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The objective of the research is to analyze the impact of the ultrasonic vibration assistance on the wear resistance due to the topography enhancement caused on Ti6Al4V cylindrical samples after surface modification through a ball burnishing process. The process parameters considered for this study are the burnishing force, the number of passes, and the addition of a 40 kHz ultrasonic assistance, which are thought to enhance the surface topography and increase the hardener effect in terms of depth. A complete screening design of 3 factors was performed, revealing that the number of passes and the vibration assistance are the most important parameters for minimizing the wear volume loss, being 170 N of burnishing force, 3 passes, and the addition of the vibration assistance as the best combination found. However, no significant difference in the friction force was observed. The topography results show that there is a decrease in the average roughness from 1.50 to 0.45 µm with optimal burnishing conditions. It was also analyzed the microstructure originated after the turning, the conventional ball burnishing, and the vibration-assisted ball burnishing, being the last optimal in terms of depth affectation to the microstructure. Therefore, these results confirm an improvement in terms of wear enhancement, friction reduction, and topography results when vibration assistance is added to a conventional ball burnishing process. Peer Reviewed Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura

Honing processes are abrasive machining processes which are commonly employed to improve the surface of manufactured parts such as hydraulic or combustion engine cylinders. These processes can be employed to obtain a cross-hatched pattern on the internal surfaces of cylinders. In this present study, fuzzy artificial neural networks are employed for modeling surface roughness parameters obtained in finishing honing operations. As a general trend, main factors influencing roughness parameters are grain size and pressure. Mean spacing between profile peaks at the mean line parameter, on the contrary, depends mainly on tangential and linear velocity. Grain Size of 30 and pressure of 600 N/cm2 lead to the highest values of core roughness (Rk) and reduced valley depth (Rvk), which were 1.741 µm and 0.884 µm, respectively. On the other hand, the maximum peak-to-valley roughness parameter (Rz) so obtained was 4.44 µm, which is close to the maximum value of 4.47 µm. On the other hand, values of the grain size equal to 14 and density equal to 20, along with pressure 600 N/cm2 and both tangential and linear speed of 20 m/min and 40 m/min, respectively, lead to the minimum values of core roughness, reduced peak height (Rpk), reduced valley depth and maximum peak-to-valley height of the profile within a sampling length, which were, respectively, 0.141 µm, 0.065 µm, 0.142 µm, and 0.584 µm.

Honing processes are usually employed to manufacture combustion engine cylinders and hydraulic cylinders. Honing provides a crosshatch pattern that favors the oil flow. In this paper, Adaptive Neural Fuzzy Inference System (ANFIS) models were obtained for tool wear, average roughness Ra, cylindricity and material removal rate in finishing honing processes. In addition, multi-objective optimization with the desirability function method was applied, in order to determine the process parameters that allow minimizing roughness, cylindricity error and tool wear, while maximizing material removal rate. The results showed that grain size and tangential velocity should be at their minimum levels, while density, pressure and linear velocity should be at their maximum levels. If only roughness, cylindricity error and tool wear are considered, then low grain size, low pressure and low linear velocity are recommended, while density and tangential velocity vary, depending on the optimization algorithm employed. This work will help to select appropriate process parameters in finishing honing processes, when roughness, cylindricity error and tool wear are to be minimized. The authors would like to thank the company Honingtec S.A. as well as Alejandro Domínguez for their help with the experimental tests. Financial support of these studies from Gdańsk University of Technology, Poland, by the DEC-6/2021/IDUB/IV.2/EUROPIUM application number 035506 grant under the IDUB - ‘Excellence Initiative - Research University’ program is gratefully acknowledged.

Purpose The purpose of this study is to use the Freeform Reversible Embedding of Suspended Hydrogels (FRESH) additive manufacturing (AM) technique for manufacturing a liver phantom which can mimic the corresponding soft living tissue. One of the possible applications is surgical planning. Design/methodology/approach A thermo-reversible Pluronic® F-127-based support bath is used for the FRESH technique. To verify how three-dimensional (3D)-printed new materials can mimic liver tissue, dynamic mechanical analysis and oscillation shear rheometry tests are carried out to identify mechanical characteristics of different 3D printed silicone samples. Additionally, the differential scanning calorimetry was done on the silicone samples. Then, a validation of a 3D printed silicone liver phantom is performed with a 3D scanner. Finally, the surface topography of the 3D printed liver phantom was fulfiled and microscopy analysis of its surface. Findings Silicone samples were able to mimic the liver, therefore obtaining the first soft phantom of the liver using the FRESH technique. Practical implications Because of the use of soft silicones, surgeons could practice over these improved phantoms which have an unprecedented degree of living tissue mimicking, enhancing their rehearsal experience before surgery. Social implications An improvement in surgeons surgery skills would lead to a bettering in the patient outcome. Originality/value The first research study was carried out to mimic soft tissue and apply it to the 3D printing of organ phantoms using AM FRESH technique.

This paper studies the problem of spurious eigensolutions in the context of the singular boundary method (SBM) formulated in the two-and-a-half-dimensional (2.5D) domain and proposes two numerical schemes to overcome this numerical difficulty. The SBM can be seen as a version of the method of fundamental solutions where the source points are located at the physical boundary. Similar to other boundary-type discretization schemes, the SBM also encounters the non-uniqueness problem at the vicinity of the eigensolutions of the corresponding interior problem. In the 2.5D domain framework, the so-called fictitious eigenfrequencies appearing in 3D problems arise in the form of spurious dispersion curves associated with propagation modes of the corresponding interior problem. The two enhanced 2.5D SBM approaches proposed in this work, based on the Burton–Miller method in one case and the dual surface method in the other, are designed to filter out the spurious eigenvalues from the simulation results and deliver accurate solutions along the wavenumber-frequency spectrum. Three benchmark examples including the radiation problems of an infinitely long cylinder under Dirichlet and Neumann boundary conditions and the radiation problem of a longitudinally infinite object with a constant star-like cross section subjected to a Dirichlet boundary condition are considered to study the proposed methods. The results demonstrate the capability of the proposed numerical schemes to successfully avoid the non-uniqueness problem when the 2.5D SBM is employed.

Specific energy consumption is an important indicator for a better understanding of the machinability of materials. The present study aims to estimate the specific energy consumption for abrasive metal cutting with ultra-thin discs at comparatively low and medium feed rates. Using an experimental technique, the cutting power was measured at four predefined feed rates for S235JR, intermetallic Fe-Al(40%), and C45K with different thermal treatments. The variation in the specific energy consumption with the material removal rate was analyzed through an empirical model, which enabled us to distinguish three phenomena of energy dissipation during material removal. The thermal treatment and mechanical properties of materials have a significant impact on the energy consumption pattern, its corresponding components, and cutting power. Ductile materials consume more specific cutting energy than brittle materials. The specific cutting energy is the minimum energy required to remove the material, and plowing energy is found to be the most significant phenomenon of energy dissipation.

La situación de alerta provocada por la Covid-19 ha hecho que la docencia universitaria tradicional pasara de ser presencial a no- presencial en menos de una semana. Este trabajo presenta los esfuerzos hechos por parte del equipo docente de Mecánica de la Escuela Técnica Superior de Ingeniería Industrial de Barcelona ( Universitat Politècnica de Catalunya) para adaptarse a la nueva realidad e intentar garantizar el aprendizaje de calidad a partir del desarrollo de nuevos materiales y la adecuación de la docencia y los sistemas de evaluación a la situación actual. Se optó para potenciar actividades orientadas al desarrollo de competencias, poniendo énfasis en la autogestión de los estudiantes y, en definitiva, promoviendo su aprendizaje activo. Para ello se creó nuevo material con el contenido teórico básico, se fomentó el uso de los foros de debate en el campus virtual y se realizaron sesiones de teoría/problemas y de aclaraciones a través de la plataforma Meet de G -Suite. Además, semanalmente los estudiantes disponían de cuestionarios de autoevaluación y de evaluaciones continuadas en formato test. Los resultados de los exámenes muestran tasas de aprobados muy similares a la de los últimos años

The present study evaluates the effects of manufacturing parameters on the tensile properties of a commercial composite material based upon polylactic acid (PLA) with wood fibers known as Timberfill. The specimens are built through fused filament fabrication (FFF), and the influence of four printing parameters (layer height, fill density, printing velocity, and orientation) is considered through a L27 Taguchi orthogonal array. Tensile tests are applied to obtain the response variable used as output results to perform the ANOVA calculations. Results show that fill density is the most influential parameter on the tensile strength, followed by building orientation and layer height, whereas the printing velocity shows no significant influence. The optimal set of parameters and levels is found, being 75% fill density, 0¿Z-axis orientation, 0.4 mm layer height, and 40 mm/s velocity as the best combination. Applying this combination, a 9.37-MPa maximum strength is the highest value obtained for the material. Additionally, five solid injection molded Timberfill specimens were tested as well and the results compared with the FFF samples. The values of the elastic modulus, elastic limit, and maximum strength of the injected samples were almost twofold of those were obtained for the FFF samples, but the maximum elongation of the injected specimens fell sharply.

The aim of the paper is to analyze the effect of nozzle diameter and infill on porosity and pore size of FDM printed specimens with rectilinear grid pattern. Two different nozzle diameters (0.2 and 0.4 mm), as well as four different infill values (20 %, 40 %, 60 % and 80 %) were used. Experimental results for pore size agree with theoretical results. On the contrary, low experimental porosity was obtained, especially for high infill values, because printed samples show fewer pores than expected. The higher infill, the lower porosity and pore size. Higher nozzle diameter implies higher pore size but similar porosity.

For comprehending tribological phenomena such as wear, friction, contact deformation and tightness of contact joints is the essential characterisation of the multiple scale topography of roughness surfaces. Wheel roughness obtained through direct measurement and then a description of wheel roughness has been obtained using the fractal function. The statistical parameters and fractal sizes for drive wheels which ran 2000 km and another ones new wheels have been analysed.By registering the results and programmable automaton of the roughness, the principal statistical characteristics were determined to be stands out the Abbott-Firestone curve and respectively, the fractal character. The appearance of roughness on the surface of the wheel causes the production of vertical vibrations that act on the complex wheel-rail system.In the analysis of the wheel irregularity, the fractal geometry was applied, so that to obtain the fractal parameters Dw, respectively Ltw (opothesy length), the method of the structure function was used [1, 2]. Therefore, the experimental measurement and obtained results processed presented.

Walking rehabilitation using exoskeletons is of high importance to maximize independence and improve the general well-being of spinal cord injured subjects. We present the design and control of a lightweight and modular robotic exoskeleton to assist walking in spinal cord injured subjects who can control hip flexion, but lack control of knee and ankle muscles. The developed prototype consists of two robotic orthoses, which are powered by a motor-harmonic drive actuation system that controls knee flexion–extension. This actuation module is assembled on standard passive orthoses. Regarding the control, the stance-to-swing transition is detected using two inertial measurement units mounted on the tibial supports, and then the corresponding motor performs a predefined flexion–extension cycle that is personalized to the specific patient’s motor function. The system is portable by means of a backpack that contains an embedded computer board, the motor drivers, and the battery. A preliminary biomechanical evaluation of the gait-assistive device used by a female patient with incomplete spinal cord injury at T11 is presented. Results show an increase of gait speed (+24.11%), stride length (+7.41%), and cadence (+15.56%) when wearing the robotic orthoses compared with the case with passive orthoses. Conversely, a decrease of lateral displacement of the center of mass (−19.31%) and step width (−13.37% right step, −8.81% left step) are also observed, indicating gain of balance. The biomechanical assessment also reports an overall increase of gait symmetry when wearing the developed assistive device.

The development of additive manufacturing (AM) during the last years has revolutionized not only the industry, but also the medical sector. This alongside the necessity in our society and in medicine to enhance the quality of life of the population has led to the creation of surgical training prototypes. They are used during surgery’s planification phase before carrying out an operation. Surgical training is a good method for medical teams to visualize and have an idea of what they can encounter in the interventions. In order to meet this objective, these prototypes should mimic as much as possible the corresponding living tissues. To achieve that, different parameters are taken into consideration: viscosity, elastic modulus, shore, etc. Nonetheless, it is difficult to achieve that aim, since until now only mono-material prototypes are accessible to hospitals due to the high cost of multi-material prototypes made with industrial proprietary AM equipment. Therefore, a deep study is done in the different multi-materials concepts within an open – and thus accessible – technology: Fused Filament Fabrication (FFF) 3D printers. Finally, a desktop multi-material AM open concept based on multiple independent extruders for surgical training prototypes is described.

The objective of this work is to analyze the influence of the vibration-assisted turning process on the machinability of S235 carbon steel. During the experiments using this vibrational machining process, the vibrational amplitude and frequency of the cutting tool were adjusted to drive the tool tip in an elliptical or linear motion in the feed direction. Furthermore, a finite element analysis was deployed to investigate the mechanical response for different vibration-assisted cutting conditions. The results show how the specific cutting energy and the material&rsquo, s machinability behave when using different operational cutting parameters, such as vibration frequency and tool tip motion in the x-axis, y-axis, and elliptical (x-y plane) motion. Then, the specific cutting energy and material&rsquo, s machinability are compared with a conventional turning process, which helps to validate the finite element method (FEM) for the vibration-assisted process. As a result of the operating parameters used, the vibration-assisted machining process leads to a machinability improvement of up to 18% in S235 carbon steel. In particular, higher vibration frequencies were shown to increase the material&rsquo, s machinability due to the specific cutting energy decrease. Therefore, the finite element method can be used to predict the vibration-assisted cutting and the specific cutting energy, based on predefined cutting parameters.

The version of record os available online at: http://dx.doi.org/10.1007/s11071-022-07807-7 The 2D motion ofarigid rimless wheel on an inclined plane has been widely studied as a first simple case of passive walker. Usually, it is modelled as a hybrid dynamical system alternating continuous smooth phases and discrete impact ones. As in other bipedal walkers, the related research is often devoted to the analysis of cyclic motions and assumes that the spoke-ground collision is a single-point one. This work focuses exclusively on the impact problem and explores the possibility of different transitions within the impact interval (single-point to double-point collisions, dynamic jamb, stick-slide transitions and sliding reversal) as a function of the spokes angular aperture, the wheel inertia, the wheel-ground friction coefficient, and the initial conditions. This analysis is done through an innovative geometrical approach based on the Percussion Centre.

The prosthetic alignment procedure considers biomechanical, anatomical and comfort characteristics of the amputee to achieve an acceptable gait. Prosthetic malalignment induces long-term disease. The assessment of alignment is highly variable and subjective to the experience of the prosthetist, so the use of machine learning could assist the prosthetist during the judgment of optimal alignment.

This research is concerned with the impact of onboard passengers’ seating arrangement on the carbody flexural vibrations of a high-speed railway vehicle. In this regard, the previously developed passenger body-seat models are used to consider the dynamic influence of the passengers. The carbody is modeled using the Euler–Bernoulli beam model to evaluate its flexural deformation. The frequency-domain analysis demonstrates that the carbody behaves almost like a rigid body when the vehicle is full of passengers. It is established that the passengers' presence causes a 31% enhancement of the ride quality determined based on EN 12299 standard for a fully occupied vehicle compared with an empty car. A scaled model of a ratio of 1:24.5 of the Shinkansen vehicle is constructed for validation purposes. The experimental results exhibit a similar trend as found by the simulations in terms of the impact of the passengers’ distribution on the carbody flexural vibrations.

In this work, the design, manufacture and measurement process of constant-breadth cams is presented. The motion law of the cam was designed by means of Bézier curves and the corresponding design desmodromic constraints. The cams were manufactured in two different materials employing two different processes: PLA cams with fused filament fabrication (FFF) and aluminium cams with computer numerical control (CNC) milling. The main aim of this work is to compare both types of cams regarding dimensional accuracy and surface finish, in order to evaluate if it would be possible to temporally replace a metallic cam with a plastic one during the repair of the first one. Dimensions were measured with micrometres and surface roughness with a contact roughness meter. The results show that, in diametral dimensions, similar dimensional error values were obtained for both the 3D-printed and the machined cams. However, in longitudinal dimensions, whose direction is perpendicular to the 3D-printed layers, the 3D-printed cams showed higher dimensional error than the machined ones. The average roughness Ra in the 3D-printed cams was 20 times higher than in the milled cams. According to the results, it would be recommended to temporally replace metallic cams with plastic ones in applications of low-power transmission. Given that in the literature little information is available about the measurement of 3D-printed desmodromic cams, this work will contribute to the study and analysis of this kind of 3D printed mechanism.

Microfluidics technology has grown rapidly over the past decades due to its high surface-to-volume ratios, flow controllability, and length scales efficiently suited for interacting with microscopic elements. However, as a consequence of the small rates of mixing and transfer they achieve due to operating under laminar flow regimes, the utilization of microfluidics for energy applications has long been a key challenge. In this regard, as a result of the hydrodynamic and thermophysical properties they exhibit in the vicinity of the pseudo-boiling region, it has recently been proposed that microconfined turbulence could be achieved by operating at high-pressure transcritical fluid conditions. Nonetheless, the underlying flow mechanisms of such systems are still not well characterized, and, thus, need to be carefully investigated. This work, consequently, analyzes supercritical microconfined turbulence by computing direct numerical simulations of high-pressure ([Formula: see text]) N2 at transcritical conditions imposed by a temperature difference between the bottom ([Formula: see text]) and top ([Formula: see text]) walls for a friction Reynolds number of [Formula: see text] (bottom wall). The results obtained indicate that microconfined turbulence can be achieved under such conditions, leading to mixing and heat transfer increments up to [Formula: see text] and [Formula: see text], respectively, with respect to equivalent low-pressure systems. In addition, it is found that the near-wall flow physics deviates from a single-phase boundary layer theory due to the presence of a baroclinic instability in the vicinity of the hot/top wall. This instability is generated by the combination of the external force driving the flow and the large variation of density across the pseudo-boiling region, which strongly modifies the flow behavior in the vicinity of the wall and renders present “law of the wall” transformation models inaccurate.

We investigate the incompressible flow past a square cylinder immersed in the wake of an upstream nearby splitter plate separating two streams of different velocity. The bottom stream Reynolds number, based on the square side, $Re_B=56$ is kept constant while the top-to-bottom Reynolds numbers ratio $R\equiv Re_T/Re_B$ is increased in the range $R\in[1,6.5]$, corresponding to a coupled variation of the bulk Reynolds number $Re\equiv(Re_T+Re_B)/2\in[56,210]$ and an {\it equivalent} nondimensional shear parameter $K\equiv2(R-1)/(R+1)\in[0,1.4667]$. The onset of vortex-shedding, at $R=2.1\pm0.1$ (corresponding to $Re=86.8\pm2.8$, $K=0.71\pm0.04$), is pushed to higher $Re$ as compared to the square cylinder in the classic configuration. The advent of three-dimensionality is triggered by a mode-C-type instability at $R\simeq3.1$ ($Re\simeq115$, $K\simeq1.02$) with wavelength $\lambda_z\simeq2.4$, much as reported for open circular rings and square cylinders placed at an incidence. The resulting solution is period-doubled and exhibits a triad of spanwise symmetries: a mirror reflection and two spatiotemporal symmetries involving the evolution by half a period (two vortex-shedding cycles) followed by either specular reflection or a half-wavelength shift. The path towards spatio-temporal chaos is initiated thereafter with a modulational period-doubling tertiary bifurcation at $R\in(3.4,3.8)$ that also doubles the spanwise periodicity. The ensuing nonlinear solution repeats only after four vortex shedding periods and retains only a spatiotemporal invariance consisting in the evolution by half a period (two vortex-shedding cycles) followed by mirror reflection about a streamwise-cross-stream plane. At slighlty higher values of $R\geq4$, the flow has become spatio-temporally chaotic, but the main features of mode C are still clearly distinguishable., Comment: 30 pages, 16 figures, under review in JFM journal

El meu treball de final de grau pretén estudiar i donar a conèixer tots els passos a seguir per poder portar a terme un projecte mecànic, i concretament, en aquest cas, una polidora de banda, des del moment que una persona té la idea fins a la fabricació de l’objecte en qüestió, amb la finalitat de poder servir de referent per a qualsevol persona interessada en la construcció d’una màquina. S’ha de tenir en compte no només el disseny sinó també els costos, tant d’ investigació, com de disseny, de gestió, dels materials, de fabricació i de muntatge, i veure si és viable econòmicament, tenint en compte els processos de fabricació, materials i tractaments, sense anar en detriment de la qualitat de les peces. Després d’un procés d’investigació del que existeix al mercat relacionat amb la nostra idea, començarem a dibuixar la màquina, els seus mecanismes...per passar a continuació amb el disseny 3D, pas previ a la realització dels plànols amb la informació de cada peça. També haurem d’anar fent càlculs tant estructurals com del cost econòmic que implicarà. A partir d’aquí es procedirà a la gestió per a la compra del material més adient tenint en compte la relació qualitat-preu, i ja es podrà començar la fabricació i ensamblatge de les diferents peces de la màquina. My end of degree thesis aims at studying and publishing all the steps to be taken into account to carry out a mechanical project, in this case, a belt grinder, from the moment the person gets the idea to the manufacturing of the machine. My project can be used as a reference by anybody interested in this procedure. Not only the design must be considered but also the costs of research, design, management, materials, assembly and it must be analyzed if it is economically viable, taking into account the manufacturing processes, materials, and the treatments, without compromising the quality of the pieces. After a market research process related to our idea, we’ll start by drawing the machine, its mechanisms, to carry on with the 3D design, step to be taken before the making of the drawings of the different pieces. The economical cost must also be considered, and then the material will be purchased after choosing the best offer from the suppliers, taking into account the relationship between quality and price. After that the manufacturing and assembling of the different pieces can be carried out.

This study examines the effects of using a gamification tool as a teaching strategy. Specifically, Kahoot! is evaluated as a tool for enhancing student learning. The activities were part of the laboratory sessions of the subject Mechanism and Machine Theory during two consecutive academic years. We analyze the effect of a gamification learning system on both, students’ grades and motivation, in a course with a large number of students (n1 = 283 students, n2 = 306 students). The students were divided into three different groups (control group, gamification group and writing group) and their results were evaluated depending on the learning method applied during the class. In terms of gamification, this project introduces real-time feedback to stimulate the interest of students and help them use the typical tools and methodologies of game-based learning. The analysis of their performance in the laboratory exam shows significant differences between the group that used gamification and the groups that did not. The results suggest that gamification in engineering lab activities has a positive effect on students’ motivation and learning outcome. The study concludes that game-based elements and competitive activities enhanced student performance

Un procés de fabricació correspon a un conjunt d'operacions necessàries per transformar una matèria primera en un producte acabat, complint amb unes especificacions donades.

Additive manufacturing (AM), also known as 3D printing is a manufacturing technology that takes the information from a computer-aided design (CAD) and builds parts in a layer by- layer style. Further to the extensive research on 3D printing of polymers and metals, ceramics have attracted the increasing attention of researchers, in sectors such as aerospace, electrical, chemical or medical. Complex shapes printing with porous structures, which are required in the medical area for prostheses, is difficult with most of the traditional manufacturing processes. However, additive manufacturing processes can achieve such geometries. Specifically, the direct ink writing (DIW) process is one of the most promising and inexpensive techniques for shaping free-form ceramic components. In this process, the material is extruded through a syringe and then deposited on a printing bed. In the present paper the redesign of an extrusion head for ceramics is presented. The main disadvantage of the original design was the limited volume of the syringe vessel barrel. For this reason, the proposed new system has higher capacity. For that, first the target specifications of the new extrusion system for larger material quantities were defined. For this purpose, the Quality Function Deployment method was used, in order to assure the required quality from the design phase. Then, these critical features and specifications were used to generate the different concepts that will ensure the quality of the printed parts when printing large volumes. The morphological matrix was used in this case. The work presented in this paper is the starting point of the development of the final design of an innovative extrusion head.

Manufacturing molds for plastic parts injection are a particular machining domain, where challenging materials, like AISI P20 steel, are forced to satisfy the highest surface quality requirements. Before mirror polishing, milling operation is a common and challenging task due to drilling and milling with the same tool. Thus, special cutting tools, like asymmetric indexable type, are often used. This tool presents two geometrically equal positive inserts – one placed horizontally and the other vertically – for the flexible machining of holes, cavities, floors, and walls. Rough-medium milling operations lead to a complicated relationship between cutting conditions and geometrical tool parameters, making it challenging to balance the tool life of both inserts. The novelty of this work is to propose a model for cutting force prediction with an asymmetric tool to explain the separated behavior of both inserts and determine a better compromise between cutting conditions and tool life. The experimental tests were done for model validation and then wear cutting tests for testing improved cutting conditions. The results predicted by the model proved that by changing the depth of cut from 0.3 mm to 0.8 mm, the wear in both inserts was more balanced, increasing chip volume up to 1.7 times.

El projecte consisteix en l’estudi i disseny d’una part d’una màquina. Aquesta part de la màquina l’anomenem mòdul i el conjunt d’aquest més altres mòduls formaran una màquina sencera. Aquesta mòdul s’anomena loading feeder “alimentador de càrrega” i la seva funció com bé diu el nom es la de subministrar safates en la zona de recollida per a que després aquestes puguin continuar el seu recorregut per la resta de la màquina. La principal funció del mòdul es elevar safates. Aquestes son elevades des d’un llit de corrons que es troba situat en la part inferior de la màquina fins a un punt de la màquina considerat ergonòmic, per a que els passatgers puguin agafar les safates amb comoditat. També, s’ha de tindre en compte que la safata per poder arribar a la zona d’elevació necessita d’un tram de rodets motoritzats per a que es posicioni en la zona correcte d’elevació. Passa el mateix en la zona superior, un cop la safata es recollida i es torna a dipositar en la màquina és necessita un tram de rodets motoritzats per a que la safata pugui continuar el seu recorregut. En aquest projecte primer s’analitzen els requisits previs que en el disseny s’hauran de complir. Un cop establerts els requisits de disseny, els quals han estat basats en les noves necessitats del mercat, s’expliquen les diferents solucions de disseny que s’han adoptat i es presenten els mecanismes. Per acabar, es calculen els esforços als quals estan sotmesos els components dels mecanismes i es comprova que estan dimensionats correctament. Al final es fa un pressupost del cost del projecte i un estudi de l’impacte medi ambiental. The project consists of the study and design of a specific module that will be part of an entire machine. This module is called loading feeder, and its function, as the name suggests, is to supply trays in the collection area so that they can continue their path through the rest of the machine. The main function of the module is to lift trays. These are raised from roller conveyor located at the bottom of the machine to a point on the machine that is considered ergonomic, so the passengers can pick up the trays comfortable. Also, keep in mind that to reach lifting area, the tray needs a roller conveyor for positioning the tray in a correct lifting area. The same happens in the upper area, once the tray is collected and deposited in the machine, a roller conveyor is needed so that the tray can continue its path. Firstly, we analyse the requirements that must be complain in the design. Once the design requirements have been established, which have been based on the market needs, the different solutions that have been adopted in the main components are explained and the mechanisms are presented. Finally, the stresses to which the components of the mechanisms are subjected, calculated and it’s verified that they are dimensioned correctly. At the end, a budget for the cost of the project and study of the environmental impact is made

Thermoplastic polyurethane (TPU) is a highly elastic linear polymer composed of soft segments, usually flexible polyester, or polyether. It is widely used in 3D printing technologies, being FFF the most common technique. However, stiffness and hardness values of 3D printed TPU in filament form are higher than would be desirable for some applications, which require softer parts. Therefore, it was seen necessary to find a new methodology for 3D printing soft TPU. In this way, the present study seeks to be the first research study that focuses on the possibility of 3D printing TPU using DIW (Direct Ink Writing) technology with UV light. Firstly, the optimal 3D printing and curing parameters to print soft TPU are determined and then two different TPU formulations are 3D printed. Then, both bulk and 3D printed TPU samples were characterized in terms of shear strength using the Warner-Bratzler shear test and hardness using the Shore hardness test. It was seen that the 3D printed samples showed higher softness than bulk samples compared to TPU filament. Finally, it was concluded that the 3D printing of TPU is challenging due to several points: (1) the viscosity of the TPU; (2) their main issue is their sticky behavior; and (3) the shrinkage which takes place after the thermal treatment and for some applications, it might be a problem. Despite that, TPU appears to be a promising material to be used in different industrial applications.

Lead-cooled fast reactor (LFR) is an important reactor type of the Generation IV nuclear energy, and the main coolant pump (MCP) is the only and most critical power equipment in primary circuit of LFR. The shutdown idling performance of the MCP, is one of the most important safety indicators in the event of a station blackout accident. When the motor loses its power supply, the MCP needs to run under the inertia of the flywheel to ensure the coolant flow for a short time. This study mainly focuses on the idling mathematical model of the MCP under power failure accidents. In this study, taking the shutdown idling performance of the MCP as the optimization goal, the parametric optimization analysis of the impeller and diffuser structure of the MCP was carried out. Specifically, based on the platform ISIGHT, the software of CFturbo, TurboGrid, CFX, Matlab and FLOWMASTER are systematically integrated, the automated 3D modeling, automatic meshing and automatic CFD calculation of different hydraulic model of the MCP are realized. And the neural network mathematical model between the geometric parameters of MCP and the idling performance indicators is established. The study shows that there is a strong linear relationship between the idling performance of the MCP and its head and shaft power, and meridian parameters of Δβ 2, Z 1, Φ 1h and the radial surface parameters of Δβ 1 and Δβ 2, Z 1 and Φ 1h have the greatest impact on the idling performance of MCP.

Rural electrification should plan the multi-stage implementation of electrification systems considering different distribution options (national grid extension and decentralized off-grid systems) with different energy sources (photovoltaic, wind, diesel, etc.). Most of the existing planning assessment tools search for a static final design and only consider economical and technical criteria, although social and environmental issues have proven essential in ensuring long-term sustainability. In this context, the objective of this paper is to investigate and define how different actions of electricity extension in a region can be gradually organized to maximize the region’s overall satisfaction, and which technology options for electricity generation and distribution should be promoted on a regional scale according to economic, technical, socio-institutional and environmental criteria. The obtained solution defines, at each planning stage, to which communities should electricity access be extended and which configuration and sources are used in each community in order to maximize the total satisfaction of the region. This total satisfaction is calculated by means of multicriteria indices that evaluate the energy provided and the suitability of the chosen system designs according to stakeholders’ opinions (experts, promoters, users, among others). A mixed-integer linear programming (MILP) model is developed to solve the regional multi-stage planning. The model is validated with a computational experiment of 540 randomly generated instances; the results highlight its efficiency. Finally, it is applied to solve a case study of 544 real non-electrified communities in Plateau State (Nigeria) calculating two electrification plans (with a more and less budget-constrained scenario) which are compared with the currently available one. The results show that the proposed new plans significantly increase the total satisfaction obtained in the electrification of the region. The consideration of a less-constrained budget scenario allows the promotion of on-grid MGs based on only photovoltaic without diesel, which is the most satisfying option for the case study from a multicriteria perspective.

Sensitivity analysis identifies the influential parameters and it is a key step in the design process. Focusing on reliability based design, the probability of a failure mode and its sensitivity to input uncertainties are obtained in a single Monte Carlo simulation using the Likelihood Ratio method. For correlated multiple failure modes, a sensitivity matrix is proposed. The dominant singular vectors of the sensitivity matrix are found to indicate the most important parameters for combined sensitivity of multiple failure modes. Therefore, the sensitivity matrix can guide resources allocation so that most uncertainties can be reduced for system reliabilities.

In this research, the effect of rail vehicle carbody’s flexural modes on the ride comfort of an example high-speed railway vehicle is investigated. The vehicle is modeled as a rigid multi-body system, where the rigid body vertical, longitudinal, pitch, and roll degrees of freedom of the carbody and bogie frames and the rigid body vertical and roll degrees of freedom of the wheelsets are considered. An Euler–Bernoulli beam theory is used to account for the flexural motion of the carbody. The longitudinal interaction between carbody and bogie through the traction rod is modeled as a nonlinear spring element. The corresponding equations of motion of the system in the frequency domain are obtained by using the equivalent linearization method. The effect of the traction rod is explored by using this model. Also, the optimal stiffness of the traction rod element that minimizes the flexural vibrations of the carbody is obtained through a genetic algorithm. With the optimal stiffness for the traction rod, the ride quality index at the center of the carbody floor is improved by 41% at a speed of 300 km/h. For the validation of numerical results, a scaled model of the vehicle with a scale factor of 24.5 was constructed, and its associated results are presented. The model was excited by random input signals, which were generated based on the power spectral density of the track irregularity function. The agreement between the simulation results and the scaled experimental outcome when compared with the measured data from other sources is found to be satisfactory. In the framework of the physical scaled model, the filtering effect due to the vehicle bogie base is also examined.

The main intention of this study is to propose general criteria for the locations of the control sources and error microphones that improve the performance of the active noise barrier. Based on the proposed criteria of this study, the greater reduction is attained when the diffracted field of the noise source is canceled with the diffracted field of the control sources, that is, it is suggested to locate the control sources on the incident side and below the path that connects the furthest point in the shadow zone to the edge of the barrier. Furthermore, it is suggested that the error microphones are most suitably placed on the shadow side of the barrier where they are under the diffracted field of both the primary and control sources. The results also show that with these general criteria, the active noise control achieves an extra reduction that varies from 14.9 to 3.9 dB (for the one-third octave bands from 63 Hz to 1 kHz) and 9.3 dB for the broadband noises.

An analysis of the existing hand-eye calibration methods reveals that most of them are far from trivial. And, what is worse, their intrinsic complexity makes it difficult to elucidate under which circumstances they fail to provide an accurate solution. Thus, although it might seem that the hand-eye calibration problem is uninspiring because it is assumed to be well-solved, we show in this letter that there was still room for improvement, both in terms of simplicity and robustness. After reviewing the most representative methods, we analyze the situations in which they fail, and we introduce a simpler closed-form alternative that accurately solves the problem in all the identified critical circumstances. Its performance is evaluated using simulated and real experimental data., This work was partially supported by the Spanish Government through project PID2020-117509GB-I00/AEI/10.13039/50110001103

This study focuses on obtaining regression models for material removal rate and tool wear in rough honing processes. For this purpose, experimental tests were carried out according to a central composite design of experiments. Five different parameters were varied: grain size or particle size of abrasive, density of abrasive or abrasive concentration, pressure of the stones against the cylinder internal surface, tangential speed (in this case, corresponding to the rotation speed of the cylinder), and linear speed of the honing head. In addition, multi-objective optimization was carried out with the aim of maximizing the material removal rate and minimizing tool wear. The results show that, within the range studied, the material removal rate depends mainly on tangential speed, followed by grain size and pressure. Tool wear is directly influenced by density of abrasive, followed by pressure, tangential speed, and grain size. According to the multi-objective optimization, if the two responses are given the same importance, it is recommended that high grain size, high density, high tangential speed, and low pressure be selected. Linear speed has less influence on both responses studied. If the material removal rate is considered to be more preponderant than tool wear, then the same values should be considered, except for high pressure. If tool wear is preponderant, then lower grain size of 128 (ISO 6106) should be selected, and lower tangential speed of approximately 166 min−1. The other variables, density and pressure, would not change significantly from the first situation.

Recent studies on ankle exoskeletons have shown the feasibility of this technology for post-stroke gait rehabilitation. The main contribution of the present work is a comprehensive experimental analysis and protocol that focused on evaluating a wide range of biomechanical, usability and users' perception metrics under three different walking conditions: without exoskeleton, with an ankle exoskeleton unpowered, and with an ankle exoskeleton powered. To carry out this study, we developed the ABLE-S exoskeleton that can provide time-adapted ankle plantarflexion and dorsiflexion assistance. Tests with five participants with chronic stroke showed that walking with the ABLE-S exoskeleton significantly corrected foot drop by 25 % while reducing hip compensatory movements by 21 %. Furthermore, asymmetrical spatial gait patterns were significantly reduced by 51 % together with a significant increase in the average foot tilting angle at heel strike by 349 %. The total time to don, doff and set-up the device was of 7.86 ± 2.90 minutes. Finally, 80 % of the participants indicated that they were satisfied with their walking performance while wearing the exoskeleton, and 60 % would use the device for community ambulation. The results of this study add to the existing body of evidence supporting that ankle exoskeletons can improve gait biomechanics for post-stroke individuals.

In this work the results about the use of innovative software in the subject Project I is presented. The subject is given in the Degree in Engineering in Industrial Technologies (GETI) in the School of Industrial Engineering of Barcelona (ETSEIB) of Universitat Politècnica de Catalunya (UPC). In Project I, small groups of 12 students or less are defined, with the purpose of developing a collaborative project along one semester. The project discussed in this work was prepared by two different departments: Mechanical Engineering and Statistics and Operative Investigation. It deals with the measurement of shaft diameters with a micrometre, in order to evaluate the measuring system employed. Traditionally, many activities of the subject were recorded in handwritten reports. The present academic year, within the frame of the project EQUIPA’T (equip yourself), innovative software was applied to the subject. As for the methodology, first the teachers attended a training course. Then, the application of innovative software to the subject was planned. Finally, it was implemented. Google forms was used in the first and last classes to gather information to prepare subgroups of students and to evaluate the subject respectively, Edpuzzle was employed to add questions to videos about two lessons of the manufacturing area: metrology and turning, and Trello was used to manage the design of a 3D printed support by different teams of students. In subsequent years, the application of new software is expected.

En este trabajo se analiza si los recursos didácticos utilizados durante el confinamiento, debido al Covid-19, han representado una innovación docente para los diferentes grupos del DEM de la UPC. Para ello se han utilizado dos encuestas: en la primera, se ha preguntado por las herramientas utilizadas, las dificultades encontradas y el interés en participar en una jornada para compartir experiencias. En la segunda, se ha preguntado por la utilización de las herramientas en cuatro períodos: antes y durante el confinamiento, a la vuelta y en la actualidad. Las conclusiones son que el uso de las distintas herramientas tuvo su punto álgido durante el confinamiento; actualmente, estas herramientas se utilizan más y se aprovechan mejor sus posibilidades puesto que la percepción que se tiene de ellas ha mejorado. Estos resultados indican que los recursos utilizados han servido para mejorar e innovar en algunos aspectos de la docencia del DEM.

Mixed-position kinematic synthesis is used to not only reach a certain number of precision positions, but also impose certain instantaneous motion conditions at those positions. In the traditional approach, one end-effector twist is defined at each precision position in order to achieve better guidance of the end-effector along a desired trajectory. For one-degree-of-freedom linkages, that suffices to fully specify the trajectory locally. However, for systems with a higher number of degrees of freedom, such as robotic systems, it is possible to specify a complete higher-dimensional subspace of potential twists at particular positions. In this work, we focus on the 3R serial chain. We study the three-dimensional subspaces of twists that can be defined and set the mixed-position equations to synthesize the chain. The number and type of twist systems that a chain can generate depend on the topology of the chain; we find that the spatial 3R chain can generate seven different fully defined twist systems. Finally, examples of synthesis with several fully defined and partially defined twist spaces are presented. We show that it is possible to synthesize 3R chains for feasible subspaces of different types. This allows a complete definition of potential motions at particular positions, which could be used for the design of precise interaction with contact surfaces.

This article presents a novel methodology conducted under controlled laboratory conditions to assess the dynamic behavior of the components of railway tracks by applying an unbalanced mass excitation force. The methodology for obtaining accurate measurements, which uses different excitation parameters, is based on an unbalanced mass device, and from these data, the transmissibility of the mass-elastomer system is estimated. For assessment of the dynamic behavior, different sine sweep rate excitations, the unbalanced mass, and background noise are considered. The experimental measurements of transmissibility with a shaker and an unbalanced mass device are performed to validate the methodology. For this, frequency-by-frequency transmissibility measurements and the swept sine were performed by the shaker, with a sine sweep from 1 to 51 Hz, using the unbalanced mass device with different sine sweep rates and unbalanced mass. The results obtained allow comparison of the transmissibility by excitation at specific frequencies and the sine sweep to validate the excitation parameters of the unbalanced mass device. Thus, a transmissibility estimation error with the sweep rate, the unbalanced mass, and the background noise is developed. By using the proposed methodology, it is possible to lower the error of the estimated transmissibility of the system with background noise.

The purpose of this paper is to present a case study whereby a hybrid experimental–numerical model is used to analyse the structure-borne radiation from a domestic product (vacuum cleaner head). The passive (including radiative) properties of the structure are modelled using the hybrid FE-SEA method. The product’s operational activity, which lies beyond the capabilities of conventional modelling methods, is characterised experimentally using inverse force identification. The identified forces and passive model are combined to form a so called hybrid FE-SEA-eXperimental model of the assembly. The FE-SEA-X model is then used to identify dominant contributions from the assembly’s sub-components This work was funded through the EPSRC Research Grant EP/ P005489/1 Design by Science

Este proyecto se ha planteado como la continuación del diseño de una garra industrial que posteriormente se ha incorporado a uno de los robots de la gama de ABB, específicamente al modelo IRB 6700, que cuenta con una alcanzabilidad de 2,45 m y un peso de 300 kg. Se ha llevado a cabo el desarrollo de una modificación en la parte inferior de uno de los subconjuntos de la garra, con la finalidad de hacerla funcional en base a las especificaciones del cliente, que en este caso es una fábrica de coches. Finalmente, en el siguiente documento se han estudiado los materiales de los que se componen los elementos de dicha modificación, así como la justificación de los cálculos requeridos, el estudio de presupuestos, el conjunto total de la garra con los cambios aplicados, su posterior mantenimiento y los respectivos planos con las acotaciones. This project has been proposed as a continuation of the design of an industrial claw that has subsequently been incorporated into one of the robots in the ABB range, specifically the IRB 6700 model, which has an achievable reach of 2.45 m and a weight of 300 kg. The development of a modification has been carried out in the lower part of one of the sub-assemblies of the claw, to make it functionally based on the specifications of the customer, which in this case is a car factory. Finally, in the following document the materials that make up the elements of said modification have been studied, as well as the justification of the required calculations, the study of budgets, the total set of the claw with the changes applied its subsequent maintenance, and the respective plans with the dimensions.

This paper aims to determine the flexural stiffness and strength of a composite made of a polylactic acid reinforced with wood particles, named commercially as Timberfill, manufactured through fused filament fabrication (FFF). The influence of four factors (layer height, nozzle diameter, fill density, and printing velocity) is studied through an L27Taguchi orthogonal array. The response variables used as output results for an analysis of variance are obtained from a set of four-point bending tests. Results show that the layer height is the most influential parameter on flexural strength, followed by nozzle diameter and infill density, whereas the printing velocity has no significant influence. Ultimately, an optimal parameter set that maximizes the material’s flexural strength is found by combining a 0.2-mm layer height, 0.7-mm nozzle diameter, 75% fill density, and 35-mm/s velocity. The highest flexural resistance achieved experimentally is 47.26 MPa. The statistical results are supported with microscopic photographs of fracture sections, and validated by comparing them with previous studies performed on non-reinforced PLA material, proving that the introduction of wood fibers in PLA matrix reduces the resistance of raw PLA by hindering the cohesion between filaments and generating voids inside it. Lastly, five solid Timberfill specimens manufactured by injection molding were also tested to compare their strength with the additive manufactured samples. Results prove that treating the wood-PLA through additive manufacturing results in an improvement of its resistance and elastic properties, being the Young’s module almost 25% lower than the injected material.

International audience; This paper is an experimental research about the mechanical effects on Ti-6Al-4V surfaces treated with an ultrasonic vibration-assisted ball burnishing process. Its aim is to define the process parameters to achieve the best surface integrity on the target workpiece, as well as identifying the effects caused by the introduction of vibrations as a means of assistance. A Taguchi orthogonal array including five factors (preload, number of passes, feed velocity, strategy and original surface texture) was applied to perform the process on ball-end milled surfaces. A comprehensive analysis of the effects was performed, by considering in depth three different facets of surface integrity, namely, topology, residual stress and hardness. Hence the extensive result datasets presented in this paper, which deliver an exhaustive description of the process effects by combining a triple approach in the results analysis section. The effect of vibrations is proved positive to enhance the texture as long as the original surface is not characterized by Sq >2 μm. Furthermore, only the preload and number of passes influence the results. In terms of residual stress, all parameters are influential in the results, especially the burnishing strategy, through which a specific direction can be reinforced. Finally, the burnishing operation proves to modify the hardness of deep layers down to 0.5 mm, applying the vibration-assisted process. The main conclusion derived from these works is a technical recommendation to treat the Ti-6Al-4 V surface through the process, aiming to find a balanced comprehensive surface integrity enhancement.

Elastic actuators feature increased energy efficiency and improved human-robot interaction compared to directly driven concepts for active orthoses and prostheses. Structure and parameters of the elastic actuation system are often designed via a model-based minimization of energy consumption based on gait data gained from healthy individuals. However, natural motion exhibits variability among individuals and may not consider requirements of persons using assistive devices. A parametric study is performed examining the impact of varying gait characteristics on the energy consumption and constraints of an optimized (clutchable) series elastic actuator of the knee joint. Furthermore, friction parameters are varied to analyze the impact on actuator constraints. Results of the parametric study indicate increased energy consumption for a slower cadence compared to the healthy gait data for both systems. The clutchable series elastic actuator is less impacted by constraints than the series elastic actuator. The utilized models are evaluated experimentally at a test bench, indicating good accordance to the measured energy consumption. The results highlight the interrelation of friction and gait parameters with energy consumption and actuator constraints and indicate that the optimization procedure for the actuator design requires detailed models of component efficiency as well as subject-specific gait characteristics.

This paper proposes a finite element model implemented in ANSYS using Lagrangian formulation to assess heat generation and friction dynamics of a friction stir welding process on AA2024-T3 aluminum plates. For that aim, the model is enriched by estimating a temperature-dependent friction coefficient using theoretical relationships, and by considering a temperaturedependent multilinear isotropic hardening equation as a plasticity model representing the material. Both quantitative determinations are confirmed through experimental data collected on the real material. Finally, the contact conditions are modeled using the modified Coulomb criterion. The results of the model are in agreement with actual results observed on experimental applications. The study proves that the rotational speed of the tool is the most determinant factor in the results. As it rises, the friction-generated heat flow is higher. This study shows that the compressive stress-strain data in strain rate of 10s-1 is a good approximation of the plasticity behavior of aluminum alloy during the friction stir welding. Peer Reviewed Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura

This article shows the design of a device to automatize an Ambu Spur II manual respirator. The aim of this compassionate medicine device is to provide an emergency alternative to conventional electric respirators—which are in much shortage—during the present COVID-19 pandemic. To develop the device, the classical method of product design based on concurrent engineering has been employed. First, the specifications of the machine have been determined, including the function determining the air volume provided at every moment of the breathing cycle, second, an adequate compression mechanism has been designed, third, the control circuit of the motor has been determined, which can be operated via a touchscreen and which includes sensor feedback, fourth, the device has been materialized with readily available materials and market components, mostly of low cost, and fifth, the machine has been successfully tested, complying with sanitary regulations and operating within desirable ranges. The device has been already manufactured to supply respirators to several hospitals around the Catalan Autonomous Community in Spain, but can also be replicated in developing countries such as Ecuador.

En la síntesis de mecanismos, habitualmente se parte de un mecanismo de barras y pares cinemáticos de clase V en el que se introducen algunas modificaciones. Una de las posibles modificaciones consiste en sustituir una de las barras por dos sólidos unidos mediante un par prismático y un mecanismo leva-palpador. Así se convierte la barra original en una “barra” de longitud variable controlada por los perfiles de la leva y el palpador. Mediante esta estrategia se diseñan mecanismos que permiten optimizar trayectorias convirtiendo mecanismos de barras en mecanismos combinados de barra y levas. En el trabajo que se presenta se analiza un mecanismo construido mediante esta técnica. Se realiza un análisis cinemático analítico para distintas sustituciones de barras y distintos perfiles de la leva. Para todas las opciones estudiadas se calculan los índices de prestaciones clásicos del mecanismo: relación de transmisión y ángulo de presión en la leva.

The problem of noise control and attenuation is of interest in a broad range of applications, especially in the low-frequency range, below 1000 Hz. Acoustic metamaterials allow us to tackle this problem with solutions that do not necessarily rely on high amounts of mass, however most of them still present two major challenges: they rely on complex structures making them difficult to manufacture, and their attenuating capabilities are limited to narrow frequency bandwidths. Here we propose the Multiresonant Layered Acoustic Metamaterial (MLAM) concept as a novel kind of acoustic metamaterial based on coupled resonances mechanisms. Their main advantages hinge on providing enhanced sound attenuation capabilities in terms of a double-peak sound transmission loss response by means of a layered configuration suitable for large scale manufacturing. This research has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Proof of Concept Grant call reference ERC-2019-PoC-25-04-2019, Proposal No. 874481) through the project “Computational design and prototyping of acoustic metamaterials for tailored insulation of noise” (METACOUSTIC). The authors also acknowledge the financial support received by the Spanish Ministry of Economy and Competitiveness, through the Research Grant DPI2017-85521-P for the project “Computational Design of Acoustic and Mechanical Metamaterials” (METAMAT) and the “Severo Ochoa Programme for Centres of Excellence in R&D ” (CEX2018-000797-S). The authors would like to acknowledge Prof. Mahmoud Hussein, for the insights behind the physics of the coupled resonances mechanism. Finally, the authors would like to gratefully acknowledge Prof. Jordi Romeu and the LEAM group for facilitating the realization of the experimental part of this work.

Este trabajo expone las medidas adoptadas en el cambio de docencia presencial a no presencial en las asignaturas de Teoría de Máquinas y Mecanismos y Vibraciones Mecánicas en la Escuela Técnica Superior de Ingeniería Industrial de Barcelona. Se mantuvo el horario habitual de las clases de los diferentes grupos, pero la primera parte de la clase estaba dedicada a que el alumnado visualizara y comprendiera vídeos de teoría o problemas y la segunda parte, en directo, a resolver dudas. El sistema de evaluación se mantuvo. El examen parcial de TMM consistió en un cuestionario secuencial síncrono de 10 preguntas multirespuesta y numéricas, no relacionadas entre ellas, y con variación aleatoria de parámetros. El examen final consistió en la resolución de tres problemas de forma secuencial, dos de corrección automática con variación de parámetros, y uno de corrección manual, con variaciones, que los alumnos debían entregar en el campus digital de la asignatura. El examen parcial de Vibraciones Mecánicas se substituyó por la resolución de dos ejercicios realizados en grupos de tres alumnos y el examen final mantuvo su formato habitual de cuestionario y problema. Una conclusión del trabajo que se presenta es que, a pesar de poner muchas dificultades para evitar la copia por parte del alumnado, la tasa de aprobados en ambas asignaturas fue muy superior a la media de los últimos años desde que se implantaron los nuevos planes de estudio.

Forging dies are crucial in forging to manufacture accurate workpieces. These dies are generally made of AISI H steel series and hardened and tempered medium carbon alloy steel. Dies are processed by using high-speed milling + polishing or electrical discharge machining + polishing. The surface quality of the workpiece depends on the surface properties of these dies, where surface roughness, material hardness, and wear evolution of their surfaces are critical aspects to consider. This research analyzes different wire electrical discharge machining surface conditions combined with polishing treatment to describe their influence on friction and wear. Wire electrical discharge machining defines the disks’ surface properties in finishing and roughing conditions, and polishing treatment varies in time and paper sand depending on the roughness. Abbott-Firestone curves and Rsk-Rku roughness parameters characterize the surface roughness of each studied configuration. Room temperature pin-on-disk tests were performed to analyze friction coefficients and wear rate for AISI 1045 pins and AISI H13 disks. On average, the highest (0.284) and the lowest (0.201) friction coefficients were found for the combination of finishing wire electrical discharge machining + polishing and roughing wire electrical discharge machining conditions, respectively. Scanning electron microscope images were taken to describe the wear tracks and pin degradation for different sliding abrasive configurations. The diagram correlating the surface morphology and the friction coefficient predicts the wear damage on initial surface conditions, which is crucial in the forging industry to determine tool maintenance or replacement. Fil: Sánchez Egea, Antonio J. Universitat Politècnica de Catalunya; España Fil: Martynenko, Vitaliy. Instituto Nacional de Tecnología Industrial. INTI-Mecánica; Argentina Fil: Simoncelli, Alejandro. Instituto Nacional de Tecnología Industrial. INTI-Mecánica; Argentina Fil: Serrancoli, Gil. Universitat Politècnica de Catalunya; España Fil: Martínez Krahmer, Daniel. Instituto Nacional de Tecnología Industrial. INTI-Mecánica; Argentina

Computational prediction of 3D crutch-assisted walking patterns is a challenging problem that could be applied to study different biomechanical aspects of crutch walking in virtual subjects, to assist physiotherapists to choose the optimal crutch walking pattern for a specific subject, and to help in the design and control of exoskeletons, when crutches are needed for balance. The aim of this work is to generate a method to predict three-dimensional crutch-assisted walking motions following different patterns without tracking any experimental data. To reach this goal, we collected gait data from a healthy subject performing a four-point non-alternating crutch walking pattern, and developed a 3D torque-driven full-body model of the subject including the crutches and foot- and crutch-ground contact models. First, we developed a predictive (i.e., no tracking of experimental data) optimal control problem formulation to predict crutch walking cycles following the same pattern as the experimental data collected, using different cost functions. To reduce errors with respect to reference data, a cost function combining minimization terms of angular momentum, mechanical power, joint jerk and torque change was chosen. Then, the problem formulation was adapted to handle different foot- and crutch-ground conditions to make it capable of predicting three new crutch walking patterns, one of them at different speeds. A key aspect of our algorithm is that having ground reactions as additional controls allows one to define phases inside the cycle without the need of formulating a multiple-phase problem, thus facilitating the definition of different crutch walking patterns.