Multi-shaker, single-axis testing can improve the quality of test, but the added complexities should be considered early in the development of a new vibration test system.
There is increasing demand to use vibration systems for transport testing of larger and more complex shaped structures, to replace the need for extensive test track proving. In such cases, the use of multiple shakers working in combination in a single axis may provide a better solution than trying to use a single bigger, higher force shaker. This is increasingly being recognised by vibration standards such as the US military environmental test standard MIL-STD-810.
When performing Multi Exciter Single Axis (MESA) testing, there are two main approaches for controlling the vibration, each with pros and cons depending upon the application. Simplistically, these approaches involve:
- Providing a common drive signal to all shakers
- Providing a different drive signal to each shaker
The latter approach requires use of a MIMO vibration controller and introduces system interactions, which may affect the choice of shakers, accelerometers, fixturing and even operational personnel. It is, therefore, important to consider these interactions as early as possible in the development of a new vibration system to ensure that the design of the system is optimized and the operational capability is understood.
This paper presents practical information on using a multiple shaker MIMO vibration testing approach for transport testing of large structures and provides guidance to organizations expanding from single shaker system testing to multiple shaker testing. It shares lessons learnt through hundreds of hours of real-world sine and random testing using a 420 kN force Quad LDS V9 vibration system in both horizontal and vertical configurations. It targets the real-world practical considerations of the test engineer/manager when defining and developing a MIMO vibration test facility for large payload testing.
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