Microsoft AR/VR patent introduces resonant scanning mirror system that is small in size and operates at low power

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(XR Navigation Network 2023年12月04日）显示系统可以利用谐振扫描镜系统来扫描来自光源的光以形成用于显示的图像。在谐振扫描镜系统中，通过反射镜的谐振振荡运动，来自光源的光以较高的速率在第一方向（例如水平方向）扫描，并根据锯齿波状控制信号以较低的速率在第二方向（例如垂直方向）扫描。通过控制反射镜的角度，以及每一个或多个光源（例如红、绿、蓝光源）的光输出强度，就能产生可见图像。

对于XR头显，紧凑的外形和低功耗操作是设计的优先事项之一，所以扫描镜系统的尺寸和功耗值得关注。所以在名为“Piezoelectrically-actuated resonant scanning mirror”的专利申请中，MicrosoftA resonant scanning mirror system that is "appropriately small in size and can operate at appropriately low power" is introduced.

In one embodiment, the invention describes a scanning mirror system that includes a mirror portion, a curved arm extending from the mirror portion, and a piezoelectric actuator support portion. Piezoelectric actuators include piezoelectric actuators for driving resonant motion of mirror portions.

The scan mirror system also includes a transmission arm extending between the flexible arm and the piezoelectric actuator support portion, wherein the transmission arm is at least partially separated from the piezoelectric actuator support portion by a gap. The scan mirror system further includes an anchor portion at least partially separated from the piezoelectric actuator support portion by a second gap.

The first and second gaps allow the piezoelectric driver support portion to be configured to match the mode shape of the scan mirror during resonant oscillation. This helps reduce mechanical damping and increase electromechanical coupling, allowing relatively low driving voltages.

Additionally, the described mirror portions may include relatively small scan angles compared to other mirror systems. So the scanning mirror system can experience less air damping during resonant oscillatory motion, further allowing the use of lower drive voltages. Using lower drive voltages could allow the use of smaller batteries than current resonant scanning mirror systems. Microsoft says this helps reduce the size and weight of the headset.

At the same time, the invention includes a tapered drive arm that can help provide a more compact scanning mirror system while maintaining curved arm length and drive arm stiffness.

FIG. 2 illustrates an exemplary display device 200 including a scanning mirror system 202. Display device 200 includes one or more light sources 204 that output light to scanning mirror system 202 . The scanning mirror system 202 is configured to scan the light in a first scanning direction 206 at a higher resonant scanning frequency and to scan the light in a second scanning direction 208 at a lower scanning frequency.

Scanning mirror system 202 may include a single mirror driven in the horizontal and vertical directions, or two mirrors driven in the horizontal and vertical directions respectively. The resulting image may be provided to output 210 for display.

In FIG. 3 , scan mirror system 300 includes a body 302 including a mirror portion 304 supported by flexible arms 306 , 308 . The body 302 also includes transmission arms 310 and 312 connected to the flexible arm 306 and transmission arms 314 and 316 connected to the flexible arm 308 .

The body 302 also includes piezoelectric actuator support portions 320, 322, 324, 326, each supporting the piezoelectric membrane and electrodes of the piezoelectric actuators 330, 3332, 3334, 336. The piezoelectric actuators 330, 332, 334, 336 can be energized through conductors connected to the electrodes to cause conformation of the piezoelectric film, thereby causing mechanical movement of the resonant scan mirror system 300.

The piezoelectric films of piezoelectric actuators 330, 332, 334, and 336 include cutout profiles as shown at 338 on piezoelectric actuator 334. Each cut profile may be shaped based on modeling of the stresses experienced by body 302 during mirror oscillations. The cutout profile can help avoid placing the piezoelectric membrane in the area of the body 302, thereby helping to reduce mechanical damping of the mirror motion. In other examples, such cutout profiles may be omitted.

In the embodiment of Figure 3, body 302 includes anchor portions 340, 342 and frame portion 348 configured to anchor scan mirror system 300 to another structure, such as a circuit board. In other examples, frame portion 348 may be omitted.

Figure 4 depicts a bottom view of scan mirror system 300 and shows adhesive 402 bonding anchor portions 340 and 342 and frame portion 348 to the underlying structure. FIG. 5 shows a side view of scan mirror system 300 mounted to circuit board 502 with adhesive 402 . Anchor portions 340 and 342 and frame portion 348 include a thicker profile than the remainder of body 302 , as indicated by dashed line 504 representing the underside of the remainder of body 302 .

Body 302 may be made from any suitable material. In one embodiment, body 302 may be formed by etching a semiconductor wafer, such as a silicon/silicon oxide/silicon multilayer wafer. In the structure, the mirror portion 304, the piezoelectric actuator support portions 320, 322, 324, 326, the flexible arms 306, 308, the actuator arms 310, 312, 314, 316, and other components are formed in what is called the device layer. upper layer.

As shown in Figure 3, the piezoelectric actuator support portion is at least partially separated from the transmission arm and anchor portion by a gap. For example, actuator arm 310 is at least partially separated from piezoelectric actuator support portion 320 by gap 350 . Additionally, anchor portion 340 is at least partially separated from piezoelectric actuator support portion 320 by gap 351 .

Likewise, piezoelectric actuator support portion 322 is at least partially separated from drive arm 312 by gap 352 and at least partially separated from anchor portion 342 by gap 353 .

Continuing, piezoelectric actuator support portion 324 is at least partially separated from drive arm 314 by gap 354 and at least partially separated from anchor portion 342 by gap 355 .

At the same time, the piezoelectric actuator support portion 326 is at least partially separated from the transmission arm 316 by a gap 356 and is at least partially separated from the anchor portion 340 by a gap 357 . Gaps 350, 3551, 352, 3553, 3554, 3555, 3556, 357 are oriented inwardly from the outer circumference of scan mirror system 300.

In the embodiment shown in Figure 3, gaps 350, 3551, 352, 3553, 3554, 3555, 3556, 357 comprise linear slits with relatively uniform widths. In other embodiments, gaps including any other suitable shape may be used.

6-7 illustrate a scanning mirror system 600 including a gap of a tapered slit. Specifically, scan mirror system 600 includes a body 602 that includes a mirror portion 604 supported by flexible arms 606,608. The body 602 includes both actuator arms 610 and 612 connected to the flexible arm 606 and actuator arms 614 and 616 connected to the flexible arm 608 .

The body 602 further includes piezoelectric actuator support portions 620, 622, 624, 626, each supporting the piezoelectric membrane and electrodes of the piezoelectric actuators 630, 632, 634, 636. Piezoelectric actuator support portions 620, 622, 624, 626 are at least partially spaced 650, 6551, 6552, 6553, 6554, 6555 in body 602 from actuator arms 610, 612, 614, 616 and anchor portions 640, 642 , 656 and 657 separately.

As shown in Figure 6, gaps 650, 652, 654, and 656 each include a tapered slit. Gaps 650, 651, 652, 653, 654, 655, 656, and 657 are oriented inwardly from the outer periphery of scan mirror system 600.

Scanning mirror system 600 omits the frame of scanning mirror system 300 . In this manner, the body 602 is configured to be mounted to another structure via the adhesive of the anchor portions 640, 642. This allows for a greater range of motion of the piezoelectric actuator support portion during operation, thereby providing less damping and lower power operation.

FIG. 7 shows a side view of scan mirror system 600 mounted to circuit board 702 with adhesive 704 . Anchor portions 640 and 642 include a thicker profile than the remainder of body 602 .

Returning to Figure 3, as mentioned above, each piezoelectric actuator 330, 332, 334, and 336 includes a piezoelectric membrane disposed between a pair of electrodes. The piezoelectric films of piezoelectric actuators 330, 332, 334, and 336 respectively convert electrical energy into mechanical energy. When the appropriate voltage is applied to each piezoelectric film through the electrodes, the lattice changes experienced by the piezoelectric films cause the body 302 to deform, causing the mirror portion 304 to tilt.

The transmission arms 310, 312 transmit motion from respective piezoelectric actuator support portions 320, 322 to the flexible arm 306. Likewise, transmission arms 314, 316 transfer motion from respective piezoelectric actuator support portions 324, 326 to flexible arm 308. Resonant oscillation of the mirror portion 304 can be achieved by modulating the voltage applied to each piezoelectric film of the piezoelectric actuator 330, 3332, 3334, 336 with a suitable phase relationship and a suitable frequency.

At the resonant frequency, the body 302 can deform according to the vibration mode of the body. The perimeter of the piezoelectric membranes of piezoelectric actuators 330, 332, 334, 336 therefore follows the modal shape profile of body 302 during resonant oscillation. This helps prevent damping of body 302 motion and/or increases electromechanical coupling, thus allowing the mirror to be driven with lower power than other resonant mirror systems.

The modal shape of body 302 may be determined at least in part by the shape and/or stiffness of piezoelectric actuator support portions 320, 322, 324, 326, which are affected by gaps 350, 3551, 352, 3553, 3554, 3555, 3556 ,357 influence. The use of gaps 351, 353, 355, 357 between the piezoelectric actuator support portions and corresponding anchor portions 340, 342 can help mitigate the movement of the body 302 compared to a resonant mirror system that does not include such gaps. Damping and can improve electromechanical coupling during use. Less damping may allow lower drive voltages to be used to operate the scan mirror system 300, thereby helping to reduce power consumption.

Scan mirror systems may experience air damping when the scan mirror oscillates. Although air damping can be mitigated by sealing the scan mirror system, sealing may add cost. Therefore, scan mirror system 300 can achieve less air damping by using relatively smaller mirrors than other scan mirror systems.

During resonant oscillation, the mirror portion 304 rotates, causing torsional strains in the flexural arms 306, 308. Torsional strains may be larger at larger scan angles and/or shorter bending lengths. Therefore, scan mirror system 300 includes features that help achieve a suitable deflection length while maintaining stiffness.

Maintaining stiffness allows for better transfer of mechanical power from the actuator to the mirror compared to other mirror systems. As shown in Figure 3, the drive arms 310, 312, 314, 316 include tapered sections, which helps increase the bending arm length compared to examples without tapered sections.

For example, actuator arm 310 tapers in segment 360 in a direction from piezoelectric actuator support portion 320 to flexure arm 306 . With the tapered section 360, the length of the curved arm 306 is longer compared to the example of the untapered section 360. A longer flex length may help keep stresses in the flexure arm 306 low, thereby increasing device reliability.

In one embodiment, the scan mirror system may include a relatively small scan angle to relieve stress in the curved arms. For a given device size, reducing the mirror scanning angle can reduce the dynamic deformation of the mirror during oscillation and improve the reliability of the device. Additionally, the relatively small scan angle helps reduce power loss due to air damping. For a given stress limit and drive voltage, if the scan angle is reduced, the overall size of the scan mirror system can be reduced. Therefore, using a lower scanning angle helps achieve a more compact scanning mirror system.

By avoiding power losses due to damping, the scan mirror system 300 can provide a relatively high quality factor. Reducing damping and providing a higher quality factor can reduce drive voltage and reduce power consumption.

Named "Piezoelectrically-actuated resonant scanning mirror"Microsoft patentThe application was originally submitted in April 2022 and was recently published by the US Patent and Trademark Office.

Generally speaking, after a U.S. patent application is examined, it will be automatically published 18 months from the filing date or priority date, or it will be published within 18 months from the filing date at the request of the applicant. Note that publication of a patent application does not mean that the patent is approved. After a patent application is filed, the USPTO requires actual review, which can take anywhere from 1 to 3 years.