JP2017016072A - Image forming apparatus - Google Patents

Abstract

CONSTITUTION: An image forming apparatus (10) is an image forming apparatus of an intermediate transfer system comprising a transfer belt (32) and a plurality of primary transfer rollers (38). Control parts (30, 80) of the image forming apparatus control a contact/separation mechanism (70) and a transfer power supply (46) when performing monochrome printing on thick paper to bring at least one of the primary transfer rollers for color printing into contact with photoreceptors for color printing without applying a voltage (S13, S15).EFFECT: Transfer shit can be prevented and film thinning of photoreceptors can be reduced.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that primarily transfers a toner image from a plurality of photoconductors arranged side by side to a transfer belt, and secondarily transfers the toner image from the transfer belt to a sheet.

  Conventionally, a toner image of each color is formed on a plurality of photoconductors arranged side by side, and these toner images are sequentially primary transferred onto a transfer belt to form a multicolor image, and then the multicolor image is transferred from the transfer belt to a sheet. 2. Description of the Related Art An intermediate transfer type image forming apparatus for performing secondary transfer and fixing is known. In the intermediate transfer type image forming apparatus, a monochrome printing mode in which only the black photoconductor is in contact with the transfer belt, a color printing mode in which all the photoconductors are in contact with the transfer belt, and a standby in which all the photoconductors are separated from the transfer belt. Displaceable to each mode position of the mode. The transfer belt is separated from or brought into contact with the photosensitive member by, for example, displacing a plurality of primary transfer rollers provided to face the plurality of photosensitive members with the transfer belt interposed therebetween.

  In such an image forming apparatus, when an image is formed on a thick paper that is thicker and stronger than plain paper, a transfer shift may occur due to an impact caused by paper conveyance. This transfer deviation is likely to occur in the monochrome printing mode. This is because, in the monochrome printing mode, the primary transfer roller that comes into contact with the photosensitive member with the transfer belt interposed therebetween is only for black, so that all the primary transfer rollers and the photosensitive member contact with each other with the transfer belt interposed therebetween. This is because the primary transfer unit including the transfer belt and the like is likely to vibrate due to an impact.

  Therefore, when forming an image on cardboard, in order to reduce transfer deviation, the color printing mode is set even when monochrome printing is performed, and all the primary transfer rollers and the photosensitive member are brought into contact with each other with the transfer belt interposed therebetween. There was a case where control to make a state was performed.

  For example, in Patent Document 1, although it is not an intermediate transfer type image forming apparatus, when the special transfer material detection unit detects that the paper is special paper or A3 size, all the photosensitive elements are used even during monochrome printing. An image forming apparatus is disclosed in which a transfer roller is moved to a pressing position (transfer position) so that a body contacts a sheet.

JP-A-2005-107407

  In the conventional image forming apparatus as disclosed in Patent Document 1, since the movement of the transfer roller to the pressing position and the application of the voltage to the transfer roller are controlled to interlock, the position of the transfer roller is color printed. When the mode is set, a transfer current flows through all the photoconductors. When a transfer current flows through the photosensitive member, the surface of the photosensitive member is reduced in molecular weight and easily vaporized, which may promote film reduction of the photosensitive member. However, this is not considered in the conventional image forming apparatus. That is, in the conventional image forming apparatus, no consideration is given to the reduction of the film thickness of the photoconductor due to the transfer current, and the life of the photoconductor may be shortened.

  Therefore, a main object of the present invention is to provide a novel image forming apparatus.

  Another object of the present invention is to provide an image forming apparatus capable of preventing transfer misalignment and reducing the film loss of the photosensitive member.

  In the first invention, a toner image is primarily transferred from a plurality of photoconductors including a black photoconductor and a plurality of color photoconductors arranged side by side to a transfer belt, and the toner image is secondarily transferred from the transfer belt to a sheet. An image forming apparatus that includes a transfer belt, a black primary transfer roller, and a plurality of color primary transfer rollers that are stretched around a plurality of rollers and arranged to face the plurality of photosensitive members. A plurality of primary transfer rollers disposed so as to face each of the photoconductors with the transfer belt interposed therebetween, a separation mechanism for separating and contacting each of the photoconductors and each of the primary transfer rollers with the transfer belt interposed therebetween, primary A transfer power source that applies a voltage to each of the transfer rollers, and a state in which no voltage is applied to at least one of the color primary transfer rollers when performing monochrome printing on thick paper In a control unit for controlling the detaching mechanism and the transfer power source so as to abut against the color photosensitive material across the transfer belt, an image forming apparatus.

  In the first invention, the image forming apparatus is an intermediate transfer type image forming apparatus including a plurality of photosensitive members, a transfer belt, a plurality of primary transfer rollers, a separation mechanism, a transfer power source, and the like. In addition to the black primary transfer roller for transferring the toner image when the monochrome printing is performed on the thick paper, the control unit of the image forming apparatus at least one of the color primary transfer rollers not used for transferring the toner image. The contact / separation mechanism and the transfer power source are controlled so that the contact member is brought into contact with the color photoconductor with the transfer belt sandwiched in a state where no voltage is applied.

  According to the first aspect of the invention, when monochrome printing is performed on a thick paper, at least one of the color primary transfer rollers is brought into contact with the photosensitive member with the transfer belt interposed therebetween, so that the vibration of the primary transfer unit during transfer is performed. Can be reduced, and the occurrence of transfer misalignment can be prevented. At this time, even if the primary transfer roller for color and the photoconductor are brought into contact with each other with the transfer belt interposed therebetween, no voltage is applied to the primary transfer roller for color, thereby reducing the film loss of the photoconductor for color. And the life of the color photoconductor can be extended.

  The second invention is dependent on the first invention, and when the monochrome printing is performed on the thick paper, the control unit is for a color in a state where no voltage is applied only when the thick paper enters the secondary transfer portion. The separation / contact mechanism and the transfer power source are controlled so that the primary transfer roller and the color photoconductor are brought into contact with each other with the transfer belt interposed therebetween.

  In the second invention, when monochrome printing is performed on the thick paper, the time for which the thick paper is subjected to the secondary transfer is the time for which the primary transfer roller for color and the color photoconductor are in contact with each other with the transfer belt interposed therebetween. This is limited to only a predetermined time before and after the time of entering the part, that is, including the moment when the leading edge of the cardboard enters the secondary transfer part. Then, the color primary transfer roller is arranged at a separated position except for a predetermined time when the cardboard enters.

  According to the second aspect of the present invention, the color primary transfer roller, the color photoconductor, the transfer belt, and the like are consumed due to the contact between the color primary transfer roller and the color photoconductor across the transfer belt. Can be minimized.

  A third invention is dependent on the first or second invention, and includes a black cleaning member and a plurality of color cleaning members provided on each of the photoconductors to remove residual toner on the photoconductor. Provided with a plurality of cleaning members and a color cleaning member, and provided with a moving mechanism for changing the contact pressure of the color cleaning member with respect to each of the color photoconductors, or changing the contact pressure. On the other hand, when performing monochrome printing, the moving mechanism is controlled so that the color cleaning member is separated from the color photoconductor or the contact pressure is weakened.

  According to a third aspect of the present invention, a cleaning member that removes residual toner on the photoconductor and a moving mechanism that moves the cleaning member in a direction to come in contact with and separate from the photoconductor are further provided. When the monochrome image is printed on the thick paper, the control unit of the image forming apparatus causes the color photosensitive member to contact at least one of the color primary transfer rollers with the transfer belt interposed therebetween. The moving mechanism is controlled so that the color cleaning member is separated from the body, or the contact pressure between the color photoconductor and the color cleaning member is weakened.

  According to the third aspect of the present invention, the film loss of the color photoconductor can be further reduced, and the life of the color photoconductor can be further extended.

  A fourth invention is dependent on the first to third inventions, and the separation / contact mechanism moves the primary transfer roller so as to separate the contact between the photoreceptor and the primary transfer roller with the transfer belt interposed therebetween. Let

  In the fourth invention, the separation / contact mechanism that separates / contacts each of the photoconductors and each of the primary transfer rollers with the transfer belt interposed therebetween is a mechanism that moves the primary transfer roller.

  The fifth invention is dependent on the first to third inventions, and the separation / contact mechanism moves the photosensitive member to separate the photosensitive member and the primary transfer roller with the transfer belt interposed therebetween. .

  In the fifth aspect of the invention, the contact / separation mechanism that separates / contacts each of the photoconductors and each of the primary transfer rollers across the transfer belt is a mechanism that moves the photoconductor.

  According to the present invention, when monochrome printing is performed on thick paper, at least one of the color primary transfer rollers is brought into contact with the photosensitive member with the transfer belt interposed therebetween, thereby reducing vibration of the primary transfer unit during transfer. This can prevent the occurrence of transfer deviation. At this time, even if the primary transfer roller for color and the photoconductor are brought into contact with each other with the transfer belt interposed therebetween, no voltage is applied to the primary transfer roller for color, thereby reducing the film loss of the photoconductor for color. And the life of the color photoconductor can be extended.

  The above object, other objects, features, and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

1 is an illustrative view showing an overall configuration of an image forming apparatus according to a first embodiment of the present invention; FIG. 2 is an illustrative view for explaining a primary transfer roller separation / contact mechanism provided in the image forming apparatus of FIG. 1, (A) shows a state in a standby mode, (B) shows a state in a monochrome printing mode, (C) shows the state in the color printing mode. FIG. 2 is a block diagram illustrating an example of an electrical configuration of the image forming apparatus in FIG. 1. It is a flowchart which shows an example of the primary transfer process which CPU of FIG. 3 performs. It is a flowchart which shows an example of the transfer process performed in the image forming apparatus of 2nd Example of this invention. FIG. 7 is an illustrative view for explaining a photoreceptor contact / separation mechanism provided in an image forming apparatus according to a fourth embodiment of the present invention, in which (A) shows a state in a standby mode and (B) shows a state in a monochrome printing mode. (C) shows the state in the color printing mode.

<First embodiment>
Referring to FIG. 1, an image forming apparatus 10 according to a first embodiment of the present invention is an intermediate transfer type color printer including a transfer device 50 including a primary transfer unit 22 and a secondary transfer roller 24. As will be described in detail later, the image forming apparatus 10 forms toner images of each color on a plurality of photoconductors 12 and sequentially transfers these toner images to a transfer belt 32 to form a multicolor image. The multi-color image is secondarily transferred from the transfer belt 32 to the paper and fixed to form an image on the paper.

  However, the image forming apparatus 10 is not necessarily limited to a color printer, and may be a copier, a facsimile, or a multifunction machine having these functions.

  As shown in FIG. 1, the image forming apparatus 10 includes components such as a photoreceptor 12, a developing device 14, a charger 16, a cleaning roller 18, an exposure device 20, a transfer device 50, and a fixing unit 40, and a paper feed tray 26. Then, an image is formed on the paper conveyed from the printer, and the image-formed paper is discharged to the paper discharge tray 28. As image data for forming an image on paper, image data input from an external computer is used. However, when the image forming apparatus 10 has a scanner function, not only image data input from the outside but also image data read from a document by a scanner can be used.

  Each of the components described above is accommodated in the housing 10a of the image forming apparatus 10. In addition, a control unit 30 including a CPU 80, a RAM 82, a ROM 84 (see FIG. 3) and the like is provided in the housing 10a. The control unit 30 transmits a control signal to each part of the image forming apparatus 10 to cause the image forming apparatus 10 to perform various operations.

  Here, the image data handled in the image forming apparatus 10 corresponds to four color images of black (K), cyan (C), magenta (M), and yellow (Y). For this reason, each of the photosensitive member 12, the developing device 14, the charger 16, and the cleaning roller 18 is provided so as to form four types of latent images corresponding to the respective colors, thereby four image stations (processes). Part). The four image stations are arranged in a line along the running direction (circumferential movement direction) of the surface of the transfer belt 32, and from the downstream side in the running direction of the transfer belt 32, black, cyan, magenta, and yellow. Arranged in order.

  Note that the subscripts K, C, M, and Y given to the symbols are used to indicate that the elements are provided for any color, and the subscripts K, C, M, and Y are respectively Each of black, cyan, magenta and yellow is shown. However, in the description of each part, when it is not particularly necessary to distinguish which color is used, the subscripts K, C, M, and Y will be omitted and the description will be made comprehensively.

  The photosensitive member 12 is a drum-shaped image bearing member in which a photosensitive layer (photosensitive film) is formed on the surface of a cylindrical substrate having conductivity, and is supported so as to be rotatable around an axis by a driving unit (not shown). . The photosensitive layer of the photoreceptor 12 is formed of a material that exhibits conductivity when irradiated with light.

  The charger 16 is a member that charges the surface of the photoreceptor 12 to a predetermined potential. The exposure device 20 is configured as a laser scanning unit (LSU) including a laser emitting unit, a reflection mirror, and the like, and exposes the surface of the charged photoreceptor 12 to expose an electrostatic latent image corresponding to image data. Are formed on the surface of the photoreceptor 12. The developing device 14 visualizes the electrostatic latent image formed on the surface of the photoreceptor 12 with toner of four colors (YMCK). The cleaning roller 18 removes toner remaining on the surface of the photoreceptor 12 after development and image transfer.

  The transfer device 50 is a device for transferring a toner image formed on the photoconductor 12 onto a sheet, and includes a primary transfer unit 22 and a secondary transfer roller 24.

  The primary transfer unit 22 includes a transfer belt (intermediate transfer belt) 32, a drive roller 34, a driven roller 36, four primary transfer rollers 38, and the like, and is disposed above the photoconductor 12.

  The transfer belt 32 is an endless belt that is stretched by a plurality of rollers such as a driving roller 34 and a driven roller 36, and is disposed so as to face the plurality of photoconductors 12. At the time of image formation (transfer), the outer peripheral surface of the transfer belt 32 is brought into contact with the surface of the photoconductor 12, and in a predetermined direction (counterclockwise in FIG. 1) as the drive roller 34 is driven to rotate. The transfer belt 32 is moved around.

  The drive roller 34 is provided so as to be rotatable around its axis by a drive unit (not shown). The driven roller 36 rotates as the transfer belt 32 rotates and applies a certain tension to the transfer belt 32 to prevent the transfer belt 32 from slackening.

  The primary transfer roller 38 is disposed at each position facing the photoconductor 12 of each color with the transfer belt 32 interposed therebetween. Each primary transfer roller 38 is displaceable in a direction in which the primary transfer roller 38 is in contact with or separated from the photosensitive member 12 by a separation mechanism 70 (see FIG. 2) described later. The transfer belt 32 is separated from and contacted with the photosensitive member 12 by the primary transfer roller 38 pressing the inner peripheral surface of the transfer belt 32 to bring the photosensitive member 12 and the transfer belt 32 into contact with each other, and the transfer belt 32. And the photosensitive member 12 are moved away from each other. That is, each of the primary transfer rollers 38 is at a pressing position where the photoconductor 12 and the primary transfer roller 38 are in contact with each other with the transfer belt 32 in between, and a separation position where the primary transfer roller 38 is separated from the photoconductor 12 and the transfer belt 32. Displaceable.

  The primary transfer roller 38 is connected to a transfer power supply 46 (see FIG. 3) for applying a voltage (primary transfer voltage). At the time of image formation, the corresponding primary transfer roller 38 is displaced to the pressing position, and the photosensitive member 12 and the primary transfer roller 38 are brought into contact with each other with the transfer belt 32 interposed therebetween. Then, a voltage having a polarity opposite to the charging polarity of the toner constituting the toner image formed on the surface of the photoreceptor 12 is applied from the transfer power supply 46 to the primary transfer roller 38. When a voltage is applied to the primary transfer roller 38, a transfer current flows from the primary transfer roller 38 to the photoconductor 12 via the transfer belt 32, and a transfer electric field is formed between the photoconductor 12 and the transfer belt 32. The toner image formed on the photoreceptor 12 is transferred (primary transfer) to the outer peripheral surface of the transfer belt 32 by the action of the transfer electric field.

  For example, when forming a color image, each color toner image formed on each photoconductor 12 is transferred to the transfer belt 32 in an overlapping manner, and a multicolor toner image is formed on the outer peripheral surface of the transfer belt 32. The On the other hand, when a monochrome image is formed, a toner image is formed only on the black photoconductor 12 </ b> K, and only the black toner image is transferred to the outer peripheral surface of the transfer belt 32.

  A secondary transfer roller 24 is disposed in the vicinity of the drive roller 34. A transfer power supply 46 is connected to the secondary transfer roller 24, and a voltage (secondary transfer voltage) is applied by the transfer power supply 46. While the sheet passes through the secondary transfer portion (nip portion) 48 between the transfer belt 32 and the secondary transfer roller 24 by the action of the transfer electric field formed by the secondary transfer roller 24 to which a voltage is applied. In addition, the toner image formed on the outer peripheral surface of the transfer belt 32 is transferred (secondary transfer) to the paper.

  The fixing unit 40 includes a heat roller and a pressure roller, and is disposed above the secondary transfer roller 24. The heat roller is set to have a predetermined fixing temperature, and when the paper passes through the fixing nip area between the heat roller and the pressure roller, the toner image transferred to the paper is melted, mixed, and mixed. The toner image is heat-fixed on the sheet by pressure contact.

  In addition, a paper conveyance path for sending the paper placed on the paper feed tray 26 to the paper discharge tray 28 via the secondary transfer roller 24 and the fixing unit 40 is provided in the housing 10 a of the image forming apparatus 10. It is formed. In this paper transport path, paper transport means such as a plurality of transport rollers 42 and registration rollers 44 are appropriately arranged.

  At the time of image formation, the sheets placed on the sheet feed tray 26 are guided to the sheet conveyance path one by one and conveyed to the registration rollers 44 by the conveyance rollers 42. The registration roller 44 conveys the sheet to the secondary transfer unit 48 between the transfer belt 32 and the secondary transfer roller 24 at the timing when the leading end of the sheet and the leading end of the toner image on the transfer belt 32 are aligned. The toner image is transferred onto the paper. Thereafter, by passing through the fixing unit 40, the unfixed toner on the paper is melted and fixed by heat, and the paper is discharged onto the paper discharge tray 28.

  Next, the separation / contact mechanism 70 provided in the primary transfer roller 38 will be described with reference to FIG. The separation / contact mechanism 70 is a mechanism that separates and contacts the photosensitive member 12 and the primary transfer roller 38 with the transfer belt 32 interposed therebetween by displacing the primary transfer roller 38. In the first embodiment, the color primary transfer rollers 38Y, 38M, and 38C are integrally displaced in conjunction with each other, and the black primary transfer roller 38 is displaced independently of the color primary transfer rollers 38Y, 38M, and 38C. It is possible.

  The separation / contact mechanism 70 basically displaces the primary transfer roller 38 to the following three mode positions based on an instruction from the control unit 30 (specifically, the CPU 80). That is, in the standby mode (non-image formation), as shown in FIG. 2A, all the primary transfer rollers 38 are arranged at the separated positions, and all the photoreceptors 12 are separated from the transfer belt 32. . In the monochrome printing mode, as shown in FIG. 2B, the color primary transfer rollers 38Y, 38M, and 38C are arranged at the separated positions, while the black primary transfer roller 38K is arranged at the pressing position. Only the black photoconductor 12K is brought into contact with the transfer belt 32. Further, in the color printing mode, as shown in FIG. 2C, all the primary transfer rollers 38 are arranged at the pressing position, and all the photosensitive members 12 are brought into contact with the transfer belt 32.

  Specifically, as shown in FIG. 2, the separating mechanism 70 includes four roller operating arms 52, a black link member 54, a color link member 56, a black cam member 58, a color cam member 60, and the like. Prepare.

  The black roller operating arm 52K is formed in an approximately L shape, and the black primary transfer roller 38K is rotatably supported at one end thereof. The bent portion of the roller operating arm 52K is rotatably supported by an apparatus frame (not shown), and the other end of the roller operating arm 52K is rotatably connected to the black link member 54.

  The black link member 54 is provided so as to be capable of reciprocating in the horizontal direction (left-right direction). A black cam member 58 that is an eccentric cam that is rotatably held by a cam shaft 66 is brought into contact with one end surface of the black link member 54 on the driven roller 36 side. A spring 62 is provided at one end of the black link member 54. One end of the spring 62 is fixed to the apparatus frame, and the other end of the spring 62 is fixed to the black link member 54. The black link member 54 is urged by the spring 62 so that the cam surface of the black cam member 58 is in pressure contact with one end surface of the black link member 54.

  On the other hand, the color roller operation arms 52Y, 52M, and 52C are formed in a substantially L shape and are mounted symmetrically with respect to the roller operation arm 52K. Color primary transfer rollers 38Y, 38M, and 38C are rotatably supported at one end portions of the roller operation arms 52Y, 52M, and 52C. The bent portions of the roller operating arms 52Y, 52M, and 52C are rotatably supported by the apparatus frame, and the other ends of the roller operating arms 52Y, 52M, and 52C are rotatably connected to the color link member 56. Is done.

  The collar link member 56 is provided so as to be reciprocally movable in the horizontal direction. A collar cam member 60, which is an eccentric cam that is rotatably held by a cam shaft 66, is brought into contact with one end surface of the color link member 56 on the drive roller 34 side. A spring 64 is provided at one end of the collar link member 56. One end of the spring 64 is fixed to the apparatus frame, and the other end of the spring 64 is fixed to the collar link member 56. The collar link member 56 is urged by the spring 64 so that the cam surface of the collar cam member 60 is in pressure contact with one end surface of the collar link member 56.

  Further, a cam motor 88 (see FIG. 3) is connected to the cam shaft 66. When the cam shaft 66 is rotated by the driving force of the cam motor 88, the black cam member 58 and the collar cam member 60 are rotated. The Then, by controlling the rotation of the black cam member 58 and the color cam member 60, the black link member 54 and the color link member 56 are moved in the left-right direction, and accordingly, the primary transfer roller 38 is moved to the photosensitive member 12. It is displaced in the contact / separation direction (vertical direction).

  For example, as shown in FIG. 2A, in the standby mode, the black link member 54 is disposed at the reference position that is to the left, and the color link member 56 is disposed at the reference position that is to the right. In this state, all the primary transfer rollers 38 are disposed at the separated positions, and all the photosensitive members 12 are separated from the transfer belt 32.

  In the monochrome printing mode, the cam shaft 66 is rotated 90 degrees counterclockwise from the state of FIG. 2A to rotate the black cam member 58 and the color cam member 60. Then, as shown in FIG. 2B, the black link member 54 is pushed by the black cam member 58 and moves to the right direction A from the reference position, and the black roller operating arm 52K uses the bent portion as a fulcrum. Rotate clockwise. As a result, the black primary transfer roller 38K moves downward and is disposed at the pressing position, and the black photoconductor 12K is in contact with the transfer belt 32.

  In the color printing mode, the cam shaft 66 is further rotated 90 degrees counterclockwise from the state shown in FIG. 2B, and the black cam member 58 and the color cam member 60 are rotated. Then, as shown in FIG. 2C, the collar link member 56 is pushed by the collar cam member 60 and moves to the left direction B from the reference position, and the color roller operating arms 52Y, 52M, and 52C are bent. It rotates clockwise with the part as a fulcrum. As a result, in addition to the black primary transfer roller 38K, the color primary transfer rollers 38Y, 38M, and 38C are moved downward and arranged at the pressing positions, and all the photoconductors 12 are in contact with the transfer belt 32. It becomes.

  Next, the electrical configuration of the image forming apparatus 10 will be briefly described with reference to FIG. As shown in FIG. 3, the image forming apparatus 10 includes a control unit 30 including a CPU 80, a RAM 82, a ROM 84, and the like. The CPU 80 is connected to the motor driver 86, the transfer power source 46, the communication unit 92, and the like via the bus 94. The motor driver 86 is connected to a cam motor 88, and an encoder 90 is connected to the cam motor 88.

  Although not shown, the CPU 80 has other processes such as a process unit including the photoconductor 12 and the like, an operation unit for a user to perform an input operation, and other image forming apparatuses 10 such as a jam sensor via a bus 94. Each part is also connected appropriately.

  The CPU 80 is responsible for overall control of the image forming apparatus 10 and comprehensively controls the operation of each part of the image forming apparatus 10. The RAM 82 is used as a work area and a buffer area for the CPU 80. The ROM 84 is a main storage device of the image forming apparatus 10, and appropriately stores a control program and data for the CPU 80 to control the operation of each part of the image forming apparatus 10. The CPU 80 writes (stores) the control program and data read from the ROM 84 in the RAM 82, and executes control of each part constituting the image forming apparatus 10 according to the control program stored in the RAM 82.

  The motor driver 86 applies a voltage to the cam motor 88 based on a control signal output from the CPU 80. The cam motor 88 is, for example, a stepping motor, and the black cam member 58 and the color cam member 60 held by the cam shaft 66 are desired by adjusting the number of pulses of the pulsed voltage applied from the motor driver 86. Rotate to an angle of. The encoder 90 outputs a pulse signal corresponding to the rotation direction and the rotation speed of the rotation shaft of the cam motor 88 to the CPU 80. The CPU 80 detects (calculates) the rotation direction and rotation speed of the rotation shaft of the cam motor 88 based on the pulse signal given from the encoder 90, and outputs a drive control signal corresponding to the calculation result to the motor driver 86.

  The transfer power supply 46 includes a primary transfer power supply and a secondary transfer power supply, and outputs a transfer voltage to be applied to the primary transfer roller 38 and the secondary transfer roller 24 based on a control signal output from the CPU 80.

  The communication unit 92 is an interface for communicating with an external computer. The CPU 80 via this communication unit 92, image data for forming an image on paper, information on whether it is monochrome printing or color printing, and whether the paper (printing medium) to be printed is plain paper or thick paper A print instruction including information on whether or not is received from an external computer.

  However, the determination of whether the paper is plain paper or thick paper (that is, the type of paper) can also be executed by providing the image forming apparatus 10 with a thickness detection unit. As the thickness detection unit, for example, an optical sensor can be used. The thickness of the sheet is detected by measuring the reflectance or transmittance of light with respect to the sheet, and the type of the sheet can be determined based on the thickness information. it can. In addition, for example, a button for selecting a paper type may be provided in an operation unit provided in the image forming apparatus 10, and the paper type may be determined based on the selection operation.

  In such an image forming apparatus 10, when printing on thick paper that is thicker and stronger than plain paper, the thick paper enters the secondary transfer portion 48 between the transfer belt 32 and the secondary transfer roller 24. Due to the impact, the primary transfer unit 22 may vibrate and transfer deviation may occur in the toner image transferred to the transfer belt 32 and the paper. This transfer deviation is likely to occur in the monochrome printing mode as shown in FIG.

  Therefore, in the first embodiment, when printing on thick paper, the toner image is appropriately transferred even on thick paper by using the color primary transfer rollers 38Y, 38M, and 38C even in monochrome printing. I can do it.

  The cardboard in the present invention refers to a paper that is thicker and stronger than plain paper, and the cardboard includes postcards, envelopes, business cards, OHP films, and the like.

  Specifically, in the first embodiment, when monochrome printing is performed on thick paper, the color primary transfer rollers 38Y, 38M, and 38C are arranged at the pressing positions in a state where no voltage is applied. That is, in addition to the black primary transfer roller 38K for transferring the toner image, the color primary transfer rollers 38C, 38M, and 38Y that are not used for the transfer of the toner image are respectively color-sensitive with the transfer belt 32 interposed therebetween. The body 12C is brought into contact with each of 12M, 12Y.

  As a result, the primary transfer unit 22 is supported by the four photoconductors 12 including black and color, so that it is difficult to vibrate even when receiving an impact. Therefore, transfer deviation of the toner image formed on the paper is appropriately prevented.

  Further, when a transfer current flows through the photoconductor 12, there is a risk that film reduction of the photoconductor 12 may be promoted. In the first embodiment, the color primary transfer rollers 38Y, 38M, and 38C are arranged at the pressing positions. However, control is performed so that no voltage is applied to the color primary transfer rollers 38Y, 38M, and 38C. That is, since no transfer current flows through the color photoconductors 12C, 12M, and 12Y, film thickness reduction of the color photoconductors 12C, 12M, and 12Y is prevented, and the life of the color photoconductors 12C, 12M, and 12Y is extended. be able to.

  The operation of the image forming apparatus 10 as described above is realized by the CPU 80 executing a control program stored in the RAM 82. Hereinafter, the primary transfer process among the image forming processes executed by the CPU 80 will be described with reference to the flowchart shown in FIG.

  As shown in FIG. 4, when a print instruction is input from a user through an external computer or the like, the CPU 80 determines whether or not monochrome printing is performed in step S1. That is, in step S1, it is determined which one of monochrome printing and color printing is included in the print instruction input by the user.

  If “NO” in the step S1, that is, if the print instruction input by the user includes an instruction to specify color printing, the process proceeds to a step S3. In step S3, all the primary transfer rollers 38 are arranged at the pressing position. That is, the CPU 80 sends a control signal to the motor driver 86 to drive the cam motor 88, and as shown in FIG. 2C, the black primary transfer roller 38K and the three color primary transfer rollers 38C, 38M, All the primary transfer rollers 38 including 38Y are brought into contact with the photoreceptor 12 via the transfer belt 32.

  In step S5, a voltage is applied to all the primary transfer rollers 38. That is, the CPU 80 sends a control signal to the transfer power supply 46 to apply the primary transfer voltage to all the primary transfer rollers 38 including the black primary transfer roller 38K and the three color primary transfer rollers 38C, 38M, and 38Y. .

  As described above, when color printing is performed, regardless of whether the paper is plain paper or thick paper, transfer processing similar to that in the conventional color printing mode is performed in steps S3 and S5. When the processes of steps S3 and S5 are completed, the process proceeds to step S17.

  On the other hand, if “YES” in the step S1, that is, if the print instruction input by the user includes an instruction to specify monochrome printing, the process proceeds to a step S7.

  In step S7, it is determined whether the paper to be printed is thick paper. That is, the CPU 80 determines whether an instruction to specify plain paper or thick paper is included in the print instruction input by the user.

  If “NO” in the step S7, that is, if the print instruction input by the user includes an instruction to specify plain paper, the process proceeds to a step S9. The black primary transfer roller 38K is disposed at the pressing position. That is, the CPU 80 sends a control signal to the motor driver 86 to drive the cam motor 88, and only the black primary transfer roller 38K is passed through the transfer belt 32 as shown in FIG. Abut.

  In step S11, a voltage is applied to the black primary transfer roller 38K. That is, the CPU 80 sends a control signal to the transfer power supply 46 and applies a primary transfer voltage to the black primary transfer roller 38K.

  Thus, when monochrome printing is performed on plain paper, transfer processing similar to that in the conventional monochrome printing mode is performed in steps S9 and S11. When the processes of steps S9 and S11 are completed, the process proceeds to step S17.

  On the other hand, if “YES” in the step S7, that is, if the print instruction input by the user includes an instruction to specify thick paper, the process proceeds to a step S13. In step S13, all the primary transfer rollers 38 are arranged at the pressing positions. That is, the CPU 80 sends a control signal to the motor driver 86 to drive the cam motor 88, and as shown in FIG. 2C, the black primary transfer roller 38K and the three color primary transfer rollers 38C, 38M, All the primary transfer rollers 38 including 38Y are brought into contact with the photoreceptor 12 via the transfer belt 32.

  In step S15, a voltage is applied to the black primary transfer roller 38K. That is, the CPU 80 sends a control signal to the transfer power supply 46 and applies a primary transfer voltage to the black primary transfer roller 38K. At this time, the primary transfer voltage is not applied to the color primary transfer rollers 38C, 38M, and 38Y.

  Thus, when performing monochrome printing on thick paper, in addition to the transfer processing similar to the conventional monochrome printing mode in steps S13 and S15, each of the color primary transfer rollers 38Y, 38M, and 38C, A process of controlling to arrange at the pressing position without applying voltage is performed. When the processes of steps S13 and S15 are completed, the process proceeds to step S17.

  In step S17, it is determined whether or not to end. For example, the CPU 80 determines whether or not printing has been completed for all sheets specified by the user. If “NO” in the step S17, the process returns to the step S1, and if “YES” in the step S17, the transfer process is ended.

  As described above, according to the first embodiment, when monochrome printing is performed on thick paper, the color primary transfer rollers 38Y, 38M, and 38C are connected to the color photoreceptors 12Y, 12M, and 38C with the transfer belt 32 interposed therebetween. Since it is brought into contact with 12C, the vibration of the primary transfer unit 22 at the time of transfer can be reduced, and the occurrence of transfer deviation can be prevented.

  At this time, even if the color primary transfer rollers 38Y, 38M, and 38C and the color photoreceptors 12Y, 12M, and 12C are brought into contact with the transfer belt 32, the color primary transfer rollers 38Y, 38M, and 38C are in contact with each other. Since no transfer voltage is applied, film loss of the color photoconductors 12Y, 12M, and 12C can be reduced, and the life of the color photoconductors 12Y, 12M, and 12C can be extended.

  In the above-described first embodiment, the color primary transfer rollers 38Y, 38M, and 38C are integrally displaced by the separation / contact mechanism 70. However, the present invention is not limited to this. The specific configuration of the separation / contact mechanism for displacing the primary transfer roller 38 can be changed as appropriate. For example, a separation / contact mechanism that can individually displace each of the color primary transfer rollers 38Y, 38M, and 38C can be employed.

Further, when each of the color primary transfer rollers 38Y, 38M, and 38C is individually displaceable, all the color primary transfer rollers 38Y, 38M, and 38C are not necessarily disposed at the pressing position when monochrome printing is performed on the cardboard. The color primary transfer rollers 38Y, 38M, and 38C may be in contact with the color photoreceptors 12Y, 12M, and 12C with the transfer belt 32 interposed therebetween.
<Second embodiment>
Next, an image forming apparatus 10 according to a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, when monochrome printing is performed on thick paper, the primary transfer rollers 38Y, 38M, and 38C for color and the photoconductors 12Y, 12M, and 12C for color are sandwiched with the transfer belt 32 interposed therebetween. It differs from the first embodiment described above in that the contact time is limited only to the time when the cardboard enters the secondary transfer section 48. Since the configuration of the other parts is the same, parts common to the first embodiment described above are given the same reference numerals, and redundant descriptions are omitted or simplified.

  In the second embodiment, when monochrome printing is performed on a thick paper, only when the thick paper enters the secondary transfer unit 48, that is, before and after the time when the leading edge of the thick paper enters the secondary transfer unit 48. The color primary transfer rollers 38Y, 38M, and 38C in a state where no voltage is applied are arranged at the pressing position only during the time, and the color primary transfer rollers 38Y, 38M, and 38C are arranged at the separated positions except for a predetermined time at the time of entry. To do.

  As an example, when the leading edge of the thick paper reaches a position near the upstream side of the secondary transfer unit 48 in the paper conveyance direction, for example, when it is detected that the leading edge of the thick paper has reached the registration roller 44, no voltage is applied. The color primary transfer rollers 38Y, 38M, and 38C are displaced to the pressed positions. Thereafter, when it is detected that the leading edge of the thick paper has passed the secondary transfer portion 48, the color primary transfer rollers 38Y, 38M, and 38C are displaced to the separated positions.

  The fact that the leading edge of the thick paper has passed through the secondary transfer section 48 is caused by, for example, an optical sensor (not shown) that detects the presence or absence of thick paper (paper) at a position near the downstream side of the secondary transfer section 48 in the paper transport direction. It is good to detect by providing. Further, for example, it is possible to detect that the leading end of the thick paper has passed through the secondary transfer unit 48 based on whether or not a predetermined time has passed since the leading end of the thick paper was sent out by the registration roller 44.

  The operation of the image forming apparatus 10 as described above will be described with reference to a flowchart. In the transfer process shown in FIG. 5, the process of step S21 and the process of steps S23 and S25 are added before and after steps S13 and S15 of the transfer process shown in FIG. In addition, since the process of step S1-step S11 is the same as the content demonstrated in 1st Example, the overlapping description is abbreviate | omitted.

  As shown in FIG. 5, if “YES” in the step S7, that is, if monochrome printing is performed on the thick paper, the CPU 80 has reached the vicinity of the secondary transfer unit 48 in step S21. Determine whether or not. For example, when the CPU 80 detects that the leading edge of the thick paper has reached the registration roller 44, the CPU 80 determines that the leading edge of the thick paper has reached the upstream vicinity of the secondary transfer unit 48 in the paper transport direction.

  If “NO” in the step S21, that is, if the leading end of the thick paper has not yet reached the vicinity of the secondary transfer portion 48, the process of the step S21 is repeated.

  On the other hand, if “YES” in the step S21, that is, if it is detected that the leading end of the thick paper has reached the vicinity of the secondary transfer portion 48, the process proceeds to a step S13.

  In step S13, all the primary transfer rollers 38 are arranged at the pressing positions. In step S15, a voltage is applied to the black primary transfer roller 38K. That is, immediately before the leading edge of the cardboard enters the secondary transfer section 48, a process is performed to control the color primary transfer rollers 38Y, 38M, and 38C so as to be arranged at the pressing position without applying a voltage.

  In a succeeding step S23, it is determined whether or not the leading end of the thick paper has passed the secondary transfer portion 48. For example, the CPU 80 determines whether or not the leading edge of the thick paper has passed through the secondary transfer unit 48 according to the detection result of the optical sensor provided in the vicinity of the downstream side of the secondary transfer unit 48 in the paper conveyance direction.

  If “NO” in the step S23, that is, if the leading end of the thick paper has not yet passed the secondary transfer portion 48, the process of the step S23 is repeated.

  On the other hand, if “YES” in the step S23, that is, if it is detected that the leading edge of the thick paper has passed the secondary transfer portion 48, the process proceeds to a step S25.

  In step S25, the color primary transfer rollers 38Y, 38M, and 38C are arranged at the separated positions. That is, the CPU 80 sends a control signal to the motor driver 86 to drive the cam motor 88, and moves the color primary transfer rollers 38Y, 38M, 38C to the separated positions as shown in FIG. Only the primary transfer roller 38 </ b> K is brought into contact with the photoconductor 12 through the transfer belt 32. When the process of step S25 ends, the process proceeds to step S17.

  As described above, according to the second embodiment, when monochrome printing is performed on thick paper, the color primary transfer rollers 38Y, 38M, and 38C and the color photoconductors 12Y, 12M, and 12C in a state where no voltage is applied. The time during which the sheet is brought into contact with the transfer belt 32 is limited to the time when the cardboard enters the secondary transfer section 48.

Therefore, the color primary transfer rollers 38Y, 38M, and 38C and the color photoconductors 12Y, 12M, and 12C are brought into contact with the transfer belt 32 between the color primary transfer rollers 38Y, 38M, and 38C, the color. It is possible to minimize the consumption of the photoconductors 12Y, 12M, 12C and the transfer belt 32.
<Third embodiment>
Next, an image forming apparatus 10 according to a third embodiment of the present invention will be described. In the third embodiment, the color cleaning rollers 18Y, 18M, and 18C are provided with a moving mechanism, and when performing monochrome printing on cardboard, the color photoconductors 12Y, 12M, and 12C are moved to the color cleaning rollers 18Y, 18M, and 18C. The point which separated 18C differs from the above-mentioned Example. Since the configuration of the other parts is the same, parts that are the same as those in the above-described embodiment are given the same reference numerals, and redundant descriptions are omitted or simplified.

  Briefly, in the third embodiment, the color cleaning rollers 18Y, 18M, and 18C are provided with moving mechanisms, and the color cleaning rollers 18Y, 18M, and 18C are respectively color photoreceptors 12Y, 12M, and 12C. It is possible to displace in the direction of separating from and contacting. As the moving mechanism, a known mechanism including an eccentric cam and a spring may be appropriately adopted.

  In the third embodiment, similarly to the first or second embodiment described above, the control unit 30 (CPU 80) controls the color primary transfer rollers 38Y, 38M, and 38C when performing monochrome printing on thick paper. Each is arranged at the pressed position without applying a voltage. In accordance with this, the moving mechanism is controlled to separate the color cleaning rollers 18Y, 18M, 18C from the color photoconductors 12Y, 12M, 12C.

  When the color primary transfer rollers 38Y, 38M, and 38C are arranged at the pressing positions and the color photoconductors 12Y, 12M, and 12C are brought into contact with the transfer belt 32, the color photoconductors are synchronized with the circumferential movement of the transfer belt 32. 12Y, 12M, and 12C are also rotated. At this time, the color photoconductors 12Y, 12M, and 12C may be accelerated by the friction with the color cleaning rollers 18Y, 18M, and 18C, but from the color photoconductors 12Y, 12M, and 12C. The film cleaning is prevented by separating the color cleaning rollers 18Y, 18M, and 18C.

  According to the third embodiment, the color cleaning rollers 18Y, 18M, and 18C are separated from the photoconductor 12 when monochrome printing is performed on thick paper, so that the film thickness of the color photoconductors 12Y, 12M, and 12C is reduced. It can be further reduced.

  In the above-described third embodiment, the color cleaning rollers 18Y, 18M, and 18C are separated from the photosensitive member 12 when monochrome printing is performed on thick paper. However, the color cleaning rollers 18Y, 18M, and 18C are not necessarily separated from each other. It is only necessary to weaken the contact pressure between the photoconductors 12Y, 12M, and 12C and the color cleaning rollers 18Y, 18M, and 18C.

Further, in each of the above-described embodiments, the cleaning roller 18 is used as a cleaning member for removing the residual toner on the photoconductor 12. However, the cleaning member may be formed in a blade shape or a brush shape.
<Fourth embodiment>
Next, an image forming apparatus 10 according to a fourth embodiment of the present invention will be described with reference to FIG. In the fourth embodiment, instead of providing the primary transfer roller 38 with a separation mechanism for separating the contact between the photoconductor 12 and the primary transfer roller 38 with the transfer belt 32 interposed therebetween, a process unit including the photoconductor 12 and the like is provided. However, it is different from the above-described embodiment. Since the configuration of the other parts is the same, parts that are the same as those in the above-described embodiment are given the same reference numerals, and redundant descriptions are omitted or simplified.

  Briefly, in this fourth embodiment, instead of providing the separation / contact mechanism 70, the separation / contact mechanism 100 is provided in the process unit including the photoreceptor 12 and the like. The separation / contact mechanism 100 is a mechanism that separates and contacts the photosensitive member 12 and the primary transfer roller 38 with the transfer belt 32 interposed therebetween by displacing the photosensitive member 12.

  The separation / contact mechanism 100 basically displaces the photoconductor 12 to the following three mode positions based on an instruction from the control unit 30 (CPU 80). That is, in the standby mode, as shown in FIG. 6A, all the photoconductors 12 are arranged at the separation positions where they are separated from the transfer belt 32. In the monochrome printing mode, as shown in FIG. 6B, the color photoconductors 12Y, 12M, and 12C are arranged at the separated positions, and the black photoconductor 12K is arranged at the pressing position. Only the black photoconductor 12K is brought into contact with the black primary transfer roller 38K. Further, in the color printing mode, as shown in FIG. 6C, all the photoconductors 12 are arranged at the pressing positions, and all the photoconductors 12 and the primary transfer roller 38 are brought into contact with each other with the transfer belt 32 interposed therebetween. The

  As shown in FIG. 6, the separation / contact mechanism 100 includes a support plate 102, a first eccentric cam 104, a second eccentric cam 106, and the like.

  The support plate 102 supports the frame of the process unit including the photoconductor 12 and the like. The first eccentric cam 104 is rotatably held by the first cam shaft 108 and is located at an end portion on the downstream side (the black photoconductor 12K side) in the running direction of the transfer belt 32 so as to contact the lower surface of the support plate 102. Placed in. Further, the second eccentric cam 106 is rotatably held by the second cam shaft 110, and is located upstream of the transfer belt 32 in the traveling direction (the yellow photoreceptor 12Y side) so as to contact the lower surface of the support plate 102. Arranged at the end. Then, by controlling the rotation of the first eccentric cam 104 and the second eccentric cam 106, the photosensitive member 12 is displaced in the contact / separation direction (vertical direction) with respect to the primary transfer roller 38.

  For example, as shown in FIG. 6A, in the standby mode, the first eccentric cam 104 and the second eccentric cam 106 support the support plate 102 at the short diameter portion. In this state, all the photoconductors 12 are arranged at the separated positions that are separated from the transfer belt 32.

  In the monochrome printing mode, the first eccentric cam 104 is rotated 90 degrees from the state shown in FIG. 6A, and the support plate 102 is supported at the long diameter portion. Then, as shown in FIG. 6B, the end of the process portion on the black photosensitive member 12K side is lifted. As a result, the black photoconductor 12K moves upward and is disposed at the pressing position, and the black photoconductor 12K and the black primary transfer roller 38K are in contact with each other with the transfer belt 32 interposed therebetween.

  Further, in the color printing mode, the second eccentric cam 106 is rotated 90 degrees from the state of FIG. 6B, and the support plate 102 is supported at the long diameter portion. Then, as shown in FIG. 6C, the end of the process unit on the yellow photoconductor 12Y side is also lifted. As a result, in addition to the black photoconductor 12K, the color photoconductors 12Y, 12M, and 12C move upward and are arranged at the pressing positions, and all the photoconductors 12 and the primary transfer roller 38 sandwich the transfer belt 32. Are in contact with each other.

  Also in the fourth embodiment, when monochrome printing is performed on thick paper, in addition to the black primary transfer roller 38K for transferring the toner image, the color primary transfer roller 38C not used for transferring the toner image. , 38M, and 38Y are brought into contact with the color photoconductors 12C, 12M, and 12Y with the transfer belt 32 interposed therebetween. That is, the color photoconductors 12Y, 12M, and 12C are arranged at the pressing positions, and the color primary transfer rollers 38Y, 38M, and 38C and the color photoconductors 12Y, 12M, and 12C are brought into contact with the transfer belt 32 interposed therebetween. However, the color primary transfer rollers 38Y, 38M, and 38C are controlled not to apply a voltage.

  According to the fourth embodiment, similarly to the first embodiment, the film loss of the color photoconductors 12Y, 12M, and 12C can be reduced while preventing transfer deviation, and the color photoconductors 12Y, 12M, and 12C can be reduced. Life can be extended.

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 12 ... Photoconductor 14 ... Developing device 16 ... Charger 18 ... Cleaning roller 22 ... Primary transfer unit 24 ... Secondary transfer roller 30 ... Control part 32 ... Transfer belt 38 ... Primary transfer roller 48 ... Secondary transfer 50: Transfer device 70, 100 ... Separation / contact mechanism 80 ... CPU

Claims (5)

An image forming apparatus that primarily transfers a toner image from a plurality of photoconductors including a black photoconductor and a plurality of color photoconductors to a transfer belt, and secondarily transfers the toner image from the transfer belt to a sheet. There,
The transfer belt stretched around a plurality of rollers so as to be able to move around, and disposed so as to face the plurality of photoconductors;
A plurality of primary transfer rollers, each of which includes a primary transfer roller for black and a plurality of primary transfer rollers for color, and is disposed so as to face each of the photoreceptors with the transfer belt interposed therebetween;
Separation / contact mechanism for separating / contacting each of the photoconductors and each of the primary transfer rollers with the transfer belt interposed therebetween,
A transfer power source that applies a voltage to each of the primary transfer rollers, and at least one of the primary transfer rollers for color is sandwiched with the transfer belt in a state in which no voltage is applied when performing monochrome printing on thick paper. An image forming apparatus comprising: a control unit that controls the separation / contact mechanism and the transfer power supply so as to be in contact with the color photoconductor.   When the monochrome printing is performed on the thick paper, the control unit removes the color primary transfer roller and the color photoconductor in a state where no voltage is applied only when the thick paper enters the secondary transfer unit. The image forming apparatus according to claim 1, wherein the separation / contact mechanism and the transfer power source are controlled so as to be in contact with each other with the transfer belt interposed therebetween. A plurality of cleaning members including a black cleaning member and a plurality of color cleaning members provided on each of the photoconductors to remove residual toner on the photoconductor; and provided on the color cleaning member, A mechanism for moving the color cleaning member to or from the color photoconductor or changing the contact pressure;
The control unit controls the moving mechanism so as to separate the color cleaning member from the color photoconductor or weaken the contact pressure when monochrome printing is performed on thick paper. The image forming apparatus described.   4. The method according to claim 1, wherein the separation / contact mechanism separates and contacts each of the photosensitive members and each of the primary transfer rollers across the transfer belt by moving the primary transfer roller. 5. Image forming apparatus.   4. The method according to claim 1, wherein the separation / contact mechanism separates and contacts each of the photoreceptors and each of the primary transfer rollers with the transfer belt interposed therebetween by moving the photoreceptor. 5. Image forming apparatus.

Images