NRAO Home  >  Green Bank  |  Wiki Topic:    GB > Operate > ActiveSurface
   Changes | Index | Contents | Search | Go

Active Surface - Introduction

  Introduction      System Overview      Power Supplies      Actuator Status      TroubleShooting   



Active Surface Operating Modes - Summary


Active Surface Operating Modes - Details

The active surface fullfils three main functions. First, it provides the zero-point corrections to position the actuators at the best position for the rigging angle, as measured by photogrammetry. Second, it can provide open-loop corrections based on an FE model to correct for residual gravitational deviations from homology as a function of elevation. (The subreflector focus-tracking model compensates for the gross motion of the primary mirror focus as a function of elevation.) Finally, the active surface may apply more advanced corrections, such as deforming the surface according to a set of input Zernike polynomials, or applying a set of random offsets. This last function is only required during PTCS testing, and should never be used during normal operation.

The active surface has no specific command to "datum" the actuators. When the VxWorks ActiveSurfaceServo system is rebooted, it reads a configuration file which contains the photogrammetry corrections, and applies these to the surface. Further adjustments (such as FE corrections) are applied on top of the zeropoints. Thus, the way to return to the photogrammetry zeropoints is simply to turn off all other corrections.

The actuators will not adopt any specific default position when the motor power supplies are turned off - they simply remain at their current position. So it is important that the FE and any other corrections are removed via the Active Surface Manager before the active surface hardware is powered down.

Given the above, the complete active surface system (Active Surface Manager, VxWorks ActiveSurfaceServo software, and the active surface hardware) has four main operating modes, as follows:


Active Surface Acceptable Operation - Summary

This section is under construction and not yet released! RMP - 8/20/04

There should be no more than 100 disabled actuators, of which no more than 50 should be within one contiguous region of the surface.


Active Surface Acceptable Operation - Details and Call-out Arrangements

This section is under construction and not yet released! RMP - 8/20/04

The performance of the GBT antenna depends on a host of variables, and the performance of the Active Surface is only only component of that. It is therefore difficult to derive performance specifications from first principles. The following are therefore somewhat arbitrary but nevertheless reasonable guidlines for when the Active Surface is within acceptable operation.

-- RichardPrestage - 19 Aug 2004

Topic ActiveSurface . { Edit | Attach | Ref-By | Printable | Diffs | r1.1 | More }
Revision r1.1 - 09 Dec 2006 - 15:30 GMT - RichardPrestage
Parents: WebHome
Content copyright © 1999-2007 by the contributing authors.
All material on this collaboration platform is the property of the contributing authors.