Design And Control Of Dielectric Elastomer Actuated High-precision XY Stages

Dielectric elastomer actuators are one of the most prevalent artificial muscles in the field of soft robotics due to their advantages of high energy density,simple structure and fast response speed.Specially,dielectric elastomer actuators can easily achieve multi-degree-of-freedom by applying different electrode pattern,which have been widely used to actuate soft robots.However,the inherent viscoelastic creep and hysteretic nonlinearity of the material and cross-coupling effect cause severe output nonlinearity in the multi-degree-of-freedom dielectric elastomer actuators,which makes it difficult for accurately tracking dynamic trajectories and control,limiting their practical applications.This thesis aims at modeling and compensating the nonlinearity of multi-degree-of-freedom dielectric elastomer actuators.To this end,this thesis firstly designs a dielectric elastomer actuated high-precision XY stage.Then,the viscoelastic creep,hysteresis and cross-coupling nonlinearity are modeled and eliminated.Further,self-sensing based control strategy is developed to achieve high-precision periodic trajectory tracking control without the additional sensor.The main research contents of this thesis are as follows:1.A dielectric elastomer actuated high-precision XY stage is designed.At first,based on a planar dielectric elastomer actuator with two pairs of electrode patterns,this thesis investigates the influences of geometric parameters and pre-stretch on the static and dynamical responses.Then,based on the optimized parameters,a dielectric elastomer actuated XY stage is designed with a workspace of 2.5 mm.Lastly,to characterize the resolution of the XY stage,the stage is used to track step trajectory with a feedback controller.The experimental results demonstrate that the resolution of out stage can reach 100 nm.2.Based on feedback control and phenomenological model,a viscoelastic nonlinearity and cross-coupling effect compensation control method of the dielectric elastomer actuated XY stage is proposed.Firstly,to remove both viscoelastic creep nonlinearity and cross-coupling effect,two PID controllers are designed,achieving static trajectory tracking control.Further,a P-I model is developed to describe the asymmetric and rate-dependent viscoelastic hysteresis nonlinearity.Based on the P-I model,two direct hysteresis compensation feedforward controllers are designed to eliminate the effect of hysteresis nonlinearity.The experimental results of tracking periodical trajectories demonstrate that this control method can reduce the trajectory tracking error by more than 90% and the stage can accurately track complex planar trajectories such as spiral and butterfly tracks.3.This thesis further achieves self-sensing based high-precision periodic trajectory tracking control of the stage.On the basis of eliminating the nonlinearity of the dielectric elastomer actuated stage,the influence of the nonlinearity on self-sensing is illuminated.Subsequently,based on the system identification model and the P-I model,self-sensing viscoelastic nonlinear feedforward compensation controllers are established and the viscoelastic hysteresis and creep nonlinearity in self-sensing are respectively eliminated.Then,through self-sensing feedback control,the dielectric elastomer actuated stage can track the periodic trajectory.The experimental result demonstrates that the trajectory tracking error is limited up to 5%.