Mechanical design and evaluation of a compact portable knee–ankle–foot robot for gait rehabilitation

• Compact, modular, portable knee–ankle–foot robot for overground gait rehabilitation
• Novel series elastic actuator with high intrinsic compliance and large output force
• Optimization of mechanism design based on human gait biomechanics
• Experiments on healthy subjects show excellent mechanical performance of the robot.

This paper presents the mechanical design and evaluation of a knee–ankle–foot robot, which is compact, modular and portable for stroke patients to carry out overground gait training at outpatient and home settings. A novel compact series elastic actuator (SEA) is developed for safe human–robot interactions. As a solution to the limitation of conventional SEA designs, one low-stiffness translational spring and a high-stiffness torsion spring are placed in series for force transmission. The springs are selected based on gait biomechanics to maintain a high intrinsic compliance for most period of a gait cycle, while retaining the capacity to provide the peak force. To achieve portability, the robotic joint mechanism is optimized based on gait biomechanics, and the mechanical structure is built with lightweight materials. This robot demonstrates stable and accurate force control in experiments conducted on healthy subjects with overground walking. The activation level of the major leg muscles of subjects is reduced as indicated by the EMG signals and the normal gait pattern is maintained during the test, which demonstrates that the robot can provide effective assistive force to the subjects during overground walking.