I would like to dedicate today’s post to a short technical study to provide some clarity on an issue that may give rise to some uncertainty.
It is sometimes the case that customers ask us to create small or very small planetary gearheads (with a diameter therefore of less than 30 mm) characterized by a low backlasch at the output shaft (less than 3’-5’).
These are requests that essentially stem from the need to obtain both a high level of accuracy and positioning repeatability. So first and foremost let’s talk about the typical needs of areas such as robotics or miniature axle movement but also – albeit more rarely – the contexts in which these particular reduction gears are used as an alternative to expensive electronic drives of the electric motors to which they are connected.
Here are a few considerations.
First of all it must be said that to obtain a low-backlash gearhead, the gears in question must be of a very high quality (namely DIN5-6) which can only be obtained with grinding of the teeth (usually following the inevitable heat treatment). The axles of satellites must also be characterized by a positioning error of a few microns, as generally happens for all assemblages of crowns, flanges clearance between satellites and plugs etc.
Today, CNC machining allows the obtaining of considerable levels of precision and this is undeniable, even if – and with this personal consideration I risk making enemies – I am convinced of the fact that when it comes to mass production, microns are more in the pencil of designers than in actual practice. Added to this is the significant barrier represented by the current practical impossibility of adjusting gears of a few millimeters in diameter due to the lack of appropriate technology, a fact which cannot be ignored.
Consider also that generally low backlash planetary gearheads of common sizes (and thus higher than the 50-60 mm in diameter) are in any case selected as it is almost impossible to obtain them for process definition. Returning then to talk about these particularly expensive non-standard products, I would recommend consulting manufacturers or dealers regarding what load applied to the reduction gear ensures the clearance (that is torsional stiffness) and for how many hours of use. This is because even normal polishing of the tooth flank after a certain period of operation can cause a number of pejorative variations.
In conclusion… In general my advice is therefore to choose products of a different type such as Harmonic Drive® reduction gears created with a different construction technology, or to accept a degree of compromise and to rely on the skilled hands of an electronic expert…