电动式振动台被广泛应用于振动测试领域，其本质是一个机电耦合换能系统。电动式振动台在低频率大位移工况下，其悬挂系统刚度和励磁电流产生的磁场分布均会随动圈位置变化而呈现显著非线性变化。这些非线性因素会导致振动台在低频或超低频振动测试时产生严重的谐波失真，并进一步导致振动台低频振动难以控制。为实现动圈低频运动的精确控制，采用基于模型的前馈控制对驱动电流进行精准补偿。为此，首先建立了考虑振动台非线性刚度及非线性力系数的集总参数模型，分析并阐述了振动台工作过程中产生非线性现象产生的机理。其次，根据集总参数模型建立了振动台的动力学方程，并结合控制目标和自治方程求解得到系统中状态变量的变化情况，利用非自治方程反推出所需的前馈控制电流。最后，将前馈控制作用下动圈的运动与控制目标进行对比分析。数值算例表明，调整后的驱动电流能够大大缩小低频或超低频工况下振动台动圈的运动状态与跟踪目标之间的差距，有效地抑制了在振动台工作过程中非线性因素带来的谐波失真。本文提出的振动台前馈控制方法能够大大提高振动台的工作精度，同时扩大振动台在低频测试时的工作行程和工作频率范围，为振动台控制设计提供了新思路。
Abstract
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.
关键词
电动振动台 /
非线性耦合 /
前馈控制 /
谐波失真
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Key words
Electrodynamic shaker /
Nonlinear coupling /
Feedforward control /
Harmonic distortion
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