64 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
A new versatile in-process monitoring system for milling
International audienceTool condition monitoring (TCM) systems can improve productivity and ensure workpiece quality, yet, there is a lack of reliable TCM solutions for small-batch or one-off manufacturing of industrial parts. TCM methods which include the characteristics of the cut seem to be particularly suitable for these demanding applications. In the first section of this paper, three process-based indicators have been retrieved from literature dealing with TCM. They are analysed using a cutting force model and experiments are carried out in industrial conditions. Specific transient cuttings encountered during the machining of the test part reveal the indicators to be unreliable. Consequently, in the second section, a versatile in-process monitoring method is suggested. Based on experiments carried out under a range of different cutting conditions, an adequate indicator is proposed: the relative radial eccentricity of the cutters is estimated at each instant and characterizes the tool state. It is then compared with the previous tool state in order to detect cutter breakage or chipping. Lastly, the new approach is shown to be reliable when implemented during the machining of the test part
Angular approach combined to mechanical model for tool breakage detection by eddy current sensors
International audienceThe paper presents a new complete approach for Tool Condition Monitoring (TCM) in milling. The aim is the early detection of small damages so that catastrophic tool failures are prevented. A versatile in-process monitoring system is introduced for reliability concerns. The tool condition is determined by estimates of the radial eccentricity of the teeth. An adequate criterion is proposed combining mechanical model of milling and angular approach. Then, a new solution is proposed for the estimate of cutting force using eddy current sensors implemented close to spindle nose. Signals are analysed in the angular domain, notably by synchronous averaging technique. Phase shifts induced by changes of machining direction are compensated. Results are compared with cutting forces measured with a dynamometer table. The proposed method is implemented in an industrial case of pocket machining operation. One of the cutting edges has been slightly damaged during the machining, as shown by a direct measurement of the tool. A control chart is established with the estimates of cutter eccentricity obtained during the machining from the eddy current sensors signals. Efficiency and reliability of the method is demonstrated by a successful detection of the damage
Advanced robot calibration using partial pose measurements
International audienceThe paper focuses on the calibration of serial industrial robots using partial pose measurements. In contrast to other works, the developed advanced robot calibration technique is suitable for geometrical and elastostatic calibration. The main attention is paid to the model parameters identification accuracy. To reduce the impact of measurement errors, it is proposed to use directly position measurements of several points instead of computing orientation of the end-effector. The proposed approach allows us to avoid the problem of non-homogeneity of the least-square objective, which arises in the classical identification technique with the full-pose information. The developed technique does not require any normalization and can be efficiently applied both for geometric and elastostatic identification. The advantages of a new approach are confirmed by comparison analysis that deals with the efficiency evaluation of different identification strategies. The obtained results have been successfully applied to the elastostatic parameters identification of the industrial robot employed in a machining work-cell for aerospace industry
OPTIMALITY CRITERIA FOR MEASUREMENT POSES SELECTION IN CALIBRATION OF ROBOT STIFFNESS PARAMETERS
International audienceThe paper focuses on the accuracy improvement of industrial robots by means of elasto-static parameters calibration. It proposes a new optimality criterion for measurement poses selection in calibration of robot stiffness parameters. This criterion is based on the concept of the manipulator test pose that is defined by the user via the joint angles and the external force. The proposed approach essentially differs from the traditional ones and ensures the best compliance error compensation for the test configuration. The advantages of this approach and its suitability for practical applications are illustrated by numerical examples, which deal with calibration of elasto-static parameters of planar manipulator with rigid links and compliant actuated joints
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