Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TENSIONLESS PLATE_LOCK-LIP
The present invention relates to offset lithographic presses and more
particularly to lock-up mechanisms for holding the thin, flexible litho
plates to the surface of the plate roll.
eack~round of the Invention
The art of printing by offset lithography involves the use of thin,
flexible plates which are basically planographic, that is without relief,
and which are treated so that the surfaces have areas which attract or
repel oil and water to create areas of image differentiation. To mount
the litho plates on the surface of the press plate rolls, it is essential
to insure that the plate conforms closely to the outer surface of the
plate roll. Mounting is usually effected by forming a longitudinal slot
in the plate roll and inserting thereinto one of a variety of biasing or
clamping devices called lockups. Often the leading edge of the plate is
bent back on itself so that the bent portion can fit over the edge formed
in the roll by the longitudlnal slot and then be held in position by some
form of spring or clamp. Alternatively, mechanisms have been provided in
which the plate leading edge has been rigidly clamped.
An example of the type of plate lock-up mechanism in which the
leading edge of the plate is clamped can be seen by referring to U.S.
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Patent 4,421,024. In this arrangemerlt, the plate leading end portion E is
held between two parts S and 6 which are of an approxi~ate trapezoidal
shape. The two parts 5 and 6 are urged inwardly to clamp the end of the
plate within slot 3 by means of the spring 8. The trailing end of the
plate, which is identified by the letter A, is held between the sloped
surface of part 6 and the similarly sloped wall 10 of slot 3.
Another example of a plate lock-up is seen in U.5. Patent 3,757,691
where the leading edge of plate 11 is held by one leaf of a spring member
16 while the trailing edge of plate 11 is held by another finger of the
spring member 16. An elongated cam 18 is used to change the spring
pressure exerted against the plate for purposes of unlocking and locking
the plate in and from operating position, respectively.
A plate lock-up mechanism which is somewhat related to that of Patent
3,757,691 is Patent 3,626,848 where a spring member is used to hold down
the leading edge of plate 11 around the undercut side of the slot and cam
40 is used to urge the hook 35 against the trailing end 13. Examples of
other plate lock up mechanisms may be found in Patents 3,608,847 and
3,095,811.
_mm~ of the_Invention
It is a principal object of this invention to provide an improved
plate lock-up mechanism in which both the leading and trailing edges of
the plate are held securely in position during operation.
An additional object of this invention is to provide a printing plate
lock-up mechanism which the plate can be installed on the plate roll and
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removed therefrom without the necessity of having installation
or removal equipment.
An additional object of this invention is to provide
S a plate lock-up mechanism in which the width of the plate gap
is held to a minimum.
~ further object of this invention i.s to provide an
improved plate lock-up mechanism which can be adapted for use
with plate rolls having longitudinal slots that were
structured for use with previously existing plate lock-up
mechanisms.
An embodiment of the invention is, in comhination a
printing cylinder in a printing press having a longitudinal
slot formed in an outer surface thereof to define at least one
undercut surface against which both ends of a flexible
printing plate are clamped to hold the plate securely against
the outer surface of the cylinder; locki.ng apparatus
including a plurality of individual cylinders substantially
evenly spaced along the length of the longitudinal slot;
individual spring biasing apparatus disposed in operative
compression between the bottom of the longitudinal slot and a
spring receivi.ng opening in each of the cylinders to urge
individually each of the cylinders outwardly against the
overlapping ends of the plate and hold them against the
undercut surface; and spacer apparatus secured to the bottom
of the longitudinal slot, the spacer apparatus including a bar
extending along the length of the slot, the bar including a
B
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plurality of evenly spaced protruding studs which receive the
individual spring biasing apparatus to hold the spring biasing
apparatus at fixed locations; the spring biasing apparatus
extending from the base of the studs to beyond the
longitudinal extent of the studs and to the full depth of the
spring receiving opening.
These and additional objects and advantages of this
invention will be in part obvious and in part explained by
reference to the accompanying specification and drawings, in
which:
Fig. 1 is a partial cross-sectional view through an
improved plate lock-up mechanism in which the plate lock-up
gap is held to a minimum;
IS Fig. 2 is a partial plan elevation of the lock-up of
Fig. l;
Fig. 3 is a cross sectional view similar to Fig. 1
showing a modified form of plate lock-up; and
Fig. 4 is a cross-sectional view similar to those of
0 Figs. 1 and 3 showing yet another modified plate lock-up.
_escription of the Preferred Embodiment
In order to more clearly understand the present
invention, reference is made to the drawings and more
particularly to Fig. 1. In this figure, numeral lQ indicates
2s a section through a portion of a plate roll upon which a plate
11 disposed. The plate roll 10 is formed with longitudinal
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groove 12 in its outer surface 13, the longitudina1 slot extending all the
way across the width of the plate roll.
Longitudinal slot 12 is shown as being undercut to define a pair of
opposed surfaces 15 which provide locking surfaces against which both the
leading and the trailing ends of plate 11 can be abutted. From the slot
inwardly, the substantially flat or planar clamping surfaces 15 terminate
in a curved wall, the shape being of no particular significance, since the
shape is largely dictated by the machining operation selected for forming
the slot.
In Fig. 1 it can be seen that the leading edge 20 of plate 11 has
been folded back at an acute angle to the plate (and to the surface of the
roll) so that it fits over the nose portion 21 of the roll 10. The
trailing edge 22 is not, unlike the leading edge~ bent back on itself but
rather extends over the opening of longitudinal slot 12 so that it is in
abutment with the innermost surface of leading edge 20.
The leading and trailing edges 20 and 22 are held against each other
and against one of the clamping surfaces 15, by the locking means 2S~
Each locking means has a curved outer surface 26 for contacting the ends
of the flexible plate and clamping them against the locking surface lS.
It will be noted that the radius of curvature of each of the locking
elements 25 is such that the contact between the curved outer surface with
the substantially planar surface 15 is one of basically line contact, so
that firm contact is made with the surface of the printing plate. By
having line as opposed to areal contact with the plate, insertion and
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removal of the plate ends from locking engagement are made easier than
would otherwise be the case.
As can be seen by referring to Fig. 2 of the drawings, the locking
means 25 are spaced at substantially equal intervals along the length of
the longitudinal slot 12 across the width of plate roll 10. It will be
appreciated by consideration of Figs. 1 and 2 together that, in the
structure shown, each of the locking elements 25 is substantially
cylindrical in shape.
In order to dispose the elements 25 at proper intervals along the
length of slot 12 and to urge them outwardly against the clamping surfaces
15, a spacer bar 30 is disposed witnin the slot. This bar has a plurality
of upwardly and outwardly extending mounting posts or spacing studs 31
each of which is surrounded by a compression spring 32. In order that the
locking elements 25 be urged outwardly and retained in position, the
bottom part of each of the elements 25 contains a cylindrical bore 33 for
reception of the upper end of a spring 32. By thls combination of stud 31
and opening 33, it is possible for the springs 32 to retain each element
25 in a predetermined or preselected location while urging the locking
element 25 curved outer surface toward engagement with a planar surface 15.
Utilizing the configuration shown in Fig. 1, where longitudinal slot
12 is formed with two undercut interlocking surfaces 15, it is possible
for the plate roll to be utilized for rotation in either a clockwise or a
counter-clockwise direction. In either case, the lock-up is performed in
the manner shown in Fig. 1, although two ends would be located on the
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right hand side of locking element 25 in case rotation in the opposite
direction were desired. In order to lock up a plate, it is necessary only
to depress the locking elements 2~ slightly by inserting the leading end
20 into the longitudinal slot. The plate is then wrapped all the way
around the roll and the trailing edge inserted into the slot so that it
rides down against the inner sur-face of leading edge 20 to arrive at the
assembled and locked position illustrated in the drawings. With this
particular configuration, it will be appreciated that upon rotation of the
plate roll against the blanket cylinder, there tends to be a flattening
and ironillg out of the plate so that it is urged tightly against the outer
surface 13 of the plate roll. The slight elongation that often occurs in
the plate then pushes the end further into the region between locking
element 25 and locking surface 15 to hold the plate in tight operating
relationship.
An important feature of the present lock-up is its ability for use in
longitudinal slots that have been used in existing plate rolls ln the
field. Figs. 3 and 4 illustrate the manner in which this can be
effected. Referring first to Fig. 3, it will be seen that the slot 35 has
been formed with only one undercut surface 36 while the other side wall of
the slot is essentially vertical. In thls case, there is shown a spacer
bar mechanism 38 that is secured into a small secondary recess by means of
a bolt 39. The use and positioning of such spacer bars is common in the
art and does not form part of this invention. In this configuration, the
generally cylindrical locking element 4~ corresponds to the locking
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element 25 of Fig. 1 and it is urged outwardly by means of compression
springs 41. In the configuration of Fig. 3, the bottom part of spring 41
is received into an appropriately formed recess 42 in the bottom of slot
33 while the upper end of spring 41 is received into a recess formed in
the bottom part of a vertically movable spacer 43. The spacer 43 is
formed with a generally arcuately formed receptacle-like surface 44 into
which the locking element 40 can be received. It should be pointed out
that the spacing element 43 contains an integrally formed wall 45 on each
end which acts to define the lateral limits of the arcuate surface 44 and
prevent locking element 40 from moving laterally in the general direction
of the length of longitudinal slot 33.
Turning now to the modification shown in Fig. 4 of the drawings,
common numbers are used to illustrate the parts that are in common with
the locking mechanism defined in Fig. 3 of the drawings. In the case of
Fig. 4, it will be obvious that the slot 35 is of a totally different
configuration than that of the slots found in Figs. 1 and 3. In this
case, the bottom of the slot is provided with cup-shaped inserts 46 which
will act to receive the lower ends of springs 41 in the same manner as do
the openings provided in the configuration of Fig. 3. Since slot 35 is
larger than that of Fig. 3, filler means 52 is mounted along one side of
the slot and held in position by means of threaded elements 53 so that one
of the undercut surfaces 15 acts to isolate the 10cking element 25 from
the adjoining undercut surface. By utilizing the spacing element, the
operation of the lock-up becomes identical to that of Fig. 3 of the
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drawings. It should be pointed out that in the cases of the lock-up shown
in Figs. 3 and 4, the plate roll 10 can be used in rotation only in one
direction since it is not possible to have the leading edge locked on the
right half of the device as seen in these Figures.
