Sheet settling system

Abstract

 In a sheet printing or coating machine, sheets 14 are travelling successively into contact with datum stops 18 carried by a rotating impression cylinder in order accurately to register, that is to say locate in position, each sheet relative to that cylinder just prior to being gripped by grippers carried by that cylinder. This enables a cylinder in rolling contact with the impression cylinder to print on or coat the sheet with accuracy as the sheet is drawn through the nip between the cylinders. However, because these machines operate at high speeds, there is a tendency for the sheets to move about as they are being fed to the datum stops, so that precise registration is not achieved. This is remedied by providing vacuum and/or magnetic forces to damp such movement by settling each sheet rapidly on a support surface 12 as it is fed into contact with the datum stops. The vacuum force is provided by drawing air through an array of holes 26 in the support surface into an underlying chamber 24 evacuated through a pipe 28 by a vacuum pump, and is adjustable either by controlling the flow rate through the pump or by controllably venting the chamber or pipe to atmosphere. The magnetic force is provided by a row of permanent or electro-magnets 22 in the support surface, and can be adjusted by varying their position perpendicular to that surface. Alternatively, in the case of electro-magnets, the magnetic force is adjustable by varying their supply of electrical power.

Description

[0001] This invention relates to a sheet settling system, and more particularly to a method of rapidly settling a sheet on a support surface of a sheet printing or coating machine, and to a machine employing the method.

[0002] The system is applicable to printing and coating machines for sheets of metal, plastics material, paper and card.

[0003] Known sheet printing and coating machines generally include two cylinders geared together so as to contra-rotate at the same constant peripheral speed in rolling contact with each other, between which the sheets are passed successively. One of the cylinders transfers an ink impression or a coating such as varnish onto each sheet. In order accurately to register, that is to say locate in position, each sheet relative to the other of the cylinders, said other cylinder carries one or more, usually two, axially-spaced datum stops or so-called front lays for the front edge of the sheet. At least one datum stop is also provided for one side of the sheet. Each sheet is fed towards the front lays on a flat infeed surface by means such as pushers carried by endless chains or the like. When the front edge of the sheet is accurately registered against the front lays, it is gripped by a plurality of cyclically-operated grippers carried by said other cylinder and the sheet is drawn through the nip of the cylinders where it is printed or coated. As the front edge of the sheet emerges from the nip it is released by the grippers and the sheet is moved onwards for further treatment or for stacking. Because these machines operate at high speeds. there is a tendency for the sheets to move or bounce about somewhat as they are being fed towards and into contact with the datum stops, as a result of which registration is not achieved with precise and consistent accuracy.

[0004] The object of the present invention is to obviate or reduce the aforesaid tendency by providing a system for rapidly settling a sheet on a support surface of a sheet printing or coating machine.

[0005] According to one aspect of the invention, a method of rapidly settling a sheet on a support surface of a sheet printing or coating machine with at least the front edge of the sheet in accurate registration with datum stops, comprises exerting an indiscernible damping force on the sheet.

[0006] The method may comprise exerting the force by vacuum means.

[0007] The method preferably comprises adjusting the vacuum force.

[0008] The method alternatively comprises exerting the force by magnet means.

[0009] The method preferably comprises adjusting the magnetic force.

[0010] The method may comprise exerting the force by both vacuum and magnet means.

[0011] According to another aspect of the invention, a sheet printing or coating machine has means for rapidly settling a sheet on a support surface thereof with at least the front edge of the sheet in accurate registration with datum stops, said means exerting an indiscernible damping force on the sheet.

[0012] Said means may be vacuum means.

[0013] The vacuum force is preferably adjustable.

[0014] Preferably, the vacuum force is provided by a vacuum chamber communicating with the support surface and evacuated by a vacuum pump, and is adjustable by controlling the evacuation flow rate of said pump.

[0015] Alternatively, the vacuum force is provided by a vacuum chamber communicating with the support surface and evacuated by a vacuum pump, and is adjustable by controlling the opening of at least one orifice in the vacuum means which opens to atmosphere.

[0016] Preferably, also, the vacuum force is additionally exerted on sheets moving along an infeed surface towards the datum stops.

[0017] In a machine for printing on or coating ferrous sheets, said means are alternatively magnet means.

[0018] The magnetic force is preferably adjustable.

[0019] Preferably, the magnetic force is adjustable by varying the position of the magnet means in a direction perpendicular to the support surface.

[0020] Alternatively, the magnetic force is electro-magnetic and is adjustable by varying the supply of electrical power to the magnet means.

[0021] A sheet printing or coating machine may have both vacuum and magnet means. This enables it to settle sheets of any material with maximum efficacy; the vacuum system sufficing to damp lighter weight non-ferrous sheets whilst being supplemented by the magnet system to damp heavier ferrous sheets.

[0022] One preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing which is a diagrammatic perspective view of a sheet (drawn transparent for clarity) in registration position on a support surface of a sheet printing or coating machine.

[0023] Referring now to the drawing, a sheet printing or coating machine, for example a machine for printing on metal sheets substantially as disclosed in our European Patent (U.K.) No. 0412720 to which reference may be made, includes a horizontal flat infeed surface constituted by a plurality of, say three as shown, parallel rails 10 which terminate in a rectangular support surface 12. The surface 12 is disposed close to the entry side of the nip between blanket and impression cylinders (not shown) which are geared together so as to contra-rotate at the same constant peripheral speed and make rolling contact with each other in well-known manner, and said surface is approximately tangential to said cylinders. The sheet 14 about to be printed is travelling in the direction of the arrow 16, being fed by a known arrangement (not shown) of pusher means carried by endless chains at approximately the same linear speed as the peripheral speed of said cylinders.

[0024] The lower, impression cylinder carries two axially-spaced non-retractable datum stops or so-called front lays 18 which act to register the front edge of the travelling sheet 14 relative to the rotating impression cylinder, and also carries two cyclically-operated grippers (not shown) which are associated with the datum stops 18. A datum stop 20 is also provided for one side of the sheet 14. A row of magnets 22 is provided near that edge of the support surface 12 adjacent to the nip. Said magnets can be either permanent magnets or electro-magnets, and the magnetic force can be adjusted by varying their position in a direction perpendicular to said surface. Alternatively, in the case of electro-magnets, the magnetic force is adjustable by varying the supply of electrical power thereto. Underlying the support surface 12 is a vacuum chamber 24 which communicates with said surface through an array of holes 26. The chamber 24 is evacuated by a conventional vacuum pump (not shown) by way of a pipe 28. The vacuum force is adjustable either by controlling the evacuation flow rate of said pump, or by controlling the opening of a number of orifices (not shown) in the vacuum chammber 24 and/or the pipe 28 which open to atmosphere The middle rail 10 is hollow with closed ends and also has an array of holes 30 in its upper surface. The interior of the middle rail 10 is connected to the pipe 28 by a branch-pipe 32.

[0025] In operation, a ferrous sheet 14 is pulled close to the rails 10 by the suction effect of the vacuum in the middle one of said rails as it travels along them. It is then rapidly settled on the support surface 12 by the combined attraction of the magnets 22 and suction effect of the vacuum in the chamber 24. Accurate registration of the sheet 14 with the datum stops 18 and 20 is thereby facilitated, after which its front edge is gripped by the grippers and it is drawn through the nip of the cylinders where it is printed. Finally, as the front edge of the sheet 14 emerges from the nip it is released by the grippers amd moved onwards for stacking. For non-ferrous sheets 14, the magnets 22 are ineffective, and if electro-magnetic can be switched off.

[0026] In one modification, further magnets are provided in other areas of the support surface 12. In another modification, the branch-pipe 32 is dispensed with and the hollow middle rail 10 communicates at one end directly with the vacuum chamber 24 and is closed at the other end.

[0027] It will be appreciated that the vacuum system can be used alone for sheets of any material, and that the magnet system can be used alone for sheets of exclusively ferrous material.

Claims

1. A method of rapidly settling a sheet on a support surface of a sheet printing or coating machine with at least the front edge of the sheet in accurate registration with datum stops, comprising exerting an indiscernible damping force on the sheet.

2. A method according to claim 1, comprising exerting the force by vacuum means.

3. A method according to claim 2, comprising adjusting the vacuum force.

4. A method according to claim 1, comprising exerting the force by magnet means.

5. A method according to claim 4, comprising adjusting the magnetic force.

6. A method according to claim 1, comprising exerting the force by both vacuum and magnet means.

7. A sheet printing or coating machine having means for rapidly settling a sheet on a support surface thereof with at least the front edge of the sheet in accurate registration with datum stops, said means exerting an indiscernible damping force on the sheet.

8. A machine according to claim 7, wherein said means are vacuum means.

9. A machine according to claim 8, wherein the vacuum force is adjustable.

10. A machine according to claim 9, wherein the vacuum force is provided by a vacuum chamber communicating with the support surface and evacuated by a vacuum pump, and is adjustable by controlling the evacuation flow rate of said pump.

11. A machine according to claim 9, wherein the vacuum force is provided by a vacuum chamber communicating with the support surface and evacuated by a vacuum pump, and is adjustable by controlling the opening of at least one orifice in the vacuum means which opens to atmosphere.

12. A machine according to any one of claims 8 to 11, wherein the vacuum force is additionally exerted on sheets moving along an infeed surface towards the datum stops.

13. A machine according to claim 7 for printing on or coating ferrous sheets, wherein said means are magnet means.

14. A machine according to claim 13, wherein the magnetic force is adjustable.

15. A machine according to claim 14, wherein the magnetic force is adjustable by varying the position of the magnet means in a direction perpendicular to the support surface.

16. A machine according to claim 14, wherein the magnetic force is electro-magnetic and is adjustable by varying the supply of electrical power to the magnet means.

17. A machine according to claim 7, having both vacuum and magnet means.

Drawing