It has always been a critical task to understand gear dynamics for gear design and condition monitoring. Many gear models have been proposed to simulate gear meshing dynamics. However, most of the theoretical models are
based on simplified gear structure and may contain approximation errors. Direct measuring of gear strain is important to gear design validation, load analysis, reliability assessment, gear condition monitoring, etc. Most of the
existing studies of tooth strain measurements are performed under static load condition. In this paper, we investigate new measuring techniques of using fiber Bragg grating (FBG) sensor and piezoelectric strain for gear dynamic
strain measurement. We conduct gear dynamic strain measurement under both low speed and normal speed condition on an industrial gearbox with relatively small module gears. Multi-combinations of speed and load conditions of the gearbox are tested and the results are discussed and analyzed. We analyze multiple factors that affect the tooth root stress, including speed, load, extended tooth meshing, etc. It is found that under low operation speed range, the tooth root strain is mainly determined by the torque, while in the mediate to high speed range, the tooth root strain is jointly affected by speed and torque. Extended tooth contact is shown in the measurement results with strong evidence. It conforms with earlier founding that the transmission error and dynamic load factor are overestimated while the operation smoothness are underestimated for spur gear under heavy load. The measured stains are also compared with numerical simulation.
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