A medium feeding device includes an imaging unit which images a medium tip end portion from a position of facing a face of the medium on a downstream side of a nipping position of the medium using a feeding unit and a separating unit; and a determining unit which determines whether or not there is transport disorder by evaluating a state of a boundary between a path member which forms a medium transport path and a medium tip end from image data obtained by the imaging unit, in which the determining unit sets a rectangular determining region including at least a part of the boundary with respect to the image data, and determines whether or not there is transport disorder based on a length of a boundary in the determining region.

A liquid ejection apparatus, including: a conveyor; and an ejector to eject a liquid; wherein each of an upstream roller pair, a first downstream roller pair, and a second downstream roller pair of the conveyor includes upper and lower rollers to respectively contact front and back surfaces of a recording medium, at least one of the upper and lower rollers being configured to give a conveyance force to the recording medium, wherein a rotation speed of the second downstream roller pair is higher than that of the first downstream roller pair, and the conveyance force of the first downstream roller pair is larger than that of the second downstream roller pair, and wherein the conveyance force of the second downstream roller pair is largest at a position thereof in the first direction which is nearest to the central position of the second downstream roller pair.

A sheet transport device includes pre-transfer sheet-transport rollers that transport a sheet to a transfer position at which an unfixed image is transferred, the pre-transfer sheet-transport rollers including a first roller in which three or more separate rollers attached to a first shaft rotate, and a second roller in which three or more separate rollers attached to a second shaft are in contact with the separate rollers of the first roller and rotate. The hardness of an inner separate roller of the first roller is lower than the hardness of end separate rollers of the first roller. The outside diameter of an inner separate roller of the second roller is greater than the outside diameter of end separate rollers of the second roller.

A document feeding device include a feeding unit feeding documents from a batch of documents on a placing tray, a separation member in pressure contact with the feeding unit and separating documents one by one, a separation swinging member supporting the separation member and displaceable in a thickness direction of the batch of documents, and a movable member supported as to be displaceable with respect to the separation swing member in the thickness direction of the batch of documents, and entering a space formed between the separation member and a document.

A medium, of which skew is appropriately corrected, is fed from an intermediate unit to a post processing unit so as to suppress an adverse effect of the skew of the medium in the post processing unit.

A paper conveying device includes: a roller shaft having a first engaging portion and configured to rotate integrally with the first engaging portion; and a roller unit having a second engaging portion and provided on the roller shaft, the roller unit being configured to convey a sheet of paper as the roller unit rotates while being in contact with the sheet of paper. In an engaged state where the first engaging portion and the second engaging portion engage with each other, the roller unit is restricted from moving in an axis direction relative to the roller shaft. In a disengaged state where the first engaging portion and the second engaging portion disengage from each other, the roller unit is movable in the axis direction relative to the roller shaft.

A paper thickness detecting device that detects a paper thickness in accordance with a detection signal of a displacement sensor, includes: a pair of paper thickness detecting rollers including a first roller and a second roller that pinch a paper conveyed via a pair of conveyance rollers; and the displacement sensor that detects a displacement amount of the pair of paper thickness detecting rollers at the time when the paper passes through the pair of paper thickness detecting rollers, wherein the paper thickness is detected on the basis of the displacement amount of the pair of paper thickness detecting rollers that follows to rotate with respect to the paper conveyed via the pair of conveyance rollers.

A document conveying apparatus includes a first conveying roller for conveying a document stacked on the document tray, a second conveying roller, provided at a downstream side with respect to the first conveying roller, for conveying a document stacked on the document tray, a separation roller, provided at a downstream side with respect to the second conveying roller, for performing separation operation of the document, a driving force transmission mechanism for transmitting the driving force to a driving shaft of the first conveying roller, a driving shaft of the second conveying roller, and a driving shaft of the separation roller, and a first blocking mechanism, provided between the first conveying roller and the driving shaft of the first conveying roller, for blocking a driving force transmitted to the driving shaft of the first conveying roller, for a first certain period of time.

A medium transportation device includes a transportation driving roller that transports a medium; a roller unit including a separation roller as a driven roller that is rotated by rotation of the transportation driving roller and a shaft which penetrates a rotation center of the separation roller; a holder that detachably holds the roller unit; and a lock mechanism that switches between an unlocked state in which the roller unit is unlocked from the holder and a locked state in which the roller unit is locked to the holder.

A sheet feeder includes: a casing; a first roller; and a pressing portion. The casing defines therein a conveying region through which a sheet is conveyed in a conveying direction. The first roller has a rotation axis extending in an axial direction crossing the conveying direction and rotatable about the rotation axis. The first roller has a portion exposed to the conveying region. The pressing portion is movable in a direction crossing the conveying region between a first position and a second position. The pressing portion is urged toward the first roller to provide the first position. The pressing portion in the first position has a portion disposed within the conveying region and spaced apart from the first roller by a prescribed distance. The pressing portion in the second position is separated from the first roller farther than in the first position.