Compact imaging head and high speed multi-head laser imaging assembly and method

• US 20020101647A1
• Filed: 05/25/2001
• Published: 08/01/2002
• Est. Priority Date: 02/01/2001
• Status: Active Grant

• Current Assignee: Kodak Polychrome Graphics GmbH (Kodak Polychrome Graphics LLC)
• Original Assignee: Kodak Polychrome Graphics Company Limited (Eastman Kodak Company)
• Inventors: Moulin, Michel
• Granted Patent: US 6,643,049 B2
• Time in Patent Office: Days
• US Class Current: 359/298
• CPC Class Codes: B41J 19/20 Positive-feed character-spacing mechanisms controlled by escapements B41J19/52
• CPC Class Codes: B41J 2/465 using masks, e.g. light-switching masks
• CPC Class Codes: B41J 2/47 using the combination of scanning and modulation of light

Abstract

Several optical heads are mounted on a common carriage adapted to scan a photosensitive printing plate. Each head is equipped with a laser source, a modulator and projection optics and can project a segment containing a plurality of pixels. The optical track of beams in each head is folded several times in such a way as to reduce the width of the head as well as its height. When the carriage moves from one edge of the plate to the other edge a swath of pixels is projected. Each head includes means to adjust the width, location, orientation and intensity of the segment it generates. Each head is accurately positioned on the carriage so that at least two abutting swaths are projected during each sweep of the carriage to produce a wider swath.

Claims

1. An imaging assembly comprising:

a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative to a desired image area; and

a plurality of imaging modules coupled to the carriage, wherein each module is adjacent to at least one other module, each module comprises at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, each module is aligned with respect to the other modules such that the plurality of modules imagewise produces laser light which is a summation of each individual light brush produced by each module, and each module comprises a signal receiver which causes a delay in the imagewise production of laser energy from each individual module.

2. The assembly of claim 1, in which the carriage is capable of traversing in a single excursion a distance greater than a desired image area, and the plurality of modules produces a continuous band of laser light which is the summation of each individual light brush produced by each module with each traverse of the carriage across the desired image area.

3. The assembly of claim 1, in which each module is vertically offset from the other modules.

4. The assembly of claim 1, in which the assembly contains four modules.

5. The assembly of claim 1, in which the modulator is a TIR modulator.

6. The assembly of claim 1, in which each module is capable of producing 256 pixels of imagewise laser light.

7. The assembly of claim 1, in which the laser light source comprises a plurality of laser diodes.

15. The imaging assembly of claim 1, in which the laser power of different modules is equalized by a shunt.

19. The assembly of claim 1, in which each module is provided with adjustable locating elements thereby enabling each module to be independently adjusted on a jig to enable location of each module brush according to x, y and z coordinates.

8. An imaging assembly comprising:

a moveable carriage; and

a plurality of imaging modules coupled to the carriage, wherein each module is adjacent to at least one other module and each module comprises a laser light source and a modulator cooperatively arranged to produce an individual light brush;

means for aligning each module with respect to the other modules such that the plurality of modules imagewise produces laser light which is a summation of each individual light brush produced by each module; and

means for delaying the imagewise production of laser energy from each individual module in response to an input signal conveying information regarding the position of the carriage relative to a desired image area.

9. An imaging system comprising:

(a) an imaging assembly comprising;

(i) a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative to a desired image area, and

(ii) a plurality of imaging modules coupled to the carriage, wherein each module is adjacent to at least one other module, each module comprises at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, and each module is aligned with respect to the other modules such that the plurality of modules imagewise produces laser light which is a summation of each individual light brush produced by each module, and each module comprises a signal receiver which causes a delay in the imagewise production of laser energy from each individual module; and

(b) a flat platesetter cooperatively arranged with the imaging assembly such that the imaging assembly imagewise provides laser energy to a printing plate residing in the platesetter.

10. An imaging system comprising:

(a) an imaging assembly comprising;

(i) a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative to a desired image area, and

(ii) a plurality of imaging modules coupled to the carriage, wherein each module comprises at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, each module is aligned with respect to the other modules such that the plurality of modules imagewise produces laser light which is a summation of each individual light brush produced by each module, and each module comprises a signal receiver which causes a delay in the imagewise production of laser energy for each individual module; and

(b) a rotating drum cooperatively arranged with the imaging assembly such that the imaging assembly imagewise provides laser energy to a printing plate residing on a surface of the rotating drum.

11. A method of preparing a printing plate comprising:

(a) providing an imaging assembly comprising;

(i) a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative to a desired image area, and

(ii) a plurality of imaging modules coupled to the carriage, wherein each module is adjacent to at least one other module, each module comprises at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, each module is aligned with respect to the other modules such that the plurality of modules imagewise produces laser light which is a summation of each individual light brush produced by each module, and each module comprises a signal receiver which causes a delay in the imagewise production of laser energy from each individual module;

(b) providing a printing plate for imaging; and

(c) imagewise providing laser light to the printing plate using the imaging assembly.

12. The method of claim 11, in which the plate resides in a flat-bed platesetter cooperatively arranged with the imaging assembly.

13. The method of claim 11, in which the plate resides on a surface of a rotating drum cooperatively arranged with the imaging assembly.

17. The assembly of claim 16, in which each module is magnetically removably attached to the carriage.

18. The assembly of claim 16, in which the locating means comprises a signal detector, an encoder, and an electronic controller which are all operatively associated to provide to locate the carriage.

14. An imaging system comprising:

a moveable carriage capable of traversing movement across the width of a radiation receptive medium;

a plurality of imaging heads selectively positioned on the carriage, wherein each head comprises at least one laser source, modulating means for modulating the laser energy and projection means for projecting the modulated laser energy cooperatively arranged such that the laser source, modulating means and projection means produce at least one individual light brush and each head produces at least one separate band of light brushes during each traverse of the carriage across the width of the medium;

compensating means for adjusting the projection of the separate bands such that the separate bands are projected during each traverse of the carriage to form a continuous band having a width equal to the cumulative width of the separate bands;

means for stepwise moving the medium in a direction perpendicular to the traversing movement of the carriage;

means for controlling the length and position of the carriage traverse across the width of the medium; and

means for detecting the location of the carriage relative to the edges of the medium and means for timing the projection of the separate bands responsive to the detecting means.

16. A laser imaging assembly comprising:

a carriage capable of moving over a photosensitive media;

a plurality of optical modules selectively positioned on the carriage wherein each module comprises a laser source and associated optical components and each module projects a brush of radiant energy wherein each module is removably attached to the carriage; and

locating means on the carriage to position each module in relation to selected reference points.

20. An optical projection head comprising:

a laser diode array having a plurality of emitters;

a TIR modulator capable of diffracting light rays from the array according to an applied electric field;

an optical mixer capable of equalizing the energy beams from the array;

a first group of optical components capable of shaping and directing energy rays from the laser array to the mixer;

a second group of optical components capable of directing rays emerging from the mixer to the modulator;

a lens capable of focalizing rays emerging from the modulator to a stop element capable of eliminating unwanted diffracted rays; and

an imaging objective assembly capable of focusing rays emerging from the stop element to a radiation sensitive media thereby producing an image wherein the optical assembly comprises means for adjusting the divergence of rays from the modulator to a selected value affecting the width of the image.

22. The head of claim 20, in which the adjusting means include a pair of lenses.

24. The head of claim 23, in which the folded beams are located in a plurality of parallel surfaces.

25. The head of claim 20, in which the modulator comprises a LiNbO₃ crystal having about 5 mol. % MgO or about 7 mol. % Zn.

27. The head of claim 20, in which the modulator is a TIR modulator having one or more drivers.

29. The head of claim 27, in which the modulator drivers are directly attached to a crystal of the modulator.

30. The head of claim 28, in which the modulator drivers are directly attached to a crystal of the modulator.

31. The head of claim 29, in which the crystal and drivers are encapsulated.

32. The head of claim 30, in which the crystal and drivers are encapsulated.

33. The head of claim 20, in which the laser diode and the stop element are cooled by a circulating coolant.

35. The head of claim 20, in which the modulator comprises a total reflection crystal having at least one prismatic edge capable of deviating rays by 90 degrees.

37. The head of claim 20, in which the objective assembly is capable of movement along the x and y axis thereby centering the objective assembly over a slit of the stop element.

40. The imaging head of claim 39, in which the laser light sources are each laser diodes having a plurality of emitters.

41. The imaging head of claim 39, in which the first optical arrangements each comprise a first lens, a second lens, a half-wave blade, a polarizing cube and a third lens.

42. The imaging head of claim 39, in which the second optical arrangement is a first common optical arrangement.

43. The imaging head of claim 42, in which the first common optical arrangement comprises a mirror, a first lens and a second lens.

44. The imaging module of claim 39, in which the third optical arrangements each comprise a mixing blade.

45. The imaging head of claim 39, in which the fourth optical arrangement is a second common optical arrangement.

46. The imaging module of claim 45, in which the second common optical arrangement comprises a first lens, a second lens, a first mirror and a second mirror.

47. The imaging head of claim 45, in which the fifth optical arrangements each comprise a first lens and a second lens.

48. The imaging head of claim 45, in which the modulators are total internal reflection modulators.

49. The imaging head of claim 45, in which the sixth optical arrangements each comprise a first lens, first and second mirrors and an imaging lens group.

50. The imaging head of claim 32, in which the head comprises two laser light energy sources, two first optical arrangements which correspondingly receive laser light from the sources, a first common optical arrangement which receives laser light from the first optical arrangements, two second optical arrangements which receive laser light from the first common optical arrangement, a second common optical arrangement which receives laser light from the second optical arrangements, two third optical arrangements which receive laser light from the second common optical arrangement, two modulators which correspondingly receive laser light from the third optical arrangements, and two fourth optical arrangements which correspondingly receive laser light from the modulators.

21. An optical projection head comprising:

a laser diode array having a plurality of emitters capable of producing energy rays along a slow axis and a fast axis which are mutually perpendicular;

a TIR modulator capable of diffracting energy rays from the array according to an applied electric field;

an optical mixer capable of equalizing the energy beams from the array;

a first group of optical components capable of shaping and directing energy rays from the laser array to the input of the mixer;

a cylindrical lens unit capable of directing and focalizing slow-axis rays emerging from the output of the mixer to the focal point of a cylindrical lens capable of directing slow-axis rays from the focal point to the modulator;

a lens capable of directing and concentrating fast-axis rays to the active zone of the modulator;

a lens capable of collecting rays emerging from the active zone to form an image of the point on a stop element capable of eliminating unwanted rays; and

an objective assembly capable of projecting an image onto a photosensitive surface.

26. The head of claim 21, in which the modulator comprises a LiNbO₃ crystal having about 5 mol. % MgO or about 7 mol. % Zn.

28. The head of claim 21, in which the modulator is a TIR modulator having one or more drivers.

34. The head of claim 21, in which the laser diode and the stop element are cooled by a circulating coolant.

36. The head of claim 21, in which the modulator comprises a total reflection crystal having at least one prismatic edge capable of deviating rays by 90 degrees.

38. The head of claim 21, in which the objective assembly is capable of movement along the x and y axis thereby centering the objective assembly over a slit of the stop element.

23. An optical head comprising:

a laser source of beams at an input end and image forming beams at the output end; and

a plurality of optical components along said beams between the input and output ends to obtain an image from the beams wherein the beams are folded a plurality of times between the input and output ends by reflecting surfaces.

39. An imaging head comprising:

a plurality of laser light energy sources;

a plurality of first optical arrangements which direct laser light from the corresponding laser light energy sources to a second optical arrangement;

a plurality of third optical arrangements which receive laser light from the second optical arrangement;

a fourth optical arrangement which receives laser light from the plurality of third optical arrangements;

a plurality of fifth optical arrangements which receive laser light from the fourth optical arrangement;

a plurality of modulators which correspondingly receive laser light from the plurality of fifth optical arrangements; and

a plurality of sixth optical arrangements which correspondingly receive laser light from the plurality of modulators.