Omni: A low-backlash planetary Wolfrom gearbox with beveloid gears for robotic applications

This article presents an innovative Wolfrom planetary gearbox for robotic applications, named “Omni”. It combines the Wolfrom planetary architecture with beveloid gears to achieve small transmission ratios (up to 1:160) in a compact shape. The key advantage of beveloid gears lies in their ability to adjust their contact position through axial movements, thus ensuring minimal torsional backlash (under 0.6 arcmin) over the entire lifespan of the gearbox. A comparison of the technologies for robot gearboxes is first reported, highlighting the advantages of the proposed solution. The article then presents the architecture and the main characteristics of the new gearbox, with a focus on the kinetostatic analysis. Two designs are proposed: one with solid and coaxial input and output shafts, and another with hollow and parallel shafts to accommodate data and supply cables. Finally, the results of validation experiments are discussed. Endurance and characterization tests confirm that Omni reaches the target performances, such as very low backlash, high stiffness, smooth motion transmission, long lifespan, and low transmission error.