The electrodynamic shaker is widely used in the field of vibration testing, and it is essentially an electromechanical coupling transducer system. Under conditions of low frequency and large displacement, the stiffness of suspensions and the magnetic field generated by the exciting current exhibit significant nonlinear variation with the displacement of the moving coil. These nonlinear factors cause severe harmonic distortion during low or ultra-low frequency vibration testing, making shakers difficult to control. To precisely control the moving coil at low frequencies, model-based feedforward control is used to accurately compensate the drive current. Therefore, a lumped parameter model considering the nonlinear stiffness and force coefficient of the shaker is established, and the mechanisms underlying the nonlinear phenomena when the shaker is working are analyzed. Then, based on the model, the dynamic equations of the shaker are established, and the changes in the state variables and the feedforward controlling current are computed. Finally, the motion of the moving coil with feedforward control is compared with the objective. The numerical examples show that the adjusted driving current can significantly reduce the gap between the motion state of the moving coil and the tracking objective at low frequency, effectively suppressing the harmonic distortion. The feedforward control method proposed in this paper can greatly improve the accuracy of the shaker and expand its frequency range of the shaker in low-frequency testing. This provides a new approach for the control design of electrodynamic shakers.
Key words
Electrodynamic shaker /
Nonlinear coupling /
Feedforward control /
Harmonic distortion
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