Image forming apparatus

Abstract

To provide an image forming apparatus that reduces the influence of the photoreceptor drum current flowing from the photoreceptor drum to the developing roller, and that can accurately determine the toner adhesion state based on the blade current flowing from the blade to the developing roller. [Solution] The ASIC 41 of the printer 1 measures the developing roller current I in a first state where the surface potential V0 of the photoreceptor drum 33 is higher than the surface potential of the developing roller 35, and the potential of the blade 37 and the surface potential of the developing roller 35 are the same (S1~S8). The ASIC 41 changes from the first state to a second state where the potential of the blade 37 is higher than the surface potential of the developing roller 35, and measures the developing roller current I in the second state (S11~S12). The ASIC 41 calculates the blade current IBLD by subtracting the current value of the first state from the current value of the second state (S13), and determines the state of toner adhesion based on the calculated current value (S17).

Description

[Technical Field]

[0001] The present application relates to a technique for determining the state of toner adhesion between a developing roller and a blade. [Background Art]

[0002] Conventionally, as an image forming apparatus that forms an image on a sheet by an electrophotographic method, there has been known an image forming apparatus that adjusts the thickness of toner carried on a developing roller by a blade (for example, the following Patent Document 1, etc.). In an image forming apparatus provided with this type of blade, there is a problem that vertical streaks occur on a sheet on which an image is formed due to toner adhesion occurring between the blade and the developing roller. The image forming apparatus of Patent Document 1 includes three current measuring units (corresponding to the current measuring circuit of the present application) that measure currents flowing respectively through the developing roller, a supply roller, and the blade, and grasps the state of toner adhesion by calculating a charge contribution ratio, which is a ratio of toner carried on the developing roller that contributes to charging. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2014-215364 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] When a current measuring unit is provided as in the image forming apparatus of Patent Document 1 described above, the current value of a current flowing from the blade to the developing roller is measured, and an attempt is made to determine the state of toner adhesion based on the measured current value, it is difficult to detect the current value of the current flowing from the blade to the developing roller due to the influence of the current flowing from a photoconductive drum to the developing roller. As a result, there arises a problem that the accuracy of determining the state of toner adhesion is reduced.

[0005] This invention was proposed in view of the above-mentioned problems, and aims to provide an image forming apparatus that reduces the influence of the photoreceptor drum current flowing from the photoreceptor drum to the developing roller, and that can accurately determine the state of toner adhesion based on the blade current flowing from the blade to the developing roller. [Means for solving the problem]

[0006] (1) To achieve the above objective, the image forming apparatus of the present invention comprises an image forming unit having a photoreceptor drum, a charger for charging the photoreceptor drum, a developing roller that contacts the photoreceptor drum and carries toner, and a blade for adjusting the thickness of the toner carried on the developing roller; a developing voltage application circuit that applies a developing voltage to the developing roller and is electrically grounded, a blade voltage application circuit that applies a blade voltage to the blade, a current measurement circuit connected between the developing roller and the developing voltage application circuit for measuring the developing roller current flowing from the developing roller to the developing voltage application circuit, and a control unit, wherein the control unit charges the photoreceptor drum with the charger, and the developing voltage application circuit and the blade voltage application circuit ensure that the surface potential of the photoreceptor drum is higher than the surface potential of the developing roller, and , a measurement process is performed in which the potential of the blade and the surface potential of the developing roller are at the same potential, and the current measurement circuit measures the first developing roller current in the first state; after the measurement process, the system is changed from the first state to a second state in which the potential of the blade is at a higher potential than the surface potential of the developing roller by the developing voltage application circuit and the blade voltage application circuit, the current measurement circuit measures the second developing roller current in the second state, and the current value of the blade current flowing from the blade to the developing roller is calculated by subtracting the current value of the first developing roller current from the current value of the second developing roller current; and a toner adhesion state determination process is performed in which the state of toner adhesion between the blade and the developing roller is determined based on the current value of the blade current calculated in the calculation process.

[0007] In the first state, no current flows between the blade and the developing roller, and a photoreceptor drum current flows from the photoreceptor drum to the developing roller, and this current flows from the developing roller to the electrically grounded ground portion of the developing voltage application circuit. The control unit measures the developing roller current using the current measurement circuit, and the measured first developing roller current can be measured as the photoreceptor drum current flowing from the photoreceptor drum to the developing roller. Next, the development voltage application circuit and the blade voltage application circuit change the first state to a second state in which the potential of the blade is higher than the surface potential of the development roller. In the second state, the photoreceptor drum current flowing from the photoreceptor drum to the development roller and the blade current flowing from the blade to the development roller merge and a current flows toward the electrically grounded ground portion of the development voltage application circuit. In the second state, the control unit can measure the merged current as the second development roller current by measuring the development roller current with the current measurement circuit. Therefore, by subtracting the current value of the first developing roller from the current value of the second developing roller, the control unit can calculate the current value of the blade current flowing from the blade to the developing roller. Then, by determining the state of toner adhesion based on the calculated blade current, the influence of the photoreceptor drum current can be reduced, and the state of toner adhesion can be determined with high accuracy.

[0008] (2) Alternatively, the configuration may further include a switching circuit connected between the blade and the blade voltage application circuit, which switches the connection between the blade and the blade voltage application circuit based on the control of the control unit.

[0009] According to this, the connection state between the blade and the blade voltage application circuit can be changed using a switching circuit, depending on whether the fixing state is being determined or an image is being formed.

[0010] (3) Alternatively, the blade voltage application circuit may be electrically grounded, and the control unit may control the switching circuit in the measurement process and the calculation process to connect the blade and the blade voltage application circuit, and in the image formation process, when toner is supplied from the developing roller to the electrostatic latent image formed on the photoreceptor drum based on the image formation job to form a toner image on the photoreceptor drum, the control unit may control the switching circuit to disconnect the blade and the blade voltage application circuit.

[0011] According to this, in the measurement and calculation processes, by connecting the blade voltage application circuit to the blade, the blade voltage can be applied to the blade from the blade voltage application circuit. Furthermore, during image formation, by disconnecting the blade and the blade voltage application circuit, the blade is disconnected from the electrically grounded part of the blade voltage application circuit and becomes electrically floating. When the blade comes into contact with the positively charged toner carried on the developing roller, the loss of charge from the positively charged toner via the blade can be suppressed.

[0012] (4) Alternatively, the control unit may, in the measurement process, control the switching circuit to connect the blade and the blade voltage application circuit, apply a blade voltage from the blade voltage application circuit to the blade that has the same voltage value as the developing voltage applied by the developing voltage application circuit to the developing roller, thereby making the potential of the blade and the surface potential of the developing roller the same potential, and in the calculation process, apply a blade voltage from the blade voltage application circuit to the blade that has a voltage value greater than the voltage value of the developing voltage applied by the developing voltage application circuit to the developing roller, thereby making the potential of the blade higher than the surface potential of the developing roller.

[0013] According to this method, in the measurement process, by applying a blade voltage with the same voltage value as the development voltage to the blade from the blade voltage application circuit, the potential of the blade and the surface potential of the development roller can be made to the same potential, thereby suppressing the flow of current between the blade and the development roller. Furthermore, in the calculation process, by applying a blade voltage with a voltage value greater than the developing voltage value to the blade from the blade voltage application circuit, the potential of the blade is made higher than the surface potential of the developing roller, allowing blade current to flow from the blade to the developing roller. Therefore, by controlling the voltage value of the blade voltage, the blade current for measurement and calculation processes can be controlled.

[0014] (5) The control unit may also be configured to stop the application of the blade voltage by the blade voltage application circuit when it is forming an image by supplying toner from the developing roller to the electrostatic latent image formed on the photoreceptor drum based on an image forming job and forming a toner image on the photoreceptor drum.

[0015] According to this, a switching circuit for disconnecting the blade and the blade voltage application circuit during image formation is unnecessary, thus reducing manufacturing costs.

[0016] (6) The image forming apparatus may also be further equipped with a sensor for detecting environmental information, which is information about the environment in which the image forming apparatus is placed. The control unit may perform a correction process to correct the current value of the blade current calculated by the calculation process based on the environmental information detected using the sensor. In the toner adhesion state determination process, the state of toner adhesion may be determined by the current value of the blade current after correction by the correction process.

[0017] The blade's resistance fluctuates in response to environmental information such as temperature and humidity. This fluctuation in blade resistance causes the blade current to fluctuate, reducing the accuracy of determining the toner's adhesion status based on the blade current. Therefore, by correcting the blade current based on environmental information detected using a sensor, and then using the corrected blade current to determine the toner's adhesion status, the toner's adhesion status can be determined with greater accuracy.

[0018] (7) The image forming unit may also further include a memory unit, wherein the toner cartridge having the developing roller is replaceable, and the control unit, upon detecting that the toner cartridge has been replaced, executes the measurement process and the calculation process, and executes a storage process to store the calculated blade current value as a threshold value in the memory unit, and in the toner adhesion state determination process, the threshold value stored in the memory unit is used to determine the state of toner adhesion.

[0019] As toner cartridges are used repeatedly, the amount of toner that accumulates between the developing roller and the blade increases, which increases the resistance between the blade and the developing roller, and decreases the blade current. With the above configuration, the state of toner accumulation can be determined based on the blade current measured when a new toner cartridge is installed in the image forming apparatus. Therefore, the state of toner accumulation can be determined based on the clean state of a new toner cartridge with no accumulation.

[0020] (8) The system may also be configured to further include a sensor for detecting environmental information, which is information about the environment in which the image forming apparatus is located, and in the storage process, the control unit corrects the current value of the blade current calculated based on the environmental information detected using the sensor, stores the corrected value as the threshold in the storage unit, and in the toner adhesion state determination process, use the corrected threshold to determine the state of toner adhesion.

[0021] According to this method, the state of toner adhesion can be determined more accurately by using the current value of the blade current, which has been corrected based on environmental information detected by a sensor, as a threshold value.

[0022] (9) Further, the charger may include a charging wire and a grid, and may further include a wire voltage application circuit that applies a wire voltage to the charging wire of the charger, wherein the control unit causes the wire voltage application circuit to apply the wire voltage to the charging wire in the first state and the second state.

[0023] According to this configuration, a scorotron charger is used to charge the photosensitive drum. Applying a wire voltage to the charging wire from the wire voltage application circuit positively charges the photosensitive drum, enabling the surface potential of the photosensitive drum to be made higher than the surface potential of the developing roller. By exposing the photosensitive drum to form an electrostatic latent image, the toner carried on the developing roller can be transferred to the electrostatic latent image on the photosensitive drum. Effects of the Invention

[0024] According to the image forming apparatus of the present application, the influence of the photosensitive drum current flowing from the photosensitive drum to the developing roller is reduced, and the state of toner fixation can be accurately determined by the blade current flowing from the blade to the developing roller. Brief Description of the Drawings

[0025] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of a monochrome laser printer according to a first embodiment. [Figure 2] 2 is a block diagram illustrating a control configuration of the monochrome laser printer of FIG. 1. [Figure 3] 3 is a diagram illustrating a connection configuration of each application circuit. [Figure 4] 4 is a flowchart illustrating the content of fixation determination mode processing. [Figure 5] 5 is a diagram illustrating voltage and current states in the first state. [Figure 6] 6 is a diagram illustrating voltage and current states in the second state. [Figure 7] 7 is a flowchart illustrating the content of new product detection processing. [Figure 8]This is a flowchart showing the printing process. [Figure 9] This diagram shows the state of toner charge when the connection state of a switching circuit is switched during the printing process. [Figure 10] This flowchart shows the contents of the adhesion determination mode processing according to the second embodiment. [Figure 11] This figure shows the voltage and current states during the printing process of the third embodiment. [Modes for carrying out the invention]

[0026] (First Embodiment) Hereinafter, a monochrome laser printer of the first embodiment, which is an embodiment of the image forming apparatus of the present invention, will be described with reference to the figures. Figure 1 is a cross-sectional view showing the schematic configuration of the monochrome laser printer 1 according to the first embodiment. Figure 2 is a block diagram showing the control configuration of the monochrome laser printer 1. The monochrome laser printer 1 is an example of the image forming apparatus of the present invention. Hereinafter, the monochrome laser printer 1 will be abbreviated as printer 1. In the following description, as shown in Figure 1, the right side of Figure 1 will be referred to as "front", the left side as "rear", the upper side as "top", and the lower side as "bottom".

[0027] Printer 1 is a laser printer that prints monochrome images onto a sheet S using an electrophotographic method. As shown in Figures 1 and 2, Printer 1 comprises a main body casing 2, a supply tray 3, a roller group 4, a main motor 5, an image forming unit 6, a fuser 7, a main circuit board 8, a high-voltage power supply board 9, etc. The main body casing 2 has a box shape and includes a transport path 11 for transporting the sheet S and an output tray 12. The supply tray 3 is detachably attached to the bottom of the main body casing 2. The sheet S is placed on the supply tray 3. The sheet S is a standard-sized sheet of paper such as A4 size. Note that the sheet S is not limited to paper media such as plain paper or cardboard, but may also be other recording media such as OHP film.

[0028] The output tray 12 is located on the top of the main housing 2, and a sheet S with an image printed on it is placed on the output tray 12. The roller group 4 includes a transport roller 13 and an output roller 15. Each roller of the roller group 4 is rotatably held by the main housing 2 and connected to a main motor 5 (see Figure 2) located inside the main housing 2 via gears, and rotates in response to the drive of the main motor 5. Figures 1 and 2 mainly show the components of the printer 1 that pertain to this invention. For this reason, some components, such as the pickup roller that supplies the sheet S from the supply tray 3, are not shown.

[0029] The transport roller 13 supplies the sheet S supplied from the supply tray 3 along the transport path 11 to the image forming unit 6. The printer 1 uses the image forming unit 6 to form a toner image on the sheet S, and then uses the fuser unit 7 to heat the sheet S on which the toner image has been formed and perform a fixing process. The printer 1 then uses the discharge roller 15 to discharge the sheet S on which the fixing process has been performed to the discharge tray 12.

[0030] The image forming unit 6 includes a laser unit 21, a toner cartridge 22, a charger 25, a transfer roller 26, etc. The laser unit 21 is located in the upper part of the main housing 2 and includes a semiconductor laser (not shown), a polygon mirror 31, a plurality of reflectors 32, and a plurality of lenses (not shown). As shown by the dashed line in Figure 1, the laser unit 21 exposes the surface of the photoreceptor drum 33 by irradiating the surface of the photoreceptor drum 33 with laser light emitted from the semiconductor laser via the polygon mirror 31, reflectors 32, and lenses. The laser unit 21 exposes the photoreceptor drum 33 according to the image data and forms an electrostatic latent image on the surface of the photoreceptor drum 33.

[0031] The toner cartridge 22 is detachably mounted to the main unit housing 2 and contains black toner. The toner cartridge 22 agitates the toner it contains using an agitator (not shown). The toner cartridge 22 also includes a photoreceptor drum 33, a supply roller 34, a developer roller 35, a toner IC 36 (see Figure 2), and a blade 37. The supply roller 34 is in contact with the developer roller 35 and rotates in conjunction with the rotation of the developer roller 35, supplying the toner from the toner cartridge 22 to the developer roller 35. The developer roller 35 is located at the toner supply port of the toner cartridge 22 and rotates in response to the drive of the main motor 5 (see Figure 2).

[0032] A positive polarity developing voltage Vb is applied to the developing roller 35 from the developing voltage application circuit 53 of the high-voltage power supply board 9 shown in Figure 3. When the developing voltage Vb is applied to the developing roller 35, the toner supplied to the developing roller 35 is carried on the developing roller 35 as it rotates and becomes positively charged.

[0033] The toner IC 36 has, for example, a memory that stores information related to the toner cartridge 22. The memory of the toner IC 36 stores identification information of the toner cartridge 22, information on the cumulative number of printed pages, and so on.

[0034] The blade 37 is, for example, a conductive metal component such as stainless steel, and is positioned to contact the developing roller 35. As the developing roller 35 rotates, the toner supplied onto it enters the space between the blade 37 and the developing roller 35, is adjusted to a predetermined thickness by the blade 37, and is then supported on the developing roller 35. The blade 37 may also have an elastic component such as rubber in the portion that contacts the developing roller 35.

[0035] As shown in Figure 3, the charger 25 is positioned above the photoreceptor drum 33 and is a scorotron-type charger, for example, in which a charging wire 27 and a grid 28 are housed in a shield case 29. The grid 28 is attached to an opening in the shield case 29 facing the photoreceptor drum 33 and is constructed by stretching conductive wires in a mesh pattern. The charging wire 27 is stretched inside the shield case 29. Therefore, the grid 28 is positioned between the photoreceptor drum 33 and the charging wire 27. Prior to forming an electrostatic latent image on the surface of the photoreceptor drum 33 during image formation, the charger 25 uniformly positively charges the surface of the photoreceptor drum 33. Note that the charger used to charge the photoreceptor drum 33 is not limited to a scorotron-type charger; other types of chargers, such as roller-type chargers, may also be used.

[0036] The photoreceptor drum 33 rotates in response to the drive of the main motor 5. The developing roller 35 is in contact with the photoreceptor drum 33 and, by rotating, supplies toner to the photoreceptor drum 33, developing the electrostatic latent image formed on the surface of the photoreceptor drum 33 and supporting a toner image. The positively charged toner supported on the developing roller 35 moves to the electrostatic latent image on the photoreceptor drum 33 due to the potential difference between the developing roller 35 and the electrostatic latent image formed on the photoreceptor drum 33, and forms a toner image.

[0037] The transfer roller 26 is positioned below the photoreceptor drum 33, facing the photoreceptor drum 33 in the vertical direction, and positioned to sandwich the sheet S. The high-voltage power supply board 9 has a transfer voltage application circuit (not shown) that applies a negative polarity transfer voltage to the transfer roller 26. The transfer roller 26 transfers the toner image supported on the surface of the photoreceptor drum 33 to the sheet S by applying the transfer voltage in accordance with the transport timing of the sheet S. Note that the transfer member that transfers the toner image to the sheet S is not limited to a roller-shaped member, but may be a member with another structure to which a transfer voltage can be applied, such as a conductive brush or a conductive leaf spring.

[0038] The sheet S onto which the toner image has been transferred is transported to the fuser unit 7. The fuser unit 7 is located behind the image forming unit 6 within the main housing 2. The fuser unit 7 includes a heating unit 39 with a heater 38 that heats the sheet S, and a pressure roller 40 that sandwiches the sheet S between the heating unit 39 and the heating unit 39. The heating unit 39 is located on the image forming surface side of the sheet S and has a heating belt that is heated by the heater 38. The pressure roller 40 rotates in accordance with the drive of the main motor 5. The heating belt of the heating unit 39 rotates in response to the rotation of the pressure roller 40 while being pressed against the sheet S. In this way, the fuser unit 7 fixes the toner image to the sheet S. The sheet S with the printed image is discharged to the discharge tray 12 by the discharge roller 15. Note that the configuration of the fuser unit 7 described above is an example. For example, the fixing device 7 may have a configuration that includes a heating roller having a heater 38 that rotates in conjunction with the rotation of the main motor 5, and a pressure roller that presses the sheet S against the heating roller and rotates in conjunction with the rotation of the heating roller.

[0039] Furthermore, the main board 8 is a control board that comprehensively controls the printer 1, and as shown in Figure 2, it has an ASIC 41, a ROM 43, a RAM 44, and a non-volatile memory 45. The ASIC 41 is an Application Specific Integrated Circuit and has a CPU, etc. The ASIC 41 is an example of the control unit of this application. Note that the control unit of this application is not limited to an ASIC, but may also be other devices such as a SoC (System on a Chip).

[0040] ROM 43 stores various control programs and setting information for controlling the printer 1. These control programs include programs for executing the sticking detection mode processing shown in Figure 4, the new product detection processing shown in Figure 7, and the printing process shown in Figure 8, which will be described later. ROM 43 also stores correction data DATA for correcting the blade current IBLD and threshold TH, which will be described later. RAM 44 is, for example, DRAM and is used as a work area for reading various control programs and as a storage area for temporarily storing image data based on print jobs. Non-volatile memory 45 is, for example, NVRAM and is used for storing setting values ​​used in various processes. For example, threshold TH, which will be described later, is stored in non-volatile memory 45. Non-volatile memory 45 is an example of a storage unit in this application. The ASIC 41 executes the control programs read from ROM 43 using the CPU, and while storing the processing results in RAM 44 and non-volatile memory 45, controls various parts of the printer 1 to perform printing and other processes.

[0041] Note that the configuration of the main board 8 shown in Figure 2 is just one example. For example, the main board 8 may have an HDD or SSD as a non-volatile storage device. Correction data DATA may be stored in the non-volatile memory 45. Control programs for executing adhesion detection processing and new product detection processing may also be stored in the non-volatile memory 45. Threshold TH may also be stored in RAM 44 or ROM 43. In this case, RAM 44 and ROM 43 are just examples of the storage units in this invention. Furthermore, the storage medium for storing the control program and threshold TH may be an external storage medium such as a USB memory stick, or a storage medium such as a CD-ROM or DVD-ROM.

[0042] Furthermore, as shown in Figure 2, the printer 1 is equipped with two temperature sensors 46 and 47 and a humidity sensor 48. For example, non-contact thermistor sensors can be used as the temperature sensors 46 and 47. The temperature sensor 46 is installed inside the main body housing 2 of the printer 1 and outputs a detection signal to the ASIC 41 according to the temperature inside the main body housing 2. As a result, the ASIC 41 can detect the temperature inside the printer 1 based on the detection signal from the temperature sensor 46. The temperature sensor 47 is installed outside the main body housing 2, or in an air intake port formed in the main body housing 2 that communicates the inside and outside, and outputs a detection signal to the ASIC 41 according to the temperature outside the main body housing 2. As a result, the ASIC 41 can detect the temperature outside the printer 1 based on the detection signal from the temperature sensor 47.

[0043] The humidity sensor 48 outputs a detection signal to the ASIC 41, for example, according to the humidity inside the main unit housing 2. This allows the ASIC 41 to detect the humidity inside the printer 1 based on the detection signal from the humidity sensor 48. The temperature sensors 46, 47, and humidity sensor 48 are examples of sensors in this application. Temperature and humidity are examples of environmental information in this application. Note that the sensor configuration described above is just an example. For example, the temperature sensor and humidity sensor may be configured as a single sensor. Alternatively, the humidity sensor 48 may be installed in a position to detect humidity outside the machine. The printer 1 may also be configured to include at least one of the temperature sensors 46, 47, and humidity sensor 48. In this case, the blade current IBLD and threshold TH, described later, may be corrected based on the detection signal from at least one sensor. Furthermore, in a configuration where the blade current IBLD and threshold TH are not corrected, as in the second embodiment described later, the printer 1 may not include the temperature sensors 46, 47, and humidity sensor 48.

[0044] As shown in Figure 1, the printer 1 is equipped with a display unit 49 on the top surface of the main body housing 2. The display unit 49 is, for example, a touch panel, connected to the ASIC 41, and displays information related to the printer 1 based on the control of the ASIC 41. In particular, in this embodiment, the display unit 49 can display a message prompting the cleaning of the blade 37. The display unit 49 also outputs a signal to the ASIC 41 in response to operation input to the touch panel. Note that the display unit 49 is not limited to a touch panel. The display unit 49 may be configured to have only a display function, such as a liquid crystal display. Furthermore, the user interface of the printer 1 is not limited to a touch panel or liquid crystal display, but may also include physical keys or switches. In addition, the printer 1 may be configured without a display unit 49 or other user interfaces.

[0045] As shown in Figure 2, the high-voltage power supply board 9 includes a wire voltage application circuit 51, a grid current detection circuit 52, a develop voltage application circuit 53, a blade voltage application circuit 54, a switching circuit 55, and a current measurement circuit 56. As shown in Figure 3, the wire voltage application circuit 51 is electrically grounded to the ground GND provided on the high-voltage power supply board 9 and is a circuit that applies a positive wire voltage Vw to the charged wire 27 of the charger 25. The wire voltage application circuit 51 changes the magnitude of the wire voltage Vw applied to the charged wire 27 according to the magnitude of the duty cycle of the PWM (Pulse Width Modulation) signal PWM_Vw input from the ASIC 41, for example. The voltage value of the wire voltage Vw is, for example, about 5.5kV to 7kV. The photoreceptor drum 33 has its rotation axis connected to the ground GND, and becomes positively charged when the wire voltage Vw is applied to the charged wire 27, and an electrostatic latent image is formed by the laser unit 21.

[0046] When a positive wire voltage Vw is applied to the charged wire 27 from the wire voltage application circuit 51, an electric field is formed between the charged wire 27 and the photoreceptor drum 33, causing corona discharge. When an electric field is formed between the charged wire 27 and the grid 28, a grid voltage Vg different from that of the charged wire 27 is generated on the grid 28, thereby controlling the strength of the electric field and thus controlling the amount of charge on the photoreceptor drum 33.

[0047] Furthermore, when a wire voltage Vw is applied to the charged wire 27, a grid current Ig flows through the grid 28. The grid current detection circuit 52 is a circuit for detecting the grid current Ig. The grid current detection circuit 52 has a resistor Rg connected between the grid 28 and the ground GND, and outputs a detection signal Sg to the ASIC 41 according to the magnitude of the grid current Ig flowing through the grid 28. The ASIC 41 changes the wire voltage Vw by changing the duty cycle of the PWM signal PWM_Vw output to the wire voltage application circuit 51 so that the current value of the grid current Ig calculated from the detection signal Sg of the grid current detection circuit 52 matches a predetermined target grid current value, and performs constant current control. As a result, the surface potential V0 of the photoreceptor drum 33 can be maintained at a predetermined target potential when performing the adhesion determination mode processing, new product detection processing, and printing processing described later. The surface potential V0 is, for example, 850V.

[0048] The developing voltage application circuit 53 is a circuit that applies a developing voltage Vb to the developing roller 35. Similar to the wire voltage application circuit 51, the developing voltage application circuit 53 is electrically grounded to the ground section GND and changes the voltage value of the developing voltage Vb according to the magnitude of the duty cycle of the PWM signal PWM_Vb input from the ASIC 41. The developing voltage Vb is, for example, +300V. When the developing voltage Vb is applied to the developing roller 35, it positively charges and holds the toner supplied from the supply roller 34, and supplies the positively charged toner to the electrostatic latent image on the photoreceptor drum 33.

[0049] The blade voltage application circuit 54 is a circuit that applies a blade voltage VBLD to the blade 37. Similar to the wire voltage application circuit 51, the blade voltage application circuit 54 is electrically grounded to the ground GND and changes the voltage value of the blade voltage VBLD according to the magnitude of the duty cycle of the PWM signal PWM_Vbld input from the ASIC 41. In this embodiment, the blade voltage application circuit 54 is changed, for example, between a state in which a blade voltage VBLD of +300V is applied and a state in which a blade voltage VBLD of +500V is applied, based on the control of the ASIC 41. Accordingly, the blade voltage application circuit 54 switches between a state in which a blade voltage VBLD with the same voltage value as the developing voltage Vb applied by the developing voltage application circuit 53 to the developing roller 35 is applied to the blade 37, and a state in which a blade voltage VBLD with a voltage value greater than the voltage value of the developing voltage Vb applied by the developing voltage application circuit 53 to the developing roller 35 is applied to the blade 37.

[0050] When a blade voltage VBLD of +300V is applied to the blade 37 and a developing voltage Vb of +300V is applied to the developing roller 35, the potential of the blade 37 and the surface potential of the developing roller 35 are the same. The surface potential of the developing roller 35 is, for example, the potential of the surface of the elastic layer when the developing roller 35 is composed of a metal rotating shaft and an elastic layer covering the outer surface of the rotating shaft. Furthermore, when a blade voltage VBLD of +500V is applied to the blade 37 and a developing voltage Vb of +300V is applied to the developing roller 35, the potential of the blade 37 is higher than the surface potential of the developing roller 35.

[0051] The switching circuit 55 is electrically connected between the blade 37 and the blade voltage application circuit 54. Based on the control signal CI of the ASIC 41, the switching circuit 55 switches between a connected state, where the blade 37 and the blade voltage application circuit 54 are connected, and a disconnected state, where the blade 37 and the blade voltage application circuit 54 are disconnected. For example, a semiconductor switch or a relay can be used as the switching circuit 55.

[0052] The surface potential V0 of the charged photoreceptor drum 33 is higher than the voltage value of the development voltage Vb. Therefore, when the wire voltage Vw is applied to the charged wire 27 and the photoreceptor drum 33 becomes positively charged, current flows from the photoreceptor drum 33 through the development roller 35 to the ground GND of the development voltage application circuit 53. Also, when a blade voltage VBLD of +500V is applied to the blade 37 from the blade voltage application circuit 54, the potential of the blade 37 becomes higher than the surface potential of the development roller 35, and current flows from the blade 37 through the development roller 35 to the ground GND of the development voltage application circuit 53. The current measurement circuit 56 is a circuit for measuring the development roller current I that flows from the development roller 35 to the development voltage application circuit 53. The current measurement circuit 56 includes, for example, a detection resistor connected between the development roller 35 and the development voltage application circuit 53, and outputs a current detection signal SI corresponding to the magnitude of the development roller current I to the ASIC 41. ASIC41 calculates the current value of the developing roller current I based on the current detection signal SI input from the current measurement circuit 56.

[0053] (Adhesion detection mode processing) Next, the toner adhesion determination mode processing performed by ASIC41 will be described. Figure 4 shows a flowchart of the adhesion determination mode processing. For example, when ASIC41 receives a predetermined operation input from the touch panel of the display unit 49, it starts the processing shown in Figure 4. By performing the adhesion determination mode processing, ASIC41 determines whether or not toner has adhered between the blade 37 and the developing roller 35 based on the current value of the blade current IBLD. Note that the conditions for starting the processing in Figure 4 are not limited to the condition of receiving operation input from the user. For example, ASIC41 may perform the processing in Figure 4 every time a predetermined number of pages are printed. The predetermined number of pages here is the number of pages on which toner adhesion may occur, for example, 1000 pages. In addition, the content, order, and execution of each step described below may be changed as appropriate depending on the change in the starting conditions.

[0054] First, when the process shown in Figure 4 is started, the ASIC41 drives the main motor 5 in step 1. Hereafter, steps will simply be referred to as S. The ASIC41 controls the main motor 5 to rotate, for example, the developing roller 35 and the photoreceptor drum 33. Note that in the adhesion determination mode process, since no actual printing is performed, it is not necessary to rotate the roller group 4 or the pressure roller 40.

[0055] After executing S1, ASIC41 activates the wire voltage application circuit 51 (S2). ASIC41 outputs a PWM signal PWM_Vw, causing the wire voltage Vw to be applied to the charged wire 27 from the wire voltage application circuit 51. After executing S2, ASIC41 changes the duty cycle of the PWM signal PWM_Vw to match the current value of the grid current Ig calculated from the detection signal Sg of the grid current detection circuit 52 to a predetermined target grid current value, and performs constant current control (S3).

[0056] Figure 5 shows the voltage and current states in the first state, which will be described later. As shown in Figure 5, the ASIC 41 performs constant current control so that, for example, the surface potential V0 of the photoreceptor drum 33 becomes +850V. The grid voltage Vg is approximately the same voltage value as the surface potential V0.

[0057] After executing S3 in Figure 4, ASIC41 controls the switching circuit 55 with the control signal CI to connect the blade voltage application circuit 54 to the blade 37 and set it to the connected state (S4). After executing S4, ASIC41 outputs the PWM signal PWM_Vbld and starts the blade voltage application circuit 54 (S5). After executing S5, ASIC41 outputs the PWM signal PWM_Vb and starts the developer voltage application circuit 53 (S6).

[0058] As shown in Figure 5, ASIC41 changes the duty cycle of the PWM signal PWM_Vbld and applies a blade voltage VBLD of +300V to the blade 37 from the blade voltage application circuit 54 (S7). Also, ASIC41 changes the duty cycle of the PWM signal PWM_Vb and applies a developing voltage Vb of +300V to the developing roller 35 from the developing voltage application circuit 53 (S7). The potential of the blade 37 and the surface potential of the developing roller 35 are at the same potential. Positively charged toner is carried on the developing roller 35. Note that in the process shown in Figure 4, ASIC41 may stop the rotation of the supply roller 34, etc., and perform the processes S1 to S9, or the processes S11 to S12 described later, with no toner carried on the developing roller 35.

[0059] By executing S2 to S7, the photoreceptor drum 33 is charged by the charger 25, and the developing voltage application circuit 53 and the blade voltage application circuit 54 bring the surface potential V0 of the photoreceptor drum 33 higher than the surface potential of the developing roller 35, and the potential of the blade 37 and the surface potential of the developing roller 35 to the same potential. In the first state, no current flows between the blade 37 and the developing roller 35, that is, no blade current IBLD flows. In addition, the photoreceptor drum current Ib flows from the photoreceptor drum 33 to the developing roller 35, and the photoreceptor drum current Ib flows through the developing roller 35 towards the electrically grounded ground portion GND of the developing voltage application circuit 53.

[0060] After executing S7, ASIC41 measures the developing roller current I based on the current detection signal SI of the current measurement circuit 56 (S8). Since the blade current IBLD is not flowing, the measured developing roller current I can be measured as the photoreceptor drum current Ib flowing from the photoreceptor drum 33 to the developing roller 35. The developing roller current I measured in S8 is an example of the first developing roller current of this application. After executing S8, ASIC41 stores the measured value measured in S8 as the current value of the photoreceptor drum current Ib in, for example, RAM44 (S9). The processing in S2 to S9 is an example of the measurement processing of this application.

[0061] After executing S9, ASIC41 changes the blade voltage VBLD to a fixed value for fixing detection (S11). ASIC41 does not change the wire voltage Vw or the developing voltage Vb. That is, the wire voltage Vw is maintained at 850V and the developing voltage Vb is maintained at 300V. The fixed value for fixing detection is a voltage value greater than the voltage value of the developing voltage Vb, for example, +500V. Therefore, by executing S11, a second state is reached in which the potential of the blade voltage VBLD is higher than the surface potential of the developing roller 35.

[0062] After executing S11, ASIC41 measures the developing roller current I based on the current detection signal SI of the current measurement circuit 56, similar to S8 (S12). Figure 6 shows the voltage and current states in the second state. As shown in Figure 6, in the second state, the photoreceptor drum current Ib flowing from the photoreceptor drum 33 to the developing roller current I and the blade current IBLD flowing from the blade 37 to the developing roller 35 merge and a current flows toward the electrically grounded ground GND of the developing voltage application circuit 53. In the second state, by measuring the developing roller current I with the current measurement circuit 56, ASIC41 can measure the merged current as the developing roller current I. This merged developing roller current I is an example of the second developing roller current of the present invention.

[0063] When the resistance between the photoreceptor drum 33 and the developing roller 35 is R0, the photoreceptor drum current Ib can be expressed by the following equation (1) using the surface potential V0 and the developing voltage Vb. Ib = (V0 - Vb) / R0 ... (1) The ASIC41 maintains the same current value for the photoreceptor drum current Ib in both processes S2-S9 and S11-S12 by maintaining the same surface potential V0 and development voltage Vb for the photoreceptor drum 33.

[0064] Furthermore, if the resistance between the blade 37 and the developing roller 35 is R, the blade current IBLD can be expressed by the following equation (2) using the blade voltage VBLD and the developing voltage Vb. IBLD = (VBLD - Vb) / R ····(2) The resistance value R increases as the amount of toner adhering between the blade 37 and the developing roller 35 increases. Therefore, by using fixed values ​​for the blade voltage VBLD and the developing voltage Vb in S11-S12, the resistance value R can be determined from the blade current IBLD. In other words, the toner adhesion state can be determined from the blade current IBLD.

[0065] The current value of the developing roller current I measured in S12 is the sum of the photoreceptor drum current Ib and the blade current IBLD. Therefore, after executing S12, ASIC41 calculates the blade current IBLD using the following equation (3) (S13). IBLD = I - Ib ... (2) ASIC41 calculates the blade current IBLD by subtracting the current value stored in RAM44, i.e., the photoreceptor drum current Ib stored in S9, from the developing roller current I measured in S12. Therefore, the blade current IBLD can be calculated by subtracting the current value of the developing roller current I measured without the blade current IBLD in S8 from the combined developing roller current I in S12. The processing in S11 to S13 is an example of the calculation process of this invention.

[0066] After executing S13, ASIC41 acquires environmental information using each sensor (S15) and obtains the current value of the blade current IBLD, which has been corrected to correspond to the environment indicated by the acquired environmental information (S16). Here, the current value of the blade current IBLD fluctuates according to the environment in which the printer 1 is located, i.e., temperature and humidity. For example, the resistance value of the metal blade 37 increases as the temperature rises and decreases as the temperature falls. Therefore, the current value of the blade current IBLD decreases when the temperature rises and the resistance value of the blade 37 increases. So, in S16, if the internal temperature detected using the temperature sensor 46 is higher than the reference temperature, ASIC41 performs a correction to increase the blade current IBLD. The correction data DATA shown in Figure 2 stores data for correcting the current value of the blade current IBLD and the threshold TH, which will be described later, based on temperature and humidity. For example, the correction data DATA stores the temperature difference between the reference temperature and the detected temperature, and the correction value to be used for that temperature difference in association with each other. The reference temperature is, for example, 25 degrees. For example, if the detected temperature is higher than the reference temperature, ASIC41 obtains a correction value from the correction data DATA corresponding to the increased temperature difference. ASIC41 adds the obtained correction value to the current value of the blade current IBLD calculated in S13. This makes the current value of the blade current IBLD larger by the amount that it has decreased from the current value of the blade current IBLD at the reference temperature. This eliminates the influence of temperature fluctuations in the blade current IBLD and allows for more accurate determination of the toner adhesion state. S16 is an example of the correction process of this invention.

[0067] The correction described above is merely an example. The ASIC41 may also correct the current value of the blade current IBLD based on the external temperature detected using the temperature sensor 47. For example, when humidity decreases, the resistance of the blade 37 increases, and when humidity increases, the resistance of the blade 37 decreases. Therefore, if the humidity detected using the humidity sensor 48 is lower than the reference humidity, the ASIC41 may perform a correction to increase the current value of the blade current IBLD. The ASIC41 may also correct the current value of the blade current IBLD by combining the temperature detected using the two temperature sensors 46 and 47 and the humidity detected using the humidity sensor 48. The same applies to the process of correcting the threshold TH in S36 of Figure 7, which will be described later, based on environmental information.

[0068] After executing S16, ASIC41 determines whether the current value of the blade current IBLD after correction in S16 is less than or equal to the threshold TH (S17). ASIC41 reads the threshold TH from the non-volatile memory 45 and compares the read threshold TH with the current value of the blade current IBLD after correction. The threshold TH is a value determined by the new product detection process described later. Note that a common value for all toner cartridges 22 may be used as the threshold TH.

[0069] If ASIC41 determines that the blade current IBLD is greater than the threshold TH (S17: NO), it terminates the process shown in Figure 4. On the other hand, if ASIC41 determines that the blade current IBLD is less than or equal to the threshold TH (S17: YES), it notifies the user to clean the blade 37 (S18). In S18, ASIC41 displays a message or cleaning method on the display unit 49, such as "Please remove the toner that has adhered to the blade." This allows the user to be prompted to clean the blade 37 depending on the amount of toner that has adhered. After executing S18, ASIC41 terminates the process shown in Figure 4.

[0070] The process in S17 is an example of the toner adhesion state determination process of the present invention. However, the method for determining the adhesion state is not limited to the method described above. For example, the ASIC41 may compare the current value of the blade current IBLD measured multiple times with a threshold value TH. Alternatively, the ASIC41 may determine the adhesion state using a value other than the current value. For example, the ASIC41 may calculate the resistance value R between the blade 37 and the developing roller 35 from the above-described equation (2), and determine the toner adhesion state by comparing the calculated resistance value R with a threshold value.

[0071] Furthermore, the notification method described in S18 above is merely an example and can be modified as needed. For example, ASIC41 may display a message on a personal computer or mobile device connected to printer 1. Alternatively, ASIC41 may send a message to the system administrator's email address.

[0072] (New product detection process) Next, the new product detection process performed by ASIC41 will be described. Figure 7 shows a flowchart of the new product detection process. When ASIC41 detects, for example, that a toner cartridge 22 installed in the image forming unit 6 has been replaced with another toner cartridge 22, it starts the process shown in Figure 7. By performing the new product detection process, ASIC41 performs the same process as the adhesion determination mode process, calculates the blade current IBLD, and updates the threshold TH with the calculated blade current IBLD. For this reason, in the following explanation of Figure 7, the explanation of the process similar to the adhesion determination mode process in Figure 4 described above will be omitted as appropriate.

[0073] Furthermore, as a method for determining whether or not the toner cartridge 22 has been replaced, for example, a method using information stored in the toner IC 36 can be employed. For example, the ASIC 41 may start the process shown in Figure 7 if the identification information of the toner cartridge 22 read from the toner IC 36 does not match before and after the replacement of the toner cartridge 22. Alternatively, the ASIC 41 may start the process shown in Figure 7 if the cumulative number of printed pages read from the toner IC 36 does not match before and after the replacement of the toner cartridge 22. Moreover, the conditions for starting the process shown in Figure 7 are not limited to the condition that the toner cartridge 22 has been replaced. For example, the ASIC 41 may start the process shown in Figure 7 based on instructions from the user.

[0074] As shown in Figure 7, when the ASIC41 starts the new product detection process, it performs the same processes as S1 to S7 in Figure 4 in S21 to S27, creating the first state shown in Figure 5. That is, it charges the photoreceptor drum 33 and creates a state in which the surface potential V0 of the photoreceptor drum 33 is higher than the surface potential of the developing roller 35, and the potential of the blade 37 and the surface potential of the developing roller 35 are at the same potential. The ASIC41 performs the same processes as S8 and S9 in Figure 4 in S28 and S29, and stores the current value of the photoreceptor drum current Ib measured using the current measurement circuit 56 in the RAM 44.

[0075] Next, ASIC41 performs the same process as in S11 in Figure 4 in S31, creating the second state shown in Figure 6. That is, it charges the photoreceptor drum 33 and creates a state in which the potential of the blade voltage VBLD is higher than the surface potential of the developing roller 35. ASIC41 performs the same processes as in S12 and S13 in Figure 4 in S32 and S33, and calculates the current value of the blade current IBLD by subtracting the current value of the photoreceptor drum current Ib stored in RAM44 from the developing roller current I measured in the second state.

[0076] ASIC41 performs the same processing as in S15 and S16 in Figure 4 in S35 and S36, correcting the calculated blade current IBLD value based on environmental information such as temperature and humidity. Then, ASIC41 updates the threshold TH stored in the non-volatile memory 45 with the corrected blade current IBLD value (S37). ASIC41 then terminates the processing shown in Figure 7. S36 and S37 are examples of the memory processing of the present invention.

[0077] Therefore, when the toner cartridge 22 is replaced with a new one, the ASIC41 sets the current value of the blade current IBLD measured in the new state as the threshold TH. The toner adhesion state can be determined based on the current value of the blade current IBLD measured in a clean state where no toner has adhered between the blade 37 and the developing roller 35. The ASIC41 may perform correction using different correction data DATA in the correction process of S16 and the correction process of S36. Alternatively, the ASIC41 may set the threshold TH as a value obtained by subtracting a predetermined value from the current value of the blade current IBLD after correction in S36. This predetermined value corresponds to the range of reduction in the blade current IBLD that is allowed from the new state until it is determined that the toner has adhered. In other words, instead of using the current value of the blade current IBLD in the new state as the threshold TH, a current value that has been corrected to correspond to a certain allowable range may be used as the threshold TH.

[0078] (Printing process) Next, we will describe the printing process performed by ASIC41. Figure 8 shows a flowchart of the printing process. When ASIC41 receives a print job, for example, instructing printer 1 to perform printing, it starts the process shown in Figure 8. By executing the printing process, ASIC41 prints the image indicated by the image data specified in the received print job onto sheet S. In the following explanation of Figure 8, the explanation of processes similar to the adhesion determination mode process in Figure 4 described above will be omitted as appropriate.

[0079] The method for accepting print jobs is not particularly limited. For example, ASIC41 may accept print jobs from a PC connected to printer 1 via a USB cable or LAN cable. Alternatively, ASIC41 may accept print jobs from a smartphone that communicates wirelessly with printer 1. Furthermore, ASIC41 may accept print jobs based on operation input to the touch panel of the display unit 49. A print job is an example of an image forming job in this invention.

[0080] As shown in Figure 8, when the printing process starts, the ASIC41 drives the main motor 5 (S41), similar to S1 in Figure 4. After executing S41, the ASIC41 controls the switching circuit 55 with the control signal CI, disconnecting the blade voltage application circuit 54 from the blade 37 and putting it into a disconnected state (S43).

[0081] The ASIC41 controls the wire voltage application circuit 51 to apply the wire voltage Vw to the charged wire 27, similar to S2 in Figure 4 (S44). Next, the ASIC41 controls the develop voltage application circuit 53 to apply the develop voltage Vb to the develop roller 35, similar to S6 in Figure 4 (S45). Positively charged toner is supported on the develop roller 35. The ASIC41 applies the develop voltage Vb, which has a voltage value determined by, for example, density correction to correct the print density (S46). The method of density correction is not particularly limited. For example, the ASIC41 may correct the voltage value of the develop voltage Vb based on the temperature and humidity detected by various sensors such as the temperature sensor 46. Alternatively, the ASIC41 may use a fixed value as the develop voltage Vb for the printing process without performing density correction.

[0082] Figure 9 shows the charge state of the toner when the connection state of the switching circuit 55 is switched during the printing process. As shown in Figure 9, for example, the developing roller 35 rotates in the counterclockwise direction shown in Figure 9. The positively charged toner carried on the developing roller 35 comes into contact with the blade 37 at a predetermined rotation position and is adjusted to a predetermined thickness. As shown in the upper part of Figure 9, if the switching circuit 55 is connected and the developing voltage Vb is applied to the developing roller 35 and it is rotated, there is a risk that the positive charge of the positively charged toner carried on the developing roller 35 will be lost via the blade 37. As a result, variations in print density will occur.

[0083] In contrast, the ASIC 41 of this embodiment, as shown in the lower diagram of Figure 9, disconnects the switching circuit 55 during the printing process, and disconnects the blade 37 from the electrically grounded ground GND of the blade voltage application circuit 54. The blade 37 becomes electrically floating (S46). This suppresses the loss of the positive charge of the positively charged toner carried on the developing roller 35 via the blade 37, thereby suppressing variations in print density and improving printing accuracy.

[0084] After executing S46, ASIC41 performs constant current control (S47) to match the current value of the grid current Ig detected by the grid current detection circuit 52 to the target grid current value, similar to S3 in Figure 4. After executing S47, ASIC41 starts printing based on the received print job (S48). ASIC41 controls the laser unit 21 to expose the photoreceptor drum 33 according to the image data instructed in the print job, and forms an electrostatic latent image on the surface of the photoreceptor drum 33. The image forming unit 6 develops the electrostatic latent image using the developing roller 35, and a transfer voltage is applied to the transfer roller 26 to transfer the developed toner image to the sheet S. The fixing device 7 fixes the toner image to the sheet S, and the discharge roller 15 discharges the sheet S with the printed image.

[0085] After starting printing in S48, ASIC41 determines whether printing is complete or not (S49). ASIC41 makes a negative determination in S49 (S49: NO) until all image data specified in the print job has been printed (S49: YES), and terminates the process shown in Figure 8 when all image data has been printed. In this way, in the first embodiment, printing accuracy can be improved by disconnecting the blade 37 from the blade voltage application circuit 54 during the printing process.

[0086] As described above, the first embodiment provides the following effects. (1) The ASIC 41 of the printer 1 in the first embodiment charges the photoreceptor drum 33 and sets it to a first state in which the surface potential V0 of the photoreceptor drum 33 is higher than the surface potential of the developing roller 35, and the potential of the blade 37 and the surface potential of the developing roller 35 are at the same potential, and measures the developing roller current I in the first state (S1~S8). After executing S8, the ASIC 41 changes from the first state to a second state in which the potential of the blade 37 is higher than the surface potential of the developing roller 35, and measures the developing roller current I in the second state (S11~S12). The ASIC 41 calculates the blade current IBLD by subtracting the current value stored in S9 from the current value measured in S12 (S13). The ASIC 41 compares the blade current IBLD calculated in S13 with the threshold TH and determines the state of toner adhesion (S17).

[0087] According to this, in the first state, the ASIC 41 can measure the photoreceptor drum current Ib by measuring the developing roller current I using the current measurement circuit 56. In the second state, the ASIC 41 can measure the combined current of the photoreceptor drum current Ib and the blade current IBLD by measuring the developing roller current I using the current measurement circuit 56. Therefore, the blade current IBLD can be calculated by subtracting the current value of the first state from the current value of the second state. Then, by determining the toner adhesion state using the calculated blade current IBLD, the influence of the photoreceptor drum current Ib can be reduced, and the toner adhesion state can be determined with high accuracy.

[0088] (2) The printer 1 also includes a switching circuit 55 that switches the connection between the blade 37 and the blade voltage application circuit 54 based on the control of the ASIC 41. According to this, the connection state between the blade 37 and the blade voltage application circuit 54 can be changed using the switching circuit 55 depending on whether the fixing state is being determined or during printing.

[0089] (3) In addition, in S4 shown in Figure 4, the ASIC 41 controls the switching circuit 55 to connect the blade 37 and the blade voltage application circuit 54. As a result, by connecting the blade voltage application circuit 54 to the blade 37, the blade voltage VBLD can be applied to the blade 37 from the blade voltage application circuit 54. Furthermore, in step S43 of Figure 8, the ASIC 41 controls the switching circuit 55 to disconnect the blade 37 from the blade voltage application circuit 54. By doing so, the blade 37 is disconnected from the electrically grounded ground portion GND of the blade voltage application circuit 54, thereby suppressing the loss of charge from the positively charged toner carried on the developing roller 35 via the blade 37.

[0090] (4) In addition, in the process shown in Figure 4, the ASIC 41 connects the blade 37 to the blade voltage application circuit 54 (S4), and applies a blade voltage VBLD with the same voltage value as the development voltage Vb to the blade 37 (S7), thereby making the potential of the blade voltage VBLD the same as the surface potential of the development roller 35. This suppresses the flow of current between the blade 37 and the development roller 35. Furthermore, in S11, the ASIC41 applies a blade voltage VBLD to the blade 37 that is greater than the voltage value of the developing voltage Vb, so that the potential of the blade 37 is higher than the surface potential of the developing roller 35. This allows the blade current IBLD to flow from the blade 37 to the developing roller 35. Therefore, by controlling the voltage value of the blade voltage VBLD, the blade current IBLD for each process can be controlled.

[0091] (5) In addition, in S16, the ASIC41 corrects the current value of the blade current IBLD calculated in S13 based on the temperature detected by the temperature sensor 46. In S17, the ASIC41 determines the state of toner adhesion based on the corrected current value. This allows for a more accurate determination of the toner's adhesion status.

[0092] (6) When the ASIC41 detects that the toner cartridge 22 has been replaced, it executes the new product detection process shown in Figure 7 and performs the same process as in Figure 4 to store the calculated blade current IBLD current value as a threshold TH in the non-volatile memory 45 (S37). In S17 of Figure 4, the ASIC41 uses the threshold TH stored in the non-volatile memory 45 to determine the state of toner adhesion. According to this method, the state of toner hardening can be determined based on a clean state where new toner has not hardened.

[0093] (7) In addition, in S36 of Figure 7, the ASIC41 corrects the current value of the blade current IBLD calculated in S33 based on temperature, etc., stores the corrected value as the threshold TH, and uses it for the determination in S17. This allows for a more accurate determination of the toner's adhesion status.

[0094] (8) In addition, in the first and second states, the ASIC 41 applies a wire voltage Vw to the charged wire 27 from the wire voltage application circuit 51. According to this, the photoreceptor drum 33 can be charged using a scorotron-type charger 25, making the surface potential V0 of the photoreceptor drum 33 higher than the surface potential of the developing roller 35.

[0095] (Second Embodiment) Next, a second embodiment of the present invention will be described. In the first embodiment described above, as shown in Figure 4, a correction process was performed to correct the current value of the blade current IBLD calculated in S13 based on environmental information such as temperature detected using the temperature sensor 46. In contrast, the second embodiment differs from the first embodiment in that no correction process is performed. In the following description of the second embodiment and subsequent embodiments, the same reference numerals are used for components and processes as in the first embodiment described above, and their descriptions are omitted as appropriate.

[0096] Figure 10 shows a flowchart of the toner adhesion determination mode processing according to the second embodiment. As shown in Figure 10, the ASIC 41 of the second embodiment executes S1 to S13 in the same way as the first embodiment, calculates the blade current IBLD in S13, and then compares the calculated blade current IBLD with a threshold value TH to determine the toner adhesion state (S17). Therefore, in the second embodiment, S15 and S16 in Figure 4 are not executed. This reduces the time required for correction processing and allows for rapid determination of the toner adhesion state. In addition, it eliminates the need to store the correction data DATA required for correction processing in ROM 43 or the like. Furthermore, it eliminates the need to provide sensors such as the temperature sensor 46 in the printer 1.

[0097] Similarly, when ASIC41 performs the new product detection process shown in Figure 7, it may skip processes S35 and S36 and execute S37 after S33. That is, it is not necessary to perform correction based on environmental information in the memory process for storing the threshold value TH. ASIC41 may update the threshold value TH in the non-volatile memory 45 with the current value of the blade current IBLD calculated in S33 (S37). This reduces the time required for the correction process and allows for rapid updating of the threshold value TH.

[0098] (Third embodiment) Next, a third embodiment of the present invention will be described. In the first embodiment described above, the printer 1 is equipped with a switching circuit 55, and in the printing process, the switching circuit 55 is controlled to disconnect the blade 37 and the blade voltage application circuit 54. In contrast, the printer 100 of the third embodiment differs from the printer 1 of the first embodiment in that it is not equipped with a switching circuit 55.

[0099] As shown in Figure 11, the printer 100 of the third embodiment does not have a switching circuit 55 between the blade 37 and the blade voltage application circuit 54. Also, the ASIC 41 of the third embodiment performs the same processing as in Figure 8, but does not execute S43. In the printing process of Figure 8, the ASIC 41 stops the application of the blade voltage VBLD by the blade voltage application circuit 54. For example, when the printing process of Figure 8 is started, the ASIC 41 maintains a state in which the output of the PWM signal PWM_Vb is stopped and stops the application of the blade voltage VBLD by the blade voltage application circuit 54. After executing S41, the ASIC 41 executes S44 and subsequent steps.

[0100] As described above, the third embodiment provides the same effects as the first embodiment. Furthermore, the third embodiment provides the following effects. (1) In the third embodiment, the ASIC 41 of the printer 100 stops the application of the blade voltage VBLD by the blade voltage application circuit 54 during the printing process. According to this, compared to the state in which the blade 37 is electrically floating as in the first embodiment, there is a possibility that the positive charge of the positively charged toner carried on the developing roller 35 may be lost via the blade 37. However, since the switching circuit 55 is not required, the manufacturing cost of the printer 100 can be reduced by eliminating the switching circuit 55. In addition, since there is no need for a port to output a control signal CI to the ASIC 41, manufacturing costs can be reduced in this respect as well.

[0101] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from its spirit. For example, the processing content and order of operations in the flowcharts shown in Figures 4, 7, 8, and 10 are just examples. For instance, in Figure 4, ASIC41 may execute S4 after S1, and then execute S2 and S3. Alternatively, ASIC41 may measure the second developing roller current first, and then measure the first developing roller current. Furthermore, in the printing process of the first to third embodiments, a positive polarity blade voltage VBLD may be applied to the blade 37. Furthermore, the configuration of the printer 1,100 in each of the above embodiments is merely an example. For instance, the printer 1 may be equipped with a communication interface such as a LAN interface. Furthermore, while a monochrome laser printer was used as the image forming apparatus in the above embodiments, the present invention is not limited to this. The image forming apparatus may also be a color laser printer. In this case, the ASIC 41 may, for example, individually set threshold values ​​TH for each of the cyan, magenta, yellow, and black toner cartridges 22 and individually determine the toner adhesion state. The image forming apparatus may also be a multifunction device equipped with multiple functions such as printing, copying, faxing, and scanning. The image forming apparatus may also be a copier or fax machine. [Explanation of symbols]

[0102] 1,100 Printer (image forming apparatus), 6 Image forming unit, 22 Toner cartridge, 25 Charger, 27 Charging wire, 28 Grid, 33 Photoreceptor drum, 35 Developing roller, 37 Blade, 41 ASIC (control unit), 45 Non-volatile memory (storage unit), 46 Temperature sensor (sensor), 47 Temperature sensor (sensor), 48 Humidity sensor (sensor), 51 Wire voltage application circuit, 53 Developing voltage application circuit, 54 Blade voltage application circuit, 55 Switching circuit, 56 Current measurement circuit, I Developing roller current, TH Threshold, V0 Surface potential, Vb Developing voltage, VBLD Blade voltage, Vw Wire voltage.

Claims

1. An image forming unit having a photoreceptor drum, a charger for charging the photoreceptor drum, a developing roller that contacts the photoreceptor drum and holds toner, and a blade for adjusting the thickness of the toner held on the developing roller, A developing voltage is applied to the developing roller, and a developing voltage application circuit is electrically grounded, A blade voltage application circuit that applies a blade voltage to the blade, A current measuring circuit is connected between the developing roller and the developing voltage application circuit for measuring the developing roller current flowing from the developing roller to the developing voltage application circuit, Control unit and Equipped with, The control unit, The photoreceptor drum is charged using the aforementioned charger, The developing voltage application circuit and the blade voltage application circuit bring the surface potential of the photoreceptor drum to a first state in which the surface potential of the photoreceptor drum is higher than the surface potential of the developing roller, and the potential of the blade and the surface potential of the developing roller are at the same potential, and in the first state, the current measurement circuit measures the first developing roller current in a measurement process, After the measurement process, the first state is changed to a second state in which the potential of the blade is higher than the surface potential of the developing roller by the developing voltage application circuit and the blade voltage application circuit, the second developing roller current is measured by the current measurement circuit in the second state, and the current value of the blade current flowing from the blade to the developing roller is calculated by subtracting the current value of the first developing roller current from the current value of the second developing roller current, and A toner adhesion state determination process is performed to determine the state of toner adhesion between the blade and the developing roller based on the current value of the blade current calculated by the calculation process described above. An image forming apparatus that performs this function.

2. The image forming apparatus according to claim 1, further comprising a switching circuit connected between the blade and the blade voltage application circuit, which switches the connection between the blade and the blade voltage application circuit based on the control of the control unit.

3. The aforementioned blade voltage application circuit is It is electrically grounded. The control unit, In the measurement process and the calculation process, the switching circuit is controlled to connect the blade and the blade voltage application circuit. The image forming apparatus according to claim 2, wherein, during image forming, toner is supplied from the developing roller to the electrostatic latent image formed on the photoreceptor drum based on an image forming job to form a toner image on the photoreceptor drum, the switching circuit is controlled to disconnect the blade and the blade voltage application circuit.

4. The control unit, In the measurement process, the switching circuit is controlled to connect the blade and the blade voltage application circuit, and the blade voltage, which is the same voltage value as the developing voltage applied by the developing voltage application circuit to the developing roller, is applied from the blade voltage application circuit to the blade, so that the potential of the blade and the surface potential of the developing roller are at the same potential. The image forming apparatus according to claim 3, wherein in the calculation process, the blade voltage is applied from the blade voltage application circuit to the blade, and the blade voltage is greater than the voltage value of the developing voltage applied by the developing voltage application circuit to the developing roller, thereby causing the potential of the blade to be higher than the surface potential of the developing roller.

5. The control unit, The image forming apparatus according to claim 1, wherein, during image forming, toner is supplied from the developing roller to the electrostatic latent image formed on the photoreceptor drum based on an image forming job to form a toner image on the photoreceptor drum, and the application of the blade voltage by the blade voltage application circuit is stopped.

6. The image forming apparatus is further equipped with a sensor for detecting environmental information, which is information about the environment in which the image forming apparatus is located. The control unit, A correction process is performed to correct the current value of the blade current calculated by the above calculation process based on the environmental information detected using the sensor. The image forming apparatus according to claim 1, wherein in the toner adhesion state determination process, the state of toner adhesion is determined by the current value of the blade current after correction by the correction process.

7. It also has a memory unit, The image forming unit is The toner cartridge having the developing roller is replaceable, The control unit, When it is detected that the toner cartridge has been replaced, the measurement process and the calculation process are executed, and the calculated blade current value is stored in the storage unit as a threshold value in a storage process. The image forming apparatus according to claim 1, wherein in the toner adhesion state determination process, the state of toner adhesion is determined using the threshold value stored in the storage unit.

8. The image forming apparatus is further equipped with a sensor for detecting environmental information, which is information about the environment in which the image forming apparatus is located. The control unit, In the memory processing described above, the calculated blade current value is corrected based on the environmental information detected using the sensor, and the corrected value is stored in the memory unit as the threshold value. The image forming apparatus according to claim 7, wherein the toner adhesion state determination process determines the toner adhesion state using the corrected threshold.

9. The aforementioned charger is Having a charged wire and grid, The device further includes a wire voltage application circuit for applying a wire voltage to the charging wire of the charger, The control unit, The image forming apparatus according to claim 1, wherein in the first state and the second state, a wire voltage is applied to the charged wire by the wire voltage application circuit.

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