Humanising robot fingers

Abstract

Background: Current challenges in the design of anthropomorphic robot fingers is the implementing of anatomically accurate tendon-ligament structures, specifically for the collateral ligaments, volar plates, and the extensor apparatus. The development of robot fingers with these structures could aid in the further understanding of the functional anatomy and biomechanics of the human finger. It has been suggested that these fibrous structures can be emulated as a set of individual, non-elastic strings. The configuration of these tendon-ligament structures result in the specific motions of the finger.
Aims: The aims of this thesis were to develop and manufacture an anthropomorphic finger prototype with fully anthropomorphic tendon-ligament systems. So the prototype could be functionally actuated as a human finger, and would perform humanoid motion mechanisms, such as the Interphalangeal joint
coupling, an ab-adduction/axial rotation coupling.
Methods: A parametric finger model was derived from CT images of human finger bones, with a focus on the soft tissue connection to the joints and the tendon pulley system attached to the phalanges. The finger segments were designed as a shell structures with functionally anthropomorphic shapes. The finger contained the metacarpal bone, the proximal, middle and distal phalanx and included
humanoid joints, tendons, and ligaments. These finger bone shells had fine rosters of perforations for the attachment of joint ligaments and supporting ligaments, implemented as a collection of individually attached dyneema strings, allowing for the precise and iterative attachment of these strings. The strings
had adjustment possibilities to accurately determine their functional lengths. This model was then produces by FDM additive manufacturing on a scale of 5:1 with PLA as a material. To reduce the friction around the joints, friction experiments were performed, where graphite in an epoxy resin was found to be an appropriate coating for the joint surfaces. The tendons and ligaments systems were developed as a collection of non-elastic Dyneema strings, where the string lengths and positioning were identified according to biomechanical finger models.
Results: The result was the creation of a finger prototype with anthropomorphically realistic pulley systems for the tendons with joint surfaces of minimal friction, so that the finger could be actuated by the tendons to simulate realistic humanoid behaviour. The humanoid motion, and coupling mechanisms
were verified with 2D motion tracking software and manual measurements by performing possible
movements done by actuating the muscle tendons of the finger prototype and by comparing the resulting
motion with that of a human finger. Where the finger prototype performed similar motions as a human finger.
Conclusions: This research project successfully developed an anthropomorphic finger with humanoid joint-ligament systems connecting the finger segments, and tendon configurations. It showed the possibility of constructing these systems and configurations as a set of individual strings that could emulate the structures found in the human body. The resulting anthropomorphic finger can form a
basis for further research in the complex mechanics, relation, and dependencies of the human hand and in doing so, aid in the study of a wide range of pathologies in the finger and the hand, as well as support surgeons in reconstructive surgery and rehabilitation.