Modelling and design of a direct-drive lift control with rope elasticity and estimation of starting torque

This paper deals with position control of a direct drive rope-based lift system at mechanical brake releasing. The electrical equipment includes a high-torque, low-speed permanent magnet synchronous motor with external rotor directly connected to the rope pulley. The drive uses only stator current sensors for torque control and an incremental encoder on the motor shaft. A detailed model of the system, which comprises also rope elasticity, is presented, as wells as a load torque estimation algorithm and a feedforward action on the torque reference signal. Such reference is used to reduce the cabin falling down at brake releasing below a perceptible threshold. Final experimental results support the mathematical theory outlined in the paper, validating the proposed control strategy.