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This paper is devoted to the design of a control system for the attenuation of vibrations in the main rotor of a helicopter in forward flight. The problem can be formulated as the one of rejecting a periodic disturbance of known frequency acting at the output of a linear time-periodic system. A solution inspired to optimal control design methods is proposed. A major preliminary issue is the estimation of the characteristics of the disturbance, for which two methods are worked out. The performance of the obtained control system is assessed by means of several simulation trials.

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In the literature, a number of interesting control schemes has been proposed for telemanipulation robotic systems. Because of the intrinsically non constant and large time delay, due to the communication channel, passivity has been largely used in these schemes in order to achieve stability of the overall teleoperation system. In this paper, the application to this context of a control scheme based on the equivalence with passive physical systems is discussed. This scheme allows to achieve stability and good performances also in cases where the time-delay is not constant. Moreover, the multi-dimensional case is taken into account, considering tasks in which not only linear motions/forces are present but also rotations and torques. Simulation results are presented and discussed.

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