1,720,963 research outputs found
Experimental identification of faults in a railway pantograph mechanism in presence of nonlinear damping (Aimeta 2017)
No full textPredictability may transform maintenance from a cost centre into a profit unit. Industries are indeed investing in innovative technologies to implement the purpose. In this paper we introduce a project meant to develop a robotic tool for the assessment of railway pantographs through a vibration based detection of faults. Nonlinearities such as intense dependence of damping on speed and non-negligible friction in joints make the applicaton particularly challenging. These phenomena could in fact drastically modify the behavior with respect to simpler linear models predictions. Experimental frequency response functions (FRFs) were hence derived for several input amplitudes so as to estimate at which extent modal parameters are related to the energy level. To discriminate the sources of nonlinearity FRFs were carried out even after the damper had been removed. Phase plots shape alteration was then observed for a couple of frequencies and as many amplitudes to delve deeper into dynamics changes. A first indication on the suitability of FRFs to detect faults is pursued considering the absence of the dashpot as an example of defect, i.e. a severe leakage, comparing modal information from the two data sets
A parallel-elastic actuation approach for wide bandwidth fingertip haptic devices
No full textWearable haptic devices are used to render sense of touch in different virtual reality, simulated or teleoperated environments. Design of these devices has to comply with dimensional constraints imposed by ergonomics and usability, introducing compromises between size of the actuators and features of the rendered haptic stimuli, such as peak forces and bandwidth. We propose a new design approach for wearable haptic devices resembling the micro-macro actuation concept: it is based on two distinct actuators with different mechanical reduction, coupled by an elastic element. We show this better matches the output range of the actuators to features of the signals used in typical haptic rendering. We investigated the approach through an analytical model, a numerical model, and physical experiments conducted after design and development of a working prototype. The theoretical and simulated models allow to better understand dynamic interaction of the system parts, and to define design guidelines for the development of the real device. The adopted design solutions were implemented and evaluated in the prototype of a highly wearable fingertip device. Final experimental results show how the implementation of the proposed method is capable of an effective haptic rendering, that better matches the desired frequency response
A Lightweight Robotic Device Based on a Micro-Macro Actuation Concept for the Inspection of Railway Pantograph
No full textFunctional verification of railway pantographs is performed within periodic maintenance programs by means of specifically designed automation and robotic devices that can check their structural integrity and correct functionality. In this paper, we present the design and validation of a new portable inspection robotic device that through structural dynamic excitation and passive movement can assess the health status of railway pantographs. The device is endowed with a new actuation system that combines the large range of force attained through a macro-Actuator with the high-frequency capabilities of a micro-Actuator while preserving lightweight structure. The reported design and experiments confirm that excitation transmission by accurate force control can be achieved in the entire frequency range, despite the interaction between actuator and structure, and that simulated defects can be revealed by low and high-frequency alterations
Rendering Fine Tactile Feedback With a Novel Hydraulic Actuation Method for Wearable Haptic Devices
Full text linkTiny contact transients prove very informative for dexterous, fine manipulation, both in virtual environments and teleoperation. Yet, it is challenging to obtain such quality of the rendering in compact and highly wearable haptic devices. To this aim we propose a novel miniature hydraulic actuator, aiming at low-noise rendering of tiny tactile signals, fully enclosed in a fingertip haptic device. Its novelty is in the use of ferrofluidic sealings, embedded within a miniature linear electromagnetic motor. The solution has two main advantages: it shows no static friction, due to the magnetohydrodynamic levitation effect of the ferrofluid, and a noiseless hydraulic reduction. Besides, the hydraulic actuator enables the use of a soft and compliant interface for transmission of signals to the fingerpad tissues. We evaluate here a prototype of the actuator implemented in a compact and soft haptic thimble: the low-noise rendering capabilities are evaluated in experiments at the bench and through perception study. Then, in a simplified teleoperation setup, we match one-to-one the pressure rendered by the device with a sensitive pneumatic pressure sensor mounted on a robotic fingertip. Results show that haptic feedback alone (no vision) is able to improve results over the visual condition in terms of maximum exerted pressure
A robotic device for the structural dynamics inspection of railway pantographs through nonlinearity tests
No full textThe railway industry is progressively embracing mechatronics solutions to improve maintenance operations. In this context, we present a robotic device that introduces structural dynamics analysis in railway pantograph inspection. Specifically, an innovative macro-micro actuation extends the bandwidth performance of actual devices, while a force control strategy proved to support the execution of nonlinearity tests via the estimation of the Frequency Response Function for different levels of the input force. Thereupon we show that the exploitation of nonlinearity can enhance the detection of even a minor localized fault
A Detection Method of Faults in Railway Pantographs Based on Dynamic Phase Plots
No full textSystems for detection of damages in railway pantographs effectively reduce the cost of maintenance and improve time scheduling. In this paper, we present an approach to design a monitoring tool fitting strong customer requirements such as portability and ease of use. Pantograph has been modeled to estimate its dynamical properties, since no data are available. With the aim to focus on suspensions health, a two Degrees of Freedom (DOF) scheme has been adopted. Parameters have been calculated by means of analytical dynamics. A Finite Element Method (FEM) modal analysis verified the former model with an acceptable error. The detection strategy seeks phase-plots topology alteration, induced by defects. In order to test the suitability of the method, leakage in the dashpot was simulated on the lumped model. Results are interesting because changes in phase plots are more appreciable than frequency-shift. Further calculations as well as experimental tests will support future developments of this smart strategy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Investigating the effect of dry-friction on damage detection tests
Full text linkThis paper investigates whether dry-friction can affect the detection of damages in the context
of structural dynamics tests. The problem is confronted through a MDOF system with a single
Coulomb contact and a harmonic excitation, in the presence of two damage scenarios, namely
the loss of a member connectivity and a reduction of the artificial damping, also considering
different locations of the frictional contact and the input excitation. In particular, we derive the
trends of the damage signature with respect to the friction-over-excitation ratio. In this way, it
was possible to correlate the amplitude of the damage signature to the properties of the system
in the stick–slip or in the stuck regime. The investigation is also pursued through experimental
tests with the same damage scenarios applying a variation of the friction ratio of one order of
magnitude. Results confirm the theoretical trends and suggest that the choice of the friction
ratio can also determine the appearance of false negatives for a given confidence level
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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