Patent Publication Number: US-3875855-A

Title: Strapping method

Description:
United States Patent Clark et al. Apr. 8, 1975 STRAPPING METHOD [57] ABSTRACT Robe&#34; flrhCheshire; Robert A fixed clamp and shear member is provided in a L81? Haven. Enfield; Franz A. combination clamping. sealer and shearing device with Kfleidl, Milfordv all Of fla strap guide opening extending through the clamp [73] Assign: The Smnley Wmks New Brimim and shear member adjacent a free end of that member Corm serving as an abutment face which cooperates with a movable clamp for clamping a leading end of strap Filedi P 1973 trained from a strap supply through the strap guide opening and into a loop about an article to be bound.  
 [2]] Appl NO&#34; 348,983 A movable shear member is mounted for sliding movement on the fixed clamp and shear member and Cl 0/ 100/33 PB is reeiprocable between a retracted position, wherein [5]] Int. Cl B65b 13/32 h strap guide opening is exposed for strap feeding i 1 Field of Search 33 33 PB, and tensioning, and an extended position wherein the IO /2 l56/l5 53/l98 R movable shear is in lapping relation to the strap guide opening of the fixed shear and clamping member to l l Relerences Cited effect strap shearing. The movable clamp in its opera- UNITED STATES PATENTS tive clamping position serves as a stop for the movable 3.269.300 8/1966 Billctt et al. IOU/33 PB and establishes a Pressmg Posmo 3 447 447 19 9 Ru)- v v u mom movable shear intermediate its retracted and extended 3.470.814 lU/l969 Tschuppu IOU/4 positions wherein the movable shear presses opposed 3.577.910 5/1971 Feldkamp 100/33 PB heated strap surfaces into a fused seal after withdrawal 3.749.622 7/l973 Sam et ill l56/l57 of a pivotubly supported heating element from be- 3-759-I69 9/1973 a 4 a IOU/33 PB tween the strap surfaces and before the movable 3.77l.436 ll/l973 Suto 100/33 PB Clamp is maimed to permit final movemem f the Prinmry E.\&#39;uminerBilly J. Wilhite Attorney. Agent, or FirmPrutzman. Hayes, Kalb &amp;  
 Chilton shear member into its extended position to shear the strap in the strap guide opening from the strap supply.  
 9 Claims. 16 Drawing Figures PMENTEUAPR BISTS SEEEET ll 0f 9 FIGS PATENIEU 81975 3, 875.855  
 FIG. /6  
 M 41; M U/ STRAPPING METHOD This invention relates to strapping articles such as boxes, cartons, bales and similar packages and particularly concerns the strapping of such articles with a length of generally flat strap formed into a loop about an article with the ends of the strap sealed face-to-face to secure the loop.  
  A primary object of this invention is to provide a new and improved method of binding an article and which is suited to provide highly reliable operation with minimum maintenance requirements with particular use in forming a high strength joint between portions of nonmetallic heat scalable strap.  
  Another object of this invention is to provide a method of the above type wherein the strap is sealed before being sheared from the strap supply.  
  Other objects will be in part obvious and in part pointed out in more detail hereinafter.  
  A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth an illustrative embodiment and is indicative of the ways in which the principles of this invention are employed.  
 In the drawings:  
  FIG. 1 is a side elevational view, partly broken away, schematically showing an exemplary strapping machine installation incorporating the present invention and installed for applying a tensioned loop of strap about a package, shown in broken lines, supported on a roller conveyor of the installation;  
  FIG. 2 is an enlarged top plan view, partly broken away, of the strapping mechanism of this invention;  
  FIG. 3 is a side elevational view, partly broken away, of the mechanism of FIG. 2;  
  FIG. 4 is a sectional view, partly broken away, of a portion of a strap re-entry rail and gate assembly of the mechanism of FIG. 2;  
  FIG. 5 is an enlarged top plan view, partly broken away and partly in section, showing a movable clamp and its linkage incorporated in the mechanism of FIG. 2;  
  FIG. 6 is an enlarged side elevational view, partly broken away, illustrating a gripper device of a strap puller unit with certain parts of its linkage shown in phantom;  
  FIG. 7 is a sectional view, partly broken away, of the gripper device of FIG. 6&#39;,  
  FIG. 8 is a schematic cross sectional side elevational view of the position of certain components of the strapping mechanism of FIG. 2 shown during strap feeding about an article to be bound;  
  FIG. 9 is a schematic top plan view of the position of certain parts of the mechanism of FIG. 2 during strap feeding;  
  FIG. 10 is an enlarged schematic view of the position of the strap clamping, sealer and shearing mechanism and its associated puller unit followig strap clamping and during strap takeup;  
  FIG. 11 shows a schematic view of the position of the puller unit during the strap tensioning and strap sealing;  
  FIG. I2 is a view similar to FIG. 10 showing the position of the parts during strap heating;  
  FIG. 13 is a schematic view shown on a relatively en larged scale of certain parts of the strap clamping, seal and shearing mechanism during strap sealing;  
  FIG. 14 is a view similar to FIG. 9 with the position of the parts shown during strap heating;  
  FIG. 15 is a view similar to FIG. 10 with the position of the parts shown during strap shearing; and  
  FIG. 16 is a view similar to FIG. I4 after strap shearing and just before completion of the strapping operation.  
  Referring to the drawings in detail, an embodiment of the machine incorporating this invention is generally denoted by the numeral 10 and is shown in a strapping machine installation in FIG. 1 for use with solid nonmetallic strap of heat scalable plastic, e.g., polypropylene or other suitable plastics such as various types of synthetic polymeric material of acceptable brittleness and tenacity and suitable elongation characteristics with a relatively low melting point. The strap used in this invention is of generally flat configuration to be applied about an article 12 supported on a roller conveyor 14.  
  The installation will be understood to include a strap supply such as a coil dispenser, not shown, from which strap 15 is paid-out to a generally rectangular strap chute 16 for encircling the article 12 with a loop of strap. The chute 16 has an entrance end 18 and a re entry end 20. The entrance end 18 is immediately above a strap sealing station 22 (best seen in FIG. 3) for receiving a free or loose leading end of strap 15 from a strap guide assembly 24 of the machine 10. The re-entry end 20 is for feeding the leading end of strap into a re-entry rail and gate assembly 26 of the machine which directs strap back into the sealing station 22.  
  The strap chute l6 and the re-entry rail and gate asembly 26 are ofa type well known to those skilled in this art and provide for guiding strap during feeding while permitting strap release from the rails onto the article 12 to be bound upon tensioning the strap 15. For the purpose of this disclosure, the term strap guideway means is intended to include the strap guide assembly 24 on the strap supply side of the sealing station, the strap chute l6 and the strap re-entry rail and gate assembly 26 of the machine.  
  In accordance with this invention, the re-entry rail and gate assembly 26 is adjustble both longitudinally as well as being laterally adjustable from side-to-side for precision feeding of strap into the strap sealing station at a desired location.  
  For this purpose a pair of rail supporting lead screws such as the one shown at 28 in FIG. 4 are received in aligned openings formed through upper and lower sections of the assembly 26 to extend through tapped holes in the rail 30 in threaded engagement with the rail. Suitable nuts 32 are threaded onto ends of each lead screw 28 projecting laterally outwardly from opposite sides of the rail 30 through elongated slots such as at 34 formed in a housing 36 of a frame of the strap clamping, seal and shearing mechanism 40. Nuts 32 are threaded onto the projecting ends of lead screws 28 to bottom against the ends of the screws. Nuts 32 may be rotated in a selected angular direction to rotate the lead screws 28 and cause the tapped rail 30 to move in a selected lateral direction to provide desired strap support and guidance into the sealing station 22, while the nuts 32 simply rotate in fixed relation to the screws 28 during such lead screw rotation and lateral adjustment of the re-entry rail 30.  
  For longitudinally adjusting the re-entry rail 30 parallel to the strap feed path through assembly 26, a jack screw mounting device is shown at 42 which includes an L-shaped bracket 44 fixed to the housing 36 with a jack screw 46 and locking nut 48 mounted on the bracket 44 to extend upwardly with the shank end of the jack screw 46 engaging a swinging end of a lever 50 supported for pivotal movement about a pin 52 secured to housing 36. The upper lead screw 28 is extended through and supported on the lever 50 to permit selective raising and lowering ofthe rail 30 responsive to ro tary adjustment of the screws 46, it being understood that a jack screw mounting device such as at 42 is provided on each side of the re-entry rail and gate assembly 26.  
  As shown, the frame 38 ofmachine is a multi-part unit for mounting various parts of the machine in proper operative association. Referring now specifically to FIG 3, the machine 10 is shown comprising in operative alignment a strap feed and takeup mechanism 54, the strap guide assembly 24 leading into the strap sealing station 22 which is upstream of the entrance end 18 of the strap chute 16 and downstream of the re-entry rail and gate assembly 26 of the machine. and the aforementioned combined strap clamping. sealer and shearing mechanism 40 at the strap sealing station 22.  
  The feed and takeup mechanism 54 includes a feed wheel 56 connected to be driven by a reversible air motor 58 mounted on the housing 36. The feed wheel 56 has a resilient driving surface for frictionally engaging the surface ofthe strap for guiding it through the combined strap clamping. sealer and shearing mechanism 40 and into the entrance end 18 ofthe strap chute 16. around the chute and into the sealing station 22. The feed wheel 56 is mounted adjacent but outwardly of the strap guide assembly 24 of the machine 10 with the driving surface of the feed wheel 56 substantially aligned with an internal guideway 60 formed within the strap guide assembly 24. A rotatable backup wheel 62 is shown mounted on the strap guide assembly 24 which is biased by a suitably anchored adjustable spring 64 to selectively set the frictional driving engagement required for the feed wheel 56 to feed strap through the strap guide assembly 24, and particularly to prevent strap damage during takeup upon stall of the air motor 58. The reversible air motor 58 is driven in one direction to feed strap 15 into a loop about the article 12 during which phase the feed wheel 56 is directly driven by the air motor 58 to provide a relatively high speed strap feedout through the chute 16. it should be noted that as strap is fed by the feed wheel 56 into the entrance end 18 of the chute 16, the strap passes through an open section of the strap guideway means at the sealing station 22 FIG. 3) between the strap guide assembly 24 of the machine 10 and the entrance end 18 of the chute 16.  
  At the sealing station 22, a combined clamp and shear plate on member 66 is secured to the frame 38 with an upper planar surface 68 (see FIG. 8, cg.) shown in the specifically illustrated embodiment as being in underlying supporting relation to an elongated movable shear slide or shear 70 mounted on the frame 38 for longitudinal reciprocable movement toward and away from the strap trained through the sealing station 22. The free ends of members 66 and 70 respectively form abutment faces 72 and 74. and a lower edge portion ofthe free end of the movable shear 70 is undercut to provide a recessed cutting edge 76 along itsjuncture with its lower planar surface 78 which is in sliding contact engagement with the upper planar surface 68 of the clamp and shear member 66. The latter has a strap guide opening 80 adjacent its abutment face 72 which passes entirely through the body of member 66 in the direction of its thickness and in alignment with the strap guide assembly 24 and the entrance end 18 of strap chute 16, whereby strap extending from the strap supply through the strap guide opening 80 will be cap tured for shearing action when the cutting edge 76 of the movable shear passes over the opening upon movement of the slide shear 70 between its retracted starting position (FIGS. 2, 3 and 8) and an extended position FIG. 15).  
  To hold the leading end of strap during withdrawal and tensioning of strap. a free end strap clamp 82 is also provided by the mechanism 40 at the sealing station 22 as shown in FIGS. 2 and 5 wherein it will be seen that actuation of the clamp 82 is provided by a clamp positioning air cylinder 84 and a clamping air cylinder 86 mounted on the frame 38 at right angles to one another for sequential power operation of clamp linkage 88 about a fixed pivot pin 89 fixed to the frame 38, the clamp 82 being integrally mounted on clamp linkage 88 in a one-piece unit. The clamp 82 is movable by a piston rod 90 of clamp positioning air cylinder 84 from an inoperative position (shown in broken lines in FIG. 5 at wherein the rod would be retracted) to its ready position (illustrated in full lines) with the rod 90 extended to position linkage 88 in its illustrated full line position. For clarity of illustration, the clamp and shear member 66 is not shown in FIG. 5, but with the clamp 82 in ready position, the clamp 82 is disposed in confronting spaced relation to the abutment face 72 of the fixed clamp and shear member 66 (FIG. 2) Upon operation of clamping air cylinder 86, its piston rod 92 will be extended against the bias of return spring 94 from its retracted position shown in FIG. 5 to swing link 96, pivotally connected to rod 92 and linkage 88, counterclockwise as viewed in FIG. 5 about fixed pivot pin 89 to drive clamp 82 via its connecting pin and linkage 88 toward the abutment face 72 and into clamping position for securing the leading end of the strap against the fixed abutment face 72 with a substantial clamping force being applied to the strap. The abutment face 72 ofthe clamp and shear member 66 is preferably grooved or serrated to ensure a positive grip on the strap when the clamp is moved into clamping position.  
  To minimize need for close tolerances while yet providing for precisely matching the abutment face 72 of member 66 with the confronting face of clamp 82, the clamp and shear member 66 is supported on a fixed underlying backup plate 102 (FlGS. 2 and 5) secured to the frame 38. Opposite sides of member 66 have cutouts at 104 for receiving corresponding projections 106 extending laterally inwardly from a pair of adjustment blocks 108 supported on backup plate 102. The adjustment blocks 108 may be moved into desired position relative to the clamp and shear member 66 within certain limits established by oversize openings at 110 in the backup plate 102 FIG. 5), for receiving shanks of releasable fasteners 112, and within the limits of predetermined clearnaces within cutouts 104. Upon adjusting the location of the fixed clamp and shear member 66 to precisely match its face 72 with that of movable clamp 82. forward walls 113, formed within cutouts 104 parallel to face 72, are engaged by adjustment block projections 106 and the fasteners 112 are secured to lock member 66 in precision alignment with the face of clamp 82.  
  With the member 66 secured in desired fixed location, the movable shear 70 may then be operatively mounted onto the upper planar surface 68 of the fixed clamp and shear member 66 with a predetermined spring loading maintaining shear 70 in continuous sliding engagement with member 66. This is achieved by an adjustable spring mounting device 114 FIG. 3) hav ing a threaded shear slide stud 116 fixed relative to the frame 38 to project upwardly through a slot 118 formed in shear 70 and having a bushing 120 fixed within the slot 118 to extend just above the upper flat surface of shear 70 where a locknut 122 threadably engaged on the stud 116 secures the head of the bushing 120 in position within the slot 118 to guide reciprocating movements of the slidable shear 70. Spring loading of the shear 70 against the fixed clamp and shear member 66 is effected under the bias of compression spring 124 coiled about stud 116 and captured between shear 70 and thrust washer 126 which is adjustably located along the length of stud 116 by and adjustable nut 128 threadably engaging the stud to selectively compress the spring 124 against the shear 70.  
  in accordance with still another feature of this invention. a heat gun assembly 130 is provided for heating the inner surfaces of the plastic strap at the sealing station 22 for forming a fused seal between lapping strap portions. The heat gun assembly 130 is fixed to a pivot arm 132 mounted for swinging movement about a pivot pin 134 secured to the frame 38 such that an elongated blade or nozzle 136 on a forward end of heat tube 138 is supported for oscillating movement in a generally horizontal plane toward and away from the sealing station between a withdrawn or remote inoperative position (FlG. 2) and an operative position (FIG. 8) wherein the nozzle 136 is inserted into the open section of the combined strap clamping, sealer and shearing mechanism 40 above the exposed strap guide opening 80 with the movable shear 70 in retracted position. The position of the nozzle 136 is controlled by a cam roller 140 (FIG 9) rotatably supported on a cam operator 142 fixed to an extendible and retractable piston rod 144 operated by a seal air cylinder 146 with its piston rod 144 in operative alignment with shear 70. The cam roller 140 is engaged for following movement by a cam plate 148 of a pivot yoke 150 (FIG. 2) and is secured by fasteners 152 to the pivot yoke 150 having an integral pivot arm 132. The cam plate 148 is urged into engagement with cam roller 140 by a spring 153 (FIG. 3) operatively connected between the frame 38 and the heat gun assembly 130. The above noted seal air cylinder 146 provides an additional function of operating the shear 70 upon movement of the piston rod 144 a sufficient distance to engage slide abutment 154 for moving the shear into its extended position and to return shear 70 to its retracted starting position (FIG. 2) upon cam operator 142 on rod 144 subsequently engaging a rear leg 156 of the shear 70, it being understood that the piston rod 144 extends through leg 156 of the shear 70 and is freely movable in relation to shear leg 156.  
  In accordance with this invention, heat gun nozzle 136 effectively provides three distinct functions. Upon being moved into its operative position (FIG. 8) in the sealing station 22 during strap feeding, the nozzle 136 itself serves to direct strap 15 through the othewise open gap between the strap guide assembly 24 and the entrance end 18 of the chute 16, thereby minimizing the frequently encountered and troublesome problem of strap buckling and jamming. In addition, the nozzle 136 has an offset projecting lip or stop plate 166 which acts as a fixed stop for a loose leading end of the fed strap after it is fed about the article 12 and into position between a free end strap clamp and the nozzle (FIG. 8). The lip 166 projects toward the clamp 82 in slightly overlying relation to the uppermost aligned edges of the clamp and abutment face 74 of the shear to ensure sufficient lapping of the leading strap end with strap trained through opening for a good seal. Finally, tube 138 of the heat gun assembly contains a heating element 158 connected by conductors contained within insulating conduit 160 to a suitable source of electrical power through a control box 162 containing the controls for the electrical and pneumatic systems of the machine. Conduit 163 provides a line for forcing air through the heat gun tube 138 and through holes 164 in opposite faces of the bladelike nozzle 136 when it is inserted into the sealing station 22 during a subsequent strap heating phase of the cycle (FIG. 12). With the nozzle 136 disposed between and in adjacently spaced, confronting relation to the surfaces of strap at the sealing station 22, and with forced heated air emanating from holes 164 in the nozzle 136, the nozzle thus serves to soften the opposed inner surfaces of the strap prior to the strap sealing phase of the cycle.  
  Another feature providing smooth, trouble-free high speed strap feedout is schematically shown in FIG. 8 for purposes of clarity wherein a strap end positioning leaf spring 168 is mounted within the guideway 60 at its exit end of the strap guide assembly 24 of the machine 10. This internal leaf spring 168 within the strap guide assembly 24 has an upper arcuate terminal portion which exerts a spring force on a leading free end of fed strap urging it toward the shear 70 at the outlet of the guideway 60 to virtually eliminate any possibility of strap being displaced out of position, due to its taking a set during storage in coiled condition, e.g., and being undesirably fed from the guideway 60 past the front face of the nozzle 136 between the nozzle and the clamp 82 rather than between the shear 70 and the nozzle 136. Also, as seen in FIG. 8, the free end strap clamp 82 is shown provided with an offset extension 170 directed angularly over the nozzle 136 in its operative position such that upon subsequent clamping and tensioning of the strap, the clamp extension 170 will separate the strap extending downstream through the strap guide opening 80 in the fixed clamp and shear member 66 in spaced apart relation to the clamp leading end of the strap to facilitate reinsertion of the nozzle 136 in the sealing station 22 following strap tensioning for subsequent heating of confronting strap surfaces by the nozzle 136 (FIG. 12).  
  Another problem frequently encountered concerns strap buckling at the sealing station such as at 22 and at other locations in the guideway means when the leading end of strap is arrested during strap feedout. To virtually eliminate such problems and related strap jamming problems within the guideway means, a builtin accumulator has been provided to receive any excess infeed of strap after the stop plate 166 terminates further movement of the strap end. For this purpose, a  
 bottom opening 172 has been formed in the strap chute 16 at the corner of the chute in adjacent upstream relation to the re-entry rail and gate assembly 26 (FIG. 1). Since plastic strap is normally stored in and fed from a coiled condition wherein it takes what is commonly called a coil set&#34; causing an arcuate bend in a length of relaxed strap, such plastic strap is fed through the chute 16 such that changes in direction of strap feed correspond to the coil set of the strap, whereby the leading strap end will pass smoothly over the bottom opening 172 at the re-entry end 20 of the chute. Opening 172, however, provides a significantly simplified, troublefree accumulator for receiving excess strap which simply buckles through the opening 172 to elimi nate undesired upstream strap buckling upon arrest of its leading end.  
  The following summary of machine operation does not specifically describe certain details of various controls, fluid logic circuitry and piping arrangements located in the control box 162 and which have been found to perform satisfactorily. for a variety of different circuits and controls may be employed in accordance with conventional techniques to effect machine operation on manual, semi-automatic or automatic program sequencing. A clear understanding of this in vention will be obtained from the following description of the sequence of operation of the mechanical components of the machine with reference to the drawings, bearing in mind that upon actuating an ON/OFF button 173 to ON, the electrical and pneumatic systems of the machine are energized to provide the desired control functioning. In addition, the various air cylinders for operating the machine components will be understood to be connected to a suitable source of compressed air through the lines schematically illustrated in FIGS. 2 and 3 connecting the cylinders to the control box 162.  
  The machine is started by actuating ON/OFF button 173 to its ON positionv At the start of each strap feeding cycle, the heating element 158 is on but the air line 163 to the heat gun nozzle 136 is shut-off, and air is exhausted through lines 174 and 176 from both sides of seal air cylinder 146 with the piston rod 144 re tracted as in FIG. 2. The line 179 to clamping air cylinder 86 is shut-off and clamp 82 is moved from inoperative position 85 (FIGS. 5 and 9) into ready position in spaced confronting relation to member 66 byline pres sure applied through air line 180 and exhausting line 182 to operate clamp positioning cylinder 84 to extend piston rod 90 to effect clamp movement. With clamp 82 in ready position, a strap end sensor circuit is established for piloting a control valve, not shown, controlling the air motor 58. As seen in FIGS. 5 and 8, lines 184, 186 establish the sensor circuit for piloting the above mentioned control valve in the control box 162 and are respectively connected to an orifice in the face of rail 30 just below clamp and shear member 66 and an opening 188 in the face of clamp 82 which are registered in alignment with one another upon moving clamp 82 into ready position. With the seal air cylinder 146 exhausted, spring 153 then extends the piston rod 144 a sufficient distance for the cam roller 140 to move across cam plate surface 178 (FIG. 9) to insert nozzle 136 into the sealing station 22 for strap support during feedout. With the nozzzle 136 in deactivated condition to prevent strap damage but in operative position at the sealing station 22, the machine 10 is then conditioned for strap feeding and the air motor 58 is energized responsive to a valve actuator 190 carried by the heat gun assembly depressing a valve 192 (FIGS. 3 and 9) connected to the control box 162 for opening an air feed line to motor 58 to drive the feed wheel 56 for strap feedout.  
  During feedout. a leading end of strap interrupts the strap end sensor circuit as it passes through the reentry rail and gate assembly 26 just upstream of the sealing station to de-energize the air motor 58 as the leading end of the strap passes into the sealing station and into abutment with the lip 166 of nozzle 136 serving as a positive stop. Interruption of the strap sensor circuit also causes line pressure to be applied to the rod side of seal air cylinder 146 through line 174 to retract piston rod 144, withdrawing gun nozzle 136 and also causes air to be supplied through lines 163 and 179 (FIG. 2) to activate the heating gun assembly 130 and to operate clamping cylinder 86 to extend its piston rod 92 (FIG. 5) to clamp the leading strap end between the shear and clamp member 66 and clamp 82 in its clamp ing position (FIG. 10). As described above, any tendency of the strap buckling and jamming is effectively minimized by the accumulator opening 172 in the chute 16 and the positive guiding assistance provided the strap during feedout by the nozzle 136 at the sealing station 22.  
  After the above described feeding of strap into a loop and when an article is in position to be bound, strap take-up is effected by momentarily depressing a takeup valve button 194 on the control box 162, causing actuation of a presettable takeup timer, not shown, in the control box 162 and to energize motor 58 to run in reverse while the leading end of the strap is held fast by the clamp 82 to pull back excess strap from the chute 16 through the machine 10, The takeup timer is preset to ensure that strap will be brought into contact with the article before the takeup timer times out. Excess strap is fed back into auxiliary accumulator 196 (FIG. 3) between the strap guide assembly 24 and the strap supply, and upon withdrawal of the extra strap back into the machine 10 and bringing the strap loop into contact with the article 12, the motor 58 will stall pre venting damage to strap from wheel slippage. The takeup timer times out providing a signal to the logic controls in control box 162, causing a gripper air cylinder 198 ofa gripper device 200 FIG. 3) to operate, reversing the normal air supply and exhaust to the cylinder 198 during feeding and takeup, whereby supply air is then fed through line 202 while line 204 is connected to exhaust to retract a piston rod 206 of gripper air cylinder 198 after feeding and takeup to apply a substantial gripping or holding force on the strap to enable a puller mechanism 207 to apply a relatively high tension pull on the strap with a low speed drive to effect resultant high elongation of the strap.  
  The puller mechanism 207 that operates this high tension, relatively low speed drive, features a gripper air cylinder-operated rotating cam 208 (FIGS. 6 and 7) in a cage 210 fixed on a carriage 211 secured to a puller piston rod 218 (FIG. 3). Carriage 211 also provides a mounting for the auxiliary accumulator 196 which is guided for reciprocable movement parallel to the feed path of the strap from the strap supply on a track 212 fixed to the frame 38. The track 212 is slotted at 214 for receiving a headed stud 216 and sideload damping spring 217 movable along the slot 214 and suspending the carriage 211 and the accumulator 196 on the track 212, while also preventing undesired rotation of carriage 211 and parts attached thereto about puller piston 218. For moving the accumulator 196 and gripper device 200, the piston rod 218 is suitably fixed to the carriage 211 and is operated by a puller air cylinder 220 which is supplied with air pressure at its rod end through line 224 and exhausted through line 222 during strap feeding and takeup with the puller piston rod 218 retracted into normal position (FIGS. 3, 8 and 10), it being understood that the supply and exhaust to cylinder 220 are switched, responsive to timing ouot of the takeup timer, to extend piston rod 218 to move it from its normal position (FIGS. 3, 8 and 10) to extended position (FIG. 11).  
  To apply a substantial holding force uniformly distributed over an extensive length of strap to ensure a tight grip on the plastic material, a gripper plate 242 is supported on the cage 210 for following movement of the cam 208 eccentrically mounted on a cam shaft 228 which is rotatable by a connecting lever 230 drivingly connected to a pivot pin connection 232 on an end of piston rod 206 ofthe gripper air cylinder 198. The grip per air cylinder 198 is pivotally supported on a bracket 234 fixed to the carriage 21] and carries an actuator 236 normally engaging a lever of a valve 238 shown mounted on the carriage 211. Thus, upon retraction of gripper air cylinder rod 206, valve actuator 236 releases valve 238 and moves gripper plate 242 into position to grip strap against strap lock surface 240 of carriage 211. This action effected by operation of the gripper air cylinder 198 produces a substantial uniformly distributed clamping force over a length of strap resulting in the plastic strap being pulled with a very high force and high elongation but without damage or breakage of the strap secured between gripper plate 242 and the strap lock surface 240 of carriage 211 as the carriage 211 is moved by extension of puller rod 218.  
  The extent of movement of the cage 210 away from its starting position determines the tension applied to the strap and may be preselected at an operator station by pressure regulation of the air supplied to puller cylinder 220 and the length of time the puller cylinder is in operation. A pull timer, not shown, is provided in the control system to operate when the takeup timer times out, to control the time of operation ofthe cylinder 220 and to operate a seal timer, not shown, when the pull timer times out. Air feed through line 222 to cylinder 220 will cease upon timing out of the pull timer, and the air will be trapped on the side of the piston in cylinder 220 during operation of the seal timer.  
  Upon timing out ofthe pull timer and start ofthe seal timer, the supply and exhaust to seal air cylinder 146 are switched by the control system to effect the following steps in the operation. Seal air cylinder rod 144 extends from retracted position to advance cam roller 140 along cam plate surface 178 onto cam surface 243, causing nozzle 136 to be reinserted into the sealing station 22, but in an activated heated condition for directing heated forced air through holes 164 against opposed inner strap surfaces adjacent opposite faces of the nozzle 136 (FIG. 12) while the strap supply end of the strap 15 is retained under tension by the puller mechanism 207. Upon moving gun nozzle 136 into operative position, a valve 244 (which was de-activated during the previous feeding phase) is engaged by actuator 190 (motor control switch 192 being de-activated by the control system during this phase of the cycle) to cause the air to exhaust from seal air cylinder 146 through line 174 to an adjustable flow control device in the control system (schematically shown at 245 in FIG. 14) to control the speed of advance of piston rod 144 and for regulating the length of time the nozzle 136 heats the strap surfaces. Upon cam roller 140 engaging cam surface 246, nozzle 136 is withdrawn, releasing valve 244 to de-activate the rod speed control device 245 and permitting the air on the rod side of the cylinder 146 to dump to atmosphere, thereby releasing rod 144 to move more rapidly into engagement with slide abutment 154 to advance shear 70 to press the melted strap surfaces together to fuse and form a seal (FIG. 13) upon cooling in a positively compressed condition. Any stretch in the strap during the heating step is accommodated by the trapped air in the piston side of puller air cylinder 220 which acts to automatically extend the piston rod 218 to maintain the strap in substantially taut condition. Advance of shear 70 is positively stopped by clamp 82 for proper cooling and forming of the seal joint, and it will be seen that the aforementioned undercut face 74 of shear 70 ensures that the cutting edge 76 of the shear 70 does not pass over guide opening 80, and the strap held in the opening 80 will be seen to be spaced apart from the upper front edge surface of the fixed clamp and shear member 66 surrounding opening 80 and also separated from the cutting edge 76.  
  Upon timing out of the seal timer following the above described sealing step, the control system causes lines 202 and 222 to be connected to exhaust, de-activating the puller air cylinder 220, and air is supplied through line 204 to gripper air cylinder 198, extending rod 206 causing disengagement of the gripper plate 242 and re laxing the strap between the heat sealed joint and the gripper plate. This action promotes joint forming, prevents damage to the strap and undesired retraction of the strap 15 through guideway toward the strap supply. To minimize any strap buckling problems retraction of rod 218 is delayed until after the start of the next strap feeding cycle. The extension of rod 206 reengages valve 238 to de-activate clamping air cylinder 86 and thereby releasing the shear to advance to its fully extended position (FIG. 15) with its cutting edge 76 passing over strap guide opening and shearing the strap in the sealing station. Valve 248 (FIGS, 2 and 16) is connected to the control system and upon being engaged by actuator 250 of shear 70 as it is fully extended (FIG. 16), the valve actuation causes retraction of the clamp positioning air cylinder 84 to withdraw the clamp 82 laterally into its inoperative position 85, releasing the sealed strap and the package, and causes retraction of the sealer air cylinder piston rod 144 into engagement with shear leg 156 and into fully retracted starting position which causes an actuator 252 of shear 70 to engage a second valve 254 to de-activate the seal air cylinder 146 and reset the control system circuitry for the next machine cycle.  
  The above described strapping machine is accordingly adapted to provide in sequence either automatically or semiautomatically, for forwardly feeding strap from a strap supply into a loop about an article, for taking up the strap to draw it into contact with the article, for tensioning the strap with high elongation, for heating confronting surfaces of strap under tensioned conditions, for pressing the heated surfaces into positive engagement with one another into a sealed joint, for relaxing the strap between the joint and the strap supply and then shearing the sealed strap from the strap supply and releasing the strap onto the article. Significant advantages are provided in the disclosed method, notably the complete elimination of any need for additional clamping components for holding strap tensioned downstream of a sealing station, as conventionally re quired while shearing and/or a relaxed supply end of the strap. Moreover, new and improved components are provided, e.g., in the gripper and puller unit for tensioning strap, and in the combined clamping, sealer and shearing device of the machine which utilize a minimum number of multi-function parts which cooperate to provide a smoothly functioning high performance operation in a compact assembly capable of being mounted as a strapping head in different locations in various installations for highly reliable operation over an extended period of time with minimum service requirements.  
  As will be apparent to persons skilled in the art, various modifications. adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.  
 We claim:  
  1. A method of binding an article with a length of heat sealable plastic strap comprising the steps of feeding the strap from a strap supply into a loop about the article with a leading end of the strap in spaced opposed lapping relation to a portion of the strap connected to the strap supply. clamping the strap adjacent its leading end. supporting the clamped leading end portion ofthe strap with a supporting member with the clamped leading end portion disposed between the supporting member and the lapping strap portion connected to the strap supply, tensioning the strap about the article. heating confronting surfaces of the lapping strap portions. sealing the heated strap surfaces by pressing the tensioned lapping strap portion connected to the strap supply into engagement with the clamped leading end portion of the strap, relaxing the strap between the sealed lapping strap portions and the strap supply while maintaining the sealed lapping portions pressed against the supporting member. and then shearing the sealed length of strap from the strap supply.  
  2. The method of claim 1 wherein the clamping and supporting steps are effected simultaneously by the supporting member by moving the supporting member against the leading end portion of the strap and into clamping relation with a fixed member engaging the strap adjacent its leading end.  
 3. A method of binding an article with a length of heat scalable plastic strap comprising the steps offeeding the strap from a strap supply through a strap guide way which includes a strap guide opening extending through a fixed clamp and shear member at a sealing station to form a loop of strap about the article, terminating strap feeding when a leading end portion of the strap is returned to the sealing station in confronting relation to a free end of the fixed clamp and shear member and in lapping spaced opposed relation to the strap trained through its strap guide opening, clamping the leading end portion of the strap by releasably securing a movable clamp in pressing engagement with the strap against the free end of the fixed clamp and shear member, heating the lapping spaced opposed surfaces of the strap, sealing the heated strap surfaces by pressing a movable shear against the strap trained through the strap guide opening of the fixed clamp and shear member to clamp and fuse the heated surfaces together between the movable shear and movable clamp, and shearing the strap from the strap supply by releasing the movable clamp to permit the movable shear to pass over the strap guide opening of the fixed clamp and shear member to cut the strap retained within its strap guide opening.  
  4. The method of claim 3 including a further step of tensioning the strap about the article after the clamping step by gripping a substantial length of strap upstream ofthe sealing station and pulling the strap in a direction opposite the direction of strap feeding.  
  5. The method of claim 4 wherein the heating and sealing steps are performed while maintaining the strap in tension,  
  6. The method of claim 5 including the step of releasing tension on the strap between the sealed strap sur faces and the strap supply after sealing but before shearing.  
  7. The method of claim 3 wherein the step of heating the lapping spaced opposed surfaces of the strap is provided by passing a heating element between the surfaces in good heat transfer relation to the strap surfaces but without contact engagement between the strap surfaces and the heating element.  
  8. The method ofclaim 7 wherein the clamping of the heated surfaces during sealing occurs substantially simultaneously with withdrawal of the heating element from between the strap surfaces to minimize cooling of the surfaces.  
  9. The method of claim 3 including the further step of releasing the sealed strap length onto the article by moving the movable clamp laterally of the path of movement of the movable shear after shearing the sealed strap length from the strap supply.  
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