Sheet storage device
When a sheet cassette ( 10 a ) is pulled out of the body of an image forming apparatus ( 100 ), winding pulleys ( 40 a and 40 b ) are rotated by the weight of a lift plate. An idle gear ( 47 ) also is rotated by a predetermined amount, so that the engagement portion ( 47 b ) thereof engages with a second arm portion ( 50 c ) of a torsion spring ( 50 ). Since a force exerted by the torsion spring ( 50 ) is set greater than the force that rotates the idle gear ( 47 ) by downward movement of lift plate ( 30 ), rotation of the idle gear ( 47 ) and winding pulley ( 40 a ) is regulated, and thus the upper surface of lift plate ( 30 ) stops in a substantially constant position with respect to sheet supply opening portions ( 31 a and 31 b ).
1. A sheet storage device comprising:
a sheet storage portion that stores a sheet;
a sheet supply opening portion that is formed from an upper end of a side wall of the sheet storage portion in a vertically downward direction;
a lift plate that is arranged in the sheet storage portion such that the lift plate can be moved up and down;
a wire with which the lift plate is hung;
a winding pulley that moves the lift plate up to a predetermined position by winding the wire;
an idle gear that engages with a gear portion formed in the winding pulley; and
a torsion spring that includes a winding spring portion which is fitted to a rotation shaft of the idle gear and a first arm portion and a second arm portion which extend from the winding spring portion and that has the first arm portion fixed to a side of the sheet storage portion,
wherein, with the sheet storage device removed from a body of an image forming apparatus, the winding pulley is reversely rotated by a weight of the lift plate, the lift plate is lowered and the second arm portion engages with an engagement portion provided on a side surface of the idle gear such that an upper surface of the lift plate on which no sheet is stacked is stopped in a substantially constant position equal to or higher than a lower end portion of the sheet supply opening portion.
2. The sheet storage device of claim 1 ,
wherein a spring constant of the torsion spring is adjusted such that, when a sheet is stacked on the lift plate, regardless of a number of sheets stacked, an uppermost surface of the sheets is constantly stopped in the position equal to or higher than the lower end portion of the sheet supply opening portion.
3. The sheet storage device of claim 1 ,
wherein a force exerted by the torsion spring is set greater than a force that rotates the idle gear by lowering of the lift plate by a weight of the lift plate.
4. The sheet storage device of claim 3 ,
wherein, when no sheet is stacked on the lift plate, the second arm portion is pressed onto a side of the sheet storage portion a predetermined angle away from a position where the first arm portion is fixed with a rotational shaft of the idle gear being a center.
5. The sheet storage device of claim 1 ,
wherein a dumper gear incorporating a torque limiter is coupled to the idle gear.
6. An image forming apparatus comprising:
the sheet storage device of claim 1 ; and
an image formation portion that forms an image on a sheet.