Design and operation of a light-based distance measuring device

Abstract

The present invention relates to an optical-based ranging device (500), the optical-based ranging device (500) comprising a light source (502), a light detector (504), a reflector (506) and a drive unit (508). The light source is configured to illuminate an object (510) using one or more light beams. The light detector is configured to detect the one or more light beams reflected from the object. The reflector has a symmetric main axis (512) and comprises at least three reflecting surfaces around the symmetric main axis. Each of the at least three reflecting surfaces is configured to first reflect each of the one or more light beams to the object and then to the light detector. The drive unit is configured to rotate the reflector about a rotation axis (514). The rotation axis is inclined at a non-zero inclination angle with respect to the symmetric main axis. The non-zero inclination angle is defined such that the one or more light beams are reflected by each of the at least three reflecting surfaces in at least a partially divergent direction towards the object. By using this configuration of the optical-based ranging device, the misalignment between the symmetric main axis of the reflector and the rotation axis of the reflector can be utilized, since the misalignment provides a divergent direction of the light beams from each of the at least three reflecting surfaces, thereby increasing the total number of scan points.

Description

Technical Field

[0001] The present invention relates to the technical field of light detection and ranging, and more particularly to a light-based ranging device capable of scanning a target object using pulsed or continuous light beams, a device for controlling the light-based ranging device, a method for operating the light-based ranging device, and a computer program product for implementing the method at the software level. Background Art

[0002] Light Detection And Ranging (LiDAR) devices are designed to measure the distance to a target object by illuminating the target object with a laser beam and measuring the time it takes for the laser beam to reach the target object and return. LiDAR devices can be used to scan buildings, rock formations, the ground, etc. to generate corresponding three-dimensional (3D) models. There are mainly two types of LiDAR devices, both based on the use of laser beams. The first type of LiDAR device uses a single laser beam for a single measurement. The second type of LiDAR device is used to scan a specific field-of-view (FOV) and measure multiple points within the FOV.

[0003] More specifically, the second type of LiDAR device can be used to generate a single laser beam, which is then reflected by a rotating mirror in several different directions. The Time-of-Flight (ToF) for each direction is calculated by a laser detector, enabling the scanning of the entire scene. An optical prism can be used instead of the rotating mirror, and the optical prism relies on light refraction to redirect the laser beam. However, such LiDAR devices only allow scanning along a single line (i.e., within a single plane).

[0004] The second type of LiDAR device can also be used to generate several laser beams (instead of just one), and each laser beam is reflected by a rotating mirror in several different directions to scan the entire FOV of the LiDAR device. Each laser beam is detected by an independent laser detector to calculate its ToF value. By using several laser beams, several distances can be measured simultaneously. However, the total number of scanned points is equal to the product of the number of laser beams and the number of different mirror positions, and this total number may not be sufficient for some applications. In some cases, a small spatial interval between the laser beams is required, which can only be achieved by increasing the number of laser beams (resulting in increased power consumption) or by restricting the FOV to be scanned. Additionally, for each scanned point, there should be a laser detector that is used to detect the corresponding laser beam reflected from the target object.

[0005] A rotating rectangular parallelepiped can be used instead of a rotating mirror. The rotating rectangular parallelepiped has four side faces, each side face being parallel to the symmetric main axis of the parallelepiped, and each side face is provided with a mirror for reflecting a laser beam. However, the axis of rotation about which the parallelepiped rotates needs to be very precisely aligned with the symmetric main axis of the parallelepiped. If any (even slight) misalignment occurs, the mirror will produce a certain swing in the vertical direction, causing the laser beam to be reflected by each mirror in a different way. This in turn will increase the necessary number of laser detectors and complicate their placement in the case of slight misalignment. Summary of the Invention

[0006] The present invention content is provided to introduce some concepts further described in the following detailed description in a simplified form. The present invention content is not intended to identify the key features or essential features of the present invention, nor is it intended to limit the scope of the present invention.

[0007] The object of the present invention is to provide a technical solution that can increase the number of scanning points and simplify the arrangement of optical detectors. Another object of the present invention is to enable the number of scanning points to be changed according to a specific application.

[0008] The above object is achieved by the features of the independent claims in the appended claims. Further embodiments and examples are obvious from the dependent claims, the detailed description, and the drawings.

[0009] According to a first aspect, there is provided an optical ranging device, the optical ranging device comprising a light source, an optical detector, a reflector, and a drive unit. The light source is configured to illuminate an object using one or more light beams. The optical detector is configured to detect the one or more light beams reflected from the object. The reflector has a symmetric main axis and comprises at least three reflecting surfaces around the symmetric main axis. Each of the at least three reflecting surfaces is configured to first reflect each of the one or more light beams to the object and then to the optical detector. The drive unit is configured to rotate the reflector about an axis of rotation. The axis of rotation is inclined at a non-zero inclination angle with respect to the symmetric main axis. The non-zero inclination angle is defined such that the one or more light beams are reflected by each of the at least three reflecting surfaces in at least a partially divergent direction to the object. By using this configuration of the optical ranging device, the misalignment between the symmetric main axis of the reflector and the axis of rotation of the reflector can be utilized, since the misalignment provides at least a partially divergent direction of the light beams from each of the at least three reflecting surfaces, thereby increasing the total number of scanning points.

[0010] In an embodiment of the first aspect, the light-based ranging device serves as a LiDAR device. In this embodiment, the light source is used to illuminate the object with the light beam that is a pulsed laser, and the light detector is used to detect the pulsed laser reflected from the object. This can make the light-based ranging device more flexible in use.

[0011] In an embodiment of the first aspect, the light source is used to illuminate the object with the light beam that is a single fan-shaped beam. This can provide higher flexibility for the configuration of the light-based ranging device. Specifically, if the fan-shaped beam is used instead of a discrete number of beams, it is not necessary to have an independent light detector for each of the light beams reflected from the object.

[0012] In an embodiment of the first aspect, if the fan-shaped beam is used, the light detector includes an array of discrete detector elements. Each of the discrete detector elements is time-division multiplexed with respect to the fan-shaped beam reflected from the at least three reflecting surfaces. In this embodiment, for each detector element, each of the at least three reflecting surfaces of the reflector produces a light detection from a different position, and the information about which of the at least three reflecting surfaces is used is used to construct the final spatial position of all the light detections.

[0013] In an embodiment of the first aspect, the light source is used to illuminate the object with a discrete number of the light beams. This can make the light-based ranging device more flexible in use.

[0014] In an embodiment of the first aspect, if the discrete light beams are used, the light detector includes an array of discrete detector elements. Each of the discrete detector elements is used to detect one of the discrete number of the light beams from the object. This can provide higher flexibility for the design of the light detector.

[0015] In an embodiment of the first aspect, the tilt angle is also defined based on the desired spatial resolution of the light detector. In this way, the tilt angle can be selected such that it is not necessary to reconfigure the light detector in any way.

[0016] In an embodiment of the first aspect, the at least three reflecting surfaces are parallel to the symmetric main axis of the reflector. This embodiment can provide higher flexibility for the design of the reflector used in the light-based ranging device. For example, the reflector can be used to have a prism-like shape.

[0017] In another embodiment of the first aspect, each of the at least three reflecting surfaces forms a different or the same angle with the symmetric main axis of the reflector. This embodiment can provide higher flexibility in the design and manufacture of the reflector used in the light-based ranging device. For example, the reflector can be implemented as a truncated pyramid.

[0018] In one embodiment of the first aspect, the light detector includes at least one single-photon avalanche diode (SPAD) detector. This can provide higher flexibility in the design and manufacture of the light detector used in the light-based ranging device.

[0019] In one embodiment of the first aspect, each of the at least three reflecting surfaces of the reflector is made reflective using one of the following techniques: mirror polishing; applying a mirror coating thereon; or attaching a mirror thereto. This can provide higher flexibility in the design and manufacture of the reflector.

[0020] According to a second aspect, there is provided a device for controlling the light-based ranging device according to the first aspect. The device includes at least one processor and a memory coupled to the at least one processor and storing processor-executable instructions. When the processor-executable instructions are executed by the at least one processor, the at least one processor is caused to perform the following operations:

[0021] - Define the non-zero tilt angle between the symmetric main axis and the rotation axis such that the one or more light beams are reflected by each of the at least three reflecting surfaces of the reflector in at least a partially divergent direction towards the object;

[0022] - Cause the drive unit to rotate the reflector about the rotation axis, the rotation axis being tilted by the non-zero tilt angle with respect to the symmetric main axis.

[0023] With this device, the tilt angle between the symmetric main axis and the rotation axis can be changed according to a specific application.

[0024] In one embodiment of the second aspect, the at least one processor is further instructed to perform the following operations:

[0025] - In the case where a sparse scan resolution is required, cause the light source to illuminate the object only when one of the at least three reflecting surfaces of the reflector is in a desired rotational position;

[0026] - In cases where a high scanning resolution is required, illuminate the object with the light source for all of the at least three reflecting surfaces of the reflector.

[0027] In this way, the number of scanning points can be changed programmatically. If a very sparse scan of the object is sufficient, drive the light source such that the light source is only turned on when a corresponding one of the at least three reflecting surfaces is in a desired rotational position, thereby reducing power consumption. For example, the sparse scan resolution may be required to detect changes in the target object or scene. Once some changes in the target object or scene are detected, the light source can be switched to a dense scan mode, in which the laser beam is generated for all of the at least three reflecting surfaces of the rotating reflector.

[0028] According to a third aspect, there is provided a method for operating an optical ranging device according to the first aspect. The method includes the following steps:

[0029] - Activate a sparse scan mode, in which the light source illuminates the object only when one of the at least three reflecting surfaces of the reflector is in a desired rotational position;

[0030] - Activate a dense scan mode, in which the light source illuminates the object for all of the at least three reflecting surfaces of the reflector.

[0031] In this way, the number of scanning points can be changed programmatically. By default, the sparse scan mode can be activated first. For example, the sparse scan mode can be used to detect changes in the target object or scene. Once some changes in the target object or scene are detected, the sparse scan mode can be changed to the dense scan mode, in which the laser beam is generated for all of the at least three reflecting surfaces of the rotating reflector. This can simplify the implementation of the method according to the third aspect, for example, in the device according to the second aspect.

[0032] According to a fourth aspect, there is provided a computer program product including a computer-readable medium storing executable code. The executable code, when executed by at least one processor, causes the at least one processor to perform the method according to the third aspect. This can simplify the implementation of the method according to the third aspect on any computing device (e.g., the device according to the second aspect).

[0033] Other features and advantages of the present invention will be apparent by reading the following detailed description and reviewing the drawings. Description of the Drawings

[0034] The essence of the present invention will be described below in conjunction with the accompanying drawings, where:

[0035] Figure 1 Schematically shows a conventional LiDAR device capable of scanning a specific FOV and providing multiple scan points;

[0036] Figure 2 Schematically shows another conventional LiDAR device capable of scanning the entire FOV and providing multiple scan points;

[0037] Figure 3 Schematically shows the various parts of a conventional LiDAR device responsible for generating a laser beam and redirecting it towards a target object;

[0038] Figure 4 Schematically shows the appearance of misalignment between the axis of rotation of a rectangular parallelepiped and the main axis of symmetry of the rectangular parallelepiped;

[0039] Figure 5 Schematically shows an optical ranging device provided by an exemplary embodiment of the present invention;

[0040] Figure 6 Shows an illustration of how to define Figure 5 A schematic diagram showing the appropriate inclination angle θ between the main axis of symmetry of a reflector included in the shown device and the axis of rotation of the reflector;

[0041] Figure 7A and Figure 7B Schematically shows how to use Figure 5 The detector element array of the photodetector included in the shown device to collect different discrete light beams reflected by a target object;

[0042] Figures 8A to 8C Schematically shows how to use Figure 5 The detector element array of the photodetector included in the shown device to collect a fan-shaped light beam emitted by a light source and subsequently reflected by a target object;

[0043] Figure 9 Schematically shows a flowchart of a method for operating Figure 5 The optical ranging device shown in the above;

[0044] Figure 10 Schematically shows a device for controlling Figure 5 The optical ranging device shown in the above. Detailed implementation

[0045] Various embodiments of the present invention are described in further detail with reference to the accompanying drawings. However, the present invention can be embodied in many other forms and should not be construed as limited to any specific structure or function disclosed in the following description. Instead, these embodiments are provided to make the description of the present invention detailed and complete.

[0046] From the detailed description, it will be apparent to those skilled in the art that the scope of the present invention includes any embodiment of the present invention disclosed herein, whether the embodiment is implemented independently or in cooperation with any other embodiment of the present invention. For example, in practice, the devices, apparatuses, and methods disclosed herein can be implemented using any number of the embodiments provided herein. In addition, it should be understood that any embodiment of the present invention can be implemented using one or more elements or steps set forth in the appended claims.

[0047] As used herein, the term "exemplary" means "serving as an illustration". Unless otherwise specified, any embodiment described herein as "exemplary" should not be construed as being preferred or having advantages over other embodiments.

[0048] According to the exemplary embodiments disclosed herein, a light-based ranging device can refer to any ranging device that is configured to perform light-based scanning relative to an associated object or scene in the presence of misalignment between the axis of rotation of a reflector included in the device and the principal axis of symmetry of the reflector. The light-based ranging device can be implemented as a LiDAR device. However, the present invention is not limited to this example of implementation, and any other device developed in the future based on this misalignment operation should be understood to fall within the scope of the present invention.

[0049] In the embodiments disclosed herein, the principal axis of symmetry can refer to an axis about which a 360° / n (or 2π / n) rotation results in the same geometric body before and after rotation. The principal axis of symmetry can also be referred to as the main axis of symmetry.

[0050] Figure 1 A conventional LiDAR device 100 that is capable of scanning a specific FOV and providing a plurality of scan points is schematically illustrated. To this end, the LiDAR device 100 includes a laser source 102, a detector 104, and a rotating mirror 106. The laser source 102 is configured to generate a single laser beam that is reflected by the rotating mirror 106 to a target object 108 (see the solid-line arrow in Figure 1 . The rotating mirror 106 is rotated about an axis of rotation 110 by a drive unit (not shown in Figure 1 ) to provide reflections of the single laser beam in different directions. After being reflected from the target object 108, the laser beam hits the rotating mirror 106 again, but is now reflected to the detector 104 disposed near the laser source 102 (see Figure 1(dashed lines in). The detector 104 is used to calculate the ToF value in each direction. Based on the ToF value, the distance to the target object 108 can be calculated and / or a visual model of the target object 108 can be obtained. An optical prism can be used instead of the rotating mirror 106, and the optical prism relies on light refraction to redirect the single laser beam. However, a disadvantage of the LiDAR device 100 is that the reflection of the single laser beam is only performed in one (horizontal) plane.

[0051] To eliminate the above disadvantages, the rotating mirror 106 can also be rotated / tilted vertically, which enables scanning to be performed in another (vertical) plane parallel to the scanning in the horizontal plane. However, the rotation / tilt of the rotating mirror 106 around another axis is difficult to achieve. In addition, although horizontal and vertical scanning can be performed, this also requires more complex mechanics to be considered in the design of the LiDAR device 100 (usually implemented using microelectromechanical system (MEMS) mirrors). As discussed below in conjunction with Figure 2 To reduce the mechanical complexity of the device design and still be able to perform scanning in the horizontal and vertical planes, a set of laser beams can be used.

[0052] More specifically, Figure 2 Another conventional LiDAR device 200 that can scan the entire FOV and provide multiple scan points is schematically shown. For this purpose, the LiDAR device 200 includes a laser source 202, a detector 204, and a rotating mirror 206. The laser source 202 is used to generate a number of laser beams that are reflected by the rotating mirror 206 onto the target object 208 (see Figure 2 the solid arrows in). Similar to the rotating mirror 106, the rotating mirror 206 is rotated around the rotation axis 210 by a drive unit ( Figure 2 not shown in) to provide the reflection of each laser beam in a different direction. Therefore, the vertical scanning of the target object 208 is provided by the number of laser beams, and the horizontal scanning of the target object 208 is provided by the rotation of the rotating mirror 206 around the rotation axis 210. After being reflected from the target object 208, the laser beams hit the rotating mirror 206 again, but are now reflected onto the detector 204 arranged near the laser source 202 (see Figure 2(the dashed lines in ). However, the total number of scanning points is equal to the product of the number of laser beams and the number of different mirror positions, and this total number may not be sufficient for some applications. In some cases, a smaller spatial interval between the laser beams emitted by the laser source 202 is required, which can only be achieved by increasing the number of laser beams (resulting in an increase in the power consumption of the laser source 202) or by restricting the FOV to be scanned. In addition, for each scanning point, there should be a detector element for detecting the corresponding laser beam reflected from the target object 208. In other words, the design of the detector 204 becomes more complex.

[0053] Figure 3 Schematically shows the parts of a conventional LiDAR device responsible for generating laser beams and redirecting them to the target object. As shown, this part includes a laser source 302 and a rotating rectangular parallelepiped 304, and the rectangular parallelepiped 304 is rotated around the rotation axis 306 by a drive unit ( Figure 3 not shown in ). There are four mirrors ( Figure 3 not shown in ), each mirror being placed on one of the sides of the rectangular parallelepiped 304, and the side is parallel to its symmetric main axis that coincides with the rotation axis 306. When the rectangular parallelepiped 304 rotates, the laser beam from the laser source 302 is only effective for a certain period of time, so that each mirror scans the entire horizontal FOV. For example, if the rectangular parallelepiped 304 rotates completely around the rotation axis 306 once per second, the horizontal FOV will be scanned four times per second. However, this type of LiDAR device requires the rotation axis 306 to be aligned very precisely with the symmetric main axis of the rectangular parallelepiped 304.

[0054] Figure 4 Schematically shows the appearance of the misalignment between the rotation axis 306 of the rectangular parallelepiped 304 and the symmetric main axis 402 of the rectangular parallelepiped 304. In this case, the four mirrors will produce a certain swing in the vertical direction, resulting in each laser beam being reflected in a different way by each of the four mirrors. This in turn increases the necessary number of laser detectors and makes it difficult to achieve their arrangement in the case of slight misalignment.

[0055] Although the symmetric main axis of the rectangular parallelepiped 304 coincides with its rotation axis (see Figure 3 and Figure 4)A slight misalignment between them will have an adverse impact on the design and operation of existing LiDAR devices (since more detector elements should be utilized and it is difficult to achieve their precise arrangement), but the authors of this article have found that such misalignment can be advantageously used to increase the number of scanning points. Specifically, according to the present invention, the inclination angle between the rotation axis of the reflector (e.g., the rectangular parallelepiped 304) and the main symmetry axis of the reflector is selected such that the laser beam is reflected from the corresponding reflecting surface of the reflector in at least a partially divergent direction, thereby (doubling) increasing the number of the scanning points.

[0056] Figure 5 Schematically shows a light-based ranging device 500 provided by an exemplary embodiment of the present invention. The light-based ranging device 500 includes a light source 502, a light detector 504, a reflector 506, and a driving unit 508. The light source 502 is used to illuminate a target object 510 with one or more light beams (see Figure 5 the thin solid arrows in, for the sake of Figure 5 avoiding overload, only one light beam is shown). The light detector 504 is used to detect one or more light beams reflected from the object 510. The reflector 506 has a main symmetry axis 512 and includes reflecting surfaces around the main symmetry axis 512. Each of the reflecting surfaces is used to first reflect each of the one or more light beams to the object 510 and then to the light detector 504. The driving unit 508 is used to rotate the reflector 506 around a rotation axis 514 (schematically shown by Figure 5 the thick solid arrow in). The rotation axis 514 is inclined at a non-zero inclination angle θ with respect to the main symmetry axis 512. The non-zero inclination angle θ is defined such that the one or more light beams are reflected by each of the reflecting surfaces to the object 510 in at least a partially divergent direction. By using this configuration of the light-based ranging device 500, the misalignment between the main symmetry axis 512 of the reflector 506 and the rotation axis 514 of the reflector 506 can be utilized because the misalignment provides at least a partially divergent direction of the light beams from each of the reflecting surfaces, thereby increasing the total number of scanning points.

[0057] The light source 502 can be implemented as a laser source, and correspondingly, the entire light-based ranging device 500 can be implemented as a LiDAR device. In addition, the light source 502 can be used to generate one or more light beams as laser pulses, each laser pulse having a frequency between 100 kHz and 5 MHz, a pulse width between 0.1 ns and 2 ns, and a pulse power between 2 W and 50 W. It should be obvious to those skilled in the art that the exact parameters (including the beam shape) of the light beams generated by the light source 502 vary according to specific applications.

[0058] As discussed above, the photodetector 504 is used to detect the light beam reflected from the object 510 and perform necessary distance calculations based on the ToF value. The photodetector 504 may include an array of discrete detector elements, and each detector element may be implemented based on at least one single-photon avalanche diode (SPAD). In addition, it should be noted that if the light beam is generated by the light source 502 as a discrete number of light beams, each of such discrete detector elements may be used to detect one of the light beams from the object 510; or, if the light beam is generated by the light source 502 as a single fan-shaped light beam, time-division multiplexing is performed with respect to the light beam from the object 510. The time-division multiplexing of the detector elements means that for each detector element, different reflecting surfaces of the reflector 506 generate light detections from different positions according to the used reflecting surface and the information about the used reflecting surface, and then can be used to construct the final spatial position of the object 510.

[0059] The reflector 506 may be made of any material that is hard enough so that the shape of the reflector 506 does not change under inertial forces during the rotation of the reflector 506 around the rotation axis 514. Some examples of such materials include metals, plastic glasses, etc. Regarding the reflecting surface of the reflector 506, one of the following techniques may be used to achieve light reflection: mirror polishing; applying a mirror coating thereon; or attaching a mirror thereto.

[0060] Although the reflector 506 is shown in Figure 5 the form of a rectangular parallelepiped having four (side) reflecting surfaces around the symmetric main axis 512, this shape is only used as a possible example and should not be regarded as any limitation of the present invention. In other exemplary embodiments, the number of the reflecting surfaces may be reduced to three, and thus, the reflector 506 may be implemented as a triangular prism; or, it may be increased to five or more, and thus, the reflector 506 may be implemented as a polygonal prism (for example, if the number of the reflecting surfaces is set to five, it is implemented as a pentagonal prism). In addition, in some other exemplary embodiments, the reflecting surfaces of the reflector 506 may not be parallel to the symmetric main axis 512, but each reflecting surface is inclined at a different or the same angle with respect to the symmetric main axis 512. This allows other geometric shapes to be used for the reflector 506, for example, as a truncated pyramid.

[0061] The driving unit 508 may be implemented in various ways. For example, the driving unit 508 may be implemented as a mechanical rotation mechanism, an electromagnetic driver, etc. The driving unit 508 may be programmed to rotate the reflector 506 around the rotation axis 514 in the clockwise or counterclockwise direction according to a specific application. For example, the rotational speed may vary within 50 - 2000 revolutions per minute, but is not limited to this exemplary numerical range.

[0062] As described above, the tilt angle θ can be defined to provide a direction in which at least a portion of the light beams reflected by each of the reflecting surfaces diverges. As will now be described in conjunction with Figure 6 what is discussed, the tilt angle θ can also be defined based on the desired spatial resolution of the light detector 504. For simplicity, Figure 6 only one light beam is referred to. Due to the tilt / misalignment between the symmetric main axis 512 and the rotation axis 514, the displacement of this light beam is represented as α. Now it is required that at a certain distance z from the light-based ranging device 500, the offset of the light beam is equal to Δ. Then, the displacement angle α can be calculated as follows: According to Figure 6 the schematic diagram shown, by adjusting the parameters α and z, the appropriate tilt angle θ that is most suitable for the target application and requirements can be selected. Alternatively, different ray-tracing software tools can be used to model the spatial distribution of the light beam at different tilt angles θ. For example, the tilt angle θ can be set to be greater than 1°.

[0063] Figure 7A and Figure 7B schematically show how to use the detector element array that constitutes the light detector 504 included in the light-based ranging device 500 to collect different discrete light beams reflected by the object 510. Specifically, Figure 7A shows the case of precise alignment between the symmetric main axis 512 and the rotation axis 514 of the reflector 506. It can be seen that, ideally, each light beam is captured by one detector element regardless of the position of the reflecting surface of the reflector 506. Figure 7B shows the case where the rotation axis 514 does not coincide with the symmetric main axis 512, that is, the case of misalignment represented by a non-zero tilt angle θ. As Figure 7B shown, the light beams at different positions of the reflecting surface of the reflector 506 do not hit the same detector element. Therefore, from Figure 7A and Figure 7B it can be seen that in the case of a non-zero tilt angle θ, the number of the detector elements should be increased, and this can be achieved, for example, by using a 2D array of detector elements. In addition, the size of the 2D array of the detector elements depends on the position of the received light beam. Therefore, the tilt angle θ between the rotation axis 514 and the symmetric main axis 512 can be selected such that the additional number of the detector elements to be added to the light detector 504 is considered. At the same time, some detector elements can collect light from two or more different light beams corresponding to several positions of the reflecting surface (as Figure 7B shown). In this case, when a detector element is activated, it is necessary to know the position where the reflector 506 is located in order to assign the correct direction in space to the corresponding scanned point cloud. This can be referred to as time-division multiplexing of the detector elements.

[0064] Figures 8A to 8C Schematically shows how to use an array of detector elements that make up a photodetector 504 included in a light-based ranging device 500 to collect a fan beam emitted by a light source 502 and subsequently reflected by an object 510. Then, splitting of the fan beam is performed on the detector side, where each detector element collects light from its own direction. In this case, the misalignment (tilt angle θ) between the symmetric main axis 512 and the rotation axis 514 should ensure that the fan beam is generated in the correct direction. Using the fan beam provides higher flexibility in the design of the device 500. In fact, if the fan beam is used instead of a discrete number of beams, for each generated beam, there is no need to have an independent detector element (as Figure 7A and Figure 7B shown). Thus, the photodetector 504 determines the resolution of the entire system (i.e., the number of scan points in the scanned point cloud). In addition, using the fan beam does not require designing and using a very complex beam splitter for the light source 502.

[0065] More specifically, Figure 8A shows a case of precise alignment between the symmetric main axis 512 and the rotation axis 514. Figure 8B shows a case where the rotation axis 514 does not coincide with the symmetric main axis 512, and the photodetector 504 is formed by a larger number of detector elements compared to Figure 8A shown (i.e., using more than 15 detector elements). Figure 8C shows a case where the rotation axis 514 does not coincide with the symmetric main axis 512, but the photodetector 504 is formed by the same number of detector elements as Figure 8A shown (i.e., also using 15 detector elements). Thus, in the case of using the fan beam, it is possible to select detector elements having the same number as in the case of precise alignment but arranged in a 2D array, or having a different number of detector elements from the case of precise alignment.

[0066] Figure 9A flowchart of a method 900 for operating a light-based ranging device 500 provided by an exemplary embodiment of the present invention is schematically shown. Specifically, the method 900 includes two steps S902 and S904, each step corresponding to a specific operation mode of the device 500. Step S902 corresponds to a sparse scan mode, in which the light source 502 is used to illuminate the object 510 only when one of the reflective surfaces of the reflector 506 is in a desired rotational position. Step S904 corresponds to a dense scan mode, in which the light source 502 is used to illuminate the object 510 for all of the reflective surfaces of the reflector. Using the two operation modes, the number of scan points can be changed according to a specific application. In an exemplary embodiment, by default, i.e., when the device 500 is turned on, the sparse scan mode (i.e., step S902) can be activated first. For example, the sparse scan mode can be used to detect changes in the object 510. Once the photodetector 504 detects some changes in the object 500, the sparse scan mode can be changed to the dense scan mode, i.e., the method 900 proceeds to step S904, in which laser beams are generated for all of the reflective surfaces of the rotating reflector 506. In another exemplary embodiment, step 902 can be omitted, and once the device 500 is turned on, the light source 502 is used to generate the beams for all of the reflective surfaces of the reflector 506.

[0067] Figure 10 A device 1000 for controlling a light-based ranging device 500 provided by an exemplary embodiment of the present invention is schematically shown. The device 1000 includes a processor 1002 and a memory 1004, and the memory 1004 is coupled to the processor 1002. The memory 1004 stores processor-executable instructions 1006, which, when executed by the processor 1002, cause the processor 1002 to perform control operations on the device 500. It should be noted that Figure 10 the number, arrangement, and interconnection of the structural elements constituting the device 1000 shown are not intended to limit the present invention, but merely to provide a general idea of how the structural elements are implemented within the device 1000. For example, if the device 1000 is implemented as a single device, it may also include a transceiver device (not shown) for performing different operations required to transmit the corresponding control information to the light-based ranging device 500.

[0068] The processor 1002 can be implemented as a central processing unit (CPU), a general-purpose processor, a special-purpose processor, a microcontroller, a microprocessor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a complex programmable logic device, etc. It should be noted that the processor 1002 can be implemented as any combination of the above. For example, the processor 1002 can be a combination of two or more CPUs, general-purpose processors, etc.

[0069] The memory 1004 can be implemented as non-volatile or volatile memory used in modern electronic computers. For example, the non-volatile memory can include read-only memory (ROM), ferroelectric random access memory (RAM), programmable ROM (PROM), electrically erasable PROM (EEPROM), solid state drive (SSD), flash memory, magnetic disk memory (e.g., hard disk drive and magnetic tape), optical disk memory (e.g., CD, DVD, and Blu-ray disc), etc. Regarding the volatile memory, examples thereof include dynamic RAM, synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), static RAM, etc.

[0070] The processor-executable instructions 1006 stored in the memory 1004 can be used as computer-executable code that causes the processor 1002 to perform certain operations. The computer-executable code is used to execute operations or example operations and can be written in any combination of one or more programming languages such as Java, C, C++, Python, etc. In some examples, the computer-executable code can be in the form of a high-level language or a pre-compiled form and is dynamically generated by an interpreter (also pre-stored in the memory 1004).

[0071] Regarding the control operations performed by the device 1000, the following can be included. The device 1000 can be connected to the drive unit 508 in a wireless or wired manner. In this case, the processor 1002 can be used, for example, to use Figure 6Define a non-zero tilt angle θ between the symmetric main axis 512 and the rotation axis 514 using the above-described model or any other ray-tracing software tool as shown, and rotate the reflector 506 about the rotation axis 514 by the drive unit 508, the rotation axis 514 being tilted by the non-zero tilt angle θ with respect to the symmetric main axis 512. Additionally, the apparatus 1000 can also be used to perform steps S902 and S904 of the method 900, i.e., control the operation of the light source 502.

[0072] It should be noted that each block, step, or operation of the method 900 and Figure 6 any combination of blocks, steps, or operations of the model shown can be implemented by various means such as hardware, firmware, and / or software. For example, one or more of the above blocks or operations can be embodied by processor-executable instructions, data structures, program modules, and other suitable data representations. Additionally, the processor-executable instructions embodying the above blocks, steps, or operations can be stored on a corresponding data carrier and executed by at least one processor implementing the functions of the apparatus 1000, etc. The data carrier can be implemented as any computer-readable storage medium readable by at least one processor to execute computer-executable instructions. Such computer-readable storage media can include volatile and non-volatile media, removable and non-removable media. By way of example, and not limitation, computer-readable media include media implemented by any suitable method or technology for storing information. More specifically, actual examples of computer-readable media include, but are not limited to, information delivery media, RAM, ROM, EEPROM, flash memory, or other memory technologies, CD-ROM, digital versatile disc (DVD), holographic media, or other optical disc storage, magnetic tape, magnetic tape cassettes, disk storage, and other magnetic storage devices.

[0073] Although exemplary embodiments of the present invention have been described herein, it should be noted that various changes and modifications can be made to the embodiments of the present invention without departing from the scope of legal protection defined by the appended claims. In the appended claims, the word "comprising" does not exclude other elements or steps, and the terms "a" or "an" do not exclude a plurality. Listing certain measures in mutually different dependent claims does not mean that a combination of these measures cannot be used advantageously.

Claims

1. An optical-based ranging device (500), characterized in that, Comprising: - A light source (502) for illuminating an object (510) using one or more light beams; - A light detector (504) for detecting the one or more light beams reflected from the object (510); - A reflector (506) having a symmetric main axis (512) and including at least three reflecting surfaces around the symmetric main axis (512), each of the at least three reflecting surfaces for first reflecting each of the one or more light beams to the object (510) and then to the light detector (504); - A drive unit (508) for rotating the reflector (506) about a rotation axis (514) that is inclined at a non-zero inclination angle with respect to the symmetric main axis (512), wherein the non-zero inclination angle is defined such that the one or more light beams are reflected by each of the at least three reflecting surfaces to the object (510) in at least a partially divergent direction, and the non-zero inclination angle is defined based on a desired spatial resolution of the light detector (504).

2. The optical-based ranging device (500) according to claim 1, characterized in that, Serving as a Light Detection and Ranging (LiDAR) device, wherein the light source (502) is for illuminating the object (510) using the light beam as a pulsed laser, and wherein the light detector (504) is for detecting the pulsed laser reflected from the object (510).

3. The optical-based ranging device (500) according to claim 1, characterized in that, The light source (502) For illuminating the object (510) using the light beam as a single sector beam.

4. The optical-based ranging device (500) according to claim 3, characterized in that, The light detector (504) includes an array of discrete detector elements, and each of the discrete detector elements is time-division multiplexed with respect to the sector beam reflected from the at least three reflecting surfaces.

5. The optical-based ranging device (500) according to claim 1, characterized in that, The light source (502) is for illuminating the object (510) using a discrete number of the light beams.

6. The optical-based ranging device (500) according to claim 5, characterized in that, The light detector (504) includes an array of discrete detector elements, and each of the discrete detector elements is for detecting one of the discrete number of the light beams from the object (510).

7. The optical-based ranging device (500) according to any one of claims 1 to 6, characterized in that, The at least three reflecting surfaces are parallel to the symmetric main axis (512) of the reflector (506).

8. The optical-based ranging device (500) according to claim 7, characterized in that, The reflector (506) includes a prism-like shape.

9. The optical-based ranging device (500) according to any one of claims 1 to 6, characterized in that, Each of the at least three reflecting surfaces forms a different or the same angle with the symmetric main axis (512) of the reflector (506).

10. The optical-based ranging device (500) according to claim 9, characterized in that, The reflector (506) is implemented as a truncated pyramid.

11. The optical-based ranging device (500) according to any one of claims 1-6, 8, 10, characterized in that, The light detector (504) includes at least one single-photon avalanche diode (SPAD) detector.

12. The optical-based ranging device (500) according to any one of claims 1-6, 8, 10, characterized in that, Each of the at least three reflecting surfaces of the reflector (506) is made reflective using one of the following techniques: mirror polishing; applying a mirror coating thereon; or attaching a mirror thereto.

13. A device (1000), characterized in that, For controlling the light-based ranging device (500) according to any one of claims 1 to 12, the apparatus (1000) includes: - At least one processor (1002); - A memory (1004), coupled to the at least one processor (1002), and stores processor-executable instructions (1006) which, when executed by the at least one processor (1002), cause the at least one processor (1002) to: Define the non-zero tilt angle between the symmetric major axis (512) and the axis of rotation (514) such that the one or more light beams are reflected by each of the at least three reflecting surfaces of the reflector (506) in at least a partially divergent direction towards the object (510); Rotate the reflector (506) about the axis of rotation (514) by the drive unit (508), the axis of rotation (514) being tilted by the non-zero tilt angle with respect to the symmetric major axis (512).

14. The device (1000) according to claim 13, characterized in that, The at least one processor (1002) is further instructed to perform the following operations: In the case where a sparse scan resolution is required, cause the light source (502) to illuminate the object (510) only when one of the at least three reflecting surfaces of the reflector (506) is in a desired rotational position; In the case where a dense scan resolution is required, cause the light source (502) to illuminate the object (510) for all of the at least three reflecting surfaces of the reflector (506).

15. A method (900), characterized in that, A method (900) for operating an optical ranging device (500) according to any one of claims 1 to 12, the method (900) comprising: - Activating (S902) a sparse scan mode in which the light source (502) illuminates the object (510) only when one of the at least three reflecting surfaces of the reflector (506) is in a desired rotational position; - Activating (S904) a dense scan mode in which the light source (502) illuminates the object (510) for all of the at least three reflecting surfaces of the reflector (506).

16. A computer program product, characterized in that, A computer-readable medium including executable code which, when executed by at least one processor, causes the at least one processor to perform the method (900) according to claim 15.

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