Patent ID: 7215114

Claim:
A rotation angle detecting device for detecting a rotation angle of a main gear, comprising: first and second detection gears having a first number of teeth and a second number of teeth, respectively, rotatable in conjunction with the main gear having a third number of teeth and a rotatable range from a first value up to a second value; a first detecting unit configured to detect a rotation angle of the first detection gear, wherein a cycle of the first detecting unit indicates the rotation angle of the main gear rotating during one revolution of the first detection gear; the second detecting unit configured to detect a rotation angle of the second detection gear, wherein a cycle of the second detecting unit indicates the rotation angle of the main gear rotating during one revolution of the second detection gear; and a third detecting unit configured to detect the rotation angle of the main gear on a basis of the rotation angle detected by the first detecting unit and the rotation angle detected by the second detecting unit, wherein a least common multiple of the cycle of the first detecting unit and the cycle of the second detecting unit is greater than or equal to the rotatable range of the main gear, wherein a first periodicity of the first detecting unit is a number of revolutions of the first detection gear during the rotation of the main gear, and a second periodicity of the second detecting unit is a number of revolutions of the second detection gear during the rotation of the main gear, the first and second periodicities being prime to each other, wherein the first number of teeth of the first detection gear is set to be a numeric value obtained by multiplying the second periodicity from the second detecting unit by a predetermined integral number, and the second number of teeth of the second detection gear is set to be a numeric value obtained by multiplying the first periodicity from the first detecting unit by the predetermined integral number, and wherein the first and second number of teeth of the first and second detection gears are dividends set to have a common whole number divisor greater than one, which results in a whole number quotient, and is different from a divisor of the third number of teeth of the main gear.