Reliability-Based Design Optimization for the Knee Joint of the Lower Extremity Exoskeleton

This paper proposes a reliability-based design optimization (RBDO) method for the knee joint of the lower extremity exoskeleton considering uncertain factors, which will provide an approach to improving the comfort and safety and even reducing energy consumption when wearing the lower extremity exoskeleton. Uncertainty quantification models for the knee joint of the lower extremity exoskeleton is established by considering the randomness from manufacture and assembly errors based on effective length model of continuous contact. After that, the time-dependent reliability for the knee joint in one gait cycle is computed using the combination of moments method and global optimization. The time-variant reliability for the knee joint is treated as the constraint, the mean value of energy consumption is identified as an optimization objective, the mean value of actuator mounting dimensions is selected as optimal variables, the reliability-based design optimization model is finally set up based on the constructed objective and constraint functions. The simplified configuration of the Berkeley Lower Extremity Exoskeleton (BLEEX) is employed to testify the effectiveness of the proposed method.