Device for forming a sequence of underlapping sheets

#This invention relates to a device for forming a sequence of underlapping sheets when conveying sheets that are cut off a paper web by means of a sheeter arranged before, to the feed table of a machine working these sheets, with a suction equipment arranged above the sheet web in the area between two draw-off equipments that are driven with different feed rates, and with a lifting equipment arranged below the sheet web, that brings the rear zone of every sheet into action with the suction equipment in order to form a guide gap for the following sheet.

#An arrangement of this kind is known from the DE-PS No. 21 37 335. With this known arrangement, suckers that are movable to and fro, are provided to form the suction equipment which is arranged above the sheet web. These suckers are in practice divided in two groups that are suspended pendulously and are connected to each other in such a way that one group is brought into the original position, while the other group is pulled in the direction of running by the sheet. This known arrangement has only shown satisfying results with low working speeds. As a result of the application of force, exerted here practically more or less pointlike, a comparatively high vacuum is required with this known arrangement in order to hold the lifted sheet securely. This has, however, a negative effect on the power input and, due to this, on the power consumption, seen in the long run. Apart from this, there is a secondary effect, that is felt to be most disadvantageous, that practically all suckers of a group of suckers will fail if only one of these suckers is not completely covered by the lifted sheet. This results in the necessity of adjusting the position of the suckers according to the size that is being worked; this not only leads to comparatively long setting times, but at the same time requires relatively high constructional expenditure. Apart from this, the arrangement as described above, proved to be too slow for increased working speeds.

#An experiment in this course in order to remove this difficulty by using continuously driven, rotating grippers, which has turned out to be quite useful for some cases of application, is described in the DE-OS No. 26 38 783. The grippers used here can, however, produce substantial noise. Besides this, the attainable distance between the scales is given firmly by the individual distance between the grippers, a fact that will prove negatively if various distances between the scales are required. Moving parts, such as the rotating grippers used here, demand moreover appropriate accident preventing devices in the form of covers etc., a fact that may cause considerable expenditure. This disadvantage is also valid for the suckers moved to and fro of the above mentioned kind. A further difficulty when using moved parts such as suckers moved to and fro or rotating grippers, is the necessity to synchronize these parts with the drive of the draw-off equipments that are decisive for the size of the scales.

#In doing so

#FIG. 1 shows the method of operation of a reel-sheet unit on principle,

#FIG. 2 shows a view of an especially preferred embodiment of the invention, partly sectional view, and

#The processing of paper reels by means of sheet-fed presses has a great amount of advantages, since especially a considerable increase of output and a decrease of costs are attained. In doing so, a paper web 2 is drawn off a paper reel 1, as indicated under FIG. 1; subsequently sheets are cut off the paper web by means of a sheeter, as indicated under 3. Subsequently the cut-off sheets are brought together by means of a device which will be explained more detailed below, to form a sequence of underlapping sheets as indicated under 4, which runs into a sheet feeding apparatus, not shown in detail, as indicated under 5; the sheet feeding apparatus feeds the sheets in cycles to a sheet working machine, as e.g. a printing machine.

#In order to form the sequence of sheets as indicated under 4, two draw-off equipments 6 and 7 are arranged subsequently to the sheeter 3, as indicated under FIG. 2, the rear draw-off equipment 6 which is near the sheeter, runs with increased speed as compared to that of the paper web, and the draw-off equipment 7 at the front runs at reduced speed, thereby forming a scale-like paper web. In the represented embodiment the rear draw-off equipment is designed as tape guide with deflection pulleys 8 and 9. The front draw-off equipment 7 is designed as a pair of rollers. In the range between the deflection pulley 8 of the shorter, top tape guide of the draw-off equipment 6 and the front draw-off equipment 7 there is, above the sheet web here being supported only by the bottom tape guide of the rear draw-off equipment 6, a suction box provided, the complete unit being specified under 10, which is connected to a vacuum supply. To do so, a connecting hose 11 is provided. The suction box 10 is bounded at the bottom by a punched plate, indicated under 12, which has a great amount of small holes 13, distributed on the entire area of the punched plate 12. As soon as there is a vacuum in the suction box 10, suction is exerted via the holes 13, which is sufficient to bring a sheet, that is near the punched plate 12, in contact with the punched plate 12. In doing so, a guide gap is formed into which each following sheet can slip in order to form a scale-like sheet web. Below the sheet web, defined by the bottom, longer tape guide of the rear draw-off equipment 6, there is a lifting device, the whole of which is represented with 14. The lifting device 14 may be designed as single blow nozzle. In the represented embodiment there is, in order to form the lifting device 14, a flap 15, supported angularly adjustable, provided, which can be operated in cycles by means of a push rod 16 in such a way as to bring the rear end of the sheet which is above in contact with the punched plate 12, as soon as the front end of this sheet is taken by the front draw-off equipment 7. FIG. 2 is based on a situation where the rear end of the front sheet A is already in action with the punched plate 12, and the following sheet B slips into the guide gap, indicated under 17. The lifting device 14 is in a delay position. The flap 15 is expediently provided with several teeth, arranged in the form of a rake between the single tapes of the bottom tape guide of the rear draw-off equipment 6. The same applies if the lifting device is operated pneumatically.

#During operation, there is a permanent vacuum in the suction box 10. Therefore the surface of the rear end of the sheet, the kind of which is indicated under A, that is brought into action with the suction box, is in contact with the punched plate 12. The retaining force exerted on this sheet via the holes 13, results at the same time in a tightening of the sheet that is conveyed further by the front draw-off equipment 7, in the course of which the rear end of the sheet slides smoothly over the punched plate 12. The punched plate 12 may be expediently polished on the range of its bottom surface in order to increase the slidability. The distribution of the holes 13 over the entire surface of the punched plate 12 not only results in an even contact of the sheet on its entire surface, but also results in a sufficient retaining force while the vacuum may be low in proportion, due to the large effective surface. The cross section of the individual holes 13 may nevertheless be comparatively small. A diameter of the holes of approximately 1.5 mm has especially held good when tests were carried out. Since already a low vacuum is sufficient to retain the sheet positively, as explained above, a sufficient retaining force is favourably guaranteed even if not all holes 13 of the punched plate 12 are covered. The length and width of the suction box 10 or of the punched plate 12 are therefore absolutely independent of the size being worked. The punched plate 12 therefore runs over the full width of the machine; due to this, lateral adjustment can be omitted. The length of the punched plate 12 corresponds to the maximum desired distance between the scales. The distance between the scales is, however, given firmly as a rule. In those cases the length of the punched plate 12 will be adapted to it.