Research On Multi-functionalization And Application Of Twisted And Coiled Polymer Fiber Artificial Muscles

Tri-co robots can realize natural interaction with the working environment,humans and other robots,and can autonomously adapt to complex dynamic environments and work collaboratively.It is one of the important research topics in the robotics field.Traditional rigid actuators such as motors and cylinders cannot meet the requirements of human-machine-environment safe interaction required by Tri-co robots.Soft actuators made of low-modulus flexible materials are suitable for the complex human-machine-environment interaction benefited from their good flexibility,infinity degrees of freedom,and strong adaptive ability.Commonly used soft actuators such as electro active polymer,shape memory materials,and fluid pressure soft actuators have output characteristics similar to biological muscles,and can meet the driving requirements of Tri-co robots to a certain extent.However,these actuators have limitations such as high driving voltage,poor output linearity,and large air source devices.Twisted and coiled polymer fiber artificial muscle(TCP)provides a new driving option for Tri-co robots with its advantages of high output linearity,low hysteresis,and simple driving devices.However,TCP have problems such as imperfect mechanical model,inaccurate temperature sensing,low integration of deformation sensing,and small deformation amplitude of TCP-driven soft robots and poor motion accuracy.To solve these problems,this work builds a mechanical model describing the relationship between temperature,load,and deformation of TCP,so as to obtain the relationship between TCP’s structure parameters and its performance;proposes carbon black conductive nylon TCP whose impedance varies with deformation and nickel wire composite wound TCP whose impedance changes with temperature;proposes deformation and temperature sensing methods of TCP by using the impedance changes of TCP itself;develops a multiple degrees of freedom soft robotic arm driven by TCP,increasing the deformation range and motion accuracy of the soft robot driven by TCP.Based on the constitutive relationship of the highly twisted polymer fiber,a thermal stress model describing the relationship between temperature and untwisting torque is established;based on the principle of virtual work,a structural deformation model describing the relationship between untwisting torque,load and deformation of TCP is established;a complete mechanical model describing the relationship between temperature,load and deformation of TCP is established by integrating the above two models.The influence law of TCP structure parameters on its performance is obtained by analyzing the mechanical model,which provides a theoretical basis for the structure design of TCP and the selection of process parameters.To realize the deformation and temperature sensing based on the impedance change of TCP itself,the carbon black conductive nylon TCP,whose resistance changes with its deformation and the nickel wire composite winding TCP,whose resistance changes with temperature are proposed.To realize the manufacturing of the above two kinds of TCPs,guided by the TCP mechanical model,the influence of TCP manufacturing process parameters on its structure and performance is explored through experiments.Based on this,the selection principle of TCP manufacturing process parameters is determined.According to the selection principle of process parameters,appropriate parameters are selected to complete the manufacturing of carbon black conductive nylon TCP and nickel wire composite winding TCP,which provides a basis for TCP deformation and temperature sensing based on its own impedance changes.A resistance sampling circuit for carbon black conductive nylon TCP is designed to realize real-time deformation sensing of TCP.The deformation sensing resolution is less than 0.466 mm.A resistance sampling circuit for the nickel wire composite winding TCP is designed to realize the real-time temperature self-sensing and control.The rise time of temperature self-sensing and control in step response is less than 1.6s,the relative steady-state error is 0.44%,and the bandwidth frequency is 0.17 Hz.Based on the temperature self-sensing and control method,a feedforward-feedback TCP deformation control system is proposed,whose rise time is less than 6 s,the relative steady-state error is 3.3%,and the bandwidth frequency is 0.13 Hz;based on the temperature self-sensing and control method,a cascade closed-loop control system for TCP output force is proposed.The rise time in step response of the cascade closed-loop control system is increased by 25%,the steady-state error is increased by 49%,and the bandwidth frequency is increased by 50.7%,compared with the single closed-loop system.These works have realized the real-time sensing of deformation and temperature by using the impedance change of TCP itself.Compared with other existing works,the proposed sensing method does not need external sensors,and has the advantages of compact structure and high system integration.A multi-degree-of-freedom soft robotic arm driven by TCP is developed.A geometric model describing the relationship between the length of TCP and the bending posture of the soft robotic arm is established,and a kinematic model describing the relationship between the bending posture of the soft robotic arm and the Euler angle at its end is established to provide a basis for the calculation of the bending posture.A statics model and a finite element analysis method describing the coordinated deformation of TCP and soft materials are established,thereby the work space of the soft robotic arm is analyzed.The experiment of the soft robotic arm is carried out.The maximum bending angle of the module is 49.1°,and the maximum output force is 147 m N.Based on the TCP temperature self-sensing control method,a bending posture closed-loop control system is established.The bandwidth frequency of the soft robotic arm in Roll and Pitch direction are 0.049 Hz and 0.058 Hz respectively;the control accuracy in Roll and Pitch direction are 2.87% and 1.18%respectively.Compared with other existing soft robots driven by TCP,the proposed soft robotic arm in this work has improved deformation range and control accuracy.