Image forming apparatus

Abstract

To provide an image forming apparatus that, in control of determining a set voltage from the amount of discharge detected from a plurality of control voltages, changes the values of a control voltage Vpp and the number of times of detection, from the difference between the amount of previous discharge and the amount of current discharge or the difference between the set voltage Vpp and the control voltage Vpp, to improve the accuracy of the amount of discharge.SOLUTION: An image forming apparatus changes a control voltage Vpp from the difference between the amount of previous discharge and the amount of current discharge. The image forming apparatus controls the control voltage Vpp so that the values of the control voltages Vpp have a target discharge amount therebetween.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an electrophotographic image forming apparatus that is applied to a copying machine, a laser printer, a facsimile, a printing device, or a combination machine of these. [Background technology]

[0002] In an image forming apparatus using an electrophotographic method, an electrostatic latent image is formed by exposing the image carrier to light after the surface of the image carrier is charged, a toner is developed on the electrostatic latent image to make it visible as a toner image, the toner image is transferred to a recording material, and the toner image is bonded to the recording material by heating or applying pressure to obtain an image. As a mechanism for charging the surface of the image carrier, there is a device that charges the image carrier by rotating a charging roller while applying a high voltage to a photoconductor.

[0003] The charging device is a charging method that stabilizes the potential convergence by superimposing DC + AC voltage on the charging roller. The applied AC voltage needs to balance the stabilization of the potential formation and the reduction of damage caused by the discharge amount to the photosensitive drum.

[0004] Therefore, in order to optimally control the AC discharge amount (Patent Document 1), multiple AC voltages are applied in the non-discharge area and the discharge area, the AC current is detected, and a linear approximation is performed from a point connecting the multiple points in the non-discharge area to the discharge area, and the AC discharge amount is calculated as the difference with the AC current detected in the discharge area. Even if the usage history changes, control is implemented that allows the AC voltage to be set so that the optimal AC discharge amount is obtained.

[0005] Also, to optimize the AC discharge amount and maintain productivity (Patent Document 2), an AC voltage is applied to one undischarged area and two discharged areas, the corresponding current waveforms are detected, the waveform is expanded in a pseudo manner from the waveform in the undischarged area to the discharge current area, the difference with the waveform detected in the discharge area is taken, the discharge amount is calculated, and the AC voltage (set voltage) that becomes the target discharge amount between the two discharged areas is determined. It is possible to achieve both precision and productivity with a small number of control operations. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-232534 [Patent Document 2] JP 2022-185544 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, problems arise in use cases where the temperature inside the device changes rapidly from 15°C to 23°C. The relationship between AC voltage and discharge amount changes significantly depending on the temperature, and it is not possible to set an AC voltage (set voltage) that will result in the target discharge amount between two points in the discharge area, and an AC voltage outside of detection is set, which may result in an excessive discharge amount.

[0008] The reason is that the impedance (temperature and humidity of the charging roller, film thickness of the photosensitive drum) changes drastically depending on the environment and usage history, so the curve of the relationship between voltage and discharge amount changes. Therefore, in order to find from a small number of points, if the discharge amount is not determined from the discharge amount detected from the control voltage near the set voltage determined by the target discharge amount, the linearity of the curve of the relationship between voltage and discharge amount will be lost, resulting in an excessive discharge amount and shortening the drum life.

[0009] As a result, even if the number of sheets used is the same, the actual life span can vary greatly depending on the user's use case. It is necessary to improve the drum CRG life span and the accuracy of life span prediction for users in a variety of usage environments.

[0010] An object of the present invention is to provide an image forming apparatus that is capable of performing more appropriate discharge current control and improving drum life even when used in an environment with rapid temperature changes. [Means for solving the problem]

[0011] In order to achieve the above object, an image forming apparatus according to one aspect of the present invention has the following configuration: That is, the image forming apparatus is a charging method for applying an AC+DC superimposed voltage to perform charging, and has a discharge calculation means for changing the control voltage Vpp at two or more points and detecting or calculating the discharge amount corresponding to the voltage, and is characterized in that in AC charging control for determining a set voltage that results in a predetermined discharge amount from the relationship between the control voltage and the discharge amount, the second and subsequent control voltages Vpp are changed based on the difference between the discharge amount corresponding to the previous control voltage and the discharge amount corresponding to the current control voltage. Effect of the Invention

[0012] According to the present invention, even when used in an environment where there is a sudden change in temperature, more appropriate discharge current control can be performed, thereby improving the drum life. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is an explanatory diagram of an overall configuration of an image forming apparatus. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of an image forming unit. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. 13 is a diagram illustrating a control flow of a comparative example. [Figure 6] FIG. 4 is a conceptual diagram of discharge control in a comparative example. [Figure 7] FIG. 2 is a diagram showing a control flow of the first embodiment. [Figure 8] FIG. 2 is a conceptual diagram of discharge control in the first embodiment. [Figure 9] FIG. 11 is a diagram showing a control flow of the second embodiment. [Figure 10] FIG. 11 is a conceptual diagram of discharge control in the second embodiment. [Figure 11] FIG. 11 is a diagram showing a control flow of the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiment may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions, and the scope of the present invention is not limited to the following embodiment.

[0015] [Example 1] §1. {Explanation of the general configuration of the image forming apparatus} <Image forming device> FIG. 1 is an explanatory diagram of the configuration of an image forming apparatus.

[0016] As shown in FIG. 1, image forming apparatus 100 is a tandem intermediate transfer type full-color printer in which yellow, magenta, cyan and black image forming units PY, PM, PC and PK are arranged along intermediate transfer belt 90.

[0017] In the image forming station PY, a yellow toner image is formed on the photosensitive drum 1Y and transferred to the intermediate transfer belt 90. In the image forming unit PM, a magenta toner image is formed on the photosensitive drum 1M and transferred to the intermediate transfer belt 90. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 1C and 1K, respectively, and transferred to the intermediate transfer belt 90.

[0018] A full-color toner image formed by superimposing four color toner images is transported to secondary transfer section 11 as intermediate transfer belt 90 rotates, and is secondarily transferred to recording material 13. Recording material 13 taken out of a recording material cassette (not shown) is separated one by one by secondary transfer section 11 and transported to registration rollers 12. Registration rollers 12 send recording material 13 to secondary transfer section 11 in synchronization with the toner image on intermediate transfer belt 90. Recording material 13 to which the full-color toner image has been secondarily transferred in secondary transfer section 11 is heated and pressurized by a fixing device (not shown) to fix the image to its surface, and then discharged outside the apparatus.

[0019] The image forming units PY, PM, PC, and PK are configured almost identically, except that the colors of toner used in the developing devices 4Y, 4M, 4C, and 4K are different. In the following, the image forming unit PY will be described, and the image forming units PM, PC, and PK will be described by replacing the Y at the end of the reference numerals of the components of the image forming unit PY with M, C, and K.

[0020] §2. {Explanation of the general configuration of the image forming unit} FIG. 2 is an explanatory diagram of the configuration of the image forming unit (PY).

[0021] As shown in FIG. 2, the image forming section PY has a charging roller 2Y, a charging roller cleaning member 8Y, an exposure device 3Y, a developing device 4Y, a cleaning blade 7Y, and a primary transfer roller 9Y arranged around a photosensitive drum 1Y.

[0022] <Configuration of charging roller 2Y> As shown in Fig. 3, the charging roller 2Y is composed of a core metal 20Y, a base layer 21Y, and a surface layer 22Y. The core metal 20Y is made of chrome-plated iron, the base layer 21Y is made of hydrin rubber, and the surface layer 22Y is made of a material based on nylon resin. The shape of the charging roller surface layer is produced by mixing it with paint containing nylon resin particles 23Y and coating it as shown in Fig. 4. The diameter of the nylon resin particles 23Y is changed to change the surface roughness. The materials and manufacturing methods of the charging roller are not limited to those mentioned above, and general rubber and resin materials can be used.

[0023] The charging roller 2Y is a rubber roller with an outer diameter of 14 mm, a volume resistivity of 10^7 (Ω·cm), and a hardness of 65° (JIS-A). In this embodiment, the surface roughness of the charging roller is Rz=12 μm, Sm: 100 μm.

[0024] Surface roughness Rz, Sm is measured in the axial direction of the charging roller surface in accordance with JIS roughness standard B0601 ('82). Measuring instrument: Tokyo Precision Surface Roughness Meter equivalent to Surfcom 480 (contact type), measuring point: one point in the longitudinal center, vertical magnification: x2000, horizontal magnification: x50, measuring conditions: cutoff λc 0.8 mm, measuring length: 4.0 mm, feed speed: 0.3 mm / s.

[0025] AC+DC are superimposed on the charging roller 2Y through the core metal 20Y, and the set voltage is determined based on the AC discharge amount control described below, with DC at -750V and AC at -750V. The voltage is adjusted so that the photoconductor surface potential is -700V. The photoconductor 1 is rotated by a drive motor (not shown) in the direction of the arrow around the central shaft at a process speed of 320mm / sec.

[0026] §3.{Determination of set voltage by controlling discharge amount} FIG. 4 shows a control block diagram required for discharge amount control (the same configuration is used for both the comparative example and the embodiment). An AC voltage Vac [Vpp] is supplied from an AC voltage power source 104 to the charging roller 2. Since the optimal AC voltage Vac [Vpp] varies depending on the operating environment, the AC discharge amount control described below is performed.

[0027] The control flow of the comparative example is shown in FIG. 5, a conceptual diagram of discharge control is shown in FIG. 6, and control data is shown in Table 2.

[0028] [Table 1]

[0029] When discharge amount control is performed, a command is issued from the CPU 101 shown in FIG. 4, and a control voltage preset in the ROM 103 and the result of the previous control are temporarily recorded in the RAM 102.

[0030] First, when the operating environment is 15°C, there is a relationship between Vac [Vpp] and the AC discharge amount, as shown by discharge curve B in Figure 6.

[0031] FIG. 5 (S501) Control voltages 1B and 2B are applied, and discharge amount detections B1 and B2 are performed.

[0032] A control voltage of 1700 Vpp is applied as control voltage 1B, and a control voltage of 1800 Vpp is applied as control voltage 2B. From the applied control voltages, a current waveform detection circuit 105 detects the current waveform, and a voltage waveform detection circuit 106 detects the voltage waveform. The detection data is stored in the RAM 102.

[0033] The discharge amount is calculated from the stored data in a discharge amount calculation unit 111. Details of the calculation method will be omitted.

[0034] As a result, the detected discharge amounts B1 and B2 corresponding to the control voltages 1B and 2B were 40 uA and 80 uA, respectively.

[0035] Figure 5 (S502) Calculates the set voltage B to achieve the target discharge amount The control voltage calculation unit 110 performs linear interpolation between the above two points and determines the set voltage B of 1750 Vpp, which gives a target discharge amount of 60 uA.

[0036] Next, when the operating environment is 23°C, there is a relationship between Vac [Vpp] and the AC discharge amount, as shown by discharge curve A in Figure 6.

[0037] A use case is considered in which the temperature detection unit 23 located near the charging roller 2 changes the temperature from 15° C. to 23° C. The control in this case where the temperature has changed to 23° C. compared to the previous control in which the temperature was controlled at 15° C. will be described.

[0038] Figure 5 (S511) Temperature difference < 3℃ As described above, when there is a temperature change, the control execution calculation unit 112 determines whether to execute discharge control since the temperature difference is 8° C.

[0039] Figure 5 (S512) Discharge amount detection A1, A2 at control voltage 1A, 2A The control voltage 1A is 1700 Vpp, and 1B is 1800 Vpp, and the corresponding detected discharge amounts A1 and A2 are 120 uA and 240 uA, respectively.

[0040] Figure 5 (S513) Calculation of set voltage A to achieve target discharge amount The set voltage B of 1600 Vpp is determined so that the target discharge amount is 60 uA. However, as shown in Figure 6, since the true discharge curve is A, the amount of discharge becomes 80 uA because A4 ⇒ A3, which is excessive discharge and increases damage to the photosensitive drum. Furthermore, if the discharge amount is also used to predict the lifespan, the prediction accuracy will decrease. The AC discharge amount control of this embodiment will be described. FIG 7 shows the control flow of the first embodiment, FIG 8 shows a conceptual diagram of the discharge control, and Table 2 shows the control data. The key point is to predict the discharge curve from the difference between the previous and current discharge amounts, and to change the control voltage so that the set voltage becomes the target discharge amount between the control voltages, thereby optimizing the discharge amount.

[0041] [Table 2]

[0042] When the operating environment is 23°C, the relationship between Vac [Vpp] and the AC discharge amount is the same as the discharge curve A in Figure 6, as shown in C. We will explain the control in the current case where the temperature has changed to 23°C compared to the previous control, which was performed at 15°C.

[0043] Figure 7 (S701) Temperature difference < 3℃ As described above, when there is a temperature change, the control execution calculation unit 112 determines that the temperature difference is 8° C., and therefore executes discharge control.

[0044] FIG. 7 (S702) Discharge amount C1 of control voltage 1C>Previous discharge amount B1 The control voltage 1C is 1700 Vpp. The detected discharge amount C1 was 120 uA, so the previous discharge amount B1 was 40 uA. By comparison, it can be seen that the current detected discharge amount C1 is larger than B1.

[0045] Figure 7 (S703) Control voltage C2 = Control voltage C1 - α Since it can be determined that the discharge characteristics have changed significantly, the control voltage C2 is set to α200V, and C2 is set to 1500Vpp. α is adjusted according to the frequency of control and the usage history.

[0046] Figure 7 (S704) Discharge amount detected by applying control voltage C2 The control voltage 2C is 1500Vpp. The detected discharge amount C2 is 40uA.

[0047] Figure 7 (S705) Calculates the set voltage B to achieve the target discharge amount The target discharge amount C is set to 60uA, and the set voltage C is set to 1550Vpp. In this way, compared to the comparative example, the optimal set voltage was determined. As shown in Figure 8, the true discharge curve C allows the optimal discharge amount to be determined.

[0048] In this way, excessive discharge can occur when the discharge curve changes due to fluctuations in the impedance of the charging roller 2 or the photosensitive drum 1. In this embodiment, explanation is given using temperature, but it is effective for various use cases such as moisture content, humidity, and usage history (photosensitive drum wear, one job length), etc.

[0049] [Example 2] The AC discharge amount control according to the second embodiment will be described.

[0050] FIG. 9 shows the control flow of the second embodiment, FIG. 10 shows a conceptual diagram of discharge control, and Table 3 shows the control data.

[0051] The point is that when a set voltage is not set between the control voltages, a control voltage is added so as to be sandwiched between the control voltages.

[0052] [Table 3]

[0053] When the operating environment is 23°C, the relationship between Vac [Vpp] and the AC discharge amount is as shown by curve D, which is the same as curve A in Figure 10. We will explain the control in this case where the temperature has changed to 23°C compared to the previous control, which was performed at 15°C.

[0054] Figure 9 (S901) Temperature difference < 3℃ As described above, when there is a temperature change, the control execution calculation unit 112 determines that the temperature difference is 8° C., and therefore executes discharge control.

[0055] Figure 9 (S902) Discharge amount detection D1 at control voltage 1D, discharge amount detection D2 at control voltage 2D The control voltage 1D is 1700Vpp. The detected discharge amount D1 is 120uA. The control voltage 2D is 1800Vpp. The detected discharge amount D2 is 240uA. Figure 9 (S903) Calculate the set voltage DD to achieve the target discharge amount The target discharge amount D is determined to be 60uA, and the set voltage DD1600Vpp is determined.

[0056] Figure 9 (S904) Set voltage DD is below control voltage 1D It can be seen that the set voltage DD1600Vpp is smaller than the control voltage 1D1700Vpp.

[0057] As shown in Figure 10, the discharge curve is D, so we can see that the DD point is shifted.

[0058] In this case, the discharge curve rises.

[0059] Figure 9 (S904) Set voltage DD is greater than control voltage 2D Although this is not the case in the present embodiment, if the control voltage is greater than the control voltage, it is assumed that the current discharge curve is flatter than the previous discharge curve.

[0060] Figure 9 (S905) Control voltage 3D = Control voltage 1D - β Since it can be determined that the discharge characteristics are increasing, in order to implement additional control, The control voltage 3D is set to β=200V, and 3D is set to 1500Vpp.

[0061] Figure 9 (S906) Discharge amount detection by applying control voltage 3D D3 The control voltage 3D is 1500Vpp. The detected discharge amount D3 is 40uA.

[0062] Figure 9 (S907) Calculates the set voltage D to achieve the target discharge amount The target discharge amount D is determined to be 60 uA, and the set voltage D1550 Vpp is determined.

[0063] In this way, the optimum set voltage could be determined in comparison with the comparative example.

[0064] Since the true discharge curve is D as shown in FIG. 10, the optimal discharge amount could be determined.

[0065] [Example 3] The AC discharge amount control of the third embodiment will be described. (See Fig. 10 for a conceptual diagram of discharge control and Table 3 for control data.) The key points are S1102 and S1103, and the number of control times is preset depending on the environment after the change.

[0066] When the operating environment is 23°C, the relationship between Vac [Vpp] and the AC discharge amount is as shown by curve D, which is the same as curve A in Figure 10. We will explain the control in this case where the temperature has changed to 23°C compared to the previous control, which was performed at 15°C.

[0067] Figure 11 (S1101) Temperature difference < 3°C As described above, when there is a temperature change, the control execution calculation unit 112 determines that the temperature difference is 8° C., and therefore executes discharge control.

[0068] Figure 11 (S1102) Temperature > 22℃ When the number of control times is preset, the discharge characteristics tend to become stronger when the temperature is 22°C or higher, so a 3D point is preset.

[0069] Figure 11 (S1103) Discharge amount detection with control voltage The control voltage 1D is 1700Vpp. The detected discharge amount D1 is 120uA. The control voltage 2D is 1800Vpp. The detected discharge amount D2 is 240uA. The control voltage 3D is 1500Vpp. The detected discharge amount D2 is 40uA. Like, if the temperature is not high, The control voltage 1D is 1700Vpp. The detected discharge amount D1 is 120uA. The control voltage 2D is 1800Vpp. The detected discharge amount D2 is 240uA. Control is carried out using

[0070] Figure 11 (S1104) Calculation of the set voltage D to achieve the target discharge amount The target discharge amount D is determined to be 60 uA, and the set voltage D1550 Vpp is determined.

[0071] In this way, the optimum set voltage could be determined in comparison with the comparative example.

[0072] · As shown in Figure 10, the true discharge curve is D, so the optimal discharge amount could be determined.

[0073] From the above, even when the control voltage that determines the amount of discharge is low and the environment changes significantly, the optimal amount of discharge can be determined, thereby minimizing damage to the drum. [Explanation of symbols]

[0074] 2. Charge roller 20 AC voltage power supply 21 Current waveform detection circuit 22 Voltage waveform detection circuit 23 Temperature detection unit 101 CPU 102 RAM 103 ROM 110 Control voltage calculation unit 111 Discharge amount calculation section 112 Control execution calculation unit

Claims

1. A charging method in which charging is performed by applying an AC+DC superimposed voltage, A discharge calculation means is provided for changing the control voltage Vpp at two or more points and detecting or calculating the discharge amount corresponding to the voltage, In an image forming apparatus, in AC charging control in which a set voltage that results in a predetermined discharge amount is determined from the relationship between the control voltage and the discharge amount, the control voltage Vpp from the second point onwards is changed based on the difference between the discharge amount corresponding to the previous control voltage and the discharge amount corresponding to the current control voltage.

2. 2. The image forming apparatus according to claim 1, wherein the control voltages from the second point onwards are changed in accordance with a temperature and a durability of the image forming apparatus.

3. 3. The image forming apparatus according to claim 1, wherein the number of times of control from the second point onwards is changed depending on a temperature and a durability number of sheets.

4. A charging method in which charging is performed by applying an AC+DC superimposed voltage, A discharge calculation means is provided for changing the control voltage Vpp at two or more points and detecting or calculating the discharge amount corresponding to the voltage, An image forming apparatus characterized in that in AC charging control in which a set voltage that provides a predetermined discharge amount is determined from the relationship between the control voltage and the discharge amount, a third and subsequent control voltages Vpp are changed based on the difference between the set voltage and the control voltage.

5. 5. The image forming apparatus according to claim 4, wherein the control voltages from the second point onwards are changed in accordance with a temperature and a durability of the image forming apparatus.

6. 6. The image forming apparatus according to claim 4, wherein the number of times of control from the second point onwards is changed depending on the temperature and the number of sheets that can be used.

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