GB2300383A - Printing press - Google Patents

Abstract

A printing unit comprises a pattern cylinder 24 arranged to be driven by a motor through a chuck assembly. The cylinder 24 is carried by a carriage which is moveable to a position in which the cylinder 24 can be replaced. A plurality of ink trays 63 are provided, each tray 63 being moveable between operative and rest positions. A washing mechanism including a moveable wash tray 71 is also provided. The unit further includes a dryer region 13 including a plurality of infrared lamps and an extraction system causing air flow past the web within the dryer region.

Description

PRINTING PRESS This invention relates to a printing press, particularly but not exclusively a multi-unit rotary gravure printing press.

Rotary gravure printing presses frequently comprise a number of in-line printing units each of which prints a different colour or pattern onto a continuous web to produce a final multi-colour image. However, in its simplest aspects the press could consist of a single printing unit, and the invention embraces the single unit, for use alone, or for use in conjunction with other units.

In conventional printing units for rotary gravure presses changing the pattern cylinder, or changing the colour of the ink applied by the pattern cylinder to the web, is a relatively lengthy and complex task, and thus the use of conventional equipment to produce relatively short print runs is uneconomic in view of the relatively long down-time involved in frequent colour and/or pattern changes.

It is an object of the present invention to provide a printing press, which may be a single printing unit, or a plurality of printing units in-line in which the foregoing disadvantages are minimised.

In accordance with the present invention there is provided a printing unit comprising a pattern cylinder for printing an ink pattern onto a web, a first ink tray moveable between a rest position, and an operative position in which the ink tray cooperates with the pattern cylinder, a second ink tray moveable between a rest position and an operative position in which the second ink tray cooperates with the pattern cylinder, and means for moving the ink trays between their rest and operative positions.

It will be understood that a colour change can be accomplished by ensuring that the first and second trays carry ink of different colours; moving the first ink tray to its rest position, cleaning the pattern cylinder, and moving the second ink tray to its operative position, the procedure being accomplished without the need to disassemble any part of the machine to substitute ink trays.

In accordance with a second aspect of the present invention there is provided a printing unit having a pattern cylinder for printing an ink pattern onto a web, means for supplying ink to the pattern cylinder, and a washing mechanism moveable between a rest position spaced from the pattern cylinder, and an operative position in which washing liquid is delivered to the pattern cylinder to wash the cylinder during an ink colour change.

It will be recognised that the washing arrangement can be used in conjunction with, or separate from, the aforementioned first and second ink trays.

In accordance with the third aspect of the present invention there is provided a printing unit comprising a rotatable pattern cylinder for transferring ink to a web to produce a printed pattern thereon, a carriage for supporting the pattern cylinder, and for moving the pattern cylinder between an outer position in which the pattern cylinder can be exchanged, and an operative position in which the pattern cylinder lies within the printing unit for cooperation with the web, and, an automatically operated chuck mechanism for gripping a drive component of the pattern cylinder when the pattern cylinder is in its operative position to drive the pattern cylinder for rotation.

In accordance with the fourth aspect of the present invention there is provided a printing unit including a printing region in which an ink pattern is transferred from a pattern cylinder to a web, and a drying region in which the web, carrying the wet ink is heated to dry the ink, the drying region incorporating a short to medium wavelength infrared heater and means for generating a flow of air across at least the printed face of the web.

The use of short to medium wavelength infrared heating in combination with a high velocity airflow across the printed face of the web is found to provide efficient ink drying in an unusually short web length. Thus a much more compact drying arrangement can be achieved than is found in conventional printing units. This advantage is of particular significance in relation to the use of water based inks which are more difficult than solvent based inks to dry, but which are preferred for environmental reasons.

One example of the invention as illustrated in the accompanying drawings in which: Figure 1 is a diagrammatic representation of part of a multi-unit printing press, and illustrates a web passing from unit to unit along the press; Figure 2 is a diagrammatic front elevational view of one of the units of Figure 1; Figure 3 is an enlarged diagrammatic view of the front plate of the frame of the unit of Figure 2; Figure 4 is a diagrammatic side elevational view of the printing unit of Figure 2 with the pattern cylinder carriage withdrawn; Figure 5 is a diagrammatic side elevational view of a pattern cylinder drive arrangement of the unit of Figure 2; Figure 6 is a diagrammatic rear elevational view, to a smaller scale, of the drive arrangement of Figure 5; Figure 7 is a view similar to Figure 2 illustrating more detail;; Figure 8 is an enlarged diagrammatic representation of part of an ink tray assembly illustrated in general in Figure 7; Figures 9, 10, 11 and 12 are diagrammatic side elevational views illustrating the operation of an ink tray change mechanism of the printing unit; Figure 13 is a diagrammatic side elevational view of part of a pattern cylinder washing mechanism of the printing unit; Figures 14 and 15 are end views showing the unit of Figure 13 in its operative and inoperative positions respectively; Figure 16 is a diagrammatic view illustrating washing of the pattern cylinder; Figures 1 7 and 18 are side and end elevational views respectively of the doctor blade assembly of the printing units; and Figures 19 and 20 are diagrammatic representations of part of the drying region of the printing unit.

The rotary gravure printing press is intended for multi-colour printing and consists of a plurality of identical print units 10 each of which is responsible for printing a single colour or pattern onto a continuous web 11 which runs in sequence through the units 10. The number of units 10 is determined by the multi-colour pattern to be printed on the web and between six and ten units would be usual. The units 10 are constructed as individually driven units but are linked by a common control mechanism so that notwithstanding their independent drive systems registration of the patterns printed by the individual units can be established and maintained. The printing units are identical to one another, and thus only one will be described.

Each printing unit 10 includes a printing region 12 and a drier region 13 mounted above the respective printing region 12. The printing region 12 has a structural frame including spaced, parallel front and rear plates 14, 15 held in position relative to one another by a plurality of transversely extending structural members 16. The plates 14, 15 are formed with respective, aligned horseshoe-shaped apertures 17 for receiving correspondingly shaped front and rear plates 18, 19 of a carriage 21.

First and second elongate structural members 22 are secured to and extend between the ends of the limbs of the plates 18, 19, each of the members 22 being mounted, through the intermediary of a linear slide arrangement, on an elongate beam 23 which in turn is mounted through further linear slides on a corresponding elongate structural member 16 of the frame of the unit. The linear slides between each member 22 and each respective beam 23, and between each beam 23 and each respective structural member 16, permit the carriage 21 to be moved between a position in which the carriage is housed within the main frame of the unit, with the plates 18, 19 occupying the apertures 17 of the plates 14, 15 respectively, to a position in which the beams 23 protrude from the front plate 14, and the carriage 21 is disposed outwardly, beyond the front plate 14 (Figure 4).

The carriage 21 is intended to support and transport the pattern cylinder 24 of the press, the pattern cylinder being the metal cylinder the surface of which is engraved with the pattern to be printed. Stub shafts 25, 26 projecting from opposite axial ends of the cylinder 24 are seated on the apical portions of the plates 18, 19 such that when the carriage 21 is in its outward position the cylinder 24 carried by the plates 18, 19 can readily be exchanged. Sliding the carriage 21 to its operative position introduces the stub shaft 25, or an appropriate adapter coupled thereto, into the collet 27 of an automatic chuck assembly 28 carried by the rear plate 15 of the main frame.A plurality of different adaptors will be provided to adapt a range of existing pattern cylinders to the chuck assembly 28, it being recognised that new cylinders will be constructed with stub shafts of appropriate length and form.

As the collet 27 is actuated to grip the stub shaft 25 or its adapter, the weight of the cylinder 24 is accepted by the chuck assembly 28, and thus is relieved from a plain brass bearing pad provided on the plate 19 of the carriage. The stub shaft 26 of the cylinder 24 is guided for rotation on a pair of spaced parallel rollers defining a bearing assembly 29 carried by the plate 18 of the carriage, and as the plate 18 is received within the aperture 17 of the plate 14 a transverse roller assembly 31 carried by the plate 14 accepts the weight of the outer end of the carriage 21 so that the positioning of the bearing 29, and thus the positioning of the stub shaft 26 is determined by the plate 14 and not by the linear slide assembly 22, 23, 16.It will be recognised therefore that when the collet 27 of the chuck 28 is closed and the chuck is rotated then the cylinder 24 is rotated about an axis defined by the axis of the chuck, and the bearings 29, both of which are supported by the plates of the unit main frame.

The unit 10 includes an impression roller 32 which in use cooperates with the pattern cylinder 24 to define a nip through which the web to be printed passes. The impression roller 32 is rotatable about an axis parallel to the axis of rotation of the cylinder 24 and comprises a steel roller within a rubber sleeve. The impression roller 32 is a free running roller, and is rotated by the passage of the web 11 through the nip. The roller 32 is rotatably supported at its opposite ends respectively in bearing assemblies 33 carried respectively on the inner faces of the front and rear frame plates 14, 15. The bearing assemblies 33 allow the impression roller 32 to be moved bodily towards and away from the pattern cylinder 24, there being a pneumatic ram 34 interposed between each bearing assembly 33 and a transverse frame member 16.The pneumatic rams 34 are fed from the same supply through a common pressure regulator, and are double-acting rams so that the roller 32 can either be loaded against the cylinder 24, or can be raised away from the cylinder 24 as will happen prior to the cylinder 24 being withdrawn on the carriage 21. In addition to the rams 34 each bearing assembly 33 incorporates a further pneumatic ram 34a the air supply of which is individually controlled. Thus the further ram 34a of each bearing assembly 33 can be used to add to, or subtract from the force generated by the main ram 34 so that more or less load can be applied at the nip selectively at either end of the impression roll 32.In effect this permits the impression roll to be skewed so that its axis is not accurately parallel to the axis of the pattern cylinder 24 to adjust the print quality at one end or the other of the pattern cylinder should this prove necessary.

Control over the supply of air pressure to either or both of the additional pneumatic rams 34a will usually be manual, and the rams will be of relatively small diameter, in order that a skilled operator can effect fine control over print quality across the width of the web.

Figures 5 and 6 diagrammatically illustrate the drive arrangement of the automatic chuck assembly 28. An a.c. servomotor 41 is carried by a bracket 42 anchored to the outer face of the rear plate 15. The output shaft of the motor 41 drives the input of a gearbox 43 also secured to the plate 15, the gearbox 43 turning the drive from the servomotor 41 through 90". An output shaft of the gearbox 43 carries a gear wheel 44 meshing with a larger diameter gearwheel 45 forming part of the chuck assembly 28.

The collet 27 of the chuck assembly 28 is of known form, and can be opened and closed to release or grip the stub shaft 25 or adapter of the cylinder 24 by longitudinal movement of an actuator rod 46. The rod 46 is connected to a pneumatic actuator 47 which can be supplied with pressurised air through a rotatable coupling (not shown). The chuck assembly 28 including the collet 27, rod 46 and actuator 47 is mounted for rotation on a carrier assembly 48 which in turn is mounted for axial movement on a bracket structure 49 secured to the outer face of the frame plate 15. The carrier 48 is moveable towards and away from the plate 15 to adjust the axial position of the collet 27 relative to a pattern cylinder 24.The gearwheel 48 has an axial thickness substantially in excess of that of the gearwheel 44 so that its teeth remain in mesh with those of the gearwheel 44 throughout its range of axial movement relative to the rear frame plate 15. Operation of the motor 41 thus drives the collet 27, and a pattern cylinder 24 clamped thereto, through the gearbox 43 and the gearwheels 44, 45. Control over the axial position of the carrier 48 and thus the collet 27 will generally be effected manually, by rotation of a worm wheel, but if desired such adjustment can be effected automatically by motorising the worm wheel, and controlling the motor from the computer control system of the press.

The pattern cylinder 24 cooperates with an ink tray containing a supply of ink into which the periphery of the pattern cylinder dips. As the pattern cylinder rotates a film of ink is carried on the surface of the cylinder and a doctor blade assembly coacts with the cylinder to remove excess ink therefrom, leaving ink in the engravings of the cylinder to be pressed onto the web in the nip of the cylinder and the impression roller.

However, in order that a rapid change in the ink colour can be effected, the unit is equipped with two ink trays and means for determining which of the trays cooperates with the pattern cylinder.

Figures 7 to 12 illustrate the ink tray arrangement. Disposed adjacent the inwardly presented face of the front frame plate 14, and anchored thereto, are first and second polished, chrome-steel rods 51, 52 disposed inclined towards one another, at approximately 600 to the horizontal on opposite sides respectively of the vertical centre line of the plate 14.

Although the upper ends of the rods do not touch, their axes intersect closely proximate the axis of rotation of the cylinder 24. A second, identical pair of rods is similarly disposed in relation to the inwardly presented face of the rear frame plate 15. A bearing sleeve 53, 54 is slidably disposed on each of the rods 51, 52, similar sleeves being positioned on the rods adjacent the plate 15. Each bearing sleeve is elongate and carries a toothed rack 55, 56 meshing with a corresponding toothed pinion 57, 58 journalled on the plate 14. Similar pinions journalled on the plate 15 mesh with the racks of the corresponding bearing sleeves associated with the rods of the plate 15.Furthermore, the pinion 57 is rotatably connected by means of an elongate shaft to the pinion associated with the right-hand rod adjacent the plate 15 and the pinion 58 is similarly coupled to the pinion associated with the left-hand rod of the plate 15. A tray carrier member extends between the sleeve 55 and the sleeve slidable on the right-hand rod of the plate 15 so that the sleeve 55, the carrier, and the sleeve of the other rod can be moved as a unit, sliding on the respective rods. A similar carrier interconnects the sleeve 56 and the sleeve of the left-hand rear rod so that again the sleeves and the carrier can move as a unit on their respective rods. The tray carriers are indicated at 59 and 61 respectively in Figures 9 to 12 and can be seen to be carrying respective ink trays 62, 63.

The arrangement of each tray 62, 63 on its respective carrier 59, 61 is the same, and is best understood with reference to Figure 8 which shows the tray 62. Each tray is a metal pressing of tapering width shaped to minimise the amount of ink stored within the tray. Naturally a tray must accommodate a range of pattern cylinder diameters and thus the amount of clearance between the walls of the tray and the periphery of the pattern cylinder will be determined by the diameter of the pattern cylinder in relation to the tray. Ink is pumped in any convenient manner from a reservoir or storage tank to a discharge bar 64 extending along one of the opposite long edges of the tray, that is to say parallel to the axis of the cylinder 24.The discharge bar has a number of apertures spaced along its length, the size and shape of the apertures being determined, in relation to the nature of the ink, to try to ensure an even discharge of ink along the length of the bar. The ink, which is normally relatively viscous, flows from the discharge bar 64 into an elongate weir 65 and overflows the weir to collect in a pool in the lower part of the tray, it being understood that in some applications it may be possible to dispense with the weir. The level 66 of ink in Figure 8 is what might be expected to occur when the cylinder 24 is not rotating. However, during rotation of the cylinder 24 the viscous nature of the ink results in ink being carried with the cylinder and so pooling to a greater depth where the cylinder periphery emerges from the ink pool.An ink return pipe 67 at the lowest part of the tray 62 returns ink to the supply so that ink not used in printing is continually circulated and does not remain stagnant in the tray. Where the ink tray is dimensioned to fit closely around a predetermined cylinder 24 then it may be possible to dispense with the ink return arrangement, the tray being supplied with ink at a rate matched to ink usage in printing. The pool of ink in the tray will thus be of small volume minimising ink wastage, and will be adequately stirred by rotation of the cylinder 24.

The tray 62 is secured to the carrier 59 by a quick release coupling 68, the coupling 68 being a screw clamp which engages an under-cut region of the base of the tray 62 and urges a flange at the opposite edge of the tray into an under-cut recess 69 of the carrier 59. It will be recognised that release of the clamping screw 68 permits the tray to be lifted from the carrier 59, the discharge bar 64 and the return pipe 67 being fitted with quick-release couplings to allow the tray to be connected to, or disconnected from the supply and return hoses.

Figures 9, 10, 11 and 12 illustrate the sequence of operations when changing ink colour. In Figure 9 the tray 62 is cooperating with the pattern cylinder 24, the sleeve 53, and the corresponding sleeve on the rod adjacent the plate 15 being driven to the upper end of their respective rods by rotation of the pinion 57. When a colour change is needed ink of the new colour is supplied to the tray 63 while printing using the tray 62 continues. Rotation of the cylinder 24 is stopped, and the impression roller 32 is lifted taking the web with it, clear of the cylinder 24. The pinion 57 is rotated to lower the tray 62 by a distance sufficient to ensure that the periphery of the cylinder 24 is just above the level of ink in the tray 62. The tray 62 is caused to pause in this position for a period of time sufficient for surplus ink to drip from the cylinder 24 back into the tray 62 (Figure 10).Thereafter the pinion 57 is rotated to lower the tray 62 to its lowermost position at which point if necessary the cylinder 24 can be manually cleaned, can be exchanged for an alternative cylinder, or can be washed as described later.

Thereafter the pinion 58 is rotated to drive the tray 63 upwardly until the tray 63 reaches the uppermost position in which it cooperates with the cylinder 24. The tray 63 is already charged with ink of the new colour different to that in tray 62 and thus printing can continue with the new colour ink. While the tray 62 is in its lowered position it can be disconnected from its supply and return pipes, and can then be removed from the carrier 59 for cleaning. If a further ink colour change is needed quickly a previously cleaned tray will be replaced on the carrier 59 and the supply and return connections to the further ink colour supply will be made. When it is necessary to switch the tray 62 for the tray 63 the procedure described above is repeated with a pause after small downward movement of the tray 63 again to allow ink to drip from the cylinder into the tray 63.

Filling the ink trays with ink of a new colour is preferably accomplished while the tray is in its rest position as described above, as this minimises operational complexity and maximises time saving. However it should be recognised that trays can be filled as they are moved to their operative position or even after they have reached the operative position.

The pin ions 57 and 58, together with their corresponding pin ions adjacent the rear plate 15, are driven by respective pneumatic motors carried by the plate 15 and controlled by the press control system.

The two trays are retained in their lowermost position for a sufficient length of time to permit either manual cleaning of the cylinder 24, replacement of the cylinder 24 if a different pattern is to be printed, or alternatively automated washing of the cylinder 24. Automated washing of the cylinder 24 speeds the colour change process even further, and removes, or greatly reduces, the need for operator intervention.

The washing arrangement is illustrated in Figures 13 to 16 from which it can be seen that there is provided a washing tray 71 which, as with the trays 62, 63, is of pressed metal construction and is long enough to accommodate the whole length of the pattern cylinder 24. Again, as with the ink trays 62, 63 the end walls of the tray 71 are recessed to receive the stub shafts of the cylinder 24. At its opposite ends respectively the tray 71 is coupled to the front and rear frame plates 14, 15 through respective parallelogram linkages 72, 73. The linkages 72, 73 are journalled to the plates 14, 15 to the right of the cylinder 24 (Figure 7) and the tray 71 can be swung, on the linkages 72, 73 from a retracted position shown in Figures 7 and 15, to an operative position shown in Figure 14.In the retracted position the tray 71 is spaced well to the right of the cylinder 74, and can be swung from that position to pass beneath the journals of the linkages to the plates 14, 15 to bring the tray upwardly underneath the cylinder 24. In order to permit this movement of the tray 71 the ink trays must both be in their lowered position, and during the movement of the tray 71 the tray itself remains in a horizontal orientation. During washing of the cylinder 24 the impression roll will be held raised from the cylinder 24 carrying the web 11 with it.

A pneumatic drive motor 74 carried by the outer face of the plate 15 drives an operating shaft 75 to which the linkages 72 and 73 are connected. Control of the motor 74 is effected by the control system of the press which ensures that the tray 71 cannot be swung to its operative position while either of the trays 62, 63 is in its operative position.

Within the tray 71 is a spray bar 76 which can, simultaneously, spray washing liquid onto one or both sides, and both ends of the pattern cylinder 24. In addition, the spray bar sprays the underside of the doctor blade assembly and ink splash guards (not shown) associated with the doctor blade assembly, and with the axial ends of the pattern cylinder 24. Washing liquid is pumped from a reservoir to the spray bar 76, and runs back from the cylinder 24 into the tray 71 from where it is returned through a return pipe system to the supply, or to a waste disposal arrangement. The washing tray can, if desired, house one or more brushes for coacting with the cylinder 24 during washing.Such brushes can be static, relying on rotation of the cylinder, or can be driven for rotation and/or reciprocation relative to the cylinder and may be resiliently biased into contact with the cylinder in use.

After washing the tray 71 is swung back to its inoperative position, and if necessary an operator wipes the cylinder 24 to remove surplus wash liquid prior to one or other of the ink trays being moved to its operative position.

It will be recognised that lifting the impression roller 32 and the web 11 away from the cylinder 24 during washing and/or ink change is desirable but not essential. If required both operations could be performed with web passing through the nip but this would lead to a scrap length within the web passing through the press.

Extending between the frame plates 14, 15 on the opposite side of the pattern cylinder 24 from the wash tray assembly is a doctor blade assembly 81. The doctor blade assembly includes, at its opposite ends, brackets 82 securing the assembly to the plates 14, 1 5 respectively, the brackets 82 including linear slide ways whereby the remainder of the assembly 81 is supported for rectilinear reciprocatory sliding movement between the plates 14, 15 parallel to the axis of the cylinder 24. The reciprocatory stroke of the moveable part of the doctor blade assembly 81 is relatively small, and the moveable part is driven in a reciprocatory manner by a crank and connecting rod 83 at the output of a gearbox 84 the input of which is driven through a belt or chain 85 from the output of the gearbox 43.

The reciprocable part of the doctor blade assembly 81 includes a first slide member 86 slidable on the bracket 82 anchored to the plate 15, the slide member 86 being connected to the end of the connecting rod and crank assembly 83 remote from the gearbox 84, the connecting rod passing through an aperture in the rear plate 15 to which the gear box 84 is mounted. A second slide member 87 is similarly slidably mounted on the bracket 82 secured to the front plate 14, the slide member 87 carrying a spiral bevel gearbox housing 88 the input of which is rotatable by a handwheel 89 projecting from the casing. A shaft 91 extends between the slide members 86, 87 parallel to the axis of the pattern cylinder 24, and is journalled at its ends for rotation in the slide members 86, 87.Rigidly secured to the shaft 91 and projecting forwardly therefrom generally towards the pattern cylinder 24 is a generally rectangular plate 92 which, at its end remote from the shaft 91, rotatably supports a shaft 93 parallel to the shaft 91. The shaft 93 has an elongate doctor blade carrier assembly 94 secured thereto, and the shaft 93 is journalled to the plate 92 such that the plane of the doctor blade carrier 94 can be adjusted relative to the plane of the plate 92.

Anchored to the shaft 91 adjacent the housing 88 is a gearwheel 95 which meshes with a gearwheel 96 carried by the output from the housing 88. Thus rotation of the handwheel 89 relative to the housing 88 drives the gear wheel 96, rotating the gearwheel 95 and the shaft 91 and raising or lowering the majority of the doctor blade assembly 81 relative to the pattern cylinder 24.

Intermediate its ends the shaft 93 extends through a gear housing 97 which is supported by the shaft 93 but anchored to the plate 92 through the intermediary of a link 98 pivotally connected at one end to the housing 97 and pivotally connected at the other end to a bracket 99 upstanding from the plate 92. The link 98 is a pneumatic ram movable between an extended condition and a retracted condition under the control of the press operator. With the length of the link 98 fixed rotation of a handwheel 101 on the housing 97 causes operation of a worm and pinion mechanism within the housing 97 to rotate the shaft 93 relative to the housing 97 thus providing a fine adjustment of the angle which the carrier 94 makes with respect to the plate 92.

The carrier 94 is an elongate clamping mechanism of known form for supporting an elongate doctor blade 102. The function of the doctor blade 102 is to wipe the surface of the cylinder 24 as the cylinder rotates to control the inking of the cylinder 24 immediately before the cylinder 24 coacts with the web 11 to print its pattern thereon. The carrier 94 includes upper and lower elongate jaws for gripping the doctor blade 102 between them, the upper jaw being urged towards the lower jaw by screw fasteners to provide the clamping action. Moreover, there is provided a screw adjustor 103 to permit minor displacement of the blade in the clamping jaws relative to the axis of the shaft 91, and thus relative to the axis of the pattern cylinder 24. The adjustor 103 thus enables the operator manually to apply more pressure between the doctor blade 102 and the pattern cylinder towards one axial end of the cylinder or the other by pivoting the blade about pin 103a in the jaws. This is an adjustment which will be used by a skilled operator to control print quality. The ram 98 is used under operator control to lift and lower the blade 102 out of and into contact with the cylinder 24. During settingup of the doctor blade the operator extends the ram fully to engage the blade with the cylinder, using the hand wheel 101 to finely adjust the position of the blade and its wiping pressure on the cylinder. Thereafter the ram is fully retracted to lift the blade 102 from the cylinder while the press is readied for printing and the extended again as printing commences.

During printing the gearbox 84 is driven while the pattern cylinder 24 rotates, and thus the doctor blade 102 is reciprocated longitudinally of the cylinder 24 continually throughout the printing process.

It is can be seen best in Figure 7, that the web 11 incoming from the supply, or from a previous printing unit 10 passes around a pair of control rollers 110, 111 before passing through the nip defined by the pattern cylinder 24 and the impression roller 32. After issuing from the nip the printed web passes around a further control roller 112 and is guided by a further roller 113 into the ink drier region 13. It will be recognised that the various rollers 110-113 extend across the full width of the web 11, and are journalled, at their ends, for rotation in the front and rear plates 14, 15 respectively. Thus their axes of rotation are parallel to the axis of rotation of the pattern cylinder 24.

The ink drier region 13 is positioned above the printing region 12 and includes cabinet 114 secured to the front and rear plates 14, 15 and having a hinged door assembly 115 extending front to back of the unit 10 and hingable to an open position to expose a narrow vertically extending gap through which the printed web 11 passes in use.The door 115, in its closed position, defines one face of the gap, and the wall of the door assembly defining the face of the gap has a rectangular, quartz window 116 the width of which slightly exceeds the width of the web 11, and behind which are positioned electrically operated infrared lamps 11 7. The lamps 11 7 are elongate spaced tubes arranged parallel to the direction of web movement, and when energised cause short to medium wavelength infrared energy to be emitted through the quartz window 116 to impinge upon the printed web which is moving in very close proximity to the window 116. It is believed that the emitted infrared energy is absorbed partly by the wet ink on the face of the web presented to the window 116, but mainly by the surface layer of the paper of the web presented to the window 116.Thereafter, it is believed that the paper acts as a heat reservoir from which heat is conducted into the ink drying the ink in effect from the inside out.

Suitable 2Kw lamps were obtained from Compact Engineering Ltd of Thirsk Industrial Park, Thirsk, North Yorkshire YO7 3BX England, identified by their order code CE/207/2/4.

Any energy passing completely through the web is reflected back to the web by a rectangular reflector 118 carried by the fixed part of the housing 114 and defining part of the face of the web gap opposite the window 116.

The heating effect produced by the lamps 117 is such that efficient cooling is called for, and the drying process is enhanced by the impingement of a high velocity airstream on the web immediately after heating by the lamps 11 7. The use of an airflow to assist drying, and for cooling of the heater assembly is also used to purge the system of vapours generated during drying of the ink.

Within the door assembly 115 there is provided ducting 119 (Figure 19) coupling upper and lower transverse extraction slots 121, 122 to an air extraction system mounted conveniently above the cabinet 114 of the drier. The slots 121 and 122 are provided in the face of the door defining the web gap, and are of a width greater than the width of the web and extend transverse to the length of the web. The slot 122 is adjacent the upper edge of the window 116, while the slot 121 is adjacent the upper edge of the door. Between the slot 122 and the window 116, and also between the slots 121 and 122 the wall of the door is perforated to provide a plurality of apertures 123 through which air can issue from the interior of the door assembly onto the printed face of the web.Internally the door is divided into upper and lower chambers by a transverse partition 124 and air from a blower fan, again conveniently mounted above the cabinet 114, enters the door assembly 115 through an inlet 125 and thus pressurises the chamber below the partition 124, this chamber containing the infrared lamps 11 7.

Behind the lamps 117 there is provided a reflector 11 7a which reflects the energy from the lamps 117 forwardly through the quartz window 116. In addition, the reflector 117 forms a duct leading to an aperture 126 in the partition 124. Thus air entering the lower chamber of the door through the inlet 125 is caused to flow upwardly between the reflector 11 7a and the quartz window 116 thus cooling the lamps 117, the reflector 11 7a, and the quartz window 116 to prevent them overheating, before flowing through the aperture 126 into the upper chamber of the door. From the upper chamber the air heated, by cooling the heating elements in the lower chamber passes through the perforations 123 to impinge at high velocity on the printed face of the web.Thus heated air circulates across the printed face of the web from the apertures 123 into the extraction slots 121, 122 so that in addition to the drying effect the drying area is continually purged of the vapours produced as the ink dries. Clearly such purging may be of crucial importance where solvent based inks, rather than water based inks are used in the printing process.

Part of the airflow from the fan or pump to the door 115 is diverted to cool the reflector 118 in the cabinet 114, and to maintain the temperature within the cabinet at an acceptable level.

The number of lamps 117 needed to effect efficient drying is dependent inter alia on web speed; ink type; and the quantity of ink transferred to the web. Moreover although as described above the lamps are arranged with their axes parallel both to the web plane and the direction of web movement,it is to be understood that other lamp orientations may prove suitable. For example it may be desirable to position the lamps with their axes parallel to the plane of the web but inclined to its direction of movement to promote more even heat distribution across the web width.

The lamps can probably be inclined at a variety of angles between parallel to web movement and transverse thereto depending on the number of lamps needed, their spacing, and the heat density required.

Opposite the region of the door above the window 116 there can, if necessary, be provided support rollers 127 to guide the web in this region of the drier.

As the web passes the upper extraction slot 121 it passes over a roller 131 journalled between the ends of a pair of elongate links 132 which, intermediate their ends, are pivoted at 132a to the front and rear walls of the cabinet 114. A spring, or counterbalance arrangement 132b acts at the end of the links opposite the roller 131 to urge the assembly of links 132 and roller 131 to pivot upwardly relative to the cabinet 114, this movement being opposed by the tension in the web 11. At its ends the roller 131 has secured thereto respective toothed wheels which cooperate with respective first and second electrical tooth sensors.

Should the web 11 break then tension in the web will be lost and the roller 131 will be swung to a position where its toothed wheels are spaced from their respective sensors, the sensors thus cease to produce a signal, and the control system of the unit 10 detects the lack of a signal, and immediately switches off the heater and pattern cylinder drive of the unit 10. It is particularly important that the heater is switched off since a stationary web within an energised heater assembly could rapidly ignite.

Assuming that tension in the web is maintained, but movement of the web ceases then again the sensors associated with the toothed wheels of the roller 131 detect the lack of movement of the web and ensure that the heater is de-energised while maintaining the air blast and extraction system operative to ensure rapid cooling of the heater assembly.

When motion of the web is recommenced the two tooth sensors independently begin to produce signals. For safety the control system will not permit the heater assembly to be energised until a predetermined one of the sensors has detected a first rotational speed, and the other of the sensors has then detected a second, higher rotational speed. In this way the control system ensures that the web speed has accelerated up to a predetermined speed before heat can be applied to the web. The heater assemblies utilised in the units 10 have a particularly high power density, and thus for fire safety reasons it is essential to monitor carefully the passage of the web through the heaters.

When it is desired to exchange the pattern cylinder 24 of the unit the drive to the pattern cylinder 24 is de-energised, the collet 27 of the chuck assembly 28 is released, both ink trays 62, 63 are lowered to their inoperative positions, and the doctor blade assembly 81 is raised away from the cylinder 24. The doctor blade assembly 81 can be moved manually, or, more desirably, a motor drive will be incorporated such that the assembly can be lifted without manual rotation of the handwheel 89. Thereafter air is fed to the rams 34 to raise the impression roller 32 and the carriage 21 can be manually withdrawn on the slides 23.The operator pulls the carriage 21 to its fully extended position and in so doing disengages the stub shaft 25 or its adapter from the collet 27 so that the stub shaft or adapter is then supported on the brass bearing pad of the end plate 19 of the carriage 21, the stub shaft 26 being supported on the bearings 29 of the plate 18. The cylinder 24 can then be lifted from the bearings of the plates 18, 19 and replaced by an alternative cylinder. A wide variety of possibilities exist for fixed or moveable support trolleys to be engaged with the front face of the front plate 14 to carry cylinders for introduction into the unit 10, and to receive cylinders withdrawn from the unit 10. Thus a single trolley could carry cylinders from a store to a series of adjacent units 10 and receive the used cylinders from those units 10 for return to the store.Alternatively a fixed support structure could be associated with each of the units 10 for holding new and used cylinders, the used cylinders then being removed when convenient by other handling equipment. The cylinder support structures, whether in the form of moveable trolleys, or fixed support structures will conveniently include guide rails which cooperate with the plates 18, 19 of the carriage 21 when the carriage 21 is fully withdrawn from the unit 10, to facility manual rolling of the cylinders 24 onto and away from the carriage 21, thereby avoiding the necessity for one or more operators actually to physically lift a cylinder into position.

As mentioned previously in its simplest configuration the rotary gravure printing press could consist of a single unit 10 for printing a single colour. More usually however there will be a plurality of units 10 operating in line, and it is desirable that one or more additional units can be added when necessary without significant difficulties.

When the press includes a plurality of units 10 it will be necessary to ensure that each unit, adding colour to generate a final multi-colour printed image, prints its colour accurately in registration with the others.

It is usually important to obtain a registration between units 10 of better than 0.1 mm. In a conventional multi-station press the registration accuracy is normally achieved by driving the pattern cylinder of each of the units from a single drive motor through the intermediary of line shafts interconnecting the units. Clearly this is an extremely complex mechanical arrangement and great accuracy is needed in the gearing in order to avoid tolerances from backlash and the like.

In a printing press comprising a plurality of the units 10 the pattern cylinder of each unit is driven by its own separate drive motor, and the synchronisation necessary for accurate printing registration is achieved by a computer control system. Such an arrangement has the advantages of mechanical simplicity, and therefore accuracy, the ability easily to add additional print units 10 to a run of existing units; the ability to avoid the need for compensator roils in, and between adjacent units to control the web between the units; and, simplicity of adjusting the register of a new cylinder fitted to one or more of the units.

Basically a main computer control generates a master synchronisation signal and the drive motor of each of the print units 10 is fitted with a resolver which in effect monitors the rotational position of the motor output, and therefore the pattern cylinder driven thereby. Each unit 10 includes, associated with the respective drive motor, a respective synchronisation computer which compares the rotational position signal produced by its own motor's resolver with the rotational position determined by the master synchronisation signal from the main computer. The difference between these two signals is used to control the speed of the motor of the unit, and thus the speed of rotation of the print cylinder of the unit.As mentioned previously the print cylinders of the unit are each driven by a respective a.c. servomotor which allows precise and responsive control, being a robust and reliable brush less permanent magnet device. Many a.c. servomotors are produced commercially with built-in resolvers. It will be appreciated therefore that each unit in effect synchronises its own pattern cylinder with a master control signal so that all the units print in registration with one another.

Although it is currently preferred to utilize a.c servomotors to drive the units 10, it is to be understood that accurate d.c. servomotors or hydraulic servomotors could prove suitable It will be recognised that if desired the master computer control could have sufficient channels to fulfil the functions of the individual synchronisation computers mentioned above. However, currently it is preferred to utilise individual synchronisation computers cooperating with the main control computer since the individual synchronisation computers can handle other functions of their individual print unit 10, for example control of ink-tray changes, nip pressure, wash sequencing, and drier safety. Each synchronisation computer can be implemented by using standard PLC (programmable logic control) modules communicating with a controller specifically designed for the functions to be implemented. A wide flexibility exists in this area to accommodate customer choice.

It will be recognised that the ink tray exchange arrangement; the washing arrangement; the cylinder exchange structure; and the drier arrangement, disclosed above can find use in presses other than those described specifically herein, and can be used separate from, or in conjunction with one another.

Claims (34)

1. A printing unit comprising a pattern cylinder for printing an ink pattern onto a web, a first ink tray moveable between a rest position, and an operative position in which the ink tray cooperates with the pattern cylinder, a second ink tray moveable between a rest position and an operative position in which the second ink tray cooperates with the pattern cylinder, and means for moving the ink trays between their rest and operative positions.

2. A unit as claimed in Claim 1, wherein the first and second ink trays are slidable upon guide means between their operative and rest positions.

3. A unit as claimed in Claim 2, wherein the guide means comprise polished rods.

4. A unit as claimed in any one of the preceding claims, wherein the means for moving comprises respective rack and pinion drive arrangements associated with the first and second ink trays.

5. A unit as claimed in any one of the preceding claims, further comprising an ink discharge bar associated with the first and second ink trays to distribute evenly the ink supplied thereto.

6. A unit as claimed in Claim 5, wherein the first and second ink trays are provided with weirs to assist even distribution of ink therein.

7. A unit as claimed in any one of the preceding claims, further comprising a doctor blade associate with the pattern cylinder.

8. A unit as claimed in Claim 7, wherein the doctor blade is reciprocable in a direction generally parallel to the axis of the pattern cylinder.

9. A unit as claimed in Claim 7 or Claim 8, wherein the angle of the doctor blade with respect of the axis of the pattern cylinder is adjustable.

10. A unit as claimed in any one of the preceding claims, further comprising a washing mechanism moveable between a rest position spaced from the pattern cylinder and an operative position in which washing liquid is delivered to the pattern cylinder to wash the cylinder during an ink colour change.

11. A unit as claimed in any one of the preceding claims, further comprising a carriage for supporting the pattern cylinder and for moving the pattern cylinder between an outer position in which the pattern cylinder can be exchanged, and an operative position in which the pattern cylinder lies within the printing unit for cooperation with the web, and an automatically operated chuck mechanism for gripping a drive component of the pattern cylinder when the pattern cylinder is in its operative position to drive the pattern cylinder for rotation.

12. A unit as claimed in any one of the preceding claims, further comprising a drying region incorporating a short to medium wavelength infrared heater and means for generating a flow of air across at least the printed face of the web.

13. A printing unit having a pattern cylinder for printing an ink pattern onto a web, means for supplying ink to the pattern cylinder, and a washing mechanism moveable between a rest position spaced from the pattern cylinder, and an operative position in which washing liquid is delivered to the pattern cylinder to wash the cylinder during an ink colour change.

14. A unit as claimed in Claim 13, wherein the washing mechanism comprises a moveable tray.

15. A unit as claimed in Claim 14, wherein the tray is supported by a parallelogram linkage arrangement.

16. A unit as claimed in any one of Claims 13 to 15, further comprising a spray bar for spraying the pattern cylinder with washing liquid.

1 7. A unit as claimed in any one of Claims 13 to 16, wherein the washing mechanism includes at least one brush.

18. A printing unit comprising a rotatable pattern cylinder for transferring ink to a web to produce a printed pattern thereon, a carriage for supporting the pattern cylinder, and for moving the pattern cylinder between an outer position in which the pattern cylinder can be exchanged, and an operative position in which the pattern cylinder lies within the printing unit for cooperation with the web, and, an automatically operated chuck mechanism for gripping a drive component of the pattern cylinder when the pattern cylinder is in its operative position to drive the pattern cylinder for rotation.

19. A unit as claimed in Claim 18, wherein the carriage is supported by a linear slide arrangement.

20. A unit as claimed in Claim 18 or Claim 19, further comprising bearings arranged to support the pattern cylinder when the pattern cylinder is in its operative position.

21. A unit as claimed in any one of Claims 18 to 20, wherein the drive component of the pattern cylinder comprises a stub shaft.

22. A unit as claimed in any one of Claims 18 to 20, wherein the drive component comprises an adapter connected to the pattern cylinder.

23. A unit as claimed in any one of Claims 18 to 22, further comprising an impression roller arranged to engage the pattern cylinder, the position of the impression roller being adjustable.

24. A unit as claimed in Claim 23, wherein the position of the impression roller is adjustable by means of a pneumatic ram.

25. A unit as claimed in Claim 24, further comprising an additional pneumatic ram for adjusting the orientation of the impression roller with respect to the axis of the pattern cylinder.

26. A unit as claimed in any one of Claims 18 to 25, wherein the chuck is pneumatically controlled.

27. A unit as claimed in any one of Claims 18 to 26, wherein the position of the chuck in the axial direction of the pattern cylinder is adjustable.

28. A printing unit including a printing region in which an ink pattern is transferred from a pattern cylinder to a web, and a drying region in which the web, carrying the wet ink is heated to dry the ink, the drying region incorporating a short to medium wavelength infrared heater and means for generating a flow of air across at least the printed face of the web.

29. A unit as claimed in Claim 28, further comprising a reflector arranged to reflect radiation from the heater towards the web.

30. A unit as claimed in Claim 29, wherein the means for generating an air flow is arranged to generate an additional air flow across the reflector.

31. A unit as claimed in any one of Claims 28 to 30, further comprising sensor means arranged to detect the presence or absence of movement of the web through the drying region.

32. A printing press comprising a plurality of printing units as claimed in any one of the preceding claims and control means arranged to control movement of the pattern cylinders of each of the printing units.

33. A printing unit substantially as hereinbefore described with reference to any one of the accompanying drawings.

34. A printing press substantially as hereinbefore described with reference to any one of the accompanying drawings.