Flip phenomena and co-existing attractors in an incremental actuator

The stepper motor converts electrical pulses into mechanical movements. The shaft of the motor rotates in discrete increments when command pulses are applied in the proper sequence. The dynamic behavior of this motor is of great importance, since instabilities lead to velocity fluctuations that are unacceptable in many applications. It is a major limitation to development of a high performance open-loop step motor system. This work represents a careful analysis of observed phenomena when this motor is operated within the chaotic regime. We report on several phenomena that have been observed in the experimental system. These phenomena, which include the alternating of the dynamics between two experimentally observable variables and the existence of co-existing attractors, greatly influence the types of control schemes that can or should be applied.