CA1080557A

CA1080557A - Sheet sensing device in a rotary printing press

Info

Publication number: CA1080557A
Application number: CA269,269A
Authority: CA
Inventors: Arno Wirz; Willi Becker
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 1976-05-13
Filing date: 1977-01-06
Publication date: 1980-07-01
Also published as: NO144915C; SE7705582L; DK143543B; DK125777A; DE2621250B1; CS192573B2; BE854635A; AU501905B2; AR211175A1; DK143543C; SE414738B; JPS5526982B2; ZA77246B; ES457023A1; FR2350959B1; AT355600B; ATA960676A; NL165113B; NO144915B; NL165113C

Abstract

Abstract of the Disclosure The specification describes a sheet sensing device for use in a rotary printing press, preferably of the perfecting type. The device includes a plurality of sheet delivery drums equipped with grippers to grip the front edge of the sheets, as well as grippers to grip the back edge of the sheet. The area of the grippers which grip the back edge of the sheets is provided with sensing nozzles which are connected to a generator operated under pneumatic pressure via a feeder system. The feeder system includes a pressure guard between the pressure generator and the sensing nozzles.

Description

The invention concerns a'sh~:Qt sensing device in a rotary printing press, particularly for perfecting. with sheet delivery drums equipped with grippers to grip the front edge of sheets and also gripping means to grip the back edge of sheets.
A sheet-fed offset printing press for perfecting, provided between the first and second printing unit with a sheet turning station consisting of two sheet transfer drums and one turning drum, is known. Below this turning drum an electronic sensing eye is provided to establish whether or not a sheet is being transfer-red by the turning drum grippers to the printing cylinder of the second printing unit.
This electronic sensing device is very susceptible to paper dust and, therefore, must be cleaned often. Sensing occurs while the sheet passes and false indications can, therefore, not be ex-cluded, particularly with higher printing speeds. The electronicsensing device, for instance, can only establish the absence of a sheet, but turned-over sheet corners which could damage the rubber blanket of the second printing unit, or a sheet which has been acquired on a slant or inadequately, would not be indicated by the known electronic sensing eye. False indications, however, cause either a machine stoppage or at least spoilage and thus possible damage to the rubber blanket. Moreover, such electronic sensing devices are very expensive.
The invention is based on the task to establish early, with certainty and at little expenditure, whether a fault-free sheet is being transferred, correctly positioned, by the sheet transfer drums or the whole sheet turning station to the following printing unit.
According to the invention this task is solved by providing in the area of the gripping means to grip the back edge of sheets .. . ~ , .

108(~557 -. senslng nozzles which are con~ec~e~ to a pne~ma~ic press~re genera-tor via a feeder system, this feeder system being equipped with a pressure monitoring means between the pressure generator and the sensing nozzles.
Sensing occurs during relative motionlesslless, i.e., the sheet on the sheet transfer drums and the sensing nozzles show practically no movement with respect to each other while sensing is in progress. Sensing, therefore, is extremely reliable. More-over, it occurs very early so that even with high printing speeds the rotary printing press can always be stopped in time, or the pressure turned off. With an arrangement of the sensing nozzles along the whole length of a sheet transfer drum not only sheets acquired on a slant can be sensed but also faults at the edge of the sheet acquired such as torn-out portions of the sheet and folded corners.
The construction of the gripping means as suction grippers and their simultaneous function as sensing nozzles constitutes a particularly advantageous development of the invention. Suction grippers and sensing nozzles are thus identical. Only the small expenditure of merely providing a pressure monitoring means in the feeder system is required to guarantee perfect super-vision of the sheet transfer by sheet transfer drums. This development of the invention is, therefore, also quite suit-able for the refitting of pneumatic sheet-transport installa tion in already existing rotary printing presses.
In an advantageous development of the invention the suction grippers extend in a row along the drum channel of the sheet -transfer drum, at least two suction grippers in the central region of the row being arranged to be offset such that they are closer -to th~ drum channel than the remaining suction grippers in the row.

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The length of a sheet can be measured hereby witll an accuracy of less than one mlllimetre. In rotary printing presses of the per-fecting type with a turning station this ensures that sheets which are too short are recognized as such and corresponding commands can be introduced for the control of the machine, e.g., the stop-ping of printing in the next unit.
One development of the invention makes provision to turn off or regulatethe suction effect of individual suction grippers or sensing nozzles, respectively, for the processing of narrower for-mats. This possibility is also of advantage for the processing ofthinner papers because in such cases the danger exists that the thin papers are sucked into the noz~les locally, leading to the possible deformation of the sheet acquired by the suction grippers and sensed.
In a particularly advantageous development of the invention the suction grippers constructed as sensing nozzles are socalled rotary suckers, constructed as discs which can be rotated by con-; trol means about an axis of rotation running at right angles to ; the axis of rotation of the sheet transfer drum and each of these discs being provided with a suction hole placed eccentrically to the axis of rotation.
The rotary suckers serve to tension the sheets on the sheet transfer drum. At the ~eginning of each tensioning process the suction holes located eccentrically with respect to the axis of rotation of each disc are farthest away from the cylinder channe~.
During the tensioning of the sheet they approach the drum channel wall. The initial position of the suction openings at the start of tensioning and sensing has the advantage that sheets which do not lie smoothly or tightly on the sheet transfer drum are not indicated as being too short, and do not result unnecessarily in ; 3 .. . . .

1(~805~;7 any fault-stops. During the senjin~ process, therefore, the sen-sing nozzles according to this embodiment move towards the drum J
channel of the sheet transfer drum and should the tensioned sheet be too short the suction openings move beyond the back edge of the sensed sheet, causing, e.g., the rotary printing press to be switched off.
A particularly advantageous development with regard to the processing of thin sheets consists in that the suction holes of those rotary suckers which are closer to the drum channel have a smaller cross-section than the suction holes of the remaining rotary suckers arranged in a row. The small cross-section of these suction openings results in a-choking effect which reduces ;
the suction force of the rotary suckers located closer to the drum channel with respect to that of the others in the row. This results in a protection of thin papers in the vicinity of the back edge of the sheet.
A development which is significant for small diameters of sheet transfer drums is distinguished by the arrangement of at least two sensiny nozzles between the gripplng means arranged in a row, and the drum channel, these sensing nozzles being connected to a pneumatic pressure generator via an air control device and an interconnected pressure monitoring me~ns.
The additional sensing nozzles can be controlled separately. ;
Thus sensing can occur under reduced pressure. Separate nozzles ~ -~
25 have the further advantage that they can be fitted better to the ~ ;
cylinder circumference, thus contributing to accurate sheet trans-fer particularly with small diameter sheet transfer drums. For should the sensing nozzles lie on a secant within the circumference of the sheet transfer drum the back edge of the sheet is sucked inwards, and the grippers lying on the clrcumference of the next 108()557 sheet transfer drum lift the ~ack edge o~ the sheet up again, re-sulting in a wavy transfer. The stronger this wavyness the yreater the danger of image deterioration in the following printing units due to a more inaccurate transfer.
With the use of sucking gripper means a particularly economic development of the invention consists in providing only one common air control device and only one pressure monitoring device for the gripping means constructed as suction grippers and the sensing nozzles which are formed into suction nozzles.
It can also be of advantage to shape the sensing nozzles as blower nozzles. Blower nozzles are self-cleaning and hence main-tenance-free. Sensing nozzles working with air-blast can be used best in connection with grippers. But they can also be used with gripper means constructed as suckers since the positive pressure used for sensing can be held low enough that the blast-pressure exerted locally exerts a force on the sheet which is less by a multiple than that of the suction grippers which grip the back edge of the sheet.
Several embodiments of the invention are explained by means of the drawing, as follows.
Figure 1 shows a sheet turning station with suction grippers to grip the back edge of sheets simultaneously constructed as sensing nozzles, Figure 2 shows a sheet turning drum with hinged suction grip-pers working as sensing nozzles, Figures 3-5 show a representation of the effect of the sensing nozzles constructed as rotary suckers, Figure 6 shows suction grippers formed as sensing nozzles of a sheet transfer drum arranged on a chain wheel shaft, Figure 7 shows a construction of a suction bar for a sheet ~ -- .

1080r~57 transEer drum accordiny to figur~ ~
Figure 8 shows a sheet turning station in which suction grip-pers and sensing nozzles are connected to separate negative pressure generators, Figure 9 shows a storage drum according to figure 8, Figure 10 shows a sheet turning station with clamping grippers to grip the back edge of sheets and with sensing nozzles constructed as blast-nozzles, and Figures 11, 12 show special arrangements of sensing nozzles.
In figure 1 a sheet turning station for a multi-colour sheet-fed rotary printing press is represented which can be switched from first printing to perfecting printing. This sheet turning station consists of three sheet transfer drums arranged between two success-ive printing units. The printing units themselves are not repre-sented. The first sheet transfer drum 1 accepts the sheet from the printing cylinder of the preceding printing unit and transfers it to the sheet transfer drum in the middle, designated as storage drum 2 in the following. In the second print position of tile sheet turning station the third sheet transfer drum, provided with a turning device and hence called turning drum 3, accepts the sheet on storage drum 2 by its back edge and feeds it, turned over! to the printing cylinder of the following printing unit.
Storage drum 2 has twice the diameter of sheet transfer drum 1 and turning drum 3. Correspondingly it is equipped with two 25- diametrically opposed drum channels 4. At the back wall of each of these drum channels 4 a row of clamping grippers 5 to acquire the front edge of sheets is provided and at the front wall a row of suction grippers 6 to hold the back edge.
Suction grippers 6 are connected with a negative pressure generator via a pressure feed 7. In order for suction grippers 6 to be al~le to work as sensing n~zzles ~he ;~rGssur~ feed 7 is Connected to a pressure monito~ing devic~ 9 controlled with respect to the sensing period.
Figure 2 also sllows a sheet turning station of a multi-colour sheet-fed rotary printing press which can be switched from first printing to perfecting printing but which consists of only a single turning drum 10. The printing cylinder 11 of the preceding printing unit, just like the printing cylinder of the following printing unit, has two printing surfaces. Turning drum 10, correspondingly, has two sheet transfer surfaces. At the back wall in the two drum channels 4 of the turnirg drum 10 clamping grippers 13 are provi-ded which are hinged and are able to accept inside drum channel 4 a sheet 15 in order to turn it over. Seen in the direction of rotation, the front wall of cylinder channel 4 is provided with a row of hinged suction grippers 14 which acquire the back edge of a sheet 15 on printing cylinder 11 and transfer it during the con- -tinued rotation of turning drum 10 to the clamping grippers 13 inside the drum channel 4. The suction grippers 14 are also con-structed as sensing nozzles.
Figure 3 shows one of the possible arrangements and uses of suction grippers 6 as sensing nozzles according to figure 1. It gives a schematic representation of a sheet guiding surface of the storage drum 2. The clamping grippers 5 have acquired the front edge 16 of the sheet 15. At the back end of this sheet guiding surface of storage drum 2 a suction bar 17 is provided, equipped with a row of disc-shaped rotary suckers 18. Each of these rotary suckers 18 has an eccentric suction hole 19 which works simultane-ously also as sensing nozzle. The suction hole 19 is arranged eccentrically with respect to the axis of rotation of the disc-shaped rotary sucker 18 and can be moved from the dash-dotted posi-tion 20 into the extended position by rotation oL the disc-shaped rotary suckers 18 over a lever system (not shown) during a sheet tensioning process. In the central area of the row of tlle rotary suckers 18 arranged along the drum channel 4 two rotary suckers 21 and 22 are arranged to be offset. They are closer to drum channel wall 23 than the normal rotary suckers 18. It is their task to determine the length of sheets.
Figure 1 shows the moment when suction grippers 6 are opposite the end of sheet 15. Suction holes 19 of rotary suckers 18 then are in the position 20 shown dash-dotted in figure 3. As is shown in figure 1 a control opening 24 has passed the front waIl of a control groove 25 such that the negative pressure generated by negative pressure generator 8 via pressure feed 7 causes suction sucking the back end of sheet 15. With continued rotation of 15 storage drum 2 rotary suckers 18, 21 and 22 are swung into the position shown as extended and pressure monitoring device 9 does not cause the printing press to be turned off, provided the sheet ~ ,- .
is without faults and has been transferred correctly. Should a portion of the back edge of the sheet be torn out, however, as shown 20 in Figure 3 at 26, these rotary suckers 18 suck fresh air and the negative pressure collapses or is reduced correspondingly. The pressure monitoring device 9 indicates a fault and the printing press switches off. Such commercially available pressure mon-itoring devices can be adjusted to the desired pressure difference.

Figures 4 and 5 show two other sources of faults leading often to malfunctions during run-on, particularly with perfecting. In figure 4 the sheet 15 is too short. It wo~ld then not be taken over correctly by the grippers of turning drum 3. In figure 4 the offset rotary suckers 21 and 22 are in their end position at the end of the tensioning phase of the sheet. The s~ction hole 19 of . .

10~0557 eacil rotary sucker 21 and 22 her~ has hal~ passed the ~ack edr~e 27 of the sheet. Tllis slight release of suction hole 19 is already sufficient, however, to lower the negative pressure enouyh for the pressure monitoring device to cause the printing press, or S printing, to be sto~ped Figure 5 shows a turned-over corner 28 of sheet 15. Already at the start of the tensionlng process suction hole 19 of the out-ermost rotary sucker 18 is not covered so that pressure mon-itoring device 9 causes the machine to be stopped as soon as negative pressure is applied.
The invention can also be used to advantage with sheet trans-fer and transport by means of chain grippers. Figure 6 shows su--h an embodiment. On chain-wheel shaft 30 of a chain gripper system 31 a sheet transfer drum 32 is arranged which is equipped at the front wall of its drum channel 33 with a suction bar 34. This serves to hold the sheet 15, fed past a turning drum 35 by chain ; gripper system 31, at its back edge until the grippers of turning drum 35 have securely gripped this back edge of sheet 15.
Figure 7 shows the construction of this suction bar 34. Suc-tion bar 34 is equipped with uniformly spaced suction holes 36which are symmetrical with respect to each other. They serve as suction grippers and as sensing nozzles at the same time. In the central region of the suction bar 34 one further sensing hole 37 each is provided, apart from the normal group of suction holes 36.
Sensing holes 37 are closest to the drum channel wall 38. If the back edge 27 of a sheet 15 is too short or if this sheet 15 is even just slightly at a slant the negative pressure syste~ of suction bar 34 is exposed to air and a pressure monitoring device, not shown, causes the rotary printing press, or the printing, to be stopped.

Figure 8 shows a sheet turning station fr~r multi-colour sheet-. ~ .

fed rotary printin~ presses where tlle print:ing unit cylinders have a relatively small diameter, i.e., ~he circ~mference of the indi-vidual drums has a relatively strong curvature.
Like that in Figure 1 this sheet turnillg station consists of the sheet transfer drum 1, the storage drum 2 and the turning drum 3. Drum channels 4 are equipped with clamping grippers 5 and suc-tion grippers 6 as per the embodiment in figure 1. Apart from suction grippers 6, however, further sensing nozzles 40 are arran-ged inside drum channels 4. They are placed in a row parallel to the row of suction grippers 6 ~see figure 11). Seen in the direc-tion of rotation of storage drum 2 they follow the suction grippers 6. The suction surface of the sensing nozzles 40 can be arranged ~ -high enough to lie right 3n the circumference of storage drum 2 such that the back edge of the sheet is not sucked inward during sensing with the consequent danger of a wavy transfer of the back edge to the grippers of turning drum 3.
Besides negative pressure generator 8, supplying control channel 25 via pressure feed 7 and suction grippers 6 via control opening 24, a further negative pressure generator 41 is provided which can generate a temporary negative pressure in sensing nozzles 40 via a pressure feed 42, a control groove 43 and a control opening 44. A pressure monitoring device 9 is connected into the pressure feed 42. Due to the arrangement of a separate negative pressure generator 41 sensing nozzles 40 are able to work with low constant pressure. It does not need to be adjusted to the various paper types to be handled, as when suction grippers are simultaneously sensing nozzles which means the pressure monitoring device 9 does also not need to be regulated.
Figure 9 shows a schematic side view of storage drum 2.

According to the representation storage drum 2 is supported in the side wall 48 of the frame on shaft-end 46 and in tl~e opposite side wall 49 of the frame on a further shaft-end 47. On the inside of the first mentioned frame side wall 48 a valve ring 50 is mounted symmetrically to shaft-end 46 and on the free frontal side 51 of which runs a valve ring 52 of the same size which is firmly anchored to storage drum 2. Valve ring 50 mounted on frame side wall 48 is equipped with control grooves 25 and 43 which are connected to their associated negative pressure generator 8 or 41 via pressure feed 7 or pressure feed 42, respectively, and the pressure mon-10 itoring device 9. The control openings 24 and 44 already mentioned are located in the valve 4ing 42 rotating with storage drum

2. Control opening 24 is connected to suction grippers 6 via a suction pipe 53 and control opening 44 to sensing nozzles 40 via another suction pipe 54.

, Sensing nozzles 40 are equipped with regulating screws 55 by means of which either the suction effect is regulated or tlle con-nection of sensing nozzle 40 to suction pipe 54 interrupted.
Should the format of a sheet 15, for instance, as shown in figure 9, be narrower than the sheet transport surface of storage drum 2, the outer sensing nozzles 40 can be turned off by screwing regula-ting screws 55 in. When there are two negative pressure generators 8 and 41, as shown in the ernbodiment according to figure 8, sensing nozzles 40 can also be constructed as blower nozzles. This has the advantage that they are self-cleaning and hence maintenance-free.
The use of blower nozzles is of particular advantage, however, in conjunction with clamping grippers, as shown in figure 10. Tllis also shows a sheet turning station, consisting of the sheet trans-fer drum l, the storage drum 2 and the turning drum 3. Drum channels 4, however, besides the clamping grippers 5 for acquisi-tion of the front edge of the sheet, are equipped with a further I w or clamping grippers 60 for the acquisition of the black edge of the sheet. Immediately next to each clamping gripper 60 a sensing nozzle formed as blower nozzle 61 is arranged as can be seen in Figure 12. The blower nozzles 61 are connected to a posi-tive pressure generator 67 via a control opening 64, a control channel 65 and a pressure feed 66. A pressure monitoring device 9 is connected into pressure feed 66. An extremely small amount of positive pressure is adequate to sense the back area of the sheet.
Even when processing air-mail paper, therefore, the back edge 0 of the sheet can be sensed without the thin sheet being blown up.
The diameter of the sensing nozzles can be kept extremely small so that even slight deviations in the lengths of the sheets or in the formation of the back edge of the sheets cause the rot-ary printing press to be turned off through the pressure mon-~ itoring device.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Sheet sensing device in a rotary printing press having a sheet transferring drum provided at respective regions thereof with gripping means for gripping the leading and trailing edges of a sheet being transferred, comprising sensing nozzles disposed in the region of the gripping means for gripping the trailing edge of a sheet, said sensing nozzles extending across the drum over a distance essentially corresponding to the width of the sheet being transferred, a line system con-necting said sensing nozzles to a pneumatic pressure-generating source, and pressure monitoring means connected in said line system between said sensing nozzles and said pneumatic pressure-generating source.

2. Sheet sensing device according to Claim 1, wherein, the gripping means for gripping the trailing edge of a sheet are constructed as suction grippers which simultaneously serve as sensing nozzles.

3. Sheet sensing device in a rotary printing press having a sheet transferring drum provided at respective regions thereof with gripping means for gripping the leading and trailing edges of a sheet being transferred, comprising sensing nozzles disposed in the region of the gripping means for grip-ping the trailing edge of a sheet, a line system connecting said sensing nozzles to a pneumatic pressure-generating source, and pressure monitoring means connected in said line system between said sensing nozzles and said pneumatic pressure-generating source, the gripping means for gripping the trailing edge of a sheet being constructed as suction grippers and serving simultaneously as said sensing nozzles, the sheet transferring drum being formed with a drum channel, said suction grippers extending in a row across the drum over a distance essentially corresponding to the width of the sheet being transferred and adjacent said drum channel, at least two of said suction grippers located substantially in the middle region of said row of suction grippers being offset with respect to the others of said suction grippers and being closer to said drum channel then the others of said suction grippers.

4. Sheet sensing device according to Claim 2 or 3, further including control means for turning off individual suction grippers and regulating individual sensing nozzles by varying the pressure differential between both the grippers and atmosphere and the nozzles and atmosphere.

5. Sheet sensing device according to Claim 2 or 3, characterized in that the suction grippers which simultaneously serve as sensing nozzles are constructed as discs which can be rotated by control means about an axis of rotation running at right angles to the axis of rotation of the sheet tran-sfer drum, each disc being provided with a suction hole placed eccentrically to the axis of rotation.

6. Sheet sensing device in a rotary printing press having a sheet transferring drum provided at respective regions thereof with gripping means for gripping the leading and trailing edges of a sheet being transferred, comprising sensing nozzles disposed in the region of the gripping means for gripping the trailing edge of a sheet and extending across the drum over a distance essentially corresponding to the width of the sheet being transferred, a line system connecting said sensing nozzles to a pneumatic pressure-generating source, and pressure monitoring means connected in said line system between said sensing nozzles and said pneumatic pressure-generating source, the gripping means for gripping the trailing edge of a sheet being constructed as suction grippers and serving simultaneously as sensing nozzles, said suction grippers serving simultaneously as sensing nozzles being rotary suckers comprising respective disc members controllably rotatable about a rotary axis extending substantially per-pendicularly to the axis of rotation of the sheet transferring drum, said disc members being formed, respectively, with a suction hole located eccentrically to the axis of rotation of the respective disc member, the sheet transferring drum being formed with a drum channel, said rotary suckers located substantially in a middle region of said row of rotary suckers being offset with respect to the others of said rotary suckers and being closer to said drum channel than the others of said rotary suckers, the suction holes respectively formed in the rotary suckers closer to said drum channel having a smaller cross section than that of the respective suction holes formed in the others of said rotary suckers.

7. Sheet sensing device as claimed in Claim 1 wherein at least two sensing nozzles are arranged in a row following said gripping means for gripping the trailing edge of a sheet with respect to the direction of rotation of the transfer drum.

8. Sheet sensing device according to claim 7 wherein only one line system and only one pressure monitoring means are provided for said gripping means and said sensing nozzles.

9. Sheet sensing device according to Claim 7, charac-terized in that the senzing nozzles are formed as blower-nozzles.