1,720,971 research outputs found
Kinematic and dynamic modeling of a helicopter rigid main rotor
No full textAnalysis of the kinematics and dynamics of a helicopter main rotor is presented in the paper. A rigid rotor type is assumed, where feathering angle of the blade is controlled by a swashplate mechanism. Kinematic constrains and links equilibrium are studied in order to determine the mechanism movement and the forces on the servoactuators which drive the swashplate position and orientation. The modeling presented is intended to be part of a simulation platform to evaluate fly-bywire actuation systems performances applied to helicopter main rotors contro
Sun follower with parallel kinematics and process for controlling such follower
Full text linkIl brevetto riguarda un inseguitore solare a cinematica parallela e il relativo sistema di controll
Evaluation of the factors affecting the optimal fiducial configurations calculated through a genetic-algorithm-based methodology in image-guided neurosurgery
No full textBackground Image-guided neurosurgery usually involves a point-pair registration between two spaces, associating the patient in the operating room with pre-operative image scans. The distribution and number of fiducial markers during registration are critical for the expected error at the target point. Methods A genetic algorithm has been designed to provide an optimal marker configuration. The solution, visualized on a 3D head reconstruction, is intended as a guideline for the surgeon to properly place the markers. However, deviations from ideal configurations occur during marker placement; moreover, the actual target is not a point, but a region. The consequent decrease of target accuracy is statistically investigated. Results A requirement on target minimum accuracy can be satisfied in the operating room not only by setting the number of markers for the optimized fiducial configuration, but also by considering the inevitable sources of error. Conclusions Quantifying the sources of error that affect a genetic-algorithmbased optimization shows that it is still convenient. Target point correct individuation is particularly important, as it strongly influences the optimization performanc
Design and test of a parallel kinematic solar tracker
Full text linkThis 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
Experimental comparison of functional methods to determine average axis of rotation in polycentric knee
No full textAn alternative technical marker set to improve pelvis tracking in clinical applications.
No full textStiffness of an EVA glove: objective evaluation and testing procedures
No full textHand fatigue is one of the major problems of astronauts during Extravehicular Activity (EVA), due to the stiffness of the space suit, in particular of the glove. In order to evaluate the stiffness of EVA gloves, different methods have been proposed in the past, mainly focused on the effects of wearing an EVA glove on hand performance when executing test protocols. In this paper, an objective method for the evaluation of the stiffness of EVA gloves is proposed, by means of a tendon-actuated finger probe. The finger probe is equipped with accelerometers, to measure the angles of its phalanges. These are actuated by applying different torques using the finger probe tendons. The EVA glove is tested in both pressurized and non pressurized conditions, thanks to a hypobaric glove box. An Orlan-DM EVA glove is tested and stiffness results are presented. This setup can be used for different kinds of gloves, not necessarily for EVA application, and allows direct, numerical measurement of their stiffnes
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