Image forming apparatus, voltage control method for image forming apparatus, and voltage control program for image forming apparatus

Abstract

To prevent a situation in which overcurrent flows and an overcurrent protection function is actuated, during setting of an initial value of applied voltage to be applied to an image carrier.SOLUTION: An image forming apparatus has: a voltage generation unit that generates applied voltage in which AC voltage is superimposed on DC voltage; an image carrier on which an electrostatic latent image is formed; a charging member that electrostatically charges the image carrier on the basis of the applied voltage from the voltage generation unit; a current detection unit that detects current flowing from the voltage generation unit to the image carrier; a storage unit that stores a previous voltage value indicating the value of the applied voltage in the previous charging of the image carrier; and a control unit that controls the operation of the voltage generation unit on the basis of the current detected by the current detection unit. When the previous voltage value stored in the storage unit is equal to or more than a reference value during setting of an initial value of the applied voltage, the control unit sets the initial value to the reference value.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, a voltage control method for an image forming apparatus, and a voltage control program for an image forming apparatus. [Background technology]

[0002] For example, in a non-image forming process in an image forming apparatus, a detection charging voltage for detecting a charging current is set within a predetermined range based on the charging voltage applied to the photoconductor drum in the previous image forming process in order to determine a charging voltage value to be used in the image forming process. If a current value detected when the charging voltage is supplied is greater than a threshold value, a control means for determining the charging voltage determines the detection charging voltage corresponding to the minimum current value as the charging voltage in the image forming process (see, for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0003] If the charging voltage in the non-image forming process is determined in a hotter and more humid environment than the previous charging voltage determination, an overcurrent may flow when the charging voltage is applied to the photoconductor drum. If an overcurrent protection function is activated due to the occurrence of an overcurrent, the time until the charging voltage is determined may become longer.

[0004] In view of the above problems, an object of the present invention is to prevent an overcurrent from flowing and activating an overcurrent protection function when setting an initial value of a voltage to be applied to an image carrier. [Means for solving the problem]

[0005] In order to solve the above technical problems, an image forming apparatus of one embodiment of the present invention has a voltage generation unit that generates an applied voltage by superimposing an AC voltage on a DC voltage, an image carrier on which an electrostatic latent image is formed, a charging member that charges the image carrier based on the applied voltage from the voltage generation unit, a current detection unit that detects a current flowing from the voltage generation unit to the image carrier, a memory unit that stores a previous voltage value indicating the value of the applied voltage when the image carrier was previously charged, and a control unit that controls the operation of the voltage generation unit based on the current detected by the current detection unit, and is characterized in that, when setting an initial value of the applied voltage, if the previous voltage value stored in the memory unit is equal to or greater than a reference value, the control unit sets the initial value to the reference value. Effect of the Invention

[0006] It is possible to prevent an overcurrent from flowing when setting the initial value of the voltage to be applied to the image carrier and activating the overcurrent protection function. [Brief description of the drawings]

[0007] [Figure 1] 1 is a diagram illustrating an overall configuration of an example of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] 2 is an explanatory diagram showing an example of a main part that performs an electrophotographic process in the image forming apparatus of FIG. 1. [Diagram 3] 2 is a functional block diagram showing an example of the configuration of a control device and a high-voltage power supply in FIG. 1. [Figure 4] 4 is a flow chart showing an example of control of a charging current by the control device of FIG. 3. [Diagram 5] 4 is a flow chart showing another example of the control of the charging current by the control device of FIG. 3. [Figure 6] 4 is a flow chart showing another example of the control of the charging current by the control device of FIG. 3. [Figure 7] 4 is a flow chart showing another example of the control of the charging current by the control device of FIG. 3. [Figure 8] 4 is a flow chart showing another example of the control of the charging current by the control device of FIG. 3. [Figure 9] 4 is a block diagram showing an example of a hardware configuration of the control device shown in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated descriptions may be omitted.

[0009] Description of an embodiment Fig. 1 is an overall configuration diagram showing an example of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 shown in Fig. 1 is, for example, a digital multifunction peripheral (MFP: Multi-Function Printer) having a copy function, a print function, a scanner function, a facsimile function, etc. The image forming apparatus 1 can switch between operation modes that respectively realize the copy function, the print function, the scanner function, and the facsimile function by using an application switching key or the like on the operation unit of the image forming apparatus 1. The image forming apparatus 1 goes into a copy mode when the copy function is selected, goes into a print mode when the print function is selected, goes into a scanner mode when the scanner function is selected, and goes into a facsimile mode when the facsimile function is selected.

[0010] In addition, the image forming apparatus 1 switches its internal state to an operating mode (operating state), a standby mode (standby state), an energy saving mode (power saving mode), etc., depending on the state of the internal circuit. Hereinafter, the energy saving mode is also referred to as an energy saving mode.

[0011] For example, the operating mode includes a copy mode or a print mode in which an image or text data is printed on a paper medium. The print mode includes an operation in a facsimile mode in which received data is printed on a paper medium. The operating mode also includes a scanner mode in which an original document is scanned, or a transmission / reception operation in a facsimile mode. The state of the internal circuitry is switched by a user's operation on the operation unit or by control within the image forming apparatus 1.

[0012] For example, the image forming apparatus 1 has an automatic document feeder 2 (ADF: Auto Document Feeder), an image reading device 3, a writing unit 4, a printer unit 5, a control device 20, a temperature and humidity sensor 25, a power supply device 30, and an operation unit 60. The printer unit 5 has a photoconductor drum 6, a developing device 7, a conveyor belt 8 (intermediate transfer belt), a fixing device 9, and a storage space for storing a paper feed tray 10. The printer unit 5 is an example of a printing unit.

[0013] As an example of the flow of image formation in the image forming apparatus 1, a case in which the operation mode is set to the copy mode will be briefly described below.

[0014] In the copy mode, multiple documents to be copied are set in the automatic document feeder 2, or a document to be copied is set on the image reading device 3. When a start button displayed on the operation unit 60 is pressed, the automatic document feeder 2 feeds the documents one by one to the image reading device 3. The image reading device 3 reads image information of each of the documents sent in sequence from the automatic document feeder 2 or the document set on the image reading device 3. The image information read by the image reading device 3 is processed by, for example, an image processing unit mounted on the control device 20.

[0015] The writing unit 4 converts the image information processed by the image processing unit into optical information. The printer unit 5 forms an electrostatic latent image by exposing the surface of the charged photoconductor drum 6 based on the image information, and forms a toner image by developing the electrostatic latent image with a developing device 7. The printer unit 5 transfers the toner image to a paper medium or the like via a conveyor belt 8 (intermediate transfer belt), and fixes the toner image transferred to the paper medium or the like with a fixing device 9. The paper medium or the like onto which the image of the original document has been copied is then discharged from a discharge section.

[0016] For example, the above-mentioned standby mode is the state in copy mode until the start button is pressed, and the operating mode is the state from when the start button is pressed until paper media or the like is discharged. After the operating mode ends, the state of the image forming device 1 returns to the standby mode, and if the standby mode continues for a predetermined time, the state of the image forming device 1 enters the energy saving mode. Then, if the operation unit 60 is operated during the energy saving mode, the state of the image forming device 1 returns to the standby mode.

[0017] The operation unit 60 accepts various inputs in response to user operations through the input unit, and displays various information on the display unit of the operation unit 60. For example, the information displayed on the display unit of the operation unit 60 is information indicating the operation for which the input was accepted, information indicating the operating status of the image forming device 1, information indicating the setting state of the image forming device 1, or the like.

[0018] The control device 20 controls the overall operation of the image forming apparatus 1, such as control of the printer unit 5, control of the power supply device 30, control of communications, and control of input to the operation unit 60, by causing a controller such as a built-in CPU (Central Processing Unit) to execute a control program. The control program may include an operation control program that controls the printer unit 5, an image processing program that processes an image formed by the printer unit 5, and a power control program that controls the power supply device 30. The control device 20 then executes the control program to perform a process of transferring an image obtained by image processing onto a paper medium or the like.

[0019] The temperature and humidity sensor 25 is provided, for example, in the printer unit 5, measures the temperature and humidity in the printer unit 5, and outputs temperature information indicating the measured temperature and humidity information indicating the measured humidity to the control device 20. Based on the temperature information and humidity information from the temperature and humidity sensor 25, the control device 20 adjusts a target value (e.g., peak value) of the AC current flowing between the high-voltage power supply 40 and the photoconductor drum 6, and controls the high-voltage power supply 40 so that the AC current value approaches the target value.

[0020] The power supply device 30 has a high-voltage power supply 40 that generates an AC voltage based on an AC voltage supplied from an AC power supply AC such as a commercial power supply, and a high-voltage power supply 50 that generates a DC voltage. The power supply device 30 supplies the generated AC voltage and DC voltage to various loads such as the printer unit 5. For example, the loads include various motors, a charger that charges the photoconductor drum 6, a developing roller of the developing device 7, and a control device 20 that includes a CPU, memory, etc.

[0021] Fig. 2 is an explanatory diagram showing an example of a main part that performs an electrophotographic process in the image forming apparatus 1 in Fig. 1. Detailed description of operations that overlap with those in Fig. 1 will be omitted.

[0022] The image forming apparatus 1 includes a photoconductor drum 6, a charging roller 11, an exposure unit 12, a developing device 7, a transfer roller 13, an intermediate transfer belt 14, a static eliminator 15, a cleaning blade 16, and high-voltage power supplies 40 and 50. The image forming apparatus 1 forms an image by an electrophotographic method. The photoconductor drum 6 is an example of an image carrier on which an electrostatic latent image is formed. The charging roller 11 is an example of a charging member.

[0023] The high-voltage power supply 40 generates a high voltage (e.g., negative voltage) by superimposing a high-voltage DC voltage and a high-voltage AC voltage, and applies the generated high voltage to the charging roller 11. The high-voltage power supply 50 generates a high DC voltage (e.g., positive voltage), and applies the generated high voltage to the transfer roller 13.

[0024] The charging roller 11 is in contact with the photosensitive drum 6 or in close proximity to it at a distance of about several tens of microns, and a high voltage applied from a high voltage power supply 40 generates a discharge between the surface of the photosensitive drum 6 and the surface of the charging roller 11. As a result, the surface of the photosensitive drum 6 is uniformly charged to a predetermined potential. In the example shown in Fig. 2, the photosensitive drum 6 rotates clockwise, and the charging roller 11 and the transfer roller 13 rotate counterclockwise.

[0025] The exposure unit 12 converts the image information processed by the image processing unit into optical information, and exposes the surface of the photosensitive drum 6 in response to an image signal to form an electrostatic latent image on the photosensitive drum 6. The developing device 7 develops the electrostatic latent image formed on the photosensitive drum 6 to form a toner image on the photosensitive drum 6. The transfer roller 13 transfers the toner image on the photosensitive drum 6 to the intermediate transfer belt 14 by a high voltage applied from a high-voltage power supply 50. The toner image transferred to the intermediate transfer belt 14 is transferred to a paper medium or the like by a transfer unit (not shown), and then fixed by the fixing device 9 in FIG. 1. As a result, an image is formed on the paper medium or the like. In the case of the direct transfer method, a paper medium or the like is placed instead of the intermediate transfer belt 14, and the toner image on the photosensitive drum 6 is directly transferred to the paper medium or the like. In the following description, the formation of an image by the image forming apparatus 1 is also referred to as printing.

[0026] The static eliminator 15 removes the charge on the surface of the photosensitive drum 6 after the toner image on the photosensitive drum 6 is transferred to the intermediate transfer belt 14. Note that the image forming apparatus 1 does not necessarily have to have the static eliminator 15. The cleaning blade 16 is elastic, and its tip is in contact with the photosensitive drum 6 at an angle, and cleans the photosensitive drum 6 by scraping off and collecting foreign matter such as toner and paper powder remaining on the photosensitive drum 6 after transfer to a paper medium or the like.

[0027] When the image forming apparatus 1 forms a color image, the printer unit (FIG. 1) has elements located on the opposite side of the intermediate transfer belt 14 from the transfer roller 13 in FIG. 2, for each of the colors yellow, magenta, cyan, and black. The image forming apparatus 1 then transfers toner images of each color in sequence, superimposed on the intermediate transfer belt 14 that is provided in common to all four colors. Thereafter, the full-color toner image on the intermediate transfer belt 14 is transferred to a paper medium or the like by a transfer section, and then fixed by a fixing device 9. This embodiment can also be applied to an image forming apparatus that forms a color image.

[0028] Fig. 3 is a functional block diagram showing an example of the configuration of the control device 20 and the high voltage power supply 40 in Fig. 1. In Fig. 3, elements used for controlling the charging of the charging roller 11 are mainly shown.

[0029] The control device 20 has a memory 21 and a comparison unit 22. The control device 20 is an example of a control unit, and the memory 21 is an example of a storage unit. The memory 21 may be provided outside the control device 20. The high-voltage power supply 40 has a charging AC voltage generation unit 41, a charging current feedback unit 42, and a charging DC voltage generation unit 43. The high-voltage power supply 40 is an example of a voltage generation unit that generates an applied voltage in which an AC voltage is superimposed on a DC voltage.

[0030] For example, the memory 21 may store a charging bias value (such as a DC voltage value, a peak-to-peak voltage value of an AC voltage, and a frequency of an AC voltage) to be generated by the high-voltage power supply 40, a previously set voltage value described below, and various parameters used in the operation of the image forming apparatus 1. For example, the memory 21 is an electrically rewritable non-volatile memory.

[0031] The control device 20 outputs to the high-voltage power supply 40 an AC control signal that causes the charging AC voltage generating unit 41 to generate an AC voltage, and a DC control signal that causes the charging DC voltage generating unit 43 to generate a DC voltage, and receives a current feedback signal from the high-voltage power supply 40.

[0032] For example, a part of the control device 20 including the comparison unit 22 may be realized by a control program executed by the control device 20. Also, a part of the functions of the high-voltage power supply 40 may be realized by cooperation between hardware and software.

[0033] The charging AC voltage generation unit 41 generates an AC voltage in response to an AC control signal from the control device 20, and outputs the generated AC voltage to the charging roller 11. For example, the AC control signal may be a PWM (Pulse Width Modulation) signal. The charging DC voltage generation unit 43 generates a DC voltage in response to a DC control signal from the control device 20, and outputs the generated DC voltage to the charging roller 11. A voltage in which the AC voltage generated by the charging AC voltage generation unit 41 and the DC voltage generated by the charging DC voltage generation unit 43 are superimposed is supplied to the charging roller 11. The voltage in which the AC voltage and the DC voltage are superimposed is an example of an applied voltage.

[0034] The charging current feedback unit 42 detects the value of the charging current flowing from the photoconductor drum 6 through the charging roller 11 to the high-voltage power supply 40 during the period when the voltage is supplied from the high-voltage power supply 40 to the charging roller 11. For example, the charging current feedback unit 42 may obtain the voltage value across both ends of a minute fixed resistor inserted into a power line that applies an AC voltage from the charging AC voltage generation unit 41 to the charging roller 11, from the charging AC voltage generation unit 41, and detect the value of the charging current based on the voltage difference across the minute fixed resistor. The charging current feedback unit 42 is an example of a current detection unit that detects the current flowing from the high-voltage power supply 40 to the photoconductor drum 6.

[0035] The charging current feedback section 42 outputs a current feedback signal indicating the detected charging current value to the control device 20. For example, the charging current feedback section 42 may output information indicating a voltage difference across a minute fixed resistor as a current feedback signal to the control device 20. Hereinafter, the voltage corresponding to the charging current indicated by the current feedback signal is also referred to as a detected FB value.

[0036] The charging current flows when the photoconductor drum 6 is charged (discharged) via the charging roller 11. For example, the charging current feedback unit 42 may detect the charging current value multiple times at a predetermined cycle while the photoconductor drum 6 makes one rotation.

[0037] The control device 20 compares the detected FB value indicated by the current feedback signal output from the charging current feedback unit 42 with a target FB value, which is a voltage value corresponding to the target value of the charging current. The control device 20 generates an AC control signal that brings the detected FB value closer to the target FB value, and outputs the signal to the charging AC voltage generation unit 41. The detected FB value and the target FB value may be compared by the comparison unit 22. The control device 20 also generates a DC control signal that causes the charging DC voltage generation unit 43 to generate a DC voltage that is an offset voltage of the voltage output to the charging roller 11, and outputs the generated DC control signal to the charging DC voltage generation unit 43.

[0038] Furthermore, the control device 20, for example, outputs AC and DC voltages from the high-voltage power supply 40, and compares the previously set voltage value stored in the memory 21 with a reference value at a predetermined timing when the photoconductor drum 6 is rotated. The reference value indicates an AC voltage value at which the circuit protection function of the overcurrent protection device provided in the image forming apparatus 1 does not operate, even in a high-temperature and high-humidity environment, and is calculated in advance by experiment.

[0039] The previously set voltage value is an AC voltage (e.g., peak-to-peak voltage) that was set when the previous job was executed to form an electrostatic latent image by charging the photoconductor drum 6. Then, the control device 20 sets the AC voltage output value, which is the value of the AC voltage output from the high-voltage power supply 40, to the reference value or the previously set voltage value according to the result of comparing the previously set voltage value with the reference value.

[0040] (First operation flow) Fig. 4 is a flow diagram showing an example of the control of the charging current by the control device 20 of Fig. 3. That is, Fig. 4 shows an example of a power supply control method of the image forming apparatus 1. For example, the operation shown in Fig. 4 may be realized by a power supply control program executed by a CPU mounted on the control device 20.

[0041] 4 is started at a predetermined timing, such as when the image forming apparatus 1 is powered on, before the photoconductor drum 6 is charged to form an electrostatic latent image, or when a change in environmental classification such as temperature or humidity is detected. For example, if the control device 20 set the AC voltage value output by the charging AC voltage generation unit 41 to 2.0 kV in the previous job in which the photoconductor drum 6 was charged to form an electrostatic latent image, the control device 20 stores 2.0 kV in the memory 21 as the previously set voltage value.

[0042] 4 starts, the control device 20 controls the charging AC voltage generator 41 and the charging DC voltage generator 43 to apply a predetermined voltage obtained by superimposing an AC voltage and a DC voltage to the charging roller 11. First, in step S10, the control device 20 reads out the previously set voltage value stored in the memory 21. Next, in step S20, the control device 20 determines, for example, by the comparison unit 22, whether or not the previously set voltage value is equal to or greater than a reference value, and if it is equal to or greater than the reference value, performs step S30, and if it is less than the reference value, performs step S40.

[0043] In step S30, the control device 20 sets the initial value of the AC voltage output value to a reference value, and executes step S50. The current leakage characteristics of the charging roller 11 change due to changes in environmental conditions such as temperature and humidity, and the charging roller 11 has a higher impedance in a low-temperature, low-humidity environment than in a high-temperature, high-humidity environment. For example, if the AC voltage value in the previous job was a value in a low-temperature, low-humidity environment and the current environment is high-temperature and high humidity, the impedance of the charging roller 11 will be low and the charging current will increase, which may activate the overcurrent protection device provided in the image forming apparatus 1.

[0044] However, by setting the initial value of the AC voltage output value to the reference value in step S30, it is possible to prevent the overcurrent protection device from operating when adjusting the AC voltage even if the previous environment was a low temperature and low humidity environment and the current environment is a high temperature and high humidity environment, thereby reducing downtime and preventing the time required for adjusting the AC voltage from becoming longer.

[0045] In step S40, the control device 20 sets the initial value of the AC voltage output value to the previously set voltage value, and executes step S50. By setting the initial value of the AC voltage output value to the previously set voltage value, which is the most recent set value, it is possible to increase the possibility that the adjustment of the AC voltage can be started from a state close to an appropriate value, and it is possible to shorten the adjustment time for adjusting the AC voltage to an appropriate value.

[0046] In steps S50 to S70, control is performed to adjust the AC voltage generated by the charging AC voltage generation unit 41. Before step S50, the control device 20 outputs an AC control signal to cause the charging AC voltage generation unit 41 to output the AC voltage output value set in step S30 or step S40.

[0047] In step S50, the control device 20 detects the AC voltage output value based on the current feedback signal indicating the charging current. For example, the control device 20 samples the AC current value at a predetermined period while the photoconductor drum 6 rotates once, and calculates a detection FB value that is the average value of the sampled current feedback signals. The detection FB value corresponds to the AC voltage output value.

[0048] Next, in step S60, the control device 20 compares the detected FB value with a target FB value, which is a target value, and determines whether the difference between the detected FB value and the target FB value is within a target range. The target FB value indicates a voltage value corresponding to the target value of the charging current (i.e., a target voltage difference across the minute fixed resistor), and corresponds to the target value of the AC voltage output value.

[0049] When the difference between the detected FB value and the target FB value is within the target range, the control device 20 determines that an appropriate AC voltage is being output from the charging AC voltage generation unit 41, and ends the process shown in Fig. 4. Then, based on an instruction to start the printing operation, the control device 20 performs a process of forming an electrostatic latent image on the photosensitive drum 6, a process of developing the electrostatic latent image, a process of transferring the toner image formed on the photosensitive drum 6 by the development onto a paper medium or the like, and a process of fixing the toner image onto the paper medium or the like.

[0050] On the other hand, when the difference between the detected FB value and the target FB value is not within the target range, the control device 20 determines that an appropriate AC voltage is not being output from the charging AC voltage generation unit 41, and executes step S70. In step S70, the control device 20 switches the output value of the AC voltage, performs control to bring the detected FB value closer to the target FB value, and returns the process to step S50. For example, the control device 20 calculates the switching amount of the output value of the AC voltage using equation (1). In equation (1), the symbol ΔVpp indicates the adjustment amount of the peak-to-peak voltage Vpp of the AC voltage, and the symbol k indicates a coefficient. ΔVpp = k × (target FB value - detected FB value) (1)

[0051] When the detected FB value is smaller than the target FB value (when the charging current is smaller than the target value), the control device 20 increases the peak-to-peak voltage Vpp of the AC voltage by ΔVpp. When the detected FB value is larger than the target FB value (when the charging current is larger than the target value), the control device 20 decreases the peak-to-peak voltage Vpp of the AC voltage by ΔVpp.

[0052] (Second operation flow) Fig. 5 is a flow diagram showing another example of the control of the charging current by the control device 20 of Fig. 3. That is, Fig. 5 shows an example of a power supply control method for the image forming apparatus 1. For example, the operation shown in Fig. 5 may be realized by a power supply control program executed by a CPU mounted on the control device 20. The same steps as those in Fig. 4 are denoted by the same step numbers, and detailed descriptions thereof will be omitted.

[0053] Fig. 5 is the same as Fig. 4 except that steps S11 and S12 are inserted between steps S10 and S20. The characteristics of the charging roller 11 indicated by the charging current vary depending on environmental conditions such as temperature and humidity, and therefore the applied voltage value from the charging roller 11 at which the overcurrent protection function operates varies depending on the environmental conditions.

[0054] 5, the control device 20 reads out the previously set voltage value from the memory 21 in step S10, and then performs an environment classification detection process to detect the current environment state in step S11. Then, in step S12, the control device 20 determines a reference value according to the detected environment classification.

[0055] For example, the control device 20 selects one of a plurality of reference values ​​stored in the memory 21 corresponding to each of a plurality of environmental classifications. For example, a relatively low reference value is stored in advance in the memory 21 corresponding to the environmental classification of high temperature and high humidity in which an increase in charging current makes the overcurrent protection device more likely to operate. Also, a relatively high reference value is stored in advance in the memory 21 corresponding to the environmental classification of low temperature and low humidity in which a decrease in charging current makes the overcurrent protection device less likely to operate.

[0056] By carrying out steps S11 and S12, it is possible to set a reference value at which the overcurrent protection device is unlikely to operate even under high temperature and high humidity conditions. This makes it possible to further improve the efficiency of charging current adjustment compared to Fig. 4, and shorten the adjustment time required to adjust the AC voltage to an appropriate value. Note that steps S11 and S12 may be carried out before step S10.

[0057] (Third operation flow) Fig. 6 is a flow diagram showing another example of the control of the charging current by the control device 20 of Fig. 3. That is, Fig. 6 shows an example of a power supply control method for the image forming apparatus 1. For example, the operation shown in Fig. 6 may be realized by a power supply control program executed by a CPU mounted on the control device 20. The same steps as those in Fig. 4 are denoted by the same step numbers, and detailed descriptions thereof will be omitted.

[0058] Fig. 6 is the same as Fig. 4 except that steps S13 and S14 are inserted between steps S10 and S20. The charging roller 11 has a characteristic that its impedance increases in proportion to the time of use. For this reason, even in the same environmental category, a new charging roller 11 and a charging roller 11 that has been used to some extent will have different charging current values. For example, the charging current value decreases as the time of use of the charging roller 11 increases.

[0059] 6, the control device 20 reads the previously set voltage value from the memory 21 in step S10, and then in step S13 checks the number of sheets printed since the charging roller 11 was new. The number of sheets printed is approximately proportional to the usage time of the charging roller 11. Then, in step S14, the control device 20 determines a reference value according to the checked number of sheets printed.

[0060] For example, the control device 20 selects one of a plurality of reference values ​​stored in the memory 21 corresponding to each of a plurality of print count categories. For example, the memory 21 stores a relatively low reference value in advance corresponding to a category with a small number of print sheets in which the charging current value is relatively large and the overcurrent protection device is likely to operate. The memory 21 also stores a relatively high reference value in advance corresponding to a category with a large number of print sheets in which the charging current value is relatively small and the overcurrent protection device is unlikely to operate.

[0061] By carrying out steps S13 and S14, it is possible to set a reference value at which the overcurrent protection device is less likely to operate, even when the charging current increases with aging of the charging roller 11. This makes it possible to further improve the efficiency of charging current adjustment compared to Fig. 4, and shorten the adjustment time required to adjust the AC voltage to an appropriate value.

[0062] Note that steps S13 and S14 may be performed before step S10. Also, the control device 20 may determine the reference value by combining the environment classification in Fig. 5 and the print count classification in Fig. 6. In this case, the control device 20 determines the reference value after sequentially performing step S11 in Fig. 5 and step S13 in Fig. 6.

[0063] (Fourth operation flow) Fig. 7 is a flow diagram showing another example of the control of the charging current by the control device 20 of Fig. 3. That is, Fig. 7 shows an example of a power supply control method for the image forming apparatus 1. For example, the operation shown in Fig. 7 may be realized by a power supply control program executed by a CPU mounted on the control device 20. The same steps as those in Fig. 4 are denoted by the same step numbers, and detailed descriptions thereof will be omitted.

[0064] Fig. 7 shows a modified example of Fig. 4, which is a flow in which steps S10, S20, and S40 are omitted from Fig. 4. In Fig. 4, the previously set voltage value is compared with a reference value, and the initial value of the AC voltage output value is set to the reference value only when the previously set voltage value is equal to or greater than the reference value. However, even when the previously set voltage value is not compared with the reference value and the AC voltage output value is unconditionally set to the reference value, it is possible to prevent the overcurrent protection device from operating.

[0065] In the flow of FIG. 7, even if the previously set voltage value is smaller than the reference value and there is no risk of the overcurrent protection device activating, the AC voltage output value is set to the reference value, so the time required to adjust the AC voltage may be longer than in FIG. 4.

[0066] (Fifth operation flow) Fig. 8 is a flow diagram showing another example of the control of the charging current by the control device 20 of Fig. 3. That is, Fig. 8 shows an example of a power supply control method for the image forming apparatus 1. For example, the operation shown in Fig. 8 may be realized by a power supply control program executed by a CPU mounted on the control device 20. The same step numbers are used for the same processes as in Figs. 4 and 5, and detailed descriptions thereof will be omitted.

[0067] FIG. 8 shows a modified example of FIG. 5, which is a flow in which steps S10, S20, and S40 are omitted from FIG. 5. In FIG. 5, the previously set voltage value is compared with a reference value, and only when the previously set voltage value is equal to or greater than the reference value, the initial value of the AC voltage output value is set to the reference value determined in step S12. However, as in FIG. 7, even when the previously set voltage value is not compared with the reference value and the AC voltage output value is unconditionally set to the reference value, it is possible to prevent the overcurrent protection device from operating. Note that steps S13 and S14 in FIG. 6 may be performed instead of steps S11 and S12 in FIG. 8.

[0068] In the flow of FIG. 8, as in the flow of FIG. 7, even if the previously set voltage value is smaller than the reference value and there is no risk of the overcurrent protection device activating, the AC voltage output value is set to the reference value. Therefore, the time required to adjust the AC voltage may be longer than that in FIG. 5.

[0069] Fig. 9 is a block diagram showing an example of a hardware configuration of the control device 20 in Fig. 3. The control device 20 has a CPU 201, a ROM (Read Only Memory) 202, and a RAM (Random Access Memory) 203. The control device 20 also has an input interface unit 204, an output interface unit 205, an input / output interface unit 206, and a communication interface unit 207.

[0070] For example, the CPU 201, the ROM 202, the RAM 203, the input interface unit 204, the output interface unit 205, the input / output interface unit 206, and the communication interface unit 207 are interconnected via a bus BUS.

[0071] The CPU 201 executes various programs such as an OS (Operating System) and applications. The ROM 202 holds basic programs and various parameters for enabling the CPU 201 to execute the various programs. The RAM 203 stores the various programs executed by the CPU 201 and data used by the programs. For example, the various programs may include an image processing program that performs image processing of an original image read by the image reading device 3 and a power supply control program that controls the power supply device 30.

[0072] For example, the input interface unit 204 is connected to an input device 61 such as an input unit mounted on the image reading device 3 and the operation unit 60 of the image forming apparatus 1. The output interface unit 205 is connected to an output device 62 such as a display unit mounted on the operation unit 60. The input / output interface unit 206 is connected to an input / output device 63 such as an auxiliary storage device and a recording medium. The communication interface unit 207 can connect the image forming apparatus 1 to a network or the like.

[0073] When various programs such as an image processing program or a power supply control program are stored in the recording medium, the programs may be transferred from the recording medium to the RAM 203 or the like via the input / output interface unit 206 to which the recording medium is connected.

[0074] As described above, in this embodiment, when the previously set voltage value is equal to or greater than the reference value, the control device 20 sets the initial value of the AC voltage output value to the reference value. This makes it possible to prevent the overcurrent protection device from activating when adjusting the AC voltage even when the previous environment was a low-temperature, low-humidity environment and the current environment is a high-temperature, high-humidity environment, thereby reducing downtime and preventing the time required for adjusting the AC voltage from becoming longer. For example, the reference value is set to a value indicating an AC voltage value at which the circuit protection function of the overcurrent protection device does not activate due to the charging current flowing through the photoconductor drum 6 when the photoconductor drum 6 is charged in a predetermined high-temperature, high-humidity environment.

[0075] When the previously set voltage value is less than the reference value, the control device 20 sets the initial value of the AC voltage output value to the previously set voltage value, which is the most recent set value. This increases the possibility that the adjustment of the AC voltage can be started from a state close to the appropriate value, and shortens the adjustment time for adjusting the AC voltage to an appropriate value.

[0076] The control device 20 sets the initial value of the AC voltage output value to one of a number of reference values ​​stored in the memory 21, depending on environmental conditions such as temperature and humidity that change the characteristics of the charging roller 11. This makes it possible to set a reference value that makes it difficult for the overcurrent protection device to operate even under high temperature and humidity conditions, further improving the efficiency of adjusting the charging current and shortening the adjustment time required to adjust the AC voltage to an appropriate value.

[0077] The control device 20 sets the initial value of the AC voltage output value to one of a number of reference values ​​stored in the memory 21, depending on the number of printed sheets, which is correlated with changes in the characteristics of the charging roller 11. This makes it possible to set a reference value at which the overcurrent protection device is less likely to operate, even when the charging current increases in accordance with changes over time in the charging roller 11, thereby further improving the efficiency of charging current adjustment and shortening the adjustment time required to adjust the AC voltage to an appropriate value.

[0078] For example, aspects of the present invention are as follows. <1> a voltage generating unit that generates an applied voltage by superimposing an AC voltage on a DC voltage; an image carrier on which an electrostatic latent image is formed; a charging member that charges the image carrier based on the applied voltage from the voltage generating unit; a current detection unit that detects a current flowing from the voltage generation unit to the image carrier; a storage unit for storing a previous voltage value indicating the value of the applied voltage when the image carrier was previously charged; a control unit that controls an operation of the voltage generating unit based on the current detected by the current detecting unit, the control unit sets the initial value of the applied voltage to the reference value if the previous voltage value stored in the storage unit is equal to or greater than a reference value when setting the initial value of the applied voltage; An image forming apparatus comprising: <2> An overcurrent protection device is provided to protect the circuit from overcurrent, the reference value is set to the applied voltage at which the circuit protection function of the overcurrent protection device does not operate due to a charging current flowing through the image carrier when the image carrier is charged under a predetermined high temperature and high humidity environment; Characterized by <1> 2. The image forming apparatus according to claim 1 . <3> A temperature and humidity sensor is provided to detect temperature and humidity. The storage unit stores a plurality of the reference values ​​corresponding to a plurality of temperature and humidity environments, when the previous voltage value stored in the memory unit is equal to or greater than a reference value at the time of setting an initial value of the applied voltage, the control unit sets the initial value to the reference value stored in the memory unit corresponding to the temperature and humidity detected by the temperature and humidity sensor; Characterized by <1> or <2> 2. The image forming apparatus according to claim 1 . <4> a printing unit that prints an image by transferring a toner image obtained by developing the electrostatic latent image formed on the image carrier onto a medium; the storage unit stores a plurality of the reference values ​​corresponding to the number of prints of an image; when the previous voltage value stored in the memory unit is equal to or greater than a reference value at the time of setting the initial value of the applied voltage, the control unit sets the initial value to the reference value stored in the memory unit corresponding to the number of prints; Characterized by <1> Or <3> 13. The image forming apparatus according to claim 12 . <5> when the previous voltage value is smaller than the reference value at the time of setting an initial value of the applied voltage, the control unit sets the initial value to the previous voltage value; Characterized by <1> Or <4> 13. The image forming apparatus according to claim 12 . <6> A method for controlling an image forming apparatus having a voltage generating unit that generates an applied voltage in the form of a DC voltage superimposed on an AC voltage, an image carrier on which an electrostatic latent image is formed, a charging member that charges the image carrier based on the applied voltage from the voltage generating unit, and a current detecting unit that detects a current flowing from the voltage generating unit to the image carrier, comprising: A control unit of the image forming apparatus, controlling an operation of the voltage generating unit based on the current detected by the current detecting unit; a previous voltage value indicating the value of the applied voltage when the image carrier was previously charged is stored in a storage unit; when setting an initial value of the applied voltage, if the previous voltage value stored in the storage unit is equal to or greater than a reference value, the initial value is set to the reference value; A voltage control method for an image forming apparatus comprising the steps of: <7> A control program for an image forming apparatus having a voltage generating unit that generates an applied voltage in the form of a DC voltage superimposed on an AC voltage, an image carrier on which an electrostatic latent image is formed, a charging member that charges the image carrier based on the applied voltage from the voltage generating unit, and a current detecting unit that detects a current flowing from the voltage generating unit to the image carrier, A control unit of the image forming apparatus includes: controlling an operation of the voltage generating unit based on the current detected by the current detecting unit; a previous voltage value indicating the value of the applied voltage when the image carrier was previously charged is stored in a storage unit; when the previous voltage value stored in the storage unit is equal to or greater than a reference value when setting an initial value of the applied voltage, setting the initial value to the reference value; A voltage control program for an image forming apparatus comprising:

[0079] Although the present invention has been described above based on the embodiments, the present invention is not limited to the requirements shown in the above embodiments. These requirements can be changed without departing from the spirit of the present invention, and can be appropriately determined according to the application form. [Explanation of symbols]

[0080] 1. Image forming device 2 Automatic document feeder 3. Image Scanning Device 4 Write Unit 5 Printer unit 6 Photoconductor drum 7. Developing device 8 Conveyor belt 9 Fixing device 10 Paper feed tray 11 Charging roller 12 Exposure section 13 Transfer roller 14 Intermediate transfer belt 15 Static eliminator 16 Cleaning blade 20 Control device 21 Memory 22 Comparison section 25 Temperature and Humidity Sensor 30 Power supply 40 High voltage power supply 41 Charging AC voltage generating unit 42 Charge current return section 43 Charging DC voltage generator 50 High voltage power supply 60 Control section 61 Input Devices 62 Output Device 63 Input / Output Device 201 CPU 202 ROM 203 RAM 204 Input interface section 205 Output interface section 206 Input / Output Interface Section 207 Communication Interface Section [Prior art documents] [Patent documents]

[0081] [Patent Document 1] JP 2008-015268 A

Claims

1. a voltage generating unit that generates an applied voltage by superimposing an AC voltage on a DC voltage; an image carrier on which an electrostatic latent image is formed; a charging member that charges the image carrier based on the applied voltage from the voltage generating unit; a current detection unit that detects a current flowing from the voltage generation unit to the image carrier; a storage unit for storing a previous voltage value indicating the value of the applied voltage when the image carrier was previously charged; a control unit that controls an operation of the voltage generating unit based on the current detected by the current detecting unit, the control unit sets the initial value of the applied voltage to the reference value if the previous voltage value stored in the storage unit is equal to or greater than a reference value when setting the initial value of the applied voltage; An image forming apparatus comprising:

2. An overcurrent protection device is provided to protect the circuit from overcurrent, the reference value is set to a voltage value at which a circuit protection function of the overcurrent protection device does not operate due to a charging current flowing through the image carrier when the image carrier is charged under a predetermined high temperature and high humidity environment; 2. The image forming apparatus according to claim 1,

3. A temperature and humidity sensor is provided to detect temperature and humidity. The storage unit stores a plurality of the reference values ​​corresponding to a plurality of temperature and humidity environments, when the previous voltage value stored in the memory unit is equal to or greater than a reference value at the time of setting the initial value of the applied voltage, the control unit sets the initial value to the reference value stored in the memory unit corresponding to the temperature and humidity detected by the temperature and humidity sensor; 3. The image forming apparatus according to claim 1, wherein:

4. a printing unit that prints an image by transferring a toner image obtained by developing the electrostatic latent image formed on the image carrier onto a medium; the storage unit stores a plurality of the reference values ​​corresponding to the number of prints of an image; when the previous voltage value stored in the memory unit is equal to or greater than a reference value at the time of setting the initial value of the applied voltage, the control unit sets the initial value to the reference value stored in the memory unit corresponding to the number of printed sheets; 3. The image forming apparatus according to claim 1, wherein:

5. the control unit sets the initial value to the previous voltage value if the previous voltage value is smaller than the reference value when setting the initial value of the applied voltage; 2. The image forming apparatus according to claim 1,

6. A method for controlling an image forming apparatus having a voltage generating unit that generates an applied voltage in the form of a DC voltage superimposed on an AC voltage, an image carrier on which an electrostatic latent image is formed, a charging member that charges the image carrier based on the applied voltage from the voltage generating unit, and a current detecting unit that detects a current flowing from the voltage generating unit to the image carrier, comprising: A control unit of the image forming apparatus, controlling an operation of the voltage generating unit based on the current detected by the current detecting unit; a previous voltage value indicating the value of the applied voltage when the image carrier was previously charged is stored in a storage unit; when setting an initial value of the applied voltage, if the previous voltage value stored in the storage unit is equal to or greater than a reference value, the initial value is set to the reference value; A voltage control method for an image forming apparatus comprising the steps of:

7. A control program for an image forming apparatus having a voltage generating unit that generates an applied voltage in the form of a DC voltage superimposed on an AC voltage, an image carrier on which an electrostatic latent image is formed, a charging member that charges the image carrier based on the applied voltage from the voltage generating unit, and a current detecting unit that detects a current flowing from the voltage generating unit to the image carrier, A control unit of the image forming apparatus includes: controlling an operation of the voltage generating unit based on the current detected by the current detecting unit; a previous voltage value indicating the value of the applied voltage when the image carrier was previously charged is stored in a storage unit; when the previous voltage value stored in the storage unit is equal to or greater than a reference value when setting an initial value of the applied voltage, setting the initial value to the reference value; A voltage control program for an image forming apparatus comprising:

Images