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This paper discusses an adaptation of modal analysis concepts to time-varying periodic systems. It will be shown that the pseudo-modal parameters preserve certain properties of the conventional modal parameters defined for LTI systems. For this reason, after definition of pseudo modal parameters for time varying systems, a new modal analysis method will be introduced in time domain and it will be shown that these parameters could explain the nature of system. For periodic time varying systems, state transition matrices are formed by an ensemble set of responses which are obtained through multiple experiments on the system with the same time varying behavior. In next step the pseudo natural frequencies of a beam with moving mass using introduced method will be extracted. In final, it will be proved that for a linear time periodic system, the pseudo natural frequency treats periodic too.

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Buckling and vibration characteristics of thin symmetrically laminated elliptical composite plates under initial in-plane edge loads and resting on Winkler-type elastic foundation are presented based on the classical laminated plate theory. The governing equations are obtained from the variational approach and solved by the Ritz method. Extensive numerical data are provided for the first three natural frequencies as a function of in-plane load for various classical edge conditions (free, clamped and simply supported). Moreover, the effects of fiber orientation on the natural frequencies and buckling loads of laminated angle-ply plates with stacking sequence of [(β /-β / β /-β)]s, are studied for chosen foundation parameter. Also, selected deformation mode shapes are illustrated. The accuracy of calculations is checked by performing good convergence studies, and the correctness of results is established by comparison with the existing results in the literature as well as FEM data.

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In this study, considering slippage between a robot end-effector and an object, adaptive control of a one-finger hand manipulating an object is explored. This system is a good sample to develop different techniques such as grasp analysis, grasp synthesis, stability analysis and designing different types of controller for cooperative manipulator systems. Due to the presence of inequality equations in frictional point contact modeling, a novel formulation is developed to replace the equality and inequality equations with a single second order differential equation with switching coefficients. Introducing this new friction contact model, an input-output conventional form is derived using the equality and inequality equations of motion of the system. Using this new form of motion equations, two adaptive controllers with simple update laws are proposed that both of them ensure the asymptotic convergence of the object position tracking as well as slippage control while compensating the system uncertainties. The first controller compensates the uncertain masses of the manipulator links and the object while the second one compensates the uncertain coefficients of friction. Numerical simulation is utilized to evaluate performance of the proposed controllers.

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Using the soft fingers increases stability and dexterity in object grasping and manipulation. This is because of the enlarged contact interface between soft fingers and object. Although slippage phenomenon has a crucial role in robust grasping and stable manipulation, in the most of previous researches in the field of finger manipulation, it is assumed that the slippage between finger and object does not occur. In this paper, slippage dynamic modeling in object grasping and manipulation using soft fingers is studied. Because of the enlarged contact interface between soft fingers and object, a frictional moment along with tangential frictional force and normal force is applied on the contact interface. Therefore, a novel method for dynamic modeling of planar slippage using the concept of Friction Limit Surface is presented. In this method, equality and inequality relations of different states of planar contact is rewritten in the form of a single second-order differential equation with variable coefficients. These coefficients are determined based on the slippage conditions. This kind of dynamic modeling of contact forces can be used for designing the controllers to cancel the undesired slippage. The method is used in study of slippage analysis of a three-link soft finger manipulating a rigid object on a horizontal surface. In order to increase the accuracy of dynamic modeling of soft finger, dynamics of soft tip is integrated with the dynamic of finger linkage. Dynamic behavior of this system is shown in the numerical simulations.

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This paper presents a new approch in the design of output feedback control system based on disturbance observer for dynamic positioning vessels. The proposed control system includes a controller and a structure of a modified notch filter and a nonlinear observer. The filter is used for estimating low-frequency motions and removing the wave-frequency motions by using vessel position mesurement. The low-frequency disturbances and vessel-velocites are estimated in nonliner observer using the low-frequency vessel motion. In this structre, wave filtering and low-frequency motion estimation are independent from the estimation of low-frequency disturbances and vessel velocities. It causes to incease the accuracy of filtering and estimation which results in desirable performance of control system. Also, filtering is independent of the vessel and low frequency disturbances models, and therefore it is not affected by modeling uncertainty. The effect of wave filtering and low-frequency disturbances estimation in DP control system from the point of reducing control signal flactutions were evaluated with numerical simulation. This is important in view of reduction of wear and tear in propaltion system and fuel consumption in a surface vessel. Futhermore, simulation results show that the proposed method has better performances in comparision with conventional method.

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This paper presents the problem of controlling multiple tasks in a prioritized scheme during accidental external physical interaction with redundant robot. This issue arises when robots are employed in social, unknown, dynamic environments for complex and critical missions. Exploiting robot redundancy to ensure safety and compliance during performing hierarchical tasks is considered in this work. A general approach to control the main task (position/orientation of the end-effector) with allocated priorities beside compliance behavior in the null space of the tasks is proposed. External interactions on the robot body are estimated with an appropriate observer without using any force/torque sensors which is further used to bring compliance in the redundant space. A novel task allocation method is proposed and the convergence of the task space error, interaction estimation error as well as null space velocities are guaranteed. Finally, the performance of the method is investigated through computer simulation and real experiments on KUKA robot arm.