Optical printer head and driving method thereof

Details Optical printer head and driving method thereof Optical printer head and driving method thereof

2001-04-17

2003-11-04

Pham, Hai (Department: 2861)

Incremental printing of symbolic information

Light or beam marking apparatus or processes

Scan of light

C347S247000

Reexamination Certificate

active

06642950

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical printer head and a driving method thereof, and more particularly to an optical printer head and a driving method thereof for use in exposure of a photosensitive member to light in an electrophotographic printer.
2. Description of the Prior Art
Conventionally, an optical printer using a line light source and a laser printer are known as electrophotographic printers. The laser printer modulates laser light in accordance with output data to produce modulated laser light which scans on a photosensitive drum using a plurality of lens systems and a polygon mirror to form an image with the light on the photosensitive drum before development of the image, thereby producing printed output.
The laser printer allows a faster speed, a higher quality image, and a lower noise level than a dot impact printer and an ink-jet printer. The laser printer is not only used for business as a printer capable of printing on plain paper, but also becoming prevalent for home use in recent years.
The optical printer with a line light source employs a line light source including light-emitting elements placed in a line, and has an advantage of no need of a scanning optical system since the aligned light-emitting elements irradiate associated spots on a photosensitive member with light, respectively. Thus, the optical printer with the line light source can realize higher reliability and a smaller size of a printer apparatus.
FIG. 1
shows a general configuration of a conventional optical printer using a line light source. In
FIG. 1
, the conventional optical printer generally comprises data input section
51
for receiving printing data, photosensitive drum
27
, optical printer head
21
for exposing photosensitive drum
27
to light in accordance with image data, converging rod lens array
24
for forming an image with the light from optical printer head
21
on photosensitive drum
27
, charger
42
, cleaner
25
, developer
43
, transferrer
44
, and charge eliminator
45
. Charger
42
, cleaning section
25
, developer
43
, transferrer
44
, and charge eliminator
45
are placed to surround photosensitive drum
27
.
The operation of the conventional optical printer using the line light source is hereinafter described with reference to FIG.
1
.
Image data output from data input section
51
is input to a driving circuit of optical printer head
21
. The output from the driving circuit causes the line light source in optical printer head
21
to emit light. The light emitted from the activated optical printer head
21
is converged by converging rod lens array
24
and irradiated to photosensitive drum
27
. The surface of photosensitive drum
27
has been uniformly charged by charger
42
such that electric charge is removed in the portions irradiated with the light from optical printer head
21
to write an electrostatic latent image on photosensitive drum
27
.
Developer
43
sprays charged particles (toner) onto the surface of photosensitive drum
27
with the electrostatic latent image written thereon to develop the electrostatic latent image, thereby forming a toner image. The toner image reaches object
26
of printing such as a sheet of paper with the rotation of photosensitive drum
27
, and is transferred onto object
26
of printing through the application of an electric field by transferrer
44
. The transferred toner image is fixed on object
26
of printing by a fixer (not shown).
The residual electric charge on the surface of photosensitive drum
27
after it passes through transferrer
44
is removed by charge eliminator
45
, and finally, cleaner
25
removes the toner remaining on the surface of photosensitive drum
27
after the transfer.
As a light source of such an optical printer, for example, Japanese Patent Laid-open Publication No. Sho 58-65682 (JP, 58065682, A) discloses the use of a light source including a number of LEDs (Light Emitting Diodes) placed in a line.
A ceramic substrate formed of alumina is primarily used as a substrate of a printer head using LEDs. The printer head is formed by placing a plurality of LED chips in a line on the ceramic substrate, performing die bonding of IC (Integrated Circuit) chips serving as driving circuits on both sides of the LED chips with conductive paste, and then making electrical connection through wire bonding. The ceramic substrate of the printer head is supplied with electric signals and power from the main body of the printer through an FPC (Flexible Printing Cable).
For the LED chips in this case, an array of LEDS for 64 dots or 128 dots and with approximately 60 &mgr;m pitches is currently used in consideration of limitations on the size of an n-type GaAsP substrate for forming part of the LED chips, yields in the manufacturing process, and the like. A plurality of such LED chips need be arranged to form a line light source of a printer head, and in such a case, highly accurate cutting technique and mounting technique on the order of micrometers are required to increase the accuracy of the arrangement.
In addition, since the n-type GaAsP substrate used is small, expensive, and even causes many defects, an attempt to increase the number of dots for light emission in a monolithic LED chip leads to reduced yields and significantly increased manufacturing cost. A method of avoiding these problems is to mass-produce LED chips for a reduced number of dots which are aligned over the length covering the printing width corresponding to an object of printing. This method, however, has mounting limitations from the issues in the arrangement of the chips and the electrical connection when a higher density is intended. As a result, the optical printer with the LEDs has limitations in providing a lower cost and higher density.
To address such problems, the use of a light-emitting element other than the LED is considered. For example, Japanese Patent Laid-open Publication No. Hei 8-108568 (JP, 08108568, A) discloses an optical printer head using an organic EL (electroluminescence) thin film light-emitting element. Since the optical printer head using the organic EL light-emitting element enables the formation of a number of light-emitting elements together on a substrate of large area as well as mass production, a lower cost can be expected. In addition, a higher density is possible due to micromachining of electrode sections in the manufacturing process.
Light-emitting elements are arranged two-dimensionally in an optical printer head to allow exposure to light in a short time even if they emit light at low luminance. For example, Japanese Patent Laid-Open Publication No. Hei 9-254437 (JP, 09254437, A) describes a printer having a printing head in which light-emitting elements are arranged two-dimensionally and a pixel array using a group of optical fibers as its front panel is used.
However, for the optical printer head using a thin film light-emitting element such as an organic EL element, the performance of the current organic EL element has a limitation of emitting light up to a luminance of several hundreds of cd/m
2
assuming that its useful life is several tens of thousands hours. In other words, when the current organic EL element is used, it is difficult to meet both needs for the amount of light required for exposure as a printer head and for the practical life. The practical life refers to the maximum number of sheets of paper required for use as a printer.
It is contemplated that a replaceable optical printer head is employed to allow light emission at a higher luminance at the expense of the useful life. However, it is difficult for a user to align a new optical printer head with a photosensitive drum and optical systems on the order of micrometers in replacing an old optical printer head.
Problems common to electrophotographic printers include the need of correction for sensitivity characteristics of a photosensitive member, the need of correction for misalignment of an object of printing, the need of correction for insufficient

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