Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-07-12
2003-01-07
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S239000
Reexamination Certificate
active
06504567
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 198 30 896.5, filed on Jul. 10, 1998, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoplotting process for high energy plotting of a computer-stored raster image on a photosensitive record carrier.
2. Discussion of Background Information
Photoplotting processes and arrangements serve, for example, to produce photographic artwork for printed circuit boards.
Photoplotters plotting a computer-stored raster image on a plane, photosensitive record carrier are known from the prior art (information sheet Xenon Plotter by the company MIVATEC Hard- und Software GmbH, Benzstrasse, 17, D71171 Schönaich, of 15.10.1996).
During said plotting, a so-called exposure head (with a plotting area of about 5×7.5 mm) is guided over a record carrier, which has a large area (up to approximately 720×600 mm) in relation thereto, for the purpose of plotting picture elements composing the raster image of the record carrier.
The exposure head is provided with an LCD matrix of light-modulation elements (LCD: liquid crystal device), each of which can be selectively controlled by electrical means in order to open or block it for transmitted light.
If transmitted light is projected onto this LCD matrix, it can only pass as a ‘light beam’ through the matrix at those elements that are controlled to admit the passage of light.
Each of the light beams admitted forms a corresponding picture element on the photosensitive record carrier. Missing light beams-equivalent to blocked elements-form ‘missing picture elements’.
The raster image of the record carrier consists of a multiplicity of picture elements, including plotted and non-plotted (missing) picture elements.
In the above arrangement light from a Xenon flash lamp is projected onto the LCD matrix.
Since the exposure head containing the LCD matrix has a much smaller area (comparable to the square of a chessboard) than the record carrier (comparable to a chessboard having many squares), said exposure head must be guided successively to all the positions of the chessboard squares so that the picture elements can be plotted there.
In view of the desired high resolution (in the range of>10 micrometers) of the raster image of the record carrier, the movement of the exposure head imposes the highest tolerance requirements with respect to the precision of the movement mechanism for displacement of the head.
Because the exposure head is moved continuously over the record carrier, there is only a very short moment to illuminate the head (by means of a Xenon flash lamp) aligned at a ‘chessboard field’ of the record carrier. A longer exposure period would lead to blurred picture elements (with ‘comet trails’) through sustained movement of the head, effectively influencing the resolution of the plotting disadvantageously.
Short exposure periods are, however, associated with minimal plotting energy, which again signifies that only photographic artwork, such as for subsequent circuit board manufacture, can be prepared. Such a comparatively small quantity of plotting energy obviates direct exposure of so-called circuit board photo-resist material.
SUMMARY OF THE INVENTION
The present invention relates to a process having a comparatively higher plotting energy, which also makes use of an exposure head being moved continuously. The plotting energy should be sufficiently high to enable direct exposure of photo-resist material.
A further object of the present invention is to propose a photoplotting process which permits plotting a raster image of the record carrier with variable image scale.
In accordance with the present invention, during relative displacement between the light modulator and the record carrier, the excursion of the light beams emanating from the light modulator and impacting a sub-area of the record carrier raster image are compensated during a time interval T by a displacable lens disposed between the light modulator and record carrier. Time interval T is above a value W
1
, which relates to the permissible maximum displacement path of the relative movement for the resolution of plotting without use of the lens, and is below a value W
2
, which relates to a time interval that begins in a current sub-area of the record carrier raster image during the projecting entry of the first half of the light modulator surface and that ends only when the second half of the light modulator surface projects into this sub-area of the record carrier raster image, reduced by the reverse period for the lens. The lens, after recording the picture elements in a record carrier raster image sub-area is displaced in a direction opposite to the compensation direction into a starting position for plotting of the next sub-area of the record carrier raster image.
Accordingly, the instant invention relates to a process for plotting of a raster image on a light-sensitive record carrier. The process includes converting a computer-stored raster image comprising raster points into controllable raster point-related light beams via a light modulator, such that picture elements corresponding to the raster points are plotted on a record carrier, matrix-like dividing of the computer raster image into imaginary computer raster image sub-areas, and matrix-like dividing of the record carrier raster image is into imaginary record carrier raster image sub-areas, wherein the sub-areas of the computer and record carrier raster image are associated with one another. The process further includes matrix-like dividing of the imaginary computer raster image sub-areas into imaginary raster point positions, matrix-like dividing of the imaginary computer raster image sub-areas into n imaginary raster point positions, and matrix-like dividing of the sub-areas of the record carrier raster image into n imaginary picture element positions. Further, the process includes assigning the picture element positions to the raster image positions, simultaneously plotting the picture elements corresponding to the raster points of a sub-area of a record carrier raster image, successively plotting the sub-areas of the record carrier raster image, continuously moving a light modulator relative to the record carrier to capture an entire surface of the record carrier according to the sub-areas of the record carrier raster image, and projecting the light modulator for each sub-area of the record carrier raster image with light. During relative displacement between the light modulator and the record carrier, an excursion of the light beams emanating from the light modulator and impacting a sub-area of the record carrier raster image are compensated during a time interval T by a displaceable lens disposed between the light modulator and record carrier. The time interval T is selected to be above a value W
1
, which relates to a maximum permissible displacement path for the relative movement for plotting resolution without use of the displaceable lens, and to be below a value W
2
, which relates to a time interval that begins when a first half of the light modulator surface projects into a specified sub-area of the record carrier raster image and that ends when only a second half of the light modulator surface projects into the specified sub-area of the record carrier raster image, and is reduced by a reverse period for the displaceable lens. The displaceable lens, after recording the picture elements in a record carrier raster image sub-area, is displaced in a direction opposite to the compensation direction into a starting position for plotting of the next sub-area of the record carrier raster image.
In accordance with a feature of the present invention, the light modulator can include a tilting mirror element semiconductor chip.
According to another feature of the present invention, the light modulator can include a liquid crystal arrangement.
According t
Greenblum & Bernstein P.L.C.
Mivatec Hard-und Software GmbH
Pham Hai
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