US20090127775A1

US20090127775A1 - Image forming system

Info

Publication number: US20090127775A1
Application number: US12/267,993
Authority: US
Inventors: Hiroyuki Takahashi; Wataru Kawata
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2007-11-15
Filing date: 2008-11-10
Publication date: 2009-05-21
Also published as: JP2009122415A

Abstract

A sheet position detecting portion which detects a position of the sheet in which the image is formed by the image forming portion, a control portion which controls a motion of the inverting portion, and a sheet post-processing apparatus which is connected to the image forming portion and receives the sheet discharged from the discharging portion so as to apply an post-processing, and the control portion can change the motion of the inverting portion based on a detected information of the sheet position detecting portion, in such a manner that an interval time of the continuous sheets becomes equal to or more than a sheet interval time which the sheet post-processing apparatus can receive the sheet.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an image forming system in which a sheet post-processing apparatus can be connected to an image forming portion.
2. Description of the Related Art
Generally, in the image forming system, in order to enhance a productivity, a subsequent sheet is sequentially fed without waiting for an image formation of a preceding sheet. Accordingly, a plurality of sheets exist in a conveying path. Further, if the preceding sheet is retarded, the subsequent sheet is temporarily stopped following the preceding sheet, in such a manner as to prevent the subsequent sheet from catching up on the preceding sheet.
Conventionally, in this kind of image forming system, an inverse conveying unit is driven at a constant speed or timing, a conveying speed and a conveying timing of a recording sheet are changed by a change of a conveying performance, and a dispersion is generated in a paper interval so as to be an obstacle in the case of increasing a continuous image forming efficiency. In other words, it is necessary to set a paper interval wide for avoiding a conveying failure due to the dispersion of the paper interval. As a result, it is hard to enhance the image forming efficiency.
In order to solve the problem mentioned above, there is an image forming apparatus structured such that a continuous image is formed always at a constant paper interval, by carrying out a conveying control correcting a change of a conveying performance of an inverse conveying unit which tends to be affected by a change such as an abrasion based on an actuation for a long term (refer to Japanese Patent Application Laid-Open No. 2002-211815).
Further, there is an image forming apparatus structured such that a conveying failure is prevented by defining a distance interval between sheets constant and inverting the sheet, in accordance with a speeding up of the image forming apparatus (refer to Japanese Patent Application Laid-Open No. 2001-240285).
In these image forming apparatuses, it is not necessary to take into consideration a dispersion at a time of setting the paper interval in the continuous image forming, it is possible to narrow down the paper interval, and it is possible to enhance the productivity of the image forming apparatus.
Further, in the conventional sheet post-processing apparatus, since the paper interval time which can execute the post-processing is narrower than the paper interval time of the image forming apparatus so as to afford, the post-processing can be executed without degrading the productivity, even if the paper interval dispersion exists within the image forming apparatus. Japanese Patent Application Laid-Open No. 2002-311659 sets the sheet interval to which the post-processing apparatus can correspond. The sheet interval set in the structure of Japanese Patent Application Laid-Open No. 2002-311659 is set while having a margin such that the post-processing apparatus can correspond even if a slip between the sheet and the conveying roller is generated within the image forming apparatus. Accordingly, there is a limit for shortening the interval between the sheets within the image forming apparatus so as to improve the productivity.
In this case, in an accessory (ACC) such as the sheet post-processing apparatus receiving the image forming apparatus having a high productivity in an in-line, the paper interval time which can execute the post-processing becomes approximately equal to the paper interval time of the image forming apparatus.
Accordingly, if the paper interval of the image forming apparatus becomes shorter than the paper interval time which the sheet post-processing apparatus can execute the post-processing, at a time when the paper interval is dispersed in the image forming apparatus, whereby the sheet is discharged from the image forming apparatus so as to be sent to the post-processing apparatus, there is a risk that the paper interval can not be corresponded by the sheet post-processing apparatus.
In the conventional paper interval dispersion suppressing unit (refer to Japanese Patent Application Laid-Open No. 2002-211815), a driving unit of an inverse conveying unit is controlled in such a manner as to detect a change of a conveying performance of the inverse conveying unit and achieve a constant conveying performance based on the detection, however, it does not take into consideration a paper interval between a preceding paper under conveying and a subsequent paper.
Accordingly, in the case that the paper interval changes suddenly, the paper is discharged from the image forming apparatus as it is without taking into consideration a receiving condition of the post-processing apparatus. In other words, in the case that the paper interval time becomes shorter over the receiving condition of the post-processing apparatus, there is a possibility that the post-processing failure is generated.
Further, in Japanese Patent Application Laid-Open No. 2001-240285, there is described that a speed of the inverting roller is adjusted in the case of correcting the paper interval dispersion by the speed of the conveying unit. However, unless a speed of a downstream roller is simultaneously adjusted, there is generated a step out of a driving motor for the roller caused by tugging the sheet from both sides, a damage applied to the sheet caused by pressing the sheet based on a speed difference between the inverting roller and the downstream roller. Further, since the sheet post-processing apparatus is not provided by taking into consideration the paper interval time which can be post-processed, for example, if the paper interval time becomes shorter than the paper interval time which the sheet post-processing apparatus can correspond to, there is a risk that the paper interval time can not be corresponded by the sheet post-processing apparatus.

SUMMARY OF THE INVENTION

A technical feature of the present invention is made by taking the circumstances mentioned above into consideration, and the present invention provides an image forming system which can detect a dispersion in a sheet conveyed within an image forming portion, and can stably carry out an post-processing while securing a high image forming productivity.
The image forming system according to the present invention has an image forming portion which forms an image in a sheet, an inverting portion which inverts the sheet in which the image is formed by the image forming portion, a discharging portion which discharges the sheet inverted by the inverting portion, a sheet position detecting portion which detects a position of the sheet in which the image is formed by the image forming portion, a control portion which controls a motion of the inverting portion, and a sheet post-processing apparatus which is connected to the image forming portion and receives the sheet discharged from the discharging portion so as to apply an post-processing, wherein the control portion can change the motion of the inverting portion based on a detected information of the sheet position detecting portion, in such a manner that an interval time of the continuous sheets becomes equal to or more than a sheet interval time which the sheet post-processing apparatus can receive the sheet.
According to the present invention, it is possible to adjust the paper interval time of the sheet discharged from the image forming portion in a range that the sheet post-processing apparatus can receive, while securing a high image forming productivity.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view of a sheet conveying path of an image forming system according to an embodiment of the present invention;

FIG. 2 is a sequence diagram at a time of conveying the sheet in the image forming system in FIG. 1;

FIG. 3 is a block diagram of a control system of the image forming system in FIG. 1;

FIG. 4 is a flow chart describing a control of the image forming system in FIG. 1; and

FIG. 5 is a flow chart describing another control of the image forming system in FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

Embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. In this case, dimensions, materials, shapes, relative arrangements and the like of constructing parts described in this embodiment are not in effect of limiting the range of this invention to them, unless otherwise specified.

First Embodiment

FIG. 1 is a view describing a sheet conveying path of one embodiment according to an image forming system of the present invention. FIG. 2 is a sequence diagram at a time of conveying the sheet in the image forming system in FIG. 1. FIG. 3 is a block diagram of a control system of the image forming system in FIG. 1. FIG. 4 is a flow chart describing a control of the image forming system in FIG. 1.
In FIG. 1, an image forming system 1 has an image forming portion 10 and a finisher 100 corresponding to a sheet post-processing apparatus. The image forming portion 10 includes an image reader which reads a document image and is not illustrated and a printer. A document feeding apparatus is mounted to the image reader. The document feeding apparatus feeds the document which is set upward on a document tray, one by one from a leading page through a reading position on a platen glass via a curved path, and discharges to an external discharge tray.
In a sheet cassette 11, a sheet S is sequentially fed out by a sheet feeding roller 12. The fed sheet S is conveyed to a registration roller 16 which stops its rotating motion by path rollers 13 and 14. The sheet S conveyed to the registration roller 16 is removed its skew feeding. In the drawing, an image reference sensor 15 is arranged in a downstream side of the path rollers 13 and 14, and serves as a sheet position detecting portion which detects a position of the fed sheet S.
A toner image formed on a photosensitive drum 21 is transferred to the sheet S in a transfer portion 20 in a state of aligning the toner image formed on the photosensitive drum 21 with a position in a conveying direction of the sheet S conveyed from the registration roller 16, by driving the registration roller 16 at a predetermined timing.
The transfer portion 20 is structured such that an endless transferring belt 22 is wound around a drive roller 22 a and a driven roller 22 b, and a corona charger (not illustrated) for transferring is arranged in an approximately opposing portion of the photosensitive drum 21 in an inner side of the transferring belt 22.
Accordingly, it is possible to transfer and convey in a state that a transferring material is adsorbed to the transferring belt 22, and the image transferred to the sheet S is fixed by a fixing portion 17. In this case, an extra toner and a paper powder on a surface of the transferring belt 22 and a surface of the photosensitive drum 21 are cleaned.
The fixing portion 17 fixes a developer image on the sheet S by thermally pressing the sheet S. The sheet S passing through the fixing portion 17 is discharged toward a finisher 100 from a discharge port 27 a corresponding to a discharge portion of the image forming portion 10 via a switching member (a flapper) 18 and a discharge roller 27. The discharge port 20 a in this case is a portion serving as a sheet delivery portion between the image forming portion 10 and the finisher 100.
The sheet S conveyed by the discharge roller 27 and discharged from the discharge port 27 a is received by a receiving roller 101 of the finisher 100, and is discharged and stacked to a sheet stack tray 104 by a discharge roller 102 while directing the image forming surface upward.
In the case of discharging to the finisher 100 while directing the image forming surface of the sheet S inversely, the sheet S discharged form the fixing portion 17 is introduced to an inverting path in which a first inverting roller 19 is arranged, by switching the switching member 18.
In this case, a trailing end of the sheet S is conveyed to a predetermined amount downstream position of the fixing portion 17 while being sped up, and a second inverting roller 24 is stopped in such a manner that the sheet trailing end is positioned at a predetermined amount upstream position (an inverting point) of the second inverting roller 24, after being conveyed at the predetermined amount.
Thereafter, the sheet S is conveyed to the discharge roller 27 side by an inverting conveying roller 26 corresponding to a conveying portion by inverting the second inverting roller 24, and is conveyed to the finisher 100. Further, in the drawing, a first inverting sensor 23 is arranged in an upstream side of the first inverting roller 19, and detects a position of the sheet S before being inverted, and a second inverting sensor 25 is arranged in a downstream side of the second inverting roller 24, and detects a position of the sheet S after being inverted.
The finisher 100 carries out each of processes such as a binding process and the like. The finisher 100 carries out a process of sequentially incorporating the sheet S discharged from the image forming portion 10, and aligning a plurality of incorporated sheets S so as to pack into one bundle, and a staple process of binding a trailing end of the packed sheet bundle by a staple 103.
Further, when the staple of the sheet bundle is selected from the operation portion, the sheet bundle is bound by the staple 103 and is discharged and stacked to the sheet stack tray 105, after finishing an post-processing of aligning the trailing end and a width direction of the sheet S.
The first and second inverting rollers 19 and 24 are respectively driven by first and second drivers 19 a and 24 a, as illustrated in FIG. 3. Further, the first and second drivers 19 a and 24 a are controlled by a control portion 30. The control portion 30 has a computing portion 31, and driving timings and sheet conveying speeds of the first and second inverting rollers 19 and 24 are calculated based on detected information of the first and second inverting sensors 23 and 25 and the image reference sensor 15.
In this case, in FIG. 2, a nominal paper interval time of the image forming portion 10 is set to A (ms) (refer to FIG. 4). Reference symbol A denotes a standard operate value calculated based on a productivity of the image forming system 1. Further, the paper interval time between a preceding sheet S1 and a subsequent sheet S2 in the image forming portion 10 including a feeding delay is set to ΔTp. The paper interval time ΔTp between the preceding sheet S1 and the subsequent sheet S2 in the image forming portion 10 in this case is calculated based on a result of detection of the preceding sheet S1 and the subsequent sheet S2 by the image reference sensor 15. The paper interval time between the preceding sheet S1 and the subsequent sheet S2 which can be received by the finisher 100 is set to be equal to or more than ΔTf. Further, the paper interval time between the preceding sheet S1 and the subsequent sheet S2 in the inverting portion is set to ΔT.
If the paper interval time at a time of receiving the sheet becomes less than ΔTf, the post-processing such as the alignment of the subsequent sheet S2, the staple 103 and the like is too later, there is a risk that the post-processing failure is generated.
In order to prevent this, the computing portion 31 determines a time ΔTs1 until the second inverting sensor 25 detects the preceding sheet S1 after the image reference sensor 15 detects the preceding sheet S1. The computing portion 31 determines a time ΔTs2 until the second inverting sensor 25 detects the subsequent sheet S2 after the image reference sensor 15 detects the subsequent sheet S2. Further, the computing portion 31 calculates a value obtained by adding the paper interval time ΔTp between the preceding sheet S1 and the subsequent sheet S2 which are detected by the image reference sensor 15, to a difference between ΔTs1 and ΔTs2, as the paper interval time ΔT between the preceding sheet S1 and the subsequent sheet S2 in the inverting portion.
As illustrated in a flowchart in FIG. 4, the control portion 30 transmits a signal to the first and second drivers 19 a and 24 a in such a manner that a paper interval time (a sheet interval time between the preceding sheet and the subsequent sheet in the discharge port 27 a) at a time of discharging the sheet S becomes equal to or more than ΔTf in correspondence to the calculated ΔT. Accordingly, the first and second inverting rollers 19 and 24 are controlled by the control portion 30, and adjust a start timing and an inverting speed of the sheet S from the inverting point. The inverting speed in this case means a conveying speed of the sheet by the second inverting roller 24 after being inverted or a conveying speed of the sheet by the inverting conveying roller 26 provided in the downstream side of the second inverting roller 24.
For example, the conveying speed of the preceding sheet S1 is slowed down due to an influence of the fixing portion 17 and a slip and an abrasion of the first and second inverting rollers 19 and 24. There is considered a case that it is delayed to reach the inverting point and the subsequent sheet S2 is conveyed faster than a target conveying speed under the transient influence of the fixing portion 17 without being affected by a reduction of a conveying efficiency (refer to a dotted portion in FIG. 2).
In this case, a start timing of the inverting portion of the subsequent sheet S2 is delayed. In other words, the start timing at the inverting point is set to be equal to or more than a paper interval time ΔTf which is a limit of receiving the finisher 100 and equal to or less than a paper interval time ΔTp at which a productivity of the image forming system 1 does not degrade. The start timing of the inverting portion means a timing for inverting the second inverting roller 24 after stopping the second inverting roller 24 in a state that the sheet rear and is positioned at a predetermined position in an upstream side of the second inverting roller 24.
With such a state, for example, in the case that a time for which the third sheet S3 reaches the inverting point is longest in the dispersion (the third sheet S3 is delayed), the inversion is started by quickening the start timing of the inverting portion while targeting at a point near ΔTf. Otherwise, in the case that the time for which the sheet S3 reaches the inverting point is shortest in the dispersion (the sheet S3 reaches earlier), the start timing of the inverting portion is delayed while targeting at ΔTp.
In other words, the paper interval time A of the image forming portion 10 is compared with ΔTp (step 1), and in the case that ΔTp is larger than the paper interval time A due to the feeding delay in the upstream side than the image forming portion, the inversion is carried out according to a normal control (step 2). In the case that ΔTp is equal to or less than the paper interval time A, ΔT is compared with ΔTp (step 3), and if the paper interval time ΔT at the inverting point becomes equal to or more than ΔTp, the start timing of the first and second inverting rollers 19 and 24 is quickened at the difference (step 4).
Accordingly, it is possible to prevent the paper interval time ΔT from becoming short at the inverting point of the subsequent sheet S2. In the case that the paper interval time ΔT at the inverting point becomes shorter than ΔTp, ΔT is compared with the paper interval time ΔTf of the receiving condition of the finisher 100 (step 5), and if ΔT is equal to or more than ΔTf, the inversion is carried out as it is in accordance with the normal control (step 6). In the case that ΔT is smaller than ΔTf, the start timing of the inverting roller (the timing at which the second inverting roller 24 is inverted) is delayed only at the difference between ΔTf and ΔT, in such a manner that the paper interval becomes equal to or more than the paper interval time ΔTf which can be received by the finisher 100 (step 7).
As mentioned above, even in the case that the paper interval dispersion is generated within the image forming portion 10, it is possible to maintain a stable conveying performance without degrading the productivity of the image forming system 1, while satisfying the receiving condition of the finisher 100.

Second Embodiment

In a second embodiment according to the present invention, in the case of discharging the sheet S to the finisher 100 while inverting the image forming surface of the sheet S after forming the image by the image forming portion 10, the sheet S is sped up in a convey region by the inverting conveying roller 26.
Further, the sheet leading end is slowed down to a speed which can received the finisher 100 at a predetermined amount upstream position of the discharge roller 27, and the sheet is discharged from the discharge port 27 a by the discharge roller 27. In this case, the computing portion 31 calculates ΔT obtained by adding ΔTp to the difference between ΔTs2 and ΔTs1. A sheet conveying speed or a speed change timing by the inverting conveying roller 26 is controlled in such a manner that the paper interval becomes equal to or more than ΔTf corresponding to the receiving condition of the finisher 100 and becomes equal to or less than ΔTp at which the productivity of the image forming system 1 does not degrade.
These controls will be specifically described with reference to FIG. 5. First, ΔTp is compared with the paper interval time A of the image forming portion 10 (step 1), and in the case that ΔTp is larger than A due to the feeding delay, the inversion is carried out in accordance with a normal control (step 2).
In the case that ΔTp is equal to or less than the paper interval time A, ΔTp is compared with the paper interval time ΔT at the inverting point (step 3), and if ΔT is equal to or more than ΔTp, a distance at which the speeding up is carried out in an inverting path is made longer at the difference, and a position starting the slowing down is set to a downstream side (step 4).
Accordingly, it is possible to prevent the paper interval time ΔT from becoming short at the inverting point of the subsequent sheet S2. In the case that the paper interval time ΔT at the inverting point becomes shorter than ΔTp, ΔT is compared with ΔTf (step 5), and it is determined whether or not ΔT is equal to or more than the paper interval time ΔTf of the receiving condition of the finisher 100.
If ΔT is equal to or more than ΔTf, the inversion is carried out as it is in accordance with the normal control (step 6). In the case that ΔT is smaller than ΔTf, the distance is made shorter by carrying out the speed-up conveying in the inverting path at the difference between ΔTf and ΔT in such a manner that the paper interval becomes equal to or more than ΔTf, and the position starting slowing down is set to an upstream side (step 7).
As mentioned above, it is possible to maintain the stable conveying performance without degrading the productivity of the image forming system 1 by controlling in such a manner as to adjust the slowing down point.
In this case, as the first embodiment, the embodiment that the paper interval is adjusted in such a manner as to be received by the finisher 100 by controlling the start timings of the first and second inverting rollers 19 and 24 is described. Further, as the second embodiment, the embodiment that the paper interval is adjusted in such a manner that the finisher 100 can receive by controlling the speed of the inverting conveying roller 26 is described. However, the structure may be made such as to adjust so as to achieve such a paper interval that the finisher 100 can receive by controlling both the start timings of the first and second inverting rollers 19 and 24 and the speed of the inverting conveying roller 26.

Third Embodiment

In a third embodiment according to the present invention, the image forming portion 10 to which a plurality of finishers 100 can be connected receives the information of the receiving time set in each of the finishers 100 by the image forming portion 10 side. It is possible to control the inverting timings of the first and second inverting rollers 19 and 24 and the conveying speed of the inverting conveying roller 26 such as to discharge at a paper interval time which is equal to or more than a lower limit value of the receiving time of the finisher 100 and equal to or more than such a paper interval time as to prevent the productivity from degrading based on the information.
As mentioned above, the information of the receiving paper interval time is received in the image forming portion 10 side from the finisher 100, and the paper interval time of the discharge is controlled in correspondence to the finisher 100. Accordingly, it is possible to obtain the image forming system 1 which can maintain the stable conveying performance in correspondence to the various accessories without degrading the productivity.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2007-296383, filed Nov. 15, 2007, which is hereby incorporated by reference herein in its entirety.

Claims

1. An image forming system comprising:

an image forming portion which forms an image in a sheet;

an inverting portion which inverts the sheet in which the image is formed by the image forming portion;

a discharging portion which discharges the sheet inverted by the inverting portion;

a sheet position detecting portion which detects a position of the sheet in which the image is formed by the image forming portion;

a control portion which controls a motion of the inverting portion; and

a sheet post-processing apparatus which is connected to the image forming portion and receives the sheet discharged from the discharging portion so as to apply an post-processing,

wherein the control portion can change the motion of the inverting portion based on a detected information of the sheet position detecting portion, in such a manner that an interval time of the continuous sheets becomes equal to or more than a sheet interval time which the sheet post-processing apparatus can receive the sheet.

2. The image forming system according to claim 1,

wherein the inverting portion includes a rotating body rotating and conveying the sheet in which the image is formed by the image forming portion, in one direction and thereafter rotating and conveying in an inverting direction, and

the control portion is capable of changing a rotation start timing of the roller in the other direction based on the detected information of the sheet position detecting portion, in such a manner that an interval between the continuous sheets becomes equal to or more than a sheet interval time which the sheet post-processing apparatus is capable of receiving.

3. The image forming system according to claim 2,

wherein the control portion delays the rotation start timing of the roller in the other direction at a time of conveying a subsequent sheet, in the case that an interval time between continuous preceding sheet and subsequent sheet detected by the sheet position detecting portion is shorter than a predetermined time.

4. The image forming system according to claim 1,

wherein the inverting portion conveys the sheet in one direction, temporarily stops the sheet and thereafter conveys the sheet in the other direction,

the inverting portion starts conveying the sheet in the other direction and thereafter conveys the sheet to the discharging portion in a state of slowing down to a predetermined speed, and

the control portion is capable of changing a timing for slowing down the conveying speed of the sheet based on the detected information of the sheet position detecting portion after the inverting portion conveys the sheet in the other direction in such a manner that an interval time of the continuous sheets becomes equal to or more than a sheet interval time which the sheet post-processing apparatus is capable of receiving.

5. The image forming system according to claim 4,

wherein the control portion sets a position starting slowing down a subsequent sheet after the inverting portion conveys the subsequent sheet in the other direction to an upstream side, in the case that the interval time between the continuous preceding sheet and subsequent sheet detected by the sheet position detecting portion is shorter than a predetermined time.

6. The image forming system according to claim 1,

wherein the control portion is capable of changing a conveying speed of the inverting portion based on the detected information of the sheet position detecting portion in such a manner that an interval time of the continuous sheets at a time of being discharged from the discharging portion becomes equal to or more than a sheet interval time which the sheet post-processing apparatus is capable of receiving.

7. The image forming system according to claim 1,

wherein the inverting portion includes a rotating body rotating and conveying the sheet in which the image is formed by the image forming portion in one direction and thereafter rotating and conveying in an inverting direction, and

the control portion controls a rotation start timing of the roller in the other direction and a sheet conveying speed by the roller based on the detected information from the sheet position detecting portion.

8. The image forming system according to claim 1,

wherein the control portion changes a motion of the inverting portion in such a manner as to achieve a paper interval time at which the sheet post-processing apparatus is capable of receiving, in the case that the interval time of the sheet detected by the sheet position detecting portion is shorter than a predetermined time.