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2 2018

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Planning task-based motions of multi-link manipulator models prone to vibration

Jarzębowska E., Augustynek K., Urbaś A.

Vibrations in Physical Systems

2018

Vol. 29

art. no. 2018029

A new method of designing tip-point trajectories for industrial manipulators with structural flexibility and friction in their supports and joints is presented in the paper. The method is based upon the formulation of the reference dynamics model of the manipulator model. The reference dynamics models are derived off-line for desired trajectories, i.e. trajectory patterns are delivered in constraint equation forms. A library of reference dynamics models can be generated off-line and serve for verification of desired motions feasibility, ability of reaching required velocities and accelerations in order to obtain the desired trajectories, and estimate power needed for desired motions execution. It enables off-line tests of a system model behavior when it moves a desired trajectory. Also, the reference dynamics enables verification of vibrations that may accompany desired motions, since at the stage of defining a desired trajectory, e.g. for performing a servicing task, a system behavior is unknown. The paper is dedicated to reference dynamics analysis, for a multi-link manipulator model, for which friction in joints is modeled by the LuGre model, the manipulator links are rigid but light and prone to vibrations. The results of the reference dynamics analysis are presented in a series of simulation studies.

Adaptive slip&slide control system design in railway applications

Uyulan Caglar

Advances in Science and Technology. Research Journal

2018

Vol. 12, no 1

207--220

Adhesion coefficient and the resultant normal force occurred at the wheel-rail contact determine braking and traction forces in railway applications. Due to the limits on controlling the resultant normal force, maximization of the adhesion coefficient is the only way to obtain larger braking and tractive works. There are various advantages of utilization of adhesion in an efficient way, such as reducing operating costs, minimizing trip time, preventing wheel-rail wear. On the other hand, the adhesion mechanism at the wheel-rail contact has a highly non-linear complex nature, whose dynamics are changed as a function of parameters like environmental conditions, vehicle speed, slip ratio etc. There is not any satisfactory accurate and trustworthy way of estimating these parameters yet. In this paper, an event based adaptive control scheme has been introduced to maximize the adhesion coefficient without requiring the exact value of those parameters. The efficient adhesion utilization can be obtained by using the proposed method while maintaining the stability. The continuous excitement of traction system and slow recuperation detection time difficulties in the former research has been overcome. The dynamics of phase shift were analyzed and an adaptive structure were built. Results acquired by using the proposed adaptive method were compared with the conventional control scheme in “Matlab&Simulink” software under various driving scenarios and wheel-rail contact conditions.