Dynamic load testing of roller screw EMAs

In the electromechanical actuators (EMA) laboratory at The University of Alabama, USA, a dynamic load test stand has been designed and built. This test stand uses large load, high bandwidth and hydraulic actuation to generate load profiles under force control. The test stand can accommodate EMAs up to six feet in length. It can generate dynamic loads of up to 100,000 lb at fundamental frequencies of up to 12 Hz against a stiff environment. This test stand has been used to generate severe loading conditions on a large roller screw in an attempt to qualify the effects of large, high frequency loads on roller screw. During the tests performed in the EMA laboratory the screw was fixed at one end and axial loads were applied to the roller nut at the other. Since the end opposite the nut was fixed, only a small amount of relative rotation between the nut and screw was achieved. This rotation was the result of elastic deformation (wind up) of the screw along the length between the fixed end and the nut. This simulates a severe, but likely, application of the roller screw. The results of the tests performed demonstrate that roller screws may be damaged by dynamic loading with load magnitudes that are well within the static load rating of the screw. While the damage that was observed is not catastrophic, it would be expected to substantially decrease the life of the screw.