Improved Method and Device for Feeding a Yarn or Thread to a Processing Machine with Constant Tension and Velocity

A method for feeding a plurality of yarns or threads to a textile machine, each yarn being respectively fed by a respective device comprising

• a rotary member,
• a sensor member,
• means for unwinding said yarn from a bobbin and entering into cooperation with the rotary member and then with the sensor member arranged to verify the tension with which the yarn is fed to and/or withdrawn by the processing machine,
• means for monitoring of the rotational velocity of the rotary member, this rotary member being driven by its own actuator and feeding the measured tension and measured velocity data being fed to a control unit which controls the yarn feed to the machine;
• wherein each yarn is fed through each respective device by a method comprising,
• unwinding the yarn from the bobbin,
• bringing the yarn into cooperation with the rotary member and directing the yarn from the rotary member to the sensor member arranged to verify the tension with which the yarn is fed to and/or withdrawn by the processing machine, with monitoring of the rotational velocity of the rotary member and hence of the feed to the machine,
• the rotary member being driven by its own actuator,
• the measured tension and measured velocity data being fed to the control unit which controls the yarn feed to the machine,
• wherein there is continuous tension control by the control unit to maintain the tension at least within a range of constant values;
• wherein if this tension condition is verified, then the yarn feed velocity is controlled and hence the yarn quantity or length fed to the machine is controlled to maintain the yarn feed velocity constant and equal to a self-determined or predefined and programmable value;
• wherein while the velocity is maintained constant, the tension value is continuously checked to verify whether the tension value remains within a range of constant values and, this control of the yarn feed to the processing machine at constant tension and constant velocity being effected either with or without synchronization with the machine, whenever the tension assumes a value outside this range, the tension is subjected to a new control procedure to return the tension to within the range of constant values, the control procedure being again followed by controlling the velocity to maintain the velocity constant;
• wherein the value of the yarn length absorbed by said devices which feed said yarns or threads is made uniform for at least part of these yarns or threads at the same value.