Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
2001-04-05
2004-12-14
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S130000
Reexamination Certificate
active
06831673
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the structure of an optical write head using light-emitting device arrays to be provided in a high-resolution electrophotographic printer, and to a method of assembling the optical write head.
An optical write head to be used in an optical printer has hitherto been equipped with light-emitting device arrays, such as light-emitting diodes. The principle of an optical printer equipped with an optical write head is illustrated in FIG.
9
. The surface of a cylindrical photosensitive drum
2
is coated with material (photosensitive material) possessing optical conductivity, such as amorphous Si or organic material. The photosensitive drum
2
rotates in accordance with a print speed. To begin with printing, the surface of photosensitive material provided over a rotating drum is charged uniformly with an electrostatic charger
4
.
Next, an optical write head
6
radiates, onto the photosensitive material, light which assumes the image of a dot to be printed, thereby neutralizing the thus-exposed portion of the photosensitive material and forming a latent image. Subsequently, a development unit
8
causes toner to adhere to the photosensitive material in accordance with the charged status of the photosensitive material. A transfer unit
10
transfers toner onto paper
14
supplied from a cassette
12
. A fixing unit
16
applies heat to the paper, thereby fixing the toner transferred on the paper. The paper is then fed to a stacker
18
. After transfer of the latent image has been completed, the entirety of the electrically-charged photosensitive drum
2
is neutralized by an erasure lamp
20
, and residual toner is removed by a cleaner unit
22
.
The optical write head which has hitherto been employed is constructed such that a plurality of light-emitting device array chips are arranged in a single line or in a staggered layout on a substrate, in accordance with specifications pertaining to a print width and such that a rod-lens array or rod-lens arrays (e.g., product name: SELFOC Lens array manufactured by Nippon Sheet Glass Co. Ltd.) having gradient index rod lenses stacked thereon in the form of one or two lines is arranged opposite the light-emitting device array chips.
FIG. 10
is a perspective view showing a rod lens array
11
having rod lenses stacked in two rows. A plurality gradient index rod lenses
24
are sandwiched between frames
26
and secured by means of resin
28
.
FIG. 11
is a cross-sectional view showing a typical example of an optical write head constructed as described above. In this example, a plurality of light-emitting device array chips
30
are arranged in a single line on a printed circuit board
32
formed from glass epoxy, in accordance with specifications pertaining to a print width. A rod-lens array
24
having gradient index rod lenses stacked thereon in the form of one or two lines is arranged opposite the light-emitting device array chips
30
. The light-emitting device array chips
30
and the rod lens arrays
34
are fixed on a housing
36
by means of a silicon filler
38
.
(I) In association with an increase in print speed and an improvement in resolution, required precision of alignment of an optical system is increased significantly. A geometrical layout or related-art mechanical components fails to maintain the precision of the mechanical components, to thereby fail to satisfy performance requirements of the optical system.
Obtaining a high-resolution image requires setting within a range of ±30 &mgr;m respective specified values of the amount of deviation between the center of an optical axis and an illumination point of each or light-emitting devices, the distance from the illumination point to the end face of a rod lens array, and the distance from a photosensitive surface to the end face of the rod lens array.
(1) The lengths of rod lenses have a variation of about ±0.4 mm in manufacture. (2) There may be a case where the rod lens array has warpage toward an image surface or an object surface. (3) Fiber-reinforced plastics (FRP) from which a frame of the rod lens array is formed has a variation of about ±0.4 mm in thickness. Even if an optical component is positioned along the mechanical components, the precision of positioning exceeds a required range of optical precision, thereby failing to satisfying optical performance.
For this reason, there has arisen a necessity of three-dimensionally aligning the position of the rod lens array to a light-emitting device array. More specifically, (1) the distance between an illumination point and the surface of a photosensitive material must be matched with a conjugate length of the rod lens array; (2) the longitudinal center of a lens belonging to the rod lens array must be set to the center of the distance; and (3) deviation between the optical axis of the rod lens array, an illumination point, and the position of the surface of a photosensitive material must be adjusted with respect to the longitudinal direction of the rod lens array.
For this reason, a space is ensured beforehand between the housing of the optical write head and the rod lens array. The rod lens array is three-dimensionally aligned. The rod lens array is secured on the housing of the optical write head by means of filling the space with a silicon-based adhesive.
However, in order to align the optical axis of the rod lens array in the longitudinal direction thereof, the alignment must be performed through use of an actuator having high positional precision. An enormous amount on alignment time is required.
The mechanical components must be formed into complicated shapes, by means of ensuring, for example, a space for effecting alignment of an optical axis. Such complicated working of the mechanical components is a contributory factor to hindering a reduction in manufacturing costs of an optical write head.
In most cases, a head housing of the related-art optical write head is molded from engineering plastics. In a case where a rod lens array having the optical axis aligned is secured to the head housing, a silicon-based adhesive is usually used. Heat contraction (a contraction of about 8% arises in volume of the adhesive), which arises after the adhesive has been tilled and cured, or distortion of material of the head housing, which is caused by contraction of the head housing with time, poses difficulty in guaranteeing the positional precision of the optical axis over a period of years.
The present invention has been conceived to solve the drawbacks set forth and is aimed at providing an optical write head which obviates a necessity of alignment operation by use of a high-precision device and a necessity of complicated mechanical components, enables lower-cost manufacture of the optical write head, and is less susceptible to time-varying changes.
(II) In principle, in a primary scanning direction (i.e., the direction in which light-emitting points are to be scanned; that is, a direction perpendicular to a sheet of FIG.
11
), the optical write head
6
having the light-emitting device array chips
30
arranged thereon must be made greater in size than a print width. In order to reduce the overall size of a printer using the optical write head
6
, demand exists for reducing the size of the printer in a sub-scanning direction (i.e., a direction in which the photosensitive drum
2
rotates) As shown in
FIG. 11
, the printed circuit board
32
having the light-emitting array chips
30
mounted thereon must be arranged perpendicular to a light-emission optical axis
39
. For this reason, a reduction in the width of the substrate
32
is effective for reducing the dimension of the printer in the sub-scanning direction.
A light-emitting diode (LED) array is commonly and widely used as a light-emitting array. Supply of a signal corresponding to an image signal output from a driver integrated circuit (IC) to LED chip arrays requires formation of bonding pads (BPs) equal in number to LED devices on the LED array chip
30
. In the case of a resolution
Arima Takahisa
Kuroda Yasunao
Kusuda Yukihisa
Oono Seiji
Wakisaka Masahide
Nippon Sheet Glass Co. Ltd.
Pham Hai
Whitham Curtis & Christofferson, P.C.
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