Compliant Structure Design for Improved Robot Motion Control Performance

Abstract

This narrative review examines how compliant structural design redistributes motion control functions between mechanical bodies and computational controllers. It synthesizes theoretical, experimental, and co-design studies on passive dynamic walking, elastic coupling, self-stabilizing locomotion, soft robots, underactuated grasping, morphological computation, and morphology-control optimization. Across these systems, compliance can store and return energy, couple joint motion, shape attracting dynamics, adapt contact geometry, and transform inputs before feedback intervenes. These mechanisms can reduce the number of independently controlled variables and the demands on sensing, modeling, and feedback. Their benefits remain conditional: excessive or poorly located compliance can reduce positioning bandwidth, force capability, repeatability, and robustness outside the intended operating range. The reviewed evidence, therefore, supports allocating compliance to specific functions rather than minimizing stiffness globally. Mechanical self-regulation should be combined with sufficient sensing and actuation for disturbances beyond the passive region, while morphology and control should be optimized jointly with manufacturability, parameter variation, and transfer from simulation to hardware taken into account.