INCORPORATION BY REFERENCE

This application is based on and claims the benefit of Japanese Patent Application No. 2020-083067 filed on May 11, 2020 and Japanese Patent Application No. 2021-057376 filed on Mar. 30, 2021, the contents of which are hereby incorporated by reference.

BACKGROUND

The present disclosure relates to a document conveying device that conveys a document toward a reading position.

Apparatuses that convey a sheet and perform a job are known. Such apparatuses include, for example, image forming apparatuses. A conveyed sheet may skew (suffer skewing). For example, if a sheet conveyed in an image forming apparatus skews, the printed image skews. Generally, a sheet is often thrust against a roller called a registration roller to correct a skew (skewed feeding). On the other hand, in some apparatuses, a sheet is intentionally not thrust against a roller. A known technology of not thrusting a sheet against a registration roller will be described below.

Specifically, a known image forming apparatus includes a transfer portion that transfer an image to a sheet, a registration roller that is provided upstream of the transfer portion in the sheet conveying direction, and a controller that controls the operation of the registration roller. The controller performs registrationless operation that does not involve thrusting the leading end of a sheet in the conveying direction against the registration roller, and then controls the swinging of the registration roller so that an image will be transferred in the right position in the sheet conveying direction. The controller performs either registrationless operation or registration operation in accordance with the shape of a sheet. The registration roller is swung in the direction perpendicular to the sheet conveying direction.

An image sensor is often used to read a document to obtain the image data of the document. For example, an apparatus provided with a copying function reads a document to generate image data and performs printing based on the generated image data.

Also often used is a document conveying device that continuously and automatically feeds one document after another toward a reading position. Using such a document conveying device allows continuous reading of a plurality of documents. A conveyed document may skew. In that case, the image in the image data obtained by reading skews. To cope with that, generally, a document conveying device includes a pair of registration rollers. In such a document conveying device, the leading end of a document is thrust against the pair of registration rollers at rest. This permits the leading end of the document to lie along the nip between the pair of registration rollers. Thus the skewing of the document is corrected. After skew correction, the pair of registration rollers starts to be rotated, so that the document with no skew is fed out.

Using a pair of registration rollers has also the advantage of making it easy to keep constant intervals between documents (sheet-to-sheet intervals). For example, the pair of registration rollers starts to be rotated at constant time intervals. For example, in a case where 30 documents are fed per minute, the pair of registration rollers starts to be rotated every two seconds. Feeding documents out at constant intervals prevents too short a sheet-to-sheet interval.

Not thrusting documents against the pair of registration rollers (not stopping documents at the pair of registration rollers) may result in too short a sheet-to-sheet interval. Specifically, a preceding document may drag the subsequent document to cause the subsequent document to protrude downstream in the conveying direction. How easily a document tends to protrude downstream depends on the paper quality of the document and how the document is set. If a subsequent document protrudes downstream in the conveying direction, it has a shorter interval from the preceding document. When documents are not stopped at the pair of registration rollers, the sheet-to-sheet interval is not adjusted. Thus not stopping documents at the pair of registration rollers may make it impossible to keep an adequate sheet-to-sheet interval.

The image forming apparatus mentioned above cannot cope with a subsequent sheet being drawn by the preceding sheet. The image forming apparatus mentioned above cannot control the sheet-to-sheet interval, often resulting in too short a sheet-to-sheet interval.

SUMMARY

According to one aspect of the present disclosure, a document conveying device includes a document tray, a first rotary member, a first motor, a second rotary member, a second motor, a document feed sensor, and a controller. On the document tray, a plurality of documents can be set. The first rotary member feeds one document after another out of the documents set on the document tray. The first motor rotates the first rotary member. The second rotary member is provided downstream of the first rotary member in a document conveying direction, and feeds the document toward a reading position. The second motor rotates the second rotary member to make it convey the document at a previously determined second conveyance speed. The document feed sensor is provided downstream of the first rotary member in the document conveying direction, upstream of the second rotary member in the document conveying direction. The controller recognizes, based on the output of the document feed sensor, the leading end of the document reaching the document feed sensor and the trailing end of the document leaving the document feed sensor. When the document starts to be conveyed, the controller starts to rotate the first motor. After the first motor starts to rotate until the leading end of the document reaches the document feed sensor, the controller rotates the first motor at a speed equal to or lower than a first rotation speed for conveying the document at a speed equal to or lower than a previously determined first conveyance speed. After the leading end of the document reaches the document feed sensor until the trailing end of the document leaves the document feed sensor, the controller changes the rotation speed of the first motor to a second rotation speed for conveying the document at the second conveyance speed. After the rotation speed of the first motor reaches the second rotation speed until the subsequent one of the documents starts to be fed, the controller stops the first motor. The controller counts as a counted time the time from the time point of the start of rotation of the first motor until the leading end of the document reaches the document feed sensor. When a time resulting from subtracting the counted time from a previously determined required sheet-to-sheet time interval is longer than a required speed change time, the controller performs deceleration and post-deceleration acceleration for the first motor to adjust the sheet-to-sheet interval between the document being fed and the preceding document. The required speed change time is the time required for speed change from the first rotation speed to the second rotation speed.

According to another aspect of the present disclosure, a method of controlling a document conveying device includes: setting a plurality of documents on a document tray; feeding, with a first rotary member, one document after another out of the documents set on the document tray; rotating, with a first motor, the first rotary member; feeding, with a second rotary member provided downstream of the first rotary member in a document conveying direction, the document toward a reading position; rotating, with a second motor, the second rotary member so that the second rotary member conveys the document at a previously determined second conveyance speed; providing a document feed sensor downstream of the first rotary member in the document conveying direction, upstream of the second rotary member in the document conveying direction; recognizing, based on an output of the document feed sensor, the leading end of the document reaching the document feed sensor and the trailing end of the document leaving the document feed sensor; starting, when the document starts to be conveyed, to rotate the first motor; rotating, after the first motor starts to rotate until the leading end of the document reaches the document feed sensor, the first motor at a speed equal to or lower than a first rotation speed for conveying the document at a speed equal to or lower than a previously determined first conveyance speed; changing, after the leading end of the document reaches the document feed sensor until the trailing end of the document leaves the document feed sensor, the rotation speed of the first motor to a second rotation speed for conveying the document at the second conveyance speed; stopping, after the rotation speed of the first motor reaches the second rotation speed until the subsequent one of the documents starts to be fed, the first motor; counting as a counted time the time from the time point of the start of rotation of the first motor until the leading end of the document reaches the document feed sensor; performing, when the time resulting from subtracting the counted time from a previously determined required sheet-to-sheet time interval is longer than a required speed change time, deceleration and post-deceleration acceleration for the first motor to adjust the sheet-to-sheet interval between the document being fed and the preceding document; and the required speed change time being the time required for speed change from the first rotation speed to the second rotation speed.

This and other objects of the present disclosure, and the specific benefits obtained according to the present disclosure, will become apparent from the description of embodiments which follows.

