Research On Position And Force Control For The Wheeled Mobile Manipulator

With the development and mutual fusion of both automation and information technology,the robot industry has developed rapidly.At the same time,the theoretical research on robot control has gradually become a hot topic.The position/force control of robot is an example.Since the wheeled mobile manipulator has larger working space and is more flexible compared with fixed-base manipulator,this paper takes the wheeled mobile manipulator as the research object.As for the three kinds of nonlinearities: flexible joint,joint deadzone and dynamic constraint that the wheeled mobile manipulator may encounter in practice,the paper analyses the system and proposes the corresponding strategies separately.Meanwhile,the solutions to the modelling error,the model uncertainty and the existence of interference in the motor model are given.For the flexible joint problem of the wheeled mobile manipulator,the dynamic model of the system is established firstly,in which the flexible joint is simplified as linear torsion spring.Then,a robust adaptive strategy is designed to guarantee the convergence of the position error and the boundness of the force.As for the modelling error,an adaptive law is given to estimate the modelling error as well.Thirdly,considering the situation where the rotational inertia of motor is unknown,an adaptive law is designed and a new robust adaptive strategy is proposed.The effectiveness of the given strategy can be proved by theoretical analysis.For the deadzone problem of the wheeled mobile manipulator,the relationship between controller output torque and joint driving torque is firstly obtained based on the model of deadzone.Secondly,an adaptive law for the width of deadzone and an adaptive strategy based on linear sliding mode are designed for the reduced dimension dynamic model.Then,the situation where the model is unknown while its upper bound exists is considered and a new robust adaptive strategy is designed to guarantee the boundness of the position and force error.For the dynamic constraint problem of the wheeled mobile manipulator,the corrected orthogonalization method is adopted to solve the problem that velocity and force are not orthogonal under dynamic constraint.By transforming the system with the designed transformation matrix,the velicity and the force are mapped to the orthogonal space.Then,a position/force strategy is designed,which drives the position and force converge to zero.Thirdly,we consider the situation where there is interference in the motor and propose the desired torque control strategy and the desired motor control strategy.The robustness of the system is enhanced.By selecting the proper Lyapunov function,the effectiveness of the proposed strategy is proved and the position error,force error and the torque error of motor converge to zero.Through simulation,the validity of the above conclusions is verified.