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%).     

Dynamic model of an overconstrained PKM with compliances: The Tripteor X7

This paper deals with dynamic modeling of a parallel kinematic machine tool: the Tripteor X7. This machine has a hybrid kinematic, so it presents a serial wrist attached to an overconstrained parallel unit. Two dynamic models are proposed in this paper. The first one is built with only rigid bodies. It aims at identifying the inertial parameters and those of the movement transformation devices. In the second model, joints and legs compliances are introduced. This model is then used to study the impact of elements deformations on the generated surfaces. All this simulations are compared to experimental measurements realized directly on the Tripteor.     

Inhibition of myo-inositol monophosphatase isoforms by aromatic phosphonates

alpha-Hydroxyphosphonates are moderately potent (Ki = 6-600 microM) inhibitors of the enzyme myo-inositol monophosphatase (McLeod et al., Med. Chem. Res. 1992, 2, 96). Hydroxy-[4-(5,6,7,8-tetrahydronaphtyl-1-oxy)phenyl]methyl phosphonate (3) was resynthesized and its inhibitory potency towards the recombinant bovine brain enzyme confirmed (Ki = 20 microM). Similar aromatic difluoro-, keto-, and ketodifluorophosphonates (5, 7, 9) were inactive. Compound 3 was 15-fold less active on the human as compared to the bovine enzyme. Molecular modeling suggested that the hydrophobic part of the inhibitor interacts with amino acid side chains that are located at the interface between the enzyme subunits in an area (amino acids 175-185) with low similarity between the two isozymes. Phe-183 in the human enzyme was replaced with leucine, the corresponding residue in the bovine isoform. The three isozymes (human wild-type, bovine wild-type and human F183L) had similar kinetic properties, except that the bovine enzyme was less effectively inhibited by high concentrations of the activator Mg2+. The F183L mutant enzyme had a twofold increased affinity for compound 3 as compared to the human wild-type form. We conclude that residue 183 contributes to the binding of aromatic hydroxyphosphonates to IMPase, but it is not the only determining factor for inhibitor specificity with respect to different isozymes.     

A study of the impact of machine tool structure on machining processes

This paper deals with parallel kinematics machine (PKM) applications for high speed machining. PKM behaviour is anisotropic, so structural deflection due to cutting loads generates different defects in the machined part, according to tool position and orientation in the workspace. The aim of the present study is the definition of a mechanical workspace where the part is machined to a specified quality level. Models of the machine tool structure, the load generated by the cutting phenomena and the machined surface are used to determine this workspace and are applied to a tricept structure with telescopic legs for grooving and drilling operations. A simulation shows that leg deflection gives rise to defects of the machined entity which are evaluated with respect to tool position and orientation. Finally, a mechanical workspace is defined for a drilling process using a tricept structure machine tool.     

Process definition of preformed part machining for taking benefit of parallel kinematic machine tool kinematic performances

In the automotive or aeronautical industries, few parallel kinematic machine tools (PKM) are used in high-speed machining (HSM). However, the dynamics of these machine tool structures could be relevant for HSM since their acceleration potential is much higher than serial kinematic machine tools. However, a particularity of PKM is to have kinematic performances depending on the tool pose in the machine workspace. Thus, this paper proposes a method to increase the productivity of performed part machining with PKM by taking advantage of their kinematic performances, with the aim of decreasing the time of the non-cutting tool movements. Process parameters defined by this method are the machined part setup, the planning of the machining operations, the control of potential redundant axis and the definition of the tool paths between cutting operations. The developed method is achieved in four successive steps based on a modelling of the kinematic behaviour of a given PKM. Each step leads to define one of the process parameters with regard to the decrease of non-cutting time. Thus, this method only requires common optimization algorithms that increase it robustness and its adaptability to different structures of PKM. It is illustrated with drilling operations on preformed parts with the Tripteor X7 machine tool developed by the PCI-SCEMM Company.     

Reduction of a parallel kinematics machine tool inverse kinematics model with regard to machining behaviour

A main limitation of parallel kinematics machine tools in machining tasks is their accuracy low level largely due to geometrical transformation errors. These errors appear due to the difference between the behaviour of the inverse kinematics model integrated into the controller and that of the real PKM. The aim of this paper is to analyse the influence of the controller IKM on PKM machining behaviour and to quantify its incidence on the assembly and machining tolerances of structural elements.     

Mice's rectum radioprotection: comparative efficacy of a series of aminothiols and aminothiol precursors

In mice, in a test of rectal gamma irradiation, cysteamine and cysteine are poor radioprotectors relative to thiazolanes or WR 2721. Among the tested prodrugs, 2-isopropyl 1,3-thiazolane was nearly as efficient as WR 2721 as soon as 15 minutes after its administration. The guarantee of radioprotection is the effective presence of the active aminothiols in the intracellular room during the irradiation. In this study, enterocytes of the rectal mucous membrane were not sufficiently permeable to exogenous cysteine or cysteamine. The cell imperviousness to these straight active aminothiols was compensated by the diffusion of their precursors across the membrane.