Jason Tarrant / November 2008 MICE Target Mechanical Design l 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

MICE Target Mechanical Design l Cross section shape »Current cruciform shape –‘+’ or ‘x’ same stiffness –For 11mm 2 CSA I = ~18mm 4 –For a round shaft with same 6mm OD I = 39mm 4 > 2 x as stiff. Jason Tarrant / November 2008

MICE Target Mechanical Design l Alternative Round or Square? Jason Tarrant / November 2008 Round For a 6mm OD tube with a CSA of 11mm 2 the ID works out to be = ~4.7mm. Calculating the second moment of area (I) = ~39mm 4. For a 0.5mm wall the OD will be 7.5mm to give 11mm 2 cross section, for this I = ~68mm 4. Square For 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 ~56mm 4 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 = 23mm 4.

Jason Tarrant / November 2008 MICE Target Mechanical Design l 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 Jason Tarrant / November 2008

MICE Target Mechanical Design l Anti-rotation device »Placement of feature (assume slot or flat on shaft) –Tubular section advantages l Stiffer than solid top section, especially with feature l Wider flat (but split) and wider deeper slot = more able to resist rotation thus preventing potential misalignment or even lock-up –Tubular section disadvantages l Cutting through tubular wall may cause relaxation of residual stress and misshapenness of shaft (follower / sprung pad cannot be part of bearing if tube is misshapen) Jason Tarrant / November 2008

MICE Target Mechanical Design l Anti-rotation device »Viable types –Slot and key l Key on shaft relies on strength of connection to shaft to prevent it parting, issues with weight & balance l Slot on shaft saves weight, key mounted elsewhere can be given a very strong connection –Flat and follower l Flat loaded with a sprung pad (could be at a bearing) l Flat loaded with a thin sprung skid –Others? Jason Tarrant / November 2008

MICE Target Mechanical Design l Anti-rotation device »Slot & key advantages –More positive rotation prevention, especially opposed to a narrow flat –A key should not impose transverse load –If shaft motion is accurately restrained by bearings the key can be sprung or loosened to minimise force required for vertical motion –Easier to machine, less operations, no feathered edges –Section is marginally stiffer & shaft more balanced (less material removed) –Might also be used as end stop for dropped shaft Jason Tarrant / November 2008

MICE Target Mechanical Design l Anti-rotation device »Slot and key disadvantages –Tight fit of key might be required to prevent hammering that is assumed to be happening with bearings –Coating the slot (or coating QA) might be difficult as the face will not be exposed (possible 1.5mm wide) Jason Tarrant / November 2008

MICE Target Mechanical Design l Anti-rotation device »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 l 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… l Target attachment »Threaded, pinned & welded Jason Tarrant / November 2008

MICE Target Mechanical Design l 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 l 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 l 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 l 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 l Solutions for ‘main function’ requirements »Constrained vertical movement –Align bearings with Target assembly l Machine separately and assemble to accurately m/c assembly (current alignment of components?) l Machine separately and assemble into assembly that allows adjustment, e.g. a gimbal type + x,y mount. l Part machine and fit to assembly / sub assembly then final machine in ‘one- shot’ (sub assembly important) l 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 l Alternative bearing hole shape that is easier to machine smooth and to tight tolerances (requires shaft change too) l Ensure that the shaft is as accurate as possible (straight, smooth, tight tolerances) l Decrease bearing misalignment (see previous) l Flexible bearing to give snug fit l Sprung device that keeps shaft in contact with bearings

Jason Tarrant / November 2008 MICE Target Mechanical Design »Minimise driving force –Minimise Friction l Low friction coating (hard wearing, not necessarily hard) l Fine surface finish (ground, polished, honed) –Minimise transverse force l Bearing alignment (see previous) l 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 l 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 l Assembly for ISIS - considerations QuestionR78 inspect & useR78 refurbishedParallel Identical How alike is the model being installed to the test model? It is the test modelMinimum 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. -Sensible Test/Run-in?