Patent Grant
8950326
The present invention relates generally to blank printing plates mounted on cylindrical rollers or mounting tables, and more particularly, is directed to a method and apparatus for laser ablating an image on mounted blank printing plates.
It is known to provide an image on a printing plate, and thereafter, mount the printing plate on a roller for a printing operation. It is also known to mount a blank printing plate on a roller or mounting table for use in a printing apparatus, and thereafter, laser ablate the printing plate to produce an image on the mounted printing plate. The present invention is directed to the latter arrangement in which a blank printing plate is mounted, and then, the image is formed thereon.
It is well-known to use mounted blank printing plates in a printing operation. The printing rollers can include one or more sleeves and/or other layers thereon. The printing plates, after being mounted on the rollers, are etched or engraved in accordance with a desired image in order to effect the printing operation. It is also known to provide such etching or engraving of the image on the printing plate by means of a laser. An example of a system for performing this operation is disclosed, for example, in U.S. Pat. No. 7,284,484, which discloses the laser ablating of a blank printing plate mounted on a printing roller.
When laser ablating an image onto the printing plate, all areas which are not image transfer areas, including edges of the printing plate, are always laser ablated to form recesses or reliefs at which no printing occurs. Thus, the areas of the printing plate outside of the image area are laser ablated to provide recesses or reliefs, which do not affect printing.
However, a problem with this operation is that the laser will oftentimes extend past an edge of the printing plate during the laser ablating operation, and inadvertently and undesirably laser ablate a portion of the roller, the sleeve mounted on the roller or the mounting table, on which the printing plate is mounted. This, however, can damage the roller, the sleeve or the mounting table.
There are several ways to avoid damage to the roller, sleeve or mounting table, including but not limited to, masking the edges of the printing plate with a reflective foil, which reflects the laser and protects the roller, sleeve or mounting table from damage. It is also possible to provide a printing plate which has significantly larger size than the area of print needed, to ensure that the laser starts and stops within the boundaries of the printing plate. However all of these methods can require additional equipment, materials, time and expense, to make them work.
Accordingly, it is an object of the present invention to provide a method and apparatus for laser ablating an image on a blank printing plate mounted on a roller, that overcomes the aforementioned problems.
It is another object of the present invention to provide a method and apparatus for laser ablating an image on a blank printing plate mounted on a roller that precisely ablates a printing plate mounted on a roller or sleeve.
It is still another object of the present invention to provide a method and apparatus for laser ablating an image on a blank printing plate mounted on a roller or sleeve and ablating precisely to the edges of the printing plate, but avoiding ablation past the boundaries of the printing plate.
It is yet another object of the present invention to provide a method and apparatus for laser ablating an image on a blank printing plate mounted on a roller that is easy and economical to use.
In accordance with an aspect of the present invention, a method for laser ablating an image on a mounted blank printing plate, includes the steps of detecting positions of at least one edge of the mounted blank printing plate, and determining positions of all edges of the blank printing plate in accordance with the step of detecting. An image area is determined within boundaries of the blank printing plate, and reliefs are laser ablated on the blank printing plate to create an image. The laser is controlled to prevent any laser ablation outside of boundaries of the edges of the printing plate, based on the step of determining positions of all edges of the printing plate.
The step of detecting positions of at least one edge of the printing plate, uses either electromagnetic radiation or a mechanical device to detect the positions.
In one embodiment, the step of detecting positions of at least one edge of the printing plate, includes the step of detecting the positions of all edges of the printing plate, and the step of determining positions of all edges of the printing plate in accordance with the step of detecting, includes the step of determining the positions of each edge of the printing plate in accordance with the detected position of each respective edge.
In another embodiment, the step of detecting positions of at least one edge of the printing plate, includes the step of detecting the position of less than all edges of the printing plate, and the step of determining positions of all edges of the printing plate in accordance with the step of detecting, includes the steps of determining the positions of each detected edge of the printing plate in accordance with the detected position of each respective edge, and calculating the positions of the remaining non-detected edges from the dimensions and shape of the printing plate and the position of at least one detected edge.
The step of determining an image area within boundaries of the printing plate, includes the step of calculating the size, shape and position of the image area such that the image area falls within the boundaries of the printing plate.
The step of controlling the laser to prevent any laser ablation outside of boundaries of the edges of the printing plate, based on the step of determining positions of all edges of the printing plate, includes the step of controlling imaging of the laser to an area within edges of the printing plate, and/or controlling power of the laser to avoid imaging outside edges of the printing plate.
In accordance with another aspect of the present invention, a method for laser ablating an image on a mounted blank printing plate having an image area, at least one edge and a peripheral tolerance region of a thickness less than the image area at at least one edge of the printing plate, includes the steps of detecting positions of at least one edge of the mounted blank printing plate, and determining positions of all edges of the blank printing plate in accordance with the step of detecting. An image area is determined within boundaries of the blank printing plate, and reliefs are laser ablated on the blank printing plate to create an image. The laser is controlled to stop any laser ablation within boundaries of the peripheral tolerance region.
The peripheral tolerance region includes one of the following: a beveled area, a stepped area, or a curved area.
In accordance with still another aspect of the present invention, apparatus for laser ablating an image on a mounted blank printing plate, includes a detector which detects positions of at least one edge of the mounted blank printing plate, a control device which determines positions of all edges of the blank printing plate in accordance with the step of detecting and which determines an image area within boundaries of the blank printing plate, a laser which laser ablates reliefs on the blank printing plate to create an image, and the control device controls the laser to prevent any laser ablation outside of boundaries of the edges of the printing plate, based on the determined positions of all edges of the printing plate.
The detector uses electromagnetic radiation or a mechanical device to detect the positions.
In one embodiment, the detector detectors the positions of all edges of the printing plate, and the control device determines the positions of each edge of the printing plate in accordance with the detected position of each respective edge.
In another embodiment, the detector detects the positions of less than all edges of the printing plate, and the control device determines the positions of all edges of the printing plate by determining the positions of each detected edge of the printing plate in accordance with the detected position of each respective edge, and calculating the positions of the remaining non-detected edges from the dimensions and shape of the printing plate and the position of at least one detected edge.
The control device determines the image area within boundaries of the printing plate, by calculating the size, shape and position of the image area such that the image area falls within the boundaries of the printing plate.
The control device controls the laser to prevent any laser ablation outside of boundaries of the edges of the printing plate, based on the determination of the positions of all edges of the printing plate, by at least one of controlling imaging of the laser to an area within edges of the printing plate, and controlling power of the laser to avoid imaging outside edges of the printing plate.
In accordance with yet another aspect of the present invention, apparatus for laser ablating an image on a mounted blank printing plate having an image area, at least one edge and a peripheral tolerance region of a thickness less than the image area at at least one edge of the printing plate, includes a detector which detects positions of at least one edge of the mounted blank printing plate, a control device which determines positions of all edges of the blank printing plate in accordance with the step of detecting and which determines an image area within boundaries of the blank printing plate, a laser which laser ablates reliefs on the blank printing plate to create an image, and the control device controls the laser to stop any laser ablation within boundaries of the peripheral tolerance region.
The peripheral tolerance region includes one of the following: a beveled area, a stepped area, or a curved area.
The above and other objects, features and advantages of the invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.
Referring to the drawings in detail, and initially to
Because printing plate 18 according to the present invention will be laser ablated, they are preferably made of materials that permit such laser ablating, including but not limited to any flexible substrate made from a photopolymer, vulcanized rubber, a thermal polymer, or any other suitable material, and including but not limited to the materials discussed in U.S. Pat. Nos. 5,804,353; 6,551,759; 6,551,762; 6,159,659; 6,627,385; 6,776,095; 6,794,115; 6,737,216; 6,178,852; and 6,797,455, the entire disclosures of which are incorporated herein by reference.
An apparatus 8 for laser ablating printing plate 18 to form an image 22 thereon includes a laser 24, such as a CO2 laser, a YAG laser or any other suitable laser, to ablate the outer surface of printing plate 18. Laser 24 is preferably mounted on a movable carriage 26 that can move along the lengthwise direction of printing plate 18 by means of a drive motor 28. Alternatively, as shown by dashed lines in
In order to control laser 24 to correctly ablate printing plate 18, it is necessary to first measure the position of printing plate 18.
In this regard, laser 24′, which is preferably also mounted on carriage 26 and driven by motor 28 to move along the surface of roller 12 as roller 12 is rotated by motor 36, focuses a beam of light 30 that is bounced off the outer surface of printing plate 18, sleeve 16 and/or roller 10, and received by a detector 32, such as an optical detector, while laser 24′ is moved with carriage 26. As an alternative, it is feasible to have scanning laser 24′ supported on a different carriage on the same machine, or even on two different machines. However, in the latter case, a point of reference would have to be established between the two systems.
Alternatively, detector 32 can provide its own source of light against sleeve 16, which is then bounced off the outer surface of printing plate 18, sleeve 16 and/or roller 10 and received by detector 32. For example, detector 32 can include a conventional photodiode which directs light against sleeve 16, and a photodetector which detects the light reflected back therefrom. Generally, any signal waves in the electromagnetic spectrum can be used for such detection operation, which include, without limitation visible light rays, infrared rays, laser light, etc.
A signal corresponding to this detection operation is then provided by detector 32 to a control device 34 which can be a computer programmed to control the ablation and relative movement of laser 24 and printing roller 10. Control device 34 controls drive motor 28 and/or drive motor 28′ to control relative lengthwise movement of printing roller 10 and laser 24′ during the measurement operation, and also controls a separate drive motor 36 to rotate cylindrical roller 12 by small increments. In this manner, the entire surface area where printing plate 18 is mounted, sleeve 16 and/or roller 10, is scanned. Alternatively, as discussed above, laser 24′ can be stationary and carriage 26, drive motor 28 and drive motor 28′ can be eliminated, and in such case, control device 34 would control stationary laser 24′ to scan across printing roller 10 in the lengthwise direction thereof.
From these measurements, the portions of the outer surface of printing plate 18 that need to be ablated in order to create the image area thereon, are determined by control device 34. Laser 24 then ablates those portions of the outer surface of printing plate 18 in accordance therewith. Thus, there is preferably relative longitudinal movement between roller 10 and laser 24, as well as rotation of roller 10 caused by drive motor 36.
In a modification thereof, second scanning laser 24′ can be eliminated and laser 24 can be used for both the measurement and the ablation operation.
As discussed above, when laser ablating an image onto printing plate 18, the edges of printing plate 18 are always laser ablated to form recesses or reliefs 40 at which no printing occurs. Thus, the areas of printing plate 18 outside of the image area are laser ablated to provide recesses or reliefs 40, which do not print.
However, a problem with this operation is that the laser will oftentimes extend past an edge of printing plate 18 during the laser ablating operation, and inadvertently and undesirably laser ablate a portion of roller 10 or sleeve 16 mounted on roller 10, on which printing plate 18 is mounted. This, however, can damage roller 10 or sleeve 16 thereon. This is because there is a sharp edge at the periphery of printing plate 18, that is, an edge which is perpendicular to the upper surface thereof.
With reference to
Generally, while roller 10 is rotated, the laser apparatus positioned thereabove laser ablates printing plate 18 to form recesses or reliefs 40 and 46, and thereby form the image to be printed by raised surfaces 48. The areas 44 of printing plate 18 outside of image area 42 which are laser ablated to provide recesses or reliefs 40, do not print.
However, a problem with this operation is that the laser will oftentimes extend past an edge, for example, edge 18a of printing plate 18 during the laser ablating operation, and inadvertently and undesirably laser ablate a portion of roller 10, or sleeve 16 mounted on roller 10 beneath printing plate 18, which could damage roller 10 or sleeve 16 thereon.
Therefore, in accordance with the present invention, printing plate 18 is first mounted on a cylindrical roller 10 in a general area where the image is to be formed, with printing plate 18 being larger than image area 42. It is verified that plate 12 is in the correct position to receive the entire image area 42 therewithin, that is, image area 42 does not extend outside of the area of plate 18.
Thereafter, at least one edge 18a of printing plate 18 is detected, and preferably all four edges 18a of printing plate 18 are detected. The detection of the edges 18a occurs by a scanning laser, for example, laser 24′, which passes over cylindrical roller 10, scanning and identifying the position of the edges of each printing plate 18 thereon. A digital template of the plate position is created by the scan, thereby setting the outer limits that the laser will engrave to coincide with edges 18a of printing plate 18. Alternatively, a mechanical detector 33, such as a mechanical finger connected to a detector, can be used to detect the edges.
The image area 42 is then ablated by laser 24 within the bounds of printing plate 18. During this process, areas 44 outside of image area 42 are ablated to provide recessed areas or reliefs 40 at which no printing occurs.
By detecting edges 18a of printing plate 18, this ensures that the laser ablating operation, when forming reliefs 40, will not extend to roller 10 and/or carrier sleeve 16, so that roller 10 and/or carrier sleeve 16 thereon will not be damaged.
It will be appreciated that, if the dimensions and shape of printing plate 18 are known, then it may only be necessary to detect one edge 18a. In such case, the positions of the remaining edges 18a can be calculated from the dimensions and shape of printing plate 18 and the position of the one detected edge 18a.
According to an important aspect of the present invention, a peripheral tolerance region 100 is provided just to the outside of edges 18a of printing plate 18, in surrounding relation to a central area 102 with the image formed thereon. As shown in
Preferably, beveled edge 18b has an inclination in the range of 5 degrees to 85 degrees; more preferably in the range of 30 degrees to 60 degrees; and still more preferably, at 45 degrees.
It will be appreciated, however, that other peripheral tolerance regions 100 can be provided. For example, as shown in
As further examples, peripheral tolerance region 100 can be a convex curved region 18d as shown in
The key is that peripheral tolerance region 100 allows for tolerances in the mechanics and in detection.
In accordance with the above, and referring to
Thereafter, image area 42 within boundaries of printing plate 18 is verified in step 108. This is accomplished by calculating the size, shape and position of an image area 42 such that the image area 42 falls within the boundaries of printing plate 18, for example, by control device 34. An image on printing plate 18 which is used for printing an image on a medium, within image area 42 is then ablated with laser 24 in step 110. Before, thereafter or simultaneously with the laser ablation of image area 42, in step 112, all areas 40 outside of image area 42 on printing plate 18 are laser ablated with laser 24 to provide a relief area 40 at which no printing on the medium will occur, based on the step of determining positions of all edges 18a of printing plate 18.
Lastly, in step 114, laser 24 is controlled by control device 34 to prevent any laser ablation outside of boundaries of edges 18a of printing plate 18, based on the step of determining positions of all edges 18a of printing plate 18. This can occur, for example, by repositioning the laser to an area within edges 18a of printing plate 18 and/or reducing or stopping power of the laser outside edges 18a of printing plate 18. This last step will occur simultaneously with the laser ablation of relief area 40.
Having described specific preferred embodiments of the invention with reference to the accompanying drawings, it will be appreciated that the present invention is not limited to those precise embodiments and that various changes and modifications can be effected therein by one of ordinary skill in the art without departing from the scope or spirit of the invention as defined by the appended claims.
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