Fotografisches Rollenkopiergerät

1312474 Photographic printing apparatus AGFA - GEVAERT AG 27 April 1970 [25 April 1969] 20109/70 Heading G2A A photographic printing apparatus includes a transport roller 8 which, when rotated by drive means (not shown), can advance a web 4 of copy material through the apparatus; a ratchet wheel 17 coupled to the roller 8; a pawl 18 which, when moved into engagement with the wheel 17 stops the roller 8 rotating; and control means capable of effecting engagement of the pawl 18 with the ratchet 17 when the web 4 has been advanced a preselected amount by the roller 8, which control means comprises a marking means and a scanning means. The roller spindle 14 carries a sprocket 16 slidably coupled thereto, the sprocket being chain driven. The pawl 18 is held out of engagement with the wheel 17 by an electromagnet 20, against the bias of a spring 19. At an exposure station 7, a known graphite marking device 12 and a photo-electric or electric scanning device 13 are provided, each of which is coupled to a movable mask of the exposure station. In the course of an exposure operation a mark is applied to the web 4 by the marking device 12. After an exposure is made, the pawl 18 is moved out of engagement with the wheel 17, and the roller 8 advances the web 4 thereby bringing the mark beneath the scanning device 13, which accordingly de-energizes the magnet 20 to free the pawl 18 and hence stop the roller 8. In another embodiment Fig. 3, (not shown), the sprocket (16) is coupled to the spindle (14) by an electromagnetically controlled coupling (21). An electromagnetic brake (22), which acts on the spindle (14), is also provided, the coupling and brake being controlled by way of a changeover contact (23) which in turn is controlled by the pawl (18). In a third embodiment Figs. 4, 5 (not shown), the spindle (14) carries a disc (28) having a magnetic recording layer on its periphery, the disc being rigidly coupled to the wheel (17). A magnetic recording head (24), a magnetic scanning head (25), and an erasing means are arranged about the disc (23), a magnetic impulse being applied to the disc when in the rest position in the course of an exposure operation. As the web is advanced, this recorded impulse is sensed by the head (25) thereby operating the pawl (18). The scanning head (25) may be adjustable in position. The arrangement of Fig. 3 can be provided with a similar magnetic control.