Development of a cascaded controller for temperature and core growth rate in vapour-phase axial deposition

A cascaded feedback control strategy for an industrial vapour-phase axial deposition (VAD) process is investigated in this paper. VAD is a widely used process in the creation of high-purity glass for optical fibre. 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 such that they deposit at the same axial rate to provide a more uniform product. This paper presents the 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.