Health monitoring of planetary gearbox using motor's control signals

Planetary gearboxes are critical components in modern machines, so it is also crucial to deploy health monitoring for their long-term running. Nevertheless, conventional health monitoring still has a high reliance on extra sensors. Control signals (CS) feedback from the motor provides a new no-extra-sensors measurement for health monitoring. However, the complex coupling relationship between the planetary gearbox and driving motor, and the complicated transmission pattern of planetary-gearbox gear faults in the control system, make the characterization of these faults in CS unclear. Given this, we establish a novel speed-torque dual-couple model, which integrates the motor's control model and the torsional vibration of the planetary gearbox under nonlinear behaviors as an electromechanical coupling system. Then, we construct a new semi-closed loop control model of this system and reveal the transmission pattern of gear faults in the motor control system. On this basis, we calculate and identify the characterization relationship in the simulation, and verify it in the experiment. The results indicate that this model can effectively characterize the impact of gear faults in planetary gearboxes on CS. In addition, the q-axis current in CS can effectively characterize the degrees of gear faults in planetary gearboxes. This paper provides a theoretical basis for the health monitoring of planetary gearboxes without extra sensors.