Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
Field of the Invention
Ths invention pertains to methods and apparatus for wrapping
objects with flexible, fusible strap.
SUMMARY OF THE_INVENTION
The principal object of the invention is to provide a high speed
strapping machine capable of strapping 80 straps a minute as compared to
typical known strapping rates of 35 straps a minute. This is accomplished
through simple mechanical movements, each combining several functions.
It is another object of this invention to provide an improved flexible
strap supply and accummulating device. Basically, this object is obtained by
driving the reel or coil or strap for discharging strap synchronously with
feed rolls for feedingsthe discharged strap into an accummulating compartment.
Another object of this invention is to provide an improved strap
feeding unit for feeding flexible strap in a strapping machine. Basically, this
object is obtained by confining the strap in an elongated transverse slot and
bringing the powered and pinch rollers together through opposed grooves at
right angles to the slot for driving the strap through the slot.
It is another object of this invention to provide an improved strap
20 tensioning mechanism. Basically, this object is obtained by providing first
means for pulling the strap around the object with a first tension, providing
second means for drawing the strap tightly around the object at a second,
greater tension, and actuating both of these means by a simple rnechanical `
movement of a common plate. In the preferred embodiment the strap is anchor-
ed from the supply end until the first predetermined tension is reached, and
then the anchor is overcome by the tension in the strap to provide removal
of additional strap from the accummulator.
Still another object of the invention is to provide a cutting and
sealing head for a strapping apparatus in which a first strap can be sealed
30 while a second strap is simultaneously being positioned around the object in
the same plane. Basically, this object is obtained by providing strap carrying
slots in a platen and grippers which are acting on the first strap so that the
~` strap can pass in a parallel path in the same plane into the track.
Still another object of this invention is to provide an improved track
.
1`~ 3
opening device for a strapping apparatus. Preferably this object is obtained
by using a rigid track and coupling tlle track at one location directly to move-ments of the members in the cutting and sealing heads so that a simple, single
operation accomplishes opening of the track.
A principal object is to provide a machine for applying flexible
sealable strapping to an object, and having means for feeding strap through a
track around the object in a loop in a cutting and sealing plane, tensioning
the strap tight on the object, cutting the supply end of the strap and sealing
the free end and supply end of the strap together, the improvement comprising:
a cutting and sealing head in the cutting and sealing plane of said track~
including means for gripping the two ends of the strap, means for sealing
the two ends together, and means for freeing the sealed ends for removal of
the strapped object all in said cutting and sealing plane; and means for feedinya new strap beneath the cutting and sealing head and in said cutting and
sealing plane around the object while the previous strap is being sealed in
said cutting and sealing plane.
BI~IEF DESCRIPTION OF THE DRAWINGS
Figure l is a front elevation of a strapping machine embodying
the principles of the invention;
Figure 2 is an isometric of a preferred strap supply and accumulator;
Figure 3 is a fragmentary enlarged side elevation of a strap tension-
ing mechanism;
Figure 4 is a fragmentary plan of the tensioning mechanism shown
in Figure 3;
Figure 5 is a side elevation of a strap feeding unit;
Figure 6 is an end elevation of the strap feeding unit shown in
Figure 5;
Figure 7 is a ~fragmentary detail of the strap feeding unit as shown
in Figure 6;
Figure 8 is an enlarged fragmentary front elevation of a cutting
and sealing head;
Figure 9 is an end elevation of the sealing and cutting head and
illustrating a common cam shaft control for operating the elements of the
cutting and sealing head;
--2--
.. .
'~` 1093953
Figure 10 is a plan of the sealing and cutting head with elements
removed for clarity;
Figure 11 is an enlarged detail of the sealing and cutting head taken
in a plane parallel to the direction of strap movement;
Figure 12 is a section of the track taken along line 12-12 of Figure 1;
Figure 13 is a section of the track taken along line 13-13 of Figure 1;
Figure 14 is a section of the track taken along line 14-14 of Figure 1;
Figure 15 is a fragmentary perspective of part of the cuttins and
sealing head;
Figure 16 is a schematic cam timing sequence; and
Figure 17 is a schematic isometric of a modified form of strap supply.
DETAILED DESCRIPTION OF Tl IE PREFERRED EMBODIMENTS
As best shown in Figure 1 the strapping machine includes a strap
track 10, a cutting and sealing head 12, a strap feed mechanism 14, a strap
supply 16, a strap accumulator 18, a strap tensioning unit 20 and a cam control
device 22. Basically, strap is fed through the strap feed mechanism 14 from the
accumulator 18 through the tensioning unit 20. The strap feeds through the
cutting and sealing head 12 around the track 10 and the free end of the strap
hits an obstruction in the cutting and sealing head to stop its travel. Strap
20 then builds up in the strap feed mechanism signalling to the cam control drive
22 to begin a cycle of sealing, cutting and tensioning. During this cycle the
free end of the strap is held while the strap is first roughly tensioned by the
tensioning unit 20 to pull the strap out of the track snugly around the object
being wrapped. Secondly, the strap is then tightly tensioned around the object
and the continuous end of the strap is clamped in the tensioned condition. Next
the continuous end which underlies the free end, and the free end are pressed
against a heating bar until the strap is melted and then the strap is pressed
tightly together with the continuous end severed. After cooling the cutting and
sealing head opens so that the strap can be removed with the object and a new
30 cycle of feeding the strap around the track is begun. The machine and the method
of strapping objects offer advantages over known prior art machines and methods
which advantages will be discussed in more detail during the description of each
of the sub-assemblies of the machine.
STRAP SUPPLY AND ACCUMULATOR
The strap supply is best shown in Figures 1 and 2 and includes a coil
3--
~093953
~ containing strap S. The coil rests on a pair of shafts 25 and 26. Shaft 26
is provided with a rubber friction cover beneath the coil and is provided with a
larger diameter roller 26a at its end. Shaft 26 thus serves as a powered feed
roll to pull the strap from the coil via guide rollers 24a and 24b and push it into
the accumulator 18. Shaft 26 is driven by a belt and pulley drive 27. A pinch
roller 28 is spring-mounted to press against the powered roller 26a.
The accumulator 18 includes a back plate 30 and a closely spaced
clear plastic front plate 31 which forms a housing for the strap. The strap is
pushed upwardly into the housing in accordion folds as best shown in Figure 1.
10 A paddle 32 is pivotally mounted and protrudes down into the top of the housing.
The paddle has a low switch operator surface 321 and a full switch operator
surface 32f. As the accordion folds build up in the housing the paddle is
raised until surface 32f closes a full switch FS to stop the feed. As strap
leaves the accumulator the level of the folds drops deactivating the full switch
and when the I eve I drops suff ici ent I y so that su rfac 321 energi zes l ow sw i tch
LS the feed roller 26a is again put into motion to increase the supply of strap
within the accumulator. An empty switch ES will stop the machine if strap no
longer is available due to an empty coil 24.
In known plastic strap supplies and accumulators the feed rolls for
20 the accumulator pull the strap from the coil by pulling directly on the strap. A
brake is then used to stop the freely rotating coil. Using this technique the
payoff speed is limited because the snap in the strap accelerates the coil and the
coast of the coil reel at the end of feeding makes the braking action very critical.
In the instant application the feed rolls for driving the coil and feeding the strap
are advantaseously very simple and require no separate brake for the coil.
The drive on the powered shaft 26 operates through a clutch which brings the
coil up to speed slowly and the coast at the end of feeding is not a concern since
it merely adds a slight amount of additional strap to the accumulator. Using
this unique technique the strapping machine is able to be run at higher speeds
30 than in the known strapping machines. A further advantage is that with known
strap supplies a separate reel is needed to hold the coil whereas in the supply
and accumulator of this invention the coil is merely set directly on the supporting
shafts 25 and 26. Still further, the strap leaves the coil at a constant linear
speed regardless of changes in diameter of the roll.
--4--
. ~ ., . , ~ , :
.
~0939S3
As best shown in Figure 17 a modified strap supply is shown. In
this embodiment a reel 300 of strap S is rotatably mounted on an axle 302
which is lifted up into support brackets 303. A belt 304 is pushed by spring 306
against the surface of the strap on the reel holding the reel into the brackets.
The belt is driven by the shaft 26 which is coupled to feed roller 26a. Thus the
belt and feed roller are rotated synchronously and the linear speed of the strap
leaving the reel and passing through the feed pinch rollers in the Same~ or as in
the embodiment of Figure 2, slightly greater at the pinch rollers, regardless of
diameter changes in the strap on the reel.
STRAP FEED MECHANISM
The strap feed mechanism 14 is best shown in Figures l and B. The
feed mechanism includes a continuously rotating powered roller 34 which rotates
in a counterclockwise direction. A spring biased pinch roller 35 actuated by
solenoid 192 presses the strap against the powered roller. The rollers 34 and
35 push the strap along a guide channel 36. As best shown in Figure 7 the guide
channel is provided with a slot 36a and the peripheral surfaces of the rolls 34
and 35 are of reduced thickness which is less than the width of the slot 36a.
The strap is thus contained at all times and is supported against buckling as it
is driven by the rollers through the channel 36. This is an advantageous feature
20 as buckling of the strap has been a problem with known strap-feeding mechanisms.
Known strap-feeding mechanisms generally interrupt the strap guide or channel
by breaking the channel upstream and downstream of the feed rollers. This
necessitates chamfering the inlet to the downstream end of the track as the strap
is fed from the feed rollers. It is in this area of the chamfer, however, where
resistance to the movement of the strap causes the tendency to buckle. As is
readily apparent in the instant invention of this application there is no chamfer
nor interription of the channel so that the buckling does not occur.
The strap feed mechanism 14 also includes a compartment 38 having
a paddle 39 that forms a portion of the channel 36 as it passes over the compart-
ment. The paddle is pivotally mounted and heldby a light spring 40 in the raisedposition. The paddle is provided with a cam 41 that engages a stop switch S.
As strap is fed by the rollers 34 and 35 through the channel 36 the free end of
the strap Passes through the cutting and sealing head 12 around the track 10
and comes to rest again in the c utting and sealing head. When the free end of
--5--
tne strap is blocked the cont;nuous end in the channel 36 begins to back up
pushing the paddle 39 downwardly and activating the stop switch S. This
de-energizes the solenoid 192 and allows a spring to move the pinch roller 35
away from the powered roller 34 to discontinue feeding of the strap and
energizes a trigger solenoid 43 (Figure 1) which pulls a trigger 44 away from
a single revolution clutch 45 which is the basic drive component for the cam
control drive 22 to begin the rest of the cycling of the machine.
TENSION!NG_ UNlT
The tensioning unit 20 is best shown in Figures 1, 3 and 4 and
10 includes a plurality of freely rotating stationary take-up rolls 48 alternated
with freely rotating movable take-up rolls 49. The strap feeds up and down
the rolls 48 and 49 as shown in Figure 3 and when the movable rolls 49 are
shifted to the phantom line position in Figure 3 it can be seen that a consider-
able amount of strap can be pulled back from the track 10 at the downstream
end of the strap. The take-up rolls provide a rough or large retraction of the
strap to pull it out of the track 10 and snugly around the object being wrapped.
At this time, of course, the free end of the strap is clamped at the cutting and
sealing head so that only the continuous end is retracted by the take-up rolls.
The strap between the take-up rol Is and the accummulator passes over a pair
20 of flanged rollers 50 in between which is fastened an anvil 51. The anvil has
a smooth end surface 51 a. A pai r of spaced anchor arms 52 are pivoted on a
plate 53 by pivot post 54. Pivotally mounted between the anchor arms is an
anchor block 56 having a protruding wedge 56a. The anchor block has a sur-
face 56b that rides against a pin 57. A spring 58 connects to the anchor arms
at a point 58a and pul ls the arms toward the anvi I to pul l the wedge 56a against
the strap and press it against the smooth end surface 51a of the anvil. The
strap is thus trapped and unable to move from the accummulator during rough
tensioning. As the strap is drawn tight on the package, however, the tension
increases so that the anchor block begins to rotate relative to the anchor arms
30 and overcomes the force of the spring 58a. When the tension reaches a preset
desired amount the anchor block swings over-center relative to the spring away
from the strap and anvil. This frees the strap for movement from the accummula~
tor as the rollers 49 continue to move toward the right. The anchor arms are
fixed to a lever 59 that is engaged by a shoulder 60 that forms part of a
T~shaped
--6--
lV939~3
, ame 61. The T-shaped frame is attached to a movable front plate 62 which
carries the movable rollers 49 and reciprocates from left to right as shown in
Figures 1 and 3. When the front plate 62 is to the left the lever 59 is rocked
counterclockwise so that the anchor block is freed from the tape. As the front
plate rnoves to the right, however, the spring 58 pulls the anchor arms 52
toward the anvil to bring the anchor block into engagement with the strap.
The front plate 62 slides on ways 64 and is pulled to the left by a
spring 65 (Figure 1). The upper end of the plate is supported by a roller 63
running in a slot in a fixed bar 63a. The front piate is coupled to a tension
10 arm 70 that is coupled to a bell crank 71. The free end of the bell crank is
provided with a cam follower 72 that follows a cam 73 which is fixed to a cam
shaft 76 that is coupled to the single revolution clutch 45. Thus the tension
arm begins to swing the front plate 62 to the right when the single revolution
clutch is energized after the free end of the strap has completely encircled the
object and has come to rest within the cutting and sealing head.
Spaced just above the front plate 62 is a knurled tension roller 80
that is coupled to a slip clutch 82 (Figure 4) such that the roller 80 is free in
the counterclockwise direction as shown in Figure 1 but will engage the clutch
82 when rotated clockwise and provide a drag to a predetermined desired amount.
20 The strap is pinched against the tension roller 80 by an eccentrically mounted
pinch roller 84. The pinch roller is connected to a tension lever 86 having a
cam follower roller 87. The lever is pulled down by a spring 88. As the
front plate 62 moves to the right during a tensioning cycle the cam roller 87
riding on the top of the plate keeps the pinch roller 84 away from the flan~3ed
tension roller 80 so that the strap can be freely drawn back by the rollers 49.
The top surface of the plate 62 has a downward ramp 92 and an upward ramp 94.
When the front plate moves to the right a distance sufficient-to allow the roller
87 to move past the downward ramp 92 the tension lever 8O swings counterclock-
wise to engage the pinch roller 84 against the tension roller 80. The strap is
30 also pushed to the right (Figure 3) by a roller which rotates on the movable
frame 61 until the tension reaches the desired load on the slip clutch 82 and
allows the strap to rotate the roller 80. Continued movement of the front plate
62 to the right draws the roller up the up ramp 94 allowing the dog 89 to seat
beneath the notch at the end of the tension lever to hold the tension lever up and
--7--
,
~ 10939S3
In an inactive position away from ramp 92 as the front plate is returned. When
the front plate is returned to the left a pin 96 engages the dog 89 to release the
tension levers so that the roller 87 returns to the top surface of the front plate
62. An adjustment bar 67 is connected to plate 62 by screws and can be moved
to the left to overlap ramp 92 with a second ramp 92a thus changing the startingtime of the final tensioning.
Known strapping machines usually employ two tensioning devices.
The first draws the strap around the package more or less loosely. The second
comes into action and draws the strap up to its final tension. In the instant
application the invention performs both of these operations by a single
mechanism requiring only a single timing sequence. This advantageously
results in simplicity of manufacture and operation and greater strapping and
tensioning speeds.
C,UTTING AND SEALING HEAD
As best shown in Figures 1 and 8-14 the cutting and sealing head 12
is provided approximately centrally in the lower run of track 10 and forms a
part thereof. The track includes a rectangular plastic straip 100 having a
groove 102 for receiving the strap. The track is abutted against a cover 104
by springs 105. The track is mounted on a pad 106 which slides on posts 107.
Stripper pins 108 pass through the track and pass into the groove 102 as the
track and pads are n~oved away from the cover. Thus the stripper pins eject
the strap from the track groove to prevent binding. The track pads are con-
nected to track bars 110 which are engaged by paddles 182 and i84 to be
described to open the track during the desired timing sequence of the strappinS
cyc l e.
The sections of track immediately adjacent the cutting and sealing
head 12 are best shown in Figures 12-14. Figure 12 which is taken along the
line 12-12 of Figure 1 shows the groove 102. Figure 12 also shows groove 36a
below the groove 102. This second groove is to allow the continuous strap to
move in beneath the captured free end of the strap and for beginning the
threading of a new strap during the seallng cycle. Figure 13 illustrates only
the groove 102 since at this location along the track there is only a single
groove as the free end of the strap is stopped in the cutting and sealing head.
The cutting and sealing head 12 is provided with a cover plate 116
--8--
,,: ;
,~
1~939~3
.hat is movable transversely of the direction of strap movement. For clarity
movements described as being transverse hereinafter will means transverse
to the path of the strap. Also in Figure 10 which is a plan view of the cuttina
and sealing head it should be understood that the cover plate 116 has been
removed for clarity. The cover plate forms an anvil for gripping and sealing
the strap as will be described. The cover plate 116 is reciprocated by a
cam follower 118 which rides on a cover plate cam 119. A left hand gripper
120 pivotally mounted in a left hand yoke 120a which is pivotally mounted for
vertical movement between an upper position as shown in Figure 11 where it
can clamp the continuous end of the strap to the cover plate. The left hand
gripper is movable into a lower position as shown in phantom lines in which
the free end of the strap engages a stop surface 121 to stop the strap as it makes
a loop around the track 10. The left hand gripper is provided with a track
groove 122 which allows feeding of new strap while the gripper 120 is raised
holding the previous loop of strap. The left hand gripper is free to move
downwardly and is held in its raised position by a cam follower 124 that rides
on a left hand cam 125. A spring 123 buffers the force between the gripper
and the gripper yoke.
A right hand gripper 128 is vertically reciprocally mounted and is
moved down by a cam follower 130 that rides on a right hand gripper cam 131.
The cam follower 130 pulls the right hand gripper down against the force of a
set of Belleville springs 134. These springs when allowed to push the riaht
hand gripper up press the gripper teeth of the right hand gripper against the
strap to anchor the free end of the strap against the cover plate 116. The
right hand gripper is provided with a track groove 136 which provides a lower
path for the strap as the free end of the strap passes between the cover plate
and the upper surface of the right hand gripper on its way to the stop surface
121 on the left hand gripper.
A platen 138 is pivotally mounted on a platen yoke 138a. The platen
yoke is pivotally mounted for movement between the left hand and right hand
grippers and between an upper position as shown in solid lines in Figure 11
in which it presses the lower continuous end of the strap against the upper
free end of the strap and against the stop plate 116 to squeeze the straps
together after melting. The platen is provided with a lower groove 140 for
_g_
:. . . ~ . .
~093953
,~
allowing the continuous end of the strap to be moved beneath the sealed loop of
strap for starting a new feeding cycle. A cam follower 142 follows a platen
cam 143 to move the platen upwardly from the phantom line lower position to
the solid line position shown in Figure 11. A spring 189 presses the platen
with a small force during heating and Belleville springs 190 press the platen
with a greater force for bonding the melted ends.
A heater bar 147 is mounted for transverse movement by a cam
follower 148 that follows a heater bar cam 149. The heater bar moves between
the two runs of strap and melts the strap as the platen presses the straps
together by spring 189 and then is removed prior to final pressing of the strapstogether by the platen through spring 190. The left hand gripper yoke 120a
and the platen yoke 138a are pivotally mounted on an inner slide 160 that is
reciprocally mounted for transverse movement. Springs 162 urge the left hand
gripper and platen to seat against their respective yokes. The inner slide is
reciprocated by a follower 153 that rides between cam surfaces on an inner
slide cam 164 and the back of cover plate cam 119. Thus while the platen and
Ieft hand gripper can move up and down they also are moved transversely by the
inner slide. Springs 170 move the cover plate to the left and the cam follower
118 moves it transversely to the right.
OPERATION
The operation of the cutting and sealing head 12 is best described
with a complete overall operation of the machine. In the start condition the
strap S has been loaded in the machine and fed around the track 10. The main
drive motor M is running. The position of all elements of the machine are
shown as in the drawings. At a signal to apply a strap the trigger solenoid
43 energizes and pulls the trigger away from the single revolution clutch ~5.
This releases the clutch and engages the drive with a cam shaft 180 on which
all of the various cams are mounted. The cam shaft begins to rotate and
releases the right hand gripper 128. The right hand gripper is driven upward
by the Belleville springs 134 and anchors the free end oF the s~rap (in from
its terminal edge) against the cover plate 116. Continued rotation of the cam
shaft causes the inner slide 160 to move transversely to the right away from
the strap. Since the platen 138 and the left hand gripper 120 are mounted on
the inner slide they also are pulled away from the strap to clear the strap area
--1 0--
:
10939S3
.or tensioning. The retraction of the inner slide also opens the strap guide
track 10. This occurs by paddles 182 and 184 which are on the platen and
left hand gripper, respectively, and which engage the track bars 110. Motion
of the track pads 106 causes the stripper pins 108 to push the strap free of thetrack groove 102. Once the platen and le ft hand gripper are clear of the
strap and the track is open the tension cam 73 drives the tension arm 70 in a
counterclockwise direction (as viewed in Figure l) and pushes the front plate
62 to the right to begin tensioning.
The first motion of the front plate allows the anchor block 56 to be
swung down and clamp the strap to the anvil 51. Continued motion of the front
plate 62 causes the strap to be drawn from the track down on the package.
The strap is drawn by the alternate sets of moving and fixed rollers 49 and 48.
When the strap is around the package and no more strap can be drawn from the
track the tension in the strap increases and trips the anchor which releases
and allows the strap to be drawn from the accummulator so that the front plate
can complete its stroke. Toward the end of the front plate movement the tension
lever roller 86 falls down the ramp 92 and allows the tension rolls 84 and 80
to close on the strap. The strap is then drawn to the final tension by the
remainder of the front plate movement.
At the beginning of the tensioning, after the inner slide is
retracted, the left hand gripper 120 and the Platen 138 drop downward in
response to the platen and left hand gripper cams. Near the end of tensioning,
the inner slide 160 moves back to its initial position. During this motion the
platen and left hand gripper, now in the lower position, come back underneath
the just tensioned strap. This motion also allows the track to close. Thus at
this moment the continuous run of the strap is confronting the trapped free end
of the strap. The left hand gripper is then raised to the up position by its
cam and clamps the continuous end of the strap against the cover plate.
At the end of the tension front plate 62 movement the tension lever
86 rolls up the ramp 94 and separates the tension rollers 80 and 84. Just as
the leit hand gripper comes up to the press the strap against the cover plate
and thus against the underside of the free end of the strap the heater blade 147moves in between the straps at the seal area. Once the heater blade is in
place the platen 138 rises to an intermediate position and presses against the
:. :
1093953
-
strap by the spring 189. During this time a cutter 186 on the surface of the
right hand gripper 128 shears the continuous end of the strap to separate it
from the suPply. At the intermediate position the platen presses the bottom
strap, heater and top strap together so that the strap is melted for sealing.
The press force is determined by a spring and plunger between the platen and
the platen lever which is pivoted on the axis 168.
At this time a switch 200 is actuated by cam 201. The activation of
this switch energizes a feed solenoid 192 that draws the pinch roller 35 against
the powered feed roller 34 by a lever 193. Because the strap is pressed
between the rolls it is fed and passes through the channel 36, the groove 112
in track 10, the groove 136 in right hand gripper 128, the groove 140 in platen
138, the groove 122 in the left hand gripper 120, the groove 102 in the tracl<
110 as it leaves the cutting and sealing head.
When the melting of the strap is complete the heater blade is pulled
back by the heater cam 149. When the heater bar is clear of the strap the
platen cam 143 drives the platen up hard against the overlapping ends of the
straps and presses the melted sections together. The Belleville springs 190
between the platen and the platen lever overcome the spring 189 and determine
the pressing force. These springs 190 do not affect the heating force from
20 spring 189, however, since they do not contact the bottom of the platen until
the cam forces the platen up into its final press. After the melted plastic has
hardened the left hand gripper 120, the platen 138, and the right hancl gripper
128 move down to their initial positions in response to their respective cams~
After the grippers and platen have started down the cover plate 116 is retracted
by its cam l l9 against the force of springs 170 to allow the sealed strap to leave
the sealing head. The cover plate immediately returns to the initial position
after the strap is free.
After the tensioning part of the cycle the front tension plate 62 is
returned by its cam 73 so that at the end of the cam shaft rotation the front plate
30 is back to its initial position and has moved the dog 89 out from under the ten-
sion lever 86 and has retracted the anchor block 56. Ready for the next cycle.
At the end of the cam shaft rotation the tripper 44 engages the single revolution
clutch 45 which then disconnects the drive from the cam shaft.
Just after the cover plate i 16 closes, the end of the new feedins strap
- 12 -
10939S3
_nters the sealing head and strikes the stop surface 121. Feeding then stopswhen the strap baclcs up into the compartment 38. This completes the cycle
of operation.
Known strapping machines start the strap feeding part of the cycle
only after the seal has been made and after the strap has been ejected from
the machine or require that the strap be shifted sideways to clear the loop
being sealed from the new strap being fed. As described above, in the inven-
tion of this application feeding of the new strap occurs in a single plane and
during the sealing operation thus shortening the total cycle time. Known
10 strapping machines also use separate actuators such as air cylinders or sole-
noids to provide the opening force for the track. In the invention of this appli-
CatiOn the motion of the gripper and platen in the sealing and cutting unit provide
this opening force and is much simpler in construction and operation and far
more reliable. Known strapping machines rely on the lateral stiffness of the
strap to keep the straps aligned with each other in the seal area. Since the
slides and guides employed in known strapping machines and always the heater
blade are moving sideways relative to the strap, there is a tendency in the
known strapping machines for the straps to be moved out of alignment thus
producing misaligned seals. In the invention of this application a stripper
20 bar 203 is advantageously provided to keep the two straps aligned rather than
solely relying on lateral stiffness of the strap. In known strapping machines
the gripper for holding the free end of the strap prior to tensioning is generally
done either by separate triggering mechanisms such as cylinders or solenoicl
or by the technique of coupling the gripper with motion of the seal head then
stopping the head for tensioning and finally restarting the head to complete the
seal after tensioning is complete. In the invention of this application the initial
gripper is applied, tensioning and sealing are all accomPlished with one revolu-
tion of a cam shaft ~iving simplicity, reliability and a very high-speed machine.
While the preferred embodiment of the invention has been illustrated
30 and described and the known advantages apparent have been discussed, it should
be understood that variations and other advantages will be apparent to one
skilled in the art without departing from the principles herein. Accordingly, the
invention is not to be limited to the specific embodiment illustrated in the
draw i ngs .
--1 3--
