JP6536088B2 - Image forming apparatus, image forming method, and program - Google Patents

Description

  The present invention relates to an image forming apparatus, an image forming method, and a program for forming an image by electrophotography. More specifically, the present invention relates to charge control in an image forming apparatus.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus for forming a toner image on a photosensitive member, various controls have been proposed to prevent image quality deterioration. For example, Patent Document 1 detects the current between the photosensitive member and the transfer member when the charging voltage is changed by the charging device as a configuration for coping with changes in the use environment and use frequency, and the detection value An arrangement is disclosed that uses the charging voltage at which is maximized to form an image.

JP, 2014-164193, A

  However, the above-described conventional techniques have the following problems. That is, in the inside of the photosensitive member, there may be a residual charge which is a charge that has not reached the surface of the photosensitive member. Then, the residual charge may offset part of the charge on the surface of the photosensitive member charged by the charging device, and the surface potential of the photosensitive member may be lower than the target surface potential. The reduction of the surface potential causes the deterioration of image quality such as density unevenness and fog. In the case of a configuration in which a contact member such as a cleaning member is brought into contact with the photosensitive member, the residual heat is easily generated due to the frictional heat accompanying the contact between the contact member and the photosensitive member.

  The present invention has been made to solve the problems of the above-described conventional apparatus. That is, an object of the present invention is to provide an image forming apparatus which forms an image by an electrophotographic method, and to provide a technique for suppressing the image quality deterioration due to the variation of the surface potential of the photosensitive member.

  An image forming apparatus made for the purpose of solving the problem includes a photosensitive body, a charging device for charging the surface of the photosensitive body, a toner supply device for supplying toner to the photosensitive body, and toner on the photosensitive body. The image forming apparatus further includes: a transfer device for transferring the image onto a material to be transferred, a contact member in contact with the photosensitive member, and a control unit, wherein the control unit is configured to rotate the photosensitive member. It is characterized in that the absolute value of the charging voltage or the absolute value of the charging current used in the charging device is set to a larger value as the charging range, which is the range charged in the charging device in the direction, increases.

  Since the image forming apparatus disclosed in the present specification includes the contact member in contact with the photosensitive member, residual charge may be generated at the contact point between the contact member and the photosensitive member. And, the more the residual charge in the charging range, the more the charge offset by the residual charge after passing through the charging range. The image forming apparatus disclosed herein increases the absolute value of the charging voltage or the absolute value of the charging current as the residual charge in the charging range increases.

  The absolute value of the surface potential of the photosensitive member after charging is increased by increasing the absolute value of the charging voltage or the absolute value of the charging current as the residual charge in the charging range increases. Therefore, even if part of the charge on the photosensitive member after charging is offset by the residual charge, it can be expected to keep the surface potential of the photosensitive member above the target surface potential. The residual charge can be estimated, for example, by the magnitude of the transfer current, the rotational speed of the photosensitive member, and the temperature of the photosensitive member.

  Further, the absolute value of the charging voltage or the absolute value of the charging current used in the charging device may be the target of the photosensitive member even if the surface potential of the photosensitive member is offset by the residual charge after passing through the charging device. It is preferable that the value be equal to or higher than the surface potential. Even if part of the charge on the photosensitive member after charging is offset by the residual charge, image quality deterioration is suppressed by using a charging voltage or charging current of a magnitude that keeps the surface potential of the photosensitive member above the target surface potential. Can be expected more surely.

  Further, it is preferable that the control unit determines that the residual charge is larger in the charging range as the transfer current used in the transfer device is larger. The larger the transfer current, the less the charge present on the photoreceptor surface after transfer. Therefore, the force for attracting the residual charge present on the photosensitive member to the photosensitive member surface is weak. For example, the charge generated on the photosensitive member at the contact point with the contact member may not reach the photosensitive member surface before reaching the charging range. Becomes higher. Therefore, it is preferable to increase the absolute value of the charging voltage or the absolute value of the charging current as the transfer current increases.

  Further, the control unit is configured to calculate a first difference which is a difference between the charging voltage in the case of the first transfer current and the charging voltage in the case of the second transfer current which is smaller by a predetermined amount than the first transfer current. A second difference which is a difference between the charging voltage in the case of the third transfer current lower than the second transfer current and the charge voltage in the case of the fourth transfer current smaller by the predetermined amount than the third transfer current. It is better to make it larger. The larger the transfer current, the lower the surface potential of the photosensitive member after transfer, so there is a high possibility that the residual charge that does not reach the surface of the photosensitive member will increase before reaching the charging range. Therefore, it is preferable to increase the amount of increase in the charging voltage as the transfer current is larger.

  Further, it is preferable that the control unit determines that the residual charge is larger in the charging range as the rotational speed of the photosensitive member is higher. The higher the rotational speed of the photosensitive member, for example, the electric charge generated at the contact point with the contact member and existing on the photosensitive member can move to the surface of the photosensitive member faster and the corresponding portion of the photosensitive member reaches the charging range Sex is high. Therefore, it is preferable to increase the absolute value of the charging voltage or the absolute value of the charging current as the rotational speed of the photosensitive member increases.

  Further, it is preferable that the control unit determines that the residual charge is larger in the charging range as the temperature of the photosensitive member is lower. The lower the temperature of the photosensitive member, the slower the moving speed of the charge moving inside the photosensitive member. Therefore, for example, there is a high possibility that the charge generated at the contact portion with the contact member and present on the photosensitive member does not reach the photosensitive member surface until the corresponding portion of the photosensitive member reaches the charging range. Therefore, it is preferable to increase the absolute value of the charging voltage or the absolute value of the charging current as the temperature of the photosensitive member decreases.

  Further, it is preferable that the control unit sets a charging voltage having a large difference with respect to a target surface potential of the photoconductor as the residual charge increases in the charging range. The absolute value of the charging voltage can be increased by setting the charging voltage with a large difference to the target surface potential of the photosensitive member.

  The control unit may set a sum of a reference charging voltage and a correction value as the charging voltage, and may increase the correction value as the residual charge increases in the charging range. The absolute value of the charging voltage can be increased by increasing the correction value.

  The contact member may be a cleaning blade for removing the toner on the photosensitive member. In the configuration in which the blade is in contact with the photosensitive member, frictional heat is apt to be generated, and a charge is apt to be generated inside the photosensitive member. Therefore, the residual charge tends to be large, and the present invention works suitably.

  Further, the correction value may be a value having an amount of charge generated by frictional heat between the photosensitive member and the cleaning blade as an upper limit. The frictional heat between the photosensitive member and the cleaning blade is the main factor causing the residual charge. Therefore, in order not to make the charging voltage too large, it is preferable to set the amount of charge generated by frictional heat as the upper limit of the correction value.

  Further, the upper limit of the correction value may be a larger value as the cumulative number of printed sheets increases. Depending on the cumulative number of printed sheets, the magnitude of the frictional heat between the photosensitive member and the cleaning blade may change. By determining the upper limit of the correction value in accordance with the cumulative number of printed sheets, a more appropriate upper limit can be set.

  Further, the correction value is not less than a value corresponding to the charge amount of the charge moving to the surface of the photosensitive member from the charging range to the supply position where the toner supply device supplies the toner among the residual charge. It should be a value. In this way, even if there is a portion where the potential drops between the charging range and the toner supply position due to the residual charge, the possibility of the toner moving to the portion where the potential drops is low. Therefore, the image quality deterioration can be suppressed.

  An image forming method for realizing the function of the image forming apparatus, a computer program, and a computer readable storage medium storing the computer program are also novel and useful.

  According to the present invention, an image forming apparatus that forms an image by an electrophotographic method, and realizes a technique for suppressing the image quality deterioration due to the variation of the surface potential of the photosensitive member.

FIG. 1 is a cross-sectional view showing a schematic configuration of a printer according to an embodiment. It is an explanatory view showing a photosensitive member of a printer. FIG. 2 is a block diagram showing an electrical configuration of a printer. FIG. 6 is an explanatory view showing the movement of charge inside the photosensitive member. 5 is a flowchart illustrating a procedure of print processing of the printer. 5 is a flowchart illustrating a procedure of charge control processing of the printer. It is a graph which shows the relationship between the transfer current value and the change of surface potential. 5 is a table showing the relationship between a transfer current value and a first correction value. It is a table | surface which shows the relationship between rotational speed and a 2nd correction value. It is a table | surface which shows the relationship between temperature and a 3rd correction value.

  Hereinafter, an embodiment in which an image forming apparatus according to the present invention is embodied will be described in detail with reference to the attached drawings. In this embodiment, the present invention is applied to a printer having an image forming function.

  The printer 100 of this embodiment is a color printer that forms a color image on a sheet as a transfer material by an electrophotographic method. As shown in FIG. 1, the printer 100 forms a toner image and transfers the sheet onto a sheet, the conveyance belt 7 conveys the sheet through the part 5, and the unfixed toner on the sheet. And a fixing device 8 for fixing the image. Further, the printer 100 includes a sheet feeding tray 91 on which the sheet before transferring the toner image is placed, and a sheet discharging tray 92 on which the sheet after forming the image is placed.

  Further, the printer 100 is provided with a conveyance path 11 which is a path of a substantially S-shaped sheet, as indicated by an alternate long and short dash line in FIG. The printer 100 further includes a sheet feeding roller 21 for conveying a sheet along the conveyance path 11, a registration roller 22, and a sheet discharging roller 23. That is, the printer 100 conveys one sheet of the sheet stored in the sheet feeding tray 91 along the conveying path 11 using the sheet feeding roller 21, the registration roller 22, the conveying belt 7, the sheet discharging roller 23 and the like. And the sheet is discharged to the sheet discharge tray 92.

  In addition, the process unit 5 of the printer 100 is provided with a configuration for forming a toner image of each color. Specifically, as shown in FIG. 1, the process unit 5 includes a black process unit 50K, a yellow process unit 50Y, a magenta process unit 50M, and a cyan process unit 50C. Along the traveling direction, they are arranged at equal intervals. The arrangement order of the process units of each color is not limited to the example shown in FIG.

  As shown in FIG. 1, the black process unit 50 K includes a drum-shaped photosensitive member 51 and a charging device 52, a developing device 54, a transfer device 55, and a cleaner 56 disposed around the photosensitive member 51. And. The process units 50C, 50M, and 50Y of the other colors have the same configuration as the process unit 50K for the black color except for the color of the toner. Furthermore, the process unit 5 has an exposure device 53 as a configuration common to the process units 50Y, 50M, 50C, and 50K of the respective colors. The photosensitive member 51 is an example of a photosensitive member, the charging device 52 is an example of a charging device, the developing device 54 is an example of a toner supply device, and the transfer device 55 is an example of a transfer device. 56 is an example of the contact member.

  The photosensitive member 51 of the printer 100 has a metal core 511 and an organic photosensitive layer 512 formed around the metal core 511, as schematically shown in FIG. That is, the metal core 511 shown on the lower side in FIG. 2 is the central part of the photosensitive member 51, and the organic photosensitive layer 512 shown on the upper side in FIG. There is. The metal core 511 is, for example, a pipe made of aluminum and is electrically grounded. In the organic photosensitive layer 512, the charge generating agent 513 and the charge transporting agent 514 are dispersed.

  In the printer 100 of the present embodiment, for example, the organic photosensitive layer 512 is made of polycarbonates as a base material, charge transport agent 513 mainly composed of phthalocyanines, charge transport mainly composed of azoquinones and arylamines And an agent having a thickness of 30 μm in the radial direction of the photosensitive member 51. The illustrated materials are not limited to these, and may be selected appropriately according to the type of toner and the like. Details of the organic photosensitive layer 512 will be described later.

  The charging device 52 is a scorotron charger including a wire and a grid, and charges the surface of the photosensitive member 51 by discharging. As a result, the surface of the photosensitive member 51 is almost uniformly charged. In the following, the grid voltage applied to the grid of the charging device 52 is referred to as charging voltage. Further, a wire current flowing through the wire of the charging device 52 is used as a charging current. Further, in the surface of the photosensitive member 51, a range that faces the charging device 52 and that receives the electric charge by the discharge of the charging device 52 at the time when it faces the charging device 52 is a charging range. The charging range moves on the surface of the photosensitive member 51 by the rotation of the photosensitive member 51.

  The exposure device 53 is a laser exposure type exposure device, and irradiates the surface of the charged photosensitive body 51 with a laser beam based on image data. As a result, an electrostatic latent image based on the print data is formed on the surface of the photosensitive member 51. Details of the exposure will be described later.

  The developing device 54 contains toner, charges the toner, and supplies it to the developing roller 541. Further, the developing device 54 applies a predetermined voltage to the developing roller 541 to provide a potential difference between the potential of the developing roller 541 and the potential of the electrostatic latent image on the photosensitive member 51, thereby making the charged toner a photosensitive member. Supply the electrostatic latent image on the V.51. Thus, a toner image is formed on the photosensitive member 51. The transfer device 55 is disposed in parallel to the photosensitive member 51 with the conveyance belt 7 interposed therebetween. The transfer device 55 electrically attracts the toner image on the photosensitive member 51 by flowing a transfer current, and transfers the toner image onto the sheet being conveyed by the conveyance belt 7.

  The cleaner 56 is a cleaning blade, one end of which is in contact with the photosensitive member 51, and removes the toner remaining on the photosensitive member 51 after transfer by scraping it. The cleaner 56 is abutted against the rotation of the photosensitive member 51 in the counter direction. For example, in FIG. 1, the photosensitive member 51 is rotated clockwise in the drawing, and the cleaner 56 has a component in the direction opposite to the traveling direction of the surface of the photosensitive member 51 at the contact point with the photosensitive member 51. It is pressed in the included direction.

  The printer 100 of this embodiment forms an image using positively chargeable one-component toner. That is, the surface of the photosensitive member 51 is positively charged by the charging device 52 when printing is performed. Next, a part of the surface of the photosensitive member 51 is exposed by the exposure device 53, whereby the potential of the part is lowered. The toner contained in the developing device 54 is charged to a positive polarity by the developing device 54 and moves to a position where the potential of the photosensitive member 51 is lowered.

  Further, when printing is performed, the printer 100 takes out the sheets placed on the sheet feeding tray 91 one by one, and conveys the sheets onto the conveyance belt 7. The transfer device 55 is set to a negative potential by the transfer current, and attracts the toner on the photosensitive member 51 in time with the conveyance of the sheet. Thus, the toner image is transferred to the sheet.

  When printing a color image, the printer 100 causes the process unit 5 to sequentially transfer the toner images of the respective colors formed on the photosensitive member 51 onto the sheet and sequentially transfer them. When printing a monochrome image, the printer 100 operates only the black processing unit 50K. Thereafter, the printer 100 conveys the sheet on which the toner image has been transferred to the fixing device 8 and thermally fixes the toner image on the sheet. Then, the sheet after fixing is discharged to the discharge tray 92.

  Subsequently, the electrical configuration of the printer 100 will be described. As shown in FIG. 3, the printer 100 according to this embodiment includes a controller 30 including a CPU 31, a ROM 32, a RAM 33, and an NVRAM (nonvolatile RAM) 34. The printer 100 further includes a process unit 5, a network interface 37, a USB interface 38, and an operation panel 40, which are electrically connected to the controller 30. Note that the controller 30 in FIG. 1 is a generic term that collectively describes hardware used for controlling the printer 100 such as the CPU 31 and does not necessarily represent a single piece of hardware actually present in the printer 100.

  The ROM 32 stores firmware, which is a control program for controlling the printer 100, various settings, initial values, and the like. The RAM 33 is used as a work area from which various control programs are read, or as a storage area for temporarily storing image data. The CPU 31 controls each component of the printer 100 while storing the processing result in the RAM 33 or the NVRAM 34 according to the control program read out from the ROM 32 and signals sent from various sensors. The CPU 31 is an example of a control unit. The controller 30 may be a control unit.

  The network interface 37 is hardware for communicating with an apparatus connected via a network using a LAN cable or the like. The USB interface 38 is hardware for communicating with a device connected via a USB cable or the like. The operation panel 40 is hardware that is responsible for displaying a notification to the user and receiving an instruction input by the user. The operation panel 40 includes, for example, a liquid crystal display and a button group including a start key, a stop key, a ten key, and the like.

  Subsequently, a method of setting the charging voltage in the printer 100 will be described. In the printer 100 of the present embodiment, if there is a portion where the surface potential is partially lowered on the photosensitive member 51 after charging and before exposure, the potential of the lowered portion is equal to the potential of the electrostatic latent image after exposure. The difference is small. On the other hand, since the charge amount of the charged toner varies, the toner having a large charge amount may move to a place where the surface potential is lowered and which is not an electrostatic latent image. Then, when toner adheres to a portion of the surface of the photosensitive member 51 other than the electrostatic latent image, for example, although it is desired to form a straight line of a certain width, it may become a partially wide straight line , May reduce the image quality. Therefore, in order to suppress the deterioration of the image quality, it is desirable that the surface potential of the photosensitive member 51 at the position immediately before development be a stable potential with little variation.

  The photosensitive member 51 has an organic photosensitive layer 512 containing a charge generating agent 513 and a charge transporting agent 514, as shown in FIG. The charge generating agent 513 receives energy such as light and heat to generate positive charge and negative charge. The generated charge is carried by the charge transfer agent 514 and moves inside the organic photosensitive layer 512. That is, due to the potential difference between the surface of the photosensitive member 51 and the metal core 511, the positive charge and the negative charge are separately separated and move to the center side and the surface side of the photosensitive member 51, respectively.

  For example, in the state where the surface of the photosensitive member 51 has a positive potential with respect to the level of the metal core 511, as shown in FIG. The positive charge moves toward the metal core 511. The higher the surface potential of the photosensitive member 51, the larger the force for attracting the negative charge, and the faster the moving speed of the negative charge. Then, when the negative charge reaches the surface of the photosensitive member 51, the negative charge is combined with the positive charge on the surface of the photosensitive member 51 to cancel the charge. As a result, the potential at that point decreases.

  Further, as described above, since the printer 100 of the present embodiment uses the positively chargeable toner, the charging device 52 positively charges the surface of the photosensitive member 51. At the time of exposure, charge of the organic photosensitive layer 512 is generated by the energy of the laser light generated from the exposure device 53. Since the surface of the photosensitive member 51 has a positive potential due to charging, the negative charge of the generated charges is attracted to the surface of the photosensitive member 51 to lower the surface potential of the photosensitive member 51 at that point. Thus, an electrostatic latent image is formed on the surface of the photosensitive member 51. Then, the developing device 54 develops a portion of the electrostatic latent image whose potential has been lowered with the positively charged toner.

  In the printer 100 of this embodiment, as described above, the cleaner 56 is in contact with the surface of the photosensitive member 51. In particular, in the printer 100 of this embodiment, a contact type blade member is used as the cleaner 56, and the cleaner 56 is in pressure contact with the surface of the photosensitive member 51. Therefore, frictional heat is generated at the contact point between the photosensitive member 51 and the cleaner 56. Then, as shown in FIG. 4A, in some cases, charges are generated in the organic photosensitive layer 512 of the photosensitive member 51 by receiving the energy of the frictional heat.

  The charge generated at the contact point with the cleaner 56 also moves in the same manner as that by the exposure described above. That is, as shown in FIG. 4B, the negative charge of the generated charges moves toward the surface side of the positively charged photosensitive member 51. Furthermore, as shown by the broken line in FIG. 4B, the negative charge reaching the surface of the photosensitive member 51 is combined with the positive charge on the surface of the photosensitive member to offset the positive charge, and the photosensitive member of that portion Decrease the potential of 51. In the printer 100, among the residual charges generated in the layer of the organic photosensitive layer 512 and not reaching the surface of the photosensitive member, the negative charge contributes to the potential drop of the photosensitive member 51. Hereinafter, among residual charges remaining in the photosensitive member 51, charges having a polarity opposite to the charging polarity are simply referred to as “residual charges”.

  If the offset of the surface potential of the photosensitive member 51 due to the residual charge occurs at a position after development and before development, the printing density may be affected. For example, as shown in FIG. 4C, when the residual charge reaches the surface of the photosensitive member 51 at the position after charging, the potential of the photosensitive member 51 at that position is lowered. The photosensitive member 51 in the portion shown in FIG. 4 is moved to the right in the figure by rotation. If there are many residual charges in the charging range, there is a high possibility that there are many residual charges reaching the surface of the photosensitive member 51 after charging. The printer 100 of this embodiment controls the charging voltage so that the surface potential of the photosensitive member 51 becomes equal to or higher than a predetermined target surface potential even if the residual charge is offset after charging.

  The contact point between the cleaner 56 and the photosensitive member 51 in the printer 100 is a position after transfer and before charging. Therefore, the negative charge of the charges generated by the frictional heat of the cleaner 56 may become a residual charge in the charging range. In particular, when the amount of charge generation is large or the movement speed of negative charge after generation is slow, there is a high possibility that the residual charge increases in the charging range. As a factor of the large amount of charge generation, the frictional heat by the cleaner 56 may be large. Further, as a factor of the slow moving speed of the negative charge after generation, the surface potential of the photosensitive member 51 before the offset is low, or the temperature of the organic photosensitive layer 512 is low.

  Next, as an example of performing charging control according to the amount of residual charge amount described above, a printing process procedure for realizing the printing operation of the printer 100 will be described with reference to the flowchart of FIG. The print process is executed by the CPU 31 when a print job is accepted.

  In the printing process, the printer 100 first starts the warm-up of the fixing device 8 and the print preparation operation of each part (S101). Further, the printer 100 executes a charging control process for determining the charging voltage to be applied to the charging device 52 (S102). The charge control process is an example of the setting step and the setting process.

  Next, the procedure of the charging control process for determining the charging voltage of the printer 100 in S102 will be described with reference to the flowchart of FIG. In the charging control process, the printer 100 first acquires a reference charging voltage (S201).

  The reference charging voltage is, for example, a charging voltage under a predetermined condition, and is stored in advance in the ROM 32 or the NVRAM 34 of the printer 100. The predetermined condition is, for example, a condition in which the printing speed is full speed in a normal temperature and normal humidity environment. In the printer 100, the reference charging voltage is slightly larger than the voltage corresponding to the target surface potential of the photosensitive member 51 after charging. In the printer 100 of this embodiment, for example, the target surface potential of the photosensitive member 51 after charging is 670 V, and the reference charging voltage is 760 V.

  Next, the printer 100 acquires a transfer current value (S203). The transfer current value is determined in advance by the setting of the received print job and the environment. The printer 100 controls the transfer device 55 by constant current control.

  The transfer current value varies depending on, for example, the humidity of the environment, the printing speed, and the paper type. When the humidity is high, the transfer current value is smaller than when the humidity is low. When the printing speed is half speed, the transfer current value is half that of full speed in order to match the amount of transfer current per unit area of the sheet with that of full speed. Also, when the paper type is thick paper, the printing speed is half speed, so the transfer current value is also half as compared to the case of plain paper, but in low humidity environment, the transfer current value is better than in the environment other than low humidity. Is a little big.

  The surface potential of the photosensitive member 51 after transfer is lower than that of the photosensitive member 51 before transfer. For example, as shown in FIG. 7, the reduction width of the surface potential of the photosensitive member 51 before and after transfer differs depending on the transfer current value, and the larger the transfer current value, the larger the reduction width. In particular, when the transfer current value exceeds 15 μA, the surface potential of the photosensitive member 51 after transfer significantly decreases. In FIG. 7, the surface potential of the photosensitive member 51 before transfer is shown by a white circle, and the surface potential of the photosensitive member 51 after transfer is shown by a black triangle.

  That is, when the transfer current value is large, the decrease in surface potential of the photosensitive member 51 after transfer is large, and the force for attracting the residual charge in the organic photosensitive layer 512 to the surface of the photosensitive member 51 is smaller than the case where the transfer current value is small. Too weak. Therefore, the moving speed of the residual charge is slow, and for example, the residual charge generated by the contact with the cleaner 56 may not reach the surface of the photosensitive member 51 before reaching the charging range. Therefore, the larger the transfer current value, the more likely the residual charge remaining on the photosensitive member 51 in the charging range.

  Therefore, the printer 100 acquires a first correction value for correcting the charging voltage in accordance with the transfer current value acquired in S203 (S204). The first correction value is one of the correction values for adding to the reference charging voltage to determine the charging voltage, as described later. That is, if the other conditions are the same, the difference between the first correction values is equal to the difference between the charging voltages. The printer 100 stores, for example, in the ROM 32 or the NVRAM 34, a table 61 indicating the first correction value corresponding to the determined transfer current value, as shown in FIG.

  As for the relationship between the transfer current value and the first correction value, as shown in FIG. 8, the larger the transfer current value, the larger the first correction value. However, the relationship between the transfer current value and the first correction value is not linear. That is, the change width of the first correction value when the transfer current value changes by the same amount is larger as the transfer current value is larger. As shown in FIG. 7, the larger the transfer current value, the larger the decrease in the surface potential of the photosensitive member 51 before and after transfer. In FIG. 8, the difference between the first correction value and the first correction value of the transfer current value before and after that is shown on the right side of the table 61 when the transfer current value is changed by 5 μA.

  For example, the first correction value is 210 V when the transfer current value is 30 μA, and the first correction value is 80 V when the transfer current value is 20 μA. And, the difference between these first correction values is 130V. On the other hand, the first correction value is 80 V when the transfer current value is 20 μA, and the first correction value is 30 V when the transfer current value is 10 μA. The difference between these first correction values is 50V. That is, when the transfer current value is changed by 10 μA, which is the same change width, the difference between the corresponding first correction values is larger as the transfer current value is larger.

  In this example, the first transfer current is 30 μA, the second transfer current and the third transfer current are 20 μA, and the fourth transfer current is 10 μA. The predetermined amount which is the change width of the transfer current value is 10 μA. The difference between the first correction value of the first transfer current and the first correction value of the second transfer current corresponds to a first difference. That is, the first difference is 130V. The difference between the first correction value of the third transfer current and the first correction value of the fourth transfer current corresponds to a second difference. That is, the second difference is 50V. Therefore, the first difference is larger than the second difference.

  Next, the printer 100 acquires the rotational speed of the photosensitive member 51 (S206). The printer 100 determines the rotational speed of the photosensitive member 51 in accordance with the print setting and the like of the print job. For example, when the printing paper is set to thick paper, the printer 100 sets the rotational speed to half speed.

  When the rotational speed of the photosensitive member 51 is high, even if the moving speed of the residual charge in the organic photosensitive layer 512 is the same, the corresponding position of the photosensitive member 51 falls within the charging range faster than the residual charge reaches the surface. There is a possibility to reach. That is, the higher the rotational speed of the photosensitive member 51, the higher the possibility that the residual charge will be large in the charging range.

  Therefore, the printer 100 acquires a second correction value for correcting the charging voltage in accordance with the rotational speed acquired in S206 (S207). The second correction value is one of the correction values for adding to the reference charging voltage to determine the charging voltage, as in the first correction value described above. For example, as shown in FIG. 9, the printer 100 stores, in the ROM 32 or the NVRAM 34, a table 62 indicating the second correction value corresponding to the acquired rotational speed.

  The relationship between the rotational speed and the second correction value is such that the larger the rotational speed, the larger the second correction value. As described above, since the reference charging voltage is determined under the condition that the rotation speed is full speed, the second correction value is 0 when the rotation speed is full speed, and the second correction value when the rotation speed is half speed The correction value is a negative value.

  Next, the printer 100 acquires the temperature of the photosensitive member 51 (S209). For example, the printer 100 acquires the temperature of the photosensitive member 51 based on the output signal of a temperature sensor that detects the temperature in the apparatus. The printer 100 may acquire the temperature of the photosensitive member 51 by, for example, directly detecting the surface temperature of the photosensitive member 51, or may estimate the temperature outside the apparatus or inside the apparatus. , And may be estimated based on the season, time, etc.

  When the temperature of the organic photosensitive layer 512 of the photosensitive member 51 is low, the moving speed of the residual charge is slow. When the moving speed is slow, it takes time for the residual charge to reach the surface of the photosensitive member 51, and there are many residual charges that do not reach the surface of the photosensitive member 51 until the corresponding portion of the photosensitive member 51 enters the charging range. there is a possibility. That is, the lower the temperature of the photosensitive member 51, the higher the possibility that the residual charge is large in the charging range.

  The printer 100 acquires a third correction value for correcting the charging voltage in response to the temperature acquired in S209 (S210). The third correction value is one of the correction values for adding to the reference charging voltage to determine the charging voltage, as with the first correction value and the second correction value described above. For example, as shown in FIG. 10, the printer 100 stores, in the ROM 32 or the NVRAM 34, a table 63 indicating the third correction value corresponding to the acquired temperature. In the relationship between the temperature and the third correction value, the lower the temperature, the larger the third correction value.

  The printer 100 corrects the reference charging voltage acquired in S201 with the first correction value acquired in S204, the second correction value acquired in S207, and the third correction value acquired in S210. The charge voltage is stored in the RAM 33 or the like (S212). That is, the printer 100 stores a value obtained by adding the first correction value, the second correction value, and the third correction value to the reference charging voltage as the charging voltage in the RAM 33 or the like, and ends the charging control process. By adding the first correction value, the second correction value, and the third correction value to the reference charging voltage, the charging voltage has a larger value as the residual charge is larger in the charging range. That is, as the residual charge in the charging range is larger, the difference between the charging voltage and the target surface potential of the photosensitive member 51 is larger.

  The total value of the correction values to be added to the reference charging voltage may have the upper limit of the charge amount estimated to be generated by the frictional heat between the photosensitive member 51 and the cleaner 56. It is not preferable to apply a charging voltage that is too large, because the service life of the printer 100 may be shortened.

  Furthermore, the upper limit of the total value of the correction values is not limited to a fixed value, and a variable value that differs according to the cumulative number of printed sheets may be used. As the cumulative number of printed sheets increases, the protective layer protecting the surfaces of the photosensitive member 51 and the cleaner 56 may peel off, the frictional resistance may increase, and the frictional heat may also increase. That is, the amount of charge estimated to be generated by the frictional heat between the photosensitive member 51 and the cleaner 56 is likely to increase according to the cumulative number of printed sheets.

  Returning to the printing process of FIG. 5, the printer 100 determines whether the warm-up has been completed (S103). Here, the completion of the warm-up is judged by whether or not the fixing device 8 has reached a predetermined temperature. If it is determined that the warm-up is not completed (S103: NO), the printer 100 continues the warm-up. On the other hand, when it is determined that the warm-up is completed (S103: YES), the printer 100 reads the charging voltage stored in the RAM 33 or the like in the charging control processing of S102 from the RAM 33 or the like, and reads the charging voltage. The voltage is applied to the grid of the charging device 52 (S105). Then, the printer 100 executes printing of one sheet (S106).

  Further, the printer 100 determines whether the printing of the received print job is completed (S107). When it is determined that the printing has not been completed (S107: NO), the printer 100 returns to S106 and prints one more sheet with the same charging voltage. The printer 100 applies a charging voltage only for a necessary period in accordance with the progress of printing and the conveyance of sheets. Then, in response to the determination that the print job has ended (S107: YES), the printer 100 ends the print processing.

  As described above in detail, the printer 100 according to the present embodiment sets the absolute value of the charging voltage to a larger value as the amount of residual charge present on the photosensitive member 51 in the charging range increases. As the amount of residual charge in the charging range increases, the voltage drop due to the residual charge tends to occur after charging. On the other hand, the larger the absolute value of the charging voltage, the larger the absolute value of the surface potential of the photosensitive member 51 after charging. Therefore, even if the residual charge reaches the surface of the photosensitive member 51 after charging and the surface potential of the photosensitive member 51 decreases, the surface potential of the photosensitive member 51 becomes equal to or higher than the target surface potential, and image quality deterioration can be expected to be suppressed.

  The present embodiment is merely an example and does not limit the present invention. Therefore, the present invention is naturally capable of various improvements and modifications without departing from the scope of the invention. For example, the present invention is not limited to a printer, and may be applied to any apparatus such as a copier, a scanner, a fax machine, etc. provided with an image forming function. Further, the present invention can be applied not only to color printers, but also to monochrome printers.

  Further, the target surface potential used in the present embodiment and the numerical values shown in the respective tables 61, 62, 63 are merely examples, and the present invention is not limited thereto. It may be appropriately selected in accordance with the material of the photosensitive member 51, the type of toner, and the like.

  Further, in the present embodiment, the printer 100 using positively chargeable toner has been described, but the present invention can also be applied to a printer using negatively chargeable toner. In such a case, the charge polarity and the polarity of the residual charge are reverse to those in the present embodiment. Therefore, each correction value for correcting the charging voltage is also a value obtained by reversing the positive and negative values with respect to the value of the present embodiment.

  The reference charging voltage is not limited to a fixed value, and may be a variable value that is changed according to humidity, temperature, and paper type. Further, in the present embodiment, one value is stored as the reference charging voltage. However, different reference charging voltages may be prepared for each transfer current value or environmental temperature. For example, a reference charging voltage to be applied may be stored for each transfer current value, and correction may be made based on the environmental temperature and the rotational speed. Alternatively, the charging voltage to be applied may be determined and stored for each combination of all the conditions, and the charging voltage may be read and set according to the conditions.

  Further, in the printer 100 according to the present embodiment, the correction value is stored for each of the various conditions. However, the correction ratio may be stored instead of the correction value. Then, the charging voltage may be determined by multiplying the reference charging voltage by the correction ratio.

  Further, in the present embodiment, the grid voltage of the charging device 52 is controlled in accordance with the amount of residual charge, but it may be controlled by controlling the wire current. That is, when it is determined that the residual charge is large in the charging range, the wire current may be increased instead of increasing the grid voltage. The present invention is applicable not only to the scorotron charging device but also to a contact charging device using a corotron charging device, a charging roller, a charging brush or the like.

  Further, not all of the transfer current, the rotational speed and the temperature may be used to set the charging voltage or the charging current. For example, one or more of these may be used to set the charging voltage or charging current.

  Further, in the printer 100 according to the present embodiment, the photosensitive body 51 has a single layer structure of the organic photosensitive layer 512 including the charge generating agent 513 and the charge transporting agent 514, but the invention is not limited thereto. For example, a two-layer structure having a transport layer containing no charge generating agent 513 and containing a charge transporting material 514 from the side of the metal core 511 and a generating layer containing a charge generating agent 513 and a charge transporting agent 514 It may be. In addition, for example, a structure of three or more layers including a surface layer and the like may be used.

  Further, the contact member is not limited to the blade-like cleaner 56. However, if the cleaner 56 is a blade member, charges tend to be generated and residual charges tend to be large in the charging range, as compared to a printer having a roller member and a brush member. Accordingly, the present invention is particularly useful in a printer 100 having a cleaner 56 by a blade member.

  Also, the charging voltage may be controlled while the job is being executed. For example, the charging voltage may be reduced if the temperature in the apparatus rises above a predetermined range during job execution. Further, for example, the charge control process may be executed for each printing of one sheet.

  Also, the processing disclosed in the embodiment may be executed by a single CPU, multiple CPUs, hardware such as an ASIC, or a combination thereof. Further, the processing disclosed in the embodiment can be realized in various modes such as a recording medium recording a program for executing the processing or a method.

31 CPU
Reference Signs List 51 photo conductor 52 charging device 54 developing device 55 transfer device 56 cleaner 100 printer

Claims (12)

With the photoreceptor,
A charging device for charging the surface of the photosensitive member;
A toner supply device for supplying toner to the photosensitive member;
A transfer device for transferring the toner on the photosensitive member to a transfer material;
A contact member in contact with the photosensitive member;
Control unit,
Equipped with
The control unit
As the residual charge, which is the charge present on the photosensitive member, increases in the charging range which is the range in which the charging device is charged in the rotational direction of the photosensitive member, the absolute value or charging value of the charging voltage used for the charging device Set the absolute value of the current to a large value,
Furthermore, the control unit
It is determined that the residual charge is greater in the charging range as the temperature of the photosensitive member is lower,
An image forming apparatus characterized by In the image forming apparatus according to claim 1,
The absolute value of the charging voltage or the absolute value of the charging current used in the charging device is the target surface potential of the photoconductor even if the surface potential of the photoconductor is offset by the residual charge after passing through the charging device. An image forming apparatus characterized by the above values. The image forming apparatus according to claim 1 or 2
The control unit
The image forming apparatus, wherein it is determined that the residual charge is larger in the charging range as the transfer current used in the transfer device is larger. In the image forming apparatus according to claim 3,
The control unit
The first difference, which is the difference between the charging voltage for the first transfer current and the charging voltage for the second transfer current that is smaller than the first transfer current by a predetermined amount, is equal to or less than the second transfer current The third embodiment is characterized in that it is larger than a second difference which is a difference between the charging voltage in the case of the third transfer current and the charging voltage in the case of the fourth transfer current which is smaller than the third transfer current by the predetermined amount. Image forming device. The image forming apparatus according to any one of claims 1 to 4,
The control unit
The image forming apparatus, wherein the residual charge is judged to be larger in the charging range as the rotational speed of the photosensitive member is higher. The image forming apparatus according to any one of claims 1 to 5,
The control unit
An image forming apparatus, wherein the charging voltage is set such that the difference with respect to the target surface potential of the photosensitive member is larger as the residual charge is larger in the charging range. The image forming apparatus according to any one of claims 1 to 5,
The control unit
An image forming apparatus, wherein a sum of a reference charging voltage and a correction value is set as the charging voltage, and the correction value is increased as the residual charge increases in the charging range. In the image forming apparatus according to claim 7,
The image forming apparatus according to claim 1, wherein the contact member is a cleaning blade that removes toner on the photosensitive member. In the image forming apparatus according to claim 8 ,
The upper limit of the correction value is a larger value as the cumulative number of printed sheets is larger. The image forming apparatus according to any one of claims 7 to 9 ,
The correction value is a value equal to or more than the charge amount of the charge moving to the surface of the photosensitive member from the charging range to the supply position where the toner supply device supplies the toner among the residual charge. An image forming apparatus characterized in that With the photoreceptor,
A charging device for charging the surface of the photosensitive member;
A toner supply device for supplying toner to the photosensitive member;
A transfer device for transferring the toner on the photosensitive member to a transfer material;
A contact member in contact with the photosensitive member;
An image forming method of an image forming apparatus comprising
As the residual charge, which is the charge present on the photosensitive member, increases in the charging range which is the range in which the charging device is charged in the rotational direction of the photosensitive member, the absolute value or charging value of the charging voltage used for the charging device Including setting steps to set the absolute value of the current to a large value,
In the setting step, it is determined that the residual charge is larger in the charging range as the temperature of the photosensitive body is lower.
An image forming method characterized by With the photoreceptor,
A charging device for charging the surface of the photosensitive member;
A toner supply device for supplying toner to the photosensitive member;
A transfer device for transferring the toner on the photosensitive member to a transfer material;
A contact member in contact with the photosensitive member;
Image forming apparatus having the
As the residual charge, which is the charge present on the photosensitive member, increases in the charging range which is the range in which the charging device is charged in the rotational direction of the photosensitive member, the absolute value or charging value of the charging voltage used for the charging device Execute setting processing to set the absolute value of the current to a large value,
In the setting process, it is determined that the residual charge is larger in the charging range as the temperature of the photosensitive member is lower.
A program characterized by

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