Image forming apparatus and its program

Abstract

To provide an image forming apparatus that can correctly set an AC voltage peak value near the start of saturation of a surface potential of an image carrier.SOLUTION: An image forming apparatus according to an embodiment comprises an image carrier, charging means, toner image forming means, transfer means, detection means, and control means. An electrostatic latent image is formed on the image carrier. The charging means includes a charging member provided in proximity to a surface of the image carrier, and applies, to the charging member, a voltage in which AC voltage is superimposed on DC voltage to uniformly electrically charge the surface of the image carrier. The toner image forming means forms a latent image of an image to be formed on the image carrier, and develops the latent image to form a toner image on the image carrier. The transfer means transfers the toner image on the image carrier onto a transfer body. The detection means detects a resistance value of the transfer means. The control means estimates a saturation value of a surface potential of the image carrier on the basis of the resistance value of the transfer means detected by the detection means, and sets a peak value of the AC voltage applied to the charging member by the charging means according to the estimated saturation value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an image forming apparatus and a program thereof.

Background Art

[0002] As an image forming apparatus placed in a workplace, an image forming apparatus using an electrophotographic method is widely used. This image forming apparatus using the electrophotographic method includes an image carrier on which an electrostatic latent image is formed, a charger that uniformly charges the surface of the image carrier by applying a voltage to a charging member close to the surface of the image carrier, an exposure device that forms a latent image on the image carrier, a developing device that performs development close to the image carrier, a primary transfer unit that transfers the toner image on the developed image carrier onto a transfer body, a secondary transfer unit that transfers the toner image transferred onto the transfer body onto paper, an image carrier cleaner that contacts the image carrier to remove residual toner after transfer, and a transfer body cleaner that contacts the transfer body to remove residual toner after transfer.

[0003] In the charger of such an image forming apparatus using the electrophotographic method, the charging roller method is adopted because the amount of ozone generated during discharge is less than that of the scorotron charging method.

[0004] In this charging roller method, an input voltage method in which an AC voltage is superimposed on a DC power supply is often selected because of a large discharge amount and stable charging performance. In order to converge the charging potential (hereinafter abbreviated as surface potential) of the surface of the image carrier near the DC voltage, it is generally known that the AC peak voltage (Vp-p), which is the peak value of the AC voltage applied to the charging roller, is set to be twice or more the DC discharge start voltage. On the other hand, when the AC peak voltage is increased, the discharge amount increases, and as the discharge amount increases, the ozone concentration near the image carrier rises, accelerating the deterioration of the image carrier, and it is known that the number of copies that can be printed extremely decreases. To solve this problem, it is desirable to set the AC peak voltage near the saturation start of the surface potential of the image carrier.

[0005] Various control methods have been proposed to set the AC peak voltage to near the point where the image carrier surface potential begins to saturate. For example, a known method involves measuring the DC or AC current flowing from the high-voltage power supply to the charging roller, comparing this to a DC or AC current reference value estimated to be near the point where the image carrier surface potential begins to saturate, and then varying the input voltage to match the current reference value. Here, the current reference value is a value estimated from the temperature and humidity at the time of measurement of the current flowing from the high-voltage power supply to the charging roller, the operation count associated with the charging roller resistance, and the image carrier film thickness information.

[0006] However, this control method includes numerous errors, such as temperature and humidity errors between the measurement location and the vicinity of the charging roller, individual differences in the resistance value of the charging roller as the number of printed sheets increases, and individual differences in image carrier film wear at a predetermined rotation speed. As a result, it may not be possible to obtain a current reference value with appropriate accuracy, and consequently, the AC peak voltage may not be set correctly.

[0007] If the AC peak voltage is set too high or too low, and the surface potential of the image carrier is also set too high or too low, problems such as white background fringing or carrier pull may occur during development by the developing unit, resulting in a significant decrease in print quality. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2006-171282 [Overview of the project] [Problems that the invention aims to solve]

[0009] The problem that the embodiments of the present invention aim to solve is to provide an image forming apparatus that can correctly set the AC voltage peak value to near the saturation start point of the image carrier surface potential. [Means for solving the problem]

[0010] In one embodiment, the image forming apparatus includes an image carrier, a charging means, a toner image forming means, a transfer means, and a detection means. Resistance sensing voltage storage unit, The system comprises control means and an image carrier on which an electrostatic latent image is formed. The charging means includes a charging member placed in close proximity to the surface of the image carrier, and uniformly charges the surface of the image carrier by applying a voltage obtained by superimposing a DC voltage on the charging member. The toner image forming means forms a toner image on the image carrier by forming a latent image of the image to be formed on the image carrier and developing it. The transfer means transfers the toner image on the image carrier onto a transfer body. The detection means detects the resistance value of the transfer means. As a voltage value Detect. The resistance-detected voltage storage unit stores the resistance-detected voltage, which is the voltage value detected by the detection means. The control means is , charged The peak value of the AC voltage applied by the means to the charged member Set do. More specifically, the control means causes the charging means to change the peak value of the AC voltage within a scanning range from a predetermined minimum value to a predetermined maximum value, while causing the detection means to detect resistance detection voltages at multiple voltage setting points set at regular intervals, storing multiple resistance detection voltages in the resistance detection voltage storage unit. Based on the changes in the multiple resistance detection voltages stored in this resistance detection voltage storage unit, the saturation value of the surface potential of the image carrier is estimated, and the peak value of the AC voltage applied by the charging means to the charging member is set according to the estimated saturation value. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a block diagram showing an example of the configuration of an image forming apparatus according to one embodiment. [Figure 2] Figure 2 shows an example of the configuration of a printer according to one embodiment. [Figure 3] Figure 3 is a graph showing the relationship between the AC peak voltage and the surface potential of the image carrier. [Figure 4] Figure 4 is a graph showing the relationship between the AC peak voltage and the surface potential of the image carrier, illustrating the effect of the resistance change of the charging roller. [Figure 5] Figure 5 is a graph showing the relationship between the AC peak voltage and the surface potential of the image carrier, illustrating the effect of changes in the thickness of the photosensitive layer of the image carrier. [Figure 6] Figure 6 is a graph showing the relationship between the surface potential of the image carrier and the resistance detection voltage. [Figure 7] Figure 7 is a graph showing the relationship between the AC peak voltage, the surface potential of the image carrier, and the resistance detection voltage. [Figure 8]FIG. 8 is a diagram showing an example of the stored content of a resistance detection voltage storage unit included in an image forming apparatus according to an embodiment. [Figure 9] FIG. 9 is a diagram showing an example of the stored content of an AC peak voltage storage unit included in an image forming apparatus according to an embodiment. [Figure 10] FIG. 10 is a flowchart showing an example of the processing operation of an image forming apparatus according to an embodiment. [Figure 11] FIG. 11 is a flowchart showing an example of the AC peak voltage control process in FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an image forming apparatus according to an embodiment will be described with reference to the drawings. Note that the scales of each part in the following drawings used for the description of the embodiment are appropriately changed. Also, each of the following drawings used for the description of the embodiment omits the configuration as appropriate for the purpose of explanation.

[0013] FIG. 1 is a block diagram showing a configuration example of an image forming apparatus 10 according to an embodiment. The image forming apparatus 10 is a multi-function peripheral (hereinafter abbreviated as MFP) placed in a workplace and having at least a scanning function and a printing function. As shown in FIG. 1, the image forming apparatus 10 includes a processor 11, a main memory 12, a storage device 13, a communication interface 14, an operation panel 15, a scanner 16, an input image processing unit 17, a page memory 18, an output image processing unit 19, a printer 20, and the like. These parts are connected to each other via a data bus or the like.

[0014] Note that, in addition to the configuration shown in FIG. 1, the image forming apparatus 10 may include a configuration as required, or a specific configuration may be excluded from the configuration shown in FIG. 1.

[0015] Processor 11 is, for example, a CPU (central processing unit), but is not limited thereto. Processor 11 may be a multi-core / multi-thread one and can execute a plurality of processes in parallel. Also, Processor 11 may be an MPU (micro processing unit). Processor 11 has a function of controlling the operation of the entire image forming apparatus 10. Processor 11 may include an internal memory and various interfaces, etc. Processor 11 realizes various processes by executing a program pre-stored in the internal memory or the storage device 13, etc.

[0016] Among the various functions realized by Processor 11 executing a program, some may be realized by various forms of hardware circuits including integrated circuits such as ASIC (Application Specific Integrated Circuit), DSP (Digital Signal Processor), FPGA (field-programmable gate array), GPU (Graphics Processing Unit), SoC (system on a chip), PLD (programmable logic device), etc. In this case, Processor 11 controls the functions executed by the hardware circuit.

[0017] Main memory 12 is a volatile memory. Main memory 12 is a working memory or a buffer memory. Main memory 12 can store various application programs based on instructions from Processor 11. Also, Main memory 12 may store control programs stored in storage device 13, data necessary for the execution of application programs, and execution results of those programs, etc. For example, Main memory 12 stores an AC peak voltage storage unit 121, etc. The AC peak voltage storage unit 121 stores an AC peak voltage which is the peak value of the AC voltage applied to a charging roller described later of the printer 20. Details of this AC peak voltage storage unit 121 will be described later.

[0018] The storage device 13 is a non-volatile memory that allows data to be written to and rewritten. The storage device 13 is composed of, for example, an HDD (Hard Disk Drive), an SSD (Solid State Drive), or flash memory. The storage device 13 stores control programs, application programs, and various data according to the operating purpose of the image forming apparatus 10. For example, the storage device 13 stores print jobs transmitted from a user terminal, described later, and the resistance detection voltage storage unit 131. A print job includes print target data such as character data and image data that form the basis of the image to be formed on the paper. The print target data may be data for forming an image on one sheet of paper, or data for forming an image on multiple sheets of paper. Furthermore, the print job may include information such as whether it is color printing or monochrome printing, the number of copies to print (number of page sets), and the number of pages to print per copy as control data. The resistance detection voltage storage unit 131 stores the resistance detection voltage of the primary transfer unit of the printer 20, described later, which is detected when the AC peak voltage is changed. Details of this resistance-sensing voltage storage unit 131 will be described later.

[0019] The communication interface 14 is an interface for communicating with external devices on the network NW. The communication interface 14 is used for communication with user terminals UT and server devices SV located in the workplace via a network NW, such as a company LAN (Local Area Network). The communication interface 14 is configured, for example, as a LAN connector. Furthermore, the communication interface 14 may also perform wireless communication with other devices according to standards such as Bluetooth® or Wi-Fi®. Note that although only two user terminals UT are shown in Figure 1, the number is not limited to these.

[0020] The control panel 15 receives various instructions from the operator of the image forming apparatus 10. The control panel 15 transmits signals indicating the instructions entered by the operator to the processor 11. The control panel 15 includes, for example, a keyboard, a numeric keypad, and a touch panel as its operating section.

[0021] Furthermore, the control panel 15 displays various information to the operator of the image forming apparatus 10. Specifically, the control panel 15 displays a screen showing various information based on signals from the processor 11. The control panel 15 includes a monitor, such as a liquid crystal display, as its display unit.

[0022] The scanner 16 optically scans the document and reads the image of the document as image data. The scanner 16 reads the document as a color image. The scanner 16 is composed of a sensor array formed in the main scanning direction. The scanner 16 moves the sensor array in the sub-scanning direction and reads the entire document.

[0023] The input image processing unit 17 processes the image data read by the scanner 16. Although not shown in Figure 1, if the image forming apparatus 10 is equipped with a reader for a storage medium such as a USB memory, the input image processing unit 17 may also process the image data read from that storage medium. Furthermore, the input image processing unit 17 converts the print target data, such as character data and image data included in the print job stored in the storage device 13, into image data that represents the image to be formed.

[0024] The page memory 18 stores the image data processed by the input image processing unit 17.

[0025] The output image processing unit 19 processes the image data stored in the page memory 18 so that the printer 20 can print the image data onto paper.

[0026] The printer 20 prints the image data processed by the output image processing unit 19 onto paper, based on the control of the processor 11. The printer 20 prints the image data onto paper, for example, using an electrophotographic method. The printer 20 also consists of a transfer body, rollers for driving the transfer body, a photosensitive drum, a resistance detection unit 21, and the like. Details of the printer 20 will be described later.

[0027] The resistance detection unit 21 detects the resistance value of the primary transfer unit as a voltage value. The resistance detection unit 21 outputs a resistance detection voltage indicating the detected voltage value to the processor 11. The processor 11 stores this resistance detection voltage in the resistance detection voltage storage unit 131, as will be described later.

[0028] Next, I will explain printer 20. Figure 2 shows an example of the configuration of printer 20. As shown in Figure 2, printer 20 consists of resistance detection units 21K, 21C, 21M, 21Y, photoreceptor drums 30K, 30C, 30M, 30Y, transfer body 31, rollers 32a, 32b, 32c, 32d, charging rollers 33K, 33C, 33M, 33Y, static eliminators 34K, 34C, 34M, 34Y, photoreceptor cleaners 35K, 35C, 35M, 35Y, and primary transfer rollers. The unit includes rollers 36K, 36C, 36M, and 36Y, a secondary transfer roller 37, a fuser 38, a transfer body cleaner 39, a developer 40K, 40C, 40M, and 40Y, agitators 41K, 41C, 41M, and 41Y, a developing roller 42K, 42C, 42M, and 42Y, a voltage application unit 43K, 43C, 43M, and 43Y, an exposure unit 44, a paper feed cassette 51, and a transport path 52, among other components.

[0029] The transfer body 31 is an intermediate transfer body. The transfer body 31 is formed in an endless belt shape. That is, the transfer body 31 is formed in an annular shape with a predetermined width.

[0030] Rollers 32a to 32d are rollers for driving the transfer body 31. Each roller 32a to 32d is formed on the inside of the transfer body 31. Each roller 32a to 32d pulls the transfer body 31 from the inside with a predetermined tension, forming it into a flat shape. Each roller 32a to 32d rotates due to the driving force from the drive unit. Each roller 32a to 32d drives the transfer body 31 by rotating. Some of the rollers 32a to 32d may rotate passively.

[0031] The printer 20 is equipped with a resistance detection unit, a photoreceptor drum, a charging roller, a static eliminator, a photoreceptor cleaner, a primary transfer roller, a developer, an agitator, a developer roller, a voltage application unit, and a laser unit within the exposure unit 44, for each toner color. Here, the printer 20 is equipped with a resistance detection unit, a photoreceptor drum, a charging roller, a static eliminator, a photoreceptor cleaner, a primary transfer roller, a developer, an agitator, a developer roller, a voltage application unit, and a laser unit for each of the cyan (C), magenta (M), yellow (Y), and black (K) toners. Note that the toner colors are not limited to the CMYK colors, but may be other colors. Also, the toner may be a special type of toner. For example, the toner may be a decolorizable toner that becomes invisible when decolorized at a temperature higher than a predetermined temperature.

[0032] In this embodiment, the printer 20 includes resistance detection units 21K, 21C, 21M, and 21Y as resistance detection units. It also includes photoreceptor drums 30Y, 30M, 30C, and 30K as photoreceptor drums. Furthermore, the printer 20 includes charging rollers 33Y, 33M, 33C, and 33K as charging rollers. Furthermore, the printer 20 includes static eliminators 34Y, 34M, 34C, and 34K as static eliminators. Furthermore, the printer 20 includes photoreceptor cleaners 35Y, 35M, 35C, and 35K.

[0033] The printer 20 also includes primary transfer rollers 36Y, 36M, 36C, and 36K. The printer 20 also includes developer units 40Y, 40M, 40C, and 40K. The printer 20 also includes agitators 41Y, 41M, 41C, and 41K. The printer 20 also includes developer rollers 42Y, 42M, 42C, and 42K. The printer 20 also includes voltage application units 43Y, 43M, 43C, and 43K.

[0034] Here, we will describe, as representative components, the resistance detection unit 21K, the photoreceptor drum 30K, the charging roller 33K, the static eliminator 34K, the photoreceptor cleaner 35K, the primary transfer roller 36K, the developer unit 40K, the agitator 41K, the developing roller 42K, and the voltage application unit 43K.

[0035] The developer unit 40K is a container that houses a developer containing toner and a magnetic carrier. The developer unit 40K receives the toner dispensed from the toner cartridge. The developer is stored in the developer unit 40K during manufacturing or at the start of use.

[0036] An agitator 41K is formed inside the developing unit 40K. The agitator 41K agitates the developer inside the developing unit 40K. The agitator 41K consists of a screw for agitating the developer and a motor for rotating the screw.

[0037] Furthermore, a developing roller 42K is formed inside the developing unit 40K. The developing roller 42K attracts the developer with a built-in magnet and rotates inside the developing unit 40K, thereby adhering the developer to the surface. The developing roller 42K is rotated by a motor or the like. The developing roller 42K is one of the rotating members for forming a toner image on the transfer body 31.

[0038] The voltage application unit 43K applies a development bias to the developing roller 42K according to the control of the processor 11. For example, the voltage application unit 43K applies a development bias to the developing roller 42K. The toner of the developer adhering to the developing roller 42K adheres to the photoreceptor drum 30K, which is the image carrier, due to the electric field generated by the development bias and the drum potential, and forms a toner image.

[0039] The charging roller 33K, which is a charging component, is placed close to the surface of the photoreceptor drum 30K and charges the surface of the photoreceptor drum 30K to a constant potential. The voltage application unit 43K applies a voltage to the charging roller 33K, which is a DC voltage superimposed on an AC voltage, according to the control of the processor 11. The charging roller 33K charges the photoreceptor drum 30K by becoming charged by the application of this voltage. The charger that uniformly charges the surface of the photoreceptor drum 30K includes the charging roller 33K and the voltage application unit 43K.

[0040] The photoreceptor drum 30K is a photoreceptor comprising a cylindrical drum and a photosensitive layer formed on the outer surface of the drum. The photoreceptor drum 30K rotates at a constant speed by power transmitted from the motor. The photoreceptor drum 30K is one of the rotating members for forming a toner image on the transfer body 31.

[0041] The photoreceptor drum 30K is charged by the charging roller 33K. While the photoreceptor drum 30K rotates, it is irradiated with a laser from the laser unit in the exposure unit 44 while charged. As a result, a bright electrostatic latent image is formed on the photoreceptor drum 30K by the laser.

[0042] The primary transfer roller 36K is formed in a position opposite the photoreceptor drum 30K, with the transfer body 31 in between. The primary transfer section includes the transfer body 31 and the primary transfer roller 36K. The primary transfer roller 36K brings the transfer body 31 into contact with the photoreceptor drum 30K and is set to a positive polarity, which is the opposite potential to the surface of the photoreceptor drum 30K, thereby attracting the toner from the surface of the photoreceptor drum 30K. As a result, the primary transfer roller 36K transfers the toner image formed on the photoreceptor drum 30K to the transfer body 31. The photoreceptor drum 30K is one of the rotating members for forming the toner image. The primary transfer roller 36K is one of the rotating members for forming the toner image on the transfer body 31. The primary transfer section, which transfers the toner image on the photoreceptor drum 30K, which is the image carrier, onto the transfer body 31, includes the transfer body 31 and the primary transfer roller 36K.

[0043] The resistance detection unit 21K detects the resistance of a resistor, including the transfer body 31 of the primary transfer unit and the primary transfer roller 36K, as a voltage value. For example, the resistance detection unit 21K detects the voltage applied to the constantly current-controlled primary transfer roller 36K. The resistance detection unit 21K outputs the detected voltage value of the applied voltage to the processor 11 as a resistance detection voltage. In the image forming apparatus 10, it is necessary to set an appropriate primary transfer voltage value for the primary transfer roller 36K in order to prevent image noise. Therefore, the resistance detection unit 21K detects the applied voltage when a predetermined positive polarity constant current is output to the primary transfer roller 36K, and the processor 11 sets the primary transfer voltage value for image formation on the primary transfer roller 36K based on the resistance detection voltage from the resistance detection unit 21K. This control process using the resistance detection unit 21 for preventing image noise will be referred to below as the resistance detection control process.

[0044] The photoconductor cleaner 35K consists of blades and other components that come into contact with the surface of the photoconductor drum 30K. The photoconductor cleaner 35K uses the blades to remove toner remaining on the surface of the photoconductor drum 30K.

[0045] The 34K static eliminator removes the residual charge potential from the 30K photoreceptor drum.

[0046] The paper feed cassette 51 is a cassette that holds paper as a medium. The paper feed cassette 51 has a structure that allows paper to be supplied from outside the housing of the image forming apparatus 10. For example, the paper feed cassette 51 has a structure that allows it to be pulled out from the housing.

[0047] The transport path 52 transports paper. For example, the transport path 52 takes out one sheet of paper at a time from the paper feed cassette 51 and transports it. For example, the transport path 52 is composed of rollers and a transport belt.

[0048] The secondary transfer roller 37 transfers the toner image formed on the transfer body 31 to the paper (secondary transfer). As shown in Figure 2, the secondary transfer roller 37 is formed in a position opposite the roller 32a, with the transfer body 31 in between. The secondary transfer roller 37 transfers the toner image on the transfer body 31 to the paper being transported by the transport path 52.

[0049] The fuser unit 38 is formed downstream of the secondary transfer roller 37 in the paper transport direction. The fuser unit 38 fixes the toner image transferred to the paper. The fuser unit 38 fixes the toner image to the paper by heating the toner image to a fixing temperature. For example, the fuser unit 38 is composed of a heater or the like.

[0050] The transfer cleaner 39 consists of a blade and other components that come into contact with the surface of the transfer body 31. The transfer cleaner 39 uses the blade to remove any toner remaining on the surface of the transfer body 31.

[0051] The exposure unit 44, also known as an LSU (laser scanning unit), irradiates each photoreceptor drum 30K, 30C, 30M, and 30Y with a laser according to control from the processor 11. By irradiating the photoreceptor drums 30K, 30C, 30M, and 30Y with a laser, the exposure unit 44 forms an electrostatic latent image on each photoreceptor drum 30K, 30C, 30M, and 30Y. For example, the exposure unit 44 consists of a laser unit, which is an irradiation device that irradiates the laser, and a polygon mirror that reflects the laser.

[0052] With the above configuration, the printer 20 forms a toner image on the transfer body 31. The printer 20 uses the secondary transfer roller 37 to transfer the toner image formed on the transfer body 31 onto the paper. The printer 20 uses the fuser 38 to heat the paper onto which the toner image has been transferred and fix the toner image to the paper. The printer 20 uses the transport path 52 to discharge the paper with the fixed toner image to the outside.

[0053] Figure 3 is a graph showing the relationship between the AC peak voltage (Vp-p), which is the peak value of the AC voltage applied to the charging roller, and the surface potential Vo, which is the charging potential of the surface of the photoreceptor drum, which is the image carrier. As mentioned above, the charging rollers 33K, 33C, 33M, and 33Y are subjected to a voltage that is a DC power supply superimposed with an AC voltage by the voltage application units 43K, 43C, 43M, and 43Y. In order to converge the surface potential Vo of the photoreceptor drums 30K, 30C, 30M, and 30Y to near the DC voltage, it is generally known that the AC peak voltage (Vp-p), which is the peak value of the superimposed AC voltage, should be set to more than twice the DC discharge start voltage. In the relationship between the AC peak voltage (Vp-p) and the surface potential Vo shown in Figure 3, it is common to set it to a value that exceeds the saturation value A. Here, the definition of the saturation value A is the inflection point in which the slope B of the relationship between the AC peak voltage (Vp-p) and the surface potential Vo decreases.

[0054] On the other hand, increasing the AC peak voltage increases the discharge rate, and this increase in discharge rate leads to an increase in ozone concentration near the photoreceptor drum at 30K, 30C, 30M, and 30Y, accelerating the degradation of the photoreceptor drum at 30K, 30C, 30M, and 30Y, which is known to drastically reduce the number of prints that can be used. To resolve this problem, it is necessary to set the AC peak voltage (Vp-p) near the saturation value A.

[0055] Figure 4 is a graph showing the effect of changes in the resistance of the charging roller. The resistance of the charging roller changes depending on temperature and humidity. The temperature and humidity of the charging roller depend on changes in ambient temperature and fluctuations in internal humidity due to the number of continuous drives or duration. When the resistance of the charging roller changes with changes in temperature and humidity, as shown in Figure 4, even if the same AC peak voltage (Vp-p) is applied to the charging roller, the surface potential of the photoreceptor drum will not be the same, and the saturation point A will change by approximately 0.6 kV. Note that the resistance of the photoreceptor drum has almost no dependence on temperature and humidity.

[0056] Figure 5 is a graph showing the effect of changes in the film thickness of the photosensitive layer on the photosensitive drum, which is the image carrier. The film thickness of the photosensitive layer on the photosensitive drum gradually thins as the number of printed sheets increases. When the film thickness of the photosensitive layer changes, as shown in Figure 5, even if the same AC peak voltage (Vp-p) is applied to the charging roller, the surface potential of the photosensitive drum will not be the same, and the saturation point A will change. For example, if the film thickness of the photosensitive layer, which was 33 μm, thins to 20 μm, the saturation point A changes by approximately 0.2 KV.

[0057] If the AC peak voltage (Vp-p) is set to a fixed value, the surface potential Vo of the photoreceptor drum will change depending on the resistance of the charging roller and the thickness of the photosensitive layer on the photoreceptor drum, as shown in Figures 4 and 5. As a result, the surface potential Vo may not reach the saturation value A at that AC peak voltage (Vp-p). If the surface potential Vo does not reach the saturation value A, problems such as white background fringing or carrier pull may occur during development by the developer.

[0058] Figure 6 is a graph showing the relationship between the surface potential Vo of the photoreceptor drum, which is the image carrier, and the resistance detection voltage To detected by the resistance detection unit 21. As mentioned above, in the image forming apparatus 10, during image formation, the appropriate primary transfer output to the primary transfer roller is set by resistance detection control using the resistance detection unit 21 to prevent image noise. When this resistance detection control is performed, the surface potential (negative polarity) of the photoreceptor drum, which is the counter electrode, is not a constant value but an arbitrary value. However, if the temperature and humidity of the surrounding environment are stable, the potential difference between the surface potential Vo and the resistance detection voltage To will be constant during the period in which the resistance detection control is performed. For this reason, as shown in Figure 6, it is known that the resistance detection voltage To fluctuates by the same amount as the fluctuation of the surface potential Vo.

[0059] Figure 7 is a graph showing the relationship between the AC peak voltage (Vp-p), the surface potential Vo of the photoreceptor drum (which is the image carrier), and the resistance detection voltage To detected by the resistance detection unit 21. As explained with reference to Figure 6, when the surface potential Vo changes, the resistance detection voltage To also changes by the same amount. Therefore, it is possible to estimate the surface potential Vo using the resistance detection voltage To. In this embodiment, the AC peak voltage (Vp-p) is scanned with multiple voltage settings set so that it passes through the surface potential saturation value A, and the amount of change in the surface potential Vo corresponding to each set voltage of the AC peak voltage (Vp-p) is detected as the amount of change in the resistance detection voltage To. This makes it possible to detect the AC peak voltage (Vp-p) that becomes the surface potential saturation value A from the saturation value of the resistance detection voltage To.

[0060] Figure 8 shows an example of the contents stored in the resistance detection voltage storage unit 131 of the image forming apparatus 10. In this embodiment, as shown in Figure 8, the resistance detection voltage storage unit 131 is a table that stores values ​​for multiple voltage settings at multiple points set to pass through the aforementioned surface potential saturation value A for each color of YMCK. The values ​​stored in this table are the resistance detection voltage To detected by the resistance detection units 21K, 21C, 21M, and 21Y of each color at the AC peak voltage (Vp-p) of each voltage setting point.

[0061] Figure 9 shows an example of the contents stored in the AC peak voltage storage unit 121 of the image forming apparatus 10. In this embodiment, as shown in Figure 9, the AC peak voltage storage unit 121 stores values ​​set as the AC peak voltage (Vp-p) applied to the charging rollers 33K, 33C, 33M, and 33Y for each color of YMCK.

[0062] Next, an example of the operation of the image forming apparatus 10 according to one embodiment will be described. Figure 10 is a flowchart showing an example of the processing operation of the image forming apparatus 10. Note that the flowchart in Figure 10 omits the printing (i.e., copying) process of scanned documents, as the only difference is the printing target; it only shows the printing process. Furthermore, the processing shown in Figure 10 and described below is just an example, and various other processes that can achieve similar results can be used as appropriate.

[0063] When power is turned on to processor 11 by turning on the power switch (not shown), the control program stored in memory device 13 is started and the processing operations shown in this flowchart are executed. Unless otherwise specified, the processing of processor 11 is assumed to transition from ACTn (where n is a natural number) to ACT(n+1).

[0064] First, in ACT1, the processor 11 performs AC peak voltage control processing. This AC peak voltage control processing sets the AC peak voltage (Vp-p) to be applied to the charging rollers 33K, 33C, 33M, and 33Y of each color in YMCK during image formation.

[0065] Figure 11 is a flowchart showing an example of the AC peak voltage control process for ACT1. In ACT11, the processor 11 sets an initial value for the target AC peak voltage (Vp-p) for which the resistance sensing voltage is to be acquired. This initial value is, for example, the smallest voltage value among the AC peak voltages (Vp-p) of multiple voltage setting points in the resistance sensing voltage storage unit 131 of the storage device 13. Therefore, in the example shown in Figure 8, the processor 11 sets the initial value of the target AC peak voltage (Vp-p) to 0.5V.

[0066] In ACT12, the processor 11 applies a DC voltage superimposed with the set target AC peak voltage (Vp-p) to the YMCK's colored charging rollers 33K, 33C, 33M, and 33Y.

[0067] In ACT13, the processor 11 acquires the resistance detection voltage To using the resistance detection units 21K, 21C, 21M, and 21Y of each color.

[0068] In ACT14, the processor 11 stores the resistance-detected voltage To for each color acquired in the resistance-detected voltage storage unit 131.

[0069] In ACT 15, the processor 11 determines whether the scanning range of the AC peak voltage (Vp-p) has ended. For example, if the largest voltage value among the AC peak voltages (Vp-p) of multiple voltage setting points in the resistance-sensing voltage storage unit 131 has been set as the target AC peak voltage (Vp-p), the processor 11 determines that the scanning range has ended.

[0070] Based on the determination that the scanning range has not been completed (ACT15, NO), the processor 11 updates the target AC peak voltage (Vp-p) in ACT16. For example, the processor 11 sets a voltage value that has not yet been set as the target AC peak voltage (Vp-p) at multiple voltage setting points in the resistance-sensing voltage storage unit 131. After that, the processor 11 proceeds to the processing operation of ACT12.

[0071] Based on the determination that the scanning range has ended (ACT15, NO), the processor 11 determines in ACT17 the AC peak voltage (Vp-p) to be applied to the YMCK colored charging rollers 33K, 33C, 33M, and 33Y. For example, for each color, the processor 11 calculates a relationship between the AC peak voltage (Vp-p) stored in the resistance-sensing voltage storage unit 131 and the resistance-sensing voltage To, and finds the inflection point where the slope of this relationship decreases. The processor 11 takes this inflection point as the saturation point A of the surface potential Vo, and determines the AC peak voltage (Vp-p) at this saturation point A as the AC peak voltage (Vp-p) to be applied.

[0072] In ACT 18, the processor 11 stores the determined AC peak voltage (Vp-p) to be applied for each color in the AC peak voltage storage unit 121 of the main memory 12. After that, the processor 11 finishes this AC peak voltage control process and moves on to the processing operation of ACT 2.

[0073] Returning to the explanation of Figure 10. In ACT2, the processor 11 determines whether or not it has received a print job from the user terminal UT via the communication interface 14. Based on the determination that it has not received a print job (ACT2, NO), the processor 11 proceeds to the processing operation of ACT4, which will be described later.

[0074] Based on the determination that a print job has been received (ACT2, YES), the processor 11 stores the received print job in the storage device 13 in ACT3. If the main memory 12 has sufficient storage capacity and there is no need to store it non-volatilely, the print job may also be stored in the main memory 12.

[0075] In ACT4, the processor 11 determines whether or not to start printing. For example, the processor 11 determines to start printing based on the user's input from the control panel 15, which includes the selection of the print job to be printed and the subsequent start operation. Note that there may be multiple print jobs selected. Based on the determination not to start printing (ACT4, NO), the processor 11 proceeds to the processing operation of ACT2.

[0076] Based on the determination to start printing (ACT4, YES), the processor 11 executes a resistance detection control process in ACT5. This resistance detection control process is a known process and is therefore not illustrated. Briefly, in this resistance detection control process, the processor 11 sets the surface potential (negative polarity) of the photoreceptor drum to an arbitrary value for each color, applies a predetermined positive constant current voltage to the primary transfer roller, and obtains the resistance detection voltage using the resistance detection unit 21K. Then, based on the resistance detection voltage obtained from the resistance detection unit 21 for each color, the processor 11 sets the voltage value to be applied to the primary transfer roller for each color during image formation.

[0077] In ACT6, processor 11 executes a print control process to execute one print job to be printed. This print control process is also a known process and is therefore not illustrated. Briefly, in the print control process, processor 11 reads one of the one or more print jobs selected by the user from among the print jobs stored in storage device 13, controls the input image processing unit 17 to convert the print target data contained in the read print job into image data, and stores it in page memory 18. Then, according to the control data contained in the print job, processor 11 controls the output image processing unit 19 to process the image data stored in page memory 18 so that the printer 20 can print the image data onto the paper, and also controls the printer 20 to print the image data processed by the output image processing unit 19 onto the paper. Upon completion of printing corresponding to the print job, processor 11 erases the print job from storage device 13.

[0078] In ACT7, processor 11 determines whether the execution of all print jobs selected by the user as print targets has finished. Based on the determination that the execution of all print targets has not finished (ACT7, NO), processor 11 proceeds to the processing operation of ACT6 and performs printing for the unexecuted print jobs.

[0079] Based on the determination that the execution of all print jobs to be printed has finished (ACT7, YES), the processor 11 determines in ACT8 whether or not to terminate the processing operation. For example, the processor 11 determines to terminate the processing operation when a power switch (not shown) is turned OFF. Based on the determination to terminate the processing operation (ACT8, YES), the processor 11 terminates the processing operation shown in the flowchart of Figure 10.

[0080] In response, the processor 11, based on the determination that it will not terminate the processing operation (ACT8, NO), proceeds to the processing operation of ACT1 and executes the AC peak voltage control processing again. In this way, the AC peak voltage control processing is repeated each time an image forming operation corresponding to one or more print jobs selected by the user is completed.

[0081] As described above, the image forming apparatus 10 according to this embodiment comprises a photoreceptor drum 30K, 30C, 30M, 30Y which is an image carrier on which an electrostatic latent image is formed, and charging rollers 33K, 33C, 33M, 33Y which are charging members that are positioned close to the surface of the photoreceptor drum 30K, 30C, 30M, 30Y, and a charger that uniformly charges the surface of the photoreceptor drum 30K, 30C, 30M, 30Y by applying a voltage obtained by superimposing a DC voltage on the charging rollers 33K, 33C, 33M, 33Y, An exposure unit 44 and developing rollers 42K, 42C, 42M, 42Y form a latent image of the image to be formed on the photoreceptor drums 30K, 30C, 30M, 30Y and develop it to form a toner image on the photoreceptor drums 30K, 30C, 30M, 30Y, and a primary transfer unit that transfers the toner image on the photoreceptor drums 30K, 30C, 30M, 30Y onto a transfer unit 31 using primary transfer rollers 36K, 36C, 36M, 36Y, and a resistor of the primary transfer unit The system includes resistance detection units 21K, 21C, 21M, and 21Y for detecting resistance values, and a processor 11 that estimates the saturation value of the surface potential of the photoreceptor drum 30K, 30C, 30M, and 30Y based on the resistance values ​​of the primary transfer unit detected by the resistance detection units 21K, 21C, 21M, and 21Y, and sets the AC peak voltage (Vp-p), which is the peak value of the AC voltage applied by the charger to the charging rollers 33K, 33C, 33M, and 33Y, according to the estimated saturation value. Thus, the charger functions as a charging means, the exposure unit 44 and the developing rollers 42K, 42C, 42M, and 42Y function as toner image forming means, the primary transfer unit functions as a primary transfer unit, the resistance detection units 21K, 21C, 21M, and 21Y function as detection means, and the processor 11 functions as a control means. Thus, in the image forming apparatus 10 according to this embodiment, which has an input voltage method in which AC is superimposed on a DC power supply by charging rollers 33K, 33C, 33M, 33Y located in close proximity to the surface of the photoreceptor drums 30K, 30C, 30M, 30Y, the AC peak voltage (Vp-p) and the saturation value A of the surface potential of the charging rollers 33K, 33C, 33M, 33Y can be detected using the change in the resistance value of the primary transfer section, so that a highly accurate AC peak voltage (Vp-p) setting can be performed. In other words, according to this embodiment, it is possible to provide an image forming apparatus 10 that can correctly set the AC voltage peak value to near the start of saturation of the image carrier surface potential. Therefore, it is possible to provide an image forming apparatus 10 that can obtain stable image quality with a long lifespan while suppressing the deterioration of the photoreceptor drums 30K, 30C, 30M, 30Y.

[0082] Here, the processor 11 causes the charger to change the AC peak voltage (Vp-p) and has the resistance detection units 21K, 21C, 21M, and 21Y detect the resistance value of the primary transfer section. Based on the changes in the resistance value of the primary transfer section detected by the resistance detection units 21K, 21C, 21M, and 21Y, the processor 11 estimates the saturation value of the surface potential of the photoreceptor drums 30K, 30C, 30M, and 30Y. Thus, the image forming apparatus 10 according to this embodiment can easily estimate the saturation value of the surface potential of the photoreceptor drums 30K, 30C, 30M, and 30Y by utilizing the state of change in resistance obtained by scanning the AC peak voltage (Vp-p) applied to the charging rollers 33K, 33C, 33M, and 33Y.

[0083] Furthermore, the resistance detection units 21K, 21C, 21M, and 21Y detect the resistance value of the primary transfer unit as a voltage value, which is the resistance detection voltage To. Therefore, the image forming apparatus 10 according to this embodiment can utilize resistance detection units 21K, 21C, 21M, and 21Y that detect the resistance detection voltage To used for resistance detection control to prevent image noise. As a result, it becomes possible to set the AC peak voltage (Vp-p) applied to the charging rollers 33K, 33C, 33M, and 33Y without adding any new components, while keeping the configuration of the existing image forming apparatus 10 unchanged. Moreover, the image forming apparatus 10 according to this embodiment can achieve both suppression of image noise and suppression of photoreceptor degradation.

[0084] Furthermore, the processor 11 estimates the saturation value of the surface potential of the photoreceptor drums 30K, 30C, 30M, and 30Y based on the saturation value of the resistance detection voltage To detected by the resistance detection units 21K, 21C, 21M, and 21Y. Thus, the image forming apparatus 10 according to this embodiment focuses on the fact that the resistance detection voltage To and the surface potentials of the photoreceptor drums 30K, 30C, 30M, and 30Y take on similar changes in response to changes in the AC peak voltage (Vp-p). By detecting the saturation value of the resistance detection voltage To, the saturation value of the surface potentials of the photoreceptor drums 30K, 30C, 30M, and 30Y can be easily estimated.

[0085] Furthermore, the primary transfer unit includes a transfer body 31 and primary transfer rollers 36K, 36C, 36M, and 36Y, which are biasing members that face the photoreceptor drums 30K, 30C, 30M, and 30Y with the transfer body 31 in between. The primary transfer rollers 36K, 36C, 36M, and 36Y bias the transfer body 31 in the direction of the photoreceptor drums 30K, 30C, 30M, and 30Y, bringing the transfer body 31 into contact with the photoreceptor drums 30K, 30C, 30M, and 30Y, thereby transferring the toner image on the photoreceptor drums 30K, 30C, 30M, and 30Y onto the transfer body 31. Each of the resistance detection units 21K, 21C, 21M, and 21Y detects the resistance value of a resistor including the transfer body 31 and the corresponding primary transfer roller 36K, 36C, 36M, or 36Y. Thus, in the image forming apparatus 10 according to this embodiment, the resistance detection units 21K, 21C, 21M, and 21Y can detect the resistance value of a resistor including the transfer body 31 and the corresponding primary transfer rollers 36K, 36C, 36M, or 36Y as the resistance value of the primary transfer unit.

[0086] Although one embodiment has been described above, the embodiments are not limited thereto. For example, in one embodiment, an image forming apparatus 10 that forms an image using four colors, YMCK, was described as an example, but the image forming apparatus may also be a monochrome image forming apparatus, such as a black image forming apparatus.

[0087] Furthermore, the resistance detection voltage storage unit 131 and the AC peak voltage storage unit 121 are not limited to storing data in a table format as shown in Figures 8 and 9.

[0088] Furthermore, while the printing operation was explained with reference to the flowchart in Figure 10, AC peak voltage control processing can also be performed in the copying operation using the scanner 16 after each copy operation of one or more originals is completed.

[0089] Furthermore, in image forming apparatuses that have a sleep function for power consumption, the AC peak voltage control processing may be performed when the apparatus wakes up from the sleep state, or according to the usage status of the image forming apparatus, such as after a certain operating time has elapsed or after a certain number of images have been formed.

[0090] Furthermore, in the AC peak voltage control process detailed in Figure 11, the determined AC peak voltage (Vp-p) may not only be stored in the AC peak voltage storage unit 121, but may also be transmitted to the server device SV via the communication interface 14. This allows the server device SV to detect potential failures of the image forming apparatus 10 by determining whether the transmitted AC peak voltage (Vp-p) is within a specified range. If there is a potential failure in the image forming apparatus 10, the server device SV can provide feedback to the image forming apparatus 10 to prevent it from using that AC peak voltage (Vp-p), or notify the maintenance personnel of the image forming apparatus 10 or a service technician from a maintenance service company.

[0091] Furthermore, in the above embodiment, it is assumed that a control program is pre-stored in the storage device 13 of the image forming apparatus 10. In this regard, a control program, which is transferred separately from the image forming apparatus 10, may be written to a writable storage device provided by the image forming apparatus 10 in response to an operation by an administrator or the like. The transfer of these control programs, etc., can be carried out by storing them on a removable computer-readable storage medium or by communication over a network. The computer-readable storage medium can take any form as long as it can store a program and is readable by the device, such as a CD-ROM or memory card.

[0092] In addition, several embodiments of the present invention have been described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments are included within the scope of the invention and within the scope of the invention and its equivalents as described in the claims. The invention described in the original claims of this application is listed below. [1] An image carrier on which an electrostatic latent image is formed, A charging means comprising a charging member positioned close to the surface of the image carrier, wherein a voltage obtained by superimposing a DC voltage on the charging member is applied to the charging member to uniformly charge the surface of the image carrier, A toner image forming means for forming a toner image on the image carrier by forming a latent image of the image to be formed on the image carrier and developing it, A transfer means for transferring the toner image on the image carrier onto a transfer body, A detection means for detecting the resistance value of the transfer means, A control means that estimates the saturation value of the surface potential of the image carrier based on the resistance value of the transfer means detected by the detection means, and sets the peak value of the AC voltage applied by the charging means to the charging member according to the estimated saturation value, An image forming apparatus comprising: [2] The control means causes the charging means to change the peak value of the AC voltage while causing the detection means to detect the resistance value of the transfer means, and estimates the saturation value of the surface potential of the image carrier based on the change in the resistance value of the transfer means detected by the detection means. [1] The image forming apparatus described above. [3] The detection means detects the resistance value of the transfer means as a voltage value. [2] The image forming apparatus described above. [4] The control means estimates the saturation value of the surface potential of the image carrier based on the saturation value of the voltage value detected by the detection means. [3] The image forming apparatus described above. [5] The transfer means comprises a transfer body and a biasing member that faces the image carrier with the transfer body in between, and the transfer means transfers the toner image on the image carrier onto the transfer body by biasing the transfer body toward the image carrier with the biasing member and bringing the transfer body into contact with the image carrier, The detection means detects the resistance value of the resistor, which includes the transfer body and the biasing member. [1] The image forming apparatus described above. [6] A processor for an image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed; a charging means for uniformly charging the surface of the image carrier by applying a voltage obtained by superimposing an AC voltage on a DC voltage to a charging member located in close proximity to the surface of the image carrier; a toner image forming means for forming a toner image on the image carrier by forming a latent image of an image to be formed on the image carrier and developing it; a transfer means for transferring the toner image on the image carrier onto a transfer material; and a detection means for detecting the resistance value of the transfer means, The detection means has a function to estimate the saturation value of the surface potential of the image carrier based on the resistance value of the transfer means detected by the detection means, The charging means has a function to set the peak value of the AC voltage applied to the charging member according to the estimated saturation value, A program to achieve this. [Explanation of Symbols]

[0093] 10…Image forming apparatus, 11…Processor, 12…Main memory, 13…Storage device, 14…Communication interface, 15…Operation panel, 16…Scanner, 17…Input image processing unit, 18…Page memory, 19…Output image processing unit, 20…Printer, 21,21K,21C,21M,21Y…Resistance detection unit, 30K,30C,30M,30Y…Photoconductor drum, 31…Transfer body, 32a,32b,32c,32d…Rollers, 33K,33C,33M,33Y…Charging rollers, 34K,34C,34M,34Y…Static eliminator, 35K,35C,35M,35Y…Photoconductor cleaner, 36K,36C,36M,36Y…Primary transfer roller, 37…Secondary transfer roller 38...Fuser, 39...Transfer cleaner, 40K, 40C, 40M, 40Y...Developer, 43K, 43C, 43M, 43Y...Voltage application unit, 44...Exposure unit, 51...Paper feed cassette, 52...Transport path, 121...AC peak voltage memory unit, 131...Resistance detection voltage memory unit, NW...Network, SV...Server device, To...Resistance detection voltage, UT...User terminal, Vo...Surface potential.

Claims

1. An image carrier on which an electrostatic latent image is formed, A charging means comprising a charging member positioned close to the surface of the image carrier, wherein a voltage obtained by superimposing a DC voltage on the charging member is applied to the charging member to uniformly charge the surface of the image carrier, A toner image forming means for forming a toner image on the image carrier by forming a latent image of the image to be formed on the image carrier and developing it, A transfer means for transferring the toner image on the image carrier onto a transfer body, A detection means for detecting the resistance value of the transfer means as a voltage value, A resistance detection voltage storage unit stores the resistance detection voltage, which is the voltage value detected by the detection means. Control means for setting the peak value of the AC voltage applied by the charging means to the charging member, Equipped with, The control means is While causing the charging means to change the peak value of the AC voltage within a scanning range from a predetermined minimum value to a predetermined maximum value, the detection means is caused to detect the resistance detection voltage at multiple voltage setting points at voltage setting points set at regular intervals, and the multiple resistance detection voltages are stored in the resistance detection voltage storage unit. Based on the change states of the plurality of resistance-detecting voltages stored in the resistance-detecting voltage storage unit, the saturation value of the surface potential of the image carrier is estimated. The peak value of the AC voltage applied by the charging means to the charging member is set according to the estimated saturation value. Image forming apparatus.

2. The control means estimates the saturation value of the surface potential of the image carrier based on the saturation value of the voltage value stored in the resistance sensing voltage storage unit. The image forming apparatus according to claim 1.

3. The transfer means comprises a transfer body and a biasing member that faces the image carrier with the transfer body in between, and the transfer means transfers the toner image on the image carrier onto the transfer body by biasing the transfer body toward the image carrier with the biasing member and bringing the transfer body into contact with the image carrier. The detection means detects the resistance value of the resistor, which includes the transfer body and the biasing member. The image forming apparatus according to claim 1.

4. A processor for an image forming apparatus comprises: an image carrier on which an electrostatic latent image is formed; a charging means for uniformly charging the surface of the image carrier by applying a voltage obtained by superimposing an AC voltage on a DC voltage to a charging member located in close proximity to the surface of the image carrier; a toner image forming means for forming a toner image on the image carrier by forming a latent image of an image to be formed on the image carrier and developing it; a transfer means for transferring the toner image on the image carrier onto a transfer material; a detection means for detecting the resistance value of the transfer means as a voltage value; and a resistance detection voltage storage unit for storing the resistance detection voltage, which is the voltage value detected by the detection means. The charging means is made to change the peak value of the AC voltage within a scanning range from a predetermined minimum value to a predetermined maximum value, and the detection means is made to detect the resistance detection voltage at multiple voltage setting points at voltage setting points set at regular intervals, thereby storing multiple resistance detection voltages in the resistance detection voltage storage unit. The function of estimating the saturation value of the surface potential of the image carrier based on the change states of the plurality of resistance-detecting voltages stored in the resistance-detecting voltage storage unit, The charging means has a function to set the peak value of the AC voltage applied to the charging member according to the estimated saturation value, A program to achieve this.

Images