JP2012098588A - Image forming apparatus and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that hardly causes a difference in size between an image formed on a first face and an image formed on a second face of a recording material even when images are formed on both of the first face and the second face of the recording material.SOLUTION: The image forming apparatus includes: toner image forming means forming a toner image; a transfer device 15 transferring the toner image onto a sheet by using a photoreceptor drum 11; a fixing unit 20 fixing the toner image to the sheet; a sheet inverting mechanism 40 inverting the sheet from a first face to a second face of the sheet after the toner image is fixed to the first face of the sheet by the fixing unit 20, and again supplying the sheet to the transfer device 15; a control unit 500 controlling the rotational speed of the photoreceptor drum 11. The control unit 500 adjusts the magnification of a toner image in a sub-scanning direction by decreasing the rotational speed of the photoreceptor drum 1 upon transferring a toner image on the second face of the sheet than the rotational speed of the photoreceptor drum 11 during transferring a toner image on the first face of the sheet.

Description

  The present invention relates to an image forming apparatus and a program.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic method, for example, a photosensitive member formed in a drum shape is uniformly charged, and the photosensitive member is exposed to light controlled based on image information. An electrostatic latent image is formed on the photoreceptor. The electrostatic latent image is converted into a visible image (toner image) with toner, and the toner image is further transferred to a recording material and fixed by a fixing device to form an image.

Japanese Patent Application Laid-Open No. 2004-228561 has a carrier that conveys a carrier to the next process area by rotation, and when the double-side transfer mode is selected, the image is transferred to the first surface of the transfer paper and fixed by a fixing unit, and then the transfer paper In the image forming apparatus for transferring an image to the second side of the sheet and fixing the image by the fixing unit, the first linear speed when the image is transferred to the first side of the transfer sheet when the double-side transfer mode is selected, and the transfer sheet There is disclosed an image forming apparatus provided with means for setting the relationship between the first linear velocity and the second linear velocity to the second linear velocity when the image is transferred to the second surface.
Japanese Patent Application Laid-Open No. 2004-228561 describes the moving speed of the first image carrier when forming the toner image transferred onto the second surface of the transfer material, and the time when forming the toner image transferred onto the first surface of the transfer material. An image forming apparatus is disclosed that is slower than the moving speed of the first image carrier.

JP-A-9-197727 Japanese Patent Laid-Open No. 11-2927

Here, images may be formed on both the first surface and the second surface of the recording material. At this time, after fixing the toner image formed on the first surface, the toner image is formed on the second surface. However, since the recording material shrinks when the toner image formed on the first surface is fixed, the size of the image formed on the first surface may be smaller than the image formed on the second surface of the recording material.
In the present invention, even when images are formed on both the first surface and the second surface of the recording material, there is a difference in the size of the image formed on the first surface of the recording material and the image formed on the second surface. An object of the present invention is to provide an image forming apparatus and the like that are unlikely to occur.

  The invention according to claim 1 is a toner image forming unit that forms a toner image, a transfer unit that transfers the toner image formed by the toner image forming unit to a recording material using a rotating body, and the transfer unit. Fixing means for fixing the toner image transferred by the recording material to the recording material, and after the toner image is fixed on the first surface of the recording material by the fixing means, the first surface and the second surface of the recording material are reversed. A reversing unit that re-feeds the recording material to the transfer unit, and a control unit that controls the rotation speed of the rotating body, and the control unit transfers the toner image to the first surface of the recording material. Adjusting the magnification in the sub-scanning direction of the transferred toner image by lowering the rotation speed of the rotating body when transferring the toner image to the second surface of the recording material than the rotating speed of the rotating body. An image forming apparatus characterized by That.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the control unit changes a rotation speed of the rotating body according to an absolute humidity value.
A third aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the fixing unit fixes the toner image of a single color on a recording material.
According to a fourth aspect of the present invention, the transfer unit transfers the toner image onto a recording material by generating an electric field, and the control unit applies a voltage applied by the transfer unit to generate the electric field. 4. The image forming apparatus according to claim 1, wherein the rotation speed of the rotating body is changed according to a value of the image forming apparatus. 5.
According to a fifth aspect of the present invention, the fixing unit includes a fixing rotator that fixes the toner image transferred by the transfer unit to a recording material while rotating the toner image, and the control unit includes the fixing rotator. 5. The image forming apparatus according to claim 1, further comprising a control for making a surface linear velocity higher than a linear velocity of the rotating body. 6.
The invention according to claim 6 further includes a recording material supply unit that accommodates the recording material, and supplies the recording material one by one to the transfer unit, and the control unit includes a leading end portion in the conveyance direction of the recording material 6. The image forming apparatus according to claim 1, wherein the linear velocity of the surface of the rotating body is continuously increased before reaching the fixing unit.

  According to a seventh aspect of the present invention, a function of controlling a toner image forming unit for forming a toner image is transferred to a recording material using a rotating body on a computer. The function of controlling the transfer means, the function of controlling the fixing means for fixing the toner image transferred by the transfer means to the recording material, and the toner image being fixed on the first surface of the recording material by the fixing means A function of controlling a reversing unit that inverts the first surface and the second surface of the recording material and supplying the recording material again to the transfer unit; and a toner image is formed on the first surface of the recording material in the transfer unit. Magnification in the sub-scanning direction of the toner image transferred by slowing the rotation speed of the rotating body when transferring the toner image to the second surface of the recording material than the rotation speed of the rotating body when transferring Make adjustments A program for forming an image by realizing function and, a.

  The invention according to claim 8 further includes a function of acquiring image forming conditions for image formation, and changes the rotational speed of the rotating body according to the image forming conditions. It is.

According to the first aspect of the present invention, an image formed on the first surface of the recording material even when images are formed on both the first surface and the second surface of the recording material, compared to the case where this configuration is not adopted. It is possible to provide an image forming apparatus in which the difference in the size of the image formed on the second surface hardly occurs.
According to the second aspect of the present invention, the transfer speed can be adjusted in accordance with the moisture content of the recording material as compared with the case where this configuration is not adopted.
According to the third aspect of the present invention, the image formed on the first surface of the recording material and the second surface are formed even when the pressure at which the toner image is fixed is small compared to the case where this configuration is not adopted. Differences in image size are less likely to occur.
According to the fourth aspect of the present invention, the moisture content of the recording material can be determined more accurately than in the case where the present configuration is not adopted.
According to the fifth aspect of the present invention, image distortion is less likely to occur even when a recording material having a predetermined thickness or more is used, compared to a case where this configuration is not adopted.
According to the sixth aspect of the present invention, compared to the case where this configuration is not adopted, even when a tensile stress is generated on the recording material by the winding mechanism or the like, the change is less likely to occur depending on the magnification of the formed image.
According to the seventh aspect of the present invention, even when an image is formed on both the first surface and the second surface of the recording material, the image formed on the first surface of the recording material and the image formed on the second surface are A computer can realize a function of forming an image so that a difference in size is less likely to occur.
According to the eighth aspect of the present invention, the computer can realize the function of adjusting the transfer speed in accordance with the moisture content of the recording material.

1 is a diagram illustrating a schematic configuration of an image forming apparatus to which the exemplary embodiment is applied. It is the enlarged view to which a part of FIG. 1 was expanded. (A)-(b) is the conceptual diagram explaining the change of the dimension of the paper at the time of double-sided printing. It is the flowchart explaining the procedure which performs double-sided printing on the paper by this Embodiment. FIG. 6 is a diagram for explaining the relationship between the moisture content of a sheet and the magnification in the sub-scanning direction of an image formed on the sheet when the transfer speed is the same on the first surface and the second surface. 6 is a flowchart illustrating a procedure for performing image formation when a sheet according to the present embodiment is a thick sheet. (A)-(b) is the figure compared with the case where it does and the case where control of step 207 of FIG. 6 is not performed. (A)-(b) is the figure which demonstrated the part of the drawing-in roll and the rolling mechanism in more detail. 6 is a flowchart illustrating a procedure for forming an image on a sheet according to the present embodiment. (A)-(b) is the figure compared about the case where the case where control of step 303 and step 304 of FIG. 9 is not performed is performed.

<Description of Entire Image Forming Apparatus>
Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus 1 to which the exemplary embodiment is applied. FIG. 2 is an enlarged view of a part of FIG. Hereinafter, the image forming apparatus 1 will be described with reference to FIGS. 1 and 2.
The image forming apparatus 1 shown in FIGS. 1 and 2 fixes an image forming unit 10 that forms a toner image on a sheet (recording material) P and a toner image formed on the sheet P by the image forming unit 10 on the sheet P. A fixing unit 20 as an example of a fixing unit to perform, a paper supply unit 30 as an example of a recording material supply unit that stores the paper P and supplies the paper P to the image forming unit 10 one by one, The main part is composed of a sheet reversing mechanism 40 that reverses the front and back sides.

Further, the image forming apparatus 1 includes a toner cartridge TC that is detachably provided and contains toner supplied to the image forming unit 10, and a paper stacking unit YS on which the paper P that has passed through the fixing unit 20 is stacked. It has been.
Further, the image forming apparatus 1 is provided with a receiving unit 400 that receives image data from a scanner 200 (image reading apparatus) provided on the upper part of the image forming apparatus 1 or a personal computer (PC) (not shown). . The image forming apparatus 1 includes an image forming unit 10, a fixing unit 20, a paper supply unit 30, a control unit 500 that controls the overall operation of the paper reversing mechanism 40, and image data received by the receiving unit 400. An image processing unit 600 that outputs image data to the image forming unit 10 after processing is provided.

  Further, the image forming apparatus 1 is provided with a user interface (UI) 700 that is configured by a display panel and receives instructions from the user and displays messages and the like to the user. The control unit 500 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an HDD (Hard Disk Drive) (all not shown). In the CPU, a processing program is executed. Various programs, various tables, parameters, and the like are stored in the ROM. The RAM is used as a work area when the CPU executes various programs.

  The image forming unit 10 is provided with a process cartridge 100. The process cartridge 100 can be removed from the image forming apparatus 1 by being pulled out to the front side (the front side in the figure) of the image forming apparatus 1. In the present embodiment, by removing the process cartridge 100, another process cartridge 100 can be mounted.

  Here, the process cartridge 100 is provided with a photosensitive drum 11, a charging device 12, a developing device 14, and a cleaning device 16. Further, the process cartridge 100 is provided with a memory M constituted by an EEPROM (Electrically Erasable and Programmable ROM) or the like. The memory M stores information indicating the type of the process cartridge 100 and information regarding the use status of the process cartridge 100 such as the number of rotations of the photosensitive drum 11. The image forming apparatus 1 according to the present embodiment includes an exposure device 13 and a transfer device that is an example of a transfer unit and transfers the toner image onto the paper P by rotating the paper P together with the photosensitive drum 11 while sandwiching the paper P. 15 are provided. Further, the image forming apparatus 1 is provided with a read / write device YK that reads information from the memory M and writes information to the memory M.

  Here, the photosensitive drum 11 provided in the process cartridge 100 has a photosensitive layer on its outer peripheral surface, and rotates in the direction of the arrow in the drawing by driving a driving source (not shown). The charging device 12 has a charging roll in contact with the photosensitive drum 11 and charges the photosensitive drum 11 to a predetermined potential. The exposure device 13 irradiates the photosensitive drum 11 with laser and selectively exposes the photosensitive drum 11 charged by the charging device 12 to form an electrostatic latent image on the photosensitive drum 11. The developing device 14 has a developing roll and forms a toner image on the photosensitive drum 11.

  More specifically, the developing device 14 contains, for example, a two-component developer including a negatively charged toner and a positively charged carrier. The developing device 14 develops the electrostatic latent image formed on the photosensitive drum 11 with toner to form a toner image on the photosensitive drum 11. The transfer device 15 has a roll-like member and rotates according to the rotation of the photoconductor drum 11 while forming an electric field between the transfer device 15 and the photoconductor drum 11 (transfer portion Tp). The toner image is transferred onto the paper P. The cleaning device 16 has a cleaning blade that contacts the photosensitive drum 11, and removes toner and the like remaining on the photosensitive drum 11 using the cleaning blade. In the present embodiment, the process cartridge 100 and the exposure device 13 can be regarded as an example of a toner image forming unit that forms a toner image.

  The fixing unit 20 fixes the toner image formed on the paper P by the image forming unit 10 to the paper P by heating. In the present embodiment, the fixing unit 20 includes a heating roll 21 that includes a heating source therein, and a pressure roll 22 that is disposed to face the heating roll 21 and sandwiches the paper P together with the heating roll 21.

  For example, a halogen heater is disposed inside the heating roll 21 as a heating source, and the surface of the heating roll 21 can be raised to a predetermined temperature by heat generated thereby. For this reason, the paper P is conveyed to the fixing unit 20 and is brought into contact with the heating roll 21, so that the paper P is heated, whereby the toner image formed on the paper P is fixed. In the present embodiment, the heating roll 21 can be regarded as a fixing rotator used for fixing the toner image transferred by the transfer unit to the recording material.

  Further, the pressure roll 22 is in close contact with the heating roll 21 to form a sandwiching portion. Here, a driving source such as a motor is connected to the heating roll 21, and when the heating roll 21 is rotated by this driving source, the pressure roll 22 is rotated accordingly. For this reason, when the paper P is transported to the sandwiching portion, the paper P can be sandwiched and transported while being sandwiched.

  The paper supply unit 30 includes a first paper supply unit 31 to a third paper supply unit 33 so that different sizes of paper P can be supplied to the image forming unit 10. The first paper feed unit 31 to the third paper feed unit 33 are configured similarly. The first paper feed unit 31 will be described as an example. The first paper feed unit 31 includes a paper storage unit 41 as an example of a recording material storage unit that stores paper P, a drawing roll 43, and a winding mechanism 44. The sheet storage unit 41 has an opening at the top and a rectangular parallelepiped shape, and stores a plurality of sheets P therein. The pull-in roll 43 comes into contact with the uppermost sheet P of the sheet bundle accommodated in the sheet accommodating unit 41 and sends out the uppermost sheet P toward the winding mechanism 44. The webbing mechanism 44 is constituted by, for example, a rotatable feed roll and a retard roll with limited rotation, and the paper P fed by the pull-in roll 43 is spread one by one.

  The paper supply unit 30 is provided with a registration roll (registration roll) 852. The registration roll 852 temporarily stops the conveyance of the sheet P in a state where the rotation is stopped, and rotates the sheet P at a predetermined timing, thereby supplying the sheet P while performing registration adjustment on the transfer portion Tp. To do. Further, the sheet supply unit 30 is an example of a conveyance unit, and is conveyed in the same manner as the first conveyance roll 55 that conveys the sheet P conveyed from the second sheet feeding unit 32 toward the registration roll 852 and the transfer unit Tp. A second transport roll 65 is provided as an example of a means for transporting the paper P transported from the third paper feed unit 33 toward the first transport roll 55.

  The paper reversing mechanism 40 reverses the front and back of the paper P that has passed through the fixing unit 20 and supplies the paper P to the transfer unit Tp again. In other words, the paper reversing mechanism 40 reverses the first surface and the second surface of the paper P after the toner image is fixed on the first surface of the paper P by the fixing unit 20 and supplies the paper P to the transfer device 15 again. It is an example of a means. The paper reversing mechanism 40 is provided with a transport roll 48 that transports the paper P on the transport path SR for reversal.

  As the sheet conveyance path of the image forming apparatus 1, a sheet conveyance path YR through which the sheet P stored in the sheet supply unit 30 passes through the registration roll 852, the transfer unit Tp, and the fixing unit 20 is provided. In the image forming apparatus 1, the sheet reversing mechanism 40 is provided with a reversing conveyance path SR that branches from the sheet conveyance path YR on the downstream side of the fixing unit 20 and merges with the sheet conveyance path YR on the upstream side of the registration roll 852. It has been. The reversing transport path SR is used when an image is formed not only on the first side of the paper P but also on the second side, that is, when the paper P is printed on both sides.

<Description of image forming operation>
Here, when an image is formed on the paper P, image data formed by a personal computer (not shown) or the like is received by the receiving unit 400, and this image data is output from the receiving unit 400 to the image processing unit 600. The The image processing unit 600 performs image processing on the image data. The image data that has been subjected to image processing is output to the exposure device 13. The exposure device 13 that has acquired the image data selectively exposes the photosensitive drum 11 charged by the charging device 12 to form an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 14 as, for example, a black (K) toner image. That is, the image forming apparatus 1 of the present embodiment develops a single color toner image.

On the other hand, in the paper supply unit 30, the drawing roll 43 rotates in synchronization with the image formation timing, and the paper P is supplied from the paper storage unit 41. Then, the sheets P that are rolled up one by one by the rolling mechanism 44 are conveyed to the registration roll 852 and are temporarily stopped. Thereafter, the registration roll 852 rotates in accordance with the rotation timing of the photosensitive drum 11, and the paper P is supplied to the transfer unit Tp. Then, the toner image formed on the photosensitive drum 11 is transferred onto the paper P in the transfer portion Tp. In this case, the photosensitive drum 11 can be grasped as a rotating body used for transferring.
Thereafter, the paper P on which the toner image has been transferred undergoes a fixing process in the fixing unit 20 and is discharged by a discharge roll 75 to a paper stacking unit YS located below the scanner 200.

  When performing double-sided printing on the paper P, the paper P that has passed through the fixing unit 20 is once conveyed toward the paper stacking unit YS by the discharge roll 75. However, the discharge roll 75 does not completely discharge the paper P and stops rotating in the middle of the paper P. Then, the discharge roller 75 rotates in the direction opposite to the direction in which the paper P is discharged in accordance with the start timing of image formation on the second surface by the image forming unit 10, and sends the paper P to the reversing conveyance path SR. Further, the sheet P passes through the sheet reversing mechanism 40 and is reversed and then supplied again to the transfer unit Tp. Then, the toner image formed on the photosensitive drum 11 is transferred to the second surface of the paper P at the transfer portion Tp. Further, the sheet P on which the toner image is transferred to the second surface is subjected to a fixing process by the fixing unit 20. Then, the paper P on which the image is formed is discharged to the paper stacking unit YS.

<Description of shrinkage of paper P during double-sided printing>
Here, the paper P contains moisture at a rate of 4 wt% to 10 wt%, for example. That is, the sheet P absorbs moisture in the atmosphere, thereby holding the amount of moisture corresponding to the environment in which the sheet P is placed. However, as described above, the fixing unit 20 performs fixing by heating the toner image transferred to the paper P. Therefore, the moisture contained in the paper P is evaporated by the heat applied by the fixing unit 20, and the moisture contained in the paper P is reduced. The moisture contained in the paper P after passing through the fixing unit 20 is, for example, 2 wt%. When the moisture contained in the paper P decreases, the paper P contracts. This phenomenon is particularly noticeable in the longitudinal direction of the paper P.

FIGS. 3A and 3B are conceptual diagrams illustrating changes in the dimensions of the paper P during double-sided printing.
First, as shown in FIG. 3A, the toner image is transferred onto the first surface of the paper P by the transfer device 15. The transferred toner image is fixed by the fixing unit 20. At this time, as shown in FIG. 3B, the paper P after passing through the fixing unit 20 contracts due to heat applied by the fixing unit 20. The shrinking length is larger in the long direction than the short direction of the paper P as described above. At this time, as the paper P contracts, the formed image is similarly reduced.
Next, the front and back of the paper P are reversed by the paper reversing mechanism 40, and the toner image is transferred onto the second surface of the paper P by the transfer device 15 as shown in FIG. Then, the sheet P passes through the fixing unit 20 again to fix the toner image on the second surface. At this time, as shown in FIG. 3D, the paper P after passing through the fixing unit 20 contracts due to the heat applied by the fixing unit 20, but most of the moisture contained in the paper P is at the time of fixing the first surface. Because of evaporation, the shrinkage rate is smaller than that of the first surface. Eventually, the image formed on the first surface of the paper P is smaller than the image formed on the second surface.

  Such a problem appears more conspicuously when a monochromatic toner is used and the monochromatic toner image is fixed on the paper P as in the present embodiment. That is, in the case of a color image forming apparatus that uses a plurality of toners, there is a pressure unit that applies pressure to the fixing unit. Then, fixing is performed by applying heat and pressure to the toner image in the pressing portion. This pressure causes the sheet P to be stretched. For this reason, the shrinkage and stretching of the paper are balanced, and the above-described problems are unlikely to occur. On the other hand, in the fixing unit 20 according to the present embodiment, a large pressure is not applied between the heating roll 21 and the pressure roll 22, and the action of stretching the paper P hardly occurs.

<Description of a method for suppressing the difference in image size between the first side and the second side of the paper P>
Therefore, in the present embodiment, the above-described problem is suppressed by the following method.
FIG. 4 is a flowchart illustrating a procedure for performing double-sided printing on the paper P according to the present embodiment.
First, when the control unit 500 (see FIG. 1) receives the image data through the receiving unit 400 (see FIG. 1), the image processing unit 600 (see FIG. 1) performs image formation on the first surface of the paper P. A command is transmitted (step 101).
Further, the control unit 500 acquires an environmental value in the image forming apparatus 1 (step 102). This environmental value is the temperature and humidity in the image forming apparatus 1 in the present embodiment, and can be obtained from a temperature sensor or a humidity sensor installed in the image forming apparatus 1 in advance. Then, the control unit 500 calculates the absolute humidity in the image forming apparatus 1 based on the acquired temperature and humidity (step 103). There are various calculation formulas for calculating the absolute humidity. For example, it can be calculated by the following formula (1).

  Next, the control unit 500 controls the image forming unit 10, the fixing unit 20, and the paper supply unit 30, conveys the paper P from the paper supply unit 30 to the transfer unit Tp, and forms a toner image on the first surface of the paper P. Then, the toner image is fixed and an image is formed on the first surface of the paper P (step 104). On the other hand, the control unit 500 transmits an image formation command for the second surface of the paper P to the image processing unit 600 (step 105). Then, the control unit 500 controls the paper reversing mechanism 40 to reverse the front and back of the paper P and transport the paper P to the transfer unit Tp (step 106). Next, the control unit 500 controls the image forming unit 10 and the fixing unit 20 to form a toner image on the second surface of the paper P, and further fix the toner image to thereby form an image on the second surface of the paper P. Form (step 107).

At this time, the control unit 500 controls the rotational speed of the photosensitive drum 11 of the image forming unit 10 at this time, and the sheet speed is higher than the rotational speed of the photosensitive drum 11 when the toner image is transferred to the first surface of the sheet P. The rotational speed of the photosensitive drum 11 when the toner image is transferred to the second surface of P is decreased. In this case, since the speed at which the toner image is formed by the toner image forming unit is not changed, the toner image formed on the photosensitive drum 11 and transferred to the second surface is contracted in the sub-scanning direction as compared with the first surface. It will be a thing. That is, the toner image formed on the photosensitive drum 11 has a smaller magnification in the sub-scanning direction.
As will be described in detail later, the rotation speed of the photosensitive drum 11 is controlled according to the absolute humidity calculated in step 103. That is, the control unit 500 performs control to change the rotation speed of the photosensitive drum 11 according to the absolute humidity value. Finally, the paper P on which image formation has been completed is discharged to the paper stacking unit YS (step 108).

  Thus, in step 107, the rotation of the photosensitive drum 11 when the toner image is transferred to the second surface of the paper P is faster than the rotational speed of the photosensitive drum 11 when the toner image is transferred to the first surface of the paper P. By reducing the speed, the toner image formed on the second surface is reduced in the sub-scanning direction (paper P transport direction). Therefore, it becomes difficult for a difference between the size of the image formed on the first surface of the paper P and the size of the image formed on the second surface to occur. In other words, the image on the first surface of the paper P is reduced when passing through the fixing unit 20 as described above. However, by performing the above-described control, the image on the first surface is reduced in the transfer unit Tp. In addition, the toner image on the second surface can be transferred.

  However, in the present embodiment, when the toner image on the second surface is formed, the size of the toner image can be changed in the sub-scanning direction of the paper P. Therefore, what is changed in this embodiment is the magnification of the toner image in the sub-scanning direction, and the magnification of the toner image in the main scanning direction cannot be changed. In other words, in the present embodiment, by adjusting the magnification in the sub-scanning direction of the toner image transferred to the second surface, the image formed on the first surface of the paper P and the image formed on the second surface are adjusted. The difference in size is suppressed. However, since it is the sub-scanning direction that reduces the length of the image on the first surface, the above method is often sufficient when transporting the paper P with the long direction of the paper P as the sub-scanning direction. . In the present embodiment, the rate at which the rotational speed of the photosensitive drum 11 is reduced when transferring the second surface to the first surface of the paper P is, for example, 0.1% to 0.5%. .

  Note that the processing performed by the control unit 500 in FIG. 4 is performed by a computer in this embodiment. In this case, a program executed by the computer has a function of controlling a toner image forming unit that forms a toner image in the computer, and a toner. A function of controlling the transfer device 15 that transfers the toner image formed by the image forming unit to the paper P using the photosensitive drum 11 and a fixing unit 20 that fixes the toner image transferred by the transfer device 15 to the paper P are provided. A control function and a paper reversing mechanism that reverses the first and second surfaces of the paper P after the toner image is fixed on the first surface of the paper P by the fixing unit 20 and supplies the paper P to the transfer device 15 again. 40, and the transfer device 15 causes the transfer device 15 to transfer the toner image onto the second surface of the paper P rather than the rotational speed of the photosensitive drum 11 when the toner image is transferred onto the first surface of the paper P. A function for adjusting the sub-scanning direction scaling ratio of the toner image transferred by slowing the rotational speed of the photosensitive drum 11 at the time of shooting, can be regarded as a program for forming an image by realizing the.

<Description of control during double-sided printing of paper P>
Next, the control of the rotational speed of the photosensitive drum 11 performed by the control unit 500 during double-sided printing of the paper P will be described in more detail.
FIG. 5 illustrates the relationship between the moisture content of the paper P and the magnification in the sub-scanning direction of the image formed on the paper P when the rotational speed of the photosensitive drum 11 is the same on the first surface and the second surface. FIG.
In FIG. 5, the horizontal axis represents the moisture content of the paper P and the weight of moisture relative to the total weight of the paper P. The vertical axis represents the magnification in the sub-scanning direction of the image formed on the paper P. This value is a relative value when the magnification in the sub-scanning direction of the first surface is 0 when the moisture content is 4.7%.
As shown in FIG. 5, the image formed on the paper P is smaller on the first side than on the second side. Furthermore, the magnification in the sub-scanning direction has a correlation with the moisture content, and decreases as the moisture content increases. That is, when the moisture content of the paper P is large, the shrinkage rate of the paper P is large.

  However, in practice, it is difficult to directly measure the moisture content of the paper P, and therefore absolute humidity correlated with the moisture content of the paper P is used. That is, it is preferable that the control of the rotational speed of the photosensitive drum 11 when the toner image is transferred to the second surface of the paper P is changed according to the absolute humidity value. Specifically, the moisture content of the paper P having a correlation is estimated from the absolute humidity value. Then, the rotational speed of the photosensitive drum 11 is reduced by the difference between the magnification value of the second surface in FIG. 5 corresponding to the moisture content and the magnification value of the first surface in the sub-scanning direction.

In the example described above, the rotational speed of the photosensitive drum 11 is controlled according to the absolute humidity value. However, the rotational speed of the photosensitive drum 11 may be controlled by introducing other parameters.
For example, the rotational speed of the photosensitive drum 11 may be changed according to the value of the voltage applied by the transfer device 15 in order to generate an electric field in the transfer portion Tp. The voltage value varies depending on the moisture content of the paper P. That is, when the moisture content of the paper P changes, the resistance value of the paper P changes accordingly. Therefore, the moisture content of the paper P can be obtained by measuring this voltage value.

Further, when a large amount of toner used for forming a toner image is used, the paper P is more difficult to reduce. In addition, when the paper P is thick paper or coated paper, the paper P is more difficult to reduce. Therefore, the rotation speed of the photosensitive drum 11 may be changed depending on the amount of toner used and the type of paper. In other words, not only the environmental values such as the temperature and humidity in the image forming apparatus 1 but also the image forming conditions including this environmental value, the value of the voltage applied by the transfer device 15 described above, the amount of toner used, the type of paper, and the like. The rotational speed of the body drum 11 may be changed.
Further, in the above-described example, the rotation speed of the photosensitive drum 11 is controlled when transferring the second surface of the paper P. However, the rotation speed of the photosensitive drum 11 is controlled when transferring the first surface. You may do it. Further, the rotational speed of the photosensitive drum 11 may be controlled on both the second surface and the first surface.

<Description of change in magnification in sub-scanning direction when paper P is thick paper>
Here, when the paper P is thicker than predetermined, the paper P may stop for a moment when the leading end of the paper P in the transport direction enters the fixing unit 20. That is, as described above, the fixing unit 20 includes the heating roll 21 and the pressure roll 22, and the heating roll 21 and the pressure roll 22 are in close contact to form a clamping unit. For this reason, when the paper P is a thick paper, when the paper P enters the pinching portion that is the entrance of the fixing portion 20, the pinching portion may become an obstacle and the paper P may stop for a moment. In this case, the paper P is also stopped at the transfer portion Tp. On the other hand, since the photosensitive drum 11 rotates, slip occurs between the paper P and the photosensitive drum 11. As a result, image dripping (so-called smear) occurs in which the toner image transferred in the transfer portion Tp is blurred in the sub-scanning direction.

  In the present embodiment, in order to suppress the occurrence of this smear, the controller 500 controls the linear velocity on the surface of the heating roll 21 to be higher than the linear velocity on the surface of the photosensitive drum 11. As a result, it is possible to suppress the phenomenon that the paper P stops for a moment when the leading end portion in the transport direction of the paper P enters the fixing unit 20. That is, since the paper P is transported by the photosensitive drum 11 at the transfer portion Tp, the transport speed when the front end portion of the paper P in the transport direction passes through the transfer portion Tp and goes to the fixing portion 20 is the photosensitive drum 11. The linear velocity of the surface. On the other hand, the linear velocity of the surface of the heating roll 21 is faster than the conveyance speed of the paper P at this time. For this reason, when the leading end portion in the transport direction of the paper P enters the holding portion of the fixing unit 20, the paper P is not easily stopped because it is drawn into the holding portion. In the present embodiment, the linear velocity on the surface of the heating roll 21 is, for example, 0.6% faster than the linear velocity on the surface of the photosensitive drum 11.

  In the present embodiment, the paper P is also conveyed by the force with which the registration roll 852 rotates. For this reason, after the rear end portion in the transport direction of the paper P is separated from the registration roll 852, the force for transporting the paper P is weakened, and the transport speed of the paper P is likely to decrease. Therefore, the above-mentioned smear may occur due to this. In the present embodiment, by controlling the linear velocity of the surface of the heating roll 21 to be higher than the linear velocity of the surface of the photosensitive drum 11, the trailing end of the paper P in the transport direction is separated from the registration roll 852. It suppresses that the conveyance speed of the paper P falls. That is, the heating roll 21 rotates thereby to generate a tensile stress that pulls the paper P in the transport direction. Therefore, the conveyance speed of the paper P is unlikely to decrease even after the rear end portion in the conveyance direction of the paper P is separated from the registration roll 852.

  In the present embodiment, it is preferable that the control unit 500 also controls to make the linear velocity of the surface of the registration roll 852 faster than the linear velocity of the surface of the photosensitive drum 11. By performing such control, the paper P is pushed out in the transport direction. For this reason, when the leading end of the sheet P in the conveyance direction enters the nipping portion of the fixing unit 20, the leading end of the sheet P is more easily pulled into the nipping portion. Therefore, it is difficult for the paper P to stop. In the present embodiment, the linear velocity of the surface of the registration roll 852 is, for example, 0.6% faster than the linear velocity of the surface of the photosensitive drum 11.

  As described above, in the present embodiment, smear that is likely to occur when the paper P is thick paper is suppressed. However, the linear velocity on the surface of the heating roll 21 or the registration roll 852 is set to the line on the surface of the photosensitive drum 11. If the speed is higher than the speed, the magnification of the paper P in the sub-scanning direction is likely to change. That is, the paper P is pushed in the transport direction by the registration roll 852 and further pulled by the heating roll 21. For this reason, slip occurs between the photosensitive drum 11 and the paper P, and the magnification in the sub-scanning direction tends to be larger at the rear end than the front end in the transport direction of the paper P. That is, an image in which the rear end portion extends in the sub-scanning direction with respect to the front end portion in the conveyance direction of the paper P is formed.

<Description of Control when Paper P is Thick Paper>
Therefore, in the present embodiment, the above-described problem is suppressed by the following method.
FIG. 6 is a flowchart illustrating a procedure for forming an image when the paper P according to the present embodiment is a thick paper.
First, when the control unit 500 (see FIG. 1) receives the image data through the receiving unit 400 (see FIG. 1), the control unit 500 (see FIG. 1) transmits a command with a content for forming an image on the paper P to the image processing unit 600 (see FIG. 1). (Step 201).

  Further, the control unit 500 acquires information on the type of the paper P (step 202). The information on the type of the paper P can be input by the user from the user interface 700 (see FIG. 1), for example. Then, the control unit 500 determines whether the thickness of the paper P is equal to or greater than a predetermined thickness depending on the type of the paper P (step 203), and the thickness of the paper P is less than the predetermined thickness. If there is, a normal image forming operation is performed (step 204). In a normal image forming operation, image formation is performed on the paper P by controlling the photosensitive drum 11, the heating roll 21, and the registration roll 852 to rotate at a constant speed. On the other hand, when the thickness of the paper P is equal to or greater than a predetermined thickness, the control unit 500 makes the linear velocity on the surfaces of the heating roll 21 and the registration roll 852 higher than the linear velocity on the surface of the photosensitive drum 11. Control is started (step 205).

  Next, the control unit 500 controls the image forming unit 10 and the paper supply unit 30 to convey the paper P from the paper supply unit 30 to the transfer unit Tp and form a toner image on the paper P (step 206). Further, the control unit 500 controls the fixing unit 20 in order to form an image on the paper P by fixing the toner image. At this time, in the present embodiment, after the leading end portion in the transport direction of the paper P reaches the fixing unit 20, that is, the sandwiching portion where the leading end portion in the transport direction of the paper P is formed between the heating roll 21 and the pressure roll 22. After entering the part, control for continuously decreasing the linear velocity on the surface of the photosensitive drum 11 is started (step 207). At this time, the control of starting the linear velocity of the surfaces of the heating roll 21 and the registration roll 852 started at step 205 to be higher than the linear velocity of the surface of the photosensitive drum 11 is performed. That is, the linear velocities on the surfaces of the heating roll 21 and the registration roll 852 are continuously reduced. Finally, the paper P on which image formation has been completed is discharged to the paper stacking unit YS (step 208).

  As described above, in step 207, the image formed on the sheet P is controlled by continuously reducing the linear velocity of the surface of the photosensitive drum 11 after the leading end of the sheet P in the conveyance direction reaches the fixing unit 20. However, the problem that the magnification in the sub-scanning direction is larger at the rear end portion than at the front end portion in the transport direction can be suppressed. That is, when the linear velocity of the surface of the photoconductive drum 11 is continuously decreased with respect to the photoconductive drum 11, the toner image forming unit does not change the speed at which the toner image is formed. The rear end portion of the paper P is contracted in the sub-scanning direction with respect to the front end portion in the conveyance direction of the paper P. That is, the toner image formed on the photosensitive drum 11 has a smaller magnification in the sub-scanning direction at the rear end than the front end in the transport direction. When this toner image is transferred to the paper P, the above-described phenomenon can be canceled. Therefore, the magnification in the sub-scanning direction of the toner image transferred onto the paper P can be adjusted.

FIGS. 7A and 7B are diagrams comparing the case where the control of step 207 in FIG. 6 is not performed and the case where it is performed.
Here, FIG. 7A is a diagram illustrating a case where the control in step 207 is not performed. FIG. 7B illustrates the case where the control in step 207 is performed. Here, the horizontal axis is the distance from the front end of the paper P in the transport direction. The vertical axis represents the magnification in the sub-scanning direction of the image formed on the paper P.
7A and 7B, it can be seen that the change in magnification in the sub-scanning direction of the image can be suppressed when the control in step 207 is performed.

  In the above-described example, the control is performed to continuously reduce the surface linear velocity of the photosensitive drum 11 after the leading end of the conveyance direction of the paper P reaches the fixing unit 20, but the present invention is not limited to this. The same control may be performed before the front end of the sheet P in the transport direction reaches the fixing unit 20. That is, in this embodiment, when the linear velocity of the surface of the registration roll 852 is made higher than the linear velocity of the surface of the photosensitive drum 11, the sub-scanning of the toner image similarly transferred onto the paper P in the transfer portion Tp is thereby performed. Sometimes the magnification of the direction changes. In this case, it is effective to perform the same control before the leading end of the sheet P in the transport direction reaches the fixing unit 20. However, in this embodiment, since the force for pushing the paper P by the registration roll 852 is weaker than the force for pulling the paper P by the heating roll 21, this control is not necessarily required. Further, it is not performed when the control of FIG. 9 described later is performed.

<Description of paper supply unit>
Next, the winding mechanism of the paper supply unit 30 will be described in more detail.
FIGS. 8A and 8B are diagrams for explaining the sheet-feeding mechanism of the paper supply unit 30. FIG.
Here, FIG. 8A shows the whirling mechanism described in FIG. 1 and FIG. As described with reference to FIGS. 1 and 2, the paper supply unit 30 includes the first paper supply unit 31 to the third paper supply unit 33, and the first paper supply unit 31 to the third paper supply unit 33 each have a drawing roll 43. And a whispering mechanism 44. Here, the whirling mechanism 44 is configured by a rotatable feed roll 44a and a retard roll 44b whose rotation is limited as shown in FIG.

  When the paper P is sent from the paper supply unit 30 toward the registration roll 852, the paper P is first sent out by the drawing roll 43. The uppermost sheet P is fed out as it is by the feed roll 44a, but the lower one is separated from the uppermost sheet by the retard roll 44b whose rotation is restricted. That is, it is possible to feed only one uppermost sheet P and feed it to the registration roll 852.

  Such an operation of the separating mechanism 44 is a load on the paper P even after the paper P is sent out. That is, since the retard roll 44b is a roll whose rotation is restricted, it becomes a load and generates a force in the direction opposite to the conveyance direction of the paper P. That is, a tensile stress that is a force for pulling the paper P is generated. This is a force that continues to work even after the sheet P passes through the registration roll 852 and enters the transfer portion Tp. For this reason, when the toner image is transferred to the paper P in the transfer portion Tp, a slip is likely to occur between the paper P and the photosensitive drum 11. When slip occurs, the image formed on the paper P has a smaller magnification in the sub-scanning direction toward the rear end than the front end in the transport direction of the paper P. That is, the image shrinks in the sub-scanning direction from the front end to the rear end in the transport direction of the paper P.

  On the other hand, when the leading end of the paper P in the transport direction reaches the fixing unit 20, the reverse phenomenon may occur. That is, when the paper P is sandwiched between the heating roll 21 and the pressure roll 22 of the fixing unit 20, the paper P starts to be conveyed by the rotational force of the heating roll 21. At this time, the force for pulling the paper P by the heating roll 21 and the pressure roll 22 is often larger than the force for pulling by the retard roll 44b. For this reason, after the leading end of the sheet P in the conveyance direction reaches the fixing unit 20, the magnification in the sub-scanning direction tends to increase toward the trailing end of the sheet P. That is, the image extends in the sub-scanning direction toward the rear end of the paper P.

  Such a phenomenon is more likely to occur when, for example, the mechanism shown in FIG. 8 (b) includes a feed roll 44a and a pad 45. In this case, when the paper P is sent from the paper supply unit 30 toward the registration roll 852, the paper P is first sent out by the drawing roll 43. The uppermost sheet P is fed as it is by the feed roll 44a, but the lower one is separated from the uppermost sheet by the frictional force generated between the sheet P and the pad 45. Therefore, it is possible to pick up and feed the sheets P one by one. Since the rolling mechanism 44 of such a mechanism generates a large frictional force with the pad 45, the load on the paper P is greater than when the above-described retard roll 44b is used, and the tensile stress acting on the paper P is also large. large.

  In the case of the present embodiment, such a phenomenon is likely to occur in the first paper feed unit 31 arranged at the uppermost stage. That is, the paper P supplied from the second paper feed unit 32 is conveyed by the first conveyance roll 55 toward the registration roll 852 and the transfer unit Tp. Further, the paper P supplied from the third paper feed unit 33 is conveyed by the second conveyance roll 65 toward the registration roll 852 and the transfer unit Tp. Therefore, the tensile stress generated by the retard roll 44b and the like due to the rotational force of the first transport roll 55 and the second transport roll 65 is canceled out. On the other hand, the first paper feed unit 31 often has no space for providing such a transport roll, and is not provided in the present embodiment. Therefore, the tensile stress generated by the retard roll 44b or the like is difficult to cancel.

<Description of Control when Forming Image on Paper P>
Therefore, in the present embodiment, the above-described problem is suppressed by the following method.
FIG. 9 is a flowchart illustrating a procedure for forming an image on the paper P according to this embodiment.
First, when the control unit 500 (see FIG. 1) receives the image data through the receiving unit 400 (see FIG. 1), the control unit 500 (see FIG. 1) transmits a command with a content for forming an image on the paper P to the image processing unit 600 (see FIG. 1). (Step 301).

Next, the control unit 500 controls the image forming unit 10 and the paper supply unit 30 to convey the paper P from the paper supply unit 30 to the transfer unit Tp and form a toner image on the paper P. At this time, it is determined whether or not the leading end of the sheet P in the transport direction has reached the fixing unit 20 (step 302). Before the leading end of the sheet P in the transport direction reaches the fixing unit 20 (No in Step 302), control is performed to continuously increase the linear velocity on the surface of the photosensitive drum 11 (Step 303).
That is, when the linear velocity of the surface of the photoconductor drum 11 is continuously increased, the toner image forming unit does not change the speed at which the toner image is formed on the photoconductor drum 11, so that the toner image formed on the photoconductor drum 11 is Thus, the rear end portion extends in the sub-scanning direction with respect to the front end portion in the conveyance direction of the paper P. In other words, the toner image formed on the photosensitive drum 11 has a larger magnification in the sub-scanning direction at the rear end than the front end in the transport direction. When this toner image is transferred to the paper P, the above-described phenomenon can be canceled. Therefore, the magnification in the sub-scanning direction of the toner image transferred onto the paper P can be adjusted. Eventually, the phenomenon that the magnification in the sub-scanning direction decreases from the front end portion to the rear end portion of the paper P before the front end portion in the transport direction of the paper P reaches the fixing unit 20 can be suppressed.

  On the other hand, after the leading end of the sheet P in the transport direction reaches the fixing unit 20 (Yes in Step 302), the control unit 500 performs control to continuously decrease the linear velocity on the surface of the photosensitive drum 11 ( Step 304). Thus, by performing the control opposite to that in step 303, the magnification in the sub-scanning direction of the toner image transferred onto the paper P can be adjusted. Therefore, the phenomenon that the magnification in the sub-scanning direction increases toward the rear end portion of the paper P after the front end portion in the transport direction of the paper P reaches the fixing unit 20 can be suppressed.

  Then, the control unit 500 controls the fixing unit 20 to fix the toner image transferred onto the paper P (step 305), and the paper P on which image formation has been completed last is discharged to the paper stacking unit YS ( Step 306).

FIGS. 10A and 10B are diagrams comparing the case where the control of step 303 and step 304 in FIG. 9 is not performed and the case where it is performed.
Here, FIG. 10A is a diagram illustrating a case where the control of step 303 and step 304 is not performed. FIG. 10B is a diagram illustrating the case where the control in step 303 and step 304 is performed. Here, the horizontal axis is the distance from the front end of the paper P in the transport direction. The vertical axis represents the magnification in the sub-scanning direction of the image formed on the paper P. Here, the dotted line is a position where the leading end of the sheet P in the transport direction reaches the fixing unit 20.
As can be seen from FIG. 10A, before the leading end of the sheet P in the transport direction reaches the fixing unit 20, the magnification in the sub-scanning direction of the image formed on the sheet P is from the leading end in the transport direction to the rear end. It gets smaller and smaller. On the other hand, after the leading end of the sheet P in the transport direction reaches the fixing unit 20, the magnification in the sub-scanning direction of the image formed on the sheet P increases toward the trailing end.
10A and 10B, it can be seen that the change in magnification in the sub-scanning direction of the image can be suppressed when the control in step 303 and step 304 is performed.

  Note that the change in magnification in the sub-scanning direction of an image formed as described above is likely to occur in the first paper feed unit 31 arranged in the uppermost stage. Therefore, such control is performed when the paper P is supplied from the first paper supply unit 31 to the transfer unit Tp, and the paper P is supplied from the second paper supply unit 32 and the third paper supply unit 33 to the transfer unit Tp. You can choose not to do it when you do it. That is, the above-described control is performed when the paper P is supplied to the transfer device 15 from the paper storage unit closest to the transfer device 15, and is not performed when the paper P is supplied to the transfer device 15 from another paper storage unit. To do.

  In the present embodiment, the processes performed in FIGS. 4, 6, and 9 can be used in combination.

In the above-described example, the driving source is connected to the photosensitive drum 11 and the control unit 500 controls the rotation speed of the photosensitive drum 11. However, the driving source is connected to the transfer device 15, and the control unit 500 is connected to the transfer device 15. The rotation speed may be controlled. In this case, the transfer device 15 can be regarded as an example of a rotating body.
Further, in the above-described example, the driving source is connected to the heating roll 21 and the control unit 500 controls the rotation speed of the heating roll 21, but the driving source is connected to the pressure roll 22, and the control unit 500 is connected to the pressure roll 22. The rotation speed may be controlled. In this case, the pressure roll 22 can be regarded as an example of a fixing rotator.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Image forming part, 11 ... Photosensitive drum, 15 ... Transfer device, 20 ... Fixing part, 21 ... Heating roll, 22 ... Pressure roll, 30 ... Paper supply part, 40 ... Paper reversing mechanism , 41 ... paper storage unit, 55 ... first transport roll, 65 ... second transport roll, 500 ... control unit, 852 ... registration roll, P ... paper, Tp ... transfer unit

Claims (8)

Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means to a recording material using a rotating body;
Fixing means for fixing the toner image transferred by the transfer means to a recording material;
A reversing unit for reversing the first and second surfaces of the recording material after the toner image is fixed on the first surface of the recording material by the fixing unit, and supplying the recording material to the transfer unit again;
A control unit for controlling the rotation speed of the rotating body;
With
The controller controls the rotational speed of the rotating body when transferring the toner image to the second surface of the recording material rather than the rotational speed of the rotating body when transferring the toner image to the first surface of the recording material. An image forming apparatus comprising: adjusting the magnification in the sub-scanning direction of the toner image transferred by being delayed.   The image forming apparatus according to claim 1, wherein the control unit changes a rotation speed of the rotating body according to a value of absolute humidity.   The image forming apparatus according to claim 1, wherein the fixing unit fixes the toner image of a single color on a recording material. The transfer means transfers the toner image to a recording material by generating an electric field,
The said control part changes the rotational speed of the said rotary body according to the value of the voltage applied by the said transfer means in order to generate the said electric field, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. Image forming apparatus. The fixing unit includes a fixing rotator that fixes the toner image transferred by the transfer unit to a recording material while rotating the toner image.
5. The image forming apparatus according to claim 1, wherein the control unit further performs control to make the linear velocity of the surface of the fixing rotator faster than the linear velocity of the rotator. 6. A recording material supply unit for storing the recording material and supplying the recording material one by one to the transfer unit;
6. The control unit according to claim 1, wherein the control unit performs control to continuously increase the linear velocity of the surface of the rotating body before the recording material conveyance direction leading end reaches the fixing unit. 2. The image forming apparatus according to item 1. On the computer,
A function of controlling toner image forming means for forming a toner image;
A function of controlling transfer means for transferring the toner image formed by the toner image forming means to a recording material using a rotating body;
A function of controlling fixing means for fixing the toner image transferred by the transfer means to a recording material;
A function of controlling a reversing unit that reverses the first surface and the second surface of the recording material after the toner image is fixed on the first surface of the recording material by the fixing unit and supplies the recording material to the transfer unit again. When,
In the transfer unit, the rotation speed of the rotating body when transferring the toner image to the second surface of the recording material is set to be higher than the rotation speed of the rotating body when transferring the toner image to the first surface of the recording material. A function of adjusting the magnification in the sub-scanning direction of the toner image transferred by delaying;
A program that performs image formation by realizing. A function of acquiring image forming conditions for image formation;
The program according to claim 7, wherein a rotation speed of the rotating body is changed according to the image forming condition.

Images