System for accurately positioning operations on conveyed products

A system for accurately controlling the start and stop positions for operations on conveyor-moved products, such as for applying glue lines, perforations or slits on sheets of paper, uses product position rather than timing to accurately control "on" and "off" operation positions on the product. The entry of a sheet of paper, for example, onto the conveyor path is noted by detecting the leading edge of the paper moving past an optical sensor. The location of the sheet is always known in a computer, due to conveyor position information continually fed to the computer. Distances which will be involved in the compensation times for the operating devices (e.g. glue heads) are calculated so that the gluing or other operation will be accurately located, but because the speed of the conveyor may vary, the "on" and "off" compensation distances are not calculated until just before the paper reaches the glue head, with current speed determined and applied to the known compensation times to calculate compensation distances.

BACKGROUND OF THE INVENTION 
The invention is in the field of timing of operations of moving workpieces 
in an assembly line process. In a specific embodiment the invention is 
concerned with operations performed on sheets of paper, such as applying 
dots or lines of glue, perforations, or slits to the paper. In accordance 
with the invention the control of the positioning of these operations is 
made more precise and waste of initial sheets is avoided. 
In manufacturing operations on moving workpieces carried on a conveyor, it 
is important that the operation be carried out at the proper location on 
the conveyed product, and this can be affected by compensation times or 
lag times of the operating devices. Such a compensation time is the delay 
between the time an electrical pulse is sent to the operating device and 
the time the operation actually takes place, and similarly, the delay to 
discontinue an action such as applying a slit or glue line. In many 
systems the timing of the operation, to allow for the compensation time, 
has simply assumed a fixed time duration between a sheet trip point and 
the operation of the device, which assumes a constant speed of the 
conveyor. More accurate encoder-driven systems base operation of the 
device as a function of position, but still base the lead time for 
operations on a selected conveyor speed. If the conveyor speed changes in 
such prior systems, or if an interruption occurs, the resulting position 
on the workpiece where the operation actually takes place will be shifted. 
If the operator decides to select a different conveyor speed, he will have 
to change the lead times for turning "on" and "off" each operating device. 
One example of such a process is the performing of operations on sheets of 
paper. In application of glue lines, for example, the conveyor moves quite 
fast and a change in speed can cause considerable inaccuracy in the 
application of the glue if compensation time is applied based on an 
assumed speed. The results are adversely affected as well simply by 
relying on timing for dispensing the glue, assuming the paper will be at 
certain positions at certain times based on assumed conveyor speed. 
Typically several settable potentiometers have been used in the operations 
of glue-applying machines, with these potentiometers being settable by the 
operator to allow for the compensation time of each glue head. However, 
the operator has typically had to discard several sheets, because he had 
to make trial and error runs of several sheets in order to correctly 
"tune" the potentiometers to apply and cut off electrical pulses at 
precisely the right times to achieve the glue pattern in the desired 
position. Also, in the actual run, once the timing of the glue heads is 
tuned, one or several more sheets may need to be thrown away because the 
conveyor is not yet up to ideal speed, affecting the location of the glue 
application. 
As such, current glue dispensing techniques and systems typically assume 
that the conveyor, and therefore the passage of the paper or other 
workpiece, maintains a constant speed during the process thereby resulting 
in both product and time losses. 
SUMMARY OF THE INVENTION 
The invention described herein overcomes problems of proper tuning of an 
operation wherein glue (or another operation) is applied to sheets of 
paper, primarily by using distance or position rather than timing, to 
govern the activation of glue heads subject to compensation times. The 
speed of operation of the conveyor can vary quite widely with the system 
of the invention, without resulting in significant errors in location of 
the glue on the paper. 
Similarly, for other operations performed by an operating device on 
products moving on a conveyor, the system of the invention assures 
accuracy and avoids extensive setup time and the use of trial and error in 
the setup. 
In accordance with the present invention, a system is provided for 
accurately controlling the start and stop positions for operations on 
conveyor-moved products, operations such as described above. The system 
uses product position rather than timing to accurately control "on" and 
"off" operation positions on the product. The entry of a sheet of paper, 
for example, onto the conveyor path is noted by detecting the leading edge 
of the paper moving past a sensor, which may be an optical sensor. A shaft 
encoder continually feeds conveyor position information to a computer, in 
which desired operation "on" and "off" positions have been prestored. 
Thus, once the sheet of paper has entered the path, its location is always 
known in the computer, assuming the paper moves with the conveyor. The 
computer calculates desired result positions for "on" and "off" for each 
cycle of operation to be performed on the paper. The operating devices, 
such as glue heads, have a known compensation time, i.e. a delay between 
the time a pulse is started to turn the glue head "on" and when glue 
actually begins to be dispensed, and a similar "off" compensation time. 
The distances which will be involved with such compensation times are 
calculated as a function of conveyor speed so that the gluing or other 
operation will be accurately located, but because the speed of the 
conveyor may vary, the "on" and "off" compensation distances are not 
calculated until just before the paper reaches the glue head, with current 
speed determined and applied to the known compensation times to calculate 
compensation distances. These distances are used to determine conveyor 
positions at which to turn the glue head (or other device) "on" and "off". 
Thus, the above speed and compensation distance calculations are completed 
immediately before the workpiece reaches the operating device, so that the 
measured conveyor speed information is as current as possible, thereby 
most accurately timing the activation of the glue head or other device. In 
a preferred embodiment the calculations are made so as to be completed an 
approximate preselected distance from the first "action" position, i.e. 
position at which an electrical pulse should be sent to turn the operating 
device "on". Such distance in one preferred embodiment is determined 
through preliminary, quick calculations which are made well in advance of 
the paper's reaching the glue head. These preliminary calculations, 
including speed of the conveyor and a calculation of approximate "advance 
distance" in front of the glue head at which the compensation distances 
should be calculated, are made repeatedly, e.g. every 50 milliseconds. 
Thus, once a position sensor has determined that a sheet of paper is on 
the belt at a known position, preliminary calculations are repeatedly 
made. These calculations include the current speed of movement of the 
belt, multiplied by the sum of a known required computation time and the 
"on" compensation time of the glue head which the paper is approaching. A 
computation time of 400 microseconds in this particular embodiment 
represents the time required to make the calculations of the first "on" 
and "off" compensation distances along with action positions at which the 
first electrical pulse "on" and "off" should occur, for the programming 
and computer used. The preliminary calculation described above gives a 
rough advance distance at which the first "on" and "off" compensation 
distance calculations should begin. This is preferably multiplied by a 
safety factor of 2 in this embodiment, to allow for any speed increases of 
the belt and also to allow for the possible need for a preliminary brief 
pulsing opening or "tickle" of the glue head, as described below. 
The paper continues in its path, with the above preliminary calculations 
repeatedly made. At a position where the computer determines that no more 
preliminary calculations can be made before the point is reached where the 
actual "on" and "off" compensation distances must be calculated, those 
compensation distance calculations are then commenced. In this way, it is 
assured that the "on" and "off" compensation distances are calculated at 
the last possible moment and position, so that the latest conveyor speed 
information is used. 
Further, a problem with glue heads is that there will be an additional 
delay if the glue head has not cycled on and off for a predetermined 
period of time, such as about one-half second. This would cause a 
positioning error. To avoid this problem, in the event the predetermined 
time has elapsed without action, as defined by the computer, the glue head 
is cycled on for about 20% of its normal compensation time (then off 
again), a short distance before the glue head is reached by the paper. 
This causes only a partial opening of the glue dispenser (such that glue 
is not dispensed), loosening it such that glue will be dispensed in a 
regular and predictable manner during its subsequent repeated on/off 
operation. The pulsing action starts a bouncing effect in the glue 
dispensing head, thus assuring more consistent time delays to operation. 
The safety factor described above leaves sufficient advance distance for 
this brief pulsing of the glue head to be carried out. 
It is therefore among the objects of the invention to achieve accuracy in 
the position of operations performed on products moved by a conveyor, 
making allowance for both the "on" and "off" compensation times for 
various operating devices, such as application of slits, perforations, 
dots or lines of glue on sheets of paper. The invention avoids the need 
for trial and error in setup and for rejection of products due to errors 
in operation positioning; it enables programming to be done by entering 
specific position values rather than on a trial and error basis. These and 
other objects, advantages and features of the invention will be apparent 
from the following description of a preferred embodiment, considered along 
with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In FIG. 1 a product 10, which may be a sheet of paper, is moving on a 
conveyor 12 toward an operating device G, which may be a glue dispensing 
head. Although the system in this embodiment is described in terms of a 
preferred application to glue lines being applied to paper, the system and 
method are much more broadly applicable, as discussed above. The movement 
of the conveyor is measured by an encoder 16 (which may be a shaft encoder 
or other encoder sensing the belt) which transmits increments of motion 
and thus conveyor position information to a computer or CPU 18. A sensor 
20, which may be an optical sensor, inductive, capacitative or other type 
of sensor, detects when the leading edge L of each paper reaches a 
position A at which the sensor 20 is located or aimed, and transmits the 
information to the CPU 18, as indicated. Each sheet of paper 10 has a 
point B (begin) at which the glue line 22 or other desired operation is to 
begin as applied by the glue head G (the position of the glue head is also 
identified as G). The sheet 10 also has a point E (end) at which the glue 
line 22 is to end, i.e. where the glue head G is to terminate its action. 
Several such glue lines or other operations may occur on a single sheet. 
In the CPU 18 are prestored a number of data, among which are (a) 
information to relate the shaft encoder readings to the position and 
movement of the conveyor; (b) the distance from A to G, the sensor 20 to 
the glue head; (c) the "on" and "off" compensation times for the glue head 
G; (d) the desired locations B and E on the sheet of paper 10 at which the 
glue line or strip is to begin and end, relative to the leading edge L of 
the paper (there may be additional glue lines as well); and (e) a known 
duration of time required for the CPU's calculation of "on" and "off" 
compensation distances along with calculation of resulting action 
positions relative to the point G, where an electrical pulse to activate 
the glue head G should begin and end. These "on" and "off" action 
positions are shown in FIG. 1 at O and F. In a preferred embodiment, the 
CPU 18 repeatedly calculates speed of the conveyor as sheets of paper 10 
and 10a progress toward the glue head G. As an example, a speed 
calculation may be performed about every 50 milliseconds, i.e. about 20 
times per second. 
Important objects of the system and method of the invention are (a) to 
accomplish triggering of an operation, e.g. the glue dispensing which 
involves a compensation time, by paper position rather than by timing, and 
(b) to accurately determine the proper triggering positions, in advance of 
the glue head, by calculating compensation distances based on conveyor 
speed as determined as recently as possible before the glue head actually 
must dispense glue onto the paper. Based on this latest up-to-date speed 
information just before the paper reaches the glue head, the computer 
calculates both "on" and "off" compensation distances for the first strip 
or dot of glue which is to be applied to the paper. In this way, all but 
the most insignificant glue positioning errors are avoided, since any 
conveyor speed changes which occur between the time of these calculations 
and the application of the glue to the paper will be relatively small. 
As the sheet of paper 10 progresses along on the conveyor 12, its leading 
edge L reaches position A, at which the paper edge sensor 20 notes the 
presence of the paper and sends a signal to the CPU 18. The computer 18 
has the information relating to the distance between A and G; the computer 
can thus use information from the encoder 16 to constantly monitor the 
position of the paper 10, via its leading edge L. The computer therefore 
constantly has the position of the paper's leading edge L and the 
remaining distance between L and G, the glue head. 
As the sheet of paper 10 moves along, conveyor speed is repeatedly 
calculated as noted above. Along with each speed calculation there 
preferably is made another calculation. Prestored "on" compensation time 
for the glue head is added to the known time required for the computer 18 
to make calculations of "on" and "off" compensation distance and resulting 
first "on" and "off" action positions. This known calculation time 
duration may be, for example, 400 microseconds. The sum of these two known 
times is multiplied by current conveyor speed, to determine an approximate 
"advance distance" in front of the glue head at which the calculations of 
compensation distance and action position should be made. To this 
calculated distance, a safety factor is applied, of 2 times (although 
other safety factors can be selected). This information is used to enable 
the calculation of compensation distances and "on" and "off" action 
positions at the last possible point before the first action position is 
actually reached, so that conveyor speed information will be as current 
and accurate as possible. 
It is noted that, if the computer requires about 400 microseconds to make 
the compensation distance and action position calculations as described, 
the repeated preliminary speed and distance calculations just described 
will take a little more than half this time, i.e. just over 200 
microseconds, because these are simpler and fewer calculations. 
When the sheet of paper reaches a position such that, based on the last 
preliminary calculation of "advance distance", no further such calculation 
can be made before the paper (or point B) enters the "advance distance" as 
just calculated. The computer commences the compensation distance and 
action position calculations. Note that the "advance distance" ordinarily 
will extend farther back than point O in FIG. 1, more than twice the 
distance between O and G. 
FIG. 1 shows a sheet of paper 10a on the conveyor, as its leading edge L 
reaches point O, a calculated first "on" action position. In accordance 
with the method described, the computer 18 has just completed the 
calculation of the location of point O, just before the paper reached this 
position. The calculations just completed have included calculation of an 
"on" compensation distance based on current speed, as well as preferably 
an "off" compensation distance based on current speed, for a first line or 
strip of glue to be applied to the paper. Using these compensation 
distances, the computer has in essence subtracted the calculated "on" 
compensation distance from the begin location B of the glue head, to 
arrive at a position in advance of G. This is shown in FIG. 1, with the 
resulting position being that position where the point B lies when the 
sheet 10a is at the position shown. To this position the computer adds 
back the distance between B and L on the paper, i.e. the distance between 
the begin point of the glue and the leading edge of the paper. This 
calculation results in the position O as shown in the drawing. Similarly, 
position F is also calculated in advance of the paper's reaching point O. 
The point F is determined by subtracting the "off" compensation distance 
from the position G, and by adding back the distance between E and L on 
the sheet of paper. This is shown with respect to a sheet of paper 
indicated in dashed lines in FIG. 1. The result of this calculation is the 
position F, which is shown beyond the point G. The paper shown in dashed 
lines has its leading edge L at the point F, so that the pulse activating 
the glue head would be turned off at this position of the paper, to 
terminate the glue strip 22. 
In many applications, more than one similar operation will be performed on 
each product, and in the case of glue applied to paper, a series of dots 
or strips of glue may be applied on a sheet. The system preferably does 
not update the speed calculation for each separate glue strip to be 
applied, but instead relies on the latest speed calculation which was used 
for the "on" and "off" compensation distance calculations. These 
calculated compensation distances are used for each of the series of glue 
lines or strips on the particular sheet of paper. Only the action 
positions (O and F) will differ for each of the glue lines. Preferably, 
after the first calculation is made the computer 18 stores the "on" and 
"off" positions O and F, the first "on" position O being put into a 
compare register in the computer. A flag is set when the computer 
determines, via the shaft encoder 16, that the paper's leading edge L has 
reached this position. The first "off" position F has also been 
calculated, as noted above, in this calculation which occurs before the 
leading edge L of the paper reaches O. When the "on" action position O is 
actually reached by the leading edge L, the electrical pulse is of course 
initiated to turn the glue head "on", and at the same time, the computer 
shifts the "off" point F location to the compare register. The computer 
then proceeds to calculate the next "on" action position, for the second 
glue line to be applied to the paper. This is done using the compensation 
distances and the positions of the beginning and end points of the second 
glue line, relative to the leading edge of the paper. Thus, the computer 
stays ahead by one calculation, in addition to the calculation for the 
immediately succeeding action. 
As noted above, as the paper 10 approaches the glue head, it may be 
determined that the glue head has not been opened for a preselected period 
of time (this may be about one-half second). If the glue head has not been 
opened for this long, it may not behave predictably, and there may be a 
further delay in initial opening of and dispensing of glue from the glue 
head. As described above, this may require an initial very brief pulsing 
of the glue head prior to the paper's reaching the position O in FIG. 1. 
Pre-calculated "advance distance" as described above is sufficiently long 
to allow a brief pulsing or "tickle" of the glue head, prior to the 
paper's reaching point O. Such a pre-pulsing of the glue head may be, as 
an example, only about 20% of the time duration of the "on" compensation 
time of the glue head. This pre-pulsing of the glue head is better 
understood with reference to FIG. 2. 
In FIG. 2, the size of the opening of a glue head dispenser is plotted as a 
function of time. Line 30 shows a normal response curve when the glue head 
has not been closed or "off" for an inordinate period of time, and 
responds in a predictable and repeatable manner. Glue dispensing starts 
when the glue head has opened to the extent indicated at the level Y.sub.1 
on the graph, and as shown, this corresponds to a duration of time 
X.sub.1. Thus, X.sub.1 is the standard "on" compensation time for the glue 
head. As indicated on the curve 30, when the glue head reaches full 
opening, it tends to "bounce" or flutter for a short period of time before 
reaching stability at the fully open position. FIG. 2 also schematically 
shows a glue pattern 32 as produced by the glue head in its normal opening 
routine, beginning at a point at time X.sub.1 and widening to the full 
pattern as the glue head opens further. 
The dashed line curve 34 in FIG. 2 shows an example of a delayed opening of 
the glue head, an opening progression which is less predictable and 
repeatable, when the glue head has not been opened for some period of time 
such as one-half second. Again, glue dispensing starts at opening level 
Y.sub.1, but this corresponds to an "on" compensation time X.sub.2, which 
is longer and less repeatable than X.sub.1. 
To remedy the problem of the longer and less predictable compensation time 
X.sub.2, the system is programmed to open the glue head for a very short 
preliminary opening, in the event the computer determines that the glue 
head has not been opened for the preselected period of time. This is shown 
at the short curve 36 in FIG. 2, where a brief "tickle" of the glue head 
is caused by a brief electrical pulse to the glue head. It has been found 
that a brief pulse having a duration of about 20% of the normal "on" 
compensation time (X.sub.1), carried out just before the prescribed 
"action" point at time 0 on the graph, is sufficient to cause the glue 
head to follow the normal opening curve 30 and normal compensation time 
X.sub.1 when the normal pulse is executed to open the glue head. This 
pre-pulse or tickle has the effect of loosening or priming the glue head, 
without dispensing any glue. As explained above, this brief pulse of the 
glue head can be performed before the sheet of paper 10a in FIG. 1 reaches 
the "on" action position O, since a sufficient safety factor is used in 
calculating the "advance distance" in which the computer should perform 
its compensation distance calculations for the operation. It is also noted 
that the computer 18 could perform this pre-pulse or "tickle" of the glue 
head during the calculations, since it can be keeping track of the opening 
and closing of the glue head independently, watching for an excessively 
long quiescent period. 
FIG. 3 shows the master CPU 18 connected to a video display 40 and keyboard 
42, thus allowing the operator to control and monitor the process. The 
master CPU 18 contains a master job memory 44 wherein are stored various 
pre-programmed jobs for current or future use. 
The master CPU 18 drives a plurality of slaves, for example, slave 46, 
slave 48, and slave 50, which operate either on separate production lines 
or with some or all on the same production line. 
As shown schematically in the drawing, each slave contains a plurality of 
job memories. Slave 1 (46), slave 2 (48) and slave N (50) are each shown 
as containing job memory 52 and job memory 54. A plurality of these job 
memories are employed within a single slave so that revised data can be 
downloaded but will not interrupt an operation in the middle of a sheet. 
The next sheet is treated according to new data if just downloaded and 
complete. 
Each slave is also connected to the encoder 16 and the product sensor 20. 
The encoder 16 continually monitors changes in position of the conveyor. 
The product sensor 20 signals the slave when the leading edge of the paper 
has reached a predetermined point on the conveyor. 
Each slave further contains a plurality of glue heads G for applying glue 
to the paper, one glue head G being shown in FIG. 1. It is noted that if 
more than one slave unit serves the same production line, so that conveyor 
speed is always common between the units, then an encoder and a sensor can 
be shared for those units. 
FIGS. 4A through 4D are a series of related flow charts representing the 
calculations and control loops used by the system of the invention. FIG. 
4A shows the start up and steady state loop. A circular queue contains 
data for several sheets' positions that may be moving between the sensor 
and glue head simultaneously. If the queue is empty, steady state 
operation continues. When the queue is occupied, calculations are made for 
position of first glue, end of the glue, and end of the sheet. At the 
appropriate position final calculations are performed and loop 2 (FIG. 4B) 
is initiated. 
FIG. 4B shows the calculations for "on" and "off" actions based on the 
compensation distance and the event locations programmed for the sheet. 
When all actions are complete, loop 1 is initiated. Loop 2 allows for 
features such as stitched action if the system is so programmed by the 
operator. 
FIG. 4C shows the interrupt structure to ensure accurate product entry 
position storage for future sheet operation. Sheets are accepted only 
after the run command is issued. This interrupt can be disabled for a 
"lockout" distance to avoid false triggering on printed material (see Loop 
1). 
FIG. 4D shows the timer interrupt loop which is used to constantly 
recalculate the current velocity of the conveyor. 
FIG. 5 shows a control unit 60 which embodies the CPU 18 indicated in FIG. 
1 and also in FIG. 3, with manual input keys and with a relatively small 
screen 59 to serve as the display 40 of FIG. 3. The screen 59 is shown 
bearing a prompt message for the operator. The control unit 60 includes a 
numerical keyboard 42, with various further keys 62, 64, 66, 68 and 70. 
Additional keys are "options" key 72, "program" key 74, "manual" key 76 
and "shift" key 78 as shown in FIG. 5. Also shown are controls indicated 
as OUTPUT 1, OUTPUT 2, OUTPUT 3 and OUTPUT 4. These are included to 
provide for individual control of up to four different operating devices 
for a given slave unit. They include on/off toggle switches 80, which 
relate to each of the operating devices served by a given slave. Shown to 
the left of these toggle switches 80 are indicator lights 81. If more than 
one slave unit is to be served by the control unit 60, additional rows of 
toggle switches and indicator lights may be included, below the switches 
and indicators 80, 81 shown in FIG. 5. The basic unit illustrated in FIG. 
5 will serve a single slave unit. 
At power on, the master CPU polls the slaves to find out how many are 
installed. Values for compensation times, sensor lead distances, sensor 
input (multiple sensors may be used on a single system), and encoder input 
(several encoders may also be used) are stored in a configuration file 
accessed from the OPTIONS key 72. Once these values are assigned, they are 
only changed if device assignments or locations are altered. The operator 
presses PROGRAM (74) and selects a job number to program (required so that 
the job can be identified for future use). The product length (lockout 
value) is requested. The master CPU prompts for information for each of 
the installed slaves. This information includes start position and run 
length as well as data for on/off sequencing within the run length and 
stitch options during the on periods (the stitch allows timed or length 
operation for spotting purposes). When all information is entered, the 
operator presses RUN (70) to download the data to the slaves and being 
operation. Changes can be made on the fly. When all changes are entered at 
the master CPU, the RUN key downloads the new data. The slaves save this 
data in a different memory area so that the changes will not affect a 
piece of product in mid-run. Only when a new piece enters the operation 
area will the new data be used. TEST (66) can be used to evaluate a job 
without the counters operating. When RUN is pressed, the lob and batch 
counters are activated (counter information is accessed via the OPTIONS 
key). The SHIFT key is used to access additional functions such as units 
of measurement, insertion or deletion of commands, to fine tune 
adjustments for setting up compensation times and sensor lead distances 
(since these may vary slightly from one device to another due to 
manufacturing and installation techniques). Some of the control keys shown 
on the unit in FIG. 5 relate to general operation of a production line and 
not to the method and system of the invention. 
Although the invention has been described in terms of one preferred 
embodiment relative to applying glue to sheets of paper, the invention 
applies much more broadly, as noted above, and can be used on other 
production lines where a workpiece or product is moved along on a 
conveyor, for one or more operations to be placed at desired locations on 
the product, those operations being subject to a lag time or compensation 
time for cycling of the operation "on" and "off". 
The above described preferred embodiments are intended to illustrate the 
principles of the invention, but not to limit its scope. Other embodiments 
and variations to this preferred embodiment will be apparent to those 
skilled in the art and may be made without departing from the spirit and 
scope of the invention as defined in the following claims.