The sheet feed device includes a sheet containing cassette with a sheet stacking plate therein, a sheet feed part enabled to feed a sheet within the sheet containing cassette set in a setting position, a first sensing mechanism, a lift mechanism, a drive mechanism, and a controller. The lift mechanism includes a cassette-side coupling member for transmitting driving force to the sheet stacking plate. The drive mechanism includes a main body-side coupling member coupled with the cassette-side coupling member. When the first sensing mechanism has sensed that no sheets are stacked on the sheet stacking plate, the controller makes the main body-side coupling member rotate reverse to move down the sheet stacking plate and, even after the sheet stacking plate lowers, makes the main body-side coupling member continue to be rotated reverse so as to move out the sheet containing cassette from the setting position.

The joint mechanism includes an engagement pin; a first coupling having a pair of projections with engagement recessed portions formed respectively, the engagement recessed portions with which both end portions of the engagement pin are freely engaged or disengaged; a second coupling including a circumferential wall having an opening portion and a pair of projecting pieces; and a biasing member. The pair of projecting pieces are arranged in the engagement recessed portions so as to be opposed, on an upstream side in a rotation direction, to opening defining surfaces of the pair of projections, with the second coupling attached to the first coupling. Both end portions of the engagement pins are engaged with the engagement recessed portions so as to be each sandwiched between each of the pair of projecting pieces being applied a biasing force of the biasing member and each opening defining surface of the pair of projections.

A sheet feeder includes a delivery roller, a supply roller, a separating member, a driving source, a first drive transmission mechanism, a second drive transmission mechanism, and a controller. The first drive transmission mechanism transmits the rotary drive power in the first direction to the delivery roller in a first drive transmission time from the start of driving of the driving source. The second drive transmission mechanism transmits the rotary drive power in the first direction to the supply roller in a second drive transmission time from the start of driving of the driving source. The second drive transmission period of the second drive transmission mechanism is longer than the first drive transmission period of the first drive transmission mechanism. When the control starts driving the driving source, the supply roller starts to rotate in the first direction after the delivery roller starts to rotate in the first direction.

A pickup roller is moved to a retracted position by rotating a feeding motor in reverse by a first predetermined amount and is moved to a contact position by rotating the feeding motor forward by a second predetermined amount.

A sheet feeder includes a delivery roller, a supply roller, a separating member, a driving source, a first drive transmission mechanism, a second drive transmission mechanism, and a controller. The first drive transmission mechanism transmits the rotary drive power in the first direction to the delivery roller in a first drive transmission time from the start of driving of the driving source. The second drive transmission mechanism transmits the rotary drive power in the first direction to the supply roller in a second drive transmission time from the start of driving of the driving source. The second drive transmission period of the second drive transmission mechanism is longer than the first drive transmission period of the first drive transmission mechanism. When the control starts driving the driving source, the supply roller starts to rotate in the first direction after the delivery roller starts to rotate in the first direction.

In a case where, for example, a certain sheet feeding operation by one of sheet delivery portions is an operation that continues from a sheet feeding operation by another one of the sheet delivery portions in a sheet feed device, a control portion delays output timing, to a feed clutch, of a control signal for feeding a first one of recording sheets, as compared to output timing of control signals for sequentially feeding a second and the following ones of the recording sheets from the same sheet delivery portion.

A roller drive transmission device includes a drive input gear, a drive transmission gear, a roller unit and a ratchet mechanism. When a rotational drive force is input to the drive input gear and the drive transmission gear is slid to a first position, the drive input gear, the drive transmission gear and the roller unit are integrally rotated in a first rotational direction. When the input of the rotational drive force to the drive input gear is cut off and the roller unit is rotated, following a sheet, the drive transmission gear is slid to a second position and the roller unit and the drive transmission gear are decoupled. The ratchet mechanism includes a load adjustment mechanism configured to make a rotational load in the first rotational direction of the drive transmission gear arranged at the second position larger than a movement load in an axial direction.

An automatic document feeder that is included in an image reader of an image forming apparatus includes a sheet conveying roller, a document feeder cover, a projection piece, a motor, a driving side gear, and a driving force transmission device including an idler gear, a driving force release gear, a slide body, a first elastic body to bias the idler gear and the driving force release gear to be separated, a second elastic body to bias the driving force release gear and the slide body to be separated, and a drive shaft. The driving force transmission device meshes the driving and driven side meshing portions together with a biasing force applied by the second elastic body when the document feeder cover is closed, and releases the driving and driven side meshing portions with a biasing force applied by the first elastic body when the document feeder cover is opened.

A conveyor includes: a first power transmitting mechanism configured to transmit one of forward rotation and reverse rotation of a motor to a first roller and not to transmit the other from a driven member to the first roller; and a second power transmitting mechanism configured to transmit the other rotation to the first roller and not to transmit the one rotation to the first roller. The first power transmitting mechanism includes a transmission delayer that does not transmit rotation of the motor from the driven member to the first roller until the motor is rotated by a particular amount from a time point at which the motor starts to be rotated in a rotational direction of the one rotation when rotation transmitted from the motor to the driven member is changed from the other rotation to the one rotation.

An automatic document feeder that is included in an image reader of an image forming apparatus includes a sheet conveying roller, a document feeder cover, a projection piece, a motor, a driving side gear, and a driving force transmission device including an idler gear, a driving force release gear, a slide body, a first elastic body to bias the idler gear and the driving force release gear to be separated, a second elastic body to bias the driving force release gear and the slide body to be separated, and a drive shaft. The driving force transmission device meshes the driving and driven side meshing portions together with a biasing force applied by the second elastic body when the document feeder cover is closed, and releases the driving and driven side meshing portions with a biasing force applied by the first elastic body when the document feeder cover is opened.