Importance

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Abstract

An apparatus for printing graphic images on sheet material has a thermal print head with a linear array of heating elements pressed into engagement with an ink web overlying the sheet material on a platen. The platen extends in the lengthwise direction of the print head across the width of the sheet material, and is rotatably driven to in turn drive the sheet material with the ink web relative to the print head. A removable cassette having a predetermined length of ink web bearing a printing ink is mounted adjacent to the print head with the ink web interposed between the sheet material and the print head for printing the graphic images on the sheet. A supply spool carrying the ink web is rotatably mounted in the cassette, and a take-up spool is also rotatably mounted in the cassette for receiving the ink web from the supply spool upon passage between the platen and print head. The take-up spool defines a first overall diameter without receiving the ink web from the supply spool, and a greater second overall diameter upon receiving the predetermined length of ink web, wherein the second overall diameter is no more than 10% greater than the first overall diameter. A spring-wrapped clutch is drivingly connected between a take-up motor and the take-up spool to impart a constant torque to the take-up spool for winding the ink web onto the spool during printing operations and to thereby maintain a substantially constant tension within the ink web.

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First Claim