A new active position sensing method for ropeless linear motor elevators

Linear motor driven elevators are desirable in high-rise buildings because of two main reasons: First, there are no theoretical limits to their length and second, more than one elevator cage can be driven by the same stator; multi-car elevators. Position sensing in multi-car elevators is difficult because no cables should be attached to the mover in a multi-car system. In this paper we propose a linear motor active position sensing method (LIMAP) inspired by linear variable differential transformer (LVDT), in which the position of the mover of a permanent magnet linear synchronous motor (PMLSM) can be measured using no electrical components on the mover, obviating the necessity of wires. A magnetic shunt is positioned at a fixed distance ahead of the mover, and the deformation it creates on the magnetic field produced by exciting one of the coils of the stator is measured through the voltages induced on the neighboring stator coils to calculate the position of the shunt, and thus the mover. A novel method on optimizing the dimensions of the magnetic shunt to give long measurement range and small position error, and a real-time measurement algorithm are also proposed. We verify our method by simulations and experimental results.