JP4722648B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic printer or a copying machine.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method such as an electrophotographic printer, a charging device uniformly charges the surface of a photosensitive drum, and an exposure device is placed on the charged photosensitive drum. Is supposed to form. Subsequently, the developing member attaches toner to the photosensitive drum to develop the electrostatic latent image into a toner image, and the transfer device transfers the toner image onto the printing medium directly or via an intermediate transfer belt. To do. The toner image transferred to the printing medium is fixed by a fixing device. Further, toner is supplied to the developing member from a toner supply member, and the toner layer thickness is regulated and the toner is charged by the toner regulating member in contact with the developing member. In the electrophotographic printer, for example, only the exposed portion on the surface of the photosensitive drum after charging is charged with the surface of the photosensitive drum so that the toner is developed. Not developed.

  In the configuration as described above, a configuration has been proposed in which the voltage applied to the toner supply member and the development member can be varied according to the environment (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 7-134477 (page 3, FIGS. 1 and 3)

  However, in actual printing, if the toner potential on the developing member becomes higher than necessary due to excessive toner supply from the toner supply member or excessive toner charging by the toner regulating member, the non-exposed portion of the image carrier is exposed. However, there is a problem in that a phenomenon of background smearing occurs in which the toner adheres and the white background is soiled.

  In addition, even if voltage correction is performed according to the environment, depending on the environment leaving time and the operating status of the apparatus, a phenomenon called background contamination that the toner adheres to the non-exposed portion of the image carrier and the white portion becomes dirty may occur. There was a problem that it occurred.

  An object of the present invention is to provide an image forming apparatus in which the print density is stable, the occurrence of background stains is prevented, and stable printing is always possible.

The image forming apparatus of the present invention includes:
An image carrier charged by a charging member to which a predetermined charging voltage is applied; an exposure member that forms an electrostatic latent image by exposing the surface of the image carrier charged by the charging member; and a predetermined voltage Corresponding to a developer layer potential control member that controls the surface potential of a developer layer on a developer member that develops the electrostatic latent image with a developer, and a non-exposed area that has not been exposed by the exposure member. a developer detecting member for detecting the developer adhering to the area, on the basis of the detection result of the developer detecting member, have a voltage control unit for controlling a voltage applied to said developer layer potential control member ,
The voltage control unit obtains a voltage at which the developer detection member detects adhesion of the developer by changing the charging voltage in a stepwise manner, and sets a preset voltage corresponding to the voltage to the development It is applied to the agent layer potential control member .

  According to the present invention, based on the detection result of the developer adhering to the non-exposed region on the image carrier or the region on the transfer member corresponding to the non-exposed region on the image carrier, the developer supply voltage, Alternatively, in order to control the developer regulation voltage, it is possible to reliably apply the developer supply voltage or the developer regulation voltage for preventing the developer from adhering to the region based on, for example, data.

Embodiment 1 FIG.
FIG. 1 is a main part configuration diagram showing the main part configuration of the image forming apparatus according to the first embodiment of the present invention.

  As shown in FIG. 1, the image forming apparatus 1 includes a photosensitive drum 11, a charging roller 12, an exposure head 13, a developing device 14, and the like arranged in order around the photosensitive drum 11 from the upstream side in the rotation direction. A density sensor 23, a transfer roller 18, and a photoconductor cleaning blade 20 are provided, and a fixing device 21 is further provided on the downstream side of the photoconductor drum 11 along the conveyance direction of the print medium 22.

  A photoconductive drum 11 as an image carrier has a photoconductive layer formed on the surface of a drum-shaped conductor such as aluminum, and is driven to rotate in the direction of the arrow in the figure by a driving means (not shown). The charging roller 12 as a charging member is covered with a conductive elastic body such as epichlorohydrin around a conductor such as stainless steel, and is disposed so as to contact the photosensitive drum 11. The exposure head 13 serving as an exposure member includes, for example, an LED element and a lens array, and is disposed at a position where irradiation light output from the LED element forms an image on the surface of the photosensitive drum 11. The photosensitive drum 11 is also a developer carrying member that carries toner.

  The developing device 14 includes a developing roller 15 that is a developing member coated with a conductive elastic body such as urethane around a conductor such as stainless steel, and a foaming elastic body such as silicone around a conductor such as stainless steel. A toner supply roller 16 that is a coated developer supply member and a toner control blade 17 that is a developer control member made of, for example, a stainless steel plate-like member, and a toner (not shown) that stores and supplies toner therein. A cartridge is provided, and the developing roller 15 is disposed so as to contact the photosensitive drum 11.

  The density sensor 23 that is a developer detection member is a photosensor including, for example, a light emitting diode and a light receiving diode, and is disposed downstream of the contact position between the photosensitive drum 11 and the developing roller 15. The transfer roller 18 covers a foaming elastic body such as silicone with a conductor such as stainless steel as an axis, and is disposed so as to contact the photosensitive drum 11. The photoreceptor cleaning blade 20 is disposed in contact with the photoreceptor drum 11 downstream of the transfer roller 18. The print medium 22 is conveyed between the photosensitive drum 11 and the transfer roller 18 and passes therethrough. The environmental sensor 24 is disposed at a predetermined position in the apparatus so as to detect the temperature and humidity in the apparatus.

  FIG. 2 is a block diagram showing a main configuration of the control system 2 of the image forming apparatus according to the first embodiment.

  As shown in the figure, the control system 2 includes a density sensor 23, a charging roller 12, a developing roller 15, a toner supply roller 16, an environmental sensor 24, a charging voltage control unit 32, a development voltage control unit 33, and a toner supply voltage control unit. 34, a calculation unit 31, and a storage unit 35.

  The charging voltage control unit 32 is connected to the charging roller 12 and applies the charging voltage set by the calculation unit 31 that is a voltage control unit to the charging roller 12. The development voltage control unit 33 is connected to the development roller 15 and applies the development voltage set by the calculation unit 31 to the development roller 15. The toner supply voltage control unit 34 is connected to the toner supply roller 16 and applies the toner supply voltage set by the calculation unit 31 to the toner supply roller 16. The density sensor 23 reads the toner reflectance on the photosensitive drum 11 and outputs the read information to the calculation unit 31. The calculation unit 31 calculates the toner reflection density based on the read information. The calculation unit 31 reads various storage data such as a print count value stored in the charging voltage environment table 36, the toner supply voltage correction table 37, and the print count storage unit 38 from the connected storage unit 35. Can do. The environmental sensor 23 measures the temperature and humidity inside the image forming apparatus 1 and outputs the measurement information to the calculation unit 31. The calculation unit 31 calculates an environmental level value to be described later based on the measurement information.

  In the above configuration, the basic operation of each unit during printing will be described.

  When executing printing, first, a predetermined charging voltage is applied to the charging roller 12 to uniformly charge the surface of the photosensitive drum 11. Next, a driving current is supplied to the exposure head 13, and the surface of the charged photosensitive drum 11 is exposed to form a desired electrostatic latent image pattern. In the developing device 14, a toner supply voltage is applied to the toner supply roller 16, and toner is supplied onto the development roller 15 by a potential difference from the development voltage also applied to the development roller 15. The toner on the surface of the developing roller 15 is thinned by the toner regulating blade 17 and simultaneously charged by friction. Then, the developing roller 15 moves the toner on the surface to the portion of the electrostatic latent image pattern on the photosensitive drum 11 and develops it. Subsequently, a transfer voltage is applied to the transfer roller 18 to transfer a toner image, which is a developer image carried on the photosensitive drum 11, onto the print medium 22. Thereafter, the toner image on the print medium 22 is fixed to the print medium 22 by the fixing device 21, and the printing operation is completed.

  Here, an example in which the image forming apparatus 1 in the initial state is operated in a normal temperature and humidity environment using negatively chargeable toner will be described. By setting the charging voltage applied to the charging roller 12 to −1000 V, the surface of the photosensitive drum 11 is charged to about −500 V. Further, by setting the developing voltage applied to the developing roller 15 to −250 V and the toner supplying voltage applied to the toner supplying roller 16 to −400 V, the toner potential on the surface of the developing roller 15 becomes about −60 V, and the developing voltage and In total, about −310 V is the charged position on the surface of the developing roller 15 in the operating state.

  On the other hand, when the photosensitive drum 11 is exposed by the exposure head 13, the surface potential of the photosensitive drum 11 that has been uniformly charged to about -500V is reduced to about -100V only in the exposed portion. For this reason, the toner moves to the surface (surface potential of about −100 V) of the exposed portion of the photosensitive drum 11 charged to the positive side with respect to the surface of the developing roller 15 (surface potential of about −310 V), and the latent image is latent. The image is visualized or developed. On the other hand, the surface potential of the non-exposed portion of the photoconductive drum 11 that is a non-exposed area that is not exposed by the exposure head 13 on the photoconductive drum 11 remains about −500 V, and therefore is charged to the negative side compared to the surface of the developing roller 15. The toner does not move to the surface of the non-exposed portion of the photosensitive drum 11.

  However, even if the operating environment is the same, the number of printed sheets, the frequency of use, the environment leaving time, the area ratio of the printed image, when adding toner, or, for example, toner, developing roller 15, toner supply roller 16, toner regulating blade 17 Depending on various factors such as a change in characteristics of an image forming process member which is a member constituting the image forming apparatus, excessive toner is supplied from the toner supply roller 16 onto the developing roller 15 even under the same voltage condition. As a result, the toner weight per unit area of the toner layer that has passed through the toner regulating blade 17 is increased, and the charged position of the toner layer is increased to the minus side.

  The surface potential of the developing roller 15 is the sum of the developing voltage applied to the developing roller 15 and the toner potential attached to the developing roller 15, and the surface potential of the non-exposed portion of the photosensitive drum 11 is the surface potential of the developing roller 15. If the value is smaller (in absolute value), the toner also adheres to the non-exposed area. Hereinafter, toner adhesion to the non-exposed portion of the photosensitive drum 11 is referred to as background smear.

  If the surface potential of the non-exposed portion of the photosensitive drum 11 is equal to the surface potential of the developing roller 15 or is larger (in absolute value) than the surface potential of the developing roller 15, if the difference is slight, the background is stained. Occurs. In other words, each toner charge on the developing roller 15 has a distribution, and some of the toner is highly charged on the negative side. In that case, when the surface potential of the non-exposed portion of the photosensitive drum 11 is equal to the surface potential of the developing roller 15 or is larger (in absolute value) than the surface potential of the developing roller 15, the difference is slight. In this case, the highly charged toner moves to the photosensitive drum 11 and scumming occurs.

Therefore, in the image forming apparatus 1 according to the first embodiment, the toner reflection density of the non-exposed portion on the photoconductive drum 11 is monitored, and the toner charge level is determined from the surface potential of the non-exposed portion of the photoconductive drum 11 where the background contamination occurs. The toner supply voltage applied to the toner supply roller 16 is corrected and applied so as to prevent the occurrence of background contamination based on the toner charging position. Then, the potential of the toner layer on the developing roller 15 is controlled. In particular,
Surface potential (−500 V) of the non-exposed portion of the photosensitive drum 11
-Surface potential of the developing roller 15 on which the toner layer is formed (about -310 V) = about -190 V
The applied voltage is corrected so that That is, the toner supply voltage is corrected and applied to the toner supply roller 16 so that the potential of the toner layer, which is the amount obtained by subtracting the development voltage of −250 V, of the surface potential of the development roller 15 is about −60 V. Thus, the toner supply roller 16 controls the potential of the toner layer on the developing roller 15 as a developer layer potential control member.

  As described above, the toner supply voltage determination process shown in FIG. 3 for the toner supply voltage determination process in the image forming apparatus 1 of the present embodiment for correcting the toner supply voltage applied to the toner supply roller 16 is described. This will be described below with reference to a flowchart showing the flow of processing.

  First, the calculation unit 31 obtains an environment level value based on the temperature and humidity information in the apparatus detected by the environment sensor 24, and obtains the obtained environment from the charging voltage environment table 36 stored in the storage unit 35. A charging voltage value corresponding to the level value is determined (step ST101).

  Here, the environmental level value is a value obtained by calculating by the calculation unit 31 from the relationship between temperature and humidity measured by the environmental sensor 24. Further, as shown in the graph of FIG. 4, the environmental areas are classified into level 1 to level 6 according to temperature and absolute humidity in stages. For example, a high temperature and high humidity environment of 30 ° C. and 80% is a level 1, 25 ° C., a 45% room temperature environment is a level 3, 10 ° C., and a low temperature and low humidity environment of 20% is a value corresponding to each level 6 area. On the other hand, FIG. 5 shows the contents of the environment table 36 for the charging voltage. For example, when the environmental level value corresponds to level 3, the charging environment table voltage value of −1000 V is selected as the charging voltage.

  FIG. 6 is a graph showing the correspondence between the charging voltage applied to the charging roller 12 and the charging potential of the surface of the photosensitive drum 11 charged thereby, according to the environment.

  Hereinafter, a method of determining the contents of the charging voltage environment table 36 will be described with reference to FIG. As shown in FIG. 6, even when the environmental level is different, the inclination of the increase in the charging potential of the photosensitive drum 11 with respect to the charging voltage applied to the charging roller 12 is the same, but the smaller the environmental level value is, the photosensitive drum 1 becomes. The charging voltage (discharge starting voltage) at which charging is started becomes lower. For example, when the photosensitive member charging potential is −500 V, the voltage value of the charging voltage to be applied is −900 V at the environmental level 1, −1000 V at the environmental level 3, and −1150 V at the environmental level 6. As described above, the charging environment table voltage of the charging voltage environment table 36 shown in FIG. 5 is stored based on the data shown in FIG. 6 at each environment level. Is.

  As the charging voltage, a voltage of a selected charging environment table voltage value (-1000 V in the environment level 3) is applied to the charging roller 24, and a constant developing voltage and toner are always applied to the developing roller 15 and the toner supply roller 16. A supply voltage is applied (step ST102). In the present embodiment, for example, a voltage of −250 V is applied as the development voltage, and a voltage of −400 V is applied as the toner supply voltage.

  Next, the toner sensor reflects the toner reflectance on the surface of the photosensitive drum 11 by the density sensor 23 while decreasing the absolute value of the applied voltage by 50 V from the charging voltage (−1000 V) determined by the environment table 36 every certain time. Is measured to obtain a toner reflection density, and a soiling detection operation is executed (step ST103). A method for performing the soiling detection operation here will be described below.

  FIG. 7 is a time chart of the charging voltage, the developing voltage, the toner supply voltage, and the output value of the density sensor 23 during the soiling detection operation, and FIGS. 8 to 12 show each time region (elapsed period) of the time chart. FIG. 3 is an operation explanatory diagram showing an operation state of the image forming apparatus 1 in FIG. Here, the environmental level is level 3, and a voltage of −250 V is applied as the developing voltage, and a voltage of −400 V is applied as the toner supply voltage, respectively.

The charging voltage is −1000 V immediately after activation, and is controlled so that the voltage decreases by 50 V in absolute value every predetermined elapsed time T. In the description, when each elapsed period T _n (n = 1, 2, 3...) Is indicated by an arrow, the time region of the specified elapsed time T is indicated.

Illustration 8 shows the operation state in the transitional period T ₁ of the time chart of FIG. 7, areas of the photoreceptor drum 11 in illustration 8 (1), by the charging roller 12 the charging voltage of -1000V is applied This is the area to be charged. In the time chart, the region number of the photosensitive drum 11 charged by the charging roller 12 is assigned to each elapsed period, and the region number of the photosensitive drum 11 detected by the density sensor 23 is assigned the same region number. is doing.

Illustration 9 shows the operation state in the age T ₂ of the timing chart of FIG. 7, areas of the photoreceptor drum 11 in illustration 9 (2), by the charging roller 12 the charging voltage of -950V is applied This is the area to be charged. Illustration 10 shows the operation state in the transitional period T ₃ of the time chart of FIG. 7, areas of the photoreceptor drum 11 of the diagram 10 (3), by the charging roller 12 the charging voltage of -900V is applied This is the area to be charged. Moreover, in the transitional period _{T 3,} the area of the density sensor 23 the photosensitive drum 11 (1) - is to monitor (region charged by the charging roller 12 of 1000V), region (1) scumming occurred in Therefore, the density sensor 23 does not output ground contamination detection. It should be noted that the density sensor 23 outputs a signal corresponding to “present” when the background dirt is not generated, and outputs a signal corresponding to “no” when the background dirt is generated. Shall.

Illustration 11 shows the operation state in the transitional period T ₄ in the time chart of FIG. 7, areas of the photoreceptor drum 11 of the diagram 11 (5), by the charging roller 12 the charging voltage of -800V is applied This is the area to be charged. Moreover, in the transitional period T _4, the area of the density sensor 23 the photosensitive drum 11 (3) - but to monitor (region charged by the charging roller 12 of 900V), region (3) in scumming occurred Therefore, the density sensor 23 does not output ground contamination detection.

Illustration 12 shows the operation state in the transitional period T ₅ of a time chart of FIG. 7, areas of the photoreceptor drum 11 of the diagram 12 (7), by the charging roller 12 the charging voltage of -700V is applied This is the area to be charged. Moreover, in the transitional period T _5, the region (5) of the density sensor 23 the photosensitive drum 11 - (the region which has been charged by the charging roller 12 of 800 V) is monitored, the area (5) in scumming occurs Therefore, the density sensor 23 outputs a signal corresponding to the background detection.

  As described above, since the density sensor 23 detects the region charged by the charging roller 12 2T before the elapsed time T based on the time lag caused by the rotation of the photosensitive drum 11, the background contamination occurs. The charging voltage in the area that is being calculated is calculated (step ST104). Here, the value of the charging voltage in the region (5) where the soiling occurs is −800V.

  Next, the toner supply voltage is determined from the charging voltage (−800 V) at the time of the occurrence of soiling obtained by the above-described soiling detection operation (step ST105). A method for determining the toner supply voltage will be described below.

  FIG. 13 is a graph showing the relationship between the difference between the developing voltage and the toner supply voltage and the toner potential on the developing roller 15. In the figure, a solid line represents a case where toner charging is normal, and a broken line represents a case where toner charging is abnormal. As shown in the graph, when the toner supply voltage increases to the minus side with respect to the development voltage regardless of whether the toner charging is normal or abnormal, the toner potential also increases to the minus side. This is because the amount of toner supplied to the developing roller 15 increases as the toner supply voltage increases to the minus side, and the amount of toner adhering to the surface of the developing roller 15 increases.

  FIG. 14 shows the detection of scumming, and the voltage applied to the developing roller 5 (development required for the charging voltage at which scumming occurs and the potential of the developing roller surface to be an appropriate potential at that time). 6 is a graph showing the relationship between the voltage and the difference between the voltage applied to the toner supply roller 6 (toner supply voltage). However, here, the development voltage is a fixed value of −250 V, and the environmental level is 3. FIG. 15 shows the contents of the toner supply voltage correction table 37 derived based on FIG. Based on the toner supply voltage correction table 37 shown in FIG. 15, the toner supply voltage and the development voltage corresponding to the charging voltage when the background contamination is detected are determined.

  The above time chart of FIG. 7 shows the result of the soiling detection operation when the toner charging is normal. In this case, the voltage correction is determined based on the following interpretation.

  From the charged voltage of −800 V at the time of occurrence of soiling, the charged potential of the surface of the photosensitive drum 11 at this time is about −300 V (see FIG. 6). On the other hand, the surface potential of the developing roller 15 is −310 V, which is the sum of the developing voltage −250 V and the normal toner charging potential −60 V (see FIG. 13), so the surface potential of the photosensitive drum 11 and the developing roller 15 is Almost equal. For this reason, it can be seen that the toner adheres to the photosensitive drum 11 and the soiling occurs. In this case, normal toner was used, and it was found that the toner potential was about -60V. However, even if it is not known, it can be estimated from the above verification result that the toner potential is around -60V. . In this case, there is no need to change the difference between the development voltage and the toner supply voltage based on the toner supply voltage correction table 37 containing the contents of FIG. 15, the toner supply voltage is −400 V, and the development voltage is −250 V. It is determined. At this time, the differential voltage between the surface potential (−500 V) of the non-exposed portion of the photosensitive drum 11 and the surface potential (−310 V) of the developing roller 15 is set to a target of −190 V.

  Next, a correction method when toner charging is abnormal will be described. FIG. 16 is a time chart of the soiling detection operation when the toner charging is abnormal. The areas (1) to (7) of the photosensitive drum 11 shown in the figure are set in the same manner as the areas of the photosensitive drum 11 set in the time chart of FIG. 7, and the density sensor 23 is also the same. In addition, the time lag due to the rotation of the photosensitive drum 11 indicates that the region charged by the charging roller 12 is detected 2T before the elapsed time T.

  According to the time chart of FIG. 16, it can be seen that the charging voltage in the region (2) where the soiling starts to occur is around −950 V, and from this, the soiling occurs from the charging voltage near −950 V. I understand that. At this time, the charged potential of the surface of the photosensitive drum 11 is about −450 V (see FIG. 6), and the potential of the surface of the developing roller 15 can be estimated to be about −450 V. Therefore, the potential of the toner at this time is It is estimated to be about -200 V obtained by subtracting the development voltage of -250 V from -450 V. Referring to the broken line in FIG. 13, when the toner is charged to -200V, if the difference between the development voltage and the toner supply voltage is set to about -50V, the toner potential becomes about -60V. Kusa is the same as normal.

  Therefore, in this case, the toner supply voltage is determined to be −300 V and the development voltage is determined to be −250 V based on the toner supply voltage correction table 37 containing the contents of FIG. In this case as well, the difference voltage between the surface potential (−500 V) of the non-exposed portion of the photosensitive drum 11 and the surface potential (−310 V) of the developing roller 15 is set to the target −190 V.

  As described above, when the correction voltage is determined, the difference between the toner supply voltage and the development voltage (for example, a fixed value = −250 V) may be determined from the charging voltage at the time of occurrence of soiling. The toner supply voltage and the development voltage shown in the toner supply voltage correction table 37 are applied. FIG. 15 is a toner supply voltage correction table for the environment level 3 shown in FIG. 5, but a toner supply voltage correction table corresponding to each environment level is prepared in the same manner as FIG.

  As described above, the determination process of the toner supply voltage by the background contamination detection by the image forming processing apparatus of the present embodiment is completed. According to this processing method, even when the charging state of the toner is changed, the difficulty of causing the background contamination is not different from that when the toner is charged normally, and the generation of the contamination can be prevented. The toner supply voltage determination process described above is performed, for example, when the apparatus is turned on, when the environmental level fluctuates, when the print count reaches a certain number, and the like. Each value shown in the present embodiment is merely an example, and the table value and the like may be set appropriately as appropriate in accordance with conditions such as the characteristics of the process material used and the process speed.

  As described above, according to the image forming apparatus of the first embodiment, the background contamination on the photosensitive drum is detected by the density sensor, and the toner supply voltage is determined from the charging voltage at which the background contamination occurs, thereby developing the image. Toner is not supplied excessively to the roller, the toner potential can be kept normal, and the occurrence of background contamination can be prevented. In the present embodiment, the surface potential of the photosensitive drum 11 is kept constant (for example, −500 V) during actual printing, so that the half pattern or gradation written on the photosensitive drum 11 by the exposure head 13 is maintained. Is appropriately written as a latent image, so that the reproducibility of the half pattern and gradation is not impaired.

Embodiment 2. FIG.
FIG. 17 is a main part configuration diagram showing a main part configuration of the image forming apparatus according to the second embodiment of the present invention.

  As shown in the figure, the image forming apparatus 101 of this embodiment is an electrophotographic color printer capable of printing four colors of black (K), yellow (Y), magenta (M), and cyan (C). It has the composition of. In the image forming apparatus 101, black (K), yellow (Y), magenta (M), and cyan (C) color toners are mounted in order from the upstream side along the conveyance path of the print medium 22. Four photosensitive drum units 111 to 114 for forming respective toner images are arranged. Each photosensitive drum unit has the same configuration. For example, as shown in the black (K) photosensitive drum unit 111, the photosensitive drum 11, the charging roller 12, the exposure head 13, and the development described in the first embodiment. The apparatus 14 includes a photosensitive member cleaning blade 20. Therefore, detailed description thereof will be omitted here.

  The transfer belt 117, which is a transfer member, is a semiconductor belt-like member made of, for example, polyamide, and is disposed so as to be in contact with the photosensitive drums 11 of the photosensitive drum units 111 to 114. Four transfer rollers 18 made of, for example, a foaming elastic body are disposed at positions facing the respective photosensitive drums 11 at the contact portions with the respective photosensitive drums 11. The transfer belt 117 is also a developer carrying member that carries toner.

  The transfer belt cleaning blade 116 is disposed on the upstream side of the rotation of the transfer belt 117 of the photosensitive drum unit 111 on the most upstream side of the medium conveyance path, and the toner transferred onto the transfer belt 117 returns to the photosensitive drum unit 111. The toner is scraped off from the transfer belt 117 so as not to be present. The density sensor 115 is a photosensor composed of a light emitting diode and a light receiving diode, as in the case of the density sensor 23 of the first embodiment described above. Here, the photosensitive drum unit 114 and the transfer belt located on the most downstream side of the medium conveyance path are here. It is disposed between the cleaning blades 116. By measuring the density of the toner image transferred onto the transfer belt 117 at this position, the toner density of all colors is measured by one density sensor 115 without being arranged corresponding to each photosensitive drum unit 111-114. Can be measured.

  A fixing device 21 is provided on the downstream side of the medium conveyance path of the transfer belt 117, and an environment sensor 24 for detecting temperature and humidity in the apparatus is disposed at a predetermined position in the apparatus. These fixing device 21 and environment sensor 24 are the same as those described in the first embodiment.

  FIG. 18 is a block diagram illustrating a main configuration of the control system 102 of the image forming apparatus 101 according to the second embodiment. The configuration of the control system 102 is connected to the four transfer rollers 8 with respect to the control system 2 (FIG. 2) of the image forming apparatus 1 according to the first embodiment, and the transfer voltage set by the calculation unit 31. Is newly added to the transfer voltage control unit 120 for applying. Further, here, for example, the charging voltage control unit 32 applies charging voltages corresponding to the four charging rollers 12 provided in the respective photosensitive drum units 111 to 114, and develops the developing voltage control unit 33 and the toner supply voltage. Similarly, the controller 34 applies charging voltages respectively corresponding to the four developing rollers 15 and the toner supply roller 16.

  In the above configuration, the basic operation of each unit during printing will be described.

  Since the operation in each of the photosensitive drum units 111 to 114 is exactly the same as the operation of the components having the same reference numerals in the image forming apparatus 1 described in the first embodiment, the description thereof is omitted here. The toner image formed on each photosensitive drum 11 is transferred onto the print medium 22 conveyed on the transfer belt 117 by the transfer roller 18 corresponding to the transfer voltage applied by the transfer voltage control unit 120. Is done. The toner image transferred onto the printing medium 12 is fixed to the printing medium 12 by the fixing device 21 and the printing operation is completed. Since the roles of the charging voltage, the developing voltage, and the toner supply voltage when printing using negatively chargeable toner are as described in the first embodiment, the description thereof is omitted here.

  Even in the image forming apparatus 101 according to the present embodiment, even if the operating environment is the same, the number of printed sheets, the frequency of use, the environment leaving time, the area ratio of the printed image, the addition of toner, or the characteristic change of the image forming process material Depending on various factors, excessive toner is supplied from the toner supply roller 16 onto the developing roller 15 even under the same voltage condition, and as a result, the toner weight per unit area of the toner layer that has passed through the toner regulating blade 17 is reduced. As a result, the toner charging position becomes larger on the negative side.

  The surface potential of the developing roller 15 is the sum of the developing voltage applied to the developing roller 15 and the toner potential attached to the developing roller 15, and the surface potential of the non-exposed portion of the photosensitive drum 11 is the surface potential of the developing roller 15. When it is smaller (in absolute value), the soiling occurs. Further, as described above, even when the surface potential of the non-exposed portion of the photosensitive drum 11 is equal to the surface potential of the developing roller 15 or larger (in absolute value) than the surface potential of the developing roller 15, the difference is slight. In this case, the highly charged toner moves to the photoconductive drum 11 and the background stain occurs.

  Therefore, the photosensitive drum 11 moves to the photosensitive drum 11 from the developing roller 15, is transferred onto the transfer belt 117, and is measured on the transfer belt 117 using a density sensor 116 that measures the density of the toner carried on the transfer belt 117. The toner reflection density carried on the portion corresponding to the non-exposed portion of the body drum 11 is monitored, the toner charged position is obtained from the surface potential of the non-exposed portion of the photosensitive drum 11 where the background contamination occurs, and the toner charged position is obtained. Based on this, the toner supply voltage to be applied to the toner supply roller 16 is corrected and applied so as not to cause background contamination by controlling the voltage condition. Then, the toner layer potential on the developing roller 15 is controlled. In the present embodiment, the print medium 22 is not transported during the soiling detection operation. Therefore, if there is toner that has been soiled and moved from the developing roller 15 onto the photosensitive drum 11, this toner is transferred from the photosensitive drum 11 to the surface of the transfer belt 117 and detected by the density sensor 116.

  A method for determining the toner supply voltage in the image forming apparatus 101 according to the present embodiment will be described below.

  First, the calculation unit 31 obtains an environment level value based on the temperature and humidity information in the apparatus detected by the environment sensor 24, and obtains the obtained environment from the charging voltage environment table 36 stored in the storage unit 35. A charging voltage value and a transfer voltage value corresponding to the level value are determined. FIG. 19 shows the contents of the charging voltage environment table 121. For example, when the environment level value is level 3, the charging environment table voltage value of −1000 V is selected as the charging voltage, and the transfer environment table voltage value of +3200 V is selected as the transfer voltage. The method of determining the charging environment table voltage in the contents of the charging voltage environment table 121 of FIG. 19 is the same as that described with reference to FIG. 6 in the first embodiment, and a description thereof is omitted here.

  A voltage having a selected charging environment table voltage value (−1000 V in the environment level 3) is applied to the charging roller 24 as the charging voltage, and a transfer environment table voltage value (+3200 V in the environment level 3) is selected as the transfer voltage. A voltage is applied to the transfer roller 18, and constant development voltage and toner supply voltage are always applied to the development roller 15 and the toner supply roller 16. In the present embodiment, for example, a voltage of −250 V is applied as the development voltage, and a voltage of −400 V is applied as the toner supply voltage.

  Next, the toner reflectivity on the surface of the transfer belt 117 is measured by the density sensor 115 while decreasing the absolute value of the applied voltage by 50 V at certain intervals from the charging voltage (−1000 V) determined by the environment table 121. The background contamination detection operation for measuring the toner reflection density is performed. The method for performing the soiling detection operation here will be described below with reference to the main configuration diagram of FIG.

  FIG. 20 is a time chart of the charging voltage, the developing voltage, the toner supply voltage, the transfer voltage, and the output value of the density sensor 115 during the soiling detection operation. Here, the environmental level is level 3, and a development voltage of −250 V is applied, a toner supply voltage of −400 V is applied, and a transfer voltage of +3200 V is applied when “on”. In addition, the region (n) (n = 11, 12,...) In the figure is sequentially charged by the charging roller 12 having a gradually decreasing charging voltage as in the case of FIG. FIG. 8 shows individual charging areas of the photosensitive drum 11 (see FIGS. 8 to 12).

  The dirt detection operation is performed from the upstream photosensitive drum unit 111 (FIG. 17). The background contamination detection operation of the photosensitive drum unit 111 is similar to the procedure described with reference to FIG. That is, the region (11) of the photosensitive drum 11 is charged by the charging roller 12 having a charging voltage value of −1000 V, and similarly, the region (12), the region (13),. It is charged by the charging roller 12 having voltage values of −950V, −900V,. These areas are sequentially transferred to the transfer belt 117 after a predetermined time lag, and the density sensor 115 (FIG. 17) monitors the transfer state to the transfer belt 117 to detect scumming. In the time chart of FIG. 20, for the sake of simplicity, it is described that the density sensor 115 monitors the state at the time of transfer to the transfer belt 117. This causes a time lag until the position of the density sensor 115 is reached.

  The voltage (developing voltage, toner supply voltage, transfer voltage, and charging voltage) is applied to the photosensitive drum unit 111 even after the background contamination detection operation of the photosensitive drum unit 111 is completed. It remains on until the dirt detection operation ends. In the case of the photosensitive drum unit 111, the occurrence of background contamination is detected in the region (15) charged by the -800V charging roller 12. In this case, as described in the first embodiment, the background contamination is detected. Since there was no charging abnormality in the detection operation, the toner supply voltage is set at the environment level 3 as the toner supply voltage even after the background contamination detection operation is completed based on the toner supply voltage correction table 122 (FIG. 18) whose contents are shown in FIG. -400V applied to the standard is continuously applied. The method for determining each applied voltage (excluding the transfer voltage) in the toner supply voltage correction table 122 of FIG. 21 is the same as that described with reference to FIGS. Is omitted

  When the background detection operation of the photosensitive drum unit 111 is completed, the background detection operation of the photosensitive drum unit 112 is continued. As in the case of the photosensitive drum unit 111, the ground contamination detection operation of the photosensitive drum unit 112 is performed by charging the region (21) of the photosensitive drum 11 with the charging roller 12 having a charging voltage value of −1000 V. 22), region (23),... Region (27) are sequentially charged by the charging roller 12 having charging voltage values of −950V, −900V,. These areas are sequentially transferred to the transfer belt 117 after a predetermined time lag, and the density sensor 115 monitors the transfer state to the transfer belt 117 to detect scumming. Here, the time lag until the transfer portion to the transfer belt 117 reaches the position of the density sensor 115 due to its movement is also omitted.

  Similar to the photosensitive drum unit 112 in the time chart of FIG. 20, each of the photosensitive drum units 111 to 114 has a development voltage, a toner supply voltage, and a transfer voltage when the soil detection operation of another photosensitive drum unit (here, 111) starts. A charging voltage is applied. The toner supply voltage here is -400 V, which is applied to the environment level 3 as a standard.

  In the case of the photosensitive drum unit 112, the occurrence of background contamination is detected in the region (25) charged by the -800V charging roller 12. In this case, as described in the first embodiment, the background contamination is detected. Since there was no charging abnormality in the detection operation, the toner supply voltage is set at the environment level 3 as the toner supply voltage even after the background contamination detection operation is completed based on the toner supply voltage correction table 122 (FIG. 18) whose contents are shown in FIG. -400V applied to the standard is continuously applied.

  Although not shown in the time chart of FIG. 20, the background contamination detection operation of the photosensitive drum unit 113 and the background contamination detection operation of the photosensitive drum 114 are performed in the same manner.

  Next, a correction method when toner charging is abnormal will be described. FIG. 22 is a time chart for the background detection operation when toner charging is abnormal. Here, the environmental level is level 3, and a development voltage of −250 V is applied, a toner supply voltage of −400 V is applied, and a transfer voltage of +3200 V is applied when “on”. In addition, the region (n) (n = 11, 12,...) In the figure is sequentially charged by the charging roller 12 having a gradually decreasing charging voltage as in the case of FIG. FIG. 8 shows individual charging areas of the photosensitive drum 11 (see FIGS. 8 to 12).

  The scumming detection operation is performed from the upstream photosensitive drum unit 111 (FIG. 17) in the same manner as in the operation of FIG. In the soil contamination detection operation of the photosensitive drum unit 111, the region (11) of the photosensitive drum 11 is charged by the charging roller 12 having a charging voltage value of −1000 V, and similarly, the region (12), the region (13),. The region (17) is sequentially charged by the charging roller 12 having charging voltage values of -950V, -900V, ... -700V. These areas are sequentially transferred to the transfer belt 117 after a predetermined time lag, and the density sensor 115 checks the transfer state to the transfer belt 117 to detect background contamination. In the time chart of FIG. 22, for the sake of simplicity, the density sensor 115 is described as checking the state immediately after the transfer to the transfer belt 117. This causes a time lag until the position of the density sensor 115 is reached.

The voltage (developing voltage, toner supply voltage, transfer voltage, and charging voltage) is applied to the photosensitive drum unit 111 even after the background contamination detection operation of the photosensitive drum unit 111 is completed. It remains on until the dirt detection operation ends. In the case of the photosensitive drum unit 111 here, the occurrence of soiling is detected in the region (12) charged by the charging roller 12 of -950V. In this case, as described in the first embodiment, since the toner charging abnormality has occurred, the toner supply voltage is set to −300 V based on the toner supply voltage correction table 122 (FIG. 18) whose contents are shown in FIG. It is determined to be corrected, at time t ₁ after the fog detecting operation is completed, the toner supply voltage is changed to -300V from -400 V.

  When the background detection operation of the photosensitive drum unit 111 is completed, the background detection operation of the photosensitive drum unit 112 is continued. As in the case of the photosensitive drum unit 111, the ground contamination detection operation of the photosensitive drum unit 112 is performed by charging the region (21) of the photosensitive drum 11 with the charging roller 12 having a charging voltage value of −1000 V. 22), region (23),... Region (27) are sequentially charged by the charging roller 12 having charging voltage values of −950V, −900V,. These areas are sequentially transferred to the transfer belt 117 after a predetermined time lag, and the density sensor 115 checks the transfer state to the transfer belt 117 to detect background contamination. Here, the time lag until the transfer portion to the transfer belt 117 reaches the position of the density sensor 115 due to its movement is also omitted.

  Similarly to the photosensitive drum unit 112 in the time chart of FIG. 22, each of the photosensitive drum units 111 to 114 has a development voltage, a toner supply voltage, and a transfer voltage when the soil detection operation of another photosensitive drum unit (here, 111) starts. A charging voltage is applied. The toner supply voltage here is -400 V, which is applied to the environment level 3 as a standard.

In the case of the photosensitive drum unit 112 here, the occurrence of background contamination is detected in the region (22) charged by the charging roller 12 of -950V. In this case, as described in the first embodiment, since the toner charging abnormality has occurred, the toner supply voltage is set to −300 V based on the toner supply voltage correction table 122 (FIG. 18) whose contents are shown in FIG. It is determined to be corrected, at time t ₂ after the fog detecting operation is completed, the toner supply voltage is changed to -300V from -400 V.

Although not shown in the time chart of FIG. 22, the same way fog detecting operation of the photosensitive drum unit 113, and fog detecting operation of the photosensitive drum unit 114 is performed.

  As described above, when determining the correction voltage, the toner supply voltage and the development voltage shown in the toner supply voltage correction table 122 containing the contents shown in FIG. FIG. 21 is a toner supply voltage correction table for the environment level 3, but a toner supply voltage correction table corresponding to each environment level is prepared in the same manner as FIG.

  As described above, the determination process of the toner supply voltage by the background contamination detection by the image forming processing apparatus of the present embodiment is completed. According to this processing method, even when the charging state of the toner is changed, the difficulty of causing the background contamination is not different from that when the toner is charged normally, and the generation of the contamination can be prevented. The toner supply voltage determination process described above is performed, for example, when the apparatus is turned on, when the environmental level fluctuates, when the print count reaches a certain number, and the like. Each value shown in the present embodiment is merely an example, and the table value and the like may be set appropriately as appropriate in accordance with conditions such as the characteristics of the process material used and the process speed.

  In this embodiment, the transfer belt also serves as a transport belt for transporting the print medium. However, the transfer belt is not limited to this configuration, and the transfer belt is transported like an intermediate transfer belt. The belt may not serve as a belt.

  As described above, according to the image forming apparatus of the second embodiment, the ground potential on the transfer belt can be detected by the density sensor with a simple configuration even in the case of a color printing apparatus or the like, and the charged potential condition for generating the ground stain. By determining the toner supply voltage from, the toner is not excessively supplied to the developing roller, so that the toner potential can be kept normal and the occurrence of background contamination can be prevented. In the present embodiment, the surface potential of the photosensitive drum 11 is kept constant (for example, −500 V) during actual printing, so that the half pattern or gradation written on the photosensitive drum 11 by the exposure head 13 is maintained. Is appropriately written as a latent image, so that the reproducibility of the half pattern and gradation is not impaired.

Embodiment 3 FIG.
FIG. 23 is a block diagram showing a main configuration of the control system 152 of the image forming apparatus according to the third embodiment based on the present invention.

  The image forming apparatus adopting the control system 152 is mainly different from the control system 2 of the first embodiment shown in FIG. 2 described above in that the toner regulating blade 17 (FIG. 1) is set by the calculation unit 31 and the toner is set. The toner regulation voltage control unit 153 for applying the regulation voltage is added, and the toner regulation voltage correction table 154 is set in the storage unit. Accordingly, in the image forming apparatus employing the control system 152, the same reference numerals are given to the parts common to the image forming apparatus of the first embodiment (FIG. 1), or the description is omitted while omitting the drawings. , Explain different points with emphasis.

  A basic operation of each unit during printing of the image forming apparatus according to the third embodiment will be described. The main configuration of the image forming apparatus according to the third embodiment is the same as that of the image forming apparatus 1 according to the first embodiment shown in FIG. 1, and therefore, the main configuration of FIG. .

In the image forming apparatus according to the third embodiment, the toner reflection density of the non-exposed portion on the photosensitive drum 11 is monitored, and the toner charged position is obtained from the surface potential of the non-exposed portion of the photosensitive drum 11 where the background contamination occurs. Based on the toner charging position, the toner is regulated and applied to the toner regulating blade 17 so as not to cause scumming by controlling the voltage condition. Then, the potential of the toner layer on the developing roller 15 is controlled. In particular,
Surface potential (−500 V) of the non-exposed portion of the photosensitive drum 11
-Surface potential of the developing roller 15 on which the toner layer is formed (about -310 V) = about -190 V
The applied voltage is corrected so that That is, the toner regulation voltage is corrected and applied to the toner regulation blade 17 so that the potential of the toner layer, which is the amount obtained by subtracting the development voltage −250 V, of the surface potential of the developing roller 15 is about −60 V. Thus, the toner regulating blade 17 controls the potential of the toner layer on the developing roller 15 as a developer layer potential control member.

  As described above, the determination processing flow shown in FIG. 24 is shown for the method of determining the toner regulation voltage in the image forming apparatus of the present embodiment for correcting the toner regulation voltage applied to the toner regulation blade 17. This will be described below with reference to the flowchart.

  First, the calculation unit 31 obtains an environment level value based on the temperature and humidity information in the apparatus detected by the environment sensor 24, and obtains the obtained environment from the charging voltage environment table 36 stored in the storage unit 35. A charging voltage value corresponding to the level value is determined (step ST201).

  Here, the environmental level value is a value obtained by calculating by the calculation unit 31 from the relationship between the temperature and humidity measured by the environmental sensor 24, and the absolute humidity is gradually changed into six values as shown in the graph of FIG. It is a level value divided into levels. For example, a high temperature and high humidity environment of 30 ° C. and 80% is level 1, a room temperature environment of 25 ° C. and 45% is level 3, a low temperature and low humidity environment of 10 ° C. and 20% is level 6. FIG. 5 shows the contents of the charging voltage environment table 36. For example, when the environment level value is level 3, the charging environment table voltage value of −1000 V is selected as the charging voltage.

  As the charging voltage, a voltage of the selected charging environment table voltage value (-1000 V at environment level 3) is applied to the charging roller 24, and the developing roller 15, the toner supply roller 16 and the toner regulating blade 17 are always constant. Development voltage, toner supply voltage, and toner regulation voltage are applied (step ST202). In the present embodiment, for example, a voltage of −250 V is applied as the development voltage, a voltage of −400 V is applied as the toner supply voltage, and −350 V is applied as the toner regulation voltage.

  Next, the toner sensor reflects the toner reflectance on the surface of the photosensitive drum 11 by the density sensor 23 while decreasing the absolute value of the applied voltage by 50 V from the charging voltage (−1000 V) determined by the environment table 36 every certain time. Is measured to obtain a toner reflection density, and a ground contamination detection operation is executed (step ST203). A method of measuring the soiling detection operation here will be described below.

  FIG. 25 is a time chart of the charging voltage, the developing voltage, the toner supply voltage, the toner regulation voltage, and the output value of the density sensor 23 during the background detection operation. The areas (1) to (7) of the photosensitive drum 11 shown in the figure are set in the same manner as the areas of the photosensitive drum 11 set in the time chart of FIG. 7, and the density sensor 23 is also the same. Further, it is shown that a region charged by the charging roller 12 2T before the elapsed time T is detected by the time lag due to the rotation of the photosensitive drum 11 (see FIGS. 8 to 12). Here, the environmental level is level 3, and the voltage of −250V is applied as the development voltage, the voltage of −400V is applied as the toner supply voltage, and the voltage of −350V is applied as the toner regulation voltage.

  The charging voltage is −1000 V immediately after activation, and is controlled so that the voltage decreases by 50 V in absolute value every predetermined elapsed time T. According to this time chart, the occurrence of scumming is recognized for the first time in the region (5) of the photosensitive drum 11, and the charging voltage applied to the charging roller 12 when the region (5) is charged is calculated ( Step ST204). Here, the value of the charging voltage in the region (5) where the soiling occurs is −800V.

  Next, the toner regulation voltage is determined next from the charging voltage (−800 V) at the time of occurrence of the soiling obtained by the above-described soiling detection operation (step ST205). A method for determining the toner regulation voltage will be described below.

  FIG. 26 is a graph showing the relationship between the difference between the development voltage and the toner regulation voltage and the toner potential on the development roller 15. In the figure, a solid line represents a case where toner charging is normal, and a broken line represents a case where toner charging is abnormal. As shown in the graph, when the toner regulation voltage increases to the minus side with respect to the development voltage regardless of whether the toner charging is normal or abnormal, the toner potential also increases to the minus side. This is presumably because the charge injected into the toner increases as the toner regulation voltage increases to the negative side. The reason why the toner potential decreases when the toner regulation voltage is increased to the plus side with respect to the development voltage is considered to be that the toner charge is discharged to the toner regulation blade side.

  FIG. 27 shows the detection of scumming detection, the charging voltage at which scumming occurs, and the voltage applied to the developing roller 5 (development) necessary for the potential of the developing roller surface to be an appropriate potential at that time. 6 is a graph showing the relationship between the voltage and the difference between the voltage applied to the toner regulating blade 17 (toner regulating voltage). However, here, the development voltage is a fixed value of −250 V, and the environmental level is 3. FIG. 28 shows the contents of the toner regulation voltage correction table 154 derived based on FIG. Based on the toner regulation voltage correction table 154 shown in FIG. 28, the toner regulation voltage and the development voltage corresponding to the charging voltage when the background contamination is detected are determined.

  The above time chart of FIG. 25 shows the result of the soiling detection operation when the toner charging is normal. In this case, the voltage correction is determined based on the following interpretation.

  From the charged voltage of −800 V at the time of occurrence of soiling, the charged potential of the surface of the photosensitive drum 11 at this time is about −300 V (see FIG. 6). On the other hand, the surface potential of the developing roller 15 is −310 V, which is the sum of the developing voltage −250 V and the normal toner charging potential −60 V (see FIG. 26), so the surface potential of the photosensitive drum 11 and the developing roller 15 is Almost equal. For this reason, it can be seen that the toner adheres to the photosensitive drum 11 and the soiling occurs. In this case, normal toner was used, and it was known that the toner potential was about −60V. However, even if it is not known, it can be inferred that the toner potential is around −60 from the above verification result. . In this case, there is no need to change the difference between the development voltage and the toner regulation voltage based on the toner regulation voltage correction table 154 containing the contents of FIG. 28, the toner regulation voltage is -350V, and the development voltage is -250V. It is determined. At this time, the differential voltage between the surface potential (−500 V) of the non-exposed portion of the photosensitive drum 11 and the surface potential (−310 V) of the developing roller 15 is set to a target of −190 V.

  Next, a correction method when toner charging is abnormal will be described. FIG. 29 is a time chart of the soiling detection operation when the toner charging is abnormal. The areas (1) to (7) of the photosensitive drum 11 shown in the figure are set in the same manner as the areas of the photosensitive drum 11 set in the time chart of FIG. 7, and the density sensor 23 is also the same. In addition, the time lag due to the rotation of the photosensitive drum 11 indicates that the region charged by the charging roller 12 is detected 2T before the elapsed time T.

  According to the time chart of FIG. 29, it can be seen that the charging voltage in the region (2) where the soiling starts to occur is around −950 V, and from this, the soiling is generated from the charging voltage near −950 V. I understand that. At this time, the charged potential of the surface of the photosensitive drum 11 is about −450 V (see FIG. 6), and the potential of the surface of the developing roller 15 can be estimated to be about −450 V. Therefore, the potential of the toner at this time is It is estimated to be about -200 V obtained by subtracting the development voltage of -250 V from -450 V. Therefore, referring to FIG. 26, in the state where the toner is charged to -200V, if the difference between the development voltage and the toner supply voltage is set to about + 50V, the toner potential becomes about -60V, and the resistance to contamination is normal. It will be the same as time.

  Therefore, in this case, based on the toner regulation voltage correction table 154 containing the contents of FIG. 28, the toner regulation voltage is determined to be −200V and the development voltage is determined to be −250V. In this case as well, the difference voltage between the surface potential (−500 V) of the non-exposed portion of the photosensitive drum 11 and the surface potential (−310 V) of the developing roller 15 is set to the target −190 V.

  Therefore, in the case of normal correction, the difference between the toner regulation voltage and the development voltage (for example, fixed value = −250 V) is determined from the charging voltage at the time of the occurrence of the soiling by the toner regulation voltage correction table 154 containing the contents of FIG. The toner regulation voltage, the development voltage, and the toner supply voltage in FIG. 28 are applied. FIG. 28 is a toner regulation voltage correction table in the case of environment level 3 in FIG. 5, but a toner regulation voltage correction table corresponding to each environment is prepared in the same manner as in FIG.

  As described above, the toner regulation voltage determination process based on the background detection by the image forming processing apparatus according to the present embodiment is completed. According to this processing method, even when the charging state of the toner is changed, the difficulty of causing the background contamination is not different from that when the toner is charged normally, and the generation of the contamination can be prevented. The toner supply voltage determination process described above is performed, for example, when the apparatus is turned on, when the environmental level fluctuates, when the print count reaches a certain number, and the like.

  In the present embodiment, as in the case of the above-described first embodiment, the background sensor is detected from the change in the toner reflection density by using the density sensor on the photosensitive drum. As shown in FIG. 2, a method is also possible in which a density sensor is provided on the transfer belt and the background is detected by a change in the toner reflection density of the transfer belt.

  Each value shown in the present embodiment is merely an example, and the table value and the like may be set appropriately as appropriate in accordance with conditions such as the characteristics of the process material used and the process speed.

  Further, in the present embodiment, the voltage control based on the detection of background contamination is targeted for the toner regulation voltage, but it is also possible to target the toner supply voltage together with the toner regulation voltage.

  As described above, according to the image forming apparatus of the third embodiment, the toner on the photosensitive drum is detected by the density sensor, and the toner regulation voltage is determined from the charging voltage at which the background is generated. Is not charged excessively, and toner is not supplied excessively to the developing roller, so that the toner potential can be kept normal, and the occurrence of soiling can be prevented. In the present embodiment, the surface potential of the photosensitive drum 11 is kept constant (for example, −500 V) during actual printing, so that the half pattern or gradation written on the photosensitive drum 11 by the exposure head 13 is maintained. Is appropriately written as a latent image, so that the reproducibility of the half pattern and gradation is not impaired.

Embodiment 4 FIG.
FIG. 30 is a flowchart showing the execution timing of the toner supply voltage or toner regulation voltage determination process of the image forming apparatus according to the fourth embodiment of the present invention.

  In the image forming apparatuses according to the first to third embodiments described above, the toner supply voltage or toner regulation voltage determination process is performed, for example, when the apparatus is turned on, when the environment level fluctuates, or when the print count is constant. I went at the timing of passing. However, for example, when the environmental level has just changed, the determination process of the toner supply voltage or the toner regulation voltage is performed and the timing until the next toner supply voltage or toner regulation voltage determination process is performed. Dirt may occur.

  In order to cope with such a situation, in the image forming apparatus according to the present embodiment, the toner density in the portion corresponding to the non-exposed portion on the photosensitive drum during printing or the non-exposed portion of the photosensitive drum on the transfer belt. By detecting the reflectance, the occurrence of background contamination during the printing process (during the printing operation) is detected, and the determination process of the toner supply voltage and the toner regulation voltage is performed as a trigger.

  The determination process of the toner supply voltage or the toner regulation voltage in the image forming apparatus according to the fourth embodiment is performed by the method described in the image forming apparatuses according to the first to third embodiments. The description here is omitted.

  Based on the flowchart of FIG. 30, the execution timing of the determination process of the toner supply voltage or the toner regulation voltage by the image forming apparatus of the present embodiment will be described below.

  First, before starting printing, for example, at a normal setting timing such as a timing when the apparatus is turned on, a timing when the environmental level fluctuates, or a timing when a certain number of print counts elapse, a toner supply voltage or A toner regulation voltage determination process is performed (step ST301). Next, a normal printing process is started (step ST302). During the process, the non-exposed portion on the photosensitive drum such as between the preceding and following printing media, or the reflectance on the transfer belt corresponding to the same portion is measured by the density sensor. (Step ST303). At this time, if an output indicating toner adhesion is output from the density sensor in spite of the non-image portion (on the non-exposed portion of the photosensitive member or on the transfer belt corresponding to the same portion) (step ST304, YES), step 301 is performed. Then, the print job is interrupted and the determination process of the toner supply voltage or the toner regulation voltage is performed again. When the output indicating the toner adhesion is not output from the density sensor (NO in step ST304), the printing is continued. These processes in steps 303 and 304 are repeated until printing is completed (step ST305).

  Therefore, in the image forming apparatus according to the fourth embodiment, when the scumming occurs during the printing process, the determination process of the toner supply voltage or the toner regulation voltage is executed at that time, and the toner supply voltage or the Apply toner regulation voltage.

  As described above, according to the image forming apparatus of the fourth embodiment, for example, the timing at which the apparatus is turned on, the timing at which the environmental level fluctuates, and the number of prints with a constant print count before printing is started. Even if the scumming occurs during the printing process between the determination process of the toner supply voltage or the toner regulation voltage at the normal setting timing such as the timing after the lapse of the stagnation, the scumming that has occurred can be eliminated immediately. .

  In each of the above-described embodiments, the present invention is shown as an example in which the present invention is adopted in an electrophotographic printer. However, the present invention is not limited to this. For example, an MFP (Multi Function Printer), a facsimile, a scanner, a copying machine The present invention can also be applied to a device such as a device. In each of the embodiments, examples of use in a one-component contact development type printer have been described. However, the present invention can also be used in a one-component non-contact development method and a two-component development method. Further, in the second embodiment, the tandem type color printer in which the medium is conveyed on the transfer belt has been described. However, a four-cycle color printer that forms a color image by sequentially repeating the transfer four times using the intermediate transfer belt. It can also be used.

1 is a main part configuration diagram showing a main part configuration of a first embodiment of an image forming apparatus according to the present invention; FIG. 2 is a block diagram illustrating a main configuration of a control system of the image forming apparatus according to the first embodiment. 4 is a flowchart illustrating a flow of toner supply voltage determination processing by the image forming apparatus according to the first embodiment. It is a graph which shows the relationship between an environmental level, temperature, and humidity. FIG. 6 is a diagram showing the contents of an environment table for charging voltage in the first embodiment. 4 is a graph showing the correspondence relationship between the charging voltage applied to the charging roller and the charging potential of the surface of the photosensitive drum charged thereby, according to the environment. 4 is a time chart of charging voltage, developing voltage, toner supply voltage, and output value of a density sensor during a background detection operation in the first embodiment. In age T ₁ of the time chart of FIG. 7 is an operation explanatory view showing an operating state of the image forming apparatus 1. In age T ₂ of the time chart of FIG. 7 is an operation explanatory view showing an operating state of the image forming apparatus 1. In age T ₃ of the time chart of FIG. 7 is an operation explanatory view showing an operating state of the image forming apparatus 1. In age T ₄ of a time chart of FIG. 7 is an operation explanatory view showing an operating state of the image forming apparatus 1. In age T ₄ of a time chart of FIG. 7 is an operation explanatory view showing an operating state of the image forming apparatus 1. 6 is a graph showing a relationship between a difference between a developing voltage and a toner supply voltage and a toner potential on a developing roller. The difference between the charging voltage at which the scumming occurs and the developing voltage applied to the developing roller and the toner supplying voltage applied to the toner supply roller, which are necessary for the potential of the developing roller surface to be an appropriate potential at that time. It is a graph showing the relationship of. It is a figure which shows the content of the toner supply voltage correction table derived | led-out based on FIG. 4 is a time chart of a background contamination detection operation when toner charging is abnormal in the first embodiment. It is a principal part block diagram which shows the principal part structure of Embodiment 2 of the image forming apparatus based on this invention. FIG. 6 is a block diagram illustrating a main configuration of a control system of an image forming apparatus according to a second embodiment. FIG. 10 is a diagram showing the contents of an environment table for charging voltage in the second embodiment. 10 is a time chart of charging voltage, developing voltage, toner supply voltage, transfer voltage, and output value of a density sensor during a background contamination detection operation in the second embodiment. 10 is a diagram illustrating the contents of a toner supply voltage correction table in Embodiment 2. FIG. 6 is a time chart of a background contamination detection operation when toner charging is abnormal in the second embodiment. It is a block diagram which shows the principal part structure of the control system of the image forming apparatus of Embodiment 3 based on this invention. 10 is a flowchart illustrating a flow of toner regulation voltage determination processing by the image forming apparatus according to the third embodiment. 10 is a time chart of a charging voltage, a developing voltage, a toner supply voltage, a toner regulation voltage, and an output value of a density sensor during a background detection operation in the third embodiment. 6 is a graph showing a relationship between a difference between a developing voltage and a toner regulation voltage and a toner potential on a developing roller. The difference between the charging voltage at which the soiling occurs and the developing voltage applied to the developing roller and the toner regulating voltage applied to the toner regulating blade, which are necessary for the potential of the developing roller surface to be an appropriate potential at that time. It is a graph showing the relationship of. It is a figure which shows the content of the toner control voltage correction table derived | led-out based on FIG. 10 is a time chart of the background contamination detection operation when toner charging is abnormal in the third embodiment. 14 is a flowchart illustrating execution timing of determination processing of a toner supply voltage or a toner regulation voltage in the image forming apparatus according to the fourth embodiment of the present invention.

Explanation of symbols

1,101 image forming apparatus,
2,102,152 control system,
11 Photosensitive drum,
12 charging roller,
13 exposure head,
14 Development device,
15 Development roller,
16 toner supply roller,
17 Toner regulating blade,
18 Transfer roller,
20 photoconductor cleaning blade,
21 Fixing unit,
22 print media,
23,115 density sensor,
24 environmental sensors,
31 arithmetic unit,
32 charging voltage controller,
33 Development voltage controller,
34 toner supply voltage control unit,
35 storage unit,
36, 121 Environmental table of charging voltage,
37, 122 toner supply voltage correction table,
38 print count storage unit,
111-114 photosensitive drum unit,
116 transfer belt cleaning blade,
117 transfer belt,
120 transfer voltage controller,
153 toner regulation voltage control unit,
154 Toner regulation voltage correction table.

Claims (14)

An image carrier charged by a charging member to which a predetermined charging voltage is applied;
An exposure member that exposes the surface of the image carrier charged by the charging member to form an electrostatic latent image;
A developer layer potential control member that controls a surface potential of a developer layer on a developer member to which a predetermined voltage is applied and develops the electrostatic latent image with a developer;
A developer detecting member that detects the developer attached to a region corresponding to a non-exposed region that was not exposed by the exposure member;
On the basis of the detection result of the developer detecting member, have a voltage control unit for controlling a voltage applied to said developer layer potential control member,
The voltage control unit obtains a voltage at which the developer detection member detects adhesion of the developer by changing the charging voltage in a stepwise manner, and sets a preset voltage corresponding to the voltage to the development An image forming apparatus, wherein the image forming apparatus is applied to an agent layer potential control member . The developer layer potential control member is a developer supply member that supplies a developer to a developer member that develops the electrostatic latent image,
The developer detection member is arranged in the rotation direction of the image bearing member downstream of said developing member, according to claim 1, characterized in Rukoto issuing detects the developer adhered to the non-exposure area on said image bearing member The image forming apparatus described. The developer layer potential control member is a developer regulating member that regulates the amount of developer on the developing member that develops the electrostatic latent image,
The developer detection member is arranged in the rotation direction of the image bearing member downstream of said developing member, according to claim 1, characterized in Rukoto issuing detects the developer adhered to the non-exposure area on said image bearing member The image forming apparatus described. A transfer member to which the developer moved from the developing member onto the image carrier is transferred;
The developer layer potential control member is a developer supply member that supplies a developer to a developer member that develops the electrostatic latent image,
The developer detecting unit according to the provided opposite to the transfer member, and wherein the Rukoto issuing detects the developer adhering to the area on the transfer member corresponding to the non-exposure area on said image bearing member Item 2. The image forming apparatus according to Item 1. A transfer member to which the developer moved from the developing member onto the image carrier is transferred;
The developer layer potential control member is a developer regulating member that regulates the amount of developer on the developing member that develops the electrostatic latent image,
The developer detecting unit according to the provided opposite to the transfer member, and wherein the Rukoto issuing detects the developer adhering to the area on the transfer member corresponding to the non-exposure area on said image bearing member Item 2. The image forming apparatus according to Item 1. A plurality of development carrier units each having the development carrier, the exposure member, and the developer layer potential control member are provided, and the developer attached to the plurality of image carriers is sequentially transferred to the transfer member. The image forming apparatus according to claim 4, wherein: 7. The image forming apparatus according to claim 6, wherein a voltage applied to each developer layer potential control member of a plurality of development carrier units is sequentially set. The absolute value of the voltage applied to the developer layer potential control member is set to be smaller as the absolute value of the voltage at which the developer is detected by the developer detection member is larger. The image forming apparatus according to claim 5. The voltage control section, any of claims 1 to 8, characterized in setting Teisu Rukoto said predetermined charging voltage to the plurality of set values based on the measurement values of the environmental sensor to measure the temperature and humidity of the internal environment An image forming apparatus according to claim 1. The voltage control unit, when the power is turned on, the voltage control unit, an image forming apparatus according to any one of claims 1 to 9, characterized in that executes processing for determining the voltage to be applied. Furthermore, a print number storage unit for storing the number of prints is provided,
When said number of printed sheets stored in the print number storage unit reaches a predetermined number, the voltage control unit, according to any of claims 1 to 9, characterized in that executes processing for determining the voltage to be applied Image forming apparatus.   The voltage control unit executes a process of determining a voltage to be applied when the developer adhering to the non-exposed area of the image carrier is detected by the developer detection member during a printing operation. The image forming apparatus according to claim 2.   A process of determining a voltage to be applied by the voltage control unit when the developer detecting member detects the developer adhering to the transfer member corresponding to the non-exposed region of the image carrier during the printing operation; The image forming apparatus according to claim 4, wherein the image forming apparatus is executed. The developer detection member, an image forming according to any one of claims 2 to 13, characterized in that a density sensor for detecting a reflection density of the developer adhering to the image bearing member or the transfer member apparatus.

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