A low cost node based on CAN I/O Expanders to detect people on escalators and moving walkways.

Safety standards oblige to know the presence of people inside an escalator and moving walkways before changing its operation state. A photoelectric curtain based on emitter/receiver photocells is a good low cost solution. As a pair of emitter/receiver must be positioned every 30 cm along the escalator, the number of detectors increases greatly in long type conveyors and also increases the assembly and wiring cost. This paper shows a solution based in a CAN slave node network distributed along both balustrades of the conveyor (Figure 1). Every CAN slave node is based on a low cost CAN Input/Output Expander chip and controls a set of detectors (emitters or receivers). There is also a master CAN node based on a PIC microcontroller that treats all messages information received from the slave CAN nodes and controls a safety relay that informs to the motor drive controller.