WO2021175440A1

WO2021175440A1 - Light-based ranging device design and operation

Info

Publication number: WO2021175440A1
Application number: PCT/EP2020/056039
Authority: WO
Inventors: Radu Ciprian Bilcu; Mikko Muukki
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2020-03-06
Filing date: 2020-03-06
Publication date: 2021-09-10
Also published as: EP4090995A1; CN115190978A

Abstract

The present disclosure refers to a light-based ranging device (500) which comprises a light source (502), a light detector (504), a reflecting body (506), and a driving 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 reflecting body has a principal axis of symmetry (512) and comprises at least three reflecting faces around the principal axis of symmetry. Each of the at least three reflecting faces is configured to reflect each of the one or more light beams first towards the object and then towards the light detector. The driving unit is configured to rotate the reflecting body about a rotation axis (514). The rotation axis is tilted relative to the principal axis of symmetry by a non-zero tilting angle. The non-zero tilting angle is defined in such a way that the one or more light beams are reflected by each of the at least three reflecting faces towards the object in at least partly diverging directions. With this configuration of the light-based ranging device, one may take advantage of the misalignment between the principal axis of symmetry of the reflecting body and the rotation axis of the reflecting body, since this misalignment provides diverging directions of the light beams from each of the at least three reflecting faces, thereby increasing the total number of scanning points.

Description

LIGHT-BASED RANGING DEVICE DESIGN AND OPERATION

TECHNICAL FIELD

The present disclosure relates to the field of light detection and ranging technology, and in particular to a light-based ranging device capable of scanning a target object with pulsed or continuous light beams, an apparatus 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 software level.

BACKGROUND

Light Detection And Ranging (LiDAR) devices are designed to measure a distance to a target object by illuminating the target object with laser beams and measuring the time required by the laser beams to travel to the target object and return back. The LiDAR devices may be used to scan buildings, rock formations, ground surfaces, etc., to produce a corresponding three- dimensional (3D) model. There are two main types of the LiDAR devices, which are based on using the laser beams. The LiDAR devices of a first type use a single laser beam to make a single measurement. The LiDAR devices of a second type are configured to scan a certain field- of-view (FOV) and measure multiple points within the FOV.

More specifically, the LiDAR devices of the second type may be configured to generate a single laser beam which is then reflected by a rotating mirror in several different directions. Time-of- Flight (ToF) for each direction is calculated by a laser detector, so that an entire scene may be scanned. Instead of the rotating mirror, one may use optical prisms, which relies on light refraction to redirect the laser beam. However, such LiDAR devices enable scanning only along one line (i.e. within one plane).

The LiDAR devices of the second type may also be configured to generate several laser beams (instead of just one), each of which is reflected by the rotating mirror in several different directions, thereby scanning the whole FOV of the LiDAR device. Each of the laser beams is detected by an independent laser detector to calculate their ToF values. By means of using the several laser beams, it is possible to measure several distances at once. However, the total number of scanning points, obtained as the number of the laser beams multiplied by the number of different mirror positions, may not be enough for some applications. In some cases, a smaller spatial separation between the laser beams is needed, which may be achieved only by either increasing the number of the laser beams (which leads to an increased power consumption) or by limiting the FOV to be scanned. Moreover, for each scanning point there should be a laser detector configured to detect the corresponding laser beam reflected from the target object.

Instead of the rotating mirror, it is possible to use a rotating rectangular parallelepiped having four side faces each parallel to a principal axis of symmetry of the parallelepiped and each provided with a mirror to reflect the laser beams. However, a rotation axis about which the parallelepiped is rotated needs to be very precisely aligned with the principal axis of symmetry of the parallelepiped. In case of any (even small) misalignment, there will be a certain swinging of the mirrors in a vertical direction, which results in a laser beam being differently reflected by each of the mirrors. This in turn will increase the necessary number of laser detectors and complicate their placement in cases of very small misalignments.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure.

It is an objective of the present disclosure to provide a technical solution that allows increasing a number of scanning points, as well as simplifies an arrangement of light detectors. It is a further objective of the present disclosure to make it possible to change the number of scanning points depending on particular applications.

The objectives above are achieved by the features of the independent claims in the appended claims. Further embodiments and examples are apparent from the dependent claims, the detailed description and the accompanying drawings.

According to a first aspect, a light-based ranging device is provided, which comprises a light source, a light detector, a reflecting body, and a driving unit. The light source is configured to illuminate an object using one or more light beams. The light detector is configured to detect the one or more light beams reflected from the object. The reflecting body has a principal axis of symmetry and comprises at least three reflecting faces around the principal axis of symmetry. Each of the at least three reflecting faces is configured to reflect each of the one or more light beams first towards the object and then towards the light detector. The driving unit is configured to rotate the reflecting body about a rotation axis. The rotation axis is tilted relative to the principal axis of symmetry by a non-zero tilting angle. The non-zero tilting angle is defined in such a way that the one or more light beams are reflected by each of the at least three reflecting faces towards the object in at least partly diverging directions. With this configuration of the light-based ranging device, one may take advantage of the misalignment between the principal axis of symmetry of the reflecting body and the rotation axis of the reflecting body, since this misalignment provides at least partly diverging directions of the light beams from each of the at least three reflecting faces, thereby increasing the total number of scanning points.

In one embodiment of the first aspect, the light-based ranging device is configured as a LiDAR device. In this embodiment, the light source is configured to illuminate the object with the light beams as pulsed laser light, and the light detector is configured to detect the pulsed laser light reflected from the object. This may make the light-based ranging device more flexible in use.

In one embodiment of the first aspect, the light source is configured to illuminate the object with the light beams as a single fan-shaped light beam. This may provide more flexibility for the configuration of the light-based ranging device. In particular, if the fan-shaped light beam is used instead of a discrete number of light beams, there is no need to have an independent light detector for each of the light beams reflected from the object.

In one embodiment of the first aspect, if the fan-shaped light beam is used, the light detector comprises an array of discrete detector elements. Each of the discrete detector elements is time- multiplexed relative to the fan-shaped light beam reflected from the at least three reflecting faces. In this embodiment, for each detector element, each of the at least three reflecting faces of the reflecting body produces light detection from a different location, and the information about which of the at least three reflecting faces was used is used to construct a final spatial location of all light detections.

In one embodiment of the first aspect, the light source is configured to illuminate the object with a discrete number of the light beams. This may make the light-based ranging device more flexible in use. In one embodiment of the first aspect, if the discrete light beams are used, the light detector comprises an array of discrete detector elements. Each of the discrete detector elements is configured to detect one of the discrete number of the light beams from the object. This may provide more flexibility for the design of the light detector.

In one embodiment of the first aspect, the tilting angle is additionally defined based on a desired spatial resolution of the light detector. By so doing, one may select the tilting angle such that there is no need to re-configure anyhow the light detector.

In one embodiment of the first aspect, the at least three reflecting faces are parallel to the principal axis of symmetry of the reflecting body. This embodiment may provide more flexibility for the design of the reflecting body used in the light-based ranging device. For example, the reflecting body may be configured to have a prism-like shape.

In another embodiment of the first aspect, each of the at least three reflecting faces is at a different or same angle to the principal axis of symmetry of the reflecting body. This embodiment may provide more flexibility in the design and fabrication of the reflecting body used in the light-based ranging device. For example, the reflecting body may be implemented as a truncated pyramid.

In one embodiment of the first aspect, the light detector comprises at least one single-photon avalanche diode (SPAD) detector. This may provide more flexibility in the design and fabrication of the light detector used in the light-based ranging device.

In one embodiment of the first aspect, each of the at least three reflecting faces of the reflecting body is made light-reflective using one of the following: mirror-polishing, applying a mirror coating thereon, or attaching a mirror thereto. This may provide more flexibility in the design and fabrication of the reflecting body.

According to a second aspect, an apparatus for controlling the light-based ranging device according to the first aspect is provided. The apparatus comprises at least one processor and a memory coupled to the at least one processor and storing processor-executable instructions. When executed by the at least one processor, the processor-executable instructions cause the at least one processor to: define the non-zero tilting angle between the principal axis of symmetry and the rotation axis such that the one or more light beams are reflected by each of the at least three reflecting faces of the reflecting body towards the object in at least partly diverging directions; and cause the driving unit to rotate the reflecting body about the rotation axis tilted relative to the principal axis of symmetry by the non-zero tilting angle.

With this apparatus, it is possible to change the tilting angle between the principal axis of symmetry and the rotation axis depending on particular applications.

In one embodiment of the second aspect, the at least one processor is further instructed to: cause the light source to illuminate the object only when one of the at least three reflecting faces of the reflecting body is in a desired rotation position if a sparse scanning resolution is required; and cause the light source to illuminate the object for all the at least three reflecting faces of the reflecting body if a dense scanning resolution is required.

By so doing, the number of scanning points may be changed programmatically. If a very sparse scan of the object is enough, then the light source is driven so that it is on only when corresponding one of the at least three reflecting faces is in a desired rotation position, thereby leading to a reduced power consumption. The sparse scanning resolution may, for example, 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 may be caused to switch to a dense scanning mode where the laser beams are generated for all the at least three reflecting faces of the rotating reflecting body.

According to a third aspect, a method of operating the light-based ranging device according to the first aspect is provided. The method comprises the steps of: activating a sparse scanning mode, at which the light source is caused to illuminate the object only when one of the at least three reflecting faces of the reflecting body is in a desired rotation position; and activating a dense scanning mode, at which the light source is caused to illuminate the object for all the at least three reflecting faces of the reflecting body.

By so doing, the number of scanning points may be changed programmatically. The sparse scanning mode may be activated first by default. For example, the sparse scanning mode may be used to detect changes in the target object or scene. Once some changes in the target object or scene are detected, the sparse scanning mode may be changed to the dense scanning mode where the laser beams are generated for all the at least three reflecting faces of the rotating reflecting body. This may simplify the implementation of the method according to the third aspect, for example, in the apparatus according to the second aspect.

According to a fourth aspect, a computer program product is provided, which comprises a computer-readable medium that stores an executable code. When executed by at least one processor, the executable code causes the at least one processor to perform the method according to the third aspect. This may simplify the implementation of the method according to the third aspect on any computing apparatus, such as the apparatus according to the second aspect.

Other features and advantages of the present disclosure will be apparent upon reading the following detailed description and reviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The essence of the present disclosure is explained below with reference to the accompanying drawings in which:

FIG. 1 schematically shows a conventional LiDAR device capable of scanning a certain FOV and providing multiple scanning points;

FIG. 2 schematically shows another conventional LiDAR device capable of scanning an entire FOV and providing multiple scanning points;

FIG. 3 schematically shows portions of a conventional LiDAR device responsible for generating and redirecting laser beams towards a target object;

FIG. 4 schematically shows appearance of a misalignment between a rotation axis of a rectangular parallelepiped and a principal axis of symmetry of the rectangular parallelepiped; FIG. 5 schematically shows a light-based ranging device in accordance with one exemplary embodiment of the present disclosure;

FIG. 6 shows a schematic depiction explaining how to define a proper tilting angle Q between a principal axis of symmetry of a reflecting body included in the device shown in FIG. 5 and a rotation axis of the reflecting body;

FIGs. 7A and 7B schematically show how different discrete light beams reflected by a target object are collected using an array of detector elements constituting a light detector included in the device shown in FIG. 5; FIGs. 8A-8C schematically show how a fan-shaped light beam emitted by a light source and then reflected by the target object is collected using the array of detector elements constituting the light detector included in the device shown in FIG. 5;

FIG. 9 schematically shows a flowchart of a method for operating the light-based ranging device shown in FIG. 5 in accordance with one example embodiment of the present disclosure; FIG. 10 schematically shows an apparatus for controlling the light-based ranging device shown in FIG. 5 in accordance with one exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

Various embodiments of the present disclosure are further described in more detail with reference to the accompanying drawings. However, the present disclosure may be embodied in many other forms and should not be construed as limited to any certain structure or function discussed in the following description. In contrast, these embodiments are provided to make the description of the present disclosure detailed and complete.

According to the detailed description, it will be apparent to the ones skilled in the art that the scope of the present disclosure encompasses any embodiment thereof, which is disclosed herein, irrespective of whether this embodiment is implemented independently or in concert with any other embodiment of the present disclosure. For example, the device, apparatus and method disclosed herein may be implemented in practice using any numbers of the embodiments provided herein. Furthermore, it should be understood that any embodiment of the present disclosure may be implemented using one or more of the elements presented in the appended claims.

The word “exemplary” is used herein in the meaning of “used as an illustration”. Unless otherwise stated, any embodiment described herein as “exemplary” should not be construed as preferable or having an advantage over other embodiments.

According to the exemplary embodiments disclosed herein, a light-based ranging device may refer to any ranging device configured to perform light-based scanning with respect to an object or scene of interest in the presence of a misalignment between a rotation axis of a reflecting body included in the device and a principal axis of symmetry of the reflecting body. The light- based ranging device may be implemented as a LiDAR device. However, the present disclosure is not limited to this implementation example, and any other devices operating based on this misalignment, which may be developed in future, should be construed as falling within the scope of the present disclosure.

In the embodiments disclosed herein, the principal axis of symmetry may refer to an axis around which a rotation by 360°/n (or 2p/h) results in an identical geometrical body before and after the rotation. The principal axis of symmetry may also be referred to as a main axis of symmetry.

FIG. 1 schematically shows a conventional LiDAR device 100 capable of scanning a certain FOV and providing multiple scanning points. For this purpose, the LiDAR device 100 comprises 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 towards a target object 108 (see the solid arrows in FIG. 1). The rotating mirror 106 is rotated by a driving unit (not shown in FIG. 1) about a rotation axis 110, thereby providing the reflection of the single laser beam in different directions. Being reflected from the target object 108, the laser beam again hits the rotating mirror 106 but now reflected towards the detector 104 arranged near the laser source 102 (see the dashed lines in FIG. 1). The detector 104 is configured to calculate a ToF value for each direction, based on which a distance to the target object 108 may be calculated and/or a visual model of the target object 108 may be obtained. Instead of the rotating mirror 106, one may use optical prisms, which rely on light refraction to redirect the single laser beam. However, the drawback of the LiDAR device 100 is that the reflection of the single laser beam is performed only in one (horizontal) plane.

To eliminate the above-indicated drawback, it is possible to rotate/tilt the rotating mirror 106 also vertically, which enables scanning in another (vertical) plane in parallel with the scanning in the horizontal plane. However, such rotation/tilt of the rotating mirror 106 about another axis is quite difficult to implement. Moreover, despite enabling scanning horizontally and vertically, this also requires more complex mechanics to be considered in the design of the LiDAR device 100 (which is usually achieved using microelectromechanical system (MEMS) mirrors). To reduce the mechanical complexity of the device design and still enable scanning in the both horizontal and vertical planes, a set of laser beams may be used, as discussed below with reference to FIG. 2.

More specifically, FIG. 2 schematically shows another conventional LiDAR device 200 capable of scanning an entire FOV and providing multiple scanning points. For this purpose, the LiDAR device 200 comprises a laser source 202, a detector 204, and a rotating mirror 206. The laser source 202 is configured to generate several laser beams that are reflected by the rotating mirror 206 towards a target object 208 (see the solid arrows in FIG. 2). Similar to the rotating mirror 106, the rotating mirror 206 is rotated by a driving unit (not shown in FIG. 2) about a rotation axis 210, thereby providing the reflection of each laser beam in different directions. Thus, the vertical scanning of the target object 208 is provided by the number of laser beams, while the horizontal scanning of the target object 208 is provided by the rotation of the rotating mirror 206 about the rotation axis 210. Being reflected from the target object 208, the laser beams again hits the rotating mirror 206 but now reflected towards the detector 204 arranged near the laser source 202 (see the dashed lines in FIG. 2). However, the total number of scanning points, obtained as the number of the laser beams multiplied by the number of different mirror positions, may not be enough for some applications. In some cases, a smaller spatial separation between the laser beams emitted by the laser source 202 is needed, which may be achieved only by either increasing the number of the laser beams (which leads to an increased power consumed by the laser source 202) or by limiting the FOV to be scanned. Moreover, for each scanning point there should be a detector element configured to detect the corresponding laser beam reflected from the target object 208. In other words, the design of the detector 204 becomes much more complicated.

FIG. 3 schematically shows portions of a conventional LiDAR device responsible for generating and redirecting laser beams towards a target object. As shown, this part comprises a laser source 302 and a rotating rectangular parallelepiped 304 rotated by a driving unit (not shown in FIG. 3) about a rotation axis 306. There are four mirrors (not shown in FIG. 3) each placed on one of side faces of the rectangular parallelepiped 304, which are parallel to its principal axis of symmetry coinciding with the rotation axis 306. As the rectangular parallelepiped 304 rotates, the laser beams from the laser source 302 are active only for a certain period of time, so that each mirror scans the entire horizontal FOV. For example, if the rectangular parallelepiped 304 makes one full rotation about the rotation axis 306 per second, the horizontal FOV will be scanned four times per second. However, this type of the LiDAR device requires that the rotation axis 306 is very precisely aligned with the principal axis of symmetry of the rectangular parallelepiped 304.

FIG. 4 schematically shows appearance of a misalignment between the rotation axis 306 of the rectangular parallelepiped 304 and a principal axis 402 of symmetry of the rectangular parallelepiped 304. In this case, there will be a certain swinging of the four mirrors in the vertical direction, which results in each laser beam being differently reflected by each of the four mirrors. This will in turn increase a necessary number of detector elements, as well as their arrangement will be difficult to implement in case of very small misalignments.

While even small misalignments between the principal axis of symmetry of the rectangular parallelepiped 304 and its rotation axis (see FIGs. 3 and 4) have an adverse impact on the design and operation of the prior art LiDAR devices (due to the fact that more detector elements should be utilized, and their exact arrangement is very difficult to implement), the present authors have found that such misalignments may be used advantageously to increase a number of scanning points. In particular, according to the present disclosure, a tilting angle between the rotation axis of a reflecting body, such as the rectangular parallelepiped 304, and the principal axis of symmetry of the reflecting body is selected such that laser beams are reflected from corresponding reflecting faces of the reflecting body in at least partly diverging directions, thereby increasing (by times) the number of scanning points.

FIG. 5 schematically shows a light-based ranging device 500 in accordance with one exemplary embodiment of the present disclosure. The light-based ranging device 500 comprises a light source 502, a light detector 504, a reflecting body 506, and a driving unit 508. The light source 502 is configured to illuminate a target object 510 using one or more light beams (see the thin solid arrows in FIG. 5 - only one light beam is shown in order not to overload FIG. 5). The light detector 504 is configured to detect the one or more light beams reflected from the object 510. The reflecting body 506 has a principal axis 512 of symmetry and comprises reflecting faces around the principal axis 512 of symmetry. Each of the reflecting faces is configured to reflect each of the one or more light beams first towards the object 510 and then towards the light detector 504. The driving unit 508 is configured to rotate the reflecting body 506 about a rotation axis 514 (which is schematically shown by the thick solid arrow in FIG. 5). The rotation axis 514 is tilted relative to the principal axis 512 of symmetry by a non-zero tilting angle Q. The non-zero tilting angle Q is defined in such a way that the one or more light beams are reflected by each of the reflecting faces towards the object 510 in at least partly diverging directions. With this configuration of the light-based ranging device 500, one may take advantage of the misalignment between the principal axis 512 of symmetry of the reflecting body 506 and the rotation axis 514 of the reflecting body 506, since this misalignment provides at least partly diverging directions of the light beams from each of the reflecting faces, thereby increasing the total number of scanning points.

The light source 502 may be implemented as a laser source and, correspondingly, the whole light-based ranging device 500 may be implemented as a LiDAR device. Furthermore, the light source 502 may be configured to generate one or more light beams as laser pulses each having a frequency from the range 100 kHz to 5 MHz, a pulse width from the range 0.1 to 2 ns, and a pulse power from the range 2 to 50 W. It should be obvious to those skilled in the art that the exact parameters, including a beam shape, of the light beams generated by the light source 502 will vary depending on particular applications.

The light detector 504 is configured to detect the light beams reflected from the object 510 and perform necessary distance calculations based on ToF values, as discussed above. The light detector 504 may comprise an array of discrete detector elements, and each detector element may be implemented based on at least one single-photon avalanche diode (SPAD). It should also be noted that each of such discrete detector elements may either be configured to detect one of the light beams from the object 510 if the light beams are generated by the light source 502 as a discrete number of light beams, or be time-multiplexed relative to the light beams from the object 510 if the light beams are generated by the light source 502 as a single fan-shaped light beam. This time-multiplexing of the detecto elements means that for each detector element, different reflecting faces of the reflecting body 506 produce light detection from different locations depending on the reflecting face used, and the information on which reflecting face was used, may be then used to construct the final spatial location of the object 510.

The reflecting body 506 may be made of any material which is hard enough, so that the shape of the reflecting body 506 does not change under inertial forces during the rotation of the reflecting body 506 about the rotation axis 514. Some examples of such a material include metal, plastic glass, etc. As for the reflecting faces of the reflecting body 506, they may be made light-reflective using one of the following techniques: mirror-polishing, applying a mirror coating on each face, or attaching a mirror to each face.

Although the reflecting body 506 is shown in FIG. 5 in the form of a rectangular parallelepiped having four (side) reflecting faces around the principal axis 512 of symmetry, this shape is used only as one possible example and should not be considered as any limitation of the present disclosure. In other exemplary embodiments, the number of the reflecting faces may be either reduced to three, for which reason the reflecting body 506 may be implemented as a triangular prism, or increased to five and more, for which reason the reflecting body 506 may be implemented as a polygonal prism (for example, a pentagonal prism if the number of the reflecting faces is set to be five). Furthermore, in some other exemplary embodiments, the reflecting faces of the reflecting body 506 may not be parallel to the principal axis 512 of symmetry but each tilted at a different or same angle relative to the principal axis 512 of symmetry. This make it possible to use other geometric shapes for the reflecting body 506, such, for example, as a truncated pyramid.

The driving unit 508 may be implemented in a variety of ways. For example, the driving unit 508 may be implemented as a mechanical rotation mechanism, an electromagnetic drive, etc. The driving unit 508 may be programmed to rotate the reflecting body 506 about the rotation axis 514 in a clockwise or counterclockwise direction depending on particular applications. A rotation speed may, for example, varies within 50-2000 revolutions per minute, but is not limited to this exemplary numerical range.

As noted above, the tilting angle Q may be defined in such a way as to provide at least partly diverging directions of the light beams reflected by each of the reflecting faces. Additionally, the tilting angle Q may be defined based on a desired spatial resolution of the light detector 504, as will be discussed now with reference to FIG. 6. For the sake of simplicity, FIG. 6 refers to only one light beam. The displacement of this light beam, due to the tilt/misalignment between the principal axis 512 of symmetry and the rotation axis 514, is denoted as a. Now let us require that at a certain distance z from the light-based ranging device 500, the shift of the light beam is equal to D. Then, the displacement angle a may be calculated as follows: a = 2 tan^-1

Tuning the parameters a and z to the schematic depiction shown in FIG. 6, one may select the proper tilting angle Q which is the best for the target application and requirements. Alternatively, different ray-tracing software tools may be used to model the spatial distribution of the light beams for different tilting angles Q. For example, the tilting angle Q may be set to be more than 1°. FIGs. 7A and 7B schematically show how different discrete light beams reflected by the object 510 are collected using an array of detector elements constituting the light detector 504 included in the light-based ranging device 500. In particular, FIG. 7A refers to the case of the perfect alignment between the principal axis 512 of symmetry and the rotation axis 514 of the reflecting body 506. As one can see, each light beam is ideally captured by one detector element regardless of the positions of the reflecting faces of the reflecting body 506. FIG. 7B refers to the case when the rotation axis 514 does not coincide with the principal axis 512 of symmetry, i.e. when there is the misalignment expressed by the non-zero tilting angle Q. As shown in FIG. 7B, the light beams for different positions of the reflecting faces of the reflecting body 506 will not hit the same detector elements. Thus, one can see from FIGs. 7A and 7B that in the case of the non-zero tilting angle Q, the number of the detector elements should be increased, and this may be achieved, for example, using a 2D array of detector elements. Moreover, the size of such a 2D array of detector elements depends on the position of the received light beams, whereupon the tilting angle Q between the rotation axis 514 and the principal axis 512 of symmetry may be selected such that it takes into account the extra number of the detector elements to be added to the light detector 504. At the same time, some detector elements may collect light from two or more different light beams corresponding to several positions of the reflecting faces (as illustrated in FIG. 7B). In this case, when one detector element is activated, it is necessary to know in which position the reflecting body 506 was, in order to assign a correct direction in space to a corresponding scanning point cloud. This may be called the time multiplexing of the detector elements.

FIGs. 8A-8C schematically show how the fan-shaped light beam emitted by the light source 502 and then reflected by the object 510 is collected using an array of detector elements constituting the light detector 504 included in the light-based ranging device 500. The split of the fan-shaped light beam is then performed on the detector side where each detector element will collect light form its own direction. In this case, the misalignment (tilting angle Q) between the principal axis 512 of symmetry and the rotation axis 514 should ensure that the fan-shaped light beam is generated in a correct direction. The use of the fan-shaped light beam provides more flexibility for the design of the device 500. Indeed, if the fan-shaped light beam is used instead of the discrete number of light beams, there is no need to have an independent detector element for each generated light beam (as shown in FIGs. 7A and 7B). Therefore, it is the light detector 504 which dictates the resolution of the whole system (i.e. the number of scanning points in the scanning point cloud). Furthermore, the use of the fan-shaped light beam does not require designing and using a very complicated beam splitter for the light source 502.

More specifically, FIG. 8A refers to the case of the perfect alignment between the principal axis 512 of symmetry and the rotation axis 514. FIG. 8B refers to the case when the rotation axis 514 does not coincide with the principal axis 512 of symmetry and the light detector 504 is formed by a bigger number of the detector elements compared to that shown in FIG. 8 A (i.e. more than 15 detector elements are used). FIG. 8C refers to the case when the rotation axis 514 does not coincide with the principal axis 512 of symmetry but the light detector 504 is formed by the same number of the detector elements as that shown in FIG. 8 A (i.e. 15 detector elements are also used). Thus, in case of using the fan-shaped light beam, one can select to have either the same number of the detector elements as in the perfectly aligned case but arranged on a 2D array, or a different number of the detector elements compared to the perfectly aligned case.

FIG. 9 schematically shows a flowchart of a method 900 for operating the light-based ranging device 500 in accordance with one example embodiment of the present disclosure. In particular, the method 900 comprises two steps S902 and S904 each corresponding to a certain operational mode of the device 500. The step S902 corresponds to a sparse scanning mode, at which the light source 502 is configured to illuminate the object 510 only when one of the reflecting faces of the reflecting body 506 is in a desired rotation position. The step S904 corresponds to a dense scanning mode, at which the light source 502 is configured to illuminate the object 510 for all the reflecting faces of the reflecting body. With such two operational modes, it is possible to change the number of scanning points depending on particular applications. In one exemplary embodiment, the sparse scanning mode, i.e. the step S902, may be activated first by default, say, when the device 500 is switched on. For example, the sparse scanning mode may be used to detect changes in the object 510. Once some changes in the object 500 are detected by the light detector 504, the sparse scanning mode may be changed to the dense scanning mode, i.e. the method 900 proceeds to the step S904, where the laser beams are generated for all the reflecting faces of the rotating reflecting body 506. In one other exemplary embodiment, the step 902 may be omitted, and the light source 502 is configured to generate the light beams for all the reflecting faces of the reflecting body 506 once the device 500 is switched on.

FIG. 10 schematically shows an apparatus 1000 for controlling the light-based ranging device 500 in accordance with one exemplary embodiment of the present disclosure. The apparatus 1000 comprises a processor 1002 and a memory 1004 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 the number, arrangement and interconnection of the constructive elements constituting the apparatus 1000, which are shown in FIG. 10, are not intended to be any limitation of the present disclosure, but merely used to provide a general idea of how the constructive elements may be implemented within the apparatus 1000. For example, if the apparatus 1000 is implemented as an individual device, it may further comprise a transceiving means (not shown) configured to perform different operations required to transmit respective control information to the light-based ranging device 500.

The processor 1002 may be implemented as a central processing unit (CPU), general-purpose processor, single-purpose processor, microcontroller, microprocessor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), digital signal processor (DSP), complex programmable logic device, or the like. It is worth noting that the processor 1002 may be implemented as any combination of the aforesaid. As an example, the processor 1002 may be a combination of two or more CPUs, general-purpose processors, etc.

The memory 1004 may be implemented as a nonvolatile or volatile memory used in modern electronic computing machines. As an example, the nonvolatile memory may 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 storage (such as hard drives and magnetic tapes), optical disc storage (such as CD, DVD and Blu-ray discs), etc. As for the volatile memory, examples thereof include Dynamic RAM, Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDR SDRAM), Static RAM, etc.

The processor-executable instructions 1006 stored in the memory 1004 may be configured as a computer executable code causing the processor 1002 to perform certain operations. The computer executable code for carrying out operations or operations for the embodiments may be written in any combination of one or more programming languages, such as Java, C, C++, Python, or the like. In some examples, the computer executable code may be in the form of a high-level language or in a pre-compiled form, and be generated by an interpreter (also pre stored in the memory 1004) on the fly. As for the control operations performed by the apparatus 1000, they may consist in the following. The apparatus 1000 may be connected wirelessly or by wire to the driving unit 508. In this case, the processor 1002 may be configured to define the non-zero tilting angle Q between the principal axis 512 of symmetry and the rotation axis 514, for example, using the above-described model shown in FIG. 6 or any other ray-tracing software tools, and to cause the driving unit 508 to rotate the reflecting body 506 about the rotation axis 514 tilted relative to the principal axis 512 of symmetry by the non-zero tilting angle Q. Furthermore, the apparatus 1000 may also be configured to perform the steps S902 and S904 of the method 900, i.e. to control the operation of the light source 502.

It should be noted that each block, step or operation of the method 900 and the model shown in FIG. 6, or any combinations of the blocks, steps or operations, can be implemented by various means, such as hardware, firmware, and/or software. As an example, one or more of the blocks or operations described above can be embodied by processor executable instructions, data structures, program modules, and other suitable data representations. Furthermore, the processor executable instructions which embody the blocks, steps or operations described above can be stored on a corresponding data carrier and executed by at least one processor implementing functions, for example, of the apparatus 1000. This data carrier can be implemented as any computer-readable storage medium configured to be readable by said at least one processor to execute the processor executable instructions. Such computer-readable storage media can include both volatile and nonvolatile media, removable and non-removable media. By way of example, and not limitation, the computer-readable media comprise media implemented in any method or technology suitable for storing information. In more detail, the practical examples of the computer-readable media include, but are not limited to information- delivery media, RAM, ROM, EEPROM, flash memory or other memory technology, CD- ROM, digital versatile discs (DVD), holographic media or other optical disc storage, magnetic tape, magnetic cassettes, magnetic disk storage, and other magnetic storage devices.

Although the exemplary embodiments of the present disclosure are described herein, it should be noted that any various changes and modifications could be made in the embodiments of the present disclosure, without departing from the scope of legal protection which is defined by the appended claims. In the appended claims, the word “comprising” does not exclude other elements or operations, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A light-based ranging device (500) comprising: a light source (502) configured to illuminate an object (510) using one or more light beams; a light detector (504) configured to detect the one or more light beams reflected from the object (510); a reflecting body (506) having a principal axis (512) of symmetry and comprising at least three reflecting faces around the principal axis (512) of symmetry, each of the at least three reflecting faces being configured to reflect each of the one or more light beams first towards the object (510) and then towards the light detector (504); and a driving unit (508) configured to rotate the reflecting body (506) about a rotation axis (514), the rotation axis (514) being tilted relative to the principal axis (512) of symmetry by a non-zero tilting angle, wherein the non-zero tilting angle is defined in such a way that the one or more light beams are reflected by each of the at least three reflecting faces towards the object (510) in at least partly diverging directions.

2. The light-based ranging device (500) of claim 1, which is configured as a Light Detection and Ranging (LiDAR) device, wherein the light source (502) is configured to illuminate the object (510) with the light beams as pulsed laser light, and wherein the light detector (504) is configured to detect the pulsed laser light reflected from the object (510).

3. The light-based ranging device (500) of claim 1 or 2, wherein the light source (502) is configured to illuminate the object (510) with the light beams as a single fan-shaped light beam.

4. The light-based ranging device (500) of claim 3, wherein the light detector (504) comprises an array of discrete detector elements, each of the discrete detector elements being time-multiplexed relative to the fan-shaped light beam reflected from the at least three reflecting faces.

5. The light-based ranging device (500) of claim 1, wherein the light source (502) is configured to illuminate the object (510) with a discrete number of the light beams.

6. The light-based ranging device (500) of claim 5, wherein the light detector (504) comprises an array of discrete detector elements, each of the discrete detector elements being configured to detect one of the discrete number of the light beams from the object (510).

7. The light-based ranging device (500) of any one of claims 1 to 6, wherein the tilting angle is additionally defined based on a desired spatial resolution of the light detector (504).

8. The light-based ranging device (500) of any one of claims 1 to 7, wherein the at least three reflecting faces are parallel to the principal axis (512) of symmetry of the reflecting body (506).

9. The light-based ranging device (500) of claim 8, wherein the reflecting body (506) comprises a prism-like shape.

10. The light-based ranging device (500) of any of the claims 1 to 7, wherein each of the at least three reflecting faces is at a different or same angle to the principal axis (512) of symmetry of the reflecting body (506).

11. The light-based ranging device (500) of claim 10, wherein the reflecting body (506) is implemented as a truncated pyramid.

12. The light-based ranging device (500) of any one of claims 1 to 11, wherein the light detector (504) comprises at least one single-photon avalanche diode (SPAD) detector.

13. The light-based ranging device (500) of any one of claims 1 to 12, wherein each of the at least three reflecting faces of the reflecting body (506) is made light-reflective using one of the following: mirror-polishing, applying a mirror coating thereon, or attaching a mirror thereto.

14. An apparatus (1000) for controlling the light-based ranging device (500) according to any one of claims 1 to 13, the apparatus (1000) comprising: at least one processor (1002); and a memory (1004) coupled to the at least one processor (1002) and storing 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 tilting angle between the principal axis (512) of symmetry and the rotation axis (514) such that the one or more light beams are reflected by each of the at least three reflecting faces of the reflecting body (506) towards the object (510) in at least partly diverging directions; and cause the driving unit (508) to rotate the reflecting body (506) about the rotation axis (514) tilted relative to the principal axis (512) of symmetry by the non-zero tilting angle.

15. The apparatus (1000) of claim 14, wherein the at least one processor (1002) is further instructed to: cause the light source (502) to illuminate the object (510) only when one of the at least three reflecting faces of the reflecting body (506) is in a desired rotation position if a sparse scanning resolution is required; and cause the light source (502) to illuminate the object (510) for all the at least three reflecting faces of the reflecting body (506) if a dense scanning resolution is required.

16. A method (900) of operating the light-based ranging device (500) according to any one of claims 1 to 13, the method (900) comprising: activating (S902) a sparse scanning mode, at which the light source (502) is caused to illuminate the object (510) only when one of the at least three reflecting faces of the reflecting body (506) is in a desired rotation position; and activating (S904) a dense scanning mode, at which the light source (502) is caused to illuminate the object (510) for all the at least three reflecting faces of the reflecting body (506).

17. A computer program product comprising a computer-readable medium that stores an executable code, wherein the executable code, when executed by at least one processor, causes the at least one processor to perform the method (900) of claim 16.