Automated Inspection of Railcar Underbody Structural Components Using Machine Vision Technology 09-2863

Monitoring the structural health of railcars is important to ensure safe and efficient railroad operation. The structural integrity of freight cars depends on the health of certain structural components within their underframes. These components serve two principal functions: supporting the car body and lading and transmitting longitudinal buff and draft forces. Although railcars are engineered to withstand large static, dynamic and cyclical loads, they can still develop a variety of structural defects. As a result, Federal Railroad Administration (FRA) regulations and individual railroad mechanical department practices require periodic inspection of railcars to detect mechanical and structural damage or defects. These inspections are primarily a manual process that relies on the acuity, knowledge and endurance of qualified inspection personnel. Enhancements to the process are possible through machine-vision technology, which uses computer algorithms to convert digital image data of railcar underframes into useful information. This paper describes research investigating the feasibility of an automated inspection system capable of detecting structural defects in freight car underframes and presents an inspection approach using machine-vision techniques including multi-scale image segmentation. A preliminary image collection system has been developed, field trials conducted and algorithms developed that can analyze the images and identify certain underframe components, assessing aspects of their condition. The development of this technology, in conjunction with additional preventive maintenance systems, has the potential to provide more objective information on railcar condition, improved utilization of railcar inspection and repair resources, increased train and employee safety, and improvements to overall railroad network efficiency. Schlake et al. 09-2863 4 INTRODUCTION In the United States, railcars undergo regular mechanical inspections as required by Federal Railroad Administration (FRA) regulations and as dictated by railroad mechanical department practices. These mechanical inspections address numerous components on the railcar including several underbody components that are critically important to the structural integrity of the railcar. The primary structural component, the center sill, runs longitudinally along the center of the car, forming the backbone of the underframe and transmitting buff and draft forces through the car (1). In addition to the center sill, several other structural components are critical to load transfer, including the side sills, body bolsters, and crossbearers. The side sills are longitudinal members similar to the center sill but run along either side of the car. Body bolsters are transverse members near each end of the car that transfer the car’s load from the car body to the trucks. Crossbearers are transverse members that connect the side sills to the center sill and help distribute the load between the longitudinal members of the car. These components work together as a system to help maintain the camber and structural integrity of the car. Mechanical Regulations and Inspection Procedures FRA Mechanical Regulations require the inspection of center sills for breaks, cracks, and buckling, and the inspection of sidesills, crossbearers, and body bolsters for breaks, as well as other selected inspection items (2). Every time a car departs a yard or industrial facility it is required under the FRA regulations to be visually inspected by either a carman or train crew member for possible defects that would adversely affect the safe operation of the train. The current railcar inspection process is tedious, labor intensive, and in general lacks the level of objectivity that may be achievable through the use of technology. In order to effectively detect structural defects, car inspectors would need to walk around the entire car and crawl underneath with a flashlight to view each structural component. Due to time constraints associated with typical pre-departure mechanical inspections, cars are only inspected with this level of scrutiny in car repair shops before undergoing major repairs. In addition to the inherent challenges of manual inspections, records of these inspections are generally not retained unless a billable repair is required, making it difficult to track the health of a car over time or to perform a trend analysis. As a result, the maintenance of railcar structural components is almost entirely reactive rather than predictive, making repairs and maintenance less efficient. Technology Driven Train Inspection (TDTI) The Association of American Railroads (AAR) along with the Transportation Technology Center, Inc. (TTCI) has initiated a program intended to provide safer, more efficient, and traceable means of rolling stock inspection (3). The object of the Technology Driven Train Inspection (TDTI) program is to identify, develop, and apply new technologies to enhance the efficiency and effectiveness of the railcar inspection, maintenance, and repair process. Examples of these new technologies include the automated inspection of railcar trucks, safety appliances and passenger car undercarriages (4, 5, 6). The ultimate objective of TDTI is to implement a network of automatic wayside inspection systems capable of inspecting and monitoring the North American Schlake et al. 09-2863 5 freight car fleet in order to maintain compliance with FRA regulations and railroadspecific maintenance and operational standards. Automated Structural Component Inspection System (ASCIS) One aspect of the TDTI initiative is the development of the Automated Structural Component Inspection System (ASCIS), which is currently underway at the University of Illinois at Urbana-Champaign (UIUC). ASCIS focuses on developing technology to aid in the inspection of freight car bodies for defective structural components through the use of machine vision. A machine-vision system collects data using digital cameras, organizes and analyzes the images using computer algorithms, and outputs useful information, such as the type and location of defects, to the appropriate repair personnel. The computer algorithms use visual cues to locate areas of interest on the freight car and then analyze each component to determine its variance from the baseline case. While manual inspections are subject to inaccuracies and delays due to time constraints and human fatigue, ASCIS will work collectively with other automated inspection systems (e.g. machine vision systems for inspecting safety appliances, truck components, brake shoes, etc.) to inspect freight cars efficiently and objectively and will not suffer from monotony or fatigue. ASCIS will also maintain health records of every car that undergoes inspection, allowing potential structural defects to be monitored so that components are repaired prior to failure. Additionally, applying these new technologies to the inspection process has the potential to enhance safety and efficiency for both train crew members and mechanical personnel. A primary benefit of ASCIS and other automated inspection systems is the facilitation of preventive, or condition-based, maintenance. Condition-based maintenance involves the monitoring of certain parameters related to component health or degradation and the subsequent corrective actions taken prior to component failure (7). Despite the advantages of condition-based maintenance, current structural component repair and billing practices engender corrective maintenance, which does not occur until after a critical defect is detected. Due to the reactive nature of corrective maintenance, repairs cannot be planned as effectively, resulting in higher expenses and less efficient repairs. For example, it is more economical to patch a cracked crossbearer before it breaks than to replace a fully broken crossbearer. Having recognized the need for preventative maintenance, railroads have begun implementing other technologies similar to ASCIS that monitor subtle indicators of railcar component health (e.g. Truck Performance Detectors and the AAR’s Fully Automated Car Train Inspection System FactISTM) (8). REGULATORY COMPLIANCE The FRA regulations for freight car bodies form the basis for which components will be inspected by ASCIS. Section 215.121 of Title 49 in the U.S. Code of Federal Regulations (CFR) governs the inspection of freight car bodies and two of the six parts in this section pertain to the inspection of structural components (2). According to the regulations, the center sill may not be broken, cracked more than 6 inches, or bent/buckled more than 2.5 inches in any 6 foot length. Specific parameters are established for the allowable magnitude of cracks or buckling because these defects may undermine the integrity of the sill, resulting in a center sill failure (9). Therefore, these regulations are intended to Schlake et al. 09-2863 6 identify potentially hazardous cars so that they will be repaired before an in-service failure. FRA structural component inspection data from the last eight years shows that on average 59% of the structural component defects are comprised of broken, cracked, bent, or buckled center sills, while the remaining 41% represent defective side sills, body bolsters, or crossbearers (Figure 1). FIGURE 1 Average number of yearly structural defects recorded by FRA inspectors as a percentage of all cars inspected in a year. Based on these data and guidance from the AAR, the primary focus of ASCIS will be on the inspection of center sills and the secondary focus will be on the inspection of the other structural components. The final goal of ASCIS is to provide data and trending information for the implementation of condition-based maintenance on all freight car structural components.