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Description  |
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BACKGROUND OF THE INVENTION
1. Field of Use
This invention relates generally to register control systems for
web-processing apparatus, such as multicolor rotogravure printing presses
which have a plurality of color decks.
In particular, it relates to register control systems for maintaining a
constant actual base repeat length at the key color deck thereby reducing
or eliminating key color repeat length errors.
2. Description of the Prior Art
The fields of publication, packaging, and newspaper printing demand high
quality color registration. Each color must be accurately applied to a
specific spot on the moving web. Prior art automatic register control
systems aim to reduce mis-register waste caused by small or large errors
which were previously detectable only after the final product was printed.
A typical register control system inspects a moving web in a printing
press and regulates servo motors to vary web length and tension and to
maintain precise registration between color units. In a typical multicolor
printing press the first significant color cylinder (usually yellow) at
the key color deck prints a small register mark on the web along with each
illustration. The marks are scanned at subsequent printing decks on the
press to detect variations in web length. Under tension, the web elongates
in various degrees, dependent upon moisture content, caliper, cylinder
sizes, dryer temperature, and any manual and automatic adjustments made to
the press during a run.
To correct for mis-register, there are two types of compensation commonly
used on presses--web compensation and cylinder compensation. On a press
using cylinder compensation, the printing cylinder is rotated to change
the location of the printing between printing decks. On a press using web
compensation, a movable compensator is operated between the printing decks
to change the length of web between two decks. As web length changes
between decks (increases or decreases), the position the cylinder prints
downstream of the preceding deck advances or retards. To advance the
printing refers to movement of the printing towards the exit end of the
press; to retard refers to movement away from the exit end of the press.
Publication gravure, letter-press, offset and packaging gravure presses
sometimes use cylinder-to-mark register control systems. Such a system
receives part of its information from a register mark printed on the web
and part of its information from a reference mark generated by or directly
related to print cylinder position. The reference mark, generated once per
cylinder revolution, is transmitted to a computer in a register control
wherein it is compared to the arrival of a scanner signal produced by the
register mark. An encoder provides for machine time increments, for
example, and sends out a series of 20,000 pulses or digits per cylinder
revolution. Signals based on the reference mark and the scanner signal
should arrive simultaneously. Any difference measured by one or more
encoder pulses is counted and sent out as a registration error signal to
operate or adjust the compensator. Accuracy of a register control system
is a function of the number of divisions into which the printing repeat
length is divided by the encoder and in this example is 1/20,000 of the
repeat length. Register control systems are used with presses which
operate at speeds up to 2500 feet of web per minute.
It is known that the majority of all intercolor register errors in
rotogravure printing is caused by changes in the actual print repeat
length in the first or key color deck and the response of sebsequent
colors to this error. Prior art printing register control systems as
hereinbefore described attempt to sequentially match intermediate colors
to the actual repeat of the first or key color. It is also known, however,
that maintenance of the desired actual print repeat length in the first or
key color deck depends on maintaining the tension level appropriate to the
condition of the web material being printed.
Variation of actual print repeat length of the first or key color may be
caused by either one of two variables; first, a variation of the tension
going into the first or key color deck caused by tension transients in the
web introduced from the unwind roll, butt splicer, infeed control, speed
changes in web speed, and second, variations in the web material being
printed, such as moisture content or board (web) caliper. All of the
above-mentioned variables, when introduced into a press operating in a
steady state condition, require the establishment of a new infeed web
tension level rather than reestablishment of a constant preset tension in
order to maintain a constant repeat length of the key color.
Thus, print register errors can occur in the key color deck that are
permanent in nature, that is, they represent a change in the print repeat
length. Thus, change in repeat length is caused by changes in the web
physical characteristics, i.e., moisture content, caliper, elasticity,
etc., and is most noticeable across a roll splice. Key color repeat length
changes can also occur on a gradual basis throughout a web roll as the web
characteristics change between the outermost wraps and the core of the web
roll.
Primary register control systems, as hereinbefore described, responding to
intermittent and cyclic print errors, operate to maintain a printed
register mark applied by the key color deck print cylinder in a fixed
position relative to a subsequent printing cylinder reference position and
thus do not correct for a fixed change in key color repeat length. The
resulting register error at each printing deck after the first color is
referred to as a phase error. Test analysis has shown that this phase
error magnitude is not a constant for each printing deck, and may be as
high as 0.030 of an inch for one color. Corrections for phase error on
presses equipped only with a primary register control system were
heretofore made manually. Unfortunately, manual corrections require
greater press operator attention and are made "after the fact," that is,
when the misregistered blanks are on the delivery table and the press is
loaded with misregistered web.
U.S. Pat. Nos. 2,082,705 and 3,025,791 are prior art examples of web
processing apparatus wherein infeed web tension is controlled
automatically in response to marks on the web. However, the prior art does
not teach repeat length or key color controls which take into account the
fact that repeat length changes sometimes represent more than transitory
changes and, in fact, are actually permanent changes which require a new
or different set of parameters within which repeat length errors of a
different magnitude are to be sensed and corrected for by establishment of
a new infeed tension level.
SUMMARY OF THE INVENTION
A key color control system in accordance with the invention is provided for
web processing apparatus, such as a multicolor rotogravure printing press
having a plurality of color decks. The key color control system maintains
a constant actual printing repeat length on the web at the first or key
color printing deck, thus minimizing the need of subsequent color decks to
adjust to a key color error. The key color control system comprises means
to detect and measure the magnitude of a repeat length error printed by
the key color deck and means to correct for the error by varying the
infeed tension level on the web ahead of the key color deck so as to
either maintain a predetermined tension level (if the change is
transitory) or establish a new tension level (if the change is permanent
or long term). The key color control system includes means for
establishing predetermined limits within which repeat length errors of
certain magnitude are likely to occur and for which correction is made by
maintaining constant repeat length by appropriate adjustment of tension
level, and means for determining and indicating that a trend in change in
magnitude of repeat length errors is occurring, which is a departure from
the predetermined limits, so that either new predetermined limits may be
estblished or a new base repeat length may be established within existing
limits so that repeat length errors of a different magnitude (usually
smaller) are likely to occur. Correction is made for repeat length errors
of a different magitude by establishing a new tension level. The system
further includes automatic reset means operable when a new base repeat
length is established within previously set limits to ensure rapid
establishment of the new tension level on the web.
The key color control system comprises scanner means, including a key color
optical scanner located after the key color deck for sensing the register
mark applied to the web in the key color deck and for providing a register
mark signal corresponding thereto; encoder and pulse generator means for
generating a reference mark signal in the form of pulses indicative of a
reference mark on the printing cylinder in the key color deck; a register
control, including digital computer means for receiving and comparing the
registration mark signal from the web and the reference mark signal from
the printing cylinder, to provide a repeat length error signal indicative
of the magnitude and direction of a repeat length error, which repeat
length error signal is converted to a control signal; and web tension
control means, including a pivotable rotatable dancer for exerting
pressure on the web to affect web tension, and dancer drive means for
moving the dancer, said drive means being responsive to said control
signal from the register control to adjust web tension accordingly, said
dancer drive means including a pneumatic cylinder connected to the dancer
and a motor-driven air regulator valve for the cylinder.
The key color system further comprises limit control means responsive to a
feedback signal resulting from the operation of the dancer drive means and
indicative of the tension being exerted on the web by the dancer. As the
repeat length printed on the web increases or decreases from the actual
cylinder repeat length, the repeat length error signal into the computer
is integrated and differentiated to determine both the direction and
magnitude of error. The output signal from the computer is a signal to the
motor which drives the air regulator valve to increase or decrease air
pressure to the pneumatic cylinder for the infeed dancer roll, thus
increasing or decreasing the tension on the web material coming into the
key color deck which causes a decrease or increase, respectively, in the
key color repeat length.
The rate and level of change to the infeed tension can be varied internally
in the key color control to accommodate both material caliper and moisture
changes in addition to dancer roll, splicer transients, and speed changes.
Thus, the key color control system also includes limit control means
including a limit circuit for establishing predetermined limits within
which repeat length errors of certain magnitude are likely to occur and
for which correction is made, and an anticipate circuit for determining
and indicating that the trend in change in magnitude of repeat length
errors is to depart from the predetermined limits, so that new
predetermined limits may be established within which repeat length errors
of a different magnitude are likely to occur, whereby the system then
corrects for repeat length errors within the new limits. The key color
control system also includes automatic reset means operable when a new
base repeat length is established within previously set limits to ensure
rapid establishment of the new tension level on the web.
The limit control means includes a limit relay circuit connected to the
register control which can be set by the press operator to establish upper
and lower limits in PLI (pounds per linear inch) within which the dancer
will exert tension. The limit control means also includes an anticipate
relay circuit which can be set by the press operator to determine that,
and provide a warning signal when, the magnitude of repeat errors is
changing to such a degree that establishment of a new set of limits or
establishing a new base repeat length for infeed tension is warranted by
the press operator because a permanent change in web condition is
appearing.
Thus, the key color control system has the ability to ascertain the
magnitude and direction of the repeat length error signal and translate
the error signal to a control signal for a tension control device (the
dancer) which then either restores a tension variation to a specific
tension level required or establishes a new tension level consistent with
that demanded for a preset printed repeat length, as dictated by a change
in the characteristic of the material printed. The tension control device
must be capable of maintaining accurate tension control of the material
being fed into the first color deck and be further capable of rapid and
proportional response to tension change demands from the measured error of
actual print repeat length in the first key color deck.
The key color control system in accordance with the invention embodies a
closed loop error feedback system principle and measures and controls the
key or first color print repeat length and maintains subsequent press
color-to-color register at a high degree of accuracy regardless of
material variations or transients due to the infeed dancer motion or butt
splicer operation.
Other advantages of a key color control system in accordance with the
invention over prior art preset infeed web tension controls using a
primary register control for intercolor tension control are that the first
or key color repeat length error is scanned and sensed after it is
printed, with the error correction initiated simultaneously with sensing.
This prevents repeat length deviations of the key color from entering the
subsequent printing decks, thus providing a more stable web condition into
the subsequent deck which reduces misregister. Furthermore, maintaining a
balanced and stable condition between the first and second printing nips
creates a more balanced condition between all other subsequent printing
nips thus minimizing further intercolor misregister.
The key color control system is adaptable to any one of the color decks of
a gravure press, and depending on the key color location, can be
implemented by positioning a selector switch to bring into play optical
scanners for repeat length control located at the several color decks.
Although the embodiment disclosed employs apparatus wherein the register
mark printed on the web is compared to a reference mark related to
printing cylinder position, it is apparent that the invention can be
employed in apparatus wherein "mark to mark" registration is employed,
i.e., apparatus wherein two spaced apart optical scanners at predetermined
locations sense and measure whether there is time registration or not
between two spaced apart register marks printed on the web.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a portion of a multicolor rotogravure
printing press with which a key color control system in accordance with
the invention is advantageously employed;
FIG. 2 is a schematic diagram of a portion of the press shown in FIG. 1 and
the key color control system in accordance with the invention;
FIG. 3 is a top plan view of a portion of the web shown in FIGS. 1 and 2
showing imprinting and register marks thereon;
FIGS. 4a through 4g are diagrams showing wave forms relating to register
marks or reference marks in certain portions of the key color control
system;
FIG. 5 is a schematic diagram of a portion of the control system shown in
FIG. 2;
FIG. 5a is a chart depicting the relationship between signal voltage and
meter readout produced by the reset control in the control system; and
FIGS. 6a through 6f are graphs depicting web infeed tension plotted against
time during different operating conditions of the press and control
system.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 shows web processing apparatus of a type with which a key color
control system in accordance with the invention is advantageously
employed. The apparatus comprises a printing press 10, having four color
printing decks A, B, C, and D; a roll stand 12; a butt splicer unit 14; a
web infeed and decurl unit 18; and a cutter unit (not shown). A web W
drawn from a web roll 20 on stand 12 passes in the direction of the arrows
H through butt splicer unit 14, web feed and decurl unit 18, the press 10
wherein it is imprinted and the cutter unit (not shown) wherein printed
segments are cut therefrom and subsequently stacked. Web W may be paper,
paperboard, plastic film, metal foil or the like, or a laminate of any two
or more such materials.
The apparatus is line-shaft driven in a conventional manner so that all
movably driven components in press 10, in the unit 18, and in the cutter
unit (not shown) are mechanically driven in synchronism at appropriate
selective speeds thereby enhancing web registration and ensuring a taut
web. Thus, as FIG. 2 shows, an electric motor 22 drives a line-shaft 23
which is connected by gear boxes 24 to power take-off shaft 25 which are
connected to the driven components in the associated units and press 10.
The printing decks A, B, C, and D are similar in construction and mode of
operation and corresponding parts are designated, where necessary, by the
same reference numeral suffixed by the letters a, b, c, and d,
respectively. In the following disclosure the first deck A, B, C, D to
imprint a color, or at least a register mark, on web W is referred to as
the first or key color deck. In practice, deck A would normally be the key
color deck in multi-color printing. However, any one of the decks A, B, C,
or D could be the key color deck.
Since the decks A, B, C, D are similar, only deck A is hereafter described
in detail. As FIGS. 1 and 2 show, deck A comprises a frame 30a upon which
are mounted a driven printing roll 31a, an impression roll 32a, a
plurality of idler rollers 33a, and a dryer 34a having suitable idler
rollers 35a therein. Deck A when in operation is provided with an ink cart
(not shown) which contains ink of an appropriate color and which is
insertable through an opening 36a in frame 30a. Compensator rollers 37 are
located between adjacent printing decks and each roller 37 is drivable in
the direction of an arrow K1 by a compensator motor 38.
Web infeed unit 18 comprises a pair of driven pull rollers 18a and 18b
between which web W passes and by means of which the web is drawn from the
roll 20. Web infeed unit 18 is provided with a dancer roll 40 which is
rotatably mounted on a pair of spaced apart support arms 41 (only one of
which is shown) which are pivotally movable in the direction of an arrow K
about a pivot point 39 by means of a piston rod 42 of a pneumatic cylinder
43 so as to apply an appropriate amount of tension on that portion of web
W between the nip of pull roller 18a and 18b and the nip of the driven
printing roll 31a and impression roll 32a, as hereinafter explained.
In operation of the apparatus, web W is drawn from roll 20 and passes
through butt splicer unit 14, web feed and decurler unit 18, and thence
between impression roll 32a and the printing roll 31a in deck A in firm
contact with both whereby a first color is imprinted. The web W is then
directed through dryer 34a where the inked pattern is heat-set or dried.
Upon leaving the dryer 34a, the web passes through the first web
compensator comprising movable compensator roller 37, and to printing deck
B. The web W, after receiving the pattern printed at deck A, which
includes a register mark R, as hereafter described, passes in succession
through decks B, C, and D in the same manner as above described with
reference to deck A. At each of the decks B, C, and D, the web W receives
a printed pattern in addition to that applied at deck A. To obtain the
desired results in the final composite copy, each of the separately
applied patterns must be held in proper spaced relationship (register) to
each other on the web. Normally, in a four-color operation such as here
illustrated, for example, deck A will print a pattern in yellow ink, deck
B in red, deck C in blue, and deck D in black, although other color
combinations could be used. The final composite copy may have areas of any
or all of these individual colors and may also have areas in which any two
or more of these individual colors are combined to form such composite
colors as, for example, orange, green, purple, brown, etc. From printing
deck D, the web W, now carrying the four-color copy, is understood to be
directed to the cutter unit (not shown) which severs blanks from the web.
The severed blanks are propelled onto a suitable collecting table (not
shown) where they are formed into a pile.
FIG. 3 shows a length of the printed web W carrying the composite printed
patterns P, which are diagrammatically illustrated by the dotted lines. In
the case illustrated, the web W is to be severed substantially along the
edges of adjacent printed patterns and the location of the cuts are
coincidental with the lines P. The first color printed (at deck A in FIGS.
1 and 2) includes the register marks indicated at R in FIGS. 2 and 3 which
are applied to the web W, preferably but not necessarily in a clear track
(devoid of other printing) along the length of the web, such as an edge
margin.
As FIGS. 1 and 2 also show, the apparatus is provided with a conventional
primary register control system which includes a primary register control
PRC for receiving signal information from a primary scanner PS located
between decks A and B and for operating a compensating motor 38 for
compensator roll 37 located ahead of deck B. The primary register control
system further includes other primary scanners OPS and other compensating
motors OCM for operating their respective dancers 37 located ahead of the
color decks C and D.
As FIGS. 1, 2, 4, and 5 further show, in accordance with the invention, a
repeat length control system is provided for use with the aforedescribed
apparatus to maintain a constant actual printing repeat length at the key
color printing deck A. Generally considered, the repeat length control
system comprises a photoelectric repeat length scanner 45 for sensing the
mark R and providing a position detect or error signal (see FIG. 4d); a
reference signal generator 44 and encoder 46 for providing a reference
signal indicative of the position of a mark M on printing cylinder 31a of
deck A (see FIGS. 4a, 4b, and 4c); a register control unit 47 for
receiving the error signals and the reference signals (see FIG. 4e); and
for providing an output or control signal, based on encoder pulses to the
error counter shown in FIG. 4g, to an electric compensator motor 48 having
a shaft 48a which operates a regulator valve 49 for controlling air
pressure from a source 49a to the pneumatic cylinder 43 for the infeed
dancer 40. FIG. 4f shows diagrammatically register mark signals which are
leading and lagging. As FIGS. 1 and 2 show, repeat length scanner 45 is
shown located after deck A which for purposes of the present description
has been selected as the key color deck. However, with deck A as the key
color deck, scanners located as at 45B or 45C could be used as the repeat
length scanner, instead of scanner 45, since they are located downstream
of the key color deck. Furthermore, any deck A, B, C, D could be selected
as the key color deck and any scanner 45, 45A, 45B, 45C could be used as
the repeat length scanner provided it is downstream of the selected key
color deck.
As FIG. 2 shows, the signals from scanner 45 and encoder 74 are directed to
the register control unit 47 which contains an electronic computer. The
manner in which the signals and encoder pulses supplied to the computer of
each console section are compared is shown graphically in FIG. 4. An
Accutrol Model 631 register control unit manufactured by Hurletron
Incorporated, Controls Division, 1938 East Fairchild, Danville, Illinois,
61832, employed in accordance with the invention as hereinbefore
explained, is suitable for use as a register control unit in accordance
with the invention. The Model 631 device is also usable as the primary
register control PRC. The Model 631 register control unit is described in
detail in an operator's and maintenance manual therfor which is available
from Hurletron Controls at the above address.
Digital output signals are derived in the computer circuits of the register
control unit 47 and are supplied to a motor control circuit for the
compensator motor 48 for the air regulator valve 49 of cylinder 43 of
infeed dancer 40. In response to the signals, the motor 48 operates in the
proper direction to cause operation of an air regulator valve 49, cylinder
43 and infeed dancer to correct the error in register by applying tension
to web W. The compensator motor 48 may be, for example, a reversible DC
motor which operates in a direction dictated by the polarity (direction of
flow) of the current supplied thereto and at a speed proportional to the
applied voltage. Register control unit 47 also contains a digital display
device comprising, for example, three electronic display tubes 75, 76, and
77. Two tubes 76 and 77 display a digit of from zero to nine, inclusive.
In normal operation, the two most significant digits of the error counts
are displayed by tubes 76 and 77. The third display tube 75 will show a
plus sign when the work applying cycle to which the numerical value of the
display applies is longer than the distance on the web between the
register marks, i.e., the repeat length. The display of a negative sign by
tube 75 indicates that the work interval involved is shorter than the
repeat length. When there is no register error, zeros are displayed.
Register control unit 47 also includes vernier adjustable thumb switches
75A, 76A, and 77A which provide a means of controlling the fine register
of each unit. Initially set, for example, at 455 at the start of a run,
the switches operate over a range of 000-999 so that the press operator
can shift the set point while on automatic control. The switch 75A
controls hundreds; the middle switch 76A, tens; and the switch 77A, units.
Changing the right hand switch 77A one digit produces a shift of register
of approximately 0.001 on a 20 inch cylinder, for example.
A memory set push button 78 is used during set-ups when the system is in
the memory set mode. The button 78 is pressed momentarily to command the
unit to count and store the number of encoder pulses or digits that are to
be included in the "main counter" sequence. The memory setting operation
is completely automatic and will be performed in the first full revolution
after the memory set small button 78 is released. The button 78 is
disabled in the automatic mode. A manual control knob 79, movable from a
spring centered manual position to either advance or retard positions, is
normally in the spring centered position. When rotated toward advance,
contacts close to operate the electric motor 48 in the compensator
actuator 47a and the motor runs at full speed as long as the switch is
made. Advance action moves the controlled printing toward the folder. When
the switch is rotated to retard, the motor runs in the reverse direction.
In automatic control, the manual switch is disabled and cannot control the
compensator actuator motor 48.
As FIG. 2 shows, register control unit 47 is provided with terminals T3 and
T73 across which the memory set push button 78 is understood to be
connected. In Applicants' invention, an automatic reset circuit,
comprising a contact VSR of a voltage sensitive relay Z and a pair of
meter contacts CRA11 and CRA22, is connected across the terminals T3 and
T73, as hereafter explained.
Contact unit 47 is also provided with terminals T76, T16A and TR16 which
are connectable, as hereafter described, to control energization of motor
48.
As FIGS. 2 and 5 best show, the repeat length control system further
comprises a limit control unit 50 which receives an input control
(feedback) signal from a potentiometer 51 which is driven by and
responsive to the position of shaft 48a of compensator motor 48. Limit
control unit 50 provides output signals to operate a low limit switch 52
and a high limit switch 53 to control the ability of the register control
unit 47 to energize the motor. Limit control unit 50 comprises a web width
selector switch 54 which receives the input control signal from
potentiometer 51 and provides control signals to an anticipate relay 55
and a limit relay 56 which are part of limit control unit 50. Switch 54
enables an indication of web tension appropriate to web width. Anticipate
relay 55 is connected to operate an anticipate alarm light 58 and to
provide a readout on a meter 60 ("B" meter) indicative of web tension
being exerted by dancer 40 in PLI (pounds per linear inch). Limit relay 56
is connected to operate a limit alarm 62 and to provide a readout on a
meter 63 ("A" meter) indicative of web tension being exerted by dancer 40
in PLI. The control signal to the relays 55 and 56 takes the form of a
voltage representative of the pounds per linear inch exerted by dancer 40
on web W as enabled by switch 54. Limit relay 56 can be preset by the
press operator to establish a predetermined range (upper and lower) within
which repeat length error signals must fall in order to effect a change in
web tension, such as for example a range between 6 PLI and 16 PLI.
Anticipate relay 55 can be preset by the press operator to establish a
range narrower than the predetermined range of the limit relay 56 (such as
for example 8 PLI and 14 PLI) so that, if repeat length error signals
begin to depart from the narrower range, the anticipate alarm 58 is
energized to warn the press operator of this fact, whereupon the press
operator knows that a change in repeat length is occurring requiring
pressure near established limit and he can reset the limit relay 56 to
provide appropriate new limits or reset the register control 47 to
establish a new base repeat length.
As FIGS. 1 and 2 show, photoelectric repeat length scanner 45 is located on
the downstream side of the deck A (which is chosen as the key color deck
in this description) to detect the recurrent register marks R. Scanner 45
provides an abrupt electrical signal upon each occurrence of mark R at the
scanned location (see FIGS. 4d and 4f). A cylinder position detector 44 is
mechanically coupled to and runs at the same rotational speed as the
printing cylinder 31a. The detector 44 provides an abrupt electrical
signal once per revolution of the cylinder to which it is coupled (see
FIG. 4d). The signal, which is fed along with encoder pulses to register
control 47 (to produce signals such as shown in FIGS. 4c, 4d, and 4e)
occurs at a predetermined, fixed angle of rotation of the cylinder 31a.
Thus, when a scanner signal occurs at scanner 45, the signal from cylinder
position detector 44 should occur before that detector has rotated through
a definite, predetermined angle. This required angle of rotation is
represented by definitely known number of pulses from the encoder 47 (see
FIG. 4e). With the drive arrangement shown in FIG. 2, it is possible to
drive the detector 44 and the encoder 47 directly from shaft 23. The
encoder 46 generates a continuous train of pulses, each of which
represents a uniform but very small increment (angle) of rotation of the
printing cylinder 31a. This train of encoder pulses is supplied to the
register control unit 47. As hereinbefore mentioned, a "mark to mark"
register system could be employed instead of that disclosed herein. As
FIG. 2 shows, the signals from scanner 45 and encoder 46 are directed to
the register control unit 47.
As will be understood with reference to FIGS. 2 and 5, the "Hi" and "Lo"
relay contacts of the "A" meter 63 and "B" meter 60 are contacts which are
related to meter needle position. The relay contacts CRB1 and CRB2 in FIG.
5 correspond to the relay contacts in meter relay 55. The relay contacts
CRA1 and CRA2 correspond to the contacts for limit relay 56. The needle of
"A" meter 63 thus controls the relay contacts CRA1 and CRA2 as follows. If
the needle of meter 63 goes to its high limit (set by the press operator),
then relay CRA1 opens its corresponding contacts and the register control
47 prevents motor 48 from operating. Similarly, if the needle of meter 63
goes to its low limit (set by the press operator), then relay CRA2 opens
its corresponding contacts and the register control 47 prevents motor 48
from operating. However, the scanner 45 is still operating and detecting
errors but is unable to cause register control 47 to operate the dancer 40
because the limits set by the operator have been reached. It should be
noted that the mechanical limit switches 52 and 53 are in series with the
relay contacts CRA2 and CRA1, respectively, and when open prevent
operation of motor 48 thereby preventing damage to components, such as
potentiometer 51, connected to shaft 48a of motor 48 thereby preventing
damage thereto.
Referring to FIGS. 2, 5, 5a, 6, and 6a-6f, the reset circuit Z for the key
color control system will now be described. As FIG. 5 shows, register
control 47 includes an internal resistor R across which a voltage signal
(0-0.5v) appears. This voltage signal is proportional to the repeat length
error. This voltage signal is fed to an operational amplifier OA in
circuit Z which in turn provides an output signal (on the order of 0-10v)
to a voltage sensitive relay VSR. The voltage sensitive relay is provided
with contacts VSR which actuate a register memory set circuit in register
counter 47. As FIG. 2 shows, contact VSR is connected in series with a
pair of contacts CRA11 and CRA22, which are parallel with each other,
across the reset terminals T3 and T73 of register control 47, as
hereinbefore described. As FIG. 5a makes clear, for example, when the
input voltage .sup.V IN and .sup.V OUT are at the levels indicated in the
table in FIG. 5a, the number count appearing as the readout on register
control 47 assumes the values indicated in the table. The reset circuit
shown in FIG. 5 operates so that, for example, when the register error
count reaches the numeral 25, then the voltage sensitive relay VSR
operates a contact in register counter 47 so as to reset register control
47 to zero. The purpose and advantage of the reset circuit is best
understood by reference to FIGS. 6a-6f.
As FIGS. 2 and 5 make clear, the relays CRA1 and CRA2 in addition to
operating their respective contacts CRA1 and CRA2, also operate the
contacts CRA11 and CRA22, respectively, in the reset circuit.
Consequently, if relay contacts CRA1 open on high limit or relay contacts
CRA2 open on low limit, either CRA11 or CRA22 would close, but if voltage
sensitive relay contact is still open, the reset circuit Z does not effect
its reset function. However, scanner 45 still senses register errors. As
the register error increases in size, the count in the register control 47
increases and the size of the error is displayed thereby. When the error
reaches a preselected numerical value determined by the design of reset
circuit Z and the new level set by the operator on thumbwheels 75A, 76A,
77A, the circuit Z effects closure of contact VSR. However, as long as the
register error exceeds the preset limit, tension on the web is at its
maximum (or minimum) value and the motor 48 and compensator 40 cannot
operate. However, as the repeat length error changes in magnitude and
comes back within the preset limits, the fact that a circuit is completed
across the terminals T3 and T73 of register control 47 (which has the same
effect as if the reset switch 78 were manually closed), the motor 48 and
compensator 40 come back into operation within the preset limits but at
such new level as to maintain the new tension level on the web.
Referring to FIG. 6a, there is depicted a condition wherein infeed tension
(in PLI) gradually increases from 10 lbs. to 18 lbs. as a period of time
elapses necessary to unwind three-quarters of the roll and then gradually
declines. Thus, the web condition requires an infeed tension which would
range from 10-18 PLI. However, if the PLI tension limit is set at 16 PLI,
it will be observed that there is a period of time during which more than
16 PLI is required but only 16 PLI is available.
Referring now to FIG. 6b there is depicted the register error readout
without the availability of the reset function provided by the circuit
shown in FIG. 5. In this situation, the register error readout is
approximately 00 until the 16 PLI limit is reached whereupon register
error readout increases since the control is not active beyond the limit
set at 16 PLI, for example. When web conditions require 16 PLI or less,
the control is active and returns the repeat length to the initial
established length.
FIG. 6c depicts the situation regarding register error readout with reset.
In this situation, register error readout remains at approximately 00
until the 16 PLI limit is exceeded whereupon register error readout begins
to increase to a readout of between 25 and 50 and then sharply drops to
near zero; this increase and sharp dropoff occurring repeatedly until the
tension level of 16 PLI is established. Note that in this case the
controller 47 has repeatedly been reset (a new repeat length established
with a new control point). The advantage here is that as soon as the web
conditions are such to require 16 PLI or less of tension, the controller
is immediately able to control eliminating the time TI shown in FIG. 6b.
The graph in FIG. 6d depicts a situation which would occur in a system in
not using a key color control system in accordance with the invention and
wherein constant tension is applied to the web.
FIG. 6e depicts a situation wherein a key color control system in
accordance with the invention but without the reset function is employed.
In this circumstance, register error readout remains at approximately 00
until the 16 PLI tension limit is exceeded, whereupon register error
readout increases until it reaches the 18 PLI limit and then recedes until
the tension level required is 16 PLI or less. However, in FIG. 6e, it will
be noted that there is a short period of time after which a register error
occurs even though there has been a return to the 16 PLI limit. It is
desirable that this period of time be eliminated and as comparison of
FIGS. 6c and 6f shows, the reset circuit shown in FIGS. 2 and 5 enables
the register controller to be immediately operative as soon as the 16 PLI
limit is returned to.
SUMMARY OF OPERATION
As is apparent from the foregoing, changes in web conditions effect changes
in print, namely, changes in repeat length of the key color. This, in
turn, results usually in excessive compensator activity, press instability
relative to the web W, and unstable registration. It is desirable,
therefore, to improve registration at the key color deck A to reduce web
spoilage. The key color register or repeat length control system in
accordance with the invention compensates for web condition changes before
the web enters the press, rather than letting the primary register control
compensate for web changes, which causes register disturbances throughout
the press 10. The repeat length control system varies infeed web tension
so that key color nip feed characteristics change to maintain constant
repeat length. The repeat length of the key color is measured and when a
change is detected, the closed loop system varies the infeed dancer
pressure to maintain constant key color repeat length. The repeat length
control system presupp | | |
