Abstract

The exact shaft angle position synchronization of two or more ordinary synchronous induction motors is provided. One motor, serving as the master, is powered directly from a source of alternating current. Each additional motor, which may be of a different size or type, is slaved to the intrinsic rotational speed of the master through the inherent electrical speed synchronization wrought by being excited by a common alternating current power source. Each slave motor is further synchronized by this invention to attain, and subsequently hold, an exact angular shaft position relative to the master. The position of the master and each slave motor shaft position is constantly measured, thereby producing several trains of electrical pulses which are compared. When an error exists, an electrical signal is produced which acts with the a.c. excitation applied to the slave motor so as to controllably retard its rotational velocity, thereby causing the angular shaft position to the slave motor to slip, or be retarded, relative to the angular position of the master motor shaft. When the angle of the slave has slipped sufficiently, and generally less than 360 degrees, the pulse train produced by the master and the slave achieve momentary coincidence and the electrical retardation of the slave motor ceases. The subsequent result is a mechanical synchronization of the angular shaft position of each motor, which is then maintained in that useful relationship by the nature of their common speed synchronization with the alternating current source frequency.