Time-control circuit for pneumatically operable devices

Abstract: A timing control circuit for a fluid pressure operable device (12) such as a strapping tool, is manually actuable to provide fluid flow to a reservoir (90) through a fluid-flow rate-controlling valve (80) from a supply (14). A line-pressure-operable, normally-open valve (60) is located in a primary fluid flow line (18) and this is closed when the pressure in the reservoir (90) builds up to the pressure to interrupt fluid flow to the device (12) to terminate its operation.

Description: The present invention provides a timing circuit for pneumatically operable strapping tool. More specifically, the present invention relates to a pneumatically operated strapping tool according to the preamble of claim 1 Tools for tightening and binding strapping about packages and articles have been utilized for many years and they include pneumatic, hydraulic and electrically driven tools. Many of the earlier tools were utilized to clinch and secure steel strapping with clips, clamps and formed interlocking notches. The introduction of plastic strapping required development of newer tools and new strap joining techniques, which included strap weldments. The tools for plastic strapping are most frequently pneumatically or electrically driven for both cost and weight considerations. The plastic strapping is constricted about a package by a mechanism which drives one end of overlapped strap portions to tighten the loop to a predetermined and sensed tensile load. Thereafter, the strap is held in position, the driving mechanism is disabled and the overlapped strap ends are secured together by fusion welding. The tools for binding and securing plastic strapping are relatively new and require special techniques to provide sound weld joints for the overlapping strap ends forming the loop about a package. Weldments avoid the use of secondary clips and fasteners to join the taut strapping looped about bundles and packages. Indicative of the early efforts at hand tools for securing looped plastic strapping is the electrically controlled hand tool taught in U.S. Patent No. 3,586,572 to Ericsson, which utilized a drive means coupled to an electric motor for tensioning the plastic strap looped about a bundle or package. Thereafter, the frictionally engaged and overlapping strap portions were rapidly oscillated to melt a surface region for fusion by interface solidification to provide weldment between the looped straps. The drive means included a rotary output shaft whose rotary motion was converted into rocking movement for intermittent rotary movement of the strap gripping member to provide oscillating movement for effecting the friction-fusion joining of the overlapping strap portions. Earlier efforts at strap fusion and welding utilizing pneumatically operated tools is exemplified by the completely automatic-type application tool taught in U.S. Patent No. 3,442,203-Kobiella, where plastic strap is automatically fed around a package from a strap supply source; the leading end of the strap is grasped; the trailing end of the strap is withdrawn to tension the strap loop; and, thereafter, the overlapping portions of the loop are friction fused. However, this apparatus is a stand-alone machine and not a completely portable hand-held tool. Hand-held, pneumatically-operated tools have been provided to accommodate joining and fusion bonding or securing plastic strapping. In these hand-held tools, the strap is manually fed about a package to bring the strapping portions into overlapping register, the strap loop is tightly cinched and the strap ends are secured by friction-fusion. Indicative of these tools are the VFL and VFM tension-weld strapping tools provided by the Signode Corporation and illustrated in catalog number 6096, where overlapping strap portions are inserted in a feedwheel mechanism and an air motor is activated by a lever operator to tighten the strap about a package to a predetermined tension noted by motor stalling. Thereafter, an eccentric handle is utilized to actuate the fusion operation. However, it has been found that the actuation time for the fusion operation will vary with the type of plastic, strap thickness, strap width, and ambient temperature, as well as operator ability to judge completion of a weldment. Pneumatically operated tools have found wide application and usage in the strap industry as well as other industries. The manufacturers and suppliers of these tools have provided control mechanisms for controlling or sensing operations based on their own initiative and in response to customer demand. In the strapping tool industry, tools are provided with means for sensing the strap tension and disengaging the drive mechanism at a predetermined strap tensile force, as well as other sophisticated controls which minimize operator judgment in providing a bound strap about a package. However, the tool manufacturers have not yet provided a means to minimize operator judgment for the time function to provide a secure weldment between the overlapped plastic straps. Therefore, a device for controlling the fusion welding operation in these hand-held tools is very desirable to cure variations in the weldments, which are now dependent upon operator judgment. Although a timing control in some form was previously conceivable, the desired device was required to be compact and easily adapted to existing friction fusion hand tools. US-A-3,093,114 discloses a pneumatic tool for tightening and loosening bolts and nuts in which a timing control arrangement is provided to reduce or cut off power to the tool after a pre-determined and adjustable period to ensure that each nut is tightened to the same degree. Engineers Digest, volume 34, No. 8, August 1973, discloses several low cost pneumatic time delay systems for pneumatic devices. According to the present invention, a pneumatically operated strapping tool for tightening and securing a loop of plastics strapping about a package, said tool including means to couple the tool to a source of fluid at a line pressure, means for constringing said loop, means for establishing a pre-determined tensile load on said strapping, means for securing overlapped portions of said strapping loop, fluid-operable means for driving said loop constringing means and said securing means, and a manually-operable, normally-closed valve coupled between said means for driving and said source of fluid; is characterised in that the strapping tool further comprises a timing control arrangement simultaneously actuable with said means for securing at said pre-determined tensile load and operable to interrupt fluid flow to said means for driving said securing means after an adjustable and pre-determinable operating period, said timing control arrangement comprising: a first conduit communicating between said manually operable, normally closed valve and said source of fluid; a manually-operable, normally-closed, three-way valve; a second conduit communicating between said source of fluid and said manually-operable, normally closed valve; an adjustable flow rate control valve for controlling a rate of fluid flow; a third conduit communicating between said manually-operable, normally closed, three-way valve and said adjustable flow rate control valve; a fluid reservoir; a fourth conduit communicating between said adjustable flow-rate control valve and said fluid reservoir; and a pressure actuable, normally-open three-way valve mounted within said first conduit between said source of fluid and said means for driving, for normally providing fluid communication through said valve at a normally open reference position, and said valve has a pressure-operable actuator coupled to said fluid reservoir and being operable by said pressure within said fluid reservoir to move to a closed position to block fluid flow to said means for driving at a pre-determined time after manual actuation of said manually operable, normally-closed three-way valve to an open position. In the Figures of the drawing, like reference numerals identify like components, and in the drawings: FIG. 1 is a perspective view of a hand-held, pneumatically driven strapping tool; FIG. 2 is a perspective view of the strapping tool of FIG. 1 in partial exploded section with an exemplary timing control circuit; and FIG.3 is a schematic diagram of a preferred embodiment of the timing control circuit for the strapping tool of FIG. 1. In FIG. 3, timing control circuit 10 is schematically illustrated in dashed outline and is coupled to hand-held and pneumatically-operable tool 12. Although hand tools are utilized for cinching or constricting steel strapping, the present illustration is particularly directed to a hand-held tool 12 for tightening and securing plastic strap about a package. The plastic strapping may be made from various chemical composition materials, and is not limited to any particular plastic composition or strap size. Hand tool 12 is coupled to a source of fluid 14 at a line pressure and has a timing control circuit 10, which is selectively actuable by eccentric handle 30 to block fluid flow after a predetermined time to terminate a tool operating cycle. A manually-operable, normally closed flow control valve 16 is directly coupled to source of fluid 14 by conduit 18. Depression of manual actuator 20 opens valve 16 for fluid communication from source 14 to drive means or air motor 22 of hand tool 12. Strapping tool 12 utilizes a feedwheel assembly 46 to constrict or shrink a strapping loop wrapped around an article to a predetermined tension, which may be sensed by a slipping clutch to limit or avoid over-tension of the overlapped strap portions. Thereafter, hand tool 12 is actuable to fusion weld the overlapped straps at the predetermined tension by engagement of vibratory welding assembly 32 in FIG. 2, which is integral with hand tool 12. The feedwheel mechanisms and welding assembly are known in the art and illustrated by pneumatically-operable Signode tension-weld strapping tool Models VFL and VFM. These tool structures and their operation are taught and illustrated in Signode catalog No. 186096, and will not be described in detail in the present application. Hand tool 12 in FIGS. 1-3 is generally equipped with both feedwheel tensioning apparatus 46 and fusion welding assembly 32 noted above, however, welding assembly 32 is actuated after attainment of the predetermined strap tension sensed by the hand tool and noted by clutch slipping or motor stalling. The fusion welding operation requires a relatively fixed period of operating time to provide sound weldment of the overlapped and pretensioned straps. Historically, the weldment period has been dependent upon operator determination to provide the operating period, which was terminated by subsequent disengagement of eccentric handle 30 for weld completion and tool disengagement from the overlapped straps. However, judgment and evaluation by an individual of good weld will vary among individuals, and, therefore, it is very desirable to provide a repetitive welding cycle operation, which is independent of operator judgment. In the illustrated embodiment, timing control arrangement 10 and welding vibrator assembly 32 for fusion welding of overlapping strap portions 50 and 52 are simultaneously actuated by rotation of eccentric handle 30, which timing control arrangement 10 may be adjusted to a desired operating period for the welding operation. The operating period is independent of operator judgment, but may be adjusted to the particular strap parameters. In FIG. 1, hand tool 12 for cinching a strap loop about a package has a motor housing 40 with an air motor 22 (not shown) secured therein. Engagement between a source of fluid 14 at a line-pressure and valve 16 is provided by depression of handle 42 to actuate manual operator 20. The exact lever coupling linkage and mechanical connections are determined by the design of the particular hand tool and are not illustrated herein. Air motor 22 in motor housing 40 is coupled to a gear transfer arrangement in gear housing 44 to drive a feed wheel at gripper 46, which gripper and feed wheel are known in the art and illustrated in the above-noted Signode Catalog 186096. Depression of lever 48 opens gripper assembly 46 for introduction of overlapping strap portions 50 and 52 generally looped or wrapped about a package or article (not shown). Release of handle 48 provides the overlapped straps in a secured position in track 47 of gripper assembly 46 and welding apparatus 32. Subsequent depression of lever 42 communicates fluid at a pressure and drives motor 22 and feedwheel 49 for cinching or shrinking of the loop about the article or package by drawing one of strap portions 50 or 52 relative to the other until a predetermined tensile load is provided in the straps, which causes motor 22 to stall. After motor stalling at the predetermined strap tension, rotation of eccentric handle 30 actuates welding assembly 32 to weld the taut, overlapping straps. Welding cycle actuation and tool operation by the operator required a certain technique matched to both the type of strapping and the gauge and/or width of the strapping to provide a proper or good weld between the overlapped strap sections. Illustrative of this technique was the requirement for rapid actuation of the eccentric handle and momentary pause at completion of the actuating movement for thin strapping, or a slightly longer pause for a thicker gauge strap of the same material. As noted above, the prior art provided a single valve 16, which was manually operable by handle 42 and actuator 20, to open fluid communication and actuate motor 22 and feedwheel 46 to tighten the strap. Thereafter, stalling of motor 22 indicated completion of strap tensioning and signalled the operator to rotate eccentric handle 30 to actuate welding assembly 32. Therefore, weld timing is critical, and timing circuit 10 removes operator judgment and evaluation of this time constraint for utilization of the hand tool and provision of a good weldment on a tightened strap. In the preferred embodiment illustrated schematically in FIG. 3 and in an as-assembled state in FIG. 2, timing control circuit 10 may be incorporated in either of the above-noted VFL or VFM tools, as an example. Timing control circuit 10 at the illustrated reference position of FIG. 3 is coupled to air supply 14 and includes normally-open, three-way, pilot valve 60, which is in-line with conduit 18 for open fluid communication between manually-operable valve 16 of hand tool 12, and source of fluid 14. Valve 60 is operable between its normally-open position for fluid flow to valve 16 and its closed position which deactivates motor 22 and exhausts valve 60 and motor 22 to the atmosphere through conduit 66. Biasing means 64 biases valve 60 to the normally-open position, as illustrated at FIG. 3, which biasing means 64 may be overcome by a force applied to pressure-operable activator 62 to move valve 60 to the closed position. Three-way valve 70 of circuit 10 is coupled to fluid source 14 through first conduit 72 and is operable by manual actuator 76 to be moved to the open position against biasing means 74 from its normally-closed position. Thus, it can be seen that fluid supply 14 is coupled along parallel conduits 18 and 72 to tool 12 and timing control circuit 10, respectively, and more specifically, fluid flow is provided to normally-closed valve 70 of circuit 10 and through normally-open pilot valve 60 to valve 16 in tool 12. Second conduit 78 couples three-way valve 70 to variable flow control valve 80, which includes an adjustable orifice restriction 82 and a check valve 84 in parallel with adjustable orifice 82 to more rapidly exhaust the downstream timing circuit elements at closure of valve 60 and deactivation of motor 22. The downstream fluid flow from valve 80 is communicated through conduit 88 to fixed volume chamber or reservoir 90. Pressure-operable actuator 62 of pilot valve 60 is coupled to conduit 88 through conduit 92 and is responsive to line-pressure above a predetermined value to close valve 60, which interrupts fluid flow through conduit 18 to deactivate motor 22 and end an operating cycle. Energization of the vibratory welding assembly 32 by rotation of eccentric handle 30 simultaneously moves manual actuator 76 and valve 70 against the bias of biasing means 74, to communicate fluid to variable orifice valve 80. Fluid at line pressure is conducted through conduit 88 and adjusted orifice 82 to fill reservoir 90 at a controlled rate and thus a known time period. As reservoir 90 is filled, the fluid pressure in conduit 88 is communicated through conduit 92 to pressure-operable actuator 62 of pilot valve 64, which moves valve 60 at a predetermined pressure to the closed position and thereby prohibits fluid communication to motor 22. Variable orifice 82 of valve 80 may be adjusted for varying the rate of fluid transfer therethrough to control the period for filling reservoir 90 and thus adjusts the time delay between the opening of valve 70 and the closing of valve 60. Check valve 84 is coupled, both upstream and downstream of variable orifice 82, to relieve the fluid pressure in conduit 88 and reservoir 90 to more rapidly evacuate these components after deactivation Of motor 22 and resetting of handle 30. Closing valve 70 exhausts conduit 78 and check valve 84 opens to expedite evacuation of conduit 88 and reservoir 90. Filter 96 in conduit 72 between source of fluid at a pressure 14 and normally-closed valve 70 filters the fluid transferred to the timing control circuit 10. In FIG. 2, timing control arrangement 10 is provided in an exemplary structure, as shown in the cutaway and exploded view. In this view, pilot valve 60 is insertable in a cylindrical passage 100 in stem 102 at the rear portion of motor housing 40, which passage 100 communicates with conduit 18 through bore 104. Fluid is communicated through conduit 18 and bore 104 to pilot valve 60 and, through and around first groove 61 to second bore 106 and conduit 72 for communication to normally-closed valve 70. Subsequent actuation of eccentric handle 30 to actuate welding or securing means assembly 32 also actuates valve 70 to the open position 0 for fluid communication through conduits 78 and 88, as well as valve 80, to reservoir 90. In the illustrated embodiment, reservoir 90 is provided by tubing of a fixed length and cross section to provide the necessary volume for fluid transfer and back-pressure communication to pilot valve 60 through conduit 92. In this illustrated embodiment, conduits 88 and 92 are not clearly distinguishable but have been integrated as extensions of tubing 90. However, it is understood that the schematic drawing and the physical embodiment of the illustrations are equivalents. Subsequent pressure transfer to cavity 98 at the base of passage 100 operates against land 110, which is operable as the manual actuator 62, to develop pressure in cavity 98 to move pilot valve 60 to the closed position. At the closed position, land 110 blocks bore 104 and disrupts fluid communication from conduit 18, which effectively terminates operation of motor 22 and tool 12 to indicate termination of a joining and welding cycle.

Claims: A pneumatically operated strapping tool (12) for tightening and securing a loop of plastics strapping (50, 52) about a package, said tool (12) including means to couple the tool to a source of fluid (14) at a line pressure, means (46) for constringing said loop, means for establishing a pre-determined tensile load on said strapping (50, 52), means (32) for securing overlapped portions of said strapping loop, fluid-operable means (22) for driving said loop constringing means (46) and said securing means (32), and a manually-operable, normally-closed valve (20) coupled between said means for driving (22) and said source of fluid (14); characterised in that the strapping tool (12) further comprises a timing control arrangement (10) simultaneously actuable with said means (32) for securing at said pre-determined tensile load and operable to interrupt fluid flow to said means (22) for driving said securing means (32) after an adjustable and pre-determinable operating period, said timing control arrangement (10) comprising: a first conduit (18) communicating between said manually operable, normally closed valve (20) and said source of fluid (14); a manually-operable, normally-closed, three-way valve (10); a second conduit (72) communicating between said source of fluid (14) and said manually-operable, normally closed valve (70); an adjustable flow rate control valve (82) for controlling a rate of fluid flow; a third conduit (78) communicating between said manually-operable, normally closed, three-way valve (70) and said adjustable flow rate control valve (82); a fluid reservoir (90); a fourth conduit (88) communicating between said adjustable flow-rate control valve (82) and said fluid reservoir (90); and a pressure actuable, normally-open three-way valve (60) mounted within said first conduit (18) between said source of fluid (14) and said means for driving (22), for normally providing fluid communication through said valve (60) at a normally open reference position, and said valve (60) has a pressure-operable actuator (62) coupled to said fluid reservoir (90) and being operable by said pressure within said fluid reservoir (90) to move to a closed position to block fluid flow to said means (22) for driving at a pre-determined time after manual actuation of said manually operable, normally-closed three-way valve (70) to an open position. A pneumatically operated strapping tool according to claim 1, wherein said adjustable flow control valve (82) has a downstream side and an upstream side, said adjustable flow control valve (82) further comprising a check valve (84) coupled between said downstream and upstream sides to more rapidly release fluid pressure in said reservoir (90) upon de-activation of said strapping tool. A pneumatically operated strapping tool according to claim 1 or 2, further comprising a filter (96) mounted in said second conduit (72) between said source of fluid (14) and said manually operable, normally closed three way valve (70). A pneumatically operated strapping tool according to any preceding claim, wherein said reservoir (90) is a coiled length of tubing coupled between said adjustable flow control valve (82) and said pressure actuable, normally open three way valve (60). A pneumatically operated strapping tool according to any preceding claim, wherein said means (32) for securing provides a fusion weldment between said overlapped strapping portions (50, 52). A pneumatically operated strapping tool according to any preceding claim, wherein said strapping tool further comprises a first manual lever (42) operable to open said manually operable, normally closed valve (20) to communicate fluid at line pressure to actuate said means (22) for driving and a second lever (30) operable to actuate said means (32) for securing, which second lever (30) simultaneously opens said manually operable, normally closed three way valve (70) for actuation of said securing means (32) for a predetermined length of time. A pneumatically operated strapping tool according to any preceding claim, wherein said strapping tool has a first housing (40) for said driving means (22) and a second housing for said securing means (32), said timing control arrangement (10) being mounted and operable in said first and second housings. A pneumatically operated strapping tool according to claim 7, wherein a cover is provided which co-operates with said first housing (40) to define a cavity for said means for driving (22), said reservoir (90) being mounted and operable in said cavity.

Inventors: CRITTENDEN DAVID E, TOPPEL ROBERT, CRITTENDEN, DAVID E., TOPPEL, ROBERT
Applicants: SIGNODE CORP, SIGNODE CORPORATION
Application year: 1991
Main classification: B29C65
IPC codes: B65B13, B29C65, F15B21