Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Patent
1997-05-19
1999-04-27
Le, N.
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
347239, H03C 308
Patent
active
058984534
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is in the field of electronic reproduction technology and is directed to a method for the point-by-point and line-by-line exposing of recording material with a light beam, and is also directed to an electronic exposing unit, also called an exposer, recorder or image setter.
In a recorder, a light beam modulated by a video signals is conducted point-by-point and line-by-line across a recording material to be exposed. The recording material is thereby fixed on a holder that moves relative to the light beam. Given an inside-the-drum device, the recording material is fixed on a stationary holder shaped like a cylindrical segment or on an exposure trough, and the light beam is conducted across the recording material point-by-point and line-by-line with a rotating light beam deflection means. However, the recorder can also be designed as a drum device or flat bed device.
A laser is often employed as a light source for generating the light beam. The modulation of the light beam dependent on the video signal occurs with a modulator, for example with an acousto-optical modulator. In the traditional technology, the drive of the modulator with the video signal occurs such that the modulator is activated line-by-line within exposure time spans wherein the light beam sweeps the lines to be recorded on the recording material and is deactivated during return time spans wherein the light beam is conducted to the next line to be exposed.
In a traditional recorder, back reflections from the modulator or the light beam deflection unit can disadvantageously occur in the direction toward the light source, and these must be prevented in order to achieve a good recording quality. Beyond this, a high efficiency of the modulator is required so that a light beam with high luminous power is available for exposing the recording medium. Further, the components that are employed must have optimally constant operating properties since, for example due to heating of the components, the optical properties of the light beam can vary, this in turn diminishing the recording quality.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to improve a method and an apparatus for exposing recording material such that an improved constancy of the operating properties is achieved while assuring a high efficiency.
According to the invention, a method is provided for exposing recording material wherein a light beam is generated in a light source. The light beam passes through an optical isolator and then through a video modulator where the light beam is modulated. The recording material is exposed point-by-point and line-by-line by the modulator light beam. The modulator is activated during each line of exposure in an exposing time span and is de-activated at least at times within a return time span for the light beam for each respective line. The optical isolator substantially prevents reflected light from reaching the light source. Internal heating in the optical isolator is compensated by activating the optical isolator not only during the exposing time span, but also during a compensation time span during at least a portion of the return time span. A sum of time extents of the exposing time span and the compensation time span is approximately constant for each line.
The invention is explained in greater detail below with reference to FIGS. 1 through 6.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block circuit diagram of an exposure device;
FIG. 2 is a schematic, sectional illustration of an exposure device on the inside drum type;
FIG. 3 shows time diagrams for illustrating the signal curves given deactivated temperature compensation (Prior Art);
FIG. 4 shows time diagrams for illustrating the signal curves given activated temperature compensation according to the invention;
FIG. 5 illustrates time diagrams with signal curves modified compared to FIG. 4, whereby the duration of the exposure time span was shortened; and
FIG. 6 shows an exemplary embodiment of the d
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Fischer Jorg Achim
Leiss Klaus Gunter
Le N.
Linotype-Hell AG
Pham Hai C.
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