Cross-coupled controllers have been proposed for improving contouring accuracy of multiaxis machine tools. However, during cross-coupled motion control, increasing contour feedrate may result in larger contour errors. In order to increase feedrate and hence productivity without sacrificing the contouring performance, this paper presents an adapative feedrate control strategy based on a linear perturbed model. The method effectively closes the feedback loop between the contour error and feedrate. An experimental biaxial control system is constructed to implement the proposed strategy. Both computer simulation and experiments have verified that desired contouring accuracy can be achieved.
A novel 8U (universal joint) parallel mechanism, being able to do omnidirectional rolling motion is proposed in this paper. This mobile mechanism owns the priority of simple structure and rolling easily on terrains with loose soil, dirt or sand with only a few actuations. Its spatial closed compact structure is described firstly. In addition, the omnidirectional locomotion accompanied with DOF (degree of freedom) alternation between one and two is revealed by mobility analysis. After that, the feasibility of rolling motion is verified theoretically by stability analysis. Finally, the omnidirectinoal rolling motion is testified both by virtual and prototype experiments.
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