Development of a Control Method for Speed Pulsation in Escalator's Chain

Chain drives are used in escalator mechanisms to transfer movement from the motor to the steps and handrails with high-efficiency and synchronization. The chain consists of rollers and links that connect the rollers. The movement of the motor is transferred to the chain by a sprocket that engages the links. However, the rigidity of the links prevent a smooth contact between the chain and sprocket while it is possible with a belt drive. Because of that, the chain winds around the sprocket in a polygonal shape that produces variation in the horizontal speed of the chain even though the sprocket rotates with a steady speed. Such changes in horizontal chain speed are referred to as pulsations. The pulsations are transferred to the steps of the escalator and decrease the comfort of passengers. The proposed approaches to suppressing pulsation include shaping the chain rail with protrusions or depressions just before the sprocket teeth to vary the horizontal speed of the escalator steps so as to maintain a constant speed within the range where passengers ride (1) and to use an inverter to control the motor rotation speed to suppress the pulsation in the horizontal section of the chain.(2) The former approach requires machining the rail into a geometrically-determined irregular shape, and the latter basically requires a means of using the sprocket phase and step speed data as feedback to satisfy the condition of constant drive speed, as well as a control circuit that uses that data to control the motor speed. Both approaches will increase system cost. This paper proposes a new method to control the pulsation of chain speed keeping the constant rotational speed in the motor. It’s a method which makes the roller speed change moving roller track adding a new type of rail next to the sprocket.