Study On Controllable And Stiffness-Variable Soft Gripper Driven By Liquid Crystal Elastomer

This paper aims at the problem that most fingers of flexible grippers are difficult to control the bending Angle when working.In order to realize the simple control of flexible fingers and increase the adaptability of grippers,a liquid crystal elastomer driven flexible gripper with variable stiffness is designed in this paper.Flexible fingers are layered in structure and play corresponding functions respectively,and the simple control of finger bending can be realized in coordination with the work.The finger structure mainly consists of the lower liquid crystal elastomer driving material,the hollow insulation layer in the middle,and the upper rubber encapsulation thermoplastic polyurethane variable stiffness layer.The three layers are bonded and formed by the binder,and the functions of each layer of the finger are improved and tested.The results are as follows:In order to improve the response speed of liquid crystal elastomers,carbon nanotubes(CNTS)were modified with strong thermal conductivity and good compatibility.Samples of0.05 wt%,0.1 wt%,0.2 wt%,0.3 wt%,0.4 wt%,0.5 wt%,0.6 wt%,0.7 wt% liquid crystal elastomeric carbon nanotube polymer were prepared.The dispersibility of the material was observed with a microscope,and the sample was heated with electricity under the same heating voltage.The experimental results show that the response speed of the polymer increases first and then decreases with the increase of carbon nanotubes,and the 0.3wt%liquid crystal elastomer-carbon nanotubes polymer has the fastest response speed.The comparison test between 0.3 wt% polymer and liquid crystal elastomer material shows that the response speed of 0.3 wt% polymer is significantly higher than that of ordinary liquid crystal elastomer material,and the modification experiment significantly improves the response speed of the material.In order to verify the variable stiffness function of fingers,a thermoplastic polyurethane sheet was fabricated using a hot pressing mechanism and encapsulated with a rubber material.Dynamic thermomechanical analysis and temperature-rising tensile test were carried out to explore the variable stiffness function of the samples.The results of dynamic thermomechanical analysis show that the energy storage modulus of the sample is 44.8387 Mpa at room temperature,and decreases to 0.4325 Mpa at 64 ℃.The loss modulus of the sample decreased from 2.0378 Mpa at room temperature to 0.1268 Mpa at the end of the test.The experimental results reflected the change characteristics of the stiffness of the sample at room temperature and after heating,that is,the stiffness decreased at temperature rise and recovered at temperature drop.The temperature rise tensile experiment aims to explore the influence of temperature on the elastic modulus of the sample.Before and after heating,the tensile test is carried out on the sample,and the results are obtained and the comparison chart of the elastic modulus gap of the sample is drawn.The experimental results indicated that the internal material of the sample was liquefied after heating,and the elastic modulus was reduced to 0.000551 Mpa.The experimental results indicated that the rubber encapsulated thermoplastic polyurethane could meet the variable stiffness function.Flexible fingers were made.While heating the driving layer in the experiment,different blocks of the variable stiffness layer were heated respectively to conduct finger bending test.The experimental results showed that fingers could bend at different angles according to the heating of different blocks of the variable stiffness limiting layer,and the maximum bending Angle was 110°.The multi-heel finger is made into a flexible gripper combined with the base,and the grasping experiment is carried out on objects of different sizes.The experimental results show that the gripper can adjust the bending Angle of the finger according to the size of the object to be grasped,so as to protect the object to be grasped.The gripper automatically releases the object after power off.Finally,abaqus simulation software was used to simulate various possible finger bending modes.