External motor drive system adjusting for creep in window covering system with continuous cord loop

Abstract

A drive system for raising and lowering a window covering includes a motor, a driven wheel configured to engage a continuous cord loop, a controller for the motor, a sensor, and a housing. The continuous cord loop includes an endless loop of flexible material and one or more sensor targets disposed on the endless loop of flexible material. The housing supports a guide rail adjacent the driven wheel. The sensor is mounted to the guide rail and is configured to generate a signal indicating presence of each sensor target when the target is located in proximity to or in contact with the sensor. The controller is calibrated to store an initial position of each sensor target along the continuous cord loop, and is configured to receive the signal indicating presence of the sensor target and to identify a drift from the initial position during continuing operation of the drive system.