Posture-dependent variable transmission mechanism for prosthetic hand inspired by human grasping characteristics

Gripping objects firmly and quickly is an important function of the human hand for everyday life. Prosthetic devices face significant challenges in replicating these capabilities, particularly in achieving a delicate balance between swift grasping and substantial grip strength while adhering to weight and form-factor constraints. To address these challenges, this study introduces a novel posture-dependent variable transmission (PDVT) that mimics the human hand’s behavior by employing a spiral-shaped spool. The PDVT’s spiral-shaped spool replicates the human hand’s quick and gentle pre-contact movements followed by a stronger force application after contact with the object. Additionally, a compressive series elastic spring enhances tendon tension across a wide range of finger postures. The manufacturing method of PDVT, utilizing both 3D printing and metal processing, enables the creation of complex spiral shapes. The PDVT demonstrates improvements in both speed and grip strength compared to conventional rigid spool mechanisms. The PDVT has the potential to be applied to various robotic grasping systems.