Image forming device having a plurality of image forming modes

An image forming device comprising:

• a main casing;
• a cartridge detachably accommodated in the main casing and including an agitator that rotates to agitate developer accommodated in the cartridge;
• a light-emitting element that emits a light into the cartridge;
• a light-receiving element that receives the light that has passed through the cartridge;
• a calculating unit that calculates a time ratio, which is a ratio of time duration, in which the light-receiving element receives the detection light within a predetermined duration, to the predetermined time duration;
• a determining unit that determines whether the time ratio calculated by the calculating unit is greater than a first threshold value, wherein the determining unit determines that the cartridge should be replaced when the time ratio calculated by the calculating unit is determined to be greater than the first threshold value;
• an image forming unit having a first image forming mode for forming images on a recording sheet while rotating the agitator at a first rotation speed and a second image forming mode for forming images on a recording sheet while rotating the agitator at a second rotation speed that is lower than the first rotation speed;
• a counting unit that counts a second value regarding image forming amount when the image forming unit is in the second image forming mode;
• and
• a detection process executing unit that determines whether the second value is greater than a predetermined count value while the image forming unit is in the second image forming mode, the detection process executing unit executing a detection process if the second value is determined to be greater than the predetermined count value while the image forming unit is in the second image forming mode;
• wherein:
• in the detection process, the detection process executing unit controls the image forming unit to change a rotation speed of the agitator from the second rotation speed to the first rotation speed, and controls the determining unit to determine whether the cartridge should be replaced while the agitator is rotating at the first rotation speed, and
• the second value is any one of a dot number printed on a recording sheet, a number of recording sheets printed with images, and a rotation number of the agitator.

An image forming device comprising:

• a main casing;
• a cartridge detachably accommodated in the main casing and including an agitator that rotates to agitate developer accommodated in the cartridge;
• a light-emitting element that emits a light into the cartridge;
• a light-receiving element that receives the light that has passed through the cartridge;
• a calculating unit that calculates a time ratio, which is a ratio of time duration, in which the light-receiving element receives the detection light within a predetermined duration, to the predetermined time duration;
• a determining unit that determines whether the time ratio calculated by the calculating unit is greater than a first threshold value, wherein the determining unit determines that the cartridge should be replaced when the time ratio calculated by the calculating unit is determined to be greater than the first threshold value;
• an image forming unit having a first image forming mode for forming images on a recording sheet while rotating the agitator at a first rotation speed and a second image forming mode for forming images on a recording sheet while rotating the agitator at a second rotation speed that is lower than the first rotation speed;
• a counting unit that counts a second value regarding image forming amount when the image forming unit is in the second image forming mode;
• a detection process executing unit that determines whether the second value is greater than a predetermined count value while the image forming unit is in the second image forming mode, the detection process executing unit executing a detection process if the second value is determined to be greater than the predetermined count value while the image forming unit is in the second image forming mode;
• and
• a reset unit that resets the second value when the agitator rotates at the first rotation speed,
• wherein, in the detection process, the detection process executing unit controls the image forming unit to change a rotation speed of the agitator from the second rotation speed to the first rotation speed, and controls the determining unit to determine whether the cartridge should be replaced while the agitator is rotating at the first rotation speed.