JP6643028B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic recording system such as a laser printer, a copying machine, a facsimile, and the like.

  2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus, a color image forming apparatus adopting an in-line method in which image forming units of respective colors are juxtaposed has been known. This color image forming apparatus includes a plurality of image forming units each including an electrophotographic photoreceptor (hereinafter, referred to as a photoreceptor drum) and process units such as a charging unit, a developing unit, and a cleaning unit that act on the photoreceptor drum. Juxtaposed. Then, images are sequentially transferred to an intermediate transfer belt or a transfer material on a transport belt which is arranged to face the plurality of image forming units.

  In such a color image forming apparatus, images are superimposed due to a difference in mechanical accuracy in an image forming unit of each color (for example, yellow (Y), magenta (M), cyan (C), black (K)). Color misalignment can occur when combined. In particular, in a configuration in which the laser scanner and the photosensitive drum are independently provided in the image forming units for each color, the positional relationship between the laser scanner and the photosensitive drum differs for each color. As a result, the laser scanning positions on the photosensitive drum cannot be synchronized with each other, causing color shift.

  To correct these color shifts, the color image forming apparatus performs color shift correction control. In Patent Document 1, a common current detection circuit is provided for independent high-voltage power supplies to be supplied to image forming units for multiple colors in order to accurately correct color misregistration generated when images of multiple colors are superimposed. An arrangement is disclosed.

JP 2012-032777 A

  However, in a circuit configuration in which a plurality of independent high-voltage power supplies are connected by a common current detection circuit as disclosed in Patent Document 1, image defects are caused by the independent high-voltage power supplies affecting each other. There was a problem that caused.

  Specifically, when the independent second high-voltage power supply is turned on while the independent first high-voltage power supply is in the ON state, the charge current generated in the second high-voltage power supply circuit is instantaneously supplied to the current detection circuit. And the potential of the input / output terminal fluctuates due to the resistance component of the current detection circuit. This potential fluctuation affects the first high-voltage power supply circuit, and the voltage value output from the first high-voltage power supply circuit fluctuates.

  Therefore, for example, when switching to the full-color mode during continuous paper feeding in the mono-color mode, the charging voltage of K fluctuates. Specifically, in the case where the charging voltage of Y, M, and C is applied while the charging voltage of K is being applied, the charging current supplied to the power supply circuit of Y, M, and C instantaneously flows into the current detection circuit. As a result, the charging voltage of Bk fluctuates. As a result, image transfer such as a horizontal streak image occurs due to the transfer of the toner to the portion where the charge output of the K photoconductor drum is reduced.

  The above problem is not limited to a circuit configuration in which an independent high-voltage power supply is connected by a common current detection circuit, and occurs in a circuit configuration in which an independent high-voltage power supply is grounded via a common resistance component. obtain. Further, for example, this may occur even when the independent high-voltage power supply is on a common board and the common board is not grounded to the frame ground (the body housing) of the apparatus main body.

  Therefore, an object of the present invention is to suppress image defects due to the influence of independent high voltage power supplies on each other in a configuration in which a plurality of independent high voltage power supplies are connected by a common current detection circuit.

  In order to achieve the above object, the present invention provides first and second photoconductors that are driven to rotate, first and second charging units that respectively charge the first and second photoconductors at charging positions, First and second developing means for attaching toner to the first and second photoreceptors at developing positions, and first and second developing means for transferring the toner images formed on the first and second photoreceptors to a member to be transferred. A transfer unit, a first power supply for supplying a charging voltage to the first charging unit, and a second power supply for supplying a predetermined voltage to at least one of the second charging unit, the second developing unit, and the second transfer unit A separating mechanism for moving the first developing unit from a contact position where the developing unit is in contact with the first photoconductor to a separating position separated from the first photoconductor, and a control unit for controlling the separating mechanism Wherein the first power supply and the second power supply Are grounded via a common resistance component, and when the first power supply is supplying the charging voltage, the second power supply does not supply a voltage at the first timing or the predetermined voltage When the supply of the predetermined voltage is started from a state in which a lower voltage is supplied, the control unit determines that the area of the first photoconductor at the charging position at the first timing reaches the developing position. Before the second timing, the first developing unit is moved to the separation position by the separation mechanism.

  According to the present invention, even if the voltage value output from the first power supply fluctuates due to the turning on of the second power supply, the development is performed before the surface potential portion of the photosensitive drum affected by the fluctuation reaches the developing means. The means is separated from the photoreceptor drum. This makes it possible to provide a good image without image defects such as horizontal stripes without transferring the developer to the surface potential portion of the photosensitive drum affected by the fluctuation.

FIG. 2 is a diagram illustrating an image forming apparatus according to a first embodiment. Sectional view of the process cartridge in the first embodiment FIG. 9 is a diagram illustrating a development contact / separation state of the process cartridge according to the first embodiment. Configuration diagram of the high-voltage power supply device in the first embodiment Configuration diagram of charging high-voltage power supply circuit and current detection circuit in the first embodiment FIG. 7 is a diagram showing a timing chart at the time of mono-full switching in the first embodiment. Configuration diagram of a high-voltage power supply device according to a modification of the first embodiment FIG. 8 is a diagram showing a timing chart at the time of mono-full switching in a modification of the first embodiment. Configuration diagram of the high-voltage power supply device in the second embodiment FIG. 10 is a diagram showing a timing chart at the time of mono-full switching in the second embodiment. Schematic view of the main body sheet metal frame in the third embodiment. Configuration diagram of the charging high-voltage power supply circuit in the third embodiment

  Hereinafter, preferred embodiments of the present invention will be illustratively described in detail with reference to the drawings. However, dimensions, materials, shapes, relative arrangements, and the like of the components described in the following embodiments should be appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

[Example 1]
<Image forming apparatus>
FIG. 1 is a schematic configuration diagram of a color image forming apparatus 100 according to Embodiment 1 of the present invention.

  In the image forming apparatus 100, a laser scanner 11, an intermediate transfer belt 13, a fixing film 24, a pressure roller 25, a paper feed tray 19, a paper feed roller 20, and the like are provided.

  Further, four process cartridges P (PY, PM, PC, PK) of a first process cartridge PY, a second process cartridge PM, a third process cartridge PC, and a fourth process cartridge PK are horizontally arranged. ing. Each of the first to fourth process cartridges P (PY, PM, PC, PK) has the same electrophotographic image forming process mechanism except that the color of the developer is different.

  Here, four process cartridges are illustrated as the plurality of image forming units. However, the number of process cartridges that can be removably mounted on the image forming apparatus is not limited to this, and can be appropriately set as needed.

  Each of the first to fourth process cartridges P (PY, PM, PC, PK) includes a developing unit 4 having a developing roller 41 for developing an electrostatic latent image on the photosensitive drum 1 as an image carrier. Having.

  The first process cartridge PY contains a yellow (Y) developer in the developing unit 4, and forms a yellow developer image on the surface of the photosensitive drum 1.

  The second process cartridge PM contains a magenta (M) developer in the developing unit 4 and forms a magenta developer image on the surface of the photosensitive drum 1.

  The third process cartridge PC accommodates a cyan (C) developer in the developing unit 4 and forms a cyan developer image on the surface of the photosensitive drum 1.

  The fourth process cartridge PK contains a black (K) developer in the developing unit 4 and forms a black developer image on the surface of the photosensitive drum 1.

  The recording medium S stacked and stored in the paper feed tray 19 is fed by a paper feed roller 20 rotating in a clockwise direction (arrow W direction) in the figure, and a contact between the belt drive roller 14 and the secondary transfer roller 18 is made. (Hereinafter referred to as “nip portion”).

  The photoreceptor drum 1 is rotating in a counterclockwise direction (direction of arrow K) in the figure, and an electrostatic latent image is sequentially formed on an outer peripheral surface thereof at an exposure position by a laser beam L from a laser scanner (exposure means) 11. It is formed. Subsequently, the electrostatic latent image is developed at a developing position by a developing roller 41 as a developing unit (toner is made to adhere), and a toner image (developer image) is formed on the photosensitive drum 1. The developing position is a position where the photosensitive drum 1 is made to adhere the toner by the developing roller 41, and is a position where the photosensitive drum 1 and the developing roller 41 face each other.

  The toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt (member to be transferred) by a primary transfer roller 17 as a transfer unit facing the photosensitive drum via an intermediate transfer belt 13 as an intermediate transfer body at a transfer position. 13 is transferred. When a color image is formed, the yellow (Y), magenta (M), cyan (C), and black (K) colors are developed on the photosensitive drum 1, and the formed toner images are transferred to an intermediate transfer belt. 13 are sequentially transferred. The transfer position is a position where the toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer belt 13, and is a position where the photosensitive drum 1 and the primary transfer roller 17 are opposed via the intermediate transfer belt 13. .

  Next, the toner image formed on the intermediate transfer belt 13 is transferred to a recording medium (sheet) S sent to a contact nip portion between the belt drive roller 14 and the secondary transfer roller 18.

  Further, the recording medium S onto which the toner image has been transferred is sent to a contact nip portion between the fixing film 24 and the pressure roller 25, where the toner image is heated and pressed, and the toner image is fixed on the recording medium S. The recording medium S on which the toner image has been fixed is discharged to a discharge tray 27 by a pair of discharge rollers 26.

<Configuration of process cartridge>
FIG. 2 is a sectional view showing a section when the process cartridge P is cut in a direction perpendicular to the axial direction of the photosensitive drum 1. In FIG. 2, the photosensitive drum 1 is rotated at a predetermined speed in a counterclockwise direction (arrow K direction) by a driving source (not shown), and the developing roller 41 is rotated in a clockwise direction (arrow L direction) at a predetermined speed.

  In this embodiment, the process cartridge P includes a cleaner unit 5 and a developing unit 4 rotatably coupled to the cleaner unit 5. The cleaner unit 5 is a first unit (photosensitive drum unit) that holds the photosensitive drum 1, and the developing unit 4 is a second unit that holds the developing roller 41.

  A charging roller (charging means) 3 provided in the cleaner unit 5 is a contact charging type charging member which abuts on the photosensitive drum 1 at a charging position and is driven to rotate. The cleaning blade (cleaning means) 51 is disposed with its tip end in contact with the photosensitive drum 1. The cleaning blade 51 serves to remove the toner remaining on the photosensitive drum 1. The transfer residual toner removed by the cleaning blade 51 is stored in a toner storage section 52 in the cleaner unit 5.

  The developing unit 4 has a developing roller 41 as a developing unit and a developing blade 42. The developing unit 4 further has a developing chamber (developer storing section) 43 for storing the toner. The developing roller 41 is disposed in the developing chamber 43, and the developing blade 42 is disposed such that the tip end thereof is in contact with the developing roller 41. The developing blade 42 functions to regulate the toner on the peripheral surface of the developing roller 41 to a thin layer.

  The developing unit 4 is urged by a pressure spring 53 which is an elastic member, and the developing roller 41 abuts on the photosensitive drum 1 with the rotation center X as a rotation axis. More specifically, the developing unit 4 is pressed in the direction of arrow G shown in FIG. 2 by the urging force of the pressure spring 53, and a moment in the direction of arrow J1 acts about the rotation center X. I have. As a result, the developing roller 41 can contact the photosensitive drum 1 with a predetermined pressure. The position of the developing roller 41 of the developing unit 4 at this time is referred to as a contact position.

  When the image forming apparatus 100 is not performing image formation (in a standby state), the developing roller 41 and the photosensitive drum 1 are separated from each other. The position of the developing roller 41 of the developing unit 4 at this time is referred to as a separation position. The reason why the developing roller 41 is maintained at the separated position in this way is to suppress the dent mark of the developing roller 41 caused by the developing roller 41 being in contact with the photosensitive drum 1 for a long period of time and an image defect due to the mark. The protruding member 44 is a member for separating the developing roller 41 and the photosensitive drum 1 from each other, and is provided at an end of the developing unit 4 in the axial direction (longitudinal direction). The developing separation mechanism for separating the developing roller 41 from the photosensitive drum 1 will be described in detail below.

<Development separation mechanism / operation>
FIG. 3 is a cross-sectional view showing the relationship between the process cartridge P and the developing separation mechanism 60. 62x and 62y are moving members located below the process cartridge P (PY, PM, PC, PK). The process cartridges PY, PM, and PC can move in the directions of arrows M and N in conjunction with the moving member 62x, and the process cartridge PK can move in the directions of the arrows M and N individually.

  Further, the moving members 62x and 62y are connected to circular cams 64x and 64y, respectively, and cam driving shafts 65x and 65y are connected to positions away from the center of a circle forming the cams 64x and 64y. The cams 64x and 64y receive driving force from a driving source (not shown) provided in the image forming apparatus 100, rotate about the cam driving shafts 65x and 65y as rotation centers, and move the moving members 62x and 62y in a substantially horizontal direction ( (In the directions of arrows M and N).

  By the rotation of the cams 64x and 64y, the moving members 62x and 62y cause the “standby state” (see FIG. 3A), the “full color image forming state” (see FIG. 3B) described below, and “ 3 (see FIG. 3C). That is, the moving members 62x and 62y are in a "standby state" in which the developing roller 41 and the photosensitive drum 1 in all the process cartridges PY, PM, PC, and PK are separated by the rotation of the cams 64x and 64y (FIG. 3A ) See). The moving members 62x and 62y rotate the cams 64x and 64y so that the developing roller 41 and the photosensitive drum 1 in all the process cartridges PY, PM, PC, and PK come into contact with each other in the "full-color image forming state" (FIG. Go to b)). In addition, the moving members 62x and 62y move to a “monocolor image forming state” (see FIG. 3C) in which only the developing roller 41 of the process cartridge PK contacts the photosensitive drum 1 by rotation of the cams 64x and 64y. .

  As described above, when image formation is not performed, the image forming apparatus 100 separates the developing roller 41 from the photosensitive drum 1 as shown in FIG. 3A (“standby”). State "). At this time, the projecting members 44 of all the process cartridges PY, PM, PC, and PK receive a pressing force from the separating member 61 of the developing separating mechanism 60 in the direction of arrow M shown in FIG. Thus, the developing unit 4 of each process cartridge P rotates about the rotation center X as a rotation axis, and the developing roller 41 and the photosensitive drum 1 are separated.

  Then, by operating the developing separation mechanism 60 once from the “standby state”, a transition is made to the “full color image forming state” (see FIG. 3B). Specifically, by moving both the moving member 62x and the moving member 62y in the direction of arrow N shown in FIG. 3A, the projecting members 44 of all the process cartridges PY, PM, PC, and PK have received the moving members 62x and 62y. The pressing force from the separating member 61 is released. As a result, the developing rollers 41 in all the process cartridges PY, PM, PC, and PK are moved from the separated position to the contact position by the force of the pressure spring 53 and contact the photosensitive drum 1. In this way, the developing rollers 41 of all the process cartridges PY, PM, PC, and PK come into contact with the photosensitive drum 1, and a full-color image can be formed.

  The developing / separating mechanism 60 is further operated once from the “full-color image forming state” to transition to the “mono-color image forming state” (see FIG. 3C). Specifically, by moving only the moving member 62x in the direction of the arrow M shown in FIG. 3A, the projecting members 44 of the process cartridges PY, PM, and PC are moved from the separating member 61 of the developing separating mechanism 60 in FIG. A pressing force is applied in the direction of arrow M shown in FIG. As a result, the developing units 4 of the process cartridges PY, PM, and PC rotate about the rotation center X as a rotation axis, and the developing roller 41 and the photosensitive drum 1 are separated. On the other hand, the process cartridge PK keeps the developing roller 41 and the photosensitive drum 1 in contact with each other. In this state, full-color image formation cannot be performed, and only mono-color image formation can be performed.

  Then, the developing / separating mechanism 60 is operated once more from the “mono-color image forming state”, so that the state shifts again to the “standby state” (see FIG. 3A). Specifically, by moving only the moving member 62y in the direction of arrow M shown in FIG. 3, the projecting member 44 of the process cartridge PK is pushed from the separation member 61 of the developing separation mechanism 60 in the direction of arrow M shown in FIG. Receive pressure. As a result, the developing unit 4 of the process cartridge PK rotates about the rotation center X as a rotation axis, and the developing roller 41 and the photosensitive drum 1 are separated. As a result, the developing rollers 41 in all the process cartridges PY, PM, PC, and PK are separated from the photosensitive drum 1.

  As described above, the image forming apparatus 100 switches from the “standby state” → “full-color image formation state” → “monocolor image formation state” → “standby state” →... ing.

<Structure of high-voltage power supply unit>
Next, the configuration of the high-voltage power supply in the image forming apparatus of FIG. 1 will be described with reference to FIG. The high-voltage power supply circuit device includes a charging high-voltage power supply circuit 33b as a first power supply for supplying a voltage (charging voltage) to the charging roller 3K of the process cartridge PK. The high-voltage power supply circuit device includes a charging high-voltage power supply circuit 33a as a second power supply for supplying a voltage (charging voltage) to the charging rollers 3Y, 3M, and 3C of the process cartridges PY, PM, and PC. Further, the high-voltage power supply circuit device includes development high-voltage power supply circuits 34Y, 34M, 34C, and 34K, a primary transfer high-voltage power supply circuit 36, and a secondary transfer high-voltage power supply circuit 38. The charging high-voltage power supply circuit 33b applies a predetermined voltage to the charging roller 3K, and the charging high-voltage power supply circuit 33a applies a predetermined voltage to the charging rollers 3Y, 3M, and 3C except for the charging roller 3K. As a result, a background potential is formed on the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K at the charging position, and the laser beam L is applied to make it possible to form an image as an electrostatic latent image potential.

  Further, the developing high-voltage power supply circuits 34Y, 34M, 34C, and 34K individually apply a predetermined voltage to the developing rollers 41Y, 41M, 41C, and 41K, respectively, so that the electrostatic latents of the photosensitive drums 1Y, 1M, 1C, and 1K are applied. The toner is placed on the image potential portion to form a toner image. The primary transfer high-voltage power supply circuit 36 applies a predetermined voltage to each of the primary transfer rollers 17Y, 17M, 17C, and 17K to transfer the toner images of the photosensitive drums 1Y, 1M, 1C, and 1K to the intermediate transfer belt 13. Transcribe. The charging means (charging roller 3K) for performing charging with the voltage supplied from the first power supply (charging high-voltage power supply circuit 33b) is a first charging means, and a photosensitive member (photosensitive drum 1K) charged by the first charging means. Is the first photosensitive member. Further, a developing unit (developing roller 41K) for attaching toner to the first photoconductor is a first developing unit, and a transfer unit (primary transfer roller 17K) for transferring a toner image from the first photoconductor is a first transfer unit. I do. A charging unit (charging rollers 3Y, 3M, 3C) for charging with a voltage supplied from a second power supply (charging high-voltage power supply circuit 33a) includes a second charging unit and a photosensitive member (photosensitive member) charged by the second charging unit. The body drums 1Y, 1M, 1C) are the second photoconductors. Further, a developing unit (developing rollers 41Y, 41M, 41C) for attaching toner to the second photoconductor is used as a first developing unit, and a transfer unit (primary transfer rollers 17Y, 17M, and 17M) for transferring a toner image from the second photoconductor is used. 17C) is a second transfer unit.

  The secondary transfer high-voltage power supply circuit 38 transfers the toner image on the intermediate transfer belt 13 to the recording medium S by applying (supplying) a secondary transfer voltage to the secondary transfer roller 18 as a third transfer unit.

  The charging high-voltage power supply circuit 33a and the charging high-voltage power supply circuit 33b are connected by a current detection circuit 37 as a common resistance component. This is to suppress a color shift of the process cartridge P (PY, PM, PC, PK). Specifically, in the process cartridge P of each color, the photosensitive drum 1 (Y, M, C, K) is separated from the photosensitive drum 1 (Y, M, C, K) while the developing roller 41 (Y, M, C, K) is separated. The surface of Y, M, C, K) is uniformly set to the background potential, and then the laser light L is irradiated. The value of the current flowing from the charging roller 3 (Y, M, C, K) to the current detection circuit 37 is different between the case where the surface of the photosensitive drum 1 (Y, M, C, K) is at the background potential and the potential of the electrostatic latent image. It differs from when. Therefore, by reading the time from the laser irradiation timing to the timing when the laser-irradiated electrostatic latent image potential portion reaches the charging roller 3 (Y, M, C, K), the laser irradiation timing of the process cartridge of each color is read. Fine-tuning to suppress color misregistration.

<Circuit diagram of high voltage power supply>
Next, the configurations of the charging high-voltage power supply circuits 33a and 33b and the current detection circuit 37 in the high-voltage power supply device of FIG. 4 will be described with reference to FIG.

  In FIG. 5, a control unit (control means) 54 includes a CPU 321, an ASIC 322, a RAM 323, and an EEPROM 322. A detailed description of the functions will be omitted. Transformers 62a and 62b boost the voltage of the AC signals generated by the drive circuits 61a and 61b to tens of times the amplitude. Rectifier circuits 51a and 52b composed of diodes 64a, 64b, 65a and 65b and capacitors 63a, 63b, 66a and 66b rectify and smooth the boosted AC signal. The rectified and smoothed voltage signal is output as a DC voltage to output terminals 53a and 53b, respectively. The comparators 60a and 60b drive the drive circuits so that the voltages of the output terminals 53a and 53b divided by the detection resistors 67a, 67b, 68a and 68b are equal to the set values 55a and 55b set by the control unit 54. The output voltages of 61a and 61b are controlled respectively. Then, according to the voltage of the output terminal 53a, a current flows through the charging rollers 3Y, 3M, 3C, the photosensitive drums 1Y, 1M, 1C and the ground. Further, according to the voltage of the output terminal 53b, a current flows through the charging roller 3K, the photosensitive drum 1K, and the ground.

  The current detection circuit 37 is inserted between the secondary circuits 50a and 50b of the transformers 62a and 62b and the ground point 57. Here, since the input terminal of the operational amplifier 70 has a high impedance and almost no current flows, the DC current flowing from the ground point 57 to the output terminals 53a and 53b via the secondary circuits 50a and 50b of the transformers 62a and 62b is: Almost all are configured to flow through the resistor 71. Further, since the inverting input terminal of the operational amplifier 70 is connected to the output terminal via the resistor 71, it is virtually grounded to the reference voltage 73 connected to the non-inverting input terminal. Accordingly, a detection voltage 56 appears at the output terminal of the operational amplifier 70 in proportion to the amount of current flowing through the output terminals 53a and 53b. The capacitor 72 stabilizes the inverting input terminal of the operational amplifier 70.

<Developing contact / separation control during printing>
In the image forming apparatus 100 having the above-described configuration, when the charging high-voltage power supply circuit 33b is turned on from OFF to ON when the charging high-voltage power supply circuit 33b is in the ON state, the charging roller 3K supplied with voltage from the charging high-voltage power supply circuit 33b. In the area of the photosensitive drum 1 </ b> K charged by the above, the surface potential fluctuates. In the following description, the region of the photosensitive drum in which the surface potential has changed is referred to as a surface potential change portion.

  Therefore, in the present embodiment, when the charging high-voltage power supply circuit 33a is switched from OFF to ON while the charging high-voltage power supply circuit 33b is in the ON state, the surface potential variation portion of the photosensitive drum 1K contacts the developing roller 41K. It is characterized in that the developing roller 41K is separated from the photosensitive drum 1K before reaching the contact portion. The operation of the developing / separating mechanism 60 for bringing the developing roller and the photosensitive drum into contact with / separating from each other is controlled by the control unit 54.

  Specifically, control of development contact / separation when switching from the mono-color mode to the full-color mode during continuous printing (hereinafter referred to as “mono-full switching”) will be described.

  FIG. 6 shows a timing chart at the time of mono-full switching in the present embodiment. In FIG. 6, the section M is printed in the mono color mode. That is, the section M is a first mode in which a toner image is formed on the photosensitive drum 1K without forming a toner image on the photosensitive drums 1Y, 1M, and 1C. Therefore, during monocolor printing, the charging high-voltage power supply circuit 33a is in the OFF state. This is to suppress unnecessary discharge deterioration of the photosensitive drums 1Y, 1M, and 1C and extend the life of the process cartridges PY, PM, and PC. That is, when the charging high-voltage power supply circuit 33a is in the OFF state, the voltage supplied to the output terminal 53a is 0 (no voltage is supplied) or a standby voltage for standby is supplied. The development contact / separation state of the image forming apparatus 100 at this time is a “monocolor image formation state” (see FIG. 3C).

  When a full-color image signal is received from a host computer (not shown) during the mono-color printing, the charging high-voltage power supply circuit 33a is prepared for the full-color printing at the timing of starting the post-rotation operation after the completion of the mono-color printing (a in FIG. 6). Turn ON. At this time, an analog signal is sent from the control unit 54 so that a desired voltage is output from the output terminal 53a to the charging rollers 3Y, 3M, 3C. Here, the post-rotation operation is an operation after the end of the primary transfer in the process cartridge P (PK) of the last page of the continuous printing.

  In the high-voltage power supply circuit of the image forming apparatus 100, when the charging high-voltage power supply circuit 33b is turned on and the charging high-voltage power supply circuit 33a is switched from OFF to ON (first timing), a voltage is sharply output to the output terminal 53a. As a result, a charging current flows through the current detection circuit 37 instantaneously. This is because the charging high-voltage power supply circuit 33a switches from the OFF state in which the standby voltage is supplied to the output terminal 53a or in which the voltage is not supplied to the ON state, so that the voltage (predetermined voltage) larger than the standby power. Is supplied to the output terminal 53a. Here, the first timing is a timing after the end of the mono-color mode (first mode) and before the start of execution of a full-color mode (second mode) described later. When this charge current flows through the resistor 71, the potentials of the output terminal and the inverting input terminal of the operational amplifier 70 change. As a result, the reference voltage value (the voltage value of A in FIG. 5) of the charging high-voltage power supply circuit 33b changes, so that the DC voltage output to the output terminal 53b, that is, the charging roller 3K changes. Due to this voltage change, the surface potential of the portion of the photosensitive drum 1K at the charging position changes. The surface potential variation portion of the photosensitive drum 1K reaches a contact portion with the developing roller 41K with the rotational driving in the direction of arrow K in FIG. 2 (c in FIG. 6). At this time, the developing roller 41K needs to be separated from the photosensitive drum 1K so that the toner does not transfer from the developing roller 41K to the surface potential changing portion of the photosensitive drum 1K. For this purpose, the developing / separating mechanism 60 may be operated once to transition from the “monocolor image forming state” to the “standby state” (see FIG. 3A). Therefore, before the timing (c in FIG. 6, the second timing) at which the surface potential changing portion at the charging position at the first timing of the photosensitive drum 1K reaches the contact portion (developing position) with the developing roller 41K. What is necessary is just to be in a "standby state". That is, it is sufficient that at least the developing roller 41K is at the separated position before the second timing (c in FIG. 6) when the surface potential changing portion of the photosensitive drum 1K reaches the contact portion with the developing roller 41K.

  In the present embodiment, the ON timing of the developing separation mechanism 60 is set to be the same as the ON timing of the charging high-voltage power supply circuit 33a (FIG. 6A). As a result, the "standby state" is set at a timing (b in FIG. 6) before the timing (c in FIG. 6) at which the surface potential changing portion of the photosensitive drum 1K reaches the contact portion with the developing roller 41K.

  Next, in order to perform printing in the full-color mode, it is necessary to operate the developing separation mechanism 60 once more to attain the “full-color image forming state”. At this time, the ON timing of the developing separation mechanism 60 is set such that the toner is not transferred from the developing roller 41K to the photosensitive drum 1K after the surface potential changing portion of the photosensitive drum 1K passes through the contact portion with the developing roller 41K. Should be fine. Therefore, the second operation of the developing separation mechanism 60 is started after the lapse of the time α for passing through the contact portion with the developing roller 41K (FIG. 6D). Then, the timing at which the developing rollers 41Y, 41M, 41C, and 41K of all the process cartridges PY, PM, PC, and PK come into contact with the photosensitive drums 1Y, 1M, 1C, and 1K to be in a “full-color image forming state” (FIG. In 6e), full-color image formation is started. The full-color image forming state is a second mode in which a toner image is formed on each of the photosensitive drums 1Y, 1M, 1C, and 1K.

  According to this control, the toner does not transfer to the surface potential variation portion of the photosensitive drum 1K generated by turning on the charging high-voltage power supply circuit 33a while the charging high-voltage power supply circuit 33b is in the ON state, thereby causing an image defect. And good images can be provided.

  In the ON state, the charging high-voltage power supply circuit 33a supplies a voltage (predetermined voltage) higher than the standby power to the output terminal 53a. The predetermined voltage is adjusted so that the photosensitive drums 1Y, 1M, and 1C are charged to a desired potential in order to form a full-color image, or an appropriate charging voltage for image formation is supplied. Adjustment voltage having a value close to the charging voltage for image formation. In the present embodiment, the predetermined voltage is set to about -1000V to -1100V.

<Operation and effect of the present embodiment>
As described above, in an image forming apparatus in which the independent first charging high-voltage power supply circuit 33b and the second charging high-voltage power supply circuit 33a are grounded via the common current detection circuit 37, the first charging high-voltage power supply When switching the second charging high-voltage power supply circuit 33a from OFF to ON while the circuit 33b is ON, the voltage output from the first charging high-voltage power supply circuit 33b by turning on the second charging high-voltage power supply circuit 33a. Values fluctuate. According to this embodiment, the voltage is supplied from the first charging high-voltage power supply circuit 33b before the surface potential portion of the photosensitive drum 1K affected by the above-mentioned fluctuation reaches the contact portion with the developing roller 41K. The developing roller 41K on the side to be cleaned is separated from the photosensitive drum 1K. As a result, it is possible to provide a good image without image defects such as horizontal stripes without transferring the developer to the surface potential fluctuation portion of the photosensitive drum affected by the fluctuation.

[Modification 1]
A modified example of the first embodiment will be described as an example. In the image forming apparatus 100 applied in the present modification, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted.

<Features of this modification>
The image forming apparatus 100 according to the present modification supplies a voltage to the primary transfer high-voltage power supply circuit 36b as a first power supply for supplying a voltage to the transfer roller 17K, and supplies a voltage to the transfer rollers 17Y, 17M, and 17C excluding the transfer roller 17K. A primary transfer high-voltage power supply circuit 36a as a second power supply exists independently of each other, and is connected by a common current detection circuit 37.

  FIG. 7 shows a configuration diagram of a high-voltage power supply device according to this modification. As shown in FIG. 7, the primary transfer high voltage power supply circuit 36a is connected so that a voltage is supplied to the transfer rollers 17Y, 17M, and 17C, and the primary transfer high voltage power supply circuit 36b is supplied with a voltage to the transfer roller 17K. It is connected to the. The primary transfer high-voltage power supply circuit 36a and the primary transfer high-voltage power supply circuit 36b are connected by a common current detection circuit 37.

  The high-voltage power supply circuit is the same as that of FIG. 5 described in the first embodiment, and a voltage is supplied from the output terminal 53a to the transfer rollers 17Y, 17M, and 17C, and from the output terminal 53b to the transfer roller 17K.

<Developing contact / separation control during printing>
Hereinafter, specific control at the time of mono-full switching in the present modified example will be described.

  FIG. 8 shows a timing chart at the time of mono-full switching in the present modified example. As in the first embodiment (FIG. 6), the section M prints in the monocolor mode, and a indicates the start timing of the post-rotation operation.

  During mono-color printing, when the primary transfer high-voltage power supply circuit 36a is in the OFF state, the voltage supplied to the output terminal 53a is 0 (voltage is not supplied) or a standby voltage for standby is supplied. When a full-color image signal is received during mono-color printing, the primary transfer high-voltage power supply circuit 36a is switched from OFF to ON at the first timing (a in FIG. 8) in preparation for full-color printing. Similarly, in the high-voltage power supply circuit of this modification, when the primary transfer high-voltage power supply circuit 36a is switched from OFF to ON while the primary transfer high-voltage power supply circuit 36b is in the ON state, the charging current is instantaneously supplied to the current detection circuit 37. Flows. This is because the primary transfer high-voltage power supply circuit 36a switches from an OFF state in which the standby voltage is supplied to the output terminal 53a or in which the voltage is not supplied to an ON state, so that a voltage larger than the standby power (predetermined voltage). This is because it operates so as to supply the voltage (voltage) to the output terminal 53a. As a result, the reference voltage value (the voltage value A in FIG. 5) of the primary transfer high-voltage power supply circuit 36b changes, so that the DC voltage output to the output terminal 53b, that is, the transfer roller 17K changes. Due to this voltage fluctuation, an overcurrent instantaneously flows from the transfer roller 17K to the photosensitive drum 1K, and a transfer memory is generated. This transfer memory cannot be suppressed by one charging unit, and the surface potential of the photosensitive drum 1K becomes uneven. Therefore, also in this modification, it is necessary to keep the developing roller 41K away from the photosensitive drum 1K so that the toner does not transfer from the developing roller 41K to the photosensitive drum 1K. For this purpose, at the first timing affected by the transfer roller whose voltage has been changed, the area of the photosensitive drum 1K (the surface potential change portion) at the transfer position is in the contact portion (development position) with the developing roller 41K. The “standby state” may be set before the arrival timing (c in FIG. 8).

  In this modification, the ON timing of the developing separation mechanism 60 is set to be the same as the first ON timing of the primary transfer high-voltage power supply circuit 36a (FIG. 8A). As a result, the "standby state" is set before the timing (c in FIG. 8) at which the surface potential changing portion of the photosensitive drum 1K reaches the contact portion with the developing roller 41K.

  Similarly, when the “full-color image forming state” is set, the ON timing of the developing separation mechanism 60 is set as long as the surface potential change portion of the photosensitive drum 1K has passed the contact portion with the developing roller 41K. Good. Therefore, after a lapse of time α that passes through the contact portion with the developing roller 41K (d in FIG. 8), the operation of the second developing separation mechanism 60 is started, and the timing when the “full-color image forming state” is reached (FIG. 8) In e), full-color image formation is started.

  According to this control, since the toner does not transfer to the surface potential variation portion of the photosensitive drum 1K generated by turning on the primary transfer high-voltage power supply circuit 36a, it is possible to provide a good image without causing image defects. it can.

  In the ON state, the primary transfer high-voltage power supply circuit 36a supplies a voltage (predetermined voltage) higher than the standby power to the output terminal 53a. The predetermined voltage is a transfer voltage for image formation for transferring a toner image from the photosensitive drums 1Y, 1M, and 1C to the intermediate transfer belt (transferred member) 13 in order to perform full-color image formation, or an appropriate image formation. This is an adjustment voltage having a value close to the transfer voltage for image formation for performing the adjustment so that the transfer voltage for the image formation can be supplied. In the present modification, the predetermined voltage is set to approximately +300 V to +500 V.

<Operation and effect of the present embodiment>
As described above, in the image forming apparatus in which the independent first primary transfer high voltage power supply circuit 36b and the second primary transfer high voltage power supply circuit 36a are grounded via the common current detection circuit 37, When the second primary transfer high-voltage power supply circuit 36a is switched from OFF to ON while the first primary transfer high-voltage power supply circuit 36b is ON, the first primary transfer high-voltage power supply circuit 36a is turned ON. The voltage value output from the primary transfer high voltage power supply circuit 36b fluctuates. According to this modification, before the surface potential variation portion of the photosensitive drum affected by the variation reaches the contact portion with the developing roller, the voltage from the first primary transfer development high voltage power supply circuit 36b is applied. Is separated from the photosensitive drum. As a result, it is possible to provide a good image without image defects such as horizontal stripes without transferring the developer to the surface potential fluctuation portion of the photosensitive drum affected by the fluctuation.

[Example 2]
In the image forming apparatus 100 applied in the present embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted.

<Features of the present embodiment>
In the image forming apparatus 100 according to the present embodiment, the charging rollers 3Y, 3M, and 3C and the developing rollers 41Y, 41M, and 41C, and the charging roller 3K and the developing roller 41K have the same high-voltage power supply. That is, a power supply for supplying a voltage to the charging roller also serves as a power supply for applying a voltage to the developing roller, and the power supply for applying a voltage to the charging roller and the developing roller is common.

  FIG. 9 shows a configuration diagram of the high-voltage power supply device of the present embodiment. As shown in FIG. 9, a voltage (development voltage) is connected to the developing rollers 41Y, 41M, and 41C so that a voltage (development voltage) is supplied to the developing rollers 41Y, 41M, and 41C from a charging and developing high-voltage power supply circuit 33a 'as a second power supply. They are connected to the charging rollers 3Y, 3M, 3C. Further, it is connected so that a voltage is supplied to the developing roller 41K from the charging developing high voltage power supply circuit 33b 'as a first power supply, and further connected to the charging roller 3K via a common resistor R2. This is intended to reduce costs by using a common charging high-voltage power supply and developing high-voltage power supply.

  The high-voltage power supply circuit is the same as that shown in FIG. 5 described in the first embodiment. The output terminal 53a connects to the charging rollers 3Y, 3M and 3C and the developing rollers 41Y, 41M and 41C, and the output terminal 53b connects to the charging roller 3K and develops. A voltage is supplied to each of the rollers 41K.

<Developing contact / separation control during printing>
Hereinafter, specific control at the time of mono-full switching in the present embodiment will be described.

  FIG. 10 is a timing chart at the time of mono-full switching in the present embodiment. As in the first embodiment, the section M prints in the monocolor mode, and a indicates the start timing of the post-rotation operation.

  When a full-color image signal is received during mono-color printing, the charging / developing high-voltage power supply circuit 33a 'is turned on in preparation for full-color printing. Similarly, in the high-voltage power supply circuit of the present embodiment, when the charging and developing high-voltage power supply circuit 33a 'is switched from OFF to ON while the charging and developing high-voltage power supply circuit 33b' is ON, the charging current is instantaneously supplied to the current detection circuit 37. Flows. As a result, the reference voltage value (the voltage value A in FIG. 5) of the charging and developing high-voltage power supply circuit 33b 'changes. At this time, in this embodiment, the DC voltage output to the charging roller 3K and the developing roller 41K fluctuates. As a result, not only the surface potential of the photosensitive drum 1K fluctuates due to the voltage fluctuation of the charging roller 3K, but also the photosensitive drum 1K is directly affected by the voltage fluctuation of the developing roller 41K. That is, the toner may transfer from the developing roller 41K to the photosensitive drum 1K. Therefore, in the present high-voltage power supply circuit, it is necessary to be in the “standby state” when the charging and developing high-voltage power supply circuit 33a ′ is switched from OFF to ON.

  Therefore, in the present embodiment, only the operation of the developing separation mechanism 60 is started at the post-rotation operation start timing (a in FIG. 10). Then, at the timing of the "standby state" (FIG. 10B), the charging / developing high-voltage power supply circuit 33a 'is switched from OFF to ON. Then, the time when the surface potential fluctuation portion affected by the charging portion of the photosensitive drum 1K reaches the contact portion with the developing roller 41k (FIG. 10C) and further passes through the contact portion with the developing roller 41K. After the lapse of α (d in FIG. 10), the second operation of the developing separation mechanism 60 is started, and the full-color image formation is started at the timing when the “full-color image forming state” is reached (e in FIG. 10).

  According to this control, the toner does not transfer to the surface potential fluctuation portion of the photosensitive drum 1K or the contact portion with the developing roller 41K generated by turning on the charging / developing high-voltage power supply circuit 33a ', thereby causing an image defect. A good image can be provided without any problem.

<Operation and effect of the present embodiment>
As described above, the independent first charging / developing high-voltage power supply circuit 33b ′ and second charging / developing high-voltage power supply circuit 33a ′ using the same high-voltage charging power supply and developing high-voltage power supply are connected via the common current detection circuit 37. When the second charging and developing high-voltage power supply circuit 33a 'is switched from OFF to ON while the first charging and developing high-voltage power supply circuit 33b' is ON in an image forming apparatus which is grounded, the second charging and developing high-voltage power supply circuit 33b 'is turned on. When the power supply circuit 33a 'is turned on, the voltage value output from the first charging and developing high voltage power supply circuit 33b' varies. According to this embodiment, before turning on the second charged developing high voltage power supply circuit 33a ', the developing roller on the side to which the voltage is supplied from the first charged developing high voltage power supply circuit 33b' is separated from the photosensitive drum. . As a result, it is possible to reduce the cost of the high-voltage power supply circuit while providing a good image without image defects such as horizontal stripes.

[Example 3]
In the image forming apparatus 100 applied in the present embodiment, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted.

<Features of the present embodiment>
The image forming apparatus 100 according to the present embodiment is characterized in that the charging high-voltage power supply circuit 33a and the charging high-voltage power supply circuit 33b are grounded to the frame ground of the main body via a common resistance component.

  FIG. 11 is a schematic view of a main body sheet metal frame of the image forming apparatus 100. In FIG. 11, reference numerals 81L and 81R denote left and right main body sheet metal frames, which are fixed by a central sheet metal frame 81C. Reference numeral 80a denotes a high-voltage board on which a high-voltage power supply circuit including a charging high-voltage power supply circuit 33a and a charging high-voltage power supply circuit 33b is pasted, and is set on a mold member 82 supported by a central sheet metal frame 81C. Reference numeral 80b denotes a high-voltage board on which a high-voltage power supply circuit including a primary transfer high-voltage power supply and a secondary transfer high-voltage power supply is pasted, and is fixed to the main body sheet metal frame 81L by a plurality of metal screws 84. Therefore, the high-voltage board 80b is grounded to the frame ground of the main body. On the other hand, since the high-voltage board 80a is connected to the high-voltage board 80b via the bundle 83, the high-voltage board 80a is grounded to the frame ground of the main body via a resistance component such as the bundle and the high-voltage board 80b.

  In the present embodiment, the current detection circuit 37 (see FIG. 5) as the resistance component described in the first embodiment is not provided. Therefore, on the high-voltage power supply circuit, the charging high-voltage power supply circuit 33a and the charging high-voltage power supply circuit 33b are not connected. However, by installing the high-voltage board 80b described above, it can be determined that the circuit configuration is as shown in FIG. Here, the Q part shown in FIG. 12 is not an actual circuit, but shows a resistance component such as the bundled wire 83 and the high-voltage board 80b as R3. That is, in this embodiment, the charging high-voltage power supply circuit 33a and the charging high-voltage power supply circuit 33b are grounded via the resistance component R3 such as the bundle 83 and the high-voltage board 80b.

<Developing contact / separation control during printing>
Hereinafter, specific control at the time of mono-full switching in the present embodiment will be described. Since the timings of various operations are the same as in FIG. 6, detailed description will be omitted.

  When a full-color image signal is received during mono-color printing, the charging high-voltage power supply circuit 33a is turned on in preparation for full-color printing at the timing of starting post-rotation operation after completion of mono-color printing (FIG. 6A). At this time, similarly to the first embodiment, when the charging high-voltage power supply circuit 33b is turned on and the charging high-voltage power supply circuit 33a is switched from OFF to ON, a voltage is sharply output to the output terminal 53a, and thus, FIG. Instantaneously, a charge current flows through the Q section. When the charge current flows through the resistor R, the voltage value of A in FIG. 12 changes, so that the DC voltage output to the output terminal 53b changes. Therefore, when the surface potential fluctuation portion of the photosensitive drum 1K that has fluctuated due to the above-described voltage fluctuation reaches the contact portion with the developing roller 41K (c in FIG. 6), the timing (c) in FIG. In FIG. 6B, the operation of the developing separation mechanism 60 is started. Then, the time when the surface potential changing portion of the photosensitive drum 1K affected by the charging portion reaches the contact portion with the developing roller 41k (FIG. 6C) and further passes through the contact portion with the developing roller 41K. After the lapse of α (d in FIG. 6), the second operation of the developing separation mechanism 60 is started. Then, the full-color image formation is started at the timing when all the developing rollers come into contact with the photosensitive drums ("e" in FIG. 6).

  According to this control, since the toner does not transfer to the surface potential fluctuation portion of the photosensitive drum 1K generated when the charging high-voltage power supply circuit 33a is turned on, a good image can be provided without causing an image defect.

<Operation and effect of the present embodiment>
As described above, in the image forming apparatus in which the independent charging high voltage power supply circuit 33a and the charging high voltage power supply circuit 33b are grounded to the frame ground of the main body via the common resistance component R3, the first charging high voltage power supply circuit 33b When the second charging high-voltage power supply circuit 33a is switched from OFF to ON in the state of ON, the voltage value output from the first charging high-voltage power supply circuit 33b is turned on by turning on the second charging high-voltage power supply circuit 33a. fluctuate. According to this embodiment, the voltage is supplied from the first charging high-voltage power supply circuit 33b before the surface potential variation portion of the photosensitive drum affected by the above-mentioned variation reaches the contact portion with the developing roller. The developing roller on the other side is separated from the photosensitive drum. As a result, similar to the first embodiment, it is possible to provide a good image without image defects such as horizontal stripes without transferring the developer to the surface potential variation portion of the photosensitive drum affected by the variation.

  Further, by sharing the charging high-voltage power supply and the developing high-voltage power supply, the cost of the high-voltage power supply circuit can be reduced as in the second embodiment.

  Further, for example, when the charged high-voltage power supply circuit and the high-voltage substrate on which the charged high-voltage power supply circuit is pasted are directly grounded to the frame ground and the impedance of the high-voltage substrate itself is high, that is, a resistance component is included between the high-voltage substrate and the frame ground. It can be applied even when

[Other embodiments]
In the above-described embodiment, the first power supply and the second power supply are the same, such as independent first and second charging high-voltage power supply circuits or independent first and second primary transfer high-voltage power supply circuits. The control method in the high voltage power supply circuit of the system was described. However, the present invention is not limited to the high-voltage power supply circuit of the same system. For example, a charging high-voltage power supply circuit for supplying a charging voltage to a first charging unit acting on a first photosensitive drum serving as a first power supply, and a primary transfer high-voltage power supply circuit or a secondary transfer high-voltage power supply circuit serving as a second power supply. It may be the case that the main body is grounded to the frame ground via a common resistance component. Further, a primary transfer high-voltage power supply circuit for supplying a transfer voltage to a first transfer unit acting on a first photosensitive drum as a first power supply, and a charging high-voltage power supply circuit or a secondary transfer high-voltage power supply circuit as a second power supply are provided. It may be the case that the main body is grounded to the frame ground via a common resistance component. In other words, the first power supply is common to the first high-voltage power supply circuit for supplying a voltage to the process means acting on the first photosensitive drum (photosensitive drum 1K) and a high-voltage power supply circuit different from the first high-voltage power supply circuit. The same can be applied as long as it is grounded to the frame ground of the main body via the above-mentioned resistance component.

  When the first power supply is a charging high-voltage power supply circuit, the first developing means may be controlled by the separating mechanism as follows. In other words, when the first power supply is supplying the charging voltage, the second power supply supplies the predetermined voltage from the state where the second power supply does not supply the voltage or supplies the voltage lower than the predetermined voltage at the first timing. When starting, the area where the first photosensitive drum is at the charging position at the first timing moves the first developing means to the separation position before the second timing when the area reaches the developing position.

  When the first power supply is a primary transfer high-voltage power supply circuit, the first developing means is controlled by the separating mechanism as follows. That is, when the first power supply is supplying the transfer voltage, the second power supply supplies the predetermined voltage at the first timing from the state where the second power supply does not supply the voltage or supplies a voltage lower than the predetermined voltage. When starting, the first developing unit is moved to the separated position before the second timing at which the area at the transfer position at the first timing of the first photosensitive drum reaches the developing position.

  By controlling the separation mechanism as described above, it is possible to suppress image defects due to disturbance of the toner image formed on the first photosensitive drum.

  In the first embodiment described above, when the second power supply is switched from OFF to ON while the first power supply is ON, the second power supply is turned on as a timing for separating the developing roller and the photosensitive drum. The configuration in which the same timing is performed is exemplified. However, the present invention is not limited to this, and the above-mentioned separation timing may be set before the surface potential variation portion of the photosensitive drum affected by the voltage variation reaches the contact portion with the developing roller. I just need.

  In the above-described embodiment, as a process cartridge detachably mountable to the main body of the image forming apparatus, a process in which a photosensitive drum and a charging unit, a developing unit, and a cleaning unit as process units acting on the photosensitive drum are integrated. The cartridge has been exemplified. However, the present invention is not limited to this. For example, it may be a process cartridge integrally including any one of a charging unit, a developing unit, and a cleaning unit in addition to the photosensitive drum.

  Further, in the above-described embodiment, the configuration in which the process cartridge including the photosensitive drum is detachable from the image forming apparatus main body is exemplified, but the present invention is not limited to this. For example, an image forming apparatus in which each component is incorporated, or an image forming apparatus in which each component is detachable, may be used.

  In the above-described embodiment, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this. For example, another image forming apparatus such as a copying machine or a facsimile machine, or another image forming apparatus such as a multifunction machine combining these functions may be used. Further, the present invention is limited to an image forming apparatus that uses an intermediate transfer member, sequentially transfers toner images of respective colors onto the intermediate transfer member, and transfers the toner images carried on the intermediate transfer member collectively to a recording medium. Not something. An image forming apparatus that uses a recording medium carrier and sequentially superimposes and transfers toner images of each color onto a recording medium as a member to be transferred carried on the recording medium carrier may be used. The same effect can be obtained by applying the present invention to these image forming apparatuses.

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum 13 ... Intermediate transfer belts 17 and 18 ... Transfer rollers 33a and 33b ... Charging high-voltage power supply circuits 33a 'and 33b' ... , 36b ... primary transfer high voltage power supply circuit 37 ... current detection circuit 38 ... secondary transfer high voltage power supply circuit 41 ... developing roller 44 ... projecting member 54 ... control unit 60 ... development separating mechanism 61 ... separating members 62x, 62y ... moving member 64x , 64y ... cams 65x, 65y ... cam drive shafts 80a, 80b ... high-voltage boards 81C, 81L, 81R ... sheet metal frames

Claims (18)

First and second photoconductors that are rotationally driven;
First and second charging means for charging the first and second photoreceptors at charging positions, respectively;
First and second developing means for attaching toner to the first and second photoreceptors at developing positions, respectively;
First and second transfer means for transferring the toner images formed on the first and second photoconductors to a member to be transferred;
A first power supply for supplying a charging voltage to the first charging unit;
A second power supply for supplying a predetermined voltage to at least one of the second charging unit, the second developing unit, and the second transfer unit;
A separation mechanism that moves the first developing unit from a contact position that contacts the first photoconductor at the development position to a separation position that is separated from the first photoconductor;
Control means for controlling the separation mechanism;
In the image forming apparatus having
The first power supply and the second power supply are grounded via a common resistance component;
When the first power supply is supplying the charging voltage, the second power supply does not supply a voltage or supplies a voltage lower than the predetermined voltage at a first timing. When the supply of the voltage is started, the control unit controls the separation mechanism to move the area of the first photosensitive member at the charging position at the first timing to the developing position before the second timing of reaching the developing position. (1) An image forming apparatus wherein the developing means is moved to the separated position.   The image forming apparatus according to claim 1, wherein the predetermined voltage is supplied to the second charging unit.   The image forming apparatus according to claim 1, wherein the predetermined voltage is supplied to the second developing unit.   The image forming apparatus according to claim 1, wherein the predetermined voltage is supplied to the second transfer unit. The first power supply supplies a developing voltage to the first developing unit,
The image forming apparatus according to claim 1, wherein the control unit moves the first developing unit to the separation position by the separation mechanism before the second timing. A first mode for forming a toner image on the first photoconductor without forming a toner image on the second photoconductor, and a second mode for forming a toner image on each of the first and second photoconductors. Can be executed,
The image according to any one of claims 1 to 5, wherein the first timing is a timing after the execution of the first mode is completed and before the execution of the second mode is started. Forming equipment.   7. The method according to claim 6, wherein the separation mechanism moves the first developing unit from the separation position to the contact position before the execution of the second mode after the second timing. An image forming apparatus according to claim 1. First and second photoconductors that are rotationally driven;
First and second charging means for charging the first and second photoreceptors, respectively;
First and second developing means for attaching toner to the first and second photoreceptors at developing positions, respectively;
First and second transfer means for transferring the toner images formed on the first and second photoconductors to a member to be transferred at a transfer position;
A first power supply for supplying a transfer voltage to the first transfer unit;
A second power supply for supplying a predetermined voltage to at least one of the second charging unit, the second developing unit, and the second transfer unit;
A separation mechanism that moves the first developing unit from a contact position that contacts the first photoconductor at the development position to a separation position that is separated from the first photoconductor;
Control means for controlling the separation mechanism;
In the image forming apparatus having
The first power supply and the second power supply are grounded via a common resistance component;
In a state where the first power supply is supplying the transfer voltage, the second power supply does not supply a voltage or supplies a voltage lower than the predetermined voltage at a first timing. When the supply of the voltage is started, the control unit determines that the area of the first photoconductor at the transfer position at the first timing reaches the developing position by the separation mechanism before the second timing of reaching the developing position. (1) An image forming apparatus wherein the developing means is moved to the separated position. The image forming apparatus according to claim 8 , wherein the predetermined voltage is supplied to the second charging unit. The image forming apparatus according to claim 8 , wherein the predetermined voltage is supplied to the second developing unit. The image forming apparatus according to claim 8 , wherein the predetermined voltage is supplied to the second transfer unit. 9. The image forming apparatus according to claim 8 , wherein the control unit moves the first developing unit to the separation position by the separation mechanism before the second timing. A first mode for forming a toner image on the first photoconductor without forming a toner image on the second photoconductor, and a second mode for forming a toner image on each of the first and second photoconductors. Can be executed,
The image according to any one of claims 8 to 12 , wherein the first timing is a timing after the execution of the first mode is finished and before the execution of the second mode is started. Forming equipment. 14. The method according to claim 13 , wherein the separation mechanism moves the first developing unit from the separation position to the contact position before the execution of the second mode is started after the second timing. An image forming apparatus according to claim 1. First and second photoconductors that are rotationally driven;
First and second charging means for charging the first and second photoreceptors at charging positions, respectively;
First and second developing means for attaching toner to the first and second photoreceptors at developing positions, respectively;
First and second transfer means for transferring the toner images formed on the first and second photoconductors to a member to be transferred at a transfer position;
Third transfer means for transferring the toner image transferred to the transfer member to a sheet,
A first power supply for supplying a charging voltage to the first charging unit;
A second power supply for supplying a predetermined voltage to at least one of the second charging unit, the second developing unit, the second transfer unit, and the third transfer unit;
A separation mechanism that moves the first developing unit from a contact position that contacts the first photoconductor at the development position to a separation position that is separated from the first photoconductor;
Control means for controlling the separation mechanism;
In the image forming apparatus having
The first power supply and the second power supply are grounded via a common resistance component;
When the first power supply is supplying the charging voltage, the second power supply does not supply a voltage or supplies a voltage lower than the predetermined voltage at a first timing. When the supply of the voltage is started, the control unit determines that the area of the first photoconductor at the charging position at the first timing reaches the developing position before the second timing reaches the developing position. (1) An image forming apparatus, wherein a developing unit is moved to the separated position. A first mode for forming a toner image on the first photoconductor without forming a toner image on the second photoconductor, and a second mode for forming a toner image on each of the first and second photoconductors. Can be executed,
The image forming apparatus according to claim 15 , wherein the first timing is a timing after the execution of the first mode is completed and before the execution of the second mode is started. First and second photoconductors that are rotationally driven;
First and second charging means for charging the first and second photoreceptors at charging positions, respectively;
First and second developing means for attaching toner to the first and second photoreceptors at developing positions, respectively;
First and second transfer means for transferring the toner images formed on the first and second photoconductors to a member to be transferred at a transfer position;
Third transfer means for transferring the toner image transferred to the transfer member to a sheet,
A first power supply for supplying a transfer voltage to the first transfer unit;
A second power supply for supplying a predetermined voltage to at least one of the second charging unit, the second developing unit, the second transfer unit, and the third transfer unit;
A separation mechanism that moves the first developing unit from a contact position that contacts the first photoconductor at the development position to a separation position that is separated from the first photoconductor;
Control means for controlling the separation mechanism;
In the image forming apparatus having
The first power supply and the second power supply are grounded via a common resistance component;
When the first power supply is supplying the transfer voltage, the second power supply does not supply a voltage or supplies a voltage lower than the predetermined voltage at a first timing. When the supply of the voltage is started, the control unit determines that the area at the transfer position at the first timing of the first photosensitive member is moved by the separation mechanism by the separation mechanism before the second timing of reaching the developing position. (1) An image forming apparatus wherein the developing means is moved to the separated position. A first mode for forming a toner image on the first photoconductor without forming a toner image on the second photoconductor, and a second mode for forming a toner image on each of the first and second photoconductors. Can be executed,
The image forming apparatus according to claim 17 , wherein the first timing is a timing after the execution of the first mode is completed and before the execution of the second mode is started.

Images