Resonant actuator assembly

Abstract

A resonant actuator assembly (1) comprising a support structure (3), a moveable part (5) capable of relative movement with respect to the support structure, and an actuator device (7) arranged to drive the relative movement of the moveable part, the resonant actuator assembly being arranged to provide a restoring force to the moveable part when the moveable part is displaced from an equilibrium position with respect to the support structure, and the actuator device being arranged to drive the relative movement of the moveable part at a resonance of the resonant actuator assembly, the restoring force being non-linearly related to the displacement.

Description

[0001] This invention relates to a resonant actuator assembly.

[0002] Actuator assemblies employ actuators to drive relative movement of movable parts relative to a supporting structure. As an example, the actuator could be one or more shape memory alloy (SMA) wires or voice coil motors, which are used in many applications requiring precise control, where the actuator assembly operates away from resonance, as resonance can affect performance. However, achieving high stroke displacement and / or high frequency with conventional actuator designs is challenging due to the cooling bandwidth of SMA wires.

[0003] In contrast, the displacement and / or frequency of the movement can be increased by configuring the actuator assembly as a resonant actuator assembly, where the resonant frequency is designed to match the desired scanning frequency. As an example only, one such application is moving optical components to scan a beam, such as in a time-of-flight sensor system, which can be used in 3D scanning applications. Another such application is providing scanning in HUD (Head-Up Display) projectors. In typical systems of this type, it may be necessary to scan at relatively high frequencies (e.g., approximately 100 Hz) to provide a high frame rate and move the movable object with a relatively large displacement range (e.g., 400 μm). Such operating parameters can be achieved using a resonant actuator assembly.

[0004] This invention relates to optimizing the design of such resonant actuator components.

[0005] According to a first aspect of the invention, a resonant actuator assembly is provided, the resonant actuator assembly including a support structure, a movable portion capable of relative movement with respect to the support structure, and an actuator device arranged to drive the relative movement of the movable portion, the resonant actuator assembly being arranged to provide a restoring force to the movable portion when displaced relative to the support structure from an equilibrium position, and the actuator device being arranged to drive the relative movement of the movable portion under resonance of the resonant actuator assembly, wherein the restoring force has a nonlinear relationship with the displacement.

[0006] A typical resonant system with a linear restoring force has a sinusoidal response (the behavior of the movable part from its equilibrium position over time). This may not be desirable in all applications. For example, in some applications (such as 3D scanning), the response with a linear restoring force can be sinusoidal. This sinusoidal waveform provides a histogram of position versus time over the resonant period, with peaks at the extremes of relatively slow displacement. Flattening the histogram of position versus time may be desirable. This can be achieved, for example, by modifying the response to make it closer to a triangular waveform. Modifying the restoring force to be non-linear with respect to displacement allows the response to be modified to flatten the histogram of position over time.

[0007] In some embodiments, the resonant actuator assembly is arranged to provide a restoring force with stiffness that increases as the magnitude of the displacement from the equilibrium position increases. For example, in embodiments where the actuator device includes an SMA line, the SMA line will excite resonance (which is designed to be close to the target frequency). Due to the nonlinearity of the system, the resulting motion is modified from a sine curve, and thus an improvement over a simple resonant actuator. The response can be modified to a triangular waveform.

[0008] In some embodiments, the resonant actuator assembly is arranged to provide a stiff restoring force that increases in stiffness as the magnitude of the displacement from the equilibrium position increases, so as to flatten the histogram of position over time during the resonant period (i.e., the probability that the actuator is located at any given point along its range of motion compared to an equivalent system with a constant restoring force). This means that the movable part spends a more equal portion of its time in each region of its travel; for example, the movable part spends more time in regions with higher probabilities.

[0009] In some embodiments, the resonant actuator assembly is arranged to provide a restoring force with increased stiffness when the magnitude of the displacement from the equilibrium position increases above a predetermined threshold. In the case of a linear restoring force, the velocity in the central region of the travel of the movable portion is approximately constant. Therefore, significant improvements can be achieved simply by changing the restoring force near the displacement extremes. This may also be simpler to achieve than changing the behavior of the element providing the restoring force.

[0010] In some embodiments that provide increased stiffness as the magnitude of the displacement from the equilibrium position increases above a predetermined threshold, the resonant actuator assembly includes a resilient bumper located between the movable portion and the support structure. This bumper is arranged to disengage when the magnitude of the displacement from the equilibrium position is below the predetermined threshold and to engage when the magnitude of the displacement from the equilibrium position increases above the predetermined threshold to provide a restoring force with increased stiffness. The resilient bumper is readily available, and existing designs can be easily adapted into actuator assemblies.

[0011] In some embodiments, the actuator device includes at least one SMA line. The SMA line provides a compact actuating element that can be easily activated by an electrical signal. The SMA line also provides greater force than other actuators of similar size. The SMA line is used to provide input drive force for a resonant actuator. Resonant actuators can achieve much longer strokes at high frequencies than non-resonant actuators.

[0012] In some embodiments, the resonant actuator assembly further includes drive circuitry arranged to provide a drive signal to at least one SMA line. In some embodiments, the drive signal includes pulses at or substantially at the resonant frequency of the resonant actuator assembly. As a result, the drive signal drives relative motion of the movable portion relative to the support structure at resonance.

[0013] In some embodiments, at least one SMA line is inclined at an acute angle relative to the axis of movement of the movable portion. This provides a transmission effect, allowing the SMA line to provide displacement of the movable portion greater than the length variation of the SMA line.

[0014] In some embodiments, the resonant actuator assembly further includes at least one intermediate section, and the actuator device includes multiple stages of at least one SMA wire, each stage being arranged to drive relative movement between two parts of the support structure, with at least one intermediate section and the movable part mechanically connected in series to additionally drive relative movement of the movable part relative to the support structure. Actuator devices with multiple stages that do not include the SMA wire can also be provided, for example, by using multiple voice coil motors instead of the SMA wire. Using multiple stages can increase design flexibility and may be more robust than using a single-stage actuator for high displacements or forces.

[0015] In some embodiments, the actuator device includes opposing SMA lines arranged to drive relative movement of the movable portion in opposite directions along the movement axis. This has the advantage that the SMA lines can be used to provide both restoring and driving forces, resulting in more symmetrical behavior.

[0016] In some embodiments, the actuator device includes opposing pairs of SMA lines, each pair of SMA lines inclined at equal and opposite acute angles relative to the axis of movement of the movable portion, in order to provide balanced force components perpendicular to the axis of movement. This means that no net force is applied to any support member that may form part of the support structure, which can reduce strain on the support member and the support structure. For example, the opposing pairs of lines can be used as support devices.

[0017] In some embodiments, the opposing SMA lines are inclined at an acute angle to provide a force component perpendicular to the axis of movement in the same direction. This may be desirable for certain types of supports that can be used as part of a support structure, which require forces applied to them to function properly.

[0018] In some embodiments, the actuator device includes at least one SMA line arranged to drive relative movement of the movable portion along a movement axis in a first direction, and no SMA line is arranged to drive relative movement of the movable portion in a second direction opposite to the first direction. This reduces the complexity of control required for the SMA lines, since the SMA lines are only used to apply force in a single direction.

[0019] In some embodiments, the resonant actuator assembly further includes an elastic element connected between the movable portion and the support structure, and arranged to provide at least a portion of the restoring force. The elastic element is readily available, for example in the form of a spring or rubber element, and thus provides a convenient means of providing the restoring force.

[0020] In some embodiments, the resonant actuator assembly further includes a support device arranged to guide relative movement of the movable portion relative to a support structure. This can provide more consistent movement of the movable portion and reduce strain on other components.

[0021] In some embodiments, the support device is arranged not to provide a restoring force. In some embodiments, the support device is arranged to provide a restoring force at least an order of magnitude smaller than that provided by the actuator device. This can be advantageous because the behavior of the movable part is entirely or almost entirely determined by another component (e.g., an elastic element or one or more SMA wires). This can simplify the design of the resonant actuator assembly.

[0022] In some embodiments, the support device is arranged to provide a restoring force at least an order of magnitude greater than that provided by the actuator device. In this case, the restoring force is almost entirely determined by the support device, which again simplifies the design of the resonant actuator assembly.

[0023] In some embodiments, the support device includes a ball bearing device. In some embodiments, the support device includes a flexural device. Both devices are readily available and provide a convenient implementation of a support for this type of actuator.

[0024] In some embodiments, the resonant actuator assembly further includes a position detection circuit arranged to obtain a measurement of the relative position of the movable portion with respect to a support structure. This can be used to guide the control of the resonant actuator assembly, particularly the control of the actuator device.

[0025] In some embodiments, the resonant actuator assembly further includes a position sensor arranged to sense the relative position of the movable part, and a position detection circuit arranged to obtain a measurement of the relative position of the movable part from the output of the position sensor. The position sensor can be used to obtain a precise measurement of the relative position of the movable part and the support structure.

[0026] In some embodiments, the actuator device includes at least one SMA line, the resonant actuator assembly further includes a resistance measurement circuit arranged to measure the resistance of the at least one SMA line, and a position detection circuit arranged to obtain a measurement of the relative position of the movable part from the output of the measured resistance. Using the resistance of the SMA line to determine the position measurement eliminates the need for a separate component to sense the position of the movable part.

[0027] In some embodiments, the movable portion is an optical component. In some embodiments, the resonant actuator assembly is arranged to scan the beam. Rapid and uniform scanning is particularly useful in certain types of optical scanning applications.

[0028] In some embodiments, the resonant frequency is at least 10 Hz. In some embodiments, the displacement ranges from at least 10 μm. These represent minimum parameters for some typical applications of this type of resonant actuator device.

[0029] According to a second aspect of the invention, a resonant actuator assembly is provided, the resonant actuator assembly including a support structure, a movable portion capable of relative movement with respect to the support structure, and an actuator device including at least one SMA line arranged to drive relative movement of the movable portion, the resonant actuator assembly being arranged to provide a restoring force to the movable portion when displaced relative to the support structure from an equilibrium position, and the actuator device being arranged to drive relative movement of the movable portion under the resonance of the resonant actuator assembly.

[0030] SMA lines provide a compact actuation element that can be easily activated by an electrical signal. SMA lines also provide greater force than other actuators of similar size. SMA lines are used to provide the input drive force for resonant actuators. Resonant actuation can achieve much higher strokes at high frequencies than non-resonant actuators, and SMA lines are particularly well-suited for this application in compact devices.

[0031] According to a third aspect of the present invention, a system is provided, the system comprising:

[0032] A sensor for sensing light, configured to provide data dependent on the sensed light; and

[0033] The resonant actuator assembly includes:

[0034] Support structure;

[0035] The movable portion is capable of relative movement with respect to the supporting structure; and the actuator device is arranged to drive the relative movement of the movable portion within a range of motion.

[0036] A resonant actuator assembly is arranged to provide a restoring force to the movable portion as it displaces relative to the support structure from its equilibrium position, and an actuator device is arranged to drive the relative motion of the movable portion under the resonance of the resonant actuator assembly, wherein the restoring force and displacement are substantially linear or nonlinear; and

[0037] The sensor is configured to stop providing data when the movable part has moved toward each end of the movement range to within 10%, 8%, or 5% of the movement range.

[0038] In some embodiments, the system is a time-of-flight (TOF) system that includes an illumination source for illuminating an object, wherein a sensor is configured to sense light scattered by the object. For example, the movable portion may include optical components for focusing (through a lens) or reflecting (through a mirror) the illumination onto the object. More specifically, oscillating movement in the movable portion can allow the illumination to scan a region of interest at the object.

[0039] The sensor can be configured to selectively provide data based on its position within its range of motion (e.g., based on its position within 40%, 42%, or 45% of its range of motion in both directions from its equilibrium position). When the sensor stops providing data, it can continue to sense light, but it cannot provide the corresponding data, or it can stop sensing altogether.

[0040] Advantageously, such an arrangement allows data to be provided only when the movable part has moved to a position in a flatter region of the histogram of the expected position over time. This means that during sensing, the movable part can spend a more equal portion of its time in each region. In particular, such an arrangement can be advantageous for resonant systems in which the restoring force has constant stiffness; however, it can also be applied to resonant systems in which the restoring force has a nonlinear relationship with the displacement of the movable part.

[0041] Various features of the many aspects of the invention listed above can be equally applied to other aspects of the invention.

[0042] For better understanding, embodiments of the invention will now be described by way of non-limiting examples with reference to the accompanying drawings, in which:

[0043] Figure 1 This is a schematic diagram of the resonant actuator assembly;

[0044] Figure 2 It is a histogram of the position of a resonant actuator component within the resonant period relative to time for certain forms of restoring force.

[0045] Figure 3 It is a graph showing the different forms of restoring force relative to their positions within the resonant actuator assembly;

[0046] Figure 4 It is a graph showing the response of the resonant actuator assembly to different forms of restoring force;

[0047] Figure 5 yes Figure 4 The extended portion of the curve graph;

[0048] Figure 6 Is for such Figure 4 and Figure 5 Histogram of the position of the resonant actuator assembly in the form of restoring force during the resonant period versus time;

[0049] Figure 7 and Figure 8 These are plan views of the first and second examples of the resonant actuator assembly;

[0050] Figure 9 These are a plan view and a side view of a third example of a resonant actuator assembly;

[0051] Figure 10 and Figure 11 These are plan views of the first and second examples of the resonant actuator assembly;

[0052] Figure 12 and Figure 13 These are circuit diagrams of different forms of resonant actuator components;

[0053] Figure 14 It is a diagram of a pulse-driven signal;

[0054] Figure 15 This is a schematic diagram of a time-of-flight sensor system that incorporates a resonant actuator assembly;

[0055] Figure 16 It is a graph showing the response in the resonant actuator assembly; and

[0056] Figure 17 Is it like this? Figure 16 The histogram of the position of the resonant actuator assembly within the resonant period versus time is shown.

[0057] Figure 1A resonant actuator assembly 1 is schematically illustrated. The resonant actuator assembly 1 includes a support structure 3. The support structure 3 may be static and may, for example, be fixed to a part of a larger assembly or device, to which the resonant actuator assembly 1 is part. The resonant actuator assembly 1 also includes a movable portion 5 capable of relative movement with respect to the support structure 3. The movable portion 5 may include an active element, such as an optical component, to be scanned by the resonant actuator assembly 1.

[0058] The resonant actuator assembly 1 also includes an actuator device 7 arranged to drive relative motion of the movable portion 5. Relative motion is the movement of the movable portion 5 relative to the support structure 3. The actuator device 7 is arranged to drive the relative motion of the movable portion 5 under the resonance of the resonant actuator assembly 1. In typical applications, the resonant frequency can be at least 10 Hz or at least 50 Hz. In typical applications, the displacement range can be at least 10 μm or at least 50 μm.

[0059] The actuator device 7 can be of any suitable type.

[0060] Actuator device 7 may include at least one SMA line 8, as shown in the following example. The SMA line provides a compact actuator that can be easily activated using an electrical signal. The SMA line also provides greater force than other actuators of similar size. The SMA line 8 is used to provide input drive force for a resonant actuator. Resonant actuation can achieve much higher strokes at high frequencies than non-resonant actuators, and the SMA line is particularly well-suited for this application in compact devices. In some embodiments, the SMA line 8 may be angled with the axis of motion M to increase its mechanical gain.

[0061] However, the actuator device 7 can be of other types, such as including a voice coil motor (VCM).

[0062] The resonant actuator assembly 1 includes a support device 9 arranged to guide relative movement of the movable portion 5 relative to the support structure 3. Depending on the nature of the resonant actuator assembly, the support device 9 can provide a restoring force to the movable portion 5. An exemplary support device 9 includes a ball bearing device, with one or more ball bearings positioned between a portion of the support structure 3 and the movable portion 5. An alternative support device 9 may be a flexure device, which may be advantageous if the support device 9 facilitates providing a restoring force to the movable portion 5. In some embodiments, the support device 9 may include a combination of different types of bearings, such as ball bearings and flexures.

[0063] The resonant actuator assembly 1 is arranged to provide a restoring force to the movable portion 5 when it is displaced relative to the support structure 3 from its equilibrium position E. The restoring force is always used to restore the movable portion 5 to its equilibrium position. An elastic element 11 connects the movable portion 5 and the support structure 3. The elastic element 11 helps provide the restoring force. The elastic element 11 does not guide the relative movement of the movable portion 5 relative to the support structure 3. However, the elastic element 11 is not necessary, and in some embodiments, the actuator device 7 can provide the restoring force. Alternatively, both the elastic element 11 and the actuator device 7 can contribute to providing the restoring force.

[0064] In summary, the restoring force is provided by one or more of the support device 9, actuator device 7, elastic element 11, and elastic buffer 13. The restoring force provided by the support device 9 and actuator device 7 depends on their design, and some examples are listed below.

[0065] For example, if an SMA line 8 is used and the SMA line 8 cannot cool rapidly after actuation, a significant restoring force can be generated from the actuator device 7. This may cause the SMA line 8 to continue exerting force on the movable part 5 even after any actuation signal has stopped. In this case, one option is to minimize any restoring force from the support device 9. In this case, the support device 9 is typically arranged to provide a restoring force at least an order of magnitude smaller than that provided by the actuator device 7. If there is no significant restoring force from the actuator device 7, the support device 9 can be designed to optimize resonance. In this case, the support device 9 is typically arranged to provide a restoring force at least an order of magnitude larger than that provided by the actuator device 7. If the design of the support device 9 and the actuator device 7 does not provide sufficient restoring force to optimize the resonant behavior of the resonant actuator assembly 1, an elastic element 11 can be included to provide an additional portion of the restoring force.

[0066] Achieving high strokes (i.e., large displacements from the equilibrium position) at high frequencies using conventional actuator designs is challenging due to the cooling bandwidth of the SMA line 8. Furthermore, the requirement for a small footprint adds additional complexity in applications involving mobile devices. Resonant actuators overcome many of these limitations, where the resonant frequency is designed to match the desired sweep frequency, and the SMA line 8 is used to provide the input driving force. The advantages of using SMA lines 8 in this type of actuator compared to other types of actuators available in small actuator assemblies are their high force and compact size.

[0067] A simple resonant system can be approximated as a simple harmonic oscillator, where the spring provides a linear restoring force as displacement increases. The response of a simple harmonic oscillator is sinusoidal when a sinusoidal driving force is present. In a scanning system, a sinusoidal response is undesirable because the flat top and bottom regions of the displacement's time dependence mean that the actuator spends disproportionately more time at extreme positions. Ideally, the actuator would spend an equal proportion of time at all positions. This would be achieved through a displacement that follows a pure triangular waveform relative to time.

[0068] Figure 2 The position histograms of a resonant system sampled at equal time intervals are shown, along with the probability that the actuator will be in any given position at random times. The displacement-time dependence of a pure sine wave, a pure triangular wave, and a smooth triangular wave are compared. The flatter the histogram (i.e., the equal probability at all positions), the better for linear sweep applications. Figure 2 This indicates that sine waves spend disproportionately more time at the extremes of motion, while triangular waves have an equal probability throughout the entire range of motion.

[0069] Advantageously, in this invention, the restoring force has a non-linear relationship with the displacement. This allows modification of the response of the resonant actuator assembly 1, which in turn allows modification of the histogram of the position. Some examples of this will now be described.

[0070] The restoring force can be plotted based on the position of the movable part 5 relative to the equilibrium position. By changing the restoring force according to the position, the response of the movable part 5 to the input driving force can be altered.

[0071] In some embodiments, the resonant actuator assembly 1 is arranged to provide a restoring force with stiffness that increases as the magnitude of the displacement from the equilibrium position increases. Here, stiffness refers to the rate of change of the restoring force with increasing displacement. This means that as the displacement becomes higher, the restoring force increases more rapidly with increasing displacement.

[0072] Figure 3 The restoring force varies with the position of the follower equilibrium position for three different dependencies of the restoring force on the displacement, as shown below.

[0073] The first curve shows linear dependence, leading to simple harmonic motion, where the restoring force is linearly proportional to the displacement.

[0074] The second curve illustrates the restoring force with cubic stiffening. In this case, the term that is cubically dependent on the displacement increases the restoring force at larger displacement magnitudes relative to the linear restoring force.

[0075] The third curve illustrates a restoring force with stiffness that increases by a step above a threshold. In this case, the effective stiffness of the "spring" providing the restoring force has a step change above a certain threshold of displacement. The dependence on displacement is linear across all displacements, but the gradient increases above the threshold. The "spring" mentioned here is merely a conceptual device for simulating the restoring force. In reality, as mentioned above, the restoring force can be provided in many different ways, without involving a spring or any elastic element. The threshold of displacement can be the desired maximum amplitude of motion. In such an embodiment, the resonant actuator assembly 1 is arranged to provide a restoring force with increased stiffness when the magnitude of the displacement from the equilibrium position increases above a predetermined threshold.

[0076] Figure 4 and Figure 5 The response of a resonant system simulated with a sinusoidal input driving force (100 Hz in this example) and a small damping term is shown. This is achieved by realizing a step change in the restoring force above a predetermined threshold (i.e., regarding the above). Figure 3 In option 3 (discussed), the sinusoidal response is distorted. Compared to the case of linear restoring force, the response becomes closer to a triangular response. This is evident in... Figure 5 The linearity of motion is evident when the displacement is less than 200 μm, where the curve of the restoring force exhibits greater linearity than that of the step change. It is also clear that the restoring force requires less time to reverse direction during a step change.

[0077] Figure 6 This demonstrates how a restoring force with a step change in stiffness flattens the position histogram compared to a linear restoring force. This confirms that a step change in the stiffness of the restoring force results in a more equal probability of migration toward each occupied position. This improvement can be quantified as the ratio between the time spent by the movable part 5 at its most extreme position and the time spent at its central equilibrium position. In the case of a linear restoring force, this ratio is approximately 3:1, so for every second the movable part 5 spends at its equilibrium position, it spends three seconds at its extreme position. In the case of a step-change restoring force, the ratio is 2:1, meaning that the time spent by the movable part 5 at its extreme position is twice the time spent at its equilibrium position. For reference, an ideal actuator could have a ratio of 1:1. Therefore, the resonant actuator assembly 1 is arranged to provide a restoring force with stiffness that increases as the magnitude of the displacement from the equilibrium position increases, thereby flattening the histogram of position versus time over the resonant period compared to an equivalent system with a restoring force having constant stiffness.

[0078] Nonlinear restoring force can be achieved in any suitable manner.

[0079] As an example, Figure 1The illustration depicts one possible manner in which a restoring force with increased stiffness is provided when the magnitude of the displacement from the equilibrium position increases above a predetermined threshold. In this example, the resonant actuator assembly 1 includes a resilient buffer 13 located between the movable portion 5 and the support structure 3. The resilient buffer 13 is arranged to disengage when the magnitude of the displacement from the equilibrium position is below the predetermined threshold and to engage when the magnitude of the displacement from the equilibrium position increases above the predetermined threshold to provide a restoring force with increased stiffness. The resilient buffer 13 can be formed in any suitable manner. Some non-limiting examples include forming the resilient buffer as a member biased by an elastic element (e.g., a spring), or forming the resilient buffer by means of an elastic material (e.g., rubber).

[0080] With linear restoring force, the natural frequency of the resonator is independent of the amplitude of the displacement from the equilibrium position. At the natural frequency, the response is purely sinusoidal, and the maximum amplitude of the displacement increases with the increase of the input driving force, but the frequency remains constant. Another advantage of providing nonlinear restoring force is that the period of the natural frequency becomes dependent on the amplitude of the oscillation. It may be desirable to change the natural frequency of the system, for example, to compensate for manufacturing variations between actuator components, or to ensure that the resonant frequency matches the desired frequency as closely as possible. Using nonlinear restoring force, the natural frequency of the resonant actuator component 1 can be dynamically adjusted by changing the amplitude of the input driving force. This can be advantageous in scanning systems such as time-of-flight (TOF) systems, where the scan rate can be synchronized with the frame rate of the sensing unit.

[0081] Figures 7 to 11 Five examples of resonant actuator assembly 1 are illustrated. In each example, the same reference numerals are used to describe the corresponding components. Some commonalities apply to multiple components in the illustrated embodiments.

[0082] The actuator device 7 includes at least one SMA line 8, and the at least one SMA line 8 is inclined at an acute angle relative to the axis of movement M of the movable part 5. Inclining the SMA line 8 in this way provides a gear effect, such that the displacement caused by the actuation of the SMA line 8 can be greater than the absolute change in the length of the SMA line 8.

[0083] exist Figures 7 to 11 In all embodiments, except Figure 10 In addition to the embodiments described herein, the actuator device 7 includes opposing SMA lines 8 arranged to drive relative movement of the movable portion 5 in opposite directions along the movement axis M. This means that the movement of the movable portion can be driven in two directions along the movement axis M.

[0084] In all embodiments, the elastic buffer 13 is disposed between the movable portion 5 and the support structure 3. The elastic buffer 13 is arranged to disengage when the magnitude of the displacement from the equilibrium position is below a predetermined threshold, and to engage when the magnitude of the displacement from the equilibrium position increases from the predetermined threshold to provide a restoring force with increased stiffness. As described above, this provides a restoring force with a step change in stiffness.

[0085] Figure 7 A mechanical implementation of a resonant actuator assembly 1 is shown, which utilizes a support structure 3 and a support device 9, the support device 9 including a low-stiffness support flexure 17 to guide movement along the movement axis M. In use, the low-stiffness support flexure 17 can preferably operate under tension. The actuator device 7 includes two opposing SMA lines 8 (which are typically relaxed in the absence of an actuation signal), arranged to drive the movable portion 5 to relative movement in opposite directions along the movement axis M. The SMA lines 8 provide the desired driving force (or thrust) in opposite directions. The SMA lines 8 are angled to the flexure 17 and the movement axis M such that the contraction of the SMA lines 8 has a high mechanical gain (i.e., the gearing effect mentioned above). This arrangement can provide a stroke exceeding 200 μm, with a footprint of 9.5 mm. Cooling plates 21 are disposed near each SMA line 8 to improve the cooling rate of the SMA lines 8. The combination of the stiffness of the SMA line 8, the mechanical gain of the system, and the stiffness of the flexure 17 contributes to the overall stiffness of the system in the central linear region around the equilibrium position of the actuator 1.

[0086] The preferred location of the movable part 5 is known, and will be discussed further below. One option for positioning the movable part 5 is to use resistive feedback via the SMA line 8. Figure 7 The implementation in the example uses a position sensor 23, which includes a Hall sensor 27 and a magnet 25, to measure position instead.

[0087] In the movable part 5 Figure 7 At the extreme points of motion, there is an elastic buffer 13 formed by a "high-stiffness" spring. The elastic buffer 13 causes a step change in the stiffness of the restoring force. Alternatively, the elastic buffer 13 can be a rubber buffer, a damping gel, or another soft elastic material. The function of these elastic buffers 13 is to significantly increase the system stiffness when the amplitude of the motion of the movable part 5 (i.e., its displacement from the equilibrium position) exceeds a predetermined threshold (e.g., a target amplitude). As shown above, this causes the movable part 5 to change direction faster than when using a purely linear restoring force.

[0088] Figure 8Another embodiment of a resonant actuator assembly 1 comprising multiple gain stages is shown. In this embodiment, the resonant actuator assembly 1 further includes at least one intermediate portion 15. The actuator device 1 includes multiple stages of at least one SMA line 8, each stage being arranged to drive relative movement between two portions of a support structure, and at least one intermediate portion 15 and a movable portion 5 are mechanically connected in series to additionally drive relative movement of the movable portion 5 relative to the support structure 3. Each of the multiple stages of at least one SMA line 8 includes a stage connected between the movable portion 5 and the intermediate portion 15 and a stage connected between the intermediate portion 15 and the support structure 3. However, additional stages may be provided.

[0089] A support device 9 is provided, comprising two sets of flexural members 17. A first set of flexural members 17 is disposed between the intermediate portion 15 and the movable portion 5, and a second set of flexural members 17 is disposed between the intermediate portion 15 and the support structure 3. The flexural members 17 help provide restoring force. This embodiment has the advantage of increasing the length of the SMA wire, which reduces stiffness and increases the wire stroke. This, in turn, means a lower mechanical gain is required.

[0090] Figure 9 One embodiment is shown in which the support device 9 does not include a flexural element and does not provide a restoring force; instead, the restoring force is provided by an actuator device 7, which includes opposing pairs of SMA lines 8. The opposing pairs of SMA lines 8 are arranged to drive relative movement of the movable portion 5 in opposite directions along a movement axis M. Each pair of SMA lines 8 is inclined at equal and opposite acute angles relative to the movement axis M of the relative movement of the movable portion 5 to provide balanced force components perpendicular to the movement axis M. The acute angle is preferably less than 10°, and more preferably less than 5°.

[0091] The intersecting SMA lines 8 are used to achieve resonance that depends only on the stiffness of the SMA lines 8 and not on the stiffness of the guide flexure 17. The four SMA lines 8 are arranged in two pairs of intersecting lines to control the movement of the movable part. This improves the linearity of the relative movement between the movable part 5 and the support structure 3. It also increases the force acting in the direction of movement, which is advantageous when high mechanical gain is required to initiate movement. An elastic damper 13 is positioned at the end of the desired range of movement to provide non-linear stiffness.

[0092] The support device 9 includes ball bearings. Due to the balanced force component perpendicular to the moving axis M from the SMA line 8, the support device 9 serves only to guide the movable part 5 along the moving axis M and prevent the movable part 5 from rotating relative to the support structure 3. Providing the support device 9 is advantageous, but remains optional.

[0093] Figure 10An embodiment is shown in which the support device 9 includes both a flexure 17 and a ball bearing. In this embodiment, the flexure is optional. The actuator device 7 includes two opposing SMA lines 8 arranged to drive relative movement of the movable portion 5 in opposite directions along the movement axis M. The opposing SMA lines 8 are inclined at an acute angle to provide a force component perpendicular to the movement axis M in the same direction. In this embodiment, the force component in the same direction loads the support assembly. In other words, the SMA lines 8 load the support device by pulling the movable portion 5 down onto the ball bearing, thereby providing low-friction guidance for the movement of the movable portion.

[0094] Figure 11 Another embodiment in which the support device 9 includes a flexure 17 is shown. The actuator device 7 includes a single SMA line 8 arranged to drive relative movement of the movable portion along a movement axis in a first direction, and no SMA line 8 is arranged to drive relative movement of the movable portion in a second direction opposite to the first direction. Figure 11 In this case, only a single SMA wire 8 is provided; however, more SMA wires 8 can be provided, for example, to increase the force acting in the direction of motion, as described above. The elastic element 11 (in this case, a spring) provides a restoring force in the direction opposite to the direction in which the SMA wire 8 drives the movable part 5.

[0095] Figure 12 and Figure 13 Two alternative circuits that can be used in any embodiment of the resonant actuator assembly 1 described above are shown; however, for simplicity, the movable part 5 and the support structure 3 are not shown. Figure 12 and Figure 13 As shown in the diagram. In each case, the resonant actuator assembly 1 also includes a drive circuit 31 arranged to provide a drive signal to the actuator device 7, which in this embodiment includes at least one SMA line 8. For simplicity, in Figure 12 and Figure 13 The diagram shows a single SMA line 8, but as mentioned above, there can also be multiple SMA lines 8.

[0096] Figure 12 and Figure 13The embodiment also illustrates a resonant actuator assembly 1, which further includes a position detection circuit 33 arranged to obtain a measurement of the relative position of the movable portion 5 with respect to the support structure 3. As mentioned above, it is generally desirable to be able to determine the position of the movable portion 5 relative to the support structure 3. For example, this position can be used to control the drive circuit 31, or, in an embodiment where the SMA lines 8 are arranged to drive relative movement of the movable portion 5 along the movement axis M in opposite directions, to control the opposing SMA lines 8.

[0097] Figure 12 One embodiment is shown in which the resonant actuator assembly 1 further includes a position sensor 23, which is arranged to sense the relative position of the movable part 5. The position sensor 23 is connected to a position detection circuit 33. The position detection circuit 33 is arranged to obtain a measurement of the relative position of the movable part 5 based on the output of the position sensor 23. The position sensor 23 may be a magnetic sensor, such as a Hall sensor 27. Figure 7 As shown, when the position sensor is a Hall sensor 27, the magnet 25 can be disposed on the movable part 5. Alternatively, the Hall sensor 27 can be placed on the movable part 5 and connected to the position detection circuit 33 via a flexible connector.

[0098] When the actuator device 7 includes at least one SMA line 8, the position measurement can be determined without using a dedicated position sensor 23. Figure 13 One embodiment is shown in which the resonant actuator assembly 1 further includes a resistance measurement circuit 35, which is arranged to measure the resistance of at least one SMA line 8 of the actuator device 7. In this embodiment, a position detection circuit 33 is arranged to obtain a measurement of the relative position of the movable portion 5 based on the output of the resistance measurement circuit 35. Since the resistance of the SMA line 8 is related to its temperature and phase, the position can be determined by determining whether the SMA line 8 is actuated based on its resistance.

[0099] The drive circuit 31 can use any suitable drive scheme to generate drive signals to actuate the actuator device 7.

[0100] Figure 14 An example is shown in which the driving signal includes a pulse at the resonant frequency. Figure 14 The pulse frequency in the middle is determined by Provided. Figure 14 The two drive signals (upper and lower) represent drive signals for actuating two opposing SMA lines 8, which are arranged in an embodiment (such as...) Figure 10In the embodiment, the movable part 5 is driven to move relative to each other in opposite directions along the moving axis M. The drive signals used to actuate the opposing SMA lines 8 (or groups of opposing SMA lines 8) are out of phase. This ensures that each SMA line 8 (or group of SMA lines 8) drives the movement of the movable part 5 only at the appropriate portion of its oscillation, to drive resonant motion (rather than suppress resonant motion). Figure 14 In the example, the pulse has a 50% duty cycle, and the two drive signals are 180° out of phase with each other. However, depending on the design of the resonant actuator assembly 1, other duty cycles can be appropriately used. The drive signals also do not necessarily have to be precisely 180° out of phase with each other. Pulse shapes other than square pulses can also be used.

[0101] Other driver solutions can be applied. For example, in Figure 13 In this case, the drive circuit 31 can generate a drive signal using resistance-based feedback control based on the output of the resistance measurement circuit 35.

[0102] Typically, the movable part 5 can be of any type and used in any application. In one type of application, the movable part 5 can be an optical component, such as a light source, lens element, or mirror. Alternatively, the optical component can be mounted on or connected to the movable part 5. When the movable part 5 is an optical component, the resonant actuator assembly 1 can be arranged to scan the beam.

[0103] Figure 15 An example is illustrated in which a resonant actuator assembly 1 is incorporated into a time-of-flight sensor system 100, which scans a beam 51 for use in a 3D scanning application. A movable portion 5 is configured to scan the beam 51 from a light source 47.

[0104] System 100 includes a light source 47. In Figure 15 In this system, light source 47 is a vertical-cavity surface-emitting laser (VCSEL); however, any type of light source can typically be used, such as a light-emitting diode (LED), laser diode, incandescent bulb, or the like. Light source 47 emits an illumination line 51 to illuminate object 101 in the field of view 49 of the time-of-flight (ToF) image sensor 43. Receiving optics 45 collect the light reflected from object 101 from light source 47 and provide it to image sensor 43. The time of flight will be measured accordingly. System 100 also includes a transmission optics system 102. Transmission optics system 102 includes light source 47, transmission optics including a lens element 46 for guiding the light emitted from light source 47, and a resonant actuator assembly 1 of the type described above.

[0105] The resonant actuator assembly 1 (which may take the form of any of the examples described above) is configured to move the illumination 51 provided by the light source 47 (VCSEL) by moving the movable portion 5 relative to the support structure 3. More specifically, the movable portion 5 moves in a direction orthogonal to the optical axis of the illumination. In this example, the movable portion 5 includes a lens element 46.

[0106] System 100 also includes a ToF image sensor 43 having a sensor surface and being configured to sense light scattered by object 101 from light source 47 and provide depth data dependent on the sensed light.

[0107] It is worth noting that system 100 also includes a position detection circuit 33. In this example, the resonant actuator assembly 1 includes the position detection circuit 33. However, in some cases, the position detection circuit 33 may be provided as a separate component to the resonant actuator assembly 1. In this example, the position detection circuit 33 determines the position data of the movable portion 5 by measuring the resistance of at least one SMA line 8 in the actuator device 7 of the resonant actuator assembly 1. A sensing resistor is connected in series with the SMA line 8, and a resistance measurement circuit 35 is provided to perform a measurement indicating the potential difference across at least one SMA line 8 (as described above). In other embodiments, alternatively, a position sensor 23, such as a Hall sensor, may be provided. System 100 also includes a processor 41 connected to the light source 47, the ToF image sensor 43, and the position detection circuit 33.

[0108] Processor 41 includes a controller. During use, light source 47 provides illumination 51 in the form of stripes and discrete flashes. The controller then provides a movement command to resonant actuator assembly 1 to move movable portion 5. This triggers drive circuitry 31 of resonant actuator assembly 1 to provide a drive signal to actuator device 7. Movement of movable portion 5 causes illumination 51 to move over at least a portion of object 101. When SMA lines 8 are heated, movable portion 5 is moved by resonant actuator assembly 1 through the contraction of at least one SMA line 8 in actuator device 7. As movable portion 5 moves illumination 51 over object 101, light source 47 continues to provide flashes of stripes of illumination 51.

[0109] It is worth noting that in this example, the position detection circuit 33 is synchronized with the light source 47. Specifically, the position detection circuit 33 includes an analog-to-digital converter (ADC), and the ADC is synchronized with the light source 47. The position detection circuit 33 provides position data of the movable part 5 (in the form of a measurement of the relative position of the movable part 5 with respect to the support structure 3) by measuring the resistance of at least one SMA line 8. Due to this synchronization, the resistance measurement is synchronized to be performed when the light source 47 emits illumination 51. Specifically, the position detection circuit 33 is synchronized to perform the resistance measurement at the start of the flash of illumination 51. However, it should be understood that the resistance measurement can be performed at any time during the flash of illumination 51, or at the end of the flash of illumination 51, as long as consistent synchronization exists. The light scattered by the object 101 is received by the ToF image sensor 43, which provides depth data dependent on the received light to the processor 41. The position detection circuit 33 provides position data to the processor 41. As illumination 51 is scanned across the object 101, multiple data points for both position and depth data are obtained, all of which are provided to the processor 41. The transmission of this data typically introduces latency from various sources. However, the impact of this latency is mitigated due to the synchronization of the position detection circuit 33 with the light source 47, as the processor 41 knows which position data points correspond to which depth data values. Therefore, the position data and depth data are correlated by the processor 41, and an accurate depth map 110 is generated as the output of the processor 41 by avoiding the impact of latency.

[0110] In some embodiments, Figure 15 The time-of-flight (TOF) system 100 may be equipped with a resonant actuator assembly 1, wherein the restoring force is substantially linearly or non-linearly related to the displacement of the movable part 5. In such an embodiment, the ToF image sensor 43 may only provide data when the movable part 5 has moved to a predetermined position, in which a relatively flat region of the histogram of position over time is anticipated. This means that during sensing, the movable part 5 may spend a more equal portion of its time in each region.

[0111] Figure 16 and Figure 17 They are Figure 15 The response curve in the resonant actuator assembly 1 and the histogram of position versus time within the resonant period of the resonant actuator assembly 1 are shown. The resonant actuator assembly 1 is arranged to have a restoring force that is substantially linearly related to the displacement of the movable part 5. Therefore, as Figure 16 As shown, the response of the resonant actuator assembly 1 can be characterized as a sinusoidal waveform.

[0112] In the first example, as indicated by dashed line 110, there is a resonant period of 10 ms. In this example, the ToF image sensor 43 is configured to continuously sense scattered light from object 101 throughout the entire range of motion, resulting in the movable part spending disproportionately much more time at the extremes of motion, such as... Figure 17 As shown.

[0113] In the second example, such as Figure 16 The solid line 210 in the figure represents a resonant period of 14 ms. In this example, a 2 ms dwell period is introduced, during which the ToF image sensor 43 is configured to stop sensing scattered light when it moves toward an extreme of motion, for example, when the movable part has moved to a position within 25 μm of the end of its range of motion. Advantageously, as Figure 17 As shown, the introduction of a dwell period results in a more equal probability of migration to each occupied location. Furthermore, during the dwell period, the ToF image sensor 43 can be given the opportunity to perform other non-sensing tasks, such as based on previously sensed light output data.

[0114] Introducing a dwell period can lengthen the resonant period. Therefore, alternatively, the resonant period can remain constant as the sensing time within the resonant period decreases. As an example, a 1ms dwell period with a shortened sensing time of 4ms can be applied to a 10ms resonant period.

Claims

1. A resonant actuator assembly, comprising: Support structure; The movable part is capable of relative movement with respect to the supporting structure; An actuator device comprising at least one SMA line, the actuator device being arranged to drive relative motion of the movable portion; A support device is arranged to guide the relative movement of the movable portion with respect to the support structure, and the support device is arranged to provide a restoring force that is at least an order of magnitude smaller than the restoring force provided by the actuator device. as well as An elastic buffer is located between the movable part and the support structure. The resonant actuator assembly is arranged to provide a nonlinear restoring force to the movable portion when it is displaced relative to the support structure from an equilibrium position, and the actuator device is arranged to drive the relative motion of the movable portion under the resonance of the resonant actuator assembly. The elastic buffer is arranged to disengage when the magnitude of the displacement from the equilibrium position is less than a predetermined threshold and to engage when the magnitude of the displacement from the equilibrium position increases from the predetermined threshold to provide the restoring force with increased stiffness.

2. The resonant actuator assembly according to claim 1, wherein, The resonant actuator assembly is arranged to provide the restoring force with stiffness that increases as the magnitude of the displacement from the equilibrium position increases, thereby flattening the histogram of position versus time within the resonant period compared to an equivalent system with a constant restoring force.

3. The resonant actuator assembly of claim 1 further includes a drive circuit arranged to provide a drive signal to the at least one SMA line.

4. The resonant actuator assembly according to claim 3, wherein, The driving signal includes a pulse at the resonant frequency of the resonance.

5. The resonant actuator assembly according to claim 1, wherein, The at least one SMA line is inclined at an acute angle relative to the axis of movement of the movable part.

6. The resonant actuator assembly according to claim 1, wherein: The resonant actuator assembly further includes at least one intermediate portion, which is movable relative to the support structure and the movable portion. The actuator device includes multiple stages of at least one SMA line, each stage being arranged to drive relative movement between two parts of the support structure, wherein the at least one intermediate part and the movable part are mechanically connected in series to additionally drive relative movement of the movable part relative to the support structure.

7. The resonant actuator assembly according to claim 1, wherein, The actuator device includes opposing SMA lines arranged to drive the movable portion to move relative to each other in opposite directions along the movement axis.

8. The resonant actuator assembly according to claim 1, wherein, The actuator device includes opposing pairs of SMA lines, each pair of SMA lines being inclined at equal and opposite acute angles relative to the axis of movement of the movable portion, so as to provide a balanced force component perpendicular to the axis of movement.

9. The resonant actuator assembly according to claim 7, wherein, The opposing SMA lines are inclined at an acute angle to provide a force component perpendicular to the axis of movement in the same direction.

10. The resonant actuator assembly according to claim 1, wherein, The at least one SMA line is arranged to drive the movable part to move relative to the other part in a first direction along the axis of movement, and no SMA line is arranged to drive the movable part to move relative to the other part in a second direction opposite to the first direction.

11. The resonant actuator assembly according to any one of claims 1 to 10, wherein, The resonant actuator assembly also includes an elastic element connected between the movable portion and the support structure, and arranged to provide at least a portion of the restoring force.

12. The resonant actuator assembly according to claim 1, wherein, The support device is arranged not to provide restoring force.

13. The resonant actuator assembly according to claim 1, wherein, The support device includes a ball bearing device.

14. The resonant actuator assembly according to claim 1, wherein, The support device includes a flexural device.

15. The resonant actuator assembly according to any one of claims 1 to 10 and 12 to 14, further comprising a position detection circuit arranged to obtain a measurement of the relative position of the movable portion with respect to the support structure.

16. The resonant actuator assembly of claim 15, wherein, The resonant actuator assembly further includes a position sensor arranged to sense the relative position of the movable part, and the position detection circuit arranged to obtain a measurement of the relative position of the movable part from the output of the position sensor.

17. The resonant actuator assembly of claim 15, wherein, The resonant actuator assembly further includes a resistance measurement circuit arranged to measure the resistance of the at least one SMA line, and the position detection circuit arranged to obtain a measurement of the relative position of the movable part from the output of the measured resistance.

18. The resonant actuator assembly according to any one of claims 1 to 10, 12 to 14, and 16 to 17, wherein, The movable part is an optical component.

19. The resonant actuator assembly of claim 18, wherein, The resonant actuator assembly is arranged to scan the beam.

20. The resonant actuator assembly according to any one of claims 1 to 10, 12 to 14, 16 to 17 and 19, wherein, The resonant frequency is at least 10 Hz.

21. The resonant actuator assembly according to any one of claims 1 to 10, 12 to 14, 16 to 17 and 19, wherein, The displacement range is at least 10 μm.

22. A resonant actuator assembly, comprising: Support structure; The movable part is capable of relative movement with respect to the supporting structure; An actuator device comprising at least one SMA line arranged to drive relative motion of the movable portion; A support device is arranged to guide the relative movement of the movable portion with respect to the support structure, and the support device is arranged to provide a restoring force that is at least an order of magnitude smaller than the restoring force provided by the actuator device. as well as An elastic buffer is located between the movable part and the support structure. The resonant actuator assembly is arranged to provide a nonlinear restoring force to the movable portion when it is displaced relative to the support structure from its equilibrium position, and the actuator device is arranged to drive the relative motion of the movable portion under the resonance of the resonant actuator assembly. The elastic buffer is arranged to disengage when the magnitude of the displacement from the equilibrium position is below a predetermined threshold and to engage when the magnitude of the displacement from the equilibrium position increases from the predetermined threshold to provide the restoring force with increased stiffness.

23. A system comprising: A sensor for sensing light, the sensor being configured to provide data dependent on the light sensed; as well as Resonant actuator assembly, the resonant actuator assembly comprising: Support structure; The movable part is capable of relative movement with respect to the supporting structure; An actuator device comprising at least one SMA line, the actuator device being arranged to drive relative motion of the movable portion within a range of motion; A support device arranged to guide the relative movement of the movable portion relative to the support structure, and the support device arranged to provide a restoring force at least an order of magnitude smaller than the restoring force provided by the actuator device; and An elastic buffer is located between the movable part and the support structure. The resonant actuator assembly is arranged to provide a nonlinear restoring force to the movable portion when it is displaced relative to the support structure from its equilibrium position, and the actuator device is arranged to drive the relative motion of the movable portion under the resonance of the resonant actuator assembly. The elastic buffer is arranged to disengage when the magnitude of the displacement from the equilibrium position is below a predetermined threshold and to engage when the magnitude of the displacement from the equilibrium position increases from the predetermined threshold to provide the restoring force with increased stiffness; and The sensor is configured to stop providing data when the movable part has moved to less than 10% of the movement range at each end of the movement range.

24. The system according to claim 23, wherein, The sensor is configured to stop providing data when the movable part has moved to within 8% of each end of the movement range.

25. The system according to claim 23, wherein, The sensor is configured to stop providing data when the movable part has moved to within 5% of each end of the movement range.

26. The system according to any one of claims 23 to 25, wherein, The system is a time-of-flight (TOF) system, which includes an illumination source for illuminating an object, wherein the sensor is configured to sense light scattered by the object, and wherein the movable portion has optical components for focusing or reflecting illumination onto the object.

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