Investigation of a parallel contact force robotic end-effector for thin-walled parts grinding and deburring with uncertain position

This paper focuses on the force overshoot problem that occurs in the initial contact phase of a robotic end-effector, a novel passive compliant constant-force end-effector designed to address the challenge of contact force stabilization and response in robotic grinding and deburring of thin-walled parts. Unlike conventional active force control methods that suffer from force overshoot due to dynamic response limitations, the proposed solution integrates a hybrid stiffness mechanism combining positive (multi-layer bending structures) and negative (inclined beams) stiffness elements to achieve sensor-less force regulation. The design features a parallel architecture with 120° distributed limbs, ensuring coaxial force distribution and vibration suppression. A comprehensive analytical model is developed, incorporating combined stiffness theory and elliptic integrals to characterize the negative stiffness beam's buckling behavior, with parameter optimization to maximize the constant-force stroke. Finite element analysis confirms uniform stress distribution under multi-axis loading (100N force/20N·m torque), while experimental validation on magnesium-aluminum alloy workpieces demonstrates the mechanism's ability to maintain contact force within ±5 % deviation over a 4.5 mm stroke range, even with ±2 mm positional errors. The passive design eliminates the need for complex control systems, offering significant advantages in cost reduction, process adaptability through quick-change couplings, and scalability for diverse thin-wall geometries. This paper provides an insight into the potential of purely passive methods in achieving accurate and smooth force control.