Interface Pressure Optimization for a Lower Limb Assistive Exoskeleton—Mechanical Modeling and Monte Carlo Simulation of Segmented Compliant Supports

The effect of the straps and support structures of a lower limb gait assist exoskeleton on pressure at the skin and soft tissue interface is examined. Because muscle atrophy may alter how loads pass between the limb and the device, a quasi-static torque and contact model for a lateral knee support model was developed. The nominal model used an assistive torque of 8 N·m and a support spacing of 0.24 m. A narrow circumferential cuff, a wide circumferential cuff, and segmented compliant pads were compared using the Markov Chain Monte Carlo method. Assistive torque, support spacing, effective contact fraction, strap preload, and a local concentration factor were varied. Under the stated model assumptions, the segmented pad concept had a median mean pressure of 8.9 kPa, with a 95% simulation interval of 6.8 to 11.5 kPa. Its peak pressure proxy had a median of 11.7 kPa, with an interval of 8.5 to 16.1 kPa. The corresponding medians for the narrow cuff were 20.6 and 36.9 kPa. Based on the comparison, an open, segmented load-bearing pad is proposed and bench testing on a limb surrogate is recommended. In the future, this study has implications on wearable pressure limits for older adults.