Image forming apparatus

An image forming apparatus that calculates an amount of positional deviation for each of a plurality of colors by:

• forming registration patterns in two arrays along a sub-scanning direction on an image carrying surface of an image carrier by a plurality of image creation units that are configured to create toner images in the respective colors, each array including for each color a registration pattern for detecting a positional deviation in the main scanning direction and a different registration pattern for detecting a positional deviation in the sub-scanning direction, each registration pattern in one of the arrays being paired with an identical registration pattern in the other array, the two arrays being arranged such that the registration patterns in each pair are side by side along the main scanning direction;
• irradiating each pair of registration patterns with light;
• and
• detecting light reflected from each pair of registration patterns,
• the image forming apparatus comprising:
• a first toner density sensor including:
• a light-emitting element configured to emit light to irradiate one of the registration patterns in each pair;
• a regular reflection photodetector configured to detect regular reflection light from the one registration pattern in the pair;
• and a diffuse reflection photodetector configured to detect diffuse reflection light from the one registration pattern in the pair, the first toner density sensor being configured to output a difference between detection signals of the reflection light detected by the respective photodetectors;
• a second toner density sensor including:
• a light-emitting element configured to emit light to irradiate the other one of the registration patterns in the pair;
• and a single photo detector that is a regular reflection photodetector configured to detect regular reflection light from the other registration pattern in the pair, the second toner density sensor being configured to output a detection signal of the regular reflection light detected by the regular reflection photodetector;
• a calculating unit configured to calculate:
• a position of the one of the registration patterns in the pair by using the difference between the respective detection signals output by the first toner density sensor;
• a position of the other registration pattern in the pair by using the detection signal of the regular reflection light output by the second toner density sensor;
• and
• a positional deviation for each registration pattern in the pair based on the respective positions calculated;
• and
• a storage unit that stores an index value indicating an amount of offset deviation estimated to occur between respective positions calculated for the registration patterns in the pair based on the respective detection signals output by the first toner density sensor and the second toner density sensor when the registration patterns in the pair are formed without any positional deviation,
• wherein the calculating unit corrects a relative positional relation between the respective positions calculated for the registration patterns in the pair in a manner that an amount of positional deviation between the respective positions is reduced by the index value.