CA1119459A - Method of unstressing a sheet - Google Patents
Method of unstressing a sheetInfo
- Publication number
- CA1119459A CA1119459A CA000326054A CA326054A CA1119459A CA 1119459 A CA1119459 A CA 1119459A CA 000326054 A CA000326054 A CA 000326054A CA 326054 A CA326054 A CA 326054A CA 1119459 A CA1119459 A CA 1119459A
- Authority
- CA
- Canada
- Prior art keywords
- grippers
- sheet
- bank
- transferred
- gripper
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41F—PRINTING MACHINES OR PRESSES
- B41F21/00—Devices for conveying sheets through printing apparatus or machines
- B41F21/10—Combinations of transfer drums and grippers
Landscapes
- Supply, Installation And Extraction Of Printed Sheets Or Plates (AREA)
- Feeding Of Articles By Means Other Than Belts Or Rollers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention concerns a method of relaxing or unstressing a sheet which is transferred from one bank of grippers in a rotary offset printing machine to the next bank of grippers. The invention reduces or eliminates stress in the front edge region of the sheet after the sheet has been transferred, yet before the next printing operation. This is accomplished by briefly opening or relaxing at least some of the grippers of the bank of grippers that are guiding the sheet. This invention reduces image imperfections caused by creasing, buckling or twisting of the sheet.
The present invention concerns a method of relaxing or unstressing a sheet which is transferred from one bank of grippers in a rotary offset printing machine to the next bank of grippers. The invention reduces or eliminates stress in the front edge region of the sheet after the sheet has been transferred, yet before the next printing operation. This is accomplished by briefly opening or relaxing at least some of the grippers of the bank of grippers that are guiding the sheet. This invention reduces image imperfections caused by creasing, buckling or twisting of the sheet.
Description
3~
The invention concerns a method of unstressing a sheet which is transferred from one bank of grippers in a xotary offset printing machine to the next bank of grippers.
In multi-colour printing incorrect sheet transfer often leads to a reduction in printing quality. Such difficulties can be expected particularly in the case of twisted paper which is not lying flat~ The following defects have been found: creasing of the sheetr reduced spacing in the case of multi-colour printing or register differences arising from printing unit to printing unit or when the same machine is passed through twice. Even in the case of a sheet which is lying flat a reason for a reduction in printing quality can be found in the fact that the sheet is transferred in a slightly crinkled condition or, in the case of a gripper transfer system with closely juxtaposed grippers r buckling occurs during transfer from a first to a second cylinder. Such incorrect sheet transfer causes stresses in the front edge region of the sheet which in turn lead to a change in the sheet during subsequent printing. This then ~esults r for example, in the above-mentioned image imperfections.
The object of the invention consists in eliminating or reducing the stresses in the front edge region of the sheet after the sheet has been transferred yet before the next start of printing.
The invention achieves this goal by the fact that, after the sheet has been transferred yet before the start of printing and before the next sheet is transferredr at least some of the grippers of the bank of grippers guiding the sheet are briefly relaxed or opened.
This brief opening and closing of all or some grippers frees the front edge of the sheet sufficiently in order to achieve the desired unstressing. Since the sheet is wrapped around the cylinder, the very fact of its curvature means that the front edge of the sheet has an inherent tendency to strai~h-ten itself anyway. This straightening force supports the unstressing of the front edge of the sheet as soon as it is released by some or all grippers~
If all the grippers of the banks of grippers are opened, it is necessary to provide an additional guide element in order to ensure that the exact register of the sheet is retained. This guide element may consist of two or more rollers which act, Eor example, on the sheet transported by the cylinder in question.
It is also possible to leave two or four grippers closed and to unstress the sheet by opening the remaining grippers. It has even been shown in tests that, in many cases, the opening merely of every other gripper permits sufficien-t unstressing of the front edge of the sheet.
In order to achieve the above-described unstressing of the sheet by means of the opening of the grippers it is merely necessary for the gripper opening cam to be of appropriate design. If the bank of grippers consists of two separately controlled groups of grippers, then each of these groups of grippers must be provided with a special control ~5 cam. It is then best for the two groups of grippers to be opened and closed once or twice alternately. This alternate opening and closing permits very effective unstressing of the front edge of the sheet.
A notably simple embodiment of the invention is explained below with the help of the drawings.
; -2-~ig. 1 shows a section through a diagrammatically presented bank of grippers according to the invention and Figs. 2 and 3 show a section through a similar bank of grippers in the area of their control elements.
The gripper 1 shown in Fig. belonging to a bank of grippers 2 of an impression cylinder 3 is fixed on a gripper housing 4 which is rotatably mounted on the gripper shaft 5.
A stop block 6 is rigidly attached to the gripper shaft 5 and connected via a compression spring 7 to the g~ipper housing 4. The compression spring 7 constantly forces the gripper 1 in the direction of the gripper contac-t shoulder 18.
Screwed into an adjustment tongue 9 of the stop block 6 is an adjusting bolt 10 whose end 11 in conjunction with a stop face 12 of the gripper housing 4 when the gripper 1 lifts off from the gripper contact shoulder 18.
The gaps 13 of the individual grippers 1 may be different so that the unstressing of the previously gripped front edge of the sheet is achieved employing an appropriately designed gripper shaft control cam 14 (see Fig. 2) by the fact that only some grippers 1 lift off while the others with a slightly larger gap 13 do not lift off yet. In the case oE a positively closing gripper system the gripper shaft control cam 14 is provided with a recess 15 whereas in the case of a non-positively closing gripper system the gripper shaft control cam 14 exhibits a prominence 16.
This measure represents a simple and low-cost way of unstressing a sheet which, for example, has been transerred to an impression cylinder 3.
After the sheet (not shown) has been transferred to the bank of grippers 2 of the impression cylinder 3, the .
cam roller 17 of the gripper shaft 5 reaches the above-mentioned slight recess 15 or prominence 16 of the gripper shaft control cam 14 and causes the l.ift-off from the gripper contact shoulder 8 oE all those grippers 1 which have a small gap 13 whereas the other grippers 1 with the larger gap 13 continue to hold the sheet in conjunction with the gripper contact shoulder 8 due to the force of the compression spring 7. The first-mentioned group of grippers 1 must have finished lifting off and reclosing before the start of printing.
The invention concerns a method of unstressing a sheet which is transferred from one bank of grippers in a xotary offset printing machine to the next bank of grippers.
In multi-colour printing incorrect sheet transfer often leads to a reduction in printing quality. Such difficulties can be expected particularly in the case of twisted paper which is not lying flat~ The following defects have been found: creasing of the sheetr reduced spacing in the case of multi-colour printing or register differences arising from printing unit to printing unit or when the same machine is passed through twice. Even in the case of a sheet which is lying flat a reason for a reduction in printing quality can be found in the fact that the sheet is transferred in a slightly crinkled condition or, in the case of a gripper transfer system with closely juxtaposed grippers r buckling occurs during transfer from a first to a second cylinder. Such incorrect sheet transfer causes stresses in the front edge region of the sheet which in turn lead to a change in the sheet during subsequent printing. This then ~esults r for example, in the above-mentioned image imperfections.
The object of the invention consists in eliminating or reducing the stresses in the front edge region of the sheet after the sheet has been transferred yet before the next start of printing.
The invention achieves this goal by the fact that, after the sheet has been transferred yet before the start of printing and before the next sheet is transferredr at least some of the grippers of the bank of grippers guiding the sheet are briefly relaxed or opened.
This brief opening and closing of all or some grippers frees the front edge of the sheet sufficiently in order to achieve the desired unstressing. Since the sheet is wrapped around the cylinder, the very fact of its curvature means that the front edge of the sheet has an inherent tendency to strai~h-ten itself anyway. This straightening force supports the unstressing of the front edge of the sheet as soon as it is released by some or all grippers~
If all the grippers of the banks of grippers are opened, it is necessary to provide an additional guide element in order to ensure that the exact register of the sheet is retained. This guide element may consist of two or more rollers which act, Eor example, on the sheet transported by the cylinder in question.
It is also possible to leave two or four grippers closed and to unstress the sheet by opening the remaining grippers. It has even been shown in tests that, in many cases, the opening merely of every other gripper permits sufficien-t unstressing of the front edge of the sheet.
In order to achieve the above-described unstressing of the sheet by means of the opening of the grippers it is merely necessary for the gripper opening cam to be of appropriate design. If the bank of grippers consists of two separately controlled groups of grippers, then each of these groups of grippers must be provided with a special control ~5 cam. It is then best for the two groups of grippers to be opened and closed once or twice alternately. This alternate opening and closing permits very effective unstressing of the front edge of the sheet.
A notably simple embodiment of the invention is explained below with the help of the drawings.
; -2-~ig. 1 shows a section through a diagrammatically presented bank of grippers according to the invention and Figs. 2 and 3 show a section through a similar bank of grippers in the area of their control elements.
The gripper 1 shown in Fig. belonging to a bank of grippers 2 of an impression cylinder 3 is fixed on a gripper housing 4 which is rotatably mounted on the gripper shaft 5.
A stop block 6 is rigidly attached to the gripper shaft 5 and connected via a compression spring 7 to the g~ipper housing 4. The compression spring 7 constantly forces the gripper 1 in the direction of the gripper contac-t shoulder 18.
Screwed into an adjustment tongue 9 of the stop block 6 is an adjusting bolt 10 whose end 11 in conjunction with a stop face 12 of the gripper housing 4 when the gripper 1 lifts off from the gripper contact shoulder 18.
The gaps 13 of the individual grippers 1 may be different so that the unstressing of the previously gripped front edge of the sheet is achieved employing an appropriately designed gripper shaft control cam 14 (see Fig. 2) by the fact that only some grippers 1 lift off while the others with a slightly larger gap 13 do not lift off yet. In the case oE a positively closing gripper system the gripper shaft control cam 14 is provided with a recess 15 whereas in the case of a non-positively closing gripper system the gripper shaft control cam 14 exhibits a prominence 16.
This measure represents a simple and low-cost way of unstressing a sheet which, for example, has been transerred to an impression cylinder 3.
After the sheet (not shown) has been transferred to the bank of grippers 2 of the impression cylinder 3, the .
cam roller 17 of the gripper shaft 5 reaches the above-mentioned slight recess 15 or prominence 16 of the gripper shaft control cam 14 and causes the l.ift-off from the gripper contact shoulder 8 oE all those grippers 1 which have a small gap 13 whereas the other grippers 1 with the larger gap 13 continue to hold the sheet in conjunction with the gripper contact shoulder 8 due to the force of the compression spring 7. The first-mentioned group of grippers 1 must have finished lifting off and reclosing before the start of printing.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Method of unstressing a sheet which is transferred from one bank of grippers in a rotary offset printing machine to the next bank of grippers wherein, after the sheet has been transferred yet before the start of printing and before the next sheet is transferred, at least some of the grippers of the bank of grippers guiding the sheet are briefly relaxed.
2. Method according to Claim 1, wherein all grippers of the bank of grippers are briefly opened and closed again and wherein, during this period, the sheet is guided by a guide element working in conjunction with the cylinder of the bank of grippers.
3. Method according to Claim 1, wherein two or more grippers of the bank of grippers remain constantly closed from the time the sheet is transferred up to the start of printing or up to the transfer of the next sheet whereas the other grippers are opened for a brief period.
4. Method according to Claim 1, wherein the bank of grippers is divided into two separately driven groups of grippers controlled in such a way that the groups of grippers open and close alternately.
5. Method according to Claim 1, wherein every other gripper is opened.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2820619.1 | 1978-05-11 | ||
| DE2820619A DE2820619C2 (en) | 1978-05-11 | 1978-05-11 | Method of relaxing an arch |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1119459A true CA1119459A (en) | 1982-03-09 |
Family
ID=6039140
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000326054A Expired CA1119459A (en) | 1978-05-11 | 1979-04-20 | Method of unstressing a sheet |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0005435B1 (en) |
| JP (1) | JPS54148609A (en) |
| AR (1) | AR220385A1 (en) |
| AT (1) | AT376176B (en) |
| AU (1) | AU523177B2 (en) |
| CA (1) | CA1119459A (en) |
| DE (1) | DE2820619C2 (en) |
| DK (1) | DK143098C (en) |
| ZA (1) | ZA792155B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4140763C2 (en) * | 1991-12-11 | 1997-06-19 | Kba Planeta Ag | Device for guiding the bow |
| DE19618029B4 (en) * | 1996-05-04 | 2006-07-27 | Heidelberger Druckmaschinen Ag | Method and device for eliminating rhythmic register errors in sheetfed presses with multi-size cylinders |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1561072B1 (en) * | 1967-03-25 | 1970-01-22 | Heidelberger Druckmasch Ag | Device on the transfer drum of sheet-fed rotary printing machines for register correction |
| AT303766B (en) * | 1969-03-10 | 1972-12-11 | Heidelberger Druckmasch Ag | Device on the transfer drum of sheet-fed rotary printing presses for register correction |
| DE2713994C2 (en) * | 1977-03-30 | 1983-01-27 | M.A.N. Maschinenfabrik Augsburg-Nürnberg AG, 8900 Augsburg | Sheet holding device of a sheet-fed rotary printing machine, which is able to slightly deform the printed sheet |
-
1978
- 1978-05-11 DE DE2820619A patent/DE2820619C2/en not_active Expired
-
1979
- 1979-03-14 EP EP79100765A patent/EP0005435B1/en not_active Expired
- 1979-03-20 AT AT0209379A patent/AT376176B/en active
- 1979-04-19 DK DK160979A patent/DK143098C/en not_active IP Right Cessation
- 1979-04-20 CA CA000326054A patent/CA1119459A/en not_active Expired
- 1979-04-24 AU AU46420/79A patent/AU523177B2/en not_active Ceased
- 1979-04-30 AR AR276353A patent/AR220385A1/en active
- 1979-05-04 ZA ZA792155A patent/ZA792155B/en unknown
- 1979-05-09 JP JP5579479A patent/JPS54148609A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| EP0005435B1 (en) | 1982-12-29 |
| DE2820619B1 (en) | 1979-10-11 |
| AT376176B (en) | 1984-10-25 |
| ATA209379A (en) | 1984-03-15 |
| DK143098B (en) | 1981-03-30 |
| AU523177B2 (en) | 1982-07-15 |
| DK143098C (en) | 1981-11-09 |
| AR220385A1 (en) | 1980-10-31 |
| JPS54148609A (en) | 1979-11-21 |
| ZA792155B (en) | 1980-06-25 |
| DK160979A (en) | 1979-11-12 |
| AU4642079A (en) | 1980-11-13 |
| DE2820619C2 (en) | 1986-03-27 |
| JPS5752232B2 (en) | 1982-11-06 |
| EP0005435A1 (en) | 1979-11-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |