JP3912967B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image by electrophotography.
[0002]
[Prior art]
Conventionally, in an image forming apparatus using this type of electrophotographic method, a metal drum having a photosensitive layer composed of a charge generation layer and a charge transport layer is generally used as an image carrier for holding toner on an electrostatic latent image. Alternatively, a photoreceptor composed of a metal belt or the like is used.
[0003]
The image carrier is driven in a certain direction by a print start signal.
[0004]
Thereafter, a bias is applied to a charging device (corona charger, charging roller, agent carrier carrying magnetic particles, etc.) to charge the surface of the image carrier to a certain potential or charge injection. The surface potential (charging potential) of the photoconductor at this time is referred to as VD potential (or Vd potential).
[0005]
Further, based on a signal from the controller, the image carrier is irradiated with LED light that is ON / OFF controlled (exposure). Since the potential is lowered at the position irradiated with light, an electrostatic latent image is formed on the surface of the image carrier. The potential of the exposed part is called VL potential (or Vl potential).
[0006]
Then, a constant developing bias (hereinafter also referred to as a developing potential) is applied to the developing device that is arranged to face the image carrier and is filled with toner, so that the toner to which a predetermined charge is applied is statically applied on the image carrier. The electrostatic latent image is visualized (development) by transferring to the electrostatic latent image. The amount of toner on the image carrier during development is determined by the relationship between the VL potential and the development bias.
[0007]
Then, a bias having a polarity opposite to that of the toner on the image carrier is applied to a transfer member such as a transfer roller or a transfer belt which is arranged adjacent to the image carrier and moves in the forward direction at substantially the same speed as the image carrier. In this state, the transfer material is passed between the image carrier and the transfer member, whereby the toner image carried on the image carrier is transferred onto the transfer material.
[0008]
In the image forming apparatus described above, the photosensitive layer of the image carrier is affected by the exposure memory due to the irradiation light. For example, the image carrier that has finished transferring the toner image repeats the above-described image forming process again, but there may be a case where a ghost (afterimage) occurs due to the influence of the exposure memory of the previous process. That is, the VL potential after exposure varies depending on the use state (exposure history) of the image carrier, which leads to a change in the amount of toner on the image carrier, and the print image density becomes uncertain.
[0009]
Therefore, conventionally, in order to suppress the exposure memory, it is common to perform so-called pre-exposure in which the image carrier is uniformly exposed by an appropriate light source (pre-exposure light source) before charging the image carrier. .
[0010]
Recently, in order to reduce the size of the apparatus, an image forming apparatus of a type that does not include a pre-exposure light source has appeared.
[0011]
In such a small image forming apparatus, in order to solve the above-described problem, exposure is performed in an exposure amount region that is 60% to 90% of the maximum latent image contrast potential difference, and a development potential or the like is adjusted in accordance with the exposure amount. A method for changing the image forming conditions is proposed. Since the exposure area under this condition is less affected by the exposure history described above, it is possible to reduce ghosts without performing pre-exposure.
[0012]
Here, the maximum latent image contrast potential difference means an exposure amount of 0.1 μJ / cm when an image bearing member charged to an arbitrary surface potential is exposed while changing the exposure amount. ² The latent image contrast potential difference (potential difference between the exposed portion and the non-exposed portion) obtained in the convergence region of the potential change in which the exposure portion potential attenuation with respect to the change amount is 50 V or less. Note that the maximum latent image contrast potential difference varies depending on the type of the photoreceptor (photosensitive layer), the surface potential (charging potential), and the like.
[0013]
By the way, as an exposure means for exposing the image carrier, a plurality of light emitting element array chips in which a plurality of light emitting elements are integrated are linearly arranged, and a plurality of rod lenses are arranged with their optical axes arranged in parallel. Using an optical print head in which a plurality of rod lens arrays arranged in a straight line are mounted on the same substrate, exposure is performed in the longitudinal direction (main scanning direction) of the image carrier. A method for forming a two-dimensional image by rotation has been proposed.
[0014]
When such an exposure means is used, the light emitting element array chip at both ends of the light emitting element array chip due to the influence of a slight gap generated when the plurality of light emitting element array chips are arranged and the influence of light emission heat flowing at both ends of the light emitting element array chip. It has been reported that the amount of exposure decreases and image defects occur.
[0015]
As a countermeasure for solving this problem, a method of setting a light emission amount of a predetermined number of light emitting elements at both ends of the light emitting element array chip to be different from a light emission amount of light emitting elements other than the end portions has been proposed. This suppresses a decrease in image density in the form of vertical stripes due to a change in the exposure amount between the element array chips and an image defect that causes image vertical white stripes when it becomes severe.
[0016]
[Problems to be solved by the invention]
However, in the case of the prior art as described above, the following problems have occurred.
[0017]
In general, the relationship (EV characteristic) between the exposure amount and the VL potential of the image bearing member (photosensitive member) shows characteristics as shown in FIG. FIG. 5 shows changes in the VL potential when the photosensitive member charged to 500 V is exposed while changing the exposure amount. The VL potential attenuates as the exposure amount is increased, but when the exposure amount becomes a certain exposure amount. The attenuation width becomes smaller and the potential attenuation becomes stable.
[0018]
In normal image formation, binary image formation is performed using an exposure amount at which the potential attenuation is substantially stabilized as an exposure setting value for normal image formation.
[0019]
On the other hand, as a ghost prevention measure, as described above, the exposure amount is reduced in the region where the influence of the exposure history is small, and the latent image contrast potential difference is equivalent to the normal image forming condition with the exposure amount. When image quality correction is performed by correcting the charging potential and development potential, the exposure amount condition is that image formation is performed at a portion where the slope of potential attenuation due to the increase in exposure amount is much steeper than in normal image formation. .
[0020]
When the light emission amount of the predetermined number of light emitting elements at the end of the light emitting element array chip and the light emission amount of the light emitting elements outside the end are corrected based on the light emission amount correction value similar to the normal condition under the exposure amount reducing condition. Since the difference in the potential attenuation amount on the photosensitive member due to the difference in light emission amount is larger than the normal condition, a new vertical streak image that has not occurred under the normal condition results in a problem.
[0021]
The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide an image forming apparatus capable of suppressing high-quality image formation by suppressing image defects such as ghosts and vertical stripes. It is to provide.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, in the image forming apparatus of the present invention,
An image carrier on which a latent image is formed;
Charging means for charging the image carrier;
The image carrier charged by the charging means by a plurality of light emitting means. Dew Light exposure means for forming a latent image;
Developing means for developing the latent image with toner;
Exposure amount switching means for switching the exposure amount of the exposure means;
A light emission amount correction unit that corrects the light emission amounts of the plurality of light emission units so as to reduce a light amount distribution difference of the exposure unit;
An image forming apparatus for forming an image on a sheet based on a toner image formed on the image carrier,
When the image carrier charged by the charging unit is exposed by the exposure unit, the amount of change in the exposed portion potential is 0.1 μJ / cm. ² The first exposure amount that is 50V or less with respect to the amount of change In A first mode for forming a latent image,
The latent image contrast potential difference between the non-exposed part and the exposed part when the image carrier charged by the charging means is exposed by the exposing means is the first mode. De 60-90% like Second exposure amount In addition to changing the exposure amount, the charging condition or development condition is changed so that the image density is substantially the same as that in the first mode. A second mode for image formation;
Is feasible Thus, when a ghost image is generated due to a sensitivity change due to an exposure history on the image carrier, the first mode can be switched to the second mode. It is characterized by that.
[0024]
A plurality of light emitting units including the plurality of light emitting means are arranged and provided,
The light emission amount correcting means is a light emission amount of the light emitting means at the end of the light emitting unit. The other Than the amount of light emitted by Set value only big To be Correction is performed, and the setting is made in the second mode than in the first mode. value small Correction to be Good.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.
[0035]
(First embodiment)
FIG. 1 is a schematic sectional view of an image forming apparatus (color image forming apparatus) according to an embodiment of the present invention. In this embodiment, a color electrophotographic copying machine using an LED exposure apparatus will be described as an example of an image forming apparatus.
[0036]
This image forming apparatus has a digital image reader unit at the top and a digital color image printer unit at the bottom.
[0037]
In the reader unit, the original 9 is placed on the original table glass 10, and the exposure CCD reading sensor is exposed and scanned to obtain a color-separated image signal from the original 9.
[0038]
This color-separated image signal is processed by a video processing unit (not shown) via a circuit (not shown) and sent to the printer unit.
[0039]
On the other hand, in the printer unit, photosensitive drums 1Y, 1M, 1C, and 1K (hereinafter abbreviated as photosensitive drums 1) as image carriers that rotate in the direction of the arrow shown in FIG. Around the chargers 2Y, 2M, 2C and 2K as charging means (hereinafter abbreviated as charger 2), and developing devices 4Y, 4M, 4C and 4K as developing means (hereinafter abbreviated as developing devices) 4), image forming means such as a transfer belt 5 is disposed.
[0040]
The photosensitive drum 1 is uniformly charged by a charger 2, and color separation is performed on the photosensitive drum 1 by exposure means 3Y, 3M, 3C, and 3K (hereinafter abbreviated as exposure means 3) including, for example, LED exposure devices. The irradiated optical image or a corresponding optical image is irradiated, and a latent image is formed on the outer surface thereof.
[0041]
Next, the electrostatic latent image on the photosensitive drum 1 is developed with a developer (toner) in the developing device 4 and is visualized as a toner image.
[0042]
When the image forming apparatus is operated as a reading instruction of the original 9 (usually in a state where the copy key is pressed) or the printer is operated, for example, when a print JOB instruction is transmitted from the PC, it is installed in the image forming apparatus. In response to a command from an internal CPU (not shown), temperature / humidity information of the environmental sensor CS1 is read and the absolute water content at this time is calculated.
[0043]
Based on the value of the water content, the CPU calculates a necessary development Vcont potential (necessary development contrast potential) in this environment from the image forming apparatus. The reason why the value of the development Vcont changes with the environment is that the physical properties of the toner used in the developing device 4, for example, the charging performance, changes with the ambient moisture content.
[0044]
In calculating the development Vcont, the relationship between the amount of water and the required development Vcont potential as shown in FIG. 2A is stored in advance as a table as shown in FIG. It calculates by linear interpolation according to the result of the calculated moisture content.
[0045]
Next, a method for calculating the latent image potential and the developing sleeve potential of the developing device will be described with reference to FIG.
[0046]
For example, when the environmental sensor CS1 shown in FIG. 1 reads 23 ° C./5%, the water content is about 1.0 (g / kg).
[0047]
At this time, according to the table of FIG. 2B, the necessary development Vcont potential is calculated as necessary development Vcont = 280V.
[0048]
When a Vback potential that is a background fog prevention potential is added to the necessary development Vcont, a necessary latent image Vcont potential (necessary latent image contrast potential) formed on the surface layer of the photosensitive drum 1 is obtained. This is expressed as follows.
Necessary latent image Vcont potential = necessary development Vcont potential + Vback = 280 V + 200 V = 480 V
[0049]
Next, a procedure for setting the charging potential and the exposure portion potential of the photosensitive drum 1 will be described.
[0050]
As described above, in the same way that the required development Vcont potential changes depending on the state of the surrounding environment, the exposure portion potential of the photosensitive drum 1 also changes because the exposure sensitivity of the photosensitive drum 1 changes depending on the relative humidity and the amount of moisture in the surrounding environment. It is necessary to find a value suitable for the environment.
[0051]
FIG. 3 shows the result of experimentally determining the change in the exposure part potential with respect to the charging potential due to the amount of water in the surrounding environment in the photoconductor according to the present exemplary embodiment.
[0052]
The image forming apparatus according to the present embodiment stores the result of FIG. 3 as table data.
[0053]
In order to obtain the calculated required latent image Vcont potential = 480 V with the moisture amount 1.0 (g / kg) calculated from the reading value of the environmental sensor CS1, the charging potential VD = 700V is obtained from the result of FIG. It can be seen that the exposed portion potential VL = 220V is obtained and the required latent image Vcont = 480V can be satisfied.
[0054]
As a result, the development potential is set to 500 V obtained by subtracting the background fog prevention potential Vback = 200 V from the charging potential VD = 700 V, so that the calculated required development Vcont potential = 280 V can be accurately obtained.
[0055]
Here, the procedure for obtaining the charging potential VD of the photosensitive drum 1, the exposure portion potential VL, and the developing potential of the developing device is summarized as follows.
[0056]
(STEP 1) Temperature / humidity information is read from the environmental sensor CS1.
[0057]
(STEP2) The absolute water content is calculated from the above information.
[0058]
(STEP 3) The required development Vcont potential is calculated from the water content value.
[0059]
(STEP 4) The necessary latent image Vcont potential is calculated from the necessary development Vcont potential and the background antifogging potential Vback.
Necessary latent image Vcont potential = necessary development Vcont potential + Vback
[0060]
(STEP 5) The charging potential VD and the exposure portion potential VL of the photosensitive drum 1 are calculated from the relationship table between the moisture amount and VD-VL.
[0061]
(STEP 6) The development potential is calculated from the charging potential VD and the background fog prevention potential Vback.
Development potential = charging potential VD-Vback
[0062]
According to the above-described processing, the image forming conditions such as the charging potential and the developing potential can be determined from the detection result of the environmental sensor and the table data. Therefore, it is necessary to provide a photosensitive drum potential detection unit, a toner image density detection unit, and the like. There is no advantage.
[0063]
As the charging method applied in the present embodiment, an injection charging method using a magnetic brush is adopted. A magnetized mag roller sleeve is provided at a certain distance (for example, 500 to 600 μm) from the surface of the photosensitive drum 1. A powder magnetic carrier (resistance value 10) prepared by pulverization or polymerization is applied to the mag roller sleeve. ^Four -10 ⁷ Ωcm (10 ² -10 ^Five Ωm)) is carried, a magnetic brush is formed from this powder magnetic carrier, and in contact with the surface of the photosensitive drum 1, injection charging is performed by applying a DC bias on which an AC component is superimposed.
[0064]
When such an injection charging method is used, since the value of the charging potential VD of the photosensitive drum 1 and the DC component bias Vdc of the mag roller are substantially equal, it is possible to obtain Vdc = VD.
[0065]
The photosensitive drum 1 used in the present embodiment is configured by applying photosensitive layers (a charge generation layer 1b, a charge transport layer 1c, and a charge injection layer 1d) on an aluminum cylinder 1a as shown in FIG. Has been. The photosensitive layer is usually an insulator, and has a characteristic of becoming conductive when irradiated with light of a specific wavelength. This is because hole-electron pairs are generated in the charge generation layer 1b by light irradiation and become charge carriers.
[0066]
The developing device 4 includes four developing devices 4Y, 4M, 4C, and 4K that individually store four color developers of yellow developer, magenta developer, cyan developer, and black developer, and the outer peripheral surface of the photosensitive drum 1. The latent image on the photosensitive drum 1 is developed using a two-component developer, which is provided at a position that is a certain distance away, for example, a distance of 300 to 600 μm.
[0067]
Here, in carrying out the present invention, a developing method such as magnetic one-component development or contact one-component development may be used instead of the developing device using the two-component developer described above.
[0068]
On the other hand, the sheet P accommodated in the paper feed cassette 13a (13b) is fed by the registration roller 14 at an appropriate timing, carried on the transfer belt 5 and conveyed in the direction of the arrow shown in the figure. A transfer voltage is applied to the sheet P by transfer application members 6Y, 6M, 6C, and 6K (hereinafter abbreviated as a transfer application member 6) disposed below the transfer belt 5, and the sheet P The toner images are sequentially transferred from yellow to black.
[0069]
The transfer belt 5 is configured by stretching a dielectric sheet or the like, and the sheet P is adsorbed to the transfer belt 5 by an adsorbing semiconductor charging roller 15 and a conductor roller.
[0070]
Then, the sheet P on which the toner image is transferred is carried on the transfer belt 5 and conveyed to the fixing device 7, and after the toner image is fixed by applying a predetermined amount of heat and pressure, the sheet P is conveyed to the conveyance tray 8. Is done.
[0071]
In the image forming apparatus of the present embodiment described above, the photosensitive drums 1Y, 1M, 1C, and 1K are exposed from the exposure units 3Y, 3M, 3C, and 3K, respectively, so that the charge generation layer 1b of the photosensitive drum 1 is positive. Hole-electron pairs are generated. The holes pass through the charge transport layer 1c, move to the charge injection layer 1d, and recombine with negative charges. As a result, the amount of negative charge on the surface of the photoreceptor (charge injection layer 1d) decreases, and the absolute value of the surface potential of the photosensitive drum 1 decreases. In this state, the surface potential on the photosensitive drum 1 becomes approximately VL potential.
[0072]
However, the VL potential on the photosensitive drum 1 that is attenuated by exposure varies depending on the exposure amount and also varies depending on the magnitude of the charging potential VD.
[0073]
Here, the exposure amount E of the photoreceptor A (μJ / cm ² ) And the VL potential (V) on the photosensitive member (EV characteristic) is shown in FIG. As shown in FIG. 5, it can be seen that the potential on the photoreceptor attenuates nonlinearly as the exposure amount increases.
[0074]
Furthermore, FIG. 6 shows the results of measurement of this EV characteristic when full exposure for two revolutions of the drum is given. As shown in FIG. 6, when the exposure amount applied to the surface layer of the photoconductor is increased, when the exposure amount value is small, the VL potential (VL potential at the second round of the drum) of the portion once exposed is the first round. However, when the exposure amount exceeds a certain exposure amount, the potential of the second round of the drum is conversely higher than that of the first round. When such a variation in the VL potential occurs, an image defect such as a decrease in density occurs.
[0075]
Further, FIG. 6 shows the results of a similar experiment performed on another photoreceptor B having different characteristics (charge generation layer, charge transport layer, charge injection layer) of the photosensitive layer. Although the EV characteristics are greatly different, it can be seen that the same result as that of the photoreceptor A is obtained with respect to the potential comparison between the first and second rounds.
[0076]
FIG. 7 shows EV characteristics when the surface potential VD on the photoconductor is changed.
[0077]
From this figure, at any VD potential, when the exposure amount is small, the VL potential at the second cycle is smaller than the VL potential at the first cycle, and when the exposure amount increases, the VL potential at the second cycle becomes larger. It can be seen that the characteristics are shown.
[0078]
Also, the exposure value at which the magnitude relationship between the VL potential in the first cycle and the VL potential in the second cycle is changed varies depending on the value of the VD potential. You can see that
[0079]
Furthermore, it can be seen from FIG. 7 that there is an exposure amount region (hereinafter referred to as a VL stable region) in which the VL potential in the first round and the VL potential in the second round are substantially the same. In this region, the VL potential is not affected by the exposure history, that is, the exposure memory. FIG. 7 shows that this region increases as the VD potential increases.
[0080]
From the above results, it has been clarified that the fluctuation of the VL potential due to exposure varies depending on the exposure amount and the surface potential VD of the photoreceptor, and there are two types of VL fluctuation due to the exposure history, an increasing direction and a decreasing direction. It has also been clarified that there is always an exposure amount region in which VL fluctuation does not occur due to the influence of exposure history, regardless of the type of photoconductor.
[0081]
FIG. 8 schematically shows the EV characteristics.
[0082]
Here, the difference between the surface potential VD of the photosensitive member and the exposed portion potential VL, that is, the potential difference between the non-exposed portion and the exposed portion is called a latent image contrast potential difference, and the exposure amount of the photosensitive member charged to the surface potential VD is changed. When exposed, 0.1 μJ / cm exposure ² The latent image contrast potential difference obtained in the potential change convergence region where the exposure portion potential change with respect to the change amount is 50 V or less is referred to as the maximum latent image contrast potential difference in VD.
[0083]
From the above experimental results, it was found that the latent image contrast potential difference in the VL stable region where the VL potential does not change with the exposure history exists in the range of about 60 to 90% of the maximum latent image contrast potential difference. It was also found that the exposure amount showing the VL stable region was an exposure amount of about 70% of the exposure amount for obtaining the maximum latent image contrast potential difference.
[0084]
Based on the above experimental results, when the image is formed with an exposure amount that obtains a latent image contrast potential difference that is substantially the same as the maximum latent image contrast potential difference under normal conditions, and a ghost image is generated on the photoconductor, the latent image contrast It can be seen that the amount of exposure should be switched to about 70% of the normal mode so that the potential difference is about 60 to 90% of the maximum latent image contrast potential difference.
[0085]
The image forming apparatus according to the present embodiment is provided so that the exposure amount can be switched between two levels of the normal mode and the ghost reduction mode by operating a changeover switch arranged on the operation panel of the apparatus.
[0086]
When the ghost reduction mode is selected, the exposure amount is reduced to about 70% of the normal mode by an exposure amount switching means (not shown) including a CPU and a memory. As a result, the latent image contrast potential difference is about 60 to 90% of the maximum latent image contrast potential difference, and image formation can be performed in a VL stable region that is not affected by the exposure history.
[0087]
However, when this ghost reduction mode is selected on the operation panel, the development contrast is reduced and the image density is reduced simply by reducing the exposure amount.
[0088]
In order to solve the problem, a relationship table between the surface potential and the VL potential in each environment as shown in FIG. 3 is prepared for the exposure amount in the ghost reduction mode and stored in the memory.
[0089]
When the ghost reduction mode is selected, the above-described processing is performed using a table corresponding to the exposure amount, and the charging potential VD of the photosensitive member and the developing device are set so that the same image density as the exposure amount in the normal mode is obtained. Image forming conditions such as development potential are determined instantaneously. As a result, even when the ghost reduction mode is switched, it is possible to output an image equivalent to the normal mode without changing the maximum image density.
[0090]
Next, the exposure unit and the light emission amount correction unit in the image forming apparatus of the present embodiment will be described in detail.
[0091]
As the exposure means 3 in the present embodiment, as shown in FIG. 9, a plurality of light emitting element array chips 30 (light emitting units) in which a plurality of light emitting elements 31 (light emitting means) are integrated are linearly arranged, An optical print head is used in which a plurality of rod lenses are arranged with their optical axes in parallel, a plurality of fixed rod lens units (not shown) are arranged in a straight line, and both are mounted on the same substrate ( FIG. 10).
[0092]
In this embodiment, a configuration is adopted in which 56 light emitting element array chips 30 each having 128 light emitting elements 31 having a wavelength of 780 nm are arranged linearly. The light emitting element 31 corresponds to the minimum pixel unit of the image forming apparatus.
[0093]
However, in the case of the exposure means 3 described above, it is very difficult to arrange a plurality of light emitting element array chips 30 to be mounted on the substrate at equal intervals, and there is a problem that gaps are generated as shown in FIG. To do. When the interval between the light emitting element array chips is increased due to this variation, it causes a decrease in the amount of light between the light emitting element array chips.
[0094]
The maximum resolution of the image forming apparatus of this embodiment is 600 dpi, and the pixel interval at that time is 42.3 μm.
[0095]
When the light emitting element array chip 30 is arranged and the distance between the end portions is larger than one pixel, a vertical streak image is generated due to a partial density decrease due to a decrease in exposure amount. When the light emitting element array chips 30 are further separated from each other, a portion where development is not performed occurs on the image, and a white streak image is generated.
[0096]
Further, as a cause of fluctuation in the light emission amount between the light emitting element array chips 30, there is an adverse effect that may be caused by heat generated by light emission of the light emitting element 31. This is a phenomenon in which the amount of light at the end of the light emitting element array chip 30 is reduced due to the generated heat moving to both ends of the light emitting element array chip 30.
[0097]
When the light amount decrease between the two light emitting element array chips 30 described above occurs, the light amount variation as shown in the model diagram of FIG. 11 occurs at the end of the light emitting element array chip 30.
[0098]
In view of this, the image forming apparatus according to the present embodiment includes a light emission amount correction unit including a CPU as a control unit and a memory as a storage unit in the apparatus main body.
[0099]
The light emission amount correction means stores the relationship between the light emission amounts of a predetermined number of light emitting elements 31 in a memory as light emission amount correction data for each pixel, and the light emission time of each light emitting element 31 is determined based on the light emission amount correction data. The amount of light between the light emitting element array chips 30 is controlled by modulation.
[0100]
At this time, by correcting the exposure unit 3 so that the amount of light is uniform, it is possible to suppress the edge light amount low phenomenon when a plurality of the light emitting element array chips 30 are arranged.
[0101]
The light amount correction data of the light emitting elements 31 other than the end portions of the light emitting element array chip 30 shown in this method is set to have a relationship as shown in the graph of the normal condition in FIG. That is, the relationship is set such that the light emission amounts of the light emitting elements at both ends of the light emitting element array chip 30 are larger than the light emission amounts of the light emitting elements other than the end portions.
[0102]
By correcting the light emission amount according to such a light emission amount correction table, it is possible to suppress a light amount fluctuation between the light emitting element array chips 30 and obtain a high-quality image without a streak image.
[0103]
By the way, as a ghost reduction mode described above, a case where image formation is performed with an exposure amount smaller than the normal condition is considered.
[0104]
In the ghost reduction mode, as shown in FIG. 8, image formation is performed in an area where the potential attenuation is large with respect to the change in exposure amount due to the EV characteristic.
[0105]
Therefore, when the light emission amount of the light emitting elements other than the end portions of the light emitting element array chip 30 is corrected with the same setting as the normal condition of FIG. The light amount correction at the end portion, which has become too large and has been used as a measure for reducing the density by reducing the exposure amount, causes the occurrence of a vertical streak image defect in which the density becomes higher.
[0106]
Further, in the exposure amount reduction condition such as the ghost reduction mode, the light emission amount of the light emitting element is reduced, so that it is considered that the influence of the generated heat is somewhat less than in the normal condition.
[0107]
From the above, it can be seen that in a region where the potential attenuation amount on the EV characteristic is large, an appropriate image cannot be obtained if the light amount correction is performed with a difference in exposure amount as in the normal condition.
[0108]
Therefore, in the light emission amount correction means of the image forming apparatus according to the present embodiment, separate light emission amount correction tables corresponding to the exposure amounts in the normal mode and the ghost reduction mode are stored in the memory, and correction is performed according to the mode. The amount is changing.
[0109]
The graph shown as the normal condition in FIG. 12 schematically represents the light emitting element light amount based on the light emission amount correction table in the normal mode, and the graph shown as the exposure amount reduction level 1 is the light emission amount for the ghost reduction mode of the present embodiment. The light-emitting element light quantity based on a correction table is typically represented.
[0110]
That is, in the ghost reduction mode, the correction amount of the light emitting element 31 at the end of the light emitting element array chip 30 is set small.
[0111]
With the above configuration, the image forming apparatus according to the present embodiment includes the light emission amount correction table according to the exposure amount. Therefore, even if exposure is performed with a small exposure amount in order to reduce ghosting, light emission is possible. A light quantity difference generated when a plurality of element array chips are arranged can be reliably corrected, and high-quality image formation without vertical stripes or white stripes can be achieved.
[0112]
(Second Embodiment)
In the first embodiment, an image forming apparatus capable of switching between two exposure levels of the normal mode and the ghost reduction mode has been described. However, in the present embodiment, a plurality of exposure amount reduction modes are provided. Shows a configuration in which the exposure level can be switched.
[0113]
Since other configurations and operations are the same as those of the first embodiment, description of the same components will be omitted.
[0114]
In the first embodiment, when a ghost image is generated, the exposure amount is reduced by the exposure amount switching unit, and further, the emission amount correction unit switches to appropriate emission amount correction data. Based on the emission amount correction data, Good image quality correction was performed by correcting the light emission amount of the light emitting element array chip 30.
[0115]
The image forming apparatus according to the present embodiment has a plurality of exposure amount reduction modes, and the level can be switched in multiple stages by the exposure amount switching means. Therefore, when the effect of reducing the ghost image is not sufficient, it is easy to The level setting can be changed.
[0116]
In that case, there is a case where image formation is performed in a region where the potential attenuation slope on the EV characteristic is larger than the exposure amount in the ghost reduction mode shown in the first embodiment.
[0117]
Accordingly, as shown in the model diagram of FIG. 12, the image forming apparatus according to the present embodiment includes a plurality of light emission amount correction data corresponding to each of the exposure amount setting values (reduction levels), and the exposure amount setting value. The light emission amount correction table is automatically switched according to the above.
[0118]
At this time, the correction amount of the light emitting element light amount is set to be smaller as the exposure amount is smaller.
[0119]
With the above configuration, in the image forming apparatus according to the present embodiment, the optimum light emission amount correction of the light emitting element array chip is performed according to the set exposure amount at any exposure amount level, and the exposure amount Image output that does not generate streak images is possible regardless of the reduction level.
[0120]
(Third embodiment)
In the present embodiment, an image forming apparatus having a plurality of function modes such as a printer, a FAX, and a copying machine will be described.
[0121]
Since the configuration and operation are substantially the same as those of the first embodiment, the description of the same components is omitted.
[0122]
In the first and second embodiments described above, when the ghost reduction mode (exposure amount reduction mode) is selected, the image forming apparatus always forms an image in the reduction mode.
[0123]
However, when a text document or the like with a small image ratio is output by the image forming apparatus, the ghost image is relatively inconspicuous, and it may not be necessary to switch to the ghost reduction mode. For example, the image ratio is small when a character document is output from a PC in the printer mode or used as a FAX.
[0124]
Therefore, it is preferable that the exposure level be selected according to the function mode of the printer, FAX, copier, etc. according to the usage status of the user's image forming apparatus. In addition, each function mode has multiple image output modes according to the type of image to be output, such as a character output mode suitable for outputting characters and line drawings, an image output mode suitable for outputting gradation images, and the like. It is preferable that the exposure level can be selected for each image output mode.
[0125]
The image forming apparatus according to the present embodiment has an independent exposure level according to each function mode or each image output mode, and the user can freely use the operation panel of the main body or the dialog screen of the PC in the printer mode. The configuration is selectable.
[0126]
In the present embodiment, the exposure level can be switched for each function mode or image output mode described above, and the individual light emission amount correction data of the light emitting element array chip is switched according to the selected exposure amount reduction level. In any function mode and image output mode, image formation without streak image generation can be performed.
[0127]
Further, since the selectable exposure level is automatically switched based on the mode selected by the user, the exposure level can be easily set according to the application of the image forming apparatus.
[0128]
【The invention's effect】
As described above, the image forming apparatus according to the present invention adjusts the correction amount of the light emission amount of the light emitting unit according to the exposure amount. Quality image formation can be performed.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention.
FIGS. 2A and 2B are diagrams showing the relationship between the amount of water in the surrounding environment and the necessary development contrast potential, where FIG. 2A is a graph and FIG. 2B is a table;
FIG. 3 is a diagram showing the relationship between VD and VL when the amount of moisture changes.
FIG. 4 is a cross-sectional view of a photosensitive drum of the image forming apparatus according to the embodiment of the present invention.
FIG. 5 is a graph showing a relationship (EV characteristics) between the exposure amount of the photosensitive member A and the VL potential on the photosensitive member.
FIG. 6 is a diagram illustrating EV characteristics of the first and second rounds of the drum.
FIG. 7 is a diagram illustrating EV characteristics of the photoconductor A when the surface potential (VD) is changed.
FIG. 8 is a diagram schematically showing an EV characteristic.
FIG. 9 is a schematic diagram showing variation in the distance between light emitting elements at the end of the light emitting element array chip.
FIG. 10 is a schematic configuration diagram of an optical print head.
FIG. 11 is a distribution model diagram of the light emission amount of the light emitting element array chip.
FIG. 12 is a model diagram showing a light emitting element light amount based on the light emission amount correction data;
[Explanation of symbols]
1 (1Y, 1M, 1C, 1K) Photosensitive drum
2 (2Y, 2M, 2C, 2K) charger
3 (3Y, 3M, 3C, 3K) Exposure means
4 (4Y, 4M, 4C, 4K) Development device
5 Transfer belt
6 (6Y, 6M, 6C, 6K) Transfer application member
7 Fixing device
8 Transport tray
9 Manuscript
10 Platen glass
13a, 13b Paper cassette
14 Registration Roller
15 Semiconductor charging roller
30 Light emitting element array chip
31 Light emitting device
32 Rod lens array unit

Claims (2)

An image carrier on which a latent image is formed;
Charging means for charging the image carrier;
An exposure means for forming the image of the bearing member exposure light latent image which has been charged by said charging means by a plurality of light emitting means,
Developing means for developing the latent image with toner;
Exposure amount switching means for switching the exposure amount of the exposure means;
A light emission amount correction unit that corrects the light emission amounts of the plurality of light emission units so as to reduce a light amount distribution difference of the exposure unit;
An image forming apparatus for forming an image on a sheet based on a toner image formed on the image carrier,
The amount of change in the potential of the exposed portion when the image bearing member charged by the charging unit is exposed by the exposure unit is 50 V or less with respect to the amount of change of the exposure amount of 0.1 μJ / cm ² . a first mode in which a latent image formed Te on exposure,
Latent image contrast potential difference between the non-exposed portion when the charged said image bearing member exposed by said exposure means and the exposure unit by the charging unit, a such that 60% to 90% of the first mode And a second mode in which image formation is performed by changing the charging condition or the development condition so that the image density is substantially the same as that in the first mode in accordance with the change in the exposure amount .
What executable der an image forming apparatus according to claim Rukoto ghost image sensitivity variation consists first mode be switched to the second mode when caused by exposure history for the image bearing member . A plurality of light emitting units including the plurality of light emitting means are arranged and provided,
The light emission amount correcting means performs a correction so that the light emission amount of the light emitting means at the end of the light emitting unit is larger than the light emission amount of the other light emitting means by a set value , and the light emission amount correcting means is more effective than the first mode. The image forming apparatus according to claim 1, wherein correction is performed so that the set value becomes smaller in the two-mode mode.

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