A drive mechanism for door hardware, such as a pushbar exit device, includes a driver for moving a component of the door hardware, a controller for controlling the operation of the driver, a sensor for detecting motion of the moving component and a spring connected between the driver and the door hardware component. The spring allows the driver to move for a period of time after the component has stopped moving. The controller monitors the sensor and moves the component until the sensor indicates that the driven component has stopped moving. The sensor produces an output signal and the controller detects an inflection point in the output signal when the component stops moving while the driver is still operating.