Image forming apparatus and image forming method

Abstract

To reduce the amount of toner unintendedly transferred to a transfer member.SOLUTION: An image forming apparatus applies a normal transfer bias to a transfer area between an image carrier 105 and a transfer member 108 to transfer a toner image on the image carrier to a recording material passing through the transfer area, thereby forming an image on the recording material. The image forming apparatus has reverse transfer bias application means that applies a reverse transfer bias having a polarity opposite to that of the normal transfer bias at a predetermined timing, and toner adhesion amount detection means 109 that detects the amount of toner adhered onto the image carrier. The image forming apparatus corrects the reverse transfer bias applied by the reverse transfer bias application means at a predetermined correction timing based on a detection result from the toner adhesion amount detection means obtained by detecting the amount of toner adhered to a predetermined toner pattern 205 for condition correction after passing through the transfer area to which the predetermined reverse transfer bias is applied.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and an image forming method.

Background Art

[0002] Conventionally, an image forming apparatus that forms an image on a recording material by applying a normal transfer bias to a transfer region between an image carrier and a transfer member and transferring a toner image on the image carrier onto the recording material passing through the transfer region is known.

[0003] For example, Patent Document 1 discloses an image forming apparatus in which a secondary transfer bias (normal transfer bias) having a polarity opposite to the normal charging polarity of toner is applied to a secondary transfer outer roller (transfer member) that forms a secondary transfer portion (transfer region) with an intermediate transfer belt (image carrier). In this image forming apparatus, a reverse transfer bias having a polarity opposite to that of the secondary transfer bias is applied in an inter-image region (inter-sheet region) for the purpose of preventing unintentional transfer of toner from the intermediate transfer belt to the secondary transfer outer roller and suppressing toner staining on the back surface of the transfer material (recording material).

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a conventional image forming apparatus, there are cases where the transfer of toner from the image carrier to the transfer member (unintentional transfer of toner) cannot be sufficiently suppressed.

Means for Solving the Problems

[0005] In order to solve the above-described problems, the present invention is an image forming apparatus that forms an image on a recording material by applying a normal transfer bias to a transfer region between an image carrier and a transfer member and transferring a toner image on the image carrier onto the recording material passing through the transfer region, and applies a reverse transfer bias having a polarity opposite to that of the normal transfer bias at a predetermined timing. In the aforementioned transfer regionThe system includes a reverse transfer bias application means for applying a reverse transfer bias and a toner adhesion amount detection means for detecting the amount of toner adhered on the image carrier. At a predetermined correction timing, the system corrects the reverse transfer bias applied by the reverse transfer bias application means based on the detection result obtained by the toner adhesion amount detection means, which detects the amount of toner adhered to a predetermined condition correction toner pattern after it has passed through the transfer region where a reverse bias with the opposite polarity to the normal transfer bias has been applied. [Effects of the Invention]

[0006] According to the present invention, even in situations where the transfer of toner from the image carrier to the transfer member cannot be sufficiently suppressed, the amount of toner transferred to the transfer member can be suppressed by modifying the bias conditions of the reverse transfer bias. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing the image formation process section (process engine section) of the printer according to the embodiment, which performs exposure, charging, development, transfer, and fixing. [Figure 2] This diagram illustrates the configuration of the image forming unit that forms the black toner image in the printer. [Figure 3] A perspective view of the intermediate transfer belt in the same printer. [Figure 4] A schematic diagram of the P / TM sensor in the printer. [Figure 5] A block diagram showing the electrical connections of each component of the printer. [Figure 6] A flowchart showing an example of toner ejection control (pattern creation process) in an embodiment. [Figure 7] (a) and (b) are explanatory diagrams showing examples of test patterns formed on the intermediate transfer belt in the embodiment. [Figure 8] A flowchart showing an example of reverse transcription bias correction control in an embodiment. [Figure 9](a) is a timing chart showing the state of the electrostatic latent image writing operation, and (b) is a timing chart showing the state of the applied bias in the secondary transfer section. [Figure 10] This graph shows the relationship between the bias conditions of the reverse transfer bias applied to the seven pattern sections that make up the test pattern, and the amount of toner deposited on each pattern section as detected by the P / TM sensor. [Figure 11] This graph shows the relationship between the bias conditions of the reverse transfer bias applied to the seven pattern sections that make up the test pattern, and the amount of toner deposited on the secondary transfer roller. [Modes for carrying out the invention]

[0008] The following describes one embodiment in which the present invention is applied to a printer as an image forming apparatus. Furthermore, the present invention is not limited to printers, as it is an image forming apparatus that applies a normal transfer bias to the transfer region between the image carrier and the transfer member, thereby transferring the toner image on the image carrier onto the recording material passing through the transfer region and forming an image on the recording material. For example, the present invention is also applicable to image forming apparatuses such as copiers, facsimile machines, and multifunction printers.

[0009] Figure 1 is a schematic diagram showing the image formation process section (process engine section) of the printer 100 in this embodiment, which performs exposure, charging, development, transfer, and fixing. In addition to the components shown in Figure 1, the printer 100 is equipped with a print controller that processes image data sent from a PC (personal computer) and converts it into exposure data, a high-voltage generator that generates high voltage, and a main unit control that controls the image formation operation. The printer 100 is also equipped with a paper feeder that supplies transfer paper 115 as recording material, a manual feed tray for manually feeding the transfer paper 115, and an output tray for ejecting the image-formed transfer paper 115.

[0010] In Figure 1, the printer 100 is equipped with an endless belt-shaped intermediate transfer belt 105, which serves as an intermediate transfer body for image carrying, and a primary transfer device 106. This intermediate transfer belt 105 has a three-layer structure consisting of a base layer, an elastic layer, and a coating layer. The base layer is composed of, for example, a fluororesin with low elongation, or a rubber material with high elongation combined with a material that does not stretch easily, such as canvas.

[0011] Furthermore, the elastic layer is composed of, for example, fluororubber or acrylonitrile-butadiene copolymer rubber and is formed on the base layer. The coating layer is formed by coating the surface of the elastic layer with, for example, a fluororesin. The intermediate transfer belt 105 is rotated by the support roller 112, which functions as a drive roller, while being stretched over four support rollers 112, 113, 114, and 119.

[0012] Four image forming units for yellow (Y), cyan (C), magenta (M), and black (K) are arranged on the tensioned portion of the intermediate transfer belt 105. The four image forming units for each color have the same configuration and are made of the same components. In Figure 1, the same components are represented by the same number in the numerical part, and the color identification code Y (yellow), C (cyan), M (magenta), and K (black) is added to the end. Photoreceptor units 103Y, 103C, 103M, and 103K and developing units 102Y, 102C, 102M, and 102K are arranged side by side in each image forming unit. Toner is supplied to the developing units 102Y, 102C, 102M, and 102K from toner bottles 104K, 104Y, 104C, and 104M.

[0013] Below these image forming units, an exposure device 200 is provided. The exposure device 200 drives a semiconductor laser from a laser exposure unit provided inside the exposure device 200 based on image information to emit writing light Lb. Then, the exposure device 200 forms an electrostatic latent image on the photosensitive drums 101Y, 101C, 101M, and 101K as latent image carriers provided in each photosensitive unit. Here, the emission of the writing light Lb is not limited to a laser, and for example, an LED (light emitting diode) may be used.

[0014] Next, the configuration of the image forming unit will be described. FIG. 2 is an explanatory diagram showing the configuration of an image forming unit that forms a black toner image. Hereinafter, an image forming unit that forms a black toner image will be described as an example, but image forming units that form toner images of other colors have the same configuration.

[0015] In FIG. 2, the constituent members of the image forming unit for black toner originally have a symbol with K at the end of the symbol, but are shown here with omission. In this image forming unit, around the photosensitive drum 101, a charging device 301 for charging the photosensitive drum, a developing device 102, and a photosensitive cleaning device 308 are provided. Also, at a position facing the photosensitive drum 101 via an intermediate transfer belt 105, a primary transfer device 106 is provided.

[0016] The charging device 301 employs a contact charging method using a charging roller, and uniformly charges the surface of the photosensitive drum 101 by applying a voltage while contacting the photosensitive drum 101. For this charging device 301, a non-contact charging method using a non-contact scorotron charger or the like can also be employed.

[0017] Also, in the developing device 102, a two-component developer composed of a magnetic carrier and a non-magnetic toner is used. Note that a one-component developer may be used as the developer. This developing device 102 can be roughly divided into a stirring unit 303 and a developing unit 304 provided in a developing case. In the stirring unit 303, a two-component developer (hereinafter simply referred to as "developer") is conveyed while being stirred and supplied onto a developing sleeve 305 as a developer carrier.

[0018] Two parallel screws 306 are provided in this stirring unit 303. Between these two screws 306, a partition plate for partitioning so that both ends communicate with each other is provided. Further, a toner concentration sensor 418 for detecting the toner concentration of the developer in the developing device 102 is attached to the developing case. On the other hand, in the developing unit 304, the toner among the developer attached to the developing sleeve 305 is transferred to the photosensitive drum 101.

[0019] The developing unit 304 is provided with a developing sleeve 305 facing the photosensitive drum 101 through an opening of the developing case, and a magnet is fixedly arranged in the developing sleeve 305. Further, a doctor blade 307 is provided so that its tip approaches the developing sleeve 305.

[0020] In this developing device 102, the developer is conveyed and circulated while being stirred by two screws 306 and supplied to the developing sleeve 305. The developer supplied to the developing sleeve 305 is pumped up and held by a magnet. The developer pumped up to the developing sleeve 305 is conveyed as the developing sleeve 305 rotates and is regulated to an appropriate amount by the doctor blade 307. The regulated developer is returned to the stirring unit 303. The developer thus conveyed to the developing area facing the photosensitive drum 101 stands up by the magnet to form a magnetic brush.

[0021] In the developing area, a developing electric field is created by the developing bias applied to the developing sleeve 305, which moves the toner in the developer to the electrostatic latent image area on the photoreceptor drum 101. As a result, the toner in the developer is transferred to the electrostatic latent image area on the photoreceptor drum 101, the electrostatic latent image on the photoreceptor drum 101 becomes a visible image, and a toner image is formed. The developer that has passed through the developing area is transported to the area where the magnetic force of the magnet is weak, away from the developing sleeve 305, and returned to the agitator 303. When the toner concentration in the agitator 303 becomes low due to the repetition of this operation, the toner concentration sensor 418 detects this and replenishes the agitator 303 with toner based on the detection result.

[0022] The primary transfer device 106 employs a primary transfer roller and is installed so as to press it against the photoreceptor drum 101 with the intermediate transfer belt 105 in between. The ends of the primary transfer roller are in contact with the intermediate transfer belt 105 in Figure 3 over a portion of the belt width corresponding to the maximum width of the transfer paper 115 (maximum paper feed width) 203.

[0023] The primary transfer device 106 does not have to be roller-shaped; it may also be conductive brush-shaped or a non-contact corona charger. The maximum paper feed width 203 is set so that the longest transfer paper (the transfer paper used to feed the largest amount of paper horizontally) in the direction perpendicular to the rotation direction of the intermediate transfer belt is sandwiched between the primary transfer device 106 and the intermediate transfer belt 105.

[0024] The photoreceptor cleaning device 308 includes a cleaning blade 309, for example, made of polyurethane rubber, positioned so that its tip is pressed against the photoreceptor drum 101. In this embodiment, a conductive fur brush 310 that contacts the photoreceptor drum 101 is also used to enhance cleaning performance.

[0025] A bias is applied to the fur brush 310 from a metal electric field roller, and the tip of a scraper is pressed against the electric field roller. The toner removed from the photoreceptor drum 101 by the cleaning blade 309 and the fur brush 310 is then collected inside the photoreceptor cleaning device 308 and recovered by the waste toner recovery device.

[0026] In the image forming unit with the above configuration, as the photoreceptor drum 101 rotates, the surface of the photoreceptor drum 101 is first uniformly charged by the charging device 301. Next, based on image information from the print controller, a laser writing light Lb is irradiated from the exposure device 200 to form an electrostatic latent image on the photoreceptor drum 101. After that, the electrostatic latent image is made visible by the developing device 102 to form a toner image.

[0027] This toner image is first transferred onto the intermediate transfer belt 105 by the primary transfer device 106. After the primary transfer, any remaining toner on the surface of the photoreceptor drum 101 is removed by the photoreceptor cleaning device 308 and used for the next image formation.

[0028] A secondary transfer roller 108 is provided as a transfer member at a position opposite the support roller 112, with the intermediate transfer belt 105 in between. The secondary transfer roller 108 transfers the toner image formed on the intermediate transfer belt 105 to the transfer paper by electrostatic force. When performing secondary transfer of the toner image on the intermediate transfer belt 105 to the transfer paper 115, the secondary transfer roller 108 is pressed against the portion of the intermediate transfer belt 105 wound around the support roller 112 to perform the secondary transfer. The secondary transfer device does not necessarily have to use a secondary transfer roller 108; it may also use other transfer members, such as a transfer belt.

[0029] The belt width of the intermediate transfer belt 105 is greater than the axial length of the secondary transfer roller 108, and the maximum paper feed width 203 is less than or equal to the axial length of the secondary transfer roller 108.

[0030] In Figure 1, a fixing device 111 is provided downstream of the secondary transfer roller 108 in the direction of transporting the transfer paper 115, for fixing the toner image transferred onto the transfer paper 115. This fixing device 111 is configured by pressing a pressure roller 118 against a heating roller 117.

[0031] A photosensor (hereinafter referred to as "P / TM sensor") 109, which serves as a toner adhesion amount detection means for detecting the amount of toner adhered to the toner pattern, is provided in the axial center of the support roller 112 at a position opposite the support roller 112 with the intermediate transfer belt 105 in between. A belt cleaning device 110 is provided at a position opposite the support roller 113 with the intermediate transfer belt 105 in between. This belt cleaning device 110 removes residual toner remaining on the intermediate transfer belt 105 after the toner image on the intermediate transfer belt 105 has been transferred to the transfer paper 115 using a cleaning blade 110a.

[0032] Figure 4 is a schematic diagram of the P / TM sensor 109. The P / TM sensor 109 of this embodiment has one light-emitting element and two light-receiving elements. The light-emitting element is an infrared LED 602. The two light-receiving elements are a specular reflection light-receiving element 603 and a diffuse reflection light-receiving element 604, which are provided at two locations on the intermediate transfer belt 105: one where specularly reflected light can be received and another where specularly reflected light cannot be received. A laser light-emitting element or the like may be used instead of the infrared LED.

[0033] Phototransistors are used as the specular reflecting light-receiving element 603 and the diffuse reflecting light-receiving element 604, but amplified photodiodes may also be used. A focusing lens 605 is provided in the middle of the optical path. In this configuration, both the specular reflecting light-receiving element 603 and the diffuse reflecting light-receiving element 604 are provided as light-receiving elements, but depending on the object to be detected and the information required, only one of them may be used.

[0034] Figure 5 is a block diagram showing the electrical connections of each part of the printer 100 in this embodiment. The printer 100 of this embodiment is equipped with a computer-configured main unit control unit 406, which controls each part. The main unit control unit 406 is configured by connecting a CPU (Central Processing Unit) 402, which performs various calculations and drive control of each part, to a ROM (Read Only Memory) 405 that stores fixed data such as computer programs in advance, and a RAM (Random Access Memory) 403 that functions as a work area for storing various data in a rewritable manner, via a bus line 409.

[0035] ROM405 stores information on the formation position and density of the toner pattern (toner deposition amount information), bias conditions for forming the gradation of the toner pattern, and a conversion LUT (Look Up Table) for converting the output of the P / TM sensor 109, which estimates the amount of toner deposited, into the amount of toner deposited.

[0036] The main control unit 406 is connected to a print controller 410, which transmits image information from PCs, fax machines, scanners, etc., to the main control unit 406 as unified image data. The A / D conversion circuit 401, which converts various sensor information into digital data, a drive circuit that drives motors and clutches, and a high-voltage generator that generates the voltage necessary for image formation are also connected to the main control unit 406.

[0037] Next, the operation of the printer 100 in this embodiment will be described. When printing using the printer 100 with the above configuration based on information from a PC, first, the printer driver on the PC is used to send a print command and image information. The print controller 410 receives the print command from the printer driver, starts the print job, processes the image information as needed, and then sends it to the main unit control 406. When the print job starts, the main unit control 406 drives the drive motor, causing the support roller 112 to rotate and the intermediate transfer belt 105 to rotate. At the same time, the main unit control 406 also drives the photoreceptor drums 101Y, 101C, 101M, and 101K of each image forming unit to rotate.

[0038] Subsequently, the main control unit 406 sends an exposure signal to the exposure unit 200 based on the image information from the print controller. The exposure unit 200 irradiates the photoreceptor drums 101Y, 101C, 101M, and 101K of each image forming unit with writing light Lb based on the exposure signal. As a result, electrostatic latent images are formed on each photoreceptor drum 101Y, 101C, 101M, and 101K, and these are made visible by the developing units 102Y, 102C, 102M, and 102K. Then, toner images of yellow, cyan, magenta, and black are formed on each photoreceptor drum 101Y, 101C, 101M, and 101K, respectively.

[0039] The toner images of each color formed in this manner are then sequentially transferred onto the intermediate transfer belt 105 by the respective primary transfer devices 106Y, 106C, 106M, and 106K, so that they overlap. As a result, a composite toner image is formed on the intermediate transfer belt 105, in which the toner images of each color overlap. Any remaining toner on the intermediate transfer belt 105 after secondary transfer is removed by the belt cleaning device 110.

[0040] Furthermore, the main unit control unit 406 rotates the paper feed roller of the paper feed device according to the transfer paper 115 selected by the user, and feeds the transfer paper 115 from one of the paper cassettes. The fed-out transfer paper 115 is separated into single sheets by the separation roller and enters the paper feed path, and is transported by the transport roller to the transport path inside the printer body. The transported transfer paper 115 is stopped when it comes into contact with the registration roller 107.

[0041] When using transfer paper 115 that is not set in the paper cassette, the transfer paper 115 set in the manual feed tray is fed out by the paper feed roller, separated into single sheets by the separation roller, and then transported through the manual feed path. It is then stopped when it comes into contact with the registration roller 107.

[0042] The registration roller 107 starts rotating in sync with the timing when the composite toner image formed on the intermediate transfer belt 105 as described above is transported to the secondary transfer section (transfer area) facing the secondary transfer roller 108. Here, the registration roller 107 is generally used in a grounded state, but a bias may be applied to remove paper dust from the transfer paper 115.

[0043] The transfer paper 115, fed by the registration roller 107, is placed between the intermediate transfer belt 105 and the secondary transfer roller 108. The secondary transfer roller 108 then transfers the composite toner image from the intermediate transfer belt 105 onto the transfer paper 115. The transfer paper 115 is then transported to the fuser unit 111 while held in place by the secondary transfer roller 108, where heat and pressure are applied to fix the toner image. After passing through the fuser unit 111, the transfer paper 115 is discharged to the output tray by the discharge roller and stacked.

[0044] Furthermore, if image formation is to be performed on the back side of the surface where the toner image has been fixed, the transport direction of the transfer paper 115 that has passed through the fixing device 111 is switched by a switching claw and sent to the paper reversal device. The transfer paper 115 is then reversed and guided again to the secondary transfer roller 108.

[0045] Next, the toner ejection control performed by the CPU 402 of this embodiment based on a computer program will be described. In this embodiment, toner is input to the belt cleaning device 110 of the intermediate transfer belt 105, and toner ejection control is performed to ensure adhesion through the dam effect and reduce friction, thereby suppressing problems such as poor cleaning and blade peeling.

[0046] In toner ejection control, for example, as shown in Figure 3, a long toner pattern 201 is formed on the intermediate transfer belt 105 in the belt width direction (main scanning direction). Then, this toner pattern 201 is moved to the belt cleaning device 110 and input to the belt cleaning device 110. In this embodiment, it is preferable that the toner pattern 201 extends across the contact width 202 of the cleaning blade 110a of the belt cleaning device 110, as shown in Figure 3. This allows toner to be input across the entire contact width 202 of the cleaning blade 110a.

[0047] The timing of toner ejection control is generally performed after the completion of a print job, but it may be performed at a different time. For example, it may be performed after the print command is entered (after the print job starts).

[0048] Furthermore, if the system is left idle without a print job being generated (without image formation operation), the amount of toner present in the belt cleaning device 110 tends to become unevenly distributed in the belt width direction (main scanning direction) of the intermediate transfer belt 105, increasing the risk of the aforementioned problems occurring. To avoid this, it is preferable to perform toner ejection control after the print command is input (after the print job starts). However, if toner ejection control is performed after the print command is input (after the print job starts), the image formation operation cannot start until the toner ejection control is completed, resulting in a problem where the first print time is delayed.

[0049] Therefore, in this embodiment, the timing of toner ejection control is set to occur after the input of the print command (after the start of the print job), but the toner pattern is formed immediately before the first image to be formed. By forming the toner pattern immediately before the first image to be formed in this way, the delay in the first print time caused by the execution of toner ejection control can be suppressed.

[0050] Figure 6 is a flowchart showing an example of toner ejection control (pattern creation process) in this embodiment. The main control unit 406 determines whether to perform toner ejection control at the timing of receiving a print command and starting a print job. Specifically, first, the CPU 402 executes the toner ejection control execution program and obtains the current travel distance stored in the ROM 405 (S101). This current travel distance is information indicating the amount of movement of the secondary transfer roller 108 and corresponds to the surface travel distance of the secondary transfer roller 108. For example, this current travel distance can be a value obtained by multiplying the cumulative time of the image forming operation (cumulative operating time of the secondary transfer roller 108) by the circumference of the secondary transfer roller 108.

[0051] Next, the CPU 402 uses the information on the travel distance at the time of the previous execution, which was stored in the ROM 405 during the previous execution of toner ejection control (when the previous toner pattern was formed), to calculate the change in travel distance ΔD1 from the time of the previous execution of toner ejection control to the present (S102). After that, the CPU 402 determines whether the calculated change in travel distance ΔD1 exceeds the execution determination threshold DC (S103).

[0052] In this determination, if the calculated change in travel distance ΔD1 does not exceed the execution determination threshold DC (No. in S103), the CPU 402 determines that toner ejection control is unnecessary and performs image formation operations according to the print job.

[0053] On the other hand, if the calculated change in travel distance ΔD1 exceeds the execution determination threshold DC (Yes in S103), the CPU 402 determines that toner ejection control is required and functions as a pattern formation processing means. The CPU 402 then performs an operation to form a predetermined toner pattern 201 as shown in Figure 3 (S104). This toner pattern 201 is formed, for example, with a single-color toner from any one of the image forming units, but it may also be formed with two or more toners. The toner pattern 201 formed on the intermediate transfer belt 105 by the image forming unit in this way passes through the secondary transfer section and is input to the belt cleaning device 110.

[0054] Furthermore, if the calculated change in mileage ΔD1 exceeds the execution decision threshold DC (Yes in S103), the CPU 402 saves the current mileage obtained in processing step S101 as the mileage at the time of the previous execution in the ROM 405 (S105). Subsequently, the CPU 402 performs image formation operations according to the print job so that the first image of the print job is formed immediately after the toner pattern 201.

[0055] Here, in order for the toner pattern formed on the intermediate transfer belt 105 to be input to the belt cleaning device 110, the toner pattern must pass through the secondary transfer section. Since the transfer paper 115 is not present in the secondary transfer section during this passage, some of the toner that makes up the toner pattern (toner not intended to be transferred to the secondary transfer roller) may adhere to the secondary transfer roller 108. If toner adheres to the secondary transfer roller 108, that toner will then adhere to the back surface of the transfer paper 115 that is subsequently transported to the secondary transfer section, soiling the back surface of the transfer paper 115.

[0056] Furthermore, if there is a means for bringing the intermediate transfer belt 105 and the secondary transfer roller 108 into contact and separate them, it is possible to separate the intermediate transfer belt 105 and the secondary transfer roller 108 when the toner pattern passes through the secondary transfer section, thereby suppressing toner adhesion to the secondary transfer roller 108. However, if the toner pattern is formed immediately before the first image formed in the print job, the means for bringing the toner pattern into contact cannot return the separated state to a contact state during the period between when the toner pattern passes through the secondary transfer section and when the composite toner image related to the first image enters the secondary transfer section. If it were possible to return the separated state to a contact state during this period, the toner pattern would need to be formed considerably earlier than the first image formed, and the delay in the first print time could not be suppressed.

[0057] Therefore, in this embodiment, during the period when the toner pattern formed on the intermediate transfer belt 105 passes through the secondary transfer section, a reverse transfer bias with the opposite polarity to the secondary transfer bias during the image formation operation is applied to the secondary transfer section. As a result, when the toner pattern on the intermediate transfer belt 105 passes through the secondary transfer section, a force toward the intermediate transfer belt 105 side (a force in the reverse transfer direction) acts on the normally charged toner constituting the toner pattern. Consequently, adhesion of the toner constituting the toner pattern to the secondary transfer roller 108 is suppressed, and soiling of the back surface of the transfer paper 115 can be suppressed.

[0058] However, in order to properly suppress the adhesion of toner (toner) constituting the toner pattern to the secondary transfer roller 108, it is necessary to apply a reverse transfer bias under appropriate bias conditions, but the optimal bias conditions for the reverse transfer bias can change over time. For example, when environmental changes such as temperature and humidity occur, the amount of charge on the toner changes, and so on, the optimal bias conditions for the reverse transfer bias to keep as much toner (toner) constituting the toner pattern as possible towards the intermediate transfer belt 105 side will change. Also, when the characteristics of the secondary transfer roller 108 (electrical resistance value, etc.) change due to wear of the secondary transfer roller 108 as it operates over time, the state of the electric field formed in the secondary transfer section by the reverse transfer bias changes. As a result, the optimal bias conditions for the reverse transfer bias to keep as much toner (toner) constituting the toner pattern as possible towards the intermediate transfer belt 105 side will change.

[0059] Therefore, in this embodiment, reverse transfer bias correction control is performed to correct the optimal bias conditions of the reverse transfer bias at a predetermined bias condition correction timing. Specifically, a test pattern, which serves as a toner pattern for predetermined condition correction, is projected onto the intermediate transfer belt 105. The amount of toner deposited on the test pattern after it has passed through a transfer region where a reverse transfer bias of predetermined bias conditions is applied is detected by the P / TM sensor 109. Based on this detection result, the bias conditions of the reverse transfer bias applied when the toner pattern 201 formed by the toner ejection control described above passes through the secondary transfer section are corrected.

[0060] Figures 7(a) and 7(b) are explanatory diagrams showing an example of a test pattern formed on the intermediate transfer belt 105 in this embodiment. Figure 8 is a flowchart showing an example of reverse transcription bias correction control in this embodiment. In this embodiment, the reverse transfer bias correction control is performed when the printer is powered on and after the print job is completed, but other timings may also be used.

[0061] When the timing for executing reverse transcription bias correction control arrives, the main control unit 406 first determines whether or not to execute reverse transcription bias correction control. A high frequency of executing reverse transcription bias correction control (frequency of test pattern formation) increases the risk of downtime. Therefore, in order to minimize the frequency of executing reverse transcription bias correction control, it is preferable to execute reverse transcription bias correction control (test pattern formation) only at times when a change in the optimal bias conditions for reverse transcription bias may occur.

[0062] Therefore, in this embodiment, the timing at which a change in the optimal bias conditions for reverse transfer bias may occur is determined as follows. Specifically, the main control unit 406 determines the timing at which a temperature change of more than or equal to a temperature change threshold T has occurred from the temperature at the time of the previous test pattern formation, the timing at which a humidity change of more than or equal to a humidity change threshold H has occurred from the humidity (which may be either relative humidity or absolute humidity) at the time of the previous test pattern formation, and the timing at which the travel distance (amount of operation of the secondary transfer roller 108) has traveled more than or equal to a travel distance threshold D2 from the travel distance (amount of operation of the secondary transfer roller 108) at the time of the previous test pattern formation. The main control unit 406 then determines that it is necessary to execute transfer bias correction control when any one of these timings has occurred. Note that the travel distance (amount of operation) of the secondary transfer roller 108 may be replaced with other information such as the number of sheets passed or the operating time, as long as it is equivalent information.

[0063] When the timing for executing reverse transfer bias correction control arrives, the CPU 402 executes the reverse transfer bias correction control execution program. The CPU 402 first obtains information on the current temperature and humidity from the temperature and humidity sensor 414, and also obtains the current travel distance stored in the ROM 405 (S201). This current travel distance is information indicating the amount of movement of the secondary transfer roller 108, and corresponds to the surface travel distance of the secondary transfer roller 108. It is the same information used to determine whether or not to execute the toner ejection control described above.

[0064] Next, the CPU 402 retrieves the information stored in the ROM 405 during the previous execution of reverse transfer bias correction control (during the previous test pattern formation), including the temperature, humidity, and mileage at the time of the previous execution. Then, using this information, the CPU 402 calculates the changes in each of these amounts from the time of the previous reverse transfer bias correction control execution to the present, namely the temperature change ΔT, the humidity change ΔH, and the mileage change ΔD2 (S202).

[0065] Subsequently, the CPU 402 determines whether the calculated temperature change ΔT, humidity change ΔH, and travel distance change ΔD2 exceed the temperature change threshold T, humidity change threshold H, and travel distance change threshold D2, respectively (S203). These thresholds T, H, and D2 are set experimentally, for example, based on changes in the characteristics of the secondary transfer roller 108.

[0066] In this determination, if none of the temperature change ΔT, humidity change ΔH, or distance change ΔD2 exceed the corresponding thresholds T, H, and D2 (No. in S203), the CPU 402 determines that reverse transfer bias correction control is unnecessary. As a result, the reverse transfer bias correction control is terminated without forming a test pattern, and the currently set bias conditions for the reverse transfer bias remain unchanged.

[0067] On the other hand, if any of the temperature change ΔT, humidity change ΔH, or distance change ΔD2 exceeds the corresponding thresholds T, H, or D2 (Yes in S203), the CPU 402 determines that reverse transfer bias correction control is necessary. The CPU 402 then functions as a bias condition correction means and performs an operation to form a predetermined test pattern 205 as shown in Figure 7 (S204).

[0068] As shown in Figure 7, the test pattern 205 in this embodiment is composed of seven pattern sections arranged in the surface movement direction (sub-scanning direction) of the intermediate transfer belt 105. In this embodiment, the bias conditions of the reverse transfer bias applied when each pattern section passes through the secondary transfer section are made different.

[0069] Figure 9(a) is a timing chart showing the state of the electrostatic latent image writing operation. Figure 9(b) is a timing chart showing the applied bias state of the secondary transfer section. If the CPU 402 determines that it is necessary to perform reverse transfer bias correction control (Yes in S203), it performs the writing operation of the test pattern 205 after the writing operation of the last image of the print job is completed, as shown in Figure 9(a). Then, as the test pattern 205, which has been developed from this electrostatic latent image and primary transferred onto the intermediate transfer belt 105, passes through the secondary transfer section, the CPU 402 applies a reverse transfer bias according to predetermined bias conditions, as shown in Figure 9(b). That is, in this embodiment, a reverse transfer bias with a different bias value is applied to each of the seven pattern sections that make up the test pattern 205, as shown in Figure 9(b).

[0070] Subsequently, the amount of toner adhering to the seven pattern areas of the test pattern 205 is detected from the output of the P / TM sensor 109 when the test pattern 205, which has passed through the secondary transfer section, passes through the P / TM sensor 109 (S204).

[0071] Next, the CPU 402 determines the bias conditions for the reverse transfer bias used during toner ejection control, based on the amount of toner deposited in the seven pattern sections of the test pattern 205, as detected by the P / TM sensor 109. Specifically, the CPU 402 calculates the bias conditions (reverse transfer bias bias value) that result in the largest amount of toner deposited in the seven pattern sections of the test pattern 205 (S205).

[0072] Figure 10 is a graph showing the relationship between the bias conditions of the reverse transfer bias applied to the seven pattern sections constituting the test pattern 205 and the amount of toner deposited on each pattern section detected by the P / TM sensor 109. Figure 11 is a graph showing the relationship between the bias conditions of the reverse transfer bias applied to the seven pattern sections constituting the test pattern 205 and the amount of toner deposited on the secondary transfer roller 108.

[0073] The amount of toner deposited on the test pattern 205 after passing through the secondary transfer section with a predetermined reverse transfer bias applied is the amount of toner deposited on the test pattern 205 before passing through the secondary transfer section minus the amount of toner deposited on the secondary transfer roller 108. Therefore, among the bias conditions of the reverse transfer bias applied to the seven pattern sections of the test pattern 205, the bias condition corresponding to the pattern section with the largest amount of toner deposited after passing through the secondary transfer section can be estimated to be the condition closest to the optimal bias condition.

[0074] In this embodiment, the CPU 402 sets the bias conditions corresponding to the pattern section with the largest amount of toner deposited after passing through the secondary transfer section as the bias conditions for the reverse transfer bias used during toner ejection control (S206), and stores them in the ROM 405. Therefore, when toner ejection control is executed again in the future, the bias conditions stored in the ROM 405 by the reverse transfer bias correction control are used as the bias conditions for the reverse transfer bias applied when the formed toner pattern 201 passes through the secondary transfer section. As a result, even if the bias conditions for the reverse transfer bias deviate from the optimal conditions, the reverse transfer bias correction control corrects the bias conditions to the optimal conditions, and toner adhesion from the toner pattern 201 to the secondary transfer roller 108 can be suppressed.

[0075] In this embodiment, toner adheres to the secondary transfer roller 108 when the test pattern 205 passes through the secondary transfer section, so a cleaning operation for the secondary transfer roller 108 is also performed (S208). Specifically, with the reverse transfer bias applied under the bias conditions set in processing step 206, the secondary transfer roller 108 is rotated idle for, for example, two turns. As a result, the toner adhering to the secondary transfer roller 108 is reverse-transferred to the intermediate transfer belt 105 side by the reverse transfer bias and recovered by the belt cleaning device 110.

[0076] Furthermore, if the CPU 402 determines that it is necessary to perform reverse transfer bias correction control, it saves the current temperature, current humidity, and current mileage obtained in processing step S201 to the ROM 405 as the temperature, humidity, and mileage at the time of the previous execution (S208).

[0077] Furthermore, if environmental conditions such as temperature and humidity change excessively, or if the characteristics of the secondary transfer roller 108 change excessively, even if the bias conditions of the reverse transfer bias are optimized, it may not be possible to sufficiently suppress toner adhesion to the secondary transfer roller 108. In such cases, even if the bias conditions of the reverse transfer bias are set to optimal conditions, each time the toner pattern 201 is formed during toner ejection control, toner will adhere to the secondary transfer roller 108, causing staining on the back side of the transfer paper 115. Therefore, in such situations, it is preferable not to perform toner ejection control.

[0078] Whether or not this situation has occurred can be determined, for example, if a means for bringing the intermediate transfer belt 105 and the secondary transfer roller 108 into contact with and separating them is provided, as follows: At a predetermined timing, a comparison toner pattern is projected onto the intermediate transfer belt 105. Then, the amount of toner deposited on the comparison toner pattern after it has passed through the secondary transfer section in a state where the intermediate transfer belt 105 and the secondary transfer roller 108 are separated by the means for bringing the intermediate transfer belt 105 and the secondary transfer roller 108 is detected by the P / TM sensor 109 and stored. Next, the reverse transfer bias described above is... correctionAfter executing the control and determining the bias conditions (bias value of the reverse transfer bias) for the pattern section with the highest toner adhesion, the difference between this highest toner adhesion and the toner adhesion of a saved comparison toner pattern is calculated. If this difference is greater than or equal to a predetermined toner adhesion amount, it is determined that optimizing the reverse transfer bias conditions will no longer be sufficient to suppress toner adhesion to the secondary transfer roller 108. As a result, toner ejection control is not executed thereafter, even when the toner ejection control execution timing (predetermined pattern creation timing) arrives.

[0079] The above is just one example; each of the following embodiments produces its own unique effects. [First aspect] The first embodiment is an image forming apparatus (e.g., printer 100) that applies a normal transfer bias (e.g., secondary transfer bias) to a transfer region (e.g., secondary transfer section) between an image carrier (e.g., intermediate transfer belt 105) and a transfer member (e.g., secondary transfer roller 108), thereby transferring the toner image on the image carrier onto a recording material (e.g., transfer paper 115) passing through the transfer region, and includes a reverse transfer bias application means that applies a reverse transfer bias having the opposite polarity to the normal transfer bias at a predetermined timing (e.g., the timing when the toner pattern 201 passes through the transfer region). The system is characterized by comprising: (for example, a high-pressure generator 416); toner adhesion amount detection means (for example, a P / TM sensor 109) for detecting the amount of toner adhesion on the image carrier; and bias condition correction means (for example, a main unit control unit 406) for correcting the bias conditions of the reverse transfer bias applied by the reverse transfer bias application means, based on the detection result obtained by the toner adhesion amount detection means from detecting the amount of toner adhesion on a predetermined condition correction toner pattern (for example, a test pattern 205) after it has passed through the transfer region in which a predetermined reverse transfer bias has been applied, at a predetermined bias condition correction timing. When applying a reverse transfer bias to the transfer area to suppress toner transfer from the image carrier to the transfer material, the optimal bias conditions for this reverse transfer bias may change over time. For example, changes in environmental conditions such as temperature and humidity can alter the optimal bias conditions for the reverse transfer bias due to changes in the toner's charge level. Furthermore, changes in the characteristics of the transfer material due to wear caused by its operation over time can alter the state of the electric field formed in the transfer area by the reverse transfer bias, thus altering the optimal bias conditions for the reverse transfer bias. If the bias conditions for the reverse transfer bias deviate from the optimal conditions, the transfer of toner from the image carrier to the transfer material cannot be sufficiently suppressed, increasing the amount of toner transferred to the transfer material and causing problems such as toner staining on the back of the recording material. In this embodiment, a predetermined condition correction toner pattern is imaged onto the image carrier at a predetermined bias condition correction timing. The amount of toner deposited on the condition correction toner pattern after it has passed through a transfer region where a predetermined reverse transfer bias is applied is detected by a toner deposit amount detection means. Based on this detection result, the bias conditions of the reverse transfer bias applied by the reverse transfer bias application means are corrected. The amount of toner deposited on the condition correction toner pattern after passing through the transfer region under a predetermined reverse transfer bias is the amount of toner deposited on the condition correction toner pattern before passing through the transfer region minus the amount of toner transferred to the transfer member. Therefore, the amount of toner transferred to the transfer member can be estimated from the detection result obtained by detecting the amount of toner deposited on the condition correction toner pattern after passing through the transfer region using the toner deposit amount detection means. Accordingly, according to this embodiment, the bias conditions of the reverse transfer bias can be corrected to a bias condition (i.e., the optimal bias condition) that sufficiently suppresses the amount of toner transferred to the transfer member. As a result, even if the bias conditions of the reverse transfer bias in the reverse transfer bias application means deviate from the optimal condition, the bias conditions of the reverse transfer bias can be corrected by the bias condition correction means to return the bias conditions of the reverse transfer bias to the optimal condition. Thus, even if the bias conditions of the reverse transfer bias in the reverse transfer bias application means deviate from the optimal condition, the amount of toner transferred to the transfer member can be suppressed.

[0080] [Second aspect] The second embodiment is characterized in that, in the first embodiment, a pattern image processing means (for example, a main unit control unit 406) is provided which performs a pattern image processing (toner ejection control) in which a toner pattern 201 that is not transferred onto the recording material is imaged on the image carrier at a predetermined pattern creation timing, and the reverse transfer bias is applied by the reverse transfer bias application means when the toner pattern passes through the transfer region, and the bias condition correction means corrects the bias conditions of the reverse transfer bias applied during the pattern image processing. According to this, even if the bias conditions of the reverse transfer bias during pattern image processing deviate from the optimal conditions, the amount of toner transferred to the transfer material by the toner pattern 201 created by the pattern image processing can be suppressed.

[0081] [Third aspect] The third embodiment is characterized in that, in the second embodiment, the pattern image processing means has means for bringing the image carrier and the transfer member into contact with and away from each other, and the pattern image processing means images a comparison toner pattern that is not transferred onto the recording material onto the image carrier, and when the difference between the detection result obtained by the toner adhesion amount detection means after the comparison toner pattern has passed through the transfer region in a state where the image carrier and the transfer member are separated by the contact / separation means and the detection result obtained by the toner adhesion amount detection means after the condition correction toner pattern has passed through the transfer region in a state where the reverse transfer bias of the bias conditions is applied, the pattern image processing is not executed even when the predetermined pattern creation timing arrives. According to this, when optimizing the bias conditions for reverse transfer bias does not sufficiently suppress toner adhesion to the transfer material, the pattern creation process can be avoided. As a result, when this situation occurs, it is possible to prevent defects such as toner staining on the back of the recording material from occurring due to the pattern creation process.

[0082] [Fourth aspect] The fourth embodiment is characterized in that, in any of the first to third embodiments, the bias condition correction means applies different predetermined reverse transfer biases to each other when the condition correction toner pattern passes through the transfer region, and corrects the bias conditions of the reverse transfer bias based on the detection results by the toner adhesion amount detection means for the amount of toner adhesion of each condition correction toner pattern corresponding to each predetermined reverse transfer bias. This makes it easier to correct the bias conditions of the reverse transfer bias, which can sufficiently suppress the amount of toner transferred to the transfer member.

[0083] [Fifth aspect] The fifth aspect is characterized in that, in any of the first to fourth aspects, the bias condition correction means corrects the bias condition for the reverse transfer bias to the bias condition that results in the largest amount of toner adhesion detected by the toner adhesion amount detection means. According to this, the bias conditions of the reverse transfer bias can be easily corrected to sufficiently suppress the amount of toner transferred to the transfer member.

[0084] [Sixth aspect] The sixth embodiment is characterized in that, in any of the first to fifth embodiments, a temperature detection means (e.g., a temperature and humidity sensor 414) is provided, and the predetermined bias condition correction timing is corrected based on the detection result of the temperature detection means (e.g., current temperature) and the timing at which a temperature change of more than a predetermined temperature difference (e.g., a temperature change threshold T) occurs from the temperature at the time of printing the previous condition correction toner pattern (e.g., the temperature at the time of the previous execution). According to this, when the optimal bias conditions for the reverse transfer bias change due to temperature changes, such as a change in the amount of charge of the toner, the bias condition correction means can correct the bias conditions of the reverse transfer bias. As a result, the frequency at which the bias condition correction means corrects the bias conditions of the reverse transfer bias at unnecessary times can be reduced, thereby suppressing downtime and other issues.

[0085] [Seventh aspect] The seventh embodiment is characterized in that, in any of the first to sixth embodiments, a humidity detection means (e.g., a temperature and humidity sensor 414) is provided, and the predetermined bias condition correction timing is corrected based on the detection result of the humidity detection means (e.g., current humidity) and the timing at which a humidity change of more than a predetermined humidity difference (e.g., humidity change threshold H) occurs from the humidity at the time of printing the previous condition correction toner pattern (e.g., humidity at the time of the previous execution). According to this, when the optimal bias conditions for the reverse transfer bias change due to changes in humidity, such as a change in the amount of charge of the toner, the bias condition correction means can correct the bias conditions of the reverse transfer bias. As a result, the frequency at which the bias condition correction means corrects the bias conditions of the reverse transfer bias at unnecessary times can be reduced, thereby suppressing downtime and other issues.

[0086] [8th aspect] The eighth embodiment is characterized in that, in any of the first to seventh embodiments, there is an operating amount detection means (e.g., CPU 402, ROM 405) for detecting the amount of operation of the transfer member (e.g., the travel distance of the secondary transfer roller), and the predetermined bias condition correction timing is corrected based on the timing when the transfer member has operated by a predetermined amount (e.g., travel distance change amount ΔD2) or more from the amount of operation when the previous condition correction toner pattern was printed (previous execution travel distance) based on the detection result of the operating amount detection means (e.g., current travel distance). According to this, as the transfer member wears down due to its operation over time, the characteristics of the transfer member change, and at the moment when the optimal bias conditions for the reverse transfer bias change, the bias condition correction means can correct the bias conditions of the reverse transfer bias. As a result, the frequency at which the bias condition correction means corrects the bias conditions of the reverse transfer bias at unnecessary times can be reduced, and downtime and other issues can be suppressed.

[0087] [Ninth aspect] The ninth aspect is an image forming method for forming an image on a recording material by applying a normal transfer bias to a transfer region between an image carrier and a transfer member, and transferring a toner image on the image carrier onto the recording material passing through the transfer region, characterized in that it comprises: a reverse transfer bias application step of applying a reverse transfer bias having the opposite polarity to the normal transfer bias at a predetermined timing; a toner adhesion amount detection step of detecting the amount of toner adhered on the image carrier; and a bias condition correction step of correcting the bias conditions of the reverse transfer bias applied in the reverse transfer bias application step, based on the detection result obtained in the toner adhesion amount detection step of the amount of toner adhered to a predetermined condition correction toner pattern after passing through the transfer region in which a predetermined reverse transfer bias has been applied, at a predetermined bias condition correction timing. According to this embodiment, the bias conditions of the reverse transfer bias can be corrected to sufficiently suppress the amount of toner transferred to the transfer member (i.e., the optimal bias conditions). As a result, even if the bias conditions of the reverse transfer bias in the reverse transfer bias application means deviate from the optimal conditions, the bias conditions can be corrected by the bias condition correction means to return the bias conditions of the reverse transfer bias to the optimal conditions. Therefore, even if the bias conditions of the reverse transfer bias in the reverse transfer bias application means deviate from the optimal conditions, the amount of toner transferred to the transfer member can be suppressed. [Explanation of Symbols]

[0088] 100: Printer 101: Photoconductor Drum 102: Developing equipment 103: Photoconductor Unit 104: Toner bottle 105: Intermediate transfer belt 106: Primary transfer device 107: Registroller 108: Secondary transfer roller 109: P / TM Sensor 110: Belt cleaning device 110a: Cleaning blade 111: Fixing device 115: Transfer paper 200: Exposure equipment 201: Toner Pattern 202: Contact width of the cleaning blade 203: Maximum paper feed width 205: Test Pattern 301: Charging device 308: Photoconductor cleaning device 402 :CPU 403 :RAM 405 :ROM 406: Main Unit Control 410: Print Controller 414: Temperature and humidity sensor 418: Toner density sensor [Prior art documents] [Patent Documents]

[0089] [Patent Document 1] Patent No. 4464092

Claims

1. An image forming apparatus that applies a normal transfer bias to a transfer region between an image carrier and a transfer member, and transfers the toner image on the image carrier onto the recording material passing through the transfer region, thereby forming an image on the recording material, A reverse transfer bias application means that applies a reverse transfer bias having the opposite polarity to the normal transfer bias to the transfer region at a predetermined timing, It has a toner adhesion amount detection means for detecting the amount of toner adhered to the image carrier, An image forming apparatus characterized in that, at a predetermined correction timing, the reverse transfer bias applied by the reverse transfer bias application means is corrected based on the detection result obtained by the toner adhesion amount detection means, which detects the amount of toner adhesion of a predetermined condition correction toner pattern after it has passed through the transfer region in which a reverse bias with the opposite polarity to the normal transfer bias has been applied.

2. In the image forming apparatus according to claim 1, The system includes a pattern image processing means that, at a predetermined pattern creation timing, images a toner pattern that is not transferred onto the recording material onto the image carrier, and applies the reverse transfer bias using the reverse transfer bias application means when the toner pattern passes through the transfer region, thereby performing a pattern image processing. The image forming apparatus is characterized in that the correction is to correct the inverse transfer bias applied during the pattern image formation process.

3. In the image forming apparatus according to claim 2, The system has means for bringing the image carrier and the transfer member into contact with and away from each other. The pattern forming processing means forms a comparison toner pattern on the image carrier that is not transferred onto the recording material, and the toner forming processing is not performed even when the predetermined pattern creation timing arrives if the difference between the detection result obtained by the toner adhesion amount detection means after the comparison toner pattern has passed through the transfer region in a state where the image carrier and the transfer member are separated by the contact / separation means, and the detection result obtained by the toner adhesion amount detection means after the condition correction toner pattern has passed through the transfer region in a state where it is formed when the reverse transfer bias is corrected and the reverse bias is applied, is greater than or equal to a predetermined toner adhesion amount.

4. In the image forming apparatus according to any one of claims 1 to 3, An image forming apparatus characterized by applying different reverse biases to each other as the condition correction toner pattern passes through the transfer region, and correcting the reverse transfer bias based on the detection results by the toner adhesion amount detection means for each toner adhesion amount of the condition correction toner pattern corresponding to each reverse bias.

5. In the image forming apparatus according to any one of claims 1 to 4, The image forming apparatus is characterized in that the correction is performed by setting the reverse bias that results in the largest amount of toner deposition detected by the toner deposition amount detection means to the reverse transfer bias.

6. In the image forming apparatus according to any one of claims 1 to 5, Having a temperature detection means, The image forming apparatus is characterized in that the predetermined correction timing includes the timing at which a temperature change of more than a predetermined temperature difference occurs from the temperature at the time of image formation of the previous condition correction toner pattern, based on the detection result of the temperature detection means.

7. In the image forming apparatus according to any one of claims 1 to 6, Having a means for detecting humidity, The image forming apparatus is characterized in that the predetermined correction timing includes the timing at which a humidity change of more than a predetermined humidity difference occurs from the humidity at the time of image formation of the previous condition correction toner pattern, based on the detection result of the humidity detection means.

8. In the image forming apparatus according to any one of claims 1 to 7, The transfer member has an operating amount detection means for detecting the amount of operation of the transfer member, The image forming apparatus is characterized in that the predetermined correction timing includes the timing at which the transfer member has operated by a predetermined amount or more from the amount of operation at the time of image formation of the previous condition correction toner pattern, based on the detection result of the operation amount detection means.

9. An image forming method for forming an image on a recording material by applying a normal transfer bias to a transfer region between an image carrier and a transfer member, and transferring the toner image on the image carrier onto the recording material passing through the transfer region, A reverse transfer bias application step in which a reverse transfer bias having the opposite polarity to the normal transfer bias is applied to the transfer region at a predetermined timing, A toner adhesion amount detection step for detecting the amount of toner adhesion on the image carrier, An image forming method characterized by comprising: a correction step, in which, at a predetermined correction timing, the amount of toner deposited on a predetermined condition correction toner pattern after passing through the transfer region in which a reverse bias of opposite polarity to the normal transfer bias is applied, is detected in the toner deposit amount detection step, and the reverse transfer bias applied in the reverse transfer bias application step is corrected based on the detection result.

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