JP2017142278A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology to reduce the number of power supplies in an image forming apparatus of an electrophotographic system.SOLUTION: A printer 100 is an image forming apparatus of an electrophotographic system comprising a photoreceptor 51, a developing part 54, a transfer part 55, and a cleaner 56. The printer 100 includes a cleaning power supply 64 that outputs a cleaning bias to the cleaner 56, a transfer power supply 66 that outputs a transfer bias to the transfer part 55, a discharge power supply 65 that outputs a discharge bias having the same polarity as the charging polarity of a toner, and a discharge switch 62. The printer 100 switches the discharge switch 62 between a first connection state where the discharge power supply 65 and the cleaner 56 are connected and the discharge power supply 65 and the transfer part 55 are not connected, and a second connection state where the discharge power supply 65 and the transfer part 55 are connected and the discharge power supply 65 and the cleaner 56 are not connected.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus. More specifically, the present invention relates to a technique for discharging toner taken in a member around the photosensitive member onto the photosensitive member and collecting the toner on the photosensitive member by a developing device.

  2. Description of the Related Art Conventionally, in an image forming apparatus that forms an image by an electrophotographic method, a technique is known in which toner taken in a member around a photoconductor is discharged onto the photoconductor and the toner on the photoconductor is collected by a developing device. . Specifically, the transfer member in contact with the photoconductor is biased with a polarity opposite to that at the time of transfer, and the toner adhering to the transfer member is returned to the photoconductor, or the cleaning member in contact with the photoconductor is cleaned. A configuration is known in which a bias having a reverse polarity is applied to return the toner adhering to the cleaning member onto the photosensitive member.

  As a document disclosing a configuration in which a bias having a polarity opposite to that at the time of image formation is applied to members around the photosensitive member, there is Patent Document 1, for example. Patent Document 1 discloses an image forming apparatus including a photosensitive drum, a cleaning roller, a transfer roller, two power sources for applying a bias to the cleaning roller, and two power sources for applying a bias to the transfer roller. Has been. Specifically, the image forming apparatus disclosed in Patent Document 1 includes a power source for applying a cleaning bias for removing toner on the photoconductor, and a cleaning for discharging the toner onto the photoconductor having a polarity opposite to the cleaning bias. A power supply for applying a discharge bias. The image forming apparatus disclosed in Patent Document 1 includes a power supply for applying a transfer bias for attracting toner on the photoconductor, and a transfer discharge bias for discharging toner onto the photoconductor that is opposite in polarity to the transfer bias. Power supply to be applied.

JP 9-325587 A

  However, the conventional technique described above has the following problems. That is, there are two power sources for the cleaning roller and the transfer roller, which are members around the photosensitive member, and the number of power sources is large. As a result, the cost increases and the configuration becomes complicated.

  The present invention has been made to solve the above-described problems of the prior art. That is, the problem is to provide a technique for reducing the number of power supplies in an electrophotographic image forming apparatus.

  An image forming apparatus designed to solve this problem includes a photosensitive member, a developing member that supplies toner onto the photosensitive member, and collects toner on the photosensitive member, and a photosensitive member on the photosensitive member. A transfer rotator for transferring the toner to the sheet, a cleaning member for removing the toner on the photoconductor from the photoconductor, and a cleaning bias for outputting a cleaning bias having a polarity opposite to the charging polarity of the toner to the cleaning member. A power supply, a transfer power supply that outputs a transfer bias that is a reverse polarity of the toner charge polarity to the transfer rotator, a discharge power supply that outputs a discharge bias that is the same polarity as the toner charge polarity, and a switch member And a control unit, wherein the control unit is in a state in which the switch member, the discharge power source and the cleaning member are connected, and the discharge power source and the transfer rotating body are not connected. A first connection state, the discharge power and said transfer rotary member is connected, the discharge power and said cleaning member and the second connection state is a state in which is not connected, switch to is characterized in that.

  An image forming apparatus disclosed in this specification includes a cleaning power source that outputs a cleaning bias to a cleaning member, a transfer power source that outputs a transfer bias to a transfer rotating member, a discharge power source that outputs a discharge bias, and a switch member. I have. The discharge power source is switched by the switch member between a state where it is connected to the cleaning member and not connected to the transfer rotator, and a state where it is connected to the transfer rotator and not connected to the cleaning member.

  That is, in the image forming apparatus disclosed in this specification, the discharge power source is switched between a state connected to the cleaning member and a state connected to the transfer rotating body. For this reason, the power source for applying the discharge bias to the cleaning member and the power source for applying the discharge bias to the transfer rotator are not separate power sources but a common discharge power source. As a result, the image forming apparatus has a smaller number of power sources than the conventional configuration.

  The present specification includes a photoconductor, a developing member that supplies toner to the photoconductor, and collects toner on the photoconductor, and a transfer that transfers the toner on the photoconductor to a sheet. A rotating member, a cleaning member that removes toner on the photosensitive member from the photosensitive member, a cleaning power source that outputs a cleaning bias that is a reverse polarity of the charging polarity of the toner to the cleaning member, and a transfer rotating member A transfer power source that outputs a transfer bias that is a bias opposite in polarity to the charge polarity of the toner, a discharge power source that outputs a discharge bias that is the same polarity as the charge polarity of the toner, a first switch member, and a second switch member A switch member; and a control unit, wherein the control unit includes a first connection state in which the discharge power source and the cleaning member are connected to each other, the discharge power source, With cleaning member The second switch member is switched to a first non-connection state that is not connected, and the second switch member is connected to the discharge power source and the transfer rotator. There is also described an image forming apparatus that switches to a second non-connected state in which the transfer rotator is not connected.

  A control method for realizing the functions of the image forming apparatus, a computer program, and a computer-readable storage medium storing the computer program are also novel and useful.

  According to the present invention, a technique for reducing the number of power supplies is realized in an electrophotographic image forming apparatus.

1 is a cross-sectional view illustrating a schematic configuration of a printer according to an embodiment. It is explanatory drawing which shows the connection structure of the power supply of the printer concerning a 1st form. FIG. 2 is a block diagram illustrating an electrical configuration of a printer. 6 is a flowchart illustrating a printing process procedure of a printer. 4 is a timing chart showing the switching timing of each switch in the printer of the first embodiment. It is explanatory drawing which shows the connection structure of the power supply of the printer concerning a 2nd form. It is a timing chart which shows the switching timing of each switch in the printer of the 2nd form.

  Hereinafter, a first embodiment in which an image forming apparatus according to the present invention is embodied will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to an electrophotographic monochrome printer.

  As shown in FIG. 1, the printer 100 according to the present embodiment includes an image forming unit 10 that prints an image on a sheet S, a paper feed tray 11 that stores a sheet S before printing, and a discharge tray that stores a printed sheet S. And a paper tray 12. Further, a sheet conveyance path 13 which is a path of the sheet S from the paper feed tray 11 to the paper discharge tray 12 through the image forming unit 10 is formed inside the printer 100.

  The image forming unit 10 forms an image on the sheet S conveyed through the sheet conveying path 13 by electrophotography. As shown in FIG. 1, the image forming unit 10 of the printer 100 includes a photoreceptor 51, a charging unit 52, an exposure unit 53, a developing unit 54, a transfer unit 55, a cleaner 56, and a fixing unit 57. The photoconductor 51 is a rotating body that rotates in the clockwise direction in FIG. 1 around a rotation axis in a direction orthogonal to the paper surface of FIG. The charging unit 52, the exposure unit 53, the developing unit 54, the transfer unit 55, and the cleaner 56 are arranged around the photoconductor 51 in this order with respect to the rotation direction of the photoconductor 51. Note that the printer 100 according to the present embodiment uses a non-magnetic one-component toner and a toner having a positive charge polarity.

  The charging unit 52 is, for example, a scorotron charger, and charges the surface of the photoreceptor 51 to a positive polarity. The exposure unit 53 is, for example, a laser exposure unit, and irradiates the photosensitive member 51 with a laser beam to reduce the absolute value of the surface potential of the photosensitive member 51, so that the photosensitive member 51 is based on image data. An electrostatic latent image is formed. The charging unit 52 and the exposure unit 53 are both arranged in non-contact with the photoconductor 51.

  The developing unit 54 includes a developing roller 541 disposed in contact with the surface of the photoreceptor 51. The developing unit 54 stores toner, develops the toner by supplying the toner to the electrostatic latent image on the photoconductor 51, and forms a toner image on the photoconductor 51. The developing roller 541 is supplied with a positive developing bias during image formation and supplies toner onto the photoconductor 51. The developing roller 541 is rotated in a direction opposite to that of the photosensitive member 51 at a slightly higher peripheral speed than the photosensitive member 51 during image formation. The developing unit 54 is an example of a developing member.

  The transfer unit 55 is, for example, a roller-like rotating member, and is disposed in contact with the surface of the photoreceptor 51. At the time of image formation, the transfer unit 55 is applied with a negative transfer bias, and electrically draws the toner image on the photoconductor 51. In addition, the transfer unit 55 is rotated in the rotation direction opposite to that of the photosensitive member 51 at the same peripheral speed as that of the photosensitive member 51 during image formation. 1, a transfer nip 551 that is a range in which the toner on the photoconductor 51 can be transferred is formed between the transfer portion 55 and the photoconductor 51. That is, the printer 100 transfers the toner image from the photoreceptor 51 to the sheet S while the sheet S being conveyed is in the transfer nip 551. The transfer unit 55 is an example of a transfer rotator.

  The cleaner 56 is a sponge roller, for example, and is disposed in contact with the surface of the photoreceptor 51. The cleaner 56 is applied with a negative cleaning bias at the time of image formation, and electrically draws residual toner remaining on the photoconductor 51 after transfer to remove it from the photoconductor 51. The cleaner 56 only needs to be rotated at a peripheral speed different from that of the photosensitive member 51, and the rotation direction may be any. The cleaner 56 is an example of a cleaning member.

  As shown in FIG. 2, the printer 100 has a configuration for applying various biases to the transfer unit 55 and the cleaner 56. Specifically, the printer 100 includes a cleaning switch 61, a discharge switch 62, and a transfer switch 63 that are three switches, and a cleaning power source 64, a discharge power source 65, and a transfer power source 66 that are three power sources. . In the printer 100 of this embodiment, the cleaning switch 61 is an example of a cleaning switch member, the discharge switch 62 is an example of a switch member, and the transfer switch 63 is an example of a transfer switch member.

  Each power source is provided with a circuit that converts power supplied from a commercial power source to generate a predetermined bias. Each power supply may be provided on the same circuit board or may be provided on different circuit boards. The various biases applied by each power source may be voltages, or may change the potential to be applied as a result of supplying current or power. Although the printer 100 has a plurality of power supplies in addition to the cleaning power supply 64, the discharge power supply 65, and the transfer power supply 66, other parts are known techniques. Only the relevant part is explained.

  The cleaning switch 61 is a switch for switching electrical connection between the cleaner 56 and the cleaning power source 64. The cleaning power supply 64 includes a power supply circuit that applies a cleaning bias, which is a bias having a polarity opposite to the toner charging polarity, to the cleaner 56. The printer 100 is controlled by the cleaning switch 61 to have a connection state in which the cleaner 56 and the cleaning power source 64 are electrically connected and a non-connection state in which the cleaner 56 and the cleaning power source 64 are not electrically connected. Switch. The connection state of the cleaning switch 61 is an example of a cleaning connection state, and the non-connection state of the cleaning switch 61 is an example of a cleaning non-connection state.

  That is, the printer 100 applies a negative cleaning bias to the cleaner 56 by setting the cleaning switch 61 to the connected state. The cleaner 56 electrically attracts the toner on the photoconductor 51 and removes the toner from the photoconductor 51 by applying a negative cleaning bias. When the cleaning switch 61 is not connected, the cleaner 56 may be connected to GND or 0V.

  The transfer switch 63 is a switch for switching the electrical connection between the transfer unit 55 and the transfer power supply 66. The transfer power supply 66 includes a power supply circuit that applies a transfer bias, which is a bias having a polarity opposite to the toner charging polarity, to the transfer unit 55. The printer 100 controls the transfer switch 63 so that the transfer unit 55 and the transfer power source 66 are electrically connected, and the transfer unit 55 and the transfer power source 66 are not electrically connected. , Switch. The connection state of the transfer switch 63 is an example of a transfer connection state, and the non-connection state of the transfer switch 63 is an example of a transfer non-connection state.

  That is, the printer 100 applies a negative transfer bias to the transfer unit 55 by setting the transfer switch 63 in the connected state. The transfer unit 55 applies a negative transfer bias to electrically attract the toner on the photoconductor 51, and transfers the toner image to the sheet S at the transfer nip 551. When the transfer switch 63 is not connected, the transfer unit 55 may be connected to GND or 0V.

  Note that the transfer power supply 66 of this embodiment is a power supply that can control the output voltage. The printer 100 changes the magnitude of the transfer bias in accordance with, for example, the type of the sheet S being conveyed. That is, by making the output voltage of the transfer power supply 66 variable, high image quality can be achieved. On the other hand, the cleaning power source 64 only needs to be able to draw the toner on the photosensitive member 51 and remove it from the photosensitive member 51, and does not require precise output control. Therefore, the cleaning power supply 64 of this embodiment is a power supply that outputs a predetermined fixed voltage.

  The discharge switch 62 is a switch for switching electrical connection between the discharge power supply 65 and the cleaner 56 or between the discharge power supply 65 and the transfer unit 55. The discharge power supply 65 includes a power supply circuit that applies a discharge bias, which is a bias having the same polarity as the charging polarity of the toner, to the cleaner 56 or the transfer unit 55.

  The printer 100 controls the discharge switch 62 so that the cleaner 56 and the discharge power supply 65 are electrically connected to each other, and the transfer unit 55 and the discharge power supply 65 are electrically connected to each other. Switch between connection status. In the first connection state, the transfer unit 55 and the discharge power supply 65 are not electrically connected. Further, in the second connection state, the cleaner 56 and the discharge power supply 65 are not electrically connected. The discharge switch 62 can also be switched to a non-connected state that is neither the first connected state nor the second connected state. When the discharge switch 62 is not connected, the discharge power source 65 is not connected to the cleaner 56 or the transfer unit 55.

  That is, the printer 100 applies a positive discharge bias to the cleaner 56 by setting the discharge switch 62 to the first connection state. The cleaner 56 electrically discharges the toner removed from the photoconductor 51 to the photoconductor 51 by applying a positive discharge bias. Further, the printer 100 applies a positive discharge bias to the transfer unit 55 by setting the discharge switch 62 to the second connection state. The transfer unit 55 electrically discharges the adhered toner to the photosensitive member 51 by applying a positive discharge bias.

  The discharge power supply 65 of this embodiment is a power supply that outputs a predetermined fixed voltage. That is, the discharge bias applied to the cleaner 56 and the discharge bias applied to the transfer unit 55 have the same voltage value. For example, a resistance member is provided between the discharge switch 62 and the cleaner 56 or between the discharge switch 62 and the transfer unit 55, and the discharge bias applied to the cleaner 56 and the transfer unit 55 are applied. The discharge bias may be different in voltage value.

  Next, the electrical configuration of the printer 100 will be described. As shown in FIG. 3, the printer 100 includes a controller 30 including a CPU 31, a ROM 32, a RAM 33, and an NVRAM (nonvolatile RAM) 34. The printer 100 includes an image forming unit 10, a network IF (network interface) 37, and an operation panel 40, and these are electrically connected to the controller 30. The image forming unit 10 includes a cleaning switch 61, a discharge switch 62, a transfer switch 63, a cleaning power supply 64, a discharge power supply 65, and a transfer power supply 66.

  The ROM 32 stores various control programs for controlling the printer 100, various settings, initial values, and the like. The RAM 33 is used as a work area from which various control programs are read, or as a storage area for temporarily storing data.

  The CPU 31 controls each component of the printer 100 while storing the processing result in the RAM 33 or the NVRAM 34 according to the control program read from the ROM 32. For example, the CPU 31 controls the states of the cleaning switch 61, the discharge switch 62, and the transfer switch 63. The CPU 31 is an example of a control unit. Further, the controller 30 may be a control unit. Note that the controller 30 in FIG. 3 is a general term that summarizes hardware used for controlling the printer 100 such as the CPU 31, and does not necessarily represent a single piece of hardware that actually exists in the printer 100.

  The network IF 37 is hardware for communicating with devices connected via the network. The communication method may be wired or wireless. The operation panel 40 is hardware that is responsible for displaying a notification to the user and receiving an instruction input by the user. The operation panel 40 includes, for example, a liquid crystal display and a button group including a start key, a stop key, a numeric keypad, and the like.

  Next, an image forming operation in the printer 100 will be described. Hereinafter, regarding the cleaning switch 61 and the transfer switch 63, the connection state is turned on, and the non-connection state is turned off. Specifically, for example, when the cleaning switch 61 is turned on, the cleaner 56 and the cleaning power source 64 are electrically connected, and when the cleaning switch 61 is turned off, the cleaner 56 In other words, the cleaning power supply 64 is not connected electrically. Further, turning on the transfer switch 63 means that the transfer unit 55 and the transfer power source 66 are electrically connected, and turning off the transfer switch 63 means that the transfer unit 55 and the transfer power source 66 are turned off. Is in a non-connected state where they are not electrically connected.

  For example, when the printer 100 receives a print instruction via the network IF 37 or the operation panel 40, the printer 100 starts a print preparation operation. Specifically, the printer 100 starts rotation of a rotating member such as the photoconductor 51, and starts up the charging unit 52 and the exposure unit 53, preheats the fixing unit 57, and the like. Note that these preparation operations may already be completed when a print instruction is received.

  The printer 100 starts the printing operation after the printing preparation operation is completed. Specifically, the printer 100 charges the surface of the photoconductor 51 with the charging unit 52 and exposes it with the exposure unit 53. As a result, an electrostatic latent image based on the print data is formed on the surface of the photoreceptor 51. Next, the printer 100 causes the developing unit 54 to supply toner to the electrostatic latent image and forms a toner image on the photoreceptor 51.

  In addition, the printer 100 feeds the sheet S from the paper feed tray 11, and transports the sheet S to the transfer nip 551 between the photoconductor 51 and the transfer unit 55 through the sheet transport path 13. Then, the printer 100 causes the transfer unit 55 to transfer the toner image on the photosensitive member 51 to the sheet S. For this purpose, the printer 100 turns on the transfer switch 63 and applies a transfer bias to the transfer unit 55 at least during a period in which the sheet S is conveyed through the transfer nip 551.

  Further, the printer 100 conveys the sheet S on which the toner image is transferred to the fixing unit 57, and the toner image is thermally fixed to the sheet S by the fixing unit 57. Then, the printer 100 discharges the sheet S on which the image is formed to the discharge tray 12.

  During printing, the printer 100 turns on the cleaning switch 61 and applies a cleaning bias to the cleaner 56. As a result, the residual toner adhering to the photoconductor 51 after the transfer is electrically attracted to the cleaner 56 and removed from the photoconductor 51. During execution of the printing operation, the printer 100 disconnects the discharge switch 62 and does not apply a discharge bias to either the cleaner 56 or the transfer unit 55.

  On the other hand, the printer 100 executes a discharge operation by applying a discharge bias to the cleaner 56 and the transfer unit 55 at any timing other than during printing. For example, the printer 100 performs an ejection operation after receiving a printing instruction and before starting a printing operation, that is, before starting development of an electrostatic latent image. Further, for example, the printer 100 executes the discharge operation after the printing operation is completed, that is, after the sheet S passes through the transfer nip 551.

  In the discharge operation, the printer 100 turns off the transfer switch 63 and then sets the discharge switch 62 in the second connection state to electrically connect the transfer unit 55 and the discharge power supply 65. As a result, the toner adhering to the transfer portion 55 is discharged onto the photoreceptor 51. Further, after turning off the cleaning switch 61, the printer 100 sets the discharge switch 62 in the first connection state to electrically connect the cleaner 56 and the discharge power supply 65. As a result, the toner attracted to the cleaner 56 and attached to the cleaner 56 is discharged onto the photoreceptor 51. Note that the order of the period for the first connection state and the period for the second connection state may be reversed.

  Further, the toner discharged onto the photoconductor 51 moves to a position facing the developing unit 54 as the photoconductor 51 rotates. In the printer 100, the toner on the photoreceptor 51 is collected by the developing unit 54 and reused. When the discharged toner is collected by the developing unit 54, for example, the surface of the photosensitive member 51 is charged by the charging unit 52 and the surface potential of the photosensitive member 51 is higher than the potential of the developing roller 541. And As a result, the toner on the photoconductor 51 is electrically moved to the developing roller 541 and collected by the developing unit 54.

  Next, a printing process procedure for realizing the printing operation including the above-described ejection operation will be described with reference to the flowchart of FIG. 4 and the timing chart of FIG. This print processing is executed by the CPU 31 when a print execution instruction is received in a state where the print preparation operation is not completed.

  In this printing process, the CPU 31 first causes each unit of the printer 100 to start a print preparation operation (S101). The CPU 31 operates a motor that rotationally drives rotating members such as the photosensitive member 51, the cleaner 56, and the transfer unit 55 in the print preparation operation. As shown in FIG. 5, at the start of the print preparation operation, both the cleaning switch 61 and the transfer switch 63 are off. Further, the discharge switch 62 is in a disconnected state. That is, neither the cleaning bias nor the discharge bias is applied to the cleaner 56. Further, neither transfer bias nor discharge bias is applied to the transfer portion 55.

  After starting the print preparation operation, the CPU 31 sets the discharge switch 62 to the second connection state (S102). Thereby, an ejection bias is applied to the transfer portion 55. Then, the CPU 31 determines whether or not the time required for one rotation of the transfer unit 55 has elapsed (S103). That is, it is determined whether or not the transfer roller has made one turn after the discharge switch 62 is in the second connection state. If it is determined that it has not elapsed (S103: NO), the CPU 31 waits until it has elapsed.

  That is, as shown in FIG. 5, the printer 100 continues the second connection state for a predetermined period Tt after setting the ejection switch 62 to the second connection state. A period Tt in FIG. 5 is a period longer than the time during which the transfer portion 55 makes one rotation. As a result, the toner is discharged over the entire circumference of the transfer portion 55.

  When it is determined that the time required for one rotation of the transfer unit 55 has elapsed (S103: YES), the CPU 31 switches the ejection switch 62 from the second connection state to the first connection state (S104). As a result, a discharge bias is applied to the cleaner 56. Then, the CPU 31 determines whether or not the time required for one rotation of the cleaner 56 has elapsed (S105). If it is determined that it has not elapsed (S105: NO), the CPU 31 waits until it has elapsed.

  That is, as shown in FIG. 5, the printer 100 continues the first connection state for a predetermined period Tc after setting the ejection switch 62 to the first connection state. A period Tc in FIG. 5 is a period longer than the time for which the cleaner 56 makes one rotation. As a result, the toner is discharged over the entire circumference of the cleaner 56.

  In the printer 100 according to the present embodiment, the discharge from the transfer unit 55 is performed first, and then the discharge from the cleaner 56 is performed. Therefore, the chance that the cleaner 56 holds the toner discharged from the transfer unit 55 unnecessarily is reduced. ing. As shown in FIG. 5, the CPU 31 keeps both the cleaning switch 61 and the transfer switch 63 off during the period in which the discharge bias is applied to the cleaner 56 and the transfer unit 55 in S102 or S104. . As a result, simultaneous application of the cleaning bias and the discharge bias to the cleaner 56 is avoided. Further, simultaneous application of the transfer bias and the discharge bias to the transfer unit 55 is avoided.

  The discharge switch 62 of this embodiment is a mechanical changeover switch, and there is a transition period that is not connected to any of the changeover switches. That is, when the discharge switch 62 is switched from one of the first connection state and the second connection state to the other, no discharge bias is applied to either the cleaner 56 or the transfer unit 55 during the period from one to the other. There is a period of disconnection. In FIG. 5, this transition period is exaggerated.

  If it is determined that the time required for one rotation of the cleaner 56 has elapsed (S105: YES), the CPU 31 switches the discharge switch 62 from the first connected state to the non-connected state (S106).

  Next, the CPU 31 determines whether or not the print preparation operation has been completed (S108). If it is determined that the print preparation operation has not been completed (S108: NO), the CPU 31 waits for the print preparation operation to be completed. If it is determined that the print preparation operation has been completed (S108: YES), the CPU 31 starts the print operation (S110).

  Then, as shown in FIG. 5, the CPU 31 turns on the cleaning switch 61 and the transfer switch 63 while keeping the discharge switch 62 in the disconnected state. The CPU 31 starts application of the cleaning bias and the transfer bias before a predetermined period Tp before the timing when the sheet S reaches the transfer nip 551. The predetermined period Tp is a time required for one rotation of the photoconductor 51. Note that a period Ts in FIG. 5 is a transfer period in which the sheet S passes through the transfer nip 551 by the printing operation.

  That is, the CPU 31 starts a printing operation so that the sheet S reaches the transfer nip 551 after a period Tp or more has elapsed after the cleaning switch 61 and the transfer switch 63 are turned on. Thereby, the charging potential of the photosensitive member 51 can be stabilized before the sheet S reaches the transfer nip 551. Either the cleaning switch 61 and the transfer switch 63 may be turned on first or simultaneously.

  Further, as shown in FIG. 5, the CPU 31 does not switch each switch during the transfer period Ts. Specifically, the CPU 31 keeps the discharge switch 62 in the disconnected state during the transfer period Ts, and switches the discharge switch 62 during a period when the sheet S is not present in the transfer nip 551. Therefore, the influence on the image quality by the switching operation of the switch is suppressed.

  After starting the printing operation, the CPU 31 determines whether or not the transfer period Ts has elapsed, the trailing edge of the sheet S has passed the transfer nip, and the passing of the sheet S has been completed (S111). For example, the printer 100 includes sensors that output different signals depending on the presence or absence of the sheet S at a plurality of locations in the conveyance path of the sheet S. The CPU 31 can acquire the timing at which the trailing edge of the sheet S has passed the transfer nip based on one output signal of the sensor. That is, the CPU 31 determines the completion of the passage of the sheet S using the positional relationship between the sensor and the transfer nip and the conveyance speed of the sheet S. When it is determined that the passage of the sheet S is not completed (S111: NO), the CPU 31 continues the printing operation until completion.

  On the other hand, when it is determined that the passage of the sheet S is completed (S111: YES), the CPU 31 sets the discharge switch 62 in the second connection state (S112). As shown in FIG. 5, the CPU 31 turns off the transfer switch 63 after a predetermined margin period Tm after the transfer period Ts. Then, the CPU 31 executes S112 after the transfer switch 63 is turned off. Thereby, simultaneous application of the transfer bias and the discharge bias to the transfer portion 55 is avoided.

  Then, the CPU 31 determines whether or not the time required for one rotation of the transfer unit 55 has elapsed (S113). If it is determined that it has not elapsed (S113: NO), the CPU 31 waits until it has elapsed.

  When it is determined that the time required for one rotation of the transfer unit 55 has elapsed (S113: YES), the CPU 31 switches the ejection switch 62 from the second connection state to the first connection state (S114). The CPU 31 turns off the cleaning switch 61 after a time period equal to or longer than the period Tp required for one rotation of the photoreceptor 51 has elapsed after the transfer period Ts. Then, the CPU 31 executes S114 after the cleaning switch 61 is turned off. As a result, simultaneous application of the cleaning bias and the discharge bias to the cleaner 56 is avoided.

  Then, the CPU 31 determines whether or not the time required for one rotation of the cleaner 56 has elapsed (S115). If it is determined that it has not elapsed (S115: NO), the CPU 31 waits until it has elapsed. When it is determined that the time required for one rotation of the cleaner 56 has elapsed (S115: YES), the CPU 31 switches the discharge switch 62 from the first connection state to the non-connection state (S116), and applies the discharge bias. Stop and end the printing process.

  As described above in detail, the printer 100 according to the first embodiment includes the cleaning power supply 64, the discharge power supply 65, the transfer power supply 66, the cleaning switch 61, the discharge switch 62, and the transfer switch 63. . The printer 100 switches the connection between the cleaner 56 and the transfer unit 55 and each power source by switching each switch. In the printer 100, the power supply for applying the discharge bias to the cleaner 56 and the power supply for applying the discharge bias to the transfer unit 55 are made common to form one discharge power supply 65. The discharge bias does not require precise control, and even the common discharge power supply 65 has little influence on the image quality. Therefore, the number of power supplies can be reduced as compared with the configuration in which the power supply for the discharge bias is separately provided in the cleaner 56 and the transfer portion 55.

  On the other hand, in the printer 100, a cleaning power source 64 that applies a cleaning bias to the cleaner 56 and a transfer power source 66 that applies a transfer bias to the transfer unit 55 are separate power sources. That is, since the transfer power supply 66 for applying the transfer bias required for precise control is provided separately from the cleaning power supply 64, the transfer bias can be suitably set according to the type of the sheet and the like, and a high-quality image is obtained. Formation can be expected.

  Next, a second embodiment in which the image forming apparatus according to the present invention is embodied will be described in detail with reference to the accompanying drawings. The printer 200 of the second embodiment has the same power supply configuration as the printer 100 of the first embodiment, but the switch configuration is different. Hereinafter, the same components as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 6, the printer 200 according to the second embodiment includes a cleaning discharge switch 68 and a transfer discharge switch 69 instead of the discharge switch 62 according to the first embodiment. In the printer 200 of this embodiment, the cleaning / discharging switch 68 is an example of a first switch member, and the transfer / discharging switch 69 is an example of a second switch member.

  The cleaning discharge switch 68 is a switch for switching an electrical connection state between the cleaner 56 and the discharge power supply 65. In other words, the printer 200 switches between a connection state in which the cleaner 56 and the discharge power supply 65 are connected and a non-connection state in which the cleaner 56 and the discharge power supply 65 are not connected by the control of the cleaning discharge switch 68. The connection state of the cleaning discharge switch 68 is an example of a first connection state, and the non-connection state of the cleaning discharge switch 68 is an example of a first non-connection state.

  The transfer discharge switch 69 is a switch for switching an electrical connection state between the transfer unit 55 and the discharge power supply 65. That is, the printer 200 switches between a connection state in which the transfer unit 55 and the discharge power supply 65 are connected and a non-connection state in which the transfer unit 55 and the discharge power supply 65 are not connected by the control of the transfer / discharge switch 69. The connection state of the transfer discharge switch 69 is an example of a second connection state, and the non-connection state of the transfer discharge switch 69 is an example of a second non-connection state.

  In this embodiment, the cleaning switch 61 is an example of a third switch member, and the transfer switch 63 is an example of a fourth switch member. The ON state of the cleaning switch 61 is an example of a third connection state, and the OFF state of the cleaning switch 61 is an example of a third non-connection state. The on state of the transfer switch 63 is an example of a fourth connection state, and the off state of the transfer switch 63 is an example of a fourth non-connection state.

  Since the printer 200 according to this embodiment includes the cleaning discharge switch 68 and the transfer discharge switch 69 separately, the cleaning discharge switch 68 and the transfer discharge switch 69 can be connected together. Therefore, unlike the printer 100 of the first embodiment, as shown in the time chart of FIG. 7, both the cleaner 56 and the transfer unit 55 can be provided with a period during which the ejection bias is applied simultaneously.

  Specifically, as shown in FIG. 7, after receiving the print instruction, the printer 200 sets the transfer discharge switch 69 to the connected state during the print preparation operation and starts the discharge from the transfer unit 55. The printer 200 sets the cleaning discharge switch 68 in the connected state after a predetermined time Ta after the transfer discharge switch 69 is set in the connected state and while the transfer discharge switch 69 is in the connected state. The predetermined time Ta is a time until a portion of the photoconductor 51 facing the transfer portion 55 reaches a position facing the cleaner 56. The arrangement of the transfer portion 55 and the cleaner 56, the photoconductor It is obtained from the peripheral speed of 51.

  The printer 200 places the transfer / discharge switch 69 in a disconnected state after the transfer / discharge switch 69 is connected, and after a period of time equal to or longer than the period Tt has elapsed. In addition, after the cleaning discharge switch 68 is set in the connected state, the printer 200 sets the cleaning discharge switch 68 in the disconnected state after a time period equal to or longer than the period Tc has elapsed. The period Tt and the period Tc are the same period as each period described in the first embodiment. In the printer 200 according to the present embodiment, an overlap can be provided between the period Tt and the period Tc. Therefore, compared to the printer 100 according to the first embodiment, the total discharge time from both the transfer unit 55 and the cleaner 56 is reduced. It can be done in a short time.

  In addition, after the printing operation is finished, the printer 200 stops applying the transfer bias to the transfer unit 55 and then discharges from the transfer unit 55 with the transfer discharge switch 69 connected. In addition, after the printing operation is finished, the printer 200 stops applying the cleaning bias to the cleaner 56, and then discharges from the cleaner 56 with the cleaning discharge switch 68 connected. Even during discharge after printing, the printer 200 turns off each switch when the period Tt or the period Tc or more elapses. Also in this case, since the period Tt and the period Tc can be overlapped, the total discharge time can be shortened compared to the printer 100 of the first embodiment.

  Also in this embodiment, simultaneous application of the cleaning bias and the discharge bias to the cleaner 56 is avoided. That is, the cleaning switch 61 is turned off while the cleaning discharge switch 68 is in the connected state. Further, simultaneous application of the transfer bias and the discharge bias to the transfer unit 55 is avoided. That is, the transfer switch 63 is turned off while the transfer discharge switch 69 is in the connected state. Further, during the transfer period Ts, the cleaning discharge switch 68 and the transfer discharge switch 69 remain in a disconnected state, and the cleaning discharge switch 68 and the transfer discharge switch 69 are switched during a period when the sheet S is not present in the transfer nip 551. . Therefore, the influence on the image quality by the switching operation of the switch is suppressed.

  As described above in detail, according to the printer 200 of the second embodiment, similarly to the printer 100 of the first embodiment, the power supply for applying the discharge bias to the cleaner 56 and the discharge bias to the transfer unit 55 are applied. A common power supply is used as one discharge power supply 65. Therefore, the number of power supplies can be reduced as compared with the conventional configuration.

  In particular, since the printer 200 of the second embodiment includes the cleaning discharge switch 68 and the transfer discharge switch 69, various connection states can be selected as compared with the first embodiment, and the time required for discharging the toner can be reduced. It can be done in a short time. On the other hand, in the first embodiment, since the number of switches is smaller than that in the second embodiment, the configuration is simple and the cost is low.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention is not limited to a printer, and can be applied to any apparatus having an image forming function in an electrophotographic system, such as a copying machine, a scanner, and a FAX apparatus.

  Further, for example, a power source having an on / off switching function may be used as each power source. In that case, the cleaning switch 61 and the transfer switch 63 may not be provided. That is, instead of the cleaning switch 61 and the transfer switch 63, a switching function of the cleaning power supply 64 and the transfer power supply 66 may be used. Further, if the printer 100 of the first embodiment uses a discharge power source 65 having an on / off switching function, a two-point switch can be used as the discharge switch 62.

  In each of the above embodiments, the cleaning power supply 64 and the discharge power supply 65 are power supplies that output a fixed voltage, but may be power supplies that can change the output voltage. The transfer power supply 66 is a power supply whose output voltage is variable, but may be a fixed voltage power supply.

  For example, in the first embodiment, a mechanical changeover switch is used as the discharge switch 62, but the present invention is not limited to this. In addition, there may be no transition period when switching from one of the first connection state and the second connection state to the other. Alternatively, there may be a period connected to both when switching.

  Further, the cleaner is not limited to the sponge roller, and can be implemented by, for example, a rubber roller, a brush roller, or the like. In addition, the cleaner may be configured by a combination of a scraping member that contacts the photosensitive member 51 and scrapes the toner, and a storage member that electrically draws the toner from the scraping member and temporarily stores the toner. . For example, the present invention can also be implemented with this configuration if the polarity of the bias applied to the storage member can be changed to switch between cleaning and discharge. In that case, the cleaner member may not be a rotating body.

  In each of the above embodiments, the toner discharge is performed before and after the printing operation. However, only one of the front and the rear may be used. If discharging is performed before the printing operation, the cleaner 56 is in a clean state at the time of printing, so that good image quality can be expected. On the other hand, if the discharge is performed after the printing operation, the discharge is performed while the charged state of the toner is good, and there is a high possibility that the amount of toner remaining in the cleaner 56 without being discharged is small.

  Further, in each of the above embodiments, the discharge bias is continuously applied for at least one rotation after the discharge bias is applied to the cleaner 56 or the transfer unit 55. However, the present invention is not limited to this. That is, the application of the discharge bias may be stopped in a time shorter than one rotation. However, it is preferable to apply a discharge bias continuously for one rotation or more because discharge can be performed over the entire circumference of each member.

  In each of the above embodiments, after the printing operation is completed, the discharge from the transfer unit 55 is performed while the cleaning bias is being applied from the cleaning power source 64 to the cleaner 56. However, the present invention is not limited to this. For example, while the cleaning bias is applied to the cleaner 56, neither the transfer unit 55 nor the cleaner 56 may discharge. In this way, the toner discharged from the transfer portion 55 is attracted to the cleaner 56, and a large amount of toner can be suppressed from being collected in the cleaner 56. However, if the cleaning bias is applied to the cleaner 56 and the discharge from the transfer portion 55 is performed simultaneously, the discharge time can be shortened.

  In each of the above embodiments, the discharge from the transfer unit 55 is started before the discharge from the cleaner 56, but the reverse order may be used. For example, after the printing operation is finished, after the application of the cleaning bias from the cleaning power source 64 to the cleaner 56 is finished, the discharge from the cleaner 56 may be performed first, and then the discharge from the transfer unit 55 may be performed.

  In addition, for example, the present invention can be applied to an image forming apparatus that uses toner having a negative polarity in charge polarity. In that case, all the various biases applied to each part may have the opposite polarities to those described in the above embodiments. Further, the toner collection method by the developing unit 54 is not limited to the examples described in the above embodiments.

  The processing disclosed in the embodiments may be executed by a single CPU, a plurality of CPUs, hardware such as an ASIC, or a combination thereof. Further, the processing disclosed in the embodiment can be realized in various modes such as a recording medium or a method recording a program for executing the processing.

31 CPU
DESCRIPTION OF SYMBOLS 51 Photoconductor 54 Developing part 55 Transfer part 56 Cleaner 61 Cleaning switch 62 Discharge switch 63 Transfer switch 64 Cleaning power supply 65 Discharge power supply 66 Transfer power supply 68 Cleaning discharge switch 69 Transfer discharge switch 100, 200 Printer

Claims (13)

A photoreceptor,
A developing member for supplying toner onto the photosensitive member and collecting toner on the photosensitive member;
A transfer rotator for transferring the toner on the photoreceptor to a sheet;
A cleaning member for removing toner on the photoconductor from the photoconductor;
A cleaning power source for outputting a cleaning bias, which is a bias having a polarity opposite to the charging polarity of the toner, to the cleaning member;
A transfer power source that outputs a transfer bias, which is a bias of a polarity opposite to the charging polarity of the toner, to the transfer rotator;
An ejection power source that outputs an ejection bias that is a bias of the same polarity as the charging polarity of the toner;
A switch member;
A control unit;
With
The controller is
The switch member includes a first connection state in which the discharge power source and the cleaning member are connected and the discharge power source and the transfer rotator are not connected, and the discharge power source and the transfer rotator are connected. , Switching to a second connection state in which the discharge power source and the cleaning member are not connected.
An image forming apparatus. An image forming apparatus according to claim 1,
The controller is
Switching the state of the switch member during a period when there is no sheet in the transfer nip between the photoconductor and the transfer rotator,
An image forming apparatus. An image forming apparatus according to claim 2,
The controller is
When a print instruction is received, the switch member is set to the second connection state before starting image formation, and then the switch member is set to the first connection state.
An image forming apparatus. An image forming apparatus according to claim 2 or claim 3, wherein
The controller is
When printing is finished, the switch member is set to the second connection state, and then the switch member is set to the first connection state;
An image forming apparatus. An image forming apparatus according to any one of claims 1 to 4, comprising:
The cleaning member is a rotating body,
The controller is
When the switch member is in the first connection state, the first connection state is continued for a time longer than the time of one rotation of the cleaning member;
An image forming apparatus. An image forming apparatus according to any one of claims 1 to 5, comprising:
The controller is
When the switch member is in the second connection state, the second connection state is continued for a time longer than a time corresponding to one rotation of the transfer rotator,
An image forming apparatus. An image forming apparatus according to any one of claims 1 to 6, comprising:
A cleaning switch member that is a switch member different from the switch member;
The controller is
Switching the cleaning switch member between a cleaning connection state in which the cleaning power source and the cleaning member are connected and a cleaning non-connection state in which the cleaning power source and the cleaning member are not connected;
While the discharge bias is applied from the discharge power source to the cleaning member, the cleaning switch member is in the cleaning non-connected state.
An image forming apparatus. An image forming apparatus according to any one of claims 1 to 7,
A transfer switch member that is a switch member different from the switch member;
The controller is
The transfer switch member is switched between a transfer connection state in which the transfer power source and the transfer rotator are connected, and a transfer non-connection state in which the transfer power source and the transfer rotator are not connected. ,
While the discharge bias is applied from the discharge power source to the transfer rotator, the transfer switch member is in the transfer non-connected state.
An image forming apparatus. An image forming apparatus according to any one of claims 1 to 8, comprising:
The controller is
While the transfer bias is applied from the transfer power source to the transfer rotator, the switch member is in a state where the discharge power source is not connected to either the cleaning member or the transfer rotator.
An image forming apparatus. A photoreceptor,
A developing member for supplying toner onto the photosensitive member and collecting toner on the photosensitive member;
A transfer rotator for transferring the toner on the photoreceptor to a sheet;
A cleaning member for removing toner on the photoconductor from the photoconductor;
A cleaning power source for outputting a cleaning bias, which is a bias having a polarity opposite to the charging polarity of the toner, to the cleaning member;
A transfer power source that outputs a transfer bias, which is a bias of a polarity opposite to the charging polarity of the toner, to the transfer rotator;
An ejection power source that outputs an ejection bias that is a bias of the same polarity as the charging polarity of the toner;
A first switch member;
A second switch member;
A control unit;
With
The controller is
The first switch member, a first connection state in which the discharge power source and the cleaning member are connected, and a first non-connection state in which the discharge power source and the cleaning member are not connected; Switch to
The second switch member includes a second connection state in which the discharge power source and the transfer rotator are connected, and a second non-connection state in which the discharge power source and the transfer rotator are not connected. And switch to
An image forming apparatus. The image forming apparatus according to claim 10, comprising:
The controller is
While the first switch member is in the first connection state, the second switch member is switched to the second connection state, or while the second switch member is in the second connection state. , Switching the first switch member to the first connection state,
An image forming apparatus. An image forming apparatus according to claim 10 or claim 11,
A third switch member;
The controller is
The third switch member, a third connection state in which the cleaning power source and the cleaning member are connected, and a third non-connection state in which the cleaning power source and the cleaning member are not connected; Switch to
While the discharge bias is applied to the cleaning member from the discharge power supply, the third switch member is brought into the third non-connected state.
An image forming apparatus. An image forming apparatus according to any one of claims 10 to 12,
A fourth switch member;
The controller is
The fourth switch member includes a fourth connection state in which the transfer power source and the transfer rotator are connected, and a fourth non-connection state in which the transfer power source and the transfer rotator are not connected. And switch to
While the ejection bias is applied from the ejection power source to the transfer rotator, the fourth switch member is brought into the fourth non-connected state.
An image forming apparatus.

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