A piezoelectric actuator, a scanning display module and a projection device

Abstract

This application discloses a piezoelectric actuator, a scanning display module, and a projection device to improve the performance of scanning devices. The piezoelectric actuator includes a piezoelectric part and driving electrodes disposed on the piezoelectric part. The piezoelectric part is a polarized piezoelectric material. The piezoelectric part includes at least one mode shape node at a set frequency. On both sides of some or all of the mode shape nodes, an electrode is disposed on the surface of the piezoelectric part on one side, and no electrode is disposed on the surface of the piezoelectric part on the other side. In this scheme, the electric field distribution formed by the driving electrodes conforms to the vibration strain characteristics of the piezoelectric part at the set frequency, avoiding the voltage doing negative work during the vibration of the piezoelectric part, thereby improving the performance of the fiber optic scanning device, reducing control difficulty, and achieving better scanning display effects.

Description

Technical Field

[0001] This application relates to the field of scanning display technology, specifically to a piezoelectric actuator, a scanning display module, and a projection device. Background Technology

[0002] Laser scanning display, as an emerging display imaging technology, can achieve scanning display using scanning devices such as micro-electro-mechanical systems (MEMS) scanning mirrors and fiber scanners. This technology can be applied to various display scenarios such as projection displays and near-eye displays.

[0003] In the actual scanning and display process, the fiber optic scanning device will be in a two-dimensional vibration state with two frequencies superimposed, thus becoming a complex vibration system. In order to achieve better display results, it is necessary to further improve the performance of the fiber optic scanning device. Summary of the Invention

[0004] This application provides a piezoelectric actuator, a scanning display module, and a projection device to improve the performance of scanning devices.

[0005] To achieve the above-mentioned objectives, the first aspect of this application provides a piezoelectric actuator, which includes a piezoelectric part and a driving electrode disposed on the piezoelectric part. The piezoelectric part is a polarized piezoelectric material. The piezoelectric part includes at least one mode node at a set frequency. On both sides of some or all of the mode nodes, an electrode is disposed on the surface of the piezoelectric part on one side, and no electrode is disposed on the surface of the piezoelectric part on the other side.

[0006] Optionally, the piezoelectric part is a piezoelectric wafer structure; the driving electrode includes an upper electrode and a lower electrode, which are respectively arranged on the upper surface and the lower surface of the piezoelectric wafer structure; on both sides of some or all of the mode nodes, an upper electrode is provided on the upper surface of one side of the piezoelectric wafer structure, and no upper electrode is provided on the lower surface of the other side of the piezoelectric wafer structure.

[0007] Optionally, the area where the lower electrode is located corresponds to the area where the upper electrode is located.

[0008] Optionally, the lower electrode is continuously arranged on the lower surface of the piezoelectric wafer structure.

[0009] Optionally, the piezoelectric part is a piezoelectric tube; the driving electrode includes an inner electrode and an outer electrode; on both sides of some or all of the mode nodes, an outer electrode is provided on the outer surface of the piezoelectric tube on one side, and no outer electrode is provided on the outer surface of the piezoelectric part on the other side.

[0010] Optionally, the inner electrode is disposed on the inner surface of the piezoelectric tube, and the area where the inner electrode is disposed corresponds to the area where the outer electrode is located.

[0011] Optionally, the internal electrodes are continuously arranged on the inner surface of the piezoelectric tube.

[0012] Optionally, at least one side region of a mode node is used to house a feedback electrode; when the piezoelectric actuator is in operation, the feedback electrode is used to detect the electrical signal generated by the deformation of the piezoelectric part.

[0013] A second aspect of this application provides a scanning display module, including a piezoelectric actuator, an optical fiber, a light source, and a control circuit as described in the first aspect; image light output from the light source is coupled into one end of the optical fiber, and the other end of the optical fiber is fixed to the piezoelectric actuator; under the control of the control circuit, the image light output from the light source is driven by the piezoelectric actuator to perform scanning display on the optical fiber.

[0014] A third aspect of this application provides a projection device, which includes one or more sets of scanning display modules as described in the second aspect.

[0015] In the embodiment of this application, the piezoelectric actuator includes a piezoelectric part and a driving electrode disposed on the piezoelectric part. The piezoelectric part is a polarized piezoelectric material. The piezoelectric part includes at least one mode node at a set frequency. On both sides of some or all of the mode nodes, an electrode is disposed on the surface of the piezoelectric part on one side, and no electrode is disposed on the surface of the piezoelectric part on the other side. In this embodiment, since the piezoelectric parts on both sides of the mode node have opposite strain characteristics, a driving electrode is disposed on one side of the mode node and no driving electrode is disposed on the other side. When the piezoelectric part is in working state, the electric field distribution formed by the driving electrode conforms to the vibration strain characteristics of the piezoelectric part at the set frequency, avoiding the voltage doing negative work during the vibration of the piezoelectric part, thereby reducing power consumption, reducing nonlinearity, improving the performance of the fiber optic scanning device, reducing control difficulty, and achieving better scanning and display effects. Attached Figure Description

[0016] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0017] Figure 1 This is a schematic diagram of an exemplary fiber optic scanner provided in an embodiment of this application;

[0018] Figure 2a This is a schematic diagram of the axial cross-sectional structure of the upper surface of the actuator 111 provided in the embodiment of this application;

[0019] Figure 2bThis is a schematic diagram of the deformation of the actuator 11 in the Y-axis direction provided in the embodiments of this application;

[0020] Figure 3 This is a schematic diagram of the vibration mode curve of the fast shaft actuator provided in the embodiment of this application;

[0021] Figure 4 This is a schematic diagram of the vibration strain characteristics of a cantilever beam under bending vibration provided in an embodiment of this application;

[0022] Figure 5 This is a schematic diagram of the positive excitation region and the negative excitation region of the actuator provided in the embodiments of this application;

[0023] Figure 6a This is a schematic diagram of the structure of the sheet-like scanning actuator provided in the embodiments of this application;

[0024] Figure 6b This is a cross-sectional schematic diagram of a possible electrode arrangement for the sheet-like scanning actuator provided in the embodiments of this application;

[0025] Figure 6c This is a cross-sectional schematic diagram showing the uniform arrangement of the lower electrodes according to an embodiment of this application;

[0026] Figure 7a This is a schematic diagram of the dual-chip structure provided in the embodiments of this application;

[0027] Figure 7b yes Figure 7a An oblique view of the first piezoelectric part 61 shown;

[0028] Figure 7c This is a cross-sectional schematic diagram showing the uniform arrangement of the lower electrodes according to an embodiment of this application;

[0029] Figure 7d yes Figure 7c An oblique view of the first piezoelectric part 61 shown;

[0030] Figure 8 This is a cross-sectional schematic diagram of another possible electrode arrangement for the sheet scanning actuator provided in the embodiments of this application. Detailed Implementation

[0031] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0032] refer to Figure 1This illustration shows an exemplary fiber optic scanner 10 according to an embodiment of this application, including an actuator 11 and an optical fiber 12. Typically, the actuator 11, also referred to as a scanning actuator, can be based on a piezoelectric material, such as piezoelectric ceramic (PZT), for actuation. Figure 1 In the example, the actuator 11 is cylindrical in shape, specifically a cylindrical tube. The tube wall can be made of piezoelectric material, and the inside of the tube can be filled with a filling material (such as resin) to fix the optical fiber 12. The optical fiber 12 passes through the actuator 11 along its longitudinal axis and extends to the front end of the actuator 11, forming a cantilever structure, i.e., an optical fiber cantilever 121. Of course, in some embodiments, the optical fiber 12 can be bonded to the surface of the actuator 11 and extends to the front end of the actuator 11 to form an optical fiber cantilever, rather than being a through-type (in this case, the filling material inside the tube may not be used). In other embodiments of this application, the optical fiber can also be arranged in a through-type or non-through-type manner, which should not be construed as a limitation of this application. Electrodes are evenly distributed on the inner and outer surfaces of the cylindrical actuator 11 (wires or printed circuits that transmit electrical signals to the electrodes are not shown in the figure). Under the action of the electrodes, the tube wall made of piezoelectric material generates an actuating force based on the inverse piezoelectric effect, and the actuator 11 can drive the optical fiber 12 to perform two-dimensional scanning. Its actuation principle will be explained in the following sections.

[0033] The actuator 11 includes a first actuating part 111 and a second actuating part 112 in a rear-to-front direction. For the actuator 11 in the working state, the first actuating part 111 is in the first direction (i.e., Figure 1 The second actuator 112 vibrates in the second direction (i.e., in the Y-axis direction of the reference coordinate system) at a first frequency, and vibrates in the second direction (i.e., in the Y-axis direction of the reference coordinate system) at a second frequency. Figure 1 The first and second frequencies (in the X-axis direction of the reference coordinate system) vibrate at a second frequency. For different scanning methods, the first and second frequencies may be the same or similar (e.g., helical scanning), or they may differ significantly (e.g., raster scanning, Lissajous scanning). Under the synergistic effect of the vibrations generated by the first actuator 111 and the second actuator 112, the fiber optic cantilever 121 is driven to sweep along the corresponding trajectory. Therefore, the first actuator 111 and the second actuator 112 can also be regarded as the two scanning axes of the fiber optic scanner. In cases where the two frequencies differ, in the embodiments of this application, the first frequency is usually less than the second frequency. Therefore, in some examples, the first actuator can also be called the slow-axis actuator, and the second actuator can also be called the fast-axis actuator.

[0034] In addition, in the embodiments of this application, when one end of the actuator is fixed, the portion from the fixed position to the free end can also be referred to as a cantilever beam.

[0035] Of course, the fiber optic scanner 10 may also include a housing, a lens, a fixed support structure, etc., and in actual operation, the fiber optic scanner 10 also needs to cooperate with other components, such as a light source and a driving circuit, in order to achieve scanning and display.

[0036] It should be understood that Figure 1 The shape of the actuator 11 in the illustrated fiber optic scanner 10 is exemplary; in other embodiments, the overall shape of the actuator 11 is not limited to [specific shape]. Figure 1 The cylindrical shape shown can also be square prism (specifically, a square tube or square rod), triangular prism (specifically, a triangular tube or triangular rod), sheet-like, etc. The size and proportions are also not limited to these. Figure 1 The structural drawings shown in the embodiments of this application are for the purpose of facilitating understanding of the solution and should not be construed as limiting the scope of this application.

[0037] For the piezoelectric material actuator in this application, the inverse piezoelectric effect can be used to achieve deformation in the d31 mode, thereby generating a bending moment to achieve bending vibration. To clearly explain the vibration mode and principle of the actuation part made of piezoelectric material, please refer to... Figure 2a The above is shown Figure 1 The axial cross-sectional structure of the upper surface of the first actuating part 111 of the actuator 11 is appropriately simplified. Figure 2a In this cross-sectional structure, a tube wall 140 made of piezoelectric material and electrodes 141 (including an outer electrode 141a and an inner electrode 141b) disposed on the inner and outer surfaces of the tube wall 140 are included. The tube wall 140 is pre-polarized. When the applied electric field between the electrodes 141 is aligned with the polarization direction of the tube wall 140, the tube wall 140 rotates along the polarization direction of the tube wall 140 based on the inverse piezoelectric effect. Figure 2a The tube wall 140 elongates along the Z-axis. When the applied electric field is opposite to the polarization direction of the tube wall 140, the tube wall 140 elongates along the Z-axis. Figure 2a The contraction occurs along the Z-axis. The elongation and shortening deformation of the tube wall 140 will generate equivalent tensile and compressive stresses along the axial direction in the overall circular tube structure, which will further enable the first actuating part 111 to drive the actuator 11 as a whole to deform in the Y-axis direction, such as... Figure 2b As shown. The actuation principle of the second actuation unit 112 is similar, so it will not be described in detail here.

[0038] Piezoelectric cantilever beams, tubes, and other forms of scanning actuators are small, stable, and high-performing, making them the preferred choice for FSD (Fiber Scanning Display) actuators. Piezoelectric cantilever beams, such as single-crystal, dual-crystal, triple-crystal, or other structural variations, primarily utilize the inverse piezoelectric effect to achieve elongation of the piezoelectric material. The actuator structure, under the bending moment generated by the equivalent tensile and compressive stresses in the axial direction, achieves vertical bending vibration.

[0039] It should be noted that for the actuators constituting a fiber optic scanner, to achieve display, resonance is typically achieved using the actuator's natural frequency. In the embodiments of this application, both the first and second actuators can have natural frequencies based on one or more attributes. Generally, the natural frequency is the inherent frequency characteristic of the device. In some examples, the natural frequency and the resonant frequency (or resonance frequency) are equivalent. The one or more attributes mentioned include, but are not limited to: material, Young's modulus, cross-sectional second distance, density, cross-sectional area, length, and / or mode constant, etc. Typically, the natural frequencies of the two actuators are different. It should also be noted that the natural frequencies of each actuator in the actuator of this application are not just a single frequency point, but a series of multiple frequency points distributed according to a certain pattern, that is, there are multiple orders. In practical applications, both the first and second actuators utilize a corresponding resonant frequency of a certain order to achieve vibration.

[0040] The applicant discovered that the aforementioned actuator exhibits dynamic deformation during vibration, manifesting as corresponding mode shapes. These mode shapes can be considered as the instantaneous structural morphology of different parts of the actuator under varying vibration or displacement states when the actuator is in a vibrating state. (Reference) Figure 3 Here, we will take the vibration modes of the fast shaft actuator at different orders as an example for explanation (of course, the vibration modes of the slow shaft actuator are similar, so we will not give separate examples). The vibration modes are represented by curves, which can also be called the vibration mode curves of the fast shaft actuator. Figure 3 The four curves shown in different colors correspond to the four modes of vibration.

[0041] from Figure 3 As can be seen, the different positions on each mode shape curve exhibit varying line shapes, representing the amplitude of deformation of the fast-shaft actuator during vibration. Positions where the displacement is always zero or essentially zero can be referred to as "mode shape nodes" or "nodes" in this application. A first-order mode shape has one node at the fixed end, i.e., the root position of the scanner, and no nodes on the cantilever beam. Correspondingly, a second-order mode shape has one node on the cantilever, a third-order mode shape has two nodes on the cantilever, and so on. In this embodiment, modes above the second order are referred to as higher-order mode shapes. At the operating frequency, the actual mode shape of the scanner is closer to the higher-order characteristics, i.e., it has at least one node. In this embodiment, the nodes of higher-order mode shapes typically do not include constraint positions (i.e., the root position). Of course, in practical applications, the nodes on the mode shape curves do not necessarily correspond to a single point on the actual actuator structure; in some cases, they can represent a small segment of the actuator structure.

[0042] Currently, for piezoelectric material shaft-type scanning actuators, the polarization direction of the piezoelectric material is usually consistent for ease of manufacturing, and the electrodes are usually evenly arranged on the entire surface of the piezoelectric material, or continuously arranged on part of the surface.

[0043] However, when the actuator vibrates at different frequencies, the tensile and compressive stresses on the surface of the actuator along the axial direction are not completely consistent, but rather vary based on different frequencies. Obviously, using a uniformly distributed conventional electrode arrangement will cause conflicts.

[0044] like Figure 4 The image shows a segment of a cantilever beam undergoing bending vibration. For ease of description, it is assumed that the dashed line in the middle divides the cantilever beam into a left and right half. The mode shape of the left half is convex, while the mode shape of the right half is concave. The mode shapes of the left and right halves exhibit opposite strain characteristics. The solid arrows represent the strain characteristics exhibited by the actual mode shapes of the cantilever beam under bending vibration, while the dashed arrows represent the strain trend under voltage.

[0045] Depend on Figure 4 It can be seen that in the left half, the upper surface of the cantilever beam undergoes tensile deformation, while the lower surface undergoes compressive deformation; the right half is the opposite, with the upper surface of the cantilever beam undergoing compressive deformation and the lower surface undergoing tensile deformation. Simultaneously, under voltage, both the upper and lower surfaces of the left and right halves exhibit a tendency towards tensile strain, while the lower surfaces exhibit a tendency towards compressive strain. This shows that in the left half of the structure, voltage excitation has a positive effect, with the vibration strain characteristics of the actuator consistent with the expected strain trend under voltage. Conversely, in the right half, voltage excitation has a negative effect, with its vibration strain characteristics opposite to the expected strain trend under voltage; that is, the voltage performs negative work. In this embodiment, the region where the strain trend under voltage is the same as the actual vibration strain characteristics is called the positive excitation region, and the region where the strain trend under voltage is opposite to the actual vibration strain characteristics is called the negative excitation region.

[0046] On the one hand, at certain locations of the actuator, voltage excitation does negative work, increasing power consumption. On the other hand, the vibration strain characteristics are opposite to the expected strain trend under the inverse piezoelectric effect, which increases the nonlinearity of the actuator under dynamic conditions. This further increases the difficulty of trajectory control of the actuator and even the optical fiber. When used for image display, the image will deteriorate, stability will decrease, and device aging may be accelerated. In addition, the physical parameters and properties of piezoelectric materials change and exhibit differences, making the cantilever beam no longer a homogeneous beam, leading to an increase in modal nonlinearity, affecting image quality, and may also cause instability and reduced fatigue characteristics.

[0047] Based on the above analysis, this application proposes an optimized electrode arrangement scheme, combined with... Figure 5 The principle of the electrode arrangement scheme in the embodiments of this application will be explained. Figure 5 The instantaneous structural morphology of the piezoelectric element has been appropriately simplified. Considering the nonlinearity of the real system and the difficulty in accurately locating the concave-convex transformation points of the mode shape, in this embodiment, the nodal positions can be approximated as distinguishing points for electrode arrangement.

[0048] In this embodiment, the piezoelectric parts on both sides of each mode node have opposite strain characteristics. That is, the two actuation part regions distributed on both sides of the node are the positive excitation region and the negative excitation region, respectively.

[0049] like Figure 5 As shown, the positive excitation region on the actuator is represented by a solid line, and the negative excitation region on the actuator is represented by a dashed line. The driving electrodes on the actuator can be arranged in an intermittent manner, including at least the following arrangement methods.

[0050] In the first arrangement, the driving electrodes are arranged in all solid line areas, and no driving electrodes are arranged in the dashed line areas.

[0051] The second arrangement method involves not arranging the driving electrodes in the solid line areas, and arranging the driving electrodes in all the dashed line areas.

[0052] The third arrangement involves arranging the driving electrodes in at least a portion of the solid-lined area.

[0053] The fourth arrangement involves arranging the driving electrodes in at least a portion of the dashed area.

[0054] The fifth arrangement involves not arranging the driving electrodes in the solid line area and the dashed line area simultaneously.

[0055] Next, the electrode arrangement of the scanning actuator in the embodiments of this application will be described in conjunction with the specific scanning actuator form.

[0056] refer to Figure 6a This illustration shows a dual-wafer structure chip scanning actuator 60 according to an embodiment of this application. The scanning actuator 60 includes a first piezoelectric part 61 and a second piezoelectric part 62 in a back-to-forward direction. In this embodiment, the first electrode 610 disposed on the first piezoelectric part 61 is used as an example for description. The first electrode 610 is set based on the vibration strain characteristics of the first piezoelectric part 61. The principle of the vibration strain characteristics has been explained in the above embodiments and will not be described in detail here.

[0057] In this embodiment, the vibration mode of the first piezoelectric part 61 corresponding to the third-order mode shape curve is used as an example for explanation. Based on this, Figure 6bThe electrode arrangement on the upper and lower surfaces of the piezoelectric wafer of the first piezoelectric part 61 is shown from a cross-sectional view along the length axis of the piezoelectric wafer. The first electrodes 610 are arranged at intervals on the surface of the first piezoelectric part 61 in a segmented manner.

[0058] In one possible electrode arrangement, such as Figure 6b As shown, at the third-order frequency, the first piezoelectric part 61 has two nodes 612 and 614, dividing it into three segments 611, 613, and 615. An upper electrode 611a is provided on the upper surface of segment 611, and a lower electrode 611b is provided on the lower surface of segment 611. Similarly, an upper electrode 615a is provided on the upper surface of segment 615, and a lower electrode 615b is provided on the lower surface of segment 615. No electrodes are provided on the surfaces of segments containing nodes 612 and 614, nor on the surface of segment 613. This arrangement of electrodes creates a segmented arrangement on the surface of the first piezoelectric part 61. Since the piezoelectric parts on either side of the mode nodes have opposite strain characteristics, this electrode arrangement ensures that the strain characteristics of the piezoelectric part during vibration are the same as the strain result generated by the electric field provided by the electrodes, preventing the voltage from doing negative work during the vibration of the actuator.

[0059] In another possible electrode arrangement, such as Figure 6c As shown, a lower electrode 61b is disposed on the lower surface of the first piezoelectric part 61. In this example, for ease of manufacturing, the lower electrode 61b can be uniformly disposed on the lower surface of the first piezoelectric part 61. Taking a piezoelectric bicrystalline structure as an example, the lower electrodes of the two piezoelectric crystals can be disposed on the inner side, or in some embodiments, the lower electrodes of the two piezoelectric crystals can share a single electrode. In this way, the voltage can also be prevented from doing negative work during the vibration of the piezoelectric part.

[0060] In this embodiment of the application, it is assumed that Figure 6a In the corresponding embodiment, electrodes are provided on the surfaces of sections 611 and 615 of the first piezoelectric part 61, while no electrodes are provided on the surface of section 613. The schematic diagram of the corresponding dual-wafer structure is shown below. Figure 7a As shown in the figure, the dual-chip structure scanning actuator is simplified, with only the piezoelectric chips and electrodes illustrated. The first piezoelectric section 61 includes two piezoelectric chips 618 and 619, which share a lower electrode 61b. The lower electrode 61b is disposed between the piezoelectric chips 618 and 619. Upper electrodes 611a and 615a are arranged alternately on the upper surface of the piezoelectric chip 618, and upper electrodes 616a and 617a are arranged alternately on the upper surface of the piezoelectric chip 619. Figure 7b As shown, Figure 7a An oblique view of the first piezoelectric part 61 shown.

[0061] Of course, in other embodiments, the lower electrode can also be arranged in segments based on the vibration strain characteristics of the first piezoelectric part 61, such as... Figure 7c As shown in 611b and 615b. Figure 7d As shown, Figure 7c The first piezoelectric part 61 is shown in a perspective view. Alternatively, the upper electrodes are uniformly and continuously arranged on the upper surface of the piezoelectric wafer, and the lower electrodes are arranged at intervals on the lower surface of the piezoelectric wafer.

[0062] It should be noted that in the embodiments of this application, the terms "upper" and "lower" in the description of the upper and lower surfaces of the piezoelectric wafer, and the upper and lower electrodes, are relative and should not be construed as a limitation on spatial position.

[0063] In another possible implementation, it is assumed that Figure 6a In the corresponding embodiment, no electrodes are provided on the surfaces of sections 611 and 615 of the first piezoelectric part 61, and the electrode arrangement of the dual-crystal structure is as follows: Figure 8 As shown, a lower electrode 613b is provided on the lower surface of section 613; upper electrodes 613a and 620a are arranged on the upper surface of section 613; similarly, no electrodes are provided on the surface of the section where the node is located.

[0064] In this embodiment, the electrodes on the second piezoelectric part 62 can be set based on the vibration strain characteristics of the second piezoelectric part 62. The setting principle is similar to that of the first electrode 610 on the first piezoelectric part 61, and will not be repeated in this embodiment.

[0065] In this application embodiment, besides the sheet-like scanning actuator, the arrangement of the inner and outer electrodes of the tubular actuator (including round tubes, square tubes, or other polygonal piezoelectric tubes) is also applicable to the electrode arrangement in this application embodiment. Similarly, the square rod actuator is also applicable to the electrode arrangement in this application embodiment. The piezoelectric part of the square rod actuator consists of a square rod-shaped substrate and a piezoelectric sheet disposed on each of the four surfaces of the square rod. It should be understood that the sheet-like scanning actuator shape in this application embodiment is only an example and should not be construed as a limitation on the actuator shape.

[0066] Furthermore, due to the system stability requirements of fiber optic scanning image display, the optical scanning trajectory needs to be detected and corrected. Therefore, at least one segment in the section divided by mode nodes can be used as the electrode arrangement for piezoelectric self-feedback. The electrical signal generated by the deformation of the piezoelectric part is detected by the feedback electrode. Since there is no signal cancellation between adjacent segments, a larger signal strength can be obtained. At the root position near the actuator (i.e., the fixed end), the vibration strain is small, but the signal anti-interference ability is strong and stable; at the free end near the actuator, the strain is large, the signal is strong, but the signal stability is poor. In this embodiment, considering the stability and strength of the signal, the segment near the middle of the structure can be selected for the arrangement of feedback electrodes.

[0067] In this embodiment, for raster scanning, the operating frequencies of the slow-axis actuator and the fast-axis actuator differ significantly, with the second frequency of the fast-axis actuator being much higher than the first frequency of the slow-axis actuator. However, for Lissajous or spiral scanning, the difference in operating frequencies between the first and second actuators is smaller. Generally, under higher-order frequency driving, the actuator's mode shape has more nodes; under lower-order frequency driving, the actuator's mode shape has fewer nodes. The number of nodes in the first actuator in this embodiment is merely illustrative and should not be construed as a limitation on the relationship between the number of nodes in the two actuators.

[0068] As described in the above embodiments, for scanning actuators, the scanning actuator has an inherent frequency based on one or more attributes. The inherent frequency is the intrinsic frequency characteristic of the device. In the embodiments of this application, the inherent frequency of each actuating part of the actuator is not just a single frequency point, but a series of multiple order frequency points distributed according to a certain pattern. For each order frequency point of the actuator, it can be determined based on one or more corresponding attributes through methods such as simulation and theoretical calculation. Of course, the specific simulation and calculation process will not be described in detail here.

[0069] Regarding the mode shape of the scanning actuator, when the scanning actuator vibrates at a set frequency, the mode shape of the actuator can be obtained by instrument detection or simulation. Assuming that the driving electrode of the actuator is set based on the vibration strain characteristics at a certain frequency, when the actuator operates with that frequency as the driving frequency, its actual mode shape during operation conforms to the mode shape curve characteristics at that frequency.

[0070] In this embodiment of the application, based on the aforementioned piezoelectric actuator, a scanning display module is also provided, including: a piezoelectric actuator, an optical fiber, a light source, and a control circuit. The control circuit may be a graphics processing unit (GPU), a central processing unit (CPU), or other chips, circuits, or combinations thereof with control and image processing functions; no specific limitation is made here.

[0071] The light source can contain multiple monochromatic lasers, for example, red (R), green (G), and blue (B) lasers, each emitting beams of different colors. The beams emitted by each laser in the light source are coupled into an optical fiber, and a piezoelectric actuator is controlled by a control circuit to sweep the beam, thereby scanning and outputting the image beam transmitted in the optical fiber. This forms a spot with corresponding image information (such as color, grayscale, or brightness) at each pixel location. Within one frame, the beam traverses each pixel location at a sufficiently fast speed to complete the scanning of one frame of the image. Due to the "visual persistence" characteristic of human vision, the human eye cannot perceive the movement of the beam at each pixel location, but instead sees a complete image frame.

[0072] It should be noted that the above embodiments illustrate the corresponding electrode arrangement in the scenario where the scanning device is a fiber optic scanner. For other types of scanning devices, such as micro-electro-mechanical systems (MEMS) scanning mirrors, the laser beam deflection (grating-type scanning trajectory or Lissajous scanning trajectory) is achieved through a two-dimensional galvanometer (which also has two scanning axes). The electrode arrangement described in this application is also applicable to such scanning devices.

[0073] In this embodiment, the scanning display module can be widely used in head-mounted AR (Augmented Reality) devices, head-mounted VR (Virtual Reality) devices, projection TVs, projectors, etc., and its applications are very wide.

[0074] It should also be noted that in the embodiments of this application, the description of "front end" is usually determined according to the direction of beam transmission, that is, the direction from front to back is consistent with the direction of beam transmission. The rear end of the actuator refers to the end of the actuator used as a fixed end, also known as the fixed end; the front end of the actuator refers to the other end of the actuator opposite to the rear end, which in some embodiments may also be called the free end, and is the part of the actuator with the most significant deformation and amplitude. Of course, the definitions and explanations of the concepts of free end, front end, or rear end here also apply to actuators, fiber optic cantilever, or other structures in other embodiments of this application. However, it should be noted that in the embodiments of this application, for some structures that do not have the above-mentioned "front" and "rear" concepts, "fixed end" and "free end" will be used directly for description. Of course, such descriptions are only for the convenience of those skilled in the art to understand accurately and intuitively, and should not be considered as a limitation of this application.

[0075] The terms "first," "second," "first," or "second" as used in the various embodiments of this disclosure may modify various components regardless of their order and / or importance, but these terms do not limit the corresponding components. The above terms are configured only for the purpose of distinguishing one component from another.

[0076] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A piezoelectric actuator, comprising a piezoelectric part and a driving electrode disposed on the piezoelectric part, wherein the piezoelectric part is a polarized piezoelectric material; characterized in that, The piezoelectric part includes at least one mode node at a set frequency; on both sides of some or all of the mode nodes, an electrode is provided on the surface of the piezoelectric part on one side, and no electrode is provided on the surface of the piezoelectric part on the other side.

2. The piezoelectric actuator as described in claim 1, characterized in that, The piezoelectric part is a piezoelectric wafer structure; the driving electrode includes an upper electrode and a lower electrode, which are respectively arranged on the upper surface and the lower surface of the piezoelectric wafer structure; on both sides of some or all of the mode nodes, the upper surface of the piezoelectric wafer structure on one side is provided with an upper electrode, and the lower surface of the piezoelectric wafer structure on the other side is not provided with an upper electrode.

3. The piezoelectric actuator as described in claim 2, characterized in that, The area where the lower electrode is located corresponds to the area where the upper electrode is located.

4. The piezoelectric actuator as described in claim 2, characterized in that, The lower electrode is continuously arranged on the lower surface of the piezoelectric wafer structure.

5. The piezoelectric actuator as described in claim 1, characterized in that, The piezoelectric part is a piezoelectric tube; the driving electrode includes an inner electrode and an outer electrode; on both sides of some or all of the mode nodes, an outer electrode is provided on the outer surface of the piezoelectric tube on one side, and no outer electrode is provided on the outer surface of the piezoelectric part on the other side.

6. The piezoelectric actuator as described in claim 5, characterized in that, The inner electrode is arranged on the inner surface of the piezoelectric tube, and the area where the inner electrode is arranged corresponds to the area where the outer electrode is located.

7. The piezoelectric actuator as described in claim 5, characterized in that, The internal electrodes are continuously arranged on the inner surface of the piezoelectric tube.

8. The piezoelectric actuator as claimed in claim 1, characterized in that, At least one side region of a mode node is used to house a feedback electrode; when the piezoelectric actuator is in operation, the feedback electrode is used to detect the electrical signal generated by the deformation of the piezoelectric part.

9. A scanning display module, characterized in that, The device includes a piezoelectric actuator as described in any one of claims 1-8, an optical fiber, a light source, and a control circuit; the image light output from the light source is coupled into one end of the optical fiber, and the other end of the optical fiber is fixed to the piezoelectric actuator; under the control of the control circuit, the image light output from the light source is scanned and displayed by the piezoelectric actuator driving the optical fiber.

10. A projection device, characterized in that, The projection device includes one or more scanning display modules as described in claim 9.

Images