Abstract:
In a strapping machine, a device for applying various levels of gripping force to a leading end of a strap during various phases of a strapping cycle is disclosed. A cam having high pressure, reduced pressure, and released pressure surfaces cooperates with an end gripper to grip a strap firmly, loosely, or not at all, depending on the requirements.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     Strap Path Access Apparatus and Method for Strapping Machine 
     Strap Severing and Ejecting Apparatus and Method for Strapping Machine 
     Obstruction Removal Apparatus and Method for Strapping Machine Inertial Strap Tensioning Apparatus and Method for Strapping Machine 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the gripping of a strap end before and during the tensioning phase of a strapping cycle of a strapping machine. 
     More particularly, the present invention relates to multiple gripping force gripping of a strap end before and during the tensioning phase of a strapping cycle of a strapping machine. 
     2. Description of Related Art 
     In the past, strapping machines were capable of exerting a single, generally high level gripping force on the leading end of a strap so as to secure the strap end during the slack removal and tensioning phase, prior to strap sealing, of the strapping machine cycle. However, the application of a high gripping force to the strap end during the rest phase of the strapping cycle, prior to the tensioning phase, increases the difficulty of pulling the strap out of the gripper if necessary, to clear a strap jam, change over the strap, or rewind the strap coil. 
     This and other problems of the prior art are solved by the invention disclosed herein. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide an end gripping device which allows for the easy removal of a leading strap end from the gripping device. 
     It is another object to provide a two force end gripping device which exerts a high gripping force on a leading end of a strap for the tensioning phase of the strapping cycle, and a reduced gripping force for the rest phase of a strapping cycle, prior to the tensioning phase of the cycle. 
     It is a further object to provide a two force end gripping device which exerts a reduced gripping force on a leading end of a strap so as to prevent the strap from bouncing back or rebounding from a sensing lever after contacting the lever. 
     These and other objects of the invention are satisfied by the apparatus and method disclosed herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various other objects, features, and attendant advantages of the present invention will be more fully appreciated from the following detailed description when considered in connection with the accompanying drawings in which like reference characters designate like or corresponding parts throughout the several views, and wherein: 
     FIG. 1 is a sectional view of the present invention in the insertion phase. 
     FIG. 2 is a sectional view of the present invention in the rest phase. 
     FIG. 3 is a sectional view of the present invention in the tensioning phase. 
     FIG. 4 is a side view of a three position cam of the present invention. 
     FIG. 5 is a side view of a four position cam of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Shown in FIG. 1 is the gripping apparatus in the pre-grip or insertion phase of the strapping cycle. An end gripper 1 in communication with a gripper spring 2 is driveable by a force acting on cam bearing 14. Gripper cam 6 is rotatable so as to present various cam surfaces to the cam bearing 14. A gripper tooth 3 may be disposed at a terminal end of the end gripper 1. An anvil 4 is positioned adjacent to the end gripper 1 in a manner which allows a strap leading end 7 to be inserted through a strap path 21 between the anvil 4 and the end gripper 1. The anvil 4 includes an anvil recess 5 which houses a strap limit sensing lever 8. A tooth anvil gap 11 in the anvil 4 receives the gripper tooth 3 during the gripping phase and may receive the gripper tooth 3 partially during the rest phase. The strap separator 12 adjacent the anvil 4 and the end gripper 1 receives the strap in an integral strap path in the separator 12. 
     In FIG. 2, the end gripper 1 is shown in a low or soft grip position, where the strap leading end 7 has travelled to and tripped the limit sensing lever 8. The strapping machine is in a rest phase of the strapping cycle at this point. The gripper cam 6 has at this time been rotated to urge a particular surface of the cam 6 against the cam bearing 14, which moves the end gripper 1 against the strap 7 in a manner which holds the strap 7 in place, but would allow the removal of the strap 7 without the necessity of repositioning the end gripper 1. This gripping mode eliminates the problem of strap recoil or bounce back after contact of the strap leading end 7 with the limit sensing lever 8, by fixing the strap 7 in place immediately at the moment the leading strap end trips the limit sensing lever 8. Also, a machine operator may easily clear strap from the end gripper 1 during this phase, because of the carefully adjusted soft grip condition achieved by the device. This facilitates the procedures of strap jam clearing, strap change over, and strap coil rewinding. 
     FIG. 3 shows the end gripper 1 in the tensioning phase. Gripper cam 6 has been rotated so as to urge a particular surface of the cam 6 against the cam bearing 14, which moves the end gripper 1 against the strap 7 in a manner which holds the strap 7 in a semi-permanent position. Gripper tooth 3 is urged against the strap 7, pushing a segment of the strap 7 into the tooth anvil gap 11 and against the anvil surface of the tooth anvil gap 11, firmly gripping the strap 7 in place. The strap 7 will at this phase remain gripped as the strapping machine executes the tensioning phase. 
     FIG. 4 shows one embodiment of the gripper cam 6. First cam surface 15 is urged against the cam bearing 14 just prior to and during the tensioning phase. Second cam surface 16 is urged against the cam bearing 14 during the strap feeding phase, and third cam surface 17 is urged against the cam beating 14 during the rest or home position phase of the strapping cycle, providing a soft grip condition. 
     FIG. 5 shows another embodiment of the gripper cam 6. Seventh cam surface 22 is urged against the cam bearing 14 during the tensioning phase. Fourth cam surface 18 is urged against the cam bearing 14 during the strap feeding phase. Fifth cam surface 19 is urged against the cam bearing 14 during the period at which the strap 7 must be held in a soft grip condition, for example to briefly prevent the bouncing or rebound of the strap leading 7 end. Subsequently, sixth cam surface 20 is urged against the cam bearing 14, dropping the end gripper 1 to release the grip force. Next, just before and also during the tensioning phase, seventh cam surface 22 is urged against the cam bearing 14. 
     The present invention also encompasses the range of equivalents to which it is entitled, and is to be limited only by the following claims.