Image forming apparatus

Abstract

To provide an image forming apparatus that executes density correction control of setting a grid voltage according to a change in at least one of temperature and humidity and subsequently setting a developing bias, and thereby can maintain print density.SOLUTION: An ASIC 61 sets set values of grid voltages GRID1 to GRID4 to be smaller as humidity detected by a temperature and humidity sensor 54 increases by using a temperature and humidity table TB1 and a grid current and voltage table TB2 (S3). With wire voltages CHG, CHGK according to the set values being supplied from wire voltage generation circuits 70, 70K (S7, S13), the ASIC 61 forms a toner image on a conveying belt 23 (S15). The ASIC 61 detects the density of the formed toner image with a density sensor 53, and sets a developing bias during printing based on a result of the detection.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present application relates to an electrophotographic image forming apparatus provided with a scorotron charger. [Background Art]

[0002] Conventionally, various technologies related to image forming apparatuses including a scorotron charger having a charging wire and a grid have been proposed. Patent Document 1 below describes an image forming apparatus that controls charging bias and developing bias based on temperature and humidity. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2003-195579 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] Since the characteristics of a scorotron charger change depending on temperature and humidity, it is necessary to set a bias according to the temperature and humidity. However, the value of the developing bias that achieves an appropriate print density also changes depending on factors such as the deterioration state of toner. The image forming apparatus of Patent Document 1 does not set the developing bias in consideration of the deterioration state of toner and the like, so there has been a risk that good print density cannot be maintained.

[0005] The present application has been made to solve the above-described problems, and an object thereof is to provide an image forming apparatus capable of maintaining print density by executing density correction control for setting a developing bias after setting a grid voltage according to a change in at least one of temperature and humidity. [Means for Solving the Problem]

[0006] To achieve the above objective, the present invention discloses an image forming apparatus comprising: a photoreceptor; a charger having a charging wire and a grid for charging the photoreceptor; an application unit connected to the charging wire for applying a wire voltage to the charging wire; a developer for developing an electrostatic latent image formed on the photoreceptor and forming a toner image; a belt in contact with the photoreceptor; a density sensor for detecting the density of the toner image formed on the belt; a humidity sensor for detecting humidity; and a control unit, wherein the control unit forms the toner image on the belt, detects the density of the formed toner image with the density sensor, and performs density correction control to set a development bias to be applied to the developer during printing based on the detection result, and in the density correction control, as the humidity detected by the humidity sensor increases, the set voltage, which is a set value of the grid voltage applied to the grid, is set to a smaller value and the wire voltage is applied by the application unit, thereby forming the toner image on the belt.

[0007] In high-humidity environments, a higher wire voltage tends to be required to obtain the target grid voltage. Higher wire voltages increase the likelihood of abnormal discharge. In the above configuration, the wire voltage can be reduced by setting a lower grid voltage and applying a lower wire voltage as the humidity detected by the humidity sensor increases. After reducing the grid voltage in response to the rise in humidity, density correction using the toner image can be performed to set the development bias. As a result, the grid voltage can be set according to the change in humidity, the development bias can be set, and the development bias can be corrected (density correction) according to toner degradation, etc., to maintain appropriate print density and enable printing.

[0008] Furthermore, the image forming apparatus is equipped with a temperature sensor for detecting temperature, and the control unit may, in the density correction control, set the set voltage to a smaller value as the temperature detected by the temperature sensor increases.

[0009] In low-temperature environments, the photoreceptor tends to become less charged, and the surface potential of the photoreceptor decreases. This makes it easier for toner to adhere to and develop areas on the photoreceptor where no image has formed, a phenomenon known as fogging. Fogging can lead to a decrease in print quality. Therefore, it is preferable to increase the grid voltage to increase the surface potential of the photoreceptor. In the above configuration, the set voltage is decreased and the wire voltage is applied as the temperature detected by the temperature sensor increases. In other words, in low-temperature environments, the set voltage can be relatively increased, and the grid voltage can be increased. After increasing the grid voltage in response to the decrease in temperature and increasing the surface potential of the photoreceptor, density correction using the toner image can be performed to set the development bias. As a result, by setting the grid voltage according to the temperature change, setting the development bias, and performing correction of the development bias (density correction) according to toner degradation, it is possible to print while maintaining appropriate print density.

[0010] Furthermore, in the concentration correction control, the control unit may set the set current, which is the set value of the grid current flowing through the grid, to a smaller value as the humidity detected by the humidity sensor increases. This reduces the grid current in high-humidity environments where abnormal discharge is likely to occur, thereby suppressing the occurrence of abnormal discharge.

[0011] Furthermore, the control unit may be equipped with a temperature sensor to detect temperature, and in the density correction control, the set current, which is the set value of the grid current flowing through the grid, may be set to a smaller value as the temperature detected by the temperature sensor increases. This allows the grid current to be relatively increased in low-temperature environments, increasing the surface potential of the photoreceptor, and then performing density correction using the toner image to set the development bias to an appropriate value.

[0012] Furthermore, the system may be equipped with a temperature sensor for detecting temperature, and the control unit may perform temperature detection using the temperature sensor, and if the difference between the detected temperature and the temperature at which the previous density correction control was performed exceeds a first temperature range, the density correction control may be performed. When the temperature changes, the characteristics of charging and developing change. In contrast, with this configuration, an appropriate print density can be maintained by performing density correction control when the temperature exceeds a predetermined first temperature range.

[0013] Furthermore, the grid voltage set in the concentration correction control is set for each second temperature range, and the second temperature range may be narrower than the first temperature range. As a result, the grid voltage is set for each second temperature range which is narrower than the first temperature range. Then, the concentration correction control is executed only when a temperature change occurs that exceeds the first temperature range which is larger than the second temperature range. This suppresses the frequent execution of the concentration correction control.

[0014] Furthermore, the control unit may detect humidity using the humidity sensor and execute the density correction control if the difference between the detected humidity and the humidity at the time of the previous density correction control exceeds the first humidity range. When humidity changes, the characteristics of charging and developing change. In contrast, with this configuration, an appropriate print density can be maintained by executing density correction control when the humidity exceeds a predetermined first humidity range.

[0015] Furthermore, the grid voltage set in the concentration correction control is set for each second humidity range, and the second humidity range may be narrower than the first humidity range. The grid voltage is set for each second humidity range that is narrower than the first humidity range. Then, the concentration correction control can be executed only when a humidity change occurs that exceeds the first humidity range which is larger than the second humidity range. This makes it possible to suppress the frequent execution of the concentration correction control.

[0016] Furthermore, the control unit may execute the density correction control if the amount of operation of the developer exceeds a predetermined amount since the previous execution of the density correction control. This allows for the maintenance of appropriate print density by appropriately executing the density correction control even if the toner deteriorates and its characteristics change due to the operation of the developer.

[0017] Furthermore, the developing unit may include a storage unit for toner, and the control unit may perform the density correction control when the storage unit is replaced. Since the characteristics of charging and development change when the toner is replaced, performing density correction control when the storage unit is replaced can maintain an appropriate print density.

[0018] Furthermore, the control unit may perform the density correction control when the photoreceptor is replaced. Since the charging and development characteristics change when the photoreceptor is replaced, performing density correction control when the photoreceptor is replaced can maintain an appropriate print density.

[0019] Furthermore, the control unit may be provided with an interface, and may execute the concentration correction control when it receives an instruction to execute the concentration correction control via the interface. This allows the concentration correction control to be performed appropriately in response to instructions from the user or others.

[0020] Furthermore, the control unit may include a plurality of photoreceptors, a plurality of chargers corresponding to the plurality of photoreceptors, an application unit that applies the wire voltage to a plurality of parallel-connected charging wires, and an adjustment circuit connected to a plurality of grids that adjusts the grid voltage. The control unit may apply the wire voltage using the application unit so that the minimum grid current among the grid currents flowing through the plurality of grids reaches a target value, and adjust the adjustment circuit so that the grid voltage of a specific charger through which the minimum grid current flows reaches the set value. By increasing the wire voltage so that the minimum grid current reaches the target value, the grid currents of the other chargers can also be reliably increased to the target value. The surface potential of all photoreceptors can be more reliably increased to the required potential.

[0021] Further, the control section may cause the adjustment circuit to perform adjustment such that the grid voltage of the chargers other than the specific charger through which the minimum grid current flows becomes a value smaller than the set voltage. This makes it possible to equalize the photoconductor charging capability of the chargers other than the specific charger through which the minimum grid current flows to the same level as the photoconductor charging capability of the specific charger through which the minimum grid current flows. Effects of the Invention

[0022] According to the image forming apparatus of the present application, density correction control for setting a developing bias after setting a grid voltage in accordance with a change in at least one of temperature and humidity can be executed, so that print density can be maintained. Brief Description of the Drawings

[0023] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of a laser printer according to an embodiment of the present application. [Figure 2] 2 is a schematic block diagram related to a high-voltage power supply device of the laser printer in FIG. 1. [Figure 3] 3 is a schematic block diagram related to a high-voltage power supply device corresponding to black color of the laser printer in FIG. 1. [Figure 4] 4 is a view showing a temperature-humidity table. [Figure 5] 5 is a view showing a grid current-voltage table. [Figure 6] 6 is a flowchart of density correction processing executed by an ASIC. Mode for Carrying Out the Invention

[0024] (Overall Configuration of Printer) Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 shows a schematic configuration of a laser printer 1 according to one embodiment of the present invention. The laser printer 1 is a color laser printer that forms a color image on a sheet P by, for example, an electrophotographic method, and is a so-called tandem laser printer that uses four toners. The recording medium, sheet P, can be printing paper or an OHP sheet. In the following description, the laser printer 1 will be simply referred to as printer 1. As shown in Figure 1, the right side of the paper in the figure is defined as the front side of printer 1, and the left side of the paper is defined as the rear side. Furthermore, the top side of the paper in Figure 1 is defined as the top side of printer 1, and the bottom side of the paper is defined as the bottom side.

[0025] As shown in Figure 1, the printer 1 has a roughly box-shaped main body housing 2, and the paper feeding unit 10, image forming unit 20, etc. are housed inside the main body housing 2. The paper feeding unit 10 has a paper feeding tray 11 capable of holding sheets P and various rollers, and drives the various rollers to feed the sheets P to the image forming unit 20. The paper feeding tray 11 is also configured to be detachable from the lower part of the main body housing 2. The sheets P supplied from the paper feeding unit 10 are transported along the transport path R shown in Figure 1. An output tray 5 is provided on the top surface of the main body housing 2. The output tray 5 stores the sheets P that have been transported along the transport path R and have had images printed on them in a stacked state.

[0026] The image forming unit 20 includes a transport unit 21, four process cartridges 30C, 30M, 30Y, and 30K, an exposure unit 35, and a fixing unit 50. The transport unit 21 is provided between the paper feeding unit 10 and the process cartridges 30C, etc., in the vertical direction, and includes a transport belt 23 and four transfer rollers 25, etc. The transport belt 23 is an endless belt formed by shaping a belt into a ring, and is wrapped around a drive roller 27 located below the rear end of the image forming unit 20 and a driven roller 29 located below the front end. The upper surface of the transport belt 23 extends substantially horizontally directly below the process cartridges 30C, etc., and contacts the back surface of the sheet P supplied from the paper feeding unit 10. The drive roller 27 rotates the transport belt 23 in a predetermined direction. Furthermore, the conveyor belt 23 becomes negatively charged when a transfer bias is applied to each transfer roller 25, and while the sheet P is attracted to its upper surface by electrostatic force, the attracted sheet P is conveyed along the conveyor path R toward the discharge tray 5.

[0027] Each of the process cartridges 30C, 30M, 30Y, and 30K corresponds to one of four colors: cyan (C), magenta (M), yellow (Y), and black (K). Each of the process cartridges 30C, 30M, 30Y, and 30K contains toner of the corresponding color (C, M, Y, K). The four process cartridges 30C, 30M, 30Y, and 30K are arranged in the order of 30Y, 30M, 30C, and 30K from front to back in printer 1.

[0028] Process cartridge 30C includes a drum-shaped photoreceptor 31, a charger 41, and a toner cartridge 33, etc. The configurations of the other process cartridges 30M, 30Y, and 30K are similar to those of process cartridge 30C, except that they contain toners of different colors. Therefore, in the following explanation, process cartridge 30C will be described as a representative example, and explanations of the other process cartridges 30M, 30Y, and 30K will be omitted as appropriate.

[0029] The photoreceptor 31 is located above the transfer roller 25, with a conveyor belt 23 sandwiched between it and the transfer roller 25 in the vertical direction. Therefore, the conveyor belt 23 is positioned in contact with the photoreceptor 31. The charger 41 is, for example, a scorotron-type charger in which a charging wire 42 and a grid 43 are housed in a shield case 45. The charging wire 42 is made of metal, for example, gold-plated tungsten or plain tungsten. The shield case 45 is formed in a roughly rectangular tubular shape, elongated in the direction of the rotation axis of the photoreceptor 31. An opening is formed in the portion of the shield case 45 facing the photoreceptor 31. The grid 43 is constructed by stretching conductive wires in a mesh pattern within the opening of the shield case 45. The charging wire 42 is stretched within the shield case 45 along the direction of the rotation axis of the photoreceptor 31, and is, for example, positioned at a distance from the upper rear side of the photoreceptor 31. Therefore, the grid 43 is positioned between the photoreceptor 31 and the charging wire 42.

[0030] The charger 41 uniformly positively charges the surface of the photoreceptor 31 during image formation. Specifically, when a voltage is applied to the charging wire 42 and the grid 43, an electric field is formed between the charging wire 42 and the photoreceptor 31, causing corona discharge. When the electric field is formed between the charging wire 42 and the grid 43, a different voltage is applied to the grid 43 than that of the charging wire 42, thereby controlling the strength of the electric field and controlling the amount of charge on the photoreceptor 31.

[0031] The exposure unit 35 is located at the top of the inside of the main housing 2 and forms an electrostatic latent image based on image data on the surface of each charged photoreceptor 31. The exposure unit 35 selectively exposes the photoreceptors 31 that have been uniformly positively charged by the charger 41. This exposure selectively removes charge from the surface of the photoreceptor 31, and an electrostatic latent image is formed on the surface of the photoreceptor 31. The exposure means of the exposure unit 35 is not particularly limited, but means using an LED head or means using a semiconductor laser can be employed as the exposure means.

[0032] The toner cartridge 33 has a developing roller 47 and a supply roller 49. For example, the toner contained in the toner cartridge 33 is positively charged between the developing roller 47 and the supply roller 49 and carried on the surface of the developing roller 47. During image formation, a developing bias is applied to the developing roller 47 to carry toner on its surface. When the developing roller 47 faces the electrostatic latent image formed on the photoreceptor 31, the potential difference between the developing roller 47 and the electrostatic latent image supplies toner to the electrostatic latent image. As a result, a toner image is formed (developed) on the surface of the photoreceptor 31. The toner cartridge 33 is also configured to be detachable from the main body housing 2 and can be replaced.

[0033] The transport unit 21 transports the sheet P toward the fixing unit 50 and applies a transfer bias to the transfer roller 25 to transfer the toner image developed on the surface of the photoreceptor 31 to the sheet P. The fixing unit 50 is located downstream of the transport path R compared to the transport unit 21. The fixing unit 50 has a heating roller 51 and a pressure roller 52. The heating roller 51 is equipped with a heat source such as a heater and is located on the image forming surface side of the sheet P. It rotates in synchronization with the transport belt 23, etc., heating the toner transferred to the sheet P while transporting the sheet P. The pressure roller 52 rotates in a driven manner, sandwiching the sheet P between itself and the heating roller 51 and pressing the sheet P toward the heating roller 51. As a result, the fixing unit 50 heats and melts the toner transferred to the sheet P and fixes it to the sheet P while transporting the sheet P along the transport path R.

[0034] The printer 1 is also equipped with a density sensor 53. The density sensor 53 is a sensor that detects a patch for density correction formed on the transport belt 23. The density sensor 53 is positioned, for example, below and behind the drive roller 27, and facing the transport belt 23. As the density sensor 53, for example, a light-reflecting sensor equipped with a light-emitting element such as an LED and a light-receiving element such as a phototransistor can be used. The ASIC (Application-Specific Integrated Circuit) 61 (see Figure 3) of the printer 1 is connected to the density sensor 53 and detects the density of the patch formed on the transport belt 23 based on the detection signal from the density sensor 53. In other words, the ASIC 61 detects the density of the toner image formed when toner is supplied to a test electrostatic latent image formed on the photoreceptor 31, i.e., the density of the patch, via the transport belt 23. The patch formed on the transport belt 23 is removed from the transport belt 23 by a belt cleaner (not shown) after the density has been detected.

[0035] Furthermore, the printer 1 is equipped with a temperature and humidity sensor 54. The temperature and humidity sensor 54 is located, for example, inside the main body housing 2, in a position close to an air intake port 55 provided in the main body housing 2. The ASIC 61 (see Figure 3) is connected to the temperature and humidity sensor 54 and detects the temperature and humidity inside the main body housing 2 based on the detection signal from the temperature and humidity sensor 54. Note that the printer 1 may be configured to have the temperature sensor and humidity sensor in separate locations. Alternatively, the printer 1 may be configured to have multiple temperature sensors or multiple humidity sensors and use the average value of multiple detection values. Alternatively, the printer 1 may be configured to have only one of the sensors, either a temperature sensor or a humidity sensor.

[0036] As shown in Figure 3, the printer 1 is equipped with a touch panel 6 and a network interface 7. The touch panel 6 is a user interface that receives operation input from the user and outputs a signal corresponding to the received operation input to the ASIC 61. The touch panel 6 also changes the display content based on the control of the ASIC 61. Note that the user interface of the printer 1 is not limited to the touch panel 6; for example, it could be a combination of an LCD and operation switches.

[0037] Network IF7 is, for example, a LAN interface and is connected to a PC or other device that issues print commands via a LAN cable. Note that Network IF7 is not limited to a LAN interface; it may also be a network interface that performs wireless communication such as Wi-Fi or Bluetooth. Furthermore, the printer 1 may be configured without at least one of the touch panel 6 and Network IF7.

[0038] (Electrical configuration of printer 1) Next, the electrical configuration of the printer 1 related to this invention will be described with reference to Figures 2 and 3. Figures 2 and 3 show a schematic block diagram of the high-voltage power supply unit 60 built into the printer 1 and the connection configuration related to the high-voltage power supply unit 60. In the following description, when distinguishing each component by color, the subscripts Y (yellow), M (magenta), C (cyan), K (black), or subscripts such as "1 to 4" (for example, grid voltage GRID1 to GRID4) will be added to the symbols of each part, and when not distinguishing, the subscripts will be omitted (for example, grid voltage GRID).

[0039] The high-voltage power supply unit 60 includes an ASIC 61, a high-voltage power supply board 62 connected to the ASIC 61, a ROM 63, and a RAM 64. The ASIC 61 is an example of the control unit of this application and, in addition to controlling the high-voltage power supply board 62, comprehensively controls the entire printer 1. The ROM 63 is a storage device that stores various control programs executed by the ASIC 61. In this embodiment, the ROM 63 stores a program PG for implementing the density correction process shown in Figure 6, which will be described later, as one of the control programs. The RAM 64 stores temporary data for various processes and image data used for printing. Note that the storage device that stores the program PG, etc., is not limited to ROM, but may also be other storage devices such as flash memory, HDD, or SSD (Solid State Drive).

[0040] Furthermore, ROM 63 stores the temperature and humidity table TB1 and the grid current and voltage table TB2. As shown in Figure 4, the temperature and humidity table TB1 is data associated with temperature t, humidity h, and parameter numbers P1 to P6, which are the identification numbers of the parameters. Also, as shown in Figure 5, the grid current and voltage table TB2 is data associated with the grid current, which is the current flowing through the grid 43, the grid voltage, which is the voltage (bias) applied to the grid 43, and parameter numbers P1 to P6. Printer 1 sets the grid current and grid voltage using the temperature and humidity table TB1 and the grid current and voltage table TB2, and then performs the development bias setting, i.e., density correction. Details of the control using the temperature and humidity table TB1, etc. will be described later.

[0041] First, the circuit for YMC will be described. The high-voltage power supply board 62 has a wire voltage generation circuit 70 and grid voltage adjustment circuits 81Y, 81M, and 81C, each equipped with grid current detection circuits 82Y, 82M, and 82C, respectively, as the circuit for YMC. The power line PL is connected to the wire voltage generation circuit 70. The YMC chargers 41Y, 41M, and 41C are connected in parallel to the power line PL. The wire voltage generation circuit 70 applies the wire voltage CHG to each charged wire 42Y, 42M, and 42C via the power line PL. The grid voltage adjustment circuits 81Y, 81M, and 81C and the grid current detection circuits 82Y, 82M, and 82C are provided in correspondence to each of the YMC chargers 41Y, 41M, and 41C.

[0042] The wire voltage generation circuit 70 includes, for example, a PWM signal control circuit 71, a transformer drive circuit 72, a boost circuit 73, and an output voltage detection circuit 78. The wire voltage generation circuit 70 generates the wire voltage CHG to be applied to the charged wires 42Y to 42C of each charger 41Y to 41C. The grid voltages GRID1 to GRID3 applied to the grid 43 are adjusted by the respective grid voltage adjustment circuits 81Y to 81C. The wire voltage CHG is, for example, approximately 5.5kV to 7kV. The grid voltage GRID is, for example, approximately 700 to 800V.

[0043] The PWM signal control circuit 71 includes, for example, a resistor and a capacitor (not shown), and smooths the PWM (Pulse Width Modulation) signal Sp1 input from port PWM1 of the ASIC61, and outputs the smoothed PWM signal Sp1 to the transformer drive circuit 72. The transformer drive circuit 72, for example, supplies the smoothed PWM signal Sp1 input from the PWM signal control circuit 71 to a drive transistor (not shown), and outputs an oscillation current to the boost circuit 73.

[0044] The transformer 74 of the boost circuit 73 is equipped with a primary winding 74a, a secondary winding 74b, and an auxiliary winding 74c. The transformer drive circuit 72 outputs an oscillation current from a drive transistor to the primary winding 74a of the transformer 74. The transformer 74 changes the voltage value of the output voltage (wire voltage CHG) output from the secondary winding 74b according to the duty cycle of the oscillation current. For example, the transformer 74 generates a wire voltage CHG with a larger voltage value as the duty cycle of the PWM signal Sp1 increases. A rectifier diode 75, a smoothing capacitor 76, and an output resistor 77 are connected to the secondary winding 74b. The boost circuit 73 boosts and rectifies the voltage generated in the primary winding 74a of the transformer 74 and applies it as a wire voltage CHG to the charging wires 42Y~42C of each charger 41Y~41C.

[0045] Furthermore, the output voltage detection circuit 78 is connected between the auxiliary winding 74c of the transformer 74 and the ASIC 61. The output voltage detection circuit 78 includes, for example, a smoothing circuit and a voltage divider resistor (not shown). The output voltage detection circuit 78 detects the output voltage v1 generated in the auxiliary winding 74c in conjunction with the generation of the wire voltage CHG. The output voltage detection circuit 78 smooths and divides the output voltage v1 and supplies it as an output voltage detection signal Sv1 to the port A / D1 of the ASIC 61.

[0046] Furthermore, each of the grid voltage adjustment circuits 81 has a voltage divider circuit 83 and an operational amplifier OP1. Note that each of the grid voltage adjustment circuits 81M and 81C has the same circuit configuration as grid voltage adjustment circuit 81Y, so some of their circuits are omitted from the illustration in Figure 2. Also, in the following explanation, the grid voltage adjustment circuit 81Y corresponding to the color Y (yellow) will be described, and the explanations of the other (M,C) grid voltage adjustment circuits 81Y and 81C will be omitted as appropriate. The voltage divider circuit 83Y has two voltage divider resistors R7 and R8 connected in series. A divided current Id1 of the grid current Ig1 flowing through the grid 43Y flows through the voltage divider resistors R7 and R8. The voltage divider circuit 83Y outputs a detection voltage Vgr1 corresponding to the grid voltage GRID1 applied to the grid 43Y from the connection point of the two voltage divider resistors R7 and R8. The voltage divider circuit 83Y supplies the detected voltage Vgr1 as a voltage divider detection signal Sid1 to the non-inverting input (+) of the operational amplifier OP1 via the output resistor R6. Capacitor C3 is connected in parallel with the voltage divider resistor R8 to form an RC filter.

[0047] Furthermore, the inverting input (-) of the operational amplifier OP1 is connected to the port PWM2 of the ASIC61 via the output resistor R9. The output side of the output resistor R9 is grounded to GND via the capacitor C4. The ASIC61 supplies the PWM signal Spp1 from port PWM2 and supplies the PWM signal Spp1 to the operational amplifier OP1 via the output resistor R9. Therefore, the ASIC61 is configured to allow the reference voltage of the operational amplifier OP1 to be changed.

[0048] A smoothing circuit, including a voltage divider resistor R4 and a capacitor C2, is connected to the output terminal of the operational amplifier OP1. The connection point of the voltage divider resistor R4 on the grid 43Y side (opposite the output terminal of the operational amplifier OP1) is grounded to GND via capacitor C2. The base of transistor Q1, which is used to stabilize the grid voltage GRID1, is connected to the connection point of the voltage divider resistor R4 on the grid 43Y side. Transistor Q1 is connected to a voltage control line Ln1, which is connected to the connection point between the voltage divider resistor R7 and the grid 43Y. Transistor Q1 is, for example, an NPN transistor, with its collector connected to the connection point on the grid 43Y side (voltage control line Ln1) and its emitter connected to the grid current detection circuit 82Y (resistor R3). Note that transistor Q1 is not limited to a bipolar transistor; for example, a FET (field-effect transistor) may also be used.

[0049] The base current of transistor Q1 is controlled by the output of operational amplifier OP1. The collector resistance of transistor Q1 changes with the base current, so transistor Q1 functions as a variable resistor. Here, collector resistance refers to the resistance value obtained by dividing the collector-emitter voltage by the collector current. For example, increasing the base current decreases the resistance, while decreasing the base current increases the resistance. This changes the collector-emitter voltage.

[0050] The operational amplifier OP1 changes the grid voltage GRID1 by changing the base voltage of transistor Q1 based on the difference between the detection voltage Vgr1 (voltage division detection signal Sid1) detected by the voltage divider circuit 83Y and the PWM signal Spp1 input from ASIC61. Therefore, ASIC61 can change the voltage value of the grid voltage GRID1 to a predetermined target voltage value (such as the setting value described later) by changing the duty cycle of the PWM signal Spp1. The grid 43Y is grounded to GND via capacitor C1.

[0051] Furthermore, a grid current detection circuit 82Y is connected to the voltage control line Ln1 to detect a line current Ir1 corresponding to the grid current Ig1 flowing through the grid 43Y. The resistor R3 of the grid current detection circuit 82Y is connected between the emitter of transistor Q1 and GND. The grid current detection circuit 82Y supplies the voltage of the positive terminal of resistor R3 as a line voltage detection signal Sir1 to the A / D2 port of the ASIC61.

[0052] Next, the circuit for K will be described. Figure 3 shows a schematic block diagram of the wire voltage generation circuit 70K, which is provided specifically for K, and the connection configuration related to the wire voltage generation circuit 70K. The configuration in Figure 3 is actually included in the configuration in Figure 2, but for convenience it has been made into a separate diagram. Therefore, in Figure 3, the same reference numerals are used for components that are the same as those in Figure 2, and their explanations are omitted as appropriate.

[0053] The wire voltage generation circuit 70K has the same configuration as the wire voltage generation circuit 70 in Figure 2, so its configuration will be omitted. The wire voltage generation circuit 70K is connected to the power line PLK. Only the charger 41K is connected to the power line PLK. The wire voltage generation circuit 70K applies the wire voltage CHGK to the charger 41K via the power line PLK.

[0054] A grid current detection circuit 82K is connected to the voltage control line Ln4 via resistor R11. This circuit detects a line current Ir4 corresponding to the grid current Ig4 flowing through the grid 43K. Resistor R11, along with resistor R3 included in the grid current detection circuit 82K, generates the grid voltage GRID4 as the line current Ir4 flows through it. The grid voltage GRID4 is approximately 700-800V, similar to the grid voltages GRID1-GRID3 described above. The line current Ir4 can be matched to a desired target value. That is, while it is possible to match any one of the line currents Ir1-Ir3 to a desired target value, it is difficult to match all of the line currents Ir1-Ir3 to their respective target values. As described above, this configuration applies a wire voltage CHG to multiple chargers 41 from a single wire voltage generation circuit 70. Therefore, if the amount of dirt adhering to each charging wire 42Y, 42M, and 42C differs, the resistance between each charging wire 42Y, 42M, and 42C and each grid 43Y, 43M, and 43C will be a different value. For this reason, grid voltage adjustment circuits 81Y, 81M, and 81C are provided to adjust the voltage values ​​of each grid voltage GRID1 to GRID3. In contrast, charger 41K is not connected in parallel with the other chargers 41, but is connected to a dedicated wire voltage generation circuit 70K. Therefore, the ASIC 61 can control the wire voltage generation circuit 70K and change the grid voltage GRID4 to match the line current Ir4 to the desired target value. Furthermore, by providing a resistor R11 with a predetermined resistance value, the desired grid voltage GRID4 can be easily obtained. Consequently, the grid voltage adjustment circuit 81 for K can be eliminated. Furthermore, by making the wire voltage generation circuit 70K for K a separate circuit from the wire voltage generation circuit 70 for YMC, the output of the wire voltage generation circuit 70 can be reduced when printing in monochrome.

[0055] ASIC61 controls the voltage value of the wire voltage CHGK supplied from the wire voltage generation circuit 70K based on the current value of the grid current Ig4. ASIC61 calculates the line current Ir4 (grid current Ig4) from the resistance value of resistor R3 included in the grid current detection circuit 82K and the voltage value of the line voltage detection signal Sir4. Based on the calculated grid current Ig4 value, ASIC61 controls the wire voltage generation circuit 70K to match the grid current Ig4 value to the desired target current value (a setting value described later). ASIC61 changes the duty cycle of the PWM signal Sp2 output from port PWM5 to match the grid current Ig4 value to the desired target current value. This makes it possible to set the grid voltage GRID4 to the desired voltage value.

[0056] The above-described configuration of the high-voltage power supply unit 60 is merely an example. The high-voltage power supply unit 60 may also be configured by connecting one wire voltage generation circuit 70 to each of the chargers 41Y, 41M, 41C, and 41K, and supplying the wire voltage CHG from this single wire voltage generation circuit 70 to the four charged wires 42Y, 42M, 42C, and 42K. Alternatively, the high-voltage power supply unit 60 may be configured to have a total of four wire voltage generation circuits 70, one for each of the charged wires 42Y, 42M, 42C, and 42K.

[0057] (Concentration correction processing) Next, the density correction process performed by ASIC61 will be explained with reference to Figures 4 to 6. Figure 6 shows a flowchart of the density correction process performed by ASIC61. For example, ASIC61 starts the process in Figure 6 by executing program PG after the printer 1 is powered on and the control program stored in ROM63 is executed to start the system. Note that the conditions for starting the process in Figure 6 are not limited to the conditions for starting the system as described above, but may also be, for example, the condition for receiving the first print command after the system has started. In the following explanation, steps will be denoted as "S" in the description of each process. In addition, ASIC61, which executes program PG, may sometimes be referred to simply by its device name. For example, the statement "ASIC61 determines predetermined conditions" means "ASIC61 executes program PG and determines predetermined conditions based on program PG."

[0058] As shown in Figure 6, first, in S1, the ASIC61 determines whether a predetermined condition is met. The predetermined condition is the condition for executing density correction control. The ASIC61 repeatedly performs the determination process in S1, making a negative determination in S1 (S1: NO) until it determines that the predetermined condition is met. Then, when the ASIC61 determines that the predetermined condition is met (S1: YES), it executes the density correction control from S3 onwards. As will be described later, the ASIC61 sets the grid current Ig and grid voltage GRID according to the temperature and humidity by executing the density correction control from S3 onwards. The ASIC61 forms a patch with the set grid current Ig and grid voltage GRID, and sets the development bias according to the density of the formed patch. The ASIC61 can print at the appropriate density by performing printing, etc., based on the print job received after the setting, with the set grid current Ig, grid voltage GRID, and development bias.

[0059] The predetermined condition in S1 is, for example, the condition for replacing the toner cartridge 33 with a new toner cartridge 33. The ASIC 61 reads the information of the IC provided in the toner cartridge 33, and if the information read from the IC includes information indicating that it is a new toner cartridge 33, it makes an affirmative decision in S1. If at least one (one color) of the four toner cartridges 33 is replaced with a new one, the ASIC 61 performs density correction control from S3 onwards.

[0060] In S3, the ASIC61 determines the set values ​​(target values) of the grid current Ig and grid voltage GRID based on the temperature and humidity. The ASIC61 detects the temperature t and humidity h inside the main housing 2 based on the detection signal from the temperature and humidity sensor 54. As shown in Figure 4, the temperature and humidity table TB1 is associated with the temperature t, humidity h, and parameter numbers P1 to P6, which are the identification numbers of the parameters, inside the main housing 2. The temperature and humidity table TB1 has temperature ranges set as the range of temperature t, namely t<10℃, 10℃≦t<15℃, 15℃≦t<20℃, 20℃≦t<25℃, 25℃≦t<30℃, and 30℃≦t, and one of the parameter numbers P1 to P6 is set for each temperature range. Therefore, in the temperature range of 10℃≦t<30℃, the temperature and humidity table TB1 has parameter numbers P1 to P6 set every 5℃ (an example of the second temperature range in this application).

[0061] Furthermore, the temperature and humidity table TB1 has humidity ranges set for the following: 0%≦h<10%, 10%≦h<20%, 20%≦h<30%, ...70%≦h<80%, and 80%≦h, and one of the parameter numbers P1 to P6 is set for each humidity range. Therefore, in the humidity range of 0%≦h<80%, the temperature and humidity table TB1 has parameter numbers P1 to P6 set for every 10% (an example of the second humidity range in this application).

[0062] Furthermore, as shown in Figure 5, the grid current-voltage table TB2 has the following settings associated with each parameter number P1 to P6: the set value of the grid current Ig for YMC (an example of the set current in this application), the set value of the grid voltage GRID for YMC (an example of the set voltage in this application), the set value of the grid current Ig4 for K (an example of the set current in this application), and the set value of the grid voltage GRID4 for K. As mentioned above, the circuit for K on the high-voltage power supply board 62 does not have a grid voltage adjustment circuit 81, as shown in Figure 3. The ASIC 61 can change the duty cycle of the PWM signal Sp2 and change the wire voltage CHGK to make the grid current Ig4 match the set value of the grid current Ig4 for K shown in Figure 5. In other words, in controlling the grid current Ig4 and grid voltage GRID4, the ASIC 61 performs control using only the set value of the grid current Ig4 and does not use the set value of the grid voltage GRID4. The voltage value of the grid voltage GRID4 of the charger 41K is determined dynamically according to the grid current Ig4. The grid voltage GRID4 setting for K shown in Figure 5 is an approximate value of the voltage that would occur if the grid current Ig4 were set to that value, and is included as reference information. Therefore, the grid current voltage table TB2 does not need to contain data for the grid voltage GRID4.

[0063] ASIC61 searches the temperature and humidity table TB1 to determine the parameter numbers P1 to P6 corresponding to the temperature and humidity detected in S3. Then, ASIC61 searches the grid current Ig and grid voltage GRID corresponding to the determined parameter numbers P1 to P6 from the grid current and voltage table TB2 to determine the set values. As shown in Figure 4, the parameter numbers increase in the order P1, P2, ... P6 as at least one of the temperature and humidity increases. Also, as shown in Figure 5, the set values ​​of the grid current Ig for YMC and K gradually decrease as the parameter numbers increase in the order P1 to P6. Similarly, the set values ​​of the grid voltage for YMC and K gradually decrease as the parameter numbers increase in the order P1 to P6. Therefore, the set values ​​of the grid current Ig and grid voltage GRID become smaller as at least one of the temperature and humidity increases.

[0064] The values ​​shown in Figure 4 (temperature / humidity table TB1) and Figure 5 (grid current / voltage table TB2) are examples. For example, the temperature / humidity table TB1 may be configured so that parameter numbers P1 to P6 are set for every temperature t less than 5°C (for example, with a second temperature range of 3°C), or so that parameter numbers P1 to P6 are set for every temperature t greater than 5°C (for example, with a second temperature range of 10°C). Alternatively, the temperature / humidity table TB1 may be configured so that the second temperature range is large at low temperatures t (for example, 10°C ≤ t < 20°C) and small at high temperatures t (for example, 20°C ≤ t < 23°C). Similarly, the humidity h in the temperature / humidity table TB1 may also be configured so that the parameter numbers are set for a second humidity range other than 10%. Furthermore, in the grid current / voltage table TB2, either the grid current Ig or the grid voltage GRID may be a fixed value. Also, the number of parameter numbers may be less than six or more than six.

[0065] For example, if the detected temperature is 17°C and the humidity is 25%, ASIC61 selects parameter number P2 based on the temperature-humidity table TB1, which corresponds to 15°C ≤ t < 20°C and 20% ≤ h < 30% (see black circle in Figure 4). ASIC61 determines the grid current Ig and grid voltage GRID from the column for parameter number P2 in the grid current-voltage table TB2. In the example shown in Figure 5, 180A is determined as the setting value for grid current Ig1 to Ig3 for YMC, and 800V is determined as the setting value for grid voltage GRID1 to GRID3 for YMC. Also, 240A is determined as the setting value for grid current Ig4 for K, and 780V is determined as the setting value for grid voltage GRID4 for K (reference information). In processing from S5 onward, ASIC61 sets the grid current Ig and grid voltage GRID based on the setting values ​​determined in S3.

[0066] In S5, ASIC61 outputs YMC PWM signals Spp1, Spp2, and Spp3 based on the YMC grid voltage GRID setting value determined in S3. Specifically, ASIC61 outputs PWM signals Spp1, Spp2, and Spp3 from ports PWM2, PWM3, and PWM4, respectively, with duty cycles where the grid voltages GRID1, GRID2, and GRID3 are set values.

[0067] Next, in S7, the ASIC61 controls the voltage value of the wire voltage CHG supplied from the wire voltage generation circuit 70 based on the current value of the grid current Ig. For example, the ASIC61 controls the wire voltage CHG based on the grid current Ig with the smallest current value among the three grid currents Ig1 to Ig3 of the YMC. The current values ​​of the grid currents Ig1 to Ig3 vary due to factors such as the adhesion of dirt to the charged wire 42. Therefore, the control of the wire voltage CHG is performed using the grid current Ig with the smallest current value as the reference. This makes it possible to set the current values ​​of all grid currents Ig1 to Ig3 to be greater than or equal to the target current value (set value) when there is variation in the amount of change of grid currents Ig1 to Ig3.

[0068] The ASIC61, for example, outputs a PWM signal Sp1 to increase the wire voltage CHG while detecting grid currents Ig1 to Ig3. The ASIC61 calculates the line current Ir1 from the resistance value of resistor R3 and the voltage value of the line voltage detection signal Sir1. The ASIC61 calculates the grid current Ig1 from the line current Ir1 and the shunt current Id1 corresponding to the grid voltage GRID1. The ASIC61 performs similar calculations for the other grid currents Ig2 and Ig3, and determines the grid current Ig with the smallest current value (hereinafter sometimes simply referred to as the smallest grid current Ig) based on the calculation results. Note that since the shunt current Id1 is smaller than the line current It1, the line current Ir1 may be used as the grid current Ig1 in the calculation.

[0069] The following describes an example where grid current Ig1 is the minimum value among grid currents Ig1 to Ig3. In this case, ASIC61 controls the wire voltage generation circuit 70 based on the detected grid current Ig1 value, and matches the minimum grid current Ig1 value to the grid current Ig set in S3. This grid current Ig set value is the grid current Ig set value for YMC, and is 180A when the parameter number P2 mentioned above is selected (see Figure 5). ASIC61 increases the duty cycle of the PWM signal Sp1 output from port PWM1 and increases the wire voltage CHG until the minimum grid current Ig1 value reaches the set value (for example, 180A). This makes it possible to more reliably increase the current values ​​of all grid currents Ig1 to Ig3 to a value greater than or equal to the set value.

[0070] Furthermore, by executing S5 described above, ASIC61 continues to output PWM signals Spp1 to Spp3 according to the set value of the grid voltage GRID. This set value of the grid voltage GRID is the set value for the YMC, and when the parameter number P2 described above is selected, it becomes 800V (see Figure 5). For this reason, the operational amplifier OP1 of each of the grid voltage adjustment circuits 81Y, 81M, and 81C changes the base voltage of transistor Q1 so that each of the grid voltages GRID1 to GRID3 matches the set value (for example, 800V).

[0071] ASIC61 executes S7 to increase the wire voltage CHG and determines whether the minimum grid current Ig1 has reached the set value (S9). Until the minimum grid current Ig1 reaches the set value, ASIC61 makes a negative determination in S9 (S9: NO) and repeatedly executes the determination process in S9 while increasing the wire voltage CHG. While ASIC61 increases the wire voltage CHG and increases the grid currents Ig1 to Ig3, the grid voltage adjustment circuits 81Y, 81M, and 81C attempt to maintain the grid voltages GRID1 to GRID3 at the set values ​​based on the PWM signals Spp1 to Spp3 input from ASIC61.

[0072] When ASIC61 determines that the current value of the minimum grid current Ig1 has reached the set value (S9:YES), it stops increasing the wire voltage CHG and executes S11. In S11, ASIC61 corrects the grid voltages GRID2 and GRID3 for colors other than the color of the minimum grid current Ig1 (in this case, Y) (M, C). In S11, for example, the grid voltage adjustment circuit 81 adjusts the grid voltages GRID2 and GRID3 so that they become smaller than the set value set in S3, the greater the current values ​​of the grid currents Ig2 and Ig3 for M and C are compared to the set value. Specifically, for example, ASIC61 lowers the duty cycle of the PWM signals Spp2 and Spp3, the greater the detected current values ​​of the grid currents Ig2 and Ig3 are compared to the set value (e.g., 180A). More specifically, ASIC61 lowers the duty cycle of PWM signals Spp2 and Spp3 compared to the duty cycle of PWM signals Spp2 and Spp3 output by S5, corresponding to the set value (e.g., 800V) set in S3. As a result, grid voltage adjustment circuits 81M and 81C lower the grid voltages GRID2 and GRID3. The ability of chargers 41M and 41C to charge photoreceptors 31M and 31C can be made to be comparable to the ability of charger 41Y to charge photoreceptor 31Y.

[0073] Next, ASIC61 sets the grid current Ig4 for K (S13). Similar to S7, ASIC61 outputs a PWM signal Sp2 from port PWM5, increasing the wire voltage CHGK. ASIC61 detects the value of the grid current Ig4 and changes the duty cycle of the PWM signal Sp2 so that the detected current value matches the set value of the grid current Ig4 for K determined in S3. For example, in the case of parameter number P2 as described above, ASIC61 increases the duty cycle of the PWM signal Sp2 until the grid current Ig4 becomes 240A. The grid voltage GRID4 is determined according to the resistance values ​​of resistors R3 and R11, etc., and will be a value that matches or is close to the set value shown in Figure 5 (for example, 780V).

[0074] Next, ASIC61 executes up to S13 to set the grid current Ig and grid voltage GRID for each color. Then, while maintaining the set grid current Ig and grid voltage GRID, it creates patches and sets the development bias (S15). For example, ASIC61 applies multiple different development biases to the development roller 47 to form multiple patches (toner images to be detected by the density sensor 53) on the photoreceptor 31 and transfers them to the transport belt 23. This is done for each of the YMCK photoreceptors 31C to 31K, and the density of the transferred patches on the transport belt 23 is detected by the density sensor 53. Based on the detected density, ASIC61 sets the development bias to be applied to the development roller 47 during printing. ASIC61 then completes the process shown in Figure 6. When ASIC61 receives a print job and prints, it executes printing with the grid current Ig, grid voltage GRID, and development bias set in the process in Figure 6. This allows printing at an appropriate print density according to temperature and humidity, improving printing accuracy. Furthermore, after completing the process shown in Figure 6, ASIC61 executes the process from S1 again. As a result, each time the predetermined conditions in S1 are met, ASIC61 appropriately sets the grid current Ig, grid voltage GRID, and development bias.

[0075] Note that the content and order of each process in the flowchart shown in Figure 6 are examples and can be changed as appropriate. For example, ASIC61 does not need to perform correction of the grid voltage GRID of the other colors in S11. Also, ASIC61 may perform the setting of K in S13 before the setting of YMC in S7, or the setting of the grid current Ig and grid voltage GRID for K and YMC may be performed in parallel.

[0076] Furthermore, in S1, if at least one of the four toner cartridges 33 (one color) is replaced with a new one, the ASIC61 performs density correction control from S3 onwards, setting (adjusting) the development bias for all colors. However, the ASIC61 may also perform development bias setting only for the color whose toner cartridge 33 has been replaced.

[0077] Furthermore, the predetermined condition in S1 is not limited to the condition in which the toner cartridge 33 is replaced with a new one. For example, the predetermined condition may be the condition in which the toner cartridge 33 is replaced with another toner cartridge 33 (new or used). For example, the ASIC 61 may read the serial number information from the IC of the toner cartridge 33, and if the serial number information read is different from the serial number information read previously, it may make an affirmative judgment in S1.

[0078] Furthermore, the predetermined conditions are not limited to conditions related to the replacement of the toner cartridge 33. For example, the predetermined conditions may be conditions in which at least one of the four photoreceptors 31 is replaced. Also, the predetermined conditions are not limited to conditions for replacing parts. For example, the predetermined conditions may be conditions in which an instruction to perform density correction control is received via the touch panel 6 or the network IF7. For example, the ASIC 61 may make an affirmative decision in S1 when it receives a predetermined operation input via the touch panel 6. Alternatively, for example, the ASIC 61 may make an affirmative decision in S1 when it receives an instruction to perform density correction control from the printer driver of a PC connected to the network IF7.

[0079] Alternatively, the predetermined condition may be a condition in which the amount of operation of the process cartridge 30 exceeds a predetermined amount since the last execution of density correction control. For example, the ASIC 61 may count the number of rotations of the developing roller 47 as the amount of operation of the process cartridge 30, and make an affirmative judgment in S1 each time the number of rotations exceeds a predetermined number since the last execution of density correction control.

[0080] Furthermore, the predetermined conditions may also be conditions in which at least one of temperature and humidity changes. ASIC61 may make a positive judgment in S1 if the difference between the detected temperature and the temperature at which the previous concentration correction control was performed exceeds a predetermined first temperature range. For example, this first temperature range can be set to a range of +6°C to -6°C. In this case, ASIC61 executes S3 and subsequent steps if the temperature difference between the previous and current temperatures exceeds ±6°C.

[0081] Furthermore, ASIC61 may make a positive judgment in S1 if the difference between the detected humidity and the humidity at the time of the previous concentration correction control exceeds a predetermined first humidity range. For example, the first humidity range can be set to a range of +10% to -10%. In this case, ASIC61 executes S3 and subsequent steps if the difference between the previous and current humidity exceeds ±10%.

[0082] Furthermore, the predetermined condition may also be a condition where the predetermined number of printed pages is exceeded. For example, when printing is completed based on a print job, ASIC61 detects the number of printed pages. If the cumulative number of printed pages exceeds the predetermined number, ASIC61 may make an affirmative decision in S1. Also, the method for counting the number of printed pages may be to count the number of pages set for the print job, or it may be a method using a sheet sensor.

[0083] Furthermore, ASIC61 may make an affirmative judgment in S1 if at least one of the above-mentioned predetermined conditions (such as component replacement, user instructions, temperature changes, humidity changes, and number of printed pages) is met. Alternatively, ASIC61 may make a judgment by combining the above-mentioned predetermined conditions. For example, ASIC61 may make an affirmative judgment in S1 if two predetermined conditions from among the multiple predetermined conditions are met.

[0084] Incidentally, in the above embodiment, printer 1 is an example of an image forming apparatus. Conveyor belt 23 is an example of a belt. Touch panel 6 and network IF 7 are examples of interfaces. Process cartridges 30C to 30K are an example of a developer. Toner cartridges 33C to 33K are an example of a storage unit. Temperature and humidity sensor 54 is an example of a humidity sensor and temperature sensor. ASIC 61 is an example of a control unit. Wire voltage generation circuits 70 and 70K are examples of application units. Grid voltage adjustment circuits 81Y to 81C are examples of adjustment circuits.

[0085] As described above, this embodiment provides the following effects. (1) In the density correction control from S3 onwards in this embodiment, the ASIC61 sets the grid voltages GRID1 to GRID4 to smaller values ​​(an example of the set voltages in this application) as the humidity detected by the temperature and humidity sensor 54 increases (see Figures 4 and 5). The ASIC61 supplies wire voltages CHG and CHGK corresponding to the set values ​​from the wire voltage generation circuits 70 and 70K (S7 and S13), creates a patch, and sets the development bias (S15).

[0086] According to this method, the grid voltage GRID is set to a lower value in response to rising humidity, and wire voltages CHG and CHGK are applied according to that set value. This allows the wire voltages CHG and CHGK to be reduced in high-humidity environments, suppressing the occurrence of abnormal discharge. Furthermore, after reducing the grid voltage GRID, density correction using a patch can be performed to set the development bias. As a result, the grid voltage GRID is set according to changes in humidity, the development bias is set, and the development bias is corrected (density correction) according to toner degradation, etc., to maintain appropriate print density and enable printing.

[0087] Here, if the printer 1 is miniaturized and the charger 41 is reduced in size, the grid 43 becomes smaller, and the portion of the grid 43 that acts as an electrode facing the charging wire 42 decreases. As a result, the spatial resistance between the grid 43 and the charging wire 42 becomes relatively larger, and in order to maintain the same amount of charge as before miniaturization, it becomes necessary to increase the wire voltages CHG and CHGK. However, increasing the wire voltages CHG and CHGK makes abnormal discharge more likely. In particular, in a high-humidity environment, wire swelling occurs, and the wire voltages CHG and CHGK may become larger than the range that can be tolerated by the wire voltage generation circuit 70, 70K, potentially causing errors. In contrast, as in the printer 1 of this embodiment, by reducing the grid voltage GRID in response to the increase in humidity, it is possible to suppress the occurrence of errors in the high-voltage generation circuit even when the printer 1 is miniaturized.

[0088] (2) The ASIC61 decreases the grid voltage GRID setting as the temperature t increases (see Figures 4 and 5). This allows the grid voltage GRID to be increased in low-temperature environments where the surface potential of the photoreceptor 31 does not rise easily, thereby increasing the surface potential of the photoreceptor 31 and suppressing the occurrence of fogging. Also, as shown in Figures 4 and 5, in this embodiment, when the temperature t is the same, the ASIC61 lowers the grid voltage GRID as the humidity increases. Also, when the humidity h is the same, the ASIC61 lowers the grid voltage GRID as the temperature increases. Therefore, the ASIC61 can change the grid voltage GRID etc. in response to changes in at least one of temperature and humidity and perform density correction.

[0089] (3) The ASIC61 reduces the set value of the grid current Ig as the humidity h increases (see Figures 4 and 5). This reduces the grid current Ig in high-humidity environments where abnormal discharge is likely to occur, thereby suppressing the occurrence of abnormal discharge.

[0090] (4) The ASIC61 decreases the set value of the grid current Ig as the temperature t increases. This allows the grid current Ig to be relatively increased in low-temperature environments, increasing the surface potential of the photoreceptor 31, and then density correction using a patch to set the development bias to an appropriate value.

[0091] (5) If the ASIC61 detects a temperature and the temperature at which the previous concentration correction control was performed exceeds a first temperature range (e.g., ±6°C) (S1:YES), it may perform concentration correction control from S3 onwards. This allows concentration correction to be performed each time the temperature exceeds a predetermined first temperature range.

[0092] (6) As shown in Figures 4 and 5, the grid voltage GRID set in the concentration correction control has set values ​​every 5°C (an example of the second temperature range in this application) in the temperature range of 10°C ≤ t < 30°C. Therefore, in this embodiment, the second temperature range (5°C) can be made narrower than the first temperature range (±6°C, total 12°C). This makes it possible to suppress the frequent execution of concentration correction control.

[0093] (7) If the difference between the detected humidity and the humidity at the time of the previous concentration correction control exceeds the first humidity range (for example, ±10%) (S1:YES), the ASIC61 may perform concentration correction control from S3 onwards. This allows concentration correction to be performed each time the humidity exceeds the predetermined first humidity range.

[0094] (8) As shown in Figures 4 and 5, the grid voltage GRID set in the concentration correction control is set at intervals of 10% (an example of the second humidity range in this application) in the humidity range of 0% ≤ h < 80%. Therefore, in this embodiment, the second humidity range (10%) can be made narrower than the first humidity range (±10%, total 20%). This makes it possible to suppress the frequent execution of concentration correction control.

[0095] (9) Alternatively, the predetermined condition may be that the number of rotations of the developing roller 47 exceeds a predetermined number since the last execution of density correction control. In this case, density correction control can be performed as appropriate in accordance with the deterioration of toner due to the operation of the developing roller 47.

[0096] (10) Alternatively, the specified conditions may also be the conditions under which the toner cartridge 33 is replaced. In this case, when the toner is replaced and the characteristics of charging and development change, density correction control can be performed to maintain the print density.

[0097] (11) The predetermined conditions may also be the conditions under which the photoreceptor 31 is replaced. In this case, when the photoreceptor 31 is replaced and the characteristics of charging and development change, density correction control can be performed to maintain the print density.

[0098] (12) In addition, if the ASIC61 receives an instruction to execute concentration correction control via the touch panel 6 or network IF7 (S1:YES), it may execute the concentration correction control from S3 onwards. This allows concentration correction control to be performed as appropriate in response to instructions from the user or others.

[0099] (13) Furthermore, the ASIC61 applies a wire voltage CHG so that the smallest grid current Ig (for example, grid current Ig1) among the YMC grid currents Ig1 to Ig3 reaches a set value, and modifies the PWM signals Spp1 to Spp3 so that the grid voltage GRID of the charger 41 through which the smallest grid current Ig flows reaches a set value, and adjusts it using the grid voltage adjustment circuit 81. This ensures that the YMC grid currents Ig1 to Ig3 are reliably increased to the target value, and the surface potential of the YMC photoreceptor 31 is increased to the required potential.

[0100] (14) The ASIC61 adjusts the grid voltage GRID of all chargers 41 except the charger 41 through which the minimum grid current Ig (e.g., grid current Ig1) flows using the grid voltage adjustment circuit 81 so that the GRID of all chargers 41 except the charger 41 through which the minimum grid current Ig flows is less than a set value (S11). This makes it possible to charge the photoreceptor 31 with chargers other than the specific charger through which the minimum grid current Ig flows (e.g., chargers 41M, 41C) to the same extent as the ability to charge the photoreceptor 31 with the specific charger through which the minimum grid current Ig flows (e.g., charger 41Y).

[0101] Furthermore, the invention of this application is not limited to the above-described embodiments, and various modifications are possible without departing from its spirit. For example, in the above embodiment, an example of the present invention being applied to an image forming apparatus using positively charged toner was described, but it is not limited to this. The present invention may also be used to create an image forming apparatus using negatively charged toner. In this case, the charging voltage of the photoreceptor 31 can be changed to match the charging polarity of the toner, and its magnitude (absolute value) can be the same as in the above embodiment. Therefore, in this invention, "setting a small setting voltage" and "setting a small setting current" mean reducing the absolute values ​​of the grid voltage GRID and grid current Ig. In the above embodiment, the wire voltage CHG applied to each charged wire 42Y~42C corresponding to the three colors Y, M, and C other than K is generated by a single wire voltage generation circuit 70, and the wire voltage CHGK applied to the charged wire 42K corresponding to the color K is generated by a wire voltage generation circuit 70K independent of the wire voltage generation circuit 70. However, the embodiment is not limited to this. For example, the wire voltage CHG applied to the charged wires 42Y~42K corresponding to all four colors, including K, may be generated by a single wire voltage generation circuit 70.

[0102] Furthermore, the second temperature range may be the same size as the first temperature range (e.g., 12°C), or it may be a larger range than the first temperature range (e.g., 15°C). Furthermore, the second humidity range may be the same size as the first humidity range (for example, 20%), or it may be a larger range than the first humidity range (for example, 25%). Furthermore, in the examples shown in Figures 4 and 5, both the grid current Ig and the grid voltage GRID were set to decrease in response to rising temperature and humidity, but this is not the only option. For example, one of the grid current Ig or grid voltage GRID could be kept at a fixed value while only the other is reduced. Furthermore, printer 1 may be configured to include only one of either a temperature sensor or a humidity sensor. The ASIC 61 may then perform control to reduce the grid current Ig or grid voltage GRID based on only one of the temperature t or humidity h.

[0103] Furthermore, in the above embodiment, a transport belt 23 that transports the sheet P to which the toner image is transferred is used as the belt of the present invention, but the invention is not limited to this. For example, as the belt of the present invention, an intermediate transfer belt may be used in which the toner image is transferred to the belt itself, and the toner image transferred to the belt is further transferred to the sheet P. Furthermore, in the above embodiment, a four-color printer was used as the image forming apparatus of the present invention, but the number of colors is not limited to four; it may be five, six, or other multiple colors. Furthermore, although a color laser printer was used as an example of the image forming apparatus in the above embodiment, the present invention is not limited to this. The image forming apparatus in the present invention may also be a monochrome printer equipped only with a photoreceptor 31K corresponding to black. In the above embodiment, a printer was used as the image forming apparatus of the present invention, but it is not limited to this. The image forming apparatus of the present invention may be a copier, scanner, facsimile machine, or a multifunction device equipped with printing, scanning, and faxing functions. The control unit of this invention is not limited to application-specific ICs such as the ASIC61, but may also be a general-purpose CPU. [Explanation of Symbols]

[0104] 1 Laser printer (image forming apparatus), 6 Touch panel (interface), 7 Network IF (interface), 23 Conveyor belt (belt), 30C~30K Process cartridge (developer), 31Y~31K Photoreceptor, 33C~33K Toner cartridge (housing section), 41Y~41K Charger, 42Y~42K Charging wire, 43Y~43K Grid, 53 Density sensor, 54 Temperature and humidity sensor (humidity sensor, temperature sensor), 61 ASIC (control unit), 70,70K Wire voltage generation circuit (application section), 81Y,81M,81C Grid voltage adjustment circuit, CHG,CHGK Wire voltage, GRID1~GRID4 Grid voltage, Ig1~Ig4 Grid current, t Temperature, h Humidity.

Claims

1. Photoreceptor and A charger having a charging wire and a grid, which charges the photoreceptor, An application unit connected to the aforementioned charging wire and for applying a wire voltage to the charging wire, A developing unit that develops the electrostatic latent image formed on the photoreceptor to form a toner image, A belt in contact with the photosensitive element, A density sensor for detecting the density of the toner image formed on the belt, A humidity sensor that detects humidity, A temperature sensor that detects temperature, Control unit and Equipped with, The control unit, The toner image is formed on the belt, the density of the formed toner image is detected by the density sensor, and density correction control is performed to set the development bias to be applied to the developer during printing based on the detection result. In the density correction control described above, the setting voltage, which is a set value of the grid voltage applied to the grid, is set to a smaller value as the humidity detected by the humidity sensor increases, and the setting voltage is set to a smaller value as the temperature detected by the temperature sensor increases, and the wire voltage is applied by the application unit to form the toner image on the belt.

2. The control unit, The image forming apparatus according to claim 1, wherein in the density correction control, the setting current, which is a set value of the grid current flowing through the grid, is set to a smaller value as the humidity detected by the humidity sensor increases.

3. A photoreceptor, A charger having a charging wire and a grid, which charges the photoreceptor, An application unit connected to the aforementioned charging wire and for applying a wire voltage to the charging wire, A developing unit that develops the electrostatic latent image formed on the photoreceptor to form a toner image, A belt in contact with the photosensitive element, A density sensor for detecting the density of the toner image formed on the belt, A humidity sensor that detects humidity, A temperature sensor that detects temperature, Control unit and Equipped with, The control unit, The toner image is formed on the belt, the density of the formed toner image is detected by the density sensor, and density correction control is performed to set the development bias to be applied to the developer during printing based on the detection result. In the density correction control described above, the setting voltage, which is a set value for the grid voltage applied to the grid, is set to a smaller value as the humidity detected by the humidity sensor increases, and the setting current, which is a set value for the grid current flowing through the grid, is set to a smaller value as the temperature detected by the temperature sensor increases, and the wire voltage is applied by the application unit to form the toner image on the belt.

4. A photoreceptor, A charger having a charging wire and a grid, which charges the photoreceptor, An application unit connected to the aforementioned charging wire and for applying a wire voltage to the charging wire, A developing unit that develops the electrostatic latent image formed on the photoreceptor to form a toner image, A belt in contact with the photosensitive element, A density sensor for detecting the density of the toner image formed on the belt, A humidity sensor that detects humidity, A temperature sensor that detects temperature, Control unit and Equipped with, The control unit, The toner image is formed on the belt, the density of the formed toner image is detected by the density sensor, and density correction control is performed to set the development bias to be applied to the developer during printing based on the detection result. In the density correction control described above, as the humidity detected by the humidity sensor increases, the set voltage, which is the set value of the grid voltage applied to the grid, is set to a smaller value, and the wire voltage is applied by the application unit to form the toner image on the belt. The temperature sensor detects the temperature, and if the difference between the detected temperature and the temperature at which the concentration correction control was previously performed exceeds the first temperature range, the concentration correction control is executed. In the concentration correction control described above, the grid voltage to be set is set for each second temperature range, The second temperature range is, An image forming apparatus having a temperature range narrower than the first temperature range.

5. A photoreceptor, A charger having a charging wire and a grid, which charges the photoreceptor, An application unit connected to the aforementioned charging wire and for applying a wire voltage to the charging wire, A developing unit that develops the electrostatic latent image formed on the photoreceptor to form a toner image, A belt in contact with the photosensitive element, A density sensor for detecting the density of the toner image formed on the belt, A humidity sensor that detects humidity, Control unit and Equipped with, The control unit, The toner image is formed on the belt, the density of the formed toner image is detected by the density sensor, and density correction control is performed to set the development bias to be applied to the developer during printing based on the detection result. In the density correction control described above, as the humidity detected by the humidity sensor increases, the set voltage, which is the set value of the grid voltage applied to the grid, is set to a smaller value, and the wire voltage is applied by the application unit to form the toner image on the belt. The humidity sensor detects the humidity, and if the difference between the detected humidity and the humidity at the time the concentration correction control was previously performed exceeds the first humidity range, the concentration correction control is executed. In the concentration correction control described above, the grid voltage to be set is set for each second humidity range, The aforementioned second humidity range is, An image forming apparatus having a range narrower than the first humidity range.

6. The control unit, The image forming apparatus according to claim 1, wherein the density correction control is performed when the amount of operation of the developer exceeds a predetermined amount since the previous execution of the density correction control.

7. The aforementioned developing unit is It has a compartment for storing toner, The control unit, The image forming apparatus according to claim 1, wherein the density correction control is performed when the housing unit is replaced.

8. The control unit, The image forming apparatus according to claim 1, wherein the density correction control is performed when the photoreceptor is replaced.

9. Equipped with an interface, The control unit, The image forming apparatus according to claim 1, which performs the density correction control when it receives an instruction to perform the density correction control via the interface.

10. Multiple photoreceptors, Multiple chargers corresponding to multiple photoreceptors, The application unit applies the wire voltage to a plurality of parallel-connected charged wires, A control circuit connected to multiple grids and adjusting the grid voltage, Equipped with, The control unit, The wire voltage is applied by the application unit so that the minimum grid current among the grid currents flowing through the multiple grids reaches the target value. The image forming apparatus according to claim 1, wherein the adjustment circuit adjusts the grid voltage of a specific charger through which the minimum grid current flows to the set value.

11. The control unit, The image forming apparatus according to claim 10, wherein the adjustment circuit adjusts the grid voltage of the chargers other than the specific charger through which the minimum grid current flows so that the grid voltage of the chargers is less than the set voltage.

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