A multi-gradient shape memory alloy actuator and a manufacturing method thereof

Abstract

The application provides a multi-gradient shape memory alloy driver and a manufacturing method thereof. The driver comprises a multi-gradient shape memory alloy layer, a heat conduction layer for heat transfer with the multi-gradient shape memory alloy layer, a thermoelectric module for temperature control of the heat conduction layer, and a packaging layer flexible substrate. The multi-gradient shape memory alloy layer and the heat conduction layer are packaged between the packaging layer flexible substrate. The multi-gradient shape memory alloy layer comprises a shape memory alloy substrate and two or more micro-protrusions. The micro-protrusions are arranged on the surface of the shape memory alloy substrate away from the heat conduction layer. The internal grain structure of each micro-protrusion is different to make the phase transition temperature different, so that the number of micro-protrusion types that occur phase transition in different temperature intervals is different, thereby realizing multi-stage deformation. The driver is lightweight, high-reliability, easy to integrate, and has a multi-gradient memory effect.

Description

Technical Field

[0001] This invention relates to the field of intelligent driving materials and flexible electronics technology, and more specifically, to a multi-gradient shape memory alloy actuator and its fabrication method. Background Technology

[0002] Bionic robots and dexterous hands are attracting widespread attention in today's society. In the field of bionic robot drive technology, efficient and adaptable drive solutions have always been a research focus. Existing drive technologies are mainly divided into pneumatic and hydraulic drives, electric drives, smart material drives, and shape memory alloy drives.

[0003] Pneumatic and hydraulic drives require complex air and hydraulic systems and external control units. Traditional mechanical transmission or fluid systems require numerous moving joints, sensors, and control circuits, leading to increased weight and decreased reliability. Motor drives rely on mechanical transmission structures such as gears and linkages, resulting in bulky size and response delays. Furthermore, they require external computers or microcontrollers for real-time closed-loop control (such as PID algorithms), increasing system energy consumption and cost. Smart material drives require high-voltage power supplies and lack sufficient mechanical strength.

[0004] Traditional shape memory alloy (SMI) actuation methods employ filament-like SMI alloy wires, using a single current to heat each wire and then cool it in air to restore its shape. Response only occurs when the SMI alloy's inherent phase transition temperature is reached, resulting in a single actuation temperature and a limited range of deformation shapes, preventing multi-gradient deformation. Furthermore, traditional SMI alloys, due to their coarse grain structure and the fact that deformation only occurs after heating to relatively high inherent phase transition temperatures, suffer from slow response times (seconds) and short cycle life (approximately 10 cycles). 4 The limitations of (number of times) make it impossible to meet the high-frequency, long-duration working requirements of bionic robots. Summary of the Invention

[0005] To overcome the shortcomings and deficiencies of the prior art, the present invention aims to provide a multi-gradient shape memory alloy actuator and its manufacturing method; the actuator is lightweight, highly reliable, easy to integrate, and has a multi-gradient memory effect.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a multi-gradient shape memory alloy actuator, comprising:

[0007] Multi-gradient shape memory alloy layer;

[0008] A thermally conductive layer is used for heat transfer with the multi-gradient shape memory alloy layer;

[0009] A thermoelectric module is used for temperature control of the heat-conducting layer;

[0010] And the flexible substrate of the encapsulation layer;

[0011] The multi-gradient shape memory alloy layer and the thermally conductive layer are encapsulated between the flexible substrate of the encapsulation layer;

[0012] The multi-gradient shape memory alloy layer includes a shape memory alloy substrate and two or more types of micro-bumps; the various micro-bumps are arranged on the surface of the shape memory alloy substrate away from the thermally conductive layer; each type of micro-bump has a different internal grain structure so that the phase transition temperature is different, so that the number and types of micro-bumps undergoing phase transition are different in different temperature ranges, thereby achieving multi-level deformation.

[0013] Preferably, each microprotrusion has the same shape and size; each microprotrusion forms a different internal grain structure through laser scanning heat treatment with different laser parameters to achieve a different phase transition temperature.

[0014] Preferably, various micro-protrusions are uniformly arranged on the surface of the shape memory alloy substrate in a periodic repeating manner.

[0015] Preferably, the multi-gradient shape memory alloy layer refers to a multi-gradient shape memory alloy layer made of nickel-titanium shape memory alloy; the flexible substrate of the encapsulation layer refers to a flexible substrate of the encapsulation layer made of polydimethylsiloxane with a base agent and curing agent ratio of 10:1.

[0016] Preferably, the thermally conductive layer is a graphene thermally conductive layer; the end of the thermally conductive layer is attached to the thermoelectric module.

[0017] Preferably, the micro-protrusions are of two or three types.

[0018] The method for fabricating the multi-gradient shape memory alloy actuator is as follows: Based on the required deformation shape of the multi-gradient shape memory alloy actuator, the structural parameters of the multi-gradient shape memory alloy layer are set, including: the shape and size of the shape memory alloy substrate, the type, number and arrangement of micro-protrusions, and the shape and size of each type of micro-protrusion.

[0019] Based on the structural parameters of the multi-gradient shape memory alloy layer, the shape of the multi-gradient shape memory alloy layer is milled out, and then cleaned and dried.

[0020] Set the phase transition temperature of various micro-protrusions; set the laser parameters for laser scanning heat treatment of various micro-protrusions according to the mapping model between phase transition temperature and laser parameters; perform laser scanning heat treatment on various micro-protrusions according to the laser parameters so that the phase transition temperature of various micro-protrusions is different.

[0021] The multi-gradient shape memory alloy layer after laser scanning heat treatment is cleaned and dried;

[0022] A thermally conductive layer is attached to a multi-gradient shape memory alloy layer;

[0023] The multi-gradient shape memory alloy layer and the thermally conductive layer are encapsulated by a double-layer sandwich encapsulation process, so as to encapsulate the multi-gradient shape memory alloy layer and the thermally conductive layer between the encapsulation layer and the flexible substrate.

[0024] Preferably, the multi-gradient shape memory alloy layer is made of nickel-titanium shape memory alloy; the mapping model between the phase transition temperature and laser parameters refers to:

[0025] The heat conduction equation for laser scanning heat treatment is:

[0026]

[0027] Where ρ is the density of the nickel-titanium shape memory alloy; Cp is the specific heat capacity; is the cooling rate; k is the thermal conductivity; T is the temperature field; Q laser The term represents the laser heat source; x, y, and z are the coordinates of the laser-scanned heat-treated object in three-dimensional space, respectively; t is the laser-scanned heat-treated time; where:

[0028]

[0029] Where P is the laser power; d is the laser spot diameter; r is the radial distance from the center of the laser spot; and η is the absorption rate of the nickel-titanium shape memory alloy to the laser.

[0030] Phase transition temperature A f The relationship with the microstructure of the multi-gradient shape memory alloy layer is as follows:

[0031]

[0032] Among them, A f0 The phase transition temperature of the multi-gradient shape memory alloy layer before laser scanning heat treatment is given; ΔH is the enthalpy change of the phase transition; T0 is the reference temperature; σ is the residual stress. a is a coefficient; K is the component sensitivity coefficient; Δx Ni This represents the change in nickel content.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] 1. This invention proposes a multi-gradient shape memory alloy actuator, which abandons traditional mechanical joints and control circuits. It utilizes the hyperelasticity and shape memory effect of shape memory alloy (SMA) to achieve adaptive deformation. By heat-treating the micro-protrusions of the multi-gradient shape memory alloy layer with different laser parameters, the internal grain structure of the micro-protrusions is made different, resulting in different martensite to austenite transformation temperatures. This makes the same shape memory alloy matrix exhibit multi-region response characteristics, and gradient graded motion can be achieved without complex external programming. Through the heating of the heat-conducting layer, the micro-protrusion structure exhibits a multi-gradient shape memory effect.

[0035] 2. The thermoelectric module of the present invention can heat and cool the multi-gradient shape memory alloy layer by changing the current;

[0036] The driving principle of the multi-gradient shape memory alloy layer is as follows: The multi-gradient shape memory alloy layer is heated to the martensitic phase transformation temperature via a thermoelectric module, triggering the shape memory effect and thus driving the layer. Due to the altered internal grain structure of the micro-protrusions after laser scanning heat treatment, the phase transformation temperature for driving is lowered, resulting in a significantly improved response speed, reaching the millisecond level. Simultaneously, the finer and more uniform grain structure obtained through laser scanning heat treatment has a longer lifespan compared to the original coarse structure, extending it to 10... 6 After multiple cycles, the multi-gradient shape memory alloy layer is driven and then cooled by a thermoelectric module instead of in the air, enabling rapid cooling recovery.

[0037] 3. This invention can be applied to bionic robot fingers, medical device drives, etc., to achieve the grasping of objects with different curvatures; the flexible wrapping structure can conform to biological soft tissue or robot surface, simulating the continuous movement pattern of muscle contraction and relaxation; therefore, this invention provides a lightweight, highly reliable, and easily integrated drive solution for bionic robot fingers, effectively overcoming the limitations of existing technologies. Attached Figure Description

[0038] Figure 1 This is an exploded view of the multi-gradient shape memory alloy actuator of the present invention;

[0039] Figure 2 This is a schematic diagram of the structure of the multi-gradient shape memory alloy layer of the multi-gradient shape memory alloy actuator of the present invention;

[0040] Among them, 1 is a multi-gradient shape memory alloy layer, 11 is the first type of micro-bump, 12 is the second type of micro-bump, 13 is a shape memory alloy substrate, 2 is a thermally conductive layer, 3 is a thermoelectric module, and 4 is a flexible substrate for encapsulation. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] like Figure 1 As shown, this embodiment of a multi-gradient shape memory alloy actuator includes:

[0044] Multi-gradient shape memory alloy layer 1;

[0045] Thermal conductive layer 2 is used for heat transfer with multi-gradient shape memory alloy layer 1;

[0046] Thermoelectric module 3 is used for temperature control of heat-conducting layer 2;

[0047] And the flexible substrate of the encapsulation layer 4.

[0048] The multi-gradient shape memory alloy layer 1 adopts an integrated structure; preferably, it is made of nickel-titanium shape memory alloy. In this embodiment, the thickness of the multi-gradient shape memory alloy layer 1 is 2 mm. The multi-gradient shape memory alloy layer 1 includes a shape memory alloy substrate 13 and two or more micro-bumps; in this embodiment, there are two types of micro-bumps, namely a first type of micro-bump 11 and a second type of micro-bump 12; the first type of micro-bump 11 and the second type of micro-bump 12 are arranged in a periodic repeating manner on the surface of the shape memory alloy substrate 13 away from the heat-conducting layer 2, such as... Figure 2 As shown. The first type of micro-protrusion 11 and the second type of micro-protrusion 12 have the same shape and size; each type of micro-protrusion forms a different internal grain structure through laser scanning heat treatment with different laser parameters to achieve different phase transition temperatures. In different temperature ranges, the types and numbers of micro-protrusions undergoing phase transitions are different, thereby achieving multi-level deformation. In this embodiment, the multi-gradient shape memory alloy actuator has two levels of bending deformation.

[0049] The thermally conductive layer 2 is preferably a graphene thermally conductive layer; the end of the thermally conductive layer 2 is attached to the thermoelectric module 3.

[0050] A multi-gradient shape memory alloy layer 1 and a thermally conductive layer 2 are encapsulated between a flexible substrate 4. The flexible substrate 4 is a flexible substrate 4 made of polydimethylsiloxane (PDMS) with a base agent to curing agent ratio of 10:1.

[0051] The principle behind this invention is the shape memory effect, which originates from the thermoelastic martensitic phase transformation and its reversibility within the material. When the temperature drops to a specific critical point (the initiation temperature of the martensitic phase transformation), the parent phase of the alloy (austenite, a high-symmetry crystal structure stable at high temperatures) transforms into the martensitic phase (a low-symmetry structure stable at low temperatures) through shear deformation. This process allows the material to undergo significant plastic deformation under external force without destroying the crystal integrity. When the material is reheated above the austenitic phase transformation temperature, the martensite reverts to the parent phase through a reverse phase transformation. The high symmetry reconstruction of the crystal structure drives the macroscopic shape to return to its initial state, thus achieving the "memory" function. If the material undergoes specific training, it can also achieve two-way shape memory (reversibly switching between two shapes) during temperature cycling. Furthermore, when the temperature is higher than the austenitic phase transformation completion temperature, external stress can directly induce the austenite to transform into martensite, which spontaneously reverses to the parent phase after unloading, exhibiting hyperelasticity (large strain reversible deformation). The essence of this phase transition behavior is thermodynamically driven lattice reconstruction, with energy changes dominated by the competition between entropy and enthalpy.

[0052] In this invention, when the heat-conducting layer is cooled, the multi-gradient shape memory alloy layer 1 does not deform, and the actuator remains flat. When the thermoelectric module 3 heats the heat-conducting layer 2, the multi-gradient shape memory alloy layer 1 undergoes gradient deformation according to the temperature, and the actuator undergoes gradient bending. After the heat-conducting layer is cooled again, the multi-gradient shape memory alloy layer can return to its initial state, and the actuator can return to its flat state.

[0053] The thermoelectric module used in this invention is made of a thermoelectric material. Thermoelectric materials can directly convert heat energy into electrical energy through the Seebeck effect (when two different conductors form a closed circuit, if the temperatures of the two junctions are different, a thermoelectric potential (thermoelectric electromotive force, the principle basis of thermocouple temperature measurement) and the Peltier effect (when current flows through a circuit composed of two different conductors, heat absorption or release occurs at the junctions (related to the direction of the current), commonly used in refrigeration or heating modules). Heating and cooling effects are achieved simply by changing the direction of the current. This invention uses the thermoelectric module to rapidly heat a multi-gradient shape memory alloy layer to its phase transition temperature to achieve bending deformation, and then rapidly cools the multi-gradient shape memory alloy layer by changing the direction of the current in the thermoelectric module, completing the recovery process.

[0054] The fabrication method of the multi-gradient shape memory alloy actuator in this embodiment is as follows:

[0055] Based on the required deformation shape of the multi-gradient shape memory alloy actuator, the structural parameters of the multi-gradient shape memory alloy layer 1 are set, including: the shape and size of the shape memory alloy substrate, the type, number and arrangement of micro-bumps, and the shape and size of each micro-bump.

[0056] The nickel-titanium shape memory alloy sheet was placed on a surface grinder and polished on both sides using 1000-grit silicon carbide sandpaper to remove the surface oxide layer and processing defects.

[0057] Based on the structural parameters of the multi-gradient shape memory alloy layer 1, the shape of the multi-gradient shape memory alloy layer 1 is milled; then it is placed in anhydrous ethanol and ultrasonically cleaned for 15 minutes to remove debris, and then the surface is dried with high-purity nitrogen.

[0058] Set the phase transition temperature for various micro-protrusions; based on the mapping model between the phase transition temperature and the multi-gradient shape memory alloy layer 1 structure, set the laser parameters for laser scanning heat treatment of various micro-protrusions;

[0059] Specifically, the mapping model between phase transition temperature and the multi-gradient shape memory alloy layer 1 structure refers to:

[0060] The heat conduction equation for laser scanning heat treatment is:

[0061]

[0062] Where ρ is the density of the nickel-titanium shape memory alloy; Cp is the specific heat capacity; is the cooling rate; k is the thermal conductivity; T is the temperature field; Q laser The term represents the laser heat source; x, y, and z are the coordinates of the laser-scanned heat-treated object in three-dimensional space, respectively; t is the laser-scanned heat-treated time; where:

[0063]

[0064] Where P is the laser power; d is the laser spot diameter; r is the radial distance from the center of the laser spot; and η is the absorption rate of the nickel-titanium shape memory alloy to the laser (for example, the absorption rate of the nickel-titanium shape memory alloy to a 1064nm laser is η≈0.3–0.5).

[0065] Phase transition temperature A f The relationship with the microstructure of the multi-gradient shape memory alloy layer 1 is as follows:

[0066]

[0067] Among them, A f0 The phase transition temperature of the multi-gradient shape memory alloy layer 1 without laser scanning heat treatment is given; ΔH is the enthalpy change of the phase transition; T0 is the reference temperature (A). f0 +273.15K); σ is the residual stress. a is a coefficient; K is the component sensitivity coefficient; Δx NiThis represents the change in nickel content; for example, the nickel-titanium shape memory alloy used in this embodiment is (55wt% nickel, 45wt% titanium, Flexinol; Dynalloy), so the change in nickel content is calculated with a nickel base of 55wt%.

[0068] Specifically, it is a two-way coupling design: phase transition temperature A f For the target → estimate σ, Δx Ni →Initial selection of laser parameters →Verification of heat conduction equation →Experimental calibration →Correction of laser parameters. If the measured phase transition temperature A... f If there is a deviation from the target, the laser parameters need to be adjusted (e.g., laser power from 20W to 25W) and the heat conduction equation needs to be recalculated.

[0069] After obtaining the laser parameters for laser scanning heat treatment of various micro-protrusions, a fiber laser (wavelength 1064nm) is used to perform laser scanning heat treatment on various micro-protrusions according to the laser parameters, so that the phase transition temperatures of various micro-protrusions are different.

[0070] Laser scanning heat treatment is confined to the top of the micro-protrusion, achieving selective control through precise positioning to ensure the phase transition temperature A. f The reliability of the gradient design is ensured. Dynamic optical path control is used to scan only the micro-protrusions of the target type, avoiding heating of adjacent areas.

[0071] For example, the laser parameters for the first type of micro-protrusion are: laser power 20W, scanning speed 1000mm / s, and laser spot diameter 31.5μm. After heat treatment, a nanocrystalline (grain size 50-100nm) strengthening layer is formed inside the first type of micro-protrusion, and the phase transition temperature increases to 80-100℃. For the second type of micro-protrusion, another set of laser parameters is used: laser power 10W, scanning speed 2000mm / s, and laser spot diameter 31.5μm. After heat treatment, a coarse-grained (grain size 5-10μm) layer is formed inside the second type of micro-protrusion, and the phase transition temperature decreases to 40-60℃.

[0072] The multi-gradient shape memory alloy layer 1 after laser scanning heat treatment was ultrasonically cleaned (anhydrous ethanol, 15 minutes) and dried to ensure that there were no residual thermal oxidation products on the surface.

[0073] A thermally conductive layer 2 is attached to a multi-gradient shape memory alloy layer 1. The surface temperature of the multi-gradient shape memory alloy layer is monitored in real time using an infrared thermal imager, and the critical transition temperatures of the first type of micro-bump (phase transition temperature T1) and the second type of micro-bump (phase transition temperature T2) are recorded to determine the driving gradient.

[0074] A dual-layer sandwich encapsulation process is used to encapsulate a multi-gradient shape memory alloy layer 1 and a thermally conductive layer 2 that are bonded together. Specifically, polydimethylsiloxane (PDMS) base agent and curing agent are mixed at a mass ratio of 10:1 and manually stirred for 5 minutes until dense and uniform fine bubbles appear. Then, the mixture is placed in a vacuum defoaming chamber and vacuum-treated for 10 minutes to eliminate bubbles, thus producing a PDMS prepolymer. The multi-gradient shape memory alloy layer 1 and the thermally conductive layer 2 (with the micro-protruding side facing up) are laid flat in a mold, and the PDMS prepolymer is poured in until it completely covers the multi-gradient shape memory alloy layer 1. The mold is placed in a 120°C oven for curing for 2 hours. After curing, the mold is peeled off and inverted so that the thermally conductive layer 2 faces up. The PDMS prepolymer is poured in again and the same curing operation is performed. After cooling to room temperature, the mold is demolded to obtain an integrated encapsulated multi-gradient shape memory alloy actuator.

[0075] Example 2

[0076] This embodiment discloses a multi-gradient shape memory alloy actuator, which differs from Embodiment 1 in that: in this embodiment, there are three or more types of microbumps; for example, three, four, or even more. Generally, the number and types of microbumps correspond to the deformation levels of the multi-gradient shape memory alloy actuator. The various microbumps are arranged in a periodic repeating pattern on the surface of the shape memory alloy substrate away from the thermally conductive layer. To facilitate the overlap of phase transition temperatures of the microbumps, it is preferable to have two or three types of microbumps.

[0077] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A multi-gradient shape memory alloy actuator, characterized in that: include: Multi-gradient shape memory alloy layer; A thermally conductive layer is used for heat transfer with the multi-gradient shape memory alloy layer; A thermoelectric module is used for temperature control of the heat-conducting layer; And the flexible substrate of the encapsulation layer; The multi-gradient shape memory alloy layer and the thermally conductive layer are encapsulated between the flexible substrate of the encapsulation layer; The multi-gradient shape memory alloy layer includes a shape memory alloy substrate and two or more types of micro-bumps; the various micro-bumps are arranged on the surface of the shape memory alloy substrate away from the thermally conductive layer; each type of micro-bump has a different internal grain structure so that the phase transition temperature is different, so that the number and types of micro-bumps undergoing phase transition are different in different temperature ranges, thereby achieving multi-level deformation; Each microprotrusion has the same shape and size; each microprotrusion undergoes laser scanning heat treatment with different laser parameters to form different internal grain structures, thereby achieving different phase transition temperatures; The multi-gradient shape memory alloy layer refers to a multi-gradient shape memory alloy layer made of nickel-titanium shape memory alloy; the flexible substrate of the encapsulation layer refers to a flexible substrate of the encapsulation layer made of polydimethylsiloxane with a base agent and curing agent ratio of 10:

1.

2. The multi-gradient shape memory alloy actuator according to claim 1, characterized in that: Various micro-protrusions are evenly arranged on the surface of the shape memory alloy substrate in a periodic manner.

3. The multi-gradient shape memory alloy actuator according to claim 1, characterized in that: The thermally conductive layer is a graphene thermally conductive layer; the end of the thermally conductive layer is attached to the thermoelectric module.

4. The multi-gradient shape memory alloy actuator according to claim 1, characterized in that: The micro-protrusions are of two or three types.

5. The method for fabricating the multi-gradient shape memory alloy actuator according to claim 1, characterized in that: Based on the required deformation shape of the multi-gradient shape memory alloy actuator, the structural parameters of the multi-gradient shape memory alloy layer are set, including: the shape and size of the shape memory alloy substrate, the type, number and arrangement of micro-bumps, and the shape and size of each micro-bump. Based on the structural parameters of the multi-gradient shape memory alloy layer, the shape of the multi-gradient shape memory alloy layer is milled out, and then cleaned and dried. Set the phase transition temperature of various micro-protrusions; set the laser parameters for laser scanning heat treatment of various micro-protrusions according to the mapping model between phase transition temperature and laser parameters; perform laser scanning heat treatment on various micro-protrusions according to the laser parameters so that the phase transition temperature of various micro-protrusions is different. The multi-gradient shape memory alloy layer after laser scanning heat treatment is cleaned and dried; A thermally conductive layer is attached to a multi-gradient shape memory alloy layer; The multi-gradient shape memory alloy layer and the thermally conductive layer are encapsulated by a double-layer sandwich encapsulation process, so as to encapsulate the multi-gradient shape memory alloy layer and the thermally conductive layer between the encapsulation layer and the flexible substrate.

6. The manufacturing method according to claim 5, characterized in that: The multi-gradient shape memory alloy layer refers to a nickel-titanium shape memory alloy; the mapping model between the phase transition temperature and laser parameters refers to: The heat conduction equation for laser scanning heat treatment is: ； Where ρ is the density of the nickel-titanium shape memory alloy; Cp is the specific heat capacity; is the cooling rate; k is the thermal conductivity; T is the temperature field; Q laser The term represents the laser heat source; x, y, and z are the coordinates of the laser-scanned heat-treated object in three-dimensional space, respectively; t is the laser-scanned heat-treated time; where: ； Where P is the laser power; d is the laser spot diameter; r is the radial distance from the center of the laser spot; and η is the absorption rate of the nickel-titanium shape memory alloy to the laser. Phase transition temperature A f The relationship with the microstructure of the multi-gradient shape memory alloy layer is as follows: ； Among them, A f0 The phase transition temperature of the multi-gradient shape memory alloy layer before laser scanning heat treatment is given; ΔH is the enthalpy change of the phase transition; T0 is the reference temperature; σ is the residual stress. , a is a coefficient; K is the component sensitivity coefficient; Δx Ni This represents the change in nickel content.

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