Image forming apparatus

Abstract

An image forming apparatus is disclosed. An image forming apparatus includes an image bearing member, a developing device, a transfer member, a transfer power supply, and a fixing device. The fixing device is provided with a heating source and a heating member in contact with a recording material in a fixing portion, and the heating source heats the recording material by the heating member by applying a voltage from an AC power source. A detector connected between the image bearing member and ground without interposing the transfer member detects the current or voltage. When the toner image is transferred from the image bearing member to the recording material in the transfer portion and the recording material is heated in the fixing portion, the controller controls the current output from the transfer power supply based on a detection result of the detection portion.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that applies an electrophotographic method, such as a printer, a copier, a fax machine, or a multifunction printer equipped with multiple functions among these functions. Background Art

[0002] In an image forming apparatus that applies an electrophotographic method, a toner image carried on an image carrier member (such as a drum-shaped photosensitive member or a belt-shaped intermediate transfer belt) is electrostatically transferred onto a recording material (such as paper or OHP) by applying a transfer voltage to a transfer member disposed opposite to the image carrier member. Thereafter, the recording material is conveyed to a fixing device, and is heated and pressurized at the fixing device, and the toner image is fixed on the recording material. The transfer member forms a transfer nip portion (transfer portion) by contacting the image carrier member, and transfers the toner image from the image carrier member to the recording material clamped by the transfer nip portion. The fixing device is provided with a heating member having a heater (heating source) and a pressing member that contacts the heating member and forms a fixing nip portion (fixing portion), and heats the recording material clamped by the fixing nip portion. When heat is generated by applying an AC voltage from a commercial power supply to the heater, the heating member is heated to a temperature at which the toner image can be fixed on the recording material.

[0003] When the recording material is clamped in the fixing nip portion while the toner image is being transferred, the current flowing from the commercial power supply to the heating member, the recording material, and the image carrier member may overlap with the transfer current in the transfer nip portion and the transfer current may swing. This phenomenon is also referred to as "AC banding". Therefore, non-uniformity of transfer properties may occur, and image defects may occur in the image transferred onto the recording material, which are uneven densities (image non-uniformity) in the sub-scanning direction (the conveyance direction of the recording material).

[0004] Japanese Patent Application Laid-Open No. 2018-97273 discloses an image forming apparatus having a configuration in which the transfer power supply is controlled based on a result of comparing a frequency obtained from a detection result of a current detection component that detects a current flowing through a transfer member with a predetermined frequency range including the frequency of a commercial power supply.

[0005] In the configuration described in JP-A 2018-97273, the current flowing from the commercial power supply through the heating member, the recording material, and the transfer member to GND is detected, and the phase and amplitude of the transfer power supply are switched. In this configuration, image non-uniformity can be suppressed under the condition that the impedance of the transfer member is low. Summary of the Invention

[0006] The above object is achieved by an image forming apparatus according to the present invention. In summary, a representative configuration of the present invention is an image forming apparatus including: an image carrier member configured to carry a toner image; a developing device configured to supply toner to the image carrier member and form a toner image on the image carrier member; a transfer member configured to contact the image carrier member to form a transfer portion and transfer the toner image from the image carrier member to a recording material in the transfer portion; a transfer power supply configured to apply a voltage to the transfer member; a fixing device disposed on a downstream side of the transfer portion with respect to a conveyance direction of the recording material and configured to form a fixing portion for sandwiching the recording material, the fixing device being provided with a heating source for heating the recording material sandwiched by the fixing portion and a heating member that contacts the recording material in the fixing portion, and the heating source being heated by applying a voltage from an AC power supply so as to heat the recording material through the heating member; a detection portion connected between the image carrier member and a ground potential without inserting the transfer member and configured to detect a current or a voltage; and a control portion configured to control the transfer power supply, wherein when the toner image is transferred from the image carrier member to the recording material in the transfer portion and the recording material is heated in the fixing portion, the control portion controls a current output from the transfer power supply based on a detection result of the detection portion.

[0007] Another representative configuration of the present invention is an image forming apparatus including: an image carrier member configured to carry a toner image; a developing device configured to supply toner to the image carrier member and form a toner image on the image carrier member; an intermediate transfer member to which the toner image is transferred from the image carrier member and which is capable of moving cyclically; an opposing member that contacts an inner peripheral surface of the intermediate transfer member; a transfer member that contacts an outer peripheral surface of the intermediate transfer member, configured to form a transfer portion by sandwiching the intermediate transfer member between itself and the opposing member, and configured to transfer the toner image from the intermediate transfer member to a recording material in the transfer portion; a transfer power supply configured to apply a voltage to the transfer member; a fixing device disposed on a downstream side of the transfer portion with respect to a conveyance direction of the recording material and configured to form a fixing portion for sandwiching the recording material, the fixing device being provided with a heating source for heating the recording material sandwiched by the fixing portion and a heating member that contacts the recording material in the fixing portion, and the heating source being heated by applying a voltage from an AC power supply so as to heat the recording material through the heating member; a detection portion connected between the opposing member and a ground potential without inserting the transfer member and configured to detect a current or a voltage; and a control portion configured to control the transfer power supply, wherein when the toner image is transferred from the intermediate transfer member to the recording material in the transfer portion and the recording material is heated in the fixing portion, the control portion controls a current output from the transfer power supply based on a detection result of the detection portion.

[0008] More features of the present invention will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Part (a) of is a schematic cross-sectional view showing an image forming apparatus according to a first embodiment of the present invention, and Figure 1 Part (b) of is a schematic diagram showing a control configuration according to the first embodiment.

[0010] Figure 2 is a graph illustrating an appropriate range of current when transferring toner to a recording material.

[0011] Figure 3 is a schematic diagram when modeling elements related to AC striping by circuit elements in an image forming apparatus according to the first embodiment.

[0012] Figure 4 is a schematic graph illustrating the current detected by a current detection part when AC striping occurs.

[0013] Figure 5 is a schematic graph illustrating the occurrence of image defects caused by AC striping.

[0014] Figure 6 is a schematic diagram illustrating image defects caused by AC striping.

[0015] Figure 7 Parts (a), (b), (c), and (d) of are schematic graphs illustrating methods of suppressing AC striping.

[0016] Figure 8 is a schematic graph illustrating gain setting in control for suppressing AC striping.

[0017] Figure 9 is a flowchart illustrating a process of control for suppressing AC striping.

[0018] Figure 10 is a schematic cross-sectional view showing an image forming apparatus according to a second embodiment. DETAILED DESCRIPTION

[0019] Hereinafter, an image forming apparatus according to the present invention will be specifically described with reference to the drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described in the following embodiments can be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. That is, the scope of the present invention is not limited to the following embodiments.

[0020] [First Embodiment]

[0021] <Configuration of the image forming apparatus>

[0022] The schematic configuration of the image forming apparatus 1 according to the embodiment will be described by using Figure 1 parts (a) and (b). Figure 1 Part (a) is a schematic cross-sectional view showing the image forming apparatus 1 according to the embodiment, and Figure 1 part (b) is a schematic view showing the control configuration of the image forming apparatus 1 according to the embodiment. The image forming apparatus 1 according to the embodiment is a laser beam printer capable of forming a monochromatic black image on a sheet-shaped recording material R by using an electrophotographic method.

[0023] The photosensitive drum 11 is rotationally driven in the direction of arrow D (clockwise direction) in the figure at a predetermined circumferential speed (processing speed) by a drum driving motor (not shown in the figure) as a driving component. The photosensitive drum 11 is a drum-shaped photosensitive member (electrophotographic photosensitive member) as an image bearing member. The surface (outer circumferential surface) of the rotating photosensitive drum 11 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in the embodiment) by a charging roller 12 which is a roller-type charging member as a charging component. The charging roller 12 is arranged to contact the surface of the photosensitive drum 11 and rotates by the rotation of the photosensitive drum 11. During the charging process, a charging voltage (charging bias) is applied to the charging roller 12 by a charging power supply (not shown in the figure) as a charging voltage applying component. The surface of the charged photosensitive drum 11 is scanned and exposed by a scanner unit (exposure device) 14 as an exposure component (light irradiation component), and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 11. The scanner unit 14 irradiates the surface of the photosensitive drum 11 with laser according to an image signal and forms an electrostatic latent image on the photosensitive drum 11. The electrostatic latent image formed on the photosensitive drum 11 is developed (visualized) by a developing device 15 as a developing component. The developing device 15 supplies toner as a developer and forms a toner image (toner picture image, developer image) on the photosensitive drum 11. The developing device 15 includes a developing sleeve 15a as a developing member (developer carrying member) and a developer container 15b for accommodating toner. The developing sleeve 15a carries the toner in the developer container 15b to a portion (developing portion) opposite to the photosensitive drum 11 and attaches the toner to the electrostatic latent image on the photosensitive drum 11 to form a toner image. During development, a developing voltage (developing bias) is applied to the developing sleeve 15a by a developing power supply (not shown in the figure) as a developing voltage applying component. In the embodiment, toner charged with the same polarity as the charging polarity of the photosensitive drum 11 (negative polarity in the embodiment) attaches to the exposed area (image portion) of the photosensitive drum 11 where the absolute value of the potential decreases after exposure following uniform charging (inversion development method). In the embodiment, the normal polarity of the toner as the main charge polarity of the toner during the developing process is negative.

[0024] The transfer roller 17 is disposed at a position opposite to the photosensitive drum 11, and the transfer roller 17 is a roller-type transfer member as a transfer component. The transfer roller 17 contacts the surface of the photosensitive drum 11 and forms a transfer nip portion (transfer portion) Nt as a contact portion between the photosensitive drum 11 and the transfer roller 17. The toner image formed on the photosensitive drum 11 is transferred to the recording material R clamped and conveyed between the photosensitive drum 11 and the transfer roller 17 in the transfer nip portion Nt. During transfer, a transfer voltage (transfer bias) is applied to the transfer roller 17 by a transfer power supply 18 as a transfer voltage application component, and the transfer voltage is a DC voltage (DC voltage) having a polarity opposite to the normal charging polarity of the toner (positive polarity in the embodiment). Recording materials (transfer materials, recording media, sheets) such as paper and OHP are accommodated in a cassette 5 as a recording material accommodation portion. A pickup roller 6 as a feeding component sends out the recording material R from the cassette 5 to a conveyance path for the recording material R. A conveyance roller pair 7 and 8 as conveyance components adjust the timing for conveying the recording material R sent out by the pickup roller 6 to the transfer nip portion Nt. And in the transfer nip portion Nt, the toner image is transferred from the photosensitive drum 11 to the recording material R conveyed by the conveyance roller pair 7 and 8. When the core metal portion of the photosensitive drum 11 is electrically connected to a sheet metal portion (not shown in the figure) such as a frame of the image forming apparatus 1, the photosensitive drum 11 is connected (electrically grounded) to GND (ground potential). And in the embodiment, a current detection portion (current detection circuit) 13 as a current detection component is provided between the core metal portion of the photosensitive drum 11 and GND. The current detection portion 13 is connected between the photosensitive drum 11 and GND without inserting the transfer roller 17. That is, the current detection portion 13 is connected between the photosensitive drum 11 and GND in a current path from the transfer power supply 18 through the transfer roller 17 and the photosensitive drum 11 to GND.

[0025] After the static charge accumulated on the surface of the recording material R is removed by the neutralization member 19, the recording material R onto which the toner image is transferred is conveyed to a fixing device 20 as a fixing component. The toner (transfer residual toner) remaining on the surface of the photosensitive drum 11 after the toner image is transferred to the recording material R is removed (cleaned) and collected from the surface of the photosensitive drum 11 by a cleaning device 16 as a cleaning component. The cleaning device 16 includes a cleaning blade 16a as a cleaning component disposed to contact the surface of the photosensitive drum 11, and a cleaning container 16b. The cleaning device 16 scrapes off the transfer residual toner from the surface of the rotating photosensitive drum 11 by the cleaning blade 16a and stores it in the cleaning container 16b.

[0026] The fixing device 20 includes a heating member 21 provided with a heat source, and a pressure roller 24 as a pressing member that contacts the heating member 21 and forms a fixing clamping portion (fixing portion) Nf. The heating member 21 is configured to include a fixing film 22 as a first fixing member (first fixing rotatable member), and a heater 23 as a heat source. The heater 23 contacts the pressure roller 24 as a second fixing member (second fixing rotatable member) via the fixing film 22. The heating clamping member is configured by the fixing film 22 as the first fixing member and the pressure roller 24 as the second fixing member. When the heater 23 generates heat by applying an alternating voltage (AC voltage) from a commercial power supply (AC power supply) 30 to the heater 23, the heating member 21 is heated to a temperature at which the toner image can be fixed on the recording material R. In addition, from the perspective of safety when contacted by the user and the breaking strength when a lightning surge is applied from the commercial power supply 30, the pressure roller 24 is connected to GND (electrical ground) via an electronic part 25. When the pressure roller 24 is pressed against the heater 23 via the fixing film 22, a fixing clamping portion Nf is formed as a contact portion between the fixing film 22 and the pressure roller 24. The pressure roller 24 is rotationally driven in the direction of arrow F (counterclockwise direction) in the figure by a fixing drive motor (not shown in the figure) as a driving component. The fixing film 22 is rotationally driven by the rotation of the pressure roller 24 while sliding on the heater 23. For the heater 23, any available configuration such as a known device can be used, for example. For example, the heater 23 includes a plate, an electrode portion to which a voltage from an AC power supply is applied, and a heating resistor formed on the surface of the plate. When current flows through the electrode portion by applying a voltage from the AC power supply to the electrode portion, the heating resistor generates heat. When heat is generated by the heating resistor, the heater 23 can heat the recording material R clamped by the fixing clamping portion Nf. The fixing device 20 heats and presses the recording material R with the toner image transferred thereon by clamping and conveying it between the fixing film 22 and the pressure roller 24 at the fixing clamping portion Nf, and fixes (melts, adheres) the toner image on the recording material R.

[0027] After the toner image is fixed by the fixing device 20, the recording material R is discharged (output) to a discharge tray 3 as a discharge portion, and the discharge tray 3 is provided on the outside (top surface) of the main unit (hereinafter simply referred to as the main unit) 2 of the image forming apparatus 1.

[0028] In an embodiment, the photosensitive drum 11, the charging roller 12 as a processing component acting on the photosensitive drum, the developing device 15, and the cleaning device 16 are configured as a processing cartridge 4 that can be detachably removed from the main assembly 2. For example, in a case where the amount of toner in the toner container 15b accommodated in the developing device 15 becomes less than a predetermined amount, in a case where the photosensitive drum 11 reaches the end of its life, or in a case where the developing sleeve 15a reaches the end of its life, etc., the processing cartridge 4 is replaced with a new processing cartridge. Incidentally, in the embodiment, the main assembly 2 is the part of the image forming apparatus 1 other than the processing cartridge 4.

[0029] The environment sensor 9 is provided in the image forming apparatus 1. In the embodiment, the environment sensor 9 is capable of detecting the temperature and humidity of the surrounding environment of the image forming apparatus 1. Incidentally, the environment sensor 9 is one example of an environment detection component (environment detection section) that detects environment information, and the environment information is at least one of the temperature or humidity in at least one of the inside or outside of the image forming apparatus 1.

[0030] In addition, the image forming apparatus 1 is provided with a control section (control circuit) 10 as a control component. The control section 10 is configured to include a CPU 10a as a calculation control section, a memory section 10b, and a transfer power control section 10c. The memory section 10b is configured by a ROM, a RAM, a non-volatile memory, etc. A print start instruction and an image signal are sent to the control section 10 from an external device (not shown in the figure) such as a personal computer. When the control section 10 controls each part of the image forming apparatus 1 based on the input print start instruction and image signal, the image forming apparatus 1 performs image formation. The memory section 10b stores programs and data related to image formation, and the CPU 10a controls each part of the image forming apparatus 1 according to the programs and data.

[0031] The detection information (detection signal) obtained by the current detection section 13 and the detection information obtained by the environment sensor 9 are respectively input to the control section 10. The current detection information input from the current detection section 13 to the control section 10 is converted into a digital value by the analog / digital (A / D) conversion section of the CPU 10a. The CPU 10a obtains the A / D-converted current detection information at a predetermined interval. The humidity and temperature information input from the environment sensor 9 to the control section 10 is also converted into a digital value by the A / D conversion section of the CPU 10a in the same manner as the current detection information, and is obtained by the CPU 10a. In addition, in the embodiment, the memory section 10b stores the cumulative number of sheets printed using the photosensitive drum 11 as the cumulative usage information of the replaceable photosensitive drum 11. In addition, in the embodiment, the memory section 10b stores the cumulative number of sheets printed using the transfer roller 17 (main unit 2) as the cumulative usage information of the transfer roller 17 (main unit 2). Incidentally, the cumulative number of printed sheets is one example of an index value (a value related to the cumulative usage information) related to the usage amount of the image forming apparatus 1 and the elements of the image forming apparatus 1. In addition, for example, the cumulative number of printed sheets can be added by counting the case where an image is formed on one surface of a recording material R of a predetermined size as one sheet. In addition, when the photosensitive drum 11 is replaced together with the charging roller 12, the developing device 15, etc., the cumulative number of sheets printed by the photosensitive drum 11 is reset to an initial value (zero in the embodiment). The CPU 10a uses the current detection information, the humidity and temperature information, and the information on the cumulative number of printed sheets, and outputs a signal required for controlling the transfer power supply 18 to the transfer power control section 10c. Details thereof will be explained later.

[0032] Incidentally, since paper is mainly used as the recording material R for the image forming apparatus 1, the recording material R is sometimes referred to as paper. However, the recording material R is not limited to paper. For the recording material R, for example, a material made of a material other than paper or including a material other than paper, such as a film mainly made of a synthetic resin or synthetic paper, or a special paper such as metallized paper including a metal layer, can also be used.

[0033] In addition, the index value (the value related to the cumulative usage information) related to the usage amount of the image forming device 1 or the elements of the image forming device 1 is not limited to the cumulative number of printed sheets. For example, it can be a value related to the amount of toner consumed or the remaining amount of toner in the developing device 15. In addition, for example, it can be the number of rotations or the rotation time of the photosensitive drum 11, the number of rotations during the charging process of the photosensitive drum 11, or the rotation time during the charging process of the photosensitive drum 11, and so on.

[0034] <Transfer mechanism>

[0035] Next, the mechanism for transferring the toner from the photosensitive drum 11 to the recording material R will be described.

[0036] When the recording material R is sandwiched between the photosensitive drum 11 and the transfer roller 17 while the toner is on the photosensitive drum 11, a voltage opposite in polarity to the toner is applied from the side of the recording material R opposite to the side where the toner is transferred. In this way, a current flows between the photosensitive drum 11 and the recording material R, and the toner is transferred to the recording material R. At this time, since the current flowing through the transfer clamping portion Nt changes according to the value of the resistance (impedance, the same applies hereinafter) of the recording material R, image defects may occur when it is not properly set.

[0037] <Method for setting transfer current and transfer voltage>

[0038] Next, by using Figure 2 and Figure 3 the method for setting the transfer voltage according to the embodiment will be described. Figure 2 is a graph showing the relationship between the resistance value of the recording material R and the current output from the transfer power supply 18. This graph shows that the appropriate range of the current flowing from the transfer roller 17 to the recording material R when transferring the toner image from the photosensitive drum 11 to the recording material R varies according to the resistance value of the recording material R. Additionally, Figure 3 is a schematic diagram modeling the elements around the transfer clamping portion Nt and the fixing clamping portion Nf according to the embodiment of the image forming apparatus 1 by using circuit elements.

[0039] In Figure 3 the capacitance (capacitance value, the same applies hereinafter) component of the heating member 21 of the fixing device 20, which is mainly the capacitance component of the heater 23 in the embodiment, is defined as the capacitor 23a, the resistance component of the pressure roller 24 is defined as the resistor 24a, the ground resistance between the pressure roller 24 and GND is defined as the resistor 25a, and the ground capacitance is defined as the capacitor 25b. Additionally, in Figure 3 the resistance component of the transfer roller 17 is defined as the resistor 17a, the capacitance component of the transfer roller 17 is defined as the capacitor 17b, the resistance component of the photosensitive drum 11 is defined as the resistor 11a, and the capacitance component of the photosensitive drum 11 is defined as the capacitor 11b. Additionally, in Figure 3 the resistor Rv represents the resistance value in the conveyance direction of the recording material R, and the resistor Rh represents the resistance value in the thickness direction of the recording material R. Additionally, as described above, the image forming apparatus 1 is provided with the current detection portion 13, and the detection result of the current detection portion 13 is input to the control portion 10. And according to the calculation result of the CPU 10a of the control portion 10, the output voltage of the transfer power supply 18 is controlled by the transfer power supply control portion 10c of the control portion 10.

[0040] Incidentally, the current detection section 13 can be configured to detect the current flowing to GND via the transfer power supply 18, the transfer roller 17, the recording material R, and the photosensitive drum 11, and the current flowing to GND via the heating member 21 (heater 23), the recording material R, and the photosensitive drum 11 (more specifically, the current in which the current flowing to GND via the transfer power supply 18, the transfer roller 17, the recording material R, and the photosensitive drum 11 and the current flowing to GND via the heating member 21 (heater 23), the recording material R, and the photosensitive drum 11 are superimposed). Specifically, for example, a high-pass filter (HPF) circuit using an application coupling capacitor and an operational amplifier or the like can be used.

[0041] Here, the resistance value and capacitance value of the recording material R and the transfer roller 17 change according to the environment. Generally, in a high-temperature and high-humidity environment, the resistance value decreases. In addition, since the photosensitive drum 11 also contacts the transfer roller 17 and the recording material R, the resistance value and capacitance value change due to wear and the like as the cumulative number of printed sheets increases. For example, as the number of printed sheets increases, the capacitance value of the photosensitive drum 11 increases. In addition, as the cumulative number of printed sheets increases, the resistance value and capacitance value of the transfer roller 17 also change due to contamination and uneven distribution of the conductive agent. For example, as the cumulative number of printed sheets increases, the resistance value of the transfer roller 17 increases.

[0042] Hereinafter, the recording material R whose resistance decreases due to moisture absorption is defined as "moisture-absorbing paper", and the recording material R whose resistance does not decrease because it has just been unpacked and has not absorbed moisture is defined as "just-opened paper". As Figure 2 shown, the appropriate range of the value of the current flowing from the transfer roller 17 to the recording material R varies according to the surrounding environment. The current flowing from the transfer roller 17 is injected into the recording material R and flows toward the photosensitive drum 11. Here, since the moisture-absorbing paper has a lower resistance than the just-opened paper, the current injected from the transfer power supply 18 via the resistor 17a into the resistor Rh flows more to the resistor RV in Figure 3 . That is, the current injected from the transfer roller 17 into the recording material R flows, for example, via the moisture-absorbing paper to the ground resistor 25a or the ground capacitor 25b between the pressure roller 24 and GND, and the current flowing from the recording material R toward the photosensitive drum 11 may be insufficient. Therefore, it is necessary to apply a higher voltage from the transfer power supply 18 to the transfer roller 17 because more current needs to be applied from the transfer roller 17 to the moisture-absorbing paper. On the other hand, since the resistance of the just-opened paper is higher than that of the moisture-absorbing paper, the current flowing from the transfer power supply 18 via the resistor 17a and the resistor Rh to the resistor Rv decreases. Therefore, the voltage applied from the transfer power supply 18 to the transfer roller 17 can be set lower than in the case of the moisture-absorbing paper.

[0043] In the case where the output voltage of the transfer power supply 18 is set to the same voltage for freshly opened paper as for moisture-absorbed paper, since the current injected from the transfer roller 17 into the recording material R and flowing to the photosensitive drum 11 becomes excessive, the polarity of the toner in the transfer nip portion Nt may be reversed, and the toner may be transferred from the freshly opened paper to the photosensitive drum 11 conversely. Therefore, as Figure 2 shown, it is preferable that the value of the current injected from the transfer roller 17 into the recording material R is within an appropriate range C (shaded area). In the embodiment, the CPU 10a of the control section 10 sets a target current using the detection result of the environment sensor 9 and the cumulative usage information stored in the memory section 10b (in the embodiment, the cumulative number of sheets printed by the photosensitive drum 11 and the cumulative number of sheets printed by the transfer roller 17) so that a current within the appropriate range C flows to the transfer nip portion Nt. And, the transfer power control section 10c of the control section 10 performs constant current control of the transfer voltage applied from the transfer power supply 18 to the transfer roller 17 so that the current of the target current flows to the transfer nip portion Nt.

[0044] <Mechanism of image defects caused by AC banding>

[0045] Next, the mechanism of how image defects are caused by AC banding will be described by using Figures 4 to 6 to.

[0046] Figure 4 is a schematic graph showing the current flowing to the transfer nip portion Nt during printing. In Figure 4 , the time T1 is the time when the recording material R enters the transfer nip portion Nt, and the time T2 is the time when the recording material R enters the fixing nip portion Nf. From the time T1 to the time before T2, the recording material R is not clamped at the fixing nip portion Nf, and the AC current from the commercial power supply 30 is not superimposed on the transfer current, so the current flowing to the transfer nip portion Nt becomes a constant current. On the other hand, after the time T2 when the recording material R is clamped at both the transfer nip portion Nt and the fixing nip portion Nf, the AC current of the commercial power supply 30 is superimposed on the transfer current via the recording material R. Therefore, the current flowing to the transfer nip portion Nt swings with the frequency cycle of the commercial power supply 30 and causes AC banding.

[0047] Figure 5 is a schematic graph showing the occurrence of image defects caused by AC banding. In addition, Figure 6 is a schematic diagram of an image in which image defects are caused by AC banding. As described above, the control section 10 considers the humidity and temperature information obtained by the environment sensor 9, etc., and as Figure 5As shown by the solid line in the figure, the transfer voltage applied from the transfer power supply 18 to the transfer roller 17 is adjusted so that the current flowing to the transfer nip portion Nt remains within an appropriate range C. However, after time T2, the current flowing from the recording material R to the photosensitive drum 11 may exceed the appropriate range C due to the addition of the AC current from the commercial power supply 30. For example, in the case where the waveform is as shown by the dashed line in the figure, since the current flowing to the transfer nip portion Nt oscillates with the period of the frequency of the commercial power supply 30, the trough portion of the waveform becomes lower than the appropriate range C of the current when transferring the toner image. Therefore, for the period of the frequency of the commercial power supply 30, the current is insufficient, and as shown in the figure, after the recording material R enters the fixing nip portion Nf, uneven density (image unevenness) may be caused in the image transferred from the photosensitive drum 11 to the recording material R for the period of the frequency of the commercial power supply 30. Figure 5 In the case where the waveform is as shown by the dashed line in the figure, since the current flowing to the transfer nip portion Nt oscillates with the period of the frequency of the commercial power supply 30, the trough portion of the waveform becomes lower than the appropriate range C of the current when transferring the toner image. Therefore, for the period of the frequency of the commercial power supply 30, the current is insufficient, and as shown in the figure, after the recording material R enters the fixing nip portion Nf, uneven density (image unevenness) may be caused in the image transferred from the photosensitive drum 11 to the recording material R for the period of the frequency of the commercial power supply 30. Figure 6 as shown in the figure, after the recording material R enters the fixing nip portion Nf, uneven density (image unevenness) may be caused in the image transferred from the photosensitive drum 11 to the recording material R for the period of the frequency of the commercial power supply 30.

[0048] <Method for Suppressing Image Defects Caused by AC Banding>

[0049] Next, a method for suppressing image defects caused by AC banding in the embodiment will be described by using Figures 7 to 9 The waveforms when AC banding occurs are all schematically shown in parts (a) to (d) of the figure, and the waveforms in the case of applying the control according to the embodiment are indicated by solid lines and the waveforms in the case of not applying the control according to the embodiment are indicated by dashed lines.

[0050] Figure 7 The waveforms when AC banding occurs are all schematically shown in parts (a) to (d) of the figure, and the waveforms in the case of applying the control according to the embodiment are indicated by solid lines and the waveforms in the case of not applying the control according to the embodiment are indicated by dashed lines. Figure 7 Part (a) of the figure shows the waveform of the current "I 进入 " flowing from the commercial power supply 30 to the transfer nip portion Nt, Figure 7 Part (b) of the figure shows the waveform of the output current "I 转印 " of the transfer power supply 18, Figure 7 Part (c) of the figure shows the waveform of the current "I Nt " in the transfer nip portion, and Figure 7 Part (d) of the figure shows the waveform of the current amplitude "ΔI" detected by the current detection portion 13.

[0051] The current (I Nt ) in the transfer nip portion Nt is the superposition of a part of the current (I 进入 ) flowing from the commercial power supply 30 to the transfer nip portion Nt and a part of the output current (I 转印 ) of the transfer power supply 18. In the case of not applying the control in the embodiment, as shown in the figure Figure 7As shown by the dashed line in part (c), the AC current (alternating current) from the commercial power supply 30 is superimposed on the DC current (direct current) from the transfer power supply 18, and the current (I Nt ) at the transfer clamping portion Nt swings. As described by using Figure 5 , when the current amplitude is large and exceeds the appropriate range C, image non-uniformity due to AC banding may occur.

[0052] Therefore, in the embodiment, as Figure 7 shown by the solid line in part (b), based on Figure 7 the current amplitude (ΔI) shown by the dashed line in part (d), the output current (I 转印 ) of the transfer power supply 18 is controlled (details will be described below). Therefore, as Figure 7 shown by the solid line in part (d), since the current amplitude (ΔI) of the current detection portion 13 decreases, as Figure 7 shown by the solid line in part (c), the fluctuation of the current (I Nt ) at the transfer clamping portion Nt can also be suppressed.

[0053] Figure 8 is a schematic graph showing an example of the current amplitude (ΔI) of the current detection portion 13 and the output current (I 转印 ) of the transfer power supply 18 when AC banding occurs.

[0054] As Figure 8 shown, when the output current of the transfer power supply 18 without suppressing AC banding is the solid line that is the same as the initial transfer target current (I S ), the detection result of the current amplitude (ΔI) of the current detection portion 13 is shown as white circles and a dotted line. In principle, AC banding can be suppressed by resetting the difference between the white circles and the dotted line of the current amplitude (ΔI) and the solid line of the initial transfer target current (I S ) as the final transfer current target value (I T ) reflecting the suppression of AC banding.

[0055] However, in practice, it is preferable to determine the correction amount of the transfer current target value (I 转印 ) of the output current (I T ) of the transfer power supply 18 by using the following three parameters.

[0056] I. The change in the current amplitude caused by the impedance of the resistance component 17a and the capacitance component 17b of the transfer roller 17, the resistance Rh of the recording material R, and the resistance component 11a and the capacitance component 11b of the photosensitive drum 11.

[0057] II. Current phase delay caused by the capacitance component 17b of the transfer roller 17 and the capacitance component 11b of the photosensitive drum 11.

[0058] III. Response delay of the circuit from the output of the transfer power supply 18 to the transfer clamping portion Nt.

[0059] The target value of the transfer current is corrected by multiplying the current amplitude (ΔI) obtained by the current detection section 13 by the gain determined by these parameters. Here, the gain can be expressed by the following formula 1.

[0060] Gain = Gain Ref x Env x K (Formula 1)

[0061] (Gain Ref : Gain in a normal temperature and humidity environment, Env: Environment coefficient, K: Cumulative usage coefficient)

[0062] Gain Ref is the correction gain as a reference and is predetermined based on factors such as the circuit response delay and circuit gain of the transfer power supply 18 and the representative temperature and humidity (e.g., 23 °C, 50% RH).

[0063] Env is a coefficient representing the change in impedance of at least one of the transfer roller 17, the recording material R, the photosensitive drum 11, etc. due to the environment, and is determined based on the humidity and temperature information (in addition, information on the type of the recording material R) obtained by the environment sensor 9. Incidentally, in the embodiment, Env is determined based on the impedance selected from a table showing the relationship between the humidity temperature information and the impedance of at least one of the transfer roller 17, the recording material R, the photosensitive drum 11, etc., and this table is pre-calculated and pre-stored in the memory section 10b. However, the method for determining Env is not limited to this. For example, Env can be determined based on the impedance calculated based on information such as the voltage of the transfer power supply 18, the humidity and temperature information, and the rate of change in the impedance of at least one of the transfer roller 17, the recording material R, the photosensitive drum 11, etc. due to the voltage of the transfer power supply 18 and the humidity and temperature information. Additionally, for example, Env can be selected from a table showing the relationship between the environment information and Env reflecting the change in impedance, which is pre-calculated and stored in the memory section 10b. Incidentally, in the embodiment, information on the type of the recording material R is input to the control section 10 from an external device together with the print start instruction, the image signal, and the print settings. Here, the type of the recording material R includes any information that can distinguish the recording material R, such as attributes based on general characteristics (i.e., so-called paper type categories) (such as plain paper, coated paper, cardboard, and synthetic paper), numerical values and numerical ranges (such as basis weight and thickness), and brand names (including manufacturers and product numbers).

[0064] K is a coefficient in the case where a phase delay of a current occurs due to a change in at least one of a capacitance component 17b of the transfer roller 17 or a capacitance component 11b of the photosensitive drum 11 caused by an increase in the cumulative usage amount through the main component 2 or toner consumption. K is determined based on the cumulative number of printed sheets stored in the memory section 10b (at least one of the information on the cumulative number of sheets printed by the photosensitive drum 11 and the information on the cumulative number of sheets printed by the transfer roller 17). In the embodiment, K is determined based on the change rate of the capacitance component selected from the following table. The table shows the relationship between the cumulative number of printed sheets (at least one of the information on the cumulative number of sheets printed by the replaceable photosensitive drum 11 and the information on the cumulative number of sheets printed by the transfer roller 17 (main component 2)) pre-calculated and pre-stored in the memory section 10b and the change rate of at least one of the capacitance components of the photosensitive drum 11 and the transfer roller 17 for each cumulative number of printed sheets (i.e., according to the increase in the cumulative number of printed sheets). However, the method for determining K is not limited to this. For example, K is determined based on the change rate of the capacitance component calculated from the following information: such as cumulative usage amount information (at least one of the cumulative usage amount information of the photosensitive drum 11 and the cumulative usage amount information of the transfer roller 17 (main component 2)) and the change rate of at least one of the capacitance components of the photosensitive drum 11 and the transfer roller 17 caused by the cumulative usage amount information. Additionally, K can be selected from a table showing the relationship between the cumulative usage information pre-calculated and stored in the memory section 10b and K reflecting the change in the capacitance component described above).

[0065] By multiplying the current amplitude (ΔI) of the current detection section 13 by the gain determined as described above, the output current (I 转印 ) of the transfer power supply 18 becomes a waveform with a phase inversion of the current amplitude (ΔI) as shown by the black circle and the dashed line in Figure 8 .

[0066] In this way, in the embodiment, the control section 10 switches the voltage applied from the transfer power supply 18 to the transfer roller 17 to match the phase of the power frequency of the commercial power supply 30. That is, within the time corresponding to the trough of the waveform of the current amplitude (ΔI), the voltage applied from the transfer power supply 18 to the transfer roller 17 is greater than the voltage applied to the transfer roller 17 when the control for suppressing AC banding is not performed. Additionally, within the time corresponding to the peak of the waveform of the current amplitude (ΔI), the voltage applied from the transfer power supply 18 to the transfer roller 17 is less than the voltage applied to the transfer roller 17 when the control for suppressing AC banding is not performed. Therefore, the voltage applied from the transfer power supply 18 to the transfer roller 17 is periodically controlled to match the phase of the power frequency of the commercial power supply 30, and as Figure 7As shown by the solid line in part (c), fluctuations in the current in the transfer clamping portion Nt can be suppressed.

[0067] Figure 9 It is a flowchart of control for detecting the current amplitude (ΔI) at the current detection portion 13 in the example and suppressing AC banding.

[0068] <Step 1>

[0069] In this step, parameters required for performing constant current control of the transfer power supply 18 are determined. First, the CPU 10a acquires, at the start of printing, the environmental information obtained by the environmental sensor 9 that has been converted into a digital value by the A / D conversion portion, and determines an environmental coefficient Env (S101) based on a table showing the relationship between humidity and temperature information and impedance, which is pre-stored in the memory portion 10b. Thereafter, similarly, the CPU 10a determines an accumulated usage coefficient K (S102) based on a table showing the relationship between the information on the accumulated number of sheets printed on the replaceable photosensitive drum 11 stored in the memory portion 10b, the information on the accumulated number of sheets printed on the transfer roller 17, and the rate of change in the capacitance component for each printed sheet number. Next, the CPU 10a determines, based on the type of the recording material R, the print setting information, etc., an initial transfer current target value (I S ) as a standard, and substitutes it with the final transfer current target value (I T ) (S103).

[0070] <Step 2>

[0071] In this step, the final transfer current target value (I T ) is calculated in consideration of suppressing AC banding. The CPU 10a acquires the current amplitude (ΔI) detected by the current detection portion 13 and converted into a digital value by the A / D conversion portion (S201). Next, the CPU 10a calculates an AC banding correction value (ΔI out [[ID=2)4]]) based on the acquired current amplitude (ΔI) and the gain calculated in Step 1 (S202). And the CPU 10a calculates the difference between the final transfer current target value (I T ) and the AC banding correction value (ΔI out ), and outputs a signal required to control the transfer power supply 18 from the transfer power supply control portion 10c so that the output current (I 转印 ) of the transfer power supply 18 becomes the final transfer current target value (I T ) (S203).

[0072] Here, the transfer power supply 18 and the transfer power supply control section 10c according to an embodiment will be briefly described. The transfer power supply 18 according to the embodiment is a power supply circuit that applies a flyback transformer, and controls the current to become a desired current while intermittently flowing the current flowing through the primary coil of the flyback transformer by a switching component. At this time, by sending a PWM signal from the transfer power supply control section 10c to the switching component, the intermittent current is sent to the primary coil of the flyback transformer. The transfer power supply 18 is provided with a constant current detection circuit section (not shown in the figure) that detects the output current (I 转印 ). And the CPU 10a adjusts the duty ratio of the PWM signal sent from the transfer power supply control section 10c to the transfer power supply 18 so that the output current (I 转印 ) detected by the constant current detection circuit section and separately input to the CPU 10a from the detection result of the current detection section 13 becomes the transfer current target value (I T ). In the embodiment, an example of applying a flyback transformer is introduced, however, it is not limited thereto. As long as the transfer power supply 18 can be controlled so that the output current (I 转印 ) of the transfer power supply 18 becomes the final transfer current target value (I T ) it is sufficient.

[0073] <Step 3>

[0074] In this step, it is determined whether to return or terminate the process according to whether printing is completed. The CPU 10a continues (waits for an update of the setting) for a predetermined period of time to set the transfer current target value (I T ) and apply the transfer voltage as performed in step 2 (S301). And the CPU 10a determines whether printing (all jobs) is completed (S302). Incidentally, a job is a series of operations that start from a single start instruction, form an image on a single or multiple recording materials R and output it from the image forming apparatus 1. And in the case where printing is not completed, the CPU 10a returns to step 2, updates the final transfer current target value (I T ) and changes the output of the transfer power supply 18. The CPU 10a repeats from step 2 to step 3 until printing is completed. On the other hand, in the case where printing is completed, the CPU 10a turns off the transfer power supply 18 and ends the operation of the image forming apparatus 1 (S303).

[0075] The loop from step 2 to step 3 is executed at a predetermined interval. Here, the predetermined interval can be an interval that can suppress AC striping. Preferably, the predetermined interval is a time that is sufficiently shorter than the period of the AC voltage of a commercial power supply with a frequency of 50 Hz (period of 20 ms) or 60 Hz (about 16.7 ms), such as 1 ms. For example, the predetermined interval can be set to a time of 0.5 ms or more and 15 ms or less, or preferably 1 ms or more and 10 ms or less.

[0076] As described above, in the embodiment, the image forming apparatus 1 is provided with an image carrier member (photosensitive drum) 11 that bears a toner image, a developing device 15 that supplies toner to the image carrier member 11 and forms a toner image on the image carrier member 11, a transfer member (transfer roller) 17 that contacts the image carrier member 11 to form a transfer portion (transfer clamping portion) Nt and transfers the toner image from the image carrier member 11 to the recording material R in the transfer portion Nt, a transfer power source 18 that applies a voltage to the transfer member 17, a fixing device 20 that is disposed on the downstream side of the transfer portion Nt with respect to the conveyance direction of the recording material R and forms a fixing portion (fixing clamping portion) Nf for clamping the recording material R. The fixing device Nf is provided with a heating source (heater) 23 for heating the recording material R clamped by the fixing portion Nf and a heating member 21 that contacts the recording material R in the fixing portion Nf, and the heating source 23 is heated by applying a voltage from the AC power source 30 so as to heat the recording material R through the heating member 21. A detection portion (current detection portion) 13 that is connected between the image carrier member 11 and the GND without inserting the transfer member 17 and detects a current or a voltage (current in the embodiment), and a control portion 10 that controls the transfer power source 18. When the toner image is transferred from the image carrier member 11 to the recording material R in the transfer portion Nt and the recording material R is heated in the fixing portion Nf, the control portion 10 controls the current output from the transfer power source 18 based on the detection result of the detection portion 13. That is, in the embodiment, the image forming apparatus 1 is connected between the image carrier member 11 and the GND in a current path from the transfer power source 18 through the transfer member 17 and the image carrier member 11 to the GND, and includes a detection portion (current detection portion) 13 that detects a current or a voltage (current in this embodiment). Further, in the embodiment, the image carrier member 11 is a photosensitive member. Further, in the embodiment, the detection portion 13 detects a current superimposed on at least a part of the current output from the AC power source 30 and at least a part of the current output from the transfer power source 18. Further, in the embodiment, the control portion 10 performs control to suppress the above-described fluctuation by correcting the output current of the transfer power source 18 based on the fluctuation amplitude obtained from the detection result of the detection portion 13 and the target value of the current supplied from the transfer power source 18 to the transfer portion Nt. Further, in the embodiment, the image forming apparatus 1 includes an environment detection portion (environment sensor) 9 that detects at least one of the temperature or humidity of at least one of the inside or outside of the image forming apparatus 1, and the control unit 10 changes the correction amount in the above-described correction based on the detection result of the environment detection portion 9. Further, in the embodiment, the image forming apparatus 1 includes a memory portion 10b that stores an index value related to the usage amount of the image forming apparatus 1, and the control portion 10 changes the correction amount in the above-described correction based on the above-described index value stored in the memory portion 10b.Here, the above-mentioned index value is, for example, a value related to the cumulative number of sheets printed by the image forming apparatus 1, or a value related to the amount of toner consumed or the amount of toner remaining in the developing device 15. Additionally, the above-mentioned index value is, for example, a value related to the cumulative use of the image carrier member 11.

[0077] As described above, in the embodiment, the image forming apparatus 1 includes a current detection section 13 between the photosensitive drum 11 and GND connected in a current path that flows from the transfer power supply 18 through the transfer roller 17 and the photosensitive drum 11 to GND. And the target current value of the transfer power supply 18 is changed and controlled based on the current detection result of the AC component caused by the current flowing from the commercial power supply 30 through the recording material R to the transfer clamping portion Nt detected by the current detection section 13. Specifically, in the embodiment, by correcting the constant current target value (I out ) of the transfer power supply 18 based on the AC striping correction value (ΔI T ), the AC amplitude of the transfer clamping portion Nt is suppressed. Therefore, according to the embodiment, image defects such as density unevenness (image unevenness) caused by AC striping due to the current from the commercial power supply 30 can be suppressed.

[0078] Incidentally, in the embodiment, the current detection section 13 is described as an example, however, a component that converts current into voltage or a voltage detection component may also be used. It is sufficient to be able to detect the fluctuation of the transfer current (AC component) caused by the current flowing from the commercial power supply 30 through the recording material R to the transfer clamping portion Nt. In this case, the image forming apparatus 1 includes a voltage detection section as a voltage detection component, which is connected between the photosensitive drum 11 and GND in a current path that flows from the transfer power supply 18 through the transfer roller 17 and the photosensitive drum 11 to GND. Moreover, in this way, similar to this embodiment, by controlling the transfer power supply 18 to suppress the fluctuation of the current flowing in the current path, the same effect as in this embodiment can be obtained.

[0079] [Second Embodiment]

[0080] Next, another embodiment of the present invention will be described. Descriptions of functions, configurations, and operations of the image forming apparatus in the embodiment that are the same as or corresponding to those of the image forming apparatus according to the first embodiment will be appropriately omitted.

[0081] <Configuration of Image Forming Apparatus>

[0082] In the first embodiment, the case where the present invention is applied to a monochrome image forming apparatus is described, however, the present invention is not limited to such a configuration. The present invention can also be applied to configurations such as a color image forming apparatus where an intermediate transfer member or a primary transfer power supply device is provided between the image carrier member and the transfer roller.

[0083] By using Figure 10 , a schematic configuration of an image forming apparatus 100 according to an embodiment will be described. Figure 10 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment. The image forming apparatus 100 according to the embodiment is a tandem type laser beam printer applying an intermediate transfer system capable of forming a full-color image on a sheet-like recording material R by using an electrophotographic method.

[0084] The image forming apparatus 100 according to the embodiment includes four image forming sections (stations) Py, Pm, Pc, and Pk as image forming members that respectively form images of yellow, magenta, cyan, and black. For elements having the same or corresponding functions or configurations provided for each color, the letters y, m, c, or k are attached to the end of the reference numeral to indicate for which color it is used. However, in the case of describing matters common to each color, the letters y, m, c, or k at the end of the reference numeral will be omitted. In the embodiment, the image forming section P is constituted by a photosensitive drum 122, a charging roller 123, a scanner unit 14, a developing device 125, etc., which will be described below. In the embodiment, the scanner unit 14 is configured as a single unit that exposes the four photosensitive drums 122y, 122m, 122c, and 122k, but may also be configured as an independent unit for each image forming section P.

[0085] The photosensitive drum 122 as an image carrier member is rotationally driven by a drum driving motor (not shown in the figure) as a driving component in the direction of arrow D (counterclockwise direction) in the figure at a predetermined circumferential speed (processing speed). The surface of the rotating photosensitive drum 122 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in the embodiment) by a charging roller 123, which is a roller-type charging member as a charging component. During the charging process, the charging roller 123 is charged with a charging voltage (charging bias) by a charging power source (not shown in the figure) as a charging voltage application component. The surface of the charged photosensitive drum 122 is scanned and exposed by a scanner unit 14 as an exposure component (light irradiation component), and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 122. The scanner unit 14 irradiates the surface of the photosensitive drum 122 with a laser 121 according to an image signal, and an electrostatic latent image is formed on the photosensitive drum 122. When a developing device 125 as a developing component supplies toner as a developer, the electrostatic latent image formed on the photosensitive drum 122 is developed (visualized), and a toner image is formed on the photosensitive drum 122 (on the image carrier member). The developing device 125 forms a toner image when attaching the toner to the electrostatic latent image by using a developing roller 124 as a developing member (developer carrier member). During development, a developing voltage (developing bias) is applied to the developing roller 124 by a developing power source (not shown in the figure) as a developing voltage application component. In the embodiment, the toner image is formed by an inversion development method. In the embodiment, the normal polarity of the toner as the main charge polarity of the toner during development is negative

[0086] An intermediate transfer belt 130, which is an intermediate transfer member composed of an endless belt, is disposed opposite to four photosensitive drums 122y, 122m, 122c, and 122k. The intermediate transfer belt 130 is stretched over tension rollers 131, an auxiliary roller 132, and a driving roller 133, which are multiple tension rollers, and is stretched with a predetermined tension. When the driving roller 133 is driven by a belt driving motor (not shown in the figure) as a driving component, the intermediate transfer belt 130 rotates (circumferentially moves) in the direction of arrow B (clockwise direction) in the figure, and the driving force is transmitted to the intermediate transfer belt 130. On the inner peripheral surface of the intermediate transfer belt 130, primary transfer rollers 126 are respectively disposed corresponding to the photosensitive drums 122y, 122m, 122c, and 122k. The primary transfer rollers 126 are roller-type primary transfer members as primary transfer components. The primary transfer rollers 126 press the intermediate transfer belt 130 against the photosensitive drums 122 and form a primary transfer clamping portion (primary transfer portion) Np, which is the contact portion between the photosensitive drums 122 and the intermediate transfer belt 130. The toner image formed on the photosensitive drum 122 is transferred (primary transfer) to the rotating intermediate transfer belt 130 through the action of the primary transfer roller 126 in the primary transfer clamping portion Np. Each of the primary transfer rollers 126y, 126m, 126c, and 126k is connected to a primary transfer power source 142 as a primary transfer voltage applying component, the auxiliary roller 132, and the driving roller 133. During primary transfer, a primary transfer voltage (primary transfer bias), which is a DC voltage with a polarity opposite to the normal charging polarity of the toner (positive polarity in the embodiment), is applied to the primary transfer roller 126. For example, when forming a full-color image, the toner images of each color of yellow, magenta, cyan, and black formed on each of the photosensitive drums 122y, 122m, 122c, and 122k are sequentially transferred so that they are superimposed on the intermediate transfer belt 130.

[0087] On the outer peripheral surface side of the intermediate transfer belt 130, a secondary transfer roller 117, which is a roller-shaped secondary transfer member as a secondary transfer part, is disposed at a position facing a driving roller 133 that also functions as a secondary transfer opposing roller serving as an opposing member. The secondary transfer roller 117 presses against the driving roller 133, contacts the driving roller 133 via the intermediate transfer belt 130, and forms a secondary transfer clamping portion (secondary transfer portion) Nt that is a contact portion between the intermediate transfer belt 130 and the secondary transfer roller 117. That is, the secondary transfer roller 117 forms the secondary transfer clamping portion Nt by sandwiching the intermediate transfer belt 130 between the secondary transfer roller 117 and the driving roller 133. The toner image formed on the intermediate transfer belt 130 is transferred (secondary transferred) to a recording material R that is conveyed by being sandwiched between the intermediate transfer belt 130 and the secondary transfer roller 117 at the secondary transfer clamping portion Nt. During secondary transfer, a secondary transfer voltage (secondary transfer bias) is applied to the secondary transfer roller 117 by a secondary transfer power source 118 that is a secondary transfer voltage application member, and this secondary transfer voltage is a DC voltage whose polarity is opposite to the normal charging polarity of the toner (positive polarity in the embodiment). A recording material R such as paper or OHT is accommodated in a cassette 5 that is a recording material accommodation portion, and is conveyed to the secondary transfer clamping portion Nt at a predetermined timing by a pickup roller 6 that is a feeding member and a pair of conveying rollers 7 and 8 that are conveying members.

[0088] After the charge accumulated on the surface of the recording material R with the toner image transferred thereon is discharged by the charge eliminating member 119, the recording material R is conveyed to the fixing device 20 which is a fixing member. The configuration of the fixing device 20 of the image forming apparatus 100 according to the embodiment is substantially the same as the configuration of the fixing device 20 of the image forming apparatus 1 according to the first embodiment. That is, the fixing device 20 is configured to include a fixing film 22 as a first fixing member (first rotatable fixing member), a heater 23 as a heating source, and a pressure roller 24 as a second fixing member (second rotatable fixing member). In addition, the fixing device 20 is provided with an electronic component 25 and a fixing control section 26. The heating member 21 is configured to include the fixing film 22 and the heater 23, and the pressure roller 24 forms a fixing nip portion (fixing portion) Nf by contacting the heating member 21. When the heater 23 generates heat by applying an AC voltage from a commercial power supply (AC power supply) 30 to the heater 23, the heating member 21 is heated to a temperature at which the toner image can be fixed to the recording material R. The fixing device 20 heats and presses the recording material R with the toner image transferred thereon by sandwiching and conveying it between the fixing film 22 and the pressure roller 24 at the fixing nip portion Nf, and the toner image is fixed (melted, adhered) to the recording material R. After the toner image is fixed by the fixing device 20, the recording material R is discharged (output) to a discharge tray 103 which is provided on the outer side (top surface) of the main assembly 102 of the image forming apparatus 100.

[0089] The toner remaining on the photosensitive drum 122 after primary transfer (primary transfer residual toner) is removed from the photosensitive drum 122 and collected by, for example, the developing device 125. In addition, an adhering material such as toner remaining on the intermediate transfer belt 130 after secondary transfer is removed from the intermediate transfer belt 130 and collected by, for example, a belt cleaning device (not shown in the figure). The belt cleaning device is provided on the downstream side of the secondary transfer nip portion Nt with respect to the rotation direction of the intermediate transfer belt 130 and on the upstream side of the most upstream primary transfer nip portion Np.

[0090] In the embodiment, the image forming apparatus 100 transfers the toner image from the intermediate transfer belt 130 to the recording material R by causing a predetermined current (transfer current) to flow from the secondary transfer power supply 118 through the secondary transfer roller 117 and the secondary transfer nip portion Nt to the driving roller 133. And, in the embodiment, the output current (I) of the secondary transfer power supply 118 转印) and the AC current superimposed on the secondary transfer current from the commercial power supply 30 via the recording material R flows from the driving roller 133 to GND via the primary transfer power supply 142. Therefore, in the embodiment, a current detection portion 113 for detecting an AC current that contributes to the AC striping of the secondary transfer current is disposed between the driving roller 133 and the primary transfer power supply 142. The current detection unit 113 is connected between the driving roller 133 and GND without inserting the secondary transfer roller 117. That is, the current detection portion 113 is connected between the driving roller 133 and GND in the current path from the secondary transfer power supply 118 through the secondary transfer roller 117 and the driving roller 133 to GND.

[0091] Incidentally, in the embodiment, the image forming apparatus 100 includes four image forming portions. However, the present invention is not limited thereto. For example, the present invention can also be applied to a color image forming apparatus that sequentially forms toner images of multiple colors on an image bearing member (such as a photosensitive drum) of one of the image forming portions and transfers the toner images to a recording material via an intermediate transfer member (such as an intermediate transfer belt).

[0092] <Method for Suppressing Image Defects Caused by AC Striping>

[0093] In the embodiment, the current detection portion 113 is provided at a position where the driving roller (secondary transfer opposing roller) 133 and the primary transfer roller 126 are connected to the primary transfer power supply 142. And in the embodiment, since the detection result of the current detection portion 113 is defined as the current amplitude (ΔI) and the output current of the secondary transfer power supply 118 is defined as (I 转印 ) , therefore the output current (I 转印 ) of the secondary transfer power supply 118 is controlled by the process described in Figure 9 in the first embodiment. That is, the CPU 10a of the control portion 10 controls the duty ratio of the PWM signal sent from the transfer power supply control portion 10c of the control portion 10 to the secondary transfer power supply 118 so that the output current (I 转印 ) of the secondary transfer power supply 118 becomes the transfer current target value (I T )

[0094] Here, the current detection section 113 in the embodiment is configured to detect current by using a current detection resistor connected in series between the driving roller 133 and the primary transfer power supply 142. In the embodiment, the primary transfer voltage is controlled as a constant voltage. Additionally, in many cases, among image forming apparatuses provided with an intermediate transfer belt 130 such as the image forming apparatus 100 in the embodiment, there is a relationship of "the secondary transfer power supply voltage is greater than the primary transfer power supply voltage". Because the recording material R is not inserted in the primary transfer clamping portion Np, but the recording material R is inserted in the secondary transfer clamping portion Nt. Therefore, the current from the primary transfer power supply 142 returns to GND through the primary transfer roller 126 and the photosensitive drum 122. Additionally, generally, the intermediate transfer belt 130 is an insulating material, and little current flows through the surface layer of the intermediate transfer belt 130. Therefore, the current from the secondary transfer clamping portion Nt flows through the current detection section 113 and merges with the current of the primary transfer power supply 142, and then returns to GND via the primary transfer roller 126 and the photosensitive drum 122.

[0095] Therefore, even in the configuration according to this embodiment, it is possible to detect the current of the AC component flowing through the secondary transfer clamping portion Nt required for suppressing AC banding by using the current detection section 113.

[0096] Incidentally, in the embodiment, the driving roller (opposing member) 133 and the primary transfer power supply 142 are configured to be connected, however, the present invention is not limited to this configuration. For example, the driving roller (opposing member) 133 may be configured to be independently connected to GND and electrically grounded. In this case, it is also possible to suppress AC banding by providing the current detection section 113 between the driving roller (opposing member) 133 and GND through similar control as described above.

[0097] Additionally, in the embodiment, the current detection section 113 is described as an example, however, as described in the first embodiment, it is also possible to use a component that converts current into voltage or a voltage detection component. It is sufficient to be able to detect the fluctuation of the transfer current (AC component) caused by the current flowing from the commercial power supply 30 through the recording material R to the transfer clamping portion Nt. In this case, the image forming apparatus 100 includes a voltage detection section as the voltage detection component, and the voltage detection section is connected between the driving roller 133 and GND in the current path where the current flows from the secondary transfer power supply 118 through the secondary transfer roller 117 and the driving roller 133 to GND. Moreover, in this way, similar to the embodiment, by controlling the secondary transfer power supply 118 to suppress the fluctuation of the current flowing in the current path, the same effect as the embodiment can be obtained.

[0098] As described above, in the embodiment, the image forming apparatus 100 is provided with: an image bearing member (photosensitive drum) 11 that bears a toner image; a developing device 15 that supplies toner to the image bearing member 11 and forms a toner image on the image bearing member 11; an intermediate transfer member (intermediate transfer belt) 130 to which the toner image is transferred from the image bearing member 11 and which is capable of moving cyclically; an opposing member (driving roller) 133 that contacts the inner peripheral surface of the intermediate transfer member 130; a transfer member (secondary transfer roller) 117 that contacts the outer peripheral surface of the intermediate transfer member 130, is configured to form a transfer portion (secondary transfer clamping portion) Nt by clamping the intermediate transfer member 130 between itself and the opposing member 133, and is configured to transfer the toner image from the intermediate transfer member 130 to the recording material R in the transfer portion Nt; a transfer power source (secondary transfer power source) 118 that is configured to apply a voltage to the transfer member 117; a fixing device 20 that is disposed on the downstream side of the transfer portion Nt with respect to the conveyance direction of the recording material R and is configured to form a fixing portion (fixing clamping portion) Nf for clamping the recording material R, the fixing device 20 being provided with a heating source 23 for heating the recording material R clamped by the fixing portion Nf and a heating member 21 that contacts the recording material R in the fixing portion Nf, and the heating source 23 being heated by applying a voltage from an AC power source 30 so as to heat the recording material R through the heating member 21; a detection portion (current detection portion) 113 that is connected between the opposing member 133 and GND without inserting the transfer member 117 and is configured to detect a current or voltage (a current in the embodiment); and a control portion 10 that is configured to control the transfer power source 118, wherein when the toner image is transferred from the intermediate transfer member 130 to the recording material R in the transfer portion Nt and the recording material R is heated in the fixing portion Nf, the control portion 10 controls the current output from the transfer power source 118 based on the detection result of the detection portion 113. That is, in the embodiment, the image forming apparatus 100 is connected between the opposing member 133 and GND in a current path from the transfer power source 118 through the transfer member 117 and the opposing member 133 to GND, and includes a detection portion (current detection portion) 113 that detects a current or voltage (a current in the embodiment). Further, in the embodiment, the intermediate transfer member 130 is an intermediate transfer belt formed of an endless belt.

[0099] As described above, according to the embodiment, similar to the monochrome image forming apparatus according to the first embodiment, even in a color image forming apparatus, image defects caused by current from a commercial power source can be suppressed.

[0100] [Other]

[0101] As described above, the present invention has been described according to specific embodiments, however, the present invention is not limited to the above embodiments.

[0102] For example, information described as being input from an external device in the above embodiments may be input from an operation unit provided in the image forming apparatus.

[0103] In addition, for example, the control for suppressing AC banding described in the above embodiments may be executed only when a predetermined condition is satisfied, such as when the current amplitude (ΔI) detected by the current detection unit exceeds a predetermined threshold.

[0104] Although the present invention has been described with reference to exemplary embodiments, it should be understood that the present invention is not limited to the disclosed exemplary embodiments. The scope of the following claims should be given the broadest interpretation to cover all such modifications as well as equivalent structures and functions.

Claims

1. An image forming apparatus, comprising: an image bearing member configured to bear a toner image; a developing device configured to supply toner to the image bearing member and form a toner image on the image bearing member; a transfer member configured to be in contact with the image bearing member to form a transfer portion and to transfer the toner image from the image bearing member to a recording material in the transfer portion; a transfer power source configured to apply a voltage to the transfer member; a fixing device disposed on a downstream side of the transfer portion with respect to a conveyance direction of the recording material and configured to form a fixing portion for clamping the recording material, the fixing device being provided with a heating source for heating the recording material clamped by the fixing portion and a heating member that comes into contact with the recording material in the fixing portion, and the heating source being heated by applying a voltage from an AC power source to thereby heat the recording material via the heating member; a detection portion connected between the image bearing member and a ground potential without interposing a transfer member and configured to detect a current or a voltage; as well as A control portion configured to control the transfer power supply, Wherein the control portion controls current output from the transfer power source based on a detection result of the detection portion when the toner image is transferred from the image bearing member to the recording material in the transfer portion and the recording material is heated in the fixing portion. 2 . The image forming apparatus according to claim 1 , wherein the image bearing member is a photosensitive member. 3 . The image forming apparatus according to claim 1 , wherein the detection portion detects the current on which at least a portion of the current output from the AC power source and at least a portion of the current output from the transfer power source are superimposed.

4. The image forming apparatus according to claim 1 , wherein the control portion performs correction of the output current from the transfer power source and controls to suppress the fluctuation based on the amplitude of the fluctuation acquired from the detection result of the detection portion and a target value of the current supplied from the transfer power source to the transfer portion.

5. The image forming apparatus according to claim 4 , further comprising an environment detecting portion configured to detect an environment as at least one of temperature and humidity of at least one of an interior and an exterior of the image forming apparatus, The control section changes a correction amount in the correction based on a detection result of the environment detection section.

6. The image forming apparatus according to claim 4 , further comprising a memory portion configured to store an index value related to a usage amount of the image forming apparatus, Wherein the control section changes a correction amount in the correction based on the index value stored in the memory section. 7 . The image forming apparatus according to claim 6 , wherein the index value is a value related to a cumulative number of printed sheets of the image forming apparatus or a value related to a toner consumption amount or a toner remaining amount of the image forming apparatus. 8 . The image forming apparatus according to claim 6 , wherein the index value is a value related to a cumulative usage amount of the image bearing member.

9. An image forming apparatus comprising: an image bearing member configured to bear a toner image; a developing device configured to supply toner to the image bearing member and form a toner image on the image bearing member; an intermediate transfer member to which the toner image is transferred from the image bearing member and which is cyclically movable; an opposing member in contact with the inner peripheral surface of the intermediate transfer member; a transfer member in contact with an outer peripheral surface of the intermediate transfer member, configured to form a transfer portion by sandwiching the intermediate transfer member between itself and an opposing member, and configured to transfer the toner image from the intermediate transfer member to a recording material in the transfer portion; a transfer power source configured to apply a voltage to the transfer member; a fixing device disposed on a downstream side of the transfer portion with respect to a conveyance direction of the recording material and configured to form a fixing portion for clamping the recording material, the fixing device being provided with a heating source for heating the recording material clamped by the fixing portion and a heating member that comes into contact with the recording material in the fixing portion, and the heating source being heated by applying a voltage from an AC power source to thereby heat the recording material via the heating member; a detection portion connected between the opposing member and a ground potential without interposing a transfer member and configured to detect a current or a voltage; as well as A control portion configured to control the transfer power supply, Wherein the control portion controls current output from the transfer power source based on a detection result of the detection portion when the toner image is transferred from the intermediate transfer member to the recording material in the transfer portion and the recording material is heated in the fixing portion. 10 . The image forming apparatus according to claim 9 , wherein the intermediate transfer member is an intermediate transfer belt constituted by an endless belt.

11. An image forming apparatus comprising: an image bearing member configured to bear a toner image; a developing device configured to supply toner to the image bearing member and form a toner image on the image bearing member; a transfer member configured to be in contact with the image bearing member to form a transfer portion and to transfer the toner image from the image bearing member to a recording material in the transfer portion; a transfer power source configured to apply a voltage to the transfer member; a fixing device disposed on a downstream side of the transfer portion with respect to a conveyance direction of the recording material and configured to form a fixing portion for clamping the recording material, the fixing device being provided with a heating source for heating the recording material clamped by the fixing portion and a heating member that comes into contact with the recording material in the fixing portion, and the heating source being heated by applying a voltage from an AC power source to thereby heat the recording material via the heating member; a detecting portion connected between the image bearing member and the ground potential in a current path from a transfer power source through the transfer member and the image bearing member to the ground potential, and configured to detect current or voltage; as well as A control portion configured to control the transfer power supply, Wherein the control portion controls current output from the transfer power source based on a detection result of the detection portion when the toner image is transferred from the image bearing member to the recording material in the transfer portion and the recording material is heated in the fixing portion.

Images