Image forming apparatus

An image forming apparatus comprising:

• an endless rotary image bearing member having a surface to bear a toner image and a potential-control toner pattern;
• an image forming unit to form the toner image and the potential-control toner pattern onto the surface of the image bearing member;
• a reflection light detector having a light source to emit light onto the surface of the image bearing member and the potential-control toner pattern formed on the image bearing member and a light-receiving element to detect the amount of light reflected from the potential-control toner pattern formed on the surface of the image bearing member as toner attraction output, and the amount of light reflected from the surface of the image bearing member as a surface output;
• and
• a controller to detect toner information of the toner image based on the toner attraction output corresponding to the detected amount of light reflected from the potential-control toner pattern formed on the image bearing member, and the surface output corresponding to the amount of light reflected from the image bearing member, the controller controlling the toner image forming unit based on the detected toner information,
• wherein the surface output comprises:
• a first surface output detected from a first time-surface of the image bearing member positioned identical to the potential-control toner pattern, the first time-surface positioned one of an integer multiple of revolutions upstream from the potential-control toner pattern in a surface movement direction in which the surface of the image bearing member is moved and an integer multiple of revolutions downstream from the potential-control toner pattern in the surface movement direction, and
• a second surface output detected from a second time-surface of the image bearing member positioned different from the potential-control toner pattern, the second time-surface positioned at a location shorter than one revolution upstream or from the potential-control toner pattern in the surface movement direction,
• wherein the controller determines whether to execute a first-surface output control, during which the reflection light detector detects at least the first time-surface of the image bearing member, or a second-surface output control, during which the reflection light detector detects only the second time-surface of the image bearing member, based on use condition of the image forming apparatus.