Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Patent
1999-07-06
2000-09-19
Le, N.
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
347130, 174 151, 357714, 357716, 372 35, B41J 245
Patent
active
061219959
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electro-optical character generator for the illumination of the surface of a photoconductor, in particular of a photoconductor in a high-performance printer, having a heat collector on whose bearer surface--facing the photoconductor--there is arranged a multiplicity of light-emitting elements, arranged in a row, for the illumination of the surface of the photoconductor, which are connected in heat-conducting fashion with the heat collector, and in which there is fashioned a hollow space running in the direction of the row, which is filled with a liquid whose quotient of supplied quantity of heat and change of temperature per unit of volume is greater than or equal to 2.5 kJ/dm.sup.3 K, and having a cooling means connected to the heat collector, for giving off the quantity of heat received by the heat collector to the environment.
2. Description of the Related Art
Electro-optical character generators are used primarily in copier machines and printers. By means of illumination on the surface of a photoconductor, they produce a latent charge image corresponding to the later print image, which image is colored in with toner particles. The colored-in charge image is subsequently transferred to a recording medium using a corona means, and is fixed on the surface thereof in a fixing means. Known character generators have a heat collector that extends in the longitudinal direction of the photoconductor and serves simultaneously as a bearer, on whose one bearing surface, facing the photoconductor, there is arranged a multiplicity of light-emitting elements in a row next to one another, as well as an optical means fastened to the heat collector, which sharply images the light points produced by the light-emitting elements on the surface of the photoconductor.
In addition, the character generator is equipped with a control electronics that drives the individual light-emitting elements independently of one another, by means of a multiplicity of integrated circuits (ICs), in such a way that the quantity of light respectively emitted by the elements is adjustable, and different charge states, and thus different grey gradations or, respectively, color gradations in the later print image, can be realized on the surface of the photoconductor.
As light-emitting elements, light-emitting diodes (called LEDs in the following) are suitable, particularly at an image point density of 600 dpi (dots per inch) and higher, which are fastened in groups of e.g. 128 LEDs on a common chip, known as LED arrays, in a line next to one another. Dependent on the width of the photoconductor, several such LED arrays are fastened next to one another on the bearer surface of the heat collector, the surface running in the longitudinal direction of the photoconductor, and are driven via the control electronics, which if warranted is also connected fixedly with the bearer.
In this LED array, power losses of up to 6 W per LED array can occur, so that in a high-performance printer that has for example a print width of 30 inches and uses approximately 140 such LED arrays for the illumination of the surface of the photoconductor, power losses of approximately 850 W occur. The heat quantity that arises in this way has to be removed, because the surface temperature of each LED may not exceed 50.degree. C. during operation. This is because if the surface temperature of the LED is higher, the quantity of light produced by the LEDs decreases, so that the surface of the photoconductor can no longer be illuminated by the LEDs with the same high quality.
For this reason, the light-emitting elements are connected in heat-conducting fashion with the heat collector, which collects the quantity of heat produced by the elements in order to keep the surface temperature of the elements below a critical temperature value, beyond which, as explained above, a high-quality illumination of the photoconductor is no longer possible. By means of a cooling means connected with the heat collector
REFERENCES:
patent: 4875057 (1989-10-01), Hediger et al.
patent: 4894709 (1990-01-01), Phillips et al.
patent: 5323292 (1994-06-01), Brzezinski
Japanese Abstract, 03221473, Sep. 30, 1991.
Japanese Abstract, 63168372, Dec. 7, 1988.
Japanese Abstract, 07169889, Apr. 7, 1995.
Le N.
Oce Printing Systems GmbH
Pham Hai C.
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