Integral Exponential Adaptive Sliding Mode Control For A 4-R?2-SS? Parallel Robot Mechanism

In recent years,China's fruit production has grown rapidly,and the realization of robotic fruit aotomatic sorting to improve fruit sorting efficiency,reduce labor intensity,and increase economic efficiency is the trend of modern agricultural development.A 4-R(2-SS)fruit sorting parallel robot which can realize the SCARA movement has been developed in our research group,and the robot has the performance advantages of high rigidity,high precision and strong carrying capacity.Considering that the kinematic control is simple to design and easy to implement,this paper takes the 4-R(2-SS)parallel robot mechanism as the research object,and focuses on the high-performance control problem of kinematics on the basis of the robot's performance advantages.At present,there are still some difficulties in the kinematic control research of parallel robot mechanisms,mainly including: the coupling problem between the branches of the parallel robot mechanism;the uncertainties in the parallel robot system such as time-varying motor model parameters and external disturbances of each branch.Therefore,in order to overcome the influence of the coupling between branches through kinematic control,this paper studies a method for calculating the equivalent inertia of the drive joints considering the coupling between branches,and converts the equivalent inertia into the equivalent load inertia of each motor,and a integral exponential adaptive sliding mode control(IEG-ASMC)method for parallel robot branch without requiring the uncertainties prior information to overcome the influence of the coupling between branches and the branch uncertainties,while effectively suppressing sliding mode control(SMC)chattering is proposed.The main works accomplished in this article are as follows:(1)A method for calculating the equivalent inertia with considering the coupling between branches of the driving joints of the parallel robot is proposed.In order to solve the coupling problem between the branches due to the characteristics of closed chain structure of the 4-R(2-SS)parallel robot mechanism,based on the of kinematic analysis,the inverse solution and the Jacobian matrix of the mechanism are established,a joint space dynamic model is established according to the principle of virtual work.Through the coupling analysis of inertia matrix in the dynamic model,a diagonally dominant characteristic index of the inertia matrix is defined,and then,a method of calculating the equivalent inertia of the drive joint with considering the coupling between the branches is proposed,which is converted into the equivalent load inertia of each motor,which can eliminate the influence of the coupling between the branches in the kinematic control and improve the kinematic control performance of the 4-R(2-SS)parallel robot mechanism.(2)A IEG-ASMC method without requiring the uncertainties prior information for parallel robot branch is proposed.Aiming at the problem of coupling between branches and the uncertainties of branches in 4-R(2-SS)parallel robot,the SMC method is introduced,and an integral exponential adaptive law without requiring uncertainty prior information that can quickly adapt to changes in uncertainties is designed based on sliding mode variables to overcome the coupling effect between branches and the influence of branch uncertainties,and at the same time effectively suppress the chattering caused by overestimation of the switching gain of SMC.The theoretical proof of the stability is accomplished and the MATLAB simulation show that : compared with fixed switching gain SMC and the IG-ASMC,the proposed IEG-ASMC method in parallel robot mechanism has good tracking control performance when there are coupling between branches and uncertainties in branches,and it can effectively suppress chattering of SMC.Compared with IEG-ASMC without considering the coupling effect,the proposed parallel robot IEG-ASMC method with considering equivalent coupling effect can overcome the influence of the coupling action between branches to improve the tracking control performance of the parallel robot.(3)The 4-R(2-SS)parallel robot control system experimental platform is constructed and the experimental verification is carried out.The VC++6.0 was used to develop 4-R(2-SS)parallel robot control system host computer program,and Pewin32Pro2 was used to develop 4-R(2-SS)parallel robot mechanism slave computer motion program.Based on the constructed 4-R(2-SS)parallel robot control system experiment platform,the motion control experiment of the 4-R(2-SS)parallel robot prototype was carried out.By compareing the proposed method and the parallel robot branch fixed switching gain SMC,the IG-ASMC,and IEG-ASMC without considering the coupling effect,the effectiveness and superiority of the proposed control method is further verify.