JP3557851B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a multifunction machine using an electrophotographic method, and more particularly, to density unevenness caused by a load variation occurring when a recording sheet is fed to a transfer position. The present invention relates to an image forming apparatus capable of reducing image quality deterioration such as color misregistration.
[0002]
[Prior art]
As an image forming apparatus of this type, a toner image formed on an orbiting photoconductor by an electrophotographic process is directly transferred to a recording sheet supplied to a transfer position of the photoconductor, and then fixed to fix a black and white or color image. And a toner image formed on the photoreceptor is primarily transferred to an intermediate transfer member that rotates in contact with the photoreceptor, and is then supplied to a transfer position of the intermediate transfer member. There is known a type which forms a black-and-white or color image after being secondary-transferred to a toner image and then fixed.
[0003]
For the purpose of improving productivity when continuously forming images on small-sized recording sheets having a relatively short length in the sheet feeding direction, for example, a type using an intermediate transfer body is used. As an image forming apparatus, an image (toner image) for a plurality of recording sheets is formed at the same time, instead of forming an image (toner image) for one small-sized recording sheet on an intermediate transfer body. One has been proposed (JP-A-4-296877).
[0004]
For example, an image forming apparatus using an intermediate transfer belt 01 as shown in FIG. 13 is used as an apparatus for executing the proposed image formation, and a small-size recording sheet P The case where the images A and B for the number of sheets are formed (FIG. 14) will be described as an example.
[0005]
In this case, first, toner images corresponding to the images A and B are formed in this order on the photosensitive drum 02, and the respective toner images are sequentially transferred to the intermediate transfer belt 01 at the primary transfer position T1, whereby the intermediate transfer belt An image A and an image B are formed at a predetermined interval on the image No. 01. Then, two recording sheets P are continuously supplied at a predetermined timing toward the secondary transfer position T2 of the intermediate transfer belt 01, and two toner images corresponding to the images A and B on the intermediate transfer belt 01 are supplied. After the images are separately transferred onto the recording sheet, the fixing process is performed through the transfer unit 05. This makes it possible to perform a continuous image forming process on a small-sized recording sheet more efficiently than in a mode in which the recording sheet is formed one by one on the intermediate transfer member.
[0006]
In this case, the two recording sheets P are continuously fed to the secondary transfer position T2 in accordance with the interval between the images A and B formed on the intermediate transfer belt 01. Normally, the sheet is fed by a registration roll 03 disposed between the sheet storage tray and the secondary transfer position T2. That is, the recording sheet conveyed from the sheet accommodating tray is temporarily stopped after the leading end portion of the recording sheet is abutted against the registration roll 03, and the conveyance posture (skew, etc.) of the recording sheet is shifted between the registration roll 03 and the conveyance roll 04. After the correction, the image forming apparatus is made to wait until the transfer timing arrives. Then, in accordance with the timing at which the image on the intermediate transfer belt 01 arrives at the secondary transfer position T2, the image is sent out by the registration roll 03 toward the secondary transfer position T2 at the same transport speed as the moving speed of the intermediate transfer belt 01. Has become.
[0007]
By the way, when the images A and B are formed on the intermediate transfer belt 01 as described above, the image forming speed (process speed) is increased, and the interval between the image forming areas C between the images A and B is reduced. By doing so, it is possible to further improve the productivity.
[0008]
However, if the process speed is simply increased to reduce the interval between the image forming areas C, it is necessary to reduce the interval between the two recording sheets P to the secondary transfer position T2 and feed the recording sheet P faster. 03, the standby time and the correction time of the recording sheet must be shortened. As a result, the second recording sheet P reaches the registration roll 03 while the first recording sheet P is sent out from the registration roll 03. This causes a problem that sheet feeding cannot be performed.
[0009]
In order to solve such a problem, for example, when the first recording sheet is sent to the secondary transfer position, the conveyance speed of the registration roll 03 is increased (increased) from the middle of the conveyance speed than usual. The rear part of the recording sheet is quickly sent out from the registration roll 03, thereby securing a standby time at the registration roll 03 for the next recording sheet, and controlling so that two recording sheets do not overlap on the registration roll 03. Can be adopted.
[0010]
[Problems to be solved by the invention]
However, in the case of this method, in order to increase the transport speed of the registration roll 03 during the transport of the recording sheet, the speed variation applies a load to the intermediate transfer belt 01, and the image quality deteriorates due to the load, that is, In the case of a black and white image, density unevenness may occur, and in the case of a color image, color unevenness and color shift may occur.
[0011]
According to the study of the present inventors, such deterioration in image quality is caused by the fact that the acceleration time E of the registration roll 03 forms a latent image of the next image D following the images A and B, as shown in FIG. When the exposure of the photoconductor 02 is performed or when the toner image of the image B on the photoconductor 02 is primarily transferred to the intermediate transfer belt 01, the load fluctuation caused by the speed increase is caused. It is supposed to be caused by causing speed fluctuation or vibration on the transfer belt 01 or the photosensitive drum 02.
[0012]
Further, even when the recording sheet is fed at a normal conveyance speed without increasing the registration roll 03 in the middle as described above, the image quality deterioration such as the density unevenness and the color shift described above may occur. is there.
[0013]
Regarding the image quality deterioration, while the recording sheet is being conveyed to the secondary transfer position of the intermediate transfer belt 01 and the secondary transfer is being performed, as shown in FIG. This load continues to increase until the recording sheet enters the secondary transfer position and immediately before it is discharged, and then disappears at the moment when the recording sheet exits the secondary transfer position. It is supposed to occur. That is, if the time when the recording sheet exits the secondary transfer position (that is, the time when the secondary transfer ends) overlaps with the exposure of the next image D or the primary transfer of the image B, the recording sheet exits at the time. It is said that the generated load fluctuation causes speed fluctuation and vibration on the intermediate transfer belt 01 and the photosensitive drum 02.
[0014]
The image quality degradation caused by the load fluctuation occurring at the moment when the recording sheet comes out of the secondary transfer position is more remarkable especially when the recording sheet is thick.
[0015]
For example, as shown in FIG. 16, yellow (Y), magenta (M), yellow (Y), and black (K) toner images are formed on the photosensitive drum 02, and are sequentially superimposed on the intermediate transfer belt 01. When a multi-toner image is transferred to form a color image by secondarily transferring the multi-toner image to a recording sheet, the timing at which the recording sheet exits the secondary transfer position is the next image. When the recording sheet overlaps at the time of exposure or transfer, the load fluctuation when the thick recording sheet comes out is increased by the thickness of the sheet, so that more remarkable color shift or color unevenness occurs. Also, when a thick recording sheet is used, if the sheet is conveyed to the secondary transfer position in a skewed state, the sheet is also skewed in the width direction of the intermediate transfer belt according to the skewed state. As a result of the distorted load, a color shift or the like due to the load may occur.
[0016]
In addition, the recording sheet sent to the secondary transfer position is sent to the fixing unit 05 after the transfer of the toner image from the front portion thereof, and as shown in FIG. Immediately upon entering the recording sheet 05, an impact is generated and transmitted to the intermediate transfer belt via the recording sheet. Such an impact also occurs when the recording sheet after the transfer comes out of the transfer position. If such impacts occur at the time of exposure or transfer of the next image, image quality degradation such as density unevenness or color misregistration may occur.
[0017]
The present invention has been made in view of such problems of the related art, and has as its object the load fluctuation occurring when a recording sheet is fed to a transfer position and the fixing of the recording sheet from the transfer position. It is an object of the present invention to provide an image forming apparatus capable of easily and surely reducing image quality deterioration such as density unevenness and color misregistration caused by a load change occurring when the sheet is conveyed to a unit.
[0018]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a rotating photosensitive member; and a toner image formed on the photosensitive member by performing charging, exposure and development according to image information in this order, on a recording sheet. Means for transferring directly to a recording sheet via a direct transfer method for transferring images directly to the recording sheet via an intermediate transfer body that rotates in contact with the photosensitive member, and a transfer position for the photosensitive member or the intermediate transfer body facing the transfer means The image forming apparatus of the direct transfer type is based on the premise that the image forming apparatus has a feeding roll that feeds a recording sheet so as to arrive at a predetermined timing and a fixing unit that fixes a toner image transferred to the recording sheet. While the rear portion of the recording sheet is set to be fed out of the feeding roll and separated while the image forming area on the photoconductor passes through the exposure position, In the transfer type image forming apparatus, the rear portion of the recording sheet is sent out from the feed roll and separated while the image forming area on the photoconductor passes at least one of the exposure position and the transfer position. Is set to.
[0019]
Here, the image forming apparatuses that are premised on the above are an image forming apparatus that employs a direct transfer method as a transfer unit (hereinafter abbreviated as “direct transfer type apparatus”) and an image forming apparatus that employs an intermediate transfer method ( Hereinafter, it is abbreviated as "intermediate transfer type device"). In either type of device, the photoreceptor may be in the form of a drum or a belt.
[0020]
In the case of a direct transfer type apparatus, the recording sheet may be conveyed to the transfer position by a method in which the recording sheet is conveyed so as to directly reach the transfer position of the photoconductor after being sent out by the feed roll, or It may be carried out by a method in which the sheet is conveyed so as to reach the transfer position of the photoreceptor while being attracted to the sheet conveying belt or the sheet conveying drum (transfer drum) after being sent out by the feed roller. When there are a plurality of photoconductors, the recording sheet may be configured to be conveyed past the transfer position of each photoconductor. On the other hand, in the case of an intermediate transfer type device, the intermediate transfer body may be any of a belt type and a drum type. Further, when there are a plurality of photoconductors, the intermediate transfer body may be configured to pass around the transfer position of each photoconductor and circulate.
[0021]
The setting as in the first aspect of the invention is sufficiently effective even if the configuration is such that only the recording sheet having the maximum feed direction size usable in the image forming apparatus is established. In the case of an intermediate transfer type device, the above setting is performed when an image forming area passes through an exposure position when an integrated drive system in which the photosensitive member and the intermediate transfer member are driven by the same drive source is adopted. When an independent driving method is used in which these are driven by different driving sources, it is preferable that the image forming area be established when the image forming areas pass the transfer position. The conditions are the same for an intermediate transfer type apparatus configured to send out a recording sheet at a higher speed, which will be described later.)
[0022]
According to a second aspect, in the apparatus according to the first aspect, when the feed roll is configured to feed the rear portion of the recording sheet at an increased speed, the exposure position and the transfer position between the image forming areas on the photoreceptor are changed. positionOne ofIs set so that the rear end of the recording sheet is sent out from the feed roll at an increased speed while passing through the sheet.
[0023]
The setting as in the second invention is most effective since productivity can be improved when a plurality of images are simultaneously formed on the photosensitive member or the intermediate transfer member. Even when one image is formed, the productivity can be improved and this is effective.
[0024]
According to a third aspect of the present invention, in the image forming apparatus similar to the above-described image forming apparatus based on the first aspect, a space between image forming areas on the photoconductor passes at least one of the exposure position and the transfer position. In between, the front portion of the recording sheet is set so as to enter the fixing means.
[0025]
The setting as in the third aspect of the invention is most effective when the fixing means is of a type in which the fixing is performed by passing the recording sheet in a state where the recording sheet is sandwiched between rolls or belts.
[0026]
Further, according to a third aspect of the present invention, in the image forming apparatus similar to the above-described image forming apparatus premised on the first aspect, the space between the image forming areas on the photoconductor passes at least one of the exposure position and the transfer position. In the meantime, the rear portion of the recording sheet is set so as to be sent out from the photoconductor or the intermediate transfer member and to be separated therefrom.
[0027]
The setting as in the third invention is effective when the transfer means or the second transfer means in the direct transfer type apparatus is a transfer roll, and is also effective when a corona discharger is used.
[0028]
[Action]
According to the apparatus of the first aspect, the time at which the rear portion of the recording sheet is sent out from the feed roll and separated does not overlap with at least one of the exposure time on the photoconductor and the transfer time. As a result, even if a load change occurs when the rear portion of the recording sheet is sent out from the feed roll and separates, the load change is transmitted to the photoconductor when at least one of exposure and transfer is performed. Therefore, density unevenness, color shift, and the like due to the load fluctuation are less likely to occur.
[0029]
Further, according to the apparatus of the first aspect, in which the feeding roll is configured to feed the rear portion of the recording sheet at an increased speed, the rear portion of the recording sheet increases in speed from the feeding roll. The timing of exposure and transfer on the photoconductor is the timing ofOne ofWill not overlap. As a result, even if a load change occurs when the rear portion of the recording sheet is fed out of the feed roll at an increased speed and separates, the load change is caused by the light exposure during at least one of exposure and transfer. Since it is not transmitted to the body, density unevenness, color shift, and the like due to the load variation are less likely to occur.
[0030]
Further, according to the apparatus of the second aspect, the timing at which the front portion of the recording sheet enters the fixing unit does not overlap with at least one of the exposure timing on the photoconductor and the transfer timing. As a result, even if a load change occurs when the front portion of the recording sheet enters the fixing unit, such a load change is not transmitted to the photoconductor when at least one of the exposure and the transfer is performed. Therefore, uneven density, color shift, and the like due to the load variation hardly occur.
[0031]
Further, according to the apparatus of the third aspect, the time when the rear portion of the recording sheet is sent out from the photoconductor or the intermediate transfer body and leaves does not overlap with at least one of the exposure time and the transfer time on the photoconductor. Become like As a result, even if a load change occurs when the rear portion of the recording sheet is sent out from the transfer unit and the photoreceptor or between the transfer unit and the intermediate transfer member and separates, such a load change is caused by at least exposure and transfer. Since the light is not transmitted to the photoconductor when one of the operations is being performed, uneven density and color shift due to the load fluctuation are unlikely to occur.
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0033]
FIG. 1 shows an image forming apparatus according to an embodiment of the present invention, and illustrates an intermediate transfer type color image forming apparatus.
[0034]
In the figure, 1 is a photosensitive drum rotating in the direction of an arrow, 2 is a charging scorotron for uniformly charging the photosensitive layer of the photosensitive drum, and 3 is an optical image corresponding to image information on the surface of the charged photosensitive drum. A rotary type developing device for developing an electrostatic latent image formed on the photosensitive drum by exposure of the exposing device with a toner of a predetermined color; A primary transfer corotron 6 for electrostatically transferring the formed toner image to an intermediate transfer belt described later, and a cleaning device 6 for removing and cleaning toner remaining on the surface of the photosensitive drum after the transfer. . The developing device 4 includes developing devices Y, M, C, and K in which toners of respective color components of yellow (Y), magenta (M), cyan (Y), and black (K) are individually stored. The four developing units can be switched to developing positions opposing the photosensitive drum 1 by rotating the rotating body in a predetermined direction.
[0035]
An image signal processing unit 10 performs predetermined image processing on input image information, and transmits the generated image signal to the laser type exposure apparatus 3 as image information. When the image forming apparatus is a copying machine or the like, the image signal processing unit 10 is provided with a document reading device 11, and receives image information of a document read by the reading device 11. When the image forming apparatus is a printer, a facsimile, or the like, an external signal input unit 12 is provided, and image information from an external device, a communication line, an information recording medium, or the like taken in from the signal input unit 12 is input. It has become. The exposure device 3 scans and exposes the photosensitive drum 1 with a laser beam based on the image information transmitted from the image signal processing unit 10.
[0036]
Further, reference numeral 20 denotes an intermediate transfer belt, which rotates in a direction indicated by an arrow in synchronization with the rotation of the photosensitive drum 1 in a state of being wound around a driving roll 21, a driven roll 22, and a backup roll 23. Reference numeral 24 denotes a cleaning device for removing and cleaning toner remaining on the surface of the intermediate transfer belt 20 after transfer. Reference numeral 25 denotes a secondary transfer roll for electrostatically transferring the toner image primarily transferred onto the intermediate transfer belt 20 to the recording sheet P. The secondary transfer roll 25 is pressed against the backup roll 23 via the intermediate transfer belt 20. It is designed to rotate. An electrode roll connected to a secondary transfer power supply (not shown) is pressed against the backup roll 23, and a transfer current is applied to the backup roll 23 via the electrode roll.
[0037]
Reference numeral 30 denotes an accommodation tray for accommodating recording sheets P such as recording paper, and is usually provided with a plurality of recording sheets P for accommodating recording sheets having different sheet sizes and accommodation directions. Reference numeral 31 denotes a feed roll for sending the recording sheet P in the storage tray 30 to the sheet conveying path, 32 denotes a sheet conveying roll (pair), and 33 denotes a recording sheet which corrects the conveying posture or temporarily stops the recording sheet and waits for a predetermined time. This is a registration roll (pair) for sending out to the secondary transfer position at a timing. A dotted line in the drawing indicates a basic transport path of the recording sheet P.
[0038]
Reference numeral 40 denotes a heating / pressing type fixing device, which is constituted by a heating roll 41 and a pressure roll 42 which are disposed so as to be in pressure contact with each other, and allows the transferred recording sheet P to pass between the rolls (nip portion). It has become. Reference numeral 45 denotes a discharge tray which discharges and stores the recording sheet after the fixing.
[0039]
In this image forming apparatus, for example, a color image is formed as follows.
[0040]
First, on the surface of the photosensitive drum 1 uniformly charged by the transfer scorotron 2, an image of the yellow component is exposed from the exposure device 3 to form a latent image thereof. The yellow component latent image is developed by a developing device Y containing yellow toner at a position facing the developing device 4 to become a yellow component toner image. Then, the toner image is electrostatically transferred to the intermediate transfer belt 20 which rotates while contacting the surface of the photosensitive drum 1 at a primary transfer position T1 facing the primary transfer corotron 5. The residual toner is removed from the photosensitive drum 1 after the transfer by the cleaning device 6 to prepare for the next toner image formation. Thereafter, the above-described yellow component image forming process is similarly repeated to form a magenta component toner image, a cyan component toner image, and a black component toner image on the photosensitive drum 1 in this order. Each toner image is transferred so as to be superimposed on the yellow component toner image on the intermediate transfer belt 20.
[0041]
While such toner image formation is being performed, a recording sheet P of a predetermined size is sent out from the storage tray 30 by the feed roll 31, and the recording sheet P stops when the sheet leading end abuts against the registration roll 33. In this state, the conveyance posture is corrected by feeding the rear portion of the sheet by the conveyance roll 32, and the sheet is on standby until the delivery timing comes.
[0042]
The multicolor toner image of four colors transferred onto the intermediate transfer belt 20 is transferred and sent out from the registration roller 33 at the timing when the toner image arrives at the secondary transfer position T2 facing the secondary transfer roll 25. The image is collectively transferred onto the recording sheet P inserted between the transfer roll 20 and the transfer roll 25 electrostatically. After the transfer, the intermediate transfer belt 20 is cleaned of residual toner and the like by the cleaning device 24 to prepare for the next transfer. When the secondary transfer is completed, the recording sheet P passes between the heating roll 41 and the pressure roll 42 of the fixing device 40, whereby the toner image is fixed to form a desired color image. The recording sheet on which the color image has been obtained in this manner is discharged onto the discharge tray 45.
[0043]
Further, in this image forming apparatus, a black and white image can be formed by forming only a black component toner image.
[0044]
In this image forming apparatus, when an image is formed on a recording sheet P having a relatively small size in the feed direction (for example, in the case of A4 size paper being fed horizontally), as shown in FIG. The setting is such that an image (toner image) of two recording sheets (two pages) can be formed on the belt 20. At this time, between the image forming areas A and B where two images are formed, there are two image forming area sections (inter-image sections) C where no image is formed as illustrated in FIG.
[0045]
In the case where an image for two recording sheets is formed on the intermediate transfer belt 20 in this manner, of the two recording sheets sent to the secondary transfer position by the registration roll 33, the rear of the first recording sheet is used. The portion is set so as to be fed at an increased speed (for example, doubled) from the normal speed of the registration roll 33.
[0046]
In this image forming apparatus, as shown in FIG. 3, a distance L from an exposure position R of the photosensitive drum 1 exposed by the exposure device 3 to a primary transfer position T1.₁ , The distance L from the primary transfer position T1 to the secondary transfer position T2 on the intermediate transfer belt 20_TwoAnd a distance L between the registration roll 33 and the secondary transfer position T2 (transfer roll 25)._ThreeAre appropriately set so as to satisfy respective conditions described later.
[0047]
<< Setting example for speed-up transfer mode >>
First, in a mode in which images of two recording sheets are formed on the intermediate transfer belt 20 and the rear portion of the first recording sheet is accelerated and fed from the registration roll 33, as shown in FIG. Acceleration period: E is a period during which no exposure or primary transfer is performed on the photosensitive drum 1 (that is, the inter-image portion on the photosensitive drum 1 corresponding to the inter-image portion C of the intermediate transfer belt 20 is moved to the exposure position). R and the time during which the sheet passes through the primary transfer position T1).₁ , L_Two , L_Three Is set.
[0048]
FIG. 4 shows a case where a color image of two recording sheets is formed on an intermediate transfer belt and is transferred to two recording sheets continuously fed to a secondary transfer position, respectively. 4 shows the operation timing of an image forming process in which the rear portion of the image forming apparatus is fed at an increased speed by a registration roll. In the drawing, Y1 is a yellow component image for the first sheet, Y2 is a yellow component image for the second sheet, M1 is a magenta component image for the first sheet, M2 is a magenta component image for the second sheet, and C1 is 1 The cyan component image for the first sheet, C2 indicates the cyan component image for the second sheet, K1 indicates the black component image for the first sheet, and K2 indicates the black component image for the second sheet.
[0049]
Here, the process speed (the speed of the photosensitive drum and the intermediate transfer belt) V (mm / s) is set, and two laterally-fed A4-size paper images are formed on the intermediate transfer belt 20 having a circumference of S (mm). Then, when two A4 size sheets are continuously fed horizontally by the registration roll 33, the rear portion 50 mm of the first sheet (length 210 mm in the feeding direction) is moved at a speed 2 · V which is twice the normal conveyance speed V. When sending at (mm / sec), what condition should be satisfied for the speed-up timing of the registration roll will be described.
[0050]
In order to simplify the description, assuming that the start of the exposure of the black image K1 as the final color for the first sheet is a reference (t = 0), each time is as follows.
・ Primary transfer start time t₁ = L₁ / V
・ Secondary transfer start time t_Two= (L₁+ L_Two ) / V
-Sheet conveyance start time: t_Three = (L₁ + L_Two -L_Three ) / V
・ Acceleration start time: t_Four = T_Three+ (210-50) / V = (L₁ + L_Two -L_Three +160) / V
・ Speed-up end time: t_Five = T_Four + (50 / 2V) = (L₁ + L_Two -L_Three +185) / V
-Length of the inter-image part: W = {S- (210 × 2)} / 2
Exposure end time of Y1 image in next cycle: t₆ = (S + 210) / V
Exposure start time of Y2 image in next cycle: t₇ = T₆ + W / V = (S + 210 + W) / V
-Primary transfer end time of K2 image: t₈ = 2t₁+ 210 / V = (2L₁ +210) / V
-Primary transfer start time of Y1 image in next cycle: t₉= T₈+ W / V = (2L₁ + 210 + W) / V
[0051]
Then, when the speed of the cashier roll increases (t)_Four ~ T_Five ) Is not exposed, that is, while the inter-image portion of the photosensitive drum is passing through the exposure position (t)₆~ T₇), "T_Four ≧ t₆ And "t_Five ≤t₇ To satisfy the relationship of₁ , L_Two , L_Three Should be set.
[0052]
Also, the speed-up time of the registration roll is set to a period during which the primary transfer is not performed, that is, while the inter-image portion of the photosensitive drum passes through the primary transfer position (t).₈~ T₉), "T_Four ≧ t₈ And "t_Five ≤t₉ To satisfy the relationship of₁ , L_Two , L_Three Should be set.
[0053]
In addition, when setting the accelerating time of this register roll, each distance L ₁ , L _Two , L _Three In addition to the setting, the speed-up speed, the ratio of the recording sheet portion to be speeded up, and the like may be adjusted.
[0054]
<< Setting example for normal transport >>
Next, in a mode in which an image for one recording sheet is formed on the intermediate transfer belt 20 and one recording sheet is fed from the registration roll 33 at a normal conveyance speed without increasing the speed, FIGS. As described above, the time when the rear portion of the recording sheet is sent out from the registration roll and leaves: F is a time when the exposure on the photosensitive drum 1 is not performed or a time when the primary transfer is not performed. In addition, each of the distances L ₁ , L _Two , L _Three Is set.
[0055]
That is, as shown in FIG. 5, the feed-out / separation timing F of the rear portion of the recording sheet is set so that the exposure is not performed, that is, the inter-image portion of the photosensitive drum passes the exposure position R. In that case, "t ₁₁ ≤t _Ten ≤t ₁₂ Relationship (t _Ten Is the separation time of the rear part of the recording sheet, t ₁₁ Is the exposure end time of the first image in the next cycle, t ₁₂ Is the exposure start time of the image next to the first image). ₁ , L _Two , L _Three Should be set. By the way, t _Ten = T _Three + Q / V = (L ₁ + L _Two -L _Three + Q) / V. In the equation, Q is the length of the recording sheet in the feed direction.
[0056]
Further, as shown in FIG. 6, the feed-out / separation timing F of the rear portion of the recording sheet may be during the time when the primary transfer is not performed, that is, while the inter-image portion of the photosensitive drum passes the primary transfer position T1. Is set to "t ₁₃ ≤t _Ten ≤t ₁₄ Relationship (t ₁₃ Is the primary transfer end time of the first image in the next cycle, t ₁₄ Is the primary transfer start time of the image following the first image). ₁ , L _Two , L _Three Should be set.
[0057]
By the way, L ₁ = 264mm, L _Two = 378mm, L _Three = 50 mm, when forming a color image on A3 size paper (420 mm in the feed direction) of the maximum size that can be used, "t ₁₁ ≤t _Ten ≤t ₁₂ To see if it satisfies the relationship. First, the sheet conveyance start time t _Three = (L ₁ + L _Two -L _Three ) / V is 2.37 sec, and the seat rear part leaving time t _Ten Is t _Three + 420 / V, so t _Ten = 2.37 + 1.68 = 4.05 sec. On the other hand, the exposure end time t of the top image Y in the next cycle ₁₁ Is (S + 420) / V, so t ₁₁ = 3.79 sec, and the exposure start time t of the image M in the next cycle ₁₂ Is 2S / V, so t ₁₂ = 4.22 sec. Therefore, in this case, “t ₁₁ ≤t _Ten ≤t ₁₂ Is satisfied, the rear portion of the recording sheet is sent out from the registration roll and is separated while the exposure of the leading image Y in the next image forming cycle is not performed.
[0058]
Thereby, as shown in FIG. 5, even if the load applied to the intermediate transfer belt due to the feeding of the recording sheet to the secondary transfer position disappears at the moment when the rear portion of the sheet comes out of the registration roll, the change in the load is reduced. It does not adversely affect the exposure on the photosensitive drum.
[0059]
Further, in the case of setting as described above, the feed-out / separation timing F of the rear portion of the recording sheet overlaps with the timing of the primary transfer as is apparent from FIG. However, if the image forming apparatus at this time is an apparatus that employs an integrated drive system in which the photosensitive drum 1 and the intermediate transfer belt 20 are driven by the same drive source, the above-described time F is set at the feeding / separation timing F at the rear of the recording sheet. Even if a load change occurs, the speed between the photosensitive drum 1 and the intermediate transfer belt 20 at the primary transfer position T1 does not easily change. Since the speed is kept almost the same, the image to be primarily transferred is hardly affected.
[0060]
From this point of view, in the image forming apparatus adopting the independent driving method in which the photosensitive drum 1 and the intermediate transfer belt 20 are driven by different driving sources, the feeding / removing timing F of the rear portion of the recording sheet is determined as shown in FIG. It is desirable that the setting be made during a period in which the primary transfer is not performed as shown in FIG. In the case of the independent driving method, if the load fluctuation described above occurs at the feeding / separation timing F at the rear portion of the recording sheet, the speed of the intermediate transfer belt 20 easily changes, but the speed of the photosensitive drum 1 hardly changes. The image exposure on the photosensitive drum is hardly affected.
[0061]
<< Other setting examples >>
In such an image forming apparatus, the distance from the secondary transfer position T2 to the fixing position (nip portion of the roll) of the fixing device 4 is L. _Four 7 (see FIG. 3), as shown in FIG. 7 and FIG. 8, the timing at which the front portion of the recording sheet after the transfer enters between the rolls of the fixing device 4 is G: the exposure on the photosensitive drum 1 is not performed. Each of the distances L is set so that the time when the transfer is not performed or the time when the primary transfer is not performed is performed. ₁ , L _Two , L _Four Is set. In this setting, the distance L between the registration roll and the secondary transfer position is set. _Three Is not directly related.
[0062]
That is, as shown in FIG. 7, the fixing rush timing G at the front portion of the recording sheet is set during the period when the exposure is not performed, that is, while the inter-image portion of the photosensitive drum passes the exposure position R. In that case, "t ₁₁ ≤t ₂₀ ≤t ₁₂ Relationship (t ₂₀ Is the time of entry into the fixing device at the front of the recording sheet, t ₁₁ , T ₁₂ Are the same as those described above). ₁ , L _Two , L _Four Should be set. By the way, t ₂₀ = T _Two + L _Four / V. Such setting is effective when performed in the case of an image forming apparatus employing the above-described integrated driving method.
[0063]
Further, as shown in FIG. 8, the fixing rush timing G at the front of the recording sheet may be during the time when the primary transfer is not performed, that is, while the inter-image portion of the photosensitive drum passes the primary transfer position T1. Is set to "t ₁₃ ≤t ₂₀ ≤t ₁₄ Relationship (t ₁₃ , T ₁₄ Are the same as those described above). ₁ , L _Two , L _Four Should be set. Such setting is effective to be performed in the case of the image forming apparatus adopting the independent driving method as described above.
[0064]
With this setting, as shown in FIGS. 7 and 8, even if the load on the intermediate transfer belt is suddenly reduced due to the front portion of the recording sheet rushing into the fixing device, such load fluctuation is not affected. There is no adverse effect on the image that has been exposed or primary transferred on the drum.
[0065]
Further, in such an image forming apparatus, as shown in FIG. 9 and FIG. 10, the time when the rear portion of the recording sheet after the transfer is sent out from between the photosensitive drum 1 and the secondary transfer roll 25 and is separated: H The distance L is set so that the exposure on the photosensitive drum 1 is not performed or the primary transfer is not performed. ₁ , L _Two , L _Four Is set. Also in this setting, the distance L between the registration roll and the secondary transfer position is set. _Three Is not directly related.
[0066]
That is, as shown in FIG. 9, the transfer position departure timing H of the rear portion of the recording sheet is set during the period when the exposure is not performed, that is, while the inter-image portion of the photosensitive drum passes the exposure position R. If you do ₁₁ ≤t ₃₀ ≤t ₁₂ (However, t ₃₀ <T _{twenty one} ) "(T ₃₀ Is the separation time from the transfer position behind the recording sheet, t _{twenty one} Is the secondary transfer end time, t ₁₁ , T ₁₂ Are the same as those described above). ₁ , L _Two , L _Four Should be set. By the way, t ₃₀ = T _Two + Q / V = (L ₁ + L _Two + Q) / V. Also, t _{twenty one} = T ₂₀ + Q / V = (L _Four + Q) / V. Such setting is effective when performed in the case of an image forming apparatus employing the above-described integrated driving method.
[0067]
Further, as shown in FIG. 10, when the transfer position leaving time H at the rear of the recording sheet is changed, the primary transfer is performed. If it is determined that there is no inter-image portion of the photosensitive drum while it is passing through the primary transfer position T1, "t ₁₃ ≤t ₃₀ ≤t ₁₄ (However, t ₃₀ <T _{twenty one} ) "(T ₁₃ , T ₁₄ Are the same as those described above). ₁ , L _Two , L _Four Should be set. Such setting is effective when performed in the case of the image forming apparatus employing the independent driving method as described above.
[0068]
In such a case, as shown in FIGS. 9 and 10, the rear portion of the recording sheet is sent out from between the photosensitive drum 1 and the secondary transfer roll 25 and is separated, so that a load is applied to the intermediate transfer belt. Even if the load is suddenly reduced, such load fluctuation does not adversely affect the image on the photosensitive drum that has been exposed or primary transferred.
[0069]
<< Setting example in other types of image forming apparatuses >>
In the above-described intermediate transfer type image forming apparatus, a drum-shaped intermediate transfer member may be used instead of the intermediate transfer belt 20. ₁ , L _Two , L _Three , L _Four The same effect can be obtained by appropriately setting.
[0070]
Further, the present invention can also be applied to a monochrome image forming apparatus of a type in which a toner image is directly transferred from a photosensitive drum 1 to a recording sheet P as illustrated in FIG. In this case, for example, an image for two small-sized recording sheets is formed on the photosensitive drum 1, or the recording sheet P is fed at an increased speed from the middle by the registration roll 33. What is necessary is just to comprise. Then, the distance (distance between the primary transfer position and the secondary transfer position) L in the intermediate transfer type image forming apparatus described above. _Two To L _Two = 0, and the above-mentioned distances L ₁ , L _Three , L _Four The same effect can be obtained by appropriately setting. In FIG. 11, reference numeral 4 denotes a developing device containing one-color toner, and reference numeral 5 denotes a transfer roll.
[0071]
Further, according to the present invention, as illustrated in FIG. 12, a toner image formed on the photosensitive drum 1 is directly transferred to a recording sheet P held and conveyed by a transfer drum 50 circulating in synchronization with the photosensitive drum 1. It can also be applied to a color image forming apparatus of the system. This apparatus can form a color image by passing the recording sheet attracted to the transfer drum 50 through the primary transfer position T1 a plurality of times and superimposing and transferring the toner image on the photosensitive drum 1.
[0072]
In this case, two small-sized recording sheets are simultaneously attracted and held on the transfer drum 50 to form an image of the two sheets, or the recording sheet P is accelerated from the middle by the registration roll 33. Then, it may be configured to feed. Then, the distance L in the intermediate transfer type image forming apparatus described above. _Two To L _Two = 0, and the above-mentioned distances L ₁ , L _Three , L _Four The same effect can be obtained by appropriately setting. 12, reference numeral 51 denotes a suction corotron for electrostatically attracting the recording sheet P to the transfer drum 50; 52, a peeling corotron for facilitating peeling of the recording sheet P from the transfer drum 50 after the final transfer; It is a static elimination corotron for drums.
[0073]
Also, in each of the above-described types of image forming apparatuses, a belt-shaped photosensitive belt may be used instead of the photosensitive drum 1.
[0074]
【The invention's effect】
As described above, according to the present invention, even if a load variation occurs when the recording sheet is fed to the transfer position or a load variation occurs when the recording sheet is transported from the transfer position to the fixing unit, Image quality deterioration such as density unevenness and color misregistration caused by such load fluctuation can be easily and reliably reduced.
[0075]
Therefore, when the apparatus of the present invention is used, the recording sheet is fed at an increased speed, Even when a thick sheet is used, it is possible to obtain a high-quality image free from uneven density and color shift.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus (intermediate transfer type color image forming apparatus) according to an example of an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing that images of a plurality of recording sheets are formed on an intermediate transfer belt.
FIG. 3 shows a distance between an exposure position and a primary transfer position, a distance between a primary transfer position and a secondary transfer position, a distance between a registration roll and a secondary transfer position, and a distance between a secondary transfer position and a fixing position. FIG.
FIG. 4 is a timing chart illustrating an example of setting a speed-up timing when a recording sheet is conveyed at an increased speed from a registration roll.
FIG. 5 is a timing chart showing an example of setting a sheet rear part leaving time (when adjusting to an inter-image part of exposure) when a recording sheet is normally conveyed from a registration roll.
FIG. 6 is a timing chart showing a setting example of a sheet rear part leaving timing when a recording sheet is normally conveyed from a registration roll (in the case of matching with an inter-image part of primary transfer).
FIG. 7 is a timing chart showing an example of setting a timing when a front portion of a recording sheet enters a fixing device (in the case of matching an exposure inter-image portion).
FIG. 8 is a timing chart showing an example of setting a timing when a front portion of a recording sheet enters a fixing device (in a case where the timing is adjusted to an inter-image portion of primary transfer).
FIG. 9 is a timing chart showing an example of setting a timing at which a rear portion of a recording sheet escapes from a transfer device and separates from the transfer device (in the case of adjusting to an exposure inter-image portion).
FIG. 10 is a timing chart showing an example of setting a timing at which a rear portion of a recording sheet escapes from a transfer device and separates from the transfer device (in the case of matching an inter-image portion of primary transfer).
FIG. 11 is a schematic diagram illustrating a configuration of an image forming apparatus (a general direct transfer type color image forming apparatus) according to another embodiment of the present invention.
FIG. 12 is a schematic diagram illustrating a configuration of an image forming apparatus (a direct transfer type color image forming apparatus using a transfer drum) according to another embodiment of the present invention.
FIG. 13 is a schematic view illustrating an example of a conventional intermediate transfer type image forming apparatus.
FIG. 14 is an explanatory diagram showing that images of two recording sheets are formed on an intermediate transfer belt in the apparatus of FIG. 14;
15A is an explanatory diagram for explaining a cause of image quality degradation that occurs when a recording sheet is transported from a registration roll at an increased speed, and FIG. 15B is an explanatory diagram illustrating image quality that occurs when a recording sheet is normally transported from a registration roller. It is an explanatory view for explaining a cause of deterioration.
FIG. 16 is an explanatory diagram for describing a cause of image quality degradation that occurs when a thick recording sheet is used.
FIG. 17 is an explanatory diagram for explaining a cause of image quality degradation that occurs when a recording sheet enters a fixing device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photoreceptor, 2 ... Charging means, 3 ... Exposure means, 4 ... Developing means, 5 and 25 ... Transfer means, 20 ... Intermediate transfer body, 33 ... Feeding roll, 40 ... Fixing means, P ... Recording sheet, R Exposure position, T1 (primary) transfer position, E: accelerated transport time of the recording sheet, F: detachment time of the recording sheet from the feed roll, G: timing of the recording sheet entering the fixing device, H: recording When the sheet leaves the transfer position.

Claims (2)

A photoreceptor that circulates, a transfer unit including a direct transfer method for directly transferring a toner image formed by performing charging, exposure and development according to image information on the photoreceptor in this order, and directly transferring the toner image to a recording sheet; A feeding roll for feeding the recording sheet so that the unit reaches the transfer position of the opposing photoconductor at a predetermined timing, and a fixing unit for fixing the toner image transferred to the recording sheet, and the feeding roll In the image forming apparatus is configured to feed the rear portion of the recording sheet at an increased speed,
While the image forming areas on the photoreceptor pass through the exposure position, the rear part of the recording sheet is set so as to be sent out at an increased speed from the feed roll and to be separated therefrom. Image forming device. A toner image formed by a photoreceptor that rotates and a charge, exposure and development according to image information performed on the photoreceptor in this order is formed on a recording sheet via an intermediate transfer member that revolves in contact with the photoreceptor. A transfer unit having an intermediate transfer system for transferring, a feeding roll for feeding a recording sheet so that the transfer unit reaches a transfer position of an opposed intermediate transfer body at a predetermined timing, and a toner image transferred to the recording sheet. An image forming apparatus comprising:
The rear portion of the recording sheet is set so as to be sent out at an increased speed from the feed roll and to be separated while the space between the image forming areas on the photoconductor passes one of the exposure position and the transfer position. An image forming apparatus comprising:

Images