JP2011095651A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a density adjusting means for detecting light reflected from a reference toner pattern formed on a photoreceptor drum and for adjusting a toner density using an output value corresponding to the reflected light, the apparatus being configured to prevent adverse effect on toner density control by suppressing firm fixing of a sleeve in the position where the reference toner pattern is formed. <P>SOLUTION: The density adjusting means is configured such that a first toner pattern is formed and a toner density control is exerted using the first reference toner pattern, the first reference toner pattern being such that the length of this pattern in its rotating direction (the length in a sub-scanning direction) is longer than L×(vp/vs), wherein L is the circumferential length of the developing sleeve 14, vs is the linear velocity of the developing sleeve 14, and vp is the linear velocity of the photosensitive drum 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus using a two-component developer, and more particularly to toner density control.

  An electrophotographic image forming apparatus using a two-component developer composed of a toner and a carrier has a toner density adjusting means for adjusting the toner density so that the ratio of the toner and the carrier stored in the developing device is appropriate. I have.

  The toner density adjusting means forms an electrostatic latent image for a reference toner pattern for detecting the toner density on the surface of a rotatable photoconductor, and the static toner for the reference toner pattern is formed by a rotatable developer carrier. The electrostatic latent image is developed, the reflected light from the developed reference toner pattern and the toner non-adhered portion on the photosensitive member is detected by the light reflection type photosensor, and the output value Vsp of the light reflection type photosensor in the reference toner pattern. (Vsp / Vsg) divided by the output value Vsg of the light reflection type photosensor in the toner non-adhering portion is configured to maintain a predetermined value set in advance.

  Specifically, when the toner adhesion amount of the reference toner pattern decreases, Vsp / Vsg rises above a predetermined value, and it is determined that the toner concentration of the developer in the developer is low, and the toner from the toner replenishing device to the developer Replenishment is executed. On the contrary, when Vsp / Vsg is lower than the predetermined value, it is determined that the toner concentration of the developer in the developing device is high, and toner replenishment from the toner replenishing device to the developing device is not executed.

  By the way, most of the required power of the image forming apparatus is power supplied to the heat source of the fixing device when the toner image is melted and fixed on the sheet-like recording material. To achieve energy saving, the lower limit fixing temperature is set. In order to meet this demand, toners having a lower fixing minimum temperature have been developed recently. For example, a fixing lower limit temperature of about 150 to 170 [° C.] has become possible with a fixing lower limit temperature of 150 [° C.] or less.

  However, the toner tends to have a strong adhesive force, and gradually adheres to the developing sleeve as the developer carrying member, which may cause the image quality to deteriorate without performing normal development (hereinafter referred to as “sticking”). This phenomenon is called sleeve sticking). Although this sleeve sticking has occurred in the conventional toner, the toner having a lower fixing minimum temperature tends to have a strong adhesive force, so that the sleeve sticking easily occurs.

  This sleeve sticking is likely to occur at a position corresponding to the non-image portion of the photoreceptor when the same document is continuously printed. This is because the toner at the position corresponding to the non-image portion of the photosensitive member is pressed against the developing sleeve by the electric field attracted by the developing sleeve itself, and is rubbed by the carrier many times until finally the fusion. It is thought to progress.

As a technique for preventing the sleeve from sticking, conventionally, for example, the developer regulating member is grounded and an electric field is formed between the developing sleeve, and thus the toner that weakly adheres to the developing sleeve is caused by this electric field. In some cases, the sleeve is prevented from sticking by shifting to (see, for example, Patent Document 1).
In addition, the gap between the photosensitive member and the developing sleeve is set to a certain extent to prevent the toner from adhering or being pressed against the surface of the developing sleeve due to the electric field effect (see, for example, Patent Document 2).

Although those described in Patent Documents 1 and 2 described above are suitable as a technique for preventing the sticking of the sleeve to the conventional toner, the toner having a strong adhesive force has no possibility of causing the sticking of the sleeve. I can't say that.
If the sleeve sticks and the occurrence location is the above-described reference toner pattern formation position, the following problems occur.

  That is, when the sleeve is fixed at the position where the reference toner pattern is formed, when the toner pattern is formed, the toner fixed to the sleeve is charged as much as the toner is fixed rather than the actual voltage. This increases and the amount of toner pattern adhering to the photoreceptor increases, so that the above-mentioned Vsp / Vsg becomes low. In this state, the toner replenishment amount tends to be smaller than the required amount.

As the sticking of the sleeve progresses, this tendency becomes conspicuous, causing a problem in density adjustment and causing problems such as a decrease in density. Further, the phenomenon that the toner adhesion amount increases due to the fixing of the sleeve is remarkable from the start of image formation until the image is formed for one rotation of the sleeve, and a phenomenon in which the circumference of the sleeve is darkened from the leading edge of the image is observed.
When the sleeve fixing progresses in this way, the toner density control is affected, and the image quality deteriorates, for example, the image density becomes thin.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that suppresses the fixation of a sleeve at a reference toner pattern formation position and does not affect toner density control. And

In order to solve the above problems, the image forming apparatus according to the present invention has the following technical means.
According to the first aspect of the present invention, an electrostatic latent image for a reference toner pattern for detecting a toner density is formed on the surface of a rotatable photosensitive member, and the electrostatic latent image is formed by a rotatable developer carrier. In the image forming apparatus, the density adjusting unit includes a density adjusting unit that detects the reflected light of the developed reference toner pattern and adjusts the toner density using an output value corresponding to the reflected light. When the length of the reference toner pattern in the rotational movement direction is L, the circumferential length of the developer carrier is L, the linear velocity of the developer carrier is vs, and the linear velocity of the photoconductor is vp. , And an image forming apparatus configured to be able to form a first reference toner pattern longer than L × (vp / vs).
According to a second aspect of the present invention, in the first aspect, the density adjusting unit is configured such that the length of the reference toner pattern in the rotational movement direction is a minimum necessary length that can detect the reflected light. The reference toner pattern can also be formed, and the toner density adjustment is executed by appropriately selecting either the first reference toner pattern or the second reference toner pattern.
According to a third aspect of the present invention, in the second aspect of the present invention, the density adjustment unit is configured to appropriately adjust the toner density using the first reference toner pattern based on toner density adjustment using the second reference toner pattern. The adjustment is executed.
According to a fourth aspect of the present invention, in any one of the first to third aspects, the density adjusting unit may detect the length of the first reference toner pattern as a detection position of the reflected light of the first reference toner pattern. Among these, it is a position that exceeds the length of L × (vp / vs) with respect to the front end side in the rotational movement direction.
According to a fifth aspect of the present invention, in any one of the first to third aspects, the density adjusting unit can detect the length of the first reference toner pattern as a detection position of the reflected light of the first reference toner pattern. Among them, a first detection position that is within the length of L × (vp / vs) with respect to the tip end side in the rotational movement direction, and a second detection position that exceeds the length of L × (vp / vs) The first reference toner pattern is used according to a difference between an output value corresponding to reflected light at the first detection position and an output value corresponding to reflected light at the second detection position. The toner density adjustment execution interval is variable.
According to a sixth aspect of the present invention, in the second or third aspect, the density adjusting unit rotates the length of the first reference toner pattern as the detection position of the reflected light of the first reference toner pattern. A first detection position that is within the length of L × (vp / vs) with respect to the leading end side in the moving direction, and a second detection position that exceeds the length of L × (vp / vs). When the difference between the output value according to the reflected light at the first detection position and the output value according to the reflected light at the second detection position is less than a threshold value, the next toner density adjustment is performed by the second toner density adjustment. A reference toner pattern is used.

  According to the present invention, it is possible to provide an image forming apparatus that suppresses the sticking of the sleeve at the formation position of the reference toner pattern and does not affect the toner density control.

1 is a schematic diagram illustrating an outline of an image forming apparatus according to an exemplary embodiment. FIG. 2 is a schematic diagram showing an outline of a process cartridge. FIG. 6 is a diagram showing a relationship between a toner density of a reference toner pattern on a photosensitive drum and an output value Vsp of a light reflection type photosensor in the reference toner pattern. It is the schematic diagram which showed the relationship between generation | occurrence | production of sleeve adhering, and a figure. FIG. 6 is a diagram showing the relationship between the number of sheets to be passed and the sleeve density. FIG. 3 is a schematic perspective view of a photosensitive drum in a state where a first reference toner pattern A is formed. FIG. 6 is a schematic perspective view of a photosensitive drum in a state where a second reference toner pattern B is formed. FIG. 6 is a diagram showing a time transition of an output voltage of a light reflection type sensor when a second reference toner pattern B is used. FIG. 6 is a diagram showing the time transition of the output voltage of the light reflection type sensor when the first reference toner pattern A is used. FIG. 5 is a diagram showing a relationship between a difference ΔVsp in output voltage of a light reflection type sensor and a sleeve density when a first reference toner pattern A is used.

An embodiment of an image forming apparatus according to the present invention will be described.
The image forming apparatus according to the present embodiment exemplifies a full-color output compatible laser printer that receives image information transmitted from the outside and forms an image on a sheet based on the image information. An outline of the forming apparatus will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1, the image forming apparatus according to the present embodiment includes four process cartridges 1 for yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K). The four process cartridges 1 have the same configuration except for the color of toner to be used. Taking the process cartridge 1 for generating a Y toner image as an example, as shown in FIG. 2, it has a photosensitive unit and a developing unit. The photosensitive unit and the developing unit can be integrally attached to and detached from the image forming apparatus main body.

FIG. 2 shows a schematic cross-sectional view of the process cartridge 1.
The photosensitive unit includes a photosensitive drum 2 as a photosensitive member, a drum cleaning device 3 that removes and collects transfer residual toner and the like adhering to the photosensitive drum 2, and a lubricant coating for setting the surface friction coefficient of the photosensitive drum 2 to a predetermined value. Brush 4 and lubricant 5 (zinc stearate), lubricant coating blade 6 for uniformly coating the lubricant 5 on the photosensitive drum 2, a charging roller 7 for uniformly charging the photosensitive drum 2, an infrared light emitting LED, etc. A light-reflective photosensor 10 that includes a light-emitting element and a light-receiving element and detects reflected light from a reference toner pattern developed on the photosensitive drum 2 and a toner non-adhering portion on the photosensitive drum 2; Yes. The details of the toner density adjusting means provided with the light reflection type photosensor 10, which is a main part of the present invention, will be described later.

  The charging roller 7 uniformly applies a charging bias obtained by superimposing a DC voltage on an AC voltage from a charging bias applying unit (not shown) to the surface of the photosensitive drum 2 that is rotated in a clockwise direction in the drawing by a driving unit (not shown). Charge. Subsequently, exposure scanning is performed with a laser beam emitted from the exposure unit 18 (FIG. 1) corresponding to the image signal to form an electrostatic latent image.

  The developing unit includes a first developer accommodating portion 8 in which a first conveying screw 11 is disposed, and a second developer accommodating portion 9 in which a second conveying screw 12 as a developer conveying screw is disposed. Yes.

  The first conveying screw 11 is rotationally driven by a driving means (not shown), and the two-component developer composed of toner and carrier in the first developer accommodating portion 8 is conveyed from the back side to the near side in FIG. Into the second developer accommodating portion 9 through a communication port (not shown) provided in the partition wall 13 erected between the first developer accommodating portion 8 and the second developer accommodating portion 9. It has become.

  The second conveying screw 12 in the second developer accommodating portion 9 is rotationally driven by a driving means (not shown), thereby conveying the two-component developer from the near side to the far side in FIG. Above the second conveying screw 12, a developing sleeve 14 as a developer carrying member is disposed in a posture parallel to the second conveying screw 12, and the developing sleeve 14 rotates counterclockwise in the figure. It is designed to be driven.

The developing sleeve 14 is formed in a cylindrical shaft shape with a nonmagnetic material (aluminum) whose surface has been roughened by sandblasting in order to enhance the conveying ability of the two-component developer. It is designed to rotate counterclockwise. A magnet roller 16 having magnetic poles 15 alternately formed in the circumferential direction is inserted inside the developing sleeve 14, and a part of the two-component developer conveyed by the second conveying screw 12 is inserted into the magnet roller. The magnetic force generated by the pump 16 is pumped up to the surface of the developing sleeve 14 and rises.
In addition to the rough surface by sandblasting, this developing sleeve 14 is provided with grooves with equal intervals (axial grooves, irises, lattices, etc.) in order to enhance the conveyance capability of the two-component developer. Is mentioned.

  Further, among the two-component developers that are pumped up and adhered to the surface of the developing sleeve 14, the doctor blade 17 as a developer amount regulating member is disposed between the developing sleeve 14 and a predetermined gap so that excess two-component developer can be scraped off. Is provided. After the developer layer thickness is regulated by the doctor blade 17, the developer drum 2 is transported to a developing area facing the photosensitive drum 2, and is applied to the developing sleeve 14 from a developing bias applying unit (not shown) by the developing bias. Toner is attached to the electrostatic latent image formed thereon, and developed into a toner image. The developer that has consumed toner by this development is returned to the second conveying screw 12 as the developing sleeve 14 rotates. And if it conveys to the back end in a figure, it will return in a 1st accommodating part through the communication port which is not shown in figure.

  Below the process cartridge 1, an exposure unit 18 is disposed as electrostatic latent image writing means. The exposure unit 18 irradiates the surface of the photosensitive drum 2 of each process cartridge 1 with laser light based on the image information. Thereby, an electrostatic latent image is formed on the photosensitive drum 2. The exposure unit 18 scans laser light emitted from a laser diode as a light source by a polygon mirror that is rotationally driven by a motor, and irradiates the photosensitive drum 2 through a plurality of optical lenses and mirrors. Instead of such a configuration, an exposure unit 18 using an LED array may be employed.

  Below the exposure unit 18, a first paper feed cassette 19 and a second paper feed cassette 20 are disposed. Each of these sheet feeding cassettes contains a sheet-like recording material, and the recording material is discharged to the sheet feeding path 22 by a sheet feeding means 21 composed of a plurality of rollers or the like. Yes.

  A registration roller pair 23 is disposed in the paper feed path 22. The registration roller pair 23 waits while sandwiching the recording material, and is driven in accordance with the timing at which a toner image formed on an intermediate transfer belt 24 described later reaches the secondary transfer nip, thereby transferring the recording material to the secondary transfer. It is designed to feed toward the nip.

  Above each process cartridge 1, an intermediate transfer belt 24 is provided, and a transfer unit that rotates the intermediate transfer belt 24 counterclockwise in the figure is disposed. Above the transfer unit, four toner bottles 25 for storing toners of respective colors Y, C, M, and K are disposed. The toner of each color stored in the toner bottle 25 is appropriately supplied to the developing unit of the process cartridge 1 of each color. These toner bottles 25 are detachable from the main body of the image forming apparatus so that they can be replaced when the remaining amount of toner in the bottles is exhausted.

  In addition to the above-described intermediate transfer belt 24, the transfer unit described above receives a belt cleaning unit 26, a primary transfer roller 27 disposed at a position where the photosensitive drums 2 of the respective colors face each other, and external driving, and receives the intermediate transfer belt 24. And a driven roller 29 provided at a predetermined interval from the driving roller 28. The drive roller 28 also serves as a counter roller for the secondary transfer roller 30.

  The primary transfer roller 27 is in contact with the photosensitive drum 2 with the lower belt of the intermediate transfer belt 24 interposed therebetween to form a primary transfer nip. The toner image on the photosensitive drum 2 is transferred onto the intermediate transfer belt 24 by applying a transfer bias having a polarity opposite to that of the toner image formed on the photosensitive drum 2 to the primary transfer roller 27. The toner images of the respective colors formed by the image forming units of the respective colors are sequentially primary transferred onto the intermediate transfer belt 24 so as to overlap with each other, and a color toner image is formed on the intermediate transfer belt 24.

A secondary transfer roller 30 is disposed at a position facing the secondary transfer counter roller, which is the drive roller 28, across the belt. The secondary transfer nip is brought into contact with the drive roller 28 with a predetermined load by a spring load. It is formed.
The color toner image formed on the intermediate transfer belt 24 is moved to the secondary transfer nip by the rotational drive of the intermediate transfer belt 24, and at the same time, is recorded in synchronization with the toner image entering the secondary transfer nip from the registration roller pair 23. The material enters the secondary transfer nip.

  The color toner image is secondarily transferred to the recording material by a secondary transfer electric field and a nip pressure formed between the secondary transfer roller 30 and the secondary transfer counter roller. The electric field for secondary transfer is formed by applying a transfer bias having the same polarity as the toner to the secondary transfer counter roller and grounding the secondary transfer roller 30.

A small amount of toner that has not been transferred to the recording material remains on the intermediate transfer belt 24 after passing through the secondary transfer nip. This is cleaned by the belt cleaning unit 26. In the belt cleaning unit 26, the cleaning blade is brought into contact with the surface of the intermediate transfer belt 24, whereby the transfer residual toner on the belt is scraped and removed.
The transfer residual toner removed from the intermediate transfer belt 24 is accommodated in the waste toner bottle 31 and discarded.

  A fixing unit is disposed above the secondary transfer nip. The fixing unit includes a fixing roller 32 including an electromagnetic induction heat generating layer, a pressure roller 33 which is in contact with the fixing roller 32 with a predetermined pressure and forms a predetermined nip width, a temperature sensor (not shown), and the like. On the left side of the fixing roller 32 in the figure, there is an IH coil unit 34 that is an electromagnetic induction means for generating heat in the electromagnetic induction heating layer in the fixing roller 32. The fixing roller 32 is heated by electromagnetic induction by an IH coil. Each roller is rotated by a pressure roller 33 in a clockwise direction and a fixing roller 32 in a counterclockwise direction by a driving source (not shown).

The recording material that has passed through the secondary transfer nip is separated from the intermediate transfer belt 24 and then fed into the fixing unit. Then, in the process of being conveyed from the lower side to the upper side in the figure while being sandwiched by the fixing nip of the fixing unit, the toner image is fixed on the recording material by being heated by the fixing roller 32 and simultaneously being pressurized by the fixing nip. It is done.
The recording material subjected to the fixing process in this manner is discharged out of the apparatus via a pair of paper discharge rollers and stacked on the upper surface of the image forming apparatus main body.

Next, the density adjusting means that is the main part of the present invention will be described in detail.
First, the basic operation of the density adjusting means will be described. The density adjusting means uses a process cartridge 1, an exposure unit 18 and the like for a reference toner pattern for detecting the toner density on the surface of the photosensitive drum 2. An electrostatic latent image is formed, the electrostatic latent image for the reference toner pattern is developed by the developing sleeve 14, and the reflected light from the developed reference toner pattern and the toner non-adhering portion on the surface of the photosensitive drum 2 is reflected by light. A value (Vsp / Vsg) obtained by dividing the output value Vsp of the light reflection type photosensor 10 in the reference toner pattern by the output value Vsg of the light reflection type photosensor 10 in the toner non-adhering portion is calculated. The calculated value is compared with a predetermined value set in advance, and toner replenishment control is performed so that the calculated value reaches a predetermined value set in advance. Going on.

In the toner replenishment control, when the toner adhesion amount of the reference toner pattern decreases, Vsp / Vsg increases from a predetermined value, and it is determined that the toner concentration of the two-component developer in the developing unit is low. Toner supply according to the comparison result is executed from a toner supply device (not shown) connected to the rear side in the drawing of one developer containing portion 8 (FIG. 1). On the contrary, when Vsp / Vsg is lower than the predetermined value, it is determined that the toner concentration of the two-component developer in the developing unit is high or appropriate, and the toner supply device supplies the first developer containing portion 8 to the first developer containing portion 8. The toner supply is not executed. That is, the relationship between the output value Vsp of the light reflection type photosensor 10 in the reference toner pattern and the toner density is determined based on the relationship as shown in FIG. 3 in terms of control.
The toner replenishment control by the density adjusting unit is performed for each process cartridge 1 for each predetermined number of image forming sheets, or when the main switch of the image forming apparatus is turned on or when the image forming operation ends.

  In this way, the toner density is adjusted by the density adjusting means. However, when the fixing of the sleeve occurs at the position where the reference toner pattern is formed, the toner fixed on the developing sleeve is charged and the effective voltage is increased. Since the amount of adhesion to the reference toner pattern (electrostatic latent image) on the photosensitive drum 2 increases, the output value Vsp of the light reflection type photosensor 10 in the reference toner pattern becomes low. Therefore, the toner density of the two-component developer in the developing unit is erroneously determined to be appropriate, so that the toner supply is insufficient and a problem arises that the image density becomes thin when a desired image is printed.

  This sleeve sticking is likely to occur in a non-image portion or an image with a small toner area in the sub-scanning direction. For example, as shown in FIG. 4, a document P having a figure a and a figure b with the same width in the main scanning direction and different lengths in the rotational movement direction (sub-scanning direction) of the photosensitive drum is used. When image formation is performed several times, the sleeve is likely to stick to the position of the developing sleeve 14 corresponding to the figure b.

FIG. 5 shows the relationship between the number of documents P (the number of images formed) and the toner density (sleeve density) at positions corresponding to the figures a and b on the developing sleeve 14. The sleeve density is measured with a reflection densitometer (RD918: manufactured by Macbeth). As is clear from FIG. 5, the figure b, whose length in the rotational movement direction (sub-scanning direction) of the photosensitive drum is shorter than the figure a, has a higher sleeve density, and is more likely to stick to the developing sleeve, and the sleeve is more likely to stick. I understand that. On the contrary, the figure a has a low sleeve density (appropriate range), and it is understood that the sleeve sticking hardly occurs.
Therefore, the density adjusting unit according to the present embodiment pays attention to the length of the reference toner pattern formed on the surface of the photosensitive drum 2 and the like.

(Embodiment 1)
In the density adjusting unit according to the first embodiment, the length of the reference toner pattern in the rotational movement direction (sub-scanning direction) is L, the circumferential length of the developing sleeve 14 is vs, the linear velocity of the developing sleeve 14 is vs, the photosensitive drum. When the linear velocity of 2 is vp, the length of the first reference toner pattern A (FIG. 6) longer than L × (vp / vs) and the rotational movement direction (sub-scanning direction) is a light-reflective photo The second reference toner pattern B (FIG. 7) having a minimum necessary length that can detect the reflected light from the sensor 10 can be formed, and toner density adjustment using the second reference toner pattern B is further possible. As a basis, toner density adjustment using the first reference toner pattern A is appropriately executed.

  As a specific example, for example, when the circumferential length L of the developing sleeve 14 is 62.8 mm and the linear velocity ratio (Vp / Vs) is 0.42, the rotational movement direction of the first reference toner pattern A (secondary) The length in the scanning direction) is set to be longer than L × (vp / vs) = about 26 mm, for example, 60 mm. In this way, the rotational movement distance of the photosensitive member corresponding to one rotation of the developing sleeve 14 is calculated, and the length of the first reference toner pattern A is set to one or more rotations of the developing sleeve 14. On the other hand, the length of the second reference toner pattern B in the rotational movement direction (sub-scanning direction) is set to 20 mm as the minimum necessary length that allows the reflected light by the light reflection type photosensor 10 to be detected. Note that the lengths of both the first reference toner pattern A and the second reference toner pattern B in the main scanning direction are both 20 mm.

As described above, according to the first embodiment, the toner of one or more rotations of the developing sleeve 14 is used for the development of the first reference toner pattern A, and the toner is periodically formed over the entire circumference of the developing sleeve 14. In addition to the original toner density control, it is possible to provide an image forming apparatus that suppresses the sticking of the sleeve and does not affect the toner density control. By performing toner density adjustment using the first reference toner pattern A as appropriate based on the toner density adjustment used, it is possible to minimize toner consumption.
In the first exemplary embodiment, the second reference toner pattern B is also used from the viewpoint of energy saving. However, the toner density adjustment may be executed using only the first reference toner pattern A. .

(Embodiment 2)
The density adjusting unit according to the second embodiment optimizes the detection position of the reflected light of the first reference toner pattern, that is, the detection timing of the light reflection type photosensor 10.

  First, the output voltage Vsp of the light reflection type photosensor 10 in the second reference toner pattern B will be described. When the vertical axis represents the output voltage Vsp and the horizontal axis represents time, the light reflection type photosensor 10 from LED-ON to OFF is shown in FIG. If the sleeve is stuck, the effective voltage is high (charge of the stuck toner is positive), so that the output voltage Vsp is lowered as shown by the broken line, and normal density adjustment is hindered. . The background portion is a surface portion of the photosensitive drum 2 where the second reference toner pattern B is not formed.

  On the other hand, the output voltage of the light reflection type photosensor 10 in the first reference toner pattern A is as shown in FIG. That is, in the case of one rotation of the developing sleeve 14, if the sleeve is stuck (separable), the output voltage Vsp (hereinafter referred to as Vsp <b> 1) decreases as described above. Since the subsequent output voltage Vsp (hereinafter referred to as Vsp2) is after the toner has been peeled off over the entire circumference of the developing sleeve 14, it is possible to detect without being affected by the fixing of the sleeve.

  Therefore, the density adjusting unit according to the second embodiment uses the first reference toner pattern A as the reference position for the detection position of the reflected light of the first reference toner pattern A, with the leading end side in the rotational movement direction as the reference. The position exceeds the length of x (vp / vs). If the specific dimensions exemplified in the first embodiment are used, a position of 26 mm or more and less than 60 mm is detected with reference to the tip side in the rotational movement direction (detection timing).

In the second embodiment, similarly to the first embodiment, the toner density adjustment using the first reference toner pattern A is appropriately performed based on the toner density adjustment using the second reference toner pattern B. It is preferable to make it.
According to the second embodiment, normal density control can be performed without being affected by the sleeve fixing.

(Embodiment 3)
In the first embodiment, the toner density adjustment using the first reference toner pattern A is appropriately performed on the basis of the toner density adjustment using the second reference toner pattern B. The density adjusting means optimizes the first reference toner pattern A creation interval (density adjustment execution interval).

  When the difference ΔVsp (= (Vsp2) − (Vsp1)) between the output voltages Vsp1 and Vsp2 in FIG. 9 described in the second embodiment is plotted on the vertical axis and the sleeve density is plotted on the horizontal axis, a diagram as shown in FIG. become. Based on this relationship, sleeve fixation can be predicted. Each time the first reference toner pattern A is created, ΔVsp is calculated, and the value is referred to the creation interval condition table of the first reference toner pattern A shown in Table 1, and the first reference toner pattern The creation interval of A is determined each time.

The higher the ΔVsp is, the more likely the sleeve fixing proceeds, and the shorter the interval for creating the first reference toner pattern A, that is, the shorter the interval at which the toner on the sleeve is peeled off, the sleeve fixing progress or the sleeve fixing. Can be prevented.
For example, when ΔVsp is 0.03 or more, the creation interval of the first reference toner pattern A is set to the 25th image formation number, and when ΔVsp is 0.02 or more and less than 0.03, the first reference toner pattern A is created. The creation interval of the toner pattern A is set to the 50th image formation number, and when ΔVsp is less than 0.02, the creation interval of the first reference toner pattern A is set to the 100th image formation number. As described above, the execution interval of the toner density adjustment using the first reference toner pattern A is varied by ΔVsp.

  On the other hand, the toner density adjustment executed when the main switch of the image forming apparatus is turned on or at the end of the image forming operation is fixed to the first reference toner pattern A, fixed to the second reference toner pattern B, or When ΔVsp is less than 0.02, the second reference toner pattern B is used. When the previous ΔVsp is 0.02 or more, the first reference toner pattern A is used.

The original execution interval of toner density adjustment executed every number of image formations is the same, and the second reference toner pattern B is used. For example, when ΔVsp is not less than 0.02 and less than 0.03, the first reference toner pattern A is created at the 50th image formation interval. In some cases, density adjustment is performed, and in this case, the second reference toner pattern B is used.
According to the third embodiment, it is possible to effectively suppress the sticking of the sleeve by changing the interval for creating the first reference toner pattern A according to the value of ΔVsp.

(Embodiment 4)
The third embodiment exemplifies the case where the interval for creating the first reference toner pattern A is changed according to the value of ΔVsp. However, the density adjusting unit according to the fourth embodiment uses the value of ΔVsp. The reference toner pattern used for the next toner density control is selected and determined as either the first reference toner pattern A or the second reference toner pattern B.

That is, when the value of ΔVsp is less than 0.02 (less than the threshold value), that is, when the sleeve fixing does not occur, or when the sleeve fixing occurs in the initial stage, the next toner density adjustment is performed using the second reference toner pattern B. Use. When the value of ΔVsp is 0.02 or more, the first reference toner pattern A is used for the next toner density adjustment.
According to the fourth embodiment, the reference toner pattern used for the next toner density control is selected and determined as the first reference toner pattern A or the second reference toner pattern B according to the value of ΔVsp. By doing so, it is possible to suppress the toner consumption in the toner density adjustment while suppressing the sticking of the sleeve.

  The image forming apparatus according to the present embodiment has been described above. However, the above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto. Various modifications can be made without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1 ... Process cartridge 2 ... Photosensitive drum 10 ... Light reflection type photo sensor 14 ... Development sleeve 18 ... Exposure unit

JP 2002-323797 A JP 2004-004209 A

Claims (6)

An electrostatic latent image for a reference toner pattern for detecting the toner density is formed on the surface of the rotatable photosensitive member, and the electrostatic latent image is developed by the rotatable developer carrier, and the developed image is developed. In an image forming apparatus including a density adjusting unit that detects reflected light of a reference toner pattern and adjusts toner density using an output value corresponding to the reflected light.
The density adjusting means is configured such that the length of the reference toner pattern in the rotational movement direction is L, the circumferential length of the developer carrier is vs, the linear velocity of the developer carrier is vs, and the linear velocity of the photoreceptor is An image forming apparatus configured to be capable of forming a first reference toner pattern longer than L × (vp / vs) when vp is set.   The density adjusting unit is configured to be capable of forming a second reference toner pattern having a minimum necessary length that allows the reflected light to be detected in the rotational movement direction of the reference toner pattern. The image forming apparatus according to claim 1, wherein toner density adjustment is executed by appropriately selecting one of a first reference toner pattern and the second reference toner pattern.   3. The toner density adjustment unit according to claim 2, wherein toner density adjustment using the first reference toner pattern is appropriately performed based on toner density adjustment using the second reference toner pattern. The image forming apparatus described.   The density adjusting unit is configured to detect the reflected light of the first reference toner pattern as the detection position of the first reference toner pattern by using the length of the first reference toner pattern as a reference, L × (vp / vs) The image forming apparatus according to claim 1, wherein the image forming apparatus is located at a position exceeding a length of the image forming apparatus.   The density adjusting unit is configured to detect the reflected light of the first reference toner pattern as the detection position of the first reference toner pattern by using the length of the first reference toner pattern as a reference, L × (vp / vs) And a second detection position that exceeds the length of L × (vp / vs), and an output value corresponding to the reflected light at the first detection position 4. The execution interval of toner density adjustment using the first reference toner pattern is varied according to a difference between the output value corresponding to reflected light at the second detection position and the second reference position. 5. The image forming apparatus according to claim 1.   The density adjusting unit is configured to detect the reflected light of the first reference toner pattern as the detection position of the first reference toner pattern by using the length of the first reference toner pattern as a reference, L × (vp / vs) And a second detection position that exceeds the length of L × (vp / vs), and an output value corresponding to the reflected light at the first detection position The second reference toner pattern is used for the next toner density adjustment when a difference between the output value corresponding to the reflected light at the second detection position is less than a threshold value. The image forming apparatus described in 1.

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