Time Domain Identification of Multi-stage Planetary Gearbox Characteristic Frequencies Using Piezoelectric Strain Sensor

Nowadays, condition monitoring of gearboxes is based on analyzing vibration signal (mostly acceleration, velocity; fewer strain) measured from mechanical components or on analyzing acoustic emission and temperature data. Strain sensors are rarely used because of their high cost, mounting difficulties and their sensitivity harsh environment. They are based on strain gage technology which implements ‘Wheatstone Bridge Conditioner’ to be able to measure strain values. This bridge circuit, unfortunately, becomes non-linear out of the measurement range resulting in significant errors. To avoid those errors, a new technology of piezoelectric strain sensors, relatively new to condition monitoring, emerges: they have good precision since the accuracy is improved and provide good results especially when attempting to do measurements at extremes of the range. In this work, a piezoelectric strain sensor mounted on an industrial planetary gearbox (PG) in vertical direction is used to acquire time domain signals. This latter is introduced to focus on the importance of the new time domain representation of a gearbox dynamic behavior by a such sensor. Finally, an analysis of the RHM sensor time domain data is conducted to identify the PG characteristic frequencies.