Vehicles equipped with omnidirectional wheels can move in any direction, which means that many driving strategies are available, even for a simple task like turning a corner. However, the characteristics of each driving strategy have not yet been explored to detect what kind of strategy is suitable for what path conditions for what reasons. This study aims to clarify and compare the phenomena that occur in the possible least-time driving strategies for an omni-wheeled vehicle while it turns a corner. Three traveling strategies are proposed according to the order of rotation and turning motion, for which the possible least-time patterns are presented. Simulations are conducted to analyze the advantages of each pattern and compare the three traveling strategies for various path and corner configurations. The results show that the strategy in which the vehicle rotates during or after turning motion costs the least time. When both the path width and corner angle are small, the vehicle should turn with a large radius to maintain a high velocity. In contrast, the vehicle should turn with a small radius when the corner angle is large, even if this requires deceleration.

Mobile parallel mechanisms (MPMs), which are parallel mechanisms with moveable bases, have previously been proposed to resolve the limited workspace of conventional parallel mechanisms. However, most previous studies on the subject focused on the kinematic analysis of some specific MPMs and did not discuss a type synthesis method for MPMs. With this in mind, we propose a screw theory-based type synthesis method to find out possible 6-degrees-of-freedom (DOF) MPM structures. In our proposed method, the 6-DOF mobility is divided into 3-DOF planar motion and 3-DOF spatial motion, both of which are realized by the transmitted planar motions of the driving units. Separately, the type synthesis of the entire MPM is divided into that of the driving unit and connecting chain. To realize 3-DOF spatial motion, two methods, applying singularity configuration and adding an additional chain, are proposed as ways to restrict undesired motions for the synthesis of the connecting chain. The driving unit is synthesized via the same type-synthesis method as the connecting chain by considering the driving unit as a planar mechanism. The method used to integrate the driving unit and the connecting chain was constructed based on whether the end pair of the connecting chain should be connected with the driving unit directly or driven by it through an actuating mechanism. As a result, 284 possible types of MPM structure are suggested and four examples of MPMs with six DOFs were synthesized to verify the feasibility of the proposed method.

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