Adjustable drive mechanism

An adjustable drive mechanism for reciprocating a pair of sealing jaws in a packaging apparatus and controlling the stroke length includes a drive belt operatively connected to move the carriage and jaws in the up and down direction. A movable pulley assembly interconnects the drive belt ends and is attached to a working arm oscillated by a linkage arrangement. The linkage arrangement includes a rocker oscillated with a crank and connecting rod. A control link pivotally connected to the rocker completes the linkage and deflects to allow raising of the working arm and driving the sealing jaws on a downward draw stroke. The upper end of the control link constitutes an adjustable pivot to vary the degree of movement imparted by the working arm to the drive belt. The adjustable pivot is carried by an annular adjustment ring mounted within an annular guide groove of a mounting plate. A control rod is provided to rotate the ring in the guide groove to selectively reposition the movable pivot for adjusting the stroke length while the apparatus is operating without affecting the home position of the sealing jaws.