The Role of Passive Mechanics in Asymmetrically Actuated Bioinspired Joints

Animal motor control relies on antagonistic muscle pairs. In many jointed animals, muscles are often asymmetrically sized, with one optimised for maximal force generation and its counterpart tuned for fine control and stability. This inherent asymmetry, combined with passive structures of the joint, integrates dexterity and power in a directionally biased manner. While conventional robotic joints are usually controlled by a single symmetrical actuator, asymmetrical actuation may offer benefits for real-world tasks. To better understand optimal design of asymmetrical actuation, we present a model that integrates active and passive mechanical properties of a joint. To obtain general insights, we use a non-dimensional framework to simulate joint performance in different dynamical regimes. Our results show that incorporating joint passive elasticity effectively compensates for the imbalance between actuators when asymmetric actuation is utilised. These results highlight a novel contribution of active-passive interactions, offering valuable insight for the design of bioinspired robotic joints.