Device for preventing overheating of electrophotographic fixing device

DETAILED DESCRIPTION OF THE DRAWINGS FIG.
1 is a perspective view of a thermal fusing device for use in a xerographic reproducing apparatus to affix powder images to a substrate such as plain paper; FIG.
2 is a cross-sectional view of the thermal fusing device illustrated in FIG.
1 and taken on the line II-II thereof; and FIG.
3 illustrates a control circuit for the fusing device illustrated in FIG.
1.
DETAILED DESCRIPTION OF THE INVENTION For a general understanding of the operation of a xerographic reproducing apparatus in which the fusing device is incorporated, reference may be had to U.
S.
Pat.
No.
3,612,820 wherein there is disclosed the various system components of such an apparatus.
In the apparatus illustrated in the aforementioned patent, a light image of a document to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon.
Thereafter, the latent image is developed with an oppositely charged developing material to form a xerographic powder image corresponding to the latent image on the plate surface.
The powder image is then electrostatically transferred to a support surface to which it is fused whereby the powder is caused to permanently adhere to the support surface, which surface usually comprises plain paper.
In such an apparatus, an original to be copied is placed upon a transparent support platen fixedly arranged in an illumination assembly and image rays are projected by means of an optical system for exposing the photosensitive surface of a xerographic plate often in the form of a drum.
The drum is mounted upon the frame of the machine and is adapted to rotate in one direction at a constant rate.
During this movement of the drum, it passes a charging station where a uniform electrostatic charge is applied to the surface thereof.
Next at an exposure station, exposure of the drum surface to the light image discharges the xerographic plate in the areas struck by light, whereby there remains on the surface a latent electrostatic image in image configuration corresponding to the light image projected from the original on the supporting platen