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

In 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.

Stiffness Computation and Identification of Parallel Kinematic Machine Tools

This paper deals with the stiffness computation and model identification of parallel kinematic machine tools (PKMs). Due to their high dynamic abilities, PKMs are subjected to high inertial and cutting loads while machining. These loads generate structure deflection, and it results in a low level of accuracy compared with serial machines. The aim of this paper is to present a “compact” and predictable model of PKM. This model could be useful to optimize part positioning in the workspace or adapt machining strategies in order to minimize the influence of structure deflections. The proposed model takes into account legs’ and joints’ compliances. Considering the geometry of most of parallel architectures, the legs are modeled as beams. The focus, here, is particularly on joints’ models. In literature, when the compliance of joints is considered, it is most of the time modeled with a constant stiffness. In this paper, a different approach is proposed, based on a technical analysis of the joints. Models proposed are applied to an existing PKM: the Tricept. The parameters of this model (i.e., the stiffness of the joints) are then identified; thanks to experimental stiffness measurements done on an ABB 940 Tricept robot. This robot is used in the industry for machining operations, such as grinding or drilling. A discussion about identifiable parameters is performed so as to best fit with experimental measurements. Finally, this model is used to define a static workspace where the machined parts are within the tolerances for a given operation.

Efficient Simulation of Parallel Kinematic Machine Tools

Today’s machine tool industry mainly consists of small and medium-sized enterprises. Thus, the simulation of new products often does not seem to be cost effective due to the small number of items produced and the high cost of simulation tools. Nevertheless, the use of simulation tools is essential in order to tap the full potential of new challenging concepts like parallel kinematic machines. This paper presents a simulation method supporting the development process of parallel kinematic machine tools from the first concept to the prototype. In order to render the method applicable for the machine tool industry, a special focus is placed on tool efficiency. A modular modeling concept will ensure that the structure of the first kinematic model of the concept phase can be enhanced during the development process and developed into more detailed models, e.g. for dimensioning calculations or to study the dynamic behavior of machine tools. Thus, the method efficiently supports the whole development process with a simulation model gradually increasing in detail according to the requirements of the machine tool designer.