Cable Robot Performance Evaluation by Wrench Exertion Capability

Although cable driven robots are a type of parallel manipulators, the evaluation of their performances cannot be carried out using the performance indices already developed for parallel robots with rigid links. This is an obvious consequence of the peculiar features of flexible cables-a cable can only exert a tensile and limited force in the direction of the cable itself. A comprehensive performance evaluation can certainly be attained by computing the maximum force (or torque) that can be exerted by the cables on the moving platform along a specific (or any) direction within the whole workspace. This is the idea behind the index-called the Wrench Exertion Capability (WEC)-which can be employed to evaluate the performance of any cable robot topology and is characterized by an efficient and simple formulation based on linear programming. By significantly improving a preliminary computation method for the WEC, this paper proposes an ultimate formulation suitable for any cable robot topology. Several numerical investigations on planar and spatial cable robots are presented to give evidence of the WEC usefulness, comparisons with popular performance indices are also provided

What is a model, why people don't trust them, and why they should

It is easier to make one�s way in the world if one has some sort of expectation of the world�s future behaviour. Even when facing a very complex problem, we are rarely in a state of full ignorance: some expectations of system behaviour and the level of risk arising from uncertainty are usually available and it is on the basis of these expectations that most decisions are taken. Humans use models, which are mental or formal representations of reality, to generate these expectations, employing an ability that is shared more or less by all forms of life. Whether it is a tree responding to shortening day length by dropping its leaves and preparing its metabolism for the winter ahead or a naked Pleistocene ape storing food in advance of winter for the same reasons, both are using models. This view leads to two outcomes. The first is that predictions, seen as an expectation of ranges of future behaviours, are not just desirable, but necessary for decision-making. The often-asked question �do models provide reliable predictions?� then shifts to �given a certain problem, what type of models provide the most useful and reliable prediction?� The second outcome is that modelling is no longer a scientist�s activity but is instead a social process. Different types of models can be employed to ensure that all available information is included in model building and that model results are understood, trusted and acted upon

The implications of the social welfare reform on the Brazilian social security

A Seguridade Social aprovada na Constituição Brasileira de 1988 não foi implementada conforme previsto na Carta Magna. As sucessivas reformas do Estado e, sobretudo, da previdência social,1 implementadas ao longo da década de 1990, justificadas sob a alegação de um suposto déficit entre receita e despesa, vêm contribuindo para descaracterizá-la enquanto sistema de proteção social, além de favorecer a fragmentação das políticas sociais que a integram: previdência, saúde e assistência. Ao tratar a previdência como seguro e não como política social, estas reformas tendem a minar e corroer as bases conceituais e financeiras da seguridade social, solapando a possibilidade de sua consolidação como propriedade social.The social security system approved in the Brazilian Constitution of 1988 was not implemented. The successive reforms of the State and, above all, of social welfare1, implemented during the 1990 decade, justified under an allegation of a supposed deficit between revenue and expenditure, have been contributing to make them to lose the characteristics of a system of social protection, and favoring, moreover, the fragmentation of the social policies that integrated: welfare, health and assistance. These reforms deal with the welfare system as insurance and not as a social policy. By doing this they tend to undermine and to waste the conceptual and financial basis of the social security, digging the possibility of its consolidation as social propriety

Intensification of barbarism and challenges to Social Work

A crise estrutural do capital agudiza as expressões da questão social e revela a barbárie cotidiana que assola sem trégua a classe trabalhadora. Avolumam-se as demandas ao Serviço Social, sobretudo em decorrência da supressão dos direitos e do processo de pauperização em contexto de avanço acelerado do reacionarismo e do conservadorismo no Brasil. Velhos e novos desafios reafirmam a pertinência do Projeto Ético-Político profissional.The structural crisis of capital intensifies the expressions of the social issue, and it reveals the daily barbarism that ravages the working class restlessly. The demands on Social Work increase, mainly due to the suppression of rights and the process of pauperization in the context of the accelerated advances in reactionarism and conservatism in Brazil. Both old and new challenges restate the relevance of the professional ethical and political project