Sheet feeding device and image forming apparatus including same

A sheet feeding device comprising:

• a main body unit;
• a sheet cassette that can be fitted into the main body unit and pulled out from the main body unit;
• a lift plate that is provided in the sheet cassette to be vertically displaceable;
• a lifting member that
• is arranged below the lift plate,
• includes a turning shaft serving as a turning support point at one end in a feeding direction and
• turns upward the other end in the feeding direction to lift the lift plate;
• a coupling member that
• is provided in the main body unit,
• includes an engagement portion which engages a portion to be engaged on a side of the turning shaft when the sheet cassette is fitted in the main body unit and
• is driven and rotated in a main rotation direction to drive and rotate, in the main rotation direction, the portion to be engaged which has been engaged by the engagement portion;
• a motor that
• is coupled to the coupling member, and
• rotates the turning shaft in the main rotation direction to turn the other end of the lifting member upward;
• a control unit that controls the motor;
• and
• an encoder that outputs a pulse signal according to the rotation of the turning shaft,
• wherein the encoder includes:
• a rotation member that
• is rotated in conjunction with the coupling member, and
• includes a plurality of detection targets arranged in a circumferential direction;
• and
• an optical sensor that
• includes a light emitting portion and a light receiving portion which are arranged opposite each other across a movement path of the detection targets, and
• changes a level of the pulse signal depending on whether light from the light emitting portion reaches the light receiving portion,
• the control unit detects a remaining number of sheets on the lift plate based on a count value of the pulse signal obtained by counting,
• the rotation member is divided into a first detection region and a second detection region,
• in the first detection region, only the detection target located at a tail end in the main rotation direction is formed longer in the circumferential direction than the other detection targets, and the detection targets are arranged at equal intervals in the circumferential direction,
• in the second detection region, the detection targets having a same circumferential length are arranged at equal intervals in the circumferential direction,
• the first detection regions and the second detection regions are alternatively arranged in the circumferential direction with a same pitch in the circumferential direction,
• a first interval in the circumferential direction between the detection target located at the tail end of the first detection region in the main rotation direction and the detection target located at a front end of the second detection region in the main rotation direction is less than a second interval in the circumferential direction between the detection target located at a tail end of the second detection region in the main rotation direction and the detection target located at a front end of the first detection region in the main rotation direction and
• the control unit rotates the rotation member in the main rotation direction from a home position located on the second interval to start detecting the remaining number of the sheets.