Method and device for feeding a thread to a textile machine with constant tension and constant velocity or quantity

A method for feeding a yarn with constant tension and constant velocity or quantity, to a textile machine the yarn processing point of which is distant from a spool or equivalent support member from which the yarn unwinds, the method comprising

• tension regulator means and first tension measurement means being provided for said yarn measuring this tension and regulating this tension at a predetermined first value prefixed at the commencement of use of the machine,
• said regulator means and said first tension measurement means being connected to control means to define a first control and regulator loop for the feed of the yarn to the textile machine,
• velocity measurement means provided in proximity to the yarn processing point or zone of the textile machine and connected to said control means to define a second control loop (15) measuring and consequently controlling the velocity in proximity to said processing point or zone of the machine at which the yarn is processed,
• said velocity control and measurement by the second control loop being utilized to regulate the yarn feed tension or the fed yarn quantity via the first regulator loop to achieve a desired and prefixed velocity value for the yarn or for the quantity thereof fed at said processing point, with compensation of the friction values to which the yarn is subjected upstream and downstream of the velocity measurement means,
• wherein the yarn feed is controlled at constant tension, then passing to constant velocity feed control mode, during this constant velocity feed control mode the control means acting on the first predetermined tension value for the purpose of making the velocity value measured in proximity to the machine processing point or zone uniform at a prefixed value, said velocity control resulting in the measured value of this velocity being made uniform at the prefixed value.