Gianluca Rossi

Measurement techniques for the acoustic analysis of synchronous belts

At present, in the automotive field, the noise generated by belt drives is evaluated by using microphones in the proximity of the belt, crankshafts, idlers and so on. Such a method can be misleading, since it may easily include the contributions of other noise sources present during the measurement. Moreover, a large amount of data is needed in order to test various layouts and various running conditions. We present a method for the analysis and prediction of the noise generated by belt drives which consists of two distinct phases in this paper. For simplicity, a two-pulley belt drive has been considered and the results have been validated at the meshing frequency, at which, as has been shown in the existing literature, the phenomenon of noise generation is mainly concentrated. In the first stage of the work, the acoustic power generation of the belt drive being tested was measured by means of acoustic intensity techniques. Subsequently, an acoustic prediction was performed by using vibration data obtained with a scanning laser Doppler vibrometer (SLDV) as inputs for a boundary element code. The SLDV was used because of its capability of measuring in-operation data on the running belt, which would not have been possible using traditional contact sensors (accelerometers and so on). The results obtained in the two phases were finally compared in order to evaluate the relation between the vibratory behaviour and the total acoustic radiation determined experimentally. The experimental and numerical data agree fairly well, adding precious information on the noise generation mechanisms and showing the feasibility of modelling the vibro-acoustic behaviour of belt drives and the possibility of a totally numerical procedure. In particular the implementation of an entirely numerical procedure using, for example, data generated through the use of codes for the dynamic characterization of mechanical systems (multi-body mechanical models and so on) seems foreseeable. In the final section of the present work, the uncertainty arising from the measurement processes of the investigation method presented is also discussed.

A new approach to the measurement of transverse vibration and acoustic radiation of automotive belts using laser Doppler vibrometry and acoustic intensity techniques

This work aims at utilizing state-of-the-art and powerful measurement techniques to develop a tool for estimating the acoustic radiation of synchronous belts during the design stage. One of the main objects of this work is that of reducing the large number of tests currently employed. Effective measurement technologies, such as laser and acoustic intensity measurement techniques, are employed to support the entire development of the predicting tool, from the analysis of the noise and vibration phenomena to the validation of the numerical models. The proposed method can also be applied successfully to the analysis of noise generating mechanisms, especially belt vibration responses. In a previous work, it has been shown that the noise radiated at meshing frequency by a belt drive, simply composed of two pulleys and driven by an electric motor, can be estimated using vibration measurements, taken by a scanning laser Doppler vibrometer, as inputs for a boundary element model. The same approach is here extended to a more complex test bench, with an internal combustion engine cylinder head giving additional excitation. The test bench has been designed and realized in order to reduce the noise radiation due to interfering sources (electric motor, cooling system etc) and to make it possible to measure the noise contribution from the belt drive only. Reference noise measurements have been performed by acoustic intensity techniques. The sound power values obtained from these measurements have been compared to those obtained from the boundary element model. The techniques employed in this work have been shown to be able to analyse resonance and meshing phenomena on a real belt drive geometry, as had not been done before, based on the literature survey reported.

Hand-arm vibration measurement by a laser scanning vibrometer

Measurement of hand-arm transmitted vibration is a relevant issue for human health and safety. Many measurement problems occur with conventional transducers. In this paper, new measurement techniques are proposed. The methodology is based on a laser scanning vibrometer. Those techniques can be applied in laboratory tests and also to perform field tests on hand-guided vibrating tools, vehicles, and machines. Results of tests performed on different subjects with their hand on three laboratory test devices, designed according to ISO standards, are presented. Comparison of simultaneous measurements performed by the vibrometer and by conventional techniques (accelerometer) has been carried out. Further work has been done in order to test film sensors for measurement of the contact force between the hand and the vibrating surface. First results are here illustrated of film sensor characterisation and mechanical impedance measurements at some points of hands of different subjects, obtained by the laser Doppler vibrometer and by the film sensor.

A New Method for the Experimental Assessment of Finger Haemodynamic Effects Induced by a Hydraulic Breaker in Operative Conditions

A New Method for the Experimental Assessment of Finger Haemodynamic Effects Induced by a Hydraulic Breaker in Operative Conditions: Matteo Valentino, et al. Clinic of Occupational Medicine, University of Ancona, Italy—The haemodynamic effects, in terms of grip force and hand‐transmitted accelerations, produced on the fingers of 10 healthy subjects by operation of a hydraulic breaker held with a low or a high grip were investigated with a new experimental set‐up. A novel apparatus consisting of a capacitive sensor matrix and a laser Doppler vibrometer was used to measure the two parameters during breaker operation. Finger blood flow in basal conditions and after each test was evaluated in the four long fingers of both hands with a photoplethysmograph and superficial skin thermometry. The amplitude of the accelerations transmitted to the hand surface was greater during the test with the low grip. Photoplethysmographic and thermometric values were significantly lower than basal values after either test. The amplitude of photoplethysmographic values during the tests was significantly lower with the low than with the high grip in 6 subjects, in both index fingers, and in the right middle finger. The authors show that the level of grip force used for holding the breaker causes transmission of vibrations of wider amplitude, resulting in greater reduction in finger blood flow. In line with the literature, stimulus magnitude, frequency and duration affected finger blood flow, especially in the index finger.

Comparison between Accelerometer and Laser Vibrometer to Measure Traffic Excited Vibrations on Bridges

The use of accelerometer based measurement techniques for evaluating bridge forced vibrations or to perform bridge modal analysis is well established. It is well known to all researchers who have experience in vibration measurements that values of acceleration amplitude can be very low at low frequencies and that a limitation to the use of accelerometer can be due to the threshold parameter of this kind of transducer. Under this conditions the measurement of displacement seems more appropriate. On the other hand laser vibrometer systems detect relative displacements as opposed to the absolute measures of accelerometers. Vibrations have been measured simultaneously by a typical accelerometer for civil structures and by a laser vibrometer equipped with a fringe counter board in terms of velocity and displacements. The accelerations calculated from the laser vibrometer signals and the one directly measured by the accelerometer has been compared.

Design and experimental characterization of a nonintrusive measurement system of rotating blade vibration

A measurement system for nonintrusive monitoring of rotating blade vibration in turbomachines based on fiber optic sensors is presented. The design of the whole system is discussed; the development of special purpose sensors, their interfacing to the data acquisition system, and the signal processing are outlined.The processing algorithms are tested by software simulation for several possible blade vibrations. Experimental tests performed on different bladed rotors are presented. Results are compared to simultaneous strain gage measurements.

Fiber optic ice sensors for refrigerators

In any kind of refrigerator, frost and ice formation has to be limited by defrosting of the evaporator surface. This paper proposes the use of fiber-optic sensor technology to successfully achieve the goal of sensing and controlling ice formation inside refrigerators, by monitoring ice thickness and servocontrolling the defrosting cycle. The main advantages of such a choice are discussed. Different fiber optic sensors are analyzed. An experimental investigation on a test bench and inside a real refrigerator is performed. The problem of cost of the sensor is also addressed.

Measurement on Rotating Mechanical Component by Thermoelasticity

In this paper a new measurement technique to perform thermoelastic stress analysis on rotating mechanical component is proposed. The idea is to use a particular realization of the Dove prism optical system, optimized to work width infrared radiation, able to give a fixed output image of a rotating surface on where a normal thermoelastic measurement system can be applied. The realization of a first prototype of this optical system is described. First results on a test case are illustrated.

Vibration measurements of tools inside fluids by laser Doppler techniques: uncertainty analysis

In this work a technique based on a laser vibrometer is examined for the vibration measurement of bodies with fluids between the measurement point and vibrometer head. Some mathematical models have been considered and the causes of uncertainty have been correlated with the optical characteristics of the various fluids employed and with their thickness. Optical test benches have been set up and comparative measurements with accelerometers have been carried out in order to verify the mathematical models and estimate other uncertainty sources. Results of the analysis have been used to perform forced vibration measurements on a machine shaft with special care in order to minimize the effect of the noise sources analysed.

Development and experimental characterization of a new non contact sensor for blade tip timing

Performances of blade tip timing measurement systems (BTT), recently used for non contact turbine blade vibration measurements, in terms of uncertainty and resolution are strongly affected by sensor characteristics. The sensors used for BTT generate pulses, to be used also for precise measurements of turbine blades time of arrival. All the literature on this measurement techniques do not address this problem in a clear way, defining the relevant dynamic and static sensor characteristics, fundamental for this application. Till now proximity sensors used are based on optical, capacitive, eddy current and microwave measuring principle. Also pressure sensors has been used. In this paper a new sensing principle is proposed. A proximity sensor based on magnetoresistive sensing element has been assembled end tested. A simple and portable test bench with variable speed, blade tip width, variable clearance was built and used in order to characterize the main sensor performances.