Transcript ECE5320 Assignment#1 - 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: [email protected];
F: (435)797-3054 (ECE Dept.)
3/11/2010
Slide-2
Outline
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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
Slide-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.
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Slide-4
Reference list
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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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To explore further
(survival pointers of web references etc)
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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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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
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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
http://www.powertransmission.com/i
ssues/0706/harmonic_fig1.jpg
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Slide-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/engl
ish/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.
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.
http://www.hds.co.jp/HDS_hp_english/engl
ish/principle/movecomp/movecomp.html
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Slide-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
200
 100 : 1
200  202
•Notice the negative sign because the flex spline
rotates in reverse of the wave generator
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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 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,
http://www.harmonicdrive.net/media/reference/operatingprincipl
and backlash.
es//diagram2.gif
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How it works: Zero Backlash
• Because the flex spline is
preloaded almost zero back
lash is achievable 6,3 or 1 arcsec 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.
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Click for
Animation
Slide-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.
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Click for
Animation
Slide-15
Configurations
http://www.powertransmission.com/issues/0706/harmonic.htm
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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
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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
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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 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)
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Advantages cont.
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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 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.
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Assembly
1.
2.
3.
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
B
A
http://www.hdinfonet.com/images/instruction-1.jpg
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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.
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http://www.hdinfonet.com/images/instruction-2.jpg
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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
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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 60º C
• Oil is generally used for :
– Higher temperatures
– Larger unites
– Vertical installations
http://www.nacharmonicdrive.com/id66.html
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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)
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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 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.
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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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