Patent Grant
10739692
This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-116174, filed on Jun. 19, 2018, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.
Embodiments of the present disclosure relate to an image forming apparatus and an image forming method.
An electrophotographic image forming apparatus is known that measures the film thickness of a photoconductor based on the voltage-current characteristics obtained when voltage is applied to the photoconductor via a charging member.
In an embodiment of the present disclosure, there is provided an image forming apparatus that includes a rotatable photoconductor, a charging device, a voltage applying device, a current detection device, and control circuitry. The charging device is configured to apply a voltage to the photoconductor to charge the photoconductor. The voltage applying device is configured to apply the voltage to the charging device. The current detection device is configured to detect a charging current that passes the charging device when the voltage applying device applies the voltage to the charging device. The control circuitry is configured to determine a film thickness of the photoconductor based on the charging current detected with the current detection device; determine an estimated film thickness being an estimated value of the film thickness, based on a previous film thickness previously determined by the control circuitry and travel information of the photoconductor after determination of the previous film thickness; determine a discharging start voltage that the voltage applying device applies to the charging device to start discharging from the charging device to the photoconductor; determine, from the estimated film thickness and the discharging start voltage, a film thickness determining voltage that the voltage applying device applies to the charging device to pass a film thickness determining current being a charging current used for determining the film thickness; and apply the film thickness determining voltage to the charging device to determine the film thickness.
In another embodiment of the present disclosure, there is provided an image forming apparatus that includes a rotatable photoconductor, charging means, voltage applying means, current detection means, and control means. The charging means charges the photoconductor by applying a voltage to the photoconductor. The voltage applying means applies the voltage to the charging means. The current detection means detects a charging current that passes the charging means when the voltage applying means applies the voltage to the charging means. The control means determines a film thickness of the photoconductor based on the charging current detected with the current detection means; determines an estimated film thickness being an estimated value of the film thickness, based on a previous film thickness previously determined by the control means and travel information of the photoconductor after determination of the previous film thickness; determines a discharging start voltage that the voltage applying means applies to the charging means to start discharging from the charging means to the photoconductor; determines, from the estimated film thickness and the discharging start voltage, a film thickness determining voltage that the voltage applying means applies to the charging means to pass a film thickness determining current being a charging current used for determining the film thickness; and applies the film thickness determining voltage to the charging means to determine the film thickness.
In still another embodiment of the present disclosure, there is provided a method of determining a film thickness of a rotatable photoconductor in an image forming apparatus. The image forming apparatus includes a charging device configured to apply a voltage to the photoconductor to charge the photoconductor, a voltage applying device configured to apply the voltage to the charging device, a current detection device configured to detect a charging current that passes the charging device when the voltage applying device applies the voltage to the charging device, and control circuitry configured to determine a film thickness of the photoconductor based on the charging current detected with the current detection device. The method includes determining an estimated film thickness being an estimated value of the film thickness, based on a previous film thickness previously determined by the control circuitry and travel information of the photoconductor after determination of the previous film thickness; determining a discharging start voltage that the voltage applying device applies to the charging device to start discharging from the charging device to the photoconductor; and determining, from the estimated film thickness and the discharging start voltage, a film thickness determining voltage that the voltage applying device applies to the charging device to pass a film thickness determining current being a charging current used for determining the film thickness.
A more complete appreciation of the disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein:
The accompanying drawings are intended to depict embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.
In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.
An image forming apparatus 100 according to the present embodiment is a multifunction device called a multifunction peripheral/printer (MFP) that has a combination of, for example, a copying function, a facsimile function, a printer function, a scanner function, a function of executing image processing on an input image (e.g., an image read by the scanner function or an image input by the scanner function or the facsimile function), and a function of storing or distributing an input image.
The image forming apparatus 100 according to the present embodiment is an electrophotographic image forming apparatus that selectively exposes a charged surface of a photoconductor to write an electrostatic latent image, adheres toner to the electrostatic latent image, and transfers the toner onto a recording medium, such as a sheet of paper. In the present embodiment, image to be processed by the image forming apparatus 100 is assumed to include not only image data but also data that does not contain image data, that is, data that contains only text information.
The controller control unit 1 controls the entire image forming apparatus 100. As an example, the controller control unit 1 is an integrated circuit (IC) that includes a central processing unit (CPU), a random access memory (RAM), and a read only memory (ROM). The CPU uses the RAM as a work area (working area) and executes a program stored in the ROM or the memory 4 to control the operation of the entire image forming apparatus 100 and achieve various functions such as the copying function, the facsimile function, the printer function, and the scanner function. Other examples of various functions include the management of communication with an external device and the instruction to start or end printing. The controller control unit 1 has a timer function and is capable of managing the time for achieving various functions.
The print engine 2, which is an example of the image forming unit, is hardware for achieving, e.g., the copying function, the facsimile function, the printer function, and the scanner function. In other words, the print engine 2 is hardware including, for example, a printer, a facsimile, and/or a scanner. The print engine 2 may include an optional device, such as a finisher that sorts printed sheets or such as an automatic document feeder (ADF) that automatically feeds an original document.
The engine control unit 3, which is control circuitry or control means, is connected to the print engine 2 to control the print engine 2 in response to an instruction from the controller control unit 1. The engine control unit 3 is, for example, an IC that includes a CPU, a RAM, and a ROM. The CPU uses the RAM as a work area (a working area) and executes a program stored in the ROM or the memory 4 to achieve various functions of the print engine 2. Examples of such various functions include printing according to an electrophotographic process.
The memory 4 as a storage device is a memory that stores programs and various data for operation of the image forming apparatus 100. The memory 4 is, for example, a ROM, a RAM, or a hard disk drive (HDD). For example, an operation system (OS) being basic software that controls the entire image forming apparatus 100, various application programs operable on the OS, and operating conditions for executing the various functions are preferably stored in the HDD or ROM as a non-volatile storage medium whose storage contents are not erased even when the image forming apparatus 100 is turned off. The memory 4 may also store operation results performed by various functions of the image forming apparatus 100 as log data each time.
In the present embodiment, the memory 4 includes a film-thickness storage unit 41, an estimated film-thickness storage unit 42, and a voltage difference storage unit 43 according to data to be stored. The film-thickness storage unit 41, the estimated film-thickness storage unit 42, and the voltage difference storage unit 43 may be different storage media or may be different storage regions of the same storage medium.
The communication I/F 5 is, for example, an interface for the image forming apparatus 100 to communicate with an external device via a network such as the Internet or a local area network (LAN). The image forming apparatus 100 accepts various data such as print instructions and image data from an external device by the communication I/F 5 and can input various data to an external device.
The control panel 6, which is an example of an operation unit, receives various inputs in response to the operation of the operator, and displays various information (e.g., information indicating received operation, information indicating the operation state of the image forming apparatus 100, and information indicating the setting state of the image forming apparatus 100). The control panel 6 is constituted by, for example, a liquid crystal display (LCD) device having a touch panel function. However, the control panel is not limited to the LCD device and may be constituted by, for example, an organic electro-luminescence (EL) display device having a touch panel function. Alternatively, in addition to or instead of the control panel 6, an operation unit such as hardware keys and an indicator such as a lamp may be provided.
The photoconductor travel distance measuring unit 7, which is the photoconductor running information acquisition unit, measures the travel distance obtained from the travel information, such as the rotation speed, of the photoconductor, and notifies the controller control unit 1 and the engine control unit 3 of the travel distance. Note that the IC itself constituting the engine control unit 3 may have a function of measuring the travel distance of the photoconductor and may function as the photoconductor travel distance measuring unit 7. The travel information is not limited to the travel distance and may be, for example, the travel time. The travel speed or the contact pressure with other members during traveling may also be used as the travel information.
The temperature-and-humidity sensor 8, which is an environment information acquisition unit, detects temperature and humidity as environment information, which is information of the environment in which the image forming apparatus 100 is installed, and notifies the controller control unit 1 and the engine control unit 3 of the temperature and humidity. The temperature-and-humidity sensor 8 is installed at an appropriate location in accordance with the specification and use of the environment information, such as the external periphery of the image forming apparatus 100, the interior of the image forming apparatus 100, and an area near a specific member inside the image forming apparatus 100, and the layout condition of the image forming apparatus 100. Note that the environment information may be one of temperature and humidity or may be obtained by using detection results of other sensors in addition to temperature and humidity.
The image forming apparatus 100 may also include an external interface to read and write an external recording medium, such as a compact disc (CD), a digital versatile disc (DVD), a secure digital (SD) memory card, or a universal serial bus (US) memory, via the external interface.
A program stored in the memory 4 is a program that can be processed by a computer. The program may be installed in the memory 4 at the time of manufacturing or shipment of the image forming apparatus 100 or may be installed after the sale. As a method of installing the program after the sale, for example, the program may be installed using an external storage medium, which stores the program, via an external storage medium or may be installed using the communication I/F 5 via the network.
As illustrated in
The print engine 2 further includes a primary transfer roller 27, an intermediate belt 28, and a neutralizer 29. Voltage is applied to the primary transfer roller 27 by the power supply from the primary transfer power source 26. The toner image on the surface of the photoconductor 23 is transferred onto the intermediate belt 28. The neutralizer 29 neutralizes the charge on the surface of the photoconductor 23 after the primary transfer.
For the operation of each part in
Further, the high voltage generated by the power supply from the primary transfer power source 26 is applied to the primary transfer roller 27, thus causing the toner image on the surface of the photoconductor 23 to be primarily transferred to the intermediate belt 28 (primary transfer). Thereafter, the toner image transferred to the intermediate belt 28 is secondarily transferred to a recording medium (secondary transfer). In the case in which the neutralizer 29 is installed as illustrated in
In the case of color printing, the photoconductors 23 for four colors are arranged side by side with respect to the intermediate belt 28. Toner images for four colors are primarily transferred separately onto the intermediate belt 28, and then the toner images are secondarily transferred onto the recording medium. Then, the toner images are fixed on the recording medium. Although various types of recording media are available in the present embodiment, the following description assumes “plain paper” as a typical recording medium. For example, coated paper, label paper, an overhead projector sheet, a film, or a flexible thin plate may be also used as the recording medium.
In
The charging power source 21 includes a current detection circuit 211 to detect the current supplied by the charging power source 21 to the charging roller 22. The current detection circuit 211, which is a current detection device or current detection means, detects an output current from the charging power source 21 to the charging roller 22 and outputs the current to the engine control unit 3 as a charging current feedback (FB) signal. The current detection circuit 211 is, for example, a circuit capable of detecting an output current of the charging power source 21 but is not limited to such a circuit if the circuit can generate the charging current FB signal. In some embodiment, the current detection circuit may be, for example, a circuit that detects the current flowing from the charging roller 22 to the photoconductor 23 and returning to the charging power source 21. The charging current FB signal is, for example, an analog signal, but it is not limited to the analog signal.
The charging roller 22 includes, for example, a metal core 22a and a conductive elastic layer (conductive rubber layer) 22b on an outer periphery of the metal core 22a. The photoconductor 23 includes, for example, a filmy photoconductive layer 23b as a charged object on an outer peripheral surface of a conductive drum substrate 23a. The thickness d of the filmy photoconductive layer 23b from the surface of the conductive drum substrate 23a in the photoconductor 23 is referred to as film thickness.
Referring to the operations of each part of
When the charging roller 22 is charged by the voltage applied to the charging roller 22 from the charging power source 21 and applied to the charging roller 22 at a certain voltage or more, the charging roller 22 starts discharging the photoconductor 23 adjacent to the charging roller 22, thus causing the surface potential of the photoconductor 23 to start to rise. Accordingly, the charging to the photoconductor 23 is performed. In this manner, the voltage at which the discharge from the charging roller 22 to the photoconductor 23 is started is referred to as discharging start voltage.
The engine control unit 3 can determine various data, such as the discharging start voltage, which is the voltage at which the charging roller 22 starts discharging, and the film thickness of the photoconductor, based on the obtained charging current FB signal. The engine control unit 3 also receives a notification of temperature and humidity from the temperature-and-humidity sensor 8.
The memory 4 can store various data for the engine control unit 3 to execute the control. The engine control unit 3 can acquire various data stored in the memory 4 and store the determined various data in the memory 4.
Here, a description is given of the relationship between the film thickness of the photoconductor and the voltage-current characteristics of the voltage applied to the charging roller and the charging current, which is the current flowing through the charging device when the voltage is applied to the charging roller. The relationship of the graph illustrated in
It is known that the relation between I=k/d (k is constant) is satisfied between the current I flowing through the charging roller in charging the photoconductor and the film thickness d of the photoconductor in a state in which the discharging is being performed from the charging roller to the photoconductor. Therefore, if the relationship of
When the slope of the voltage-current characteristics of the voltage applied to the charging roller and the charging current is calculated at a certain point in time, a plurality of different voltages being at least equal to or greater than the discharging start voltage may be applied to the charging roller to detect the charging current when each of the different voltages is applied. For example, the charging currents detected on application of four different voltages are plotted as illustrated in (1), (2), (3), and (4) of
First, the engine control unit 3 determines an estimated film thickness of the photoconductor 23 as an estimated-film-thickness determining step (step S1). For example, the engine control unit 3 acquires, from the photoconductor travel distance measuring unit 7, the travel distance TD of the photoconductor after determining the previous film thickness. The engine control unit 3 also acquires the film thickness previously determined, from the film-thickness storage unit 41. The engine control unit 3 determines the estimated film thickness with reference to the table illustrated in
Next, as a threshold current determining step, the engine control unit 3 determines a threshold current I0 which is a lower limit of the charging current in which the film thickness of the photoconductor can be measured (step S2). In the present embodiment, the threshold current I0 of the photoconductor 23 is previously stored in the memory 4, and the engine control unit 3 acquires the threshold current I0 from the memory 4 to determine the threshold current I0. The threshold current I0 is set so as to be a threshold value that can determine the film thickness without being affected by noise and current detection accuracy. In other words, when the current is too small, various noises and current detection accuracy on the detection may affect the accuracy of the film thickness measurement. Therefore, the lower limit of the charging current, at which the film thickness of the photoconductor can be measured, is determined. The threshold current I0 may be set by a theoretical value or may be set by experiments in advance, or may be set by a simulation.
The engine control unit 3 determines the discharging start voltage Vth as the discharging start voltage determining step (step S3). That is, the voltage-current characteristics are determined from the charging current obtained when a plurality of different voltages, for example, the four different voltages illustrated in
The engine control unit 3 determines a minimum voltage V1 that is the minimum value among the film-thickness determining voltages for passing the current having the threshold current I0 or greater as a first film-thickness determining voltage determination step (step S4). For example, as illustrated in
As described above, an estimated film thickness, which is an estimated value of the film thickness, is determined based on a previous film thickness, which is a previously-determined film thickness, and travel information of the photoconductor after the previous film thickness is determined. The discharging start voltage, which is the voltage with which discharging from the charging device to the photoconductor is started, is determined. From the estimated film thickness and the discharging start voltage, the film-thickness determining voltage is determined that is a voltage to be applied by the voltage applying device to flow the film-thickness determining current, which is a charging current used for determining the film thickness. The film-thickness determining voltage is applied to the charging device to determine the film thickness. Such a configuration can determine the film thickness with high accuracy without deviating from the load range as the power source of the charging power source.
The control unit sets a voltage obtained by adding a predetermined voltage to the threshold voltage, which is a threshold voltage necessary for flowing a threshold current being a minimum current usable for determining the film thickness, to the minimum voltage being the minimum value of the film-thickness determining voltage. If the voltage applied to determine the film thickness is too close to the discharging start voltage, noise and current measurement accuracy may affect the film thickness determined. The discharging start voltage varies with the film thickness of the photoconductor and the environmental conditions. Therefore, the voltage obtained by adding an excess voltage corresponding to the predetermined voltage is set to the minimum voltage of the film-thickness determining voltage. Such a configuration can reliably perform discharging and flow a charging current sufficient to detect the film thickness without the influence of the noise and the current measurement accuracy. Such a configuration can determine the film thickness with high accuracy.
The engine control unit 3 further determines n film-thickness determining voltages of V2 and V3 (step S5) as the second film-thickness determining voltage determination step. For example, the engine control unit 3 adds a predetermined voltage β to the minimum voltage V1 to determine the voltage V2. Then, the engine control unit 3 adds a predetermined voltage γ, which is determined in advance, to the voltage V2 to determine the voltage V3. In other words, the engine control unit 3 adds a predetermined voltage β+γ, which is determined in advance, to the voltage V1 to determine the voltage V3. In the present embodiment, the predetermined voltages β and γ are previously stored in the voltage difference storage unit 43. The engine control unit 3 acquires the predetermined voltages β and γ from the voltage difference storage unit 43 to determine the voltage V2 and the voltage V3.
In such a manner, the engine control unit 3 determines a plurality of film-thickness determining voltages including the minimum voltage V1, V2, and V3, which are the minimum voltage V1 and the different film-thickness determining voltages V2 and V3 obtained by adding different predetermined voltages, for example, predetermined voltages β and β+γ to the minimum voltage V1. The engine control unit 3 determines voltage-current characteristics based on a plurality of charging currents flowing on application of the plurality of film-thickness determining voltages, and determines the film thickness of the photoconductor from the slope of the voltage-current characteristics. Although at least two points are used to determine the slope, the above-described configuration determines the film-thickness based on more measurement points, thus reducing sampling errors due to, for example, noise and abrasion wear of the photoconductor. In the present embodiment, the measurement points are three points of V1, V2 and V3 but are not limited to the three points. The film thickness may be determined by a greater number of measurement points than the present embodiment.
The engine control unit 3 determines the film thickness of the photoconductor as a film thickness determining step (step S6). For example, the engine control unit 3 controls the charging power source 21 to apply the determined film thickness determining voltages V1, V2, and V3 to the charging roller 22. When currents I1, I2, and I3 are detected for the film thickness determining voltages V1, V2, and V3, respectively, the voltage-current characteristics as illustrated in
The engine control unit 3 stores the measured film thickness in the film-thickness storage unit 41 (step S7) and terminates the process flow.
The predetermined voltages α, β, and γ may be fixed values, such as α=β=γ=100V, but may also be variable values stored in a table format. That is, as the film thickness is larger and the temperature is lower, the discharge voltage Vth is greater. Therefore, variable values are set so as to vary so that the predetermined voltages α, β, and γ become smaller as the estimated film thickness is greater or the temperature is lower. Such a configuration can set the film-thickness determining voltages to a value not exceeding the rated voltage of the charging power source 21, that is, within the raged voltage range.
If the predetermined voltages β and γ are too low, the accuracy of the film thickness determined would be reduced by the influence of the sampling error. On the other hand, if the predetermined voltages β and γ are too high, the predetermined voltages β and γ would exceed the rated voltage of the charging power source 21. Therefore, the predetermined voltages β and γ are determined in consideration of the above-described condition.
In the present embodiment, all steps of the processing flow are executed by the engine control unit 3. In some embodiments, for example, a part of the processing flow may be executed by another control unit, such as the controller control unit 1, in the image forming apparatus 100.
Here, a first variation of the film thickness determining process is described below. In the description of
Estimated film thickness=Previous film thickness−Film thickness abrasion rate×Photoconductor travel distance (Formula 1)
The film thickness abrasion rate is a film thickness value that is worn by a constant travel distance and is, for example, 0.15 μm/km. At this time, if the previous film thickness value is 20 μm and the photoconductor travel distance is 10 km, the present film thickness can be determined to be d=20 μm−(0.15×10)=18.5 μm.
Next, a second variation of the film thickness determining process is described. In the description of
Next, a third variation of the film thickness determining process is described. In the description of
In the second variation and the third variation, the environment information is determined using the detection results of the temperature-and-humidity sensor 8 but the environment information is not limited to the detection results of the temperature-and-humidity sensor 8. That is, a sensor that detects an environmental factor that may affect the discharging start voltage, such as a sensor that detects a substance that floats in the air and adheres to the surface of the photoconductor 23 and affect the characteristics of the surface of the photoconductor 23, may be suitably provided to determine the environment information and the corresponding discharging start voltage. In the second variation and the third variation, the environment information includes LL, MM, and HH, which are codes converted from the detection results of the sensor. In some embodiments, a table may be used in that the detection results of the sensor themselves are associated with the discharging start voltages.
Although the first variation, the second variation, and the third variation of the present embodiment are described above, another example of the film thickness determining process flow may execute the first variation as step S1 and the second variation as step S3 of the flowchart illustrated in
The present invention is not limited to embodiments described above. Various modifications can be made without departing from the scope of the technical gist of the present invention. The present invention includes all technical matters included in the technical idea described in the scope of the claims. The above-described embodiments are examples. A person skilled in the art can implement various alternatives, alternations, modifications, or improvements from the contents disclosed in the present specification, and these are to be included in the technical scope described in the scope of the accompanying claims. The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above. Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions.
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