APT'07 International Conference on Applied Production Technology, 17.09.-19.09.07, Bremen
In milling operations the productivity is partly related to the machine dynamics and the achievable path accuracy at the tool center point (TCP). Considering large parts, this objectives yield to a conflict. Long ranges demand huge machine dimensions and high accuracy demands a high stiffness leading to mechanisms with high inertia and a therefore bad dynamic behavior in consequence. New design concepts like parallel kinematic machines (PKM) are studied intensively to overcome this restriction. When the kinematic chains are closed loops, a higher structural stiffness is proposed with a lower amount of moved masses but unfortunately the working space of PKM is strongly restricted when linear motions with high speed and high accuracy are demanded. Underlaid serial axes with long travel can carry a PKM and thus spread the local advantages over a wide range. Resulting redundant degrees of freedom (DOF) contribute to further optimization concerning agility and precision. The paper presents a general design method for trace segregation filters that restrict travels and velocities of the sub-kinematics and fulfill important trace preparation features with a general decrease of individual acceleration demands and an automatic centering of the small sub-space. Machining time estimations for some kinematic concepts are introduced to aid the process of structural synthesis of the partial mechanisms. An experimental milling machine with kinematic redundancy in the plane demonstrates the effectiveness of the proposed methods.