ELECTROPHOTOGRAPHIC IMAGE FORMING APPARATUS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a structure of an electrophotographic image forming apparatus with a photosensitive device integrated with an exposure source.

2. Description of the Related Art

In an electrophotographic process, a photosensitive member is uniformly charged and then exposed to light with a desired pattern based on image information so as to form a charge density distribution (latent image) on a surface of the photosensitive member. After that, the charge density distribution thus formed is developed with toner, to thereby obtain a visible image.

As a product to which the electrophotographic process is applied, a laser printer and an LED printer are widely used.

In the laser printer, a semiconductor laser is used as an exposure source, and a laser beam of the semiconductor laser is reflected by a rotating polygon mirror to thereby perform scanning on the photosensitive member.

In this case, in the following description, a main scanning direction of the rotary drum-shaped photosensitive member indicates a longitudinal direction of the drum (drum generatrix direction). Further, a sub-scanning direction of the rotary drum-shaped photosensitive member indicates a circumferential direction of the drum.

In the LED printer, there is employed a method in which the required number of light emitting diode (LED) pixels are arranged in a laser scanning direction (main scanning direction) of the laser printer, thereby forming an image on the surface of the photosensitive member by use of an imaging device.

The LED printer is characterized in that image positioning accuracy is enhanced because main scanning involved in the laser printer is not performed in the LED printer.

However, in both the laser printer and the LED printer, accuracy of sub-scanning is determined depending on a relative position and a relative speed between the photosensitive drum and the exposure source. Accordingly, unevenness in pitch is generated in a sub-scanning direction due to, for example, vibration of the exposure source, decentering of the photosensitive drum, and fluctuation in rotational speed.

In order to enhance the accuracy of the sub-scanning, it is possible to reduce a relative speed between the exposure source and the photosensitive member to zero. Specifically, it is possible that the exposure source and the photosensitive member are to be integrated with each other. As examples of the method of obtaining the integrated structure, the following methods have been employed.

(1) An example of a flat-plate photosensitive device in which a photoconductive layer is stacked on a light emitting device through an intermediate buffer layer

Japanese Patent Application Laid-Open No. H05-221018 discloses introduction of the intermediate buffer layer, as a method of stacking an a-Si photoconductive layer (amorphous silicon photoconductive layer) with high hardness on a thin-film electroluminescence (EL) layer.

(2) An example of a flat-plate photosensitive device in which an a-Si photoconductive layer is stacked on a light emitting array layer through an insulating layer.

Japanese Patent Application Laid-Open No. H06-095456 discloses a top emission structure of an inorganic LED in which a pixel thin-film-transistor (TFT) matrix is formed on a glass substrate.

(3) An example of a photosensitive drum in which a photoconductive layer is stacked on an electroluminescence (EL) device including a pixel TFT

Japanese Patent Application Laid-Open No. 2001-018441 discloses a device transfer process as a method of forming the EL device including a TFT layer on a cylindrical substrate.

In this case, the rotary drum-shaped photosensitive member, in which the exposure source and the photosensitive member are integrated with each other, that is, the drum integrated with the exposure source, in which pixels are formed on the photosensitive member so as to eliminate the factor of deviation in positional accuracy of an image not only in the main scanning direction but also in the sub-scanning direction, is hereinafter referred to as a digital photosensitive drum.

It is appropriate for a direction of technical development to employ the method of using the digital photosensitive drum in view of the technical transition from point scanning with a laser beam to an LED array in which the main scanning direction is fixed, and further, from the LED array to a pixel matrix system in which the sub-scanning direction is also fixed.

However, in a laser scanner for performing laser scanning and in the LED array for an LED system, the exposure source is spatially fixed and an image of the light source is formed on a spatially predetermined position. On the other hand, in the digital photosensitive drum, scanning lines are rotated with the drum. For this reason, there arises a problem to be solved for image formation. In other words, in a case of image formation using the digital photosensitive drum, as a first problem, it is necessary to employ a method of determining a scanning line to be exposed to light from an outside from the necessity that an exposure process is performed between a charging process and a development process for the image formation. As a second problem, in an in-line color image forming apparatus, in a case of correction control for matching positions of colors in a sub-scanning direction, it is necessary to provide a unit for determining a scanning line to be used after the correction, to each digital photosensitive drum for each color.

In the laser scanner for performing laser scanning and in the LED array for the LED system, the exposure source is spatially fixed and the image of the light source is formed on a spatially predetermined position.

However, in the digital photosensitive drum, the exposure source is rotated with the drum. Accordingly, in the case of image formation using the digital photosensitive drum, it is necessary to determine which exposure source performs an exposure process from the outside.

For the image formation, it is necessary to perform the exposure process between the charging process and the development process, and to perform exposure at a timing between the charging process and the development process. Further, in the in-line color image forming apparatus, it is necessary to determine an exposure timing for each drum so as to match the positions of the colors in the sub-scanning direction.

A conventional system is disadvantageous in the above-mentioned problems. In other words, in structures disclosed in Japanese Patent Application Laid-Open Nos. H05-221018 and H06-095456, a flat-plate device having the exposure source and the photosensitive member which are integrated with each other is used. Accordingly, in the first place, the structures are unsuitable for the electrophotographic image forming apparatus which is required to perform a continuous printing operation.

Further, in the structure of the digital photosensitive drum disclosed in Japanese Patent Application Laid-Open No. 2001-018441, a self-luminous device is wound around the drum substrate, so a seam is formed in the circumferential direction of the drum. For this reason, there is a description that a rotation start position (home position) of the drum is detected, and then, the image formation is performed after the elapse of predetermined time. However, with the structure, an exposing position (selection of scanning line) depends on time. Accordingly, when an image forming speed (rotational speed of drum) is changed, an error is generated in the exposure timing.

SUMMARY OF THE INVENTION

The present invention provides an electrophotographic image forming apparatus mounted with a digital photosensitive drum having an exposure source and a photosensitive member which are integrated with each other, in which, even when the rotational speed of the electrophotographic photosensitive drum is changed, an appropriate exposure source can be selected.

The present invention provides an electrophotographic image forming apparatus, including: an electrophotographic photosensitive drum that is rotatably disposed and includes a light emitting element matrix layer including multiple light emitting pixel portions, and a photoconductive layer in which a latent image is formed by light emission of the light emitting pixel portions; a charging device for charging the electrophotographic photosensitive drum at a charging position thereof; a developing device for developing the latent image at a developing portion with a developer; a rotary portion that rotates with the electrophotographic photosensitive drum and has multiple phase detecting patterns of the electrophotographic photosensitive drum, the multiple phase detecting patterns including adjacent phase detecting patterns which form an angle with respect to a rotation center of the rotary portion, the angle being set within an angle formed between the charging position and the developing position with respect to the rotation center of the electrophotographic photosensitive drum; and a control portion that controls light emission of the multiple light emitting pixel portions and is capable of changing an interval between a timing for light emission of a first light emitting pixel portion among the multiple light emitting pixel portions and a timing for light emission of a second light emitting pixel portion which is positioned at a downstream side of the first light emitting pixel portion in a rotation direction of the electrophotographic photosensitive drum, based on detection results of the multiple phase detecting patterns during the formation of the latent image so as to correspond to a single transfer material.

According to the present invention, in the electrophotographic image forming apparatus mounted with the digital photosensitive drum having the exposure source and the photosensitive member which are integrated with each other, even when the rotational speed of the electrophotographic photosensitive drum is changed, an appropriate exposure source can be selected.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a schematic cross-sectional diagram illustrating a schematic structure of an electrophotographic image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged diagram illustrating portions of an image forming unit and an intermediate transfer belt unit which are provided in the electrophotographic image forming apparatus.

FIG. 3 is an exploded schematic diagram illustrating first to fourth process cartridges which are mounted to the image forming unit, and the intermediate transfer belt unit.

FIG. 4 is an enlarged schematic cross-sectional diagram illustrating a schematic structure of a single cartridge.

FIG. 5A is a longitudinal sectional diagram of a digital photosensitive drum; FIG. 5B is an enlarged diagram of one end side (driving side) of the digital photosensitive drum; and FIG. 5C is an enlarged diagram of the other end side (non-driving side) of the digital photosensitive drum.

FIG. 6 is a perspective view illustrating a drive portion and a phase detecting portion of the digital photosensitive drum.

FIG. 7 is a schematic diagram of a layered structure of a digital photosensitive drum according to an embodiment of the present invention.

FIG. 8 is a schematic diagram of a longitudinal and lateral lattice-like structure including a signal line group of a single line layer and a signal line group of a scanning line layer.

FIG. 9 is a flowchart of an outline of a manufacturing process for the digital photosensitive drum.

FIG. 10A is a schematic process chart illustrating the manufacturing process for device transfer; FIG. 10B is a schematic process chart illustrating the manufacturing process for formation of an insulating layer; FIG. 10C is a schematic process chart illustrating the manufacturing process for formation of via holes; FIG. 10D is a schematic process chart illustrating the manufacturing process for formation of through hole electrodes; FIG. 10E is a schematic process chart illustrating the manufacturing process; FIG. 10F is a schematic process chart illustrating the manufacturing process; FIG. 10G is a schematic process chart illustrating the manufacturing process for formation of a partition wall; FIG. 10H is a schematic process chart illustrating the manufacturing process for formation (deposition) of an organic electroluminescence (EL) layer; FIG. 10I is a schematic process chart illustrating the manufacturing process for formation (sputtering) of a scanning line; FIG. 10J is a schematic process chart illustrating the manufacturing process for formation (deposition) of a transparent insulating/barrier layer; and FIG. 10K is a schematic process chart illustrating the manufacturing process for formation (sputtering) of a transparent conductive layer.

FIG. 11A is a schematic process chart illustrating the manufacturing process; FIG. 11B is a schematic process chart illustrating the manufacturing process; FIG. 11C is a schematic process chart illustrating the manufacturing process; FIG. 11D is a schematic process chart illustrating the manufacturing process; and FIG. 11E is a schematic process chart illustrating the manufacturing process.

FIG. 12 is a block diagram of a drive circuit of the digital photosensitive drum.

FIG. 13 is a drive timing chart for the digital photosensitive drum.

FIG. 14 is a block diagram illustrating data transfer.

FIGS. 15A, 15B, and 15C are diagrams for describing detection of a rotary phase of the digital photosensitive drum.

FIGS. 16A, 16B, and 16C are diagrams for describing detection of the rotary phase of the digital photosensitive drum.

FIGS. 17A and 17B are diagrams for describing detection of the rotary phase of the digital photosensitive drum.

FIG. 18 is a plan diagram of the digital photosensitive drum.

DESCRIPTION OF THE EMBODIMENT

Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.

Embodiment 1

(1) Image Forming Portion

FIG. 1 is a schematic cross-sectional diagram illustrating a schematic structure of an electrophotographic image forming apparatus A according to an embodiment of the present invention. FIG. 2 is an enlarged diagram illustrating portions of an image forming unit 1 and an intermediate transfer belt unit (ITB unit; hereinafter, referred to simply as “belt unit”) 7 which are provided in the electrophotographic image forming apparatus A. FIG. 3 is an exploded schematic diagram illustrating first to fourth process cartridges (hereinafter, referred to simply as “cartridge”) PY, PM, PC, and PK which are mounted to the image forming unit 1, and the intermediate transfer belt unit 7. FIG. 4 is an enlarged schematic cross-sectional diagram illustrating a schematic structure of a cartridge P (Y, M, C, K).

The image forming apparatus A according to the embodiment of the present invention is a full-color digital electrophotographic printer of a four-drum-tandem type using an endless belt as an intermediate transfer member.

The printer A is capable of forming a full-color image or a mono-color image corresponding to electrical image data (image information signal), which is input from an external device (host device) C connected to a main body control circuit portion B, on a surface of a sheet-like recording material S, and outputting (printing out) the sheet material S.

The external device C is a personal computer, an image reader, a facsimile machine, or the like.

The main body control circuit portion (controller) B exchanges various electrical information signals with the external device C. In addition, the main body control circuit portion B performs processing for the electrical information signals input from image forming process devices, sensors, and the like and for command signals sent to the image forming process devices and the like, and performs a predetermined image forming sequence control. Further, the main body control circuit portion B executes an operational control of the entire printer according to a control program and a reference table which are stored in a ROM or a RAM.

The image forming unit 1 is disposed above the belt unit 7 and has a structure of a horizontal tandem type in which the first to fourth cartridges PY, PM, PC, and PK are arranged in series from the left side to the right side of the drawing. Each cartridge P (Y, M, C, K) can be individually detachably mountable and replaceable with respect to a unit frame (not shown) of the image forming unit 1.

The first to fourth cartridges PY, PM, PC, and PK each form a color separation component image of a full-color image, that is, a toner image of each of yellow, magenta, cyan, and black. In the embodiment of the present invention, the cartridges for forming the toner images of yellow, magenta, cyan, and black are arranged in order of image formation to be executed. However, the order of colors in which the image formation is to be performed is not limited thereto, and the cartridges may be arranged in order of arbitrary colors.

With reference to FIG. 4, each cartridge P (Y, M, C, K) has the same structure in an electrophotographic process mechanism, and includes a drum-shaped electrophotographic photosensitive member (hereinafter, referred to simply as “drum”) 2 which has a major role in an image forming process.

Each drum 2 is a digital photosensitive drum in which a photoconductive layer is stacked on a matrix layer of a light emitting device, and an exposure source and a latent image forming device are integrated with each other. At the time of executing the image forming process, each drum 2 is rotationally driven counterclockwise at a predetermined angular velocity around a drum shaft (central spindle) 2a thereof. The digital photosensitive drum 2 is described later.

Further, each cartridge P (Y, M, C, K) includes a charging roller (charging device) 4, a developing unit (developing device) 4, and a drum cleaning device (cleaning device) 5, which are electrophotographic process unit operating on the drum 2. Note that a yellow toner as a developer is contained in the developing unit 4 of the first cartridge PY. A magenta toner as a developer is contained in the developing unit 4 of the second cartridge PM. A cyan toner as a developer is contained in the developing unit 4 of the third cartridge PC. A black toner as a developer is contained in the developing unit 4 of the fourth cartridge PK.

Each charging roller 3 has a roller portion made of a conductive rubber provided on a metal shaft portion thereof, and is disposed substantially in parallel with the drum 2 so as to be brought into pressure contact with the drum 2 with a predetermined pressing force. Thus, each charging roller 3 is driven by the rotation of the drum 2 to be rotated. A DC voltage of, for example, −700 V as a dark potential Vd with respect to a substrate potential of the drum 2, is applied as a charging bias, from a power supply portion (not shown) to the metal shaft portion of the charging roller 3. Then, at a charging position “a” which is a contact portion between the drum 2 and the charging roller 3, on the surface of the drum 2 having a dielectric coating film, a uniform surface charge distribution with a potential of about −450 V can be formed.

With respect to the drum surface with the uniform surface charge distribution, a light emitting device of the drum corresponding to image data is lit, thereby exposing a spot pattern from a back surface of the photosensitive member at a position between the charging position “a” and a developing position “b”, that is, an exposure point “c” which is in the vicinity of an uppermost position in the vertical direction of the drum 2 in FIG. 4. The developing position “b” corresponds to a portion at which the drum 2 is exposed to the action of development by the developing unit 4, and corresponds to a portion at which a developing roller 4a is in contact with the drum 2 in the embodiment of the present invention.

In the photoconductive layer of the drum 2 exposed to light through the lighting of the light emitting device, carriers are generated in a carrier generation layer (CGL) and holes are moved in a carrier transport layer (CTL) under the action of an electric field due to charges on the uniformly charged surface, thereby neutralizing the surface charges. As a result, there is formed a surface charge density distribution in which a potential (light potential) Vl at an exposed portion of the photosensitive member of the drum 2 is about −50 V and a potential (dark potential) Vd at a non-exposed portion thereof is about −400 V. In other words, an electrostatic latent image is formed on the surface of the drum 2.

In this manner, in the first cartridge PY, on the surface of the rotating drum 2, an electrostatic latent image corresponding to a yellow color component image of the full-color image is formed, and the electrostatic latent image thus formed is developed as a yellow toner image by the developing unit 4.

In the second cartridge PM, on the surface of the rotating drum 2, an electrostatic latent image corresponding to a magenta color component image of the full-color image is formed, and the electrostatic latent image thus formed is developed as a magenta toner image by the developing unit 4.

In the third cartridge PC, on the surface of the rotating drum 2, an electrostatic latent image corresponding to a cyan color component image of the full-color image is formed, and the electrostatic latent image thus formed is developed as a cyan toner image by the developing unit 4.

In the fourth cartridge PK, on the surface of the rotating drum 2, an electrostatic latent image corresponding to a black color component image of the full-color image is formed, and the electrostatic latent image thus formed is developed as a black toner image by the developing unit 4.

For each developing unit 4, a so-called non-magnetic one-component contact development process is employed in the embodiment of the present invention. Each developing unit 4 includes the developing roller 4a having the roller portion made of conductive rubber. The developing roller 4a is disposed substantially in parallel with the drum 2 so as to be brought into pressure contact with the drum 2 with the predetermined pressing force. The developing roller 4a is driven independently of the drum 2 by a drive mechanism (not shown). Tangential speed directions of the developing roller 4a and the drum 2 at the developing position “b”, which is the contact portion between the developing roller 4a and the drum 2, are the same, but a tangential speed ratio between the developing roller 4a and the drum 2 is about 2:1.

To the developing unit 4 of each cartridge P (Y, M, C, K), a toner is supplied from a toner tank (toner cartridge) 6 set above each cartridge P at a predetermined control timing. The toner supplied to the developing unit 4 is subjected to contact electrification due to interaction among a supply roller 4b and a trimmer 4c, which are disposed to be brought into contact with the developing roller 4a, and the developing roller 4a. Then, the toner is coated on a surface layer of the developing roller 4a, and a mass of coated toner per unit area is regulated so as to obtain a desired value. After that, the toner is carried to the developing position “b” through the rotation of the developing roller 4a. To the developing roller 4a, a predetermined developing bias is applied from a power supply portion (not shown). For example, between the developing roller 4a and the substrate of the drum 2, a developing bias of, for example, −200 V is applied. As a result, under the above-mentioned latent image conditions, when a development contrast Vc is set to 150 V and a back contrast Vbc is set to 200 V, the latent image is developed with toner, thereby enabling formation of the toner image on the drum 2.

The belt unit 7 includes an intermediate transfer belt (hereinafter, referred to simply as “belt”) 8 made of an endless dielectric member with flexibility. The belt 8 is hung around three rollers, that is, a drive roller 9, a tension roller 10, and a secondary transfer opposing roller 11, which are substantially in parallel with each other, as suspension members, under tension. The three rollers are disposed so as to be rotatably borne by a belt unit frame 7a. Inside the belt 8, four primary transfer rollers 12 corresponding to each cartridge P (Y, M, C, K) are provided. The primary transfer rollers 12 each have a roller portion which is made of conductive rubber and is provided to a metal shaft portion thereof, and are arrayed substantially in parallel with the corresponding drums 2. Further, the primary transfer rollers 12 are each brought into pressure contact with a lower surface portion of each drum 2 with a predetermined pressing force through the belt 8. A contact nip portion between the drum 2 and the belt 8 corresponds to a primary transfer position “d”. Also the primary transfer rollers 12 are each disposed so as to be rotatably borne by the belt unit frame 7a.

At the time of executing the image forming process, the belt 8 is rotationally driven clockwise as indicated by the arrow at a predetermined speed. A speed criterion of the drum 2 of each cartridge P (Y, M, C, K) at the time of executing the image forming process is synchronous with the tangential speed of the belt 8. In the embodiment of the present invention, in order to synchronize the speed criterion with the image formation of each cartridge P (Y, M, C, K), a drive transmission method using a timing belt is employed. Specifically, a transfer drive pulley provided above a shaft of the primary transfer roller of each cartridge P (Y, M, C, K) is driven by the timing belt to which a driving force is transmitted from a pulley provided above a belt drive shaft. In addition, a transfer roller gear and a drum gear are engaged with each other, thereby transmitting the driving force to the drum shaft 2a, that is, the drum 2.

On each drum 2 of the first to fourth cartridges PY, PM, PC, and PK, color toner images of yellow, magenta, cyan, and black, which are color separation component images of the full-color image, are respectively formed at the predetermined control timing. At the primary transfer position “d”, the yellow toner image formed on the drum 2 of the first cartridge PY is primarily transferred onto the belt 8 which is rotationally driven. At the primary transfer position “d”, the magenta toner image formed on the drum 2 of the second cartridge PM is primarily transferred onto the yellow toner image formed on the belt 8 in a superimposed manner. At the primary transfer position “d”, the cyan toner image formed on the drum 2 of the third cartridge PC is primarily transferred onto the yellow toner image and the magenta toner image which are formed on the belt 8 in a superimposed manner. At the primary transfer position “d”, the black toner image formed on the drum 2 of the fourth cartridge PK is primarily transferred onto the yellow toner image, the magenta toner image, and the cyan toner image, which are formed on the belt 8 in a superimposed manner. In other words, the four color toner images of yellow, magenta, cyan, and black are sequentially superimposedly (multi-layeredly) transferred onto the predetermined position of the belt 8, thereby synthesizing and forming a full-color unfixed toner image (mirror image).

At the primary transfer position “d” of each cartridge P (Y, M, C, K), the toner images are primarily transferred onto the belt 8 from each drum 2 by the action of the electric field formed by a predetermined transfer bias applied to each primary transfer roller 12 from each power supply portion (not shown).

In each cartridge P (Y, M, C, K), untransferred toner remaining on each drum 2 after the transfer of the toner images onto the belt 8 is scraped off as waste toner from the drum surface by using a cleaning blade 5a, which is made of polyurethane rubber, of the drum cleaning device 5. The waste toner thus scraped off is recovered by a waste toner screw 5b into a waste toner container (not shown) provided to the image forming unit 1.

The full-color unfixed toner image thus synthesized and formed on the belt 8 is carried through the continuous rotation of the belt 8, and reaches a secondary transfer position “e” which is a contact portion between the belt 8 and the secondary transfer roller 13. The secondary transfer roller 13 has a roller portion which is made of conductive rubber and is provided to a metal shaft thereof, and is disposed substantially in parallel with the secondary transfer opposing roller 11 so as to sandwich the belt 8, thereby being brought into pressure contact with the secondary transfer opposing roller 11 with a predetermined pressing force. Then the secondary transfer roller 13 is rotated in a forward direction with respect to a belt movement direction at the same speed as that of the belt 8.

On the other hand, in response to a demand for an image forming (printing) operation, by a separation feed roller 16 provided in a sheet feed/transport unit 15, only a top recording material of the sheet-like recording materials (recording papers) S as a transfer material, which are stacked in a sheet feed cassette 14 disposed at a lower portion of the printer main body, is separated. The recording material S passes through a transport roller pair 17 to be fed to a registration unit 18. The registration unit 18 allows the recording material S to be fed to the secondary transfer position “e” at a timing when a position of a leading end of the toner image formed on the belt 8 is synchronized with a position of a leading edge of the recording material S. The recording material S entering the secondary transfer position “e” is sandwiched and transported at the secondary transfer position “e”. During the transportation process, a predetermined transfer bias is applied to the secondary transfer roller 13 from a power supply portion (not shown), thereby sequentially performing collective transfer of the four-color toner images superimposed on the belt 8.

The recording material S passing through the secondary transfer position “e” is separated from the surface of the belt 8, and is introduced to a fixing unit 20 of a heat and pressure type by a transport unit 19. The unfixed full-color toner image formed on the recording material S is applied with heat and pressure by the fixing unit 20, thereby being fused, mixed, and fixed onto the recording material. Then, the recording material S passes through a longitudinal transporting unit 21 and a delivery unit 22 and is delivered onto a face-down delivery tray 23 as a full-color image formed material.

Further, the untransferred toner remaining on the belt 8 after the transfer of the toner image onto the recording material S is removed and recovered by a belt cleaning device 24.

The above description relates to a full-color image forming mode. In a case of a mono-color image forming mode for forming a monochromatic image or the like, a cartridge for a designated color operates for image formation. The other cartridges do not operate for image formation while each drum 2 thereof is rotationally driven.

In FIG. 1, a multiple feed unit (manual feed unit) 25 is provided on a side of a right-side surface of the printer A. The multiple feed unit 25 is disposed so as to be capable of being opened and closed with respect to the printer main body. When in non-use, the multiple feed unit 25 is shifted to a state of being closed with respect to the printer main body, and when in use, the multiple feed unit 25 is shifted to a state of being opened with respect to the printer main body. Further, in FIG. 1, a face-up delivery tray 26 is provided on a side of a left-side surface of the printer A. The face-up delivery tray 26 is disposed so as to be capable of being opened and closed with respect to the printer main body. When in non-use, the face-up delivery tray 26 is shifted to a state of being closed with respect to the printer main body, and when in use, the face-up delivery tray 26 is shifted to a state of being opened with respect to the printer main body.

The printer A according to the embodiment of the present invention has a drawer structure capable of drawing the secondary transfer roller 13, the sheet feed/transport unit 15, the registration unit 18, and the multiple feed unit 25, as one unit, from the right side (multiple feed unit side) of the printer main body shown in FIG. 1. In addition, the image forming unit 1 is mounted above the drawer. At the time of replacing toner, the drawer is drawn out and a toner tank 6, which is provided above the image forming unit 1 and is drawn out, is replaced, thereby facilitating the replacement of the toner. Similarly, each cartridge P (Y, M, C, K) can also be easily replaced by drawing out the drawer and replacing the cartridge which is provided above the image forming unit 1 and is drawn out. In the printer according to the embodiment of the present invention, the toner tank (toner cartridge) has a toner capacity of 3,000 sheets of A4 size sheets in the coverage rate of 5%, and the durable number of sheets is 50,000 in each cartridge P (Y, M, C, K).

(2) Digital Photosensitive Drum 2

FIG. 5A is a longitudinal sectional diagram of the digital photosensitive drum 2. FIG. 5B is an enlarged diagram illustrating one end side (driving side) of the digital photosensitive drum 2. FIG. 5C is an enlarged diagram illustrating the other end side (non-driving side) of the digital photosensitive drum 2. FIG. 6 is a perspective view illustrating a drive portion and a phase detecting portion of the digital photosensitive drum 2.

The digital photosensitive drum 2 is a rotary drum-shaped photosensitive device in which a self-luminous device portion, which is a light emitting element matrix layer, a functional separation portion, and a photosensitive portion are stacked on a cylindrical substrate, and in which the exposure source and the latent image forming device are integrated with each other. At both opening portions of the drum 2, cylindrical flanges 31a and 31b are press-fitted coaxially with the drum 2 to be fixed and mounted. Between the flanges 31a and 31b, the drum shaft 2b is inserted to be mounted. The flanges 31a and 31b are fixed to the drum shaft 2a in an integrated manner. An axis of the drum 2 and an axis of the drum shaft 2a are coaxially matched with each other. Both end portions of the drum shaft 2a are allowed to protrude to an outside from the flanges 31a and 31b, respectively, and protruding shaft portions are fitted with bearings 32a and 32b, respectively. In addition, at the protruding shaft portion on a driving side, a drum gear G2 is coaxially fitted with the drum shaft 2a to be fixed thereto in an integrated manner. Further, on an outer peripheral portion (outer diameter portion) of an end portion of the flange 31a on the driving side, an encoder wheel portion 33 (rotary portion) for phase detection is provided. The encoder wheel portion 33 rotates together with the drum 2. The bearings 32a and 32b are held by frames Pa and Pb, respectively, of each process cartridge P (Y, M, C, K).

In a state where each process cartridge P (Y, M, C, K) is mounted to a predetermined position of the printer main body, a drum gear G2 of each process cartridge is engaged with a transfer roller gear G12 on a side of the corresponding primary transfer roller as illustrated in FIG. 6. A driving force is transmitted from the transfer roller gear G12 to the drum gear G2, thereby rotationally driving the drum shaft 2a. That is, the drum 2 is rotationally driven. As described above, torque of the belt drive roller 9 of the belt unit 7 is transmitted to each primary transfer roller 12 through a power transmission mechanism of the pulley and the timing belt, thereby rotating each primary transfer roller 12. The transfer roller gear G12 is coaxially fixed to a shaft 12a of the primary transfer roller 12 in an integrated manner, thereby being rotated integrally with the primary transfer roller 12. The rotation of the transfer roller gear G12 is transmitted to the drum gear G2, thereby rotationally driving the drum 2. The speed criterion of the drum 2 of each cartridge P (Y, M, C, K) at the time of executing the image forming process is synchronized with the tangential speed of the belt 8.

FIG. 7 is a schematic diagram of a layered structure of the digital photosensitive drum 2 according to the embodiment of the present invention. The digital photosensitive drum 2 is a rotary drum-shaped photosensitive device with the exposure source and the latent image forming device that are integrated with each other, which has three functional layers, that is, a self-luminous device portion 50 which is a light emitting element matrix layer, a functional separation portion 60, and a photosensitive portion 70 that are stacked on a cylindrical substrate 40. FIG. 7 is a planar cross-sectional diagram of the drum 2, which includes a drum axis of the drum 2 and one of second electrode wires formed in parallel with the drum axis.

In the following description, for convenience of description, a first electrode wire annularly formed in a circumferential direction of the cylindrical substrate, which is included in the self-luminous device portion 50, is referred to as “signal line,” and a second electrode wire linearly formed in a longitudinal direction of the cylindrical substrate, which is included in the self-luminous device portion 50, is referred to as “scanning line.”

(2-1) Cylindrical Substrate 40

As the cylindrical substrate 40, a cylinder (hereinafter, referred to as “drum cylinder”) made of aluminum is used in the embodiment of the present invention.

(2-2) Self-Luminous Device Portion 50

The self-luminous device portion 50 includes a control circuit 51 for controlling a voltage applied to the signal line (first electrode wire) and the scanning line (second electrode wire), a signal line layer (first electrode wire layer) 52, an electroluminescence (EL) layer 53, and a scanning line layer (second electrode wire layer) 54. The control circuit 51, the signal line layer 52, the EL layer 53, and the scanning line layer 54 are stacked in the stated order from an inner side to an outside with respect to an outer peripheral surface of the drum cylinder 40.

The signal line layer 52 is a layer formed of a signal line group (sub-scanning signal line group) including multiple signal lines 52e. The signal lines 52e each extend annularly in the circumferential direction of the cylindrical substrate. The signal lines 52e are separated from each other by insulating members 52g and are arrayed at equal predetermined intervals in the longitudinal direction of the cylindrical substrate.

The scanning line layer 54 is a layer formed of a scanning line group (main scanning signal line group) including multiple scanning lines 54a. The scanning lines 54a each extend in the longitudinal direction of the cylindrical substrate. The scanning lines 52a are each separated by an insulating member 54b (see FIG. 11E), and are arrayed at equal predetermined intervals in the circumferential direction of the cylindrical substrate.

The annular signal line group of the signal line layer 52 and the linear scanning line group of the scanning line layer 54 form a longitudinal and lateral lattice-like structure, and an intersecting point between each of the signal lines 52e and each of the scanning lines 54a becomes a pixel portion.

The control circuit 51 has a function of performing an on/off control of each of the signal lines 52e of the signal line layer 52 and each of the scanning lines 54a of the scanning line layer 54. The control circuit 51 controls a gate 51b of a drive TFT 51d of a final stage, thereby turning on/off each of the signal lines 52e and each of the scanning lines 54a. In other words, the control circuit 51 controls each pixel independently. A source electrode of the drive TFT 51d is connected to an electrode pad 51e. The drive TFT 51d illustrated in FIG. 7 is a transistor of the control circuit for controlling each of the signal lines. Each drive TFT 51d illustrated in FIGS. 11A to 11E is a transistor of the control circuit for controlling each of the scanning lines.

The control circuit 51 is obtained by transferring a control circuit, which is formed on a glass substrate by a poly-Si process, onto the drum cylinder 40 by a so-called device transfer process. A polysilicon layer (insulating layer) 51a of the circuit formed by the poly-Si process is joined to a surface of the drum cylinder 40. Drivers (constant current circuit, lighting time control circuit, shift register, buffer, and the like) for driving the drive TFT 51d are formed on the same device.

The signal line layer 52 includes interlayer insulating layers (insulating films) 52a and 52b, the multiple annular signal lines 52e, and a through hole electrode (large) 52c and a through hole electrode (small) 52d which are interlayer electrodes for connecting each of the multiple annular signal lines 52e to the electrode pad 51e of the drive TFT 51d.

Each of the signal lines 52e of the embodiment of the present invention is an Ag electrode having a width of 10 μm. As FIG. 8 illustrates the schematic diagram of the longitudinal and lateral lattice-like structure of the annular signal line group of the signal line layer 52 and the linear signal line group of the scanning line layer 54, the signal lines 52e are each annularly formed around the drum cylinder 40. The annular signal lines 52e are separated from each other by partition walls 54b and a large number of annular signal lines 52e are disposed at equal predetermined intervals in the longitudinal direction of the drum cylinder. In the embodiment of the present invention, each interval between the annular signal lines 52e is about 42 μm (image resolution of 600 dpi), 5,120 annular signal lines 52e (corresponding to A4-size portrait printing) are disposed so that the axis of the annular signal lines 52e matches the axis of the drum shaft 2a. The signal lines 52e are each connected to the electrode pad 51e of the drive TFT 51d via the through hole electrodes 52d and 52c.

The EL layer 53 forms a fluorescent light emitting device of a charge injection type with an organic EL layer. In the embodiment of the present invention, a side of the signal lines 52e is set as a cathode of a metal electrode (Ag), and a side of the scanning lines 54a is set as an anode of a metal oxide (ITO). Accordingly, there is employed a four-layered structure in which an electron transport layer (ETL), an emissive layer (EML), a hole transport layer (HTL), and a hole injection layer (HIL) are formed in the stated order from the signal line 52e side toward the scanning line 54a side.

The scanning lines 54a of the scanning line layer 54 each have a width of 10 μm, and are linear pattern electrodes each extending in the longitudinal direction of the drum cylinder. The scanning lines 54a are separated from each other by each partition wall 54b which is an insulating member, and a large number of scanning lines 54a are disposed at equal predetermined intervals in the circumferential direction of the cylindrical substrate. The scanning lines 54a are each made of a transparent conducting oxide (ITO). In the embodiment of the present invention, each interval between the scanning lines 54a is about 42 μm (resolution (number of pixels) of 600 dpi), and 1,800 scanning lines 54a (with a drum having a diameter of 24 mm and at phase angle of 0.2°) are disposed in parallel with the drum axis or disposed with a crossing angle with respect to the drum axis. The scanning lines 54a are each connected to the electrode pad 51e of the drive TFT 51d via the through hole electrodes 54c and 52c as illustrated in FIG. 11E.

(2-3) Functional Separation Portion 60

The functional separation portion 60 includes: a transparent insulating/gas barrier layer (hereinafter, referred to as “transparent insulating/barrier layer”) 61 which is a transparent insulating layer for electrically insulating the self-luminous device portion 50 and the photosensitive portion 70; and a transparent conductive layer (transparent conductive film) 62 formed on the transparent insulating/barrier layer 61. The transparent insulating/barrier layer 61 has a multilayer stacked structure including an organic polymer film and a metal oxide thin film (Al₂O₃). The transparent conductive layer 62 is obtained by depositing ITO on a surface (cylindrical outer peripheral surface side) of the transparent insulating/barrier layer 61. As a result, in the functional separation portion 60, a visible light transmittance of 85% (λ=520 nm) and a high gas barrier property are maintained.

(2-4) Photosensitive Portion 70

The photosensitive portion 70 is an organic photoconductor (OPC) in which an undercoat layer (UCL) 71, a carrier generation layer (CGL) 72, a carrier transport layer (CTL) 73, and a protection layer 74 are sequentially stacked in the stated order on the transparent conductive layer 62 of the functional separation portion 60.

A fundamental structure of the above-mentioned digital photosensitive drum 2 according to the embodiment of the present invention includes the substrate, the control circuit, the signal lines, the EL layer, the scanning lines, the transparent insulating layer, the transparent conductive layer (ITO), and the OPC. A signal line driver serving as a control circuit portion for controlling the voltage of each signal line is separated into multiple parts. Between the signal line driver and each signal line, there is formed a vertical contact structure with a through hole. A scanning line driver serving as a control circuit portion for controlling the voltage of each scanning line is disposed outside an image-forming area of the drum 2. Each scanning line is made of ITO or of ITO and an auxiliary electrode, and has a top emission structure.

In the digital photosensitive drum 2 of the embodiment of the present invention, the self-luminous device portion 50 includes the control circuit 51 and the signal line layer 52 formed on the control circuit 51. In other words, a distance between the control circuit 51 and each signal line 52e is shorter than a distance between the control circuit 51 and each scanning line 54a. When the distance between the control circuit 51 and each signal line 52e is shorter, the electrical signal hardly attenuates, thereby enabling stable control of each signal line 52e.

If the organic EL layer 53 is formed between the signal lines 52e and the scanning lines 54a, it is possible to cause the EL layer 53 to emit light by a PM process. Accordingly, in the case where the control circuit 51 is formed on the cylindrical substrate 40, it is possible to control light emission with a layered structure (1) in which the control circuit 51, the signal line layer 52, the EL layer 53, and the scanning line layer 54 are formed in the stated order from a side of the cylindrical substrate 40. In addition, it is also possible to control light emission with a layered structure (2) in which the control circuit 51, the scanning line layer 54, the EL layer 53, and the signal line layer 52 are formed in the stated order from the cylindrical substrate 40 side. In other words, with any one of the structures (1) and (2), it is possible to control light emission. However, it can be said that the structure (1) is better than the structure (2), because the signal lines 52e are controlled more rapidly (with short period of time) than the scanning lines 54a. Specifically, a position of the EL layer 53 in the longitudinal direction of the drum 2 to be caused to emit light is determined by a image data signal, and the control of the signal lines 52e has to be performed based on the image data. Meanwhile, the scanning lines 54a are associated with a position of the EL layer 53 in the circumferential direction of the drum 2 to be caused to emit light, so the control of the scanning lines 54a is not changed based on the image data. Thus, the signal lines 52e controlled rapidly (with short period of time) are disposed near the control circuit 51, with the result that the attenuation of the data signal can be suppressed. In particular, the control circuit 51 is formed on the substrate 40, so the signal lines 52e and the control circuit 51 can be formed to be close to each other.

Further, in the digital photosensitive drum 2 according to the embodiment of the present invention, the scanning lines 54a of the scanning line layer 54 are each made of a transparent conductive oxide (ITO). The scanning lines 54a are each transparent, so it is impossible to prevent the light emitted in the EL layer 53 from advancing to the photosensitive portion 70. As described above, the EL layer 53 is formed between the signal lines 52e and the scanning lines 54a. Accordingly, at least one of the signal line 52e and the scanning line 54a is to be formed on the EL layer 53. In this case, the signal lines 52e are each annularly formed, so it is difficult to form the signal lines made of ITO by sputtering or the like. On the other hand, the scanning lines 54a are linearly formed in the longitudinal direction of the drum 2, so the electrode wires made of ITO can be formed more easily than the annular signal lines 52e. Accordingly, when there is employed a structure in which the scanning lines 54a are formed on the EL layer 53, and the scanning lines 54a are each made of the transparent conductive oxide (ITO), the light emitted in the EL layer 53 can be irradiated on the photosensitive portion 70 without interference.

With the simple structure as described above, it is possible to mount the digital photosensitive drum, which includes the exposure source and the photosensitive member integrated with each other, in the conventional structure employing the electrophotographic image forming process. Then, even if the rotation speed of the electrophotographic photosensitive drum is changed, an image forming apparatus which can select an appropriate exposure source can be obtained. In addition, writing start position correction or sub-scanning registration correction of an inline color machine can be performed without being affected by fluctuation in image forming speed.

(3) Process of Manufacturing Digital Photosensitive Drum 2

FIGS. 9, 10A to 10K, and 11A to 11E illustrate an outline of a process of manufacturing the digital photosensitive drum 2 according to the embodiment of the present invention. FIG. 9 is a flowchart of the outline of the manufacturing process, FIGS. 10 A to 10K and 11A to 11E are schematic process charts of the manufacturing process.

FIGS. 10A to 10K are diagrams taken along the longitudinal direction of the digital photosensitive drum 2 so as to contain the scanning lines 54a. A horizontal direction of FIGS. 10A to 10K corresponds to the longitudinal direction of the digital photosensitive drum 2.

FIGS. 11A to 11E are diagrams taken along the circumferential direction of the digital photosensitive drum 2 so as to contain the control circuit 51 for controlling each of the scanning lines formed in an end portion in the longitudinal direction. A horizontal direction of FIGS. 11A to 11E corresponds to the circumferential direction of the digital photosensitive drum 2.

FIG. 18 is a plan diagram of the digital photosensitive drum 2. FIGS. 10A to 10K are views as looking from a direction indicated by the arrow XA of FIG. 18. FIGS. 11A to 11E are views as looking from a direction indicated by the arrow XIA of FIG. 18.

Process P1: Formation of Control Circuit

On an original substrate (glass substrate), by employment of the poly-Si process, a control circuit (device) for controlling each of the signal lines and scanning lines, which is a circuit that drives each of the signal lines and includes an interface (I/F), is formed.

Process P2: Device Transfer

The device is removed from the original substrate and is transferred onto the outer peripheral surface of drum cylinder 40. Specifically, the control circuit 51 is formed on the outer peripheral surface of the drum cylinder 40 (see FIG. 10A).

The device is bonded and fixed onto the outer peripheral surface of the drum cylinder 40 so as to be wound around the outer peripheral surface. In this case, a tolerance between an outer diameter dimension of the drum cylinder 40 and a winding perimeter of the device is absorbed, so a wound and bonded portion of the device still has a seam with an interval of 250 μm or smaller.

Process P3: Formation of Insulating Layer 52a

At both ends of the drum cylinder 40, the flanges 31a and 31b (see FIG. 5A) are mounted. On the outer peripheral surface of the drum on which the control circuit 51 is formed, an organic polymer layer as the interlayer insulating layer 52a is formed (see FIG. 10B).

In the embodiment of the present invention, a polyimide film is coated with a thickness of 10μ as the insulating layer 52a by dipping. Through the process, the seam portion is filled, and the outer peripheral surface of the drum becomes a seamless continuous curved surface.

Process P4: Formation of Signal Line Layer 52

On the insulating layer 52a, toward the center of the signal line electrode pad 51e of the drive TFT 51d of the control circuit 51, each via hole (large through hole) 52f is formed by laser beam machining (see FIG. 10C).

Then, an electrode is embedded in each via hole 52f by using conductive paste. Specifically, each through hole electrode (large) 52c is formed (see FIG. 10D).

Further, also on a side of the scanning line drive circuit, formation of each through hole (large) 52f for the scanning lines 54a and formation of each through hole electrode 52c are performed in the same manner (see FIGS. 11A and 11B).

The outer peripheral surface formed of the insulating layer 52a and the through hole electrode 52c is polished by a CMP process to be smoothed.

Then, by the photolithography process, multiple signal lines (first electrode wires) 52e are formed in such a manner that the signal lines 52e are annularly formed with no seam in the circumferential direction of the drum cylinder, are separated from each other by each insulating member 52g, and are arrayed in the longitudinal direction of the drum cylinder (see FIGS. 10E and 10F).

Reference symbol 52f denotes the through hole (small), and reference symbol 52g denotes the partition wall of the insulating member for patterning the signal lines. The through hole electrode 52d, which is formed in the through hole (small) 52f, is formed simultaneously with the signal lines 52e. The signal lines 52e are each connected to the electrode pad 51e of the drive TFT 51d via the through hole electrodes 52d and 52c.

Further, also on a side of the scanning line drive circuit, each through hole (small) 52f is formed (see FIG. 11C).

Process P5: Formation of Organic EL Layer 53

On the surface of the signal line layer 52, multiple partition walls 54b, each of which is an insulating member for patterning the scanning lines, are formed linearly in the longitudinal direction of the drum cylinder, and at predetermined intervals and widths in the circumferential direction of the drum cylinder (see FIGS. 10G and 11D).

Next, the EL layer 53 is formed by vapor deposition (FIG. 10H).

Process P6: Formation of Scanning Line Layer 54

By use of a shadow mask, the scanning lines 54a are patterned and formed by sputtering using ITO (see FIGS. 10I and 11E). In this case, each of through hole electrodes (interlayer electrode) 54c is also formed between the scanning lines 54a and the through holes (large) 52c formed on the scanning line drive circuit side.

By the above-mentioned processes P1 to P6, on the outer peripheral surface of the drum cylinder 40, the control circuit 51, the signal line layer 52, the EL layer 53, and the scanning line layer 54 are sequentially stacked in the stated order, thereby forming the self-luminous device portion 50.

Process P7: Formation of Transparent Insulating/Barrier Layer 61

On the outer peripheral surface of the self-luminous device portion 50 formed as described above, the polymer (PEN) layer and the metal oxide (Al₂O₃) layer are alternately formed as the transparent insulating/barrier layer 61 by a continuous vapor deposition process (see FIG. 10J).

Process P8: Formation of Transparent Conductive Layer 62

On the outer peripheral surface of the transparent insulating/barrier layer 61, the ITO is formed as the transparent conductive layer 62 by sputtering (see FIG. 10K).

By the above-mentioned processes P7 and P6, on the outer peripheral surface of the self-luminous device portion 50, the functional separation portion 60 having a gas barrier property, a surface conductivity, and a visible light transmittance is formed.

Process P9: Formation of Photosensitive Portion 70

On the outer peripheral surface of the functional separation portion 60, an organic photoconductor (OPC) layer in which the undercoat layer (UCL) 71, the carrier generation layer (CGL) 72, the carrier transport layer (CTL) 73, and the protection layer 74 are stacked is formed as the photosensitive portion 70 by dipping coating.

All the processes of film formation, photolithography, and formation of the through hole electrodes, for forming the self-luminous device portion 50, the functional separation portion 60, and the photosensitive portion 70 are processes performed from the outer peripheral surface side of the drum.

By the above-mentioned manufacturing processes P1 to P9, the digital photosensitive drum 2 which has a small diameter and has no seam in the circumferential direction of the drum can be realized.

Specifically, before execution of the process P2 in which the device is transferred to form the control circuit for controlling the signal lines and scanning lines onto the drum cylinder 40, a discontinuous portion, that is, a seam is left on the periphery of the drum. However, the outer diameter portion of the drum obtained after the interlayer insulating layer 52a is formed in the process P3, a seamless cylindrical surface shape is obtained. Further, in the subsequent steps, the signal lines 52e are each annularly formed, and the scanning lines 54a are arranged symmetrically with respect to the drum rotational axis.

With the above-mentioned structure, there is formed a seamless pixel matrix having light emitting points (pixels) in the vicinity of each intersecting point between each of the signal lines 52e and each of the scanning lines 54a. Specifically, the digital photosensitive drum 2 which has a small diameter and has no seam is manufactured. As a result, it is possible to realize downsizing of the printer main body in which the exposure device is contained. Stability of the output image with respect to vibration and load fluctuation is improved.

(4) Driving Method for Digital Photosensitive Drum 2

FIG. 12 is a block diagram illustrating the drive circuit of the digital photosensitive drum 2.

Exchange of the electrical information signals containing the image data between the main body control circuit portion B of the printer A and the control circuit portion provided on the side of the digital photosensitive drum 2 rotationally driven, is performed by using a wireless interface.

In the embodiment of the present invention, in order to drive the light-emitting pixels formed on the drum 2 side, passive matrix (PM) drive is performed by sequentially selecting the scanning lines 54a. Specifically, the drive circuit sequentially selects the scanning lines 54a of the scanning line layer 54, thereby driving the signal lines 52e of the signal line layer 52 in synchronism with the selection of the scanning lines 54a. Thus, the drive circuit drives the signal lines 52e by using a line-sequential system in which the light-emitting pixel portions in the vicinity of each intersecting point between each of the scanning lines 54a and each of the signal lines 52e are caused to emit light, thereby forming a light-emitting pattern corresponding to the image data.

In the embodiment of the present invention, 1,800 scanning lines 54a are sequentially selected at each scanning line interval of about 42 μm (resolution of 600 dpi), at an image forming speed of 120 mm/s, and with a stationary scanning period of about 352 μs (scanning frequency of 2.8 KHz).

Control is performed such that a scanning line potential becomes a positive potential at the time of selection, and becomes 0 V (ground voltage (GND)) at the time of non-selection. In synchronism with the selection of the scanning lines, turning on/off of the signal lines is controlled, thereby forming the light-emitting pattern corresponding to the image data on the scanning lines. In the embodiment of the present invention, the scanning line potential is set to about 0 V (GND) at the time of selection of the signal lines 52e, and is set to +5 V at the time of non-selection. The potential at the time of non-selection of the scanning lines 54a and the potential at the time of selection of the signal lines 52e are set to substantially equal to each other, thereby preventing light emission on the scanning lines at the time of non-selection.

FIG. 6 illustrates a phase detection structure of the digital photosensitive drum 2 according to the embodiment of the present invention. FIG. 6 illustrates a part in vicinity of the driving-side end portion of the digital photosensitive drum 2 and a part of the belt unit 7, which is a target to which the drum 2 is positioned.

The drum 2 has an encoder wheel portion 33 for phase detection, which is provided at the outer diameter portion of the driving-side drum flange 31a that is fixed coaxially with the drum 2 at the end portion of the drum cylinder 40. Accordingly, when the drum 2 is rotationally driven, the encoder wheel portion 33 is also rotated together with the drum 2. A rotation central axis of the encoder wheel portion 33 is provided coaxially with the central axis of the drum 2.

A phase division pattern of the encoder wheel portion 33 is held in a phase relationship between the scanning lines 54a of the scanning line layer 54 of the drum 2.

The encoder wheel portion 33 corresponds to an etching pattern of black color Cr formed in the outer diameter portion of the drum flange 31a made of an aluminum alloy. In the embodiment of the present invention, the number of divisions is 1,800 (900 divisions for each of A and B phases) and a Z-phase for detecting 0 point is included.

On the other hand, a phase detector 34 is a reflective photodetector with a detector for the Z-phase, and is disposed so as to be fixed to the belt unit frame 7a. The phase division pattern of the encoder wheel portion 33 is detected by the phase detector 34. Detection signals of the phase detector 34 are input to a phase detecting circuit internal counter (see FIG. 12) of the main body control circuit portion B.

In the embodiment of the present invention, as illustrated in FIG. 4, the exposure point “c” is positioned between the charging position “a” and the developing position “b”, that is, in the vicinity of an uppermost portion in a vertical direction of the cross section of the drum. A phase detecting point by the phase detector 34 is positioned in the vicinity of a lowermost portion in the vertical direction of the cross section of the drum, which corresponds to the primary transfer position “d”.

A rotation angle of the drum 2 is obtained by accumulating A/B phase outputs detected by the phase detector 34 to the internal counter of the main body control circuit portion B. The internal counter is operated in a mode in which the internal counter is reset when the Z-phase, which is a reference position of the drum 2, is detected.

In the main body control circuit portion B, which is a control portion, when a trigger for starting image formation is issued, a scanning line selection control portion (see FIG. 12) detects a current phase of the drum 2 based on a current value of the internal counter to thereby select the scanning line 54a to be exposed and driven. Specifically, at the time of image formation, the main body control circuit portion B calculates the phase with respect to the belt unit 7 (printer main body) of the drum 2 in response to the output signals from the phase detector 34, thereby determining the scanning line to be driven based on the calculated value. When a writing start trigger is issued, the scanning line 54a to be written on the drum is selected based on the current phase of the drum 2. In synchronism with a current phase pulse of the drum 2, writing scanning is performed.

FIG. 13 illustrates a drive timing. One (1) strobe period corresponds to a scanning line selection period. In the embodiment of the present invention, all the 5,120 signal lines are divided into 5 segments to be controlled. For this reason, in the case of light emission, time-shared drive is performed in which a time of about 50 μs is allocated to each segment to be sequentially driven.

In the light-emitting pixel data, LINEn+1 data is latched with a frame in which the scanning line LINEn emits light. 1,024 pieces of light-emitting data (4-bit data containing light-emitting time information) of each segment are transferred to the signal drive circuit by the time-sharing, thereby being latched to a buffer.

FIG. 14 is a block diagram illustrating the data transfer. Each segment (Segment) is selected based on an address (ADDR) generated in the control portion, and is transferred to the segment corresponding to the data. In this case, a frequency of a clock for transferring (CLK) data is 20 MHz.

With the above-mentioned structure, in the self-luminous device portion 50, through the sequential selection of the scanning lines 54a and the drive for turning on/off the signal lines 52e in synchronism with the selection of the scanning lines 54a, fluorescent spots are generated in the organic EL layer 53 in the vicinity of each portion at which each of the scanning lines 54a and each of the signal lines 52e of the selection pixel intersects with each other. With the fluorescent spots, the photosensitive portion 70 stacked on the fluorescent spots is directly exposed, thereby forming the charge density distribution on the surface of the photosensitive member, that is, an electrostatic latent image.

With reference to FIGS. 15A to 15C, 16A to 16C, and 17A and 17B, detailed description is given of detection of a rotary phase of the drum 2 with respect to the printer main body.

For example, as illustrated in FIG. 15A, the charging position “a” and the developing position “b” are positioned with 120° with respect to the drum 2. A middle position between the charging position “a” and the developing position “b” is set as the exposure point “c”. A position 180° opposite from the exposure point “c” is set as the transfer position “d”. A rotational angular velocity of the drum 2 is set to 120°/second. It is assumed that, between an area 2) and an area 3) of the drum 2, there is only one patch (so-called home position detection) M for position detection, and that, at a position corresponding to the transfer position “d”, there is a phase detector 34 for detecting the patch.

In FIG. 15A, when the phase detector 34 detects the patch M at the transfer position “d”, it becomes apparent that an area 1) is positioned between the charging position “a” and the developing position “b”. It is necessary to perform the exposure between the charging position “a” and the developing position “b”, so the main body control portion B determines that the area 1) is an area in which a latent image can be formed. As illustrated in FIG. 15B, an area 2) is subjected to exposure after the elapse of one (1) second from the detection of the patch M.

Thus, in the case of starting the exposure based on time, there arises no problem when the rotational speed of the drum 2 is constant. However, when the rotational speed of the drum 2 rapidly decreases, as illustrated in FIG. 15C, even in a case where there is a portion which is not ready to be subjected to exposure (portion which is not ready to be written), there is a possibility that the portion is to be subjected to exposure. In other words, there is a possibility that the formation of the latent image is not satisfactorily performed due to the fluctuation in angular velocity of the drum 2.

Specifically, in the related art, the exposure is started based on time, and in a case of forming a latent image corresponding to a single recording material, among multiple light emitting pixel portions, an interval between a timing for light emission of a certain light emitting pixel portion and a timing for light emission of a light emitting pixel portion which is positioned downstream in a rotation direction of the drum 2 is constantly the same. As a result, when the rotational speed of the drum 2 is fluctuated, the exposure may be started at a timing when the latent image is not able to be formed yet in some cases.

In view of the above, an interval between division patterns (patterns corresponding to patches M of FIGS. 15A to 15C) for phase detection is set within 120° between the charging position “Na” and the developing position “b”, thereby reducing the effect of the fluctuation in speed of the drum 2 on the encoder wheel portion 33 of the above embodiment. In FIGS. 16A to 16C, patterns (patches) M1, M2, and M3 for phase detection are provided at boundaries (every 120°) between the areas 1), 2), and 3), respectively.

In FIG. 16A, when the phase detector 34 detects the patch M3 at the transfer position “d”, it is apparent that there is the area 1) between the charging position “a” and the developing position “b”.

Further, as illustrated in FIG. 16B, when the subsequent pattern M2 is detected after the elapse of one (1) second, it is apparent that there is the area 2) between the charging position “a” and the developing position “b”.

Thus, by providing the patterns M1, M2, and M3, it is possible to determine which area of the drum 2 is currently positioned between the charging position “a” and the developing position “b”. As a result, the timing of the exposure can be determined not based on the time but based on the patterns M1, M2, and M3. In other words, the exposure is started by using the detected patterns M1, M2, and M3 as a trigger.

In the above-mentioned method, even when the rotational speed of the drum 2 rapidly decreases, as illustrated in FIG. 16C, the subsequent pattern does not reach the transfer position “d”, that is, the phase detector 34, so it is apparent that there is a portion which is not ready for the exposure in the area 2).

Accordingly, it is possible to determine that the exposure is not executed in the area 2), thereby preventing the situation where the exposure is performed even when there is the portion which is not ready for the exposure.

In the above embodiment, during the formation of the latent image with respect to a single transfer material, it is possible to change a light emission interval between the light emission of a certain light emitting pixel portion (first light emitting pixel portion) and the light emission of a light emitting pixel portion (second light emitting pixel portion) which is positioned at a downstream side of the first light emitting pixel portion in the rotation direction of the drum 2. Accordingly, during the formation of the latent image with respect to a single transfer material, even when the rotational speed of the drum 2 is fluctuated, the exposure timing can be optimally controlled.

As a matter of course, when the number of divided patterns of the encoder wheel portion 33 is further increased, the accuracy for detecting the position of the drum 2 is increased. For example, as illustrated in FIG. 17A, there are provided 10 patterns M1 to M10, the rotational phase position of the drum 2 can be detected in 10 divisions. Accordingly, ideally, if there are the same number of patterns as that of the scanning lines 54a contained in the scanning line layer 54, it is possible to recognize the patterns and the scanning line 54a based on one-to-one correspondence.

In FIG. 16A, it is assumed that, when the interval between the adjacent patterns is set to be equal to or smaller than the angle formed between the charging position “a” and the developing position “b”, it is possible to detect which area of the drum 2 is positioned at least between the charging position “a” and the developing position “b”. In a case where the exposure is to be performed only in a specific area between the charging position “a” and the developing position “b”, it is effective to increase the number of patterns. For example, in a case where there is an area suitable for the exposure between the charging position “a” and the developing position “b”, assuming that it is not desirable to perform the exposure immediately after the charge position “a” or immediately before the developing position “b”, when the number of patterns is increased by division, it is possible to perform the exposure in the area suitable for the exposure. For example, as illustrated in FIG. 17B, when the area suitable for the exposure has a central angle 30°, 360°÷30°=12 is established. When the pattern of the encoder wheel portion 33 is divided into 12 patterns, the exposure can be performed in the area suitable for the exposure.

Thus, it is effective that each interval between the patterns for detecting the rotational phase of the drum of the encoder wheel portion 33, that is, the divided number of phase detection is further increased, because the exposure can be performed in the specific area (area suitable for exposure) between the charging position “a” and the developing position “b”.

In this manner, each interval (divided number of phase detection) between patterns for detecting the rotational phase of the drum of the encoder wheel portion 33 is set within the interval between the charging position “a” and the developing position “b” of the drum 2.

The control portion B controls the exposure of the pixel portions based on detection results obtained through the detection of the phase detecting patterns of the encoder wheel portion 33 by the phase detector, and based on the image data input from the external device (host device) C. As a result, it is possible to provide an image forming apparatus capable of selecting an appropriate light emitting pixel portion even when the rotational speed of the electrophotographic photosensitive drum is changed.

Further, in a case where the rotational speed of the drum 2 decreases, light emitting positions of the light emitting pixel portions may be changed. For example, when the rotational speed of the drum 2 is high, the exposure is performed at the position “c” of FIG. 15C, and when the rotational speed of the drum 2 is low, the exposure is performed at the position at the downstream side of the position “c” of FIG. 15C in the rotation direction of the drum 2. As a result, a time interval between the time when the drum 2 is subjected to exposure and the time when the drum 2 reaches the developing position can be uniformly set.

Accordingly, the writing start position correction for the exposure or the sub-scanning registration correction for the in-line color image forming apparatus can be performed without the effect of the fluctuation in image forming speed.

In the embodiment of the present invention, the encoder wheel portion is provided to an outer peripheral portion (outer diameter portion) of an end portion of the flange 31a on the driving side. However, the structure is not limited thereto, and any structure may be employed as long as the encoder wheel portion is rotated through the rotation of the drum 2 and detects the phase detecting patterns of the encoder wheel portion, to thereby enable detection of the phase of the drum 2.

(5) Others

(1) The image forming apparatus according to the embodiment of the present invention is the in-line color image forming apparatus, but the image forming apparatus can be applied to a color image forming apparatus of a single-drum system and to a monochromatic image forming apparatus.

(2) The charging unit of the drum 2 is not limited to the contact charging using the charging roller according to the embodiment of the present invention. A corona discharge device of a non-contact type can also be used.

(3) The developing unit of the drum 2 is not limited to the non-magnetic one-component contact development process of the embodiment of the present invention. It is possible to employ various types of development processes including a contact type and a non-contact type using one-component developer or two-component developer.

(4) It is also possible to use an image forming apparatus with no cleaner, in which a dedicated cleaning unit is not provided, and the residual toner remaining after the transfer is developed by a developing unit of a developing-and-cleaning type (in which cleaning is carried out simultaneously with developing).

(5) In the image forming apparatus according to the embodiment of the present invention, the light emitting pixels are driven by the passive matrix drive, but may be driven by active matrix drive.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2006-328096, filed Dec. 5, 2006, and Japanese Patent Application No. 2007-293103, filed Nov. 12, 2007, which are hereby incorporated by reference herein in their entirety.

Number	Date	Country	Kind
2006-328096	Dec 2006	JP	national
2007-293103	Nov 2007	JP	national

ELECTROPHOTOGRAPHIC IMAGE FORMING APPARATUS

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