Sensing, Actuating & Interacting Through Passive Body Dynamics: A Framework for Soft Robotic Hand Design

Abstract

Robotic hands have long strived to reach the performance of human hands. The physical complexity and extraordinary capabilities of the human hand, in terms of sensing, actuation and cognitive abilities, makes achieving this goal challenging. At the heart of the physical structure of the hand is its’ passive behaviours. Seen most clearly in soft robotic hands, these behaviours influence and affect the mechanical, sensing and control functionalities. With this perspective, we present a framework through which passivity in robot hands can be understood, by concretely identifying the role of passivity in the design, fabrication and control of soft hands. In this framework we focus on the interactions between the physical hand and the: environment, internal actuation, sensor morphology and wrist control. Taking these surrounding systems away, we are left with a passive soft hand whose behaviours emerge from external interactions. Inspired by the human hand, we define the role of these four key interacting pillars and review how state-of-the art robot hands utilize these four elements to aid functionality. We show how these pillars promote hybrid soft-rigid hands with rich behaviours, providing benefits in terms of the increased adaptability to uncertain environments, improved scalability and reduction in the cost of actuation, sensing and control. This review provides a conceptual framework for approaching hand design and analysis through consideration of the passive behaviours. This highlights not only the advances that can be made by approaching the problem in this way, but also the outstanding challenges that stem from this outlook.