Abstract
Parallel manipulators (PMs) have been there for more than half a century and they have been subject of intensive research. In comparison with their serial counterparts, PMs consist of several kinematic chains that connect the fixed base to the moving platform. The interest in such architectures is due to the several advantages they offer, among which we mention: high rigidity and payload-to-weight ratio, elevated dynamical capabilities due to reduced moving masses (especially when the actuators are at or near the base), better precision, higher proper frequencies, etc. Nevertheless, despite of the aforementioned merits, their exploitation as machine tools is still timid and limited, in which they most often do not exceed the research and prototyping stages at university laboratories and machine tool manufacturers. The main drawbacks that hinder the widespread of parallel kinematic machines (PKMs) are the following: limited operational workspace and tilting capacity, presence of singular configurations, design complexities, calibration difficulties, collision-related problems, sophistication of control (especially in the case of actuation redundancy), etc. Besides, though PMs have met a great success in pick-and-place applications, thanks to their rapidity (acceleration capacity), still their precision is less than what has been initially anticipated. On the other hand, extremely precise PMs exist, but unfortunately with poor dynamic performance. Starting from the aforementioned problematics, the current thesis focuses on obtaining PKMs with a good compromise between rapidity and precision. We begin by providing a survey of the available literature regarding PKMs and the major advancements in this field, while emphasizing the shortcomings on the level of design as well as performance. Moreover, an overview on the state of the art regarding performance evaluation is presented and the inadequacies of classical measures, when dealing with redundancy and heterogeneity predicaments, are highlighted. In fact, if finding the proper architectures is one of the prominent issues hindering PKMs' widespread, the performance evaluation and the criteria upon which these PKMs are dimensionally synthesized are of an equal importance. Therefore, novel performance indices are proposed to assess precision, kinetostatic and dynamic capabilities of general manipulators, while overcoming the aforementioned dilemmas. Subsequently, several novel architectures with 3T-2R and 3T-1R degrees of freedom (T and R signify translational and rotational degrees of freedom), namely MachLin5, ARROW V1, and ARROW V2 with its mutated versions ARROW V2 M1/M2, are presented. Furthermore, the dimensional synthesis of the executed PKM, namely ARROW V2 M2, is discussed with its preliminary performances and possible future enhancements, particularly regarding precision amelioration.