Patent ID: 8810187

Claim:
A method for misstep detection and motor step recovery in a stepper motor operating in synchronous, open-loop mode, comprising the steps: operating a stepper motor in synchronous, open-loop mode to produce movement along a trajectory comprised of commanded target positions; establishing a range of load angle values that are representative of normal motor operation, with load angle values outside of said established range being indicative of the occurrence of at least one misstep; periodically, in the course of movement of the stepper motor along said trajectory, accessing feedback signals, generated by a position-feedback device, to determine the actual position of the motor shaft; periodically, in the course of movement of the stepper motor along said trajectory, computing deviations from commanded positions by subtracting actual shaft positions, indicated by said accessed feedback signals generated by the position-feedback device, from corresponding commanded positions; utilizing each computed position deviation solely to determine if it corresponds to a load angle value that lies either within or beyond said established range of load angle values; if, throughout each period of position-indicating feedback signal access, said corresponding load angle value is determined to lie within said range of established load angle values, maintaining normal stepper operation of the motor along said trajectory, without adjustment; and if, during any period of position-indicating feedback signal access, said corresponding load angle value is determined to lie beyond said established range, immediately taking action for recovery of lost motor steps.