Design, modeling and implementation of a biphasic media variable stiffness actuator

Nowadays, an increasing number of industrial processes are expected to have robots interacting safely with humans and the environment. Compliance control of robotic systems strongly addresses these scenarios. This thesis develops a variable stiffness actuator (VSA) whose position and stiffness can be controlled independently. Actuator’s stiffness is controlled by changing pressure of control fluid into distribution lines. The used control fluid is biphasic, composed of separated gas and liquid fractions with predefined ratio. Firstly, an approach for the mathematical model is introduced and a model-based control method is implemented to track the desired position and stiffness. Results from force loaded and unloaded simulations proved the feasibility of these methods. Based on the previous outcome, a compliant revolute joint mechanism was modeled and implemented in order to use it as a test bench for the VSA. The mechanism is able to track position and stiffness accurately; however, better mechanical design and manufacturing methods are suggested in order to avoid excessive friction. Later on, a momentum-based collision detection and reaction algorithm is proposed, simulated and tested on the mechanism. Experimental results confirm that this method can be used to attain a higher level of safety in the system. Finally, a compliant cable-driven revolute joint using biphasic media variable stiffness actuators is modeled and simulated. This cable-driven mechanism is characterized by a wide range of stiffness and high-power output

Seismic Behavior of Cross laminated Timber (CLT) Structural Systems: from Traditional Steel Connections to Low-Damage Solutions

Timber buildings have always showed great performances, even if past timber structural systems are no longer adequate to fulfil modern building standards. The key aspect of CLT buildings, as for timber constructions in general, are the connection systems. Nowadays, design of CLT wall connections is based on the hypothesis that hold-down connection is subjected only to tension, while angle bracket only to shear. Nevertheless, experimental highlighted that the two types of connection may be subjected to significant displacements in both directions, thus to coupled actions. The first part of this study presents results from an extensive experimental campaign conducted on traditional connections for CLT buildings using a specific setup that allowed to impose prescribed levels of displacements in secondary direction, varying at the same time the main direction displacement in a cyclic and monotonic manner. A total of fifteen specimens, for each connection type, are presented and critically discussed in terms of load-displacement curves, strength, stiffness, energy dissipation, strength degradation and ductility. The second part of the thesis focuses on an experimental and numerical investigation of a two storey 2/3 scaled CLT hybrid rocking wall. The applicability and the response of this relatively new low-damage solution has been studied for the first time applied on a CLT shear wall. The CLT wall included post-tensioned bars to provide self-centring capabilities and replaceable external steel dissipaters to accommodate energy dissipations. Furthermore, an experimental solution for the dissipater-wood panel link has been implemented. Results are presented in terms of achieved lateral force, overturning moment capacity, variation in the post-tension force, oscillation of the neutral axis depth and energy dissipation. Lastly, a numerical simulation accompanied experimental evidences, to examine the response of the rocking system for higher level of drifts, going beyond test limits