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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 UniversityE: [email protected];
F: (435)797-3054 (ECE Dept.)
3/11/2010
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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
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Introduction
Harmonic Drives (HD) were invented in the late 1950 byC. 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 gearingmechanisms.
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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.
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http://en.wikipedia.org/wiki/Harmonic_drivehttp://en.wikipedia.org/wiki/Harmonic_drive8/10/2019 adaptive sterr
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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
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http://www.hdinfonet.com/harmonic_drive.htmlhttp://www.powertransmission.com/issues/0706/harmonic.htmhttp://en.wikipedia.org/wiki/Harmonic_drivehttp://www.nacharmonicdrive.com/index.htmlhttp://www.harmonicdrive.net/http://www.roymech.co.uk/Useful_Tables/Drive/Harmonic_Gears.htmlhttp://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://machinedesign.com/article/sometimes-it-pays-to-be-eccentric-0518http://www.roymech.co.uk/Useful_Tables/Drive/Harmonic_Gears.htmlhttp://www.harmonicdrive.net/http://www.nacharmonicdrive.com/index.htmlhttp://en.wikipedia.org/wiki/Harmonic_drivehttp://www.powertransmission.com/issues/0706/harmonic.htmhttp://www.hdinfonet.com/harmonic_drive.html8/10/2019 adaptive sterr
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Major applications
Robotics Ground Robotics (chaosAutonomous 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
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http://www.hdinfonet.com/applications.html
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Basic Working Principle
All harmonic drives consist
of the same three basic
elements:
A Circular Spline
B Flex Spline
C Wave Generator
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http://www.powertransmission.com/issues/0706/harmonic_fig1.jpg
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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 bearingso that the bearing conforms to the
plugs elliptical shape.
The WG is pressed into the flex
spline.
The WG is attached to the drive inputin the most common configuration.
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http://www.hds.co.jp/HDS_hp_english/english/principle/movecomp/movecomp.html
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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.
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http://www.hdinfonet.com/images/instruction-4.jpg
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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.
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http://www.hds.co.jp/HDS_hp_english/english/principle/movecomp/movecomp.html
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How it works: Reduction
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The gear reductions are aresult of the flex spline
having two less teeth than
the circular spline.
1:100202200
200
Notice the negative sign because the flex splinerotates in reverse of the wave generator
Click forAnimation
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How it works: Flexing
The Harmonic Drive
mechanism relies upon the
elastic properties of the the flex
spline material (steel).
The resulting deformation iswell 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.
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http://www.harmonicdrive.net/media/reference/operatingprinciples//diagram2.gif
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How it works: Zero Backlash
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Because the flex spline ispreloaded 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 forAnimation
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How it works: Efficiency
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Standard gear mechanismshave contact between only a
couple of teeth at any given
time.
The unique design of theharmonic 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 forAnimation
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Configurations
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http://www.powertransmission.com/issues/0706/harmonic.htm
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Sample Application
Exoskeletal Robotics is an idealapplication 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 hightorque and low weight.
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http://www.cyberdyne.jp/English/robotsuithal/index.html
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Major Specifications
There is not limitation of type motor to providethe input actuation.
Input/output torque requirements
Hollow shaft vs. solid shaft
Input Power
Lubrication types and operating temperatures
Size and Weight
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Advantages
Simple construction (3 piece) Light weight (up to 50% lighter than conventional
reducers)
Compact (single stage, pancake style, coaxial input output shafts)
High efficiency in gear ratios between 60:1 to 250:1
efficiencies of 65% to 95% are achievable.
High positional accuracy (0.008)
High torque-to-weight ratio (100:1, 160:1, 200:1)
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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.
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Limitations
Gear reductions below 30:1 are limited because ofthe 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.
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Assembly
1. The ball bearing is pressed aroundthe wave generator plug and
conforms to the elliptical shape of
the plug.
2. The wave generator Ais inserted
into the flex cup B. The cup alsoconforms to the elliptical shape of
the WG.
3. The flex cup Bis inserted into the
circular spline C.
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A
A
B
B
C
http://www.hdinfonet.com/images/instruction-1.jpg
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Installation Issues
When installing the waveflex spline into the
circular spline care must
be taken to ensure a
concentric meshing of thegears.
Can be verified by
inspecting the gap on theminor axis.
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http://www.hdinfonet.com/images/instruction-2.jpg
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Installation Issues
Care must be taken toallow the Flex spline cup
enough clearance to
deflect normally
The outer wall
The bottom of the cup
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http://www.hdinfonet.com/application_notes.html
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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 60 C
Oil is generally used for : Higher temperatures
Larger unites
Vertical installations
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http://www.nacharmonicdrive.com/id66.html
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Selection
Harmonic Drives have many specifications but the basicsare:
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)
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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 ableto reduce the requirements for the motor and the
savings in size and weight.
Based on the myriad of configuration possibilitiesit is recommended to contact a sales rep for actual
pricing.
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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/
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http://www.harmonicdrive.net/http://www.hdinfonet.com/firstpage.htmhttp://www.harmonicdrive.de/en/index.htmhttp://www.harmonicdrive.de/en/index.htmhttp://www.hdinfonet.com/firstpage.htmhttp://www.harmonicdrive.net/