Abstract
The invention relates to a laser based printing apparatus (100) using laser light sources (111, 112, 113, 402, 404, 406, 604, 606, 808, 810) for supplying energy to a target object (120) to form an image. The printing apparatus (100) comprises a laser light source arrangement (110, 400, 600) comprising a plurality of laser light sources (111, 112, 113, 402, 404, 406, 604, 606, 808, 810) arranged such that laser beams (114, 410, 805, 806) of the laser light sources (111, 112, 113, 402, 404, 406, 604, 606, 808, 810) intersect a surface (121) of a target object (120) at different target points (123, 24, 125, 412, 414, 416, 616, 610, 802) along a moving direction (122), a transport mechanism (130) for moving the target object (120) and the laser light sources (111, 12, 113, 402, 404, 406, 604, 606, 808, 810) relatively to each other in the moving 10 direction (122) and a controlling arrangement (140), which is realized to control the laser light sources (111, 112, 113, 402, 404, 406, 604, 606, 808, 810) and/or the transport mechanism (130) based on image data (150) in such a way, that the energy level of a target point (123, 124, 125, 412, 414, 416, 616, 610, 802) is stepwise increased by irradiation of at least two different laser light sources along the moving direction (122). The invention also describes a method for controlling such a laser based printing apparatus (100).
Claims
1. A printing apparatus using laser light sources for supplying energy to a target object to form an image, comprising a laser light source arrangement comprising a plurality of laser light sources arranged such that laser beams of the laser light sources intersect a surface of a target object at different target points along a moving direction, a transport mechanism for moving at least one of the target object and the laser light sources relative to each other in the moving direction, wherein with each movement of the at least one of the laser light sources and the target object a selected one of the different target point is irradiated by at least one of the plurality of laser light sources, wherein multiple target points can be printed simultaneously, and a controlling arrangement configured to: control the plurality of laser light sources based on data associated with the image wherein an energy level at the selected target point is stepwise increased by irradiation of at least two different laser light sources along the moving direction, wherein the laser light sources are operated at a defined power operating point dependent upon a texture of the target object.
2. The printing apparatus according to claim 1, wherein the controlling arrangement wherein controlling of the laser light sources is synchronised with the movement of the target object.
3. The printing apparatus according to claim 1, wherein the controlling arrangement is configured to individually control a subset of the laser light sources based on the data associated with the image.
4. The printing apparatus according to claim 1, wherein the transport mechanism moves the target object and the laser light sources relative to each other wherein each laser light source is irradiating the selected target point only once.
5. The printing apparatus according to claim 1, wherein the power operating point being a fraction of a maximum output power of the laser light sources.
6. The printing apparatus according to claim 1, wherein the laser light source arrangement comprises subsets of laser light sources, wherein corresponding laser beams of the subsets of laser light sources irradiate target points transversely to the moving direction.
7. The printing apparatus according to claim 1, wherein at least one subset of the laser light sources is controlled as a single entity.
8. The printing apparatus according to claim 1, wherein at least a first laser light source continuously irradiates the selected target point and at least a second laser light source is individually controlled based on the image data to irradiate the selected target point.
9. The printing apparatus according to claim 1, wherein a laser beam of at least one continuously irradiating laser light source is optically superimposed with a laser beam of at least one individually controlled laser light source at the selected target point.
10. The printing apparatus according to claim 1, wherein at least one of the laser light sources comprises a VCSEL.
11. A method of controlling a printing apparatus using laser light sources for supplying energy to a target object to form an image, comprising moving at least one of the target object and the laser light sources relative to each other wherein laser beams of the laser light sources intersect a surface of the target object at different target points along a moving direction, wherein with each movement of at least one of the laser light sources and the target object more than one target point is irradiated at a same time such that multiple printing image points can be printed simultaneously, regulating an irradiation intensity of a selected target point in accordance with the motion of at least one of the target object and the laser light sources, wherein an energy level at the selected target point is stepwise increased by irradiation of at least two different laser light sources along the moving direction based on data associated with the image, wherein the laser light sources are operated at a defined power operating point dependent upon a texture of the target object.
12. The method of controlling a printing apparatus according to claim 11, wherein at least a first laser light source is continuously irradiating the target object and at least a second laser light source is individually controlled based on the image data.
13. The method of controlling a printing apparatus according to claim 11, wherein a heat load at the selected target point is distributed between subsets of individually controllable laser light sources according to defined load distribution rules.
14. The method of controlling a printing apparatus according to claim 11, wherein missing output power of failing one of the laser light sources is compensated by other laser light sources, which are irradiating the same selected target point at an increased output power according to defined compensation rules.
15. The method of controlling a printing apparatus according claim 11, wherein at least one of a power level and a pulse width of individually controllable laser light sources are controlled individually according to defined image quality rules.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a schematic representation of a prior art solution with optical superposition only;
(2) FIG. 2 schematically shows an embodiment of a printing apparatus according to the invention;
(3) FIG. 3 shows an intensity profile generated by the printing apparatus depicted in FIG. 2;
(4) FIG. 4 schematically shows a laser light source arrangement for printing with pre-heating;
(5) FIG. 5 shows an intensity profile generated by the laser light source arrangement depicted in FIG. 4;
(6) FIG. 6 schematically shows an alternative laser light source arrangement for printing with pre-heating;
(7) FIG. 7 shows an intensity profile generated by the laser light source arrangement depicted in FIG. 6;
(8) FIG. 8 schematically shows an alternative laser light source arrangement with optical superposition and pre-heating;
(9) FIGS. 9a and 9b show two alternative intensity profiles generated by a row of laser light source arrangements as depicted in FIG. 8;
(10) In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.
DETAILED DESCRIPTION OF THE EMBODIMENTS
(11) For better understanding of the spatial orientation in the Figures, these include a miniature Cartesian coordinate system at the bottom right.
(12) FIG. 1 is a schematic representation of a prior art solution with optical superposition only. Three laser light sources 300 are arranged such that their laser beams 305, 306 are superimposing at one target point 302 on a surface 121 of a target object 120. Thus the power density at that target point 302 can be approximately three times as high as the power density of each single laser beam. This might help to overcome the shortcomings of laser light sources with low power density like VCSELs. But this approach requires a specific geometrical arrangement of the laser light sources as shown in FIG. 1 and/or the use of additional lenses, which implicates a significantly more complex and therefore less cost-effective system architecture. Furthermore it becomes clear from FIG. 1 that geometrical restrictions limit the number of lasers beams, which can be superimposed. Also the general limitation in terms of solid angles and Etendue is well known. In addition lasers beams coming from the sides 305 have non-perpendicular incidence and therefore can be absorbed differently and can show a distorted illumination pattern.
(13) FIG. 2 schematically shows an embodiment of a printing apparatus 100 according to the invention. Depicted is direct printing, i.e. printing onto the final printing medium. The printing apparatus 100 comprises a laser light source arrangement 110, a transport mechanism 130 and a controlling arrangement 140 electrically connected to the laser light source arrangement 110 and the transport mechanism 130. The transport mechanism 130 moves a target object 120 in a moving direction 122 to a proper position for irradiation by the laser light sources 111, 112, 113. The motion mechanics of the transport mechanism 130 is realized in such a way, that precision and accuracy of the movement are adequate for the desired printing resolution and image quality. Here the target object 120 is also the final printing medium, i.e. a plane paper with a special surface 121 suitable for laser light printing. The transport mechanism 130, here only depicted schematically, can be realized for example by means of a transfer roller.
(14) The laser light source arrangement 110 comprises three subsets of multiple laser light sources in the form of rows arranged in x-direction. Thereby, three laser light sources, one of each row, form a laser light source column parallel to the moving direction 122. One laser light source column 111, 112, 113 is explicitly depicted in FIG. 2. The remaining laser light source columns of the arrangement, not explicitly shown in FIG. 2, are working according to the same principle. To avoid gaps in the optical power output in x-direction, the laser light sources may be mounted in close proximity. Here, the laser light sources are cost-effective and simply controllable semiconductor laser diodes, namely Vertical Cavity Surface Emitting Lasers VCSELs, but other kinds of laser light sources may be applied as well. Each row of laser light sources may be constructed as a sub-module with an independent cabling in such a way, that each sub-module can be exchanged easily in order to simplify maintenance and repair. Also neighboring laser light rows may be positioned close together, for example on a printed circuit board, building a laser light source module. Neighbouring laser rows may also be build monolithically on one and the same semiconductor chip.
(15) The laser beams 114 emitted by the laser light sources 111, 112, 113 are focused onto to the surface 121 of the target object 120 by means of microlenses 115. The output of a typical semiconductor laser like a VCSEL, due to its small diameter, diverges almost as soon as it leaves the aperture, at an angle of anything up to 50. However, such a divergent beam can be transformed into a focussed beam by means of a lens. Dependent on the printing application e.g. printing on packages, offset plate writing or laser sintering, the laser light sources 111, 112, 113 are irradiating different kinds of target surfaces. Thereby different physical effects are produced on each kind of target surface, e.g. change of the electrical property or melting of small particles of powdered material like plastic, metal, ceramic or glass. Therefore the laser light sources are mounted according to their physical properties in a proper position to the target surface 121 such that effective irradiation of the target object with adequate resolution can be assured.
(16) The controlling arrangement 140 comprises an image data interface 141, an image data converter 143 and a power control module 142. The power control module 142 controls the power supply 160 of the laser light sources. The power supply supplies electrical or other types of energy to the laser light sources. In FIG. 2 the power supply is shown as one module, but in reality there can be different power supplies for each individually controlled laser light source. Groups of continuously irradiating laser light sources, which require the same power can share a single power supply. It may be advantageous that the power control module provides power regulation within a range from zero to maximum power. But in order to keep the system simple binary on-off regulation can be considered as well. The controlling arrangement 140 controls the transport mechanism 130 to move the target object 120 in moving direction 122. FIG. 2 depicts one target point 123, 124, 125 at three different stages during the printing process. Thereby the target point 123, 124, 125 passes the focus of the laser beam 114 of the three affected laser light sources 111, 112, 113 one after the other. Here, the target point 123, 124, 125 is also the image point, since printing onto the final printing medium is depicted. As soon as the target point passes an affected laser light source, based on image data 150 the power control module 142 drives the power supply (160) of that laser light source to supply optical power to that target point according to a defined control algorithm. The first laser light source 111 of the laser light source column irradiates the target point first, the second laser light source 112 irradiates the target point second and the third laser light source 113 irradiates the target point last. This way the energy level of the target point is increased within three steps to a desired level adequate for printing the image. The control algorithm can be stored in the controlling arrangement 140.
(17) The controlling arrangement 140 of the printing apparatus 100 gets image data 150 via the image data interface 141 encoded in one or any number of special description languages or formats, e.g. CAD files, Adobe PostScript, text-only data or bitmaps. The image data converter 143 transforms the image data 150 into an internal printing format suitable for the controlling arrangement to control the laser light sources adequately. Alternatively the transforming may be done prior to the printing process by some external background system; in other words, the controlling arrangement can also receive image data already in internal printing format without using the image data converter 143 at all.
(18) FIG. 3 shows an example of an intensity profile 200 generated by the laser light source arrangement 110 of the printing apparatus 100 depicted in FIG. 2 during the printing process. It illustrates how the controlling arrangement 140 via the power control module 142 controls the laser light sources to irradiate the target surface 121 based on the image data 150. The intensity profile comprises three bars of black and white areas 202 in x-direction relating to the three rows of laser light sources 111, 112, 113 of the laser light source arrangement 110. The white areas 205 show where laser light sources of the laser light source arrangement are not supplying any optical output power onto the target surface 121 at that moment. The black areas show where laser light sources of the laser light source arrangement 110 is supplying full optical output power onto the target surface 121 at that moment. It can be seen from the intensity profile 200 that in this embodiment all rows of the laser light source arrangement 110 comprise individually controlled laser light sources 111, 112, 113. Thus the final energy level of the printed image line is determined by the total amount of the optical output power of all of the three rows of laser light sources 111, 112, 113 according to their depicted intensity profiles.
(19) FIG. 4 schematically shows a laser light source arrangement 400 of an embodiment of a printing apparatus according to FIG. 2 for printing with pre-heating and FIG. 5 shows an exemplary intensity profile 500 generated by that laser light source arrangement 400. The laser light source arrangement 400 comprises three subsets of multiple laser light sources in the form of rows 401, 403, 405 arranged in x-direction. Three laser light sources 402, 404, 406, one of each row, form a laser light source column 503 parallel to the moving direction 122. The remaining laser light source columns, not explicitly shown in FIG. 4, are working according to the same principle. The last laser light source 406 of the laser light source column 503 is individually controllable according to the image data 150, i.e. it is a printing laser light source. The first 402 and second 404 laser light sources are pre-heating the surface 121 of the target object 120. The rows of pre-heating laser light sources 402, 404 are controlled as one single entity or as separate lines, since they act the same way, i.e. they are providing the same output power at the same time, thus simplifying the controlling and the system architecture. During the printing process the target object is moved in y-direction 122 and each target point 412, 414, 416 is passing the focus of each laser beam 410 of the three laser light sources 402, 404, 406 one after the other. FIG. 4 depicts one target point 412, 414, 416 at three different stages during the printing process. Thereby the first laser light source 402 is taking on the first step of pre-heating the target point 412, 414, 416 and the second laser light source 404 is taking on the second step of pre-heating the target point 412, 414, 416. Finally the last laser light source 406 is printing the image point, i.e. it irradiates the target point 412, 414, 416 across the energy threshold to the final energy level based on the image data 150. Thus it is the row 405 of printing laser light sources 406, which determines the final target image. The pre-heating is carried out such that the laser light source 404 doing the second step of pre-heating is irradiating the target point 412, 414, 416 again in time before cooling and thermal diffusion of the target surface 121 decreases the energy level of the target point 412, 414, 416 significantly.
(20) The intensity profile 500 shown in FIG. 5 is represented the same way as in FIG. 3. The target object 120 is moved in y-direction. In comparison to the intensity profile 200 depicted in FIG. 3 in FIG. 5 the intensity profile 500 shows two completely black bars 502, representing the two rows 401, 403 of pre-heating laser light sources 402, 404 of the laser light source arrangement 400 in FIG. 4. Thus the final energy level of the printed image line is determined by the total amount of the optical output power of the two rows 401, 403 of pre-heating laser light sources 402, 404 and the row 405 of printing laser light sources 406 according to their depicted intensity profiles.
(21) FIG. 6 schematically shows an alternative embodiment to the laser light source arrangement 400 depicted in FIG. 4 and FIG. 7 shows an exemplary intensity profile 700 generated by that laser light source arrangement 600. Compared to the laser light source arrangement 400 in FIG. 4, this laser light source arrangement 600 comprises one row 601 of larger area pre-heating laser light sources 604 instead of two rows 401, 403 of smaller pre-heating laser light sources 402, 404. Larger area laser light sources may advantageously replace multiple smaller laser light sources when it comes to pre-heating. Pre-heating is about increasing the energy level of an area 610 of the target surface 121 rather than to irradiate a target point 612. Using larger area laser light sources 604 for pre-heating may simplify the system architecture and therefore be more cost-effective, since less laser light sources may be needed for each laser light source arrangement 600 altogether. Analogous to the laser light source arrangement 400 depicted in FIG. 4 the last laser light source 606 in y-direction is a printing laser light source, i.e. it irradiates a target point 616 across the energy threshold according to the image data 150.
(22) The intensity profile 700 shown in FIG. 7 is represented the same way as in FIG. 3. The target object 120 is moved in y-direction. In comparison to the intensity profile 500 depicted in FIG. 5 in FIG. 7 the intensity profile 700 shows one broader completely black bar 702 instead of the two narrow ones 502 depicted in FIG. 5. The broad black bar 702 is representing the row 601 of pre-heating larger area laser light sources 604 of the laser light source arrangement 600 in FIG. 6. Thus according to this intensity profile 700 the laser light source arrangement 600 is pre-heating one broad area for further printing and prints one line of image data 150 onto the target surface.
(23) FIG. 8 schematically shows a sub-module of laser light sources 800 with optical superposition and offset-heating, i.e. basic heating independent from image data 150. The sub-module may replace single printing laser light sources within the laser light source arrangements 110, 400, 600 of FIG. 1, FIG. 4 or FIG. 6. Instead of one laser light source of a laser light source row, three laser light sources 808, 810or three rows of such light sources 808, 810are arranged in a sub-module 800 such that their laser beams 805, 806 are superimposing at one target point 802 on a surface 121 of a target object 120. One central laser light source 808 irradiating the target surface 121 perpendicularly is used as the printing laser light source. The two tilted laser light sources 810 arranged on both sides of the central laser light source 808, are simultaneously offset-heating the target surface 121. Since the two tilted laser light sources 810 are only offset-heating and not printing, the problem of producing a distorted illumination pattern according to a non-perpendicular incidence angle as discussed in FIG. 1 is not relevant here.
(24) FIG. 9a and FIG. 9b show two exemplary intensity profiles 901, 902 generated during printing with pre-heating by a row of laser light sub-modules 800 as depicted in FIG. 8, which is extending in x-direction. The intensity profiles 900, 910 are represented the same way as in FIG. 2. The intensity profile of FIG. 9a is generated by a row of laser light sub-modules 800 according to FIG. 8 with tilted offset-heating laser light sources 810. Thereby the controlling arrangement 140 is switching on all tilted offset-heating laser light sources 810 of the row. Thus areas of the target surface 121 though not irradiated by printing laser light sources are offset-heated nevertheless. Accordingly the relating intensity profile in FIG. 9a shows also grey areas 906, which illustrate that just offset-heating below the energy threshold takes place without final printing. This may have advantages in simplicity of the system architecture and therefore costs.
(25) Alternatively FIG. 9b illustrates an intensity profile generated by a row of laser light sub-modules 800 with two rows of tilted individually controlled laser light sources, instead of the two rows of tilted offset-heating laser light sources 810 depicted in FIG. 8. Thereby the controlling arrangement 140 is addressing only such tilted laser light sources that support printing laser light sources 808 irradiating a target point. Thus areas of the target surface 121 not irradiated by printing laser light sources 808 are not offset-heated. This can be derived from the intensity profile in FIG. 9b, which shows either white areas 907 without activity or black areas 908 with full optical power output of all three laser light sources. This approach is more energy efficient, because only areas are irradiated where needed.
(26) For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and use of the word comprising does not exclude other steps or elements. A unit or module can comprise a plurality of units or modules, respectively. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
(27) The control of the printing apparatus in accordance with the method of controlling the printing apparatus can be implemented as program code means of a computer program and/or as dedicated hardware.
(28) A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.
(29) Any reference signs in the claims should not be construed as limiting the scope.
