1.0 Purpose

The purpose of this procedure is to provide the information required to replace the Tracker Y slew motor.

2.0 Scope

This procedure defines the steps, parts, hardware, and equipment for removing the existing Tracker Y slew motor and installing the new Y slew motor.

3.0 Applicable Documents

The following documents are applicable to the extent specified herein:

a. 1010-0020 Tracker Beam Assembly

b. TM-12774 HET Project Safety plan

c. TM-12725 HET Tracker Installation Procedure

d. TM-13058 HET Tracker Servicing Procedure

4.0 Safety Precautions

Y slew motor replacement will be performed at the University of Texas, McDonald Observatory. Measures shall be taken to prevent, or reduce to a minimum, personnel exposure to hazardous conditions and environments. A safe servicing area will be maintained during the Y slew motor replacement. The following personnel and facility safety precautions shall be observed:

a) One engineer shall be designated as the Installation Director and will be responsible for the safety of the personnel and equipment during conduct of the replacement procedure.

b) Secure the area from unnecessary traffic.

c) Protective equipment shall be worn as required by established safety practice.

d) Prior to working with electrical circuits, remove all jewelry, watches, rings, and metal objects.

e) Personnel shall read and understand safety precautions outlined in reference documents.

f) Personnel involved with elevated work shall wear fall restraint equipment as specified in Section 9 of TM-12774 or per HET facility procedures.

g) All personnel on the ground level shall wear protective equipment as defined in TM-12774 per HET facility procedures.

h) Prior to any lifting or work on the Tracker, a protective cover or shield shall be in place to protect the primary mirror.

i) The Installation Director shall review the complete procedure with the participants.

1) One (1) 5000 lb minimum sling. Length to reach the top of the carriage, when at 3 feet from the top of travel, and routed under the top cross member of the Y beam to the dome crane hook.

2) Two (2) 3000 lb minimum slings. 3 to 5 feet long.

3) Compressed air supply to the reach the Y axis tracking brake. With fitting to attach to the brake air input.

4) Brake caliper shim (Provided with Tracker)

5) Three (3) D size sheets of mylar (0.004 to 0.010 thick)

6) One (1) wood V-block (Provided with Tracker) or high enough to reach the roller screw at the floating bearing mount (-Y end). V cut to fit roller screw.

7) Bearing retainer installation/removal tool – spanner (Delivered with Tracker)

8) Large ratchet driver for item 7.

9) Large adjustable wrench and “cheater bar” (Pipe to extend lever arm of adjustable wrench).

10) Torque wrench with a socket driver head (Used on bearing retainer installation/removal tool). Torque required is minimum 116 Ft-lbs.

6.0 Slew Motor Replacement

6.1 Preparation

A minimum of two (2) people are required to perform these operations. Three (3) are preferred.

1) The Installation Director shall review this portion of the procedure with all participants. All necessary drawings, procedures, equipment, etc shall be available for use during this briefing and the work.

2) Load all special equipment required into the manlift.

3) Run the compressed air line to the Y track brake.

4) Drive the Carriage in the +Y direction to the roller screw fixed bearing mount. (Track motor). Apply all brakes.

5) Position the dome crane at the top (+Y) end of the Y beam. Lower the crane hook to within reach of the top of the Y beam.

6) Two (2) slings (3000 lb min rating) are required. Attach one (1) sling at the bottom on each side of the carriage around the Y beam vertical truss member. Leaving approximately 24 inches of slack to lower the carriage in the –Y direction.

7) Attach one (1) sling (5000 lb min rating) around the upper crossmember of the carriage in the center. Run the sling under the top cross-member X beam of the Y beam and attach that end to the crane.

8) Gently pull the strap tight with the crane.

9) Release the Y track brake as follows: disconnect the air line to the brake if not already removed; connect the air line from the portable tank to the brake; open the air supply valve until the brake releases then shut the air valve again. If the carriage begins to back-drive excessively set the brake by opening the vent valve. Repeat steps 8 and 9 until the crane has the downhill weight of the carriage.

6.2 Slew Motor Removal

A minimum of two (2) people are required to perform these operations. Three (3) are preferred.

1) Locate the brake caliper spacer provided with the Tracker and keep it near by. Make sure there is enough service loop in the air line to remove the brake and set it aside.

2) While holding the track brake housing, remove the track brake housing mounting bolts. Do not remove the brake mounting plate.

3) Release the track brake calipers by applying air pressure to the brake. Lift the track brake assembly off the brake housing mount and set in the manlift. Insert the spacer between the brake pads and release the air pressure.

4) Remove the center portion of the flexible coupling. Note the orientation and location of the spherical washers for assembly later. Do not loose or drop the bolts and washers. Keep the disc packs intact. The roller screw shaft may rotate slightly due to the back driving force from the carriage. Alternately, the track motor and coupling may be removed together off the roller screw.

5) Loosen the screws that clamp the coupling to the roller screw shaft. Remove the coupling flange attached to the roller screw shaft. The coupling attached to the track motor can remain on the motor shaft.

6) Loosen clamp screws on the track brake and slide the disc off the roller screw shaft. NOTE: THE BRAKE DISC IS KEYED TO THE SHAFT.Do not drop the key.

7) Remove the fixed roller screws (+Y) bearing cover and v-seal from the fixed bearing mount.

8) Remove the bellows mounting screws from the roller screw (+Y) fixed bearing mount. Compress the bellows and measure the compressed length. The roller screw must be removed from the bearing mount by greater than this length.

9) One person now is required at the floating bearing end (-Y) of the roller screw.

10) At the floating bearing end (-Y), remove the bellows mounting screws and push the bellows in the +Y direction approximately 18 inches.

11) At the floating bearing end (-Y), tightly wrap the roller screw with Mylar on the exposed threaded portion of the shaft.

12) At the floating bearing end (-Y), locate the wooden v-block under the roller screw on the +Y side of the floating bearing mount (at the -Y end of the roller screw).

13) Remove the v-seal and bearing cover from the floating bearing mount.

14) At the fixed bearing end (+Y), attach the bearing retainer removal tool (spanner) to the bearing retainer on the fixed bearing (+Y end). Attach the ratchet driver.

15) At the floating bearing end (-Y), attach the adjustable wrench on the flats on the end of the roller screw shaft. Slip cheater bar over wrench handle for additional leverage.

16) Remove the Ringfeder clamp on the roller screw shaft.

17) With one person securely holding the adjustable wrench, loosen the fixed bearing retainer by rotating the ratchet counter clockwise. Remove the retainer. Do not attempt to remove the bearings from the bearing mount.

18) Do not attempt to remove the bearings or retainer from the roller screw on the floating roller screw end (-Y end).

19) Remove the adjustable wrench from the roller screw shaft.

20) Grab the roller screw shaft on both sides of the bearing mount at the floating end of the roller screw (-Y). Be prepared to support the roller screw as it moves through the bearing mount (-Y end).

21) While supporting the floating bearing end of the roller screw shaft, slowly lower the crane hook and therefore let the carriage and roller screw shaft move in the-Y direction. The fixed bearings remain in their mount with the shaft moving out of the bearings. The floating bearings will be pushed out of their mount but remain on the roller screw shaft.

22) An alternate method to remove the roller screw is to rotate the roller screw from the coupling end (+Y) to back the shaft through the bearing mounts.

23) Slide the shaft in the –Y direction until the shaft drive end (+Y) is away from the fixed bearing mount a few inches more than the bellows length measured in step 8. Stop the crane.

24) Remove the screws attaching the bellows to the slew motor cover. Slide the bellows off the roller screw shaft.

25) Wrap the threaded portion of the shaft with Mylar.

26) Disconnect the slew motor connector from the cable. DONE

27) Remove the Cover, Motor-Slew screws. Carefully remove the cover off the roller screw shaft. DO NOT KNICK THE THREADS ON THE SHAFT.

28) Wrap the remaining threaded portion of the shaft with Mylar up to the slew motor rotor.

29) If desired, insert Mylar in the air gap between the slew motor rotor and stator.

30) Slide the slew motor stator out of the Spacer, Motor-Slew.

31) Remove the slew motor rotor clamp screws and the clamp.

32) Remove the rotor from the Drive Coupling, Slew Motor.

33) Inspect the motor mounting area for varnish that may have melted and coated the inside of the mounting area. Clean with an appropriate solvent such as Acetone. Clean the Spacer, Motor-Slew and Retainer, Duplex Bearing.

34) If required for cleaning, remove the Spacer, Motor-Slew (spacer).

35) If necessary remove and clean the Retainer, Duplex Bearing attached to the Drive Coupling, Slew Motor.

6.3 Slew Motor Replacement

These Stator Assembly tasks should be performed on a bench.

1) Verify the new motor stator cable fits through the slot in the Cover, Motor-Slew. If not, widen the slot on a milling machine or with a hand file. Touch up with black paint.

2) Attach the Clamp, Install, Y-Slew (HET 0003) to the Spacer, Stator, Y-Slew (HET 0002) using the 0.625 inch long screws. Slide a Shaft, Installation through the two (2) sets of 0.25 inch diameter holes. Align the clamp so the shaft slides smoothly through. Hand tighten.

3) Align the keyways in the stator and Spacer, Stator, Y-Slew. Install the stator in the Spacer, Stator, Y-Slew. Insert the new key. The key should protrude out the end.

4) Take all parts and assemblies up to the Tracker for installation.

5) Install the Retainer, Duplex Bearing if it was removed for cleaning. Apply Loctite to the screws. Torque the screws as specified on drawing 1010-0020.

6) Install the Spacer, Motor-Slew if it was removed for cleaning. Do not install the 45º and 135º (CCW) screws. Apply Loctite or use the lock washers to the remaining screws. Torque the screws as specified on drawing 1010-0020.

7) If the Spacer, Motor-Slew was not removed, remove the 45º and 135º (CCW) screws.

8) Perform a trial fit of the new stator with spacer on the existing Spacer, Motor-Slew. Use steps 13 and 14 below.

9) Align the keyways of the rotor with the Drive Coupling, Slew Motor. Slide the new rotor on the Drive Coupling, Slew Motor. Install the new key.

10) Using the rotor and the key for alignment, slide the Spacer, Rotor, Y-Slew (new part) inside the rotor.

11) Using eight (8) 1.75 inch long cap screws with Loctite applied, clamp the rotor onto the coupling. Torque the screws to 75 in-lbs. Use a “star pattern” when tightening.

12) Wrap the rotor magnets with one (1) wrap of Mylar.

13) Install the one Shaft, Installation (HET 0004) in each of the 45º and 135º (CCW) holes in the Housing, Slew Drive.

14) Get a firm grip on the assembly, holding the front of the stator so it will not “jump” axially out of the Spacer, Stator, Y-Slew. Slowly slide the assembly over the rotor using the shafts as a guide. About half way over the rotor the magnetic force may push the stator back axially away from the rotor. Verify the key is sliding into the Spacer, Motor-Slew. Keep pushing until the stator assembly is seated.

15) Loosely install a few screws. Remove the Clamp, Install, Y-Slew.

16) Remove the two (2) Shaft, Installation.

17) Apply Loctite or use the lock washers. Install the two (2) mounting screws in the Spacer, Motor-Slew and Housing, Slew. Torque to 75 in-lbs.

18) Push the Spacer, Stator, Y-Slew tight against the Spacer, Motor-Slew. Apply Loctite to the 0.625 mounting screws. Insert the screws to attach the Spacer, Stator, Y-Slew to the Spacer, Motor-Slew. Torque to 75 in-lbs. Use a “star pattern” when tightening.

19) Remove Mylar from the rotor.

20) Slide the Cover, Motor-Slew over the roller screw shaft. Fit the connector through the cover and place the cover on the stator. Apply Loctite or use lock washers on the screws. Install the screws and torque to 70 in-lbs. Use a “star pattern” when tightening.

21) Remove the mylar form the upper roller screw shaft.

22) Slide the bellows over the roller screw. DO NOT KNICK THE THREADS ON THE SHAFT. Compress the bellows towards the slew housing.

23) Position a person at the –Y (floating bearing) and the +Y ends of the roller screw.

24) While supporting the roller screw at the –Y end, use the crane to pull the carriage in the +Y direction until the roller screw shaft is at the fixed bearing mount. Stop the crane.

25) While guiding the floating bearings into their mount, rotate the roller screw so the screw shaft moves into the fixed bearings. Shake the roller screw as the floating bearings move into their mount. The shaking will prevent binding of the bearings as they move into the bearing mount. This technique will work on the fixed bearing side also. The installation may push the fixed bearings partially out of the housing.

26) Verify the shaft and bearings are correctly seated. The floating bearings should be approximately centered in their housing.

27) Perform steps in Note 12 on drawing 1010-0020. Slide the bearing clamp on the roller screw shaft and snug up against the bearing.

28) Attach the bearing retainer removal tool (spanner) to the bearing retainer on the fixed bearing (+Y end). Attach the torque wrench to the installation tool.

29) At the floating bearing end (-Y), attach the adjustable wrench on the flats on the end of the roller screw shaft. Slip the cheater bar over wrench handle for additional leverage.

30) With one person securely holding the adjustable wrench, incrementally tighten the fixed bearing retainer by rotating the ratchet clockwise. Use steps of 25, 50, 75, 100, 116 Ft-lbs.

31) Remove the wrenches and remaining Mylar.

32) Slide the Cover, Retaining Nut on the drive end of the roller screw and seat on the fixed bearing outer race. Install the screws with the flat and lock washers. Torque to the required values (75 in-lbs) on 1010-0020. Use a “star pattern” when tightening.

33) Apply a thin coat of silicone grease (DC-55 or equivalent) to the v-ring seal. Slide the seal onto the roller screw shaft and seat against the bearing cover.

34) Slide the Cover, Retaining Nut on the floating end of the roller screw shaft. The cover should not touch the bearings. Install the screws with flat and lock washers. Torque to 40 in-lbs.

35) Apply a thin coat of silicone grease (DC-55 or equivalent) to the v-ring seal. Slide the seal onto the roller screw shaft and seat against the bearing cover.

36) Install the brake disc per Section 5.10

37) Install the track motor if it was removed. Check alignment and install the coupling per Section 5.11 steps b through i.

38) Install the track brake assembly using Section 5.12 steps b through f.

39) Attach the roller screw bellows to their respective mounts.

40) Attach all air lines that were removed.

1. Verify all brakes are engaged.

2. Reduce tension on the crane strap to allow for a 20 millimeter move in –Y.

3. Test for alignment by commanding a –10 mm move in Y. Listen for clicking from the track drive coupling. If clicking is detected, notify the Installation Director. Align the Y drive coupling per the alignment procedure and repeat this step. Continue the alignment procedure and test until no clicking is heard from the Y track drive coupling.

4. The step 5 and steps 6 through 8 may be performed in parallel.

5. Install the standard algorithm pmac card.

6. Tension the crane strap to hold the carriage in position.

7. Using the portable air tank, release the Y slew brake. The Y stage may back drive slightly. Listen for rubbing noises from the newly installed Y slew motor.

8. Using extreme care, slowly lower the crane to allow the Y stage to back drive about 10 millimeters. Listen for rubbing noises. The motion should be smooth and quite. If unacceptable noise is heard, stop the operation, reset the Y slew brake and contact the Installation Director.

9. Once steps 5 though 8 are completed, it is time to test the new Y slew motor electrically. You must have the Installation Directors permission to proceed.

10. Command a +10 mm move of the Y slew motor. Watch for proper motion. The brakes must release prior to or concurrently with the Y slew motor energizing. If a following or other error occurs, notify the Installation Director to determine additional actions. If no error occurs and motion is successful, remove the following equipment.

11. Disconnect the crane and safety straps from the carriage.

12. Remove the safety tarp.