One of the many advantages of a harmonic drive is the lack of backlash due to the unique style. However, the actual fact that they are light-weight and intensely compact is also important.
High gear reduction ratios as high as 30 times that achieved with planetary gears are feasible in the same space.
C W Musser designed strain wave gearing back 1957 and by 1960 he was already selling licenses so that industry giants could use his patented item.
harmonic drive assembled The harmonic drive is a type of gear arrangement often referred to as a strain wave gear due to the way it works. It really is some sort of reduction equipment mechanism comprising at the least three main components. These parts interact in a manner that allows for high precision reduction ratios that could otherwise require a lot more complicated 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 taken to the desk. Musser determined the potential of his invention at an early stage and in 1960 began selling licenses to manufacturers so they could use his patented product. Nowadays, there are only a small number of manufacturers in the USA, Germany, and Japan who are holding the license to produce harmonic drives, doing so at their top-notch facilities and generating ultimate quality stress gears for the whole world.
harmonic drive exploded viewThe workings of a harmonic drive
The rotational movement originates from an input shaft that can be a servo motor axis for instance. This is connected to an element called “wave era” which includes an elliptical shape and is definitely encircled by an elliptical ball bearing. As the shaft rotates, the edges change position, so that it looks like it really is generating a movement wave. This part is inserted inside a flex spline that is made out of a torsionally stiff yet flexible materials. The material takes up this wavy motion by flexing according to the rotation of the insight shaft and in addition creates an elliptical shape. The outer advantage of the flex spline features equipment tooth that are suitable for transferring high loads with no issue. To transfer these loads, the flex spline is installed in the circular spline which is a round gear featuring internal tooth. This outer band is definitely rigid and its own internal size is marginally larger than the main axis of the ellipse shaped by the flex spline. This implies that the circular spline will not believe the elliptical form of the other two parts, but rather, it simply meshes its inner teeth with those of the external flex spline aspect, leading to the rotation of the flex spline.
The rate of rotation would depend on the rotation of the input shaft and the difference in the number of teeth between the flex spline and the circular spline. The flex spline has fewer teeth compared to the circular spline, so that it can rotate at a very much reduced ratio and in the contrary 
path than that of the insight shaft. The decrease ration is distributed by: (amount of flex spline teeth - number of circular spline tooth) / amount of flex spline teeth. So for instance, if the flex spline has 100 tooth and the circular spline has 105, the decrease ratio is (100 - 105) / 100 = -0.05 which means that the flex spline ration is -5/100 (minus indicates the contrary direction of spin). The difference in the amount of teeth could be changed to support different decrease ratios and thus different specialized wants and requirements.
Advantages
Achieving decrease 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 by any 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 used. That is mainly thanks to the elliptical bearing fitted on the external rim of the insight shaft allowing 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 the need to improve anything, plus they wthhold the same positional accuracy in both spin directions.
The efficiency of the harmonic drive measured on real shaft to shaft studies by the producer goes up to 90%. There are extremely few mechanical engineering components that may claim this operational performance level.
Uses for a harmonic drive
In a nutshell a harmonic drive can be used “in virtually any gear reduction software where small size, low weight, zero backlash, high precision and high reliability are needed”. Examples include aerospace applications, robotics, electric automobiles, medical x-ray and stereotactic devices, milling and lathe devices, flexo-printing machines, semiconductor apparatus, optical measuring devices, woodworking devices and camera mind pans and tilt axes. The most notable examples of harmonic drive applications are the wheels of the Apollo Lunar Rover and the winches of the Skylab space station.