Abstract: A storage system with movable units is equipped with emitters for providing a series of radiant energy beams directed along an array of parallel paths through passages beneath the movable units. A control computer stops movement of the movable units in response to blockage of any path. Additionally, the system compares the identities of paths blocked on one cycle with those blocked on a prior cycle to determine whether unblocking of a path is due to a person or other object leaving the work area or is due by a condition in which the system has lost track of the person or object. In the latter case, the system inhibits operation of the movable units even if all paths are unblocked.

Abstract: A locking mechanism for a system of movable storage units is actuated passively to prevent the storage units from moving back toward one another once an access aisle has been created therebetween. The locking mechanism includes a first gear which rotates with the operating handle during movement of a storage unit and a floating gear mounted to a support plate so that it meshes with the first gear. After a storage unit has been moved in one direction to create an access aisle, rotating the operating handle to move the storage unit in the opposite direction to close the aisle will cause the support member and floating gear to pivot toward a position in which the floating gear is engaged with an arresting member, whereupon the storage unit will be locked from movement in that opposite direction. A logic system controls the actuation of the locking mechanism responsive to the position of the storage unit with respect to adjacent storage units.