Constrained Trajectory Generation and Control for a 9-Axis Micromachining Center With Four Redundant Axes

Abstract

A control strategy and trajectory generation algorithm for a novel 9-axis micromachining center is presented. The micromachining center consists of a 3-axis gantry type micromill and a six degree of freedom magnetic rotary table. The micromill is modeled as a rigid body and controlled with a sliding mode controller and feedfoward friction compensator. The rotary table is modeled as a rigid body with flexible connections and controlled using a combination of notch filters, loop shaping controllers, and integrators. To improve the performance of the micromill, the tracking error of the micromill is sent as reference commands to the rotary table. The trajectory generation algorithm consists of a kinematic module and a feedrate optimizer. The kinematic module resolves the redundancies of the 9-axis micromachine while respecting the stroke limits and avoids singularities. The generated position commands by the kinematic module are optimized without violating the physical limits of the drives. A two dimensional contouring experiment has been carried out to validate the improved tracking error performance of the proposed strategy. A freeform surface has been machined to demonstrate the overall performance of the 9-axis machine tool.