Wrist joint driven by polyvinyl chloride-based artificial muscle

Abstract

The invention discloses a wrist joint driven by polyvinyl chloride-based artificial muscles, which adopts a hemispherical pair structure as a connecting part, realizes two-degree-of-freedom movement of the wrist joint by utilizing traction force of an axial driver of a dielectric elastomer, and aims to provide a more flexible, efficient and comfortable solution. The dielectric elastomer is prepared through a solution blending method, and silanized barium titanate / polyvinyl chloride composite gel is adopted. By means of the high dielectric constant of barium titanate, the defect that the dielectric constant of polyvinyl chloride gel is low is overcome, and therefore the working voltage needed by the polyvinyl chloride gel electric actuator is effectively reduced. Besides, the dispersity of the barium titanate modified by the silane coupling agent in a dielectric elastomer and the interface adhesive force of the barium titanate and a matrix are remarkably improved, so that the dielectric property and the mechanical property of the composite material are improved, and the stability of the electric actuator is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of artificial muscles, and in particular relates to a wrist joint driven by a polyvinyl chloride-based artificial muscle, and a preparation method and application thereof. Background Art

[0002] The wrist joint is the most flexible joint in the human body. Its high flexibility enables us to complete a variety of tasks from fine manipulation to large-scale movements. How to design a robotic device that can mimic the natural wrist movement of the human body has become an important research direction in the field of modern robotics and rehabilitation engineering.

[0003] At present, the research on wrist robots mainly focuses on the use of traditional drive methods such as electric drives, pneumatic drives, and hydraulic drives. Although these traditional drive technologies can provide a certain degree of precise control, they often have some obvious disadvantages: the electric drive system drives the wrist joint movement through a servo motor or a stepper motor, which can achieve high-precision control, but its large size and heavy weight limit the flexibility and comfort of the system, and the rigid structure of the electric drive often makes it difficult to simulate the complex wrist joint movement of the human body. Traditional drive systems (especially electric and hydraulic systems) usually require larger drives and power sources, resulting in a larger overall system size and weight. For wrist robots that require flexible movement, especially in application scenarios with high requirements for weight and comfort, existing technologies are difficult to provide solutions that meet the needs.

[0004] CN 107139208 A discloses a dielectric elastomer mechanical wrist joint, comprising: a movable disk, a fixed disk, a mounting seat and a plurality of dielectric elastomer conical drive units evenly distributed on the fixed disk. A flexible dielectric elastomer is used to replace the traditional motor, and the soft artificial muscle is controlled by an electric field to achieve low-impact and lightweight drive similar to biological joints. However, there are problems such as structural volume redundancy and significant force transmission path loss, which lead to limited clinical adaptability.

[0005] The present invention proposes a wrist joint driven by a polyvinyl chloride-based artificial muscle, which uses a hemispherical substructure as a connecting part and utilizes the traction of a dielectric elastomer axial driver to achieve two-degree-of-freedom movement of the wrist joint, aiming to provide a more flexible, efficient and comfortable solution. The dielectric elastomer is prepared from polyvinyl chloride gel filled with silanized barium titanate. This method significantly improves the dielectric constant of the polyvinyl chloride gel and effectively suppresses its viscoelastic behavior, thereby greatly improving the driving displacement performance and stability. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a wrist joint driven by a polyvinyl chloride-based artificial muscle. The movement of the human wrist joint is simulated by the meshing of hemispherical gears, and the pulling effect of the tendons is simulated by a dielectric elastomer to achieve the movement of the wrist joint in two degrees of freedom. The dielectric elastomer is prepared by a solution blending method, using a silanized barium titanate / polyvinyl chloride composite gel. Barium titanate, with its high dielectric constant, makes up for the deficiency of the low dielectric constant of polyvinyl chloride gel, thereby effectively reducing the required working voltage of the polyvinyl chloride gel electric actuator. In addition, the barium titanate modified by a silane coupling agent significantly improves its dispersibility in the dielectric elastomer and its interfacial adhesion with the matrix, thereby improving the dielectric properties and mechanical properties of the composite material and improving the stability of the electric actuator.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions: A wrist joint driven by a polyvinyl chloride-based artificial muscle comprises a movable disk, a hemispherical gear at the upper end of the wrist, a hemispherical gear at the lower end of the wrist, a fixed disk and a dielectric elastomer axial driver, wherein the hemispherical gear at the upper end of the wrist is fixedly connected to the movable disk, the hemispherical gear at the lower end of the wrist is fixedly connected to the fixed disk, and the hemispherical gear at the upper end of the wrist is meshed with the hemispherical gear at the lower end of the wrist, the fixed disk is fixedly connected to a base via a column, the upper end of the dielectric elastomer axial driver is fixedly connected to the movable disk, and the lower end of the dielectric elastomer axial driver is fixedly connected to the base.

[0008] Furthermore, there are four dielectric elastomer axial drivers, namely dielectric elastomer axial driver one, dielectric elastomer axial driver two, dielectric elastomer axial driver three, and dielectric elastomer axial driver four. The dielectric elastomer is made of silanized barium titanate / polyvinyl chloride composite gel, and the dielectric elastomer axial driver extends after power is supplied.

[0009] The working method of the wrist joint driven by the polyvinyl chloride-based artificial muscle described in the present invention is as follows: when in use, an alternating current signal is introduced by a high-voltage power supply, and is passed into two adjacent dielectric elastomer axial drivers, so that the two adjacent dielectric elastomer axial drivers generate in-plane actuation under the electric field, and the other two dielectric elastomer axial drivers will contract because they are in a pre-stretched state in the initial state, thereby driving the hemispherical gear at the upper end of the wrist to rotate toward the contraction direction of the dielectric elastomer axial driver.

[0010] Furthermore, the wrist joint driven by the polyvinyl chloride-based artificial muscle has two degrees of freedom and can bend in four directions around the hemispherical gear at the lower end of the wrist. The hemispherical gear at the upper end of the wrist is tightly meshed with the hemispherical gear at the lower end of the wrist, and adjacent dielectric elastomer axial drivers are used in pairs. When dielectric elastomer axial driver one and dielectric elastomer axial driver two are energized and extended, dielectric elastomer axial driver three and dielectric elastomer axial driver four will contract because they are in a pre-stretched state in the initial state, driving the hemispherical gear at the upper end of the wrist to rotate to one side of the contraction direction of dielectric elastomer axial driver three and dielectric elastomer axial driver four, thereby achieving the function of wrist bending.

[0011] Furthermore, the dielectric elastomer axial driver is made of silanized barium titanate / polyvinyl chloride composite gel, and conductive silicone grease electrodes are coated on both sides of the composite gel; wherein, The silanized barium titanate / polyvinyl chloride composite gel is prepared by a solution blending method of polyvinyl chloride and silanized barium titanate. The dielectric constant of the barium titanate used in preparing the silanized barium titanate is 1000-2000.

[0012] Furthermore, the thickness of the silanized barium titanate / polyvinyl chloride composite gel is 0.3-0.5 mm, the elastic modulus is 0.12-0.73 MPa, and the dielectric constant is 4-11; the thickness of the conductive silicone grease electrode is 0.1-0.2 mm, the diameter is 40 mm, and the surface resistance is 1000-3000Ω / sq.

[0013] Furthermore, the dielectric elastomer axial actuator can generate an in-plane actuation displacement of 0.21-8.23 mm under an alternating current signal with an electric field strength of 5.4 V / μm-17.8 V / μm and a frequency greater than 0.5 Hz.

[0014] Furthermore, the preparation method of the silanized barium titanate / polyvinyl chloride composite gel is as follows: (1) dissolving silanized barium titanate nanoparticles in N,N-dimethylformamide to obtain a mixed solution A; dissolving polyvinyl chloride and di-n-butyl adipate in N,N-dimethylformamide to obtain a mixed solution B; (2) uniformly mixing the mixed solutions A and B to obtain a mixed solution C; (3) Pour the mixed solution C into a glass culture dish and heat it in a vacuum drying oven until the solvent is completely evaporated to obtain a silanized barium titanate / polyvinyl chloride composite gel.

[0015] Furthermore, the amount of di-n-butyl adipate used is 2 to 4 times the mass of polyvinyl chloride, and the content of silanized barium titanate in the composite gel is 6.25 wt% to 20 wt%.

[0016] Among them, the typical preparation method of silanized barium titanate / polyvinyl chloride composite gel is as follows: (a) Take a beaker filled with 20 ml of N,N-dimethylformamide, add 0.3 g of barium silane titanate, and ultrasonicate at room temperature for 1 h. Then weigh 1.5 g of polyvinyl chloride powder and pour it into the barium silane titanate solution, and stir it continuously at room temperature for 3 h. Finally, weigh 3 g of di-n-butyl adipate and add it to the beaker, continue stirring for 1 h, and complete the preparation of the composite solution.

[0017] (b) Take a glass petri dish with a diameter of 90 mm and a flat bottom, and wipe it clean with alcohol. Pour the composite solution prepared in method (a) into the glass petri dish, and then let it stand at room temperature for one hour, and finally dry it in a vacuum drying oven at 60°C for 24 h. Use a square mold to cut the composite gel into samples with a size of 10 mm × 10 mm, and store them in a clean environment.

[0018] Further, a typical preparation method of silanized barium titanate nanoparticles is as follows: (a) 1.5 g of barium titanate nanoparticles were dispersed in 20 ml of hydrogen peroxide aqueous solution (30%), the dispersion temperature was raised to 106 °C under normal pressure, and then the dispersion was stirred at 106 °C for 6 h. The dispersion was then cooled to room temperature, centrifuged, and dried at 80 °C for 12 h to obtain hydroxylated barium titanate nanoparticles.

[0019] (b) 1.5 g of hydroxylated barium titanate nanoparticles were dispersed in 20 mL of anhydrous ethanol, the dispersion was ultrasonicated at room temperature for 1 h, and then 5 wt% of 2-cyanoethyltriethoxysilane was slowly added to the dispersion, and the dispersion was stirred at 60 °C for 6 h. Finally, the product was washed with deionized water three times and dried in a vacuum oven at 80 °C for 6 h to obtain silanized barium titanate nanoparticles.

[0020] Furthermore, the preparation method of conductive silicone grease electrode slurry is as follows: dilute components A and B of conductive silicone grease respectively with silicone oil, evenly mix the diluted A and B components, and stir continuously until there are no particles in the conductive silicone grease to obtain conductive silicone grease, and the mass ratio of component A, component B, and silicone oil is 1:1:3.

[0021] The beneficial effects of the present invention are: 1. The wrist joint driven by the polyvinyl chloride-based artificial muscle is driven by a silanized barium titanate / polyvinyl chloride composite gel electric actuator, which greatly reduces the weight of the robot, and the flexible driver makes its force softer. 2. The dielectric properties of the silanized barium titanate / polyvinyl chloride composite gel proposed in the present invention are significantly improved, and the dielectric constant is greatly improved compared to that of pure PVC gel, which is beneficial to the electric actuation performance of the silanized barium titanate / polyvinyl chloride gel electric actuator under low voltage. 3. The mechanical properties of the silanized barium titanate / polyvinyl chloride composite gel proposed in the present invention are significantly improved. Compared with pure PVC gel, the viscoelasticity is reduced, which is beneficial to the stability and rapid recovery ability of the silanized barium titanate / polyvinyl chloride gel electric actuator. 4. The silanized barium titanate / polyvinyl chloride composite gel electric actuator proposed in the present invention can work stably under low electric fields, and respond to changes in frequency and voltage at the same time, and has good controllability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The working process diagram of the dielectric elastomer axial actuator.

[0023] Figure 2 The driving platform is a dielectric elastomer axial actuator.

[0024] Figure 3 Infrared spectrum of CN@BT nanoparticles.

[0025] Figure 4 This is the stress-strain curve of CN@BT / PVC composite gel.

[0026] Figure 5 is the dielectric constant and dielectric loss of CN@BT / PVC composite gel.

[0027] Figure 6 Schematic diagram of electron microscopy of CN@BT / PVC composite gel.

[0028] Figure 7 is the actuation displacement curve of the dielectric elastomer axial actuator.

[0029] Figure 8 The preparation process of the dielectric elastomer axial actuator.

[0030] Fig. 9 Schematic diagram of the pre-compression device of the dielectric elastomer axial actuator.

[0031] Fig.10 Schematic diagram of the wrist joint structure.

[0032] Fig.11 It is a schematic diagram of the movable disk structure.

[0033] Fig.12It is a schematic diagram of the fixed plate and the base.

[0034] Among them, 1 is a movable disk, 2 is a hemispherical gear at the upper end of the wrist, 3 is a hemispherical gear at the lower end of the wrist, 4 is a fixed disk, 5.1 is a dielectric elastomer axial driver 1, 5.2 is a dielectric elastomer axial driver 2, 5.3 is a dielectric elastomer axial driver 3, 5.4 is a dielectric elastomer axial driver 4, 5.5 is an acrylic frame, 5.6 is a CN@BT / PVC composite gel 1, 5.7 is an electrode 1, 5.8 is a CN@BT / PVC composite gel 2, 5.9 is an electrode 2, 5.10 is a pre-compression device, 5.10.1 is an upper nut, 5.10.2 is a nylon upper cap, 5.10.3 is a compression spring, 5.10.4 is a screw, 5.10.5 is a nylon lower cap, and 5.10.6 is a lower nut. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention, and those skilled in the art in this field can make some non-essential improvements and adjustments based on the content of the above invention.

[0036] Example 1 Preparation of silanized barium titanate nanoparticles (CN@BT) (a) 1.5 g of barium titanate BT nanoparticles were dispersed in 20 ml of hydrogen peroxide aqueous solution (30%), the dispersion temperature was raised to 106 °C under normal pressure, and then the dispersion was stirred at 106 °C for 6 h. The dispersion was then cooled to room temperature, centrifuged, and dried at 80 °C for 12 h to obtain hydroxylated barium titanate BT-OH nanoparticles.

[0037] (b) 1.5 g of hydroxylated barium titanate nanoparticles were dispersed in 20 mL of anhydrous ethanol, the dispersion was ultrasonicated at room temperature for 1 h, and then 5 wt% of 2-cyanoethyltriethoxysilane was slowly added to the dispersion, and the dispersion was stirred at 60 °C for 6 h. Finally, the product was washed with deionized water three times and dried in a vacuum oven at 80 °C for 6 h to obtain silanized barium titanate CN@BT nanoparticles.

[0038] Example 2 Preparation of PVC gel (Sample 1) Take a 100 ml clean beaker, add 20 ml of N,N-dimethylformamide, 1.5 g of polyvinyl chloride powder and 3 g of di-n-butyl adipate, and stir continuously at room temperature for 6 hours to obtain a completely dissolved polyvinyl chloride mixture. Take a glass petri dish with a diameter of 90 mm and a flat bottom, and wipe it clean with alcohol. Pour the polyvinyl chloride mixture into the glass petri dish, then let it stand at room temperature for one hour, and finally dry it in a vacuum drying oven at 60°C for 24 h. Obtain unmodified pure polyvinyl chloride composite gel, record it as sample 1, and store it in a clean and dry environment.

[0039] Example 3 Preparation of silanized barium titanate / polyvinyl chloride CN@BT / PVC composite gel (sample 2) Take a beaker with 20 ml of N,N-dimethylformamide, add 0.1 g of barium silane titanate; ultrasonically treat at room temperature for 1 h. Then weigh 1.5 g of polyvinyl chloride powder and pour it into the barium silane titanate solution, and stir it continuously at room temperature for 3 h. Finally, weigh 3 g of di-n-butyl adipate and add it to the beaker, continue stirring for 1 h, and complete the preparation of the composite solution. Take a glass petri dish with a diameter of 90 mm and a flat bottom, and wipe it clean with alcohol. Pour the polyvinyl chloride mixture into the glass petri dish, then let it stand at room temperature for one hour, and finally dry it at 60℃ in a vacuum drying oven for 24 h. A polyvinyl chloride composite gel with a mass fraction of 6.25 wt% is obtained, which is recorded as sample 2. The composite gel is cut into samples of 10 mm × 10 mm in size using a square mold and stored in a clean and dry environment.

[0040] Example 4 Preparation of CN@BT / PVC composite gel (Sample 3) The mass of the silanized barium titanate in this example is 0.2 g, and the remaining steps are the same as those in Example 3, to obtain a polyvinyl chloride composite gel with a mass fraction of 11.8 wt%, which is recorded as Sample 3.

[0041] Example 5 Preparation of CN@BT / PVC composite gel (sample 4) The mass of the silanized barium titanate in this example is 0.3 g, and the remaining steps are the same as those in Example 3, to obtain a composite gel of polyvinyl chloride with a mass fraction of 16.7 wt%, which is recorded as Sample 4.

[0042] Example 6 Preparation of CN@BT / PVC composite gel (Sample 5) The mass of the silanized barium titanate in this example is 0.4 g, and the remaining steps are the same as those in Example 3, to obtain a polyvinyl chloride composite gel with a mass fraction of 21.1 wt%, which is recorded as Sample 5.

[0043] Example 7 Preparation of CN@BT / PVC composite gel (Sample 6) The mass of the silanized barium titanate in this example is 0.5 g, and the remaining steps are the same as those in Example 3, to obtain a polyvinyl chloride composite gel with a mass fraction of 25 wt%, which is recorded as Sample 6.

[0044] 1. Chemical structure analysis of CN@BT / PVC composite gel Figure 3 Infrared spectra of BT nanoparticles and CN@BT particles, BaTiO 3 The particle has a stretching vibration at 482 cm due to the Ti-O bond. -1 and 524cm -1 A strong absorption peak appears at the modified BaTiO 3 At 1100cm -1 and 1199cm -1 The absorption peaks at 2 -R group, which is the characteristic peak of silane coupling agent, at 2250cm -1 With 2230cm -1 The absorption peak at belongs to C≡N. The above results fully demonstrate that the cyanosilane coupling agent was successfully synthesized on BaTiO 3 surface.

[0045] 2. Mechanical properties analysis of CN@BT / PVC composite gel The mechanical properties of the prepared samples 1 to 6 were tested and analyzed. The samples were cut into dumbbell shapes and tensile tested using a universal tensile machine. The stress-strain curves are shown in Figure 2. Figure 4 shown.

[0046] The introduction of barium titanate as an inorganic filler with a high dielectric constant can significantly improve the rigidity and tensile strength of the composite gel. Since the silanization treatment improves the bonding force between barium titanate and the PVC matrix, the barium titanate particles are evenly dispersed in the composite material, thereby reducing the aggregation and interaction between particles, avoiding local stress concentration, and improving the overall mechanical strength of the composite gel. Although the barium titanate particles provide rigidity, PVC as a flexible matrix can maintain the ductility and toughness of the composite material. The silanization treatment improves the compatibility between the two, so that the composite material can effectively disperse stress when subjected to external forces, avoid brittle fracture, and improve the impact resistance and durability of the material.

[0047] 3. Dielectric properties analysis of CN@BT / PVC composite gel The dielectric constant has a significant effect on the driving performance of DEA. Figure 5 The dielectric properties of samples 1 to 6 are shown. Figure 5 (a) It can be seen that at room temperature, the dielectric constant of each composite gel sample decreases with the increase of frequency, which may be caused by interface polarization and dipole polarization. Sample 1 has the lowest dielectric constant, which is 10 3 Hz, and then with the increase of fillers, the dielectric constant continues to increase. Sample 6 is 7.1 at 10 3 The dielectric constant at Hz is 10.2, which is 43% higher than that of sample 1. Figure 5 (b) shows the change of dielectric loss value of different samples when the frequency is 10 2 Hz to 10 4 In the Hz range, the dielectric loss decreases with increasing frequency, which is due to the migration of polymer chains and the dipole polarization of the composite gel. As the filler content increases, the dielectric loss of the sample also increases. The dielectric loss value of sample 1 without filler is the lowest, and the dielectric loss of sample 6 is the highest.

[0048] 4. SEM of CN@BT / PVC composite gel The cross-sectional morphology of the CN@BT / PVC samples was observed using a scanning electron microscope. Figure 6 (a) shows the connection between the middle layer substrate film and the electrode. After adding the curing agent to the silicone rubber electrode, it can be cured at 60°C. It can be seen in the figure that the electrode and the substrate film are tightly bonded without falling off or damage. Figure 6 (b) and Figure 6 (c) shows the filler dispersion of the CN@BT / PVC elastomer composite film. The CN@BT particles are firmly bonded to the PVC matrix, and no holes, cracks or other structural defects are observed, indicating that the composite film maintains high quality and stability during the preparation process. It can be seen that the modified filler is well dispersed in the matrix film, which is more conducive to improving the dielectric constant of the composite film. The electron microscope image fully demonstrates that the CN@BT / PVC composite gel is successfully prepared, and the CN@BT / particles are evenly dispersed in the matrix without large-scale agglomeration. This is one of the main reasons why the CN@BT / PVC composite gel has excellent electromechanical properties.

[0049] Example 8 Preparation of Conductive Silicone Grease Electrode Slurry Dilute 2 g of conductive silicone grease with 3 g of silicone oil, stirring continuously until no particles are present in the conductive silicone grease. Specifically, add 1 g of conductive silicone grease component A, 1 g of conductive silicone grease component B, and 3 g of silicone oil into a clean disposable plastic cup, stirring continuously to evenly disperse components A and B in the silicone oil until no conductive particles are visible.

[0050] Example 9 Preparation of CN@BT / PVC composite gel electric actuator The composite gel was pre-stretched in an equibiaxial manner with a stretching ratio of 2 times its original size and prepared into an axial actuator to test its driving performance.

[0051] The manufacturing method of the dielectric elastomer axial driver is as follows: like Figure 8 As shown, the 10 mm × 10 mm size CN@BT / PVC composite gel 1.5.6 was subjected to equibiaxial pre-stretching to a size of 20 mm × 20 mm, and fixed on an acrylic frame with an outer frame size of 20 mm × 10 mm and an inner frame size of 18 mm × 8 mm. The excess part was cut off for later use. The release paper with an inner frame size of 18 mm × 8 mm was used as a mask, and the electrode slurry prepared in Example 8 was evenly coated on one side of the composite gel, and dried in an oven at 60°C for 2 h to prepare electrode 1.5.7. Repeat the above steps, and apply CN@BT / PVC composite gel 2.5.8 and electrode 2.5.9 on it in turn, thereby obtaining a four-layer (CN@BT / PVC composite gel 1-electrode 1-CN@BT / PVC composite gel 2-electrode 2) film structure.

[0052] The pre-compression device 5.10 is placed on the four-layer film structure, the prepared four-layer film structure is rolled on the pre-compression device 5.10, and the dielectric elastomer axial driver is obtained after connecting the copper wire. Specifically, the copper wires are led out from the two ends of the two electrodes and connected to the positive and negative electrodes of the power supply respectively, which can drive the film to deform, so that the spring rebounds to achieve driving.

[0053] like Fig. 9 As shown, the pre-compression device 5.10 includes an upper end nut 5.10.1, a nylon upper end cap 5.10.2, a compression spring 5.10.3, a screw rod 5.10.4, a nylon lower end cap 5.10.5, and a lower end nut 5.10.6. The nylon upper end cap 5.10.2-compression spring 5.10.3-nylon lower end cap 5.10.5 are sequentially fixed on the screw rod 5.10.4 by the upper end nut 5.10.1 and the lower end nut 5.10.6, and the compression spring 5.10.3 is in a compressed state, so as to support the four-layer film structure. After winding, remove the upper nut 5.10.1, screw 5.10.4 and lower nut 5.10.6. At this time, the compression spring 5.10.3 will rebound partially, and the pre-compression of the spring will continue to be limited by the four-layer film of the dielectric elastomer and the nylon upper end cap 5.10.2 and nylon lower end cap 5.10.5 at both ends of the compression spring 5.10.3. Lead copper wires from both ends of the two electrodes to connect the positive and negative poles of the power supply, which can drive the film to deform, so that the spring rebounds to achieve driving.

[0054] according to Figure 2 The driving platform of the dielectric elastomer axial actuator was built, and the electro-actuation performance of the composite gel electro-actuator was analyzed. Figure 1 As shown in the figure, during the experiment, a signal generator is first used to generate a driving signal. The function of the signal generator is to provide an adjustable input signal, usually an AC signal, and the frequency and amplitude of these signals can be adjusted according to the experimental requirements. The generated driving signal is then sent to the signal amplifier, which amplifies the voltage of the input signal to a level sufficient to drive the dielectric elastomer axial actuator. The amplified high-voltage signal is applied to the electrodes of the dielectric elastomer actuator, generating an electric field and exciting the material to deform. The actuator begins to move axially under the action of the electric field. In order to monitor the movement of the actuator in real time, the system uses a laser displacement sensor. This sensor measures the displacement change of the dielectric elastomer actuator with high precision by emitting a laser beam and receiving reflected light. The laser displacement sensor can provide micron-level accuracy to ensure accurate acquisition of the actuator displacement data. At the same time, the system is also equipped with a stress sensor to detect the stress change of the actuator under the action of the electric field. The stress sensor can sense the mechanical stress that the dielectric elastomer material is subjected to during the driving process and convert this data into an electrical signal. All the collected displacement and stress data will be transmitted to the computer in real time for analysis.

[0055] The electro-actuation performance of the composite gel electric actuator prepared in Example 9 (CN@BT / PVC composite gels of Sample 1, Sample 2, Sample 3, Sample 4, Sample 5 and Sample 6, respectively) was tested. The test conditions were: electric field strength 17.8V / μm, frequency 1 Hz. The in-plane actuation displacement of the center of the weight was recorded by a laser displacement sensor, and the curve is shown in Figure 7 As shown. It can be seen from the figure that when the electric field strength is 17.8V / μm, the driving displacement of the composite film electric actuator increases first and then decreases with the increase of CN@BT content. Combined with the summary data in Table 1, it can be seen that the driving displacement of pure PVC (sample 1) is only 1.34 mm, while the driving displacement of sample 4 reaches a maximum value of 8.23 ​​mm. It is 6.14 times the driving displacement of sample 1. After adding CN@BT filler, the driving effect of the composite film electric actuator is significantly improved. This is because CN@BT particles not only improve the interface bonding force between the filler and the matrix, but also effectively improve the dielectric constant of the barium titanate filler. Since barium titanate itself has a high dielectric constant, the modified barium titanate can better store and release electrical energy. Therefore, under the action of the electric field, the electrical energy storage capacity and driving performance of the composite material are enhanced. In addition, the modified barium titanate filler improves the distribution of the electric field in the material due to interface modification, so that the electric field can act more evenly and effectively on the entire composite material. When an external electric field is applied, the modified filler can better store and conduct electrical energy, improving the responsiveness and efficiency of electric field drive. Especially under high-frequency electric field drive, the performance of the composite material is more prominent, and the response speed and driving effect are improved.

[0056] Table 1. Actuation displacement of CN@BT / PVC composite gel electric actuator at different voltages Example 10 like Fig.10 As shown, a wrist joint driven by a polyvinyl chloride-based artificial muscle comprises a movable disk 1, a hemispherical gear 2 at the upper end of the wrist, a hemispherical gear 3 at the lower end of the wrist, a fixed disk 4 and a dielectric elastomer axial driver, wherein the hemispherical gear 2 at the upper end of the wrist is fixedly connected to the movable disk 1, the hemispherical gear 3 at the lower end of the wrist is fixedly connected to the fixed disk 4, and the hemispherical gear 2 at the upper end of the wrist is meshed with the hemispherical gear 3 at the lower end of the wrist, the fixed disk 4 is fixedly connected to the base 7 through a column 6, the upper end of the dielectric elastomer axial driver is fixedly connected to the movable disk 1, and the lower end of the dielectric elastomer axial driver is fixedly connected to the base 7, there are four dielectric elastomer axial drivers, namely, dielectric elastomer axial driver one 5.1, dielectric elastomer axial driver two 5.2, dielectric elastomer axial driver three 5.3, and dielectric elastomer axial driver four 5.4, the dielectric elastomer is made of silanized barium titanate / polyvinyl chloride composite gel, and the dielectric elastomer axial driver extends after power is supplied.

[0057] The movable plate 1 and the upper hemispherical gear 2 of the wrist are integrally formed by 3D printing of nylon material, and the lower hemispherical gear 3 and the fixed plate 4 are integrally formed by 3D printing of nylon material. Specifically, Fig.11 and 12 As shown, the movable disk is provided with four small holes corresponding to the four dielectric elastomer axial drivers, and the nylon upper end cap at the upper end of the dielectric elastomer axial driver is fixed to the movable disk 1 by interference fit with the small holes. Similarly, the base 7 is provided with four small holes corresponding to the four dielectric elastomer axial drivers, and the nylon lower end cap at the lower end of the dielectric elastomer axial driver is fixed to the base 7 by interference fit with the small holes. Since the distance between the movable disk 1 and the base 7 is slightly larger than the length of the dielectric elastomer axial driver, the dielectric elastomer axial driver needs to be axially stretched during the installation process, and the dielectric elastomer axial driver is in a pre-stretched state after being fixed.

[0058] The wrist joint driven by the polyvinyl chloride-based artificial muscle has two degrees of freedom and can bend in four directions around the hemispherical gear at the lower end of the wrist. The working principle is as follows: the dielectric elastomer axial drive is in a pre-stretched state, the hemispherical gear 2 at the upper end of the wrist is tightly meshed with the hemispherical gear 3 at the lower end of the wrist, and the adjacent dielectric elastomer axial drives are used in pairs. When in use, an AC signal is introduced by a high-voltage power supply and passed into two adjacent dielectric elastomer axial drivers, so that the two adjacent dielectric elastomer axial drivers produce in-plane actuation under the electric field, and the other two dielectric elastomer axial drivers will contract due to their initial pre-stretched state, thereby driving the hemispherical gear at the upper end of the wrist to rotate toward the contraction direction of the dielectric elastomer axial driver.

[0059] Specifically, when the dielectric elastomer axial driver 1 5.1 and the dielectric elastomer axial driver 2 5.2 are energized and extended, the dielectric elastomer axial driver 3 5.3 and the dielectric elastomer axial driver 4 5.4 will contract due to their initial pre-stretched state, driving the hemispherical gear 2 at the upper end of the wrist to rotate toward the contraction direction of the dielectric elastomer axial driver 3 5.3 and the dielectric elastomer axial driver 4 5.4, thereby achieving the function of wrist bending. Similarly, the wrist joint driven by polyvinyl chloride-based artificial muscles can achieve bending in four directions around the hemispherical gear at the lower end of the wrist.

[0060] The flexible artificial muscle-driven wrist joint based on silanized barium titanate / polyvinyl chloride composite gel proposed in the present invention can achieve low-voltage driven bidirectional flexion and extension and deflection movements, can assist patients in safe and gentle wrist joint rehabilitation training, solves the problems of bulky size and high impact force of traditional rigid drivers, and has both precise motion adaptability and wearing comfort.

[0061] The wrist joint driven by artificial muscle prepared by CN@BT / PVC composite gel (sample 4) of the present invention can achieve a continuous range of motion from 30° flexion to 30° extension in the sagittal plane flexion and extension dimension; the ulnar and radial deviation dimension of the coronal plane can achieve a range of motion from 25° adduction to 25° abduction. When performing a two-degree-of-freedom compound motion, the end effector (active disc) can form a spherical working envelope with a diameter of 100 mm in three-dimensional space, and its maximum synthetic deflection angle reaches ±50°.

[0062] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A wrist joint driven by polyvinyl chloride-based artificial muscle, characterized in that The invention comprises a movable disk (1), a hemispherical gear (2) at the upper end of the wrist, a hemispherical gear (3) at the lower end of the wrist, a fixed disk (4) and a dielectric elastomer axial driver, wherein the hemispherical gear (2) at the upper end of the wrist is fixedly connected to the movable disk (1), the hemispherical gear (3) at the lower end of the wrist is fixedly connected to the fixed disk (4), and the hemispherical gear (2) at the upper end of the wrist and the hemispherical gear (3) at the lower end of the wrist are meshed together, the fixed disk (4) is fixedly connected to a base (7) via a column (6), the upper end of the dielectric elastomer axial driver is fixedly connected to the movable disk (1), and the lower end of the dielectric elastomer axial driver is fixedly connected to the base (7).

2. The wrist joint driven by polyvinyl chloride-based artificial muscle according to claim 1, characterized in that: There are four dielectric elastomer axial drivers, namely dielectric elastomer axial driver one (5.1), dielectric elastomer axial driver two (5.2), dielectric elastomer axial driver three (5.3), and dielectric elastomer axial driver four (5.4). The dielectric elastomer is made of silanized barium titanate / polyvinyl chloride composite gel, and the dielectric elastomer axial driver extends after power is supplied.

3. The working method of the wrist joint driven by polyvinyl chloride-based artificial muscle according to claim 2, characterized in that: When in use, an alternating current signal is introduced by a high-voltage power supply and passed into two adjacent dielectric elastomer axial drivers, so that the two adjacent dielectric elastomer axial drivers are actuated in a plane under the electric field, and the other two dielectric elastomer axial drivers are contracted because they are in a pre-stretched state in the initial state, thereby driving the hemispherical gear (2) at the upper end of the wrist to rotate in the contraction direction of the dielectric elastomer axial driver.

4. The method for operating a wrist joint driven by polyvinyl chloride-based artificial muscle according to claim 3, characterized in that: The wrist joint driven by the polyvinyl chloride-based artificial muscle has two degrees of freedom and can bend in four directions around the hemispherical gear at the lower end of the wrist. The hemispherical gear (2) at the upper end of the wrist is tightly meshed with the hemispherical gear (3) at the lower end of the wrist. Adjacent dielectric elastomer axial drivers are used in pairs. When dielectric elastomer axial driver one (5.1) and dielectric elastomer axial driver two (5.2) are energized and extended, dielectric elastomer axial driver three (5.3) and dielectric elastomer axial driver four (5.4) will contract due to their initial pre-stretched state, driving the hemispherical gear (2) at the upper end of the wrist to rotate toward the contraction direction of dielectric elastomer axial driver three (5.3) and dielectric elastomer axial driver four (5.4), thereby achieving the function of wrist bending.

5. The polyvinyl chloride-based artificial muscle-driven wrist joint according to claim 1 or 2, characterized in that: The dielectric elastomer axial driver is made of silanized barium titanate / polyvinyl chloride composite gel, and conductive silicone grease electrodes are coated on both sides of the composite gel; wherein, The silanized barium titanate / polyvinyl chloride composite gel is prepared by a solution blending method of polyvinyl chloride and silanized barium titanate. The dielectric constant of the barium titanate used in preparing the silanized barium titanate is 1000-2000.

6. The wrist joint driven by polyvinyl chloride-based artificial muscle according to claim 5, characterized in that: The thickness of the silanized barium titanate / polyvinyl chloride composite gel is 0.3-0.5 mm, the elastic modulus is 0.12-0.73 MPa, and the dielectric constant is 4-11; the thickness of the conductive silicone grease electrode is 0.1-0.2 mm, the diameter is 40 mm, and the surface resistance is 1000-3000Ω / sq.

7. The polyvinyl chloride-based artificial muscle-driven wrist joint according to claim 5, characterized in that: The dielectric elastomer axial actuator can generate an in-plane actuation displacement of 0.21-8.23 mm under an alternating current signal with an electric field strength of 5.4 V / μm-17.8 V / μm and a frequency greater than 0.5 Hz.

8. The polyvinyl chloride-based artificial muscle-driven wrist joint according to claim 5, characterized in that: The preparation method of the silanized barium titanate / polyvinyl chloride composite gel is as follows: (1) dissolving barium titanate silane in N,N-dimethylformamide to obtain a mixed solution A; dissolving polyvinyl chloride and di-n-butyl adipate in N,N-dimethylformamide to obtain a mixed solution B; (2) uniformly mixing the mixed solutions A and B to obtain a mixed solution C; (3) Pour the mixed solution C into a glass culture dish and heat it in a vacuum drying oven until the solvent is completely evaporated to obtain a silanized barium titanate / polyvinyl chloride composite gel.

9. The wrist joint driven by polyvinyl chloride-based artificial muscle according to claim 8, characterized in that: The amount of di-n-butyl adipate used is 2 to 4 times the mass of polyvinyl chloride, and the content of silanized barium titanate in the composite gel is 6.25 wt% to 20 wt%.

10. The polyvinyl chloride-based artificial muscle-driven wrist joint according to claim 5, characterized in that: The preparation method of the conductive silicone grease is as follows: components A and B of the conductive silicone grease are diluted with silicone oil respectively, and the diluted components A and B are evenly mixed to obtain the conductive silicone grease, wherein the mass ratio of component A, component B and silicone oil is 1:1:3.

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