JP3957992B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic system or an electrostatic recording system, and more particularly to an image forming apparatus such as a copying machine, a printer, and a FAX.
[0002]
[Prior art]
In general, a developing device as a developing unit included in an image forming apparatus of an electrophotographic system or an electrostatic recording system has a one-component developer containing magnetic toner as a main component, or a non-magnetic toner and a magnetic carrier as main components. A two-component developer is used. In particular, in an image forming apparatus that forms a full-color or multi-color image by an electrophotographic method, most developing devices use a two-component developer from the viewpoint of the color of the image.
[0003]
As is well known, the toner concentration of the two-component developer (the ratio of the toner weight to the total weight of the carrier and toner) is a very important factor in stabilizing the image quality. The toner of the developer is consumed during development, and the toner density of the developer is reduced. For this reason, it is necessary to detect the toner density or image density in the developer in a timely manner, to replenish the toner in accordance with the change, to always control the toner density or image density to be constant, and to maintain the image quality.
[0004]
In view of this, various types of density control devices have been proposed in the past in which toner replenishment control is performed on a developing device having a reduced toner density to control the toner density or image density to be constant.
[0005]
For example, as a method of making the toner concentration in the developer in the developing container of the developing device constant, a method of detecting and controlling the toner concentration of the developer in the developing container from the amount of reflected light (developer reflection control), development There is a method (inductance control) for detecting and controlling the magnetic permeability of the developer magnetic carrier in the container.
[0006]
However, in the method of making the developer toner concentration constant, it is possible to keep the developer toner concentration constant in order to directly detect the developer toner concentration. When the toner or the magnetic carrier is changed and the triboelectric charge amount (tribo) of the toner is changed, the developability is changed, so that the image density is also changed.
[0007]
For this reason, in recent image forming apparatuses, a density detection means for forming a reference image (hereinafter referred to as a “patch image”) on a photosensitive drum as an image carrier and setting the toner adhesion amount facing the photosensitive drum. In general, a method (patch detection control) in which the developer density is controlled by detecting with an optical detection sensor is used. In this patch detection control method, the toner density of the patch image on the photoconductive drum is detected and replenishment control is performed, so that the image density can be kept almost constant. It is known to be affected.
[0008]
This will be specifically described with reference to FIG. FIG. 3 is an EV characteristic in which the vertical axis indicates the drum potential (V), the horizontal axis indicates the laser level, and is divided into 8 bits. In FIG. 3, the photosensitive drum sensitivity before and after the endurance is shown. From the figure, it can be seen that the halftone sensitivity deteriorates after the endurance of the photosensitive drum used in this study. Further, the patch image density used in the patch detection control is a halftone density from the viewpoint of the optical detection sensor characteristics and the image stability.
[0009]
For this reason, when patch detection control is performed on a photoconductor drum after durability with reduced sensitivity, the halftone latent image potential, that is, the patch latent image potential, is higher than the initial value, so the contrast potential of the patch image decreases. Accordingly, the development characteristics of the patch image are deteriorated as compared with those before the endurance, and the control means repeats the toner replenishment in order to compensate for the deterioration of the development characteristics. As a result, when the initial development characteristic was recovered, the development characteristic curve as shown in FIG. 4 was changed. Note that the image density in FIG. 4, that is, the patch image density, was 0.8 using an X-rite reflection densitometer.
[0010]
[Problems to be solved by the invention]
By the way, as described above, the toner and the magnetic carrier in the developer change due to long-term use, and it becomes difficult to recover by toner replenishment control, or the developer is replaced before that. When the developer is replaced (including the replacement of the toner supply container that can be attached to and detached from the image forming apparatus and contains toner to be supplied to the developing apparatus), the initial state of the developer is detected and the patch image density is detected. The reference value is set (hereinafter referred to as “initial setting”). This initial setting is a very important sequence because it becomes the target value of the amount of toner on the photosensitive drum thereafter, but the initial setting is in a state where the photosensitive drum sensitivity varies due to individual differences of each photosensitive drum and durability deterioration. If it is set, it will greatly affect the image density transition after setting.
[0011]
Also, at the normal initial setting, the patch laser level determined by the installation environment and environmental history of the apparatus is stored and used in the apparatus main body with a table or the like, but the initial stage after changing the developer with the patch laser level fixed is used. Since it was also used at the time of setting, the initial setting was performed in a state where the latent image potential of the patch image was not compensated.
[0012]
As described above, in the conventional patch detection control at the initial setting after the developer replacement or the like, the development characteristic curve after the endurance changes due to the setting failure at the initial setting accompanying the change in the photosensitivity characteristic of the photosensitive drum. As a result, the image density may change greatly.
[0013]
An object of the present invention is to provide an image forming apparatus capable of optimizing the potential of an electrostatic latent image for detection even if the photosensitivity characteristics of an image carrier have changed due to durability.
[0014]
Another object of the present invention is to provide an image forming apparatus capable of optimizing the amount of developer to be supplied to the developing means.
[0015]
Another object of the present invention is to provide an image forming apparatus capable of optimizing the target value to be compared with the output of the density detecting means.
[0016]
Further objects of the present invention will become apparent upon reading the following detailed description.
[0017]
[Means for Solving the Problems]
  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention
  Image carrierWhen,
  Developing means for developing the electrostatic latent image formed on the image carrier with a developerWhen,
  Potential detection means for detecting the potential of the electrostatic latent image for detection on the image carrierWhen,
  Potential control means for controlling the potential of the electrostatic latent image for detection according to the output of the potential detection meansWhen,
  Density detection means for detecting the density of the developer image for detectionWhen,
  Developer amount control means for controlling the amount of developer to be replenished to the developing means in accordance with the output and target value of the density detecting means;
  Have
  After the developer replacement, the density detection unit detects the density of the detection developer image obtained by developing the detection electrostatic latent image controlled by the potential control unit by the development unit, An initial setting is made to correct the target value based on the output of the density detecting means by the detection.An image forming apparatus characterized by the above.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.
[0020]
Example 1
A first embodiment of the present invention will be described with reference to FIGS.
[0021]
First, the image forming apparatus of this embodiment will be described with reference to FIG. For the sake of simplicity, a single image forming station (photosensitive drum 40 as an image carrier, pre-exposure device 18, primary charger 19 as charging means, developing device 20 as developing means, and In the case of a color image forming apparatus, for example, cyan, magenta, yellow, and black developing devices are sequentially arranged facing the photosensitive drum 40 in the case of a color image forming apparatus. It is set as the installed configuration.
[0022]
In this embodiment, the case of an electrophotographic digital color copying machine will be described. However, the present invention is applicable to various other image forming apparatuses of an electrophotographic system or an electrostatic recording system, and an image forming apparatus for forming a monochrome image. It goes without saying that it is equally applicable.
[0023]
First, an image of an original is read by a CCD (not shown), and a binarized image signal that is pulse-width modulated in accordance with the obtained image signal is directly input to the laser drive circuit 12 and is a laser diode that is an exposure means. 13 is used as an on / off control signal for light emission. The laser light emitted from the laser diode 13 is scanned in the main scanning direction by a known polygon mirror 14, passes through the f / θ lens 15 and the reflection mirror 16, and onto the photosensitive drum 40 rotating in the arrow direction. Irradiates to form an electrostatic latent image.
[0024]
On the other hand, the photosensitive drum 40 is uniformly discharged by the pre-exposure device 18 and is uniformly charged, for example, negatively by the primary charger 9. Thereafter, an electrostatic latent image corresponding to the image signal is formed by the irradiation of the laser beam described above. The electrostatic latent image is developed as a visible image (toner image) by the developing device 20 by a reversal development method. The toner image formed on the photosensitive drum 40 is transferred by the action of the transfer charger 22 onto the recording material P conveyed to the photosensitive drum 40 by the recording material carrying belt 17 as a recording material carrying member. The recording material carrying belt 17 is stretched around two rollers 25a and 25b, and is driven endlessly in the direction of the arrow in the figure to convey the recording material P carried thereon to the photosensitive drum 40. After the transfer, the transfer residual toner remaining on the photosensitive drum 40 is scraped off by the cleaner 24.
[0025]
In addition, after performing the image formation, in order to perform the patch detection control which is the image density stabilization control, first, a single gradation density level (0.8 in this embodiment using an X-rite reflection densitometer) is placed on the photosensitive drum 40. A reference patch image T) is developed and developed, and the density of the patch image T is measured by a density sensor 27 serving as a density detection means having a light emitting portion and a light receiving portion disposed opposite to the photosensitive drum 40. The detected value is sent to the CPU 6.
[0026]
The CPU compares the detected value Sgnl with an initial density reference value (SgnlInit) stored in advance in a ROM as a storage unit, and a toner excess necessary for returning the toner density to the initial density reference value (SgnlInit). Calculate the deficiency. Specifically, it is calculated by the following formula.
[0027]
Toner excess / deficiency = (SgnlInit−Sgnl) / (Signal level difference Δ of toner concentration 1%) × (toner amount of toner concentration 1%)
The amount of toner excess / deficiency calculated here is positive / negative. For example, it is determined that the toner is in an insufficient toner state when positive, and an excessive toner state when negative.
[0028]
When it is determined that the toner is in a shortage state, the toner conveying screw 30 connected via the gear train 28 is rotationally driven by the motor 7, whereby the replenishing toner 29 in the replenishing tank 8 is conveyed and entered into the developing device 20. Supplied.
[0029]
Next, a method for determining a reference value (target value) of patch latent image potential control and patch detection density at the time of initial setting after replacing the developer 21 in the developing device 20, which is a characteristic part of the present invention, is shown in FIG. It demonstrates using the flowchart of these.
[0030]
In this embodiment, first, after replacing the developer 21 or after replacing a replenishing container that can be attached to and detached from the image forming apparatus and contains the developer to be replenished to the developing apparatus (S100), the developer tribo (per unit weight) The developer is agitated by the agitating / conveying screw 20b in the developing container 20a (S101). Thereafter, the environmental patch latent image potential Vref is determined based on the environment where the apparatus is placed or the environmental history (S102). Then, a patch latent image is formed at a certain laser level (exposure time) (S103), and the patch latent image potential Vp is measured by the surface potential sensor 23 as potential detecting means (S104). Next, a patch latent image potential difference Vdif (= Vref−Vp) is calculated (S105). If the potential difference is within a predetermined potential difference (± 5 V in this embodiment), a developing bias is applied to the developing device 20 to develop the patch latent image. (S108) The patch latent image density detection result by the sensor 27 is stored in the ROM as the initial density reference value SgnlInit (S109).
[0031]
When the patch latent image potential difference Vdif (= Vref−Vp) is calculated by the CPU (S105), if Vdif is greater than 5V, it is determined that the patch latent image potential Vp is higher than the predetermined potential, and the patch latent image is first displayed. The laser level at the time of formation is increased by one step (S106), a patch latent image is formed again, and the patch latent image potential Vp is detected (S104). Conversely, if Vdif is less than −5V, it is determined that the patch latent image potential is lower than the predetermined potential, the laser level is lowered by one step (S107), a patch latent image is formed again, and the patch latent image potential Vp Is detected (S104).
[0032]
When the patch latent image potential difference Vdif is outside the predetermined range, the CPU repeats the above sequence. When Vdif falls within the predetermined potential difference (when the patch latent image potential Vp falls within the predetermined range), the same as described above. The developing device 20 is applied with a developing bias to develop a patch latent image appropriately controlled in potential, the patch sensor 27 detects a patch density signal value, and the measurement result is stored as an initial density reference value SgnlInit. Stored in the ROM.
[0033]
Finally, the patch laser level necessary for forming a patch latent image with the potential controlled and the potential optimized obtained in the initial setting sequence is stored in the ROM (S110). Used as patch laser level.
[0034]
As described above, since the initial setting is performed under the patch image forming conditions at which a predetermined patch latent image potential is obtained, adverse effects due to variations in the photosensitivity characteristics of the photosensitive drum can be eliminated, and the conditions obtained at the initial setting can be eliminated. Since the subsequent patch formation is performed, the toner replenishment control to the developing device can be performed satisfactorily, and the image density fluctuation can be suppressed.
[0035]
Example 2
Next, a second embodiment of the present invention will be described.
[0036]
In the first embodiment, when the patch latent image potential difference Vdif is greater than or equal to a predetermined potential difference, when determining the next patch laser level, control is performed to change the laser level by one step in any case. However, in this control method, when Vdif is very large, the predetermined potential difference is not easily accommodated, and it takes time to perform the initial setting sequence, resulting in an increase in downtime.
[0037]
Therefore, in this embodiment, the control is performed by changing the change amount of the patch laser level in accordance with the obtained patch latent image potential difference. Specifically, the laser level change amount obtained by the following equation was obtained, and the patch laser level was changed from this value.
[0038]
Laser level change = Patch potential difference / 10V
As a result, an image forming condition capable of obtaining a predetermined patch latent image potential can be quickly found, and an initial setting sequence can be smoothly performed.
[0039]
Example 3
In this embodiment, after ensuring the bright part and dark part potentials on the photosensitive drum before performing the initial setting sequence, the patch latent image potential measurement was performed to perform the initial setting. That is, as shown in FIG. 3, in the case where the laser level is 0 (minimum) and the case where the laser level is 256 (maximum), the above-described potential control is performed so that the potential on the photosensitive drum becomes a predetermined potential. An initial setting sequence was performed.
[0040]
Thus, the patch latent image potential can be determined with very high accuracy because it is an initial setting sequence after guaranteeing the bright portion potential and the dark portion potential based on the sensitivity of the surface of the photosensitive drum.
[0041]
Example 4
In the fourth embodiment, the laser exposure intensity was changed in order to set the patch latent image potential to a predetermined potential.
[0042]
Specifically, when the patch latent image potential difference Vdif shown in FIG. 2 is larger than 5V, the laser power is increased by one step. When the patch latent image potential difference Vdif is smaller than −5V, the laser power is decreased by one step. The same effect was obtained.
[0043]
Example 5
First, the potential control method employed also in the first to fourth embodiments will be described.
[0044]
The potential control is a control for preventing a change in the maximum image density and a deterioration in white fog by detecting and correcting a change in the durability characteristic of the photosensitive drum. Specifically, from the contrast potential that can guarantee the maximum image density, This is control for obtaining the grid potential of the charging means and the developing bias potential of the developing means.
[0045]
Here, regarding the potential control method, the relationship between the grid potential and the photosensitive drum surface potential will be described with reference to the graph of FIG. 8, and the potential measurement flowchart will be described with reference to FIG.
[0046]
First, the grid potential is set to Vg1 = −300 V (S1), and the photosensitive drum surface potential (dark portion potential) Vd when scanned with the light emission pulse level of the semiconductor laser as the exposure means being minimized, the light emission of the semiconductor laser. The photosensitive drum surface potential (light portion potential) Vl when the pulse level is maximized is measured with a surface potentiometer (S2 to S5).
[0047]
Similarly, Vd and Vl when the grid potential is set to Vg2 = −500V and Vg3 = −700V are measured in the same manner as described above (S6 to S15). Next, the grid potential -300V data and -500V data, and the grid potential -500V and -700V data are interpolated and extrapolated to obtain the relationship between the grid potential and the photosensitive drum surface potential (S16).
[0048]
The development bias potential Vdc is set by providing a difference between the surface potential Vd and Vback (here, 150 V) set so that fog toner does not adhere to the image (S17).
[0049]
Next, the contrast potential (Vcont + Vback) required at the time of image formation is obtained by calculating the amount of water from the temperature and humidity of the apparatus detected by the environmental sensor provided in the apparatus. Here, Vcont is a differential voltage between Vdc and Vl.
[0050]
From this contrast potential, it is possible to calculate how many V grid potential is required and how many V development bias potential is necessary from the relationship shown in FIG. Control for obtaining this potential data is potential control.
[0051]
However, if potential control is performed at the start of each copy sequence, it is possible to compensate for changes in the sensitivity of the photoconductor at any time. However, since the printout throughput is reduced, the above-described potential control is usually performed by the main power supply of the image forming apparatus. Immediately after entering, or after the elapse of a predetermined time, that is, after elapse of, for example, 2 hours of the previous potential control, the control is performed using the previously obtained grid potential and developing bias potential.
[0052]
However, due to problems such as complicated control of a plurality of patches and an increase in downtime, the actual patch detection control is configured to control the toner density in the developing container by one-patch control (hereinafter referred to as “one-patch toner density control”). Is common. However, in order to improve the printout throughput even with one patch toner density control, patch detection trial frequency, replenishment control between patch detections, and image defect countermeasures by increasing or decreasing the toner density in the developing container are also important image formation requirements. It has become.
[0053]
Further, in the apparatus using the two controls described above, the patch detection control is performed in a state where the bright portion and dark portion potentials are compensated by the potential control method but the halftone potential cannot be compensated. For this reason, the image density largely changes due to a halftone sensitivity difference (such as before and after endurance) of the photosensitive drum that changes with time.
[0054]
For this reason, when patch detection control is performed on a photoconductor drum after durability with reduced sensitivity, the halftone latent image potential, that is, the patch latent image potential, is higher than the initial value, so the contrast potential of the patch image decreases. Accordingly, the development characteristics of the patch image are deteriorated as compared with those before the endurance, and the control means repeats the toner replenishment in order to compensate for the deterioration of the development characteristics. As a result, when the initial development characteristic was recovered, the development characteristic curve as shown in FIG. 4 was changed. It should be noted that the patch image density is set to 0.8 level as measured by a reflection densitometer (manufactured by X-rite). In addition, this characteristic was remarkable in a durable drum, that is, a photosensitive drum after long-term use or in a high moisture content environment.
[0055]
Therefore, in this embodiment, in the image forming apparatus shown in FIG. 5 (the image forming apparatus having substantially the same configuration as that in FIG. 1, the same members as those in FIG. When the normal image formation (same as in the first to fourth embodiments) is completed, a post-rotation sequence, that is, a patch image formation step is performed, and the detection result of the patch latent image potential obtained at this time is fed back at the next patch image formation. By doing so, the downtime of the apparatus is made as short as possible.
[0056]
The post-rotation sequence will be described with reference to the flowchart of FIG.
[0057]
When the post-rotation sequence is entered, the laser level is first determined from the current detection result of the environmental sensor 10 and the environmental history in order to form a patch of a certain density level on the photosensitive drum 40 (S100). In this embodiment, a density patch that is 0.8 in the X-rite reflection densitometer is used as the density level. However, the density level is not limited to this, and a level of 0.5 to 1.2 is preferable. Used for.
[0058]
Next, similarly to the normal image formation, the photosensitive drum 40 is uniformly charged by the primary charger 19, and a patch latent image is formed at the previously determined laser level (S101).
[0059]
Thereafter, when the patch latent image passes through the potential sensor 23, the patch latent image potential is detected (S102) and compared with the initial patch latent image potential (S103). Then, when it is higher than the initial patch latent image potential, ErrFlag = 1 is set, and when it is lower, ErrFlag = −1 is set (S104) and sent to the controller 6.
[0060]
When the patch latent image reaches the development position, it is developed by the two-component developer in the developing device 20 (S105). When the developed patch image passes over the optical sensor 27, the patch image density is detected (S106), and the detection result is sent to the controller 6, compared with the initial density (S107), and determined to be lower than the initial density. In the case where the toner is supplied, the toner 7 is rotated by the motor 7 so that the replenishment toner in the replenishing tank 22 is replenished to the developing device 20 by a necessary amount (S108). A stop signal is generated (S109), and the post-rotation sequence is terminated.
[0061]
Next, a reference image forming condition feedback method will be described. Here, the control when the patch latent image potential is higher than the initial potential in the post-rotation sequence described above, that is, when the next post-rotation sequence is entered with ErrFlag = 1 will be described.
[0062]
In this embodiment, after entering the post-rotation sequence, the laser level is first determined by the environmental sensor 10 that detects the temperature and humidity of the atmosphere in the laser level determination step, and then the laser drive circuit 12 is used to lower the patch latent image potential. The laser level was increased by 1 to form a patch latent image. The subsequent sequence is the same as the post-rotation sequence described above.
[0063]
As a result of this control, the patch latent image potential can be lowered from the previous patch latent image potential in the patch latent image potential detection step (S102). After the patch latent image potential is detected in the subsequent rotation sequence, if the patch latent image potential is kept high, the process proceeds to S105 without re-creating the patch latent image unlike the first to fourth embodiments. . As a result of the patch latent image potential detected in S102, the laser level may be raised by one step in the next post-rotation sequence (when the patch latent image is next formed).
[0064]
By repeatedly performing the patch latent image potential control after this rotation, the patch latent image potential can be brought close to the initial potential in the long term without increasing the downtime of the apparatus. It has become possible to reduce changes in developability due to changes in the durability of the photosensitive drum.
[0065]
Accordingly, since the time during which a normal image cannot be formed can be shortened as much as possible, a decrease in image formation throughput can be suppressed as much as possible. This is particularly effective when images are continuously formed on a plurality of recording materials P.
[0066]
Here, the case where the patch latent image potential is higher than the initial potential, that is, the case where ErrFlag = 1, has been described, but it is needless to say that the control can be performed in the opposite manner to the above sequence even when the potential is low.
[0067]
Example 6
In Example 5, when determining the laser level, control was performed by changing the laser level by one step using ErrFlag. However, the patch detection control is halftone control, and as is apparent from the development characteristics shown in FIG. 4 described above, the development characteristics in the vicinity of this density change sharply. Therefore, a laser level change of one stage may be accompanied by a very large density fluctuation. As a result, in an image forming apparatus that forms an image using a plurality of photosensitive drums, there is a possibility that a color variation or the like occurs.
[0068]
Therefore, in this example, the patch potential difference represented by the following formula (1) was calculated.
[0069]
Patch potential difference = patch latent image potential-initial potential (1)
Then, the patch laser level was changed according to the obtained patch potential difference. Specifically, in this embodiment, the laser level change amount obtained by the following equation (2) is obtained, and the patch laser level is changed from this value.
[0070]
Laser level change amount = patch potential difference / 10 (V) (2)
As a result, it was possible to achieve durable concentration stabilization without causing a large concentration change.
[0071]
In this embodiment, the laser level change amount is obtained by the equation (2). However, the laser level change amount may be changed according to the characteristics of the photosensitive drum, or the laser level change amount may be controlled in advance using a table based on environmental conditions and patch potential differences. It doesn't matter.
[0072]
Example 7
Next, this embodiment will be described with reference to FIG.
[0073]
In this embodiment, the patch latent image potential measurement and the patch laser level determination were performed immediately after the potential control, other than during post-rotation. Since the potential control sequence is normally performed at the time of pre-rotation during the copy operation, the following description will be made as a sequence at the time of pre-rotation.
[0074]
First, after the bright part and dark part potentials are compensated by the potential control sequence described above (S200), a patch latent image is formed at the laser level calculated from the current environment and environmental history (S201, S202). The image potential is detected (S203) and compared with the patch initial potential (S204). Then, when it is higher than the patch initial potential, ErrFlag = 1 is set, and when it is lower, ErrFlag = −1 is set (S205). From this result, when ErrFlag = 1, the patch laser level is increased by one step, and ErrFlag = In the case of -1, the level is lowered by one step (S201), a latent image is formed again (S202), the electrostatic potential is measured (S203), and the laser level is searched to be the same as the initial potential. Did that.
[0075]
According to the above control, the patch latent image potential can be compensated in a state where the bright part potential and the dark part potential are compensated, so that a better result can be obtained. Further, by storing the patch laser level determined here in the controller, it becomes possible to find a desired patch laser level relatively easily even when the sensitivity of the photosensitive drum thereafter changes.
[0076]
Example 8
In the above embodiment, the patch latent image potential is made the same as the initial potential by changing the laser level, that is, the laser exposure time. In this embodiment, the patch exposure image potential is changed by changing the laser exposure intensity.
[0077]
Specifically, in steps S104 and S205 shown in FIGS. 6 and 7, when ErrFlag = 1, the laser power is increased by one step, and when ErrFlag = −1, the laser power is decreased by one step. The same effects as in the example could be obtained.
[0078]
Example 9
In Examples 1 to 8, an organic photoreceptor is used as the image carrier, but an amorphous silicon photoreceptor may be used. In such an image forming apparatus using an amorphous silicon photoconductor, the patch latent image potential control described in Examples 1 to 8 was performed.
[0079]
The amorphous silicon photoreceptor has a Vickers hardness of 1500 to 2000 kg / cm.²(= 1.5 × 10²~ 2.0 × 10²It is known that it has a very large dark decay as a photosensitive drum characteristic. For this reason, in an image forming apparatus using an amorphous silicon drum and patch detection control, a large number of tables are prepared for dark attenuation and sensitivity change correction, and the durability development characteristics fluctuate due to the complexity and control of initial settings. There was such a big problem.
[0080]
However, according to the first to fourth embodiments, since the initial setting is performed after determining the image forming conditions for obtaining a predetermined patch latent image potential at the time of initial setting, the table prepared in the apparatus of the present embodiment is the environment patch latent image. Only the electric potential is required, and it is possible to suppress fluctuations in image density after long-term use.
[0081]
Further, according to the fifth to eighth embodiments, since the patch latent image potential is always controlled to be the same as the initial potential, the same effect can be obtained without the trouble of preparing a large number of tables. I was able to.
[0082]
Further, the present invention is an image forming apparatus employing a tandem system having a plurality of image carriers (in the case where a plurality of image forming stations are provided in FIGS. The present invention is particularly effective when applied to a configuration in which toner images are sequentially superimposed and transferred to form a color image. That is, since the output image density can be optimized for each image forming station, it is possible to obtain a high-quality image with no color variation in the formed color image. Further, the toner image transferred from each image carrier is not limited to the recording material P but may be a so-called known intermediate transfer member. In this case, the color image that has been primary-transferred sequentially and superimposed on the intermediate transfer member from each image carrier is then transferred to the recording material P in a batch manner.
[0083]
Although this invention was demonstrated as what can be embodied in the said Examples 1-9, the application range is not restricted to this, All modifications are possible if it is in the range of the thought of this invention.
[0084]
【The invention's effect】
  As described above, the present inventionAn image carrier, a developing unit that develops the electrostatic latent image formed on the image carrier with a developer, a potential detector that detects a potential of a detection electrostatic latent image on the image carrier, and a potential Potential control means for controlling the potential of the electrostatic latent image for detection according to the output of the detection means, density detection means for detecting the density of the developer image for detection, and the output and target value of the density detection means A developer amount control means for controlling the amount of developer to be replenished to the developing means, and after the developer replacement, the developing electrostatic latent image for detection whose potential is controlled by the potential control means is developed by the developing means. Then, the density of the developer image for detection obtained in this way is detected by the density detection means, and the target value is corrected based on the output of the density detection means by the detection, and the initial setting is performed.So
(1) Even if the photosensitivity characteristic of the image carrier changes due to durability, the potential of the electrostatic latent image for detection can be optimized.
(2) The amount of developer to be replenished to the developing means can be optimized.
(3) The target value to be compared with the output of the density detecting means can be optimized.
(4) Therefore, it is possible to suppress image density fluctuation and always obtain a high quality image.
Such effects can be achieved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a flowchart showing an embodiment of patch latent image potential control at the time of initial setting.
FIG. 3 is a characteristic diagram illustrating an example of a potential fluctuation state of the photosensitive drum.
4 is a diagram showing development characteristics before and after endurance due to potential fluctuation of the photosensitive drum in FIG. 3; FIG.
FIG. 5 is a schematic configuration diagram illustrating another example of the image forming apparatus according to the present invention.
FIG. 6 is a flowchart showing an embodiment of a post-rotation sequence.
FIG. 7 is a flowchart showing an embodiment of a pre-rotation sequence.
FIG. 8 is a graph showing the relationship between the grid potential and the photosensitive drum surface potential.
FIG. 9 is a flowchart showing an example of a conventional potential control sequence.
[Explanation of symbols]
13 Laser diode (exposure means)
19 Primary charger (charging means)
20 Developing device (developing means)
20a Developer container
23 Surface potential sensor (surface potential detection means)
27 Patch detection sensor (concentration detection means)
40 Photosensitive drum (image carrier)

Claims (12)

And the image bearing member,
Developing means for developing the electrostatic latent image formed on the image carrier with a developer ;
And potential detection means for detecting the potential of the electrostatic latent image for detection on the image bearing member,
A potential control means for controlling the potential of the electrostatic latent image for detection according to the output of the potential detection means ;
Density detecting means for detecting the density of the developer image for detection ;
Developer amount control means for controlling the amount of developer to be replenished to the developing means in accordance with the output and target value of the density detecting means;
Have
After the developer replacement, the density detection unit detects the density of the detection developer image obtained by developing the detection electrostatic latent image controlled by the potential control unit by the development unit, An image forming apparatus , wherein an initial setting is performed to correct the target value based on an output of the density detection means by the detection . The image forming apparatus according to claim 1 , wherein the developer is a two-component developer including a toner and a carrier. 3. The image forming apparatus according to claim 1 , wherein in the initial setting, the potential control unit controls the potential of the electrostatic latent image for detection according to an output of the potential detection unit and a target value. . The image forming apparatus further includes a latent image forming unit that forms an electrostatic latent image for detection on the image carrier. In the initial setting, the potential control unit uses the latent image forming unit according to the output of the potential detecting unit. the image forming apparatus according to claim 1 or 2, characterized in that to control the latent image forming conditions. 5. The image forming apparatus according to claim 4 , wherein an amount of changing the latent image forming condition by the potential control unit is variable according to an output of the potential detection unit. Is the latent image forming means includes an exposure means for exposing said image bearing member, said potential control means according to claim 4, characterized in that for controlling the exposure conditions by the exposure means in accordance with the output of said potential detection means Image forming apparatus. The image forming apparatus according to claim 6 , wherein the exposure condition is an exposure time. The image forming apparatus according to claim 6 , wherein the exposure condition is exposure intensity. Wherein a and a containing means for containing the developer to be replenished to the developing unit further houses means detachably mountable to the image forming apparatus main body, wherein the developer exchange, characterized in that it is a replacement of said containing means the image forming apparatus according to claim 1 or 2. The image forming apparatus according to claim 1 or 2, characterized in that said image bearing member is an amorphous silicon photoconductor. The image forming apparatus according to claim 1 or 2 concentration of the developer image for detection is equal to or formed to have a halftone density. 12. The image forming apparatus according to claim 11 , wherein the density of the developer image for detection is formed to be a level of 0.5 to 1.2 as measured by a reflection densitometer.

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