In context
By late 2023, underactuated robot hands had advanced to combine parallel pinch and self-adaptive grasping, but most designs traced circular end-phalanx paths, limiting their ability to pick flat objects from surfaces. This gap motivated research into mechanisms that could deliver straight-line motion without complex control or extra actuators.
What was reported
Researchers from China Agricultural University, Tsinghua Shenzhen International Graduate School, and X-Institute proposed a novel underactuated finger—the Watt finger—that integrates a Watt linkage for straight-line end-phalanx motion, parallel linkages to maintain orientation, and a triangular differential linkage for adaptive grasping. The finger has three joints and transitions automatically from straight parallel pinch to self-adaptive enveloping when the first or second phalanx is blocked.
Kinematic analysis using SAM software showed that during a 100 mm horizontal displacement of the contact point, vertical deviation was only 1.8 mm, confirming near-straight-line motion. The mechanism also exhibited a large workspace and stable velocity, enhancing grasp reliability. A two-finger prototype, the Watt hand, was built and tested, demonstrating effective straight parallel pinch and adaptive grasping across various object shapes and sizes.
Force analysis provided contact force distributions for both grasp modes, and design parameters were optimized for stable grasping. The mechanism avoids sliding joints, improving structural stability and manufacturability compared to prior designs.
Why it mattered
This work offered a simpler, more robust solution for straight-line parallel pinch in underactuated hands, potentially expanding the applicability of robot grippers in industrial settings where picking objects from flat surfaces is common. The design's larger grasp space and stability could reduce the need for precise positioning, lowering system costs and complexity.
“The straight-line trajectory makes the hand have a larger grasp space and a wider range of adaptation.”
Source: 《机器人》期刊 (robot.sia.cn) · Published 2023-11-10 · “差动瓦特连杆直线平夹自适应抓持器”