Variable-rigidity flexible wheel of manned lunar rover based on shape memory alloy

Abstract

The invention provides a manned lunar rover variable-stiffness flexible wheel based on shape memory alloy, and relates to the technical field of aircrafts for cosmic sailing, the manned lunar rover variable-stiffness flexible wheel comprises a hub, a tread and a support body; the support body is connected between the hub and the tread, and the structure of the support body simulates the arrangement mode of cobweb radial wires and spiral wires; the tread and the supporting body are both made of shape memory alloy with a hyperelastic effect; the peripheral wall of the tread is provided with ground gripping teeth, and the ground gripping teeth can retract into the outer wall of the tread when the lunar rover runs on the lunar surface with good conditions; the ground gripping teeth can further extend outwards in the direction perpendicular to the outer wall of the tread when the lunar rover runs on the complex lunar surface. The distribution density and the thickness of the supporting bodies are gradually changed from large to small from the position close to the hub to the position close to the tread, so that the wheel can be subjected to self-adaptive rigidity adjustment; energy is absorbed through the tread and the supporting body, and mechanical energy is converted into heat energy to be dissipated, so that the riding comfort is improved; and the ground gripping teeth are designed on the tread, so that the traction capability of the wheel can be improved.

Description

Technical Field

[0001] This invention relates to the field of spacecraft technology for space travel, and more particularly to variable stiffness flexible wheels for manned lunar rovers based on shape memory alloys. Background Technology

[0002] Manned lunar rovers are one of the key pieces of equipment in current lunar exploration technology and have become a hot research topic worldwide. my country has successfully completed the Chang'e-3 mission and plans to achieve a manned lunar landing by 2030. However, the extreme environment on the lunar surface (temperature difference of -180℃ to 130℃, low gravity, sharp lunar regolith, and strong radiation) poses severe challenges to the wheels of manned lunar rovers. Traditional metal or rubber materials are prone to embrittlement / aging due to temperature changes and loss of elasticity, and rigid structures are prone to sinking or slippage. Manned missions have significantly higher requirements for wheel load capacity (carrying astronauts and equipment), terrain adaptability (crossing rocks and craters), and long lifespan (resistance to fatigue and lunar dust wear) than unmanned lunar rovers.

[0003] The most widely used and relatively mature type of wheel in current lunar exploration missions is the rigid wheel, which is usually composed of a hub, spokes, and rim. It has the advantages of simple structure, high strength and good pressure resistance. However, it has defects such as poor traction, insufficient cushioning performance and poor smoothness of movement. These shortcomings restrict the application of rigid wheels in manned lunar rovers. Summary of the Invention

[0004] In view of this, the present invention proposes a variable stiffness flexible wheel for manned lunar rovers based on shape memory alloys, in order to solve the technical problems mentioned in the background art, in which lunar rovers typically use rigid wheels, resulting in poor traction, insufficient cushioning performance, and poor smoothness of movement.

[0005] The technical solution of this invention is implemented as follows: This invention provides a variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy, comprising a hub, a tread, and a support structure, wherein: The support body is connected between the wheel hub and the tire tread. The structure of the support body imitates the arrangement of radial and spiral filaments of a spider web. The distribution density and thickness of the support body are designed to gradually decrease from the position near the wheel hub to the position near the tire tread. Both the tread and the support are made of shape memory alloy with superelastic effect, and their austenite termination temperature is designed to be lower than the common working temperature on the lunar surface. The tread is equipped with grip teeth on its peripheral wall. These grip teeth can retract into the outer wall of the tread when the rover is traveling on a lunar surface with good conditions, so that the outer wall of the tread forms a smooth driving surface. The grip teeth can also extend outward perpendicular to the outer wall of the tread when the rover is traveling on a complex lunar surface, so as to penetrate soft lunar soil or climb rocks.

[0006] In some optional embodiments, preferably, the grip teeth are fixedly installed on the outer wall of the tread. The grip teeth are made of nickel-titanium shape memory alloy with a two-way shape memory effect. Through a thermomechanical training process, the grip teeth have the following two preset shapes: the first shape is a curved and contracted shape in high-speed mode, in which the grip teeth are in a low-temperature martensitic phase and are closely attached to the tread substrate or are streamlined and curved, so that the outer wall of the tread forms a smooth driving surface; the second shape is an upright grip shape in passing mode, in which the grip teeth are in a high-temperature austenitic phase and extend outward perpendicular to the tread surface, forming a rigid protrusion for penetrating soft lunar soil or climbing rocks.

[0007] In some optional embodiments, preferably, a first electrode and a circuit switch are also included. The first electrode is installed on the inner wall of the tread and extends into the grip teeth. The circuit switch is used to control the circuit of the first electrode to be open or closed. When the circuit switch controls the circuit of the first electrode to be open and no current flows through the first electrode, the grip teeth are in a low-temperature martensitic phase and are close to the tread matrix or are streamlined and curved. When the circuit switch controls the circuit of the first electrode to be closed, the first electrode is energized and heats the grip teeth, causing the grip teeth to be in a high-temperature austenitic phase and extend outward perpendicular to the tread surface.

[0008] In some optional embodiments, preferably, the tread is provided with a guide groove in the radial direction, and the grip teeth are slidably installed in the guide groove; It also includes two return springs and two shape memory alloy springs; the two ends of the return springs are respectively connected to the grip teeth and the tread, and the two return springs are respectively located on both sides of the grip teeth in the thickness direction; the two ends of the shape memory alloy springs are respectively connected to the grip teeth and the tread, and the two shape memory alloy springs are respectively located on both sides of the grip teeth in the width direction. When the lunar rover travels on the lunar surface where conditions are favorable, the shape memory alloy springs are in an unexcited, released state, and the gripping teeth retract into the tread under the elastic force of the return spring. When the lunar rover travels on the complex lunar surface, the shape memory alloy spring is excited and contracts. The shape memory alloy spring undergoes a phase change and generates a retraction driving force. After the driving force of the shape memory alloy spring overcomes the elastic force of the return spring, the gripping teeth extend out of the outer wall of the tread.

[0009] In some alternative implementations, preferably, the length of the grip teeth extending beyond the outer wall of the tread is determined by the force balance between the shape memory alloy spring and the return spring.

[0010] In some optional embodiments, preferably, the return spring has a diameter of 3-5 mm, a wire diameter of 0.3-1.2 mm, a pitch of 1.5-2.5 mm, and an effective number of coils of 8-12; the shape memory alloy spring has a diameter of 2-4 mm, a wire diameter of 0.2-0.6 mm, a pitch of 0.5-1.5 mm, and an effective number of coils of 10-20.

[0011] In some alternative embodiments, preferably, the support body is divided into multiple grounded and ungrounded regions, each region is equipped with a second electrode, and the second electrode of each region can be energized independently.

[0012] In some alternative embodiments, preferably, the support body has multiple layers, the multiple layers of the support body are arranged parallel to each other along the axial direction of the hub, and there are staggered angles between the multiple layers of the support body.

[0013] In some optional embodiments, preferably, a controller is also included. This controller acquires the wheel slip ratio and sink depth, the height of obstacles on the lunar regolith surface, estimates the gravel particle size, and normalizes the acquired parameters to obtain a lunar regolith softness index S, an obstacle index R, and a gravel particle size index G. The controller then calculates the target extension ratio λ by combining the influence weights of these three indices on the traction tooth extension control, and calculates the target extension length x of the traction tooth based on the target extension ratio λ and the maximum extension length. des .

[0014] In some alternative embodiments, preferably, the support body includes a plurality of annular bars and spokes, the plurality of annular bars being coaxially arranged with the hub, and the spokes being arranged between two adjacent annular bars along the radial direction of the hub, with adjacent two rings of spokes being staggered.

[0015] The variable stiffness flexible wheel for manned lunar rovers based on shape memory alloys of the present invention has the following advantages over existing technologies: (1) The structure of the support body mimics the arrangement of radial and spiral filaments in a spider web. The distribution density and thickness of the support body are designed to gradually decrease from large to small along the position near the wheel hub to the position near the tire tread. This allows the outer ring area near the tire tread to undergo large deformation first when the wheel is under pressure to absorb the impact and increase the contact area, while the inner ring area near the wheel hub provides stable support. This achieves an adaptive stiffness effect of "softening upon contact with the ground and hardening under load" in a single passive structure. Both the tire tread and the support body are made of shape memory alloy with superelastic effect, and their austenitic... The end temperature is designed to be lower than the common operating temperature on the lunar surface, ensuring that the material remains in a superelastic state under lunar conditions. When the wheel rolls over an obstacle or is subjected to impact, the support deforms, and the stress induces the austenite to martensite phase transformation, absorbing energy. When the stress is relieved, the martensite undergoes a reverse phase transformation back to austenite, and the structure automatically returns to its original shape without permanent deformation. The significant hysteresis effect in this phase transformation process can effectively convert mechanical energy into heat energy and dissipate it, thereby greatly improving the vehicle's ride comfort. The tire tread is designed with grip teeth to increase adhesion to the lunar soil and improve the wheel's traction. (2) The grip teeth are fixedly installed on the outer wall of the tread. The grip teeth are made of nickel-titanium shape memory alloy with two-way shape memory effect. The grip teeth have the following two preset shapes through thermomechanical training process: the first shape is the curved and folded shape in high-speed mode. At this time, the grip teeth are in low-temperature martensite phase and are close to the tread matrix or in a streamlined curve so that the outer wall of the tread forms a smooth driving surface; the second shape is the upright grip shape in passing mode. At this time, the grip teeth are in high-temperature austenite phase and extend outward perpendicular to the tread surface to form a rigid protrusion for penetrating soft lunar soil or climbing rocks. The system can automatically judge the road conditions and change its shape at the best time, thereby realizing intelligent switching between high-speed smooth driving and high passability, and improving the passability and smoothness of the wheel. (3) The tread is provided with a guide groove in the radial direction, and the grip teeth are slidably installed in the guide groove; it also includes two return springs and two memory alloy springs; the two ends of the return springs are respectively connected to the grip teeth and the tread, and the two return springs are respectively located on both sides of the thickness direction of the grip teeth; the two ends of the memory alloy springs are respectively connected to the grip teeth and the tread, and the two memory alloy springs are respectively located on both sides of the width direction of the grip teeth; when the lunar rover travels on the lunar surface with good conditions, the memory alloy springs are in an unexcited released state, and the grip teeth are retracted into the tread by the elastic force of the return springs; when the lunar rover travels on the complex lunar surface, the memory alloy springs are excited and contracted, and the memory alloy springs undergo a phase change to generate a retraction driving force. After the driving force of the memory alloy springs overcomes the elastic force of the return springs, the grip teeth extend out of the outer wall of the tread; (4) The support body is divided into multiple grounded and non-grounded areas. Each area is equipped with a second electrode. The second electrode of each area can be energized independently. When the lunar rover turns, the grounded area of ​​the outer wheel can be heated separately to harden it to reduce deformation and sideslip, while keeping the inner wheel soft to provide comfort, thus realizing intelligent anti-roll and differential control. (5) The support body is provided in multiple layers, and the multiple layers of the support body are arranged parallel to the axis of the wheel hub. There are staggered angles between the multiple layers of the support body. The low stiffness mode (suitable for soft lunar soil) can adopt a configuration with fewer layers (such as 2-3 layers). In this mode, the wheel ground contact area is large and the ground pressure is small, which can effectively prevent the wheel from sinking and significantly improve the passability on soft terrain. The high stiffness mode (suitable for hard rocks or high-speed driving) can adopt a configuration with more layers (such as 4-5 layers or more). In this mode, the wheel deformation is small and the rolling resistance is low, which can provide stable support and efficient drive, and is suitable for high-speed movement on flat and hard lunar rock surfaces. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the variable stiffness flexible wheel of the manned lunar rover based on shape memory alloy in an embodiment of the present invention. Figure 2 This is a schematic diagram of the shape memory alloy gripping teeth before and after excitation in an embodiment of the present invention. Figure 3 This is a schematic diagram of the structure of the gripping teeth, the return spring, and the shape memory alloy spring in an embodiment of the present invention; Figure 4 For the present invention Figure 3 Enlarged view of part A in the middle; Figure 5 This is a schematic diagram of the structure of the support body in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of the support in different stacking states in the embodiments of the present invention.

[0018] Explanation of reference numerals in the attached diagram: 1-Wheel hub, 2-Tread, 3-Support body, 4-Grip teeth, 5-Return spring, 6-Memory alloy spring; 21-Guide groove; 31-Ring bar, 32-Spoke. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0021] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0023] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided in this invention; however, those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0025] The technical solution will now be explained in detail: Reference Figures 1-6 As shown, a first aspect of the present invention proposes a variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy, comprising a hub 1, a tread 2, and a support 3, wherein: The support 3 is connected between the wheel hub 1 and the tread 2. The structure of the support 3 imitates the arrangement of radial and spiral threads of a spider web. The distribution density and thickness of the support 3 are designed to gradually decrease from large to small along the position near the wheel hub 1 to the position near the tread 2. Both the tread 2 and the support 3 are made of shape memory alloys with superelastic effects, and their austenite termination temperature is designed to be lower than the common working temperature on the lunar surface. Both the tread 2 and the support 3 can be made of nickel-titanium shape memory alloys, whose elastic modulus is a function of its phase and temperature, and varies greatly in different phases. Its high-temperature austenitic phase has a high elastic modulus (50-80 GPa), and its low-temperature martensitic phase has a low elastic modulus (20-40 GPa). Of course, shape memory alloys can also be made of FeMnSi, CuZnSi, TiNb, etc. The tread 2 is equipped with grip teeth 4 on its peripheral wall. The grip teeth 4 can retract into the outer wall of the tread 2 when the lunar rover is traveling on a lunar surface with good conditions, so that the outer wall of the tread 2 forms a smooth driving surface. The grip teeth 4 can also extend outward perpendicular to the outer wall of the tread 2 when the lunar rover is traveling on a complex lunar surface, so as to penetrate soft lunar soil or climb rocks.

[0026] This embodiment proposes a variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy. The structure of the support body 3 mimics the arrangement of radial and helical filaments in a spider web. The distribution density and thickness of the support body 3 are designed to gradually decrease from large to small near the hub 1 towards the tread 2. This allows the outer region near the tread 2 to undergo large deformation first when the wheel is under pressure to absorb impact and increase the contact area, while the inner region near the hub 1 provides stable support. This achieves an adaptive stiffness effect of "softening upon contact with the ground and hardening under load" in a single passive structure. Furthermore, both the tread 2 and the support body 3 are made of highly elastic materials. Made of shape memory alloy with an austenite termination temperature designed to be lower than the common working temperature on the lunar surface, ensuring that the material remains in a superelastic state in the lunar environment. When the wheel rolls over an obstacle or is subjected to an impact, the support 3 deforms, and the stress induces the austenite to transform into martensite, absorbing energy. When the stress is relieved, the martensite undergoes a reverse transformation back to austenite, and the structure automatically restores its original shape without permanent deformation. The significant hysteresis effect in this phase transformation process can effectively convert mechanical energy into heat energy and dissipate it, thereby greatly improving the ride comfort of the vehicle. The tread 2 is designed with grip teeth 4 to increase adhesion to the lunar soil and improve the traction of the wheel.

[0027] In some embodiments, the grip teeth 4 are fixedly mounted on the outer wall of the tread 2. The grip teeth 4 are made of a nickel-titanium shape memory alloy with a two-way shape memory effect. Through a thermomechanical training process, the grip teeth 4 have the following two preset shapes: the first shape is a curved and contracted shape in high-speed mode, in which the grip teeth 4 are in a low-temperature martensitic phase and are closely attached to the tread 2 substrate or are streamlined and curved, so that the outer wall of the tread 2 forms a smooth driving surface; the second shape is an upright grip shape in pass-through mode, in which the grip teeth 4 are in a high-temperature austenitic phase and extend outward perpendicular to the surface of the tread 2, forming a rigid protrusion for penetrating soft lunar soil or climbing rocks. The system can automatically judge the road conditions and change its shape at the optimal time, thereby achieving intelligent switching between high-speed smooth driving and high passability.

[0028] The thermomechanical training process for obtaining the preset shape of the gripper tooth 4 is as follows: The gripper tooth 4 is made of NiTi shape memory alloy sheet. First, the gripper tooth 4 is kept upright at room temperature and placed in a solidification mold. In this state, it is heated to 400 ℃ in a resistance furnace and held for 20 min. After being removed, it is quenched in room temperature water within 3 seconds. The above solidification process is repeated 3 times to make the gripper tooth 4 remember its upright shape in the austenitic state. Then, the solidified gripper tooth 4 is cooled to about 0 ℃. In the martensitic state, the gripper tooth 4 is bent into a closed shape that adheres to the tread 2 substrate using a bending jig and locked. In the above bent and locked state, the gripper tooth 4 assembly is placed in a temperature control chamber and subjected to thermal cycling training between 0 ℃ and 80 ℃: the temperature is increased from 0 ℃ to 80 ℃ at a rate of 5–10 ℃ / min, held for 3–5 min, and then naturally cooled back to 0 ℃ and held for 2–5 min. The above heating-holding-cooling-holding process constitutes one training cycle, which is repeated 30 times. After this thermo-mechanical training, the gripping tooth 4 can automatically recover its bent and folded shape when cooled to 0 ℃ or in the low temperature environment of the lunar surface, and can automatically recover its upright gripping shape when electrically heated, thus obtaining a stable two-way shape memory effect.

[0029] In a further embodiment, the variable stiffness flexible wheel of the manned lunar rover based on shape memory alloy also includes a first electrode and a circuit switch. The first electrode is installed on the inner wall of the tread 2 and extends into the grip teeth 4. The circuit switch is used to control the on / off state of the circuit of the first electrode. When the circuit switch controls the circuit of the first electrode to be open, and no current flows through the first electrode, the grip teeth 4 are in a low-temperature martensitic phase and are closely attached to the tread 2 matrix or are streamlined and bent. When the circuit switch controls the circuit of the first electrode to be closed, the first electrode is energized and heats the grip teeth 4, causing the grip teeth 4 to be in a high-temperature austenitic phase and extend outward perpendicular to the surface of the tread 2. The triggering mechanism uses an electronic sensor to energize the first electrode to apply excitation, causing the grip teeth 4 to heat up, thereby causing the grip teeth 4 to transform from a low-temperature martensitic phase to a high-temperature austenitic phase.

[0030] In other embodiments, such as Figure 3 ( Figure 3 The example only selects one location of the traction tooth 4, and the number and distribution of the traction teeth 4 are similar to those in the example. Figure 1 )and Figure 4 As shown, the tread 2 is provided with a guide groove 21 in the radial direction, and the grip teeth 4 are slidably installed in the guide groove 21; The manned lunar rover's variable stiffness flexible wheel based on shape memory alloy also includes two return springs 5 ​​and two shape memory alloy springs 6; the two ends of the return springs 5 ​​are respectively connected to the grip teeth 4 and the tread 2, and the two return springs 5 ​​are respectively located on both sides of the grip teeth 4 in the thickness direction; the two ends of the shape memory alloy springs 6 are respectively connected to the grip teeth 4 and the tread 2, and the two shape memory alloy springs 6 are respectively located on both sides of the grip teeth 4 in the width direction. When the lunar rover travels on the lunar surface where conditions are favorable, the shape memory alloy spring 6 is in an unexcited and released state, and the gripping teeth 4 are retracted into the tread 2 by the elastic force of the return spring 5. When the lunar rover travels on the complex lunar surface, the shape memory alloy spring 6 is excited and contracts. The shape memory alloy spring 6 undergoes a phase change and generates a retraction driving force. After the driving force of the shape memory alloy spring 6 overcomes the elastic force of the return spring 5, the gripping teeth 4 extend out of the outer wall of the tread 2.

[0031] In this embodiment, the grip teeth 4 are designed as radially sliding piston structures, and a shape memory alloy spring 6 is used as its core driving and locking element, thereby achieving continuous, active, and adjustable precise control over the extension length of the grip teeth 4. Each grip tooth 4 is no longer fixed to the tread 2, but is installed as an independent sliding unit in the radial guide groove 21 of the tread 2 base, and can slide freely along the guide groove 21.

[0032] In some embodiments, the length of the grip tooth 4 extending beyond the outer wall of the tread 2 is determined by the force balance between the shape memory alloy spring 6 and the return spring 5. Let x be the radial extension of the grip tooth 4, and kr be the equivalent stiffness of the return spring 5. Then, the return spring 5 generates a spring force F. reset The formula for calculating (x) is: F reset (x)=k r ·x (1).

[0033] This invention treats the temperature of the shape memory alloy spring 6 as a function of the electric drive conditions, and controls the spring temperature T(I,t) by adjusting the current magnitude and the energizing time: (2); In equation (2), T0 is the initial temperature, R is the resistance of the shape memory alloy spring 6, A is the surface area of ​​the shape memory alloy spring 6, h is the heat dissipation coefficient of the shape memory alloy spring 6, m is the mass of the shape memory alloy spring 6, and c is the specific heat capacity of the shape memory alloy spring 6.

[0034] Shape memory alloy spring 6: shape memory alloy phase transformation strain with temperature M s ~A f Approximately linear between them: (3); In equation (3), εtr (T) represents the phase transformation strain at temperature T, A f With M s These are the temperatures at which the austenitic phase transformation of shape memory alloys completes and the martensitic phase transformation begins, respectively, ε. max This represents the maximum phase transition strain of the shape memory alloy spring 6.

[0035] The amount of contraction x of the shape memory alloy spring 6 free (T) is calculated using the following formula: (4); In equation (4), L0 is the effective initial length.

[0036] The balanced extension amount x(I,T) of the gripper tooth 4 is determined by the balance between the driving force of the shape memory alloy and the elastic force of the return spring 5, and the expression is: (5); In equation (5), k s (T(I,t)) represents the equivalent axial stiffness of the shape memory alloy spring.

[0037] The extension amount of the grip teeth 4 can be infinitely adjusted by regulating the driving current and the duration of energization. Under complex lunar surface conditions, the driving current increases, causing T(I,t) to rise. The shape memory alloy enters the austenitic state, and its driving force exceeds the elastic force of the return spring 5, pushing the grip teeth 4 out of the tread 2. Under good lunar surface conditions, heating is stopped, T(I,t) drops to the martensitic state, the driving force decreases, and the return spring 5 retracts the grip teeth 4 back into the tread 2.

[0038] In some embodiments, due to space constraints of the lunar rover wheels, preferably, the return spring 5 has a diameter of 3-5 mm, a wire diameter of 0.3-1.2 mm, a pitch of 1.5-2.5 mm, and an effective number of coils of 8-12; the shape memory alloy spring 6 has a diameter of 2-4 mm, a wire diameter of 0.2-0.6 mm, a pitch of 0.5-1.5 mm, and an effective number of coils of 10-20.

[0039] In some embodiments, the support 3 is divided into multiple grounded and ungrounded regions, each region being equipped with a second electrode, and each second electrode in each region can be independently energized. By controlling the energizing time and current magnitude of the second electrode, the temperature of the matrix material is controlled, thereby actively controlling its elastic modulus and enabling the wheel's stiffness to be actively adjusted during operation. For example, when the lunar rover turns, the grounded region of the outer wheel can be heated separately to harden it and reduce deformation and sideslip, while keeping the inner wheel soft to provide comfort, thus achieving intelligent anti-roll and differential control.

[0040] In some embodiments, the support body 3 has multiple layers, which are arranged parallel to each other along the axial direction of the hub 1, and there are staggered angles between the multiple layers of support bodies 3. The low-stiffness mode (suitable for soft lunar soil) can use a configuration with fewer layers (e.g., 2-3 layers). In this mode, the wheel's contact area is large, the ground pressure is low, effectively preventing the wheel from sinking and significantly improving passability on soft terrain. The high-stiffness mode (suitable for hard rocks or high-speed travel) can use a configuration with more layers (e.g., 4-5 layers or more). In this mode, the wheel deformation is small, the rolling resistance is low, providing stable support and efficient drive, suitable for high-speed movement on flat, hard lunar rock surfaces. Figure 6 As shown, the support structure can be arranged in five identical layers, six layers evenly staggered at 5°, or seven layers alternating at 15°. The specific stagger angle can be set according to actual design requirements.

[0041] Based on the equivalent beam theory, the spokes of the biomimetic spider web structure are simplified into a variable cross-section cantilever beam, whose stiffness K1 is expressed as: (6); In equation (6), E eq I is the equivalent elastic modulus of the shape memory alloy matrix material. eq Let L be the equivalent moment of inertia of the cross section, and L be the effective length of the spokes. If the multi-layered structures are arranged identically, the total stiffness K of the biomimetic spider web structure is... total It can be viewed as a single-layer structure in parallel: (7); In equation (7), n is the number of layers in the biomimetic spider web structure, and k i Let be the stiffness of the i-th layer; In the actual design, to improve the smoothness of the lunar rover wheels, there are staggered angles between the layers, and the deformation between the layers affects each other. A coupling coefficient α is introduced to address this. ij To describe the stiffness influence relationship between layers: (8); In equation (8), F n For the load borne by the nth layer, δ n For the deformation of the nth layer, α ij This is the coupling stiffness term, which is related to factors such as the stagger angle of the interlayer arrangement.

[0042] In some optional embodiments, preferably, the variable stiffness flexible wheel of the manned lunar rover based on shape memory alloy further includes a controller. The controller acquires the wheel slip ratio and sinking depth, the height of obstacles on the lunar soil surface, estimates the sand and gravel particle size, and normalizes the acquired parameters to obtain the lunar soil softness index S, the obstacle index R, and the sand and gravel particle index G. The controller then calculates the target extension ratio λ by combining the influence weights of the three indices on the extension control of the gripping tooth 4, and calculates the target extension length x of the gripping tooth 4 based on the target extension ratio λ and the maximum extension length. des .

[0043] The controller can acquire wheel slip ratio and sinking depth through wheel speed sensors, vehicle speed sensors, motor current sensors, and sinking detection units, and obtain the height of obstacles on the lunar regolith surface through a forward vision / laser ranging module. Optionally, it can estimate the sand and gravel particle size through close-range vision, and normalize the acquired parameters to obtain the lunar regolith softness index S, obstacle index R, and sand and gravel particle size index G. (9); In equation (9), sat [0,1] Let s be the saturation function used to control the calculation results within the interval [0,1], and let s and z represent the slip rate and subsidence depth of the wheel in the lunar soil, respectively. ref and z ref w1 and w2 are reference values ​​for slip ratio and settlement depth, respectively, and w1 and w2 are the weighting coefficients used to adjust slip ratio and settlement depth in the calculation of softness index. (10); In equation (10), h obs with h ref These represent the height of the detected obstacle features and a reference value, respectively. (11); In equation (11), d and d ref These are the characteristic particle sizes and reference values ​​of sand and gravel on the lunar soil surface; The target extension ratio λ is calculated based on environmental conditions, using the following formula: (12); In equation (12), a 1. a 2 and a 3 represents the weights of the influence of lunar soil softness, obstacle conditions, and sand and gravel particle characteristics on the extension control of gripping teeth 4, respectively. Target extension length x of gripper tooth 4 des : (13); In equation (13), x maxThe maximum length of the grip tooth 4 extending beyond the tire.

[0044] Due to the geometric parameter limitations of this invention, the extension length of the grip tooth 4 is approximately 12–25 mm.

[0045] In some embodiments, the support body 3 includes a plurality of annular strips 31 and spokes 32. The plurality of annular strips 31 are coaxially arranged with the hub 1, and the spokes 32 are arranged between two adjacent annular strips 31 along the radial direction of the hub 1, with adjacent rings of spokes 32 staggered. Each layer of the support body 3 is independently designed to mimic the gradient density distribution characteristics of a spider web in nature, that is, from the inner ring connected to the hub 1 to the outer ring connected to the tread 2, the width, thickness, and distribution density of its annular strips 31 and spokes 32 decrease.

[0046] The working principle of the variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy in this invention embodiment is as follows: The structure of the support body 3 mimics the arrangement of radial and helical filaments in a spider web. The distribution density and thickness of the support body 3 are designed to gradually decrease from large to small along the path from near the hub 1 to near the tread 2. This allows the outer ring area near the tread 2 to undergo large deformation first when the wheel is under pressure to absorb the impact and increase the contact area, while the inner ring area near the hub 1 provides stable support. This achieves an adaptive stiffness effect of "softening upon contact with the ground and hardening under load" in a single passive structure. Both the tread 2 and the support body 3 are made of materials with… Made of a shape memory alloy with superelastic effect, its austenite termination temperature is designed to be lower than the common working temperature on the lunar surface, ensuring that the material is always in a superelastic state in the lunar environment. When the wheel rolls over an obstacle or is subjected to impact, the support 3 deforms, and the stress induces the austenite to transform into martensite, absorbing energy. When the stress is relieved, the martensite undergoes a reverse phase transformation back to austenite, and the structure automatically restores its original shape without permanent deformation. The significant hysteresis effect in this phase transformation process can effectively convert mechanical energy into heat energy and dissipate it, thereby greatly improving the ride comfort of the vehicle. The tread 2 is designed with grip teeth 4 to increase the adhesion to the lunar soil and improve the traction of the wheel.

[0047] The variable stiffness flexible wheel for the manned lunar rover based on shape memory alloy proposed in this embodiment has the following advantages: (1) By using a wide-temperature-range shape memory alloy material and integrating embedded electrodes, the wheel can reliably achieve stiffness transformation by actively adjusting the material phase state through active electrothermal control in the extreme lunar environment of -180℃ to 130℃. This technology effectively overcomes the problems of low-temperature embrittlement, high-temperature creep and performance degradation of traditional materials, and ensures the environmental adaptability and functional reliability of the wheel in the entire lunar surface temperature range. (2) In response to the problem of limited adaptability to complex terrain, this invention uses a biomimetic spider web gradient stiffness structure and shape memory alloy active stiffness technology to enable the wheel to intelligently adjust its stiffness according to the softness and hardness of the terrain. It automatically softens on soft lunar soil to increase the ground contact area and prevent sinking, and actively hardens on hard rocks to reduce deformation and improve efficiency, thus achieving optimal self-adaptation of a single wheel to all terrains.

[0048] (3) To address the difficulty in balancing lightweight and high load-bearing capacity, this invention achieves high-strength support in an extremely lightweight thin-walled topology through a shape memory alloy biomimetic spider web structure; its superelastic effect can completely recover up to 8% of the strain, and it also has excellent energy absorption capacity, thus ensuring the mass of the ultra-light single wheel while achieving reliable load-bearing under extreme loads. (4) In response to the problem of complex lunar surface, the present invention realizes intelligent switching of tread shape 2 through the active deformation capability of shape memory alloy grip teeth 4: it shrinks on flat road surfaces to ensure smooth driving; it quickly stands upright and penetrates when encountering soft lunar soil or obstacles, significantly improving traction and obstacle crossing ability. (5) To address the difficulty in achieving wheel stiffness, this invention utilizes the electrothermal modulating properties of shape memory alloys and employs embedded electrodes to actively control the phase change state of the material, thereby achieving stepless and precise adjustment of wheel stiffness. This technology does not require complex mechanical structures; it can intelligently switch between the flexible martensitic state and the rigid austenitic state simply by controlling the current.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy, characterized in that, Includes the wheel hub, tire tread, and support structure, among which: The support body is connected between the wheel hub and the tire tread. The structure of the support body imitates the arrangement of radial and spiral filaments of a spider web. The distribution density and thickness of the support body are designed to gradually decrease from the position near the wheel hub to the position near the tire tread. Both the tread and the support are made of shape memory alloy with superelastic effect, and their austenite termination temperature is designed to be lower than the common working temperature on the lunar surface. The tread is equipped with grip teeth on its peripheral wall. These grip teeth can retract into the outer wall of the tread when the rover is traveling on a lunar surface with good conditions, so that the outer wall of the tread forms a smooth driving surface. The grip teeth can also extend outward perpendicular to the outer wall of the tread when the rover is traveling on a complex lunar surface, so as to penetrate soft lunar soil or climb rocks.

2. The variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy as described in claim 1, characterized in that, The grip teeth are fixedly installed on the outer wall of the tread. The grip teeth are made of nickel-titanium shape memory alloy with two-way shape memory effect. Through thermomechanical training process, the grip teeth have the following two preset shapes: The first shape is the curved and folded shape in high-speed mode. At this time, the grip teeth are in the low-temperature martensitic phase and are close to the tread substrate or in a streamlined curve so that the outer wall of the tread forms a smooth driving surface; The second shape is the upright grip shape in passing mode. At this time, the grip teeth are in the high-temperature austenitic phase and extend outward perpendicular to the tread surface to form a rigid protrusion for penetrating soft lunar soil or climbing rocks.

3. The variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy as described in claim 2, characterized in that, It also includes a first electrode and a circuit switch. The first electrode is installed on the inner wall of the tread and extends into the grip teeth. The circuit switch is used to control the circuit of the first electrode to be open or closed. When the circuit switch controls the circuit of the first electrode to be open and no current flows through the first electrode, the grip teeth are in a low-temperature martensitic phase and are close to the tread matrix or are streamlined and curved. When the circuit switch controls the circuit of the first electrode to be closed, the first electrode is energized and heats the grip teeth, so that the grip teeth are in a high-temperature austenitic phase and extend outward perpendicular to the tread surface.

4. The variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy as described in claim 1, characterized in that, The tread is provided with a guide groove in the radial direction, and the grip teeth are slidably installed in the guide groove; It also includes two return springs and two shape memory alloy springs; the two ends of the return springs are respectively connected to the grip teeth and the tread, and the two return springs are respectively located on both sides of the grip teeth in the thickness direction; the two ends of the shape memory alloy springs are respectively connected to the grip teeth and the tread, and the two shape memory alloy springs are respectively located on both sides of the grip teeth in the width direction. When the lunar rover travels on the lunar surface where conditions are favorable, the shape memory alloy springs are in an unexcited, released state, and the gripping teeth retract into the tread under the elastic force of the return spring. When the lunar rover travels on the complex lunar surface, the shape memory alloy spring is excited and contracts. The shape memory alloy spring undergoes a phase change and generates a retraction driving force. After the driving force of the shape memory alloy spring overcomes the elastic force of the return spring, the gripping teeth extend out of the outer wall of the tread.

5. The variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy as described in claim 4, characterized in that, The length of the grip teeth extending beyond the outer wall of the tire tread is determined by the force balance between the shape memory alloy spring and the return spring.

6. The variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy as described in claim 4, characterized in that, The return spring has a diameter of 3-5 mm, a wire diameter of 0.3-1.2 mm, a pitch of 1.5-2.5 mm, and an effective number of coils of 8-12; the memory alloy spring has a diameter of 2-4 mm, a wire diameter of 0.2-0.6 mm, a pitch of 0.5-1.5 mm, and an effective number of coils of 10-20.

7. The variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy as described in claim 1, characterized in that, The support is divided into multiple grounded and ungrounded areas, each of which is equipped with a second electrode, and each second electrode in each area can be energized independently.

8. The variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy as described in claim 1, characterized in that, The support body has multiple layers, which are arranged parallel to each other along the axial direction of the hub, and there are staggered angles between the multiple layers of support bodies.

9. The variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy as described in claim 1, characterized in that, It also includes a controller that acquires the wheel slip ratio and sinking depth, the height of obstacles on the lunar soil surface, estimates the sand and gravel particle size, and normalizes the acquired parameters to obtain the lunar soil softness index S, the obstacle index R, and the sand and gravel particle index G. The controller then calculates the target extension ratio λ by combining the influence weights of these three indices on the traction tooth extension control, and calculates the target extension length x of the traction tooth based on the target extension ratio λ and the maximum extension length. des .

10. The variable stiffness flexible wheel for a manned lunar rover based on shape memory alloy as described in any one of claims 1-9, characterized in that, The support body includes multiple annular bars and spokes. The multiple annular bars are coaxially arranged with the hub, and the spokes are arranged between two adjacent annular bars along the radial direction of the hub. Adjacent spokes are staggered.

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