Tensioning apparatus for pliable material

Claim 1

APPARATUS FOR APPLYING AND MAINTAINING UNIFORM TENSION IN A MOVING PLIABLE MATERIAL COMPRISING A DEVICE FOR APPLYING FRICTIONAL RESISTANCE TO THE MOVEMENT OF SAID MATERIAL THERETHROUGH, SAID DEVICE INCLUDING MEANS ENGAGING SUBSTANTIALLY OPPOSITE SIDES OF THE MATERIAL IN A SUCCESSION OF SPACED POINTS ALONG ITS PATH OF TRAVEL AND CAUSING THE MATERIAL TO MOVE IN A TORTUOUS PATH, FLUID-PRESSUREOPERATED MEANS INCLUDING A FIRST BLEED-OFF VALVE OPERATIVELY CONNECTED TO SAID ENGAGING MEANS FOR VARYING THE TORTUOSITY OF THE MATERIAL TO VARY PROPORTIONALLY THE FRICTIONAL RESISTANCE APPLIED TO THE MATERIAL, A MOVABLE SENSING ELEMENT ENGAGING AND FORMING A LOOP IN SAID MATERIAL AFTER IT PASSES SAID DEVICE, MEANS FOR APPLYING A PREDETERMINED CONTROL FLUID PRESSURE TO SAID FLUID-PRESSURE-OPERATED MEANS SUCH AS TO CAUSE SAID ENGAGING MEANS TO EFFECT SUCH TORTUOSITY IN THE MATERIAL THAT THE FRICTIONAL RESISTANCE SO APPLIED TO THE MATERIAL INDUCES AN OPTIMUM TENSION THEREIN, AND MEANS INCLUDING A SECOND BLEED-OFF VALVE RESPONSIVE TO MOVEMENT OF SAID SENSING ELEMENT RELATIVE TO AN OPTIMUM POSITION AT WHICH SAID OPTIMUM TENSION EXISTS IN THE MATERIAL FOR CORRESPONDINGLY VARYING THE EXTENT OF BLEED-OFF OF PRESSURE BY SAID FIRST BLEED-OFF VALVE AND TO VARY THE PRESSURE IN SAID FLUID-PRESSURE-OPERATED MEANS WITH RESPECT TO SAID CONTROL FLUID PRESSURE.