Device for connecting the overlapping ends of a strap put around a package

Abstract

 In a package strapping tool for jointing metal strapping, crimping jaws 22 on which embrace opposite edges of overlapping ends of a loop of strapping around a package and which are actuated through a toggle linkage 32, 34 by a fluid pressure operated piston and cylinder assembly 27 are moved from the fully open position to grip the edges of the overlapping strapping ends by a small partial-close cylinder and piston assembly 71 and 72. The partial-close piston 72 acts coaxially upon the main piston 28 and its full stroke movement is limited to the main piston movement necessary for the jaws to grip the strapping tightly enough to locate it while the strapping is tensioned. Compressed air supplying an air motor (not shown) for driving a rotary tensioning dog (not shown) is applied simultaneously to the partial close cylinder72 so that the jaws 22 grip the strapping from the start of tensioning A valve (not shown) may be provided to put the partial-close assembly out of action when not required.

Description

[0001] This invention relates to package strapping tools of the kind in which a joint between the overlapping ends of a loop of metal strapping tensioned around a package is made by a crimping jaw mechanism operated by a piston and cylinder assembly actuated by fluid pressure, usually pneumatic but sometimes hydraulic.

[0002] The crimping jaw mechanism comprises a pair of crimping jaws which in use embrace opposite edges of the overlapped strapping portions (which may or may not be surrounded by a metal seal) and are pivoted about axes parallel to one another and to the edges of the strapping. Usually the crimping jaws are connected to the piston of the piston and cylinder assembly by toggle linkages. Such package strapping tools are referred to hereinafter as package strapping tools of the kind described.

[0003] In package strapping tools of the kind described, it is known to provide a spring to act upon the piston and cause the crimping jaws to close partially and grip the edges of a seal surrounding the overlapped portions and hold the strapping in place between the jaws while the strapping is being tensioned. To overcome the friction of the piston and cylinder assembly which is necessarily large and of the linkage connecting the crimping jaws, the spring has to be heavy. The spring takes up much space and increased operating pressure (or greater piston area) is required to compress it and open the jaws fully at the end of the jointing operation so as to enable the completed joint to be separated from the tool.

[0004] A package strapping tool of this kind according to the present invention is characterised by a secondary fluid pressure cylinder and piston arranged to act, when energised, upon the crimping jaw mechanism to cause the crimping jaws to grip the edges of the overlapping portions of strapping or of a seal surrounding the overlapping portions.

[0005] A secondary piston and cylinder of very much smaller diameter than the main piston is adequate to move the main piston, the connecting linkage and the crimping jaws to bring the crimping jaws to the gripping position. A relatively short stroke only is needed. For eventual return to the fully open position of the jaws the secondary piston and cylinder is vented to atmosphere, or in the case of a hydraulic system is open freely to a fluid return conduit, and offers little resistance to movement of the main piston.

[0006] The secondary cylinder is preferably disposed co-axially on, or in, the cylinder head of the main cylinder and arranged so that the secondary piston, or a piston rod extending from the secondary piston, can bear directly on the main piston, the secondary piston having a full stroke sufficient to move the main piston through part of its stroke away from the position corresponding to the fully open position of the crimping jaws to the position corresponding to the gripping position of the crimping jaws.

[0007] In a tool which includes fluid-pressure operated tensioning means for tightening the loop of strapping prior to the making of the joint between the overlapping portions, fluid-pressure supplied to operate the tensioning means is preferably applied simultaneously to the secondary cylinder.

[0008] Means may be provided for putting the secondary piston and cylinder out of action when the partial close action is not required. This means may be a simple valve for closing the passage through which pressure air is supplied to the secondary cylinder. In a strapping tool according to the invention therefore it is simple to make provision for partial closing of the crimping jaws to be an optional feature for use only when required. In the known strapping tools in which a heavy spring is provided for partial closing of the crimping jaws it is difficult to make the partial close action optional.

[0009] Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a front view of one form of strapping tool according to the invention,

Figure 2 is a rear view and

Figure 3 an end view in the direction of arrow 3 in Figure 1,

Figure 4 is a view similar to Figure 1 but partly in section,

Figure 5 is a fragmentary view of part of Figure 4 with the inclusion of package strapping,

Figure 6 is a partial section on line 6-6 of Figure 1,

Figure 7 is a section on line 7-7 of Figure 1,

Figures a and 9 are sections similar to Figure 7 showing different stages in the operation of the tool,

Figure 10 is a perspective view of a completed package strapping joint made by the strapping tool of Figures 1 to 9,

[0010] The strapping tool illustrated in Figures 1 to 9 of the drawings is operated by compressed air and is of the so-called "pusher bar" type which avoids the use of a base plate interposed between the strapping and a package being secured. The strapping tool comprises an air-driven tensioning motor assembly 20 for tightening a metal strap 21 (Figures 5 and 10) around the package, a crimping device 22 for securing together overlapping portions of the strap 21 within a surrounding metal seal 23 and a valve assembly 24 by which the operation of the strapping tool is controlled.

[0011] The tensioning motor assembly 20 and the crimping device 22 are both pivoted to a frame 25 to enable the tool to be opened for easier engagement with a loop of strapping and closed for operating upon it.

[0012] The crimping device 22 is operated by a large double acting piston and cylinder assembly 27 with a piston 28 (Figure 4) working in a cylinder formed in a housing 29. The piston 28 is mounted on a piston rod 30 which extends through the bottom of the housing 29 to be connected by a transverse pin 31 (Figures 4 to 7) to a pair of links 32 of a toggle linkage 33 for operating crimping jaws 34. A front plate 35 lies on one side of the toggle linkage. An intermediate plate 36 and a back plate 37, in contact with one another, lie parallel to the front plate 35 on the opposite side of the toggle linkage. The plates 35, 36 and 37 are secured to the housing by bolts 38 and further bolts 39 near the lower corners of the plate provide pivots for the jaws 34.

[0013] The bolts 39 also support fixed blades 40 against each face of each jaw 34 with which they co-operate to crimp the seal and make the joint in the strapping.

[0014] A seal stop 41 is slidably mounted in the intermediate plate 36 and urged towards a projecting position by a spring 42. A gap 43 (Figure 4) is provided in the bottom edge of the seal stop 41 to receive the strapping so that the seal stop 41 straddles it and acts as a guide during tensioning as well as providing an abutment for the rear end of the seal. In the face of the back plate 37 that is against the intermediate plate 36 is formed a slideway for a cutter 44. As visible in Figure 4 the transverse pin 31 projects through a slot in the intermediate plate 36 to engage a hole in the cutter 44 which is therefore moveable along the slideway by the pin 31.

[0015] The crimping device 22 is pivoted to the frame 25 by a pivot pin 45 which passes through lugs 46 projecting from the back plate 39 and a bore in the frame 25. Forming part of the frame 25 is a strap foot 47 which tapers towards a toe 48. In the closed position of the tool the toe 48 bears against the bottom edge of the back plate 37 and the front edge projects forward to a position in which it co-operates with the cutter 44 in severing surplus strapping from the completed joint.

[0016] The motor assembly 20 is pivoted to the frame 25 by a pivot pin 49. A rotary dog 50 (Figures 1, 3 and 4) for tensioning the strap is driven by an air motor 51 of the motor assembly 20 through suitable gearing. There is a roller 52 rotatably mounted in the strap foot 47 opposite the rotary dog 50 to support the strap against the pressure of the rotary dog during tensioning. The roller 52 is rotatable with the object of reducing friction.

[0017] A hand lever 53 rigidly mounted on the frame 25 extends above the body of the motor 51. By squeezing the hand lever 53 and motor 51 together, the motor 5₁ can be raised to lift the rotary dog 50 away from the strap foot to enable the strap to be inserted between the rotary dog 50 and the roller 52. A barrel-shaped compression spring 54 mounted between a bracket 55 rigid with the hand lever 53 and a lug 51' on the casing of the motor assembly urges the rotary dog 50 towards the roller 52. An outrigger bracket 56 supported by the motor pivot 49 carries an outer end bearing for the shaft on which the rotary dog 50 is mounted. A downward projection 57 of the outrigger bracket forms an outer edge strap guide and an upwardly inclined tail 58 on the strap guide provides a guide for the inner edge of the strap. Outside the outrigger bracket 56 a strap foot restrainer 59 (Figures 1, 3 and 4) is swivelly mounted on the motor pivot 49. On its inner face the strap foot has an arcuate groove 60 to receive a lateral projection 61 on the strap foot when the strap foot restrainer 59 is swung downwards. The under face of the projection 61 has a curved surface centred on the motor pivot 49 and engages the facing side of the groove 60 to resist deflection of the strap foot during strap tensioning. A link 62 couples the strap foot restrainer 59 to an auxiliary double-acting piston and cylinder assembly 63. The link 62 is pivotally connected to the strap foot restrainer 59 and to a piston rod 64. A cylinder 65 (Figure 4) of the piston and cylinder assembly 63 is formed in a body 66 of the valve assembly 24 and its piston 67 is connected to the piston rod 64. In its outstroking direction the piston 67 swings the strap foot restrainer 59 clockwise (as viewed in Figures 1 and 4) engaging the lateral projections 61 with the groove 60. The movement continues until the strap foot restrainer 59 meets a peg 68 protruding from the outrigger bracket 56 on which it acts to urge the motor assembly 20 about the motor pivot 49 in a clockwise direction (as shown in Figure 4) so as to urge the rotary dog 50 harder against the strapping. If frictional contact between the strap foot restrainer 59 and the strap foot 47 has not already caused the strap foot 47 to move towards the crimping device 22, force applied to the strap foot 47 through the rotary dog 50, by the action of the auxiliary piston and cylinder assembly 63, will urge the toe 48 of the strap foot 47 towards the back plate 37.

[0018] In the opposite direction the auxiliary piston and cylinder assembly 63 moves the strap foot restrainer 59 anti-clockwise disengaging its groove 60 from the lateral projections 61 and out of the way of the strap being inserted between the rotary dog 50 and the roller 52. Towards the end of the anti-clockwise movement of the strap foot restrainer 59 a tail 69 of the strap foot restrainer 59 engages an abutment 70 (Figures 1 and 4) on the frame 25 so that the strap foot restrainer 59 and the frame 25 together move anti-clockwise about the pivot pin 45 swinging the strap foot 47 away from the back plate 33 ready for engagement of the tool with the loop of strapping.

[0019] In the cylinder housing 29 above the large piston 28 is a small co-axial partial-close, cylinder 71 (Figures 4 and 7 to 9) with a piston 72 which abuts the large piston 28 when the piston 28 is at the top of its stroke. When air under pressure is admitted to the top of the partial close cylinder 71, the piston 72 moves from the position shown in Figure 7 and bears on the large piston 28 and moves the piston rod 30 to close the crimping jaws 34 around the seal 23 (as shown in Figure 8) whilst strap tensioning takes place. By this means the seal 23 is retained and prevented from being pulled out of the jaws as a result of curvature or irregularities in the packaging surface.

[0020] At the bottom of the cylinder housing 29 a plunger 73 (Figure 4) is slidably mounted for movement parallel to the piston rod 30. It is spring biased to project into the cylinder. Towards the lower end of its stroke the piston 28 depresses the plunger 73 indicating that the crimping operation powered by the piston and cylinder assembly 22 has been completed. The way in which use is made of this indication will be described later.

[0021] The valve assembly 24 comprises a tension valve 74 and a sealing valve 75. The tension valve has a slidable valve spool 76 (Figure 6) urged upwards by a spring 77 against a pivoted tension valve lever 78 by which the spool 76 can be manually depressed. Moving the tension valve spool downwards supplies compressed air under pressure to the top of the piston 67 of the auxiliary piston and cylinder assembly 63, and opens its underside to atmosphere, supplies air to the air motor 51 and to the top of the co-axial cylinder 71 through a passage 99 (Figure 4). The underside of the large piston 28 is also opened to atmosphere. The passage 99 includes a screw-down valve 100 which enables the passage 99 to be closed so that pressure air can be prevented from reaching the co-axial cylinder 71 if the previously described action of the piston 72 in partly closing the crimping device is not required.

[0022] Similarly a pivoted sealing valve lever 79 provides manual control of a valve spool 80 of the sealing valve 75. The valve spool 80 is urged upwards by a spring 81. Moving the sealing valve spool 80 downwards supplies pressure air to the top of the cylinder of the main piston and cylinder assembly 27. A catch 82 (Figures 1, 4 and 6) pivotally mounted between the levers 78 and 79 is urged by a spring 82' anti-clockwise (as viewed in Figure 6) towards the tension valve lever 78 and has a notch 83 to engage a recess 84 in the tension valve lever 78. The notch 83 of the catch 82 self-engages the recess 84 when the tension valve lever 78 is depressed and retains that lever in the depressed position. The catch 82 also has a tail 85 which lies under the sealing valve lever 79. When the sealing valve lever is depressed it engages the tail 85 and trips the catch 82 disengaging its notch 83 from the recess 84. However, rigid with the sealing valve lever 79 is a hold-down pin 86 (Figures 1, 3 and 4) which projects over the tension valve lever 78. When the catch 82 is tripped the tension valve lever 79 rises into engagement with the hold-down pin 86 but not sufficiently to alter the effective position of the tension valve spool 76.

[0023] A cranked lever 87 (Figures 2, 3 and 4) is pivotally mounted about a pivot pin 88 on the body 66 of the valve assembly 24. The lower end of the cranked lever 87 extends under the edge of the cylinder housing 29 and has a lateral extension 89 which is bifurcated and embraces a circumferential groove 90 in the plunger 73 where it projects below the cylinder housing 29. The upper end of a helical compression spring 91 surrounds a spigot 92 at the lower end of the plunger 73. The lower end of the spring 91 is received in a pocket 93 in a lug 94 projecting from the back plate 37. The spring 91 urges the plunger 73 upwards and the cranked lever 87 in an anti-clockwise direction in Figure 2. At its upper end the cranked lever 87 has a lateral projection 95 (Figure 3) which extends towards the sealing lever 79 and lies in the path which a lateral projection 96 on the sealing lever 79 follows when the sealing lever 79 is depressed. Meeting faces 97, 98 (Figure 2) on the projections 95 and 96 respectively are complementarily inclined so that when the sealing lever 79 is depressed the projection 95 on the sealing lever deflects the projection 96 moving the cranked lever 87 (clockwise in Figure 2) against the action of the spring 91 until the projection 95 has passed the projection 96 when the spring urges the projection 96 to overlie the projection 95 and retain the sealing lever 79 in the operative position. The plunger 73, cranked lever 87, spring 91 and the overlapping projections 95, 96 thus constitute a self-engaging latch to retain the sealing lever 79 in the operative position until the plunger 73 is engaged by the piston 28 at the end of its downward movement. The piston 28 reaches this position when the sealing operation has been completed. Depression of the plunger 73 by the piston 28 releases the latch so that the sealing lever 79 withdraws the hold-down pin 86 from the tension lever 78 which, too, returns to its initial position under the pressure of the tension valve spool spring 77.

[0024] A summary of the full cycle of the operation of the strapping tool is as follows. In the starting condition shown in Figures 1 and 7 pressure air is being supplied through the sealing valve spool 80 to the underside of the piston 28 so that the crimping jaws 34 are held wide open. Pressure air is also being supplied by the tension valve spool 76 to the underside of the piston of the auxiliary piston and cylinder assembly 63. This holds the strap foot restrainer 59 in its upper position and the toe 48 of the strap foot 47 is separated from the back plate 37.

[0025] A metal seal 23 is slipped over the end of a length of strapping 21 drawn from a supply reel. The strapping is pulled through the seal and is looped around a package. The free end is threaded again through the seal below the supply end of the strapping loop and the projecting portion 101 (Figures 5 and 10) bent back under the seal. The end of the loop nearest the supply reel is inserted sideways into the tool between the rotary dog 50 and the roller 52. To create a gap for this purpose between the rotary dog 50 and the roller 52 the air motor 51 is lifted by squeezing together the air motor 51 and the hand lever 53. The seal 23 is arranged under the crimping jaws 34 and the strap foot occupies the angle between the strapping of the loop and the portion leading to the supply. The slack in the strapping is pulled up manually until the end of the seal abuts against the seal stop 41.

[0026] The tension lever 78 is then depressed and is held in this position by the catch 82. The resulting reversal of the pressure air supply to the auxiliary piston and cylinder assembly 63, so that it is now applied to the top of the piston, closes the strap foot restrainer 59 (as shown in Figure 4), urges the strap foot towards the back plate 37, and urges the rotary dog 50 against the strapping. Air pressure is simultaneously applied to the partial-close cylinder 71 partially to close the crimping jaws 34 to grasp and locate the seal, as shown in Figure 8, and to the air motor 51 which drives the rotary dog 50 to tension the strapping.

[0027] The strapping is fully tensioned when the motor stalls. The operator then depresses the sealing lever 79 to apply air pressure to the top of the piston 28. The crimping jaws 34, as shown in Figure 9, form the joint between the overlapping ends of the loop of the strapping and the cutter 44 co-operates with the toe 48 of the strap foot to cut off the loop from the supply of strapping. When the main piston 28 reaches the bottom of its stroke, on completing the crimping and cutting off operation, it strikes the plunger 73 so that the sealing lever 79 is released as previously described.

[0028] Release of the sealing lever 79 also releases the tension lever 78 allowing the respective spool springs to restore the sealing valve spool 70 and tension valve spool 76 to their initial positions. Back in their initial positions, the valve spools cut-off the pressure air supply to the motor and supply it instead to the underside of the main piston 28, re-opening the crimping jaws 34 so that the tool can be removed from the package, and to the top of the piston of the auxiliary piston and cylinder assembly 63 swinging the strap foot restrainer 59 up into the open position and bringing its tail 69 into engagement with the abutment 70 to withdraw the strap foot 47 from the back plate 37 ready for the next loop of strapping. The form of the resulting joint is shown in Figure 10.

[0029] The screw-down valve 100 allows air from the tension valve spool 76 to be cut off from the partial close cylinder 71 so that the intermediate movement of the crimping jaws 34 to grip the seal 23 as shown in Figure 8 does not take place. This may be desirable for various operational reasons, for example, to run the tool along the strapping 21 for some distance up to the seal 23.

Claims

₁. A package strapping tool of the kind in which a joint between the overlapping ends of a loop of metal strapping tensioned around a package is made by a crimping jaw mechanism operated by a piston and cylinder assembly actuated by fluid pressure and comprising a pair of crimping jaws which in use embrace opposite edges of the overlapped strapping portions, and are pivoted about axes parallel to one another and to the edges of the strapping characterised by a secondary fluid pressure cylinder (71) and piston (72) arranged to act, when energised, upon the crimping jaw mechanism (22) to cause the crimping jaws (34) to grip the edges of the overlapping portions of strapping or of a seal surrounding the overlapping portions.

2. A package strapping tool according to claim 1 characterised in that the secondary fluid pressure cylinder (71) and piston (72) are arranged to act, when energised, upon the crimping jaw mechanism (22) through the main piston (28) operating the crimping jaws (34).

3. A package strapping tool according to claim 2 characterised in that the secondary cylinder (71) is disposed co-axially on, or in, the cylinder head (99) of the main cylinder (29) and arranged so that the secondary piston (72), or a piston rod extending from the secondary piston (72), can bear directly on the main piston (29), the secondary piston (71) having a full stroke sufficient to move the main piston (29) through part of its stroke, away from the position corresponding to the fully open position of the crimping jaws (34) to the position corresponding to the gripping position (Figure 8) of the crimping jaws (34).

4. A package strapping tool according to any preceding claim and which includes fluid-pressure operated tensioning means for tightening the loop of strapping prior to the making of the joint between the overlapping portions characterised in that fluid-pressure supplied to operate the tensioning means (20) is applied simultaneously to operate the secondary piston and cylinder (71, 72).

5. A package strapping tool according to any preceding claim wherein means (100) is provided for putting the secondary piston and cylinder out of action when the partial close action is not required.

Drawing