Efficient and comprehensive haptic information for grasp control in upper-limb prosthetics

Abstract

Defining the Self is a long-standing quest, which has been addressed by psychologists, mathematicians and philosophers. Prosthetics has become an exciting branch of robotics that carries the potential of answering this question, usinga synthetic or robotic framework, due to the controllability of the relation between the prosthetic device and the human wearer in the interaction with the environment. The incorporation of the robotic prosthesis as part of the wearer’s body has been found to be a sensorimotor artificial transformation subjected to complex technological challenges due to the unstructured environments in which humans operate. This thesis addresses the technological and information-related challenges of haptic interfaces - both haptic sensing and displays - for upper-limb prostheses. It introduces the notion of efficient feedback in prosthetics, a concept through which, technologically, morphology in the design of tactile sensors and haptic displays enhances the relayed information using minimal resources (e.g., electronical, computational and physical). Within the same concept, extended to the information dimension of sensing, this thesis proposes the nature of haptic information which needs to be provided to the prosthesis wearer for acomprehensive environmental representation and an efficient grasp. We show that a quantitative feedback description of proprioceptive sensing,e.g., grip force strength, and exteroceptive sensing, e.g., object slip speed, for prosthetic hands, endows prosthesis users with a robust guidance towards stable grasp, i.e., grip force within safe margins against slip. Additionally, we show the distinct role of grip force and slip speed feedback in regulating the artificial grasp. Following up on these ideas, we developed a haptic device that displays both force and slip in a quantitative way and reveals efficient design principles for prosthetics. We also look at efficient design principles of tactile sensing systems for extracting enhanced haptic information. Ridged patterns on an artificial skin are inspected for their potential to encode haptic stimuli in their morphology during static and dynamic events. We developed a ridged artificial skin that detects stimulus force, slip occurrence, speed and location, by using a single force sensor. Based on evolutionary algorithms, we provide insights into the trade-off between tactile sensing resolution and sensitivity, as an expression of the number and spatial distribution of ridges, respectively. The thesis deepens the understanding of artificial sensorimotor transformations in prosthetic systems and shows the potential of exploiting morphology for efficient sensory feedback schemes in prosthetics.