Wayside system for wheel–rail contact forces measurements D. Milkovic ´ a,⇑ , G. Simic ´ a ,Z ˇ . Jakovljevic ´ a , J. Tanaskovic ´ b , V. Luc ˇanin a a University of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, 11120 Belgrade, Serbia b Innovation Center of Faculty of Mechanical Engineering, University of Belgrade, Kraljice Marije 16, 11120 Belgrade, Serbia article info Article history: Received 18 February 2013 Received in revised form 8 May 2013 Accepted 14 June 2013 Available online 27 June 2013 Keywords: Wheel–rail contact forces Contact point position Wayside measurement system Strain-gauges measurement Independent component analysis (ICA) abstract The system for assessment of the wheel–rail contact forces can be used for multiple pur- poses, among them for estimation of the train running safety, for train axle load measuring or wheel flats detection, as well as for the other research analyses. As the wheel–rail rolling contact moves along the track during train motion, it is very difficult to establish a reliable and accurate system for measuring of contact forces. Measurement principle of the way- side system, presented in this paper, is based on rail strains measurements using strain gauges, connected into the Wheatstone bridges in a smart way, in order to achieve signal proportional to applied load. This principle uses independent component analysis (ICA) model in combination with system calibration for successful separation of vertical and lat- eral contact forces from recorded strain signals. In addition, the system provides identifi- cation of the contact point position on the rail during train passing over it, which further expands the possibilities of its application to wheel–rail wear analysis, contact geometry optimization etc. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Systems for measurement of the wheel–rail contact forces are indispensable information provider in studying of railway vehicle dynamics. These systems could be used for multiple purposes, among them for health monitoring of the rolling stock, as well as for the train axle load mea- surements, without interrupting train regular service. Measurements of the wheel–rail contact forces are also important in the process of experimental verification of the dynamic behaviour of rail vehicles, as some of the cri- teria for evaluating the dynamic behaviour and train run- ning safety are based on the values of these forces [1]. For example, derailment mechanism is based on the anal- ysis of the ratio between lateral and vertical forces. As the wheel–rail contact during train motion travels along the track, it is very difficult to establish a measuring device or a system that would enable acceptably accurate measurements of the contact forces. So far developed methods and principles of measurements can be classified into two categories: 1. Vehicleside methods – allowing continuous measuring of the forces during train motion, using specially adapted wheels and/or wheelset [1,2], 2. Wayside methods – allowing discrete contact forces measurements, using devices installed on track [3–8]. Vehicleside methods are mainly based on measuring strains using special instrumented wheelset. Systems based on these methods provide measuring with one vehi- cle over the whole railroad network. The system drawback is the volume of work required for its preparation includ- ing calibration process, as well as the high costs related to the requirement of the expert knowledge and usually specific design of the wheelset, dependant on the vehicle type. Wayside methods are less expensive, consequently pro- viding less research possibilities. Wayside systems are uti- lized for measuring of contact forces at single point, or at relatively short rail length, with all vehicles passing over 0263-2241/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.measurement.2013.06.017 ⇑ Corresponding author. Tel.: +381 11 3370 351. E-mail address: dmilkovic@mas.bg.ac.rs (D. Milkovic ´). Measurement 46 (2013) 3308–3318 Contents lists available at SciVerse ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement