Note: Descriptions are shown in the official language in which they were submitted.
TORQUE-ASSIST SYSTEM FOR PRINTING BELTS
BACKGROUND OF THE INVENTION
This application relates to the art of drive mechanisms
and, more particularly, to drive mechanisms for driving a
belt past a cylinder around which the belt extends. The in- ~
- vention is particularly applicable for use with belt-type of ` -
- printing machines and will be particularly described with
reference thereto. However, it will be appreciated that the
~ ~ invention has broader aspects and may be used for driving
belts in general and is not limited to use~for drivLng belts
.
in belt-type of printing machines.
One example of a belt-type of printing machine is dis-
, . . .
closed in U.S. Pat. No. 3,518,940 issued July 7, 1970, to ~ -
Stroud et al. A continuous belt extends around rolls and is
,i :
.
q driven through a nip between plate and impressLon cylinders.
The belt carries flexible printing plates which transfer
:,
5 images to a web of paper or the like passing through the nip
around-the impression cylinder. For halftones and multi- -`.
color printing, along with accurate slit~ing of the printed
web, it is necessary to maintain accurate registration be-
tween the belt and the belt drive. One drive arrangement for
maintaining accurate registration includes belt drive sprock-
ets at opposite ends of the plate cylinder and having sprocket
teeth engageable with longitudinally-spaced holes adjacent
the longitudinal edges of the belt.
In the earliest drive arrangements of the type described,
the~sprockets were secured directly to the opposite ends of
the plate cylinder and rotatably driven in unison therewith
'~
~ :
.
so the plate cylinder also transmitted drive traction to the
belt. ~s a practical matter, it is not possible to machine
the plate cylinder to such accurate dimensions that the plate
cylinder would drive the belt at precisely the same speed as
the drive sprockets. If the plate cylinder drives the belt
slightly faster or slower than the drive sprockets, the belt
and drive sprockets will slip relative to one another and
registration will be lost, or the belt will break. In order
to overcome this problem, as disclosed in the aforementioned
Stroud patent, the belt drive sprockets are mounted for rota-
tion independently of the plate cylinder. Torque is supplied
from the drive sprockets to the plate cylinder through
clutches. In addition, the outer surface of the plate cylin-
der is highly polished so it will slip easily relative to the
belt. With this arrangement, it was believed that any ten-
dency for relative movement between the belt and drive sprock-
ets would be overcome by relatively easy slippage between the
belt and plate cylinder. However, it has been found that
such phenomenon as 8queezing of the flexible printing plates
between the nip produces a drag on the belt intermediate the
drive sprockets and this drag cannot be overcome by relative
slippage between the belt and plate cylinder, or between the
plate cylinder and drive sprockets. Therefore, it has been
found that registration is sometimes lost due to jumping of
the sprockets relative to the belt.
It would be desirable to have an arrangement for pre-
vénting relative movement between the belt and belt drive
sprockets in order to maintain accurate registration of the
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~ ~ 3 ~
belt and printing plates carried thereby.
SUMMARY OF THE INVENTION
A belt-type of printing machine of the type described
has a supplemental torque-assist drive for the plate cylinder
which is selectively operated for supplying supplemental
torque to the plate cylinder when there is impending rela-
tive movement between the belt and drive sprockets. This
~ ~ .
arrangement provides supplemental traction to the belt
through the plate cylinder for preventing loss of registration.
In a preferred arrangement, the outer surface of the
.
plate cylinder is provided with traction material having a
~,.....
high coefficient of friction for suppiying driving traction
to the belt.
In accordance with another aspect of the invention, ;
sensing means is provided for sensing impending relative
movement between the belt and the belt drive sprockets and
then selectively operating ehe torque-assist drive for pre- i-
venting such relative movement.
The torque-assist drive may take many forms, and the
sen~ing means may also be of many different designs. In
fact, it is possible to manually operate the torque-assist
drive upon visual observation of impending slippage or
visual observation of gauges or the liké connected with the
belt drive for showing impending slippage.
The torque-assist drive can be capable of imparting ~ ;
either positive or negative traction to the belt for posi-
tively driving or braking the belt depending upon the di-
rection of impending relative movement between the belt and
drive sprockets.
It is a principal object of the present invention to
provide an improved belt drive mechanism.
It is an additional object of the invention to provide
a belt-type printing machine with an improved belt drive
mechanism which p~events loss of belt registration.
It is another object of the invention to provide an
improved method of driving a belt and of maintaining regis-
tration of a belt in a belt-type of printing machine. ~-
It is also an object of the invention to provide an
improved belt drive mechanism which is relatively simple in
operation. ~ ;
BRIEF DESCRIPTION OF THE DR~WING
Figure 1 is a schematic perspective illustration of a
printing belt carrying flexible printing plates, and passing
~ ~.
through a nip between plate and impression cylinders; `
Figure 2 is a partial cross-sectional elevational view
showing a flexible printing plate carried by the belt passing
through the nip between the plate and impression cylinders;
Figure 3 is a cross-sectional elevational view showing
one orm of drive mechanism constructed in accordance with
the present application;
Figure 4 is a partial cross-sectional elevational view
showing another drive mechanism;
Figure 5 is a cross-sectional elevational view taken
generally on line 5-5 of Figure 4;
Figure 6 is a schematic illustration of another drive
arrangement;
- . ,: . . . . .
~3q~9
Figure 7 is a schematic illustration of still another
drive arrangement;
Figure 8 is a schematic illustration of still another
drive arrangement;
Figure 9 is a partial cross-sectional elevational view
showing a drive arrangement at one end of a plate cylinder;
. ~
Figure 10 is a partial cross-sectional elevational view
similar to Figure 9 and showing the drive arrangément at the
other end of a plate cylinder;
Figure 11 is a partial cross-sectional elevational
view taken generally on line 11-11 of Figure 9;
Figure 12 is a partial cross-sectional elevational view :~
taken generally on line 12-12 of Figure 9;
Figure 13 is a top plan view taken generally on line
13-13 of Figure 12; and
Figure 14 is a schematic of a control arrangement for
the drive system of Figures 9-13.
DESCRIPTION OF PREFERRED EMBODIMENTS
, With reference to the drawing, Figure 1 shows a con-
tinuous flexible belt of synthetic plastic material or the
like having a plurality of flexible printing plates 12 :~
mounted thereon. Printing belt A extends around a belt
drive and plate cylinder assembly B which cooperates with an ;~
impression cylinder 14 to define a nip between which print-
ing belt A and printing plates 12 pass for transferring
images to a continuous web of paper or the like 18. An ink-
ing assembly is generally indicated at 20 for inking printing
plates 12 which travel counterclockwise in Figllre 1 with
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' ' ! . ' ' ~
~ ~ 3 ~
printing belt A and the belt drive and plate cylinder
assembly B.
Figure 2 shows printing belt A traveling from right to
left through the nip between impression cylinder 14 and the
belt drive and plate cylinder assembly 8. Flexible printing
plates 12 are squeezed as they pass through the nip and this
causes a bulge in flexible printing plate 12 at the nip en-
trance, and such bulge is shown exaggerated at 24 in Figure
2. This bulge creates a very high drag or resistance to
movement of printing belt A through the nip and the high `~
torque required to move the bulge through the nip can result
in jumping of the drive sprockets ahead of the printing belt
A. Due to the highly polished surface of the plate cylinder,
sufficient drive traction cannot bei~mparted to the printing
belt by the plate cylinder for overcoming the drag caused by
the bulge. Placing traction material having a high coeffi-
cient of friction on the plate cylinder would provide suffi-
cient supplemental traction but would again cause the problem
of the plate cylinder driving the belt at a different speed
than the drive sprockets.
In order to overcome the aforementioned problem and pre-
vent relative movement between the belt and the positive belt
drive, supplemental torque-assist means is provided for im-
parting supplemental torque to the plate cylinder. Gne ar-
rangement for accomplishing this is shown in Figure 3. Plate
cylinder 30 has journals 32 rotatably supported in support
bearing assemblies 34. The outer surface of plate cylinder
30 i8 coated or covered with traction material 38 having a
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~3'~
high coefficient of friction. Traction material 38 may be a
natural or synthetic rubber or other suitable traction ma-
terial, and preferably covers the entire outer surface of
plate cylinder 30 because discontinuities in traction ma-
terial 38 can result in printing problems. Traction material
38 is capable of supplying high traction to printing belt A
for driving same through the nip definèd by impression cylin-
der 14 and plate cylinder 30. It will be recognized that
other traction increasing arrangements could also be provided.
For example, it is possible to provide a plurality of very
small holes extending from the surface of plate cylinder 30
to an interior vacuum chamber suitably connected with a
vacuum so that printing belt A would be held against plate
cylinder 30 by the vacuum. The holes should be very small
so the plate cylinder still provides nearly continuous backup
support for the belt to prevent any printing problems due to
discontinuities. In effect, the plate cylinder would be
porous with the inner ends of the pores being connected to
the interior of the plate cylinder which would be under a
vacuum.
Belt drive means C are located at opposite ends of
plate cylinder 30 and include hubs 40 rotatably mounted on
journals 32, and sprockets 42 suitably secured to hubs 40.
Sprockets 42 have circumferentially-spaced sprocket teeth 46 -
which e~tend through longitudinally-spaced holes shown at 50
in Figure 1 adjacent the longitudinal side edges of printing ~-
belt A.
Drive gears 54 are rotatably mounted on journals 32
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~l3~
outwardly of drive hubs 40 and are suitably drivingly con-
nected as by a train of gears with machine power shaft 60.
Drive gears 54 are connected by electrical load cells 62 with
drive hubs 40. Electrical load cells 62 are simply similar
to electrical strain gauges and are characterized by having a
variable resistance to flow of electricity therethrough de-
pending upon the stress to which the loàd cell is subjected.
Slip rings 66, 68 connected with load cells 62 are connected
through electrical brushes 70, 72 with a control circuit and
with a source of electricity.
Signals from load cells 62 are fed to a signal amplifier
74 connected to a comparator 76 having a reference signal im-
pressed thereon by an adjustable reference signal device 78.
The comparator 76 comparesthe reference signal with the load
cell signal and sends any resultant signal to a differentiator
80 which determines whether the difference signal is positive
or negative. Positive difference signals are fed through am-
plifier 84 to magnetic particle drive clutch 86, while nega- -
tive difference signals are fed through amp~ifier 88 to
magnetic particle brake 90.
Magnetic particle clutch 86 is of a known type and sim-
ply includes an outer rotating member on input shaft 96 which
i8 ratially spaced from an inner rotating member on output
shaft 98. The radial space between the inner and outer ro-
tating members is filled with magnetically attractive powder,
and an electrical coil in the stator of the clutch surrounds
the rotating members. Energization of the electrical coil
produces a magnetic field which causes the powder to form a
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.. .: . - . ~ - :
~ ~ 3 ~ ~ ~
drive link between the inner and outer rotating members for
transmitting torque. The amount of torque transmitted varies
in accordance with the strength of the magnetic field which
in turn varies in accordance with the current flow through
. .
the eIectrical coil. Magnetic particle brake 90 is similarly
constructed and the rotating member on the output shaft 102
is simply radially spaced from a stationary member, and the
radial space is filled with magnetically attractive powder. ~-
~Energization of the coil in the magnetic particle brake 90
.
forms a link between the rotating member on the output shaft
102 and the stationary member for~applying a variable braking
torque. The braking torque varies in accordance with the ~ ;
strength of the magnetic field which in turn varies in ac-
- .
cordance with the~current supplied to the coil.
Input shaft 96 of magnetic particle clutch 86 is driven `
~,.
from machine drive shaft 60 as by a toothed belt 106 extend- -
ing around suitable gears on drive shaft 60 and input shaft - -
- ~ . . .
~ 96. Output shaft 98 of magnetic particle clutch 86 and out- ~ ~-
:- .
- put shaft 102 of magnetic particle brake 90 are connected by
a toothed belt 112 extending around suitable gears on those
.
shafts. A drive belt 114 extends around suitable gears on
clutch output shaft 98 and a gear or pulley 116 fixed to the ~ -
:~ :
outer end of Journal 32 on plate cylinder 30.
In operation of the apparatus, driving torque is sup- ~ -
plied to drive gears 54 from machine drive shaft 60. Driving
torque is transmitted from drive gears 54 through load cells
62 to drive hubs 40. This rotates sprockets 42 which posi-
tively drive printing belt A. The controls may be set so
_g_
.
~ ~ ~l3~
that magnetic particle clutch 86 is normally supplying suf-
ficient torque to plate cylinder 30 to maintain rotation of
same. In the event of a drag on printing belt A as previous-
ly described, additional driving torque will be required from
drive gears 54 to drive hubs 40. This will cause additional
deflection of load cells 62 so the load cell signal received
by comparator 76 will exceed the reference signal from refer-
ence signal generating device 78. The positive signal is fed
to differentiator 80 which in turn feeds it to magnetic parti-
cle c~ut~h 86 for supplying supplemental torque to plate cylin-
der 30 which in turn supplies supplemental traction to print-
ing belt A for positively driving same at a slightly greater
speed than sprockets 42 for relieving the excessive load on
the sprockets. As the load on the sprockets is relieved, the
necessary torque from drive gears 54 to drive hubs 40 is re-
duced and this relaxes load cells 62 so the load cell signal
again drops off for reducing the torque transmitted by mag-
netic particle clutch 86. If the printing machine is stopped
ra~idly, as under emergency conditions, the momentum of the
belt and plate cylinder could cause printing belt A to be
driven past sprockets 42 so that registration would be lost.
However, a condition of that type will result in hubs 40 tend-
ing to drive back through load aells 62 to drive gears 54 so
that load cells 62 are completely relieved of stress or
stressed in an opposite direction. The load cell signal from
comparator 76 is then sent by differentiator 80 to magnetic
particle brake 90 for applying a braking force to plate cylin-
der 30 for preventing printing belt A from slipping past
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. ~ ~
3~ 29
sprockets 42.
Instead of having fully automatic operation of a drive
system in the manner described, it will be recognized that it
is also possible to simply have visible gauges or the like in ;;
place of load cells 62 and to manually operate controllers for
controlling the torque transmitted by magnetic particle clutch
86 and magnetic particle brake 90. The sensing means defined -
by the load cells 62 senses impending relative movement or
slippage between printing belt A and drive means C. The sen- -
sing means also senses relative rotational movement between ~;
~, drLve gears 54 and~drive hubs 40. Indirectly, the sensing
means also senses a change in the speed of the belt at its
longitudinal edges as compared to the central portion of the - -
printing belt between the drive sprockets. ~The sensing means
automatically operates to operate the plate cylinder drive ~,
means or torque-assist means defined by magnetic particle
clutch 86 and magnetic particle brake 90. Supplemental ~ -
torque Ls then selectivcly supplied to plate cylinder 30 for -
supp}yLng supplemental traction to printing belt A to prevent
the impending relative movement between the belt and belt
drive means. The traction supplied to the printing belt by
plate ¢ylinder 30 can be either positive drive traction or
braking traction.
Figures 4 and 5 show another arrangement wherein belt
drive means C' includes a combined hub and drive gear 154 ro-
tatably mounted on journal 32 and drivingly connected with
machine drive shaft 60 by a toothed drive belt 156. As shown
in Figure 5, a roller 158 is biased against the tension side
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,
!. '. . ,~' ., .: ., ':, ' . ' ~ . ~ ' ' . '
~ ~ 3~
of drive belt 156 for normally deflecting same. Roller 158 is
biased by a cylinder 160 which also has an internal resistance
which varies in accordance with the projecting length of
cylinder shaft 162 carrying roller 158. Control signals pass-
ing through cylinder 160 are fed to an electric motor 170
drivingly connected by gear 172 with a drive gear 174 fixed
on plate cylinder journal 32 for supplying torque-assist to
plate cylinder 30. As the resistance to movement of the
printing belt increases, additional torque is required on
sprockets 42 and this increases the tension in that portion
of drive belt 156 engaging roller 158 so that roller 158 de-
flects to the right in Figure 5 for increasing the signal sent
to motor 170 which then increases its driving torque to plate
cylinder 30 for relieving the drag on the pr~nting belt.
When the tension in that portion of belt 156 engaging roller
158 is relieved, roller 158 again extends outwardly and the
signal provided to electric motor 170 is reduced so the driv-
ing torque to plate cylinder 30 is reduced. Although motor
170 itself provides a braking drag when energized at very low
levels, it will be recognized that it is also possible to
provide an additional motor or generator to function as a
brake for supplying braking traction to plate cylinder 30.
It will be recognized that many other automatic sensing
devices may be used for sensing impending relative movement
between the belt and belt drive means for automatically op-
erating a torque-assist means for supplying supplemental
torque to the plate cylinder which in turn supplies supple-
mental traction to the printing belt for preventing the
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.-
~3~
relative slippage.
Instead of having the belt drive and plate cylinder co-
operating with an impression cylinder to define the nip
through which the printing belt moves, it will be recognized
that many other arrangements are possible, and only a few of
such alternative arrangements will be described. Figure 6 ~;
shows a rotatable impression cylinder 14 cooperating with a
rotatable idling plate cylinder 230 having printing belt A
extending therearound, and driven by a drum and sprocket sys-
tem 232 corresponding to the sprocket and plate cylinder
driving arrangements described with respect to Figures 1-5.
An arrangement of this type is not as good as the preferred
arrangement because the elasticity of printing belt A makes
registration difficult and the printing belt joint is sub-
jected to extreme tension.
Figure 7 shows an arrangement wherein a sprocket and
drum drive 232 located much closer to idling plate cylinder
230. An additional idler roll 234 completes the system.
This reduces errors in registration and increases the minimum
belt length that can be accommodated. However, a severe load
would still be placed on the belt joint.
Figure 8 shows a direct lithography system in which belt
A contains lithographic images of a planographic nature which
are transferred to web 18 extending around a rubber covered
impression drum 14'. Even if the lithographic image on belt
A is formed by ri~i~ plates of metal or plastic, the rubber
covered drum 14' produces the same bulging effect requiring
the supplemental drive to the central drum located between
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~3~
the opposite drive sprockets in drive assembly 232.
In all of the arrangements described, the belt drive sys-
tem includes belt drive means located at opposite ends of a
cylinder around which the belt extends. The belt drive means
is rot3table independently of the cylinder and sensing means
is provided for sensing impending relative movement between
the belt and belt drive means. The sensing means is used for
operating torque-assist means which supplies supplemental
torque to the cylinder for imparting supplemental traction to
the belt and preventing the impending slippage between the
belt and belt drive means. The supplemental traction sup-
plied from the cylinder to the belt may be either driving
traction or braking traction.
Figures 9-14 show another plate cylinder drive arrange-
ment and a control syste~ therefor. With reference to Figures
9 and 10, plate cylinder 330 has its outer cylindrical surface
coated or covered with a material having a high coefficient of
frlction as described with reference to plate cylinder 30 of
Figures 3 and 4. Plate cylinder 330 has opposite end journals
332 and 333 rotatably mounted in supports 334 by bearing as-
semblies 335. Bearing holders 336, 337 are received in suit-
able openings 338 in supports 334 for supporting bearings 335.
Longitudinal grooves 339 extending radially of openings 338
receive keys 341 on bearing holders 336, 337 for preventing
rotation of such holders relative to supports 334, while al-
lowing longitudinal movement of holders 336, 337 relative to
supports 334. Outer bearing retainers 342, 343 are secured
to bearing holders 336, 337.
-14-
~3~
A cup member 346 suitably secured to support 334 over
outer bearing retainer 342 has an opening therein aligned
with the longitudinal axis of plate cylinder 330 and a
threaded nut 348 received in such hole is also suitably se-
cured to cup 346 against rotational or longitudinal movement
relative thereto. A threaded shaft 350 on a hand wheel 352
extends threadably through nut 348. A bearing 354 is posi-
tioned between shaft 350 and periphery of a hole in outer
bearing retainer 342. Relative axial movement between shaft
350 and bearing 354 is prevented by a shoulder 356 on shaft
350 and an outer retainer 358 secured on shaft 350. Rela-
tive axial movement between bearing 354 and outer retainer
342 is prevented by opposite retainers 360 suitably secured
to retainer 342. ThuS, shaft 350 can rotate relative to re-
tainer 342 but cannot move axial~y relative thereto. A lock
nut 364 threaded on shaft 350 has one or more handles 366 ~;~
attached thereto. Movement of lock nut 364 securely against
nut 348 prevents rotation of shaft 350. ~oosening of lock
n~t 364 allows rotation of shaft 350 by operation of hand
wheel 352 for shifting bearing retainer 342 axially. This
also shifts bearings 335 axially and results in limited axial
movement of plate cylinder 330 for properly aligning the belt
and the printing plates carried thereby. For multi-color
printingj it is necessary to obtain very accurate alignment
of the printing plates at the various printing stations. The
limited axial movement of the plate cylinder allows a fine
adjustment of the printing plates to insure alignment at the
various printing stations.
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.
.. . .. , . . ~ .
~3~
Drive gears 370 are suitably drivingly connected with
the main drive shaft of the press. Drive gears 370 are
bolted to electrical ring holders 372 on which four electri-
cal rings 374-377 are mounted in spaced-apart relationship.
Electrical ring holders 372 are rotatably mounted on journals
332, 333 by bearings 380 and 382.
Plate discs 384 are suitably bolted to bearing holders
336, 337 as by the same bolts which secure inner bearing re-
tainers 386 to holders 336, 337. Thus, plate discs 384 are
fixed against rotation. Plate extensions 388 extend from
plates 384 substantially parallel to the longitudinal axis of
plate cyIinder 330 in outwardly-spaced relationship to drive
gears 370. Extensions 388 completely span drive gears 370
and have inwardly extending members 390 connected with the
outer ends thereof, and extending inwardly on the opposite
side of drive gears 370 from plates 384. Brush supports 392
are attached to the free ends of members 390 and extend away
from drive gears 370 substantially parallel to the longitu-
dinal axis of plate cylinder 330 for supporting four electri-
cal brushes 404-407 which cooperate with electrical rings
374-377.
Transducer mounting plates 412 are suitably bolted to
ring holders 372 in opposed relationship to transducer mount-
ing plates 4~4 which are suitably bolted to holders 416 for
belt drive sprockets 418 having sprocket teeth 420 thereon
for engaging the holes in the longitudinal edges of the
printing belt on which the printing plates are mounted. Belt
drive sprocket holders 416 are rotatably mounted on journals
-16-
. . ,- . . . :
~ 4
332, 333 as by bearings 422, 424.
With reference to Figures 12 and 13, the upper edges of
each plate 412, 414 have a clevis 432~ 434 therein for making
pinned connections with rods 436, 438 attached to a transducer
440 whose electrical resistance varies in accordance with the
tension to which it is subjected. Wires indicated generally
by numeral 444 in Figure 11 connect transducer 440 with
brushes 404-407 to control the excitation of an electric motor
drivingly connected with a gear 450 in Figure 10 on a stub
shaft 452 attached with journal 333 on plate cylinder 330.
The electric motor directly drives plate cylinder 330 through
gear 450 and shaft 452. Driving torque for belt drive sprock-
ets 418 is transmitted through transducers 440 and their
mounting plates 412-414 from drive gears 370.
Four brushes 404-407 and cooperating rings 374-377 are
used simply to insure continuous conductivity. One pair of
brushes and rings is used for transducer input and the other
pair for transducer output. Thus, operation of the apparatus
is not affected by momentary interruptions in conductivity
between one brush and ring of each pair due to such things .
as ring irregularity or brush bounce. :.
A voltage source generally indicated at 460 in Figure
14 applies a voltage to transducers 440 through brushes 404,
405 and their associated rings 374, 375. The current through
transducers 440 varies in accordance with the stress on the
transducers, and the output passes through brushes 406, 407
and their associated rings 376, 377 to amplifiers 4~2. The
sprockets 42 or 418 are individually mechanically adjustable
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, ~ . . . .
.. . .
^ ~ 3~
to be sure that equal driving force is applied to both of the
opposite edge portions of the printing belt. For purposes of
this mechanical sprocket adjustment, the signals from ampli-
fiers are supplied to torque meters 464 which indicate the
pounds of stress on the individual transducers, and visually
inform the operator that sprocket adjustment is necessary.
Sprocket adjustment is carried out until the driving force
applied at both edge poreions of the printing belt is equal-
ized as indicated by equal readings on the torque meters 464.
The signals from amplLfiers 462 also pass to voltage
sensitive relays 466 which operate, when the transducers are
subjected to excessive stress, for shutting down the main
drive for the entire apparatus by opening normally closed
contacts 468 which are suitably connected between the power
supply and the main drive motor.
The signals from amplifiers 462 are also fed to a sum-
ming and trimming device 470 which sums the two signals from
the amplifiers 462 and compares:the sum with a reference sig-
nal provided by either an adjustable low torque input set pot
472 or an adjustable high torque set pot 474.
Impression cylinder 14 is movable toward and way from
plate cylinder B or 330. When 6tarting up the press, impres-
sion cylinder 14 is in a position moved away from the plate
cylinder. A limit switch operated by the position of impres-
sion cylinder 14 has a contact 476 between law set pot 472
and device 470 which is normally closed when impression cylin-
der 14 is in its position away ~rom plate cylinder 330. The
limit switch has contacts 478 between high set pot 474 and
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3~9
device 4iO which are open when impression cylinder 14 is in
its position away from plate cylinder 330, and are closed -.
when impression cylinder 14 is moved to its cooperative posi-
tion ad~?acent plate cylinder 330. When the apparatus is
started up, the low torque set pot provides the signal to de- :
vice 470. Impression cylinder 14 moves toward plate cylinder
330 and eventually reaches its operating position. At that
time, the limit switch operates for opening contacts 476 and
closing contacts 478 so that during operation of the apparatus
the reference signal is provided to device 470 by high set :
pot 474. The desirable input signal from high torque set pot
474 is compared by device 470 with the sum of the signals
actually received from transducers 440. The resulting differ- ~:
ence signal, if any, is fed to a comparator device 480 which:`:
;; : -
also receives signals from a tachometer 482 connected with the :`
main drive for belt A and a tachometer 484 connected with
electric motor 486 which is drivingly connected to gear 450 : :
;,
of~Figure lO for directly driving the shaft of plate cylinder ~ .:
330. Electric motor 486 is connected with the gear 450 of ~;
20Flgure 10 through a gear box 488 shown in Figure 14. An idler
roll 492 is indicated in Figure 14 for printing belt A simply
for convenience of illustration. ~-~
The signals fed to comparator device 480 are compared and
any difference signal is then fed to a motor control device
500 which provides signals to adjust the armature voltage of -`
motor 486 for operating same to maintain the speed of plate
cylinder 330 approximately the same as the speed of belt A.
If excessive torque is being exerted on belt A by sprockets
-19-
~3~9
418, the higher stress on transducers 440 will result in more
driving torque being provided to motor 486 for providing more
driving torque directly to plate cylinder 330. If the signal
provided by transducers 440 is less than that set in high
torque set pot 474, this means that the sprockets are trying
to unload. That is, the driving force provided by the sprock-
ets is diminishing below the level required for proper opera-
tion of the apparstus. This may result from a number of dif-
ferent reasons, including the possibility that the driving
force being imparted directly to the belt by plate cylinder
330 is too high. Therefore, motor 486 will act as a generator ;
and provide a braking force on plate cylinder 330 to prevent
plate cylinder 330 from driving belt A past sprockets 418.
Trimming device 470 provides greater sensitivity and more
accurate control of the motor 486 than would be possible
using only signals from tachometers 482 and 484.
. ~.
Although the invention has been shown and described wi~h `-
, -
` respect to certain preferred embodiments, it is obvious that ~
.; ~
equivalent alterations and modifications will occur to others ~ -
8killed in the art upon the reading and understanding of this
specification. The present invention includes all such equiva-
lent alterations and modifications, and is limited only by
the scope of the claims.
.
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