Shedding drive arrangement

A shedding drive arrangement having a dobby driving the upper and lower sheds symmetrically and with a coupling arrangement, coupling jack levers of the dobby with the heald frames, the coupling arrangement comprising first and second arms, each jack lever having a first arm and a second arm operatively connected with it, the second arm being pivotably mounted at one end about a stationary pivot and at its other end secured by means of a second pivot in pivotable manner to one end of the first arm, the other end of said first arm being pivoted to and driven by means of said associated jack lever, said jack lever, when in motion, producing a reciprocating movement which is carried out over a predetermined distance, said movement producing at the first arm a force directed in the longitudinal direction of the said first arm and by which there is brought about a movement of the said end of the first arm that is connected to said second arm, which is unsymmetrical in relation to that position of the said one end of the first arm in which the plane defined by the axis of the second pivot and by the longitudinal direction of the first arm is in a tangential situation at the locus of the axis of the second pivot relative to the said stationary pivot.