JP7443137B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile machine using an electrophotographic method.

Conventionally, in image forming devices such as copiers and page printers that use electrophotography, a toner image formed on a photoreceptor is first transferred onto an intermediate transfer body, and then secondarily transferred to a transfer material such as recording paper. An intermediate transfer method is known. As the intermediate transfer body, an intermediate transfer belt composed of an endless belt is often used. In a color image forming device capable of forming a full-color image, a plurality of photoreceptors are arranged side by side along the conveyance direction of the intermediate transfer member, and toner images of different colors formed on each photoreceptor are transferred onto the intermediate transfer member. The primary transfer is performed so that the two images are superimposed on each other.

In such image forming apparatuses, there is a need to improve the running stability of the intermediate transfer member in order to suppress the occurrence of color misregistration and improve image quality. A factor that disturbs the running stability of the intermediate transfer member is the contact pressure (primary transfer pressure) between the photoreceptor and the intermediate transfer member in the primary transfer portion.

By arranging the primary transfer member offset from the photoreceptor to the downstream side in the conveyance direction of the intermediate transfer member and preventing the primary transfer member from coming into pressure contact with the photoreceptor via the intermediate transfer member, the primary transfer pressure can be reduced. An image forming apparatus has been proposed (Patent Document 1).

Japanese Patent Application Publication No. 2007-286270

Incidentally, image forming apparatuses are required not only to have high image quality but also to have a long life. Generally, the electrical resistance of an intermediate transfer member increases as the amount of repeated use increases. Therefore, in order to extend the life of the image forming apparatus, it is required to be able to form high-quality images even when the intermediate transfer member has a high resistance.

However, in the above-described configuration in which the primary transfer member is placed in a position where it is not in pressure contact with the photoreceptor via the intermediate transfer member, in situations where the intermediate transfer member has a high resistance, such as at the end of its life and in a low temperature and low humidity environment, Image defects may occur due to abnormal discharge. In other words, with this configuration, it may be necessary to apply a relatively high primary transfer voltage to the primary transfer member in situations such as those described above, and in that case, abnormal discharge may occur between the primary transfer member and the photoreceptor. is more likely to occur, and image defects due to abnormal discharge are more likely to occur.

Therefore, an object of the present invention is to suppress image defects due to abnormal discharge in a configuration in which the primary transfer member is disposed at a position where it does not come into pressure contact with the photoreceptor via the intermediate transfer member.

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides a rotatable photoconductor that carries a toner image, a charging member that charges the surface of the photoconductor, a charging voltage application unit that applies a voltage to the charging member, and a charge voltage application unit that applies a voltage to the photoconductor. a movable intermediate transfer member that transports the toner image that has been primarily transferred from the photoreceptor to a transfer material; A primary transfer member that primarily transfers a toner image to the intermediate transfer member, the contact area between the photoreceptor and the intermediate transfer member, and the primary transfer member and the intermediate transfer member with respect to the moving direction of the intermediate transfer member. and a primary transfer voltage applying section that applies a voltage to the primary transfer member. a current detection unit that detects a current flowing through the charging member when a voltage is applied to the charging member by the charging voltage applying unit; Execute a detection operation to obtain a detection result of the current detection unit when the surface of the photoconductor that has passed through the primary transfer unit is being charged by the charging member in a state where is applied, and the detection result is an image forming apparatus comprising: a control unit capable of changing operation settings of the image forming apparatus based on information regarding occurrence of discharge between the primary transfer member and the photoreceptor; It is.

According to the present invention, image defects due to abnormal discharge can be suppressed in a configuration in which the primary transfer member is disposed at a position where it does not come into pressure contact with the photoreceptor via the intermediate transfer member.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. FIG. 3 is a schematic cross-sectional view of an image forming section. FIG. 3 is a schematic diagram for explaining the mechanism of occurrence of abnormal discharge. FIG. 3 is a flowchart of control in the first embodiment. FIG. 2 is a graph diagram showing the relationship between primary transfer voltage and primary transfer efficiency. FIG. 3 is a flowchart of control in Example 2. FIG. FIG. 3 is a graph diagram showing the relationship between the temperature of the intermediate transfer belt and the impedance of the primary transfer section. FIG. 7 is a flowchart of control in Example 3;

Hereinafter, the image forming apparatus according to the present invention will be explained in more detail with reference to the drawings.

[Example 1]
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem type (in-line type) laser beam printer that uses an intermediate transfer method and can form a full-color image using an electrophotographic method.

The image forming apparatus 100 has a plurality of image forming units (stations), first, second, and It has third and fourth image forming sections PY, PM, PC, and PK. For elements with the same or corresponding functions or configurations in each image forming unit PY, PM, PC, and PK, the suffix Y, M, C, and K are omitted to indicate that they are elements for one of the colors. This may be explained comprehensively. FIG. 2 is a schematic cross-sectional view showing one representative image forming section P. In this embodiment, the image forming section P includes photosensitive drums 1 (1Y, 1M, 1C, 1K), charging rollers 2 (2Y, 2M, 2C, 2K), and exposure devices 3 (3Y, 3M, 3C, 3K), which will be described later. ), a developing device 4 (4Y, 4M, 4C, 4K), a primary transfer roller 5 (5Y, 5M, 5C, 5K), a drum cleaning device 6 (6Y, 6M, 6C, 6K), etc. .

A photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) electrophotographic photosensitive member (photosensitive member) serving as an image carrier that carries a toner image, is rotated around a predetermined circumference in the direction of arrow R1 (clockwise) in the figure. Rotationally driven at speed. In this embodiment, for example, when the transfer material S is plain paper, the photosensitive drum 1 is driven to rotate at a peripheral speed of 300 mm/s. The surface of the rotating photosensitive drum 1 is charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 2, which is a roller-shaped charging member serving as a charging means. During the charging process, a predetermined negative charging voltage (charging bias) is applied to the charging roller 2 from a charging voltage applying section (charging power source) 70. In this embodiment, the image forming apparatus 100 is configured such that the charging current detection section 71 can detect the current flowing through the charging roller 2 (charging voltage application section 70). In this embodiment, the charging voltage applying section 70 and the charging current detecting section 71 are individually provided for each image forming section P. The charged surface of the photosensitive drum 1 is scanned and exposed based on an image signal by an exposure device (laser scanner unit) 3 serving as an exposure means, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. Ru. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by being supplied with toner as a developer by a developing device 4 serving as a developing means, and a toner image is formed on the photosensitive drum 1. The developing device 4 includes a developing roller 41 as a developer carrier, and a toner container 42 that stores toner. During development, a predetermined negative development voltage (development bias) is applied to the development roller 41 from a development voltage application section (development power supply) (not shown). In this example, the exposed area (image area) on the photosensitive drum 1, whose absolute value has decreased by being exposed to light after being uniformly charged, has the same polarity as the charged polarity of the photosensitive drum 1 (in this example). In this example, negatively charged toner is attached (reversal development).

An intermediate transfer belt 8 made of a flexible endless belt is disposed so as to be movable (rotatable) in contact with each photosensitive drum 1 of each image forming section P. The intermediate transfer belt 8 is an example of an intermediate transfer body that transports a toner image that has been primarily transferred from an image carrier to a transfer material for secondary transfer. The intermediate transfer belt 8 is stretched around a plurality of driving rollers 9 and driven rollers 10 as tension rollers (supporting members), and is stretched with a predetermined tension. When the drive roller 9 is rotationally driven, the intermediate transfer belt 8 moves at a peripheral speed (surface movement) corresponding to the peripheral speed (surface movement speed) of the photosensitive drum 1 in the direction of arrow R2 (counterclockwise) in the figure. Rotate (move in circles) at a speed). In this embodiment, for example, when the transfer material S is plain paper, the intermediate transfer belt 8 rotates (circularly moves) at a peripheral speed of 300 mm/s corresponding to the peripheral speed of the photosensitive drum 1. On the inner peripheral surface side of the intermediate transfer belt 8, a primary transfer roller 5, which is a roller-shaped primary transfer member serving as a primary transfer means, is arranged corresponding to each photosensitive drum 1. In this embodiment, the primary transfer roller 5 is arranged offset to the downstream side in the conveyance direction (surface movement direction) of the intermediate transfer belt 8 with respect to the corresponding photosensitive drum 1. That is, the primary transfer roller 5 is arranged so that the contact area between the photosensitive drum 1 and the intermediate transfer belt 8 and the contact area between the primary transfer roller 5 and the photosensitive drum 1 do not overlap with respect to the conveying direction of the intermediate transfer belt 8. has been done. Further, in the primary transfer roller 5, the contact area between the primary transfer roller 5 and the intermediate transfer belt 8 is located downstream of the contact area between the photosensitive drum 1 and the intermediate transfer belt 8 in the conveying direction of the intermediate transfer belt 8. It is arranged like this. Thereby, the primary transfer roller 5 is placed at a position where it does not come into pressure contact with the corresponding photosensitive drum 1 via the intermediate transfer belt 8. The primary transfer roller 5 is biased to press the intermediate transfer belt 8 toward the photosensitive drum 1, and forms a primary transfer portion N1 where the photosensitive drum 1 and the intermediate transfer belt 8 are in contact. The toner image formed on the photosensitive drum 1 as described above is primarily transferred onto the rotating intermediate transfer belt 8 at the primary transfer portion N1. During the primary transfer, the primary transfer roller 5 is supplied with a polarity opposite to the normal charging polarity of the toner (the charging polarity of the toner during development) (positive polarity in this embodiment) from the primary transfer voltage applying section (primary transfer power source) 50. A primary transfer voltage (primary transfer bias) which is a DC voltage is applied. In this embodiment, the image forming apparatus 100 is configured such that the primary transfer current detection section 51 can detect the current flowing through the primary transfer section N1 (primary transfer voltage application section 50). In this embodiment, the primary transfer voltage applying section 50 and the primary transfer current detecting section 51 are individually provided for each image forming section P. For example, when forming a full-color image, toner images of yellow, magenta, cyan, and black formed on each of the photosensitive drums 1Y, 1M, 1C, and 1K are sequentially superimposed on the intermediate transfer belt 8. Primary transfer is performed.

On the outer peripheral surface side of the intermediate transfer belt 8, a secondary transfer roller 11, which is a roller-shaped secondary transfer member serving as a secondary transfer means, is arranged at a position facing the drive roller 9, which also serves as a secondary transfer opposing roller. ing. The secondary transfer roller 11 is pressed toward the drive roller 9 via the intermediate transfer belt 8, and forms a secondary transfer portion N2 where the intermediate transfer belt 8 and the secondary transfer roller 11 come into contact. As described above, the toner image formed on the intermediate transfer belt 8 is transferred to a transfer material (recording paper) such as recording paper that is being conveyed between the intermediate transfer belt 8 and the secondary transfer roller 11 in the secondary transfer section. material, sheet) S. During the secondary transfer, a secondary transfer voltage application unit (secondary transfer power source) (not shown) supplies the secondary transfer roller 11 with a polarity that is opposite to the normal charging polarity of the toner (positive polarity in this embodiment). A secondary transfer voltage (secondary transfer bias) which is a DC voltage is applied. The transfer material S is loaded and stored in a transfer material cassette 13, is fed from the transfer material cassette 13 by a feeding roller 14 of a feeding/conveying device 12, and transferred to a pair of registration rollers by a pair of conveying rollers 15 of the feeding/conveying device 12. 16. Then, this transfer material S is supplied to the secondary transfer portion N2 by the pair of registration rollers 16 in synchronization with the toner image on the intermediate transfer belt 8. In this embodiment, for example, when the transfer material S is plain paper, the transfer material S is transported at a transport speed of 300 mm/s corresponding to the peripheral speed of the intermediate transfer belt 8.

The transfer material S onto which the toner image has been transferred is conveyed to a fixing device 17 as a fixing means. The fixing device 17 fixes (melts, fixes) the toner image on the surface of the transfer material S by heating and pressurizing the transfer material S carrying the unfixed toner image. Thereafter, the transfer material S is discharged (output) by a pair of discharge rollers 18 onto a discharge tray 19 provided outside the apparatus main body 110 of the image forming apparatus 100 .

Further, primary transfer residual toner remaining on the photosensitive drum 1 during the primary transfer is removed from the photosensitive drum 1 and collected by a drum cleaning device 6 serving as a photosensitive member cleaning means. The drum cleaning device 6 includes a drum cleaning blade 61 as a cleaning member and a collected toner container 62. The drum cleaning device 6 uses a drum cleaning blade 61 to scrape off primary transfer residual toner from the surface of the rotating photosensitive drum 1 and stores it in a collected toner container 62 . The drum cleaning blade 61 is in contact with the surface of the photosensitive drum 1 in a direction counter to the rotational direction of the photosensitive drum 1 . In addition, deposits such as toner remaining on the intermediate transfer belt 8 during secondary transfer (secondary transfer residual toner) and paper powder adhering to the intermediate transfer belt 8 from the transfer material S are removed from the belt as an intermediate transfer body cleaning means. It is removed from the intermediate transfer belt 8 by the cleaning device 20 and collected. The belt cleaning device 20 includes a belt cleaning blade 21 as a cleaning member and a collected toner container 22. The belt cleaning device 20 uses a belt cleaning blade 21 to scrape secondary transfer residual toner from the surface of the rotating intermediate transfer belt 8 and stores it in a collected toner container 22 . The belt cleaning blade 21 is in contact with the surface of the intermediate transfer belt 8 in a counter direction to the rotation direction of the intermediate transfer belt 8.

Image forming apparatus 100 includes a control section (controller) 80. The control section 80 includes a CPU as an arithmetic control means, a memory such as a ROM or RAM as a storage means, an input/output circuit that controls input/output of signals between the control section 80 and each section, and the like. The control unit 80 comprehensively controls the operations of each unit of the image forming apparatus 100 by having the CPU execute processing based on programs and data stored in the memory. The control section 80 controls each section of the image forming apparatus 100 to execute image formation based on image information input from an external device connected to the image forming apparatus 100, such as an image reading apparatus or a personal computer.

The image forming apparatus 100 also detects the temperature inside the main body 110 of the image forming apparatus 100 (inside the machine) as an environment detection means for detecting at least one of temperature and humidity inside or outside the image forming apparatus 100. It has an in-machine temperature sensor 90 for sensing. The in-machine temperature sensor 90 detects the in-machine temperature and outputs a signal related to the detection result to the control unit 80.

In this embodiment, in each image forming section P, the photosensitive drum 1, the charging roller 2, the developing device 4, and the drum cleaning device 6 as process means that act on the photosensitive drum 1 are integrally connected to the apparatus main body 110. A removable process cartridge 7 is configured. Further, in this embodiment, the intermediate transfer belt 8, drive roller 9, driven roller 10, primary transfer rollers 5Y, 5M, 5C, 5K, etc. are integrated into an intermediate transfer unit 30 that is detachable from the apparatus main body 110. It consists of

Further, the toner used in this example is a substantially spherical toner (one-component nonmagnetic developer) with an average particle size of 5 to 8 μm. In this embodiment, since a total of two transfers, primary transfer and secondary transfer, are performed, a spherical toner with good transferability is used as the toner. The toner used in this example is manufactured by a polymerization method. This toner has a substantially spherical shape due to the manufacturing method. Furthermore, the toner used in this example has a core containing wax, a binder resin layer on the core made of styrene-butyl acrylate, and an outermost resin layer on the core made of styrene-polyester. is used. Furthermore, external additives are added to the toner in order to stabilize charging performance and provide lubricity. Note that as the binder resin for the toner, it is possible to use a vinyl copolymer made of styrene resin and acrylic resin, polyester resin, or the like.

2. Transfer Configuration In this embodiment, as described above, the primary transfer roller 5 is arranged at a position where it does not come into pressure contact with the corresponding photosensitive drum 1 via the intermediate transfer belt 8. In particular, in this embodiment, the primary transfer roller 5 is arranged offset to the downstream side in the conveyance direction of the intermediate transfer belt 8 with respect to the photosensitive drum 1 . In this embodiment, the primary transfer roller 5 is a metal roller made of metal. Particularly, in this embodiment, as the primary transfer roller 5, a plated SUM material (free-cutting steel) having an outer diameter of 6 mm was used. Note that the primary transfer roller 5 may be formed using Al (aluminum), SUS (stainless steel), or the like in addition to the SUM material. In this embodiment, in each image forming portion P, the primary transfer roller 5 and the intermediate transfer belt 8 are The distance between the contact area and the upstream end of the contact area is 3 mm.

By arranging the primary transfer roller 5 at a position where it does not come into pressure contact with the photosensitive drum 1 via the intermediate transfer belt 8, the primary transfer pressure can be reduced and the running stability of the intermediate transfer belt 8 can be easily improved. Furthermore, by arranging the primary transfer roller 5 at a position where it does not come into pressure contact with the photosensitive drum 1 via the intermediate transfer belt 8, it is possible to use a metal roller as the primary transfer roller 5, and it is possible to use a configuration using a foamed roller or the like. It is easier to reduce costs compared to Further, in this embodiment, the primary transfer roller 5 is arranged offset to the downstream side in the conveyance direction of the intermediate transfer belt 8 with respect to the photosensitive drum 1. Thereby, discharge (pre-discharge) occurring between the photosensitive drum 1 and the intermediate transfer belt 8 on the upstream side of the primary transfer portion N1 with respect to the conveyance direction of the intermediate transfer belt 8 is suppressed, and image disturbance is easily reduced.

Further, in this embodiment, the intermediate transfer belt 8 has a base layer and a surface layer. In particular, in this embodiment, the intermediate transfer belt 8 is composed of two layers: a base layer and a surface layer formed on the base layer. The surface layer is a layer provided closer to the outer peripheral surface of the intermediate transfer belt 8 than the base layer, and has a surface that supports (holds) the toner transferred from the photosensitive drum 1.

In this embodiment, the intermediate transfer belt 8 has a thickness of 70 μm, a volume resistivity of 1.0×10 ⁹ Ω·cm, and a surface resistivity of 1.0×10 ¹⁰ Ω/□. The electrical characteristics were measured using Hiresta UP MCP-HT450 (manufactured by Mitsubishi Chemical Corporation) at an applied voltage of 250 V in an environment of a temperature of 23° C. and a relative humidity of 50%. Note that the surface resistivity is a value measured from the back surface side (inner peripheral surface side) of the intermediate transfer belt 8.

In this example, a belt formed using polyethylene naphthalate was used as the base layer of the intermediate transfer belt 8. In addition to the above materials, examples of materials used for the base layer of the intermediate transfer belt 8 include polycarbonate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polymethylpentene-1, polystyrene, polyamide, polysulfone, polyarylate, and polyethylene terephthalate. , polybutylene terephthalate, polyimide, polybutylene naphthalate, polyphenylene sulfide, polyether sulfone, polyether nitrile, thermoplastic polyimide, polyether ether ketone, thermotropic liquid crystal polymer, polyamic acid, and other thermoplastic resins. Two or more of these can also be used in combination. Further, in this embodiment, an ion conductive material is melted and kneaded as a conductive material into the base material (such as the above-mentioned thermoplastic resin) of the base layer of the intermediate transfer belt 8. In this example, an ionic liquid was used as the ion conductive material. However, the ion conductive material is not limited thereto, and in addition to the above, conductive oligomers, quaternary ammonium salts, and the like can be mentioned. Note that as the conductive material, an electronically conductive material may be used, or an electronically conductive material and an ionically conductive material may be used. Examples of electronically conductive materials include particulate, fibrous, or flake carbon-based conductive fillers, particulate, fibrous, or flake metal-based conductive fillers, and particulate metal oxide-based conductive fillers. can be mentioned.

The surface layer of the intermediate transfer belt 8 may be thermosetting or hardened by irradiation with energy rays such as ultraviolet rays or electron beams, from the viewpoint of increasing the surface hardness of the intermediate transfer belt 8 and improving durability (wear resistance). A curable material is used. In particular, curable materials that are hardened by highly curable ultraviolet rays or electron beams are preferred, but the material is not limited thereto. In this example, acrylic resin was used as the curable material. However, it is not limited to this, and in addition to the above, examples of organic materials include curable resins such as melamine resins, urethane resins, alkyd resins, and fluorine curable resins. Examples of inorganic materials include alkoxysilane/alkoxyzirconium materials, silicate materials, and the like. Examples of the organic/inorganic hybrid material include organic polymer materials with inorganic fine particles dispersed therein, organoalkoxysilane materials with inorganic fine particles dispersed therein, acrylic silicone materials, organoalkoxysilane materials, and the like. Among curable materials, resin materials are preferable from the viewpoint of abrasion resistance and crack resistance of the surface layer of the intermediate transfer belt 8, and among curable resins, acrylic materials obtained by curing an acrylic copolymer containing unsaturated double bonds are preferred. Resins are preferred. The unsaturated double bond-containing acrylic copolymer is available, for example, as Lucifral (trade name, manufactured by Nippon Paint Co., Ltd.), which is an acrylic ultraviolet curable hard coat material.

3. Primary transfer voltage control In this embodiment, the image forming apparatus 100 performs primary transfer voltage control so as to be able to stably apply an optimal primary transfer voltage by correcting environmental fluctuations, electrical resistance unevenness, etc. of the intermediate transfer belt 8. conduct. In this embodiment, the image forming apparatus 100 performs control to determine the primary transfer voltage during image formation by so-called ATVC control (Auto Transfer Voltage Control) as primary transfer voltage control. In other words, when the non-image area on the photosensitive drum 1 is passing through the primary transfer part N1 during a pre-rotation operation before image formation as a time of non-image formation, the voltage applied to the primary transfer roller 5 is set in advance. Constant current control is performed using the set current value. The impedance fluctuation in the primary transfer portion N1 can be detected by the fluctuation of the generated voltage value at this time. When forming an image, constant voltage control of the voltage applied to the primary transfer roller 5 is performed using a voltage value determined by arithmetic processing of the previously generated voltage value. The arithmetic processing includes determining the average value of the generated voltage values and further multiplying the average value by a predetermined coefficient. Such control makes it possible to apply an appropriate primary transfer voltage during image formation, making it possible to stably output a good image.

Note that ATVC control can be performed in at least one image forming section P among the plurality of image forming sections P. The process may be performed by any one image forming part P among the plurality of image forming parts P, or may be performed by a plurality of (or all) image forming parts P. When ATVC control is performed in any one image forming section P (for example, image forming section PK for black) among the plurality of image forming sections P, the result can be reflected on all the image forming sections P. At this time, the same primary transfer voltage value may be set for all the image forming parts P based on the results, or different primary transfer voltage values may be set for at least one image forming part P (or all of them may be used) based on the results. You may also set a value. Further, when ATVC control is performed in a plurality of image forming sections P, the primary transfer voltage of each image forming section P may be set respectively based on the results obtained in each image forming section.

Here, the image forming apparatus 100 executes a job (print job) that is a series of operations to form and output an image on a single or multiple transfer materials S, which is started by one start instruction. . A job generally includes an image forming process, a pre-rotation process, a paper spacing process when images are formed on a plurality of transfer materials S, and a post-rotation process. The image forming process is a period in which the electrostatic image of the image to be actually formed on the transfer material S and output, the formation of the toner image, the primary transfer, and the secondary transfer of the toner image are performed. Refers to the period. More specifically, the timing during image formation differs depending on the position where the electrostatic image formation, toner image formation, toner image primary transfer, and secondary transfer steps are performed. This corresponds to the period during which the image area above 8 passes through each of the above positions. The pre-rotation process is a period from when a start instruction is input until actually starting to form an image, during which preparatory operations are performed before the image forming process. The inter-sheet process is a period corresponding to the interval between the transfer materials S when images are continuously formed on a plurality of transfer materials S (continuous printing, continuous image formation). The post-rotation process is a period in which organizing operations (preparatory operations) are performed after the image forming process. The non-image forming time is a period other than the image forming time, and includes the pre-rotation process, paper interval process, post-rotation process, and preparatory operations when the image forming apparatus 100 is turned on or returned from a sleep state. This includes a pre-multi-rotation process. More specifically, the timing during non-image formation is such that the non-image area on the photosensitive drum 1 or the intermediate transfer belt 8 is formed during the formation of the electrostatic image, the formation of a toner image, the primary transfer of the toner image, and the secondary transfer of the toner image. This corresponds to the period during which the vehicle passes through each position where each process is performed. Note that the image area on the photosensitive drum 1 or the intermediate transfer belt 8 is an area where an image can be formed to be transferred to the transfer material S and output from the image forming apparatus 100, and the non-image area is an area other than the image area. It is an area.

In this embodiment, the control unit 80 typically performs the primary transfer voltage control in the pre-rotation process or the pre-multi-rotation process. However, the present invention is not limited to this, and the primary transfer voltage control may be performed in the paper interval process or the post-rotation process. Further, in the present embodiment, the control unit 80 typically performs an operation of measuring the charging current I (an operation for detecting the occurrence of abnormal discharge), which will be described later, in the pre-rotation process or the pre-multi-rotation process. However, the present invention is not limited to this, and the operation of measuring the charging current I may be performed in the paper interval process or the post-rotation process.

4. Mechanism of Occurrence of Abnormal Discharge FIG. 3 is an enlarged schematic cross-sectional view of the vicinity of the primary transfer portion N1. When a high potential difference occurs between the primary transfer roller 5 and the photosensitive drum 1, abnormal discharge may occur between the primary transfer roller 5 and the photosensitive drum 1. The potential of the area on the photosensitive drum 1 that has experienced this abnormal discharge may become a positive potential that is opposite to the normal charging polarity of the photosensitive drum 1. In the area on the photosensitive drum 1 that has received this abnormal discharge, a history of the above-mentioned potential reversal remains even after being charged by the charging roller 2, and toner is supplied by the developing roller 41 and developed as discharge traces. Sometimes. In other words, in the configuration of this embodiment, the area on the photosensitive drum 1 that has received the discharge has a smaller absolute value of potential than the surrounding area (even after the charging process by the charging roller 2). (can only be charged up to a negative potential with a small value). Therefore, similar to the image area exposed by the exposure device 3 to reduce the absolute value of the potential, toner also adheres to the area subjected to the discharge. Furthermore, even if the area on the photosensitive drum 1 that has received the discharge becomes an image area, image unevenness may occur because the potential after exposure by the exposure device 3 is different from the potential of the surrounding image area.

The intermediate transfer belt 8 containing an ion conductive material tends to have an increased electrical resistance under a low temperature and low humidity environment or due to an increase in the amount of repeated use. In particular, in a configuration in which the primary transfer roller 5 is disposed at a position where it does not come into pressure contact with the photosensitive drum 1 via the intermediate transfer belt 8, the electrical resistance of the intermediate transfer belt 8 is approximately equal to the impedance of the primary transfer portion N1. Therefore, in a situation where the electrical resistance of the intermediate transfer belt 8 increases as described above, a high potential difference is required between the primary transfer roller 5 and the photosensitive drum 1 in order to supply the desired primary transfer current. Abnormal discharge is more likely to occur.

Here, the abnormal discharge that occurs between the primary transfer roller 5 and the photosensitive drum 1 due to the above-described mechanism may be simply referred to as "abnormal discharge."

5. Detection of occurrence of abnormal discharge The intermediate transfer belt 8 in this embodiment has a surface resistivity of 1.0×10 ^10.7 Ω/□ under an environment of a temperature of 15° C. and a relative humidity of 10% (low temperature and low humidity environment). However, depending on the value of the primary transfer voltage, abnormal discharge may occur. Note that this surface resistivity is the surface resistivity after the intermediate transfer belt 8 is used for printing 150,000 sheets. The method for measuring surface resistivity is the same as the method described above.

When abnormal discharge occurs, the potential of the photosensitive drum 1 is reversed to positive polarity, and the charging current detected by the charging current detection section 71 increases accordingly. Table 1 shows the relationship between the presence or absence of abnormal discharge and the charging current I detected by the charging current detection section 71 in the configuration of this embodiment. As this charging current I, the average value of the charging current for one revolution of the photosensitive drum 1 when the primary transfer voltage is applied to the so-called solid white image (non-image area) on the photosensitive drum 1 was used. . In this embodiment, the operation of determining the charging current I takes about 4 seconds.

In addition, from the viewpoint of improving accuracy, it is preferable to measure the charging current I over one revolution of the photosensitive drum 1 or more, but the measurement is not limited to this. It is sufficient if it can be detected. Further, the number of rotations of the photosensitive drum 1 for measuring the charging current I is typically 5 or less, preferably 3 or less, in order to prevent the control time from becoming too long. Here, one revolution of the photosensitive drum 1 means, more specifically, that after the position on the photosensitive drum 1 that has been charged to a predetermined charging potential equivalent to that at the time of image formation passes through the primary transfer portion N1, This is one revolution of the photosensitive drum 1 after reaching the charging position. Here, the charging position is a position in the rotational direction of the photosensitive drum 1 where the surface of the photosensitive drum 1 is charged by the charging roller 2 . In this embodiment, the photosensitive drum 1 is exposed to light due to an electric discharge generated at least in one of the small gaps between the charging roller 2 and the photosensitive drum 1 at the upstream and downstream sides of the rotational direction of the photosensitive drum 1 at the contact portion between the charging roller 2 and the photosensitive drum 1. The surface of the drum 1 is charged. However, for simplicity, the contact portion between the charging roller 2 and the photosensitive drum 1 may be regarded as the charging position.

When abnormal discharge occurs, the charging current I increases to 60 μA or more. Therefore, the presence or absence of abnormal discharge can be detected by setting the threshold value Ith of the charging current I to 60 μA. That is, when the charging current I is 60 μA or more, it can be determined that abnormal discharge has occurred. Furthermore, if the charging current I is less than 60 μA, it can be determined that no abnormal discharge occurs. Since the charging current I tends to stably change in the direction of increasing as abnormal discharge occurs, the occurrence of abnormal discharge can be easily detected by using the charging current I as an index.

Note that the threshold value Ith of the charging current I may be changed as appropriate so that it can be determined whether or not abnormal discharge has occurred. For example, depending on the configuration of the image forming apparatus 100 to which the present invention is applied, the threshold value Ith may be changed as appropriate so that it can be determined whether or not abnormal discharge has occurred. In addition, in the image forming apparatus 100, the threshold value Ith is appropriately changed in accordance with the environment and the amount of repeated use of the image forming apparatus 100 (photosensitive drum 1, etc.) so that it can be determined at that point whether or not abnormal discharge has occurred. It's okay. Note that the environment may be at least one of temperature and humidity inside or outside of the image forming apparatus 100.

6. Switching Control to Abnormal Discharge Suppression Mode In the present embodiment, the image forming apparatus 100 has a normal mode (first mode) and an abnormal discharge suppression mode (second mode) as print modes. It is configured such that it can be used for printing. Here, the procedure for switching the print mode will be explained, and the contents of the normal mode and the abnormal discharge suppression mode will be described later.

FIG. 4 is a flowchart schematically showing a procedure for switching operation (processing) between the normal mode and the abnormal discharge suppression mode during execution of one job. The control unit 80 acquires the detection result of the charging current I by the charging current detection unit 71 (S101). Next, the control unit 80 determines whether the charging current I is greater than or equal to the threshold value Ith (whether abnormal discharge is occurring) (S102). When the control unit 80 determines in S102 that the charging current I is greater than or equal to the threshold value Ith (I≧Ith) (abnormal discharge has occurred), printing is performed in the abnormal discharge suppression mode (S103). Then, the control unit 80 repeats printing in the abnormal discharge suppression mode until the last image of the job (S104), and ends the job after printing up to the last image of the job. On the other hand, if the control unit 80 determines in S102 that the charging current I is not greater than or equal to the threshold value Ith, that is, it is less than the threshold value Ith (I<Ith) (no abnormal discharge has occurred), the control unit 80 operates in the normal mode. Printing is performed (S105). Then, the control unit 80 repeats printing in the normal mode until the last image of the job (S106), and ends the job after printing up to the last image of the job. Note that after printing one image in the normal mode or the abnormal discharge suppression mode, it is also possible to return to the process of detecting the charging current each time (S101).

More specifically, in this embodiment, when starting a job, the control unit 80 executes primary transfer voltage control in the pre-rotation process or the pre-multi-rotation process to determine the primary transfer voltage in the normal mode. . In addition, when starting a job, the control unit 80 controls the process speed in the normal mode described later and the primary transfer voltage setting in the normal mode determined by the primary transfer voltage control in the pre-rotation process or the pre-multi-rotation process, as described above. The charging current I is measured as follows. Thereby, the control unit 80 detects whether abnormal discharge occurs between the primary transfer roller 5 and the photosensitive drum 1 (S102). To measure the charging current I, the photosensitive drum 1 is charged, and the charged surface (solid white image) of the photosensitive drum 1 is passed through the primary transfer portion N1 with the primary transfer voltage applied to the primary transfer roller 5. . Then, the surface of the photosensitive drum 1, which has passed through the primary transfer portion N1 as described above, passes through the charging position for a period sufficient to determine the charging current I as described above (approximately 4 seconds in this embodiment). Do it like this. Then, depending on the detection result of the occurrence of abnormal discharge, printing in the normal mode or the abnormal discharge suppression mode is started (S103 to S106).

Note that detection of the occurrence of abnormal discharge (measurement of charging current) can be performed in at least one image forming section P among the plurality of image forming sections P. It may be performed in any one image forming part P (for example, image forming part PK for black) among the plurality of image forming parts P, or in a plurality (or all of them) of the image forming parts P. When detecting the occurrence of abnormal discharge in multiple image forming units P, if abnormal discharge is detected to occur in a predetermined number or more (for example, one or more) of the image forming units, abnormal discharge is suppressed. mode can be switched. Alternatively, when measuring charging current (detecting the presence or absence of abnormal discharge) at multiple image forming units P, the average value (or maximum value) or A representative value such as the minimum value) can be determined and used to determine whether abnormal discharge has occurred. In this embodiment, detection of the occurrence of abnormal discharge (measurement of charging current) is performed at all image forming units P, and if it is detected that abnormal discharge has occurred in one image forming unit P, an abnormal discharge is detected. Switch to discharge suppression mode.

7. Abnormal Discharge Suppression Mode Abnormal discharge is more likely to occur as the potential difference between the primary transfer roller 5 and the photosensitive drum 1 increases. Therefore, in this embodiment, in the abnormal discharge suppression mode, the absolute value of the primary transfer voltage applied to the primary transfer roller 5 is controlled to be smaller than in the normal mode.

In the abnormal discharge suppression mode, the process speed can further be made slower than in the normal mode. In this embodiment, the peripheral speed of the intermediate transfer belt 8 (and the corresponding peripheral speed of the photosensitive drum 1) corresponds to the process speed of the image forming apparatus 100. That is, as described above, by reducing the absolute value of the primary transfer voltage, it is possible to obtain the effect of suppressing abnormal discharge. However, if the absolute value of the primary transfer voltage is made smaller than the absolute value of the primary transfer voltage in the normal mode, which is usually set to the optimum value, the primary transfer efficiency may decrease depending on the image, causing image quality deterioration.

FIG. 5 is a graph showing the relationship between the primary transfer voltage and the primary transfer efficiency when the process speed is 300 mm/s and 100 mm/s in the configuration of this example. The primary transfer efficiency is the ratio (percentage) of the amount of toner primarily transferred to the intermediate transfer belt 8 out of the total amount of toner of the toner image formed on the photosensitive drum 1 . For example, a predetermined test toner image is formed on the photosensitive drum 1. Then, the image density of the toner image on the photosensitive drum 1 before the primary transfer and the image density of the toner image remaining on the photosensitive drum 1 after the primary transfer are transferred to a transparent adhesive tape. Measurement is performed using a commercially available image density measuring device. Thereby, primary transfer efficiency can be measured. Here, the normal mode determined by the primary transfer voltage control is performed using the intermediate transfer belt 8 after printing 150,000 sheets in an environment with a temperature of 15° C. and a relative humidity of 10% (low temperature and low humidity environment). As an example, the primary transfer voltage is approximately 2500 to 3000V. Further, at this time, it is assumed that plain paper is used as the transfer material S, and the process speed in the normal mode is 300 mm/s. Note that, herein, this condition is also simply referred to as "a condition under which abnormal discharge occurs."

As shown in FIG. 5, when the process speed is 300 mm/s, if the primary transfer voltage is lowered to 2500 V or less in order to avoid abnormal discharge, the primary transfer efficiency becomes approximately 96% or less. Depending on the image, uneven density may be visible. On the other hand, when the process speed is slowed down to 100 mm/s, the primary transfer efficiency remains at about 99% even if the primary transfer voltage is lowered to 1500 V to avoid occurrence of abnormal discharge. That is, by setting the process speed to 100 mm/s, the occurrence of abnormal discharge can be avoided while reducing density unevenness compared to when the process speed is 300 mm/s. In this manner, by lowering the process speed and lowering the primary transfer voltage, it is possible to suppress the occurrence of abnormal discharge while suppressing image quality deterioration.

Table 2 shows the effects of this example under conditions where abnormal discharge occurs. In a comparative example in which printing is performed in normal mode (primary transfer voltage 2500 to 3000 V, process speed 300 mm/s), image defects occur due to abnormal discharge. On the other hand, in Example 1-1 (primary transfer voltage 1500 V, process speed 300 mm/s) in which the absolute value of the primary transfer voltage is reduced in the abnormal discharge suppression mode, abnormal discharge can be suppressed. Furthermore, in Example 1-2 (primary transfer voltage 1500 V, process speed 100 mm/s) in which the primary transfer voltage is lowered and the process speed is slowed down, abnormal discharge can be suppressed and the primary transfer efficiency can be maintained at the optimum primary transfer efficiency. Transfer can be performed. In other words, the image quality in Example 1-2 is better than that in Example 1-1.

Note that, depending on the configuration of the image forming apparatus 100 to which the present invention is applied, for example, it is possible to appropriately select which of the above embodiments 1-1 and 1-2 to apply, or by combining them. May be applied. When combining Example 1-1 and Example 1-2, the following may be considered. For example, if the control unit 80 acquires image information and the image quality does not deteriorate even if the absolute value of the primary transfer voltage is decreased (or the image deterioration is not noticeable), the absolute value of the primary transfer voltage is decreased. Embodiment 1-1 is applied. On the other hand, in the case of images where image quality deterioration occurs (or image deterioration is easily noticeable) by simply reducing the absolute value of the primary transfer voltage, it is recommended to reduce the process speed in addition to reducing the absolute value of the primary transfer voltage. Embodiment 1-2 is applied. Here, an example of an image in which the above-mentioned image deterioration does not occur (or in which image deterioration is not noticeable) is an image with a low printing rate where the printing rate is less than a predetermined threshold value. Further, an example of an image in which the image deterioration occurs (or in which image deterioration is noticeable) is an image with a high printing rate where the printing rate is equal to or higher than the predetermined threshold value. Here, "printing rate" is the ratio of the total image data of pixels in the unit area, when the total image data when the image data of all pixels in the unit area are at the highest density level is 100%. (image ratio). The printing rate correlates with the amount of toner per unit area of the toner image.

Further, the primary transfer voltage (difference between the primary transfer voltage in the normal mode) and the process speed in the abnormal discharge suppression mode may be changed as appropriate so as to suppress the occurrence of abnormal discharge. For example, depending on the configuration of the image forming apparatus 100 to which the present invention is applied, the primary transfer voltage and process speed in the abnormal discharge suppression mode may be changed as appropriate so as to suppress the occurrence of abnormal discharge. In addition, in the image forming apparatus 100, the primary transfer voltage in the abnormal discharge suppression mode is set so that the occurrence of abnormal discharge can be suppressed at that time depending on the environment and the amount of repeated use of the image forming apparatus 100 (such as the photosensitive drum 1). or the process speed may be changed as appropriate.

8. Effects As described above, in this embodiment, the image forming apparatus 100 transfers a toner image from the photoreceptor 1 to the intermediate transfer member 8 at the primary transfer portion N1 where the outer circumferential surface of the photoreceptor 1 and the intermediate transfer member 8 are in contact with each other. It has a primary transfer member 5 for primary transfer. The primary transfer member 5 is located at a position where the contact area between the photoreceptor 1 and the intermediate transfer member 8 and the contact area between the primary transfer member 5 and the intermediate transfer member 8 do not overlap with respect to the moving direction of the intermediate transfer member 8. It comes into contact with the inner circumferential surface of the intermediate transfer body 8 . The image forming apparatus 100 includes a current detection section 71 that detects the current flowing through the charging member 2 when a voltage is applied to the charging member 2 by the charging voltage applying section 70, and a control section 80. This control unit 80 controls, during non-image formation, the charging member 2 to charge the surface of the photoconductor 1 that has passed through the primary transfer portion N1 while being charged by the charging member 2 and applying a voltage to the primary transfer member 5. The image forming apparatus 100 performs a detection operation to obtain the detection result of the current detection unit 71 when It is possible to change the operation settings. In this embodiment, the control unit 80 can switch the operation settings during image formation between the first mode and the second mode based on the above information. In particular, in this embodiment, if the absolute value of the current detected by the current detection section 71 in the detection operation is less than a predetermined threshold, the control section 80 sets the operation setting during image formation to the first mode, and sets the operation setting during image formation to the first mode. If the absolute value of the current detected by the current detection unit 71 in the detection operation is equal to or greater than the threshold value, the operation mode during image formation is set to the second mode. In this embodiment, the absolute value of the voltage applied by the primary transfer voltage applying unit 50 to the primary transfer member 5 in the second mode is greater than the absolute value of the voltage applied to the primary transfer member 5 by the primary transfer voltage applying unit 50 in the first mode. The absolute value of the voltage is smaller. Further, the process speed in the second mode may be slower than the process speed in the first mode. In this embodiment, the intermediate transfer body 8 contains an ion conductive material. In addition, in this embodiment, the primary transfer member 5 has a contact area between the primary transfer member 5 and the intermediate transfer body 8 which is larger than a contact area between the photoreceptor 1 and the intermediate transfer body 8 with respect to the moving direction of the intermediate transfer body 8. is located on the downstream side.

According to this embodiment, image defects due to abnormal discharge can be suppressed by detecting the occurrence of abnormal discharge and printing by switching between normal mode and abnormal discharge suppression mode according to the detection result. .

[Example 2]
Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are given the same reference numerals as those of the image forming apparatus of Embodiment 1. Detailed explanation will be omitted.

This embodiment differs from the first embodiment in that, in addition to the configuration of the first embodiment, whether or not to detect the occurrence of abnormal discharge is switched depending on the result of detecting the impedance of the primary transfer portion N1.

1. Determining whether or not to detect abnormal discharge occurrence The impedance of the primary transfer portion N1 is the impedance between the primary transfer roller 5 and the photosensitive drum 1, and depends on the surface resistivity of the intermediate transfer belt 8. The control unit 80 can detect the impedance of the primary transfer unit N1 from the value of the voltage output by the primary transfer voltage application unit 50 and the value of the current detected by the primary transfer current detection unit 51 at that time. can. In this embodiment, the control section 80 detects the impedance of the primary transfer section N1 in the pre-rotation process or the pre-multi-rotation process when starting a job. The impedance detection operation of the primary transfer portion N1 can be performed in synchronization with the primary transfer voltage control (ATVC control). The detection results of voltage values and current values obtained in primary transfer voltage control (ATVC control) may be used.

Table 3 shows the relationship between the impedance of the primary transfer portion N1 and the occurrence of abnormal discharge in the configuration of this embodiment. When the impedance R becomes 110 MΩ or more, abnormal discharge is likely to occur. Therefore, whether or not the abnormal discharge occurrence detection can be executed can be determined by setting the threshold value Rth of the impedance R to 110 MΩ. That is, when the impedance R is 110 MΩ or more, it can be determined that abnormal discharge occurrence detection should be performed. Furthermore, if the impedance R is less than 110 MΩ, it can be determined that there is no need to detect the occurrence of abnormal discharge.

Note that the threshold value Rth of the impedance R may be changed as appropriate so that it can be determined whether or not to detect the occurrence of abnormal discharge. For example, depending on the configuration of the image forming apparatus 100 to which the present invention is applied, the threshold value Rth may be changed as appropriate so that it can be determined whether or not to detect the occurrence of abnormal discharge. In addition, in the image forming apparatus 100, a threshold value Rth is set so that it can be determined whether or not to detect the occurrence of abnormal discharge at that time, depending on the environment or the amount of repeated usage of the image forming apparatus 100 (such as the photosensitive drum 1). It may be changed as appropriate.

2. Control of Switching to Abnormal Discharge Suppression Mode FIG. 6 is a flowchart showing an outline of the procedure of switching operation (processing) between the normal mode and the abnormal discharge suppression mode during execution of one job. The control unit 80 detects the impedance R of the primary transfer unit N1 (S201). Specifically, the control unit 80 acquires the value of the voltage output by the primary transfer voltage application unit 50, and when the primary transfer voltage application unit 50 is outputting the voltage, the control unit 80 controls the primary transfer unit N1 (primary transfer The value of the current flowing through the current detection unit 51) is acquired from the primary transfer current detection unit 51. The value of the voltage output by the primary transfer voltage application section 50 is obtained from the setting value of the output voltage of the primary transfer voltage application section 50 by the control section 80 or the detection result of the voltage detection section included in the primary transfer voltage application section 50. be able to. Then, the control section 80 determines the impedance R of the primary transfer section N1 based on the obtained voltage value and current value. Next, the control unit 80 determines whether the impedance R of the primary transfer unit N1 is equal to or greater than the threshold value Rth (whether or not detection of the occurrence of abnormal discharge can be performed) (S202). If the control unit 80 determines in S202 that the impedance R of the primary transfer unit N1 is not greater than or equal to the threshold value Rth, that is, it is less than the threshold value Rth (R<Rth) (the abnormal discharge occurrence detection is not performed), the control unit 80 performs normal operation. Printing is performed in the mode (S203). Then, the control unit 80 repeats printing in the normal mode until the last image of the job (S204), and ends the job after printing up to the last image of the job.

On the other hand, if the control unit 80 determines in S202 that the impedance R of the primary transfer unit N1 is equal to or higher than the threshold value Rth (R≧Rth) (the abnormal discharge detection is performed), the charging current detection unit 71 The detection result of the current I is acquired (S205). Next, the control unit 80 determines whether the charging current I is greater than or equal to the threshold value Ith (whether abnormal discharge is occurring) (S206). If the control unit 80 determines in S206 that the charging current I is not greater than or equal to the threshold value Ith, that is, less than the threshold value Ith (I<Ith) (abnormal discharge has not occurred), printing is performed in the normal mode. (S203). Then, the control unit 80 repeats printing in the normal mode until the last image of the job (S204), and ends the job after printing up to the last image of the job. Further, when the control unit 80 determines in S206 that the charging current I is equal to or higher than the threshold value Ith (I≧Ith) (abnormal discharge has occurred), printing is performed in the abnormal discharge suppression mode (S207). Then, the control unit 80 repeats printing in the abnormal discharge suppression mode until the last image of the job (S208), and ends the job after printing up to the last image of the job.

A case where the impedance R of the primary transfer portion N1 is less than 110 MΩ will be described. In the configuration of this embodiment, it takes about 4 seconds to detect the occurrence of one abnormal discharge, whereas it takes only 0.2 seconds to detect the impedance of the primary transfer portion N1. In the first embodiment, since the presence or absence of abnormal discharge is detected, it takes about 4 seconds to print in the normal mode. On the other hand, in this embodiment, only the impedance of the primary transfer portion N1 is detected without detecting the presence or absence of abnormal discharge, so it takes only 0.2 seconds to print in the normal mode.

In this way, by determining whether or not to detect the presence or absence of abnormal discharge occurrence according to the impedance detection result of the primary transfer portion N1, the number of times the detection of the presence or absence of abnormal discharge occurrence is executed is minimized, and a decrease in printing speed is suppressed. (reducing downtime when printing cannot be performed).

Note that the operation of measuring the charging current I and the contents of the normal mode and the abnormal discharge suppression mode are the same as those described in Example 1, and therefore redundant explanation will be omitted.

Further, the impedance of the primary transfer portion N1 can be detected by at least one image forming portion P among the plurality of image forming portions P. It may be performed in any one image forming part P (for example, image forming part PK for black) among the plurality of image forming parts P, or in a plurality (or all of them) of the image forming parts P. In the case where a plurality of image forming sections P are used, a representative value such as an average value (or maximum value or minimum value) can be determined and used based on the results obtained at each image forming section P. In this embodiment, the impedance detection result of the primary transfer portion N1 in the black image forming portion PK is used.

Furthermore, although the impedance of the primary transfer portion N1 is obtained here as information regarding the electrical resistance of the primary transfer portion N1, the present invention is not limited to this. As information regarding the electrical resistance of the primary transfer portion N1, any index value that correlates with the electrical resistance (impedance) of the primary transfer portion N1 can be used. For example, this index value may be the value of the current flowing through the primary transfer section N1 (primary transfer voltage application section 50) when the primary transfer voltage application section 50 is outputting a predetermined voltage. Further, this index value may be the value of the voltage output by the primary transfer voltage application section 50 when a predetermined current is flowing through the primary transfer section N1 (the primary transfer voltage application section 50).

3. Effects As described above, in this embodiment, the image forming apparatus 100 includes an electrical resistance detection section (in this embodiment, the primary transfer current detection section 51) that detects an index value correlated with the electrical resistance of the primary transfer section N1. The control unit 80 can switch whether or not to perform a detection operation (operation for detecting the presence or absence of abnormal discharge) based on the detection result of the electrical resistance detection unit 51. In this embodiment, the control unit 80 executes the above-mentioned detection operation when the electrical resistance of the primary transfer portion N1 indicated by the detection result of the electrical resistance detection unit 51 is equal to or greater than a predetermined threshold value.

According to this embodiment, the same effects as in the first embodiment can be obtained, and the number of times the abnormal discharge detection is performed can be reduced, thereby suppressing a decrease in printing speed.

[Example 3]
Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are given the same reference numerals as those of the image forming apparatus of Embodiment 1. Detailed explanation will be omitted.

In addition to the configuration of Embodiment 2, in this embodiment, when a temperature rise of the intermediate transfer belt 8 is detected during continuous printing of multiple sheets in the abnormal discharge suppression mode, the presence or absence of abnormal discharge is detected again. This embodiment differs from the second embodiment in that if no discharge occurs, the mode is returned to the normal mode.

1. Judgment to return from abnormal discharge suppression mode to normal mode The temperature of intermediate transfer belt 8 has a high correlation with the temperature inside (inside the machine) of main body 110 of image forming apparatus 100, and in this embodiment, the temperature of intermediate transfer belt 8 is detected by internal temperature sensor 90. There is a high correlation with the value of the cabin temperature. Therefore, in this embodiment, an in-machine temperature sensor 90 is used as intermediate transfer body temperature detection means for detecting the temperature of the intermediate transfer belt 8. Note that the temperature of the intermediate transfer belt 8 can be calculated by converting the internal temperature of the machine into the temperature of the intermediate transfer belt 8 using a predetermined table showing the relationship between the internal temperature of the machine and the temperature of the intermediate transfer belt 8, or by using the image forming history. It is also possible to use a method of predicting. Further, a temperature sensor that directly detects the temperature of the intermediate transfer belt 8 with or without contact may be used.

Since the electrical resistance of the intermediate transfer belt 8 has temperature characteristics, the impedance of the primary transfer portion N1 changes depending on the temperature of the intermediate transfer belt 8. The intermediate transfer belt 8 in this embodiment has a surface resistivity of 1.0×10 ^10.7 Ω/□ under an environment of a temperature of 15° C. and a relative humidity of 10% (low temperature, low humidity environment). Note that this surface resistivity is the surface resistivity after the intermediate transfer belt 8 is used for printing 150,000 sheets.

FIG. 7 is a graph diagram showing the relationship between the temperature of the intermediate transfer belt 8 and the impedance of the primary transfer portion N1 in the configuration of this embodiment. When the temperature T of the intermediate transfer belt 8 is 16° C. or higher, the impedance R becomes less than 110 MΩ, and no abnormal discharge occurs (see Table 3 of Example 2). Therefore, whether or not to return from the abnormal discharge suppression mode to the normal mode during continuous printing in the abnormal discharge suppression mode can be determined by setting the threshold value Tth of the temperature T of the intermediate transfer belt 8 to 16°C. In other words, when the temperature T of the intermediate transfer belt 8 becomes 16° C. or higher during continuous printing in the abnormal discharge suppression mode, detection of the occurrence of abnormal discharge is performed, including determining whether or not to detect the occurrence of abnormal discharge. can do.

2. Switching Control to Abnormal Discharge Suppression Mode FIG. 8 is a flowchart diagram showing an outline of the procedure of switching operation (processing) between the normal mode and the abnormal discharge suppression mode during execution of one job. The control unit 80 detects the impedance R of the primary transfer unit N1 (S301). Next, the control unit 80 determines whether the impedance R of the primary transfer unit N1 is equal to or greater than the threshold value Rth (whether or not detection of the occurrence of abnormal discharge can be performed) (S302). If the control unit 80 determines in S302 that the impedance R of the primary transfer unit N1 is not greater than or equal to the threshold value Rth, that is, it is less than the threshold value Rth (R<Rth) (the abnormal discharge occurrence detection is not performed), the control unit 80 performs normal operation. Printing is performed in the mode (S303). Then, the control unit 80 repeats printing in the normal mode until the last image of the job (S304), and ends the job after printing up to the last image of the job.

On the other hand, if the control unit 80 determines in S302 that the impedance R of the primary transfer unit N1 is equal to or higher than the threshold value Rth (R≧Rth) (the abnormal discharge detection is executed), the charging current detection unit 71 The detection result of the current I is acquired (S305). Next, the control unit 80 determines whether the charging current I is greater than or equal to the threshold value Ith (whether or not abnormal discharge is occurring) (S306). If the control unit 80 determines in S306 that the charging current I is not greater than or equal to the threshold value Ith, that is, it is less than the threshold value Ith (I<Ith) (abnormal discharge has not occurred), printing is performed in the normal mode. (S303). Then, the control unit 80 repeats printing in the normal mode until the last image of the job (S304), and ends the job after printing up to the last image of the job. Further, when the control unit 80 determines in S306 that the charging current I is equal to or higher than the threshold value Ith (I≧Ith) (abnormal discharge has occurred), printing is performed in the abnormal discharge suppression mode (S307). Next, the control unit 80 obtains the temperature T of the intermediate transfer belt 8 based on the detection result of the internal temperature by the internal temperature sensor 90, and determines whether the temperature T of the intermediate transfer belt 8 is equal to or higher than the threshold value Tth ( S308). As described above, the control unit 80 treats the detection result of the internal temperature by the internal temperature sensor 90 as the temperature T of the intermediate transfer belt 8, or performs predetermined processing based on the detection result of the internal temperature to determine the temperature of the intermediate transfer belt 8. You can also find T. When the control unit 80 determines in S308 that the temperature T of the intermediate transfer belt 8 is equal to or higher than the threshold value Tth (T≧Tth), the control unit 80 returns to the process in S305 and detects the charging current I. Further, if the control unit 80 determines in S308 that the temperature T of the intermediate transfer belt 8 is not equal to or higher than the threshold value Tth, that is, less than the threshold value Tth (T<Tth), the image printed this time is the last image of the job. It is determined whether or not (S309). If the control unit 80 determines in S309 that the image is not the last image of the job, the control unit 80 returns to the process of S307 and prints in the abnormal discharge suppression mode, and if it determines that the image is the last image of the job, the control unit 80 end.

For example, the printing time under the following conditions will be explained. That is, in a job of printing 100 sheets, the temperature T of the intermediate transfer belt 8 increases from 14.degree. C. to 16.degree. C. or higher after the 50th sheet. In the abnormal discharge suppression mode, the process speed is reduced from 300 mm/s in the normal mode to 100 mm/s. The printing time per sheet at a process speed of 300 mm/s is 1 second, the printing time per sheet at a process speed of 100 mm/s is 3 seconds, and the process speed switching operation takes about 4 seconds. In this case, with the configuration of Example 2, it takes about 300 seconds to complete the job. On the other hand, in the configuration of this embodiment, since the process speed is returned to 300 mm/s after the 51st sheet, it takes only about 204 seconds to complete the job. In other words, according to this embodiment, the printing time can be reduced by about 96 seconds compared to the second embodiment.

In this way, when an increase in the temperature of the intermediate transfer belt 8 is detected, the occurrence of abnormal discharge is detected again, and if no abnormal discharge has occurred, the mode is returned to the normal mode, thereby suppressing a decrease in printing speed ( (reducing downtime when printing cannot be performed). If the change in impedance due to the temperature of the intermediate transfer belt 8 is sufficiently large and the image forming apparatus 100 is equipped with means for detecting an index correlated with the temperature of the intermediate transfer belt 8 (such as the internal temperature in this embodiment), It is preferable to apply this embodiment.

Note that the operation of measuring the charging current I and the contents of the normal mode and the abnormal discharge suppression mode are the same as those described in Example 1, and therefore redundant explanation will be omitted. Further, since the operation of detecting the impedance R of the primary transfer portion N1 is the same as that described in the second embodiment, a redundant explanation will be omitted.

Further, in this embodiment, the threshold value Tth is set to 16° C., which corresponds to the absolute value of the temperature of the intermediate transfer belt 8, but the present invention is not limited to this. Since the surface resistivity of the intermediate transfer belt 8 has individual variations, a threshold value may be set as appropriate depending on the intermediate transfer belt 8. Further, the amount of impedance change with respect to the amount of temperature change of the intermediate transfer belt 8 tends to be constant regardless of the surface resistivity. Therefore, the difference between the initial impedance detection result of the primary transfer portion N1 and the impedance at which abnormal discharge no longer occurs (110 MΩ in the configuration of this embodiment) can be converted into the amount of temperature change until abnormal discharge no longer occurs. can. The temperature threshold Tth may be set by adding the amount of temperature change to the initial temperature.

3. Effects As described above, the image forming apparatus 100 has a temperature detection section (in-machine temperature sensor 90 in this embodiment) that detects an index value correlated with the temperature of the intermediate transfer body 8, and the control section 80 has a It is possible to switch whether or not to perform a detection operation (operation for detecting the presence or absence of abnormal discharge) based on the detection result of the detection unit 90. In this embodiment, the control section 80 executes the above-mentioned detection operation when the temperature of the intermediate transfer body 8 indicated by the detection result of the temperature detection section 90 is equal to or higher than a predetermined threshold value. In particular, in this embodiment, the image forming apparatus 100 includes an electrical resistance detection section (in this embodiment, the primary transfer current detection section 51) that detects an index value correlated with the electrical resistance of the primary transfer section N1, and an intermediate transfer body 8. and a temperature detection section (in-machine temperature sensor 90 in this embodiment) that detects an index value correlated with the temperature of the vehicle. The control unit 80 executes the above-mentioned detection operation when the electrical resistance of the primary transfer portion N1 indicated by the detection result of the electrical resistance detection unit 51 is equal to or higher than a predetermined electrical resistance threshold, and in the detection operation, the current detection unit 71 detects the electrical resistance. If the absolute value of the current detected is less than a predetermined current threshold, image formation is executed with the operation setting set to the first mode, and if the absolute value of the current detected by the current detection unit 71 in the detection operation is greater than or equal to the current threshold. In this case, image formation is executed with the operation setting set to the second mode. Then, when image formation is executed in the second mode, the control unit 80 performs the above-mentioned detection operation when the temperature of the intermediate transfer body 8 indicated by the detection result of the temperature detection unit 90 exceeds a predetermined temperature threshold. is executed, and if the absolute value of the current detected by the current detection unit 71 in the detection operation is less than the current threshold value, the operation setting is changed to the first mode and subsequent image formation is executed, and the detection operation is performed. If the absolute value of the current detected by the current detection unit 71 is equal to or greater than the current threshold value, the operation setting is maintained in the second mode and subsequent image formation is performed.

According to this embodiment, the same effects as in the second embodiment can be obtained, and it is also possible to return from the abnormal discharge suppression mode to the normal mode by detecting that the situation is such that abnormal discharge is unlikely to occur. This makes it possible to perform more appropriate control. Specifically, by not implementing the abnormal discharge suppression mode more than necessary, it becomes possible to apply an appropriate primary transfer voltage, and it is possible to further suppress a decrease in printing speed.

In this embodiment, similarly to the second embodiment, a configuration has been described in which the impedance R of the primary transfer portion N1 is detected and it is determined whether or not to detect the occurrence of abnormal discharge based on the detected value. This refers to the control corresponding to S301 and S302 in the sequence of FIG. However, the present invention is not limited to this, and whether or not to implement the abnormal discharge suppression mode is determined based on the detection result of the charging current without detecting the impedance R of the primary transfer section N1, and based on the detection result of the temperature detection section 90. A configuration may also be adopted in which the execution mode is determined again. That is, between S103 and S104 in FIG. 4 described in Example 1, control may be performed to return from the abnormal discharge suppression mode to the normal mode based on the detection result of the temperature detection unit 90 described in this example. . As a result, the same effect as in Example 1 can be obtained, and it is possible to detect a situation in which abnormal discharge is less likely to occur and return from the abnormal discharge suppression mode to the normal mode, thereby making it more appropriate. It becomes possible to apply a primary transfer voltage. Further, by not implementing the abnormal discharge suppression mode more than necessary, it is possible to further suppress a decrease in printing speed.

[others]
Although the present invention has been described above with reference to specific examples, the present invention is not limited to the above-mentioned examples.

In the above embodiment, in order to reduce the potential difference between the primary transfer roller 5 and the photosensitive drum 1 in the abnormal discharge suppression mode and suppress abnormal discharge between them, the primary transfer voltage applied to the primary transfer roller 5 is Reduced the absolute value of voltage. However, the present invention is not limited to this, and in order to reduce the potential difference between the primary transfer roller 5 and the photosensitive drum 1 (non-image area) and suppress abnormal discharge between them, charging It is also possible to reduce the absolute value of the voltage. In this case, it is also possible to reduce the absolute value of the development voltage and to increase the amount of exposure light so as to obtain appropriate development contrast and back contrast. Here, the development contrast is the potential difference between the image area (exposed area) on the photosensitive drum 1 and the development voltage (development roller 41). Further, the back contrast is the potential difference between the non-image area (unexposed area) on the photosensitive drum 1 and the developing voltage (developing roller 41). In other words, the absolute value of the charging potential of the surface of the photoreceptor 1 charged by the charging member 2 in the second mode is greater than the absolute value of the charging potential of the surface of the photoreceptor 1 charged by the charging member 2 in the first mode. The absolute value of may be smaller. In the abnormal discharge suppression mode, the primary transfer voltage and charging voltage may be changed from the normal mode.

Further, instead of printing in the abnormal discharge suppression mode explained in the above embodiment, or in addition to this, as an operation of the abnormal discharge suppression mode, warm air is applied to increase the temperature of the intermediate transfer belt 8. You may drive. Thereby, it becomes possible to actively lower the impedance of the primary transfer portion N1, and it becomes possible to suppress the occurrence of abnormal discharge. Examples of warm-up operations include: Examples of things that interrupt printing are as follows. For example, a heating element (heater) included in the image forming apparatus 100, such as a heating element included in the fixing device 17 or another heating element, may be made to generate heat, or the photosensitive drum 1 may be placed on standby or in a state where the amount of heat generated is higher than usual. Alternatively, the intermediate transfer belt 8 may be rotated idly. Further, the following can be mentioned as things that are executed while printing operations are being performed. Examples of this include causing a heating element (heater) included in the image forming apparatus 100 to generate heat, or increasing the amount of heat generated than usual. In addition, the air inside the image forming apparatus 100 may be raised by stopping the operation or slowing down the rotation speed of the fan that takes in air from the outside to the inside of the image forming apparatus 100 or exhausts air from the inside to the outside. One example is to make it easier to warm up. At this time, a heating element (heater) included in the image forming apparatus 100 may be made to generate heat, or the amount of heat generated may be increased more than usual. That is, the control unit 80 performs image formation based on information regarding the occurrence of discharge between the primary transfer member 5 and the photoreceptor 1 based on the detection result of the current detection unit 71 in the detection operation (operation for detecting the presence or absence of abnormal discharge occurrence). It is possible to perform a warm-up operation that increases the temperature inside the device 100. The control unit 80 can perform the warm-up operation when the absolute value of the current detected by the current detection unit 71 in the detection operation is equal to or greater than a predetermined threshold value. Further, the warm-up operation can be ended when the absolute value of the current detected by the current detection section 71 in the detection operation becomes less than the predetermined threshold value. The threshold value for determining whether or not to execute this warm-up operation may be the same as or different from the threshold value for determining whether or not to switch from the first mode to the second mode in the above-described embodiment. good.

1 Photosensitive drum 2 Charging roller 3 Exposure device 4 Developing device 5 Primary transfer roller 8 Intermediate transfer belt 50 Primary transfer voltage application section 51 Primary transfer current detection section 70 Charging voltage application section 71 Charging current detection section 90 Internal temperature sensor 100 Image forming device

Claims (15)

a rotatable photoconductor that carries a toner image;
a charging member that charges the surface of the photoreceptor;
a charging voltage applying section that applies a voltage to the charging member;
a movable intermediate transfer member that transports the toner image primarily transferred from the photoreceptor to a transfer material;
A primary transfer member that primarily transfers a toner image from the photoreceptor to the intermediate transfer member at a primary transfer portion where the photoreceptor and the outer circumferential surface of the intermediate transfer member are in contact with each other, with respect to the moving direction of the intermediate transfer member, The primary transfer member contacts the inner circumferential surface of the intermediate transfer member at a position where a contact area between the photoreceptor and the intermediate transfer member and a contact area between the primary transfer member and the intermediate transfer member do not overlap. ,
a primary transfer voltage application unit that applies a voltage to the primary transfer member;
In an image forming apparatus having
a current detection unit that detects a current flowing through the charging member when a voltage is applied to the charging member by the charging voltage application unit;
During non-image formation, the surface of the photoconductor is charged by the charging member and has passed through the primary transfer section while a voltage is being applied to the primary transfer member. Execute a detection operation to obtain a detection result of a current detection unit, and change operation settings of the image forming apparatus based on information regarding occurrence of discharge between the primary transfer member and the photoreceptor based on the detection result. a control unit capable of
An image forming apparatus comprising: The control unit is capable of switching operation settings during image formation between a first mode and a second mode based on the information. Image forming device. The control unit sets the operation setting during image formation to the first mode if the absolute value of the current detected by the current detection unit in the detection operation is less than a predetermined threshold, and controls the current detection in the detection operation. 3. The image forming apparatus according to claim 2, wherein when the absolute value of the current detected by the unit is equal to or greater than the threshold value, the operation mode during image formation is set to the second mode. The absolute value of the voltage that the primary transfer voltage applying section applies to the primary transfer member in the second mode is greater than the absolute value of the voltage that the primary transfer voltage applying section applies to the primary transfer member in the first mode. The image forming apparatus according to claim 3, wherein the value is smaller. The charging potential of the surface of the photoreceptor that has been charged by the charging member in the second mode is greater than the absolute value of the charging potential of the surface of the photoreceptor that has been charged by the charging member in the first mode. The image forming apparatus according to claim 3 or 4, wherein the absolute value of is smaller. 6. The image forming apparatus according to claim 3, wherein the process speed in the second mode is slower than the process speed in the first mode. 7 . The control unit according to claim 1 , wherein the control unit is capable of executing a warm-up operation for increasing the internal temperature of the image forming apparatus based on the information. Image forming device. The image forming apparatus according to claim 7, wherein the control unit executes the warm-up operation when the absolute value of the current detected by the current detection unit in the detection operation is equal to or greater than a predetermined threshold. The image forming apparatus includes an electrical resistance detection section that detects an index value that correlates with electrical resistance of the primary transfer section,
9. The control unit is capable of switching whether or not to execute the detection operation based on the detection result of the electrical resistance detection unit. Image forming device. The image forming apparatus according to claim 9, wherein the control section executes the detection operation when the electrical resistance of the primary transfer section indicated by the detection result of the electrical resistance detection section is equal to or higher than a predetermined threshold value. Device. The image forming apparatus includes a temperature detection unit that detects an index value correlated with the temperature of the intermediate transfer body,
The image according to any one of claims 1 to 8, wherein the control unit is capable of switching whether or not to execute the detection operation based on the detection result of the temperature detection unit. Forming device. The image forming apparatus according to claim 11, wherein the control unit executes the detection operation when the temperature of the intermediate transfer member indicated by the detection result of the temperature detection unit is equal to or higher than a predetermined threshold. The image forming apparatus includes an electrical resistance detection section that detects an index value that correlates with the electrical resistance of the primary transfer section, and a temperature detection section that detects an index value that correlates with the temperature of the intermediate transfer body,
The control unit includes:
Executing the detection operation when the electrical resistance of the primary transfer section indicated by the detection result of the electrical resistance detection section is equal to or higher than a predetermined electrical resistance threshold, and the absolute value of the current detected by the current detection section in the detection operation. is less than a predetermined current threshold, image formation is performed with the operation setting set to the first mode, and when the absolute value of the current detected by the current detection unit in the detection operation is equal to or greater than the current threshold, the operation setting is performing image formation in the second mode;
When image formation is executed in the second mode, if the temperature of the intermediate transfer body indicated by the detection result of the temperature detection section exceeds a predetermined temperature threshold, the detection operation is executed, and the detection is performed. If the absolute value of the current detected by the current detection section during operation is less than the current threshold value, the operation setting is changed to the first mode and subsequent image formation is performed, and in the detection operation, the current detection section 7. If the absolute value of the current detected by is equal to or greater than the current threshold, the operation setting is maintained in the second mode and subsequent image formation is performed. The image forming apparatus described in . 14. The image forming apparatus according to claim 1, wherein the intermediate transfer body contains an ion conductive material. In the primary transfer member, a contact area between the primary transfer member and the intermediate transfer body is located downstream of a contact area between the photoreceptor and the intermediate transfer body, with respect to a moving direction of the intermediate transfer body. The image forming apparatus according to any one of claims 1 to 14, characterized in that the image forming apparatus is arranged so as to perform the following operations.

Images