Apparatus and method for register control in web processing apparatus

Register control apparatus for a rotogravure color printing press positions an adjustably movable web (or cylinder) compensator mechanism to, in effect, adjust the web length between printing roller nips in successive printing decks to correct for printing registration errors. The register control apparatus employs the principle that there is a predetermined position of the compensator mechanism for any given length of web wherein register error is eliminated. The register control apparatus, which is initially provided or programmed with electronic signal information representative of web length and compensator mechanism position (null position) wherein no registration error occurs, also includes electrical devices and circuitry for sensing and electronically processing incoming signal information relative to web speed; direction, magnitude and rate of registration error; and change of position of the compensator mechanism. The register control apparatus performs computing operations on the programmed signal information and incoming signal information and provides an output signal which locates the compensator mechanism in a position wherein register error is eliminated. The computing operation includes: ascertaining the proportion between the register error and compensator mechanism position; ascertaining the derivative (i.e., relationship) between the rate of change of register error and the rate of change of compensator mechanism position; and integrating to establish the average magnitude of register error and relating it to the average (optimum) position requirement of the compensator mechanism.

BACKGROUND OF THE INVENTION 
1. Field of Use 
This invention relates generally to apparatus and methods for register 
control in web processing apparatus, such as multi-deck rotogravure color 
printing presses, or the like, which employ adjustably positionable web or 
cylinder compensator mechanisms for varying web length between printing 
decks to eliminate register errors. 
2. Description of the Prior Art 
Some prior art register control systems sense and measure only the 
magnitude and direction of register errors and adjust the compensator 
mechanism position accordingly to effect a change in web length and 
thereby eliminate register error. In such prior art systems, compensation 
is relatively slow and allows considerable register error to accumulate 
while a correction is being made. Attempts to increase compensator rate of 
change in such systems result in instability, oscillation and poor 
registration. In effect, such prior art systems involve random (trial and 
error) positioning of the compensator until an optimum position of the 
compensator is found wherein register error is eliminated, but due to the 
cyclic nature of the process, this optimum position is rarely achieved. 
One type of prior art register control system employs a strain gauge for 
measuring web tension between successive roller nips and operates to 
locate the compensator in a position wherein a desired web tension, 
considered to be indicative of no register error, is maintained. However, 
there are many variables which affect web characteristics and web tension, 
such as moisture and humidity, and therefore the last-mentioned prior art 
systems allow register errors to occur, even though a predetermined web 
tension is being maintained, because web conditions are actually changing. 
SUMMARY OF THE PRESENT INVENTION 
Applicants have discovered in connection with register control apparatus 
for web processing apparatus, such as printing presses, that there is an 
important and usable relationship between the length of web between the 
printing roller nips in successive printing decks, the magnitude (length) 
of a register error, and the position of the compensator mechanism which 
acts upon the web between decks to adjust web length therebetween. To put 
it another way, for every web length between successive pairs of roller 
nips, there is an optimum position for the compensator mechanism wherein a 
desired web length is established and register error is eliminated and 
this optimum compensator mechanism position can be ascertained and 
established by means of register control apparatus and method in 
accordance with the present invention. For example, if the length of web 
between printing roller nips to provide correct registration is known to 
be 30 feet (i.e. 15 repeats of 24" repeat length each), and if the 
register error is ascertained to be 0.006 inch per foot of web, then the 
length of the web path must be changed 0.18 inch to eliminate the register 
error. If the position of the compensator mechanism is already known, then 
a calculation can be made as to how far the compensator mechanism must be 
moved in the appropriate direction to a new position necessary to effect 
the decimal change in web length to eliminate register error. Thus, 
instead of moving the compensator mechanism randomly in a trial and error 
process until the register error is eliminated, as in prior art register 
control apparatus and methods, it is possible, in accordance with the 
present invention, to employ apparatus and method for register control 
which employs the above principles in conjunction with relevant signal 
information (both preprogrammed and incoming) to move the compensator 
mechanism directly to a definite predetermined (calculated) new position 
wherein the register error is eliminated. 
Furthermore, for a register error of given magnitude the compensator 
mechanism can be moved to the new position within a predetermined time 
interval to correct the register error within a minimum web length. 
Also, because of the changes in the modulus of elasticity in a web, long 
term (as well as short term) register error can occur. In the case of 
nominal boxboard material, for example, the actual printed repeat length 
can vary by as much as 0.007 inch throughout a roll. Since the nominal 
position of the compensator mechanism is directly related to repeat 
length, then as the repeat length changes, so must the position of the 
compensator mechanism change. Therefore, additional signal information to 
the compensator mechanism is required than was furnished in prior art 
system. Compensation rate is also directly proportional to web speed. 
Accordingly, the following signal information is sensed, evaluated and 
computed in accordance with the system and method of the present 
invention: web speed; magnitude, direction, and rate of change of register 
error; compensator position and rate of change of compensator position. 
In accordance with the invention there is provided web processing apparatus 
such as a rotogravure color printing press which includes means for 
adjusting web length between pairs of printing roller nips in successive 
printing decks to correct for registration errors. The said means, in one 
embodiment includes an adjustably positionable compensator mechanism and 
in another embodiment includes an angularly adjustable cylinder. The 
register control system includes means for sensing, measuring, and 
providing signal information relative to web speed; the direction, 
magnitude and rate of register error; and the position and rate of change 
of position of the compensator. The register control system, which relies 
on the principle that there is a predetermined compensator position for a 
given web length wherein register error is eliminated, also includes means 
for performing computing operations on the aforesaid signal information to 
provide a control signal for adjusting compensator position. Such 
computing operations include: 
ascertaining the proportion between the error signal and compensator 
position; ascertaining the derivative (i.e., relationship) between the 
rate of change of register error and the rate of change of compensator 
position; and integrating to establish the average magnitude of the 
register error and relating it to the average (optimum) position 
requirement of the compensator. 
The method for achieving register control broadly involves the steps of 
placing the compensator in a nominal (initial) position relative to the 
pairs of printing roller nips wherein no register error occurs and 
identifying that first position (by setting the computer to a zero or null 
condition), measuring the web length between the pair of printing roller 
nips with no register error present (i.e., providing a web length 
factor--a gain constant signal supplied to computer), measuring the 
magnitude of a register error when such occurs, calculating on the basis 
of measured web length factor, the nominal or initial or null position of 
the compensator, and register error magnitude a new position for the 
compensator needed to change web length an amount sufficient to eliminate 
register error, and moving the compensator to the new position. 
A register control system in accordance with the invention results in the 
elimination of long term and short term register errors and provides 
improved printing press performance by properly positioning the 
compensator mechanism at the proper rate to achieve correct registration 
with a minimum time and with minimum web waste. 
A register control system in accordance with the invention can be embodied 
in web processing apparatus, such as printing presses, during manufacture 
or in the field and is economical to manufacture, and reliable in use. 
A register control in accordance with the invention effects register error 
correction regardless of the fact that the web is still being subjected to 
variables which affect web characteristics, such as moisture, humidity, or 
other machine induced variables. 
A register control system in accordance with the invention distinguishes 
between long-term and short-term errors and in the case of the former 
shifts the compensator mechanism from one nominal position to a new 
nominal position. 
Other objects and advantages of the invention will hereinafter appear.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 schematically shows a portion of a web processing apparatus, such as 
rotogravure color printing press 10, with which a register control system 
in accordance with the invention is advantageously employed. Press 10 
comprises successive spaced apart printing decks 11 and 12 through which a 
continuous web 13, such as paper, paperboard, or foil, passes in the 
direction of arrow 14. A web compensating mechanism 15 is located between 
decks 11 and 12 and includes an adjustably movable compensator 17, in the 
form of a roll, which engages the changes web length and a servo-drive 
motor 18 which moves compensator roller 17 to effect web compensation, 
i.e. a short-term application of longitudinal strain on the web 13 for the 
purpose of accurate registration. Instead of the web compensating 
mechanism 15, however, a cylinder compensating mechanism of the type 
schematically shown in FIG. 5 may be employed. Each deck comprises a 
framework 19 and a rotatably driven etched printing or gravure cylinder 21 
and an impression roll 20 which holds the web 13 against the gravure 
cylinder. Each deck also comprises other rollers (unnumbered) which guide 
the web 13 therethrough. The cylinder 21 and roll 20 define a nip, i.e., a 
line along which the web 13 is gripped, and the nips in decks 11 and 12 
are designated respectively, as the preceding nip 23 and the succeeding 
nip 24. The term "web length" as used herein refers to the length of the 
web between the nips 23 and 24 and this length varies with the position of 
the web compensator 17 and the repeat length. Repeat length is one 
impression or copy and corresponds to the circumference of the gravure 
cylinder 21. 
As FIG. 2 shows, web compensating mechanism 15 specifically comprises, in 
addition to compensator roller 17 and motor 18, a gear reducer 30 which is 
driven by motor 18 and connected by means of a belt drive 31 and a 
right-angle worm gear drive set 32 to compensator 17. Set 32 comprises a 
drive shaft 33 having gears 34 thereon which engage gears 35 on lead 
screws 36 which are connected to effect movement of compensator 17 in 
advance (arrow 38) and retard (arrow 39) directions. 
As FIGS. 3, 4 and 5 show, the web compensation or cylinder compensation 
principle relates directly to the elastic characteristics of the web 13. 
It is this property that allows one to position a mark previously printed 
41 (41A or 41B) on the web 13 with respect to a mark 40 that is being 
printed. Since there is no web slippage at the gravure nips 23 and 24 in 
web compensation, the web compensator 17 is employed to strain the web 13. 
As FIG. 5 shows, however, in cylinder compensation, the cylinders 20A and 
21A are angularly shifted relative to the web to impose a strain on the 
web. It is this momentary change in the longitudinal dimension (web 
length) or strain of the web 13 that accomplishes registration. 
By definition, as a positive strain is applied to the web 13 by the 
compensator 17, the previously printed mark 41A is retarded with respect 
to the mark being printed 40. Conversely, as a negative strain is applied, 
the previously printed reference mark 41B is advanced with respect to the 
mark being printed 40. Reference mark 41A is retarded with respect to the 
mark 40. As the web entering the nip is relaxed, the reference mark 
advances toward position 41B. The position of the mark 40 does not change, 
only the position of the reference mark (41A or 41B) changes. The 
designations "advance" or "retard" refer to the operation of the controls 
to effect the indicated web movement. 
During compensation, the web tension between the gravure nips 23 and 24 
changes momentarily. Since the compensator velocity is always proportional 
to the web speed, the web tension or stress change is limited to about 10 
percent of the established level. These web tension changes are an 
indirect result of compensator mechanism position change. Therefore a 
definite compensator mechanism position is established for any given 
register error independent of web characteristics. 
The application of an electronic register control for servo-motor 18, as 
hereinafter explained, enables one to accurately obtain a specific 
position for the compensator roll 17 to establish its proper short-term 
web strain position and long-term position. 
By applying the basic principles of stress/strain relationships in 
accordance with the invention and the technique of positional 
servo-control, web compensated print-to-print registration can be 
accomplished. 
FIG. 6 is a schematic diagram of a register control system for rotogravure 
color printing press 10 which includes the adjustably positionable 
compensator mechanism 15 for adjusting web length between the successive 
printing nips 23 and 24 to correct for registration errors. The register 
control apparatus employs the principle that there is a predetermined 
position of the compensator mechanism for any given length of web wherein 
register error is eliminated. The register control apparatus, which is 
initially provided or programmed with electronic signal information 
representative of web length and compensator mechanism position (null 
position) wherein no registration error occurs, also includes electrical 
devices and circuitry for sensing and electronically processing incoming 
signal information relative to web speed; direction, magnitude and rate of 
registration error; and change of position of the compensator mechanism 
15. The register control apparatus performs computing operations on the 
programmed signal information and incoming signal information and provides 
an output signal which locates the compensator mechanism in a position 
wherein register error is eliminated. The computing operation includes: 
ascertaining the proportion between the register error and compensator 
mechanism position; ascertaining the derivative (i.e., relationship) 
between the rate of change of register error and the rate of change of 
compensator mechanism position; and integrating to establish the average 
magnitude of register error and relating it to the average (optimum) 
position requirement of the compensator mechanism. 
More specifically, FIGS. 6 and 6C show that the register control system 
comprises two web scanners 51 and 52. Scanner 51 senses the previously 
printed color location mark 41A or 41B which is indicative of a preceding 
color placement on the web 13 and provides location signals to a mark 
location comparator 53. Mark location comparator 53 compares a mark 
location from scanner 51 to the signal from scanner 52 which senses the 
mark 40 being printed. That difference signal is compared to a programmed 
location for the two marks. As FIGS. 6 and 6C show, the system also 
comprises a cylinder angular velocity/position transducer 54 which 
provides a basis for retaining the programmed mark location requirement. 
This programmed mark location requirement is a memorized count value that 
is the pre-programmed required relationship between the two marks that are 
scanned by scanners 51 and 52. As FIGS. 6 and 6B show, a mark location 
scalar and vector computer 55 is provided to scale the mark change in 
location into a unit of linear measurement in magnitude and direction. 
Computer 55 provides a series of binary pulses that are counted in one 
direction or another to determine the direction of the register error and 
magnitude of register error. This pulse count is stored on a continuing 
basis. More specifically, the relationship between the two marks is 
counted in pulses and stored and compared to a previously established 
compensator position requirement. The difference between previous position 
requirements and the current output from the error computer 55, indicative 
of a register error, is a signal comprised of a magnitude component and a 
direction component. As FIGS. 6 and 6D show, a compensator position 
computer 56 is provided to translate the change in mark location into a 
compensator position change requirement, as a function of compensating web 
length. The error count (a binary count) represents magnitude and 
direction of register error and is converted to a binary coded decimal 
(BCD) indication or display signal for the operator. The binary signal 
value is translated to a hexadecimal value and is used to compute the 
required compensator position change. As used herein the term hexadecimal 
means a series of counts 1 to 16 that the computer program uses because it 
is more convenient and accurate to manipulate numbers with that number 
base. As FIGS. 6 and 6D show, a compensator position regulator 57 is 
provided to command and control a compensator position change which will 
return the mark to its location requirement. More specifically a digital 
signal provides digital counts which are used to position the compensator 
regulator and these counts are matched by the counts that are received 
from the velocity/position transducer 58 for the purpose of determining 
what the actual movement of the compensator is relative to the command. As 
FIGS. 6, 6A and 6D show, a compensator velocity/position transducer 58 is 
provided to provide scalar and vector information of compensator velocity 
and position. Transducer 58A provides digital pulse signals which indicate 
the position change of the compensator 15 from its initial nominal 
position. As a practical matter, in operation, the range of corrective 
movement of the compensator 15 in inches would be typically on the order 
of 30,000 of an inch, although the total possible movement of the computer 
can be up to about 40 inches for set-up of press to establish initial web 
length. A compensator velocity regulator 59 is provided to command a 
velocity of compensator speed which is proportional to web speed and to 
position error. The compensator velocity regulator 59 receives input 
signals and provides an output signal at 59d. Signal 59a is signal 
proportional to web speed. Signal F is a digital to analog converted 
signal of plus and minus value, such as zero to five volts, and represents 
the velocity command from the position regulator 57. Signal g represents 
an analog signal which is proportional to the velocity of movement of the 
compensator 15. The output signal 59d is an analog signal that commands 
the motor control power unit 61 to provide power to the DC motor 18 which 
moves the compensator 15. The combination of signals c and F comprise one 
signal F which is compared to the signal g. The combination of two signals 
provides the velocity regulator 59 with analog information of the velocity 
error between its command F and its feedback signal g. A web speed 
transducer (i.e., a tachometer) 60, responsive to web speed at roller 64, 
provides a signal to maintain the compensator velocity proportional to web 
speed. The position regulator velocity command signal F is a function of 
register error and web speed. The web speed signal is provided by the web 
speed transducer 60 and takes the form of digital pulse information that 
is frequency related to and representative of the speed of the web. A 
motor control amplifier 61 is provided to amplify the low level control 
signal from velocity regulator 59 to motor 18. Motor 18 converts amplified 
signals into mechanical motion of compensator 17. The web compensator 
mechanism 15 thus imparts longitudinal strain to the web 13 in a tensive 
direction of varying magnitudes, the result of which is to relocate the 
preceding previously printed color location mark 41. The effect of 
imparting longitudinal strain on web 13 is a result of compensator 
movement and has the effect of stretching the web 13 between the pair of 
roller nips 23 and 24. As the web is stretched, the effect is to retard 
the position of the previously printed mark 41A with respect to the mark 
40 being printed. The purpose of imposing strain is to effect an immediate 
change in the registration from the preceding mark 41A to the mark 40 
being printed. After a period of time, when all web between the pair of 
spaced apart nips 23 and 24 is replaced by a new web, the resulting 
displacement in the color (mark) placement is permanent, even after strain 
or stretch imparted to the web goes away. In an alternative embodiment 
shown in FIG. 5, when using an adjustable roller to achieve web 
compensation, the effect of the angular shifting of the rollers 20A and 
21A is to stretch the web but there is no web slippage relative to the 
rollers. 
The method of registration error calculation involves comparing a 
calibrated number of encoder pulses to successive pulse inputs. The 
reference-to-mark calibration method uses the zero reference signal to 
start the pulse count and the sensed color mark to stop the count. Any 
deviation from the calibrated count is register error. This "BCD" error 
magnitude must be converted, by the control, to inches of error based on 
the repeat length calculation. 
The scaled signal must be further compared and conditioned. The error in 
pulse counts has "high" and "low" frequency components associated with it. 
The high frequency variations (0.5-8.33 HZ) are to be filtered out based 
on their amplitude and frequency. When a significant difference in error 
occurs there is to be no velocity command issued. If the error returns to 
a value below the "impulse limit" with the next impression the auto 
compensation will resume. If, however, the error remains above the limit 
after four impressions, auto operation must then resume (as the error may 
no longer be considered transient). 
FIGS. 12, 13 and 14 depict actual color register charts recorded during 
three production runs and under identical conditions. These charts show 
the register of two colors during production at a web speed of 400 feet 
per minute. The heavy horizontal line A indicates zero register. Each 
small division indicates one thousandths of an inch. Each "blip" or dot 
indicates the register reading of one imprinting. There are 320 
imprintings recorded between each heavy vertical line B. FIG. 12 shows 
register variation without register control. FIG. 13 shows register 
variation with slow response, as in existing prior art systems. FIG. 14 
shows register variation with a register control system in accordance with 
the present invention. 
FIGS. 15, 16 and 17 are graphs which depict the cyclic nature of register 
error in a rotogravure press on a short term basis. The curve in FIG. 15 
is a typical cyclic register depiction and relates the random variation in 
printed repeat length relative to time. The two curves in FIGS. 16 and 17 
represent compensator movement related to time for register errors of the 
type shown occurring in the curve of FIG. 15. 
As FIG. 16 shows, typical prior unidirectional control compensator motors 
can move only in one direction relative to horizontal reference line H for 
a given polarity of register error. The result is that as the register 
polarity crosses over, the compensator is in the wrong position at zero 
register. It is this factor that requires that unidirectional control 
systems operate with very slow response. 
As FIG. 17 shows, the velocity/position register error control system in 
accordance with the invention has the capability to move the compensator 
roller 17 in either direction (above or below reference line H) for any 
given polarity of register error. This is accomplished as a result of 
sensing the register error trend as shown in the curve in FIG. 15, as well 
as providing for the compensator position. Thus, a system sensing the 
register trend, actual register error, and computing positional change 
requirements is constantly capable of returning to the nominal position 
irrespective of register polarity. This capability permits high 
compensation rates, for example, five inches of web compensation per 
minute, which is a factor of at least ten times greater than some existing 
controls. 
As FIG. 6 shows, the control system includes means for providing 
proportional, integral, and derivative command signals to the compensator 
15, as a function of the wave form of the BCD register error input signal. 
The mathematical representation of this position command is explained 
below. The graph in FIG. 18 shows a wave from W representing a register 
error and the derivative, integral and proportional terms (labelled in 
FIG. 18) referred to herein are discussed relative to that wave from W. 
The equation that represents the position command is: (EQ-1) position 
command, 
##EQU1## 
Where: P=Position command in inches 
e=Register error in inches 
x=Repeat length in inches 
t=Time in seconds 
A.sub.0 e.sub.1 (inches)=proportional command 
##EQU2## 
The repeat length refers to the circumference of the gravure cylinder 21. 
It is a variable that must be computed each time a new set of gravure 
cylinders 21 is placed in the press. The method employed is to first 
measure the linear speed of the web 13 and then divide by the impression 
rate. (EQ-2) Repeat length=x=Web speed (IN/SEC)/Impression Speed (RE/SEC) 
Therefore: 
##EQU3## 
The web speed measuring tachometer 64 is located on the web 13 for this 
purpose. In regard to equation (EQ-1), the proportional gain (A.sub.0), 
derivative gain (A.sub.1), and integral gain (A.sub.2), values are 
required to be fully independent and adjustable. 
As an aid in understanding the present invention, the register control may 
be considered as performing a transfer function according to the block 
diagrams shown in FIGS. 20 and 21 and in accordance with the analysis of 
FIG. 18. The transfer function is comprised of three terms (see FIG. 21) 
which, when summed, become the position command. 
Where: 
e.sub.1 (inches)=existing register error 
e.sub.0 =previous register error 
x=repeat length (inches) 
A.sub.0 e.sub.1 (inches)=proportional command 
##EQU4## 
Therefore the general equation for the position command is: 
##EQU5## 
The gain constants A.sub.0, A.sub.1 and A.sub.2 have been introduced here 
by realizing that the ultimate system response is a function of the length 
of web that the web compensator must control. This web length factor is 
the nip-to-nip web length less the web resistence of the idler rolls it 
contacts. By analysis it has been found that the derivative gain (A.sub.1) 
is large in magnitude compared to the other two (A.sub.0 and A.sub.2). 
The practical maximum gain for A.sub.1 is the web length in inches from 
nip-to-nip and this must be expressed in the same unit distance by which 
the derivative term is computed. For example, A.sub.1 =Nip-to-Nip web 
length=384 inches is typical. 
The maximum gain for A.sub.0 and A.sub.2 would be the theoretical value of 
1 (one). In practice, these gains are varied for system stability and 
usually are less than unity gain. 
A.sub.1 presents itself as the most significant factor for determining the 
ultimate performance of the register control system. This is true because 
register errors are always changing in a sinusoidal pattern, as FIG. 18 
shows. 
The control system performs the transfer function and positional control on 
each repeat length. The repeat length and the web speed define the time 
period of position control, because the error is sampled once per repeat. 
Each time the web compensator 17 moves, the registration error wave form 
changes (i.e., as regards slope and magnitude). It would be impractical to 
attempt to predict the required compensator position between the sample 
periods for each repeat length. As a result the nature of this 
servocontrol is incremental, in that it can only compute a position 
command once per repeat length. It is impractical to attempt programming 
it to anticipate error trends between repeats. Therefore, in practice, the 
operation of this control system is limited by the fact that the register 
error is sampled once per repeat length; that is, the control must assume 
that, having computed a position command, error causing conditions do not 
change significantly from one repeat length to the next. This is a valid 
assumption based on actual field testing. The largest error recorded in 
field testing was 0.001 of an inch per foot of web. Therefore, the present 
control would allow the worst case error of 0.003 inch in a longest 
typical repeat length of 36 inches. The nominal register error was 
recorded during field testing was 0.0002 inch/foot. 
In graphical form the result of a properly implemented transfer function 
will take the form of that illustrated in FIG. 19, A large step error is 
shown to illustrate compensation under magnified conditions. In the graph 
shown in FIG. 19 wherein feet of web is plotted against register error in 
inches, the curve A depicts the register error per unit feet of web 
passing through the printing roller as was described before. Curve B 
depicts the position change in inches of the compensator relative to the 
sheet of web passing through the printing roller. The graph in FIG. 19 
depicts the proper function of a compensator such as 15 which will reduce 
the initial register error to zero in as short a time as possible. 
By taking into account one more variable, which is the wrap angle of the 
web 13 on the compensator roll 17, as being a constant of 180.degree., the 
actual transfer equation can be expressed as: 
##EQU6## 
By substitution from equation (EQ-3) we obtain: 
##EQU7## 
A functional representation of the algorithm as implemented by an 
electronic circuit is shown in FIG. 21 and should be considered in 
conjunction with equation (EQ-5 and EQ-5A). 
OPERATION 
Referring to FIG. 6, the initial conditions for operation assume that the 
control system is set in the manual mode and the register error 
measurement control is set in the memory set mode. The memory set mode 
establishes the physical relationship between mark 40 and mark 41. The 
digital pulse signal L from scanner 52 generated by mark 40 enters into 
the circuit block 53 on signal line e. 
The pulse generator signal M from scanner 51 generated by mark 41 enters 
into the circuit block 53 on signal line m. The relationship between mark 
40 and mark 41 is recorded and stored in the memory to later be compared 
to the ongoing relationship sensed relative to the continuous repeat of 
mark 40 and mark 41. In the memory set mode the compensator 15 is jogged 
into position by means of a manual advance and retard pushbutton 70A under 
operator control. While the press 10 is running at a low production speed, 
the compensator 15 is jogged to an initial position to establish the 
desired relationship between mark 40 and mark 41. Once this occurs the 
control is switch to automatic control (70) and the error measurement 
counter is switched to the automatic mode (71). 
As soon as the operator jogs the compensator 15 into the correct position 
by means of switch 70A the desired relationship between mark 40 and mark 
41 is established. The relationship between marks 40 and 41 as established 
by the operator, is memorized by means of the cylinder position pulse 
count which is produced by the encoder 54 which is geared or connected in 
a one-to-one relationship with the gravure cylinder 21. The pulses from 
the cylinder encoder 54 are counted and the relationship between marks 40 
and 41 is digitally computed, representing a particular count value in 
binary coded decimal (BCD) terms, which is memorized and available to be 
compared automatically to the continuous BCD count value between mark 40 
and mark 41. The control circuit 53 computes any difference in count 
between the memorized count and the continuous on-going count per repeat 
length between marks 40 and 41. At the same time the control circuit 57 
begins controlling the relationship between the marks 40 and 41 as a 
result of a BCD error count signal B which comes initially from circuit 53 
as a result of the aforementioned computation. See FIGS. 8 and 6B. The BCD 
error signal B is a plus and minus count value which represents the error 
or difference in position between marks 40 and 41. The serial BCD 
information is transmitted as a signal on line B in circuit 55-4 via an 
asynchronous transmitted mounted in the error measurement control 53. It 
transmit the BCD error signals by means of a UART LSI integrated circuit 
55-4 in serial format through line drivers and line receivers to the UART 
located at 55-4. The output of the receiving UART is a BCD signal which 
contains information identical to that which had been transmitted from the 
transmitting UART. It is provided to the computer as required and is 
represented as a hexidecimal error value for use in the UART SVC routine 
provided by circuit 55-1. The hexidecimal error value must be converted to 
a value of error in inches for the purposes of proportional control. This 
is accomplished by the ASEQ routine of circuit 55-2 (FIG. 7). The circuit 
55-2 needs a signal from the circuit 55-3 which is a signal represented in 
hexidecimal form and which is a count value of the repeat length of the 
web 13 being printed. The repeat length is computed in circuit 55-6 by 
means of incoming signals at lines A and C. The signal at line A 
represents an input from the cylinder reference pulse generator 54. This 
is a digital pulse which signifies one revolution of the gravure cylinder 
23. The other signal at line C comes from the web speed encoder 60. These 
pulses represent a calibrated value in terms of a given number of pulses 
per inch and that value is counted or computed between reference pulses in 
circuit 55-6. The computation in circuit 55-6 represents a calibrated 
pulse count of the repeat length in inches. The repeat length in inches is 
applied to the data bus of the computer and it is called for by the INIT 
routine circuit 55-3. The repeat length is also called for by the circuit 
55-2, for the purposes of error computation in inches. The circuit 55-2 
performs that error computation in inches by the shown formulas and 
outputs the error value in inches on signal line D which goes to the 
circuit 56 that is programmed to compute the required position change 
relative to the register error of the compensator 15. (FIG. 6D) The ASEQ 
routine of circuit 56-2 is programmed to execute equation (EQ-5) (FIG. 
10). The ASEQ routine receives the web length factor from the data bus as 
set by circuit 56-1. The computer is provided with the web length factor 
by means of circuit 56-1. The web length factor is a BCD word or signal to 
the computer. The computer uses this value represented in hexidecimal form 
to compute the compensator position requirement through the ASEQ routine 
in circuit 56-2. The signal at line i is a hexidecimal count value which 
represents the position change requirement for the compensator 15. It is a 
digital value that represents both the direction and the magnitude of the 
required position change. The position change value i is received from the 
data bus by the ASEQ routine circuit 57-6 and that value is compared on an 
interrupt basis to the signal e entered on the data bus which represents 
the position change of the compensator. This signal is provided by circuit 
57-2 (FIG. 11) which represents the input from the compensator position 
encoder 58A. The compensator position encoder signal from 58A provides two 
pulse trains which are 90.degree. out of phase with each other. Phase A 
leads phase B in the clockwise direction. This provides directional 
information as well as magnitude information of compensator position in 
the form of digital pulses. Circuit 57-2 provides the pulses on an 
interrupt basis directly to the central processing unit 57 of the 
computer. Through the C pulse counter routine of pulse counter circuit 
57-7, these pulses are counted and the relationship of these pulses with 
respect to the magnitude and direction of motion of the web compensator 15 
are stored for the purposes of providing the ASEQ routine circuit 57-6 
with the proper information to compare the position command signal to the 
actual position signal of the compensator 15 as it is being commanded to 
change. The ASEQ routine of circuit 57-6 outputs the difference of the two 
pulses, (Signal i minus the pulses form signal e) to the velocity limit 
logic control circuit 57-4, which is again in the ASEQ routine circuit 
which is programmed to limit the velocity reference signal count directly 
proportional to web speed. This portion of the ASEQ routine of circuit 
57-5 receives these velocity count values represented in hexidecimal form 
from the UPDATE routine of circuit 57-5 (FIG. 7). The UPDATE routine 
simply counts the number of pulses in a given time period and according to 
a calibrated value determines actual speed of web 13 for the purposes of 
this value being called by the ASEQ routine circuit to limit the velocity 
pulse count wth respect to web speed (see web tachometer roll dia. cal. 
(FIG. 7). The ASEQ routine provides digital pulses to the digital to 
analog converter circuit 57-3 (FIG. 9) which represents the velocity 
command in digital form. The count value of the digital pulses represents 
the velocity requirement for the web compensator 15 or the cylinder 
compensator. The length of time that those pulses are present at output F 
(FIG. 6D) determines the position requirement for the velocity control. A 
plus and minus 5-volt DC signal is provided as a signal at line F a period 
(time) proportional to register error and the magnitude proportionate to 
web speed. The signal at line F goes to circuit 59 (FIG. 6A) which 
represents the velocity command voltage. It is summed through a 
differential amplifier 59a with the analog voltage zero to plus and minus 
13 volts DC signal at line g which represents zero to plus and minus 1,860 
RPM of the compensator drive motor 18. This signal at line g which is the 
velocity tachometer signal is provided by device 58-B which is a DC 
tachometer whose output is 7 volts per thousand RPM. The two signals are 
compared through this differential operational-amplifier 59a and the 
output becomes a signal at line 59d which is a current reference which is 
an amplitude modulated plus and minus DC signal for control of the DC 
amplifier 61 that controls DC motor 18. Motor 18 is mechanically coupled 
through the compensator mechanism 17. When the DC motor 18 turns clockwise 
the compensator 15 is driven in a direction which advances the position of 
the mark 40 (which is the mark being printed) with respect to the mark 41 
(which is the mark that has previously been printed). 
As a general comment to the discussion of the circuit of FIG. 6, all inputs 
to the computer are provided when the computer routine requests that 
particular data. The only exception to this is the data from the 
compensator position encoder 58A. This data is received by circuit 57 on 
an interrupt basis. 
FIGS. 3 and 5 are schematic representations of web compensation and 
cylinder compensation mechanisms, respectively. As FIG. 3 shows, in web 
compensation, movement of compensator 15 in a direction and magnitude of 
1/2.times. will produce an eventual register change of mark 41 with 
respect to mark 40 which is a distance x from an initial mark 41 position 
in line with mark 40. The number of cylinder revolutions that occur before 
full correction results is defined by the ratio of the web length in path 
to the circumference of the gravure cylinder 21. For example, with respect 
to FIG. 5, 
##EQU8## 
if the web length is 30 feet, and the cylinder circumference of 21 is two 
feet. Then the number of revolutions=30 ft./2 ft.=15 ft. for full 
correction of x to take place as seen on the web 13 exiting from cylinder 
21A. 
From this example, it is apparent that as far as the upstream web path is 
concerned, the concept of register control is equivalent between cylinder 
and web compensation, and the register control system in accordance with 
the invention, as hereinbefore described, is applicable to a cylinder 
compensation system such as is shown in FIG. 5, wherein angular rotation 
of cylinder 21A in the appropriate direction is the corrective action 
taken, instead of movement of a compensator 15, such as is shown in FIG. 
4.