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In the applicant's own prior U.S. Pat. No. 3,749,011, which issued July 31,
1973, there is disclosed a dampening system including a fountain roller,
intermediate roller, distributor roller and form roller in which the form
and intermediate rollers are mounted upon separate levers for control of
throw-off by separate actuators. It is found that as a result of lack of
coordination of the two throw-off mechanisms it is possible to have either
too much or too little dampening fluid on the form roller when it is
reapplied to the plate. Thus, where the second actuator is delayed
following throw-off of the first, it is possible for excess water to be
built up on the distributor roller resulting in the possibility of
flooding of the plate with water when the form roller is prompltly
reapplied. Conversely, after a long period of throw off, during which the
dampening fluid has evaporated from the rollers, any delay in restoring
the second actuator to working position after the first, runs risk that
the form roller may be in substantially dry condition when it is applied
to the plate, resulting in undesired pick-up of ink from the plate and
tending to degrade the function of the form roller when the regular water
flow is finally re-established. Coordinating the operation of the
throw-off levers under all possible conditions has required a large amount
of manipulative skill.
Moreover, adjusting means are provided in the prior patent for adjusting
the degree of engagement of the various rollers in the system, but such
adjusting mechanism has been found to be relatively expensive and
unnecessarily complex. Finally, it is found that residual moisture on the
surfaces of the rollers during throw-off tends to contract into droplets
which show up in the subsequently printed product.
It is, accordingly, an object of the present invention to provide an
improved system of the above type which is relatively simple and foolproof
in operation employing a single actuator for pressure-disengagement of all
of the rollers in a predetermined throw-off sequence and for restoring the
rollers to working position in converse sequence, with each sequence being
accomplished automatically and out of the press operator's control so that
each roller, upon being backed-off from the remaining rollers and
subsequently re-engaged has deposited thereon precisely the right amount
of water with the form roller neither in flooding or starving condition at
the time it is re-applied to the plate. It is a more specific object to
provie a dampening system which is capable of immediately re-establishing
moisture conditions for optimum printing regardless of whether the period
of throw-off is short or long. Thus, in the case of momentary throw-off
the amount of moisture left on the individual rollers as they are
thrown-off in sequence corresponds substantially to the running condition
so that when the running condition is re-established promptly the
dampening system can take up where it left off. However, under conditions
where the period of throw-off has been so long as to permit evaporation of
the moisture from the rollers, the sequencing of roller re-engagement is
such that the water path is completed through the rollers starting at the
fountain roller, with the form roller engaging the plate as a last step,
thereby to insure that the form roller will be rewetted to the proper
degree before being applied to the plate.
Thus, stated in other terms, it is an object of the invention to provide a
dampening system in which the form roller and intermediate roller are
mounted upon separte throw-off levers with the intermediate roller
throw-off lever being effectively in the path of final movement of the
form roller throw-off lever, thereby insuring that intermediate roller
throw-off occurs last during the throw-off movement and first during
restoration.
It is another object of the invention to provide a dampening system which
includes a biasing spring for biasing of the rollers into working position
and which includes a single power actuator for the throw-off, the biasing
spring being so arranged that the reaction force thereof following
throw-off need not be resisted by the actuator, permitting use of an
actuator of the type which is capable of generating only momentary thrust
for throwing into the opposite condition.
It is yet another object of the present invention, in its preferred form,
to provide a dampening system including fountain, intermediate,
distributor and form rollers in which, under the condition of throw-off,
pressureless "kissing" contact is retained between the intermediate
roller, and the fountain roller and between the distributor roller and the
form roller, to insure that residual moisture on the surfaces of the
rollers does not contract into droplets affecting the quality of the
printed product.
Other objects and advantages of the invention will become apparent upon
reading the attached detailed description and upon reference to the
drawings, in which:
FIG. 1 is an elevational view of a dampening system constructed in
accordance with the present invention, partly diagrammatic, and with the
parts in normal working position;
FIG. 2 is a view similar to FIG. 1 but showing the dampening mechanism in
the condition of throw-off;
FIG. 3 is a stop motion view showing engagement of the intermediate roller
with the fountain roller and distributor roller during the initial portion
of the restoration stroke of the actuator;
FIG. 4 is a further stop motion view taken a brief moment following that of
FIG. 3 and showing the form roller in contact with the distributor roller
for rewetting of the form roller prior to contact of the form roller with
the plate.
While the invention has been described in connection with a preferred
embodiment, it will be understood that we do not intend to be limited to
the embodiment shown but intend, on the contrary, to cover the various
alternative and equivalent constructions included within the spirit and
scope of the appended claims.
Turning now to FIG. 1, there is disclosed a dampening system, or mechanism,
10 for the purpose of applying a film of water or equivalent dampening
fluid to a lithographic plate 11 secured to plate cylinder 12. The
dampening mechanism includes a series of rollers supported between a pair
of frame plates 15. In the base of the frame is a trough or fountain 20
which may, for example, contain a charge of water and alcohol. Dipping
into the fountain is a fountain roller 21 having a shaft 22 which is
journaled in the frame 15 and which has a connection 23 to a separate
adjustable slow speed drive 24 which may, for example, consist of an
electric motor with a step-down drive train plus means for adjusting the
motor speed, a matter well known in the art. The fountain roller 21 is
conventionally formed of metal or other hard surfaced material.
Running in engagement with the fountain roller 21 is an intermediate roller
25 having a shaft 26, the intermediate roller, in accordance with
conventional practice, being resiliently surfaced. The intermediate roller
25, in turn, engages a distributor roller 31 having a shaft 32 which is
fixedly journaled in the frame. The distributor roller 31 is hard surfaced
and has a rotary drive connection 33 to the press drive 34. The
distributor roller 31, in addition to being driven positively at "press
speed", preferably has an associated "vibrating" mechanism (not shown) for
periodic reciprocation thereby to improve the distribution of the moisture
in the longitudinal direction.
The distributor roller, in turn, is in rolling engagement with a water form
roller 35 which is resiliently surfaced and which, finally, applies the
film of water to the plate 11. The means for applying a corresponding film
of ink to the plate will be understood to be conventional and therefore
has not been shown.
In operation, the form roller 35, which is freely rotatable, is rotated at
"press speed" by the surface of the distributor roller 31 and by
engagement with the printing plate 11. The intermediate roller 25 is also
freely rotatable and is driven at "press speed" by the distributor roller.
The fountain roller 21 is driven by its drive 24 at a slower speed
resulting in slippage between the rollers 21, 25, the degree of slippage
being inversely related to the rate at which water is fed from the
fountain.
In accordance with the present invention, the form roller 35 and the
intermediate roller 25 are mounted on respective throw-off levers for
broadwise swinging movement from the pressurized working condition, which
is illustrated in FIG. 1, and the throw-off condition, which is
illustrated in FIG. 2, in which all of the rollers are out of pressure
engagement, with rollers 25 and 31 being completely separated from one
another and with the form roller being out of contact with the printing
plate, the form roller throw-off lever being operated by a single actuator
between its respective positions and the intermediate roller throw-off
lever being effectively in the path of final movement of the form roller
throw-off lever for actuation by the latter in predetermined sequence.
Thus, referring to FIG. 1, the form roller 35, having a shaft 36, is
mounted upon a rockable lever 40 having a first arm 41 which carries the
roller 35 and a second or actuating arm 42 which is connected to a
pneumatic or equivalent actuator 43 having a plunger 44. The lever 40
rocks about an axis 45 centered within a rockable mounting ring 46 which
is journaled, as indicated, in the frame 15. The working position of the
form roller 35, and consequently the amount of pressure which is applied
to the printing plate, is determined by the adjustment of a stop screw 47
which threadedly engages the frame and the tip of which engages a stop
surface 48 on the arm 41 of the lever.
For the purpose of fine adjustment of the pressure of roller 35 with
respect to the distributor roller 31 and plate 11, an eccentric bushing 50
having shallow eccentricity is interposed between the mounting ring 46 and
lever 40, the phase of the eccentric bushing being determined by a worm
wheel adjustment including a worm 51 having an adjusting knob 52.
For the purpose of supporting the intermediate roller 25 between respective
throw-off and working positions, a second throw-off lever 60 is provided
which is arranged in the effective path of movement of the throw-off lever
40 and subject only to the final portion of movement of the latter in the
direction of throw-off. The lever 60 is swingable about a shaft 61 at its
upper end journaled in the frame 15. The lower end 62 is engaged by a
biasing spring 63 which urges the lever 60 clockwise into working
position, with the spring force being established by the setting of an
adjusting screw 64 which is interposed between the spring and the frame of
the device. An adjustable stop in the form of a screw 65, which engages a
stop surface 66 on the lever, determines the running position of the
roller 25 with respect to the roller 31. Fine adjustment of the roller
position is determined by an eccentric bushing 70 which is interposed
between the lever 60 and the shaft 61 upon which it is mounted, the
phasing of bushing being determined by an adjustable worm 71 under the
control of an adjusting knob 72.
For swinging the lever 60 clockwise only during the final portion of the
throw-off movement of the lever 40, a cam 80 is interposed between those
two members, being secured to the right-hand edge of the lever 40 and
engaging a stop or abutting surface 81 on the lever 60. It is one of the
features of the invention, as illustrated in FIG. 2, that under the
condition of throw-off the line of action of the reaction force F between
the levers originating in the biasing spring 63 is directed along a line
82 which intersects the axis of rotation 45 of the lever 40. Since the
reaction force intersects the lever axis it does not have any moment arm
with respect to the lever 40 and the reaction force does not, therefore,
have to be resisted by the power actuator 43 during conditions of
throw-off. Thus, where the actuator 43 is of the pneumatic type and where
a leak may exist in the line, the biasing spring 63 will not have the
effect of constantly urging the actuator in the direction of its working
position. This makes it possible to use an actuator of the type which
applies only a momentary thrust to achieve throw-over between its
respective end positions.
The operating sequence during a typical throw-off cycle may be reviewed as
follows: The mechanism, initially, will be understood to be in the
condition of FIG. 1, with a film of water being fed through the series of
rollers to the surface of the printing plate. When throw-off is desired,
either momentary or for extended shut down, the actuator 43 is energized
in the direction to retract the rod 44, thereby rocking the throw-off
lever 40 clockwise about its axis 45. During the initial portion ot the
movement, separation will immediately take place between the form roller
and the plate. Contact between the form roller and the distributor roller
31 may persist just long enough for the form roller to undergo one or more
revolutions to establish an optimum film on the surface of the form roller
following which the form roller disengages itself from the surface of the
distributor roller 31, such disengagement coming about by the fact that
the center of rocking movement 45 of the lever 40 is spaced from the fixed
center of rotation of the distributor roller, that is, the center of shaft
32.
The rocking movement of throw-off lever 40 mentioned thus far has had no
effect upon the throw-off lever 60. However, during the final portion of
the clockwise movement of the lever 40, the cam 80 thereon engages the
cooperating surface 81 at the edge of the lever 60, causing the latter to
rock counterclockwise through a small angle against the restoring force of
the spring 63. The initial portion of throw-off movement of the lever 60
causes the intermediate roller 25 to disengage itself from the distributor
roller 31, leaving the latter with an adequate film of water. As the final
event of throw-off, the intermediate roller 25 is wipingly moved out of
engagement with respect to the fountain roller 21, the intermediate roller
receiving an adequate film of water, before final disengagement. As a
result, all of the rollers may be separated from one another and charged
with a film of water of optimum thickness. It will be assumed that the
distributor roller 31 continues to operate at "press speed" and that the
fountain roller 21 continues to be driven by its drive 24.
Thus, where the rollers are restored to the working condition of FIG. 1
after only a brief period of throw-off, and before substantial evaporation
has taken place, all of the rollers will be in moisture transmitting
condition to take up the furnishing of water to the plate where they left
off and free of any possibility of flooding.
It is to be noted that the charging of the individual rollers with water
incident to throw-off and the re-engagement of the rollers in water
transmitting relation is brought about automatically by a single
energization and de-energization of the actuator 43 without care or
attention on the part of the operator. This is to be distinguished from
the prior patent mentioned above which requires separate actuators for
separate portions of the rollers in the water train, which actuators must
be operated, with exercise of skill, in a coordinated fashion.
It is one of the features of the present invention that an assured film of
water exists on the form roller 35 at the time that the form roller is
brought into contact with the plate regardless of the length of the period
of throw-off and even where the water on the rollers has completely
evaporated. This will be made clear upon considering the stop motion
views, FIGS. 3 and 4. FIG. 3 shows the condition of the rollers a moment
after the actuator 43 has been energized in a direction to restore the
working condition, that is, energized in a direction to impart
counterclockwise movement to the throw-off lever 40. The initial portion
of the movement releases the throw off lever 60, allowing the intermediate
roller 25 first to come into pressure contact with the fountain roller 21
and then into seated contact with the distributor roller 31, with the
final position being determined by the setting of the stop 65. This
completes a water feed path from the fountain roller 21 to the distributor
roller 31, causing the latter to be wetted to the proper degree.
Shortly thereafter, as the plunger 44 of the actuator continues its outward
movement, the distributor roller 31, with a film freshly formed thereon,
is pressed into the surface of the form roller 35, with the two undergoing
one or more revolutions together for re-formation of the film on the form
roller prior to engagement with the plate, which is the condition
illustrated in FIG. 4.
The final portion of the outward movement of the actuator plunger results
in the seating of the form roller 35, with its proper degree of moisture,
and prerotated by the distributor roller 31, into contact with the surface
of the printing plate 11. The above sequence, as stated, assures that the
form roller 35 is wetted to proper degree, avoiding either flooding or
dryness, and pre-rotated, as it is brought into its working relation to
the plate, the condition which is shown in FIG. 1.
While the timing and sequence of breaking of contact during the throw-off
stroke, and the timing and sequence of engagement, is automatically
determined by a simple triggering of a power actuator 43 in one direction
or the other, it will be understood that the present invention is not
limited to use of a power actuator and manual means, for example a single
handle coupled to the lever 40, may, if desired, be used; accordingly, the
term "actuator" is not limited to a powered device. However, where manual
actuation is used the operator should be instructed to swing the lever 40
smartly and consistently between its end positions, in imitation of a
powered device, in order to insure the precise timing which has been
described.
While it is one of the features of the present mechanism that the throw-off
lever 60 is located in the path of final movement of the throw-off lever
40, it will be understood that what is referred to its the "effective"
path of final movement. It will be understood, for example, that the cam
80, instead of directly engaging the lever 60, may, and normally will,
engage a cam follower secured thereto. It will be further understood that
the illustrated levers and associated elements will be repeated at both
sides of the frame.
Comparing the above mechanism with that shown in, say, FIG. 1 of the prior
patent it is apparent that a large degree of simplification and economy
have been achieved accompanied by precise and automatic sequencing which
achieves the proper water feed conditions regardless of whether throw-off
is momentary or for an extended period of time upon simple triggering of
the actuator and without exercise of care or skill on the part of the
operator.
For the sake of easy understanding it has been temporarily assumed in the
above discussion that the rollers are thrown between a pressurized
"working" condition in which each roller exerts pressure against its
neighbor and an alternate throw-off condition in which each roller is
separated from its neighbor. However, it is one of the features of the
present invention, in its preferred aspect, that under the throw-off
condition pressure is relieved at the engaged surfaces of all of the
rollers but all of the rollers are not moved out of touching contact with
one another. More specifically, and as shown in FIG. 2, the form roller 35
is completely disengaged from the plate by a rather wide spacing and the
intermediate roller 25 is physically separated, and spaced from, the
cooperating distributor roller 31. However, light "kissing" contact is
permitted to occur between the form roller 35 and distributor roller 31 on
the one hand and between the intermediate roller 25 and the fountain
roller 21 on the other hand. By "kissing" contact is meant that the
pressure between the rollers is reduced, by relative shifting of the
roller centers, to an extremely low value, a value which is sufficient to
cause the pairs of rollers to rotate idly together free of any indenting
effect. That is, under the preferred condition of throw-off, the form
roller 35 will be rotated in idle, substantially pressureless, contact
with the associated distributor roller 31 as the latter continues to be
driven from the drive 34. Similarly, under the throw-off condition, the
intermediate roller 25 will tend to be idly rotated by substantially
pressureless "kissing" engagement with the fountain roller 21, the latter
being driven by the drive 24.
Such light "kissing" contact insures that the residual moisture which
exists upon the surfaces of the rollers at the moment of cut-off will
persist in the form of a film and will not have opportunity to contract
into droplets, by reason of surface tension, which droplets have a
degrading effect upon the initially printed copies when the fountain is
subsequently restored to its running condition in which pressure exists
between all of the rollers in the series.
Restricting the separating movement between the form roller 35 and
distributor roller 31 and between the intermediate roller 25 and the
fountain roller 21 during throw-off in order to maintain the "kissing"
engagement discussed above is a matter well within the skill of the art.
That is to say, in FIG. 2 the rollers 35, 31 and rollers 25, 21 are
retained in substantially pressureless contact. It will be appreciated by
one skilled in the art that the reduction in axial separation required to
retain "kissing" contact between the selected rollers under the throw-off
condition is a matter of geometrical adjustment, primarily a slight
shifting of roller centers and slight adjustment of eccentricity. Thus, to
reduce the separation between the rollers 35, 31 for a given swing of the
arm 42 to retain "kissing" contact, the "throw" between the centers 45, 32
may be reduced by rotation of bushing 50 while to retain substantially
pressureless contact between the rollers 25, 21 the eccentric bushing 70
may be similarly rotated.
It is one of the features of the invention, in its preferred form, that the
intermediate roller 25 operates at two different speeds in the running and
throw-off conditions. During normal running (FIG. 1) the roller 25 is
driven at press speed, with slippage between the roller and the fountain
roller. However, during throw-off, the substantially pressureless contact
between the intermediate roller 25 and the fountain roller 21 is,
nevertheless, sufficient for the roller 25 to operate at the peripheral
speed of the fountain roller which continues to be driven, at slower than
press speed, by the drive 24. (FIG. 2).
In contrast, a fountain roller 35 continues to operate at press speed
during both running and throw-off conditions. In the latter condition the
"kissing" contact suffices to cause the form roller to operate at press
speed. In any event, both of the rollers 35, 25 being constantly
pre-rotated, and with the water film being constantly reformed thereon are
in a position to be restored to running condition by snap action of the
actuator 43 without the usual time delay of conventional dampening
systems.
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