Frequency domain processing consistent in high

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frequency domain processing, consistent in high accuracy synchronous FFT transform, filtering resonance band of workpiece and tool, Hilbert transform [12], [13], [14] followed by Inverse Fast Fourier Transform (IFFT). Next the FFT analyses of the envelope ensure high precision description of the milling tool to identify the type and amplitude of asymmetry and wear. Each cutter tooth asymmetry is automatically qualified through the harmonic components with a lower frequency than the principal frequency equivalent of teeth number. To detect structural defects that may occur in these machine components, spectral analysis of the signal’s envelope has been widely employed [ 13], [14]. This is based on the consideration that structural impacts induced by a localized defect often excite one or more resonance modes of the structure and generate impulsive vibrations in a repetitive and periodic way. Frequencies related to such resonance modes are often located in higher frequency regions than those caused by the robot-borne vibrations, and are characterized by an energy concentration within a relatively narrow band centred at one of the harmonics of the resonance frequency. By utilizing the effect of mechanical amplification provided by structural resonances, defect- induced vibration features can be separated from the background noise and interference for diagnosis purpose [15]. The resonance filter band for envelope method is between 2000 - 3000Hz. Figure 19: The envelope time signal and the spectrum frequency envelope on X, Y, Z direction during the milling process in P 1 position After the application of envelope is emphasized amplitude low frequency range contained in 7 - 11 Hz that is generated by varying cutting forces resulting in excitation resonance frequency of the robot. High-frequency amplitude modulation generated by the contact tool/chip/workpiece allows the Hilbert transform [16] their impact frequency identification robot. An important perspective is to locate the source of these lower frequency vibrations. This robot can validate that increases rigidity to the P 1 position from position P 2 .
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12 ICASAAM 2011 7-10 September 2011 Bucharest Romania Figure 20: The envelope time signal and the spectrum frequency envelope on X, Y, Z direction during the milling process in P 2 position 6 Conclusions Robots are increasingly used in machining applications where the performance of position and orientation of the tool center point is important. The use of robots in machining applications takes a large scale, in particular in the aerospace industry. Knowing that the dynamic behavior of robots used in processing materials is poor in comparison with a CNC gantry, a detailed approach is required concerning the dynamical behavior induced by the cutting process. This paper aims at characterizing the dynamics change of the robot dynamical behavior through several points of the workspace. Especially the evolution of its stiffness for different configurations of the workspace is analyzed. An experimental protocol was designed and developed to
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