Dexterous Three-Finger Gripper based on Offset Trimmed Helicoids (OTHs)
Qinghua Guan, Hung Hon Cheng, Josie Hughes
TL;DR
This work introduces offset-trimmed helicoids (OTH) as soft fingers with a tunable deformation center and dual helically routed tendons to achieve in-plane bending and lateral transitions, yielding a large, tunable workspace and reduced actuation effort in a TPU-based finger. The authors develop PCC-based kinematics, FEM-informed design guidance, and a workspace analysis to optimize tendon configurations and offset distance, selecting $D_c=10\\\ \mathrm{mm}$ and a $90^{\\circ}$ twist for a three-finger gripper. Experimental validation with TPU fingers demonstrates strong agreement between model and reality, tunable fingertip compliance, and the ability to perform grasping, rotation, and spinning tasks, including rapid in-hand rotation on the order of $60^{\\circ}$ in $15\\mathrm{ms}$ and in-hand manipulation of a rod. The results highlight a path toward dexterous soft manipulation with relatively simple actuation, while indicating opportunities to improve autonomy through vision, tactile sensing, and learning-based control. The work has implications for adaptable, soft robotic hands capable of dynamic manipulation across object geometries and speeds.
Abstract
This study presents an innovative offset-trimmed helicoids (OTH) structure, featuring a tunable deformation center that emulates the flexibility of human fingers. This design significantly reduces the actuation force needed for larger elastic deformations, particularly when dealing with harder materials like thermoplastic polyurethane (TPU). The incorporation of two helically routed tendons within the finger enables both in-plane bending and lateral out-of-plane transitions, effectively expanding its workspace and allowing for variable curvature along its length. Compliance analysis indicates that the compliance at the fingertip can be fine-tuned by adjusting the mounting placement of the fingers. This customization enhances the gripper's adaptability to a diverse range of objects. By leveraging TPU's substantial elastic energy storage capacity, the gripper is capable of dynamically rotating objects at high speeds, achieving approximately 60 in just 15 milliseconds. The three-finger gripper, with its high dexterity across six degrees of freedom, has demonstrated the capability to successfully perform intricate tasks. One such example is the adept spinning of a rod within the gripper's grasp.