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Prepared by: Zeke Susman Dept. of Electrical and Computer Engineering Utah State University

ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Harmonic Drive. Prepared by: Zeke Susman Dept. of Electrical and Computer Engineering Utah State University E: zeke.susman@gmail.com ; F: (435)797-3054 (ECE Dept.). 3/11/2010. Outline . Introduction

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Prepared by: Zeke Susman Dept. of Electrical and Computer Engineering Utah State University

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  1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Harmonic Drive Prepared by: Zeke Susman Dept. of Electrical and Computer Engineering Utah State University E: zeke.susman@gmail.com; F: (435)797-3054 (ECE Dept.) 3/11/2010

  2. Outline • Introduction • Reference list • To probe further • Major applications • Basic working principle illustrated • A typical sample configuration • Major specifications • Advantages • Limitations • Assembly and Installation • Selection • Cost • Suppliers ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  3. Introduction • Harmonic Drives (HD) were invented in the late 1950 by C. Walton Musser. • HD have become a primary choice when precise positional accuracy and repeatability are required. • HD is capable of high gear ratios, zero backlash, and high torque-to-weight ratios. • HD are very compact with torque-to-weight ratios 50% smaller and 30% greater efficiencies than other gearing mechanisms. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  4. Reference list • A. Lauletta, “The Basics of Harmonic Drive Gearing”, Gear Product News, April 2006. pp. 32-36 • Wikipedia, “Harmonic Drive”, Widipedia, [Accessed: March, 8, 2010] , [Online] http://en.wikipedia.org/wiki/Harmonic_drive. • KAZEROONI, H. “Dynamics and control of instrumented harmonic drives”, Journal of dynamic systems, measurement, and control. 1995, vol. 117, no1, pp. 15-19 (8 ref.) American Society of Mechanical Engineers, New York,  1971. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  5. To explore further (survival pointers of web references etc) • http://www.hdinfonet.com/harmonic_drive.html • http://www.powertransmission.com/issues/0706/harmonic.htm • http://en.wikipedia.org/wiki/Harmonic_drive • http://www.nacharmonicdrive.com/index.html • http://www.harmonicdrive.net/ • http://www.roymech.co.uk/Useful_Tables/Drive/Harmonic_Gears.html • http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518 • http://machinedesign.com/article/flexible-gears-minimize-gearhead-backlash-for-life-0607 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  6. Major applications • Robotics • Ground Robotics (chaos – Autonomous solutions) • Prosthetics /Cybernetics – (Cyberdyne, Honda) • Industrial Robotics (car manufacturing, silicon wafer production) • Aerospace • Satellites, Aircraft • Medical Equipment (mri equipment, microscope positioning) • Communications • Radar and satellite tracking systems http://www.hdinfonet.com/applications.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  7. Basic Working Principle All harmonic drives consist of the same three basic elements: • A – Circular Spline • B – Flex Spline • C – Wave Generator http://www.powertransmission.com/issues/0706/harmonic_fig1.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  8. Wave Generator • The wave generator (WG) consists of two parts: (yellow inner ring) • An elliptically shaped steel plug • Ball bearing • The plug is pressed into the bearing so that the bearing conforms to the plugs elliptical shape. • The WG is pressed into the flex spline. • The WG is attached to the drive input in the most common configuration. http://www.hds.co.jp/HDS_hp_english/english/principle/movecomp/movecomp.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  9. Flex Spline • The flex spline (FS) is a thin walled steel cylindrical cup. • It has teeth machined into outside upper rim of the cup. • The FS has a large diameter to allow radial flexibility while maintaining high torsional stiffness. • In common configuration rotates in reverse of the wave generator plug. • The rotating output element in the common configuration. http://www.hdinfonet.com/images/instruction-4.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  10. Circular Spline • The Circular Spline is a rigid circular ring with teeth on the inside edge that mate with the teeth of the flex spline (blue outer ring). • It is the non-rotating element in the common configuration. http://www.hds.co.jp/HDS_hp_english/english/principle/movecomp/movecomp.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  11. How it works: Reduction • The gear reductions are a result of the flex spline having two less teeth than the circular spline. Click for Animation • Notice the negative sign because the flex spline rotates in reverse of the wave generator ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  12. How it works: Flexing • The Harmonic Drive mechanism relies upon the elastic properties of the the flex spline material (steel). • The resulting deformation is well below the endurance limits of the material, if the peak torque is kept below the rated maximum. • This flexing preloads the gears and helps reduce noise, friction, and backlash. http://www.harmonicdrive.net/media/reference/operatingprinciples//diagram2.gif ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  13. How it works: Zero Backlash • Because the flex spline is preloaded almost zero back lash is achievable 6,3 or 1 arc-sec depending on size and reduction ratio. • The amount of backlash between mating teeth remains constant over the lifetime of the drive because the preloading and the relative motion of the gears. Click for Animation ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  14. How it works: Efficiency • Standard gear mechanisms have contact between only a couple of teeth at any given time. • The unique design of the harmonic drive allows for 30% of the teeth to be in contact at any give time. • Increases torque transfer efficiency to be between 65% and 90% highest of any gear transfer mechanism. Click for Animation ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  15. Configurations http://www.powertransmission.com/issues/0706/harmonic.htm ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  16. Sample Application Exoskeletal Robotics is an ideal application of Harmonic Drive technologies. The Japanese company Cyberdyne is producing these suits and are using HD at each joint. Each blue circle represents an integrated stepper and a harmonic drive. Because the drive and the motor are coaxially aligned a very compact assembly is achievable with very high torque and low weight. http://www.cyberdyne.jp/English/robotsuithal/index.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  17. Major Specifications • There is not limitation of type motor to provide the input actuation. • Input/output torque requirements • Hollow shaft vs. solid shaft • Input Power • Lubrication types and operating temperatures • Size and Weight ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  18. Advantages • Simple construction (3 piece) • Light weight (up to 50% lighter than conventional reducers) • Compact (single stage, pancake style, coaxial input out put shafts) • High efficiency in gear ratios between 60:1 to 250:1 efficiencies of 65% to 95% are achievable. • High positional accuracy (0.008º) • High torque-to-weight ratio (100:1, 160:1, 200:1) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  19. Advantages cont. • Zero backlash • Infinite lifetime w/ constant performance • Cost effective • Hollow Shaft • Quiet operation because low tooth impact, elliptical shape keeps gears tight and smooth. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  20. Limitations • Gear reductions below 30:1 are limited because of the possibility of fatiguing the flexspline. • Restricted to input power levels below 6000W. • Large models experience lower efficiency • High ratio drives are non-backdrivable • Must be careful of operating temperatures, and lubrication techniques. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  21. Assembly • The ball bearing is pressed around the wave generator plug and conforms to the elliptical shape of the plug. • The wave generator A is inserted into the flex cup B. The cup also conforms to the elliptical shape of the WG. • The flex cup B is inserted into the circular spline C. A B C A B http://www.hdinfonet.com/images/instruction-1.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  22. Installation Issues • When installing the wave flex spline into the circular spline care must be taken to ensure a concentric meshing of the gears. • Can be verified by inspecting the gap on the minor axis. http://www.hdinfonet.com/images/instruction-2.jpg ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  23. Installation Issues • Care must be taken to allow the Flex spline cup enough clearance to deflect normally • The outer wall • The bottom of the cup http://www.hdinfonet.com/application_notes.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  24. Lubrication • Lubrication types include oil and grease. • The type of lubrication required depends on the size of the unit and operating temperature and the ambient temperature difference. • Temperature difference must be kept below 60º C • Oil is generally used for : • Higher temperatures • Larger unites • Vertical installations http://www.nacharmonicdrive.com/id66.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  25. Selection Harmonic Drives have many specifications but the basics are: • Input/output Torque Ratio • Lubrication Type • Output Rpm • Physical size and weight • Maximum Backlash (6,3,1 arc/sec) • Maximum Transmission Error (6,3,1 arc/sec) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  26. Cost • Harmonic Drives range in cost based on size, lubrication, and configuration type. • The drive costs a bit more than other reduction devices, but the savings is made up by being able to reduce the requirements for the motor and the savings in size and weight. • Based on the myriad of configuration possibilities it is recommended to contact a sales rep for actual pricing. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  27. Suppliers • Harmonic Drive - http://www.harmonicdrive.net/ • Harmonic Drive Gearing - http://www.hdinfonet.com/firstpage.htm • Harmonic Drive AG - http://www.harmonicdrive.de/en/index.htm • Heason - http://www.heason.com/ ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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