PRINTING UNIT

Abstract: A printing unit has two parallel frame sides (1), between which transverse, rotatable rollers (3, 8, 13) are supported in bearing brackets (6, 11, 16) which are arranged in each frame side and displaceable in the plane thereof under the action of a power unit (31) for clamping the bearing brackets in the machine frame. Each frame side (1) has a recess (27), in which the bearing brackets (6, 11, 16) are arranged and which is defined by two abutment portions (28, 29), between which the clamping forces act. The power unit (31) in each frame side has a contact point in a gap (34) between one abutment portion (28) and the neighbouring bearing bracket (16).

Description: PRINTING UNIT Technical Field The present invention relates to a printing unit for printing a continuous web. The invention relates especially, but not exclusively, to so-called flexo- graphic printing units. Background Art Printing units of the above-mentioned type are well- known to those skilled in the art and usually comprise a machine frame having two parallel frame sides, between which transverse, rotatable rollers or cylinders are supported in bearing brackets. The terms roller and cylinder will below be used as synonyms. A flexographic printing unit comprises as a rule the following rollers/cylinders: (a) an inking roller which is inked by, for instance, a chamber doctoring system, (b) a stereo roller, and (c) an impression cylinder. In the operative (active) position, the bearing brackets of the rollers/cylinders are set, such that the cylinders/ rollers rotate towards each other, the generatrices being related to each other in a manner which is optimal for transferring ink from the inking roller to the web to be printe . In a flexographic printing unit, the ink is transferred from the inking roller to the web to be printed by means of a compressible stereo arranged as a jacket on the stereo roller. This stereo jacket, which covers either the whole periphery of the stereo roller or a part thereof, usually has a thickness of a few millimetres. The height of the ink-transferring parts of the stereo always deviates more or less from the ideal height. Therefore, the stereo must be compressed, on the one hand, when being inked by the inking roller and, on the other hand, when applying ink to the web to be printed, to an extent corresponding to the difference in height between the lowest printing point and the highest print- ing point (apex). The web to be printed is supported by the impression cylinder so as to be correctly positioned relative to the stereo when ink is transferred from the stereo. When the printing operation is temporarily interrupted, the stereo can be damaged if the web that is being printed dries and gets stuck to the stereo, the ink acting as adhesive, or if the inking roller drags itself along the stereo when, during the interruption, rotated by a separate motor, such that the ink does not dry on the inking roller. To obviate these problems, it should be possible to set the printing unit to a non-operative position in case of interruption of the printing. This means that the generatrices of the impression cylinder, stereo roller and inking roller are separated from each other about a millimetre. Printing units of this type are disclosed in Applicant's Patent Publications DE-C-2, 746, 878, EP-A-132,246 and EP-A-280, 668. In these prior-art printing units, which in fact function well, the force providing the clamping of the bearing brackets and, thus, the rollers/ cylinders is generated by means of lever mechanisms and/ or chains passed around guide pulleys. In certain applications, this clamping can be felt to be complicated and inefficient, and therefore there is a need of a new, simplified and improved clamping technique. In flexographic printing units, it is also a general wish that the rollers/cylinders should be easily replaceable to facilitate shifting between different printing jobs. A known solution to this problem is presented US-A- 3,792,658 which discloses a printing unit having the rollers/cylinders mounted in bearing brackets. As is evident from Fig. 1 of this US patent, the impression cylinder is supported between two upright arms belonging to two fixed, L-shaped bearing brackets, on which the stereo roller bearing brackets, which are also L-shaped, are arranged. The bearing brackets of the inking roller are in turn arranged on the L-shaped bearing brackets of the stereo roller. Each of the bearing brackets of the stereo roller and the inking roller is horizontally displaceable by a power unit in the form of pneumatic cylinders in combination with precise adjustment members. The nominal adjustment of each bearing bracket is determined by a rod preselected from a set of rods of different lengths. The purpose of the precise adjustment member is to adjust the distance of the rollers/cylinders in respect of devia- tions of stereo thicknesses and varying material thicknesses. The purpose of the power units is on the one hand to lock, together with the rods adapted to the diameter of the impression cylinder, the bearing brackets relative to each other when the printing unit is operative and, on the other hand, to move the bearing brackets of the stereo roller and the inking roller between the operative and the non-operative position. During operation of these prior-art printing units, when the bearing brackets of the rollers thus are locked relative to each other, certain drawbacks arise. In the printing unit according to US-A-3, 792, 658, the power units do not act in the same plane as the forces arising when the stereo is being compressed. The moments and transverse forces arising owing to the forces acting in different planes cause vibrations and elastic deformations in the printing unit, above all in the bearing brackets of the stereo roller. This leads, in turn, to the generatrices of the cylinders/rollers being urged away from the position that yields optimal ink transfer. Deformations of this type always result in a deterioration of the printing quality. A further problem in printing units having an L-shaped stereo roller bearing bracket is that supplementary locking mechanisms in the form of screws or other power units are required to lock the bearing brackets of the stereo roller and the inking roller relative to the bearing brackets of the impression cylinder when the printing unit is operative. There is thus a need of arranging the rollers/cylinders so as to obviate the above-mentioned problems. In printing units of the design as described above, it is desirable first to be able to effect a nominal adjustment of the rollers/cylinders according to the current diameters thereof and then to correct the nominal adjustment in respect of deviations from the ideal stereo height and the current material thickness. To this end, various bearing bracket arrangements are utilised. EP-A- 363,293 discloses a flexographic printing unit which, for the above-mentioned purpose, is provided with devices for rough and precise adjustments, respectively. These adjustment devices, however, are complicated and besides connected to each other, which renders a separate nominal or correction adjustment impossible. Moreover, the bearing brackets are interconnected, which makes the exchange of rollers considerably more difficult since also the complicated adjustment devices have to be dismounted. The printing unit of EP-A-363, 293, in which the rolling bearing brackets are supported by two parallel, subjacent guide shafts, offers no satisfactory solution to the problem of providing a rational adjustment of the printing unit in combination with efficient absorption of the forces arising during the deformation of the stereo. Summary of the Invention The object of the present invention thus is to provide a printing unit while obviating the above-mentioned drawbacks, the clamping of the bearing brackets being possible without requiring any complicated lever mechanisms and/or chain arrangements and the rollers/cylinders being easily replaceable for different printing jobs, and nominal adjustment and correction adjustments being inde- pendent of one another. Moreover, the clamping of the bearing brackets should be of such a type that neither horizontal nor vertical forces (for instance, exerted by gear wheels ) can affect the set mounting position of the cylinders/rollers during operation. A further object of the invention is to provide a reliable printing unit which is composed of as few and simple components as possible. These and other objects, which will appear from the description below, have now been achieved by means of a printing unit having the features as defined in appended claim 1. Preferred embodiments of the invention are stat- ed in the appended subclaims. A great number of advantages are achieved according to the invention. The inventive printing unit is of simple mechanical design and will therefore be easy to manufacture. The replacement of rollers/cylinders as well as the adjustment can be carried out very easily and quickly. Internal forces (compression of the stereos) are absorbed by self-locking means and therefore cannot affect the correction adjustment members. The bearing brackets are horizontally locked by a horizontal force, while vertical locking is provided by the friction between the bearing brackets that arises when they are compressed by the horizontal force. Owing to the large force-transmitting surfaces which absorb the horizontal force, the bearing brackets are not deformed, i.e. the nominal measurement is affected negligibly by the clamping force. Since the stereos as well as inks and inking systems, inking rollers and chamber doctoring systems have been further developed, the requirements placed on the mechanical performance as well as the stability and adjustability of the printing unit increase. Thus, it is important that the parameters affecting the printing result (e.g. the roller/cylinder distance) can be determined numerically, which is achieved by the invention. Brief Description of the Drawings The invention will now be described in more detail with reference to the accompanying schematic drawings which, for the purpose of exemplification, show the currently preferred embodiments of the invention. Fig. 1 is a side view of a printing unit according to a first embodiment of the invention in its operative position. Fig. 2 shows a spring means and is an enlargement of a detail of Fig. 1. Fig. 3 is a part-sectional view of a power means and is an enlargement of a detail of Fig. 1. Fig. 4 is a view, corresponding to Fig. 1, of the printing unit in its non-operative, idle-running position. Figs 5 and 6 show the spring means and the power means in Fig. 4 and are enlargements of details similar to Figs 2 and 3. Fig. 7 is a view of the printing unit in the position for replacement of rollers, corresponding to Figs 1 and 4. Figs 8 and 9 illustrate the spring means and the power means in Fig. 7 and are enlargements of details corresponding to Figs 2-3 and 5-6, respectively. Fig. 10 is a sectional view taken along line X-X in Fig. 1. Fig. 11 is a side view of a printing unit according to a second embodiment of the invention. Fig. 12 is an end view XII-XII of a frame side of the printing unit illustrated in Fig. 11. Description of the Preferred Embodiments Figs 1-10 illustrate a first embodiment of the invention in the form of a flexographic printing unit which comprises a machine frame having two parallel frame sides, which are generally designated 1 and 2 and between which transverse, rotatable rollers or cylinders are supported. An impression cylinder 3 has its stub shafts 4 and 5 mounted in bearing brackets 6 and 7. A stereo roller 8 has its stub shafts 9 and 10 mounted in bearing brackets 11 and 12, and an inking roller 13 has its stub shafts 14 and 15 mounted in bearing brackets 16 and 17. In connection with the inking roller 13, there is an inking device, preferably a chamber doctoring system (not shown), which need not be described in more detail here. The machine frame also comprises two crossbars 18, 19 connecting the frame sides 1, 2 with each other. Between the bearing brackets 16, 17 of the inking roller 13 and the bearing brackets 11, 12 of the stereo roller 8, there are first spacers or gauge blocks 20, 21, and between the bearing brackets 6, 7 of the impression cylinder 3 and the bearing brackets 11, 12 of the stereo roller 8, there are second spacers or gauge blocks 22, 23. The gauge blocks 20-23 are included in a device for nominal adjustment of the bearing brackets 6, 7, 11, 12, 16, 17 according to the diameter of the rollers/cylinders 3, 8, 13, as will be described below. To accomplish a correction adjustment of the rollers/cylinders 8 and 13, there is, in connection with the bearing brackets 11, 12, 16, 17 in each frame side 1, 2, an eccentric-acting lever mechanism 24, 25 which preferably is of the type as described in EP-A-280,668 which was mentioned by way of introduction and which is incorporated herein by reference. A continuous web of material 26, which is to be printed between the impression cylinder 3 and the stereo roller 8, is indicated by a dash-dot line in Figs 1, 4 and 7. Since the two frame sides 1, 2 are identical, it suffices to describe below one frame side 1 as shown in Figs 1, 4 and 7. In this frame side 1, the bearing brackets 6, 11, 16 of the rollers/cylinders 3, 8, 13 and the gauge blocks 20-23 are arranged in a rectangular recess 27, which has an open side (here upwardly open) and which is defined by two upright, opposite and spaced- apart counterportions or abutment portions 28 and 29. The recess 27 is also defined by a horizontal bottom portion 30, which extends between the vertical abutment portions 28 and 29 and on which the bearing brackets 6, 11 are slidably displaceable in the plane of the frame side 1, as well as the gauge blocks 20 and 22 arranged therebetween. The frame side 1 thus can be regarded as a U-shaped cradle, in which the bearing brackets 6, 11, 16 and the gauge blocks arranged therebetween are placed. To produce a force for clamping the bearing brackets 6, 11, 16 and the gauge blocks 20, 22 arranged therebetween, in the recess 27 between the abutment portions 28 and 29, a pressure cylinder 31 is arranged in the bearing bracket 16. The pressure cylinder 31, which preferably is hydraulic or pneumatic and of standard type, cooperates with a screw 32 which is screwed in a threaded hole in the abutment portion 28. Some sort of spacer 33 is preferably arranged between the pressure cylinder 31 and the screw 32. For clamping into the operative position of the printing unit, the pressure cylinder 31 is activated and extended from the bearing bracket in the direction of the abutment portion 28. The end of the pressure cylinder 31 then abuts the spacer 33 of the screw 32 and thus has a contact point in or adjacent to a gap 34 between the abutment portion 28 and the neighbouring bearing bracket 16, as will be best seen from the part-sectional view in Fig. 3. For reasons of symmetry, there is a pressure cylinder 31 in each frame side 1, 2, as will be seen from Fig. 10. The two pressure cylinders 31 thus form a power unit for generating the clamping force discussed above. It should be emphasised that this power unit can, of course, be designed in some other manner. For instance, the pressure cylinders can instead be arranged in the opposite abutment portions and abut the neighbouring bearing brackets . As is evident from Fig. 1, the longitudinal axes of the rollers/cylinders 3, 8, 13 extend in substantially the same plane as the longitudinal axes of the pressure cylinders 31 and the screws 32, and said force contact point is also positioned in this plane. This results in a very simple distribution and absorption of forces. Horizontal forces are absorbed directly by the pressure cylinder 31, and vertical forces by frictional forces between the bearing brackets and the gauge blocks, which results in reliable clamping and absorption of forces as well as moments. Adjacent to the bearing bracket 11 of the stereo roller 8, there is a spring arrangement comprising four spring means in the form of helical springs 36, of which one is shown in detail in Figs 2, 5 and 8. In the operative position (Fig. 1) of the printing unit, the springs 36 are pressed against the gauge blocks 20 and 22 arrang- ed on both sides of the bearing bracket 11, and apply bias on these. In the idle-running position (Fig. 4) of the printing unit, when the web is not being printed, the impression cylinder 3, the stereo roller 8 and the inking roller 13 are separated from each other, such that the stereo does not contact the web 26 and the inking roller 13. In the non-operative position, the clamping force is relieved by the pressure cylinders 31 being retracted into the bearing brackets 16 (Fig. 6), the springs 36 applying their bias on the neighbouring gauge blocks 20 and 22, such that a gap 37 forms between the bearing bracket 11 and the neighbouring gauge blocks 20 (see Fig. 5). In Fig. 7, the printing unit is shown in its position for replacement of a roller, for instance replace- ment of the stereo roller 8. In this case, the clamping forces are completely relieved by loosening the adjustment screws 32, and the contact between their spacers 33 and the neighbouring pressure cylinder 31 ceases completely and a gap forms therebetween (Fig. 9). In this position, the springs 36 are also out of contact with the neighbouring gauge blocks 20 and 22 (see Fig. 8). Subsequently, the eccentric-acting lever mechanism 24 is removed by simple operations, whereupon the stereo roller 8 and the associated bearing blocks 11, 12 can be taken out of the recess 27. In the inventive printing unit, the replacement of a roller can be carried out in a much simpler and quicker manner than in prior-art printing units. Moreover, it is very easy in the inventive printing unit to change to rollers/cylinders of a different diameter since the nominal adjustment of distance is effected by means of readi- ly exchangeable gauge blocks. Alternatively, gauge blocks and bearing brackets can be made as a single unit, having dimensions adapted to the diameter of the roller/cylinder. Of course, also the width of the bearing brackets can be adapted to the desired clamping. The gauge blocks 20, 22 thus form, together with the adjustment screws 32, a device for nominal adjustment. Preferably, the spacers 33 arranged at the two ends of the adjustment screws are replaceable, which means that such spacers 33 of different thicknesses (dimensions) can be used for the nominal adjustment. When the nominal adjustment of the printing unit is finished, a correction adjustment of the stereo roller 8 and the inking roller 13 is carried out by means of the two eccentric-acting lever mechanisms 24 and 25. The two lever mechanisms 24, 25, which are connected to the stub shafts 9, 10 and 14, 15, respectively, of the stereo roller 8 and the inking roller 13, thus form a simple and reliable device for correction adjustment. According to the above-described first embodiment of the printing unit according to the invention, the two abutment portions 28, 29 defining the recess 27 constitute fixed parts of each frame side 1 and 2. According to a second embodiment of the invention, an alternative is presented as shown in Figs 11 and 12. In this case, one abutment portion 29' still constitutes a fixed part of the frame side 1 , whereas the other abutment portion 28 ' is movable (arrow A). The distance between these two abutment portions 28 ' and 29 ' , which define the recess 27' for the bearing brackets and the gauge blocks, thus is adjustable. The movable abutment portion 28' carrying the adjustment screw 32' constitutes an upright part of an L-shaped element generally designated 38, whose horizontal part 39 is adjustably arranged in or adjacent to the frame side 1. In this embodiment, there is no power means adjacent to the gap 34 between the abutment portion 28 ' and the neighbouring bearing bracket 16 ' , but instead the clamping force indicated by arrow F is generated by means of a schematically illustrated power means 40 which is connected to the horizontal part 39 of the L-shaped element 38. The printing unit designed according to the second embodiment will thus function substantially according to the principle of a vice. In a third variant (not shown), the L-shaped element of the second embodiment is arranged in another way, its horizontal part being arranged on and overlaying the brackets and the gauge blocks. The outer abutment por- tion thus extends downwardly. Of course, the overlaying L-shaped element is removable for replacement of rollers and bearing brackets . The features that are essential to the invention, however, are the same for both embodiments by the bear- ing brackets being arranged in a recess 27, 27' defined by two preferably upright, spaced-apart abutment portions 28, 28' and 29, 29', respectively, between which the clamping force acts. The clamping-force-generating power unit 31, 40 of the two embodiments has in each frame side a contact point in or adjacent to the gap 34 between one abutment portion 29, 29' and the neighbouring bearing bracket 16, 16'. In the second embodiment, the operative power means 40, however, is spaced from said contact point adjacent to the gap 34. An advantage of the new clamping technique compared to previous techniques (lever and chain) is that the vertical forces will be absorbed, in both abutment portions, by the frictional force. If the compressed bearing brackets are regarded as a beam, this will have a support for the vertical forces at each end owing to the new clamping technique. In prior-art embodiments, the vertical forces are absorbed at one end only. One may compare the outward bending of the free end of a beam fixedly clamped at one end, with a beam that is supported at both ends. It should finally be pointed out that the inventive concept is in no way restricted to the embodiments de- scribed above, and several modifications are possible within the scope of the inventive idea as reflected in the appended claims. The power means preferably consist of fluid-operated pressure cylinders, especially pneumatic or hydraulic such cylinders, but the expert rea- uses that alternative power means can be used. Furthermore, it will be appreciated that alternative solutions of details can be used to provide the nominal adjustment and the correction adjustment. For printing various inks at the same time on a web, a plurality of printing units can be arranged successively, horizontally or vertically. It may be convenient that the recesses in the frame sides are not horizontally arranged, but make a suitable angle with the horizontal plane. When printing units coupled together are used for printing the same web, it is suit- able that the recesses in the frame sides make a certain angle with each other. It should also be pointed out that the invention is not bound to the arrangement of rollers as described above, but several alternatives are feasible within the scope of the invention. According to the desired printing, for instance the impression cylinder and the inking roller can change places, and additional rollers and cylinders may be included in the printing uni . The number of gauge blocks may also vary, and it should espe- cially be mentioned that gauge blocks can be arranged between the outer abutment portion and the neighbouring bearing bracket.

Claims: CLAIMS 1. A printing unit comprising a machine frame hav- ing two parallel frame sides (1, 2), between which transverse, rotatable rollers (3, 8, 13) are supported in bearing brackets (6, 11, 16) which are arranged in each frame side and displaceable in the plane thereof under the action of a unit (31; 40) for generating forces for clamping the bearing brackets in the machine frame, ch a r ac ter i s ed in that each frame side ( 1 , 2 ) has a recess (27; 27') in which bearing brackets belonging to each frame side are arranged, each recess being defined by two spaced-apart abutment portions (28, 29; 28', 29'), between which said clamping forces act, and the power unit (31; 40) in each frame side having a contact point in or adjacent to a gap (34) between one of the abutment portions (28; 28') and the neighbouring bearing bracket (16; 16'). 2. The printing unit as claimed in claim 1, wherein each abutment portion (28, 29) of each recess (27) is a fixed part of the frame side ( 1 ) . 3. The printing unit as claimed in claim 1, wherein one abutment portion (29') is fixed, while the other abutment portion (28') is movable, and the power unit ( 40 ) is arranged to displace the movable abutment portion ( 28 ' ) for providing said clamping of the bearing brackets . 4. The printing unit as claimed in any one of claims 1-3, wherein the power unit comprises two power means (31; 40), each actuating the bearing brackets in the associated frame side. 5. The printing unit as claimed in claims 2 and 4, wherein each power means (31) is arranged in connection with the associated gap (34) in the frame side. 6. The printing unit as claimed in claim 5, wherein each power means (31) is arranged in said neighbouring bearing bracket (16) adjacent to the gap (34). 7. The printing unit as claimed in claims 3 and 4, wherein each power means (40) is arranged in the associated frame side and spaced from said contact point adjacent to the gap (34). 8. The printing unit as claimed in claim 7, wherein each power means (40) is connected to one leg (39) of an L-shaped element (38), which is arranged in or adjacent to the associated frame side and whose other leg (28') constitutes said movable abutment portion. 9. The printing unit as claimed in any one of claims 4-8, wherein the power means (31; 40) are fluid-operated pressure cylinders. 10. The printing unit as claimed in any one of claims 1-9, further comprising a device (20, 22, 32) for nominal adjustment of the bearing brackets according to the diameter of the rollers (3, 8, 13). 11. The printing unit as claimed in claim 10, wherein the device for nominal adjustment comprises gauge blocks (20, 22) between the bearing brackets and/or between the outer bearing brackets and the abutment portions. 12. The printing unit as claimed in claim 11, wherein the device for nominal adjustment comprises additional adjusting members (32; 32' ) which are mounted in each of the abutment portions (28; 28') closest to the gap (34) and which are pressable against said neighbouring bearing brackets (16; 16' ). 13. The printing unit as claimed in claim 12, wherein said additional adjusting members consist of adjustment screws (32; 32 ' ) which are screwed in threaded holes in the abutment portions (28; 28') closest to said gap (34). 14. The printing unit as claimed in any one of claims 10-13, further comprising a device (24, 25) for correction adjustment of the rollers (3, 8, 13) according to the character of the circumferential surfaces thereof and the web of material (26) to be printed. 15. The printing unit as claimed in claim 14, where- in the device for correction adjustment consists of eccentric-acting lever mechanisms (24, 25) which are connected to the stub shafts (4, 5, 9, 10, 14, 15) of the rollers. 16. The printing unit as claimed in any one of the preceding claims, wherein the longitudinal axes of the rollers (3, 8, 13) and said contact points are essentially in the same plane.

Inventors: STENQVIST JAN, STENQVIST, JAN
Applicants: STENQVIST JAN, STENQVIST, JAN
Application year: 1997
Main classification: B41F5
IPC codes: B41F5, B41F13