Research On The Applications In Soft Robotics And Design Of Dielectric Elastomer Actuators

Compared with conventional robots that based on hard materials,the soft robots that utilize soft materials or flexible structures have more excellent biomimetic performance,higher degree-of-freedom in motion and better environment adaptivity.Soft robots can move in confined space and sustain external impact without failure in structure and functions.Based on the characteristics of the utilized materials,the self-healing,self-sensing and self-assembly can also be endowed with soft robots.Most reported soft robots are driven by smart materials or smart structures that have controllable active deformation.Although having particular advantages in soft robotics applications,limitations exist in the practical applications of each smart materials or smart structures.For example,the heating/cooling process is required for temperature-controlled smart materials,which increases the response time of the system;the pump and valves are required for pneumatically actuated structures,which increases the volume and weight of the system and also brings noises.Dielectric elastomers are typical electro-active polymers that can response to external electric field and have the advantages of large deformation,fast response,light weight and high energy density,making them promising materials for artificial muscles.The fast response of dielectric elastomer is beneficial for increasing the dexterity of the soft robots and can realize the rapid switch and control between different motion modes or functions of the soft robots.This dissertation investigates the dielectric elastomer actuators based soft robots and human-machine interaction.For the concerned dielectric elastomer actuator structures,mechanical models are established to analyze their deformation and failure behavior under external voltage.The influences of the design parameters on the performances of the actuators are investigated to realize the design and optimization of the parameters of actuators,depending on the application requirements and experimental conditions.The details are following.The spring-roll bending actuator is a typical dielectric elastomer actuator,which is mainly composed of a spring as the core and the dielectric elastomer film wrapping around the spring,and can be used as the driving element of soft robots.To perform the design and optimization of the structure parameters of the dielectric elastomer spring-roll bending actuators,a theoretical model is firstly established based on the ideal dielectric elastomer model.The state equations of the bending actuator are formulated to analyze its deformation under external voltage.Critical criterions for typical failure modes of dielectric elastomers,including electrical breakdown,electromechanical instability,loss of tension and limiting stretch,are given and thus the allowable states of the actuator is determined.The influences of the design parameters of the bending actuator on its electrically induced deformation performance are discussed and the parameter optimization is conducted,considering several optimization goals.For some simplifications that are adopted in model establishment,the complicated deformation of the films in actuator is considered for model improvement.The theoretical predictions based on the improved model can well fit the test data.Based on the experimental conditions and theoretical predictions,the dielectric elastomer spring-roll bending actuator is fabricated with selected parameters,which can generate large bending deformation when subjected to external voltage.The deformation and lateral output force of the actuator under different applied voltages are tested.Integrated with 3D printed structures,applications of the bending actuators in soft robotics are preliminarily demonstrated by using the bending actuators as driving elements.A three-finger flexible gripper is fabricated with the capability to rapidly grasp and release objects under the control of the voltage.An inchworm inspired crawling robot is also fabricated,which can crawl under the alternative signals due to the anisotropic frictions that provide by the oriented fiber bundles.To realize the human-machine interaction between human and dielectric elastomer biomimetic structures,the electrophysiological signals are acquired,processed and amplified to control the deformation and functions of the dielectric elastomer biomimetic structures.The electrocardiogram-like signal is utilized to make a dielectric elastomer heart-shaped structure deform following the heartbeat.This verified the feasibility of using electrophysiological signals to control the dielectric elastomer biomimetic structures.Then a novel human-machine interface between human eyes and a dielectric elastomer biomimetic lens is further developed.Mimicking the working mechanism of human eyes,a dielectric elastomer biomimetic lens is designed and fabricated.The central part of the biomimetic lens is a soft tunable lens that mimics the human's crystalline lens.The focal length of the tunable lens can be adjusted by voltage,with a comparable focal length change ratio to that of human's crystalline lens.Actuated by the surrounding films that mimic the extraocular muscles,the tunable lens can have motions like planar movements and rotations.The eye movement recognition is performed by acquiring and processing the electrooculographic signals.Then the control of the biomimetic lens by eye movements is realized.The eye rotations can control the movements of the biomimetic lens to corresponding directions.Double blink can be used to adjust the focal length of the biomimetic lens,thus realize the switch between near vision mode and distance vision mode.For the unexpected responses that generated from errors in eye movement recognition,the method to reset the system by eye movements is also proposed.The aforementioned soft tunable lens is composed of lens frame,soft active film and passive film adhered on both sides of the frame and the enclosed transparent fluid.When the voltage is applied,the curvatures of the films on both sides will change,thus the focal length of the lens is tuned.The theoretical model of the tunable lens is established adopting ideal dielectric elastomer model and the theoretical results fit well with the experimental data.Based on the established model,the focus tuning performance and failure of the tunable lenses with circular and annular electrode configurations are compared.The influences of different design parameters on the focus tuning performances of both types of lens are discussed,providing references for the design of the soft tunable lens.