JP2005092117A - Charging device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformly charge a photoreceptor while suppressing failures such as an abnormal image and filming on the photoreceptor due to a discharge to the minimum. <P>SOLUTION: In a contact charging or non-contact charging device 113, intensity of light generated in a gap H between an image carrier (photoreceptor 103) and a charging member 104 is detected by an optical sensor 110, and a discharge condition is controlled based on the correlation between the light intensity detected by the optical sensor 110 and a discharge condition as a target. Thus, discharge energy applied on the photoreceptor 103 from the charging member 104 is accurately estimated, and the device is controlled so that the discharge energy may become the optimum value, and the occurrence of failures such as the abnormal image and filming due to the increase of loads applied on the photoreceptor 103 can be suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a charging device that charges an image carrier as part of an electrophotographic process, a process cartridge having a charging device, and an image forming apparatus.

  2. Description of the Related Art Conventionally, a contact charging type charging device that charges a photosensitive member by bringing a charging member into contact with the photosensitive member has been proposed and put into practical use. In such a charging device, for example, a roller-shaped charging member is contacted and driven on the photosensitive member to charge the photosensitive member (see Patent Document 1). Such a contact charging method is much less in the amount of generated discharge products than the widely used corona charging method, and the applied voltage is low, so the cost of the power supply is reduced. Has advantages such as being easy.

  However, the contact charging method is inferior to the corona discharge method in terms of charging uniformity. Therefore, in order to improve the uniformity of charging, a method is known in which an AC voltage having an amplitude voltage more than twice the charging start voltage when this DC voltage is applied is superimposed on the DC voltage applied to the charging member. (See Patent Document 2).

  In the contact charging method, foreign matter is caught between the charging member and the photosensitive member, the charging member is contaminated and charging failure occurs, or the roller is in direct contact with the photosensitive member. There is a problem that the photosensitive member is contaminated, which causes image defects such as horizontal stripes.

  On the other hand, in order to improve the problem such as contamination of the charging member due to contact charging, a method is known in which the charging member is disposed close to the surface of the photosensitive member with a certain gap (see Patent Document 3). .

  However, even in such a non-contact charging method, a voltage application method in which an AC voltage is superimposed on a DC voltage is desirable in consideration of problems such as variations in charging potential due to minute gap fluctuations and discharge stability.

JP 63-167380 A JP-A 63-149668 JP 2001-194868 A Japanese Patent Publication No. 7-7224 Toshiharu Nakamura et al., “Charging mechanism of charging roller”, Journal of Electrophotographic Society, Vol. 30, No. 3, 1991

  In the contact charging method and the non-contact charging method as described above, it is necessary to apply a sufficient amplitude voltage to the charging member in order to maintain the uniformity of charging. On the other hand, as the amplitude voltage increases, it is applied to the photoconductor. The load increases and problems such as abnormal images and filming are likely to occur. For this reason, it is desirable that the amplitude voltage in the non-contact charging method of the AC superposition method is set to a minimum necessary size to achieve uniform charging. However, since the electrical characteristics such as the resistance value and dielectric constant of the charging member change according to the usage environment such as temperature and humidity, the amplitude voltage value that satisfies the above conditions varies according to such a change. There is.

  On the other hand, a conventional technique for controlling an applied voltage in a charging process is known (see Patent Document 4). In such a conventional technique, in order to control the surface potential of the photoreceptor, the discharge current of the charging member and the inflow current of the photoreceptor are detected, and the applied voltage is feedback-controlled from the current ratio. However, such a feedback control method cannot accurately measure the current flowing in the discharge space between the photosensitive member and the charging member, and therefore cannot accurately control the applied voltage. That is, between the photosensitive member and the charging member, as shown in FIG. 15, the current (region A in FIG. 15) flowing between the charging member and the photosensitive member directly related to the charging potential control and the charging potential control A capacitor component current (region B in FIG. 15) flows as charges accumulated in the charging member and the photosensitive member, which are not directly related. For this reason, when an ammeter is set between the photosensitive member and the charging member, the sum of the current values of the region A and the region B is detected, and the current values of the region A and the region B are measured separately. I can't do it. For this reason, according to the method for detecting the current, the degree of discharge can be approximately evaluated, but the degree of discharge cannot be accurately evaluated.

  An object of the present invention is to uniformly charge a photoconductor while minimizing problems on the photoconductor due to discharge such as abnormal images and filming.

  According to a first aspect of the present invention, there is provided a charging device that applies a voltage from a voltage application unit to a charging member that is in contact with or close to the image carrier and charges the image carrier by proximity discharge. An optical sensor for detecting the intensity of light generated in a gap between the member and a control means for controlling the discharge condition based on a correlation between the light intensity detected by the optical sensor and a target discharge condition. It has.

  According to a second aspect of the present invention, in the charging device according to the first aspect, the voltage application unit simultaneously applies a DC voltage and an AC voltage to the charging member, and calculates an absolute value of an amplitude voltage of the AC voltage as a discharge start voltage. It is specified to be at least twice the absolute value of.

  According to a third aspect of the present invention, there is provided the charging device according to the second aspect, wherein the control means includes a light intensity generated when the voltage applying unit applies a target amplitude voltage to the charging member, and the optical sensor. The feedback control amount for the amplitude voltage is determined from the difference from the detected light intensity, and the amplitude voltage is feedback controlled with the determined feedback control amount.

  According to a fourth aspect of the present invention, in the charging device according to the first aspect, the light intensity detected by the optical sensor has an adjustment mechanism that variably adjusts a gap between the image carrier and the charging member. The gap is variably adjusted based on the correlation between the gap and the gap.

  According to a fifth aspect of the present invention, in the charging device according to any one of the first to fourth aspects, the control means monitors the light intensity detected by the optical sensor when the voltage application unit is activated, and discharge conditions To control.

  According to a sixth aspect of the present invention, in the charging device according to any one of the first to fourth aspects, the control means detects the light intensity detected by the optical sensor when the voltage application unit is restarted after being temporarily stopped. To control the discharge conditions.

  According to a seventh aspect of the present invention, in the charging device according to any one of the first to fourth aspects, the control means monitors the light intensity detected by the photosensor and controls a discharge condition at a specified time. To do.

  According to an eighth aspect of the present invention, in the charging device according to any one of the first to fourth aspects, the control means monitors the light intensity detected by the photosensor at a specified period to control the discharge condition. .

  According to a ninth aspect of the present invention, in the charging device according to the first aspect, the optical sensor is disposed downstream of the charging member in the rotation direction of the image carrier as viewed from an exposure position with respect to the image carrier. ing.

  According to a tenth aspect of the present invention, in the charging device according to the first aspect, the optical sensor is disposed upstream of the charging member in the rotation direction of the image carrier as viewed from an exposure position with respect to the image carrier. ing.

  The process cartridge according to claim 11 supports the image carrier and the charging device according to any one of claims 1 to 10 for uniformly charging the image carrier, and is attached to and detached from the main body of the image forming apparatus. It is free.

  According to a twelfth aspect of the present invention, in the process cartridge according to the fourteenth aspect, the member that contacts the image carrier is supported.

  According to a thirteenth aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier; a charging device according to any one of claims 1 to 10 that uniformly charges the image carrier; and after uniform charging based on image data. An exposure device for exposing the image carrier to form an electrostatic latent image, a developing device for developing the electrostatic latent image formed on the image carrier, and using the developed electrostatic latent image as a recording material And a transfer device for transferring.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to the thirteenth aspect, the image carrier is made of amorphous silicon.

  According to a fifteenth aspect of the present invention, in the image forming apparatus according to the thirteenth aspect, the image carrier is made of OPC in which a filler is dispersed in a surface layer.

  According to a sixteenth aspect of the present invention, in the image forming apparatus according to the thirteenth aspect, an electrostatic latent image for a plurality of colors is formed on the image carrier, and the electrostatic latent image for a plurality of colors is developed with a plurality of colors. The recording material is transferred to form a color image on the recording material.

  According to the first aspect of the present invention, it is possible to accurately evaluate the energy of discharge applied from the charging member to the image carrier, and to control the discharge energy to an optimum value. It is possible to suppress the occurrence of problems such as abnormal images and filming due to an increase in load.

  According to the second aspect of the present invention, when the amplitude voltage of the AC voltage is high, problems such as an abnormal image and filming of the image carrier increase. On the other hand, when the amplitude voltage is too low, a uniform potential is applied to the image carrier. In contrast, by defining the absolute value of the amplitude voltage of the AC voltage to be at least twice the absolute value of the discharge start voltage, the image carrier can be uniformly charged, and an abnormal image of the image carrier can be obtained. And minimizing defects such as filming.

  According to the third aspect of the invention, when the amplitude voltage of the AC voltage is high, abnormalities such as an abnormal image and filming of the image carrier increase. On the other hand, when the amplitude voltage is too low, a uniform potential is applied to the image carrier. However, the feedback control amount for the amplitude voltage is determined from the difference between the light intensity generated when the voltage application unit applies the target amplitude voltage to the charging member and the light intensity detected by the optical sensor. In addition, the amplitude voltage is feedback-controlled with the determined feedback control amount, so that the image carrier can be uniformly charged and the malfunction of the image carrier such as an abnormal image and filming can be minimized. be able to.

  According to the fourth aspect of the present invention, when the amplitude voltage of the AC voltage is high, problems such as abnormal images and filming of the image carrier increase. On the other hand, when the amplitude voltage is too low, a uniform potential is applied to the image carrier. In contrast, the gap between the image carrier and the charging member is variably adjusted based on the correlation between the light intensity detected by the optical sensor and the gap, thereby making the image carrier uniform. It is possible to achieve both charging and minimizing problems such as abnormal images and filming on the image carrier.

  According to the fifth aspect of the present invention, when the resistance of the charging member varies depending on the temperature and humidity, and the temperature and humidity when the power is turned off are different from the temperature and humidity when the power is turned on thereafter, the charging member Focusing on the fact that the optimal discharge energy applied to the image carrier is not uniform, the discharge applied to the image carrier from the charging member by monitoring the light intensity detected by the photosensor when starting the voltage application unit By controlling the energy, it is possible to optimize the discharge energy applied from the charging member to the image carrier, thereby causing problems such as abnormal images and filming due to an increased load on the image carrier. Can be suppressed.

  According to the invention described in claim 6, when the apparatus is stopped due to occurrence of an abnormality or the like, paying attention to the fact that the voltage application command value or the like in the voltage application unit may fluctuate due to the influence of noise or the like. Discharge applied from the charging member to the image carrier by monitoring the light intensity detected by the optical sensor and controlling the discharge energy applied from the charging member to the image carrier when the application unit is restarted after being temporarily stopped. It is possible to optimize the energy, thereby suppressing the occurrence of problems such as abnormal images and filming due to an increase in the load on the image carrier.

  According to the seventh aspect of the present invention, when the charging device is continuously used, the optimum discharge applied from the charging member to the image carrier is caused by the resistance of the charging member fluctuating or the surface of the charging member becoming dirty. Focusing on the fact that the energy is not uniform, etc., the light intensity detected by the optical sensor is monitored at specified time intervals, and the discharge energy applied from the charging member to the image carrier is controlled, so that the image from the charging member It is possible to optimize the discharge energy applied to the carrier, thereby suppressing the occurrence of problems such as abnormal images and filming due to an increase in the load on the image carrier.

  According to the eighth aspect of the present invention, when the charging device is continuously used, the optimum discharge applied from the charging member to the image carrier is caused by the resistance of the charging member fluctuating or the surface of the charging member becoming dirty. Paying attention to the fact that the energy is not uniform, etc., by monitoring the light intensity detected by the optical sensor at a specified period and controlling the discharge energy applied from the charging member to the image carrier, the image carrier from the charging member It is possible to optimize the discharge energy applied to the body, thereby suppressing the occurrence of problems such as abnormal images and filming due to an increase in the load on the image carrier.

  According to the ninth aspect of the present invention, attention is paid to the fact that if the light for exposing the image carrier is detected by the optical sensor, an accurate monitoring result by the optical sensor cannot be obtained. By disposing the optical sensor on the downstream side in the rotation direction of the image carrier relative to the charging member as seen from the position, the light for exposing the image carrier to the detection of the optical sensor can be less affected, Therefore, it is possible to optimize the discharge energy applied to the image carrier from the charging member controlled by monitoring the light intensity detected by the optical sensor. The occurrence of problems such as images and filming can be suppressed.

  According to the invention described in claim 10, when the light for exposing the image carrier is detected by the optical sensor, an accurate monitoring result by the optical sensor cannot be obtained. By disposing the optical sensor upstream of the charging member in the rotation direction of the image carrier as viewed from the position, the light for exposing the image carrier to the detection of the optical sensor can be less affected, and therefore The discharge energy applied to the image carrier from the charging member that is controlled by monitoring the light intensity detected by the optical sensor can be optimized, whereby an abnormal image due to an increase in the load on the image carrier. The occurrence of problems such as filming can be suppressed.

  According to the eleventh aspect of the present invention, when the charging device and the image carrier are detached and replaced separately, the proximity gap between the charging member and the image carrier cannot be maintained constant at the time of replacement, and the gap can be controlled. Focusing on the possibility of deviating from the range, the image carrier and the charging device according to any one of claims 1 to 10 that uniformly charges the image carrier are supported together to form an image. By making it detachable from the main body of the apparatus, the proximity gap between the charging member and the image carrier can be kept constant in advance, and the proximity between the charging member and the image carrier can be maintained even when the process cartridge is replaced. The fluctuation of the gap can be prevented, and thus a stable charged state can be obtained.

  According to the twelfth aspect of the present invention, when replacing the member that contacts the image carrier, the image carrier must be touched. At this time, the proximity gap between the charging member and the image carrier varies. By supporting the member that contacts the image carrier, the fluctuation of the proximity gap between the charging member and the image carrier can be prevented even when the process cartridge is replaced. Therefore, a stable charged state can be obtained.

  According to the thirteenth aspect, the charging device according to any one of the first to tenth aspects has the effect.

  According to the fourteenth aspect of the present invention, the use of amorphous silicon for the image carrier can dramatically improve the smoothness of the image carrier, and therefore the proximity between the charging member and the image carrier. The gap can be made uniform, and thus a stable charged state can be obtained.

The invention of claim 15 uses OPC in which a filler is dispersed in the surface layer on the image carrier,
It is possible to prevent gap fluctuation of the proximity gap between the charging member and the image carrier, in particular, discharge instability (shift to streamer discharge) due to gap enlargement, and thus a stable charged state can be obtained. .

  According to the sixteenth aspect of the present invention, in the case of a color image forming apparatus, the charging uniformity of the image carrier is more important than the monochromatic image forming apparatus, whereas the charging uniformity is kept stable over a long period of time. In addition, since the image carrier is less likely to deteriorate, image quality deterioration can be prevented.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic diagram illustrating an electrophotographic process unit in an image forming apparatus. The image forming apparatus 101 has an electrophotographic process unit 102 in a main body housing (not shown). The electrophotographic process unit 102 includes a roller-shaped charging member 104, an exposure device 105, a developing device 106, a transfer device 107, around a photosensitive member 103 as an image carrier that is driven to rotate clockwise in FIG. A cleaning unit 108, a static elimination device 109, and an optical sensor 110 are arranged.

  The electrophotographic process unit 102 further includes a voltage application unit 111 that applies a voltage to the charging member 104 and a voltage control device 112 as a control unit that controls the voltage application unit 111. The voltage application unit 111 applies a voltage using the power source PS as a source to the charging member 104, and the voltage control device 112 controls the voltage that the voltage application unit 111 applies to the charging member 104. The charging member 104, the voltage application unit 111, and the voltage control device 112 constitute a charging device 113.

  The image forming apparatus 101 includes a paper feed cassette that stores recording paper as a plurality of recording materials. The recording paper in the paper feed cassette is fed by a paper feed roller and separated one by one by a separation mechanism. Then, after the timing is adjusted by the registration roller pair, it is sent out between the transfer device 107 and the photosensitive member 103 (none is shown).

  The image forming apparatus 101 rotates the photosensitive member 103 in the clockwise direction in FIG. 1, uniformly charges the charging member 104, and then irradiates a laser beam modulated with image data by the exposure device 105 to electrostatically A latent image is formed. Then, the electrostatic latent image formed on the photosensitive member 103 is developed by attaching toner to the developing device 106. Thereafter, the toner image is transferred onto a recording sheet by the transfer device 107, and the recording sheet onto which the toner image has been transferred is conveyed to a fixing unit (not shown). Therefore, the recording paper on which the toner image is transferred is discharged onto a paper discharge tray (not shown) after the toner is fixed by the fixing unit.

  Simultaneously with the discharge operation of the image-formed recording paper, the image forming apparatus 101 further rotates the photoconductor 103 after the toner image is transferred to the recording paper by the transfer device 107. In the process, after the toner remaining on the surface of the photoconductor 103 is scraped off and removed by the cleaning unit 108 having a blade configuration, the photoconductor 103 is neutralized by the static eliminator 109. The cleaning unit 108 is not limited to a structure in which the residual toner on the photoconductor 103 is scraped off with a blade, but may be a unit that scrapes off the residual toner on the photoconductor 103 with a fur brush, for example.

  In this way, the electrophotographic process for one rotation of the photosensitive member 103 is completed. Thereafter, the photosensitive member 103 after charge removal is uniformly charged again by the charging member 104, and the subsequent electrophotographic process is executed by the same processing. .

  FIG. 2 is a front view of the process cartridge. In the image forming apparatus 101 of this embodiment, a process cartridge 114 is provided in which a photosensitive member 103, a charging member 104, a developing device 106, and a cleaning unit 108 as a member that contacts the photosensitive member 103 are supported by one unit. ing. The process cartridge 114 is configured to be detachable from the main body of the image forming apparatus 101.

  FIG. 3 is a cross-sectional view of the photoconductor 103. The photoconductor 103 of this embodiment is an amorphous silicon photoconductor. As an example, such a photoconductor 103 is configured by laminating a photoconductive layer 103b made of a-Si: H, X and having photoconductivity on a support 103a (FIG. 3A). . As another example, the photoconductor 103 is configured by laminating a photoconductive layer 103b made of a-Si: H, X and having photoconductivity on a support 103a, and an amorphous silicon-based surface layer 103c. (FIG. 3B). As another example, the photosensitive member 103 includes an amorphous silicon-based charge injection blocking layer 103d, a photoconductive layer 103b made of a-Si: H, X and having photoconductivity on the support 103a, and amorphous silicon. The system surface layer 103c is laminated (FIG. 3C). As yet another example, the photoconductor 103 is configured by laminating a photoconductive layer 103b on a support 103a. The photoconductive layer 103b includes a charge generation layer 103ba made of a-Si: H, X and a charge transport layer 103bb, and an amorphous silicon based surface layer 103bc is provided thereon.

  FIG. 4 is a front view showing the positional relationship between the photoconductor 103 and the charging member 104. FIG. 5 is a side view showing the positional relationship between the photoconductor 103 and the charging member 104. As shown in FIG. 4, the charging member 104 is not in contact with the photosensitive member 103 and is disposed with a gap H between the charging member 104 and the photosensitive member 103. In order to realize such an arrangement, in this embodiment, as shown in FIG. 5, a pair of spacers 115 are provided on both sides of the charging member 104, and the charging member 104 is interposed via these spacers 115. In contact with the photosensitive member 103. As an example of the structure in which the charging member 104 is brought into contact with the photosensitive member 103, a biasing member 116 in the form of a coil spring is provided in the present embodiment. In FIGS. 4 and 5, for convenience of explanation, the cylindrical photoconductor 103 is expressed in a planar shape. Therefore, the charging device 113 of this embodiment is a non-contact roller charging method.

  Here, the non-contact roller charging method as in the present embodiment relates to the charging uniformity with respect to the photoconductor 103, similarly to the contact roller charging method in which the roller-shaped charging member 104 is arranged in contact with the photoconductor 103. Is inferior in comparison with the corona discharge method. Therefore, in the present embodiment, in order to improve the uniformity of charging with respect to the photoconductor 103, the voltage application unit 111 adds the DC voltage applied to the charging member 104 to twice the charging start voltage when this DC voltage is applied. An AC voltage having the above amplitude voltage is superimposed.

  However, if the voltage application unit 111 is configured to superimpose an AC voltage having an amplitude voltage more than twice the charging start voltage at the time of application of the DC voltage on the DC voltage applied to the charging member 104, another implementation is possible. As a form, a contact roller charging method in which a roller-shaped charging member 104 is disposed in contact with the photosensitive member 103 may be employed.

  Next, the optical sensor 110 detects the intensity of light generated in the gap H between the photoconductor 103 and the charging member 104. That is, the non-contact roller charging type charging device 113 generates light in the gap H between the photoconductor 103 and the charging member 104 when the voltage application unit 111 applies a voltage to the charging member 104. The optical sensor 110 thus detects the intensity of the light generated in the gap H. In the present embodiment, such an optical sensor 110 is disposed downstream of the charging member 104 in the rotation direction of the photoconductor 103 when viewed from the exposure position of the exposure device 105 with respect to the photoconductor 103.

  On the other hand, as another embodiment, as shown in FIG. 6, which is a schematic diagram showing the electrophotographic process unit 102 in the image forming apparatus 101, the optical sensor 110 has an exposure position of the exposure apparatus 105 with respect to the photosensitive member 103. From the viewpoint, the charging member 104 may be disposed upstream of the photosensitive member 103 in the rotation direction.

  Such an arrangement position of the optical sensor 110 shown in FIG. 1 or FIG. 6 is an accurate monitor when the light from the exposure device 105 for exposing the photosensitive member 103 is detected by the optical sensor 110. It is decided by paying attention to the fact that results cannot be obtained. That is, the light for exposing the photoconductor 103 has an influence on the detection of the photosensor 110 regardless of the arrangement position of the photosensor 110 shown in FIG. 1 or the arrangement position of the photosensor 110 shown in FIG. Can be hard to affect.

  Here, when light is generated in the gap H between the photosensitive member 103 and the charging member 104 when the voltage applying unit 111 applies a voltage to the charging member 104, the light has a spectrum as illustrated in FIG. With distribution. As is clear from FIG. 11, the spectrum of the light generated in the gap H between the photoconductor 103 and the charging member 104 is light in the wavelength range from visible to ultraviolet. Therefore, the optical sensor 110 needs to be able to detect light in such a wavelength range. As the optical sensor 110 having such a structure, for example, a photodiode, a phototransistor, a CdS cell, a photomultiplier tube, a phototube, a CCD image sensor, an image intensifier, or a combination thereof can be used.

  FIG. 7 is a flowchart illustrating an example of a processing procedure in the voltage control device 112. The voltage control device 112 is a digital circuit having a processor configuration for executing a predetermined process. However, a microcomputer configuration may be used as necessary.

  The voltage control device 112 drives and controls the voltage application unit 111 to apply a voltage to the charging member 104 (step S101), and then outputs an output signal of the optical sensor 110, that is, between the photosensitive member 103 and the charging member 104. A signal relating to the intensity of light generated in the gap H is received, and the light intensity I is detected (step S102). Then, the detected light intensity I is compared with the reference intensity Iref (step S103). This reference intensity Iref is defined as the intensity of light that can be uniformly charged by the charging member 104 and that is generated when an amplitude voltage of an alternating voltage that minimizes a malfunction such as an abnormal image is applied. Therefore, if the absolute value of the difference between the light intensity I and the reference intensity Iref is within a specified value range as a result of the comparison between the detected light intensity I and the reference intensity Iref (Y in step S103), the process is performed as it is. Exit. In this case, as an example, a range of a predetermined value to which the absolute value of the difference between the light intensity I and the reference intensity Iref should be compared is a value obtained by multiplying the reference intensity Iref by 0.05. On the other hand, when the absolute value of the difference between the light intensity I and the reference intensity Iref is out of the range of the specified value (N in step S103), the absolute difference between the light intensity I and the reference intensity Iref Based on the value, a feedback control amount for the amplitude voltage Vpp of the AC voltage applied to the charging member 104 is determined (step S104), and the voltage application unit 111 is driven and controlled in a state in which the amplitude voltage Vpp is feedback controlled with the determined feedback control amount. Then, a voltage is applied to the charging member 104 (step S101). As a result, it is possible to achieve both charging of the photoconductor 103 uniformly and minimization of defects such as abnormal images and filming on the photoconductor 103. The reason is as follows.

  As described above, when the photosensitive member 103 is charged by proximity discharge by the charging member 104 that is in contact with or close to the photosensitive member 103, the visible to ultraviolet wavelength region is in the gap H between the photosensitive member 103 and the charging member 104. Light is generated. In the graph shown in FIG. 11 described above, an optical fiber is installed at a position of about 1 cm from the gap H between the photoconductor 103 and the charging member 104, and the gap H between the photoconductor 103 and the charging member 104 is in the gap H. It is an optical spectrum measured by introducing generated light into a spectroscope using a photomultiplier tube as a detector through an optical fiber. The voltage application conditions of the charging member 104 and the type of the charging member 104 when performing such a measurement experiment are as follows.

Applied bias to charging member 104:
AC component: Vpp 2.2kV f1.35kHz
DC component: -600V
Moreover, JASCO Corporation FP6500 was used for the spectroscope.

Charging member 104: non-contact type hard type charging roller The intensity of the light spectrum shown in the graph of FIG. 11 varies depending on the voltage application condition. FIG. 12 is a graph showing the light intensity of a wavelength of 337 nm generated in the gap H between the photosensitive member 103 and the charging member 104 when the amplitude voltage Vpp is changed. The experimental conditions are described below.

Bias applied to charging member 104 AC component: Vpp 1.4 to 3.0 kV f1.35 kHz
DC component: -600V
As is clear from the graph shown in FIG. 12, it is understood that the light intensity I increases when the amplitude voltage Vpp is increased. Therefore, the amplitude voltage Vpp is determined from the light intensity I. Therefore, the amplitude Vpp can be controlled by detecting the light intensity I. The control amount in this case may be determined with reference to the value of the graph shown in FIG.

  That is, the inventor of the present invention has shown that between the light intensity I of the light generated in the gap H between the photoconductor 103 and the charging member 104 and the amplitude voltage Vpp of the AC voltage applied to the charging member 104 as shown in FIG. It was confirmed by experiment that there is a correlation as shown in the graph. Therefore, in the present embodiment, the voltage control device 112 is configured so that both charging the photoreceptor 103 uniformly and minimizing defects such as abnormal images and filming on the photoreceptor 103 can be achieved. Control discharge conditions. More specifically, the feedback control amount for the amplitude voltage Vpp of the AC voltage applied to the charging member 104 is determined based on the absolute value of the difference between the light intensity I and the reference intensity Iref (step S104 in FIG. 7). In a state where the amplitude voltage Vpp is feedback-controlled by the feedback control amount, the voltage application unit 111 is driven and controlled to apply a voltage to the charging member 104 (step S101 in FIG. 7). As a result, it is possible to suppress the occurrence of problems such as abnormal images and filming due to an increase in the load on the photosensitive member 301.

  Here, in the present embodiment, the necessity of controlling the discharge conditions will be added.

  First, a description will be given of a problem of fluctuation due to the temperature and humidity of the gap H between the photoconductor 103 and the charging member 104. Considering the working environment, it is considered that the use environment limit that moisture absorption promotes most in the office is about 30% at a temperature of 30 ° C. and about 80% of humidity. Similarly, the low humidity environment limit assumed in the office is considered to be about 20% humidity at a high temperature of about 30 ° C. The charging device of the present invention is considered to provide the charging device 113 that is excellent in quality over time under such environmental conditions.

  When a small gap H is formed between the photosensitive member 103 and the charging member 104 under the conditions of a temperature of 30 ° C. and a humidity of 20% where the influence of moisture absorption is small, using a conventional rubber charging roller, FIG. As shown in part A, the gap H between the charging member 104 and the photosensitive member 103 may be narrowed due to hygroscopic expansion of the intermediate resistance layer due to the hygroscopic action. This is because, in the case of the non-contact roller charging method, the charging member 104 cannot be extended due to the presence of the spacers 115 provided on both sides of the charging member 104, and the moisture absorption site indicated as part B is at the center of the charging member 104. It occurs for reasons such as being concentrated. The occurrence of a portion such as the portion A can be reduced by imparting stretchability to the spacer 115, whereas the moisture absorption portion indicated as the portion B should be concentrated in the center of the charging member 104 of the charging member 104. In the method of imparting stretchability to the spacer 115, the expansion of the portion B cannot be reduced.

  Accordingly, Table 1 shows the relationship between the environment and the gap H as a comparison when a rubber roller and a hard roller are used as the charging member 104.

  As is clear from Table 1, when the charging member 104 is a hard roller made of a hard material, the gap H does not change even when the environment is changed, whereas when the charging member 104 is a rubber roller, the high humidity environment. Below, the gap H has become very narrow. The narrowing of the gap H may be due to the possibility that the charging member 104 is in contact with the photosensitive member 103, and therefore, the toner on the charging member 104 may be contaminated. Therefore, in order to maintain the charging uniformity, the charging member 104 is preferably a hard type that ensures the maintenance of the gap H.

  In order to avoid toner contamination of the charging member 104, it is also effective to use a spherical toner with high transfer efficiency.

  Next, the roller resistance dependency of the photosensitive member charging potential will be described. As apparent from Table 1, the characteristics of the charging member 104 made of resin or the like are likely to change depending on the environment of temperature and humidity. In particular, the resistance easily changes due to moisture, and when the resistance changes, the potential charged on the photoconductor 103 also changes. FIG. 14 is a graph showing the charging potential of the photoconductor 103 when a constant AC voltage is applied to the charging member 104 and the resistance of the charging member 104 is changed. As can be seen from this graph, the charging potential of the photoconductor 103 rapidly decreases at a certain threshold as the roller resistance of the charging member 104 increases. Therefore, since the charging potential of the photoconductor 103 easily varies depending on the temperature and humidity environment, it is necessary to control the change in the charging potential due to the environmental change by changing the amplitude voltage Vpp.

  Next, in the present embodiment, as shown in FIG. 7, light generated in the gap H between the photoconductor 103 and the charging member 104 is detected immediately after the start of charging, for example, in the self-check mode immediately after the start of discharging. The discharge conditions are controlled. This is because if the resistance of the charging member 104 varies depending on the temperature and humidity, and the temperature and humidity at the time of power-off are different from the temperature and humidity when the power is turned on after that, the charging member 104 changes to the photosensitive member 103. This is because the optimum discharge energy to be applied is not uniform. When the voltage application unit 111 is activated, the discharge intensity applied from the charging member 104 to the photoconductor 103 is controlled by monitoring the light intensity I detected by the optical sensor 110 and controlling the discharge energy applied from the charging member 104 to the photoconductor 103. It is possible to optimize the energy, and thus it is possible to reliably suppress the occurrence of problems such as abnormal images and filming due to an increase in the load on the photoconductor 103.

  On the other hand, other timings can be defined as the timing for controlling the discharge conditions. Various examples of controlling discharge conditions at different timings will be described with reference to the flowcharts of FIGS. In this case, the same parts as those in the flowchart shown in FIG.

  First, in FIG. 8, a voltage is applied to the charging member 104 and a copy operation is being executed (step S11). After the voltage application unit 111 is temporarily stopped due to an abnormal process such as a paper jam (step S12), the voltage is applied to the charging member 104 again. Is applied (step S101) and, for example, a process of detecting light generated in the gap H between the photosensitive member 103 and the charging member 104 when the self-check mode is set (step S102) is executed. This timing example focuses on the fact that the voltage application command value in the voltage application unit 111 may fluctuate due to the influence of noise or the like when the apparatus stops due to the occurrence of an abnormality or the like. In this case, when the voltage application unit 111 is restarted after being temporarily stopped, the light intensity I detected by the optical sensor 110 is monitored and the discharge energy applied from the charging member 104 to the photoconductor 103 is controlled to thereby charge the charging member. It is possible to optimize the discharge energy applied from 104 to the photoconductor 103, thereby reliably suppressing the occurrence of problems such as abnormal images and filming due to an increase in the load on the photoconductor 103. .

  Next, in FIG. 9, when a voltage is applied to the charging member 104 and a copying operation is being executed (step S11), when a certain number of copies, in this case 200 copies, is copied (step S21), the gap between the photosensitive member 103 and the charging member 104 is reached. A process of detecting light generated in the gap H (step S102) is executed. In this timing example, when the charging device 113 continues to be used, the optimum discharge energy applied from the charging member 104 to the photosensitive member 103 due to fluctuations in the resistance of the charging member 104 or contamination of the surface of the charging member 104. Is also not uniform. In this case, the light intensity I detected by the optical sensor 110 is monitored and the discharge energy applied from the charging member 104 to the photoconductor 103 is controlled at every specified time, so that the charge member 104 provides the photoconductor 103. It is possible to optimize the discharge energy, and thus it is possible to reliably suppress the occurrence of problems such as abnormal images and filming due to an increase in the load on the photoconductor 103.

  Next, in FIG. 10, after the processing shown in the flowchart of FIG. 7 is performed, the power is turned on and the copying operation is continued (step S11), and always between the photosensitive member 103 and the charging member 104 (at a specified cycle). A process of detecting light generated in the gap H (step S201) is executed. That is, when the light intensity I is detected from the output signal of the optical sensor 110 (step S201), the detected light intensity I is compared with the reference intensity Iref (step S202). This reference intensity Iref is defined as the intensity of light that can be uniformly charged by the charging member 104 and that is generated when an amplitude voltage of an alternating voltage that minimizes a malfunction such as an abnormal image is applied. Therefore, as a result of the comparison between the detected light intensity I and the reference intensity Iref, if the absolute value of the difference between the light intensity I and the reference intensity Iref is within a predetermined value range (Y in step S202), the process is performed as it is. Exit. In this case, as an example, a range of a predetermined value to which the absolute value of the difference between the light intensity I and the reference intensity Iref should be compared is a value obtained by multiplying the reference intensity Iref by 0.05. On the other hand, if the absolute value of the difference between the light intensity I and the reference intensity Iref is outside the range of the specified value (N in step S202), the absolute difference between the light intensity I and the reference intensity Iref A feedback control amount for the amplitude voltage Vpp of the AC voltage applied to the charging member 104 is determined based on the value (step S203), and the voltage application unit 111 is driven and controlled in a state where the amplitude voltage Vpp is feedback-controlled with the determined feedback control amount. Then, a voltage is applied to the charging member 104 (step S101). In this timing example, when the charging device 113 continues to be used, the optimum discharge energy applied from the charging member 104 to the photosensitive member 103 due to fluctuations in the resistance of the charging member 104 or contamination of the surface of the charging member 104. Is also not uniform. In this case, the discharge applied from the charging member 104 to the photoconductor 103 is controlled by monitoring the light intensity I detected by the optical sensor 110 and controlling the discharge energy applied from the charging member 104 to the photoconductor 103 at a predetermined cycle. It is possible to optimize the energy, and thus it is possible to reliably suppress the occurrence of problems such as abnormal images and filming due to an increase in the load on the photoconductor 103.

  In the implementation, an adjustment mechanism (not shown) that variably adjusts the gap H between the photoconductor 103 and the charging member 104 is provided, and the correlation between the light intensity I detected by the optical sensor 110 and the gap H is provided. The gap H may be variably adjusted based on the above. As a result, when the amplitude voltage Vpp of the AC voltage is high, problems such as abnormal images and filming on the photoconductor 103 become large. On the other hand, if the amplitude voltage Vpp is too low, a uniform potential cannot be applied to the photoconductor 103. On the other hand, the gap H between the photoconductor 103 and the charging member 104 is variably adjusted based on the correlation between the light intensity I detected by the optical sensor 110 and the gap H, thereby making the photoconductor 103 uniform. It is possible to achieve both charging and minimizing problems such as abnormal images and filming on the photoconductor 103.

  Further, in the present embodiment, the photoconductor 103 made of amorphous silicon is exemplified, but in the implementation, the photoconductor 103 made of OPC having a filler dispersed in the surface layer may be used.

  In addition, a color image that forms an electrostatic latent image for a plurality of colors on the photosensitive member 103, develops the electrostatic latent images for a plurality of colors in a plurality of colors, transfers the images to recording paper, and forms a color image on the recording paper. You may apply to a formation apparatus.

It is a schematic diagram showing an electrophotographic process section in the image forming apparatus of the present embodiment. It is a front view of a process cartridge. 2 is a cross-sectional view of an image carrier (photoconductor). FIG. FIG. 3 is a front view showing an arrangement relationship between an image carrier (photoconductor) and a charging member. FIG. 3 is a side view showing a positional relationship between an image carrier (photoconductor) and a charging member. It is a schematic diagram of the electrophotographic process part which shows another structural example regarding the arrangement position of an optical sensor. It is a flowchart which shows an example of the process sequence in a voltage control apparatus. It is a flowchart which shows another example of the process sequence in a voltage control apparatus. It is a flowchart which shows another example of the process sequence in a voltage control apparatus. It is a flowchart which shows another example of the process sequence in a voltage control apparatus. 6 is a graph showing a spectral distribution of light generated in a gap between an image carrier (photoconductor) and a charging member. It is a graph showing the light intensity of the wavelength of 337 nm generated in the gap between the image carrier (photoconductor) and the charging member when the amplitude voltage Vpp is changed. FIG. 3 is a schematic diagram of an image carrier (photosensitive member) illustrating a charging member that is hygroscopically expanded and a charging member. 6 is a graph showing the charging potential of the photosensitive member when a constant AC voltage is applied to the charging member and the resistance of the charging member is changed. A current (region A) flowing between the charging member and the photosensitive member that directly relates to the charging potential control flowing between the photosensitive member and the charging member, and a charging member and a photosensitive member that are not directly related to the charging potential control, respectively. 6 is a graph showing a capacitor component current (region B) that becomes a charge accumulated in the capacitor.

Explanation of symbols

101 Image forming apparatus 103 Image carrier (photosensitive member)
DESCRIPTION OF SYMBOLS 104 Charging member 105 Exposure apparatus 106 Developing apparatus 107 Transfer apparatus 111 Voltage application part 113 Charging apparatus 110 Optical sensor 112 Control means (voltage control apparatus)
114 process cartridge H gap I intensity of light

Claims (16)

In a charging device that applies a voltage from a voltage application unit to a charging member brought into contact with or close to the image carrier, and charges the image carrier by proximity discharge.
An optical sensor for detecting the intensity of light generated in the gap between the image carrier and the charging member;
Control means for controlling the discharge condition based on the correlation between the light intensity detected by the optical sensor and the target discharge condition;
A charging device comprising:   The voltage application unit applies a DC voltage and an AC voltage simultaneously to the charging member, and defines an absolute value of an amplitude voltage of the AC voltage to be twice or more an absolute value of a discharge start voltage. 1. The charging device according to 1.   The control means determines a feedback control amount for the amplitude voltage from the difference between the light intensity generated when the voltage application unit applies the target amplitude voltage to the charging member and the light intensity detected by the optical sensor. 3. The charging device according to claim 2, wherein the amplitude voltage is feedback-controlled with the determined feedback control amount.   An adjustment mechanism that variably adjusts the gap between the image carrier and the charging member, and the gap is variable based on the correlation between the light intensity detected by the optical sensor and the gap; The charging device according to claim 1, wherein the charging device is adjusted.   5. The charging device according to claim 1, wherein when the voltage application unit is activated, the control unit monitors a light intensity detected by the optical sensor to control a discharge condition. 6.   5. The control unit according to claim 1, wherein when the voltage application unit is restarted after being temporarily stopped, the light intensity detected by the optical sensor is monitored to control a discharge condition. The charging device described.   5. The charging device according to claim 1, wherein the control unit monitors the light intensity detected by the optical sensor and controls a discharge condition at regular time intervals.   5. The charging device according to claim 1, wherein the control unit monitors a light intensity detected by the optical sensor at a predetermined cycle to control a discharge condition. 6.   The charging device according to claim 1, wherein the optical sensor is disposed downstream of the charging member in a rotation direction of the image carrier as viewed from an exposure position with respect to the image carrier.   The charging device according to claim 1, wherein the optical sensor is disposed upstream of the charging member in the rotation direction of the image carrier as viewed from an exposure position with respect to the image carrier.   A process car which supports both the image carrier and the charging device according to any one of claims 1 to 10 which uniformly charges the image carrier and is detachable from the main body of the image forming apparatus. Tridge.   The process cartridge according to claim 14, wherein a member that contacts the image carrier is supported. An image carrier;
The charging device according to any one of claims 1 to 10, which uniformly charges the image carrier;
An exposure apparatus that exposes the image carrier after uniform charging based on image data to form an electrostatic latent image;
A developing device for developing an electrostatic latent image formed on the image carrier;
A transfer device for transferring the developed electrostatic latent image to a recording material;
An image forming apparatus comprising:   The image forming apparatus according to claim 13, wherein the image carrier is made of amorphous silicon.   The image forming apparatus according to claim 13, wherein the image carrier is made of OPC having a filler dispersed in a surface layer. Forming an electrostatic latent image for a plurality of colors on the image carrier, developing the electrostatic latent images for a plurality of colors in a plurality of colors, transferring the images to a recording material, and forming a color image on the recording material; The image forming apparatus according to claim 13.

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