US Patent 9509243 Automatic actuator calibration using back EMF

A self-calibrating linear actuator is configured to control a spring return valve with variable stroke. The actuator includes a motor, a spindle coupled to an output of the motor, a motor controller coupled to the motor, a microcontroller coupled to the motor controller, and a back electromotive force (BEMF) circuit, coupled to the motor, configured to provide to the microcontroller a BEMF value for each motor step. The microcontroller is configured to determine a difference of a number of motor steps during operation of the actuator and to store the difference as a calibrated touch point for the actuator.