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Document Title

DOCUMENT NUMBER 52D003S ISSUE 03 CATEGORY SOFTWAREELECTRONICS STAUS AUTHOR

Document Number:

5.2d003S

Issue:

0.3

Category:

Software/Electronics

Staus:


Author:

Stewart McLay & Alan Pickup

Date:

2002-08-05





Document Title

Filter Paddle Interlocking Specification

Document Number

5.2d003S

Issue

0.3

Date

2002-08-05




Document Prepared By:

Stewart McLay

Alan Pickup

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TABLE OF CONTENTS

1. Introduction 5

2. OPERATIONAL CONSIDERATIONS 5

3. Electronics Requirements 6

4. Software Requirements 6

5. Questions 7

6. Appendix 7

6.1 XYCOM XVME-240 Digital I/O Card Input Signals 7

6.2 XYCOM XVME-240 Digital I/O Card Output Signals 8

6.3 OMS VME58-8 motor card input signals 9



1.Introduction

This document outlines the results of a discussion on the recommended requirements for the interlocking system controlling the filter paddle mechanisms in WFCAM. Present at the meeting on 2002 July 31 were Ken Laidlaw, Alan Pickup, Andy Vick, Brian Woodward and Stewart McLay.


2.OPERATIONAL CONSIDERATIONS

The following operational considerations were noted:


  1. Each mechanism (focus/filter paddle) has two limit switches. These limit switches are placed at either end of travel where the low limit switch is placed at the end nearest to the datum switches and the high limit switch is at the opposite end.

  2. Each mechanism (focus/filter paddle) has two datum switches; a primary and secondary (backup) datum switch. Although these are located close together, they will probably not activate at the same step transition. If we define the edge of the primary datum switch as step 0, say, the calibration will likely differ from that achieved by defining the edge of the secondary switch as step 0. If the difference in calibration is less than the required positioning accuracy of the filter, then this would not matter. Otherwise, the software would need to know which switch is in use and what the associated datum position should be.

  3. The datum switches serve a dual purpose: the edge of the switch activation region marks the datum position; and, while the switch is activated, the filter is regarded as parked. After each filter paddle mechanisms has been datumed, it will then be parked by moving into the region where the datum switch is activated. The distance it is moved into the region must be sufficient to ensure that any flexure during the movement of WFCAM on the telescope does not cause the switch to be deactivated.

  4. The datum switch used by the electronics and the software will be selected by a jumper setting. The output from the selected datum switch will be fed into both the VME58-8 motor card and the interlocking hardware. If the software cannot sense the state of the selected switch via the motor card, it may be necessary to connect the switch also to the digital I/O card - this is to be investigated.

  5. Interlocking will be implemented on an electronics board. It will have one input for each filter paddle datum switch. To accommodate a situation where both datum switches are broken, it will be possible to disconnect that particular filter mechanism from the hardware interlock system.

  6. The interlock will be activated when more than one filter paddle mechanism is not in a parked position (i.e. when more than one datum switch is not activated). When activated the interlock system prevents the mechanisms from being driven. The state of this interlock will be output also to the digital I/O card so that it is available to the software system. The software will report the interlock state via a continuously-updated colour-coded status display on a DM screen.

  7. It will be possible to override the interlock system by using a hardware switch, the interlock override switch. This will allow the mechanisms to be driven into the parked region even though more than one mechanism is not parked. Activation of this switch will permit the recovery of the mechanisms so they can be driven into a safe configuration. The setting of the interlock override switch will be output to the digital I/O card to be available to the software system. The software will report the state of the interlock override switch via a continuously-updated colour-coded status display on a DM screen.

  8. Any attempt to datum the filter mechanisms, or to select a filter, while the interlock is activated will be rejected by the software with an error message. This is the case even if the override switch is enabled. In addition, the software will make its own check of the datum switch states prior to datuming or selecting a filter and it will reject the operation with an error message if it more than one filter is not parked.

  9. The software will provide a command to allow the system to recover from situations where more than one filter mechanism is not parked. This will move all deployed filters out of the beam and towards their parked region in as safe a way as possible to avoid paddles colliding, perhaps by moving them all slowly and simultaneously until all but one are within their park regions. Activation of this command requires that the interlock override switch be enabled - otherwise it is rejected with an error.


3.Electronics Requirements

Below is a summary of the consequential electronics requirements:


  1. Jumpers will be used to select whichever datum switch is to be used for each filter. The signal will be routed to theVME58-8 motor board and the interlock hardware. Depending on further investigations, it may be necessary to route this also to the digital I/O board.

  2. It must be possible to disconnect any filter mechanism from the interlock hardware so that the state of its datum switch is ignored by the interlock system.

  3. The interlock hardware will prevent any filter motor from driving if more than one filter datum switch is not activated. The state of the interlock signal will be routed to the digital I/O board.

  4. An interlock override switch will be provided to allow the filters to be moved irrespective of the state of the interlock. The state of this switch will also be routed to the digital I/O board.


4.Software Requirements

The consequential software requirements are:


  1. In normal circumstances, no more than one filter will be deployed at any time. The selection of a different filter will require that the currently deployed filter be parked before the new filter is deployed.

  2. The requirement that no two filters be away from their park regions at any time, means that the eight filter mechanisms must be datumed in series rather than in parallel, with a consequent increase in the time taken to datum.

  3. Any attempt to datum the filter mechanisms, or to select a filter, while the interlock is activated will be rejected by the software with an error message. This is the case even if the override switch is enabled. In addition, the software will make its own check of the datum switch states prior to datuming or selecting a filter and it will reject the operation with an error message if it more than one filter is not parked.

  4. The software will provide a command to allow the system to recover from situations where more than one filter mechanism is not parked. This will move all deployed filters out of the beam and towards their parked region in as safe a way as possible to avoid paddles colliding, perhaps by moving them all slowly and simultaneously until all but one are within their park regions. Activation of this command requires that the interlock override switch be enabled - otherwise it is rejected with an error.


5.Questions

Below is a list of questions that need to be answered.


  1. Can we sense the state of a datum switch via the VME58-8 motor card?

  2. What is the separation in steps between the primary and secondary datums, and is this small enough to be ignored considering the positional accuracy required?

  3. When more than two filters are away from their park positions, what is the safest way to move them to minimise the possibility of collision? This should also take into consideration that the mechanism might be loosing steps.

  4. How far into the park region, and away from the edge of the datum switch, should we park each filter?

  5. What can we safely assume about the mechanism over the course of a night, i.e. is it possible that a filter paddle might move due to the force of gravity, especially when the telescope is being moved?

6.Appendix

6.1XYCOM XVME-240 Digital I/O Card Input Signals

Input Signal

Polarity

Status

Comments

Filter paddle 1 datum

HIGH

Micro-switch open

Also indicates mechanism is NOT parked


LOW

Micro-switch closed

Also indicates mechanism is parked

Filter paddle 2 datum

HIGH

Micro-switch open

Also indicates mechanism is NOT parked


LOW

Micro-switch closed

Also indicates mechanism is parked

Filter paddle 3 datum

HIGH

Micro-switch open

Also indicates mechanism is NOT parked


LOW

Micro-switch closed

Also indicates mechanism is parked

Filter paddle 4 datum

HIGH

Micro-switch open

Also indicates mechanism is NOT parked


LOW

Micro-switch closed

Also indicates mechanism is parked

Filter paddle 5 datum

HIGH

Micro-switch open

Also indicates mechanism is NOT parked


LOW

Micro-switch closed

Also indicates mechanism is parked

Filter paddle 6 datum

HIGH

Micro-switch open

Also indicates mechanism is NOT parked


LOW

Micro-switch closed

Also indicates mechanism is parked

Filter paddle 7 datum

HIGH

Micro-switch open

Also indicates mechanism is NOT parked


LOW

Micro-switch closed

Also indicates mechanism is parked

Filter paddle 8 datum

HIGH

Micro-switch open

Also indicates mechanism is NOT parked


LOW

Micro-switch closed

Also indicates mechanism is parked

Focus datum

HIGH

Micro-switch open



LOW

Micro-switch closed


Interlock

HIGH

Interlock activated

Interlock electronic protection system has been activated


LOW

Interlock NOT activated

Interlock electronic protection system has NOT been activated

Interlock Override

HIGH

Interlock override activated

Electronic switch for interlock override has been switched on


LOW

Interlock override NOT activated

Electronic switch for interlock override has been switched off


6.2XYCOM XVME-240 Digital I/O Card Output Signals

Output Signal

Polarity

Status

Filter paddle 1 power

HIGH

Power ON


LOW

Power OFF

Filter paddle 2 power

HIGH

Power ON


LOW

Power OFF

Filter paddle 3 power

HIGH

Power ON


LOW

Power OFF

Filter paddle 4 power

HIGH

Power ON


LOW

Power OFF

Filter paddle 5 power

HIGH

Power ON


LOW

Power OFF

Filter paddle 6 power

HIGH

Power ON


LOW

Power OFF

Filter paddle 7 power

HIGH

Power ON


LOW

Power OFF

Filter paddle 8 power

HIGH

Power ON


LOW

Power OFF

Focus power

HIGH

Power ON


LOW

Power OFF


6.3OMS VME58-8 motor card input signals

All low limit switches, high limit switches and datum switches will be connected to the ports for all mechanisms.


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