Sectional rigidity-adjustable shape memory alloy driving actuator and control method thereof

Abstract

The invention belongs to the technical field of intelligent actuators and flexible drivers, and relates to a sectional rigidity-adjustable shape memory alloy driving actuator and a control method thereof. The actuator comprises a flexible shell, an isolation element, a shape memory alloy driving element and a phase change rigidity regulation and control material, the isolation element divides the flexible shell into multiple sections of cavity structures which are axially arranged, all cavities are filled with the phase change rigidity regulation and control material, the phase change temperatures are not completely the same, and all temperature parameters and driving force meet the preset matching relation. According to the control method, the heating temperature of the shape memory alloy driving element is controlled, so that the phase change stiffness regulation and control materials are subjected to phase change in sequence to achieve sequential unlocking of the equivalent stiffness of the cavity, and multi-section controllable equivalent stiffness regulation can be achieved under a single driving source. The actuator is simple in structure, programmable in response and suitable for the fields of soft robots, deformable supporting structures, intelligent execution systems and the like.

Description

Technical Field

[0001] This invention belongs to the field of intelligent actuators and flexible actuators, and relates to a segmented shape memory alloy drive actuator with adjustable stiffness and its control method. Background Technology

[0002] Shape memory alloy actuators, with their advantages of high output force and compact structure, are widely researched and applied in flexible actuation fields such as soft robotics, wearable rehabilitation medical devices, and intelligent flexible support structures, and are one of the core components of flexible actuation systems. In these applications, actuators need to possess both support capabilities and structural compliance. Shape memory alloy actuators with a single constant equivalent stiffness cannot meet the dynamic equivalent stiffness control requirements at different working stages. Therefore, variable equivalent stiffness technology has become a key research and development direction for this type of actuator, and existing technologies have proposed various equivalent stiffness control schemes.

[0003] Patent application CN117961967A discloses a flexible rod structure and actuator with variable equivalent stiffness. This technology adjusts the equivalent stiffness of the flexible rod by changing the number, size, and arrangement of shape memory alloys, or by combining different elastomers to control the modulus distribution, utilizing the deformation of the shape memory alloys to adapt to the equivalent stiffness requirements of various scenarios. However, this technology has significant drawbacks: its equivalent stiffness adjustment relies on the independent movement of multiple shape memory alloys, requiring a multi-channel current control system. This not only leads to a complex overall actuator structure and high operating energy consumption, but also presents challenges in the coordinated control of multiple driving components and a high failure rate. Furthermore, this solution relies on changes in the modulus of the elastomers to achieve equivalent stiffness adjustment, which can only change gradually and with limited amplitude, achieving only a few times modulus change. It cannot achieve a "lock-unlock" type abrupt change in equivalent stiffness, making it difficult to meet the application scenarios such as soft robots and flexible support structures that have strict requirements for abrupt changes in equivalent stiffness. Furthermore, this technology lacks the ability to work synergistically with "local compliance + overall support". When the shape memory alloy adjusts the equivalent stiffness, it will cause the overall equivalent stiffness of the flexible rod to change synchronously. It cannot achieve the effect of compliant deformation in local areas and rigid support in other areas, and cannot meet the actual needs of soft robots, wearable devices and other devices that require precise control of local equivalent stiffness.

[0004] Overall, existing technologies related to variable equivalent stiffness in shape memory alloy actuators mostly rely on structural modulus distribution control or multi-drive control to achieve equivalent stiffness changes. They generally struggle to achieve independent adjustment of multiple equivalent stiffness segments under a single drive source, and lack effective sequential and gradient equivalent stiffness control mechanisms. Furthermore, they suffer from limited equivalent stiffness variation range and lack the ability to precisely control local equivalent stiffness. These limitations make them unsuitable for applications such as soft robots and wearable rehabilitation devices, which require simple actuator structures, segmented sequential equivalent stiffness control, and a balance between local compliance and overall support. Therefore, there is an urgent need to develop a novel shape memory alloy driven actuator to address these issues. Summary of the Invention

[0005] The purpose of this invention is to solve the problems existing in the prior art and to provide a segmented adjustable stiffness shape memory alloy drive actuator and its control method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A segmented, adjustable stiffness shape memory alloy driven actuator, comprising:

[0008] A flexible outer shell with a hollow columnar structure;

[0009] An isolation element consisting of a cavity structure that divides the hollow portion of a flexible shell into at least two segments arranged sequentially along the axial direction of the flexible shell;

[0010] Shape memory alloy drive element that runs through all cavity structures along the axial direction of the flexible shell;

[0011] The phase change stiffness control material is filled in each cavity structure. The phase change stiffness control material is a material that has a phase change temperature, is rigid when it is below the phase change temperature, and is soft when it is above or equal to the phase change temperature.

[0012] The phase transition temperatures of the phase transition stiffness control materials within different cavity structures are not entirely the same; the lowest phase transition temperature is denoted as T. min The highest phase transition temperature is denoted as T. max The austenitization completion temperature of shape memory alloy drive components is denoted as A. f The highest stable temperature that a shape memory alloy driving element can reach after being energized is denoted as T. s The ambient temperature is denoted as T. e T min A f T max All are greater than T e And less than T s ;

[0013] Along a certain direction parallel to the axis of the flexible shell, for any two adjacent cavity structures, the phase transition temperature of the phase transition stiffness control material located in the first cavity structure is greater than or equal to the phase transition temperature of the phase transition stiffness control material located in the second cavity structure.

[0014] The driving force generated by the shape memory alloy driving element during the austenitization process is greater than the minimum force required for the flexible shell to undergo reversible deformation, and greater than the structural resistance when any phase transformation stiffness control material is in a softened state (including the residual equivalent stiffness of the phase transformation stiffness control material in a softened state, the elastic resistance of the flexible shell, and the structural friction force), and less than the structural resistance when any phase transformation stiffness control material is in a rigid state. This ensures that structural deformation is preferentially concentrated in the softened cavity structure area, while the unsoftened cavity structure area remains rigidly locked, achieving precise local controllable deformation.

[0015] As a preferred technical solution:

[0016] As described above, a segmented adjustable stiffness shape memory alloy driven actuator has a seamless gap between the shape memory alloy driving element and the isolation element to prevent the phase change stiffness control materials in adjacent cavity structures from mixing.

[0017] As described above, a segmented shape memory alloy drive actuator with adjustable stiffness, T e <T min ≤A f ≤T max <T s .

[0018] The above temperature parameter matching relationship (T) e <T min ≤A f ≤T max <T s In the context of shape memory alloy drive elements, the austenitization completion temperature A is... f Located within the phase transition temperature range of multi-stage phase transition stiffness control materials (i.e., satisfying T... min ≤A f ≤T max This allows at least a portion of the phase change stiffness control material to soften before the shape memory alloy driving element during temperature rise, achieving segmented equivalent stiffness control. To further ensure the control accuracy of sequential unlocking, the phase change temperatures of the phase change stiffness control materials in each cavity structure arranged sequentially along the axial direction of the flexible shell are labeled in ascending order as T1, T2, ..., T... i T i+1 ... T n Where n is the total number of segments in the cavity structure, and T1 is T min T n That is, Tmax By rationally designing the phase transformation temperatures of each stage, the austenitization completion temperature A is achieved. f Satisfy, T i f <T i+1 The matching relationship is used to ensure that the phase transition temperature is ≤T i The preceding cavity first completes the softening process; the driving action of the shape memory alloy driving element only occurs in the softened cavity section, with a phase transition temperature ≥ T. i+1 The subsequent cavities maintain high equivalent stiffness, forming a "soft-hard collaborative driving structure." This avoids the problem of all cavities softening simultaneously or failing to soften at all due to improper temperature matching, thus preserving the core effect of segmented unlocking. Simultaneously, the electrical input power of the shape memory alloy driving element is set to overcome the latent heat of phase change in the phase change stiffness control material and system heat dissipation losses, ensuring its highest stable temperature T after energization. s Higher than the highest phase transition temperature T of all phase transition stiffness modulated materials max .

[0019] As described above, the segmented adjustable stiffness shape memory alloy drive actuator has a phase transition temperature of 40-100℃ for the phase transition stiffness control material. This temperature range is compatible with the achievable heating temperature of the shape memory alloy drive element and can cover the phase transition range of various phase transition stiffness control materials. This ensures that the segmented adjustable stiffness shape memory alloy drive actuator maintains a high structural equivalent stiffness under normal temperature conditions and can achieve stable and controllable segmented equivalent stiffness adjustment when electrically heated.

[0020] As described above, a segmented shape memory alloy driven actuator with adjustable stiffness undergoes solid-liquid phase transition, glass-rubber transition, solid-solid phase transition, crystallization-melting transition, or reversible crosslinking transition when the phase transition temperature is above or equal to the phase transition temperature.

[0021] As described above, in a segmented adjustable stiffness shape memory alloy driven actuator, the phase change stiffness control material is a phase change material, or a phase change composite material formed by combining a phase change material with a thermally conductive filler; the phase change material is selected from at least one of metallic phase change materials, metallic alloy phase change materials, organic phase change materials, inorganic salt phase change materials, thermoplastic polymer phase change materials, and hydrogel phase change materials.

[0022] As described above, the segmented adjustable stiffness shape memory alloy driven actuator has a flexible shell structure that is a hollow cylinder, a hollow elliptical cylinder, or a hollow polygonal prism (with a polygonal cross-section). The material is silicone rubber, polyurethane elastomer, thermoplastic elastomer, natural rubber, or synthetic rubber. The thickness is within a range that allows the shell to undergo elastic deformation under the drive of the shape memory alloy driven element while maintaining the sealing of the cavity structure.

[0023] ​As described above, in a segmented shape memory alloy drive actuator with adjustable stiffness, the isolation element is a heat insulation layer or a thermal resistance structure to reduce thermal coupling.

[0024] As described above, a segmented adjustable stiffness shape memory alloy drive actuator uses a shape memory alloy drive element that is a shape memory alloy spring or a shape memory alloy fiber.

[0025] The segmented adjustable stiffness shape memory alloy drive actuator described above further includes:

[0026] A power supply module for powering shape memory alloy drive components;

[0027] The control module is used to control the magnitude and duration of the power supply current of the power module. By adjusting the magnitude and duration of the power supply current, the control module controls the phase change process of the phase change stiffness regulating material in each cavity structure, thereby realizing the segmented control of the equivalent stiffness of the actuator.

[0028] As described in any of the preceding claims, a drive control method for a segmented adjustable stiffness shape memory alloy drive actuator continuously supplies power to the shape memory alloy drive element until T... s >T max During this process, the temperature of the shape memory alloy driving element sequentially reaches the phase transition temperature of the phase transition stiffness control material in different cavity structures, thereby realizing the graded unlocking of the equivalent stiffness of each cavity structure, and thus realizing the segmented deformation and controllable equivalent stiffness adjustment of the actuator.

[0029] In the initial state, the phase transformation stiffness control materials in each cavity structure are in an environment below their own phase transformation temperature, and are in a solid or high modulus rigid state, so the actuator as a whole exhibits high equivalent stiffness; at this time, the shape memory alloy driving element is in the martensitic state, and the overall structure of the actuator maintains a stable shape.

[0030] When power is continuously supplied to the shape memory alloy driving element, the current generates Joule heat through the driving element, causing its temperature to gradually rise. Since the phase change stiffness control materials in each cavity structure have different phase change temperatures and are orderly distributed along the actuator axis, as the temperature of the driving element rises, the material in the cavity structure with the lowest phase change temperature reaches the phase change temperature first, undergoes a phase change, and changes from a rigid state to a softened state. The equivalent stiffness of the corresponding cavity region is significantly reduced, thus unlocking the stiffness of that section.

[0031] As the temperature of the drive element continues to rise, it gradually undergoes a martensitic-austenitic phase transformation and generates recovery strain and driving force during the austenitization process. When the driving force is greater than the structural resistance of the softened cavity region, the drive element will cause the softened region to deform, while the cavity that has not reached the phase transformation temperature will still maintain a high equivalent stiffness locked state. The deformation is preferentially concentrated in the softened region, realizing the local controllable deformation of the actuator.

[0032] As the power supply continues, the temperature of the drive element rises further, reaching higher phase change temperatures in sequence. The phase change stiffness control material in each cavity structure undergoes phase change gradually in a preset order, and the low equivalent stiffness region of the actuator gradually expands along the axial direction. Under continuous driving action, the shape memory alloy drive element drives each softened section to undergo segmented deformation in sequence, ultimately realizing the segmented equivalent stiffness control and controllable shape change of the entire actuator.

[0033] When the power supply is stopped, the shape memory alloy drive element and actuator as a whole gradually cool down, the drive element undergoes a reverse phase transformation and gradually returns to the martensitic state; at the same time, the phase transformation stiffness control material in each cavity structure returns to the rigid state, the equivalent stiffness of each cavity region gradually recovers, the actuator regains high overall equivalent stiffness, and completes a reversible stiffness control cycle.

[0034] From a mechanical equivalence perspective, the actuator as a whole can be considered as being composed of multiple cavity units with different equivalent stiffnesses connected in series. Let the equivalent stiffness of the nth cavity unit be k. i When the phase transition stiffness control material in a certain cavity undergoes a phase transition, its equivalent stiffness k i This will significantly reduce, thus leading to a decrease in the overall equivalent stiffness K of the actuator. ep Consequently, the stiffness decreases; as the number of phase-change unlocked cavities increases, the overall equivalent stiffness of the actuator decreases in a stepwise manner, achieving a segmented adjustable equivalent stiffness response. By rationally designing the phase change temperature, cavity size, and structural layout of the phase change stiffness control material in each cavity, precise control of the actuator's equivalent stiffness change sequence, deformation position, and driving process can be achieved, constructing an intelligent execution structure with programmable segmented equivalent stiffness control capabilities.

[0035] Beneficial effects:

[0036] (1) This invention uses a single shape memory alloy driving element in conjunction with phase change stiffness control materials with different phase change temperatures to unlock the equivalent stiffness in sequence by naturally forming the temperature gradient. Only one current adjustment is needed to achieve multi-segment equivalent stiffness control, which simplifies the control system structure and effectively reduces energy consumption and equipment failure rate.

[0037] (2) The present invention relies on the phase change of the phase change stiffness control material to achieve the equivalent stiffness change. The elastic modulus of the material before and after the phase change is significantly different, which can achieve a step change in the equivalent stiffness and achieve the equivalent stiffness control effect of "lock-unlock".

[0038] (3) The present invention can unlock the equivalent stiffness of each cavity structure in sequence by controlling the heating temperature of the shape memory alloy driving element, thereby achieving the effect of compliant deformation of local cavity areas while maintaining rigid support in other areas, and has the ability to coexist in the state of "local compliance + overall support".

[0039] (4) The present invention reduces the thermal coupling between the cavity structures by setting isolation elements. At the same time, the driving force of the shape memory alloy driving element matches the resistance of the flexible shell and the phase change stiffness control material, ensuring the accuracy and stability of the equivalent stiffness segment control. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the segmented adjustable stiffness shape memory alloy driven actuator of Example 1;

[0041] Figure 2 This is a schematic diagram showing the position or connection relationship of the isolation element, flexible shell, shape memory alloy driving element, first phase change stiffness control material, second phase change stiffness control material, and three-phase change stiffness control material in Example 1.

[0042] Figure 3 This is a top view of the isolation element in Example 1;

[0043] Figure 4 This is a schematic diagram of the flexible shell structure in Example 1;

[0044] Figure 5 This is a schematic diagram of the shape memory alloy driving element in Example 1;

[0045] Figure 6 This is a front view structural schematic diagram of the first phase change stiffness control material, the second phase change stiffness control material, and the third phase change stiffness control material in Example 1.

[0046] Figure 7 This is a top view schematic diagram of the first phase change stiffness control material, the second phase change stiffness control material, and the third phase change stiffness control material in Example 1.

[0047] Figures 1-7In the middle, 1-power module, 2-control module, 3-wire, 4-isolation element, 5-flexible shell, 6-shape memory alloy driving element, 7-first phase change stiffness control material, 8-second phase change stiffness control material, 9-third phase change stiffness control material, 10-A-section cavity structure, 11-B-section cavity structure, 12-C-section cavity structure.

[0048] Figure 8 This is a schematic diagram of the sequential stiffness unlocking and deformation process of the segmented adjustable stiffness shape memory alloy driven actuator in Example 1; where a corresponds to the initial state, b corresponds to the single-segment local deformation state after the stiffness of segment A cavity structure is unlocked, c corresponds to the two-segment sequential deformation state after the stiffness of segment A cavity structure and segment B cavity structure is unlocked, and d corresponds to the full-segment deformation state after the stiffness of segment A cavity structure, segment B cavity structure and segment C cavity structure are all unlocked. Detailed Implementation

[0049] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0050] The following are the test methods for the relevant performance indicators in each embodiment:

[0051] Phase transformation temperature: For phase transformation materials of metallic alloys (such as Bi-In-Sn low-melting-point alloys), the phase transformation temperature refers to the melting point, which is the characteristic temperature at which the material undergoes a solid-liquid phase transformation, changing from a solid to a liquid state. It is also the key temperature at which its equivalent stiffness decreases significantly from a rigid state to a softened state. The test method refers to the standard ASTM E794-24: A sample of a certain mass is placed in the sample crucible of a differential scanning calorimeter (TA Q2500), and heating and cooling scans are performed under an inert atmosphere. The heating rate and cooling rate are both set to 10℃ / min, and the scanning temperature range covers the phase transformation range of the material (the phase transformation range can be set to 0-150℃). By analyzing the position of the endothermic peak in the DSC curve, the melting point of the material is determined as the phase transformation temperature.

[0052] For thermoplastic polymers, the phase transition temperature refers to the glass transition temperature, which is the characteristic temperature at which the material undergoes a glass-to-rubber transition and its equivalent stiffness decreases significantly. The test method refers to the standard ASTM E1356-08: Differential scanning calorimeter (TA Q2500) is used for testing. The sample is placed in the test device, and a programmed temperature scan is performed under inert atmosphere conditions. The heating rate is set to 10℃ / min. The glass transition temperature is determined as the phase transition temperature by analyzing the baseline abrupt change or modulus abrupt change point that appears in the heat flow curve or storage modulus change curve.

[0053] For low-melting-point metal particle-polymer microcapsule composite phase change materials, the phase change temperature refers to the overall melting point of the material, that is, the characteristic temperature at which the internal low-melting-point metal phase undergoes a solid-liquid phase change, significantly reducing the overall equivalent stiffness of the material. The test method refers to the standard ASTM E794-24: a certain mass of sample is placed in the sample crucible of a differential scanning calorimeter (TA Q2500), and heating and cooling scans are performed under inert atmosphere. The heating and cooling rates are both set to 10℃ / min, and the scanning temperature range covers the phase change range of the material (the phase change range can be set to 0-150℃). The melting point of the material is determined by analyzing the position of the endothermic peak in the DSC curve as the phase change temperature.

[0054] Whether the thermal stability requirements are met: Place the sample in a constant temperature test chamber and increase the temperature in stages from 25℃ to 50℃ to 75℃ to 100℃ to 125℃ to 150℃, holding each temperature stage for 30 minutes. Observe whether the sample shows cracking, melting, deformation or a significant decrease in elastic modulus. If the sample still maintains structural integrity at the highest test temperature of 150℃, it is determined that the thermal stability requirements are met.

[0055] Austenitizing completion temperature A f Referring to standard ASTM E794-24, a differential scanning calorimeter (TA Q2500) was used for testing. Under a nitrogen protective atmosphere, temperature scans were performed within the range of 0-200℃ at heating and cooling rates of 10℃ / min. The austenitizing completion temperature A was determined by analyzing the positions of the endothermic and exothermic peaks in the DSC heat flow curves. f .

[0056] Maximum stable temperature T sThe sample was connected to a current-driven circuit, and the driving current was gradually increased to raise the sample temperature. The sample temperature was recorded in real time using an infrared thermal imager (FLIR E96), and the changes in driving force were simultaneously acquired using an Instron 5966 material testing machine. The sample was sequentially held at temperature steps of 30℃, 60℃, 90℃, 120℃, and 150℃ for 3 minutes each, and the shape recovery ability and structural stability of the sample were observed. If the sample could stably cycle and actuate at this temperature without significant performance degradation, then this temperature was determined to be the highest stable temperature To of the shape memory alloy's electrothermal response. s Sample temperature measurement and cycle performance evaluation were performed in accordance with standard ASTM F2082-19.

[0057] Monofilament drive output force: Referring to standard GB / T 1040.2-2022, the sample is fixed between the fixtures of the mechanical testing device (Instron 5966) and an initial pre-deformation is applied so that the sample is just under tension. The sample is then heated to the highest stable temperature T. s The sample generates restoring force under the shape memory effect. The force change curve is recorded in real time by a force sensor. The maximum output restoring force (i.e., the single-filament drive output force) is tested and recorded to characterize the actuation performance of the drive element.

[0058] Equivalent stiffness: Fix one end of the sample, apply a small displacement Δx to the other end, measure the corresponding reaction force F, and calculate the equivalent stiffness using the formula... Calculate the equivalent stiffness k ep The heating of different cavity segments is controlled by shape memory alloy driving elements, so that the phase change stiffness control material reaches the phase change temperature in sequence. The overall equivalent stiffness of the structure after each segment is activated is measured, and the relationship curve between the equivalent stiffness and the number of segments is plotted. To ensure the repeatability of the test, each test is performed in 3 cycles and the average value is taken. The test method is adapted to the standards ASTM E111-17 and ASTM D575-91 (2018).

[0059] Bending angle: Fix one end of the sample and keep the other end free. Heat the sample by applying current and temperature (phase change temperature of each phase change material) to induce bending deformation. Record the bending state of the sample using an image acquisition device or angle measuring instrument, and calculate the bending angle using geometric measurement or image analysis methods. To ensure test repeatability, the initial length of the sample, the fixed position, and the ambient temperature must be recorded. Multiple cyclic tests can be performed. The test method is adapted to ASTM F2082-23.

[0060] Bending angle control accuracy: Conduct multiple repeated drive tests under the same driving conditions and record the actual angle when the target bending angle is reached each time; evaluate the bending angle control accuracy by statistically analyzing the deviation and standard deviation between the target angle and the actual angle; the test method is adapted to ASTM F2082-19.

[0061] Phase transition unlocking response time: The sample is placed in an initial rigid state and heated by passing a fixed working current (the optimal working current can be determined by testing different currents). The sample is monitored synchronously by an infrared thermal imager (FLIR E96) and a displacement sensor. The time interval from the start of heating to the softening of the phase transition stiffness control material and the generation of measurable deformation in the structure is recorded. This time interval is the phase transition unlocking response time.

[0062] Axial recovery deformation: A preset tensile deformation is applied to the sample until it is just under tension, then it is fixed and heated to the austenitization completion temperature A. f The above describes the process of recording sample length changes using a displacement measuring device and calculating the deformation required for the sample to return to its original length. The test method is adapted to the standard ASTM F2082-19.

[0063] Example 1

[0064] A segmented shape memory alloy driven actuator with adjustable stiffness, such as Figures 1-7 As shown, it includes a flexible shell 5, an isolation element 4, a first phase change stiffness control material 7, a second phase change stiffness control material 8, a third phase change stiffness control material 9, a power supply module 1, and a control module 2.

[0065] The flexible shell 5 has a hollow cylinder structure with an outer diameter of 15mm, an axial length of 120mm, a wall thickness of 2mm, and is made of silicone rubber with thermal stability that meets the requirements (manufacturer: Smooth-On, grade: Ecoflex 00-30).

[0066] The insulating element 4 divides the hollow part of the flexible shell 5 into three cavity structures arranged sequentially along the axial direction. The three cavity structures are referred to as cavity structure A 10, cavity structure B 11, and cavity structure C 12, respectively. The axial length of each cavity structure is the same. The insulating element 4 is a silicone rubber heat insulation layer (material is the same as that of the flexible shell 5), and the thickness of the insulating element 4 is 4mm.

[0067] The shape memory alloy driving element 6 runs through all the cavity structures along the axial direction of the flexible shell 5; the shape memory alloy driving element 6 is a shape memory alloy wire (manufacturer: Jiangyin Peier Technology Co., Ltd.), with a diameter of 0.8 mm, a length of 120 mm, and an austenitization completion temperature A. f The highest stable temperature is 90℃, and the highest stable temperature is T. sThe temperature is 150℃, the single-wire drive output force is 3.8N, and the shape memory alloy wire is covered with a 1mm thick silicone rubber insulation layer (material is the same as the flexible shell 5).

[0068] The first phase transformation stiffness control material 7 is filled in the cavity structure 10 of section A. The first phase transformation stiffness control material 7 is a Bi-In-Sn low-melting-point alloy (Bi 50wt%, In 36wt%, Sn 14wt%) with a phase transformation temperature of 60℃ and an equivalent stiffness of 11.2GPa. The second phase transformation stiffness control material 8 is filled in the cavity structure 11 of section B. The second phase transformation stiffness control material 8 is a Bi-In-Sn low-melting-point alloy (Bi 46wt%, In 42wt%, Sn 12wt%) with a phase transformation temperature of 80℃ and an equivalent stiffness of 12GPa. The third phase transformation stiffness control material 9 is filled in the cavity structure 12 of section C. The third phase transformation stiffness control material 9 is a Bi-In-Sn low-melting-point alloy (Bi 40wt%, In 48wt%, Sn 12wt%) with a phase transformation temperature of 100℃ and an equivalent stiffness of 12.5GPa.

[0069] The positive and negative terminals of the power module 1 are each connected to the control module 2 via a wire 3. The two ends of the shape memory alloy driving element 6 are each connected to the control module 2 via a wire 3. The power module 1 is used to supply power to the shape memory alloy driving element 6, and the control module 2 is used to control the power supply current and power supply time of the power module 1.

[0070] At ambient temperature T e At 25℃, power is continuously supplied to the shape memory alloy driving element. When the temperature rises to 60℃, the phase change stiffness control material in the A-section cavity structure reaches the phase change temperature, undergoes a solid-liquid phase change, and the equivalent stiffness drops to 50MPa, entering a softening state. The stiffness of this cavity structure is unlocked. At this time, the phase change stiffness control material in the B-section and C-section cavity structures is still in a rigid locked state. The deformation of the shape memory alloy driving element is concentrated only in the softened upper cavity. The upper section of the drive actuator undergoes bending deformation, with a bending angle of up to 30°, realizing single-segment local deformation and equivalent stiffness control.

[0071] When the temperature of the shape memory alloy driving element continues to rise to 80°C due to continuous power supply, the phase change stiffness control material in the B-segment cavity structure reaches the phase change temperature, undergoes a solid-liquid phase change, and the equivalent stiffness drops to 50MPa, entering a softening state. The stiffness of this segment cavity structure is then unlocked. At this point, only the C-segment cavity structure remains rigidly supported. The shape memory alloy driving element drives the A-segment and B-segment cavity structures to bend and deform simultaneously, with a bending angle of up to 50°, achieving sequential deformation and equivalent stiffness control of the two segments.

[0072] Continue to supply power until the temperature of the shape memory alloy driving element rises to 100°C. When the phase change stiffness control material in the C-section cavity structure reaches the phase change temperature, a solid-liquid phase change occurs, the equivalent stiffness drops to 50MPa, and it enters a softening state. All cavity structures complete stiffness unlocking, and the shape memory alloy driving element can drive the entire actuator to undergo bending deformation with a bending angle of up to 80°.

[0073] In this embodiment, the phase change unlocking response time of each cavity structure is approximately 2-3 seconds, and the control process is stable and controllable. After the actuator completes the target action, the power supply is stopped, and the shape memory alloy driving element and the actuator as a whole cool naturally. The driving element undergoes a reverse phase change and returns to the martensitic state. At the same time, the phase change stiffness control material in each cavity structure resolidifies into a rigid state as the temperature decreases. The equivalent stiffness of each cavity structure gradually recovers, and the actuator finally returns to the initial high equivalent stiffness state, completing one reversible equivalent stiffness control cycle.

[0074] The segmented adjustable stiffness shape memory alloy drive actuator of this embodiment can achieve sequential stiffness unlocking of the three-section cavity structure with a single shape memory alloy wire, realizing efficient multi-segment equivalent stiffness adjustment and drive control. This not only effectively improves the actuation accuracy of the actuator, but also significantly reduces the structural and control complexity of the multi-drive system. It can be applied to flexible mechanical fingers or soft robot arms to simulate sequential grasping actions.

[0075] Example 2

[0076] A segmented adjustable stiffness shape memory alloy driven actuator includes a flexible housing, an isolation element, a shape memory alloy driving element, a phase change stiffness control material, a power module, and a control module.

[0077] The flexible shell has a hollow cylindrical structure with an outer diameter of 16mm, an axial length of 120mm, and a wall thickness of 2mm. The material is silicone rubber with thermal stability that meets the requirements (manufacturer: Smooth-On, grade: Ecoflex 00-30).

[0078] The insulating element divides the hollow portion of the flexible shell into three axially arranged cavity structures, denoted as cavity structure A, cavity structure B, and cavity structure C, respectively. The axial lengths of cavity structures A, B, and C are 30mm, 40mm, and 50mm, respectively. The insulating element is a thin-film thermal insulation layer (the film is a polyimide film, manufacturer: DuPont, brand: Kapton HN), and the thickness of the insulating element is 0.2mm.

[0079] The shape memory alloy driving element runs through all the cavity structures along the axial direction of the flexible shell; the shape memory alloy driving element is a shape memory alloy wire (manufacturer: Jiangyin Peier Technology Co., Ltd.), with a diameter of 0.35mm, an axial length of 120mm, and an austenitization completion temperature A. f The highest stable temperature is 80℃, and the highest stable temperature is T. s The temperature is 150℃, the single-wire drive output force is 1.8N, and the shape memory alloy wire is covered with a 1mm thick silicone rubber insulation layer (material is the same as the flexible shell).

[0080] Phase change stiffness control materials are filled into each cavity structure. The phase change stiffness control material in cavity A is a thermoplastic polyurethane (manufacturer: Sigma-Aldrich, grade: Desmopan 9370A) with a phase change temperature of 50℃ and an equivalent stiffness of 60MPa; the phase change stiffness control material in cavity B is a thermoplastic polyurethane (manufacturer: Covestro, grade: Elastollan 1185A) with a phase change temperature of 70℃ and an equivalent stiffness of 55MPa; and the phase change stiffness control material in cavity C is polylactic acid (manufacturer: Nature Works, grade: Ingeo 4032D) with a phase change temperature of 90℃ and an equivalent stiffness of 55MPa.

[0081] The power module is used to power the shape memory alloy drive element;

[0082] The control module is used to control the power supply current and power supply time of the power module.

[0083] At ambient temperature T e At 25°C, power is continuously supplied to the shape memory alloy driving element. When the temperature rises to 50°C, the phase transition stiffness control material in the A-section cavity structure reaches the phase transition temperature, such as... Figure 8 From middle a to Figure 8 As shown in Figure b, a glass-to-rubber transition occurs, and the equivalent stiffness decreases to 5 MPa, entering a softened state. The stiffness of this cavity structure is unlocked. At this time, the phase change stiffness control material in the cavity structures of sections B and C is still in a rigid locked state. The deformation of the shape memory alloy drive element is only concentrated in the softened section A cavity. The upper section of the drive actuator undergoes axial recovery deformation of 15 mm, and the bending angle can reach 25°, realizing single-segment local deformation and equivalent stiffness control.

[0084] When the temperature of the shape memory alloy drive element continues to rise to 70°C due to continuous power supply, the phase transition stiffness control material in the B-segment cavity structure reaches the phase transition temperature, such as... Figure 8 From middle b to Figure 8As shown in section c, a glass-to-rubber transition occurs, and the equivalent stiffness decreases to 5 MPa, entering a softened state. The stiffness of this cavity structure is unlocked. At this time, only the cavity structure of section C still maintains rigid support. The shape memory alloy driving element drives sections A and B to bend simultaneously, increasing the bending angle by 20°, thus realizing the sequential deformation of the two sections and the control of the equivalent stiffness.

[0085] Continue supplying power until the temperature of the shape memory alloy drive element rises to 90°C, at which point the phase transition stiffness control material within the C-segment cavity structure reaches its phase transition temperature, such as... Figure 8 From middle C to Figure 8 As shown in d, a glass-to-rubber transition occurs, the equivalent stiffness decreases to 5MPa, and it enters a softening state. All cavity structures have completed stiffness unlocking, and the shape memory alloy drive element can drive the entire actuator to undergo bending deformation, with a bending angle of up to 70°.

[0086] In this embodiment, the phase change unlocking heating time for each cavity structure is approximately 3-5 seconds. After the actuator completes the target action, the power supply is stopped, and the shape memory alloy driving element and the actuator as a whole cool naturally. The driving element undergoes a reverse phase transformation and returns to the martensitic state. At the same time, the phase change stiffness control material in each cavity structure returns to the glassy rigid state as the temperature decreases. The equivalent stiffness of each cavity structure gradually recovers, and the actuator finally returns to the initial high equivalent stiffness state, completing one reversible equivalent stiffness control cycle.

[0087] The segmented adjustable stiffness shape memory alloy actuator of this embodiment can be applied to wearable rehabilitation devices to achieve precise control of the equivalent stiffness and flexibility of the human wrist during flexion. Furthermore, because a thermoplastic polymer is used as the phase change stiffness control material, the polymer has the characteristic of being lightweight, which makes the total weight of the actuator device <50g, making it more suitable for actual wearable application scenarios.

[0088] Example 3

[0089] A segmented adjustable stiffness shape memory alloy driven actuator includes a flexible housing, an isolation element, a shape memory alloy driving element, a phase change stiffness control material, a power module, and a control module.

[0090] The flexible shell has a hollow cylindrical structure with an outer diameter of 12mm, an axial length of 100mm, and a wall thickness of 1.5mm. The material is silicone rubber with thermal stability that meets the requirements (manufacturer: Smooth-On, grade: Ecoflex 00-30).

[0091] The insulating element divides the hollow portion of the flexible shell into three axially arranged cavity structures, denoted as cavity structure A, cavity structure B, and cavity structure C, respectively. The axial length of each cavity structure is the same. The insulating element is a low thermal conductivity insulation layer (polyimide film, manufacturer: DuPont, brand: Kapton HN), and the thickness of the insulating element is 0.15mm.

[0092] The shape memory alloy driving element runs through all the cavity structures along the axial direction of the flexible shell; the shape memory alloy driving element is a shape memory alloy wire (manufacturer: Jiangyin Peier Technology Co., Ltd.), with a diameter of 0.35mm, an axial length of 100mm, and an austenitization completion temperature A. f The highest stable temperature is 85℃, and the highest stable temperature is T. s The temperature is 150℃, the single-wire drive output force is 1.8N, and the shape memory alloy wire is covered with a 0.5mm thick silicone rubber insulation layer (material is the same as the flexible shell).

[0093] Phase change stiffness control materials are filled into each cavity structure. The phase change stiffness control material in cavity A is a low-melting-point metal particle-polymer microcapsule composite phase change material with a phase change temperature of 55℃ and an equivalent stiffness of 70MPa; the phase change stiffness control material in cavity B is a low-melting-point metal particle-polymer microcapsule composite phase change material with a phase change temperature of 75℃ and an equivalent stiffness of 70MPa; the phase change stiffness control material in cavity C is a low-melting-point metal particle-polymer microcapsule composite phase change material with a phase change temperature of 95℃ and an equivalent stiffness of 70MPa.

[0094] The preparation process of a low-melting-point metal particle-polymer microcapsule composite phase change material with a phase change temperature of 55℃ and an equivalent stiffness of 70MPa is as follows:

[0095] (1) A Bi-In-Sn low-melting-point alloy (Bi 51wt%, In 34wt%, Sn 13wt%) with a phase transformation temperature of 55℃ and an equivalent stiffness of 11.0GPa is heated to about 10-20℃ above its phase transformation temperature under an inert atmosphere to form a molten metal liquid, and then prepared into low-melting-point metal particles with a particle size of 50-100μm by gas atomization or mechanical ball milling.

[0096] (2) The low melting point metal particles are added to the polysorbate aqueous solution (concentration of 1-5 wt%; manufacturer of polysorbate: Sigma-Aldrich, brand: Tween 80) and dispersed and emulsified under the action of a high-speed shear emulsifier (3000-6000 rpm) to form a stable suspension system of low melting point metal particles in the aqueous phase; wherein, the mass ratio of low melting point metal particles to emulsifier solution is 1:10.

[0097] (3) Under continuous stirring, add urea-formaldehyde resin aqueous solution (prepared by diluting urea-formaldehyde resin aqueous solution with an initial solid content of 37wt% to 20wt%-30wt% with deionized water; the urea-formaldehyde resin aqueous solution with an initial solid content of 37wt% was purchased from Sigma-Aldrich, catalog number 419755) to the system, adjust the pH value to 3-4, stir and react at 60℃ for 2h to form a dense polymer coating layer on the surface of low melting point metal particles, and obtain low melting point metal microcapsules; wherein, the mass ratio of urea-formaldehyde resin aqueous solution to low melting point metal particles is 2:1;

[0098] (4) The low-melting-point metal microcapsules are filtered, washed and vacuum dried at 50-60℃ to obtain low-melting-point metal microcapsule powder with uniform particle size;

[0099] (5) Disperse the low melting point metal microcapsules uniformly in a flexible polymer matrix (silicone rubber, manufacturer Smooth-On, brand name Ecoflex 00-30) at a mass fraction of 40wt%-70wt%. After mechanical stirring and vacuum degassing, inject the microcapsules into a preset cavity structure (the shape and size of the cavity are designed according to the segmented adjustable stiffness shape memory alloy driven actuator: the structure is a hollow cylinder with an outer diameter of 12mm, an axial length of 100mm, and a wall thickness of 1.5mm) and cure it to obtain the low melting point metal particle-polymer microcapsule composite phase change material.

[0100] The preparation process of the low-melting-point metal particle-polymer microcapsule composite phase change material with a phase change temperature of 75℃ and an equivalent stiffness of 70MPa is basically the same as the above steps (1) to (5), except that: in step (1), the Bi-In-Sn low-melting-point alloy with a phase change temperature of 55℃ and an equivalent stiffness of 11.0GPa is replaced with the Bi-In-Sn low-melting-point alloy with a phase change temperature of 75℃ and an equivalent stiffness of 11.7GPa (Bi 48wt%, In 40wt%, Sn 12wt%); in step (3), the temperature of the stirring reaction is 70℃;

[0101] The preparation process of the low-melting-point metal particle-polymer microcapsule composite phase change material with a phase change temperature of 95℃ and an equivalent stiffness of 70MPa is basically the same as the above steps (1) to (5), except that: in step (1), the Bi-In-Sn low-melting-point alloy with a phase change temperature of 55℃ and an equivalent stiffness of 11.0GPa is replaced with the Bi-In-Sn low-melting-point alloy with a phase change temperature of 95℃ and an equivalent stiffness of 12.3GPa (Bi 42wt%, In 46wt%, Sn 12wt%); in step (3), the stirring reaction temperature is 80℃;

[0102] The power module is used to power the shape memory alloy drive element;

[0103] The control module is used to control the power supply current and power supply time of the power module, and to precisely regulate the temperature of the shape memory alloy drive element through the current.

[0104] At ambient temperature T e At 25℃, power is continuously supplied to the shape memory alloy driving element. When the temperature rises to 55℃, the phase change stiffness control material in the A-section cavity structure reaches the phase change temperature, undergoes a solid-liquid phase change, and the equivalent stiffness decreases by 80%, entering a softened state. The stiffness of this cavity structure is unlocked. At this time, the phase change stiffness control material in the B and C sections of the cavity structure is still in a rigid locked state. The deformation of the shape memory alloy driving element is only concentrated in the softened A-section cavity. The upper section of the drive actuator undergoes an axial recovery deformation of 10mm, realizing single-segment local deformation and equivalent stiffness control.

[0105] When the temperature of the shape memory alloy driving element continues to rise to 75°C due to continuous power supply, the phase change stiffness control material in the B-section cavity structure reaches the phase change temperature, undergoes a solid-liquid phase change, and the equivalent stiffness decreases by 80%, entering a softening state. The stiffness of this section of the cavity structure is unlocked. At this time, only the C-section cavity structure still maintains rigid support. The shape memory alloy driving element drives the A and B sections to deform simultaneously, and the cumulative axial recovery deformation increases by 15mm, realizing the sequential deformation and equivalent stiffness control of the two sections.

[0106] Continue to supply power until the temperature of the shape memory alloy driving element rises to 95°C. When the phase change stiffness control material in the C-section cavity structure reaches the phase change temperature, a solid-liquid phase change occurs, the equivalent stiffness decreases by 80%, and it enters a softening state. All cavity structures complete stiffness unlocking, and the shape memory alloy driving element can drive the entire actuator to bend and deform. The bending angle control accuracy can reach ±2°.

[0107] In this embodiment, the phase change unlocking response time of each cavity structure is approximately 2 seconds, which is fast. After the actuator completes the target action, the power supply is stopped, and the shape memory alloy driving element and the actuator as a whole cool naturally. The driving element undergoes a reverse phase change and returns to the martensitic state. At the same time, the phase change stiffness control material in each cavity structure resolidifies into a rigid state as the temperature decreases. The equivalent stiffness of each cavity structure gradually recovers, and the actuator finally returns to the initial high equivalent stiffness state, completing one reversible equivalent stiffness control cycle.

[0108] The segmented adjustable stiffness shape memory alloy driven actuator of this embodiment uses a low melting point metal particle-polymer microcapsule composite phase change material as the phase change stiffness control material. This composite material effectively improves thermal conductivity and photothermal conversion efficiency, making the heating of the shape memory alloy driven element more uniform. It can also achieve sequential and compliant deformation of the three-section cavity structure under the drive of a single shape memory alloy wire, making it suitable for practical application scenarios of flexible gripping devices.

[0109] Example 4

[0110] A segmented adjustable stiffness shape memory alloy driven actuator includes a flexible shell, an isolation element, a shape memory alloy driving element, a phase change stiffness control material, and a photothermal drive control module.

[0111] The flexible shell has a hollow cylindrical structure with an outer diameter of 18mm, an axial length of 160mm, and a wall thickness of 2mm. The material is silicone rubber with thermal stability that meets the requirements (manufacturer: Smooth-On, grade: Ecoflex 00-30).

[0112] The insulating element divides the hollow portion of the flexible shell into four cavity structures arranged sequentially along the axial direction. These four cavity structures are denoted as cavity structure A, cavity structure B, cavity structure C, and cavity structure D, respectively. The axial length of each cavity structure is the same. The insulating element is a silicone rubber heat insulation layer (material same as the flexible shell), and the thickness of the insulating element is 5mm.

[0113] The shape memory alloy driving element runs through all the cavity structures along the axial direction of the flexible shell; the shape memory alloy driving element is a shape memory alloy wire (manufacturer: Jiangyin Peier Technology Co., Ltd.), with a diameter of 0.35mm, an axial length of 160mm, and an austenitization completion temperature A. f The highest stable temperature is 50℃, and the highest stable temperature is T. s The temperature is 150℃, the single-wire drive output force is 1.8N, and the shape memory alloy wire surface is coated with a polydopamine and silver nanowire photothermal coating. The coating process is as follows:

[0114] (1) A dopamine reaction solution was prepared using DA-HCl, NaIO4 and sodium acetate buffer (composed of sodium acetate, hydrochloric acid and deionized water, with a sodium acetate concentration of 0.1M and a pH of 5-6). Silver nanowires with an average aspect ratio of 120 were added to the dopamine reaction solution and stirred until homogeneous to obtain a mixed reaction solution. The mass ratio of DA-HCl to NaIO4 was 1:1, the mass ratio of DA-HCl to sodium acetate buffer was 1:100, and the mass ratio of DA-HCl to silver nanowires was 20:1.

[0115] (2) The pretreated shape memory alloy wire was placed in anhydrous ethanol and deionized water in sequence, and ultrasonic cleaning was used to remove surface impurities. After cleaning, it was dried. Then the dried shape memory alloy wire was placed in a HarrickPlasma PDC-002 plasma cleaner for hydrophilic treatment to improve the hydrophilicity of the alloy wire surface. The shape memory alloy wire was completely immersed in the mixed reaction solution and reacted for 2 hours under magnetic stirring conditions at 25°C and 300 rpm to make the polydopamine-silver nanowire composite coating uniformly loaded on the surface of the alloy wire.

[0116] Phase transformation stiffness control materials are filled into each cavity structure. The phase transformation stiffness control material in cavity A is a Bi-In-Sn low-melting-point alloy (Bi 56wt%, In 26wt%, Sn 18wt%) with a phase transformation temperature of 40℃ and an equivalent stiffness of 10.5GPa. The phase transformation stiffness control material in cavity B is a low-melting-point metal (Bi 50wt%, In 36wt%, Sn 14wt%) with a phase transformation temperature of 60℃ and an equivalent stiffness of 11.2GPa. The phase transformation stiffness control material in cavity C is a low-melting-point metal (Bi 46wt%, In 42wt%, Sn 12wt%) with a phase transformation temperature of 80℃ and an equivalent stiffness of 12.0GPa. The phase transformation stiffness control material in cavity D is a low-melting-point metal (Bi 40wt%, In 42wt%, Sn 12wt%) with a phase transformation temperature of 100℃ and an equivalent stiffness of 12.5GPa. 48wt%, Sn 12wt%)

[0117] The photothermal drive control module provides controllable light source irradiation, regulates the heating rate and maximum temperature of the shape memory alloy drive element, and the light source power is adjustable within the range of 50-150 mW / cm². 2 .

[0118] At ambient temperature T e At 25℃, the actuator is continuously irradiated with a controllable light source. The shape memory alloy driving element completes photothermal conversion and heating through the surface photothermal coating. When the temperature rises to 40℃, the phase change stiffness control material in the A-section cavity structure reaches the phase change temperature, undergoes a solid-liquid phase change, and the equivalent stiffness drops to 50MPa, entering a softening state. The stiffness of this section of the cavity structure is unlocked. At this time, the phase change stiffness control materials in the B, C, and D sections of the cavity structure are still in a rigid locked state. The deformation of the shape memory alloy driving element is only concentrated in the softened A-section cavity, realizing single-segment local deformation and equivalent stiffness control.

[0119] When the temperature of the shape memory alloy driving element continues to rise to 60°C due to continuous irradiation, the phase change stiffness control material in the B-segment cavity structure reaches the phase change temperature, undergoes a solid-liquid phase change, and the equivalent stiffness decreases to 50MPa, entering a softening state. The stiffness of this segment of the cavity structure is unlocked. At this time, the C and D segments of the cavity structure still maintain rigid support. The shape memory alloy driving element drives the A and B segments to deform simultaneously, realizing the sequential deformation of the two segments and the control of the equivalent stiffness.

[0120] When the temperature of the shape memory alloy driving element continues to rise to 80°C due to continuous irradiation, the phase change stiffness control material in the C-section cavity structure reaches the phase change temperature, undergoes a solid-liquid phase change, and the equivalent stiffness drops to 50MPa, entering a softening state. The stiffness of this cavity structure is unlocked. At this time, only the D-section cavity structure still maintains rigid support. The shape memory alloy driving element drives the A, B, and C sections to deform simultaneously, realizing three-segment sequential deformation and equivalent stiffness control.

[0121] Continue irradiation until the temperature of the shape memory alloy driving element rises to 100℃. When the phase change stiffness control material in the D-section cavity structure reaches the phase change temperature, a solid-liquid phase change occurs, the equivalent stiffness drops to 50MPa, and it enters a softening state. All cavity structures complete stiffness unlocking, and the shape memory alloy driving element can drive the entire actuator to deform, realizing full-section equivalent stiffness control.

[0122] In this embodiment, the phase transformation unlocking response time for each cavity structure is approximately 2 seconds. After the actuator completes the target action, the light source illumination is stopped, and the shape memory alloy driving element and the actuator as a whole cool naturally. The driving element undergoes a reverse phase transformation and returns to the martensitic state. At the same time, the phase transformation stiffness control material in each cavity structure resolidifies into a rigid state as the temperature decreases. The equivalent stiffness of each cavity structure gradually recovers, and the actuator eventually returns to its initial high equivalent stiffness state, completing one reversible equivalent stiffness control cycle.

[0123] The segmented adjustable stiffness shape memory alloy actuator in this embodiment achieves non-contact actuation through a photothermal actuation control module. The polydopamine + silver nanowire photothermal coating on the surface of the shape memory alloy actuator can significantly reduce actuation energy consumption and effectively improve the response speed of phase change unlocking and actuator deformation. It is suitable for applications such as remote micro-operation and wearable flexible exoskeletons.

[0124] Example 5

[0125] A segmented adjustable stiffness shape memory alloy driven actuator includes a flexible housing, an isolation element, a shape memory alloy driving element, a phase change stiffness control material, a power module, and a control module.

[0126] The flexible shell has a hollow cylindrical structure, formed by a composite of silicone tubing and flexible fiber fabric. The silicone tubing is located in the inner layer, and the flexible fiber fabric covers the outside of the silicone tubing to form a reinforcing layer with a thickness of 0.5 mm. The flexible fiber fabric is aramid fiber fabric (manufacturer: DuPont, grade: Kevlar 49), used to improve the mechanical strength and tear resistance of the flexible shell while maintaining the flexibility of the overall structure. The silicone tubing has an outer diameter of 20 mm, an axial length of 200 mm, a wall thickness of 2 mm, and is made of silicone rubber (manufacturer: Smooth-On, grade: Ecoflex00-30) that meets the requirements for thermal stability.

[0127] The insulating element divides the hollow portion of the flexible shell into five axially arranged cavity structures, denoted as cavity structure A, cavity structure B, cavity structure C, cavity structure D, and cavity structure E, respectively. The axial length of each cavity structure is the same. The insulating element is a thin-film thermal insulation layer (polyimide film, manufacturer: DuPont, brand: Kapton HN), with a thickness of 0.2 mm.

[0128] The shape memory alloy actuating element runs through all the cavity structures along the axial direction of the flexible shell; the shape memory alloy actuating element is a shape memory alloy fiber (manufacturer: Jiangyin Peier Technology Co., Ltd.), with a diameter of 0.35mm, an axial length of 200mm, and an austenitization completion temperature A. f The highest stable temperature is 50℃, and the highest stable temperature is T. s The temperature is 150℃, the single-filament drive output force is 1.8N, and the shape memory alloy fiber is covered with a 0.5mm thick silicone rubber insulation layer (material is the same as the flexible shell).

[0129] Phase transformation stiffness control materials are filled into each cavity structure. The phase transformation stiffness control material in cavity A is a Bi-In-Sn low-melting-point alloy (Bi 56wt%, In 26wt%, Sn 18wt%) with a phase transformation temperature of 40℃ and an equivalent stiffness of 10.5GPa. The phase transformation stiffness control material in cavity B is a low-melting-point metallic phase transformation material (Bi 52wt%, In 32wt%, Sn 16wt%) with a phase transformation temperature of 50℃ and an equivalent stiffness of 10.8GPa. The phase transformation stiffness control material in cavity C is a low-melting-point metallic phase transformation material (Bi 50wt%, In 36wt%, Sn 14wt%) with a phase transformation temperature of 60℃ and an equivalent stiffness of 11.2GPa. The phase transformation stiffness control material in cavity D is a low-melting-point metallic phase transformation material (Bi 50wt%, In 36wt%, Sn 14wt%) with a phase transformation temperature of 70℃ and an equivalent stiffness of 11.5GPa. 49wt%, In 38wt%, Sn 13wt%); The phase change stiffness control material in the cavity structure of section E is a low melting point metal phase change material (Bi 46wt%, In 42wt%, Sn 12wt%) with a phase change temperature of 80℃ and an equivalent stiffness of 12.0GPa.

[0130] The power module is used to power the shape memory alloy driving element, and the output current control range is 0.5-1.2A;

[0131] The control module is used to control the power supply current and power supply time of the power module.

[0132] At ambient temperature T e At 25℃, power is continuously supplied to the shape memory alloy driving element. When the temperature rises to 40℃, the material in the cavity structure of section A undergoes a solid-liquid phase transition, and the equivalent stiffness decreases to 50MPa, entering a softening state. The stiffness of this cavity structure is unlocked, and the upper section of the drive actuator undergoes bending deformation with a bending angle of up to 15°. At this time, the phase transition stiffness control material in the cavity structures of sections B, C, D, and E is still in a rigid locked state. The cavity structure of section B maintains its structural support capacity, realizing the local deformation and equivalent stiffness control of a single section.

[0133] Continuous power supply causes the temperature of the shape memory alloy driving element to continue to rise, sequentially reaching the phase transition temperatures of the phase transition stiffness control material within the cavity structure in segments B (phase transition temperature 50℃, equivalent stiffness decreases to 50MPa, maximum bending angle can reach 30°), C (phase transition temperature 60℃, equivalent stiffness decreases to 50MPa, bending angle can reach 45°), D (phase transition temperature 70℃, equivalent stiffness decreases to 50MPa, bending angle can reach 60°), and E (phase transition temperature 80℃, equivalent stiffness decreases to 50MPa, bending angle can reach 75°). The corresponding cavity structures complete phase transition softening and unlocking in a preset order. The shape memory alloy driving element drives the softened cavity segments to undergo segmented bending deformation in sequence until all cavity structures complete stiffness unlocking.

[0134] In this embodiment, the phase transformation unlocking heating time for each cavity structure is approximately 2-4 seconds, ensuring local control accuracy. After the actuator completes the target action, the power supply is stopped, and the shape memory alloy driving element and the actuator as a whole cool naturally. The driving element undergoes a reverse phase transformation and returns to the martensitic state. At the same time, the phase transformation stiffness control material in each cavity structure returns to a rigid state as the temperature decreases. The equivalent stiffness of each cavity structure gradually recovers, and the actuator finally returns to the initial high equivalent stiffness state, completing one reversible equivalent stiffness control cycle.

[0135] The segmented adjustable stiffness shape memory alloy actuator of this embodiment can be applied to finger / arm assistive devices. It can realize multi-segment sequential bending deformation of a five-segment cavity structure. Moreover, the actuator can take into account both structural support and deformation compliance, and is suitable for the actual application needs of wearable rehabilitation medical devices.

Claims

1. A segmented, adjustable stiffness shape memory alloy driven actuator, characterized in that, include: A flexible outer shell with a hollow columnar structure; An isolation element consisting of a cavity structure that divides the hollow portion of a flexible shell into at least two segments arranged sequentially along the axial direction of the flexible shell; Shape memory alloy drive element that runs through all cavity structures along the axial direction of the flexible shell; The phase change stiffness control material is filled in each cavity structure. The phase change stiffness control material is a material that has a phase change temperature, is rigid when it is below the phase change temperature, and is soft when it is above or equal to the phase change temperature. The phase transition temperatures of the phase transition stiffness control materials within different cavity structures are not entirely the same; the lowest phase transition temperature is denoted as T. min The highest phase transition temperature is denoted as T. max The austenitization completion temperature of shape memory alloy drive components is denoted as A. f The highest stable temperature that a shape memory alloy driving element can reach after being energized is denoted as T. s The ambient temperature is denoted as T. e T min A f T max All are greater than T e And less than T s ; Along a certain direction parallel to the axis of the flexible shell, for any two adjacent cavity structures, the phase transition temperature of the phase transition stiffness control material located in the first cavity structure is greater than or equal to the phase transition temperature of the phase transition stiffness control material located in the second cavity structure. The driving force generated by the shape memory alloy driving element during the austenitization process is greater than the minimum force required for the flexible shell to undergo reversible deformation, greater than the structural resistance of any phase transformation stiffness control material in a softened state, and less than the structural resistance of any phase transformation stiffness control material in a rigid state.

2. The segmented adjustable stiffness shape memory alloy drive actuator according to claim 1, characterized in that, T e <T min ≤A f ≤T max <T s 。 3. The segmented adjustable stiffness shape memory alloy drive actuator according to claim 1, characterized in that, The phase transition temperature of the phase transition stiffness control material is 40-100℃.

4. A segmented adjustable stiffness shape memory alloy drive actuator according to claim 1, characterized in that, At temperatures above or equal to the phase transition temperature, phase transition stiffness control materials undergo solid-liquid phase transitions, glass-rubber transitions, solid-solid phase transitions, crystallization-melting transitions, or reversible crosslinking transitions.

5. A segmented adjustable stiffness shape memory alloy drive actuator according to claim 4, characterized in that, The phase change stiffness regulating material is a phase change material, or a phase change composite material formed by combining a phase change material with a thermally conductive filler. The phase change material is selected from at least one of the following: metallic phase change materials, metallic alloy phase change materials, organic phase change materials, inorganic salt phase change materials, thermoplastic polymer phase change materials, and hydrogel phase change materials.

6. A segmented adjustable stiffness shape memory alloy drive actuator according to claim 1, characterized in that, The flexible shell has a hollow cylinder, hollow elliptical cylinder, or hollow polygonal prism structure, and is made of silicone rubber, polyurethane elastomer, thermoplastic elastomer, natural rubber, or synthetic rubber.

7. A segmented adjustable stiffness shape memory alloy drive actuator according to claim 1, characterized in that, The insulating element is a heat insulation layer or a thermal resistance structure.

8. A segmented adjustable stiffness shape memory alloy drive actuator according to claim 1, characterized in that, The shape memory alloy driving element is a shape memory alloy spring or a shape memory alloy fiber.

9. A segmented adjustable stiffness shape memory alloy drive actuator according to claim 1, characterized in that, Also includes: A power supply module for powering shape memory alloy drive components; A control module used to control the magnitude of the power supply current and the power supply time of the power module.

10. A drive control method for a segmented adjustable stiffness shape memory alloy drive actuator as described in any one of claims 1 to 9, characterized in that, Power is continuously supplied to the shape memory alloy driving element, causing its temperature to gradually rise and sequentially reach the phase transition temperature of the phase transition stiffness control material in each cavity structure, thereby realizing the sequential unlocking and segmented control of the equivalent stiffness of each cavity structure.

Images