How does a Harmonic Drive work? Why are they used?

Among the many benefits of a harmonic drive may be the insufficient backlash because of the unique design. However, the fact they are lightweight and intensely compact can be important.
High gear reduction ratios of up to 30 instances that achieved with planetary gears are feasible in the same space.
C W Musser designed strain wave gearing back in 1957 and by 1960 he was already selling licenses to ensure that industry giants could use his patented product.
harmonic drive assembled The harmonic drive is a kind of gear arrangement often referred to as a strain wave gear because of just how it works. It is some sort of reduction gear mechanism consisting of at the least three main parts. These parts interact in a manner that allows for high precision decrease ratios that would otherwise require a lot more complex and voluminous mechanisms.

As a product, the harmonic drive was invented by the American engineer Clarence Walton Musser in 1957, and it quickly conquered the industry with a variety of advantages that it brought to the table. Musser discovered the potential of his invention at an early stage and in 1960 started selling licenses to producers so they could use his patented product. Nowadays, there are just a handful of manufacturers in the USA, Germany, and Japan who are holding the license to produce harmonic drives, doing this at their top-notch services and making ultimate quality stress gears for the whole world.

harmonic drive exploded viewThe workings of a harmonic drive
The rotational motion originates from an input shaft which can be a servo motor axis for instance. This is linked to an component called “wave era” which includes an elliptical form and is usually encircled by an elliptical ball bearing. As the shaft rotates, the edges modification position, so it looks like it really is generating a movement wave. This part is inserted in the flex spline that’s made out of a torsionally stiff yet flexible materials. The material takes up this wavy motion by flexing based on the rotation of the input shaft and also creates an elliptical form. The outer edge of the flex spline features gear tooth that are suitable for transferring high loads with no issue. To transfer these loads, the flex spline is installed inside the circular spline which really is a round gear featuring internal teeth. This outer ring is definitely rigid and its internal diameter is marginally bigger than the major axis of the ellipse formed by the flex spline. This means that the circular spline does not believe the elliptical form of the additional two parts, but instead, it simply meshes its internal tooth with those of the outer flex spline side, leading to the rotation of the flex spline.

The rate of rotation is dependent on the rotation of the input shaft and the difference in the amount of teeth between the flex spline and the circular spline. The flex spline provides fewer teeth compared to the circular spline, so it can rotate at a much decreased ratio and in the contrary direction than that of the insight shaft. The reduction ration is distributed by: (quantity of flex spline tooth – quantity of circular spline teeth) / number of flex spline tooth. So for example, if the flex spline has 100 tooth and the circular spline has 105, the reduction ratio is (100 – 105) / 100 = -0.05 which means that the flex spline ration is -5/100 (minus indicates the opposite direction of spin). The difference in the amount of teeth could be changed to accommodate different decrease ratios and therefore different specialized requires and requirements.

Achieving decrease ratios of 1/100 and up to even 1/300 simply by using such a compact light arrangement of gears cannot be matched by any various other gear type.
The harmonic drive is the only gear arrangement that doesn’t feature any backlash or recoil effect, or at least they are negligible in practice. That is mainly thanks to the elliptical bearing installed on the external rim of the insight shaft enabling the free rotation of the flex spline.
The positional accuracy of harmonic drives even at an extreme number of repetitions is extraordinary.
Harmonic drives can accommodate both forward and backward rotation without necessity to improve anything, plus they retain the same positional accuracy in both spin directions.
The efficiency of a typical harmonic drive measured on real shaft to shaft studies by the manufacturer goes up to 90%. There are extremely few mechanical engineering components that may claim such an operational efficiency level.
Uses for a harmonic drive
In short a harmonic drive can be used “in any gear reduction application where little size, low weight, zero backlash, very high precision and high reliability are needed”. Examples include aerospace applications, robotics, electric automobiles, medical x-ray and stereotactic machines, milling and lathe machines, flexo-printing machines, semiconductor gear, optical measuring devices, woodworking machines and camera mind pans and tilt axes. The most known examples of harmonic drive applications include the tires of the Apollo Lunar Rover and the winches of the Skylab space station.


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