JP2014130190A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device which forms an excellent image even if resistance change occurs in a transfer member, and an image forming apparatus.SOLUTION: A transfer device includes: a photoreceptor for carrying a toner image; developing means for forming the toner image on the photoreceptor; a transfer sheet rotated at a predetermined speed or an intermediate transfer belt; and a transfer roller which is in contact with the inside of the transfer sheet or the intermediate transfer belt to apply transfer bias for transferring the toner image from the photoreceptor to the transfer sheet or the intermediate transfer belt. The transfer device includes: a driving source for driving the transfer roller independently; a transfer current sensor 69 which measures transfer current during predetermined image formation; and rotation control means 62 which controls rotation of the transfer roller according to information on the measured current.

Description

  The present invention relates to an image forming apparatus configured as a transfer apparatus and an electronic copying machine, a printer, a facsimile, or a multifunction machine having at least two of these functions in an electrophotographic image forming apparatus.

  In the image forming apparatus of the above type, a so-called tandem type color copying machine in which a plurality of image forming units are arranged in parallel along one running side of an endless belt-like intermediate transfer member is well known. When creating a color print in this type of color image forming apparatus, first, color toner images of black, cyan, magenta, and yellow are formed on an image carrier in an image forming unit for each color. Next, the intermediate transfer member is brought into contact with the image carrier of each color, and a bias is applied to the primary transfer roller disposed opposite to the image carrier and in contact with the inner surface of the intermediate transfer member to form a transfer electric field. Primary transfer is performed in which the toner images are sequentially superimposed on the intermediate transfer member. The color toner image obtained by the primary transfer arrives at the secondary transfer portion in which the secondary transfer roller is arranged on the outside as the intermediate transfer member moves. The secondary transfer unit is provided with a counter roller facing the secondary transfer roller and contacting the inner side of the intermediate transfer member. The intermediate transfer member is sandwiched between the counter roller and the secondary transfer roller. Yes. A ground transfer is connected to the opposing roller inside the intermediate transfer body, while a secondary transfer bias is applied to the secondary transfer roller outside the intermediate transfer body. Thereby, a secondary transfer electric field for electrostatically moving the toner image from the former side to the latter side is formed between the counter roller and the secondary transfer roller. Then, the toner image on the intermediate transfer belt is secondarily transferred to the recording medium fed into the secondary transfer nip at a timing synchronized with the toner image on the intermediate transfer member by the action of the secondary transfer electric field. The toner on the recording medium is fixed by a fixing device, thereby creating a color print.

  By the way, the above-mentioned primary transfer roller is often made of an elastic roller having a metal core and a conductive sponge layer fixed on the surface thereof. At this time, a predetermined initial resistance of the primary transfer roller is used, and a bias to be applied is also determined. However, such a transfer roller has high resistance due to deterioration due to low-temperature and low-humidity environment or use over time, and thus it is difficult to obtain good image quality in a device whose bias is controlled by constant current control or constant voltage control. There was a problem.

  Therefore, Patent Document 1 describes an image forming apparatus that corrects a transfer bias voltage applied to an intermediate transfer member in accordance with potential information of the carrier and environmental conditions in order to prevent image defects due to uneven resistance of the transfer member. Has been.

  Patent Document 2 discloses image formation in which a transfer bias current control device performs control to switch a target value of a primary transfer bias current based on a detection result of a surface potentiometer that is a potential detection unit that detects a surface potential of a photoreceptor. A device is described. In the apparatus of Patent Document 2, a stable transfer electric field can be formed even when the resistance of the transfer member fluctuates, and the toner yield can be improved by forming a good transfer electric field.

  Furthermore, Patent Document 3 discloses an image forming system including a transfer device that changes a voltage value generated from a constant voltage circuit in accordance with properties of a transfer material (resistance variation due to temperature and humidity, longitudinal size, thickness, and the like). An apparatus is described. In the apparatus of Patent Document 3, a good transfer image can be obtained without causing a transfer image of various sizes, double-sided high-resistance paper, and a fuzzy image due to transfer failure or excessive transfer current even under the worst condition of toner loading. Can be obtained.

  However, in these techniques, when the resistance of the transfer roller is increased, the applied bias is increased in order to obtain a transfer electric field necessary to form a good image. There was a problem that image degradation occurred.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a transfer device and an image forming apparatus capable of solving the above-described conventional problems and capable of forming a good image even when the resistance variation of the transfer member occurs.

  In order to solve the above-described problems, the present invention provides an image carrier for carrying a toner image, a developing means for forming a toner image on the image carrier, and a transfer object rotated at a predetermined speed, or A transfer roller that contacts a transfer object transport unit and a transfer object or a transfer object transport unit and applies a transfer bias for transferring a toner image from the image carrier to the transfer object or the transfer object transport unit. A drive source for independently driving the transfer roller, means for measuring a transfer current during predetermined image formation, and rotation control for controlling the rotation of the transfer roller in accordance with information on the measured current And a transfer device.

  According to the present invention, it is possible to obtain a good image without image deterioration without applying a high bias even if a variation in which the resistance of the transfer member increases occurs.

1 is a schematic cross-sectional view illustrating an example of an image forming apparatus to which the present invention is applied. It is explanatory drawing which shows the image forming unit of the image forming apparatus. It is a graph which shows an example of the transfer voltage current characteristic at the time of changing the rotation speed of a transfer roller. It is a schematic block diagram which shows a main controller, a drive system control part, etc. It is a flowchart of the rotation speed control in one Embodiment of this invention. It is a schematic sectional drawing of the image forming apparatus which shows another embodiment of this invention. It is a flowchart of rotation speed control in another embodiment of the present invention. It is a flowchart of the rotation speed control in another embodiment of this invention. It is a graph which shows the relationship between the temperature of environmental conditions, and a transfer voltage current.

Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing an example of an image forming apparatus configured as an electronic copying machine, a printer, a facsimile, or a complex machine to which the present invention is applied. The image forming apparatus shown here includes four image forming units 1Y, 1M, 1C, and 1K for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. An intermediate transfer unit 20 is included. Further, the image forming apparatus includes an optical writing unit 35, a fixing device 40, and a paper feeding device 50.

  The four image forming units 1Y, 1M, 1C, and 1K use Y, M, C, and K toners of different colors, but have the same configuration. Here, an image forming unit 1K for forming a black (K) toner image will be described as an example.

FIG. 2 is an explanatory view showing an image forming unit for forming a black (K) toner image.
In FIG. 2, a drum-shaped photosensitive member 2K as a latent image carrier, a drum cleaning device 3K, a charge eliminating device (not shown), a charging device 6K, a developing device 8K, and the like are provided. These devices are integrated to form one cartridge, and can be replaced when the cartridge reaches the end of its life.

  The photoreceptor 2K has a drum shape with an outer diameter of about 60 mm in which an organic photosensitive layer is formed on the surface of a drum base, and is driven to rotate in the clockwise direction in the drawing by a driving means (not shown). The charging device 6K generates a discharge between the charging roller 7K and the photosensitive member 2K while bringing the charging roller 7K to which a charging bias is applied into contact with or in proximity to the photosensitive member 2K, thereby making the surface of the photosensitive member 2K uniform. Charge like this. In the reference form, the toner is uniformly charged to the same negative polarity as the normal charging polarity of the toner. As the charging bias, one in which an AC voltage is superimposed on a DC voltage is employed. The charging roller 7K is formed by coating a metal cored bar with a conductive elastic layer made of a conductive elastic material. Instead of a method in which a charging member such as a charging roller is brought into contact with or close to the photoreceptor 2K, a method using a charging charger may be adopted. The uniformly charged surface of the photosensitive member 2K is optically scanned by a laser beam emitted from the optical writing unit 35 to carry an electrostatic latent image for K.

  The electrostatic latent image for K is developed by a developing device 8K using K toner (not shown) to become a K toner image. The developing device 8K includes a developing unit that encloses the developing roller 9K, and a developer transport unit that stirs and transports a K developer (not shown). The developer transport section includes a first transport chamber that houses the first screw member 10K and a second transport chamber that houses the second screw member 11K.

  The drum cleaning device 3K removes transfer residual toner adhering to the surface of the photoreceptor 2K after the primary transfer step (primary transfer nip described later). It includes a cleaning brush roller 4K that is driven to rotate, a cleaning blade 5K that abuts the free end of the cleaning brush roller 4K in a cantilevered state, and the like. The transfer residual toner is scraped off from the surface of the photoreceptor 2K by the rotating cleaning brush roller 4K, and the transfer residual toner is scraped off from the surface of the photoreceptor 2K by the cleaning blade. The cleaning blade is in contact with the photosensitive member 2K in the counter direction in which the cantilevered support end side is directed downstream of the free end side in the drum rotation direction.

  The static eliminator neutralizes the residual charge on the photoreceptor 2K after being cleaned by the drum cleaning device 3K. By this charge removal, the surface of the photoreceptor 2K is initialized and prepared for the next image formation.

  Above the image forming units 1Y, 1M, 1C, and 1K, an optical writing unit 35 serving as a latent image writing unit is disposed. The optical writing unit 35 optically scans the photoreceptors 2Y, 2M, 2C, and 2K with laser light emitted from a laser diode based on image information sent from an external device such as a personal computer. By this optical scanning, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 2Y, 2M, 2C, and 2K. Specifically, the portion of the uniformly charged surface of the photoreceptor 2Y that has been irradiated with laser light attenuates the potential. Thereby, an electrostatic latent image is obtained in which the potential of the laser irradiation portion is smaller than the potential of the other portion (background portion). The optical writing unit 35 irradiates the photosensitive member through a plurality of optical lenses and mirrors while polarizing the laser light L emitted from the light source in the main scanning direction by a polygon mirror rotated by a polygon motor (not shown). To do. You may employ | adopt what performs optical writing by the LED light emitted from several LED of the LED array.

  Below the image forming units 1Y, 1M, 1C, and 1K, an intermediate transfer unit 20 is disposed as a transfer device that moves the endless intermediate transfer belt 21 endlessly in the counterclockwise direction in the drawing. Yes. The intermediate transfer unit 20 includes, in addition to the intermediate transfer belt 21 which is an image carrier and a transfer medium conveying unit, a driving roller 22, a secondary transfer back roller 23, a cleaning backup roller 24, and four primary transfer rollers 25Y and 25M. , 25C, 25K, secondary transfer roller 26, belt cleaning device 27, potential sensor 28, and the like.

  The intermediate transfer belt 21 is stretched by a driving roller 22, a secondary transfer back roller 23, a cleaning backup roller 24, and four primary transfer rollers 25Y, 25M, 25C, and 25K disposed inside the loop. . Then, it is moved endlessly in the same direction by the rotational force of the driving roller 22 that is driven to rotate counterclockwise in the figure by a driving means (not shown). As the intermediate transfer belt 21, a belt having the following characteristics is used. That is, the thickness is about 20 [μm] to 200 [μm], preferably about 60 [μm]. Further, the volume resistivity is about 1e6 [Ωcm] to 1e12 [Ωcm], preferably about 1e9 [Ωcm] (measured with Mitsubishi Chemical Hiresta UP MCP HT45 under an applied voltage of 100 V). The material is made of carbon-dispersed polyimide resin.

  The four primary transfer rollers 25Y, 25M, 25C, and 25K sandwich the intermediate transfer belt 21 that is moved endlessly between the photoreceptors 2Y, 2M, 2C, and 2K. As a result, primary transfer nips for Y, M, C, and K in which the front surface of the intermediate transfer belt 21 and the photoreceptors 2Y, 2M, 2C, and 2K abut are formed. A primary transfer bias is applied to the primary transfer rollers 25Y, 25M, 25C, and 25K by a transfer bias power source (not shown). As a result, a transfer electric field is formed between the Y, M, C, and K toner images on the photoreceptors 2Y, 2M, 2C, and 2K and the primary transfer rollers 25Y, 25M, 25C, and 25K. Similarly to the image forming unit 1K for K, Y, M, and C toner images are formed on the photoreceptors 2Y, 2M, and 2C, and the Y toner that is first formed on the surface of the photoreceptor 2Y for Y is photosensitive. As the body 2Y rotates, it enters the primary transfer nip for Y. Then, the image is primarily transferred from the photoreceptor 2Y to the intermediate transfer belt 21 by the action of the transfer electric field and nip pressure. The intermediate transfer belt 21 on which the Y toner image has been primarily transferred in this way then passes sequentially through the primary transfer nips for M, C, and K. Then, the M, C, and K toner images on the photoreceptors 2M, 2C, and 2K are sequentially superimposed and superimposed on the Y toner image. A four-color superimposed toner image is formed on the intermediate transfer belt 21 by this superimposing primary transfer.

  The primary transfer rollers 25Y, 25M, 25C, and 25K are made of an elastic roller having a metal core and a conductive sponge layer fixed on the surface thereof, and have the following characteristics. Have. That is, the outer shape is 16 [mm]. The diameter of the mandrel is 10 [mm]. Further, from a current I that flows when a voltage of 1000 V is applied to the primary transfer roller mandrel while a grounded metal roller having an outer diameter of 30 [mm] is pressed against the sponge layer with a force of 10 [N]. The resistance R of the sponge layer calculated based on Ohm's law (R = V / I) is about 3E7Ω. A primary transfer bias is applied to such primary transfer rollers 25Y, 25M, 25C, and 25K by constant current control.

  The secondary transfer roller 26 of the intermediate transfer unit 20 is disposed outside the loop of the intermediate transfer belt 21. An intermediate transfer belt 21 is disposed between the secondary transfer back roller 23 facing the inner side of the loop.

  The secondary transfer roller 26 is grounded, whereas a secondary transfer bias power source 29 applies a secondary transfer bias to the secondary transfer back roller 23. As a result, a secondary transfer electric field for electrostatically moving a negative polarity toner from the secondary transfer back roller 23 side to the secondary transfer roller 26 side between the secondary transfer back roller 23 and the secondary transfer roller 26. Is formed.

  The secondary transfer back roller 23 has the following characteristics. That is, the outer diameter is about 24 [mm]. The diameter of the cored bar is about 16 [mm]. The surface of the metal core is covered with a conductive NBR rubber layer, and its resistance R is 1e6 [Ω] to 1e12 [Ω], preferably about 4E7 [Ω]. The resistance R is a value measured by the same method as that for the primary transfer roller.

  The secondary transfer roller 26 has the following characteristics. That is, the outer diameter is about 24 [mm]. The diameter of the cored bar is about 14 [mm]. The surface of the metal core is covered with a conductive NBR rubber layer, and its resistance R is 1E6Ω or less. The resistance R is a value measured by the same method as that for the primary transfer roller. The primary transfer rollers 25Y, 25M, 25C, and 25K and the secondary transfer roller 26 are driven by independent motors ((drive sources)).

  A sheet feeding device 50 is disposed below the intermediate transfer unit 20. The transfer paper P, which is a sheet-like non-transfer body, is conveyed and hits the timing roller pair 51. The timing roller pair 51 stops the rotation of both rollers as soon as the conveyed transfer paper P is sandwiched between the rollers. Then, rotation driving is resumed at a timing at which the sandwiched transfer paper P can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 21 in the secondary transfer area, and the transfer paper P is moved to the secondary transfer area. Send it out.

  The four-color superimposed toner image on the intermediate transfer belt 21 is secondarily transferred onto the transfer medium P by a secondary transfer electric field to form a full-color toner image. The transfer target P having the full-color toner image formed on the surface in this manner is separated from the secondary transfer roller 26 and the intermediate transfer belt 21 by the curvature when passing the secondary transfer region.

  Untransferred toner that has not been transferred to the transfer medium P adheres to the intermediate transfer belt 21 that has passed through the secondary transfer region. This is cleaned from the belt surface by a belt cleaning device 27 in contact with the front surface of the intermediate transfer belt 21. The cleaning backup roller 24 disposed inside the loop of the intermediate transfer belt 21 backs up the cleaning of the belt by the belt cleaning device 27 from the inside of the loop.

  The potential sensor 28 is disposed outside the loop of the intermediate transfer belt 21. In the entire area of the intermediate transfer belt 21 in the circumferential direction, the intermediate transfer belt 21 is opposed to the grounded driving roller 22 with a gap of about 4 mm. Then, when the toner image primarily transferred onto the intermediate transfer belt 21 enters a position facing the intermediate transfer belt 21, the surface potential of the toner image is measured. As the potential sensor 28, EFS-22D manufactured by TDK Corporation is used.

  A fixing device 40 is disposed on the right side of the secondary transfer region in the drawing. The fixing device 40 forms a fixing nip with a fixing roller 41 containing a heat source such as a halogen lamp and a pressure roller 42 that rotates while contacting with the fixing roller 41 with a predetermined pressure. The transfer target P fed into the fixing device 40 is sandwiched between the fixing nips in a posture in which the unfixed toner image carrying surface is in close contact with the fixing roller 41. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed. The transfer target P discharged from the fixing device 40 passes through a post-fixing conveyance path and is then discharged outside the apparatus.

  When a monochrome image is formed, a support plate (not shown) that supports the primary transfer rollers 25Y, 25M, and 25C for Y, M, and C in the intermediate transfer unit 20 is moved to move the primary transfer roller 25Y, 25M, 25C, and 25K are moved away from the photoreceptors 2Y, 2M, and 2C. As a result, the front surface of the intermediate transfer belt 21 is separated from the photoreceptors 2Y, 2M, and 2C, and the intermediate transfer belt 21 is brought into contact with only the K photoreceptor 2K. In this state, among the four image forming units 1Y, 1M, 1C, and 1K, only the K image forming unit 1K is driven to form a K toner image on the photoreceptor 2K.

  When the image forming apparatus as described above is used over time, the transfer roller resistance increases due to deterioration, the transfer current decreases with the same applied bias, and a necessary transfer electric field cannot be formed during constant voltage control. Therefore, during constant current control, a discharge due to application of a high bias may occur and the image may deteriorate.

  The inventors have made various studies in order to make full use of such a high resistance roller. As a result, it has been found that changing the rotational speed of the intermediate transfer belt 21 rotating at a predetermined speed and the transfer roller rotating at a constant speed has the same effect as lowering the roller resistance.

FIG. 3 shows an example of transfer voltage current characteristics when the rotation number of the transfer roller is changed.
The transfer roller 25 rotates at the same speed as the intermediate transfer belt 21, but if the number of rotations per unit time of the transfer roller 25 is increased or decreased, the transfer current increases even with the same applied bias, and the roller resistance is lowered. It was found that there is an effect equivalent to. This effect made it possible to use the high resistance roller.

  FIG. 4 is a schematic block diagram showing a main controller, a drive system control unit and the like in the image forming apparatus which is a full color printer. The control unit includes a main controller 61 including a microcomputer.

  A user interface (I / F) unit 68 including a numeric keypad, an LCD, and the like is connected to the main controller 61. The user I / F unit 68 is operated by the user to give instructions regarding image formation and the like. Done. At the same time, it is possible to notify the user of information such as image formation via the user I / F unit 68.

  A drive system control unit 62 connected to the main controller 61 includes a photosensitive drum rotation drive unit 63, a cleaning device swing drive unit 64, a primary transfer rotation drive unit 65, an intermediate transfer rotation drive unit 66, and a secondary transfer roller rotation. Each drive unit 67 is connected. The drive system controller 62 controls the operation of each connected drive unit. The main controller 61 is connected to a transfer current sensor 69, an environment sensor 70, and the like.

  The present invention controls the rotation of the primary transfer roller when the transfer current value of the primary transfer current sensor decreases due to use over time or the like. In this embodiment, the rotational speed of the primary transfer roller 25 is changed. Is controlling.

The control flow of the rotation speed is shown in FIG.
In FIG. 5, the primary transfer current at a constant voltage is measured by the transfer current sensor 69 (S1). Next, it is determined whether the measured current measured has fallen below a predetermined value (S2). When the transfer current becomes lower than a predetermined current, the rotation speed of the primary transfer roller 25 is controlled. As the rotation speed control, the rotation speed of the primary transfer roller 25 is changed by changing the drive current input to the transfer motor (S3). The control unit includes a non-volatile memory as storage means, and the non-volatile memory stores a transfer current and a drive current value of the transfer motor in association with each other.

  Next, a specific rotation control example for controlling the rotation speed of the primary transfer roller 25 will be described. First, when a primary transfer roller having an initial resistance of 1E7 [Ω] is used, the transfer current when 2000 V is applied is 20 μA. When this was used over time and the transfer current value when 2000 V was applied again was measured, the transfer current was as low as 10 μA. When an image on the primary transfer roller 25 at the time of use over time (constant current control with a primary transfer current of 20 μS) was confirmed, a part of the image defect due to uneven discharge occurred. Therefore, when the rotation control of the primary transfer roller 25 was performed and the number of rotations per unit time of the primary transfer roller was doubled, the transfer current value increased to 20 μA. Further, when an image at the time of rotation control (constant current control of primary transfer current 20 μA) was checked, no image defect occurred.

  In this embodiment, when the resistance of the transfer roller becomes high due to use over time and the transfer current becomes low, the roller resistance is reduced by controlling the number of rotations of the transfer roller and increasing the linear speed difference with the intermediate transfer belt. By doing so, an appropriate transfer electric field is formed. Therefore, a good image can be obtained even when the resistance of the transfer roller increases due to use over time.

  In the above embodiment, the transfer device that performs primary transfer has been described. However, the present invention can also be applied to a transfer device that performs secondary transfer.

FIG. 6 is a schematic sectional view of an image forming apparatus showing another embodiment of the present invention.
The image forming apparatus shown in FIG. 6 is the same as the apparatus shown in FIG. 1 except for the configuration of the secondary transfer apparatus provided with the transfer member conveyance belt 30, and the other components are the same. In addition, in order to avoid duplication of explanation, explanation of the same part is omitted.

  The secondary transfer roller 26 of the intermediate transfer unit 20 is disposed outside the loop of the intermediate transfer belt 21 and is inscribed inside the loop of the transfer member conveyance belt 30. An intermediate transfer belt 21 and a transfer member transport belt 30 are arranged between the secondary transfer back roller 23 inside the loop.

  The secondary transfer roller 26 is grounded, whereas a secondary transfer bias power source 29 applies a secondary transfer bias to the secondary transfer back roller 23. As a result, a secondary transfer electric field that electrostatically moves negative polarity toner from the secondary transfer back roller 23 side to the secondary transfer roller 26 side between the secondary transfer back roller 23 and the secondary transfer roller 26. Is formed.

  The secondary transfer back roller 23 has the following characteristics. That is, the outer diameter is about 24 [mm]. The diameter of the cored bar is about 16 [mm]. The surface of the metal core is covered with a conductive NBR rubber layer, and its resistance R is 1e6 [Ω] to 1e12 [Ω], preferably about 4E7 [Ω]. The resistance R is a value measured by the same method as that for the primary transfer roller. The transfer member conveyance belt 30 is stretched by a plurality of rollers such as a secondary transfer roller 26, a transfer member driving roller 31, and a transfer member driven roller 32 disposed inside the loop. Then, it is endlessly moved in the same direction by the rotational force of the driven roller 31 that is driven to rotate in the clockwise direction in the drawing by a driving means (not shown). As the transfer / conveying belt 30, a belt having the following characteristics is used. That is, the thickness is about 20 [μm] to 200 [μm], preferably about 60 [μm]. Further, the volume resistivity is about 1e6 [Ωcm] to 1e12 [Ωcm], preferably about 1e9 [Ωcm] (measured with Mitsubishi Chemical Hiresta UP MCP HT45 under an applied voltage of 100 V). The material is made of carbon-dispersed polyimide resin.

  The secondary transfer roller 26 has the following characteristics. That is, the outer diameter is about 24 [mm]. The diameter of the cored bar is about 14 [mm]. The surface of the metal core is covered with a conductive NBR rubber layer, and its resistance R is 1E6Ω or less. The resistance R is a value measured by the same method as that for the primary transfer roller.

  The output terminal of the secondary transfer bias power source 29 is connected to the core metal of the secondary transfer roller 26. The potential of the metal core of the secondary transfer roller 26 becomes almost the same value as the output voltage value from the secondary transfer bias power source 29. Further, the core metal of the secondary transfer back roller 23 is grounded (ground connection).

FIG. 7 shows a control flow of the rotational speed.
In FIG. 7, the secondary transfer current is measured by the transfer current sensor 69 (S1). Next, it is determined whether the measured current value has fallen below a predetermined value (S2). When the transfer current becomes lower than a predetermined current, the rotational speed of the secondary transfer roller is controlled. As the rotation speed control, the rotation speed of the secondary transfer roller 26 is changed by changing the drive current input to the transfer motor (S2).

  As described above, in this embodiment, when the resistance of the secondary transfer roller 26 increases and the transfer current decreases, the roller resistance is reduced by controlling the number of rotations of the transfer roller and increasing the linear velocity difference with the intermediate transfer belt. By lowering, an appropriate transfer electric field is formed. Therefore, even if the resistance of the secondary transfer roller 26 is high, this can be corrected and a good image can be obtained.

  Next, a specific rotation control example for controlling the rotation speed of the secondary transfer roller 26 will be described. First, when the secondary transfer roller 26 having an initial resistance of 4E7 [Ω] was used, the transfer current when applying 500 V was 20 μA. When this was used over time and the transfer current value when 500 V was applied again was measured, the transfer current was as low as 15 μA. When the image at the time of constant current control with the secondary transfer current 30 μA at the time of use was observed, it was confirmed that some image defects due to discharge unevenness occurred. Therefore, when the rotation control of the secondary transfer roller 26 is performed and the rotation speed is halved, the transfer current value is increased to 20 μA, and the image at the time of constant current control is confirmed with the secondary transfer current 30 μA. There was no image defect.

  In this embodiment, when the resistance of the transfer roller becomes high due to use over time and the transfer current becomes low, the roller resistance is reduced by controlling the number of rotations of the transfer roller and increasing the linear speed difference with the intermediate transfer belt. By doing so, an appropriate transfer electric field is formed. Therefore, a good image can be obtained even when the resistance of the transfer roller increases due to use over time.

Incidentally, the resistance of the transfer roller increases even in a low temperature and low humidity environment.
Therefore, an embodiment in which the influence of the increase in roller resistance that occurs in a low-temperature and low-humidity environment in the configuration of the above-described two embodiments will be described.

FIG. 8 is a block diagram showing a method for controlling the primary transfer roller 25 when an environmental sensor for detecting an environmental state is used.
In FIG. 8, temperature and humidity are measured by the environmental sensor 70 (S1). Next, it is determined whether the measured temperature / humidity has fallen below a predetermined value (S2). When the transfer current becomes lower than a predetermined current, the rotation speed of the primary transfer roller 25 is controlled. As the rotation speed control, the rotation speed of the primary transfer roller 25 is changed by changing the drive current input to the transfer motor (S2). Such control can also be used for controlling the secondary transfer roller 26.

The control system of this embodiment is provided with temperature and humidity detection means for detecting temperature and humidity as environmental conditions. The temperature / humidity detection means is arranged in the vicinity of the transfer body. However, if there is no heat source or air blowing mechanism nearby and the environmental conditions are relatively stable, it may be installed in another place. Good.
The temperature and humidity are detected by the temperature and humidity detection means, and the transfer roller rotation amount is corrected using the detected temperature and humidity data, thereby forming an appropriate transfer electric field according to the environmental conditions.

  FIG. 9 is a characteristic diagram showing the relationship between the temperature of the environmental conditions and the transfer voltage current. The vertical axis shows the transfer current and the horizontal axis shows the transfer voltage. Compared with the current voltage in a normal environment, the slope of the voltage-current characteristic is reduced to about ½ under low temperature and low humidity conditions. However, even in such an environment, it is possible to make the transfer current characteristic the same as in a normal state by increasing the number of rotations of the transfer roller and the belt to about 4 times.

  As described above, as the environmental condition becomes low temperature and low humidity (LL), an appropriate transfer electric field can be formed by reducing the roller resistance by controlling the rotation speed of the transfer roller, and a good image can be obtained. .

  Next, a specific example of rotation control for controlling the number of rotations of the transfer roller against a decrease in temperature and humidity will be described. First, in the MM environment, when a secondary transfer roller having a resistance of 1E8 [Ω] was used, a secondary transfer current of 15 μA was measured when 500 V was applied.

  Next, when the transfer current value when 500 V was applied was measured similarly in the LL environment, the transfer current was as low as 5 μA. Further, when an image sample controlled at a constant current to a secondary transfer current of 30 μA in the LL environment was examined, it was confirmed that a part of image defect due to discharge unevenness occurred. Therefore, when line control of the secondary transfer roller was performed and the number of rotations was quadrupled, the transfer current value increased to 15 μA. In addition, no image defect occurred even in the image sample controlled at a constant current of the secondary transfer current 30 μA in the LL environment.

  In this embodiment, when the resistance of the transfer roller becomes high and the transfer current becomes low due to the LL environment, the roller resistance is lowered by controlling the number of rotations of the transfer roller and increasing the linear velocity difference from the intermediate transfer belt. Thus, an appropriate transfer electric field is formed. Therefore, a good image can be obtained even when the resistance of the transfer roller is high at low temperatures and low humidity.

  In the above-described embodiment, the effect of resistance fluctuation of the transfer rollers 25 and 26 is reduced by providing a difference in linear velocity between the belts in contact with the transfer rollers 25 and 26. 21 may fluctuate and the image may be disturbed. Therefore, it is desirable to stabilize the belt conveyance speed by making the pressing force of the belt driving roller 32 to the belt stronger than the pressing force of the transfer rollers 25 and 26.

For example, when the primary transfer roller rotation control mechanism is installed, if the nip pressure of the primary transfer roller 25 is 10N, the pressing force of the drive roller is increased to about 15N.
In the above-described embodiment, the influence of the roller resistance fluctuation is eliminated by decreasing or slightly increasing the number of rotations of the transfer roller. However, depending on the roller material, the resistance variation is large, and there is a case where a desired transfer current cannot be obtained unless the linear velocity difference of the belt member in contact with the transfer roller is increased. Therefore, if the rotation speed of the roller is increased while keeping the rotation direction of the belt member in contact with the transfer roller in the same direction, the belt bends and an abnormal image is generated.

  In such a case, when the rotation speed of the transfer roller is controlled, it is necessary to reversely rotate the transfer roller by switching the transfer roller drive bias between positive and negative to make the rotation speed larger than usual.

  Next, an example of rotation control will be described. First, when using a secondary transfer roller having a resistance of 1E7 [Ω] in an MM environment, a secondary transfer current of 20 μA was measured when 500 V was applied. Next, when the transfer current value when 500 V was applied was measured similarly in the LL environment, the transfer current was as low as 5 μA. Further, when an image sample prepared by constant current control with a secondary transfer current of 30 μA in the LL environment was examined, it was confirmed that uneven transfer discharge occurred. Therefore, when the rotation direction of the secondary transfer roller is changed to the rotation direction opposite to the conveying belt and the number of rotations is increased by five times, the transfer current value is increased to 20 μA, and the secondary transfer current is fixed to 30 μA in the LL environment. No image defect occurred in the image sample prepared by current control.

  As described above, an appropriate transfer electric field is formed by reducing the roller resistance by reversely rotating the transfer roller by switching the positive / negative of the transfer roller drive bias, etc., and obtaining a good image. Can do.

  In the present invention, a transfer charger, a transfer brush, or the like may be employed in place of the primary transfer rollers 25Y, 25M, 25C, and 25K in an apparatus that controls the rotation of only the secondary transfer roller 26.

2 Photoreceptor 8 Developing means 21 Intermediate transfer belt 25 Primary transfer roller 26 Secondary transfer roller 62 Rotation control means 69 Transfer current sensor P Transfer paper

Japanese Patent No. 3449122 JP 2010-26083 A Japanese Patent Laid-Open No. 2000-3101

Claims (5)

An image carrier for carrying a toner image, and developing means for forming a toner image on the image carrier;
A transferred object or transferred object conveying means that rotates at a predetermined speed and an inner side of the transferred object or transferred object conveying means, and a toner image is transferred from the image carrier to the transferred object or transferred object conveying means. In a transfer apparatus having a transfer roller for applying a transfer bias for transferring,
A drive source for independently driving the transfer roller;
Means for measuring a transfer current during predetermined image formation;
And a rotation control means for controlling the rotation of the transfer roller in accordance with the information of the measured current. An image carrier for carrying a toner image, and developing means for forming a toner image on the image carrier;
A transferred object or transferred object conveying means that rotates at a predetermined speed and an inner side of the transferred object or transferred object conveying means, and a toner image is transferred from the image carrier to the transferred object or transferred object conveying means. In a transfer apparatus having a transfer roller for applying a transfer bias for transferring,
A drive source for independently driving the transfer roller;
An environmental sensor for detecting the environmental condition in the device body;
And a rotation control means for controlling the rotation of the transfer roller in accordance with information from the environmental sensor.   3. The transfer apparatus according to claim 1, further comprising a driving roller for driving the transfer body or the transfer body conveying means, wherein the transfer roller or the transfer body is pressed against the transfer body or the transfer body conveying means. A transfer device characterized by being smaller than a pressure of a driving roller for driving a conveying means.   3. The transfer device according to claim 1, wherein the rotation control unit controls the rotation number of the transfer roller to change per unit time.   3. The transfer apparatus according to claim 1, wherein the rotation control unit controls the rotation direction of the transfer roller to be changed to a direction different from the rotation direction of the transfer medium or the transfer object transport unit. apparatus.

Images