Multiple-Input Multiple-Output (MIMO) Vibration Control on Sentek Dynamics Three-axis Shaker Table

Vibration testing has been performed since the 1860’s and in recent decades, single shaker vibration testing has been performed for all types of industries and contributed significantly to the progress of modern industries. Many products have been qualified to survive their launching, operating or transportation environmental conditions mainly through single shaker vibration control testing. 

With the development of multiple shaker table systems and the availability of the Multiple-Input Multiple-Output (MIMO) controllers, Multiple-Input Multiple-Output (MIMO) vibration control emerged a couple decades ago. Due to the readiness of the standards, (e.g., MIL-STD 810G Method 527 and IEST DTE 022 Working Group Recommendation) MIMO testing has gained a huge momentum in the past decade. Not only are military, defense, and space exploration organizations such as NASA adopting MIMO testing, automotive and commercial industries are utilizing multiple shaker testing systems as well.

The following photo illustrates a three-axis shaker system (MA-1000-4H) provided by Sentek Dynamics.

Figure 1. MA-1000-4H Three-Axis Shaker system

Figure 1. MA-1000-4H Three-Axis Shaker system

In the real world, structural vibrations are excited due to sources in all directions. To simulate the real world vibration environment, the testing needs to be performed in more than only one direction simultaneously. For many applications, MIMO Testing is required for different reasons: For a large structure testing that cannot be excited with a single shaker without extensive fixturing, or large structure testing with a single shaker does not provide sufficient force. Also, there are tests that require simultaneous multi-axis excitation (translations only, or translations with rotations). MIMO testing is recommended when SDOF testing is inadequate to properly distribute the vibration energy to satisfy this specific requirement.

MIMO testing with multiple shakers exciting along multiple directions at the same time reduces the overall testing time and eliminates the time required to change the fixing of the DUT to the table and change shaker orientations (e.g., from vertical to horizontal) in the case of single shaker testing arrangement. In general, MIMO testing provides a distribution of vibration energy to the test article in more than one axis in a controlled manner without relying upon the dynamics of the test article for such distribution. The physical configuration of the test article is such that its slenderness ratio is high, and Single Exciter Testing must rely upon the dynamics of the test article to distribute energy. For large and heavy test articles, more than one exciter may be necessary to provide sufficient energy to the test item.

Crystal Instruments’ Spider MIMO Vibration Control System takes use of multiple shakers, and multiple control channels are individually assigned with a defined profile. The control process of MIMO Control is expanded into an advanced Matrix fashion compared to the Scalar fashion of the single shaker control.

MIMO Random Control, like MIMO Sine Control, can control phase between shakers and between axes. By maintaining a multi-dimensional system matrix, the Spider system is always capable of determining the contribution from each shaker to the overall response and properly differentiating for each shaker so that proper, accurate, safe control is assured. In a Random test, MIMO Random control produces true gaussian random with one control per profile. The same quality of control offered by Single Shaker Random control is inherent to MIMO Random control. Adaptive control guarantees rapid equalization and accurate control when non-linear responses occur in the shaker system. This also reduces the time required to achieve full level testing.

The following MIMO Random control screenshot displays the common carrier transportation profiles used to control the transverse, longitudinal and vertical direction vibration on a three-axis shaker system.

MIMO Random Vibration Control