Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2000-09-29
2004-06-15
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S237000, C347S247000
Reexamination Certificate
active
06750895
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical printer head to expose a photosensitive body in a xerography-type printer.
2. Description of the Related Art
Conventionally, as a xerography-type printer, a laser printer and/or line-illuminant type optical printer are known. The laser printer produces printed outputs by causing modulated laser light generated through modulation of laser light based on data to be output to scan on a photosensitive drum, using two or more lens systems and polygon mirrors, to expose an image and to develop it. Since the laser printer can provide a higher speed, higher image quality and lower noise when compared with a dot-impact type printer or ink-jet type printer or a like and allows printing on ordinary paper, it is not only widely used for business applications but also is finding widespread use in households in recent years.
The line-illuminant type optical printer is a printer which uses a line illuminant composed of light emitting devices arranged in a form of a line. Since each of the arranged light emitting devices irradiates a corresponding spot on a photosensitive body, it has an advantage in that a scanning optical system is not required, which serves to implement high reliability and miniaturization of optical printers.
FIG. 13
is a side view showing overall configurations of conventional optical printer using a line illuminant. The conventional optical printer using the line illuminant, as shown in
FIG. 13
, is chiefly composed of a data inputting device
101
, an optical printer head
102
, a converging rod lens array
103
, a photosensitive drum
104
, a charging device
105
, a developing device
106
, a transferring device
107
, a charge removing device
108
and a cleaning device
109
.
Operations of the optical printer using the line illuminant will be hereinafter described by referring to FIG.
13
.
Print data fed from the data inputting device
101
is input to a driving circuit (not shown) of the optical printer head
102
. An output from the driving circuit activates the optical printer head
102
to cause the line illuminant to emit light. The photosensitive drum
104
is irradiated with light emitted by the activation of the optical printer head
102
and converged by the converging rod lens array
103
. A surface of the photosensitive drum
104
is uniformly pre-charged by the charging device
105
. A charge is removed from an area of the surface irradiated with the light by the optical printer head
102
and an electrostatic latent image is written to the photosensitive drum
104
. Electrically charged fine grains (toner) are deposited on a surface of the photosensitive drum
104
to which the electrostatic latent image has been written and the electrostatic latent image is developed by the developing device
106
and a toner image is generated. The toner image having reached an object to be printed
110
through rotation of the photosensitive drum
104
is transferred to the object to be printed
110
by electric fields applied from the transferring device
107
and then a transferred toner image is fixed on the object to be printed
110
by a fixing device (not shown). Residual charge being left on the surface of the photosensitive drum
104
after it has passed through the transferring device
107
is removed by the charge removing device
108
and finally the toner being left on the surface of the photosensitive drum
104
after it has been transferred is removed by the cleaning device
109
.
Moreover, a line-illuminant type optical printer head is disclosed in Japanese Patent Application Laid-open No. Sho58-65682 in which an LED (Light Emitting Diode) arranged in a form of a line is used as a line illuminant. An LED-type optical printer head uses a ceramic substrate made from alumina on which LED chips are arranged in the form of a line. IC (Integrated Circuit) chips operating as driving circuits are die-bonded to both sides of the ceramic substrate by using a conductive paste and then electrical connections are established by wire bonding and electrical signals and power are supplied through a FPC (Flexible Printing Cable) from a printer proper to the ceramic substrate. Due to size limitation imposed by an n-type GaAsP (Galium Arsenide Phosphide) substrate and to yield limitation imposed by manufacturing processes, LED chips of 64 dots or 128 dots with about 60 &mgr;m pitches are used presently. Therefore, to form the line illuminant of the optical printer head, it is necessary to arrange a plurality of such LED chips and, if accuracy of arrangement must be increased, cutting and/or mounting technologies with a high accuracy in the order of microns are required. Moreover, the n-type GaAsP substrate is small and costly and further has many defects. That is, in a case of monolithic type LED chips, an increase of numbers of light-emitting dots causes a lowered yield of LED chips and a rise in manufacturing costs. To avoid this, LED chips having the small number of light-emitting dots are mass-produced and are arranged by a length being equivalent to a printing width required by an object to be printed. However, an increase in density of the optical printer head by this method leads to packaging limitation imposed by arrangements and electrical connections of the LED chips. Therefore, the LED-type optical printer head has limits to lower manufacturing costs and higher density.
Therefore, a possibility of using light-emitting devices other than the LED is examined. For example, an optical printer head using an organic EL (electroluminescence) thin-film light emitting device is disclosed in Japanese Patent Application No. Hei8-108568. In a case of the optical printer head using the organic EL thin-film light emitting device, a large number of light-emitting devices can be formed, collectively and at comparatively lower costs, on a substance with a large area and mass production of the optical printer head is made possible. Moreover, by microfabrication of an electrode of the optical printer head, the density of the optical printer head is made higher.
Generally, in the optical printer head, even if an emitting device has a small light-emitting luminance, by arranging light-emitting devices in two dimensions, it can be used for short time exposure processes. For example, in Japanese Patent Application No. Hei9-254437, an optical printer head is disclosed in which light-emitting devices are arranged in two dimensions and a picture element array with a cluster of optical fibers incorporated on a front panel is used as a printer head.
However, the optical printer head using thin-film emitting devices such as organic EL devices or a like has a problem. That is, since a maximum light emitting luminance of present organic EL devices is hundreds cd/m
2
for a lifetime of scores of thousands of hours, when used for a printer head, it is difficult to satisfy both of requirements of light amounts required for exposure and practical lifetime (to be measured by required pieces of paper to be printed) at a same time. Though light-emitting operation with high luminance would be made possible by sacrificing the requirement of the lifetime and by using a replacement-type optical printer head, it is impossible to perform exact positioning among the optical printer head, photosensitive drum and optical system with an accuracy in the order of microns at a user level.
The followings are problems common to xerography-type printers:
(1) Correction is needed to a sensitivity characteristic of a photosensitive body.
(2) Correction is needed to a positional displacement of an object to be printed.
(3) Correction is needed to insufficient development that may occur in a region having small exposure amounts when printing on multiple gray scales is performed.
Since a characteristic of a surface potential of the photosensitive body does not always correspond linearly to the amount of exposure, the printer must be driven in accordance with the characteristic of a photosensitive body. Moreover, sinc
Asada Hideki
Otose Tomohiko
Uezono Tsutomu
Pham Hai
Whitham Curtis & Christofferson, P.C.
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