Design of a Biomimetic Robotic Hand with Dexterous Grasping and Manipulation Capabilities

Ang, Edmund Er Wen (2020) Design of a Biomimetic Robotic Hand with Dexterous Grasping and Manipulation Capabilities. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

This research describes the design and development process of a biomimetic robotic hand. The main motivation of this research is to increase the dexterity of robotic hands such that it can increase the functionality of existing prosthetic hands while taking in consideration of cost and complexity. Along with functionality, the appearance of these hands must be made to seem more life-like such that it can be a potential solution for actual limb replacement. Hence, the hand’s mechanical design is intended to mimic human hand architecture as well as its biomechanical features, which includes having the bones, ligaments, muscles and tendons. The final design and prototype of the biomimetic robotic hand has demonstrated that the appearance and functionality of the human hand could be replicated artificially with low-cost approaches. Using 3D printed plastic, the bones, actuator housing and assembly parts of the hand were fabricated. With soft rubber sheets, elastic and inelastic ribbons as the joints, a hand with passive compliance, appropriate range of motions and structural stability was developed. The actuation network of the human hand was also replicated with braided fishing lines used as the force transmission medium to mimic tendon muscles’ core functionality. More importantly, the actuation scheme and tendon routing of the hand is ensured to represent both essential extrinsic and intrinsic muscles of the human hand. The actuation scheme consists of a hybrid of active servo and passive elasticity, with 13 active servomotors used. The ring and little finger are coactuated via differential pulley transmission due to their collaborative relationship in grasping. With comparison to a grasping taxonomy developed by Feix et al. (2016), the developed hand prototype is able to achieve 28 out of 33 grasps types, with varying grasp qualities. The factors of unsuccessful grasp and poor performance include incorrect orientation and tendon routing of the thumb, inconsistent and inaccurate range of motion of finger joints due to non-parametric fabrication of ligaments, lack of corrugation of skin layer to increase contact area. The developed hand demonstrated in-hand manipulation capabilities through the rotation of a rectangular sponge in the z-axis, with a range of motion of -45°/55°, actuated by the coupled movement of thumb flexion and index finger abduction. The trajectory of the index finger has a logarithmic spiral curve and highly matches to human data, demonstrating excellent biomimicry. Besides, a novel sensor implementation based on a series elastic sensor design has been investigated through an experiment that utilises both a force sensitive resistor (FSR) sensor and the developed series elastic (SE) sensor in an index-thumb ring grasp of a masking tape ring. A high amount of power loss, in the tendon cable is discovered when the SE sensor is mounted in series with an actuator. The SE sensor has more practical suitability to the developed biomimetic robotic hand in terms of mechanical mounting compared to the FSR sensor. However, both FSR sensor and the SE sensor demonstrated good linearity, with FSR sensor having higher sensitivity.