H. Chanal

Tool path smoothing of a redundant machine: Application to Automated Fiber Placement

Automated Tape Laying and Fiber Placement of composite materials are the two principal automated processes used for fabrication of large composite structures in aeronautical industry. The aluminum parts produced by High Speed Machining tend to be replaced by carbon fiber composite parts realized with these processes. However, structural parts present reinforcement zones which disturb the tool path follow-up and generate an increase of the manufacturing time. Thus, this paper deals with the optimization of tool paths of a 7-axis machine tool of Fiber Placement with the objective of reducing the manufacturing time while ensuring the requested quality of the final part. In this paper, two complementary methods are detailed. The first method takes advantage of the degree of redundancy of the machine tool to decrease the kinematic loads of the control joints. The second method aims to smooth the orientation of the machine head along the tool path while ensuring quality constraints. These two methods are then applied on a test tool path and bring to a significant decrease of the manufacturing time (32.9%).

HSM-ADAPTED TOOL PATH CALCULATION FOR POCKETING

High-speed milling imposes a precise choice of cutting conditions, because the feed rate and the radial depth of cut influence the maximum forces on cutting edges. But the control of these cutting conditions for pocket machining is very difficult due to the complex tool path shape. Our work is focused on the improvement of the geometrical definition of the tool path, in order to ensure a better respect of the cutting conditions required for HSM. Initially, we study variations in the radial depth of cut and the real feed rate, when the tool follows usual tool paths for pocketing. Numerical simulations and experimental measurements are used. Next, a new tool path computation method that increases the real feed rate and respects radial depth of cut requirements is proposed. The computation takes into account both the geometrical requirements and the HSM dynamic requirements. Such tool paths reduce machining time and respect initial cutting parameters which are favorable for process reliability and tool life.

Definition of a new static model of Parallel Kinematic Machines: Highlighting of overconstraint influence

This paper deals with static behaviour modelling of Parallel Kinematic Machines (PKMs). Due to their high dynamic abilities, PKMs are subjected to high inertial and cutting loads while machining. These loads generate structure deflection, and thus tool pose defects. The aim of this article is to present a predictable model of PKMs. 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 modelled as beams. The focus, here, is particularly on joint models. In the literature, when the compliance of joints is considered, it is always modelled with a constant stiffness. In this paper, a different approach is proposed, based on a technical analysis of the joints and non linear models are chosen. 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 a ABB 940 Tricept robot. Finally, a second architecture is studied. This machine is overconstrained even if it is very close to the Tricept architecture. The same modelling method is applied and the static behaviours of the two machines are compared. Thus, the effect of overconstraint on static behaviour is analysed.

Scintillation Signal in XEMIS2, a Liquid Xenon Compton Camera with 3γ Imaging Technique

The XEMIS project (XEnon Medical Imaging System), which makes use of 3γ imaging technique and liquid xenon Compton camera, aims to make a precise 3D localization of a specific radioactive emitter and to reduce drastically (100 times less) the injected activity to the patient in cancer diagnosis. The 3γ imaging is characterized by the simultaneous detection of 3 γ-rays emitted by 44Sc which is a (β+, γ) emitter. The second prototype XEMIS2 is a liquid xenon cylindrical camera for small animal imaging. The active volume of XEMIS2 is surrounded by a set of VUV-sensitive Hamamatsu photomultipliers, for the scintillation signals detection. A pulse-shaping amplifier was tested in XEMIS1 for the readout of the scintillation signal of the PMT. The typical output pulse shows a relatively good performance of the pulse-shaping amplifier providing a possible solution for XEMIS2 scintillation DAQ. Meanwhile, the pulse-shaping amplifier and the constant fraction discriminator (CFD) have lay the foundation of the preliminary design of XEMIS2 scintillation signal detection chain.

XEMIS: Liquid Xenon Compton Camera for 3γ Imaging

An innovative liquid xenon Compton camera project, XEMIS (XEnon Medical Imaging System) has been proposed by SUBATECH laboratory, for a new functional medical 3γ imaging technique based on the detection in coincidence of 3 γ-rays. The purpose of this 3γ imaging modality is to obtain a 3D image using 100 times less activity than in current PET systems. The combination of a liquid xenon time projection chamber (LXe TPC) and a specific (β+, γ) radionuclide emitter 44Sc is investigated in this concept. In order to provide an experimental demonstration for the use of a LXe Compton camera for 3γ imaging, a succession of R&D programs, XEMIS1 and XEMIS2, have been carried out using innovative technologies. The first prototype XEMIS1 has been successfully validated showing very promising results for energy, spatial and angular resolutions with an ultra-low noise front-end electronics. The second phase dedicated to a 3D imaging of small animals, XEMIS2, is now under installation and qualification, while the characterizations of ionization signal using Monte Carlo simulation has shown preliminary good performances for energy measurement.