EP2921299A1

EP2921299A1 - Apparatus particularly suitable for cleaning the cliché plate of flexographic printing machines

Info

Publication number: EP2921299A1
Application number: EP15159603.8A
Authority: EP
Inventors: Marco Corti; Riccardo Fumagalli
Original assignee: Elettra Srl
Current assignee: Elettra Srl
Priority date: 2014-03-21
Filing date: 2015-03-18
Publication date: 2015-09-23

Abstract

Apparatus having unwinding and winding reels (25, 26) for a cleaning cloth (P), which when passing between the two reels is set under longitudinal tension on a roller or other linear counteracting means (24) against which this cloth is made to rub in reverse direction on the surface to be cleaned of the cliché plate (2) of the printing cylinder (1) of a flexographic machine. Said roller or other linear counteractingacting means (24) has a rigid surface contacting the cloth (P) and facing the printing cylinder (1, 2) and in that the displacement means of the carriage, that supports the cloth cleaning device, to move this device towards and then away from this printing cylinder (1, 2), are means suitable to produce an accurate movement, so that during the cliché plate (2) cleaning step the cloth, set on this roller or other linear counteractingacting means (24), touches with its outer surface the exposed surface (S) of the cliché plate (2), the interference with this surface (S) being minimum. In the active step of cleaning the cliché plate (2) of the printing cylinder, the means that provide for the unwinding of the cloth (P) under tension cause the cloth to move forward with small continuous or intermittent movements.

Description

The invention relates to the cliché plate cylinder or printing cylinder of flexographic machines for printing on cardboard or other types of substrate, which receives the ink from the anilox roller and then transfers it onto the substrate to be printed supported on the opposite face by support and unwinding means. The cliché plate is generally formed of a preformed plate made of plastic material, of variable thickness, which is removably fixed to the support surface of the printing cylinder. In order to improve the performance of the cliché plate while it is in use and at the end of each operating cycle, is to be cleaned; currently, this is carried out also using mechanised systems that make use of, for example, rotating brushes or, alternatively, that act on the surface of the cliché plate with the presence of cleansing fluid and with the action, in the right phase, of suction means to remove any fluid with the dirt and to dry the clean surface. This procedure requires long operating times, can only be carried out with the machine at a standstill and often the results are unsatisfactory due to the difficulty in completely eliminating the dirt that can accumulate in recessed areas of the exposed surface of the cliché plate. Attempts have also been made to clean the cliché plate during operation of the machine, with electrostatic or cryogenic cleaning systems, which have proved costly, difficult to use and, consequently, have not had the expected success.
The applicant has a high level of know-how and holds numerous Italian and foreign patents covering processes and systems for cleaning the rubber cylinders of printing machines or the central drum of flexographic machines, which provide for the use of a cleaning cloth of the same width as the width of the cylinder to be cleaned (see below), of the type known commercially with the name SONTARA DUPONT, pre-wetted or wetted during use with a cleansing fluid, unwound from and wound on unwinding and winding reels parallel to the cylinder to be cleaned. By means of a presser, also parallel to the axis of the cylinder to be cleaned, a transverse portion of said clean and wetted cloth is put into contact with the lateral surface of the cylinder to be cleaned, which continues to rotate, so that the dirt on this cylinder is wetted by the fluid of the cloth and collected by the same portion of cloth that is in contact with this cylinder and that has a length usually varying from 2 to 15 cm, guaranteed by the structure, pliability and elasticity of the presser, due to which contact is distributed over the whole of the width between cloth and cylinder, without requiring precision assembly operations and the use of precise movement mechanisms. It is also known from the patent JPH5162295 to move the cloth cleaning device and presser with an alternating transverse movement, parallel to the axis of the cylinder, to spread out the dirt on the transverse extension of this cylinder, to reduce concentrated dirt, such as any vertical lines, i.e. those lines caused by dirt that accumulates laterally at the longitudinal edges of substrates to be printed. After this operation to spread the dirt, the cloth is fed for one or more short portions and the presser remains in static position and is thrust against the cylinder, which continues to rotate, until all the dirt has been removed.
If this method were to be used to clean the cliché plate of flexographic machines, most of the dirt would be pushed into the recessed areas of the plate, which would gradually fill up and themselves become receptive of the ink dispensed by the anilox roller, with evident negative and unacceptable consequences for print quality.
To be able to use a cloth device and presser to clean the cliché plate of a flexographic machine for printing on cardboard or other types of substrate, it was necessary to resolve the following technical problem: preventing the dirt collected by the cloth during rubbing of the exposed surface of the cliché plate from entering the recessed areas of this plate, and ensuring that is it completely and promptly removed by this cloth.
This technical problem is resolved with the solution summarised in the appended main claim and with the following idea of solution. The cleaning cloth is guided under sufficient longitudinal tension on a counteractingacting roller parallel to the axis of the cylinder to be cleaned, which unlike the counteractingacting rollers used in the prior art, see for example prior art publications WO 2013/160288 , DE 100 08 214 A1 and DE 10 2004 002 521 A1 , in which rollers also perform the function of presser and have the lateral surface coated with a sufficiently elastic and pliable materials (latex, silicone, butyl rubber or another elastomer), with a hardness of approximately 30-80 Shore, in the innovative solution in question the lateral surface of this counteractingacting roller is made of rigid material, such as metal, and its diameter is such as to ensure that this roller has high flexural strength, a large surface in contact with the cloth and at the same time such as to have a contact area with the active surface of the cylinder to be cleaned, substantially of linear type, that touches the cliché plate on the whole of its width, but the amplitude of which is substantially limited to a contact line. Through precision movement means, the surface of the counteractingacting roller, covered intimately by the cloth under tension, is made to touch the exposed surface of the cliché plate with a small degree of interference between the outer surface of the cloth and the active surface of the cliché plate and with a relative reverse movement between the two surfaces, so that the cloth picks up the dirt and removes it rapidly from the cliché plate, due to adequate longitudinal unwinding imparted to the cloth, so that a clean portion of cloth gradually comes into contact with the cliché plate and a corresponding quantity of soiled cloth is moved away from this cliché plate and also due to the substantially linear contact between cloth and cliché plate, so that the soiled cloth is promptly moved away from this cliché plate due to the curvature of the rigid counteractingacting roller, which after having put the tightly stretched outer surface of the cloth into light contact with outer surface of the cliché plate, immediately removes the cloth with the dirt from this cliché plate. Instead of said counteractingacting roller with rigid lateral surface, any equivalent means can be used, such as a roller of small diameter supported rotatably by a sturdy flat beam, to form the rounded and rotatable operating edge of a substantial doctor blade, or a sturdy doctor blade with a rounded edge coated with a material with low friction coefficient can be used, on which the cloth under tension is made to slide, or other suitable rigid counteractingacting means capable of ensuring precise positioning of the cloth in relation to the cliché plate to be cleaned can be used.
Other and further features of the invention and of the advantages deriving therefrom will be more apparent from the following description of a preferred embodiment thereof, illustrated purely by way of non-limiting example in the figures of the five accompanying drawings, wherein:

Fig. 1 is a side view and with a sectional view of parts of the cleaning device during cooperation with the cliché plate of the printing cylinder of the machine;
Fig. 2 shows an enlargement of the main operating components of the device shown in Fig. 1, to provide a better understanding of the operating principle of this cleaning device;
Fig. 3 shows the cleaning device mounted on the shoulders of the machine, in a front view according to the arrow K3 of Fig. 1;
Fig. 4 shows other details of the device as in Fig. 3, in a top plan view according to the arrow K4 and with a sectional view of some parts and a cutaway view of other parts to provide a better understanding of some components;
Fig. 5 shows details relating to one of the components for transverse oscillation of the cleaning device, shown along the line of section V-V of Fig. 4;
Fig. 6 shows a side elevation according to the arrow K6 of Fig. 3, of the means that provide for longitudinal unwinding of the cleaning cloth under tension.

In Fig. 1, the number 1 indicates the printing cylinder, for example having a diameter of approximately 430-450mm, which carries on its circumference the cliché plate 2, which rotates in the direction indicated by the arrow, which receives ink from the anilox roller and then transfers this ink to the substrate to be printed, indicated schematically by the arrow 4, supported by known positioning and unwinding means, not shown. In the portion of printing cylinder 1 that runs between the printing area of the substrate 4 and the inking roller 3, there is positioned the cleaning device according to the invention, supported by the side panels 5 of the machine (Figs. 3, 4, 5) by means of inner plates 6 that carry respective precision rectilinear guide and slide units 7, for example of recirculating ball type, horizontal and orthogonal to the axis of the cylinder 1, adapted to allow the cleaning device to move towards and away from the cylinder 1, to pass from a withdrawn rest position to the nearby operating position, and vice versa. To simplify the description of the invention, the reference drawings only show one of the side panels 5 of the machine with the parts associated thereto and nearby of the cleaning device, it being understood that on the other side panel 5, not shown, there are associated symmetrical parts of the same device indicated with the same numbers. On the slides of the units 7 there are fixed the primary side panels 8 supporting the cleaning device (see below), which are interconnected by a torsion shaft 9 supported rotatable with bearings by the same primary side panels 8, and which project from the outer side thereof with hubs, on which there are fitted toothed wheels of the same diameter 10 that mesh with racks 11 parallel to the guide and slide units 7 and fixed to supports 111, in turn fixed on the plates 6 with adjusting means, described below. One of the primary side panels 8 supports a gear motor unit 12, for example with a reduction ratio of 1/40, preferably with electric motor to control the speed and the phase, with encoder and brake, connected to a unwinding and control unit 13, to which information relating to the thickness of the cliché plate mounted on the cylinder 1, and therefore related to the stroke of the cleaning device towards this cylinder, can be provided. The shaft of the gear motor unit 12 projects from the outer side of the supporting side panel 8 and a toothed wheel 14 that meshes with a toothed wheel 10 of the synchronization shaft 9 is fitted thereon. It is evident how the rotation in one direction of the motor unit 12, 14 corresponds to turning of the toothed wheels 10 on the respective racks 11, for example in the direction that carries the side panels 8, and with these the whole cleaning device, to move towards the cylinder 1, while reverse rotation of the same motor unit 12, 14 will return the cleaning device to the withdrawn rest position. To prevent using costly components in the rack and pinion movement system described above and to provide for automatic take-up of clearances and correction of any small misalignments in the two rack and pinion mechanisms, the stroke of the carriage with the two primary side panels 8 towards the cylinder 1 is opposed by elastic means capable of providing a counteractingacting thrust so that the teeth of the rack and pinion systems are always in contact with each other with the side panels that determine the movement of the cleaning device towards the cylinder 1. For this purpose, as shown in Figs. 3 and 4, the front of the primary side panels 8 facing the cylinder to be cleaned 1 is involved during centring by one of the ends of opposing cylindrical coil springs 15, parallel to the racks 11 and housed and guided with the other end in the seats 16 of respective supports 17 having a square shaped base and fixed on the inner sides of the nearby plates 6. Good results have been obtained using springs 15 capable of providing a thrust of approximately 20-30 kg and a gear motor unit 12 capable of providing a thrust of approximately 100-120 kg. From Fig. 4 it can be seen that the supports 111 of the racks 11 (Fig. 4) are fixed to the plates 6 with screws 18 passing through longitudinal slots 19 of these supports, to allow adequate adjustment of the two rack and pinion mechanisms described above, in the installation step of the apparatus in question.
On the inner faces of the two primary side panels 8 of the device there are fixed, in a cantilever fashion and perpendicularly, pairs of guide rods 20 on which there slide with respective recirculating ball bushings 21, the secondary side panels 22 of the cleaning device (Figs. 1, 3-5), fixed mutually by means of at least one cross member 23 and on which there is mounted rotatable with their ends the counteractingacting roller 24 parallel to the cylinder 1, having a rigid lateral surface, for example made of metal and/or another suitable material not elastic and pliable as in the prior art and with a diameter suitable to ensure high flexural strength and linearity of the outer generatrix, for example an outer diameter of approximately 150-200 mm. These secondary side panels 22 support with the known possibilities of rapid and simplified assembly and disassembly, the axes 125 and 126 of reels 25 and 26, respectively to unwinding clean cloth and to collect soiled cloth, the first reel preferably being positioned at the bottom so that the clean cloth P unwound therefrom can travel upwards, rubbing on a cleansing fluid dispensing bar 27 of known type, fixed to the cross member 23, so that this cloth suitably wetted with fluid can curve through about 180° around the counteractingacting roller 24 and can finally reach the axis 126 to form the winding up reel 26. For correct operation of the device, the axis 125 of the unwinding reel is controlled by clutch and, optionally, braking means, indicated schematically with 28, of mechanical or other known type, and the axis 126 of the soiled cloth winding up reel is connected to continuous or intermittent rotation means, to take up cloth P from the unwinding reel 25, which being clutched, causes this cloth P to be pulled longitudinally to intimately touch the wetting bar 27 and then the counteractingacting roller 24. To ensure unwinding of portions of web of a predetermined and constant length, even when the diameter of the winding up reel 26 varies, good results have been achieved with a device that is now described with reference to Fig. 6 and that, in connection with one of the ends of the axis 126, with the interposition of a free wheel 29, has a lever 30 placed on the outer face of the nearby side panel 22 (see also Figs. 3, 5), oriented downwards and connected with its end 130 to the rod 131 of a piston-cylinder unit 31, in turn hinged with the base of its body, in 32, to the side panel 22. The cylinder 31 can be of single-acting type with spring return and in the active stroke of extension of its rod 131, due to the free wheel 29 causes a corresponding clockwise rotation of the axis 126 and of the reel 26, to produce the necessary unwinding of the cloth P under tension. From Fig. 6 it can be noted that the side of the lever 30 facing the cylinder 31 has a cam profile 33 with which there cooperates the rounded end of a stroke limiting eccentric 34 rotatable on the side panel 22 by means of a pin 35 passing through a support placed on this side panel, which extends parallel to the axis 126 of the reel 26 with a portion to which there is fixed the end of a blade 36 that is stressed by a spring 37 to circumferentially touch this reel 26 to detect variations in its diameter. It is apparent how when the diameter of the winding up reel 26 increases the blade 36 oscillates downwards causing the stroke limiting eccentric 34 to oscillate downwards proportionally, to progressively decrease the reverse stroke of the rod 131 and consequently to decrease the subsequent active stroke of extension of this rod towards the fixed position of maximum extension indicated by the line K, thereby decreasing the angle of rotation of the axis 126 to ensure the unwinding of constant quantities of cloth P. Good results have been obtained by activating the cylinder 31 to perform one extension per second of its rod, with cyclical and constant unwinding of the cloth P of about 2 mm. It can be appreciated how the use of the stroke limiting device 34 to limit the return stroke at rest of the lever 30 and of the related cylinder 31, provides the great advantage of preventing early wear of these stroke limiting means, due to the substantial absence of mechanical stresses in the contact between the parts. The stroke limiting device 34 or other analogous component provided on the other secondary side panel 22 of the cleaning device, with a related blade 36 and related spring 37 associated to detect the diameter of the winding up reel 26, can be combined with a sensor (not shown) that detects when this reel 26 has reached a maximum predetermined diameter and must be replaced together with installation of a new unwinding reel 25 of new clean cloth.
It is understood that within the scope of the invention it would also be possible to use reels 25 of cloth pre-wetted with cleansing fluid, so that the cleaning device may be without the dispensing bar 27.
With reference to Fig. 5, it can be seen that the counteractingacting roller 24 is formed by a sturdy metal sleeve 124, for example made of aluminium or steel alloy, which carries fixed on both ends (hereinafter, in order to simplify illustration, only one end of the roller 24 is considered, it being understood that identical symmetrical components identified by the same number are mounted on the other end) bushings 38 on which there is fixed with screws and with an intermediate flange 139 thereof a cylindrical bell housing 39, which with its end passes, with a small amount of clearance, through a bore 40 of the side panels 22 to project sufficiently from the outer side of this side panel and to allow fixing of a flange 41 through which the counteractingacting shaft 24 is constrained to the plate 22 with a small amount of clearance that permits it to rotate. It is understood that, instead of this simplified solution, there could be fixed in the bore 40 of the outer ring a double-acting bearing (not shown), suitable both for radial loads and for axial loads, for example of ball type or of cross roller type, on the inner ring of which there can be fixed the flange of the bell housing 39 and the flange 41, so as to prevent all axial and radial clearance between the side panel 22 and the parts constraining the counteractingacting roller 24 thereto, with resulting advantages of silent operation and reduced wear. The flange 41 is preferably equipped with circumferential teeth, which can be detected by a sensor 42 fixed on the outer face of the side panel 22, to indicate the rotation and the extent of this rotation of the roller 24 to the electronic means for programming and controlling operation of the device, not shown. In the bell housing 39 there is mounted coaxially, with interposition of a bearing 43, for example of recirculating ball type, a cylindrical barrel 44 that with the outer end thereof is fixed to the inner face of the nearby primary side panel 8 on which there is fixed externally, opposite and in axial alignment with said barrel 44, the body 45 of a pneumatic cylinder in which there slides a piston 145 integral with a hollow rod 245 that enters the barrel 44 axially, which is screwed to an extension 46 constrained to the bottom of the bell housing 39 with the interposition of a thrust bearing 47 and a circlip 48 and of any other adjusting means, not shown, all so that said extension 46 is constrained axially to the bell housing 39 and does not receive therefrom the rotation deriving from the counteractingacting roller 24. The hollow rod 245 is provided with a seat of larger diameter open on the piston 145, in which there is housed a cylindrical coil spring 49 that interacts between the bottom of said seat and the head of a tie rod 50 that passes axially through this spring, which projects therewith for a sufficient portion from the piston 145 and which passes axially through the narrowest part of the seat of the rod 245 to project therefrom and to rest externally thereon with a nut 250. The extension 46 is provided with a cavity 51 to allow free axial movement therein of the tie rod 40 and of the related nut 250 each time the head of this tie rod contacts the bottom of the body 45 of the pneumatic cylinder and compresses the spring 49, which acts as shock absorber and as energy buffer, to return the energy accumulated through compression each time the axial stroke of the counteractingacting roller 24, together with the related carriage with the secondary side panels 22 and the unwinding and winding up reels of the cloth, is reversed.
In Fig. 5, the piston 145 is shown with a continuous line in an intermediate operating position and with a dashed line in the two different right and left stroke end positions, which are purely theoretical as reversal of the stroke of the opposed pneumatic cylinders 45 is controlled before the piston reaches said stroke end positions, for example when a proximity sensor 52 is covered by the portion of the rod 245 with largest external diameter, as switching from the supply to the discharge step and vice versa of the mouth 534 of these pneumatic cylinders 45, which can in this way be of the single-acting type, takes place in this step.
It can be appreciated how partial insertion into the ends of the counteractingacting roller 24 of the piston cylinder units 45, 145 that cause transverse oscillation of the cleaning device, makes it possible to obtain a noteworthy reduction in the overall dimensions of the apparatus as a whole, making ordinary and extraordinary maintenance of the apparatus simpler and safer.
With the means described above it will be possible to impart to the cloth cleaning device transverse oscillations with a stroke of the required length, for example in the order of approximately 70 mm, and with the required frequency, for example approximately 4-6 strokes per second.
The device as described operates as follows. Normally, the cleaning device is withdrawn from the printing cylinder 1 and has, downstream of the bar 27, if present, and on the first portion of the counteractingacting roller 24, a portion of cloth P sufficiently wetted with cleansing fluid. As the processor 13 is aware of the thickness of the cliché plate 2 mounted on the cylinder 1 (see also Fig. 2), when cleaning of this cliché plate 2 is required, said processor 13 activates the gear motor unit 12 to move the cleaning device towards this cylinder 1 by a predetermined amount, so that the tightly stretched cloth P reaches a condition of intimate contact with extremely limited interference with the active and exposed surface S of the cliché plate 2, from which the dirt D is to be removed.
Interference between the outer surface of the tightly stretched cloth P and the outer surface S of the cliché plate to be cleaned can be in the range of 10-50% of the thickness this tightly stretched cloth P, for example in the order of approximately 0.1-0.2 millimetres. Good results have been obtained by providing a thrust against the cliché plate 2 of the counteractingacting roller 24 covered with the cloth P of approximately 1-3 Newton. Considering said interference is approximately 0.2 mm between the cliché plate 2 with related carrying roller 1 with a diameter of approximately 500 mm, and the counteractingacting roller 24 with a diameter of approximately 150-200 mm, the value of said thrust will be in the order of approximately 5-15 Newton/cm². At these thrust values, and bearing in mind that the bearing surfaces between roller 24 and cliché plate 2 are variable from a minimum of a few centimetres, in the central position, to the whole of the width of these components, the maximum allowed flexure of the counteractingacting roller 24 must remain below 0.05 mm. For these purposes, it is useful to perform a precise movement of the device towards the cliché plate 2 of the printing cylinder 1 with the aforesaid means employing a precision motor and a drive train with automatic take up and compensation of clearances through said opposing springs 15. However, it is understood that the system can use redundant control means, for example in the form of stroke limiting means adjustable as a function of the thickness of the cliché plate 2 mounted on the cylinder 1, with which at least one of the side panels 8 comes into contact in their stroke towards this cylinder 1. When the dirt D reaches the contact area between the raised surfaces of the cliché plate 2 and the cloth P, supported by the rigid counteractingacting roller 24 that ensures correct and uniformly distributed positioning between cloth and cliché plate, also due to the adequate longitudinal tension to which the cloth P is subjected in order to oblige it to intimately and uniformly mate with the rigid contact surface of the roller 24, this dirt D touches the cloth P and remains thereon while this cloth P is fed in reverse direction by approximately 2mm per second, with rotation of the counteractingacting roller 24 in the direction of the arrow F2 and while the printing cylinder 1 rotates in the direction of the arrow F1 with a speed, for example, of approximately 3 rpm. It is evident that, due to the curvature of the rigid roller 24 and to the unwinding of the cloth P, the dirt D is promptly removed from the cliché plate 2 and cannot enter the recessed areas 102 of the active surface of this cliché plate 2. It is understood that the scope of invention also includes the constructional variant, not shown, in which the axis 126 of the reel 26 is operated at the opposite ends by respective devices as shown in Fig. 6, that alternate in the active unwinding movements of the cloth, to ensure substantially continuous unwinding of the cloth, always in the order of approximately 2 mm per second. The scope of the invention also covers the use of alternative means to the rotating counteractingacting roller 24, both of means with rolling contact with the cloth P and of means with sliding contact with this cloth. In the first case, a there could be used a roller of small diameter supported in rotation by a sturdy flat beam, to form the rounded and rotating operating edge of a substantial doctor blade. In the second case the counteractingacting roller 24 could be replaced by the edge, rounded and optionally coated with a material with a low friction coefficient, of a sturdy doctor blade, on the edge of which the cloth is guided, tightly stretched and made to slide. These means have not been illustrated as they are apparent to those skilled in the art based on the description above.
To make use of the cleaning cloth P on the whole of its transverse extension, the whole cleaning device can be made to oscillate transversely with alternate activation of the aforesaid pneumatic cylinders 45, there being provided for this purpose the use of a cloth of equal or greater width to the width of the cliché plate 2 and of the oscillating stroke of the device with the means described with reference to Fig. 6, so that at the end of each stroke the cliché plate substantially does not exit from the transverse dimensions of the cloth. During the step of transverse oscillation of the device to prevent the cleaning cloth P from forming folds or wrinkles on the roller 24 that would interfere anomalously with the surface of the cliché plate to be cleaned, this counteractingacting roller 24 is provided with an outer lateral surface with a friction coefficient with the cloth of a value suitable to avoid the formation of said wrinkles and for this purpose the outer lateral surface of the roller 24 is machined, for example with sanding and subsequent hard anodising treatments, so as to have a roughness Ra with an average value between 3 and 6. Again to prevent the formation of said wrinkles, the cloth must be subjected by said unwinding means to a longitudinal tension of adequate value, preferably between 0.05 and 1 kg per linear centimetre.
It is understood that the scope of the invention also includes the constructional variant according to which the device is only provided with the movements towards and away from the printing cylinder (1, 2) and not also with the transverse oscillation movement, and in this case the counteractingacting roller 24 can have an outer surface with the aforesaid roughness or substantially smooth.

Claims

Cleaning device to clean the cliché plate (2) of the printing cylinder (1) of flexographic machines, of the type comprising a first reel (25) to unwinding a cloth (P) of the same width as the width of the printing cylinder (1) with the cliché plate to be cleaned, which comprises a second reel (16) to collect the collecting cloth unwound from said first reel and which comprises a rectilinear counteractingacting means (24) on which there is guided a portion of the cloth (P) comprised between said first and said second reel, these reels (25, 26) and this rectilinear counteractingacting means (24) being arranged with their axis parallel to that of the printing cylinder (1) with the cliché plate (2) and being supported by the side panels (22) of a carriage provided with means for movement towards and away from this printing cylinder with cliché plate (1, 2), so that in the movement towards the cylinder the cloth guided on said rectilinear counteractingacting means (24) touches and rubs the surface to be cleaned of the cliché plate of the printing cylinder, there being provided on this carriage means that provide for the longitudinal unwinding of the cloth under tension, so that it is stretched transversely and longitudinally and adheres intimately on said rectilinear counteracting means (24) and this unwinding of the cloth being opposite to the direction of rotation (F1) of the printing cylinder with the cliché plate (1, 2) and being provided with means (27) for wetting the same cloth unwound from the unwinding reel with a fluid useful for cleaning the cliché plate (2) of the printing cylinder (1), or this cloth of the unwinding reel (25) being pre-wetted with a said cleansing fluid, characterised in that said rectilinear counteracting means (24) has a rigid surface in contact with the cleaning cloth (P) and facing the cliché roller to be cleaned (2) and has a transverse profile sufficiently curved and convex and in that said means for movement of the carriage that supports the cleaning device are means capable of performing a precision movement, so that in the active cleaning step of the cliché plate (2) of the printing cylinder (1), the outer surface of the cloth (P)guided on said linear counteracting means (24) is in a contact state with the exposed surface (S) of the cliché plate and with minimum interference with this surface (S), and it has been provided that during this active step of cleaning of the cliché plate of the printing cylinder the unwinding means of the cloth (P) under tension cause this cloth to be fed with brief, continuous or intermittent movements, said rectilinear counteracting means (24) consisting of a roller with the lateral surface made of metal or another hard material, this counteracting roller being static or preferably being rotatable about its axis and having a diameter suitable to ensure that this counteracting roller has high flexural strength and linearity of the outer generatrix thereof, so that in the operating step of thrust of the cloth (P) against the surface of the cliché plate (2) to be cleaned, the maximum allowed flexure of this counteracting roller (24) remains below 0.05 mm.
Device according to claim 1), wherein the longitudinal unwinding means of the cloth (P) are such that in the operating step the cloth is fed by a few millimetres per second, for example by at least two millimetres per second or by another amount correlated to the rotation speed of the cylinder (1) with the cliché plate to be cleaned.
Device according to claim 1), wherein the unwinding reel (25) of the clean cloth (P) is placed under the counteracting roller (24) and is sufficiently withdrawn from this and the cloth (P) is unwound from the lower part of this reel (25), is guided on an optional fluid dispensing bar (27) fixed on a cross member (23) of the carriage of the cleaning device and finally is guided from the bottom upwards on the counteracting roller (24), to involve this roller for approximately 180° of its circumference and finally the cloth is fastened to the lower part of the axis (126) of the reel (26) for winding up the soiled cloth, placed substantially at the same height and in the vicinity of the counteracting roller (24), all so that even when the diameter of the unwinding and winding reels (25, 26) of the cloth varies, this cloth (P) involves said counteracting roller (24) with a large contact surface.
Device according to claim 1), wherein the unwinding means of the cleaning cloth (P) under tension comprise clutch means (28) to control the rotation axis of the unwinding reel (25) of the clean cloth and comprise a free wheel (29), a lever (30) and a piston-cylinder pneumatic unit (31) that make use of the stroke of extension of the rod of this unit (31) to wind the soiled cloth on the corresponding reel (26), there being provided eccentric means (34) whose angular position is modified by a blade (36), which by elastic means (37) is made to read the diameter of the winding up reel (26) of the soiled cloth and said eccentric being arranged to limit the oscillation of said lever (30) during the stroke of retraction of the rod of said unit (31), so that when the position (K) of maximum extension of the rod remains fixed, the winding up reel (26) is rotated with decreasing angular movements as its diameter increases, to ensure cyclical and constant unwinding of the cloth (P).
Device according to claim 4), wherein the axis of the winding up reel (26) can be provided on both ends with a cyclical rotation device and the pneumatic units (31) of these devices are connected to supply and discharge means that are mutually offset, to ensure continuous unwinding of the cleaning cloth (P).
Device according to claim 1), wherein the side panels (22) of the carriage of the cleaning device are provided with at least a pair of bushings (21) with axis parallel to the axis of the reels (25, 26) and of the counteracting roller (24) and in which there slide guide rods (20) fixed in a cantilever fashion and perpendicularly on the inner sides of corresponding primary side panels (8) sliding horizontally by means of respective guide and slide units (7) on support plates (6) fixed on the inner faces of the side panels (5) of the printing machine, it being provided that between these plates (6) and said primary side panels (8) said means that provide for movement of the cleaning device towards and away from the cliché plate (2) of the printing cylinder (1) act with a precise movement towards it, and on these primary side panels (8) there being provided alternate movement means, to impart to the carriage with the secondary side panels (22) that support the cloth cleaning means (P) a transverse oscillation of amplitude and frequency such as to facilitate removal of the dirt (D) from the active surface (S) of the cliché plate (2) of the printing cylinder (1), and which ensures more efficient use of the cloth on its transverse extension.
Device according to claim 6), wherein the means for movement of the cleaning device towards and away from the printing cylinder (1, 2) to be cleaned comprise a torsion shaft (9) supported rotatable and transversely by said primary side panels (8) and provided on both ends with equal toothed wheels (10) that cooperate with racks (11) fixed with adjustable supports (111) on the plates (6) with said guide and slide units (7), parallel to these units (7), one of said toothed wheels (10) being connected to the output toothed wheel (14) of a gear motor unit (12) fixed on a primary side panel (8) and provided with an electric motor to control the speed and the phase, with an encoder and if necessary with a brake, connected to an electronic control unit (13), to which there is provided with any suitable means data relating to the thickness of the cliché plate (2) mounted on the related cylinder (1), and therefore related to the precision movement that this motor must impart to the cleaning device in the step of movement towards this printing cylinder (1, 2).
Device according to claim 7), wherein there is provided the use of opposing springs (15) supported by supports (17) constrained to the plates (6) fixed to the side panels (5) of the printing machine, to oppose the movement towards the printing cylinder (1, 2) of the primary side panels (8) of the cleaning device, to take up small clearances and any small misalignments in the two pinion (10, 14) and rack (11) mechanisms and consequently to ensure the necessary precision in the performance of said movement towards the cylinder.
Device according to claim 6), wherein the means for transverse oscillation of the secondary carriage with the side panels (22) that support the unwinding and winding up reels (25, 26) of the cloth (P) and the counteracting roller (24) comprise piston-cylinder pneumatic units (45, 145) mounted on the outer side of the primary side panels (8), and which with their rod cooperate, with the interposition of bearings (43, 47), with parts inside the two ends of the counteracting roller (24) produced with a metal sleeve (124) and supported rotatable by these ends by the side panels (22) of the secondary carriage, there being provided in said piston-cylinder units (45, 145) elastic shock absorbers (49, 50) useful as dampers and which cyclically yield the energy accumulated to the oscillating system each time that means (52) cause reversal of the supply and discharge phases in said pneumatic units (45, 145).
Device according to one or more of the preceding claims, in particular according to claim 6), characterized in that the counteracting roller (24) has an outer lateral surface with a roughness (Ra) with an average value between 3 and 6 and in that the cleaning cloth (P) is stretched tightly longitudinally on this roller (24) and is fed with a tension in the order of 0.05 to 1 kg per linear centimetre.