f/8 tip-tilt mechanism and handling cart P. Schurter December 2012

WBS 1.5 TaskDurationDependencyResourcesNotesStatus 1.5 New drive screw assemblies 11 w + 4 w proc Get specs from Deliver to 2.7 when done. PS, 1 IM Assembly integrates drive screw, motor, encoder, power and signal connections. Starts after WBS Specify new drive screw 1 w PS To meet positioning requirements. Done. Using old drive screw 1.5.1b Check operation of system 2wRequirementsPS Will the current design meet the requirements? Done. Yes, barely Design assembly 2 w Deliver to PS Almost done. Need to design mount for new encoder. ETA 1 week 1.5.3Procure parts4 w proc PS Parallel tasksPending 1.5.4Fabricate parts4 w 1 IM 1.5.5Assembly2 w PS, 1 IM Pending 1.5.6Rework2 w From Deliver to PS, 1 IM After bench test. Includes design, fabrication, assembly. Contingency. Pending 2

Design issues f/8 mechanism is over constrained 3 Cylindrical roller Spherical roller 9 radial supports, 3 spherical, 6 cylindrical

Radial support detail The radial supports are not compliant 4

And three axial actuators Axial actuator 5

What happens when a tilt command is given Radial displacement But rollers are not compliant and cell is very stiff… 6

The radial rollers (over)define the rotation axis of the cell Inducing radial loading and displacement of the leadscrew 7 Rollers oppose the tilting, they do not want to tilt! Control system may have a hard time reaching the tilt demand

Effect of tilt and focus If a focusing movement is started, the distance between the rollers and the cell will change. The rollers do not follow and they will jam on one side and become loose on the other. Also will induce radial displacement of the axial actuators 8

The existing system Ø5/8”-10 ACME lead screw Aluminum bronze nut The radial displacement of the actuator tip induces a radial load on the aluminum –bronze nut, increasing wear over time. The system keeps working, but increases its inaccuracy 9

Further mechanical issues 10 Existing ball joint design Flat face in ball joint limits rotation of lead screw. This is needed, but as a side effect it also restricts movement of ball joint to one axis

Orientation of ball joints 11 Arrangement of ball joints makes tilting impossible…

Except for play 12 There is enough play (50µm) in the mechanism to allow for 0.56° - we need 0.2 °

But…. 13 This also means a little play on the lead screw (0.27°), which may lead to control problems: the motor moves, but the actuator doesn’t

Conclusions 14 Existing design of tilt actuators will work, with limitations. It is the only way to have it working in time. Perhaps upgrade the system later? Tilting will be done much more frequently, ~30 times per night. This will increase wear on nut, so we should expect to change the nut more frequently

WBS 4 Status 4 Handling cart8 w RGP input safety requirements PS, RR, 1 IMSchedule before WBS Design and fabricate 6 w PS, RR, 1 IM In process Design safety review 1 w Various Design reviewed by external reviewers Done Design2 w PS, RR Eng design done; fab dwgs needed Done Fabricate4 w 1 IM Materials bought. Drawings sent to the shop 15

Overview LARGER BASE AND SECTION ROTATION HANDLE LOCKING PIN NEW DESIGN INCLUDES DECAM ADAPTER PLATE 16

SIDE VIEW FLOOR CLEARANCE IS OVER 3 INCHES 17

TOP VIEW CART IS LARGER THAN INSTRUMENT IN BOTH X AND Y DIMENSIONS 18

CENTER OF MASS IS PLACED ON THE AXIS OF ROTATION DOES NOT CHANGE WITH INSTRUMENT ROTATION 19

ROTATION MECHANISM ROTATION HANDLE PLACES OPERATOR OUTSIDE POTENTIALLY DANGEROUS AREA SAFETY PIN MUST BE DISENGAGED TO ROTATE INSTRUMENT SHAFT CLAMP MUST BE DISENGAGED TO ROTATE INSTRUMENT 20

CONNECTION TO INSTRUMENT 21 INSTRUMENT IS BOLTED ON 8 POINTS

SAFETY 22 INSTALLATION POINTS HAVE WARNING IN ENGLISH AND SPANISH WELDED LUG IMPEDES INSTALLATION ON THIS SIDE