Proceedings of 2008 ISFA 2008 International Symposium on Flexible Automation Atlanta, GA, USA June 23-26, 2008 ISFA2008U_108 AXIAL DEPOSITION CONTROL IN VAPOR-PHASE AXIAL DEPOSITION Hodge E. Jenkins Dept. of Mechanical and Industrial Engineering Mercer University 1400 Coleman Ave. Macon, GA 31207 USA jenkins_he@mercer.edu Mark L. Nagurka Dept. of Mechanical Engineering Marquette University P.O. Box 1881 Milwaukee, WI 53201 -1881 USA mark.nagurka@marquette.edu ABSTRACT An advanced feedback control strategy for a vapor-phase axial deposition (VAD) is investigated in this paper. VAD is a widely used process in the creation of high purity glass for optical fiber. In previous work a soot tip surface temperature controller was developed for the VAD process to reduce the effects of core soot temperature variation on deposition geometry, leading to a more stable process. However, it is desired to regulate both the core soot and clad soot deposition such that they deposit at the same axial rate to provide a more uniform product. This paper presents the design and development of a cascaded controller strategy and process model to couple and regulate the surface temperature and deposition rates of core and clad soot. Simulation studies demonstrate a potential improvement in the uniformity of the core and clad soot geometry over the soot product length. NOMENCLATURE A Area, effective heat flow normal area D Clad diameter of preform d Core diameter of preform G CORE Core axial deposition function G LENGTH Core tip length function G P Plant transfer function ∆H 2 to T CORE G PI PI controller transfer function G TEMP Core temperature function k TH Thermal conductivity K i Integral gain K p Proportional gain L CORE Length of core soot tip L 0 Initial length of core substrate soot tip PI Proportional, integral control Pull speed Rate of preform deposition axial growth q CLAD,SS Heat flow from clad substrate Q CLAD Volumetric deposition rate of clad torch T CORE,0 Core soot substrate temperature initial T CORE Core soot substrate temperature T CLAD Clad soot substrate temperature VAD Vapor-phase Axial Deposition CORE X & Core soot axial growth rate, or pull speed CLAD X & Clad soot axial growth rate β Heat flux (constant) ∆H 2 (s) Hydrogen flow rate change to core torch ∆L Change in length of core soot section ∆T CORE_LENGTH Core substrate temperature change from core tip length change INTRODUCTION This paper proposes a process control improvement for a vapor-phase axial deposition (VAD) process, a commonly used multi-step process for the manufacture of high quality glass for optical fiber. The process deposits a glass soot mixture of silicon-dioxide and germanium-dioxide to create the light guide core and cladding around the core. It is desirable to maintain consistent core and clad geometry throughout the manufacturing process to create a high performance optical fiber product for high bandwidth data transmission. Common practice in the VAD process is for the core and clad soot deposition rates, as well as the related surface temperature, to run essentially open-loop while regulating constant flow rates of gases and chemicals to the deposition torches. This situation yields varying diameters of core and clad soot regions reducing the usable length of the final glass and lowering product yield. VAD was invented at NTT Laboratories in Japan and is the dominant process for Japanese manufacturers of optical fiber. VAD is an improvement of the Corning OVD (outside vapor deposition) process [1,2]. The VAD process has been the 1 Copyright © 2008 by ASME