PID Control and Stability Analysis of an ith leg of a Six Degree of Freedom Machining Bed

Abstract

Process of material removal from work piece to get desired shape is usually termed as machining. Operations such as milling, drilling and turning are categorized as machining. Current spindle techniques allow quick material removal. Performance envelope is limited in such case for higher spindles. The high speed tools are also vulnerable to external and internal vibrations. Cuts made and parts created in existence of these vibrations will result in dimensional inaccuracy and imprecise measurements. A solution of these problems is to restrict the tool motion in a single dimension and instead give Six-DOF to the machine bed. A six degree of freedom robotic mechanism is proposed to tackle this problem to be used as a bed for machining. Proposed machining bed is a six degree of freedom parallel manipulator known as Stewart Platform, in which the tool is fixed and work piece is mounted on a movable top plate which gives controlled motion in six degrees of freedom. Overview of design for a six degree of freedom machining bed is discussed in this paper. The analysis of machining bed is done on MATLAB®. Close loop response, stability through Bode Plot, Nyquist Plot and Root Loci and selection of a controller when working in open loop conditions is discussed in detail in this paper. The results verify that a six degree of freedom bed can be used for the purpose of machining.