In this paper, a passive exoskeleton is developed to strengthen the motion ability of the knee joint bearing four times the body weight during climbing mountains or stairs. With the novel design, an inverted cam mechanism is designed to transform foot-strike energy to joint positive work of the knee joint, a type-selection mechanism for spring steel bars, and further their application model based on the linear elastic theory of metal materials are established, and to attach the exoskeleton assistance torque to the energy consumption characteristics of the knee joint, the moment-arm variation and the cam profile of the inverted cam mechanism are investigated. In addition, this paper proposes the potential link between the utilization of foot-strike energy and discrete power assistance for the knee joint, which creates simplifying conditions for exoskeleton designs with clutch mechanisms. Finally, to verify the effectiveness of the exoskeleton design, two exoskeleton prototypes were used for respiratory metabolism tests, in which 75% of the test results obtained an average power-assistant efficiency of 14.15%.
Keywords: Foot-strike energy; Inverted cam mechanism; Knee exoskeleton; Power assistance; Stair climbing.