One of the many advantages of a harmonic drive is the insufficient backlash because of the unique design. However, the fact that they are lightweight and intensely compact can be important.
High gear reduction ratios of up to 30 times 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 had been selling licenses so that industry giants might use his patented item.
harmonic drive assembled The harmonic drive is a kind of gear arrangement often referred to as a strain wave gear due to just how it works. It really is some sort of reduction gear mechanism comprising a minimum of three main elements. These parts interact in a way that allows for very high precision decrease ratios that would otherwise require much 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 the countless advantages that it brought to the table. Musser discovered the potential of his invention at an early on stage and in 1960 began offering licenses to producers so they could use his patented item. Nowadays, there are just a small number of manufacturers in the USA, Germany, and Japan who are holding the license to produce harmonic drives, doing this at their top-notch facilities and producing 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 which can be a servo electric motor axis for instance. This is connected to an component called “wave era” which includes an elliptical form and is normally encircled by an elliptical ball bearing. As the shaft rotates, the edges switch position, so that it looks like it is generating a movement wave. This component is inserted in the flex spline that is made out of a torsionally stiff yet flexible material. The material takes up this wavy motion by flexing based on the rotation of the input shaft and in addition produces an elliptical form. The outer edge of this flex spline features gear teeth that are ideal for transferring high loads with no issue. To transfer these loads, the flex spline is installed inside the circular spline which is a round equipment featuring internal teeth. This outer ring can be rigid and its own internal diameter is marginally larger than the major axis of the ellipse produced by the flex spline. This means that the circular spline will not believe the elliptical shape of the various other two components, but instead, it simply meshes its internal teeth with those of the outer flex spline side, 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 amount of teeth between the flex spline and the circular spline. The flex spline provides fewer teeth compared to the circular spline, so that it can rotate at a very much reduced ratio and in the opposite path than that of the insight shaft. The decrease ration is given by: (number of flex spline tooth – amount of circular spline teeth) / amount of flex spline tooth. So for example, if the flex spline provides 100 teeth and the circular spline offers 105, the decrease ratio is (100 – 105) / 100 = -0.05 which implies that the flex spline ration is -5/100 (minus indicates the contrary direction of spin). The difference in the number of teeth can be changed to accommodate different reduction ratios and thus different specialized requires and requirements.
Achieving decrease ratios of 1/100 or more to even 1/300 simply by using such a concise light set up 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 used. That is mainly thanks to the elliptical bearing installed on the external rim of the insight shaft permitting the free of charge 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 with no need to improve anything, plus they retain the same positional accuracy about 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 elements 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 app where small size, low weight, zero backlash, high precision and high reliability are required”. Examples include aerospace applications, robotics, electric automobiles, medical x-ray and stereotactic devices, milling and lathe devices, flexo-printing machines, semiconductor tools, optical measuring machines, woodworking machines and camera head pans and tilt axes. The most known types of harmonic drive applications include the wheels of the Apollo Lunar Rover and the winches of the Skylab space station.