Minutes of Tray Assembly Meeting Aug. 3, 2000 Posted at: http://scipp.ucsc.edu/groups/glast/meeting/non_periodical/ Present: Eduardo, Ossie, Roman, Andrea, Alessandro, Gwelen We built on last weeks meeting which identified a concept for placing ladders on trays. Ossie presented a concept CAD drawing of the idea which Pisa had. The general concept is one where individual ladders are aligned on a stage relative to some pin holes. A transfer tool is aligned to the pin holes and picks up the ladder with vacuum. Finally, the transfer tool is moved to the tray which is mounted (aligned) to a base with the same alignment holes. Using this method, the ladders are held in X,Y,Z relative to tray during adhesive curing. The tool which needs to sit with the detector during curing is relatively simple and many could be made. The optical, or mechanical alignment stage is a separate apparatus which can support alignment of ladders for many trays. Some input on the alignment stage: 1) Alessandro suggested a 3 axis manual micrometer with 2 CCD cameras 2) Ossie asked if pins would be sufficient. i.e, no 3 axis movement. CCD cameras would have an error box on their display which gives visual verification that the detector edge is within the specified distance from the detector edge. 3) It was agreed that the merits of these two options need to be evaluated with real ladders. Pisa will go ahead and start with a 3 axis stage for prototyping. 4) If the alignment is done with CCD cameras with error boxes, then we should capture the images for a later calculation of the distance from fiducial to detector edge (by counting pixels). We discussed what type of ladder survey would be useful for tray assembly. Some people want a measurement of fiducial to edge of detector. The alignment stage above, with CCD image capture would produce this measurement, albeit late in the game. There were varying opinions about how the prototyping should progress at SLAC or Pisa. Everyone agreed that there needs to be collaboration on creating and reviewing CAD drawings. Ossie suggested BJ as a central archive for drawings. Ossie and Eduardo said it would be nice to have SLAC build their own prototype soon in the game to get a feel for the system and to help them give input. Gwelen was worried about duplication of effort and suggested that Pisa go ahead with initial drawings and prototypes and when the bugs are worked that SLAC does design review. Ossie said there are two options for duplicating the tools. 1) One group builds all the tools, calibrates them, and ships them. 2) Drawings and calibration are perfectly documented so that tools can be re-produced anywhere. To start on the tool, accurate tray dimensions are needed. It would be nice to have a final number soon which should be easy since the detector size is fixed. It was agreed to assume the fixture will use the tray corner post pin holes for now and that alternate datum targets will be discussed and possibly incorporated into the tray later. There was also a discussion about Ladder Assembly: Alessandro likes the tool, thinks it is fast and wants to do QC by surveying the ladder before curing glue. The ladders would be under vacuum of course. This lead to a long sharing of views about the production schedule. It was agreed that we need milestones for completion of various parts before resource need can be estimated (people, space, equipment, jigs). Everyone wants more detail in the schedule. The need for documentation and compliance with various standards was discussed. Ossie said that we don't have to comply with NASA contractor specs, but we do have to follow Stanford's "Contamination Control Plan". This will require extremely detailed documentation of procedures. It was noted that before flight qualified hardware (ladders) are being built, that procedures need to be finalized, documentation finished, and a database implemented to track production. This is hard to imagine being done by the time detector procurement starts this spring. Lastly, we talked about adhesive testing. There was fairly common agreement that we should use 2 types of epoxy to glue the ladders down. One epoxy would be non-conductive and have the optimum properties (shear modulus, and shear strength) to mediate the thermal mismatch induced stress. The second epoxy would be conductive and have a modulus much less than the other epoxy to minimize shear stress on the conductive bond. No one was identified to find epoxies that fit this plan. Gwelen pointed out that it would be nice to have Hytec's plots for shear stress in the adhesive bond ( HTN-102050-017) for adhesives with shear modulus between 250psi and 50ksi. Roman is looking into testing apparatus available on Stanford campus. Pisa may have access to some equipment also. Another meeting, hopefully soon, will be needed to divide the effort for finding adhesives and testing them.