Metrological characterization of MEMS accelerometers by LDV

Abstract In this work two calibration methodologies, able to characterize the digital sensitivity of MEMS accelerometers, are presented and compared, to identify the contributions for the evaluation of the reproducibility in the low frequency range. The methodologies are different from the point of view of test bench, test procedure and data processing method. In particular, different vibration actuators are used, a linear slide and an electro-dynamic shaker, different sensors as a reference for the calibration, piezoelectric accelerometers and a Laser Doppler Vibrometer (LDV). A group of 5 accelerometers is tested for the purpose of developing the calibration techniques and evaluate a first reproducibility estimate. The experimental results provided by the two calibration procedures show significant differences. Some elements that could explain these differences have been identified, and will be further investigated in future work

Physical and Metrological Approach for Feature’s Definition and Selection in Condition Monitoring

In this paper, a methodology is described aiming at emphasizing physical and metrological criteria in feature selection for condition monitoring of a real scale mechatronic system. The device is used for packaging applications according to the movements of its end effector, driven by a couple of brushless servomotors and a kinematic mechanical linkage. The approach is hybrid, meaning that the starting feature set is built with reference to both experimental data from different sensors and to the indication of a simplified kinematic and dynamic model of the mechanical linkage itself. A critical comparison and mixing of theoretical and experimental data, based also on a physical interpretation of differences, suggests some more features, with respect to the classical ones, of hybrid type, which could be mostly correlated to the effects of statuses and defects of the system to be identified. The whole procedure is step by step validated, in order to evaluate the variability of features, throughout the whole procedure. The variability is analyzed depending on the actions that are realized in order to define, select, and use the proposed features for data processing by advanced algorithms, like the most typically used classifiers and artificial neural networks. A comparison with the state-of-the-art automatic feature’s selection procedure is also presented. Experimental results show that the proposed methodology is able to classify with high accuracy many statuses of the mechatronic system, which are only slightly different as for set-up settings and/or mechanical wear and lubrication conditions of mechanical parts of the mechatronic system. Issues to be pursued to a more effective generalization of the method are also discussed

Effect of uncertainty of reliability data of instrumentation on risk assessment and prediction in process plant applications

Some aspects are discussed concerning the uncertainty causes in risk assessment techniques of industrial interest. Particular attention has been paid to the evaluation of the effect of uncertainty of reliability data of devices and instruments to be used in process plants on the evaluation of the occurrence frequency of the top event. The influence of measuring equipment, whose contribution to the whole uncertainty appears in some cases very important, has been analysed with reference to both operative and environmental aspects

Uncertainty Evaluation in Vision-Based Techniques for the Surface Analysis of Composite Material Components

In this paper, a methodology is discussed concerning the measurement of yarn’s angle of two different glass-reinforced polypropylene matrix materials, widely used in the production of automotive components. The measurement method is based on a vision system and image processing techniques for edge detection. Measurements of angles enable, if accurate, both useful suggestions for process optimization to be made, and the reliable validation of the simulation results of the thermoplastic process. Therefore, uncertainty evaluation of angle measurement is a mandatory pre-requisite. If the image acquisition and processing is considered, many aspects influence the whole accuracy of the method; the most important have been identified and their effects evaluated with reference to two different materials, which present different optical-type characteristics. The influence of piece geometry has also been taken into account, carrying out measurements on flat sheets and on a semi-spherical object, which is a reference standard shape, to verify the effect of thermoforming and to tune the process parameters. Complete uncertainty in the order of a few degrees has been obtained, which is satisfactory for purposes of simulation validation and consequent process optimization. The uncertainty budget also allowed individuation of the most relevant causes of uncertainty for measurement process improvement

Uncertainty of slip measurements in a cutting system of converting machinery for diapers production

In this paper slip measurements are described between the peripheral surfaces of knife and a not driven anvil cylinders in a high velocity, high quality cutting unit of a diaper production line. Laboratory tests have been carried out on a test bench with real scale components for possible on line application of the method. With reference to both starting and steady state conditions correlations with the process parameters have been found, achieving a very satisfactory reduction of the slip between the knife cylinder and the not driven anvil one. Accuracy evaluation of measurements allowed us to validate the obtained information and to evaluate the detection threshold of the measurement method in the present configuration The analysis of specific uncertainty contributions to the whole uncertainty could be also used, to further reduce the requested uncertainty of the measurement method

Selective and validated data processing techniques for performance improvement of automatic lines

Optimization of the data processing techniques of accelerometers and force transducers allowed to get information about actions in order to improve the behavior of a cutting stage of a converting machinery for diapers production. In particular, different mechanical configurations have been studied and compared in order to reduce the solicitations due to the impacts between knives and anvil, to get clean and accurate cuts and to reduce wear of knives themselves. Reducing the uncertainty of measurements allowed to correctly individuate the best configuration for the pneumatic system that realize the coupling between anvil and knife. The size of pipes, the working pressure and the type of the fluid used in the coupling system have been examined. Experimental results obtained by means of acceleration and force measurements allowed to identify in a reproducible and coherent way the geometry of the pushing device and the working pressure range of the hydraulic fluid. The remarkable reduction of knife and anvil vibrations is expected to strongly reduce the wear of the cutting stage components

Selective and validated data processing techniques for performance improvement of automatic lines

Optimization of the data processing techniques of accelerometers and force transducers allowed to get information about actions in order to improve the behavior of a cutting stage of a converting machinery for diapers production. In particular, different mechanical configurations have been studied and compared in order to reduce the solicitations due to the impacts between knives and anvil, to get clean and accurate cuts and to reduce wear of knives themselves. Reducing the uncertainty of measurements allowed to correctly individuate the best configuration for the pneumatic system that realize the coupling between anvil and knife. The size of pipes, the working pressure and the type of the fluid used in the coupling system have been examined. Experimental results obtained by means of acceleration and force measurements allowed to identify in a reproducible and coherent way the geometry of the pushing device and the working pressure range of the hydraulic fluid. The remarkable reduction of knife and anvil vibrations is expected to strongly reduce the wear of the cutting stage components