The Minimum Energy option of MIMO Random is implemented to handle the nonlinearity of a multi-shaker table and provide fast convergent control.

Utilizing a three-axis shaker system for any prolonged period of time causes the nonlinearity issue and some control issues. A typical example in the following screenshot illustrates the overshooting issue along a low frequency end.

When the MIMO Random test on the three-axis shaker table is ramped up to -6 dB, it becomes obvious that the controls along the X, Y, and Z axes show very high levels of overshoot along the low frequency end. As test continues, the overshoot is mitigated by the update of the system FRF matrix and the non-linear control algorithm. This process can take over three minutes until the overshoot is totally compensated and the control reaches its target for all three axes control.

In order to mitigate the overshooting issue, the Minimum Energy option is implemented. With this option, two main actions are taking place: the H update rate is set to 100% and the off-diagonal terms of the FRF matrix are forced to be zero. These actions take place in the defined low frequency range. The high H update ratio generally results in a fast update of the FRF matrix. While nulling the off-diagonal FRFs relates to the name of this option, the minimum energy option treats the three-axis shaker table system as three independent shakers. The whole operation is accomplished from low frequency to the user defined frequency.

To use this option, users can check the option to “Set minimum energy control freq(Hz)” and enter the upper frequency of the option, as illustrated in the following screenshot.

With the Minimum Energy option turned on from 10 Hz to 100 Hz, the following screenshot displays the three-axis MIMO Random test going into -6 dB.

The above screenshot demonstrates a limited overshoot for all three axis control channels. This is attributed to the application of the Minimum Energy option.

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