Scanning mirror assembly with torsion spring for improved non-linearity

Abstract

Embodiments of the present specification provide a scanning mirror assembly for an optical sensing system. The scanning mirror assembly can include a scanning mirror configured to rotate about a rotation axis. The scanning mirror assembly can also include a plurality of torsion springs connected to at least one side of the scanning mirror along the rotation axis. In certain aspects, the plurality of torsion springs can collectively have a nonlinear spring constant and a linear spring constant. In certain other aspects, a ratio of the nonlinear spring constant to the linear spring constant can satisfy a predetermined threshold.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Patent Application No. 17 / 226,667, filed April 9, 2021, entitled “SCANNING MIRROR ASSEMBLY WITH TORSION SPRINGS DESIGNED TO IMPROVE NON-LINEARITY”, and U.S. Patent Application No. 17 / 226,071, filed April 8, 2021, entitled “SYSTEM AND METHODFOR DESIGNING A SCANNING MIRROR ASSEMBLY WITH AN OPTIMIZED FREQUENCYBANDWIDTH BASED ON SPRING CONSTANT INFORMATION”. The contents of both priority applications are expressly incorporated herein by reference in their entirety. Technical Field

[0003] This specification relates to the design of scanning mirrors used in optical sensing systems, and in particular to enabling scanning mirror assemblies to have optimized frequency bandwidth by forming torsion springs with linear and nonlinear spring constants that optimize the frequency bandwidth of the scanning mirror assembly. Background Technology

[0004] Optical sensing systems, such as lidar (LiDAR) systems, are widely used in advanced navigation technologies, such as assisted autonomous driving and high-definition map generation. For example, a typical lidar system measures the distance to a target by illuminating it with a pulsed laser beam and using sensors to measure the reflected pulses. Differences in the laser's return time, wavelength, and / or phase can be used to construct a digital three-dimensional (3D) representation of the target. Because using a narrow laser beam as the incident light allows for the mapping of physical features at very high resolution, LiDAR systems are particularly suitable for applications such as autonomous driving sensing and high-definition map measurement.

[0005] A lidar system may include a transmitter configured to emit a beam to scan an object, and a receiver configured to receive the beam reflected from the object. The transmitter and receiver can use optical components (such as scanning mirrors) to direct the beam in multiple directions. The scanning mirror can be a single micromirror or an array of micromirrors integrated into a micromechanical mirror assembly made of semiconductor materials, such as those using microelectromechanical systems (MEMS) technology. In some applications, MEMS mirrors can operate at or near a resonance region. Using resonance allows the optical sensing system to achieve a larger mirror scanning angle in a relatively short time compared to non-resonant mirrors. MEMS mirrors can resonate at or near their characteristic vibrational frequency, which can be determined by design parameters associated with the scanning mirror, scanner, and / or transmitter.

[0006] These design parameters may include mirror size, Q coefficient, number of comb teeth, inter-comb tooth distance, comb tooth length, drive frequency and amplitude, spring size, linear spring constant k1, nonlinear spring constant k3 and / or spring constant ratio r3 (where r3 = k3 / k1), and the above are just some examples. These design parameters can be adjusted during the design phase to ensure that the scanning mirror assembly meets one or more target performance characteristics, such as target mirror scanning angle, characteristic vibration frequency, target vibration frequency bandwidth, etc.

[0007] Therefore, it is beneficial to be able to accurately and efficiently calculate the target performance characteristics during the design phase of a scanning mirror. However, current techniques for calculating performance characteristics during the design phase are only applicable to rigid scanning mirror assemblies. For example, for torsion spring design, conventional techniques cannot calculate the nonlinear spring constant k3 and spring constant ratio r3 with high precision. Therefore, conventional torsion spring design fails to consider the associated nonlinear spring constant k3 (and spring constant ratio r3) and vibration frequency bandwidth. Consequently, conventional torsion springs lack the required nonlinearity, and using conventional torsion springs may limit the performance of related scanning mirror assemblies.

[0008] Therefore, the structural characteristics of a torsion spring cannot satisfy the desired nonlinear spring constant k3 (and spring constant ratio r3) and vibration frequency bandwidth. Summary of the Invention

[0009] Embodiments of this specification provide a scanning mirror assembly for an optical sensing system. The scanning mirror assembly may include a scanning mirror configured to rotate about a rotation axis. The scanning mirror assembly may also include a plurality of torsion springs connected along the rotation axis to at least one side of the scanning mirror. In some aspects, the plurality of torsion springs may collectively have a nonlinear spring constant and a linear spring constant, the ratio of the nonlinear spring constant to the linear spring constant satisfying a predetermined threshold.

[0010] Embodiments of this specification provide an optical sensing system. The optical sensing system may include a laser emitter configured to emit optical signals. The optical sensing system may also include a scanning mirror assembly configured to reflect the optical signal into the environment in one or more directions. The scanning mirror assembly of the optical sensing system may include a scanning mirror configured to rotate about a rotation axis. The scanning mirror assembly of the optical sensing system may also include a plurality of torsion springs connected along the rotation axis to at least one side of the scanning mirror. The optical sensing system may also include a receiver configured to receive at least a portion of the optical signal reflected from the environment. In some aspects, the plurality of torsion springs may collectively have a nonlinear spring constant and a linear spring constant, the ratio of the nonlinear spring constant to the linear spring constant satisfying a predetermined threshold.

[0011] Embodiments of this specification provide a method for assembling a scanning mirror assembly. The method may include connecting the scanning mirror to a gimbal to allow the scanning mirror to rotate about a rotation axis. The method may also include connecting a plurality of torsion springs along the rotation axis to one side of the scanning mirror, having predetermined gaps between the scanning mirrors and in a predetermined direction. In some aspects, the plurality of torsion springs may collectively have a nonlinear spring constant and a linear spring constant, the ratio of the nonlinear spring constant to the linear spring constant possibly satisfying a predetermined threshold.

[0012] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not constitute a limitation of this specification. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of an exemplary lidar system according to some embodiments of this specification.

[0014] Figure 2A This is a top view of an exemplary scanning mirror design based on some embodiments shown in this specification.

[0015] Figure 2B This is a first perspective view of an exemplary scanning mirror assembly shown according to some embodiments of this specification.

[0016] Figure 2C This is a second perspective view of an exemplary scanning mirror assembly shown according to some embodiments of this specification.

[0017] Figure 2D This is based on some embodiments shown in this specification. Figure 2B The first unfolded view of an exemplary torsion spring of the scanning mirror assembly shown.

[0018] Figure 2E It is based on some embodiments shown in this specification for determining Figure 2DThe first graph shows the linear and nonlinear spring constants of an exemplary torsion spring.

[0019] Figure 2F This is based on some embodiments shown in this specification. Figure 2B A second unfolded view of an exemplary torsion spring of the scanning mirror assembly shown.

[0020] Figure 2G It is based on some embodiments shown in this specification for determining Figure 2F The second graph shows the linear and nonlinear spring constants of the exemplary torsion spring.

[0021] Figure 2H This is based on some embodiments shown in this specification. Figure 2B The third unfolded view of the exemplary torsion spring of the scanning mirror assembly shown.

[0022] Figure 2I It is based on some embodiments shown in this specification for determining Figure 2H The third graph shows the linear and nonlinear spring constants of the exemplary torsion spring.

[0023] Figure 2J This is a first partial view of an exemplary scanning mirror assembly with an angular torsion spring, as shown in some embodiments of this specification.

[0024] Figure 2K This is a second partial view of an exemplary scanning mirror assembly with an angular torsion spring, as shown in some embodiments of this specification.

[0025] Figure 3 This is an exemplary lookup table that associates inertial force / torque and angular displacement, as shown in some embodiments of this specification.

[0026] Figure 4 This is a graph showing the frequency bandwidth associated with different spring constant ratios, according to some embodiments of this specification.

[0027] Figure 5 This is a flowchart illustrating an exemplary method for assembling a scanning mirror according to some embodiments of this specification. Detailed Implementation

[0028] Reference will now be made in detail to exemplary embodiments, examples of which are shown in the accompanying drawings. Where possible, the same reference numerals will be used throughout the drawings to refer to the same or similar parts.

[0029] LiDAR is an optical sensing technology that enables autonomous vehicles to "see" the world around them, creating virtual models of the environment for decision-making and navigation. Optical sensors (such as LiDAR transmitters and receivers) use laser beams and time-of-flight (ToF) distance measurements to create 3D maps of the surrounding environment. ToF, one of the working principles of LiDAR, provides distance information by measuring the time it takes for a collimated laser beam to reflect off an object and return to the sensor. The reflected light signals are measured and processed on the vehicle to detect, identify, and decide how to interact with or avoid objects.

[0030] A lidar system may include a transmitter configured to emit a beam to scan an object, and a receiver configured to receive the beam reflected from the object. The transmitter and receiver can use optical components (e.g., scanning mirrors) to direct the beam in a range of directions. The scanning mirror can be a single micromirror or an array of micromirrors integrated into a micromechanical mirror assembly made of semiconductor materials, such as those using microelectromechanical systems (MEMS) technology. In some applications, MEMS mirrors can operate at or near resonance. Using resonance allows the optical sensing system to achieve a larger mirror scanning angle in a relatively short time compared to non-resonant mirrors. MEMS mirrors can resonate at or near their characteristic vibrational frequency, which can be determined by design parameters associated with the scanning mirror assembly, scanner, and / or transmitter.

[0031] These design parameters may include mirror size, Q coefficient, number of comb teeth, comb tooth spacing, comb tooth length, drive frequency and amplitude, spring size, linear spring constant, nonlinear spring constant, and spring constant ratio. These design parameters can be adjusted during the design phase to ensure that the scanning mirror meets one or more target performance characteristics, such as target mirror scanning angle, characteristic vibration frequency, and target vibration frequency bandwidth.

[0032] The vibration frequency bandwidth is a frequency characteristic range within which the scanning mirror assembly can be driven to vibrate about a rotation axis. This characteristic range may include the characteristic vibration frequency of the scanning mirror assembly itself and a set of frequencies located on either side of the characteristic vibration frequency.

[0033] Various design parameters can affect the vibration frequency bandwidth of a scanning mirror assembly. Examples of such design parameters include the linear spring constant k1 and the nonlinear spring constant k3 associated with the torsion spring contained in the scanning mirror assembly. As shown later, the ratio of the nonlinear spring constant k3 to the linear spring constant k1, r3 = k3 / k1 (also known as the “spring constant ratio”), controls the vibration frequency bandwidth (also known as the “frequency response bandwidth”).

[0034] For example, the spring constant ratio r3 is proportional to the vibration frequency bandwidth; therefore, the larger r3 is, the wider the vibration frequency bandwidth. Developing design parameters to maximize the relevant vibration frequency bandwidth of the scanning mirror assembly while maintaining the desired characteristic vibration frequency may be advantageous during use by controlling the scanning mirror angle by adjusting the drive frequency in the accompanying scanner electronics.

[0035] For a rigid scanning mirror assembly, r3 follows formula (1), which is a formula for controlling the rigid body motion that maintains a single mode (or "angular displacement"):

[0036]

[0037] Where θ is the angular displacement, J is the mirror moment of inertia, d is the damping coefficient, k is the rotational spring constant, N is the number of driving comb units, f(θ) is the functional relationship between the electrostatic force driven by a single comb tooth under unit voltage and the angular displacement, and L i is the equivalent arm length of the comb drive relative to the rotating shaft, r3 is the ratio of the nonlinear spring constant k3 to the linear spring constant k1, and V(t) is the driving voltage.

[0038] However, scanning mirror assemblies made of these or similar materials are typically flexible and therefore non-rigid.

[0039] Therefore, the shape of the scanning mirror assembly formed from these materials is composed of multiple patterns of the structure (also known as "angular displacement") or multiple cross sections (also known as "nodes") with different angular displacements at the same point during operation, such as... Figure 2C As shown. This specification uses a novel method to calculate the nonlinear spring constant k3 and the spring constant ratio r3 to achieve high-precision torsion spring design. The torsion spring design provided by this method can be customized to achieve the desired spring constant ratio r3, maximizing the vibration frequency bandwidth and thus improving component performance. For example, as... Figures 1-5 As shown, for the design of these torsion springs, it may be beneficial to be able to calculate the spring constant ratio r3 with high accuracy and efficiency during the design phase. A system and method for accurately and efficiently calculating the spring constant ratio and adjusting design parameters based thereon are disclosed in U.S. Application No. 17 / 226,071, filed April 8, 2021, the entire contents of which are incorporated herein by reference.

[0040] The following description of exemplary embodiments refers to scanning mirrors used in LiDAR systems, but the applications of the scanning mirror assemblies disclosed in this specification are not limited to LiDAR systems. Rather, those skilled in the art will understand that the following descriptions, embodiments, and techniques are applicable to any type of optical sensing system known in the art (e.g., biomedical imaging, 3D scanning, tracking and targeting, free-space optical communication (FSOC), and telecommunications, the above being merely some examples) without departing from the scope of this specification.

[0041] Figure 1 This is a block diagram of an exemplary lidar system 1000 according to some embodiments of this specification. The lidar system 1000 may include a transmitter 1002 and a receiver 1004. The transmitter 1002 may emit laser beams in multiple directions. The transmitter 1002 may include one or more laser sources 1006 and scanners 1008.

[0042] like Figure 1 As shown, transmitter 1002 can continuously emit pulsed laser beams in different directions within a scanning range (e.g., an angular range). Laser source 1006 can be configured to provide laser beam 1007 (also referred to as a "native laser beam") to scanner 1008. In some embodiments of this specification, laser source 1006 can generate pulsed laser beams in the ultraviolet, visible, or near-infrared wavelength range.

[0043] In some embodiments of this specification, the laser source 1006 may include a pulsed laser diode (PLD), a vertical-cavity surface-emitting laser (VCSEL), a fiber laser, etc. For example, the PLD may be a semiconductor device similar to a light-emitting diode (LED), wherein the laser beam is generated at the junction of the diode. In some embodiments of this specification, the PLD includes a PIN diode, wherein the active region is located in the intrinsic (I) region, and charge carriers (electrons and holes) are pumped into the active region from the N and P regions, respectively. Depending on the semiconductor material, the wavelength of the incident laser beam 1007 provided by the PLD may be greater than 700 nm, such as 760 nm, 785 nm, 808 nm, 848 nm, 905 nm, 940 nm, 980 nm, 1064 nm, 1083 nm, 1310 nm, 1370 nm, 1480 nm, 1512 nm, 1550 nm, 1625 nm, 1654 nm, 1877 nm, 1940 nm, 2000 nm, etc. It is understandable that any suitable laser source can be used as the laser source 1006 for emitting the laser beam 1007.

[0044] Scanner 1008 can be configured to emit a laser beam 1009 toward object 1120 in a direction within a scanning angle range. In some embodiments consistent with this specification, scanner 1008 may include a micromechanical mirror assembly with a scanning mirror, such as MEMS mirror 1100. In some embodiments, at each point in time during the scanning process, scanner 1008 can emit a laser beam 1009 toward object 1120 in a direction within a scanning angle range by rotating the micromechanical mirror assembly. At its rotation angle, MEMS mirror 1100 can deflect a laser beam 1007 generated by laser source 1006 into a desired direction, becoming laser beam 1009. The micromechanical mirror assembly may include, in addition to these, various components that enable rotation of MEMS mirror 1100. For example, the micromechanical mirror assembly may include the following components: a scanning mirror (e.g., MEMS mirror 1100), a first set of anchors, one or more actuators connected to the anchors in the first set of anchors, a second set of anchors, at least one torsion spring connected to at least one anchor in the anchor set, and a substrate, to name only a few examples.

[0045] Certain design parameters of the MEMS mirror 1100 can affect its performance. These parameters may include mirror size, Q-factor, number of comb teeth, comb tooth spacing, comb tooth length, drive frequency and amplitude, spring size, linear spring constant, nonlinear spring constant, torsional spring constant, spring constant ratio, torsional spring size, number of torsional springs, angle of the torsional spring relative to one or more anchors, gimbal and / or scanning mirror angles, to name just a few. Therefore, adjusting design parameters during the design phase to meet target performance requirements can be beneficial for the design of the MEMS mirror 1100.

[0046] This specification provides torsion spring designs that consider nonlinearity, allowing for optimization of the spring constant ratio r3 and vibration frequency bandwidth for their associated scanning mirror assemblies, such as one or more MEMS mirrors 1100, scanners 1008, and / or transmitters 1002. These torsion spring designs can be customized to achieve a target spring constant ratio r3′ and / or vibration frequency bandwidth for the scanning mirror assembly. For example, an initial spring constant ratio calculated for an initial design parameter set can be compared to a target nonlinear spring constant ratio. When the calculated initial nonlinear spring constant ratio meets the target nonlinear spring constant ratio, the initial design parameter set can be the parameters used to manufacture the torsion spring and scanning mirror assembly. Otherwise, when the initial nonlinear spring constant does not meet the target spring constant ratio r3′, an adjusted design parameter set can be proposed, changing the size, shape, or number of torsion springs, and the simulation can be re-run to determine whether the adjusted torsion spring design parameter set achieves the target spring constant ratio r3′.

[0047] The design parameter set can be adjusted until a torsion spring design that meets the target spring constant ratio r3′ is achieved. In some embodiments, design changes to the initial torsion spring design can be determined by comparing the calculated spring constant ratio r3 with the target spring constant ratio r3′. An adjusted design parameter set can be selected for torsion spring design to keep the characteristic vibration frequency and linear spring constant k1 constant, while changing only the nonlinear spring constant k3, for example, as shown in Figure 2 below. Figure 5 Provide detailed additional information.

[0048] Continue to refer to Figure 1 The object 1120 can be made of a variety of materials, including, for example, non-metallic objects, rocks, rainwater, compounds, aerosols, clouds, and even single molecules. In some embodiments of this specification, the scanner 1008 may also include optical components (e.g., lenses) that can focus the pulsed laser into a narrow laser beam to improve scanning resolution.

[0049] In some embodiments, receiver 1004 can be configured to detect a laser beam 1110 returning from object 1120. The returning laser beam 1110 may have a different direction than laser beam 1009. Receiver 1004 can collect the laser beam returning from object 1120 and output an electrical signal reflecting the intensity of the returning laser beam. Upon contact with the object, the laser beam can be reflected by object 1120 via backscattering (e.g., Raman scattering and / or fluorescence). Figure 1 As shown, receiver 1004 may include lens 1140 and photodetector 1121. Lens 1140 may be configured to collect light from various directions within its field of view and focus the laser beam before it is received by photodetector 1122. At each point in time during the scan, lens 1140 may collect the returning laser beam 1110. The returning laser beam 1110 may return from object 1121 and has the same wavelength as laser beam 1009.

[0050] Photodetector 1110 can be configured to detect a laser beam 1110 returning from object 1120. In some embodiments, photodetector 1121 can convert laser light collected by lens 1140 (e.g., the returning laser beam 1110) into an electrical signal 1190 (e.g., a current or voltage signal). The electrical signal 1190 may be generated when photons are absorbed by a photodiode included in photodetector 1121. In some embodiments of this specification, photodetector 1121 may include a PIN detector, a PIN detector array, an avalanche photodiode (APD) detector, an APD detector array, a single-photon avalanche diode (SPAD) detector and a SPAD detector array, a silicon photomultiplier (SiPM / MPCC) detector, a SiP / MPCC detector array, etc.

[0051] The lidar system 1000 may further include one or more signal processors 1124. The signal processor 1124 may receive electrical signals 1190 generated by the photodetector 1121. The signal processor 1124 may process the electrical signals 1190. For example, it may determine the distance information carried by the electrical signals 1190. The signal processor 1124 may construct a point cloud based on the processed information. The signal processor 1124 may include a microprocessor, microcontroller, central processing unit (CPU), graphics processing unit (GPU), digital signal processor (DSP), or other suitable data processing device.

[0052] Figure 2A This is a top view of an exemplary scanning mirror design 200 shown according to some embodiments of this specification. Various aspects of the scanning mirror design 200 can be used (e.g., during the design phase) to calculate the performance characteristics of the scanning mirror 202 (e.g., MEMS mirror 1100).

[0053] For example, the scanning mirror design 200 may include an initial design parameter set that can be used to calculate associated nonlinear spring constants. In some embodiments, the initial design parameter set may be associated with one or more components of the scanning mirror assembly. These components may include at least one of the following: a scanning mirror 202 (e.g., a MEMS mirror 1100), a first set of anchors 204a, a second set of anchors 204b, fixed comb-like drive teeth 206a connected to the anchors 204b, sliding comb-like drive teeth 206b connected to the scanning mirror 202, one or more torsion springs 208, and / or a substrate 211.

[0054] In some embodiments, the initial design parameter set may be parameters of these components, and any changes to these parameters may affect the linear spring constant k1, the nonlinear spring constant ratio k3, and the spring constant ratio r3, thereby affecting the vibration frequency bandwidth of the components. For example, the initial design parameter set may include the dimensions of the aforementioned components (e.g., length, width, and thickness), such as the dimensions of the scanning mirror 202 and the drive comb, and the distances between these components, such as the distance between the scanning mirror 202 and the anchor 204b. Other examples of the initial design parameter set may include one or more materials of these components, the characteristic frequency of the scanning mirror 202, the total overlap area of ​​all comb-like drive teeth 206a, 206b, the air gap spacing between components (e.g., the air gap spacing d0 between the fixed comb-like drive teeth 206a and the sliding comb-like drive teeth 206b), the drive voltage frequency, silicon density, and the moment of inertia of the scanning mirror; the above are just a few examples.

[0055] In some embodiments, the linear spring constant k1, the nonlinear spring constant k3, and the spring constant ratio r3 can be calculated using an initial design parameter set and calculation formulas, such as formulas (2)-(5) listed below.

[0056] To achieve numerical simulation for calculating the linear spring constant k1, nonlinear spring constant k3, and spring constant ratio r3 of the flexible scanning mirror assembly, this specification provides a computer model that can convert the aforementioned dimensional formula (1) into a dimensionless formula (2). Calculating the solution of the dimensionless formula (2) simplifies the calculations in the scanning mirror simulation process. For vibration frequencies, units of Hz (1 Hz = 1 revolution per second) or kHz are typically used. However, the unit Hz is numerically incompatible for mathematical calculations; therefore, this computer model can use dimensionless "radians." The computer model in this specification can be configured to divide time steps (e.g., two time steps, ten time steps, 20 time steps, 100 time steps, etc.) to numerically integrate formula (2):

[0057]

[0058] Where τ is a dimensionless time, the natural frequency of equation (2) becomes 2π. When the scanning mirror assembly is driven at or near its natural frequency, the magnitude of the angular displacement θ is mainly controlled by the quality factor Q of the scanning mirror. The magnitude of the angular displacement is linearly proportional to the driving torque and inversely proportional to the torsional spring constant k, which can also be called the "linear spring constant". For the vibration of the reflector, the linear spring constant is the torsional spring constant because the motion is rotational. In other words, the "k" in formula (2) is the same as the "k" in formula (1).

[0059] As the scanning mirror assembly rotates, tension is applied along the spring, which is due to the nonlinear spring constant k3.

[0060] Due to the symmetry of the scanning mirror assembly design, the nonlinear spring constant k3 is cubic (third order). If the nonlinear spring were quadratic (second order), the scanning mirror assembly would be asymmetrical and would experience different torques when rotating in the positive or negative direction.

[0061] Both the linear spring constant k1 and the nonlinear spring constant k3 are functions of the spring's size and shape. Therefore, computer models and / or users can change the size and shape of the spring to find the target linear spring constant k1′ and the target nonlinear spring constant k3′.

[0062] Assuming the torsion spring is a cubic nonlinear spring, the relationship between torque and angular displacement θ can be expressed by a polynomial, as shown in formula (3):

[0063] torque=k1θ 1 +k3θ 3 =kθ(1+r3θ) 2 (3)

[0064] Where Q is the quality factor, r3 is the ratio of the nonlinear spring constant k3 to the linear spring constant k1, and k is the torsional spring constant.

[0065] As mentioned earlier, to obtain high accuracy in solving for the linear spring constant k1, nonlinear spring constant k3, and spring constant ratio r3 of a flexible scanning mirror assembly, the relevant motion control formulas must consider the flexibility of the assembly. To calculate these parameters, this method uses a computer model that considers the assembly's flexibility to simulate its vibration. For example, the following will combine... Figures 2B-5 Please provide a detailed explanation.

[0066] Figure 2B An exemplary scanning mirror assembly 210 in the primary vibration mode is described. Figure 2C An exemplary scanning mirror assembly 212 in an advanced vibration mode according to an embodiment of this specification is described. Figure 2B and 2C It may describe the vibration of the same scanning mirror assembly in different vibration modes, such as primary vibration mode and advanced vibration mode. Figure 2D An embodiment according to this specification is shown. Figure 2C An unfolded view 221 of the first torsion spring configuration of an exemplary scanning mirror assembly 212. Figure 2E Based on the embodiments of this specification and Figure 2D The first curves of linear torque versus angular displacement and nonlinear torque versus angular displacement associated with the first torsion spring configuration are shown in Figure 230. Figure 2F An embodiment according to this specification is shown. Figure 2C An unfolded view 240 of the second torsion spring configuration of an exemplary scanning mirror assembly 212. Figure 2G Based on the embodiments of this specification and Figure 2F The second torsion spring configuration is associated with linear torque versus angular displacement and nonlinear torque versus angular displacement, as shown in Figure 250. Figure 2H An embodiment according to this specification is shown. Figure 2C An unfolded view 260 of the third torsion spring configuration of the exemplary scanning mirror assembly 212. Figure 2I Based on the embodiments of this specification and Figure 2H The third curves of linear torque versus angular displacement and nonlinear torque versus angular displacement associated with the third torsion spring configuration are shown in Figure 260. Figure 2J An embodiment according to this specification is shown. Figure 2C An unfolded view 280 of the fourth torsion spring configuration of the exemplary scanning mirror assembly 212. Figure 2K An embodiment according to this specification is shown. Figure 2CAn unfolded view 290 of the fifth torsion spring configuration of the exemplary scanning mirror assembly 212. Figures 2B-2K They will be explained together.

[0067] Figure 2B An exemplary scanning mirror assembly 210 is shown, which includes an elliptical scanning mirror 202 and a gimbal 214, a set of comb-shaped drive teeth 206b connected to the gimbal 214b, and a torsion spring 208 connecting the gimbal 214b to an anchor 204a. During vibration, each point (also referred to as a “node”) on the surface of the scanning mirror assembly 210 has the same angular displacement associated with a given angular acceleration, also referred to as a “primary vibration mode”.

[0068] on the other hand, Figure 2C An exemplary scanning mirror assembly 220 is shown, whose components, size, and shape are similar to... Figure 2B The exemplary scanning mirror assembly 210 described herein is similar, except that the scanning mirror assembly vibrates in an advanced vibration mode. For simplicity, the comb-like drive teeth 206b are not shown here. During vibration, as... Figure 2C As shown, different points, sections, regions, or nodes on the surface of the scanning mirror assembly 220 may have different angular displacements associated with a given angular acceleration; these are also referred to as "advanced vibration modes." When vibrating in advanced modes, the surface of the scanning mirror assembly 220 may not remain flat due to a lack of rigidity. Physically, the shape of the scanning mirror can be a combination of primary modes and one or more advanced modes (e.g., there may be multiple advanced vibration modes). Therefore, the scanning mirror may never truly be flat during vibration. Therefore, this specification can calculate the linear spring constant k1 and the nonlinear spring constant k3 by averaging these values ​​across the entire surface of the scanning mirror 202.

[0069] In some embodiments, the linear spring constant k1, nonlinear spring constant k3, and spring constant ratio r3 of the flexible scanning mirror assembly 220 can be calculated using an initial design parameter set and calculation methods, for example, formulas (4) and (5) listed below. Computer models (such as ANSYS ADPL, Simulink Ordinary Differential Equation (ODE) solvers, etc.) can use the solutions of formulas (4) and (5) to solve the numerical simulation of the dimensionless formula (2) above. Once a solution to the dimensionless formula (2) is found, it can be converted back to a dimensional quantity to solve formula (1).

[0070] More specifically, the computer model can generate a simulation of the flexible scanning mirror assembly based on an initial set of design parameters. This initial set of design parameters can be input into the computer model by the user, or the computer model can select initial design parameters from a sample set of design parameters. The computer model can then simulate the angular acceleration applied to the simulated flexible scanning mirror assembly 220. You can choose to simulate angular acceleration This is to simulate the scanning mirror 202 rotating at a predetermined angle (e.g., 5 mechanical degrees). Under angular acceleration... Under these conditions, the simulated scanning mirror 202, the universal joint 214, and the torsion spring 208 may deform in their natural shapes, such as Figure 2C As shown, the natural shapes are the same as or similar to those associated with the vibrational motion during the scanning process.

[0071] To simplify the calculations related to determining torque as a function of angular displacement θ, the computer model can first calculate the average angular displacement θ of all nodes across the entire surface of the scanning mirror 202. For example, for a given angular acceleration, the computer model can determine the average angular displacement θ of all nodes using formula (4):

[0072]

[0073] Where n is the total number of nodes on the surface of scanning mirror 202 in the numerical model (also known as the "simulation"), and z i It is the vertical displacement of node i, y i It is the distance from node i to the rotation axis.

[0074] Then, at the same angular acceleration The torque of all rotating bodies in the assembly (e.g., scanning mirror 202, universal joint 214, comb-shaped drive teeth 206b) can be calculated using the following formula (5):

[0075]

[0076] Where r is the distance between the node (also called the "mass element") and the rotation axis "dm".

[0077] Then, angular acceleration It can change incrementally; the average angular displacement θ can be calculated for each increment of angular acceleration. Angular acceleration This can be acceleration related to different scanning angles. The computer model can then calculate the torque of the entire scanning mirror assembly as a function of the average angular displacement associated with that angular acceleration, and so on, until the torque as a function of angular displacement is calculated for each simulated angular acceleration. The computer model can save the resulting data as a lookup table that associates torque and angular displacement, for example... Figure 3 As shown. This lookup table can include torque and angular displacement values, which are used to plot polynomial curves to calculate the linear spring constant k1 and the nonlinear spring constant k3, for example, as follows: Figure 2D , Figure 2F and Figure 2H As shown. In some embodiments, the angular displacement can be converted from degrees to radians before performing polynomial curve fitting.

[0078] Finally, for the design of a scanning mirror assembly using an initial set of design parameters, given the relationship between angular displacement and torque for a specific design, the computer model can calculate the linear spring constant k1 and the cubic nonlinear spring constant k3 using cubic polynomial curve fitting. Figure 2E , Figure 2G and Figure 2I These examples are depicted in the text. The spring constant ratio r3 can be calculated as r3 = k3 / k1.

[0079] The computer model can compare the calculated r3 for the initial design parameter set with the target spring constant ratio r3′ to determine whether these design parameters have achieved the expected results. If the initial design parameter set meets the target linear spring constant k1′, the target nonlinear spring constant k3′, and the target spring constant ratio r3′, the computer model may output such an indication. Otherwise, if the initial design parameter set does not meet one or more target nonlinear spring constants k3′ and / or the target spring constant ratio r3′, an adjusted design parameter set can be proposed by the computer model or input as user input for the torsion spring, and then the simulation can be rerun.

[0080] The adjusted set of design parameters may include, for example, at least one structural change to at least one torsion spring. More specifically, at least one structural change may include a change in the size of at least one spring, a change in the number of springs in at least one spring, a change in the spacing between two or more springs in at least one spring, a change in the angle between at least one spring and the scanning mirror assembly, or a change in the type of the scanning mirror assembly, such as... Figure 2D , 2F As shown in 2H.

[0081] In achieving the target linear spring constant k1′ and thus the target characteristic vibration frequency through the initial design parameter set, structural modifications can be selected to adjust the nonlinear spring constant k3′ (to increase the spring constant ratio r3) without changing the linear spring constant k1, thereby increasing the vibration frequency bandwidth without changing the characteristic vibration frequency of the scanning mirror assembly.

[0082] For example, suppose the initial design parameter set includes a torsion spring 208 with dimensions as follows: Figure 2D As shown. Figure 2D This shows half of the symmetrical structure of the elliptical scanning mirror design, with its central torsion spring 208 appearing as a "rectangle". The spring stiffness and the characteristic frequency requirements of the specific scanning mirror assembly application determine the selection of the spring length L and spring width w.

[0083] Figure 2EThis illustrates torque as a function of angular displacement curves (as shown in the first curve, Figure 230) related to the initial design parameter set. One is a linear curve that can be calculated by neglecting nonlinearities in the calculation. The second is a calculated nonlinear curve that includes geometric nonlinearities as the scanning mirror assembly rotates. As the mirror angle increases, additional torque is required; this phenomenon is also known as "spring stiffening." Physically, nonlinearity is caused by the stretching of material along its length towards the upper or lower edge of the spring. Therefore, a wider torsion spring 208 is more nonlinear than a narrower torsion spring. For a linear spring, the design parameter set can include a relatively small w and a larger L.

[0084] Assuming the target characteristic vibration frequency is 1.7 kHz, it can be achieved experimentally and by correctly selecting the values ​​of L and w. Figure 2E As shown, for L of 500 μm and w of 300 μm, 6.2 × 10 8 The linear spring constant k1 will produce the desired frequency of 1.7 kHz, while the nonlinear spring constant k3 is 8.6 × 10⁻⁶. 9 In this example, the spring constant ratio r3 is 14, as... Figure 2E As shown. Without departing from the scope of this specification, the following can be used. Figure 2D Other dimensions besides the L and w values ​​given.

[0085] For example, suppose the target spring constant ratio r3′ is 20 (e.g., a predetermined threshold). In this example, Figure 2D The initial design parameter set did not achieve the target spring constant ratio. Therefore, the computer model can suggest an adjusted design parameter set, or the user can input the adjusted design parameter set.

[0086] For ease of explanation, assume the adjusted design parameter set includes Figure 2F The parameters shown. Figure 2F The image shows half of the symmetrical structure of the elliptical scanning mirror design, with the central torsion spring 208 comprising a "three-spring design". Figure 2F The triple torsion spring includes a central torsion spring 208' and two outer torsion springs 208'. For example... Figure 2F As shown, the triple spring design includes four dimensions that can be used to adjust the nonlinear spring constant k3. These dimensions include, for example, a central torsion spring 208' with a length L of 700 μm and a width w1 of 120 μm, and outer torsion springs 208" with a width w2 of 120 μm. The gap h between the central torsion spring 208' and each outer torsion spring 208" is 260 μm. Assuming the target characteristic vibration frequency is 1.7 kHz, these four spring dimensions can be adjusted to keep the linear spring constant k1 at 6.2 × 10⁻⁶. 8 The nonlinear spring constant k3 is increased. This is achieved by increasing the number of design parameters from... Figure 2D Two of them were added to Figure 2F The number of possible design parameter combinations that design engineers can customize to achieve target linear and nonlinear spring constants can also be increased from two to four. Increasing the number of possible design parameter combinations to achieve target linear and nonlinear spring constants simplifies the design engineer's search for design parameters to achieve these target spring constants. In addition to... Figure 2F Other dimensions may be used in addition to the values ​​of L, w1, w2 and clearance h given in this specification, without departing from the scope of this specification.

[0087] Considering that the spring is composed of an infinite number of fibers, the fibers along the axis of rotation contribute only to the linear spring constant k1. All other fibers contribute to both the linear spring constant k1 and the nonlinear spring constant k3. The fibers in the outermost layer of the spring have the greatest influence on the nonlinearity. Therefore, in general, a larger w1, a smaller w2, and a smaller h contribute to a larger linear spring constant k1, while a smaller w1, a larger w2, and a larger h contribute to a larger nonlinear spring constant k3. Thus, by splitting a torsion spring into a central torsion spring 208' and two outer torsion springs 208'", and moving the outer torsion springs 208' away from the central torsion spring 208', the nonlinearity of the torsion spring (central torsion spring 208' and outer torsion springs 208') can be increased.

[0088] Therefore, as Figure 2G As shown, Figure 2F The adjusted design parameter set shown reduces the nonlinear spring constant k3 from 8.6 × 10⁻⁶. 9 Increased to 1.0×10 10 .and Figure 2D Compared to the initial design parameter set shown, the spring constant ratio r3 increases to 17.

[0089] Still assuming the target spring constant ratio r3′ is 20, Figure 2F The adjusted design parameter set also failed to achieve the target spring constant ratio. Therefore, the computer model can suggest an adjusted design parameter set, or the user can input the adjusted design parameter set.

[0090] For ease of explanation, assume the adjusted design parameter set includes Figure 2H The parameters shown. Figure 2H The image shows half of the symmetrical structure of the elliptical scanning mirror design, with the central torsion spring 208 featuring a "double spring design". Figure 2F The central torsion spring shown has been removed. (By removing from...) Figure 2H The torsion spring design shown removes Figure 2F The central torsion spring 208' in the middle, the nonlinearity of the torsion spring may be... Figure 2HThis can be further increased. For this spring design, three parameters can be adjusted (e.g., length L = 800 μm, width w = 95 μm, gap h = 1000 μm) to increase the nonlinear spring constant k3 without changing the linear spring constant k1. For example... Figure 2I As shown, the adjusted design parameter set adds the nonlinear spring constant k3, and... Figure 2F Compared to the spring design shown, from 8.6×10 9 Increased to 1.2 × 10 10 Here, the target spring constant ratio r3′ is achieved to be 20. Without departing from the scope of this specification, the following methods can be used: Figure 2H Other dimensions besides the L, w, and h values ​​given.

[0091] Figure 2J and 2K The adjusted set of design parameters shown includes tilting the spring "inward" or "outward" to change the linear spring constant k1 and the nonlinear spring constant k3. The tilt amount of the torsion spring 208 depends on the target requirements of the specific application.

[0092] For each spring constant ratio r3, the frequency response curve can be simulated by applying all other design parameters to the computer model and applying a sinusoidal drive voltage (e.g., as shown below). Figure 4 As shown), this curve covers a frequency range from slightly below the natural frequency to well above the natural frequency. Simulations were repeated for r3 = 14, 17, and 20 under the same design parameter values, as... Figure 4 The three frequency response curves are shown. The effect of the spring constant ratio r3 is that the vibration frequency bandwidth of the scanning mirror assembly design increases with the increase of the spring constant ratio r3. As mentioned above, designing the torsion spring such that this set of design parameters maximizes the associated vibration frequency bandwidth while maintaining the desired characteristic vibration frequency may be advantageous for controlling the scanning mirror angle during use by adjusting the drive frequency in the accompanying scanner electronics.

[0093] Figure 5 A flowchart illustrating an exemplary method 500 for designing a scanning mirror according to embodiments of this specification is provided. Method 500 can be performed by an assembly system configured to assemble a scanning mirror assembly. For example, the assembly system may include a MEMS assembly system, or any other assembly system configured to assemble the scanning mirror assembly using micromechanical and / or MEMS processing technologies. As described below, method 500 may include steps S502-S510. It is worth noting that some steps may be optional, some steps or sub-steps may be performed simultaneously, or in different ways. Figure 5 Execute in the order shown.

[0094] In step 502, the assembly system connects the scanning mirror to a gimbal to allow the scanning mirror to rotate about a rotation axis. For example, refer to... Figure 2F , Figure 2H , Figure 2J and Figure 2K The scanning mirror 202 can be connected to the universal joint 214 via a torsion spring 208. Connecting the scanning mirror to the universal joint may include forming the scanning mirror connected to the universal joint using micromechanical and / or MEMS processing techniques.

[0095] In step 504, the assembly system may connect multiple torsion springs along a rotation axis to one side of the scanning mirror, the multiple torsion springs having a predetermined gap and in a predetermined direction. Connecting the multiple torsion springs may include forming multiple torsion springs connected to one or more universal joints, scanning mirrors, and / or anchors. For example, refer to... Figure 2F , Figure 2H , Figure 2J and Figure 2K ,like Figure 2F As shown, multiple torsion springs 208 are connected to one side of the elliptical scanning mirror 202 or the universal joint 214 assembly, such that a gap of distance h separates the torsion springs 208 from the rotation axis, or as... Figure 2H As shown, the gap of distance h separates the torsion spring 208. Step 504 may include sub-steps 506-510.

[0096] In step 506, the assembly system can be achieved by connecting multiple external torsion springs on both sides of the rotation axis to one side of the scanning mirror, while connecting multiple torsion springs along the rotation axis to one side of the scanning mirror. For example, refer to... Figure 2F , Figure 2H , Figure 2J and Figure 2K A pair of external torsion springs are connected to the scanning mirror 202 or universal joint 214 assembly on both sides of the rotating shaft. Although Figure 2F , 2H Multiple external torsion springs are depicted on both sides of the rotating shaft in 2J and 2K, but without departing from the scope of this specification, there may be more than one external torsion spring on both sides of the rotating shaft.

[0097] In step 508, the assembly system can connect multiple torsion springs to one side of the scanning mirror via a central torsion spring that overlaps with the rotation axis, connecting them along the rotation axis to one side of the scanning mirror. For example, refer to... Figure 2F The central torsion spring 208' is located on the rotation axis between the outer torsion springs 208".

[0098] In step 510, the assembly system can connect multiple external torsion springs along the rotation axis to one side of the scanning mirror by means of multiple external torsion springs tilted inward or outward relative to the rotation axis. For example, refer to Figure 2J and2K The torsion spring 208 is tilted inward or outward relative to the axis of rotation, such as Figure 2J As shown.

[0099] Another aspect of this specification relates to a non-transitory computer-readable medium storing instructions that, when executed, cause one or more processors to perform the methods described above. The computer-readable medium may include volatile or non-volatile, magnetic, semiconductor-based, magnetic tape-based, optical, removable, non-removable, or other types of computer-readable media or computer-readable storage devices. For example, the computer-readable medium may be a storage device or storage module storing disclosed computer instructions. In some embodiments, the computer-readable medium may be an optical disc or flash drive storing computer instructions.

[0100] It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and related methods. Other embodiments will be readily apparent to those skilled in the art upon consideration of the specifications and practices of the disclosed system and related methods.

[0101] This specification and examples are to be considered exemplary only, and the true scope is indicated by the following claims and their equivalents.

Claims

1. A scanning mirror assembly for an optical sensing system, comprising: The scanning mirror is configured to rotate about a rotation axis; as well as Multiple torsion springs are connected along the rotation axis to at least one side of the scanning mirror. Among them, the plurality of torsion springs collectively possess both nonlinear spring constants and linear spring constants, and The ratio of the nonlinear spring constant to the linear spring constant satisfies a predetermined threshold, and the plurality of torsion springs include a plurality of external torsion springs located on both sides of the rotation axis. The plurality of external torsion springs are connected to one side of the scanning mirror along the rotation axis to increase the nonlinear spring constant without changing the linear spring constant.

2. The scanning mirror assembly according to claim 1, wherein, All of the plurality of torsion springs are parallel to the rotation axis.

3. The scanning mirror assembly according to claim 1, wherein, At least one of the plurality of torsion springs is not parallel to the axis of rotation.

4. The scanning mirror assembly according to claim 3, wherein, At least one of the plurality of torsion springs is tilted inward toward the axis of rotation.

5. The scanning mirror assembly according to claim 3, wherein, At least one of the plurality of torsion springs is tilted outward away from the axis of rotation.

6. The scanning mirror assembly according to claim 1, wherein: The plurality of torsion springs also includes a central torsion spring that overlaps with the rotation axis; and The plurality of external torsion springs are oriented toward both sides of the central torsion spring and are equidistant from the central torsion spring.

7. The scanning mirror assembly according to claim 1, further comprising: The gimbal connected to the scanning mirror, The plurality of torsion springs are connected to the scanning mirror via the universal joint.

8. The scanning mirror assembly according to claim 1, wherein: The linear spring constants of the plurality of torsion springs are selected to achieve the target characteristic vibration frequency; as well as The nonlinear spring constants of the plurality of torsion springs are selected to achieve the target vibration frequency bandwidth.

9. An optical sensing system, comprising: A laser emitter configured to emit optical signals; A scanning mirror assembly configured to reflect the optical signal into the environment in one or more directions, the scanning mirror assembly comprising: The scanning mirror is configured to rotate about a rotation axis; and Multiple torsion springs are connected along the rotation axis to at least one side of the scanning mirror. The receiver is configured to receive at least a portion of the optical signal returned from the environment. Among them, the plurality of torsion springs collectively possess both nonlinear spring constants and linear spring constants, and The ratio of the nonlinear spring constant to the linear spring constant satisfies a predetermined threshold, and the plurality of torsion springs include a plurality of external torsion springs located on both sides of the rotation axis. The plurality of external torsion springs are connected to one side of the scanning mirror along the rotation axis to increase the nonlinear spring constant without changing the linear spring constant.

10. The optical sensing system according to claim 9, wherein, All of the plurality of torsion springs are parallel to the rotation axis.

11. The optical sensing system according to claim 9, wherein, At least one of the plurality of torsion springs is not parallel to the axis of rotation.

12. The optical sensing system according to claim 11, wherein, At least one of the plurality of torsion springs is tilted inward or outward relative to the axis of rotation.

13. The optical sensing system according to claim 9, wherein: The plurality of torsion springs also includes a central torsion spring that overlaps with the rotation axis, and The plurality of external torsion springs are oriented toward both sides of the central torsion spring and are equidistant from the central torsion spring.

14. The optical sensing system according to claim 9, wherein: The linear spring constants of the plurality of torsion springs are selected to achieve the target characteristic vibration frequency, and The nonlinear spring constants of the plurality of torsion springs are selected to achieve the target vibration frequency bandwidth.

15. A method for assembling a scanning mirror assembly, comprising: Connect the scanning mirror to the gimbal so that the scanning mirror rotates about the rotation axis; as well as A plurality of torsion springs are connected to one side of the scanning mirror along the rotation axis, the plurality of torsion springs having a predetermined gap between them and in a predetermined direction. The plurality of torsion springs together possess both nonlinear and linear spring constants. Wherein, the ratio of the nonlinear spring constant to the linear spring constant exceeds a predetermined threshold, and the plurality of torsion springs include a plurality of external torsion springs located on both sides of the rotation axis, the plurality of external torsion springs being connected along the rotation axis to one side of the scanning mirror to increase the nonlinear spring constant without changing the linear spring constant.

16. The method according to claim 15, wherein, The step of connecting the plurality of torsion springs to one side of the scanning mirror includes: The plurality of external torsion springs on both sides of the rotating shaft are connected to one side of the scanning mirror.

17. The method according to claim 16, wherein, The method of connecting the plurality of torsion springs to one side of the scanning mirror also includes: A central torsion spring, which overlaps with the rotation axis, is connected to one side of the scanning mirror.

18. The method according to claim 17, wherein, The method of connecting the plurality of torsion springs to one side of the scanning mirror also includes: The plurality of external torsion springs are tilted inward or outward relative to the rotation axis.

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