Sheet Conveying Mechanism and Image Forming Apparatus

This application claims the benefit of priority to Chinese Patent Application No. 202410686714.6, filed on May 30, 2024 with China National Intellectual Property Administration, and entitled “SHEET CONVEYING MECHANISM AND IMAGE FORMING APPARATUS”, the entire disclosure of which is incorporated herein by reference.

The present disclosure relates to the field of printing technology, and more particularly to a sheet conveying mechanism and an image forming apparatus.

In an image forming apparatus, a sheet detection unit is configured to scan an external dimension and a surface of a sheet. When there is a conveying abnormality of the sheet in a sheet feeding unit of the image forming apparatus, an abnormal sheet is discharged to a sheet discharging tray through a sheet discharging channel.

On the one hand, in order to ensure an image detection performance of the sheet, it is necessary to maintain a certain distance between the sheet and the sheet detection unit. Usually, a height of a sheet conveying path of a conveying track of the image forming apparatus is within 1 mm, and a distance between the sheet and a centerline of the conveying track is within ±0.5 mm. However, when a thickness of the sheet does not exceed 0.6 mm, if a sheet jam is caused by a sheet multi-feed, i.e., simultaneous feeding of two or more sheets, a maximum thickness of two sheets can reach 1.2 mm. Considering a dimensional tolerance of the conveying track, in order to ensure a sheet multi-feeding performance, the height of the sheet conveying path of the conveying track needs to be at least 2 mm.

On the other hand, in order to ensure the image detection performance, it is necessary for the sheet to have a certain degree of movement accuracy relative to the sheet detection unit. The sheet detection unit takes photos and reads images of the sheet during moving the sheet. The greater the change in the direction of sheet conveying, the greater the impact on the external dimension of the sheet and the accuracy of image reading. However, in order to prevent slipping in heavy sheet multi-feed and suppress conveying errors during conveying process, a conveying roller pair needs to have a conveying pressure (clamping force), usually around 30N. If the conveying pressure of the conveying roller pair is too high, when a front end of the sheet protrudes into the conveying roller pair, the impact changes greatly, and the speed of the front end of the sheet changes greatly.

Therefore, the existing image forming apparatus has following problems: (1) the image detection performance requires the sheet conveying path of the conveying track to be less than 1 mm, while the sheet multi-feeding performance requires the sheet conveying path of the conveying track to be greater than 2 mm; (2) the image detection performance requires a low conveying pressure of the conveying roller pair, while the sheet multi-feeding performance requires a high conveying pressure of the conveying roller pair.

The existing image forming apparatus cannot simultaneously ensure the image detection performance and the sheet multi-feeding performance.

In order to resolve above-mentioned problem, an embodiment of the present disclosure provides a sheet conveying mechanism and an image forming apparatus, which can simultaneously ensure an image detection performance and a sheet multi-feeding performance of a sheet.

According to an aspect of the present disclosure, a sheet conveying mechanism, includes: a sheet feeder that conveys a sheet to a sheet conveying path; a conveying track that defines the sheet conveying path of the sheet; and a conveying roller pair that conveys the sheet along the sheet conveying path. The sheet conveying mechanism further includes: a conveying track separator that adjusts a height of the sheet conveying path, wherein the sheet conveying path has at least a first height and a second height, and the second height is greater than the first height; and a conveying roller separator that adjusts a clamping force of the conveying roller pair, wherein the conveying roller pair has at least a first clamping force and a second clamping force, and the second clamping force is smaller than the first clamping force.

According to another aspect of the present disclosure, an image forming apparatus, includes: a sheet conveying mechanism according to the above-described aspect, that conveys a sheet; and an image former that forms an image on the sheet

The implementation and application of specific embodiments will be discussed in detail below. However, it should be understood that the specific embodiments discussed only exemplarily illustrate specific ways of implementing and applying the present disclosure, and are not limiting the scope of the present disclosure. In the following description, some directional representations, such as “left”, “right”, “top”, “bottom”, “front”, “back”, are used with reference to the directions shown in the drawings. When the components are arranged as shown in the drawings, these directional representations are appropriate, but when the positions of the components in the drawings change, these directional representations also change accordingly.

In an image forming apparatus (i.e., image former), a sheet detection unit (i.e., sheet detector) is configured to scan an external dimension and a surface of a sheet. In a sheet conveying mode, the sheet is conveyed from a sheet feeding unit (i.e., sheet feeder) to an image forming unit through the sheet detection unit. When there is a conveying abnormality of the sheet, such as a sheet multi-feed, in the sheet feeding unit, the apparatus switches to a sheet discharging mode and an abnormal sheet is discharged to a sheet discharging tray through a sheet discharging channel.

The existing image forming apparatus has following problems: (1) the image detection performance requires the sheet conveying path of the conveying track to be less than 1 mm, while the sheet multi-feeding performance requires the sheet conveying path of the conveying track to be greater than 2 mm; (2) the image detection performance requires a low conveying pressure of the conveying roller pair, while the sheet multi-feeding performance requires a high conveying pressure of the conveying roller pair.

Accordingly, an embodiment of the present disclosure provides a sheet conveying mechanism. The sheet conveying mechanism includes: a sheet feeding unit configured to convey a sheet to a sheet conveying path; a conveying track configured to define the sheet conveying path of the sheet; and a conveying roller pair configured to convey the sheet along the sheet conveying path. The sheet conveying mechanism further includes: a conveying track separation device (i.e., conveying track separator) configured to adjust a height of the sheet conveying path, wherein the sheet conveying path has at least a first height and a second height, and the second height is greater than the first height; and a conveying roller separation device (i.e., conveying roller separator) configured to adjust a clamping force of the conveying roller pair, wherein the conveying roller pair has at least a first clamping force and a second clamping force, and the second clamping force is smaller than the first clamping force.

In order to simultaneously ensure the image detection performance and the sheet multi-feeding performance, the embodiment of the present disclosure provides a conveying track separation device and a conveying roller separation device. An optimal design based on sheet type, sheet size, scheduled time and sheet conveying mode can ensure an appropriate height of the sheet conveying path and the clamping force of the conveying roller pair. By optimizing the height of the sheet conveying path and the clamping force of the conveying roller pair, the image detection performance of the image forming apparatus can be improved, the sheet multi-feeding performance can be ensured, and the sheet handling capability of the image forming apparatus can be enhanced.

As shown in, an image forming apparatusincludes a sheet conveying mechanismand an image forming unit. The sheet conveying mechanismis configured to convey a sheet, and the image forming unitmay be a printing body, configured to form an image on the sheet.

The sheet conveying mechanismincludes a sheet feeding unit, a conveying track, a conveying roller pair, a conveying track separation device and a conveying roller separation device. The sheet feeding unitis configured to convey a sheet to a sheet conveying path. The conveying track is configured to define the sheet conveying path of the sheet. The conveying roller pair is configured to convey the sheet along the sheet conveying path. The conveying track separation device is configured to adjust a height of the sheet conveying path. The sheet conveying path has at least a first height and a second height, and the second height is greater than the first height. The conveying roller separation device is configured to adjust a clamping force of the conveying roller pair. The conveying roller pair has at least a first clamping force and a second clamping force, and the second clamping force is smaller than the first clamping force.

In some embodiments, the sheet conveying mechanism further includes a control unit (i.e., hardware processor) configured to have a sheet conveying mode and a sheet discharging mode. In a normal conveying state, the control unit is in the sheet conveying mode, and the sheet is conveyed to the image forming unitand then an image is printed on the sheet. When a conveying abnormality occurs, the control unit switches to the sheet discharging mode and the abnormal sheet is discharged through a vertical conveying pathto a sheet discharging tray.

In some embodiments, during a sheet conveying process, a sheet grammage and/or a size of each sheet are automatically detected by a sheet detection sensor. When there is a significant difference between a real-time detection results and parameters set for printing, it is determined that the sheet is an incorrect sheet and needs to be automatically discharged, and the sheet conveying mechanism switches to the sheet discharging mode.

As shown in, the sheet feeding unitis provided with a sheet multi-feeding detection sensorconfigured to detect whether a sheet multi-feed has occurred in the sheet feeding unit. When the sheet multi-feeding detection sensordetects a sheet multi-feed in the sheet feeding unit, the control unit switches from the sheet conveying mode to the sheet discharging mode, and the abnormal sheet is discharged through the vertical conveying pathto the sheet discharging tray.

In some embodiments, the sheet conveying mechanismfurther includes a sheet detection unitconfigured to detect the sheet. The sheet detection unitmay be a sheet image scanner based on a contact image sensor (CIS). The conveying roller pair includes an upstream conveying roller pairand a downstream conveying roller pairlocated on two sides of the contact image sensor. During continuous sheet conveying process, the sheet is scanned by the contact image sensorto obtain an image of an external shape of the sheet, and an external dimension of the sheet are calculated by scanning the image.

In some embodiments, the sheet conveying mechanismfurther includes multiple position detection sensors PS, PS, PS, PSand PSconfigured to detect whether the sheet has arrived or passed through a conveying roller pair adjacent to the position detection sensors. For example, the position detection sensors PSand PSare located on two sides of the upstream conveying roller pair, and the position detection sensor PSis located at downstream of the downstream conveying roller pair.

In some embodiments, in the sheet conveying mode, the sheet conveying path has the first height, and in the sheet discharging mode, the control unit is configured to switch the sheet conveying path from the first height to the second height.

In some embodiments, in the sheet discharging mode, the control unit is configured to further determine whether to switch the sheet conveying path from the first height to the second height based on a conveying abnormality of the sheet.

Specifically, in the sheet discharging mode, when a sheet multi-feed is detected, the control unit is configured to switch the sheet conveying path from the first height to the second height.

In some embodiments, in the sheet discharging mode, the control unit is configured to further determine whether to switch the sheet conveying path from the first height to the second height based on a sheet grammage of the sheet.

Specifically, in the sheet discharging mode, when the sheet grammage of the sheet exceeds 300 gsm or a thickness of the sheet exceeds 0.3 mm, the sheet conveying path is switched from the first height to the second height.

In some embodiments, in the sheet discharging mode, when a sheet multi-feed is detected, the control unit is configured to further determine whether to switch the sheet conveying path from the first height to the second height based on the sheet grammage of the sheet.

In some embodiments, as shown in, the control unit is configured to perform the following operations:

In some embodiments, as shown in, the control unit is configured to perform the following operations:

In some embodiments, as shown in, the control unit is configured to perform the following operations:

In some embodiments, when starting to convey the sheet from the sheet feeding unit, if a conveying abnormality occurs, the sheet will conveyed to a designated position and wait for a clearing operation. When it is determined that a sheet multi-feed occurs, it is necessary to determine whether to increase the height of the sheet conveying path by the conveying track separation device.

In some embodiments, as shown in, the control unit is configured to perform the following operations:

In some embodiments, a status of the multi-feed sheet when starting multi-feeding inspection is determined by determining whether the sheet has reached the conveying roller. If the front end of the multi-feed sheet is greatly offset, the front end of the multi-feed sheet has already reached the furthest downstream conveying roller when starting the multi-feeding inspection. The multi-feed sheet in this state is not suitable for automatic discharging, and it is safer to manually deal with the fault.

In some embodiments, in the sheet conveying mode, before a front end of the sheet enters the conveying roller pair, the conveying roller pair has the first clamping force, when the front end of the sheet enters the conveying roller pair, the conveying roller pair has the second clamping force, and after the front end of the sheet enters the conveying roller pair, the conveying roller pair has the first clamping force. In the sheet discharging mode, the conveying roller pair has the first clamping force.

In some embodiments, in the sheet conveying mode, before a rear end of the sheet leaves the conveying roller pair, the conveying roller pair has the first clamping force, when the rear end of the sheet leaves the conveying roller pair, the conveying roller pair has the second clamping force, and after the rear end of the sheet leaves the conveying roller pair, the conveying roller pair has the first clamping force. In the sheet discharging mode, the conveying roller pair has the first clamping force.

In practical applications, whether the front end of the sheet enters the conveying roller pair and whether the rear end of the sheet leaves the conveying roller pair are detected by position detection sensors, such as multiple position detection sensors PS, PS, PS, PSand PS. By switching the clamping force of the conveying roller pair from the first clamping force to the second clamping force when the sheet enters and leaves the conveying roller pair, an impact on the sheet is reduced.

In some embodiments, the sheet conveying mechanismfurther includes a sheet detection unitconfigured to detect the sheet. The sheet detection unitincludes a contact image sensor. The conveying roller pair includes an upstream conveying roller pairand a downstream conveying roller pairlocated on two sides of the contact image sensor. In the sheet conveying mode, before the front end of the sheet enters the downstream conveying roller pair, the downstream conveying roller pairhas the first clamping force. When the front end of the sheet enters the downstream conveying roller pair, the downstream conveying roller pairhas the second clamping force. After the front end of the sheet enters the downstream conveying roller pair, the downstream conveying roller pairhas the first clamping force. Before the rear end of the sheet leaves the upstream conveying roller pair, the upstream conveying roller pairhas the first clamping force. When the rear end of the sheet leaves the upstream conveying roller pair, the upstream conveying roller pairhas the second clamping force, and after the rear end of the sheet leaves the upstream conveying roller pair, the upstream conveying roller pairhas the first clamping force. When the rear end of the sheet leaves the upstream conveying roller pair, if the pressure of the conveying roller pair is small, the posture of the rear end of the sheet is more stable, which is more conducive to scanning the image of the sheet.

In the sheet discharging mode, the upstream conveying roller pairand the downstream conveying roller pairhave the first clamping force.

In some embodiments, when the front end of the sheet reaches a first predetermined position, the conveying roller separation device adjusts the clamping force of the downstream conveying roller pair, and when the rear end of the sheet reaches a second predetermined position, the conveying roller separation device adjusts the clamping force of the upstream conveying roller pair.

In some embodiments, the sheet conveying mechanism further includes a first detection sensor and a second detection sensor. The first detection sensor is configured to detect whether the front end of the sheet has reached the first predetermined position, and the second detection sensor is configured to detect whether the rear end of the sheet has reached the second predetermined position.

illustrates a working timing diagram of a control unit of a sheet conveying mechanism according to another embodiment of the present disclosure.

t: When the front end of the sheet reaches PSfor a certain time t, the front end of the sheet reaches the CIS detection sensor, and the sheet image scanner begins to detect.

t: When the front end of the sheet reaches PSfor a certain time t, the front end of the sheet reaches the downstream conveying roller pair, and the conveying track separation device of the downstream conveying roller pairacts to switch the clamping force of the downstream conveying roller pairfrom the first clamping force to the second clamping force.

t: When the front end of the sheet protrudes into the downstream conveying roller pairfor a certain time t, the conveying track separation device of the downstream conveying roller pairacts to switch the clamping force of the downstream conveying roller pairfrom the second clamping force to the first clamping force.

t: When the rear end of the sheet leaves PSfor a certain time t, the rear end of the sheet leaves the upstream conveying roller pair, and the conveying track separation device of the upstream conveying roller pairacts to switch the clamping force of the upstream conveying roller pairfrom the first clamping force to the second clamping force.

t: When the conveying track separation device of the upstream conveying roller pairacts for a certain time t, the rear end of the sheet leaves the upstream conveying roller pair, and the conveying track separation device of the upstream conveying roller pairacts to switch the clamping force of the upstream conveying roller pairfrom the second clamping force to the first clamping force.

t: When the rear end of the sheet leaves PSfor a certain time t, the rear end of the sheet leaves the CIS detection sensor, and the detection of the sheet image scanner ends.

In some embodiments, as shown in, the control unit is configured to perform the following operations:

In some embodiments, as shown in, the conveying track separation deviceincludes a first driving motor, a first driving beltand a first rotary cam. The first driving motordrives the first rotary camto rotate through the first driving belt. When the first rotary camrotates, the first rotary camdrives a track mounting plateto move up and down to adjust the height of the sheet conveying path of the conveying track. For example, an upper track of the conveying track is installed on the track mounting plate, which drives the upper track to move up and down to adjust a distance between the upper track and a lower track, so as to adjust the height of the sheet conveying path. The first driving motormay adopt a high-precision stepper motor, a servo motor, etc. The driving transmission method may adopt a driving belt, a driving gear, a rack, etc. The separation action may be achieved by sliding the rotary cam up and down, or by rotating the rotary cam and a rotary shaft.