Abstract:
A strapping head having a feed unit for advancing a strap downstream and tensioning the strap around an object to be strapped and a crimp unit downstream of the feed unit for crimping two sections of the strap to each other has for each of the units an electric drive motor. In addition the head is provided with an electronic programmable controller connected to both of the units for operating same in accordance with a resettable program.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to copending provisional application 61/431,465 filed 11 Jan. 2011. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a strapping head. More particularly this invention concerns a device for securing a loop of strap around a workpiece, for instance a coil of steel wire or a bundle of steel bars. 
       BACKGROUND OF THE INVENTION 
       [0003]    Strapping machines in the steel industry are typically used to strap coils and bundles of bar materials. Coils are typically formed on a wire rod mill and are then compacted in a compactor machine and then strapped as part of this process; the heads are incorporated in to this machine. Bar Bundles are generally processed through a cooling bed and then collected in a bundle area to be strapped together in predetermined bundle weights. 
         [0004]    Typically these two types of machine use very different strapping technology and thus strapping heads, the compactor strapping head can be very complex, incorporating various custom hydraulic manifolds and cylinders. The bundle heads are typically somewhat less complex due to the simpler requirements of the bundling area. 
         [0005]    Both types of strapping head rely on hydraulic and pneumatic media and feedback from proximity sensors to determine if the commands given are carried out and the strapping sequence has been completed. Thus these machines can be considered dumb or open-loop systems as they cannot make adjustments themselves and must report to an off machine programmed logic controller (PLC) to control them. 
         [0006]    Furthermore, no adjustment for operating conditions can be made by the operator either without dismantling the machine and refurbishing it in a workshop. 
       OBJECTS OF THE INVENTION 
       [0007]    It is therefore an object of the present invention to provide an improved strapping head for sheet-steel coils or steel bars. 
         [0008]    Another object is the provision of such an improved strapping head for sheet-steel coils or steel bars that overcomes the above-given disadvantages, in particular that addresses the problems above. 
       SUMMARY OF THE INVENTION 
       [0009]    A strapping head having a feed unit for advancing a strap downstream and tensioning the strap around an object to be strapped and a crimp unit downstream of the feed unit for crimping two sections of the strap to each other has according to the invention for each of the units an electric drive motor. In addition the head is provided with an electronic programmable controller connected to both of the units for operating same in accordance with a resettable program. 
         [0010]    In accordance with the invention each of the motors has its own respective such electronic controller. Furthermore according to the invention the head has a clamping unit for arresting the strap during crimping by the crimper. The clamping means or unit having its own electric drive motor. 
         [0011]    With this system, because of the on-board intelligence, the heads themselves hold the programming to complete the process. They do not rely on the outside control of a PLC, and each motion within in the head handshakes with the next until the process is complete. If a motion is not complete the head captures this and restarts the process until it is completed, or switches to a manual mode so that an operator can trouble shoot the system and complete the actions manually. 
         [0012]    Each part of the overall process is the responsibility of a respective movement controller coupled to an actuator, and each movement controller controls only the movements required for the defined process and tells the next controller via a handshake signal that the movements are complete. If the handshake is not complete the controller tries again or switches to manual and alerts the operator that there is an issue with the particular motion or part of the process. 
         [0013]    The prior-art heads controlled via hydraulic media can not do this and the operator has no way of knowing what is wrong in the process and the whole sequence must be started again, or the strap scraped and the whole binding process started again. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0014]    The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which: 
           [0015]      FIGS. 1 ,  2 , and  3  are perspective views from different angles of the strapping head according to the invention; 
           [0016]      FIG. 4  is a section taken through the crimper of the head as shown by line IV-IV of  FIG. 6 ; 
           [0017]      FIG. 5  is a section taken through the clamp of the head as shown by line V-V of  FIG. 6 ; and 
           [0018]      FIG. 6  is a longitudinal section through the head taken along line VI-VI of  FIGS. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    As seen in  FIGS. 1 ,  2 ,  3 , and  6 , the apparatus of this invention basically comprises a feeder FE, a guide GU, a crimper CR ( FIG. 4 ), and a clamp CL ( FIG. 5 ). 
         [0020]    The feeder FE at the upstream end of the strapping head has a master controller  1  that holds the master program and that is used for handshaking with all the other below-mentioned movement controllers. It also controls the pinch of the unillustrated strap fed in from the left in  FIGS. 1 ,  2 , and  6 . 
         [0021]    Furthermore the feeder FE has an electric hybrid stepping motor  2  whose torque and angular position is controlled by the master controller  1  and that is connected to a multiscrew actuator  3 . A movement controller  6  reporting to the master controller  1  is effective via another hybrid stepping motor  5  to a lower pinch roller  8  cooperating with an upper pinch roller  7  to advance the unillustrated strap downstream through a guide track  9  of the guide GU. 
         [0022]    At the downstream end the clamp CL has a movement controller  10  and a hybrid stepping motor  11  effective through a multiscrew actuator  12  on movable clamp jaws  13  cooperating with a clamp anvil  15 . 
         [0023]    The crimper CR downstream of the clamp CL has a movement controller  15  reporting like the movement controllers  6  and  10  to the master controller  1  and effective through another hybrid motor  16  and multiscrew actuator  17  on binding/cutting jaws  19  cooperating and forming a quick-release coupling  20  with an anvil  18  on a mount  29 . The coupling  20  has pivot shafts  21  extending between a front plate  30  and back plate  31 . 
         [0024]    Other movement controllers  22  for secondary crimp are connected through their own hybrid stepping motors  23  and multiscrew actuators  24  to crimp jaws  25 . A quick-release pin  26  and a crimp slide block  27  are connected via crimp links  28 . Similarly clamp links  32  are connected to a clamp link block. 
         [0025]    Due to the onboard intelligence and the configuration of the movement controllers, it is possible for the process to be tailored to individual strapping processes. This makes the system easy to adapt to different processes. 
         [0026]    The use of this configuration of movement controllers makes it possible for the crimp/binding depth to be easily reset. This important for two distinct reasons. 
         [0027]    1. Binding strength: The shallower the deformations in the strap the stronger the joint. For example with a 3 mm indentation/perforation the strength of the binding can be as high as 92% of the parent material. With a indentation/perforation of 3.5 mm the strength reduces to 88% of the parent material. This has been proved with actual binding samples tested to destruction. 
         [0028]    2. Jaw wear: The jaws wear over time and eventually will not bind the material. With a conventional head there is no way to compensate for this. But with the use of individual movement controllers the travel of the jaw stack can be increased to compensate for jaw wear thus increasing the usable time of the machine between rebuilds. 
         [0029]    This adjustability is also carried through to the strap feed pinch roll. Strap feed speeds, strap tension torque and strap pinch forces are all variable. This allows the machine to operate with various different strap media without significant adjustments to valves flow control and pressure control. All of the above items are infinitely variable, within the desired operating range. 
         [0030]    Since the heads incorporate their own on board intelligence and movement controllers there is no need for an external control structure. This allows the strapping head to be incorporated into any strapping process be it coil, bar or other. The only signals required to make the head operate in any process architecture are a go signal from the machine they are incorporated into. Thus the heads return a complete signal when the process is complete or an error signal when the heads switch to manual mode. 
         [0031]    The mechanical features of the machine are similar to the current state of the art strapping heads available on the market with the following differences: 
         [0032]    1. Quick release Jaw stack: There is no need to strip the machine in order to replace the jaw stack and anvil. This can now be completed with the strapping head in place on the compactor or bundling machine. 
         [0033]    2. Removal of oil from the coil and bars being strapped. 
         [0034]    3. Reduced maintenance and operator intervention. 
         [0035]    4. Jaw design for wear compensation. 
         [0036]    The machine functions as follows: 
         [0037]    The master movement controller  1  located on the strap pinch axis holds the overall program sequence. The master movement controller  1  then handshakes with the other movement controllers  6 ,  10 , and  15  in the desired sequence. Each movement controller  6 ,  10 , and  15  contains the parameters needed for its move or operation and then handshakes back to the master controller  1  to confirm the moves completeness or error function. If there is an error function the master controller  1  resets the sequence and it is tried again. If this fails the master controller  1  switches to manual mode and alerts the external operating system of the machine it is incorporated into that manual moves are required. 
         [0038]    At the start of a cycle a ready signal given to an external operating system and a remote I/O is given to start sequence from the external system. 
         [0039]    The pinch then is closed by the master movement controller  1  and the strap is fed around the external guide track by the feed unit movement controller  4 . The length of strap is determined by step counts or en external switch dependent on the application. 
         [0040]    As the strap is fed the main crimp axis movement controller  15  closes the crimp jaws 50% to aid in guiding the strap by the movement controller  15 . On completion of strap feeding the clamp is closed via the movement controller  10 . The strap is then tensioned pulled in reverse until controller  6  attached to the lower roller  8  detects a stall condition at full torque or a specified torque value. 
         [0041]    At this stage the main crimp and cut movement controller is actuated by the controller  15 . This action then creates the crimp and cuts the strap from the main reel, in that sequence but from the same axis. At this time the tension motor  5  stops pulling the strap as the crimp movement controller tells the movement controller  6  at the pinch rolls  7  and  8  to stop. Once the tension motor  6  stops, the secondary crimps are actuated by the movement controller  22 . 
         [0042]    On completion of this action all movement controllers  6 ,  10 , and  15  return to the home position, but not the master controller  1 . Instead the master controller  1  then relays a signal to the external system that the process is complete and any other external actions can be completed as required. 
         [0043]    This sequence of operations is different from the current state of the art hydraulic heads as they signal a dumb relay solenoid and rely on a dumb proximity switch to signal a process is complete. Instead, the head according to the invention continuously monitors position, torque, and current and thus can be deliver real-time feed back to the master controller  1  as needed to ensure the process is completed correctly without the use of an external PLC system or extra external hardware. 
         [0044]    Thus this system with its intelligent platform or architecture, is fully adjustably configurable without mechanical intervention or disassembly. It can run without the use of external PLC controllers, and the head is interchangeable with any platform. The head can compensate for jaw wear without mechanical intervention. It can also vary binding strength based on indentation crimp depth our competitors can not it is a fixed variable for each crimp. 
         [0045]    The operation cycle for the machine resides in the machine itself so there is no need for an external PLC to control the head and or heads if working in unison. Each movement controller informs the next that its task is complete within the head without the need for external I/O or PLC interaction in the process. Furthermore the machine process can be changed without manual intervention or physically altering the machine by shimming or adjusting mechanical parts. The removal of all hydraulic and pneumatic consumable media from the working area greatly simplifies its hookup and servicing. Furthermore the machine can be adapted into any existing strapping process or machine without having to re-configure the existing control architecture or PLC logic. 
         [0046]    A final advantage of the inventive system is reduced energy consumption as no hydraulic media power pack required to feed the heads. In fact, the head consume on average 1.5 kW total power during operation compared to 5-10 kW for the hydraulic prior-art equivalents.