Driving a motion platform with a vibration control software for multi-axis environmental testing: challenges and solutions.

Multiple-Input Multiple-Output (MIMO) vibration control testing is nowadays recognized, in the environmental testing community, as an effective test methodology to accurately replicate the vibration environment a structure needs to withstand during its operational life. For these applications, the control process typically takes place in the frequency domain, within the data acquisition hardware's embedded processor. Multiple analogue voltages (the so called ‘drives’) are computed and streamed to the exciters in order to obtain a controlled response of a Unit Under Test (UUT) for a set of multiple control channels (the so called ‘Controls’, typically acceleration recordings). The multi-input excitation can be simultaneously applied with a set of multiple independent shakers or with multi-degrees of freedom (DOFs) shaking tables. In this case the drives are translated in the shaking table’s DOFs in the three dimensional space. Advanced state-of-the-art hydraulic and electrodynamic multi-axis shakers are nowadays available to excite the UUT in all the six DOFs. On the other hand six DOFs motion platforms are widely used in motion simulation, where the aim is to use the platform to replicate the motion of an object in the three dimensional space. This is typically performed with a dedicated algorithms, running on real time hardware that communicates with the platform’s internal controller via Internet Protocol. Theoretically, the only step to combine this type of hardware with a data acquisition system and a vibration control software is to translate the drives in actuators displacements. However, adding layers to the communication chain, brings practical challenges. First of all, in order to establish any communication, it is mandatory to cope with the platform’s protocol and real time requirements. Then, for any environmental testing application, it is fundamental to guarantee that the information sent is not inconsistently distorted or delayed in the communication process.
This work aims to show the challenges and the solutions to combine a six DOFs motion simulation platform with an advanced off-the-shelf MIMO vibration control software and data acquisition hardware. The case study will show the possibility of (i) use the motion simulation platform for low frequency environmental testing and (ii) use the MIMO vibration control software to replicate a pre-defined motion in the three dimensional space.