Scanner control for LiDAR systems

Abstract

A scanner (120) for a laser radar system (100) and a method for controlling the scanner (120) are provided. The method includes: generating a trigger signal by a position sensor of the scanner (120); generating a single drive signal including a first component of a first frequency and a second component of a second frequency, the first component and the second component being superimposed at a fixed phase relationship by means of the trigger signal; sending the single drive signal to the scanner (120), the scanner (120) having a resonant response at the first frequency; and actuating the scanner (120) to perform a first periodic motion around a first axis at the first frequency and a second periodic motion around a second axis at the second frequency.

Description

Background Art

[0001] LiDAR (Light Detection and Ranging) technology can be used to obtain three-dimensional information about the environment by measuring the distance to an object. A LiDAR system may include at least one light source configured to emit light pulses and at least one detector configured to receive returning light pulses. The returning light pulse or light beam may be referred to as an echo beam. Based on the elapsed time (i.e., time of flight) between the emission of the light pulse and the detection of the returning light pulse, the distance may be obtained. The light pulse may be generated by a laser transmitter and then shaped (collimated or focused) by a lens or lens assembly. The returning light pulse may be received by a detector located near the laser transmitter. The returning light pulse may be scattered light from the surface of an object.

[0002] In some cases, multiple light pulses or sequences of light pulses can be emitted into an environment to scan a large area. In some cases, lidar systems can utilize scanners to steer one or more light beams in one or more directions according to a scanning pattern. It would be important to provide lidar systems with improved scanner control to increase the efficiency of sampling the environment or providing adaptive scanning patterns. Summary of the Invention

[0003] There is a need for improved lidar systems for three-dimensional measurement. There is also a need for lidar systems with fine-grained controllable scan patterns. In some cases, lidar systems can utilize a scanner to direct one or more light beams in one or more directions, which may require that the movement of the scanner be controlled by an improved control system. In some cases, to achieve a desired scan pattern, the movement of the scanner can be controlled at a fine-grained level. The provided lidar system can meet the above needs by providing an improved scanner that is configured to direct light pulses according to a configurable scan pattern. In some cases, to achieve a desired scan pattern, the disclosed system or method provides a mechanism for controlling the scanner, thereby improving the efficiency of sampling the environment and allowing automatic adaptation to various real-time conditions. In particular, the scan pattern / path and / or measurement resolution can be adapted to real-time conditions (e.g., environmental conditions). The provided lidar system is capable of dynamically adjusting the resolution of sampling points emitted into a selected area in 3D space, as well as the x and / or y resolution of pixels in a selected area of a 3D point cloud image. The provided methods and apparatus can be used in conjunction with light source control so that the light beam can be emitted into space based on the movement of the scanner. By integrating the control of the scanner and the light source, the pixel (point) distribution or resolution in selected areas of the image frame can be dynamically controlled in the x- and y-directions. In addition, the provided mechanism can allow the stabilization of LiDAR images or point cloud images across image frames.

[0004] In one aspect of the present invention, a method for controlling a scanner of a laser radar system is provided. The method may include: generating a trigger signal from a position sensor of the scanner; generating a single drive signal including a first component at a first frequency and a second component at a second frequency, wherein the first component and the second component are superimposed at a fixed phase relationship by means of the trigger signal; transmitting the single drive signal to the scanner, wherein the scanner has a resonant response at the first frequency; and actuating the scanner to perform a first periodic motion about a first axis at the first frequency and a second periodic motion about a second axis at a second frequency.

[0005] In some embodiments, the scanner includes a single multi-axis mirror portion. In some embodiments, a first periodic motion is performed about the first axis at a first resonant frequency of the scanner. In some embodiments, a second periodic motion is performed about the second axis at a second resonant frequency of the scanner. In some embodiments, the second component includes a ramp waveform. In some cases, the second component includes a low-frequency waveform component and a high-frequency waveform component. In some examples, the frequency of the high-frequency waveform component is twice the first frequency of the first component, and the high-frequency waveform component and the low-frequency waveform component are synchronized with the aid of a trigger signal. Alternatively, the high-frequency waveform component has a variable amplitude, and the high-frequency waveform component and the low-frequency waveform component are combined in a predetermined phase relationship. In some cases, the high-frequency waveform component is generated in response to a real-time condition. Such a real-time condition can include detection of a target.

[0006] In some embodiments, the trigger signal is generated at the beginning or end of a sweep cycle of the first periodic motion. In some embodiments, the second component is generated in response to receiving the trigger signal. In some embodiments, the position sensor is an optical position sensor or a position sensitive detector.

[0007] In some embodiments, the scanner directs the sequence of light pulses along a scanning pattern that approximates a raster scanning pattern. In some cases, the method may further include dynamically adjusting the scanning pattern along a second axis based on real-time conditions. For example, adjusting the scanning pattern along the second axis includes varying the second periodic motion by superimposing a high-frequency waveform component onto the single drive signal. In this case, the amplitude or frequency of the high-frequency waveform component is determined based on real-time conditions. In some cases, the method may further include dynamically adjusting the scanning pattern along a first axis based on real-time conditions. For example, adjusting the scanning pattern along the first axis includes varying the time interval between emitting the sequence of light pulses.

[0008] Another aspect of the present disclosure provides a scanner for a laser radar system. The scanner may include: a scanner actuated to perform a first periodic motion around a first axis at a first frequency and a second periodic motion around a second axis at a second frequency; a position sensor configured to generate a trigger signal; and a controller configured to generate a single drive signal to actuate the scanner, wherein the single drive signal includes a first component at the first frequency and a second component at a second frequency, wherein the first component and the second component are superimposed with a fixed phase relationship with the aid of the trigger signal.

[0009] In some embodiments, the scanner includes a single multi-axis mirror section. In some cases, the single multi-axis mirror section includes a scanning plate suspended on a gimbal by one or more torsion arms. For example, the one or more torsion arms are H-shaped.

[0010] In some embodiments, the first periodic motion occurs about the first axis at a first resonant frequency of the scanner. In some embodiments, the second periodic motion occurs about the second axis at a second resonant frequency of the scanner. In some embodiments, the second component comprises a ramp waveform. In some cases, the second component comprises a low-frequency waveform component and a high-frequency waveform component. For example, the frequency of the high-frequency waveform component is twice the first frequency of the first component, and in some cases, the high-frequency waveform component and the low-frequency waveform component are synchronized with each other via a trigger signal. In some cases, the high-frequency waveform component has a variable amplitude. For example, the high-frequency waveform component and the low-frequency waveform component are combined in a fixed phase relationship or the high-frequency waveform component is generated in response to a real-time condition. For example, the real-time condition can include the detection of a target.

[0011] In some embodiments, the position sensor is an optical position sensor or a position sensitive detector. In some embodiments, the position sensor is used to detect the movement of the scanner. In some embodiments, a trigger signal is generated at the beginning or end of a sweep period of the first periodic motion. In some embodiments, the controller is configured to generate the second component in response to receiving the trigger signal. In some embodiments, the scanner guides the sequence of light pulses along a scanning pattern that approximates a raster scanning pattern. In some cases, the scanning pattern is dynamically adjusted along the second axis direction based on real-time conditions. In some cases, the scanning pattern is adjusted by superimposing a high-frequency waveform component on the single drive signal to change the second periodic motion. For example, the amplitude or frequency of the high-frequency waveform component is determined based on real-time conditions. In one example, the real-time conditions include detection of a target.

[0012] In some embodiments, the position sensor is an optical position sensor or a position sensitive detector. In some embodiments, the position sensor is configured to detect movement of the scanner. In some embodiments, a trigger signal is generated at the beginning or end of a sweep period of the first periodic motion. In some embodiments, the controller is configured to generate the second component in response to receiving the trigger signal.

[0013] In some embodiments, the scanner directs the sequence of light pulses along a scanning pattern that approximates a raster scan pattern. In some cases, the scanning pattern is dynamically adjusted along the second axis based on real-time conditions. In some cases, the scanning pattern is adjusted by superimposing a high-frequency waveform component onto the single drive signal to alter the second periodic motion. In some cases, the amplitude or frequency of the high-frequency waveform component is determined based on real-time conditions. In some cases, the scanning pattern is dynamically adjusted along the first axis based on real-time conditions. In some cases, the scanning pattern is adjusted by varying the time interval between the emission of the sequence of light pulses.

[0014] Other aspects and advantages of the present disclosure will become readily apparent to those skilled in the art from the following detailed description, wherein exemplary embodiments of the present disclosure are shown and described only by way of illustration of the best mode contemplated for carrying out the present disclosure. It should be understood that the present disclosure is susceptible of other and different embodiments, and that its several details are capable of modification in various obvious respects, all without departing from the present disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive.

[0015] Incorporated by Reference

[0016] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The novel features of the present invention are set forth with particularity in the appended claims. The features and advantages of the present invention will be better understood with reference to the following detailed description and accompanying drawings which set forth illustrative embodiments in which the principles of the invention are utilized, wherein:

[0018] Figure 1 An example of a lidar system according to some embodiments of the present invention is schematically shown.

[0019] Figure 2 Examples of distorted scan patterns and raster scan patterns are shown.

[0020] Figure 3 Examples of multi-axis scanning mirrors according to some embodiments of the present invention are schematically shown.

[0021] Figure 4 Examples of multi-axis scanning mirrors according to some embodiments of the present invention are schematically shown.

[0022] Figure 5 Example components of a scanning mirror according to an embodiment of the present invention are shown.

[0023] Figure 6 Examples of sensors configured to provide signals for synchronizing or combining drive signal components or separate waveforms are shown.

[0024] Figure 7 Examples of waveforms for driving a scanning mirror according to some embodiments of the present invention are shown.

[0025] Figure 8 Examples of waveforms for driving a scanning mirror with raster pinch correction according to some embodiments of the present invention are shown.

[0026] Figure 9 Another example of a composite drive signal illustrated by a single waveform in accordance with some embodiments of the present invention is shown.

[0027] Figure 10 An example of changing a drive signal corresponding to a slow scan motion according to some embodiments of the present invention is schematically shown.

[0028] Figure 11 An example of a scan pattern with configurable pixel distribution is shown.

[0029] Figure 12 An example of dynamically configuring the distribution and / or density of pixels / measurement points in response to real-time conditions is schematically shown.

[0030] Figure 13 A block diagram of a control system for a scanner according to some embodiments of the present invention is schematically shown. Detailed Description of the Invention

[0032] Although preferred embodiments of the present invention have been shown and described herein, it will be apparent to those skilled in the art that these embodiments are provided as examples only. Without departing from the present invention, those skilled in the art will now appreciate that many variations, changes, and replacements may be employed in practicing the present invention.

[0033] LiDAR systems can be referred to as laser ranging systems, laser radar systems, LIDAR systems, or laser detection and ranging (LADAR or ladar) systems. LiDAR is a range-finding sensor characterized by long detection range, high resolution, and minimal environmental interference. LiDAR has been widely used in intelligent robots, drones, and autonomous or self-driving vehicles. LiDAR operates by estimating distance based on the round-trip time (i.e., time of flight) of electromagnetic waves between a source and a target.

[0034] In some cases, a lidar system may include a transmitting device that emits laser pulses into an environment to scan space. The sequence of laser pulses may be emitted according to a scanning pattern. A scanning pattern (which may be referred to as an optical scanning pattern, an optical scanning path, or a scanning path) may refer to a pattern or path along which a laser beam or laser beam spot is directed. Along the scanning pattern, multiple laser beam spots may be evenly distributed or unevenly distributed. The scanning pattern may be controlled by various factors, such as the movement of a scanner or the arrangement of multiple light sources.

[0035] In some embodiments, the scanner may include one or more scanning mirrors that are configured to rotate, oscillate, tilt, pivot, or move at an angle around one or more axes. In some cases, the scanner may be a two-dimensional (2D) scanner. The scanner may use a single scanning mirror that is driven to rotate around two scanning axes. In some cases, the scanning mirror may be driven to perform a fast scan along one axis and a slow scan along another axis. The two axes may be orthogonal to each other. Traditionally, a fast scan sweeps back and forth horizontally in the field of view (FOV), while a slow scan sweeps back and forth vertically in the field of view. The fast scan runs at a relatively high scan rate, while the slow scan runs at a scan rate equal to the video frame rate. In some cases, the fast scan runs resonantly, while the slow scan provides a basic sawtooth pattern, gradually scanning down the frame for a (large) portion of the frame time, then returning to the top of the frame to restart or scanning back from bottom to top in a continuous manner. In other cases, staggered sawtooth scanning, triangle wave scanning, sine scanning, and other waveforms may be used to drive one or both axes. A full sweep along the fast axis can be in any range, such as over an angular range of ±60°, ±50°, ±40°, ±30°, ±20°, ±10°, or any value therebetween. A full sweep along the slow axis can be in any range, such as over an angular range of ±60°, ±50°, ±40°, ±30°, ±20°, ±10°, or any value therebetween.

[0036] A single scanning mirror can be controlled to follow a scan path that substantially covers a field of view (FOV). For example, the scan path may result in pixels of a point cloud that substantially cover the FOV. The pixels may be distributed across the entire FOV according to a scan pattern. In some cases, by controlling the movement of the scanning mirror, the pixels may have a specific non-uniform distribution (e.g., pixels may have a higher density in one or more selected areas of the FOV). Alternatively or in addition, by controlling the movement of the scanning mirror, the pixels may be evenly distributed along the scan pattern.

[0037] In some cases, a pixel or measurement point may correspond to a light pulse. In alternative cases, a pixel or measurement point may correspond to multiple light pulses. A pixel or measurement point may be a distance measurement point. In some cases, a distance measurement point may be generated using a single light pulse. In some cases, a measurement point may be obtained by emitting a sequence of coded light pulses emitted over a short duration, such that the sequence of light pulses may be used to derive a distance measurement point. For example, a lidar may be used for three-dimensional (3D) imaging (e.g., a 3D point cloud) or for detecting obstacles. In this case, the distance measurement associated with the sequence of light pulses may be considered a pixel, and the collection of continuously emitted and captured pixels (i.e., a "point cloud") may be rendered as an image or analyzed for other reasons (e.g., detecting obstacles). The light pulse train can be generated and emitted for a duration of, for example, at least 10 ns, 20 ns, 30 ns, 40 ns, 50 ns, 60 ns, 70 ns, 80 ns, 90 ns, 100 ns, 200 ns, 300 ns, 400 ns, 500 ns, 600 ns, 700 ns, 800 ns, 900 ns, 1 μs, 2 μs, 3 μs, 4 μs, 5 μs, 50 μs, 100 μs, 200 μs, 300 μs, 400 μs, 500 μs, or longer. In some cases, the time interval between consecutive trains can correspond to the temporal resolution of the 3D imaging. The temporal resolution of the point cloud image can also affect the pixel resolution in the horizontal or fast scan direction. The time interval between trains can be constant or variable.

[0038] It should be noted that the fast scan direction does not need to be aligned with the horizontal direction (rotated around the vertical scan axis), and the slow scan direction does not need to be aligned with the vertical direction (rotated around the horizontal scan axis). The fast scan direction and / or the slow scan direction can be in any orientation relative to the ground reference system.

[0039] As used herein, unless the context indicates otherwise, the terms "light pulse sequence," "pulse sequence," "signal sequence," and the like are used interchangeably throughout the specification. Unless the context indicates otherwise, the terms "measurement signal," "measurement pulse," "signal light," "output light beam," and the like may refer to light pulses emitted from a transmitting device of a lidar system. The terms "return beam," "return signal," "return pulse," and the like may refer to light pulses received by a detector of a lidar system and are used interchangeably throughout the specification, unless the context indicates otherwise.

[0040] The output beam, or signal light, can then be directed into space for measurement. For example, the output beam can have an average power of approximately 1 mW, 10 mW, 100 mW, 1 W, 10 W, or any other suitable average power. As another example, the output beam can include pulses with a pulse energy of approximately 0.1 μl, 1 μl, 10 μl, 100 μl, 1 mJ, or any other suitable pulse energy. As another example, the output beam can include pulses with a peak power of approximately 10 W, 100 W, 1 kW, 2 kW, 5 kW, 10 kW, or any other suitable peak power. A light pulse with a duration of 400 ps and a pulse energy of 1 μl has a peak power of approximately 2.5 kW. If the pulse repetition frequency is 500 kHz, the average power of the output beam with a 1 μJ pulse is approximately 0.5 W. In some cases, the wavelength of the output beam can be in the range of 900 nm to 1600 nm, or in any other suitable range. In some cases, the wavelength of the output beam can be in the range of 1530 nm to 1570 nm to provide eye-safe laser light.

[0041] Figure 1 An example of a laser radar system 100 is schematically shown. In some embodiments, the laser radar system 100 may include a transmitting module 110, a receiving module, a scanner 120, and a plurality of optical components, such as lens assemblies 161, 165, and a mirror 163.

[0042] The transmitting module 110 may include at least one light source configured to generate a laser beam or light pulse. Depending on the specific application, the wavelength of the laser beam may be within any suitable range. In some cases, the light source may include an eye-safe laser. An eye-safe laser may refer to a laser whose emission wavelength, average power, peak power, peak intensity, pulse energy, beam size, beam divergence, or exposure time is such that the light emitted from the laser has little or no risk of causing damage to the human eye. For example, the light source may be classified as a Class 1 laser product (as defined by the 60825-1 standard of the International Electrotechnical Commission (IEC)) or a Class I laser product (as defined in Section 1040.10 of Title 21 of the United States Code of Federal Regulations (CFR)), which are safe under all normal use conditions. In some embodiments, the light source may include an eye-safe laser (e.g., a Class 1 or Class I laser) configured to operate at any suitable wavelength between about 1400 nm and about 2100 nm. In some cases, the light source may include an eye-safe laser operating at a wavelength between about 1400 nm and about 1600 nm. In some cases, the light source may include an eye-safe laser operating at a wavelength between about 1530 nm and about 1560 nm.

[0043] The light source may include a laser diode. The light source may include any suitable type of laser, such as a Fabry-Perot laser diode, a quantum well laser, a distributed Bragg reflector (DBR) laser, a distributed feedback (DFB) laser, or a vertical cavity surface emitting laser (VCSEL). In some cases, the light source may include a fiber laser module. In one example, the fiber laser module may include a current-modulated laser diode having a peak wavelength of approximately 1550 nm, followed by a single-stage or multi-stage erbium-doped fiber amplifier (EDFA). The fiber laser module may include a seed laser, a pump laser, an optical amplifier (e.g., a gain fiber or fiber amplifier), and other components.

[0044] The output beam or signal light may be directed to one or more optical elements (e.g., reflectors) and / or through a lens assembly 161 (e.g., a collimating lens, a collimating lens assembly) for collimating or focusing the beam 111. The lidar system 100 may include any suitable optical components, such as one or more lenses, mirrors, filters (e.g., bandpass or interference filters), beam splitters, polarizers, polarizing beam splitters, wave plates (e.g., half-wave or quarter-wave plates), diffraction elements or holographic elements, telescopes, to expand, focus, or collimate the output beam 111 to a desired beam diameter or divergence.

[0045] Similarly, the return beam 131 may pass through one or more optical components 165 so that the return beam can be directed and focused onto an active area of a detector of the detection module 130. The one or more optical components may include, for example, one or more mirrors (e.g., plane mirrors, concave mirrors, convex mirrors, parabolic mirrors) or lenses / lens assemblies for directing the return beam to the detector.

[0046] LiDAR system 100 may include a mirror portion 163 configured to allow signal light 111 to pass through the mirror portion while directing return light 131 toward a detector. In some cases, mirror portion 163 may include a hole, slot, or aperture that allows signal light 111 to pass through the mirror portion. In some cases, mirror portion 163 may be configured such that at least a portion (e.g., at least 90%, 80%, 70%, 60%, etc.) of signal light 111 passes through the mirror portion and at least a portion (e.g., at least 90%, 80%, 70%, 60%, etc.) of return light 131 is reflected by mirror portion 163. In some cases, mirror portion 163 may provide that signal light 111 and return light beam 131 are substantially coaxial, such that the two beams travel along substantially the same optical path but in opposite directions. For example, mirror portion 163 may include a hole, slot, or aperture through which signal light 111 passes and a reflective surface that reflects at least a portion of return light beam 131 toward an active area of detector 130.

[0047] The detection module 130 may include one or more detectors configured to receive the return beam 160. The detector may be a photoreceiver, an optical receiver, a light sensor, a photodetector, or a light detector. In some cases, the detection module may include one or more avalanche photodiodes (APDs) or one or more single photon avalanche diodes (SPADs). In some cases, the receiving module may include one or more PN photodiodes (e.g., a photodiode structure formed by a p-type semiconductor and an n-type semiconductor) or one or more PIN photodiodes (e.g., a photodiode structure formed by an undoped intrinsic semiconductor region located between a p-type region and an n-type region).

[0048] The returned light beam can be directed to the active area of the detector. The active area can have any suitable size or diameter, such as a diameter of approximately 25 μm, 50 μm, 80 μm, 100 μm, 200 μm, 500 μm, 1 mm, 2 mm, or 5 mm. In some cases, the mirror portion 163 can have a substantially flat reflective surface or the reflective surface can be curved (e.g., the mirror portion can be an off-axis parabolic mirror portion configured to focus the input light beam 131 onto the active area of the receiver). The reflective surface of the mirror portion 163 can include a reflective metal coating (e.g., gold, silver, or aluminum) or a reflective dielectric coating, and the reflective surface can have any suitable reflectivity R at the operating wavelength of the light source (e.g., R greater than or equal to 70%, 80%, 90%, 95%, 98%, or 99%).

[0049] In some embodiments, the lidar system 100 may include an optical receiving device 165 (e.g., a focusing lens, a focusing lens assembly), one or more optical elements (e.g., a reflector) 163 that allow reflected light from external objects to pass through the optical receiving device and then be received by the detection module 130. The received optical signal may be converted into an electrical signal and processed by the controller 140.

[0050] The lidar system 100 may include a scanner 120 to direct the output beam 111 in one or more directions. The scanner 120 may be configured to scan the output beam 111 within a certain angular range. In some cases, the scanner 120 may be configured to scan the output beam 111 within a 5-degree angular range, a 20-degree angular range, a 30-degree angular range, a 60-degree angular range, or any other suitable angular range. As an example, the scanning mirror may be configured to periodically oscillate or rotate back and forth within a 15-degree range, which causes the output beam 111 to scan within a 30-degree range (e.g., a rotation of the scanning mirror Θ degrees results in a 2Θ-degree angular scan of the output beam). In some embodiments, the field of view (FOR) of the lidar system 100 may refer to an area, region, or angular range that the lidar system may be configured to scan or capture distance information. As an example, a lidar system having an output beam 111 with a 30-degree scanning range may be referred to as having a 30-degree angular field of view. As another example, a lidar system 100 having a scanning mirror that rotates within a 30-degree range can generate an output beam 111 that scans within a 60-degree range (e.g., a 60-degree FOR). In certain embodiments, the lidar system 100 can have a FOR of approximately 10°, 20°, 40°, 60°, 120°, or any other suitable FOR. In some cases, the FOR can be referred to as a full scan area.

[0051] In some embodiments, the scanner 120 may include one or more scanning mirrors that are configured to rotate, oscillate, tilt, pivot, or move in an angular manner around one or more axes. In some cases, a plane scanning mirror 125 may be attached to a scanner actuator or mechanism that actuates the mirror portion to scan within a specific angular range. In some cases, the scanner 120 may include a resonant scanning mirror or a galvanometer 125. In some cases, the scanner may be a two-dimensional (2D) scanner. The scanner may use a single scanning mirror that is driven to rotate around two scanning axes. In some cases, the scanning mirror may be driven to perform a fast scan along one axis and a slow scan along another axis. The two axes may be orthogonal to each other. The scanning mirror 125 may be designed so that the single scanning mirror has a resonant response at one or more frequencies of the drive signal to produce a desired periodic motion. For example, the resonant frequency and amplification factor of the scanning mirror may be independently selected on each of the two axes by distributing its mass differently around each axis and by designing a support structure (e.g., a support arm or torsion arm having different torsional stiffnesses on each axis). Details on the design of the scanning mirror and drive signals will be described later.

[0052] The scanner can be actuated by any suitable actuator or mechanism, such as a galvanometer scanner, a piezoelectric actuator, a polygon scanner, a rotating prism scanner, a voice coil motor, an electric motor (such as a DC motor, a brushless DC motor, a synchronous motor or a stepper motor), or a microelectromechanical system (MEMS) device, etc.

[0053] A resonant scanner (which may be referred to as a resonant actuator) may include a spring-like mechanism driven by an actuator to produce periodic oscillations at a substantially fixed frequency. The periodic oscillation frequency associated with the fast scan axis may be the same as the resonant frequency about the fast scan axis. The periodic oscillation frequency of the scanning mirror rotating about the slow scan axis may be the resonant frequency or a detuned frequency component about the slow scan axis. The oscillation frequency about the fast scan axis may be approximately 1 kHz. The fast scan oscillation frequency may be any value below 1 kHz or above 1 kHz. The slow scan oscillation frequency may be any value in the range of approximately 10 Hz to 100 Hz. The slow scan oscillation frequency may be any value below 10 Hz or above 100 Hz. In some cases, the fast scan oscillation frequency and the slow scan oscillation frequency may have a predetermined relationship. For example, the fast scan oscillation frequency can be at least about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, or 100 times the slow scan oscillation frequency.

[0054] Scanner 120 can include a scanning mirror 125, which can have any suitable geometry or size so that the scanning mirror can oscillate at a resonant frequency about one or more axes in response to a drive signal. In some cases, the scanning mirror can include a scanning plate having a diameter or width between approximately 3 mm and 15 mm. In some cases, the scanning mirror can also receive return beam 131 and direct the return beam to mirror portion 163.

[0055] The scanning mirror can be rotated by any suitable actuation mechanism, such as using electromagnetic actuation. In an example, the scanning mirror can be actuated by a voice coil motor (which may be referred to as a voice coil actuator), which may include a magnet and a coil. When current is supplied to the coil, a translational force is applied to the magnet, which causes the scanning mirror attached to the magnet to move or rotate. A galvanometer scanner (which may be referred to as a galvanometer actuator) may include a galvanometer-based scanning motor having a magnet and a coil. When current is supplied to the coil, a rotational force is applied to the magnet, which causes the mirror portion attached to the galvanometer scanner to rotate. The current supplied to the coil can be controlled to dynamically change the position of the galvanometer.

[0056] In some embodiments, the scanner 120 may include a scanner control unit 121 that can control the scanning mirror to direct the output beam 111 in a desired direction or along a desired scanning pattern. The scanner control unit 121 can generate a drive signal to actuate the scanning mirror 125. The drive signal that actuates the scanning mirror may include one or more components having different frequencies or one or more separate waveforms. In some cases, the drive signal can be a single drive signal including multiple frequency components (e.g., multiplexed frequencies) such that at least one of the frequency components is modulated at a resonant frequency for fast scanning and at least one of the frequency components is used for slow scanning. The frequency of the slow scan may or may not be a resonant frequency around the slow scan axis. The signal component for the slow scan may be a superimposed waveform including different frequency components. Alternatively, separate drive signals corresponding to the two scanning axes can be provided to the scanning mirror. Details about the drive signal and waveform (frequency) components will be described later.

[0057] In some cases, the scanner 120 may also include one or more sensors 123 configured to detect the angular position and / or angular motion of the scanning mirror. A position signal 150 may be transmitted to the scanner control unit 121 to control the drive signal of the scanner. In some embodiments, the position signal 150 can be used to synchronize the oscillations on the two axes, thereby stabilizing the point cloud image frame by frame. For example, with the help of the position signal, the zero-speed position of the horizontal oscillation cycle is synchronized with the start or end of the vertical oscillation cycle, so that the pixel (point) coordinates across different frames are substantially the same.

[0058] Any suitable sensor can be used to detect the motion or angular position of the scanning mirror. For example, a piezoresistive sensor, a photodetector, an optical position sensor (OPS), a position sensitive detector (PSD), or other sensor can be used to sense motion or position. In some cases, a PSD can be used to measure the angular position of the scanning mirror. The angular position can be measured with an angular resolution of no more than 0.01 degrees, 0.05 degrees, 0.1 degrees, or any value less than 0.01 degrees or greater than 0.1 degrees.

[0059] In an optional embodiment, the position signal 150 or the sensor signal generated by the position sensor 123 can also be used by the transmitter module 110 to coordinate the light pulses and the movement of the scanning mirror. This can advantageously allow the distribution or resolution of pixels (measurement points) in the selected area to be adjusted in the fast scan and slow scan directions.

[0060] In the case of a 2D resonant scanner, the resonant scanner's scan speed varies continuously in both the horizontal and vertical directions. Like a pendulum, the scanner can accelerate toward the center and then decelerate toward the end of the sweep. It then reverses the cycle. This can result in non-straight horizontal lines (i.e., fast scan lines) and / or an undesirable pixel distribution in the scan pattern. Figure 2 Examples of a scan pattern 201 that suffers from raster pinch distortion and a raster scan pattern 203 that has had the distortion corrected are shown. Scan pattern 201 without raster pinch correction is "pinched" at the outer edges of the field of view in the horizontal direction. That is, the spacing of pixels near the edges of the scan pattern is uneven during the successive forward and reverse sweeps of the light pulse. This uneven spacing can cause pixels to overlap or leave gaps between adjacent rows of pixels. The distribution of horizontal lines is also uneven in the vertical direction, resulting in sparse pixels towards the center of the field of view and denser pixels towards the top and bottom of the field of view.

[0061] The provided scanner or lidar system can provide improved scanner control such that measurement points along a scan pattern can be stabilized across image frames, the scan pattern can be better approximated as a raster pattern using a built-in raster shrinkage correction feature, and / or the distribution (resolution) of pixels along a slow scan direction (i.e., the fast scan period along the slow scan direction) can be configured and controlled substantially in real time. As will be described later herein, the scan path followed by a light pulse in response to a ramped vertical scan (exemplified by a single waveform including a low-frequency component and a high-frequency component twice that of the fast scan) can be approximated as a raster scan pattern.

[0062] In some embodiments of the present invention, a single scanning mirror can be used to perform oscillatory motion about two or more axes. The scanning mirror can be a resonant mirror, whose geometry, mass distribution, and structure are designed so that the scanning mirror can oscillate at a resonant frequency about one or more axes in response to a drive signal. The two axes can correspond to a fast scan axis and a slow scan axis.

[0063] Figure 3 An example of a multi-axis scanning mirror 300 according to some embodiments of the present invention is schematically shown. Scanning mirror 300 can be actuated to rotate about a fast scan axis 301 and a slow scan axis 303. In the example shown, movement about fast scan axis 301 can produce a horizontal scan cycle, and movement about slow scan axis 303 can result in a periodic vertical scan.

[0064] In some embodiments, the scanning mirror 300 may include a scanning plate 317. The scanning plate 317 may include a mirror portion formed thereon or attached thereto. The scanning plate 317 may have a diameter or width between approximately 3 mm and 15 mm. The scanning plate 317 may have any form factor, such as circular, oval, rectangular, square, and various other shapes. The movement of the scanning plate 317 may be controlled by the system to direct the incident light pulse in a desired direction, such as to follow a scanning pattern.

[0065] Scanning mirror 300 can be coupled to an actuator or mounting structure via a torque arm 315. For example, torque arm 315 can be mechanically connected to a fixed base or mounting structure to receive a drive signal. Torque arm 315 can be coupled to a gimbal 316. Gimbal 316 can be of any form factor, such as circular, rectangular, elliptical, etc.

[0066] For a given drive frequency, the amplitude of motion of the gimbal 316 (and other structures suspended therefrom) can be proportional (although not necessarily linearly proportional) to the voltage of the drive signal and the mechanical amplification factor of the rotating mass at the drive frequency. For drive frequency components at or near the resonant frequency of the gimbal (and the suspended structure), the rotational motion about the slow axis 303 can be amplified. For detuned drive frequency components, the amplitude of the gimbal's rotation can be reduced and, in certain frequency ranges, reversed. In some cases, the frequency of the drive signal can be selected not to be at the resonant frequency of the slow axis to avoid frequency drift during operation. In an alternative case, the resonant frequency drive component can be used to drive an oscillatory response about the slow scan axis.

[0067] Inner gimbal ring 318 can be suspended from gimbal mount 316 via torsion arm 311, allowing the inner gimbal ring and the components carried thereon to rotate relative to gimbal mount 316 about fast scan axis 301. The combined mass and mass distribution of the components including scan plate 317, inner gimbal ring 318, and the stiffness of torsion arm 311 can determine the resonant frequency and amplification factor for rotation of scan plate 317 about fast scan axis 301. Any suitable resonant frequency and amplification factor for the fast scan axis or both axes can be selected by varying the mass distribution and mass of the components and / or the stiffness of the torsion arm. The oscillation frequency about the fast scan axis can be the resonant frequency, which can be approximately 1 kHz. The fast scan oscillation frequency can be any value below 1 kHz or above 1 kHz. The slow scan oscillation frequency can be any value within the range of approximately 10 Hz to 100 Hz. The slow scan oscillation frequency can be any value below 10 Hz or above 100 Hz. In some cases, the fast scan oscillation frequency and the slow scan oscillation frequency can have a predetermined relationship. For example, the fast scan oscillation frequency can be at least about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, or 100 times the slow scan oscillation frequency.

[0068] In some embodiments, the scan plate 317 can be coupled to the inner gimbal ring 318 via a torque arm 313. The torque arm can be coupled to two opposing sides of the scan plate 317. As can be seen, the scan plate 317 is suspended from the inner gimbal ring 318 via the torque arm 313, allowing the scan plate 317 to rotate relative to the inner gimbal ring 318 about the slow scan axis 303. The introduction of the torque arm 313 and the inner gimbal ring 318 can allow the scan plate 317 to have an auxiliary mode at twice the resonant frequency of the fast scan axis, thereby correcting for raster pinch distortion. For example, to correct for raster pinch distortion, the drive signal can be a single composite drive signal that includes a vertical drive waveform at a low frequency (e.g., the resonant frequency of the slow scan axis) and a vertical drive sawtooth waveform at twice the resonant frequency of the fast scan axis. The inner gimbal ring 318 can oscillate at the resonant frequency in Mode 2 due to the torsion arm and the inner gimbal ring.

[0069] Scanning mirror 300 may include or be actuated by an actuator (e.g., a coil). The actuator may be driven to produce rotational motion of gimbal 316, inner gimbal ring 318, and suspended scanning plate 317 about axes 301, 303. In some cases, a combination of coils may be included to drive motion of the scanning mirror about two axes. Alternatively or in addition, separate coils may be driven to produce rotational motion of scanning plate 317 about a fast scan axis and rotational motion of the assembly including gimbal, inner gimbal ring, and scanning plate about a slow scan axis. When the coil receives a signal that is periodically driven at a rate corresponding to the resonant frequency of scanning plate 317 about the fast scan axis (or any frequency that produces a suitable response), the amplitude of rotation of the scanning plate about the fast scan axis can be enhanced due to a mechanical amplification factor. In a similar manner, when the coil receives a signal that is periodically driven at a rate corresponding to the resonant frequency of the assembly comprising the scan plate, torque arm, inner gimbal, and gimbal, the assembly can oscillate with increased amplitude about the slow scan axis due to the mechanical amplification factor, thereby achieving a greater angular range with a relatively small amount of input energy. Alternatively, the oscillation frequency associated with the slow scan axis can be at or near the resonant frequency to avoid frequency drift during operation.

[0070] Figure 4 Another example of a multi-axis scanning mirror 400 according to some embodiments of the present invention is schematically shown. Figure 3 As shown in FIG. 4 , the scanning mirror 400 can be actuated to rotate about a fast scan axis 401 and a slow scan axis 403. In the example shown, periodic motion about the fast scan axis 401 can produce a horizontal scan cycle, and periodic motion about the slow scan axis 403 can produce a periodic vertical scan. The scanning mirror 400 can have different structures to provide a high frequency response about the slow scan axis, thereby allowing for an overall compact design of the scanning mirror or an increased effective / active area of the scanning plate.

[0071] The scanning mirror 400 can be Figure 3 The scanning plate is coupled to an actuator or mounting structure via a torque arm 415 in a manner similar to that described in

[15] . For example, the torque arm 415 can be mechanically connected to a fixed base plate or mounting structure to receive a drive signal. The torque arm 415 can be coupled to a gimbal 416 that serves as a support structure for the scanning plate. The gimbal 416 can be of any form factor, such as circular, rectangular, oval, square, etc.

[0072] For a given drive frequency, the amplitude of motion of the gimbal 416 (and other structures suspended therefrom) can be proportional (although not necessarily linearly proportional) to the voltage of the drive signal and the mechanical amplification factor of the rotating mass at the drive frequency. For drive frequency components at or near the resonant frequency of the gimbal (and the suspension structure), the rotational motion about the slow axis 403 can be amplified. For detuned drive frequency components, the amplitude of the gimbal's rotation is reduced and, within certain frequency ranges, reversed. In some cases, the frequency of the drive signal can be selected to be off-harmonic with respect to the slow scan axis to avoid frequency drift during operation. Alternatively, the resonant frequency can be used to drive motion about the slow scan axis to achieve a larger angular range. For example, the combined mass and mass distribution of the assembly including the scan plate 417, any components disposed between the scan plate and the torque arm 415, and the stiffness of the torque arm 415 can determine the resonant frequency and amplification factor for rotation of the scan plate 417 about the slow scan axis 403.

[0073] The scanning plate 417 can be suspended on the gimbal 416 via a first pair of torque arms 413a, 413b and a second pair of torque arms 411a, 411b, allowing the scanning plate 417 to rotate relative to the gimbal 416 about the fast scan axis 401 and the slow scan axis 403. In the illustrated example, the scanning plate 417 can be coupled to the gimbal 416 via an H-shaped structure provided on opposite sides of the scanning plate 417. Figure 3 In the example shown, the introduction of torsion arms 413a and 413b allows the scanning plate 417 to have an auxiliary mode at twice the resonant frequency of the fast scan axis, thereby correcting for grating pinch distortion. As shown in the side view 420, a vibration response at the resonant frequency around the slow scan axis in mode 2 can be achieved. By replacing the inner gimbal ring and torsion arms with H-shaped torsion arms, a compact design or a scanning plate with increased effective area can be provided at a small cost to the overall size of the scanning mirror.

[0074] The combined mass and mass distribution of the components including scan plate 417, torsion arms 413a, 413b, and the stiffness of torsion arms 411a, 411b can determine the resonant frequency and amplification factor for rotation of scan plate 417 about fast scan axis 401. Any suitable resonant frequency and amplification factor for the fast scan axis or both axes can be selected by varying the mass distribution and mass of the components. The oscillation frequency about the fast scan axis can be the resonant frequency, and in some cases, the resonant frequency can be approximately 1 kHz. The fast scan oscillation frequency can be any value below 1 kHz or above 1 kHz. The slow scan oscillation frequency can be any value in the range of approximately 10 Hz to 100 Hz. The slow scan oscillation frequency can be any value below 10 Hz or above 100 Hz. In some cases, the fast scan oscillation frequency and the slow scan oscillation frequency can have a predetermined relationship. For example, the fast scan oscillation frequency can be at least about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, or 100 times the slow scan oscillation frequency.

[0075] The scanning mirror 400 may include or be actuated by an actuator (e.g., a coil). The actuator may be driven to generate rotational motion of the gimbal 416, the H-shaped torsion structure, and the suspended scanning plate 417 about the axes 401, 403. In some cases, a combination of coils may be utilized to drive motion about both axes. Alternatively or in addition, separate coils may be driven to generate rotational motion of the scanning plate 417 about the fast scan axis and rotational motion of the assembly including the gimbal, the H-shaped torsion structure, and the scanning plate to rotate about the slow scan axis. When the coil receives a signal that is periodically driven at a rate corresponding to the resonant frequency of the scanning plate 417 about the fast scan axis (or any frequency that produces a suitable response), the amplitude of the rotation of the scanning plate about the fast scan axis may be enhanced due to a mechanical amplification factor. In a similar manner, when the coil receives a signal that is periodically driven at a rate corresponding to the resonant frequency of the assembly comprising the scan plate, torque arm, gimbal, and any components carried thereon, the assembly can oscillate about the slow scan axis with an increased amplitude due to the mechanical amplification factor, thereby achieving an increased angular range with a relatively small amount of input energy. Alternatively, the oscillation frequency associated with the slow scan axis can be at or near the resonant frequency to avoid frequency drift during operation.

[0076] Figure 5An example assembly of a scanning mirror according to an embodiment of the present invention is shown. The scanning mirror 500 can be the same scanning mirror as described above. For example, the scanning mirror 500 can include a scanning plate 505 coupled to a gimbal 501 via a torque arm 503. The scanning mirror can be attached to or secured to a substrate or mounting unit via a torque arm as described elsewhere herein. In some cases, the scanning mirror, actuator (not shown), and mounting structure can be enclosed in a housing 507, 508. The housing can have at least one surface 507 with an opening or aperture so that light pulses can be incident on the scanning mirror 500 and directed in one or more directions.

[0077] As described above, to correct for raster pinch distortion and / or stabilize the image frame, the drive signals for the slow-scan axis and the fast-scan axis can be synchronized such that there is a substantially fixed phase difference between their oscillations. In some cases, the oscillation frequency of the fast scan can be n times the oscillation frequency of the slow scan, where n can be an integer, such as 2, 3, 4, 5, 6, 7, 8, 10, 15, 20, 25, 30, 25, 40, 45, 50, 60, 70, 80, 90, 100, or more. In some cases, the oscillatory motions about the two axes can be synchronized, and the phase difference can be zero.

[0078] In some embodiments, the sensor (e.g. Figure 1 The synchronization is achieved with the help of a position sensor 123 in the scanner. The sensor may be a position sensor for controlling the motion of the scanning mirror. The position signal generated by the position sensor may be used by the scanner control unit to generate a drive signal for the scanner. For example, the scanning motion of the scanning plate may be detected by the position sensor and used to synchronize or combine multiple components of the drive signal. A position signal may be generated when the scanning plate reaches the end of the sweep (e.g., the beginning or the end). In some cases, a position signal may be generated when the scanning plate reaches the beginning or the end of the horizontal sweep and used to trigger a cycle of vertical scanning, thereby synchronizing the oscillatory motion along the two scanning axes. The position signal may be generated at the beginning or the end of a horizontal (i.e., fast scanning) sweep cycle. In some embodiments, the position signal may be generated by a controller that is connected to a controller. Figure 1 Alternatively, the position signal may be generated by any other sensor capable of detecting the angular position of the scanner.

[0079] Figure 6An example of a sensor 610 configured to provide a signal for synchronizing or combining drive signal components or separate waveforms is shown. For example, the sensor signal can be used as a trigger signal to synchronize a periodic slow scanning motion with a periodic fast scanning motion. As described above, the sensor 610 can be used to detect the angular position and / or angular motion of the scanning mirror 620. The scanning mirror 620 can be configured to rotate, tilt, pivot, or move in an angular manner about one or more axes. The scanning mirror 620 can be the same as the scanning plate described elsewhere herein. Any suitable sensor (e.g., a position sensitive detector) can be used to detect the motion or angular position of the mirror portion. For example, a piezoresistive, photodetector, optical position sensor (OPS), or other sensor can be used to sense the motion or angular position. In some embodiments, the position sensor can be a position sensitive detector (PSD).

[0080] In some cases, the transmitter module can also use the position signal to control the light source. For example, the position signal can be used by the transmitter module to coordinate the movement of the light pulse and the scanning mirror. This provides the advantage of providing a trigger signal that is used by both the light source controller and the scanner controller without introducing additional components into the lidar system.

[0081] In the example shown, the position sensor 610 can be located on a side 621 of the scanning mirror that is opposite to a side 623 on which the output light beam 111 is incident on the scanning mirror 620. The position sensor 610 can be an optical position sensor that may not be in direct contact with the scanning mirror 620. In the example shown, the position sensor 610 can include a light source 612 configured to generate measurement light. The measurement light can be incident on the side 621 of the scanning mirror 620, directed back to the position sensor 610 and captured by the detector component 618. The measurement light can be pulsed light or continuous light. In some cases, the side 621 of the scanning mirror that faces the position sensor 610 can have a reflective surface so that the measurement light can be directed back to the position sensor.

[0082] The light source 612 and the detector assembly 618 can be arranged at an angle such that the measurement light emitted by the light source can be captured by the active area of the detector assembly 618. In some cases, support elements 615, 616, 617 can be used to position the light source and the detector assembly at a predetermined angle relative to each other and / or relative to the scanning mirror 620. The light source 612 and / or the detector assembly 618 can be permanently fixed to such a support element or can be removably coupled to such a support element.

[0083] Light source 612 can be any suitable light source for generating measurement light. For example, the light source can include lasers such as solid-state lasers, gas lasers, liquid lasers, semiconductor lasers, fiber lasers, and the like. Detector component 618 can be a position-sensitive detector that can measure the position of a light spot on a sensor surface in one or two dimensions. Based on the position of the light spot, the angle of the scanning mirror can be calculated. Angular position can be measured with an angular resolution of no more than 0.01 degrees, 0.05 degrees, 0.1 degrees, or any value below 0.01 degrees or above 0.1 degrees.

[0084] In some cases, position sensor 610 may include other components, such as optical filter 614 or connection board 619, to enhance the measurement signal or provide electrical connections and various other functions.

[0085] As mentioned above, the fast scan can be run at a relatively high scan rate, while the slow scan can be run at a scan rate equal to the video frame rate. In some applications, the fast scan operates in a resonant manner, while the slow scan provides a basic sawtooth pattern, scanning down the frame in steps for a (large) portion of the frame time, then flying back to the top of the frame to start over or scanning back from bottom to top in a continuous manner. In other applications, interlaced sawtooth scans, triangle wave scans, sine scans, and other waveforms can be used to drive one or both axes. The drive signal can be a composite signal comprising multiple components or separate waveforms.

[0086] One or more components of the drive signal may be synchronized by a clock signal or combined with a fixed phase relationship by means of a clock signal. Figure 7 Examples of waveforms for driving a scanning mirror are shown. As shown in example 700, the drive signals for generating rotational motion about the fast scan axis and the slow scan axis can be synchronized by a clock signal 720. Clock signal 720 can have the same frequency as the fast scan as described above, or a predetermined multiple n of the fast scan frequency (n = 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.). The clock signal can be a pulse signal, a digital signal, a continuous signal, or any other form. As shown in example 700, a slow scan waveform 701 can begin in response to clock signal 720 generated when a fast scan sweep reaches the beginning / end.

[0087] In some cases, the drive signal for actuating many embodiments of the present invention may involve a combination of waveforms. For example, waveform 703 is a high-frequency signal / component for driving a first oscillatory motion about a first axis at a corresponding high resonant frequency. In this case, waveform 703 may be the drive frequency component for fast scanning. Waveform 701 is a lower-frequency signal for driving a second oscillatory motion about a second axis at a corresponding lower (resonant) frequency. In this case, waveform 701 may be the drive frequency component for slow scanning. The slow scan waveform 701 and the fast scan waveform 703 may be composite frequency components of the drive signal provided to the scanning mirror.

[0088] In some cases, the pixel distribution (vertical resolution) along the vertical direction or slow scan direction can be controlled by changing the drive signal for the slow scan motion. As shown in example 710, the waveform 710 used to drive the oscillatory motion about the slow scan axis can be a composite signal 711 including a low-frequency component 713 and a high-frequency component 715. These two components can be combined with a predetermined phase relationship so that the superimposed signal 711 can drive the scanning plate to rotate at an increasing / decreasing speed within a selected time interval (within the vertical scan period), thereby reducing / increasing the pixel density in the selected area. With the help of a clock signal 720, these two components can be synchronized or combined with a fixed phase relationship.

[0089] Figure 8 An example of a waveform 801 for driving a scanning mirror with raster pinch correction is shown. The waveform used to actuate the slow scan motion can be a ramped waveform. The path followed by the scanning beam or series of light pulses in response to the ramped vertical scan can approximate a raster pattern. The waveform used to drive the oscillatory motion about the slow scan axis can be a composite signal 801 comprising a low-frequency component 803 and a high-frequency component 805. The low-frequency component 803 can be a resonant signal superimposed with an off-harmonic frequency signal, for example, as an approximate sawtooth waveform 805. The low-frequency component 803 may or may not be at or near the resonant frequency about the slow scan axis. In some cases, the low-frequency component can be at the resonant frequency to achieve a wider range of deflection angles. Alternatively, the low-frequency component can be an off-harmonic frequency to avoid frequency drift during operation. The high-frequency component 805 can approximate a sawtooth waveform and can be twice the resonant frequency of the fast scan axis. The high-frequency component 805 can be used to drive the scanning plate to rotate at twice the resonant frequency of the fast scan, with the phase synchronized by a clock signal. By combining a high-frequency component, which is twice as fast as the rapid scanning motion, with a low-frequency component and synchronizing them with the help of a clock signal, the scanning mirror can deflect light pulses along essentially parallel paths, including left-to-right and right-to-left scanning directions, essentially eliminating raster pinch distortion.

[0090] Figure 9Another example of a composite drive signal 901 illustrated by separate waveforms 903 and 905 is shown. As shown in the example, the waveform used to drive the oscillatory motion about the slow scan axis can be a composite signal 901 that includes a low-frequency component 903 and a high-frequency component 905. These two components can be combined with a predetermined phase relationship so that the superimposed signal 901 can drive the scanning plate to move at an increasing / decreasing speed within a selected time interval (within the vertical sweep), thereby reducing / increasing the pixel density in the selected area. In some cases, the high-frequency component can have a varying amplitude, so that the waveform / amplitude of the combined signal can be adjusted at a fine-grained control level. It should be noted that the high-frequency component 905 can have any arbitrary waveform, as long as the resulting composite signal 901 can have the desired waveform for slowing down or accelerating the speed in the vertical direction.

[0091] Figure 10 Schematically illustrates an example of changing the drive signal corresponding to the slow scan motion. Figure 9 The drive signal 901 in FIG. 1 adjusts the pixel distribution / density in the vertical direction shown in the scanning pattern 1001, thereby increasing the vertical resolution in the middle region 1005. This also means that more dense measurement pulses are emitted to the middle region 1005 of the field of view. This advantageously allows for increased efficiency in sampling the environment.

[0092] It should be noted that the drive signals described above can be combined in any suitable manner to produce the desired effect. For example, by combining the signal components described above, raster shrinkage correction and pixel distribution change can be performed simultaneously. Figure 11 An example of a scan pattern with a configurable measurement point distribution or pixel resolution is shown. The scan pattern 1101 can be dynamically adjusted by generating a drive signal to the scan mirror. The drive signal can include multiple signal components, wherein a first component has a resonant frequency of the fast scan to generate motion about the fast scan axis, a second component has a (resonant) frequency of the slow scan to generate motion about the slow scan axis, a third component has a frequency that is twice the fast scan frequency to generate a high-frequency movement about the slow scan axis (to correct for raster pinch distortion), and a fourth component has a frequency and / or waveform that is used to change the speed of the slow scan motion (to adjust the pixel density of the selected area in the vertical direction).

[0093] Multiple components can be combined with a fixed phase difference or synchronized with the help of a position signal as described elsewhere in this document. For example, a first component with a fast scan resonant frequency can be synchronized with a second component to actuate a low-frequency motion of a slow scan with zero phase difference (i.e., when the vertical scan is at its start / end position, the horizontal scan reaches its start / end position). This can also be achieved by selecting the resonant frequency and / or the oscillation frequency for the oscillatory motion in the two directions so that one frequency is a predetermined multiple of the other. Similarly, the first component can also be synchronized with a third component with a frequency twice the frequency of the first component to correct for grating pinch distortion. The fourth component and the second component can have a controllable or configurable phase relationship or amplitude relationship so that the slow scanning motion of the scanning mirror can be dynamically controlled based on real-time conditions.

[0094] In some cases, the pixel distribution along the horizontal or fast scanning direction can also be adjusted. This can be achieved by controlling the light source to generate light pulses at a desired time interval. For example, when using a fiber laser, the time interval between seed light pulses can be controlled to achieve a variable time interval.

[0095] In some cases, a non-uniform pixel (point) distribution may be preferred so that a denser light spot can be emitted into a selected area in a controllable manner. For example, the light spot may preferably be denser in the middle of a line scan, or denser in an area where a target object is detected and detail is desired. This advantageously provides adjustable resolution over a selected area, thereby improving the sampling and computational efficiency of the lidar imaging. As an example, the pixel distribution and / or scan pattern can be dynamically adjusted in response to the detection of a potential target. The scan pattern or pixel distribution can be dynamically determined based on one or more real-time conditions, including environmental conditions or conditions of the lidar system.

[0096] Figure 12 An example of dynamically configuring the distribution and density of pixels / measurement points in response to real-time conditions is schematically shown. In some cases, during a first operating setting 1201, an object of interest 1205 may be identified and may require more information for further identification. In response to identifying the position of the object in the field of view, the provided system may adopt a second operating setting 1203 and adjust the drive signals generated to the scanning mirror and light source accordingly. The second operating setting may result in a higher density of pixels or measurement points allocated to the object area of interest.

[0097] In some cases, the scanning pattern or pixel distribution can be dynamically changed to improve the energy efficiency of the lidar system. For example, when the lidar system detects that it is in a less complex environment (e.g., rural areas), a scanning pattern or resolution with fewer pixels distributed toward the edge of the field of view can be selected. This can be achieved by changing the drive signal or changing one or more components of the drive signal used to actuate the slow scanning motion and / or adjusting the control signal of the light source.

[0098] Figure 13 A block diagram of a control system 1300 for a scanner according to some embodiments of the present invention is schematically shown. The control system 1300 may be used with Figure 1 13. Scanning mirror 1301 can be controlled by control system 1300. The scanning mirror can be the same as the scanning mirror described elsewhere in this document. For example, the scanning mirror can include a single multi-axis scanning mirror. In some embodiments, scanning mirror 1303 can be actuated to rotate about a fast scan axis and a slow scan axis.

[0099] The slow scan motion can be detected by a position sensor. In some cases, the slow scan motion can be analyzed by a signal analyzer 1305. In some cases, the slow scan motion can be a ramped vertical scan at a frequency twice the resonant frequency of the fast scan axis. The various waveforms associated with the slow scan motion (characteristics of the oscillatory motion) can be extracted by the signal analyzer and fed to a controller 1307 for further adjustment or generation of control signals to the slow scan control unit.

[0100] In some cases, the controller 1307 can communicate with a main controller or an external control entity. For example, the controller 1307 can receive instructions from the main controller to adjust the drive signal in order to change the slow scan motion of the scanning mirror. For example, when a target is detected, the controller 1307 can receive an instruction containing information about the position (coordinates) of the target. In response to the instruction, the controller 1307 can generate an instruction to the slow scan waveform generator 1311 to generate a waveform or component waveform of the drive signal for changing the vertical / slow scan motion of the scanning mirror. For example, a high-frequency component with a varying amplitude or a separate high-frequency waveform can be generated and added to the signal component for driving the slow scan motion, thereby reducing the speed of movement in the target position. With the assistance of the clock signal generated by the clock 1309, the variable high-frequency waveform can be combined with other components.

[0101] The separate waveform associated with the slow scan motion may then be sent to the slow scan control unit 1313 to generate a control signal.A drive signal component for actuating the slow scan motion may be generated and combined with a drive signal component for actuating the fast scan motion.

[0102] The fast scan motion of the scanning mirror 1301 can be monitored and detected by the position sensor described above. The fast scan motion can be used to generate a clock signal for synchronizing the slow scan motion with the fast scan motion, as described elsewhere herein. In some embodiments, the clock signal can be generated by the clock 1309 and provided to the slow scan waveform generator 1311 to trigger the control signal for the slow scan motion. The clock signal can also be used to synchronize or combine the various signal components of the composite drive signal for various purposes as described above.

[0103] The rapid scanning motion can be fed as feedback information to the rapid scanning control unit 1303 for generating a control signal. The rapid scanning control unit 1303 can dynamically adjust the control signal or generate a drive signal for actuating the rapid scanning motion based on the feedback information.

[0104] In some cases, a combined drive signal including the outputs from fast scan control unit 1303 and slow scan control unit 1313 may be sent to the drive circuitry of the scanning mirror.

[0105] The control unit, functions, algorithms, operations, circuits, or methods may be implemented using software, hardware, or firmware, or a combination thereof. In some embodiments, the control unit may include one or more processors and at least one memory for storing program instructions. The processor may be a component of the laser radar system. Alternatively, the processor may be external to the laser radar system but in communication with the laser radar system. The processor may be a single or multiple microprocessors, a field programmable gate array (FPGA), or a digital signal processor (DSP) capable of executing a specific instruction set. Computer-readable instructions may be stored on a tangible, non-transitory computer-readable medium, such as a floppy disk, a hard disk, a CD-ROM (compact disc read-only memory) and MO (magneto-optical), a DVD-ROM (digital versatile disk read-only memory), a DVD RAM (digital versatile disk random access memory), or a semiconductor memory. The control unit may be a stand-alone device or system that communicates with the laser radar system. Alternatively, the control unit may be a component of the laser radar system. The methods disclosed herein, such as generating variable vertical scanning motion in response to real-time conditions, may be implemented in hardware components or a combination of hardware and software (e.g., an ASIC, a dedicated computer, or a general-purpose computer).

[0106] The provided laser control or stabilization methods and mechanisms can be used in conjunction with various lidar systems or for a variety of applications. For example, when a denser spot size is desired in a given area, the vertical scanning motion can be altered. In this case, the methods and mechanisms can also provide scanner stability and raster shrinkage correction.

[0107] The laser radar system equipped with the scanner control mechanism can be placed on a movable object to sense the environment around the movable object. Alternatively, the laser radar system can be installed on a stationary object.

[0108] The movable objects of the present invention can be configured to move in any suitable environment, such as in air (e.g., a fixed-wing aircraft, a rotary-wing aircraft, or an aircraft with neither fixed wings nor rotary wings), in water (e.g., a ship or submarine), on the ground (e.g., a motor vehicle such as a car, truck, bus, van, motorcycle, bicycle; a movable structure or frame such as a stick, fishing rod; or a train), underground (e.g., a subway), in space (e.g., a space shuttle, a satellite, or a probe), or any combination of these environments. The movable object can be a vehicle, such as a vehicle described elsewhere herein. In some embodiments, the movable object can be carried by a living being or launched from a living being, such as a human or animal.

[0109] In some cases, the movable object may be an autonomous vehicle, which may be referred to as an autonomous car, a driverless car, a self-driving car, a robot car, or a driverless car. In some cases, an autonomous vehicle may refer to a vehicle that is configured to sense its environment and navigate or drive with little or no human input. For example, an autonomous vehicle may be configured to drive to any suitable location and control or perform all safety-critical functions (e.g., driving, steering, braking, parking) throughout the entire journey without the driver being expected to take control of the vehicle at any time. As another example, an autonomous vehicle may allow a driver to safely divert their attention from the task of driving in a particular environment (e.g., on a highway), or an autonomous vehicle may provide control of the vehicle in all but a few environments, requiring little or no input or attention from the driver.

[0110] In some cases, a lidar system can be integrated into a vehicle as part of an autonomous vehicle driving system. For example, a lidar system can provide information about the surrounding environment to the autonomous vehicle's driving system. In one example, the lidar system can provide a 360-degree horizontal field of view of the vehicle. The autonomous vehicle driving system can include one or more computing systems that receive information about the surrounding environment from the lidar system, analyze the received information, and provide control signals to the vehicle's driving system (e.g., steering wheel, accelerator, brake, or turn signal).

[0111] As used herein, A and / or B include one or more of A or B, and combinations thereof, such as A and B. It should be understood that although the terms "first," "second," "third," etc. are used herein to describe various elements, components, regions, and / or parts, these elements, components, regions, and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, or part from another element, component, region, or part. Therefore, without departing from the teachings of the present invention, the first element, component, region, or part discussed herein may be referred to as a second element, component, region, or part.

[0112] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that when used in this specification, the terms "comprise" and / or "comprises" or "includes" and / or "comprising" specify the features, regions, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and / or groups thereof.

[0113] References throughout this specification to "some embodiments" or "one embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases "in some embodiments" or "in one embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0114] Although preferred embodiments of the present invention have been shown and described herein, it will be apparent to those skilled in the art that these embodiments are provided as examples only. Without departing from the present invention, many variations, changes, and replacements will now occur to those skilled in the art. It should be understood that various substitutions to the embodiments of the present invention described herein may be adopted in practicing the present invention. A variety of different combinations of the embodiments described herein are possible, and such combinations are considered to be part of this disclosure. In addition, all features discussed in conjunction with any embodiment herein can be easily applied to other embodiments herein. The following claims are intended to define the scope of the present invention, and are intended to encompass methods and structures within the scope of these claims and their equivalents.

Claims

1. A method for controlling a scanner of a laser radar system, comprising: generating a drive signal including a first component at a first frequency and a second component at a second frequency; sending the drive signal to the scanner, wherein the scanner has a resonant response at a first frequency; actuating the scanner to perform a first periodic motion about a first axis at the first frequency and a second periodic motion about a second axis at a second frequency; as well as Dynamically adjust the drive signal of the scanning mirror according to real-time conditions to change the resolution in the selected area; The selected area includes an area of interest, and the step of changing the resolution in the selected area includes: increasing the resolution within the selected area; and / or the selected area includes an edge area of the field of view of the lidar, and the step of changing the resolution in the selected area includes: reducing the resolution within the selected area.

2. The method according to claim 1, wherein The scanner includes a single multi-axis mirror section.

3. The method according to claim 1, wherein: The first periodic motion occurs about the first axis at a first frequency of the scanner.

4. The method according to claim 1, wherein The second periodic motion occurs about the second axis at a second frequency of the scanner.

5. The method according to claim 1, wherein The second component includes a ramp waveform.

6. The method according to claim 5, wherein: The second component includes a low-frequency waveform component and a high-frequency waveform component.

7. The method of claim 6, wherein: The frequency of the high-frequency waveform component is twice the first frequency of the first component.

8. The method of claim 7, wherein: The high-frequency waveform component and the low-frequency waveform component are synchronized with the aid of a trigger signal.

9. The method of claim 6, wherein: The high frequency waveform component has a variable amplitude.

10. The method of claim 9, wherein: The high-frequency waveform component and the low-frequency waveform component are combined in a predetermined phase relationship.

11. The method of claim 9, wherein: The high frequency waveform component is generated in response to real-time conditions.

12. The method of claim 11, wherein: The real-time condition includes detection of a target.

13. The method of claim 1, wherein: The trigger signal is generated at the beginning or end of the sweep cycle of the first periodic motion.

14. The method of claim 1, wherein: The second component is generated in response to receiving a trigger signal.

15. The method of claim 1, wherein: The scanner directs a train of light pulses along a scan pattern that approximates a raster scan pattern.

16. The method of claim 15, further comprising dynamically adjusting the scanning pattern along the second axis according to real-time conditions.

17. The method of claim 16, wherein: Adjusting the scanning pattern along the second axis direction includes changing the second periodic motion by superimposing a high-frequency waveform component to the drive signal.

18. The method of claim 17, wherein: The amplitude or frequency of the high-frequency waveform component is determined based on the real-time condition.

19. The method of claim 15, further comprising dynamically adjusting the scanning pattern along the first axis according to real-time conditions.

20. The method of claim 19, wherein: Adjusting the scanning pattern along the first axis includes changing a time interval for emitting the sequence of light pulses.

21. The method of claim 1, further comprising: A trigger signal is generated by a position sensor of the scanner, wherein the first component and the second component are superimposed with a fixed phase relationship by means of the trigger signal.

22. The method of claim 21, wherein: The position sensor is an optical position sensor or a position sensitive detector.

23. The method of claim 1, wherein: The region of interest includes the area of the target of interest in the field of view of the laser radar.

24. The method of any one of claims 1-23, wherein the real-time condition comprises identifying an area of interest or detecting an environmental condition surrounding a lidar.

25. A scanning device for a laser radar system, comprising: a scanner actuated to perform a first periodic motion about a first axis at a first frequency and a second periodic motion about a second axis at a second frequency; as well as a controller configured to generate a drive signal to actuate the scanner, wherein the drive signal includes a first component at a first frequency and a second component at a second frequency; The controller is configured to dynamically adjust the drive signal of the scanning mirror according to real-time conditions to change the resolution in the selected area; The selected area includes an area of interest, and the changing of the resolution in the selected area includes: increasing the resolution within the selected area; and / or the selected area includes an edge area of the field of view of the lidar, and the changing of the resolution in the selected area includes: reducing the resolution within the selected area.

26. The scanning device of claim 25, wherein: The scanner includes a single multi-axis mirror section.

27. The scanning device of claim 26, wherein: The single multi-axis mirror section includes a scan plate suspended on a gimbal by one or more torsion arms.

28. The scanning device of claim 27, wherein: The one or more torque arms are H-shaped.

29. The scanning device of claim 25, wherein: The first periodic motion occurs about the first axis at a first frequency of the scanner.

30. The scanning device of claim 25, wherein: The second periodic motion occurs about the second axis at a second frequency of the scanner.

31. The scanning device of claim 25, wherein: The second component includes a ramp waveform.

32. The scanning device of claim 31, wherein: The second component includes a low-frequency waveform component and a high-frequency waveform component.

33. The scanning device of claim 32, wherein: The frequency of the high-frequency waveform component is twice the first frequency of the first component.

34. The scanning device of claim 33, wherein: The high-frequency waveform component and the low-frequency waveform component are synchronized with the aid of a trigger signal.

35. The scanning device of claim 32, wherein: The high frequency waveform component has a variable amplitude.

36. The scanning device of claim 35, wherein: The high-frequency waveform component and the low-frequency waveform component are combined in a fixed phase relationship.

37. The scanning device of claim 35, wherein: The high frequency waveform component is generated in response to real-time conditions.

38. The scanning device of claim 37, wherein: The real-time condition includes detection of a target.

39. The scanning device of claim 25, wherein: The position sensor is an optical position sensor or a position sensitive detector.

40. The scanning device of claim 25, wherein: A position sensor is used to detect the movement of the scanner.

41. The scanning device of claim 25, wherein: The trigger signal is generated at the beginning or end of the sweep cycle of the first periodic motion.

42. The scanning device of claim 25, wherein: The controller is configured to generate the second component in response to receiving a trigger signal.

43. The scanning device of claim 25, wherein: The scanner directs a train of light pulses along a scan pattern that approximates a raster scan pattern.

44. The scanning device of claim 43, wherein: The scanning pattern is dynamically adjusted along the second axis according to real-time conditions.

45. The scanning device of claim 44, wherein: The scanning pattern is adjusted by superimposing a high-frequency waveform component on the driving signal to change the second periodic motion.

46. The scanning device of claim 45, wherein: The amplitude or frequency of the high-frequency waveform component is determined based on real-time conditions.

47. The scanning device of claim 43, wherein: The scanning pattern is dynamically adjusted along the first axis according to real-time conditions.

48. The scanning device of claim 45, wherein: The scanning pattern is adjusted by changing the time intervals at which the sequence of light pulses is emitted.

49. The scanning device of claim 25, further comprising a position sensor configured to generate a trigger signal, wherein the first component and the second component are superimposed in a fixed phase relationship with the aid of the trigger signal.

50. The scanning device of claim 25, wherein: The region of interest includes the area of the target of interest in the field of view of the laser radar.

51. The scanning device of any one of claims 25-50, wherein the real-time condition comprises identifying an area of interest or detecting an environmental condition surrounding a laser radar.

52. A laser radar system comprising: a transmitting module configured to generate a laser beam; Detection module; The scanning device according to any one of claims 25 to 51, wherein the scanning device is configured to receive the laser beam and scan it outward into the external environment, and receive an echo of the laser beam after it is reflected by an obstacle and reflect it to the detection module; The transmitting module is further configured to: dynamically adjust the driving signal of the transmitting module according to real-time conditions to change the resolution in the selected area; The selected area includes an area of interest, and the changing of the resolution in the selected area includes: increasing the resolution within the selected area; and / or the selected area includes an edge area of the field of view of the lidar, and the changing of the resolution in the selected area includes: reducing the resolution within the selected area.

53. The laser radar system of claim 52, wherein: The region of interest includes the area of the target of interest in the field of view of the laser radar.

54. The laser radar system of any one of claims 52-53, wherein: The real-time conditions include identifying an area of interest or detecting environmental conditions around the lidar.

55. A laser radar system comprising: a transmitting module configured to generate a laser beam; Detection module; a scanning device configured to receive the laser beam and scan it out into the external environment, and receive an echo of the laser beam after it is reflected by an obstacle and reflect it to the detection module; a control device configured to dynamically adjust the drive signal of the transmitting module according to real-time conditions to change the resolution in the selected area; and / or dynamically adjusting the drive signal of the scanning device according to real-time conditions to change the resolution in the selected area; The selected area includes an area of interest, and the changing of the resolution in the selected area includes: increasing the resolution within the selected area; and / or the selected area includes an edge area of the field of view of the lidar, and the changing of the resolution in the selected area includes: reducing the resolution within the selected area.

56. The laser radar system of claim 55, wherein: The region of interest includes the area of the target of interest in the field of view of the laser radar.

57. The laser radar system of any one of claims 55-56, wherein the real-time conditions include identifying an area of interest or detecting environmental conditions around the laser radar.

58. A control method for a laser radar, comprising: Launching a laser beam through a launch module; receiving the laser beam through a scanning device and scanning the laser beam into the external environment; The scanning device receives the echo of the laser beam reflected by the obstacle and reflects it to the detection module; Dynamically adjust the drive signals of the transmitting module and / or the scanning device according to real-time conditions to change the resolution in the selected area; The selected area includes an area of interest, and the changing of the resolution in the selected area includes: increasing the resolution within the selected area; and / or the selected area includes an edge area of the field of view of the lidar, and the changing of the resolution in the selected area includes: reducing the resolution within the selected area.

59. The control method according to claim 58, wherein: The region of interest includes the area of the target of interest in the field of view of the laser radar.

60. The control method according to any one of claims 58 to 59, wherein: The real-time conditions include identifying an area of interest or detecting environmental conditions around the lidar.

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