Innovative gearboxes with beveloid gears for robotic applications

This thesis investigates the Omni planetary gearbox, for which Bonfiglioli Riduttori holds a patent and carried out validation tests. The design adopts a Wolfrom planetary architecture combined with preloaded axial beveloid gears to achieve a backlash of under 1 arcminute. The Omni gearbox is available in two versions—OH (with central hole for cable routing) and OS (solid shaft). It is designed in ten sizes (010–100, by payload capacity) and four ratios (1:80, 1:100, 1:125, 1:160). The validation process for the Omni began with the development of preliminary sizing tools. These included an analytical kinetostatic model, a KISSsoft model for beveloid gear pairs based on their midsection geometry, and a model of the main bearing based on the standard ISO 281. A more detailed design was then created using multibody, finite-element and KISSsys models. These models enabled the optimisation of the gearbox design and the definition of validation experiments. The latter, focused on endurance and characterisation, were performed on OH prototypes, size 060, with a 1:125 ratio. Results were generally positive, with minor issues related to efficiency and service life. These are currently being addressed by optimising lubrication, refining gear flank geometry, and adjusting spring preload. The beveloid gear design adds complexity to parameter optimisation because there are no standard sizing procedures. Two analytical models were built to address this issue: the first used the minimum potential energy principle to evaluate contact-stresses in parallel-axis straight beveloid gears; the second predicted pitting in parallel-axis helical beveloid gears in accordance with ISO 6336-1 (Annex E) and ISO 6336-2. These models support the optimisation of design parameters to minimise contact pressure. A simple (non-planetary) parallel-axis gearbox including helical beveloid gears was chosen as a case study to validate the second model through endurance tests. Preliminary test results confirm the expected lifetime.