Planetary mechanisms based on worm and spiroid gears

Abstract

The paper considers two new planetary mechanisms based on worm and spiroid gears. The mechanisms provide an extremely high reduction (from dozens of thousands up to hundreds of thousands in one stage), smoothness of operation, possibility to adjust or eliminate the backlash due to combining many advantages of common multi-stage planetary gears and multi-stage usual (nonplanetary single-row) worm and spiroid gears. One of the mechanisms implies simultaneous meshing of the spiroid satellite worm with two sun gearwheels (movable and fixed). As for the second mechanism, each of two spiroid satellite worms (in general, different from each other) is meshing with one of two sun gearwheels: one spiroid worm with the movable gearwheel and the other spiroid worm with the fixed one. Formulas are derived for calculating the total gear ratio that allow for providing its large values by small difference in gear ratios for meshing of spiroid satellite worms with sun gears. The method of analyzing the forces acting in the worm and spiroid gearing and the efficiency of the mechanism is described. Numerical investigation showed that one should aim at greater reduction at the worm stage of the mechanism, at interaxial angles close to 90o, and at low ratios of the gearwheel diameter and the interaxial distance. The second of the proposed mechanisms is comparable with simple stationary-axes multi-stage worm-type mechanisms by the efficiency; and they provide smaller sizes and coaxial alignment of the input and output shafts.