Measurement of short shaft power based on a digital speckle correlation method

This paper proposes a new method of using a camera to monitor changes in short shaft power. First, the camera is used to collect a sequence of images of the shaft surface without torque in advance as reference images. Then strain patterns of the shaft surface under the action of torque are collected and displacements between two adjacent frames are calculated to get the rotation speed by a digital speckle correlation method; a gradient algorithm is used to measure sub-pixel displacements between two ends of the strain images, and the torque is obtained. Finally, shaft power is obtained from rotational speed and torque. To verify the accuracy of measurement, bench experiments using different rotational speeds and torques are done, which are compared with standard sensor measurement. The measurement errors of speed, torque and shaft power are 0.1%-0.11%, 7.79%-10.91% and 7.7%-10.82%, respectively. Results show that the measurement system of shaft power based on a digital industrial camera has high precision. In comparison to the state-of-the-art methods, the proposed method has overcome the shortcomings of traditional methods whose installation is complex and whose signals easily interfere. It is characterized by simple construction, and applied to monitor dynamic short shaft power online.