Patent ID: 7894737

Claim:
An image-forming device comprising: a first driving unit that provides a first driving force; an endless belt that is rotated by the first driving force; a plurality of photosensitive drums opposing the endless belt; a second driving unit that provides a second driving force; a plurality of input couplings that receives the second driving force; a plurality of output couplings corresponding to both the plurality of input couplings and the plurality of photosensitive drums respectively, the second driving force being transmitted from each input coupling to the corresponding output coupling to rotate the corresponding photosensitive drum when each input coupling is positioned at a predetermined position for the corresponding output coupling; a first detecting unit that detects a position of each input coupling before the first driving unit begins to provide the first driving force and the second driving unit begins to provide the first driving force; a second detecting unit that detects a position of each output coupling before the first driving unit begins to provide the first driving force and the second driving unit begins to provide the first driving force; a calculating unit that calculates, based on the position of each input coupling and the position of each output coupling, a first start timing when a first photosensitive drum starts to rotate and a second start timing when a second photosensitive drum starts to rotate, the first photosensitive drum being the photosensitive drum that starts to rotate first when the second driving unit provides the second driving force, the second photosensitive drum being the photosensitive drum that starts to rotate last when the second driving unit provides the second driving force; and a controlling unit that controls the first driving unit to begin to provide the first driving force after the first start timing and before the second start timing.