Sheet feeder and image forming apparatus provided with same

A sheet feeder, comprising:

• a casing;
• a sheet stacking portion arranged in the casing and on which sheets are to be placed;
• a sheet conveyance path arranged in the casing and in which the sheets stacked on the sheet stacking portion are fed in a predetermined sheet feeding direction;
• a feed roller mounted in the casing to face a downstream side of the sheet stacking portion in the sheet feeding direction from above and feeds the sheet toward the sheet conveyance path;
• a separation pad arranged to face the feed roller so that a nip portion is defined between the feed roller and the separation pad, the sheets being fed one by one through the nip portion in the sheet feeding direction;
• a holder mountable into and removable from the casing and fixedly supporting the separation pad, the holder including a first supporting plate that supports the separation pad, a second supporting plate facing the first supporting plate and a biasing spring compressed between the first and second supporting plates,
• the first supporting plate includes:
• a first supporting portion extending vertically, and
• a second supporting portion inclined toward a downstream side in the sheet feeding direction as the second supporting portion extends up from an upper end of the first supporting portion, the second supporting portion defining a part of the first supporting plate that holds the separation pad,
• a pair of shaft portions projecting respectively in a sheet width direction from opposite sides of a lower end part of the first supporting portion of the holder in the sheet width direction, each shaft portion having an outer circumferential surface, a pair of holes arranged on the same axis as the shaft portions,
• the second supporting plate includes a pair of projecting portions respectively projecting in the sheet width direction from opposite sides of a lower end side of the second supporting plate in the sheet width direction, the first supporting plate being supported rotatably on the second supporting plate with the projecting portions as pivots by inserting the projecting portions into the holes;
• a mounting portion arranged in the casing, and the holder being mounted into the mounting portion, the mounting portion including a wall portion standing at a side downstream of the holder in the sheet feeding direction and defining a side surface at a downstream side in the sheet feeding direction, the second supporting plate facing the wall portion of the mounting portion and the biasing spring biasing the separation pad toward the feed roller when the sheet passes through the nip portion;
• and
• a guiding member arranged in the mounting portion and guiding the holder, the guiding member having a pair of guide surfaces arranged at an upstream side of the mounting portion in the sheet feeding direction and extending in a vertical direction while facing the holder, the guide surfaces being arranged on opposite sides of the mounting portion in the sheet width direction intersecting the sheet feeding direction;
• wherein, a posture of the holder is changeable between a first posture in which predetermined clearances are formable between the guide surfaces of the guiding member and the outer circumferential surfaces of the shaft portions when the holder is mounted into the mounting portion and a second posture in which the outer circumferential surfaces of the shaft portions are pressed directly against the guide surfaces of the guiding member when the sheet passes through the nip portion after the holder is mounted into the mounting portion, the biasing spring biases the separation pad toward the feed roller when the sheet passes through the nip portion;
• and
• the outer circumferential surfaces of the shaft portions are guided by the guide surfaces when the holder is mounted.