harmonic gear

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 actuators

Basic Working Principle

All harmonic drives consist of the same three basic elements:

A Circular SplineB Flex SplineC Wave Generator

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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-*


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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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.

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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


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.

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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.

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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.

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Configurations*Slide-*


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-*


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)

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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.

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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-*


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-*


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-*


harmonic gear

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