JP2011191512A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that suppresses a change in the charging performance of a photoreceptor drum, resulting from a decrease in a quantity of destaticizing light. <P>SOLUTION: The image forming apparatus includes: the photoreceptor drum (18) having a surface layer of amorphous silicon and used for transferring a toner image, formed on the surface layer through electrification and exposure by its rotating drive, to a transfer material; a charger (20) for charging the photoreceptor drum; a destaticizing unit (19) having a light source for emitting destaticising light to the surface layer before the charging of the drum, thereby removing electric charges left on the surface layer after the transfer; and a control means (92) for controlling a drive current so as to offset a decreased quantity of destaticizing light based on a relation between the drive current for causing the light source to emit light and the charging current applied to the charger. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that outputs a toner image on a photosensitive drum to an intermediate transfer member or paper.

  In this type of image forming apparatus, an electrophotographic system is used. When the charger precharges the photosensitive drum and the exposure unit irradiates the surface layer of the photosensitive drum with light, an electrostatic latent image is formed on the surface layer. An image is formed. Further, the developing device carries toner, and when a developing bias voltage is applied, the toner is excited and adheres to the electrostatic latent image, and a toner image is formed on the surface layer of the photosensitive drum. Then, the visualized toner image is transferred and fixed on a sheet or a sheet via an intermediate transfer member.

  Here, a structure for irradiating the surface layer of the photosensitive drum with static elimination light is known (for example, see Patent Document 1). This is because a memory image is generated unless the exposure history of the photosensitive drum is eliminated. Therefore, before the light source of the static elimination unit reaches charging, it is irradiated with static elimination light to remove charges (residual charges) remaining on the surface layer of the photosensitive drum after transfer.

  In addition, if the film thickness of the surface layer of the photosensitive drum is reduced or the usage environment is changed, the charging performance of the photosensitive drum cannot be maintained. Therefore, in this technology, the charge removal amount is adjusted according to the usage period of the photosensitive drum and the temperature / humidity of the photosensitive drum to maintain the charging performance of the photosensitive drum.

JP 2008-158024 A

  Incidentally, the photosensitive drum has a long-life structure having an amorphous silicon-based surface layer in addition to the OPC photosensitive member having an organic surface layer in which film loss is likely to occur. That is, according to this photosensitive drum, the film thickness of the amorphous silicon surface layer does not decrease, and the charging performance of the photosensitive drum hardly changes even when the usage environment changes. It is not necessary to adjust the amount of static elimination according to the period of use, temperature and humidity.

However, there is a problem that the charging performance of the photosensitive drum becomes difficult to maintain due to a decrease in the amount of charge removed from the light source. This is because the memory image is generated as described above when the amount of charge to the surface layer is reduced.
In this case, if the drive current of the light source is increased and the amount of static elimination light is simply set to a large value that does not produce a memory image to compensate for the decrease, the charging current, i.e. The current flowing from the charger to the photosensitive drum increases, the conductive agent protecting the surface layer of the photosensitive drum deteriorates, and the resistance value of the surface layer increases, so the charging performance also changes.

  Thus, in order to suppress the change in the charging performance due to the decrease in the amount of static elimination in the photosensitive drum having the amorphous silicon surface layer, attention is paid to the light source itself, in other words, the driving current of the light source. It is necessary to compensate for the reduction in the amount of static elimination light from the viewpoint of the charging current determined by the magnitude of the drive current. However, in the above-described conventional technique that simply adjusts the amount of static elimination light from the viewpoint of the photosensitive drum, There is no special consideration.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of solving the above-described problems and suppressing a change in charging performance of a photosensitive drum due to a decrease in the amount of charge removed.

  A first invention for achieving the above object is a photosensitive drum having an amorphous silicon-based surface layer and transferring a toner image formed on the surface layer by charging or exposure to a transfer material by rotational driving thereof. And a charger for charging the photosensitive drum, and a charge eliminating unit for removing charges remaining on the surface layer after the transfer, having a light source that irradiates the surface layer with charge eliminating light before reaching the charge. And a control means for controlling the drive current so as to compensate for the decrease in the light amount of the static elimination light based on the relationship between the drive current for causing the light source to emit light and the charging current applied to the charger.

According to the first invention, in the photosensitive drum having an amorphous silicon surface layer, the surface layer has a high hardness and hardly loses its thickness. The relationship between the amount of charge removed to irradiate the layer and the charging current applied to the charger is substantially constant.
Here, the amount of charge removal is determined by the drive current that causes the light source to emit light, and is proportional to the magnitude of this drive current.

  However, when the light source is deteriorated, even if a drive current having the same magnitude as that at the beginning of use is supplied to the light source, the amount of static electricity removed at the same magnitude as that at the beginning of use cannot be obtained. Always less than the initial static charge. That is, in order to obtain the charge removal amount at the beginning of use, a driving current larger than that at the beginning of use must be supplied to the light source.

Note that this reduction in the amount of static elimination also occurs due to an increase in the environmental temperature. The amount of static elimination when the temperature rises decreases and is always below the initial level of static elimination.
If the relationship between the drive current and the amount of charge removed is the relationship between the charge amount and the charge amount that is substantially constant as described above, the charge current when the light source is deteriorated or when the environmental temperature is increased is the charge at the beginning of use. Since the current is always lower than the current, if the drive current when the light source is deteriorated or the environmental temperature is increased is always set to be larger than the drive current at the beginning of use, the amount of reduction in the amount of charge can be compensated.

  Therefore, in the present invention, the control means controls the drive current so as to compensate for the reduction in the amount of static elimination light based on the relationship between the drive current and the charging current. Therefore, it is possible to secure the amount of static elimination at the beginning of use and maintain the charging performance of the photosensitive drum. As a result, stable image forming performance can be obtained.

According to a second aspect of the present invention, in the configuration of the first aspect, the control unit obtains a characteristic curve from the charging current and the drive current when a predetermined period of the light source has elapsed or when the environmental temperature of the image forming apparatus has increased. A curve acquisition unit is provided.
According to the second invention, in addition to the operation of the first invention, the control means further includes a characteristic curve acquisition unit, which is used for static elimination when the light source is deteriorated or the environmental temperature is increased. The relationship between the amount of light that is always lower than the amount of static elimination at the beginning of use is applied to the relationship between the amount of static elimination and the charging current, which is almost constant as described above, and a characteristic curve based on the light source drive current-charging current is obtained. Clarify that the charging current when the temperature rises is always below the initial charging current. As a result, the amount of reduction in the charge removal amount as seen from the charging current is clarified, and this reduction can be compensated for surely.

According to a third aspect of the present invention, in the configuration of the first or second aspect of the invention, the control means uses the charging current usage range determined from the elimination of the exposure history of the surface layer and the life of the charger, And a drive current range setting unit for setting a drive current range for compensating for the above.
According to the third invention, in addition to the operation of the first and second inventions, the control means further includes a drive current range setting unit, which is a minimum for preventing memory images. Using a range from a necessary charging current to an upper limit value of the charging current that does not shorten the life of the charger, a driving current is set to compensate for a decrease in the amount of charge removal. As a result, the amount of reduction in the charge removal amount as seen from the drive current is clarified, and this reduction can be compensated more reliably.

According to a fourth aspect of the invention, in the configuration of the third aspect of the invention, the drive current range setting unit uses the charging current usage range determined from the elimination of the exposure history of the surface layer and the life of the charger, and The drive current range before the decrease is set.
According to the fourth aspect of the invention, in addition to the action of the third aspect of the invention, the drive current range setting unit sets the range of the drive current at the beginning of use, for example, before the light amount of the neutralizing light is reduced by the light source. The relationship between the drive current at the time of deterioration and the rise in environmental temperature always exceeds the drive current at the beginning of use. Therefore, it is possible to set the drive current for making up for the reduction in the amount of static elimination light more clearly.

A fifth invention is characterized in that, in the configurations of the first to fourth inventions, the light source is a plurality of LED chips having substantially the same light emission characteristics along the rotation axis of the photosensitive drum.
According to the fifth invention, in addition to the effects of the first to fourth inventions, when the light source is an LED chip, the transparent resin encapsulating the LED chip is deteriorated by the heat of the chip, for example. The reduction in the amount of static elimination becomes remarkable due to “deterioration of the light source” in which the transparency is reduced and “increase in environmental temperature” in which the light emission efficiency of the chip is reduced due to temperature rise. However, if the above-described control means is used, the amount of reduction in the amount of static elimination can be compensated, so that the amount of static elimination at the beginning of use can be sufficiently secured.

  The present invention provides an image forming apparatus that can maintain the charging performance of the photosensitive drum even when the amount of charge removal is reduced because the reduction amount of the charge removal amount is compensated by the relationship between the drive current of the light source and the charging current. be able to.

1 is a schematic configuration diagram of a printer according to an embodiment. It is a block diagram including the controller of the printer of FIG. FIG. 2 is a cross-sectional view around the image forming unit in FIG. 1. It is explanatory drawing of the static elimination light quantity control part of FIG. It is a figure explaining the relationship between a static elimination light quantity and a charging current. It is a figure explaining the relationship between a static elimination light quantity and the optical memory potential of a photosensitive drum. It is a figure explaining the relationship between the drive current of a light source, and the static elimination light quantity. It is a figure explaining the relationship (characteristic curve) of the drive current and charging current of a light source. It is explanatory drawing of optical memory electric potential.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
FIG. 1 schematically shows the structure of a printer 1 capable of color printing, which is an example of an image forming apparatus. The cross section shown in the figure is seen from the left side of the printer 1. For this reason, the front surface of the printer 1 is positioned on the right side and the rear surface of the printer 1 is positioned on the left side.

As shown in FIG. 1, a paper discharge tray 36 is provided above the apparatus main body 2 of the printer 1, and a plurality of operation keys used for various operations by the user are provided near the paper discharge tray 36. A front cover 5 on which a screen for displaying various types of information is arranged is provided.
Further, a sheet feeding cassette 4 is disposed below the apparatus main body 2, and sheets of sheets are stored in the storage unit 40 in a stacked state. As shown in the figure, a paper feed roller 46 is provided on the upper right side of the container 40.

Then, the sheet is sent toward the upper right of the sheet feeding cassette 4 in FIG. 1, and the sent sheet is conveyed upward along the front surface of the printer 1 inside the apparatus main body 2.
Further, the paper feed cassette 4 is configured to be able to be pulled out to the front side of the printer 1, that is, in the right direction in FIG. 1, and in this pulled out state, a new sheet can be replenished to the storage section 40. The paper can be replaced with another type of paper.

Inside the apparatus main body 2, a transport roller 10, a registration roller 14, an image forming unit 16, and a secondary transfer unit 30 are sequentially arranged on the downstream side in the paper transport direction from the paper feed cassette 4.
The image forming unit 16 includes four image forming units 17 arranged in parallel, and each image forming unit 17 is provided with a photosensitive drum 18 (FIGS. 1 and 3). The photosensitive drum 18 is rotatably installed and is driven clockwise in FIGS. 1 and 3 by a driving motor (not shown).

The photosensitive drum 18 of the present embodiment is an a-Si drum formed with a diameter of, for example, 30 mm and having an amorphous silicon-based surface layer on the surface thereof.
An exposure unit 15 is provided between the photosensitive drum 18 and the paper feed cassette 4 (FIG. 1), and laser light is irradiated from the exposure unit 15 toward the photosensitive drums 18 respectively. Is done. As shown in FIGS. 1 and 3, the charger 20, the developing device 24, the intermediate transfer roller 13, the cleaning unit 50, and the eraser (static elimination unit) 19 are disposed at appropriate positions around each photosensitive drum 18. Are provided.

  As shown in FIG. 3, the charger 20 is positioned below the image forming unit 17 and includes a charging roller 21 that is in contact with the photosensitive drum 18 and a brush that cleans the surface of the charging roller 21 by grinding and rubbing. It has a rubbing roller 22 and directly contacts the surface layer of the photosensitive drum 18 to be charged. The charging roller 21 is made of, for example, epichlorohydrin rubber, and has a diameter of, for example, φ12 mm.

Further, the developing device 24 is disposed on the left side of the image forming unit 17 in FIGS. 1 and 3, and has a developing roller 25 facing the photosensitive drum 18. The developing roller 25 is driven counterclockwise in FIGS. 1 and 3 by a driving motor (not shown).
The image forming unit 16 includes an intermediate transfer belt (transfer material) 12. The intermediate transfer belt 12 is disposed above each photosensitive drum 18, and 4 between the intermediate transfer belt 12 and the paper discharge tray 36. A single toner container 23 is disposed (FIG. 1). These toner containers 23 are arranged in the order of magenta, cyan, yellow, and black from the back side to the front side of the printer 1, and the toner container for black has the largest capacity. Is done.

The secondary transfer unit 30 includes a secondary transfer roller 31, and the secondary transfer roller 31 is configured to be able to press against the intermediate transfer belt 12 from obliquely below. The intermediate transfer belt 12 and the secondary transfer roller 31 form a nip portion for transferring a toner image onto a sheet.
A fixing unit 32, a discharge branching unit 34, and a paper discharge tray 36 are sequentially arranged on the downstream side of the secondary transfer unit 30 in the paper transport direction.

In this embodiment, a duplex printing conveyance path 38 is formed between the secondary transfer unit 30 and the manual feed tray 3. The duplex printing conveyance path 38 branches from the discharge branching portion 34 on the front side of the apparatus main body 2 and extends downward, and is connected to the upstream side of the registration roller 14.
As shown in FIG. 3, the cleaning unit 50 includes a cleaning blade 52 and a rubbing roller on the downstream side of the transfer position with the intermediate transfer roller (primary transfer roller) 13 as viewed in the rotation direction of the photosensitive drum 18. A roller 56 and a toner recovery unit 80 are provided.

Specifically, the rubbing roller 56 is driven counterclockwise in FIG. 3 by a driving motor (not shown), and rubbing and polishing the surface layer of the photosensitive drum 18 after the toner image is transferred in the trail direction. As a result, the rubbing roller 56 removes residual toner and the like adhering to the amorphous silicon surface layer.
The cleaning blade 52 is composed of a galvanized steel body fixed to the lower end of the housing 51 and a polyurethane rubber blade welded to the body. The edge of the blade is in contact with the photosensitive drum 18 in the counter direction. Residual toner adhering to the surface layer is scraped off.

The residual toner scraped off from the surface layer of the photosensitive drum 18 by the cleaning blade 52 and the rubbing roller 56 is accumulated in the housing 51 and is conveyed by a screw 88 extending along the rotational axis direction of the photosensitive drum 18. , Collected in a collection container (not shown).
The above-described eraser 19 is arranged at the upper end of the housing 51 located on the upstream side of the charger 20, specifically, the upstream side of the cleaning unit 50 as viewed in the rotational direction of the photosensitive drum 18. Immediately after that, the charge removal light is irradiated to the surface layer of the photoconductive drum 18, and the charge remaining on the surface layer of the photoconductive drum 18 is sandwiched by a cleaning process by the cleaning unit 50 between this charge removal and the next charging. (Residual charge) is removed.

More specifically, the eraser 19 has an erase substrate 19 a extending along the rotational axis direction of the photosensitive drum 18, and the erase substrate 19 a has a drive circuit for supplying a drive current to a plurality of LED chips (light sources) 74. Is formed.
Each LED chip 74 is encapsulated in a transparent resin, and is disposed on the erase substrate 19a at substantially equal intervals along the rotation axis direction of the photosensitive drum 18, and emits light with a driving current from the driving circuit.

  By the way, the light emission characteristics of these LED chips 74 are substantially the same when the eraser 19 is manufactured. However, when the transparency of the transparent resin is reduced, the amount of electricity removed decreases (deterioration of the light source). Further, when the temperature in the printer 1 rises, the light emission efficiency of the LED chip 74 is lowered, and the amount of static elimination light is temporarily lowered (increased environmental temperature) until this temperature is lowered.

Therefore, in this embodiment, the decrease in the amount of static electricity removed from the LED chip 74 due to the deterioration of the light source and the increase in the environmental temperature is compensated for by the drive signal from the controller 90 shown in FIG. Is done.
Note that the principle of correcting the reduction in the amount of static elimination light of the LED chip 74 will be described in detail later with reference to FIGS. 5 to 8. Here, the configuration of the controller 90 according to FIGS. 2 and 4 will be mainly described. .

The controller 90 includes a static elimination light quantity control unit (control means) 92 (FIG. 2), and controls the magnitude of the drive current that causes the LED chip 74 to emit light so as to ensure the static elimination light quantity at the beginning of use. More specifically, as shown in FIG. 4, the charge removal amount control unit 92 of this embodiment includes a characteristic curve acquisition unit 94 and a drive current range setting unit 96.
The characteristic curve acquisition unit 94 acquires a characteristic curve (light source driving current-characteristic curve based on charging current) formed by the relationship between the driving current Iled that causes the LED chip 74 to emit light and the charging current I applied to the charging roller 21. .

This is because when the charge removal amount E from the LED chip 74 is measured by a light amount measuring device, the relationship between the charge removal amount E and the charging current I applied to the charging roller 21 is substantially constant in the a-Si drum 18 as will be described later. It focuses on the point that becomes.
This charge removal amount E can be obtained from the magnitude of the drive current Iled input to the drive circuit. The charging current I can be obtained from, for example, an average value obtained by measuring the current flowing from the charging roller 21 to the surface layer of the a-Si drum 18 for one round of the a-Si drum 18.

As a result, the characteristic curve acquisition unit 94 acquires a characteristic curve based on the light source driving current-charging current and outputs the acquisition result to the driving current range setting unit 96.
The characteristic curve is acquired when the printer 1 is turned on. This is because the deterioration of the LED chip 74 occurs on a scale of 2000 to 3000 hours, and in view of this scale, it is sufficient to obtain the characteristic curve when the power is turned on.

Next, the drive current range setting unit 96 sets the range of the drive current Iled input to the drive circuit using the use range of the charging current I.
Specifically, the charging current I is used in the range of the minimum charging current Imin necessary for eliminating the exposure history on the surface layer of the a-Si drum 18 and the upper limit charging current that does not make the charging roller 21 short-lived. Imax is used to determine the range of the driving current Iled input to the driving circuit by applying the charging current I usage range Imin to Imax to the characteristic curve of the light source driving current-charging current. The setting result is output to the drive circuit of the eraser 19.

Further, the drive current range setting unit 96 according to the present embodiment sets the drive current range Iled_min to Iled_max in advance of the range of the drive current Iled before the reduction of the charge removal amount of the LED chip 74, for example, at the beginning of use. 98.
Thereafter, when the charge removal amount of the LED chip 74 is lowered, the drive current range Iled_min to Iled_max before the charge removal light amount reduction is called from the memory 98, and the drive current range Iled'_min after the charge removal light amount is lowered. This is because it can be easily recognized how much the amount of electricity removed from the LED chip 74 has decreased as compared to ~ Iled'_max.

  The driving current at the beginning of use can be set to any value as long as it is within the range of driving currents Iled_min to Iled_max before the amount of static elimination light is reduced. For example, an average value of these values (Iled_min + Iled_max) / 2 is set. In this case, it is desirable that a margin can be provided for the upper limit value Iled_max and the lower limit value Iled_min.

  Returning to FIG. 1 again, when the printer 1 performs printing, the paper feed roller 46 separates and feeds the paper from the paper feed cassette 4 one by one. The sent paper reaches the registration roller 14. The registration roller 14 corrects the oblique feeding of the paper and measures the image transfer timing with the toner image formed by the image forming unit 16, while feeding the paper to the secondary transfer unit 30 at a predetermined paper feed timing. Send it out.

On the other hand, the input port 91 in FIG. 2 is configured to be able to receive image data as a printing source from the outside. This image data is data in which various images such as characters, codes, figures, symbols, diagrams, and patterns are converted into data. Based on this data, the controller 90 controls light irradiation and the like.
Specifically, the LED chip 74 of the eraser 19 is turned on to remove the static electricity from the surface layer of each photosensitive drum 18, and the charger 20 charges the surface layer of the photosensitive drum 18.

Next, when the exposure unit 15 irradiates the surface layer of the photosensitive drum 18 with laser light, an electrostatic latent image is formed on the surface layer of each photosensitive drum 18, and this electrostatic latent image is applied by applying a developing bias voltage. Thus, a toner image of each color is formed.
Each toner image is superimposed on the intermediate transfer belt 12 (primary transfer) and is secondarily transferred to a sheet by the secondary transfer unit 30. The toner remaining on the surface layer of the photosensitive drum 18 is removed by the cleaning unit 50 or the like.

Subsequently, the sheet is fed toward the fixing unit 32 with an unfixed toner image carried thereon, and is heated and pressed by the fixing unit 32 to fix the toner image. Thereafter, the sheet sent from the fixing unit 32 is discharged to the discharge tray 36 via the discharge roller 35 and stacked in the height direction.
When double-sided printing is performed on this single-sided printing, the conveyance direction of the paper discharged from the fixing unit 32 is switched by the discharge branching unit 34.

That is, the sheet printed on one side is pulled back into the apparatus main body 2 and conveyed to the duplex printing conveyance path 38. Subsequently, the sheet is sent toward the upstream side of the registration roller 14 and is sent again toward the secondary transfer unit 30. As a result, the toner image is transferred to the surface of the paper that has not been printed.
As described above, according to this embodiment, since the surface layer of the a-Si drum 18 has a high hardness and hardly loses its thickness, the LED chip 74 of the eraser 19 irradiates this surface layer. The relationship between E and the charging current I applied to the charging roller 21 is substantially constant.

  Specifically, as shown in FIG. 5, when the charge removal light amount E is small, the charging current I changes greatly with respect to the change in the charge removal light amount E, while when the charge removal light amount E increases, the a-Si drum 18. Since the amount of carriers generated in the surface layer gradually saturates, the amount of current flowing from the charging roller 21 to the surface layer of the a-Si drum 18 also gradually saturates, and the change in the charging current I is small with respect to the change in the charge removal amount E. Become.

Next, if the charge removal amount E is small, the previous exposure history cannot be eliminated on the surface layer of the a-Si drum 18, and a memory image is generated, causing image degradation. The optical memory potential (hereinafter referred to as memory potential) will be described with reference to FIG. The surface potential V in FIG. 9 is obtained by measuring the surface potential of the a-Si drum 18 at the development position. The surface potential Vo is charged in the first round, and the solid image is exposed in the second round. The surface potential of the exposed part (exposure area) decreases to VL. After static elimination, recharging is performed, but if the amount of static elimination is not sufficient, the residual charge of the photocarrier cancels the charge in the charging process due to the influence of the residual charge of the photocarrier that is excessively generated in the photosensitive layer in the exposure process, The surface potential after recharging becomes Vr, which is lower than Vo. On the other hand, the surface potential after recharging of the non-exposed region is charged to the surface potential Vo because no cancellation due to the residual charge of the photocarrier occurs. This potential difference Vmr is a memory potential. When the memory potential Vmr is increased, the surface potential after recharging of the solid image portion is greatly decreased, so that fogging occurs and image deterioration is caused. If the amount of static elimination is sufficiently large, a large amount of light carriers are generated in both the exposed and non-exposed areas of the solid image area in the static elimination process, so the difference between the residual optical carriers in the exposed and non-exposed areas of the solid image area is small. Therefore, the memory potential Vmr becomes small.
In the relationship between the charge removal amount E shown in FIG. 6 and the memory potential V of the a-Si drum 18, the charge removal amount when the lower limit value of the surface potential generated by the memory image is Vm is Emin. When Emin is applied to FIG. 5, the minimum charging current Imin necessary for preventing the memory image is determined.

On the other hand, in order not to shorten the life of the charging roller 21, an upper limit value Imax of the charging current is necessary.
Here, the charge elimination light amount E is determined by the drive current Iled that causes the LED chip 74 to emit light, and is proportional to the magnitude of the drive current Iled (FIG. 7).
However, when the transparent resin encapsulating the LED chip 74 deteriorates due to heat of the LED chip 74, for example, and its transparency is lowered, as shown in FIG. 7, the drive current Iled0 having the same magnitude as the initial use is applied to the LED chip. Even if it flows to 74, the amount of static elimination light E0 having the same size as that at the beginning of use cannot be obtained, and the amount of static elimination light E ′ when the LED chip 74 is deteriorated decreases and is always lower than the amount of static elimination light E0 at the beginning of use. That is, in order to obtain the charge elimination light amount E0 at the beginning of use, a drive current Iled ′ larger than that at the beginning of use must be passed through the LED chip 74.

Further, the reduction of the amount of static elimination E is also caused by the increase of the environmental temperature. The amount of static elimination E when the temperature rises decreases and is always lower than the amount of static elimination E0 at the beginning of use.
Then, when the relationship between the drive current Iled and the charge removal light amount E is seen from the above-described relationship between the charge removal light amount E and the charging current I, the characteristics due to the light source drive current-charge current as shown in FIG. A curve is obtained, and the charging current when the LED chip 74 deteriorates or the environmental temperature rises is always lower than the charging current at the beginning of use, so the drive current Iled ′ when the LED chip 74 deteriorates or the environmental temperature rises is If it is always set larger than the drive current Iled0 at the beginning of use, it is possible to compensate for the decrease in the charge removal amount E.

  Therefore, in this embodiment, the range of the drive current Iled is controlled by the charge elimination light quantity control unit 92 so as to compensate for the reduction in the charge elimination light quantity based on the relationship between the drive current Iled and the charging current I. Therefore, it is possible to secure the amount of static elimination E0 at the beginning of use and maintain the charging performance of the a-Si drum 18. As a result, stable image forming performance can be obtained.

  The charge elimination light amount control unit 92 includes a characteristic curve acquisition unit 94. The characteristic curve acquisition unit 94 uses the charge removal light amount E 'when the LED chip 74 is deteriorated or when the environmental temperature rises. In other words, the relationship in which the drive current Iled ′ required when the LED chip 74 deteriorates or the environmental temperature rises always exceeds the drive current Iled0 at the beginning of use is substantially equal to the above-described static elimination light amount E. By applying the relationship with the charging current I, the characteristic curve by the light source driving current-charging current in FIG. 8 is obtained, and the charging current when the LED chip 74 is deteriorated or when the environmental temperature is rising is always the initial charging current. Clarify below points. As a result, the amount of reduction in the charge removal amount as seen from the charging current I is clarified, and the amount of decrease can be reliably compensated.

  Further, the charge elimination light amount control unit 92 includes a drive current range setting unit 94. The drive current range setting unit 94 performs charging that does not shorten the life of the charging roller 21 from the minimum charge current Imin necessary to prevent memory images. Using the range up to the upper limit value Imax of the current, the drive current Iled'_min (indicated by a black circle in FIG. 8) to Iled'_max (indicated by a black square in FIG. 8) is set to compensate for the decrease in the amount of static elimination light. To do. As a result, the amount of reduction in the charge removal amount as seen from the drive current Iled is clarified, and this reduction can be more reliably compensated.

  Furthermore, the drive current range setting unit 94 ranges from the drive current Iled_min (shown by a circle in FIG. 8) to Iled_max (shown by a □ in FIG. 8) before the amount of electricity removed by the LED chip 74 is reduced (for example, at the beginning of use). Is stored in the memory 98, and the relationship in which the drive current Iled 'when the LED chip 74 is deteriorated or when the environmental temperature rises always exceeds the drive current Iled0 at the beginning of use is clarified. Therefore, the range from the drive current Iled′_min (indicated by the mark ● in FIG. 8) to Iled′_max (indicated by the mark ■ in FIG. 8) for making up for the reduction in the amount of light removed can be set more clearly.

Further, when the LED chip 74 is used as in the present embodiment, the amount of static elimination light is significantly reduced due to the deterioration of the LED chip 74 and the increase of the environmental temperature. However, if the above-described static elimination light amount control unit 92 is used, the reduction in static elimination light amount can be compensated, so that the static elimination light amount E0 at the beginning of use can be sufficiently secured.
In addition, various numerical values in the present embodiment are specified. First, the drum linear velocity of the a-Si drum 18 is 400 [mm / sec], and the optical memory potential V is 5 [V].

  The charging roller 21 has a charging DC voltage of 490 [V], a voltage amplitude of 1000 [V], a charging voltage frequency of 2.75 [kHz], a charging current upper limit Imax of 250 [μA], and a charging current lower limit Imin. Is 200 [μA]. Further, the time from the irradiation position of the LED chip 74 to the charging roller 21 is 80 [mmsec].

The drive current lower limit Iled_min at the beginning of use is 17 [mA] and the drive current upper limit Iled_max is 60 [mA], while the drive current lower limit Iled′_min after the static elimination light source deterioration is 40 [mA] and the drive current upper limit. Iled'_max is 100 [mA].
The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims.

For example, in the above embodiment, the eraser 19 having the LED chip 74 has been described. However, the light source of the present invention may be a laser diode or an organic EL element. This is because, in these cases, the amount of static elimination light is reduced due to the deterioration of the light source.
In the above-described embodiment, the printer 1 using the intermediate transfer belt is described. However, the present invention can also be applied to a case where the toner image on the photosensitive drum 18 is directly transferred to a sheet, and the transfer material of the present invention may be a sheet.

Furthermore, in this embodiment, an example in which a printer is embodied as an image forming apparatus is shown. However, the image forming apparatus of the present invention is naturally applicable to a multifunction machine, a copying machine, a facsimile machine, and the like.
In any of these cases, similarly to the above, it is possible to suppress the change in the charging performance of the photosensitive drum due to the decrease in the amount of charge removal.

1 Printer (image forming device)
12 Intermediate transfer belt (transfer material)
18 Photosensitive drum 19 Eraser (static elimination unit)
20 Charger 74 LED chip (light source)
90 controller 92 static elimination light quantity control unit (control means)
94 Characteristic curve acquisition unit 96 Drive current range setting unit

Claims (5)

A photosensitive drum having an amorphous silicon-based surface layer and transferring a toner image formed on the surface layer through charging and exposure to a transfer material by rotational driving;
A charger for charging the photosensitive drum;
A static elimination unit having a light source for irradiating the surface layer with static elimination light before reaching the charge, and removing charges remaining on the surface layer after the transfer;
Control means for controlling the drive current so as to compensate for a decrease in the light amount of the charge removal light based on a relationship between a drive current for causing the light source to emit light and a charging current applied to the charger. An image forming apparatus. The image forming apparatus according to claim 1,
The control unit includes a characteristic curve acquisition unit that obtains a characteristic curve from the charging current and the driving current when a predetermined period of the light source has elapsed or when the environmental temperature of the image forming apparatus has increased. Image forming apparatus. The image forming apparatus according to claim 1, wherein
The control means uses the charging current usage range determined from the elimination of the exposure history of the surface layer and the life of the charger, and sets the driving current range to compensate for the decrease in the light amount of the static elimination light. An image forming apparatus comprising a current range setting unit. The image forming apparatus according to claim 3, wherein
The drive current range setting unit sets a range of the drive current before a reduction in the amount of static elimination light by the light source, using a charging current usage range determined from elimination of the exposure history of the surface layer and the life of the charger. An image forming apparatus. An image forming apparatus according to any one of claims 1 to 4,
The image forming apparatus according to claim 1, wherein the light source is a plurality of LED chips having substantially the same light emission characteristics along a rotation axis of the photosensitive drum.

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