Jason Tarrant / November 2008 MICE Target Mechanical Design Contents » Shaft Bearing Redesign – Cross section shape – Anti-rotation device and location – Target shape and attachment – Bearing design – Assembly issues with alternative shaft and bearings » Assembly for ISIS Jason Tarrant / November 2008
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Jason Tarrant / November 2008 MICE Target Mechanical Design l Contents »Shaft Bearing Redesign –Cross section shape –Anti-rotation device and location.
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Jason Tarrant / November 2008
MICE Target Mechanical Design Contents
» Shaft Bearing Redesign– Cross section shape– Anti-rotation device and location– Target shape and attachment– Bearing design– Assembly issues with alternative shaft and bearings
» Assembly for ISIS
Jason Tarrant / November 2008
Jason Tarrant / November 2008
MICE Target Mechanical Design Cross section shape
» Current cruciform shape– ‘+’ or ‘x’ same stiffness– For 11mm2 CSA I = ~18mm4
– For a round shaft with same CSA @ 6mm OD I = 39mm4 > 2 x as stiff.
Jason Tarrant / November 2008
Jason Tarrant / November 2008
MICE Target Mechanical Design Alternative Round or Square?
Jason Tarrant / November 2008
RoundFor a 6mm OD tube with a CSA of 11mm2 the ID works out to be = ~4.7mm. Calculating the second moment of area (I) = ~39mm4. For a 0.5mm wall the OD will be 7.5mm to give 11mm2 cross section, for this I = ~68mm4.
SquareFor a square tube the cross corner dim will be ~8.5mm for a square section that has an across flats dim of 6mm. For the square section with an A/F of 6mm the A/F of the ID will be 5mm (0.5mm wall) and the I will be ~56mm4 in both the horizontal/vertical and 45deg orientations, however overall it does fall outside 6mm. For a shaft with across corner measurement of 6mm I = 23mm4.
Jason Tarrant / November 2008
MICE Target Mechanical Design
Alternative Round or Square?» Round advantages
– Various standard sizes– Easier to finish a round shaft and produce hole to
tight tolerances / fine finish– Techniques for joining (threads, orbital welding)
easier than square
» Round disadvantages– Square shaft easier to control rotation
» Possible location– Shaft movement keeps permanent
magnet within stator = possible length to keep slot inside w/o passing thro bearing? Move bearing?
– Key, part of stator tube or similar components?
– If flexible key, could be vertical cantilever
Jason Tarrant / November 2008
MICE Target Mechanical Design
Target Shape» Round tubular end as target» Formed flat target from tubular end» Separate component of any shape
attached to round section that requires attachment…
Target attachment» Threaded, pinned & welded
Jason Tarrant / November 2008
Jason Tarrant / November 2008
MICE Target Mechanical Design
Bearing Function» Allow constrained vertical movement
– Keep permanent magnet aligned with stator– Target tip in beam– Optical grating w.r.t optical sender / receiver
» Minimise free horizontal movement of shaft – To prevent rattling / hammering
» Minimise driving force– Allow low driving force of shaft– No frictional heating
Jason Tarrant / November 2008
MICE Target Mechanical Design
Requirements w.r.t main functions» Allow constrained vertical movement
– Coaxiality of bearings with assembly components (x,y & orientation), especially stator.
» Minimise free horizontal movement of shaft – Minimal clearance between bearings and shaft
» Minimise driving force– Low friction between shaft and bearing– No transverse force on shaft by bearings (good
location and fit)
Jason Tarrant / November 2008
MICE Target Mechanical Design
Other essential requirements» Durable
– For required life of target
» Compatible– Radiation– Non-magnetic– Compatible with material/coating of shaft– Compatible with adjacent part materials
Jason Tarrant / November 2008
MICE Target Mechanical Design
Possible supplementary functions» Prevent rotation of the shaft» Damping to prevent vibration issues» End-stop for a dropped shaft
Jason Tarrant / November 2008
MICE Target Mechanical Design Solutions for ‘main function’ requirements
» Constrained vertical movement– Align bearings with Target assembly
Machine separately and assemble to accurately m/c assembly (current alignment of components?)
Machine separately and assemble into assembly that allows adjustment, e.g. a gimbal type + x,y mount.
Part machine and fit to assembly / sub assembly then final machine in ‘one-shot’ (sub assembly important)
At least one bearing flexibly mounted to take up misalignment (even dynamic misalignment)
Jason Tarrant / November 2008
MICE Target Mechanical Design
» Minimise free horizontal movement– Reducing the clearance between shaft and bearing
Alternative bearing hole shape that is easier to machine smooth and to tight tolerances (requires shaft change too)
Ensure that the shaft is as accurate as possible (straight, smooth, tight tolerances)
Decrease bearing misalignment (see previous) Flexible bearing to give snug fit Sprung device that keeps shaft in contact with bearings
Jason Tarrant / November 2008
MICE Target Mechanical Design
» Minimise driving force– Minimise Friction
Low friction coating (hard wearing, not necessarily hard) Fine surface finish (ground, polished, honed)
– Minimise transverse force Bearing alignment (see previous) Bearing clearance (see previous)
– Also minimise mass in shaft
Jason Tarrant / November 2008
MICE Target Mechanical Design
» Assembly issues with round shaft & slot/key– Passing target through bearing– Engaging key in slot– Other….
Jason Tarrant / November 2008
MICE Target Mechanical Design Assembly for ISIS» 3 Choices
– 1/ R78 after long test, inspect, predict life, install in ISIS if prediction OK, problems/issues?
– 2/ R78 refurbished, shaft and bearings from same batch as test model, problems/issues?
– 3/ Parallel identical assembly made at same time as R78 test model, problems/issues?
Jason Tarrant / November 2008
MICE Target Mechanical Design Assembly for ISIS - considerations
Question R78 inspect & use R78 refurbished Parallel Identical
How alike is the model being installed to the test model?
It is the test model Minimum difference in all components to test model (easy to be ~ identical)
Many new components = biggest difference (can it really be made identical?)
Is it known to work? Known to work for reasonable no. of cycles
Expected to work based on previous test, potentially only shaft bearing issues
Expected to work based on R78 model but potential for many differences (shaft, bearing, driving, electrics)
What components are worn?
Potential for wear hence reduced life throughout (or is it run-in?)
Shaft & bearings replaced but still many components part worn
All components fresh
Expected life? Can shaft, bearing, drive wear/damage be gauged?
Can drive be judged for wear/damage?
Relies on being same as the R78 offline model
Other Implications? -How fast can the offline target produce ‘x’ cycles?-How identical is the offline model? Could be a reverse problem to using parallel identical model in ISIS.
-Sensible Test/Run-in?-Offline model identical, could be a reverse problem.