Driving device and image forming apparatus

[0030]First Embodiment of the present invention will be described with reference to FIGS. 1 to 8. First, an image forming apparatus in this embodiment will be described with reference to FIG. 1. Incidentally, as the image forming apparatus to which the present invention is applicable, in addition to an electrophotographic image forming apparatus, those of a plurality of types including, e.g., an offset print type, an ink jet type, and the like. Of these types, an image forming apparatus 1 shown in FIG. 1 is a color image forming apparatus of the electrophotographic type. Further, the image forming apparatus 1 is a so-called intermediary transfer and tandem type image forming apparatus in which image forming portions 2 for four colors of yellow (Y), magenta (M), cyan (C) and black (Bk) are disposed side by side on an intermediary transfer belt 3 as an image bearing member. Such an image forming apparatus has gone mainstream in recent years from the viewpoint of excellence in thick paper

[0062]Second Embodiment of the present invention will be described with reference to FIGS. 10, 11, 12(a) and 12(b). In this embodiment, a flywheel 44 which is an inertial member is fixed on the rotation shaft 31c of the follower gear 31. Other constitutions and functions are similar to those in the above-described First Embodiment, thus being omitted from detailed description. Generally, it has been known that an inertial effect of the inertial member having the same weight and the same radius is achieved as the square of the rotational speed ratio. For this reason, by mounting the flywheel 44 on the follower gear 31 rotating at the speed higher than that of the photosensitive member gear 30 as in this embodiment, a sufficient inertial effect can be obtained even when the flywheel 44 has a small diameter.

[0063]Further, in this embodiment, by using the follower gear 31 as the scissors gear to sandwich the photosensitive member gear 30, rigidity of the engaging portion between the follow