Patent ID: 8723504

Claim:
A remaining sheet quantity detection device, comprising: a sheet housing part for housing sheets; a tray which is provided for placing the sheets and is movable in a vertical direction within the sheet housing part; a motor for moving the tray in the vertical direction; a distance measuring sensor which is provided opposite to an upper face of the tray, outputs a measurement signal indicating a vertical distance between the distance measuring sensor and the upper face of the tray as a voltage value, and has output characteristics where the voltage value becomes a peak value when the vertical distance between the distance measuring sensor and the upper face of the tray is a predetermined peak distance, the voltage value sequentially increases as the vertical distance between the distance measuring sensor and the upper face of the tray increases when the vertical distance between the distance measuring sensor and the upper face of the tray is less than the peak distance, and the voltage value sequentially decreases as the vertical distance between the distance measuring sensor and the upper face of the tray increases when the vertical distance between the distance measuring sensor and the upper face of the tray exceeds the peak distance; a detection unit for detecting that the vertical distance between the distance measuring sensor and the upper face of the tray is less than the peak distance and that the vertical distance between the distance measuring sensor and the upper face of the tray exceeds the peak distance; a storage unit for storing first information which associates the vertical distance between the distance measuring sensor and the upper face of the tray with the voltage value in a distance range less than the peak distance, and second information which associates the vertical distance between the distance measuring sensor and the upper face of the tray with the voltage value in a distance range exceeding the peak distance; a distance acquisition unit for acquiring a vertical distance between the distance measuring sensor and the upper face of the tray that is associated with the voltage value obtained by the distance measuring sensor in the first information when the detection unit detects that the vertical distance between the distance measuring sensor and the upper face of the tray is less than the peak distance, and acquiring a vertical distance between the distance measuring sensor and the upper face of the tray that is associated with the voltage value obtained by the distance measuring sensor in the second information when the detection unit detects that the vertical distance between the distance measuring sensor and the upper face of the tray exceeds the peak distance; and a remaining quantity detection unit for detecting a remaining quantity of the sheets by using the vertical distance between the distance measuring sensor and the upper face of the tray acquired by the distance acquisition unit.