Fault Modeling of Harmonic Reducers Based on Current Signal Under Time Varying Conditions

The harmonic reducer is often used in the industrial robot due to the characteristics of large deceleration ratio and high transmission efficiency. Flexible thin-wall bearing is one of the core structures of the harmonic reducer, and compared with ordinary bearings, its inner and outer rings have unique thin-wall structure, which deforms periodically under the extrusion of the elliptical camshaft and the alternating load. The above characteristic and working conditions make it the most vulnerable part of the reducer. What's more, the harmonic reducer is subjected to the influence caused by the changing speed and load under practical operating conditions of industrial robots, which can increase the possibility to damage. Therefore, we propose a fault model of harmonic reducer for industrial robots based on current signal under varying load and speed. The proposed model considers the vibration of flexible bearing caused by the long and short axes changing alternately. In addition, the working condition of varying load and speed is also considered in the fault frequency model. The experiment of harmonic reducer is conducted in case of three common parts damage on the flexible bearing, and the effectiveness of the proposed model is also verified. Results show that this model can clearly reflect the actual fault situation of the harmonic reducer used in industrial robots.