Study of surface relief optimization for improving the durability of RV reducers of industrial robots under thermomechanical loading

Abstract

The service life of an RV reducer in a robot joint drive is governed by its cycloid-pin mesh, and a surface microrelief is proposed for lowering friction and wear, which parts of the cycloid wheel flank may carry it remains unclear once load and thermal state are treated together. The study computes how contact, kinematic and lubrication quantities vary along that flank and delimits the parts where a microrelief leaves the peak contact pressure unchanged. The modelling unit is a point of the working flank of the cycloid wheel of a model RV reducer. For 720 mesh positions the pin load sharing, the Hertzian pressure, the entrainment and sliding velocities, the film thickness parameter from the Dowson-Higginson relation at two bulk temperatures and the friction energy density per pass were computed. The calculated peak contact pressure is 1315 MPa at an arc coordinate of 3.31 mm; the calculated friction energy density peaks at 10.30 kJ/m² only 0.01 mm away, and the calculated share of the flank under boundary lubrication grows from 55.9% to 65.8% upon heating. The zone admissible for a microrelief under the peak-pressure criterion covers 91.8% of the loaded flank and 66.9% of the friction work. The calculations show that the most heavily loaded part of the flank is also the part of highest frictional heat release and thinnest film, so a position-dependent relief belongs upstream of it, covering two thirds of the friction work at an unchanged peak pressure.