JP3994610B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus represented by a copying machine, a printer, and the like, and in particular, adjustment of a sheet conveyance speed in a transfer unit that transfers an image to a sheet and a sheet conveyance unit upstream and downstream of the transfer unit. It is about.
[0002]
[Prior art]
As an image forming apparatus such as a copying machine or a printer using an electrophotographic system, as illustrated in FIG. 10, an image carrier 100 including a photosensitive drum or the like that carries an image (toner image) to be transferred to a sheet P, A transfer body 120 including a transfer roll, a transfer belt, and the like that rotates while forming a transfer nip N in contact therewith and is applied with a transfer bias, and allows the sheet P to pass through the transfer nip N therebetween. There is a method of electrostatically transferring the toner image on the image carrier 100 to the paper P. In the drawing, reference numeral 130 denotes an upstream side sheet conveyance body 130 that holds and conveys the sheet P so as to be fed to the nip portion N on the upstream side in the sheet conveyance direction (the chain line with arrows) of the transfer nip N. A pair of registration rolls 140 is a fixing roll pair as a downstream paper transport body 140 that sandwiches and transports the paper P so as to be sent out from the nip portion N on the downstream side of the transfer nip N in the paper transport direction.
[0003]
In such an image forming apparatus that performs transfer using the contact-type transfer body 120, when a relatively hard material (such as an OHP sheet or cardboard) is used as the paper P, the center of the image in the transfer process is used. There is a problem that a so-called hollow-out phenomenon (also referred to as a “hollow character”), which is transferred in a state where the portion is missing, is likely to occur.
[0004]
As a means for preventing such a hollowing out phenomenon, for example, Japanese Patent Laid-Open No. 4-70785 discloses that a transfer material is conveyed upstream and downstream of a transfer portion while the transfer material (paper P) is conveyed and transferred. An image forming apparatus is proposed which is held by at least one of the conveying means (130, 140) and the transfer material is conveyed at a speed higher by 5% or less than the speed of the transfer means (100, 120). ing. In this image forming apparatus, as shown in the embodiment, the rotation speed of the image carrier and the rotation speed of the contact type transfer means are set to the same speed.
[0005]
[Problems to be solved by the invention]
However, in the proposed image forming apparatus, the conveyance speed of the paper is always maintained to be higher than the speed of the transfer unit, and when plain paper (including thin paper) is used as the paper P. However, there is a problem that the magnification of the image fluctuates in the paper conveyance direction, that is, the vertical direction of the paper during the transfer (the image expands or contracts), or paper wrinkles are likely to occur during fixing after the transfer.
[0006]
Incidentally, means for relatively shifting the rotational speed of the image carrier and the rotational speed of the contact type transfer body have been proposed in order to prevent the above-described hollowing out phenomenon (for example, Japanese Patent Laid-Open Nos. 7-319302 and 7). -248686). However, in this case, although the hollowing out phenomenon is eliminated, the transfer member rubs against the image carrier due to the relative speed difference, so that the life of the image carrier (photosensitive member) is particularly worn and its life is shortened. In addition, there is a problem in that the stability of the sheet conveyance at the transfer nip N is deteriorated, so that a misalignment of the transferred image occurs, or a phenomenon that the image is blurred (smear) by shifting the sheet at the time of transfer occurs. .
[0007]
The present invention has been made in view of such circumstances, and as one of its purposes, there is no occurrence of voids, and there are no fluctuations in image magnification during transfer or paper wrinkles during fixing. In addition, an object of the present invention is to provide an image forming apparatus that can perform good image formation without shortening the life of the image carrier and without causing image blur due to paper misalignment during transfer. In addition, as another object, an image that can be arbitrarily selected depending on a user's usage mode, such as a case where priority is given to prevention of a hollowing out phenomenon or a case where priority is given to extending the life of an image carrier, etc. It is to provide a forming apparatus.
[0008]
[Means for Solving the Problems]
The present invention (first invention) for achieving the above-described object is to provide an image carrier that rotates while carrying an image to be transferred onto a sheet, and to form a transfer nip in contact with the image carrier. On the premise of an image forming apparatus comprising a rotating transfer body, and an upstream paper transport body and a downstream paper transport body that rotate and transport while sandwiching paper on the upstream and downstream sides of the transfer nip in the paper transport direction, Recognizing means for recognizing that the paper is either plain paper or special paper, and when the recognizing means recognizes that the paper is plain paper, the rotation speed of the transfer body and the rotation of the upstream paper transport body Both the conveyance speed is the same as the rotation speed of the image carrier and the rotation conveyance speed of the downstream paper conveyance body is lower than the rotation speed of the image carrier. Paper When recognized, the rotational speed of the transfer body is made the same as the rotational speed of the image carrier, and the rotational transport speeds of the downstream paper transport body and the upstream paper transport body are set to the rotational speed of the image carrier. The present invention is characterized in that a control means for performing control for higher speed is provided.
[0009]
Here, the image carrier is usually a photoreceptor or the like on which an image is also formed, but may be an intermediate transfer member that carries an image intermediately and conveys it to a transfer portion to a sheet. The transfer body is a transfer roll, a transfer belt, or the like. Further, the upstream sheet conveying body and the downstream sheet conveying body are usually composed of a pair of rolls in which the rolls are pressed against each other, but a combination of rolls and belts or a pair of belts combining the belts. Also good.
[0010]
The plain paper includes thin paper in addition to what is generally called plain paper. One special paper is OHP sheet, cardboard (basis weight 100g / m ² The above-mentioned recording medium is a type of recording medium that is relatively easily subject to hollowing out. The recognition means for recognizing the plain paper and the special paper is, for example, provided with a selection means capable of selecting and specifying a paper type to be used by a user or the like and recognizing selection information from the selection means. Of course, a detection unit that can automatically detect the plain paper and the special paper may be used to recognize the detection information.
[0011]
Furthermore, the said control means should just be what can perform speed control which satisfy | fills each above conditions (relationship). In general, a drive source that can rotationally drive the image carrier, transfer body, paper transport body, or the like, or a device that can adjust the rotational speed of a drive transmission system is used. Also, when using plain paper, if the rotational speed of the downstream paper transport body is set lower than the rotational speed of the image carrier, the ratio of the low speeds includes voids, image magnification fluctuations, paper wrinkles, etc. From the viewpoint of ensuring prevention, it is preferable to set the rotational conveyance speed of the downstream paper conveyance body to about 99.6 to 99.8% when the rotation speed of the image carrier is 100%. On the other hand, when using the special paper, if the rotational transport speeds of the downstream paper transport body and the upstream paper transport body are made higher than the rotational speed of the image carrier, the ratio of the high speed is determined to be a dropout, image From the viewpoint of reliably preventing magnification fluctuations, smears, paper wrinkles, and the like, it is preferable to set the rotational conveyance speed of both paper conveyance bodies to be about 101 to 105%.
[0012]
According to the image forming apparatus of the first invention, in the case of plain paper, in addition to the fact that it is difficult for the hollows to occur, the plain paper is looped between the downstream side paper transport member that rotates at a low speed from the transfer nip. Since the sheet is fed to the downstream sheet conveyance body while forming the image, fluctuations in image magnification during transfer and paper wrinkles on the downstream sheet conveyance body are less likely to occur. In the case of special paper, the special paper is transported between the upstream paper transport body and the transfer nip in such a state that the special paper is pushed into the transfer nip by the upstream paper transport body that rotates at a high speed. The special paper is transported between the transport bodies in a state where it is pulled out by the downstream paper transport body rotating at a high speed. As a result, the conveyance speed of the special paper in the transfer nip becomes slightly faster than the rotation speed of the image carrier, so that it is difficult for image voids to occur.
[0013]
In the first aspect of the present invention, the rotational speeds of the upstream paper transport body and the downstream paper transport body when the paper is recognized as the special paper are set for the control means. It is preferable to perform control so that the rotation conveyance speed is higher than the rotation conveyance speed of the upstream sheet conveyance body. The high speed ratio at this time is preferably set so that the rotational transport speed of the downstream paper transport body is about 101 to 103% when the rotational transport speed of the upstream paper transport body is 100%.
[0014]
In such a configuration, the special paper is strongly pulled out from the transfer nip and conveyed by the downstream paper conveyance body that rotates at a relatively high speed, so that the image void is less likely to occur. .
[0015]
On the other hand, the present invention (second invention) for achieving the latter object described above is the image forming apparatus based on the first invention, wherein the image carrier is provided between the image carrier and the transfer body. A speed-up gear train that increases the rotational power of the image and transmits it to the transfer body side is detachably provided, and the rotational speed of the transfer body is transmitted to the transfer body through the speed-up gear train. Between the rotation speed of the image carrier and the rotational speed of the image carrier by removing at least one gear and rotating the transfer body with respect to the image carrier. It is characterized by having a structure.
[0016]
Here, the speed-up gear train may be any one as long as the rotational power of the image carrier can be accelerated and transmitted to the transfer body side, and at least one of them can be attached and detached. A simple configuration in which one large-diameter gear attached to the image carrier side and one small-diameter gear attached to the transfer body side are meshed is preferable.
[0017]
According to such an image forming apparatus of the second invention, when priority is given to prevention of the hollowing out phenomenon, the rotational power of the image carrier is transmitted to the transfer member via the speed increasing gear train. The rotational speed of the transfer body becomes higher than the rotational speed of the image carrier, so that an image (toner) breaking action at the time of transfer can be obtained with certainty, and the omission of the image is accurately prevented. On the other hand, when priority is given to extending the life of the image carrier, the transfer member can be removed by removing at least one gear of the speed increasing gear train and rotating the transfer member relative to the image carrier. The rotation speed of the image carrier becomes the same as that of the image carrier, so that the transfer member does not rub against the image carrier and the life of the image carrier is extended. In this way, it is possible to easily and clearly respond to the user's usage (request) by attaching or removing the speed increasing gear train.
[0018]
In the second invention, when the rotational speed of the transfer body is set to be higher than the rotational speed of the image carrier, the rotational speeds of the upstream paper transport body and the downstream paper transport body are both set to the rotational speed of the transfer body. It is preferable to provide a control means for performing control to make the speed higher than the rotation speed of each sheet conveying body when the rotation speed is the same as the rotation speed of the image carrier.
[0019]
When configured in this manner, it is possible to perform more optimal paper conveyance that is less likely to cause smear and paper wrinkles in plain paper.
[0020]
In addition, this invention is good also as what was comprised combining the above-mentioned 1st invention and 2nd invention as needed. For example, on the premise of the second invention, when the rotational speed of the transfer body is the same as the rotational speed of the image carrier, the first invention is applied. Shi May be.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
FIG. 1 shows a main part of an image forming apparatus according to an embodiment of the present invention. In this image forming apparatus, an image forming unit 2 for forming a toner image corresponding to image information and a sheet P for transferring a toner image formed by the image forming unit 2 are formed in the apparatus main body 1. The sheet feeding unit 3 to be supplied to the transfer position of the unit 2 and the fixing unit 4 for fixing the toner image transferred to the paper P supplied from the sheet feeding unit 3 are mainly equipped.
[0022]
The image forming unit 2 includes a photosensitive drum (image carrier) 10 having an organic photosensitive layer formed on the surface thereof and driven to rotate in the direction of arrow A by a driving source (not shown), and a charging roll disposed around the photosensitive drum 10. 11, an image exposure device 12, a developing device (developing roll 13), a transfer roll 14, and peripheral devices such as a cleaning device (cleaning blade 15). In such an image forming unit 2, when an image is formed, the surface of the photosensitive drum 10 is first uniformly charged by the charging roll 11, and then an optical image based on image information input from a document reading device or an externally connected device. (In this example, a laser beam Bm) is exposed and scanned from the image exposure device 12, and an electrostatic latent image is formed on the surface of the charged photosensitive drum 10. Subsequently, the electrostatic latent image is visualized with a developer (toner) supplied by a developing roll 13 of a developing device that is rotated by applying a developing bias, and is formed as a toner image. The image is conveyed and supplied from the sheet feeding unit 3 between a transfer nip N formed between the photosensitive drum 10 and a transfer roll (transfer body) 14 that is pressed against and rotates and is applied with a transfer bias. The sheet P is electrostatically transferred to the sheet P. After the transfer, the photosensitive drum 10 is cleaned by removing the toner adhering to the surface thereof by the cleaning device 15.
[0023]
The paper feeding unit 3 is disposed in a support structure that can be inserted into and removed from the apparatus main body 1 at a lower portion of the image forming unit 2, and paper P having a predetermined size, feeding direction, type, and the like is appropriately distributed. A plurality of paper feed trays 30 to 32 to be accommodated, and a paper feed path for conveying predetermined paper P one by one from the paper feed trays 30 to 32 to the image forming section 2 are provided. The paper feed unit 3 is also equipped with a manual feed tray (not shown) that is mounted so as to protrude from the apparatus main body 1. In such a sheet feeding unit 3, when an image is formed, the sheet P is fed one by one by a feed roll 33 from predetermined sheet feeding trays 30 to 32 containing sheets P of desired conditions to be used for the image formation. Thereafter, the sheet is conveyed to a registration roll pair (upstream sheet conveyance body) 36 by a sheet conveyance roll pair 34, 35 and the like constituting the sheet feeding path and is temporarily stopped. Thereafter, the paper P is fed to the transfer position (transfer nip N) of the image forming unit 2 in accordance with the image forming (especially transfer process) timing of the image forming unit 2 while being sandwiched by the resist roll pair 36. It is designed to be conveyed. When image formation is performed using the paper P stacked on the manual feed tray, the paper P stacked on the manual feed tray is also registered in the same manner as the paper feed from the paper feed tray by a feed roll (not shown). The roll pair 36 is conveyed. In the figure, reference numerals 37 and 38 denote paper conveyance guides that constitute the paper feed path, and an alternate long and short dash line indicates a conveyance path for the paper P.
[0024]
The paper P supplied from the paper feeding unit 3 to the transfer nip N of the image forming unit 2 through the registration roll pair 36 is sandwiched between the photosensitive drum 10 and the transfer roll 14 that form the transfer nip N. Thus, the toner image formed on the photosensitive drum 10 is electrostatically transferred. The sheet P after the transfer is discharged from the transfer nip N and sent to the fixing unit 4.
[0025]
The fixing unit 4 is disposed at a position on the upper side of the fixing nip N in the image forming unit 2, and a heating roll 41 that is heated and maintained at a predetermined temperature, and is in pressure contact with the heating roll 41. And a fixing roll pair 40 (downstream sheet transport body) including a pressure roll 42 that rotates while forming a fixing nip. Reference numeral 43 in the figure denotes a cover. In such a fixing unit 4, the transferred paper P is fed into a fixing nip formed by the fixing roller pair 40 and conveyed while being sandwiched between the heating roller 41 and the pressure roller 42. Thereby, the toner image on the paper P is heated and pressed to be fixed. After the fixing is completed, the paper P is discharged from the fixing nip of the fixing unit 4 and then discharged and conveyed to the paper discharge unit 1 a formed in the apparatus main body 1 by the paper discharge roll pair 45. In this way, basic image formation is completed.
[0026]
In this image forming apparatus, the rotation state of the transfer roll 14 can be arbitrarily switched.
[0027]
That is, as shown in FIG. 2, the transfer roll 14 in the image forming section 2 receives the rotational driving force of the photosensitive drum 10 by the speed increasing gear train 5 and rotates at a higher speed, and rotates in contact with the photosensitive drum 10. Either one of the cases can be switched to. The speed increasing gear train 5 is coaxially attached to one end of a photosensitive drum 10 that is rotationally driven by a rotational driving source such as an electric motor (not shown), and a first gear 51 having a diameter slightly larger than the diameter of the drum, A small-diameter second gear 52 that is detachably attached to the rotation shaft 14 a of the transfer roll 14 and meshes with the first gear 51 is configured.
[0028]
2A, when the second gear 52 is attached to the rotation shaft 14a of the transfer roll, the rotational power of the photosensitive drum 10 is increased to the transfer roll 14 via the speed increasing gear train 5. Therefore, the transfer roll 14 rotates at a higher speed than the photosensitive drum 10. On the contrary, as shown in FIG. 2B, when the second gear 52 is removed from the rotation shaft 14a of the transfer roll, the rotational power of the photosensitive drum 10 is transmitted to the transfer roll 14 via the speed increasing gear train 5. Since the transfer roll 14 is only brought into pressure contact with the photosensitive drum 10, the transfer roll 14 is driven to rotate with the photosensitive drum 10 and rotates at the same speed. In addition, the selection of the attachment and removal of the second gear 52 in the speed increasing gear train 5 can be performed in accordance with the use mode (request) of the user. To do.
[0029]
Further, in this image forming apparatus, as shown in FIGS. 4 to 5, the rotation speed of the heating roll 41 in the registration roll pair 36 and the fixing unit 4 is controlled according to the type of paper P to be used. ing.
[0030]
That is, when the paper P uses what is called “plain paper” such as plain paper or thin paper (plain paper mode), the paper P is called “special paper” such as an OHP sheet, cardboard, postcard, or label paper. The special paper mode and the special paper mode are controlled so that the rotational speeds of the resist roll pair 36 and the heating roll 41 are slightly different between the normal paper mode and the special paper mode. Yes.
[0031]
Of these, whether the paper P belongs to the plain paper group or the special paper group, a special paper selection switch (not shown in FIG. 4) arranged on an operation panel (not shown) of the apparatus body 1. Reference numeral 6) is recognized when the user turns on (or turns off). Further, regarding the drive system of the resist roll pair 36 and the heating roll 41, in the case of this image forming apparatus, as conceptually shown in FIG. The pulleys 55a, 56a, 36a, 41a attached to the drive shafts and the rotation shafts of the rolls 36, 41 and the rotation transmission belts 57, 58 appropriately stretched between the pulleys 55a, 56a, 36a, 41a. The resist roll pair 36 (one of the rolls) and the heating roll 41 are transmitted to each of them, and the rotational speeds of the respective roll pairs 36 and 41 are adjusted by adjusting the rotational speeds of the respective drive sources 55 and 56. Is adjusted accordingly.
[0032]
FIG. 4 shows the configuration of the control device 7 that controls the drive system of the registration roll pair 36 and the heating roll 41 corresponding to the type of the paper P. The control device 7 generally includes a central processing unit 70 connected to the special paper selection switch 6, a driving system driver 75 that controls the driving conditions of the driving source 55 of the registration roll pair 36, and a heating roll 41. Is connected to a driving system driver 76 for controlling the driving conditions of the driving source 56.
[0033]
The central processing unit 70 performs arithmetic processing according to the drive system control program stored in the memory unit (ROM or the like) according to the information signal input from the special paper selection switch 6. A predetermined control signal is transmitted to the drive system driver 77 (75, 76). Thereby, the rotational speed of the drive source 55 of the resist roll pair 36 and the heating roll 41 is adjusted, and the rotational speed of both the rolls 36 and 41 is controlled accordingly. In this example, according to the control flow as shown in FIG. 5, based on the determination, each rotational speed is set based on the control program as shown in FIG. In particular, the setting data relating to the control program shown in FIG. 6 is contents used when the second gear 52 of the speed increasing gear train 5 is removed and the transfer roll 14 is rotated at the same speed as the photosensitive drum 10. In addition, the rotational speed of the registration roll pair 36 is set to be 0.2% higher than the rotational speed of the fixing roll pair 40 (heating roll 41).
[0034]
Next, the operation of the image forming apparatus corresponding to this drive system control device will be described.
[0035]
First, as shown in FIG. 5, the control device 7 determines whether or not the special paper mode is selected by the special paper selection switch 6 (step 10: S10). If it is not selected, it is regarded as the plain paper mode, and the drive system setting for the plain paper mode as shown in FIG. 6 is performed (S20). On the other hand, when the selection mode is selected by the selection switch 6, the drive system setting for the special paper mode is performed as shown in FIG. 6 (S30).
[0036]
When the plain paper mode is selected, the “plain paper mode” as shown in FIG. 6 is set, and the registration roll pair 36 and the fixing roll 40 are rotated at a steady speed (S20). . That is, assuming that the rotation speed of the photosensitive drum 10 (and the transfer roll 14) is 100%, the rotation speed of the resist roll pair 36 is set to “100%” to be the same speed as the photosensitive drum 10, and the fixing roll 40 (heating roll 41). The control is performed such that the rotation speed is set to “99.8%” to be lower than that of the photosensitive drum 10.
[0037]
Accordingly, as shown in FIG. 7, the plain paper P (N) is rotated at each rotation speed as indicated by the dotted line by the registration roll pair 36, the roll pair of the photosensitive drum 10 and the transfer roll 14, and the fixing roll pair 40. The paper is conveyed in a state where it receives a paper conveying force according to. Particularly in this case, the plain paper P (N) is slightly fixed in a state in which a loop is formed between the roll pair of the photosensitive drum 10 and the transfer roll 14 and the fixing roll pair 40 due to the rotational speed difference between the two. It is conveyed so as to be pushed into the fixing nip of the pair 40.
[0038]
On the other hand, when the special paper mode is selected, the “special paper mode” as shown in FIG. 6 is set, and the registration roll pair 36 and the fixing roll 40 are rotated at high speed (S30). ). That is, the rotational speed of the resist roll pair 36 is set to “101%” and the rotational speed of the fixing roll 40 (heating roll 41) is set to “101.4%”. Is called. In this example, it is 1.4% faster than the rotational speed of the photosensitive drum (transfer roll).
[0039]
As a result, as shown in FIGS. 8a to 8d, the special paper P (S) has each of the resist roll pair 36, the roll pair of the photosensitive drum 10 and the transfer roll 14, and the fixing roll pair 40 as indicated by dotted arrows. The paper is transported in a state of receiving a paper transport force corresponding to the rotational speed. Particularly in this case, the special paper P (S) is pushed into the transfer nip by the resist roll pair 36 due to the rotational speed difference between the resist roll pair 36 and the roll pair of the photosensitive drum 10 and the transfer roll 14. It is conveyed in such a state. Further, the photosensitive drum 10 and the transfer roll 14 are transported between the roll pair and the fixing roll pair 40 so as to be pulled out from the transfer nip by the fixing roll pair 40 due to a difference in rotational speed between the two.
[0040]
FIG. 9 shows the results of tests performed using this image forming apparatus.
[0041]
In FIG. 9a, the rotational speed A (corresponding to the paper transport speed) A of the resist roll pair 36 is equivalent to the paper transport speed B (corresponding to the rotational speed of the photosensitive drum 10) at the transfer nip N. After making various changes and settings as shown in the chart, plain paper (Fuji Xerox Office Supply: L paper) and special paper (OHP sheet, cardboard: basis weight 16 g / m) ² ) (Sample Nos. (1) to (5)), the obtained image (including characters) is hollowed out, and the parallelism as the variation in image magnification (in the paper transport direction) Image distortion occurring at both left and right edges / vertical magnification (image distortion occurring at the leading and trailing edges in the paper transport direction) and smear (image distortion caused by paper misalignment at the transfer nip) It shows the result of examining each occurrence situation. On the other hand, FIG. 9B shows various changes in the rotational speed C (corresponding to the paper transport speed) C of the fixing roll pair 40 with respect to the paper transport speed B at the transfer nip N as shown in the chart, When image formation is performed using paper (Sample Nos. A to e), the obtained image is hollowed out, parallelism / vertical magnification as image magnification variation, and paper wrinkle (paper generated at the fixing nip) The results of examining the occurrence of wrinkles) are shown. Each result shown in the chart is evaluated based on the following criteria.
○: Good, Δ: Within allowable level, ×: Unacceptable level.
[0042]
From the results shown in FIGS. 9a and 9b, it can be confirmed that when plain paper is used, the combination of the test sample (2) and the test sample a gives a good result. That is, it has been found that the registration roll pair 36 should be at the same speed as the photosensitive drum 10 (and the transfer roll 14; the same applies hereinafter), while the fixing roll pair 40 should be at a lower speed than the photosensitive drum 10.
[0043]
In addition, when special paper is used, it can be confirmed that good results are obtained when the test samples (3) and (4) and the test samples c and d are appropriately combined. That is, it has been found that both the registration roll pair 36 and the fixing roll pair 40 should be faster than the photosensitive drum 10.
[0044]
Further, in this test, the transfer roll 14 is rotated at the same speed as the photosensitive drum 10 (by driven rotation) regardless of whether plain paper or special paper is used. Problems caused by rubbing 10 (problems described in the description of the prior art) can be surely avoided.
[0045]
Incidentally, from the viewpoint of obtaining good results regardless of whether plain paper or special paper is used, for example, test sample (3) and test sample d in the speed setting examples shown in FIG. It is good to combine.
[0046]
In this image forming apparatus, when there is a strong demand for the user to give priority to prevention of image dropout, the transfer roller 14 is rotated at a higher speed than the photosensitive drum 10 by the speed increasing gear train 5. . In this case, if the rotational speeds of the resist roll pair 36 and the heating roll 31 are both higher than the rotational speeds (rotational speeds of the photosensitive drum 10) when the transfer roll 14 is set to the same speed as the photosensitive drum 10. Good. Specifically, when the rotation speed of the photosensitive drum 10 is 100%, the rotation speed of the resist roll pair 36 and the heating roll 31 is preferably about 100.2 to 100.5%.
[0047]
[Other embodiments]
In the first embodiment, the case where the present invention is applied to an image forming apparatus for black and white is exemplified, but the present invention may be applied to an image forming apparatus for color. Further, the method of the image forming apparatus is not particularly limited.
[0048]
【The invention's effect】
As described above, according to the image forming apparatus of the first invention, no matter where plain paper or special paper is used, there is no hollowing out, and the magnification fluctuation or fixing of the image during transfer is fixed. It is possible to perform good image formation in which there is no occurrence of paper wrinkles at the time, and the life of the image carrier is shortened and image blur due to paper misalignment during transfer is not generated. According to the image forming apparatus of the second invention, the image carrier and the case where priority is given to the prevention of the hollowing out phenomenon or the like only by switching the use of the speed increasing gear train or not depending on the use mode of the user. A case where priority is given to extending the life of the user can be arbitrarily selected and can be easily and accurately handled.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a main part of an image forming apparatus according to a first embodiment.
FIG. 2 is an explanatory diagram of a main part showing a configuration of a drive transmission system for a photosensitive drum of a transfer roll.
FIG. 3 is a conceptual diagram illustrating a main part of a configuration of a rotational drive system of a resist roll pair and a fixing roll pair.
FIG. 4 is a block diagram showing a control device related to a drive system for a resist roll pair and a fixing roll pair.
FIG. 5 is a flowchart showing the control contents of a drive system for a registration roll pair and a fixing roll pair.
FIG. 6 is a chart showing the control setting contents for the rotational speed of each roll pair and the like.
FIG. 7 is an explanatory diagram showing a paper conveyance state by each roll pair or the like when plain paper is used.
FIG. 8 is an explanatory diagram showing a paper conveyance state by each roll pair when special paper is used.
FIG. 9 is a chart showing a test performed using the image forming apparatus according to the first embodiment and a result thereof;
FIG. 10 is a conceptual diagram showing a main part of a conventional image forming apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 5 ... Speed increasing gear train, 6 ... Special paper selection switch (recognition means), 7 ... Control device (control means), 10 ... Photosensitive drum (image carrier), 14 ... Transfer roll (transfer body), 36 ... Resist Roll pair (upstream side paper transport body), 40... Fixing roll pair (downstream side paper transport body), 52... 2nd gear (removal gear), P... Paper, P (N) ... plain paper, P (S). Special paper.

Claims (4)

An image carrier that rotates while carrying an image to be transferred to a sheet, a transfer body that rotates while forming a transfer nip in contact with the image carrier, and an upstream side and a downstream side of the transfer nip in the sheet conveyance direction. Bei example an upstream sheet conveying member and the downstream paper transport member rotates conveyed while sandwiching the paper, said and said sheet is conveyed is pinched at the same time between the upstream sheet conveying member and the transfer nip In an image forming apparatus that may be sandwiched and conveyed at the same time between a transfer nip and the downstream sheet conveyance body ,
A recognition means for recognizing that the paper is either plain paper or special paper stronger than the plain paper ;
When the recognition means recognizes that the paper is plain paper, both the rotational speed of the transfer body and the rotational transport speed of the upstream paper transport body are set to the same speed as the rotational speed of the image carrier and the downstream side. When the recognizing means recognizes that the paper is a special paper, the rotational speed of the transfer body is set to be lower than the rotational speed of the image carrier. And a control means for controlling the rotational transport speeds of the downstream paper transport body and the upstream paper transport body to be higher than the rotational speed of the image carrier. An image forming apparatus. The apparatus of claim 1.
The control means determines the rotational transport speeds of the upstream paper transport body and the downstream paper transport body when the paper is recognized as special paper, and further the rotational transport speed of the downstream paper transport body is the upstream paper transport. An image forming apparatus that performs control so as to be faster than a rotational conveyance speed of a body. The apparatus of claim 1 .
An accelerating gear train that increases the rotational power of the image carrier and transmits it to the transfer body between the image carrier and the transfer body is provided detachably.
In addition, by transmitting the rotational power of the image carrier to the transfer body via the speed increasing gear train, the rotational speed of the transfer body is made higher than the rotational speed of the image carrier, and at least the speed increasing gear train The structure is such that the rotational speed of the transfer body can be switched to the same speed as that of the image carrier by removing one gear and rotating the transfer body with respect to the image carrier. An image forming apparatus. The apparatus of claim 3.
When the rotational speed of the transfer body is set to be higher than the rotational speed of the image carrier, the rotational speed of the upstream paper transport body and the downstream paper transport body is set to the rotational speed of the transfer body. An image forming apparatus comprising a control unit that performs control to make the speed higher than the rotational speed of each paper transport when the speed is the same as the speed.

Images