A method for controlling an image reading device, comprising:
- providing an optical sensor including a light emitting portion and a light receiving portion, the light receiving portion being arranged at a distance from a light emission surface of the light emitting portion and outputting an output signal;
- radiating light toward a document with a lamp provided in a carriage;
- rotating an endless belt by transmitting, via a first transmission gear, a drive of a stepping motor to a driving gear around which the belt is wound;
- moving the carriage fitted to the belt in a sub-scanning direction by rotation of the driving gear;
- meshing a second transmission gear with a rotary shaft of the stepping motor or with one of the gears of a moving portion;
- rotating, based on a driving force of the second transmission gear, a pulse generating gear provided with a plurality of light shielding teeth along a circumference thereof;
- controlling rotation and magnetic excitation of the stepping motor;
- making the light receiving portion output the output signal at a first level when light from the light emitting portion is not intercepted and output the output signal at a second level when the light is intercepted;
- providing in the carriage a light shielding plate which passes through a gap between the light emitting portion and the light receiving portion and which, while passing therethrough, shields an optical path from the light emitting portion to the light receiving portion;
- arranging the pulse generating gear at a position at which the pulse generating gear, while rotating, alternately transmits and intercepts light along the optical path with the light shielding teeth by the light shielding teeth passing through the gap;
- setting a first width and a second width such that a movement amount of the pulse generating gear resulting from the stepping motor rotating one step is equal to or larger than both the first width and the second width,
- the first width is a width of each of the light shielding teeth in a rotation direction of the pulse generating gear,
- the second width is a width of an interval between adjacent light shielding teeth in the rotation direction of the pulse generating gear,
- keeping the carriage on standby at a home position which is a position at which the light shielding plate does not shield the optical path;
- recognizing a deviation in a position of the carriage when, during standby of the carriage at the home position, a level of the output signal changes;
- and
- determining whether or not phase adjustment of the stepping motor is required based on the recognition.