Trajectory Planning And Coordination Control Strategies Of Bilateral Upper-Limb Rehabilitation Robots

Robot-assisted rehabilitation has received increasing attention and interest from researchers throughout the world due to its advantages of high precision,quantification,strong repeatability and rich training modes over conventional physiotherapy.This can greatly improve the efficiency of rehabilitation training.The robotic system for unilateral upper limb rehabilitation has a mature theoretical basis and technical support,and has obtained a wide range of clinical applications.In contrast,while the research on robot-assisted bilateral upper limb rehabilitation is still in early stage,it has been attracting increasing attention worldwide.Medical research data show that coordination training helps to promote the neuronal plasticity of the brain,which to some extent supports the in-depth exploration and development of new robot-assisted rehabilitation technologies such as bilateral upper limb robotic system.In terms of mechanical structure,bilateral rehabilitation robots can be divided into the asynchronous system and the synchronous one.Asynchronous robot systems are usually composed of two multi-degree-of-freedom independent robotic subsystems,and thus they usually have larger workspace and enable multi-movement modes due to two individually controlled handles.However,they suffer from the risk of linkage interference during the robotic movement,making the planning of training trajectories relatively complex.Differently,the synchronous bilateral robot is characterized with two handles rigidly connected through the robotic end effector.This brings a certain coupling to the two robotic handles,and thus this type of robot is more suitable for upper limb coordination training.However,existing robot-assisted bilateral upper limb rehabilitation technology still lacks in-depth exploration in motion control,trajectory planning,coordination mode and other aspects,especially in the lack of subject-specific adaptability and normalized integration of incentive mechanism with coordination training implementation.Thus,it is greatly essential and significant to address the following scientific issues: including how to establish normalized trajectory planning theories for bilateral upper limb rehabilitation robots;how to propose new interactive control methods with subjectspecific workspace consideration;and how to deliver upper limb coordination trainings with enhanced rehabilitation efficacy.This study is based on the development research fund project of the University of Auckland,New Zealand.Taking two typical bilateral upper limb rehabilitation robots for examples,this study is dedicated to researching their trajectory planning and coordination control strategies.Firstly,the normalized trajectory planning method was investigated through analyzing human upper limb kinematics and robotic workspace.Then,based on the proposed trajectory planning method,the position control,interactive control algorithms,and coordination strategies of synchronous bilateral upper limb robots were investigated and analyzed.Finally,a series of human tests were conducted in evaluating some key issues of trajectory planning and interactive coordination control of bilateral rehabilitation robots.The main research work of this study includes the following aspects:(1)Due to the lack of normalization theories in trajectory planning for bilateral upper limb rehabilitation robots,a new three-stage trajectory planning strategy was proposed in this study.Firstly,a seven-dof upper limb kinematics model was established by analyzing individual joint movement,aiming to derive the workspace of human upper limbs.Combining with the robotic workspace,the feasible region of effective workspace of human upper limbs can be obtained by integrating the intersection of the robot workspace and human upper limb workspace.Then,the rehabilitation training trajectories with multi-movement modes were defined within the feasible region for enhanced training safety.Finally,the spatial interference possibility was analyzed and compared by calculating the position relation of each link of the robot.This work aims to provide theoretical guidance for developing safe robot-assisted bilateral upper limb training environment.(2)To increase workspace of the robot,an optimization method was adapted using an external point penalty function.It enables the establishment of an optimization model of asynchronous robots with the objective function of maximizing the feasible region of effective workspace between humans and robots.Furthermore,to solve the issue that the three-stage trajectory planning strategy cannot completely avoid spatial interference,an inverse kinematics model of the robot was established based on the optimization model of the robot with the constraint condition of avoiding spatial interference.Simulation results show that the algorithm can effectively improve the feasible region and thus improve the proposed three-stage trajectory planning strategy by avoiding spatial interference of robots.(3)To further validate the applicability of the proposed trajectory planning method and improve bilateral coordination training strategies,this study set up a new type of portable synchronous upper limb bilateral robot platform where accurate and robust position control was achieved with subject-specific adaptation.Firstly,through kinematics analysis,software and hardware development,a synchronous bilateral robot was built and its two handles were rigidly connected through a mechanical link.Then,due to the coupling problem of the synchronous robot,two control methods were investigated respectively based on decoupling PID and kinematic proportional voltage.Furthermore,a passive training mode was implemented using the minimum jerk method and also with the integration of subject-specific workspace.Experimental results show that the synchronous robot can achieve stable and accurate motion control in the personalized workspace.(4)The interaction control implementation of the synchronization robot still lacks the integration of subject-specific workspace.By combining the concept of feasible region and compliance control methods,this study proposed an adaptive compliance control algorithm with linear parameter adjustment.This method enables the compliance change of the robot by regulating the robotic position with the reference trajectory in real time.Further,to avoid abrupt change of the robotic compliance when there is an irregular feasible region boundary,an adaptive control method was proposed based on the BPNN algorithm.It created the corresponding relationship between the position within the feasible region and control parameters,and reduced the chattering due to abrupt parameter changes.Finally,human experiments show that the proposed method can effectively improve the safety and compliance of human-robot interaction.(5)To enable more advanced coordination training strategy implementation,this study established a new coordination training model for bilateral upper limb rehabilitation.Since people have different movement capacities,and thus for different applications two control schemes were respectively proposed and implemented.One is the triggered position control based on a virtual channel and the other is the adaptive compliance control.Furthermore,to reduce the laziness of patients caused by redundant assistive force from robots,an iterative control method was proposed based on task performance.On the premise of not intervening human upper limb movement,this method tried to search optimal control parameters on an individual basis through the approximation of a limited number of times.The results of human tests show that this method can stimulate patients' consciousness of active movement and thus improve the efficiency of rehabilitation training.