High speed labeling machine having a constant tension driving system

A high speed labeling machine is provided which includes a constant tensioning device for maintaining tension downstream of the metering roll at a substantially constant predetermined level thereby improving both metering and dispensing of labels. The constant tensioning device may also function as a driver for pulling the continuous web of material through the labeling machine thereby reducing the driving load on the metering roll, thus both providing more effective and accurate metering at a given web speed while also allowing higher web speeds to be achieved.

TECHNICAL FIELD
 This invention relates to an improved high speed labeling system having a
 constant tension driving system capable of maintaining a substantially
 constant tension in the web material so as to ensure accurate metering of
 the web and effective dispensing of labels.
 BACKGROUND OF THE INVENTION
 The application of labels to articles and products has been and continues
 to be an important step in providing product identification, specific
 product information and marketing advantages. Manufacturers of various
 products are continually seeking a more efficient and effective manner in
 which to apply labels to articles or items, such as cartons, containers or
 any other packages or products Laving a surface capable of securely
 receiving an adhesive label.
 Numerous methods have been employed in the past to mark articles, such as
 color-coded ink sprays and manually applied stickers. The introduction of
 adhesive-backed pressure sensitive labels and hand-held, manually operated
 applicators has greatly facilitated the marking of articles in that the
 applicators provide a simple means for applying an adhesive-backed label
 to an article. Such hand-held label applicators are well known and used
 extensively in various industries, for example, for marking the price of
 articles to be sold. Their use, however, in manufacturing, assembling and
 distributing applications is limited because of the necessity for marking
 many items at a high rate of speed. In these applications, the articles to
 be labeled are transported along a conveyor past a number of stations, one
 of which often entails the application of a label to each article as it
 passes by or while the conveyor is stopped. Use of a hand-held label
 applicator in this type of high speed operation would be unacceptably
 slow, inefficient, labor intensive and therefore, inipractical due to the
 time constraints associated with high volume production.
 As a result, relatively high speed labeling machines have been developed to
 apply labels to articles advancing by a labeling station on, for example,
 a conveyor belt. The pressure-sensitive labels are commonly precut and
 carried on a continuous web of material often called backing material
 which is rolled into a roll for mounting on the labeling machine. The
 backing material is somewhat more flexible than the label itself. This
 allows the label to be separated from the backing material, or dispensed,
 simply by bending the backing material sharply away from the label, which
 is usually done by drawing the backing over a fairly sharp stripping or
 peeling edge of a peeling bar or plate. The less flexible label then
 separates from the backing material and remains relatively straight for
 application to the article by some type of applicator. For example, U.S.
 Pat. Nos. 3,321,105 to Marano and 5,022,954 to Plaessmann disclose
 automated labeling machines which operate at relatively high speed when
 compared to manual application.
 Although some present labeling machines function adequately at certain high
 speeds, there is an ongoing need for labeling machines capable of labeling
 at extremely high speeds so as to increase the number of labels applied
 per unit time, thereby increasing the efficiency of the manufacturing
 process. One method of increasing the labeling capacity of a machine is to
 increase the speed at which the web moves through the machine. The higher
 the moving or feed speed of the web through the machine, the greater the
 number of labels dispensed per unit time. A common form of driving means
 for pulling the web through the labeling machine is a nip roller assembly
 driven by, for example, a stepper motor such as disclosed in both Marano
 '105 and Plaessmann '954. The web passes through a nip formed between a
 driver roller, powered by the stepper motor, and a driven or nip roller
 biased against the driver roller. In this manner, the rollers engage the
 web so that intermittent operation of the stepper motor causes
 intermittent movement of the web through the labeling machine. Increasing
 the speed of the stepper motor will, therefore, increase the speed of the
 web through the dispenser, i.e., over the peeler bar. However, the web
 feed speed will certainly be limited by the maximum operational speed and
 capacity of the driver of the nip roller assembly. Although a single
 driving device, such as a stepper motor, capable of achieving higher
 speeds and torque capacities, may be available, these drivers are often
 too large and too expensive. Therefore, it has been found that many
 labeling machines are incapable of achieving extremely high labeling
 speeds while minimizing costs. Moreover, as with the labelers disclosed in
 Marano '105 and Plaessmann '954, the nip roll assembly is often used as
 both a driving means and a metering means. In this instance, the driver
 roller must function to both pull the web through the machine while also
 stopping and starting the movement of the web so as to properly meter the
 correct length of web over the peeler bar as required to dispense the next
 label(s). However, the ability of the nip roll assembly to accurately and
 effectively meter the proper length of web is impaired, especially at high
 speeds, by the requirement of the assembly to also provide the pulling
 force necessary to pull the web through the machine. As a result, at very
 high speeds, these driving and metering nip roll assemblies often fail to
 provide accurate and effective metering of the web.
 The labeling machines disclosed in Marano '105 and Plaessmann '954 include
 a tensioning device downstream of the metering roll for maintaining a
 continuous tension in the web between the metering roll and a take-up
 drum. Specifically, the Marano tensioning device is a slipping belt/pulley
 arrangement attached to a take-up drum for continually rotating the
 take-up drum with a light rotational load. The Plaessmann reference
 discloses an idler arm-type assembly positioned between the metering roll
 and take-up drum for applying a light tensioning load to the web. In both
 embodiments, the tensioning device functions as a speed compensator
 between the take-up drum and the metering roll which do not move in
 complete synchronization. In this manner, the slip belt/pulley device and
 the idler arm device both insure that there are no loops or kinks in the
 web before it goes to the take-up drum by maintaining a continuous tension
 in the web. However, the continuous tension in the web caused by these
 tensioning devices varies throughout the operation of the labeling
 machine. As the web material accumulates on the take-up drum, the diameter
 of the take-up roll of material gradually increases, thereby continually
 increasing the moment arm through which the accumulating force of the
 take-up drum acts on the web. As a result, the force applied on the web by
 the take-up drum gradually decreases as the diameter of the roll
 increases, thus gradually decreasing the tension in the web. Also, the
 spring force biasing the idler arm of the Plaessmann '954 device varies
 throughout movement of the arm thus varying the tension in the web.
 Moreover, the continuous stopping and starting of the metering roll causes
 variations in the web tension downstream of the metering roll. These
 variations in web tension downstream of the driving and metering roll
 cause undesirable variations in web tension through the labeling machine.
 These tension variations adversely affect the ability of the metering roll
 to accurately and effectively meter the web thereby also adversely
 affecting ihe dispensing of labels by, for example, failing to pull the
 proper length of web across the peeler bar. Moreover, the web tension
 variations felt upstream at the peeler bar disadvantageously affect the
 dispensing of labels by making it more difficult for the metering means to
 accurately and repeatedly pull the web over the peeler bar with the
 optimum amount of constant web tension necessary for effective dispensing
 of labels at a given web speed. In addition, the above-noted adverse
 affects of web tension variations are exacerbated at higher web speeds at
 which substantially constant web tension becomes critical to achieving
 accurate metering and dispensing of labels.
 Many labeling machines also include a printing device upstream of the
 dispenser for printing indicia on the labels as the web passes through the
 printer. The printing devices used are often "off-the-shelf" items having
 a metering/driving roll incorporated therein. As a result, it is often
 more cost effective and easier to use this existing metering/driving roll
 as the primary metering/driving roll for the labeling machine. However,
 the driver for the driving/metering roll found in many printers often
 lacks the power/torque capable of: 1) accurately metering the web at
 higher web speeds while maintaining high printing quality; and/or 2)
 creating a pulling force sufficient to overcome the inertia of a large
 supply roll of continuous web, as used in large capacity labeling, so as
 to effectively pull the web from the supply roll while accurately metering
 the web.
 SUMMARY OF THE INVENTION
 It is an object of the present invention, therefore, to overcome the
 disadvantages of the prior art and to provide a labeling machine capable
 of accurately and effectively metering and applying labels to articles at
 a very high speed.
 It is another object of the present invention to provide a labeling machine
 with a constant tension driving system capable of maintaining a
 substantially constant tension in the web material downstream of the
 metering roll so as to ensure accurate metering and effective dispensing
 of labels.
 It is yet another object of the present invention to provide a labeling
 machine having a constant tension driving system which reduces the driving
 load on the driver/metering roll to allow the metering roll to more
 accurately meter the web while achieving the same web speed.
 It is a further object of the present invention to provide a high speed
 labeling machine with a constant tension system capable of maintaining
 substantially constant tension in the web between the driving roll and the
 take-up drum to minimize tension variations in the web throughout the
 labeling machine.
 Still another object of the present invention is to provide a labeling
 machine capable of achieving higher labeling or web speeds while providing
 effective metering and dispensing of labels.
 Yet another object of the invention is to provide a labeling machine for
 printing and dispensing labels which permits the metering roll of an
 "off-the-shelf" printer to be used as an effective driving and metering
 roll for high capacity labeling.
 A further object of the invention is to provide a labeling machine with a
 constant tension driving system which maintains tension in the web
 material downstream of the metering roll and the label dispenser at
 substantially constant levels.
 Still yet another object of the present intention is to provide a
 high-speed labeling machine capable of effectively maintaining the proper
 amount of tension in the continuous web of labeling material to effect the
 proper dispensing.
 A further object of the present invention is to provide a high-speed
 labeling machine which minimizes the required tension force applied to the
 web of backing material necessary for dispensing each label.
 Another object of the present invention is to provide a high-speed labeling
 machine capable of minimizing the frictional forces applied to the web by
 the peeler bar while ensuring effective label dispensing.
 Yet another object of the present invention is to provide a labeling and
 printing machine which permits more effective and consistent printing of
 labels throughout operation.
 A further object of the present invention is to provide a labeling and
 printing machine which minimizes tension variations in the web at the
 printer, thereby allowing more effective and consistent printing.
 These and other objects are achieved by providing a labeling machine for
 dispensing labels from a continuous web of material traveling along a feed
 path and applying the labels to a plurality of articles, comprising a
 supply roll for providing a supply of the continuous web of material
 having the labels affixed thereto, a dispenser positioned along the feed
 path downstream of the supply roll for removing the labels from the
 continuous web, a metering roll positioned along the feed path for
 metering the web from the supply roll and a constant tensioning device
 positioned along the feed path downstream of the metering roll for
 maintaining tension in the web immediately downstream of the metering roll
 at a substantially constant predetermined level. The constant tensioning
 device may also function as a driving device for imparting a pulling force
 on the continuous web of material for pulling the material from the supply
 means thereby assisting an upstream driving device. The metering roll may
 function as the upstream driving device and the labeling machine may
 further include a take-up drum downstream of the dispenser for
 accumulating the web material. The metering and driving roll may be
 positioned along the feed path, either between the supply roll and the
 dispenser or between the dispenser and the take-up drum. Preferably, the
 pulling force supplied by the constant tensioning device equals at least
 20% of the total pulling force necessary to pull a given web through the
 labeling machine at a given speed. The substantially constant pulling
 force imparted by the constant tensioning device may be equal to
 approximately one-half the maximum driver pulling force imparted on the
 web by the driving and metering roll at full capacity. The labeling
 machine may include a printer positioned upstream of the dispenser for
 printing indicia on the labels. The constant tensioning device may be a
 power dancer positioned along the feed path between the dispenser and the
 take-up drum. The power dancer may include a lever arm having a roller
 mounted on one end thereof and a biasing spring operatively connected to
 the lever arm for biasing the arm against the web of material. The lever
 arm may be pivotable between two positions so as to allow the spring to
 move the arm as the web is indexed through the metering roll. The take-up
 drum may be operable to move the lever arm back to the first position upon
 reaching the second position thereby recocking the arm. The dispenser may
 include a peeler bar having a peeling edge for contacting the web of
 material so as to cause the label to dispense from the web. A rotatable
 roller may be positioned immediately adjacent the peeling edge of the bar
 for supporting the portion of the web exiting the peeler bar thereby
 reducing frictional forces across the peeler bar.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring to FIG. 1, there is shown the high speed labeling machine of the
 present invention indicated generally at 10 for accurately metering a
 continuous web of material 12 while effectively dispensing labels 14 for
 application to various items or articles (not shown). Labeling machine 10
 generally includes a supply roll 16 of labels affixed to the continuous
 web of backing material 12, a dispensing unit 18 for removing the labels
 from the backing material 12, an applicator 20 for applying the labels to
 the articles, a driving and metering roll 22 for pulling the web from
 supply roll 16 in accurately metered lengths so as to dispense labels 14
 as needed, a constant tensioning device 24 for assisting the driving and
 metering roll 22 in pulling the web through the labeling machine while
 maintaining substantially constant tension downstream of the driving and
 metering roll 22, and an accumulating or take-up drum 26 for accumulating
 the waste backing material.
 Supply roll 16 is rotatably mounted on a spindle 28 extending from a main
 support frame 30 of labeling machine 10. The web 12 from supply roll 16
 passes around a first idler roller 32 and extends upwardly toward a second
 idler roller 34. Web 12 then passes over second idler roller 34 downwardly
 toward dispensing unit 18. Idler roller 34 is mounted on a conventional
 idler arm 36 biased upwardly by a small biasing force created by for
 example, a biasing spring. The lightly loaded idler arm 36 maintains a
 minimal amount of tension in web 12 so as to ensure smooth, taut delivery
 of web 12 to dispensing unit 18.
 Two small idler rollers 38 and 40 direct the downwardly fed web toward
 dispensing unit 18. Dispensing unit 18 includes a dispensing device in the
 form of a peeler bar assembly 42 which includes a peeler bar 44 having a
 peeling edge against which the web is moved to separate the label from the
 web of backing material. A delivery roller 46 mounted on dispensing unit
 18 directs web 12 toward peeler bar 44. A rotatable reduction roller 48
 mounted on unit 18 and positioned immediately adjacent the portion of the
 web exiting the peeling edge of peeler bar 44, is positioned to receive
 the exiting portion of the web to minimize the frictional forces on the
 web as it is pulled over the peeling edge, thereby minimizing the required
 tension in the web necessary to effectively dispense labels 14. Applicator
 20 may be any conventional applicator device for applying labels 14 to
 articles. For example, applicator may be a conventional vacuum blow
 applicator which alternates between creating a vacuum for acquiring labels
 dispensed from peeler bar 44 and supplying pressurized air for blowing the
 dispensed labels onto articles at the appropriate moment.
 As shown in FIG. 1, driving and metering roll 22 includes a driver roller
 50 operated by, for example, a stepper motor 52 controlled by an
 electronic control unit (ECU) 54. ECU 54 controls driver roller 50 so as
 to rotate and pull the web through the nip formed between driver roller 50
 and a nip roller 56 biased against driver roller 50 by a biasing spring
 58. An idler roller 60 mounted on main support 30 receives the web from
 nip roller 56 of driving and metering roll 22 and directs the web upwardly
 toward constant tensioning device 24 and take-up drum 26.
 As shown in FIGS. 1 and 2, constant tensioning device may be in the form of
 a power dancer device 24 including a pivotable lever arm 62 rotatably
 mounted at a fixed end 64 to main support 30 by a pin 66. The pin 66
 extends through a support wall 68 of main support 30 and through the
 center of a spacer collar 70. Pin 66 extends outwardly from spacer collar
 70 to connect with a pivotable link 72 on the opposite side of support
 wall 68. Lever arm 62 and link 72 are both rigidly attached to pin 66 so
 that movement of either arm 62 or link 72 causes corresponding movement of
 the other. The outward end of link 72 includes an extension pin 74 which
 extends laterally outward from link 72. Power dancer 24 also includes a
 biasing means, such as a coil spring 76, which connects at one end to
 extension pin 74. The opposite end of spring 76 connects to one end of a
 support rod 78 which extends laterally from, and is rigidly attached to,
 support wall 68. Lever arm 62 also includes a pivotable end 80 having a
 link roller 82 connected thereto and extending laterally outwardly for
 supporting the web received from idler roller 60 and redirecting the web
 toward take-up drum 26. As described more fully hereinbelow, power dancer
 device 24 is designed so that a substantially constant load is placed on
 the web by the biasing force of spring 76 acting through link 72 and lever
 arm 62 throughout the movement of arm 62.
 Take-up drum 26 is mounted on a rotatable shaft of a motor which operates
 to rotate drum 26 in the clockwise direction as shown in FIG. 1 for
 accumulating the waste backing material into a roll. Drum 26 is
 intermittently operated depending on the position of pivotable lever arm
 62. As shown in FIG. 1, when lever arm 62 is in the lower position
 indicated at I, take-up drum 26 is not rotating. As the web is indexed
 through the labeling machine as dictated by the operation of stepper motor
 52 and driver roller 50, lever arm 62 moves from the lower position I
 pivotally upwardly to an upper position indicated at II. When lever arm 62
 reaches upper position II, a limit switch (not shown) activates the motor
 driving take-up drum 26 to begin rotating take-up drum 26 causing lever
 arm 62 to pivot downwardly back into the lower position I at which time
 take-up drum 26 stops rotating. Therefore, the pivoting action of lever
 arm 62 avoids the need to continuously operate take-up drum 26 or,
 alternatively, to intermittently cycle take-up drum 26 each time the web
 is indexed through metering roll 22.
 Power dancer device 24 performs at least two important functions for
 accomplishing accurate metering and effective dispensing of labels. First,
 power dancer 24 maintains a constant load or tension in the web traveling
 between take-up drum 26 and driving and metering roll 22. Power dancer
 device 24 produces a substantially constant tension in web 12 by
 maintaining a substantially constant torque on lever arm 62 throughout its
 pivotal movement. As shown in FIG. 1, this substantially constant torque
 is achieved by positioning spring 76 relative to link 72 so that the force
 component of the total spring pulling force on link 72, which causes the
 rotation of link 72, that is, the rotational force component, increases as
 the spring force on spring 76 decreases during movement of lever arm 62.
 This rotational force component is that component of the total spring
 force which is tangential to the circular path of rotation of link 72
 around the pivot axis at pin 66, which, in this case, is also
 perpendicular to link 72. As shown in FIG. 1, with lever arm 62 in the
 lower position I, the spring force pulling on link 72 acts at such an
 angle to link 72 to create both a radial force component (parallel to the
 longitudinal axis of link 72) and the rotational force component.
 Therefore, the total spring force is proportioned between the radial
 component and rotational (tangential) component based on the angle of the
 spring relative to link 72. As lever arm 62 moves from the lower position
 I to the upper position II during indexing of web 12 through metering roll
 22, link 72 rotates towards spring 76. As lever arm 62 moves toward upper
 position II, the force applied by spring 76 gradually becomes more
 perpendicular to link 72 and tangential to the circular path of rotation
 of link 72 around pin 66 so that causing the rotational force component to
 increase relative to the radial force component. As a result, a greater
 portion of the total spring force of spring 76 is transmitted through link
 72, pin 66, lever arm 62, and support roller 82 to the web. However, as
 link 72 moves towards spring 76, the total spring force decreases as the
 spring is relaxed towards its normal untensioned position. Therefore, the
 decrease in the total spring force applied to the link is compensated by
 the increase in the rotational force component's share of the total force
 spring force applied to the link due to the varying position of the spring
 relative to the link 72. It has been found that by positioning the spring
 76 relative to link 72 so that the rotational force component's share of
 the total force acting on link 72 varies inversely to the changing spring
 force throughout the movement of lever arm 62, the resultant force by
 roller 82 on web 12 can be maintained substantially constant throughout
 the movement of lever arm 62 thereby maintaining tension in web 12 at a
 substantially constant level. By maintaining tension in the web between
 the take-up drum 26 and metering roll 22, power dancer 24 significantly
 reduces tension variations in the web downstream of the metering roll 22.
 As a result, metering roll 22 is able to more accurately and effectively
 meter or pull the web intermittently through the machine. Moreover, it has
 been found that tension variations downstream of metering roll 22 are
 transmitted through the web upstream of metering roll 22. Since
 maintaining optimum tension across peeler bar 44 is critical to the proper
 dispensing of labels, tension variations in the web adversely affect the
 ability of the peeler bar to dispense labels effectively. Power dancer 24
 substantially reduces variations throughout the machine by maintaining
 tension in the web downstream of the metering device at a substantially
 constant level. Also, the need for maintaining substantially constant
 tension in the web increases as the web speed increases since at higher
 web speeds, metering roll 22 and peeler bar 24 are more sensitive to
 changes in web tension.
 The second important function performed by power dancer 24 is as a driving
 means for pulling web 12 through the labeling machine from supply roll 16.
 As previously mentioned, metering roll 22 also functions as a driver for
 pulling the web through the labeling machine. For a given web size and a
 given driver, such as stepper motor 52, the motor 52 can be operated at
 maximum capacity to achieve a maximum driver pulling force resulting in a
 maximum web speed. To increase the web speed beyond the capacity of
 stepper motor 52, a new higher capacity, more expensive stepper motor or
 driving device would be needed. However, by using the power dancer 24 of
 the present invention, higher web speeds can be more effectively obtained
 with the existing driving and metering roll 22 and stepper motor 52
 without undue costs. In order to create a significant driving force for
 assisting metering roll 22, spring 76 of power dancer 24 is chosen so as
 to apply a significant torque to lever arm 62 resulting in a significant
 pulling force on web 12 tending to pull the web through metering roll 22.
 This power dancer generated force may be at least 20%, and preferably
 approximately 50%, of the total force needed to pull the web through the
 labeling machine at a given speed. In this manner, both driving and
 metering roll 22 and power dancer 24 apply pulling forces on the web to
 pull the web through the machine. As a result, power dancer 24 reduces the
 driving load required by driving and metering roll 22. For example, if at
 a maximum capacity, driving and metering roll 22 is capable of pulling web
 12 with a pulling force of 20 pounds, and power dancer 24 is set by
 choosing the appropriate spring to achieve a substantially constant force
 on web 12 immediately downstream of metering roll 22 of approximately 10
 pounds, then the total pulling force on the web at dispensing unit 18
 would be approximately 30 pounds each time the metering roll shifts into a
 driving mode to pull web 12 through the machine. This use of power dancer
 24 as a driver for applying a significant pulling force to web 12 has two
 significant advantages. First, since power dancer 24 acts as a second
 driver, stepper motor 52 of driving and metering roll 22 can be operated
 at less than its full capacity to achieve the same web speed. Therefore,
 since the total pulling force on the web is greater due to the combination
 of drivers, a higher web speed can be achieved. For example, in the
 example described hereinabove, without power dancer 24, driving and
 metering roll 22 may operate at a first web speed corresponding to the
 maximum pulling force of 20 pounds. However, when combined with power
 dancer 24, the maximum pulling force on the web is 30 pounds; 10 pounds
 created by power dancer 24 and 20 pounds created by driving and metering
 roll 22 during the driving mode. It should be noted that during the
 braking mode of driving and metering roll 22 as it stops, stepper motor 52
 operates to resist the pulling force of power dancer 24. However, although
 the tension upstream of driving and metering roll 22 increases and
 decreases with the operation of roll 22, the tension in the continuous web
 of material downstream of driving and metering roll 22 is maintained at a
 substantially constant level by power dancer 24 as described hereinabove.
 The second major advantage achieved by utilizing power dancer 24 as a
 driver for applying a significant pulling force on web 12, is that power
 dancer 24 reduces the driving load required by driver and metering roll
 22. The greater the driving requirements placed on the driving and
 metering roll 22, the more difficult it is for stepper motor 52 to
 accurately stop and start movement of the web. This metering effect is
 extremely important to the proper dispensing of labels, especially at high
 speeds at which the window of opportunity for precise starting and
 stopping is decreased substantially. By decreasing the driving load on the
 driving and metering roll 22, the present invention enables roll 22 and
 stepper motor 52 to more accurately and effectively perform its metering
 function. If driving and metering roll 22 is capable of achieving a given
 web speed with a maximum pulling force of 20 pounds, the same web speed
 can be achieved using the present invention by setting the power dancer to
 impart a pulling force of 10 pounds on the web from metering roll 22 and
 operating the stepper motor at half capacity so as to result in a total
 pulling force of 20 pounds during the driving mode of metering roll 22.
 Thus, the same web speed is achieved while reducing the driving load on
 driving and metering roll 22, thereby ultimately obtaining more accurate
 and effective metering and dispensing of labels.
 Referring to FIGS. 3 and 4, a second embodiment of the present invention is
 shown and includes a labeling machine similar to the previous embodiment
 in that a supply roll 102 of labels mounted on a web of backing material
 is supplied to a dispensing unit 104 and applicator 106 for applying
 labels to articles (not shown). Also, labeling machine 100 includes a
 power dancer device 108 and a talce-up drum 110. However, in this
 embodiment, a printer 112 is positioned along the feed path of the web
 between the supply roll 102 and dispenser 104 for printing indicia on the
 labels as the web passes through the printer. Printer 112 is typically an
 "off-the-shelf" printer having a built-in driving and metering roll 114
 for pulling the web through the printer. However, it has been found that
 the driving and metering roll 114 of most printers are operated by small
 drivers, such as a low power stepper motor, lacking the power to
 effectively pull the web from the large supply roll 102 as used in large
 capacity labeling. The present invention assists driving and metering roll
 114 by using power dancer 108 to create a pulling force in the web thereby
 alleviating the driving load on roll 114. As a result, the built-in
 driving and metering roll 114 of printer 112 can be used without incurring
 the costs and burden of modifying the machine to include a larger driving
 and metering roll or driving means. Moreover, power dancer 108 maintains
 tension in the web downstream of the driving and metering roll 114 at a
 substantially constant levels. Also, although the tension level in the web
 downstream of dispenser 104 will be larger than the tension immediately
 downstream of driving and metering roll 114 due to the frictional losses
 across peeler bar 116 of dispenser 104, dancer 108 also maintains the
 tension immediately downstream of peeler bar 116 at a substantially
 constant level. As discussed above in relation to the embodiment of FIG.
 1, since the load on the driving and metering roll 114 is reduced and the
 tension in the web immediately downstream of roll 114 is maintained at a
 substantially constant level, more accurate metering of the web can be
 achieved. In this embodiment, improvements in metering translates into
 improvements in the printing of labels by the printer. In addition, the
 substantially constant tension level at the peeler bar permits more
 effective dispensing of labels.
 Referring to FIGS. 3 and 4, power dancer 108, although structurally
 different from that of the previous embodiment, functions substantially in
 the same manner to maintain tension in the web downstream of metering roll
 114 at a substantially constant level while providing a driving pulling
 force on the web. Power dancer 108 includes a pivotable lever arm 118
 having a rotatable roller 120 attached to one end thereof for pivotable
 movement between a first position I and a second position II. The opposite
 end of lever arm 118 includes a pin 122 extending perpendicular from lever
 arm 118 transversely through a first wall 124 and a second wall 126. Pin
 122 is supported by bearings 128 attached to each wall for allowing pin
 122 to freely rotate. A link 130 is rigidly attached at one end to pin 122
 so that movement of lever arm 118 rotates link 130. The opposite end of
 link 130 includes a small hole (not shown) for attachment to one end of a
 spring 132. The opposite end of spring 132 is positioned in a U-shaped
 groove formed in the outer circumferential portion of a wheel 134 mounted
 on a rod 136 extending from second wall 126 toward first wall 124. A
 threaded pin 138 extends radially outward from wheel 134 for connection
 with the end of spring 132. Wheel 134 is rotatably adjustable into a
 variety of locked positions to allow the tension in spring 132 to be
 varied to achieve the optimum driving force while still maintaining a
 substantially constant tension level throughout the movement of lever arm
 118. As can be seen in FIG. 3, as lever arm 118 moves toward the second
 position II, the force applied by spring 132 gradually becomes more
 tangential to the axis of rotation around pin 122 so that a greater
 portion of the total spring force is used to rotate lever arm 118.
 However, as with the previous embodiment, as link 130 moves towards spring
 132, the total spring force decreases as the spring is relaxed towards its
 normal untensioned position. Therefore, the increase in the rotational
 force due to the varying position of the spring 132 relative to the link
 130 is compensated by the decrease in the total spring force applied to
 the link. Therefore, by positioning wheel 134 and therefore spring 132
 relative to link 130 so that the rotational force component's share of the
 total force acting on link 130 varies inversely to the changing spring
 force throughout the movement of lever arm 118, the resultant torque and,
 therefore, the resultant force by roller 120 on web 12 can be maintained
 substantially constant throughout the movement of lever arm 118, thereby
 maintaining tension in the web at a substantially constant level.
 INDUSTRIAL APPLICABILITY
 The disclosed high speed labeling machine having a constant tension driving
 system finds particular utility when positioned along a conveyer as a
 labeling station in a manufacturing, distribution, or packaging
 application. The high speed labeling machine of the present invention is
 especially useful in labeling and printing applications in which effective
 and accurate metering and dispensing of labels is a priority.