1,752 research outputs found
Machining of complex-shaped parts with guidance curves
Nowadays, high-speed machining is usually used for production of hardened
material parts with complex shapes such as dies and molds. In such parts, tool
paths generated for bottom machining feature with the conventional parallel
plane strategy induced many feed rate reductions, especially when boundaries of
the feature have a lot of curvatures and are not parallel. Several machining
experiments on hardened material lead to the conclusion that a tool path
implying stable cutting conditions might guarantee a better part surface
integrity. To ensure this stability, the shape machined must be decomposed when
conventional strategies are not suitable. In this paper, an experimental
approach based on high-speed performance simulation is conducted on a master
bottom machining feature in order to highlight the influence of the curvatures
towards a suitable decomposition of machining area. The decomposition is
achieved through the construction of intermediate curves between the closed
boundaries of the feature. These intermediate curves are used as guidance curve
for the tool paths generation with an alternative machining strategy called
"guidance curve strategy". For the construction of intermediate curves, key
parameters reflecting the influence of their proximity with each closed
boundary and the influence of the curvatures of this latter are introduced.
Based on the results, a method for defining guidance curves in four steps is
proposed
Efficiency Improvement of Measurement Pose Selection Techniques in Robot Calibration
The paper deals with the design of experiments for manipulator geometric and
elastostatic calibration based on the test-pose approach. The main attention is
paid to the efficiency improvement of numerical techniques employed in the
selection of optimal measurement poses for calibration experiments. The
advantages of the developed technique are illustrated by simulation examples
that deal with the geometric calibration of the industrial robot of serial
architecture
Industry-oriented Performance Measures for Design of Robot Calibration Experiment
The paper focuses on the accuracy improvement of geometric and elasto-static
calibration of industrial robots. It proposes industry-oriented performance
measures for the calibration experiment design. They are based on the concept
of manipulator test-pose and referred to the end-effector location accuracy
after application of the error compensation algorithm, which implements the
identified parameters. This approach allows the users to define optimal
measurement configurations for robot calibration for given work piece location
and machining forces/torques. These performance measures are suitable for
comparing the calibration plans for both simple and complex trajectories to be
performed. The advantages of the developed techniques are illustrated by an
example that deals with machining using robotic manipulator
Design of Calibration Experiments for Identification of Manipulator Elastostatic Parameters
The paper is devoted to the elastostatic calibration of industrial robots,
which is used for precise machining of large-dimensional parts made of
composite materials. In this technological process, the interaction between the
robot and the workpiece causes essential elastic deflections of the manipulator
components that should be compensated by the robot controller using relevant
elastostatic model of this mechanism. To estimate parameters of this model, an
advanced calibration technique is applied that is based on the non-linear
experiment design theory, which is adopted for this particular application. In
contrast to previous works, it is proposed a concept of the user-defined
test-pose, which is used to evaluate the calibration experiments quality. In
the frame of this concept, the related optimization problem is defined and
numerical routines are developed, which allow generating optimal set of
manipulator configurations and corresponding forces/torques for a given number
of the calibration experiments. Some specific kinematic constraints are also
taken into account, which insure feasibility of calibration experiments for the
obtained configurations and allow avoiding collision between the robotic
manipulator and the measurement equipment. The efficiency of the developed
technique is illustrated by an application example that deals with elastostatic
calibration of the serial manipulator used for robot-based machining.Comment: arXiv admin note: substantial text overlap with arXiv:1211.573
Modelling of the gravity compensators in robotic manufacturing cells
The paper deals with the modeling and identification of the gravity
compensators used in heavy industrial robots. The main attention is paid to the
geometrical parameters identification and calibration accuracy. To reduce
impact of the measurement errors, the design of calibration experiments is
used. The advantages of the developed technique are illustrated by experimental
result
Identification of geometrical and elastostatic parameters of heavy industrial robots
The paper focuses on the stiffness modeling of heavy industrial robots with
gravity compensators. The main attention is paid to the identification of
geometrical and elastostatic parameters and calibration accuracy. To reduce
impact of the measurement errors, the set of manipulator configurations for
calibration experiments is optimized with respect to the proposed performance
measure related to the end-effector position accuracy. Experimental results are
presented that illustrate the advantages of the developed technique.Comment: arXiv admin note: substantial text overlap with arXiv:1311.667
Robust algorithm for calibration of robotic manipulator model
The paper focuses on the robust identification of geometrical and elastostatic parameters of robotic manipulator. The main attention is paid to the efficiency improvement of the identification algorithm. To increase the identification accuracy, it is proposed to apply the weighted least square technique that employs a new algorithm for assigning of the weighting coefficients. The latter allows taking into account variation of the measurement system precision in different directions and throughout the robot workspace. The advantages of the proposed approach are illustrated by an application example that deals with the elasto-static calibration of industrial robot.AN
Spectator 1951-03-08
xii, 611 hlm.; 21 c
Usual and unusual antibacterial effects of quinolones
Recently documented antibacterial effects of quinolones are reviewed. DNA gyrase is most likely to be the primary target site for these agents. Quinolones rapidly kill susceptible bacteria; the mechanisms of the bactericidal activity, still poorly understood, probably involve new protein synthesis. Quinolones alter membrane integrity before cell death, leading to leakage of cytoplasmic constituents. In Gram-negative bacteria, quinolones act as chelating agents for outer membrane divalent cations, disorganizing the bacterial lipopolysaccharide layer and facilitating the further entry of quinolone molecules in a ‘self-promoted' pathway. Quinolones inhibit plasmid replication and reduce the efficacy of plasmid conjugation. Subinhibitory concentrations of quinolones can interfere with bacterial virulence factors, such as bacterial adherence to the host cell, phagocytosis and production of enzymes implicated in virulence. Recent studies also indicate synergism of quinolones with oxacillin against methicillin-resistant staphylococci and describe improved activity of newer compounds against Gram-positive pathogen
Experimental Study of tool Wear Mechanisms in Conventional and High Pressure Coolant Assisted Machining of Titanium Alloy Ti17
Titanium alloys are known for their excellent mechanical properties, especially at high temperature. But this specificity of titanium alloys can cause high cutting forces as well as a significant release of heat that may entail a rapid wear of the cutting tool. To cope with these problems, research has been taken in several directions. One of these is the development of assistances for machining. In this study, we investigate the high pressure coolant assisted machining of titanium alloy Ti17. High pressure coolant consists of projecting a jet of water between the rake face of the tool and the chip. The efficiency of the process depends on the choice of the operating parameters of machining and the parameters of the water jet such as its pressure and its diameter. The use of this type of assistance improves chip breaking and increases tool life. Indeed, the machining of titanium alloys is generally accompanied by rapid wear of cutting tools, especially in rough machining. The work done focuses on the wear of uncoated tungsten carbide tools during machining of Ti17. Rough and finish machining in conventional and in high pressure coolant assistance conditions were tested. Different techniques were used in order to explain the mechanisms of wear. These tests are accompanied by measurement of cutting forces, surface roughness and tool wear. The Energy-dispersive X-ray spectroscopy (EDS) analysis technique made it possible to draw the distribution maps of alloying elements on the tool rake face. An area of material deposition on the rake face, characterized by a high concentration of titanium, was noticed. The width of this area and the concentration of titanium decreases in proportion with the increasing pressure of the coolant. The study showed that the wear mechanisms with and without high pressure coolant assistance are different. In fact, in the condition of conventional machining, temperature in the cutting zone becomes very high and, with lack of lubrication, the cutting edge deforms plastically and eventually collapses quickly. By contrast, in high pressure coolant assisted machining, this problem disappears and flank wear (VB) is stabilized at high pressure. The sudden rupture of the cutting edge observed under these conditions is due to the propagation of a notch and to the crater wear that appears at high pressure. Moreover, in rough condition, high pressure assistance made it possible to increase tool life by up to 400%.Authors would like to thank « Région des pays de la loire » for funding of the project which is part of a PhD thesi
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