Roads are among the most important pieces of a nation’s infrastructure. To ensure the continued use of these systems they must be monitored and understood using various technologies. A weigh-in-motion (WIM) system is one such device which is used to obtain traffic flow and vehicle weight data. This sensor monitors all traffic traveling over a stretch of road without requiring the vehicles to stop for measurement. As a result, it can be used to reduce the number of overloaded trucks through enforcement of weight requirements. This will create a safer driving environment, prolong road life, and reduce maintenance costs.
The largest deterrent to implementing current weigh-in-motion technologies is the large costs incurred through purchase, installation, and maintenance. In addition, these systems currently require wires to be routed through the road pavement for the purpose of data travel and power.
This paper focuses on the creation of a low cost WIM sensor being developed for the addition of battery-less wireless implementation in the future. Such a system would allow for broader use of the technology and reduce the aforementioned problems caused by overloaded trucks. The final product would not only reduce costs due to road damage but also those costs associated with sensor maintenance.
There are many challenges associated with the practical design of a WIM system. First, this system must be large enough to contain the full contact patch of the largest operating vehicle on the road while preventing this design from yielding under vehicle weight. Second, the sensor must be as accurate or more accurate than current WIM technologies under all operating conditions. Finally, it must have a simple and cost effective construction.
In the design of such a sensor, the author implemented a two layer design to reduce the number of piezo-electric patches and thus obtain an inexpensive system. The top layer was a frame large enough to bear the weight of the full contact patch of the vehicle. The lower beams served as a mounting location for the piezos. Both layers had to withstand the full weight of the dynamic vehicle load without yielding. The design process also included resonant frequency analysis to understand if the vehicle velocity would cause a change in output of the sensor. Finally, electronics had to be developed to monitor, store, and reset piezo readings for continued operation.
In addition to the aforementioned challenges, finding the means to test such a piece of equipment was extremely difficult. First, a stretch of road had to be identified which could be modified for the installation of the sensors. Equipment had to be procured to cut and remove concrete, and pour a new slab before sensor testing could begin. Additionally, vehicles of various weights had to be obtained and a driver found certified to drive them in order to test the equipment at multiple speeds. Finally, this construction and testing had to be completed during the winter outside.
University of Minnesota M.S. thesis. August 2011. Major: Mechanical engineering. Advisor: Rajesh Rajamani. 1 computer file (PDF); viii, 103 pages, appendices 1-12.
Pruden, Sean Michael.
Development of a piezoelectric weigh-in-motion system for battery-less wireless operation..
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