Design of soft exoskeleton structure for hand rehabilitation actuated by shape memory alloy

Based on the previously designed hand rehabilitation exoskeleton structure, we propose a wearable soft hand rehabilitation device (HRD) actuated by shape memory alloy (SMA) wires. In order to accommodate the force and strain required for finger flexion and extension, the HRD with SMA wires-driven range extension mechanism has been redesigned to be 36.7% less long than the previous structure. In addition, we also designed the supporting structure for the SMA wires to stabilize the length of SMA wires and keep them tight to ensure the best actuation effect. Compared to previous work, the Coupled statics model is justified by analyzing the relationship between finger joint angles and fingertip forces during grasping. The experimental results show that the maximum sum of joint angle of the metacarpophalangeal (MCP) joint, proximal interphalangeal (PIP) joint, and distal interphalangeal (DIP) joint of the index finger is about 150°. The maximum fingertip forces of different fingers are different, ranging from 2 N to 7 N, depending on the geometrical size of each finger. The maximum operating temperature of the device is 31.7°C, which is within the safe range. This study demonstrates the feasibility of using the HRD to assist hand function rehabilitation.