Pavement marking materials provide delineation on highways around the world. The condition of the marking materials is very important for the driver's safety as well as the comfort and the driving expenses. Currently thermoplastic pavement marking materials (TPMM) are widely used in states. Measuring the thickness of TPMM on pavement is an essential index to monitor the contractors, calculate durability of marking materials, and provide better information for the pavement marking evaluation.
In recent years to measure the thickness of TPMM, a procedure involving pre-embedded plates sprayed with the marking materials has been widely accepted. This method is labor intensive, and cannot obtain a continuous-thickness profile. Therefore there are demands to develop a high-speed automatic measuring system for determining the thickness and uniformity of marking materials.
In this paper, a laser range sensor based on auto-synchronized laser scanning is proposed for the thermoplastic pavement marking material thickness measurement. Compare to classical triangulation method, this approach doesn't scarify the system resolution for large field of view and it is more suitable for highway speed measurement. To achieve high speed measurement, PSD (Position Sensitive Detector) is used in the prototype system instead of CCD (Charge Couple Device) in traditional auto-synchronized system. The standoff distance and transverse scan range of the prototype system both are 1 foot. The lab test results show that the prototype system can measure the thermoplastic type thickness with error in 5mil at laser scanning rate up to 50Hz.
Thermo-plastic tape (TPT) provides delineation on highways around the world. The thickness of TPT on pavement is a very important parameter to control the quality of TPT, calculate durability of TPT, and provide information for the maintenance and replacement of TPT. Traditionally, the thickness measurement is conducted by using pre-embedded plates and measuring the thickness of TPT after spraying of the TPT marking materials. This method is labor intensive and cannot obtain a continuous-thickness profile. Developing an automatic thickness measurement system for TPT marking materials is critical to pavement management and public safety.
The measurement system developed in this paper uses laser triangulation technique to detect the thickness of TPT. A dedicated digital laser signal processing circuit is developed to restore thickness information. The thickness measurement system provides continuous real-time thickness measurement of TPT. Lab and field tests under various conditions with TPT marking materials on real pavement surfaces were conducted. The test results showed that the measurement system is capable of reaching the resolution of 5 mils on pavement. The developed system for thickness measurement of TPT has a 267 KHz working frequency, which is the highest among similar devices. The high speed allows the system to provide higher accuracy and more flexibility in various applications.