Fundamentals for the application of eccentric joints in parallel kinematic machine tools

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Parallel kinematic machine tools have advantages relating stiffness and motion dynamics com- pared to serial kinematic machines. However their application range is still limited. Looking for rea- sons often yields a non-efficient provision of motion accuracy as well as an insufficient workspace. In either case the passive joints used in the kinematic structure pose essential weak points. In general the intersection of the rotational joint axes is claimed. This simplifies the kinematic model but also has drawbacks. The design potentials are strongly limited, as a matter of principle. High joint stiffness and a large pivoting range are conflicting demands. The design and manufacturing of the joints is constrained to compromises. As of today optimized solutions lead to expensive special purpose designs, which restrict their economic application.Aim of the project is the enhancement of the application range of PKMs by avoiding joint specific drawbacks using an alternative joint design. The approach is to abandon the claim of intersecting joint axes, leading to eccentric joints. As a consequence a large pivoting range and a high joint stiffness are no longer conflicting demands. Though the idea of eccentric joint axes is not really new, their use in PKMs still lacks basics in theory, design as well as application specific aspects. In this project these basics are developed and proved by experimental investigations of eccentric joint as single parts as well as applied to a PKM. The working program is divided into two sections. The first section of the project focused on eccen- tric joints as single parts. Herein, promising results have been reached. The second section of the project now has its focus on the overall system of the PKM with eccentric joints. Application specific basics are to be developed and investigated. This relates on the one hand to control specific requirements for a safe and accurate usage of the enhanced motion capabilities and on the other hand to the derivation of statements about the enhancement of overall system properties realizable with eccentric joints. Extensive experimental investigations are planned here on the example of the hexapod FELIX of the IWM Dresden. This test bed ensures for investigations of different joint con- figurations in the same machine structure with identical conditions and thus for an optimal comparability of the results.