Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Utility Patent
1999-01-27
2001-01-02
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S242000, C347S130000
Utility Patent
active
06169564
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical printhead for use in, for example, an electrophotographic printer.
DESCRIPTION OF THE RELATED ART
An LED head is one type of an optical print head. For example, Japanese Patent Preliminary Publication (KOKAI) No. 6-64227 discloses one such type of printhead. The printhead includes a rod lens array, a printed circuit board, and a base. The rod lens array (e.g., Selfoc Lens Array or SLA, manufactured by NIPPON ITA GARASU) focuses light emitted from LEDs on the surface of a photoconductive body. The printed circuit board has LED chips and driver ICs mounted thereon. The driver ICs selectively drive the LED chips to emit light in accordance with print data. The base serves as a heat sink and a datum or reference for positioning the aforementioned structural elements.
The LED printhead must be longer than the width of a print medium. For example, if the maximum size of the print paper that a printer can accept is A4 (210 mm×297 mm), then the length of the LED printhead should be in the range from 260 to 280 mm. If the maximum size is A3 (297 mm×420 mm), then the length of the LED printhead should be in the range from 350 to 370 mm. Thus, the SLA, holder, LED array unit, and base are all necessarily long.
An LED printhead must be designed to form a line of uniformly focused spots of light on the surface of a photoconductive body along the length of the photoconductive body. The line should be accurately straight so that the line of spots do not wave or is not curved.
The base is rigid and serves as a reference, so that the entire structure of the printhead is sufficiently rigid and straight. The resin-molded holder is mounted together with the SLA and LED array unit to the base for integral construction, so that the overall structure of the print head is accurately straight. The SLA has a lateral end surface abutting an SLA-supporting portion formed on the holder, the lateral end surface being in the same plane as the light incident surfaces of the rod lenses of the SLA. As a result, a line of the light incidence surfaces of the rod lenses is parallel to a row of LED array units. Conventionally, special care had to be taken in order to form an accurately straight base and a precision SLA-supporting portion so that the lines of focal points of the SLA is accurately straight and therefore the line of spots focussed on the surface of the photoconductive body.
The LED printhead of the aforementioned construction is placed to oppose the photoconductive body and forms a line of spots of light focussed on the photoconductive body, the line not waving or not being out of the straight.
However, in order to obtain an adequately straight line of focused spots of images, the SLA must not deviate more than several tens microns, preferably less than
20
microns, from a true straight line. This implies that the SLA-supporting portion must not deviate more than several tens microns from the true straight line. The holder is molded from a resin. A long molded article such as one used in an LED printhead suffers from distortion and warp resulting from partial shrinkage of the article after molding. Therefore, a highly accurate mold is needed. Stringent dimensional requirements imposed on the article and the mold lead to a high cost of the mold. In the mass production of the article, the mold must be frequently maintained so as to ensure high dimensional accuracy.
SUMMARY OF THE INVENTION
An object of the invention is to provide a printhead in which a line of focussed images of LEDs is very straight.
A circuit board holds a line of a plurality of light emitting elements mounted thereon. The light emitting elements are at a predetermined height from the surface of the circuit board. A rod lens array (SLA) longitudinally extends and forms images of the light emitting elements on a photoconductive body such that the images and the light emitting elements form pairs of conjugate points with respect to the rod lens array. A holder holds the rod lens array relative to the light emitting elements.
A plurality of supporting members are mounted to the holder at a plurality of locations along a length of the rod lens array (SLA) and hold the rod lens array relative to the circuit board so that the images form a substantially straight line on the photoconductive body. Each of the plurality of supporting members substantially independently supports the rod lens array relative to the circuit board. The supporting members has a first reference portion and a second reference portion, the first reference portion abutting a lower surface of the rod lens array (SLA) and the second reference portion abutting the surface of the circuit board on which the light emitting elements are carried.
The supporting member of different heights may be assembled to the holder along the length of the rod lens array so that any warp and/or distortion of the base is accommodated, thereby allowing images of light emitting elements are on a very straight line.
Further scope of applicability of the present invention will become apparent form the detailed description given hereinafter. However, it should be understood that the detailed description and specific example, while indicating a preferred embodiment of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5023442 (1991-06-01), Taniguchi et al.
patent: 5321429 (1994-06-01), Ono et al.
patent: 06-064-227 (1994-03-01), None
Nakajima Norio
Tsukagoshi Hisashi
Le N.
Nguyen Lamson D.
Oki Data Corporation
Rabin & Champagne PC
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