(19)
(11) EP 2 037 328 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
18.04.2012 Bulletin 2012/16

(43) Date of publication A2:
18.03.2009 Bulletin 2009/12

(21) Application number: 08252838.1

(22) Date of filing: 28.08.2008
(51) International Patent Classification (IPC): 
G03G 15/01(2006.01)
 G03G 15/00(2006.01)
(84) Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MT NL NO PL PT RO SE SI SK TR
Designated Extension States:
AL BA MK RS

(30) Priority: 14.09.2007 JP 2007239604

(71) Applicant: Ricoh Company, Ltd.
Tokyo 143-8555 (JP)

(72) Inventors:
  • Nishikawa, Tetsuji
    Machida-shi Tokyo (JP)
  • Kikura, Makoto
    Yokohama-shi Kanagawa (JP)
  • Suzuki, Kazuki
    Yokohama-shi Kanagawa (JP)
  • Maehata, Yasuhiro
    Sagamihara-shi Kanagawa (JP)
  • Ishida, Masahiro
    Sagamihara-shi Kanagawa (JP)

(74) Representative: Leeming, John Gerard 
J A Kemp 14 South Square Gray's Inn
London WC1R 5JJ
London WC1R 5JJ (GB)

   


(54) Image forming apparatus


(57) Time Ti since an immediately preceding rotational reference position 16a1 is calculated by a timer in accordance with a detection signal at a rotational reference position 16a1, and then it is stored. When a black photosensitive drum 2K is stopped in a monochrome mode using the stored time Ti, the phase of the black photosensitive drum 2K is matched with the phases of the photosensitive drums 2Y, 2C, and 2M whose rotations are stopped in a color mode, thereby making it possible to prevent positional shifts between color toner images and a black toner image.







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