| UK Astronomy Technology Centre | Chris Tierney |
| Royal Observatory, Edinburgh | 31st March 2001 |
The filter assembly comprises a rotary stage housing up to six filters.
This filter selection wheel is indexed to a home switch.
Safety
All the NAOMI mechanism control screens display two buttons - a red "Emergency" button
and a green "Safe" button - in the top right corner of the screen.
Left clicking an "Emergency" button will immediately stop any motion by any part of the wavefront sensor or calibration unit. Thereafter, any demands for motion are rejected, until the user left clicks on any of the "Safe" buttons. Many mechanisms will then demand to be re-indexed before allowing the execution of any other motions.
Note: This safety feature has no effect on the motion of the Durham deformable mirror (DM) or fast beam-steering mirror (FSM), nor any component of the electronics associated with NAOMI.
For more information, see the NAOMI mechanism software
safety page.
Commands to the filter assembly
Before any operations are performed on this assembly, it must be initialised by left-cicking
the Mode button "Init", followed by Directive "Start". The user should see the status
display "Command accepted - record state is busy". The record state will return to
"idle" when initialisation is complete.
For all commands, in normal operation the user should see the status display "Command accepted - record state is busy" when the command starts. When the command is complete, the record state should change to "idle".
A status of "Command rejected" indicates that the command was not started. A status of "record state is error" indicates that the command did not complete succesfully. In both cases an error message will indicate the cause of the failure.
After initialisation, the mechanism should be indexed. This is started by clicking the "Index" Mode followed by "Start" Directive. The filter selection wheel will be indexed to its home switch during this process.
After these operations have been performed, the assembly is now available for normal use. The user should left-click the "Move" Mode button. Thereafter, clicking the "Start" Directive button will cause the assembly to move the filter selection wheel to the specified position (see below).
The "Stop" Directive button can be clicked at any time to bring the assembly to a controlled stop.
Parameter input/output
Before executing a move command, the user must input the desired (angular) position of the selection wheel in the "Demand
Position" input field, in degrees. The position is assumed relative to the home switch position by the software.
The "Demand Position" field accepts as input a filter name (for example, "red"), which is translated internally into an angular position before being passed on the the wheel device. The list of accepted named positions, and their numerical equivalents, is determined by the software during initialisation using the filter assembly lookup table. Details of the lookup tables used by the NAOMI mechanism control software are available on the NAOMI mechanism control software lookup tables page included in this documentation.
The "Current Position" indicator field displays the current position of the filter selection wheel device, in degrees.
The "Current Velocity" indicator is included to inform the user of the angular velocity (degree/sec) used by the device.
Menu items
One item is provided in the Device displays menu - to access the deviceControl screen for the
filter selection wheel device.
Status and Higher displays menus give access to further assembly information and the top-level screens, respectively.