Yarn supply apparatus with electronic yarn tension control, particularly for knitting machines having rapidly varying yarn supply requirements

Yarn supply apparatus for a yarn utilization textile machine, particularly for knitting machine, with electronic yarn tension control, having

• a rotatable yarn supply means (5,152) supplying yarn under essentially slipless conditions;
• a drive motor (3) rotatably coupled to the yarn supply means, and operating under respectively steady state and transient operating conditions, including starting, acceleration, retarding and stopping;
• variable frequency generating means (54,55,56) coupled to the motor and supplying the motor with power at variable frequency in which the frequency controls the operating speed and condition of the motor;
• yarn tension sensing means (20,21,28) coupled to the yarn at a position between the yarn supply means and the yarn utilization textile machine, said yarn tension sensing means providing an electrical tension signal representative of yarn tension;
• and
• a control unit (52) coupled to receive the tension signal and providing an output signal controlling the variable frequency generating means to provide power to the motor at the frequency at which the yarn tension has a predetermined command value,
• and comprising in accordance with the invention
• yarn reserve forming means (15,16,19) located in the path of the yarn from the yarn supply means to the utilization machine,
• said yarn reserve forming means having a yarn capacity sufficient to supply yarn from said yarn reserve under starting conditions of the motor (3) and before the motor has reached the speed in which, under control of said command value, it can supply yarn at said tension command value;
• yarn reserve sensing means (28,52) controlling said motor (3) to reestablish a predetermined yarn reserve in the yarn reserve forming means after change of yarn reserve from said predetermined reserve upon a transient operating condition of the motor;
• and
• circuit means (63,64) forming part of said control unit (52) limiting the rate of change of control of the variable frequency generating means, at least under starting condition of the motor (3), to a rate at which the motor, with the yarn supply means (5,152) coupled thereto, can operate in synchronism with the frequency of the supply power to thereby remain in step with said frequency.