Patent ID: 6916076

Claim:
A cartridge for an image forming device that includes a carriage that mounts the cartridge thereon and moves along with the cartridge, a sensor that detects an amount of reflected light reflected from the cartridge, the sensor including a light emitting unit that irradiates a light onto the cartridge and a light receiving unit that receives the reflected light, a detection unit that detects an amount of an ink contained in the cartridge based on the amount of the reflected light detected by the sensor, and a reading unit that controls the carriage to move to a predetermined position where the light irradiated from the light emitting unit is irradiated onto the cartridge and reads levels of reflected light from a waveform for the amount of reflected light at a reading interval, based on which the detection unit detects the amount of the ink contained in the cartridge, the cartridge comprising: a casing having a light receiving portion that receives the light from the light emitting unit, the light receiving portion being provided with prisms in a shape that repeatedly alternates in peaks and valleys, wherein adjacent two of the valleys are separated by a predetermined valley interval, wherein the predetermined valley interval is a non-integral fraction of the reading interval.