JP4899672B2 - Image forming apparatus - Google Patents

Description

  In the present invention, the surface of an image carrier is uniformly charged to a predetermined potential by a charging bias voltage in which a DC voltage and an AC voltage are superimposed. The present invention relates to an image forming apparatus that forms an image, develops an electrostatic latent image formed on the image carrier with toner, and transfers the developed toner image to a recording medium to form an image.

  Conventionally, image forming apparatuses such as laser printers, facsimile machines, and copiers are provided with a photosensitive drum as an image carrier, and the surface of the photosensitive drum is uniformly charged, and then a light beam based on image data is irradiated. Then, an electrostatic latent image is formed on the photosensitive drum, the electrostatic latent image is developed using toner, and the image developed on the photosensitive drum is appropriately transferred to a recording medium via an intermediate transfer member. Some formed an image.

  In this type of image forming apparatus, when the developed image on the photosensitive drum is transferred to an intermediate transfer body or the like, all the toner cannot be transferred, and the toner is not transferred onto the photosensitive drum after transfer. Remains slightly. The toner adhering to the photosensitive drum after the transfer may adhere to a charger or an exposure device provided around the photosensitive drum, or may be mixed into the developing device. Will interfere.

  For this reason, a cleaner having a mechanism for collecting toner on the photosensitive drum and a mechanism for discarding the collected toner is disposed around the photosensitive drum on the downstream side of the transfer position.

  Here, in this type of image forming apparatus, in order to uniformly charge the photosensitive drum, a contact-type charger is used, and charging is performed by applying a voltage in which an AC voltage is superimposed on a DC voltage. is there. As a result, although the photosensitive drum can be uniformly charged, discharge products such as NOx are generated. The discharge product accumulates on the surface of the photosensitive drum and easily absorbs moisture in the air. For this reason, if the discharge product is left attached to the surface of the photosensitive drum, the electric resistance of the surface of the photosensitive drum is lowered, the charge holding ability is remarkably reduced, and the electric charge leaks on the surface of the photosensitive drum. The latent image collapses and a phenomenon (image flow) in which an image is not formed occurs.

  In particular, in order to achieve a long life and high reliability, a protective layer is provided on the surface of the photoconductor to suppress the film reduction rate (abrasion rate) and the generation of scratches. Since it is difficult to remove the discharge product as compared with a soft photoconductor without a protective layer, the occurrence of the above-described image flow becomes remarkable.

  In order to prevent the image flow due to the discharge product, the applicants set a difference between the moving speed of the photosensitive member and the moving speed of the intermediate transfer member, and the toner is transferred between the photosensitive member and the intermediate transfer member. It has been proposed to roll and collect the discharge product with toner.

  In this proposal, it has been confirmed that the greater the difference in speed between the photosensitive member and the intermediate transfer member, the higher the effect of suppressing image flow.

Conventionally, as a technique for providing a predetermined moving speed difference between the moving speed of the photosensitive drum and the moving speed of the intermediate transfer belt, density unevenness, voids, color unevenness, and the like due to transfer defects are prevented. Accordingly, it has been proposed to change the moving speed difference in accordance with the environmental temperature and humidity, the number of image formations, the type of photosensitive member, the type of image, and the like (see, for example, Patent Document 1).
JP 2004-117722 A

  However, when the technique described in Patent Document 1 is applied, if the speed difference is increased as described above from the viewpoint of image drift prevention, the frictional force between the photosensitive member and the intermediate transfer member increases, and the intermediate transfer member. There is a problem that the moving speed is not constant and minute speed fluctuations occur.

  That is, minute speed fluctuations of the intermediate transfer member cause the positional deviation of the transferred image and the occurrence of jumping, leading to deterioration of the graininess of the formed image. Further, when a color image is formed, it may cause a color shift.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of efficiently preventing the occurrence of an image flow without impairing the image quality.

In order to solve the above-mentioned problems, the invention of claim 1 is characterized in that an electrostatic latent image is obtained by scanning a light beam on the image carrier while the surface of the image carrier is uniformly charged to a predetermined potential by a charging means. The electrostatic latent image formed on the image carrier is developed with a toner containing an external additive by a developing means, and the developed toner image is transferred to an intermediate transfer member. an image forming apparatus for forming an image by transferring the further recording medium the toner image on the body, a charging bias voltage to a DC voltage and an AC voltage at the time of image formation is superimposed is applied to the charging unit, the image forming At other times, a charging bias voltage applying means for applying to the charging means a voltage in which a DC voltage and an AC voltage are superimposed or a DC voltage as a charging bias voltage, and a developing bias voltage in which the AC voltage is superimposed on the DC voltage are developed. Apply to means Development bias voltage application means, environmental condition detection means for detecting relative humidity as an environmental condition in the image forming apparatus, and application of an alternating voltage with respect to the total time during which the charging bias voltage is applied by the charging bias voltage application means In order to suppress the image flow of the electrostatic latent image caused by the state acquisition means for acquiring the time ratio as information relating to the voltage application state to the charging means, and the discharge product adhering to the image carrier. Based on the relative humidity detected by the environmental state detection unit and the information acquired by the state acquisition unit, the difference between the movement speed of the image carrier and the intermediate transfer member and the development bias voltage Setting means for setting the amplitude of the AC voltage, and the moving speed difference set by the setting means and the amplitude of the AC voltage of the developing bias voltage And control means for controlling the execution of the image formation was, and a, and a recovery means for recovering the toner remaining on the image bearing member surface after transfer to the intermediate transfer member the toner image.

According to a second aspect of the present invention, the state acquisition unit uses the average number of prints per job as information relating to the voltage application state to the charging unit , instead of the ratio .

According to a third aspect of the present invention, in the state acquisition means, instead of the ratio , the ratio of the application time of the charging bias voltage to the charging means with respect to the rotation time of the image carrier is the voltage application state to the charging means. It is characterized by information .

The invention of claim 4 is characterized in that the setting means sets the moving speed difference within 5%.

The invention of claim 5 is characterized in that the setting means sets the moving speed difference within 3%.

The invention of claim 6 is characterized in that the developing means uses a two-component developer containing the toner and a carrier.

The invention of claim 7 is characterized in that a protective layer is provided on the surface of the image carrier.

  The present invention has an excellent effect of providing an image forming apparatus capable of efficiently preventing the occurrence of image flow without impairing image quality.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a configuration of an image forming apparatus 10 according to the present embodiment. As shown in the figure, the image forming apparatus 10 has an endless belt-like intermediate transfer belt 14 that is stretched around a plurality of winding rollers 12 and conveyed in the direction of arrow E by driving a motor (not shown). A plurality of image forming units 15 (details will be described later) are arranged along the longitudinal direction.

  Note that the image forming apparatus 10 in the present embodiment also supports color image formation, and toners corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K). Image forming units 15Y, 15M, 15C, and 15K that form images are provided. Hereinafter, the members provided for each color are shown by adding alphabets (Y / M / C / K) indicating the respective colors at the end of the reference numerals. The description will be made by omitting the alphabet at the end of the code.

  The different color toner images formed by the image forming units 15 are transferred onto the intermediate transfer belt 14 so as to overlap each other on the belt surface of the intermediate transfer belt 14. As a result, a color toner image is formed on the intermediate transfer belt 14. In this embodiment, the toner image in which the four color toner images are transferred in a superimposed manner is referred to as a final toner image.

  On the downstream side of the four image forming units 15 in the conveying direction of the intermediate transfer belt 14, a transfer device 26 including two rollers 26A and 26B facing each other is disposed. The final toner image formed on the intermediate transfer body belt 14 is sent between the rollers 26A and 26B, taken out from the paper tray 29 provided at the bottom of the image forming apparatus 10, and is similarly supplied to the rollers 26A and 26B. It is transferred to the paper 28 that has been conveyed in between.

  In addition, a fixing device 30 including a pressure roller 30A and a heating roller 30B is disposed on the conveyance path of the paper 28 onto which the final toner image has been transferred. The paper 28 conveyed to the fixing device 30 is nipped and conveyed by the pressure roller 30A and the heating roller 30B, whereby the toner on the paper 28 is melted and pressed against the paper 28 to be fixed. As a result, a desired image (color image) is formed on the paper 28. The paper 28 on which the image is formed is discharged out of the apparatus.

  On the other hand, a cleaner 32 that collects the toner remaining on the intermediate transfer belt without being transferred to the paper 28 by the transfer device 26 is disposed downstream of the transfer device 26 in the transport direction of the intermediate transfer belt 14. Yes. The cleaner 32 is provided with a blade 34 so as to be in contact with the intermediate transfer belt 14, and collects residual toner by rubbing it.

  A sensor unit 36 for detecting the density of the toner transferred to a predetermined position other than the image forming area on the intermediate transfer belt 14 is provided on the downstream side of the image forming unit 15 in the conveyance direction of the intermediate transfer belt 14. It has been.

  FIG. 2 shows the configuration of the image forming unit 15. Since the configuration of the image forming unit 15 for each color is the same, the description will be made with the last symbol indicating each color omitted.

  As shown in the figure, the image forming unit 15 includes a photosensitive drum 16 that is disposed in contact with the intermediate transfer belt 14 and rotates at a predetermined speed in the arrow F direction.

  In the present embodiment, it is preferable to apply a low-abrasion material as the photosensitive drum 16. With a low-abrasion photoconductor drum, for example, when an image is formed for 1000 revolutions using a cleaning blade as a diameter Φ30 mm, the surface is worn by about 1 to 10 nm. Depending on the specification) This low-abrasion photoconductor drum is worn only about one-tenth as compared with a photoconductor drum of the type used while scraping the surface.

  A charging roller 18 for charging the photosensitive drum 16 is disposed on the circumferential surface of each photosensitive drum 16. The charging roller 18 is a conductive roller, and its peripheral surface is in contact with the peripheral surface of the photosensitive drum 16, and is arranged so that the axial direction of the charging roller 18 coincides with the axial direction of the photosensitive drum 16. Has been.

  A predetermined voltage (DC voltage −650 V in the present embodiment) in which the DC voltage and the AC voltage are superimposed is applied to the charging roller 18, and the charging roller 18 rotates so as to follow the rotation of the photosensitive drum 16. The surface of the photosensitive drum 16 is uniformly charged to a predetermined potential (in this embodiment, about −700 V).

  Further, an exposure device 20 for forming an electrostatic latent image on the photosensitive drum 16 is provided on the peripheral surface downstream of the charging roller 18 in the rotational direction F of each photosensitive drum 16. The exposure device 20 includes an LED array in which a plurality of LEDs (light emitting diodes) are arranged, and light based on image data in the axial direction of the photosensitive drum 16 uniformly charged by the charging roller 18. Irradiate while scanning the beam. The potential of the region irradiated with the light beam from the exposure device 20 rises (in this embodiment, about −300 V), and an electrostatic latent image is formed on the photosensitive drum 16. Here, it is described that “the potential of the region irradiated with the light beam increases”, but only the absolute value is taken out in the sense that the charging potential is close to 0 V, and “the region of the region irradiated with the light beam is extracted. It is also said that the electric potential drops.

  Further, an electrostatic latent image formed on the photosensitive drum 16 is provided in a predetermined color (yellow / magenta / cyan / black) around the exposure device 20 in the rotation direction F of each photosensitive drum 16. A developing device 22 is provided for developing with toner and forming a toner image. In the present embodiment, a developer including two components of a negative polarity toner and a positive polarity carrier is applied. In order to achieve both improvement in development efficiency and transfer efficiency, which will be described later, and cleaning properties, the toner particles preferably have a shape factor SF of 125 to 135.

  The shape factor SF is expressed by the following equation (1) where the absolute maximum length ML of the toner particles and the projected area A of the toner particles are assumed.

SF = 100 × π × ML ² / 4A (1)

  As shown in the figure, the developing unit 22 includes a developing roller 38 and a blade 40 that are disposed close to the photosensitive drum 16. The developing roller 38 is applied with a developing bias in which an AC voltage is superimposed on a DC voltage, is charged to the same polarity as the surface of the photosensitive drum 16 (negative polarity in the present embodiment), and is loaded in the developing device 22. The toner adheres to the peripheral surface by the positive polarity carrier. Further, the developing roller 38 is driven to rotate in the same direction as the rotation direction F of the photosensitive drum 16 (in the direction of arrow G in the figure), and the toner adhered excessively to the developing roller 38 is dropped by the blade 40 and developed. It adheres uniformly.

  By the rotation of the developing roller in the rotation direction G, the toner attached to the developing roller 38 is conveyed to the surface of the photosensitive drum 16, and the surface of the photosensitive drum 16 and the toner are moved in the opposite directions. As a result, the toner is rubbed against the photosensitive drum 16, so that the electrostatic latent image formed on the photosensitive drum 16 is efficiently developed.

  When the surface potential Vh of the unexposed portion of the photosensitive drum 16 is −700 V and the surface potential Vl of the exposed portion is −300 V, a bias voltage is applied to the developing roller 38 to develop the surface potential Vdev of the developing roller 38. Is set to −600 V, the toner adhering to the developing roller 38 adheres to the exposed portion on the photosensitive drum 16. Therefore, the electrostatic latent image formed on the photosensitive drum 16 is reversely developed.

  Further, a transfer roller 25 for transferring the toner image on each photoconductive drum 16 to the intermediate transfer belt 14 is provided around the downstream side of the developing device 22 in the rotation direction F of each photoconductive drum 16. . The transfer roller 25 rotates in the direction indicated by the arrow H, conveys the intermediate transfer belt 14 at a predetermined speed, and sequentially opposes the photosensitive drum 16. Further, the transfer roller 25 is positively charged and transfers the toner on the photosensitive drum 16 onto the intermediate transfer belt 14.

  Here, the transfer roller 25 cannot transfer all of the toner on the photosensitive drum 16 to the intermediate transfer belt 14, and a slight amount of toner remains on the photosensitive drum 16 that has passed through the transfer roller 25. (Transfer residual toner).

  There is also toner (retransfer toner) whose polarity is reversed to plus by the transfer roller 25 and reattached on the photosensitive drum 16. In addition, when the other color toner image has already been transferred onto the intermediate transfer belt 14 when passing through the transfer roller 25, the retransfer toner includes the other color toner.

  Therefore, a cleaning blade 24 that collects residual toner such as transfer residual toner and retransfer toner on the photosensitive drum 16 is disposed downstream of the transfer roller 25 on the peripheral surface of the photosensitive drum 16. The cleaning blade 24 is disposed so that one side thereof is in contact with the photosensitive drum 16, and scrapes off the toner or the like on the surface of the photosensitive drum 16 to collect it.

  The toner contains inorganic fine particles such as lubricants and polishing aids as external additives, and some of the inorganic fine particles remain on the photosensitive drum 16 after transfer, as in the toner. .

  Incidentally, the AC bias component of the voltage applied to the charging roller 18 described above causes discharge products to be generated on the surface of the photosensitive drum 16 during charging. Since the discharge product absorbs moisture and induces image flow when the humidity is increased, accumulation of the discharge product on the photosensitive drum 16 needs to be prevented.

  In particular, in the present embodiment, since a low-abrasion photoconductor having a protective layer on the surface is used, the surface of the photoconductor may be scraped by the cleaning blade 24 as compared with a photoconductor having no protective layer. Since there is almost no discharge product, it is also difficult to remove. Therefore, image flow is also likely to occur, which is a big problem.

  Therefore, in the present embodiment, a difference (peripheral speed difference) is provided between the circumferential speed of the photosensitive drum 16 and the circumferential speed of the intermediate transfer belt 14, so The discharge product is peeled off from the photosensitive drum 16 by the rotational sliding of the toner by utilizing the rotational sliding of the toner.

  Further, by providing the peripheral speed difference, a shearing force acts on the toner image formed on the photosensitive drum, and the transfer efficiency of the toner to the intermediate transfer belt 14 is increased. However, since inorganic fine particles such as a lubricant and a polishing aid developed together with the toner on the photosensitive drum 16 are difficult to be transferred to the intermediate transfer belt, the inorganic fine particles in the toner remaining on the photosensitive drum 16 are not transferred. The concentration increases, and the effect of removing discharge products can be enhanced by the action of these abrasives and lubricants in the cleaning blade.

  On the other hand, if the peripheral speed difference is too large, hollowing out, misalignment, etc. occur at the time of transfer and the image quality deteriorates. Therefore, by controlling the peripheral speed difference according to the environment and operating conditions, both transfer and image formation are performed. Can be done well.

  For this reason, the image forming apparatus 10 has an environmental sensor 48 (not shown in FIG. 1) for detecting the temperature (degree) and the relative humidity (%) in the environment where the image forming unit 15 is disposed in the vicinity of the image forming unit 15. , See FIG. 3).

  FIG. 3 shows a control block diagram related to peripheral speed difference control in the image forming apparatus 10 of the present embodiment.

  As shown in FIG. 1, the image forming apparatus 10 includes a peripheral speed difference control unit 50 that is controlled by a control unit (not shown) that controls the entire image forming apparatus 10. The peripheral speed difference control unit 50 is connected to the environment sensor 48, the charging control unit 60, the photosensitive drum rotation control unit 64, the exposure control unit 66, and the development control unit 68, respectively.

  In this embodiment, the peripheral speed difference is changed by changing the rotational speed of the photosensitive drum 16. For this reason, the writing timing at the time of exposure is changed in accordance with the change in the rotational speed of the photosensitive drum 16.

  Further, the peripheral speed difference control unit 50, the charging control unit 60, the photosensitive drum rotation control unit 52, the exposure control unit 66, and the development control unit 68 are provided for each image forming unit 15 of each color.

  Accordingly, each image forming unit 15 can independently control the peripheral speed difference.

  The charging control unit 60 controls charging of the photosensitive drum 16 by controlling application and rotation of a voltage to the charging roller 18. The charging controller 60 applies a charging bias voltage obtained by superimposing an AC voltage on a DC voltage when charging at least the image forming area. However, the AC voltage may not be superimposed in processing other than during image formation.

The charging controller 60 includes an operation history memory 62 . The operation history memory 62 stores, as an operation history, a voltage application time and an AC bias application time to the charging roller 18 in image formation for the most recent predetermined number of sheets. The operation history stored in the operation history memory 62 is updated and stored so as to delete the oldest history and store the latest history every time one-sheet image formation is executed.

  The photosensitive drum rotation control unit 64 controls the photosensitive drum 16 to rotate in the direction of arrow F at a predetermined speed.

  The exposure controller 66 controls the lighting of the LED based on the input image data at a timing corresponding to the rotational speed of the photosensitive drum 16, and forms an electrostatic latent image on the photosensitive drum 16.

  The development control unit 68 executes voltage application control and rotation control to the developing roller 38 in order to develop the electrostatic latent image with toner.

  The peripheral speed difference control unit 50 includes an environment level setting unit 52, a characteristic value level setting unit 54, and a control parameter setting unit 56. The environment level setting unit 52 and the characteristic value level setting unit 54 are respectively controlled. It is connected to the parameter setting unit 56.

  The environmental level setting unit 52 sets the environmental level based on the environmental temperature and the environmental humidity detected by the environmental sensor 48. The environment level is set using an environment level setting table as shown in Table 1 below. Information indicating the set environment level is output to the control parameter setting unit 56.

  In the present embodiment, image flow does not occur when the relative humidity is lower than 60%. Therefore, the environment level setting unit 52 outputs a default parameter setting instruction to the control parameter setting unit 56 without setting the environment level when the relative humidity is lower than 60%.

  That is, as shown in Table 1, environment level 1 is an environment where the humidity is low enough to prevent image flow, and environment level 2 is an environment where the humidity is high enough to cause image flow. Environment level 3 is an environment in which the humidity is 90% or more and image flow is particularly likely to occur.

  The characteristic value level setting unit 54 sets a characteristic value level indicating an operation state related to the generation of discharge products, and uses a characteristic value level setting table as shown in Table 2 below. Is set. Information indicating the set characteristic value level is output to the control parameter setting unit 56.

  The characteristic value level is not set when the relative humidity is lower than 60%, like the environmental level.

  Here, it is known that a large amount of discharge products are generated on the photosensitive drum 16 by applying an AC bias to the charging roller 18. In the present embodiment, the amount of discharge products deposited on the photosensitive drum 16 is the AC bias application time with respect to the voltage application time to the charging roller 18 in the most recent predetermined number of image forming processes. It is applied as an operating state related to. The AC bias application time with respect to the voltage application time can be obtained by dividing the AC bias application time by the voltage application time and multiplying by 100.

  Therefore, the characteristic value level 1 is a state in which the AC bias application time is 60% or less with respect to the voltage application time, and the number of discharge products is relatively small. In the characteristic value level 2, the possibility that the discharge product exists on the photosensitive drum 16 is slightly higher than the characteristic value level 1, and in the characteristic value level 3, the amount of the discharge product existing on the photosensitive drum 16 is high. Most likely.

  Further, the control parameter setting unit 56 determines a control parameter related to the peripheral speed difference in accordance with the environment level set by the environment level setting unit 52 and the characteristic value level set by the characteristic value level setting unit 54.

  As described above, as the peripheral speed difference increases, the transfer efficiency of the toner to the intermediate transfer belt 14 increases, and the transfer residual toner having a high concentration of abrasive or lubricant can be supplied to the cleaning blade. Removability is improved.

  For this reason, when a large amount of discharge products are present on the photosensitive drum 16 or when the relative humidity is high and the discharge products easily absorb moisture, a large amount of inorganic fine particles may be present on the photosensitive drum 16. preferable.

  The inorganic fine particles fly on the photosensitive drum 16 during development. The amount of the inorganic fine particles flying onto the photosensitive drum 16 increases as the amplitude Vp-p (peak to peak voltage) of the AC component (hereinafter referred to as “developing AC bias”) of the developing bias applied to the developing roller 38 increases. Become more.

  FIG. 4A shows the measurement result of the recovered amount of inorganic fine particles in the cleaning blade 24 when the amplitude Vp-p of the development AC bias is changed. The toner ratio is obtained by dividing the amount of abrasive or lubricant recovered by the cleaning blade by the total amount of recovered material.

  As shown in the figure, the toner ratio increases as the amplitude Vp-p of the developing AC bias increases in both the image portion and the non-image portion.

  In FIG. 4B, measurement was performed under the conditions of a relative humidity of 90%, an applied voltage time ratio (AC / DC) of 80%, a voltage application time of 80% to the charging roller 18 with respect to the rotation time, and 1000 pv / job. FIG. 5 shows the state of occurrence of image flow due to the change in the amplitude Vp-p of the developing AC bias when the peripheral speed difference is 0.3%, 3%, and 5%. Note that the grade shown in the figure indicates a state where the influence of image flow does not appear in the image as it is closer to grade 0, and the state where the influence of image flow is large and appears in the image as it is closer to grade 5. Further, grades 0 to 2 are such that deterioration of image quality due to image flow is not discernable by human eyes. In the present embodiment, even if the image flow is affected within the range up to grade 2, the image flow is affected. It will be described as being allowed.

  As shown in the figure, when the amplitude Vp-p of the developing AC bias is 0.9 kV, the influence of the image flow cannot be suppressed to an allowable range even if the peripheral speed difference is increased to 5%. When the developing AC bias amplitude Vp-p is 1.5 kV, the influence of image flow can be suppressed to an allowable range even when the peripheral speed difference is 0.3%.

  When the peripheral speed difference is increased, the transfer efficiency of the toner is increased, but the transfer efficiency of the inorganic fine particles is not significantly changed.

  Therefore, in this embodiment, a control parameter setting table as shown in Table 3 below is used to control the peripheral speed difference and the amplitude Vp-p of the developing AC bias to prevent the occurrence of image flow. A predetermined control parameter is set according to the environment level and the characteristic value level.

  In other words, in a situation where image flow is likely to occur, the amplitude Vp-p of the development AC bias is increased to minimize the increase in the peripheral speed difference and prevent the deterioration of the image quality.

  When the relative humidity is lower than 60% and the environmental level is not set, the characteristic value level is not set, and the control parameter setting unit 56 uses a peripheral speed difference of 0.3% as a default control parameter. A developing AC bias amplitude Vp-p 0.9 kV is set.

  If the peripheral speed difference is too large, transfer defects such as toner scattering and color misregistration between toner images transferred in each image forming unit 15 will be caused. For this reason, in this embodiment, the amplitude Vp-p of the development AC bias is set so that the peripheral speed difference is within 3%.

  The peripheral speed difference control unit 50 outputs a control signal based on the parameters set by the control parameter setting unit 56 to the charging control unit 60, the photosensitive drum rotation control unit 64, the exposure control unit 66, and the development control unit 68.

  As a result, the charging control unit 60, the photosensitive drum rotation control unit 64, the exposure control unit 66, and the development control unit 68 execute rotation control and voltage application, respectively, according to the control signal.

  Hereinafter, the operation of the present embodiment will be described.

  When a print job is input, the image forming apparatus 10 executes print processing based on the input image data in accordance with the print conditions in units of print jobs.

  The peripheral speed difference control unit 50 also determines the difference in peripheral speed between the peripheral speed of the photosensitive drum 16 and the peripheral speed of the intermediate transfer belt 14 in the printing process, and the amplitude Vp of the developing AC bias applied to the developing roller 38. The peripheral speed difference control process is executed in which the magnitude of -p is appropriately changed according to the environment and the operating state.

  FIG. 5 shows a processing flow of a peripheral speed difference control processing program executed mainly by the peripheral speed difference control unit 50. Hereinafter, the peripheral speed difference control process according to the present embodiment will be described with reference to FIG.

  First, in step 200, relative humidity information indicating the relative humidity detected by the environmental sensor 48 is acquired. In the next step 202, it is determined whether or not the relative humidity indicated by the acquired relative humidity information is less than 60%. judge.

  Here, when the relative humidity is less than 60%, even if the discharge product exists on the photosensitive drum 16, the discharge product does not absorb moisture, and thus no image flow occurs.

  If the determination in step 202 is negative, the process proceeds to step 204 to prevent image flow. In step 204, the environment level is set, and then the process proceeds to step 206. This environmental level is determined in advance according to the relative humidity, and is set using an environmental level setting table as shown in Table 1 above.

In the next step 206, the operation history indicating the voltage application state to the charging roller 18 by the charging control unit 60 in the printing process for the latest predetermined number of sheets (500 sheets in the present embodiment) is read from the operation history memory 62. And then the process proceeds to step 208.

  In step 208, a characteristic value level is set based on the acquired operation history, and then the process proceeds to step 210.

  On the other hand, if the determination in step 204 is affirmative, the process proceeds to step 210 without executing the processing in steps 204 to 208.

  In step 210, control parameters are set according to the set environment level and characteristic value level, or default parameter setting instructions.

  In the next step 212, a control signal is output to each part so that image formation is executed with the peripheral speed difference and the development AC bias amplitude Vp-p according to the set control parameter, and then the peripheral speed difference The control processing program is terminated.

As described above in detail, according to this embodiment, and uniformly charges the photoreceptor drum 16 surface to a predetermined potential by the charging roller 18 and the DC voltage and AC voltage is applied as a static-bias voltage In this state, the photosensitive drum 16 is scanned with a light beam to form an electrostatic latent image, and externally charged by a developing roller 38 to which a developing bias voltage in which a DC voltage and an AC voltage are superimposed is applied. The electrostatic latent image formed on the photosensitive drum 16 is developed with the toner containing the agent, the developed toner image is transferred to the intermediate transfer belt 14, and the toner image on the intermediate transfer belt 14 is further transferred to the paper When forming an image by transferring a 28, as environmental conditions in the device to detect the relative humidity by the environmental sensor 48, D the most recent 500 sheets of image formation is updated and stored in the operation history memory 62 Based on the bias application time and the AC bias application time, the characteristic value level setting unit 54 sums the time when the DC voltage is applied as information on the voltage application state to the charging roller 18 in the image formation for the most recent predetermined number of sheets. The ratio of the time during which the AC voltage is applied to is derived, and the peripheral speed between the peripheral speed of the photosensitive drum 16 and the peripheral speed of the intermediate transfer belt 14 is determined based on the detection result by the environmental sensor 48 and information on the application state. The difference and the amplitude Vp-p of the development AC bias are set, and each part is controlled to execute image formation with the set peripheral speed difference and the amplitude Vp-p of the development AC bias. It is possible to efficiently prevent the occurrence of image flow without damaging it.

  That is, if the image flow is likely to occur according to the environmental conditions, the peripheral speed difference is increased and the developing AC bias amplitude Vp-p is also increased. Since the speed difference is reduced and the amplitude Vp-p of the developing AC bias is also reduced, the image flow is generated as compared with the case where the control for preventing the image flow is executed by changing only the peripheral speed difference. Both image quality degradation and image quality degradation can be prevented.

  In addition, according to the present embodiment, the control parameter setting unit 56 sets the peripheral speed difference within 3%. Therefore, the toner scattering and the toner images obtained by the image forming units 15 are set. The occurrence of transfer defects such as color misregistration can be prevented.

  In the present embodiment, the ratio of the time during which the AC voltage is applied to the total time during which the DC voltage is applied is applied as information regarding the voltage application state to the charging roller 18 in the image formation for the most recent predetermined number of sheets. Although the embodiment has been described, the present invention is not limited to this.

  For example, the ratio of the application time of the charging bias voltage to the charging roller 18 with respect to the rotation time of the photosensitive drum 16 may be applied as information regarding the state of voltage application to the charging roller 18.

  In this case, it is necessary to be able to grasp the rotation time of the photosensitive drum 16 in image formation for the most recent predetermined number of sheets. For this reason, for example, an operation history memory is provided in the photosensitive drum rotation control unit 64 so as to update and store the rotation control time of the photosensitive drum 16 in the latest image formation for a predetermined number of sheets.

  Further, the characteristic value level setting unit 54 replaces the table shown in Table 2 used in the above-described embodiment as a table used when setting the characteristic value level indicating the operation state related to the generation of the discharge product. For example, the table shown in Table 4 below may be used.

  Here, when the photosensitive drum 16 rotates in a state where no voltage is applied to the charging roller 18, a refresh effect is activated. Therefore, it can be considered that the longer the voltage application time to the charging roller 18 with respect to the photosensitive member rotation time, the greater the possibility that the discharge product adheres to the surface of the photosensitive drum 16.

  Further, the average number of prints per job may be applied as information regarding the voltage application state to the charging roller 18.

  The image forming apparatus 10 starts the image forming operation when the execution of the job is instructed, and stops the image forming operation when the printing is finished. Therefore, when a plurality of prints are included in one job, the print The number of image forming operations are continuously executed. Normally, in the image forming apparatus, various operations for rotating the photosensitive drum 16 without applying a voltage to the charging roller 18 are performed when an operation start instruction and stop are performed. For this reason, even if the same number of images are formed, it can be said that the smaller the number of prints per job, the more frequently the refresh effect will work, and the smaller the amount of discharge product attached.

  In such a configuration, it is necessary to store a predetermined number of prints of the most recently executed job in a memory (not shown) or the like. That is, since the number of prints per job varies from job to job, the number of jobs corresponding to the predetermined number of pages is not constant.

  Further, the characteristic value level setting unit 54 replaces the table shown in Table 2 used in the above-described embodiment as a table used when setting the characteristic value level indicating the operation state related to the generation of the discharge product. For example, the table shown in Table 5 below may be used.

  The configuration of the image forming apparatus 10 according to the above-described embodiment (see FIG. 1) is an example, and can be changed as appropriate without departing from the spirit of the present invention.

  For example, a single image forming unit 15 may be provided and monochrome printing may be performed.

  In this case, since it is not necessary to consider the color misregistration between the image forming units, the setting range of the peripheral speed difference may be expanded to 5%.

  The flow of each process according to the above embodiment (see FIG. 5) is also an example, and can be appropriately changed without departing from the gist of the present invention.

  For example, in the present embodiment, a mode has been described in which the rotation speed of the photosensitive drum 16 is changed and the exposure timing is changed accordingly, but the present invention is not limited to this. . In other words, the peripheral speed difference may be varied, and the peripheral speed of the intermediate transfer belt 14 may be changed to change the conveyance speed of the paper 28, the control parameters of the fixing device, and the like.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. 1 is a schematic diagram illustrating a configuration of an image forming unit according to an embodiment. It is a block diagram regarding the peripheral speed difference control according to the embodiment. (A) is a graph showing the ratio of the abrasive and lubricant contained in the toner collected by the cleaning blade when the amplitude of the development AC bias is changed, and (B) is the amplitude of the development AC bias. 6 is a graph showing the evaluation result of the degree of deterioration of image quality due to the occurrence of image flow. It is a flowchart which shows the flow of a process of the circumferential speed difference control processing program concerning embodiment.

Explanation of symbols

10 Image forming apparatus 14 Intermediate transfer belt (intermediate transfer body)
16 Photosensitive drum (image carrier)
18 Charging roller (charging means)
20 exposure unit 22 development unit (development means)
24 Cleaning blade 48 Environmental sensor (environmental state detection means)
50 Peripheral speed difference control unit (control means)
52 Environment Level Setting Unit 54 Characteristic Value Level Setting Unit (State Acquisition Unit)
56 Control parameter setting section (setting means)
60 Charge Control Unit 62 Operation History Memory 64 Photosensitive Drum Rotation Control Unit 66 Exposure Control Unit 68 Development Control Unit

Claims (7)

An electrostatic latent image is formed by scanning the image carrier with a light beam in a state where the surface of the image carrier is uniformly charged to a predetermined potential by the charging means, and the static image formed on the image carrier is formed. The electrostatic latent image is developed with a toner containing an external additive by a developing unit, the developed toner image is transferred to an intermediate transfer member, and the toner image on the intermediate transfer member is further transferred to a recording medium. An image forming apparatus for forming
The charging bias voltage and a DC voltage and an AC voltage at the time of image formation is superimposed is applied to the charging unit, except in the time of image formation, a DC voltage and an AC voltage and a voltage is superimposed or DC voltage as the charging bias voltage the Charging bias voltage applying means for applying to the charging means;
A developing bias voltage applying means for applying a developing bias voltage in which an alternating voltage is superimposed on a direct current voltage to the developing means;
Environmental condition detection means for detecting relative humidity as an environmental condition in the image forming apparatus;
State acquisition means for acquiring the ratio of the application time of the AC voltage to the sum of the time when the charging bias voltage is applied by the charging bias voltage application means as information relating to the state of application of the voltage to the charging means;
In order to suppress the image flow of the electrostatic latent image caused by the discharge product attached on the image carrier, the relative humidity detected by the environmental state detection unit and the information acquired by the state acquisition unit A setting means for setting a difference between the moving speed of the image carrier and the moving speed of the intermediate transfer body and the amplitude of the AC voltage of the developing bias voltage;
Control means for controlling execution of image formation in accordance with the moving speed difference set by the setting means and the amplitude of the AC voltage of the developing bias voltage;
Recovery means for recovering toner remaining on the surface of the image carrier after the transfer of the toner image to the intermediate transfer member;
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the status acquisition unit uses the average number of prints per job as information regarding a voltage application state to the charging unit instead of the ratio.   The state acquisition means uses the ratio of the application time of the charging bias voltage to the charging means with respect to the rotation time of the image carrier as information relating to the state of voltage application to the charging means instead of the ratio. The image forming apparatus according to claim 1.   4. The image forming apparatus according to claim 1, wherein the setting unit sets the difference in moving speed within 5%.   4. The image forming apparatus according to claim 1, wherein the setting unit sets the difference in moving speed within 3%.   The image forming apparatus according to claim 1, wherein the developing unit uses a two-component developer including the toner and a carrier.   The image forming apparatus according to claim 1, wherein a protective layer is provided on a surface of the image carrier.

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