Image forming apparatus

Abstract

To provide an image forming apparatus that prevents reversal of a cleaning blade.SOLUTION: An image forming apparatus comprises: a photoreceptor drum; an electrifying roller; an exposure unit; a developing unit; a transfer roller; a fixing unit; a cleaning blade; an electrification bias power supply that applies voltage to the electrifying roller; a transfer bias power supply that applies voltage to the transfer roller; and a control section. When an effective electrification width in an axial direction on a surface of the photoreceptor drum is defined as A, a contact width in the axial direction of the cleaning blade in contact with the photoreceptor drum is defined as B, and a contact width in the axial direction of the transfer roller in contact with the photoreceptor drum is defined as C, A<B<C. The control section performs reversal prevention control of applying voltage in which AC voltage is superimposed on DC voltage, to the transfer roller in a non-image forming period.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] Electrophotographic image forming apparatuses that form images using electrophotographic technology are widely used in copiers, printers, facsimile machines, and the like.

[0003] Conventionally, in an image forming apparatus using an electrophotographic process, a cleaning blade is installed to remove residual toner on the surface of the photosensitive drum. In an image forming apparatus equipped with a cleaning blade, there is a problem that the cleaning blade may reverse when the frictional force between the photosensitive member and the cleaning blade becomes excessive.

[0004] On the other hand, in order to reduce the frictional force between the photosensitive member and the cleaning blade, a technique of applying a lubricant to the surface of the cleaning blade is known. For example, Patent Document 1 describes an image forming apparatus in which a lubricant is applied to the surface of the cleaning blade.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when the lubricant on the cleaning blade peels off, there is a problem that the cleaning blade may reverse due to a difference in the coefficient of friction between the charged area and the non-charged area in the area where the cleaning blade contacts the photosensitive member.

[0007] One aspect of the present invention aims to provide an image forming apparatus that prevents the cleaning blade from reversing.

Means for Solving the Problems

[0008] An image forming apparatus according to one aspect of the present invention includes a photoreceptor drum, a charging roller that charges the surface of the photoreceptor drum, an exposure unit that exposes the surface of the photoreceptor drum to form an electrostatic latent image on the surface of the photoreceptor drum, a developing unit that supplies toner to the electrostatic latent image to form a toner image, a transfer roller that transfers the toner image onto a sheet, a fixing unit that fixes the toner image onto the sheet, a cleaning blade disposed to contact the surface of the photoreceptor drum, a charging bias power source that applies a voltage to the charging roller, a transfer bias power source that applies a voltage to the transfer roller, and a control unit. The image forming apparatus is configured such that, when an effective charging width in the axial direction on the surface of the photoreceptor drum is A, an axial contact width of the cleaning blade in contact with the photoreceptor drum is B, and an axial contact width of the transfer roller in contact with the photoreceptor drum is C, A < B < C, and the control unit performs anti-reversal control in which a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the transfer roller during non-image formation.

Effects of the Invention

[0009] According to the image forming apparatus according to one aspect of the present invention, it is possible to prevent the cleaning blade from reversing.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the embodiments will be described with reference to the drawings. Regarding the drawings, the same or equivalent elements are denoted by the same reference numerals, and duplicate explanations are omitted.

[0012] FIG. 1 is a cross-sectional view schematically showing an image forming unit in an image forming apparatus according to an embodiment. FIG. 2 is a cross-sectional view schematically showing the entirety of the image forming apparatus according to the embodiment.

[0013] The image forming unit 1 shown in Fig. 1 includes a photosensitive drum 10, a charging roller (charging means) 11, an exposure unit 12, a developing unit (developing means) 13, a transfer roller 14, a charge elimination lamp 15, a cleaning unit 16, a charging bias power supply 21, a developing bias power supply 22, a transfer bias power supply 23, and a control unit 24.

[0014] In the image forming unit 1, around the photosensitive drum 10, a charging roller 11, an exposure unit 12, a developing unit 13, a transfer roller 14, a charge elimination lamp 15, and a cleaning unit 16 are arranged along the rotation direction of the photosensitive drum 10 (the direction of arrow R in the figure).

[0015] The charging roller 11 is a contact roller type charging part that contacts the surface of the photosensitive drum 10 and charges the surface of the photosensitive drum 10. An output voltage (charging bias) from the charging bias power supply 21 is applied to the charging roller 11.

[0016] The exposure unit 12 irradiates and exposes light corresponding to image data output from an image processing unit (not shown) onto the surface of the photosensitive drum 10 that is uniformly charged. Thereby, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 10.

[0017] The developing unit 13 visualizes the electrostatic latent image formed on the photosensitive drum 10 with toner and includes a developing roller 131 disposed opposite to the photosensitive drum 10. That is, in the developing unit 13, the developer is supplied from the inside of the developing unit 13 to the outer periphery of the developing roller 131, and the electrostatic latent image formed on the photosensitive drum 10 is visualized with toner (a toner image is formed on the photosensitive drum 10). At this time, an output voltage (developing bias) from the developing bias power supply 22 is applied to the developing roller 131.

[0018] The developer used in the developing unit 13 includes a two-component developer in which a carrier and toner are mixed, and a one-component developer composed only of toner. The developing unit 13 according to the embodiment may use a two-component developer or a one-component developer.

[0019] The transfer roller 14 has a conveyance path for the recording paper (not shown in FIG. 1) between it and the photosensitive drum 10, and can convey the incoming recording paper while pressing it against the photosensitive drum 10. Further, an output voltage (transfer bias) from the transfer bias power supply 23 is applied to the transfer roller 14 to transfer the toner image on the photosensitive drum 10 onto the paper. The paper with the transferred toner image is conveyed to the fixing unit 150 shown in FIG. 2, and the transferred toner image is fixed.

[0020] The charge elimination lamp 15 irradiates the surface of the photosensitive drum 10 with uniform light to remove the residual charge of the photosensitive drum 10. The cleaning unit 16 includes a cleaning blade 161 whose one end is arranged in contact with the surface of the photosensitive drum 10, and the cleaning blade 161 removes the residual toner on the surface of the photosensitive drum 10.

[0021] The charging bias power supply 21, the developing bias power supply 22, and the transfer bias power supply 23 are connected to the control unit 24. That is, the control unit 24 controls the charging bias power supply 21, the developing bias power supply 22, and the transfer bias power supply 23 to perform voltage control of the charging bias, the developing bias, and the transfer bias, and executes an image forming operation and an inversion suppression control during non-image formation. The control unit 24 executes an image forming operation using the image forming unit 1 and prints an image on a recording sheet. Further, the control unit 24 counts the number of printed sheets from the start of use of the photosensitive drum 10. Also, the number of printed sheets is reset to 0 when the photosensitive drum 10 is replaced. The control unit 24 performs an inversion suppression control of applying a bias in which an AC voltage is superimposed on a DC voltage to the transfer roller 14 during non-image formation (when toner removal is executed). The control unit 24 is, for example, a processor such as a CPU (Central Processing Unit) or a logic circuit (hardware) formed in an integrated circuit (IC (Integrated Circuit) chip) or the like.

[0022] As shown in FIG. 2, the image forming apparatus 101 includes an image forming unit 1, a paper feed roller 130, a paper discharge roller 130a, a tray 140, and a fixing unit 150. The image forming apparatus 101 is, for example, an electrophotographic printer or a multifunction peripheral.

[0023] A tray 140 for accommodating paper is disposed below the image forming unit 1. The paper in the tray 140 is conveyed by a plurality of paper feed rollers 130 to a transfer position where the image forming unit 1 faces the transfer roller 14. The arrow P indicates the conveyance direction of the paper.

[0024] A fixing unit 150 for fixing the image (toner image) transferred to the paper onto the paper is provided on the downstream side of the transfer roller 14 in the paper conveyance direction P. And, a paper discharge roller 130a for discharging the paper on which the image is fixed from the image forming apparatus is provided further downstream of the fixing unit 150 in the paper conveyance direction P. In such a configuration, the image formed by the image forming unit 1 is transferred to a sheet conveyed by the paper feed roller 13 at the transfer position where the photosensitive drum 10 and the transfer roller 14 are in contact, and then fixed to the sheet by the fixing unit 150. The sheet on which the image is fixed is discharged from the image forming apparatus 101 by the paper discharge roller 130a.

[0025] FIG. 3 is a diagram schematically showing a process layout according to the embodiment.

[0026] As shown in FIG. 3, let the effective charging width in the axial direction on the surface of the photosensitive drum 10 charged by the charging roller 11 (the length of the charging roller 11) be A, the contact width in the axial direction where the cleaning blade 161 contacts the photosensitive drum 10 (the length of the cleaning blade 161) be B, and the contact width in the axial direction where the transfer roller 14 contacts the photosensitive drum 10 (the length of the transfer roller 14) be C. In the embodiment, A, B, and C satisfy A < B < C. That is, the contact width B in the axial direction where the cleaning blade 161 contacts the photosensitive drum 10 is larger than the effective charging width A in the axial direction on the surface of the photosensitive drum 10 charged by the charging roller 11. The contact width C in the axial direction where the transfer roller 14 contacts the photosensitive drum 10 is larger than the contact width B in the axial direction where the cleaning blade 161 contacts the photosensitive drum 10.

[0027] As a result, in the region on the surface of the photosensitive drum 10 that contacts the transfer roller 14 (the contact width C in the axial direction where the transfer roller 14 contacts the photosensitive drum 10), due to the energization fatigue caused by the transfer roller 14 during non-image formation, the difference in the friction coefficient is suppressed in the entire region of the contact region in the axial direction where the cleaning blade 161 contacts the photosensitive drum 10, and the reverse rotation of the cleaning blade 161 is prevented.

[0028] The axial contact width C of the transfer roller 14 in contact with the photoreceptor drum 10 is preferably 10 mm or more longer than the axial contact width B of the cleaning blade 161 in contact with the photoreceptor drum 10. Since the ends of the transfer roller 14 tend to have a high resistance and it is difficult for current to flow, by using a transfer roller 14 that is 10 mm or more longer than the cleaning blade 161, the transfer current can flow uniformly throughout the entire area of the cleaning blade contact region B. Also, since there is no further effect even if the length of the transfer roller 14 is made 20 mm or more longer than the cleaning blade 161, the axial contact width C of the transfer roller 14 in contact with the photoreceptor drum 10 is preferably 10 - 20 mm longer than the axial contact width B of the cleaning blade 161 in contact with the photoreceptor drum 10.

[0029] Here, the detection of the torque of the photoreceptor drum 10 will be described.

[0030] FIG. 4 is a diagram for explaining the torque detection of the photoreceptor drum in the image forming apparatus according to the embodiment.

[0031] The image forming unit 1 further includes a DC (Direct Current) motor 17 and a torque detection unit 18. The photoreceptor drum 10 is rotationally driven at a constant speed by the DC motor 17.

[0032] The torque detection unit 18 detects the current value (torque current value) of the DC motor 17. The torque detection unit 18 detects the torque applied to the photoreceptor drum 10 by reading the current value of the DC motor 17. The torque detection unit 18 outputs a torque current value indicating the torque applied to the photoreceptor drum 10 to the control unit 24.

[0033] The control unit 24 determines whether to execute the reverse rotation suppression control described later according to whether the torque value detected by the torque detection unit 18 is equal to or greater than a predetermined threshold value. Specifically, for example, the control unit 24 determines whether to execute the reverse rotation suppression control described later according to whether the torque current value detected by the torque detection unit 18 is equal to or greater than a predetermined threshold value.

[0034] FIG. 5 is a flowchart of control processing of the image forming apparatus according to the embodiment.

[0035] In step S201, the control unit 24 prints an image on a recording sheet using the image forming unit 1.

[0036] In step S202, the control unit 24 determines whether the number of printed sheets is a specified value. If it is determined that the number of printed sheets is the specified value, the control proceeds to step S203. If it is determined that the number of printed sheets is not the specified value, the control proceeds to step S204. Note that the specified value is set in advance, and a plurality of specified values may be set.

[0037] In step S203, the control unit 24 executes reverse suppression control. Specifically, in the reverse suppression control, the control unit 24 controls the charging bias power supply 21 and the transfer bias power supply 23, and applies a voltage (bias) obtained by superimposing an AC voltage on a DC voltage to the transfer roller 14 during non-image formation. Note that the control unit 24 executes the reverse suppression control for an execution time corresponding to the number of printed sheets. The execution time of the reverse suppression control corresponding to the number of printed sheets will be described later.

[0038] In step S204, the torque detection unit 18 detects (measures) the torque applied to the photosensitive drum 10. The control unit 23 determines whether the detected torque is equal to or greater than a threshold value. Specifically, for example, the control unit 23 determines whether the torque current value of the DC motor 17 indicating the torque applied to the photosensitive drum 10 detected by the torque detection unit 18 is equal to or greater than the threshold value. If it is determined that the detected torque current value is equal to or greater than the threshold value, the control proceeds to step S205. If it is determined that the detected torque current value is less than the threshold value, the process ends.

[0039] In step S205, the control unit 24 executes reverse suppression control. For example, the threshold value is 1.20 mA. When the torque current value of the DC motor 17 is 1.20 mA or more, it is determined that the torque current value is equal to or greater than the threshold value (step S204: Yes), and the reverse suppression control is executed.

[0040] FIG. 6 is a table showing the relationship between the number of printed sheets and the execution time of the reverse suppression control. In the table shown in FIG. 6, a plurality of numbers of printed sheets (0, 5,000, 10,000, 15,000, 20,000, 25,000, 30,000) corresponding to the specified values are described.

[0041] In the reverse suppression control of steps S203 and S205, the control unit 24 performs the reverse suppression control for a time corresponding to the number of printed sheets. For example, the control unit 24 performs the reverse suppression control for the execution time of the reverse suppression control corresponding to the number of printed sheets shown in the table of FIG. 6. For example, as shown in the table of FIG. 6, when the number of printed sheets reaches 5,000, the control unit 24 performs the reverse suppression control for 60 seconds. When the number of printed sheets reaches 10,000 and 15,000, the control unit 24 performs the reverse suppression control for 45 seconds. When the number of printed sheets reaches 20,000, 25,000, and 30,000, the control unit 24 performs the reverse suppression control for 30 seconds. As shown in FIG. 6, the execution time of the reverse suppression control when the number of printed sheets reaches 5,000 is 60 seconds. When the number of printed sheets reaches 10,000, the execution time of the reverse suppression control decreases to 45 seconds. When the number of printed sheets reaches 20,000, the execution time of the reverse suppression control decreases to 30 seconds. Thus, each time the number of printed sheets reaches a predetermined number, the execution time of the reverse suppression control becomes shorter. The reason why the execution time of the reverse suppression control decreases as the number of printed sheets increases is that the difference in the friction coefficient between the non-charged region and the charged region in the contact area between the cleaning blade 161 and the photoreceptor is larger when the number of printed sheets is small.

[0042] FIG. 7 is a diagram showing the applied voltages to the charging roller and the transfer roller during image formation and non-image formation.

[0043] In the embodiment, during image formation, a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging roller 11. During image formation, the applied voltage to the charging roller 11 is, for example, a DC voltage Vdc = -600V, an AC voltage Vpp = 1.1kV, and a frequency Vf = 1.3kHz. Only a DC voltage is applied to the transfer roller 14. The applied voltage to the transfer roller 14 is, for example, a DC voltage Vdc = 2500V.

[0044] Also, in the inversion suppression control (when not forming an image), only a DC voltage is applied to the charging roller 11. The strength of the voltage applied to the charging roller 11 in the inversion suppression control (when not forming an image) is not particularly limited, but it is more desirable that it be smaller than the DC voltage applied to the charging roller 11 during image formation. For example, the DC voltage is Vdc = -450V. The reason for making the strength of the voltage applied to the charging roller 11 smaller than during image formation is that applying a voltage to the charging roller 11 can damage the photoreceptor, so it is more preferable to apply a voltage to such an extent that problems such as carrier buildup do not occur. To the transfer roller 14, a voltage obtained by superimposing an AC voltage on a DC voltage is applied. The voltage applied to the transfer roller 14 is, for example, DC voltage Vdc = 3000V, AC voltage Vpp = 1.0kV, and frequency Vf = 1.3kHz. It is more desirable that the amplitude of the AC voltage Vpp applied to the transfer roller 14 be in the range of 0.75 to 5.25kV. The reason for it being more desirable that the amplitude of the AC voltage Vpp applied to the transfer roller 14 be in the range of 0.75 to 5.25kV is that when the amplitude of the AC voltage Vpp is greater than 5.25kV, the difference in the friction coefficient becomes smaller, but the damage to the photoreceptor becomes larger.

[0045] In the inversion suppression control, the application time of the charging bias to the charging roller 11 and the application time of the transfer bias to the transfer roller 14 are set to be approximately the same. Also, these application times are appropriately set according to the number of printed sheets, the torque of the photoreceptor drum, the temperature and humidity of the surrounding environment, etc. Incidentally, when the inversion suppression control is executed (when not forming an image), the DC voltage applied to the charging roller 11 is set to an output value smaller than the DC voltage applied during image formation, and the DC voltage applied to the transfer roller 14 is set to an output value larger than the DC voltage applied during image formation.

[0046] In the conventional process arrangement, inversion occurs from the end of the cleaning blade because there is a difference in the friction coefficients between the non-charged area and the charged area in the area where the cleaning blade contacts the photoreceptor. The reason for the difference in the friction coefficients is that in the charged area, due to fatigue caused by AC charging, the binder on the outermost surface of the photoreceptor breaks, increasing the friction coefficient. In the embodiment, the transfer roller 14 is arranged to be longer than the cleaning blade 161, and by applying a bias voltage in which an AC voltage is superimposed on a DC voltage to the transfer roller 14 during non-image formation, the friction coefficient can be increased due to charging fatigue even in the non-charged area outside the effective range of the charging roller 11. Thereby, the image forming apparatus 101 according to the embodiment can prevent the inversion of the cleaning blade 161 by suppressing the occurrence of a difference in the friction coefficient in the entire area where the cleaning blade 161 contacts the photoreceptor.

[0047] The image forming apparatus 101 may further include a humidity detection unit (not shown) that detects the humidity (absolute humidity) around the image forming apparatus 101. Further, the control unit 24 may count the time (stop time) during which no image forming operation has been performed from the end of the previous image forming operation to the present. The control unit 24 may determine the execution time of the inversion suppression control based on the humidity and the stop time as described below, and execute the inversion suppression control. Since the inversion of the cleaning blade 161 is likely to occur depending on the humidity and the stop time, the inversion of the cleaning blade 161 can be further prevented by performing the inversion suppression control based on the humidity and the stop time.

[0048] FIG. 8 is a modified example of a flowchart of the control process of the image forming apparatus according to the embodiment. FIG. 9 is a table showing the execution time of the inversion suppression control for combinations of the stop time and the absolute humidity.

[0049] First, it is assumed that the control unit 24 counts the time (stop time) during which no image forming operation has been performed from the end of the image forming operation to the present.

[0050] In step S211, the power of the image forming apparatus 101 is turned on.

[0051] In step S212, a humidity detection unit (not shown) detects the absolute humidity around the image forming apparatus 101. The control unit 24 determines the execution time of the inversion suppression control based on the detected absolute humidity and the stop time. For example, the control unit 24 uses the table shown in FIG. 9 to determine the execution time of the inversion suppression control according to the combination of the stop time and the absolute humidity. The table shown in FIG. 9 describes the execution time of the inversion suppression control for the combination of the stop time (hours) and the absolute humidity (g / m 3 ). For example, in the table shown in FIG. 9, when the stop time is 30 hours and the absolute humidity is 10 g / m 3 , the execution time of the inversion suppression control is 15 seconds.

[0052] In step S213, the control unit 24 executes the inversion suppression control for the execution time determined in step S212.

[0053] In step S214, the control unit 24 starts the image forming operation.

[0054] Hereinafter, the control proceeds to step S201 in FIG. 5.

[0055] Next, the experimental results of Examples 1 to 7 and Comparative Examples 1 to 3 will be described.

[0056] FIG. 10 is a table showing the experimental results in Examples 1 to 7 and Comparative Examples 1 to 3. In the table of FIG. 10, the effective charging width A in the axial direction on the surface of the photosensitive drum 10 charged by the charging roller 11 is denoted as the length A of the charging roller 11, the contact width B in the axial direction where the cleaning blade 161 contacts the photosensitive drum 10 is denoted as the length B of the cleaning blade 161, and the contact width C in the axial direction where the transfer roller 14 contacts the photosensitive drum 10 is denoted as the length C of the transfer roller 14, respectively.

[0057] In the experiment, a durability test (printing durability test) was conducted using a modified digital copying machine (manufactured by Sharp Corporation, model: MX-M3531) at the charging voltage and transfer voltage shown in the table of FIG. 10, and it was confirmed whether blade reversal occurred before 30,000 prints were completed.

[0058] Regarding the contact angle (°) of the outermost surface layer (charge transport layer) of the photoreceptor, the contact angle (°) of the charge transport layer was measured at a temperature of 20°C and a humidity of 50% using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., model: CA-X) and pure water (temperature 20°C) as the reagent. Here, the contact angle measured in the experiment will be explained using a figure.

[0059] FIG. 11 is a diagram showing the contact angle of the surface of the charge transport layer of the photoreceptor with respect to pure water.

[0060] As shown in FIG. 11, the contact angle θ of the surface of the charge transport layer of the photoreceptor with respect to pure water is the angle between the tangent to the end of the pure water droplet dropped from the nozzle and the charge transport layer of the photoreceptor. Note that details of the contact angle are described in Japanese Patent Application Laid-Open No. 2023-143015.

[0061] In Example 1, as shown in FIG. 10, the process arrangement is defined such that A (length of charging roller) < B (length of cleaning blade) < C (length of transfer roller). Under an environment with an absolute humidity of 6, during image formation, the DC voltage of the charging bias is -600V, the frequency of the AC voltage is 1.8 kHz, the AC voltage is 1800V, and the DC voltage of the transfer bias is 2500V, and each bias is applied. During the reverse rotation suppression control during non-image formation, the DC voltage of the charging bias is -450V, the DC voltage of the transfer bias is 3000V, the AC frequency is 1.8 kHz, and the AC voltage is 1800V, and each bias is applied to perform an idling operation. As a result, the cleaning blade did not reverse.

[0062] In Example 2, as shown in FIG. 10, the process arrangement is defined such that A (length of the charging roller) < B (length of the cleaning blade) < C (length of the transfer roller). In an environment with an absolute humidity of 12, during image formation, a DC voltage of -600V is applied to the charging bias, an AC frequency of 1.8 kHz, an AC voltage of 1800V, and a DC voltage of 2500V is applied to the transfer bias, and each bias is applied. In the reverse suppression control during non-image formation, a DC voltage of -450V is applied to the charging bias, a DC voltage of 3000V is applied to the transfer bias, an AC frequency of 1.8 kHz, and an AC voltage of 1800V, and each bias is applied to perform an idling operation. As a result, the cleaning blade did not reverse.

[0063] In Example 3, as shown in FIG. 10, the process arrangement is defined such that A (length of the charging roller) < B (length of the cleaning blade) < C (length of the transfer roller). In an environment with an absolute humidity of 16, during image formation, a DC voltage of -600V is applied to the charging bias, an AC frequency of 1.8 kHz, an AC voltage of 1800V, and a DC voltage of 2500V is applied to the transfer bias, and each bias is applied. In the reverse suppression control during non-image formation, a DC voltage of -450V is applied to the charging bias, a DC voltage of 3000V is applied to the transfer bias, an AC frequency of 1.8 kHz, and an AC voltage of 1800V, and each bias is applied to perform an idling operation. As a result, the cleaning blade did not reverse.

[0064] In Example 4, as shown in FIG. 10, the process arrangement is defined such that A (length of the charging roller) < B (length of the cleaning blade) < C (length of the transfer roller). In an environment with an absolute humidity of 12, during image formation, a DC voltage of -600V is applied to the charging bias, an AC frequency of 1.8 kHz, an AC voltage of 1800V, and a DC voltage of 2500V is applied to the transfer bias, and each bias is applied. In the reverse suppression control during non-image formation, a DC voltage of -450V is applied to the charging bias, a DC voltage of 3000V is applied to the transfer bias, an AC frequency of 1.8 kHz, and an AC voltage of 600V, and each bias is applied to perform an idling operation. As a result, the cleaning blade did not reverse.

[0065] In Example 5, as shown in Fig. 10, the process arrangement is defined such that A (length of charging roller) < B (length of cleaning blade) < C (length of transfer roller). In an environment with an absolute humidity of 12, during image formation, a DC voltage of -600V is applied to the charging bias, an AC frequency of 1.8 kHz, an AC voltage of 1800V, and a DC voltage of 2500V is applied to the transfer bias, and each bias is applied. In the reverse suppression control during non-image formation, a DC voltage of -450V is applied to the charging bias, a DC voltage of 3000V is applied to the transfer bias, an AC frequency of 1.8 kHz, and an AC voltage of 800V, and each bias is applied to perform an idling operation. As a result, the cleaning blade did not reverse.

[0066] In Example 6, as shown in Fig. 10, the process arrangement is defined such that A (length of charging roller) < B (length of cleaning blade) < C (length of transfer roller). In an environment with an absolute humidity of 12, during image formation, a DC voltage of -600V is applied to the charging bias, an AC frequency of 1.8 kHz, an AC voltage of 1800V, and a DC voltage of 2500V is applied to the transfer bias, and each bias is applied. In the reverse suppression control during non-image formation, a DC voltage of -450V is applied to the charging bias, a DC voltage of 3000V is applied to the transfer bias, an AC frequency of 1.8 kHz, and an AC voltage of 5000V, and each bias is applied to perform an idling operation. As a result, the cleaning blade did not reverse.

[0067] In Example 7, as shown in Fig. 10, the process arrangement is defined such that A (length of charging roller) < B (length of cleaning blade) < C (length of transfer roller). In an environment with an absolute humidity of 12, during image formation, a DC voltage of -600V is applied to the charging bias, an AC frequency of 1.8 kHz, an AC voltage of 1800V, and a DC voltage of 2500V is applied to the transfer bias, and each bias is applied. In the reverse suppression control during non-image formation, a DC voltage of -450V is applied to the charging bias, a DC voltage of 3000V is applied to the transfer bias, an AC frequency of 1.8 kHz, and an AC voltage of 6000V, and each bias is applied to perform an idling operation. As a result, the cleaning blade did not reverse.

[0068] In Comparative Example 1, as shown in FIG. 10, the process arrangement is defined such that A (length of charging roller) < B (length of cleaning blade) < C (length of transfer roller). In an environment with an absolute humidity of 12, during image formation, a DC voltage of -600 V for the charging bias, an AC frequency of 1.8 kHz, an AC voltage of 1800 V, and a DC voltage of 2500 V for the transfer bias were applied, and anti-reversal control was not executed during non-image formation. As a result, cleaning blade reversal occurred.

[0069] In Comparative Example 2, as shown in FIG. 10, the process arrangement is defined such that C (length of transfer roller) < A (length of charging roller) < B (length of cleaning blade). In an environment with an absolute humidity of 12, during image formation, a DC voltage of -600 V for the charging bias, an AC frequency of 1.8 kHz, an AC voltage of 1800 V, and a DC voltage of 2500 V for the transfer bias were applied, and anti-reversal control was not executed during non-image formation. As a result, cleaning blade reversal occurred.

[0070] In Comparative Example 3, as shown in FIG. 10, the process arrangement is defined such that C (length of transfer roller) < A (length of charging roller) < B (length of cleaning blade). In an environment with an absolute humidity of 12, during image formation, a DC voltage of -600 V for the charging bias, an AC frequency of 1.8 kHz, an AC voltage of 1800 V, and a DC voltage of 2500 V for the transfer bias were applied. During non-image formation (anti-reversal control), a DC voltage of -450 V for the charging bias, a DC voltage of 3000 V for the transfer bias, an AC frequency of 1.8 kHz, and an AC voltage of 1800 V were applied, and an idling operation was executed. As a result, cleaning blade reversal occurred.

[0071] FIG. 12 is a diagram showing the process arrangements of the conventional and the embodiment.

[0072] The upper side of FIG. 12 shows the conventional process arrangement, and the lower side shows the process arrangement of the embodiment.

[0073] FIG. 13 is a graph of the contact angles of the conventional and the embodiment respectively.

[0074] The horizontal axis of FIG. 13 indicates the position from the end of the photoreceptor drum (the left end of the photoreceptor drums 10 and 10a in FIG. 12), and the vertical axis indicates the contact angle. The solid line graph indicates the contact angle of the embodiment (with reverse suppression control), and the dotted line graph indicates the contact angle of the conventional (without reverse suppression control). The contact angle is the same as the above description. Also, there is a relationship that as the friction coefficient of the photoreceptor surface increases, the contact angle decreases.

[0075] In the conventional process arrangement, A (the length of the charging roller 11a) < C (the length of the transfer roller 14a) < B (the length of the cleaning blade 161a).

[0076] In the conventional process arrangement, due to the difference in the friction coefficients between the non-charged area (1) and the charged areas (2) and (3), the reversal of the end of the cleaning blade 161a occurs.

[0077] The reason for the difference in the friction coefficients is that in the charged areas (2) and (3), due to the fatigue caused by AC charging, the binder resin on the photoreceptor surface is cut and the friction coefficient increases.

[0078] In the embodiment, the process arrangement is A (the length of the charging roller 11) < B (the length of the cleaning blade 161) < C (the length of the transfer roller 14).

[0079] In the embodiment, the transfer roller 14 is arranged to be longer than the cleaning blade 161, and a bias voltage obtained by superimposing an AC voltage on a DC voltage is applied to the transfer roller 14 during non-image formation, thereby increasing the friction coefficient of the non-charged area (1) of the photoreceptor drum 10 due to charging fatigue. The middle photoreceptor drum 10 in FIG. 12 shows the state before charging fatigue, and the middle photoreceptor drum 10 shows the state after charging fatigue.

[0080] As shown in the graph of FIG. 13, conventionally, the difference in the contact angle between the non-charged region (1) and the charged regions (2) and (3) is large. That is, conventionally, the difference in the friction coefficient between the non-charged region (1) and the charged regions (2) and (3) is large. On the other hand, in the embodiment, the difference in the contact angle between the non-charged region (1) and the charged regions (2) and (3) is small. That is, in the embodiment, the difference in the friction coefficient between the non-charged region (1) and the charged regions (2) and (3) is small.

[0081] Thus, according to the image forming apparatus according to the embodiment, by reducing the difference in the friction coefficient in the entire contact region of the photoreceptor drum 10, the reversal of the end portion of the cleaning blade 161 can be suppressed.

[0082] Next, the configurations of the charging bias power source 21 and the transfer bias power source 23 will be described.

[0083] FIG. 14 is a diagram showing the configurations of the charging bias power source and the transfer bias power source in the image forming apparatus according to the embodiment.

[0084] The charging bias power source 21 includes a charging DC power source 21a that applies a DC voltage to the charging roller 11 and a charging AC power source 21b that applies an AC voltage to the charging roller 11.

[0085] The transfer bias power source 23 includes a transfer DC power source 23a that applies a DC voltage to the transfer roller 14 and a charging AC power source 23b that applies an AC voltage to the transfer roller 14.

[0086] The control unit 24 controls the charging DC power source 21a, the charging AC power source 21b, the transfer DC power source 23a, and the charging AC power source 23b, thereby performing voltage control of the charging bias and the transfer bias.

[0087] Further, the charging bias power source 21 and the transfer bias power source 23 may have the following configurations.

[0088] FIG. 15 is a diagram showing a modified example of the configuration of a charging bias power source and a transfer bias power source in the image forming apparatus according to the embodiment.

[0089] The charging bias power source 21 includes a charging DC power source 21a that applies a DC voltage to the charging roller 11 and an AC power source 2123b that applies an AC voltage to the charging roller 11.

[0090] The transfer bias power source 23 includes a transfer DC power source 23a that applies a DC voltage to the transfer roller 14 and an AC power source 2123b that applies an AC voltage to the transfer roller 14.

[0091] In the modified example, the AC power source 2123b is shared by the charging bias power source 21 and the transfer bias power source 23.

[0092] The control unit 24 controls the charging DC power source 21a, the transfer DC power source 23a, and the AC power source 2123b, thereby controlling the voltages of the charging bias and the transfer bias. Specifically, the control unit 24 controls the AC power source 2123b and can switch the supply destination of the AC voltage by the AC power source 2123b. During image formation, the control unit 24 applies an AC voltage to the charging roller 11 by the AC power source 2123b, and during non-image formation, it applies an AC voltage to the transfer roller 14.

[0093] According to the image forming apparatus according to the modified example, an AC voltage can be applied to the charging roller 11 and the transfer roller 14 with one AC power source 2123b. Thereby, the cost can be reduced.

[0094] Note that the present invention is not limited to the above-described embodiment and can be modified, and the above configuration can be replaced with a configuration having substantially the same configuration, the same operational effects, or a configuration capable of achieving the same object.

Explanation of Reference Numerals

[0095] 1 Image forming unit 10 Photosensitive drum 11 Charging roller 12 Exposure Unit 13 Development Unit 131 Development Roller 14 Transfer Roller 15 Desiccation Lamp 16 Cleaning Unit 21 Charging Bias Power Supply 22 Development Bias Power Supply 23 Transfer Bias Power Supply 24 Control Unit 101 Image Forming Apparatus

Claims

1. A photoreceptor drum, a charging roller for charging the surface of the photoreceptor drum, an exposure unit for exposing the surface of the photoreceptor drum to form an electrostatic latent image on the surface of the photoreceptor drum, a developing unit for supplying toner to the electrostatic latent image to form a toner image, a transfer roller for transferring the toner image onto a sheet of paper, a fixing unit for fixing the toner image onto the sheet of paper, a cleaning blade disposed so as to contact the surface of the photoreceptor drum, a charging bias power source for applying a voltage to the charging roller, a transfer bias power source for applying a voltage to the transfer roller, a control unit, and an image forming apparatus comprising: when an effective charging width in the axial direction on the surface of the photoreceptor drum is A, a contact width in the axial direction where the cleaning blade contacts the photoreceptor drum is B, and a contact width in the axial direction where the transfer roller contacts the photoreceptor drum is C, A < B < C, the control unit performs inversion suppression control for applying a voltage obtained by superimposing an AC voltage on a DC voltage to the transfer roller during non-image formation. An image forming apparatus.

2. The image forming apparatus according to claim 1, wherein in the inversion suppression control, only a DC voltage is applied to the charging roller and no AC voltage is applied.

3. The image forming apparatus according to claim 2, wherein in the inversion suppression control, the DC voltage applied to the charging roller is made smaller than the DC voltage applied to the charging roller during image formation.

4. The image forming apparatus according to claim 1, wherein the amplitude of the AC voltage applied to the transfer roller is in the range of 0.75 to 5.25 kV.

5. The image forming apparatus according to claim 1, further comprising an AC power source capable of switching the supply destination of the AC voltage to the charging roller or the transfer roller.

6. The image forming apparatus according to claim 1, further comprising a torque detection unit for detecting the torque applied to the photoreceptor drum, wherein the control unit executes the inversion suppression control based on the detected torque.

7. The image forming apparatus according to claim 1, wherein the control unit counts the number of printed sheets and executes the inversion suppression control based on the counted number of printed sheets.

8. The image forming apparatus according to claim 7, wherein the control unit executes the inversion suppression control every time the counted number of printed sheets reaches a predetermined number, and the execution time of the inversion suppression control becomes shorter every time the counted number of printed sheets reaches the predetermined number.

9. ​ The image forming apparatus further includes a humidity detection unit that detects the humidity around the image forming apparatus, The control unit determines the time for executing the reverse suppression control based on the detected humidity and the time during which no image forming operation has been performed since the previous image forming operation ended, and executes the reverse suppression control for the determined time. The image forming apparatus according to claim 1.

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