Design and kinematic analysis of a chopstick-like metamorphic mechanism for positioning,grasping and flipping

LU Junjie; DAI Zhongyu; XIE Jin

doi:10.16578/j.issn.1004.2539.2026.06.012

Abstract：[Objective]Chopstick-like mechanisms in medical and daily life applications require integrated capabilities of positioning,grasping and flipping,while the mobility requirements of the moving platform differ across these functional modes.A novel spatial parallel metamorphic mechanism RR(P)C-4U(P)S-U(P)SP/rSPS based on reconfigurable spherical(rS)joint was proposed to achieve smooth transitions between multiple working modes.[Methods]Firstly,the flipping trajectory of chopsticks was measured through tests,and the variation range of human chopstick flipping angles was determined to provide a basis for the dimensional parameter design of the mechanism.Secondly,the kinematic model of the mechanism was established using screw analysis method,and the inverse kinematic solution and velocity Jacobian matrix were derived,followed by the analysis of workspace boundaries and singular configuration distribution.Finally,a virtual prototype was constructed using Adams software,and kinematic simulation verification was performed for both positioning and flipping modes.[Results]The results show that the moving platform of the proposed mechanism has two distinct mobility configurations:3T2R and 2T2R.The 3T2R cconfiguration corresponds to the positioning working mode,while the 2T2R configuration can realize the grasping and flipping functions.The flipping angle range of chopsticks can reach[-0.352,0.352]rad,which meets the design requirements.The number of motion inputs in each mode is strictly equal to the expected mobility of the moving platform,and there is no forward kinematic singular configuration in the entire workspace.