Dipartimento di Ingegneria Industriale DIN

This paper studies the trajectory planning for underactuated cable-driven parallel robots (CDPRs) in the case of rest-to-rest motions, when the motion time and the path geometry are prescribed. For underactuated manipulators, it is possible to prescribe a control law only for a subset of the generalized coordinates of the system. However, if an arbitrary motion is prescribed for a suitable subset of these coordinates, the constraint deficiency on the end-effector motions leads to the impossibility of bringing the system at rest in a prescribed time. In addition, the behavior of the system may not be stable, that is, unbounded oscillatory motion of the end-effector may arise. In this paper, we propose a novel trajectory-planning technique that allows the end-effector to track a constrained geometric path in a specified time, and allows it to transition between stable static poses. The design of such a motion is based on the solution of a Boundary Value Problem, formulated as the problem of finding a solution to the differential equations of motion, with constraints on position and velocity at start and end times. To prove the effectiveness of such a method, the trajectory planning of a 6-Degree-of-Freedom spatial CDPR suspended by 3 cables is investigated. Trajectories of a reference point on the moving platform are designed so as to ensure that the assigned path is tracked accurately and the system is brought to a static condition in a prescribed time. Experimental validation is presented and discussed.

The stability of superconducting wires is a crucial task in the design of safe and reliable superconducting magnets. These magnets are prone to premature quenches due to local releases of energy. In order to simulate these energy disturbances, various heater technologies have been developed, such as coated tips, graphite pastes, and inductive coils. The experiments studied in the present work have been performed using a single-mode diode laser with an optical fiber to illuminate the superconducting strand surface. Minimum quench energies and voltage traces at different magnetic flux densities and transport currents have been measured on an LHC-type, Cu/NbTi wire bathed in pool boiling helium I. This paper deals with the numerical analysis of the experimental data. In particular, a coupled electromagnetic and thermal model has been developed to study quench development and propagation, focusing on the influence of heat exchange with liquid helium.

ABSTRACT This paper is focused on methods to indicate the environmental impact in terms of air pollutants of CHP (Combined Heat and Power) systems. The aim is to combine the energy saving achievement with information concerning the environmental benefit, in comparison with the non-CHP scenario. Environmental impact of CHP production both on global and local scale should be taken into account. In particular, the method of the "Avoided Heat Generator" is highlighted in this study as a proper approach for CHP and is used for a local-scale environmental impact evaluation. This approach calculates the reduction of emission due to CHP operation, taking into account the amount of pollutant emitted by an equivalent heat generator, which provides the same thermal power of the CHP prime mover. Moreover, the recommended approach is compared in the paper with another proposed method, based on the PSI (Pollutant Saving Index) value, which is suitable to estimate the global-scale environmental impact. Numerical evaluations of the CUP environmental benefits, in terms of NOx, CO and CO2 emissions, are shown for several CHP systems with different technologies and electric power sizes, in order to provide a comprehensive overview of current CUP prime mover environmental performance and to serve as an application reference example of the two methods potential use, in the framework of the CUP units authorization procedure. The significant effect of the reference comparative scenario is also highlighted.

Load and wind energy profiles are totally uncorrelated, therein lies the problem of variable energy sources. Managing load with increasing wind penetration may call for operational ranges that conventional systems cannot readily access. Storage technologies could allow tolerating the unsteadiness of renewable sources with smaller fossil fuel plants capacity.