Development and Simulation of an Active Load Cell Test Rig

In industrial machinery, fluid-film bearings are used to support high-speed rotating masses in a low friction environment. As technology progresses, the need for higher machine speeds and loading conditions is a driving factor behind many cutting edge designs. Accurate knowledge of fluid-film bearing stiffness and damping coefficients can assist in vibration analysis to prevent a dangerous, costly, and time-consuming machine failure. Test rigs have been developed throughout the past three decades with the sole purpose of identifying these coefficients experimentally, however there is a need for higher accuracy measurements. The effective determination of fluid film bearing force is a necessary precursor to making accurate dynamic coefficient measurements, particularly at high frequencies. Current methods of force identification are indirect and subject to significant errors that compound at high frequencies to render these measurements inaccurate.

The "Active Load Cell" is a new experimental method of determining fluid-film bearing force without the need for inertial correction. A control algorithm works in conjunction with accelerometer readings and an electrodynamic shaker to adaptively cancel the motion of the bearing housing. This measurement method has the potential to determine bearing forces directly, to a higher degree of accuracy than previous force identification methods. This research details the development and simulation of an Active Load Cell Test Rig, which will be used to validate this concept prior to implementation within full-scale equipment. The results documented here suggest that bearing force amplitude and phase can be determined within 1% of true values across a wide range of test frequencies, stiffness, and dynamic loading conditions.