An image recognition measurement approach and uncertainty for overspeed governors employed in elevator safety

Elevator safety is closely related to public safety. Overspeed governor is a crucial part of the elevator safety system. Its inspection and calibration involve the measurement of tripping velocity. The frequently-used contact-type measurement method has risks. This paper proposes a non-contact image-recognizing measurement method by the camera, which includes the processes of rotor centre recognition, feature points matching, and tripping switches recognition. The velocity curve can be obtained by feature points displacement based on the rotor centre. Tripping switches recognition can determine the electrical and mechanical tripping velocities in the speed curve. The experimental results demonstrate that the proposed method has no significant difference from the common contact-type measurement method, while it significantly eliminates the risks of physical damage and improves measurement safety. Moreover, this paper proposes the deduction and calculation of measurement uncertainty decided by camera performance. Due to the enhancement of measuring safety, the proposed method will have further application in the field of elevator inspection.