Robust Control Of Micro-hand Nonlinear Systems Based On Operator Theory

With the development of the science,soft robot has become a research topic in the field of robotics.With the development of medical technology and the emergence of an aging society,the research on soft robot has been attracting more and more attention.As an important branch of soft robots,soft actuators have high safety to fragile objects and affinity to human because it is made of flexible material,which is more concerned and respected by scientists.Micro-hand,as the representative of the research of soft actuators,is made of silicon rubber,which has the shape of a bellows and is a flexible pneumatic actuator.Besides,it only needs one air tube to generate curling motion in two ways under positive and negative pressure.However,due to the nonlinear characteristics of the actuator,it is very difficult for the actuators to be accurately modelled and stably controlled,as well as tracking control.Therefore,in this paper,the robust right coprime factorization method based on operator theory is used to study the robust control and tracking control of Micro-hand nonlinear systems.Firstly,because the Micro-hand actuator system is nonlinear,the operator theory is adopted to describe the Micro-hand system model,only the relationship between the input pressure and the bending angle of the actuator is considered,and the effective factorization is carried out based on isomorphism.Furthermore,the least square identification algorithm is used to identify the rubber radius,which ameliorates the shortage of constant rubber radius in existing literature.Secondly,because the air pressure changes nonlinearly with time,which brings certain challenges to the real-time accurate control of the Micro-hand.The passivity-based control design of the Micro-hand nonlinear system is considered from an energy perspective,that is,robust right coprime factorization method based on operator theory and passivity-based control method are used to design robust controllers to maintain the robust stability of the system.Meanwhile,among the studies of Micro-hand nonlinear system,the tracking problem of the system has not been perfectly solved.Therefore,based on the newly established Micro-hand systemmodel,two tracking controllers are designed,one of which is an adaptive tracking controller with the ability to automatically modify its own characteristics to adapt to the dynamic change of the system.On the other hand,because the integral sliding mode control has fast response speed and strong robustness for the uncertainty,and the introduction of integral term can eliminate the steady-state error caused by the sliding mode approaching state and enhance the robustness of the system,another integral sliding mode tracking controller is designed to refer to the Micro-hand nonlinear system.Finally,MATLAB simulation is performed on the designed controller using real experimental data,from the simulation results,it can be seen that the designed controllers basically meets the robust stability requirements with good tracking performance.From the simulation results,it is find that the robust stability can be guaranteed by the two types tracking control scheme,while the tracking error by using the integral sliding mode controller is much smaller than the adaptive controller.That is,it is better for the Micro-hand nonlinear systems to maintain the stability and the tracking performance by using the integral sliding mode control.