Crack detection on an escalator handrail

In the course of an escalator inspection the service crew checks the surface of the handrails. This surface has to be smooth without any cracks to prevent injuries of passengers. The inspection is still carried out manually as no sensors are on the market to fulfil this safety critical task. A low target price, harsh environmental conditions, and a high reliability impede the use of standard off-the-shelf sensors for such a crack detection. The paper compares the potential of different types of sensors to reliably detect cracks on escalator handrails. The benefits and drawbacks of non-contacting sensing techniques like ultrasonic, inductive, capacitive, and optical are discussed. Finally, a new low-cost optoelectronic prototype device is presented together with some measurement results. This prototype sensor reliably detects cracks on escalator handrails.