Printing – Stenciling – Stencils
Reexamination Certificate
1999-04-22
2001-04-24
Yan, Ren (Department: 2854)
Printing
Stenciling
Stencils
C101S477000
Reexamination Certificate
active
06220155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stencil making device for perforating a stencil sheet supplied from a rolled stencil sheet.
2. Description of the Related Art
FIG. 7
illustrates a conventional stencil making device. A rolled base sheet S for stencil printing (hereinafter referred to as a stencil sheet S) is supported in a master holder
106
. The stencil sheet S supplied from the rolled stencil sheet S is in a shape of a continuous strip. The stencil sheet S changes conveying direction while turning on a set guide shaft
100
. Then, the sheet is sandwiched between a thermal head
101
and a platen roller
102
, and subsequently held between an upper roller
104
and a lower roller
105
after turning on a roller
103
, and then conveyed to an initial stop position.
When the stencil sheet S is conveyed, tension in an opposite direction to the conveying direction is exerted on the stencil sheet S by a back-tension unit
107
disposed to the master holder
106
, so that a portion of the sheet sandwiched between the thermal head
101
and the platen roller
102
does not wrinkle. The rolled stencil sheet S is attached to the back tension unit
107
.
While being perforated by the thermal head
101
, the stencil sheet S is conveyed only by a driving force of the platen roller
102
holding the sheet on the thermal head
101
. The perforated stencil sheet S is guided downward by the roller
103
to move to a reservoir box
108
. The perforated stencil sheet S is stored in the reservoir box
108
until the perforation by the thermal head
101
finishes.
On completion of perforating, the thermal head
101
moves upward to release the stencil sheet S held on the platen roller
102
. The perforated stencil sheet S is conveyed by the upper and the lower rollers
104
,
105
until a leading end thereof reaches a clamp plate
110
of a printing drum
109
. The leading end of the stencil sheet S is held on the printing drum
109
by the clamp plate
110
. When the printing drum
109
rotates simultaneously with rotation of the upper and the lower rollers
104
,
105
, the stencil sheet S is conveyed and wound around the circumferential surface of the printing drum
109
. After the sheet is wound around the drum, a cutter unit
111
cuts the stencil sheet S.
The present device combines stencil printing function with the stencil making function. A part of the constitution for stencil printing is not illustrated in the drawings. A part of a circumferential wall of the printing drum
109
is ink-permeable. Ink supplying means is disposed inside the printing drum
109
for supplying ink to an inner surface of the circumferential wall. Pressing means is disposed under the printing drum
109
for pressing printing sheet against the printing drum
109
. When the printing drum
109
rotates, the printing sheet is supplied between the printing drum
109
and the pressing means at a predetermined timing, so that the printing sheet is pressed against an image area of the stencil sheet S. The ink supplied to the inner surface of the printing drum
109
passes through the circumferential wall of the printing drum
109
, and then transferred to the printing sheet through perforations of the stencil sheet S to form an image thereon.
According to the conventional stencil making device as illustrated in
FIG. 7
, the back tension unit
107
comprises a silicon oil damper. The rolled stencil sheet S is perforated by a perforating section comprising the platen roller
102
and the thermal head
101
, and conveyed to the downstream side. Then, the back tension unit
107
exerts back tension on the stencil sheet S held between the back tension unit
107
and the perforating section.
The tension changes according to a diameter of the rolled stencil sheet S. The tension is small when the diameter of the rolled stencil sheet S is long, and it increases as the diameter decreases. Torque required to rotate the silicon oil damper for exerting the back tension is constant. A product of the tension exerted on the stencil sheet unrolled from the most outer portion of the rolled stencil sheet and the diameter of the rolled stencil sheet is balanced with torque required to rotate the silicon oil damper. Accordingly, when the diameter of the rolled stencil sheet decreases, the tension exerted on the unrolled stencil sheet increases.
The increased tension exerted on the stencil sheet may cause a slip between the platen roller
102
and the stencil sheet S. If such a slip occurs, the stencil sheet moves in shorter distance than rotational distance of the platen roller
102
. The slip results in shortening the size of the perforated area in the stencil sheet than a predetermined size (a size of an original), thereby causing shrinkage in print-image.
If torque of the silicon oil damper is set at smaller level to lower the tension exerted on the stencil sheet when the diameter of the rolled stencil sheet is shorter, the stencil sheet may wrinkle in perforating when the diameter of the rolled stencil sheet is longer since the tension exerted on the stencil sheet is excessively small.
The present invention is made in view of the aforementioned problems. An object of the present invention is to provide a stencil making device capable of exerting appropriate tension on the stencil sheet S in perforating to avoid wrinkling the stencil sheet.
SUMMARY OF THE INVENTION
A stencil making device as defined in the first aspect of the present invention comprises supporting means for rotatably supporting a rolled stencil sheet, perforating means for perforating the stencil sheet conveyed from the supporting means to form an image therein, a pair of rollers rotatably disposed between the supporting means and the perforating means to hold the stencil sheet therebetween, and torque applying means attached to one of the rollers to apply a predetermined torque to the roller when the roller rotates.
According to a stencil making device as defined in the second aspect of the present invention, in the stencil making device of the first aspect, the torque applying means is a torque limiter.
According to a stencil making device as defined in the third aspect of the present invention, in the stencil making device of the first aspect, the torque applying means is a damper.
According to a stencil making device as defined in the fourth aspect of the present invention, in the stencil making device of the first aspect, the pair of rollers comprises a tension roller rotatably disposed at a predetermined position and a nip roller vertically movably and rotatably disposed over the tension roller, the nip roller is urged downwardly to contact the tension roller, and the torque applying means provides the predetermined torque to the tension roller.
According to a stencil making device as defined in the fifth aspect of the present invention, in the stencil making device of the fourth aspect, the nip roller is urged to the tension roller by its self weight.
According to a stencil making device of the sixth aspect of the present invention, in the stencil making device of the fourth aspect, the stencil making device further comprises an elastic member to elastically urge the nip roller to the tension roller.
According to the aforementioned stencil making device, back tension exerted on the stencil sheet in perforating is constant regardless of the diameter of the rolled stencil sheet. Accordingly, the stencil sheet does not wrinkle in perforating and the size of perforated area in the stencil sheet does not shrink.
REFERENCES:
patent: 3977512 (1976-08-01), Teagarden et al.
patent: 5438347 (1995-08-01), Shishido et al.
patent: 5443556 (1995-08-01), Hasegawa et al.
patent: 5662040 (1997-09-01), Mori et al.
patent: 5694841 (1997-12-01), Sato
patent: 5893324 (1999-04-01), Kimura
patent: 0 841 184 (1998-05-01), None
Kanesaka & Takeuchi
Riso Kagaku Corporation
Yan Ren
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