Design of Robot Leg with Variable Reduction Ratio Crossed Fourbar Linkage Mechanism Generally, large knee joint torque is required when a leg is flexed. However, the large torque motor will increase the robot size and total weight. Also, a large reduction ratio gear box to realize the large torque will decrease output speed and lower backdrivability of the joint. It makes the robot difficult to perform agile and flexible motion like animals. In this paper, we propose a robot leg with a knee joint mechanism consisting of a variable reduction ratio crossed fourbar linkage mechanism (VRRCFLM) based on cruciate ligament of an animal. The VRRCFLM is to increase the reduction ratio for large knee flexion postures without greatly reducing the total backdrivability. In this paper, we developed a robot leg with a knee joint mechanism consisting of the VRRCFLM. In order to design the link parameters of the leg mechanism, optimization design aimed at maximizing the jumping height of the robot was performed. The robot model with the designed mechanism was evaluated through the dynamics simulations. Thanks to the VRRCFLM, the required torque of the knee motor at the large flexion postures was decreased. Moreover, the vertical jumping height was improved by 24.6 % comparing with a model without the mechanism. In experiments using the prototype, the required static torque was decreased as in simulation, and the jumping height was more than one leg length.

Design and Optimization of Singledegreeoffreedom Six bar Mechanisms for Knee Joint of Lower Extremity Exoskeleton Robot * The irregular contact surface between the femur and the tibia of the human body produces Jshaped instantaneous centers of rotation (ICR) of the knee joint. Therefore, two single degreeoffreedom (SDOF) sixbar mechanisms, which are composed of a trajectory fitting fourbar mechanism and a transmission fourbar mechanism, are used to fit the centers of the human knee joint and increase the loadbearing performance. Firstly, the displacements of ICR of the human knee joint are measured and calculated for the sake of the dimensional synthesis of the trajectory fitting fourbar mechanism. Then, two structural layouts of transmission fourbar mechanism are designed according to different selection of the driving rod in the trajectory fitting fourbar mechanism, and both the transmission fourbar mechanisms are optimized. The results show that after the two step optimization, the SDOF sixbar mechanism with the crank as the driving rod in the trajectory fitting fourbar mechanism has a better performance in smoothing the knee joint torque curve and superior transmission efficiency.