1. Field of the Invention
This invention relates to a non-impact printer and more specifically to a thermal printer.
2. Description of the Prior Art
Alignment of the thermal printhead and the application of even pressure forcing the printhead to print on the print medium has been a problem in the prior art. Exacting tolerances have been required for the printhead and for the printhead's positioning on the heat sink bracket, and also with respect to the printhead carriage for moving the printhead across the print medium.
A common prior art mechanism for forcing the printhead against the print medium is a spring, secured at opposite sides of the print medium, the spring positioned to force the printhead against the print medium. However, the force applied at the outer edges of the print medium is different from the force applied at, for example, the center of the print medium. This uneven force results in uneven printing.
This inventive printer overcomes these shortcomings by providing an adjustment for moving the supporting bracket, and the printhead, relative to the printhead carriage and relative, vertically, to the print medium. This adjusting mechanism enables much looser tolerances than in the prior art.
To apply even pressure to the printhead in its entire traverse of the print medium, a torsion spring has been positioned to bear against the printhead carriage and the bracket to force the bracket in a direction toward the print medium, thereby causing the printhead to contact the print medium at a constant force throughout its traverse. The spring tension is selected to apply the desired force of the printhead against the print medium.