Gearbox with adjustable backlash enables pre-tensioning as required

A gearbox with adjustable backlash enables multifunctional use. The team at Roschiwal + Partner Ingenieur GmbH has been working on a corresponding solution and has now presented variants for planetary gears and cycloidal gears. We describe the design in detail.

The issue of backlash in the gearbox is not an easy one. If a planetary gearbox is designed with as little backlash as possible or even with preload, the pressure on the gear configurations is so high that they can no longer cope with higher speeds. If the gearbox is speed-resistant, the positioning accuracy leaves a lot to be desired. So the only option is either - or?

This question captivated a team from Roschiwal + Partner Ingenieur GmbH in Augsburg so much that the engineering firm - in contrast to its usual practice - started its own development. ‘Our aim was to make the gearbox backlash controllable and thus obtain multifunctional gearbox solutions,’ reports former Managing Director Robert Merk. After a good three years of development work, the team achieved its goal and applied for a patent for the solution.

This is what the planetary gearbox with electronically adjustable preload looks like:

As with already known principles, the gears of a planetary gear in the Roschiwal solution are tensioned against each other in order to eliminate any play between the tooth flanks.

An elastically deformable ring gear is hydraulically pressurised so that the planetary gears move towards the centre axis of the gearbox and are braced against the sun gear. In the relaxed state, the outside of the ring gear rests against the housing so that the gearbox can work like a conventional planetary gearbox. ‘The principle is similar to a hydraulic clamping device for tool holders, as is common in machine tool construction,’ Robert Merk draws a parallel. In order to enable the planetary gears to deflect, the planet carriers are designed for elasticity in the micrometre range in the radial direction. At the same time, they have the torsional rigidity required for power transmission in the direction of rotation.

The required hydraulic oil pressure is generated by an electrically operated system that is fully integrated into the gearbox housing - only the electrical connection is visible from the outside.
Open for future co-operation

The concept of dynamic tensioning of a cycloidal or planetary gearbox has now been developed to such an extent that it can be adapted to industry-specific applications and prototypes can be built. ‘Because we have developed this globally unique solution on our own initiative, we are also open to future cooperation,’ says former Managing Director Merk, signalling the engineering firm's fundamental willingness to engage in dialogue.