Note: Descriptions are shown in the official language in which they were submitted.
CA 02173931 2001-12-19
METHOD AND APPARATUS FOR REGISTRATION
OF A SEAL AND PERFORATION ON A PLASTIC BAG
FIELD OF THE INVENTION
The invention relates generally to the art of
plastic bag making machines. Specifically, the present
invention relates to a bag machine which employs a rotary
sealing drum which is adjustable in size to produce bags of
different lengths and in which the locations of seals are
detected and used as references for forming perforations.
CA 02173931 2001-12-19
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BACKGROUND OF THE INVENTION
Many different types ef plastic bag making
machines are known in the art of producing plastic bags for
industrial and indivi~3ua1 consumers for many different
applications (e.g. small sandwich bags and trash bags;?.
While the present invention has a wide range of applications
for the production of such products, the related art will be
explained by reference to one particular class of bags i.e.,
polyethylene trash bags or, garbage bags and wastebasket
liners of the type usually sold in boxes of folded bags or
rolls of bags.
Further discussion of the history and operation of
these machines can be found in Zx.S. Patent No. 4,642,084
(the '084 patent) entitled "Plastic Bag Making Machine",
issued to Peter J. CJietman, Jr., on February 10, 1987, and
assigned to Custom Machinery Design, Inc. The '084 patent
discloses a bag machine which includes a rotary drum with
seal bars attached thereto and which includes a gear
mechanism adapted for. analog variation of the drum diameter
between a first smaller diameter and a second larger
diameter. Manual rotation of a hex nut assembly while the
machine is stopped increases or decreases the drum's
diameter through a series of appropriately mounted mitre
217393
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gears and ring gears. Once this adjustment is made, the
machine begins operation. Readjustment of the drum diameter
can only be accomplished by stopping the machine to adjust
the hex nut assembly.
Additionally, very small errors in drum diameter
size can lead to acute problems, particularly an error in
the seal to print registration distance that accumulates
every revolution of the drum. An error of a fraction of an
inch leads to serious problems when the bag width is only
several inches across and the speed of the film moving
through the machine is 500-900 bags per minute. By the time
the error is detected, a considerable amount of film (or
web) is wasted.
The control of the spacial relationship between a
repetitive print pattern on the web and the repetitive seals
the machine is placing across the web is referred to as the
"registration" of the seal to the print on the web. This
spacial relationship may also be referred to as the "phase"
between the repetitive print and seal occurrences on the
web.
Similarly, the control of the spatial relationship
between the repetitive seals placed across the web and the
repetitive perforations the machine is placing across the
web is referred to as the "registration" of the perforation
to the seal on the web. This spacial relationship may also
be referred to as the "phase" between the repetitive
perforations and the repetitive seals across the web. The
distance between a seal and a perforation is commonly called
the "skirt length" of the finished bag.
213931
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Another prior art device described in U.S. Patent
No. 4,934,993 (the '993 patent), also issued to Peter J.
Gietman, Jr. and assigned to the assignee of the present
invention, allows for adjusting the drum diameter while the
bag making machine is in operation. The '993 patent
requires the operator to preset the drum diameter
corresponding to the nominal bag length, but will correct
for slight variations in the bag length. If the seal is not
properly registered to the printing on the bag the diameter
of the drum is temporarily increased or decreased. When the
registration is correct the drum returns to the preset
diameter. One disadvantage of this system is that "hunting"
(the drum diameter will continually change) will occur if
the average bag varies more than slightly from the preset
length. Hunting will be particularly prevalent at higher
speeds.
When a bag making machine such as that described
in the '993 patent is used to adjust the drum diameter, any
device (such as a perforator, die cutter, punching station,
or folding station) on the bag making machine that processes
the plastic downstream of the drum may become out of proper
synchronization with the sealing process occurring in the'
drum while the drum is changing diameter. For example a
perforator will be slightly out of synchronization causing
~5 perforation to seal registration (skirt length) to vary.
According to the '993 patent the skirt length may be
adjusted manually. However, by the time the error is
detected and the manual correction made, a considerable
amount of film may be wasted.
-5-
Another device, disclosed in U.S. Patent No.
5,292,299 (the '299 patent), uses a proximity detector and
an encoder to determine where each seal will be placed.
However, the '299 patent does not actually sense and
determine the location of a seal; the '299 patent "fixes"
the distance between the point of application of the seal
and the point of perforation at a constant minimum distance
instead of detecting it. Because the actual location of the
seal is not known, the user is required manually to
initialize the skirt length, which requires time to
accomplish and may result in errors and undue waste.
Likewise, if synchronization is lost, errors will occur in
the placement of the perforation.
In any event, the prior art and the '299 patent
demonstrate the desirability of determining the location
where the perforation should be placed, with respect to the
seal.
As one alternative, this may be done by detecting
a printed mark, and locating both the seal and perforation
with respect to the printed mark. One known arrangement for
detecting printed marks, such as registration marks, on film
(or web) materials involves the use of a light source
aligned generally perpendicular to the web and a sensor
positioned substantially collinear with the light source.
While this prior art method indirectly locates the
perforation with respect to the seal, it would be
advantageous to directly place the perforation with respect
to the seal. However, known print detectors are not
successful at detecting features in certain sheet materials,
and in plastic film materials in particular. Accordingly,
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it would be desirable to provide the capability to detect a
seal in a plastic film and control film perforation such
that perforations are directly registered with respect to
the seal.
However, in the past, it has been difficult to
detect the presence of a seal in a moving film accurately
and consistently. Thus, it would be desirable to provide a
seal detection method and arrangement which can accurately
and consistently detect a seal in a moving film, even where
the film is moving at linear speeds in excess of 600 feet
per minute. Additionally, it may be desirable to detect a
perforation for properly separating bags being removed from
a roll of bags and/or folded.
A bag making machine which overcomes the foregoing
shortcomings and satisfies these needs would represent a
considerable advancement in the art.
OBJECTS AND SUMMARY OF THE INVENTION
It is a primary object of the present invention to
provide a plastic bag making machine which can adjust for
different bag sizes without requiring the machine to be
stopped and to adjust the registration of downstream process
devices.
It is another object of the present invention to
provide a plastic bag making machine which automatically
compensates for errors in sizing of bags by adjusting its
sealing apparatus to the bag size being produced without
having to stop the machine.
According to the present invention a plastic bag
making machine includes a cylindrical drum with a variable
21'3931
diameter. A plurality of seal bars define the circumference
of the drum, and are substantially parallel to the drum's
rotational axis. The bags are made from a plastic film that
includes registration marks thereon. The marks are detected
by a detector disposed near the film. A detector also
detects each revolution of the drum. An encoder provides
signals indicative of the position of the film. A
controller determines the distance between the registration
marks using the output of an encoder as a position signal
and adjusts the diameter of the drum in response to the
determined distance. The controller also determines the
position of the seal bars relative to the registration marks
and adjusts the diameter of the drum in response to the
relative position. A downstream device includes a
perforation to seal registration controller with a
registration control input. The controller provides a
control signal to the registration control input in response
to changes in the diameter of the drum.
To properly locate the perforations with respect
to the seal, the machine preferably includes an arrangement
for detecting seals in the moving sheet material. The
arrangement includes a support surface disposed on a first
side of the material to support the moving sheet material, a
radiation source disposed on the second side of the moving
sheet material for emitting radiation towards the material,
and a radiation receiver disposed on the second side of the
material for receiving a portion of the radiation. The
apparatus further includes a signal processor unit adapted
to produce a signal representative of the intensity of the
portion of the radiation. The controller uses this
_g_
information ~.o dei.ermine she ioc;ation o~ a seal, and to
locate the perforation with respect to the seal.
J~ESC:l~IPTIUiV UF' 'rHF 1W1W1NCiS
For a better understanding of the invention,
reference is made t~ tie ac:c:~ulpamyinc~ czrawiy5, in whieii
like numerals designate corresponding elements or sections
throughout, and in which:
Figure 1 is a schematic illustration of the bag
making machine according to a preferred embodiment of the
present invention;
Figure 2 is a longitudinal elevation (partially in
section) of the expandable sealing drum according to the
preferred embodiment of the present invention;
Figure 3 is a cross-sectional view taken along the
line 3-3 of Figure 2;
Figure 4 is a perspective view of a Length of
printed plastic film as used in the preferred embodiment of
the present invention;
Figure 5 is a graph showing drum error versus
time;
Figure 6 is a graph showing phase rate versus time
for the drum error of Figure 5;
Figure 7 is a graph showing phase error versus
time for the drum error of Figure 5;
Figure 8 is a graph showing drum error versus
time;
Figure 9 is a graph showing phase rate versus time
for the drum error of Figure 8;
_. 2~7393~
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Figure 10 is a graph showing phase error versus
time for the drum error of Figure 8;
Figure 11 is a diagram of control corrections for
different cases for a control algorithm used to implement
the present invention;
Figure 12 is a schematic illustration of the bag
making machine according to an alternative preferred
embodiment of the present invention;
Figure 13 is an illustration of an arrangement for
detecting a seal in a moving film for use with the machines
illustrated in Figure 1 or 12, where the arrangement
includes a movable backing or support surface; and
Figure 14 is an illustration of an arrangement for
detecting a seal or perforation in a moving film, where the
arrangement includes a stationary backing or support
surface.
To improve the clarity of the description of the
major features of the present invention, only general
descriptions are provided for components which are well
known in the art, and could be variously embodied by one of
ordinary skill in the art after reading and understanding
the principles of the present invention, and/or are
specifically described in the '084 and '993 patents.
DESCRIPTION OF PREFERRED EMBODIMENTS
Before explaining at least one embodiment of the
invention in detail it is to be understood that the
invention is not limited in its application to the details
of construction and the arrangement of the components set
forth in the following description or illustrated in the
2~~393~
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drawings. The invention is capable of other embodiments or
of being practiced or carried out in various ways. Also, it
is to be understood that the phraseology and terminology
employed herein is for the purpose of description and should
not be regarded as limiting.
The major elements of a bag making machine 10
include a dancer and idler assembly 12, a sealing drum and
blanket assembly 14, a chill roll 16, a controller 15, a
punching station 17, a folding station 18, a pull roll
i0 system 20, a perforator/cutting station 22 and a phase
variator assembly 24.
The elements of the system shown in Figure 1 may
be configured in other ways, including removing elements
shown therein. Likewise, the bag making machine 10 may have
other elements added depending on the type of product being
produced. For purposes of illustration, the basic system of
the '084 patent will be used herein but should not be deemed
limiting in any way. As noted above, this system can be
employed in any mechanism wherein certain functions are to
be performed in a specific spacing relationship to
preprinted matter on a stream of pliable material.
Film 11 is fed in the direction of the arrows from
a source of plastic tubing 13 through a dancer roll 12a and
an idler roll 12b into the sealing drum and blanket assembly
14. Source 13 may be any source for printed plastic
material such as an extruder, a preprinted roll of plastic
film, or a printer on which the plastic is imprinted.
Dancer roll 12a and idler roll 12b maintain proper tension
and speed for the bag making system.
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The sealing drum and blanket assembly 14 consists
of a cylindrical drum 28, which is capable of being varied
in diameter. That feature is illustrated in Figure 1 by the
dotted circle illustrating a smaller diameter. A number of
sealing bars 30 are also shown in Figure 1 and periodically
form cross seals across the flattened film tube 11. Sealing
bars 30 are of conventional design and are disclosed in
detail with respect to construction and operation in the
'084 patent. A blanket 32 is mounted on rollers 34, 35, 36
and 37 for surrounding a portion of drum 28 in such a way
that the film 11 passes between blanket 32 and drum 28 while
seals are being formed. Rollers 34 and 35 are mounted to an
elongate frame 39 which is pivotable between the solid and
dotted line positions shown in Figure 1. Frame 39 includes
a perpendicular plate 40 near its midsection, the latter
being coupled to an air cylinder 42 having an extensible rod
43. It will be appreciated that extension of rod 43 causes
rollers 34 and 35 to move to the dotted line position when
the drum diameter decreases, thereby maintaining tension of
blanket 32 against drum 28.
Roller 37 is driven from a gear motor 44 by belt
45 to drive blanket 32, and in turn blanket 32 will rotate
drum 28 due to the tension between these components. Motor
44 includes an encoder 47 which generates a position signal
during revolution of motor 44. Alternative encoder
locations are on roller 37 or roller 36 or any machine
roller such that the film 11 being processed is in direct
contact with that roller, the roller circumference moves
with the film 11, and the film 11 will not slip against the
roller. A detector 23, such as an electric eye or magnetic
_ 217331
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sensor is positioned directly above drum 28 and generates a
signal when a small metal or magnetic protrusion 26 on drum
28 passes, i.e. for each revolution of drum 28. From the
output of encoder 47 and detector 23 the circumference of
drum 28 and the linear travel of film 11 are determined by
controller 15. In an alternative embodiment encoder 47 may
be mounted via a pulley to roller 37 or roller 36.
After passing chill roll 16, the film 11 next
passes through an optional punching station 17 which punches
preselected hole and handle configurations in the film.
Thereafter, the film may be further processed as shown or in
any other appropriate manner.
Variator system 24 is driven from a gear box 63 by
belt 64. Gear box 63 is driven by drum 28 through belt 65.
Variator system 24 also includes a pair of gears 66 and 67,
used to vary the phase of the perforator/cutting station 22
and punching station 17, respectively, or any other type of
downstream station. Adjustments in the perforation to seal
phase are made at the perforator/cutting station 22 by
activating motor 69 which drives gears 66 and 67. As will
be explained below, the phase may be automatically adjusted
when the diameter of drum 28 is adjusted, in order to keep
the skirt length appropriate. In an alternative embodiment
the adjustment may be made by hand.
Proceeding now to the more detailed description of
the preferred embodiment of the present invention, reference
is also made to Figures 2 and 3 to illustrate the expandable
sealing drum 28. Drum 28 is generally cylindrical and is
comprised of a plurality of elongate slats 70 and a
plurality of sealing bars 30. Each slat 70 includes a steel
_ ~173~3t
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base 72 having a slightly curved exterior surface. A rubber
lagging 71 is provided on the exterior surfaces to assist in
maintaining proper traction between blanket 32 and drum 28.
Drum 28 also has a pair of generally circular end
plates 75 and axial shaft sections 77a and 77b extending
through the center of drum 28 and mounted in suitable
bearings to permit rotation of drum 28. Mounting plates 79
having holes therein are attached to the interior sides of
each of end plates 75 near the outer edge thereof, the axis
of the openings of each plate 79 being at 90 degrees with
respect to the axis of shaft sections 77a and 77b. Similar
plates 80 are affixed to end plates 75 inwardly of plates 79
so that the pairs of spaced apart mounting plates (79 and
80) are disposed equidistantly around each end plate 75. In
one embodiment 6 pairs of mounting plates are used. In a
second embodiment 12 pairs, or a different number, of
mounting plates are used.
A threaded rod 82 is placed through holes in each
pair of plates 79 and 80. A mitre gear 85 is mounted on the
inner end of rod 82. Rotation of mitre gear 85 causes
rotation of rod 82.
A pair of mitre ring gears 88 are rotatably
mounted to a machined surface of shaft sections 77a and 77b
on bearings 89 and are constructed and arranged to mesh with
mitre gears 85. Rotation of ring gears 88 causes rotation
of all mitre gears 85 and threaded rods 82 which are coupled
to each mitre gear ring 88.
Slats 70 are coupled to and supported by threaded
rods 82 by a threaded plate 92 fastened to each end of slats
70. Rotation of the rods 82 will cause plates 92 to travel
2~'~393~~.
_14_
up and down the length of the rods. Rotation of a rod 82 in
one direction will cause the slats 70 to move radially
inward, reducing the drum diameter, while rotation in the
opposite direction will cause a drum diameter expansion. In
alternative embodiments supports other than threaded rods
may be used, such as ball nuts and ball screws.
Rotation of rods 82 is accomplished by a motor 46
mounted in tube 48. Tube 48 is a hollow tubular section
coaxially joining shaft sections 77a and 77b. Pinion 38 on
gear box 49 is run by motor 46 and engages a gear 50 mounted
on a rod 62. Rod 62 extends the length of drum 28 and
pinion gears 90 at each end of rod 62 engage ring gears 88.
Rotation of pinion 38 by motor 46 causes rod 62 to
rotate ring gear 88 and rods 82, thereby reducing or
enlarging the diameter of drum 28. Motor 46 is energised by
controller 15 through wires 54 which are connected to wires
extending through shaft section 77b and tube 48 via slip
rings 55.
In an alternative embodiment rod 62 may be
replaced with a chain which directly drives one rod 82 at
each end of drum 28. The chain driven rod 82 then drives
ring gear 88, which in turn drives the remaining rods 82.
Controller 15 preferably includes a CPU (or any
other digital logic device) and receives as inputs the
outputs from a detector 19, detector 23 and encoder 47.
Controller 15 could alternatively include analog logic
Circuits or any other device that provides the proper
outputs in response to the inputs. Detector 19 is an
electric eye that detects a plurality of registration marks
100 on film 11, and is located above the path of film 11. A
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firmly mounted and flat surface provides a consistent
optical background for detector 19 so that registration
marks 100 on the film 11 can be read accurately. In an
alternative embodiment the detector 19 may detect a
distinguishing feature in the printed pattern rather than a
specific mark for such purpose. And in a further
alternative embodiment, the controller can ignore detection
of printed matter on the web between specific selected
features in the printed matter or between marks printed for
the purpose of registration to the printed pattern.
While the operation of the bag machine of the
present invention will be described with specific reference
to the configuration of the '084 patent and a machine for
producing plastic bags, it should be understood that the
principles taught herein have numerous other applications.
Therefore, application of the subject matter should not be
limited just to plastic bag making machines.
Controller 15 includes an input from an operator
interface 110, such as a VDT (video display terminal) and a
keyboard. Operator interface 110 allows the operator to use
one or more of a variety of features, such as, but not
limited to, automatic nominal or average bag length
detection, preset average or nominal bag length, automatic
adjustment for variations in bag length, manual adjustment
for variations in bag length, automatic phase control for
skirt length and manual phase control for skirt length.
Initially, film 11 is fed in the direction of the
arrows from film source 13 through the dancer and idler
rolls to the blanket and drum assembly 14. As the film 11
passes over the idler roll 12b, detector 19 reads the
_.
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position of the registration mark 100 relative to the
activated sealing bars' position generated by detector 23,
determined from the input from encoder 47. In the fully
automated mode, controller 15 can determine the nominal bag
length (spacing between marks), as well as variations from
the nominal bag length. Appropriate activation of motor 46
and adjustment to the drum size is then made, as well as the
appropriate phase adjustment for controlling the seal to
print registration. For example, if the seal bar position
is progressively moving away upstream from the registration
mark on the film, then the drum size is too large and motor
46 will be activated to decrease the drum diameter. When
the seal bar holds its position relative to the registration
mark 100, drum 28 is then set at the proper diameter.
At this point, seal bar spacing, as measured along
the drum circumference, is equal to registration mark
spacing, but the registration of the seal on the web with
respect to the registration mark may not be correct. A
shift may then be required to bring each seal and
corresponding registration mark 100 into proper spacing.
This is also accomplished with controller 15 through its
automatic control of the drum size. Similarly, the
perforator/cutting station 22 should also be adjusted to
control the perforation to seal registration (skirt length).
In order to change the seal to registration mark
spacing the drum size is altered temporarily to allow the
registration mark 100 to "move" closer to the seal. As an
example, if the registration mark needs to be moved closer
to the seal, the drum size is altered to establish a known
rate of advancement of the registration mark 100 toward the
_.. 2~ °~39~1
-17-
seal on each revolution of drum 28. When enough revolutions
are completed, drum 28 is returned to its proper size arid
normal operation ensues. However, the temporary change in
drum size to correct the seal to registration mark spacing
will cause a temporary shift in the perforation to seal
spacing (skirt length). Thus, the phase of
perforator/cutting station 22 is temporarily adjusted to
maintain the skirt length at the desired value. The
following example is illustrative of how this is
accomplished, but is not in any way limiting on the use of
the equipment or the components therein.
If the seal location with respect to the
registration mark is six inches from the desired seal
lOCatlOn Wlth reSpeCt tU the reglStratlOn mark, the drllm
circumference may be reduced by 1/2 inch. Thus, after every
revolution of drum 28, the registration mark is 1/2 inch
closer to the seal. After 12 revolutions, the seal and
registration mark will be properly spaced. Drum 28 is then
expanded to the original circumference and normal operation
of the machine may recommence.
While the proper drum diameter and seal to
registration mark spacing are being obtained by controller
15 the skirt length should be temporarily adjusted. The
perforator/cutting station 22 is mechanically linked to drum
28. When the diameter of drum 28 may be changed the speed
of perforator/cutting station 22 is simultaneously changed.
However, there is a propagation delay while the bag at drum
28 travels along the film path until it reaches
perforator/cutting station 22. During this propagation
delay the phase of the perforator/cutting station should be
X173931
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corrected to compensate for the instantaneous change in the
speed of the perforator cutting station. Controller I5
provides the proper signal to motor 69 to temporarily
compensate for the propagation delay at the time it sends
the signal to adjust the diameter of drum 28.
Controller 15 also allows the presetting of the
nominal bag length prior to threading film 11 through the
machine. The operator can input the desired length, and
controller 15 can cause the diameter of the drum to be
adjusted until the preset diameter is obtained. Of course,
the machine must be running in order to accomplish this.
In summary, controller 15 determines the spacing
between print registration marks using inputs from detector
19 and encoder 47 determines the circumference of drum 28
using inputs from detector 23 and encoder 47. Controller 15
then calculates the arc length distance between active seal
bars along the circumferential path of drum 28 and adjusts
the drum circumference so that the arc length distance
between active seal bars matches the distance between print
registration marks. Controller 15 also measures the
position of the seal bar relative to the print registration
mark and automatically adjusts the relative placement of the
seals in relationship to the print registration mark to a
fixed distance, responding to changes in the print mark
spacing on the printed web as they occur.
The location of a seal bar with respect to the
print registration mark is determined by first counting
encoder pulses from the time detector I9 detects a
registration mark until the time detector 23 detects
protrusion 26, located on the circumference of a drum end
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plate 75, in direct radial alignment with a seal bar
location. Secondly, the distance from the detector 19
position along the web path to the lowest point on the drum
circumference is known as a function of drum ciroumferenoe.
Using the encoder measurement, the known path length, and
the known mark spacing, the actual and desired spacing
between seal and registration mark can be calculated and
compared.
During normal operation of the machine, plastic
film 11 is fed from the roll 13 through the dancer roll 12a
and idler roll 12b to the blanket and drum assembly 14 where
heat seals are applied. The plastic film may be configured
so that the seals define the bottoms of plastic bags being
formed. Alternatively, the seals may define the sides of
the bags. In this situation, the plastic film 11 is slit
longitudinally down the middle, the middle slit being the
top opening of each bag being formed.
Utilizing the drum sizing and the seal to
registration mark registration functions of controller 15,
seals may be consistently placed in proper orientation to
any printed matter appearing on the film. As the film 11
leaves the blanket and drum assembly 14, it encounters chill
roll 16 which cools the heat seals.
The plastic is next fed to punching station 17
where handles may be punched into or out of the plastic and
the bag's configuration may be further defined. For
example, "t-shirt" bags are quite popular in supermarkets
and grocery stores at present. These bags have a lower bag
section and two handles that resemble the shoulder straps of
- 21'~393~
a tank top t-shirt. This configuration may be punched on
the apparatus shown.
From punching station i7, the film may be fed to
folding station i8 as disclosed in the '084 patent. From
folding station 18 film 11 may next move to the
perforator/cutting station 22 where perforations can be
placed between bags or where the bags may be completely
separated. As shown in the '084 patent, the separation
between bags may also be partially slit, partially
perforated. The bags then move o~ to a packaging operation.
In the preferred embodiment, punching station 17
and perforator/cutting station 22 and any other downstream
devices are run off of the same gear box ~3 connected to
drum 28. As described above controller 15 causes
adjustments to be made to variator system ~4 so that there
is no phase variance between seals, handle cuttings and
perforation or cutting.
As an alternative embodiment, a separate servo
motor is used to drive the perforator/cutting station 22 and
~0 a further separate servo motor is used to drive the punching
station 1~. In this embodiment, the controller maintains
the relative speed a~.d position of the two added servo
motors to the rest of the machine using encoder feedback
signals from each servo motor and a master encoder signal
from an encoder connected either directly or indirectly via
belt and pulleys to the dr~n shaft 111.
The currently preferred embodiment is to mount the
encoder to the end of the blanket drive roll 37 in Figure 1
or Figure 12. This is because it is desirable to measure
film displacement between seal occurrences, which is the
217393I
distance between seals which equals the product length. The
control system then adjusts the perforator/cutting station
22 to make exactly one revolution per product length,
automatically adjusting (that is "registering") this motion
ratio and the perforator/cutting station ~2 cut position to
maintain consistent perforation to seal distance, as the
product may change from one product to the next.
In a second alternative embodiment the variator
system 24 may be composed of a special planetary gear box
system known as a phase variator. ~s a third alternative
embodiment, there may be two of these phase variator
devices, one in the drive system to the punching station and
one in the drive system to the perforation/cutting station.
Thus, the punching station may also have a motor on its
phase variator to allow the controller 15 to control punch
to seal registration independently from perforation to seal
registration.
Controller 15 serves at least one other function
during operation of the machine. Through detectors 19 and
23, controller 15 continuously calculates averages of mark
to mark spacing (bag length), seal to registration mark
spacing (phase), and/or perforation to seal spacing (skirt
length). These averages are used as filters to minimize
control system "hunting" if widely varied sequential values
are measured. carious types of averaging may be used,
including a recursive filter known as a low pass filter.
Such averaging or filtering methods will be well known to
anyone knowledgeable in the art of digital filtering. The
controller also detects and rejects erroneous readings and
2I73~~~
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sends alarm signals to operators if readings vary too much
or too frequently.
When the discrepancy between the nominal bag
length and the mark to mark spacing reaches a preselected
limit, controller 15 resets the nominal spaEing and
instructs motor 4~ to make a minor adjustment in the size of
drum 28 to compensate. The drum diameter may be slightly
increased or decreased. This compensation function is
continuous and ongoing so that the printed matter 101 is
maintained in a consistent position on the bags.
The seal to mark registration control scheme
described first may be summarized as first adjusting the
diameter of the drum to be appropriate for the actual bag
length, and then temporarily adjusting the diameter to
correct phase error. An alternative control provides for
adjusting the drum diameter in such a way as to concurrently
correct for both bag length and phase error.
To better understand this type of control, a more
in depth analysis of the relationship between drum diameter,
bag length, and phase error, as well as the changes to each
over time is useful.
drum error (or bag length error) may be defined as
the desired drum circumference less the actual drum
circumference, and may have either a positive or negative
sign. An i~Erease in the magnitude of the error does not
change the sign (direction) of the error. drum error does
not change unless the drum diameter is changed.
Phase error, the distance between the desired and
actual seal positions, also has a positive and negative
sign. if the actual seal position is trailing the desired
_ 21'~393~.
-23-
seal position, then the phase error is defined to be
positive. If the actual seal position is leading the
desired position, then the phase error is defined to be
negative.
The phase error will change with each revolution
~zniess the drum error is zero. For example, assuming there
is a zero phase error and a non-zero drum error before the
first drum revolution, a phase error dependent on the drum
offset is added after one revolution. After two
revolutions, there is two times the phase error, after three
revolutions, three times the phase error, etc. A
description of this is that the phase is "walking."
fi~hen the phase is walking the seal can move closer
to the preceding or following desired seal location. This,
what begins as a positive error may increase until it
eventually becomes closer to the following seal position.
At that time the error may be described as a negative error,
and viewed as preceding the following desired seal location.
This is much like an angle of +315 degrees being described
as an angle of -45 degrees. ~'or example, if the bag length
is 8~ inches, then:
Measured Phase Error Corrected Phase Error
+38 inches +38 inches
+42 inches -38 inches
-38 inches -38 inches
-42 inches +38 inches
The phase error could be defined as always positive or
always negative, but this would mean that the phase
correction could be as large as a bag length. It is more
- 213931
-24-
efficient to limit the maximum phase error to be half of a
bag length as is done above.
The phase will walk even while drum adjustments
are being made, unless the drum correction is completed
prior to the next revolution (or the next seal bar if there
are multiple seal bars per revolution). An example of the
phase walking over a correction interval is demonstrated in
Figures 5, 6, and 7. Figure 5 shows the drum error as a
function of time with an initial drum error of positive 30
inches. Figure ~ shows the phase rate as a function of time
for the drum error of Figure 5. The phase rate is the rate
at which the phase changes or walks and is also a function
of drum circumference. Phase rate is defined as the drum
error divided by the current drum circumference (and is then
multiplied by line speed to convert from inches per inch to
inches per second to convert to a time base). Since the
actual drum circumference is changing over time, the drum
error (which is the desired drum circumference minus the
actual drum circumference) is also changing over time.
Assuming that the desired drum circumference is constant
over the correction interval, the phase rate is changing
logarithmically. Figure 7 shows the phase error as a
function of time for an initial phase error of positive 10
inches and the drum error of Figure 5.
Figures 5-7 show the time interval over which the
drum error is eliminated, and assumes a constant rate of
drum circumference change. Figures 5 and ~ show that as the
drum error gets smaller, the phase rate decreases, and goes
to zero when the drum error is zero.
- 21°3931
-25-
because the phase is walking when the correction
is made the phase error at the end of the correction time
will be the initial phase error plus the phase error added
due to the phase walking. The added phase is actually the
area under the phase rate curve (the accumulated phase
error . Once the actual drum circumference is equal to the
desired drum circumference, the drum error and the phase
rate will both be zero, and the phase will no longer walk.
Given an initial drum error and an initial phase
error, the objective of the controller of this alternative
is to force these errors to be as close to zero as possible,
and to drive them there somewhat concurrently. since there
are variations in raw materials, namely normal variation of
the length of registration marks, the thickness of the film,
etc., it is impossible to drive these errors to exactly
zero. The controller should therefore maintain these errors
to be within tolerance limits.
A control strategy that accomplishes this
objective may be implemented with a controller that utilizes
an algorithm which uses the initial drum error and the
initial phase error as inputs and uses drum correction
direction (increase or decrease drum circumference) and
length of time for correction as outputs. This algorithm is
computed in the controller, which then controls the drum
circumference.
A drum correction motor is turned on for a
specified length of time in response to the output of the
controller. The controller can run the motor either forward
or backward, which corresponds to increasing or decreasing
the dr~n circumference. The time and direction are
217393
-2 6-
calculated by a control algorithm so that when the
corrections have been completed the phase error and the drum
error are both zero (or within specified tolerance limits).
This is done by adjusting the drum so that the initial phase
error plus the phase error added by the time it takes to
correct the drum error is equal to the phase error incurred
by the intentional offset.
Figures 8-10 illustrate this concept. Figure 8
shows drum error as a function of time with an initial drum
error of 2 inches. Figure 9 shows the phase rate as a
function of time for the drum error of Figure 8, and Figure
10 shows the phase error as a function of time for the drum
error of Figure 8.
In the example shown there is a positive drum
error and a positive phase error. The time t1 in each graph
is the time it takes to correct for the initial drum error.
At time t1 the drum error is zero but the phase error has
walked to a larger value than it had initially. The drum
thus needs to continue to be increased and then decreased so
that it will walk the phase error back to zero and it will
return the drum error to zero. The drum is thus increased
over the time interval from t1 to t2, and is then decreased
over the time interval from t2 to t3 as shown in Figure 8.
Figure 9 shows the area under the phase rate curve
for these time intervals. The area Cl is the amount of
additional phase error that occurs just correcting for the
initial drum error. Therefore, in accordance with the
control strategy the area ~2 and the area ~3 is forced to be
equal to the area ~1 plus the initial phase error. The
_ 21 ~393Z
-27-
value of C2 and C3 is opposite in sign (negative in this
case) to the value of C1 and the initial phase error.
fhe example illustrated in Figures 8-1~ assumed
that the drum error and phase error were both initially
positive. 'Ihe inventors have found that an effective
control algorithm may be based on dividing the universe of
initial conditions into the following six possible cases:
Case 1: positive drum error, positive phase
error
Case 2: negative drum error, negative phase
error
Case 3: positive drum error, negative phase
error (area of IC11>Iphase errorl)
Case 4: negative dru~i error, positive phase
error (area of IC11>lphase errorl)
Case 5: positive drum error, negative phase
error (area of IC11<Iphase errorl)
Case 6: negative drum error, positive phase
error (area of IC11<Iphase errorlj
2U Case 1 is described above in conjunction with
Figures 8-10. similarly, a negative initial drum error and
initial phase error (Case 2) would result in initially
reducing the drum circumference beyond the desired drum
circumference, and then returning it to its proper drum
circumference. Both Cases 1 and 2 result in the initial
phase error increasing in magnitude as the drum is adjusted
to its proper circumference. In other words, the drum error
is of a polarity (sign) that causes the initial phase error
to walk even farther from zero as the drum error is being
corrected.
~17393i
-28-
The six cases are illustrated on the graph of
Figure 11. In Figure 11, the horizontal axis shows drum
error (positive to the right), and the vertical axis shows
phase error (positive upwards). As may be seen on Figure
11, Cases 3-6 have initial drum errors such that the phase
error accumulated while the drum error is being corrected
has a polarity (sign) opposite that of the initial phase
error.
For these cases, the area C1 is opposite in sign
to that of the initial phase error. That is, the initial
drum error is causing the initial phase error to walk closer
to zero. In Cases 3 and ~, the magnitude of Cl is greater
than the magnitude of the initial phase error. This means
that by the time the drum error is reduced to zero, the
phase error will have walked past zero and continue to grow
in the opposite direction that it started from. This means
that the control action will be that of Cases 1 and 2,
namely, the drum will go past the desired drum circumference
and then return.
In Cases 5 and 6, the magnitude of C1 is less than
the magnitude of the initial phase error. This means that
the drum error is walking the phase error towards zero, but,
at the time the drum error has been reduced to zero, the
phase error has not yet reached zero. In these cases, the
drum error can be left as is for a period of time to allow
the phase error to walk toward zero before the drum error is
corrected. The time the walking is allowed should be
selected such that by the time the drum error is corrected
to zero, the phase error is also corrected to zero. Another
approach is to adjust the drum circumference so that the
- 2173931
-29-
initial drum error is actually increased. This would also
increase the phase rate and thus reduce the time that it
takes to walk the phase error to zero.
Figure 11 shows points (del, pel) and (de2, pet)
which correspond to the point at which the magnitude of Cl
is equal to the magnitude of the initial phase error. There
is one point for every drum error which has a value of phase
error which corresponds to this point. At this point, the
time it takes to adjust the drum circumference to its
desired value is equal to the time it takes to walk the
phase to zero error. Therefore, only the correction
interval t1 would be needed.
Figure 11 also shows a zone of no correction.
This represents the fact that the drum error and phase error
will never actually be zero, and therefore tolerance limits
are be set. If the drum error is within 0.030 inches and
the phase is within 0.100 inches, no corrective action is
taken. These numbers are purely illustrative and should not
be considered critical or limiting.
According to another alternative embodiment, when
the drum error is large initially, the drum error is reduced
to a predetermined limit before concurrent or simultaneous
drum error and phase error corrections are made. One such
limit that has been found to be acceptable empirically is 2
inches. There are two reasons simultaneous drum error and
phase error adjustments with large initial drum errors are
avoided. First, the time to make both changes
simultaneously is much greater than first getting the drum
within this limit and then doing both changes
simultaneously. Second, for large drum errors the phase
_ ~17393~
error will walk too far during the correction period, and
can even walk across the entire bag length multiple times.
One implementation of an algorithm that satisfies
the above described control scheme, using a linear phase
rate assumption, involves the solution of a quadratic
equation to derive the time that the drum correction motor
should be on for. The solution of this quadratic yields a
complex number. The magnitude of the complex number is used
for the time and the direction in which the correction motor
is run is determined by the initial drum and phase error.
If the initial drum error is opposite in sign of the initial
phase error, then the direction of drum correction is
determined by the magnitude of C1 relative to the initial
phase error.
his one skilled in the art will readily recognize,
many control equations will satisfy the concerns addressed
above, and come within the scope of the present invention.
One such equation that is acceptable has been developed by
the inventors, and is given below. The equation is merely
illustrative, and should not be construed as limiting the
scope of this invention.
In the equations below T1 is the time it takes to
initially drive the drum error to zero (t1 on Figures 8-10j
and T2 is the time from when the drum rate error is zero
until the drum motor direction is reversed (t2 - t1 on
Figures 8-10). Ttot is the total correction time. For the
following equations it is
assumed that T2 occurs
drum set - drumcirco
- midway between T1 and Ttot .
drumrate
2I'~393~
-31-
~ ( k ~ s ~ dramrate ~ ~/k 2 ~ s 2 ~ drvmrate 2 - 9 ~ k ~ s ~ drum set ~ IPS ~
drumrate )
2 ~ s ~ dr~mrate ~ IPS
TZ - -1
2 ~ s ~ dramrate ~ Ipg ' (k ~ s ~ drvmrate . yk ~ s ~ dr~amrate - 4 ~ k ~ s ~
drum-set ~ IPS ~ drumrate j
and Ttot = s ~ T1+2 - T2
where:
drumcirc = measured circumference of drum
drumcirco = initial circumference of drum
drumrate = rate at which drum circumference changes
drum set = desired circumference of drum
s = +/- 1 depending on the direction of the
correction
k = initial phase error + phase error accumulated
during correction time T1
drum err = drum circumference error (drum set-
drumcirc)
drum erro = initial drum error
phaserate = rate at which phase is changing
IPS = line speed
In the above embodiments the time that the fixed
speed drum diameter motor is turned on is varied in response
to the phase error and drum size error. Zn another
embodiment, in addition to or instead of controlling the on
_ ~~ 73~3I
-32-
time of the motor, the motor speed is varied in response to
the phase error and drum size error.
One alternative embodiment places the print
detector 19 between the drum 28 and perforator/cutting
station 22. This configuration is advantageous because it
places the detector closer to the perforator/cutting system.
However, this configuration allows errors in the skirt
length because the drum is upstream of the detector 19.
Specifically, this configuration can cause random errors
because excess film can accumulate in the seal drum area
when the film tension is too relaxed in this area. When
sufficient excess film accumulates, a fold in the film (or
web) can occur and will pass through the rest of the system
as an undetected length of film. Subsequent areas of the
machine will provide enough film tension to pull this fold
open again, thus lengthening the film possibly after
measurement and before perforation or cutting.
In a particularly preferred alternative
embodiment, shown in Figure 12, print detector 19 is placed
upstream of the drum 28 and a seal detecting station,
designated generally at 112, and described in detail below,
is located upstream of the perforator/cutting station 22 for
detecting the seals formed by sealing bars 30. This
configuration has the advantage of precise and direct
control of the skirt length because the seal can be placed
with respect to the registration mark and the perforation
can be placed with respect to the seal. The highly
desirable precise and direct control of the skirt length can
be achieved because the location at which the perforation is
_ 2173931
-33-
applied is directly controlled with respect to the actual,
detected location of the seal.
In such an arrangement print detector i9 is used
to determine the desired diameter of drum 28, in the manner
described above with respect to Figures 1-11. As described
above, the actual diameter of drum 28 determines the
distance between seals, and the distance from the seal to
the registration mark. Additionally, seal detecting station
112 determines the location of each seal. This information
is used to locate the perforation with respect to the seal,
by adjusting the speed of the perforator/cutting station 22
as described above, and preferably independently of the drum
diameter adjustments.
The above-described embodiment utilizes a print
detector 19 to indirectly control the location
(registration) of the seal with respect to the mark (print).
The print location is detected and the seal location is
adjusted to be placed in what the controller 15 indicates
will be the correct location. However, the actual seal-to-
print registration is not directly monitored or directly
controlled.
Another alternative embodiment uses the seal
detecting station 112 to directly control seal-to-mark
(print) registration. In this embodiment, the seal
detecting station 112 and the print detector 19 are located
downstream of the seal drum 28. The detectors 19, 112 and
controller 15 are used to locate and determine the actual
distance between the seal and the print. The actual
distance is compared to a desired distance and the
controller 15 adjusts the drum diameter accordingly. A
- 21'3931
-34-
signal indicative of the distance may be obtained by
counting encoder pulses from the time the print is detected
until the seal is detected, or vice versa.
The desired seal-to-print distance may be obtained
in a variety of ways, including entering the desired
distance into the controller 15 through a keypad, mouse, or
other user-interface 110. Alternatively, the user can
adjust the distance while the machine 10 is making bags, and
when the desired distance is obtained, the controller will
store that distance.
The preferred arrangement of seal detecting
station 112 will now be described with reference to Figures
13 and 14. Referring first to Figure 13, seal detecting
station 112 includes a roller 122, a radiation source such
as a fiber optic sender 124, a radiation receiver such as a
fiber optic receiver 126, an interface unit 128, a power
supply 120, a dropping resistor 121, and a support structure
123. The radiation source typically includes a light
emitting diode (LED), while the receiver may include a photo
diode of known type. These may be included in a single
unit. By way of example only, sender 124 and receiver 126
unit may be of the type manufactured by MICROSWITCH having
Part No. FE-T2A3, power supply 120 may be a 24 volt DC
supply, resistor 121 may be a 2200 ohm carbon resistor, and
structure 123 may be incorporated into the frame of bag
making machine 10. Moreover, certain control or signal
processing elements, such as interface unit 128, may be
included in controller 15. Interface unit 128 may include a
number of elements manufactured by MICROSWITCH, including:
a plug-in base, Part No. MPS33; a plug-in receptacle, Part
._. ~173~~~
-35-
No. MPB 11; a control head, Part No. MPF6; and a multi-
function timer/logic card, Part No. MPA133.
In one preferred embodiment, the sensor system
consists of the following Tri-Tronics Company, Inc.
components:
Model PIC-1 Product Inspection Control which is
used to convert the sensor electrical output pulse
to a fixed width pulse to assure detection by the
machine control system or "CPU".
~ Model SEIF1 Optical sensor with infrared light
source, infrared light detector, "enhanced dynamic
range" adjustment, and optical fiber cable
adapter.
Model BF-P-36P fiber optic light guide assembly
with bifurcated fiber bundle 0.010 x 1.50 inch.
In general, radiation source or sender 124,
receiver 126 and unit 128 interact such that when a seal
passes a sensing position "A" below sender 124 and receiver
126, unit 128 drops the potential between signal line 125
and common line 127 from substantially 24 volts to
substantially 0 volts. Additionally, upon detection of a
seal, unit 128 also changes the potential between power line
130 and signal line 125 from substantially 0 volts to
substantially 24 volts. In general, the detection of a seal
results in the change in reflectance of the film.
Sender 124 and receiver 126 preferably each
include a linear light wave guide arranged along a line
substantially parallel to the heat seals in film 11. More
specifically, in reference to Figure 13, the heat seals in
film 11 are substantially parallel with the longitudinal
- 2I'~3~3i
-36-
axis 132 of roller 122 and are perpendicular to the line of
travel L-L of film 11 (see also Figure 14}. The linear
light wave guide portions of sender 124 and receiver 125 are
coupled to unit 128 via fiber optic cables 131 and 133,
respectively. Sender 124 provides a form of radiation such
as infrared, visible green light or visible red light to the
sensing position "A", where the light strikes the film and a
portion of the light is reflected back to receiver 126. The
type of light implemented may depend upon the type of film
being processed. Additionally, the light source may be of
continuous or pulsed light. Sender 124 and receiver 12~ are
fastened to support structure 123 with clamps 135.
Referring to Figure 13, roller 122 has a
substantially cylindrical shape having a width wider than
the width of film 11. Roller 122 includes a shaft 134 which
rotatably supports roller 122 between a pair of bearings 136
mounted to frame 123. Roller 122 may be a solid roller
fabricated from aluminum and having a specially treated
surface 137 to provide the proper light transmission between
sender 124 and receiver 126. The transmission of light may
include reflection from film 11 and surface 137. In
particular, the surface may be a colored surface, preferably
black, which is hardened and impregnated with Teflon''. This
surface reduces friction between roller 122 and film 11, and
also provides an effect upon light transmitted from sender
124 which enhances the ability of the arrangement to sense
seals in film 11 (particularly more translucent and
transparent films) moving at relatively high speeds (in
excess of 600 linear feet per minute). By way of example,
the roller surface may be treated with a hard lube
_ 21739~~
-37-
impregnating process provided by Wisconsin Hard Coats of
Milwaukee, Wisconsin.
As discussed above, unit 128 includes a
photoelectric sensor head and a signal interface module.
The photoelectric sensor head provides the source of
radiation, such as light, directed to sender 124 over fiber
131 and also includes an arrangement for monitoring the
intensity of light received from receiver 126 via fiber 133.
The signal interface module detects changes in the intensity
of light provided to unit 128 by fiber 133. The signal
interface module allows for the adjustment of sensitivity to
changes in light intensity, changes in the duration of time
for which the potentials between lines 130 and 125, and 125
and 127 are changed due to the detection of a seal, and
allows for the adjustment of a time delay between the time a
seal is sensed and the time the changes in potential between
lines 125, 127 and 130 take place.
Hy way of example, unit 128 may include a timer
logic card of the type manufactured by MICROSWITCH having
Part No. MPA133. The timer logic card includes adjustments
to provide the above-described ability to control the
duration of potential changes between lines 125, 127 and 130
(pulse-width control), as well as the time delay for the
purpose of delaying the point in time when unit 18 causes
potential changes between lines 125, 127 and 130 due to the
detection of a formation. The sensitivity of unit 127 to
changes in the intensity of light provided by receiver i26
is controlled by the sensitivity adjustment on the control
head.
2173~3~.
-38-
Detecting a seal in a moving film 11 using sender
124 and receiver 126 depends upon the type of film and the
underlying surface 137 supporting moving film 11 at the
interface between film 11 and surface 137 (surface 143 in
the Figure 2 embodiment). More specifically, the light
directed by sender 124 is directed along a plane "S" of
sender 124 and strikes film 11 at the line where plane "S"
intersects film 11 (position "A" at the interface). The
characteristics of the combination of film Ii and underlying
surface 137 affect the intensity of the light which is
directed (reflected) back to receiver 126 along a plane "R"
of receiver 126. Light affecting characteristics (e. g.
reflection, absorption, and scattering properties) of film
11 and underlying surface 137 affect the intensity of the
light which is received by receiver 126 and monitored by
unit 128 for the purpose of providing a pulse via lines 125,
127 and 130.
To compensate for differences in light affecting
characteristics of different films 11 in combination with
surface 137, the orientation of the planes "S" and "R" of
sender 124 and receiver 126 respectively are adjustable.
More specifically, an angle 138 between plane "S" and a
perpendicular plane "P", and an angle 140 between plane "j
and plane "P" are adjustable. Plane "P" is perpendicular to
surface 137 at position "A". The adjustment of angles 138
and 140 has been performed based upon empirical data, and
depends upon the type of surface 127 on roller 122 and color
and type of film 11. Furthermore, without base surface 137,
a consistent distance between sender 124, receiver 126 and
film 11 is difficult to maintain, as are angles 138 and 140.
- 2~.'~3~3~
-39-
Accordingly, without surface 137, it has been found that the
detection of a formation such as a seal in moving film 11
cannot be performed with sufficient consistency or accuracy
to be useful for the purpose of seal detection in a high
speed bag making machine. Additionally, properly selected,
surface treatment for surface i37, such as a black hard Iube
coat, provides increased accuracy in detecting seals for a
relatively large range of colors and types of film 11.
By way of example, the following Table A includes
a list of materials where ranges for angles 138 and 140 have
been determined based upon testing using infrared light.
The materials tested were LLDPE (linear low density
polyethylene), HDPE (high density polyethylene), and LDPE
(low density polyethylene). This testing was conducted
using a support structure 123 where the tips of sender 124
and receiver 126 were a distance D of approximately 3/8 of
an inch from point "A".
TABLE A
MATERIAL RANGE OF RANGE OF
TYPE ANGLE 38 ANGLE 40
LLDPE - Clear 13.5 - 77.5 13.5 - 77.5
HDPE - Clear 13.5 - 77.5 13.5 - 77.5
LDPE - Black 13.5 - 77.5 13.5 - 77.5
LDPE - Orange 13.5 - 45.0 13.5 - 45.0
~ ~
By way of further example, the following Table B
includes a list of materials where the sensitivity
adjustment of the control head has been determined at
- 21'~3~3i
-40-
various distances v, and angles 138 and 140. The values in
Table B are turns of the adjustment screw in a MICROSWITCH
control head model number MPF6.
TABLE B
Distance
D (inches),
ATERIAL Angles
138 &
140 (degrees)
11/32,
17/32,
9/16,
5/8,
3/4,
17 13
17 45
45
LDPE - Orange 5.5 1.5 3.5 4.5 4.5
LDPE - Clear 3.0 1.5 0.0 0.0 3.0
LDPE - Black 8.0 6.0 8.5 7.0 8.0
HDPE - Clear 1.0 1.5 0.0 0.0 0.0
Testing with the film disposed over a flat surface
has revealed an optimum optical fiber head angle to the film
surface of approximately 5 degrees from perpendicular,
toward the trailing side of film motion. Additionally, an
optimum distance to the plastic film of 0.156 inch has been
determined.
Figure 14 illustrates a modified arrangement for
sensing a formation such as a seal in moving film 11. The
modification includes replacing roller 122 with a fixed
support 142 over which film 11 may travel. Support 142 may
be fabricated from aluminum to include an interface surface
143 which includes a Hard Lube treatment as does surface 137
of roller 122. Additionally, film 11 or surface 143 may be
provided with lubricants to facilitate the sliding of film
11 relative to surface 143. Support 142 is fastened to
~173~3i
-41-
support structure 123 with an appropriate fastener
arrangement 144.
The embodiments of the arrangements described in
reference to Figures 13 and 14 may be modified to include
automatic positioning of sender 124 and receiver 126. More
specifically, positioners such as stepping motors may be
used to position sender 124 and receiver 126. In a
preferred embodiment, sender 124 may be mounted upon the
shaft of a stepping motor 146 and receiver 126 may be
5 mounted upon the shaft of a similar stepping motor 148.
Stepping motors 146 and 148 are controlled by a main control
unit 150 (included in controller 15j. By providing
controller 150 with data relating to the type of film 11 for
which seals are being detected, controller 150 may cause
stepping motors 146 and 148 to rotate such that angles 138
and 140 are set to optimize the seal detection capability of
the arrangement for a selected film 11. Of course, stepping
motors 146 and 148 may include gear reductions to enhance
the ability of the system to set angles 138 and 140.
Depending upon the application, stepping motors
146 and 148 may be replaced with other positioning
arrangements such as linkages in combination with an air or
hydraulic cylinder.
