Ribbon tension control for a ribbon cartridge

Claim 1

In a serial printer having a platen, a laterally movable carrier for traversing a printing line, printhead means supported on said carrier for impacting with said platen to print characters, ribbon feed means supported on said carrier for feeding an ink ribbon past said printhead means, and a ribbon cartridge supported on said carrier, wherein said ribbon cartridge includes means for rotatably supporting a ribbon supply spool, means for rotatably supporting a ribbon take-up spool and means for transferring said ribbon between said supply spool and said take-up spool; the improved ribbon tension control comprising: a stationary frictional drag means extending radially across and positioned in frictional engagement with all the edges of at least one side of the ribbon positioned on the supply spool, said frictional drag means being of a shape to effect a substantially uniform tension in said ribbon during its transfer, said shape comprising a generally curved section which is coaxial with the ribbon supply spool and a straight-line tapered section extending radially outwardly from the generally curved section and extending approximately to the periphery of the ribbon material on the supply spool, the generally curved section having a width in the radial direction of about 0.16 times the width in the radial direction of the tapered section and said tapered section having a width in the circumferential direction of the spool which decreases by a factor of about 0.5 from its inner extremity to its outer extremity, said generally curved section is positioned against said spool to provide a predetermined area of contact between said spool and said generally curved section regardless of the amount of ribbon remaining on said spool.