Controlled system for supplying weft yarn in a loom, comprising supply control means of the weft yarn, unwinding means (1) of the weft yarn wound on a reel, measuring and accumulating means (2) of anunwound section of length of the weft yarn comprising first sliding means (21) adapted to deviate the weft yarn with respect to second sliding means (22), further measuring and accumulating means (3,4) of an unwound section of length of the weft yarn, connected to a drive (100, 200, 300) controlled by the supply control means of the weft yarn, said further measuring and accumulating means (3, 4)comprising oscillating means (30, 40), in strict relationship with the motion of said unwinding means (1) and in strict relationship with the motion of the inserting means of the weft in the pitch, said oscillating means (30, 40) comprising at least one oscillating arm (31, 41) with respect tod a rotation axis, said at least one oscillating arm (31, 41) comprising third sliding means (32, 42) adapted to allow deviating the weft yarn with respect to fourth sliding means (33, 43), said at least one oscillating arm (31, 41) is connected to a motor which moves approximately with a constant torque.