Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2002-09-17
2004-11-23
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
Reexamination Certificate
active
06822668
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a multibeam laser source with a plurality of laser light sources arranged in an array.
To set images on image carriers formed with a flat or curved surface, in particular printing forms in a printing form exposer or a direct imaging printing unit of a printing machine, use is frequently made of multibeam light sources, typically multibeam laser light sources, such as semiconductor laser or diode laser arrays, in particular. Depending upon the image information to be set, each individual light source and each individual emitter is switched on or the variables that influence the light intensity for each image point to be set on the image carrier is set or prescribed, respectively, so that each individual emitter produces a projection point with a specific light intensity. As an option, provision is frequently also made of imaging or reproduction optics for projecting the light emitted by the light sources onto the image carrier, frequently by changing the propagation direction of the light and by beam shaping, respectively.
For precise and simple image-setting or imaging of the printing form by the plurality of heretoforeknown imaging methods, it is desirable that the image points of the light sources on the image carrier lie on one projection line for the one-dimensional case, preferably on a straight line, which typically, if the image carrier is a printing form and is accommodated on a so-called printing form cylinder or printing plate cylinder, is parallel to the axis of the cylinder and, for the two-dimensional case, forms an orthogonal, in particular Cartesian projection field, respectively. Furthermore, it is particularly advantageous if the spacings between adjacent image points are uniform. Due to influences or effects arising during manufacture, the spacings of the light sources from one another frequently do not meet these requirements. Possible causes therefor are position errors of individual emitters on a substrate or a change in the geometry during fastening to a holding element, for example. In addition, reproduction or imaging errors in the reproduction or imaging optics arranged downstream to project the light sources onto image points in a projection plane often lead to deviations in the spacings from desired prescriptions thereof.
While the use of micro-optical components in reproducing or imaging optics, i.e., individual optical components which, respectively, act upon a light beam originating from only one emitter or from a few emitters, in principle, permits the light path or the course of the beam to be varied, in particular in relation to another beam from another emitter or several other emitters, there exist technical reasons which hamper a practicable realization of this concept, amongst others due to the small geometric dimensions of the micro-optical components or of the lack of a permanent fixing.
Because, in general, the image carrier upon which an image is to be set is movable relative to the image-setting or imaging device with the multibeam light source, there is a further possible way of varying the position of image points to be set on the image carrier located in the projection plane, in that the time control of the individual light sources in the multibeam light source is selected to be different so that the projection points of the light sources come to lie at desired coordinate points on the image carrier. In this way, for example with a number of light sources distributed non-uniformly in the direction of the relative movement, a number of image points distributed uniformly in this direction or distributed as desired can be produced. In the non-prepublished German Patent Application No. De 101 24 215.8 known only in-house at the corporate assignee of the instant application, an image-setting or imaging device of this general type with a plurality of light sources is described, to which a time delay device is assigned, which shifts the triggering point for driving each light source as a function of the respective spacing of the light source from a subject line in such a way that image points are produced in a projection line of the subject line on a printing form.
Electronic correction of the position of the image point by time-delayed control, using the movement of the image carrier with respect to the image-setting or imaging device, is, however, possible for a number of projection points only in the sense that a one-dimensional arrangement on the surface of the image carrier is achieved; for a multibeam light source, the light sources of which are arranged in a one-dimensional array, only a (one-dimensional) curve or else a straight or sectionally straight line can be predefined or prescribed on the (two-dimensional) surface of the image carrier. Time-delayed driving or control of the light sources takes place in such a way that triggering of the light source occurs when, during the relative movement between the image-setting or imaging device and the image carrier, the assigned projection point thereof intersects the curve on the surface. Accordingly, the image point that is produced lies on the curve. In general, with the hereinaforementioned procedure, however, it is not possible, for fundamental reasons, to influence the position of the image points produced along the curve, because, in the geometric sense, this is a (one-dimensional) projection of the position of the projection points on the surface onto the curve for non-delayed driving or control of the light sources along the direction of the relative movement. What is involved, therefore, is an only one-dimensional correction of the image point position. For a multibeam laser light source with light sources arranged in a two-dimensional array, this property therefore applies correspondingly to each line in the arrangement.
As is known, the radiation characteristic of a laser light source is influenced by the geometric arrangement of the resonator. An introduction to laser structures of semiconductor lasers is given, for example, in “Integrierte Optoelektronik” (Integrated Opto-electronics) by K. J. Ebeling (Springer, Heidelberg, 1992). Furthermore, particularly for gain-guided laser diodes, it is known that the active region wherein laser activity occurs is determined by the region through which current flows, i.e., that region wherein pump energy is provided.
U.S. Pat. No. 4,791,646 discloses that a gain-guided diode laser can have a spatial distribution of the pump energy in the resonator, so to say, a tailor-made pump energy distribution. This is achieved by a two-dimensional pattern of current-guiding contacts and insulating regions on one side of the laser. The location-dependent pumping within the resonator of a large-area diode laser leads to a narrow intensity distribution in the remote field.
U.S. Pat. No. 4,719,623 describes a gain-guided diode laser with a spatial pump energy distribution, which has a nonuniform pattern of current-carrying contacts and insulating regions on one side of the laser. Although the laser is described as a field with a plurality of partial lasers, what is involved is a single-beam light source, because the individual partial lasers are coupled. Due to the feature of a nonuniform pump current distribution, oscillation of the laser in the fundamental super mode of the coupled partial lasers formed by the individual pump currents is promoted, so that a spatially narrow remote field is generated.
The aforedescribed gain-guided diode lasers are single-beam laser light sources. Although, with the aforedescribed measures, an effect upon the intensity distribution of the remote field of the diode lasers is achieved, no lateral beam offset in a direction perpendicularly to the emission direction of the resonator can be achieved. However, this property is desirable in particular for the use of a multibeam laser light source for setting an image on an image carrier, in particular for the efficient setting of an image on a printing form in a printing form exposer or a direct
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Locher Ralph E.
Pham Hai
Stemer Werner H.
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