Driving Characteristics Research And Application Of The Twisted And Coiled Actuator

As a kind of soft actuators,artificial muscles can contract and extend like biological muscles,so it has a high application value in the field of soft robots,bionic robots,rehabilitation robots,etc.However,most of the traditional artificial muscles such as shape memory alloys(SMA),dielectric elastomer actuators(DEA),carbon nanotube artificial muscles(CNT)and ionomer-metal composites(IPMC)have large hysteresis,low cycle life,limited deformation and output force,and also costly.A recently-discovered polymeric artificial muscle,twisted and coiled actuator(TCA)which can be easily fabricated from polymer fibers such as nylon fibers can provide large tensile stroke and stress.merits of TCA also include high energy density,long cycle life and small hysteresis.These advantages provide the TCA enormous potentials for applications in soft robots.In this study,the twisted and coiled actuator is taken as the research object,the structure and actuating principle of the TCA are studied and analyzed;starting from the basic structure of the TCA,the formation process of the spiral structure is analyzed,the actuating principle of the length change of the TCA caused by the temperature change is analyzed.Based on the force analysis model of the spring structure,the static model of the TCA is established.The model reveals how the material properties,size,structure,load conditions,and the recovered torque influence the amount of deformation of the TCA.Manufacture methods of fabricate a variety of polymer fibers into TCAs are explored,the nylon 6,6 polymer fiber is used as an example to demonstrate the process of fabeicating TCA in a natural spiral way and winding around a mandrel.Two ways to make TCA with attached heating wire and the way to control the wire attachment density are introduced.The sensory and control system of TCA is studied.Based on the TCA with attached heating wire,a temperature self-sensing method for TCA is presented,and the temperature measurement error was less than 3.2%.A self-sensing temperature closed-loop control system for artificial muscle is established,and the average steady-state error of the step response is less than 1.15%.Based on the temperature closed-loop control system,a position control system of the TCA is established.In the open-loop condition,without using other sensors,only relying on the temperature self-sensing characteristics of the TCA,the deformation of TCA can be controlled accurately and steadily,which lays the foundation for the actual use and control of TCA.Under the closed-loop condition,the dual closed-loop control system with both position closed-loop control and temperature closed-loop control realized a very precise and stable position control of the TCA,the steady-state error of the step response is less than 0.1%.The TCA is applied to the actuating of soft robots,a general soft robot module that driven by TCAs with the ability to bend in any direction is designed and manufactured.,soft robots with complex functions can be created by assembling multiple modules together.A bending posture control system for the soft robot module is established,and the precise control of the bending angle of the soft robot module is realized.This soft robot module has been successfully applied to a two-finger soft manipulator to verify the possibility of assembling the soft robot module into a soft robot,and the grabbing ability of the manipulator is tested.The related results lay a theoretical and practical foundation for the specific actuate control and application of TCAs.