency of the actuator 300 does not match the resonance frequency. FIG. [Figure 18] 10 is a diagram for explaining an example of a spot S formed on a scanning line by pulsed light emission from an LD, and a group G set for the spot S. FIG. [Figure 19] 19A to 19D are diagrams showing examples of the relationship between the light projection timing of each spot in the group G(n, x) shown in FIG. 18 and the corresponding light detection timing. [Figure 20] 10 is a histogram showing an example of a total of the detection results of TOF corresponding to each spot S in a group G(n, x). [Figure 21] 2 is a diagram illustrating in more detail the configuration of the light receiving section 40 in FIG. 1 and the optical path of the return light L4. FIG. [Figure 22]1, the relationship between the configuration of the light receiving element 43 and the incident position of the return light L4, and a detection signal output by the light receiving element 43. FIG. [Figure 23] 19 is a diagram showing the positional relationship of a plurality of groups G in the example shown in FIG. 18. FIG. [Figure 24] 2 is a flowchart showing an example of a process for object detection executed by the processor 53 shown in FIG. 1. [Figure 25] FIG. 10 is a diagram illustrating an example of setting a group G in a first modified example of the first embodiment. [Figure 26] FIG. 10 is a diagram showing an example of setting a group G in the second modified example. [Figure 27] FIG. 10 is a diagram showing an example of setting a group G in the third modified example. [Figure 28] FIG. 13 is a diagram showing an example of setting a group G in the fourth modified example. [Figure 29] 25 is a flowchart of a process executed by a processor 53 in a fifth modified example of the present invention, the process corresponding to FIG. 24. [Figure 30] FIG. 13 is a diagram showing another example of setting a group G in the fifth modified example. [Figure 31] FIG. 13 is a schematic diagram for explaining the configuration of scanning lines formed in the field of view by the scanning unit 30 in a sixth modified example. [Figure 32] FIG. 10 is a diagram illustrating yet another example of setting the group G. [Figure 33] 25 is a flowchart of a process corresponding to FIG. 24, which is executed by a processor 53 in yet another modification of the present invention. [Figure 34] 10 is a diagram showing another example of the configuration of the actuator in the scanning unit 30. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] An embodiment of the present invention will be described with reference to the drawings. 1. Overall configuration of the object detection device (Figs. 1 to 4) First, the overall configuration of an object detection device according to one embodiment of the present invention will be described with reference to Figures 1 and 2, with the main components divided according to their functions. Figure 1 is a block diagram showing the main components of the object detection device divided according to their functions. Figure 2 is a diagram for explaining the principle of object detection in the object detection device.

[0022] An object detection device 10, which is one embodiment of the object detection system of the present invention, projects a laser beam to the outside, detects the laser beam reflected by an external object and returns, and detects the distance to an object on the optical path of the laser beam and the direction of the object based on the difference between the timing of the projection and the timing of the detection of the reflected light. As shown in Figure 1, this object detection device 10 includes a light projecting unit 20, a scanning unit 30, a light receiving unit 40, a front-end circuit 51, a TDC (Time-to-Digital Converter) 52, a processor 53, and an input / output unit 54.

[0023] Of these, the light projecting unit 20 is a module for projecting a laser beam to the outside, and includes an LD (laser diode) module 21, a laser driving circuit 22, and a light projecting optical system . The LD module 21 is a laser light source that outputs laser light in response to a drive signal applied from a laser drive circuit 22. Here, a laser module with multiple light-emitting points is used to increase the output intensity, but a single light-emitting point may also be used. There are no particular restrictions on the wavelength of the laser light, but it is conceivable to use, for example, near-infrared laser light. Laser light is an example of a light beam. The laser drive circuit 22 is a circuit that generates a drive signal for turning on the LD module 21 at a timing according to parameters supplied from the processor 53, and applies the signal to the LD module 21. The LD module 21 is turned on intermittently by a pulse wave.

[0024] The projection optical system 23 is an optical system for converting the laser light output by the LD module 21 into a beam of parallel light, and in this embodiment, a collimating lens made of a convex lens whose focal point is located at the center of the multiple light-emitting points provided in the LD module 21 is used. In addition, the laser beam L1 formed by the projection optical system 23 passes through the through hole 41a of the mirror 41 of the light receiving unit 40, is reflected by the mirror 31 of the scanning unit 30, and is output to the outside of the object detection device 10 as emitted light L2.

[0025] Next, the scanning unit 30 is a module for deflecting the laser beam output by the light projecting unit 20 to scan a predetermined field of view (FOV) 70, and includes an actuator 32 having a mirror 31 that is a reflective material. The actuator 32 periodically changes the direction of the projection of the laser beam by periodically changing the orientation of the mirror 31 provided on the optical path of the laser beam.

[0026] Although only one actuator 32 is shown in FIG. 1, in reality, the actuator 32 is composed of two actuators 300 and 380, each of which swings a mirror around a different axis, as shown in FIG. 3. The actuator 300 is driven to reciprocate and is responsible for scanning in the main scanning direction (first direction), forming main scanning direction (horizontal) scanning lines 71 and 72, while the actuator 380 changes the orientation of the mirror at the end of the main scanning direction scanning to adjust the scanning position in the sub-scanning direction. Note that the scanning line 71 scans from left to right in the figure, and the scanning line 72 scans from right to left in the figure. Here, the former is called the forward scanning and the latter the backward scanning, but this is simply to distinguish between the two, and the forward and backward scanning may be reversed.

[0027] It should be noted that since the LD module 21 is turned on intermittently, the scanning lines 71 and 72 are not actually continuous lines but are a collection of beam spots. A reflecting portion 66 is provided on the optical path of the emitted light L2. The reflecting portion 66 is a member that reflects at least a portion of the emitted light L2 toward the incident optical path of the emitted light L2 at a predetermined position in the main scanning direction. The reflecting portion 66 will be described in detail later. The light projecting unit 20 and scanning unit 30 constitute an optical scanning device.

[0028] Next, light receiving unit 40 is a module for detecting light incident from outside object detection device 10, and includes a mirror 41, a condenser lens 42, a light receiving element 43, and an aperture 44. The light to be detected by light receiving unit 40 is a laser beam that is emitted from object detection device 10 and reflected back by an external object, and a laser beam that is reflected back by reflecting unit 66. The laser beam reflected by the external object is diffused at the object surface, and only the component of the laser beam that is reflected in the opposite direction to the optical path taken when the light was emitted returns to object detection device 10 as return light L3. This return light L3 travels in the opposite direction along substantially the same path as emitted light L2, and reaches mirror 41 as return light L4.

[0029] Similarly, the component of the laser beam reflected by the reflector 66 and returning is reflected in the opposite direction to the optical path taken when the beam was projected, and reaches the mirror 41 as return light L4. The only difference from when the laser beam is reflected by an external object is essentially the travel distance of the laser beam.

[0030] The mirror 41 is a fixed mirror that has a through hole 41a for passing the laser beam output from the light-projecting unit 20, and also guides the return light L4 to the light-receiving element 43. Here, the laser light output from the LD module 21 generally does not become a completely parallel beam even when passing through a collimating lens, and has a small divergence angle. Therefore, at the position of the mirror 41, the return light L4 has a larger divergence than the laser beam L1, so it hits the mirror 41 over a wider area than the through hole 41a, and the component that hits positions other than the through hole 41a is reflected toward the light-receiving element 43.

[0031] The condenser lens 42 is a lens that condenses the return light L4 reflected by the mirror 41 onto a predetermined focal plane. The light receiving element 43 is a photodetector that outputs a detection signal according to the intensity of light incident on a predetermined light receiving surface. In this embodiment, a silicon photomultiplier (SiPM) is used as the light receiving element. This will be described in detail later.

[0032] Aperture 44 is disposed on the focal plane of condenser lens 42 and blocks light other than that at the opening, thereby preventing ambient light from entering light receiving element 43. More specifically, aperture 44 allows a component of return light L4 that is incident on mirror 41 in the direction opposite to the optical path at the time of light projection and reflected by mirror 41 to pass through with a predetermined diameter, while blocking other light. Therefore, even if the laser beam reflected by reflecting portion 66 in a direction different from the incident optical path of output light L2 reaches mirror 41, it is blocked by aperture 44 and does not reach light receiving element 43. Similarly, the ambient light is blocked by the aperture 44 except for a small component that happens to be incident along approximately the same path as the return light L4, and does not reach the light receiving element 43. Therefore, the aperture 44 can cut out most of the ambient light. Of the above, the mirror 41, the condenser lens 42, and the aperture 44 constitute a light receiving optical system. The mirror 31 in addition to the light receiving optical system corresponds to a light guide section.

[0033] Next, the front-end circuit 51 is a circuit that shapes the detection signal output by the light receiving element 43 into a waveform suitable for timing detection by the TDC 52 . The TDC 52 is a circuit that generates a digital output indicating the time difference between the timing t0 of the lighting pulse of the laser beam L1, which is the emitted light, and the timing t1 of the pulse of the corresponding returned light L4, based on the drive signal supplied from the laser drive circuit 22 and the shaped detection signal supplied from the front-end circuit 51. The TDC 52 functions as a measurement unit that measures the time difference between the projection of the laser light and the reception of the light by the light-receiving element 43.

[0034] As will be described later, if a photon of disturbance light incident along substantially the same path as the return light L4 reaches the light-receiving element 43, this also causes the light-receiving element 43 to output a detection signal. For this reason, the time difference measured by the TDC 52 may be the time difference between the projection of the laser light and the detection of the disturbance light. Based on this premise, one of the features of this embodiment is a configuration for distinguishing between the time difference due to the return light L4 and the time difference due to the disturbance light and specifying the time difference due to the return light L4.

[0035] Since there is a time difference between the emitted light pulse and the returned light pulse, which is the time it takes for the light to reach an object on the optical path and return, if the time difference due to the returned light L4 can be identified, the distance s from the object detection device 10 to the object can be calculated based on the time difference Δt (hereinafter, this Δt will also be referred to as "TOF (Time of Flight)") as s = c(Δt) / 2, as shown in Fig. 2, where c is the speed of light. To be precise, the above s is the optical path length from the object to the light receiving element 43. When the laser beam is reflected by the reflecting unit 66 and returns, s is basically the optical path length from the reflecting unit 66 to the light receiving element 43. However, when the distance from the LD module 21 to the mirror 41 and the distance from the mirror 41 to the light receiving element 43 are significantly different, it is preferable to appropriately correct the error due to this difference in distance.

[0036] The processor 53 is a control unit that controls the operation of each unit shown in FIG. 1. It may be configured as a general-purpose computer equipped with a CPU, ROM, RAM, etc., that executes software, or it may be configured as dedicated hardware, or a combination thereof. For example, the processor 53 calculates the distance to the object based on the output signal from the TDC 52, and calculates the direction of the object based on the timing of scanning by the scanning unit 30 (the projection direction of the emitted light L2) at the time of detecting the returned light. As will be described in detail later, the processor 53 also performs an adjustment process to align the drive frequency of the actuator 300 with its resonance frequency, and a process to distinguish between a time difference due to the returned light L4 and a time difference due to ambient light and identify the time difference due to the returned light L4.

[0037] The input / output unit 54 is a module that inputs and outputs information to and from the outside. The input / output of information here includes wired or wireless communication with an external device, receiving user operations using buttons, a touch panel, etc., and presenting information to the user using a display, lamp, speaker, vibrator, etc. Examples of information that the input / output unit 54 should output to the outside include, for example, information about a detected object (which may be raw data on distance and direction, or information indicating that an object has been detected based on the raw data, such as a predetermined size, position, and moving speed), and information about the operating state and setting state of the object detection device 10. Examples of information that the input / output unit 54 should receive as input from the outside include, for example, information about the operating settings of the object detection device 10.

[0038] Possible communication partners via the input / output unit 54 include, for example, mobile objects such as automobiles and drones equipped with autonomous driving systems, and wearable devices used in the field of augmented reality (AR). If information about objects detected by the object detection device 10 is supplied to an autonomous driving system, the autonomous driving system can refer to the information and plan a driving route that avoids the detected object. If information about objects detected by the object detection device 10 is supplied to a wearable device, the positions of surrounding objects can be detected with higher accuracy than when surrounding objects are estimated from image information captured by a camera, and artificially processed information can be combined with the object image.

[0039] It is also possible to implement the present invention as a system including the object detection device 10 and its communication partner, such as an automobile, drone, aircraft, wearable device, etc. The embodiment described here is particularly useful when the object detection device 10 is mounted on a wearable device, which is in high demand for miniaturization and low power consumption.

[0040] Next, the general structure of the object detection device 10 will be described with reference to Figures 3 and 4. Figure 3 is an exploded perspective view showing the structure of the main components of the object detection device, and Figure 4 is a perspective view showing the appearance of the object detection device. 3 and 4, the object detection device 10 has an exterior formed by joining a top cover 61 and a rear cover 62 with two cover clips 63, 63. The top cover 61 also has a window for passing the emitted light L2, and a protective material 64 that is transparent to the wavelength of the emitted light L2 is fitted into the window to prevent dust from entering. A reflecting portion 66 is provided on the inner surface of this protective material 64.

[0041] The components shown in Fig. 1 are stored inside these housings. Note that the actuator 32 shown in Fig. 1 is shown as two actuators: actuator 300 responsible for scanning in the main scanning direction, and actuator 380 responsible for scanning in the sub-scanning direction. Mirror unit 301 is a mirror included in actuator 300. Although not shown in FIG. 1, the mirror 48 is an optical element located between the mirror 41 and the condenser lens 42 for changing the direction of the return light L4. Chain line with symbol 65 indicates the field of view of the object detection device 10 (the scanning range of the emitted light L2), and corresponds to the field of view 70 in Fig. 1. Circuits such as the laser drive circuit 22 and the processor 53 and wiring between modules are omitted in Fig. 3 to make the drawing easier to see. The description of the overall configuration has now been completed, and below, some of the components of the object detection device 10 will be described individually.

[0042] 2. Configuration of the Actuator 300 (FIG. 5) As already mentioned, the scanning unit 30 includes the actuators 300 and 380, but the actuator 300 will be explained first. As shown in FIG. 3, the actuator 300 and the actuator 380 are significantly different in configuration. Since the actuator 380 is used to deflect the emitted light L2 in the sub-scanning direction, it does not require very high speed movement, and therefore an actuator called a galvanometer mirror, which rotates the mirror 381 around a physical axis, is used.

[0043] On the other hand, since the actuator 300 is used to deflect the emitted light L2 in the main scanning direction, it is required to have high speed movement and durability to be able to continue this high speed movement for a long period of time. Therefore, an actuator suited to these purposes is used as the actuator 300.

[0044] FIG. 5 shows the mirror of the actuator 300 shown in FIG. unit 3 shows a cross section perpendicular to the rotation axis of 301. In outline, actuator 300 is configured by fixing mirror unit 301 to one surface of torsion spring 302 having a linear protrusion so as to straddle the protrusion, and fixing one end of torsion spring 302 to top yoke 314 serving as a support member. Then, due to the action of permanent magnet 321 and drive coil 316 arranged on the other surface of torsion spring 302, torsion spring 302 and mirror unit 301 rotate around rotation axis 304 located approximately in the center of the protrusion of torsion spring 302 in accordance with the voltage applied to drive coil 316, and perform reciprocating motion within a predetermined angular range.

[0045] That is, permanent magnet 321 is fixed to the surface of torsion spring 302 opposite protrusion 302c so that north pole 321n is positioned on one side across the protrusion and south pole 321s is positioned on the other side. One end of the shaft of the drive coil 316 faces the midpoint between the north pole 321n and south pole 321s of the permanent magnet 321 through the opening in the top yoke 314.

[0046] In this state, when current is applied to drive coil 316 and, for example, the end facing permanent magnet 321 becomes an N pole, S pole 321s of permanent magnet 321 is attracted to drive coil 316 and N pole 321n repels drive coil 316, and a force acts on permanent magnet 321 to rotate it clockwise as viewed in Figure 5. This force causes torsion spring 302 to rotate and twist clockwise around imaginary rotation axis 304 located near the center of the cross section of protrusion 302c. Accordingly, mirror unit 301 fixed to torsion spring 302 also rotates clockwise around rotation axis 304. The rotation stops at a position where the magnetic force generated between the drive coil 316 and the permanent magnet 321 is balanced with the restoring force of the torsion spring 302. The speed of this rotation and the stop position can be adjusted by changing the strength of the current flowing through the drive coil 316.

[0047] When the direction of current flow to the drive coil 316 is reversed, the torsion spring 302 and the mirror unit 301 similarly rotate counterclockwise. By periodically reversing the direction of the voltage or current of the drive signal applied to the drive coil 316, the mirror unit 301 can be caused to alternately rotate clockwise and counterclockwise as shown by arrow V in Fig. 5, thereby performing reciprocating rotational motion within a predetermined angular range around the rotation axis 304. This makes it possible to realize the periodic deflection of the laser beam L1 required for scanning in the main scanning direction, as described with reference to Fig. 1.

[0048] The sensing coil 317 detects the current flowing due to the induced electromotive force caused by the fluctuation of the magnetic field strength generated by the oscillation of the permanent magnet 321, and detects the current flowing due to the induced electromotive force generated by the fluctuation of the magnetic field strength generated by the oscillation of the permanent magnet 321. unit It is provided to detect the rotational angular velocity of 301. If this detection is not performed, the sensing coil 317 is not necessary. As the actuator 300 described above, for example, the one proposed by the present applicant and described in Japanese Patent No. 6519033 (Patent Document 7) can be used.

[0049] [3. Adjusting the actuator drive frequency (Figs. 6 to 14)] Next, we will explain the operation related to adjustment to match the drive frequency of the actuator to the resonant frequency, which is performed by the above-mentioned object detection device 10. This operation will be explained using the above-mentioned actuator 300 as an example, but similar adjustment can be applied to any type of actuator that has a resonant frequency, including actuator 400 described below.

[0050] FIG. 6 shows an example of the waveform of the drive signal drv_p applied to the drive coil 316 to drive the actuator 300. The drive signal drv_p used here is a square wave in which voltages of +v and -v repeat at a fixed cycle, as shown in Fig. 6. When the reciprocal of this cycle (referred to herein as the "drive frequency") matches the resonance frequency of the mover 320, which includes the mirror unit 301 (hereinafter referred to as the "mirror 301"), the mirror 301 of the actuator 300 can be driven efficiently, that is, with low power consumption. Furthermore, the main scanning direction positions of each spot on the main scanning line can be easily matched between the forward and backward passes. The resonance frequency of the mover including the reflecting material in the actuator as described above will be referred to as the "resonance frequency of the actuator."

[0051] 7 to 9 show the relationship between the scan angle of mirror 301 and the absolute value of the angular velocity for several cases. Fig. 7 shows an example where the drive frequency matches the resonant frequency of actuator 300, while Figs. 8 and 9 show examples where the drive frequency deviates from the resonant frequency of actuator 300. In Figs. 7 to 9, the horizontal axis represents the position on the oscillation path of mirror 301 (expressed as a rotation angle based on an appropriate position, and this is called the "scan angle"), and the vertical axis represents the absolute value of the angular velocity at that position, showing changes in velocity. The relationship during forward scanning is shown by a solid line 501, and the relationship during backward scanning is shown by a dashed line 502. In the following description, unless otherwise specified, the term "velocity" or "angular velocity" refers to the absolute value of the velocity or angular velocity.

[0052] It is known that the moving speed of mirror 301 oscillated by actuator 300 is not constant. Because mirror 301 stops at the ends of the oscillation path and moves in other parts, it is clear that there are fluctuations in the moving speed, but according to experiments conducted by the inventors, the speed is generally slower toward the ends of the oscillation path and faster toward the center, as shown in Figures 7 to 9.

[0053] Furthermore, experiments by the inventors have shown that in the case of Figure 7, where the drive frequency is (almost) the same as the resonant frequency of actuator 300, whether the rotation is clockwise or counterclockwise, i.e., whether it is forward scanning or backward scanning, the angular velocity is approximately the same at the same position, except that the direction of movement is different. Also, the angular velocity peaks at the center position of the main scanning. For this reason, in Figure 7, solid line 501 and dashed line 502 overlap, and only solid line 501 is shown in the figure.

[0054] On the other hand, experiments by the inventors have also shown that when the drive frequency is deviated from the resonant frequency of actuator 300, the relationship between the scan angle and the angular velocity differs between the forward scan and the backward scan, as shown in Figure 8 or Figure 9. In this case, the peak of the angular velocity in each scan also deviates from the center position of the main scan. In the example of Fig. 8, the peaks of the angular velocity are shifted rearward from the center position in both the forward scan and the backward scan, whereas in the example of Fig. 9, the peaks are shifted forward from the center position.

[0055] Experiments conducted by the inventors have revealed that when the drive frequency and the resonant frequency of the actuator 300 are relatively close to each other, by gradually bringing the drive frequency closer to the resonant frequency (or to what is assumed to be the resonant frequency) and changing it beyond the resonant frequency, the relationship between the scan angle and the angular velocity in reciprocating scanning changes as follows:

[0056] That is, initially, one of the relationships shown in Figures 8 and 9 is observed, and as the drive frequency approaches the resonance frequency, the difference between the forward scan and the backward scan becomes smaller, and when it reaches a certain value, the relationship shown in Figure 7 is observed. This value is considered to be the resonance frequency. After that, when the drive frequency passes the resonance frequency, the other relationship shown in Figures 8 and 9 is observed, and as the drive frequency moves away from the resonance frequency, the difference between the forward scan and the backward scan becomes larger.

[0057] In this embodiment, the drive frequency of the actuator 300 is controlled by utilizing the relationship between the scanning angle and angular velocity of the mirror 301, in order to match the drive frequency of the actuator 300 with the resonance frequency of the actuator 300. The reflecting section 66 shown in Figures 1 and 4 is provided for this drive frequency control.

[0058] Next, the principle of this drive frequency control will be explained with reference to FIGS. FIG. 10 shows the relationship between the scanning range of the emitted light L2, the position where the reflecting portion 66 is provided, and the position of the effective reflecting area 66a. As shown in FIG. 10, the scanning range of the emitted light L2 is indicated by the two-dot chain line. (Field of view range) A rectangular line 65 is formed in a protective material 64 through which the emitted light L2 can pass. In the figure, the horizontal direction is the main scanning direction and the vertical direction is the sub-scanning direction. Reference numerals 71 and 72 denote examples of the main scanning lines on the outgoing and returning passes, respectively.

[0059] The reflecting portion 66 is provided in a predetermined area that is a portion of the scanning range of the emitted light L2 in the main scanning direction and has an extent in the sub-scanning direction large enough for at least one round trip of the main scanning line to pass through. The reflecting portion 66 is formed to specularly reflect the incident emitted light L2. As a result, when viewed in the main scanning direction, the emitted light L2 that enters the effective reflection area 66a is reflected along the same optical path as the emitted light L2. Conversely, the position where the emitted light L2 is incident on the reflecting surface almost perpendicularly becomes the effective reflecting area 66a, and the reflecting portion 66 should be formed in a range in the main scanning direction that includes this effective reflecting area 66a.

[0060] FIG. 11 is an explanatory diagram of a method for detecting the timing at which the emitted light L2 is reflected by the effective reflection area 66a. 1, when the object detection device 10 performs object detection, the LD module 21 is intermittently turned on to form scanning lines 71 and 72 as a set of beam spots 73. When the beam spot 73 is incident on the effective reflection area 66a and reflected by the effective reflection area 66a, the TDC 52 outputs a signal of the time difference corresponding to the distance from the effective reflection area 66a to the light receiving element 43, as the time difference between the timing t0 of the lighting pulse and the timing t1 of the corresponding pulse of the return light L4. When the processor 53 detects a signal of this time difference for a certain beam spot, it can determine that the emitted light L2 of that beam spot has been reflected by the effective reflection area 66a.

[0061] Because the effective reflection area 66a has a fixed width in the main scanning direction, when a main scanning line passes through the effective reflection area 66a, a fixed number of the beam spots that make up the main scanning line are reflected by the effective reflection area 66a. These spots are hatched in Figure 11. From the lighting timing of each spot reflected by the effective reflection area 66a, the processor 53 can identify the time range during one main scanning scan during which the output light L2 is incident on the effective reflection area 66a. Although noise due to external light may be mixed in, reflection by the effective reflection area 66a occurs continuously over a certain range of the main scanning direction, and therefore noise due to external light can be easily eliminated by monitoring the time difference signals for multiple beam spots that are continuous in the main scanning direction.

[0062] 11 to 14, this time range is hatched, and the timing corresponding to the left end of the effective reflection area 66a in Fig. 10 is indicated by Ra, and the timing corresponding to the right end is indicated by Rb. Ra and Rb can be said to be the timings of the optical ends at which the detection of reflected light by the light receiving element 43 switches between being detected and not being detected.

[0063] The processor 53 can also refer to the timing of voltage inversion of the drive signal drv_p of the actuator 300 as the timing of the start and end of each main scan. In Figures 11 to 14, the start and end of the forward main scan are indicated by Ts and Te, respectively, and the start and end of the backward main scan are indicated by Ts' and Te'. As described above, the processor 53 can obtain information on the time range during which the laser beam was reflected by the effective reflection area 66a during each main scan by using almost the same hardware and algorithms used for object detection.

[0064] In reality, the periods of forward scanning and backward scanning may not be continuous when viewed from the main scanning line as a reference, for example, because the ends of the main scanning line are cut off. However, when adjusting the drive frequency, one main scan is counted from the time when the reciprocatingly rotating mirror 301 starts rotating at one end of its oscillation path until it rotates to the other end, stops, and changes direction of rotation, and the forward scanning and backward scanning are considered to be continuous. In other words, the following explanation will be based on the assumption that Te of the forward scan and Ts' of the next backward scan are the same, and that Te' of the backward scan and Ts of the next forward scan are the same.

[0065] 12 to 14 respectively show the time range during which reflected light from the effective reflection area 66a is detected during one main scan when the scan angle and angular velocity of the mirror 301 are as shown in Figures 7 to 9. It is assumed that the drive frequency is not changed between the forward scan and the backward scan, and the time required for one main scan (Te-Ts or Te'-Ts') is the same for both the forward scan and the backward scan.

[0066] 12, in a state in which the drive frequency (almost) matches the resonance frequency of mirror 301, in forward scanning, as shown in graph 511, emitted light L2 is reflected by effective reflection area 66a slightly earlier than the center of the scanning period, and the reflected light is detected by light receiving element 43. This corresponds to the fact that reflecting portion 66 is disposed in the first half of the path of forward scanning. Conversely, in backward scanning, as shown in graph 512, the reflected light is detected by light receiving element 43 slightly later than the center of the scanning period.

[0067] In addition, in this state, the relationship between the scanning angle and angular velocity of the mirror 301 is the same in the forward and backward scans as shown in FIG. 7, so if the output of the TDC 52 for each beam spot in the backward scan is arranged in reverse order, it is considered to (almost) match the output in the forward scan, as shown in graph 513.

[0068] That is, the time difference between the timing at which the emitted light L2 is reflected by the edge of the effective reflection area 66a (first reference timing) and the timing at which the scan reaches the edge of the scan line (second reference timing: the timing at which the mirror 301 changes its rotation direction at the end of the oscillation path) is the same in the forward scan and the backward scan. However, the "edge" here refers to the edge (specific edge) located on the same side of the field of view. That is, for example, Ra - Ts in the forward scan is equal to Te' - Ra in the backward scan. Also, Te - Rb in the forward scan is equal to Ts' - Rb in the backward scan.

[0069] In contrast to the example in Figure 12, under conditions where the angular velocity increases in the latter half of the scan as in Figure 8, as shown in Figure 13, the timing at which reflected light from the effective reflection area 66a is detected shifts to the latter half of the scan for both the forward scan and the backward scan compared to the case in Figure 12. Conversely, under conditions where the angular velocity is large in the first half of the scan as in Fig. 9, the timing at which reflected light from the effective reflection area 66a is detected shifts toward the first half of the scan for both the forward scan and the backward scan, as shown in Fig. 14, compared to the case of Fig. 12. In Figs. 13 and 14, the positions indicated by the virtual lines are the positions of the detection timing in Fig. 12.

[0070] Therefore, when the drive frequency does not match the resonance frequency of the mirror 301, the time difference between the first reference timing and the second reference timing will be different. Furthermore, if the difference between the drive frequency and the resonance frequency becomes smaller, the difference in the time lag also becomes smaller. From the above, if the drive frequency of the actuator 300 is adjusted so that the time difference between the first reference timing and the second reference timing matches in the forward scan and the backward scan, the drive frequency can be matched with the resonant frequency of the mirror 301.

[0071] In actual adjustment, for example, if the time difference between the first reference timing and the second reference timing does not match between the forward scan and the return scan, the drive frequency can be slightly adjusted in an appropriate direction to increase or decrease the difference between the forward and return scans, and the drive frequency can be adjusted in the direction that reduces the difference until the difference becomes zero. A specific method for adjusting the drive frequency as described above can be, for example, that disclosed in Japanese Patent No. 7097647 (Patent Document 6) proposed by the present applicant.

[0072] 4. Reduction of noise caused by ambient light (Figs. 15 to 22) Next, an operation performed by the object detection device 10 described above for reducing the influence of noise due to ambient light during object detection will be described.

[0073] First, FIG. 15 shows the configuration of scanning lines formed within the field of view by the scanning unit 30. 15, the scanning unit 30 forms a number of parallel main scanning lines 71, 72 within the field of view 65, including the main scanning lines that pass through the reflecting unit 66 shown in FIG. 10. The main scanning lines 71 resulting from the forward scanning and the main scanning lines 72 resulting from the backward scanning are arranged alternately in the sub-scanning direction. This is achieved by driving the actuator 380 when the main scanning reaches the end of the main scanning range to rotate the mirror 381 by an angle corresponding to the interval between the main scanning lines, and then repeating the main scanning in the opposite direction.

[0074] Here, scanning in the sub-scanning direction is performed from top to bottom in Fig. 15. After the scanning in the sub-scanning direction reaches the bottom end, the actuator 380 is rotated in the opposite direction to that during the sub-scanning, so that the mirror 381 faces the sub-scanning start position, and the next frame is scanned. As described above, while the emitted light L2 is scanning the main scanning lines 71 and 72, a pulsed drive signal is applied to the LD module 21 to cause the LD to emit pulsed light, and the emitted light L2 forms multiple spots on each of the scanning lines 71 and 72.

[0075] Here, if the drive frequency of actuator 300 matches the resonance frequency, the position in the main scanning direction of each spot on the forward main scanning line 71 can be aligned with that of each spot on the backward main scanning line 72 by controlling the light emission timing of the LD so that the light emission intervals of the LD during one main scanning period match on each main scanning line. That is, for any natural number x from 1 to the number of spots on one main scanning line X, the position in the main scanning direction of the x-th spot from the beginning on the forward main scanning line 71 and the x-th spot from the end on the backward main scanning line 72 can be aligned approximately.

[0076] That is, in this case, as shown in FIG. 7, the relationship between the scanning angle and the angular velocity is the same for the forward and backward passes and is symmetrical with respect to the central position of the main scanning, so when the LD is turned on at the same light emission interval, the distribution of the spots becomes symmetrical with respect to the central position of the main scanning, which is common to the forward and backward passes.

[0077] Therefore, in this case, the spots are substantially distributed in a state aligned not only in the main scanning direction but also in the sub-scanning direction within the field of view 65. Even if the light emission interval of the LD varies depending on the position on the main scanning line, the same can be said as long as the distribution of the light emission interval on the main scanning line is symmetrical with respect to the center position of the main scanning.

[0078] This state is shown schematically in Figure 16. The dashed lines in Figure 16 indicate the position in the main scanning direction of the xth spot from the beginning on main scanning line 71 on the outgoing path, which is approximately at the position where it is incident on object 80, and the position in the main scanning direction of the xth spot from the end on main scanning line 72 on the return path, which coincide with each other. Therefore, by simply regarding both of these as the "pixel at the xth position in the main scanning direction" and combining the position and distance of object 80 obtained from the forward and backward scanning, an object image 81 that reflects the position and shape of object 80 can be obtained with a resolution that combines the scanning lines in both directions.

[0079] On the other hand, if the drive frequency of the actuator 300 does not match the resonance frequency, the relationship between the scanning angle and the angular velocity will be different on the forward and backward passes, as shown in Figures 8 and 9. Therefore, even if the light emission timing of the LD is controlled so that the light emission intervals of the LD during one main scanning period match on each main scanning line, the positions in the main scanning direction will not match between the spots on the main scanning line 71 on the forward pass and the spots on the main scanning line 72 on the backward pass. For example, in the case of the relationship shown in Figure 8, the spots are dense on the left side of Figure 15 on the forward pass and sparse on the right side, and conversely, on the backward pass they are sparse on the left side and dense on the right side. However, as long as stable reciprocating scanning is possible, the positions of the spots on each main scanning line in the main scanning direction will generally match between the forward passes and between the backward passes.

[0080] This state is shown schematically in Figure 17. As in Figure 16, the dashed lines in Figure 17 indicate the position in the main scanning direction of the xth spot from the beginning on main scanning line 71 on the outgoing pass, and the position in the main scanning direction of the xth spot from the end on main scanning line 72 on the return pass. However, these do not generally coincide. Which is on the right side depends on the situation and the position in the main scanning direction. Therefore, if we simply consider both of these as "the pixel at the xth position in the main scanning direction" and combine the position and distance of object 80 obtained from the forward and backward scanning, we will end up with an object image that is a mixture of object image 82 obtained from the forward scanning and object image 83 obtained from the backward scanning, which is different from object image 82. However, each of the object images 82 and 83 has half the resolution in the sub-scanning direction as compared with the object image 81 in FIG. 16, but each reflects the position and shape of the object 80.

[0081] In order to reduce the influence of noise due to ambient light during object detection, object detection device 10 aggregates the TOF detection results of reflected light corresponding to multiple spots, and calculates the distance to the object in the direction corresponding to the multiple spots based on the aggregated results. This collection of multiple spots will be called a "group" of spots.

[0082] FIG. 18 shows an example of group settings. In Figure 18, the symbols for the outgoing main scanning line 71 and the returning main scanning line 72 are each assigned a branch number indicating the number of the main scanning line from the top in Figure 15. For example, main scanning line 71-n indicates the nth main scanning line. This number is counted without distinguishing between the outgoing and returning passes. For this reason, the main scanning line immediately below main scanning line 71-n is the returning main scanning line 72-(n+1).

[0083] Also, the xth spot from the left on the nth main scanning line in Fig. 15 is labeled S(n, x). The xth spot from the left corresponds to the xth spot from the beginning on the forward pass and the xth spot from the end on the backward pass. Furthermore, a group G of spots S is indicated by the position of the spot located at the top left corner of the group. For example, if the top left corner spot is spot S(n,x), it is indicated by the symbol G(n,x).

[0084] 18 shows an example in which two spots in each of the main scanning direction and the sub-scanning direction, for a total of 2 × 2 = 4 spots, are defined as group G(n, x). Group G consists of four spots: S(n, x), S(n, x+1), S(n+1, x), and S(n+1, x+1). If the spots are located close to each other like this (i.e., have close projection directions), then if there is an object in the projection direction, the light will be incident on the object at close positions, and the TOF values ​​will likely be close.

[0085] 19A to 19D are diagrams showing an example of the relationship between the light projection timing of each spot in group G(n, x) shown in Fig. 18 and the corresponding light detection timing by light receiving element 43. In this example, it is assumed that the distances from object detection device 10 to the object are approximately equal at the positions where four spots S are incident.

[0086] First, the light reflected from the object should be detected at a time T, which corresponds to the TOF, after the timing of the LD drive signal's lighting pulse, for each spot. In each figure, this detection signal is shown by a PD output pulse. However, if the amount of reflected light is small and no photons are returned, it is possible that the reflected light pulse will not be detected, as shown in Figure 19D.

[0087] On the other hand, photons originating from ambient light are also incident on the light-receiving element 43, unrelated to the lighting pulse, and when such photons are incident, the light-receiving element 43 outputs a detection signal. The pulse itself cannot be distinguished from a detection signal generated when reflected light is received. Furthermore, it is not possible to predict the timing at which the detection signal will be generated. In the examples of Figures 19A to 19D, a disturbance light detection signal is output at a timing T1 after the lighting pulse in Figure 19A, and at a timing T2 after the lighting pulse in Figure 19B. In the examples of Figures 19C and 19D, a disturbance light detection signal is not output.

[0088] 19A and 19B, the light receiving element 43 can detect multiple light receptions corresponding to one lighting pulse and output a corresponding detection signal for each. For example, the light receiving element 43 can be configured to output a pulse as a detection signal when light (photons) is incident within each time range corresponding to a predetermined resolution, and to output a flat signal indicating that no light is incident when the light is not incident.

[0089] 1 calculates the TOF of the reflected light corresponding to each spot based on the output signal output from the light receiving element 43 within a predetermined time period shorter than the interval between the lighting pulses corresponding to each spot and shaped by the front-end circuit 51, and passes the calculated TOF to the processor 53. There may be multiple TOF values ​​corresponding to one spot. For each group, the processor 53 counts the TOF values ​​corresponding to each spot in the group for each predetermined class.

[0090] Next, FIG. 20 shows an example of the totalization of the TOF detection results shown in FIG. 20, the counting results are shown as a histogram, with the horizontal axis representing the TOF class and the vertical axis representing the frequency. Of course, the processing by the processor 53 only needs to determine the frequency for each TOF class. When the TOF values ​​corresponding to the four spots shown in Fig. 19 are tallied, the frequency of the class containing T is 3, and the frequencies of the classes containing T1 and T2 are each 1, as shown in Fig. 20. In this way, for the light reflected from the object, a common TOF is detected in multiple spots, so the frequency of that part is thought to be large.

[0091] Therefore, processor 53 determines the distance to the object by taking the representative value of the class with a frequency equal to or greater than a predetermined threshold (2 in the example of FIG. 20) as the TOF of reflected light from an object present in the light projection direction of the group. The representative value may be the center value of the class or any other value within the class. If there is no class with a frequency equal to or greater than the predetermined threshold, it is determined that no reflected light is returned from the light projection direction of the group and that there is no object that can be detected in that direction.

[0092] Note that, since there are cases where reflected light cannot be detected, as shown in Figure 19D, it is advisable to set the threshold to a value smaller than the number of spots in the group. Since low-frequency class values ​​can be considered to be detections of randomly incident ambient light, it is preferable to set the threshold to a value that is almost never reached by ambient light. However, even if ambient light is mistaken for reflected light from an object in a small number of groups as a result of using a small threshold, this usually does not have a significant impact on the overall composition of the object image.

[0093] The light projection direction of a group may be set to the average value of the light projection directions of the spots in the group, or may be set to the light projection direction of any one of the spots in the group. By detecting the direction in which an object is present and the distance to the object based on the light projection direction for each group and the frequency for each class obtained by tallying the light, the detection signal derived from ambient light output by the light receiving element 43 can be efficiently removed, enabling object detection that is less susceptible to the influence of ambient light.

[0094] The TOF scales used for aggregation may be the same as the resolution used for TOF measurement, or may be coarser than the resolution. If the scales are too fine, the TOFs of the reflected light from the object will be classified into different scales due to slight differences in the distance to the object for each spot, so it is preferable that the TOF scales be coarser than the resolution used for TOF measurement. Furthermore, when determining the TOF corresponding to a group, the average value of all TOFs classified into classes with frequencies above a threshold can be used, so that the TOF resolution can be maintained at the value at the time of measurement even if the classes are coarse.

[0095] Furthermore, instead of obtaining one TOF corresponding to a group, it is possible to use, among the TOFs corresponding to each spot constituting the group, a TOF classified into a class with a frequency equal to or greater than a threshold in the aggregation of Fig. 20 as the TOF of reflected light from an object present in the projection direction of the spot. In this way, even when performing the aggregation of Fig. 20, it is possible to obtain the distance to the object for each spot rather than for each group. In this case, there will be multiple projection directions corresponding to one group, but object detection will still be performed based on the projection direction for each group and the frequency for each class obtained by aggregation.

[0096] 21 shows the configuration of the condenser lens 42, light receiving element 43, and aperture 44 of the light receiving unit 40, and the optical path of the return light L4 in more detail than in FIG. 1. Also, FIG. 22 is a diagram for explaining the relationship between the configuration of the light receiving element 43 and the incident position of the return light L4, and the detection signal output by the light receiving element 43. 1, in the light receiving unit 40, the returning light L4 reflected by the mirror 41 is collected by the collecting lens 42 onto a focal plane located at the position of the aperture 44, as shown in FIG. 21. The aperture 44 has an opening with an extremely small diameter corresponding to the focal diameter that can be formed by the collecting lens 42, and the returning light L4 passes through this opening. The returning light L4 that has passed through the aperture 44 is incident on the light receiving surface of the light receiving element 43 as a slightly widened spot.

[0097] The SiPM used as the light receiving element 43 in this embodiment has a configuration in which an array of avalanche photodiodes (APDs) 43a operating in Geiger mode is provided on the light receiving surface as shown in Fig. 22. The light receiving element 43 is positioned so that the return light L4 is incident on substantially the entire area where the APD 43a is formed.

[0098] The scanning unit 30 and the light receiving unit 40 are configured to guide the light that enters the mirror 31 along an optical path opposite to the projected outgoing light L2 to the light receiving element 43, so that after the mirror 41, the returning light L4 can be made to enter the same position on the light receiving element 43 along the same optical path regardless of the projection direction of the outgoing light L2. Therefore, the returning light L4 can always be detected by the entire array of APDs 43a, and therefore the returning light L4 can be detected with sufficient sensitivity without using a particularly large array, making it possible to reduce the size and cost of the light receiving element 43, and ultimately the entire object detection device 10.

[0099] Each APD 43a can output a pulse signal in response to the incidence of one photon. The light receiving element 43 has output signal lines 43b corresponding to each APD 43a, and outputs a signal obtained by adding up the output signals from all the output signal lines 43b as a detection signal 46 from the output signal line 43c. In the object detection device 10, there is no need to change the range of the APD 43a to which the output signals are added depending on scanning conditions such as the interval between scanning lines or spots, the scanning period, etc., so that the detection signal can be output from such a single output signal line 43c, thereby simplifying the hardware configuration and reducing costs.

[0100] Next, FIG. 23 shows an example of the arrangement of multiple groups. In the object detection device 10, the processor 53 tally up the TOFs for each spot in the group for each group as described above, and based on the tallying results, determines the distance to an object in the light projection direction of each group (or each spot in the group). For this reason, the groups are densely arranged without any gaps within the field of view 65, as shown in Fig. 23. In the example of Fig. 23, only four groups, G(n, x), G(n, x+2), G(n+2, x), and G(n+2, x+2), are shown, but similar 2 x 2 spot groups are set above, below, left, and right of these. Note that even if a spot that does not belong to any group is placed between a certain group and an adjacent group, there is no problem other than a decrease in object detection resolution, and object detection itself is possible.

[0101] Note that the object to be detected usually has unevenness and is not directly facing the object detection device 10. Therefore, if the spots are far apart, the distance to the object is more likely to change. Therefore, it is preferable that each group be made up of spots whose light projection directions are as close as possible. On the other hand, especially when the amount of ambient light is large, it is difficult to distinguish between the ambient light and the light reflected by the object unless at least about four spots are grouped together.

[0102] In this case, if a group were composed of only spots on the same main scanning line, for example, the spots at both ends would be spaced farther apart, which would be inconvenient. Therefore, in this embodiment, as shown in Figures 18 and 23, a group is set to span multiple adjacent main scanning lines, so that it is composed of spots whose projection directions are as close as possible. In this case, each group includes spots illuminated during the forward main scanning pass and during the return main scanning pass that follows the forward main scanning pass.

[0103] 16 and 17, however, unless the drive frequency of the actuator 300 matches the resonant frequency, it is difficult to determine which spot on the forward main scanning line 71 is closest to which spot on the backward main scanning line 72. Therefore, in the object detection device of this embodiment, the drive frequency adjustment is performed as described above to match the drive frequency of the actuator 300 with the resonant frequency before starting object detection, and object detection is performed after the match is confirmed. In other words, when the match is confirmed, the TOF count results are used for object detection. If this coincidence is confirmed, it is possible to create groups of spots whose projection directions are close to each other based on the number of times each spot has been turned on during the forward scan or the backward scan, as shown in Figures 18 and 23. Alternatively, the projection directions of the spots in each group created in advance in this way will actually be close to each other.

[0104] 24 shows a flowchart of the above-described process for object detection with reduced influence of ambient light, which is executed by the processor 53 of the object detection device 10. This process can be realized by software or dedicated hardware. This process is related to the object detection method of the present invention. When processor 53 detects an object detection start instruction due to some trigger such as a user operation or a request from another process or another device, it starts the processing shown in FIG.

[0105] In this process, the processor 53 first activates the actuators 300 and 380, the LD module 21, and the light receiving element 43, and thereafter places them in a state where their operations can be controlled by control signals from the processor 53 (S11). If this state has already been reached at the start of the process, step S11 can be omitted.

[0106] Next, the processor 53 adjusts the drive frequency of the actuator 300 to match the resonant frequency of the actuator 300 using the method described with reference to Figures 6 to 14 (S12). The processor 53 determines whether the drive frequency matches the resonant frequency, and if they match (Yes in S13), proceeds to step S14 and subsequent steps. If the result of step S13 is Yes, the processor 53 creates a group of spots as described with reference to FIGS. 18 and 23 for each spot within the field of view 65 used for object detection (S14).

[0107] Then, for each light emission of the LD, the time difference (TOF) between the light emission timing and the subsequent light detection timing of the light receiving element 43 is obtained (S15), and the obtained time differences are tallied for each group created in step S14 and for each class of time difference value as described using Figure 20 (S16).

[0108] Thereafter, for each group, if there is a class whose frequency is equal to or greater than the threshold, the representative value of that class is recorded as the TOF value of the light reflected from the object in that group (S17), and the direction of the detected object and the distance to the object are calculated and output based on the TOF value of each group (S18). This output may, for example, be a combination of the direction and distance to the object corresponding to each group. Alternatively, as described above, a combination of the direction and distance to the object corresponding to each spot constituting the group may be output. If object detection is to be continued, the process returns to step S15 and is repeated, and if object detection is to be ended, the process of FIG. 24 is ended (S19).

[0109] The above process is for performing object detection based on the light projection direction and frequency for each class for each group when the determination is Yes (match) in step S13. Conversely, while the determination is No in step S13, not only are the light projection direction and frequency for each class for each group not used for object detection, but object detection itself is not performed and the results are not output.

[0110] In the above process, step S12 is an adjustment procedure, step S13 is a determination procedure, step S14 is a group creation procedure, step S16 is a counting procedure, and steps S17 and S18 are object detection procedures. In these procedures, processor 53 functions as an adjustment unit, a determination unit, a group creation unit, a counting unit, and an object detection unit, respectively. It should be noted that instead of creating and storing groups in advance before step S15, it is also possible to prepare rules for creating groups in advance, and then after step S15, divide each light into groups according to those rules and perform the counting in step S16.

[0111] According to the embodiment described above, when a predetermined field of view is scanned with pulsed laser light and an object is detected based on the timing of receiving reflected light, the effects of ambient light can be efficiently eliminated and accurate object detection can be performed using the compact object detection device 10. Furthermore, the processing required for this is not particularly complicated, which also reduces the cost of the object detection device 10, including the software and hardware. In experiments conducted by the inventors, the object detection device 10 of the embodiment described above caused a slight amount of false detection when attempting to detect an object outdoors in the direction of the sun, but in other cases it was able to properly eliminate the effects of ambient light and detect objects.

[0112] 5. First to Fourth Modifications (FIGS. 25 to 28) Next, first to fourth modified examples of the above-described embodiment will be described. These modified examples differ from the above-described embodiment only in the method of setting groups, and only this point will be described. Unless otherwise specified, common reference numerals will be used for parts that are common to or correspond to the above-described embodiment. This also applies to the other modified examples.

[0113] 25 to 28 show examples of spot group settings according to the first to fourth modified examples, respectively. In these figures, the code for each main scanning line is written to the left of the corresponding main scanning line. In the first modified example, as shown in Fig. 25, groups are set so that the ranges of multiple groups overlap in the main scanning direction. The size of each group is 2 x 2 = 4 spots, as in the case of Fig. 23. In this example, group G(n, x+1) is set to the right of group G(n, x), shifted by one spot. Therefore, spots S(n, x+1) and S(n+1, x+1) are included in both groups. Similarly, group G(n+2, x+1) is set to the right of group G(n+2, x), shifted by one spot.

[0114] In the second modified example, as shown in Fig. 26, groups are set so that the ranges of multiple groups overlap in the sub-scanning direction. The size of each group is 2 x 2 = 4 spots, as in Figs. 23 and 25. In this example, group G(n+1, x) is set below group G(n, x), shifted by one spot (one main scanning line). Therefore, spots S(n+1, x) and S(n+1, x+1) are included in both groups. Similarly, group G(n+1, x+2) is set below group G(n, x+2), shifted by one spot.

[0115] When outputting object direction and distance information for each group, if the groups are arranged so that they do not overlap, as in Figure 23, the object detection resolution will be reduced by the number of spots in each group. However, if the groups are arranged so that they overlap, as in Figures 25 and 26, the reduction in resolution can be prevented. Of course, the groups may be arranged so that their ranges overlap in both the main scanning direction and the sub-scanning direction. For example, for all spots except the rightmost and bottommost, 2 x 2 spot groups are set so that the corresponding spots are located in the upper left corner. In this way, object detection can be performed without reducing resolution and while eliminating the effects of ambient light.

[0116] In the third modified example, 3 × 3 = 9 spots are grouped into one group, as shown in Fig. 27. The ranges of each group are designed not to overlap, so that the group G(n, x) is immediately to the right of group G(n, x+3), and the groups G(n+3, x) and G(n+3, x+3) are immediately below this. Increasing the number of spots in one group in this way makes it possible to obtain a higher frequency in the aggregation of Fig. 20 for return light L4 having approximately the same TOF compared to randomly incident disturbance light, even if the light intensity of the return light L4 is smaller than that of the disturbance light. Therefore, the TOF of the return light L4 can be identified with high accuracy.

[0117] In the fourth modified example, spots located two main scanning lines apart are grouped together, as shown in Fig. 28. This is because a group is made up of only spots on the main scanning line on the outgoing path and only spots on the main scanning line on the returning path. That is, in the example of FIG. 28, two spots on the outgoing main scanning line 71-n and the nearest other outgoing main scanning line 71-(n+2) are grouped as group G(n,x). Similarly, two spots on the return main scanning line 72-(n+1) and the nearest other return main scanning line 72-(n+3) are grouped as group G(n+1,x+2). Although not shown for convenience of illustration, a group G(n+1,x) is set adjacent to the left side of group G(n+1,x+2) and one spot downward from group G(n,x). Similarly, a group G(n,x+2) is set adjacent to the right side of group G(n,x) and one spot upward from group G(n+1,x+2).

[0118] Therefore, in the example of Fig. 28, the groups are arranged without gaps so as not to overlap each other, as in the case of Fig. 23. Also, as in the case of Fig. 23, each group contains spots that are included in different main scanning passes. Although this is inferior to the example in Figure 23 in terms of making the light projection directions of each spot within the group as close as possible to each other, even if a group is formed from spots in such discontinuous positions, it is possible to eliminate the effects of ambient light in the same way as in the above-mentioned embodiment.

[0119] Furthermore, by forming a group from only the spots on the outgoing main scanning line and only the spots on the returning main scanning line in this way, it is possible to perform the tallying shown in Fig. 20 without any problems even if the drive frequency of actuator 300 does not match the resonance frequency. This is because even in this state, the positions of the spots on each main scanning line in the main scanning direction are aligned as long as they are aligned with each other on the outgoing main scanning lines or the returning main scanning lines.

[0120] 6. Fifth Modification (FIGS. 29 and 30) Next, a fifth modification of the above-described embodiment will be described. The fifth modification can be applied when a group is formed of only spots on the main scanning line on the forward pass or only spots on the main scanning line on the backward pass, as in the fourth modification, and differs from the above-described embodiment only in that the processing shown in Fig. 29 is executed instead of the processing shown in Fig. 24, so only this point will be described.

[0121] FIG. 29 is a flowchart of the process executed by the processor 53 in the fifth modified example of the present invention, which corresponds to FIG. Similar to the processing in FIG. 24, processor 53 starts the processing shown in FIG. 29 when it detects an instruction to start object detection.

[0122] In this process, the processor 53 first activates the actuators 300 and 380, the LD module 21, and the light receiving element 43 (S31), similarly to step S11 in Fig. 24. If this state is already reached at the start of the process, step S31 can be omitted. Next, processor 53 creates a group of spots as described with reference to FIG. 24 for each spot within field of view 65 used for object detection (S32, S33).

[0123] Thereafter, the drive frequency of the actuator 300 may be adjusted to match the resonance frequency (S34) in the same manner as in step S12 of Fig. 24, but this is not essential. Even if adjustment is performed, the process may proceed to step S35 and subsequent steps without waiting for the adjustment to be completed. The processing in steps S35 to S37 is the same as that in steps S15 to S17 in FIG. 24, except that the group configuration is different.

[0124] After step S37, processor 53 determines whether the drive frequency of actuator 300 matches the resonant frequency (S38). If they match, processor 53 calculates and outputs the direction and distance to the detected object based on the TOF values ​​of each group on both the forward and backward journeys (S39). If they do not match, processor 53 calculates and outputs the direction and distance to the detected object based on the TOF values ​​of each group on either the forward or backward journey (S40). After that, in either case, if object detection is to be continued, the process returns to step S34 and the process is repeated, and if object detection is to be ended, the process of FIG. 29 is ended (S41).

[0125] In the above processing, only one of the forward and backward passes is used in step S40 because, as explained using Figure 17, in this state, the object detection results based on the forward pass main scanning lines and the object detection results based on the backward pass main scanning lines show different object images. However, by performing the above processing, object detection can be performed without adjusting the drive frequency of actuator 300 to match the resonant frequency, or even if adjustment is made, before the adjustment is completed, while the accuracy is lower than in the above-mentioned embodiment, and the influence of ambient light can be eliminated.

[0126] This modification is useful when it is desired to omit the function of adjusting the drive frequency or when it is desired to shorten the time from startup of the object detection device to object detection. It is also conceivable to perform the processing of Figure 29 at startup, and then reset the groups and proceed to the processing of Figure 24 after the drive frequency of actuator 300 matches the resonant frequency. Also, in the processing of FIG. 29, modifications similar to those described with reference to FIG. 24 can be applied.

[0127] FIG. 30 shows another example of group setting applicable to the fifth modified example. 30, three consecutive spots in the main scanning direction on the same main scanning line are grouped together. Group G(n,x) and its adjacent group G(n,x+3) are set on the outgoing main scanning line 71-n, and group (n+1,x) and its adjacent group G(n+1,x+3) are set just below that on the returning main scanning line 72-(n+1).

[0128] Even if the groups are set in this way, the groups are still made up of only the spots on the main scanning line in the forward pass and only the spots on the main scanning line in the backward pass, and the processing in FIG. 29 can be applied. Furthermore, when performing the processing of FIG. 24, it is also possible to set groups as shown in FIG.

[0129] [7. Sixth Modification (Fig. 31)] Next, a sixth modified example of the above-described embodiment will be described. The sixth modified example differs from the above-described embodiment in that the scanning unit 30 does not perform scanning in the sub-scanning direction but only scans in the main scanning direction, and only this point will be described. FIG. 31 shows the configuration of scanning lines formed within the field of view by the scanning unit 30 in the sixth modified example.

[0130] 31, in the sixth modified example, there are only two scanning lines: a scanning line 171 for object detection and a scanning line 172 for driving frequency adjustment. A reflecting portion 66 is provided at a position where the scanning line 172 passes. Both scanning lines scan the same position on the outward and return paths. The scanning lines 171 and 172 do not need to be located close to each other, and do not need to be parallel to each other. Only when adjusting the drive frequency without using the actuator 380 shown in Fig. 3, some optical element such as a mirror or a prism may be inserted in the optical path of the output light L2 to move the scanning line to a position passing through the reflecting unit 66.

[0131] When a two-dimensional field of view is not required, even in an object detection device 10 that does not perform scanning in the sub-scanning direction and has only one scanning line 171 for object detection, it is possible to eliminate the effects of ambient light in the same way as in the above-described embodiment. In this case, the frame boundaries are not particularly defined, but just as in the above-described embodiment, spots are formed by the forward scan and the subsequent return scan, and if the drive frequency of the actuator 300 matches the resonant frequency, the main scanning direction positions of each spot match on the forward and return scans.

[0132] Therefore, it is possible to set groups similar to those in Fig. 23, Fig. 25 to Fig. 28, and even Fig. 30, and execute the processing in Fig. 24 or Fig. 29. The scanning lines shown in these figures can be considered to be scanning lines that scan the same position at different scanning timings, such as the nth time, the (n+1)th time, etc. Furthermore, if a group is set to span n scans, when the n scans are completed, the TOFs for that group can be tallied and the direction of the object and the distance to the object can be output based on the tallied results.

[0133] 8. Other Modifications (FIGS. 32 to 34) Next, other modifications of the embodiment described above will be described. First, in the above-described embodiment and each modified example, the group boundary in the main scanning direction is common regardless of the position in the sub-scanning direction. However, as shown in Fig. 32, the group boundary in the main scanning direction may differ depending on the position in the sub-scanning direction.

[0134] In Figure 32, groups G(n, x) and G(n, x+2) are set on the nth and n+1th main scanning lines, while groups G(n+2, x+1) and G(n+2, x+3) are set on the n+2nd and n+3rd main scanning lines, one spot apart in the main scanning direction. Even when the groups are set in this way, the effect of eliminating the influence of ambient light can be obtained, as in the above-described embodiment and each of the modifications.

[0135] Furthermore, in the above-described embodiment, an example in which object detection itself is not performed when the drive frequency does not match the resonance frequency has been described with reference to FIG. 24, but this is not essential. Fig. 33 shows a flowchart of the processing executed by processor 53 in this modified example, which corresponds to Fig. 24. In Fig. 33, the same steps as in Fig. 24 are given the same step numbers, and the description of these steps will be omitted.

[0136] In FIG. 33, similarly to the case of FIG. 29, it is not essential to perform the adjustment (S12) for matching the drive frequency of the actuator 300 to the resonance frequency. Then, steps S14 and S15 are executed without going through the determination of step S13, and after step S15, a determination is made, similar to step S13, as to whether the drive frequency of the actuator 300 matches the resonance frequency (SA). If this is Yes, the processes from step S16 onwards are carried out as in the case of Fig. 24. If the answer is No in step SA, groups are not used, and the direction of the detected object and the distance to the object are calculated and output based on the TOF value corresponding to each light emission (spot).

[0137] 24, object detection itself is performed and the results are output even if the drive frequency does not match the resonant frequency. When step SB is executed, no groups are used, so the effect of eliminating the effects of ambient light cannot be obtained. However, in a dark environment with little ambient light, the accuracy of object detection may not be significantly affected. Therefore, this modification is useful when you want to shorten the time from startup of the object detection device to object detection, even if you are initially willing to accept the risk of the effects of ambient light. As in the case of FIG. 29, when the drive frequency does not match the resonance frequency, object detection may be performed based on the TOF value corresponding to the light emission on one of the scanning lines on the forward or backward path.

[0138] Furthermore, an actuator using a magnetic spring can also be used as the actuator responsible for scanning in the main scanning direction. FIG. 34 shows an example of the configuration of the scanning unit 30 using such an actuator 400. 34 is configured such that a mirror 401 is fixed to a permanent magnet 410, and the permanent magnet 410 is held by bearings 403 and 405. The interaction between the magnetic force of the permanent magnet 410, a yoke 430 arranged around the permanent magnet 410, and a current flowing through a drive coil arranged between the permanent magnet 410 and the yoke 430 causes the permanent magnet 410 and the mirror 401 to rotate together around a rotation axis 404 passing through the center of the permanent magnet 410 in accordance with the voltage applied to the coil, and to reciprocate within a predetermined angular range. In this type of actuator 400, the movable part including the mirror 401 also has a resonant frequency. Specifically, it is conceivable to use an actuator proposed by the present applicant and described in Japanese Patent No. 6830698 (Patent Document 4) or Japanese Patent Laid-Open No. 2021-132416 (Patent Document 5).

[0139] In the above-described embodiment, an example has been described in which processor 53 performs the process of calculating the direction of an object and the distance to the object. However, processor 53 may perform the process of acquiring the TOF value corresponding to each spot (up to step S15 in FIG. 24 or step S35 in FIG. 27) and determining whether the drive frequency matches the resonant frequency, and output the results to an external device via input / output unit 54. The external device may then set groups, tally TOFs, calculate the direction of an object and the distance to the object based on the tally results for each group, and graphically display an object image based on the above. In this case, object detection device 10 and the external device constitute an object detection system.

[0140] In addition to the above, in this invention, the specific configuration of the device, the specific operating procedures, the specific shapes of the parts, etc. are not limited to those described in the embodiments. Furthermore, the features described in each of the above items can be applied independently to devices and systems.

[0141] Furthermore, an embodiment of the program of the present invention is a program that causes one computer, or multiple computers working together, to control the required hardware and realize some or all of the functions related to the drive frequency adjustment and elimination of the effects of ambient light that have been described above, or that executes the processing described in the above-mentioned embodiment.

[0142] Such a program may be stored in a ROM or other non-volatile storage medium (flash memory, EEPROM, etc.) that is included in the computer from the beginning. It may also be provided by recording it on any non-volatile storage medium such as a memory card, CD, DVD, or Blu-ray disc. Furthermore, it may be downloaded from an external device connected to a network, installed on a computer, and executed.

[0143] Furthermore, the configurations of the embodiments and modified examples described above can be implemented in any combination as long as they are not mutually contradictory, and it goes without saying that only some of them can be taken out and implemented. [Explanation of symbols]

[0144] 10...object detection device, 20...light-emitting unit, 21...LD module, 22...laser drive circuit, 23...light-emitting optical system, 30...scanning unit, 31...mirror, 32...actuator, 40...light-receiving unit, 41...mirror, 42...condensing lens, 43...light-receiving element, 43a...APD, 43b, 43c...output signal line, 44...aperture, 46...detection signal, 51...front-end circuit, 52...TDC, 53...processor, 54...input / output unit, 61...top cover, 62...rear cover, 63...cover clip, 64...protective material, 65...field of view range, 66...reflecting unit, 66a...effective reflector irradiated area, 70...field of view, 71, 72...scanning line, 73...beam spot, 80...object, 81-83...object image, 300, 380, 400...actuator, 301...mirror unit, 302...torsion spring, 304, 404...rotation axis, 316...drive coil, 317...sensing coil, 320...mover, 321...permanent magnet, 321s...south pole, 321n...north pole, 381, 401...mirror, 403, 405...bearing, 410...permanent magnet, 430...yoke, G...group, L1...laser beam, L2...emitted light, L3, L4...returned light, S...spot

Claims

1. an optical scanning unit that scans a predetermined field of view with a pulsed light beam by reflecting the light beam off a first reflecting material that is periodically driven to rotate back and forth around a first rotation axis by a first actuator, the scanning including a reciprocating scan in a first direction corresponding to the rotation direction of the first reflecting material; a light detection unit that receives and detects light at a predetermined position; a light guide section that guides light incident on the first reflecting material to the light detecting section along an optical path opposite to the light beam projected; a measuring unit that measures the time difference between the projection of the light beam and the reception of the light by the light detecting unit; a counting unit that counts the time difference measured by the measurement unit for each of a group of lightings of the light beam a plurality of times in which the projection directions are close to each other, the lightings including lightings in a forward scan in the first direction and lightings in a backward scan following the forward scan, for each class of the value of the time difference; and an object detection unit that performs object detection to detect the direction in which an object exists and the distance to the object based on the projection direction of the light beam and the frequency for each class obtained by the aggregation for each of the plurality of groups set within the field of view.

2. 10. The object detection system of claim 1, an adjustment unit that adjusts the frequency of the drive signal applied to the first actuator so that the frequency of the drive signal matches a resonance frequency of the first actuator; a determination unit that determines whether a frequency of the drive signal matches a resonance frequency of the first actuator, The object detection system is characterized in that, when the determination unit determines that the frequency of the drive signal matches the resonant frequency of the first actuator, the object detection unit uses the frequency obtained by the aggregation for the object detection.

3. 3. The object detection system of claim 2, The light beam is pulsed in the same pattern in the forward scanning in the first direction and in the backward scanning following the forward scanning, An object detection system comprising: a group creation unit that creates the plurality of groups based on the number of times each light beam is lit during the forward scan or the return scan.

4. 10. The object detection system of claim 1, the optical scanning unit further includes a second reflecting member that is rotationally driven around a second rotation axis that is not parallel to the first rotation axis, the scanning of the light beam includes a main scanning in the first direction and a sub-scanning corresponding to a rotation of the second reflecting material; An object detection system, characterized in that the lighting during the forward scanning and the lighting during the return scanning included in each group are lightings whose light projection directions are adjacent to each other in the sub-scanning direction.

5. 5. The object detection system of claim 4, an adjustment unit that adjusts the frequency of the drive signal applied to the first actuator so that the frequency of the drive signal matches a resonance frequency of the first actuator; a determination unit that determines whether a frequency of the drive signal matches a resonance frequency of the first actuator, The object detection system is characterized in that the object detection unit uses the count obtained by the aggregation for the detection when the determination unit determines that the frequency of the drive signal matches the resonant frequency of the first actuator.

6. 6. The object detection system of claim 5, The light beam is pulsed in the same pattern during a forward scan in the main scanning direction and during a backward scan at a position adjacent to the forward scan in the sub-scanning direction; An object detection system comprising: a group creation unit that creates the plurality of groups based on the number of times each light beam is lit during the forward scan or the return scan.

7. an optical scanning unit that scans a predetermined field of view with a pulsed light beam by reflecting the light beam off a first reflecting material that is periodically driven to rotate back and forth around a first rotation axis by a first actuator, the scanning including a reciprocating scan in a first direction corresponding to the rotation direction of the first reflecting material; a light detection unit that receives and detects light at a predetermined position; a light guide section that guides light incident on the first reflecting material to the light detecting section along an optical path opposite to the light beam projected; a measuring unit that measures the time difference between the projection of the light beam and the reception of the light by the light detecting unit; a counting unit that counts the time difference measured by the measurement unit for each of a group of lightings of the light beam that are adjacent to each other in the first direction, the lightings being a plurality of times with projection directions close to each other, for each class of value of the time difference; and an object detection unit that performs object detection to detect the direction in which an object exists and the distance to the object based on the projection direction of the light beam and the frequency for each class obtained by the aggregation for each of the plurality of groups set within the field of view.

8. an optical scanning unit that scans a predetermined field of view with a pulsed light beam by reflecting the light beam off a first reflecting material that is periodically driven to rotate back and forth around a first rotation axis by a first actuator, the scanning including a reciprocating main scan in a first direction corresponding to the rotation direction of the first reflecting material; a light detection unit that receives and detects light at a predetermined position; a light guide section that guides light incident on the first reflecting material to the light detecting section along an optical path opposite to the light beam projected; a measuring unit that measures the time difference between the projection of the light beam and the reception of the light by the light detecting unit; a counting unit that counts the time differences measured by the measurement unit for each of a group of lightings of the light beam that are close to each other in projection directions and that are included in different main scanning times, for each class of the value of the time differences; an object detection unit that performs object detection to detect a direction in which an object exists and a distance to the object based on the projection direction of the light beam and the frequency for each class obtained by the aggregation for each of the plurality of groups set within the field of view; an adjustment unit that adjusts the frequency of the drive signal applied to the first actuator so that the frequency of the drive signal matches a resonance frequency of the first actuator; a determination unit that determines whether a frequency of the drive signal matches a resonance frequency of the first actuator, The object detection system is characterized in that, when the determination unit determines that the frequency of the drive signal matches the resonant frequency of the first actuator, the object detection unit uses the frequency obtained by the aggregation for the object detection.

9. 9. The object detection system of claim 8, the light detection unit detects light for each pixel using a plurality of pixels, each of which is an avalanche photodiode operated in Geiger mode, detects incident light corresponding to each lighting of the light beam using the same plurality of pixels, and outputs a sum of outputs corresponding to the light detection from each of the plurality of pixels as the detection result of the incident light during the detection period.

10. an optical scanning step in which a pulsed light beam is reflected by a first reflecting material that is periodically driven to rotate back and forth around a first rotation axis by a first actuator, and projected to scan a predetermined field of view with the light beam, the scanning including a reciprocating scan in a first direction corresponding to the rotation direction of the first reflecting material; a light detection step of receiving and detecting light, at a predetermined position, by a light detection unit, the light that is incident on the first reflecting material along an optical path opposite to the projected light beam and is guided by a light guiding unit; a measurement procedure for measuring a time difference between the projection of the light beam and the reception of the light by the light detection unit; a counting step of counting the time differences measured in the measurement step for each of a group of lightings of the light beam a plurality of times in which the projection directions are close to each other, the lightings including lightings in a forward scan in the first direction and lightings in a backward scan following the forward scan, for each class of the value of the time differences; and an object detection procedure for detecting the direction in which an object exists and the distance to the object based on the projection direction of the light beam and the frequency for each class obtained by the aggregation for each of the plurality of groups set within the field of view.

11. an optical scanning step in which a pulsed light beam is reflected by a first reflecting material that is periodically driven to rotate back and forth around a first rotation axis by a first actuator, and projected to scan a predetermined field of view with the light beam, the scanning including a reciprocating scan in a first direction corresponding to the rotation direction of the first reflecting material; a light detection step of receiving and detecting light, at a predetermined position, by a light detection unit, the light that is incident on the first reflecting material along an optical path opposite to the projected light beam and is guided by a light guiding unit; a measurement procedure for measuring a time difference between the projection of the light beam and the reception of the light by the light detection unit; a counting step of counting the time differences measured in the measurement step for each of a group of lightings of the light beam, the lightings being adjacent to each other in the first direction, for each class of values ​​of the time differences; and an object detection procedure for detecting the direction in which an object exists and the distance to the object based on the projection direction of the light beam and the frequency for each class obtained by the aggregation for each of the plurality of groups set within the field of view.

12. an optical scanning procedure in which a pulsed light beam is reflected by a first reflecting member that is periodically driven to rotate back and forth around a first rotation axis by a first actuator, and projected to scan a predetermined field of view with the light beam, the scanning including a reciprocating main scan in a first direction corresponding to the rotation direction of the first reflecting member; a light detection step of receiving and detecting light, at a predetermined position, by a light detection unit, the light that is incident on the first reflecting material along an optical path opposite to the projected light beam and is guided by a light guiding unit; a measurement procedure for measuring a time difference between the projection of the light beam and the reception of the light by the light detection unit; a counting step of counting the time differences measured in the measurement step for each of a group of lightings of the light beam, the lightings being close to each other in projection directions and included in different main scanning times, for each class of the value of the time differences; an object detection step of detecting a direction in which an object exists and a distance to the object based on the projection direction of the light beam and the frequency for each class obtained by the aggregation for each of the plurality of groups set within the field of view; an adjustment step of adjusting a frequency of the drive signal applied to the first actuator so that the frequency of the drive signal matches a resonance frequency of the first actuator; a determination step of determining whether or not a frequency of the drive signal matches a resonance frequency of the first actuator, The object detection method is characterized in that the object detection procedure is a procedure in which, if it is determined in the determination procedure that the frequency of the drive signal matches the resonant frequency of the first actuator, the frequency obtained by the aggregation is used for the object detection.

13. a processor controls an optical scanning device that scans a predetermined field of view with a pulsed light beam by reflecting the light beam off a first reflecting material that is periodically driven to rotate back and forth around a first rotation axis by a first actuator, and projecting the light beam, the optical scanning device comprising: an optical scanning unit that performs a reciprocating scan in a first direction corresponding to the rotation direction of the first reflecting material; an optical detection unit that receives and detects light at a predetermined position; and a light guiding unit that guides light that is incident on the first reflecting material to the optical detection unit along an optical path opposite to the projected light beam, A program for executing the object detection method according to any one of claims 10 to 12.

14. The processor an acquisition procedure for acquiring measurement results of the time difference between the projection of the light beam and its reception by the light detection unit for each projection of the light beam, the measurement results being generated by an optical scanning device comprising: an optical scanning unit that scans a predetermined field of view with the light beam by reflecting the light beam off a first reflecting material that is periodically driven to rotate back and forth around a first rotation axis by a first actuator, the first reflecting material being rotated back and forth around a first rotation axis, the first reflecting material being rotated back and forth in a first direction corresponding to the rotation direction of the first reflecting material; an optical detection unit that receives and detects light at a predetermined position; and a light guiding unit that guides light that is incident on the first reflecting material to the optical detection unit along an optical path opposite to the projected light beam; a counting step of counting the time differences acquired in the acquisition step for each of a group of lightings of the light beams, the lightings being a plurality of times with projection directions close to each other, the lightings including lightings in a forward scan in the first direction and lightings in a backward scan following the forward scan, for each class of value of the time differences; and an object detection procedure for detecting the direction in which an object exists and the distance to the object as seen from the optical scanning device, based on the projection direction of the light beam and the frequency for each class obtained by the aggregation, for each of the plurality of groups set within the field of view.

15. The processor an acquisition procedure for acquiring measurement results of the time difference between the projection of the light beam and its reception by the light detection unit for each projection of the light beam, the measurement results being generated by an optical scanning device comprising: an optical scanning unit that scans a predetermined field of view with the light beam by reflecting the light beam off a first reflecting material that is periodically driven to rotate back and forth around a first rotation axis by a first actuator, the first reflecting material being rotated back and forth around a first rotation axis, the first reflecting material being rotated back and forth in a first direction corresponding to the rotation direction of the first reflecting material; an optical detection unit that receives and detects light at a predetermined position; and a light guiding unit that guides light that is incident on the first reflecting material to the optical detection unit along an optical path opposite to the projected light beam; a counting step of counting the time differences acquired in the acquisition step for each of a group of lightings of the light beams, the lightings being adjacent to each other in the first direction, for each class of values ​​of the time differences; and an object detection procedure for detecting the direction in which an object exists and the distance to the object as seen from the optical scanning device, based on the projection direction of the light beam and the frequency for each class obtained by the aggregation, for each of the plurality of groups set within the field of view.

16. The processor an acquisition step of acquiring measurement results of a time difference between the projection of the light beam and its reception by the light detection unit for each projection of the light beam, and a determination result of whether or not a frequency of a drive signal for the first actuator matches a resonance frequency of the first actuator, the measurement results being generated by an optical scanning device comprising: an optical scanning unit that scans a predetermined field of view with the light beam by reflecting the light beam off a first reflecting material that is driven to rotate back and forth periodically around a first rotation axis by a first actuator, the scanning including a reciprocating scan in a first direction corresponding to the rotation direction of the first reflecting material; an optical detection unit that receives and detects light at a predetermined position; and a light guiding unit that guides light that is incident on the first reflecting material to the light detection unit along an optical path opposite to that of the projected light beam; a counting step of counting the time differences acquired in the acquisition step for each of a group of lightings of the light beams, the lightings being close to each other in projection directions and included in different main scanning times, for each class of the value of the time differences; A program for executing an object detection procedure that detects the direction in which an object exists and the distance to the object as seen from the optical scanning device based on the projection direction of the light beam and the frequency for each class obtained by the aggregation for each of the multiple groups set within the field of view, and an object detection procedure that uses the frequency obtained by the aggregation for the object detection when the judgment results obtained in the acquisition procedure are a match.

Images