US 2933040 A
Description (OCR text may contain errors)
April 19, 1960 R. w. Hr-:LMIG 2,933,'O40
SHEET GRIPPER ELEMENT Filed Dec. 19, 1958 INVENTOR,
,ZP/emma 14./ A452 41/4 a/w wy' ATTORNEY Unit. Sttes Patent O sHEET GRrPrnR ELEMENT Richard W. Helmig, Shaker Heights, Ohio, assignor to Harris-Intertype Corporation, Cleveland, Ohio, a corporation of Delaware Application December 19, 1958, Serial No. 781,802
2 Claims. (Cl. 101-412) This invention relates generally to Sheet gripping devices adapted for use in a multicolor Sheet fed printing press, and in particular to a gripper post or other Sheet gripping. element having a gripping surface capable of positively grasping and holding a Sheet during passage through the press.
To obtain high quality printing in a multicolor printing press, i.e., accuracy of registration between the printing units or between one color and the next, it is necessary that each Sheet be positively gripped and maintaned in its gripped position without relative movement between the Sheet and the Sheet gripping members during transfer between the several units of the press. Numerous attempts have been made to provide either the gripping fingers or the posts with which they cooperate to grip a Sheet, with surfaces having a coeflicient of friction which prevents sheet movement. In the past, gripper posts have been serrated, knurled, Sandblasted, provided with rubber inserts, provided with an emery cloth strip, etc. However, none of these has proven completely effective for all types of paper, cardboard, or other Stock. This is particularly true in a lithographic press in which very tacky inks are often used. These inks, when transferred from a blanket cylinder to sheets held by gripper-s on an impression cylinder, tend to cause the sheets to adhere or stick to the blanket.` In many printing presses, the sheet is still undergoing printing at the time 'that the grippers on the impression cylinder are transferring the Sheet to other grippers on the next adjacent Sheet receiving member. 'There occurs a tendency for the Sheet to pull out of these latter 'grippers, or at least be slightly displaced relative to the grippers due to the pullof the tacky ink on the blanket cylinder. The slightest displacement of a Sheet will obviously alect the registration between printing units or colors adversely.
lt is therefore the principal object of 'this invention to provide accuracy of registration of print between the several units or colors of a multicolor Sheet fed printing press. r
A more specific object of the invention is to eliminate or minimize the relative movement between a Sheet and the Sheet gripping members during travel of the' Sheet through a printing press.
Other objects will be apparent from the following de- Scription in which reference iszmade to the accompanying drawings. i
According to the invention, the gripper posts with which the customary sheet gripping fingers on a printing press cylinder cooperate, are etched to provide the posts with a multiplicity of minute peaks having relatively coplanar tops. When a gripping finger and post grip a Sheet, the peaks of the post positively grip the Sheet and prevent displacement of the Sheet relative to the gripping members while the Sheet is undergoing the printing process.
In the drawings:
Fig. 1 is an elevational sectional view of a gripping finger and cooperating gripping post mounted on a portion of a cylinder of a printing press.
Fig. 2 is an enlarged fragmentary view of the gripper post of Fig. 1.
`Fig. 3 is a view looking from above at the post of Fig. 2.
Fig. 4- is a greatly enlarged elevational sectional view of one of the peaks of the post.
Fig. 5 is a plan view of the top of the peak of Fig. 4.
The environment of the gripper post of the invention is shown in Fig. l, and will be described only to the extent necessary to fully illustrate the invention. A cylinder 16, which may be an impression cylinder of a rotary printing press, carries an oscillatable gripper Shaft 11. The gripper shaft 11 carries along its length a plurality of gripper fingers 12 which cooperate with a similar plurality of fixed gripper posts 13, to grip a sheet S and assist in carrying it through the press The posts 13 may be Secured to the cylinder by means of capscrews 14.
The gripper finger 12 has spaced sides each of which is Seated on a fianged bearing 15 journaled on the Shaft 11. A gripper dog 16 is secured to the Shaft 11 between the sides of the finger 12 by means of a clamping Screw 17. A compression spring 18 intermediate the finger and dog urges the gripper finger clockwise as viewed in Fig. l away from a seat 19 in the gripper dog 16, this clock- Wise movement being resisted when abutments 20 on the gripper finger and 21 on the dog engage at the time the gripper finger is out of contact with a Sheet. When the Shaft 11 is oscillated to its position shown in Fig. l to gripca Sheet, the tp of the finger 12 engages the Sheet S and a very slight separation of the abutments 20 and 21 will occur, allowing the spring 18 to clamp the Sheet between the finger tip and the top of the post 13 with a preselected force. Referring now to Figs. 2 and 3, it will be seen that the top surface of the gripper post 13 is provided with a multiplicity of peaks 22 having valleys between the peaks, and preferably is further provided with flat summits or plateaus 23 on the peaks. It will be noted that the plateaus 23 of the various peaks 22 are substantially planar and that the tops of the peaks provide a substantially level or planar surface for the post at the top thereof.
The manufacture of the top surface of the posts is Substantially the Same as that used in making halftone printing plates for many years. The top of the post 13 is Originally flat, and is preferably coated with an etch resistant light Sensitive material capable of being harclened upon exposure to intense light. A fine screen having areas of transparency which correspond only to the particular Size and number of peaks desired is placed over the posts having the coating thereon, and light is passed through the transparent areas. The light Sensitive material is hardened upon exposure to the light and adheres to the top surface of the post 13. The unhardened portions of the light Sensitive material are then washed off or otherwise removed and an etching material is applied to the surface of the post. As mentioned previously, the hardened areas of the light Sensitive material are etch resistant, and therefore only the areas previously covered by the unhardened portions of the light Sensitive material are etched away into the stock of the gripper post 13. The tops of the peaks may be ground after etching whenever it iS desired that the peaks 22 have coplanar plateaus which are accurately coplanar. The posts are preferably hardened to minimize their wear due to abrasion from the Sheet stock and also from constant pounding of the gripper fingers.
I have found that a screen capable of producing 2000 points per square inch makes a very fine gripping surface for most materials ranging from the flimsiest papers to the heaviest coated stocks. I also find that the plateaus 23, if made approximately .005" across, and if the etchng is .0l deep, Will provide side walls on the peaks v22 which are very ragged as shown in Fig. 4 and are generally perpendicular to the plateaus 23. While I prefer themto be perpendicular, they appear to provide a satisfactory gripping surface up to about an angle of 120 between a plateau and side wall. This is probably. true because the ragged etched surface apparently provides a substantial gripping surface for the fibers of paper orrcardbo'ard. These ragged edges plus the fact that the peaks are relatively small in cross-section area,and also the additional fact that this process of manufacturing enables me to obtain a great many peaks in a very small area, 'permits me to grip sheets without noticeable displacement between the sheets and the gripper posts and fingers. I prefer that a scatter pattern of peaks be provided, but obviously, a uniform pattern may perform equally well. Furthermore, the plateaus may be of any configuration.
While I have shown and described peaks in a, certain quantity, shape, and size, and valleys of a certain depth,
it'v is obvious that numerous other arrangements are possible .and capable of producing the desired result. For example, the peaks need not necessarily be furnished with plateaus, even though the latter provide a desirable relatively level gripping surface. Furthermore, the gripping surface may be produced on a thin plate and then cemented, brazed, or otherwise fastened to the main body of the post.
Various other modifications and changes may be made in lthe details of construction and process of manufacturing' Without departing from the spirit and scope of the nvention.
' -Having described my invention, I claim: A 1. A sheet gripping device having a pair of relatively movable and cooperating gripping elements at least one of which has a hardened gripping surface comprising a multiplicity of minute peaks distributed throughout said gripping surface and having generally coplanar tops, and valleys surrounding the peaks, at least said one element being made by a process comprising the steps of coating the areas corresponding to the peak tops with an etch resistant material, and subjecting the uncoated areas to an etch to remove stock to a depth sufficient to form the valleys between the peaks,
2. A sheet gripper post adapted to cooperate with a relatively movable gripper fin'ger to grip sheets, said post having a hardened gripping surface comprising a multiplicity of peaks distributed throughout said surface and having minute relatively coplanar tops, and valleys surrounding the peaks, said post being made by a process comprising the steps of coating a surface of the post With a light Sensitive etch resistant material, exposing the areas corresponding to the tops to light to harden the coating in those areas, removing the unhardened areas of said coating, and subsequently subjecting the areas previously coveredrby the unhardened coating to an etch to remove stock to a depth suificient to form the valleys between the peaks.
OTHER REFERENCES Modem Photoengraving by Flader and Mertle. Published by Modem Photoengraving Publishers, 1948. Pages 1, and 181.