A Scaled-Bogie Test Bench to Understand and Demystify Wheel-Rail Contact Dynamics

It is a well-known fact that railway dynamics is far from being trivial, mostly because of the wheel/rail contact phenomenon. Except for specialists in this field who are obviously familiar with notions like wheelset equivalent conicity, hunting motion, limit cycles, etc., most of people, including engineers, have no or few idea about the guidance principle of railway vehicles equipped with standard bogies with rigid wheelsets. The present project has been initiated at the Center for Research in Mechatronics of the Université catholique de Louvain within the framework of a master thesis under our supervision. The main objective is essentially educational and led us to build an experimental bench to highlight the wheel/rail guidance phenomenon of railway vehicles

Comparison of functional methods for estimating joint positions of human limb

Accurate knowledge of the center of rotation (CoR) of anatomical joints is required for many research and application fields of biomechanics. However the location of the CoR can be difficult to estimate in vivo. Several methods have been developed over the last thirty years, using 3D motion capture devices. Two main approaches are commonly used to localize the CoR of upper and lower limb joints: predictive methods and functional methods. Functional methods, which can be divided into spherefit methods and coordinate transformation (CT) methods, are reported to show better precision and repeatability than predictive approaches. Many studies focused on the comparison between several functional methods for the estimation of the shoulder or hip joint but, to our knowledge, none of them compared functional methods for estimating joint positions and segmental body lengths of a whole human limb. This paper aims at comparing four functional methods (two spherefit and two CT) for locating shoulder, elbow and wrist joint centers according to the movement characteristics. Various simulations were performed in order to analyze the sensitivity of these methods to the noise level, type of movements, dataset size and computational cost. Experimental measurements were also performed. Five subjects repeated 10 cycles of three different movements (circumduction, flexion-extension and adduction-abduction). On this experimental data, analyses focused on precision and repeatability of 3D localization of the upper limb joint centers. Our study shows that spherefit methods are faster than CT methods. However CT methods seems to be less sensitive to both noise level and dataset size, and their repeatability is more reliable

Design of a Rehabilitation Robot for Hemiplegic Patients via Multibody Modelling and Analysis

Multibody dynamics maturity presently allows engineers to deal with new families and applications for which there is still a lack of understanding of dynamical phenomena: this is obviously the case of biomechanics. By referring to the recent scientific literature, it is rather impressive — and this is a real source of motivation — to see how multibody dynamics has been rapidly and deeply involved in biomechanical and surgical issues. From about ten years now, the expertise of our team (UCL, Louvain-la-Neuve) in the field of multibody systems has been exploited in close collaboration with physiotherapists and surgeons of the Cliniques Saint-Luc (UCL, Brussels) for medical research projects in which dynamical issues have to be solved. The present application, namely a rehabilitation robot for upper limbs of hemiplegic patients, has been recently analysed via a multibody approach, thanks to kinematic and dynamic models symbolically generated by the ROBOTRAN program

Automatic Resonance Tuning and Feedforward Learning of Biped Walking using Adaptive Oscillators

In this contribution, we propose a novel approach to achieve two fundamental features of adaptive control in rhythmic movements: The automatic locking of the controller to the system’s resonance frequency, and the progressive transfer from feedback to feedforward control. This is realized by using adaptive oscillators, i.e. mathematical tools capable of synchronizing to a periodic input and learning this input’s main features (frequency, amplitude). In particular, these concepts are illustrated here on a simulated walking task. Automatic resonance tuning emerges from the interaction between the plant (the biped walker), the controller, and the movement phase directly estimated by the adaptive oscillator. Progressive transfer to feedforward control is realized by learning the control pattern (initially provided by the feedback controller) with local filters. In conclusion, this paper illustrates to potential relevance of using adaptive oscillators as central elements in adaptive control of rhythmic tasks

Dynamic analysis of intervertebral efforts in scoliosis : a multibody modeling approach

A biomechanical model, using the multibody dynamics approach, is developed to calculate the intervertebral efforts in spine. The latter are computed, via inverse dynamics, using kinematic information from gait. Optimization process is required in order to convert that information, expressed in absolute coordinates from the optometric sensors, into relative joint coordinates, in order to calculate joint forces and torques