Machining performance optimization of Parallel Kinematic Machines tools with regard to their anisotropic behaviour

Today, Parallel Kinematic Machines tools (PKMs) appear in automotive and aeronautic industries. These machines allow a benefit of productivity due to their higher kinematics performances than Serial Kinematic Machines tools (SKMs). However, their machining accuracy is lower. Moreover, the compensation of the defects which penalizes the machined parts quality is difficult due to their anisotropic behaviour. Thus, this article deals with the development of methods improving the machined parts quality and the productivity. In order to improve parts quality, the static behaviour of the machine structure is considered with a model taking into account joints and legs compliances. Then, it allows determining a static workspace. About the productivity, the improvement of kinematics performances is performed through an optimization work of the non productive tool path between cutting operations. The computed tool path must verify a minimum time constraint and avoid collisions between the tool and the machined part. All the methods are illustrated with the PKM Tripteor X7 developed by PCI