Printing – Flexible-sheet-securing devices
Reexamination Certificate
2002-02-06
2003-12-30
Evanisko, Leslie J. (Department: 2854)
Printing
Flexible-sheet-securing devices
C101S378000, C101S409000, C271S277000
Reexamination Certificate
active
06668722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet member holding apparatus wherein a pair of arms, which extend in opposite peripheral directions from a fulcrum attached to a part of a peripheral surface of a rotary body, are pivoted about the fulcrum by a centrifugal force generated by rotation of the rotary body, one of the arms approaches the peripheral surface of the rotary body, and a sheet member wound around the peripheral surface of the rotary body is held by a clamp section attached to the one of the arms.
2. Description of the Related Art
For printing, a photosensitive printing plate (hereinafter, “printing plate”), in which a photosensitive layer is formed on a sheet-type supporting body such as a thin plate made of aluminum, is generally used. As such printing plates, printing plates having different longitudinal and breadthwise dimensions according to printing size are used.
An image exposure apparatus for performing image exposure on a printing plate includes an apparatus which winds a printing plate around a rotary drum and then emits a light beam based on image data to the printing plate while rotating the printing plate integrally with the rotary drum, so as to scan-expose the printing plate.
When the printing plate is wound around the rotary drum, the printing plate is nipped and fixed to the rotary drum by holding apparatuses (chucks) for clamping both ends, in the peripheral direction of the rotary drum, of the printing plate (nipping the plate between the chucks and the peripheral surface of the rotary drum).
That is, a holding apparatus corresponding to one end of the printing plate along the drum peripheral direction (for example, the end at a winding front end side) is attached to a predetermined position of the rotary drum, and, after the printing plate has been wound around the rotary drum, a holding apparatus corresponding to the other end of the printing plate (here, the end at a winding rear end) is attached to a position according to the size of the printing plate.
Here, the holding apparatus for attaching the printing plate to the rotary drum at the position according to the size has a fixing barrel (stanchion) which can be inserted into an arbitrary position of an attachment groove which is formed along the peripheral direction in the peripheral surface of the rotary drum. The fixing barrel attached to the holding apparatus is freely movable relative to the attachment groove and can nip the ends of printing plates having various sizes in suitable positions.
When the printing plate wound around the rotary drum is to be exposed, the printing plate is closely contacted with the peripheral surface of the rotary drum and rotated at high speed together with the rotary drum.
At this time, in order to prevent lifting of the end of the printing plate fixed by the clamp section of the holding apparatus due to centrifugal force, a structure in which the centrifugal force is utilized to instead increase holding force of the clamp section has been suggested (for example, see Japanese Patent Application Laid-Open No. 2000-112142).
In this publication (of the prior art), because force is applied by the centrifugal force to portions to be held, a ratio of lengths from a fulcrum to the ends of a seesaw-type arm (a mechanism where a center portion is the fulcrum and the arm pivots about the fulcrum) is prescribed, and a strong holding force is applied at a distal end of the arm at a clamp section side thereof. In this prior art, a combined structure in which the sheet material is adsorbed to the rotary drum when wound around the rotary drum is also used.
However, in the above prior art, holding of the sheet material is mainly due to the adsorption, and holding reinforcement due to the centrifugal force is utilized supplementarily. Moreover, the publication discloses only prescription of the lengths of the arms and simply describes the well-known law of moment. Therefore, a position of the center of gravity in the holding apparatus, a coefficient of friction between the holding apparatus and the sheet material at the time of holding the sheet material, a coefficient of friction between the sheet material and the rotary drum, and the like are not taken into consideration.
However, in a case where the sheet material is not adsorbed to the rotary drum, the above coefficients of friction and the like can be important conditions, and the centrifugal force cannot be utilized effectively merely by prescribing the lengths of the arms.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus which utilizes centrifugal force effectively so as to be capable of holding a sheet member securely.
There will now be explained a first principle with reference to a model shown in
FIGS. 1A and 1B
.
FIG. 1A
shows a state in which a sheet member
202
is wound around a peripheral surface of a rotary body
200
. A radius of the rotary body
200
is r, a thicknesswise dimension of the sheet member
202
is t, and density of material of the sheet member
202
is c.
A holding apparatus
204
of the present invention is provided at an end of the sheet member
202
, and a pair of arms
208
and
210
are provided extending from a fulcrum
206
in opposite directions along a peripheral direction of the rotary body
200
. A first of the arms
208
(left of the fulcrum
206
in
FIG. 1A
) is pivoted on the fulcrum
206
by centrifugal force generated at a time of rotation of the rotary body
200
so as to approach the peripheral surface of the rotary drum
200
, and the sheet member
202
is consequently pressed by a clamp section
212
. As a result, the sheet member
202
is nipped and held between the peripheral surface of the rotary body
200
and the clamp section
212
.
There is a coefficient of friction &mgr;
1
between the clamp section
212
and the sheet member
202
, and a coefficient of friction &mgr;
2
between the sheet member
202
and the rotary body
200
.
FIG. 1B
is an enlarged diagram of the holding apparatus
204
of the present invention.
Length of the first arm
208
(from the fulcrum
206
to the clamp section
212
) is L
1
, length of the second arm
210
(from the fulcrum
206
to a center of gravity
214
) is L
2
, and a unit weight of the center of gravity (weight per unit length of the arm in an axial direction of the rotary body) is m.
Here, when the rotary body
200
rotates, a centrifugal force m×r×&ohgr;
2
is applied at the center of gravity
214
in an upward direction of FIG.
1
B. Here, &ohgr; is angular velocity.
This centrifugal force effects a holding force at the clamp section
212
of the first arm
208
to the sheet member
202
, and when a ratio of the lengths of the first arm
208
and the second arm
210
is taken into consideration, theoretically, the sheet member
202
is nipped by a force of (L
2
/L
1
)×m×r×&ohgr;
2
.
Further, because the coefficients of friction &mgr;
1
and &mgr;
2
are effective at the clamp section
212
, when the coefficients of friction &mgr;
1
and &mgr;
2
are combined, the holding force of the clamp section
212
generated by the rotation of the rotary body
200
can be represented by the following expression.
(&mgr;
1
+&mgr;
2
)×(L
2
/L
1
)×m×r×&ohgr;
2
On the other hand, as a force which acts at the sheet member
202
during the rotation of the rotary body
200
, a force due to the centrifugal force and acting to pull the sheet member out of the clamp section
212
may be considered. This force can be represented by the density c and thicknesswise dimension t of the sheet member
202
, and the radius r and angular velocity &ohgr; of the rotary body
200
in the following expression.
c×r
2
×t×&ohgr;
2
In order to hold the sheet member
202
securely by the clamp section
212
, the following relationship must hold:
(&mgr;
1
+&mgr;
2
)×(
L
2
/L
1
)×
m×r×&ohgr;
2
>c×r
2
×t×&ohgr;
2
When common denominators (r and &oh
Evanisko Leslie J.
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
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