JP2006072208A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent transfer memory from being caused and to prevent an image defect accompanying it. <P>SOLUTION: An image forming apparatus is equipped with an image carrier and a transfer means which abuts against it, and performs constant-current control over the transfer means with a set current in a paper non-feed state wherein no recording material is present at a transfer position where the both abut against each other and varies conveyance intervals of recording materials according to the voltage at this time. Further, the image forming apparatus is equipped with the image carrier and transfer means which abuts against it, and performs the constant-current control over the transfer means with a set voltage in the paper non-feed state wherein no recording material is present at the transfer position where the both abut against each other and widens conveyance intervals of recording materials when the voltage at this time is not larger than a prescribed value. Furthermore, the image forming apparatus is equipped with the image carrier and transfer means which abuts against it, and performs the constant-current control over the transfer means with the set voltage in the paper non-feed state wherein no recording material is present at the transfer position where the both abut against each other and varies conveyance intervals of recording materials according to the current at this time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer.

  A conventional image forming apparatus is shown in FIG.

  In FIG. 2, the image forming apparatus includes a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is rotationally driven at a predetermined process speed in the direction of an arrow by a main body drive motor (not shown) which is a driving means.

  Around the photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a transfer roller 5 as a transfer device, and a cleaning device 6 are arranged in this order along the rotation direction.

  Further, a paper feed cassette 13 that stores a recording material P such as paper is disposed at the lower part of the apparatus main body. A paper feed roller 8, a transport roller 9, and a photosensitive drum 1 are sequentially arranged along the transport path of the recording material P. And a transfer roller 5, a fixing device 7, a paper discharge roller 10, and a paper discharge tray.

  Next, the operation of the image forming apparatus having the above-described configuration will be described.

  The photosensitive drum 1 that is rotationally driven in the direction of the arrow by the main body drive motor is uniformly charged to a predetermined polarity and a predetermined potential by the charging roller 2. The surface of the charged photosensitive drum 1 is subjected to exposure L based on image information by the exposure device 3 of the laser optical system on the surface, and the electric charge of the exposed portion is removed to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 4. The developing device 4 has a developing roller, and a developing bias is applied to the developing roller to attach toner to the electrostatic latent image on the photosensitive drum 1 and develop (develop) it as a toner image.

  The toner image is transferred to the recording material P such as paper by the transfer roller 5. The recording material P is stored in the paper feed cassette 13, fed by the paper feed roller 8, transported by the transport roller 9, and transported to the transfer nip portion between the photosensitive drum 1 and the transfer roller 5. At this time, the recording material P is synchronized with the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the recording material P.

  The recording material P carrying the unfixed toner image on the surface by transfer is conveyed to the fixing device 7 where the unfixed toner is heated and pressurized and fixed on the recording material P.

  The recording material P after the toner image is fixed is discharged onto a discharge tray on the upper surface of the apparatus main body by a discharge roller 10.

  On the other hand, after the toner image is transferred, the toner remaining on the surface without being transferred to the recording material P is removed by the cleaning blade of the cleaning device 6, and the next image formation is performed.

  By repeating the above operation, image formation can be performed one after another.

  When an image is formed on both sides of a recording material by the image forming apparatus, the following operation is performed.

  The recording material on which the image on the first side has been formed is heated by the fixing device 7 and conveyed to the paper discharge roller 10. After the trailing edge of the recording material passes through the fixing device 7, the rotation direction of the paper discharge roller 10 is reversed. The recording material is conveyed from the rear end of the first surface to the double-sided conveyance path P2 indicated by a one-dot oblique line in the figure, and is fed to the conveyance roller 9 in a state where the first surface of the recording material on which the image is formed is reversed so as to be the back surface. Sent. Thereafter, double-sided printing is automatically performed by performing image formation similar to that for the first side.

  Next, the configuration of the transfer device in the conventional image forming apparatus will be described with reference to FIG.

  The transfer roller 5 is a roller in which a conductive elastic layer 52 is formed on a metal core 51 and is pressed against the photosensitive drum 1 to form a transfer nip portion. A transfer power source 11 that applies a voltage to the transfer roller is connected to the transfer roller 5, and the voltage applied to the transfer roller is controlled by a control device 12.

  The recording material P is fed to the nip portion between the transfer roller 5 and the photosensitive drum 1 in synchronization with the movement of the toner image on the photosensitive drum 1 by the rotation on the photosensitive drum, and is transferred to the transfer roller 5 via the core metal by the transfer bias power source 10. 5 is applied to the back surface of the recording material by the action of the voltage applied to the recording material 5, and the toner image on the photosensitive drum 1 is transferred to the recording material by this charge.

  As a method for controlling a transfer unit in a conventional image forming apparatus, an automatic transfer voltage control method (hereinafter referred to as an ATVC method) that can always obtain good transfer performance even when environmental conditions change with respect to the voltage of a transfer roller. Is proposed in Patent Document 1. In this ATVC method, prior to the image forming process, the photosensitive drum is rotated, a voltage is applied to the transfer roller during this rotation (pre-rotation), and the output current value at this time is measured with an ammeter. The measured value is fed back to the controller. The bias voltage of the power supply is adjusted by the controller so that the output current value becomes a predetermined value, and the constant voltage of the adjusted voltage as it is or corrected by a coefficient or the like is transferred at the time of transfer. Even if the resistance value of the transfer roller varies greatly depending on the environment, an appropriate transfer bias can always be obtained.

Japanese Patent No. 2704277

  However, when an image is formed on both sides of the recording material in the conventional image forming apparatus, the image is defective due to the transfer memory in which the toner adheres to the end region in the longitudinal direction of the recording material and the end of the recording material becomes dirty (hereinafter referred to as the image defect). , Edge fogging) may occur. This edge fog phenomenon occurs remarkably when images are continuously formed on both sides of the recording material.

  FIG. 6 is a diagram showing the state of the edge fogging when the recording material passes through the transfer unit.

  As shown in the drawing, when the transfer process is performed on the recording material P having a narrow width with respect to the longitudinal width of the transfer roller 5, the sheet passing region Tp through which the recording material passes and the non-sheet passing region through which the recording material does not pass. A difference occurs in the transfer current flowing at T0. In the sheet passing area Tp, a transfer current flows through the recording material, whereas in the non-sheet passing area, there is no recording material, so the transfer current flowing in the non-sheet passing area T0 increases.

  In the reversal development type image forming apparatus, the photosensitive drum is charged to negative polarity by the charging means, and the voltage applied to the transfer roller is positive. If the transfer current in the transfer process is increased, the surface of the photosensitive drum is greatly charged in the positive direction. Even if a negative charging is performed by a subsequent charging unit, it cannot be charged to the original charging potential. Some toner adheres to the photosensitive drum.

  When image formation is performed on both sides of a recording material, in the case of an image forming apparatus having a configuration in which the conveyance reference of the recording material is changed between image formation on the first surface and image formation on the second surface, the recording material in the transfer process as shown in FIG. Since the transfer position of the image on the first surface differs from the image formation on the second surface, the toner on the photosensitive drum due to the transfer memory generated in the non-sheet passing area of the preceding recording material adheres to the end of the subsequent recording material. It becomes bad dirt.

  Even in the configuration of the image forming apparatus in which the recording material conveyance reference is not changed in the image formation on the first side and the second side, when the conveyance of the recording material is obliquely inclined, the position of the end portion of the recording material is shifted. Therefore, the same phenomenon may occur.

  In particular, this phenomenon is likely to occur when the transfer current flowing through the non-sheet passing portion is increased, and is particularly likely to occur when the recording material has a high resistance value and a transfer roller resistance value is low.

  When the resistance value of the recording material is high, the transfer voltage must be increased in order to obtain a transfer current in the sheet passing area. As a result, the transfer current in the non-sheet passing area increases. When image formation is performed on both sides of the recording material, since the heat treatment is performed in the fixing device during image formation on the first surface, the moisture content of the recording material is reduced, and the resistance value of the recording material for the second surface printing is increased. Transfer memory is likely to occur.

  Further, when the resistance value of the transfer roller is low, the difference between the transfer currents in the paper passing area and the non-paper passing area depending on the presence or absence of the recording material becomes large. When image formation is performed on both sides of the recording material, the recording material is heated by the fixing device when the first image of the recording material is formed. When the material passes, the temperature of the transfer roller rises due to the heat of the recording material. Therefore, the current in the non-sheet passing area increases, and a transfer memory is likely to occur.

  As a transfer roller used in recent years, an elastic layer of a polymer conductive rubber material is used. The polymer conductive rubber material has a characteristic that the resistance value tends to decrease with increasing temperature, so that when the image is continuously formed on both sides of the recording material, the temperature of the transfer roller increases. Since the resistance value decreases, transfer memory is more likely to occur.

  Due to the above reasons, a transfer memory may occur when images are continuously formed on both sides of a recording material in the image forming apparatus.

  An object of the present invention is to solve the above-described problems, and an object of the present invention is to prevent the generation of a transfer memory and to prevent image defects associated therewith.

  In order to achieve the above-mentioned object, the invention according to claim 1 is set at the time of non-sheet passing including an image carrier and a transfer means in contact with the image carrier, and a recording material does not exist at a transfer portion in contact with the image carrier. The transfer unit is controlled at a constant current by the current, and the recording material conveyance interval is changed according to the voltage at this time.

  The invention according to claim 2 includes an image carrier and a transfer unit that contacts the image carrier, and the transfer unit is set with a set voltage when no recording material is present at a transfer site where both of them contact. Voltage control is performed, and when the voltage at this time is less than a predetermined value, the recording material conveyance interval is widened. According to a third aspect of the present invention, an image carrier and a transfer unit that contacts the image carrier are provided, and the transfer unit is fixed with a set voltage when no recording material is present at the transfer part that contacts both of them. Voltage control is performed, and the recording material conveyance interval is changed according to the current at this time.

  According to a fourth aspect of the present invention, an image carrier and a transfer unit abutting against the image carrier are provided, and the transfer unit is fixed with a set voltage when no recording material is present at a transfer site where both of them abut. Voltage control is performed, and when the current at this time exceeds a predetermined value, the recording material conveyance interval is widened.

  According to a fifth aspect of the invention, in the invention according to any one of the first to fourth aspects, the image is formed a plurality of times on the recording material.

  According to the present invention, by changing the interval of the recording material in accordance with the resistance value of the transfer means, it is possible to prevent image defects caused by the transfer memory on the photosensitive drum.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
The image forming apparatus shown in FIG. 2 includes a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of the arrow at a predetermined process speed (PS = 150 mm / s) by a main body driving motor as a driving means.

  Around the photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a transfer roller 5 as a transfer device, and a cleaning device 6 are arranged in this order along the rotation direction.

  Further, a paper feed cassette 13 that stores a recording material P such as paper is disposed at the lower part of the apparatus main body. A paper feed roller 8, a transport roller 9, and a photosensitive drum 1 are sequentially arranged along the transport path of the recording material P. And a transfer roller 5, a fixing device 7, a paper discharge roller 10, and a paper discharge tray.

  Next, the operation of the image forming apparatus having the above-described configuration will be described.

  The photosensitive drum 1 that is rotationally driven in the direction of the arrow by a main body drive motor (not shown) is uniformly charged to a predetermined polarity and a predetermined potential by the charging roller 2. The surface of the charged photosensitive drum 1 is subjected to exposure L based on image information by the exposure device 3 of the laser optical system on the surface, and the electric charge of the exposed portion is removed to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 4. The developing device 4 has a developing roller, and a developing bias is applied to the developing roller to attach toner to the electrostatic latent image on the photosensitive drum 1 and develop (develop) it as a toner image.

  The toner image is transferred to the recording material P such as paper by the transfer roller 5. The recording material P is stored in a paper feed cassette 7, fed by a paper feed roller 8, transported by a transport roller 9, and transported to a transfer nip portion between the photosensitive drum 1 and the transfer roller 5. At this time, the recording material P is synchronized with the toner image on the photosensitive drum 1, and a transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is given a predetermined value on the recording material P. Transcribed into position.

  The recording material P carrying the unfixed toner image on the surface by transfer is conveyed to the fixing device 11 where the unfixed toner is heated and pressurized and fixed on the recording material P.

  The recording material P after the toner image is fixed is discharged onto a discharge tray on the upper surface of the apparatus main body by a discharge roller 10.

  On the other hand, after the toner image is transferred, the toner remaining on the surface without being transferred to the recording material P is removed by the cleaning blade of the cleaning device 6, and the next image formation is performed.

  By repeating the above operation, image formation can be performed one after another.

  Next, the operation during automatic duplexing for forming images on both sides of the recording material will be described.

  In the image forming apparatus according to the present embodiment, images can be formed on both sides of the recording material, and the conveyance path P1 on the first surface of the recording material in FIG. 2 is indicated by a broken line, and the conveyance path P2 on the second surface is indicated by a one-dot broken line.

  The operation of the double-sided image forming apparatus will be described below.

  The recording material is fed from the recording material cassette 13 below the image forming apparatus and reaches the conveying roller 9. The conveyance roller 9 conveys the recording material P to the transfer unit in synchronization with the image formed on the photosensitive drum 1, and the recording material P reaches the paper discharge unit via the transfer unit and the fixing device 7. After the recording material trailing edge passes through the fixing device 7, the rotation direction of the paper discharge roller 10 is reversed, and the recording material is conveyed to the double-sided conveyance path P2 with the trailing edge of the first surface of the recording material as the leading edge. The first surface of the material is fed to the transport roller 9 in an inverted state so as to be the back surface. Thereafter, image formation is automatically performed on both sides of the recording material by performing image formation similar to that on the first surface.

  FIG. 1 is a diagram showing the relationship of the sheet passing position of the recording material with respect to the longitudinal direction of the photosensitive drum and the transfer roller and the interval between the recording materials. A4 size (width 210 mm) was used as the recording material.

  The recording material in the image formation on the first surface of the recording material is conveyed on the basis of the center so that the center of the transfer roller coincides with the center of the recording material in all paper sizes.

  The conveyance of the recording material in the image formation on the second surface of the recording material is designed such that the conveyance of the second surface of the recording material of LTR size (215.9 mm) is coincident with the center of the transfer roller. All sizes are conveyed with the position of the LTR size end as a reference.

  Therefore, since the recording material on the second side is conveyed by the double-sided conveyance path P2, the recording material is regulated by the double-sided reference of the end portion, so when the A4 size recording material is conveyed at the transfer portion at the time of image formation on the second side. On the other hand, the sheet is transported at different positions with a deviation of 6 mm from the first side and the sheet passing area.

  With respect to the order of the recording materials when the double-sided image forming operation is continuously performed in the configuration of the present embodiment, the first side of the first sheet, the second side of the first sheet, and the next 1 of the second sheet Image formation is performed alternately on the first side and the second side, such as the first side and then the second side of the second sheet.

  In the state where the resistance value of the transfer roller is not lowered, the interval between the recording materials on the second surface and the first surface is set to 60 mm. The recording material interval is set to the shortest recording material interval in order to maximize the output of the recording material. The interval between the recording materials on the first side and the second side is sufficiently longer than the interval between the second side and the first side because there is a time required for reversing the recording material.

  Next, the voltage control of the transfer roller 5 and the control method for conveying the recording material will be described.

  FIG. 3 is a schematic configuration part of the transfer part of the image forming apparatus.

  Reference numeral 5 denotes a transfer roller, 11 denotes a transfer bias power source, and 12 denotes a control device for controlling the transfer bias power source and the like.

  The operation will be described below.

  First, the driving of the image forming apparatus is started, and the transfer bias power source 11 is controlled at a constant current value of 8 μA at the time of the pre-rotation before the recording material P reaches the transfer portion in the non-sheet passing state. The voltage generated at that time is set as a constant current detection voltage Vt0, and the information is sent to the control device 12. This constant current detection voltage Vt0 is processed to determine the transfer voltage Vt when the recording material is passed, and the transfer bias power supply 11 is fixed when the recording material is passed through the photosensitive drum 1 and the transfer roller 5 section. Control the voltage.

  Further, the transfer voltage is obtained by the following control equation.

First surface of recording material: Vt = 0.75 × Vt0 + 1.5 (kV)
Recording material second side: Vt = 0.85 × Vt0 + 1.8 (kV)
Further, during the image formation on both sides, the transfer bias power source 12 is controlled at a constant current value of 8 μA in the same manner as in the pre-rotation at the non-sheet passing interval between the first side and the second side of the recording material. The voltage generated at that time is set as a constant current detection voltage Vt0, the information is sent to the control device 12, the transfer voltage is determined by the above formula at the non-sheet passing interval of the recording material, and resetting is performed.

  Further, the recording material interval between the second surface and the first surface of the recording material is changed as shown in Table 1 according to the constant current detection voltage Vt0.

図１は定電流時検知電圧Ｖｔ０が１. ４ｋＶ以上のときの記録材間隔を表わす図、図４は定電流時検知電圧Ｖｔ０が１. ０ｋＶ以上１. ４ｋＶ以下のときの記録材間隔を表わす図、図５は定電流時検知電圧Ｖｔ０が１. ０ｋＶ以下のときの記録材間隔を表わす図である。

FIG. 1 shows the recording material interval when the constant current detection voltage Vt0 is 1.4 kV or more, and FIG. 4 shows the recording material interval when the constant current detection voltage Vt0 is 1.0 kV or more and 1.4 kV or less. FIG. 5 and FIG. 5 are diagrams showing the recording material interval when the constant current detection voltage Vt0 is 1.0 kV or less.

  As can be seen from Table 1 and FIGS. 1, 4 and 5, when the detection voltage during constant current control is 1.4 kV or more, the image forming and recording materials can be recorded at the shortest recording material interval of 60 mm of the image forming apparatus. Transport. When the constant current detection voltage is 1.0 kV or more and 1.4 kV or less, image formation and recording material conveyance are performed at a recording material interval of 95 mm. Since the outer diameter of the photosensitive drum 1 in this embodiment is 30 mm, the photosensitive drum makes one round with a recording material interval of 95 mm.

  When the detection voltage at constant current is 1.0 kV or less, image formation and recording material conveyance are performed at a recording material interval of 190 mm. Since the outer diameter of the photosensitive drum is 30 mm, the photosensitive drum makes two rounds with a recording material interval of 190 mm.

  With the above control, the resistance value of the transfer roller is obtained from the detection voltage of the constant current control when the recording material is not passed, and when the detection voltage Vt0 at the constant current is 1.0 kV or more and 1.4 kV or less (the transfer roller resistance value is When the recording material is low, the transfer current flowing through the non-sheet passing portion increases and the photosensitive drum is charged to a polarity opposite to the charged polarity. Since the interval to the first surface is equal to or more than one rotation of the photosensitive drum, the charging process is performed twice until the photosensitive drum position at the rear end position of the second recording material is used for image formation on the first surface of the next recording material. pass. As a result, the memory on the photosensitive drum is eliminated and the charging potential is maintained at a predetermined level, and no image defect occurs at the end of the recording material.

  When the constant current detection voltage Vt0 is 1.0 kV or less (when the transfer roller resistance value is further lower), the recording material interval from the second recording material to the first recording material after the second recording material is two revolutions of the photosensitive drum. Because of the above interval, the charging process is passed three times until the photosensitive drum position at the rear end position of the second surface of the recording material is used for image formation on the first surface of the next sheet. As a result, the memory on the photosensitive drum is eliminated and the charging potential is maintained at a predetermined level, and no image defect occurs at the end of the recording material.

  In this embodiment, the interval between the recording materials is changed to 95 mm (one turn) and 190 mm (two turns), which are integral multiples of the photosensitive drum peripheral length. The same effect can be obtained with an integral multiple as long as the circumference of the photosensitive drum is one or more times, such as 1.2 times or 1.5 times the circumference.

<Embodiment 2>
The second embodiment of the present invention will be described below. The configuration and dimensions of the image forming apparatus used in the present embodiment are the same as those in the first embodiment, and a description thereof will be omitted.

  With respect to the order of the recording materials when the image forming operation on both sides is continuously performed in the configuration of the present embodiment, the first surface of the first sheet, the second surface of the first sheet, and the first sheet of the second sheet Image formation is performed alternately on the first side and the second side, such as the first side and then the second side of the second sheet.

  In the state where the resistance value of the transfer roller is not lowered, the interval between the recording materials on the second surface and the first surface is set to 60 mm. The recording material interval is set to the shortest recording material interval in order to maximize the output of the recording material. The interval between the recording materials on the first side and the second side is sufficiently longer than the interval between the second side and the first side because of the time required for reversing the recording material.

  Next, the voltage control of the transfer roller 5 and the control method for conveying the recording material will be described.

  FIG. 3 is a schematic configuration part of the transfer part of the image forming apparatus.

  Reference numeral 5 denotes a transfer roller, 11 denotes a transfer bias power source, and 12 denotes a control device for controlling the transfer bias power source and the like.

  The operation will be described below.

  First, the driving of the image forming apparatus is started, and the transfer bias power source 11 is controlled at a constant current value of 8 μA at the time of the pre-rotation before the recording material P reaches the transfer portion in the non-sheet passing state. The voltage generated at that time is set as a constant current detection voltage Vt0, and the information is sent to the control device 12. This constant current detection voltage Vt0 is processed to determine the transfer voltage Vt when the recording material is passed, and the transfer bias power supply 11 is fixed when the recording material is passed through the photosensitive drum 1 and the transfer roller 5 section. Control the voltage.

  Further, the transfer voltage is obtained by the following control equation.

First surface of recording material: Vt = 0.75 × Vt0 + 1.5 (kV)
Recording material second side: Vt = 0.85 × Vt0 + 1.8 (kV)
Further, when forming a double-sided image, the transfer bias power source 12 is controlled at a constant voltage value of 2 kV at a non-sheet passing interval between the first and second sides of the recording material. The current generated at that time is set as a constant voltage detection current It0, and the information is sent to the control device 12. According to the constant pressure detection current It0, the recording material interval between the second surface and the first surface of the recording material is shown in Table 2. Change as follows.

図１は定電流時検知電圧Ｉｔ０が１１. ４μＡ以下のときの記録材間隔を表わす図、図４は定電圧時検知電流Ｉｔ０が１１. ４μＡ以上１６μＡ以下のときの記録材間隔を表わす図、図５は定電圧時検知電流Ｉｔ０が１６μＡ以上のときの記録材間隔を表わす図である。

FIG. 1 is a diagram showing the recording material interval when the constant current detection voltage It0 is 11.4 μA or less, and FIG. 4 is a diagram showing the recording material interval when the constant voltage detection current It0 is 11.4 μA or more and 16 μA or less. FIG. 5 is a diagram showing the recording material interval when the constant-current detection current It0 is 16 μA or more.

  As can be seen from the above Table 2 and FIGS. 1, 4 and 5, when the detection voltage at the time of constant voltage control is 11.6 μA or less, the image forming and recording materials are recorded at the shortest recording material interval of 60 mm of this image forming apparatus. Transport. When the detection current at the time of constant voltage is 11.6 μA or more and 16 μA or less, image formation and recording material conveyance are performed at a recording material interval of 95 mm. Since the outer diameter of the photosensitive drum 1 in this embodiment is 30 mm, the photosensitive drum makes one round with a recording material interval of 95 mm.

  When the constant current detection current is 16 μA or more, image formation and recording material conveyance are performed at a recording material interval of 190 mm. Since the outer diameter of the photosensitive drum is 30 mm, the photosensitive drum makes two rounds with a recording material interval of 190 mm.

  With the above control, the resistance value of the transfer roller is obtained from the detection current of the constant voltage control when the recording material is not fed. When the detection current It0 at the constant voltage is 11.6 μA or more and 16 μA or less (when the transfer roller resistance value is low) ), The transfer current flowing through the non-sheet passing portion when the recording material is passed increases, and the photosensitive drum is largely charged to the opposite polarity to the charged polarity, but the first side of the next recording material after the second side of the recording material. Since the interval until the photosensitive drum is equal to or longer than the circumference of the photosensitive drum, the charging process passes twice until the photosensitive drum position at the rear end position of the second recording material is used for image formation on the first recording material. . As a result, the memory on the photosensitive drum is eliminated and the charging potential is maintained at a predetermined level, and no image defect occurs at the end of the recording material.

  When the constant voltage detection current It0 is 16 μA or more (when the transfer roller resistance value is further lower), the recording material interval to the first surface of the next recording material after the second recording material is equal to or more than two photosensitive drums. Because of the interval, the charging process passes three times until the photosensitive drum position at the rear end position of the second surface of the recording material is used for image formation on the first surface of the next sheet. As a result, the memory on the photosensitive drum is eliminated and the charging potential is maintained at a predetermined level, and no image defect occurs at the end of the recording material.

<Embodiment 3>
The third embodiment of the present invention will be described below. The configuration and dimensional relationship of the image forming apparatus used in the present embodiment are the same as those in the first embodiment, and description thereof will be omitted.

  The transfer bias power supply 11 is controlled at a constant current value of 8 μA at the constant current value of 8 μA in the same manner as in the pre-rotation at the non-sheet passing interval on the first and second sides of the recording material. The voltage generated at that time is set as the constant current detection voltage Vt0, and the information is sent to the control device 12, the transfer voltage is reset at the non-sheet passing interval of the recording material, and the start timing of conveyance of the recording material is changed.

  As described above, when the detection voltage at the constant current is 1.4 kV or more, image formation and recording material conveyance are performed with the shortest sheet interval of 60 mm of the image forming apparatus. When the detection voltage at a constant current is 1.4 kV or more, the feeding of the next recording material is temporarily stopped.

  The rotational driving operation of the photosensitive drum 1, the transfer roller 5 and the like is continuously performed, and the constant current control is continuously performed with the transfer bias power source 11 at a constant current value of 8 μA as in the previous rotation. When the constant-current detection voltage Vt0 becomes 1.5 kV or higher, the next recording material is transported and the image forming operation is restarted.

  With the above control, the resistance value of the transfer roller can be obtained from the detection voltage of the constant current control when the recording material is not fed. When the constant-current detection voltage Vt0 is 1.4 kV or less (when the transfer roller resistance value is low), no image is formed at the edge of the recording material because the next image formation is not performed.

It is a figure which shows conveyance of the recording material which concerns on embodiment of this invention. 1 is a cross-sectional configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a schematic block diagram of the transfer roller part which concerns on the Example of this invention. It is a figure which shows conveyance of the recording material which concerns on the Example of this invention. It is a figure which shows conveyance of the recording material which concerns on the Example of this invention. It is a figure which shows the state of the transfer part which concerns on a prior art example. It is a figure which shows conveyance of the recording material which concerns on a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 5 Transfer roller 11 Transfer bias power supply 12 Control part P Recording material

Claims (5)

  The image bearing member and a transfer means that abuts the image carrier, and the transfer means is controlled at a constant current by a set current when no recording material is present at the transfer portion where both abut, and the voltage at this time An image forming apparatus characterized in that the recording material conveyance interval is changed according to the above.   An image carrier and a transfer means that contacts the image carrier, and the transfer means is controlled at a constant voltage with a set voltage when no recording material is present at the transfer portion where both of them contact, and the voltage at this time An image forming apparatus characterized in that the recording material conveyance interval is widened when the value is less than a predetermined value.   An image carrier and a transfer unit that contacts the image carrier, and the transfer unit is controlled at a constant voltage with a set voltage when no recording material is present at the transfer part that contacts the image carrier. An image forming apparatus characterized in that the recording material conveyance interval is changed according to the above.   An image carrier and a transfer unit that contacts the image carrier, and the transfer unit is controlled at a constant voltage with a set voltage when no recording material is present at the transfer part that contacts the image carrier. An image forming apparatus characterized in that the recording material conveyance interval is widened when the value exceeds a predetermined value.   The image forming apparatus according to claim 1, wherein the image formation is performed a plurality of times on the recording material.

Images