2 Refitting the Front Optical
Bench
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Check that the cryostat is rotated to the correct angle (5 degrees
past the vertical) and remove the six M8 bolts with invar spacers
from the interface surface of the main optical bench (MOB).
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Mounting the Front Optical Bench onto
the Main Optical Bench.
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Position the front optical bench (FOB) on a storage
table in front of the cryostat with the filter assembly end facing
the MOB, Fit an eyebolt and shackle to the upper-centre of the FOB
(if not already there) and attach a single lifting hook from the overhead
crane. Carefully lift the filter end of the FOB using the crane whilst
two people support Its weight using the handles, the storage table
can now be slid from underneath, The two people holding the handles
can now gently lower the top end of the FOB so that it is freely supported
by the crane (~50kg) ensuring that it does not swing against the cryostat. |

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With one or two people guiding using the handles, bring the
FOB into position in front of the MOB adjusting its height and position
as required with the crane.
Remove
the perspex cover over the field rotator optics and the taped cover
over the entrance to the spectrometer camera through the nitrogen
can.
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Slowly guide the FOB towards the MOB using the trolley
facility on the crane, ensure that the baffle plates on each side
interleave properly and that they are not causing obstruction, Check
also that the three reference pads are not causing an interference.
Once the two interface surfaces have been properly mated together
insert and partially tighten the six M8 bolts remembering the invar
spacers, three per side. |
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Remove the lifting hook and eyebolt from the instrument
and rotate the cryostat until the FOB/MOB interface is about 10 degrees
off the horizontal with the filter assembly end lowest this will allow
the weight of the FOB to push itself into the corner defined by the
three reference pads, Slacken the six M8 bolts and check that the
FOB is sitting properly against the three reference pads on the MOB
this defines its position to the rest of the instrument, once this
check has been completed the bolts can be tightened to a torque of
36.2Nm. |

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Connect the two twisted copper strand thermal wicks to the filter
wheel motors using the screws and washers which should be in place
there.
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Make sure that the control racks are depowered then connect
the six stepper motor cables and the one datum status cable, checking
that the labels on each cable corresponds to the engraved identification
on each of the connector plates, Refit the long panel cover over
the joint between the FOB/MOB interface at the JT side this should
also be taped up.
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Refit the baffle plate along the gap between the
FOB and the detector box radiation shield. |
3. Removing Focus Translation
Mechanism from Front Optical Bench
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3.1. If necessary remove the fore optics (See
Fore Optics procedure) This is only required to be done
if the focus motor connector cannot be undone by hand.
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3.2 Disconnect
focus motor connector and copper wick.
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3.3 Disconnect translation
motor connector and copper wick
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3.4. Access to screws
for wick through translation support frame
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3.5 Disconnect
status connector through radiation shield.
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3.6 Undo M8 hex
socket head screws through translation support frame.
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3.7 Undo 5 M6 hex
socket head screws fixing translation support frame to front optical
bench and remove.
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3.8 Remove baffle plate (2 M3 hex
socket screws) beside image extract motor to gain access to one
of the screws fixing the focus/translation support plate to front
optical bench.
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3.9 Support and the weight of the
mechanism and undo the six M6 hex socket head screws fixing the
focus/translation support plate to the front optical bench wedge.
Remember the two screws beside the translation motor.
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3.10 Carefully remove the focus/translation
mechanism from the front optical bench and put down as shown.
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3.11 Check through the blackened detector
baffle that the image extract mirror has been retracted. Then cover
the aperture (use motor coupling to retract mirror if required).
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3.12 To refit the focus/translation mechanism,
ensure that the support plate is correctly positioned against the
three X and Y defining pads before tightening the six M6 hex socket
head screws to a torque of 14.7 Nm.
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3.13 Take care when inserting the baffle on the
back of the detector box into the baffle on the front optical
bench.
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3.14. Refit baffle plate as per 3.7
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3.15. Refit support plate as per 3.5
and 2.6
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3.16. Connect status connector as per 3.4
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3.17. Connect translation connector as wick as per
3.3
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3.18. Connect focus translation motor and wick as
per 3.2.
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4 Removing the Filter Assembly
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4.1 Position the front optical bench on it's four supporting
feet on a flat level surface.
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4.2 Completely remove the sections of copper
wick which connect both motors to the front optical bench replacing
the screws and washers when finished.
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4.3 Disconnect both of the motor connectors
and the status connector.
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4.4 remove the four M6 screws
on the base plate adjacent to the motors, then using the handles
withdraw the filter assembly carefully from its recess in the bottom
of the front optical bench, once removed replace eh screws in the
front optical bench. Lay the assembly down flat
supported along each side edge with motor connectors facing upwards. Check
through the entrance hole of the filter assembly to see if there
are filters are filters in position, if so manually turn the coupling
on each motor until the blank positions are reached then tape a
cover over the hole on each side.
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5 Refitting the filter assembly
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5.1 Fit the three different length extended support
feet to the front optical bench at the M12 lifting eye positions. The
shortest is fitted in eh central position at the filter end of the
front optical bench.
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5.2 The longest support is positioned at the opposite
end adjacent to the image extract motor. To fit
this support move the black M12 screw to the vacant hole below the
copper wick then fit the support in the hole previously occupied
by the screw.
REMEMBER
TO REPLACE THE SCREW IN ITS ORIGINAL HOLE WHEN THE SUPPORT IS REMOVED.
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5.3 The last support is fitted on the opposite
side in the hole adjacent to the translation motor. Two
people can now move the front optical bench up on to its side and
then turn it over to stand on its three support feet, this gives
access to the imager assemblies, care should be taken as there are
now exposed mirrors (See Imager Assembly procedure).
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5.4 With the front optical bench positioned
this way up, it is possible to slide the filter assembly into its
recess in the front optical bench and to locate it properly against
eh three defining pads. Secure the filter assembly
in position by tightening the four M6 screws to a torque of 14.7
Nm. Reconnect the motor and status connectors and
refit the two copper wicks.
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6 Removing the Imager assemblies
from the Front Optical Bench
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The Michelle imager consists of four mechanism assemblies
and two optical assemblies, These are all fitted to the side of the
front optical bench (FOB) which interfaces to the main optical bench
(MOB).
In order to get access to the imager assemblies it is necessary
to remove the FOB
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Once the FOB has been removed it should be positioned on a flat
stable surface in one of two ways.
1. Up on its side, the side without the stepper motor connectors,
securely clamped to a heavy angle bracket.
2. Fit the three extended support feet (see refitting
the filter assembly) and sit the FOB down flat.
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The assemblies can be split into two groups |
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1. The upper optics housing and the image extract mirror with
its associated drive mechanism.
2. The lower optics housing and the image inject mirror with its
associated drive mechanism.
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Gloves
should be worn and extreme care should be taken during this procedure
as you will be handling assemblies with vulnerable exposed mirrors. |
Before removing any of the above assemblies ensure
that the image extract and inject mirrors have been parked in the
spectroscopy position, This can be done manually by turning the coupling
on each motor shaft. |
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To remove the upper optics housing first disconnect the datum
status switch connector and remove the three P-clips attaching the
wiring harness to the top of the optics housing replace the screws
in the housing for safe keeping.
Remove the wiring harness P-clip fixings which are securing
the captive grey baffle plate to the FOB.
Undo the three M5 socket head screws which are securing the
upper housing to the FOB and remove the housing with the baffle
plate. This assembly contains the toroid mirror and a small flat
mirror and should be stored safely.
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To remove the lower optics housing disconnect its
datum status switch connector and undo the three M5 socket head screws
which are securing the lower housing to the FOB, As one of the screws
is partially obstructed behind the micro-switch assembly this screw
should be undone last as you lift the housing from its mounting. This
assembly contains the aspheric mirror and should be stored safely. |
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When refitting both optics housings it is important
to ensure that they are mounted properly located hard against the
machined alignment features provided by the FOB. |
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Both the extract and inject mirror assemblies are
mounted similarly to the FOB on dowels and secured by four socket
head screws at the bevel gear end of the assembly (extract M4 &
inject M3). To remove these assemblies disconnect its associated datum
switch connector and undo the four fixing screws, remove the P-clip
fixing from the extract mirror assembly, Lift the assemblies squarely
until they are free from the dowels turning the gears as necessary.
These assemblies have flat mirrors mounted to them and should be stored
safely. |

Image inject mirror retracted showing pupil stop and location
of temperature sensor
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Both the motor assemblies have to be removed from the other
side of the FOB, The inject motor assembly is located in a recess
beneath the focus translation mechanisms and the extract motor protrudes
from the FOB adjacent to the detector housing.
To remove the motor assemblies first undo the M3 screws fixing
the twisted copper braid thermal wicks and disconnect the stepper
motor connectors then remove any aluminium tape and undo the four
M4 socket head screws which secure the assemblies and baffle plates
to the FOB.
Remember
to replace any tape removed when replacing the motor assemblies.
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7 Removing cold pupil stop from
the Front Optical Bench
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7.1 Sit the front optical bench down
on a flat level surface using the four support feet on the imager
side of the front optical bench.
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7.2 Ensure the imager inject mirror
is in its spectroscopy position, manually retract the mirror by
turning the motor coupling through the recess in the front optical
bench if the mirror is observed to be in its imaging position.
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7.3 Remove the fore optics module (see section
1) and the filter module (see section 3)
to gain access to the cold pupil stop access hole in the front
optical bench.
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7.4 Remove the black clamp nut which is securingthe
pupil stop in position through the access hole in the front optical
bench using the tool supplied. Additional access
through the filter drawer recess can be used.
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7.5 Remove the pupil stop through the access hole
using the tool supplied, this is done by engaging the threaded
end of the tool in one of the two tapped holes on the top of the
pupil stop and withdrawing it from the recess carefully. The
pupil stop has an orientation defining feature which is located
in a slot in the pupil stop recess, this must be properly engaged
when refitting the pupil stop.
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