PATENT DOCUMENT

Publication Number: US-10739460-B2
Application Number: US-201715451431-A
Country: US
Kind Code: B2

Title: Time-of-flight detector with single-axis scan

Abstract:
Apparatus for mapping includes an illumination assembly, which projects a line of radiation extending in a first direction across a scene. A detection assembly receives the radiation reflected from the scene within a sensing area that contains at least a part of the line of the radiation, and includes a linear array of detector elements and objective optics, which focus the reflected radiation from the sensing area onto the linear array. A scanning mirror scans the line of radiation and the sensing area together over the scene in a second direction, which is perpendicular to the first direction. Processing circuitry processes signals output by the detector elements in response to the received radiation in order to construct a three-dimensional (3D) map of an object in the scene.

Claims:
The invention claimed is: 
     
       1. Apparatus for mapping, comprising:
 an illumination assembly, which is configured to project, via an exit pupil, a line of radiation extending in a first direction across a scene; 
 a detection assembly, which is configured to receive the radiation reflected from the scene within a sensing area that contains at least a part of the line of the radiation, and which comprises a linear array of detector elements and objective optics, which focus the reflected radiation from the sensing area via an entrance pupil onto the linear array, wherein the line of the radiation and the sensing area have respective axes that are collinear in a plane containing the exit and entrance pupils; 
 a scanning mirror, which is configured to scan the line of radiation and the sensing area together over the scene in a second direction, which is perpendicular to the first direction; and 
 processing circuitry, which is configured to process signals output by the detector elements in response to the received radiation in order to construct a three-dimensional (3D) map of an object in the scene. 
 
     
     
       2. The apparatus according to  claim 1 , wherein the linear array has an array axis that is aligned along the first direction. 
     
     
       3. The apparatus according to  claim 2 , wherein the scanning mirror is configured to rotate about a mirror axis, and wherein the illumination assembly comprises at least one radiation source, which is arranged in a plane defined by the array axis and the mirror axis together with the linear array and the scanning mirror. 
     
     
       4. The apparatus according to  claim 1 , wherein the illumination assembly comprises a further linear array of radiation sources, which are configured to emit respective beams of radiation, and projection optics which are configured to collect and focus the emitted beams to form the line of the radiation. 
     
     
       5. The apparatus according to  claim 4 , wherein the radiation sources emit pulses of radiation in mutual synchronization. 
     
     
       6. The apparatus according to  claim 1 , wherein the scanning mirror is a second scanning mirror, while the illumination assembly comprises a radiation source, which is configured to emit a beam of radiation, and a first scanning mirror, which is configured to receive and scan the emitted beam in the first direction. 
     
     
       7. The apparatus according to  claim 6 , wherein the first scanning mirror scans at a first speed, and the second scanning mirror scans at a second speed, which is slower than the first speed. 
     
     
       8. The apparatus according to  claim 1 , wherein the illumination assembly is configured to emit pulses of radiation, and wherein the signals output by the detector elements are indicative of respective times of flight of the pulses from points in the scene, and the processing circuitry is configured to construct the 3D map responsively to the times of flight. 
     
     
       9. The apparatus according to  claim 8 , wherein the detector elements comprise avalanche photodiodes. 
     
     
       10. The apparatus according to  claim 8 , wherein the detector elements comprise single-photon avalanche diodes. 
     
     
       11. The apparatus according to  claim 8 , wherein the processing circuitry comprises a pulse amplifier, which is configured to amplify the signals output by the detector elements, and a multiplexer, which is configured to select the detector elements for connection to the pulse amplifier in synchronization with a scan rate of the apparatus. 
     
     
       12. The apparatus according to  claim 1 , wherein the scanning mirror is rotatable so as to scan the line of radiation and the sensing area both over a first scene on a first side of the apparatus and over a second scene on a second side of the apparatus, opposite the first side. 
     
     
       13. The apparatus according to  claim 12 , wherein the scanning mirror has first and second opposing reflective surfaces, and wherein the scanning mirror rotates so that the line of radiation and the sensing area reflect from the first reflective surface when scanning over the first scene and from the second reflective surface when scanning over the second scene. 
     
     
       14. The apparatus according to  claim 12 , wherein the second reflective surface is smaller than the first reflective surface. 
     
     
       15. A method for mapping, comprising:
 projecting, via an exit pupil, a line of radiation that extends in a first direction over a scene; 
 receiving, via an entrance pupil, the radiation reflected from the scene within a sensing area of a detector assembly, which comprises a linear array of detector elements, wherein the sensing area contains at least a part of the line of the radiation, and wherein the line of the radiation and the sensing area have respective axes that are collinear in a plane containing the exit and entrance pupils; 
 scanning, using a scanning mirror, both the line of radiation and the sensing area over the scene in a second direction, which is perpendicular to the first direction; and 
 processing signals output by the detector elements in response to the received radiation in order to construct a three-dimensional (3D) map of an object in the scene. 
 
     
     
       16. The method according to  claim 15 , wherein receiving the radiation comprises aligning an array axis of the linear array along the first direction. 
     
     
       17. The method according to  claim 15 , wherein projecting the line of radiation comprises applying a linear array of radiation sources to emit respective beams of radiation, and collecting and focusing the emitted beams to form the line of the radiation. 
     
     
       18. The apparatus according to  claim 15 , wherein projecting the line of radiation comprises scanning a beam along the line in the first direction. 
     
     
       19. The method according to  claim 18 , wherein scanning the beam comprises scanning the beam along the line at a first speed, and wherein scanning using the scanning mirror comprises scanning the line of radiation and the sensing area over the scene at a second speed, which is slower than the first speed. 
     
     
       20. The method according to  claim 15 , wherein scanning the line of radiation comprises scanning pulses of radiation, and wherein the signals output by the detector elements are indicative of respective times of flight of the pulses, and wherein processing the signals comprises constructing the 3D map responsively to the times of flight.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application 62/319,810, filed Apr. 8, 2016, and of U.S. Provisional Patent Application 62/353,581, filed Jun. 23, 2016. This application is also a continuation-in-part of U.S. patent application Ser. No. 14/749,654, filed Jun. 25, 2015, which is a continuation of U.S. patent application Ser. No. 13/810,451, filed Jan. 16, 2013 (now U.S. Pat. No. 9,098,931), in the national phase of PCT Patent Application PCT/IB2011/053560, filed Aug. 10, 2011, which claims the benefit of U.S. Provisional Patent Application 61/372,729, filed Aug. 11, 2010, and U.S. Provisional Patent Application 61/425,788, filed Dec. 22, 2010. All of these related applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to three-dimensional (3D) mapping, and particularly to devices and methods for 3D mapping based on projection and sensing of a beam of radiation. 
     BACKGROUND 
     Various methods are known in the art for optical 3D mapping, i.e., generating a 3D profile of the surface of an object by processing optical radiation received from the object. This sort of 3D profile is also referred to as a 3D map, depth map or depth image, and 3D mapping is also referred to as depth mapping. “Optical radiation” includes any and all electromagnetic radiation in the visible, infrared and ultraviolet portions of the spectrum. In the description that follows, the term “radiation” should be understood as referring to optical radiation. 
     Some 3D mapping techniques are based on measurement of the time of flight of optical pulses. For example, U.S. Patent Application Publication 2013/0207970, whose disclosure is incorporated herein by reference, describes a scanning depth engine, in which mapping apparatus includes a transmitter, which emits a beam comprising pulses of light, and a scanner, which is configured to scan the beam, within a predefined scan range, over a scene. A receiver receives the light reflected from the scene and generates an output indicative of a time of flight of the pulses to and from points in the scene. A processor is coupled to control the scanner so as to cause the beam to scan over a selected window within the scan range and to process the output of the receiver so as to generate a 3D map of a part of the scene that is within the selected window. 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide improved devices and methods for 3D mapping. 
     There is therefore provided, in accordance with an embodiment of the invention, apparatus for mapping, including an illumination assembly, which is configured to project a line of radiation extending in a first direction across a scene. A detection assembly is configured to receive the radiation reflected from the scene within a sensing area that contains at least a part of the line of the radiation, and includes a linear array of detector elements and objective optics, which focus the reflected radiation from the sensing area onto the linear array. A scanning mirror is configured to scan the line of radiation and the sensing area together over the scene in a second direction, which is perpendicular to the first direction. Processing circuitry is configured to process signals output by the detector elements in response to the received radiation in order to construct a three-dimensional (3D) map of an object in the scene. 
     In the disclosed embodiments, the linear array has an array axis that is aligned along the first direction. In some embodiments, the scanning mirror is configured to rotate about a mirror axis, and the illumination assembly includes at least one radiation source, which is arranged in a plane defined by the array axis and the mirror axis together with the linear array and the scanning mirror. 
     In one embodiment, the illumination assembly includes a further linear array of radiation sources, which are configured to emit respective beams of radiation, and projection optics which are configured to collect and focus the emitted beams to form the line of the radiation. Typically, the linear arrays of the detector elements and of the radiation sources have respective axes that are mutually parallel. 
     Alternatively, the scanning mirror is a second scanning mirror, while the illumination assembly includes a radiation source, which is configured to emit a beam of radiation, and a first scanning mirror, which is configured to receive and scan the emitted beam in the first direction. In a disclosed embodiment, the first scanning mirror scans at a first speed, and the second scanning mirror scans at a second speed, which is slower than the first speed. 
     In some embodiments, the illumination assembly is configured to emit pulses of radiation, and the signals output by the detector elements are indicative of respective times of flight of the pulses from points in the scene, and the processing circuitry is configured to construct the 3D map responsively to the times of flight. In one embodiment, the detector elements include avalanche photodiodes. Alternatively, the detector elements include single-photon avalanche diodes. In a disclosed embodiment, the processing circuitry includes a pulse amplifier, which is configured to amplify the signals output by the detector elements, and a multiplexer, which is configured to select the detector elements for connection to the pulse amplifier in synchronization with a scan rate of the apparatus. 
     In some embodiments, the scanning mirror is rotatable so as to scan the line of radiation and the sensing area both over a first scene on a first side of the apparatus and over a second scene on a second side of the apparatus, opposite the first side. In a disclosed embodiment, the scanning mirror has first and second opposing reflective surfaces, and the scanning mirror rotates so that the line of radiation and the sensing area reflect from the first reflective surface when scanning over the first scene and from the second reflective surface when scanning over the second scene. In one embodiment, the second reflective surface is smaller than the first reflective surface. 
     There is also provided, in accordance with an embodiment of the invention, a method for mapping, which includes projecting a line of radiation that extends in a first direction over a scene. The radiation reflected from the scene within a sensing area of a detector assembly is received by the detector assembly, which includes a linear array of detector elements. Using a scanning mirror, both the line of radiation and the sensing area are scanned over the scene in a second direction, which is perpendicular to the first direction. Signals output by the detector elements in response to the received radiation are processed in order to construct a three-dimensional (3D) map of an object in the scene. 
     In a disclosed embodiment, receiving the radiation includes aligning an array axis of the linear array along the first direction. 
     In some embodiments, projecting the line of radiation includes applying a linear array of radiation sources to emit respective beams of radiation, and collecting and focusing the emitted beams to form the line of the radiation. 
     In other embodiments, projecting the line of radiation includes scanning a beam along the line in the first direction. In a disclosed embodiment, scanning the beam includes scanning the beam along the line at a first speed, and scanning using the scanning mirror includes scanning the line of radiation and the sensing area over the scene at a second speed, which is slower than the first speed. 
     In a disclosed embodiment, scanning the beam of radiation includes scanning pulses of radiation, and the signals output by the detector elements are indicative of respective times of flight of the pulses, and processing the signals includes constructing the 3D map responsively to the times of flight. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic pictorial illustration of a 3D mapping system, in accordance with an embodiment of the invention; 
         FIG. 2  is a schematic pictorial illustration showing details of a 3D mapping module, in accordance with an embodiment of the invention; 
         FIG. 3  is a block diagram that schematically shows processing circuitry used in 3D mapping, in accordance with an embodiment of the invention; 
         FIG. 4  is a schematic frontal view of a 3D mapping module, in accordance with another embodiment of the invention; 
         FIG. 5  is a schematic pictorial illustration showing details of the 3D mapping module of  FIG. 4 , in accordance with an embodiment of the invention; and 
         FIG. 6  is a schematic pictorial illustration showing a rear view of the 3D mapping module of  FIG. 4 , in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In some 3D mapping systems based on time-of-flight measurement, such as that described in the above-mentioned U.S. Patent Application Publication 2013/0207970, the same scanning mirror is used to scan both the pulsed beam that is transmitted toward the scene and the sensing area of the detector, which senses the reflected radiation, in both horizontal and vertical directions. This approach is advantageous in ensuring that the transmitted and received beam axes are mutually aligned, but it imposes difficult constraints on the optical design of the system. In other systems, separate mirrors are used to scan the transmitted beam and the sensing area of the detector, thus relaxing the optical constraints but giving rise to possible difficulties in alignment and synchronization of the sensing area with the transmitted beam. 
     Embodiments of the present invention address these difficulties by projecting a line of radiation and capturing the reflected radiation using a linear array of detectors, with a scanning mirror that scans both the line of radiation and the sensing area of the detectors together over a scene. This approach both simplifies the optical design of the scanning module and obviates mechanical problems associated with rapid scanning, while enabling compact, robust module designs. In some of these embodiments, the scanning mirror can be rotated so as to scan the emitted beams and the sensing area both over a first scene on one side of the apparatus and over a second scene on the opposite side of the apparatus, making it possible to create 3D maps of either or both of these scenes. 
     In the disclosed embodiments, mapping apparatus comprises an illumination assembly, which projects a line of radiation extending in a certain direction across a scene that is to be mapped, for example in a horizontal direction. In some of the embodiments described below, the illumination assembly comprises a linear array of radiation sources, which emit respective beams of radiation, with projection optics that collect and focus the emitted beams to form the line of radiation. Alternatively, however, the illumination assembly may comprise a single radiation source with suitable optics. 
     A detection assembly receives the radiation reflected from the scene within a sensing area that contains the projected line of the radiation (or at least a part of the projected line). For this purpose, the detection assembly comprises a linear array of detector elements and objective optics, which focus the reflected radiation from the sensing area onto the linear array. The sensing area is typically long and narrow, parallel to and in alignment with the line of radiation. For this purpose, the axis of the array of detector elements may also be aligned along the same direction as the line of radiation. 
     A scanning mirror scans the line of radiation and the sensing area together over the scene in a direction that is perpendicular to the line of radiation. Thus, for example, if the illumination assembly projects a horizontal line, the mirror scans the line vertically, or vice versa. This arrangement is advantageous in that the mirror can scan relatively slowly (for example, at 30 Hz to enable mapping at standard video refresh rates), and no high-speed scanning components are required. 
     Other embodiments of the present invention use a hybrid approach, combining a scanning illumination beam with a fixed array of detector elements for sensing the reflected radiation. A first scanning mirror scans the emitted beam in a first direction over a scene, while a second scanning mirror, as described above, scans both the emitted beam and the sensing area of the detector array over the scene in a second direction, perpendicular to the first direction. 
     Processing circuitry processes the signals output by the detector elements in response to the received radiation in order to construct a 3D map of an object in the scene. In the embodiments described below, the illumination assembly emits pulses of radiation, and the detector elements output signals that are indicative of respective times of flight of pulses from points in the scene, which are used by the processor in constructing the 3D map. Alternatively, the apparatus and techniques described herein may be applied, mutatis mutandis, in other sorts of 3D mapping systems. 
       FIG. 1  is a schematic, pictorial illustration of a system for 3D mapping, in accordance with an embodiment of the invention. The system is built around a 3D mapping module  20 , which is described in greater detail with reference to the figures that follow. Module  20  may be used, for example, in or together with a computing device for mapping a hand  24  of a user for purposes of gesture detection. This is just one possible, non-limiting application of the present embodiment, and module  20 , as well as other sorts of apparatus based on the principles described herein, may similarly be applied in other types of systems and used to map various other types of objects. 
     As shown in  FIG. 1 , module  20  emits a pulsed beam  26  of radiation through an exit aperture  28  toward a scene that includes hand  24 . Module  20  scans the beam over the scene in a predefined scan pattern  32 , such as a raster scan, which is generated by cooperative operation of two scanning mirrors as shown in  FIG. 2 . Each pulse emitted from exit aperture  28  illuminates a successive spot  30  in the scene along the scan pattern, and the spots in each row of scan pattern  32  define a projected line of radiation. Radiation  34  that is reflected from the scene at each spot  30  is collected through an entrance aperture  36  of module  20  and detected by a detection assembly in the module, which is likewise shown in the figures that follow. Processing circuitry in or associated with module  20  processes the signals output by the detection assembly in response to the reflected radiation  34  that is received through aperture  36  in order to construct a 3D map of hand  24  and/or other objects in the scene. 
     For convenience in the description that follows, the frontal plane of module  20  is taken to be the X-Y plane, as illustrated in  FIG. 1 , while the Z-axis corresponds to the direction of propagation of beam  26  when undeflected, i.e., roughly at the center of scan pattern  32 . Module  20  scans beam  26  across an X-Y plane. In pattern  32 , the X-axis of the scan is taken to be the “fast” axis, which is traversed by beam  26  many times in the course of each scan over the scene, while the Y-axis is taken to be the “slow” axis. These choices of the axes are arbitrary, however, and module  20  can be configured to generate other scan patterns, with different scan axes, as will be apparent to those skilled in the art after reading the present description. 
       FIG. 2  is a schematic pictorial illustration showing details of 3D mapping module  20 , in accordance with an embodiment of the invention. Mapping module  20  comprises an illumination assembly, comprising a radiation source  40 , which emits beam  26 , and a scanning mirror  42 , which receives and reflects beam  26  from source  40 . In a typical implementation, radiation source  40  comprises a laser diode, which emits ultra-short pulses, having a duration on the order of 1 ps. To minimize the size and weight of module  20  and enable high-speed scanning, mirror  42  in this embodiment is typically small (for example, less than 10 mm in diameter). Such mirrors can be made by micro-electro-mechanical systems (MEMS) techniques, as described, for example, in the above-mentioned U.S. Patent Application Publication 2013/0207970, with an electromagnetic, electrostatic, or piezoelectric drive. Alternatively, mirror  42  may comprise a rotating polygon or any other suitable type of scanning mirror that is known in the art. 
     In an alternative embodiment (not shown in the figures), multiple radiation sources can share mirror  42 , with the sources arranged so that their beams strike the mirror at different angles, thus scanning over different parts of the scene and increasing the pixel throughout of module  20  while decreasing the required mirror scan amplitude. 
     Mirror  42  rotates about an axis  44 , causing beam  26  to scan over the scene in the X-direction. A second mirror  46 , which rotates about an axis  48 , causes beam  26  to scan over the scene in the Y-direction. Typically, the small, lightweight mirror  42  rotates at high speed, possibly in a resonant scanning mode, while mirror  46  rotates at a slower speed. Mirror  46  may thus comprise a MEMS device or any other suitable sort of rotating mirror. 
     If the beam output by source  40  is not well collimated, optics  50  may be added in the beam path to improve collimation. Optics  50  may be positioned either where shown in  FIG. 2  or at any other suitable location, for example, between source and mirror  42  or between mirror  42  and mirror  46 . Additionally or alternatively, optics  50  may be used to enhance the scan range, as described, for example, in the above-mentioned U.S. Pat. No. 9,098,931. Furthermore, the distance between mirrors  42  and  46  is typically smaller than that shown in  FIG. 2 , with mirror  42  in or near the plane of the entrance pupil of the optical receiver. 
     Reflected radiation  34  from each of spots  30  is received by a detection assembly, comprising a linear array  54  of detector elements  56  and objective optics  52 , which focus the reflected radiation onto the detector elements. Optics  52  typically comprise a multi-element lens with a wide acceptance angle and may be positioned between array  56  and mirror  46 , rather than in the position shown in  FIG. 2 . It is desirable that the entrance pupil of the lens be close to mirror  46  to achieve a compact design. Additionally or alternatively, optics  52  comprise a narrowband filter, which passes the wavelength of source  40  while preventing ambient radiation from reading detector elements  56 . 
     Optics  52  thus define the sensing area of the detection assembly, which is essentially the optical projection by optics  52  of the area of detector elements  56 . Mirror  46  scans this sensing area over the scene, including hand  24 , in the Y-direction, simultaneously with scan pattern  32  of transmitted beam  26 . At least one of detector elements  56  will then capture the radiation reflected from each of spots  30  in the scan pattern. There is thus no need for a collection mirror to scan the sensing area at high speed in the X-direction. 
     In the pictured embodiment, array  54  comprises a single row of detector elements  56  arranged along an array axis, which in this example is parallel to the X-direction, i.e., parallel to axis  48  of mirror  46 . Alternatively, the array may comprise multiple, parallel rows of detector elements arranged in this way. In this geometry, as shown in  FIG. 2 , it is possible to arrange most of the key elements of module  20 , including radiation source  40 , mirrors  42  and  46 , and array  56 , in the X-Y plane that contains both the array axis and mirror axis  48 . This planar arrangement of the array elements is useful in achieving a compact design of module  20 , with a low profile in the Z-direction, as is shown in  FIG. 1 . 
       FIG. 3  is a block diagram that schematically shows processing circuitry used in or with 3D mapping module  20 , in accordance with an embodiment of the invention. This circuitry processes the signals output by detector elements  56  in response to received radiation  34  in order to construct the 3D map of hand  24  (or of other objects in the scene). The signals output by the detector elements are indicative of respective times of flight (TOF) of the pulses emitted by radiation source  40 , and the processing circuitry constructs the 3D map by measuring these times of flight. 
     For this purpose, detector elements  56  typically comprise sensitive, high-speed photodetectors, such as avalanche photodiodes or single-photon avalanche diode (SPAD) devices. When avalanche photodiodes or similar sorts of detectors are used, one or more pulse amplifiers, such as high-speed transimpedance amplifiers (TIAs), amplify the signals output by detector elements  56  in order to generate sharp output pulses for TOF measurement. Although it is possible to couple a respective TIA to each detector element  56 , in practice only one detector will actually receive reflected radiation at any given time: the detector whose sensing area is aligned along the X-axis with the current location of transmitted beam  26  and the corresponding spot  30 . Therefore, in the pictured embodiment, module  20  comprises only a single pulse amplifier  62 , and a multiplexer  60  selects detector elements  56  for connection to pulse amplifier  62  in synchronization with the scan of scanning mirror  42  about axis  44 . In other words, at any point during the scan, multiplexer  60  connects the input of amplifier  62  to the output of the detector element  56  that is aligned with transmitted beam  26  at that point. 
     The pulse output of amplifier  62  is input to a TOF circuit  64 , which compares the arrival time of each pulse at detector  56  to a reference signal indicating the time at which the pulse was emitted by transmitter  40  and generates a corresponding delay value. TOF circuit  64  may comprise a time-to-digital converter (TDC), for example. A depth processing circuit  66  collects the TOF values over the entire scan pattern  32  and combines them into a 3D map of the scene begin scanned. 
     When detector elements  56  comprise SPAD devices, no TIA is needed, and instead event timing histograms are created and analyzed in order to determine the TOF values for each pixel. 
     Since the beam from transmitter  40  in this embodiment is scanned over the scene, the resolution of module  20  is determined not by the pitch or number of detector elements  56  in array  54 , but rather by the accuracy of sensing and angular pointing, along with the pulse frequency. This feature is especially valuable when detector elements  56  comprise APD sensors, since APDs can be bigger than the required pixel size. 
     Alternatively, other sorts of processing circuitry, including one or multiple pulse amplifiers, may be coupled to the output of detector elements  56 . Furthermore, although the disclosed embodiments are directed specifically to TOF-based 3D mapping, the principles of the present invention may similarly be applied in other types of 3D mapping, such as the sort of pattern-based matching that is described in U.S. Pat. No. 9,098,931, as well as other applications of high-speed optical scanners and detectors. 
     Reference is now made to  FIGS. 4 and 5 , which schematically illustrate a 3D mapping module  120 , in accordance with another embodiment of the invention.  FIG. 4  is a frontal view, while  FIG. 5  is a pictorial illustration showing details of the components of the module. For convenience in the description that follows, as in the preceding embodiment, the frontal plane of module  120  is taken to be the X-Y plane, while the Z-axis corresponds to the direction of propagation of a line  122  of radiation emitted from module  120  when undeflected, i.e., roughly at the center of the scan pattern of the module. Line  122  is oriented along the X-direction and is scanned by module  120  in the Y-direction. These choices of the axes are arbitrary, however, and are used solely for the sake of clarity and convenience in the present description. 
     Mapping module  120  comprises an illumination assembly  123 , comprising a linear array  124  of radiation sources, which emit respective beams of radiation, and projection optics  126 , which collect and focus the emitted beams to form line  122 . (The term “line” is used in this context to mean a long, narrow area that is illuminated by the combined beams from array  124  or, alternatively, by the scanned beam in the preceding embodiment.) In the present embodiment, the axis of array  124  is oriented along the X-axis on the lower surface of a case  128  of module  120 ; and optics  126  comprise a pair of turning mirrors  130 ,  132  with a collimating lens  134  between them. (Turning mirrors  130 ,  132  shift the beam axes into closer proximity with the sensing area of an array  136  of detector elements, as described further hereinbelow.) Alternatively, array  124  may be mounted, for example, on the side of case  128 , in which case turning mirror  130  may be eliminated. In a typical implementation, the radiation sources in array  124  comprise laser diodes, which emit ultra-short pulses of infrared radiation in mutual synchronization, having a duration on the order of 1 ps. 
     A scanning mirror  138  reflects line  122  of radiation that is formed by optics  126  through a window  140  in case  128  toward the scene that is to be mapped. Mirror  138  rotates about a mirror axis  142  that is oriented along the X-direction, thus causing line  122  to scan over the scene in the Y-direction. In the pictured embodiment, mirror  138  is mounted on bearings  143  and is rotated at the desired scan rate by a suitable mechanism  144 , such as a motor or magnetic drive. Alternatively, mirror  138  may comprise a MEMS device, as is known in the art, or any other suitable sort of beam deflector. 
     Mirror  138  also reflects the radiation returned from the scene toward a detection assembly  145 , comprising linear array  136  of detector elements and objective optics  146 , which focus the reflected radiation from a sensing area  148  within the scene onto array  136 . (For enhanced compactness and reduction of undesirable geometric effects, turning mirror  132  may be formed on an oblique surface of one of the lenses in objective optics  146 .) Sensing area  148  corresponds to the projection by optics  146  of the area of the detector elements in array  136  onto the scene being mapped. Line  122  and sensing area  148  overlap in the plane of the scene that is being mapped. For good imaging and tracking between line  122  and sensing area  148  in the embodiment shown in the figures, an exit pupil  150  of projection optics  126  and an entrance pupil  152  of objective optics  146  are coplanar and located in close proximity to one another. To minimize the size of module  120  and reduce triangulation effects between the transmitted beams and the sensing areas, it is desirable that the plane of pupils  150  and  152  be located roughly midway between optics  146  and mirror  138 , and that the axes of the array of transmitted beams and of the sensing area be collinear in this plane. 
     In the pictured embodiment, array  136  comprises a single row of detector elements arranged along an array axis, which is likewise parallel to the X-axis, i.e., parallel to axis  142  of mirror  138 , as well as to the axes of line  122  and array  124  in this example. Alternatively, array  136  may comprise multiple, parallel rows of detector elements arranged in this way. In this geometry, as shown in the figures, it is possible to arrange most of the key elements of module  120 , including arrays  124  and  136  and mirror  138 , in the X-Y plane that contains both the array axes and mirror axis  142 . This planar arrangement is useful in achieving a compact design of module  120 , with a low profile in the Z-direction. Arrays  124  and  136  may conveniently be mounted on a common printed circuit substrate  154 , as shown in  FIG. 4 . 
     Processing circuitry (such as depth processing circuit  66  or other sorts of processing circuitry described above) used in or with 3D mapping module  120  processes the signals output by the detector elements in array  136  in response to the radiation reflected from sensing area  148 , in order to construct a 3D map of an object or objects in the scene. The signals output by the detector elements are indicative of respective times of flight (TOF) of the pulses emitted by the radiation sources in array  124 , and the processing circuitry constructs the 3D map based on these times of flight. For this purpose, the detector elements in array  136  typically comprise sensitive, high-speed photodetectors, such as avalanche photodiodes or single-photon avalanche diode (SPAD) devices. The configuration and uses of these detector types in module  120  are similar to those described above with reference to module  20 . 
     As in the preceding embodiment, other sorts of processing circuitry may be coupled to the outputs of the detector elements, and the principles of the present embodiment may similarly be applied in other types of 3D mapping, as well as other applications of high-speed optical scanners and detectors. 
       FIG. 6  is a schematic pictorial illustration showing a rear view of 3D mapping module  120 , in accordance with an embodiment of the invention. Scanning mirror  138  is rotatable so as to scan line  122  of radiation and sensing area  148  both over the scene on the front side of module  120  that is shown in  FIGS. 4 and 5  and over another scene on the opposite, rear side of module  120 , which is shown in  FIG. 6 . (The terms “front” and “rear” are used arbitrarily, for the sake of clarity, and may just as well be reversed in devices in which module  120  is installed.) The same illumination assembly  123  and detection assembly  145  are used in both front and rear scanning configurations. 
     To scan the rear side of module  120 , it is possible simply to rotate mirror  138  about mirror axis  142  so that the same reflective surface faces the rear side. To make module  120  still more compact, however, in the present embodiment mirror  138  has two opposing reflective surfaces: a front surface  156  that is shown in  FIGS. 4 and 5 , and a rear surface  158  that is shown in  FIG. 6 . Mirror  138  rotates about axis  142  so that line  124  and sensing area  148  reflect from front surface  156  when scanning over the scene on the front side of module, and from rear surface  158  when scanning over the scene on the rear side. As a consequence of this structure, mirror  138  need never rotate through the horizontal (X-Z) plane, and module  120  may thus be made very thin, for example less than 5 mm thick in the Z-direction. 
     To reduce the size of module  120  still further, rear surface  158  can be made smaller than front surface  156 , as illustrated in  FIG. 6 , so that mirror  138  has a profile in the Y-Z plane that is roughly trapezoidal. When mapping the scene on the rear side of module  120 , rear surface  158  reflects line  124  and sensing area  148  through a window  160  in the rear side of case  128 . The smaller rear surface  158  means that the collection aperture of objective optics  146 , and hence the sensitivity of detection assembly  145 , are smaller in the rear scanning configuration than in the front scanning configuration. This tradeoff of sensitivity against module size may be acceptable, for example, when the rear scanning configuration is used primarily for nearby scenes, in which the intensity of the radiation reflected back from sensing area  148  is relatively high. 
     Furthermore, the reduced aperture of optics  146  in the rear scanning configuration is useful in increasing the depth of field, which may include objects very close to module  120 . To increase the depth of field still further, rear surface  158  of mirror  138  may be masked, to decrease the light collection aperture still further. Alternatively or additionally, objective optics  146  may have different, adjustable focal positions for short- and long-range mapping. 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Metadata:
Filing Date: 20170307
Publication Date: 20200811
Grant Date: 20200811
Priority Date: 20100811
Inventors: SHPUNT, ALEXANDER
GERSON, YUVAL
Assignee: APPLE INC
CPC Classifications: [{"code": "G01C15/002", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01S17/42", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01B11/2518", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01C15/002", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06T17/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4817", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01B11/2518", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S7/4816", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06T17/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01C15/002", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/42", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01B11/2518", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S7/4817", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4816", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/89", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 59065099