Angular dynamic model for fault detection of the outer raceway of the RV reducer main bearings under low-speed conditions

Abstract Because industrial robot joints typically operate at low speeds, conventional vibration-based fault detection techniques are unsuitable for detecting the fault of the main bearing in an industrial robot joint or rotary vector (RV) reducer. This study aims to assist in the development of the instantaneous angular speed (IAS) based main bearing fault detection method by investigating the angular response patterns caused by RV reducer main bearings with spall on the outer raceway under low-speed conditions. This study establishes an angular dynamic model to explain the IAS jitters caused by the main bearing with spall on the outer raceway under low-speed conditions. First, the radial and axial deformations arising from the contact between the roller and raceway were analyzed using Hertz contact theory. Subsequently, formulas for the induced tangential force and moment generated by the contact deformation were derived, considering the additional displacement and torque resulting from the impact force. The IAS jitters reveal the torque changes associated with the spall under low-speed conditions, enabling the estimation of the spall size by determining the start and end points of the IAS jitters. The model contribute to developing IAS-based main bearing fault detection methods for industrial robot joints.