Variable stiffness flexible gripper and brush writer based on composite dielectric elastomer film

Abstract

The present application provides a variable stiffness flexible gripper based on composite dielectric elastomer film and a brush writing device based on the variable stiffness flexible gripper. The variable stiffness flexible gripper comprises a plurality of stiffness adaptive flexible drivers, each of which comprises an actuating layer, a stiffness adjusting layer and a flexible frame layer arranged in layers. The actuating layer and the stiffness adjusting layer are both composite dielectric elastomer films with flexible electrodes coated on the upper and lower surfaces. The flexible frame layer is the outermost layer and is used to adjust the bending degree of the stiffness adaptive flexible driver. The actuating layer and the stiffness adjusting layer are respectively connected with an external power supply. By adjusting the voltage and frequency applied to the actuating layer and the stiffness adjusting layer, the integrated change of the actuating displacement and the stiffness of the flexible gripper is realized.

Description

Technical Field

[0001] This invention relates to the field of artificial muscles, and more particularly to a variable stiffness flexible gripper and a brush pen writing device based on a composite dielectric elastomer film. Background Technology

[0002] Artificial muscles are soft actuators that mimic the characteristics of natural muscles and are widely used in the manufacture of robots with more efficient and natural forms of movement. Artificial muscles with emotional feedback are crucial for the development of robot intelligence and human-computer interaction. Although existing artificial muscle materials can match or even surpass human muscles in some individual properties, they struggle to mimic muscle states under different emotions. For example, the strokes of a human hand writing the same word differ between relaxed and tense states because of variations in muscle tension, resulting in slight differences in the expressed movement. Among these, flexible grippers with adjustable stiffness, due to their structural flexibility and environmental adaptability, have become a vehicle for biomimetic robots to achieve more accurate and diverse movements and emotional transmission, but their responsiveness and integration remain challenging.

[0003] To achieve adaptability to different loads without sacrificing the compliance of soft actuators and robots in robot-object interactions, stiffness-tunable materials are being applied to flexible robotic systems. These materials include shape memory polymers (SMPs), electrorheological materials (ER), low-melting-point alloys (LMPAs), particulate or layered interference structures, and elastomers filled with electro / magnetically active liquids. The stiffness of thermally responsive SMPs can be adjusted by the temperature of the glass transition region, switching from a deformable, soft-hot state (~MPa) to a high-load-bearing, hard-cold state (~GPa). To achieve stable actuation and significant stiffness adjustment in flexible grippers, researchers have combined shape memory polymers with another stimulus-responsive material, obtaining stiffness-tunable actuators through combinations of different thermally responsive materials. However, this approach inevitably suffers from long thermal response times and low efficiency, along with complex structures that hinder integration. These issues impede the practical application of actuation materials in the field of artificial muscles. Summary of the Invention

[0004] This invention provides a variable stiffness flexible gripper based on a composite dielectric elastomer film, to at least solve one of the problems existing in related technologies. To achieve this objective, this invention is implemented through the following technical solution.

[0005] One embodiment of the present invention provides a variable stiffness flexible gripper based on a composite dielectric elastomer film. The variable stiffness flexible gripper includes multiple stiffness-adaptive flexible actuators. Each stiffness-adaptive flexible actuator includes an actuation layer, a stiffness adjustment layer, and a flexible frame layer stacked together. The actuation layer and the stiffness adjustment layer are both composite dielectric elastomer films with flexible electrodes coated on their upper and lower surfaces. The flexible frame layer is the outermost layer and is used to adjust the bending degree of the stiffness-adaptive flexible actuator. The actuation layer and the stiffness adjustment layer are respectively connected to an external power source. By adjusting the voltage and frequency applied to the actuation layer and the stiffness adjustment layer, the integrated change of the actuation displacement and stiffness of the flexible gripper is realized.

[0006] Furthermore, the composite dielectric elastomer film is a film made from a silicone rubber elastomer prepolymer containing giant electrorheological particles. The giant electrorheological particles are urea-encapsulated barium titanyl oxalate particles obtained by co-precipitation of carbon quantum dots. The giant electrorheological particles are mixed with dimethyl silicone oil in a mass ratio of 4:1 to 1:1 to form a suspension. The suspension is mixed with a silicone rubber mixture to obtain the silicone rubber elastomer prepolymer. The giant electrorheological particles account for 5-50% of the mass of the silicone rubber elastomer prepolymer.

[0007] Furthermore, the giant electrorheological particles in the composite dielectric elastomer film of the actuation layer account for 20-25% of the mass of the silicone rubber elastomer prepolymer.

[0008] Furthermore, the actuation layer comprises at least two layers of the composite dielectric elastomer film.

[0009] Furthermore, the giant electrorheological particles in the composite dielectric elastomer film of the stiffness adjustment layer account for 40-45% of the mass of the silicone rubber elastomer prepolymer.

[0010] Furthermore, the thickness of the composite dielectric elastomer film of the actuation layer is 0.2mm-0.7mm, and the thickness of the composite dielectric elastomer film of the stiffness adjustment layer is 0.8mm-1.2mm.

[0011] Furthermore, the range of coordinated stiffness variation between the stiffness adjustment layer and the actuation layer is 16.4–30.4 mN / mm.

[0012] Furthermore, the composite dielectric elastomer film of the actuation layer and the stiffness adjustment layer is formed integrally by silicone adhesion, and the flexible frame layer is adhered to the stiffness adjustment layer.

[0013] Furthermore, when a voltage is applied to the stiffness adjustment layer, an actuation coupling is generated between the actuation layer and the stiffness adjustment layer.

[0014] When a voltage is applied to the actuation layer, a stiffness increase effect is generated simultaneously in the actuation layer and the stiffness adjustment layer, but the stiffness increase of the actuation layer is less than that of the stiffness adjustment layer.

[0015] When a voltage is applied simultaneously to the actuation layer and the stiffness adjustment layer, stiffness coupling is generated between the actuation layer and the stiffness adjustment layer.

[0016] Furthermore, the resonant frequency when voltage is applied to the stiffness adjustment layer is 7Hz, the resonant frequency when voltage is applied to the actuation layer is 9Hz, and the resonant frequency when voltage is applied to both the stiffness adjustment layer and the actuation layer is 8Hz.

[0017] Another aspect of the present invention provides a brush writing device based on the above-described variable stiffness flexible gripper.

[0018] The embodiments of the present invention have the following beneficial effects:

[0019] (1) By introducing carbon quantum dot-modified urea-coated barium titanyl oxalate particles (giant current rheological particles) into silicone rubber elastomers, a composite dielectric elastomer film was obtained that simultaneously possesses high dielectric properties and giant current rheological properties. Functional conversion and performance amplification were achieved by adjusting the particle concentration in the giant current rheological particles. A composite dielectric elastomer film with a particle concentration of 20-25% as the actuation layer exhibited high actuation performance: an area strain of 33% at an electric field of 15.6 kV / mm. A composite dielectric elastomer film with a particle concentration of 40-45% as the stiffness adjustment layer achieved a higher energy storage modulus increment: ΔG' = 1.5 MPa. The synergy of the two functional layers enabled the actuator based on this composite dielectric elastomer film to exhibit superior actuation and current rheological performance compared to existing actuators under low electric fields.

[0020] (2) The stiffness-adaptive flexible actuator based on the composite dielectric elastomer film has excellent electromechanical conversion capability and can simultaneously achieve direct control of enhanced actuation and stiffness adjustment capability (stiffness increased by 2.4 times); and the superposition of the two functional layers, the actuation layer and the stiffness adjustment layer, can achieve the coupling effect of actuation and stiffness change when voltage is applied at the same time, making its actuation or stiffness change significantly better than applying voltage to only a single functional layer, and the response time is in the millisecond range.

[0021] (3) The stiffness-adaptive flexible actuator based on this composite dielectric elastomer film also exhibits good frequency response. Under a certain electric field, each functional layer shows a distinct displacement resonance region with frequency variation. The individual stiffness adjustment layer and actuation layer have resonance frequencies of 7Hz and 9Hz, respectively, while the resonance frequency of the functional layers when an electric field is applied simultaneously is 8Hz. Since coupling can affect the resonance properties of the system and cause a shift in the resonance frequency, the resonance frequencies of the functional layers have a certain coupling correlation.

[0022] (4) An integrated variable stiffness flexible bionic gripper and brush writer based on stiffness adaptive flexible actuator can achieve rapid response to brush grasping and writing actions based on actuation and stiffness adjustment; under the same stroke trajectory, the actuation and stiffness change response can be coordinated by combining voltage and frequency in an independent or on-demand control interactive manner, thereby obtaining a variety of different emotional brush strokes and realizing the diversification of emotional expression in calligraphy writing.

[0023] (5) The variable stiffness flexible gripper based on composite dielectric elastomer film has the characteristics of performance stability. The stiffness adaptive flexible actuator can operate stably for at least 1 million driving cycles. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 This is a schematic diagram of the structure of a variable stiffness flexible gripper based on a composite dielectric elastomer film according to an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of the structure of SAFA according to an embodiment of the present invention;

[0027] Figure 3 (a) and (b) respectively display 1 to 10 7 The dielectric constant (ε) of the composite dielectric elastomer GERDE thin film in the Hz frequency range. r The trends of dielectric loss (tanδ) and frequency variation;

[0028] Figure 4 (a) and (b) show the stress-strain curves and Young's modulus of the composite dielectric elastomer GERDE as a function of BTRU concentration, respectively.

[0029] Figure 5 (a) Relationship between the area change rate and out-of-plane actuated displacement of different concentrations of GERDE under the same electric field (5 kV / mm); 5(b) Correlation between the storage modulus increment ΔG' and particle concentration; 5(c) Electromechanical coupling coefficient k of different concentrations of GERDE and PDMS; 5(d) VHB (3M commercial acrylic tape) TM Comparison of DEA (dielectric elastomer actuator) actuation displacement (25% pre-stretch) and relative ER effect of four elastomers: 4910, PDMS, PDMS / TiO2, and GERDE;

[0030] Figure 6(a) Displacement and stiffness responses of each functional layer of SAFA in the embodiment of the present invention under voltage; 6(b) Actuation displacement of each functional layer of SAFA in the embodiment of the present invention under applied voltage; 6(c) Curve of force varying with displacement of SAFA before and after power-on.

[0031] Figure 7 Schematic diagrams of the initial, grasping, and writing actions of the brush writing device with a variable stiffness flexible gripper according to the embodiment of the present invention.

[0032] Figure 8 (a) Variation of blocking force of different functional layers under an electric field in this embodiment; 8(b)效果图 of the regular script calligraphy character '中' written by the bionic flexible gripper in this embodiment. Detailed implementation manners

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will elaborate on each implementation manner of the present invention in conjunction with the accompanying drawings. However, those of ordinary skill in the art can understand that in each implementation manner of the present invention, many technical details are proposed for the better understanding of the readers. However, even without these technical details and various changes and modifications based on the following implementation manners, the technical solutions claimed in the present application can still be achieved. The division of the following various embodiments is for convenience of description and should not constitute any limitation to the specific implementation manners of the present invention. The various embodiments can be combined and cited with each other on the premise of no contradiction.

[0034] In the embodiment of the present invention, by introducing giant current-variable particles (BTRU) into a silicone rubber elastomer, a giant current-variable dielectric elastomer (GERDE) with both high dielectric and giant current-variable properties is obtained. At the same time, the designed and prepared stiffness adaptive flexible actuator (SAFA) achieves direct control and coupling effects of enhanced driving and stiffness adjustment capabilities (a 2.4-fold increase in stiffness), and the response time is in the millisecond level. Finally, an integrated variable stiffness bionic gripper structure is constructed based on SAFA, which can respond to the grasping and writing actions of the brush respectively based on actuation and adjustable stiffness, and obtain more than three different emotional calligraphy traces, realizing the diversification of emotional expression in calligraphy writing. And the SAFA bionic gripper shows significant long-term stability in at least 1 million driving cycles.

[0035] The embodiment of the present invention provides a variable stiffness flexible gripper based on a composite dielectric elastomer film. Figure 1 Schematic diagram of the structure of the variable stiffness flexible gripper based on the composite dielectric elastomer film according to the embodiment of the present invention. Figure 2 Schematic diagram of the structure of SAFA according to the embodiment of the present invention. As Figure 1 and Figure 2As shown, the variable stiffness flexible gripper comprises multiple SAFAs, each SAFA including a stacked actuation layer ACL10, a stiffness adjustment layer VSL 20, and a flexible frame layer 30.

[0036] The actuation layer 10 is a composite dielectric elastomer film with flexible electrodes 11 coated on its upper and lower surfaces. Its preparation method involves pre-stretching the composite dielectric film using a rigid frame (e.g., a pre-stretch ratio of 150% x 125% length x width), followed by coating the upper and lower surfaces of the film with flexible carbon grease electrodes. For example, the flexible carbon grease electrodes can be coated by imprinting. Preferably, as... Figure 2 As shown, a two-layer composite dielectric film stacked structure is used to improve overall actuation. The actuation layer 10 has a film thickness of 0.2mm-0.7mm. The stiffness adjustment layer 20 is also a composite dielectric elastomer film with flexible electrodes 11 coated on both its upper and lower surfaces, and its preparation method is the same as that of the actuation layer 10. In this embodiment, the film thickness of the stiffness adjustment layer 20 is 0.8mm-1.2mm. The composite dielectric elastomer films of the actuation layer 10 and the stiffness adjustment layer 20 are bonded together with silicone (e.g., PDMS) to form a whole. The flexible frame layer 30 is bonded to the stiffness adjustment layer 20 and is used to adjust the curvature of the SAFA. The material of the flexible frame layer 30 can be, for example, silicone rubber (e.g., PDMS). The actuation layer 10 and the stiffness adjustment layer 20 are respectively connected to an external power source. By adjusting the voltage and frequency applied to the actuation layer 10 and the stiffness adjustment layer 20, the integrated change of the actuation displacement and stiffness of the flexible gripper is achieved.

[0037] In this embodiment, the composite dielectric elastomer film is a film made from a silicone rubber elastomer prepolymer containing giant electrorheological particles. The giant electrorheological particles are urea-encapsulated barium titanyl oxalate particles (BTRU) prepared by co-precipitation, denoted as BTRU particles. The BTRU particles are mixed with dimethyl silicone oil at a mass ratio of 4:1 to 1:1 to form a suspension. The suspension is then mixed with a silicone rubber mixture to obtain the silicone rubber elastomer prepolymer. The giant electrorheological particles account for 5-50% of the mass of the silicone rubber elastomer prepolymer.

[0038] The method for preparing a composite dielectric elastomer film according to an embodiment of the present invention includes the following steps:

[0039] Step 1: The prepared BTRU particles and dimethyl silicone oil are premixed using a high-energy ball mill at a specific mass ratio to obtain a uniformly dispersed suspension. The ball milling time is 10-30 minutes, and the mass ratio of BTRU particles to silicone oil is 4:1 to 1:1. The BTRU particles are essentially urea-coated barium titanyl oxalate particles, prepared by a co-precipitation method. The viscosity of the dimethyl silicone oil is 5-100 mPa·s.

[0040] Step 2: Mix components A and B of commercial silicone rubber Ecoflex-0030 (Smooth-On, USA) in a 1:1 ratio to obtain a mixture. Stir the mixture and the above suspension at a specific mass ratio until homogeneous, and use a vacuum pump to remove excess air bubbles to obtain the composite dielectric elastomer prepolymer. Ecoflex-0030 (0030) is a two-component silicone rubber with a fixed A:B mixing ratio of 1:1. The elastic modulus after curing is approximately 68.95 kPa. The amount of particles added accounts for 5% to 50% of the mass of the composite dielectric elastomer prepolymer.

[0041] Step 3: Set the relevant parameters on the automatic coating machine and pour the composite dielectric elastomer prepolymer onto the PET (polyethylene terephthalate) substrate for coating. The parameters set on the automatic coating machine include: expected film thickness of 0.5–1 mm, coating speed of 10–100 mm / s, coating distance of 10–50 cm, and substrate heating temperature of 25–60 °C.

[0042] Step 4: After the coating is completed, the prepolymer will be cured to obtain a composite dielectric elastomer film with uniform thickness.

[0043] Furthermore, the composite dielectric elastomer film was fabricated into a ring-shaped film actuator to test the out-of-plane actuation displacement of the dielectric elastomer, thereby evaluating the dielectric properties, mechanical properties and storage modulus changes of the composite dielectric elastomer film under different particle contents (5wt.% to 50wt.%), and at the same time evaluating the actuation of the composite dielectric elastomer film under different particle concentrations.

[0044] (1) Dielectric properties

[0045] Figure 3 (a) and (b) show the dielectric constant (ε) of the composite dielectric elastomer GERDE film in the frequency range of 1–107 Hz. r The trends of dielectric loss (tanδ) and frequency variation. Figure 3 In (a), as the frequency increases, the ε of samples with different particle concentrations... r The dielectric properties gradually decrease and then tend to stabilize. This is mainly because the dielectric properties of materials at low frequencies depend on interfacial polarization. As the frequency increases further, interfacial polarization weakens, and dipole polarization becomes dominant. Figure 3In (b), at low frequencies, the dielectric loss of the composite elastomer material is mainly due to conductivity loss caused by leakage current. At 1 kHz, the tanδ of silicone rubber is 0.02, while the tanδ of the 20 wt.% and 50 wt.% composite materials are 0.4 and 2.15, respectively. With further increases in frequency, significant dielectric loss peaks appear in the 10³–10⁴ Hz range for different samples, primarily due to increased molecular dipole orientation polarization. Therefore, the dielectric constant of the elastomer composite material increases with increasing BTRU particle concentration, attributed to the enhanced overall polarization caused by the increased particle concentration. However, as the particle concentration increases, the dielectric loss of the system also continuously increases, and the energy conversion efficiency decreases, which is detrimental to improving the actuation performance of the elastomer.

[0046] (2) Mechanical properties

[0047] Figure 4 (a) and (b) show the stress-strain curves and Young's modulus of the composite dielectric elastomer GERDE as a function of BTRU concentration, respectively. Increasing particle content typically leads to an increase in Young's modulus. Therefore, to achieve a lower modulus increase in the GERDE film under high doping levels and maximize the actuation performance of the GERDE actuator, this embodiment of the invention adds a high content of silicone oil as a particle dispersant and composite film softener while doping with BTRU particles. Tensile test results show that, with increasing particle concentration and silicone oil content, the Young's modulus of the GERDE elastomer increases from an initial 0.15 MPa (0% GERDE particle mass content, denoted as GERDE-0) to 0.21 MPa (10% GERDE particle mass content, denoted as GERDE-10), and finally decreases to 0.06 MPa (50% GERDE particle mass content, denoted as GERDE-50), showing a trend of first increasing and then decreasing.

[0048] (3) Changes in storage modulus

[0049] To assess stiffness changes, the storage modulus increment (ΔG' = G'E - G'0) and the relative ER (electro-variable) effect are typically used.

[0050] The relative ER (electro-reflective) effect is defined by the following formula.

[0051]

[0052] Among them G' E G and G'0 are the storage moduli when there is an electric field and when there is no electric field, respectively. Figure 5(b) The correlation between ΔG' and particle concentration is shown. ΔG' is small at low mass fractions but increases significantly with increasing particle concentration. As particle content increases, the distance between particles decreases, and the electrostatic attraction between particles is essentially a short-range force, thus ΔG' increases rapidly. Simultaneously, higher mass fractions increase the chance of particle chain formation, leading to longer and denser structures in the presence of an external electric field. However, excessively high content can cause uneven particle dispersion, even separation from the polymer matrix, resulting in a decrease in ΔG'. At a constant concentration, the ΔG' of the GERDE film increases with increasing electric field strength. This is because initially, the particles are randomly distributed and need to migrate towards the direction of the electric field. Due to the presence of polymer chains around the particles, their fluidity is poor, requiring the addition of silicone oil for regulation and control. However, at low voltages, the attraction between particles is still small, making it difficult to overcome the elastic force of the matrix, resulting in a small ΔG'; as the electric field increases, the attraction between particles strengthens, and the ΔG' value rises rapidly. Compared to traditional electrorheological fluids (ERE), where the energy storage modulus increment ΔG' is positively correlated with the square of the electric field (ΔG'∝E2), GERDE's modulus is not (ΔG'∝Eα). The higher the particle mobility, the larger the α value (α>2). Therefore, GERDE-45 (45% GERDE particle content) achieves a ΔG' of 1.5 MPa and a relative ER efficiency of 11237%, demonstrating excellent stiffness adjustment capability.

[0053] The flexible electrodes on the upper and lower surfaces of the composite dielectric elastomer layer are led out through conductive tape and connected to an external high-voltage power supply, thereby controlling the device's gripping and stiffness adjustment. The coordinated stiffness variation range of the stiffness adjustment layer 20 and the actuation layer 10 can reach 16.4–30.4 mN / mm.

[0054] (4) Actuation performance

[0055] To evaluate the energy conversion capability between electrical and mechanical energy in GERDE thin films, the electromechanical coupling coefficient (k) can be calculated based on the above measurements. The results show that the electromechanical coupling coefficient increases continuously with increasing concentration. Figure 5 d), of which GERDE-25 and GERDE-45 have the highest electromechanical sensitivity ( Figure 5 c) The values ​​reached 39.22 and 156.11 respectively, which are 1.9 and 7.4 times higher than those of the commercially available 3M VHBTM4910 (k=21), demonstrating higher electromechanical conversion capability. Subsequently, the DEA-induced displacement (25% pre-stretch) and relative ER effect of four elastomers—VHB, PDMS, PDMS / TiO2, and GERDE—were compared. Figure 5d) The results show that GERDE has high advancement in low-voltage actuation and ER effect. More importantly, GERDE generated a large-area strain of 33% (25% pre-stretch, 15.6kV / mm) under a low electric field of 15.6kV / mm, achieving the same actuation strain effect as the commercial VHBTM4910 (400% pre-stretch, 70kV / mm) under a high electric field.

[0056] Driven area strain and out-of-plane driven displacement are important components for evaluating DEA actuation performance. Out-of-plane driven displacement is measured by applying a certain prestress to the DEA surface, while the area strain test method is explained in the actuation characterization. Based on the measured area change rate and out-of-plane driven displacement (e.g., ) of different concentrations of GERDE under the same electric field (5 kV / mm), [further details are needed]. Figure 5 a) indicates that with the increase of particle concentration, the out-of-plane actuation displacement and area change rate of the GERDE actuator show a trend of first increasing and then decreasing, and reach the maximum at a concentration of 25 wt% (GERDE-25), with an area change rate of 19.5% and an out-of-plane actuation displacement of 2.9 mm. The area change rate is 2.7 times higher than that of the pure matrix, and the out-of-plane actuation displacement is 2.1 times higher.

[0057] In this embodiment, the giant electrorheological particles in the composite dielectric elastomer film of the actuation layer 10 account for 20-25% of the mass of the silicone rubber elastomer prepolymer (e.g., Figure 2 Designated as GERDE-25, according to the comparison of actuation test results, a high actuation performance can be obtained at this concentration; concentrations higher or lower than this will cause a decrease in actuation performance. The giant electrorheological particles in the composite dielectric elastomer film of the stiffness adjustment layer 20 account for 40-45% of the mass of the silicone rubber elastomer prepolymer (e.g., Figure 2 The ER effect (denoted as GERDE-45) is essentially a process force. Increasing the particle content is beneficial to enhancing the ER effect. Therefore, within this concentration range, more BTRU particles can be added. However, excessive particle addition will prevent the polymer from agglomerating to form an elastomer. Thus, a higher increase in storage modulus can be obtained at this concentration. The synergy of the two functional layers enables the actuator based on this composite dielectric elastomer film to exhibit superior actuation performance and electrorheological performance under low electric fields compared to existing actuators.

[0058] Then, several of the above-mentioned SAFAs are assembled into a flexible gripper. In this embodiment, a flexible gripper with two fingers is used as an example. After the electrodes have cured, two GERDE films with different particle concentrations are adhered together using silicone to form a whole. Finally, a flexible silicone rubber frame is adhered to the GERDE film of the stiffness adjustment layer 20 to form a SAFA. The upper and lower electrodes of the GERDE film are led out using fine conductive tape and connected to the positive and negative terminals of an external high-voltage power supply. A clamp is designed and manufactured, using a PMMA (polymethyl methacrylate) plate to fix the SAFA unit (finger) at a predetermined position with a bending angle as a component of the biomimetic flexible gripper. Copper nails are used as circuit connection points to apply circuitry to the two SAFAs simultaneously. Finally, the two SAFAs are fixed to the PMMA and the bending angle is adjusted to form the fingers.

[0059] The following describes the performance testing of the variable stiffness flexible gripper.

[0060] (1) Actuation and stiffness response of each functional layer of SAFA

[0061] To better illustrate the actuation and stiffness response performance of the variable stiffness flexible gripper, the main body of the SAFA was pre-tested for changes in stiffness and actuation under different voltages and different functional layers. The displacement and stiffness response of each functional layer of the SAFA under different voltages were then tested. Figure 6 (a) shows that as the voltage of the stiffness adjustment layer 20 increases, the SAFA displacement continuously increases, achieving displacement superposition between the actuation layer 10 and the stiffness adjustment layer 20, i.e., actuation coupling. Simultaneously, increasing the voltage of the actuation layer 10 also increases the stiffness of the SAFA structure, but the increase is small, far less than that of the stiffness adjustment layer 20. However, when voltage is applied to both layers simultaneously, the stiffness improvement effect is better than single-layer stiffness adjustment, and at 4kV, the SAFA structure stiffness increases to 2.4 times the initial stiffness, achieving stiffness coupling between the actuation layer 10 and the stiffness adjustment layer 20. Furthermore, Figure 6 (c) It can be shown more intuitively that the force-displacement change curve of SAFA before and after energization can be divided into the normal zone (no energization) and the stiffness adjustment zone (energization). By adjusting the voltage during the test, the stiffness of SAFA can be rapidly changed, and the stiffness adjustment before and after voltage application can be reversible.

[0062] Subsequently, by applying voltage-response actuation displacement to each functional layer of SAFA ( Figure 6(b) It can also be seen that when the actuation layer 10 is driven under a 4kV, 0.1Hz electric field, the SAFA actuation displacement reaches 10mm. When a 4kV voltage is applied to both functional layers simultaneously, the actuation displacement reaches 10.8mm, which is better than the actuation of the actuation layer 10 alone. Therefore, the superposition of the two functional layers has a certain degree of coupled actuation. Since silicone rubber elastomers have good time and frequency response, GERDE also has this characteristic well. By testing its actuation response, the results show that under an electric field, its response time is about 150ms, which is similar to the response time of the electrostatic composite gripper. Therefore, SAFA has excellent actuation response and can achieve rapid response strain. However, its recovery time is relatively long (~1.5s). This is because when the GERDE-45 elastomer is subjected to an electric field, a strong and stable microstructure is formed between the particles. This structure leads to a significant hysteresis effect, so more time or external force is needed to consume the stored energy and eventually recover to the initial state. Nevertheless, SAFA still holds significant advantages compared to thermotropic stiffness (response and recovery >30s) and liquid crystal polymers (>4s). Furthermore, SAFA exhibits good frequency response; under a given electric field, each functional layer displays a distinct displacement resonance region with frequency variation. The individual stiffness adjustment layer 20 and actuation layer 10 have resonance frequencies of 7Hz and 9Hz, respectively, while the resonance frequency is 8Hz when all functional layers are simultaneously subjected to an electric field. Since coupling can affect the system's resonance properties and cause a shift in resonance frequency, the resonance frequencies of the functional layers exhibit a certain degree of coupling correlation.

[0063] (2) Resistance test

[0064] Another embodiment of the present invention provides a brush writing device based on the above-mentioned variable stiffness flexible gripper, such as... Figure 7 As shown.

[0065] The gripping force of the robot gripper is directly related to the resistance force of SAFA (e.g., Figure 8 (a) and (b)) By testing the change of the blocking force under the electric field of different functional layers, it can be seen that the blocking force of the stiffness adjustment layer 20 alone reaches about 31mN under a voltage of 4kV, while the clamping force of the coupling effect between the stiffness adjustment layer 20 and the actuation layer 10 reaches about 50mN, which can realize the robot gripper to stably grasp the pen-type calligraphy brush.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A variable stiffness flexible gripper based on a composite dielectric elastomer film, characterized in that, The variable stiffness flexible gripper includes multiple stiffness-adaptive flexible actuators. Each actuator comprises a stacked actuation layer, a stiffness adjustment layer, and a flexible frame layer. The actuation layer and the stiffness adjustment layer are composite dielectric elastomer films with flexible electrodes coated on their upper and lower surfaces. The flexible frame layer is the outermost layer and is used to adjust the bending degree of the stiffness-adaptive flexible actuator. The actuation layer and the stiffness adjustment layer are respectively connected to an external power source. By adjusting the voltage and frequency applied to the actuation layer and the stiffness adjustment layer, the flexible gripper can achieve [variable function / adjustment]. The method enables integrated changes in displacement and stiffness, wherein the composite dielectric elastomer film is a film made from a silicone rubber elastomer prepolymer containing giant electrorheological particles, wherein the giant electrorheological particles are urea-encapsulated barium titanyl oxalate particles obtained by co-precipitation of carbon quantum dots, the giant electrorheological particles are mixed with dimethyl silicone oil at a mass ratio of 4:1 to 1:1 to form a suspension, the suspension is mixed with a silicone rubber mixture to obtain the silicone rubber elastomer prepolymer, and the giant electrorheological particles account for 5-50% of the mass ratio of the silicone rubber elastomer prepolymer.

2. The variable stiffness flexible gripper based on a composite dielectric elastomer film according to claim 1, characterized in that, The giant electrorheological particles in the composite dielectric elastomer film of the actuation layer account for 20-25% of the mass of the silicone rubber elastomer prepolymer.

3. The variable stiffness flexible gripper based on a composite dielectric elastomer film according to claim 2, characterized in that, The actuation layer comprises at least two layers of the composite dielectric elastomer film.

4. The variable stiffness flexible gripper based on a composite dielectric elastomer film according to claim 1, characterized in that, The giant electrorheological particles in the composite dielectric elastomer film of the stiffness adjustment layer account for 40-45% of the mass of the silicone rubber elastomer prepolymer.

5. The variable stiffness flexible gripper based on a composite dielectric elastomer film according to claim 1, characterized in that, The composite dielectric elastomer film of the actuation layer has a thickness of 0.2mm-0.7mm, and the composite dielectric elastomer film of the stiffness adjustment layer has a thickness of 0.8mm-1.2mm.

6. The variable stiffness flexible gripper based on a composite dielectric elastomer film according to claim 1, characterized in that, The range of coordinated stiffness variation between the stiffness adjustment layer and the actuation layer is 16.4~30.4 mN / mm.

7. The variable stiffness flexible gripper based on a composite dielectric elastomer film according to claim 1, characterized in that, When a voltage is applied to the stiffness adjustment layer, an actuation coupling is generated between the actuation layer and the stiffness adjustment layer. When a voltage is applied to the actuation layer, a stiffness increase effect is generated simultaneously in the actuation layer and the stiffness adjustment layer, but the stiffness increase of the actuation layer is less than that of the stiffness adjustment layer. When a voltage is applied simultaneously to the actuation layer and the stiffness adjustment layer, stiffness coupling is generated between the actuation layer and the stiffness adjustment layer.

8. The variable stiffness flexible gripper based on a composite dielectric elastomer film according to claim 1, characterized in that, The resonant frequency when voltage is applied to the stiffness adjustment layer is 7 Hz, the resonant frequency when voltage is applied to the actuation layer is 9 Hz, and the resonant frequency when voltage is applied to both the stiffness adjustment layer and the actuation layer is 8 Hz.

9. A calligraphy brush writing device based on a variable stiffness flexible gripper, characterized in that, The variable stiffness flexible gripper is the variable stiffness flexible gripper based on a composite dielectric elastomer film according to any one of claims 1-8.

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