Research On Motion Control Strategy For An Omnidirectional Lower-limb Rehabilitation Robot

The global population aging is increasingly serious and patients with lower-limbdysfunction caused by various diseases, injuries and traffic accidents have increasedsignificantly. Correct, scientific rehabilitation for these patients plays an important role, inaddition to early treatments and necessary drug treatments. In this dissertation, the kinematic,dynamic modeling of an omnidirectional lower-limb rehabilitation robot and the trajectorytracking control under the centre-of-gravity shift during walking training are studied based onthe research projects of Liaoning Provincial Department of Education and Liaoning ProvincialNatural Science Foundation. This research, which our country is short of, so has a broad outlookand can provide theoretical and technical base for the application of the omnidirectional lower-limb rehabilitation robot.The omnidirectional lower-limb rehabilitation robot is a strongly coupled, complexnonlinear system including many uncertainties. The robot’s motion is affected by mechanicalerrors of actuators, mass and inertia, environments, the sliding and friction between the wheeland ground and mechanical vibration. Especially, the center of gravity of the omnidirectionalmobile robot during rehabilitation affected by load factors is uncertain. The motion control todeal with the centre-of-gravity shift has become an important problem in such field. Thisdissertation mainly includes the following aspects:(1) Mathematical modeling of omnidirectional lower-limb rehabilitation robot with regardfor centre-of-gravity shift. Combined with the analyzing of the kinematics and dynamicscharacteristics of a four wheeled omnidirectional robot, the models of the robot kinematics anddynamics are established, respectively the ideal case with no load, with consideration of themass of the load, but not consideration of the centre-of-gravity shift and with regard for thecentre-of-gravity shift.(2) For the omnidirectional lower-limb rehabilitation robot, a new controller by using theacceleration and velocity information effectively of the target trajectory is proposed. This new controller is proposed by using the relation equations of certain physical matrices of the systemdynamic model perfectly. By including the acceleration and velocity information, the speed ofcvergence and accuracy of the tracking error are well improved. The stability of this controllerwas proved by Lyapunov theorem under the condition of the constant mass of the patient. Thecontroller was simulated to verify the correctness by comparison with PD controller.(3) A robust control strategy under the unknown and time-varying of the centre-of-gravityis proposed. Considering that the centre-of-gravity of the robot is always unknown and time-varying, a robust compensation control strategy aimed to solve the time-varying and unknownof the centre-of-gravity shift is developed. By developing an adaptive robust controller withH∞tracking performance to eliminate the time-varying and unkown part of the system, themotion performance and the interference suppression of the rehabilitation robot has both beenimproved. Based on specifying constraint relationship on four wheels’ control force, the newstrategy broke the previous limitation and dependence of the controller to the time-varyingmatrix of the system model.(4) Experimental platform and research on trajectory tracking control of theomnidirectional lower-limb rehabilitation robot. Based on the platform consisting of the robotdesigned by Kochi University of Technology, the camera and the computer, the feasibilities ofthe above proposed trajectory tracking control algorithms of chapter3and chapter4arevalidated through tracking basic line trajectory.The research on the omnidirectional lower-limb rehabilitation robot and its motion controlalgorithms are yet to start in our country. The effectiveness of the algorithms is also closelyrelated to the hardware of robot, online, reliability and real-time. The purpose of this dissertationis to improve the effect of rehabilitation based on control methods during the centre-of-gravityshift and to provide modest promotion to the development of lower-limb rehabilitation robot.