Apparatus for controlling the tension in a flexible material as it is being wound onto or unwound from a drum

Claim 1

A LAPPING HEAD FOR APPLYING A FLEXIBLE INSULATING TAPE TO AN ELECTRIC CONDUCTOR COMPRISING (A) MEANS FOR ROTATING A PAD OF SAID TAPE AROUND SAID CONDUCTOR, (B) MEANS FOR GUIDING SAID TAPE FROM THE PAD ON TO THE CONDUCTOR, AND (C) A REVERSIBLE ELECTRIC MOTOR COUPLED TO THE PAD IN SUCH A WAY AS TO DRIVE THE PAD, (D) A SENSING DEVICE RESPONSIVE TO CHANGES IN TENSION OF THE INSULATING TAPE IN ITS PATH BETWEEN THE PAD AND THE CONDUCTOR, (E) A VARIABLE RESISTANCE COUPLED TO THE SENSING DEVICE IN SUCH A WAY THAT VARIATIONS IN THE RESPONSE OF SAID DEVICE VARY THE VALUE OF THE RESISTANCE, (F) A MULTI-STAGE HIGH GAIN D.C. AMPLIFIER CONSISTING ESSENTIALLY OF A SUCCESSION OF TRANSISTOR AMPLIFYING STAGES CONNECTED IN CASCADE HAVING THE VARIABLE RESISTANCE IN THE INPUT CIRCUIT OF THE LAST OF SAID STAGES AND HAVING THE OUTPUT CIRCUIT OF THE LAST OF SAID STAGES CONNECTED TO THE REVERSIBLE MOTOR TO SUPPLY SUBSTANTIALLY THE WHOLE CURRENT FOR AT LEAST ONE ELEMENT OF THE MOTOR, THE ELEMENTS CONSISTING OF THE ARMATURE AND FIELD, TO DRIVE THE MOTOR IN ONE DIRECTION WHEN THE VARIABLE RESISTANCE IS ABOVE A PREDETERMINED VALUE AND IN THE REVERSE DIRECTION WHEN IT IS BELOW SAID VALUE, WITH A TORQUE DEPENDENT ON THE VALUE OF SAID RESISTANCE, AND (G) A RESISTANCE/CAPACITANCE STABILISATION NETWORK, DESIGNED TO INHIBIT HUNTING IN THE SYSTEM, CONNECTED IN THE INPUT CIRCUIT OF THE FIRST OF SAID AMPLIFIER STAGES.