Image forming apparatus with conveyance belt movement correction

An image forming apparatus comprising:

• a conveyance belt;
• an image forming portion that forms an image on paper that is conveyed on the conveyance belt;
• a belt moving mechanism that moves the conveyance belt in a width direction of the conveyance belt;
• an optical sensor including a light emitting portion, and a light receiving portion in which a plurality of light receiving elements are aligned in the width direction of the conveyance belt, so that the number of light receiving elements that receive light irradiated by the light emitting portion differs depending on a position of a side face of the conveyance belt, the light receiving portion being configured to output a light receiving signal having a value that corresponds to the number of light receiving elements that receive light irradiated by the light emitting portion;
• a current generation portion that generates an electric current that is supplied to the light emitting portion;
• a position detection portion that causes the light emitting portion to emit light by causing the current generation portion to generate a light emitting current, which is the current supplied to the light emitting portion, when detecting the position of the side face of the conveyance belt, and detects the position of the side face of the conveyance belt based on the value of the light receiving signal output from the light receiving portion;
• a belt movement control unit that moves the conveyance belt to correct skewing of the conveyance belt, by controlling the belt moving mechanism based on the position of the side face of the conveyance belt detected by the position detection portion;
• a reference value storage portion storing in advance a reference value, which is the value of the light receiving signal output from the light receiving portion and is used as a reference when correcting a value of the light emitting current;
• a base current measurement portion that, in a case where a condition for correcting the value of the light emitting current is satisfied, monitors a decrease in the value of the light receiving signal while decreasing the current generated by the current generation portion, in a state where the conveyance belt is not positioned between the light emitting portion and the light receiving portion, and, in a case where the value of the light receiving signal reaches the reference value stored in the reference value storage portion, measures a value of a base current, which is the current generated by the current generation portion;
• an initial value storage portion storing in advance an initial value of the base current that is measured by the base current measurement portion;
• and
• a correction value determination portion that determines a correction value of the light emitting current, so that the value of the light emitting current increases, depending on an amount by which the value of the base current measured by the base current measurement portion increases relative to the initial value stored in the initial value storage portion,
• wherein the position detection portion, in a case of detecting the position of the side face of the conveyance belt after the correction value determination portion determines the correction value, utilizes the correction value determined by the correction value determination portion as the value of the light emitting current.