1.  Field of the Invention
The present invention relates to a fuser device used with an imaging system for setting toner on a recording media, and more especially to a fuser device which can tension a film based on a control structure. 
2.  Description of Related Art
Fuser devices are used in electronic imaging apparatus such as laser printers, copier and so on for setting toner, which is coated on thermally conductive thin films, on paper under proper pressure at proper temperature. 
Please refer to FIG.  1 illustrating a fuser device for an imaging system disclosed in U.S. Pat.  No.  5,525,775.  The fuser device include a pressure roller 10a, a thin film guiding element 13 and a heater 19 disposed on a bottom of an insulating base 20a.  The thin film guiding element 13 includes a flat-bottom portion 14, a front supporting wall 15 and a rear supporting wall 16.  The front supporting wall 15 and the rear supporting wall 16 extend longitudinally from two ends of the flat-bottom portion 14 respectively and are arc-shaped.  A thermally conductive thin film 21a covers the thin film guiding element 13. 
When printing, the pressure roller 10a turns in the anticlockwise direction and drives the thermally conductive thin film 21a to turn in the clockwise direction, thereby driving paper P to pass through the fuser area between the heater 19 and the pressure roller 10a.  The heater 19 gives out heat and transfers the heat to the paper P and the toner Ta through the thermally conductive thin film 21a after electrodes (not shown) of the heater 19 are electrified.  Under the influence of the heat and the pressure from the pressure roll 10a, the toner Ta melts to be set on the paper P.
In the course of printing, the thermally conductive thin film 21a contacts with the front supporting wall 15 in an area B. The contact in the large area causes the wear of the thermally conductive thin film 21a relative to the thin film guiding element 13. 
Additionally, the thermally conductive thin film 21a is affected by the tensile force only in the area A and the area B, and is in the tension relaxation state in the other areas.  Since the tensile force on the thermally conductive thin film 21a varies, the movement of the thermally conductive thin film 21a is unstable, so that the portion of the thermally conductive thin film 21a which contacts with the paper P has unstable dynamic characteristics when it enters and leaves the fuser area, which affects the set quality of the toner.  Also, the contact force between the thermally conductive thin film 21a and the thin film guiding element 13 is unstable, so the thermally conductive thin film 21a and the thin film guiding element 13 collide with each other, thereby their wear increases.