Design, dynamic analysis and experimental evaluation of a hybrid parallel-serial polishing machine with decoupled motions

Abstract

Abstract In this paper, a novel six degrees-of-freedom (DOF) hybrid kinematic machine (HKM) is designed, analyzed and evaluated for precision polishing. The design adopts a three DOF tripod-based parallel manipulator (PM) to locate the workpiece, a two DOF serial manipulator (SM) to orient the polishing tool and a functional extension limb to provide a redundant DOF for the workpiece with an axially symmetrical shape. Compared with the existing HKMs, the most distinctive feature is that the position and orientation adjustments of the tool with respect to the workpiece are decoupled during the synchronous machining, thus allowing the rotational tool center point (RTCP) function to be conveniently realized. For the developed HKM, the kinematics are studied systematically, including position, velocity, acceleration and workspace. The dynamic model of the PM is derived by employing the principle of virtual work. For a pre-defined trajectory, the required driving forces are obtained through dynamic simulation. Based on these analyses, a laboratory prototype of the HKM is designed and developed. Preliminary accuracy assessment of the HKM is implemented with a double ball-bar and a series of polishing experiments are conducted to show the capacity and feasibility of the developed HKM.