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Experimental apparatus for film thickness and friction measurements on gear teeth and cam-follower contacts
No full textGear teeth and cam-follower couplings are typical non-conformal contacts working under transient elastohydrodynamic conditions undergoing variations of load, speed and geometry. Therefore, both numerical and experimental simulation of these contacts are difficult. Experimental results can validate numerical results and furnish useful indications for design optimization of gears and cam systems.
In this work, a new test rig is presented that has been purposely designed for investigations on lubricated contacts working under transient conditions, as gear teeth and cam-follower contacts.
Some theoretical/numerical simulations has been performed to investigate the dynamic behaviour of the apparatus to obtain important indications for its design.
The contact is formed between a specimen of suitable shape moved by an electric motor and a flat counterface. The load is applied thanks to a lever system and calibrated springs. Film thickness and contact forces are the main quantities measured by the experimental apparatus. Film thickness and shape are estimated using optical interferometry; interference images are recorded using a microscope connected with a computer controlled high-speed camera when using glass counterfaces. A complex dynamometric system with load cells has been realised for measuring all components of the contact force. An air cooled insulated base is used for thermal insulation. A real-time controller and data acquisition system are used
Sviluppo di un’attrezzatura per la simulazione di contatti fra camma e piattello e fra denti di ingranaggi
No full textI sistemi costituiti da camma-piattello e denti di ingranaggi sono tipici contatti non conformi, che lavorano sotto condizioni elastoidrodinamiche transitorie a causa della variazione di carichi, velocità e geometria. Per questo motivo sia la simulazione numerica che quella sperimentale di tali contatti sono difficoltose. I risultati sperimentali sono fondamentali per validare quelli numerici e fornire utili indicazioni per l'ottimizzazione dei sistemi a camme.
In questo lavoro è descritta una nuova attrezzatura sperimentale, progettata per lo studio di contatti lubrificati in condizioni di transitorio, proprio come il contatto camma-piattello e quello fra denti di ingranaggi. Sono state effettuate alcune simulazioni teorico-numeriche per studiare il comportamento dinamico dell'attrezzatura utilizzando profili di camme diversi e variando velocità di rotazione
Experimental study on circular eccentric cam-follower pairs
Full text linkExperimental verifications of cam-follower contacts are very important because of the difficulties for a reliable simulation due to the continuous variation of load, speed and geometry of the lubricated contact. Some experiments have been carried out with a new apparatus, specifically designed and realised for investigation on cam-follower and gear teeth contacts, in order to test its capability to measure film thickness and contact forces. Circular eccentric cams have been used because they feature lower transient effects and comparison of the results with the theoretical/numerical ones is easier. The tests have been performed using cams with two different eccentricities and surface roughness, and two different followers, one made of steel and one made of glass.
The behaviour of the cam-follower contacts at several different rotational speeds, ranging from 50 to 500 rpm, and different pre-loads have been investigated. Lubrication regimes ranged from boundary to complete, being most of the tests performed under mixed lubrication conditions. Localised wear has occurred during some tests. Data of all contact force and moment components as well as of the cam shaft driving torque have been acquired at high acquisition frequency. Some methodologies for numerical data elaboration have been identified. Optical interference images have been correctly recorded at the desired frequency. The trends of the normal and friction forces measured in the different tests are presented in the paper, as well as the evaluated trends of the friction coefficient. Some sample optical interference images are also shown. The results furnish encouraging indications about the capabilities of the experimental apparatus
Dynamic aspects of a new experimental apparatus for tribological investigations on cam-follower pairs
No full textThe cam-follower mechanism is one of the most complex lubricated contacts, due to its continuous variations of load, velocity and geometry. Both theoretical-numerical and experimental studies are very difficult to perform and need to be often done in parallel. Numerical simulations need an experimental verification and experiments need often a dynamic simulation for a better interpretation of the experimental results and also for design purposes. In this work the importance of the dynamic behaviour of the whole system connected to a cam-follower pair is evidenced. A new experimental apparatus has been designed with the aid of a simulation programme contemporaneously developed. Different versions of the apparatus have been analysed with purposely developed versions of the programme, particularly for a correct estimation of the contact load. Some sample results obtained for a cam with a spline profile used with two versions of the apparatus are presented. The influence of the dynamic effects particularly on the contact load is shown
Investigation on cam–follower lubricated contacts
Full text linkAbstract: The Investigation on cam–follower contact is one of the most complex lubricated non-conformal contact due to its continuous variation of load, speed, and geometry. The com-plexity of the phenomena occurring in the camshaft systems makes experimental verifications very important. In this study, an already existing versatile experimental apparatus for the inves-tigation of non-conformal lubricated contacts, able to measure film thickness using the optical interference method and friction force trough a load cell, has been modified in order to test cam– follower contacts. Some tests have been carried out for investigating the behaviour of some fundamental components of the rig. A theoretical/numerical simulation has been performed to investigate the dynamic behaviour of the system and in order to provide some indications for the interpretation of the experimental results. Purposely developed versions of the pro-gramme have been also an important support for the design of a new apparatus specifically addressed to the cam–follower contact with increased potentialities capable of more detailed measurements of film thickness and contact forces. The apparatus is able to reproduce a cam– follower mechanism that uses a rocker as a link device between the cam follower set and the valve
Set-up of a test rig for lubricated cam simulation
No full textExperimental tests are necessary in order to understand the behaviour of the lubricated contact between the cam and the follower. Some experimental works were made in the past. A study for the realization of a new experimental rig started at the University of Pisa. The new rig is basically able to measure two fundamental quantities of the lubricated contacts: the film thickness and contact force. Due to the continuous movement of the cam-follower contact point, particular problems are related to the contact force measurement and to the interference images detection. A measurement group has been specifically designed able to measure all components of the contact force. The film thickness and shape is estimated by interferometric method using a microscope that can be connected to a high-speed camera; the whole system is moved with specific laws by a computer controlled XYZ positioner. The main problems faced for the preliminary set-up of these two fundamental groups are described in this work
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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