Vehicle Weigh-in-Motion Technology

These days, the volumes of ground transportation keep increasing with the fast development of the industry and commerce and the competition between transport companies was even more drastic. As a result, vehicles overloaded illegally already become a widespread social problem. Thus, the vehicle weigh-in-motion (WIM), a technology can measure the traffic loads, attracted more attention currently. The most of the existing weighing sensors are mainly suitable to be installed for permanent applications. Although some of them are portable, the heavy weight, large volumes limited the application. In this paper, a novel capacitance weighing sensor was developed by using conductive fabrics as electrodes and insulating rubber sandwiches between two electrodes. This design significantly reduces the volume and weight of the WIM sensor. Moreover, because of this striking feature, the whole system can be easily to carry even to rolled up due to its flexibility. Based on the analysis results of the relationship among stress, strain and time, and the influence of geometrical form of force part, a number of experiments were tested. The conclusion can be drawn that the whole system is suitable for the application to weigh vehicles in motion. In addition to, according to the analysis of hard sensors on the traditional WIM systems, a model with three degree of freedom was been established. Then a six order mathematics' model based on system identification induced from it was used to the system. The experiment results proved the feasibility of the method. The main research achievements are showed as follows:1. A novel capacitive flexible weighing sensor was proposed. The "3+2" structure and charging and discharging circuit were presented for reducing the influence of edge effects and parasitic capacitance. The compensated circuit was used to offset the natural capacitance since the variation of capacitance would be much smaller than the natural capacitance of the sensor.2. According to the viscoelasticity properties for the sensor's material, the behavior of the sensor was simulated based on the Maxwell-Kelvin model and the relationship between variation of capacitance and weight were derived. The relationship between variation of capacitance and geometrical form of force part was further studied since in some cases the flexible sensor would be affected by geometrical form of force part.3. The wavelet transform was applied to filter the high frequency noise appeared in the axle load signals which were sampled by the AD card. A number of static and dynamic experiments were tested. The results showed that Maxwell-Kelvin model was capable of describing mechanical response of the capacitive flexible weighing sensor presented in the paper and the appliance of this system to weigh in motion.4. A model with three degree of freedom was established based on current vehicles and weighing sensors and a six order model based on system identification was developed. The experiment results showed the method can be used for the rapid prediction of an applied mass in the vehicle Weigh-in-Motion system. The feasibility and limitation for the SVM method were also been presented in the study.