A Multi-Objective Simulation-Optimization Framework for the Design of a Compliant Gravity Balancing Orthosis

Flexion-synergy is a stereotypical movement pattern that inhibits independent joint control for those who have been affected by stroke; this abnormal co-activation of elbow flexors with shoulder abductors significantly reduces range of motion when reaching against gravity. While wearable orthoses based around compliant mechanisms have been shown to accurately compensate for the arm at the shoulder, it is unclear if accurate compensation can also be achieved while minimizing device bulk. In this work, we present a novel, multi-objective simulation-optimization framework towards the goal of designing practical gravity-balancing orthoses for the upper-limb. Our framework includes a custom built VB.NET application to run nonlinear finite element simulations in SolidWorks, and interfaces with a MATLAB-based particle swarm optimizer modified for mul-tiple objectives. The framework is able to identify a set of Pareto-optimal compliant mechanism designs, confirming that compensation accuracy and protrusion minimization are indeed conflicting design objectives. This Pareto set is compared to an approximation of the current state-of-the-art. The execution of the simulation-optimization framework demonstrates a capability of achieving designs that compensate for more than 90% of the arm's gravity, as well as those that exhibit an average protrusion of 15 % of the arm length if not lower, with different trade-offs between these two objectives.