Dobby mechanism for looms

Claim 1

A dobby having cams of a varying ratio for looms having heddles and operable at high working speeds, in combination comprising a case, a rotary cam carrying drum in said case and adapted for interchangeably carrying a plurality of independent chain cam driving wheels replaceable with disc cams according to number of repetitions of pattern to be obtained, chain cams driven by said chain cam driving wheels, an idle drum for the rotating chain cams parallel to and spaced apart from said firstmentioned drum, and cam follower means subjected to resilient return means and operatively connected with a lever system for controlling the movement for the heddles of the loom, said dobby also comprising guide means for said idle drum and tension means operating on the latter for positioning at the desired position along said guide means adjusting the tension in said chain cams, each of the chain cams comprising a plurality of composable profile links having rises and dwells corresponding in height to those of said disc cams, said links being pivoted with each other and defining a continuous profile of the chain itself to provide a continuously engaging surface supporting said cam follower means with length thereof depending on the determined waft ratio.