Image forming apparatus with a toner supply unit
阅读说明：本技术 图像形成设备 (Image forming apparatus with a toner supply unit ) 是由 富士良太 加藤正则 尾崎善史 于 2019-11-07 设计创作，主要内容包括：一种图像形成设备,包括：图像载体,在该图像载体中形成潜像；显影装置,该显影装置将色调剂从与所述图像载体相对的显影构件转移至所述潜像,并使所述潜像显影；显影电源,该显影电源在所述图像载体和所述显影构件之间施加显影电压；周期检测器,该周期检测器检测所述显影构件和所述图像载体在周向方向上的周期性信息；以及校正器,该校正器基于所述周期检测器检测到的所述周期性信息校正所述显影电压或所述潜像的曝光量。所述显影装置和所述显影电源中的至少一者被设定成使得所述色调剂的电荷向图像的实心区域中的所述潜像的供应率达到80％以上。(An image forming apparatus includes: an image carrier in which a latent image is formed; a developing device that transfers toner from a developing member opposed to the image carrier to the latent image and develops the latent image; a developing power supply that applies a developing voltage between the image carrier and the developing member; a period detector that detects periodic information of the developing member and the image carrier in a circumferential direction; and a corrector correcting the developing voltage or the exposure amount of the latent image based on the periodicity information detected by the period detector. At least one of the developing device and the developing power supply is set so that a supply rate of the charge of the toner to the latent image in a solid area of an image reaches 80% or more.)
1. An image forming apparatus, comprising:
an image carrier in which a latent image is formed;
a developing device that transfers toner from a developing member opposed to the image carrier to the latent image and develops the latent image;
a developing power supply that applies a developing voltage between the image carrier and the developing member;
a period detector that detects periodic information of the developing member and the image carrier in a circumferential direction; and
a corrector correcting the developing voltage or the exposure amount of the latent image based on the periodicity information detected by the period detector,
wherein at least one of the developing device and the developing power supply is set so that a supply rate of the charge of the toner to the latent image in a solid area of an image reaches 80% or more.
2. The image forming apparatus according to claim 1,
wherein at least one of the developing device and the developing power supply is set so that a supply rate of the charge of the toner to the latent image in the solid area reaches 90% or more.
3. The image forming apparatus according to claim 1 or 2,
wherein the developing voltage is a superimposed voltage in which an AC voltage is superimposed on a DC voltage, and
the amplitude Vpp of the AC voltage is set to 0.8kV or more and 2.2kV or less.
4. The image forming apparatus according to claim 3,
wherein the amplitude Vpp of the AC voltage is set to 1.0kV or more and 2.1kV or less.
5. The image forming apparatus according to any one of claims 1 to 4, further comprising:
a detector that detects a toner concentration in the developer in the developing device,
wherein the amount of the toner in the developer is increased in accordance with the toner concentration detected by the detector.
6. The image forming apparatus according to any one of claims 1 to 5,
wherein, in an area where the image carrier and the developing member are opposed to each other, a peripheral speed of the developing member is set to be faster than a peripheral speed of the image carrier.
7. The image forming apparatus according to claim 6,
wherein, in the area where the image carrier and the developing member are opposed to each other, a ratio of a peripheral speed of the developing member to a peripheral speed of the image carrier is in a range of 1.4 to 2.5.
Technical Field
The present disclosure relates to an image forming apparatus.
Background
Japanese unexamined patent application publication No. 2015-004875 discloses an image forming apparatus that detects information about a periodic change that occurs with a period of vibration of a developing sleeve and corrects a developing bias, thereby adjusting image quality.
Disclosure of Invention
In a conventional image forming apparatus, a gap between a roller-shaped developing member and an image carrier (e.g., a photoreceptor) (hereinafter, referred to as "DRS") is periodically changed due to vibration and eccentricity of the developing member and the image carrier, and periodic density unevenness (so-called banding) occurs at a position where the gap is large or small.
To cope with the periodic density unevenness, for example, the period of the gap between the developing member and the image carrier is detected, and the developing amount is corrected by adjusting the exposure amount (in other words, the potential difference between the developing member and the image carrier) on the basis of the period.
However, in the case of periodic density unevenness (so-called banding), the density difference between the high density region and the low density region changes depending on the area coverage. The higher the area coverage, the larger the concentration difference. Therefore, when the correction amount is controlled with the exposure amount that is constant in the axial direction of the image carrier, the effectiveness of the density correction is different for each area coverage because the density difference is changed according to the area coverage. Note that the area coverage refers to a value (%) indicating the amount of a toner used per unit area of an image formed on the photoreceptor.
An object of the present disclosure is to provide an image forming apparatus that reduces image density unevenness occurring in an axial direction of an image carrier, as compared with a case where a supply rate of charges of toner to a latent image in a solid area of an image is less than 80%.
Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments need not address the above advantages, and aspects of the non-limiting embodiments of the present disclosure may not address the above advantages.
According to a first aspect of the present disclosure, there is provided an image forming apparatus including: an image carrier in which a latent image is formed; a developing device that transfers toner from a developing member opposed to the image carrier to the latent image and develops the latent image; a developing power supply that applies a developing voltage between the image carrier and the developing member; a period detector that detects periodic information of the developing member and the image carrier in a circumferential direction; and a corrector correcting the developing voltage or the exposure amount of the latent image based on the periodicity information detected by the period detector. At least one of the developing device and the developing power supply is set so that a supply rate of the charge of the toner to the latent image in a solid area of an image reaches 80% or more.
A second aspect of the present disclosure provides the image forming apparatus according to the first aspect of the present disclosure, wherein at least one of the developing device and the developing power supply is set so that a supply rate of the charge of the toner to the latent image in the solid area reaches 90% or more.
A third aspect of the present disclosure provides the image forming apparatus according to the first or second aspect of the present disclosure, wherein the developing voltage is a superimposed voltage in which an AC voltage is superimposed on a DC voltage, and a magnitude Vpp of the AC voltage is set to 0.8kV or more and 2.2kV or less.
A fourth aspect of the present disclosure provides the image forming apparatus according to the third aspect of the present disclosure, wherein the amplitude Vpp of the AC voltage is set to 1.0kV or more and 2.1kV or less.
A fifth aspect of the present disclosure provides the image forming apparatus according to any one of the first to fourth aspects of the present disclosure, further comprising a detector that detects a toner concentration in the developer inside the developing device. The amount of the toner in the developer is increased according to the toner concentration detected by the detector.
A sixth aspect of the present disclosure provides the image forming apparatus according to any one of the first to fifth aspects of the present disclosure, wherein a peripheral speed of the developing member is set faster than a peripheral speed of the image carrier in an area where the image carrier and the developing member are opposed to each other.
A seventh aspect of the present disclosure provides the image forming apparatus according to the sixth aspect of the present disclosure, wherein a ratio of a peripheral speed of the developing member to a peripheral speed of the image carrier is in a range of 1.4 to 2.5 in an area where the image carrier and the developing member are opposed to each other.
According to the first aspect of the present invention, banding in the image that occurs in the axial direction of the image carrier is reduced as compared with the case where the supply rate of the charge of the toner to the latent image in the solid areas of the image is less than 80%.
According to the second aspect of the present disclosure, banding in the image that occurs in the axial direction of the image carrier is reduced as compared with the case where the supply rate of the charge of the toner to the latent image in the solid area of the image is less than 90%.
According to the third aspect of the present disclosure, banding in an image that occurs in the axial direction of the image carrier is reduced as compared with the case where the amplitude Vpp of the AC voltage is less than 0.8 kV. In addition, less energy is consumed than in the case where the amplitude Vpp of the AC voltage is higher than 2.2 kV.
According to the fourth aspect of the present disclosure, banding in an image that occurs in the axial direction of the image carrier is reduced as compared with the case where the amplitude Vpp of the AC voltage is less than 1.0 kV. In addition, less energy is consumed than in the case where the amplitude Vpp of the AC voltage is higher than 2.1 kV.
According to the fifth aspect of the present disclosure, banding in an image occurring in the axial direction of the image carrier is reduced as compared with the case where the toner amount is changed irrespective of the toner concentration in the developer.
According to the sixth aspect of the present disclosure, banding in an image occurring in the axial direction of the image carrier is reduced as compared with the case where the peripheral speed of the developing member is the same as the peripheral speed of the image carrier in the region where the image carrier and the developing member are opposed to each other.
According to the seventh aspect of the present disclosure, banding in an image occurring in the axial direction of the image carrier is reduced as compared with the case where the ratio of the peripheral speed of the developing member to the peripheral speed of the image carrier is less than 1.4 in the region where the image carrier and the developing member are opposed to each other. In addition, the dispersion of the toner from the developing area is less occurred as compared with the case where the ratio of the peripheral speed of the developing member to the peripheral speed of the image carrier is greater than 2.5 in the area where the image carrier and the developing member are opposed to each other.
Drawings
Exemplary embodiments of the present disclosure will be described in detail based on the following drawings, in which:
fig. 1 is a schematic configuration diagram showing an example of an image forming apparatus according to an exemplary embodiment;
FIG. 2 is a configuration diagram showing a monochrome unit of an image forming apparatus according to an exemplary embodiment;
fig. 3 is a block diagram showing a hardware configuration of the control system;
fig. 4 is a diagram showing an example of periodic density unevenness of an image formed on a recording medium;
FIG. 5 is a diagram illustrating an embodiment of a solid image and a low area coverage image formed on a recording medium;
fig. 6 is a graph illustrating a relationship between a gap difference between the photosensitive body and the developing roller and a density difference between a high density region and a low density region according to a high area coverage and a low area coverage;
fig. 7A is a graph showing a density difference between a high density region and a low density region according to a high area coverage and a low area coverage, and fig. 7B is a graph showing a corrected density difference between a high density region and a low density region according to a high area coverage and a low area coverage;
fig. 8 is a graph showing a relationship between a potential difference between the photosensitive body and the developing roller and a density (D) of an image;
fig. 9A is a schematic image illustrating the states of the photosensitive body and the developing roller before development, and fig. 9B is a schematic image illustrating the development process caused by a potential difference between the photosensitive body and the developing roller;
fig. 10A is a schematic image showing a development state by a potential difference between the photoreceptor and the developing roller in the solid area, and fig. 10B is a schematic image showing a development state by a potential difference between the photoreceptor and the developing roller with a low area coverage;
FIG. 11A is a schematic image showing a development state when the supply rate of toner obtained from a potential difference between the photoconductor and the development roller in the solid area is low, and FIG. 11B is a schematic image showing a development state when the supply rate of toner obtained from a potential difference between the photoconductor and the development roller having a low area coverage is low;
FIG. 12 is a graph showing a relationship between a change amount of a gap between the photoconductor and the developing roller and a necessary correction amount of a potential difference between the photoconductor and the developing roller according to a difference in area coverage when a supply rate of toner to a latent image is low;
FIG. 13 is a graph showing a relationship between a change amount of a gap between the photoconductor and the developing roller and a necessary correction amount of a potential difference between the photoconductor and the developing roller according to a difference in area coverage when a supply rate of toner to a latent image is high;
fig. 14 is a graph showing a density difference between a high density region and a low density region according to a difference in area coverage in the image forming apparatus of the comparative example and the image forming apparatus of the exemplary embodiment;
fig. 15 is a graph showing correction amounts of density differences between high density regions and low density regions according to differences in area coverage in the image forming apparatus of the comparative example and the image forming apparatus of the exemplary embodiment;
fig. 16 is a graph showing corrected density differences between the high density region and the low density region according to the difference in area coverage in the image forming apparatus of the comparative example and the image forming apparatus in the exemplary embodiment;
FIG. 17A is a graph showing a density difference between a high density region and a low density region according to a high area coverage and a low area coverage, and FIG. 17B is a graph showing a density difference between a high density region and a low density region according to a difference in area coverage generated by increasing a supply rate of toner to a latent image;
FIG. 18 is a graph showing a density difference between a high density region and a low density region according to a high area coverage and a low area coverage when a supply rate of toner to a latent image in a solid region of an image is 100%;
FIG. 19 is a diagram showing an embodiment of an image former for measuring a supply rate of toner to a latent image;
FIG. 20 is a graph showing a value obtained by subtracting a density difference between a high density region and a low density region from a gap between the photoconductor and the developing roller when changing the supply rate of toner to the latent image and the area coverage;
FIG. 21 is a graph showing evaluation of image quality when the supply rate and area coverage of toner to a latent image are changed;
FIG. 22 is a graph showing a relationship between the amplitude Vpp of the AC voltage of the developing voltage and the supply rate of the toner charge; and
FIG. 23 is a graph showing the relationship between the peripheral speed ratio of the developing roller to the photoconductor and the supply rate of toner charge.
Detailed Description
Hereinafter, embodiments for carrying out the present disclosure (hereinafter, referred to as exemplary embodiments) will be described. In the following description, a direction indicated by an arrow symbol X in the drawings is referred to as an apparatus width direction, and a direction indicated by an arrow symbol Y in the drawings is referred to as an apparatus height direction. A direction (arrow sign Z direction) perpendicular to each of the device width direction and the device height direction is referred to as a device depth direction.
First exemplary embodiment
An image forming apparatus according to a first exemplary embodiment will be described with reference to fig. 1 to 22.
Fig. 1 shows an example of an image forming apparatus 10 in an exemplary embodiment. First, the overall configuration of the image forming apparatus 10 in the exemplary embodiment will be described. Next, the developing
< general configuration of image Forming apparatus >
As shown in fig. 1, the image forming apparatus 10 is an electrophotographic system-based apparatus, and includes a recording medium storage 12, a toner image former 14, a transfer device 16, a recording medium conveying device 18, a fixing device 20, and a control device 70.
The recording medium memory 12 has a function of storing paper P as a recording medium before forming an image.
The toner image former 14 has a function of forming a toner image carried by an intermediate transfer belt configured by a transfer device 16 described later by performing charging, exposure, and development steps. As an example, the toner image former 14 includes monochrome units 21Y, 21M, 21C, and 21K that form toner images on each of the photoconductors 22 using toners of different colors (Y (yellow), M (magenta), C (cyan), and K (black)). For example, the toner image former 14 can form toner images composed of a plurality of colors from image data. The photoreceptors 22 are all embodiments of image carriers.
The monochrome units 21Y, 21M, 21C, and 21K have the same structure except for the color of the toner image formed by each monochrome unit. Hereinafter, when it is not necessary to distinguish the monochrome units 21Y, 21M, 21C, and 21K and their compositions, a description will be given by omitting the letters (Y, M, C and K) of the monochrome units 21Y, 21M, 21C, and 21K. Each monochrome unit 21 includes a photoconductor 22, a charging device 24, an exposure device 26, a developing
The transfer device 16 has a function of carrying a toner image of each color formed by each monochrome unit 21 and transferring the toner image onto the conveyed sheet P. The transfer device 16 includes an intermediate transfer belt 30, four transfer rollers 32, a drive roller 38, a secondary transfer unit 36, and a tension roller 34. The intermediate transfer belt 30 is endless. The four transfer rollers 32 form a nip portion by sandwiching the intermediate transfer belt 30 together with the photoreceptor 22. The intermediate transfer belt 30 is circumferentially moved in the arrow mark direction by a drive roller 38. In the exemplary embodiment, as an example, the single-color units 21Y, 21M, 21C, and 21K are arranged in order from the upstream side toward the downstream side in the circumferential moving direction of the intermediate transfer belt 30. Thus, the toner images formed by the monochrome units 21Y, 21M, 21C, and 21K on each of the photoconductors 22 are superimposed on the intermediate transfer belt 30 and transferred by the transfer roller 32.
On the downstream side of the monochrome units 21Y, 21M, 21C, and 21K and on the upstream side of the secondary transfer unit 36 in the circumferential moving direction of the intermediate transfer belt 30, a
The secondary transfer unit 36 includes: a transfer roller 54 which is in contact with a surface holding the toner image of the intermediate transfer belt 30; and an opposing roller 56 disposed opposite to the transfer roller 54 with the intermediate transfer belt 30 interposed therebetween. The secondary transfer unit 36 is designed to transfer the toner image of each color carried by the intermediate transfer belt 30 onto the conveyed paper sheet P.
The recording medium conveying device 18 has a function of conveying the sheet P so that the sheet P passes through a nip N1 of the secondary transfer unit 36 and a nip N2 of the fixing device 20. The recording medium conveying device 18 includes a plurality of conveying rollers 44, and further includes a conveying belt 46. The conveying roller 44 is formed of a pair of rollers arranged in a contact state. The conveying roller 44 is designed to convey the sheet P stored in the recording medium storage 12 along the conveying path 18A.
The conveyor belt 46 has a configuration in which an endless belt is wound around a pair of rollers arranged separately. The conveying belt 46 is arranged on the downstream side of the secondary transfer unit 36 and on the upstream side of the fixing device 20 in the conveying direction of the paper P. The conveyance belt 46 is designed to convey the sheet P, on which the toner image is transferred by the secondary transfer unit 36, to the fixing device 20 along the conveyance path 18A.
The fixing device 20 has a function of fixing the toner image, which has been transferred (secondary transfer) onto the sheet P by the transfer device 16, at the nip portion N2. The fixing device 20 includes a heater 62 and a pressure roller 64, the endless belt moves circumferentially in the heater 62, and the pressure roller 64 is in pressure contact with the heater 62. The sheet P is conveyed to a nip N2 between the heater 62 and the pressure roller 64, and thus the toner image of the sheet P is fixed by heating and pressing.
The control device 70 has a function of controlling each component of the image forming apparatus 10. For example, the control device 70 is designed to control each component of the image forming apparatus 10 (so that each component performs a corresponding operation) in accordance with job data received from an external device (not shown). The job data includes image data (image information) for causing each monochrome unit 21 to form a toner image and necessary data for other image forming operations.
The image forming apparatus 10 includes a plurality of toner cartridges 140Y, 140M, 140C, and 140K that store toners of different colors (Y (yellow), M (magenta), C (cyan), K (black)). In addition, the image forming apparatus 10 includes a toner conveying device 142, and the toner conveying device 142 conveys the toner T of each color from the toner cartridges 140Y, 140M, 140C, and 140K to the developing devices of the monochrome units 21Y, 21M, 21C, and 21K. The toner transfer device 142 includes: a conveyance path 144 connecting the toner cartridges 140Y, 140M, 140C, and 140K and the developing
< operation of image Forming apparatus >
Next, the operation of the image forming apparatus 10 will be described.
The control device 70, which receives job data from an external device (not shown), causes the toner image former 14, the transfer device 16, the recording medium conveyance device 18, and the fixing device 20 to operate. In the toner image former 14, each of the photoconductors 22 is charged by a corresponding charging device 24, the photoconductors 22 are exposed by a corresponding exposure device 26 to form a latent image (i.e., an electrostatic latent image), and then the latent image of each of the photoconductors 22 is developed into a toner image by a corresponding developing
Next, a voltage (primary transfer voltage) is applied from a power source (not shown) to each transfer roller 32. The drive roller 38 driven by a drive source (not shown) moves the intermediate transfer belt 30 circumferentially in the arrow mark direction.
Thus, the toner images of each color are superimposed and primarily transferred onto the intermediate transfer belt 30.
Further, the recording medium conveying device 18 delivers the sheet P to the nip N1 at the timing when the toner image of each color carried on the intermediate transfer belt 30 moving in the circumferential direction reaches the nip N1. In the secondary transfer unit 36, a voltage (secondary transfer voltage) is applied from a power source (not shown) to a power source roller (not shown) that is in contact with the outer periphery of the counter roller 56, and thus a toner image of each color is secondary-transferred onto the sheet P passing through the nip portion N1.
Next, the recording medium conveying device 18 conveys the sheet P on which the toner images of each color have been secondarily transferred to the nip N2. Accordingly, the toner images of the respective colors are fixed to the sheet P passing through the nip portion N2 by the fixing device 20, thereby forming an image on the sheet P. Subsequently, the sheet P is discharged to the discharge unit 66 by the conveying rollers 44.
< developing apparatus >
Next, the developing
As shown in fig. 2, the developing
As shown in fig. 2, as an example, the developer G is composed of a two-component developer including a negatively charged nonmagnetic toner T and a positively charged magnetic carrier CA.
The housing 102 has a developing roller chamber 122, the developing roller chamber 122 storing the developing roller 106 and a developer stirring conveyor 125 (a first stirring conveyance chamber 123 and a second stirring conveyance chamber 124), the developer stirring conveyor 125 being disposed obliquely below the developing roller chamber 122. A partition wall 103 is formed in the housing 102, and the partition wall 103 partitions the first agitation and conveyance chamber 123 and the second agitation and conveyance chamber 124. The housing 102 is provided with an inflow opening (not shown) that is connected to the first agitation and conveyance chamber 123 and the second agitation and conveyance chamber 124 at both ends of the partition wall 103 in the Z direction.
The developing roller 106 has: a magnet roller 106A which is cylindrical and fixedly supported by the housing 102 via a shaft (not shown); and a cylindrical developing sleeve 106B movably supported in the circumferential direction outside the magnet roller 106A. The magnet roller 106A is provided with a plurality of magnetic poles (not shown) in the circumferential direction of the outer peripheral surface. A gear (not shown) is fixed to an end portion of the developing sleeve 106B in the axial direction, the rotational force is transmitted from the developing motor 134 to the gear, and the developing sleeve 106B is rotated in the direction of an arrow mark R1 in fig. 2 via the gear.
The first auger 109 includes a rotary shaft 109A arranged in the Z direction and a helical conveyance blade 109B supported on the outer periphery of the rotary shaft 109A. The first auger 109 rotates in, for example, the R2 direction, thereby conveying the developer G while agitating the developer G.
The second auger 111 includes a rotating shaft 111A arranged in the Z direction and a conveying screw blade 111B supported on the outer periphery of the rotating shaft 111A. The second auger 111 rotates in the R3 direction, for example, to convey the developer G in the opposite direction to the first auger 109 while agitating the developer G.
The developing roller 106 is electrically connected to a developing power source 130, and the developing power source 130 applies a developing voltage to the photosensitive body 22 and the developing roller 106. A superimposed voltage in which an alternating current component (AC) serving as an alternating current voltage is superimposed on a direct current component (DC) serving as a direct current voltage is applied as a developing voltage from the developing power supply 130 to the developing roller 106. Note that, in the exemplary embodiment, the waveform of the AC component is a rectangular wave. However, without being limited thereto, the waveform may be a triangular wave or a sine wave. The frequency of the AC component is preferably in the range of, for example, 5kHz or more and 20kHz or less.
The amplitude Vpp of the AC voltage is preferably, for example, 0.8kV or more and 2.2kHz or less, more preferably 1.0kV or more and 2.1kHz or less, and further preferably 1.3kV or more and 2.0kHz or less. In an exemplary embodiment, the amplitude Vpp of the AC voltage is set to 1.5 kHz.
In the image forming apparatus 10, the developing voltage applied from the developing power supply 130 is set so that the supply rate of the charge of the toner T to the latent image in the solid area of the image of the photoconductor 22 is 80% or more. The latent image in the solid area of the image refers to a latent image having an area coverage of 100% of the photoconductor 22. The supply rate of the charge of the toner T to the latent image refers to a neutralization rate for neutralizing the latent image potential with the charge of the toner T, and may be hereinafter simply referred to as "neutralization rate".
As shown in fig. 22, as the amplitude Vpp of the AC voltage of the developing voltage increases, the supply rate (i.e., neutralization rate) of the charge of the toner T to the latent image increases. For example, by setting the amplitude Vpp of the AC voltage to 0.8kV or more, the supply rate of the charge of the toner T to the latent image in the solid area of the image of the photoconductor 22 becomes 80% or more. The supply rate (i.e., neutralization rate) of the charge of the toner T to the latent image in the solid area of the image of the photoconductor 22 is preferably 80% or more, and more preferably 90% or more. The supply rate of the charge of the toner T will be described in detail later.
The bottom of the housing 102 is provided with a magnetic permeability sensor 132, and the magnetic permeability sensor 132 detects the concentration of the toner T in the developer G (hereinafter referred to as "toner concentration"). The magnetic permeability sensor 132 is a sensor that detects the toner concentration in the developer G by detecting the magnetic permeability of the developer including the nonmagnetic toner and the magnetic carrier. Magnetic permeability sensor 132 is an embodiment of a detector.
Although illustration is omitted, a conveyance path 144 (see fig. 1) for replenishing new toner is connected to an upper portion of the housing 102 of the developing
< operation of developing apparatus >
Next, the operation of the developing
In the developing
When the developer G is supplied to the developing roller 106, the developer G is conveyed by the rotation of the developing sleeve 106B in the R1 direction with the developer G held on the developing sleeve 106B by the plurality of magnetic poles of the magnet roller 106A. The developer G held on the developing sleeve 106B enters between the outer circumferential surface of the developing sleeve 106B and the leading end of the layer thickness regulating member 108, so that the thickness of the layer is regulated, and the developer G is conveyed to the region opposed to the photosensitive body 22.
In the development region where the photoconductor 22 and the development roller 106 are opposed to each other, application of a development voltage from the development power source 130 to the photoconductor 22 and the development roller 106 causes the toner T of the developer G of the development sleeve 106B to be transferred to the latent image of the photoconductor 22. For example, the toner is supplied (in other words, transferred) to the latent image formed on the photoconductor 22 by a difference potential Vcln between the photoconductor surface potential Vs and the development voltage Vdev as the development bias applied to the development roller 106. As a result, a toner image is formed on the photoconductor 22.
< control System >
Next, the hardware configuration of the control system of the image forming apparatus 10 will be described with reference to fig. 3.
As shown in fig. 3, the control device 70 of the image forming apparatus 10 is constructed by a computer, for example. The control device 70 includes a Central Processing Unit (CPU)71, a Read Only Memory (ROM)72, a Random Access Memory (RAM)73, a nonvolatile memory 77, and an input/output interface (I/O) 75. The CPU 71, ROM 72, RAM 73, nonvolatile memory 77, and I/O75 are coupled to each other via a bus 76.
The CPU 71 is a central processing unit, and executes various programs and controls components. Specifically, the CPU 71 reads the program from the ROM 72 or the nonvolatile memory 77, and executes the program using the RAM 73 as a work area. In the exemplary embodiment, an execution program for executing various types of processing is stored in the nonvolatile memory 77.
The ROM 72 stores various programs and various types of data. The RAM 73 serving as a work area temporarily stores programs and/or data. The nonvolatile memory 77 is an embodiment of a storage device that holds stored information even if power is turned off. For example, a semiconductor memory is used, but a hard disk may be used.
The toner image former 14, the communication unit 82, the exposure device 26, the
The control device 70 adjusts the potential difference between the photosensitive body 22 and the developing roller 106 by controlling the developing bias applied from the developing power source 130 to the photosensitive body 22 or the exposure amount applied from the exposure device 26 to the photosensitive body 22 based on the periodicity information detected by the
The image forming apparatus 10 controls a density difference in an output image in the axial direction of the photosensitive body 22 using an area ratio of an exposure pattern in the output pattern formed by one developing
< operations and effects >
Next, the operation and effect of the exemplary embodiment will be described. First, before describing the operation and effects of the exemplary embodiment, an image forming apparatus of a comparative example will be described.
In the image forming apparatus of the comparative example, the amplitude Vpp of the AC voltage of the developing voltage applied from the developing power source was set to 0.6 kV. In the region where the developing roller and the photosensitive body are opposed to each other, the peripheral speeds of the developing roller and the photosensitive body are set to be equal.
In general, in an image forming apparatus, as shown in fig. 4, a gap (DRS) between a developing roller and a photoreceptor changes periodically due to vibration and eccentricity of the developing roller and the photoreceptor, so that periodic density unevenness (so-called banding) occurs at a position where the gap is large or small in a printing direction (i.e., a circumferential direction). Since the developing electric field depends on the distance between the developing roller and the photoconductor, when the distance between the developing roller and the photoconductor is changed, the developing amount of toner is also changed. Therefore, when the gap between the developing roller and the photoreceptor is large, the density of the image decreases, and when the gap between the developing roller and the photoreceptor is small, the density of the image increases.
In the image forming apparatus of the comparative example, the period sensor detects the periodicity information due to the periodic change of the gap between the developing roller and the photosensitive body, and controls the exposure amount of the exposure device to the photosensitive body (specifically, the potential difference between the developing member and the image carrier) based on the periodicity information. Therefore, the developing amount of toner is corrected.
However, in the case of periodic concentration unevenness (so-called banding), the concentration difference (Δ D) between the high concentration region and the low concentration region changes depending on the area coverage (Cin). Fig. 5 shows a solid image with 100% area coverage and an image with low area coverage. As shown in fig. 6, as the difference in gap between the photoreceptor and the developing roller (Δ DRS) increases, the density difference (Δ D) increases for higher area coverage.
Therefore, as shown in fig. 7A and 7B, when the correction amount is controlled with the exposure amount (correcting the potential difference between the developing roller and the photosensitive body) being constant in the axial direction of the photosensitive body, the effectiveness of the density correction is different for each area coverage because the density difference varies with the area coverage. As shown in fig. 7B, particularly when the area coverage is high, the correction is insufficient, and the density difference (Δ D) may increase. It is to be noted that, in the image forming apparatus of the comparative example, the potential difference V between the developing roller and the photoconductor was constant in the axial direction of the photoconductor, and the control of the density difference in the output image of the photoconductor in the axial direction was achieved by changing the area coverage. Fig. 8 shows a relationship between the potential difference V on the photoconductor and the developing roller and the density D.
In the image forming apparatus of the comparative example, the correction was performed at an average of the area coverage of 20% and the area coverage of 80%. In this case, the area coverage includes one area coverage in which correction of the developing amount of the toner is excessively effective and the other area coverage in which correction of the developing amount of the toner is insufficient. When both the over-correction and the under-correction exist, the density difference (Δ D) increases, and the correction may cause an unexpected decrease in print quality.
For example, a method may be employed in which the area coverage is assumed in accordance with the output image pattern, and the exposure amount is adjusted at the position of the photoconductor in the axial direction. However, the complexity and cost of the image forming apparatus are inevitably increased, such as an increase in the capacity of a computing memory.
The reason why the density difference (Δ D) with respect to the gap change between the photoconductor and the developing roller differs depending on the area coverage includes a difference in the supply rate (i.e., neutralization rate) of the charge of the toner to the latent image. The charge supply rate of the toner indicating the occupancy of the toner to the latent image changes due to the movement of the toner in the development nip. As shown in fig. 9A, when there is no potential difference between the developing roller and the photoconductor, the toner T of the developing roller having the negative polarity does not move to the photoconductor. As shown in fig. 9B, when there is a potential difference between the developing roller and the photoconductor (for example, the potential of the developing roller < the potential of the photoconductor), the toner T of the developing roller moves to a portion of the photoconductor having a positive potential (specifically, a latent image in an exposed portion).
As shown in fig. 10A, when the potentials of the toner layers attached on the surfaces of the developing roller and the photoconductor are equal (in other words, when the potential difference disappears), the developing process is stopped. This state is defined as a supply-limited state of the toner T, in other words, a state in which a supply rate of the charge of the toner to the latent image (i.e., neutralization rate) reaches 100%. In this case, even when the gap between the photoconductor and the developing roller is changed, no potential difference occurs between the developing roller and the photoconductor (i.e., the toner layer adhering to the photoconductor), and no force for supplying toner is applied. Therefore, when the supply rate of the charge of the toner to the latent image is high, the influence of the change in the gap between the photoconductor and the developing roller on the density difference (Δ D) is low.
In contrast, as shown in fig. 10A and 10B, when a latent image is formed with the same exposure amount with different area coverage (i.e., when the potential difference between the developing roller and the photosensitive body is the same), the necessary amount of charge per unit area is changed. As shown in fig. 10B, when the area coverage is low, the necessary charge amount per unit area decreases. In contrast, as shown in fig. 10A, when the area coverage is high, a larger amount of charge supply per unit area is required. In other words, when the area coverage is low, the amount of toner T required for the photoreceptor is reduced as compared with the case of a solid image (i.e., the area coverage is 100%).
Therefore, when the area coverage is low, the supply rate of the electric charge of the toner T (i.e., the neutralization rate) is likely to increase (see fig. 11B), and when the area coverage is high, the supply rate of the electric charge of the toner T is likely to decrease (see fig. 11A). Therefore, a high or low supply rate of the charge of the toner for each area coverage causes a density difference (Δ D) with respect to a gap change between the photoconductor and the developing roller.
For example, when the developing electric field for scattering the toner in the developing nip portion is low, or when the toner amount is small, the toner supply performance is low, and the supply rate of the charge of the toner (that is, the neutralization rate) cannot be increased. In this case, as shown in fig. 11B, when the area coverage is low, the amount of toner T required for the photoconductor is small, the supply-limited state of the toner T is likely to be reached, and the supply rate of the charge of the toner increases. When the toner supply restricted state is reached, the dependency of the developing electric field almost disappears, and the toner is less likely to scatter. Therefore, a density change with respect to a gap change between the photoconductor and the developing roller is less likely to occur (see fig. 6).
However, as shown in fig. 11A, when the area coverage is high, the amount of toner T required for the photoconductor is large, it is impossible to reach the supply-limited state of toner T, and the supply rate of the charge of toner T (i.e., neutralization rate) is lowered. When the toner supply restricted state is not reached, the toner is likely to be scattered at a position where the clearance (DRS) between the photoconductor and the developing roller is small, and the toner is less likely to be scattered at a position where the clearance (DRS) between the photoconductor and the developing roller is large. Therefore, a density change with respect to a gap change between the photoconductor and the developing roller is likely to occur (see fig. 6).
In the image forming apparatus 10 of the exemplary embodiment, the toner T is more efficiently developed during the nip passage in the developing
More specifically, in the image forming apparatus 10, the amplitude Vpp of the AC voltage of the developing voltage applied from the developing power supply 130 is set to 0.8kV or more (1.5 kV in the exemplary embodiment). Therefore, the scattering performance of the toner T from the developing roller 106 to the photoconductor 22 is enhanced, so that the toner supply performance is improved, and the supply rate of the charge of the toner T (i.e., the neutralization rate) is improved even in the case of a high area coverage. As shown in fig. 22, in the image forming apparatus 10, the amplitude Vpp of the AC voltage of the developing voltage is set to 1.5kV, and therefore, the supply rate of the electric charge of the toner T (i.e., the neutralization rate) reaches 97% or more. Therefore, the supply rate of the charge of the toner is maintained at a high level for all the area coverage, and an image whose density is stable for the gap change between the photoconductor 22 and the developing roller 106 is output.
The supply ratio of the toner charge in the solid area (i.e., the neutralization ratio in the solid area) is calculated according to the following expression:
the neutralization ratio in the solid region (toner layer potential after passing through the nip-latent image potential)/(developing roller potential-latent image potential) × 100%
In an exemplary embodiment, the supply rate of the charge of the toner in the solid area is set to a percentage or more, which is the area coverage of the outline referred to as the density correction standard.
Fig. 12 shows a relationship between a variation amount of the gap (DRS) between the photoconductor and the developing roller and a necessary correction amount of the potential difference (V) between the photoconductor and the developing roller according to the difference in the area coverage (Cin) in the image forming apparatus of the comparative example. The amount of change in the gap (DRS) between the photoreceptor and the developing roller has the same meaning as the difference in the gap (Δ DRS) between the photoreceptor and the developing roller. In the image forming apparatus of the comparative example, as described above, the amplitude Vpp of the AC voltage of the developing voltage applied from the developing power supply is set to 0.6kV, and the supply rate of the charge of the toner T (i.e., the neutralization rate) is low. As shown in fig. 12, in the image forming apparatus of the comparative example, in the case of a solid area (
Fig. 13 shows a relationship between the amount of change of the gap (DRS) between the photoconductor 22 and the developing roller 106 and the necessary amount of correction of the potential difference (V) between the photoconductor 22 and the developing roller 106 according to the difference in the area coverage (Cin) in the image forming apparatus of the exemplary embodiment. In the image forming apparatus 10, the amplitude Vpp of the AC voltage of the developing voltage applied from the developing power supply 130 is set to 1.5kV, and the supply rate (i.e., neutralization rate) of the charge of the toner T is high (see fig. 22). As shown in fig. 13, in the image forming apparatus 10, in the case of a solid area (area coverage of 100%), the necessary correction amount of the potential difference (V) between the photoconductor 22 and the developing roller 106 is lower for the change amount of the gap (DRS) between the photoconductor 22 and the developing roller 106 than in the image forming apparatus of the comparative example.
Fig. 14 shows a density difference (Δ D) according to a difference in area coverage (Cin) when the gap (DRS) between the photoconductor 22 and the developing roller 106 is changed at 50 μm in the image forming apparatus of the comparative example and the image forming apparatus 10 of the exemplary embodiment. As shown in fig. 14, in the image forming apparatus 10 in the exemplary embodiment, the density difference (Δ D) with the area coverage of 100% is smaller than that in the image forming apparatus of the comparative example.
Fig. 15 shows correction amounts for the density difference (Δ D) according to the difference in the area coverage (Cin) when the gap (DRS) between the photoconductor 22 and the developing roller 106 is changed at 50 μm in the image forming apparatus of the comparative example and the image forming apparatus 10 of the exemplary embodiment. In fig. 15, the density difference (Δ D) was corrected with an average of 20% area coverage and 80% area coverage.
Fig. 16 shows the density difference (Δ D) corrected according to the difference in the area coverage (Cin) when the gap (DRS) between the photoconductor 22 and the developing roller 106 is changed at 50 μm in the image forming apparatus of the comparative example and the image forming apparatus 10 of the exemplary embodiment. In fig. 16, the corrected density difference (Δ D) is obtained by subtracting the correction amount of the density difference (Δ D) shown in fig. 15 from the density difference (Δ D) shown in fig. 14. As shown in fig. 16, in the image forming apparatus 10 of the exemplary embodiment, the density difference (Δ D) is smaller for all area coverages including 100% of the area coverage than in the image forming apparatus of the comparative example. In particular, in the image forming apparatus 10 in the exemplary embodiment, the density difference (Δ D) for 100% area coverage is smaller than that in the image forming apparatus of the comparative example.
Fig. 17A shows a density difference (Δ D) according to a difference in area coverage in the printing direction. Fig. 17B shows a density difference (Δ D) according to a difference in area coverage in the printing direction when the supply rate of the charge of the toner T (i.e., neutralization rate) increases. As shown in fig. 17B, the density difference (Δ D) according to the difference in the area coverage in the printing direction is reduced by increasing the supply rate of the electric charge of the toner T.
Fig. 18 shows the density difference (Δ D) according to the difference in the area coverage in the printing direction when the supply rate of the charge of the toner T in the solid area (i.e., neutralization rate) is 100%. As shown in fig. 18, when the supply rate of the charge of the toner T in the solid region having the area coverage of 100% is 100%, the density difference (Δ D) according to the difference in the area coverage disappears.
In the image forming apparatus 10 of the exemplary embodiment, the developing power source 130 is set so that the supply rate of the charge of the toner T to the latent image in the solid area of the image reaches 80% or more. Therefore, in the image forming apparatus 10, the image density unevenness occurring in the axial direction of the photoconductor 22 is reduced as compared with the case where the supply rate of the charge of the toner to the latent image in the solid area of the image is less than 80%.
In addition, in the image forming apparatus 10 of the exemplary embodiment, the developing voltage applied from the developing power supply 130 is a superimposed voltage in which an AC voltage is superimposed on a DC voltage, and the amplitude Vpp of the AC voltage is set to 0.8kV or more and 2.2kHz or less. Therefore, in the image forming apparatus 10, the image density unevenness occurring in the axial direction of the image carrier is reduced as compared with the case where the amplitude Vpp of the AC voltage is lower than 0.8 kV. In addition, less energy is consumed compared to the case where the amplitude Vpp of the AC voltage is higher than 2.2 kV.
Exemplary embodiments
By using the image forming apparatus 300 shown in fig. 19, the supply rate of the electric charge of the toner T (i.e., the neutralization rate) is controlled to be 75%, 80%, 90%, 100% by replacing the amplitude Vpp of the AC voltage of the developing voltage with one in the range of 0.4, 0.6, 1.0, 1.2 kV. The supply rate of the charge of the toner T (i.e., neutralization rate) is fixed, and images having all halftones (area coverage of 20%, 50%, 80%, 100%) are output.
The gap (DRS) between the photoconductor body 22 and the developing roller 106 was set to 230 μm and 330 μm, and the concentration was measured. Data were obtained with Δ D as the concentration difference. Further, the image quality is evaluated from the image having the halftone.
As shown in fig. 19, in the image forming apparatus 300, the potential sensor 302 for the photosensitive body 22 is provided in the developing
Fig. 20 is a graph showing a value obtained by subtracting the density difference (Δ D) from the difference (Δ DRS) in the gap between the photoconductor 22 and the developing roller 106 for each area coverage and each supply rate (i.e., neutralization rate) of the charge of the toner T.
Fig. 21 is a graph showing evaluation of the quality of an image having a halftone for each area coverage and each supply rate of electric charge of the toner T (i.e., neutralization rate). Here, "o" represents a level at which the periodic bands cannot be clearly recognized by visual observation, and "x" represents a level at which the periodic bands can be clearly recognized by visual observation. Between the graph shown in fig. 20 and the graph shown in fig. 21, the numerical values do not correspond to each other. This is because the absolute value of the density is changed according to an image having a halftone, and thus a difference in visibility occurs, and the halftone is easily seen. As shown in fig. 21, by setting the supply rate of electric charges (i.e., neutralization rate), it can be confirmed that, by setting the supply rate of electric charges of the toner T to 80% or more, no periodic band of density is recognized in an image having halftone in a solid area with an area coverage of 100%.
Second exemplary embodiment
Next, an image forming apparatus according to a second exemplary embodiment will be described. Note that the same components as those in the first exemplary embodiment described above are denoted by the same reference numerals, and description thereof is omitted.
In the image forming apparatus 10 in the first exemplary embodiment, the amplitude Vpp of the AC voltage of the developing voltage applied from the developing power supply 130 is set to be high. However, unlike this, in the image forming apparatus 10 in the second exemplary embodiment, in the region where the photoconductor 22 and the developing roller 106 are opposed to each other, the peripheral speed of the developing roller 106 is set higher than the peripheral speed of the photoconductor 22. In the second exemplary embodiment, as an example, in a region where the photosensitive body 22 and the developing roller 106 are opposed to each other, the peripheral speed of the developing roller 106 is set to be 1.8 times the peripheral speed of the photosensitive body 22. In other words, the circumferential speed ratio of the developing roller 106 to the photoconductor 22 is set to 1.8. In the image forming apparatus 10 in the second exemplary embodiment, the rotational force from the developing motor 134 is transmitted to the developing sleeve 106B of the developing roller 106, and thus the developing sleeve 106B moves circumferentially.
In the image forming apparatus 10 in the second exemplary embodiment, the amplitude Vpp of the AC voltage of the developing voltage applied from the developing power supply 130 is set to 0.6 kV.
In fig. 23, the relationship between the peripheral speed ratio of the developing roller and the photoconductor and the supply rate of toner charge is shown in a graph. As shown in fig. 23, as the peripheral speed ratio of the developing roller to the photoconductor increases, the supply rate (i.e., neutralization rate) of the charge of the toner T to the latent image increases. For example, by setting the peripheral speed ratio of the developing roller to the photoconductor to 1.4 or more, the supply rate (i.e., neutralization rate) of the charge of the toner T to the latent image in the solid area of the image of the photoconductor 22
In the region where the photoconductor 22 and the developing roller 106 are opposed to each other, the ratio of the peripheral speed of the developing roller 106 to the peripheral speed of the photoconductor 22 is preferably in the range of 1.4 to 2.5, more preferably in the range of 1.5 to 2.2, and further preferably in the range of 1.7 to 2.0.
In the image forming apparatus 10 in the second exemplary embodiment, the developing
In the image forming apparatus 10 in the second exemplary embodiment, in the region where the photosensitive body 22 and the developing roller 106 are opposed to each other, the peripheral speed of the developing roller 106 is set to be faster than the peripheral speed of the photosensitive body 22. Therefore, the image density unevenness occurring in the axial direction of the photoconductor 22 is reduced as compared with the case where the peripheral speed of the developing member and the peripheral speed of the image carrier are the same in the region where the image carrier and the developing member are opposed to each other.
In the image forming apparatus 10 in the second exemplary embodiment, in the region where the photoconductor 22 and the developing roller 106 are opposed to each other, the ratio of the peripheral speed of the developing roller 106 to the peripheral speed of the photoconductor 22 is in the range of 1.4 to 2.5. Therefore, compared to the case where the ratio of the peripheral speed of the developing member to the peripheral speed of the image carrier is less than 1.4, the image density unevenness occurring in the axial direction of the photoconductor 22 is reduced. In addition, the dispersion of the toner T from the development area is less occurred as compared with the case where the ratio of the peripheral speed of the developing member to the peripheral speed of the image carrier is higher than 2.5.
Third exemplary embodiment
Next, an image forming apparatus according to a third exemplary embodiment will be described. Note that the same components as those in the first exemplary embodiment described above are denoted by the same reference numerals, and description thereof is omitted.
In the image forming apparatus 10 in the first exemplary embodiment, the amplitude Vpp of the AC voltage of the developing voltage applied from the developing power supply 130 is set to be high. However, unlike this, in the image forming apparatus 10 in the third exemplary embodiment, the toner concentration in the developer G in the developing
In image forming apparatus 10 in the third exemplary embodiment, as shown in fig. 3, the toner concentration in developer G in developing
In the image forming apparatus 10 in the third exemplary embodiment, the developing
Note that a configuration may be adopted in which any two or more settings between the setting of the developing power source 130 and the setting of the developing
The configuration of each member in the image forming apparatuses in the first to third exemplary embodiments may be modified.
Although certain exemplary embodiments of the present disclosure have been described in detail, the present disclosure is not limited to those exemplary embodiments, and it is apparent to those skilled in the art that other various exemplary embodiments may be implemented within the scope of the present disclosure.
The foregoing description of the exemplary embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise disclosure. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
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