The Design of Parallel Kinematic Machine Tools Using Kinetostatic Performance Criteria

International audienceMost industrial machine tools have a serial kinematic architecture, which means that each axis has to carry the following one, including its actuators and joints. High Speed Machining highlights some drawbacks of such architectures: heavy moving parts require from the machine structure high stiffness to limit bending problems that lower the machine accuracy, and limit the dynamic performances of the feed axes. That is why PKMs attract more and more researchers and companies, because they are claimed to offer several advantages over their serial counterparts, like high structural rigidity and high dynamic capacities. Indeed, the parallel kinematic arrangement of the links provides higher stiffness and lower moving masses that reduce inertia effects. Thus, PKMs have better dynamic performances. However, the design of a parallel kinematic machine tool (PKMT) is a hard task that requires further research studies before wide industrial use can be expected. Many criteria need to be taken into account in the design of a PKMT. We pay special attention to the description of kinetostatic criteria that rely on the conditioning of the Jacobian matrix of the mechanism. The organisation of this paper is as follows: next section introduces general remarks about PKMs, then is explained why PKMs can be interesting alternative machine tool designs. Then are presented existing PKMTs. An application to the design of a small-scale machine tool prototype developed at IRCCyN is presented at the end of this paper

Parametric stiffness analysis of the Orthoglide

This paper presents a parametric stiffness analysis of the Orthoglide. A compliant modeling and a symbolic expression of the stiffness matrix are conducted. This allows a simple systematic analysis of the influence of the geometric design parameters and to quickly identify the critical link parameters. Our symbolic model is used to display the stiffest areas of the workspace for a specific machining task. Our approach can be applied to any parallel manipulator for which stiffness is a critical issue

Kinematic Modeling, Linearization and First-Order Error Analysis

This chapter deals with a modular method for the kinematic analysis of parallel kinematic machines (PKM) at discrete points within their workspace. Firstly, a modular approach is presented for calculating the forward kinematic transmission function of some widely used parallel kinematic machines. This includes the well-known Stewart-Gough-platforms of general geometry, the Delta-robots, and parallel machines with legs of constant length. The kinematic analysis is based on the kinetostatic method and permits to calculate the position, velocity, and acceleration transmission from the articulated joints towards the moveable platform of the machine. Furthermore, a force transmission is defined based on kinetostatic duality. By means of a simple numerical calculation schema, a comprehensive first-order sensitivity analysis is performed. Finally, it is shown how to set up the stiffness matrix for the aforementioned robots. Computational examples of the proposed algorithms are presented

Technology-Oriented Optimization of the Secondary Design Parameters of Robots for High-Speed Machining Applications

International audienceIn this paper, a new methodology for the optimal design of the secondary geometric parameters (shape of links, size of the platform, etc.) of parallel kinematic machine tools is proposed. This approach aims at minimizing the total mass of the robot under position accuracy constraints. This methodology is applied to two translational parallel robots with three degrees-of-freedom (DOF): the Y-STAR and the UraneSX. The proposed approach is able to speed up the design process and to help the designer to find more quickly a set of design parameters