PROBLEM TO BE SOLVED: To improve reliability of a mechanism for detecting that a drive gear is on an origin position and to prevent an electric circuit from being complicated.SOLUTION: A rotational position detection apparatus includes a measuring gear 62 having a different number of teeth to be engaged with a drive gear 32, a drive gear sensor 67 for detecting one position in a circumferential direction of the drive gear 32 and a measuring gear sensor 64 for detecting one position in a circumferential direction of the measuring gear 62. When the drive gear 32 is on an origin position, the measuring gear 62 is also on the origin position and both the sensors 67 and 64 are in detection states. When the drive gear 32 is rotated by 360°×n from the origin position and the drive gear sensor 67 is in a detection state, the measuring gear 62 is rotated over 360°×m from the origin position and the measuring gear sensor 64 is in an undetectable state.COPYRIGHT: (C)2014,JPO&INPIT【課題】本発明は、駆動歯車が原点位置にあることを検出する機構の信頼性を向上させるとともに、電気回路が複雑化しないようにすることである。【解決手段】本発明に係る回転位置検出装置は、駆動歯車32と噛合する歯数が異なる測定歯車62と、駆動歯車32の円周方向における一箇所を検出する駆動歯車用センサ67と、測定歯車62の円周方向における一箇所を検出する測定歯車用センサ64とを有し、駆動歯車32が原点位置にあるときは、測定歯車62も原点位置にあって、両センサ67,64が共に検出状態であり、駆動歯車32が原点位置から360°×nだけ回転して、駆動歯車用センサ67が検出状態のときには、測定歯車62が原点位置から360°×mを超えて回転し、測定歯車用センサ64が検出不能状態である。【選択図】図5
