Image formation apparatus

Abstract

To reduce the number of extensions of a first print time being a time required after starting print until finishing the print of the first sheet as much as possible by suppressing the generating of a negative ghost due to a photoreceptor and performing pre-exposure at required timing while maintaining the high image quality and life of a development device to improve productivity.SOLUTION: Control means controls transfer separation means so as to put an image carrier and transfer means into a separation state before performing this image formation operation and controls to perform the pre-exposure for exposing the image carrier by exposure means according to a leaving time after finishing the last image formation operation until starting this image formation operation and information stored in storage means after controlling development separation means so as to put the image carrier and a developer carrier into a separation state.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an image forming apparatus. Here, the image forming apparatus forms an image on a recording material (recording medium) using an electrophotographic image forming method. Examples of the image forming apparatus include a copying machine, a printer (such as a laser beam printer, an LED printer, etc.), a facsimile apparatus, a word processor, and a multifunction machine (multifunction printer) thereof.

Background Art

[0002] Image forming apparatuses such as copying machines and laser beam printers using the electrophotographic method form an electrostatic latent image by irradiating a uniformly charged photoreceptor surface (on the image carrier) with laser light corresponding to image data. Then, the image forming apparatus supplies a developer (hereinafter referred to as "toner") from a developing device to this electrostatic latent image and visualizes it as a toner image on the photoreceptor surface. This toner image is transferred from the photoreceptor surface to a transfer material such as recording paper by a transfer device and fixed on the transfer material by a fixing device, thereby forming a recorded image. After the transfer material is separated, the photoreceptor surface is cleaned by scraping off the remaining toner by a cleaning device and is repeatedly used for image formation.

[0003] By the way, in an electrophotographic image forming apparatus, various charges are generated in the photoreceptor, such as the transfer of charges due to rubbing or discharging with a member in contact with the photoreceptor surface, and the generation of charges inside the photoreceptor by laser light. As shown in FIG. 10, the photoreceptor has a structure in which a charge generation layer that generates photocarriers (plus in the figure) when light hits and a charge transport layer through which the photocarriers move overlap. As shown in FIGS. 11(a) and 11(b), the potential of the exposed portion drops below the charging potential (Vd), and an electrostatic latent image is formed. However, when the exposure is strong, photocarriers remain in the exposed portion (FIGS. 11(c) and 11(d)). The remaining photocarriers inhibit the movement of new photocarriers to the charge transport layer (FIGS. 11(e) and 11(f)), and an image called a negative ghost as shown in FIG. 12(a) may occur.

[0004] In order to prevent negative ghosts, a pre-exposure means using an LED or the like is arranged on the downstream side in the rotation direction of the photoreceptor in the transfer unit and on the upstream side of the charging unit in the rotation direction, and the surface of the photoreceptor before charging is exposed over the entire longitudinal direction of the photoreceptor. According to this method, even if photocarriers exist in the charge transport layer or the charge generation layer, since the entire area is exposed and the photocarriers are uniformly present, they do not appear as ghost images. However, in this method, since it is necessary to arrange the pre-exposure means separately from the exposure means in the image forming apparatus, problems such as an increase in the size of the apparatus itself and an increase in cost occur. Therefore, for example, as described in Patent Document 1, there is a method of exposing the photoreceptor before image formation using the exposure means instead of the pre-exposure means. This is a method of exposing the surface of the photoreceptor before image formation using the exposure means for forming a latent image during normal image formation.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the prior art, since the developing roller also rotates during pre-exposure, the deterioration of the toner is promoted and the life of the developing device is shortened. Therefore, it is conceivable to separate the developing roller from the photoreceptor and further stop the rotation of the developing roller to perform pre-exposure without shortening the life of the developing device. However, even in that case, when a slight speed difference is created between the photoreceptor and the transfer member, there is a risk of defective images such as horizontal streak images due to uneven exposure. This is because the supply of toner that has been acting as a lubricant between the photoreceptor and the transfer member is lost, causing both members to vibrate. In such a situation, it is necessary to suppress the generation of negative ghosting due to the photoreceptor while maintaining high image quality and the life of the developing device.

[0007] Under such circumstances, an object of the present invention is to minimize the number of times of extending the first print time, which is the time required from the start of printing to the completion of the first print, by performing pre-exposure at the necessary timing, and to improve productivity.

Means for Solving the Problems

[0008] In order to solve the above-described problems, an image forming apparatus of the present invention includes the following configuration.

[0009] An image carrier, an exposure unit for forming an electrostatic latent image on the image carrier by exposing the image carrier, a developer carrier for carrying a developer, and a developing unit for supplying the developer by the developer carrier to develop the electrostatic latent image to form a developer image, a transfer unit for transferring the developer image, a developing separation unit for enabling a contact state in which the image carrier and the developer carrier are in contact with each other and a separation state in which the image carrier and the developer carrier are separated from each other, a transfer separation unit for enabling a contact state in which the image carrier and the transfer unit are in contact with each other and a separation state in which the image carrier and the transfer unit are separated from each other, a storage unit for storing information regarding the thickness of the charge generation layer of the image carrier, and a control unit for controlling the exposure unit, the developing separation unit, and the transfer separation unit. The control unit controls the transfer separation unit to separate the image carrier and the transfer unit into a separated state before performing the current image forming operation, and controls the developing separation unit to separate the image carrier and the developer carrier into a separated state. After that, the control unit controls to execute pre-exposure for exposing the image carrier by the exposure unit according to the elapsed time from the end of the previous image forming operation to the start of the current image forming operation and the information stored in the storage unit.

Effects of the Invention

[0010] According to the present invention, by solving the above problems and performing pre-exposure at the necessary timing, the number of times of extending the first print time, which is the time from the start of printing to the completion of the first print, can be minimized as much as possible, and productivity can be improved.

Brief Description of the Drawings

[0011]

Figure 1

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Figure 12

Embodiments for Carrying Out the Invention

[0012] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are examples, and the present invention is not limited to the content of the embodiments. Also, in the following figures, components that are not necessary for the description of the embodiments are omitted from the figures.

[0013] <Regarding Negative Ghosts> Here, the generation of negative ghosts will be described in detail. FIG. 10 is a schematic cross-sectional view schematically showing the layer structure of the photoreceptor. As shown in FIG. 10, the photoreceptor has a structure in which a drum substrate, an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) overlap from the central part toward the circumferential part (surface). When light hits the charge generation layer, it generates photocarriers (positive charges in the figure). The charge transport layer is a layer through which photocarriers move.

[0014] FIG. 11 shows the charge generation layer and the charge transport layer of the photoreceptor above and the surface potential (V) of the photoreceptor below, both showing the state after exposure. As shown in FIGS. 11(a) and 11(b), after the surface of the photoreceptor is charged by a charging member, photocarriers are generated in the charge generation layer in the exposed portion by an exposure device. Here, let the potential after charging be the charging potential Vd. The photocarriers generated in the charge generation layer cancel out the negative charges accumulated on the surface of the photoreceptor due to charging. As a result, the potential of the exposed portion becomes lower in absolute value than the charging potential Vd, and an electrostatic latent image is formed. Here, the potential whose absolute value has decreased by being exposed is called the exposure potential Vl.

[0015] However, as shown in FIGS. 11(c) and 11(d), when the exposure is strong, the amount of photocarriers generated in the charge generation layer also increases. Therefore, photocarriers may remain in the exposed portion without being able to combine with the negative charges on the surface of the photoreceptor. Hereinafter, the photocarriers remaining in the charge generation layer after exposure are also referred to as residual photocarriers. In such a case, as shown in FIG. 11(e), the residual photocarriers may inhibit the movement of newly generated photocarriers to the charge transport layer by the next exposure. Then, as shown in FIG. 11(f), only the portion where the residual photocarriers are present may not have the absolute value of the potential decrease compared to the normal potential, and an image called a negative ghost as shown in FIG. 12(a) may be generated. FIG. 12(a) shows a state in which a negative ghost is generated at a position corresponding to one circumference of the photoreceptor in the image under the influence of the residual photocarriers from one week ago. As shown in FIG. 12(a), the negative ghost is a phenomenon in which the image formed on the photosensitive drum 1 one week ago becomes thin (white) and is visualized.

[0016] To prevent negative ghosts, in the rotation direction of the photoreceptor, pre-exposure means using an LED (Light Emitting Diode) or the like may be arranged on the downstream side of the transfer portion and the upstream side of the charging portion. The pre-exposure means exposes the surface of the photoreceptor before charging over the entire area in the longitudinal direction of the photoreceptor. According to this method, even if photocarriers are present in the charge transport layer or the charge generation layer, since the entire area is exposed by the pre-exposure means, the photocarriers in the charge generation layer will be uniformly present and will not appear as ghost images. However, in this method, since it is necessary to arrange the pre-exposure means separately from the exposure means in the image forming apparatus, problems such as an increase in the size of the apparatus itself and an increase in cost occur. Therefore, for example, a method of exposing the photoreceptor before image formation using the exposure means instead of the pre-exposure means can be mentioned. This is a method of exposing the surface of the photoreceptor before image formation using the exposure means for forming a latent image during normal image formation.

[0017] <First Embodiment> [1. Image Forming Apparatus] The overall configuration of an electrophotographic image forming apparatus will be described. FIG. 1(a) is a schematic cross-sectional view of the image forming apparatus 100, and FIG. 1(b) is a cross-sectional view of the process cartridge 7 as seen along the longitudinal direction (axis of rotation direction) of the photosensitive drum 1 as a rotating body. The image forming apparatus 100 is a full-color laser printer adopting an in-line method and an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a recording material P (for example, recording paper, plastic sheet, cloth, etc.) according to image information. The image information is input into the image forming apparatus 100 from an image reading apparatus (not shown) connected to the image forming apparatus 100 or a host device (not shown) such as a personal computer communicably connected to the image forming apparatus 100.

[0018] The image forming apparatus 100 has first, second, third, and fourth image forming units SY, SM, SC, and SK for forming images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) as a plurality of image forming units. Hereinafter, members contributing to the formation of toner images of respective colors are given suffixes Y, M, C, and K that distinguish colors in the reference numerals, but the suffixes Y, M, C, and K may be omitted except when explaining a specific color. In the present embodiment, the image forming apparatus 100 has a photosensitive drum 1 which is four drum-type electrophotographic photoreceptors arranged side by side in a direction intersecting with the vertical direction as a plurality of image carriers. The photosensitive drum 1 is integrated with the image forming unit S to form a process cartridge 7.

[0019] The rotatable photosensitive drum 1, which is an image carrier carrying an electrostatic latent image, is rotationally driven in the direction of arrow A by a drum driving motor 80 (see FIG. 2), which is drum driving means. The charging roller 2, which is charging means, is a single-layer roller composed of a conductive core bar and a conductive rubber layer. For example, the outer diameter is φ7.5 mm, and the volume resistivity is 10 3 ~10 6It is Ω·cm. Then, by applying a charging voltage of, for example, -1000 V to the charging roller 2 by the charging voltage power supply 71 (see Fig. 2), the surface of the photosensitive drum 1 is uniformly charged to -500 V (see Fig. 11(a)). A DC voltage composed of Vd + Vth is applied to the charging roller 2, and the photosensitive drum 1 is uniformly charged with the charging potential Vd by discharge. The charging potential Vd at this time is, for example, -500 V. Vth is the discharge start voltage. When the applied charging voltage is small, the surface potential on the photosensitive drum 1 does not increase due to discharge, but the surface potential starts to increase due to discharge from the discharge start voltage Vth. That is, the discharge start voltage Vth in this embodiment is -500 V.

[0020] After the surface of the photosensitive drum 1 is charged by the charging roller 2, the surface of the photosensitive drum 1 is irradiated with the laser beam L from the exposure unit 30. The exposure unit 30 is an exposure means for irradiating the laser beam L based on the image information to form an electrostatic latent image on the surface of the photosensitive drum 1. The surface of the photosensitive drum 1 irradiated with the laser beam L changes the surface potential to, for example, -100 V as the exposure potential Vl, and an electrostatic latent image is formed (see Fig. 11(b)).

[0021] The process cartridge 7 is composed of a developing unit 3 as developing means and a photosensitive drum unit 13. In the developing unit 3, a developing roller 4 as a developer carrier and a toner supply roller 5 as a toner supply member are respectively arranged. The developing unit 3 is provided with a developing chamber 3a, a toner storage section 3b, a developing blade 6, and a toner transfer member 22 for transferring toner 10, which is a developer, to the developing chamber 3a by rotating in the direction of arrow G. By receiving the driving force of a developing drive motor 79 (see FIG. 2) which is developing drive means, the developing roller 4 starts to rotate in the direction of arrow D, and the toner supply roller 5 starts to rotate in the direction of arrow R. Then, a voltage of, for example, -300 V is applied as a developing voltage from a developing voltage power source 72 (see FIG. 2) to the developing roller 4. Thereby, toner 10 is supplied and developed by the developing roller 4 to the electrostatic latent image formed on the surface of the photosensitive drum 1, that is, the portion of the above-described exposure potential Vl. Note that a developing clutch 84 (see FIG. 2) for transmitting and blocking the driving force of the developing drive motor 79 is provided, and the driving timing of each color developing unit can be changed.

[0022] The developer image (toner image) developed on the surface of the photosensitive drum 1 is transferred to an intermediate transfer belt 31 which is an intermediate transfer member shown in FIG. 1(a). The intermediate transfer belt 31 formed of an endless belt as an intermediate transfer member is a member for transferring the toner image on the photosensitive drum 1 to a recording material P while facing the photosensitive drum 1 of each image forming section S. The intermediate transfer belt 31 abuts on the photosensitive drum 1 of each image forming section S and circulates (rotates) in the direction of arrow B (counterclockwise direction).

[0023] On the inner peripheral surface side of the intermediate transfer belt 31, transfer members as primary transfer means, i.e., primary transfer rollers 32, are respectively arranged so as to face each photosensitive drum 1. A voltage having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 32 from a primary transfer voltage power source 76 (see FIG. 2). Thereby, the toner image on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 31. In this embodiment, the polarity of the toner has the normal polarity as the negative polarity. Therefore, primary transfer can be performed by applying a positive-polarity voltage as the primary transfer voltage (transfer voltage). Note that the intermediate transfer belt 31 and the primary transfer roller 32 can be brought into contact with (contact state) or separated from the photosensitive drum 1 (can take a separated state) via a primary transfer contact / separation mechanism 83 (see FIG. 2) as primary transfer separation means. Further, in this embodiment, the driving of both the photosensitive drum 1 and the intermediate transfer belt 31 is obtained from a drum driving motor 80, and the ON / OFF of the driving of each of the photosensitive drum 1 and the intermediate transfer belt 31 can be switched by a drum clutch 85 (see FIG. 2).

[0024] Also, a secondary transfer roller 33 as secondary transfer means is disposed on the outer peripheral surface side of the intermediate transfer belt 31. A voltage of a polarity opposite to that of the toner is applied to the secondary transfer roller 33 from a secondary transfer voltage power source 77 (see FIG. 2) as a secondary transfer voltage application unit. Thereby, the toner image on the intermediate transfer belt 31 is transferred (secondary transfer) to the recording material P. Hereinafter, the position where the toner image is secondarily transferred to the recording material P is referred to as a secondary transfer portion. For example, at the time of full-color image formation, the above-described process is sequentially performed in the image forming units SY, SM, SC, and SK, and the toner images of respective colors are sequentially superimposed and primarily transferred onto the intermediate transfer belt 31. Thereafter, the recording material P is conveyed to the secondary transfer portion in synchronization with the movement of the intermediate transfer belt 31. Then, by the action of the secondary transfer roller 33 in contact with the recording material P via the intermediate transfer belt 31, the four-color toner image on the intermediate transfer belt 31 is secondarily transferred onto the recording material P all at once. The recording material P onto which the unfixed toner image has been transferred is conveyed to a fixing device 34. By applying heat and pressure to the recording material P in the fixing device 34, the toner image is fixed to the recording material P, and the recording material P is discharged outside the image forming apparatus 100.

[0025] Also, the toner remaining on the surface of the photosensitive drum 1 without being transferred by the primary transfer roller 32 is scraped off from the surface of the photosensitive drum 1 by a cleaning blade 8 which is a cleaning member in contact with the photosensitive drum 1. The toner scraped off by the cleaning blade 8 is stored in a waste toner storage chamber 9 provided below the cleaning blade 8. The toner that is not transferred to the recording material P by the secondary transfer roller 33 and remains on the intermediate transfer belt 31 is conveyed to a belt cleaning device 35 for the intermediate transfer belt 31 as a cleaning device and stored in a waste toner storage container 36. The control unit 202 will be described later.

[0026] [2. Schematic Configuration of Process Cartridge] The overall configuration of the process cartridge 7 mounted on the image forming apparatus 100 of this embodiment will be described in detail with reference to FIG. 1(b). The process cartridge 7 is detachable from the image forming apparatus 100 via mounting means such as a mounting guide (not shown) and a positioning member (not shown) provided in the image forming apparatus 100. In other words, the photosensitive drum 1 is insertable and removable with respect to the image forming apparatus 100. In this embodiment, all the process cartridges 7 for each color have the same shape. In each process cartridge 7 for each color, toners 10 of each color of yellow (Y), magenta (M), cyan (C), and black (K) are accommodated. In this embodiment, the process cartridge 7 will be described. However, a configuration may be adopted in which the developing unit 3 has a developing cartridge that can be detachably attached to the image forming apparatus 100 alone. Note that in this embodiment, the configurations and operations of the process cartridges 7 for each color are substantially the same except for the type (color) of the accommodated toner 10.

[0027] The process cartridge 7 includes a developing unit 3 including a developing roller 4 and the like, and a photosensitive drum unit 13 including a photosensitive drum 1. In this embodiment, the developing unit 3 and the photosensitive drum unit 13 are integrated into the process cartridge 7, but the present invention is not limited to this. For example, each of them may be configured to be detachable from the image forming apparatus 100 as a developing cartridge and a photosensitive drum cartridge.

[0028] The developing unit 3 is roughly divided into a developing chamber 3a and a toner storage section 3b. The toner storage section 3b is provided with a toner conveying member 22 for conveying the toner 10 to the developing chamber 3a. The toner conveying member 22 conveys the toner 10 to the developing chamber 3a by rotating in the direction of arrow G in the figure. In the developing chamber 3a, a developing roller 4 as a developer carrier that contacts the photosensitive drum 1 and rotates in the direction of arrow D in the figure is provided. In this embodiment, the developing roller 4 and the photosensitive drum 1 rotate so that their surfaces move in the same direction in the opposing developing section. Also, inside the developing chamber 3a, a toner supply roller 5 and a developing blade 6 are arranged. The toner supply roller 5 supplies the toner 10 conveyed from the toner storage section 3b to the developing roller 4. The developing blade 6 is a toner regulating member that regulates the coating amount and imparts charge to the toner 10 on the developing roller 4 supplied by the toner supply roller 5.

[0029] Independent voltages are applied from the power supply to the developing roller 4, the toner supply roller 5, and the developing blade 6 (see Figure 2). The toner 10 supplied to the developing roller 4 by the toner supply roller 5 is charged by rubbing between the developing roller 4 and the developing blade 6, charge is imparted, and the layer thickness is regulated. The toner 10 on the developing roller 4 with the regulated layer thickness is conveyed to the opposing portion with the photosensitive drum 1 by the rotation of the developing roller 4, and the electrostatic latent image on the photosensitive drum 1 is developed and visualized as a toner image.

[0030] During the image forming operation, a predetermined DC voltage (developing voltage: Vdc) applied to the developing roller 4 is set to -300V. Also, by applying a voltage (toner supply voltage: Vr = -450V) to the toner supply roller 5, the potential difference (ΔVr) between the toner supply roller 5 and the developing roller 4 is adjusted to adjust the supply amount of the toner 10 to the developing roller 4. In this embodiment, ΔVr = Vdc - Vr is set to +150V (=-300V - (-450V)), and a potential setting is made such that the negatively charged toner easily moves from the toner supply roller 5 to the developing roller 4. When developing and visualizing the electrostatic latent image on the photosensitive drum 1 as a toner image, the developing roller 4 is rotationally driven so as to contact the circumferential surface of the photosensitive drum 1.

[0031] In the photosensitive drum unit 13, a photosensitive drum 1 is rotatably attached via a bearing (not shown). The photosensitive drum 1 is rotationally driven in the direction of arrow A in Fig. 1(b) by receiving the driving force of a drum driving motor 80. Further, in the photosensitive drum unit 13, a charging roller 2 and a cleaning blade 8 as a plate-shaped elastic body are arranged so as to contact the circumferential surface of the photosensitive drum 1. One end of the cleaning blade 8 is fixed to a plate-shaped metal sheet metal, and the other free end abuts against the rotation of the photosensitive drum 1 in the counter direction, forming a cleaning nip portion which is the contact portion with the photosensitive drum 1. The surface of the photosensitive drum 1 is rubbed by the cleaning blade 8 to scrape off the toner 10 and fine particles remaining in the transfer process and store them in the waste toner storage chamber 9. Thereby, contamination of the charging roller 2 and image defects caused by the toner 10 being carried around on the photosensitive drum 1 are prevented.

[0032] [3. Structure of Photosensitive Drum] The photosensitive drum 1 is composed of a cylindrical metal support having conductivity, a conductive layer as an undercoat layer of the support, a photosensitive layer (charge generation layer, charge transport layer) formed on the undercoat layer, and a protective layer formed on the photosensitive layer. The photosensitive drum 1 is configured by providing a photosensitive material such as OPC (organic photoconductor), amorphous selenium, or amorphous silicon on a drum substrate on a cylinder having an outer diameter of φ24 mm formed of aluminum, nickel, or the like as a support. Further, in order to improve the wear resistance, the photosensitive drum 1 in this embodiment is provided with a wear-resistant protective layer on the outermost layer. By providing the protective layer, the durability can be improved. In this embodiment, the protective layer is provided, but it may not be provided.

[0033] The protective layer preferably contains conductive particles and / or a charge transport material and a resin. Examples of the conductive particles include particles of metal oxides such as titanium oxide, zinc oxide, tin oxide, and indium oxide. Examples of the charge transport material include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, and resins having groups derived from these substances. Among these, triarylamine compounds and benzidine compounds are preferred. Examples of the resin include polyester resins, acrylic resins, phenoxy resins, polycarbonate resins, polystyrene resins, phenolic resins, melamine resins, and epoxy resins. Among them, polycarbonate resins, polyester resins, and acrylic resins are preferred.

[0034] Also, the protective layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of the reaction in this case include thermal polymerization reaction, photopolymerization reaction, and radiation polymerization reaction. Examples of the polymerizable functional group of the monomer having a polymerizable functional group include an acrylic group and a methacrylic group. A material having a charge transport ability may be used as the monomer having a polymerizable functional group.

[0035] The protective layer may contain additives such as an antioxidant, an ultraviolet absorber, a plasticizer, a leveling agent, a slipperiness imparting agent, and a wear resistance improving agent. Specifically, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, boron nitride particles, etc. may be mentioned. The average film thickness of the protective layer is preferably 0.5 μm or more and 10 μm or less, and more preferably 1 μm or more and 7 μm or less.

[0036] The protective layer can be formed by preparing a coating liquid for the protective layer containing each of the above-mentioned materials and a solvent, forming this coating film, and drying and / or curing it. Examples of the solvent used in the coating liquid include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. In this example, the average film thickness of the protective layer was set to 3 μm.

[0037] [4. Control Modes of the Image Forming Apparatus] Next, the control modes of the image forming apparatus 100 will be described. FIG. 2 is a block diagram showing a schematic control mode of the main part of the image forming apparatus 100 of this example. The control unit 202 is a control means for controlling the operation of the image forming apparatus 100, and exchanges various electrical information signals. Further, the control unit 202 processes electrical information signals input from various process devices and sensors, and processes command signals to various process devices. The controller 200 exchanges various electrical information with a host device (not shown), and comprehensively controls the image forming operation of the image forming apparatus 100 via the interface 201 according to a predetermined control program and reference table by the control unit 202. The control unit 202 is configured to include a CPU (Central Processing Unit) 155, a memory 15, a timer 156, and the like. The CPU 155 is a central element that performs various arithmetic processes. The memory 15 is a storage element such as a RAM (Random Access Memory) and a ROM (Read Only Memory). The timer 156 measures time. In the RAM, detection results of sensors, count results of counters, calculation results, etc. are stored, and in the ROM, a control program, a data table obtained in advance by experiments, etc. are stored. To the control unit 202, each control target, sensor, counter, etc. in the image forming apparatus 100 are connected.

[0038] The control unit 202 controls the transmission and reception of various electrical information signals, the driving timings of each unit, etc., and performs control such as of a predetermined image formation sequence. For example, the control unit 202 controls the following high-voltage power supplies and devices in order to form a toner image on the surface of the photosensitive drum 1. The control unit 202 controls the charging voltage power supply 71 that applies a charging voltage, the developing voltage power supply 72 that applies a developing voltage, and the toner supply voltage power supply 73 that applies a toner supply voltage to the toner supply roller 5. Also, the control unit 202 controls the developing blade voltage power supply 74 that is the power supply for the developing blade 6 which is a toner regulating member. Further, the control unit 202 controls the exposure unit 30 and the like. Additionally, the control unit 202 controls the primary transfer voltage power supply 76, the secondary transfer voltage power supply 77, etc. for forming a toner image on the recording material P. Also, the control unit 202 controls the developing drive motor 79 that controls the driving of the developing unit 3, and the drum drive motor 80 that controls the driving of the intermediate transfer belt 31 and the photosensitive drum 1. Moreover, the control unit 202 controls the developing clutch 84 for transmitting or blocking the driving force of the developing drive motor 79 to the developing unit 3, and the drum clutch 85 for transmitting or blocking the driving force of the drum drive motor 80 to the photosensitive drum 1. Also, the control unit 202 controls the developing contact / separation mechanism 82 as a developing separation means for controlling the contact / separation between the developing roller 4 and the photosensitive drum 1, and the primary transfer contact / separation mechanism 83 for controlling the contact / separation between the photosensitive drum 1 and the intermediate transfer belt (primary transfer roller 32).

[0039] [5. Characteristics and Execution Feasibility Judgment Procedure of the Pre-Exposure Sequence] In this embodiment, the process cartridge 7 is provided with a memory 15 as a storage means. As the storage means, any form such as a contact non-volatile memory, a non-contact non-volatile memory, a volatile memory having a power supply, etc. can be used. In this embodiment, a memory 15 which is a non-contact non-volatile memory is mounted on the process cartridge 7. The memory 15 has an antenna (not shown) which is an information transmission means on the memory side, and can read and write information by communicating wirelessly with a control unit 202 provided in the main body of the image forming apparatus 100. In this embodiment, the control unit 202 has the functions of an information transmission means on the main body side of the image forming apparatus 100 and a means for reading and writing information of the memory 15. Information regarding the sensitivity of the photosensitive drum 1 described later is stored in this memory 15. In this embodiment, it is characterized in that whether to execute the pre-exposure sequence is determined according to the information regarding the sensitivity of the photosensitive drum 1 stored in the memory 15.

[0040] As described above, after charging the surface of the photosensitive drum 1 by the charging roller 2, photocarriers are generated in the portion of the photosensitive drum 1 that has received exposure by the exposure unit 30, and the negative charges accumulated on the surface of the photosensitive drum 1 due to this photocarrier and charging cancel each other out. As a result, the potential of the exposed portion on the photosensitive drum 1 drops below the charging potential (Vd), and an exposure potential (Vl) is formed.

[0041] <Relationship between the film thickness (thickness) of the charge generation layer and negative ghost> [1] When the film thickness of the charge generation layer is thin As described above, negative ghost is generated in the process of accumulation of photocarriers. When the film thickness of the charge generation layer is thin, the amount of generated photocarriers is small, and it takes time until the residual photocarriers accumulate, so negative ghost is generated.

[0042] The details will be described below. When printing a completely black area with strong exposure in a state where there are no residual photo carriers (new product or after being left for a long time), the normal potential is obtained as described in the background art. However, when exposure is continued, photo carriers remain in the exposed areas without being able to combine with the negative charges on the surface of the photosensitive drum 1 (Figs. 11(c) and 11(d)). In such a case, the residual photo carriers inhibit the movement of new photo carriers to the charge transport layer (Fig. 11(e)). Then, only in that part, the potential does not drop compared to the normal potential (Fig. 11(f)), and an image called a negative ghost as shown in Fig. 12(a) may occur.

[0043] After that, since photo carriers remain, negative ghosts do not occur even when exposure is continuously repeated. That is, when the entire surface of the photosensitive drum 1 is exposed and photo carriers remain throughout the area, no potential difference is generated between the exposed area and the unexposed area, and negative ghosts do not occur.

[0044] 〔2〕When the film thickness of the charge generation layer is thick When the film thickness of the charge generation layer is thick, the amount of generated photo carriers is large, and residual photo carriers quickly accumulate, so negative ghosts do not occur.

[0045] The details will be described below. When printing a completely black area with strong exposure in a state where there are no residual photo carriers (new product or after being left for a long time), since the amount of generated photo carriers is large, photo carriers remain without being able to combine with the negative charges on the surface of the photosensitive drum 1 in the first exposure immediately after that (Figs. 11(c) and 11(d)). In such a case, even in the first exposure, the potential does not drop compared to the normal potential. However, since photo carriers similarly remain even when exposure is continuously repeated, as a result, the difference in exposure potential Vl between the first and second exposures is small, and negative ghosts do not occur.

[0046] <Relationship between the film thickness of the charge generation layer and positive ghosts> When the film thickness of the charge generation layer is thick, positive ghosts occur. By repeating the exposure, the remaining photo carriers become stronger, and when charging next, the charging potential Vd cannot be increased to the normal potential due to the influence of the remaining photo carriers. Since the charging potential Vd of the exposed part decreases and the exposure potential Vl decreases accordingly, an image called a positive ghost as shown in Fig. 12(b) may occur. As shown in Fig. 12(b), a positive ghost is a phenomenon in which the image formed on the photosensitive drum 1 one cycle ago becomes dark (black) and is visualized. Therefore, from the viewpoint of positive ghosts, it is desirable that the film thickness of the charge generation layer be as thin as possible.

[0047] <Film Thickness of Charge Generation Layer and Measurement Method> In this embodiment, a charge generation layer with a thin film thickness [1] that does not generate positive ghosts is adopted. The generation timing of negative ghosts varies depending on the film thickness of the charge generation layer. For this reason, information regarding the film thickness of the charge generation layer that correlates with the sensitivity of the photosensitive drum 1 is stored in the memory 15 of the process cartridge 7.

[0048] The method for measuring the film thickness of the charge generation layer will be described. A calibration curve is obtained from the density value measured by pressing a spectro densitometer (trade name: X-Rite504 / 508, manufactured by X-Rite) against the surface of the photosensitive drum 1 and the film thickness measurement value obtained by observing the cross-sectional SEM image of the charge generation layer. By converting the density value of each point of the photosensitive drum 1 using the obtained calibration curve, the film thickness distribution of the charge generation layer was precisely and simply measured. The film thicknesses of the charge generation layer adopted in this embodiment are 0.60, 0.70, and 0.80.

[0049] <Relationship between Standby Time and Negative Ghosts> Although photo carriers disappear over time, if there are few remaining photo carriers, the time until they disappear becomes shorter. That is, the thinner the film thickness of the charge generation layer, the fewer the remaining photo carriers, so the time until they disappear becomes shorter, and negative ghosts occur after disappearance.

[0050] <Procedure for Judging Whether to Execute Pre-Exposure Sequence> In this embodiment, as shown in Table 1, the execution conditions based on the film thickness of the charge generation layer and the standing time T (standing time) are stored in the ROM on the image forming apparatus 100 side. The control unit 202 determines whether the pre-exposure sequence can be executed according to the information regarding the sensitivity of the photosensitive drum 1 (film thickness of the charge generation layer) stored in the memory 15 and the standing time since the end of the printing operation.

Table 1

[0051] Table 1 shows the determination of whether the pre-exposure sequence can be executed when the film thickness of the charge generation layer is less than 0.65, less than 0.75, and less than 0.85, respectively, and the standing time is less than 3 hours, less than 6 hours, less than 9 hours, and less than 12 hours, respectively. For example, when the film thickness of the charge generation layer is 0.70 (predetermined thickness) classified as 0.65 or more and less than 0.75, if the standing time is less than 6 hours, it is determined that the pre-exposure sequence is not executed. On the other hand, if the standing time is 6 hours or more (predetermined time or more), it is determined that the pre-exposure sequence is executed. When the film thickness of the charge generation layer is the predetermined film thickness, it is determined that the pre-exposure sequence is executed as the standing time becomes longer.

[0052] Also, for example, even if the standing time is 3 hours or more and less than 6 hours, if the film thickness of the charge generation layer is less than 0.65, it is determined that the pre-exposure sequence is executed, and if it is 0.65 or more, it is determined that the pre-exposure sequence is not executed. Thus, even with the same standing time (predetermined time), it is determined that the pre-exposure sequence is executed as the film thickness of the photosensitive drum 1 becomes thinner (less than the predetermined thickness).

[0053] A procedure for determining whether to execute the pre-exposure sequence will be described. FIG. 7 is a flowchart for determining whether to execute the pre-exposure sequence of the present embodiment. In the present embodiment, after the printing operation ends, the ghost countermeasure sequence from S101 and later is executed by the control unit 202. The control unit 202 executes the processing from S101 and later when the image formation ends. In S101, the control unit 202 initializes the timer 156 (T = 0) and starts measuring time by the timer 156 after the image formation ends. In S102, the control unit 202 receives a print start request signal from the controller 200. In S103, the control unit 202 acquires the time T measured by the timer 156.

[0054] In S104, the control unit 202 communicates with the memory 15 mounted on the process cartridge 7 by the CPU 155, and reads information regarding the sensitivity of the process cartridge 7 (the film thickness of the charge generation layer). In S105, the control unit 202 determines whether the execution conditions are satisfied based on the content of the ROM on the main body side of the image forming apparatus 100 (Table 1), the film thickness of the charge generation layer read in S104, and the elapsed time T started to be measured in S103.

[0055] If the control unit 202 determines in S105 that the execution conditions are satisfied, the process proceeds to S106. In S106, the control unit 202 executes the pre-exposure sequence. After the pre-exposure sequence in S106 ends, in S107, the control unit 202 starts a normal image forming operation in response to the print start request signal received in S102.

[0056] If the control unit 202 determines in S105 that the execution conditions are not satisfied, the pre-exposure sequence is not executed, and a normal image forming operation is started in S107. When the image forming operation ends in S108, the control unit 202 returns the process to S101. The control unit 202 resets the value of the elapsed time T (T = 0) in S101, starts measuring the elapsed time T again by the timer 156, and prepares for the reception of the next print start request signal.

[0057] For example, when the film thickness of the photosensitive drum 1 read from the memory 15 of the process cartridge 7 is less than 0.65 and the standing time T measured by the timer 156 is 3 hours or more and less than 6 hours, the control unit 202 determines that the execution conditions are satisfied from Table 1. Also, for example, when the film thickness of the photosensitive drum 1 read from the memory 15 of the process cartridge 7 is less than 0.65 and the standing time T measured by the timer 156 is less than 3 hours, the control unit 202 determines that the execution conditions are not satisfied from Table 1.

[0058] [6. Execution Procedure of Pre-Exposure Sequence] Next, the execution procedure of the pre-exposure sequence in S106 of FIG. 7 will be described. FIG. 3 is a time chart of the pre-exposure sequence of this embodiment. In FIG. 3, (i) shows the state (stop, low-speed rotation) of the photosensitive drum 1, (ii) shows the application state of the charging voltage (V), and (iii) shows the exposure state (ON, OFF). Also, (iv) shows the contact / separation state of the intermediate transfer belt 31, (v) shows the driving state (ON, OFF) of the intermediate transfer belt 31, and (vi) shows the application state of the primary transfer voltage (V). Further, (vii) shows the contact / separation state of the developing roller 4 with the photosensitive drum 1, (viii) shows the driving state (ON, OFF) of the developing roller 4, and (ix) shows the application state of the developing voltage (V). The horizontal axis all indicates time. t1 to t5 indicate timings (times).

[0059] First, at timing t1, the photosensitive drum 1 starts to rotate at a low speed by the drum drive motor 80. Here, the image forming apparatus 100 of this embodiment can perform an image forming operation at a plurality of image forming speeds. The control unit 202 rotates the photosensitive drum 1 at the slowest image forming speed among the plurality of image forming speeds and executes a pre-exposure sequence. In this way, the rotation speed of the photosensitive drum 1 is the slowest among the speeds operable during image formation. By rotating the photosensitive drum 1 at a slow speed, it is possible to enhance the effect of reducing negative ghost while suppressing an increase in the number of rotations of the photosensitive drum 1. Also, since the driving of the intermediate transfer belt 31 is taken from the drum drive motor 80, the intermediate transfer belt 31 also starts to be driven together with the start of rotation of the photosensitive drum 1. Also, the intermediate transfer belt 31 and the photosensitive drum 1 are in a separated state by the primary transfer contact and separation mechanism 83 before the execution of this sequence, but at this time as well, the intermediate transfer belt 31 and the photosensitive drum 1 maintain the separated state. Also, the primary transfer voltage by the primary transfer voltage power supply 76 is 0 V (OFF). Also, the developing roller 4 and the photosensitive drum 1 are in a separated state by the developing contact and separation mechanism 82 before the execution of this sequence, but at this time as well, the developing roller 4 and the photosensitive drum 1 maintain the separated state. The developing voltage by the developing voltage power supply 72 is 0 V.

[0060] Next, at timing t2, a charging voltage is applied to the charging roller 2 by the charging voltage power supply 71. The charging voltage at this time is -1000 V. Then, at timing t3, which is the timing when the portion charged at timing t2 reaches the exposure position, exposure of the photosensitive drum 1 is started by the exposure unit 30. Here, the exposure in the longitudinal direction of the photosensitive drum 1 is performed over the entire area equal to or larger than the image forming width, the laser light amount is the same as that during image formation at the normal speed, and is stronger than the laser light amount during image formation in the low speed mode. As a result, a stronger laser light hits the photosensitive drum 1, thereby enhancing the effect of reducing negative ghost. Also, by rotating the photosensitive drum 1 at a low speed, the generation of vibration can be suppressed, and the occurrence of exposure unevenness can be suppressed.

[0061] Also, in accordance with the timing when exposure for approximately one rotation (one circumference) of the photosensitive drum 1 in the circumferential direction is completed, first, the charging voltage is stopped at timing t4, and then, exposure is stopped at timing t5, and the process proceeds to the normal image forming operation as it is. Note that, in this embodiment, the control unit 202 stops exposure within the time corresponding to one circumference of the photosensitive drum 1, but the timing for stopping exposure may be a timing corresponding to one circumference or more of the rotation of the photosensitive drum 1.

[0062] In this embodiment, the rotation speed of the photosensitive drum 1 during the pre-exposure sequence was set to the slowest speed among the speeds operable during image formation, and the sequence was executed. However, this is not a limitation, and the sequence may be executed at a low speed at which driving is stable.

[0063] [7. Verification of Effects] To verify the effects of this embodiment, a printing test was conducted in an environment of normal temperature and humidity (temperature 23°C, humidity 50%). In this verification, the film thickness of the charge generation layer was 0.60, the circumferential speed of the photosensitive drum 1 during image printing was 321 mm / sec, and the circumferential speed of the photosensitive drum 1 during the pre-exposure sequence was 91 mm / sec. At this time, when the printed image was checked, no occurrence of horizontal streak images due to negative ghosting or uneven exposure was observed in the printed images after 5 hours of stop and after 8 hours of stop because the pre-exposure sequence was executed based on Table 1.

[0064] To clarify the effects of this embodiment, as a comparative example, a similar printing test was conducted with a configuration in which the photosensitive drum 1 and the intermediate transfer belt 31, which is the transfer means, do not separate during the pre-exposure sequence. FIG. 4 is a diagram showing the sequence of the comparative example, and (i) to (ix) are the same as (i) to (ix) of FIG. 3. Also, t11 to t19 indicate timings.

[0065] As shown in FIG. 4, in this comparative example, (iv) exposure is performed while the photosensitive drum 1 and the intermediate transfer belt 31 are in contact with each other. At timing t11, both the photosensitive drum 1 and the intermediate transfer belt 31 are started to rotate. Then, at timing t12, a charging voltage is applied to the charging roller 2 by the charging voltage power supply 71. Next, at timing t13, a primary transfer voltage similar to that during image formation is applied to the primary transfer roller 32 from the primary transfer voltage power supply 76. Then, at timing t14, the intermediate transfer belt 31 is brought into contact with the photosensitive drum 1 by the primary transfer contact / separation mechanism 83. And at timing t15, the exposure unit 30 starts to expose the photosensitive drum 1. In accordance with the timing when the exposure for approximately one rotation of the photosensitive drum 1 is completed, first, the charging voltage is stopped at timing t16, and then the exposure is stopped at timing t17. Then, the intermediate transfer belt 31 is separated from the photosensitive drum 1 at timing t18, and the primary transfer voltage is stopped at timing t19.

[0066] In this comparative example, the predetermined time for executing the pre-exposure sequence was set to 6 hours, and if 6 hours or more had elapsed since the end of the previous image formation, the pre-exposure sequence was executed. Also, in this printing test, the peripheral speed of the photosensitive drum 1 during image printing was 321 mm / sec, and the peripheral speed of the photosensitive drum 1 during the execution of the pre-exposure sequence was 91 mm / sec. At this time, when the printed image was checked, negative ghosts were generated in the printed image after a 5-hour stop. On the other hand, although no generation of negative ghosts was observed in the printed image after an 8-hour stop, horizontal streak images due to uneven exposure were generated.

[0067] As described above, when a predetermined time or more has elapsed since the end of the previous (immediately preceding) image formation operation, the following control is performed. That is, the photosensitive drum 1 and the intermediate transfer belt 31 are separated, and further, the photosensitive drum 1 and the developing roller 4 are separated, the rotation of the developing roller 4 is stopped, and the pre-exposure sequence is performed at a speed slower than that during normal image formation with the same laser light amount as during normal image formation.

[0068] In the first embodiment, it is determined whether the pre-exposure sequence can be executed according to the information regarding the sensitivity of the photosensitive drum 1 (film thickness of the charge generation layer) stored in the memory 15 and the elapsed time since the end of the printing operation. By doing so, it is possible to suppress the occurrence of negative ghosting and exposure unevenness. Furthermore, it is possible to minimize the influence on the life of the photoreceptor and the developing device by performing this sequence. Furthermore, since the pre-exposure sequence is executed at the necessary timing, it is possible to minimize the number of times the first print time, which is the time required from the start of printing to the completion of the first print, is extended, and productivity can be improved. Note that there is a correlation between the sensitivity of the photosensitive drum 1 and the film thickness of the charge generation layer. In Example 1, the film thickness of the charge generation layer was adopted as the information regarding the sensitivity of the photosensitive drum 1 stored in the memory 15, but it is not limited to this, and any information that has a correlation with the sensitivity of the photosensitive drum 1 may be used.

[0069] As described above, according to Example 1, it is possible to suppress the occurrence of negative ghosting by the photoreceptor while maintaining high image quality and the life of the developing device. Furthermore, since the pre-exposure sequence is executed at the necessary timing, it is possible to minimize the number of times the first print time, which is the time required from the start of printing to the completion of the first print, is extended, and productivity can be improved.

[0070] <Second Embodiment> In this embodiment, the amount of residual photo carriers is calculated based on the information regarding use (hereinafter referred to as use information), and the pre-exposure sequence is executed when the calculated amount of residual photo carriers is less than a threshold value. In this embodiment, parts overlapping with the first embodiment will not be described, and the method for calculating the residual photo carriers unique to this embodiment will be described.

[0071] <Method for Calculating the Amount of Residual Photo Carriers> A method for calculating the amount of residual photo carriers will be described. As described above, negative ghosting occurs during the process of photo carrier accumulation (when the amount is small). When exposure is repeated, photo carriers remain (accumulation amount) in the exposed areas without being able to combine with the negative charges on the surface of the photosensitive drum 1. Also, the remaining photo carriers decay over time (decay amount). That is, the amount of residual photo carriers at the start of image formation can be calculated and estimated from the accumulation amount and the decay amount.

[0072] Figure 8(a) shows the relationship between the amount of photo carriers generated during single-sided printing and the amount of residual photo carriers (accumulation amount) after single-sided printing. When the amount of photo carriers generated is small, the amount of residual photo carriers tends to be small. Also, the amount of photo carriers generated is correlated with the film thickness of the charge generation layer and the printing rate. The thinner the film thickness and the lower the printing rate, the smaller the amount. Note that the printing rate indicates the ratio of the area where the electrostatic latent image is formed to the entire area of the image formation region. Therefore, based on usage information such as the number of printed sheets and the printing rate, the accumulation amount of residual photo carriers can be calculated. Also, Figure 8(b) shows the relationship between the amount of residual photo carriers and the standing time. The amount of residual photo carriers decays with the passage of time (standing time) (decay amount).

[0073] Therefore, the above-described measurement data (Figure 8(a), Figure 8(b)) are stored in advance in the ROM on the main body side of the image forming apparatus 100. From the amount of residual photo carriers (accumulation amount) at the end of the previous image formation and the standing time T (decay amount) from the end of the previous image formation to the start of the current image formation, the amount of residual photo carriers at the start of image formation is calculated. The calculated amount of residual photo carriers is stored in the memory 15.

[0074] Specifically, this will be described with reference to FIG. 8(c). FIG. 8(c) shows the amount of residual photocarriers when image formation and leaving it idle are repeated. The horizontal axis represents the number of image formations, and the vertical axis represents the amount of residual photocarriers. In FIG. 8(c), the portion where the amount of residual photocarriers decreases without the number of sheets changing indicates that it has been left idle. When image formation is performed, the amount of residual photocarriers increases according to the relationship in FIG. 8(a), and when left idle, it decreases according to the relationship in FIG. 8(b). Furthermore, by repeating image formation and leaving it idle, the amount of residual photocarriers gradually increases. However, when the idle time becomes long, the amount of residual photocarriers significantly decreases (A), and negative ghosting occurs. In this embodiment, negative ghosting occurred when the amount of residual photocarriers was below that shown by the broken line in FIG. 8(c). Therefore, in this embodiment, the amount of residual photocarriers shown by the broken line is set as the threshold, and when the amount of residual photocarriers at the start of image formation becomes below the threshold, the ghost countermeasure sequence is executed.

[0075] <Procedure for determining whether to execute the pre-exposure sequence> In this embodiment, the amount of residual photocarriers is calculated based on the usage information, and it is determined whether to execute the pre-exposure sequence according to the calculated result. This sequence is performed before the sequence of the first embodiment above. The procedure for determining whether to execute the pre-exposure sequence will be described.

[0076] FIG. 9 is a flowchart for determining whether to execute the pre-exposure sequence of this embodiment. In this embodiment, the amount of residual photocarriers at the start of image formation is calculated from the amount of residual photocarriers at the end of the previous image formation and the idle time T from the end of the previous image formation to the start of the current image formation. Then, when the calculated amount of residual photocarriers is below the threshold, the ghost countermeasure sequence is executed. When image formation ends, the control unit 202 executes the processing after S201. In S201, the control unit 202 initializes the timer 156 (T = 0) and starts measuring time with the timer 156 after the end of image formation. In S202, the control unit 202 receives a print start request signal from the controller 200. In S203, the control unit 202 acquires the time T measured by the timer 156.

[0077] In S204, the control unit 202 communicates with the memory 15 mounted on the process cartridge 7 by the CPU 155, and reads the amount of residual photocarriers at the end of the previous image formation. In S205, the control unit 202 calculates the amount of residual photocarriers from the content of the main body side ROM of the image forming apparatus 100 in which the data of FIGS. 8(a) and 8(b) are stored in advance by the CPU 155, the amount of residual photocarriers (accumulated amount) read in S204, and the elapsed time T (attenuation amount).

[0078] In S206, the control unit 202 determines whether or not the amount of residual photocarriers calculated in S205 is equal to or less than the threshold value. If the control unit 202 determines in S206 that the calculated amount of residual photocarriers is equal to or less than the threshold value, the process proceeds to S207. In S207, the control unit 202 executes the pre-exposure sequence. After the pre-exposure sequence in S207 ends, in S208, the control unit 202 starts the normal image forming operation in response to the print start request signal received in S202. If the control unit 202 determines in S206 that the calculated amount of residual photocarriers is greater than the threshold value, the control unit 202 does not execute the pre-exposure sequence, proceeds the process to S208, and immediately starts the normal image forming operation.

[0079] In S210, when the image formation in S209 ends, the control unit 202 calculates the amount of residual photocarriers at the end of image formation based on usage information such as the number of printed sheets and the printing rate in the same manner as in S205, stores it in the memory 15, and returns the process to S201. The amount of residual photocarriers stored in the memory 15 in S210 is read in S204 before the start of the next image formation and used to determine whether or not to execute the next pre-exposure sequence.

[0080] As described above, in this embodiment, the amount of residual photocarriers is calculated based on usage information, and whether to execute the pre-exposure sequence is determined according to the calculated amount of residual photocarriers. Thereby, the occurrence of negative ghosts and exposure unevenness can be suppressed. Further, since the pre-exposure sequence is executed at the necessary timing, the number of times of extending the first print time, which is the time from the start of printing to the completion of the first print, can be minimized as much as possible, and productivity can be improved.

[0081] Note that the usage information may be information obtained based on the following two pieces of information. The first piece of information may be any one of, for example, the number of recording materials (number of printed sheets) on which an image forming operation has been performed, the number of rotations of the photosensitive drum 1, and the number of recording materials that have passed through the image forming apparatus 100. The second piece of information is information on the printing rate regarding the amount of charge generated in the charge generation layer of the photosensitive drum 1 during the image forming operation.

[0082] As described above, according to this embodiment, while suppressing the occurrence of negative ghosts due to the photoreceptor, high image quality can be maintained and the life of the developing device can also be maintained. Further, since the pre-exposure sequence is executed at the necessary timing, the number of times of extending the first print time, which is the time from the start of printing to the completion of the first print, can be minimized as much as possible, and productivity can be improved.

[0083] <Third Embodiment> In this embodiment, an environmental sensor is provided inside the main body of the image forming apparatus 100, and it is characterized in that whether to execute the pre-exposure sequence is determined according to the environment (for example, temperature and humidity) in which the image forming apparatus 100 is installed. In this embodiment, parts that overlap with the previous description will be omitted from the description, and parts specific to this embodiment will be described.

[0084] In a high-temperature and high-humidity environment, since the charge is immediately removed and no charge accumulates in the photosensitive drum 1, negative ghosts are unlikely to occur. Therefore, in a high-temperature and high-humidity environment, since it is not necessary to execute the pre-exposure sequence, the environmental sensor is used to control so as not to execute the pre-exposure sequence in the case of a high-temperature and high-humidity environment.

[0085] [Control Mode of Image Forming Apparatus] FIG. 5 is a schematic block diagram showing the control mode of the image forming apparatus 100 of the present embodiment. As shown in FIG. 5, in the present embodiment, in addition to the apparatus of the first embodiment, an environment sensor 86 which is an environment detection means is connected to the control unit 202. The environment sensor 86 is installed inside the main body of the image forming apparatus 100, and can acquire temperature and humidity information inside the main body of the image forming apparatus 100. Next, the procedure for determining whether the pre-exposure sequence can be executed will be described.

[0086] [Determination of Executability of Pre-Exposure Sequence] FIG. 6 is a flowchart for determining whether the pre-exposure sequence of the present embodiment can be executed. In the present embodiment, when the printing operation ends, the control unit 202 executes the ghost countermeasure sequence after S301.

[0087] In S301, after the image formation is completed, the control unit 202 initializes the timer 156 (T = 0) and starts measuring time by the timer 156. In S302, the control unit 202 receives a print start request signal from the controller 200.

[0088] In S303, the control unit 202 acquires temperature and humidity information based on the detection result of the environment sensor 86. In S304, the control unit 202 calculates the absolute moisture content W by the CPU 155 using the temperature and humidity information acquired in S303. In S305, the control unit 202 determines whether the absolute moisture content W calculated in S304 is less than or equal to a predetermined absolute moisture content (predetermined value) stored in the memory 15.

[0089] In S305, when the control unit 202 determines that the absolute moisture content W is greater than the predetermined value, the process proceeds to S309. In S305, when the control unit 202 determines that the absolute moisture content W is less than or equal to the predetermined value, the process proceeds to S306.

[0090] In S306, the control unit 202 acquires the elapsed time T measured by the timer 156.

[0091] In S307, the control unit 202 reads out the predetermined time recorded in the memory 15, and determines whether or not the elapsed time T acquired in S306 is equal to or longer than the predetermined time. If the control unit 202 determines in S307 that the elapsed time T is equal to or longer than the predetermined time, the process proceeds to S308. In S308, the control unit 202 executes a pre-exposure sequence. After the pre-exposure sequence in S308 ends, in S309, the control unit 202 starts a normal image forming operation in response to the print start request signal received in S302.

[0092] If the control unit 202 determines in S307 that the elapsed time T is less than the predetermined time, the process proceeds to S309. At this time, the control unit 202 starts a normal image forming operation in S309 without executing the pre-exposure sequence. When the image formation ends in S310, the control unit 202 returns the process to S301. The control unit 202 resets the value of the elapsed time T (T = 0) in S301, starts measuring the elapsed time T again by the timer 156, and prepares for reception of the next print start request signal.

[0093] Note that due to power saving control or the like of the controller 200, the control unit 202 may shift to the sleep mode and the power supply on the control unit 202 side may be turned off. In this case, time may be measured on the controller 200 side, and the determination of the availability of this sequence operation may be made using the time obtained by correcting the time of the timer 156 based on the time acquired from the controller 200. Note that the pre-exposure sequence in S308 executes the same control as that in FIG. 3.

[0094] In this embodiment, the predetermined time is set to 3 hours and the pre-exposure sequence is executed when the stop time is 3 hours or longer. However, this is not restrictive, and the setting of the predetermined time may be changed according to the characteristics of the photosensitive drum 1.

[0095] Note that the sequence of this embodiment using the environmental sensor is executed before the sequences described in the first and second embodiments.

[0096] As described above, according to the environment in which the image forming apparatus 100 is installed, it is determined whether the pre-exposure sequence can be executed. As a result, when the usage environment is equal to or less than a predetermined absolute moisture content and a predetermined time or more has elapsed since the previous image formation, the pre-exposure sequence is executed. That is, the photosensitive drum 1 and the intermediate transfer belt 31 are separated, and further, the photosensitive drum 1 and the developing roller 4 are separated, the rotation of the developing roller 4 is stopped, and the pre-exposure sequence is performed at a speed slower than that during normal image formation with the same laser light amount as during normal image formation. Thereby, the occurrence of negative ghost and exposure unevenness can be suppressed. Further, the influence on the life of the photoreceptor and the developing device due to performing this sequence can be minimized.

[0097] As described above, according to the third embodiment, it is possible to suppress the occurrence of negative ghost due to the photoreceptor while maintaining high image quality and the life of the developing device.

[0098] The disclosure of this embodiment includes the following configurations. (Configuration 1) An image carrier, Exposure means for forming an electrostatic latent image on the image carrier by exposing the image carrier, A developing agent carrier for carrying a developing agent, and developing means for supplying the developing agent by the developing agent carrier to develop the electrostatic latent image to form a developing agent image, Transfer means for transferring the developing agent image, Developing separation means for enabling a contact state in which the image carrier and the developing agent carrier are in contact with each other and a separation state in which the image carrier and the developing agent carrier are separated from each other, Transfer separation means for enabling a contact state in which the image carrier and the transfer means are in contact with each other and a separation state in which the image carrier and the transfer means are separated from each other, Storage means for storing information regarding the thickness of the charge generation layer of the image carrier, Control means for controlling the exposure means, the developing separation means, and the transfer separation means, An image forming apparatus comprising: Before performing the current image forming operation, the control means controls the transfer separation means so as to separate the image carrier and the transfer means, and controls the development separation means so as to separate the image carrier and the developer carrier, and then The control means controls to determine whether to execute or not to execute pre-exposure for exposing the image carrier by the exposure means according to a stand-by time from the end of the previous image forming operation to the start of the current image forming operation and the information stored in the storage means. An image forming apparatus characterized by the above. (Configuration 2) When the stand-by time is equal to or longer than a predetermined time, the control means controls to execute the pre-exposure regardless of the thickness of the charge generation layer of the image carrier. The image forming apparatus according to Configuration 1, characterized in that. (Configuration 3) The control means When the stand-by time is a predetermined time and the thickness of the charge generation layer of the image carrier is less than a predetermined thickness, the pre-exposure is executed. When the stand-by time is a predetermined time and the thickness of the charge generation layer of the image carrier is equal to or more than a predetermined thickness, the control means controls not to execute the pre-exposure. The image forming apparatus according to Configuration 1, characterized in that. (Configuration 4) An image carrier, Exposure means for forming an electrostatic latent image on the image carrier by exposing the image carrier, A developer carrier for carrying a developer, and developing means for supplying the developer by the developer carrier to develop the electrostatic latent image to form a developer image, Transfer means for transferring the developer image, Development separation means for enabling a contact state in which the image carrier and the developer carrier are in contact with each other and a separation state in which the image carrier and the developer carrier are separated from each other, Transfer separation means for enabling a contact state in which the image carrier and the transfer means are in contact with each other and a separation state in which the image carrier and the transfer means are separated from each other, Storage means for storing information regarding the use of the image carrier; Control means for controlling the exposure means, the developing separation means, and the transfer separation means; An image forming apparatus comprising: Before performing the current image forming operation, the control means controls the transfer separation means so as to separate the image carrier and the transfer means, and controls the developing separation means so as to separate the image carrier and the developer carrier. After that, The control means controls to determine whether to execute pre-exposure for exposing the image carrier by the exposure means according to the elapsed time from the end of the previous image forming operation to the start of the current image forming operation and the information stored in the storage means. An image forming apparatus characterized by the above. (Configuration 5) The information regarding the use of the image carrier is information obtained based on any one of the number of recording materials on which the image forming operation has been performed, the number of rotations of the image carrier as a rotating body, and the number of recording materials that have passed through the image forming apparatus, and information regarding the amount of charge generated that remains during the current image forming operation out of the amount of charge generated in the charge generation layer of the image carrier during the previous image forming operation. The image forming apparatus according to Configuration 4, characterized by the above.

Explanation of Signs

[0099] 1 Photosensitive drum 2 Charging roller 4 Developing roller 30 Exposure unit 32 Primary transfer roller 82 Developing contact / separation mechanism 83 Primary transfer contact / separation mechanism 100 Image forming apparatus 202 Control unit

Claims

1. An image carrier, exposure means for forming an electrostatic latent image on the image carrier by exposing the image carrier, a developer carrier for carrying a developer, and developing means for supplying the developer by the developer carrier to develop the electrostatic latent image to form a developer image, transfer means for transferring the developer image, developing separation means for enabling a contact state in which the image carrier and the developer carrier are in contact with each other and a separation state in which the image carrier and the developer carrier are separated from each other, transfer separation means for enabling a contact state in which the image carrier and the transfer means are in contact with each other and a separation state in which the image carrier and the transfer means are separated from each other, storage means for storing information regarding the thickness of the charge generation layer of the image carrier, control means for controlling the exposure means, the developing separation means, and the transfer separation means, An image forming apparatus comprising: Before performing the current image forming operation, the control means controls the transfer separation means to separate the image carrier and the transfer means, and controls the developing separation means to separate the image carrier and the developer carrier. After that, The control means controls to determine whether to execute pre-exposure for exposing the image carrier by the exposure means according to the elapsed time from the end of the previous image forming operation to the start of the current image forming operation and the information stored in the storage means. An image forming apparatus characterized by this.

2. When the elapsed time is equal to or longer than a predetermined time, the control means controls to execute the pre-exposure regardless of the thickness of the charge generation layer of the image carrier. The image forming apparatus according to claim 1, characterized by this.

3. The control means executes the pre-exposure when the elapsed time is a predetermined time and the thickness of the charge generation layer of the image carrier is less than a predetermined thickness, and controls not to execute the pre-exposure when the elapsed time is a predetermined time and the thickness of the charge generation layer of the image carrier is equal to or more than the predetermined thickness. The image forming apparatus according to claim 1, characterized by this.

4. An image carrier, exposure means for forming an electrostatic latent image on the image carrier by exposing the image carrier, a developer carrier for carrying a developer, and developing means for supplying the developer by the developer carrier to develop the electrostatic latent image to form a developer image, transfer means for transferring the developer image; developing separation means for enabling the image carrier and the developer carrier to assume a contacting state in which they are in contact with each other and a separated state in which they are separated from each other; transfer separation means for enabling the image carrier and the transfer means to assume a contacting state in which they are in contact with each other and a separated state in which they are separated from each other; storage means for storing information regarding the use of the image carrier; control means for controlling the exposure means, the developing separation means, and the transfer separation means; An image forming apparatus comprising: Before performing the current image forming operation, the control means controls the transfer separation means so that the image carrier and the transfer means are in a separated state, and controls the developing separation means so that the image carrier and the developer carrier are in a separated state. After that, The control means controls to determine whether or not to execute pre-exposure for exposing the image carrier by the exposure means according to a stand-by time from the end of the previous image forming operation to the start of the current image forming operation and the information stored in the storage means. An image forming apparatus characterized by this.

5. The information regarding the use of the image carrier is information obtained based on any one of the number of recording materials on which the image forming operation has been performed, the number of rotations of the image carrier as a rotating body, and the number of recording materials that have passed through the image forming apparatus, and information regarding the amount of charge generated that remains during the current image forming operation out of the amount of charge generated in the charge generation layer of the image carrier during the previous image forming operation. The image forming apparatus according to claim 4, characterized in that.

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