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Abstract: Instantaneous Angular Speed (IAS) has recently appeared as an original and promising tool for monitoring mechanical parts of rotating machines. Mechanisms running under non-stationary conditions, such as wind turbine, are especially suited to this method since the issued signal is intrinsically sampled in the angular domain. Although processing tools are developed to enhance its use in the industry, this method is lacking a proper identification of its limitations and this paper aims at precisely understanding two of its main shortcomings: the aliasing and the quantization phenomena. After having presented the measurement method, both the aliasing and the quantization error are theoretically dissected. Formula is proposed to estimate their influence in the spectral observation of the IAS, and a good signal-to-noise ratio appraisal for this measurement technique is finally obtained. It can eventually be used as a first guide to conveniently design an IAS based control/monitoring system. [Copyright &y& Elsevier]

In machining, tool condition monitoring (TCM) is one of the major trends of development of process efficiency. By monitoring tool wear and detecting tool-teeth break, TCM is able to protect tool, machine and workpiece, which corresponds to important savings. Cutting forces are often considered as the best indicator for detecting tool wear and damage, but they are very difficult and expensive to measure directly in industrial cases. The aim of this work is to develop a new method using standard transducers available on actual machines for a better monitoring of cutting process. This method analyses instantaneous variations in rotational frequency so as to observe milling operation. Experimental cutting tests were performed on a milling machine. On one hand, cutting forces were acquired through common dynamometer. On the other hand, signal from spindle integrated rotary encoder is acquired using specific angular-sampling methodology. Spindle rotational frequency is then easily computed using rudimentary signal processing tools. Correspondence between cutting force magnitude and variation in spindle rotational frequency is noted: when a tooth goes in material, cutting force suddenly increases, and rotational frequency starts to decrease until cutting force becomes low enough. Thus, apparition of tool wear can be observed by monitoring variations in rotational frequency according to the different teeth of the tool. Moreover, a sudden variation in the amplitude of slow-down due to a tooth allows detection of tooth breakage. Instantaneous variations in spindle rotational frequency are shown to be very effective indicators for tool condition in comparison with cutting force, so they must be very useful for TCM systems. [ABSTRACT FROM AUTHOR]

In the present contribution, experimental and numerical methodologies concerning orthogonal cutting are proposed in order to study the dry cutting of an aeronautic aluminium alloy (A2024-T351). The global aim concerns the comprehension of physical phenomena accompanying chip formation with respect to cutting speed, such as chip segmentation and fragmentation. For experimental validation, series of tests are carried out concerning geometrical analysis of the chip; video sequences of chip formation with a high-speed camera, and high-frequency sampling measurements of the cutting force signal are realised. For the numerical approach, the material and its ductile shear failure behaviour are based on the Johnson-Cook laws. The material failure model exploited considers both damage evolution and energy coupling. Numerical results concerning cutting force and segmentation frequency are compared to experimental ones. Moreover,an analysis of damage distributions is presented. [ABSTRACT FROM AUTHOR]

We investigate the influence of phase mismatch on the performance of a spectral inverter based on four-wave mixing in a commercial dispersion-shifted fiber. The inverter operates at 10 Gb/s. When the pump wave is tuned ±0.3 mn around the zero-dispersion wavelength of the fiber, the power penalty at 10-9 bit-error rate remains within the range of 1-2 dB, although the conjugate power is reduced considerably by almost 6 dB. A numerical calculation of the inverter's efficiency is also presented, which takes into account longitudinal variation of the zero-dispersion wavelength along the fiber [ABSTRACT FROM PUBLISHER]

All-optical Boolean XOR is demonstrated on a high-speed serial bit stream with a three-optical input fiber Sagnac interferometer switch, which uses a semiconductor optical amplifier. Full duty cycle bit switching has been demonstrated up to 5 GHz with contrast ratio as high as 14.6 dB [ABSTRACT FROM PUBLISHER]

Abstract: The detection of chatter is crucial in the machining process and its monitoring is a key issue to ensure a better surface quality, to increase productivity and to protect both the machine and the workpiece. An investigation of chatter monitoring in the high speed machining process on the basis of the analysis of cutting forces and instantaneous angular speeds (IAS) in the angular domain is presented in this paper. Experimental cutting tests were carried out on slot milling operation of aluminum alloy. Our experimental set-up allows for, on the one hand, the acquisition of the angular cutting force and, on the other hand, the measurement of IAS. The latter is computed from the signal delivered by the standard encoder mounted on the spindle motors. The same signal is used as a base for synchronous angular sampling. The acquisition methodology is described and discussed in this paper. Data analysis confirms the relevance of cutting forces for chatter monitoring and the good correlation between cutting forces and IAS of the spindle. Two chatter indicators are developed in the angular domain from the periodic and residual parts of angular speed and cutting force signals. They are used successfully for the detection of the chatter phenomenon. The indicator based on IAS is very convenient because it does not require additional sensors and can be realized without increasing the cost of the manufacturing system. [Copyright &y& Elsevier]