A micro bistable actuator based on shape memory alloy wire driving assembly

Abstract

The application provides a micro bistable actuator based on a shape memory alloy wire driving assembly, relates to the technical field of tactile display and micro actuator, and comprises a mounting frame, a rotating part and a contact element, and the core is that two shape memory alloy wires arranged in an antagonistic mode drive the rotation of an eccentric cam body. In a power-off state, the cam body is kept in a first stable state or a second stable state by using the mass distribution and friction of the cam body, and no continuous power consumption or additional locking structure is needed. The shape memory alloy wire is firmly connected with the cam body through spiral winding and laser welding, zero-power-consumption bistable state keeping is realized, and the problems of large power consumption, large size or low assembly yield of traditional micro actuators are solved. The application has the characteristics of small size, fast response, low power consumption and high production yield, and is suitable for Braille display, micro valve and portable tactile feedback equipment.

Description

Technical Field

[0001] This invention relates to the fields of tactile display technology and micro actuator technology, and particularly to a micro bistable actuator based on a shape memory alloy wire drive assembly. Background Technology

[0002] Tactile display devices enable visually impaired individuals to perceive information such as text and graphics through their fingertips via a retractable array of contact points. Existing micro actuators are mainly divided into the following two categories: 1. Electromagnetic drive actuators: These use an electromagnetic coil and a permanent magnet to drive an eccentric wheel to rotate, and an additional locking block and limit block are used to achieve self-locking upon power failure. Although this type of solution can achieve contact point lifting control, it has the following problems: (1) The electromagnetic coil is large in size and difficult to further miniaturize; (2) An additional locking structure is required, which increases the number of parts and assembly complexity; (3) Continuous or pulsed current is required during operation, resulting in high power consumption. 2. Piezoelectric drive actuators: These utilize the inverse piezoelectric effect of piezoelectric ceramics to generate displacement, which has the advantage of fast response, but the displacement is small (usually at the micrometer level), requiring a displacement amplification mechanism, and the driving voltage is high (tens to hundreds of volts), making them unsuitable for portable devices.

[0003] Shape memory alloys (SMAs), as a novel smart material, have attracted attention in the field of micro-actuators due to their advantages such as high power density, small size, and no noise. However, most existing SMA actuators adopt a single-pass drive plus spring reset structure, which requires continuous power to maintain the state, resulting in high power consumption; moreover, the displacement of SMAs is limited (usually 4%-8% of the material length), making it difficult to directly generate millimeter-level strokes.

[0004] Based on the above analysis, most micro actuators in the existing technology cannot maintain their current state after power failure and require continuous power consumption to maintain their operation. In order to achieve power failure self-locking, the existing solutions require additional structures such as locking blocks, which is not conducive to extreme miniaturization. At the same time, the displacement of SMA material itself is limited, making it difficult to meet the stroke requirement of about 0.5mm. In addition, during high-speed switching, the contacts may temporarily detach from the eccentric wheel due to inertia, resulting in jumping and wear. Summary of the Invention

[0005] This invention provides a miniature bistable actuator based on a shape memory alloy wire drive assembly, specifically comprising: The mounting frame comprises a mounting frame, a rotating part, and contact elements. The mounting frame is assembled from a base, a lower frame, and an upper frame stacked sequentially from bottom to top. The cam body of the rotating part is rotatably mounted inside the lower frame via a rotating shaft. The cam body has a first steady-state position and a second steady-state position. In the power-off state, the cam body maintains either the first or second steady-state position through its own mass distribution and friction. The contact elements are vertically mounted inside the upper frame, and the bottom surface of the contact body in the contact elements contacts the outer circumferential surface of the cam body. A drive assembly body is provided on the cam body, and the drive assembly body has two shape memory alloy wires. One end of each shape memory alloy wire is connected to the cam body via a metal component, and the other end is fixed to the base or circuit board. When one shape memory alloy wire is energized and contracts, it drives the cam body to rotate towards the first steady-state position, and when the other shape memory alloy wire is energized and contracts, it drives the cam body to rotate towards the second steady-state position. The two shape memory alloy wires are arranged in an antagonistic manner relative to the rotation axis of the cam body, and the contraction directions of the two shape memory alloy wires are opposite.

[0006] Preferably, the cam body has a first end and a second end, the first end being the position on the outer circumference of the cam body that is farthest from the rotation axis, and the second end being the position on the outer circumference of the cam body that is closest to the rotation axis; the eccentricity of the cam body is configured such that when the cam body rotates from the first steady-state position to the second steady-state position, the lifting stroke of the contact element is equal to the displacement generated by the cam body rotating 180°.

[0007] Preferably, the cam body includes a first end section, a second end section, and a metal component located between the first end section and the second end section. The diameters of the first end section and the second end section are larger than the diameter of the metal component, and two shape memory alloy wires are wound and fixed to the metal component.

[0008] Preferably, the ratio of the diameter of the metal component to the diameter of the first end segment is 1:1.5 to 1:3.

[0009] Preferably, the center of mass of the cam body is offset from its rotation axis, so that the cam body has a local minimum potential energy in both the first steady-state position and the second steady-state position, and the potential barrier height corresponding to the local minimum potential energy is greater than the energy that the external disturbance can provide.

[0010] Preferably, a preload mechanism is also included, which applies a preload force to the contact element toward the cam body, so that the contact element is frequently in contact with the outer circumferential surface of the cam body.

[0011] Preferably, the pre-tightening mechanism is selected from one of a magnetic pre-tightening mechanism, an elastic pre-tightening mechanism, or a vacuum adsorption pre-tightening mechanism.

[0012] Preferably, the magnetic preload mechanism includes a second magnetic element disposed within the contact element and a first magnetic element disposed on the base or cam body of the mounting frame, wherein the second magnetic element and the first magnetic element attract each other, and the attraction force is configured to be greater than the inertial force of the contact element at the highest switching frequency.

[0013] Preferably, the second magnetic component is a permanent magnet microsphere, the cam body is made of a magnetically conductive material, and the first magnetic component is a permanent magnet embedded in the base.

[0014] Preferably, the elastic preload mechanism includes a limiting spring connecting the contact element and the mounting frame, wherein the elastic force of the limiting spring causes the contact element to frequently adhere to the cam body.

[0015] Preferably, a limiting mechanism is also included, which is used to limit the rotation angle of the cam body to prevent it from exceeding the first steady-state position or the second steady-state position.

[0016] Preferably, the limiting mechanism is selected from one of mechanical limiting surface, magnetic limiting or elastic limiting.

[0017] Preferably, the mechanical limiting surface includes a first limiting surface α and a second limiting surface β disposed within the lower frame, corresponding to the first steady-state position and the second steady-state position of the cam body, respectively.

[0018] Preferably, the gap between the first limiting surface α and the second limiting surface β and the cam body is less than 0.05 mm.

[0019] Preferably, the two shape memory alloy wires are fixedly connected to the metal components on the cam body by winding and laser welding, wherein the number of winding turns is 0.5-3 turns.

[0020] Preferably, the system also includes a control circuit that applies a pulsed current to the two shape memory alloy wires. The width of the pulsed current is configured to be sufficient to cause the shape memory alloy wires to complete phase change contraction and drive the cam body past the dead point or limit point, and is less than the overheat damage threshold of the shape memory alloy wires.

[0021] Preferably, the pulse current has a width of 10-200ms and an amplitude of 30-300mA.

[0022] Preferably, the ratio of the overall height of the actuator to the lifting stroke of the contact element is less than or equal to 4:1.

[0023] As a preferred alternative to the two shape memory alloy wires, one option is to use a single shape memory alloy wire in conjunction with a return spring that provides a restoring force opposite to that of the shape memory alloy wire.

[0024] Preferably, the return spring is selected from one of a torsion spring, a compression spring, or a spring sheet. Preferably, when using the torsion spring, the torsion spring is disposed outside the rotating shaft and connects the rotating shaft and the lower frame.

[0025] Preferably, when using the compression spring, one end of the compression spring is connected to the metal component, and the other end is connected to the inner wall of the lower frame.

[0026] The working principle of this invention is as follows: Initially, both shape memory alloy wires are in a cooled and relaxed state, and the cam body is stable in a certain steady state. When it is necessary to switch to the raised state, a pulse current is applied to either shape memory alloy wire. This wire contracts upon heating, pulling the cam body to rotate in the raised direction. After the eccentric wheel passes the "dead point or limit point" in the middle, it automatically rotates to the first steady state under the action of inertia and gravity, with the farthest end lifting the contact point, which extends to the highest position. When the pulse ends, the shape memory alloy wire is de-energized and cooled, and the cam body is mechanically self-locked to maintain the raised state. When it is necessary to switch back to the second steady state, a pulse current is applied to the other shape memory alloy wire, driving the eccentric wheel to rotate in the opposite direction and pass the dead point or limit point, finally stabilizing in the second steady state, with the contact point falling back to the lowest position. The entire switching process requires only a short pulse, and neither steady state requires continuous power consumption to maintain, achieving zero power consumption.

[0027] Beneficial effects 1. In this invention, the eccentric mass distribution design of the cam body is utilized to make it have local minimum potential energy in both the first and second steady-state positions. Combined with the mechanical or magnetic limiting mechanism described in the text, self-locking retention in the power-off state is achieved without the need for continuous power consumption to maintain the state, thus solving the problem of high standby power consumption of traditional electromagnetic actuators.

[0028] 2. In this invention, by precisely configuring the eccentricity of the cam body, the lifting stroke of the contact element is precisely controlled during the 180° rotation of the actuator. Combined with the magnetic pre-tightening mechanism (attraction force of about 0.02-0.05N) or the elastic pre-tightening mechanism, the contact gap between the contact element and the cam body is effectively eliminated.

[0029] The embodiments show that the structure has no jumping under 100Hz high-frequency switching, which not only ensures the reliability of contact action, but also achieves fast response through the antagonistic arrangement of the driving method (dual shape memory alloy wires or shape memory alloy wires with a reset spring), meeting the core requirements of miniaturized devices for efficient and low-power driving. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below.

[0031] The accompanying drawings described below are only related to some embodiments of the invention and are not intended to limit the invention.

[0032] In the attached diagram: Figure 1 A theoretical structural schematic diagram of a cam driven by a shape memory alloy wire in a bistable actuator according to an embodiment of the present invention is shown. Figure 2 A three-dimensional structural schematic diagram of a bistable actuator according to an embodiment of the present invention is shown.

[0033] Figure 3 A partial cross-sectional schematic diagram of a bistable actuator according to an embodiment of the present invention is shown.

[0034] Figure 4 A three-dimensional structural schematic diagram of the rotating part according to an embodiment of the present invention is shown.

[0035] Figure 5 A schematic diagram showing the position of the limiting plane of a bistable actuator according to an embodiment of the present invention is shown.

[0036] Figure 6 A flowchart illustrating the state switching process of a bistable actuator according to an embodiment of the present invention is shown.

[0037] Figure 7 A schematic diagram of two preload methods for a bistable actuator according to an embodiment of the present invention is shown.

[0038] Figure 8 The diagram illustrates two alternative schemes for a bistable actuator using a single shape memory alloy wire and a return spring, according to an embodiment of the present invention.

[0039] List of main reference numerals 1. Drive component main body; 101. Metal component; 102. Shape memory alloy wire; 4. Rotating part; 401. Cam body; 402. Rotating shaft; 4021. Torsion spring; 5. Mounting frame; 501. Lower frame; 5011. Compression spring; 502. Upper frame; 5021. Limiting spring; 503. Base; 5031. First magnetic component; 6. Contact element; 601. Contact body; 602. Second magnetic component. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] In this document, “illustrative” means “serving as an example, illustration or description”, and any illustration or implementation described herein as “illustrative” should not be construed as a more preferred or advantageous technical solution.

[0042] To keep the drawings concise, only the parts relevant to this application are shown schematically in each drawing, and they do not represent the actual structure of the product. In addition, to make the drawings concise and easy to understand, in some drawings, only one of the components with the same structure or function is shown schematically, or only one of them is labeled.

[0043] In this document, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; unless otherwise specified or explained, the term "multiple" refers to two or more; the terms "connected," "fixed," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0044] Example: Please refer to Figures 1 to 8 : like Figure 1 and Figure 2 As shown, this invention proposes a miniature bistable actuator based on a shape memory alloy wire drive assembly, comprising: The mounting frame 5 comprises a rotating part 4 and a contact element 6. The mounting frame 5 is assembled from a base 503, a lower frame 501, and an upper frame 502, stacked sequentially from bottom to top. The cam body 401 of the rotating part 4 is rotatably mounted inside the lower frame 501. The cam body 401 has a first stable position and a second stable position. In the power-off state, the cam body 401 is maintained in either the first or second stable position by its own mass distribution and friction, without the need for an additional locking structure. The contact element 6 is vertically mounted inside the upper frame 502, with the bottom surface of the contact body 601 in the contact element 6 contacting the outer circumferential surface of the cam body 401. A drive assembly body 1 is provided on the cam body 401, and this drive assembly body 1 has… The structure of the two shape memory alloy wires 102: one end of each shape memory alloy wire 102 is connected to the cam body 401 via a metal component 101, and the other end is fixed to the base 503 or a circuit board. When one shape memory alloy wire 102 is energized and contracts, it drives the cam body 401 to rotate to a first steady-state position. When the other shape memory alloy wire 102—hereinafter referred to as the second shape memory alloy wire 102—is energized and contracts, it drives the cam body 401 to rotate to a second steady-state position. The first shape memory alloy wire 102 and the second shape memory alloy wire 102 are arranged in an antagonistic manner relative to the rotation axis 402 of the cam body 401, and the contraction directions of the first shape memory alloy wire 102 and the second shape memory alloy wire 102 are opposite.

[0045] like Figure 6 As shown, the working principle of this invention is as follows: In the initial state, it can be referred to... Figure 6 As shown in Figure a, both shape memory alloy wires 102 are in a cooled and relaxed state, and the cam body 401 is stable in a certain steady state. When it is necessary to switch to the raised state, refer to... Figure 6 As shown in Figure b, when a pulsed current is applied to any shape memory alloy wire 102, the wire 102 contracts upon heating, pulling the cam body 401 to rotate in the protruding direction; see reference. Figure 6 As shown in Figure c, after the cam body 401 passes the intermediate "dead point or limit point," it automatically rotates to the first steady state under the action of inertia and gravity, with the farthest end lifting the contact point, which extends to its highest position. When the pulse ends, the shape memory alloy wire 102 is de-energized and cooled, and the cam body 401 is mechanically self-locked to maintain the protruding state. When it is necessary to switch back to the second steady state, as... Figure 6 As shown in Figure d, a pulsed current is applied to another shape memory alloy wire 102, driving the cam body 401 to rotate in the opposite direction and pass through the dead point or limit point, eventually stabilizing in the second steady state, and the contact point falls back to the lowest position, as shown in Figure d. Figure 6 As shown in Figure e. The entire switching process requires only a brief pulse, and neither of the two steady states requires continuous power consumption to maintain, achieving zero power consumption.

[0046] In the above embodiment, the mounting frame 5 is precision injection molded from liquid crystal polymer and is assembled from three parts from bottom to top, with an internal receiving cavity; the cam body 401 is made of 17-4PH stainless steel, prepared by micron-level powder injection molding process, and then finely machined after sintering; the two cam bodies 401 with a diameter of 1mm are connected by a metal neck, which can be regarded as the metal component 101 in the drive component body 1, and forms a drive component with two shape memory alloy wires 102; wherein, the diameter of the metal neck is 0.5mm and the total length is 1.5mm; the eccentricity e of the cam body 401 is 0.25mm, corresponding to a stroke of 0.5mm for the contact body 601; the diameter of the rotating shaft 402 is 0.15mm; the contact body 601 is a POM plastic column with a diameter of 1.0mm and a spherical bottom surface.

[0047] It should be noted that in the above embodiments, the shape memory alloy wire 102 is fixedly connected to the metal neck (which can be regarded as a metal component 101) on the cam body 401 by winding and laser welding, as can be referred to Figure 1 The specific connection method and parameters can be adapted and set according to the structure of the matching driver components.

[0048] The shape memory alloy wire 102 is made of NiTi alloy with a diameter of 0.05 mm and a phase transformation temperature of 70-90℃. The first shape memory alloy wire 102 and the second shape memory alloy wire 102 are respectively wound around the opposite sides of the metal neck of the cam body 401. The connection method between the two shape memory alloy wires 102 and the metal neck adopts the preparation method of the drive component in the above embodiment. For the specific structure, please refer to... Figure 3 As shown.

[0049] The control circuit applies a pulsed current to the shape memory alloy wire 102. The pulse parameters are configured to be sufficient to cause the alloy wire to complete phase change contraction and drive the cam body 401 past the dead point or limit point. In this embodiment, the pulse width is 50ms, the pulse current is 120mA, the driving voltage is 5V, the switching time is about 50ms, and the natural cooling time is about 200-300ms.

[0050] Based on the above embodiments, a magnetic pre-tightening mechanism can be added, which can be referred to as follows: Figure 7 As shown in Figure a; the contact body 601 has a 0.6mm diameter neodymium iron boron permanent magnet microsphere embedded inside as the second magnetic component 602, which is fixed by bonding. The cam body 401 is made of magnetically conductive 17-4PH stainless steel and heat-treated to improve its magnetic permeability; a 0.8mm×0.8mm×0.3mm neodymium iron boron sheet is embedded in the bottom groove of the base 503 as the first magnetic component 5031, which adopts a post-magnetization process: first assembling the unmagnetized permanent magnet, and then magnetizing and activating the whole after all assembly is completed.

[0051] It should be noted that this invention can be combined with supporting core technologies, especially the supporting post-magnetization process, to achieve complete working functions.

[0052] Magnetic force estimation: When the gap between the contact body 601 and the cam body 401 is approximately 0.05mm, the attractive force is approximately 0.02-0.05N, which is much greater than the inertial force of the contact body 601—its mass is approximately 0.01-0.02g. At an acceleration of 0.5mm / 30ms, the inertial force is approximately 5.6×10⁻⁶. -6 N. In the 100Hz high-speed switching test, the sample without magnetic bonding showed an approximately 5% probability of contact jump; the sample with magnetic bonding did not show any jump in 100,000 tests.

[0053] The embodiments show that the structure has no jumping under 100Hz high-frequency switching, which not only ensures the reliability of contact action, but also achieves fast response through the antagonistic arrangement of the driving method (dual shape memory alloy wires or shape memory alloy wires with a reset spring), meeting the core requirements of miniaturized devices for efficient and low-power driving.

[0054] As an alternative to magnetic preload, this embodiment employs an elastic preload mechanism, such as... Figure 7 As shown in Figure b, a limiting spring 5021 is provided between the contact body 601 and the upper frame 502. One end of the limiting spring 5021 is fixed to the upper frame 502, and the other end is pressed against the top of the contact body 601. The limiting spring 5021 is a micro spring made of beryllium bronze with a thickness of 0.03 mm, a width of 0.5 mm, and a cantilever length of 1.2 mm. The elastic force of the limiting spring 5021 is about 0.01-0.03 N, which is sufficient to ensure that the contact body 601 always fits against the cam body 401.

[0055] This embodiment adds a mechanical limiting mechanism to the above embodiment, such as... Figure 5 a and Figure 5 As shown in Figure b; a first limiting surface α is set within the mounting frame 5 corresponding to the stable position of the protrusion, and a second limiting surface β is set corresponding to the stable position of the smoothing; the distance between the limiting surface and the end face of the cam body 401 is 0.02mm, which is only used to prevent overshoot and does not provide locking force; the limiting surface material is soft polyurethane to reduce impact noise.

[0056] As an alternative to mechanical limiting, this embodiment adopts a magnetic limiting mechanism; a permanent magnet is set on the cam body 401, a first magnetic conductor is set in the mounting frame 5 corresponding to the first steady-state position, and a second magnetic conductor is set in the second steady-state position; when the cam body 401 rotates to the steady state, the magnetic force between the permanent magnet and the magnetic conductor helps to maintain the position and prevent overshoot.

[0057] As an alternative to the antagonistic actuation of two shape memory alloy wires 102, this embodiment uses a single shape memory alloy wire 102 in conjunction with a return spring, such as... Figure 8 As shown in Figure a; one end of the first shape memory alloy wire 102 is connected to the cam body 401, and the other end is fixed to the base 503; the reset spring is connected to the other side of the cam body 401 and provides a restoring force opposite to that of the shape memory alloy wire.

[0058] It should be noted that, as Figure 8 As shown in b, the reset spring can be either a torsion spring 4021 (installed at the pivot) or a compression spring 5011 (installed on the side wall of the mounting frame 5); when the shape memory alloy wire 102 is energized and contracts, it overcomes the spring force and drives the cam body 401 to rotate in the protruding direction; after the power is cut off, the reset spring pushes the cam body 401 to reset.

[0059] The above description is merely a specific embodiment of this application. Under the guidance of the above teachings, those skilled in the art can make other improvements or modifications based on the above embodiments. Those skilled in the art should understand that the above specific description is only to better explain the purpose of this application, and the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A miniature bistable actuator based on a shape memory alloy wire drive assembly, characterized in that, include: Mounting frame (5), rotating part (4) and contact element (6); The mounting frame (5) is composed of a base (503), a lower frame (501) and an upper frame (502) stacked and assembled from bottom to top; The cam body (401) of the rotating part (4) is rotatably mounted inside the lower frame (501) via a rotating shaft (402). The cam body (401) has a first steady-state position and a second steady-state position. In the power-off state, the cam body (401) is maintained in the first steady-state position or the second steady-state position by its own mass distribution and friction. The contact element (6) is vertically mounted inside the upper frame (502), and the bottom surface of the contact body (601) in the contact element (6) contacts the outer circumferential surface of the cam body (401). The cam body (401) is provided with a drive assembly body (1), and the drive assembly body (1) has two shape memory alloy wires (102); one end of the two shape memory alloy wires (102) is connected to the cam body (401) through a metal component (101), and the other end is fixed to a base or circuit board. When one of the shape memory alloy wires (102) is energized and contracts, it drives the cam body to rotate to a first steady-state position, and when the other shape memory alloy wire (102) is energized and contracts, it drives the cam body (401) to rotate to a second steady-state position. The two shape memory alloy wires (102) are arranged in an antagonistic manner relative to the rotation axis (402) of the cam body (401), and the two shape memory alloy wires (102) contract in opposite directions.

2. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 1, characterized in that, The cam body (401) has a first end and a second end. The first end is the position on the outer circumference of the cam body (401) that is farthest from the rotation axis (402), and the second end is the position on the outer circumference of the cam body (401) that is closest to the rotation axis (402). The eccentricity of the cam body (401) is configured such that when the cam body (401) rotates from the first steady-state position to the second steady-state position, the lifting stroke of the contact element (6) is equal to the displacement generated by the cam body (401) rotating 180°.

3. A micro bistable actuator based on a shape memory alloy wire drive assembly according to claim 2, characterized in that, The cam body (401) includes a first end section, a second end section, and a metal component (101) located between the first end section and the second end section. The diameters of the first end section and the second end section are larger than the diameter of the metal component (101). Two shape memory alloy wires (102) are wound and fixed to the metal component (101).

4. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 3, characterized in that, The ratio of the diameter of the metal component (101) to the diameter of the first end segment is 1:1.5 to 1:

3.

5. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 1, characterized in that, The center of mass of the cam body (401) is offset from its rotation axis (402), so that the cam body (401) has local minimum potential energy in both the first steady state position and the second steady state position. The potential barrier height corresponding to the local minimum potential energy is greater than the energy that external disturbance can provide.

6. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 1, characterized in that, It also includes a pre-tightening mechanism that applies a pre-tightening force to the contact element (6) toward the cam body (401) so that the contact element (6) always fits against the outer circumferential surface of the cam body (401).

7. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 6, characterized in that, The pre-tightening mechanism is one of a magnetic pre-tightening mechanism, an elastic pre-tightening mechanism, or a vacuum adsorption pre-tightening mechanism.

8. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 7, characterized in that, The magnetic preload mechanism includes a second magnetic element (602) disposed in the contact element (6) and a first magnetic element (5031) disposed on the base (503) or cam body (401) of the mounting frame (5). The second magnetic element (602) and the first magnetic element (5031) attract each other, and the attraction force is configured to be greater than the inertial force of the contact element (6) at the highest switching frequency.

9. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 8, characterized in that, The second magnetic component (602) is a permanent magnet microsphere, the cam body (401) is made of a magnetically conductive material, and the first magnetic component (5031) is a permanent magnet embedded in the base (503).

10. A micro bistable actuator based on a shape memory alloy wire drive assembly according to claim 7, characterized in that, The elastic preload mechanism includes a limiting spring (5021) connecting the contact element (6) and the mounting frame (5), the elastic force of which causes the contact element (6) to frequently conform to the cam body (401).

11. A micro bistable actuator based on a shape memory alloy wire drive assembly according to claim 1, characterized in that, It also includes a limiting mechanism, which is used to limit the rotation angle of the cam body (401) to prevent it from going beyond the first steady-state position or the second steady-state position.

12. A micro bistable actuator based on a shape memory alloy wire drive assembly according to claim 11, characterized in that, The limiting mechanism adopts one of mechanical limiting surface, magnetic limiting or elastic limiting.

13. A micro bistable actuator based on a shape memory alloy wire drive assembly according to claim 12, characterized in that, The mechanical limiting surface includes a first limiting surface (α) and a second limiting surface (β) disposed within the lower frame (501), which correspond to the first steady-state position and the second steady-state position of the cam body (401), respectively.

14. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 13, characterized in that, The gap between the first limiting surface (α) and the second limiting surface (β) and the cam body (401) is less than 0.05 mm.

15. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 1, characterized in that, Two shape memory alloy wires (102) are fixedly connected to the metal component (101) on the cam body (401) by winding and laser welding, wherein the number of winding turns is 0.5-3 turns.

16. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 1, characterized in that, It also includes a control circuit that applies a pulsed current to the two shape memory alloy wires (102), the width of which is configured to enable the shape memory alloy wires (102) to complete phase change contraction and drive the cam body (401) past the dead point or limit point, and is less than the overheat damage threshold of the shape memory alloy wires.

17. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 16, characterized in that, The pulse current has a width of 10-200ms and an amplitude of 30-300mA.

18. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 1, characterized in that, The ratio of the overall height of the actuator to the lifting stroke of the contact element (6) is less than or equal to 4:

1.

19. A micro bistable actuator based on a shape memory alloy wire drive assembly according to claim 1, characterized in that, Two alternatives to the shape memory alloy wire (102) include using a single shape memory alloy wire (102) in conjunction with a reset spring that provides a restoring force opposite to that of the shape memory alloy wire.

20. A micro bistable actuator based on a shape memory alloy wire drive assembly according to claim 19, characterized in that, The reset spring is selected from one of the following: torsion spring (4021), compression spring (5011), or spring sheet.

21. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 20, characterized in that, When the torsion spring (4021) is used, the torsion spring (4021) is disposed outside the rotating shaft (402) and connects the rotating shaft (402) and the lower frame (501).

22. A miniature bistable actuator based on a shape memory alloy wire drive assembly according to claim 20, characterized in that, When the compression spring (5011) is used, one end of the compression spring (5011) is connected to the metal component (101), and the other end is connected to the inner wall of the lower frame (501).

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