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IntroductionHarmonic 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.Slide-*
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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Basic Working Principle
All harmonic drives consist of the same three basic
elements:
A Circular SplineB Flex SplineC Wave Generator
Slide-*
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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Wave GeneratorThe wave generator (WG) consists of two parts:
(yellow inner ring)An elliptically shaped steel plugBall bearingThe
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.Slide-*
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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Flex SplineThe 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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ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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Circular SplineThe 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.
Slide-*
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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How it works: Reduction*ECE5320 Mechatronics. Assignment#1
Survey on sensors and actuatorsSlide-*The gear reductions are a
result of the flex spline having two less teeth than the circular
spline.
Notice the negative sign because the flex spline rotates in
reverse of the wave generatorClick for Animation
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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How it works: FlexingThe 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.
Slide-*
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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How it works: Zero BacklashSlide-*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
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How it works: Efficiency*Slide-*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
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Configurations*Slide-*
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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Major SpecificationsThere is not limitation of type motor to
provide the input actuation. Input/output torque requirementsHollow
shaft vs. solid shaftInput PowerLubrication types and operating
temperaturesSize and WeightSlide-*
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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AdvantagesSimple 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 (0.008)High torque-to-weight ratio (100:1,
160:1, 200:1)
*Slide-*
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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Advantages cont.Zero backlashInfinite lifetime w/ constant
performanceCost effectiveHollow ShaftQuiet operation because low
tooth impact, elliptical shape keeps gears tight and smooth.
Slide-*
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LimitationsGear 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 efficiencyHigh
ratio drives are non-backdrivableMust be careful of operating
temperatures, and lubrication techniques.Slide-*
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SelectionHarmonic Drives have many specifications but the basics
are:Input/output Torque RatioLubrication TypeOutput RpmPhysical
size and weightMaximum Backlash (6,3,1 arc/sec)Maximum Transmission
Error (6,3,1 arc/sec)*Slide-*
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CostHarmonic 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.Slide-*
ECE5320 Mechatronics. Assignment#1 Survey on sensors and
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