The instantaneous rotational speed (IRS) of a rotating machine is key information to understand the machine operation and diagnose the potential faults. A novel nonprojection fringe vision-based system was proposed to realize the measurement of IRS, which was simply composed of an artificial linearly varying-density fringe pattern (LVD-FP) as a sensor and a high-speed camera as a detector. The designed LVD-FP, printed by a normal printer, was pasted around the surface of the rotary shaft completely along the fringe density change direction. Part of the LVD-FP was captured by the high-speed camera. The fringe period density of each imaged LVD-FP intensity changed due to the rotation of the shaft, from which the rotational angle could be obtained. Subsequently, both the instantaneous angular speed (IAS) between two adjacent frames and the IRS could be accurately and efficiently obtained. The influences of the key parameters of the proposed system on the measurement accuracy were investigated by simulations and experiments. Both the simulation and experimental results demonstrated that the proposed system can accurately measure the IAS and correctly track the wide range IRS with the advantage of noncontact and cost effective. In addition, the rotation direction of the shaft could be directly obtained from the sign of the IRS curves. Therefore, the proposed system could provide a novel vision-based approach for IRS measurement, especially when the conventional speed sensor cannot be installed on the rotary shaft. The good performance of the system in IRS measurement makes it attractive for fault diagnosis of rotating machinery.

A non-projection fringe vision measurement system suitable for vibration monitoring was proposed by using the concept of a 2D optical coherence vibration tomography (2D-OCVT) technique. An artificial quasi-interferogram fringe pattern (QIFP), similar to the interferogram of the 2D-OCVT system, was pasted onto the surface of a vibrating structure as a sensor. Image sequences of the QIFP were captured by a high-speed CMOS camera that worked as a detector. It was possible to obtain both the in-plane and out-of-plane vibration simultaneously. The in-plane vibration was obtained by tracking the center of the imaged QIFP using an image cross-correlation method, whilst the out-of-plane vibration was obtained from the changes in period density of the imaged QIFP. The influence of the noise sources from the CMOS image sensor, together with the effect of the imaging distance, the period density of the QIFP and also the key parameters of the fringe density enhanced by the spectrum correction method on the accuracy of the displacement measurement, were investigated by numerical simulations and experiments. Compared with the results from a conventional accelerometer-based measurement system, the proposed method was demonstrated to be an effective and accurate technique for measuring structural vibration without introducing any extra mass from the accelerometer. The significant advantages of this method include its simple installation and real-time dynamic response measurement capability, making the measurement system ideal for the low- and high-frequency vibration monitoring of engineering structures.