Wheel diameter adjustable trolley with sensing-deformation composite spokes and control method

Abstract

The invention discloses a wheel diameter adjustable trolley with sensing-deformation composite spokes and a control method. Each wheel of the trolley is composed of a wheel axle and a plurality of wheel spokes distributed in a circumferential array mode, and the wheel spokes are of a three-layer composite structure: a driving layer composed of a liquid crystal elastomer is responsible for generating deformation under thermal stimulation; the rigidity-variable layer formed by a rigidity-adjustable polymer realizes hardening locking through ultraviolet irradiation, and realizes reversible adjustment of rigidity through heating; the sensing layer is formed by a multi-walled carbon nanotube grid, can be integrally formed with the driving layer and is used for monitoring the wheel diameter change in real time; according to the control method, the trolley can be switched between the high obstacle crossing ability of the large wheel form and the high load stability of the small wheel form. According to the method, the motion performance under the complex terrain is remarkably improved, and the method has wide application prospects in the field of adaptive mobile robots.

Description

Technical Field

[0001] This invention relates to the field of soft robots, specifically to a mobile robot with adaptive terrain capabilities, and particularly to a vehicle with adjustable wheel diameter featuring a sensing-deformation composite spoke and a control method thereof. Background Technology

[0002] Traditional wheeled robots face significant limitations in their mobility on complex, unstructured terrains such as sand, steps, narrow spaces, and discontinuous surfaces. Their fixed wheel diameters make it difficult to balance the need for high obstacle-crossing capability with large wheel diameters with the requirement for high stability, a low center of gravity, and small wheel diameters. While some research has attempted to achieve wheel diameter changes through complex mechanical structures, these generally suffer from system complexity, heavy weight, slow response, and a lack of state self-awareness.

[0003] The development of soft materials such as liquid crystal elastomers has provided a new approach to solving the above problems. Liquid crystal elastomers can produce reversible, large-amplitude deformations under stimuli such as heat and light, but they usually lack the ability to maintain their shape. How to combine the driving characteristics of materials with the stability, controllability, and state sensing capabilities of structures to manufacture simple, reliable, and intelligent variable wheel diameter systems has become a pressing technical problem in this field. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a wheel diameter adjustable vehicle with sensing-deformation composite spokes and a control method. Through the multi-physics response and synergistic effect of its core component—the sensing-deformation composite spokes—it solves the problems of existing wheeled robots in adapting to complex terrain, such as fixed shape, single function, lack of state perception, and the need for complex mechanical structures for motion mode switching.

[0005] The technical solution for achieving the objective of this invention is as follows: I. A wheel diameter adjustable vehicle with sensing-deformation composite spokes It includes two wheels, two drive motors, and a vehicle frame; Each wheel is connected to a drive motor and a corresponding end of the vehicle body frame, and the two wheels and two drive motors are arranged symmetrically about the vehicle body frame. Each wheel includes multiple curved composite spokes and an axle, all of which are evenly distributed circumferentially on the outer periphery of the axle, and all of which are curved in the same direction and to the same degree.

[0006] The composite spokes have a multi-layered structure, including: A sensing layer, a driving layer, and a variable stiffness layer are stacked sequentially, with the driving layer fixedly connected to the sensing layer and the variable stiffness layer, respectively. The driving layer comprises a liquid crystal elastomer material that deforms under thermal stimulation; The variable stiffness layer includes a stiffness-adjustable polymer material whose stiffness is adjusted with temperature and whose shape is locked by heating followed by cold quenching. The sensing layer includes an array of insulating microstructure units and a conductive carbon nanotube network filling the trenches between the insulating microstructure units; the conductive carbon nanotube network forms a connected grid array, and electrodes for extracting the resistance signal of the conductive carbon nanotube network are installed at both ends of the sensing layer.

[0007] The driving layer uses a main-chain liquid crystal elastomer material pre-oriented through a stretching-UV crosslinking process. The raw materials for its preparation, by weight, include: 100 parts of mesocrystalline unit (RM257), 5.5-6.5 parts of pentaerythritol tetra(3-mercaptopropionate) (PETMP), 20-23 parts of 2,2'-(ethylenedioxy)diethylthiol (EDDET), 0.5-0.8 parts of 2-hydroxy-2-methylphenylacetone (HHMP), and 0.2-0.4 parts of catalyst (DPA). The initial state of the driving layer is achieved by heating above its phase transition temperature to form a contractile deformation state, which is then cooled below its phase transition temperature to restore the initial state. The stiffness-adjustable polymer material is a UV-curable shape memory polymer system. Its raw materials, by weight, include: 12-18 parts aliphatic polyurethane acrylate resin (AUD), 30-38 parts tricyclodecanediethanol diacrylate (TCDDA), 35-40 parts epoxy resin (E-51), 10-15 parts polyetheramine (D230), and 0.3-0.8 parts photoinitiator benzoin dimethyl ether (DMPA). The sensing layer is a conductive mesh array structure formed by filling the gaps and trenches between insulating microstructure units with multi-walled carbon nanotubes. The insulating microstructure units are made of NOA photoresist material, formed through a micro-nano imprinting process, specifically by imprinting the NOA photoresist using a polydimethylsiloxane (PDMS) mold and then curing it under UV light.

[0008] The driving layer and the variable stiffness layer are connected by an adhesive, which is a silicone adhesive. In the ultraviolet light irradiation hardened state, the variable stiffness layer softens after being heated above its glass transition temperature in the initial state, while the drive layer shrinks and deforms after being heated above its phase transition temperature, causing the softened variable stiffness layer to deform as well, resulting in spoke deformation and an increase in wheel diameter. In rapid cold quenching with a cooling rate greater than 40°C / s, the variable stiffness layer quickly hardens and locks in, restricting the recovery of the drive layer, which is still in a state of shrinkage and deformation, and locking the spoke shape. In natural environmental cooling, the drive layer gradually recovers and drives the variable stiffness layer to recover to its initial state together.

[0009] The vehicle has at least two switchable modes: Small wheel configuration: wherein the composite spokes of the wheel are all at a first degree of curvature, and the radius of the wheel is a first radius, suitable for a first motion scenario; The wheel is a large wheel, wherein the composite spokes of the wheel are all at a second degree of curvature greater than the first degree of curvature, and the radius of the wheel is the second radius greater than the first radius, which is suitable for the second motion scenario.

[0010] II. A control method for a wheel-diameter adjustable trolley with sensing-deformation composite spokes. The wheel switches between small and large wheel shapes through repeated heating and cooling processes to adapt to different motion scenarios. The wheel radius is monitored and controlled by mapping the resistance signal transmitted by the electrodes of the sensing layer with the degree of bending of the composite spokes.

[0011] The steps for switching from a small wheel shape to a large wheel shape are as follows: all the composite spokes are heated to soften the variable stiffness layer and shrink the drive layer, causing all the composite spokes to extend from the first degree of curvature to the second degree of curvature, increasing the wheel radius from the first radius to the second radius. Then, all the composite spokes at the second degree of curvature are cold-quenched to lock all the composite spokes at the second degree of curvature, locking the wheel radius at the second radius, and the wheel diameter adjustable vehicle adapts to the second motion scenario. The steps for switching from a large wheel configuration to a small wheel configuration are as follows: heating the composite spokes locked at the second degree of curvature to release the locking state of all the composite spokes; then cooling all the composite spokes in the environment and driving all the composite spokes to return from the second degree of curvature to the first degree of curvature, so that the wheel radius decreases from the second radius to the first radius, and the wheel diameter adjustable vehicle adapts to the first motion scenario.

[0012] The heating methods include hot air convection heating and infrared radiation heating; the quenching methods include ice water bath immersion cooling, vortex tube airflow cooling, and cryogenic spray cooling.

[0013] The resistance of the composite spokes changes during bending and recovery. The electrodes of the sensing layer transmit the resistance change of the flexible actuator through a signal. The resistance signal output by the sensing layer of the composite spokes has a definite mapping relationship with the change in the radius of the wheel. Based on this mapping relationship, the monitoring and control feedback of the wheel radius is realized.

[0014] The beneficial effects of this invention are: Compared with the prior art, the present invention has the following significant advantages: 1. Deep functional integration, achieving a leap from "complex machinery" to "material intelligence". Existing variable wheel diameter technologies mostly rely on complex mechanical structures such as motors, connecting rods, and gears, resulting in bulky systems, slow response, and susceptibility to damage. This invention pioneers a three-layer integrated composite spoke design combining "drive-variable stiffness-sensing," integrating drive, shape locking, and state sensing functions into a single material structure. This fundamentally eliminates complex mechanical transmissions, achieving extreme simplification of the system structure and a significant reduction in weight.

[0015] 2. Possesses bistable characteristics, enabling a leap from "continuous energy consumption" to "energy-saving lock-in". Existing actuators based on software actuators typically require continuous energy input to maintain the deformed state, resulting in high energy consumption and a high risk of material fatigue. This invention utilizes the difference between the phase transition dynamics of the driving layer (liquid crystal elastomer) and the glass transition dynamics of the variable stiffness layer. Through a "heating-rapid cooling" control strategy, the wheel can be stably switched to the large wheel configuration. Through a "heating-ambient cooling" control strategy, the wheel can be stably switched to the small wheel configuration. Maintaining the stable configuration requires no energy input, achieving true bistable operation and zero static power consumption, significantly improving the vehicle's range and reliability.

[0016] 3. Possessing intrinsic perception capabilities, enabling a leap from "blind action" to "intelligent controllability". Existing variable wheel diameter mechanisms or flexible actuators generally lack real-time monitoring capabilities for their own state, operating on an "open-loop" control basis and unable to accurately determine the current configuration. This invention, through a multi-walled carbon nanotube sensing layer integrally formed with the drive layer, transforms the entire composite spoke into a distributed strain sensor, enabling real-time, in-situ monitoring of precise changes in the wheel radius without any external sensors. This invention significantly improves motion performance in complex terrain and has broad application prospects in the field of adaptive mobile robots.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the overall structure of the wheel-diameter adjustable cart with sensing-deformation composite spokes according to the present invention. Figure 2 This is an exploded view of the structure of the wheel-diameter adjustable trolley described in this invention; Figure 3 This is a schematic diagram of the composite spoke morphology switching described in this invention; Figure 4 This is a schematic diagram illustrating the mode switching (wheel diameter adjustment) of the wheel-diameter adjustable trolley described in this invention; Figure 5 This is a schematic diagram illustrating the manufacturing process of the adjustable wheel of the present invention; Figure 6 This is a physical image of the multi-walled carbon nanotube mesh microstructure of the sensing layer described in this invention; Figure 7 These are physical images of the large and small wheels of the adjustable wheel diameter trolley described in this invention. Figure 8 This is a physical image of the composite spoke morphology switching process described in this invention; Figure 9 This is a graph showing the correspondence between the wheel radius and spoke resistance value of the adjustable wheel diameter trolley described in this invention. Figure 10 This is a comparison chart of the load-bearing capacity of the vehicle described in this invention under different configurations. Figure 11 These are comparison images of the vehicle described in this invention under different configurations, tested on sand. Figure 12 These are comparison images of the vehicle described in this invention under different configurations, obtained through a step test. Figure 13 These are comparison images of the vehicle described in this invention under different configurations, passing through a height restriction tunnel. Figure 14 These are comparison images of the vehicle described in this invention under different configurations, tested on a slope. Figure 15 These are comparative images of the vehicle described in this invention under different configurations, tested on discontinuous ground. Figure 16 These are comparative images showing the crawling test of the vehicle described in this invention in different configurations in water. Figure 17 These are comparative images showing the vehicle described in this invention swimming in water under different configurations.

[0019] In the figure: wheel 1, drive motor 2, vehicle body support 3, drive layer 11, variable stiffness layer 12, sensing layer 13, wheel axle 14, insulating microstructure array 15. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] like Figure 1 and Figure 2 As shown, a wheel diameter adjustable vehicle with sensing-deformation composite spokes includes two wheels 1, two drive motors 2, and a vehicle frame 3; Each wheel 1 is connected to a corresponding drive motor 2 and one end of the vehicle body bracket 3, and the two wheels 1 and the two drive motors 2 are arranged symmetrically about the vehicle body bracket 3; the drive motor 2 is mounted on the vehicle body bracket and provides power to the wheel 1.

[0022] like Figure 3 As shown, each wheel 1 includes multiple curved composite spokes and axle 14. All composite spokes are evenly distributed circumferentially on the outer periphery of axle 14 to form a circumferential array, and all composite spokes have the same curvature direction and degree. The number of composite spokes is specifically six.

[0023] The composite spokes are multi-layered functional components, including: The sensing layer 13, the driving layer 11, and the variable stiffness layer 12 are stacked in sequence, and the driving layer 11 is fixedly connected to the sensing layer 13 and the variable stiffness layer 12 respectively. The driving layer 11 includes a liquid crystal elastomer material that generates driving deformation under thermal stimulation; The variable stiffness layer 12 includes a thermally responsive stiffness-adjustable polymer material whose stiffness can be reversibly adjusted with temperature changes, and whose shape can be locked by rapid cold quenching after heating. The sensing layer 13 is a conductive multi-walled carbon nanotube mesh microarray structure, which is used to sense the deformation of the actuator through its resistance change.

[0024] The insulating microstructure unit 15 is formed by a micro-nano imprinting process, specifically: it is formed by imprinting NOA photoresist cured on the surface of the driving layer 11 through a polydimethylsiloxane (PDMS) mold and then curing it under ultraviolet light.

[0025] The driving layer 11 of the composite spokes serves as the power source for switching spoke morphologies. It is composed of a liquid crystal elastomer material, specifically a liquid crystal elastomer film with a uniaxial orientation structure. The liquid crystal units within this film achieve a macroscopically ordered arrangement during the fabrication process through a stretching-crosslinking technique. Its working mechanism is as follows: when subjected to external stimuli such as heating, or when heat is generated by the absorption of specific wavelengths of light through doping with photothermal agents / its own properties, the degree of order of the liquid crystal molecules changes, causing the film to undergo significant and reversible contraction along its orientation direction. After the stimulus is removed and the film cools, it returns to its initial length. This reversible contraction-recovery behavior provides the core, large-amplitude driving force for the composite spokes.

[0026] The variable stiffness layer 12 of the composite spokes is crucial for achieving deformation locking and is composed of a thermally responsive, adjustable stiffness polymer. Before UV curing, its cross-linking density is initially low, and its glass transition temperature is below room temperature, exhibiting soft and highly elastic properties, facilitating programming the spoke shape in a mold. After being placed in a pre-designed spoke shape mold and cured by UV irradiation, its cross-linking density significantly increases, and its glass transition temperature rises far above room temperature, making the material rigid. This polymer possesses unique dynamic mechanical properties; its elastic modulus is extremely sensitive to temperature changes. When heated above its glass transition temperature or phase transition temperature, the polymer chain segments become active, and the material transitions from a rigid to a soft state with a significantly reduced modulus. At this point, even a small stress generated by the drive layer can induce responsive deformation. When the temperature is rapidly cooled below the transition temperature, the polymer chain segment movement is frozen, and the material returns to a high-modulus rigid state, effectively resisting the elastic recovery forces of the drive layer and other components, thus "locking" the overall shape of the composite spokes in its current deformation state. Unlocking is achieved simply by reheating. By controlling the temperature change of the composite spokes, a controllable form switching is achieved: "After heating, it quickly cools and switches to the large wheel form; after being heated again to unlock, it switches to the small wheel form as it cools with the environment."

[0027] The sensing layer 13 of the composite spokes acts as the "nerve" system, enabling real-time, passive monitoring of its own deformation and wheel radius. It is not an independent layer, but rather a microstructured functional layer directly constructed on the surface of the drive layer. Specifically, it is constructed by forming negative grid-like microchannels on the surface of a liquid crystal elastomer film using micro-nano fabrication techniques, such as PDMS soft molds and NOA UV-curable photoresist. Multi-walled carbon nanotube solution is then filled into the channels using a blade coating method, and after drying, a continuous and stable grid-like conductive microstructure is formed. Its sensing mechanism is based on the resistance strain effect: when the spoke shape changes, the multi-walled carbon nanotube grid on its surface undergoes microscopic deformation, including changes in the contact resistance between carbon nanotubes and changes in the grid geometry. These factors collectively cause a reliable and measurable change in the resistance value of the entire conductive network. By monitoring this resistance signal in real time and establishing a calibration relationship between resistance, deformation, and wheel radius, the real-time information of the wheel radius can be accurately and in-situ obtained without relying on any external sensors.

[0028] The main body of the vehicle frame 3 is a baffle, with connection ports for connecting the drive motor 2 installed at two corners on the same side of the baffle. The adjustable wheel diameter vehicle of this invention is driven by an external power supply to the drive motor 2: the red lead is connected to a 5.0V positive terminal, and the black lead is grounded at 0V. When the motor is energized in the forward direction, the wheel 1 rotates in the forward direction; when energized in the reverse direction, the wheel 1 rotates in the reverse direction. By adjusting the polarity of the input voltage, the vehicle can move forward, backward, turn, and make U-turns.

[0029] The driving layer 11 uses a liquid crystal elastomer material that is a main-chain liquid crystal elastomer pre-oriented by a stretching-ultraviolet crosslinking process. The raw materials for its preparation include, by weight, 100 parts of mesocrystalline unit (RM257), 5.5~6.5 parts of pentaerythritol tetra(3-mercaptopropionate) (PETMP), 20~23 parts of 2,2'-(ethylenedioxy)diethylthiol (EDDET), 0.5~0.8 parts of 2-hydroxy-2-methylphenylacetone (HHMP), and 0.2~0.4 parts of catalyst (DPA). The initial state of the driving layer 11 is formed by heating above its phase transition temperature to a shrinkage deformation state along its molecular orientation direction. The shrinkage deformation state is restored to its initial state by natural cooling in the environment to below its phase transition temperature. The reversible shrinkage strain range is between 40% and 50%. The stiffness-adjustable polymer material is a UV-curable shape memory polymer system. Its raw materials, by weight, include: 12-18 parts aliphatic polyurethane acrylic resin (AUD), 30-38 parts tricyclodecanedimethylethanol diacrylate (TCDDA), 35-40 parts epoxy resin (E-51), 10-15 parts polyetheramine (D230), and 0.3-0.8 parts photoinitiator benzoin dimethyl ether (DMPA). The stiffness-adjustable polymer material undergoes a synergistic curing treatment combining thermosetting and UV curing. The synergistic curing process involves: first, a first-stage thermosetting at 80℃ for 4 hours, followed by a second-stage post-curing at 120℃ for 4 hours; finally, curing with a wavelength of 365nm and an intensity of 50mW / cm². 2 The third stage of irradiation was carried out under ultraviolet light for 300 seconds.

[0030] The sensing layer 13 is a conductive multi-walled carbon nanotube mesh microarray structure, which is used to sense the deformation of the actuator through its resistance change.

[0031] The insulating microstructure unit 15 is formed by a micro-nano imprinting process, specifically: NOA photoresist cured on the surface of the driving layer 11 is imprinted using a polydimethylsiloxane (PDMS) mold and then cured under ultraviolet light. The multi-walled carbon nanotube mesh microstructure of the sensing layer 13 of the composite spokes is formed by imprinting photoresist to form channels, then coating and filling with a multi-walled carbon nanotube solution and then curing.

[0032] The driving layer 11 and the variable stiffness layer 12 are bonded together by an adhesive to form an initial planar sheet structure. The adhesive is a silicone adhesive Sil-Poxy, whose Young's modulus matches the modulus of the driving layer 11 and the variable stiffness layer 12 in the uncured state to ensure effective strain transfer. The variable stiffness layer 12 in the hardened state is irradiated with ultraviolet light. In the initial state, the variable stiffness layer 12 softens after being heated to a temperature exceeding its glass transition temperature, while the driving layer 11 shrinks and deforms after being heated to a temperature exceeding its phase transition temperature, causing the softened variable stiffness layer 12 to deform together. The variable stiffness layer 12 is then rapidly quenched to a temperature below room temperature to form a hardened locked state. The hardened locked state is released by reheating to a temperature exceeding its glass transition temperature. The nematic phase transition characteristics allow the driving layer 1 to return to its original state before heating during the natural and slow cooling process after heating. During rapid cold quenching, the glass transition dynamics of the variable stiffness layer 12 take precedence over the nematic phase transition of the driving layer 11. This causes the driving layer 11 to be unable to recover in time compared to the variable stiffness layer 12, resulting in the variable stiffness layer 12 hardening and locking, while the driving layer 11 remains in a state of contraction and deformation. In a natural environment, slow cooling allows the driving layer 11 sufficient time to recover, thereby driving the variable stiffness layer 12 to recover to its initial state. The sensing layer 13 deforms along with the driving layer 11 and the variable stiffness layer 12, thus realizing the deformation of the composite spokes.

[0033] The wheel diameter adjustable vehicle with sensing-deformation composite spokes has at least two switchable modes: Small wheel configuration: The composite spokes of wheel 1 are all at the first degree of curvature, and the radius of wheel 1 is the first radius. It is suitable for the first motion scenario, that is, it is suitable for motion scenarios with high load capacity requirements, discontinuous terrain, and height restrictions. It is not suitable for motion scenarios with high obstacle crossing ability. The large wheel design, in which the composite spokes of wheel 1 are all at a second degree of curvature greater than the first degree of curvature, and the radius of wheel 1 is the second radius greater than the first radius, is suitable for the second motion scenario, that is, motion scenario requiring high obstacle crossing ability, but not suitable for motion scenario requiring high load capacity, discontinuous terrain, or height restrictions.

[0034] Specifically, after heating the composite spokes, the variable stiffness layer 12 softens, and the drive layer 11 contracts, causing the spokes to stretch. Then, rapid quenching locks the spoke shape, and the wheel switches to a larger wheel form. This is because the phase transition kinetics of the liquid crystal elastomer in the drive layer 11 and the stiffness-tunable polymer in the variable stiffness layer exhibit significant differences: the first-order phase transition of the liquid crystal elastomer is time-dependent, and rapid quenching delays its phase transition process, keeping it in a contracted state; while the glass transition of the stiffness-tunable polymer is a kinetically controlled second-order transition, relatively insensitive to the cooling rate, and can quickly recover its high-modulus state during rapid cooling. Based on this mechanism, after the spokes deform due to heat: if slow cooling is used, the order of the liquid crystal elastomer gradually recovers, and the drive actuator returns to its initial shape; if rapid quenching is implemented, the variable stiffness layer 12 solidifies first and locks the mechanical state of the system, while the drive layer 11 remains in a contracted state, thus effectively fixing the spoke deformation. The spokes can be unlocked by reheating and then fully restored to their original shape through a subsequent cooling process, allowing the wheel to switch back to its initial small wheel configuration. Figure 4 This describes the overall shape change of the car when switching between small-wheel and large-wheel configurations.

[0035] Figure 5 This describes the manufacturing process for wheels with adjustable diameters. The sheet-like composite material comprises a stiffness-tunable polymer that has not been cured by ultraviolet light, a liquid crystal elastomer, a multi-walled carbon nanotube mesh microstructure, and a photoresist substrate.

[0036] The manufacturing of wheel 1 includes the following steps: Preparation of liquid crystal elastomer thin films; Multi-walled carbon nanotube mesh microstructures were prepared on the surface of a liquid crystal elastomer film by imprint lithography and blade coating processes to form a driving layer preform with integrated sensing layer 11. A prepolymer of a stiffness-adjustable polymer was prepared and cured to obtain a preform of variable stiffness layer 12. The preform of the drive layer 11 with integrated sensing layer and the preform of the variable stiffness layer 12 are bonded together with adhesive to obtain a sheet-like flexible actuator. The sheet-like flexible actuator is placed in an arc-shaped mold, and the variable stiffness layer 12 is hardened under ultraviolet light to shape the composite spokes into a preset arc-shaped structure. Multiple shaped composite spokes are circumferentially arrayed and mounted on the wheel axle to assemble wheel 1.

[0037] The preparation method of the stiffness-tunable polymer is as follows: 1.5g AUD, 3.45g TCDDA, 3.75g E-51, and 0.05g DMPA are mixed in a beaker and heated at 80°C for 5 minutes. Then, 1.25g D230 is added to the beaker. After stirring the mixture for 1 minute, it is degassed in a vacuum chamber for approximately 5 minutes to obtain a prepolymer of the stiffness-tunable polymer. Next, the obtained prepolymer is poured into a 60mm*10mm*1mm mold. It is then thermocured at 80°C for 4 hours, followed by post-curing at 120°C for 4 hours. Finally, a stiffness-tunable polymer that has not been cured by ultraviolet light is obtained.

[0038] The preparation method of liquid crystal elastomer (LCE) is as follows: 5.75 g of RM257 and 1.28 g of toluene are mixed in a beaker and heated in an oven at 85 °C for about 20 minutes. Then, 0.037 g of HHMP is added to the beaker. After the mixture clarifies, 0.342 g of PETMP and 1.238 g of EDDET are mixed together and then added to the above mixture. Subsequently, 0.018 g of PDA is poured into the beaker. The solution is stirred for about 1 minute, degassed in a vacuum chamber for about 5 minutes, and poured into a 60 mm * 10 mm * 1 mm mold. Next, the mold is placed in a dark environment for 24 hours. In a subsequent step, the cured film-like LCE is placed in an oven at 85 °C for 12 hours to evaporate the solvent. Finally, the LCE film is stretched to three times its original length and irradiated with 365 nm, 10 mW / cm² UV light for 10 minutes.

[0039] The method for preparing carbon nanotube microstructures is as follows: A prepared liquid crystal elastomer film is taken, and a certain amount of photoresist is drop-coated onto the surface of the film. A lattice structure PDMS mold is then imprinted onto the photoresist, and the film is irradiated with 365nm UV light at 10mW / cm² for 2 minutes. After the photoresist has cured, a quantitative multi-walled carbon nanotube solution is drop-coated onto the imprinted photoresist. The solution is then evenly scraped into the microchannels using a blade. The solution is left in the air for 120 minutes until it is completely dry. The solid multi-walled carbon nanotubes outside the microchannels are then wiped away with alcohol. After the alcohol evaporates, the multi-walled carbon nanotube microstructure is obtained, as shown below. Figure 6 As shown.

[0040] A liquid crystal elastomer film with a multi-walled carbon nanotube microstructure was bonded to a stiffness-tunable polymer using Sil-Poxy adhesive to form a sheet-like composite material. This material was placed in a 3D-printed curved mold, and the stiffness-tunable polymer was hardened using ultraviolet light to fix its shape, resulting in a composite spoke. Six composite spokes were then mounted on a wheel axle to obtain a wheel with an adjustable diameter.

[0041] A control method for a wheel diameter adjustable trolley with sensing-deformation composite spokes is as follows: By repeatedly heating and cooling, the wheel 1 switches between small wheel and large wheel shapes to adapt to different motion scenarios. The wheel radius is monitored and controlled by the mapping relationship between the resistance signal transmitted by the electrodes of the sensing layer 13 and the degree of bending of the composite spokes.

[0042] The steps for switching from a small wheel shape to a large wheel shape are as follows: all composite spokes are heated to soften the variable stiffness layer 12 and shrink the drive layer 11, causing all composite spokes to extend from the first degree of curvature to the second degree of curvature, increasing the radius of wheel 1 from the first radius to the second radius. Then, all composite spokes at the second degree of curvature are subjected to rapid cold quenching. The rapid glass transition dynamics of the variable stiffness layer 12 are utilized to complete the nematic phase transition before the drive layer 11, thereby locking all composite spokes at the second degree of curvature and locking the wheel radius at the second radius. The wheel diameter adjustable vehicle adapts to the second motion scenario. The steps for switching from a large wheel shape to a small wheel shape are as follows: The composite spokes locked at the second degree of curvature are heated to release the locking state of the variable stiffness layer 12, thereby releasing the locking state of all composite spokes; then all composite spokes are slowly cooled in the environment, and the dynamic characteristics of the slow nematic phase transition of the drive layer 11 are used to drive all composite spokes to return from the second degree of curvature to the first degree of curvature, so that the wheel radius is reduced from the second radius to the first radius, and the wheel diameter adjustable vehicle adapts to the first motion scenario.

[0043] Heating methods include hot air convection heating and infrared radiation heating; quenching methods include ice water bath immersion cooling, vortex tube cryogenic airflow cooling, and cryogenic spray cooling.

[0044] Heating is achieved by directly heating the variable stiffness layer 12, directly heating the drive layer 11, or heating the environment in which the vehicle is located.

[0045] During the bending and recovery process, the resistance of the composite spokes changes constantly. The electrodes of the sensing layer 13 transmit the resistance change of the flexible actuator through a signal. The resistance signal output by the sensing layer 13 of the composite spokes has a definite mapping relationship with the change in the radius of the wheel. Based on this mapping relationship, real-time passive monitoring and control feedback of the wheel radius can be achieved.

[0046] like Figure 7 As shown, the car can freely switch between small-wheel and large-wheel configurations. Figure 8 As shown, the initial radius of the cart wheel is 22.5 mm. After heating, the spokes expand, and then rapid cooling locks the spoke shape, transforming the cart into a large wheel with a radius of 34 mm. Upon reheating, the spoke locking is released, and the spokes return to their initial small wheel shape as they cool with the environment.

[0047] like Figure 9As shown, the change in the resistance of the spokes can reflect the change in the radius of the car wheel. Let the initial wheel shape be the initial state, where the resistance of a single spoke is R0. After heating, the spokes unfold, increasing the contact area of ​​the multi-walled carbon nanotube mesh microstructure and decreasing the resistance. As the environment cools, the spokes gradually return to their initial state, decreasing the contact area of ​​the multi-walled carbon nanotube mesh microstructure and increasing the resistance.

[0048] like Figure 10 As shown, the load-bearing capacity of the car differs between the small-wheel and large-wheel configurations, with the spoke shape in the small-wheel configuration exhibiting better load-bearing capacity. The weight of a single spoke is approximately 1.0g. In the large-wheel configuration, the wheel deforms noticeably when a single wheel is loaded with 100g; in the small-wheel configuration, the wheel remains undeformed when a single wheel is loaded with 200g, and while it deforms when loaded with 500g, it still maintains its basic shape.

[0049] like Figure 11 As shown, in sandy terrain, larger wheels have a larger radius and spoke shape, which is more conducive to passage through sand, while smaller wheels are more prone to getting stuck. Figure 12 As shown, in stepped terrain, the larger wheel configuration performs better. The car can pass through a 30mm high step in the larger wheel configuration, but cannot in the smaller wheel configuration. Figure 13 As shown, in the small-wheel configuration, the wheel radius is smaller, making it easier to pass through height-restricted tunnels. Facing a 50mm height-restricted tunnel, the car can pass through in the large-wheel configuration, but cannot in the small-wheel configuration. (See diagram). Figure 14 As shown, because the small car has a higher center of gravity and experiences greater undulations in its large-wheel configuration, the small-wheel configuration is more advantageous on sloping terrain, while the large-wheel configuration is prone to slippage and has lower climbing efficiency. Figure 15 As shown, on discontinuous terrain, in the form of a large wheel, the outer contour of the wheel is discontinuous, and the spokes are prone to getting stuck in dents. However, in the form of a small wheel, the outer contour of the wheel is continuous, and this does not occur. Figure 16 As shown, because the overall density of the car is greater than that of water, it will sink to the bottom and crawl along the surface. Due to the larger wheel radius in the large wheel configuration, it can crawl faster at the same motor speed. Figure 17 As shown, after attaching foam to the toy car, its movement in the two configurations can be compared. In the large-wheel configuration, the wheel radius is larger and the spoke shape is closer to that of a paddle, resulting in better performance and higher swimming efficiency. In summary, the small-wheel configuration performs better in tunnels with height restrictions, slopes, and discontinuous terrain, while the large-wheel configuration performs better in sand, steps, and water, as shown in Table 1.

[0050] Table 1: Comparison of the performance of the vehicle with large wheel configuration and small wheel configuration in different terrains This invention provides a technical solution for a three-layer integrated composite spoke based on "drive-variable stiffness-sensing," achieving the following through the inherent properties of the material and a unique control strategy: Fusion of drive and lock: The reversible large deformation drive of liquid crystal elastomer is combined with the ultraviolet light programmable lock and thermo-induced reversible stiffness adjustment characteristics of stiffness-adjustable polymer, so that the wheel can actively and reliably switch between two stable configurations: large wheel diameter with high obstacle crossing ability and small wheel diameter with high load and high stability. This solves the problem that traditional flexible actuators need to continuously consume energy to maintain the deformation state.

[0051] Programmable customization of configuration and function: By using ultraviolet light to harden the variable stiffness layer, the initial configuration of the spokes can be precisely programmed; by controlling the thermal stimulation and cooling rate, the different thermodynamic response dynamics of the drive layer and the variable stiffness layer can be used to achieve programmed control of the configuration switching path and final state.

[0052] Intrinsic sensing capabilities: Through a carbon nanotube sensing grid integrated with the drive layer, the wheel radius and spoke shape can be monitored in real time and in situ without the need for external sensors, providing closed-loop feedback for precise configuration control and autonomous decision-making by the robot.

[0053] The wheel diameter adjustable trolley of the present invention has a high degree of flexibility and adaptability in wheel diameter adjustment, specifically manifested in: Flexible cooling control: Composite spokes can be cooled using various methods, such as passive natural cooling, active air cooling, water cooling, and semiconductor cooling, depending on the cooling rate requirements of the actual application. This diverse cooling strategy provides an important guarantee for achieving precise deformation control and stiffness adjustment.

[0054] Fully reversible working mechanism: Based on the reversible driving characteristics of liquid crystal elastomers and the reversible thermal phase transition of variable stiffness polymers, the deformation generation and stiffness control process of composite spokes are both fully reversible, ensuring that the trolley can achieve long-term stable cyclic operation.

[0055] Diverse composite spoke deformation control modes: By adjusting the stimulation method of the drive layer and the local stiffness of the variable stiffness layer, the composite spokes can achieve repeated and reversible controlled deformation, enabling stepless adjustment of the wheel diameter. The variable stiffness layer's properties allow for zero-power maintenance of the deformed state, overcoming the technical challenge of continuous energy consumption required for traditional wheel shape switching to maintain deformation.

[0056] This invention ultimately provides a wheel-diameter adjustable vehicle with programmable configuration, switchable form, and self-sensing state, achieving intelligent and energy-saving improvements in motion performance in complex mixed terrain.

[0057] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, or improvements made by those skilled in the art within the spirit and principles of this invention should be included within the scope of protection of the claims of this invention. The scope of protection of this invention should be determined by the claims.

Claims

1. A wheel-diameter adjustable vehicle with sensing-deformation composite spokes, characterized in that: It includes two wheels (1), two drive motors (2) and a vehicle frame (3); Each of the wheels (1) is connected to one end of the vehicle body bracket (3) via a drive motor (2), and the two wheels (1) and the two drive motors (2) are arranged symmetrically about the vehicle body bracket (3); Each wheel (1) includes multiple curved composite spokes and axle (14), all of which are evenly distributed circumferentially on the outer periphery of the axle (14), and all of which are curved in the same direction and to the same degree.

2. The wheel diameter adjustable cart with sensing-deformation composite spokes according to claim 1, characterized in that: The composite spokes have a multi-layered structure, including: A sensing layer (13), a driving layer (11), and a variable stiffness layer (12) are stacked in sequence, and the driving layer (11) is fixedly connected to the sensing layer (13) and the variable stiffness layer (12) respectively. The driving layer (11) includes a liquid crystal elastomer material that deforms under thermal stimulation; The variable stiffness layer (12) includes a stiffness-adjustable polymer material whose stiffness is adjusted with temperature and whose shape is locked by heating followed by quenching. The sensing layer (13) includes an array of insulating microstructure units (15) and a conductive carbon nanotube network filling the trenches between the insulating microstructure units; the conductive carbon nanotube network forms a connected grid array, and electrodes for extracting the resistance signal of the conductive carbon nanotube network are installed at both ends of the sensing layer (13).

3. The wheel diameter adjustable cart with sensing-deformation composite spokes according to claim 2, characterized in that: The driving layer (11) uses a liquid crystal elastomer material that is a main-chain liquid crystal elastomer pre-oriented by a stretching-ultraviolet crosslinking process. The raw materials for its preparation include, by weight, 100 parts of mesocrystalline unit (RM257), 5.5~6.5 parts of pentaerythritol tetra(3-mercaptopropionate) (PETMP), 20~23 parts of 2,2'-(ethylenedioxy)diethylthiol (EDDET), 0.5~0.8 parts of 2-hydroxy-2-methylphenylacetone (HHMP), and 0.2~0.4 parts of catalyst (DPA). The initial state of the driving layer (11) is formed by heating above its phase transition temperature to form a shrinkage deformation state. The shrinkage deformation state is cooled to below its phase transition temperature to restore the initial state. The stiffness-adjustable polymer material is a UV-curable shape memory polymer system. The raw materials for its preparation include, by weight, 12-18 parts of aliphatic polyurethane acrylic resin (AUD), 30-38 parts of tricyclodecanediethanol diacrylate (TCDDA), 35-40 parts of epoxy resin (E-51), 10-15 parts of polyetheramine (D230), and 0.3-0.8 parts of photoinitiator benzoin dimethyl ether (DMPA). The sensing layer (13) is a conductive grid array structure formed by filling the gaps and grooves of the insulating microstructure unit (15) with multi-walled carbon nanotubes. The insulating microstructure unit (15) is made of NOA photoresist material, which is formed by micro-nano imprinting process, specifically by imprinting NOA photoresist with a polydimethylsiloxane (PDMS) mold and then curing it with UV light.

4. The wheel diameter adjustable cart with sensing-deformation composite spokes according to claim 3, characterized in that: The driving layer (11) and the variable stiffness layer (12) are connected by an adhesive, which is a silicone adhesive. The variable stiffness layer (12) in the UV-cured state softens after being heated to a temperature exceeding its glass transition temperature, while the driving layer (11) shrinks and deforms after being heated to a temperature exceeding its phase transition temperature, causing the softened variable stiffness layer (12) to deform as well, resulting in spoke deformation and an increased wheel diameter. During cold quenching, the variable stiffness layer (12) quickly hardens and locks, restricting the recovery of the driving layer (11) which is still in a state of shrinkage and deformation, thus locking the spoke shape. During natural cooling, the driving layer (11) gradually recovers and causes the variable stiffness layer (2) to recover to its initial state. The cooling rate of the quenching process is greater than 40℃ / s.

5. A wheel-diameter adjustable cart with sensing-deformation composite spokes according to claim 4, characterized in that, It has at least two switchable modes: Small wheel configuration: wherein the composite spokes of the wheel (1) are all at the first degree of curvature, and the radius of the wheel (1) is the first radius, suitable for the first motion scenario; The wheel is in the form of a large wheel, wherein the composite spokes of the wheel (1) are all in a second degree of curvature greater than the first degree of curvature, and the radius of the wheel (1) is the second radius greater than the first radius, which is suitable for the second motion scenario.

6. A control method for a wheel-diameter adjustable cart with sensing-deformation composite spokes as described in any one of claims 1-5, characterized in that: The wheel (1) is switched between small wheel and large wheel forms by repeated heating and cooling to adapt to different motion scenarios. The wheel radius is monitored and controlled by the mapping relationship between the resistance signal transmitted by the electrodes of the sensing layer (13) and the degree of bending of the composite spokes.

7. The control method for a wheel-diameter adjustable cart with sensing-deformation composite spokes according to claim 6, characterized in that, Includes the following steps: The steps for switching from a small wheel shape to a large wheel shape are as follows: all the composite spokes are heated to soften the variable stiffness layer (12) and shrink the drive layer (11), causing all the composite spokes to stretch from the first degree of curvature to the second degree of curvature, so that the radius of the wheel (1) increases from the first radius to the second radius. Then, all the composite spokes in the second degree of curvature are cold-quenched to lock all the composite spokes in the second degree of curvature, so that the radius of the wheel is locked in the second radius, and the wheel diameter adjustable car adapts to the second motion scenario. The steps for switching from a large wheel configuration to a small wheel configuration are as follows: heating the composite spokes locked at the second degree of curvature to release the locking state of all the composite spokes; then cooling all the composite spokes in the environment and driving all the composite spokes to return from the second degree of curvature to the first degree of curvature, so that the wheel radius decreases from the second radius to the first radius, and the wheel diameter adjustable vehicle adapts to the first motion scenario.

8. The control method for a wheel-diameter adjustable cart with sensing-deformation composite spokes according to claim 6, characterized in that: The heating methods include hot air convection heating and infrared radiation heating; the quenching methods include ice water bath immersion cooling, vortex tube airflow cooling, and cryogenic spray cooling.

9. The control method for a wheel-diameter adjustable cart with sensing-deformation composite spokes according to claim 6, characterized in that: The resistance of the composite spoke changes during bending and recovery. The electrodes of the sensing layer (13) transmit the resistance change of the flexible actuator through a signal. The resistance signal output by the sensing layer (13) of the composite spoke has a definite mapping relationship with the radius change of the wheel. Based on this mapping relationship, the monitoring and control feedback of the wheel radius is realized.

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