DESIGN AND CONTROL OF A 6-DOF PARALLEL MANIPULATOR FOR HIGH-PRECISION MICRO-ASSEMBLY IN SEMICONDUCTOR FABRICATION

Abstract

Parallel kinematic machines (PKMs) offer superior stiffness, accuracy, and dynamic performance compared to serial robots of equivalent payload capacity, making them attractive for precision micro-assembly tasks in semiconductor and MEMS fabrication. This thesis presents the complete kinematic and dynamic modelling, structural optimisation, and model-based control design of a 6-DOF Stewart-Gough platform (SGP) intended for sub-micron wafer alignment. A closed-form inverse kinematics solution is derived analytically, and a Jacobian-based velocity mapping is validated against MATLAB Robotics Toolbox simulations. Structural optimisation of the platform legs using Topology Optimisation (SIMP method in ANSYS Mechanical) reduced leg mass by 38% while maintaining first natural frequency above 180 Hz. A model-based feedforward + PD feedback controller achieved positioning accuracy of 0.15 μm RMS in translation and 0.8 μrad RMS in rotation across a 50 mm × 50 mm × 10 mm workspace, validated on a physical prototype with piezoelectric linear actuators (PI P-628). The design meets SEMI Standard E57 positioning repeatability requirements for 300 mm wafer handling.