There are a number of U.S. patents that disclose electronic apparatus for printing indicia on labels, some of these are restricted to hand held units and others that disclose tabletop units. Hand held label printers, such as disclosed in U.S. Pat. No. 6,113,293, and tabletop printers, such as disclosed in U.S. Pat. Nos. 6,266,075 and 5,078,523, include the same general combination of elements, a print head, means for feeding label media to be printed past the print head, a microprocessor, a read only memory programmed with appropriate instructions to operate the microprocessor, a random access memory, a keyboard with letter, number, and function keys for the entry of alphanumeric information and instructions concerning the indicia to be printed, and a visual display such as a light emitting diode (LED) or liquid crystal display (LCD) unit to assist the operator in using the printer. In a hand held printer, these components may all be enclosed in a single housing.
The label media comprises a series of labels that are attached to a carrier strip. The carrier strip is fed through the printer and legends, alphanumeric characters, and other indicia, are printed on the labels. The labels are then removed from the carrier and attached to the objects needing identification. As there are many types of label applications, there are many combinations of labels and carrier strips that provide labels of varying sizes, colors and formats.
A particular type of print head employs thermal transfer printing technology. Thermal transfer printing uses a heat generating print head to transfer a pigment, such as wax, carbon black, or the like, from a thermal transfer ribbon to a label media. By using digital technology, characters are formed by energizing a sequence of pixels on the print head which in turn melts the wax or other pigment on the ink ribbon transferring the image to the label media.
In a known thermal transfer printer such as a label printer, label media and ink ribbon are simultaneously fed past the print head by a platen roller in an overlay relationship between the print head and the platen roller. The platen roller is rotatably driven by a drive mechanism that may also rotatably drive ink ribbon take up and supply spools to maintain tension in the ink ribbon.
In a cartridge-based printing system, such as disclosed in U.S. Pat. No. 6,113,293, it is desirable to have a consistent label media path. In order to accomplish this, many cartridge-based printing systems have the label media path defined by a point tangent to the outside diameter of a roll of label media, such as a label media drive roller. This method, however, presents a problem as the label media is consumed. In particular, as the label media is consumed the diameter of the roll decreases and the beginning point of the label media path changes.
This problem is solved by pivotally mounting the label media, such that as the diameter of the label media decreases, the label media pivots to maintain the label media in contact with the label media drive roller. Unfortunately, as the label media is jostled or jarred, the label media can lose contact with the label media drive roller and retract into the cartridge. As a result, the end of the label media may be difficult to retrieve from the cartridge for use. Accordingly, a need exists for an improved printer cartridge that can carry label media that remains in contact with a label media drive roller even when jarred or jostled.