No abstract

No abstract

No abstract

This paper proposes some new nonlinear dynamic models for single-link flexible manipulators that experience large deflections. These models are developed under the assumption of a very lightweight arm with all its mass concentrated at the tip. Two models are proposed that are validated experimentally. The first of them is the typical linear model. The second one is a new nonlinear model that exhibits the advantages of being very simple while being very accurate too. Compared with the previously defined models, which are based on finite elements numerical techniques, our models are described by nonlinear ordinary differential equations that are well suited for analysis and design of closed loop control systems for tip positioning.

This article deals with feedforward control of very lightweight, flexible robotic arms. In particular, we develop a new, objective method of designing a trajectory that can be used as a modified input, to cancel tip vibrations during robot manoeuvres. This method takes into account the constraints found in real actuators (DC-motors), such as the maximum torque the motor can supply, and also those due to the mechanical limits of the link, like the maximum deflection before reaching the elastic limit of the link. The parameters of the internal control of the actuators are also derived from the design process, achieving the fastest performance possible without saturating the motor. Lastly, we show some experimental results which clearly demonstrate the benefits of the new trajectories by comparing them to a ramp one.

No abstract

Throughout the last decades, collaborative schemes, under an amalgam of different acronyms (ECR, CPFR, VMR, etc.), have been developed to mitigate the problematic Bullwhip effect. Essentially, companies work together by either sharing information, making joint decisions, or sharing benefits to reach potential synergies. This work aims at reviewing these works through a systematic literature review process to investigate the different collaborative models from an operational perspective. A total of 92 articles have been classified into 3 categories: Information Exchange; Vendor Managed Replenishment; and Synchronized Supply Chain. For each category, we have identified the type of research, supply chain structures, forecasting models, demand characteristics, replenishment policies and assumptions employed in the considered articles. This article identifies the main results achieved and the gaps and opportunities to be developed as further research.Among the SCM challenges, one of the most fascinating problems is the Bullwhip effect, which can be defined as the demand variability amplification as one move upwards in the supply chain. These fluctuations reduce supply chain effectiveness, decrease the service level and raise costs [10][11][12]. The first time Forrester, the forefather of the debate in the literature for over six decades, mentioned this phenomenon dates back to 1958 [13,14], but the term Bullwhip effect (BWE) or Forrester effect was not coined until 1997 by [16]. Note that Forrester effect [14] is more related with the Demand Signal Processing called in the past Demand Amplification. For the interested reader, see reference [15]. Sometimes, it is also referred as "the first law of supply chain dynamics" [11]. This effect and its consequences have been subject of numerous studies [16][17][18][19][20][21].BWE is very related to the uncertainty that takes place in a company when executes its own processes, keeping in mind only the information they have in their stand-alone Enterprise Resource Planning (ERP) system within the supply chain [22]. It is considered one of the major causes of inefficiency in SCM [23]. BWE has pernicious effects such as: excessive inventory investments along the supply chain, lower customer service, lost revenues due to shortages, and reduced productivity of capital investment, amongst other inefficiencies [24]; and causes losses of up to 30% of manufacturing profits [17]. Surveys of the BWE literature can be found in [22, 23]. Giard and Sali [23] study 53 articles between 1997 and 2011 and explore 13 axes of analysis such as supply chain structure or demand and inventory control models in order to analyze the causes of the BWE in the productive part of the automotive industry supply chain. Wang and Disney [22] cited 150 articles out of 455 papers that were reviewed. In that reference, the methodologies employed in BWE research were categorized into: empirical, experimental, analytical and simulation-based. The influence of demand, type of forecasting technique, time delay and ...

Resumen: Este breve trabajo pone de relieve la importancia de la educación para la ciudadanía a la vez que plantea la necesidad de revisar su sentido a la luz de nuevas demandas y retos, tanto sociales como políticos. Pero también llama la atención sobre los límites de cualquier sistema educativo visto como solución directa a los mismos. Asimismo, esta contribución sirve para presentar el monográfico «Educación para la ciudadanía: significado y experiencias». Se trata de un número especial que, en su primera parte, plantea algunos análisis y reflexiones teóricas que ayudan a entender qué se debe o se puede esperar de una educación ciudadana. A continuación, dos artículos analizan la formación inicial del profesorado en educación para la ciudadanía en distintos niveles educativos. Por último, se ofrece una panorámica sobre algunas líneas y contextos de investigación en educación para la ciudadanía así como de experiencias prácticas relacionadas con la temática tanto dentro como fuera de los centros educativos.Palabras clave: ciudadanía; educación ciudadana; educación para los derechos humanos; democracia; política.Abstract: This brief paper highlights the importance of education for citizenship while raises the need to revise its sense in light of new demands and challenges, both social and political. But it also draws attention to the limits of any education system seen as a direct solution to them. With this contribution the monographic «Citizenship Education: meaning and experiences» is presented. This is a special issue that in its first part presents some analysis and theoretical reflections that help to understand what should or can be expected of a civic education. The following are two articles analyze the initial teacher training on citizenship education in different educational levels. Finally, an overview of some lines and research contexts about citizenship education and practical experiences related to the topic both inside and outside of schools is offered.