Weft-braking device for yarn feeders provided with a stationary drum

A weft-braking device for installation on a yarn feeder provided with a stationary drum having a plurality of yarn loops wound thereon which are to be unwound upon request from a downstream machine, comprising:

• a first annular plate coaxially supported in front of a delivery end of the drum, and
• a second annular plate which is coaxially biased against said first annular plate by driving means,
• said yarn being adapted to run between said annular plates to receive a braking action by friction from them,
• wherein said driving means comprise at least one piezoelectric actuator which is a flat, piezoelectric bending actuator deformable by bending in response to a voltage applied thereto and has a movable operative end which is operatively connected to said second annular plate and a stationary operative end which is anchored to a stationary support,
• wherein said piezoelectric actuator has an annular profile and is a multilayer, monolithical-type actuator formed by a plurality of layers made of a piezoelectric material alternated to layers of a conductive material, said layers being bonded to one another by sintering.