JP2007219270A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus appropriately carrying out setting of surface potential for an image carrier according to an arbitrary image carrier and even according to a variation in the resistance value of a charging roller. <P>SOLUTION: The image forming apparatus is provided with the image carrier, the charging roller charging the image carrier and a voltage applying means applying the voltage obtained by superposing AC voltage on DC voltage to the charging roller. The image forming apparatus is provided with; an effective current value measuring means measuring an effective current value which is the total of an effective value of the AC current flowing in the image carrier and the DC current value, a storing means storing a reference effective current value, an AC voltage correcting means correcting the AC voltage applied to the charging roller on the basis of the measured effective current value by the effective current value measuring means and the reference effective current value stored in the storing means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that appropriately sets a surface potential of an image carrier.

In an electrostatic copying type image forming apparatus, an electrostatic latent image is formed on an image carrier using charging means, and this is developed into toner to form a toner image. The toner image is transferred onto a transfer sheet, whereby image formation is performed. Therefore, it is known that unless an appropriate voltage is applied to the charging means, an appropriate surface potential cannot be applied to the image carrier, and the quality of the formed image is lowered.
In the electrostatic copying type image forming apparatus described in Patent Document 1, a DC voltage is applied to a charging unit that rotates in contact with the image carrier to discharge it, thereby charging the image carrier. In this case, the resistance value in the charging means greatly depends on the environmental conditions. Therefore, when measuring the inflow current value of the image carrier in contact with the charging means from the charging means and measuring the resistance value of the charging means, the temperature in the vicinity of the charging means is measured, and the temperature in the vicinity of the charging means and the temperature Accordingly, a plurality of applied voltage values to be applied to the charging means are stored in advance, so that the surface potential can be easily set based on the stored values.
JP 2000-338749 A

On the other hand, a photoconductive drum provided in an image forming apparatus is applied to a charging roller necessary to give a predetermined surface potential to the photoconductive drum, such as an organic photo conductor (OPC). If the relationship between the voltage to be measured and the resistance value of the system from the charging roller to the photosensitive drum measured when the voltage is applied to the charging roller is determined, any of the photosensitive An appropriate surface potential can also be set for the body drum regardless of the temperature near the charging roller.
However, it is known that an amorphous silicon (hereinafter referred to as a-Si) drum used in an image forming apparatus in recent years has a different resistance value measured for each a-Si drum. That is, when a voltage is applied to the charging roller to give an appropriate surface potential to the a-Si drum, the current flowing through the charging roller is different for each a-Si drum even with the same charging roller. Different resistance values. For this reason, even if the voltage applied to the charging roller according to the temperature is stored in order to give an appropriate surface potential to a predetermined photosensitive drum by using the technique described in Patent Document 1, the same charging roller is used. In combination with the photosensitive drum, an appropriate surface potential cannot be applied even if a stored voltage is applied.

On the other hand, it is known that charging unevenness is less when charging the charging roller by applying a voltage in which DC voltage and AC voltage are superimposed than when charging only the DC voltage. ing.
This is because, when only a DC voltage is applied to the charging roller, the amount of discharge is small, so that the surface of the charging roller to which the voltage is applied and the surface of the photosensitive drum in contact with the charging roller or the surface of the charging roller adhere to the surface. It is easily affected by foreign matter and is difficult to charge uniformly. However, when a voltage with DC voltage and AC voltage superimposed is applied to the charging roller, reverse discharge occurs when an AC voltage twice the discharge start voltage is applied. This is because it has the effect of smoothing charges.
In this way, image quality deteriorates when there is uneven charging. Therefore, there are many types of image forming apparatuses that apply a voltage obtained by superimposing a DC voltage and an AC voltage with little charging unevenness to a charging roller.
In the image forming apparatus described in Patent Document 1, only a DC voltage is applied to the charging roller, and the resistance value of the system from the charging roller to the photosensitive drum is measured. Therefore, it is necessary to provide a DC voltage that is high enough to provide the surface potential.
On the other hand, in an image forming apparatus that applies a predetermined surface potential to a photosensitive drum by applying a voltage obtained by superimposing a DC voltage and an AC voltage to a charging roller, as described above, a predetermined surface potential is applied to the photosensitive drum. In order to use the technique described in Patent Document 1 above, it is necessary to measure the resistance value of the system from the charging roller to the photosensitive drum, even though it is not necessary to apply a high DC voltage. Therefore, it is necessary to apply a high DC voltage component, so that a member corresponding to a high voltage is required, and there is a problem that costs increase.
Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide an image forming apparatus that applies a voltage obtained by superimposing a DC voltage and an AC voltage to a charging roller at a low cost and arbitrarily. It is an object of the present invention to provide an image forming apparatus capable of appropriately setting the surface potential of an image carrier corresponding to the image carrier and corresponding to the change in the resistance value of the charging roller.

That is, in the present invention, an image carrier that carries an image to be developed by a developer, a charging roller that charges the image carrier by rotating in contact, and an AC voltage and a DC voltage are superimposed on the charging roller. The present invention relates to an image forming apparatus including a voltage applying unit that applies the applied voltage. In order to achieve the above object, in the present invention, an effective current value measurement that measures the effective current value that is the sum of the effective value of the alternating current and the direct current value that flows through the image carrier charged by the charging roller. Means, storage means for storing a reference effective current value by which the image carrier charged by the charging roller can obtain a predetermined surface potential, effective current value measured by the effective current value measuring means, and storage means AC voltage correcting means for correcting the AC voltage applied to the charging roller by the voltage applying means on the basis of the reference effective current value stored in.
The normal effective current value is a current value obtained by converting an alternating current into a direct current, and is a value obtained by multiplying the maximum value of the alternating current by a predetermined ratio (for example, a constant such as 0.707). Here, since the AC component and the DC component are superposed, the AC current multiplied by a predetermined constant is added to the DC current component, which is called the effective current value.
With the configuration as described above, the voltage applied to the charging roller necessary to give a predetermined surface potential to the image carrier, and the resistance of the image carrier measured when the voltage is applied to the charging roller. Even in an image forming apparatus provided with an image carrier having a variation in value relationship, the voltage applied to the charging roller can be corrected appropriately. That is, the surface potential of the image carrier can be appropriately set.
Further, temperature detection means for detecting the temperature in the vicinity of the charging roller and / or humidity detection means for detecting the humidity in the vicinity of the charging roller, and temperature detected by the temperature detection means and / or the humidity detection means. It is conceivable to include environmentally friendly voltage correction means for correcting the AC voltage applied to the charging roller by the voltage application means based on the humidity.
With this configuration, the surface potential of the image carrier can be set according to environmental changes. That is, since the resistance value of the charging roller varies depending on the temperature and humidity in the vicinity of the charging roller, the voltage applied to the charging roller is changed by the voltage applying means in accordance with the temperature and humidity in the vicinity of the charging roller. is there.
Further, the voltage applied to the charging roller by the voltage applying unit is corrected by the environmental voltage correcting unit based on the temperature detected by the temperature detecting unit and / or the humidity detected by the humidity detecting unit. For this reason, it is conceivable that the AC voltage correcting means corrects the AC voltage applied to the charging roller by the voltage applying means.
Accordingly, the voltage applied to the charging roller by the voltage applying unit by the AC voltage correcting unit is synchronized with the correction of the voltage applied to the charging roller by the voltage applying unit according to the environmental change. Can be corrected.
Further, based on the effective current value measured by the effective current value measuring means and the reference effective current value stored in the storage means, the DC voltage applied to the charging roller by the voltage applying means is corrected. It is preferable to provide DC voltage correcting means.
With such a configuration, even if the voltage applied to the charging roller is corrected by the voltage applying unit by the AC voltage correcting unit, an appropriate surface potential cannot be applied to the image carrier. Further, by correcting the DC voltage applied to the charging roller by the voltage applying means by the DC voltage correcting means, it is possible to give an appropriate surface potential to the image carrier.
The reference effective current value is preferably measured in the manufacturing process of the image forming apparatus.
When measured in the manufacturing process of the image forming apparatus, the image carrier provided in the image forming apparatus and the charging roller are not deteriorated, that is, the quality of the formed image is not deteriorated. By using the effective current value as a reference, an accurate reference value can be obtained, and an appropriate voltage can be set later when correction is performed.
The AC voltage correcting means is applied to the charging roller by the voltage applying means by the difference between the effective current value measured by the effective current value measuring means and the reference effective current value stored in the storage means. It is conceivable to correct the voltage.
This is because the large difference between the effective current value measured by the effective current value measuring means and the reference effective current value stored in the storage means means that the same voltage is applied to the charging roller. This is because the value is far from the reference effective current value. That is, since the resistance value is increased due to the deterioration of the charging roller or the adhering foreign matter, a larger voltage must be applied to the charging roller. In addition, if the voltage is applied by the difference instead of specifically determining the applied voltage value with respect to the effective current value, the value of the voltage applied to the charging means corresponding to the effective current value flowing through an arbitrary image carrier. Since it is not necessary to store a large number of images, the cost is low.
Furthermore, in order to use the technique described in Patent Document 1, it is necessary to actually measure the resistance value of the charging roller. In that case, it is not necessary to apply a DC voltage that is high enough to give a predetermined surface potential to the image carrier only by the DC voltage as described above, and a voltage obtained by superimposing the DC voltage and the AC voltage is not necessary. In an image forming apparatus that applies a predetermined surface potential to the image carrier by applying it to the charging roller, in order to actually measure the charging roller resistance, a high voltage is used only to measure the charging roller resistance. A member corresponding to is required, and costs are increased. However, with the above configuration, the resistance value of the charging roller is not actually measured, but the effective current value of the current flowing through the image carrier charged by the charging roller is measured. It is not necessary to prepare a member corresponding to a high voltage only for measuring the value, and the cost is low. In addition, it is possible to provide an image forming apparatus capable of appropriately setting the surface potential of the image carrier in accordance with an arbitrary image carrier and corresponding to the change in the resistance value of the charging roller.

  According to the present invention, in an image forming apparatus that applies a voltage obtained by superimposing a DC voltage and an AC voltage to a charging roller, the resistance value of the charging roller can be changed at a low cost according to an arbitrary image carrier. In addition, it is possible to provide an image forming apparatus capable of appropriately setting the surface potential of the image carrier corresponding to the above.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a schematic diagram showing a schematic configuration of an image forming unit G of the image forming apparatus X according to the embodiment of the present invention, and FIG. 2 is an image forming unit of the image forming apparatus X according to the embodiment of the present invention. 3 is a block diagram of a control system in G. FIG. 3 shows a reference setting process executed by the control unit 20 of the jig Y and a voltage applied to the charging roller 12 executed by the control unit 6 of the image forming apparatus X according to the embodiment of the present invention. FIG. 4 is a diagram showing environment / AC voltage setting correspondence information, FIG. 5 is a diagram showing effective current value difference / AC voltage setting information, and FIG. 7 is a graph showing the relationship between the surface potential and effective current value of the photosensitive drum 11 provided in the image forming apparatus X according to the embodiment of the present invention and the AC voltage applied to the charging roller 12. FIG. FIG.
In the present invention, an image forming apparatus X of a type that applies a voltage obtained by superimposing a DC voltage and an AC voltage to a charging roller is used.
The effective current value flowing through the photosensitive drum 11 used in the present embodiment is the sum of the effective value of the alternating current (maximum alternating current value × 0.707) and the direct current value.

First, the schematic configuration of the image forming unit G provided in the image forming apparatus X according to the embodiment of the present invention will be described with reference to the schematic diagram of FIG. 1 and the block diagram of FIG.
As shown in the block diagram of FIG. 2, the image forming unit G includes an effective current value measuring unit 1 that is a current measuring circuit that measures an effective current value of a current flowing through the photosensitive drum 11 described later, and a later described control system. A voltage application unit 2 that applies a voltage obtained by superimposing a DC voltage and an AC voltage to the charging roller 12, and an application voltage value (DC application voltage value, AC application voltage) that is applied to the charging roller 12 by the voltage application unit 2. Value) and the like, a temperature detection sensor 4 for detecting the temperature of the charging roller 12 or the vicinity thereof, a humidity detection sensor 5 for detecting the humidity in the vicinity of the charging roller 12; A surface potential measuring unit 7 which is a measuring instrument for measuring the surface potential of the photosensitive drum 11 and a control unit 6 for comprehensively controlling them are provided. As shown in the schematic diagram of FIG. 1, the hardware includes a photosensitive drum 11 that carries an image, and a charging roller that rotates while contacting the photosensitive drum 11 to charge the surface of the photosensitive drum 11. 12, an exposure unit 13 for irradiating the photosensitive drum 11 with a laser beam to form an electrostatic latent image, and a toner contained in a developer is attached to the electrostatic latent image to form a toner image on the photosensitive member. A developing unit 14 formed on the surface of the drum 11; a transfer roller 15 pressed against the photosensitive drum 11 via a recording sheet (not shown) to which a toner image developed on the photosensitive drum 11 is transferred; , A cleaning unit 16 for cleaning the photosensitive drum 11 after transfer, and a charge eliminating unit 17 for removing a potential remaining on the photosensitive drum 11 after transfer.
Here, a unit that includes the photosensitive drum 11, the charging roller 12, and the storage unit 3 and that can be mounted on the image forming apparatus main body is referred to as a drum unit.
The storage unit 3 stores environmental information, which is information on the temperature and humidity in the vicinity of the charging roller 12, and AC voltage setting information including the value of the AC voltage applied to the charging roller 12 in association with each other. Has been. FIG. 4 shows an example. Hereinafter, the information stored in advance in the storage unit 3 as shown in FIG. 4, that is, the information in which the environment information and the AC voltage setting information are associated is referred to as environment / AC voltage setting correspondence information.
Further, the storage unit 3 includes a difference between a reference effective current value I0 and a measured effective current value, which will be described later, and a correction value of an AC voltage applied to the charging roller 12 that is corrected according to the effective current value difference. Are stored in association with each other. FIG. 5 is an example. Hereinafter, information shown in FIG. 5 stored in advance in the storage unit 3, that is, information in which the difference between the reference effective current value I0 and the measured effective current value and the AC voltage setting information are associated with each other will be described. , Effective current difference / AC voltage setting information.
The photosensitive drum 11 is an a-Si drum here, but is not particularly concerned with this.
The charging roller 12 is a molded product provided with an epichlorohydrin rubber elastic layer so that the diameter of the roller is φ12 on a φ6 cored bar. As an example, the epichlorohydrin rubber elastic layer has a thickness of 3 mm. As an example, the elastic layer has an electric resistance of 3 × 10 7 Ωcm and a rubber hardness of 40 (JIS-A). Here, the charging roller 12 is made of such a material, but is not limited thereto.
The charging roller 12 is not an insulator as described above but has a predetermined electric resistance. However, as described above, the resistance value varies depending on the environmental conditions and the degree of contamination thereof. Therefore, in the present invention, when an electric current is passed through the charging roller 12 to uniformly charge the surface of the photosensitive drum 11 to, for example, +250 V, the electrical conditions given to the charging roller 12 are corrected as described below. The charging roller 12 is pressed in the direction of the photosensitive drum 11 by a spring (not shown), and is adjusted so that the distance between the photosensitive drum 11 and the charging roller 12 is appropriate. The charging roller 12 is in contact with the photosensitive drum 11, and is synchronized with the rotation of the photosensitive drum 11 in the clockwise direction (the direction of the arrow P1) in FIG. (In the direction of arrow P2).
The developing unit 14 includes a developing roller 14-1 carrying a developer. The developing roller 14-1 is disposed at a position facing the photosensitive drum 11 in a non-contact manner.
The transfer roller 15 is a recording sheet on which the toner image developed on the photosensitive drum 11 is conveyed between the photosensitive drum 11 and the transfer roller 15 by applying a voltage of −2.5 kV, for example. It is intended for transfer to.

In the developing unit 14, a DC voltage is applied to the developing roller 14-1, so that toner is carried on the surface of the developing roller 14-1. Further, when an AC voltage having an amplitude of 1.7 kV, a frequency of 2.5 kHz, and a DUTY ratio of 45% is applied to the developing roller 14-1, for example, toner attached to the surface of the developing roller 14-1 is transferred to the photosensitive drum. 11 is easily transferred to the electrostatic latent image on the surface. As a result, a fine toner image is formed on the photosensitive drum 11. The photosensitive drum 11 rotates clockwise (in the direction of arrow P1) in FIG. Further, as described above, the toner image is transferred to a recording paper (not shown) conveyed between the photosensitive drum 11 and the transfer roller 15 by applying a voltage to the transfer roller 15. .
A cleaning unit 16 is disposed downstream of the transfer roller 15 in the rotation direction of the photosensitive drum 11 (in the direction of the arrow P1 in FIG. 1), and toner remaining on the surface of the photosensitive drum 11 The deposits are removed.
A neutralization unit 17 is provided on the downstream side of the cleaning unit 16 in the rotation direction of the photosensitive drum 11, and the potential remaining on the photosensitive drum 11 is removed.
On the other hand, the toner image formed on the recording paper or the like is heated on a fixing roller (not shown) and fixed on the recording paper or the like.

As described above, the quality of the image formed by the image forming unit G depends on the surface potential of the photosensitive drum 11 and the voltage applied to the developing roller 14-1.
Therefore, an appropriate surface potential must be given to the photosensitive drum 11.
However, the resistance value of the charging roller 12 for charging the photosensitive drum 11 varies depending on the environment (temperature and humidity in the vicinity of the charging roller 12), deterioration of the charging roller 12, adhesion of foreign matters, and the like. The photosensitive drum 11 also has a different resistance value measured for each product. That is, even when the same voltage is applied to the charging roller 12 in order to give an appropriate surface potential to the photosensitive drum 11, the same charging roller 12 is also described above depending on each photosensitive drum or environmental conditions. Since the current flowing through the charging roller 12 is different, the voltage to be applied to the charging roller 12 changes.

Here, the voltage applied to the charging roller 12 is a voltage obtained by superimposing a DC voltage and an AC voltage. I've omitted the reason because I already explained it. In the present invention, the AC voltage applied to the charging roller 12 is changed to make the surface potential of the photosensitive drum 11 charged in contact with the charging roller 12 uniform. In order to give a predetermined surface potential to the photosensitive drum 11, the DC voltage applied to the charging roller 12 is also changed if necessary.
Here, the reason why the AC voltage applied to the charging roller 12 is adjusted in order to make the surface potential of the photosensitive drum 11 uniform will be described.
FIG. 6 is a graph showing the relationship between the surface potential and effective current value of the photosensitive drum 11 and the AC voltage applied to the charging roller 12.
As shown in FIG. 6, the vertical axis represents the surface potential of the photosensitive drum 11 and the effective current value flowing through the photosensitive drum 11, and the horizontal axis represents the AC voltage applied to the charging roller 12 by the voltage application unit 2. The effective current value increases linearly according to the AC voltage. According to experiments, it has been confirmed that the surface potential and effective current value of the photosensitive drum 11 are constant from a certain point in time (referred to as point C) even if the applied AC voltage is increased. This means that the point C matches the reverse discharge start condition when a voltage obtained by superimposing a DC voltage and an AC voltage is applied to the charging roller 12 by the voltage application unit 2. ing. Such a constant value is obtained after the start of reverse discharge, and the charge transfer between the charging roller 12 and the photosensitive drum 11 is performed, whereby the surface of the photosensitive drum 11 is uniformly charged. Such a uniformly charged and stable surface potential is hereinafter referred to as a saturated surface potential. Here, as an example, it is 250V.
In FIG. 6, while the AC voltage applied to the charging roller 12 up to point C and the surface potential of the photosensitive drum 11 increase linearly, that is, while positive discharge is performed, the saturated surface Since the potential is not reached, the photosensitive drum 11 is not uniformly charged, so that the quality of the formed image is not good. Further, as indicated by point C in FIG. 6, when the photosensitive drum 11 is at the saturated surface potential, the photosensitive drum 11 is uniformly charged and is in a stable state. However, as shown on the right side from point C in FIG. 6, even if the photosensitive drum 11 has the saturated surface potential, if a high voltage is applied to the charging roller 12, the charging roller 12 or There is a problem that the photosensitive drum 11 is easily deteriorated or the amount of ozone and nitrogen oxides generated is increased. Therefore, when the minimum necessary AC voltage (here, the AC voltage at the point C in FIG. 6) capable of giving the saturated surface potential to the photosensitive drum 11 is applied to the charging roller 12, the charging roller 12 and A uniform surface potential can be applied to the photoconductor drum 11 while suppressing deterioration of the photoconductor drum 11 and generation amounts of ozone and nitrogen oxides. Subsequently, the DC voltage is changed to obtain a predetermined surface potential (here, +350 V). The predetermined surface potential is a surface potential at which toner can easily transfer from the developing roller 14-1 to the photosensitive drum 11, and image formation can be performed with appropriate image quality. As described above, the AC voltage applied to the charging roller 12 is the optimum AC voltage at the point A in FIG. 6, that is, when the reverse discharge is started. At this time, the DC voltage applied to the charging roller 12 is the optimum DC voltage. The effective current value flowing through the photosensitive drum 11 at this time (point A in FIG. 6) is stored as a reference effective current value I0. That is, if an AC voltage and a DC voltage applied to the charging roller 12 are set so that an effective current value flowing through the photosensitive drum 11 becomes a reference effective current value I0, an appropriate surface of the photosensitive drum 11 can be obtained. A potential can be applied.
That is, if there is a difference between the measured effective current value and the reference effective current value I 0, an appropriate surface potential cannot be applied to the photosensitive drum 11, so that it is applied to the charging roller 12 as described later. It is necessary to correct the AC voltage and DC voltage that are generated.
An appropriate surface potential can be applied to the photosensitive drum 11, and the minimum AC voltage applied to the charging roller 12 required for starting reverse discharge is not fixed at the point A in FIG. Instead, it may be, for example, a point A1 in FIG. 6 depending on an arbitrary photosensitive drum or depending on the environment and the degree of deterioration of the charging roller 12.
Therefore, the AC voltage applied to the charging roller 12 to give an appropriate surface potential to the photosensitive drum 11 is not fixed. It varies depending on the environmental conditions and the situation of the photosensitive drum 11 or the charging roller 12. Therefore, an effective current value for obtaining an appropriate surface potential is measured for each drum unit when the deterioration of the photosensitive drum 11 and the charging roller 12 is not progressing, such as in the manufacturing process of the image forming apparatus, and this is measured as the reference effective current. Stored as a value I0, the AC voltage applied to the charging roller 12 is corrected based on the difference from the measured effective current value.
As described above, according to the present invention, the AC voltage applied to the charging roller 12 in accordance with the change in the resistance value between the photosensitive drum 11 and the charging roller 12 which is known by the change in the effective current value of the current flowing through the photosensitive drum 11. In addition, by setting the DC voltage, an appropriate surface potential is given to the photosensitive drum 11.

Next, a schematic configuration of the jig Y used in the present embodiment will be described with reference to the block diagram of FIG.
The jig Y is an assembly line (manufacturing process) of a factory where the image forming apparatus is manufactured, and is used to adjust the surface potential of the photosensitive drum provided in the drum unit when the drum unit is mounted on the image forming apparatus. It is a jig.
As shown in the block diagram of FIG. 7, the jig Y is mounted with an effective current value measuring unit 21 which is a current measuring circuit for measuring an effective current value flowing through the photosensitive drum provided in the mounted drum unit. In order to charge the charging roller provided in the drum unit, a voltage applying unit 22 that applies a voltage to the charging roller, a temperature detection sensor 24 that detects the temperature of the charging roller or its vicinity, and a humidity near the charging roller The operator starts processing, a humidity detection sensor 25 for detecting the above, a drive motor 26 which is a motor for rotating the photosensitive drum, a surface potential measuring unit 27 which is a measuring instrument for measuring the surface potential of the photosensitive drum, and an operator starts processing. The operation input unit 28 capable of performing an input operation such as the above instruction and the control unit 20 that comprehensively controls them are configured.
In actual measurement, the storage unit 3 provided in the installed drum unit is connected to the control unit 20 as shown in FIG.

Hereinafter, a method for setting an appropriate voltage applied to the charging roller 12 will be described.
First, with the jig Y, the environment (temperature and humidity in the vicinity of the charging roller 12) and the resistance value of the charging roller 12 change (the resistance value of the charging roller 12 increases due to deterioration of the charging roller 12 and adhesion of foreign matter). The outline of the process for appropriately setting the surface potential of the photosensitive drum 11 by adjusting the voltage applied to the charging roller 12 according to FIG.
(1) At the time of assembly in the factory, a voltage obtained by superimposing an AC voltage corresponding to the environment (temperature and humidity near the charging roller 12) and a predetermined DC voltage is applied to the charging roller 12 with the jig Y, and the reference DC Processing to store voltage values.
A rubber roller that is often used as a charging roller that contacts a photosensitive drum and charges the photosensitive drum has a higher resistance value as the temperature and humidity are lower. Therefore, as the temperature and humidity are lower, a saturated surface potential cannot be applied to the photosensitive drum 11 in contact with the charging roller 12 unless a higher voltage is applied to the charging roller 12. Therefore, in order to give a saturated surface potential to the photosensitive drum 11, it is necessary to apply a voltage to the charging roller 12 in accordance with the temperature and humidity in the vicinity of the charging roller 12.
First, when the image forming apparatus X is assembled at a factory, an operator attaches the image forming apparatus X to the image forming apparatus X in order to store information necessary for giving a saturated surface potential to the photosensitive drum 11 in the storage unit 3 of the drum unit. The drum unit to be processed is mounted on the jig Y.
Subsequently, the temperature and humidity in the vicinity of the charging roller 12 provided in the drum unit mounted on the jig Y are measured by the temperature detection sensor 24 and the humidity detection sensor 25 of the jig Y. A predetermined AC voltage (see FIG. 4; Vpp0 in FIG. 6) determined in advance according to the measured temperature and humidity, and a predetermined DC voltage (value capable of giving a surface potential of B1 volts in FIG. 6) Is applied by the voltage application unit 22 and the charging roller 12 is charged, so that the photosensitive drum 11 in contact with the charging roller 12 is also charged. If the saturation surface potential of the photosensitive drum 11 (for example, the surface potential at point C in FIG. 6 + 250V) does not reach a predetermined surface potential (for example, + 350V), the DC voltage applied to the charging roller 12 is changed. Thus, the photosensitive drum 11 is adjusted to have a predetermined surface potential (+350 V). When a predetermined surface potential (+350 V) is applied to the photosensitive drum 11, the DC voltage applied to the charging roller 12 is stored in the storage unit 3 as a reference DC voltage value. In other words, an appropriate DC voltage at the time of assembly in a factory where there is no change over time or adhesion of foreign matter is stored as a reference value to prepare for later correction. In the future, in order to adjust the surface potential due to changes in the environment and resistance, first, the reference DC voltage value is given to the charging roller 12, and then the AC voltage is changed so as to become the saturated surface potential, thereby making the charge uniform. Further, when the saturated surface potential is not a predetermined surface potential, the DC voltage is changed.
Note that the predetermined AC voltage shown in FIG. 4 is obtained by measuring the AC voltage applied to the charging roller at the start of the reverse discharge using a plurality of charging rollers and a photosensitive drum in various environments in advance. The reference AC voltage calculated as
(2) During assembly at the factory, the jig Y measures and stores the effective current value that is the sum of the effective value of the alternating current flowing through the photosensitive drum 11 (maximum alternating current value × 0.707) and the direct current value. processing.
A change in the resistance value of the charging roller 12 (an increase in the resistance value of the charging roller 12 due to deterioration of the charging roller 12 or adhesion of foreign matter) can be understood by a change in the effective current value of the current flowing through the photosensitive drum 11. The effective current value of the current flowing through the photosensitive drum 11 as a reference is measured.
As described above, the AC voltage applied to the charging roller 12 when reverse discharge is started between the photosensitive drum 11 and the charging roller 12, and a predetermined voltage when the AC voltage is applied. A voltage obtained by superimposing a DC voltage that becomes a surface potential is necessary and optimum for applying a predetermined surface potential to the photosensitive drum 11. The effective current value flowing through the photosensitive drum 11 at this time is stored as a reference effective current value I0. That is, as an index for setting the optimum AC voltage to be applied to the charging roller 12, the effective current value measuring unit 21 of the jig Y can effectively measure the current flowing through the photosensitive drum 11 during assembly at the factory. The process for measuring and storing the current value is executed.
In this way, when the image forming apparatus X is assembled at the factory, a direct current voltage is applied to the charging roller 12 so that the photosensitive drum 11 provided in the drum unit mounted on the jig Y has a predetermined surface potential. The effective value (maximum alternating current) of the alternating current flowing through the photosensitive drum 11 charged by the charging roller 12 in a state where a voltage superposed with the alternating voltage is applied (to this point is executed in (1)). Current value × 0.707) and the effective current value which is the sum of the DC current values are measured. The measured effective current value is stored in the storage unit 3 as the reference effective current value I0.
(3) A process of applying an alternating voltage to the charging roller 12 according to the environment (temperature and humidity in the vicinity of the charging roller 12) when used by a user.
As described above, the resistance of the charging roller 12 varies depending on the environment. Therefore, in order to give a saturated surface potential to the photosensitive drum 11 charged by the charging roller 12, a predetermined DC voltage (here, a reference DC voltage value stored in the storage unit 3), an environment, It is necessary to apply to the charging roller 12 a voltage obtained by superimposing an alternating voltage according to the above. If the saturated surface potential is not a predetermined surface potential, the DC voltage is changed.
Specifically, when the user uses the image forming apparatus X, the temperature at or near the charging roller 12 and the humidity near the charging roller 12 are measured. A predetermined AC voltage is applied to the charging roller 12 according to the measured temperature and humidity with reference to FIG. When the power of the image forming apparatus X is turned on, when the controller 6 is energized from the energization cut-off state (when returning from the so-called sleep mode), at predetermined time intervals, during predetermined operation input processing, near the charging roller 12 It is performed at an appropriate time, such as when the environment (temperature and humidity) changes.
(4) When the user is used, the effective current value of the current flowing through the photosensitive drum 11 is measured, and the AC voltage applied to the charging roller 12 is corrected according to the difference between the measured effective current value and the reference effective current value I0. To do.
If the measured effective current value is different from the reference effective current value I0, a predetermined surface potential is applied to the photosensitive drum 11 due to the deterioration of the charging roller 12 or the increase of the resistance value of the charging roller 12 due to the adhesion of foreign matter. It is thought that it was not possible. Therefore, it is necessary to first give a saturated surface potential to the photosensitive drum 11 by correcting the AC voltage applied to the charging roller 12.
When the user uses the image forming apparatus X, the sum of the effective value (maximum alternating current value × 0.707) of the alternating current flowing through the photosensitive drum 11 charged by the charging roller 12 and the direct current value. The effective current value is measured by the effective current value measuring unit 1. The measured effective current value measured is compared with the reference effective current value I0 stored in the storage unit 3 in (2). The AC voltage applied to the charging roller 12 is corrected according to the difference between the measured effective current value and the reference effective current value I0 with reference to FIG.
When a saturated surface potential is given by correcting the AC voltage in this way, the DC voltage is corrected so as to be a predetermined surface potential unless the saturated surface potential is a predetermined surface potential.
Hereinafter, processing procedures by the control unit 20 and the control unit 6 for executing the processes (1) to (4) will be described.

  The drum unit including the photosensitive drum 11, the charging roller 12, and the storage unit 3 is detached from the image forming apparatus X by an operator and attached to the jig Y. Here, a reference DC voltage value applied to the charging roller 12 to give a saturated surface potential to the photosensitive drum 11 and a predetermined surface potential to the photosensitive drum 11 are given by the jig Y. Sometimes, the reference effective current value flowing through the photosensitive drum 11 is stored in the storage unit 3. An example in which the drum unit including the storage unit 3 in which the reference DC voltage value and the reference effective current value are stored by the jig Y is attached to the image forming apparatus X will be described.

(1) At the time of assembly in the factory, a voltage obtained by superimposing an AC voltage corresponding to the environment (temperature and humidity near the charging roller 12) and a predetermined DC voltage is applied to the charging roller 12 with the jig Y, and the reference DC Processing to store voltage values.
FIG. 3A illustrates an example of a processing procedure by the control unit 20 of the reference setting process of the voltage applied to the charging roller 12 in order to give a predetermined surface potential to the photosensitive drum 11 according to the environment. It is a flowchart of.
In the figure, S10, S20,... Indicate process procedure (step) numbers, and the process starts from step S10.
In the assembly line of the factory where the image forming apparatus X is manufactured, the operator can place the photosensitive drum 11, the charging roller 12, and the storage unit on the jig Y that can be mounted on the image forming apparatus X according to the embodiment of the present invention. 3 is installed. At this time, the jig Y is configured as shown in FIG. 7, and the control unit 20 stores data in the storage unit 3 provided in the drum unit mounted on the jig Y.
The following steps S10 to S50 are preferably performed at the time of assembly in a factory where the image forming apparatus X is manufactured.
This is because, when the image forming apparatus X is assembled at the factory, the change over time (deterioration, etc.) and the adhesion of foreign matters due to the use of the photosensitive drum 11 and the charging roller 12 provided in the image forming apparatus X It is possible to obtain an accurate reference value based on the effective current value when there is no image quality, that is, the quality of the formed image is not deteriorated, and set an appropriate voltage when correcting later. Because you can.

First, a predetermined surface potential value and a predetermined DC voltage value are input by the operator through the operation input unit 28.
In step S <b> 10, a predetermined surface potential value (here, +350 V) input by the operator through the operation input unit 28 is stored as a predetermined surface potential in the storage unit 3. Subsequently, a DC voltage having a predetermined value input by the operator through the operation input unit 28 is applied to the charging roller 12 provided in the drum unit mounted on the jig Y by the voltage application unit 22. The process proceeds to step S20.

  In step S20, the temperature detection sensor 24 of the jig Y detects the temperature of the charging roller 12 or the vicinity thereof, and the humidity detection sensor 25 of the jig Y detects the humidity of the vicinity of the charging roller 12. . The temperature detected by the temperature detection sensor 24 and the humidity detected by the humidity detection sensor 25 are stored in the storage unit 3 provided in the drum unit attached to the jig Y by the control unit 20 of the jig Y. And the process proceeds to step S30.

  In step S30, the control unit 20 of the jig Y collates the environment information stored in step S20 with the environment / AC voltage setting correspondence information (FIG. 4) stored in advance in the storage unit 3, An AC voltage set for the charging roller 12 is determined. The determined AC voltage is applied by the control unit 20 to the charging roller 12 provided in the drum unit mounted on the jig Y by the voltage applying unit 22 of the jig Y, and the process proceeds to step S40. In this way, a voltage obtained by superimposing the DC voltage and the AC voltage is applied to the charging roller 12. Here, the photosensitive drum 11 has a saturated surface potential.

  In step S40, the photosensitive drum 11 is rotated by the drive motor 26 of the jig Y by the control unit 20 of the jig Y, and a predetermined surface potential (here, + 350V) stored in the storage unit 3 on its surface. ) Is determined. That is, the surface potential measurement unit 27 of the jig Y shown in FIG. 7 measures the surface potential of the photosensitive drum 11 provided in the drum unit mounted on the jig Y, and the control unit 20 of the jig Y controls the surface potential. If the surface potential of the photosensitive drum 11 measured by the surface potential measuring unit 27 is determined to be a predetermined surface potential (Yes side in step S40), it is determined to be the predetermined surface potential. The value of the DC voltage applied to the charging roller 12 is stored in the storage unit 3 as a reference DC voltage value, and the process proceeds to step S50. If the control unit 20 determines that the surface potential of the photosensitive drum 11 measured by the surface potential measurement unit 27 is not a predetermined surface potential (No side of step S40), the process proceeds to step S51. The DC voltage applied to the charging roller 12 is changed until the surface potential of the photosensitive drum 11 reaches a predetermined surface potential.

  In step S51, the DC voltage applied to the charging roller 12 by the voltage application unit 22 is changed by the control unit 20 of the jig Y, and the process returns to step S40.

(2) During assembly at the factory, the jig Y measures and stores the effective current value that is the sum of the effective value of the alternating current flowing through the photosensitive drum 11 (maximum alternating current value × 0.707) and the direct current value. processing.
In step S50, the effective value (maximum alternating current value × 0) of the alternating current flowing through the photosensitive drum 11 in a state where the effective current value measuring unit 21 of the jig Y obtains a predetermined surface potential as described above. .707) and the effective current value which is the sum of the DC current values is measured. The effective current value measured by the effective current value measuring unit 21 is stored as a reference effective current value I0 in the storage unit 3 provided in the drum unit mounted on the jig Y by the control unit 20 of the jig Y. , The process ends.
The drum unit provided with the charging roller 12, the photosensitive drum 11, and the storage unit 3 for which the storage process has been completed is removed from the jig Y by an operator and attached to the image forming apparatus X. Then, the image forming apparatus X equipped with the drum unit is shipped. When the image forming apparatus X is used by a user, the reference DC voltage value stored in step S40 is applied to the charging roller 12 by the voltage application unit 2. The charging roller 12 is applied with the reference DC voltage value by the voltage application unit 2 and also with an AC voltage corrected in the following procedure according to the environment. At this time, if the photosensitive drum 11 does not reach the predetermined surface potential, the DC voltage is also corrected.

(3) A process of applying an alternating voltage to the charging roller 12 according to the environment (temperature and humidity in the vicinity of the charging roller 12) when used by a user.
Next, an example of a procedure for correcting the AC voltage applied to the charging roller 12 according to the environment and the difference in effective current value will be described with reference to the flowchart of FIG. The correction process is performed when the image forming apparatus X is shipped and a user uses the image forming apparatus X.
FIG. 3B is a flowchart for explaining an example of a processing procedure by the control unit 6 for correcting a voltage applied to the charging roller 12 according to a difference in environment or effective current value.
In the figure, S100, S110... Indicate processing procedure (step) numbers, and the processing starts from step S100.
The following steps S100 to S140 are performed when a predetermined operation is performed every predetermined time when the image forming apparatus X is turned on, when it is energized from the power-off state by the control unit 6 (when returning from the so-called sleep mode). This is performed at an appropriate time, such as during input processing or when the environment (temperature or humidity) in the vicinity of the charging roller 12 changes.

  In step S100, the reference DC voltage stored in the storage unit 3 is applied to the charging roller 12 by the voltage application unit 2.

  In step S110, the temperature detection sensor 4 detects the temperature of the charging roller 12 or the vicinity thereof, and the humidity detection sensor 5 detects the humidity of the charging roller 12 vicinity. The temperature detected by the temperature detection sensor 4 and the humidity detected by the humidity detection sensor 5 are temporarily stored as environment information in the storage unit 3 by the control unit 6, and the process proceeds to step S120. Is done. In addition, whenever a temperature is newly detected by the temperature detection sensor 4 and a new humidity is detected by the humidity detection sensor 5, the environmental information temporarily stored in the storage unit 3 is deleted, The newly detected temperature and humidity are stored.

In step S120, the control unit 6 collates the environment information stored in step S110 with the environment / AC voltage setting correspondence information (FIG. 4) stored in advance in the storage unit 3, and the charging roller The AC voltage set to 12 is determined. The control unit 6 applies the determined AC voltage to the charging roller 12 by the voltage application unit 2, and the process proceeds to step S130. As described above, the voltage application unit 2 applies a voltage in which a DC voltage and an AC voltage are superimposed on the charging roller 12.
The process of correcting the AC voltage according to the environmental information in steps S110 and S120 is executed every time the environment (temperature and humidity) in the vicinity of the charging roller 12 changes.
Note that the value of the environment / AC voltage setting correspondence information in FIG. 4 is an example.
Here, the voltage application unit 2 applies the charging roller 12 based on the temperature detected by the temperature detection sensor 4 and the humidity detected by the humidity detection sensor 5 in steps S110 and S120. The control unit 6 that performs the process of correcting the AC voltage is an example of an environment-compatible voltage correction unit.

(4) When the user is used, the effective current value of the current flowing through the photosensitive drum 11 is measured, and the voltage applied to the charging roller 12 is corrected according to the difference between the measured effective current value and the reference effective current value I0. processing.
In step S130, the effective current value measuring unit 1 measures an effective current value that is the sum of the effective value of the alternating current flowing through the photosensitive drum 11 (maximum alternating current value × 0.707) and the direct current value. . The effective current value measured by the effective current value measuring unit 1 is temporarily stored in the storage unit 3 as a measured effective current value by the control unit 6, and the process proceeds to step S140.

  In step S140, the measured effective current value measured by the effective current value measuring unit 1 in step S130 and temporarily stored in the storage unit 3, and stored in the storage unit 3 in step S50 of the reference setting process. The difference X (referred to as effective current value difference X) with the reference effective current value I0 calculated is calculated by the control unit 6 and temporarily stored in the storage unit 3, and the process proceeds to step S150. The fact that the effective current value difference X is not 0 means that the photosensitive drum 11 does not have a predetermined surface potential due to a change in the resistance value of the charging roller 12, and in subsequent steps S150 and S160. The AC voltage and DC voltage applied to the charging roller 12 are corrected.

In Step S150, the effective current value difference X temporarily stored in Step S130 and the effective current value difference / AC voltage setting information stored in advance in the storage unit 3 by the control unit 6 (FIG. 5). And the AC voltage set for the charging roller 12 is determined. The AC voltage determined by the control unit 6 is applied to the charging roller 12 by the voltage application unit 2, and the measured effective current value and the effective current value difference X temporarily stored in the storage unit 3 are: Erased. Thus, by correcting the AC voltage applied to the charging roller 12 by the voltage application unit 2, a saturated surface potential is applied to the photosensitive drum 11, and the process proceeds to step S160.
In addition, the value of the effective current value difference / AC voltage setting information in FIG. 5 is an example.
In accordance with the difference between the measured effective current value measured by the effective current value measuring unit 1 and the reference effective current value I0 stored in the storage unit 3 in steps S130 to S150, the voltage applying unit 2 The control unit 6 that performs processing for correcting the AC voltage applied to the charging roller 12 is an example of AC voltage correcting means.
The AC voltage correction process executed in accordance with the effective current value difference in steps S130 to S150 may be periodically performed separately from the voltage correction process executed in accordance with the environmental information in steps S110 and S120. Here, it is executed in synchronization with the voltage correction process executed according to the environmental information in steps S110 and S120.

In step S160, it is determined whether or not a predetermined surface potential (here, +350 V) stored in the storage unit 3 is applied. That is, the surface potential of the photosensitive drum 11 is measured by the surface potential measuring unit 7 shown in FIG. 2, and the surface potential of the photosensitive drum 11 measured by the surface potential measuring unit 7 is measured by the control unit 6. Is determined to be the predetermined surface potential (Yes in step S160), the process ends.
If the controller 6 determines that the surface potential of the photosensitive drum 11 measured by the surface potential measuring unit 27 is not a predetermined surface potential (No side of step S160), the process proceeds to step S161. The DC voltage applied to the charging roller 12 is changed until the surface potential of the photosensitive drum 11 reaches a predetermined surface potential.

In step S161, the control unit 6 changes the DC voltage applied to the charging roller 12 by the voltage application unit 2, and the process returns to step S160.
Here, in the state where the AC voltage corrected based on the effective current value measured by the effective current value measuring unit 1 and the reference current value I0 stored in the storage unit 3 is applied, the voltage The control unit 6 that corrects the DC voltage applied to the charging roller 12 by the applying unit 2 corresponds to an example of a DC voltage correcting unit.

As described above, the voltage applied to the charging roller 12 is not determined with respect to the specifically measured effective current value, but can be arbitrarily determined by applying a voltage to the charging roller 12 according to the effective current value difference. Since it is not necessary to store a large number of voltage values applied to the charging roller 12 corresponding to the effective current value flowing through the photosensitive drum, the cost is low.
In the present invention, the resistance value of the charging roller 12 is not actually measured, but the effective value of the alternating current flowing through the photosensitive drum 11 charged by the charging roller 12 (maximum alternating current value × 0.707). ) And the DC current value are measured to determine the change in the resistance value of the charging roller 12 based on the change in the effective current value. If the resistance value of the charging roller 12 is actually measured instead of the method of the present invention, a DC voltage that is high enough to give a predetermined surface potential to the photosensitive drum 11 is required. It is not necessary to apply a DC voltage that is high enough to give a predetermined surface potential to the photosensitive drum 11 with only the DC voltage, and a voltage obtained by superimposing the DC voltage and the AC voltage is applied to the charging roller. In the image forming apparatus X of the type that gives a predetermined surface potential to the photosensitive drum, it is necessary to apply a high DC voltage component only to measure the resistance value of the charging roller 12, so that a member corresponding to the high voltage is used. It becomes necessary. However, in the present invention, since the resistance value of the charging roller 12 is not actually measured, the effective current value of the current flowing through the photosensitive drum 11 charged by the charging roller 12 is measured. Since it is not necessary to use a DC high voltage compatible member corresponding to a DC voltage that is high enough to give a predetermined surface potential to the photosensitive drum 11, it is inexpensive.
In addition, the surface potential of the photosensitive drum 11 is appropriately set according to an arbitrary photosensitive drum and corresponding to a change in the resistance value of the charging roller 12 due to deterioration of the charging roller 12 or adhesion of foreign matter. be able to.

  In the image forming apparatus X, as the environmental information of the charging roller 12, both the temperature and humidity in the vicinity of the charging roller 12 are detected and the values are used, but only the temperature in the vicinity of the charging roller 12 or Only the humidity in the vicinity of the charging roller 12 may be used.

1 is a schematic diagram showing a schematic configuration of an image forming unit G of an image forming apparatus X according to an embodiment of the present invention. FIG. 3 is a block diagram of a control system in the image forming unit G of the image forming apparatus X according to the embodiment of the present invention. An example of the procedure of the reference setting process executed by the control unit 20 of the jig Y and the process of applying a voltage to the charging roller 12 executed by the control unit 6 of the image forming apparatus X according to the embodiment of the present invention will be described. The flowchart for doing. The figure which shows environmental and alternating voltage setting correspondence information. The figure which shows effective current value difference and alternating voltage setting information. 3 is a graph showing the relationship between the surface potential and effective current value of the photosensitive drum 11 provided in the image forming apparatus X according to the embodiment of the present invention, and the AC voltage applied to the charging roller 12. The block diagram of the jig Y. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,21 ... Effective current value measurement part 2,22 ... Voltage application part 3 ... Storage part 4,24 ... Temperature detection sensor 5,25 ... Humidity detection sensor 6,20 ... Control part 7,27 ... Surface potential measurement part 11 ... Photoreceptor drum 12 ... Charging roller 13 ... Exposure unit 14 ... Development unit 15 ... Transfer roller 16 ... Cleaning unit 17 ... Charging unit 26 ... Drive motor

Claims (6)

An image carrier that carries an image to be developed by the developer, a charging roller that charges the image carrier by rotating in contact, and a voltage obtained by superimposing an AC voltage and a DC voltage on the charging roller An image forming apparatus comprising:
Effective current value measuring means for measuring an effective current value that is a sum of an effective value of an alternating current flowing through the image carrier charged by the charging roller and a direct current value;
Storage means for storing a reference effective current value by which the image carrier charged by the charging roller can obtain a predetermined surface potential;
An AC voltage that corrects an AC voltage applied to the charging roller by the voltage applying unit based on the effective current value measured by the effective current value measuring unit and the reference effective current value stored in the storage unit. Correction means;
An image forming apparatus comprising:   Temperature detecting means for detecting the temperature in the vicinity of the charging roller and / or humidity detecting means for detecting the humidity in the vicinity of the charging roller, temperature detected by the temperature detecting means and / or humidity detected by the humidity detecting means The image forming apparatus according to claim 1, further comprising: an environmentally-friendly voltage correction unit that corrects an alternating voltage applied to the charging roller by the voltage application unit.   The voltage applied to the charging roller by the voltage application unit is corrected by the environmental voltage correction unit based on the temperature detected by the temperature detection unit and / or the humidity detected by the humidity detection unit. The image forming apparatus according to claim 2, wherein the AC voltage correcting unit corrects the AC voltage applied to the charging roller by the voltage applying unit.   DC voltage for correcting the DC voltage applied to the charging roller by the voltage applying means based on the effective current value measured by the effective current value measuring means and the reference effective current value stored in the storage means. The image forming apparatus according to claim 1, further comprising a correction unit.   The image forming apparatus according to claim 1, wherein the reference effective current value is measured in a manufacturing process of the image forming apparatus.   The AC voltage correcting means is applied to the charging roller by the voltage applying means by the difference between the effective current value measured by the effective current value measuring means and the reference effective current value stored in the storage means. The image forming apparatus according to claim 1, which corrects a voltage.

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