JP4735126B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus and a control method thereof, and more particularly to an image forming apparatus and a photoconductor that are intended to extend the life of a photoconductor and prevent image defects caused by wear of the photoconductor layer. The present invention relates to a film thickness detection method and a charging control method for a charging roll using the same.

JP 2002-72633 A Japanese Patent Laid-Open No. 05-223513

  In general, in an image forming apparatus such as a printer or a copying machine, it is desired to extend the service life due to a recent increase in the frequency of use in offices or the like, and a demand for maintenance-free. In order to realize a long life of the image forming apparatus, it is a big problem to extend the life of the photoreceptor.

  In order to cope with such a problem, an image forming apparatus that attempts to extend the life by controlling charging of a photosensitive member has been proposed (for example, see Patent Document 1).

  In this Patent Document 1, the amount of discharge charge generated between the photosensitive member and the charging roll is controlled to be constant regardless of the film thickness of the photosensitive member and the contamination of the charging roll, the stress on the photosensitive member is reduced, and its long life An image forming apparatus is disclosed which is designed to be simplified.

  In addition, a photoconductor film thickness detection method for detecting the lifetime of the photoconductor has also been proposed (see, for example, Patent Document 2).

  This Patent Document 2 discloses a film thickness detection method in which the film thickness is detected by measuring the current that flows when the potential is changed from zero to a predetermined potential over the entire circumference of the photoreceptor.

  However, the prior art disclosed in the above patent document has the following problems.

  In general, it is known that the amount of discharge charge is the main cause of white-point image defects due to photoconductor wear and charging failure. That is, if the discharge charge amount is large, the wear of the photoreceptor is promoted and the life thereof is shortened. On the other hand, if the discharge charge amount is small, white spot-like image defects due to poor charging occur. For this reason, as in the prior art disclosed in Patent Document 1, it is possible to control the voltage and current applied to the charging roll so as to obtain a constant discharge charge amount that does not cause white spot-like image defects due to defective charging. This is an effective method for extending the life of the photoreceptor.

  However, in the prior art disclosed in Patent Document 1, when the surface of the photoconductor is changed from an initial thick film state to a thin film state with use, white point image defects due to charging failure occurring at the time of thick film are prevented. When the control target discharge charge amount is determined and the applied voltage / current is controlled so as to achieve the target discharge charge amount even in the case of a thin film, there is a problem that the charge becomes insufficient and density unevenness occurs. Further, the film thickness unevenness of the photoreceptor existing from the manufacturing stage is amplified as the wear progresses, and in the case of a thin film, there has been a problem that the density unevenness is remarkably generated due to the film thickness unevenness due to the uneven wear.

  On the other hand, when a sensor for detecting the film thickness of the photoconductor is provided in order to detect the life of the photoconductor, there arises a problem that the apparatus becomes large and the cost increases. On the other hand, according to the prior art disclosed in Patent Document 2, such a problem can be avoided. However, in the prior art, when the charging roll becomes dirty and a resistance change occurs, it is correct. There has been a problem that the film thickness cannot be detected.

  In addition to the film thickness detection method disclosed in Patent Document 2, a method of detecting the film thickness from the amount of charge until the current is saturated from the state where the photoreceptor potential is 0 V is also conceivable. Since it is necessary to detect over the circumference, there has been a problem that wear is promoted by continuously applying stress to the photosensitive member during the discharge.

  Therefore, the present invention has been made in view of the above-described problems of the prior art, and the object of the present invention is to extend the life of the photoreceptor and prevent image defects depending on the use environment. An object of the present invention is to provide an image forming apparatus capable of supplying an optimum bias voltage / current compatible with both at a low cost with a simple configuration.

  Another object of the present invention is to provide a film thickness detection method for detecting the film thickness of a photoreceptor at a low cost with a simple configuration without adding a new sensor for film thickness detection, and the film thickness detection. It is an object of the present invention to provide a charge control method for supplying an optimum bias voltage / current using the method.

  In order to achieve the above object, an image forming apparatus according to the present invention has a photosensitive member coated with a photosensitive layer on which an electrostatic latent image is formed, and an AC voltage / current superimposed on a DC voltage / current. In an image forming apparatus having a charging roll to which a bias voltage / current is applied to charge the photosensitive member to a predetermined potential, a discharge charge amount detection for detecting a charge amount of a discharge generated between the photosensitive member and the charging roll A film thickness detecting means for detecting the film thickness of the photosensitive layer of the photoconductor, an environment detecting means for detecting temperature and humidity in the apparatus, and a detection result of the film thickness detecting means and the environment detecting means. Discharge charge amount setting means for setting a predetermined discharge charge amount, and AC application to the charging roll so that the discharge charge amount becomes a predetermined discharge charge amount set by the discharge charge amount setting means Voltage / current change control It is characterized in further comprising a charge control unit that.

  Here, the predetermined discharge charge amount is a lower limit value of the discharge charge amount that does not cause white spot-like image defects due to poor transfer of toner accompanying charging failure.

  In the image forming apparatus of the present invention configured as described above, the predetermined discharge charge amount is set by the discharge charge amount setting means based on the detection results of the film thickness detection means and the environment detection means. It is possible to optimally set the discharge charge amount that achieves both long life and prevention of image defects according to the film thickness of the photoconductor that wears and thins with use. The discharge charge amount that becomes stress is detected by the discharge charge amount detection means, and the AC applied voltage / current to the charging roll is changed by the charge control means so that the discharge charge amount becomes a predetermined discharge charge amount according to the film thickness. Since the change control is performed, it becomes possible to supply the optimum bias voltage / current that achieves both the long life of the photoconductor and the prevention of image defects according to the use environment, and at the same time, the wear of the photoconductor progresses. Due to uneven wear It is possible to suppress the degree uneven.

  In addition, a contamination grade setting unit that sets a contamination level of the charging roll is further provided, and the film thickness detection unit is configured to output the output condition based on outputs of the environment detection unit, the discharge charge amount detection unit, and the contamination grade setting unit. The film thickness of the photoconductor may be detected.

  When configured in this way, it further comprises a fouling grade setting means for setting the fouling level of the charging roll, and the film thickness detecting means is based on the outputs of the environment detecting means, the discharge charge amount detecting means and the fouling grade setting means. Since the film thickness of the photoconductor under the output conditions is detected, the film thickness of the photoconductor can be detected according to the fouling status of the charging roll and the change in the surrounding environment and the amount of discharge charge in the status. It becomes possible to more appropriately detect the film thickness of the photoconductor according to the use environment.

  Further, the contamination grade setting means may set the contamination grade of the charging roll based on the history information of the photoreceptor.

  Here, the history information of the photosensitive member is cumulative charging history information of the photosensitive member, and is substantially equivalent to the cumulative number of prints and the cumulative rotation number of the photosensitive member.

  When configured in this way, the contamination grade setting means sets the contamination grade of the charging roll based on the accumulated number of prints, for example, the history information of the photoconductor, so that the contamination level of the charging roll is detected. The contamination grade can be set without adding any new sensor, which can contribute to cost reduction and downsizing.

  The discharge charge amount setting means calculates the target discharge charge amount by calculation and detects the target discharge charge amount when the film thickness detected by the film thickness detection means is less than a specified value. When the film thickness exceeds the specified value, the target discharge charge amount may be set to a predetermined value.

  In general, the amount of discharge charge that achieves both long life of the photoconductor and prevention of image defects is a constant value when the film thickness exceeds a predetermined thickness, and when the thickness is below a predetermined thickness Has been found to increase with decreasing film thickness.

  Therefore, in such a configuration, the discharge charge amount setting means calculates the target discharge charge amount by calculation and calculates the film thickness when the film thickness detected by the film thickness detection means is not more than the specified value. When the film thickness detected by the detection means exceeds the specified value, the target discharge charge amount is set to a predetermined value, so that more appropriate charge control according to the wear state of the film thickness is realized. Thus, the arithmetic processing can be simplified.

  Further, the method for detecting the film thickness of the photoconductor of the present invention comprises a photoconductor having a photoconductor layer on which an electrostatic latent image is formed, and a bias voltage obtained by superimposing an AC voltage / current on a DC voltage / current. A charging roll that charges the photosensitive member to a predetermined potential by applying a current, sets a contamination grade of the charging roll based on history information of the photosensitive member, and sets a predetermined bias voltage / current to the charging roller. When applied to a roll, the charge amount of discharge generated between the photoreceptor and the charging roll, ambient temperature and humidity are measured, and the film thickness of the photoreceptor is measured based on these measurement results and the contamination grade. Is detected.

  According to the photoconductor film thickness detection method of the present invention configured as described above, the film thickness of the photoconductor is detected based on the contamination status of the charging roll, the change in the surrounding environment, and the amount of discharge charge in the status. The film thickness of the photoconductor according to the state can be detected appropriately. In addition, by detecting the film thickness based on the discharge charge amount, it is not necessary to provide a separate detection cycle for detecting the film thickness, and the film thickness detection can be performed together with the measurement of the discharge charge amount during charge control. It is possible to reduce the stress on the photoconductor and extend the life of the photoconductor.

  The charging roll charging control method of the present invention detects the film thickness, ambient temperature and humidity of the photoreceptor by the film thickness detection method, and discharges based on the detection results of the film thickness, ambient temperature and humidity. A target value of a charge amount is set, and a bias voltage / current applied to the charging roll is controlled so that a charge amount of discharge generated between the photosensitive member and the charging roll becomes the target value. Is.

  According to the charging control method of the present invention configured as described above, the target value of the discharge charge amount is set based on the change in the film thickness of the photoconductor and the surrounding environment according to the use state, and the target value is set. Since the bias voltage / current applied to the charging roll is controlled, the optimum discharge charge amount corresponding to the environmental change taking into account the contamination condition of the charging roll is realized, and the life of the photosensitive member is extended and the image defect is prevented. It is possible to supply the optimum bias voltage / current that is compatible with each other according to the usage environment, and it is also possible to suppress uneven density due to uneven wear due to the progress of wear on the photoreceptor.

  According to the image forming apparatus of the present invention, according to the film thickness situation of the photoreceptor, the amount of discharge charge that achieves both the long life of the photoreceptor and the prevention of image defects is worn and thinned with use. In addition to being able to set optimally, it is possible to supply the optimum bias voltage / current according to the usage environment, and at the same time, density unevenness due to uneven wear due to the progress of wear on the photosensitive member can be suppressed. It becomes possible.

  Further, according to the method for detecting the film thickness of the photoreceptor of the present invention, the film thickness can be detected together with the measurement of the discharge charge amount during charge control by detecting the film thickness based on the discharge charge amount. Reduces stress on the photoconductor, extends the life of the photoconductor, and appropriately adjusts the photoconductor thickness according to usage conditions without adding a new sensor for film thickness detection. Can be calculated.

  Further, according to the charging control method of the charging roll of the present invention, the target value of the discharge charge amount is calculated based on the change in the film thickness of the photoconductor and the surrounding environment according to the use state, so that the target value is obtained. Since the bias voltage / current applied to the charging roll is controlled, the optimum discharge charge amount corresponding to the environmental change taking into account the contamination condition of the charging roll is realized, and the life of the photosensitive member is extended and the image defect is prevented. It is possible to supply the optimum bias voltage / current that is compatible with each other according to the usage environment, and it is also possible to suppress uneven density due to uneven wear due to the progress of wear on the photoreceptor.

  Embodiments according to the present invention will be described below with reference to the drawings.

  First, a schematic configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of a tandem color image forming apparatus 100 according to the present invention.

  In this image forming apparatus 100, color image information of a color original read by the image reading apparatus 102, color image information sent from a personal computer or an image data input device (not shown), and the like are input, and the input image Image processing is performed on the information.

  In FIG. 1, 1Y, 1M, 1C, and 1K are image forming units that form toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The endless intermediate transfer belt 9 stretched by a roll is arranged in series in the order of 1Y, 1M, 1C, and 1K along the traveling direction. The intermediate transfer belt 9 is an intermediate transfer body to which toner images of respective colors sequentially formed by these image forming units 1Y, 1M, 1C, and 1K are transferred in a state of being superimposed on each other. The primary transfer rolls 6Y, 6M, 6C, and 6K disposed to face the photosensitive drums 2Y, 2M, 2C, and 2K, which are electrostatic latent image carriers corresponding to 1Y, 1M, 1C, and 1K, respectively. It is inserted between them and formed so as to be able to circulate in the direction of the arrow. The toner images of each color transferred onto the intermediate transfer belt 9 in a multiple manner are collectively transferred onto a recording sheet 18 as a recording medium fed from a paper feed cassette 17 or the like, and then transferred by a fixing device 15. The recording paper 18 fixed on the recording paper 18 and having a color image formed thereon is discharged to the outside. Note that the symbol CR is a device controller that includes a CPU, a ROM, a RAM, and the like, and controls overall processing in the image forming apparatus 100.

  Here, the image reading apparatus 102 illuminates a document placed on the platen glass with a light source (not shown), and reflects a reflected light image from the document with an image reading element including a CCD sensor or the like via a scanning optical system. It is configured to read at a predetermined resolution.

  The image forming units 1Y, 1M, 1C, and 1K are configured in the same manner. Broadly speaking, the photosensitive drums 2Y, 2M, 2C, and 2K that rotate at a predetermined rotational speed in the direction of the arrow, Charge rollers 3Y, 3M, 3C, and 3K as charging means for uniformly charging the surfaces of the photosensitive drums 2Y, 2M, 2C, and 2K, and corresponding colors on the surfaces of the photosensitive drums 2Y, 2M, 2C, and 2K Exposure devices 4Y, 4M, 4C, and 4K for exposing the formed images to form electrostatic latent images, and developing devices 5Y for developing the electrostatic latent images formed on the photosensitive drums 2Y, 2M, 2C, and 2K, 5M, 5C, 5K, toner cartridges 10Y, 10M, 10C, 10K that are detachably disposed and supply toner of a predetermined color to the developing devices 5Y, 5M, 5C, 5K, and cleaning devices 7Y, 7M, 7C, 7K etc. It is constructed from.

  Further, in the present embodiment, the photosensitive drums 2Y, 2M, 2C, and 2K are made of an organic photosensitive material, an amorphous selenium photosensitive material, an amorphous silicon photosensitive material, or the like on the surface of a metal drum that rotates in the direction of the arrow. The photosensitive layer is coated, and the charging rolls 3Y, 3M, 3C, 3K are in contact with the surfaces of the photosensitive drums 2Y, 2M, 2C, 2K, and the AC voltage / current is superimposed on the DC voltage / current. The photoconductor layer is configured to be charged to a predetermined potential by a bias.

  The image forming process in the image forming apparatus configured as described above will be described using the image forming unit 1Y that forms a yellow toner image as a representative example.

  First, the surface (photoreceptor layer) of the photosensitive drum 2Y is uniformly charged by applying a bias voltage / current obtained by superimposing an AC voltage / current to a predetermined DC voltage / current to the charging roll 3Y. Is done. Next, for example, based on the image information read by the image reading device 102, scanning exposure corresponding to the yellow image is performed by the laser beam output from the exposure device 4Y, and the surface (photosensitive layer) of the photosensitive drum 2Y is formed. An electrostatic latent image corresponding to the yellow image is formed.

  The electrostatic latent image corresponding to the yellow image is converted into a yellow toner image by the developing device 5Y, and is primarily transferred onto the intermediate transfer belt 9 by the pressing force and electrostatic attraction force of the primary transfer roll 6Y constituting a part of the primary transfer unit. Is done. The yellow toner remaining on the photosensitive drum 2Y after the primary transfer is scraped off by the drum cleaning device 7Y. Thereafter, the surface of the photosensitive drum 2Y is neutralized by the neutralization device 8Y and then charged again by the charging roll 3Y for the next image forming cycle.

  In the present image forming apparatus 100 that performs multicolor image formation, an image forming process similar to the above is performed at the timing in consideration of the relative position difference between the image forming units 1Y, 1M, 1C, and 1K. This is also performed in 1M, 1C, and 1K, and a full color toner image is formed on the intermediate transfer belt 9 in a superimposed state. As the intermediate transfer belt 9, for example, a flexible synthetic resin film such as polyimide is formed in a strip shape, and both ends of the synthetic resin film formed in the strip shape are connected by means such as welding, thereby being endless. A belt-shaped one is used.

  The full-color toner image primarily transferred onto the intermediate transfer belt 9 is placed on a recording paper 18 that is conveyed to a secondary transfer position at a predetermined timing, and a backup roll 13 that supports the intermediate transfer belt 9 and the backup roll 13. The secondary transfer is performed by the pressure contact force and electrostatic attraction force with the secondary transfer roll 12 that is in pressure contact with each other at a predetermined timing.

  On the other hand, recording paper 18 having a predetermined size is fed by a paper feed roll 17a from a paper feed cassette 17 serving as a recording paper storage unit disposed in the lower part of the image forming apparatus 100. The fed recording paper 18 is conveyed to a secondary transfer position of the intermediate transfer belt 9 by a plurality of conveying rolls 19 and registration rolls 20 at a predetermined timing. Then, as described above, the full color toner images are collectively transferred from the intermediate transfer belt 9 to the recording paper 18 by the backup roll 13 and the secondary transfer roll 12 as secondary transfer means.

  The recording paper 18 on which the full-color toner image is secondarily transferred from the intermediate transfer belt 9 is separated from the intermediate transfer belt 9 and then conveyed to the fixing device 15 disposed on the downstream side of the secondary transfer unit. The fixing device 15 fixes the toner image on the recording paper 18 with heat and pressure. The recording sheet 18 after fixing is discharged onto a discharge tray 24 through a discharge roll 23.

  Further, the residual toner on the intermediate transfer belt 9 that could not be transferred onto the recording paper 18 by the secondary transfer means is transported to the belt cleaning device 14 while adhering to the intermediate transfer belt 9 as it is, and this belt cleaning device 14 Thus, the image is removed from the intermediate transfer belt 9 to prepare for the next image formation.

  By the way, in the image forming apparatus configured as described above, when a bias voltage / current is applied to the charging rolls 3Y, 3M, 3C, 3K, the charging rolls 3Y, 3M, 3C, 3K and the corresponding photosensitive members are used. Discharge occurs between the photosensitive drums 2Y, 2M, 2C, and 2K, and the photosensitive drums 2Y, 2M, 2C, and 2K are charged to a predetermined potential by this discharge. When this bias voltage / current is applied, especially when the AC voltage / current component is increased, the amount of discharge charge is increased, the wear of the photosensitive drums 2Y, 2M, 2C, and 2K is promoted, and the life thereof is shortened. End up. This is presumably because the surface of the photoreceptor is more damaged by the amplitude of the AC component.

  On the other hand, if the AC voltage / current component in the bias voltage / current is reduced, the amount of discharge charge is reduced, charging failure occurs in a spot manner, and white spot-like image defects occur.

  Accordingly, in order to extend the life of the photosensitive drum and prevent white spot-like image defects due to charging failure, the photosensitive drums 2Y, 2M, 2C, 2K and the charging rolls 3Y, 3M, 3C, 3K It is necessary to control the applied bias voltage / current so that the amount of discharge generated during the period of time becomes a predetermined amount of discharge charge. The predetermined amount of discharge charge depends on the photosensitive drums 2Y, 2M, 2C, It has been found by the present inventors that the thickness varies depending on the film thickness of the 2K photoreceptor layer, the fouling status of the charging rolls 3Y, 3M, 3C, and 3K and the ambient temperature / humidity.

  Therefore, in the image forming apparatus according to the present invention, a predetermined discharge charge amount corresponding to the thickness (hereinafter also referred to as a film thickness) of the photoreceptor layer of the photoreceptor drum is obtained, and this discharge charge amount is realized. In addition, the AC voltage / current is changed and controlled while the DC voltage / current in the bias voltage / current applied to the charging roll is kept constant.

  Hereinafter, the charging control content of the charging roll according to the present invention will be described with reference to FIG. FIG. 2 is a block diagram schematically showing the configuration of charging control according to the present invention. Here, the image forming units 1Y to 1K have the same configuration, and these components (for example, the photosensitive drums 2Y to 2K) have the same structure. Notation (for example, photosensitive drum 2) is used.

  As shown in FIG. 2, the image forming apparatus according to the present embodiment is in contact with the surface of the photosensitive drum 2 and a contact-type charging roll 3 to which a predetermined bias voltage / current is applied, and the charging roller 3. Charge control means 30 comprising a high voltage power supply 30a for supplying a bias voltage / current to the roll 3 and a power supply controller 30b for controlling the supply voltage / current supplied by the high voltage power supply 30a, and an environment for detecting the temperature and humidity in the apparatus The sensor S, the contamination grade setting means 33 for setting the contamination level (grade) according to the contamination status of the charging roll 3, and the charging roller 3 and the photosensitive drum 2 when the bias voltage / current is applied. Based on the output of the discharge charge amount detection means 35 for measuring the charge amount of the generated discharge, and the environmental sensor S, the contamination grade setting means 33, and the discharge charge amount detection means 35, the photosensitive A film thickness detecting means 37 for detecting the film thickness of the drum 2 and a discharge charge amount setting means 39 for setting a target value of the optimum discharge charge amount based on the outputs of the environmental sensor S and the film thickness detecting means 37 are provided. ing.

  Here, the charging roll 3 is configured by covering the surface of a metal core 3a made of metal such as stainless steel with a conductive layer 3b made of conductive synthetic resin or synthetic rubber whose resistance value is adjusted to a predetermined value. As necessary, a release layer is formed on the surface of the conductive layer 3b. Then, by applying, for example, an AC voltage on which a DC voltage is superimposed to the metal core 3a from the high voltage power source 30a, a gap discharge is generated in the minute gap between the charging roll 3 and the photosensitive drum 2, and the discharge Thus, the surface of the photosensitive drum 2 is charged. In the present embodiment, the contact-type charging roll 3 is exemplified, but the present invention is not limited to such a contact-type charging roll 3 and can be applied to a non-contact type charging roll. It is.

  As the voltage applied to the charging roll, for example, the DC voltage is set to about 700 to 800 V DC, which is substantially equal to the charging potential of the photosensitive drum 2, the AC voltage is set to 1.5 to 2.0 kV, and the frequency is set to about 1.3 kHz. ing. As a result, an AC current Iac in which an AC component is superimposed on a DC component flows through the charging roll 3 during gap discharge.

  The discharge charge amount detection means 35 detects the alternating current Iac flowing through the charging roll 3 via the high-voltage power supply 30a, and discharges between the photosensitive drum 2 and the charging roll 3 based on the alternating current Iac. The charge amount is calculated.

  That is, the discharge charge amount detection means 35 according to the present embodiment is configured to easily detect the discharge charge amount at the time of gap discharge without adding any special sensor for detecting the discharge charge amount. As a result, the number of parts can be reduced, and the size and cost can be reduced.

  Further, the contamination grade setting means 33 is configured to set a contamination grade according to the contamination status of the charging roll 3 based on the history information of the photosensitive drum 2. Here, the fouling grade of the charging roll 3 is set in accordance with the cumulative charging history of the photosensitive drum 2, and is substantially set in accordance with the cumulative number of printed sheets and the cumulative rotational speed of the photosensitive member. Is. Therefore, as the history information of the photosensitive drum 2, for example, a measurement result of a conventionally known print number counter or a cumulative rotation number counter of the photosensitive drum 2 can be used.

  That is, in the contamination grade setting means 33 according to the present embodiment, the contamination grade of the charging roll 3 is set without providing any new sensor.

  Further, the discharge charge amount setting means 39 sets the lower limit value of the discharge charge amount at which the white spot due to charging failure disappears, that is, the lower limit value of the discharge charge amount at which no white spot-like image defect occurs, according to the environment. Is. As the environment sensor S, a conventionally known temperature / humidity sensor can be used.

  The control function of each of these constituent means may be realized by diverting the apparatus controller CR, or of course, may be realized by providing a dedicated controller.

  Next, specific contents and operations of each constituent unit configured as described above will be described with reference to FIGS.

  First, the configuration and operation of the film thickness detection means 37 according to the present invention will be described with reference to the functional block diagram of FIG.

  As shown in FIG. 3, the film thickness detection means 37 according to the present invention determines the film thickness of the photosensitive drum 2 based on the outputs of the environmental sensor S, the contamination grade setting means 33, and the discharge charge amount detection means 35. It is configured to calculate.

  In calculating the film thickness, in the image forming apparatus according to the present embodiment, the correlation between the discharge charge amount and the photoreceptor film thickness is obtained for each fouling grade of the charging roll 3 as shown in FIG. A film thickness database (for example, a table or a graph) is provided.

This film thickness database shows the relationship between the discharge charge amount and the photoreceptor film thickness when a prescribed alternating voltage / current is applied within a predetermined use range (for example, AC 1.5 to 2.5 kV). It is determined for each fouling grade and predetermined usage environment (temperature / humidity) range. Specifically, the relationship between the discharge charge amount and the photoreceptor film thickness with respect to the reference voltage V _{0 as} a reference is obtained for each fouling grade and a predetermined use environment (temperature / humidity) range, For example, the relationship shown in FIG. 4 is that discharge is performed for each fouling grade (in this example, fouling grades 1, 3, and 5) when the specified voltage V _{0 is} 1.5 kV AC, the temperature is 20 ° C., and the humidity is 40%. The relationship between the charge amount and the photoreceptor film thickness is obtained.

When detecting the film thickness, first, a specified voltage / current (in this example, which serves as a reference for the above-described film thickness database) is supplied from the AC power supply 30a via the power controller 30b constituting the charging control means 30. A specified voltage V ₀ : 1.5 kV) is applied to the charging roll 3.

When the specified voltage V ₀ is applied, the discharge charge amount Q ₀ generated between the photosensitive drum 2 and the charging roll 3 is detected by the discharge charge amount detection means 35, and the ambient temperature is detected by the environment sensor S. / Humidity is measured, and the contamination grade of the charging roll 3 is set by the contamination grade setting means 33 with reference to the history information of the photosensitive drum 2 as shown in FIG. In FIG. 5, the contamination grade of the charging roll 3 increases as the cumulative number of printed sheets increases, and the contamination roll numerical value increases, and the contamination of the charging roll 3 progresses (its resistance value increases). Show.

  In FIG. 5, the fouling grade of the charging roll 3 is indirectly set according to the cumulative number of printed sheets, which is an example of the history information of the photosensitive drum 2. For example, the cumulative rotational speed of the photosensitive drum 2 is used. A fouling grade may be set according to the conditions. Further, the contamination grade of the charging roll 3 may be set directly by irradiating the surface of the charging roll 3 with a conventionally known optical sensor and directly measuring the reflectance.

Next, the film thickness detection unit 37 sets the contamination grade of the charging roll 3 and the ambient environment temperature / humidity that change depending on the use state based on the detection result of the contamination grade setting unit 33 and the environmental sensor S and the discharge charge amount Q _0. The corresponding photoconductor film thickness is detected by referring to the relational database (FIG. 4) between the discharge charge amount and the photoconductor film thickness described above, or based on this database by a simple calculation such as an interpolation method. Calculate appropriately.

As described above, according to the film thickness detection unit 37 according to the present embodiment, the film thickness is detected based on the discharge charge amount Q ₀ based on the specified voltage V ₀ corresponding to the film thickness database. There is no need to provide a separate detection cycle for film thickness detection, and it is possible to perform film thickness detection when measuring the amount of discharge charge during charge control, reducing stress on the photoconductor, Long service life is possible. In addition, since it is not necessary to provide a film thickness detection sensor for film thickness detection, it is possible to reduce the number of parts and reduce the cost.

  Next, charging control of the charging roll based on the photoreceptor film thickness detected as described above will be described step by step with reference to the flowchart of FIG.

  S1: First, the film thickness detection means 37 detects the film thickness of the photosensitive drum 2 in use, and the environment sensor S detects the ambient temperature / humidity at that time.

  In the present embodiment, as described above, the film thickness detection unit 37 is used to detect the film thickness, but naturally, a conventionally known film thickness sensor or film thickness detection cycle is separately provided. The film thickness of the photosensitive drum 2 may be detected.

  S2: Next, based on the detection results of the film thickness detection means 37 and the environment sensor S, the discharge charge amount setting means 39 sets a target value for the discharge charge amount. Here, the target value of the discharge charge amount is set based on the following relationship.

  Generally, the optimum target discharge charge amount Qp for extending the life of the photosensitive drum 2 without applying stress and preventing charging failure due to insufficient charging varies depending on the thickness of the photosensitive drum. . Specifically, as shown in FIG. 7, the optimum target discharge charge amount Qp is substantially constant (in this example) until the photosensitive member film thickness reaches a predetermined thickness (in this example, about 25 μm). In this case, the optimum target discharge charge amount Qp tends to increase almost in proportion to the decrease amount of the photoreceptor film thickness.

  Here, FIG. 7 shows the temperature of the photoconductor and the target discharge under the conditions of temperature: 20 ° C., humidity: 40%, allowable film thickness range (thickness range in which the photoconductor drum 2 can be used): about 15 to 40 μm. It is an example which calculated | required the relationship with the electric charge amount Qp. Such a relationship changes depending on the surrounding environment. Specifically, when the ambient temperature / humidity increases, the polygonal line L in FIG. 7 translates substantially downward.

  Therefore, the discharge charge amount setting means 39 according to the present embodiment includes a discharge charge amount database in which the relationship between the target discharge charge amount Qp and the film thickness is obtained for each appropriate ambient temperature / humidity range. The optimum target discharge charge amount Qp is appropriately set by referring to this discharge charge amount database from the film thickness detected by the film thickness detection means 37 and the ambient temperature / humidity detected by the environmental sensor S, or an interpolation method or the like. Is calculated by the following. As a result, it is possible to reduce the stress on the photosensitive drum 2 to extend the life, and to optimally set the target discharge charge amount Qp for preventing charging failure according to the use state.

  In setting the target discharge charge amount Qp, the optimum target discharge charge amount Qp is a substantially constant value until the photosensitive member film thickness reaches a specified value (about 25 μm in this example) as described above. (In this example, about 50 μC) (see FIG. 7), the film thickness detected (calculated) by the film thickness detecting means 37 is defined from the viewpoint of simplifying the arithmetic processing and reducing the burden on the CPU. When it exceeds the value (about 25 μm in this example), a predetermined constant value (for example, about 50 μC) is set by the discharge charge amount setting means 39 and detected (calculated) by the film thickness detection means 37. The film thickness may be calculated by calculation only when the film thickness is equal to or less than the specified value.

  S3: Next, an arbitrary AC voltage is applied to the charging roll 3 by the power supply controller 30b and the high-voltage power supply 30a within the use range (for example, AC 1.5 to 2.5 kV in this example).

  S4: The discharge charge amount Q at this time is measured by the discharge charge amount detection means 35.

  S5: The measured discharge charge amount Q is compared with the target discharge charge amount Qp. If the discharge charge amount Q does not reach the target discharge charge amount Qp, the AC bias voltage is increased and the target discharge charge amount is increased. When Qp is exceeded, the AC bias voltage is decreased. Such a step is repeated until the discharge charge amount Q converges to coincide with the target discharge charge amount Qp.

  S6: Image formation is started when the discharge charge amount Q coincides with the target discharge charge amount Qp.

  According to the charging control method according to the present embodiment configured as described above, the target value Qp of the discharge charge amount is calculated based on the change in the film thickness of the photosensitive drum 2 and the surrounding environment according to the use state, and this Since the bias voltage / current applied to the charging roll 3 is controlled so as to be the target value Qp, the optimum discharge charge amount corresponding to the environmental change in consideration of the contamination state of the charging roll 3 is realized, and the photosensitive drum 2 It is possible to supply the optimal bias voltage / current that achieves both long life and prevention of image defects according to the operating environment, and also suppresses uneven density due to uneven wear due to the progress of photoconductor wear. It becomes possible.

  In this embodiment, in calculating the film thickness and the target discharge charge amount, each calculation is set by referring to the related database. However, the correlation between the change factors of the film thickness and the target discharge charge amount is set. When a predetermined relational expression (function) can be set, naturally, the film thickness and the target discharge charge amount may be calculated based on this relational expression.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. It is a block diagram which shows typically the structure of the charge control which concerns on this invention. It is a functional block diagram which shows the structure and effect | action of film thickness detection which concern on this invention. It is a figure which shows the relationship between the discharge charge amount in a predetermined environment, and a photoreceptor film thickness. It is a figure which shows the relationship between the accumulated number of prints which is an example of photoreceptor history information, and the contamination grade of a charging roll. It is a flowchart which shows the content of the charging control which concerns on this invention. It is a figure which shows the relationship between the photoreceptor film thickness in a predetermined environment, and target discharge charge amount.

Explanation of symbols

1Y-1K: image forming unit, 2Y-2K: photosensitive drum, 3Y-3K: charging roll, 3a: cored bar, 3b: conductive layer, 4Y-4K: exposure device, 5Y-5K: developing device, 6Y-6K : Primary transfer roll, 7Y-7K: drum cleaning device, 8Y-8K: neutralization device, 9: intermediate transfer belt, 10Y-10K: toner cartridge, 12: secondary transfer roll, 14: belt cleaning device, 15: fixing device 17: paper cassette, 18: recording paper, 30: charging control means, 30a: high voltage power supply, 30b: power supply controller, 33: contamination grade setting means, 35: discharge charge amount detection means, 37: film thickness detection means, 39: Discharge charge amount setting means, 100: Image forming apparatus, CR: Apparatus controller, Qp: Target discharge charge amount, S: Environmental sensor, V ₀ : Specified voltage

Claims (3)

A photosensitive member coated with a photosensitive layer on which an electrostatic latent image is formed, and a bias voltage / current obtained by superimposing an alternating voltage / current on a direct current voltage / current are applied to bring the photosensitive member to a predetermined potential. In an image forming apparatus having a charging roll for charging,
A discharge charge amount detecting means for detecting a charge amount of discharge generated between the photoreceptor and the charging roll;
A film thickness detecting means for detecting the film thickness of the photoconductor layer of the photoconductor;
Environment detection means for detecting temperature and humidity in the device;
A discharge charge amount setting means for setting a predetermined discharge charge amount based on the detection results of the film thickness detection means and the environment detection means;
Charge control means for changing and controlling the AC applied voltage / current to the charging roll so that the discharge charge amount becomes a predetermined discharge charge amount set by the discharge charge amount setting means. Image forming apparatus. Further comprising a fouling grade setting means for setting a fouling level of the charging roll;
2. The film thickness detection unit detects the film thickness of the photosensitive member under the output conditions based on outputs of the environment detection unit, the discharge charge amount detection unit, and the contamination grade setting unit. Image forming apparatus.   The discharge charge amount setting means calculates the target discharge charge amount by calculation when the film thickness detected by the film thickness detection means is not more than a specified value, and the film detected by the film thickness detection means. 2. The image forming apparatus according to claim 1, wherein when the thickness exceeds a specified value, the target discharge charge amount is set to a predetermined value.

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