Overview of Status of Analysis, Design, Fabrication, Tests, etc.
Basic acrylic prototype created
Purchase request being processed for eight bearings, six of which will arrive by ~ Thursday (2-7-13), to arrive during 7th week
Purchase request being processed for 12"x24"x0.5" aluminum plate, will arrive by ~ Tuesday (2-12-13)
Test rigs near ready for fabrication (BOMs complete)
Accomplishments from Previous Week
Tolerance analysis of timing belt at high temperatures -- acceptable level of expansion/contraction within our temperature range
General bearing type researched and finalized -- thin steel or ceramic fixed to plate flush with top surface
Designs for heat, cold test rigs complete; cycle test rig research near complete
Goals for Next Week (list names after each item). Use specific and measurable objectives.
Develop complete design so that fabrication/assembly of prototype may begin when aluminum plate stock arrives next Tuesday
Finalize puck hard-stop design
Finalize compliance design
Find out required stroke length necessary for Airpot pneumatic actuator so that we can order pistons asap
Finish all test rigs
Begin initial fabrication/assembly on parts and rigs
Sponsor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Meeting with Ernest on Jan. 31, 13:
Actuator:
Contact Ken Lafleur from Airpot; order cylinder pre-assembled instead of part by part
Large bearing design:
As long as there is at least 1mm of material between DUT chips and outside edge of puck, the outside diameter of the puck can be changed (we have ~1.7mm)
Ernest would rather we ordered a few different bearing materials of the same dimensions to see just how (un)necessary full ceramic bearings are
440C stainless and ZrO2 ceramic have very close thermal expansion coefficients, so design wouldn't be any different.
Bearing mounting usually requires 1 ring is clearance fit, 1 is interference fit; we should not go for an interference fit, but instead use e.g. a screw as a retainer
For timing belt, ID of bearing will be "interference" fit to puck, OD of bearing will be clearance fit with plate
Look into Smalley snap rings with springs to maintain force on (without constraining) the bearing in the clearance fit
Look into Loctite to turn clearance into a press fit
Belt drive:
Timing belt concern is more than it will fail on the low-temp side (brittle failure); our job would be to find the min. bending radius at -55C
We could have a plate underneath the main plate, but it should be small (not the full 10"x7.25"), and for specific purposes (e.g. to mount compliance rollers to)
Instructor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Actuator:
Suggested pneumatic cylinder has a pivot on back so piston doesn't bind (same as Ernest's suggestion)
Compliance:
Spring-loaded rollers between pucks could give system needed compliance
a bow-shaped piece of metal, bent for preloaded tension, attached to rollers could provide compliance
Still working on possible design flaws/failures or alternatives, if necessary
Expressed concern with press-fitting a ceramic bearing to an aluminum plate
Response: see comments from sponsor.
Risks and Areas of Concern
Don't yet know how to find the minimum bending radius of silicone at -55C (rough calculations say it may be 1.5mm; rough calculations not trusted)
Spring properties and tolerance requirements still unknown
1-2 week (flexible with some pleading) lead time on Airpel actuator
Resources or Information Required but not Available
Resources from component room, undergrad mech labs
Schedule
Proof of Concept presentations
Work out timing belt length and stroke length so belt and actuator can be ordered (by the end of week 5)
Ordering stock aluminum for plate and bearings in week 5
Finalize design (week 5 and 6)
Preliminary fabrication/ assembly can start week 6
Budget (list amount spent and amount remaining)
All listed below are still pending:
$742.33 on assorted 8x bearings from Boca Bearing Co.
$109.58 on 12" x 24" x 0.5" 6061-T6 aluminum plate from OnlineMetals
Total spent: $851.92
Remaining: $2648.09
Progress on Report and Webpage
Abstract, table of contents, project description complete