Printing – Work supporting members – Grippers
Reexamination Certificate
2001-01-24
2002-07-16
Evanisko, Leslie J. (Department: 2854)
Printing
Work supporting members
Grippers
C101S415100, C271S082000, C271S277000
Reexamination Certificate
active
06418849
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a chuck and a fixing device for holding a sheet body in a state in which the sheet body is wound onto a periphery of a rotation body, and to an image recording device.
2. Description of the Related Art
In general, in printing, a photosensitive printing plate (referred to as a printing plate hereinafter) in which a photosensitive layer is formed on a support body formed of a sheet such a thin aluminum plate and the like is used. This printing plate is used as a printing plate for printing after an image is recorded due to exposure, and a development process or the like is carried out.
This type of printing plate includes one in which, in the image exposure device for carrying out image exposure, the printing plate is wound onto a rotation drum and held, then while the rotation drum is rotated at a high speed, a light beam is radiated onto the printing plate in accordance with the image data for recording on the printing plate, to thereby scan-expose the printing plate.
Image exposure devices in which a rotation drum is used to expose the printing plate include a type which uses a fixing device which, when the printing plate is wound onto the rotation drum, clamps the non-image portions of both ends of the printing plate which are along a circumferential direction of the rotation drum, between the drum and itself. In this type of a fixing device, the printing plate, generally, the clamp portion which opposes the printing plate is urged in the circumferential direction of the rotation drum by an urging force, and the printing plate is thereby nipped between the clamp portion and the rotation drum.
In this case, by the clamp portion being fit into a plurality of grooves which are provided in the circumferential direction of the rotation drum, the grooves serve as support points and the clamp portion is fixed to the rotation drum.
However, when the rotation drum is rotated at a high speed in a state in which a sheet body such as a printing plate is wound onto the rotation drum, a centrifugal force is exerted on the clamp portion causing the holding force to decrease.
It may be thought that if the number of support points is increased, the clamp portion will be firmly held onto the rotation drum, but if the number of support points is increased, the number of grooves on the rotation drum also has to be increased. If maintaining the continuity of a surface such that there are no uneven portions when winding the printing plate onto the peripheral surface of the drum is considered, the number of grooves that can be formed is limited. Thus, it becomes necessary to form a clamp that is formed of a material having high rigidity.
As a result of this, the weight is increased, and due to increase in the rotational torque, it becomes necessary to increase the driving force of the clamp. It also becomes necessary to increase the durability and the like of the support structure and this causes obstruction in other sections. It is therefore not preferable that the clamp be formed of a material having high rigidity.
In view of the above, the object of the present invention is to provide a sheet body fixing device in which when a sheet body such as a printing plate or the like is wound onto a rotation drum, the sheet body is securely fixed to the rotation drum and the coming up of the sheet off the drum surface after the fixing is kept at a minimum.
SUMMARY OF THE INVENTION
The invention according to a first aspect of the present invention is a sheet fixing device for holding a sheet in a state in which the sheet is wound around a peripheral surface of a rotation drum, the sheet fixing device comprising:
a clamp portion disposed along an axial direction at one portion of the peripheral surface of the rotation drum, at least one of a leading end portion and a trailing end portion of the sheet being nipped between the clamp portion and the peripheral surface of the rotation drum; and
a fixing element which fixes the clamp portion to the peripheral surface of the rotation drum at a plurality of support points along an axial direction of the rotation drum,
wherein when the clamp portion is fixed to the rotation drum by the fixing element, if the pitches between the support points at which the clamp portion is fixed to the rotation drum are L
1
(
1
) . . . L
1
(n) where n is an integer not less than 1, and the pitches between both end portions of the clamp portion and supports closest to the both end portions thereof are L
2
(
1
) and L
2
(
2
), then L
1
(
1
) . . . L
1
(n) and L
2
(
1
)and L
2
(
2
) are set so that the maximum deformation amounts &Dgr; L
1
(
1
) . . . &Dgr;
0
L
1
(n) and &Dgr; L
2
(
1
) and &Dgr; L
2
(
2
) for the respective pitches during the rotation of the drum are substantially equal.
In the invention according to the first aspect and a second aspect of the present invention, when the rotation drum is rotated in a state in which a sheet is clamped by the clamp portion, due to a so-called centrifugal force being exerted, a force operates which causes the clamp portion to tend to come up off the surface of the rotation drum. In this case, because the supports are firmly fixed to the surface of the rotation drum, the deformation amount is insignificant, and the maximum amount of deformation is at the center of the length between the support points and is an arch-shaped deformation.
On the other hand, deformation of the length between the support points closest to the end portions and said end portions differ from the deformation of the length between the support points.
Even if deformation cannot be totally eliminated, extreme deformation of one portion in the longitudinal direction of the clamp portion (the axial direction of the rotation drum) can be avoided, and one side of the sheet (for example, the leading side) is thereby held by a substantially uniform nipping force. Thus, the coming up of the sheet from off the surface of the drum can be controlled.
In the first aspect of the present invention, as a means for avoiding extreme deformation of one portion, given that the pitches between the support points at which the clamp portion is fixed to the rotation drum are L
1
(
1
) . . . L
1
(n) where n is an integer not less than 1, and the pitches between both end portions of the clamp portion and support points closest to the both end portions is L
2
(
1
) . . . L
2
(
2
), then L
1
(
1
) . . . L
1
(n) and L
2
(
1
) and L
2
(
2
) are set so that the maximum deformation amounts &Dgr;L
1
(
1
) . . . &Dgr;L
1
(n) and &Dgr;L
2
(
1
) and &Dgr;L
2
(
2
) for the respective pitches during the rotation of the drum are substantially equal.
Further, the second aspect of the present invention is the invention according to the first aspect of the present invention, wherein L(
1
) . . . L
1
(n) are all set to be substantially equal to L
1
, and L
2
(
1
) and L
2
(
2
) for both end portions are set to be substantially equal to L
2
, and one of L
1
and L
2
is set, with the other of L
1
and L
2
as a reference, such that a deformation amount &Dgr;L
1
of L
1
and deformation amount &Dgr;L
2
of L
2
are substantially equal.
As a result, the deformation amounts &Dgr;L
1
between the support points are made substantially equal, and in order for &Dgr;L
1
, as well as the deformation amount &Dgr;L
2
which occurs between a support point and one end portion (L
2
) to be made substantially the same, one of L
1
and L
2
is set with the other of the two as a reference. That is, even for clamps having the same amount of support points, by causing the relationship between L
1
and L
2
to be fixed, the maximum deformation amount is reduced.
The invention according to a third aspect of the present invention is the invention according to the second aspect of the present invention, wherein a dimension L
2
between a support point and an end portion, is set by using a dimension L
1
between support points, as a reference.
According to the third aspect of the present invention, by first setting L
1
Evanisko Leslie J.
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
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