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 light, as well as a program for causing a computer to control necessary hardware to execute procedures related to such object detection. [Background technology]

[0002] Conventionally, there has been known an object detection device that detects an object on the optical path of the laser light and the distance to the object based on the time from the irradiation to the detection of the reflected light (TOF: Time of flight) by irradiating a pulse of laser light to the outside and detecting the returned laser light reflected by an object. 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, disturbance light noise is a problem in object detection by LIDAR because when the light detection unit detects incident light, it is not possible to distinguish, based only on the presence or absence of light, whether the detected light is reflected light of the irradiated light or disturbance light that is incident independently of the irradiated light. As a technique for dealing with this problem, a technique using a histogram is known, as described in Patent Documents 1 and 2. Moreover, a technique using a histogram is also disclosed in Patent Document 3. In addition, Patent Documents 4 to 7 are also known as publications related to the applicant's patents or patent applications. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-91377 A [Patent Document 2] JP 2020-112443 A [Patent Document 3] JP 2020-26969 A [Patent Document 4] Patent No. 6830698 [Patent Document 5] JP 2021-132416 A [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 the pulsed light is received is measured repeatedly or using multiple SPADs (Single Photon Avalanche Diodes), a histogram of the time differences 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 are related to a type of LIDAR that does not perform scanning with light, but irradiates a measurement target with light that has a wide area and covers it, 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 illumination light is emitted, or by changing the direction in which the illumination light is emitted to multiple directions per one light receiving position for receiving reflected light.

[0007] However, the technology described in Patent Document 3 addresses the problem that components such as lenses and holders used in optical distance measuring devices may deform in response to the ambient temperature, which may result in the reflected light not being properly received within the light receiving range, and enables distance measurement to be performed even if the light receiving position is slightly shifted. It is unclear whether this technology is also useful for reducing the effects of external light. In addition, a large light receiving element array is used to receive reflected light at different positions depending on the direction of the light projection, making it difficult to apply to small devices. Furthermore, it is assumed that complex control of the light receiving position and the light irradiation direction is performed, which makes it difficult to reduce the cost.

[0008] The present invention aims to solve these problems and to reduce the effects of ambient light using a small, low-cost method when scanning a predetermined field of view range with pulsed laser light and detecting objects 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 via 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, the group including lighting during a forward scan in the first direction and lighting during a return scan following the forward scan, for each class of the time difference value, 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 of the drive signal matches the resonant frequency of the first actuator, and a determination unit that determines whether or not the frequency of the drive signal matches the resonant frequency of the first actuator, and 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 tallying for the object detection.

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

[0013] Alternatively, the optical scanning unit may further include a second reflective 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 reflective 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 each other in the sub-scanning direction.

[0014] The device further includes 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 or not the frequency of the drive signal matches the resonant frequency of the first actuator, and 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 counted frequency for the detection.

[0015] Furthermore, it is preferable to provide a group creation unit which 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 has been 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 which 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 the projection direction and adjacent to each other in the first direction, for each class of the value of the time difference. Alternatively, instead of the above-mentioned counting unit, a counting unit may be provided which counts the time difference measured by the measurement unit for each of a group of lightings of the light beam that include multiple lightings that are close to each other in the projection direction and that are each included in different main scans, by class of the value of the time difference.

[0017] Furthermore, in each of the above 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 illuminations 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 a detection result of the incident light during the detection period.

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

[0019] According to the present invention as described above, when a predetermined field of view is scanned with a pulsed laser light and an object is detected based on the timing of receiving reflected light, the influence of disturbance light can be reduced using a compact and low-cost method. [Brief description 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. [Diagram 2] 1 is a diagram for explaining the principle of object detection in the object detection device 10. FIG. [Diagram 3] 1 is an exploded perspective view showing the structure of main components of an object detection device 10. FIG. [Figure 4] 1 is a perspective view showing the appearance of an object detection device 10. FIG. [Diagram 5] 4 is a cross-sectional view of the actuator 300 shown in FIG. 3, taken along a cross section perpendicular to the rotation axis of the mirror unit 301. FIG. [Figure 6] 4 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] 1 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 shows another example different from that of FIG. 7. [Figure 9] FIG. 8 is a diagram corresponding to FIG. 7 and showing yet another example. [Figure 10] 13 is a schematic diagram showing the relationship between the scanning range of the output light L2, the position where the reflecting portion 66 is provided, and the position of the effective reflecting area 66a. FIG. [Figure 11]13 is a diagram for explaining a method of detecting the timing at which output light L2 is reflected by an effective reflection area 66a of a reflecting portion 66. FIG. [Figure 12] 8 is a diagram showing a time range during 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. 7. FIG. [Figure 13] 9 is a diagram showing a time range during 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. 8. FIG. [Figure 14] 10 is a diagram showing the time range during 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 within 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 coincides with 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 resonant frequency. FIG. [Figure 18] 1 is a diagram for explaining an example of a spot S formed on a scanning line by pulsed emission of 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] 11 is a histogram showing an example of a total of detection results of each spot S in a group G(n,x) and the corresponding TOF. [Figure 21] 2 is a diagram showing in more detail the configuration of the light receiving section 40 in FIG. 1 and the optical path of the return light L4. [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. [Diagram 25] FIG. 13 is a diagram illustrating an example of setting a group G in a first modified example of the first embodiment. [Figure 26] FIG. 13 is a diagram showing an example of setting a group G in the second modified example. [Figure 27] FIG. 13 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. [Diagram 30] FIG. 13 is a diagram showing another example of setting the group G in the fifth modified example. [Diagram 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 the sixth modified example. [Diagram 32] FIG. 13 is a diagram showing yet another setting example of group G. [Diagram 33] 25 is a flowchart of a process corresponding to FIG. 24 and executed by a processor 53 in still another modified example of the present invention. [Diagram 34] 13 is a diagram showing another example of the configuration of an actuator in the scanning unit 30. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 an embodiment of the present invention will be described with reference to Figures 1 and 2, with main components divided according to their functions. Figure 1 is a block diagram showing 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 projection timing and the detection timing of the reflected light. As shown in Fig. 1, this object detection device 10 includes a light projection 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 projection 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 projection 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 light source with multiple light emitting points is used to increase the output intensity, but a single light emitting point may be used. There is no particular restriction on the wavelength of the laser light, but it is possible to use, for example, a near-infrared laser light. The laser light is an example of a light beam. The laser driving circuit 22 is a circuit for generating a driving signal for turning on the LD module 21 at a timing according to parameters supplied from the processor 53, and applying the driving 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 the emitted light L2.

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

[0026] Also, while only one actuator 32 is shown in FIG. 1, in reality, the actuator 32 is composed of two actuators 300, 380 that swing the mirror around different axes as shown in FIG. 3. The actuator 300 is driven to reciprocate and is responsible for scanning in the main scanning direction (first direction) to form horizontal scanning lines 71, 72, and 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. 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 forward scanning and the latter is called backward scanning, but this is simply to distinguish between the two, and the forward and backward scanning may be reversed.

[0027] Incidentally, 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. In addition, 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 part of the emitted light L2 toward the incident optical path of the emitted light L2 at a predetermined position that is a part of 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, the light receiving unit 40 is a module for detecting light incident from outside the 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 the light receiving unit 40 is a laser beam projected from the object detection device 10 and reflected back by an external object, and a laser beam reflected back by the reflecting unit 66. The laser beam reflected by the external object is diffused on the object surface, and only the component of the laser beam reflected in the opposite direction to the optical path at the time of projection returns to the object detection device 10 as return light L3. This return light L3 travels in the opposite direction along substantially the same path as the emitted light L2, and reaches the 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 at the time of projection and reaches the mirror 41 as return light L4. The only difference with the case where 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 having a through hole 41a for passing the laser beam output from the light projector 20, and for guiding the return light L4 to the light receiving element 43. Here, the laser light output from the LD module 21 is generally not completely parallel 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 is more divergent than the laser beam L1, so that it hits the mirror 41 over a wider range than the through hole 41a, and the component that hits a position 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 light detecting element 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 disturbance light from entering light receiving element 43. More specifically, aperture 44 passes a component of return light L4 that enters mirror 41 in the opposite direction to the optical path at the time of light projection and is reflected by mirror 41 with a predetermined diameter, and blocks other light. Therefore, even if the laser beam reflected by reflecting portion 66 in a direction different from the optical path of incidence 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, except for a small component that happens to be incident along substantially the same path as the return light L4, is blocked by the aperture 44 and does not reach the light receiving element 43. For this reason, 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 light receiving optical system plus the mirror 31 correspond to a light guiding 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 return 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 its reception by the light receiving element 43.

[0034] As described later, when a photon of disturbance light incident on substantially the same path as the return light L4 reaches the light receiving element 43, the light receiving element 43 also outputs a detection signal. Therefore, 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. On this premise, one of the features of this embodiment is a configuration for distinguishing between the time difference caused by the return light L4 and the time difference caused by the disturbance light and specifying the time difference caused by 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 required 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 as s = c(Δt) / 2, as shown in Fig. 2, based on the time difference Δt (hereinafter, this Δt will also be referred to as "TOF (Time of Flight)"), 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. and executing software, or may be configured as dedicated hardware, or may be a combination of them. 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 at the time of detecting the return light (the projection direction of the emitted light L2). In addition, as will be described in detail later, it also performs a process of adjusting the drive frequency of the actuator 300 to match its resonance frequency, and a process of distinguishing between the time difference caused by the return light L4 and the time difference caused by the disturbance light and identifying the time difference caused by the return 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, acceptance of an operation from a user using a button or a touch panel, and presentation of information to a user using a display, a lamp, a speaker, a vibrator, and the like. Examples of information that the input / output unit 54 should output to the outside include information on 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 on distance and direction, such as a predetermined size, position, and moving speed), and information on the operating state and setting state of the object detection device 10. Examples of information that the input / output unit 54 should accept as input from the outside include information on the operating settings of the object detection device 10.

[0038] Possible communication partners via the input / output unit 54 include, for example, moving objects such as automobiles and drones equipped with an automatic driving system, and wearable devices used in the field of Augmented Reality (AR). If information on objects detected by the object detection device 10 is supplied to an automatic driving system, the automatic driving system can refer to the information and plan a driving route that avoids the detected object. If information on 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 a communication partner such as an automobile, a drone, an aircraft, a 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 Fig. 3 and Fig. 4. Fig. 3 is an exploded perspective view showing the structure of the main components of the object detection device, and Fig. 4 is a perspective view showing the appearance of the object detection device. 3 and 4, the object detection device 10 has an exterior in which a top cover 61 and a rear cover 62 are joined by 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 at the wavelength of the emitted light L2 is fitted into the window to prevent dust from entering. The reflecting portion 66 is provided on the inner surface of the 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: an actuator 300 responsible for scanning in the main scanning direction, and an actuator 380 responsible for scanning in the sub-scanning direction. The mirror unit 301 is a mirror provided in the actuator 300. 1, mirror 48 is an optical element located between mirror 41 and condenser lens 42 for changing the direction of return light L4. Dashed line 65 indicates the field of view (the scanning range of emitted light L2) of object detection device 10, and corresponds to field of view 70 in Fig. 1. Circuits such as laser driver circuit 22 and processor 53 and wiring between modules are omitted in Fig. 3 to make the drawing easier to see. The overall configuration has now been described, 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. Of these, the actuator 300 will be described first. As shown in FIG. 3, the actuator 300 and the actuator 380 are significantly different in configuration. Since 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 that rotates 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 a cross-sectional view of the actuator 300 shown in FIG. 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 an 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 side 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 response to 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 such 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 the south pole 321s of the permanent magnet 321 through an 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 clockwise as viewed in Fig. 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 drive coil 316 and permanent magnet 321 is balanced with the restoring force of torsion spring 302. The speed of this rotation and the stop position can be adjusted by changing the strength of the current passed through 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 the arrow V in Fig. 5, and can be caused to perform reciprocating rotational motion within a predetermined angle 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 is provided to detect the rotational angular velocity of the mirror 301 rotating together with the permanent magnet 321 by detecting the current that flows due to the induced electromotive force caused by the fluctuation in the strength of the magnetic field generated by the oscillation of the permanent magnet 321. If this detection is not performed, the sensing coil 317 is not necessary. As the actuator 300 as 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. Adjustment of the actuator drive frequency (Figs. 6 to 14)] Next, an explanation will be given of an operation related to adjustment for matching the drive frequency of the actuator to the resonant frequency, which is executed by the above-mentioned object detection device 10. This operation will be explained using the above-mentioned actuator 300 as an example, but a similar adjustment can be applied to any type of actuator having a resonant frequency, including the actuator 400 described later.

[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 are repeated at a constant period, as shown in Fig. 6. When the reciprocal of this period (referred to as the "drive frequency" in this specification) matches the resonance frequency of the mover 320 including the mirror unit 301 (hereinafter referred to as the "mirror 301"), which is the mover, the mirror 301 of the actuator 300 can be driven efficiently, that is, with low power consumption. In addition, the main scanning direction positions of the spots on the main scanning line can be easily matched between the forward and backward passes. The resonant frequency of the mover including the reflective material in the actuator as described above will be referred to as the "resonant 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 in several cases. Fig. 7 shows an example in which the drive frequency matches the resonant frequency of actuator 300, while Figs. 8 and 9 show examples in which the drive frequency deviates from the resonant frequency of actuator 300. In Figs. 7 to 9, the horizontal axis shows 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 shows the absolute value of the angular velocity at that position, to illustrate the change 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, "velocity" or "angular velocity" refers to the absolute value of the velocity or angular velocity.

[0052] Here, it is known that the moving speed of mirror 301 oscillating by actuator 300 is not constant. Since mirror 301 stops at the ends of the oscillation path and moves in other parts, it is clear that there is a fluctuation in the moving speed, but according to experiments 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, the inventors' experiments have shown that in the case of Fig. 7 where the drive frequency is (almost) the same as the resonant frequency of the actuator 300, whether the actuator rotates clockwise or counterclockwise, i.e., whether the actuator is scanning forward or backward, the angular velocity is almost the same at the same position, except that the direction of movement is different. Also, the central position of the main scan is the peak of the angular velocity. For this reason, the solid line 501 and the dashed line 502 overlap in Fig. 7, and only the solid line 501 is shown in the figure.

[0054] On the other hand, experiments by the inventors have also found 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] The inventors' experiments have revealed that when the drive frequency and the resonant frequency of the actuator 300 are relatively close to each other, by gradually approaching the drive frequency to the resonant frequency (or to what is assumed to be the resonant frequency) and then changing the drive frequency 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 in Figures 8 and 9 is observed, and as the drive frequency approaches the resonant 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 resonant frequency. After that, when the drive frequency passes the resonant frequency, the other relationship in Figures 8 and 9 is observed, and as the drive frequency moves away from the resonant 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 to match the drive frequency of the actuator 300 with the resonant frequency of the actuator 300 by utilizing the relationship between the scanning angle and angular velocity of the mirror 301. 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 output light L2, the position where the reflecting portion 66 is provided, and the position of the effective reflecting area 66a. 10, the scanning range 65 of the emitted light L2 indicated by the two-dot chain line is formed in a rectangular shape within 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. 71 and 72 indicate examples of the main scanning lines on the outgoing and return paths, respectively.

[0059] The reflecting portion 66 is provided in a predetermined area that is a part of the scanning range of the emitted light L2 in the main scanning direction and has a width 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 incident on the effective reflection area 66a is reflected toward 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 detects an object, the LD module 21 is turned on intermittently to form the scanning lines 71, 72 as a set of the beam spot 73. Then, when the beam spot 73 enters the effective reflection area 66a and is reflected by the effective reflection area 66a, the TDC 52 outputs a signal of a 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 may determine that the emitted light L2 of that beam spot has been reflected by the effective reflection area 66a.

[0061] Since the effective reflection area 66a has a certain width in the main scanning direction, when a main scanning line passes through the effective reflection area 66a, a certain number of the beam spots constituting the main scanning line are reflected by the effective reflection area 66a. These spots are hatched in Fig. 11. The processor 53 can specify the time range during which the output light L2 is incident on the effective reflection area 66a during one main scanning scan from the lighting timing of each spot reflected by the effective reflection area 66a. Although noise due to external light may be present, reflection from 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 signal for multiple consecutive beam spots 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. It can be said that Ra and Rb are the timings of the optical ends at which the detection of reflected light by the light receiving element 43 is switched between presence and absence.

[0063] Furthermore, the processor 53 can 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 point of the forward main scan is indicated by Ts and the end point by Te, and the start point of the return main scan is indicated by Ts' and the end point by Te'. As described above, the processor 53 can obtain information about 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 period of forward scanning and the period of backward scanning may not be continuous when viewed from the main scanning line as a reference, for example, because the end of the main scanning line is cut off. However, when adjusting the drive frequency, one main scan is counted from when the mirror 301, which rotates back and forth, starts rotating at one end of the swing path to when it rotates to the other end, stops, and changes its rotation direction, and the forward scanning and backward scanning are considered to be performed continuously. In other words, the following explanation will be given assuming that Te of the forward path and Ts' of the next backward path match, and Te' of the backward path and Ts of the next forward path match.

[0065] Figures 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. Note that the drive frequency is not changed between the forward scan and the return scan, and the time required for one main scan (Te-Ts or Te'-Ts') is the same for the forward scan and the return scan.

[0066] 12, in a state in which the drive frequency (almost) coincides with the resonance frequency of mirror 301, in forward scanning, as shown in graph 511, the emitted light L2 is reflected by effective reflection area 66a at a point 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 the forward scanning. Conversely, in backward scanning, as shown in graph 512, the reflected light is detected by light receiving element 43 at a point slightly later than the center of the scanning period.

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

[0068] That is, the time difference between the timing when the emitted light L2 is reflected by the end of the effective reflection area 66a (first reference timing) and the timing when the scan reaches the end of the scan line (second reference timing: the timing when 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 "end" here refers to an end (a specific end) 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 in which the angular velocity is greater in the latter half of the scan as in Figure 8, 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 return scan as shown in Figure 13, 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 to the first half of the scan for both forward and backward scans as shown in Fig. 14 compared to the case of Fig. 12. In Figs. 13 and 14, the positions indicated by virtual lines are the positions of the detection timing in Fig. 12.

[0070] Therefore, when the drive frequency does not match the resonant frequency of the mirror 301, the time difference between the first reference timing and the second reference timing will differ. Furthermore, if the difference between the drive frequency and the resonant frequency becomes smaller, the difference in the time lag also becomes smaller. From the above, if the drive frequency of 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 return scan, the drive frequency can be matched with the resonant frequency of 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 is slightly adjusted in an appropriate direction to increase or decrease the difference between the forward and return scans, and the drive frequency is then adjusted in the direction that reduces the difference until the difference becomes zero. As a specific method for adjusting the drive frequency as described above, for example, the method proposed by the present applicant and described in Japanese Patent No. 7097647 (Patent Document 6) can be used.

[0072] 4. Reduction of noise caused by ambient light (Figs. 15 to 22) Next, an operation performed by the above-described object detection device 10 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. As shown in FIG. As shown in Fig. 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 line that passes through the reflecting unit 66 shown in Fig. 10. The main scanning lines 71 from the forward scan and the main scanning lines 72 from the backward scan are arranged alternately in the sub-scanning direction. This is achieved by driving the actuator 380 when the main scan 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 the top to the 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 scanning the main scanning lines 71, 72 with the emitted light L2, 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, 72.

[0075] Here, if the drive frequency of actuator 300 matches the resonant frequency, the positions in the main scanning direction of each spot on main scanning line 71 in the forward pass and each spot on main scanning line 72 in the backward pass can be aligned by controlling the light emission timing of LD so that the light emission interval of LD during one main scanning period matches 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 positions in the main scanning direction of the x-th spot from the beginning on main scanning line 71 in the forward pass and the x-th spot from the end on main scanning line 72 in the backward pass can be approximately aligned.

[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. Therefore, 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 an aligned state 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 diagrammatically in Figure 16. The dashed lines in Figure 16 indicate the position in the main scanning direction of the xth spot from the start on main scanning line 71 on the outgoing pass, which is approximately at the position where it enters 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 pass, 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 return scans, it is possible to obtain an object image 81 that reflects the position and shape of object 80 with a resolution combining the scan lines in both directions.

[0079] On the other hand, when the drive frequency of the actuator 300 does not match the resonant frequency, the relationship between the scanning angle and the angular velocity differs between 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 do not match between each spot on the main scanning line 71 on the forward pass and each spot 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 performed, the positions in the main scanning direction of each spot on each main scanning line will generally match between the forward passes and between the return passes.

[0080] This state is shown diagrammatically 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 start 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 were to simply regard 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 would end up obtaining 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 the object image 81 in FIG.

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

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

[0083] Also, the x-th spot from the left on the n-th main scanning line in Fig. 15 is labeled S(n,x). The x-th spot from the left corresponds to the x-th spot from the beginning on the forward pass and the x-th spot from the end on the backward pass. Furthermore, a group G of spots S is indicated using the position of the spot located at the upper left corner within the group. For example, if the upper 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 each in the main scanning direction and the sub-scanning direction, totaling 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 light projection directions), then if there is an object in the direction of the light projection, the light will be incident on close positions on the object, and the TOF values ​​will 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 reflected light from the object should be detected at a timing common to all spots, time T equivalent to the TOF, after the timing of the light-on pulse of the LD drive signal. In each figure, this detection signal is shown by a pulse of the PD output. 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 regardless of 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. In addition, it is not possible to predict the timing at which the detection signal will be generated. In the examples of Fig. 19A to Fig. 19D, the disturbance light detection signal is output at a timing T1 after the lighting pulse in Fig. 19A, and at a timing T2 after the lighting pulse in Fig. 19B. In the examples of Fig. 19C and Fig. 19D, the disturbance light detection signal is not output.

[0088] 19A and 19B, the light receiving element 43 can detect a plurality of light receptions corresponding to one lighting pulse and output a corresponding detection signal. For example, the light receiving element 43 may be one that outputs a pulse as a detection signal when light (photons) is incident within a time range corresponding to a predetermined resolution, and outputs a flat signal indicating that no light is 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 tallies up the TOF values ​​corresponding to each spot in the group for each predetermined class.

[0090] Next, FIG. 20 shows an example of a compilation 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 need only 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 including T is 3, and the frequencies of the classes including T1 and T2 are each 1, as shown in Fig. 20. In this way, for the reflected light from the object, a common TOF is detected in multiple spots, so the frequency of that part is considered to be high.

[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 may be 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 therefore no object is detectable in that direction.

[0092] In addition, since there are cases where reflected light cannot be detected as shown in Fig. 19D, it is preferable to set the threshold value to a value smaller than the number of spots in the group. Since it can be considered that randomly incident disturbance light has been detected as a value of a low frequency class, it is preferable to set the threshold value to a value that is hardly reached by disturbance light. However, even if disturbance light is mistaken for reflected light from an object in a small number of groups as a result of adopting a small threshold, this usually does not have a significant effect on the overall composition of the object image.

[0093] The light projection direction of a group may be set to an average value of the light projection directions of the individual 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 up the light, it is possible to efficiently remove the detection signal derived from ambient light output by the light receiving element 43, and perform object detection that is less susceptible to the effects of ambient light.

[0094] The TOF classes used for counting may be the same as the resolution used for TOF measurement, or may be coarser than the resolution. If the classes are too fine, the TOFs of the reflected light from the object will be classified into different classes due to slight differences in the distance to the object for each spot, so it is preferable that the TOF classes are coarser than the resolution used for TOF measurement. In addition, 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] Also, instead of obtaining one TOF corresponding to a group, a TOF corresponding to each spot constituting a group, which is classified into a class having a frequency equal to or greater than a threshold value in the tabulation of Fig. 20, may be adopted as the TOF of reflected light from an object present in the projection direction of the spot. In this way, even when performing the tabulation of Fig. 20, the distance to the object can be obtained for each spot, not for each group. In this case, there are multiple projection directions corresponding to one group, but object detection is still performed based on the projection direction for each group and the frequency for each class obtained by tabulation.

[0096] Fig. 21 shows the configurations of the condenser lens 42, the light receiving element 43, and the aperture 44 of the light receiving section 40, and the optical path of the return light L4 in more detail than Fig. 1. 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. As described in the explanation of Fig. 1, in the light receiving unit 40, the return light L4 reflected by the mirror 41 is collected by the collecting lens 42 and collected on a focal plane 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 the collecting lens 42 can form, and the return light L4 passes through the opening. The return light L4 that passes through the aperture 44 is incident on the light receiving surface of the light receiving element 43 as a slightly broadened spot.

[0097] The SiPM used as the light receiving element 43 in this embodiment has an array of avalanche photodiodes (APDs) 43a operating in Geiger mode provided on the light receiving surface as shown in Fig. 22. The light receiving element 43 is disposed at a position where 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 guide the light incident on the mirror 31 to the light receiving element 43 along an optical path opposite to the projected outgoing light L2, so that after the mirror 41, the return light L4 can be made to be incident on the same position of the light receiving element 43 along the same optical path regardless of the projection direction of the outgoing light L2. Therefore, the return light L4 can always be detected by the entire array of the APD 43a, so that the return light L4 can be detected with sufficient sensitivity without using a particularly large array, and the size and cost of the light receiving element 43, and therefore the entire object detection device 10, can be reduced.

[0099] Each APD 43a can output a pulse signal in response to the incidence of one photon. The light receiving element 43 includes output signal lines 43b corresponding to each APD 43a, and outputs a signal obtained by adding up the output signals of all the output signal lines 43b as a detection signal 46 from the output signal line 43c. In the object detection device 10, since there is no need to change the range of the APD 43a to which the output signals are added according to scanning conditions such as the interval between scanning lines or spots, the scanning period, etc., 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 an arrangement of multiple groups. In the object detection device 10, the processor 53 compiles the TOFs for each spot in the group for each group as described above, and determines the distance to an object in the light projection direction of each group (or each spot in the group) based on the compilation results. 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 2x2 spot groups are set above, below, left, and right. 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 objects to be detected usually have projections and recesses, and are not directly facing the object detection device 10. For this reason, if the positions of the spots are far apart, there is a high possibility that the distance to the object will change. Therefore, it is preferable that each group is composed of spots whose projection directions are as close as possible. On the other hand, particularly when the amount of disturbance light is large, it is difficult to distinguish between the disturbance light and the reflected light from the object unless at least about four spots are grouped.

[0102] In this case, if a group is composed of only spots on the same main scanning line, for example, the interval between the spots on both ends will be large, which is inconvenient. Therefore, in this embodiment, as shown in Figures 18 and 23, the 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 in the forward main scanning and lights in the return main scanning following the forward main scanning.

[0103] 16 and 17, however, unless the drive frequency of the actuator 300 matches the resonant frequency, it is difficult to grasp which spot on the forward main scanning line 71 is adjacent 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 to match the drive frequency of the actuator 300 with the resonant frequency as described above before starting object detection, and object detection is performed after the match is confirmed. In other words, when the match is confirmed, the TOF counting result is used for object detection. If the agreement 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 forward scanning or backward scanning, 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 by 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, processor 53 starts the process 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 these in a state in which 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 by the method described with reference to Figures 6 to 14 so that it matches the resonant frequency of the actuator 300 (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 from the LD, the time difference (TOF) between the light emission timing and the subsequent light detection timing by 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 values ​​as described with reference to FIG. 20 (S16).

[0108] Thereafter, if there is a class for each group whose frequency is equal to or exceeds the threshold value, the representative value of that class is recorded as the TOF value of the reflected light 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). For example, this output is output for each group as a combination of the direction and the distance to the object corresponding to each group. In addition, as described above, it may be output as a combination of the direction and the distance to the object corresponding to each spot constituting the group. 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 the frequency of each class for each group when it is determined as Yes (match) in step S13. In other words, while it is No in step S13, not only are the light projection direction and the frequency of each class for each group not used for object detection, but object detection itself is not performed and the result is not output.

[0110] In the above process, step S12 is an adjustment procedure, step S13 is a judgment 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, the processor 53 functions as an adjustment unit, a judgment unit, a group creation unit, a counting unit, and an object detection unit, respectively. It should be noted that instead of creating and storing the groups in advance prior to step S15, it is also possible to prepare only the rules for creating groups in advance, and then after step S15, divide the lights into groups according to those rules and perform the tallying in step S16.

[0111] According to the embodiment described above, when detecting an object based on the timing of receiving reflected light while scanning a predetermined field of view with a pulsed laser light, it is possible to efficiently eliminate the influence of disturbance light and perform accurate object detection with the small object detection device 10. Furthermore, the processing required for this is not particularly complicated, and it is possible to reduce 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 few false detections when attempting to detect an object outdoors in the direction of the sun, but in other cases was able to properly eliminate the effects of external light and detect objects.

[0112] 5. First to Fourth Modifications (FIGS. 25 to 28) Next, first to fourth modified examples of the above-mentioned embodiment will be described. These modified examples differ from the above-mentioned 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 common to or corresponding to the above-mentioned embodiment. This point is also the same for the other modified examples.

[0113] 25 to 28 respectively show examples of setting the spot groups according to the first to fourth modified examples. In these figures, the reference numerals for each main scanning line are 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, which is the same as in Fig. 23. In this example, group G(n, x+1) is provided on the right side of group G(n, x) at a position shifted by one spot. Therefore, spots S(n, x+1) and S(n+1, x+1) are included in both of these groups. Similarly, group G(n+2, x+1) is provided on the right side of group G(n+2, x) at a position 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, which is the same as in Figs. 23 and 25. In this example, group G(n+1, x) is provided below group G(n, x) at a position shifted by one spot (one main scanning line). Therefore, spots S(n+1, x) and S(n+1, x+1) are included in both of these groups. Similarly, group G(n+1, x+2) is provided below group G(n, x+2) at a position shifted by one spot.

[0115] When outputting information on the direction and distance of an object for each group, if the groups are arranged so that they do not overlap as in FIG. 23, the resolution of object detection will decrease by the number of spots in one group. However, if the groups are arranged so that they overlap as in FIG. 25 and FIG. 26, the decrease in resolution can be prevented. Of course, the groups may be set so that the ranges of the groups overlap in both the main scanning direction and the sub-scanning direction. For example, for all spots except the rightmost and bottommost spots, 2×2 spot groups are set so that the relevant spots are located at the upper left corner. In this way, object detection can be performed without decreasing the resolution and excluding 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. Since the ranges of each group do not overlap, the group G(n,x) is adjacent to the right of group G(n,x+3), and the groups below them are group G(n+3,x) and group G(n+3,x+3). In this way, by increasing the number of spots in one group, even if the amount of light of the return light L4 is smaller than that of the disturbance light, a higher frequency can be obtained for the return light L4 having approximately the same TOF when counting in Fig. 20 compared to the disturbance light that is randomly incident. Therefore, the TOF of the return light L4 can be identified with high accuracy.

[0117] In the fourth modified example, as shown in Fig. 28, spots located two main scanning lines apart are grouped into one group. This is because a group is made up of only spots on the main scanning line on the forward pass and only spots on the main scanning line on the return pass. That is, in the example of FIG. 28, two spots on the forward main scanning line 71-n and the nearest other forward main scanning line 71-(n+2) are grouped as group G(n,x). Also, 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 omitted for convenience of illustration, a group G(n+1,x) is set at a position shifted one spot downward from the group G(n,x) and adjacent to the left side of the group G(n+1,x+2). Similarly, a group G(n,x+2) is set at a position shifted one spot upward from the group G(n+1,x+2) and adjacent to the right side of the group G(n,x).

[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 includes spots that are included in different main scanning passes. Although this is inferior to the example in Figure 23 in terms of the light projection directions of each spot in a group being 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 external light in the same way as in the above-mentioned embodiment.

[0119] Furthermore, by forming a group from only the spots on the forward main scanning lines and only the spots on the backward main scanning lines in this way, even if the drive frequency of the actuator 300 does not match the resonant frequency, the tallying in Fig. 20 can be performed without any problems. This is because even in this state, the positions in the main scanning direction of the spots on each main scanning line are aligned as long as they are aligned with the forward main scanning lines and the backward main scanning lines.

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

[0121] FIG. 29 is a flowchart of a process corresponding to FIG. 24, which is executed by the processor 53 in the fifth modified example of the present invention. 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, the processor 53 determines whether the drive frequency of the actuator 300 matches the resonant frequency (S38). If they match, the processor 53 calculates and outputs the direction of the detected object and the distance to the object based on the TOF values ​​of each group on both the forward and backward routes (S39). If they do not match, the processor 53 calculates and outputs the direction of the detected object and the distance to the object based on the TOF values ​​of each group on either the forward or backward route (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, the reason why only one of the forward and return passes is used in step S40 is that, as explained using FIG. 17, in this state, the object detection results based on the main scanning lines of the forward pass and the object detection results based on the main scanning lines of the return pass show different object images. However, by performing the above processing, it is possible to perform object detection without adjusting the drive frequency of actuator 300 to the resonant frequency, or before the adjustment is completed, with accuracy lower than that of the above-mentioned embodiment, while eliminating the effects of ambient light.

[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 possible to perform the process of Fig. 29 at startup, and after the drive frequency of the actuator 300 matches the resonant frequency, to reset the group and move to the process of Fig. 24. Also in the above 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 return 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 lines on the forward pass and only the spots on the main scanning lines on the backward pass, and the process in FIG. 29 can be applied. When performing the process 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 a 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 the driving frequency is adjusted 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 portion 66.

[0131] When a two-dimensional field of view is not required, even in an object detection device 10 that does not scan 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 a manner similar to that of 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 a forward scan followed by a return scan, and if the drive frequency of actuator 300 matches the resonant frequency, the main scanning direction positions of each spot will 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 further Fig. 30, and execute the processes in Fig. 24 and Fig. 29. The scanning lines shown in these figures can be regarded as scanning lines that scan the same position at different scanning timings, such as the nth time, the n+1th time, etc. Furthermore, when 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 variations 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 be different depending on the position in the sub-scanning direction.

[0134] In Figure 32, group G(n, x) and group G(n, x+2) are set on the nth and n+1th main scanning lines, while group G(n+2, x+1) and group G(n+2, x+3) are set on the n+2nd and n+3rd main scanning lines, shifted one spot in the main scanning direction from these groups. Even if 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 modified examples.

[0135] In the above embodiment, the example in which object detection itself is not performed when the drive frequency does not match the resonant frequency has been described with reference to FIG. 24, but this is not essential. Fig. 33 shows a flowchart of the process executed by processor 53 in this modified example, which corresponds to Fig. 24. In Fig. 33, the same processes as in Fig. 24 are given the same step numbers, and the description of these processes 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 actuator 300 to the resonant frequency. Then, steps S14 and S15 are executed without going through the determination of step S13, and after step S15, a determination is made (SA) as to whether or not the drive frequency of the actuator 300 coincides with the resonant frequency, similar to step S13. If Yes, the processes from step S16 onwards are carried out as in the case of Fig. 24. If No in step SA, the groups are not used, and the direction of the detected object and the distance to the object are calculated and output based on each emission (spot) and the corresponding TOF value.

[0137] That is, unlike the case of Fig. 24, even if the drive frequency does not match the resonant frequency, object detection itself is performed and the result is output. In the case where step SB is executed, since no group is used, the effect of eliminating the influence of disturbance light cannot be obtained, but in a dark environment with little disturbance light itself, the accuracy of object detection may not be affected very much. Therefore, this modified example is useful when you want to shorten the time from starting up the object detection device to detecting an object, even if you are willing to accept the risk of the influence of disturbance light at first. As in the case of FIG. 29, when the drive frequency does not match the resonant frequency, object detection may be performed based on the TOF value corresponding to the emission of light on one of the scanning lines on the forward or backward path.

[0138] Also, an actuator using a magnetic spring can be used as the actuator responsible for scanning in the main scanning direction. FIG. 34 shows an example of the configuration of a scanning unit 30 using such an actuator 400. 34, a mirror 401 is fixed to a permanent magnet 410, and the permanent magnet 410 is held by bearings 403 and 405. The permanent magnet 410 and the mirror 401 rotate together around a rotation axis 404 passing through the center of the permanent magnet 410 in response to the voltage applied to the coil due to 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, and 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 possible to use, for example, 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 the processor 53 performs the process of calculating the direction of an object and the distance to the object. However, the 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 result to an external device via the input / output unit 54, and the external device may set groups, tally up the TOFs, calculate the direction of an object and the distance to the object based on the tally results for each group, and graphically display the object image based on the above. In this case, the object detection system is composed of the object detection device 10 and the external device.

[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 embodiment. 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 for causing one computer, or multiple computers working in cooperation, to control the required hardware and realize some or all of the functions relating to the drive frequency adjustment and elimination of the effects of ambient light described above, or for executing 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 recording 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 and installed on a computer to be 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 inconsistent, 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 projection unit, 21... LD module, 22... laser driving circuit, 23... light projection 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, 66... ​​reflecting unit, 66a... effective reflector Shooting area, 70...field of view, 71, 72...scanning line, 73...beam spot, 80...object, 81 to 83...object image, 300, 380, 400...actuator, 301...mirror unit, 302...torsion spring, 304, 404...rotation axis, 316...driving 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...return 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.

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