On the Cross Axis Responses in SISO and MIMO Random Vibration Control Testing

In random vibration control testing, the nowadays common practice to recreate in the laboratory the multi-directional nature of a real vibration environment is the sequential Single-Input Single-Output (SISO) control testing: the test specimen is sequentially rotated and each axis is individually excited using a single axis shaker. In SISO control configuration, just the drive axis of vibration is feedback controlled and in order to verify the validity of the single axis test, the cross axis responses (the two axes orthogonal to the main axis) should not exceed acceptable thresholds. Significant advances in test hardware and control software, in addition to test facility designed for multi-axial excitation testing, have made possible to perform single axis testing using Multiple-Input Multiple-Output (MIMO) control strategy. The MIMO control configuration allows the simultaneous control of the vibration levels on the main axis and on the two cross axes. This paper presents a part of an test campaign carried out using two different test facilities with the same performance characteristics: a single axis shaker and a three-axial shaker. The aim of the work is to compare the results in term of cross axis responses obtained performing sequential single axis test with SISO and MIMO control strategies.