A New 3-DOF Spatial Parallel Mechanism for Milling Machines with Long X Travel Dragan S. Milutinovic 1 (2), Milos Glavonjic 1 , Vladimir Kvrgic 2 , Sasa Zivanovic 1 1 Mechanical Engineering Faculty, University of Belgrade, Serbia and Montenegro 2 LOLA System, Belgrade, Serbia and Montenegro Abstract It is well known that the shape and volume of the workspace are one of the greatest weaknesses of parallel kinematic machine tools (PKM). Hexaglide and Triaglide mechanisms are examples where workspace extension is achieved by elongating one axis as a principal motion axis that is a common feature of all Cartesian machines. With the idea of principal axis of motion in mind, a new 3-DOF spatial parallel mechanism for horizontal and vertical milling machines has been developed. In comparison with similar developed mechanisms it has several advantages such as: rather regular shape of the workspace (slightly modified block) similar to serial machines; greater stiffness by nature of the struts arrangement; good force and speed ratio through the entire mechanism’s workspace. The paper describes the structure of the mechanism, modelling approach and simulation on a developed vertical milling machine prototype. Keywords: Parallel mechanism, Modelling, Milling machine 1 INTRODUCTION Compared with conventional machine tools, PKMs have many advantages, e.g. higher stiffness and higher ratio of force - to - weight. This is regarded as a revolutionary concept for machine tools. Many research works about diverse aspects of PKMs have been published. The search for a machine tool structure with superior performance in the key areas of accuracy dynamics and price in comparison with conventional design is clearly underway [1]. Many different PKM topologies with 3 to 6 DOF have been used [2,3,4]. However, 5 - axis CNC machining is not always needed for the most parts with moderate shape complexities. Researches in industry and institutes have recently focused on PKMs with less than 6-DOF [5]. Different machine tool manufacturers, motivated by physical and commercial limits of conventional machining centers are currently investigating capabilities of PKM as kinematic structures for high speed 3 - axes machining centers as well [1]. It is well known that workspace shape and volume are one of the greatest PKM weaknesses. In addition to advantages offered by fixed leg lengths, Hexaglide and Triaglide mechanisms [4,6] are examples where parallel guide ways are used and where workspace extension is achieved by elongation of one axis as a principal motion axis which is a common feature of all Cartesian machines. With the idea of principal axis of motion in mind, a new 3- DOF spatial parallel mechanism for horizontal and vertical milling machines has been invented by the first three authors of this paper. The paper describes the mechanism’s structure, modelling approach and simulation on a developed vertical milling machine prototype. 2 OUTLINE OF THE MECHANISM A CAD model of the initial version of the mechanism is shown in Figure 1. This is a combined representation of the initial physical model and the analytically obtained workspace. Due to the specific topology of the mechanism, physical model has been used for an initial functioning test, i.e., checking of mechanism’s stability. As may be seen from Figure 1 the mechanism consists of the mobile platform, three joint parallelograms c 1 , c 2 and c 3 , and a stationary base with two parallel guideways. Two crossed parallelograms c 1 and c 2 , with spherical and/or universal joints, i.e., cardan joints, are connected with one of their Figure 1: Initial mechanism’s version CAD model. ends attached to the mobile platform, and with their other ends to independent sliders s 1 and s 2 which, with one common guideway, make two powered and controlled translatory joints. The third joint parallelogram c 3 is connected with one of its ends, through passive translatory-rotating joints with 2-DOF, to the mobile platform. Its other end is connected with rotating joints to the slider s 3 , which, with the base guideway, makes the third powered and controlled translatory joint. The actuation of sliders s 1 , s 2 and s 3 offers three degrees of freedom to the mobile platform, i.e., the tools, so that the platform in its motion through the space remains parallel to itself, meaning that it retains constant orientation in the space. The specificity of the mechanism’s topology is reflected in the use of passive translatory-rotating joints, i.e., passive translatory degrees of freedom in Y direction for connection of joint parallelogram c 3 to the platform and its primary movement in Z direction. In this way a specific decoupling of the interacting impact of the platform’s motion in Z and Y directions takes place. In this way exceptional workspace regularity is obtained, e.g., Z min =constant and Z max =constant on its boundaries for each of Y min YY max . The position of the joint parallelogram c 3 , the shape of its segments and joint distribution may provide great force and stiffness in Z