Sheet feeding device, and document feeding device in image reading apparatus comprising the same

Abstract

A sheet feeding device, and a document feeding device including the sheet feeding device have a pickup roller which can elevate and lower between an operative position and a standby position, a sheet feeding rotating device that separably feeds each sheet from the roller, and a registration roller that registers the sheet from the sheet feeding rotating device. A carry-in roller conveys the sheet to a predetermined processing position, and a carry-out roller carries the sheet from the processing position. The pickup roller and sheet feeding rotating device are drivingly coupled to a first driving motor. The registration roller and carry-in roller are coupled to a second driving motor via a sliding friction clutch. The sliding friction clutch is configured so that the registration roller is rotated by rotating the second driving motor and transmission of a driving force is blocked by rotating the first driving motor.

1 . A sheet feeding device comprising:
 a placement tray on which sheets are placed;   pickup roller means configured to move up and down between an operative position where the pickup roller means engages a sheet and a standby position located above the operative position;   sheet feeding rotating means for separably feeding each sheet from the pickup means;   a registration roller located downstream of the sheet feeding rotating means to register the sheet from the sheet feeding rotating means;   a carry-in roller located downstream of the sheet feeding rotating means to transfer the sheet to a predetermined processing position;   a carry-out roller for carrying the sheet out from the processing position;   a first driving motor for rotating the pickup roller means and the sheet feeding rotating means;   a second driving motor for rotating the registration roller and the carry-in roller; and   sliding friction clutch means situated between the second driving motor and the registration roller, the sliding friction clutch means being coupled to the registration roller so that the registration roller is drivingly rotated by operating the second driving motor, and transmission of a driving force to the registration roller is blocked by operating of the first driving motor.   
   
   
       2 . The sheet feeding device according to  claim 1 , wherein the sliding friction clutch means comprises a rotating shaft connected to the registration roller; and a coil spring wound around the rotating shaft, and
 rotation of the second driving motor is frictionally transmitted to the rotating shaft via the coil spring, and frictional transmission of rotation of the rotating shaft with the coil spring is cancelled by rotating the first driving motor in a predetermined direction.   
   
   
       3 . The sheet feeding device according to  claim 2 , wherein the coil spring is wound around the rotating shaft so as to be freely compressed and loosened,
 the second driving motor and the first driving motor are coupled to the coil spring so as to rotate in a compressing direction and in a loosening direction, respectively, and   transmission of a driving force from the second driving motor to the rotating shaft is controlled on a basis of a difference in rotation speed between the first driving motor and the second driving motor which act on the coil spring.   
   
   
       4 . The sheet feeding device according to  claim 1 , wherein the pickup roller means is attached to a swinging arm member supported by a rotating support shaft,
 the rotating support shaft is coupled to the first driving motor, and   the swinging arm member is coupled to the rotating support shaft so that the pickup roller means is moved from the standby position to the operative position by rotating the first driving motor forward and from the operative position to the standby position by rotating the first driving motor backward.   
   
   
       5 . The sheet feeding device according to  claim 1 , wherein the first driving motor is configured to rotate forward and backward,
 the pickup roller means and the sheet feeding rotating means are coupled together so as to be rotated by rotating the first driving motor forward,   the pickup roller means is coupled to the sheet feeding rotating means so as to be moved from the standby position to the operative position by rotating the first driving motor forward and from the operative position to the standby position by rotating the first driving motor backward, and   the sliding friction clutch means is configured so that transmission of a driving force from the second driving motor to the registration roller is blocked by rotating the first driving motor forward.   
   
   
       6 . A document feeding device in an image reading apparatus, comprising:
 a placement tray on which sheets are placed;   a sheet feeding path for guiding a sheet from the placement tray to a reading position;   a sheet discharging path for guiding the sheet from the reading position to a sheet discharging tray;   pickup roller means located above the placement tray and configured to move up and down between an operative position where the pickup roller means engages the sheet and a standby position located above the operative position;   sheet feeding rotating means for separably feeding each sheet from the pickup roller means;   a registration roller located on the sheet feeding path to register the sheet from the sheet feeding rotating means;   a carry-in roller located on the sheet feeding path for transferring the sheet from the registration roller to the reading position;   a carry-out roller located on the sheet discharging path to carry the sheet out from the reading position;   a sheet discharging roller located on the sheet discharging path, for carrying the sheet from the carry-out roller out to the sheet discharging tray;   a first driving motor configured to rotate forward and backward to drivingly rotate the pickup roller means and the sheet feeding rotating means, wherein the pickup roller means and sheet feeding rotating means are coupled to the first driving motor so as to be drivingly rotated in a sheet feeding direction by rotating the first driving motor forward, and the pickup roller means is coupled to the first driving motor so as to move from the standby position to the operative position by rotating the first driving motor forward and to move from the operative position to the standby position by rotating the first driving motor backward;   a second driving motor configured to rotate forward and backward to drivingly rotate the registration roller, carry-in roller, carry-out roller, and sheet discharging roller, wherein the registration roller, carry-in roller, carry-out roller, and sheet discharging roller are coupled to the second discharging motor so as to drivingly rotate in the sheet feeding direction by rotating the second driving motor forward; and   sliding friction clutch means situated between the second driving motor and the registration roller, for transmitting a driving force from the second driving motor to the registration roller, the sliding friction clutch means being configured so that transmission of the driving force from the second driving motor to the registration roller is blocked by rotating the first driving motor forward.   
   
   
       7 . The document feeding device according to  claim 6 , wherein a circulation path for guiding the sheet from the sheet discharging roller to the sheet feeding path is connected to the sheet discharging path,
 the sheet discharging roller is coupled to the second driving motor so that the sheet is carried out to the sheet discharging tray by rotating the second driving motor forward, and the sheet is reversed and conveyed to the circulation path by rotating the second driving motor backward, and   the registration roller is coupled to the second driving motor via a one-way clutch so as to be drivingly rotated in the sheet feeding direction by rotating the second driving motor forward.