Vibration Analysis for Improving Powertrain Design and Contact Measurements of a Roller Rig

This paper provides two vibration analyses on a scaled roller rig that is under construction at the Railway Technologies Laboratory of Virginia Tech (VT) for evaluating wheel/rail contact mechanics. The scaled vertical rig includes a wheel that is placed on a roller with similar profile of a U.S. 136 weight rail. Two independent AC servomotors enable controlling the relative speed of the disks to a high degree of precision. Linear actuators allow for adjusting the simulated load, wheel angle of attack, rail cant, and lateral position of the wheel with respect to the rail, including flanging. Rotation of each disk is dominated by internal dynamics of the motors, gearheads, couplers, and flexible shafts. As a result, dynamics of each component has direct effect on the relative speed of the wheel and the roller at the contact patch. On the other hand, it is essential to make sure that the measurements are only caused by the particular subject of study, and not any intermittent source of disturbance such as unbalanced rotation. Electromechanical models of the rig components have been developed in previous works of the authors for studying the overall behavior of the coupled drivelines. This study aims to fulfill the previous studies by analyzing the effect of incorporating compliant joints in the drivelines, as well as unbalanced dynamics in the disks. Appropriate consideration is given to providing an accurate mathematical model of each phenomenon. The mathematical models are solved numerically to carry out parametric studies that represent actual working conditions of the rig. The results of these studies indicate that incorporation of constant velocity joints in sensitive instruments like the roller rig, leads to inevitable axial vibrations that affect both driver and driven sides. This paper also provides a tool for filtering the undesired vibrations from the contact measurements due to unbalanced rotation or other sources of the same nature.