MIT2_72s09_lec11

MIT2_72s09_lec11 - Martin Culpepper, All rights reserved 4...

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MIT OpenCourseWare http://ocw.mit.edu 2.72 Elements of Mechanical Design Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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2.72 Elements of Mechanical Design ‘Lecture’ 11: Screw drives
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Schedule and reading assignment Quiz ± Bolted joint qualifying Thursday March 19 th Topics ± Screw drive group activity - 90% hands on Reading assignment Read: 13.1 – 13.7 17.1 & 17.3 Skim: Rest of Ch. 17 © Martin Culpepper, All rights reserved 2
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Screws Convert rotary motion into linear motion: Types of “lead screws”: ± Sliding contact thread lead screws ± Ball screws ± Hydrostatic lead screws ± Others © Martin Culpepper, All rights reserved 3
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Typical screw types Image by jgelens on Flickr. Images removed due to copyright restrictions. Please see http://news.thomasnet.com/images/large/455/455175.jpg http://www.danahermotion.com/website/com/eng/img/product/LeadScrew2Nut.jpg
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Unformatted text preview: Martin Culpepper, All rights reserved 4 Errors Some error sources Misalignment Bearings, Carriage Geometry Straightness Varying pitch diameter (periodic error and backlash) Errors in thread-contacting elements Loads Elastic Vibration Active error management Periodic errors can be mapped Linear position sensors Martin Culpepper, All rights reserved 5 Preload why Nut-screw: Backlash Use two nuts that are preloaded against each other Use oversize rolling elements Use a split-circumferentially clamped nut Screw-machine: Backlash Buckling Straightness Vibration Martin Culpepper, All rights reserved 6 Cross feed design exercise Kinematic (trade off) Loads and power (limits) Constraints (bearing, flexure?) Preload (Nut-screw and screw-machine) Stress/fatigue Errors (Causes, systematic, random) Martin Culpepper, All rights reserved 7...
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MIT2_72s09_lec11 - Martin Culpepper, All rights reserved 4...

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