The JCMT active surface control system - Implementation

The James Clerk Maxwell Telescope (JCMT) on the summit of Mauna Kea in Hawaii is a 15 meter sub-millimeter telescope which operates in the 350 microns to 2 millimeter region. The primary antenna surface consists of 276 panels, each of which is positioned by 3 stepper motors. In order to achieve the highest possible surface accuracy we are embarking upon a project to actively control the positions of the panels to compensate for variations in temperature and homology errors as a function of elevation. The current panel adjuster system is based on a 6809 micro connected to the control computer by a GPIB interface. This system is slow and inflexible and it would prove difficult to build an active surface control system with it. Part of the upgrade project is to replace the existing micro with a 68060 VME micro. The poster paper will describe how the temperature of the antenna is monitored with the new system, how a Finite Element Analyses package transforms temperature changes into a series of panel adjuster moves, and how these moves are then applied to the surface. The FEA package will run on a high end Sun workstation. A series of DRAMA (Distributed Real time AAO Monitor for Astronomy) tasks distributed between the workstation and the Baja 68060 VxWorks Active Surface Control System micro will control the temperature monitoring, FEA and panel adjustment activities. Users can interact with the system via a Tcl/TK based GUI.