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

Among the many benefits of a harmonic drive is the lack of backlash due to the unique style. However, the actual fact they are light-weight and extremely compact is also important.
High gear reduction ratios of up to 30 moments that achieved with planetary gears are feasible in the same space.
C W Musser designed strain wave gearing back 1957 and by 1960 he had been selling licenses to ensure that industry giants could use his patented product.
harmonic drive assembled The harmonic drive is a type of gear arrangement also known as a strain wave gear because of the way it works. It is some sort of reduction equipment mechanism consisting of at the least three main parts. These components interact in a manner that allows for high precision reduction ratios that could otherwise require a lot more complex and voluminous mechanisms.

As something, 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 taken to the desk. Musser recognized the potential of his invention at an early stage and in 1960 started selling licenses to manufacturers so they might use his patented product. Today, there are only a handful of manufacturers in america, Germany, and Japan who are keeping the license to create harmonic drives, doing so at their top-notch services and making ultimate quality strain gears for your world.

harmonic drive exploded viewThe workings of a harmonic drive
The rotational motion comes from an input shaft that can be a servo engine axis for example. This is linked to an element called “wave generation” which has an elliptical form and is definitely encircled by an elliptical ball bearing. As the shaft rotates, the edges transformation position, so it appears like it is generating a motion wave. This part is inserted inside a flex spline that’s crafted from a torsionally stiff however flexible materials. The material occupies this wavy movement by flexing based on the rotation of the insight shaft and also creates an elliptical shape. The outer advantage of the flex spline features equipment tooth that are suitable for transferring high loads with no problem. To transfer these loads, the flex spline is fitted in the circular spline which really is a round gear featuring internal tooth. This outer band is rigid and its internal size is marginally bigger than the main axis of the ellipse created by the flex spline. This implies that the circular spline does not presume the elliptical form of the additional two elements, but rather, it basically meshes its inner tooth with those of the external flex spline aspect, resulting in 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 your flex spline and the circular spline. The flex spline offers fewer teeth than the circular spline, so it can rotate at a much decreased ratio and in the opposite direction than that of the input shaft. The reduction ration is distributed by: (amount of flex spline teeth – number of circular spline tooth) / quantity of flex spline teeth. So for instance, if the flex spline offers 100 teeth 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 support different decrease ratios and therefore different specialized wants and requirements.

Advantages
Achieving reduction ratios of 1/100 and up to even 1/300 by simply using such a compact light set up of gears can’t be matched simply by any additional 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. This is mainly thanks to the elliptical bearing fitted on the outer rim of the input 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 forwards and backward rotation without the need to change anything, and they wthhold the same positional accuracy on both spin directions.
The efficiency of the harmonic drive measured on real shaft to shaft tests by the producer rises to 90%. There are very few mechanical engineering components that can claim such an operational effectiveness level.
Uses for a harmonic drive
In short a harmonic drive can be utilized “in any gear reduction software where little size, low weight, zero backlash, very high precision and high reliability are needed”. Examples include aerospace applications, robotics, electric vehicles, medical x-ray and stereotactic machines, milling and lathe devices, flexo-printing devices, semiconductor equipment, optical measuring machines, woodworking devices and camera mind pans and tilt axes. The most notable examples of harmonic drive applications are the tires of the Apollo Lunar Rover and the winches of the Skylab space station.