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HETDEX Linear Drive Design<br />Tim Beets, PE<br />University of Texas<br />Center for Electromechanics<br />t.beets@cem.u...
Tracker Linear Actuators<br />2 Bridge actuators (X)<br />SKF 60x10 precision roller screw w/preloaded nut<br />18,800kg P...
Unique Design Considerations<br />Operation:<br />1) Slow-speed, precise positioning (tracking) and 2) high-speed, coarse ...
Roller Screw Concerns<br />Rotordynamic analysis predicted screw behavior<br />Tracking speed is well below critical speed...
Low-Temperature Trials<br />Temperature effects cause large variation in drive performance<br />Current requirements doubl...
Subsequent discussion with SKF resulted in changing grease in roller screw and slew drive bearings
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Advisory panel 2011 beets

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Advisory panel 2011 beets

  1. 1. HETDEX Linear Drive Design<br />Tim Beets, PE<br />University of Texas<br />Center for Electromechanics<br />t.beets@cem.utexas.edu<br />(512) 232-4285<br />
  2. 2. Tracker Linear Actuators<br />2 Bridge actuators (X)<br />SKF 60x10 precision roller screw w/preloaded nut<br />18,800kg Payload<br />4 meters travel<br />1 Trolley actuator (Y)<br />SKF 60x10 precision roller screw w/non-preloaded nut<br />35° Inclination<br />9,000kg Payload<br />4 meters travel<br />Bridge and trolley ride THK linear bearing rails<br />Upper X Drive<br />Y Drive<br />Trolley<br />Lower X Drive<br />Bridge<br />
  3. 3. Unique Design Considerations<br />Operation:<br />1) Slow-speed, precise positioning (tracking) and 2) high-speed, coarse positioning (slewing)<br />Low temperatures atypical for roller screw applications<br />Components:<br />Long roller screws are prone to rotordynamic instabilities and tend to sag along unsupported length<br />HET structure is flexible with limited alignment capabilities and presents transient alignment issues under dynamic loading (i.e., tracker traverse)<br />COTS drive components<br />Upper X drive model and analysis of screw sag<br />
  4. 4. Roller Screw Concerns<br />Rotordynamic analysis predicted screw behavior<br />Tracking speed is well below critical speed<br />Screw is not rotated during slewing (high-speed traverses) and nut speed is reduced at center of travel<br />Sag of screw adds considerable load to nut<br />Analyses predicted unacceptable stresses at screw ends when nut was aligned at screw center<br />A single d.o.f. was added to allow the nut to pivot while traversing the sag region<br />Resulting stresses are much lower—increased component life, controller consistency<br />Slew drive pivot bearings<br />
  5. 5. Low-Temperature Trials<br />Temperature effects cause large variation in drive performance<br />Current requirements doubled for velocity-controlled runs<br />Random behavior such as velocity spikes were observed at lower temperature<br /><ul><li>Test results drove decision to increase drive torque capacity to achieve performance targets at lower temperatures
  6. 6. Subsequent discussion with SKF resulted in changing grease in roller screw and slew drive bearings
  7. 7. Erratic low-temperature operation significantly complicates precision control</li></ul>Slew drive velocity at 70°F (blue) and 20°F (green) with constant current (2A) applied<br />
  8. 8. Technical Collaboration<br />MDO HET engineers<br />HET actuator design/operation experience<br />HETDEX operating requirements<br />SKF roller screws, bearings, lubricants<br />THK linear bearings, lubricants<br />Danaher (Kollmorgen) motors, gearheads<br />R+W couplings/torque limiters<br />Branham restraining brakes<br />H&M Mfg. pulleys, belts<br />Upper X slew drive operation during testing<br />

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