Abstract: This paper introduces the design and fabrication of a smart and Hybrid Composite Finger (HCF) to achieve finger-like motions, such as holding and tapping motions. Bionic research on tapping motion of the index finger was conducted to obtain its structural and tapping parameters. The HCF, actuated by Shape Memory Alloy (SMA) wires, possesses a hybrid structure which is composed of a rigid structure to be its metacarpal part and a deformable structure to produce bending movement just like the function of the finger. Owing to an adhesive bonding technology, the HCF was fabricated with a composite structure which is reliable under impulsive responses, and had a worklife of more than 630000 times. A bending model was built by synthesizing the phase transformation dynamic model of the SMA wires and quasi-static analysis of the HCF. Structural optimization of the HCF was conducted by synthesizing the bending model together with experimental analyses. To produce a holding motion like as the finger, a holding heating strategy was proposed to adaptively heat the HCF to keep holding state based on the resistance feedback of SMA wires and a Proportion Differentiation (PD) algorithm. Besides, we used an impulsive heating method to heat the HCF to produce a high fidelity tapping motion with a maximum tapping force (6.83 N) at a response time (43 ms) which considerably coincided with those (about 
5.8 N, 45 ms) from tapping bionics of the index finger. Finally, a soft prosthetic hand system which had a hand-like appearance was manufactured based on the HCFs and several tests like as anthropomorphic gesture motions and human-like tapping motions to tap a keyboard were conducted to prove potential application of the HCF.

Key words: soft robotics, soft prosthetic hand, biomimetic, artificial muscle, composite structure, SMA wires