This paper presents the design and control strategy of a novel assistive system,FEXO Knee,which combines functional electrical stimulation(FES)with a compliant exoskeleton for better physical rehabilitation of knee joint.The knee exoskeleton and FES work in asynergetic manner that attempts to allow arbitrary torque allocation between them via regulating a tunable gain.Currently the study focuses on controlling human rhythmic movements,i.e.,the swing of shank,to demonstrate the assistance efficiency of the hybrid FES-exoskeleton rehabilitation,and thus two muscle groups(Vasti and Hamstrings)were stimulated to produce active torque for knee joint.The reference trajectories of the exoskeleton and FES were provided by central pattern generator that acts as a phase predictor to deal with unexpected phase confliction between the two compliant mechanisms(the human shank and the exoskeleton).The modulated pulse width of FES stimulator is controlled by a model-based feed-forward controller.The elastic cable-driven actuator of knee exoskeletonallows safe interaction with the patients and avoids abruptly large torque shocks,which we think is more important than absolutely accurate position tracking in robotic-assisted rehabilitation.The movement command of the knee exoskeleton was produced by a classical proportional-integral-derivative controller.The joint angle is the only feedback signal that needs to be measured in the control frame.The mutual torque was also measured during the swing but it is merely for the purpose of performance evaluation.Four healthy subjects participated in the initial evaluation experiments and the results showed good performance of the hybrid FES-exoskeleton system.