JP2010026189A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress an image quality defect caused by fluctuation of a resistance value when electric resistance of a transfer roller is largely fluctuated due to environmental change and change with the lapse of time. <P>SOLUTION: An image forming apparatus includes: a belt type image carrier; a primary transfer roller rotating in the same direction as the belt type image carrier while in contact with the belt type image carrier; and a photoreceptor drum which is provided to face the primary transfer roller across the belt type image carrier and comes in contact with the belt type image carrier: A detection means for measuring the electric resistance of the primary transfer roller is provided to adjust nip width formed by the primary transfer roller and the photoreceptor drum so that the electric resistance value of the primary transfer roller may be always constant on the basis of the electric resistance of the primary transfer roller measured by the detection means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, and more particularly, a transfer type image forming apparatus that transfers a toner image carried on a belt-like image carrier onto a transfer material using a transfer belt. It is about.

  In the transfer type image forming apparatus, in order to appropriately transfer the toner to the transfer material, it is necessary to apply an appropriate electric field to the toner. If the transfer bias applied to the toner is insufficient, an electric field sufficient to transfer the toner to the transfer material cannot be created, resulting in transfer failure. On the other hand, when the transfer bias applied to the toner is excessive, an electric field is generated at the entrance to the nip or in the vicinity of the exit of the nip, so that a discharge occurs, and the toner is scattered by this discharge to cause a transfer failure.

  Therefore, an appropriate transfer bias must be applied to the toner to provide an optimum electric field for transfer. However, the electrical resistance of the transfer roller varies greatly due to environmental fluctuations and deterioration of energization over time. Since the electric resistance value of the transfer roller fluctuates, even when the same transfer current is applied, the transfer voltage applied to the entire transfer portion varies greatly. Therefore, there has been a problem that the above-mentioned transfer failure occurs.

  In order to solve this problem, when the transfer roller resistance value is low, the transfer current is set high, and conversely, when the transfer roller resistance value is high, the transfer current is set low. A method for preventing defects has been proposed.

  In addition, in order to cope with environmental fluctuations, a plurality of transfer rollers are prepared, and when there is a fluctuation in the environment, it has a mechanism that can be changed to a transfer roller according to the environment. A method for preventing this has been proposed.

Japanese Patent Laid-Open No. 2005-134487 JP 2006-91481 A Japanese Patent Laid-Open No. 6-308441

  However, the following problems can be considered in the conventional technology. In the system that suppresses transfer defects by changing the transfer current in response to environmental fluctuations, when the resistance value of the transfer roller increases due to environmental fluctuations, abnormal images due to discharge near the exit and entrance of the nip are suppressed. In order to achieve this, since it is necessary to set the transfer current low, there is a problem in that a sufficient transfer electric field cannot be formed at the nip portion and transfer failure occurs.

  In addition, the method of replacing the transfer roller according to the environment requires a plurality of transfer rollers and requires a mechanism for replacing the transfer rollers, which complicates the configuration of the transfer unit and increases costs. Is a problem.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can eliminate such drawbacks of the prior art and effectively suppress image quality defects due to fluctuations in the resistance value of a transfer roller.

In order to achieve the above object, a first means of the present invention includes a belt-like image carrier, a primary transfer roller that contacts the belt-like image carrier and rotates in the same direction as the belt-like image carrier, and the belt An image forming apparatus including a photosensitive drum provided in a position facing the primary transfer roller with the image carrier interposed therebetween and in contact with the belt image carrier;
Detection means for measuring the electrical resistance of the primary transfer roller is provided, and based on the electrical resistance of the primary transfer roller measured by the detection means, the electrical resistance value of the primary transfer roller is always constant. A nip width formed by the primary transfer roller and the photosensitive drum is adjusted.

  The second means of the present invention has a mechanism for receiving the shaft of the primary transfer roller by a cam as a mechanism for changing the nip width in the first means, and the nip width by rotating the cam. It is characterized by changing.

  According to a third means of the present invention, in the first means, a measuring means for measuring the temperature and humidity in the image forming apparatus is provided, and the primary transfer is performed based on the temperature and humidity measured by the measuring means. The nip width formed by the roller and the photosensitive drum is changed.

According to a fourth aspect of the present invention, there is provided a belt-like image carrier, a secondary transfer roller that contacts the belt-like image carrier and rotates in the same direction as the belt-like image carrier, and sandwiches the belt-like image carrier. In the image forming apparatus provided with a secondary facing roller that is provided at a position facing the secondary transfer roller and is in contact with the belt-like image carrier,
A detecting means for measuring the electric resistance of the secondary transfer roller is provided, and based on the electric resistance of the secondary transfer roller measured by the detecting means, the electric resistance value of the secondary transfer roller is always constant. A nip width formed by the secondary transfer roller and the secondary opposing roller is adjusted.

  According to a fifth means of the present invention, in the fourth means, as the mechanism for changing the nip width, there is a mechanism for receiving the shaft of the secondary transfer roller by a cam, and the nip width is obtained by rotating the cam. It is characterized by changing.

  According to a sixth means of the present invention, in the fourth means, a measuring means for measuring the temperature and humidity in the image forming apparatus is provided, and the secondary transfer is performed based on the temperature and humidity measured by the measuring means. The nip width formed by the roller and the secondary opposing roller is changed.

  The present invention is configured as described above, and can provide an image forming apparatus capable of effectively suppressing image quality defects due to fluctuations in the resistance value of the transfer roller.

  Examples of the present invention are shown below.

  Hereinafter, an embodiment in which the present invention is applied to a color copying machine as an image forming apparatus will be described. FIG. 2 is a schematic configuration diagram of the entire color copying machine according to the present invention. First, the configuration and operation of an image forming unit and a transfer unit, which are main parts of a color copying machine, will be described with reference to FIG.

  The image forming unit and the primary transfer unit include chargers 10a to 10d, exposure units 11a to 11d, development units 12a to 12d, static eliminators 13a to 13d, cleaners 14a to 14d, photoconductors 15a to 15d, and primary transfer roller 16a. The intermediate transfer belt 100 is a belt-like image carrier.

  The photoreceptors 15a to 15d rotate in the illustrated direction. The intermediate transfer belt 100 is stretched by rollers 30 and 31 and is in contact with the photoreceptors 15a to 15d. Each of the image forming units is disposed around the photoconductors 15a to 15d with respect to the rotation direction of the photoconductor 15 from the point of contact with the intermediate transfer belt 100, and the static eliminators 13a to 13d, the cleaners 14a to 14d, and the chargers 10a to 10d. The exposure units 11a to 11d and the development units 12a to 12d are arranged in this order. The primary transfer rollers 16a to 16d are arranged to be pressed from the back side of the region where the photoconductors 15a to 15d are in contact with the intermediate transfer belt 100. In this embodiment, the roller for driving the belt is the roller 30, and the intermediate transfer belt 100 is moved in the direction of the arrow by the roller 30.

  Next, an image forming method and a primary transfer method will be described. The photoreceptor 15 is charged by the charger 11. Thereafter, an electrostatic latent image is generated on the charged photosensitive member 15 by irradiating a laser beam from the exposure device 11 based on image data from the scanner and the PC. Thereafter, the toner charged by the developing device 12 is adhered onto the photoreceptor 15 to develop the electrostatic latent image. The toner image formed on the photoreceptor 15 is transferred onto the intermediate transfer belt 100 by applying a transfer electric field with a current or voltage controlled by a constant current or a constant voltage to the primary transfer roller 16.

  After the toner image is transferred onto the intermediate transfer belt 100, the residual charge remaining on the photoconductor 15 is removed by the static eliminator 13, and the toner remaining on the photoconductor 15 is removed by the cleaner 14. Repeat the back process.

  In the embodiment of FIG. 2, an image forming unit is arranged for each of the four colors of cyan, magenta, yellow, and black, and the toner image formed on the photoreceptor 15a is subjected to primary transfer onto the intermediate transfer belt 100. After that, the intermediate transfer belt 100 moves to the photoconductor 15b and transfers the toner image formed by the photoconductor 15b onto the toner image transferred by the photoconductor 10a. Thereafter, the photoconductors 15c and 15d and the toner image are sequentially superposed and transferred.

  The toner image transferred onto the intermediate transfer belt 100 is transferred by the registration rollers 22 and 23 at the secondary transfer portion formed by the secondary opposing roller 103 and the secondary transfer roller 102 that hold the intermediate transfer belt 100. Transferred to the material 104.

  In the secondary transfer unit, a current is applied to the secondary transfer roller 102, and the transfer current flows into the secondary facing roller 103, whereby the toner on the intermediate transfer belt 100 is transferred to the transfer material 104. Can do.

  However, the resistance value of the primary transfer roller 16 greatly fluctuates due to environmental fluctuations and deterioration of energization over time. Due to the fluctuation of the electric resistance value, the voltage value at the transfer point largely fluctuates, and there is a problem that an appropriate transfer current cannot be applied to the toner, resulting in a transfer failure.

  Therefore, in this embodiment, the electric resistance of the primary transfer roller 16 is detected by applying a constant current to the primary transfer portion. In the present embodiment, the detection of the electric resistance is not shown, but is assumed to be measured by a voltmeter. The electric resistance R is given by R = Rv × d / (m × L) where the width L of the transfer roller, the thickness d of the rubber layer of the transfer roller, and the nip width are m. Here, Rv is the volume resistivity of the transfer roller. From the above equation, it can be seen that the resistance value of the transfer roller is inversely proportional to the nip width.

  In this embodiment, as shown in FIG. 1, the primary transfer is performed so that the electrical resistance becomes constant after the electrical resistance of the primary transfer roller 16 is detected by applying a constant current to the primary transfer portion. A mechanism for changing the nip width of the primary transfer portion by receiving the shaft of the roller 16 by the cam 17 is provided.

  When the detected electrical resistance value is lower than the target electrical resistance value, the cam 17 receiving the shaft of the primary transfer roller 16 is rotated to reduce the nip width L and make the electrical resistance value the same as the target value. To be. Conversely, when the detected electrical resistance value is higher than the target electrical resistance value, the nip width L is increased by rotating the cam 17 so that the electrical resistance value becomes the same as the target value. As a result, transfer can be performed with a constant transfer bias under any conditions, and transfer defects can be suppressed.

  The timing for detecting the electrical resistance is performed immediately before adjusting the image density. Since the image density is adjusted with respect to the image transferred onto the intermediate transfer belt 100, the image density on the intermediate transfer belt 100 is not stable when an appropriate primary transfer bias is not applied. For this reason, by adjusting the electrical resistance and adjusting the nip width based on the detection result before adjusting the image density, the image density can always be adjusted under optimum transfer conditions.

  In this embodiment, the configuration and operation of the image forming section and the transfer section, which are the main parts of the color copying machine described with reference to FIG.

  The resistance value of the secondary transfer roller 102 greatly fluctuates due to environmental fluctuation and deterioration of energization over time. Due to the fluctuation of the electric resistance value, the voltage value at the transfer point largely fluctuates, and there is a problem that an appropriate transfer current cannot be applied to the toner, resulting in a transfer failure.

  Therefore, in this embodiment, the electric resistance of the secondary transfer roller 102 is detected by applying a constant current to the secondary transfer portion. In the present embodiment, the detection of the electric resistance is not shown, but is assumed to be measured by a voltmeter. The electric resistance R is given by R = Rv × d / (m × L) where the width L of the transfer roller, the thickness d of the rubber layer of the transfer roller, and the nip width are m. Here, Rv is the volume resistivity of the transfer roller. From the above equation, it can be seen that the resistance value of the transfer roller is inversely proportional to the nip width.

  In this embodiment, as shown in FIG. 3, the secondary transfer roller is configured so that the electrical resistance becomes constant after the electrical resistance of the secondary transfer roller 102 is detected by applying a constant current to the secondary transfer portion. A mechanism for changing the nip width of the secondary transfer portion by receiving the shaft 102 by the cam 18 is provided.

  If the detected electrical resistance value is lower than the target electrical resistance value, the cam 18 receiving the shaft of the secondary transfer roller 102 is rotated to reduce the nip width and make the electrical resistance value the same as the target value. To be. Conversely, when the detected electrical resistance value is higher than the target electrical resistance value, the cam 18 is rotated to narrow the nip width so that the electrical resistance value becomes the same as the target value. As a result, transfer can be performed using a constant transfer bias under any conditions, and transfer defects can be suppressed.

  The timing for detecting the electrical resistance is performed immediately before adjusting the same image density as the timing for detecting the electrical resistance of the primary transfer in the first embodiment. Taking time just to detect the electrical resistance of the secondary transfer portion during printing reduces the productivity of printing, and also detects the electrical resistance of the primary transfer and the nip width in Example 1. Since the adjustment can be performed independently, it is performed immediately before adjusting the image density from the viewpoint of productivity.

  By using this method, the electric resistance of the primary transfer roller 16 is detected by applying a constant current to the primary transfer portion. When the detected electrical resistance value is lower than the target electrical resistance value, the electrical resistance value is reduced by rotating the cam receiving the shaft of the primary transfer roller to reduce the nip width. To be the same as the target value. Conversely, if the detected electrical resistance value is higher than the target electrical resistance value, the electrical resistance value is made equal to the target value by rotating the cam and reducing the nip width. Accordingly, transfer can be performed using a constant transfer bias under any conditions, and transfer defects can be suppressed.

  By using this method, the electric resistance of the secondary transfer roller 102 is detected by applying a constant current to the secondary transfer portion. When the detected electric resistance value is lower than the target electric resistance value, the electric resistance value is reduced by rotating the cam receiving the shaft of the secondary transfer roller to reduce the nip width. To be the same as the target value. Conversely, if the detected electrical resistance value is higher than the target electrical resistance value, the electrical resistance value is made equal to the target value by rotating the cam and reducing the nip width. Accordingly, transfer can be performed using a constant transfer bias under any conditions, and transfer defects can be suppressed.

It is an enlarged view of the primary transfer part which concerns on Example 1 of this invention. 1 is an overall schematic view of a color copying machine according to an embodiment of the present invention. It is an enlarged view of the secondary transfer part which concerns on Example 2 of this invention.

Explanation of symbols

10a to 10d: Y, M, C, and K charging devices 11a to 11d: Y, M, C, and K color exposure devices 12a to 12d: Y, M, C, and K developing devices 13a to 13d: Y , M, C, K color neutralizers 14a-14d: Y, M, C, K color cleaners 15a-15d: Y, M, C, K photoconductors 16a-16d: Y, M, C, K Primary transfer roller for each color 17: Primary transfer roller movable cam 18: Secondary transfer roller movable cam 20, 21: Fixing roller 22, 23: Registration roller 24: Static elimination brush 30, 31: Intermediate transfer belt stretching roller 100: Intermediate transfer belt 102: Secondary transfer roller 103: Secondary counter roller 104: Transfer material 105: Toner image

Claims (6)

A belt-like image carrier, a primary transfer roller that contacts the belt-like image carrier and rotates in the same direction as the belt-like image carrier, and faces the primary transfer roller across the belt-like image carrier. In an image forming apparatus provided with a photosensitive drum provided at a position and in contact with the belt-shaped image carrier,
Detection means for measuring the electrical resistance of the primary transfer roller is provided, and based on the electrical resistance of the primary transfer roller measured by the detection means, the electrical resistance value of the primary transfer roller is always constant. An image forming apparatus characterized by adjusting a nip width formed by the primary transfer roller and the photosensitive drum.   The image forming apparatus according to claim 1, wherein the mechanism for changing the nip width includes a mechanism for receiving a shaft of the primary transfer roller by a cam, and changing the nip width by rotating the cam. An image forming apparatus.   2. The image forming apparatus according to claim 1, further comprising a measuring unit for measuring temperature and humidity in the image forming apparatus, and based on the temperature and humidity measured by the measuring unit, the primary transfer roller and the photoconductor. An image forming apparatus characterized by changing a nip width formed by a drum. A belt-like image carrier, a secondary transfer roller that contacts the belt-like image carrier and rotates in the same direction as the belt-like image carrier, and faces the secondary transfer roller across the belt-like image carrier In an image forming apparatus provided with a secondary opposing roller provided at a position and in contact with the belt-like image carrier,
A detecting means for measuring the electric resistance of the secondary transfer roller is provided, and based on the electric resistance of the secondary transfer roller measured by the detecting means, the electric resistance value of the secondary transfer roller is always constant. An image forming apparatus characterized by adjusting a nip width formed by the secondary transfer roller and the secondary opposing roller.   5. The image forming apparatus according to claim 4, wherein the nip width is changed by a mechanism that receives a shaft of the secondary transfer roller by a cam, and the nip width is changed by rotating the cam. An image forming apparatus.   5. The image forming apparatus according to claim 4, further comprising a measuring unit that measures temperature and humidity in the image forming apparatus, and based on the temperature and humidity measured by the measuring unit, the secondary transfer roller and the secondary An image forming apparatus characterized by changing a nip width formed by a counter roller.

Images