Variable pitch cyclindrical cam mechanism for controlling the motion of a weft insertion member

An apparatus for controlling the motion of a weft insertion member in a shuttleless loom comprising:

• a multiple-threaded variable pitch cylindrical cam, adapted to be secured to the weft insertion member, said multiple-threaded variable pitch cylindrical cam being a triple-threaded variable pitch cylindrical cam;
• a slider having a plurality pairs of frustoconical rollers by which said slider is drivingly engaged to said multiple-threaded variable pitch cylindrical cam with each pair of said frustoconical rollers engaged to each thread of said multiple-threaded variable pitch cylindrical cam, each roller having an angle of inclination formed whereby the profile of each thread of said variable cylindrical cam is in a conjugate relation with the surface of each pair of said frustoconical rollers to obtain smooth transmission from rectilinear reciprocating motion of said slider to rotary reciprocating motion of said variable pitch cylindrical cam, said plurality pairs of frustoconical rollers being three pairs of frustoconical rollers;
• three roller seats adapted to receive six frustoconical rollers of said three pairs of frustoconical rollers mounted on the slider, wherein said six frustoconical rollers are divided into three groups, each group having two frustoconical rollers, and wherein each group of two frustoconical rollers is rotatably received by one roller seat and is located between two adjacent threads of said triple-threaded variable pitch cylindrical cam with a different one of the two frustoconical rollers contacting said different one of the two adjacent threads whereby said three pairs of frustoconical rollers are formed with each pair of frustoconical rollers constituted by two frustoconical rollers from two different groups of said three groups of two frustoconical rollers;
• and
• three needle bearings for connecting said three roller seats to said slider, said needle bearings providing a rotary degree of freedom between said roller seats and said slider whereby one of the two frustoconical rollers received by said roller seat will intimately contact one thread of said two adjacent threads when the other of the two frustoconical rollers received by the same roller seat is forced to drivingly engage to the other thread of said two adjacent threads of said triple-threaded variable pitch cylindrical cam, and whereby the frustoconical rollers will be in immediate contact with the threads at the moment when the motion of the slider is reversed, thereby eliminating any backlash that may exist between said cylindrical cam and said frustoconical rollers in the reciprocating motion of said slider.