JP2006003625A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which excess carrier or developer replenishment is prevented by replacing a carrier or developer on the basis of information on the deteriorated state of the developer, accordingly a charge amount of a toner is made stable and proper and an image having good graininess and no surface stain over a prolonged period of time can be obtained without causing toner scattering. <P>SOLUTION: In the image forming apparatus having a developing case 53 for converting an electrostatic latent image on an image bearing member 4 to a toner image with a developing sleeve 54 which holds a magnet roller fixed therein and rotates, and a device for replenishing a carrier or developer to the developing case 53, a toner scattering detection sensor 71 is disposed near the developing device and the carrier or developer is properly replenished on the basis of a signal from the toner scattering detection sensor 71. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing method using a two-component developer comprising a magnetic carrier and a nonmagnetic toner. Furthermore, the present invention relates to an image forming apparatus such as a copying machine or a printer that forms an image by an electrophotographic method using this developing method.

Generally, a toner image is formed by applying a two-component developer composed of toner and carrier to an electrostatic latent image formed electrostatically on the surface of an image carrier, and then the toner is applied to a transfer material such as paper. In an image forming apparatus that repeats the image transfer process, it is important that the toner always maintains a stable charge amount in order to obtain a high-quality image stably over a long period of time.
However, when a two-component developer is used, the repetition is received from a developer regulating member that is generally a plate-like blade provided to optimize the amount of developer on the developer carrier. Due to the stress, the external additive on the toner surface is buried in the toner or detached from the surface, or the toner component is fixed (spent) on the carrier surface.

  Among the above defects, when the external additive of the toner is buried or detached, and the external additive is not present on the toner surface, the non-electrostatic adhesion between the toner and the carrier increases, There is a problem that the developing ability as a developer lacks stability because it adheres firmly to the carrier. In addition, since the adhesion force between the toner and the carrier increases, the replacement with the newly supplied toner hardly occurs, and the supplied toner cannot contact the carrier or is weakly charged by contact between the toners. It will be transported to the development area while maintaining the reverse charge. The weakly charged and reversely charged toner generated in this manner is not preferable because it easily separates from the carrier and causes abnormal images such as image background stains and in-machine contamination due to toner scattering. Further, when transferring from a photosensitive member or an intermediate transfer material to paper, the transfer rate is lowered, which leads to a decrease in image graininess and a non-uniform solid image.

In particular, when an image having a low image area ratio is formed repeatedly, the developer must repeatedly pass through the developer regulating member, so that the additive on the toner surface is likely to be buried inside the toner. There is a problem that defects are likely to occur.
In addition, if the toner component adheres to the surface of the carrier during the repeated stress as described above, the charge imparting ability of the carrier to the toner is reduced. It is difficult to obtain a sufficient amount of charge, and as a result, it causes image background contamination and toner scattering.

  In order to solve the above problems, for example, in the inventions described in Patent Documents 1 and 2, the carrier is replenished together with the toner to be replenished during repeated image formation, and the developer in the developing container is constant. A technique is described in which the developer in the developing container is gradually replaced by overflowing when the amount is exceeded, and the charging ability in the developing container is kept substantially constant.

JP 2001-042624 A Japanese Patent No. 0937445

However, in the inventions described in Patent Documents 1 and 2, since the carrier is continuously replenished as needed, not only the deteriorated carrier but also the carrier that sufficiently retains the ability to impart charge to the toner is discharged. There is a problem. In addition, when images are formed repeatedly with a low image area, the supply of carriers becomes insufficient, and it is difficult to suppress the occurrence of defects due to the deterioration of the developer. Further, when an image with a large image area is continuously output, the carrier is excessively replenished, so that there is a problem that the cost for image formation increases significantly.
In addition, since the degree of deterioration of the developer varies depending on the usage conditions such as the environment, it is possible to improve the image quality of all the machines in the market for a long time simply by continuing to replenish the developer quantitatively as in the carrier replenishment method described above. It is difficult to make it possible to get across.

  Therefore, in view of the above circumstances, the present invention causes an increase in cost by preventing excessive carrier or developer replenishment by replacing the carrier or developer based on information on the deterioration state of the developer. However, the charge amount of the toner used for development is kept stable and uniform over a long period of time, thereby preventing the occurrence of abnormal images, and stabilizing and optimizing the toner charge amount even during repeated image formation. It is an object of the present invention to provide an image forming apparatus which can obtain an image having good graininess and no background stain for a long period of time without causing toner scattering.

The features of the present invention, which is a means for solving the above problems, are listed below.
1. The image forming apparatus of the present invention includes an image carrier that is rotationally driven, a charging unit that charges the surface of the carrier to a desired potential, an exposure unit that forms an electrostatic latent image corresponding to an image on the image carrier, A two-component developer composed of a non-magnetic toner and a magnetic carrier is built in, and a toner image is visualized as an electrostatic latent image on the image carrier by a developer carrier that is rotatably held with a magnet roller fixed inside. In an image forming apparatus having a developing device and a device for supplying a carrier or developer to the developing device,
A toner scattering detection sensor is provided in the vicinity of the developing device, and a carrier or developer is appropriately replenished based on a signal from the detection sensor.
2. The image forming apparatus according to the present invention includes: The image forming apparatus according to claim 1, wherein the toner scattering detection sensor is an optical sensor including a light emitting unit that emits light and a light receiving unit that receives reflected light and converts it into an electrical signal. .
3. The image forming apparatus according to the present invention includes: Or 2. In the image forming apparatus, the toner scattering detection sensor is installed in the vicinity of the developing unit formed between the developer carrier and the image carrier and downstream in the rotation direction of the developer carrier. Features.

  Therefore, by the means for solving the above, the image forming apparatus of the present invention can be used for development without causing an increase in cost by replacing the carrier or the developer based on the information on the deterioration state of the developer. The amount of toner charged is kept stable and uniform over a long period of time, thereby preventing the occurrence of abnormal images. Furthermore, even in repeated image formation, the image has good graininess and no background stains over a long period of time. Can be obtained.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows an electrophotographic full-color printer as an image forming apparatus according to the present invention. In FIG. 1, a plurality of photoconductor units 2Y, 2M, 2C, and 2K as image carrier units are detachably attached to the apparatus body 1 in a box-shaped apparatus body 1. A transfer belt 3 as a recording material carrier is disposed obliquely in the diagonal direction of the apparatus main body 1 at a substantially central portion in the apparatus main body 1. The transfer belt 3 is provided so as to be rotatively driven in a direction indicated by an arrow A, spanned by a plurality of rollers to which the rotational driving force is transmitted.
The photoreceptor units 2Y, 2M, 2C, and 2K have drum-like photoreceptors 4Y, 4M, 4C, and 4K as image carriers, and the belts are arranged so that the surface of each photoreceptor is in contact with the transfer belt 3. It is arrange | positioned above. The arrangement of the photoreceptor units 2Y, 2M, 2C, and 2K is in the order of 4Y, 4M, 4C, and 4K so that the photoreceptor unit 2Y is located on the sheet feeding side and the photoreceptor unit 2K is located on the fixing device 9 side. Yes. As the photoconductors 4Y, 4M, 4C, and 4K, belt-like photoconductors or the like may be used.

  The developing devices 5Y, 5M, 5C, and 5K serving as the developer supply means are disposed to face the photoreceptors 4Y, 4M, 4C, and 4K, respectively. The developing devices 5Y, 5M, 5C, and 5K are a two-component developer having a plurality of colors, for example, yellow (hereinafter referred to as Y) and a carrier, a two-component developer having magenta (hereinafter referred to as M) and a carrier, and cyan (hereinafter referred to as C). ) And a two-component developer having a carrier, and black (hereinafter referred to as K) and a two-component developer having a carrier are supplied to the electrostatic latent images on the photoreceptors 4Y, 4M, 4C, and 4K, respectively. Is developed.

  A writing device 6 as an exposure unit is disposed above the photoreceptor units 2Y, 2M, 2C, and 2K, and a duplex unit 7 is disposed below the photoreceptor units 2Y, 2M, 2C, and 2K. Below the duplex unit 7, paper feed cassettes 13 and 14 that can store transfer materials P of different sizes are disposed. A reversing unit 8 is disposed on the left side of the apparatus main body 1, and a manual feed tray 15 is provided on the right side of the apparatus main body 1 so as to be opened and closed in the direction of arrow B. A fixing device 9 is disposed between the transfer belt 3 and the reversing unit 8. A reversal conveyance path 10 is branched and formed on the downstream side of the fixing device 9 in the transfer material conveyance direction, and the sheet-like transfer material P is discharged at the upper portion of the apparatus by a paper discharge roller 11 disposed in the reverse conveyance path 10. Guide to the paper tray 12.

The photoreceptor units 2Y, 2M, 2C, and 2K are units for forming toner images of Y, M, C, and K colors on the photoreceptors 4Y, 4M, 4C, and 4K, and are disposed in the apparatus main body 1. The configuration is the same except for the location. For example, the photoconductor unit 2Y has a unit configuration in which a photoconductor 4Y, a charging roller as a charging unit that contacts the photoconductor 4Y, and a cleaning device that cleans the surface of the photoconductor 4Y with a brush roller and a cleaning blade are integrated. And is detachably attached to the apparatus main body 1. A description of the configuration of the photoreceptor units 2M, 2C, and 2K is omitted.
In the writing device 6, two rotary polygon mirrors (not shown) arranged on the same axis are rotated by a polygon motor. The rotating polygon mirror includes a laser beam for Y modulated by Y image data from laser diodes as two laser light sources (not shown), a laser beam for M modulated by M image data, and the other two laser light sources. The C laser light modulated by the C image data from the laser diode and the K laser light modulated by the K image data are distributed to the left and right and reflected.
The Y laser light, the M laser light, the C laser light, and the K laser light from the rotary polygon mirror each pass through two layers of fθ lenses, and the laser light from the fθ lenses is reflected by the mirror and is long. After passing through the scale WTL, the photoconductor of the photoconductor unit is irradiated through a mirror provided separately from the mirror.

As shown in FIG. 1, the duplex unit 7 includes a pair of transport guides 41 and 42 and a plurality of transport roller pairs 43. In the double-sided image forming mode in which images are formed on both sides of the transfer material P, the double-sided unit 7 is conveyed to the reverse conveying path 44 of the reversing unit 8 after being formed on one side, and is then transferred back and back. The transfer material P to be reversed is received, and is conveyed again to a transfer portion formed between the photoconductors 4Y, 4M, 4C, and 4K and the transfer belt 3.
The reversing unit 8 includes a plurality of conveying rollers and a plurality of conveying guide plates. In the double-sided image forming mode, the reversing unit 8 reverses the front and back and sends the transfer material P to the double-sided unit 7. It has a function of discharging the formed transfer material P to the outside of the apparatus in the same direction, and a function of discharging the transfer material P after the image formation to the outside of the apparatus with its front and back reversed. In the paper feed unit in which the paper feed cassettes 13 and 14 are arranged, separation paper feed units 45 and 46 for separating and feeding the transfer material P on the paper feed cassettes 13 and 14 one by one are provided. Yes. Inside the transfer belt 3, transfer brushes 47, 48, 49, and 50 as transfer means are provided so as to face the photoreceptors 4Y, 4M, 4C, and 4K.

In this embodiment, when image formation is instructed by an operation unit (not shown), the photoconductors 4Y, 4M, 4C, and 4K are rotated by a drive source (not shown) to rotate clockwise. The charging rollers of the photoconductor units 2Y, 2M, 2C, and 2K are charged with a charging bias from a power source (not shown) to uniformly charge the photoconductors 4Y, 4M, 4C, and 4K, respectively. The photoreceptors 4Y, 4M, 4C, and 4K are each uniformly charged by a charging roller and then exposed to laser light modulated by image data of each color of Y, M, C, and K by the writing device 6, An electrostatic latent image is formed on each surface. The electrostatic latent images on the photoconductors 4Y, 4M, 4C, and 4K are developed by developing devices 5Y, 5M, 5C, and 5K to become toner images of Y, M, C, and K colors.
One transfer material P is separated from the selected one of the paper feed cassettes 13 and 14, and is supplied to a registration roller 51 disposed on the paper feed unit side of the photoreceptor unit 2Y. Paper. In this embodiment, a manual feed tray 15 is disposed on the right side of the apparatus main body 1, and a transfer material can be fed from the manual feed tray 15 to the registration roller 51. The registration roller 51 sends each transfer material onto the transfer belt 3 at a timing when the leading edge of the transfer material coincides with the toner image on the photoreceptors 4Y, 4M, 4C, and 4K. The transferred transfer material P is electrostatically attracted to the transfer belt 3 charged by the paper suction roller 52 and conveyed to each transfer unit.
When the transferred transfer material P passes through the transfer portions in order, the toner images of the respective colors Y, M, C, and K on the photoreceptors 4Y, 4M, 4C, and 4K are sequentially transferred by the transfer brushes 47 to 50. By superimposing and transferring, a full-color toner image with four colors superimposed is formed. The transfer material P on which the full-color toner image is formed is fixed to the full-color toner image by the fixing device 9 and then reversely discharged to the discharge tray 12 through the discharge path corresponding to the designated mode. The toner goes straight from the fixing device 9 and passes through the reversing unit 8 and is discharged straight.

In the image forming apparatus, when the double-sided image forming mode is selected, the transfer material P has a reversal conveyance path 44 in the reversing unit 8 after the toner image is formed on one side and the toner image is fixed by the fixing device 9. Then, after being switched back, the sheet is transported to the duplex unit 7, and is fed again from there, and an image is formed on the back surface and discharged in the same manner as in the front surface image formation.
The above image forming operation is an operation when the full color mode for superimposing four colors is selected by an operation unit (not shown). However, when the full color mode for superimposing three colors is selected by the operation unit, a K toner image is formed. Is omitted, and a full color image is formed on the transfer material by superimposing Y, M, and C three color toner images. When the monochrome image forming mode is selected on the operation unit, only the K toner image is formed and a monochrome image is formed on the transfer material.

Since the developing devices 5Y, 5M, 5C, and 5K have the same configuration except that only the toner color is different, the configuration of the developing device 5Y will be described as a representative. FIG. 2 is a diagram of the developing device 5Y as viewed from the developer conveyance direction side.
In FIG. 2, the developing device 5 </ b> Y opposes the photoconductor 4 </ b> Y through a developing case 53 containing a two-component developer having Y toner and a carrier and an opening of the developing case 53 disposed in the developing case 53. A developing sleeve 54 as a developer carrying member arranged in such a manner, and multiple screw members 55 and 56 as stirring members which are arranged in the developing case 53 and convey the developer while stirring. .
The developing case 53 is divided by a partition wall 57 into a first space portion 65 located on the developer supply side to the photoreceptor 4Y and a second space portion 64 side receiving supply of replenishment toner from the supply port 62. Has been. The screw member 56 is disposed in the space portion 65, and the screw member 55 is disposed in the space portion 64, and is rotatably supported by a bearing member (not shown) provided in the developing case 53. Of course, the developing sleeve 54 is also rotatably supported by the developing case 53 via a bearing member (not shown). The developing sleeve 54 rotates when a rotational driving force is transmitted from a driving unit (not shown).

As shown in FIG. 2, the screw members 55 and 56 extend in the width direction of the transfer material P and are arranged in parallel to each other. At one end of the screw members 55 and 56, gears 66 and 68 having the same number of teeth are mounted so as to mesh with each other. In this embodiment, the rotational driving force from the drive motor 69 is transmitted to the gear 66, so that the screw members 55 and 56 are rotationally driven in directions opposite to each other. In FIG. 2, the screw member 55 rotates in a direction to convey the developer from left to right, and the screw member 56 rotates in a direction to convey the developer from right to left.
Between the one end of the partition wall 57 and the inner side surface 53 a of the developing case 53, a transfer portion 59 for sending the developer from the space portion 65 to the space portion 64 is formed, and the other end of the partition wall 57 and the inner side surface of the developing case 53 are formed. Between the space portions 53b, transfer portions 59 for feeding the developer from the space portion 64 to the space portion 65 are formed. The developing case 53 is provided with a T sensor (not shown) as toner concentration detecting means for detecting and outputting the toner concentration in the developer.

The operation of the developing device 5Y having such a configuration will be described with respect to developer conveyance. The two-component developer in the developing case 53 is conveyed from the right to the left in FIG. 2 while being agitated when the screw members 55 and 56 rotate at a constant speed, and is a space in which the conveying screw 56 is disposed from the transfer portion 59. Sent to part 65. The two-component developer sent from the transfer section 59 to the space section 65 is stirred by the transport screw 56 and simultaneously transported to the right in FIG. 2 and then sent from the transfer section 58 to the space section 64 side, and again. While being agitated by the conveying screw 55, it is conveyed leftward in FIG. By transporting the developer while stirring in this way, the Y toner and the carrier are frictionally charged by stirring while the developer circulates in the developing device 5Y.
The conveying screw 56 supplies a part of the developer to the developing sleeve 54, and the developing sleeve 54 carries the developer magnetically and conveys it. The electrostatic latent image on the photoreceptor 4Y is developed with Y toner on the developing sleeve 54 to become a Y toner image.
When the toner concentration (ratio of toner and carrier) of the developer in the developing case 53 reaches a predetermined value, Y toner is supplied from the toner supply port 62 to the space 64 in the developing case 53. The Y toner is mixed with the developer by stirring with the screw member 55.

  FIG. 3 is a cross-sectional view of the developing case 53. The developer accommodated inside is agitated and conveyed by the screw members 55 and 56 in a state adjusted to an appropriate toner concentration. The developer is pumped up by the developing sleeve 54 on the surface of the developer carrying member holding a fixed magnet inside, and the carrier holding the toner around after being regulated to an appropriate amount of developer forms a magnetic brush on the sleeve. The toner image is formed by contacting the image carrier 4 and attaching the toner to the latent image. Here, a toner scattering detection sensor 71 is installed below the developing area between the developing sleeve 54 and the image carrier 4 and on the downstream side in the rotation direction of the developing sleeve. The toner scattering detection sensor 71 is preferably in the vicinity of the developing device, and further preferably below the developing device and downstream in the rotational direction of the developing sleeve 54, but may be above the developing device or upstream in the rotational direction of the sleeve. Alternatively, the toner scattering may be detected by the toner scattering detection sensor 71 located at a remote position by sucking and conveying the air in the vicinity of the developing device.

  FIG. 4 is a schematic diagram of the toner scattering detection sensor 71. The toner scattering detection sensor 71 includes a light emitting unit 72, a light receiving unit 73, and a lens 74. When the toner scatters, the toner splattered from the developing device passes between the light emitting unit 72 and the light receiving unit 73. At this time, the light emitted from the light emitting unit 72 is reflected by the toner, and the reflected light is read by the light receiving unit 73 and output in the form converted into an electrical signal.

FIG. 5 shows detection results of toner scattering by the toner scattering detection sensor 71. This is the relationship between the toner scattering density and the sensor output when developers having different levels of toner scattering are used and installed in the developing device. According to this result, it can be seen that the toner scattering amount of the developing device can be accurately detected from the output value of the toner scattering detection sensor.
Here, the toner scattering is a phenomenon in which the toner having a low charge amount or charged in the reverse polarity is detached from the carrier in the magnetic brush that is raised due to the centrifugal force generated by the rotation of the developing sleeve 54 and scattered outside the developing device. . FIG. 7 shows the relationship of toner scattering density to the amount of weakly charged and reversely charged toner. As shown here, as the amount of weakly charged and reversely charged toner in the developer increases, the toner scattering worsens.
Generally, the weakly charged / reversely charged toner in the developer tends to increase over time as the developer continues to be stressed during repeated image formation. The main causes are that the coat layer on the carrier surface is scraped, and that the toner component adheres to the carrier surface. Therefore, deterioration of toner scattering with time can be considered as deterioration of the carrier of the developer.
Therefore, in this embodiment, a new carrier is replenished according to the amount of scattered toner, and the carrier in which the charging ability is lowered is discharged so that the carrier in the developing device can be always replaced. The carrier may be replenished alone or in a state where the carrier and toner are mixed.

FIG. 6 is a flowchart showing toner scattering detection, carrier or developer supply operation in the configuration according to the present invention. First, when an image formation is instructed, the developer carrier starts to be driven simultaneously with the formation of the latent image on the image carrier. At that time, the toner scattering detection sensor is activated to output the toner scattering state, and when the output value exceeds the reference value, carrier supply and discharge are started. When the output value is lower than the reference voltage, no carrier supply is performed. To prepare for the next image formation. Further, it is more effective if the carrier replenishment amount is made variable by the output of the toner scattering detection sensor.
By passing through the above steps, even when images are repeatedly formed over a long period of time, by continuing to be stressed, the carrier whose ability to impart charge to the toner has been reduced is discharged out of the developing device, and a new carrier is replenished. Thus, it is possible to prevent the carrier deterioration in the developing device from progressing. In addition, it is possible to prevent the occurrence of weakly charged or reversely charged toner and to always provide an appropriate charge amount to the toner, so that image formation can be performed over a long period of time without causing problems such as toner scattering and background contamination. It becomes possible to repeat. In addition, toner scattering is detected, the deterioration of the developer is grasped, and the carrier or developer is replenished. Become.

1 shows an electrophotographic full-color printer as an image forming apparatus according to the present invention. FIG. 6 is a diagram of the developing device 5Y viewed from the developer conveyance direction side. 4 is a cross-sectional view of the developing device 53. FIG. 3 is a schematic diagram of a toner scattering detection sensor 71. FIG. This is a detection result of toner scattering by the toner scattering detection sensor 71. 4 is a flowchart showing toner scattering detection, carrier or developer supply operation in the configuration according to the present invention. This shows the relationship of toner scattering density to the amount of weakly charged and reversely charged toner.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Apparatus main body 2Y, 2M, 2C, 2K Photoconductor unit 3 Transfer belt 4 Image carrier 4Y, 4M, 4C, 4K Photoconductor 5Y, 5M, 5C, 5K Developing device 6 Writing device 7 Duplex unit 8 Reversing unit 9 Fixing device DESCRIPTION OF SYMBOLS 10 Reverse conveyance path 11 Paper discharge roller 12 Paper discharge tray 13, 14 Paper feed cassette
15 Manual feed tray 41, 42 Conveying guide 43 Conveying roller pair 44 Reverse conveying path 45, 46 Separating paper feeding unit 47, 48, 49, 50 Transfer brush 51 Registration roller 52 Paper adsorbing roller 53 Developing case 53a, 53b Inner side surface 54 Developing sleeve 55, 56 Screw member 57 Partition wall 58, 59 Delivery portion 62 Toner supply port 64, 65 Space portion 66, 68 Gear 69 Drive motor 71 Toner scattering detection sensor 72 Light emitting portion 73 Light receiving portion 74 Lens P Transfer material

Claims (3)

An image carrier that is driven to rotate;
Charging means for charging the surface of the carrier to a desired potential;
Exposure means for forming an electrostatic latent image corresponding to the image on the image carrier;
A two-component developer composed of a non-magnetic toner and a magnetic carrier is built in, and a toner image is visualized as an electrostatic latent image on the image carrier by a developer carrier that is rotatably held with a magnet roller fixed inside. A developing device;
In an image forming apparatus having a device for supplying a carrier or developer to a developing device,
An image forming apparatus, wherein a toner scattering detection sensor is provided in the vicinity of the developing device, and a carrier or a developer is appropriately replenished based on a signal from the detection sensor. The image forming apparatus according to claim 1.
The toner scattering detection sensor is an optical sensor including a light emitting unit that emits light and a light receiving unit that receives reflected light and converts it into an electrical signal. The image forming apparatus according to claim 1,
The toner scattering detection sensor is installed in the vicinity of a developing unit formed between a developer carrier and an image carrier and downstream in the rotation direction of the developer carrier.

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