Abstract:
A small profile strapping tool includes a body defining a cylinder housing, a piston disposed within a cylinder in the cylinder housing, a pneumatic weld motor operably connected to the piston for actuation during a weld cycle, a pneumatic tensioning motor for actuation during a tensioning cycle, and a pneumatic module removably mounted to the cylinder housing. Within the module, a pilot valve controls a flow of gas into the module, a tensioning motor valve controls gas flow to the tensioning motor to draw tension in the strap, a weld cycle valve controls gas flow to the weld motor and piston, a timer and an accumulator are configured to isolate gas flow to the weld motor upon reaching a predetermined pressure in the accumulator following actuation, and a pneumatic signal circuit disposed between the cylinder and a bleed valve includes a signal valve that controls actuation of the bleed valve to route gas to the tension motor to maintain tension in the strap following the weld cycle.

Description:
BACKGROUND OF THE INVENTION 
   The present invention pertains to an improved small profile tool for tightening strap around an object or load and adhering the strap onto itself. More particularly, the present invention is directed to a pneumatic circuit and module for a strapping tool that is configured to tension a strap around a load, weld or melt-adhere the strap onto itself and sever the strap from a strap source (e.g., supply). 
   Strapping tools are well-known in the art. These tools come in a wide variety of types, from fully manual tools to automatic, table-top tools. Tools are generally designed for use with either metal strapping or plastic/polymeric strapping. 
   Strappers for applying plastic or polymeric strapping materials can be of the automatic table-top or hand-held devices and are either electrically or pneumatically driven. This is necessary in order to provide energy for tensioning the strapping material and adhering the strap onto itself. Typically, the adhering function is provided by melting or otherwise welding a section of the polymeric (plastic) strapping material onto itself. Such melting or welding operations are generally carried out using ultrasonic or vibrational-type weld assemblies. The movement or vibrational motion can be provided by electrical, electromechanical or fluid drive (hydraulic or pneumatic) systems. 
   In one exemplary tool, a pneumatic system is used to drive the motors to tension the strap (driving a tensioning wheel), and to move a vibrating element that is in contact with interfacial surfaces of overlapping plastic strap portions. The tool includes a pneumatic circuit to route the compressed gas (air) to the appropriate functional elements (clamps and motors) through valves and the like. 
   In such a tool, the various functional elements are large and as such can be cumbersome. In addition, many such tools use one or more large (and heavy) mechanical clutch(es) to hold or clamp the strap following tension. 
   Accordingly, there exists a need for a pneumatic strapping tool that uses separate pneumatic motors (one motor for tensioning or feeding strap and another for welding the strap material onto itself) in a small or low profile package. Desirably, such a tool incorporates a pneumatic circuit that allows eliminating the clutch (and thus the weight) otherwise necessary for clamping the strap during welding and roll-back to facilitate operation. Most desirably, for ergonomic considerations, the pneumatic module is of a two button design to facilitate operation and to prevent actuation of the tensioning cycle (motor) during the sealing cycle. 
   BRIEF SUMMARY OF THE INVENTION 
   A small profile strapping tool is configured for tensioning a strap around a load, adhering the strap onto itself, and cutting a feed end of the strap. The tool uses separate pneumatic motors (one motor for tensioning or feeding strap and another for welding the strap material onto itself) in a small or low profile package. The tool incorporates a pneumatic circuit that allows eliminating the clutch (and thus the weight) otherwise necessary for clamping the strap during welding and roll-back to facilitate operation. 
   The pneumatic module is of a two button design to facilitate operation and to prevent actuation of the tensioning cycle (motor) during the sealing cycle. The tool includes a body defining a cylinder housing, a piston disposed within a cylinder in the cylinder housing, a pneumatic weld motor operably connected to the piston for actuation during a weld cycle to adhere the strap onto itself and a pneumatic tensioning motor for actuation during a tensioning cycle to tension the strap prior to adhering the strap onto itself. 
   The pneumatic module is removably mounted to the cylinder housing and includes a compressed gas inlet to the module and a pilot valve in flow communication with the gas inlet for controlling the flow of compressed gas into the module. A tensioning motor valve controls compressed gas flow to the tensioning motor and a weld cycle valve controls compressed gas flow to the weld motor and piston. The tension motor and the weld motor are in flow communication with (receiving gas from) the pilot valve. 
   A tensioning motor valve switch (one of the two buttons) actuates the tensioning motor valve to draw tension in the strap. The weld cycle valve switch (the second button) is then depressed to actuate the weld cycle valve and initiate the weld cycle. A timer and an accumulator in parallel with the weld motor are configured to isolate gas flow to the weld motor following actuation of the weld motor valve, upon reaching a predetermined pressure in the accumulator (corresponding to a predetermined amount of time). A pneumatic signal circuit is disposed between the piston cylinder and a bleed valve and includes a signal valve in the signal circuit. The signal valve controls the actuation of the bleed valve to route gas to the tension motor to maintain tension in the strap following the weld cycle during the cooldown cycle, thus eliminating the need for a mechanical clutch in the tensioning motor. 
   In a preferred strapping tool, the module is self-contained. The timer and the accumulator isolate gas flow to the pilot valve upon reaching a predetermined pressure in the accumulator (again, corresponding to a predetermined period of time). Another timer is disposed between the weld motor and the piston cylinder to delay venting of the piston cylinder following isolation of gas flow into the piston cylinder. 
   The tensioning motor valve is biased to close the valve to isolate flow to the tension motor and the weld motor valve is biased to close the valve to isolate flow to the weld motor. Compressed gas is introduced to the tension motor valve to assist the bias to close the valve and compressed gas is introduced to the weld motor valve against the bias to maintain the valve in an open condition. 
   These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein: 
       FIG. 1  is a perspective view of an improved small profile strapping tool embodying the principles of the present invention, the tool being shown with a strap material positioned in the tool, and showing the direction of movement of the material during tensioning; 
       FIG. 2  is a schematic illustration of the tool on a load to be strapped, with the strap material encircling the load; 
       FIG. 3  is a pneumatic circuit diagram illustrating the pressurized lines (in bold) when the tool is in a neutral state; 
       FIG. 4  is the pneumatic circuit diagram illustrating the pressurized lines (in bold) when the tool is in tension mode; 
       FIG. 5  is the pneumatic circuit diagram illustrating the pressurized lines (in bold) when the tool is in weld mode after tensioning; 
       FIG. 6  is the pneumatic circuit diagram illustrating the pressurized lines (in bold) when the tool is in cooldown mode after tensioning and welding; 
       FIG. 7  is the pneumatic circuit diagram illustrating the pressurized lines (in bold) when the tool weld mode is actuated without tensioning; and 
       FIG. 8  is the pneumatic circuit diagram illustrating the pressurized lines (in bold) when the tool is in cooldown mode after welding and without tension in the strap. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated. 
   It should be further understood that the title of this section of this specification, namely, “Detailed Description Of The Invention”, relates to a requirement of the United States Patent Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein. 
   Referring now to the figures and in particular to  FIG. 1 , there is shown a pneumatic motor strapper or strapping tool  10  of a design similar to that of the present invention. The illustrated strapper  10  shows, generally, the construction of a strapping tool that is configured to tension a strap S around a load L, weld the strap S material onto itself and sever a feed end F of the strap. For purposes of the present disclosure, the strap material will be referred to as having a feed end F which is the supply end of the material and a free or trailing end T which is that end of the material that is fed around the load L and reinserted into the strapping tool  10  for welding. 
   The tool includes, generally, a body  12 , a foot  14 , a weld motor  16  and housing  18 , a tensioning motor  20 , a cylinder housing  22  and a pneumatic module  24  having a circuit embodying the principle of the present invention. The tool  10  includes a handle  26  and grip  28  for ease of handling and use. The pneumatic module  24 , as will be discussed in more detail below, is mounted to the body  12  and provides pneumatic pathways between the module  24  and the weld and tensioning motors  16 ,  20  for introducing and venting a compressed gas, such as compressed air, to and from the motors. The module  24  is readily mounted to and removed from the body  12  by a plurality of fasteners such as bolts and the like. 
   The pneumatic module  24  is removably mounted to the body  12  and includes a plurality of components (e.g., switches, such as tension motor switch  30  and weld motor switch  32 , valves, accumulators) to control the overall operation of the strapper  10 . The module  24  is configured to readily mount to and be removed from the body  12  by, for example, bolts or like fasteners for ease of maintenance, removal and repair. In this manner, the module  24  can be removed and a spare installed on the tool  10  for continued use. 
   Referring to  FIG. 3 , a pneumatic schematic is shown in which the tool  10  is in a neutral state. Air enters the tool  10  through a compressed air supply  40  and enters a pilot valve  42 . The pilot valve  42  is a two position valve (on-off) that is biased to the on position (as shown). The on position routes air to a juncture  44  at which the air supply splits with one branch  46  routing air to a tension motor valve  48  and the other branch  50  routing air to a weld cycle valve  52 . A tee  54  in the air supply, prior to the pilot valve  42  is routed to a bleed valve  56  and is routed to a back end of the tension valve (as indicated at  58 ). The bleed valve  56 , as set forth below is used to bleed air to the tension motor  16  during welding and cooling. In the neutral position, air flows to the tension  48  and weld cycle  52  valves and to the bleed valve  56 ; however, the tension and weld cycle valves  48 ,  52  and the bleed valve  56  are all in the closed position and thus the system is pressurized. 
   Referring to  FIG. 4 , depressing or actuating the tensioning motor switch  30  moves the tensioning motor valve  48  into the open position, routing air through a variable orifice  62  to the tensioning motor  16 . Referring briefly to  FIG. 1 , a pivoting latch  31  is positioned between the tension and seal valve motor switches  30 ,  32  that pivots to lock the tension motor valve  48  in the actuated position and releases the tension motor valve upon actuation, e.g., depression of, the weld motor switch  32 . The variable orifice  62  is adjustable to provide control of the tensioning motor  16  power output. Note that the tensioning motor valve  48  is shown in the off or closed position, and is biased to this position. At the same time, air is routed from a tee  61  between the tensioning valve  48  and the tension adjusting orifice  62  to a signal valve orifice  64  in series with an orifice  66  and check valve  68  that route air to a signal valve  70 . The signal valve  70  resides in an air line  72  between the piston chamber  60  and the bleed valve  56  and serves to allow or not allow a signal to open or close the bleed valve  56  dependent upon the pressure in the piston chamber  60 . The air routed from the tension portion of the system does not flow through the signal valve  70  proper, but moves the signal valve  70  to the open position (against a bias) to provide a signal flow path from the piston chamber  60  to open and close the bleed valve  56 . The signal flow (path) is used to move the bleed valve to the open position (also against a bias). This routes air to the tensioning motor  16  to maintain tension in the strap during the weld cycle (as seen in  FIG. 5 ). 
   Releasing the tensioning motor switch  30  closes the tensioning motor valve  48 , terminating the air feed to the tensioning motor  16 . The air entering the back end of the tensioning motor valve (at  58 ) assists (the spring bias) in moving the tensioning valve  48  to the closed position following release of the valve switch  30 . At this point in time, however, even though the tensioning motor  16  has stopped (the tensioning valve  48  is closed), a portion of the tensioning portion of the system remains pressurized with air routed to the signal valve  70  to maintain the signal valve in the open position as long as there is sufficient pressure in the line  69  between the orifice  66  and the signal valve  70 . 
   Referring to  FIG. 5 , a weld cycle switch  32  operates the weld cycle valve  52 . Depressing the switch  32  moves the valve  52  to the on position. (Note that the valve is shown in the off or closed position and is biased to this position.) The weld cycle valve  52  is a contact or maintain valve. In the on position, air is routed through the second line branch  50  to the valve  52 . Air enters the valve  52  and is routed to the weld motor  20 . A line tee  76  from the weld motor line is routed back to the weld cycle valve (at  78 ) to “hold” the valve  52  in the on position. Although the valve  52  is biased to the closed position, the air pressure “holding” the valve  52  open is sufficiently high to overcome the spring force. 
   As air is provided to the weld motor  20 , air is also routed to the weld cylinder  60  (to the top of the piston) to maintain pressure on the piston  34  (which assures that sufficient pressure is applied by the weld element on the strap S). The air is routed to the top of the weld cylinder  60  through a check valve  92 . As set forth above, after welding is complete, the strap S must be allowed sufficient time to cool to assure integrity of the weld. Cool down, which is shown schematically in  FIG. 6 , is accomplish with pressure applied by the weld element on the strap S (by applying pressure via the piston  34 ), without the vibrational motion of the element being imparted. 
   In addition, as air is routed to the piston chamber  60  (weld piston chamber), air also flows through the signal line  72  and the signal valve  70  to in turn open the bleed valve  56  which routes air back to the tension motor  16  to maintain tension (not further tension) in the strap during welding and to signal valve  70  to maintain its open position. 
   At the same time that air is routed to the weld motor  20  and piston chamber  60 , air is directed to a volume chamber or accumulator  80 , through a weld timer  82  and check valve  84  for weld timing. The weld timer  82  is a restriction device such as the illustrated variable orifice. In this manner, air flow into the accumulator  80  is restricted (and thus timed) in that flow through the orifice  82  is limited or restricted. A line  86  from the accumulator  80  is routed to the pilot valve, so that as the pressure in the accumulator  80  increases, air flows to the pilot valve  42 . When the air in the accumulator  80  reaches a predetermined pressure, the pilot valve  42  closes, thus stopping air flow to the weld cycle valve  52 . This stops operation of the weld motor  20 . 
   When air flow is terminated to the weld cycle valve  52 , the pressure exerted to maintain the valve  52  open (through line  78 ) also drops, and the valve  52  returns to the closed position by action of the bias. 
   Referring to  FIG. 6 , the cool down timer  90  maintains pressure on the piston  34  without vibrational motion of the weld element, which is accomplished by isolating air to the weld motor  20  (thus ceasing vibration). The air routed to the top of the weld cylinder  60  is slowly vented from the cylinder  60  by a restricted vent path from the top of the cylinder  60 . The cool down timer includes a check valve  92  in parallel with a restriction device  94  such as a variable orifice. In this manner, although the weld motor  20  has stopped, the pressure exerted by the piston  34  is maintained and is slowly released by the timed venting from the cylinder  60 . In addition, during cool down, the air pressure holding the bleed valve  56  also declines (in a slow, timed manner by action of restricted flow through orifice  94 ) allowing the bleed valve  56  to return to the closed position. This in turn isolates air flow through line  88  to the tension motor  16  and the signal valve  70  which in turn is urged closed. In addition, the volume chamber  80  is vented through seal valve  52  allowing the pilot valve  42  to reset to the open position. 
   One of the advantages of the present system is the “fail-safe” mode of operation seen in  FIG. 7 , in which nothing occurs (that is, no tensioning) when the weld cycle valve  52  is actuated without first actuating the tensioning cycle valve. This also prevents inadvertently actuating the tensioning motor  16  during the weld cycle. 
     FIG. 8  illustrates the cooldown cycle without strap tension (air is isolated from the tension motor  16 ). In this mode, air is isolated from the weld motor  20  and is bled from the piston  60  through orifice  94 . 
   Continuing through the pneumatic circuit, the accumulator  80  is routed to the pilot valve  42  to close the pilot valve  42  when the accumulator  80  is under pressure. The accumulator  80  vents through the weld cycle valve  52  when the valve is in the off position. The pilot valve  42  is maintained in the open position by a line that tees from the tee line to the weld cycle valve. 
   Those skilled in the art will recognize and understand that the various references to “lines”, “vent paths” and the like are provided by a plurality of openings formed, e.g., machined, in the module. 
   All patents referred to herein, are hereby incorporated herein by reference, whether or not specifically do so within the text of this disclosure. 
   In the present disclosure, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular. 
   From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.