Key coupling device for high-speed rotary dobbies

A control device for a high-speed rotary dobby comprising a main crank arm which has a small end hinged to a main lever of the dobby and a big end mounted idly on a drive shaft driven with intermittent motion with pauses at every 180.degree. of rotation by a modulation mechanism via a cam which is rigidly connected alternately to said crank arm or to said shaft by a key which is housed in a radial groove in said cam and an end of said key during said pauses in the drive shaft is inserted into or is maintained inserted in one of two opposing radial grooves in said big end of the main crank arm or one of two opposing radial grooves in said drive shaft, in accordance with instructions of a programmer, by a control ring coaxial to said shaft, said ring cooperating with walls of a transverse groove in the key, wherein said transverse groove in the key has a width equal to the sum of the thickness of said control ring and length of travel undergone by the key in its insertion into or withdrawal from said radial grooves, said control ring being of elliptical shape with its major axis positioned along an axis of said opposing radial grooves in said big end of the main crank arm and fixed onto an operating lever the fulcrum of which lies on a prolongation of the minor axis of said elliptical control ring, said operating lever cooperating with a V-shaped spring which has ends of its two arms inserted in a cavity facing the lever fulcrum and provided in the body of the lever, and which is mounted preloaded between two fixed shoulders positioned symmetrically about an axis of symmetry of said spring, which passes through said fulcrum of said operating lever, this latter comprising a second cavity opposite the preceding cavity and cooperating with a slide to which there is hinged a lower end of a sector which rocks symmetrically about said axis of symmetry of the V-shaped spring, said sector comprising in its upper part two valleys arranged symmetrically about said axis of symmetry of the V-shaped spring and cooperating with a lower end of an overlying pusher rod which is hinged at its upper end to an arm projecting from a shaft made to rock by a control mechanism synchronized with said modulation mechanism, said overlying pusher rod is slidingly inserted between two pins of a needle selector which cooperates with a port of the programmer by the action of a thrust spring and a return extractor comb made to rock by a second control mechanism and also synchronized with said modulation device.