JP2009075357A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which weight and cost reductions are achieved by reducing the number of components. <P>SOLUTION: The image forming apparatus includes: a plurality of image carriers disposed along a conveyance path for a transfer body and carrying a toner image; and at least one charge supply member for supplying charges to the transfer body in order to transfer each toner image to the transfer body. In the image forming apparatus, the charge supply member is disposed not to be opposite to at least one of the image carriers. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms a color image by transferring toner images formed on a plurality of image carriers to a transfer body.

  In image forming apparatuses such as printers and copiers that perform color image formation by electrophotography, a plurality of photosensitive drums and transfer rollers are opposed to each other along a conveyance path of a transfer medium such as a recording medium or an intermediate transfer belt. Arranged. Each photosensitive drum is provided with a toner cartridge for supplying toner of each color, and a charging drum and an exposure device arranged around the photosensitive drum form an electrostatic latent image on the surface of the photosensitive drum. Toner is supplied to the electrostatic latent image to form a toner image.

When the transfer body is transported between each photoconductor drum and the transfer roller, a transfer output is applied to the transfer roller, and a charge having a polarity opposite to the charge polarity of the toner image formed on the surface of the photoconductor drum. Is applied to the transferred transfer body. As a result, the toner images on the respective photosensitive drums are sequentially transferred to the transfer body, and a color image is formed on the transfer body.
JP 2005-70138 A

  However, in the conventional image forming apparatus described above, since it is necessary to provide a transfer roller corresponding to each photosensitive drum, there is a problem that the number of parts increases and costs increase.

  Therefore, there has been a demand for an image forming apparatus capable of reducing the number of parts and reducing the weight and cost.

  The present invention adopts the following configuration in order to solve the above points.

<Constitution>
An image forming apparatus according to the present invention is arranged along a transfer path of a transfer body, and supplies a plurality of image carriers that carry a toner image and charges to the transfer body in order to transfer the toner image to the transfer body. At least one charge supply member, and the charge supply member is disposed at a position not facing the at least one image carrier among the plurality of image carriers.

  According to the image forming apparatus of the present invention, the charge supply member such as the transfer roller can be disposed at a position not facing the image carrier such as the photosensitive drum, so that the charge supply member corresponds to each image carrier. Therefore, it is possible to reduce the number of installed charge supply members. Therefore, the weight reduction and cost reduction of the image forming apparatus are realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, a case where the present invention is applied to an intermediate transfer type color printer will be described as an example.

FIG. 1 is a schematic cross-sectional view of a color printer according to Embodiment 1 of the present invention.
The color printer 10 of this embodiment forms a color image as an image forming apparatus by superposing four color toners of black, yellow, magenta, and cyan.

  In the color printer 10, as shown in FIG. 1, four independent printing mechanisms 12K, 12Y, 12M, and 12C are sequentially arranged along the traveling direction of the intermediate transfer belt 11 as a belt member. .

  The printing mechanisms 12K, 12Y, 12M and 12C are electrophotographic LED printing mechanisms for black, yellow, magenta and cyan, respectively. In this embodiment, as shown in FIG. . Thereafter, when distinguishing the same components of the printing mechanisms 12K, 12Y12M, and 12C, K, Y, M, and C are added to the symbols, respectively, but when referring collectively, only the symbols are shown. Each symbol is shown in the printing mechanism 12C of FIG.

  Each of the printing mechanisms 12K, 12Y, 12M, and 12C includes an image forming unit 13 that forms a toner image and an LED head 14 that serves as an exposure unit.

  The image forming unit 13 is detachably disposed and includes a photosensitive drum 15 as an image carrier. The photosensitive drum 15 is exposed at the lower part of the image forming unit 13, and the surface thereof is disposed in contact with the intermediate transfer belt 11.

  The LED head 14 includes an LED array, a substrate on which a drive IC for driving the LED array and a register group for holding data are mounted, and a SELFOC lens array that collects light from the LED array. In response to an image data signal input from an LED head interface unit 50 (FIG. 3), which will be described later, the LED array emits light, thereby exposing the surface of the uniformly charged photosensitive drum 15 to electrostatic latent image. Form an image.

  Inside the image forming unit 13, a charging roller 16 as a charger for uniformly charging the surface of the photosensitive drum 15 around the photosensitive drum 15, and a developing roller 17 as a developer carrier. Are disposed in contact with the surface of the photosensitive drum 15. Further, around the photosensitive drum 15, a static elimination light source 18 that neutralizes residual charges by irradiating the surface of the photosensitive drum 15 with light on the downstream side of the contact portion between the photosensitive drum 15 and the intermediate transfer belt 11. is set up.

  Inside the image forming unit 13, a sponge roller 19 as a developer supplying member and a developing blade 20 as a layer regulating member are arranged around the developing roller 17 so as to contact the surface of the developing roller 17. Has been.

  A toner cartridge 21 as a toner container is detachably mounted on the upper part of the image forming unit 13, and toner 22 as a developer is supplied from the toner cartridge 21 into the image forming unit 13. In this embodiment, the material of the toner 22 is selected in advance so as to be negatively charged by frictional charging.

Further, as described above, the intermediate transfer belt 11 is disposed below the image forming unit 13. The structure of the intermediate transfer belt 11 is shown in FIG.
FIG. 2 is an explanatory diagram illustrating the structure of the intermediate transfer belt according to the first exemplary embodiment.

  As shown in FIG. 2, the intermediate transfer belt 11 of the present embodiment is made of a plastic film formed in a seamless endless shape, and includes a belt driving roller 23, a belt driven roller 24, and a secondary transfer backup as support members. It is stretched around the roller 25. As shown in FIG. 2, the intermediate transfer belt 11 has a two-layer structure of a high resistance layer 65 made of a high resistance material and a conductive layer 66 made of a low resistance material. As described above, the belt drive roller 23 is driven to rotate while the outer peripheral surface upper part is in contact with the surface of the photosensitive drum 15.

In this embodiment, the high resistance layer 65 of the intermediate transfer belt 11 is formed by mixing carbon in polyamideimide (PAI) so that the volume resistivity is 10 ¹¹ to 10 ¹³ Ω · cm. Further, in this embodiment, the conductive layer 66 of the intermediate transfer belt 11 is formed by rolling an aluminum thin film as a conductive member so that the volume resistivity is 10 ⁴ Ω · cm or less. It is formed by bonding or vapor deposition.

  The belt driving roller 23, the belt driven roller 24, and the secondary transfer backup roller 25 are all formed of a conductive member, and are connected to a primary transfer voltage control unit 56 (FIG. 3) described later as a charge supply member.

  A sheet feeding mechanism 26 is provided below the intermediate transfer belt 11. The paper feed mechanism 26 includes a recording medium accommodation cassette 28 that accommodates a plurality of recording media 27, a hopping roller 29, a paper feed sensor 30, a registration roller 31, a pinch roller 32, and a guide 33. Paper is fed to the next transfer unit 34.

  The hopping roller 29 is rotationally driven by a hopping motor 59 (FIG. 3), and conveys the recording medium 27 selected one by one from the recording medium accommodating cassette 28 by the discriminating means (not shown) between the registration roller 31 and the pinch roller 32. . The paper feed sensor 30 detects the arrival of the recording medium 27 between the registration roller 31 and the pinch roller 32 and notifies a printer control unit 58 (FIG. 3) described later. The registration roller 31 is rotationally driven by a registration motor 60 (FIG. 3), and the pinch roller 32 is driven to rotate as the registration roller 31 is driven. The guide 33 conveys and feeds the recording medium 27 conveyed by the registration roller 31 and the pinch roller 32 to the secondary transfer unit 34.

  A secondary transfer roller 35 is disposed in the secondary transfer portion 34 so as to face the secondary transfer backup roller 25 with the intermediate transfer belt 11 interposed therebetween. The secondary transfer roller 35 contacts the outer peripheral surface of the intermediate transfer belt 11, that is, the high resistance layer 65. When the recording medium 27 fed by the paper feeding mechanism 26 reaches this contact portion, that is, the nip portion, the intermediate transfer belt The toner image transferred onto the transfer belt 11 is secondarily transferred onto the surface of the recording medium 27.

  The recording medium 27 onto which the toner image has been transferred in the secondary transfer unit 34 is separated from the intermediate transfer belt 11 and conveyed to the guide 36. A position detection sensor 37 for detecting the rear end position of the recording medium 27 is provided on the downstream side in the conveyance direction of the recording medium 27. The recording medium 27 that has failed to be separated from the intermediate transfer belt 11 is provided with this position detection sensor. 37. The recording medium 27 separated from the intermediate transfer belt 11 is further guided to the fixing mechanism 38 by the guide 36.

  The fixing mechanism 38 includes a heat roller 39 and a pressure roller 40. The heat roller 39 is rotationally driven by the heater motor 62 (FIG. 3), and the pressure roller 40 is driven to rotate as the heat roller 39 is driven. A thermistor 41 is disposed near the surface of the heat roller 39 to monitor the temperature of the heat roller 39. The recording medium 27 conveyed to the fixing mechanism 38 is heated and pressed by the heat roller 39 and the pressure roller 40, and the toner images of the respective colors transferred in the secondary transfer unit 34 are fixed on the surface of the recording medium 27. Is done. In addition, a discharge sensor 42 is provided on the downstream side of the heat roller 39 to monitor the winding of the recording medium 27 around the heat roller 39 and the occurrence of a jam in the fixing mechanism 38.

  A guide 43 for conveying the recording medium 27 discharged from the fixing mechanism 38 is provided further downstream of the discharge sensor 42. The recording medium 27 on which the toner image is fixed by the fixing mechanism 38 is conveyed and discharged by the guide 43 to a stacker 44 provided at the upper part of the color printer 10.

  A cleaning blade 45 is disposed in contact with the side surface of the intermediate transfer belt 11 that contacts the belt driven roller 24. The cleaning blade 45 is made of, for example, a flexible rubber material or plastic material, and scrapes off toner, dust, and the like attached to the surface of the intermediate transfer belt 11 as the intermediate transfer belt 11 rotates. The scraped toner, dust, and the like are accommodated in a waste toner tank 46 installed under the cleaning blade 45.

  In addition, an environmental temperature / humidity sensor 47 is further provided inside the color printer 10. The environmental temperature / humidity sensor 47 has a function of detecting the temperature and humidity inside the color printer 10, and is mounted on, for example, a high-pressure board installed on the side surface of the color printer 10.

Next, the control system of the color printer 10 of this embodiment will be described in detail.
FIG. 3 is a block diagram illustrating a functional configuration of the color printer according to the first embodiment of the invention.
In FIG. 3, symbols K, Y, M, and C correspond to the printing mechanisms 12 for black, yellow, magenta, and cyan.

  As shown in FIG. 3, the color printer 10 includes a host interface unit 48, a command / image processing unit 49, an LED head interface unit 50, a motor control unit 51, a fixing mechanism temperature control unit 52, a high voltage control unit 53, a charging bias, and the like. A control unit 54, a development bias control unit 55, a primary transfer voltage control unit 56, a secondary transfer voltage control unit 57, and a printer control unit 58 are provided.

  The host interface unit 48 is a part that bears an interface in a physical layer with a host device such as a PC (not shown), and is composed of a connector, a communication chip, and the like. The host interface unit 48 receives a command for instructing execution of print processing, image data to be printed, and the like from the host device, and sends them to the command / image processing unit 49.

  The command / image processing unit 49 performs interpretation processing of commands received from the host device via the host interface unit 48, processing for developing image data described in PDL (Page Description Language), etc. into bitmap data, and the like. A processing unit configured by a microprocessor, a RAM, and the like. The command interpreted by the command / image processing unit 49 is output to the printer control unit 58, and the developed bitmap data is output to the LED head interface unit 50.

  The LED head interface unit 50 has a function of processing the bitmap data input from the command / image processing unit 49 according to the interface of each LED head 14K, 14Y, 14M, and 14C, and is semi-custom It is composed of LSI, RAM, and the like.

  The motor control unit 51 controls driving of each motor such as a hopping motor 59, a registration motor 60, a belt motor 61, a heater motor 62, and a drum motor 63.

  The hopping motor 59 is a drive unit that rotationally drives the hopping roller 29. The registration motor 60 drives the registration roller 31 to rotate. The belt motor 61 rotationally drives the belt driving roller 23 to rotate the intermediate transfer belt 11. The heater motor 62 rotationally drives the heat roller 39 provided in the fixing mechanism 38. The drum motor 63 rotationally drives the photosensitive drums 15K, 15Y, 15M, and 15C provided in the image forming units 13K, 13Y, 13M, and 13C.

  The fixing mechanism temperature control unit 52 controls the temperature of the fixing mechanism 38 in order to maintain the temperature of the heat roller 39 detected by the thermistor 41 at the fixing temperature notified by the printer control unit 58 described later.

  The fixing mechanism heater 64 is composed of a halogen lamp, is disposed inside the heat roller 39, and receives power supply from a power supply unit (not shown) under the control of the fixing mechanism temperature control unit 52 to heat the heat roller 39.

  The high voltage control unit 53 is constituted by a microprocessor or a custom LSI, controls supply of charging bias and developing bias to the image forming units 13K, 13Y, 13M and 13C, and transfers in the primary transfer unit and the secondary transfer unit 34. In order to control the supply of voltage, the charging bias controller 54, the developing bias controller 55, the primary transfer voltage controller 56, and the secondary transfer voltage controller 57 are controlled.

  The charging bias controller 54 controls supply and stop of charging bias to the charging rollers 16K, 16Y, 16M, and 16C.

  The development bias controller 55 controls supply and stop of development bias to the development rollers 17K, 17Y, 17M, and 17C.

  The primary transfer voltage control unit 56 controls supply and stop of the primary transfer voltage to the belt driving roller 23, the belt driven roller 24, and the secondary transfer backup roller 25 as charge supply members. The primary transfer voltage control unit 56 determines an appropriate output voltage based on the temperature and humidity inside the color printer 10 detected by the environmental temperature / humidity sensor 47, and performs constant voltage control.

  The secondary transfer voltage control unit 57 controls the supply and stop of the secondary transfer voltage to the secondary transfer roller 35. The secondary transfer voltage controller 57 determines an appropriate output voltage based on the temperature and humidity inside the color printer 10 detected by the environmental temperature / humidity sensor 47 and performs constant voltage control.

  The printer control unit 58 controls each unit of the color printer 10 based on the command received from the command / image processing unit 49. The printer control unit 58 notifies the internal temperature and humidity of the color printer 10 detected by the environmental temperature / humidity sensor 47 to the high-pressure control unit 53 and, based on the temperature and humidity, optimizes the fixing mechanism 38. The fixing temperature is determined and notified to the fixing mechanism temperature control unit 52.

Next, the operation of the color printer 10 of this embodiment will be described.
Here, the flow of processing when the color printer 10 performs printing processing will be described.

  In the color printer 10, when the host interface unit 48 receives a print request command and image data transmitted from a host device such as a PC (not shown), the print request command and image data are sent to the command / image processing unit 49. .

  Based on the received print request command, the command / image processing unit 49 sends a print start instruction to the printer control unit 58 and develops image data to convert the bitmap data for each page into each color, that is, black. , Yellow, magenta, and cyan are generated and stored.

  When the printer control unit 58 receives the print start instruction, the printer control unit 58 refers to the output from the environmental temperature / humidity sensor 47 to determine the optimum fixing temperature and notifies the fixing mechanism temperature control unit 52 of the fixing temperature. The fixing mechanism temperature control unit 52 refers to the output from the thermistor 41 and turns on / off the fixing mechanism heater 64 to maintain the notified fixing temperature.

  When one page of bitmap data is generated and stored in the command / image processing unit 49 and the output from the thermistor 41 reaches the optimum fixing temperature in the fixing mechanism 38, the printer control unit 58 starts the printing process. Accordingly, the high voltage control unit 53 is instructed to start supplying the charging bias, the developing bias, and the primary transfer voltage, and the motor control unit 51 is instructed to start driving the motor.

  The high voltage control unit 53 instructs the charging bias control unit 54 to supply a charging bias. Upon receiving this instruction, the charging bias controller 54 supplies a charging bias to the charging rollers 16K, 16Y, 16M, and 16C, and charges the surfaces of the photosensitive drums 15K, 15Y, 15M, and 15C.

  The high voltage control unit 53 also instructs the development bias control unit 55 to supply a development bias. In response to this instruction, the developing bias controller 55 supplies the developing bias to the developing rollers 17K, 17Y, 17M, and 17C.

  The high voltage controller 53 further instructs the primary transfer voltage controller 56 to supply the primary transfer voltage. At that time, the high voltage control unit 53 notifies the primary transfer voltage control unit 56 of the output information from the environmental temperature / humidity sensor 47 notified by the printer control unit 58. The primary transfer voltage control unit 56 determines an output voltage based on the notified output information, and supplies the primary transfer voltage to the belt driving roller 23, the belt driven roller 24, and the secondary transfer backup roller 25. Here, a case where the primary transfer voltage control unit 56 supplies +1000 V as the primary transfer voltage to the belt driving roller 23, the belt driven roller 24, and the secondary transfer backup roller 25 will be described as an example.

  Upon receiving a voltage output from the primary transfer voltage control unit 56, a voltage of +1000 V is applied to the belt driving roller 23, the belt driven roller 24, and the secondary transfer backup roller 25 made of a conductive member. Further, as shown in FIG. 2, the conductive layer 66 of the intermediate transfer belt 11 comes into contact with the surfaces of the belt driving roller 23, the belt driven roller 24, and the secondary transfer backup roller 25 as shown in FIG. The same voltage, that is, a voltage of +1000 V is applied.

  When instructed to start driving the motor, the motor control unit 51 drives the belt motor 61 and the drum motor 63. When the belt motor 61 is driven, the belt driving roller 23 starts rotating, and the intermediate transfer belt 11 starts rotating. When the drum motor 63 is driven, in each image forming unit 13, the photosensitive drum 15, the charging roller 16, the developing roller 17, and the sponge roller 19 start to rotate.

  As the photosensitive drum 15 and the charging roller 16 rotate, the surface of the photosensitive drum 15 is uniformly charged. For example, when a voltage of −1000 V is applied to the charging roller 16, the photosensitive drum 15 is charged to −500V. Further, the toner 22 supplied from the toner cartridge 21 reaches the developing blade 20 as the sponge roller 19 rotates. As the developing roller 17 rotates, a toner layer thinned by the developing blade 20 is formed on the outer periphery of the developing roller 17. At that time, the toner 22 is negatively charged due to friction between the developing roller 17 and the developing blade 20. For example, a voltage of −200 V is applied to the developing roller 17.

  After the surface of the photosensitive drum 15 is uniformly charged and a toner layer is formed on the developing roller 17, when a voltage of +1000 V is applied to the intermediate transfer belt 11 by supplying the primary transfer voltage, the command / Based on the control of the printer control unit 58, the image processing unit 49 reads black bitmap data for one line at a predetermined timing and outputs it to the LED head interface unit 50.

  Here, in the command / image processing unit 49, after the voltage of +1000 V is applied to the intermediate transfer belt 11 by supplying the primary transfer voltage, the contact portion of the photosensitive drum 15 with the intermediate transfer belt 11 is the primary transfer voltage. Bitmap data is transmitted at the timing when the rotation from the transfer unit to the exposure unit by the LED head 14 is performed. The reason is as follows. That is, when the primary transfer voltage is supplied, that is, when a voltage is applied to the intermediate transfer belt 11, charge movement based on the potential difference between the photosensitive drum 15 and the intermediate transfer belt 11 occurs in the primary transfer portion. . Along with the movement of the charge, the surface potential of the photosensitive drum 15K is different from that when the supply of the primary transfer voltage is stopped. The occurrence of such a difference in surface potential creates a density difference in the toner image formed on the photosensitive drum 15K, and as a result, there is a possibility of causing image deterioration. Therefore, the command / image processing unit 49 transmits bitmap data after the surface potential of the photosensitive drum 15K is stabilized.

  When receiving the bitmap data input from the command / image processing unit 49, the LED head interface unit 50 processes the bitmap data in accordance with the interface of the LED head 14K, generates an image data signal, and generates the image data. A signal is output to the LED head 14K.

  The LED head 14K causes the corresponding LED array to emit light based on the input image data signal. As a result, the uniformly charged surface of the photosensitive drum 15K is exposed, and an electrostatic latent image for one line is formed. For example, the surface potential of the photosensitive drum 15K that is exposed by the LED head 14K and has an electrostatic latent image formed thereon is set to about −50 to 0V.

  As described above, the bitmap data sent for each line is sequentially converted into an electrostatic latent image on the surface of the photosensitive drum 15K, and an electrostatic latent image for one page is formed on the photosensitive drum 15K. The A black toner 22K is attached to the electrostatic latent image by electrostatic force from a developing roller 17K charged with a developing bias. At this time, since the surface of the photosensitive drum 15K on which no electrostatic latent image is formed is charged to −500 V, the toner 22K does not adhere to the surface. As a result, a black toner image is formed on the surface of the photosensitive drum 15K.

  For yellow, magenta, and cyan colors, bitmap data is similarly transmitted at the timing based on the arrangement interval of each printing mechanism 12, and yellow, magenta, and cyan are transferred to the surfaces of the photosensitive drums 15Y, 15M, and 15C. Each toner image is formed.

Subsequently, the toner image formed on each photosensitive drum 15 is transferred to the intermediate transfer belt 11 in the primary transfer portion. The flow of primary transfer will be described with reference to the drawings.
FIG. 4 is an explanatory diagram of an electric field generated in the primary transfer portion.

  As shown in FIG. 4, the photosensitive drum 15 includes a surface layer 67 made of a photoconductive member and an aluminum tube 68. The aluminum tube 68 of the photosensitive drum 15 is grounded as shown in FIG.

  By supplying the primary transfer voltage, a voltage of +1000 V is applied to the conductive layer 66 of the intermediate transfer belt 11. Therefore, a potential difference is generated between the grounded aluminum tube 68 and the conductive layer 66 of the intermediate transfer belt 11. Due to this potential difference, an electric field is generated between the photosensitive drum 15 and the intermediate transfer belt 11 in the direction indicated by the arrow in FIG. 4, that is, in the direction from the intermediate transfer belt 11 toward the photosensitive drum 15.

  The toner 22 attached to the surface of the photosensitive drum 15 is negatively charged. Therefore, in the primary transfer portion, the toner 22 receives an electrostatic force from the photosensitive drum 15 toward the intermediate transfer belt 11 based on the electric field shown in FIG. As a result, the toner image formed on the photosensitive drum 15 is transferred to the intermediate transfer belt 11.

  When transferring the toner image in each printing mechanism 12, the printer control unit 58 turns on the respective static elimination light sources 18 and irradiates light toward the downstream side of the primary transfer unit of the photosensitive drum 15. Residual charges on the photosensitive drum 15 are neutralized by irradiation with light from the neutralizing light source 18. When the charge-removed photosensitive drum 15 is charged again by the charging roller 16, it can be more uniformly charged to a predetermined potential.

  In this way, the black, yellow, magenta, and cyan toner images are sequentially transferred onto the intermediate transfer belt 11 with a time difference based on the arrangement interval of the printing mechanisms 12, and full-color undetermined on the intermediate transfer belt 11. A contact toner image is formed. The intermediate transfer belt 11 further rotates and the transfer surface on which the unfixed toner image is transferred reaches the secondary transfer portion 34.

  On the other hand, the printer control unit 58 supplies the motor control unit 51 with the timing when the transfer surface reaches the secondary transfer unit 34, that is, the nip portion of the secondary transfer roller 35 and the secondary transfer backup roller 25. Give paper instructions.

  When receiving a paper feed instruction, the motor control unit 51 starts driving the hopping motor 59 and rotates the hopping roller 29. The recording medium 27 accommodated in the recording medium accommodating cassette 28 is selected by a discriminating means (not shown) and is sent out by the rotation of the hopping roller 29. When the recording medium 27 is detected by the paper feed sensor 30 and reaches between the registration roller 31 and the pinch roller 32, the motor control unit 51 stops driving the hopping motor 59. Thereby, the hopping roller 29 stops its rotation.

  Based on the output from the position detection sensor 37, the transmission start timing of bitmap data, the driving speed of the belt driving roller 23, the distance from the primary transfer unit to the secondary transfer unit 34, etc. The timing at which the unfixed toner image transfer surface on the transfer belt 11 reaches the secondary transfer portion 34 is measured. Then, the printer control unit 58 feeds paper to the secondary transfer unit 34 in accordance with this timing. The motor control unit 51 starts driving the registration motor 60 and the heater motor 62, and the recording medium 27 between the registration roller 31 and the pinch roller 32 is conveyed to the guide 33 along with the rotation of the registration roller 31. Guided by the guide 33 and fed to the secondary transfer section 34. As the heater motor is driven, the heater roller 39 starts rotating in the fixing mechanism 38.

  When the recording medium 27 reaches the secondary transfer unit 34, the high voltage control unit 53 starts supplying the secondary transfer voltage by the secondary transfer voltage control unit 57 based on an instruction from the printer control unit 58. The secondary transfer voltage control unit 57 determines the output voltage based on the output information from the environmental temperature / humidity sensor 47 notified by the high voltage control unit 53 and the medium information such as the thickness and material of the recording medium 27. A secondary transfer voltage is supplied to the secondary transfer roller 35. Note that the medium information used by the secondary transfer voltage control unit 57 is input by, for example, an operation panel (not shown) or a host device.

FIG. 5 shows the state of the electric field generated in the secondary transfer portion 34 when the secondary transfer voltage is supplied.
FIG. 5 is an explanatory diagram of an electric field generated in the secondary transfer portion.

  In the present embodiment, a primary transfer voltage of +1000 V is applied to the secondary transfer backup roller 25 in the secondary transfer unit 34 by the output from the primary transfer voltage control unit 56. Therefore, in order to transfer the negatively charged toner from the intermediate transfer belt 11 toward the recording medium 27, it is necessary to supply a secondary transfer voltage higher than +1000 V to the secondary transfer roller 35. In this embodiment, the secondary transfer roller 35 is supplied with a voltage of +3000 V as the secondary transfer voltage.

  In FIG. 5, the secondary transfer roller 35 is charged to +3000 V by the supply of the secondary transfer voltage. On the other hand, the secondary transfer backup roller 25 and the conductive layer 66 of the intermediate transfer belt 11 are charged to +1000 V by the supply of the primary transfer voltage. Therefore, a potential difference is generated between the secondary transfer roller 35 and the conductive layer 66 of the intermediate transfer belt 11, and the direction indicated by the arrow in FIG. 5, that is, the direction from the secondary transfer roller 35 to the intermediate transfer belt 11. In addition, an electric field is generated.

  Based on this electric field, the unfixed toner image on the intermediate transfer belt 11 receives an electrostatic force from the intermediate transfer belt 11 toward the secondary transfer roller 35. On the other hand, the recording medium 27 is fed to the nip portion between the intermediate transfer belt 11 and the secondary transfer roller 35 in the secondary transfer portion 34. Therefore, the toner image on the intermediate transfer belt 11 moves toward the secondary transfer roller 35 based on the electrostatic force and is transferred onto the surface of the recording medium 27.

  The intermediate transfer belt 11 continues to rotate. The recording medium 27 onto which the toner image has been transferred is separated from the intermediate transfer belt 11, conveyed to the guide 36, and further guided to the fixing mechanism 38.

  In the fixing mechanism 38, the heat roller 39 is maintained at an optimal fixing temperature and is rotated together with the pressure roller 40 under the control of the fixing mechanism temperature control unit 52. The recording medium 27 is heated and pressed by the heat roller 39 and the pressure roller 40, and the toner image transferred in the secondary transfer unit 34 is fixed on the surface of the recording medium 27.

  Thereafter, the recording medium 27 is discharged from the fixing mechanism 38, conveyed by the guide 43, and discharged to the stacker 44. When the discharge sensor 42 detects the rear end position of the recording medium 27 and grasps the discharge of the recording medium 27, the printer control unit 58 instructs the motor control unit 51 to stop driving the motor. Further, the high voltage control unit 53 stops the supply of the primary transfer voltage by the primary transfer voltage control unit 56 when the intermediate transfer belt 11 stops running, and 2 when the recording medium 27 passes through the secondary transfer unit 34. The supply of the secondary transfer voltage by the next transfer voltage control unit 57 is stopped. Further, the high-voltage control unit 53 stops the supply of the charging bias by the charging bias control unit 54 and the supply of the developing bias by the development bias control unit 55 with the rotation of each drum being stopped. Thereby, the printing process in the color printer 10 is completed.

  As described above, after the toner image formed on each photoconductive drum 15 is transferred onto the intermediate transfer belt 11, the toner image is secondarily transferred to the recording medium 27 fed from the paper feed mechanism 26, and a color image is formed. It is formed.

  As described above, in the color printer of this embodiment, the intermediate transfer belt having the conductive layer is stretched around the belt driving roller, the belt driven roller, and the secondary transfer backup roller made of a conductive member, and these belt driving rollers. The primary transfer voltage is applied to the intermediate transfer belt via the belt driven roller and the secondary transfer backup roller. As a result, the primary transfer voltage is also supplied to the conductive layer in contact with the belt driving roller, the belt driven roller, and the secondary transfer backup roller. Therefore, in the primary transfer portion, the transfer is performed at a position facing each photosensitive drum. There is no need to newly provide a charge supply member such as a roller. Therefore, the number of parts is reduced, and the cost can be reduced and the apparatus can be reduced in weight. Further, since the pressure contact force from the transfer roller to the intermediate transfer belt and the photosensitive drum in the conventional color printer is removed, the wear of the intermediate transfer belt and the photosensitive drum is prevented and the driving load of the intermediate transfer belt is reduced. And stable running is possible.

  In order to bring the intermediate transfer belt 11 and the photosensitive drum 15 into close contact, a guide member that presses the intermediate transfer belt 11 from the conductive layer 66 side toward the photosensitive drum 15 is disposed at a position facing each of the photosensitive drums 15. You may set up. In this case, the adhesion between the intermediate transfer belt 11 and the photosensitive drum 15 is increased, so that the occurrence of transfer omission and the like is suppressed, and better image formation is realized.

  In the color printer 10 according to the first embodiment, the intermediate transfer belt 11 having the conductive layer 66 is stretched around the belt driving roller 23, the belt driven roller 24, and the secondary transfer backup roller 25 made of a conductive member, thereby transferring the transfer roller. The transfer voltage can be supplied without the need for an image.

  However, as the four color toner images are sequentially transferred onto the intermediate transfer belt 11, electric charges are generated between the photosensitive drum 15 and the intermediate transfer belt 11, and electric charges due to contact between the photosensitive drum 15 and the intermediate transfer belt 11. This movement causes a problem that negative charges accumulate on the transfer surface of the intermediate transfer belt 11, that is, the high resistance layer 65, resulting in a shortage of transfer voltage in the primary transfer portion.

  Therefore, in order to solve the above problem, in this embodiment, the color printer 70 is configured as follows.

FIG. 6 is a schematic sectional view of a color printer according to Embodiment 2 of the present invention.
The color printer 70 of this embodiment is different from that of the first embodiment in the configuration in which belt neutralizing light sources 72K, 72Y, and 72M are added.
In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

  As shown in FIG. 6, the color printer 70 includes four independent printing mechanisms 12K, 12Y, 12M, and 12C arranged along the traveling direction of the intermediate transfer belt 71 as a belt member. I have.

FIG. 7 is an explanatory diagram illustrating the structure of the intermediate transfer belt according to the second embodiment.
As shown in FIG. 7, the intermediate transfer belt 71 of this embodiment is formed in a seamless endless shape, and includes a photoconductive layer 74 made of a photoconductive member and a conductive layer 66 made of a conductive member. It has a layer structure.

  In this embodiment, the photoconductive layer 74 of the intermediate transfer belt 71 is formed of the same photoconductive member as the surface layer 67 of the photosensitive drum 15 (FIG. 4).

  Between the printing mechanisms 12K, 12Y, 12M, and 12C, belt neutralizing light sources 72K, 72M, and 72C are arranged as shown in FIG. Each of the belt neutralization light sources 72K, 72M, and 72C, as a neutralization member, irradiates the surface of the intermediate transfer belt 71 with light to neutralize the accumulated negative charge.

FIG. 8 is a block diagram illustrating a functional configuration of the color printer according to the second embodiment of the present invention.
In addition to the functions of the printer control unit 58 of the first embodiment, the printer control unit 73 further controls turning on and off of the belt charge removal light sources 72K, 72Y, and 72M.

Next, the operation of the color printer 70 of this embodiment will be described.
Here, the flow of printing processing in the color printer 70 will be described only for parts different from the first embodiment.

  The processing flow for transferring the toner image on the photosensitive drum 15K to the intermediate transfer belt 71 is the same as that in the first embodiment. In the present embodiment, the printer control unit 73 turns on the belt static elimination light source 72K when the printing mechanism 12K starts to transfer the toner image formed on the photosensitive drum 15K to the intermediate transfer belt 71.

When the toner image on the photosensitive drum 15K is transferred to the intermediate transfer belt 71, negative charges may adhere to the intermediate transfer belt 71 due to the generation of electric discharge or the movement of electric charges due to contact as described above. Here, the surface of the intermediate transfer belt 71 in contact with the photosensitive drum 15, that is, the transfer surface is composed of a photoconductive layer 74 as shown in FIG. 7, and a conductive layer 66 is formed on the back side thereof. Yes. By irradiating the transfer surface of the intermediate transfer belt 71 with light from the belt neutralizing light source 72K, the negative charge attached on the photoconductive layer 74 in the primary transfer portion is neutralized.
The negative charge of the toner image is not neutralized even when irradiated with light from the belt neutralization light source 72K. Therefore, during the primary transfer of the toner image on the photosensitive drum 15Y in the printing mechanism 12Y, the black toner image transferred onto the intermediate transfer belt 71 maintains its negative charge, and the black toner image contained in the toner image is maintained. The reverse transfer of the toner 22K to the photosensitive drum 15Y is prevented.

  Thereafter, the same processing is repeated in the printing mechanisms 12Y, 12M, and 12C, and a full-color toner image is formed on the intermediate transfer belt 71. Thereafter, the full-color toner image is transferred to the recording medium 27 in the secondary transfer unit 34 and then fixed in the fixing mechanism 38. When the recording medium 27 is discharged to the stacker 44, the printing process in the color printer 70 ends.

  It is also possible to similarly install a belt static elimination light source on the downstream side of the printing mechanism 12C. However, in this embodiment, since a new toner image is not transferred on the downstream side of the printing mechanism 12C, the color printer 70 is configured to have only three belt static elimination light sources.

  As described above, in the color printer of this embodiment, the transfer surface of the intermediate transfer belt is used as a photoconductive layer, and the belt neutralizing light source is installed between the printing mechanisms, so that accumulation is performed by repeating primary transfer. It is possible to remove the charge on the intermediate transfer belt and prevent a shortage of transfer voltage. At this time, since the negative charge of the toner is not neutralized, the problem that the toner image transferred by the upstream printing mechanism is reversely transferred to the downstream photosensitive drum is also prevented. Therefore, it is possible to obtain a higher quality printing result.

  In this embodiment, the belt static elimination light source 72 is installed on the photoconductive layer 74 side of the intermediate transfer belt 71, but the present invention is not limited to this. For example, by forming the conductive layer 66 of the intermediate transfer belt 71 from a transparent conductive member, the belt charge removal light source 72 can be installed on the conductive layer 66 side.

  Further, in this embodiment, the belt static elimination light source 72 is installed between the printing mechanisms 12, but the present invention is not limited to this. For example, it is possible to adopt a configuration in which installation is limited, such as installation only between the printing mechanisms 12M and 12C. Further, in order to stabilize the primary transfer condition in the printing mechanism 12K, it is also possible to install a belt static elimination light source 72 on the upstream side of the printing mechanism 12K.

  In the color printer 70 of the second embodiment, the transfer surface of the intermediate transfer belt 71 is a photoconductive layer 74, and belt static elimination light sources 72K, 72Y, and 72M are installed between the printing mechanisms 12K, 12Y, 12M, and 12C. By eliminating the negative charge adhering to the intermediate transfer belt 71 during the primary transfer, it is possible to solve the shortage of the primary transfer voltage and obtain a high-quality primary transfer result.

  However, the color printer 70 according to the second embodiment has a problem in that the secondary transfer unit 34 is insufficiently charged negatively on the intermediate transfer belt 71 and causes toner scattering.

  Therefore, in this embodiment, the color printer 80 is configured as follows in order to solve the above-described problem.

FIG. 9 is a schematic cross-sectional view of a color printer according to Embodiment 3 of the present invention.
The color printer 80 of this embodiment is different from that of the second embodiment in the configuration in which a corona charger 81 is added.
In the present embodiment, the same components as those in the first embodiment or the second embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

  As shown in FIG. 9, the color printer 80 includes four independent printing mechanisms 12K, 12Y, 12M, and 12C that are disposed along the traveling direction of the intermediate transfer belt 71 as a belt member. I have.

  Between the printing mechanisms 12K, 12Y, 12M, and 12C, as shown in FIG. 9, belt neutralizing light sources 72K, 72Y, and 72M are installed as neutralizing members. A corona charger 81 as a charging member is installed on the downstream side of the printing mechanism 12C.

FIG. 10 is a block diagram illustrating a functional configuration of the color printer according to the third embodiment of the present invention.
The corona charger 81 discharges the intermediate transfer belt 71 under the control of the high-pressure control unit 82 and charges the intermediate transfer belt 71 negatively.

Next, the operation of the color printer 80 of this embodiment will be described.
Here, only a portion different from the second embodiment will be described with respect to a flow of processing when the color printer 80 performs printing processing.

  In the color printer 80 of the present embodiment, when the primary transfer operation is started in the printing mechanism 12 </ b> C, the high voltage control unit 82 starts supplying voltage to the corona charger 81 based on an instruction from the printer control unit 83. In this embodiment, a voltage of −4000 V is applied to the corona charger 81, and the surface of the intermediate transfer belt 71 is charged to about −600 V as the voltage is applied to the corona charger 81. At this time, the toner image transferred onto the intermediate transfer belt 71 is also charged together with the intermediate transfer belt 71. However, since a negative charged charge increases, problems such as reverse charging polarity do not occur. Unlike frictional charging, charging is performed by the corona charger 81, so that the toner image is not damaged by friction.

  The intermediate transfer belt 71 and the toner image that are negatively charged by the corona charger 81 reach the secondary transfer section 34 as the intermediate transfer belt 71 rotates. At this time, the blank portion of the intermediate transfer belt 71 is negatively charged, and the toner image is more strongly negatively charged. Therefore, toner scattering is unlikely to occur in the secondary transfer portion 34, and reliable secondary transfer is realized.

  As described above, in the color printer of this embodiment, by installing the corona charger further downstream of each printing mechanism, toner scattering due to insufficient negative charging of the intermediate transfer belt is generated in the secondary transfer unit. It becomes possible to suppress. In addition, the toner image is more strongly charged by the corona charger without changing the charging polarity, so that the secondary transfer can be reliably performed, and a higher-quality printing result can be obtained.

  In this embodiment, a corona charger is used as the charging member, but the present invention is not limited to this. For example, a charging roller that performs contact charging can be used as the charging member.

FIG. 11 is a schematic cross-sectional view of a color printer according to Embodiment 4 of the present invention.
The color printer 90 according to the present exemplary embodiment includes neutralizing light sources 91 </ b> K, 91 </ b> Y that can neutralize the photosensitive drum 15 and the intermediate transfer belt 71 instead of the neutralizing light sources 18 </ b> K, 18 </ b> Y, 18 </ b> M, 18 </ b> C and the belt neutralizing light sources 72 </ b> K, 72 </ b> Y, 72 </ The configuration in which 91M and 91C are provided and the light shielding plates 92K, 92Y, 92M, and 92C are added is different from the third embodiment.
In the present embodiment, the same components as those in the first to third embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

  As shown in FIG. 11, the color printer 90 includes four independent printing mechanisms 93K, 93Y, 93M, and 93C disposed along the traveling direction of the intermediate transfer belt 71 as a belt member. I have.

  Each of the printing mechanisms 93K, 93Y, 93M, and 93C includes an image forming unit 94 and an LED head 14.

  The image forming unit 94 includes a photosensitive drum 15 as an image carrier, a charging roller 16, a developing roller 17, a sponge roller 19, a developing blade 20, and a toner cartridge 21.

  Inside the image forming unit 94, a static elimination light source 91 is installed on the downstream side of the contact portion between the photosensitive drum 15 and the intermediate transfer belt 71. This static elimination light source 91 has a finger-light characteristic capable of simultaneously irradiating the photosensitive drum 15 and the intermediate transfer belt 71 with light, and irradiates the surface of the photosensitive drum 15 with light to neutralize residual charges, The surface of the transfer belt 71 is irradiated with light to remove the accumulated negative charge.

  Further, in the image forming unit 94, in order to block the light from the static elimination light source 91 from being irradiated to the contact portion between the photosensitive drum 15 and the intermediate transfer belt 71, that is, the upstream side of the primary transfer portion. A light shielding plate 92 is installed as a shielding member. If the light from the static elimination light source 91 leaks to the upstream side of the primary transfer portion, there is a possibility that toner scattering may occur due to insufficient primary transfer voltage. The light shielding plate 92 of this embodiment is installed in each image forming unit 94 in order to prevent the occurrence of toner scattering in the primary transfer portion.

FIG. 12 is a block diagram illustrating a functional configuration of the color printer according to the fourth embodiment of the present invention.
The printer control unit 95 controls turning on and off of each static elimination light source 91.

Next, the operation of the color printer 90 of this embodiment will be described.
Here, the flow of the printing process in the printing mechanism 93 </ b> K of the color printer 90 will be described only for parts different from the third embodiment.

  When the printing operation is started in the printing mechanism 93K, the printer control unit 95 turns on the static elimination light source 91K. The neutralization light source 91K irradiates the photosensitive drum 15K and the intermediate transfer belt 71 with light to neutralize charges remaining on the surface of the photosensitive drum 15K after the primary transfer, and at the primary transfer portion, the light of the intermediate transfer belt 71 is discharged. The negative charge adhering to the conductive layer 74 is removed. Further, the light shielding plate 92K prevents light from the static elimination light source 91K from leaking to the upstream side of the primary transfer portion and causing toner scattering.

  As described above, the color printer of this embodiment can reduce the number of parts by sharing the static elimination light source that neutralizes residual charges on the photosensitive drum and the static elimination light source that neutralizes the intermediate transfer belt. Therefore, it is possible to reduce the cost and reduce the weight of the apparatus without deteriorating the image quality.

  In each of the above-described embodiments, the description has been made by taking the intermediate transfer type electrophotographic color printer as an example, but the present invention is not limited to this. For example, the present invention can be applied to a direct transfer type electrophotographic color printer in which a recording medium is adsorbed and conveyed on a transfer conveyance belt and a toner image is transferred from the image carrier to the recording medium.

  In each of the above-described embodiments, the case where the belt driving roller, the belt driven roller, and the secondary transfer backup roller are employed as the charge supply member and the primary transfer voltage is supplied to the belt driving roller has been described as an example. It is also possible to adopt a configuration in which the primary transfer voltage is applied only to any of the belt driving roller, the belt driven roller, and the secondary transfer backup roller. It is also possible to newly provide a charge supply member and apply a primary transfer voltage to the charge supply member. Furthermore, in any three of the four printing mechanisms, a transfer roller as a charge supply member is installed at a position facing the photosensitive drum, or a charge supply member is installed between each of the yellow and magenta printing mechanisms. The structure etc. to perform are also possible.

1 is a schematic sectional view of a color printer according to Embodiment 1 of the present invention. FIG. 3 is an explanatory diagram illustrating a structure of an intermediate transfer belt of Example 1. 1 is a block diagram illustrating a functional configuration of a color printer according to a first embodiment of the invention. It is explanatory drawing about the electric field which generate | occur | produces in a primary transfer part. It is explanatory drawing about the electric field which generate | occur | produces in a secondary transfer part. It is a schematic sectional drawing of the color printer which concerns on Example 2 of this invention. FIG. 6 is an explanatory diagram illustrating a structure of an intermediate transfer belt of Example 2. It is a block diagram which shows the function structure of the color printer which concerns on Example 2 of this invention. It is a schematic sectional drawing of the color printer which concerns on Example 3 of this invention. It is a block diagram which shows the function structure of the color printer which concerns on Example 3 of this invention. It is a schematic sectional drawing of the color printer which concerns on Example 4 of this invention. It is a block diagram which shows the function structure of the color printer which concerns on Example 4 of this invention.

Explanation of symbols

10, 70, 80, 90 Color printer 11, 71 Intermediate transfer belt 18, 91 Static elimination light source 23 Belt drive roller 24 Belt driven roller 25 Secondary transfer backup roller 35 Secondary transfer roller 65 High resistance layer 66 Conductive layer 72 Belt static elimination light source 74 Photoconductive layer 81 Corona charger 92 Shading plate

Claims (14)

A plurality of image carriers that are arranged along the transfer path of the transfer body and carry toner images, and at least one charge supply that supplies charges to the transfer body in order to transfer each of the toner images to the transfer body An image forming apparatus comprising a member,
The image forming apparatus, wherein the charge supply member is disposed at a position not facing the at least one of the plurality of image carriers. The transfer body comprises a belt member conveyed in contact with the plurality of image carriers.
The charge supply member supplies the charge to the belt member;
The image forming apparatus according to claim 1, wherein each toner image is transferred to the belt member at a contact portion between the belt member and each image carrier. The belt member is stretched and conveyed on a plurality of support members,
The image forming apparatus according to claim 2, wherein the at least one charge supply member includes any one of the plurality of support members.   The image forming apparatus according to claim 2, further comprising a charging member that charges a transfer surface onto which each of the toner images is transferred. The belt member has at least one conductive layer,
The image forming apparatus according to claim 2, wherein the conductive layer is formed on a surface opposite to a contact surface including a contact portion with the plurality of image carriers on the belt member. The image forming apparatus according to claim 5, wherein the conductive layer is made of a conductive member having a volume resistivity of 10 ⁵ Ω · cm or less. The belt member has a photoconductive layer made of a photoconductive member,
The photoconductive layer is formed on a contact surface including a contact portion with the plurality of image carriers in the belt member,
The image forming apparatus according to claim 2, further comprising a neutralizing member that neutralizes the photoconductive layer.   The image forming apparatus according to claim 7, wherein the neutralizing member further neutralizes a surface of the image carrier. The static elimination member comprises a static elimination light source that performs static elimination by irradiating the photoconductive layer of the belt member with light, and further radiating light on the surface of the image carrier.
The image forming apparatus according to claim 7, further comprising a light shielding member for shielding light from the static elimination light source to a contact portion between the belt member and the image carrier. A belt member disposed to face the plurality of image carriers;
The transfer body is composed of a recording medium conveyed by the belt member,
The charge supply member supplies the charge to the transfer body via the belt member;
The image forming apparatus according to claim 1, wherein each of the toner images is transferred to the recording medium. The belt member is stretched and arranged on a plurality of support members,
The image forming apparatus according to claim 10, wherein the at least one charge supply member includes any one of the plurality of support members. The belt member has at least one conductive layer,
The image forming apparatus according to claim 10, wherein the conductive layer is formed on a surface of the belt member opposite to a conveyance surface of the recording medium. The image forming apparatus according to claim 12, wherein the conductive layer is made of a conductive member having a volume resistivity of 10 ⁵ Ω · cm or less. The transfer body comprises a transfer belt having a conductive layer,
The image forming apparatus according to claim 1, wherein the charge supply member includes a transfer voltage supply unit that supplies a transfer voltage to the transfer belt.

Images