Patent Description:
Document <CIT> discloses a LADAR system with lookdown and loitering capabilities. The sensor is mounted on a gimbal and capable of scanning in azimuth.

Document <CIT> discloses an FLIR/laser targeting and imaging system including an opto-electronic subsystem that employs a single pitch bearing and a common pitch/yaw afocal for both the laser energy and the IR energy.

Document <CIT> discloses a vehicle-based lidar system using multiple lasers. Each laser in an array of lasers can be sequentially activated.

Document <CIT> discloses a ranging device including a transmission optical system and a reception optical system. The system also includes a vibration isolation lens and a driving mechanism therefor.

Three-dimensional sensors can be applied in autonomous vehicles, drones, robotics, security applications, and the like. Scanning lidar sensors may achieve high angular resolutions appropriate for such applications at an affordable cost. However, scanning lidar sensors may be susceptible to external vibration sources as well as internal vibration sources. For example, when applied in an autonomous vehicle, scanning lidar sensors may be exposed to external vibrations from uneven roads, road noise, and engine noise. Internal noise from the scanning mechanism may also interfere with the operations of scanning lidars. Therefore, it may be desirable to include systems for mitigating vibrations and active vibration management systems in scanning lidar sensors.

The above is achieved by the combination of features of independent claim <NUM>.

According to the present invention, a scanning lidar system according to claim <NUM> includes an external frame, an internal frame attached to the external frame by vibration-isolation mounts, and an electro-optic assembly movably attached to the internal frame and configured to be translated with respect to the internal frame during scanning operation of the scanning lidar system.

According to some embodiments of the present invention, a scanning lidar system may include an external frame, an internal frame attached to the external frame by vibration-isolation mounts, an electro-optic assembly movably attached to the internal frame and configured to be translated with respect to the internal frame during scanning operation of the scanning lidar system, a counterweight movably attached to the internal fame, a driving mechanism mechanically coupled to the counterweight, a first sensor couple to the internal frame for measuring an amount of motion of the internal frame, and a controller coupled to the first sensor and the driving mechanism. The controller may be configured to cause a motion of the counterweight with respect to the internal frame based on the amount of motion of the internal frame measured by the first sensor.

According to some embodiments of the present invention, a scanning lidar system may include an external frame, an internal frame attached to the external frame by vibration-isolation mounts, an electro-optic assembly movably attached to the internal frame and configured to be translated with respect to the internal frame during scanning operation of the scanning lidar system, a counterweight movably attached to the internal fame, a driving mechanism mechanically coupled to the counterweight, a first sensor couple to the external frame for measuring an amount of motion of the external frame, and a controller coupled to the first sensor and the driving mechanism. The controller may be configured to cause a motion of the counterweight with respect to the internal frame based on the amount of motion of the external frame measured by the first sensor.

<FIG> illustrates schematically a lidar sensor <NUM> for three-dimensional imaging. The lidar sensor <NUM> includes an emitting lens <NUM> and a receiving lens <NUM>, both being fixed. The lidar sensor <NUM> includes a laser source 110a disposed substantially in a back focal plane of the emitting lens <NUM>. The laser source 110a is operative to emit a laser pulse <NUM> from a respective emission location in the back focal plane of the emitting lens <NUM>. The emitting lens <NUM> is configured to collimate and direct the laser pulse <NUM> toward an object <NUM> located in front of the lidar sensor <NUM>. For a given emission location of the laser source 110a, the collimated laser pulse <NUM>' is directed at a corresponding angle toward the object <NUM>.

A portion <NUM> of the laser pulse <NUM> is reflected off of the object <NUM> toward the receiving lens <NUM>. The receiving lens <NUM> is configured to focus the portion <NUM> of the laser pulse <NUM> reflected off of the object <NUM> onto a corresponding detection location in the focal plane of the receiving lens <NUM>. The lidar sensor <NUM> further includes a photodetector 160a disposed substantially at the focal plane of the receiving lens <NUM>. The photodetector 160a is configured to receive and detect the portion <NUM> of the laser pulse <NUM> reflected off of the object at the corresponding detection location. The corresponding detection location of the photodetector 160a is conjugate with the respective emission location of the laser source 110a.

The laser pulse <NUM> may be of a short duration, for example, <NUM> ns pulse width. The lidar sensor <NUM> further includes a processor <NUM> coupled to the laser source 110a and the photodetector 160a. The processor <NUM> is configured to determine a time of flight (TOF) of the laser pulse <NUM> from emission to detection. Since the laser pulse <NUM> travels at the speed of light, a distance between the lidar sensor <NUM> and the object <NUM> may be determined based on the determined time of flight.

The laser source 110a may be raster scanned to a plurality of emission locations in the back focal plane of the emitting lens <NUM>, and is configured to emit a plurality of laser pulses at the plurality of emission locations. Each laser pulse emitted at a respective emission location is collimated by the emitting lens <NUM> and directed at a respective angle toward the object <NUM>, and incidents at a corresponding point on the surface of the object <NUM>. Thus, as the laser source 110a is raster scanned within a certain area in the back focal plane of the emitting lens <NUM>, a corresponding object area on the object <NUM> is scanned. The photodetector 160a is raster scanned to a plurality of corresponding detection locations in the focal plane of the receiving lens <NUM>. The scanning of the photodetector 160a is performed synchronously with the scanning of the laser source 110a, so that the photodetector 160a and the laser source 110a are always conjugate with each other at any given time.

By determining the time of flight for each laser pulse emitted at a respective emission location, the distance from the lidar sensor <NUM> to each corresponding point on the surface of the object <NUM> may be determined. In some embodiments, the processor <NUM> is coupled with a position encoder that detects the position of the laser source 110a at each emission location. Based on the emission location, the angle of the collimated laser pulse <NUM>' may be determined. The X-Y coordinate of the corresponding point on the surface of the object <NUM> may be determined based on the angle and the distance to the lidar sensor <NUM>. Thus, a three-dimensional image of the object <NUM> may be constructed based on the measured distances from the lidar sensor <NUM> to various points on the surface of the object <NUM>. In some embodiments, the three-dimensional image may be represented as a point cloud, i.e., a set of X, Y, and Z coordinates of the points on the surface of the object <NUM>.

The intensity of the return laser pulse is measured and used to adjust the power of subsequent laser pulses from the same emission point, in order to prevent saturation of the detector, improve eye-safety, or reduce overall power consumption. The power of the laser pulse may be varied by varying the duration of the laser pulse, the voltage or current applied to the laser, or the charge stored in a capacitor used to power the laser. In the latter case, the charge stored in the capacitor may be varied by varying the charging time, charging voltage, or charging current to the capacitor. The intensity may also be used to add another dimension to the image. For example, the image may contain X, Y, and Z coordinates, as well as reflectivity (or brightness).

The angular field of view (AFOV) of the lidar sensor <NUM> may be estimated based on the scanning range of the laser source 110a and the focal length of the emitting lens <NUM> as, <MAT> where h is scan range of the laser source 110a along certain direction, and f is the focal length of the emitting lens <NUM>. For a given scan range h, shorter focal lengths would produce wider AFOVs. For a given focal length f, larger scan ranges would produce wider AFOVs. In some embodiments, the lidar sensor <NUM> may include multiple laser sources disposed as an array at the back focal plane of the emitting lens <NUM>, so that a larger total AFOV may be achieved while keeping the scan range of each individual laser source relatively small. Accordingly, the lidar sensor <NUM> may include multiple photodetectors disposed as an array at the focal plane of the receiving lens <NUM>, each photodetector being conjugate with a respective laser source. For example, the lidar sensor <NUM> may include a second laser source 110b and a second photodetector 160b, as illustrated in <FIG>. In other embodiments, the lidar sensor <NUM> may include four laser sources and four photodetectors, or eight laser sources and eight photodetectors. In one embodiment, the lidar sensor <NUM> may include <NUM> laser sources arranged as a <NUM>×<NUM> array and <NUM> photodetectors arranged as a <NUM>×<NUM> array, so that the lidar sensor <NUM> may have a wider AFOV in the horizontal direction than its AFOV in the vertical direction. According to various embodiments, the total AFOV of the lidar sensor <NUM> may range from about <NUM> degrees to about <NUM> degrees, or from about <NUM> degrees to about <NUM> degrees, or from about <NUM> degrees to about <NUM> degrees, depending on the focal length of the emitting lens, the scan range of each laser source, and the number of laser sources.

The laser source 110a may be configured to emit laser pulses in the ultraviolet, visible, or near infrared wavelength ranges. The energy of each laser pulse may be in the order of microjoules, which is normally considered to be eye-safe for repetition rates in the KHz range. For laser sources operating in wavelengths greater than about <NUM>, the energy levels could be higher as the eye does not focus at those wavelengths. The photodetector 160a may comprise a silicon avalanche photodiode, a photomultiplier, a PIN diode, or other semiconductor sensors.

The angular resolution of the lidar sensor <NUM> can be effectively diffraction limited, which may be estimated as, <MAT> where λ is the wavelength of the laser pulse, and D is the diameter of the lens aperture. The angular resolution may also depend on the size of the emission area of the laser source 110a and aberrations of the lenses <NUM> and <NUM>. According to various embodiments, the angular resolution of the lidar sensor <NUM> may range from about <NUM> mrad to about <NUM> mrad (about <NUM>-<NUM> degrees), depending on the type of lenses.

The laser sources and the photodetectors may be scanned using relatively low-cost flexure mechanisms, as described below.

<FIG> illustrates schematically a flexure mechanism <NUM> that may be used for scanning one or more laser sources 110a-110d and one or more photodetectors 160a-160d in the lidar sensor <NUM> illustrated in <FIG>. In this example, four laser sources <NUM>10a-<NUM>10d and four photodetectors 160a-160d are mounted on a same rigid platform <NUM>. The positions of the laser sources 110a-110d and the photodetectors 160a-160d are arranged such that each laser source 110a, 110b, 110c, or 110d is spatially conjugate with a corresponding photodetector 160a, 160b, 160c, or 160d. The platform <NUM> is coupled to a first base plate <NUM> by a first flexure comprising two flexure elements 220a and 220b. The flexure elements 220a and 220b may be deflected to the left or right by using a single actuator, such as the voice coil <NUM> and the permanent magnet <NUM> as shown in <FIG>, or by a piezoelectric actuator, and the like. The first base plate <NUM> may be coupled to a second base plate <NUM> by a second flexure comprising two flexure elements 270a and 270b. The flexure elements 270a and 270b may be deflected forward or backward by using a single actuator, such as the voice coil <NUM> and the permanent magnet <NUM> as shown in <FIG>, or by a piezoelectric actuator, and the like.

Thus, the laser sources 110a-110d and the photodetectors 160a-160d may be scanned in two dimensions in the focal planes of the emitting lens <NUM> and the receiving lens <NUM>, respectively, by the left-right movements of the flexure elements 220a and 220b, and by the forward-backward movements of the flexure elements 270a and 270b. Because the laser sources 110a-110d and the photodetectors 160a-160d are mounted on the same rigid platform <NUM>, the conjugate spatial relationship between each laser-photodetector pair is maintained as they are scanned, provided that the lens prescriptions for the emitting lens <NUM> and the receiving lens <NUM> are essentially identical. It should be appreciated that, although four laser sources <NUM>10a-<NUM>10d and four photodetectors 160a-160d are shown as an example in <FIG>, fewer or more laser sources and fewer or more photodetectors may be mounted on a single platform <NUM>. For example, one laser source and one photodetector, or two laser sources and two photodetectors, or eight laser sources and eight photodetectors may be mounted on a single platform <NUM>. Eight laser sources may be arranged as a <NUM>×<NUM> array, and eight photodetectors may be arranged as a <NUM>×<NUM> array, all mounted on the same rigid platform <NUM>.

A first position encoder <NUM> may be disposed adjacent the platform <NUM> for detecting coordinates of the laser sources 110a-110d in the left-right direction (i.e., the x-coordinates), and a second position encoder <NUM> may be disposed adjacent the first base plate <NUM> for detecting coordinates of the laser sources <NUM>10a-<NUM>10d in the forward-backward direction (i.e., the y-coordinates). The first position encoder <NUM> and the second position encoder <NUM> may input the x-y coordinates of the laser sources 110a-110d to the processor <NUM> to be used for constructing the three-dimensional image of the object <NUM>.

Other types of flexure mechanisms may be used in a scanning lidar sensor. Additional description related to a scanning lidar sensor is provided in <CIT>. Instead of using refractive lenses for collimating and focusing the laser pulses, reflective lenses or mirrors may be used for collimating and focusing the laser pulses. One of ordinary skill in the art would recognize many variations, alternatives, and modifications.

Scanning lidars, such as those described above in relation to <FIG> and <FIG>, may be susceptible to vibrations caused by the scanning mechanisms. For example, in the scanning lidar system illustrated in <FIG>, the back and forth scanning motions of the platform <NUM> in the left-right direction or the forward-back direction may cause vibrations of the whole lidar system. Such vibrations can impair the performance of the lidar system. For example, three-dimensional images acquired by the lidar system may be unstable due to such vibrations. Therefore, embodiments of the present invention may employ counter-balance techniques in scanning lidar systems for mitigating vibrations.

<FIG> illustrates a schematic cross-sectional view of a scanning lidar system <NUM>. The lidar system <NUM> may include a fixed frame <NUM>, a first platform <NUM> flexibly attached to the fixed frame <NUM>, and a second platform <NUM> flexibly attached to the fixed frame <NUM>. The lidar system <NUM> may further include a lens assembly attached to the first platform <NUM>. The lens assembly may include a first lens <NUM> and a second lens <NUM> mounted in a lens mount <NUM>. Each of the first lens <NUM> and the second lens <NUM> may include a single lens element, or multiple lens elements as illustrated in <FIG>. The first lens <NUM> may define a first optical axis in a first direction (e.g., in the direction of the Z-axis) and a first focal plane (e.g., in an X-Y plane). The second lens <NUM> may define a second optical axis substantially parallel to the first optical axis and a second focal plane (e.g., in an X-Y plane). The first lens <NUM> and the second lens <NUM> may have substantially the same focal length, so that the first focal plane and the second focal plane may be substantially coplanar.

The lidar system <NUM> may further include an electro-optic assembly attached to the second platform <NUM>. The electro-optic assembly may include one or more laser sources <NUM> and one or more photodetectors <NUM> mounted on the second platform <NUM>. The second platform <NUM> can be, for example, a printed circuit board including electric circuits for driving the one or more laser sources <NUM> and the one or more photodetectors <NUM>. The second platform <NUM> may be flexibly attached to the fixed frame <NUM> and positioned apart from the first platform <NUM> in the direction of the first optical axis or the second optical axis (e.g., in the Z direction), such that the one or more laser sources <NUM> lie substantially at the first focal plane of the first lens <NUM>, and the one or more photodetectors <NUM> lie substantially at the second focal plane of the second lens <NUM>. Each photodetector <NUM> may be positioned apart from a corresponding laser source <NUM> on the second platform <NUM> so as to be optically conjugate with respect to each other, as described above.

The first platform <NUM> may be flexibly attached to the fixed frame <NUM> via a first flexure <NUM>, such that the first platform <NUM> may be translated in a first plane (e.g., an X-Y plane) using a first actuator <NUM>. The second platform <NUM> may be flexibly attached to the fixed frame <NUM> via a second flexure <NUM>, such that the second platform <NUM> may be translated in a second plane (e.g., an X-Y plane) using a second actuator <NUM>. Each of the first actuator <NUM> and the second actuator <NUM> may comprise a voice coil and a magnet, a piezo motor, or the like.

The lidar system <NUM> may further include a controller <NUM> coupled to the first actuator <NUM> and the second actuator <NUM>. The controller may be configured to translate the first platform <NUM> to a plurality of first positions in the first plane through the first actuator <NUM>, and to translate the second platform <NUM> to a plurality of second positions in the second plane through the second actuator <NUM>. Each respective second position of the second platform <NUM> may correspond to a respective first position of the first platform <NUM>. In some embodiments, the motion of the second platform <NUM> may be substantially opposite to the motion of the first platform <NUM>, as illustrated by the arrows in <FIG>. In this manner, any vibration caused by the motion of the lens assembly may cancel any vibration caused by the motion of the electric-optic assembly to certain degree. Therefore, the lidar system <NUM> may impart a minimal net vibration to an external frame.

The first platform <NUM> and the second platform <NUM> may be translated with respect to each other such that a momentum of the lens assembly and a momentum of the electro-optic assembly substantially cancel each other. For example, the amount of motion of the first platform <NUM> may be inversely proportional to a mass of the lens assembly, and the amount of the motion of the second platform <NUM> may be inversely proportional to a mass of the electro-optic assembly. In this manner, the lidar system <NUM> may impart a negligible net vibration to an external frame.

<FIG> illustrates a schematic cross-sectional view of a scanning lidar system <NUM>. The lidar system <NUM> is similar to the lidar system <NUM> illustrated in <FIG>, but may further include a post <NUM> attached to the fixed frame <NUM> and a linkage member <NUM> attached to the post <NUM>. The linkage member <NUM> may mechanically couple the first flexure <NUM> and the second flexure <NUM> to each other so as to facilitate reciprocal motions between the first platform <NUM> and the second platform <NUM>. In some embodiments, a single actuator <NUM> may be coupled to either the first platform <NUM> or the second platform <NUM> for controlling both the motion of the first platform <NUM> and the motion of the second platform <NUM> through the linkage member <NUM>.

The linkage member <NUM> may be configured to force the first platform <NUM> and the second platform <NUM> to move in opposite directions. For example, the linkage member <NUM> may include an arm <NUM> attached to the post <NUM> at a pivot point <NUM>, as illustrated in <FIG>. As the second platform <NUM> is translated through the second flexure <NUM> using the actuator <NUM>, the arm <NUM> may rotate about the pivot point <NUM>, which may in turn cause the first platform <NUM> to move in an opposite direction with respect to the motion of the second platform <NUM> through the first flexure <NUM>. The linkage member <NUM> may pivot about the pivot point <NUM> by means of a bearing or a flexure attachment, which may allow pivot motions without adding frictional losses. The arm <NUM> of the linkage member <NUM> may also be attached to the first platform <NUM> and the second platform <NUM> by means of bearings or flexures. It should be noted that although the actuator <NUM> is depicted as attached to the second platform <NUM> in <FIG>, the actuator <NUM> may be attached to the first platform <NUM> in some other embodiments, such that a motion of the first platform <NUM> may cause a reciprocal motion of the second platform <NUM> through the linkage member <NUM>.

The linkage member may be configured such that a rate of motion of the first platform <NUM> is substantially inversely proportional to the mass of the lens assembly, and a rate of motion of the second platform <NUM> is substantially inversely proportional to the mass of the electro-optic assembly, so that a momentum of the lens assembly and a momentum of the electro-optic assembly substantially cancel each other. Therefore, the lidar system <NUM> may impart a negligible net vibration to an external frame. For example, as illustrated in <FIG>, the pivot point <NUM> may be positioned such that a ratio of the distance a from the pivot point <NUM> to the end of the arm <NUM> that is attached to the first flexure <NUM> and the distance b from the pivot point <NUM> to the other end of the arm <NUM> that is attached to the second flexure <NUM> may be inversely proportional to a ratio of the mass of the lens assembly and the mass of the electro-optic assembly.

<FIG> illustrates a schematic cross-sectional view of a scanning lidar system <NUM> according to some further embodiments of the present invention. The lidar system <NUM> is similar to the lidar system <NUM> illustrated in <FIG>, but here the first platform <NUM> and the second platform <NUM> are coupled to each other via the actuator <NUM>. The actuator <NUM> may be configured to cause the first platform <NUM> and the second platform <NUM> to move in opposite directions. For example, the actuator <NUM> may include a voice coil and a first magnet attached to the first flexure <NUM>, as well as a second magnet <NUM> attached to the second flexure <NUM>. Activation of the voice coil may cause the first platform <NUM> to move in one direction and the second platform <NUM> to move in the opposite direction, as illustrated by the arrows in <FIG>.

<FIG> is a simplified flowchart illustrating a method <NUM> of three-dimensional imaging using a scanning lidar system. The method <NUM> may include, at <NUM>, translating a lens assembly to a plurality of first positions. The lens assembly may include a first lens defining a first optical axis in a first direction and a first focal plane, and a second lens defining a second optical axis substantially parallel to the first optical axis and a second focal plane.

The method <NUM> may further include, at <NUM>, translating an electro-optic assembly to a plurality of second positions, wherein the electro-optic assembly moves in a direction substantially opposite to motion of the lens assembly. Each respective second position corresponds to a respective first position of the lens assembly. The electro-optic assembly may include a first laser source positioned substantially at the first focal plane of the first lens, and a first photodetector positioned substantially at the second focal plane of the second lens. The first laser source and the first photodetector are spaced apart from each other so as to be optically conjugate with respect to each other.

The method <NUM> may further include, at <NUM>, at each of the plurality of second positions, emitting, using the first laser source, a laser pulse; and at <NUM>, collimating and directing, using the first lens, the laser pulse towards one or more objects. A portion of the laser pulse may be reflected off of the one or more objects. The method <NUM> further includes, at <NUM>, receiving and focusing, using the second lens, the portion of the laser pulse reflected off of the one or more objects to the first photodetector; at <NUM>, detecting, using the first photodetector, the portion of the laser pulse; and at <NUM>, determining, using a processor, a time of flight between emitting the laser pulse and detecting the portion of the laser pulse. The method <NUM> further includes, at <NUM>, constructing a three-dimensional image of the one or more objects based on the determined times of flight.

The lens assembly and the electro-optic assembly may be translated with respect to each other such that a momentum of the lens assembly and a momentum of the electro-optic assembly substantially cancel each other. In some embodiments, the lens assembly and the electro-optic assembly may be mechanically coupled to each other via a linkage member so as to facilitate reciprocal motions between the lens assembly and the electro-optic assembly, and translating the lens assembly and translating the electro-optic assembly are performed through an actuator coupled to one of the lens assembly or the electro-optic assembly. In some other embodiments, the lens assembly and the electro-optic assembly may be mechanically coupled to each other via an actuator, and translating the lens assembly and translating the electro-optic assembly are performed through the actuator.

Translating the lens assembly may include raster scanning the lens assembly in one dimension, and translating the electro-optic assembly may include raster scanning the electro-optic assembly in one dimension. In some other examples, translating the lens assembly may include raster scanning the lens assembly in two dimensions, and translating the electro-optic assembly may include raster scanning the electro-optic assembly in two dimensions.

As discussed above, scanning lidar systems may be susceptible to external vibrations as well as internal vibrations. According to the present invention, a scanning lidar system utilizes vibration isolation mounts and may utilize active vibration management systems to mitigate effects of vibrations.

<FIG> illustrates schematically a system <NUM> for vibration management in a scanning lidar sensor according to some embodiments of the present invention. The system <NUM> includes an external frame <NUM> and an internal frame <NUM>. A lidar sensor <NUM> may be attached to the internal frame <NUM>. The lidar sensor <NUM> may include moving parts for scanning. For example, the lidar sensor <NUM> may include a lens assembly and an electro-optic assembly, either or both of which may be translated with respect to the internal frame <NUM>, similar to the lidar sensors illustrated in <FIG>. The internal frame <NUM> can be a housing for the lidar sensor. The external frame <NUM> can be a vehicle, a drone, or the like where the lidar sensor is utilized for three-dimensional sensing. For example, in an autonomous vehicle, the external frame <NUM> may be a front bumper of the vehicle on which the internal frame <NUM> of the lidar sensor <NUM> is mounted. The external frame <NUM> may also be a housing larger in size than the internal frame <NUM>. The internal frame <NUM> is attached to the external frame <NUM> using vibration isolation mounts <NUM> and <NUM>. The vibration isolation mounts <NUM> and <NUM> may include rubber dampers, springs, or other types of shock absorbers.

The system <NUM> may further include active vibration management mechanisms. In some embodiments, the system <NUM> may include a first sensor <NUM> coupled to the internal frame <NUM> for measuring residual motions of the internal frame <NUM> caused by external vibrations. The first sensor <NUM> may also be used to measure motion and vibration resulting from the internal scanning mechanism of the lidar sensor <NUM>. The first sensor <NUM> may be referred to as an internal sensor. The first sensor <NUM> may comprise an accelerometer that can measure motions along one axis, two axes, or three axes (e.g., along the X-, Y-, and/or Z-axes). In some other embodiments, the first sensor <NUM> may comprise a displacement sensor, such as an encoder, a capacitive sensor, a Hall sensor, or the like.

The system <NUM> may further include one or more actuators <NUM> and <NUM> coupled to the internal frame <NUM> for moving the internal frame <NUM> with respect to the external frame <NUM>. For example, a first actuator <NUM> may be configured to move the internal frame <NUM> up or down (e.g., along the Z-axis) with respect to the external frame <NUM>, and a second actuator <NUM> may be configured to move the internal frame <NUM> forward or backward (e.g., along the X-axis) with respect to the external frame <NUM>, as illustrated in <FIG>. Similarly, a third actuator (not shown in <FIG>) may be configured to move the internal frame <NUM> left or right (e.g., along the Y-axis) with respect to the external frame <NUM>. Each of the first actuator <NUM> and the second actuator <NUM> may comprise a voice coil motor, a piezo motor, or the like.

The system <NUM> may further include a controller <NUM> coupled to the first sensor <NUM>, the first actuator <NUM>, and the second actuator <NUM> The controller <NUM> may be configured to provide "feedback" compensation for the residue motions of the internal frame <NUM> caused by external or internal vibrations. For example, the controller <NUM> may cause the internal frame <NUM> to be translated up or down (e.g., along the Z-axis) through the first actuator <NUM>, or be translated forward or back (e.g., along the X-axis) through the second actuator <NUM>, based on the amount of motion of the internal frame <NUM> measured by the first sensor <NUM>.

The system <NUM> may further include a second sensor <NUM> coupled to the external frame <NUM> for measuring vibration motions of the external frame <NUM> before such motions are attenuated by the vibration isolation mounts <NUM> and <NUM>. The second sensor <NUM> may be referred to as an external sensor. For example, when applied in an autonomous vehicle, the vibration motions of the external frame <NUM> can be due to uneven roads, road noise, engine noise, and the like, as well as internal noise from the scanning mechanism of the lidar system. The second sensor <NUM> may comprise an accelerometer that can measure motions along one axis, two axes, or three axes (e.g., along the X-, Y-, and/or Z-axes). In some other embodiments, the second sensor <NUM> may comprise a displacement sensor, such as an encoder, a capacitive sensor, a Hall sensor, or the like.

In some embodiments, the controller <NUM> may also be coupled to the second sensor <NUM> and configured to provide "feedforward" compensation based on the amount of motion of the external frame <NUM> measured by the second sensor <NUM>. Modeling of the system response to external vibrations and resonances may be used to control the feedforward corrections. Feedforward corrections are proactive, and therefore may respond faster as compared to feedback corrections, which are reactive.

In some cases, translational motions of the internal frame <NUM> may not adequately compensate for large motions caused by the vibration of the external frame <NUM>. For example, when a car hits a large pot hole, the car may have a large rocking motion in its pitch (e.g., a rotation about the Y-axis). If left uncompensated, this rocking motion may cause a lidar to aim upward toward the sky or downward toward the ground, instead of aiming toward the front of the car. Therefore, the internal frame <NUM> may be tilted up or down (and/or left or right) to compensate for such tilting motions of the external frame <NUM>. For example, if the first actuator <NUM> is positioned off-center between the vibration isolation mounts <NUM> and <NUM>, the internal frame <NUM> may be tilted up or down about the Y-axis through the first actuator <NUM>.

The signals from the first sensor <NUM> and/or the second sensor <NUM> may be used for image stabilization, either mechanically or digitally. Mechanical image stabilization for the most part may be achieved through vibration cancellation as described above. However, due to the complexity of mechanical vibration modes, the controller <NUM> may utilize a model or empirical approach to its feedback control in order to more effectively provide image stabilization. Additionally, signals from the first sensor <NUM> (and the second sensor <NUM> if available) may be sent to an image processing unit for the lidar sensor <NUM>. Residual errors detected by the first sensor <NUM> and/or the second sensor <NUM> can be used by the image processing unit to digitally shift the image, thus providing a digital image stabilization function.

<FIG> illustrates schematically a system <NUM> for vibration management in a scanning lidar sensor according to some embodiments of the present invention. The system <NUM> is similar to the system <NUM> illustrated in <FIG>, but may further include a third actuator <NUM> positioned apart from the first actuator <NUM>. The controller may be further coupled to the third actuator <NUM>, and configured to compensate pitch motions (e.g., rotations about the Y-axis) of the external frame <NUM> by pushing the first the internal frame <NUM> by the first actuator <NUM> and pulling the internal frame <NUM> by the third actuator <NUM>, or vice versa. Similarly, the system <NUM> may further include a fourth actuator (not shown in <FIG>) positioned apart from the second actuator <NUM> (e.g., along the Y-axis), for compensating the yaw motions (e.g., rotations about the Z-axis) of the external frame <NUM>.

According to some embodiments of the present invention, counter-moving masses may be used for active vibration management. <FIG> illustrates schematically a system <NUM> for vibration management in a scanning lidar sensor according to some embodiments of the present invention. The system <NUM> may include a counter-mass <NUM> movably attached to the internal frame <NUM>. The system <NUM> may further include a first actuator <NUM> mechanically coupled to the counter-mass <NUM> for moving the counter-mass <NUM> along the Z-axis (e.g., up or down). The first actuator <NUM> may comprise a voice coil motor, a piezo motor, or the like.

A controller <NUM> may be coupled to the first sensor <NUM> and the first actuator <NUM>, and configured to control the first actuator <NUM> based on the amount of motion of the internal frame <NUM> as measured by the first sensor <NUM>. For example, in response to the first sensor <NUM> sensing an upward motion (e.g., along the positive Z direction) of the internal frame <NUM>, the controller <NUM> may cause the counter-mass <NUM> to move downward (e.g., along the negative Z direction) with respect to the internal frame <NUM>, so that a net movement of the internal frame <NUM> may be substantially zero. The counter-mass <NUM> may preferably be positioned near the center of mass of the internal frame <NUM> including the mass of the lidar sensor <NUM> and other associated parts.

The system <NUM> may also include a second actuator <NUM> mechanically coupled to the counter-mass <NUM> for moving the counter-mass <NUM> along the X-axis (e.g., forward or backward). The controller <NUM> may be further coupled to the second actuator <NUM> and configured to cause the counter-mass <NUM> to move along the X-axis based on the amount of motion of the internal frame <NUM> along the X-axis as measured by the first sensor <NUM>, so as to result in a nearly zero net motion of the internal frame <NUM> along the X-axis. Similarly, the system <NUM> may also include a third actuator (not shown in <FIG>) for moving the counter-mass <NUM> along the Y-axis.

The controller <NUM> may also be coupled to the second sensor <NUM> (i.e., the external sensor) and configured to provide "feedforward" compensation of the external vibrations by moving the counter-mass <NUM> accordingly based on the amount of motions of the external frame <NUM> as measured by the second sensor <NUM>. As discussed above, feedforward corrections may respond faster than feedback corrections.

In some examples, more than one counter-masses may be deployed for active vibration management. <FIG> illustrates schematically a system <NUM> for vibration management in a scanning lidar sensor according to some embodiments of the present invention. Similar to the system <NUM> illustrated in <FIG>, the system <NUM> may include a first counter-mass <NUM> movably attached to the internal frame <NUM>, a first actuator <NUM> mechanically coupled to the first counter-mass <NUM> for moving the first counter-mass <NUM> along the Z-axis, and a second actuator <NUM> mechanically coupled to the first counter-mass <NUM> for moving the first counter-mass <NUM> along the X-axis. In addition, the system <NUM> may include a second counter-mass <NUM> movably attached to the internal frame <NUM>, a third actuator <NUM> mechanically coupled to the second counter-mass <NUM> for moving the second counter-mass <NUM> along the Z-axis, and a fourth actuator <NUM> mechanically coupled to the second counter-mass <NUM> for moving the second counter-mass <NUM> along the X-axis. The system <NUM> may be able to account for the fact that a single actuator may not act in line with the center of mass of the internal frame <NUM>. Also, the relative movements of the first counter-mass <NUM> and the second counter-mass <NUM> with respect to each other may cause a torsional motion of the internal frame <NUM>, such as a rotation about the Y-axis (i.e., a pitch motion) or a rotation about the X-axis (i.e., a roll motion) of the internal frame <NUM>, so as to compensate for torsional vibrations.

A plurality of laser sources and/or a plurality of photodetectors may be mounted on a platform in a configuration that accounts for the field curvature of a lens. Field curvature, also known as "curvature of field" or "Petzval field curvature," describes the optical aberration in which a flat object normal to the optical axis cannot be brought properly into focus on a flat image plane. Consider a single-element lens system for which all planar wave fronts are focused to a point at a distance f from the lens, f being the focal length of the lens. Placing this lens the distance f from a flat image sensor, image points near the optical axis may be in perfect focus, but rays off axis may come into focus before the image sensor. This may be less of a problem when the imaging surface is spherical. Although modern lens designs, for example lens designs that utilize multiple lens elements, may be able to minimize field curvature (or to "flatten the field") to a certain degree, some residue field curvature may still exist.

In the presence of field curvature of a lens, if a plurality of laser sources <NUM>10a-<NUM>10d are mounted on a planar surface, such as illustrated in <FIG>, laser pulses emitted by laser sources that are positioned off from the optical axis may not be perfectly collimated by the emission lens <NUM> due to field curvature of the emission lens <NUM>. Similarly, if a plurality of photodetectors 160a-160d are mounted on a planar surface as illustrated in <FIG>, the laser pulses reflected off of objects may not be brought into perfect focus by the receiving lens <NUM> at the photodetectors that are positioned off from the optical axis due to field curvature of the receiving lens <NUM>.

<FIG> illustrates a schematic cross-sectional view of a mounting configuration for optical components in a scanning lidar system that may take into account lens field curvatures. A lens <NUM> may be mounted on a lens holder <NUM>. The lens <NUM> may be characterized by an optical axis <NUM> that passes through the lens center <NUM>, and a surface of best focus <NUM> at a distance f from the lens <NUM>, f being the focal length of the lens <NUM>. The surface of best focus <NUM> may be curved due to field curvature as discussed above, and may be referred to as a curved "focal plane" of the lens <NUM>. A plurality of laser sources <NUM> may be mounted on a surface <NUM> of a platform <NUM> positioned approximately at the distance f from the lens <NUM> along the optical axis <NUM>. The surface <NUM> of the platform <NUM> may have a curved shape that substantially matches the surface of best focus <NUM> of the lens <NUM>, so that an emission surface <NUM> of each of the plurality of laser sources <NUM> may lie approximately at the surface of best focus <NUM> of the lens <NUM>. By mounting the plurality of laser sources <NUM> in this configuration, laser pulses emitted by each laser source <NUM> may be nearly perfectly collimated by the lens <NUM> even if the laser source <NUM> is positioned off from the optical axis <NUM>.

For example, assuming that the surface of best focus <NUM> of the lens <NUM> has a spherical shape, the surface <NUM> of the platform <NUM> may be configured to have a spherical shape so that an emitting surface <NUM> of each laser source <NUM> may lie substantially on the surface of best focus <NUM> of the lens <NUM>. In cases where the surface of best focus <NUM> of the lens <NUM> has a curved shape other than spherical, such as ellipsoidal, conical, or wavy shaped, the surface <NUM> of the platform <NUM> may be shaped accordingly.

Similarly, the plurality of laser sources <NUM> illustrated in <FIG> may be replaced by a plurality of photodetectors, so that a detection surface <NUM> of each of the plurality of photodetectors <NUM> may lie substantially at the surface of best focus <NUM> of the lens <NUM>. In this configuration, laser pulses reflected off of objects may be brought into near perfect focus by the lens <NUM> at the detection surface <NUM> of each photodetector <NUM> even if the photodetector <NUM> is positioned off from the optical axis <NUM> of the lens <NUM>.

A plurality of laser sources and a plurality of photodetectors may share a same lens. The photodetectors may be placed closely adjacent to their corresponding lasers, such that some of the returning light is intercepted by the photodetector. Positions either to the side, in front of the laser, or behind the laser are possible. Because the laser beam typically has a narrow angular distribution and only utilizes the central portion of the lens, certain lens aberrations, such as spherical aberration, may be employed to advantage to direct some returning light, from the outer portions of the lens, to the photodetectors without overly disturbing the focus properties of the outgoing laser beam. In an alternative design, a beam splitter may be utilized to separate the outgoing and incoming beams. This may allow the lasers and detectors to share a conjugate point of the lens without physically overlapping in space.

<FIG> illustrates a schematic cross-sectional view of a mounting configuration for optical components in a scanning lidar system. Here, a platform <NUM> may have a planar surface <NUM>, and the plurality of laser sources (or photodetectors) <NUM> may be mounted on the planar surface <NUM> of the platform <NUM>. The plurality of laser sources <NUM> may have varying heights h depending on their positions with respect to the optical axis <NUM> of the lens <NUM>, such that an emitting surface <NUM> of each respective laser source <NUM> may lie substantially on the surface of best focus <NUM> of the lens <NUM>. For example, for a spherical-shaped surface of best focus <NUM>, the laser sources <NUM> farther away from the optical axis <NUM> may have greater heights than those of the laser sources <NUM> closer to the optical axis <NUM>, as illustrated in <FIG>, so as to account for the curvature of the surface of best focus <NUM>. As an example, each laser source <NUM> (or photodetector die) may be placed in a respective surface-mount package that places the die at a respective height h above the bottom of the package. The respective height h may vary depending on the position of the laser source <NUM> (or photodetector die) with respect to the optical axis <NUM>. The packages are then subsequently soldered to a printed circuit board placed and positioned so that each die is correctly located at an image point of the lens <NUM>.

<FIG> illustrates a schematic cross-sectional view of a mounting configuration for optical components in a scanning lidar system. Here, the plurality of laser sources (or photodetectors) <NUM> may have substantially the same height h. But the platform <NUM> may have a surface <NUM> with a stepped profile, such that an emitting surface <NUM> of each respective laser source <NUM> may lie substantially on the surface of best focus <NUM> of the lens <NUM>.

Laser sources and photodetectors may be mounted in a configuration that also takes into account possible distortion and vignetting of a lens. <FIG> illustrates a schematic cross-sectional view of a mounting configuration for optical components in a scanning lidar system. Similar to the mounting configuration illustrated in <FIG>, a plurality of laser sources (or photodetectors) <NUM> may be mounted on a curved surface <NUM> of a platform <NUM> so that the emission surface <NUM> of each laser source <NUM> lies substantially at the surface of best focus <NUM> of the lens <NUM>. In addition, the plurality of laser sources <NUM> are tilted at varying angles, such that a normal of the emission surface <NUM> of each laser source <NUM> may point substantially toward the lens center <NUM>. In this configuration, laser pulses emitted by laser sources <NUM> that are positioned off from the optical axis <NUM> may be collimated by the lens <NUM> with minimal distortion and vignetting. It should be understood that the term "lens center" may refer to the optical center of the lens <NUM>. The lens center <NUM> may be a geometrical center of the lens <NUM> in cases where the lens <NUM> can be characterized as a thin lens. Some compound lenses may be partially telecentric, in which case the preferred orientation of the normal to the laser emission or detector surface may not point toward the geometric center of the lens, but rather the optical center of the lens, which will typically be at an angle closer to the optical axis of the lens.

A plurality of photodetectors may be mounted on a planar surface of the platform <NUM>. A plurality of photodetectors may be mounted on the curved surface <NUM> of the platform <NUM>, so that the detection surface of each photodetector may point substantially toward the lens center <NUM>. Thus, image rays may impinge on the photodetectors substantially perpendicular to the detection surfaces of the photodetectors so that optimal detection efficiencies may be achieved. <FIG> illustrates a schematic cross-sectional view of a mounting configuration for optical components in a scanning lidar system. Here, a platform <NUM> may have a surface <NUM> that includes a plurality of facets with varying orientations, such that the normal of each facet <NUM> substantially points toward the lens center <NUM> of the lens <NUM>. Each of the plurality of laser sources may include a surface-emitting laser, such as a vertical-cavity surface-emitting laser (VCSEL), or a side-emitting laser mounted in a package in an orientation such that its light is emitted vertically with respect to the package.

<FIG> shows a schematic cross-sectional view of a laser source <NUM> that may be utilized. The laser source <NUM> may include a surface-emitting laser chip <NUM> mounted on a chip base <NUM> with a leveled surface <NUM>. The laser source <NUM> may be covered with a transparent cover <NUM>, and may include solder pads <NUM> and <NUM> on chip base <NUM>. The laser source <NUM> may, for instance, be a package that is designed to be soldered to the surface of a printed circuit board.

<FIG> illustrates a schematic cross-sectional view of a mounting configuration for optical components in a scanning lidar system. Here, a plurality of laser sources <NUM> are mounted on a platform <NUM> with a planar surface <NUM>. The plurality of laser sources <NUM> may have varying heights h and varying surface slanting angles depending on the position of each respective laser source <NUM> with respect to the optical axis <NUM>, such that the normal of the emission surface <NUM> of each respective laser source <NUM> points substantially toward the lens center <NUM>.

<FIG> show schematic cross-sectional views of some exemplary laser sources <NUM> and <NUM> that may be utilized. Each of the laser sources <NUM> and <NUM> may include a surface-emitting laser chip <NUM> surface-mounted on a chip base <NUM> or <NUM> with a slanted surface <NUM> or <NUM>. The surface slanting angle α and the base height h can vary depending on the position of the laser source with respect to the optical axis as discussed above. For example, a laser source positioned closer to the optical axis <NUM> may have a relatively smaller slanting angle α as illustrated in <FIG>, and a laser source positioned farther away from the optical axis <NUM> may have a relatively larger slanting angle α as illustrated in <FIG>. The laser source <NUM> or <NUM> may be covered with a transparent cover <NUM>, and may include solder pads <NUM> and <NUM> on chip base <NUM> or <NUM>. The laser source <NUM> or <NUM> may, for instance, be a package that is designed to be soldered to the surface of a printed circuit board. A side-emitting laser chip may also be used, in which case the laser chip may be oriented in the package such that its light is emitted perpendicular to the surface <NUM> or <NUM>.

<FIG> illustrates a schematic cross-sectional view of a mounting configuration for optical components in a scanning lidar system. Here, a plurality of laser sources <NUM> are mounted on a platform <NUM> with a substantially planar surface <NUM>. The plurality of laser sources <NUM> may have substantially the same height h but varying surface slanting angles depending on the position of each respective laser source <NUM> with respect to the optical axis <NUM> of the lens, such that the normal of the emission surface <NUM> of each respective laser source <NUM> points substantially toward the lens center <NUM>. As illustrated, the emission surface <NUM> of each respective laser source <NUM> may lie substantially at a focal plane <NUM> of the lens <NUM>.

<FIG> illustrates a schematic cross-sectional view of a mounting configuration for optical components in a scanning lidar system. Here, a plurality of laser sources <NUM> are mounted on a platform <NUM> with a substantially planar surface <NUM>. Each of the plurality of laser sources <NUM> may be tilted at a respective tilting angle, such that the normal of the emission surface <NUM> of each respective laser source <NUM> points substantially toward the lens center <NUM>. As illustrated, the emission surface <NUM> of each respective laser source <NUM> may lie substantially at a focal plane <NUM> of the lens <NUM>.

<FIG> illustrates a schematic cross-sectional view of a mounting configuration for optical components in a scanning lidar system. The lidar system may include a first lens <NUM> and a second lens <NUM>. The first lens <NUM> has a lens center <NUM>, and is characterized by a first optical axis <NUM> along a first direction and a first surface of best focus <NUM>. The second lens <NUM> has a lens center <NUM>, and is characterized by a second optical axis <NUM> substantially parallel to the first optical axis <NUM> and a second surface of best focus <NUM>. The lidar system may further include a plurality of surface-emitting laser sources <NUM> and a plurality of photodetectors <NUM> mounted on a platform <NUM>. The platform <NUM> may be a printed circuit board. The platform <NUM> is spaced apart from the first lens <NUM> and the second lens <NUM> along the first direction. The platform <NUM> may have a surface <NUM> (extending substantially in the direction perpendicular to the paper, i.e., the Z direction) that includes a plurality of first facets <NUM>. Each surface-emitting laser source <NUM> may be mounted on a respective first facet <NUM>. The plurality of first facets <NUM> may be positioned and oriented such that an emission surface <NUM> of each respective laser source <NUM> lies substantially at the first surface of best focus <NUM> of the first lens <NUM> and its normal points substantially toward the lens center <NUM> of the first lens <NUM>. The surface <NUM> of the platform <NUM> may further include a plurality of second facets <NUM>. Each photodetector <NUM> may be mounted on a respective second facet <NUM>. The plurality of second facets <NUM> may be positioned such that a detection surface <NUM> of each respective photodetector <NUM> lies at a respective position on the second surface of best focus <NUM> of the second lens <NUM> that is optically conjugate with a respective position of a corresponding laser source <NUM>. The plurality of second facets <NUM> may be oriented such that the normal of the detection surface <NUM> may point substantially toward the lens center <NUM> of the second lens <NUM>.

Claim 1:
A scanning lidar system (<NUM>; <NUM>) comprising:
an external frame (<NUM>);
an internal frame (<NUM>) attached to the external frame (<NUM>) by vibration-isolation mounts (<NUM>, <NUM>); and
an electro-optic assembly (<NUM>) including a first laser source (110a) and a first photodetector (160a),
characterized in that
the electro-optic assembly (<NUM>) is movably attached to the internal frame (<NUM>) and configured to be translated with respect to the internal frame (<NUM>) during scanning operation of the scanning lidar system (<NUM>, <NUM>).