9a 34 can maintain the platforms 16a 39 and 16a 34 in such positions that these platforms cannot interfere with the transport of packs 1 through the storing unit 6 and on toward the inlet of the processing machine 3 analogously the various stops are held in retracted or inoperative positions so that the packs 1 are transported at the speed of movement of the conveyor 4 the photocell l4 monitors the path for movement of packs with the upper reach of the conveyor 4 and transmits appropriate signals to the computer 41 during each of a series of successive intervals whose duration is determined by the computer thus the photocell l4 is active at all times to indicate whether or not successive packs 1 on the conveyor 4 are separated from each other by gaps or requisite width when the computer 41 receives such signals during each of the aforementioned intervals the operation of the production line is 34 normal 34 and the storing unit 6 is idle if the processing machine 3 is defective e g if the machine 3 is stopped due to a malfunction which can be detected automatically or by an attendant the switch 42 in the conductor means u is actuated.