While a few proposed control strategies have shown their acceptable effectiveness, performance improvement on stability and robustness of unmanned helicopters are still imperative and a great challenge due to strong nonlinearities, extensive parameter uncertainties and external disturbances when the flight condition is terrible, such as flight on a windy day. Because acceleration feedback control is advantageous in terms of simple controller structure and easy implementation, we attempt to incorporate it into the tracking control of an unmanned helicopter that is highly nonlinear and underactuated. In this paper, we use a prefilter to formulate a new acceleration feedback control and then use it as a robust enhancement for the H 1 algorithm to attenuate uncertainties and external disturbances involved in the tracking control of an unmanned helicopter. We conduct simulations with an unmanned model helicopter and compare the tracking performance of the helicopter with and without acceleration feedback control. The results show that the use of acceleration feedback control does enhance tracking performance greatly compared to the standard H 1 control.
A kinetostatic model and a dynamics model of a parallel ma丑 ipulator (PM) with three grippers are establ四hed and a丑alyzed in the light of its application. First, the coordinative kinematics of this manipulator and three grippers are analyzed. Second, the kinetostatic formulae are derived for transforming the coordinative kinematics and forces applied on the grippers into the workloads applied on the movi吨 platform and the active/co丑 strained forc臼 and torques applied onto active legs. Third, the dynamics formulae are derived for solving dynamic active wrench of grippers a丑d PM by considering inertial mass of the grippers, legs and platform. Finally, a numerical example is given for illustrating application of kinetostatic model and dynamics formulae , and the dynamics solutions of this manipulator are veri丑ed by simulatio丑.
KeyWordsParallel manipulator with multi grippers, coordinative dynamics, coordinative kinetostatics Notation DoF -degree of freedom; PM -paralle1 manipu1ator m , B -p1atform and base of PM 队 , Bi -joints on m and B (i= 1, 2, 3) ωi -the ith claw
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