JP2008096601A - Transfer device and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer device which is inexpensive, can be made compact and is suitable for a high speed machine, without causing failures such as the damage of a high voltage source in the transfer device. <P>SOLUTION: A power source circuit section 95 supplying a high voltage to a transfer roller 74 has a constant voltage control power source circuit composed of the high voltage source 100 and a constant current control circuit 96 and a constant current control power source circuit composed of the high voltage source 100 and a constant voltage control circuit 97. A control section 101 performs control so as to connect only one of the two power source circuits to the transfer roller 74 and connects the constant voltage control power source circuit to the transfer roller 74, in the separate state of a transfer unit 90 from a photoreceptor 23 and connects the constant current control power source circuit to the transfer roller 74, in the contact state of the transfer unit 90 with the photoreceptor 23. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transfer device and an image forming apparatus including the transfer device, and in particular, adsorbs a recording sheet (sheet) on a transfer belt and applies a transfer electric field with a transfer roller disposed on the back surface of the transfer belt. The present invention relates to a transfer device that transfers a toner image formed on a photosensitive member to a recording sheet, and an image forming apparatus including the transfer device.

  Conventionally, in an image forming apparatus using an electrophotographic system, an electrostatic latent image is formed on a photosensitive drum by irradiating an optical image, and then the electrostatic latent image is developed into a toner image. Printing is performed by transferring an image onto a recording sheet.

  In such an image forming apparatus, a transfer device that transfers a toner image on a photoreceptor onto a recording sheet charges the recording sheet with a polarity opposite to that of the toner, and adsorbs and transfers the toner onto the recording sheet. The transfer device needs to perform stable transfer in order to provide an image with stable print quality.

  As a method of the transfer device, there are a corona charging method, a roller transfer method, a belt transfer method, and the like depending on a method for charging the recording paper. In the corona method, for example, as disclosed in Patent Document 1, a corona charger is disposed so as to face the photosensitive member, and a recording sheet is passed between the corona charger and the photosensitive member. An electric field is applied for charging.

  In the roller transfer method, the recording paper is passed between the transfer roller and the photosensitive member, and charged by applying a transfer electric field when passing. In the belt transfer system, a transfer belt is wound around a driving roller and a driven roller, and the transfer roller is disposed inside the transfer belt. The recording sheet is adsorbed on the surface of the transfer belt and passes through a region where the transfer roller and the photoconductor face each other. When the recording sheet passes, a transfer electric field is applied through the transfer belt and charged.

  By the way, in recent years, in such an image forming apparatus, development of high-speed machines has been actively performed. For example, in high-speed machines up to several years ago, the number of sheets processed per minute when A4 recording paper was transported sideways (the direction perpendicular to the transport direction is the length of the recording paper) was 50 to 70 sheets. However, the number of high-speed machines in recent years has increased to 100 to 120, and there is a direction to advance from the field of image forming apparatuses to the field of light printing.

  As a transfer device mounted on a high-speed machine, a roller transfer method or a belt transfer method in which a recording paper is brought into contact with a photosensitive member at the time of transfer is employed, and among them, many devices adopt a belt transfer method. The reason is that by using the transfer belt, the width of the nip portion where the photosensitive member, called the transfer nip, and the transfer belt come into contact with each other can be easily set to a width required from the process speed or the like. In the case of a high-speed machine, the width of the transfer nip part is wide because the process speed is faster than that of the low-speed machine. In the roller transfer type device, in order to ensure the necessary width of the transfer nip part, The diameter of the transfer roller must be large.

  However, the belt transfer system has a problem of image fogging because the transfer belt contacts the photoconductor. That is, the surface of the transfer belt is in direct contact with the photosensitive member at a portion other than the width in the direction perpendicular to the conveyance direction of the conveyed recording paper in the transfer nip portion. Therefore, the fog toner on the photoconductor moves at the time of contact, and is transferred onto the recording paper at the time of the next image formation, and the image is soiled.

  In order to avoid such a deterioration in image quality due to fog toner, conventionally, a cleaning for cleaning the surface of the transfer belt is usually performed immediately after the end of printing JOB and every time transfer to one sheet of recording paper is completed. The Cleaning methods mainly include mechanical cleaning and electrical cleaning.

  In mechanical cleaning, the toner is scraped and collected by bringing a blade into contact with the surface of the transfer belt. In the electrical cleaning, an electric field having the same polarity as the toner (hereinafter referred to as a cleaning electric field) is applied to the transfer belt so that the fog toner can be easily separated, and the photosensitive member or a storage portion arranged on the outer periphery of the transfer belt is used. It is to be collected.

  In particular, in high-speed machines, an electrical cleaning technique in which cleaning is performed in a non-contact manner is frequently used due to problems such as wear and damage, or meandering of the transfer belt. Conventionally, such a cleaning electric field is applied using a roller different from the transfer roller provided so as to be in contact with the transfer belt.

  Further, an attracting electric field for attracting the recording paper to the surface of the transfer belt is also applied to the transfer belt. The suction electric field is applied to suck the first recording sheet of the print job. In the second and subsequent recording sheets, since the transfer belt is already charged by the transfer electric field applied to the previous recording sheet, it is not necessary to apply the adsorption electric field. Conventionally, such an attracting electric field is also applied using a roller different from the transfer roller provided so as to be in contact with the transfer belt.

  Further, in many belt transfer type transfer apparatuses, a transfer belt and a group of rollers including a transfer roller around which the transfer belt is wound are unitized to form a transfer unit. The transfer unit is separated from / contacted to the photosensitive member by a separation / contact mechanism. This is because, when the transfer belt and the photosensitive member are always in contact with each other, a curve along the shape of the photosensitive member is attached to the transfer belt, which affects the conveyance of the recording paper and the transfer of the toner image. .

The transfer electric field for transferring the toner image on the photosensitive member to the recording paper is applied in a state where the transfer unit is in contact with the photosensitive member. Applied in a state separated from the body.
Japanese Patent Laid-Open No. 07-140813

  However, the above-described conventional transfer device has a problem that the cost is high and further miniaturization cannot be achieved.

  That is, in the conventional configuration, a cleaning electric field or an adsorption electric field is applied using a roller different from the transfer roller that applies the transfer electric field. Therefore, a power supply circuit is connected to each roller other than the transfer roller that applies a cleaning electric field and each roller that applies an adsorption electric field, and the number of power supply circuits increases.

  In order to secure a space for arranging a large number of power supply circuits, the size of the apparatus must be increased, and it is difficult to further reduce the size, resulting in an increase in cost.

  Therefore, the applicant of the present application has considered to eliminate the roller for applying the cleaning electric field and the roller for applying the attracting electric field by applying the cleaning electric field or the attracting electric field by the transfer roller as a configuration for solving the above problem.

  However, when a configuration in which a cleaning electric field or an adsorption electric field is simply applied by a transfer roller is used, there is a new problem that a high-pressure source may be destroyed.

  This is because many of today's transfer apparatuses are equipped with a constant current control power supply circuit adopting a constant current control system as a power supply circuit for applying a voltage to the transfer roller. In the constant current control method, a voltage value is applied to the transfer roller so that the current value flowing from the transfer roller to the photoconductor becomes a set value. Since the value of the current flowing from the transfer roller to the photoconductor changes due to the resistance change between the transfer roller and the photoconductor, the constant current control power supply circuit changes the applied voltage so that the current according to the set value flows. .

  However, as described above, the application of the cleaning electric field and the adsorption electric field is performed in a state where the transfer unit is separated from the transfer belt, and the transfer belt and the photoconductor are not in contact with each other when the cleaning electric field is applied. Therefore, the air layer acts as an infinite resistance layer between the photosensitive member and the transfer belt, and the constant current electric control power supply circuit transfers the current until the current flowing between the photosensitive member of the transfer roller reaches a predetermined value. As a result of increasing the voltage applied to the roller, the high voltage source is destroyed.

  The power supply circuit includes a constant voltage control power supply circuit that adopts a constant voltage control method in addition to the constant current control method described above. In the constant voltage control method, a set voltage is applied to the transfer roller. Therefore, even if an air layer is interposed between the photosensitive member and the transfer belt, the applied voltage value is fixed, so that the high voltage source is not destroyed.

  However, as described above, the value of the current flowing from the transfer roller to the photoconductor changes due to a resistance change between the transfer roller and the photoconductor. Therefore, in the constant voltage control power supply circuit, it is necessary to switch the set voltage in accordance with the resistance value of each recording sheet such as thick paper, thin paper, and OHP. As a result, a constant current control power supply circuit has been conventionally employed as the power supply circuit for the transfer roller.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a transfer device suitable for a high-speed machine that is low in cost and can be miniaturized, and an image forming apparatus including the transfer device.

  In order to solve the above problems, the transfer device according to the present invention or the transfer device provided in the image forming apparatus according to the present invention has a transfer belt wound around a plurality of rollers, and is attracted to the transfer belt. In the transfer device for transferring the toner image formed on the photoreceptor onto the sheet conveyed by applying an electric field by a transfer roller disposed on the back side of the transfer belt, the transfer belt and the transfer roller are A separation / contact mechanism for separating and contacting the transfer unit as a unit with respect to the photosensitive member; and a power supply circuit unit for supplying a high voltage to the transfer roller, wherein a voltage set to the transfer roller is applied. A power supply circuit section having a constant voltage control power supply circuit and a constant current control power supply circuit for applying a voltage having a value corresponding to a current set to the transfer roller; and the two power supply circuit sections A control unit that controls connection between the power supply circuit and the transfer roller, and the control unit controls so that only one of the two power supply circuits is connected to the transfer roller. In the state where the transfer unit is separated from the photosensitive member, the transfer roller and the constant voltage control power supply circuit are connected.

  According to this, the power supply circuit unit for supplying a high voltage to the transfer roller has a constant voltage control power supply circuit and a constant current control power supply circuit. The control unit controls so that only one of the two power supply circuits is connected to the transfer roller, and at least in a state where the transfer unit is separated from the photoconductor, Connect the constant voltage control power supply circuit.

  Therefore, according to the above configuration, the constant current control power supply circuit continues to apply a voltage to the transfer roller in a state where the transfer unit and the photosensitive member are separated from each other, thereby destroying the high voltage source in the power supply circuit unit. It is possible to apply various electric fields from the transfer roller without inviting them. That is, it is possible to apply a cleaning electric field or an adsorption electric field using a transfer roller that applies a transfer electric field without destroying the high-pressure source.

  Thus, it is possible to provide a transfer device suitable for a high-speed machine and an image forming apparatus provided with the transfer device that is low in cost and can be reduced in size without causing a problem that destroys a high-voltage source in a power supply circuit unit. Is possible.

  In the transfer device of the present invention, the control unit connects the transfer roller and the constant current control power supply circuit when the transfer unit is in contact with the photoconductor, and the transfer unit is connected to the photoconductor. It is preferable that the transfer roller and the constant voltage control power supply circuit be connected when they are further apart.

  According to this, in the toner image transfer process in which the transfer unit comes into contact with the photosensitive member, the transfer roller and the constant current control power supply circuit are connected. Therefore, the advantage of applying the transfer electric field with the constant current control power source, that is, the advantage that it is not necessary to switch the set voltage according to the resistance value of the sheet for each type of thick paper, thin paper, OHP, etc. is also lost. In addition, it is possible to provide a transfer device suitable for a high-speed machine that is low in cost and can be miniaturized.

  In the transfer device of the present invention, the control unit further connects the transfer roller and the constant current control power supply circuit in a transfer step of applying the toner image formed on the photoreceptor to the sheet. Other than the transfer step, the transfer roller and the constant voltage control power supply circuit are connected.

  According to this, in the toner image transfer process, the transfer roller and the constant current control power supply circuit are connected. Therefore, the advantage of applying the transfer electric field with the constant current control power source, that is, the advantage that it is not necessary to switch the set voltage according to the resistance value of the sheet for each type of thick paper, thin paper, OHP, etc. is also lost. In addition, it is possible to provide a transfer device suitable for a high-speed machine that is low in cost and can be miniaturized.

  In the transfer device of the present invention, in a single print job in which only one sheet is conveyed, the separation / contact mechanism is configured such that the front end of the sheet adsorbed to the transfer belt is connected to the photosensitive member and the transfer device. The transfer unit comes into contact with the photoconductor when it reaches the transfer nip portion facing the roller, and the transfer unit is separated from the photoconductor when the trailing edge of the sheet exits the transfer nip portion. The transfer unit is separated, and the control unit controls the constant voltage control of the power supply circuit connected to the transfer roller at the timing when the leading edge of the sheet adsorbed to the transfer belt reaches the transfer nip portion. Switch from the power supply circuit to the constant current control power supply circuit, and switch to the constant voltage control circuit again when the trailing edge of the sheet exits the transfer nip. Configuration and it should be.

  Further, in a continuous print job in which a plurality of sheets are continuously conveyed, the separation / contact mechanism is configured such that the leading edge of the first sheet of the continuous print job attracted to the transfer belt is transferred to the photoconductor and the transfer. The transfer unit contacts the photoconductor at the timing when it reaches the transfer nip facing the roller, and keeps contact until the trailing edge of the final sheet of the continuous print job exits the transfer nip. The transfer unit was separated and contacted so that the transfer unit was separated from the photoconductor at the timing when the trailing edge of the final sheet of the print print job exited the transfer nip, and the control unit was attracted to the transfer belt. When the leading edge of the first sheet of the continuous print job reaches the transfer nip portion, the power supply circuit connected to the transfer roller is connected to the constant voltage control. Switching from the power supply circuit to the constant current control power supply circuit, again at the timing when the trailing edge of the last sheet of the continuous printing print job has exited the transfer nip portion, it may be configured to switch to the constant voltage control circuit.

  Further, a transfer electric field that is an electric field for transferring the toner image to the sheet is applied from the constant current power supply circuit, and a cleaning electric field for cleaning the surface of the transfer belt is applied from the constant voltage power supply circuit. Alternatively, in addition to this, an adsorption electric field for adsorbing the first sheet conveyed to the transfer belt can be applied.

  As described above, the transfer device according to the present invention or the transfer device provided in the image forming apparatus according to the present invention has a transfer unit in which the transfer belt and the transfer roller are unitized with respect to the photoconductor. A separation / contact mechanism for separating and contacting, a power supply circuit unit for supplying a high voltage to the transfer roller, a constant voltage control power supply circuit for applying a voltage set to the transfer roller, and a set for the transfer roller A power supply circuit unit having a constant current control power supply circuit for applying a voltage having a value corresponding to a current; and a control unit for controlling connection between the two power supply circuits in the power supply circuit unit and the transfer roller, The controller controls so that only one of the two power supply circuits is connected to the transfer roller, and at least when the transfer unit is separated from the photoconductor, A structure for connecting the transfer roller and the constant-voltage control power source circuit.

  Thus, it is possible to provide a transfer device suitable for a high-speed machine and an image forming apparatus provided with the transfer device that is low in cost and can be reduced in size without causing a problem that destroys a high-voltage source in a power supply circuit unit. Is possible.

  An embodiment of the present invention will be described below with reference to the drawings.

  FIG. 2 is a schematic explanatory diagram showing the overall configuration of the multifunction machine 1 including the image forming apparatus according to the present embodiment. The multifunction device 1 includes a document feeder (hereinafter referred to as SPF: Single Pass Feeder) 2 and an image forming apparatus 3.

  The image forming apparatus 3 forms a monochrome image on a recording sheet (sheet) in accordance with image data obtained by scanning a document conveyed by the SPF 2 or image data input from the outside. The image forming apparatus 3 includes a scanner unit (document reading device) 11, a printer unit 12, and a paper feed unit 13.

  The printer unit 12 includes an optical writing unit 21, a developing device 22, a photosensitive member 23, a charger 24, a cleaner unit 25, a transfer device 26, a fixing unit 27, a recording paper conveyance path 28, a paper discharge tray 29, and a manual feed tray 30. I have. The paper feed unit 13 includes a paper feed cassette 41 and a large capacity paper feed (LCC) 42. These paper feed cassette 41 and large-capacity paper feed cassette 42 contain recording paper used for image formation.

  The scanner unit 11 includes a document placing table 51 made of glass on the upper surface, and includes a light source holder 52, a mirror group 53, and a CCD (imaging device) 54 below the document placing table 51. In the scanner unit 11, when scanning a document sent from the SPF 2, the light source holder 52 and the mirror group 53 are stopped at a position on one end side of the document placing table 51. In this case, when the document is conveyed from the SPF 1, light is emitted from the light source of the light source holder 52 to the document, and reflected light from the document is imaged on the CCD 54 via the mirror group 53, and an electronic image is obtained by the CCD 54. Converted to data. In order to perform such an operation, a reading window is formed at one end of the upper surface of the scanner unit 11.

  In the printer unit 12, the charger 24 uniformly charges the surface of the photoconductor 23 to a predetermined potential. Although the image forming apparatus 3 uses the charger type charger 24, a contact type roller type or brush type charger can also be used.

  The optical writing unit 21 adopts a two-beam system including two laser irradiation units 61a and 61b in order to cope with high-speed printing processing, and the burden associated with increasing the irradiation timing is reduced. The optical writing unit 21 irradiates laser light from the laser irradiation units 61a and 61b in accordance with input image data. The laser light is irradiated to the uniformly charged photoconductor 23 through the mirror groups 62a and 62b, and the photoconductor 23 is exposed. As a result, an electrostatic latent image corresponding to the image data is formed on the surface of the photoreceptor 23.

  In the image forming apparatus 3, a laser scanning unit (LSU) including laser irradiation units 61 a and 61 b and mirror groups 62 a and 62 b is used as the optical writing unit 21, but the light emitting elements are arranged in an array. An EL write head or an LED write head can also be used.

  The developing device 22 is arranged to face the photoconductor 23 and visualizes the electrostatic latent image formed on the surface of the photoconductor 23 with black toner. The cleaner unit 25 removes and collects toner remaining on the surface of the photoconductor 23 after development and image transfer.

  The transfer device 26 is formed on the surface of the photosensitive member 23 on a recording sheet that is attracted to and transported by a transfer belt (transfer belt) 71 by applying an electric field having a polarity opposite to the electric charge of the electrostatic latent image. The transferred toner image is transferred. For example, when the electrostatic latent image has a charge of (−) polarity, an electric field of (+) polarity is applied. The transfer device 26 will be described later.

  The fixing unit 27 heats and melts the toner image transferred onto the recording paper and fixes it on the recording paper. The fixing unit 27 includes a heating roller 81 and a pressure roller 82. The heating roller 81 has a built-in heat source, and the pressure roller 82 is pressed against the heating roller 81 with a predetermined pressure.

  A recording sheet on which an image is printed is discharged to the discharge tray 29. Instead of the paper discharge tray 29, it is also possible to arrange a post-processing device (staple, punch processing, etc.) or a multi-stage paper discharge tray as an option.

  The paper feed cassette 41 and the large-capacity paper feed cassette 42 are for storing recording paper (sheets) used for image formation. For high-speed printing processing, the paper feed cassette 41 disposed below the printer unit 12 can store 500 to 1500 sheets of standard size recording paper. On the other hand, the large-capacity paper feed cassette 42 arranged outside the housing of the image forming apparatus 3 can store a large amount of a plurality of types of recording paper. The manual feed tray 30 is for feeding recording paper of an irregular size.

  Next, the transfer device 26 will be described in detail. The transfer device 26 includes a transfer unit 90 as shown in FIG. The transfer unit 90 includes a transfer belt 71, a driving roller 72, a driven roller 73, a transfer roller 74, and a tension roller 78 in a transfer unit case 91. These belts and roller groups are integrated by being incorporated in the unit case 91.

The transfer belt 71 sucks and conveys recording paper (sheet) on the surface thereof. The transfer belt 71 has a resistance value in the range of 10 × 10 ⁸ to 1 × 10 ¹² Ω · cm. The transfer belt 71 is wound around a driving roller 72, a driven roller 73, a transfer roller 74, and a tension roller 78.

  The transfer roller 74 is provided between the driving roller 72 and the driven roller 73 and at a contact portion between the photosensitive member 23 and the transfer belt 71. The transfer roller 74 applies a transfer electric field for transferring the toner image formed on the surface of the photoreceptor 23 onto the recording paper. The transfer roller 74 is made of an electrically conductive roller that is elastically supported. Since the transfer roller 74 has elasticity, the photoreceptor 23 and the transfer belt 71 can be brought into surface contact having a predetermined width (transfer nip) instead of line contact, and the transfer efficiency of the toner image onto the recording paper can be improved. It has improved.

  The drive roller 72 is a driven roller 73 that rotates the transfer belt 71. Here, as shown in FIGS. 3A and 3B, the driving roller 72 is connected to the ground, and the recording paper is peeled off to remove the recording paper from the transfer belt 71 by removing the charge of the recording paper. Also functions as a roller. The tension roller 78 applies tension to the transfer belt 71.

  Further, as shown in FIGS. 3A and 3B, a cleaning unit 79 is attached to the transfer unit case 91. That is, the cleaning unit 79 is also a part of the transfer unit 90. The cleaning unit 79 removes and collects toner adhering to the surface of the transfer belt 71.

  Further, as shown in FIGS. 3A and 3B, the transfer device 26 has a separation / contact mechanism 75 that separates and contacts the transfer unit 90 with respect to the photosensitive member 23. The separation / contact mechanism 75 displaces the transfer unit 90 between a contact position where the transfer unit 90 is in contact with the photoconductor 23 and a retracted position separated from the photoconductor 23.

  As shown in FIG. 3A, the contact position is a position where the transfer belt 71 and the photoconductor 23 are in contact with each other. More specifically, the transfer belt 71 is pressed against the photoconductor 23 by the transfer roller 74. Position. When the transfer unit 90 is in this state, the toner image on the photosensitive member 23 is transferred onto a recording sheet that passes through the transfer nip portion. The transfer nip portion is an area where the transfer roller and the photoconductor 23 face each other and the transfer belt 72 is pressed against the photoconductor 23.

  On the other hand, as shown in FIG. 3B, the retracted position is a position where the transfer belt 71 is farthest from the photoconductor 23, for example, a position about 5 mm away from the photoconductor 23. Except when the transfer device 26 performs a transfer operation, such as when the image forming apparatus 3 is in a standby state, the transfer unit 90 is disposed at the retracted position.

  For example, as shown in FIGS. 3A and 3B, the separation / contact mechanism 75 can be constituted by an eccentric cam 75a and a rotation mechanism (not shown) that rotates the eccentric cam 75a.

  FIG. 4 shows a schematic configuration in the vicinity of the transfer device 26 in the image forming apparatus 3 on which the transfer device 26 is mounted. Here, the operation around the transfer device 26 at the time of transferring the toner image will be described with reference to FIG.

  The recording paper reaches the transfer belt 71 via the paper guide 103 by the conveying force of the registration roller 102. The recording paper that has reached the transfer belt 71 is adsorbed on the surface thereof, and is conveyed to the transfer nip portion where the photoconductor 23 and the transfer roller 74 face each other as the transfer belt 71 rotates.

  Here, the registration roller 102 feeds the recording sheet at a predetermined timing so that the position of the toner image on the surface of the photoconductor 23 and the position of the recording sheet coincide with each other. Further, when the print job is a single print job in which only one recording sheet is conveyed, the transfer unit 90 is arranged so that the transfer belt 71 contacts the photoconductor 23 at the timing when the recording sheet reaches the transfer nip portion. The separation / contact is controlled. On the other hand, in the case of a continuous print job in which a plurality of recording sheets are continuously conveyed, the separation and contact are performed so that the transfer belt 71 contacts the photoconductor 23 at the timing when the first recording sheet reaches the transfer nip portion. Be controlled.

  While being transferred through the transfer nip portion, the toner image on the surface of the photoconductor 23 is transferred onto the recording paper by the transfer electric field applied from the transfer roller 74. When the leading edge of the recording sheet is conveyed to the drive roller 72, the recording sheet is separated from the surface of the transfer belt 71 from the leading end side and conveyed to the fixing unit 81 shown in FIG.

  Further, in the case where the print job is a single print job that transports only one sheet of recording paper, the transfer unit 90 causes the transfer belt 71 to move away from the photoconductor 23 at the timing when the trailing edge of the recording paper exits the transfer nip portion. In addition, the separation / connection is controlled. On the other hand, in the case of a continuous print job in which a plurality of recording sheets are continuously conveyed, the state in which the transfer belt 71 is in contact with the photoconductor 23 is maintained until the toner image is transferred to the final recording sheet. Control is performed so that the transfer belt 71 is separated from the photoconductor 23 at the timing when the trailing edge of the recording sheet exits the transfer nip portion.

  In FIG. 4, a member indicated by a member number 107 is a peeling claw for forcibly peeling the recording paper attached to the surface of the photoconductor 23 from the surface of the photoconductor 23.

  The configuration so far is the same as the conventional transfer device. Hereinafter, a characteristic configuration of the transfer device 26 according to the present embodiment will be described.

  A characteristic configuration of the transfer device 26 according to the present embodiment is that a transfer roller 74 that applies a transfer electric field to a cleaning electric field and an adsorption electric field, which has been conventionally applied from a roller different from the transfer roller, is used. This is a point to be applied.

  The cleaning electric field is an electric field for removing the toner attached to the transfer belt 71 for cleaning. Since the toner is removed by the action of repulsive force, the polarity of the cleaning electric field is the same as that of the toner. On the other hand, the attracting electric field is an electric field for electrostatically attracting the first recording sheet of the print job to the transfer belt 71. The polarity of the attracting electric field may be any as far as the function of attracting the recording paper is concerned, but it is preferable that the polarity of the attracting electric field is the same as that of the transfer electric field in order to perform good transfer in the subsequent transfer process.

  However, as described above, when a cleaning electric field and an adsorption electric field are applied by the constant current control power supply circuit connected to the transfer roller, the resistance of the air layer between the photosensitive member and the transfer belt causes a high voltage. The source is destroyed.

  In order to avoid such destruction, the transfer device 26 of this embodiment includes a power supply circuit unit 95 including a constant current control circuit 96 and a constant voltage control circuit 97 as shown in FIG. 74 is provided as a power supply circuit section for supplying high voltage to 74.

  The constant current control circuit 96 adjusts the high voltage supplied from the high voltage source 100 to a voltage at which a preset current flows between the transfer roller 74 and the photoconductor 23. More specifically, the constant current control circuit 96 sets the voltage applied to the transfer roller 74 from the high-voltage source 100 so that a preset amount of current flows between the transfer roller 74 and the photoconductor 23. To be adjusted. The constant current control circuit 96 and the high voltage source 100 constitute a constant current control power supply circuit that applies a voltage having a value corresponding to the current set to the transfer roller 74.

  On the other hand, the constant voltage control circuit 97 adjusts the high voltage supplied from the high voltage source 100 to a voltage preset as a voltage value applied to the transfer roller 74. The constant voltage control circuit 97 and the high voltage source 100 constitute a constant voltage control power supply circuit that applies a set voltage to the transfer roller 74.

  The outputs of the constant current control circuit 96 and the constant voltage control circuit 97 are supplied to the transfer roller 74 via the switching unit 98. The switching unit 98 switches a counterpart control circuit connected to the transfer roller 74. Only one of the outputs of the constant current control circuit 96 and the constant voltage control circuit 97 is connected to the transfer roller 74 by the switching unit 98.

  The switching operation of the switching unit 98 is controlled by the control unit 101. The control unit 101 includes a CPU and a ROM and a RAM attached thereto, and is also a control center that controls the operation of each part in the image forming apparatus 3.

  Therefore, in the present embodiment, the control unit 101 controls the operation of the separation / connection mechanism 75 as well as the switching operation of the switching unit 98. When a print request is issued, the control unit 101 moves the transfer unit 90 to a contact position at a predetermined timing to contact the photoconductor 23. After the transfer is completed, the control unit 101 moves the transfer unit 90 at a predetermined timing. Separated from the photoreceptor.

  In the present embodiment, a signal from a sensor 102 that detects the position of a recording sheet conveyed on the conveyance path in the image forming apparatus 3 is input to the control unit 101. Then, the separation / contact mechanism 75 is driven in accordance with the position of the recording paper to be conveyed, and the separation / contact of the transfer unit 90 is controlled.

  As described above, when the print job is a single print job that conveys only one recording sheet, the control unit 101 transfers the transfer unit 90 (specifically, the belt 71 at the timing when the recording sheet reaches the transfer nip portion). ) Is brought into contact with the photoreceptor 23. Then, the transfer unit 90 is separated from the photoconductor 23 at the timing when the trailing edge of the recording sheet exits the transfer nip portion.

  On the other hand, in the case of a continuous print job in which a plurality of recording sheets are continuously conveyed, the transfer unit 90 is brought into contact with the photoconductor 23 at the timing when the first recording sheet reaches the transfer nip portion. The transfer belt 71 is kept in contact with the photoconductor 23 until the toner image is transferred to the final recording paper, and the transfer belt is at a timing when the rear end of the final recording paper exits the transfer nip portion. 71 is separated from the photoreceptor 23.

  The timing when the leading edge of the recording paper reaches the transfer nip and the timing when the trailing edge of the recording paper exits the transfer nip are the distance from the registration roller to the transfer nip, the width of the transfer nip, the length of the recording paper, The control unit 101 calculates based on the re-rotation timing of the registration roller 102, the process speed, and the like.

  The control unit 101 controls the transfer roller 74 so that only one of the two control circuits is connected. At least when the transfer unit 90 is separated from the photoconductor 23, the transfer roller 90 The switching unit 98 is controlled so that 74 and the constant voltage control circuit 96 are connected.

  Thus, the constant current control circuit 96 continues to apply a voltage to the transfer roller 74 in a state where the transfer unit 90 and the photoconductor 23 are separated from each other without causing a situation where the high voltage source 100 is destroyed. Various electric fields can be applied from the transfer roller 74. That is, it is possible to apply a cleaning electric field or an adsorption electric field using the transfer roller 74 that applies a transfer electric field without destroying the high-voltage source 100.

  Further, as a more preferable configuration, when the transfer unit 90 is in contact with the photoconductor 23, the control unit 101 connects the transfer roller 74 and the constant current control circuit 96 so that the transfer unit 90 is separated from the photoconductor 23. In this case, the switching unit 98 is controlled so that the transfer roller 74 and the constant voltage control circuit 97 are connected.

  Further, as a more preferable configuration, the control unit 10 performs switching so that the transfer roller 74 and the constant current control circuit 76 are connected in the transfer process of transferring the toner image formed on the photoconductor 23 to the sheet. The unit 98 is controlled.

  With such a configuration, in the toner image transfer process in which the transfer unit 90 comes into contact with the photosensitive member 23, the transfer roller 74 and the constant current control circuit 96 are connected. There is no loss of the advantage of applying with the power source, that is, the advantage that it is not necessary to switch the set voltage according to the resistance value of the sheet for each type of thick paper, thin paper, OHP, and the like.

  The control unit 101 can determine whether or not the transfer unit 90 is in contact with the photoconductor 23 according to the operation of the separation / contact mechanism 75, for example. Specifically, for example, if the separating / connecting mechanism 75 is composed of the above-described eccentric cam 75a and a rotating mechanism that rotates the eccentric cam 75a, the eccentric cam 75a is shown in FIG. When it is in the upward state shown, it is determined that it is in contact, and when it is in the sideways state shown in FIG. 3B rotated 90 degrees from the state of FIG. To do.

  When the control unit 101 determines that the transfer unit 90 and the photoconductor 23 are in contact with each other based on the direction of the eccentric cam 75a, the switching unit 98 is connected so that the transfer roller 74 and the constant current control circuit 96 are connected. To control. On the other hand, if it is determined that the transfer unit 90 is separated from the photoreceptor 23, the transfer roller 74 and the constant voltage control circuit 97 are connected.

  Furthermore, in the present embodiment, the control unit 101 determines the contact state between the transfer unit 90 and the photoconductor 23 in more detail than the direction of the eccentric cam 75a as well as the direction of the eccentric cam 75a. The switching unit 98 is controlled.

  More specifically, in the single print job in which only one sheet of recording paper is transported, the control unit 101 uses the separation / contact mechanism 75 so that the leading edge of the recording paper attracted to the transfer belt 71 enters the transfer nip portion. The transfer unit 90 is brought into contact with and separated from the photosensitive member 23 so that the transfer unit 90 comes into contact with the photosensitive member 23 at the arrival timing and the transfer unit 90 is separated from the photosensitive member at the timing when the trailing edge of the recording sheet exits the transfer nip portion.

  In accordance with such separation / contact control of the transfer unit 90, in the single print job, the control unit 101 transfers the transfer unit at the timing when the leading edge of the recording paper adsorbed to the transfer belt 71 reaches the transfer nip portion. 90, the photosensitive member 23 is judged to have contacted, and the control circuit connected to the transfer roller 74 is switched from the constant voltage control circuit 97 to the constant current control circuit 96. Then, it is determined that the transfer unit 90 is separated from the photoconductor 23 at the timing when the trailing edge of the recording sheet exits the transfer nip portion, and a control circuit connected to the transfer roller 74 is fixed from the constant current control circuit 96. Switch to voltage control circuit 97.

  In a continuous print job in which a plurality of recording sheets are continuously conveyed, the control unit 101 uses the separation / contact mechanism 75 so that the leading end of the recording sheet attracted to the transfer belt 71 reaches the transfer nip portion. The transfer unit 90 comes into contact with the photosensitive member 23 at the timing to hold the contact state until the trailing edge of the final recording paper of the continuous printing job passes the transfer nip portion, and the trailing edge of the final recording paper of the continuous printing job. Then, the transfer unit 90 is brought into and out of contact so that the transfer unit 90 is separated from the photoconductor 23 at the timing when the toner passes through the transfer nip.

  In accordance with such separation / contact control of the transfer unit 90, the control unit 101 performs transfer at the timing when the leading edge of the first recording sheet attracted to the transfer belt 71 reaches the transfer nip portion in a continuous print job. It is determined that the unit 90 and the photoconductor 23 are in contact with each other, and the control circuit connected to the transfer roller 74 is switched from the constant voltage control circuit 97 to the constant current control circuit 96. Then, it is determined that the transfer unit 90 is separated from the photoconductor 23 at the timing when the trailing edge of the final recording sheet exits the transfer nip portion, and the control circuit connected to the transfer roller 74 is changed from the constant current control circuit 96. Switch to constant voltage control circuit 97.

  Further, the control unit 101 supplies an applied voltage to the transfer roller 74 from the constant current control circuit 96 to the transfer roller 74 at a preset timing. The voltage application timings of the constant current control circuit 96 and the constant voltage control circuit 97 are also controlled so that the cleaning electric field is applied.

  FIG. 5 shows a change in the charging state of an arbitrary portion of the transfer belt 71 by voltage application control to the transfer roller 74 by the control unit 101. FIG. 5 is for a continuous print job, and L shown in the drawing corresponds to the circumferential length of the transfer belt 71.

  In transferring a toner image onto a recording sheet, first, an attracting electric field is applied. The application of the adsorption electric field is performed before the transfer unit 90 is brought into contact with the photoconductor 23. Therefore, the transfer roller 74 is connected to the constant voltage control circuit 97 in the power supply circuit unit.

  The polarity of the adsorption electric field is the same as that of the transfer electric field. Here, the reverse development using the negatively charged toner is illustrated, and thus the negative polarity is used. Note that the electric field strength (applied voltage) is smaller than the transfer electric field, as long as the recording paper can be adsorbed. Such an adsorption electric field is applied while passing through the transfer nip portion.

  After exiting the transfer nip portion, the charge accumulated on the transfer belt 71 gradually attenuates. By reaching the position of the driving roller 72 connected to the ground, the amount of attenuation increases, but the negative roller is held and the position of the tension roller 78 and then the position of the driven roller 73 are reached. The recording paper is adsorbed.

  When the leading edge of the recording sheet reaches the transfer nip with the recording sheet adsorbed, a transfer electric field is applied. At this time, immediately before the transfer electric field is applied, the transfer unit 90 and the photoconductor 23 come into contact with each other, and the control circuit in the power supply circuit unit 25 connected to the transfer roller 74 receives a constant current from the constant voltage control circuit 97. The control circuit 96 is switched to. The transfer electric field is applied while passing through the transfer nip portion.

  After exiting the transfer nip portion, the charge accumulated on the transfer belt 71 gradually attenuates. By reaching the position of the driving roller 72, the amount of attenuation increases as described above, but the position of the tension roller 78 and then the position of the driven roller 73 are reached while holding a negative charge. Then, the next recording sheet is sucked.

  Also, immediately before reaching the position of the tension roller 78, the toner adhering to the transfer belt 71 is collected by the cleaning unit 79. At this time, since the transfer belt 71 is positively charged but is attenuated, the adhesion between the transfer belt 71 and the toner is weakened and can be cleaned.

  Thereafter, the same change occurs until the last recording sheet of the continuous print job is sucked and transferred. Then, when the trailing edge of the final recording sheet exits the transfer nip portion, a cleaning electric field is applied. At this time, immediately before the cleaning electric field is applied, the transfer unit 90 and the photosensitive member 23 are separated from each other, and the control circuit connected to the transfer roller 74 is switched from the constant current control circuit 96 to the constant voltage control circuit 97. . The cleaning electric field is applied while passing through the transfer nip portion. The polarity of the cleaning electric field is negative with the same polarity as the toner.

  The charges accumulated on the transfer belt 71 after exiting the transfer nip portion are gradually attenuated in this case. By reaching the position of the drive roller 72, the amount of attenuation increases as described above, but the negative charge is held, the cleaning unit 79 is reached, and the toner adhering to the transfer belt 71 is collected. At this time, since the transfer belt 71 is negatively charged, the transfer belt 71 tends to be separated from the toner, and good cleaning becomes possible.

  The flowchart of FIG. 6 shows a control circuit switching procedure of the power supply circuit unit in the transfer device 26 by the control unit 101.

  When the operation start of the drive source of the image forming apparatus is instructed during standby (S1), the control unit 101 determines whether or not the transfer belt 71 needs to be rotated (S2). If rotation is not required, the process returns to the standby state.

  On the other hand, if rotation is necessary, it is determined whether or not the application of an electric field from the transfer roller 74 is necessary (S3). The electric field applied from the transfer roller 74 includes a transfer electric field, an adsorption electric field, and a cleaning electric field. Again, if no application is required, the process returns to the standby state.

  When it is necessary to apply an electric field from the transfer roller 74, it is determined whether or not the transfer unit 90 is in contact with the photoconductor 23 (S4). This determination can be made based on, for example, the direction of the eccentric cam 75a in the separation / contact mechanism 75.

  In S4, the case where the transfer unit 90 is in contact with the photoconductor 23 is a transfer process. On the other hand, in S4, the case where the transfer unit 90 is separated from the photoconductor 23 is a pre-rotation process performed before the transfer process.

  When the transfer unit 90 is in contact with the photosensitive member 23, the constant current control circuit 96 is selected as a control circuit mounted on the power supply circuit unit 95 of the transfer device 26, and the constant current control circuit 96 and the transfer roller 74 are connected. Connect (S5).

  Then, the control unit 101 performs constant current control, continues constant current control using the constant current control circuit 96, and applies a transfer electric field (S6). Thereafter, the control unit 101 continues the constant current control until it is determined that the constant current control is finished (S7). Here, when the trailing edge of the recording sheet exits the transfer nip and the application of the transfer electric field is completed, the control unit 101 determines that the constant current control is completed, and the process proceeds to S8.

  In S8, it is determined whether it is necessary to continuously apply an electric field from the transfer roller 74. If it is a continuous print job, the transfer to the next recording sheet is performed, so that the process returns to S2. In the case of the second and subsequent pages, the contact state is determined in S4. If it is a single print job, the transfer to the next recording sheet is not performed, so that it is not necessary and returns to the standby state.

  On the other hand, if the transfer unit 90 is separated from the photosensitive member 23 in the determination of S4, that is, in the pre-rotation process, the constant voltage control circuit 97 mounted on the power supply circuit unit 95 of the transfer device 26 is selected. Then, the constant voltage control circuit 97 and the transfer roller 74 are connected (S10).

  Then, the control unit 101 performs constant voltage control, continues constant voltage control using the constant voltage control circuit 97, and applies a cleaning electric field applied in the pre-rotation step (S11). Thereafter, the control unit 101 continues the constant voltage control until it is determined that the constant voltage control has ended (S12). Here, the control unit 101 determines that the constant voltage control has ended by confirming the end of the application of the cleaning electric field by the pre-rotation, and the process proceeds to S8.

  In S8, it is determined whether it is necessary to continuously apply an electric field from the transfer roller 74, and the process returns to S2 for a subsequent print job after the previous rotation. If it is after the pre-rotation process, since it is necessary to apply an adsorption electric field by constant voltage control in order to adsorb the first recording sheet, the process proceeds to S10 to S12. In S12, at the timing when the leading edge of the recording paper reaches the transfer nip, it is determined that the application of the attracting electric field to the transfer roller 72 is finished and the constant voltage control is finished. The second and subsequent recording sheets are the same as described above.

  As described above, in the image forming apparatus 3 of the present embodiment and the transfer device 26 provided in the image forming apparatus 3, the power supply circuit unit 95 that supplies a high voltage to the transfer roller 74 includes the high-voltage source 100 and constant current control. A constant voltage control power supply circuit configured to apply a voltage set to the transfer roller 74, which includes the circuit 96, and a value corresponding to a current set to the transfer roller 74, which includes the high voltage source 100 and the constant voltage control circuit 97. A constant current control power supply circuit that applies a voltage having the same, and the control unit 101 controls the transfer roller 74 so that only one of the two power supply circuits is connected, and at least the transfer unit 90. Is separated from the photoconductor 23, the transfer roller and the constant voltage control power supply circuit are connected, and more preferably, the transfer unit 90 and the photoconductor 23 are in contact with each other, or the transfer The extent, to the transfer roller 74 and the constant current control power supply circuit are connected, a configuration for switching.

  As a result, the transfer device is suitable for a high-speed machine that is low-cost and can be miniaturized without incurring problems that destroy the high-pressure source 100 in the transfer device.

1, showing an embodiment of the present invention, is a block diagram illustrating a main configuration of a power supply circuit unit in a transfer device. FIG. It is a longitudinal cross-sectional view which shows schematic structure of the multifunction machine provided with the said transfer apparatus. It is explanatory drawing which shows the contact position and retracting position which the said transfer apparatus can take. 2 is a diagram illustrating a schematic configuration in the vicinity of a transfer device in an image forming apparatus on which the transfer device is mounted. 6 is a diagram illustrating a change in a charging state of an arbitrary portion of a transfer belt of the transfer device during a continuous print job. 4 is a flowchart showing a switching procedure of a control circuit of a power supply circuit unit of the transfer device in the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multifunction machine 3 Image forming apparatus 26 Transfer apparatus 71 Transfer belt 74 Transfer roller 75 Separation / contact mechanism 79 Cleaning unit 90 Transfer unit 95 Power supply circuit section 96 Constant current control circuit (constant current control power supply circuit)
97 Constant voltage control circuit (constant voltage control power supply circuit)
98 switching unit 100 high voltage source (constant current control power supply circuit, constant voltage control power supply circuit)
101 Control unit

Claims (8)

A transfer belt wound around a plurality of rollers, and a toner image formed on a photoreceptor on a sheet adsorbed and conveyed by the transfer belt is transferred by a transfer roller disposed on the back side of the transfer belt. In a transfer device that transfers by applying an electric field,
A separation / contact mechanism for separating / contacting a transfer unit formed by unitizing the transfer belt and the transfer roller with respect to the photoreceptor;
A power supply circuit unit for supplying a high voltage to the transfer roller, the constant voltage control power supply circuit for applying a voltage set to the transfer roller, and a voltage having a value corresponding to the current set to the transfer roller A power supply circuit unit having a constant current control power supply circuit for applying
A control unit for controlling connection between the two power supply circuits in the power supply circuit unit and the transfer roller;
The controller controls the transfer roller so that only one of the two power supply circuits is connected, and at least the transfer unit is separated from the photoconductor, A transfer device, wherein a constant voltage control power supply circuit is connected.   The control unit connects the transfer roller and the constant current control power supply circuit when the transfer unit is in contact with the photoconductor, and transfers the transfer unit when the transfer unit is separated from the photoconductor. The transfer device according to claim 1, wherein a roller and the constant voltage control power supply circuit are connected.   2. The control unit according to claim 1, wherein the control unit connects the transfer roller and the constant current control power supply circuit in a transfer step of transferring a toner image formed on the photoreceptor to a sheet. Transfer device. In a single print job where only one sheet is transported,
The separation / contact mechanism is configured such that the transfer unit contacts the photoconductor at a timing when the leading edge of the sheet adsorbed to the transfer belt reaches a transfer nip portion where the photoconductor and the transfer roller are opposed to each other. The transfer unit is separated and contacted so that the transfer unit is separated from the photoconductor at the timing when the trailing edge of the sheet exits the transfer nip.
The control unit transfers a power supply circuit connected to the transfer roller from the constant voltage control power supply circuit to the constant current control power supply when the leading edge of the sheet adsorbed to the transfer belt reaches the transfer nip portion. 2. The transfer apparatus according to claim 1, wherein the transfer device is switched to a circuit, and is switched to the constant voltage control circuit again at a timing when the trailing edge of the sheet exits the transfer nip portion. In continuous print jobs that transport multiple sheets continuously,
The separation / contact mechanism is configured such that the transfer unit moves the photosensitive member and the transfer roller at the timing when the leading edge of the first sheet of the continuous print job attracted to the transfer belt reaches the transfer nip portion where the photosensitive member and the transfer roller face each other. The contact is maintained until the trailing edge of the final sheet of the continuous print job exits the transfer nip, and the trailing edge of the final sheet of the continuous print job exits the transfer nip. Separate the transfer unit so that the transfer unit is separated from the photoreceptor,
The controller controls the power supply circuit connected to the transfer roller at the timing when the leading edge of the first sheet of the continuous print job adsorbed on the transfer belt reaches the transfer nip, and supplies the constant voltage control power source. 2. The circuit is switched from a circuit to a constant current control power supply circuit, and is switched to the constant voltage control circuit again at the timing when the trailing edge of the last sheet of the continuous print job exits the transfer nip portion. The transfer apparatus described.   The constant current power supply circuit applies a transfer electric field that is an electric field for transferring the toner image to the sheet, and the constant voltage power supply circuit applies a cleaning electric field for cleaning the surface of the transfer belt. The transfer device according to claim 1.   The transfer apparatus according to claim 6, wherein the constant voltage power supply circuit further applies an adsorption electric field for adsorbing the first sheet conveyed to the transfer belt. In an image forming apparatus that forms an electrostatic latent image on a surface of a photoreceptor, develops the electrostatic latent image with toner to form a toner image, and transfers the toner image onto a sheet.
An image forming apparatus comprising the transfer device according to claim 1.

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