Sébastien Murer

Numerical determination of the mechanical stiffness of a force measurement device based on capacitive probes: Application to roller bearings

Abstract Bearings allow external loadings to be transferred from one raceway to the other through rolling elements, which induces strains in the bearing constituents. In order to measure the radial component of these forces, the fixed ring is inserted within a housing equipped with capacitive probes able to measure displacements with very high sensitivity. This work mainly focuses on determining the optimal housing shape using FE simulations and their influence on the global stress state undergone by the structure. Finally, an averaged global stiffness is computed, allowing proper calculation of the contact forces involved in the bearing.

Model of the risk assessment of hand-arm system vibrations in cycling: Case of cobblestone road

Vibrations experienced by the human body are a well-known and widely studied risk factor in the industrial world. These are transmitted to the whole body or parts of it (like the hand-arm system) and are measured and limited according to international standards and European directives. However, despite the ubiquity of vibrations, their effects are little studied in sport. Vibrations can induce discomfort, thus degrading performance, or even cause musculoskeletal disorders. This article presents a numerical methodology to estimate the vibration total value transmitted to the hand-arm system during the practice of cycling over cobblestone roads. This assessment is achieved using a modeling of the excitation source representing the displacement over the cobblestone, as well as the vibratory behavior of the cycle. The influence of the model parameters will be discussed. Finally, the estimated vibration total value will be compared to values obtained from field test conditions.

Numerical simulation and experimental comparison of flaw evolution on a bearing raceway: Case of thrust ball bearing

Abstract Bearings are essential elements in the design of rotating machines. In an industrial context, bearing failure can have costly consequences. This paper presents a study of the rolling contact fatigue damage applied to thrust ball bearings. It consists in building a dynamic three-dimensional numerical model of the cyclic shift of a ball on an indented rolling surface, using finite element analysis (FEA). Assessment of the evolution in size of a surface spall as a function of loading cycles is also performed using FEM coupled with fatigue laws. Results are in good agreement with laboratory tests carried out under the same conditions using a fatigue test cell dedicated to ball bearings. This study may improve knowledge about estimating the lifetime of rolling components after onset of a spall using FEA and accounting for structural damage state.

Validation of a High Sampling Rate Inertial Measurement Unit for Acceleration During Running

The musculo-skeletal response of athletes to various activities during training exercises has become a critical issue in order to optimize their performance and minimize injuries. However, dynamic and kinematic measures of an athlete’s activity are generally limited by constraints in data collection and technology. Thus, the choice of reliable and accurate sensors is crucial for gathering data in indoor and outdoor conditions. The aim of this study is to validate the use of the accelerometer of a high sampling rate (1344Hz) Inertial Measurement Unit (IMU) in the frame of running activities. To this end, two validation protocols are imposed: a classical one on a shaker, followed by another one during running, the IMU being attached to a test subject. For each protocol, the response of the IMU Accelerometer (IMUA) is compared to a calibrated industrial accelerometer, considered as the gold standard for dynamic and kinematic data collection. The repeatability, impact of signal frequency and amplitude (on shaker) as well as the influence of speed (while running) are investigated. Results reveal that the IMUA exhibits good repeatability. Coefficient of Variation CV is 1%8.58±0.06m/s2 on the shaker and 3%26.65±0.69m/s2 while running. However, the shaker test shows that the IMUA is affected by the signal frequency (error exceeds 10% beyond 80Hz), an observation confirmed by the running test. Nevertheless, the IMUA provides a reliable measure in the range 0–100 Hz, i.e., the most relevant part in the energy spectrum over the range 0–150 Hz during running. In our view, these findings emphasize the validity of IMUs for the measurement of acceleration during running.

Optimization and Ergonomics of Novel Modular Wheelchair Design

The Manual Wheelchair (MW) is an important device which provides technical assistance to people affected by mobility impairments. This mode of displacement is neither natural nor easy and the environments, whether natural or built, can present various obstacles, which will restrict mobility and the social participation of MW users. Users complete autonomy depends on their capacity to cope with the many obstacles of their daily life, such as pavements or unleveled grounds. Ever since its invention the MW as an economical mobility solution, it has gone through many improvements, yet its technological innovation slowed down during the recent years. In this study, we present a novel design of MW. Its conception includes innovative kinematics with genuine lifting and folding systems. A lever system mounted on hubless-wheels is dedicated to the propulsion mechanism. The objective of this new concept is the optimization of MW mechanism to be more user friendly and to take into account the ergonomics considerations in an attempt to improve the user’s daily life.

Experimental Investigations and Finite Element Modelling of the Vibratory Comportment of a Manual Wheelchair

This paper presents the comparison between the numerical results provided by the finite element model of a manual wheelchair and the vibration experiments performed on the same actual wheelchair. Two patients having different corpulence participated in this study while sitting on different types of cushions. The tests were carried out using a vibrating table with white noise as the input, in an attempt to simulate the entire vibration spectrum that the user of the chair could undergo. A numerical approach based on the finite element method has made it possible to create a numerical model of the wheelchair that can then anticipate structural problems resulting from these vibratory constraints. The objective of this work is to characterize the structure of the wheelchair as well as the vibration disturbances suffered by the user according to the daily life tasks. This first study will later allow the development of a design strategy oriented towards patient’s comfort with regard to vibrations and also to develop a new type of wheelchair using an adapted structure guaranteeing a longer material life.

EMG Comparison of Sport Manual Wheelchair Propelled by Lever Drive and Push Rims and Possible Consequences for Rehabilitation: A Case Study

The goal of this paper is to demonstrate a comparison of EMG muscle activity of a subject who conducted two 4 min long rides on a manual wheelchair using push rims and lever drive. The tests were carried out on a mechanical treadmill which allowed for maintaining constant ride conditions regarding slope and velocity of the wheelchair. The resulting muscle activity is presented in % MVC as a function of elbow joint position in deg. From this case study we conclude that it is possible that using lever drive for wheelchair propulsion activates muscles of a subject differently from push rims thus enabling a different way of muscle rehabilitation.

The Musculoskeletal Contribution in Wheelchair Propulsion Systems: Numerical Analysis

Although many improvements are still being investigated in the Manual Wheelchair (MWC), a number of criticisms are formulated by a vast majority of daily users. One of the most significant concerns are related to the handrim propulsion system, which is responsible for micro-traumas. The numerical study described in this paper compares two types of propulsion systems: the classical handrim and the lever propulsion. The purpose is to assess the force required for propulsion and the related consequences on involved muscles in the case of a paraplegic patient. Numerical results on lever propulsion demonstrates improved force distribution and reduced muscle activity compared to the classic handrim propulsion. In our view, these results constitute a promising initial step for demonstrating the superiority of lever propulsion from an ergonomics viewpoint.