High-Speed 3D Railroad Tie Deflection Mapping in Real-Time Using an Array of Air-Coupled Non-contact Transducers

An ultrasonic sonar-based ranging technique is introduced for measuring railroad tie 3D surface deflections. Tie deflection profiles can be used for flagging defective conditions of rail tracks such as center-binding, that can cause train derailments. The technique utilizes an array of air-coupled capacitive ultrasonic transducers oriented parallel to the tie with a minimum clearance of 3-in. from the rail to ensure contactless inspection. The proposed technique has the potential for detecting both the static and dynamic behavior of ties. The transducers are used in pulse-echo mode and the distance between the transducer to the tie surface is computed by tracking the time-of-flight of the reflected wave from the tie surface. An adaptive, reference-based, cross-correlation operation is used for measuring relative tie deflections. Multiple measurements along the width of the tie allow the measurement of twisting deformations as well. An acoustic signal strength-based and an image-based classifier are used in tandem to differentiate signals coming from ties and ballast. Data acquisition and processing are performed using a LabVIEW real-time module. Field tests on a replica test track, at walking speeds, were performed at the Rail Defect Testing Facility. The initial results indicate the potential of this system to measure full-field tie deflections in 3D at walking speeds (~3 mph).