This article was published in the Journal of Sound and Vibration [© Elsevier] and the definitive version is available at: http://dx.doi.org/10.1016/0022-460X(89)90705-0The application of Laser Doppler Velocimetry (LDV) to the measurement of\ud normal-to-surface vibration of a solid surface is now established as a technique\ud complementary to the use of an accelerometer. Several practical systems have been\ud developed and a number are now commercially available. Each velocirneter relies on\ud the same principle of operation, namely the detection of a Doppler shift, fD, in\ud the light scattered from a vibrating target. Fig. 1 shows a typical vibrometer\ud arrangement. Since the photodetector cannot respond quickly enough to detect the\ud light frequency directly, scattered light from the vibrating surface is mixed\ud with a reference beam and heterodyned on the detector surface. In addition, in\ud order to resolve the sign of the vibration velocity, it is necessary to pre-shift\ud the reference beam by a known amount, fR, resulting in an optical beat at the\ud detector of frequency (fR ± fD). An appropriate Doppler signal processor then\ud demodulates the detector signal to produce a time-resolved analogue of the target\ud vibration velocity (in the direction of the incident beam). Systems differ in the\ud method adopted to produce the reference beam frequency shift. Bragg cells [1],\ud diffraction gratings [2] rotating scattering discs [3] and frequency modulation\ud of the laser beam itself [4] have all been used successfully... (continues)

The fundamental mechanism by which speckle noise is generated in laser vibrometry before describing a new numerical simulation for prediction of speckle noise level in a real measurement is considered. Factors within the simulation include rate of change of phase within individual speckle transitions, low-pass filtering to match the frequency range of experimental data with which comparison is to be made, a track-and-hold facility for periods of low signal amplitude, and wavefront curvature effects. The simulation data provide real insight into the phase and amplitude modulation of the Doppler signal, and good agreement is found in the final comparison with experimental data from a measurement on a rotating target.

Three types of thin, flexible force sensor were studied under a variety of loading conditions to determine their suitability for measuring grip force. Static accuracy, hysteresis, repeatability, and drift errors were established, the effects of shear force and surface curvature were considered, and dynamic accuracy and drift were measured. Novel tests were developed to consider dynamic accuracy and sensitivity to shear loadings. Additionally, three sensors were evaluated in a real-life gripping scenario, measuring grip force during a golf shot. Comments are made on sensor performance, ease of use, and durability.

This is an Open Access Article. It is published by Elsevier as Open Access at: http://dx.doi.org/10.1016/j.ymssp.2014.11.012Piston slap is a major source of vibration and noise in internal combustion engines. Therefore, better understanding of the conditions favouring piston slap can be beneficial for the reduction of engine Noise, Vibration and Harshness (NVH). Past research has attempted to determine the exact position of piston slap events during the engine cycle and correlate them to the engine block vibration response. Validated numerical/analytical models of the piston assembly can be very useful towards this aim, since extracting the relevant information from experimental measurements can be a tedious and complicated process.In the present work, a coupled simulation of piston dynamics and engine tribology (tribodynamics) has been performed using quasi-static and transient numerical codes. Thus, the inertia and reaction forces developed in the piston are calculated. The occurrence of piston slap events in the engine cycle is monitored by introducing six alternative concepts: (i) the quasi-static lateral force, (ii) the transient lateral force, (iii) the minimum film thickness occurrence, (iv) the maximum energy transfer, (v) the lubricant squeeze velocity and (vi) the piston-impact angular duration. The validation of the proposed methods is achieved using experimental measurements taken from a single cylinder petrol engine in laboratory conditions. The surface acceleration of the engine block is measured at the thrust- and anti-thrust side locations. The correlation between the theoretically predicted events and the measured acceleration signals has been satisfactory in determining piston slap incidents, using the aforementioned concepts. The results also exhibit good repeatability throughout the set of measurements obtained in terms of the number of events occurring and their locations during the engine cycle

This article was published in the journal, Optics and Lasers in Engineering [© Elsevier] and the definitive version is available at: http://dx.doi.org/10.1016/j.optlaseng.2008.06.010When coherent light scatters from a surface, which is rough on the scale of the wavelength of the light, a speckle pattern is produced. The Laser Vibrometer measures target vibration velocity in the direction of the incident laser beam and typically samples a region of a speckle pattern on its photodetector. Target motions can cause the speckle pattern to change on the photodetector surface, particularly when target motions are non-normal to the direction of the laser beam. This speckle motion modulates the Doppler signal and adds noise to the demodulated output signal. Periodic target motions can cause the speckle noise to become pseudo-random and produce harmonic peaks, with the same fundamental frequency as the genuine target vibrations, which can be indistinguishable from the genuine target vibrations. Typical speckle noise levels are generally considered to be low-level, but they have not so far been adequately quantified. This paper reports preliminary results quantifying speckle noise levels using controlled experimental configurations incorporating periodic in-plane and tilt target motions. Working with commercial Laser Vibrometers, various target surface finishes and treatments are considered and speckle noise maps are produced for each configuration. For a tilting surface, speckle noise has been quantified at approximately 1 μm s−1/deg s−1 while, for surfaces with in-plane motion, the sensitivity to speckle noise has been estimated pessimistically at 0.1% of the in-plane velocity. Ultimately, these speckle noise maps will form a valuable practical resource for the Laser Vibrometer user