Gabriele Biondi

Design and test of a parallel kinematic solar tracker

This article proposes a parallel kinematic solar tracker designed for driving high-concentration photovoltaic modules. This kind of module produces energy only if they are oriented with misalignment errors lower than 0.4°. Generally, a parallel kinematic structure provides high stiffness and precision in positioning, so these features make this mechanism fit for the purpose. This article describes the work carried out to design a suitable parallel machine: an already existing architecture was chosen, and the geometrical parameters of the system were defined in order to obtain a workspace consistent with the requirements for sun tracking. Besides, an analysis of the singularities of the system was carried out. The method used for the singularity analysis revealed the existence of singularities which had not been previously identified for this kind of mechanism. From the analysis of the mechanism developed, very low nominal energy consumption and elevated stiffness were found. A small-scale prototype of the system was constructed for the first time. A control algorithm was also developed, implemented, and tested. Finally, experimental tests were carried out in order to verify the capability of the system of ensuring precise pointing. The tests have been considered passed as the system showed an orientation error lower than 0.4° during sun tracking.

Control of a Noncooperative Approach Maneuver Based on Debris Dynamics Feedback

Space Debris removal is a critical issue related to space research. One of the key requirements for a removal mission is the assessment of the target rotational dynamics. Ground observations are no...

Vision-based localization of the center of mass of large space debris via statistical shape analysis

The current overpopulation of artificial objects orbiting the Earth has increased the interest of the space agencies on planning missions for de-orbiting the largest inoperative satellites. Since this kind of operations involves the capture of the debris, the accurate knowledge of the position of their center of mass is a fundamental safety requirement. As ground observations are not sufficient to reach the required accuracy level, this information should be acquired in situ just before any contact between the chaser and the target. Some estimation methods in the literature rely on the usage of stereo cameras for tracking several features of the target surface. The actual positions of these features are estimated together with the location of the center of mass by state observers. The principal drawback of these methods is related to possible sudden disappearances of one or more features from the field of view of the cameras. An alternative method based on 3D Kinematic registration is presented in this paper. The method, which does not suffer of the mentioned drawback, considers a preliminary reduction of the inaccuracies in detecting features by the usage of statistical shape analysis.

Analysis of Constraint Singularities of a 2-DOF Spatial Parallel Mechanism

This paper considers the kinematic analysis of a 2 dof closed-loop chain for the night-sky observation known as the Canterbury tracker. Closed-loop mechanisms are characterized by a higher number of joints than dofs, so kinematic constraints act to make dependent their configurations. For some configurations of the joints, it is possible that one or more constraints become redundant, giving instantaneously extra dofs to the mechanism. Thus, conventional input-output singularities do not represent the unique possibility of having controllability issues. In this paper, the screw theory is exploited to determine singular configurations of the proposed trackers. According to the results of this analysis, the geometric parameters of the mechanism are chosen to make it suitable for solar tracking purpose, taking into account the existence of these singular configurations to avoid tracking failures.