Artificial Muscles Design Methodology Applied to Robotic Fingers

In the domain of prosthetic robots, main challenges are related to the flexibility and adaptability of devices allowing people to achieve daily tasks. Particularly for robotic hand prosthesis, these challenges can be addressed from two approaches: the soft robotic and the utilization of smart materials. In this paper we propose a methodology to design artificial muscles for robotic fingers, showing the implementation feasibility of smart materials for precision grasping tasks. This work is part of the ProMain project that concerns the modeling and the design of a soft robotic hand prosthesis, actuated by artificial muscles and controlled with surface Electromyography (EMG) signals. In a first stage, we designed a robotic finger based on the equivalent mechanical model of the human finger. The model considers three phalangeal joints to perform flexion and extension movements. The robotic finger has three Degrees of Freedom (DoF), is under-actuated and is driven by tendons. i.e. only one actuator activates the whole finger, and the motor is coupled to the finger mechanism through two flexible wires. Then we carry out two experiments: the first experiment measures the pinch force of the human finger and the second measures kinematics and force of our robotic finger. We enhance experimental results with the mathematical model of the finger, to identify and quantify the main parameters of the artificial muscle. An approach to design an shape memory alloy based artificial muscle is introduced and justified.