Time domain sinusoidal acceleration controller for an electrodynamic shaker

Abstract

A digital acceleration controller for sine vibration testing using electrodynamic shakers is presented. The control purpose is to reproduce a specified acceleration profile at the shaker table close to the device under test (magnitude and frequency). The difficulty in sine testing is that the load dynamics are unknown and can severely modify the shaker response. Since a logarithmic frequency sweep is usually involved, the controller needs to be not only robust to unmodelled dynamics but also sufficiently fast to hold the specified magnitude acceleration within predefined limits during the sweep. In contrast to the typical frequency domain control approach of industrial shaker controllers, the proposed solution is implemented on a sample-by-sample basis, which reduces the time required to update the shaker drive signal in response to the controlled acceleration. A cascade of compensators is designed to attenuate the shaker structural resonances and obtain asymptotic reference tracking. The controller structure is developed based on the usual vibration testing power amplifier technology and on the typical frequency range of automotive and aerospace tests. A practical procedure is presented to identify the shaker dynamic model parameters and to design the acceleration controller. Different from other solutions presented in the literature for sine testing, the experimental performance is also investigated with resonant loads.