A novel approach to gearbox condition monitoring by using drive rectifier input currents

Gearboxes are widely used and subjected to progressive deterioration which makes box condition monitoring a relevant topic in the servodrive industry. This paper proposes a novel scheme for performing integral condition monitoring in a drive containing a gearbox. The proposed scheme is based on a modified MCSA scheme (motor current signature analysis) that uses the drive rectifier input currents instead than the machine currents, as in the case of the conventional scheme. The approach is based on the principle that any fault signature generated due to a faulty component (machine, load, mains, or power converters) propagates through the drive´s main components (rectifier-inverter). In most of the cases the fault signatures should be detectable at the input side by carefully looking at the rectifier supply currents. The proposed scheme allows not only condition monitoring of the gearbox and the machine, but other drive´s components at no extra cost. An experimental investigation is carried out to demonstrate the feasibility of the scheme to detect a faulty gearbox in a PM servo drive operating under different working conditions. Important differences in magnitude for those frequencies related to the gearbox and system unbalances were found at the input side when the test was repeated with faulty gearbox, which demonstrates the feasibility of the scheme.