Webcam-Based Tachometer for In-field Induction Motor Load Estimation, Proc The International Conference of Electrical Machines Association Fernando José Pimentel Lopes ICEM, Lausanne, Switzerland, Vol. 1, pp. 1 - 9, September, 2016.
Abstract -- Rotational speed measurement is a key issue in most industries, either for process control, characterization or fault diagnosis. In electric motor driven systems it can be used, for example, to estimate the motor load or pulley-belt transmission slip. Encoders and resolvers are typically used for continuous speed monitoring, requiring mechanical coupling with the rotating shaft/part. If the speed is to be measured at a given instant or during a few moments, noninvasive contactless optical tachometers can be used, using optical reflection or stroboscopic principles. In most cases, stroboscopic tachometers require no reflective elements/strips in the rotating part. However, if the user wants to continuously measure the speed of a given rotating part during the audit/characterization period, with real-time data logging and without sticking reflective strips or introducing shaft-coupled encoders/resolvers, there is no low-cost commercial solution to perform such task. For example, if the user’s aim is to continuously estimate the load variation of an induction motor over a day or week, on the basis of the slip/speed value, it is not possible with conventional commercial low-cost contactless equipment, unless the user uses expensive online-operation equipment estimating the speed by means of input voltage/current. Moreover, in some rotating systems/parts not directly driven by an electric motor, the online equipment cannot be used and it is not practical, and in some cases even impossible, to couple an encoder/resolver or stick some reflective strips. In this paper, an innovative nonintrusive low-cost webcam-based tachometer is proposed, developed and experimentally tested. It can be used to easily estimate and record the speed over time in, for example, electrical motors, pulleys, shafts and wind turbines.