Minutes of the Tracker
Meeting
April 22, 2004
Action Items:
1.
John
Ku: make a priority in the next days to analyze the Grid bushing
2.
Sandro
and Riccardo: review the top tray closeout/insert drawings tomorrow and send
approval back to SLAC
3.
Sandro:
get lead time for the insert manufacture
4.
Sandro:
send a sample of facesheet material to Ben Rodini
5.
Martin:
use the as-built thickness +-50um for the facesheet drawings
6.
Sandro:
send Martin a fax regarding facesheet drawing issues
7.
Arthur:
analyze and plot the eccentricity sensitivity vs angle
8.
Sandro
and Riccardo: review and sign off on the cone/stud drawings with understanding
that additional drawings will be made asap for lower-eccentricity cones
9.
Robert:
make a top-level agenda for next week
10.Nanda: detailed PRR/TRR
agendas
11.Riccardo: send mid-tray
as-built measurements to Martin
12.Dave: send Tom V the WIP
status from Teledyne
13.Sandro: send containers back
to Jeff
14.Jeff: send INFN details as
to what is needed regarding fastener specs
Agenda:
- Martin/Riccardo: top tray drawing sign-off/resolution of
insert counterbore issue
- Jim: 7075-T76 for top/bottom tray inserts
- PRR/TRR planning; Pisa meeting agenda; readiness matrix;
expectations
- Mid-tray production status
- Mid-tray "as-built" measurement & verification.
- Mid-tray design- INFN to supply red-line mark-up of design
per as-built conditions
- G&A Status: MCM installation & alignment. Wire bonding characterization results
- Menning/Sandro/Ku: grid bushing design and magnitude of
eccentric offset.
- Status of bottom tray closeouts, Ti parts, MCMs, BT cores,
bias circuits etc. (see the new status chart at
http://www-glast.slac.stanford.edu/Tracker-Hardware/Actions/Tracker_SLAC_Status.pdf)
- Jeff: new drawing tree
- A.O.B.
John Ku presented the status
of the static test work. They are
starting with the z axis and have run 3 load cases. The main problems are with instrumentation and making sure of
recovery of accurate data. They are
writing all lessons learned into the procedure. Overall it is progressing well, but they need to work on the
LVDTs, which don’t have enough precision.
They are now changing to the lateral axis. After finishing they will leave it set up in the lateral
case. The work is in the same room as
ESPI testing. John estimates that they
could do the acceptance test in 1 day in the worst case. Andrea is preparing a procedure for mounting
the bottom tray into the fixture to avoid damage to closeouts.
John had some action items
regarding the Grid bushing but hasn't had time to look at them.
1. how tight does the fit
between stud and bore have to be to give acceptable stress margins in aluminum?
2. how high are stresses in
the Grid wall if a bushing is pushed in?
3. can a split bushing be
used?
John will make a priority of
doing the work himself in the next days.
Martin said that a 1.4 mil interference fit is preferred. But is the stress in the Grid too high? Is a split bushing preferred? There will be a meeting Friday on these
issues.
Martin said that the insert
and closeout drawings are all out for sign-off. The counterbore depth is consistent with the mid-tray
design. Inserts are not flush on the
backsides. Sandro said that Riccardo
was only concerned about 1 particular insert.
There would be a small simplification of the tool if this insert flange
were increased in thickness. However,
at this point the drawings are complete and Martin would not have time to
revise them before leaving for Italy.
The decision was for everybody to review the drawings as they are and
get them released so that work can proceed.
Martin and Riccardo will discuss the particular insert again in Pisa.
Sandro said that he and
Riccardo will review the top tray closeout/insert drawings tomorrow.
There was general agreement
to move forward with using 7075-T76 aluminum for bottom and top tray
inserts. The T6 material has not been
approved by NASA for that use, and at this point the T76 material is in
Pisa. Sandro said that the week after
next they will start to make the parts.
Sandro needs to get the lead time from the machine shop.
The discussion then turned
to face sheet thickness. Sandro said
that the actual thickness are 200um for 4 plys and 290um for 6 plys. Sandro
also said that the old PCI facesheets were very much the same thickness. That is quite a bit more than what Ben
predicted, so he thinks then that the fiber volume must be less than 60%. Sandro will send a sample to Ben for
analysis. Ben said that he has seen the
prepreg material spec at Plyform.
Martin will use Sandro’s numbers and will put +-50 micron tolerance on
thickness. Sandro will send Martin a
fax with other issues that he has with the facesheet drawings that are out for
review. Ben noted a subtle asymmetry in
the way the facesheets are made and then put onto the trays, but he thought
that it probably was not a big deal.
There was a long discussion
of eccentricity. Martin derived the
need for the large eccentricity of 20 mils per cone based on tolerance
stackup. A major part of the stackup was
the tolerance on tilt of the corner-bracket/flexure assembly relative to the
bottom tray. Sandro requested an
eccentricity less than half as much based on his concern that the angular
setting accuracy that could realistically be obtained would result in too much
error in offset. Arthur said that even
with the large eccentricity the offset is not very sensitive to the angle if
the needed offset is small. High
sensitivity comes in only when one gets near the full extension with both cones
offset the same direction (the dependence of offset on angle is highly
nonlinear). But one goes to that
extreme position only if needed, in which case a lower eccentricity would not
even give a solution. He said that he would
perform some more analysis of the adjustment angles and make plots illustrating
his points. Sandro suggested making two
sets of cones with differing eccentricities.
Mike echoed that as a good possibility.
However, the first priority is to evaluate the 2 cone/stud sets due to
arrive tomorrow. In parallel the
existing drawings need to be signed off for release and procurement
started. After the evaluation of the
first 2 sets that arrive tomorrow Arthur can prepare drawings for cones of
reduced eccentricity.
Regarding next week’s
meetings, Robert sent out a revised PRR matrix including some comments and also
sent comments on several of the procedure drawings. At Nanda’s request he can make a top-level agenda, but the
detailed presentation agenda for the individual PRRs need to come from INFN. Robert suggested that prior to the PRRs
there should be some discussion of the design to try to close out issues there.
Chris asked when the EM vibe
TRR will take place. Robert said that
it is gated by the Grid bushing issue, which is preventing a new vibe fixture
from being made and by the cone procurement.
The TRR should be a week or two before the test, but when we will be
ready for the test is unclear at the moment due to the above issues.
Mid-tray production status:
3 mid trays are in Pisa, 1
of them heavy. They have been tested by
ESPI and dimensional checks were done.
3 more are at Plyform.
Production is going well. A
summary of the as-built measurements requested will be sent to Martin tomorrow
by Riccardo.
Mid tray drawings still need
redlines to be sure they reflect the as-built trays. We will work out a plan next week to get this done.
At G&A the special
mock-ups are complete. The tools to
align the MCM is ready for the first trays.
They need 2 weeks for characterization of the wire bonding. The final procedure should be ready the 2nd
week of May.
MCM status: 6 units are to
ship from Teledyne today, so thermal cycles and burn-in should start on
Friday. 9 more units should ship next
week. After the first 6 units there was
some delay in the schedule due to a production halt to work on inspection
criteria for pitch-adapters. Also, a
high than expected chip failure rate has required rework and slowed down
completion of the first lot (otherwise 5 more should arrive the next day after
the first 6, and etc.) Dave will send
Tom V the WIP status.
The new EGSE was
successfully tested with the mini-tower.
2 sets should ship in the next days to Pisa.
Jeff reported that the new
bottom tray cores are on order as of a few days ago but will have 4-week
turn-around, and then they have to go to SLAC for inspection and ship to Pisa.
Jeff asked Sandro to return
containers sent to INFN.
INFN (Nanda) will supply
specs for the 2.5 and 4mm fasteners so that Jeff can add the info to the
procurement spec. He will send an email
with specific requests.
Jeff reported that the
updated new drawing tree is, as always, available on the Tracker we site.
Bottom tray closeouts are on
their way to Pisa.
Titanium flexures and corner
brackets and bias circuits should arrive at SLAC tomorrow and will be hand
carried to Pisa. That will be 2.5 sets
of titanium parts and 45 bias circuits (1/4-oz).