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Active Surface - System Overview

This page is intended to give a brief overview of how the Active Surface works.

Software

• The VxWorks software - PTCS.ActiveSurfaceServo. This is the low-level software that sends demand for each actuator to the hardware, closes the servo loops, checks for hardware faults and so on. This is not a manager, although it has some manager-like features, and in particular uses the M&C message system. Within the message system, this appears as "DeviceName = PTCS.ActiveSurface" and "Host = gbtas0". This software can be restarted using the ResetBox application.

• The Active Surface Manager. This is the higher level control manager. It is responsible for generating actuator demands (e.g. on the basis of the current elevation and the Finite Element model of the surface, and sending them to the PTCS.ActiveSurfaceServo for execution. This software also appears in the M&C message system with "DeviceName = PTCS.ActiveSurface", but in this case "Host = vortex". The Active Surface Manager can be stopped and started using the TaskMaster application.

• User Interfaces. The main ones are the "Active Surface Manager CLEO window", which controls the Manager, and the "showSurface GUI", which talks directly to the PTCS.ActiveSurfaceServo. The CLEO window is used for normal operation of the active surface, but the showSurface GUI can be used to turn on/off power supplies, and to find the detailed status of individual actuators. The Active Surface Manager may also be configured through the new ObservingAPI the config_tool, or DeviceExplorer. Currently, this will normally only happen as part of PTCS system tests. Finally, it is possible to telnet in to the console of the VxWorks Active Surface Master Computer (gbtas0). This is primarily used to run diagnostics, or execute the "rs" command (see TroubleShooting?)

Hardware

A simplified hardware block diagram is as follows:

The main input to the system is a command vector of desired actuator lengths for each of the 2209 actuators. The main outputs are the lengths of the actuators. The Active Surface Master Computer (gbtas0) receives the commands and processes them in several ways. Initially the commands undergo a sanity check. Following this, the "ideal" commands are turned into "real" commands by compensating for the temperature, gain, and offset characteristics of the actuators. In the control system, the actuators are labelled by their rib and hoop locations on the physical structure. The Active Surface Master Computer therefore has to permute the commands to account for the mapping of telescope ribs and hoops to control system addresses.

"real" position commands are transmitted to the Slave Computers (gbtas1 and gbtas2), whose main task is to close the position loops. To control the actuators, the Slave Computers communicate with Intelligent I/O Processors (IIOPs), which basically interface the VME computer bus to proprietary serial busses. In turn, the serial busses communicate with two types of control modules, the LVDT Module, and the H-drive Module. An LVDT module functions as a readout for 16 Linear Variable Differential Transformers, or LVDTs, (the actuator position transducers), while an H-Drive module functions as a motor driver for 16 DC Brush motors (the actuator motors). Thus, a pair of modules (one LVDT Module + one H-Drive module) contains the control electronics for 16 actuators. The system requires 139 pairs of modules to control the entire complement of actuators. Within the active surface servo room, the hardware is divided into four bays, with two IIOPs in each bay. Finally, there are 20 actuator motor power supplies, and four transet (what is this) power supplies.

Thus:

• Each of 4 bays contains 2 IIOPS and 35 LVDT/H-Drive Modules, five motor power supplies and one transnet power supply.
• Each of 8 IIOPs controls 17 or 18 LVDT/H-Drive Modules and 2 or 3 power supplies.
• Each LVDT/H-Drive Module controls 16 actuators.

-- RichardPrestage - 19 Aug 2004