The Development of a New Synthetic Finger for Robotics Applications

The quest to replicate the human hand's extraordinary dexterity has significantly propelled the development of robotic systems designed to mimic human hand functionalities. These systems find applications across diverse fields, from healthcare and personal assistance to teleoperation, collaborative industrial processes, and prosthetic devices. Central to achieving such functionalities is a deep understanding of the mechanical and tribological mechanisms involved in human hand precision grasping interactions. This thesis explores these underlying mechanisms to inform the development of synthetic fingers that closely replicate human finger interactions for robotic systems. The approach includes a comprehensive literature review, synthetic finger design development, a comparison of stiffness and frictional behaviour between human and synthetic fingers, and an analysis of the contact mechanics of synthetic fingers under quasi-static and dynamic loading conditions. Supported by the broader Tribology as an Enabling Technology (TrEnT) research project, this work applies tribological principles to address design challenges in robotic systems aiming to enhance their dexterity. The literature review emphasises the importance of understanding the interplay between friction, contact area and shear responses in ensuring grasp stability. It highlights the potential of Finite Element (FE) modelling in enhancing simulations of finger-object interactions. Additionally, it reviews state-of-the-art synthetic finger technologies with embedded sensors mimicking human mechanoreceptors, identifying limitations in enabling dexterous grasping. The review underscores significant gaps in standardised testing methods for evaluating synthetic finger performance, advocating for the integration of friction and contact area analysis to advance these systems. Chapter 3 details the design development of a novel synthetic finger inspired by human fingers. A simplified cylindrical geometry with a hemispherical tip was adopted, with SLA 3D printing enabling the creation of ridges that mimic human fingerprints. Material selection and evaluation identified a silicone variant that closely mimics the compressive stiffness of the human finger. Chapter 4 compares the frictional behaviours of human and synthetic fingers with different elastic moduli on micro-grit abrasive papers. Insights are provided into how stiffness and texturing can enable synthetic fingers to mimic the frictional behaviour of human fingers and enhance tactile feedback. Chapter 5 investigates the contact mechanics of synthetic fingers under quasi-static loading through an integrated experimental and modelling approach. A high-resolution contact area quantification method is introduced, aiding the validation of analytical and FE contact area predictions. The findings demonstrate the importance of precise contact area quantification for enhancing predictive models of synthetic finger interactions, enabling design optimisation and improved control strategies for robotic manipulators. Chapter 6 examines the frictional dynamics and shear response of synthetic fingers interacting with glass, using both experimental and FE modelling approaches. Friction tests evaluate the effects of material properties, normal force, sliding velocity, contact angle and surface texture on frictional behaviour. A novel experimental approach combines contact area quantification with friction tests, providing detailed insights into the interaction dynamics. This technique is directly compared with FE simulations, to examine the impact of varying the coefficient of friction on simulation accuracy. Comparative assessments of material properties and texturing on the contact area behaviour of synthetic fingers are conducted using both FE simulation and experimental data. Additionally, FE simulations explore design parameters – such as the impact length, size, and bone inclusion – which are time-intensive to evaluate experimentally. The recommendations provided through this study guide the optimisation of synthetic finger designs, emphasising tailored material properties, textures, and dimensions to meet diverse functional requirements for robotic grasping and tactile applications. In conclusion, this research provides a foundation for advancing tactile robotics by enhancing understanding of synthetic finger mechanics and establishing methodologies to evaluate and improve future designs