The present invention relates to a mechanism for adjusting tension of an inked ribbon of a printer.
The thermal printer which produces printed impressions by using an inked ribbon is well known.
There are two tension applying mechanisms, one of which is provided for applying a back tension to a feeding ribbon, and the other is provided for applying a winding-up tension. The value of the tension applied to the ribbon has influence on the quality of the printing.
When the tension is too low, the ribbon wrinkles, causing printer failures in dots.
If the tension is too high, the ribbon slips and can not be fed.
Japanese Patent Application Laid Open 7-89172 discloses a mechanism for controlling tension applied to an inked ribbon to a constant value by detecting the fluctuation of the tension of the inked ribbon which is caused by the change of diameter of the rolled ribbon during the printing operation.
In the conventional system, there must be provided a sensor for detecting the ribbon tension, and tension adjusting driving mechanisms in both of the ribbon feeding side and ribbon winding-up side. Consequently, the system becomes complicated in construction.