Typewriting machines – Sheet or web – Including friction-feed means
Reexamination Certificate
1998-12-28
2001-09-11
Hilten, John S. (Department: 2854)
Typewriting machines
Sheet or web
Including friction-feed means
C400S641000, C492S033000, C492S036000
Reexamination Certificate
active
06287033
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet conveying apparatus. More particularly, the present invention relates to a sheet conveying mechanism which is capable of preventing occurrence of deviation of registration (hereinafter called “registration deviation”) in a printer.
The present application is based on Japanese Patent Applications Nos. Hei. 9-360925 and 10-356282, the content of which is incorporated hereinto by reference.
2. Description of the Related Art
Conveyance of paper in a thermal printer has been mainly performed by any one of three methods which are a grip roller drive method, a platen roller drive method and a drum drive method. Among the foregoing methods, printers adaptable to a somewhat large sheet size of about A3-size employ the grip roller method structured as shown in FIG.
15
. Referring to
FIG. 15
, reference numeral
101
represents a platen roller disposed opposite to a thermal head
100
and arranged to rotate counterclockwise so as to convey sheets
103
and apply a predetermined pressure to the thermal head
100
so as to press the recording sheet
103
and a toner ribbon
102
guided by a guide roller
104
. Moreover, a roller pair comprised of a capstan roller
105
and a pinch roller
106
forms a conveying mechanism having a large holding force so as to convey the sheet
103
from a recording portion to a discharge portion. A backup roller
107
is an adjustment roller.
When a color recording operation of a plurality of images is performed by superimposing the images in a plane sequential manner such that confirmation of registration (position alignment) is performed by using registration marks “+” as shown in
FIG. 16
, so-called registration deviation occurs if the sheet conveying mechanism cannot realize a required conveyance accuracy. In this case, there arises problems in that color shift and bleeding occur.
In order to ensure a required conveyance accuracy of a recording sheet conveyed in the grip roller drive method, the surface of the capstan roller
105
is devised (e.g. a roll having a random spray deposit surface) to increase the friction with the reverse side of the sheet
103
. As an alternative to this, the material of the surface of the pinch roller
106
is devised to increase the friction with the right side of the sheet
103
. Another contrivance has been employed in which the pressure is increased to enlarge the frictional force while the friction factor is maintained.
FIGS. 18A and 18B
show the surface condition of a capstan roller having a spray deposit surface:
FIG. 18A
is an enlarged view of the spray deposit surface; and
FIG. 18B
is an enlarged sectional view thereof. As shown in
FIGS. 18A and 18B
, the spray deposit surface is uneven in a random fashion, which has made it unsatisfactory to ensure that a sheet of paper is surely conveyed.
An improvement of the grip belt method shown in
FIG. 17
has been employed such that the pair of the rollers is changed to a belt structure. A rubber capstan belt
110
is attached around a pair of rollers
108
and
109
. A rubber pinch belt
113
is attached around a pair of rollers
111
and
112
. Thus, the area of contact for conveying the sheet is enlarged so as to enlarge the frictional force.
However, there is no definite method capable of improving the registration accuracy in the above described methods. The reason for this lies in that the contrivances of the grip roller method such that the surfaces of the capstan roller
105
and the pinch roller
106
are modified cannot attain a satisfactory effect.
When the pressure is increased, the shaft of the grip roller is warped, and therefore uniform pressure cannot be applied. Although the backup roller
107
may be employed or a separable comb-toothed roller may be employed to press the central portion, delicate adjustment must be performed in the above-mentioned case. Therefore, there arises a problem in that a satisfactory effect cannot be obtained.
When the frictional force is enlarged by changing the grip roller to a belt structure, the area of contact of the belt can be enlarged. However, such a structure can merely obtain almost the same effect as the structure in which the two pairs of grip rollers are provided.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a sheet conveying mechanism for a printer which is capable of accurately conveying a recording sheet by griping the sheet without the problems raised in the methods according to the related art so as to prevent color shift and bleeding when a color image is recorded and which is capable of improving the dimension accuracy of a monochrome image.
In order to achieve the above object, according to an aspect of the present invention, there is provided a sheet conveying mechanism which comprises: a hard pinch roller; and a capstan roller confronting the pinch roller, the capstan roller associating with the pinch roller to convey at least one sheet, and the capstan roller having a surface on which a plurality of projections are formed, wherein height of the projections is 60 &mgr;m±40 &mgr;m, a projection pitch in an axial direction of the capstan roller is 0.5 mm±0.2 mm, and the projections are arranged on half or more of the area of the surface of the capstan roller. More specifically, the pinch roller has a hardness of as high as 55 degrees to 85 degrees (where the hardness is measured by hardness meter JIS K-6301A). This structure enables a sheet conveying mechanism adapted to a grip roller method incorporating the capstan roller and the pinch roller to have enlarged holding force and permits an improvement in the conveyance accuracy to accurately convey a sheet.
According to the other aspect of the present invention, it is preferable that the height of the projections is 60 &mgr;m±15 &mgr;m. This structure enables the sheet conveying mechanism to have enlarged holding force with optimum frictional force and permits an improvement in the paper conveyance accuracy.
According to the other aspect of the present invention, arrangement of the projections may have an angle of 0° with respect to the axial direction of the capstan roller. In this case, it is preferable that the projections are arranged so that one or two projection lines of the projection are simultaneously brought into contact with the pinch roller. Further, according to the other aspect of the present invention, it is preferable that each of the projections has a substantially tree stump shape. On the other hand, each of the projections may have a substantially quarter-spherical shape. In this case, the plurality of quarter-spherical projections may be arranged such that the cross sections of substantially half the quarter-spherical projections face opposite in direction to the cross sections of the rest of substantially half the quarter-spherical projections. This structure ensures that greater holding force is maintained when a sheet is conveyed.
According to the other aspect of the present invention, it is preferable that the sheet conveying mechanism further comprises a backup roller contacting with a substantially central portion of the pinch roller, and pressing the pinch roller toward the capstan roller. In this case, it is preferable that end portions of the backup roller are chamfered and rounded off. According to this structure, concurrent use of even one backup roller realizes similar holding force to what is obtainable from a comb-toothed roller and prevents the surface of the pinch roller from being injured by the end portions of the roll.
The foregoing sheet conveying mechanism according to the present invention is used to convey a sheet in a printer, in particular, to convey a sheet in a thermal printer, to convey a thermoadhesive image receiving sheet, to convey a color thermosensitive sheet and to convey a sheet having a PET support member. When the sheet conveying mechanism according to the present invention is employed in any one of the foregoing printers, the re
Hatakeyama Seiji
Sawano Mitsuru
Colilla Daniel J.
Fuji Photo Film Co. , Ltd.
Hilten John S.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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