P. Toni

Experimental campaign on a servo-actuated pantograph

Many interesting technical problems arise from the development of high speed trains current collection is one of the more important. The dynamic behaviour of a pantograph-catenary system make the electrical contact between the catenary and the contact-shoe unreliable. An insufficient quality of current collection causes a lot of negative consequences such as: insufficient current pick up, excessive wear of contact shoes and wires, power and control electronics malfunction, high EMI. Many Researchers have investigated the problem of optimum current pick up and many different solutions have been proposed in the past years. Since 1993 the Researchers of University of Florence have proposed the idea of a servo-actuated pantograph. The purpose of these studies was the development of a system including sensors and actuators able to regulate the value of relevant variables, such as contact force, at an optimum level researchers of Italian Railways found the proposal of a servo-actuated pantograph very interesting so the two groups began to co-operate. After the development of simulation models to evaluate performance and robustness of some control techniques for a servo-actuated pantograph, the authors arranged an experimental campaign in order to verify the results of simulations and to develop a first prototype of servo-actuated pantograph. This paper describes some simulation and experimental results obtained during the campaign which is currently going on.

A Comparison of Stationary and Non-stationary Mathematical Models for the Ring-spinning Process

A generalized non-stationary mathematical model of the ring-spinning process is proposed and compared with the stationary model commonly used for predicting process characteristics. Special attention is focused on defining the proper boundary conditions, which differ considerably from those of the stationary case. Numerical procedures are described in order to solve the problem, and the results of a sample case are presented.

A numerical model of a HIL scaled roller rig for simulation of wheel–rail degraded adhesion condition

Scaled roller rigs used for railway applications play a fundamental role in the development of new technologies and new devices, combining the hardware in the loop (HIL) benefits with the reduction of the economic investments. The main problem of the scaled roller rig with respect to the full scale ones is the improved complexity due to the scaling factors. For this reason, before building the test rig, the development of a software model of the HIL system can be useful to analyse the system behaviour in different operative conditions. One has to consider the multi-body behaviour of the scaled roller rig, the controller and the model of the virtual vehicle, whose dynamics has to be reproduced on the rig. The main purpose of this work is the development of a complete model that satisfies the previous requirements and in particular the performance analysis of the controller and of the dynamical behaviour of the scaled roller rig when some disturbances are simulated with low adhesion conditions. Since the scaled roller rig will be used to simulate degraded adhesion conditions, accurate and realistic wheel–roller contact model also has to be included in the model. The contact model consists of two parts: the contact point detection and the adhesion model. The first part is based on a numerical method described in some previous studies for the wheel–rail case and modified to simulate the three-dimensional contact between revolute surfaces (wheel–roller). The second part consists in the evaluation of the contact forces by means of the Hertz theory for the normal problem and the Kalker theory for the tangential problem. Some numerical tests were performed, in particular low adhesion conditions were simulated, and bogie hunting and dynamical imbalance of the wheelsets were introduced. The tests were devoted to verify the robustness of control system with respect to some of the more frequent disturbances that may influence the roller rig dynamics. In particular we verified that the wheelset imbalance could significantly influence system performance, and to reduce the effect of this disturbance a multistate filter was designed.

Probabilistic analysis of braking performance in railways

Abstract To increase safety and efficiency in the management of railway traffic, a new speed control system, named SCMT, is currently being developed by RFI and Trenitalia for the Italian Railways. Other innovative speed supervision systems are being developed in Europe, such as the ETCS/ERTMS, which will also be installed on the new high-speed line Roma-Napoli. All traffic management systems are generally based on a set of supervision curves relating the allowed velocity of the train to the running distance, in order to ensure the respect of speed restrictions on the line by ‘soft’ or ‘hard’ intervention such as an acoustic and visual warning to the driver (soft) and/or service or emergency braking (hard) in the case of train velocity exceeding the permitted one. To elaborate this set of supervision curves, the on-board unit requires train deceleration depending on time and speed as basic information about the braking behaviour of the train. The implementation of a speed supervision system requires a preliminary definition of braking models that allow the conversion of the general parameters affecting the braking performances of trains (such as a braked weight percentage, goods/passenger brake position, brake equipment, train length, etc.) into a basic deceleration profile as a function of time, during the deceleration rise phase, and of speed, during fully developed braking. The deceleration used to evaluate braking curves is obtained by applying a proper safety margin to the nominal deceleration value (which depends on train characteristics). In this paper a probabilistic analysis of train deceleration is carried out, starting from probability distributions of parameters affecting the braking. For the major parameters, the probability distribution was determined on the basis of technical knowledge and experimental results. The aim of this work is to determine the probability that the real deceleration is lower than the nominal value multiplied by a given safety margin.

Train speed and position evaluation using wheel velocity measurements

A security system called SCMT, to be installed on trains circulating on Italian railways is being developed. One of the components of SCMT is a module for estimating train speed and positions between two subsequent viapoints equipped with balises which communicate to the train the distance to next target(s) and velocity requirement(s) at target(s). The module uses two wheels equipped with incremental encoder-type sensors. We describe an algorithm for position and velocity estimation capable of compensating for poor wheel-rail adhesion conditions due to rain, fog, ice, leaves, and so on, where conventional odometry algorithms fail. The system was designed and trained using a wide set of experimental data, conducted using different types of vehicles and conditions (in particular, degraded adhesion conditions were investigated). In each experimental test the velocities of four wheels and the real train were measured. The main goal of the system proposed in the paper is to evaluate the train speed and position on the basis of two wheel velocities information also in the case of wheel slipping or skidding. The system can estimate train speed and position also in case of failure of one of the two velocity sensors. The velocities of the two wheels must be periodically re-aligned to the real train speed, during a phase in which wheels are not slipping, in order to compensate for variations of wheel diameters.

Preliminary Field Testing Of A Servoactuated Pantograph

One of the main problems concerning high speed running on Italian railways is the current pick up. The contact force between the pantograph and the overhead contact line increases its amplitude and frequency as the speed increases. The frequent detachments generated by this situation cause not only the temporary interruption of power transmission and wire and contact shoe erosion and produce electromagnetic pollution. A frequent method to reduce detachments is based on the progressive increase of uplift force with the increasing speed. This solution can^t be used in high speed running as the excessive contact force necessary to avoid detachments causes a very quick erosion of contact shoes. Furthermore, operating in the above mentioned condition, the amplitude of contact shoe oscillations may cause impact with the suspension devices of overhead line. An alternative approach to solve these problems is the use of a servo actuated pantograph able to maintain the contact force at a given value. In order to obtain the above mentioned result a FS pantograph was modified applying a brushless servomotor connected by a wire to the contact strip. This actuator, adding its force to the effect of the traditional air bellow, is able to properly regulate the contact force. In the paper the preliminary experimental results, obtained by a special test rig in a FS laboratory, are reported and discussed. Transactions on the Built Environment vol 34,

A TEST RIG FOR EVALUATING ODOMETRY ALGORITHMS

Odometry is a fundamental task to perform in modern systems for monitoring and control of trains. However, odometry becomes difficult to perform when wheel/rail adhesion is not good and the train is braking or accelerating. To improve the performance of odometry systems, the use of sensors in addition to axle-mounted encoder-type sensors (such as longitudinal accelerometers and radar Doppler sensors) is being tested on prototype onboard systems. This paper describes work being conducted by researchers of TRENITALIA S.p.A. and the Section of Applied Mechanics of the University of Florence for the design and realization of a test rig for odometry techniques.

Identification of a wheel--rail adhesion coefficient from experimental data during braking tests

The forces that occur in the wheel–rail interface significantly affect vehicle dynamics, especially in the longitudinal direction. Conventionally, the tangential component of the force exchanged between the rail and the wheel is expressed as the product of the normal component of the force, and the so-called adhesion coefficient. This ratio depends on several parameters that are usually summarized in the term ‘adhesion conditions’. When the adhesion conditions are degraded (for example, in cases of rain, fog, ice, dead leaves, etc.), and the vehicle is accelerating or braking, pure rolling conditions between the wheels and the rails do not hold any more, and macroscopic sliding occurs on one or more of the wheels. The aim of this work is to identify a relationship between adhesion coefficient and some parameters, namely wheel sliding and train speed, starting from a set of experimental measurements, obtained from test runs conducted with artificially degraded adhesion conditions.