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(11) | EP 2 085 223 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 153(4) EPC |
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| (54) | METHOD FOR POSITIONAL ADJUSTMENT OF PRINTER BODIES IN FLEXOGRAPHIC PRINTING MACHINES |
| (57) The invention relates to a method for positional adjustment of printing bodies in
flexographic printing machines comprising: a) moving a first printing roller (5), linearly, via guide arrangements (17), towards the support drum (1) by means of a linear motor (M1); b) detecting that a point of contact between said first printing roller (5), or a printing plate secured around it, and the sheet material (2) supported on the support drum (1) has been reached; c) rotating the support drum (1) and allowing the rotation of the first printing roller (5) moved by the support drum (1) by friction, through the sheet material (2), or rotating both the support drum (1) and the first printing roller (5) in a synchronized manner; and d) detecting the linear towards/away positions on said guide arrangements (17) of the first printing roller (5). |
Field of the Art
[0001] The present invention generally relates to a method for positional adjustment of printing bodies in flexographic printing machines, applicable to flexographic printing machines with a series of linear motors for moving each of the rollers of the printing units, and particularly to a method of reading the embossment of printing plates assembled on printing rollers.
Prior State of the Art
[0002] Flexographic printing machines using linear motors for moving the different rollers forming the printing units thereof to the printing position are known.
[0003] Said machines have positioning systems, for the purpose of specifying as much as possible the printing position to be taken by the rollers in order to ensure sufficient pressure to print but not causing damage of the printing plate by pressing excessively against the support drum.
[0004] Most of said positioning systems require a visual evaluation by an operator in the printing job performed, although there are also proposals which replace the mentioned manual evaluation with artificial viewing systems.
[0005] In addition, due to the different types and numbers of printing plates to be used by a flexographic machine to perform different printing jobs, it is desirable to know the development and arrangement of each of them with respect to the printing plates carrier roller, or printing roller, carrying the printing plate or plates, thus knowing the outer embossment of said roller, for several purposes such as improving the precision of the mentioned positioning, or for supplying power to the linear motors in a more controlled and precise manner, etc.
[0006] Proposals relating to performing the mentioned positional adjustment by means of detecting different linear towards/away positions taken by a printing roller with respect to the support drum when contact with one or the other area of a printing plate, or directly with the bare surface of the printing roller, occurs, are not known.
[0007] Proposals relating to ascertaining the mentioned development and arrangement of the printing plates with respect to the printing rollers to know their outer embossments are not known either.
Description of the Invention
[0008] It is necessary to offer an alternative to the state of the art by means of providing a method the application of which allows carrying out the mentioned positional adjustment, as well as the mentioned ascertainment of the development and arrangement of the printing plates with respect to the printing rollers.
[0009] To that end the present invention provides a method for positional adjustment of printing bodies in flexographic printing machines with a rotating support drum on which there is supported a sheet material to be printed, and a series of printing rollers each of which carrying one or more printing plates, and each associated to a respective inking roller, belonging to respective printing units, arranged around said support drum and spaced out along its perimeter, said printing rollers and inking rollers being coupled to respective guide arrangements, through mobile supports which can be operated by respective linear motors for moving each of said rollers, linearly and independently, in a towards/away direction with respect to said support drum, said method comprising, starting from initial positions in which there is no contact between the printing rollers and the support drum, nor between the inking rollers and the printing rollers, sequentially performing the following steps:
- a) moving at least a first of said printing rollers through said mobile supports, linearly, through said guide arrangements, towards the support drum by means of a corresponding linear motor;
- b) detecting that a point of contact between said first printing roller, or a printing plate secured around it, and the sheet material supported on the support drum has been reached;
- c) rotating the support drum and allowing the rotation of the first printing roller moved by the support drum, by friction, through the sheet material, or rotating both the support drum and the first printing roller in a synchronized manner; and
- d) detecting the linear towards/away positions on said guide arrangements of the first printing roller.
[0010] In a preferred embodiment, the method comprises carrying out said step a) by means of applying a corresponding power supply to said linear motor and maintaining, at least during said steps c) and d), the power supply of the linear motor with sufficient minimum intensity to overcome the frictional resistance on the guide arrangements and in a direction corresponding to the towards movement, but allowing the towards-away movement of the first printing roller with respect to the support drum without damaging the printing plate or printing plates assembled on the first printing roller.
[0011] Said away position occurs because the mobile support of the first printing roller is allowed to move away backwards in the event of collision of the printing plate with the support drum or, where appropriate, with the sheet material carried by the support drum, after a position of the first printing roller closer to the support drum, generally contacting with the bare surface of the first printing roller.
[0012] For the purpose of carrying out the mentioned ascertainment of the arrangement and development of the printing plate, and therefore of the embossment or projecting surface of the printing plate with respect to the outer surface of the printing roller, the method comprises carrying out said step d) to perform said detections of the linear towards/away positions of the first printing roller in correspondence with the angular positions thereof (detected by means of corresponding angular position detectors), thus obtaining a substantial representation of the embossment of at least said printing plate assembled on the first printing roller with respect to the angular positions thereof, and hence of the outer embossment of the first printing roller if it rotates a complete turn in step c).
[0013] Although the previous steps have been described for a first printing roller, the method can likewise be applied to the remaining printing rollers.
[0014] Due to the mentioned possibility of the backward movement of the first printing roller, and also of the remaining printing rollers, through the mentioned mobile supports, with respect to the guide arrangements, at least one linear away position is detected in said step d) whenever a printing plate carried by the printing roller contacts with the support drum, and at least one towards position is detected whenever said contact of the printing plate with the support drum does not exist, at which time it is generally the bare outer surface of the printing roller which contacts with the support drum, although for a case in which the printing plate extends over virtually the entire circumferential outline of the printing roller, the outer surface of the printing roller may not contact with the support drum in the towards position.
[0015] In addition to said towards and away positions, the method comprises detecting a series of intermediate towards/away positions for different areas of contact of the printing plate with the sheet material for the case of a printing plate with an irregular embossment, it being possible to ascertain said irregular embossment by means of the relationship of said detected positions with the angular positions of the printing roller on which the printing plate is assembled.
Brief Description of the Drawings
[0016] The previous and other features and advantages will be more fully understood from the following detailed description of several embodiments with reference to the attached drawings, which must be taken as being illustrative and non-limiting, in which:
Figure 1 is a schematic elevational depiction of part of a flexographic machine with four printing units, in which some of the most relevant elements to be taken into account by the method proposed by the present invention for one embodiment can be seen,
Figure 2a is a schematic depiction of part of the machine of Figure 1 for three different positions of one of the printing rollers with respect to the support drum, for one embodiment,
Figure 2b is a representative graph of the positions of the printing roller illustrated in Figure 2a,
Figure 3a is a schematic perspective depiction of part of the machine of Figure 1, including one of the printing rollers illustrated therein and part of the support drum, for an embodiment for which said printing roller carries two printing plates, one in each one of two areas spaced out longitudinally,
Figure 3b shows two representative graphs of the positions of the printing roller for each of the two areas of the embodiment of Figure 3a,
Figure 4a is a schematic perspective depiction of part of the machine of Figure 1, including one of the printing rollers therein illustrated and part of the support drum, for one embodiment for which said printing roller carries a single printing plate in an area close to an end, and
Figure 4b shows two representative graphs of the positions of two end areas of the printing roller for the embodiment of Figure 4a.
Detailed Description of Specific Embodiments
[0017] The present invention relates to a method for positional adjustment of the printing bodies in flexographic printing machines such as that illustrated in Figure 1, with a rotating support drum 1 on which there is supported a sheet material 2 to be printed, and a series of printing rollers 5-8 each of which carrying one or more printing plates Cl1 (see Figures 2a, 3a and 4a), and each associated to a respective inking roller 9-12, belonging to respective printing units, arranged around said support drum 1 and spaced out along its perimeter, said printing rollers 5-8 and inking rollers 9-12 being coupled to respective guide arrangements 17, through mobile supports 18a, 18b which can be operated by respective linear motors M1-M8, at least one per roller, for moving each of said rollers 5-12, linearly and independently, in a towards/away direction with respect to said support drum 1.
[0018] The method comprises, starting from initial positions in which there is no contact between the printing rollers 5-8 and the support drum 1, nor between the inking rollers 9-12 and the printing rollers 5-8, sequentially performing the following steps:
- a) moving a first 5 of said printing rollers 5-8, linearly, through said guide arrangements 17, towards the support drum 1;
- b) detecting that a point of contact between said first printing roller 5, or a printing plate Cl1 secured around it, and the sheet material 2 supported on the support drum 1 has been reached;
- c) rotating the support drum 1 and allowing the rotation of the first printing roller 5 moved by the support drum 1, by friction, through the sheet material 2, or rotating both the support drum 1 and the first printing roller 5 in a simultaneous and synchronized manner; and
- d) detecting the linear towards/away positions on said guide arrangements 17 of the first printing roller 5.
[0020] As mentioned above, the method comprises performing step a) by means of a corresponding power supply of the linear motor M1, and maintaining the power supply with sufficient minimum intensity to cause said movement, overcoming the resistance of the guide arrangements 17 (see Figure 1), but allowing a backward away movement in the event of a collision with the support drum 1.
[0021] Figure 2a shows the first printing roller 5 in three different positions with respect to the support drum 1:
- a first position, or position A, in which the printing plate Cl1 is located in an immobile position of contact with the support drum 1 (or with the sheet material 2 if this were the case), also immobile,
- a second position, or position B, in which both the support drum 1 and the first printing roller 5 are rotating, according to said step c), and in which the first printing roller 5 has moved linearly towards the former until its bare outer surface has contacted with the support drum 1, and
- a third position, or position C, in which both the support drum 1 and the first printing roller 5 continue to rotate, and in which the first printing roller 5 has moved linearly away due to the thrust received upon contacting the printing plate Cl1 with the support drum 1.
[0022] Figure 2b shows by means of a graph the different linear positions, in this case in correspondence with the angular positions, of the first printing roller 5 along a complete turn, including said positions A, B and C. As can be observed, the section going from B to C is different from the rest of the graph; this is because in said section what contacts with the support drum 1 is the bare surface of the printing roller 5, whereas in the rest of the graph the contact occurs through the printing plate Cl1.
[0023] For one embodiment the method comprises, after said step d), performing the following steps:
e) analyzing the variations of the linear positions detected in step d) which for the embodiment shown in Figures 2a and 2b, are caused by the different linear positions taken by the first printing roller 5 when the printing plate Cl1 contacts with the sheet material 2 supported on the support drum 1 and when the bare outer surface of the printing roller 5 does so directly, and
f) considering, out of the positions detected in step d), the linear position of the first printing roller 5 farthest away from the support drum 1 as substantially the position to be reached by the first printing roller 5 in future operations of the machine.
[0024] In other words, according to the embodiment shown in Figures 2a and 2b, any of the positions included in sections A-B and C-A corresponding to the away position, are those considered in step f) as the position to be reached by the first printing roller 5.
[0025] To carry out said step f), i.e., to ascertain the position to be reached by the first printing roller 5, it is not necessary to detect angular positions nor is it necessary therefore to relate them with the linear positions (unlike the embodiment shown in Figure 2b), since it is only required to detect the linear position taken by the first printing roller 5 when the printing plate contacts with the sheet material 2.
[0026] For one embodiment, the method comprises recording said positions detected in step d) prior to said analysis of the variations experienced by them, or after such analysis.
[0027] The mentioned detection of linear positions of step d) is performed through the reading of one or more linear position detectors (not shown) associated to each roller, the levels of the graph shown in Figure 2b (as well as those shown in Figures 3b and 4b) corresponding to the values of, for example, voltage supplied by one of said linear position detectors associated to the first printing roller 5, which will have one or another value depending on the thickness of printing plate Cl1, which causes a movement away from the support drum 1 to a greater or lesser extent.
[0028] The angular positions are also detected by means of one or more corresponding angular position detectors associated to each roller, showing the readings made with one of said angular position detectors associated to the first printing roller 5, represented in degrees in Figures 2b, 3b and 4b, corresponding to certain voltage values supplied by the detector.
[0029] For one embodiment the method comprises using two linear motors per roller, one at each end, whereby it is possible to move each end of each roller independently by means of corresponding independent regulations of each of said two motors or, for another embodiment making the two linear motors operate in a synchronized manner.
[0030] The method proposed by the invention is applied to the positional adjustment of a printing roller carrying a printing plate with at least two differentiated areas or carrying at least two printing plates Cl1, Cl2 arranged in two differentiated areas, spaced out at least longitudinally, as occurs in the first printing roller 5 shown in Figure 3a.
[0031] For the case mentioned in which the first printing roller 5 has two linear motors, one per end, the method comprises performing steps a), b), c) and d) simultaneously or sequentially at the two ends of the first printing roller 5 through the two corresponding linear motors, and
e) analyzing the variations of the linear positions detected in the two ends of the first printing roller 5 in step d),
said step f) comprising considering, out of the positions detected in step d), the linear positions of the two ends of the first printing roller 5 farthest away from the support drum 1 as substantially the positions to be reached by the first printing roller 5 in future operations of the machine.[0032] For the embodiment shown in Figures 3a and 3c, the first printing roller 5 carries two printing plates Cl1, Cl2, each in an area close to one of the two ends movable by two respective linear motors, and the graphs shown in Figure 3b have been obtained by means of, as mentioned, performing steps a) to d) simultaneously or sequentially at the two ends of the first printing roller 5 through the two mentioned corresponding linear motors, having carried out step d) to perform the detections of the linear towards/away positions of each of the two ends of the first printing roller 5 in correspondence with the angular positions thereof.
[0033] The upper graph of Figure 3b is representative of the movement indicated as X1 in Figure 3a when, respectively, a first printing plate Cl1 located in a first of said two areas close to the ends contacts with the sheet material 2 supported on the support drum 1 and when the bare outer surface of the printing roller 5 comprised by said first area does so directly, and the lower graph of Figure 3b is representative of the movement indicated as X2 in Figure 3a, when a second printing plate Cl2 located in a second of said two areas contacts with the sheet material 2 supported on the support drum 1 and when the bare outer surface of the printing roller 5 comprised by said second area does so directly.
[0034] Both graphs of Figure 3b represent the positions of the first printing roller 5 farthest away from the support drum 1, with a level greater than that of the towards positions. Also, the same references X1, X2 have been used to indicate both the directions of the linear movements of both end areas of the first printing roller 5, and to name the signal resulting from the readings taken by means of respective linear position detectors, each of them arranged in each of the two areas close to the ends of the first printing roller 5.
[0035] For the embodiment shown in Figures 4a and 4b, steps a) to d) have also been performed at the two ends of the first printing roller 5 through the two mentioned corresponding linear motors, also having carried out step d) to perform the detections of the linear towards/away positions of each of the two ends of the first printing roller 5 in correspondence with the angular positions thereof.
[0036] Since the first roller of Figure 4a carries only one printing plate Cl1, arranged in an area close to one of the two ends, the upper graph of Figure 4b only shows a variation of linear positions, i.e., for X1, whereas in the lower part, i.e., X2, there is no positional discrepancy, simply showing the position in which the bare surface of the area close to the end of the first roller not carrying the printing plate contacts with the sheet material 2 supported on the support drum 1. In this case and for the purpose of arranging the first printing roller 5 parallel with the support drum 2 so that the printing pressure is homogenous, the proposed method comprises, for the present embodiment, performing an alternative step to the mentioned step f), comprising considering, out of the positions detected in step d), only the linear position farthest away from the support drum 1 of the end of the first printing roller 5 where the printing plate Cl1 is close to, as substantially the position to be reached by both ends of the first printing roller 5 in future operations of the machine.
[0037] Although the illustrated embodiments only refer to the application of the method on a printing roller, specifically the first printing roller 5, the method proposed by the present invention can also be applied to the inking rollers 9-12, to which end it comprises, before or after said steps a) to f), sequentially performing the following steps:
g) moving a first 9 of said inking rollers 9-12, linearly, through said guide arrangements 17 (see Figure 1), towards the first associated printing roller 5,
h) detecting that a point of contact between said first inking roller 9 and the first printing roller 5, or a printing plate Cl1 secured around it, has been reached,
i) rotating at least the first printing roller 5 or the first inking roller 9, one causing the rotation of the other due to the contact between them, or rotating the two of them 5, 9 in a synchronized manner;
j) detecting by means of one or more linear position detectors, the relative linear towards/away positions between the printing roller 5 and the first inking roller 9, and analyzing the variations of the linear positions detected and caused by the different linear positions taken by the first inking roller 9 when it contacts with said printing plate Cl1 of the first printing roller 5 and when it does so directly with the bare outer surface of the first printing roller 5, and
k) considering, out of the positions detected in step d), the linear position of the first inking roller 9 farthest away from the first printing roller 5 as substantially the position to be reached by the first inking roller 9 in future operations of the machine.
[0038] The proposed method comprises carrying out said movement of said step g) by means of the power supply of a corresponding linear motor M5 associated to said first inking roller 9, and maintaining, at least during said steps i) and j), the power supply of said linear motor M5 with sufficient minimum intensity to overcome the frictional resistance on the guide arrangements 17, allowing the towards-away movement of the first inking roller 9 with respect to the printing roller 5.
[0039] For one embodiment, the method comprises carrying out said step j) to perform said detections of the relative linear towards/away positions between the first two rollers 5, 9 in correspondence with the angular positions of the first printing roller 5, to obtain a substantial representation of the embossment of at least said printing plate Cl1 assembled on the first printing roller 5 with respect to the angular positions thereof.
[0040] With respect to said detection of said contact of said step b) and/or said detection of said contact of said step h), they are carried out automatically, in different ways depending on the embodiment.
[0041] For one embodiment, said automatic detection of said step b) and/or of said step h) comprises analyzing the variations in consumption of said linear motor or motors M1, M5.
[0042] For another alternative embodiment, said automatic detection of said step b) and/or of said step h) comprises maintaining the linear motor M1, M5 in current regulation, with a minimum intensity to overcome the resistance of the guide arrangements 17, and starting an initial movement and detecting the collision by the stop of the movement at constant intensity.
[0043] Though the method has been explained for the first printing roller 5 and for the first inking roller 9, it has been done in such a manner for the purpose of simplifying the explanation, since the method comprises performing all the steps for the remaining printing rollers 6-8 and/or inking rollers 10-12 in the same way as for said first printing roller 5 and/or inking roller 9.
[0044] For one embodiment, the method comprises performing all the steps for all the printing rollers 5-8 simultaneously, and for another embodiment performing all the steps for all the inking rollers 9-12 also simultaneously.
[0045] The proposed method comprises using the results of said step d) or of step j) to calculate the development of said printing plate or plates Cl1, Cl2 for different purposes, one of which consists of consulting said calculated printing plate development in a data structure relating known developments of printing plates with other features or formats associated to said known developments, such as the thickness of the adhesive plus that of the printing plate, the radius of the liners, etc.
[0046] Knowing the development of the printing plate according to the proposed method offers several advantages, such as enabling a more precise control of the linear motors, increasing the power supply voltage only when necessary, i.e., when the printing plate Cl1 contacts with the sheet material 2 wrapped around the support drum 1 and therefore proceeds to print, and maintaining it at a lower level when the part facing the sheet material 2 is the bare outer surface of the printing roller.
a) moving at least a first (5) of said printing rollers (5-8), linearly, through said guide arrangements (17), towards the support drum (1) by means of a corresponding linear motor (M1);
b) detecting that a point of contact between at least said first printing roller (5), or at least one printing plate (Cl1) secured around it, and the sheet material (2) supported on the support drum (1) has been reached;
c) rotating the support drum (1) and allowing the rotation of the first printing roller (5), moved by the support drum (1), by friction, through the sheet material (2), or rotating both the support drum (1) and the first printing roller (5) in a synchronized manner; and
d) detecting the linear towards/away positions on said guide arrangements (17) of at least the first printing roller (5).
e) analyzing the variations of the linear positions detected in step d), and
f) considering, out of the positions detected in step d), the linear position of the first printing roller (5) farthest away from the support drum (1) as substantially the position to be reached by the first printing roller (5) in future operations of the machine.
e) analyzing the variations of the linear positions detected at the two ends of the first printing roller (5) in step d),
said step f) comprising considering, out of the positions detected in step d), the linear positions of the two ends of the first printing roller (5) farthest away from the support drum (1) as substantially the positions to be reached by the first printing roller (5) in future operations of the machine.
g) moving at least a first (9) of said inking rollers (9-12), linearly, through said guide arrangements (17), towards the first associated printing roller (5),
h) detecting that a point of contact between at least said first inking roller (9) and the first printing roller (5), or a printing plate (Cl1) secured around it, has been reached,
i) rotating at least the first printing roller (5) or the first inking roller (9), one causing the rotation of the other due to the contact between them, or rotating the two of them (5, 9) in a synchronized manner;
j) detecting the relative linear towards/away positions between the printing roller (5) and the first inking roller (9), and analyzing the variations of the linear positions detected and caused at least by the different linear positions taken by the first inking roller (9) when it contacts with at least said printing plate (Cl1) of the first printing roller (5) and when it does so directly with the bare outer surface of the printing roller (5), and
k) considering, out of the positions detected in step j), at least the linear position of the first inking roller (9) farthest away from the first printing roller (5) as substantially the relative position to be reached by the first inking roller (9) in future operations of the machine.