Research On Multifunctional Soft Robots Based On Supercoiled Polymer Artificial Muscle

As a new type of artificial muscles,supercoiled polymer(SCP)artificial muscle is capable of producing reversible mechanical deformation under external stimuli such as temperature field,infrared light,magnetic field and microwave depending on its fabrication process,among which SCP made from conductive nylon yarn with silver-plated surface is the most common and easy to use.SCP has many advantages such as large deformation,high output force,low hysteresis,low cost,easy actuation,long service life,and small size,which make it valuable for applications in soft robots,bionic robots,and rehabilitation robots.This paper takes the SCP as the research subject and starts from its structure and coiling method to reveal the actuation principle that temperature change leads to the contraction/extension of the whole SCP by decreasing/increasing the distance between the spiral coil and coil of the SCP.An analysis of the principles and differences in sensing methods of resistive wire accompanied twisting SCP and conductive fiber coiling SCP is conducted.The differences and properties between the multiple SCPs with various structures are described.The fabrication method of the SCP using nylon 66 fiber is investigated,and the fabricated SCP samples are characterized experimentally in terms of strain and force.To address the multiple challenges of current soft robots,including actuation methods optimization,stiffness modulation,and the lack of sensing mechanisms,three different soft robot prototypes based on SCP,a new type of actuator and sensor,are designed and fabricated with the aim of mitigating the shortcomings of current soft robots,as described below:(1)Development of a new hybrid actuation method combining SCP and gearmotor,and integration of this actuation method into a soft robotic finger.The stiffness and force output characteristics of the soft robotic finger in three configurations are tested experimentally.The experiment demonstrates the superiority of this actuation method in terms of compliance(compared with gearmotor & kiteline),output force(especially compared with SCP),and shows the potential of this new actuation method for grasping and manipulation in soft robots.(2)Proposition of a soft robotic finger with variable stiffness and multimode bending capability by integrating two types of thermally responsive polymers,i.e.,shape memory polymer(SMP)and SCP,into the finger design.The variable stiffness structure composed of thermoplastic SMP and Polyimide(PI)electrothermal film is used for stiffness modulation,and SCP is used for finger actuation.The electrothermally activated properties of SMP and SCP enable a more compact structure for the soft robotic finger.A stiffness model of the soft robotic finger is developed based on the thermomechanical constitutive model of SMP.In experimental section,the performance of the finger is tested to verify the validity of the stiffness model.The variable stiffness and multimode grasping performance of the two-finger robotic gripper is demonstrated,showing the potential of the proposed design in soft robotic gripper and robot design.(3)Based on the actuation and sensing characteristics of SCP,a soft robot module with proprioceptive capability actuated by SCP is proposed.The module can bend in two opposite directions and an internal soft strain sensor(SCP)can be used to sense the bending deformation of the module.From the bionic perspective,an inchworm crawling robot and a soft robotic gripper are designed and prototypes are fabricated using a single module as the basic unit.The experimental part tests the performance of the crawling robot and the soft robotic gripper,while demonstrating the integrated actuation-sensing capability.The results show the high application value of the soft robot module with proprioceptive function in the actuation/sensing of the soft robots and bionic robots,and the modular design enables it to be applied to more kinds of soft robots.