3 Real-Time State Detection in Highly Dynamic Systems 31 Instrumented Bar Interfacial Material Low Friction Material Striker Bar PZT Low Friction Rail Material Cart Stop Fig. 3.2 CAD model of the experimental setup Laser Extensometer PZT Striker Bar Instrumented Bar Fig. 3.3 Overall view of the experimental setup An important consideration in the design of the test setup was to make the components modular. This includes the options of changing aspects of the experiment such as the bar lengths and materials. Of particular importance to this research is the configuration of the boundary conditions of the instrumented bar. The non-contact side of which can be configured as a cantilever or with springs of varying stiffness. The impacted side of the instrumented bar can have an elastic material bonded to it, thus adding an interface between the two bars during impact. This is of significant interest because it could be possible to detect the varying levels of compression the elastic interfacial material would undergo during impact. Most importantly though, the modular design allows others to investigate state detection in highly dynamic environments as well by allowing them to make non-permanent changes to the experimental setup to suit the needs of their own research. Another design consideration was the choice of materials to use for the various parts of the structure. Aluminum was chosen for the bars because it was inexpensive, lightweight, and readily available. The geometry of both the instrumented bar and impactor bar were chosen to meet certain criteria. For example, the end of the impactor bar that strikes the instrumented bar is slightly rounded, sometimes called “bull nosed,” in order to ensure a good impact even if there are small misalignment issues. Another consideration was the bonding of the PZT onto the instrumented bar. PZTs are very brittle ceramics that are commercially available primarily as flat discs or wafers. It is possible to buy PZTs with custom geometry, but it is, in this case, a needlessly expensive option. So, a square cross section was chosen for the bars so a relatively inexpensive PZT would be easy to mount. Another important aspect of the experimental setup is the equipment used for data acquisition. The FPGA DAQ used for this test setup is an NI PXIe-7965R with a NI 5781 adapter module which is capable of measuring at 100 MS/s. These are housed in an NI PXIe-1082 chassis that also holds an NI PXIe-8133 controller running a real-time OS. This controller is connected via an ethernet cord to a normal laptop running the programming software LabVIEW on a Windows OS. The controller running the real-time OS adds more real-time computing resources that can be leveraged. The most important of
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