Sheet feeding device, image forming apparatus, and method for controlling sheet feeding device

A sheet feeding device comparing:

• a cassette including a sheet placing plate having an upper surface on which paper sheets are set, the cassette being detachable and attachable;
• a first sensor unit including a first conductive plate and a first coil circuit board on which a coil pattern is printed, the first coil circuit board being applied with a voltage so that a magnetic field is generated, and so that the first sensor unit outputs a first output value corresponding to a position of the first conductive plate;
• a first moving mechanism arranged to move the first conductive plate so that a facing area between the first coil circuit board and the first conductive plate is increased or decreased according to remaining quantity of paper sheets in the cassette;
• a storage unit arranged to store remaining quantity detection data for determining current remaining quantity of paper sheets corresponding to the first output value, and a reference value for determining whether or not the cassette is attached;
• and
• a control unit arranged to recognize a magnitude of the first output value, wherein
• the first conductive plate is attached to the cassette,
• the first coil circuit board is disposed at a position facing the first conductive plate in a non-contact manner when the cassette is attached, but is not attached to the cassette, and
• the control unit determines the current remaining quantity of paper sheets based on the magnitude of the first output value and the remaining quantity detection data, and determines whether or not the cassette is attached based on the magnitude of the first output value and the reference value.