Image formation apparatus

Abstract

To provide a charging device and an image formation apparatus that enable removal of deposits from a photoreceptor without complicating a structure.SOLUTION: Photoreceptor drums (28k, 28c, 28m, 28y) are charged by a charging roller (48). An image forming apparatus is provided with a DC charging circuit (56) that DC-charges the photoreceptor drums with a DC voltage in a first period related to image formation processing and an AC charging circuit (58) for grinding that superimposes an AC voltage on the DC voltage for superimposition-charging in order to grind the surfaces of the photoreceptor drums in a second period other than the first period. The DC charging circuit (56) is provided with DC power supplies (57k, 57c, 57m, 57y) as many as the photoreceptor drums (28k, 28c, 28m, 28y), allowing individual DC-charging of the corresponding photoreceptor drums. The AC charging circuit (58) for grinding is provided with AC power supplies (59) which is less in number than the DC power supplies.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to an image forming apparatus, and more particularly to an image forming apparatus that removes foreign matter (for example, charging products, ozone products, etc.), toner, developer, and other adhering matter adhering to the surface of a photoconductor drum. [Background technology]

[0002] This type of background art is disclosed in Patent Document 1. In Patent Document 1, a rubbing polishing roller is provided, and polishing is performed by applying pressure to remove deposits. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-065434 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the background art of Patent Document 1, it is necessary to provide a structure such as a polishing roller, which makes the structure complicated.

[0005] Therefore, an object of the present disclosure is to provide a novel image forming apparatus.

[0006] Another object of the present disclosure is to provide an image forming apparatus that enables removal of deposits on a photoconductor without complicating the structure. [Means for solving the problem]

[0007] In order to solve the above problems, the present disclosure employs the following configurations. Note that the reference symbols and supplementary explanations in parentheses indicate the corresponding relationship with the embodiments described to facilitate understanding of the present disclosure, and are not intended to be limiting.

[0008] The first embodiment is an image forming apparatus having a charging device that charges a photosensitive drum via a charging roller, the image forming apparatus having a DC charging circuit that charges the photosensitive drum with a DC voltage during a first period related to image formation processing, and a grinding AC charging circuit that outputs an AC voltage to grind the surface of the photosensitive drum during a second period other than the first period and superimposes it on the DC voltage to provide superimposed charging.

[0009] In the first embodiment, an image forming apparatus (10: reference symbols illustrating corresponding parts in the embodiments, not intended to be limiting; the same applies below) includes photoconductor drums (28k, 28c, 28m, 28y), each of which is supplied with a charging voltage via a charging roller (54). A DC charging circuit (56) charges the photoconductor drum with a DC voltage during a first period related to image formation processing. A grinding AC charging circuit (58) outputs an AC voltage to grind the surface of the photoconductor drum during a second period other than the first period, and superimposes the AC voltage on the DC voltage to perform superimposed charging.

[0010] According to the first embodiment, a DC charging method that does not easily scrape the surface of the photosensitive drum is adopted during image formation processing, making it possible to use a relatively inexpensive photosensitive drum, and a superimposed charging method is adopted using an AC charging circuit only for removing adhesions, so that it is possible to remove more adhesions from the photosensitive drum surface than expected with an inexpensive circuit configuration and output precision of the DC charging method, and to improve image deterioration at a relatively low cost.

[0011] The second embodiment is an image forming apparatus dependent on the first embodiment, and includes a plurality of photosensitive drums each corresponding to a different color. The DC charging circuit has a plurality of DC power supplies that apply a DC voltage to each of the plurality of photosensitive drums. The grinding AC charging circuit has a smaller number of AC power supplies than the DC power supplies.

[0012] In the second embodiment, for example, when four photoconductor drums (28k, 28c, 28m, 28y) are provided to form a four-color image, the DC charging circuit (56) is provided with four DC power supplies (57k, 57c, 57m, 57y) corresponding to the four photoconductor drums, respectively. On the other hand, the grinding AC charging circuit (58) is provided with one, two or three AC power supplies (59, 59kc, 59my, 59k, 59c), which is less than the number of DC power supplies.

[0013] According to the second embodiment, the number of AC power sources in the grinding AC charging circuit is made smaller than the number of DC power sources in the DC charging circuit, thereby making it possible to reduce costs.

[0014] A third embodiment is an image forming apparatus dependent on the first embodiment, further comprising an image formation number counter which counts the number of times an image forming operation has been performed, and a first judgment unit which judges whether the count value of the image formation number counter has reached a predetermined value, and when the first judgment unit judges that the count value of the image formation number counter has reached the predetermined value, an AC charging circuit for grinding is activated.

[0015] In the third embodiment, the image formation counter (88d) counts the number of times that an image formation operation using a photosensitive drum has been performed. The first determination unit (S2) determines whether the count value (i) of the image formation counter has reached a predetermined value (N). When the first determination unit (S2) determines that the count value (i) has reached the predetermined value (N), the grinding AC charging circuit (58) is operated in a second period.

[0016] According to the third embodiment, the grinding AC charging circuit is operated at a timing when the possibility of image deterioration due to deposits on the surface of the photosensitive drum increases, so that deposits on the surface of the photosensitive drum can be effectively removed.

[0017] The fourth embodiment is an image forming apparatus subordinate to the first embodiment, and further includes a process control execution unit that executes process control using a patch image, and a second judgment unit that judges whether the patch image has density unevenness, and when the second judgment unit judges that the patch image has density unevenness, an AC charging circuit for grinding is activated.

[0018] In the fourth embodiment, a process control execution unit (86e, S4) executes process control using a patch image. A second determination unit (S5) determines whether or not there is density unevenness as a result of the process control processing. When the second determination unit (S5) determines that there is density unevenness, the grinding AC charging circuit (58) is activated.

[0019] According to the fourth embodiment, by performing grinding of the photosensitive drum during image formation when patch density unevenness is detected during process control, it is possible to improve image deterioration at a relatively early timing.

[0020] The fifth embodiment is an image forming apparatus dependent on the first embodiment, further including a limiting unit that limits the number of rotations of the photosensitive drum when the AC voltage is superimposed on the DC voltage during the second period to perform superimposed charging.

[0021] In the fifth embodiment, a grinding rotation number counter (88e) is provided, and a limiting unit (S33, S34) stops superimposed charging by the grinding AC charging circuit when the count value of this counter reaches a predetermined value (X).

[0022] According to the fifth embodiment, it is possible to prevent the photosensitive drum from being excessively ground. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram showing an image forming apparatus according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic diagram showing an example of the periphery of one image station including a charging roller in the embodiment shown in FIG. [Diagram 3]FIG. 3 is a circuit diagram showing a main part of a first example of a charging device according to the embodiment. [Figure 4] FIG. 4 is a circuit diagram showing a main part of a second example of a charging device according to the embodiment. [Diagram 5] FIG. 5 is a circuit diagram showing a main part of a third example of a charging device according to the embodiment. [Figure 6] FIG. 6 is a block diagram showing an example of the electrical configuration of the image forming apparatus according to the embodiment. [Figure 7] FIG. 7 is an illustrative view showing an example of a memory map of the memory (RAM) of the first embodiment. [Figure 8] FIG. 8 is a flow chart showing an example of the operation in the first embodiment. [Figure 9] FIG. 9 is an illustrative view showing an example of a memory map of a memory (RAM) according to the second embodiment. [Figure 10] FIG. 10 is a flow chart showing an example of the operation in the second embodiment. [Figure 11] FIG. 11 is a flow chart showing an example of the operation in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 1, an image forming apparatus 10 according to an embodiment of the present disclosure is, for example, a multifunction peripheral (MFP) having a copy function, a printer function, a scanner function, a facsimile function, etc. However, it should be noted in advance that the present disclosure can be applied to any image forming apparatus having one or more of these functions. In addition, although the present disclosure is directed to a charging device of such an image forming apparatus, the overall configuration will be outlined here to the extent necessary for understanding the embodiment.

[0025] The image forming apparatus 10 includes a main body 12 and an image reading unit 14 disposed above the main body 12. A document table 16 is disposed above the image reading unit 14, and a document (not shown) placed on the document table 16 is read by a scanner 18 included in the image reading unit 14. For example, the surface of the document is exposed to light by a light source unit 18a including a plurality of LEDs arranged in the main scanning direction, and the light reflected from the surface of the document is guided by a mirror unit 18b to an imaging lens of an imaging unit 18c, which then forms an image of the reflected light on a light receiving element of a line sensor such as a CCD or CIS by the imaging lens. The line sensor detects the luminance and chromaticity of the reflected light imaged on the light receiving element, and image data based on the image of the document surface is generated.

[0026] An original pressing cover is provided above the original table 16 so as to be freely opened and closed, and the original pressing cover is further provided with an ADF (original document feeder) 22 that feeds originals placed on an original placement tray 20 one sheet at a time to an original reading position P1. When the original passes through the original reading position P1, it is read by a scanner 18.

[0027] A control unit (FIG. 6) and an image forming unit 24 are provided in the main body 12 of the image forming apparatus 10. As shown in FIG. 6, the control unit includes a computer or the like that functions as a main control unit 66, and transmits control signals to each part of the image forming apparatus 10 in response to input operations to an operation unit 74, causing the image forming apparatus 10 to perform various operations.

[0028] The image forming section 24 includes an exposure unit 26, a photoconductor drum 28, a charging device 30, a developing device 32, a cleaning unit 36 ​​including a cleaning blade 34, a transfer belt 38, a transfer roller 40, a fixing section 42, and the like.

[0029] The transfer belt 38 of the image forming unit 24 is stretched over a driving roller 44a and a driven roller 44b, and is moved in the direction of the arrow A by the driving roller 44a being driven by a motor 78 (FIG. 6) according to an appropriate transmission ratio by a gear train (not shown). The transfer belt 38 is arranged so as to come into contact with the photosensitive drum 28. Although details will be described later, a toner image is formed on the photosensitive drum 28 by the developing device 32, and the toner image formed on the photosensitive drum 28 is primarily transferred onto the surface of the transfer belt 38. The toner image primarily transferred onto the transfer belt 38 is supplied from a paper feed cassette 48a or a manual paper feed tray 48b constituting the paper feed unit 46 at a contact portion N with the transfer roller 40 that rotates clockwise, is conveyed by a conveying roller 50, and is secondarily transferred onto a sheet (recording medium) conveyed via a path P2. The toner image transferred onto the sheet is heated / melted by the fixing unit 42 and fixed onto the sheet, and the sheet with the fixed toner image is discharged onto the discharge tray 52.

[0030] Image data for forming an image on paper may be image data read by the image reading unit 14 or image data sent from an external computer. Path P3 is used as a paper inversion location when printing on both sides of the paper.

[0031] The image data handled by the image forming apparatus 10 corresponds to color images of four colors: black (K), cyan (C), magenta (M), and yellow (Y). For this reason, four photoconductor drums 28, charging devices 30, developing devices 32, and cleaning units 36 are provided, one for each color, so as to form four types of latent images corresponding to each color, and these constitute four image stations.

[0032] Referring also to FIG. 2, each image forming station includes the photoconductor drum 28, the charging device 30, the developing device 32, the cleaning unit 36 ​​having the cleaning blade 34, a charge removing section (not shown), and the like, as described above.

[0033] The photoconductor drum 28 is an example of an image carrier, and has a base, which is a cylindrical conductive member made of a conductive material such as aluminum. This base is grounded through the main body 12 of the image forming apparatus 10. A photosensitive layer is formed on the surface (outside) of the base of the photoconductor drum 28. The photosensitive layer is insulating when not irradiated with light, and becomes conductive only in the irradiated area when irradiated with light. The photoconductor drum 28 is provided so that the outer peripheral surface of the photosensitive layer (sometimes referred to as the surface of the photoconductor drum 28 or the outer peripheral surface of the photoconductor drum 28) abuts against the outer surface of the transfer belt 38.

[0034] The charging device 30 uniformly charges the surface of the photoconductor drum 28 to a predetermined potential (for example, −550 V). To this end, the charging device 30 has a charging roller 54 to which a charging voltage is applied. The charging roller 54 has a base body that is a cylindrical conductive member and a conductive elastic member provided on the surface (outer circumferential surface) of the base body, and is provided so that the conductive elastic member abuts against the surface of the photoconductor drum 28. When the photoconductor drum 28 rotates, the charging roller 54 is rotated in the direction opposite to the rotation direction of the photoconductor drum 28.

[0035] The charging device 30 includes a DC charging circuit 56, which is a DC voltage source, and an AC charging circuit 58 for grinding. During the image formation process, a DC voltage Vdc generated by the DC charging circuit 56 is supplied to the charging roller 54, and the photosensitive drum 28 is DC-charged.

[0036] The AC voltage Vac generated by the grinding AC charging circuit 58 is supplied to the charging roller 54 via a coupling capacitor 60 when the photosensitive drum 28 is ground as necessary during periods other than image formation processing.

[0037] In other words, the DC power supply 56 and the AC power supply 58 of the charging device 30 can be turned on / off individually, and the on / off is controlled by a computer (CPU) 70 (FIG. 6) described later depending on whether the image formation process is in progress or not.

[0038] Furthermore, the peak-to-peak voltage value Vpp of the AC voltage Vac can also be adjusted (controlled) by the computer (CPU) 70. The DC voltage Vdc is a negative voltage with respect to the ground potential, for example, −550 V. This DC voltage Vdc becomes the charging potential of the photoconductor drum 28. The value of the output voltage Vdc from the DC power supply 56 can also be adjusted (controlled) by the computer (CPU) 70.

[0039] The frequency of the AC voltage Vac varies depending on conditions, but is, for example, 1950 Hz. The AC voltage Vac is, for example, a sine wave voltage, and its peak-to-peak voltage value Vpp is set to a voltage necessary for grinding at least the surface of the photoconductor drum 28, for example, 1.5 kVpp.

[0040] The surface of the photoconductor drum 28 thus charged is exposed according to an image to be output by an exposure unit 26 (FIG. 1) having a light-emitting portion. The exposed area of ​​the photosensitive layer of the photoconductor drum 28 becomes conductive, and the potential is removed from the grounded substrate, dropping from -550 V to a potential VL of -100 V or less, forming an electrostatic latent image whose surface potential varies according to the image data.

[0041] The developing device 32 includes a stirring member that conveys and stirs a developer (two-component developer) containing granular carriers made of a magnetic material and non-magnetic, insulating toner having a particle size smaller than that of the carrier, and a developing roller (magnetic roller) 62 that carries the developer on its surface. The stirring member stirs the toner together with the carrier, thereby frictionally charging the toner so that the toner has a predetermined charge, and conveys the toner to the developing roller 62. The developing roller 62 is made of a non-magnetic conductive material (for example, aluminum), and is rotatably supported by the developing device 32. A plurality of magnets (not shown) are fixedly disposed inside the developing roller 62 so as not to rotate with the developing device 32. A magnetic brush made of carriers and toner is formed on the surface of the developing roller 62 by the magnetic force of the plurality of magnets. When the developing roller 62 rotates, the magnetic brush containing the toner rotates together with the developing roller 56, and is sent to the photoconductor drum 28. A developing bias voltage Vd of, for example, −475 V is supplied to the developing roller 62 from a developing bias power supply (bias power supply) 64. When the magnetic brush approaches the surface of the photosensitive drum 28 while the developing bias voltage Vd is being supplied to the developing roller 62, the toner contained in the magnetic brush is separated from the magnetic brush and electrostatically moves toward the photosensitive drum 28 due to the potential difference between the potential VL, which is the image area of ​​the electrostatic latent image formed on the circumferential surface of the photosensitive drum 28, and the developing bias voltage Vd, forming a toner image.

[0042] The toner image formed on the peripheral surface of the photoconductor drum 28 is primarily transferred to the transfer belt 38, and then secondarily transferred at a contact portion N between the transfer belt 38 and the transfer roller 40 onto the paper transported from the paper feed unit 46 by the transport roller 50. The toner image transferred onto the paper is heated / melted by the fixing unit 42 and fixed onto the paper, and the paper with the fixed toner image is discharged onto the discharge tray 52.

[0043] Residual toner remaining on the peripheral surface of the photoconductor drum 28 after the primary transfer is scraped off by a cleaning blade 34 and collected by a cleaning unit 36 ​​.

[0044] During the image forming process, the static electricity on the surface of the photoconductor drum 28 is then removed by a charge removing device (not shown), and the steps following charging by the charging device 30 are repeated.

[0045] 2, one grinding AC charging circuit 58 is provided for one DC charging circuit 56. Therefore, for example, in an image forming apparatus having four image forming stations, four grinding AC charging circuits 58 are provided.

[0046] However, the grinding AC charging circuit 58 in this embodiment is not used for superimposed charging of DC and AC during image formation processing, but is used only to remove deposits from the surface of the photosensitive drum 28. Therefore, in the embodiment of FIG. 3, only one AC power supply 59 is used for the four DC power supplies 57k, 57c, 57m and 57y.

[0047] More specifically, the DC charging circuit 56 in this embodiment is provided with four DC power sources 57k, 57c, 57m and 57y corresponding to the four color images of black (K), cyan (C), magenta (M) and yellow (Y), and in the image forming process, a DC charging voltage is supplied to the photoconductor drum 28k, the photoconductor drum 28c, the photoconductor drum 28m and the photoconductor drum 28y of each station, respectively.

[0048] In contrast, in the grinding AC charging circuit 58, only one AC power source 59 is provided, and when the photoconductor drums 28k, 28c, 28m, and 28y are to be ground outside the image formation processing period, the grinding AC voltage from the AC power source 59 is superimposed on the DC voltage from the DC power sources 57k, 57c, 57m, and 57y of the DC charging circuit 56 via coupling capacitors 60k, 60c, 60m, and 68y, and supplied to the photoconductor drums 28k, 28c, 28m, and 28y through their respective charging rollers.

[0049] As is well known, the DC charging method discharges less electricity to the photoconductor than the AC charging method, and the surface of the photoconductor is hardly scraped away, so the photoconductor has a relatively long life, but on the other hand, when foreign matter (charged products, ozone products, etc.) adheres to the surface of the photoconductor, it is difficult to remove such adhesions. In addition, the DC charging method has the characteristic that the required voltage precision (for example, ±1.0%) can be relatively easily ensured.

[0050] In the AC charging system, the amount of discharge to the photoconductor is larger than in the DC charging system, and the surface of the photoconductor is easily scraped, so the life of the photoconductor is relatively short, and photoconductors that are expensive and difficult to grind are generally used. In addition, the AC charging system is characterized by the requirement for relatively strict voltage accuracy.

[0051] Therefore, in this embodiment, a DC charging method that is less likely to scrape the surface of the photosensitive drum is adopted during image formation processing, making it possible to use a relatively inexpensive photosensitive drum, and a superimposed charging method using an AC charging circuit is adopted only for removing adhering substances.

[0052] In detail, during timing related to image formation, the grinding AC charging circuit 58 is not operated (output), and the photosensitive drums 28 (28k, drums 28c, 28m and 28y) are charged only with the DC component from the DC charging circuit 56 to form an image.

[0053] On the other hand, to address image deterioration due to adhesions on the surfaces of the photosensitive drums 28 (28k, 28c, 28m and 28y), the grinding AC charging circuit 58 is operated (output) while rotating the photosensitive drums 28 (28k, 28c, 28m and 28y) at a timing unrelated to image generation (image forming process), and a high-voltage output in which the AC component from the grinding AC charging circuit 58 is superimposed on the DC component from the DC charging circuit 56 is applied to the photosensitive drums 28 (28k, 28c, 28m and 28y) via coupling capacitors 60 (60k, 60c, 60m and 60y).

[0054] This control method makes it possible to remove more than expected amounts of adhesion from the photoconductor surface using an inexpensive circuit configuration and the output precision of a DC charging method, thereby improving image deterioration at a relatively low cost.

[0055] In addition, since the grinding AC charging circuit 58 operates (outputs) at a timing unrelated to image formation, the output voltage precision of the AC component is not required very much. It is sufficient if the output voltage precision is such that the photoconductor is not ground unevenly, so it is considered that a precision of ±5% or less is not particularly problematic.

[0056] Incidentally, in the case of a superimposed charging method in which a DC voltage and an AC voltage are superimposed during image formation, the AC component voltage generally needs to be applied at about 1.5 kVpp, and if the voltage accuracy needs to be ±10 Vpp, then a tolerance of ±0.67% is required. In other words, in the case of the conventional superimposed charging method, the voltage accuracy of the AC component needed to be at most ±1.0% or less.

[0057] In contrast, in the case of the AC charging circuit 58 for grinding of the embodiment, a voltage accuracy of about ±2.0% or more and ±5.0% or less is sufficient, and an inexpensive circuit can be used as the AC charging circuit 58 for grinding.

[0058] Another feature of this embodiment is that the number of AC power sources 59 in the grinding AC charging circuit 58 is less than the number of DC power sources 57 in the DC charging circuit 56 (four, 57k, 57c, 57m and 57y in this embodiment).

[0059] That is, in the first example shown in FIG. 3, the number of DC power supplies 57 is four, whereas the number of AC power supplies 59 is one.

[0060] As a second example, it is possible to use four DC power supplies 57 and two AC power supplies 59.

[0061] As a third example, it is possible to provide four DC power supplies 57 and three AC power supplies 59.

[0062] In either example, by making the number of AC power sources 59 of the grinding AC charging circuit 58 less than the number of DC power sources 57 of the DC charging circuit 56, it is possible to reduce costs.

[0063] 4 shows a second example, in which one AC power source 59kc is provided for the photoconductor drums 28k and 28c, and one AC power source 59my is provided for the photoconductor drums 28m and 28y. An AC voltage from the AC power source 59kc is superimposed on a DC voltage from the DC power sources 57k and 57c through coupling capacitors 60k and 60c and applied to the photoconductor drums 28k and 28c, respectively, and an AC voltage from the AC power source 59my is superimposed on a DC voltage from the DC power sources 57m and 57y through coupling capacitors 60m and 60y and applied to the photoconductor drums 28m and 28y, respectively.

[0064] 5 shows a third example, in which one AC power source 59k is provided for photoconductor drum 28k, one AC power source 59c is provided for photoconductor drum 28c, and one AC power source 59my is provided for photoconductor drums 28m and 28y. Then, the AC voltage from AC power source 59k is superimposed on the DC voltage from DC power source 57k through coupling capacitor 60k and applied to photoconductor drum 28k, the AC voltage from AC power source 59c is superimposed on the DC voltage from DC power source 57c through coupling capacitor 60c and applied to photoconductor drum 28c, and the AC voltage from AC power source 59my is superimposed on the DC voltage from DC power sources 57m and 57y through coupling capacitors 60m and 60y and applied to photoconductor drums 28m and 28y, respectively.

[0065] Furthermore, in the second example in which the number of AC power sources is two, in addition to the case in which one AC power source is used to power each of two photosensitive drums as in FIG. 4, one AC power source may be used to power, for example, one photosensitive drum 28k, and one AC power source may be used to power the remaining three photosensitive drums 28c, 28m, and 28y.

[0066] In the third example in which the number of AC power sources is three, either way, as shown in FIG. 5, two AC power sources each power one photosensitive drum, the remaining AC power source powers two photosensitive drums, and the remaining two photosensitive drums are powered by one AC power source.

[0067] Referring to FIG. 6, the image forming apparatus 10 includes a main control unit 66, which is connected to various components by a bus 68.

[0068] The main control unit 66 is essentially a computer, and includes a CPU 70 and a memory 72. The memory 72 includes a RAM, a ROM, a HDD (hard disk drive), etc., although details are not shown. The memory 72 and an operation unit 74 are electrically connected to the CPU 70 via a bus 68. The CPU 70 executes various computer programs in response to instructions from the operation unit 74, etc., to perform the operations of each unit of the image forming apparatus 10. The various computer programs described above are stored in advance in the ROM or HDD, and are expanded into the RAM and executed as necessary.

[0069] The operation unit 74 is provided, for example, on the front side of the document table 16 of the main body 12 shown in FIG. 1, and is used to select functions such as copy, scan, fax, etc., and to input an instruction for the number of copies, for example, through a touch display (not shown).

[0070] The operation unit 74 may also be provided with a photoconductor grinding instruction button 75 used in a third embodiment shown in FIG. 11, which will be described later.

[0071] The bus 68 is further electrically connected to the image reading unit 14, the image forming unit 24, the paper feeding unit 46, and the like.

[0072] As described above, the image reading unit 14 reads image information from an original placed on the original table 16 (FIG. 1) and outputs image data to the main control unit 66. The image forming unit 24 prints an image represented by the image data on paper, and as described above, includes the photoconductor drum 28, the charging device 30, etc.

[0073] The image forming apparatus 10 further includes a DC charging circuit 56 , an AC charging circuit for grinding 58 , a motor control unit 76 , and a communication unit 80 .

[0074] The DC charging circuit 56, in accordance with instructions from the main control unit 66, ie, the CPU 70, controls the on / off of each of the DC power supplies 57 (57k, 57c, 57m, 57y) and controls the output voltage of each of them.

[0075] The grinding AC charging circuit 58 follows instructions from the main control unit 66, ie, the CPU 70, to control the on / off of each of the AC power sources 59 (59kc, 59my, 59k, 59c) and to control the output voltage of each.

[0076] The motor control unit 76 controls the on / off and rotation speed of the motor 78 according to commands from the main control unit 66, i.e., the CPU 70. The motor 78 drives the photosensitive drum 28 and also drives the driven parts such as the drive roller 44a (FIG. 1) of the transfer belt 38 and the transfer roller 40 according to a transmission ratio suited to each of them. In other words, it rotates the process unit.

[0077] The communication unit 86 is for communicating data with external computers, mobile terminals, etc. via a network cable, wirelessly, etc., and when image data to be printed is sent from an external computer or mobile terminal, the CPU 70 of the main control unit 66 controls the image forming unit 24 to form an image from the sent image data.

[0078] Fig. 7 is a diagram showing an example of a memory map of the RAM of the memory 72 in the embodiment shown in Fig. 6. As shown in Fig. 7, the RAM includes a program storage area 82 and a data storage area 84. The program storage area 82 stores a control program for the image forming apparatus 10.

[0079] The control programs for the image forming apparatus 10 include a display control program 86a, an operation detection program 86b, an image forming program 86c, and a grinding charge control program 86d.

[0080] The display control program 86a is a program that generates display screen data necessary to display various screens on the screen of a touch display (not shown) included in the operation unit 74 based on the display image generation data in the display image generation data memory area 88a described below, and uses the display screen data to display images on the touch display.

[0081] The operation detection program 86b is a program for detecting operation data corresponding to an operation on the operation unit 74 and storing the operation data in an operation data storage area 88b described later. For example, when the touch display is touched, the main control unit (computer) 66 acquires touch coordinate data output from the touch display as operation data in accordance with the operation detection program 86b and stores the data in the operation data storage area 88b. When a hardware button or key (not shown) provided on the operation unit 74 is pressed or operated, the main control unit 66 acquires operation data resulting from the pressing or operation of the button or key in accordance with the operation detection program 86b and stores the data in the operation data storage area 88b.

[0082] The image forming program 86c is a program that controls the image forming unit 24 to print image data on recording paper supplied from a paper feed unit. However, this image forming program 86c controls the motor control unit 76 shown in FIG. 6. That is, when a print job is commanded from the operation unit 74, the image forming program 86c controls the motor control unit 76 to turn on the motor 78. This rotates the process unit (a unit formed of a photosensitive drum, etc.). When the motor 78 is turned off, the rotation of the process unit is stopped.

[0083] In detail, this image forming program 86c executes image forming processing by controlling the image reading unit 14 to read the document, controlling the charging device 30 to perform DC charging by the DC charging circuit 56, controlling the paper feed unit 40 to feed paper and also to control the transport of the fed recording paper, developing the electrostatic latent images on the photosensitive drums 28k, 28c, 28m and 28y, controlling the transfer device including the transfer belt 38 and transfer roller 40, and controlling the fixing unit 42 to fix the toner image on the recording paper. This series of operational controls is already well known, and detailed explanations will be omitted.

[0084] The grinding charging program 86d is a program for controlling the DC charging circuit 56 and the grinding AC charging circuit 58 to supply a superimposed DC voltage and an AC voltage to each photosensitive drum when the surfaces of the photosensitive drums 28k, 28c, 28m and 28y should be ground outside of the image processing period.

[0085] Although not shown, the program storage area 74 also stores other programs necessary for controlling the image forming apparatus 10.

[0086] In the data memory area 84, there are set a display image generation data memory area 88a, an operation data memory area 88b, a temporary memory area 88c, an image formation number counter 88d, a grinding rotation number counter 88, a downtime counter 88e, and the like.

[0087] The display image generation data in the display image generation data storage area 88a includes polygon data and texture data for generating a display image, etc. The display image generation data also includes image data corresponding to software keys, image generation data for displaying each screen, etc.

[0088] The operation data in the operation data storage area 88b is operation data detected according to the operation detection program 86b, and is stored in chronological order. Note that the operation data is deleted after being used in the processing of the main control unit 66.

[0089] The temporary storage area 88c temporarily stores image data read by the scanner 18, for example, for image processing by the image processing program 78d.

[0090] The data memory area 84 further includes an image formation count counter 88d, which is incremented each time an image formation operation is performed, and counts how many times the image formation operation (printing operation) has been performed to date.

[0091] The grinding rotation number counter 88e counts how many times the photoconductor drums 28 (28k, 28c, 28m, and 28y) have rotated while the grinding AC charging circuit 58 (FIG. 2) is operating.

[0092] In addition, the data storage area 84 may store other data required for executing the control program of the image forming apparatus 10, and may also be provided with flags and other counters required for executing the control program.

[0093] The operation of the embodiment will be described with reference to Fig. 8. This operation starts when a print job (image forming job) is received based on a user instruction from the operation unit 74 or a print instruction from an external computer or mobile terminal.

[0094] In step S1 of the image forming process, in step S11, the CPU 70 of the main control unit 66 commands the motor control unit 76 to start rotating the motor 78. This causes the process unit including the photoconductor drums 28k, 28c, 28m, and 28y to rotate.

[0095] In the next step S12, the CPU 70 controls the DC charging circuit 56 of the charging device 30 to DC-charge the photoconductor drums 28k, 28c, 28m and 28y, and outputs the developing bias 64 shown in FIG.

[0096] In the next step S13, electrostatic latent images according to the image data are formed on the photoconductor drums 28k, 28c, 28m, and 28y. At this time, since the developing bias has already been output, the electrostatic latent images on the photoconductor drums 28k, 28c, 28m, and 28y are developed to form toner images.

[0097] In the next step S14, paper is fed from the paper feed section 40 and conveyed by the conveying rollers 50.

[0098] In the next step S15, the transfer belt 38 and the transfer roller 40 are used to transfer the toner image onto the conveyed recording paper.

[0099] In the next step S16, the toner image is fixed onto the recording paper by the fixing unit 42, and the paper is discharged.

[0100] A series of image forming processes is completed up to this point, and if there is unprocessed image data, steps S12 to S16 are repeated.

[0101] When there is no more unprocessed image data, the CPU 70 stops the motor 78 in step S18, thereby stopping the process unit.

[0102] Then, in step S19, the image formation number counter 88d in the data memory area 84 is incremented. However, although step S19 is provided at the end of step S1 (image formation process) in Fig. 8, this is for convenience, and in reality, this counter 88d is incremented every time an image formation operation is performed.

[0103] When the image formation process in step S1 is completed, in the next step S2, it is determined whether or not the count value i of the image formation number counter 88d has reached a predetermined value N. Here, the predetermined value N is a value determined depending on the photosensitive drum used, and is a value at which it can be assumed that image unevenness will appear and that grinding of the photosensitive drum will be necessary.

[0104] If "NO" is determined in step S2, the process ends.

[0105] However, if the answer is "YES", the process proceeds to the next grinding process step S3. However, it should be noted that the grinding process step S3 is executed at a timing (period) that is not related to image formation. This is the same in the second embodiment shown in FIG. 10 and in the third embodiment shown in FIG. 11.

[0106] In the first step S31, similarly to the previous step S11, the process rotation is started.

[0107] In the next step S32, the CPU 70 operates the DC charging circuit 56 and the grinding AC charging circuit 58 of the charging device 30, and as described with reference to Figures 3 to 5, the DC voltage from the DC charging circuit 56 and the AC voltage from the grinding AC charging circuit 58 are superimposed and applied to each of the rotating photoconductor drums 28k, 28c, 28m, and 28y in step S33. As described above, by applying an AC voltage, the surfaces of the photoconductor drums 28k, 28c, 28m, and 28y can be ground, and adhesions that have adhered during image formation processing using only DC charging can be effectively removed.

[0108] Incidentally, in step S32 as well, the developing bias 64 (FIG. 2) is output in order to prevent the residual toner on the photoconductor drums 28k, 28c, 28m, and 28y from scattering.

[0109] In this grinding-superimposed charging process, if the photosensitive drum is rotated more than necessary, it will be ground excessively, so in step S33, the grinding-superimposed charging process is stopped when the photosensitive drums 28k, 28c, 28m, and 28y reach a predetermined number of rotations X. According to experiments by the inventors, it has been found that approximately 10 rotations is sufficient, although this varies depending on the material of the photosensitive drum. Therefore, when the grinding-superimposed charging process is started, the CPU 70 increments the grinding rotation number counter 88e in the data storage area 84 for each rotation of the photosensitive drum, and when the count value of the counter 88e reaches the predetermined value X, in step S34, the grinding-superimposed charging is stopped and the development output is also stopped.

[0110] However, it should be noted that although the grinding rotation number counter 88e is incremented for each rotation of each photosensitive drum in step S3, for the sake of convenience, this is shown collectively as step S33 in FIG.

[0111] In the first embodiment of the present disclosure shown in FIGS. 7 and 8, when the number of image forming operations estimated to require removal of adhesions from the photosensitive drum reaches a predetermined value N, superimposed charging for grinding is performed.

[0112] In other words, the grinding superimposed charging process step S3 is executed at a timing when the possibility of image deterioration due to accumulation of foreign matter (charge products / ozone products, etc.) and developer / toner on the photosensitive member surface becomes high, based on the count value of the image formation count counter 88d.

[0113] In addition, such timing is predicted while observing the life condition of the photosensitive drum (mileage and / or elapsed time since installation), and the grinding-use superimposed charging processing step S3 is executed at regular life cycles or at shorter execution intervals in the latter half of the life, and at a timing other than the period related to the image formation processing.

[0114] Since the photosensitive drum has a tendency that improvement in image deterioration is less likely (improvement becomes more difficult) in the latter half of its life, it is desirable to narrow the gap in the latter half.

[0115] In the second embodiment shown in FIGS. 9 and 10, process control is performed, and when image unevenness or the like actually occurs, superimposed charging for grinding is performed.

[0116] For this purpose, a process control processing program 86e is set in the program storage area 82 as shown in FIG.

[0117] As is well known, in the process control processing program 86e, a patch image is formed and its density is detected, thereby making it possible to detect the presence or absence of density unevenness.

[0118] In this embodiment, such process control processing is performed in step S4 of Fig. 10, and it is determined whether or not there is density unevenness in step S5. If "YES" is determined in this step S5, the process proceeds to step S20 of superimposed charging for grinding, which is the same as in the previous embodiment.

[0119] In the process control step S4, process rotation is started in step S41, and DC charging is performed by the DC charging circuit 56 in step S32, and a developing bias is output.

[0120] Thereafter, steps S33, S34, S35 and S36 are executed to form a patch image on transfer belt 38 (FIG. 2), and the density of the patch image is detected by a density sensor (not shown) provided at a predetermined position, for example, near driven roller 44b.

[0121] Such process control processing using patch images is well known, and a further detailed explanation will be omitted.

[0122] Then, in step S37, the DC charging and the developing bias are stopped, and in step S38, the process rotation is stopped.

[0123] In the second embodiment, the process control is performed in step S4 of Fig. 10, and it is determined whether or not there is density unevenness in step S5. If "YES" is determined in step S5, the process proceeds to step S3 of superimposed charging for grinding, which is the same as in the previous embodiment.

[0124] If "NO" is determined in step S5, the process ends.

[0125] As in the first embodiment, by simply predicting the possibility of image deterioration based on the number of image formations, there is a limit to predicting the timing of image deterioration due to unexpected accumulation of foreign matter on the photosensitive drum surface.

[0126] Therefore, as in the second embodiment, by performing grinding of the photosensitive drum during image formation when uneven patch density is detected during process control, it is possible to improve image deterioration at a relatively early stage.

[0127] In addition, in this case, in order to focus on grinding the photosensitive drum of the color for which patch density unevenness has been detected, the DC voltage when superimposed on the grinding AC voltages of the other colors is lowered, thereby making it possible to reduce unnecessary photosensitive drum grinding and extend the life of the photosensitive drum.

[0128] In the third embodiment of the present disclosure, the superimposed electrification step for grinding S3 can be executed whenever the user desires.

[0129] For this purpose, as described above, the photoconductor grinding instruction button 75 is provided on the operation unit 74 (FIG. 6).

[0130] When the operation data of this button 75 is input, the CPU 70 judges "YES" in step S6 of FIG. 11, and then proceeds to the superimposed electrification for grinding step S3, where the superimposed electrification for grinding is performed in the same manner as in the previous embodiment.

[0131] As in the third embodiment, a forced photoconductor grinding mode (a mode in which the grinding AC charging circuit 58 is activated at a timing unrelated to image formation) is provided as a method of improving image deterioration that cannot be detected even by uneven patch density during process control, making it possible to deal with even subtle image deterioration.

[0132] In the above embodiment, the monochrome photoconductor drum 28k and the color photoconductor drums 28c, 28m and 28y are adapted to carry out the superimposed charging for grinding at the same timing.

[0133] Alternatively, for example, the number of times a monochrome image is formed and the number of times a color image is formed may be counted separately, and the output method of the DC charging circuit 56 for each color may be adjusted.

[0134] Specifically, since the color (C / M / Y) process is stopped (not charged) during monochrome image formation, the possibility of foreign matter adhering to the surfaces of the color photoconductor drums 28c, 28m and 28y is lower than that of the monochrome photoconductor drum 28k.

[0135] For this reason, the image formation count counter 88d may be provided with a monochrome image formation count counter and a color image formation count counter, and the degree (level) of the possibility of foreign matter adhering to the color photosensitive drums 28c, 28m and 28y may be predicted (calculated) based on the total count value of each counter or the ratio thereof. The higher the possibility of foreign matter adhering (the ratio of color image formation, etc.), the higher the output voltage of the DC charging circuit 56 when operating the grinding AC charging circuit 58 may be adjusted, and the lower the possibility of foreign matter adhering to the color photosensitive drums 28c, 28m and 28y, the lower the output voltage of the DC charging circuit 56 at this time.

[0136] This is because it is known that even if the AC voltage has the same magnitude (Vpp), the photosensitive drum is more likely to be ground as the superimposed DC voltage becomes higher.

[0137] When it is considered that there is no need to grind the color photoconductor drums 28c, 28m, and 28y very much, the operation of the grinding AC charging circuit 58 can be suppressed, thereby preventing excessive grinding of the color photoconductor drums 28c, 28m, and 28y and extending their lifespan.

[0138] Furthermore, the specific numerical values ​​given in the above embodiments are merely examples and can be changed as appropriate depending on the actual product. [Explanation of symbols]

[0139] 10...Image forming device 14 … Image reading section 24 … Image forming section 28, 28k, 28c, 28m, 28y ... Photoconductor drum 30 ... Charging device 48 ...Charging roller 56 … DC charging circuit 57k, 57c, 57m, 57y...DC power supply 58 …AC charging circuit for grinding 59, 59kc, 59my, 59k, 59c...AC power supply 70...CPU 86d … Grinding charge control program 86e ... Programming program S3 … Superimposed electrostatic treatment step for grinding

Claims

1. An image forming apparatus including a charging device that charges a photoconductor drum via a charging roller, a DC charging circuit that charges the photosensitive drum with a DC voltage during a first period related to an image forming process; and an AC charging circuit for grinding that outputs an AC voltage to grind the surface of the photosensitive drum during a second period other than the first period and superimposes the AC voltage on the DC voltage to provide a superimposed charge.

2. Equipped with multiple photoconductor drums that correspond individually to each color, the DC charging circuit includes a plurality of DC power sources that apply a DC voltage to each of the plurality of photosensitive drums, 2. The image forming apparatus according to claim 1, wherein said grinding AC charging circuit has a number of AC power supplies less than said number of DC power supplies.

3. an image formation counter for counting the number of times an image formation operation has been performed; and a first determination unit that determines whether or not a count value of the image formation counter has reached a predetermined value; 2. The image forming apparatus according to claim 1, wherein when said first judging section judges that the count value of said image formation number counter has reached a predetermined value, said grinding AC charging circuit is activated.

4. a process control execution unit that executes process control using patch images; and a second determination unit that determines whether or not the patch image has density unevenness; 2. The image forming apparatus according to claim 1, wherein the grinding AC charging circuit is activated when the second judging section judges that the patch image has density unevenness.

5. 2. The image forming apparatus according to claim 1, further comprising a limiting unit that limits the number of rotations of the photosensitive drum when the AC voltage is superimposed on the DC voltage to perform superimposed charging during the second period.

Images