Apparatus and method for controlling linear motors

Abstract

A reciprocatable shuttle employed to advance a variable number of article carriers through successive work stations is driven on forward and return movements by a plurality of energizable linear motor stators for which the shuttle forms a common reactor. Energization of the stators is controlled by a programmable logic contoller in response to inputs from velocity measuring circuits which determine the difference in the actual velocity of the shuttle relative to a desired maximum forward velocity, return velocity and creep velocity; to inputs from distance measuring curcuits which determine the distance travelled by the shuttle relative to a forward deceleration point and to a return deceleration point; to inputs which establish the return or forward position of the shuttle; and, to inputs which count the number of article carriers to be advanced. The programmable logic causes the stators to be progressively energized at timed intervals in response to a velocity ON signal to accelerate the shuttle to that velocity; to maintain the shuttle at that velocity; and, in response to a distance signal, to reversely energize the stators until the shuttle reaches the creep velocity. The maximum number of stators energizable is limited in accordance with the article carrier count, and the sequence in which the stators are energized is rotated on each forward-advance movement cycle of the shuttle.