Side sealing mechanism for a packaging machine

Heat sealing bars are spaced circumferentially around a rotatable drum and seal together two face-to-face strips of material as the strips are drawn continuously around the drum. The sealing bars are automatically moved radially inwardly and outwardly to change the circumferential distance between the bars and the effective diameter of the drum and thereby keep the bars in register with printed material on the strips.

BACKGROUND OF THE INVENTION 
This invention relates to a side sealing mechanism for a packaging machine 
of the type in which a flexible web of heat-sealable material is advanced 
and folded to form two face-to-face strips which are sealed together at 
longitudinally spaced positions to convert the web into series of 
interconnected pouches. The pouches subsequently are separated by cutting 
through the side seals and then are advanced through a filling station 
where product such as a food product is deposited into the pouches. 
The invention has more particular reference to a sealing mechanism for a 
continuous motion packaging machine. In such a machine, the web, the 
folded strips and the severed pouches are advanced with continuous motion 
as the pouch forming and filling operations are performed. A typical 
continuous motion machine is disclosed in Nutting et al U.S. Pat. No. 
3,230,687 and such a machine is capable of operating at significantly 
higher speeds than an intermittent motion machine in which the various 
operations are carried out when the web and the pouches dwell between 
successive steps. 
In most instances, the web is pre-printed with a repeating pattern of 
labeling information, decorative artwork, advertising material and the 
like which ultimately appears on the outer sides of the finished pouches. 
In order for each pouch to have the proper appearance, it is necessary 
that the side seals register correctly with the printing on the web. In 
other words, each side seal should be located exactly at the proper area 
of repeat of the printed pattern on the web so that all pouches will be of 
proper and uniform appearance. 
To keep the packaging machine operating in registration with the printing 
on the web, it is conventional for the web to be preprinted with 
photoelectric targets which are spaced longitudinally from one another in 
accordance with the width of the pouches. Photoelectric detectors sense 
the targets and produce signals which are used to control the operation of 
various mechanisms of the machine. Packaging machines in which 
photoelectric detectors sense preprinted targets to maintain web 
registration are disclosed in Lense U.S. Pat. No. 3,500,726, in Johnson et 
al U.S. Pat. No. 3,545,166 and in Johnson et al U.S. Pat. No. 3,553,934. 
Difficulty is encountered in obtaining proper registration of the side 
seals because, in many instances, the printed pattern and the 
photoelectric targets may not repeat at exactly the same interval 
throughout the entire length of the web. Variations in the repeat interval 
may be caused by the web being stretched or tensioned by different amounts 
during its advance, by temperature fluctuations, by imperfections in the 
printing process itself and by other factors. While the variation of the 
repeat interval within a given group of pouches may be very minute, the 
cumulative variations that may occur in a web which is several hundred 
feet in length can result in the side seals being formed out of 
registration with the printed material and thereby ruin the appearance of 
the pouches. 
SUMMARY OF THE INVENTION 
The general aim of the present invention is to provide a new and improved 
side sealing mechanism which is especially adapted for use with a high 
speed continuous motion packaging machine and which is particularly 
characterized by its ability to form the side seals in virtually perfect 
registration with the printing of the web regardless of any variations 
that might be present in the repeat interval. 
A more detailed object is to provide a side sealing mechanism in which the 
side seals are formed by angularly spaced heat sealing bars which are 
carried on a rotary drum, the circumferential spacing between the sealing 
bars being adjusted automatically to compensate for variations in the 
repeat interval. 
A more detailed object is to adjust the circumferential spacing between the 
seal bars by automatically moving the bars radially inwardly or outwardly 
relative to the drum in response to signals resulting from detection of 
the photoelectric targets on the web. 
The invention also resides in the provision of unique mechanism for 
radially adjusting and radially retracting the seal bars. 
These and other objects and advantages of the invention will become more 
apparent from the following detailed description when taken in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings for purposes of illustration, the invention is 
embodied in a packaging machine 20 for forming, filling and closing 
pouches 21 each composed of two rectangular panels disposed face-to-face 
and joined together at their margins, preferably by a fold and a heat seal 
24 at the bottom and by heat seals 25 at the sides. The pouches may range 
in width from 41/2 inches to 7 inches and are adapted to be handled by the 
machine at rates as high as 250 pouches per minute. 
Herein, the pouches 21 are made from a web of sheet material either 
composed of or coated on one side with a thermoplastic material and drawn 
off of a supply roll (not shown) rotatable about a horizontal axis. As the 
web is advanced, it is folded longitudinally and upwardly to form two 
face-to-face strips 26 and 27 (FIG. 2) which are joined at their bottom 
margins by a fold. The strips are disposed in a vertical plane and, in the 
present instance, are advanced with high speed continuous motion as 
opposed to slower intermittent or step-by-step motion. For this purpose, 
two pair of continuously rotating feed rolls 28 and 28a (FIG. 1) engage 
opposite sides of the strips and respectively draw the web material off of 
the supply roll and through the pouch forming section of the machine 20. 
As the strips 26 and 27 are advanced by the feed rolls 28 and 28a, the 
strips are guided around a continuously rotating sealing drum 29 (FIG. 1) 
having a heated, ring-like sealing bar 30 which engages the forward strip 
26 to seal the bottom margins of the strips together and form the bottom 
seal 24. Thereafter, the strips are guided past a side sealing mechanism 
31 which forms the side seals 25 by sealing the strips together along 
vertical bands located at equally and longitudinally spaced positions 
along the strips. The strips then are guided around a continuously 
rotating cooling drum 32 which chills the newly formed seals. 
At periodic intervals, a cutter 34 severs successive pouches 21 from the 
leading end portion of the strips 26 and 27 by cutting through the seals 
25 intermediate their edges so that each seal 25 forms the trailing side 
seal of one pouch and the leading side seal of the next pouch. The cutter 
has been shown only schematically in FIG. 1 since its details form no part 
of the present invention. It should be understood, however, that the 
cutter is of the type which is capable of cutting through the strip while 
the latter is advanced with continuous motion. Reference may be had to the 
abovementioned Nutting et al patent for a disclosure of a cutter which 
acts on a continuously moving pouch strip. That patent also contains a 
detailed disclosure of mechanisms for folding, sealing and advancing a 
pouch strip. The specific cutter of the present machine 20 is disclosed in 
detail in Burton U.S. Pat. No. 4,299,151. 
After being separated from one another, the pouches 21 are accelerated to a 
desired spacing and are gripped by carriers 35 attached to a continuously 
moving chain 36 which advances the pouches through a filling station where 
a quantity of product such as food product is deposited into the open 
upper ends of the pouches. Thereafter, the upper ends of the pouches are 
sealed to enclose the product in the pouches. Reference also may be had to 
the aforementioned Nutting et al patent for a detailed disclosure of 
apparatus for advancing and filling the pouches and for sealing the upper 
ends thereof. 
Conventionally, the lower side of the web which is drawn off of the supply 
roll is pre-printed with a repeating pattern of labeling information and 
decorative material, the pattern having a repeat interval which is 
substantially equal to the width of the pouches 21. When the web is 
folded, the printed material appears on the outer sides of the strips 26 
and 27 as a series of longitudinally spaced blocks and ultimately appears 
on the outer sides of the pouches. In order for the pouches to have the 
proper appearance, it is necessary for each side seal 25 to register with 
or to be centered precisely on the space between adjacent blocks of the 
printed material so that each pouch contains a complete block which is 
centered with respect to the pouch. Also, it is necessary for the cutter 
34 to separate the pouches substantially at the middle of each side seal. 
In order to enable the pouches 21 to be sealed and cut in registration with 
the printed blocks, it is conventional practice to pre-print the web with 
photoelectric targets 37 (FIG. 1) which are spaced from one another in 
accordance with the pitch of the blocks. As the strips 26 and 27 are 
advanced, a photoelectric detector 38 senses the targets and produces an 
electrical signal or pulse each time one of the targets passes the 
detector. The frequency of the output pulses from the detector is 
indicative of the spacing between the targets and thus is indicative of 
the pitch of the printed blocks. Such photoelectric detection systems are 
per se well known and are per se widely used in the art of packaging 
machines. In the present machine 20, the signals resulting from detection 
of the targets are used to control the speed of the feed rolls 28a in 
accordance with operation of the cutter 34 so as to cause the feed rolls 
to present a side seal to the cutter each time the latter is actuated. 
While the targets 37 and the photoelectric detector 38 are very useful in 
maintaining proper registration, a problem is created by the fact that the 
spacing between the targets and the printed blocks may not be exactly 
equal or may not be precisely at an optimum value throughout the entire 
length of the web. For example, the web may be stretched by different 
amounts as it is advanced. Changes in temperature may result in the 
spacing between the targets being greater or less than optimum. Also, the 
process by which the web is printed may not be absolutely perfect and may 
result in variations in the spacing of the targets 37. Thus, there is no 
assurance that the spacing between the targets 37 (and thus the printed 
blocks) is perfectly uniform throughout the length of the web or from 
web-to-web. 
In accordance with the present invention, provision is made of a unique 
drum-type side sealing mechanism 31 which is capable of forming the side 
seals 25 at high speeds and preferably with continuous motion and which is 
capable of automatically adjusting to compensate for any variations in the 
spacing between the targets 37 and the printed blocks. As a result, the 
side sealing mechanism forms the side seals in proper registration with 
the printed material even though the spacing between adjacent printed 
blocks may not be uniform throughout the length of the web. 
More specifically, the side sealing mechanism 31 comprises a drum 40 
adapted to rotate continuously in a counterclockwise direction (FIG. 2) 
and about an upright axis. Carried by the drum are several (herein, eight) 
electrically heated sealing bars 41 which are spaced circumferentially 
around the drum in accordance with the longitudinal spacing between the 
side seals 25. As the strips 26 and 27 are advanced, they are guided 
around the forward half of the drum and are maintained under tension. The 
rear side of the rear strip 27 frictionally engages the group of seal bars 
on the forward half of the drum and, as a result of such engagement, the 
rear strip causes the drum to turn about its axis. At the same time, the 
seal bars seal the rear strip 27 to the forward strip 26 to form the side 
seals 25. As the strips first become tangent to the drum, a pressure 
roller 43 (FIG. 2) acts against the forward strip and presses the rear 
strip against the sealing bars 41 as each bar approaches a nine o'clock 
position. The roller is rotatably supported by a pivoted bracket 44 and 
may be released from the strips by swinging the bracket in a 
counterclockwise direction (FIG. 2) by means of a pneumatic actuator 45 
which is attached to the bracket. 
As shown in FIG. 3, the drum 40 comprises a vertical cylindrical shell 46 
whose top is closed by a plate 47 and whose bottom is closed by a ring 48. 
Screws 49 fasten the ring 48 to a lower ring 50 rotatably supported by a 
bearing 51 which, in turn, is mounted in a bearing block 52 secured to the 
main support or frame 53 of the machine 20. 
For a purpose which will become apparent subsequently, a gear 54 (FIG. 3) 
is sandwiched between the rings 48 and 50 and is secured rigidly thereto 
by the screws 49. The gaer meshes with a pinion 55 which is keyed to an 
upright shaft 56 journaled in the frame 53 by a bearing 57. The lower end 
of the shaft is connected to a right angle gear box 58 (FIG. 1) whose 
output shaft 59 is connected by gears 60 to a shaft 61 which forms one 
input of a differential gear box 62. The other input of the differential 
is formed by a reversible electric correction motor 63. 
Each seal bar 41 is located within a vertically elongated slot formed in a 
shoe 65 (FIG. 2) which defines the peripheral surface of the drum 40. The 
outer face of each of the eight shoes is convex and is arcuately curved 
about the axis of the drum. The outer face of each sealing bar corresponds 
in shape to the side seal 25. 
At the upper and lower end portions of each shoe 65, two screws 66 (FIG. 4) 
are located on opposite sides of the seal bar 41 and secure the shoe to an 
inner mounting plate 67 which closes off the inner side of a cavity formed 
in the shoe. The heads of the screws are accommodated within small 
recesses which are formed in the shoe. 
An electrical resistance heating element 68 (FIGS. 3 and 4) is associated 
with each sealing bar 41 and is adapted, when energized, to heat the 
sealing bar to a high temperature. Electrical current may be conducted to 
the several heating elements by way of a slip ring assembly (not shown) 
coaxial with the drum 40. A thermal isolation block 69 (FIG. 4) is located 
within the cavity of each shoe 65 to insulate the shoe thermally from the 
heating element and the sealing bar. 
As shown in FIG. 3, upper and lower rods 70 are secured to and project 
inwardly from the mounting plate 67 of each seal bar 41 and are fastened 
together by a verticval strap 71 located within the drum 40. In carrying 
out the invention, the rods lie along radii of the drum and are supported 
for in and out radial sliding by guide bushings 72 mounted in the shell 46 
of the drum. Rotatably mounted on and depending from the inner ends of the 
rods 70 are cam followers or rollers 73 which coact with two vertically 
spaced actuators 74 to effect in and out movement of the seal bars 41. 
Herein, each actuator 74 is in the form of a disc having eight angularly 
spaced identical cam surfaces which are defined by curved slots 75 formed 
in the upper side of the disc. The rollers 73 fit into the slots 75 and, 
when the discs are turned either clockwise or counterclockwise, the slots 
and the rollers coact to either advance the seal bars outwardly (FIG. 4) 
or retract the bars inwardly (FIG. 5). Since the rods 70 lie along radii 
of the drum, the circumferential spacing between the bars 41 is increased 
whlen the bars are advanced outwardly and, in addition, the effective 
outer diameter of the drum 40 is increased. Conversely, the 
circumferential spacing between the bars and the effective outer diameter 
of the drum are decreased when the bars are retracted inwardly. When the 
bars are in their innermost positions, there is only a very small gap 
between the ends of adjacent shoes 65 (see FIG. 5). 
The discs 74 are telescoped on and are keyed to the upper end portion of an 
upwardly extending tubular shaft 80 (FIG. 3) which is coaxial with the 
drum 40. A sleeve bearing 81 journals the shaft within the rings 48 and 50 
and the gear 54 while a ball bearing 82 rotatably supports the lower end 
portion of the shaft on the frame 53. A gear 83 is secured to the lower 
end portion of the shaft 80 and meshes with a pinion 84 which is secured 
to a vertical shaft 85 whose upper end portion is journaled in the frame 
by a ball bearing 86. As shown in FIG. 1, the lower end portion of the 
shaft 85 is connected into a right angle gear box 87 having a shaft 88 
which forms the output of the differential 62. 
OPERATION 
The correction motor 63 of the differential 62 is de-energized as long as 
the circumferential spacing between the seal bars 41 coincides with the 
spacing between the targets 37 on the strips 26 and 27 and as long as the 
side seals 25 are being formed in registration with the printed material 
on the strips. As the drum 40 is rotated by the advancing strips, the gear 
54 acts through the pinion 55, the shaft 56, the gear box 58, the shaft 59 
and the gears 60 to backdrive the input shaft 61 of the differential 62 in 
timed relationship with the drum. As long as the correction motor 63 is 
de-energized, the output shaft 88 of the differential 62 is rotated in 
phase with the input shaft 61 and acts through the gear box 87, the shaft 
85, the pinion 84 and the gear 83 to rotate the shaft 80 in phase with the 
drum. The ratio of the various gears are such that the shaft 80 is rotated 
in the same direction and at the same R.P.M. as the drum 40 when the 
correction motor 63 is de-energized. As a result, the cam discs 74 are 
rotated in unison with the drum 40 and the seal bars 41 and thus the discs 
do not effect any change in the radial position of the seal bars. 
Because of one or more of the factors mentioned previously, it is possible 
that, sometime during operation of the machine 20, there may be a tendency 
for the side seals 25 to be formed out of perfect registration with the 
printed material on the strips 26 and 27. For example, slippage of the 
strips or the cumulative effect of printing tolerances could, if left 
uncompensated, result in the side seals 25 being formed either slightly 
ahead of or slightly behind the spaces between the blocks of printed 
material. If this tends to occur, the photoelectric detector 38 causes the 
correction motor 63 to be momentarily energized in one direction or the 
other. When energized, the correction motor acts through the differential 
62 and, depending upon its direction of rotation, acts to mementarily 
advance or momentarily retard rotation of the shafts 88 and 80 with 
respect to the input normally applied via the shaft 61. If rotation of the 
shaft 80 is advanced, the cam discs 74 are rotated clockwise relative to 
the drum 40 (while still rotating with the drum) and cause the seal bars 
41 to advance outwardly to increase the circumferential spacing between 
the seal bars and increase the effective diameter of the drum (see FIG. 
4). Retardation of the shaft 80 results in the discs turning 
counterclockwise relative to the drum so as to retract the seal bars and 
decrease their circumferential spacing and the effective diameter of the 
drum as shown in FIG. 5. 
In this way, the circumferential spacing between the seal bars 41 can be 
changed automatically to match the spacing between the printed blocks on 
the strips 26 and 27. Thus, proper registration can be maintained between 
the side seals 25 and the printed blocks even though the repeat interval 
of the blocks may not be uniform throughout the length of the web. 
Importantly, changing of the circumferential spacing between the seal bars 
41 does not result in any relative circumferential movement between the 
seal bars and the inner strip 27 and thus no "smearing" of the seals 25 
occurs when the bars are adjusted. When the bars are moved outwardly to 
increase the circumferential spacing therebetween, the bars simply 
increase the effective diameter of the drum and push the strips outwardly 
without moving relative thereto. Any surplus material which might be 
necessary to enable the bars to push the strips outwardly can be gained 
from the material accumulated in the tension roll system (not shown) 
upstream of the bottom sealing drum 29. The tension roll system also takes 
up any slack and keeps the strips tensioned around the bars when the bars 
are moved radially inwardly and decrease the effective diameter of the 
drum 40. 
The details of the specific system for controlling the correction motor 63 
do not form part of the present invention and many such systems are 
commercially available. Simply by way of a brief example, the pulses from 
the detector 38 may be routed as a command signal to electronic circuitry 
having a comparator 90 (FIG. 1) operable to control the correction motor 
63. Pulses representative of the actual spacing between the seal bars 41 
may be produced by a second photoelectric detector 91 located adjacent the 
rear side of the drum 40, such pulses being routed to the comparator as a 
feedback signal. As long as the command and feedback pulses are in phase, 
the output of the comparator is zero and thus no signal is supplied to the 
correction motor 63. If the feedback pulses either lag or lead the command 
pulses, the comparator produces an error signal of proper polarity to 
energize the correction motor in a direction to advance or retard the 
shaft 80 until the error is reduced to zero. The circuitry may include 
suitable averaging, filtering and/or threshold networks to impart 
stability to the operation of the correction motor.