METHOD AND APPARATUS FOR POSITIONING SHEET MATERIAL ON A SUPPORT TABLE TO MAKE HOLES BY PUNCHING

Abstract: The invention relates to a method and apparatus for punching register holes in sheets provided with adjustment marks. The apparatus comprises a punching table (1) having punches (27) and sensors (28) on the punching table, a vacuum table (25) being provided in the punching table substantially in the plane thereof, said vaccuum table being adjustable in two mutually perpendicular directions in the plane of the punching table and being rotatable about an axis perpendicular to said plane. Adjustment means for the adjustment of the vacuum table are operatively connected to the sensors to control the operation thereof via a microprocessor in dependence of the adjustment marks being sensed by the sensors. When the method is practised the sheet is attached by suction to the vacuum table, and this table and thus the sheet is positioned by the adjustment of the vacuum table, the positioning being controlled in dependence of the position of the adjustment marks being sensed. After positioning the sheet is punched, the sheet then being released from the vacuum table and removed from the punching table.

Description: METHOD AND APPARATUS FOR POSITIONING SHEET MATERIAL ON A SUPPORT TABLE TO MAKE HOLES BY PUNCHING. The invention relates to method and apparatus for punching register holes in sheet material, this term as used herein relating not only to paper sheets but also to plastics sheets, photographic plates, metal sheets, film and the like used in the graphic industry. Henceforth reference will be made to sheet when sheet material of said kinds is referred to. The register holes are used for exact positioning of sheets in a predetermined position when sheets are handled for treatment or use thereof in different ways in lithographic processes. For example, positioning of photographic plates, masks and films in making printing plates for offset printing may be concerned. It is a necessary pre-requisit in order to obtain finally a satisfactory result, for example good register of the colours of a product of multi-colour printing, that the punched register holes are located in an exact predetermined position on the sheet. Today the sheet is positioned in the punching apparatus completely manually. On the sheet there are provided adjustment marks or other reference points, and in computer type setting this can be done already in the computer. By means of these adjustment marks and sensors with video optics the sheet is positioned in the intended position on a punching table with the greatest conceiv¬ able accuracy, the sheet then being fixed to the punching table and being punched. A manual operation of this type is time consuming and makes great demands on the operator performing the operation. The object of the invention is to replace the manual operation by an automatic operation which with an accuracy unsurpassed so far provides positioning of the sheet in the intended position before punching. For this object there is provided according to the invention a method for punching register holes in sheet material wherein the sheet material is positioned on a punching table in relation to fixedly located punches by guidance of adjustment marks on the sheet material, said method having obtained the characterizing features according to claim 1. According to the invention there is also provided an apparatus for working the method in accordance with claim 3. In order to explain the invention in more detail reference is made to the accompanying drawings in which FIG. 1 is plan view of an apparatus according to the invention, FIG. 2 is a side view of the apparatus in FIG. 1, FIG. 3 is a perspective view of a punching table with punches and sensors, FIG. 4 is a diagrammatic plan view of an adjustable section placed on the punching table, and FIG. 5 is a plan view of a sheet with adjustment marks. The apparatus shown in FIGS. 1 and 2 comprises a frame 10 having three separate sections, viz. a picking magazine 11, a punching table 12, and a finished product magazine 13. The picking magazine 11 has guides 14 which may be adjustable for adjustment to different sheet sizes, and in FIG. 1 there is indicated by dot-and-dash lines 15 a sheet pile in this magazine. The finished product magazine 13 has in a corresponding way guides 16, and the sheet pile in this magazine is indicated by dot- and-dash lines 17. Two guides 21 are supported by means of flanges 18, 19 and 20 projecting from the frame 10, said guides extending along the frame over the punching table 12 and the finished magazine 13 and over the portion of the picking magazine 11, which is next to the punching table 12. Two suction ramps 22 and 23 are displaceably guided on the guides 21 and are connected to linear drive means 24, e.g. a double acting pneumatic ram, to be driven by said means along the guides, fixedly spaced from each other. The suction ramps can be displaced by the drive means 24 from the left end position shown in FIGS. 1 and 2, wherein the suction ramp 22 is located over the sheet pile 15 at the right end thereof and the suction ramp 23 is located over a vacuum table 25 at the same level as the puching table 12, at the right end thereof, to a left end position wherein the suction ramp 22 has been dis¬ placed to the position where the suction ramp 23 is located in FIG. 1, and the suction ramp 23 has been dis¬ placed to the finished product magazine 13 where it is located over the pile 17 at the right end thereof the suction ramp being indicated by dot-and-dash lines 23' in said position. The suction ramps can be displaced between these end positions in order that the suction ramp 22 will grip the uppermost sheet of the pile 15 and will pull said sheet onto the punching table 12 and will posi¬ tion the sheet over the vacuum table 25 as indicated by dot-and-dash lines 15' . At the same time the sheet indi- cated on the punching table 12 will be gripped by the suction ramp 23 and will be pulled into the finished pro¬ duct magazine 13 to be deposited therein to form together with other sheets transferred to the finished product magazine the pile 17 which thus will comprise punched sheets. In order to facilitate pulling of the sheet from the picking magazine 11 pressure rollers 26 are mounted in a conventional way in this magazine. Referring also to FIGS. 3 to 5 the elements for positioning the sheet 15' on the punching table 12 and for punching this sheet after accurate positioning thereof on the punching table will be explained in more detail, said elements forming part of the apparatus. The vacuum table 25 can be of a conventional con- struction and is constructed to attach a sheet against the plane surface thereof when the vacuum table is put under vacuum, i.e. activated. In the apparatus according to the invention the vacuum table is made adjustable in the punching table 12 so as to be displaced in the direc- tions X and Y indicated by double arrows in FIG. 4, and to be rotated in the direction Z indicated by a double arrow. Said adjustment of the vacuum table can be effected by electric step motors which provide the greatest accuracy in the positioning of the vacuum table. On the punching table 12 there is provided adjacent the vacuum table at the longitudinal edges thereof four punch assemblies 27 of conventional type. On the punching table there are also provided two cameras with the objectives thereof directed downwards towards the punching table, and these cameras form sensors for sensing the position of the sheet located on the punching table 15' by guidance of adjustment marks 29 (FIG. 5), which are found on each sheet in the picking magazine. The adjustment marks can be of different types. The marks are shown here as crosses but they can comprise also dots, circles, squares or the like, or combinations thereof. For the control of the different steps in working the method according to the invention in the apparatus described the cameras 28 should be connected to a micro¬ processor to forward to the microprocessor input signals by guidance of the adjustment marks 29, said input signals indicating the position of the sheet 15 laying on the punching table 12. According to a program stored in the microprocessor and in dependence of the input signals received from the cameras, the microprocessor will control the drive means 24 and the step motors connected to the vacuum table 25. The programming and construction of microprocessors for the performance of such control can be effected on the basis of common knowledge of the skilled man on the present state of the computer art and accordingly will not be described in more detail here. In order to explain the method of the invention when the apparatus described is being used it is assumed initially that the vacuum ramp 22 has positioned the sheet 15' on the punching table 12 and has returned to the left position shown in FIGS. 1 and 2. The positioning of the sheet 15' is controlled from the microprocessor which stops the movement of the sheet onto the punching table 12 when the cameras 28 sense the adjustment marks 29. Then, the sheet 15' can be positioned on the punching table 12 with an accuracy of »1.0 mm, but this accuracy is not satisfactory for punching the sheet and thus a fine adjustment has to take place. This fine adjustment of the position of the sheet 15' is obtained by means of the vacuum table 25 which will be activated as soon as the sheet 15' has been positioned on the punching table 12. In dependence of signals from the cameras adjustment of the vacuum table 25 and thus of the sheet 15' attached to the vacuum table will be effected via the micro¬ processor as required in the directions X, Y and Z in order that the two adjustment marks 29 will be centered below the cameras or in relation to zero marks provided on the positioning table, the positions of the adjustment marks being sensed continuously by the cameras during the positioning by means of the step motors in the directions X, Y and Z. This positioning can be performed at an accuracy of »0.01 mm, and when the positioning has been closed the punch assemblies 27 will be activated in dependence of a signal from the micro processor for punching of the sheet. When this has been done the acti¬ vation of the vacuum table 25 will be ceased and the drive means 24 will displace the suction ramps 22 and 23 to the right end position for deposition of the punched sheet 15' in the finished product magazine 13 and with¬ drawal of a new sheet from the picking magazine 11 for punching on the punching table 12. The sensors for sensing the adjustment marks on the sheets can comprise for example inductive, mechanical or other known types of sensors instead of cameras as shown herein. Also the adjustment means for the vacuum table can of course comprise other means then electric step motors, e.g. hydraulic or mechanical adjustment means.

Claims: CLAIMS 1. Method for punching register holes in sheets (15') provided with adjustment marks (29), c h a r a c- t e r i z e d in that the sheet (15') is taken from a picking magazine (11) and is located on a vacuum table (25) arranged substantially in the same plane as a punching table (12) , that the sheet is attached by suction to the vacuum table, that the vacumm table and thus the sheet is positioned by adjusting the vacuum table in mutually perpendicular directions (X, Y) in the plane of the punching table and rotation (Z) of the vacuum table about an axis perpendicular to said plane, that the positioning is controlled by a microprocessor in dependence of the position of the adjustment marks being sensed, and that the sheet is punched and the punched sheet after having been released from the vacuum table is removed from the punching table. 2. Method according to claim 1, c h a r a c t e r- i z e d in that the sheet (15') is moved linearily from the picking magazine (11) to the punching table (12) and therefrom to a finished product magazine (13). 3. Apparatus for punching register holes in sheets (15') provided with adjustment marks (29), comprising a punching table (12) having punches (27) and sensors (28) for sensing the position of the sheet on the punching table, c h a r a c t e r i z e d by a vacuum table (25) mounted in the punching table (12) substantially in the plane thereof, said vacuum table being adjustable in two mutually perpendicular directions (X, Y) in the plane of the punching table and being rotatable about an axis (Z) perpendicular to said plane, and that adjustment means for adjustment of the vacuum table are operatively connected to the sensors for controlling the operation thereof via a microprocessor in dependence of the adjust¬ ment marks being sensed by the sensors. 4. Apparatus according to claim 3, c h a r a c¬ t e r i z e d in that the sensors comprise cameras (28) having the objectives thereof directed towards the punching table (12) for optical sensing of the adjustment marks (29). 5. Apparatus according to claim 3 or 4, c h a r a c¬ t e r i z e d in that a picking magazine (11) for non- punched sheets and a finished product magazine (13) for punched sheets are provided one at each side of the punching table (12) and that means (22, 23, 24) are provided for rectilinear displacement of the sheets from the picking magazine to the punching table and therefrom to the finished product magazine. 6. Apparatus according to claim 5, c a r a c¬ t e r i z e d in that the said means comprise two linea ily guided suction ramps (22, 23) mounted at a fixed spacing from each other.

Inventors: PERSSON JOHNNY, PERSSON, JOHNNY
Applicants: PERSSON JOHNNY, PERSSON, JOHNNY
Application year: 1992
Main classification: B26D5
IPC codes: B26D7