Packaging machine seal mechanism apparatus/method and control

A packaging machine of the type having a mechanism for tubulating a belt-like film and a conveyor for transferring products into the tubular film is typically equipped with a pair of sealing bars which produce transverse seals between the products being packaged. The present invention relates to a mechanism which is able to control the length and speed of the stroke of the sealing bars and the speed of the film dependent on the length of the product being packaged which assures more uniform heating of the seals resulting overall in more uniform transverse seals.

FIELD OF THE INVENTION 
The invention relates to packaging apparatus and methods for wrapping 
longitudinally conveyed products in a tubular formed heat sealable film 
which is heat sealed transverse to the direction of movement between the 
products and more particularly to an apparatus and method for controlling 
the stroke and speed of the transverse sealing mechanism when the length 
of the package is changed. 
BACKGROUND OF THE PRIOR ART 
A conventional product packaging machine which utilizes a heat sealable 
film, moves both the product and the film in a longitudinal direction, 
bonds the film edges together to form a tube around the product and seals 
the tube transversely has generally the construction shown in FIGS. 11 and 
12. The term "product" is used to refer to any product, item, material or 
anything else that might be packaged by the type machines being presently 
and hereafter described. Referring further to FIGS. 11 and 12, a 
thermoplastic film in a roll 1 supported by rolling shafts 2 is supplied 
by a pullout roller 3 and a tension belt 4 and establishes film tube 7 of 
this belt-like film 5 by passing it over a cylinder making former 6. A 
continuous stream of to-be-wrapped products 10 are supplied, equidistantly 
spaced, into the tubular film 7 by the pushing force of attachments 9 
disposed on endless chains of a chain conveyor 8, and the tubular film 7 
is clamped and fused transversely between the to-be-wrapped products 10 by 
a pair of seal bars 11, 12 disposed transversely across the tubular film 
7. 
As seen in FIG. 12, a lever 15, supported pivotally by a pin 14 on a 
machine frame 13, is connected by a link 18 to a reciprocating frame 17, 
supported slidably on a guide 16, and the lever 15 is caused to swing back 
and forth by the rotation of a grooved cam 19. Accordingly, the 
reciprocating frame 17 reciprocates along the guide 16 as represented by 
an arrow. On the other hand, the seal bars 11, 12 connected by links 21, 
22 are brought close to, and then away from, one another by the rocking 
operation of the bell crank 20 as generated by internal mechanism (not 
shown). Consequently, the seal bars 11, 12 move along a pair of elliptical 
paths as represented by an arrow 23 in FIG. 11 enabling a transverse 
sealing of tubular film 7 for an extended time. 
When the length of the to-be-wrapped products 10 sent by the chain conveyor 
8 is changed, a sensor 24 reads the length of the to-be-wrapped products 
10 and inputs this length value as a digital value to a microcomputer 25. 
The microcomputer 25 generates signals 26, 27 corresponding to the length 
of the to-be-wrapped products by its arithmetic operation. Signal 26 is 
sent to a first motor 28 (FIG. 11) and the signal 27 is sent to a second 
motor 29 (FIG. 12). These motors change the rotating speeds of the pullout 
roller 3, the tension belt 4 and the grooved cam 19. In other words, since 
a third conveyor drive motor 30 in FIG. 11 always keeps a fixed speed to 
drive products through the machine, the film speed must be lowered in the 
case of a product 10a having a small length in order to keep constant the 
gaps 31, 32 between the adjacent products 10b in FIG. 13, and the film 
speed must be increased, on the contrary, in the case of a product 10b 
having a greater length. The reciprocating speed of the seal bars 11, 12 
is synchronized with the film speed thus changed. 
PROBLEM TO BE SOLVED BY THE INVENTION 
The seal mechanism control apparatus described above involves the problem 
that the heating time to form the transverse seams is changed whenever the 
length of the to-be-wrapped product is changed. In other words, the 
reciprocation stroke of the frame 17 is always constant in the apparatus 
of FIG. 12. Therefore, when the rotating speed of cam 19 is increased so 
as to increase the speed of the frame 17, the contact time of both seal 
bars naturally decreases accordingly. There is a problem in that the seam 
seal time becomes shorter and the seal cannot be effectively reliable. 
SUMMARY OF THE INVENTION 
To solve the problems described above, there is provided a packaging 
machine which includes a mechanism for gradually tubulating a belt-like 
film in a longitudinal direction of the film and conveying the film, a 
feed conveyor for equidistantly transferring to-be-wrapped products into 
the tubular film, a mechanism for transmitting going motion of a main 
lever swinging through a selected arc to a frame through a connecting link 
and reciprocating the frame in the direction in which the tubular film is 
being transferred and a sealing mechanism for transversely clamping the 
tubular film by a pair of seal bars supported on the frame and which heat 
and seal the film as the frame moves synchronously with the tubular film 
and in the same direction. An operation control apparatus for the seal 
mechanism has a screw shaft disposed on the main lever and connected to a 
first drive motor. The frame is connected to a slider by a link. The 
slider is threadably meshed with the screw shaft. A control mechanism for 
the described packaging machine of the invention, according to a first 
embodiment (FIG. 8) for generating control signals to control the first 
motor and a second motor adapted for conveying the film is disposed so as 
to receive and calculate a value of the length of to-be-wrapped products 
transferred from the feed conveyor into the tubular film as input data, 
and to let the position of the slider on the main lever and the transport 
speed of the film correspond to the value of the length of the 
to-be-wrapped product. 
The control mechanism for the described packaging machine of the invention 
is configured according to a second embodiment (FIG. 9) wherein, after the 
value of the length of the to-be-wrapped product transferred from the feed 
conveyor into the tubular film is accepted by the control mechanism as 
input data, the rotating angle of the first drive motor is first 
controlled on the basis of this input data and then the rotating speed of 
the second motor is controlled in proportion to the operating state of the 
first motor feedback from a rotation angle detector connected to the first 
motor to the control mechanism so that the position of the slider on the 
main lever and the transport speed of the film correspond to the value of 
the length of the to-be-wrapped product. 
The control mechanism for the described packaging machine of the invention 
is configured according to a third embodiment (FIG. 10) so that, after the 
value of the length of the to-be-wrapped product transferred from the feed 
conveyor into the tubular firm is accepted by the control mechanism as the 
input data, the rotating speed of the second motor is first controlled on 
the basis of the input data, and then the rotating angle of the first 
motor is controlled in proportion to the operating speed of the second 
motor fed back from a rotation speed detector connected to the second 
motor to the control mechanism so that the position of the slider on the 
main lever and the transport speed of the film correspond to the value of 
the length of the to-be-wrapped product. 
In the invention of the apparatus described according to the first 
embodiment, when the value of the length of the to-be-wrapped products 
transferred from the feed conveyor into the tubular film is digitized and 
inputted to the control mechanism, an arithmetic unit of the control 
mechanism controls the stroke of the seal bars in the reciprocating 
direction and the transport speed of the film in such a manner that they 
correspond to the digital signals. In other words, the control signal sent 
from the control mechanism to the first motor causes the first motor to 
rotate the screw shaft and causes displacement of the slider engaged with 
the screw shaft along the main lever. The swinging distance of the slider 
becomes smaller as the slider gets closer to the pivotal point of the main 
lever, and the swing speed is proportionally reduced. The swing distance 
and the speed become greater, on the contrary, as the slider is moved 
farther from the pivotal point of the main lever. Since the slider is 
interconnected to the sealing bars frame through the connecting link, the 
motion of the slider is directly transmitted to the frame. On the other 
hand, the speed of the film is controlled corresponding to the 
reciprocating speed of the frame by the control signal sent from the 
control mechanism to the second motor. Accordingly, when the length of the 
to-be-wrapped product is changed to a greater value, the reciprocating 
speed of the seal bars supported by the frame increases, so that the film 
speed, too, is increased by a proportional amount. Since the film clamping 
time of the seal bars becomes longer in proportion to the increase of the 
speed of the frame, control can be made so that the heating time of the 
film by the seal bars can be kept always constant irrespective of the size 
of the to-be-wrapped products.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Making reference initially to FIGS. 6 and 7, there is shown a preferred 
packaging machine apparatus used with each of the later described three 
embodiments of the control mechanism of the invention. A feed conveyor 45 
is constituted by a number of equidistantly spaced attachments 42 on an 
endless chain 41 driven at a predetermined speed by a motor 40 and forming 
grooves 44 at the center of the upper surface of frames 43, 43 disposed on 
both sides of the chain 41. The feed conveyor 45 can slide each 
to-be-wrapped product 46 pushed by each attachment 42 inside the groove 44 
and can transfer the product 46 to a conveyor 47 as represented by an 
arrow. A pair of side chains 48, 48 are each supported by two sprockets 
49, 50 and one tension wheel 51, respectively, on both sides of the 
conveyor 47. As shown in FIG. 6, side chains 48 are disposed in such a 
manner as to incline downward in the transferring direction of product 46, 
and each side chain 48 is equipped with a large number of equidistantly 
spaced clampers 52. These clampers 52 have a structure similar to that of 
known document clips, wherein a clamping force is provided ordinarily by a 
spring, and this clamping force is released only when the clamper 52 is in 
touch with a round cam (not shown) disposed at each sprocket 49, 50. 
In FIG. 6, a supply roll 56 of a heat sealable film 60 is supported on two 
rod-like rollers 54, 55 disposed rotatably on a machine frame 53. The film 
60 is guided to a position between side chains 48, 48 by a drive roller 58 
receiving the rotating power of a motor 57 and passes around a roller 59 
to change the film direction. The belt-like film 60 is drawn diagonally 
downward by the motion of both chains 48, 48 while being supported along 
its edges by the series of clampers 52. The gap between side chains 48, 48 
is expanded in the vicinity of the tension wheels 51 (FIG. 5B) at the 
intermediate portion of the chains 48. As a result the film 60 is 
stretched laterally and is put on top of the to-be-wrapped product 46. 
Both side edges of the film 60, which are released from the clampers 52 by 
releasing cams located proximate the sprockets 50, are pulled to the 
center by the rotation of a pair of opposed, high-friction belts 61, 61 
disposed in a V shape as viewed in FIG. 7 and the film side edges are 
fused to each other by heat and clamping force applied by a pair of heat 
sealing rollers 62, 62. As a result, a continuous stream of products 46 
are wrapped while being arranged equidistantly inside the tubular film 63, 
and a pair of seal bars 65, 66 operate along a pair of mirror-image 
elliptical paths 64, 64 (represented by arrows), with the film tube and 
product movement being further assisted by side belts 67, 67 on both sides 
of conveyor 47. The tubular film 63 is fused between successive products 
46 in a direction transverse to the axis of film tube 63. The packaging 
machine thus far described in reference to FIGS. 6 and 7 is not novel in 
most of its structures, and is disclosed in U.S. Pat. No. 4,144,697, the 
teachings of which are incorporated herein by reference. 
As an addition to and modification of the basic packaging machine described 
above, the invention provides a novel mechanism for operating the seal 
bars 65, 66 in an elliptical path and is constructed as illustrated in 
FIGS. 1A, 1B, 2, 3 and 4. Further, as later described, the invention 
provides three embodiments of a control mechanism (FIGS. 8, 9 and 10) for 
the novel sealing mechanism of the invention. 
In detail, as shown in FIG. 3, two rod-like guides 73 are fixed in parallel 
to each other between four bracket members 70 and 71 fixed on the upper 
surface of a base 80 so that a frame 74 is slidably supported on the 
guides 73 to be movable in the direction indicated by arrows. Upper and 
lower bars 77 and 78, as shown in FIG. 2, engage at both ends of frame 74 
with vertical guide rails 76 longitudinally formed at the inner surfaces 
of two wall plates 75 of frame 74. An upper seal bar 65 is provided at the 
lower surface of the upper bar 77 and is cushioned through cushion springs 
79, and a lower seal bar 66 is firmly provided at the upper surface of the 
lower bar 78. Also, as shown in FIG. 3, a reversing shaft 97 is rotatably 
supported by a pair of bosses 96 formed at the wall plate 75 on both sides 
of the frame 74, with bell cranks 98 fixed to both axial ends thereof. 
As shown in FIG. 1A, pins at both ends of each bell crank 98 and both ends 
of upper and lower bars 77 and 78 are connected by links 110 and 111. As 
shown in FIG. 3, a driving shaft 100 is rotatably supported by a bearing 
99 attached to wall plate 75. The reversing shaft 97 and driving shaft 100 
are connected with each other through a bevel gear set 112. A gear 103 is 
rotatably supported in a support structure 102 which is fixed to the base 
80, and spline 107, axially formed at the peripheral surface of the 
driving shaft 100, slidably engages a spline bore 108 formed within the 
gear 103. Two lever bars 88 are fixedly attached to a shaft 91 which is 
rotatably supported between a pair of bearings 87 on the upper surface of 
the base 80. The lever bars 88 and both sides of the frame 74 are 
connected through two parallel rods 89. As shown in FIG. 1B, two 
shaft-like guides 94 are provided along a main lever 85 supported by a 
bracket 83 through a pin 84. A slider 90 is slidably supported on the 
guides 94. A driven lever 92, fixed to one end of the shaft 91 is 
connected to slider 90 through a rod 93. A pin 86 formed at the lateral 
side of main lever 85 engages an endless grooved cam 82. As shown in FIG. 
3, the grooved cam 82 is supported by a bearing 105 through a shaft 104, 
and the shaft 104 is driven by a motor 81 through a chain 106. Therefore, 
when motor 81 rotates the grooved cam 82 shown in FIG. 1B, the main lever 
85 swings at the upper end thereof around the lower pin 84. This swinging 
motion oscillates both the shaft 91 through the connecting rod 93 and the 
driven lever 92. In FIGS. 1A and 3, the shaft 91 is cyclically reversed so 
as to swing the upper ends of the two swinging levers 88, 88. As a result, 
the frame 74 through the connecting rods 89 repeats a corresponding motion 
along the rod-like guides 73. In this case, the driving shaft 100 axially 
slides in the spline bore 108 through the center of gear 103. 
A second grooved cam 113 is fixed to the second end of the shaft 104 
supporting the grooved cam 82. A pin 116 provided at the lateral surface 
of a swinging arm 115 supported at one end by a bracket 114 engages the 
second grooved cam 113. As shown in FIG. 4, the opposite end of the arm 
115 and the inner end of a gear segment 118, pivoted to the support 
structure 102 through a pin 117, are connected through a connecting rod 
119. A circular-arc gear 120 is fixed to the other end of the gear segment 
118 and engages with the gear 103. Therefore, the second grooved cam 113 
rotates to vertically move the arm 115 at the outer end thereof so as to 
actuate the gear segment 118 around the pin 117, so that the gear 103 
transmits reciprocating power to the driving shaft 100 throughout its 
sliding motion and further to reversingly move the shaft 97 and bell 
cranks 98, seen in FIG. 3, thereby moving both the bars 77 and 78 toward 
or away from each other. Accordingly, when both bars 77 and 78 move close 
to each other, the frame 74 is moved in the transportation direction of a 
wrapped product 46. When the frame 74 moves backwardly with respect to the 
transportation direction, both the bars 77 and 78 separate and remain away 
from each other, whereby the seal bars 65 and 66, mounted to the bars 77 
and 78 travel along a long elliptical path 64 (see FIG. 6). 
Returning to FIG. 1B, an internally threaded bore formed through the slider 
90 engages with a screw shaft 121, rotatably provided between the two 
rod-like guides 94 of the main lever 85, so that the first motor 122 
rotates screw shaft 121 through gear box 126 so as to move the slider 90 
linearly along the rod-like guides 94. When a pusher 125 assembled onto 
the slider 90 comes into contact with either of the microswitches 123 or 
124 provided on the main lever 85, the motor 122, and consequently slider 
90, stop, thus providing a selected maximum moving range for slider 90 
corresponding to the distance between the pair of switches 123 and 124. 
The shaft of the first motor 122 is connected through a belt 127 to a 
rotation angle detector 128 formed of an encoder. 
A power supply switch 130, shown in the electrical diagram of FIG. 5, is 
manually closed to start the apparatus. Closing of switch 130 causes a 
relay coil 132 to be energized through a normally closed switch 131 and 
which acts to close a switch 133, thereby starting rotation of the first 
motor 122. First motor 122 rotates in the direction of lowering the slider 
90 by the rotation of screw shaft 121, shown in FIG. 1B, which causes the 
slider 90 to contact and close the first switch 124 shown in FIG. 5. As a 
result, relay coil 132 is energized which causes switch 131 to open. This 
in turn causes switch 133 to open and the first motor 122 to stop, thus 
position-compensating the slider 90 in the zero point. In other words, 
regardless of the initial position of slider 90, it is lowered to the 
position where the first switch 124 contacts with the slider 90, thereby 
initializing the circuit. Thereafter, the operator operates a keyboard 136 
to convert a known length of the wrapped product 46 into digital form and 
input it to a counter 137 in a microcomputer 150, and thereafter a second 
switch 138 is closed. This causes a relay coil 139 to close switch 140 and 
a relay coil 141 relationally closes a switch 142, whereby the first motor 
122 starts its reverse rotation. Hence, the slider 90 in FIG. 1B starts to 
move upwardly along the rod-like guides 94. In FIG. 5, the rotation angle 
detector 128, driven by the rotation of the shaft of the first motor 122, 
gradually reduces numerical values stored by microcomputer 150 in the 
counter 137, so that simultaneously, when the stored numerical value of 
the counter 137 becomes zero, a switch 143 closes and energizes a relay 
coil 144 to open a normally closed switch 145. As a result, the switch 142 
is opened by reason of relay coil 141 being energized to stop the first 
motor 122. Thus, in FIG. 1B, the slider 90 shifts only by an amount each 
time a command is given, always starting at the zero point. In addition, 
the upper switch 123 acts as a safety so as to prevent the slider 90 from 
moving further upward. In FIG. 5, simultaneously when the counter 137 
excites the relay coil 144 through the switch 143, motors 40, 57 and 81 
all operate to start the entire packaging apparatus. 
Reverting to FIG. 1B, as the slider 90 shifts upwardly along the main lever 
85, driven lever 92 is able to swing through a greater arc. Conversely, as 
the slide 90 shifts downwardly, the swinging angle of the driven lever 92 
become smaller, so that the stroke amount of the frame 74, in the 
direction of reciprocation, changes in proportion to a change in the 
swinging angle of the driven lever 92. Moreover, the greater the stroke 
amount of the frame 74 is, the faster the stroke speed thereof becomes. 
Conversely, when the frame 74 reduces its stroke amount, the stroke speed 
is smaller in proportion to the stroke amount. 
In FIG. 6, as mentioned above, when a length of the wrapped product 46 is 
input to the microcomputer 150 as a numerical value from the keyboard 136, 
the microcomputer 150 automatically controls the speed of the pair of the 
seal bars 65 and 66 along the elliptical paths 64. Simultaneously, the 
microcomputer 150 controls the rotation of the second motor 57 so as to 
coordinate the feeding speed of film roll 56 with the stroke speed of the 
seal bars 65, 66. In other words, as shown in the diagram of FIG. 8 
according to the first embodiment of the control mechanism, when the 
length of the wrapped product 46 is input 151 as data, the microcomputer 
processes the input 151 in data processing 152 to obtain a rotation angle 
153 by computation and an instruction 154 which is given to the first 
motor 122 to displace the slider 90, and encoder 128 feeds back the 
rotation angle of motor 122 to the microcomputer. Simultaneously, the 
microcomputer computes 155 the control speed of the second motor 57 to 
give an instruction 156 thereto, and an encoder 72 feeds back 158 the 
speed of motor 57. In addition, in this case, rotation elements 47, 48, 61 
and 62 (see FIG. 6) in contact with the film each are changed in speed to 
be synchronized thereto. 
In the second embodiment of the control mechanism as shown in FIG. 9, when 
the microcomputer receives the data relating to the length of the 
to-be-wrapped product, it starts controlling the rotating angle of the 
screw shaft 121 by the rotation of the first motor 122 and represents that 
the feed speed of the film can be controlled by the second motor 57 on the 
basis of the feed-back signal 157 from the rotating angle detector 128. On 
the other hand, according to the third embodiment of the control mechanism 
as shown in FIG. 10, the film speed is first controlled by the second 
motor 57 and the rotating angle of the first motor 122 is controlled on 
the basis of the feed-back signal 158 from the encoder 72. 
In summary, the apparatus of the present invention controls the angle of 
the screw shaft disposed along the main lever to be controlled in 
proportion to the length value of the to-be-wrapped product, changes the 
position of the slider by this screw shaft, increases the stroke of the 
frame supporting the seal bars in the reciprocating direction by this 
slider position control, and controls the speed and stroke of the sealing 
bars in proportion to the film speed. When the length of the to-be-wrapped 
product is to be increased, for example, the speed and stroke of the frame 
are increased proportional to the film speed. Accordingly, even when the 
film speed changes, the time of heating the film can always be kept 
constant, and production of products having inferior transverse seals can 
be prevented. 
As described above, the preferred embodiment is intended as an example of 
the invention, and not as a limitation of its scope. Further variations as 
will be apparent to those skilled in the art, including the specific 
details of the control steps, are to be construed as within the principles 
taught herein and defined by the claims below.