A conveyance device includes a sheet stacker, a pickup roller, a feed roller, a first drive source, a first encoder, a first drive controller, a separation roller, a second drive source, a second encoder, a second drive controller, a separation pressure provider, and a torque estimation device. The torque estimation device estimates a torque of the second drive source with an applied voltage to the second drive source from the second drive controller after calculating a turning angle speed from a rotation amount of the second drive source detected by the second encoder based on a relational expression between a motor rotation speed and an applied voltage that are measured beforehand for the second drive source and a torque of the second drive source.

A sheet conveyor includes a separation roller, a retard roller forming a nip with the separation roller, and a load application device configured to apply a load to the retard roller. The load application device includes a motor, a first drive train, a second torque limiter isolated from the first drive train, and a controller. The first drive train includes a plurality of gears for transmitting a driving force from the motor to the retard roller, a first torque limiter, and a clutch disposed between the motor and the first torque limiter. The second torque limiter is configured to communicate with the retard roller. The controller is configured to, during conveyance of a sheet, control the clutch to allow transmission of the driving force from the motor for a predetermined time period and to interrupt transmission of the driving force from the motor after expiration of the predetermined time period.

A sheet conveying device includes a sheet pickup body, a first sheet conveyor, and a second sheet conveyor, which are disposed in this order along a sheet conveyance direction, and circuitry. The first sheet conveyor includes a first sheet feed roller, a second sheet feed roller, and a first motor. The second sheet conveyor includes a conveyance roller and a second motor. The circuitry is configured to determine a sheet conveyance state of a sheet based on at least one of torque of the first motor of the first sheet conveyor and torque of the second motor of the second sheet conveyor. The first sheet conveyor is configured to interpose the sheet between the first sheet feed roller and the second sheet feed roller and convey the sheet to the second sheet conveyor as the first sheet feed roller rotates.

A paper separation mechanism, comprising a separation roller assembly having a separation roller, a torque limiter connected to the separation roller, and a separation gear arranged between the separation roller and the torque limiter; a transmission gear assembly having a first transmission gear which is able to mesh or separate with the separation gear, a second transmission gear meshed with the first transmission gear, and a connecting part connected the first transmission gear and the second transmission gear; and a motor connected to the transmission gear assembly for applying forward or reverse torque; wherein when the motor is applying the forward torque, the connecting part rotates forward to mesh the first transmission gear with the separation gear; and when the motor is applying the reverse torque, the connecting part rotates reverse to separate the first transmission gear with the separation gear.

A sheet feeding device includes a conveyance rotator, a separation rotator, a torque applier, a torque control circuit, and a torque transmission switcher. The conveyance rotator conveys a sheet in a sheet feeding direction. The separation rotator sandwiches the sheet together with the conveyance rotator. The torque applier applies a reverse torque to the separation rotator in a sheet reversing direction to reverse the sheet. The torque control circuit controls the reverse torque applied to the separation rotator to be equal to or less than a given value. The torque transmission switcher switches, between a transmission state and a non-transmission state, a state of a torque transmission path between the torque applier and the separation rotator. The transmission state is a state in which the reverse torque is transmitted. The non-transmission state is a state in which the reverse torque is not transmitted.

A paper feed apparatus. The paper feed apparatus can include a stack of paper, the stack of paper having an uppermost sheet of paper and a second sheet of paper being disposed below the uppermost sheet of paper. A driven pick roller is suitably arranged in contact with the uppermost sheet of paper and is suitably rotatable in a first roller direction to convey the uppermost sheet of paper in a first paper direction. A nip defined by a driven feed roller and a separation roller is suitably disposed downstream from the pick roller, the nip having a gap sufficient for the uppermost sheet of paper to pass through, the gap being sufficient for the separation roller to be in frictional engagement with the second sheet of paper to prevent it from passing through the nip. A rotating element having a plurality of radially extending brush elements is suitably disposed between the driven pick roller and the driven feed roller and rotatable in a second direction opposite the first roller direction to urge the second sheet of paper under the influence of the plurality of radially extending brush elements in a second paper direction opposite the first paper direction.

A document feeder includes a lift plate, a pickup roller, a lift motor, a retard roller, and a control unit. In a manual feed mode, the control unit rotates the retard roller to feed a document in a document conveyance direction. Further, the control unit causes the lift motor to start lowering the lift plate while the pickup roller is feeding a document after the rotation of the pickup roller is started.

The document feeder includes a lift plate, a pickup roller, a lift motor, a retard roller, and a control unit. In a manual feed mode, the control unit rotates the retard roller to feed a document in a document conveyance direction. Further, the control unit causes the lift motor to start lowering the lift plate while the pickup roller is feeding a document after starting to rotate the pickup roller. When there is a document set on the lift plate at the time when the pickup roller stops, the control unit automatically resumes the feeding in the manual feed mode.

A sheet feeder includes a separation roller, a retard roller, and a return latch. The separation roller rotates in a forward direction to separate a sheet and transport the separated sheet in a sheet transport direction. The retard roller forms, together with the separation roller, a nip point and rotates in a reverse direction to return a sheet in a direction opposite to the sheet transport direction. The return latch moves from a retracted position to a protruding position to return a sheet remaining after separation by the separation roller to a position upstream of the nip point in the sheet transport direction. The return latch, when at the retracted position, is retracted from a sheet transport path and, when at the protruding position, protrudes to the sheet transport path.

Provided are: a sheet feed device that is capable of suppressing the occurrence of a sheet feeding fault by changing the pressing contact force of a retard roller against a feed roller; and an image formation device equipped with the same. This sheet feed unit (50) is provided with: a pickup roller (29); a feed roller (31); a retard roller (32); a holding member (40) that holds the retard roller (32); a first biasing member (42) that biases the holding member (40); and a pressing contact force changing mechanism (60) that changes the pressing contact force of the retard roller (32) against the feed roller (31). The pressing contact force changing mechanism (60) has: a rotary shaft (61) disposed parallel to the axial direction of the retard roller (32); a cam member (70) that rotates with the rotary shaft (61); and a movable member (80) that contacts the cam member (70), moves in the axial direction in conjunction with the rotation of the cam member (70), and changes the biasing force generated by the first biasing member (42).