Deflection device for LISSAJOUS scanning

Abstract

A deflection device for Lissajous scanning, the deflection device comprising a frame and a micromirror. The micromirror is movably arranged in a recess of the frame by a suspension mount comprising one or more springs. The micromirror is operable to oscillate back and forth about each of two or three axes at respective eigenfrequencies, for reflecting incident light at different angles to form a two-dimensional Lissajous pattern. The deflection device can comprise a drive device for exciting the micromirror in oscillatory motion about each of two or three axes at respective or near respective eigenfrequencies. Each of the one or more springs has a shape along a path segment of a circumference of the micromirror that collectively covers more than 360 degrees. The arrangement of the one or more springs provides the micromirror with a compact suspension and a large tilt angle.

Description

Technical Field

[0001] This invention relates to the field of optical communication, and more specifically, to a deflection device for a micro-electro-mechanical-system (MEMS) scanner with lissajous scanning capability. Background Technology

[0002] In the field of optics, Micro-Electrical-Mechanical-System (MEMS) technology has been an enabling tool for many cutting-edge optical communication devices. MEMS scanners, capable of two-dimensional optical scanning, play a crucial role in a variety of low-power and compact scanning applications, including projection, sensing, and imaging. Lissajous scanning is particularly useful for compact laser projectors because the micromirrors used for this type of scanning resonate and oscillate on two axes to achieve a larger amplitude than non-resonant operating scanners. For scanning-type laser projection systems, a larger amplitude equates to higher optical resolution. Therefore, laser projection based on the resonant operation of MEMS scanners is widely adopted because it can simultaneously achieve considerable amplification of micromirror oscillation amplitude and low power consumption. Unlike raster scanning MEMS scanners, lissajous MEMS scanners operate at high scanning frequencies on both axes, offering advantages such as simple manufacturing, high mechanical stability, and uniform scan quality.

[0003] MEMS scanners typically consist of micromirrors suspended by springs for movement along one or more axes. One of the key aspects to consider when using MEMS scanners for commercial purposes is compactness. To achieve compactness, 2D MEMS micromirrors without gimbal mounts have been proposed. Alternatively, 2D MEMS micromirrors have been proposed that suspend the micromirrors directly from the surrounding chip frame using springs. However, these architectures can still lead to underutilization of available chip space during suspension. Ideally, the deflection device used for the scanner should contain the smallest possible components while meeting all the requirements for achieving good scan resolution.

[0004] The inventors have recognized that, in providing a deflection device for Lissajous scanning, it is necessary to address the aforementioned technical deficiencies in the prior art. Summary of the Invention

[0005] One object of the present invention is to provide a deflection device for Lissajous scanning, the device having an optimized compact design to achieve high scanning resolution. The compact design of the deflection device achieves a large tilt angle through a long suspension, occupying less space and thus reducing chip size.

[0006] A first aspect provides a deflection device for Lissajous scanning. The deflection device includes a frame and a micromirror. The micromirror is movably arranged in a recess in the frame via a suspension mount comprising one or more springs. One end of each spring is connected to the micromirror, and the other end is connected to the frame. Each spring has a shape with a path segment along the circumference of the micromirror, such that the total path segments of all springs cover more than 360 degrees. The arrangement of one or more springs along the circumference of the micromirror reduces the space required for micromirror suspension, thereby reducing chip size.

[0007] One or more springs enable the micromirrors to oscillate back and forth around each of two or three axes at their respective intrinsic frequencies. The intrinsic frequencies associated with the two or three axes can be equal or substantially equal. The micromirrors reflect the light beam at different angles, forming a two-dimensional lissajous pattern to provide high-quality images with high scanning speeds.

[0008] In a first possible implementation of the deflection device, the deflection device includes a driving device for exciting the micromirror to oscillate around each of the two or three axes at its respective or similar intrinsic frequencies. The driving device is used to control the resonant operation of the micromirror on the two or three axes.

[0009] The driving device may include one or more piezoelectric actuators. Each spring may be connected to one of the piezoelectric actuators. The one or more piezoelectric actuators are used to move the one or more springs with a high actuation force when actuated with a low driving voltage.

[0010] The driving device can be used to excite oscillating motion by applying periodic drive signals to one or more piezoelectric actuators. The periodic drive signals can include drive signals for each of two or three axes of the micromirror's oscillating motion. The drive signals can include frequencies that are the same as or close to the intrinsic frequencies associated with the respective axes. The drive signals can transfer energy to achieve oscillating motion of the micromirror about each of the two or three axes. The equal or substantially equal frequencies of the drive signals provide high scan curve fill factors, which can support high scan display resolution.

[0011] In a second possible implementation of the deflection device, the suspension mount comprises two or more staggered nested helical springs. These staggered nested helical springs can be a subset of one or more springs. The staggered nested helical springs reduce the space required to suspend the micromirror.

[0012] The two or more staggered nested helical springs can be connected to the micromirror with equal angular spacing. This equal angular spacing provides an improved scan trajectory fill factor and eliminates the need for a gimbal structure in the gimbal-mounted micromirror.

[0013] In a second possible implementation of the deflection device, the suspension mount comprises three staggered nested helical springs attached to the micromirror, spaced 120 degrees apart. Each staggered nested helical spring covers a circular segment exceeding 120 degrees. Each of the three staggered nested helical springs has a longer length and a smaller cross-sectional area, providing a longer suspension for the micromirror. This longer suspension facilitates a larger tilt angle without reaching the breaking limit of the three staggered nested helical springs.

[0014] In a third possible implementation of the deflection device, the suspension mount comprises four staggered nested helical springs attached to the micromirror, spaced 90 degrees apart. Each staggered nested helical spring covers a circular segment exceeding 90 degrees. The increased number of staggered nested helical springs helps compensate for the lower overall stiffness of each individual spring, thereby enabling a high scan frequency.

[0015] In a fourth possible implementation of the deflection device, two or more staggered, nested helical springs are interlaced around the micromirror in an Archimedean spiral configuration. This Archimedean spiral configuration provides a compact suspension mount for the micromirror, thereby reducing chip size.

[0016] The spring stiffness of at least one interleaved helical spring can differ from the spring stiffness of the remaining interleaved helical springs. This difference in spring stiffness provides minimal difference between the micromirror resonant frequencies.

[0017] At least one of the width, length, thickness, and / or material properties of the at least one interleaved helical spring may differ from the width, length, thickness, and / or material properties of the remaining interleaved helical springs. Reducing the cross-sectional area of ​​the interleaved helical springs and increasing their length helps to achieve a larger tilt angle without reaching the spring's breaking limit. To compensate for the overall lower stiffness of each helical spring, the number of interleaved helical springs can be increased to achieve the desired overall spring stiffness.

[0018] In a fifth possible implementation of the deflection device, two or more staggered nested helical springs are arranged with rotational or mirror symmetry relative to the micromirror. Any number of N springs is achieved by rotating the next corresponding nested helical spring by an angle of 2πN, where N is the number of springs. The two or more staggered nested helical springs may include a first helical spring that is staggered with an adjacent second, third, fourth, or nth helical spring. The two or more staggered nested helical springs provide a tightly packed helical spring arrangement, allowing the suspension to effectively utilize available chip space for optimized compactness.

[0019] At least one of the interlocked helical springs can be a torsion spring. A torsion spring provides uniform tension, thus enabling repeatable vibrations. The torsion spring has a shape with a path segment along the circumference of the micromirror to minimize space requirements.

[0020] In a sixth possible implementation of the deflection device, the micromirrors are configured to have different moments of inertia on at least two axes, which can be used to adjust for any differences between the frequencies of the drive signals associated with the respective axes.

[0021] The geometry of a micromirror can differ relative to at least two axes. The geometry of the micromirror can be selected to achieve a tight package, thereby reducing chip size.

[0022] Micromirrors can be elliptical. The moment of inertia of a micromirror can be modified by using an elliptical mirror that includes one or more springs with the same construction.

[0023] In a seventh possible implementation of the deflection device, a drive device is used to limit the amplitude of the micromirror's oscillation motion. The amplitude of the oscillation motion can be kept within the resonant range of the micromirror.

[0024] The driving device may include a control loop for controlling the frequency of a periodic drive signal based on the measured phase position of the micromirror, such that the maximum amplitude of the oscillation motion is maintained within the resonant range of the micromirror. The frequency level can be determined by a predefined scan resolution and a predefined scan repetition rate, and the periodic drive signals can have the same or different scan repetition rates. The frequency of the periodic drive signal continuously varies with the resonant frequency of the micromirror. The frequency of the periodic drive signal permanently adapts to the instantaneous resonant frequency of the micromirror to generate a lissajous trajectory, thereby achieving good image overlap.

[0025] In an eighth possible implementation of the deflection device, the drive device further includes a drive electrode connected to each spring and / or micromirror. The drive electrode is used to move one or more springs with a high actuation force when actuated with a low drive voltage.

[0026] The drive device may include one or more piezoelectric actuators connected to (e.g., arranged on) one or more interleaved helical springs. The one or more piezoelectric actuators may be arranged on two or more interleaved helical springs to achieve a compact construction.

[0027] The micromirror can be vacuum-packaged. Vacuum-packaged micromirrors provide low damping to achieve higher resonant amplitudes. Vacuum-packaged micromirrors offer larger achievable scanning angles, reduce power consumption by several orders of magnitude, achieve higher usable scanning frequencies, and lower electrostatic or piezoelectric actuator drive voltages.

[0028] This invention solves a technical problem in the prior art, namely, the ineffective utilization of chip space for suspending micromirrors. This invention also solves another technical problem in the prior art, namely, the lack of long suspensions with greater rigidity.

[0029] Therefore, compared with the prior art, the deflection device for Lissajous scanning provided by the present invention has an optimized and compact design for achieving high scanning resolution. The compact design of the deflection device achieves a large tilt angle through a long suspension, occupying less space and thus reducing the chip size.

[0030] These and other aspects of the invention will be apparent from the implementations described below. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the present invention or prior art implementations, the accompanying drawings required for describing the prior art implementations are briefly described below. Obviously, the drawings in the following description only show some implementations of the present invention; those skilled in the art can still obtain other drawings based on these drawings without any creative effort.

[0032] Figure 1 This is a schematic diagram of a deflection device for Lissajous scanning according to an implementation of the present invention;

[0033] Figure 2 According to the implementation of the present invention, Figure 1 A schematic diagram of the micromirror of the deflection device, including four springs connected to the micromirror, each spring covering a circular segment of more than 90 degrees;

[0034] Figure 3 According to the implementation of the present invention, Figure 1 A schematic diagram of the micromirror of the deflection device, including three springs connected to the micromirror, each spring covering a circular segment of more than 120 degrees;

[0035] Figure 4 According to the implementation of the present invention, Figure 1 A schematic diagram of the micromirror of the deflection device includes four springs connected to the micromirror, each spring covering a circular segment of more than 120 degrees.

[0036] Specific implementation method

[0037] The present invention provides a deflection device for Lissajous scanning, the deflection device having an optimized compact design to achieve a large tilt angle through a long suspension, while still reducing space requirements and chip size to achieve high scanning resolution.

[0038] To facilitate understanding of the present invention by those skilled in the art, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described implementations are only a part, not all, of the present invention. All other implementations obtained by those skilled in the art based on the implementations of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0039] To aid in understanding how the invention is implemented, this document first defines several terms that will be introduced in the description of how the invention is implemented.

[0040] The terms “first,” “second,” “third,” and “fourth” (if any) used in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular sequence or order. It should be understood that such terms are interchangeable where appropriate, for example, to allow implementations of the invention described herein to be implemented in sequences other than those shown or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to the steps or units expressly listed, but may include other steps or units not expressly listed or inherent to such processes, methods, products, or apparatuses.

[0041] Figure 1This is a schematic diagram of a deflection device 100 for Lissajous scanning according to an implementation of the present invention; the deflection device 100 includes a frame 102 and a micromirror 104. The micromirror 104 is movably arranged in a recess in the frame 102 by a suspension mount including one or more springs 110. The frame 102 may be fixed and sealed by a first transparent surface 112 and a second transparent surface 114, respectively, thereby forming a vacuum-sealed sealed chamber 108. The vacuum-sealed sealed chamber 108 provides low damping to achieve a higher resonant amplitude of the micromirror 104. Each of the one or more springs 110 is connected at one end to the micromirror 104 and at the other end to the frame 102. Each of the one or more springs 110 has a path segment shape along the circumference of the micromirror 104, such that the path segments of the one or more springs 110 can collectively cover more than 360 degrees. The deflection device 100 can deflect the light beam from the incident axis.

[0042] The micromirror 104 can be used to oscillate back and forth around each of two or three axes at their respective intrinsic frequencies to reflect incident light at different angles. The intrinsic frequencies associated with the two or three axes are equal or substantially equal.

[0043] When the micromirrors 104 are illuminated by a light beam, they can oscillate back and forth around each of two or three axes at their respective intrinsic frequencies, reflecting the light beam at different angles in two dimensions to form a two-dimensional lissajous pattern. Compared to grating patterns, two-dimensional lissajous patterns provide high-quality images with lower power consumption and faster scanning speeds.

[0044] The deflection device 100 includes a drive device 106 for exciting the micromirror 104 to oscillate about each of two or three axes at its respective intrinsic frequency or a similar intrinsic frequency. The drive device 106 may include one or more piezoelectric actuators. Each of one or more springs 110 is connected to one of the one or more piezoelectric actuators. The drive device 106 can be used to exciting the oscillating motion by applying a periodic drive signal to the one or more piezoelectric actuators connected to the one or more springs 110. In an exemplary implementation, the one or more piezoelectric actuators act on one or more springs 110 to exciting the micromirror 104 to oscillate about each of two or three axes at its respective intrinsic frequency or a similar intrinsic frequency. The one or more piezoelectric actuators utilize low drive voltages, thereby reducing power consumption by several orders of magnitude.

[0045] The periodic drive signals include drive signals for each of two or three axes. The drive signals may include frequencies that are the same as or close to the intrinsic frequencies associated with the respective axes. Drive signals having the same or close to the intrinsic frequencies associated with the respective axes may differ at least in terms of a predefined scan resolution and a predefined scan repetition rate.

[0046] According to a first implementation of the deflection device 100, the drive device 106 further includes a drive electrode connected to each of one or more springs 110 and / or the micromirror 104. The drive electrode may be an electrostatic drive unit connected at one end to the frame 102 and at the other end to each of the one or more springs 110. The one or more springs 110 may be arranged in a tightly spiral configuration around the micromirror 104. This tight spiral arrangement of the one or more springs 110 around the micromirror 104 significantly reduces the chip space requirements for suspending the micromirror 104, thereby enabling a more cost-effective component by reducing chip size. The suspension mount may include two or more staggered nested helical springs. The two or more staggered nested helical springs may be a subset of the one or more springs 110. The two or more staggered nested helical springs can reduce the space required for suspension. The two or more staggered nested helical springs may be connected to the micromirror 104 at equal angular distances.

[0047] According to a second implementation of the deflection device 100, two or more staggered nested helical springs are arranged with rotational or mirror symmetry relative to the micromirror 104. Any number of N springs is achieved by rotating the next corresponding nested helical spring by an angle of 2πN, where N is the number of springs. The two or more staggered nested helical springs can be staggered around the micromirror 104 in the form of an Archimedean spiral to provide a compact suspension mount for the micromirror 104. The Archimedean spiral is a spiral form in which the radius moves linearly outward along the length of the spiral.

[0048] In an exemplary implementation of the deflection device 100, four helical springs with higher stiffness and wider cross-sectional areas are arranged by rotating the next spring 90 degrees relative to the preceding helical spring. These four springs define two orthogonally tilted eigenmodes of the micromirror 104. To further increase the stiffness and scanning speed of the mirror 104 at a constant tilt axis, a fixed number of N additional springs with smaller cross-sectional areas can be implemented between the first four springs. At least one of the interleaved helical springs may have the same width, length, thickness, and / or material properties. One or more piezoelectric actuators can be arranged on two or more interleaved helical springs with minimal inter-electrode distance for efficient engagement with each electrode.

[0049] Figure 2According to the implementation of the present invention, Figure 1 A schematic diagram of the micromirror 104 of the deflection device 100 includes four springs connected to the micromirror 104, each spring covering a circular segment exceeding 90 degrees. The micromirror 104 includes a suspension mount 206 comprising a first spring 208A, a second spring 208B, a third spring 208C, and a fourth spring 208D. The first spring 208A includes a first end 212A and a second end 212B. The first spring 208A is connected to the micromirror 104 via the first end 212A and to the frame 102 via the second end 212B. The second spring 208B includes a first end 214A and a second end 214B. The second spring 208B is connected to the micromirror 104 via the first end 214A and to the frame 102 via the second end 214B. The third spring 208C includes a first end 216A and a second end 216B. The third spring 208C is connected to the micromirror 104 via a first end 216A and to the frame 102 via a second end 216B. The fourth spring 208D includes a first end 218A and a second end 218B. The fourth spring 208D is connected to the micromirror 104 via a first end 218A and to the frame 102 via a second end 218B. The first spring 208A, the second spring 208B, the third spring 208C, and the fourth spring 208D can be connected to the micromirror 104 at an equal angular distance of 90 degrees, and each spring covers a circular segment exceeding 90 degrees.

[0050] The first spring 208A, the second spring 208B, the third spring 208C, and the fourth spring 208D can be staggered in a helical manner around the micromirror 104, thereby forming an interlocking helical spring structure around the micromirror 104. The first spring 208A, the second spring 208B, the third spring 208C, and the fourth spring 208D can be staggered in an Archimedean spiral pattern around the micromirror 104 to provide a compact suspension mount for the micromirror 104. The stiffness of at least one of the first spring 208A, the second spring 208B, the third spring 208C, or the fourth spring 208D can differ from the stiffness of the remaining springs. The difference in stiffness of the first spring 208A, the second spring 208B, the third spring 208C, and / or the fourth spring 208D provides minimal difference between the resonant frequencies of the micromirror 104.

[0051] The width, length, thickness, and / or material properties of at least one of the first spring 208A, the second spring 208B, the third spring 208C, or the fourth spring 208D may differ from the width, length, thickness, and / or material properties of the remaining springs. Optionally, increasing the length (l) of the first spring 208A, the second spring 208B, the third spring 208C, and / or the fourth spring 208D reduces the cross-sectional area of ​​the first spring 208A, the second spring 208B, the third spring 208C, and / or the fourth spring 208D. Reducing the cross-sectional area of ​​at least one of the first spring 208A, the second spring 208B, the third spring 208C, or the fourth spring 208D and increasing its length helps to achieve a larger tilt angle without reaching the breaking limit of the first spring 208A, the second spring 208B, the third spring 208C, or the fourth spring 208D.

[0052] To compensate for the relatively low overall stiffness of each of the first spring 208A, second spring 208B, third spring 208C, and fourth spring 208D, multiple springs can be added to achieve the desired overall spring stiffness. The first spring 208A, second spring 208B, third spring 208C, and fourth spring 208D can be arranged with rotational or mirror-symmetrical arrangement relative to the micromirror 104. Any number of N springs can be achieved by rotating the next corresponding nested helical spring by an angle of 2πN, where N is the number of springs. The first spring 208A, second spring 208B, third spring 208C, or fourth spring 208D can be a torsion spring.

[0053] When the micromirror 104 is illuminated by a light beam, it can be used to oscillate back and forth around each of the two or three axes at its respective intrinsic frequency, reflecting the incident light at different angles to form a two-dimensional lissajous pattern. Compared to grating patterns, two-dimensional lissajous patterns provide high-quality images with lower power consumption and faster scanning speeds. The intrinsic frequencies associated with the two or three axes can be equal or substantially equal. The driving device 106 can be used to excite the micromirror 104 to oscillate around each of the two or three axes at its respective intrinsic frequency or similar intrinsic frequencies by applying periodic driving signals to the first piezoelectric actuator 210A, second piezoelectric actuator 210B, third piezoelectric actuator 210C, and fourth piezoelectric actuator 210D, which are respectively connected to the first spring 208A, second spring 208B, third spring 208C, and fourth spring 208D. The periodic drive signal may include a drive signal with the same or close frequency as the intrinsic frequency associated with the corresponding axis for each of two or three axes.

[0054] The drive device 106 can be used to limit the amplitude of the oscillating motion of the micromirror 104. The amplitude of the oscillating motion can be maintained within the resonant range of the micromirror 104. The micromirror 104 is configured to have different moments of inertia on at least two axes to adjust for any differences between the frequencies of the drive signals associated with the respective axes. The geometry of the micromirror 104 can be different relative to at least two axes. The geometry of the micromirror 104 can be determined by the beam size and the type of application, such as projection or imaging. The micromirror 104 can be elliptical relative to at least two axes. The moment of inertia can be modified by an elliptical mirror comprising a compact suspension mount having a first spring 208A, a second spring 208B, a third spring 208C, and a fourth spring 208D, the mounts of which can have the same construction.

[0055] The first piezoelectric actuator 210A, the second piezoelectric actuator 210B, the third piezoelectric actuator 210C, and the fourth piezoelectric actuator 210D can be arranged on the first spring 208A, the second spring 208B, the third spring 208C, and the fourth spring 208D in an interleaved nested helical spring structure to obtain a compact construction.

[0056] Figure 3 According to the implementation of the present invention, Figure 1 A schematic diagram of the micromirror 104 of the deflection device 100 includes three springs connected to the micromirror 104, each spring covering a circular segment exceeding 120 degrees. The micromirror 104 includes a suspension mount 306 comprising a first spring 308A, a second spring 308B, and a third spring 308C. The first spring 308A includes a first end 312A and a second end 312B. The first spring 308A is connected to the micromirror 104 via the first end 312A and to the frame 102 via the second end 312B. The second spring 308B includes a first end 314A and a second end 314B. The second spring 308B is connected to the micromirror 104 via the first end 314A and to the frame 102 via the second end 314B. The third spring 308C includes a first end 316A and a second end 316B. The third spring 308C is connected to the micromirror 104 via the first end 316A and to the frame 102 via the second end 316B. The first spring 308A, the second spring 308B, and the third spring 308C can be connected to the micromirror 104 at an equal angular distance of 120 degrees, and each spring covers a circular segment of more than 120 degrees.

[0057] The first spring 308A, the second spring 308B, and the third spring 308C can be staggered in a helical manner around the micromirror 104, thereby forming an interlocking helical spring structure around the micromirror 104. The first spring 308A, the second spring 308B, and the third spring 308C can be staggered in an Archimedean spiral pattern around the micromirror 104 to provide a compact suspension mount for the micromirror 104. The stiffness of at least one of the first spring 308A, the second spring 308B, and / or the third spring 308C can differ from the stiffness of the remaining springs. The difference in stiffness among the first spring 308A, the second spring 308B, and / or the third spring 308C provides minimal difference in the resonant frequencies of the micromirror 104.

[0058] The width, length, thickness, and / or material properties of at least one of the first spring 308A, the second spring 308B, or the third spring 308C may differ from the width, length, thickness, and / or material properties of the remaining springs. Optionally, increasing the length (l) of the first spring 308A, the second spring 308B, and / or the third spring 308C, and decreasing the cross-sectional area of ​​the first spring 308A, the second spring 308B, and / or the third spring 308C, can help achieve a larger tilt angle without reaching the breaking limit of the first spring 308A, the second spring 308B, or the third spring 308C.

[0059] To compensate for the relatively low overall stiffness of each of the first spring 308A, the second spring 308B, and the third spring 308C, multiple springs can be added to achieve the desired overall spring stiffness. The first spring 308A, the second spring 308B, and the third spring 308C can be arranged with rotational or mirror-symmetrical arrangement relative to the micromirror 104. The first spring 308A, the second spring 308B, or the third spring 308C can be a torsion spring.

[0060] When the micromirror 104 is illuminated by a light beam, it can be used to oscillate back and forth around each of the two or three axes at its respective intrinsic frequency, reflecting the incident light at different angles to form a two-dimensional lissajous pattern. Compared to grating patterns, two-dimensional lissajous patterns provide high-quality images with lower power consumption and faster scanning speeds. The intrinsic frequencies associated with the two or three axes can be equal or substantially equal. The driving device 106 can be used to excite the micromirror 104 to oscillate around each of the two or three axes at its respective intrinsic frequency or a similar intrinsic frequency by applying periodic driving signals to the first piezoelectric actuator 310A, the second piezoelectric actuator 310B, and the third piezoelectric actuator 310C, which are respectively connected to the first spring 308A, the second spring 308B, and the third spring 308C. The periodic driving signals can include driving signals with the same or similar frequencies as the intrinsic frequencies associated with the corresponding axes for each of the two or three axes.

[0061] The drive device 106 can be used to limit the amplitude of the oscillating motion of the micromirror 104. The amplitude of the oscillating motion can be maintained within the resonant range of the micromirror 104. The micromirror 104 is configured such that its moment of inertia is different on at least two axes to adjust for any differences between the frequencies of the drive signals associated with the respective axes. The geometry of the micromirror 104 can be different relative to at least two axes. The micromirror 104 can be elliptical relative to at least two axes. The moment of inertia can be modified by an elliptical mirror comprising a suspension mount having a first spring 308A, a second spring 308B, and a third spring 308C, the mounts of which can have the same construction.

[0062] The first piezoelectric actuator 310A, the second piezoelectric actuator 310B, and the third piezoelectric actuator 310C can be arranged on the first spring 308A, the second spring 308B, and the third spring 308C in an interleaved nested helical spring structure to obtain a compact construction.

[0063] Figure 4 According to the implementation of the present invention, Figure 1A schematic diagram of the micromirror 104 of the deflection device 100 includes four springs connected to the micromirror 104, each spring covering a circular segment exceeding 90 degrees. The micromirror 104 includes a suspension mount 406 comprising a first spring 408A, a second spring 408B, a third spring 408C, and a fourth spring 408D. The first spring 408A includes a first end 412A and a second end 412B. The first spring 408A is connected to the micromirror 104 via the first end 412A and to the frame 102 via the second end 412B. The second spring 408B includes a first end 414A and a second end 414B. The second spring 408B is connected to the micromirror 104 via the first end 414A and to the frame 102 via the second end 414B. The third spring 408C includes a first end 416A and a second end 416B. The third spring 408C is connected to the micromirror 104 via a first end 416A and to the frame 102 via a second end 416B. The fourth spring 408D includes a first end 418A and a second end 418B. The fourth spring 408D is connected to the micromirror 104 via a first end 418A and to the frame 102 via a second end 418B. The first spring 408A, the second spring 408B, the third spring 408C, and the fourth spring 408D can be connected to the micromirror 104 at an equal angular distance of 90 degrees, and each spring covers a circular segment exceeding 90 degrees.

[0064] The first spring 408A, the second spring 408B, the third spring 408C, and the fourth spring 408D can be staggered in a spiral around the micromirror 104, thus forming an interlocking helical spring structure around the micromirror 104. The first spring 408A, the second spring 408B, the third spring 408C, and the fourth spring 408D can be staggered in an Archimedean spiral curve around the micromirror 104 to provide a compact suspension mount for the micromirror 104.

[0065] When the micromirror 104 is illuminated by a light beam, it can be used to oscillate back and forth around each of the two or three axes at their respective intrinsic frequencies, reflecting the incident light at different angles to form a two-dimensional lissajous pattern. Compared to grating patterns, two-dimensional lissajous patterns provide high-quality images with lower power consumption and faster scanning speeds. The intrinsic frequencies associated with the two or three axes are equal or substantially equal. The driving device 106 can be used to excite the micromirror 104 to oscillate around each of the two or three axes by applying periodic driving signals to the first piezoelectric actuators 410A, 410B, 410C, and 410D, respectively connected to the first spring 408A, second spring 408B, third spring 408C, and fourth spring 408D, at their respective intrinsic frequencies or close to their intrinsic frequencies. The periodic driving signals can include driving signals with a frequency equal to or close to the intrinsic frequency associated with the corresponding axis for each of the two or three axes. The micromirror 104 is configured to have different moments of inertia on at least two axes to accommodate any differences between the frequencies of the drive signals associated with the respective axes.

[0066] The first piezoelectric actuator 410A, the second piezoelectric actuator 410B, the third piezoelectric actuator 410C, and the fourth piezoelectric actuator 410D can be arranged on the first spring 408A, the second spring 408B, the third spring 408C, and the fourth spring 408D in an interleaved nested helical spring structure to obtain a compact construction.

[0067] Micromirror 104 can be a micro-electro-mechanical system (MEMS) micromirror. Micromirror 104 can have a diameter ranging from 0.5 mm to 10 mm. Micromirror 104 can include a flat reflective surface and can be coated with a thin film containing a reflective material such as gold, aluminum, or silver to obtain strong reflection of visible and infrared wavelengths. Micromirror 104 can reflect electromagnetic waves radiated from a light source while changing the angle of its reflective surface. The motion of micromirror 104 can optionally be a superposition of two or three independent oscillating motions (e.g., one per axis). This decomposition of independent oscillating motions may only be applicable to relatively small amplitudes (e.g., rotation of no more than a few degrees per axis). Micromirror 104 can be excited by electromagnetic forces in a moving coil device. Micromirror 104 can be excited by electromagnetic forces in a moving magnet device.

[0068] The first transparent surface 112 and the second transparent surface 114 of the encapsulated micromirror 104 can be made of a transparent material because the incident light can come from one or both sides of the surface of the micromirror 104.

[0069] In one example, when using a high-quality micromirror 104 with a quality factor greater than 3000, the resonance of the micromirror's amplitude response increases significantly, and the corresponding phase response decreases significantly. Therefore, even with a small resonant frequency shift, the amplitude of the high-quality micromirror 104 changes very significantly, making even a small temperature change sufficient to cause the micromirror 104 to de-resonate. In this case, a drive signal with a fixed frequency will no longer produce an acceleration effect, but rather a deceleration effect. Therefore, the drive device 106 may include a control loop for controlling the frequency of a periodic drive signal. The periodic drive signal depends on the measured phase position of the micromirror 104, such that the phase and maximum amplitude of the oscillating motion remain within the resonant range of the micromirror 104. The phase and amplitude of the oscillating motion can be kept constant by the control loop. Optionally, two independent phase control loops are provided. Therefore, the frequency of the periodic drive signal is not fixed but continuously varying. They respond to all changes occurring within the resonant frequency of the micromirror 104. The frequency (i.e., repetition rate) of the periodic drive signal is actively varied in the closed-loop control. Depending on the refresh rate of the scanning display, the frequency values ​​of the periodic signals are nearly equal, with a frequency difference ranging from approximately 30 Hz to 120 Hz. This frequency difference is a small value, ranging from a few kHz to 100 kHz, compared to the typical drive frequency. The permanent adaptation of the drive signal frequency to the instantaneous resonant frequency of the micromirror 104 generates a moving Lissajous trajectory, thereby describing all areas of the projection screen with image data to achieve good image overlay. For lower-quality micromirrors, such as those with a quality factor greater than 300, temperature-induced phase control can be performed.

[0070] In an exemplary implementation, a predefined scan resolution and a predefined scan repetition rate for the permissible range of amplitude modification can be determined based on the characteristics of the micromirror 104 and the resolution of the field of view. For example, the modification range is predefined as the inverse of the minimum resolution in the axis. For a definition using pixels, the amplitude change may be less than one pixel width. For example, in the case of a minimum resolution of 480x640 pixels, the amplitude change of the micromirror 104 may be less than 1 / 480 (0.00283) and 1 / 640 (0.00146). The amplitude change can be at least one of less than 1%, less than 0.5%, or less than 0.3%. A drive signal having a frequency equal to the intrinsic frequency associated with the corresponding axis can activate circular or elliptical scanning. To cover the entire projection area, amplitude modulation of the diameter of the circle or ellipse may be required, continuously varying the diameter.

[0071] In the exemplary implementation, each interleaved nested helical spring is described in polar coordinates as

[0072] r(θ) = a + b.θ

[0073] Where r is the radius, a is the initial radius, b is the measure of radius growth, and θ is the angle θ = 0.n.2. n = the number of turns of the interlocking helical springs.

[0074] In Cartesian coordinates, interleaved nested helical springs can be designed and described as follows:

[0075] x component =r·cos(θ)=(a+b·θ)·cos(θ)

[0076] y component =r·sin(θ)=(a+b·θ)·sin(θ)

[0077] The growth factor (b) can be expressed using the final radius a. final and initial radius a initial The difference is described by the ratio of the required number of turns n:

[0078] b = (a final -a initial ) / (2·π·n)

[0079] Two or more staggered nested helical springs include a first helical spring that is staggered with an adjacent second, third, fourth, or nth helical spring to provide a densely packaged helical spring arrangement, allowing the suspension to effectively utilize available chip space, thereby achieving optimized compactness.

[0080] Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A deflection device for Lissajous scanning, characterized in that including a frame and a micromirror, said micromirror is movably arranged in a recess of the frame by a suspension mount comprising one or more springs, one end of each of said springs is connected to the micromirror and the other end is connected to the frame, and each of said one or more springs has a shape of a path segment along a circumference of said micromirror such that the path segments of said one or more springs in total cover more than 360 degrees; said suspension mount comprises two or more interleaved nested coil springs, said two or more interleaved nested coil springs are a subset of said one or more springs; said deflection device comprises a drive device for exciting said micromirror to a wobble motion around each of two or three axes at a respective eigenfrequency or at a close eigenfrequency; said drive device comprises one or more piezoelectric actuators, each of said one or more springs is connected to one of said one or more piezoelectric actuators; said drive device is for exciting said wobble motion by applying a periodic drive signal to said one or more piezoelectric actuators, said periodic drive signal comprises a drive signal for each of said two or three axes having the same or a close frequency to the eigenfrequency associated with the respective axis; said drive device is for limiting an amplitude of said wobble motion; said drive device comprises a control loop for controlling a frequency of said periodic drive signal depending on a measured micromirror phase position, wherein a level of said frequency is determined by a predefined scan resolution and a predefined scan repetition rate, wherein said periodic drive signal has the same or different scan repetition rates.

2. Deflection device according to claim 1, characterized in that said one or more springs enable said micromirror to wobble back and forth around each of two or three axes at a respective eigenfrequency, and said eigenfrequencies associated with said two or three axes are equal or substantially equal.

3. Deflection device according to claim 1, characterized in that said two or more interleaved nested coil springs are connected to said micromirror at equal angular distances.

4. Deflection device according to claim 3, characterized in that said suspension mount comprises three interleaved nested coil springs, said coil springs are connected to said micromirror at an angular distance of 120 degrees, each spring covers a circular segment of more than 120 degrees.

5. Deflection device according to claim 3, characterized in that said suspension mount comprises four interleaved nested coil springs, said coil springs are connected to said micromirror at an angular distance of 90 degrees, each spring covers a circular segment of more than 90 degrees.

6. Deflection device according to any one of claims 3 to 5, characterized in that said two or more interleaved nested coil springs are interleaved in the form of an Archimedean spiral around said micromirror.

7. Deflection device according to any one of claims 3 to 5, characterized in that a spring stiffness of at least one of said two or more interleaved nested coil springs is different from a spring stiffness of the remaining interleaved nested coil springs.

8. Deflection device according to any one of claims 3 to 5, characterized in that at least one of a width, a length, a thickness and / or a material property of at least one of said two or more interleaved nested coil springs is different from a width, a length, a thickness and / or a material property of the remaining interleaved nested coil springs.

9. Deflection device according to any one of claims 3 to 5, characterized in that said two or more interleaved nested coil springs are arranged in rotational or mirror symmetry with respect to said micromirror.

10. Deflection device according to any of claims 3-5, characterized in that at least one of said two or more interleaved nested coil springs is a torsion spring.

11. Deflection device according to any one of claims 3-5, characterized in that The micromirror is configured such that its moment of inertia differs in at least two of the two or three axes for adjusting any differences between the frequencies of the drive signals associated with the respective axes.

12. Deflection device according to claim 11, characterized in that The geometry of the micromirror differs with respect to at least two of the two or three axes.

13. Deflection device according to claim 12, characterized in that The micromirror is elliptical.

14. The deflection apparatus of claim 1, wherein, The drive apparatus further comprises a drive electrode connected to each of the one or more springs and / or the micromirror.

15. Deflection device according to claim 14, characterized in that The drive apparatus comprises one or more piezoelectric actuators connected to the one or more interleaved nested coil springs.

16. The deflection apparatus of claim 1, wherein, The micromirror is vacuum encapsulated.

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