Tension sensing mechanism for strapping tool

A tension sensing mechanism for a strapping tool for tensioning a loop of strapping having first and second strap portions about an article, said tool having a frame and tensioning means supported from said frame for engaging said first strap portion and effective when operated for drawing said first strap portion relative to the second strap portion to progressively constrict and tension the loop, said tension sensing mechanism comprising:

• means for gripping said second strap portion and restraining it from movement relative to said frame and said first strap portion;
• a first arm pivotally mounted to said frame for pivoting movement in a first direction and in a second, opposite direction;
• first biasing means for biasing said first arm in said first direction;
• a second arm pivotally mounted on said first arm for pivoting movement in the first and second directions away from and towards said strap portions, respectively;
• second biasing means for biasing said second arm in said second direction;
• said tensioning means connected with said second arm on said first arm for being pivoted with said second arm to engage said first strap portion and for being operated to tension the loop when said second strap portion is restrained by said gripping means whereby, at a predetermined tension level, the loop tension reaction force transmitted from said second arm to said first arm urges said first arm to overcome said first biasing means and pivot relative to said frame in said second direction;
• and
• control means responsive to the pivoting movement of said first arm in said second direction for terminating the operation of said tensioning means at the predetermined loop tension level.