JP2011191378A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus efficiently transferring toner images of a photoreceptor drum on the surface of a recording medium. <P>SOLUTION: The image forming apparatus 1 is provided with: the photoreceptor drums 5K, 5Y, 5M, 5C; an exposure part for forming electrostatic latent images on charged photoreceptor drums; a developing part for using a developer on the photoreceptor drums forming the electrostatic latent images to form developer images; and a transfer belt 7 for transferring the developer images on a medium 17. The image forming apparatus also has speed differences between peripheral speeds S1, S2, S3, S4 of the photoreceptor drums and a linear speed S5 of the transfer belt. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus with improved transfer efficiency.

  2. Description of the Related Art Conventionally, an image forming apparatus such as an electrophotographic printer charges a plurality of photosensitive drums, holds an electrostatic latent image corresponding to a print image on the charged photosensitive drums, and adds a toner image to the electrostatic latent image. The toner image is transferred to the recording medium by generating a charge (transfer voltage) having a polarity opposite to that of the toner on the recording medium conveyed by the transfer belt. Therefore, in this image forming apparatus, it is important to improve the transfer efficiency of toner to the recording medium.

  For example, the technique disclosed in Patent Document 1 detects a leak current flowing from a recording medium to a transfer belt and suppresses the leak current to improve transfer efficiency.

JP 2008-083233 A

  However, since the image forming apparatus of Patent Document 1 is based on the premise that the circumferential speed of each photosensitive drum and the linear speed of the transfer belt are the same in the transfer process, when transferring a toner image to a recording medium, Depending on the position of the photosensitive drum, the toner image (developer image) on the photosensitive drum may not be sufficiently transferred to the recording medium, and the print image quality may deteriorate.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of transferring a developer image on a photosensitive drum onto the surface of a recording medium with high efficiency.

  In order to achieve the object, an image forming apparatus of the present invention includes a photosensitive drum (image carrier), an exposure unit that forms an electrostatic latent image on the charged photosensitive drum, and the electrostatic latent image is formed. An image forming apparatus comprising: a developing unit that forms a developer image on the photosensitive drum, and a transfer belt that transfers the developer image onto a medium, wherein the peripheral speed of the photosensitive drum and the linear speed of the transfer belt And a speed difference between the two.

  The medium is a recording medium conveyed by the transfer belt and the photosensitive drum, and the transfer belt and the photosensitive drum transfer the image to the recording medium.

  According to the present invention, it is possible to provide an image forming apparatus capable of transferring a developer image on a photosensitive drum onto the surface of a recording medium with high efficiency.

1 is a cross-sectional view for explaining a schematic configuration of an image forming apparatus according to a first embodiment. FIG. 3 is a configuration diagram for explaining a transfer unit of the image forming apparatus according to the first embodiment. 3 is a set condition table for the peripheral speed of the photosensitive drum according to the first embodiment. FIG. 6 is a configuration diagram for explaining a transfer unit of an image forming apparatus according to a second embodiment. 10 is a set condition table for the peripheral speed of the photosensitive drum according to the second embodiment. FIG. 10 is a configuration diagram (part 1) for explaining a transfer unit of an image forming apparatus according to a third embodiment. 12 is a setting condition table (No. 1) of a peripheral speed of a photosensitive drum according to a third embodiment. FIG. 10 is a configuration diagram (No. 2) for explaining a transfer portion of an image forming apparatus according to a third embodiment. 14 is a set condition table (No. 2) of the peripheral speed of the photosensitive drum according to the third embodiment. FIG. 2 is a cross-sectional view for explaining a schematic configuration when the present invention is applied to an intermediate transfer type image forming apparatus.

  An embodiment of the present invention will be described with reference to FIGS. In the drawings, the same components are denoted by the same reference numerals. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view for explaining a schematic configuration of the image forming apparatus of the present embodiment. FIG. 2 is a configuration diagram for explaining a transfer portion of the image forming apparatus of the present embodiment. FIG. 3 is a setting condition table for the peripheral speed of the photosensitive drum in the present embodiment. In addition, about the component which is not directly related to this embodiment, illustration is abbreviate | omitted for convenience.

(Constitution)
With reference to FIG. 1 and FIG. 2, the configuration of the image forming apparatus of the first embodiment is shown.
As shown in FIG. 1, the image forming apparatus 1 (1a) according to the present embodiment overlaps toners as developers of four colors of black (K), yellow (Y), magenta (M), and cyan (C). It is a tandem color printer that obtains a color image by printing together.

  In FIG. 1, an image forming apparatus 1 includes photosensitive drums 5K, 5Y, 5M, and 5C (hereinafter referred to as photosensitive drums 5) for carrying an image, and a charger 2K for negatively charging the photosensitive drum 5. 2Y, 2M, 2C (hereinafter referred to as charger 2) and exposure units 3K, 3Y, 3M, 3C (hereinafter referred to as exposure unit 3) for writing an electrostatic latent image on the photosensitive drum 5. ) And developing units 4K, 4Y, 4M, and 4C (hereinafter referred to as developing unit 4) for visualizing the electrostatic latent image on the photosensitive drum 5 with a negatively charged toner as a developer. Each of them is configured to have four colors of black, yellow, magenta, and cyan.

  Transfer rollers 6K, 6Y, 6M, and 6C (hereinafter referred to as transfer roller 6) are arranged on the inner peripheral side of an endless belt-shaped transfer belt 7, and a photosensitive drum is sandwiched between the transfer belts 7. 5 is pressed against. The transfer roller 6 is connected to a transfer power source (not shown).

  The transfer belt 7 is supported by the tension of the drive roller 8 and the idle roller 9, and the surface where the photosensitive drum 5 and the transfer belt 7 are in contact with each other is arranged smoothly.

  The recording medium 17 is set on a support plate member 18, and the support plate member 18 is pushed up by a spring 19 to press the recording medium 17 against the hopping roller 14.

  A broken line in FIG. 1 is a conveyance path of the recording medium 17, and the first conveyance roller 11, the second conveyance roller 12, and the writing sensor 15 are arranged along the conveyance path.

  The fixing device 10, the discharge sensor 16, and the discharge roller 13 are disposed downstream of the transfer belt 7 in the medium conveyance direction.

The print control unit 20 controls the image forming apparatus 1 (see FIG. 2).
The print controller 20 is connected to the charger 2, the exposure device 3, the developing device 4, the fixing device 10, the writing sensor 15, and the discharge sensor 16.

  The print control unit 20 includes a microprocessor, a ROM, a RAM, an input / output port, a timer, and the like.

  The photosensitive drum 5, the hopping roller 14, the first transport roller 11, the second transport roller 12, the drive roller 8, the fixing device 10, and the discharge roller 13 are rotating members, and a drive (not shown) configured by a motor or the like. Connected to the device. The drive device is connected to and controlled by the print control unit 20.

Next, the configuration of the transfer unit will be described with reference to FIG.
The photosensitive drums 5K, 5Y, 5M, and 5C for the respective colors are mechanically connected to the photosensitive drum driving units 21K, 21Y, 21M, and 21C for the respective colors, and the photosensitive drum driving units 21K, 21Y, 21M, and 21C for the respective colors are The print controller 20 is electrically connected.

  Each of the photosensitive drum driving units 21K, 21Y, 21M, and 21C includes a rotation driving device such as a motor and a speed reduction device such as a gear. The photosensitive drums 5K, 5Y, 5M, and 5C are rotated at a desired rotation speed. The speed of the outer peripheral surface of the photosensitive drum at this time is called a peripheral speed.

  The peripheral speeds of the photosensitive drums 5K, 5Y, 5M, and 5C are controlled to desired peripheral speeds by controlling the rotational speeds of the motors of the photosensitive drum driving units 21K, 21Y, 21M, and 21C according to instructions from the print control unit 20. Is done. Further, since the rotational speeds of the photosensitive drum driving units 21K, 21Y, 21M, and 21C for the respective colors can be controlled independently, the peripheral speeds of the photosensitive drums 5K, 5Y, 5M, and 5C are controlled independently. Can do.

(Operation)
The operation of the present embodiment will be described with reference to FIG. 1, FIG. 2, and FIG.
In the image forming apparatus 1, the following operation is controlled by the print control unit 20.

  As shown in FIG. 1, the print control unit 20 processes, for example, print instruction images, transport control of the recording medium 17, and charging control in accordance with a print instruction from a host controller such as a PC connected to the image forming apparatus 1. Then, exposure control, development control, transfer control, and fixing control are performed, and as a result, printing is performed on the recording medium 17.

  To explain in sequence, the print controller 20 starts the control of the fixing device 10 and can use the fixing device 10 when receiving a print instruction signal from a host controller such as a PC connected to the image forming apparatus 1. Heat control to temperature.

  When the temperature at which the fixing device 10 can be used is reached, the print control unit 20 controls the photosensitive drum driving units 21K, 21Y, 21M, and 21C to rotate the photosensitive drums 5K, 5Y, 5M, and 5C, and the peripheral speed thereof is increased. Acceleration is performed until the peripheral speeds S1, S2, S3, and S4 during printing are reached.

  The print control unit 20 simultaneously controls the drive device to start the rotation of the drive roller 8 and rotates the transfer belt 7 by the drive roller 8. The linear velocity of the transfer belt 7 is equal to the recording medium 17 at the time of printing. Until the transfer speed S5 is reached.

  The printing control unit 20 controls the charger 2 at the timing when the photosensitive drum 5 starts to rotate, and applies a negative voltage to the photosensitive drum 5 to charge the surface of the photosensitive drum 5 to, for example, −600V.

  Then, the print control unit 20 controls the developing device 4 to be in a developable state at a timing when a portion charged to −600 V of the photosensitive drum 5 passes through the developing area of the developing device 4 by rotation. For example, in the case of a contact development method using a development roller, a voltage of −200 V is applied to the development roller to which negatively charged toner adheres, thereby enabling development.

  The image forming apparatus 1 is ready for printing when a portion charged to −600 V of the photosensitive drum 5 reaches the transfer nip portion by rotation under the control of the print control unit 20.

  Next, the printing control unit 20 rotates the hopping roller 14 with a driving device, and separates and conveys the recording medium 17 one by one.

  When the printing control unit 20 controls the driving device, the separated recording medium 17 is transported to the second transport roller 12 through the first transport roller 11, and the second transport roller 12 and the transfer belt 7 are in contact with each other. The writing sensor 15 disposed between them detects the timing when the leading edge of the recording medium 17 passes the position of the writing sensor 15, and a detection signal is notified from the writing sensor 15 to the print control unit 20.

  The print control unit 20 separates an image to be printed on the recording medium 17 into each color of black, yellow, magenta, and cyan based on the print instruction signal received from the host controller. Conversion to image data that can be written as an electrostatic latent image.

Then, the recording medium 17 is conveyed onto the transfer belt 7 after passing through the writing sensor 15.
The print control unit 20 detects the timing at which the writing sensor 15 detects the leading edge of the recording medium 17, the distance from the writing sensor 15 to the transfer nip of each color, and the distance from the exposure location on the photosensitive drum 5 to the transfer location. Then, the electrostatic latent image is written on the photosensitive drum 5 by controlling the exposure device 3 at the timing when the image to be printed is transferred to a desired position on the recording medium 17 according to the conveyance speed of the recording medium 17.

  On the transfer belt 7, distances L1K, L1Y, and the distances from the center position of the idle roller 9 of the transfer belt 7 with which the leading end portion of the recording medium 17 contacts to the contact portion with each photosensitive drum 5 (center position of the photosensitive drum) The contact area between the recording medium 17 and the transfer belt 7 is determined by L1M and L1C (L1K <L1Y, L1M, and L1C). That is, the front end portion of the recording medium 17 has a contact area between the transfer belt 7 and the portion from the most upstream photosensitive drum 5K to the center position of the idle roller 9 from the photosensitive drums 5Y and 5M other than the most upstream photosensitive drum 5K. The contact area between the portion up to the center position of the idle roller 9 and the transfer belt 7 is smaller.

  Further, on the transfer belt 7, distances L2C and L2M from the center position of the drive roller 8 of the transfer belt 7 in contact with the rear end portion of the recording medium 17 to the contact portions (center positions of the photosensitive drums) with each photosensitive drum 5. , L2Y, L2K (L2C <L2M, L2Y, L2K) determine the contact area between the recording medium 17 and the transfer belt 7. That is, the rear end portion of the recording medium 17 has a contact area between the transfer belt 7 and the portion from the most downstream photosensitive drum 5C to the center position of the drive roller 8, and the photosensitive drums 5Y and 5M other than the most downstream photosensitive drum 5C. To the center position of the drive roller 8 and the contact area between the transfer belt 7 and the contact area.

  The exposure device 3 uses, for example, an LED head or the like, and irradiates, for example, spot light having a pitch of 600 dpi onto a portion on the photosensitive drum 5 where a toner image is to be obtained. Then, the surface of the photosensitive drum 5 charged to −600 V has a potential of about −50 V, and an electrostatic latent image is formed on the photosensitive drum 5.

  The surface of the photosensitive drum 5 on which the electrostatic latent image is written by the exposure device 3 is moved to the position of the developing device 4 by the rotation operation, and the developer is exposed to a portion where the absolute value of the surface potential is reduced by exposure. 4, the negatively charged toner as the developer adheres to the photosensitive drum 5 by the Coulomb force, so that a visible toner image is formed.

  Then, the surface of the photosensitive drum 5 to which the developed toner image adheres is conveyed to the transfer nip portion by a rotating operation.

  A transfer voltage for printing is applied to the transfer roller 6 during a period in which the recording medium 17 is in the transfer nip portion. For example, a positive voltage having a polarity opposite to that of the toner image, for example, 1500 V to 3000 V is applied. The

  Then, the toner image on the photosensitive drum 5 receives a coulomb force by a positive voltage applied to the transfer roller 6 at the transfer nip portion, and is transferred onto the recording medium 17.

  These operations are sequentially performed for black, yellow, magenta, and cyan. Then, the recording medium 17 to which the toner image is transferred is conveyed to the fixing device 10, and the toner is melted by the heat and pressure of the fixing device 10. As a result, the toner image is fixed on the surface of the recording medium 17.

  The recording medium 17 that has passed through the fixing device 10 is detected by the discharge sensor 16 to pass through the rear end of the recording medium 17 and is discharged out of the image forming apparatus 1 by the discharge roller 13.

  When the print control unit 20 receives the detection signal of the rear end passage of the recording medium 17 from the discharge sensor 16, the rotation operation of each roller, the chargers 2K, 2Y, 2M, and 2C, the developing devices 4K, 4Y, and 4M. 4C and the transfer power supply (not shown) are stopped, and the printing operation of the image forming apparatus 1 is terminated.

  Further, when the passage timing of the recording medium 17 is abnormal, the print control unit 20 performs measures such as stopping the operation of the image forming apparatus 1. This abnormality detection of the passage timing is similarly performed by the presence / absence detection operation of the recording medium 17 by the writing sensor 15.

  Next, operations of the photosensitive drum driving units 21K, 21Y, 21M, and 21C when the toner image is transferred to the recording medium 17 will be described with reference to FIGS.

In the present embodiment, the linear velocity S5 of the recording medium 17 at the time of printing and the peripheral velocity of the photosensitive drums 5K, 5Y, 5M, and 5C for each color have the relationship shown in FIG.
That is, the peripheral speeds S1 and S4 of the photosensitive drums 5K and 5C for developing the black toner and the cyan toner among the photosensitive drums 5 are 0.1% faster than the linear speed S5 of the recording medium 17 (S5 + S5 × 0). .1%) is set. Further, the peripheral speeds S2 and S3 of the photosensitive drums 5Y and 5M for developing yellow toner and magenta toner are set 0.2% faster (S5 + S5 × 0.2%) than the linear speed S5 of the recording medium 17. .

  As an actual operation, the printing control unit 20 controls the transfer belt 7 to the linear velocity of S5 during the printing operation, and independently controls the motors of the photosensitive drum driving units 21K, 21Y, 21M, and 21C to perform each color. The photosensitive drums 5K, 5Y, 5M, and 5C are controlled to have peripheral speeds S1, S2, S3, and S4, respectively. Since printing is performed at such a peripheral speed of the photosensitive drum 5 and the linear speed of the transfer belt 7, the black toner photosensitive drum 5 </ b> K exhibits a speed difference of 0.1% of the peripheral speed relative to the linear speed of the recording medium 17. Printed in the hold state. Similarly, the other yellow toner photosensitive drum 5Y, magenta toner photosensitive drum 5M, and cyan toner photosensitive drum 5C are 0.2%, 0.2%, and 0.1% of the linear velocity S5 of the recording medium 17, respectively. Printed with a difference in peripheral speed.

By performing the control in this way, the following operation is performed in the transfer unit.
The recording medium 17 is placed on the transfer belt 7 and conveyed, and is first conveyed to a transfer nip formed by the photosensitive drum 5K, the transfer belt 7, and the transfer roller 6K. Here, the black toner on the photosensitive drum 5K is transferred to the recording medium 17. However, since the peripheral speed S1 of the photosensitive drum 5K is 0.1% faster than the linear speed S5 of the recording medium 17, the black toner on the photosensitive drum 5K. Is in a state of being rubbed (subject to sliding friction) on the recording medium 17. During this rubbing, the black toner rotates or moves slightly, so that the force adhering to the photosensitive drum 5K due to mirror image force, van der Waals force, etc. is easily cut off. Therefore, the toner on the photosensitive drum 5K is easily transferred to the recording medium 17.

  Next, the recording medium 17 is conveyed to the transfer belt 7 and conveyed to a transfer nip portion formed by the photosensitive drum 5Y, the transfer belt 7, and the transfer roller 6Y. Here, as in the case of black toner, the yellow toner on the photosensitive drum 5Y is transferred to the recording medium 17, but the peripheral speed S2 of the photosensitive drum 5Y is 0.2% faster than the linear speed S5 of the recording medium 17. Therefore, the yellow toner on the photosensitive drum 5Y is in a state of being rubbed against the recording medium 17. During this rubbing, the yellow toner rotates or moves slightly, so that the force adhering to the photosensitive drum 5Y due to mirror image force, van der Waals force, or the like can be easily cut off. Therefore, the toner on the photosensitive drum 5Y is easily transferred to the recording medium 17.

  Further, when the black toner already transferred to the recording medium 17 comes into contact with the yellow photosensitive drum 5Y, it adheres to the yellow photosensitive drum 5Y by the mirror image force or van der Waals force with respect to the photosensitive drum 5Y. A reverse transfer phenomenon may occur in which the recording medium 17 returns to the photosensitive drum 5Y.

  However, in this embodiment, a speed difference is made between the peripheral speed of the yellow photosensitive drum 5Y and the linear speed of the recording medium 17, so that toner rotation and minute position movement occur in the transfer nip portion, and the photosensitive drum 5Y It is easy to cut off the mirror image force and the van der Waals force that are generated between the toner and the black toner easily stays on the recording medium 17, thereby suppressing the reverse transfer phenomenon. This effect is effective for thin lines that are susceptible to blurring due to reverse transfer, particularly vertical thin lines, and generation of blurring of the thin lines can be suppressed, so that a good image can be obtained.

  Next, the recording medium 17 is sequentially conveyed to the transfer nip portion of the photosensitive drum 5M for magenta toner and the photosensitive drum 5C for cyan toner. However, the recording medium 17 is similarly good in transfer efficiency and little toner has already been transferred to the recording medium 17. Good print quality can be obtained by reverse transfer.

  The larger the difference in the peripheral speed of the photosensitive drum 5 with respect to the linear speed of the recording medium 17, the better the transfer efficiency and the reduction of reverse transfer. However, although the recording medium 17 is mounted on the transfer belt 7 and conveyed, if the contact area is small, a slip may occur between the recording medium 17 and the transfer belt 7 due to this speed difference. . Since this slip generates a color position shift of each color, a problem of color shift occurs.

As described above, in the present embodiment, both the front end portion and the rear end portion of the recording medium 17 are formed between the photosensitive drums 5 </ b> K and 5 </ b> C and the portion of the idle roller 9 or the drive roller 8 and the transfer belt 7. The contact area is smaller than the contact area between the transfer belt 7 and the portions from the photosensitive drums 5Y and 5M other than the photosensitive drums 5K and 5C to the center position of the idle roller 9 or the drive roller 8. For this reason, both the front end portion and the rear end portion of the recording medium 17 are more likely to cause color shift than the center portion.
Therefore, in this embodiment, the peripheral speed of the black photosensitive drum 5K and the cyan photosensitive drum 5C and the linear speed of the transfer belt 7 as the most upstream photosensitive drum and the most downstream photosensitive drum in the moving direction of the transfer belt 7 are described. Is set smaller than the speed difference between the photosensitive drums 5Y and 5M (+ 0.1%), thereby suppressing the occurrence of this problem.

  On the other hand, in the yellow photosensitive drum 5Y and the magenta photosensitive drum 5M as photosensitive drums other than the most upstream photosensitive drum and the downstream downstream photosensitive drum in the moving direction of the transfer belt 7, the recording medium 17 and the transfer belt 7 The contact area always increases. Therefore, in the photosensitive drum 5Y and the photosensitive drum 5M, the close contact between the recording medium 17 and the transfer belt 7 is hard to be displaced, and the possibility of color misregistration is reduced. Therefore, the transfer efficiency is improved and the reverse transfer is reduced. As can be seen, the speed difference between the peripheral speed of the photosensitive drum and the linear speed of the transfer belt is set large (+ 0.2%).

  In the present embodiment, in order to prevent color misregistration at the front end portion and the rear end portion of the recording medium, the mode in which the peripheral speed of the photosensitive drum is increased with respect to the linear speed of the recording medium has been described. On the other hand, the same effect can be obtained even if the peripheral speed of the photosensitive drum is decreased.

  Therefore, according to the image forming apparatus of the present embodiment, transfer efficiency can be increased by performing transfer in a state where there is a speed difference by changing the peripheral speed of the photosensitive drum with respect to the linear speed of the recording medium. Furthermore, it is possible to suppress a phenomenon in which the toner once transferred to the recording medium is reversely transferred to the photosensitive drum downstream in the recording medium conveyance direction. For this reason, it is possible to obtain a good image with thin lines, particularly vertical thin lines, where blurring is likely to occur.

  This effect is particularly significant under conditions where the adhesion force of the toner increases, such as when many printings are continuously performed. Further, as in the present embodiment, the speed difference between the linear speed of the recording medium and the peripheral speed of the photosensitive drum is reduced with respect to the photosensitive drum having a small area where the recording medium is in close contact with the transfer belt. A good image can be obtained by good transfer and low reverse transfer while suppressing the amount of color misregistration in the recording medium conveyance direction.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a configuration diagram for explaining the transfer unit of the image forming apparatus according to the present embodiment, and FIG. 5 is a setting condition table for the peripheral speed of the photosensitive drum according to the present embodiment.

(Constitution)
Since the configuration of the second embodiment has many parts in common with the configuration of the first embodiment, only different parts will be described.

The present embodiment is different from the first embodiment in that a humidity detection unit 22 is further provided as shown in FIG. 4, and the humidity detection unit 22 is connected to the print control unit 20. It is a point.
The humidity detector 22 has a function of detecting the relative humidity value of the environment where the image forming apparatus 1b is installed.

(Operation)
With reference to FIGS. 4 and 5, the operation of the image forming apparatus 1 in the present embodiment will be described. Since the operation of this embodiment has many parts in common with the operation of the image forming apparatus 1 of the first embodiment, only different parts will be described.

  The humidity detection unit 22 is disposed in the image forming apparatus 1, detects the relative humidity value of the environment where the image forming apparatus 1 is installed, and transmits the detected relative humidity value to the print control unit 20. .

  When receiving a print instruction from a host controller such as a PC connected to the image forming apparatus 1, the print control unit 20 starts a printing operation as in the first embodiment.

  This embodiment is different from the first embodiment in that the print controller 20 determines the peripheral speed of the photosensitive drum during printing from the relative humidity value received from the humidity detector 22 in a humid environment as shown in FIG. It is a point set so that it can respond to. Other operations are the same as those in the first embodiment.

  Specifically, the print control unit 20 determines whether the linear velocity S5 of the transfer belt 7 and the peripheral velocity of each photosensitive drum when the relative humidity value detected by the humidity detector 22 is 70% RH or higher. The operation of the image forming apparatus 1 is controlled by setting the speed difference larger than that in the case where the humidity is less than 70% RH.

  Under a high humidity environment, the adhesion force between the photosensitive drum 5 and the toner increases, so that the transfer efficiency is lowered and the reverse transfer phenomenon in which the toner once transferred to the recording medium returns to the photosensitive drum 5 easily occurs. Therefore, by increasing the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of the photosensitive drum 5, the toner in the transfer nip is rotated, causing a slight positional movement, and between the photosensitive drum 5 and the toner. It is possible to easily cut off the mirror image force and the van der Waals force that are generated by the above, and improve the transfer efficiency and reduce the reverse transfer to obtain a good printing result.

  In this embodiment, when the relative humidity is 70% RH or more, the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of each photosensitive drum 5 is increased by 0.05% compared to the case where the humidity is less than 70% RH. However, this condition is appropriately adjusted according to the material of the photosensitive drum 5, the material of the toner, and the material of the recording medium.

  In this embodiment, the mode in which the peripheral speed of the photosensitive drum 5 is increased with respect to the linear speed of the recording medium 17 has been described. However, the peripheral speed of the photosensitive drum 5 is decreased with respect to the linear speed of the recording medium 17. However, the same effect can be obtained.

  Accordingly, the speed difference is increased by changing the peripheral speed of the photosensitive drum 5 with respect to the linear speed of the recording medium 17 in a humid environment where the adhesion force of the toner to the photosensitive drum 5 tends to be larger than in a low humidity environment. Transfer efficiency can be increased by performing transfer in such a state. Further, it is possible to suppress a phenomenon in which the toner once transferred to the recording medium 17 is reversely transferred to the photosensitive drum 5 downstream in the conveyance direction of the recording medium 17. For this reason, it is possible to obtain a good image with thin lines, particularly vertical thin lines, which are susceptible to blur.

  This effect is particularly significant under conditions where the adhesion force of the toner increases, such as when many printings are continuously performed. Further, as in this embodiment, the speed difference between the linear speed of the recording medium 17 and the peripheral speed of the photosensitive drum 5 is different from that of the photosensitive drum 5 where the area where the recording medium 17 is in close contact with the transfer belt 7 is small. By reducing the image quality, a good image can be obtained by good transfer and low reverse transfer while suppressing the amount of color misregistration in the conveyance direction of the recording medium 17 to a small amount.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIGS.

  Since the configuration of the third embodiment has much in common with the configuration of the first embodiment, only different points will be described.

  As shown in FIG. 6, the third embodiment is different from the first embodiment in that the recording medium information that can be input from the outside by the user, for example, the measured value of the recording medium, the thickness of the recording medium, and the like. In addition, a sheet information acquisition unit 22a that can directly input the type of recording medium and the like from the operation panel to the print control unit 20 is further provided. In the present embodiment, the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of each photosensitive drum 5 is changed in the image forming apparatus 1 based on information from the paper information acquisition unit 22a.

  That is, in the present embodiment, the image forming apparatus 1c has a structure that allows the user to set information on the recording medium 17. As setting information from the user, for example, as shown in FIG. 7, the basis weight value of the recording medium 17 can be set.

  Specifically, the user sets the basis weight value of the recording medium 17 on the image forming apparatus 1c from the operation panel, and directly instructs the print control unit 20 from a host controller such as a PC. With such a configuration, the print control unit 20 can obtain information on the state of the recording medium.

  Since the operation of the image forming apparatus according to the third embodiment has many operations that are the same as those of the first embodiment, only different operations will be described.

  In the third embodiment, control is performed to change the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of the photosensitive drum 5 by setting the basis weight of the recording medium 17. Other operations are the same as those in the first embodiment.

  The print control unit 20 obtains information on the recording medium from the user from the operation panel. In this embodiment, the basis weight information of the recording medium 17 is obtained.

  If the basis weight of the recording medium 17 to be printed is 200 gsm or more, the print control unit 20 increases the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of the photosensitive drum 5 as compared with the case where the basis weight is less than 200 gsm. Control. Here, gsm indicates the number of grams per square meter.

  This is because a recording medium having a large basis weight is generally thick, and a thick recording medium causes a reverse transfer phenomenon in which the toner once transferred to the recording medium returns to the photosensitive drum 5 rather than a thin recording medium. Cheap. Therefore, by increasing the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of the photosensitive drum 5, the toner is rotated at the transfer nip portion to cause a minute position movement between the photosensitive drum 5 and the toner. It is possible to easily cut off the mirror image force and van der Waals force, which are generated adhesion forces, improve transfer efficiency, reduce reverse transfer, and obtain good printing results.

  In this embodiment, as shown in FIG. 7, when the basis weight of the recording medium is 200 gsm or more, the speed difference between the linear velocity of the transfer belt 7 and the peripheral speed of each photosensitive drum 5 is larger than when the basis weight is less than 200 gsm. 0.05% larger. This condition is appropriately adjusted depending on the material of the photosensitive drum, the material of the toner, and the material of the recording medium.

  Further, in the present embodiment, as shown in FIG. 8, a thickness detection sensor is attached as a thickness detection unit 22b for inputting the thickness information of the recording medium 17 to the print control unit 20 of the image forming apparatus 1d. By obtaining information from the thickness detection sensor, the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of each photosensitive drum 5 may be controlled by the thickness of the recording medium 17.

  The thickness detection unit 22b is provided, for example, in a conveyance path between the writing sensor 15 and the second conveyance roller 12 in FIG. 1 and detects the thickness of the recording medium 17 being conveyed. Information regarding the thickness of the recording medium 17 detected by the thickness detector 22 b is sent to the print controller 20.

  Further, by adding a configuration for setting the type of the recording medium 17 by the user and adding a configuration for automatic detection, the type information of the recording medium 17 is obtained, and as shown in FIG. It is also effective to control the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of each photosensitive drum 5.

  This is because the adhesion between the toner and the recording medium 17 differs depending on the type of the recording medium 17, so that the transfer efficiency and the susceptibility to reverse transfer are different.

  As shown in FIG. 9, when a surface coat film is used as the recording medium 17, the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of each photosensitive drum 5 is 0.05% compared to the case of plain paper. It is set large.

  In the surface-coated film medium, the toner tends to adhere to the film medium and the reverse transfer phenomenon occurs more easily than the plain paper. Therefore, if the speed difference between the linear speed of the transfer belt 7 and the peripheral speed of each photosensitive drum 5 is increased. Thus, it is possible to improve the transfer efficiency and suppress reverse transfer to obtain a good printing result.

  In this embodiment, the example in which the peripheral speed of the photosensitive drum 5 is increased with respect to the linear speed of the recording medium 17 has been described. However, the peripheral speed of the photosensitive drum 5 is decreased with respect to the linear speed of the recording medium 17. However, the same effect can be obtained.

  In the image forming apparatuses 1c and 1d of the present embodiment, depending on the basis weight, thickness, and type of the recording medium 17, the toner tends to have a large adhesive force on the photosensitive drum 5 with respect to the linear velocity of the recording medium 17. Thus, transfer efficiency can be increased by changing the peripheral speed of the photosensitive drum 5 and performing transfer with a speed difference. Further, it is possible to suppress a phenomenon in which the toner once transferred to the recording medium 17 is reversely transferred to the photosensitive drum downstream in the conveyance direction of the recording medium 17. For this reason, it is possible to obtain a good image with thin lines, particularly vertical thin lines, where blurring is likely to occur.

  This effect is particularly significant under conditions where the adhesion force of the toner further increases, such as when many printings are continuously performed. Further, as in this embodiment, the speed difference between the linear speed of the recording medium 17 and the peripheral speed of the photosensitive drum 5 is different from that of the photosensitive drum 5 where the area where the recording medium 17 is in close contact with the transfer belt 7 is small. By reducing the size of the recording medium 17, it is possible to obtain a good image with good transfer and low reverse transfer while suppressing the amount of color misregistration in the conveyance direction of the recording medium 17.

  The present embodiment can be applied to MFPs, facsimile machines, and copiers as long as the apparatus has a configuration for developing and transferring a developer by an electric field.

  In this embodiment, an example of a four-color printer is shown, but the present invention can be similarly applied to an image forming apparatus of three colors or five or more colors.

  Further, in the present embodiment, the tandem type direct transfer type image forming apparatus 1 has been described. However, the present invention is not limited to this type of image forming apparatus, and as shown in FIG. It can also be applied to the image forming apparatus. FIG. 10 is a cross-sectional view for explaining a schematic configuration when the present invention is applied to an intermediate transfer type image forming apparatus. In the example shown in FIG. 10, the image forming apparatus arranges the transfer belt 7 as an intermediate transfer belt, transfers the toner images from the photosensitive drums 5K, 5Y, 5M, and 5C, and then again these developer images. Are further provided with a secondary transfer roller 6Aa and a secondary transfer backup roller 6Ab for retransferring the recording medium in a lump, and the recording medium 17 is passed between the secondary transfer roller 6Aa and the secondary transfer backup roller 6Ab. 17 is a tandem type intermediate transfer system that performs batch transfer to 17.

  In this tandem type intermediate transfer type image forming apparatus, in the step of transferring the toner images from the photosensitive drums 5K, 5Y, 5M, and 5C to the intermediate transfer belt, the peripheral speed of each photosensitive drum 5 and the line of the intermediate transfer belt. A speed difference is provided between the speed. The present invention is also effective in this tandem type intermediate transfer type image forming apparatus.

1 (1a), 1b, 1c, 1d Image forming apparatus 2, 2K, 2Y, 2M, 2C Charger 3, 3K, 3Y, 3M, 3C Exposure unit 4, 4K, 4Y, 4M, 4C Developer 5, 5, 5K, 5Y, 5M, 5C Photosensitive drum (image carrier)
6, 6K, 6Y, 6M, 6C Transfer roller 7 Transfer belt 8 Drive roller 9 Idle roller 10 Fixing device 11 First transport roller 12 Second transport roller 13 Discharge roller 14 Hopping roller 15 Write sensor 16 Discharge sensor 17 Recording medium 18 Support Plate member 19 Spring 20 Print control unit 21K, 21Y, 21M, 21C Photosensitive drum drive unit 22 Humidity detection unit 22a Paper information acquisition unit (operation panel)
22b Thickness detection unit (thickness detection sensor)
S1, S2, S3, S4 Peripheral speed of photosensitive drum S5 Linear speed of transfer belt

Claims (11)

An image carrier;
An exposure unit for forming an electrostatic latent image on the charged image carrier;
A developing unit that forms a developer image using a developer on the image carrier on which the electrostatic latent image is formed;
An image forming apparatus comprising a transfer belt for transferring the developer image to a medium,
An image forming apparatus having a speed difference between a peripheral speed of the image carrier and a linear speed of the transfer belt. The medium is a recording medium conveyed by the transfer belt and the image carrier,
The image forming apparatus according to claim 1, wherein the transfer belt and the image carrier transfer the image onto the recording medium. The medium is the transfer belt itself,
The image forming apparatus further includes a retransfer roller configured to retransfer the transferred developer image onto the recording medium while conveying the recording medium interposed between the transferred transfer belt itself. Item 2. The image forming apparatus according to Item 1. Three or more image carriers are arranged in order on the transfer belt,
The difference between the peripheral speeds of the most upstream image carrier and the most downstream image carrier in the moving direction of the transfer belt and the linear speed of the transfer belt is the difference between the peripheral speeds of the other image carriers and the line of the transfer belt. The image forming apparatus according to claim 1, wherein the image forming apparatus is smaller than a speed difference from the speed. When providing the speed difference by making the peripheral speed of the image carrier faster than the linear speed of the transfer belt,
5. The image forming apparatus according to claim 4, wherein peripheral speeds of the most upstream image carrier and the most downstream image carrier are slower than peripheral speeds of the other image carriers. When providing the speed difference by making the peripheral speed of the image carrier slower than the linear speed of the transfer belt,
The image forming apparatus according to claim 4, wherein peripheral speeds of the most upstream image carrier and the most downstream image carrier are faster than peripheral speeds of the other image carriers. Further comprising a humidity detection means for detecting the relative humidity value of the environment in which it is installed;
7. The image formation according to claim 1, wherein when the relative humidity value detected by the humidity detection unit is high, the speed difference is set larger than when the relative humidity value is low. apparatus. It further comprises recording medium information detecting means for detecting recording medium information inputted from the outside,
The image forming apparatus according to claim 1, wherein the speed difference is changed according to the recording medium information detected by the recording medium information detection unit. The recording medium information detecting means detects a weighing value of the recording medium information;
The image forming apparatus according to claim 8, wherein when the detected weighing value is heavy, the speed difference is set to be larger than when the weight value is light. The recording medium information detecting means detects the thickness of the recording medium information;
9. The image forming apparatus according to claim 8, wherein when the detected recording medium is thick, the speed difference is set larger than when the recording medium is thin. The recording medium information detecting means detects the type of the recording medium information;
The image forming apparatus according to claim 8, wherein the speed difference is changed according to the type of the detected recording medium.

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