JP2015152762A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to prevent a streaky image defect from being generated due to separation and contact between image holding bodies of imaging apparatus and a rotating annular belt passing through the image holding bodies sequentially, in changing of a mode between first mode and second mode during consecutive image forming operation.SOLUTION: An image forming apparatus includes control means which controls power source means to supply a switch voltage, which is smaller than a transfer voltage for image formation, in a period from the start to the end of separation or contact between image holding bodies of inactive imaging apparatuses and an annular belt and a transfer member, when a mode is changed during consecutive image forming operation, between first mode which forms an image by use of all the imaging apparatuses and second mode which forms an image by using some of the imaging apparatuses, while separating the annular belt and the transfer member from the image holding bodies of the inactive imaging apparatuses.

Description

  The present invention relates to an image forming apparatus.

  Conventionally, a first mode (or color mode or the like) for forming a multicolor (mainly full color) image by using all of a plurality of image forming apparatuses that respectively form toner images of different colors on different image carriers, and a plurality of As an image forming apparatus capable of forming an image by switching to a second mode (or monochrome mode or the like) for forming a monochromatic image using a part of the image forming apparatus, for example, the following are known. It has been.

  One of them is an image forming apparatus that uses an intermediate transfer member or a recording material transport unit, and when performing switching (transition process) from the first mode to the second mode during continuous operation, The image forming apparatus is configured to perform the transfer in a state where the transfer unit is once completely separated from the intermediate transfer member or the recording material conveying unit, or in a state where the transfer power supply of the transfer unit is turned off and application of the transfer voltage to the transfer unit is stopped. (Patent Document 1). According to Patent Document 1, according to this image forming apparatus, toner contamination that occurs when switching between a first mode typified by a full color mode and a second mode typified by a monocolor mode is prevented, and a high-quality image is obtained. It has been shown that can be formed.

  As a direct tandem image forming apparatus, when the color mode is switched to the monochrome mode, the color transfer roller is separated from the transfer belt of the transfer target member with the transfer bias applied. There is an image forming apparatus that performs the image formation (Patent Document 2). This Patent Document 2 shows that it is possible to suppress the occurrence of reverse transfer ghost (a phenomenon in which a black toner image reversely transferred to a color photoconductor is retransferred to a transfer member such as paper) in the monochrome mode. .

JP 2004-341399 A JP 2012-63597 A

  In the present invention, when switching between the first mode and the second mode in the middle of the continuous image forming operation, an image carrier of each image forming device and an annular belt (intermediate belt) that sequentially rotates and passes through each image carrier. Suppressing the occurrence of streak-like image quality due to separation or contact with the transfer belt or the paper transport belt without increasing the waiting time until the image forming operation in the mode after the switching is started. An image forming apparatus capable of performing the above is provided.

The image forming apparatus of the present invention (A1)
A plurality of image forming apparatuses including at least an image holding body and an image forming device that forms a toner image on the image holding body;
An annular belt rotating in sequence through the image carrier of each of the imaging devices;
A recording target in which the outer peripheral surface of the annular belt is brought into contact with the image carrier of each image forming device and the toner image on each image carrier is conveyed by the outer peripheral surface of the annular belt or the annular belt. A plurality of transfer members each transferred to the material;
Power supply means for supplying a common transfer voltage to each of the transfer members and capable of changing an output voltage;
A first mode in which an image is formed using all of the plurality of image forming devices; and an annular shape from an image holding body of an image forming device that uses a part of the plurality of image forming devices and does not use the image forming device. When switching between the second mode in which the image is formed while the belt and the transfer member are separated from each other during the continuous image forming operation, the image carrier of the unused image forming device, the annular belt, and the transfer Control means for controlling the power supply means to supply a switching voltage changed to a value smaller than the transfer voltage at the time of image formation from the start of the separation operation or contact operation with the member to the completion of the operation. It is characterized by having.

  In the image forming apparatus of the invention (A2), in the image forming apparatus of the invention A1, the voltage at the time of switching is between the image holding body of the unused image forming apparatus and the annular belt or between the image holding body and the image forming apparatus. The voltage is smaller than the discharge start voltage between the transfer member facing the image carrier.

  According to the image forming apparatus of the invention A1, when switching between the first mode and the second mode in the middle of the continuous image forming operation, the image holding body of each image forming apparatus and each image holding body are sequentially passed. The occurrence of streak-like image quality defects due to separation or contact with the rotating annular belt is suppressed without increasing the waiting time until the image forming operation in the mode after the switching is started. Can do.

  In the image forming apparatus of the invention A2, the effect of the invention A1 can be obtained more reliably than when the configuration of the invention is not provided.

FIG. 2 is a schematic diagram schematically showing the configuration of the image forming apparatus according to Embodiment 1 (state when performing an image forming operation in a first mode). FIG. 2 is a conceptual diagram schematically illustrating a component that supplies power to an image forming device of each image forming apparatus in the image forming apparatus of FIG. 1. FIG. 2 is a block diagram illustrating main components related to a control unit in the image forming apparatus of FIG. 1. FIG. 2 is a schematic diagram schematically showing a configuration of the image forming apparatus in FIG. 1 (state when performing an image forming operation in a second mode). FIG. 6 is a flowchart showing a flow of main control operations when a first mode and a second mode are switched during a continuous image forming operation. FIG. 6 is a timing chart showing main operation contents in each image forming apparatus when switching from the first mode to the second mode and when switching from the second mode to the first mode during the continuous image forming operation. It is a chart which shows a test result. It is explanatory drawing which shows the state in the case of changing an output voltage in a primary transfer electric power feeding part, (a) shows a state when changing an output voltage from 0V to +2.0 kV, (b) shows an output voltage +0. The state when changing from 8 kV to +2.0 kV is shown.

  Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as “embodiments”) will be described with reference to the accompanying drawings.

<Embodiment 1>
FIG. 1 schematically shows the configuration of the image forming apparatus according to the first embodiment, FIG. 2 schematically shows the components that supply power to each image forming device in the image forming apparatus, and FIG. 3 shows the image forming apparatus. The main components related to the control unit in FIG.

  The image forming apparatus 1 according to Embodiment 1 includes a plurality of image forming apparatuses 2 that form toner images developed with toner as a developer based on input image information in an internal space of a housing 10, and each image forming apparatus 2. An intermediate transfer device 3 that holds the toner image formed by the image device 2 and finally transfers it to a recording paper 9 as a recording material, and a required recording paper to be conveyed to the secondary transfer position of the intermediate transfer device 3 A paper feeding device 4 that accommodates and supplies 9 and a fixing device 5 that fixes the toner image by passing the recording paper 9 on which the toner image has been transferred by the intermediate transfer device 3 are installed. Reference numeral 6 in FIG. 1 denotes a central control unit that comprehensively controls the operation of each component of the image forming apparatus 1, reference numeral 8 denotes a power supply device, and reference numeral 11 denotes a planar shape inclined on the upper surface of the housing 10. 2 shows a discharge storage portion that stores the recording paper 9 formed after image formation. Also, the alternate long and short dash line in FIG. 1 indicates the main transport path when the recording paper 9 is transported.

  The plurality of image forming apparatuses 2 includes four image forming units 2Y, 2M, 2C, and 2K that respectively form toner images having four colors of yellow (Y), magenta (M), cyan (C), and black (K). These are arranged in series at a required interval (for example, the same interval) and arranged in an inclined manner in the order of the above four colors so as to incline toward the left shoulder. Further, each of the four image forming units 2 (Y, M, C, K) includes a photosensitive drum 21, a charging device 22, an exposure device 23, a developing device 24, a primary transfer device 25, a drum cleaning device (not shown), and the like. Each has.

  The photosensitive drum 21 is formed by forming an image holding surface having a photoconductive layer (photosensitive layer) made of an organic photosensitive material on the peripheral surface of a cylindrical or columnar conductive substrate to be grounded, not shown. It receives power from the rotation drive device (image forming device drive unit 29) and rotates in the direction indicated by the arrow. The charging device 22 charges the image holding surface of the photosensitive drum 21 to a required charging potential, and a charging voltage is applied from the charging power supply unit 13 to a contact member disposed in contact with the image holding surface. It is a contact type charging device. As the charging voltage, when the developing device 23 performs reversal development, a voltage having the same polarity as the charging polarity of the toner supplied from the developing device is supplied.

  The exposure device 23 irradiates the charged image holding surface of the photosensitive drum 21 with light composed of the four color components based on the image information input to the image forming apparatus 1. An electrostatic latent image having a required latent image potential is formed. As this exposure apparatus 23, for example, a non-scanning exposure apparatus configured by using a light emitting diode and an optical component is applied. Further, the exposure device 23 receives an image signal for forming a latent image from an image processing device 14 that performs a required process on image information input to the image forming device 1 from an externally connected device such as a personal computer terminal. It has become.

  The developing device 24 includes a developer container that stores a two-component developer (a developer including a non-magnetic toner and a magnetic carrier) that is an example of a developer, and the developer stored in the developer container. The developing roller 24a that holds the rotating member and conveys it to the developing region that is close to and faces the photosensitive drum 21, and the agitating and conveying member that conveys the two-component developer contained in the developing roller 24a to the developing roller 24a while rotating and stirring. A member, a layer thickness regulating member for regulating the amount (layer thickness) of the developer held on the developing roll, and the like are provided. Further, the developing device 24 is supplied with a developing voltage from the developing power supply unit 15 to the developing roll 24a, and the developing roll 24a and the agitating / conveying member are not shown in the drawing with a rotation driving device (imaging device driving unit 29). It receives power from and is rotated in the required direction. As the development voltage, for example, a direct current on which an alternating current is superimposed is supplied. The developer toner is agitated by the agitating / conveying member in the developer container and rubs against the carrier to be frictionally charged to a required polarity (negative polarity in the first embodiment).

  The primary transfer device 25 rotates in contact with the developed image holding surface of the photosensitive drum 21 (with the intermediate transfer belt 31 interposed) and is supplied with a primary transfer voltage from the primary transfer power supply unit 16. It is a contact type transfer device provided with a member. The contact member is a primary transfer roll that is driven to rotate while pressing an intermediate transfer belt 31 described later against the image holding surface of the photosensitive drum 21. As the primary transfer voltage, a DC voltage (a DC voltage having a polarity opposite to the charging polarity of the toner) is supplied.

  The intermediate transfer device 3 is arranged so as to exist at a position above the four image forming devices 2 (Y, M, C, K). The intermediate transfer device 3 passes through the primary transfer position between the photosensitive drum 21 and the primary transfer device 25 (contact member) in each image forming device 2 (Y, M, C, K) in the direction indicated by the arrow. A rotating intermediate transfer belt 31, a plurality of support rolls 32 to 35 that hold the intermediate transfer belt 31 in a desired state from its inner surface and rotatably support the intermediate transfer belt 31, and the intermediate transfer belt 31 supported by the support roll 33 A secondary transfer roll 36 that rotates in contact with a predetermined pressure and a belt cleaning device 37 that removes toner and the like remaining on the intermediate transfer belt 31 after passing through the secondary transfer roll 36 are mainly configured. ing.

  As the intermediate transfer belt 31, for example, a belt formed of a predetermined thickness using a material in which a resistance adjusting agent such as carbon is dispersed in a synthetic resin such as polyimide resin is used. The support roll 32 is configured as a drive roll, the support roll 33 is configured as a secondary transfer backup roll, the support roll 34 is configured as a tension applying roll, and the support rolls 35a and 35b are configured as transfer surface exposing rolls. The support roll 32 as a drive roll is rotated in a required direction by receiving power from a rotation drive device (intermediate transfer device drive unit 39) (not shown). A secondary transfer voltage is supplied from the secondary transfer power supply unit 17 to the support roll 33 or the secondary transfer roll 36. As the secondary transfer voltage, a DC voltage having the same polarity as the toner charging polarity is supplied when supplied to the support roll 33, and is opposite to the toner charging polarity when supplied to the secondary transfer roll 36. A polar DC component is supplied.

  The sheet feeding device 4 is disposed so as to exist at a position below the intermediate transfer device 3. The paper feeding device 4 is attached so that it can be pulled out to the front side (side surface that the user faces when operating) of the housing 10 and accommodates a recording paper 9 of a desired size, type, etc. A plurality of containers 41 and a feeding device 42 that feeds the recording paper 9 from the containers 41 one by one are mainly configured. Reference numeral 45 in FIG. 1 denotes a paper feed conveyance path for conveying the recording paper 9 delivered from the paper feed device 4 to the secondary transfer position of the intermediate transfer device 3 (between the intermediate transfer belt 31 and the secondary transfer roll 36). As shown, the paper feed conveyance path 45 includes a plurality of conveyance roll pairs 46, 47,... And a conveyance guide material (not shown). The transport roll pair 47 is configured as a feed roll pair having functions such as correcting the transport timing and transport state of the recording paper 9. The delivery device 42 and each pair of conveyance rolls are rotated in required directions by receiving power from a rotation drive device (paper conveyance system drive unit 49) (not shown).

  The fixing device 5 is disposed so as to exist in a spatial position above the secondary transfer roll 36 in the intermediate transfer device 3. The fixing device 5 rotates in a direction indicated by an arrow inside the casing 51 and is heated by a heating unit so that the surface temperature is maintained at a predetermined temperature. And a pressurizing rotator 53 such as a roll type or a belt type that is driven and rotated by being brought into contact with a predetermined pressure in a state substantially along the axial direction of the heating rotator 52. A required heating voltage is supplied from the fixing power supply unit 18 to the heating means of the heating rotator 52. The heating rotator 52 is rotated in a required direction by receiving power from a rotation driving device (fixing device driving unit 59) (not shown). Reference numeral 55 in FIG. 1 denotes a paper discharge conveyance path for conveying the fixed recording paper 9 to be discharged to the discharge accommodating portion 11, and this paper discharge conveyance path 55 is not shown with a plurality of conveyance roll pairs 56 and 57. It consists of a conveyance guide material.

  The central control unit 6 includes storage means including a ROM (read only memory) 65 shown in FIG. 3 and an external storage device, an arithmetic processing device (not shown), an input / output device, a control device, and the like. Necessary control operations are executed according to the contents of programs, data, etc.

  As shown in FIG. 3, the central control unit 6 is connected to an input unit 71 for inputting information relating to an image forming operation and the like, and other detection units such as various sensors (not shown). Information and detection information are input. Further, the central control unit 6 drives the image processing unit 14 that performs a required process on image information input from an externally connected device connected to the image forming apparatus 1 and a drive that controls the operation of the drive components in the image forming apparatus 1. The control unit 61, the power control unit 62 that controls the operation of the power supply device in the image forming apparatus 1, and the exposure control unit that receives the image signal from the image processing unit 14 and controls the operation of the exposure device 23 in each image forming device 2. 63 and the like, and necessary control signals are transmitted to the respective control units.

  For example, the drive control unit 61 controls the drive unit 29 of each image forming device 2, the drive unit 39 of the intermediate transfer device 3, the drive unit 59 of the fixing device 5, paper such as the paper feed device 4 and the conveyance path. It is connected to the transport system drive unit 49 and the like, and controls the operation of each drive unit. The power supply control unit 62 is connected to the above-described charging power supply unit 13, exposure power supply unit 14, development power supply unit 15 (A, B), primary transfer power supply unit 16, secondary transfer power supply unit 17, fixing power supply unit 18, and the like. And controls the operation of each power feeding section. Among these, the development power supply unit 15 supplies a common (same) development voltage to the development roll 24a of each development device 24 in the three image forming devices 2 (Y, M, C) from the first development power supply unit 15A. A developing voltage is separately supplied from the second developing power supply unit 15B to the developing roll 24a of the developing device 24 in the image forming device 2K. The primary transfer power supply unit 16 is configured to supply a common (identical) primary transfer voltage to the primary transfer rolls of the primary transfer devices 25 in the four image forming devices 2 (Y, M, C, and K). ing.

  Further, the image forming apparatus 1 is a full-color image composed of toner images of four colors (Y, M, C, K) formed by using all four image forming apparatuses 2 (Y, M, C, K). The first mode (full color mode), which is an image forming pattern for forming the image, and one color toner image formed using one of the four image forming devices 2 (Y, M, C, K). It has at least a second mode (monochrome mode) that is an image forming pattern for forming a monochromatic image. The monochrome mode in the first embodiment is set as a monochrome mode for forming a monochrome image composed of a black (K) toner image.

  In the image forming apparatus 1, the first mode and the second mode can be switched in the middle of the continuous image forming operation, and image formation in each mode can be performed continuously. The mode switching instruction at this time is input, for example, as part of information included in image information transmitted from a terminal device connected to the image forming apparatus 1 or when the image forming apparatus 1 is used as a document reading apparatus. May be input as control information determined by the image content of the read original or may be input from the input means 71 as selection instruction information. This mode switching instruction is input to at least the central control unit 6 and recognized.

  As shown in FIG. 4, when the image forming apparatus 1 executes an image forming operation in the black and white mode, which is the second mode, the image forming apparatuses 2Y, 2M, and 2C that are not used in the image forming operation in that mode are used. The primary transfer devices (primary transfer rolls of contact members) 25Y, 25M, and 25C together with a part of the intermediate transfer belt 31 existing between the primary transfer roll groups, and the photosensitive drums in the image forming devices 2Y, 2M, and 2C that are not used. 21 are set to be in a state of being separated from each other.

  The primary transfer devices 25Y, 25M, and 25C in the image forming devices 2Y, 2M, and 2C that are not used are brought into contact with and separated from the respective photosensitive drums 21 by the contact / separation (displacement) mechanism 19. It has a structure that can be displaced. In the first embodiment, the upstream contact surface-developing roll 35a is similarly displaced by the contact / separation mechanism 19. The contact / separation mechanism 19 is composed of, for example, a cam mechanism, and is composed of devices such as a rotating cam, a drive motor, and a clutch (not shown). Further, the separation mechanism 9 is a position constituted by a device such as a position identification sensor that detects that the primary transfer devices 25Y, 25M, and 25C have reached the preset contact position and separation position, respectively, when they are displaced. Detection means 72 is provided.

  As shown in FIGS. 5 and 6, when the central control unit 6 switches between the first mode and the second mode in the middle of the continuous image forming operation, the image forming apparatus 1 has the second one. In the image forming apparatuses 2Y, 2M, and 2C that are not used in the image forming operation in the mode (black and white mode), an operation to separate or contact the photosensitive drums 21, the intermediate transfer belt 31, and the primary transfer rolls 25Y, 25M, and 25C is started. Before the operation is completed until the operation is completed, the primary transfer power supply unit 16 outputs and supplies the switching voltage changed to a value smaller than the primary transfer voltage at the time of image formation. . The change of the voltage supplied from the primary transfer power supply unit 16 is actually controlled by the power supply control unit 62. Specifically, the power supply control unit 62 performs control related to the voltage supply ON / OFF operation and the output voltage setting change operation in the primary transfer power supply unit (for example, a constant voltage control type power supply device) 16. Details of the above control operation will be described later.

  The switching between the first mode and the second mode is recognized by a switching instruction input to at least the central control unit 6 via the image processing unit 14, the input means 71, and the like. Further, as shown in FIG. 3, the central control unit 6 is connected to a separation control unit 64 that controls the operation of the separation mechanism (separation drive unit) 19 and the position detection means 72 described above. The central control unit 6 receives the position information of the primary transfer roll 25 and the like to be displaced by the separation mechanism 19 from the position detection unit 72, and transmits a necessary control signal to the separation control unit 64. It is supposed to be. Further, when the switching mode is switched between the first mode and the second mode in the middle of the continuous image forming operation, the photosensitive voltages in the image forming apparatuses 2Y, 2M, and 2C that are not used in the second mode image forming operation are used. A voltage (not 0 V) with a value that does not cause streak-like image quality defects caused by discharge that occurs when the drum 21 and the intermediate transfer belt 31 and the primary transfer rolls 25Y, 25M, and 25C are separated or contacted by the separation operation or contact operation. Is preset.

  Hereinafter, a basic image forming operation by the image forming apparatus 1 will be described.

  First, an operation in the case of forming a full color image in the first mode full color mode will be described as an example.

  First, at the time of image formation in the full color mode, as shown in FIG. 1 and the like, in each of the four image forming apparatuses 2 (Y, M, C, K), the photosensitive drums 21 are rotated in the directions indicated by the arrows, respectively. The charging device 22 charges the image holding surface of each photosensitive drum 21 to a required polarity (negative polarity in the first embodiment) and a potential according to the charging voltage. Next, each exposure device 23 of the image forming device 2 (Y, M, C, K) is based on an image signal that is separated into each color component (Y, M, C, K) with respect to the photosensitive drum 21 after charging. Exposure is performed to form an electrostatic latent image of each color component having a predetermined potential on the image holding surface of the photosensitive drum 21.

  Subsequently, each developing device 24 of the image forming device 2 (Y, M, C, K) has a predetermined polarity (minus polarity) with respect to the electrostatic latent image portion of each color component formed on the photosensitive drum 21. Development is performed by supplying charged toner of each color (Y, M, C, K) from the developing roll 24a and electrostatically adhering them with a developing electric field including a developing voltage. As a result, toner images of any of four colors (Y, M, C, K) are formed on the image holding surface of each photosensitive drum 21 in the image forming device 2 (Y, M, C, K). The That is, for example, a yellow toner image is formed on the photosensitive drum 21 of the image forming device 2Y, and a magenta toner image is formed on the photosensitive drum 21 of the image forming device 2M.

  Subsequently, at each primary transfer position of each image forming device 2 (Y, M, C, K), the primary transfer device 25 converts the four color toner images formed on the respective photosensitive drums 21 to primary transfer voltages. By the transfer electric field formed in this way, primary transfer is performed in order (in the order of Y, M, C, K) to the intermediate transfer belt 31 of the intermediate transfer device 3. At this time, the primary transfer devices (primary transfer rolls) 25 in the four image forming devices 2 (Y, M, C, and K) are moved to their respective contact positions, and as shown in FIG. 31 is in contact with each photosensitive drum 21. Next, after the intermediate transfer device 3 conveys the toner image primarily transferred to the intermediate transfer belt 31 to the secondary transfer position by rotating it in the direction indicated by the arrow of the intermediate transfer belt 31, the intermediate transfer belt 31 at the secondary transfer position The secondary transfer roll 36 (or the support roll 33) is applied to the recording paper 9 conveyed from the paper feeding device 4 via the paper feeding conveyance path 45 by a transfer electric field formed by the secondary transfer voltage. Secondary transfer at once.

  Subsequently, the intermediate transfer device 3 peels the recording paper 9 on which the toner image has been secondarily transferred from the intermediate transfer belt 31 and then sends it to the fixing device 5. Next, in the fixing device 5, the recording paper 9 onto which the toner image has been transferred is heated and pressed through the contact portion between the heating rotator 52 and the pressing rotator 53, thereby melting the toner image. Then, it is fixed on the recording paper 9. Next, in the case of an operation in which the fixing device 5 sends out the recording paper 9 on which the toner image is fixed to the discharge conveyance path 55 and forms an image on one side of the recording paper 9, The recording paper 9 is discharged to the outside of the housing 10 through the discharge conveyance path 55 and finally stored in the discharge container 11.

  Through the above operation, one sheet of recording paper 9 on which a full color image formed by combining four color toner images is formed on one side is output, and the image forming operation in the full color mode which is the first mode is completed.

  Next, the operation when forming a black and white image in the black and white mode of the second mode will be described as an example.

  First, at the time of image formation in the monochrome mode, as shown in FIG. 4, primary transfer rolls 25Y and 25M in the image forming apparatuses 2Y, 2M, and 2C that are not used among the four image forming apparatuses 2 (Y, M, C, and K). , 25C are displaced by the separation mechanism 19 to positions separated from the respective photosensitive drums 21 in the respective image forming apparatuses. Further, at the time of image formation in the monochrome mode, as shown in FIG. 6, the rotation of the photosensitive drums 21 in the unused image forming devices 2Y, 2M, and 2C by the driving unit 29 is stopped, and the image forming devices 2Y. , 2M, 2C, the supply of the charging voltage from the primary transfer power supply unit 16 to each charging device 22 is stopped. Further, the supply of the developing voltage from the first developing power supply unit 15A to the developing roll 24a of each developing device 24 in the unused image forming devices 2Y, 2M, 2C is also stopped.

  Only the image forming device 2K to be used operates in the same manner as the operation of the image forming device in the full color mode described above, and forms a black toner image on the image holding surface of the photosensitive drum 21. Next, the primary transfer device (primary transfer roll) 25K in the image forming device 2K primarily transfers the black toner image formed on the photosensitive drum 21 to the intermediate transfer belt 31. Next, the intermediate transfer device 3 secondarily transfers the black toner image primarily transferred to the intermediate transfer belt 31 onto the recording paper 9 at the secondary transfer position.

  Subsequently, after the intermediate transfer device 3 sends the recording paper 9 onto which the black toner image has been secondarily transferred toward the fixing device 5, the fixing device 5 fixes the toner image on the recording paper 9. Next, the fixing device 5 sends the recording paper 9 on which the toner image has been fixed to the discharge conveyance path 55. The recording paper 9 at this time is finally stored in the discharge container 11.

  With the above operation, one sheet of recording paper 9 having a black and white image composed of a black toner image formed on one side is output, and the image forming operation in the black and white mode, which is the second mode, is completed.

  Next, a control operation when the first mode and the second mode are switched during the continuous image forming operation will be described.

  Here, a case will be described as an example in which the first mode full color mode can be switched to the second mode monochrome mode.

  First, in the central control unit 6, as shown in FIG. 5, it is time to switch based on a switching instruction between the first mode and the second mode (actually a switching instruction from the first mode to the second mode). (Step 10; hereinafter, this is also abbreviated as “ST10”. The subsequent steps are also abbreviated in the same manner.) When it is determined that the switching time has come, It is continuously determined whether or not the last primary transfer (primary transfer of the black toner image at the most downstream position) in the image forming operation in the mode (here, “first mode / full color mode”) is completed (ST11). As the switching time at this time, for example, a time (for example, time t1 illustrated in FIG. 6) at which an image forming operation in the first mode (final page) that is a mode before switching is started is set.

  When it is determined in step 11 that the last primary transfer has been completed (for example, the last primary transfer voltage supply end time t2 has been reached), the central control unit 6 via the power supply control unit 62 performs the primary transfer power supply unit 16. Then, the output voltage of the primary power supply unit 16 is changed from “primary transfer voltage” to “switching voltage”, and the switching voltage is controlled to be supplied to at least the primary transfer roll 25K (ST12). In the first embodiment, the same switching voltage is supplied to the four primary transfer rolls.

  At this time, the power supply control unit 62 changes the output voltage of the primary transfer power supply unit 16 to the switching voltage, and when the output voltage is settled to the switching voltage (voltage A), the primary supplied before that time. Instead of the transfer voltage (voltage 1), the switching voltage (voltage A) is actually output and supplied. At this time, as indicated by a solid line in FIG. 6, the central control unit 6 moves to the primary transfer roll 25 in the image forming apparatuses 2Y, 2M, and 2C that are not used (not used) in the second mode that is the mode after switching. In the first embodiment, since there is only one primary transfer power supply unit 16, as shown by a two-dot chain line in FIG. 6, the primary image in the black image forming device 2K is stopped. A voltage common to the voltage (voltage A) supplied to the transfer roll 25K is supplied in the same manner.

  Subsequently, the central control unit 6 operates the separation mechanism (drive unit) 19 via the separation control unit 63 after the supply of the switching voltage is started (for example, when time t3 is reached). Then, the operation of separating the photosensitive drum 21 from the primary transfer rolls 25Y, 25M, 25C and the intermediate transfer belt 31 in the image forming apparatuses 2Y, 2M, 2C not used in the second mode is started (ST13). At this time, the upstream transfer surface projecting roll 35a is also displaced by the separation mechanism 19 to assist the separation operation (FIG. 1 → FIG. 4).

  Subsequently, the central control unit 6 uses the detection information from the position detection means 72 as to whether or not the primary transfer rolls 25Y, 25M, and 25C in the image forming devices 2Y, 2M, and 2C have reached the separation positions by the separation operation in Step 13. Based on the determination (ST14), when the arrival at the separation position is confirmed (for example, when the arrival at the separation position is confirmed at time t4), the operation of the separation mechanism 19 is controlled via the separation control unit 63. As a result, the separation operation is stopped (ST15). With this separation operation, as shown in FIG. 4, the primary transfer rolls 25Y, 25M, and 25C in the image forming apparatuses 2Y, 2M, and 2C that are not used in the second mode, together with a part of the intermediate transfer belt 31, are connected to the respective image forming apparatuses. 2Y, 2M, and 2C are separated from the photosensitive drum 21.

  Subsequently, after stopping the separation operation, the central control unit 6 changes the output voltage of the primary transfer power feeding unit 16 from the “switching voltage” to the “primary transfer voltage” via the power supply control unit 62. Control is performed so that the primary transfer voltage is supplied to the four primary transfer rolls 25 (Y, M, C, K) (ST16).

  At this time, the power supply control unit 62 changes the output voltage of the primary transfer power supply unit 16 to the primary transfer voltage, and when the output voltage is settled to the primary transfer voltage (voltage 2), the switching that has been supplied so far Instead of the hour voltage, the primary transfer voltage is actually output and supplied. At this time, as shown in FIG. 6, the central control unit 6 does not use the second mode at the time after the separation operation is completed (for example, at time t5 after confirmation of arrival at the separation position). The rotation of the photosensitive drum 21 in the image devices 2Y, 2M, and 2C is stopped and the voltage supply to the charging device 22 is stopped (turned off). Note that the rotation of the photosensitive drum 21 and the voltage supply to the charging device 22 in the image forming device 2K used in the second mode after switching are continued without interruption as shown in FIG.

  Thus, the control operation in the case of switching from the full color mode of the first mode to the black and white mode of the second mode is completed. The image forming operation in the black and white mode that is the second mode after the switching is performed as described above.

  Next, the case where the mode is switched from the black and white mode of the second mode to the full color mode of the first mode will be described as an example.

  Also in this case, first, the central control unit 6 performs switching based on a switching instruction between the first mode and the second mode (actually a switching instruction from the second mode to the first mode) as shown in FIG. The determination is continued until the time comes (ST10). When it is determined that the switching time has come, the last primary in the image forming operation in the mode before the switching (here, “second mode / monochrome mode”). It is determined whether or not the transfer (primary transfer of the black toner image) has been completed (ST11). As the switching time at this time, for example, a time when the image forming operation in the second mode (final page) which is the mode before switching is started is set.

  When it is determined in step 11 that the last primary transfer has been completed (for example, the time t6 at which the supply of the primary transfer voltage for the primary transfer of the last page has been completed) is reached, the central control unit 6 turns on the power supply control unit 62. And controlling the primary transfer power supply unit 16 to change the output voltage of the primary power supply unit 16 from the primary transfer voltage to the switching voltage, and to supply the switching voltage to at least the primary transfer roll 25K (ST12). ). In the first embodiment, the same switching voltage is supplied to the four primary transfer rolls. At this time, the power supply control unit 62 changes the output voltage of the primary transfer power supply unit 16 to the switching voltage, and when the output voltage is settled to the switching voltage (voltage B), the primary supply that has been supplied so far Instead of the transfer voltage (voltage 2), the switching voltage (voltage B) is actually output and supplied.

  Subsequently, the central control unit 6 operates the separation mechanism (drive unit) 19 via the separation control unit 63 after the supply of the switching voltage is started (for example, when time t7 is reached). Then, the operation of bringing the photosensitive drum 21, the primary transfer rolls 25Y, 25M, and 25C, and the intermediate transfer belt 31 into contact with each other in the image forming apparatuses 2Y, 2M, and 2C that are not used in the second mode that is the mode before switching is started ( ST13: The part in parentheses is applicable.) At this time, the upstream transfer surface-developing roll 35a is also displaced by the separating mechanism 19 to assist the contact operation (FIG. 4 → FIG. 1). Further, as shown in FIG. 6, the central control unit 6 performs the second mode at a time (for example, a time between time t6 and time t7) before the end of the last primary transfer and before starting the contact operation. In the image forming apparatuses 2Y, 2M, and 2C that are not used, rotation of the photosensitive drum 21 is started and voltage supply to the charging device 22 is started (turned on).

  Subsequently, the central control unit 6 uses the detection information from the position detection unit 72 as to whether or not the primary transfer rolls 25Y, 25M, and 25C in the image forming apparatuses 2Y, 2M, and 2C have reached the contact position by the contact operation in Step 13. Based on the determination (ST14, the part in parentheses is applicable) and confirming the arrival at the contact position (when the arrival at the contact position is confirmed at time t8), via the separation control unit 63 The contact operation is stopped by controlling the operation of the separation mechanism 19 (ST15, the portion in parentheses corresponds). By this contact operation, as shown in FIG. 1, the primary transfer rolls 25Y, 25M, and 25C in the image forming apparatuses 2Y, 2M, and 2C that are not used in the second mode interpose the intermediate transfer belt 31, and the respective image forming apparatuses. 2Y, 2M, and 2C are in contact with the photosensitive drums 21, respectively.

  Subsequently, after stopping the contact operation, the central control unit 6 controls the primary transfer power supply unit 16 via the power supply control unit 62, and changes the output voltage of the primary power supply unit 16 from the switching voltage to the primary transfer voltage. Then, the primary transfer voltage is controlled to be supplied to the four primary transfer rolls 25 (Y, M, C, K) (ST16).

  At this time, the power supply control unit 62 changes the output voltage of the primary transfer power supply unit 16 to the primary transfer voltage, and when the output voltage is settled to the primary transfer voltage (voltage 1), the switching that has been supplied so far Instead of the hourly voltage (voltage B), the primary transfer voltage (voltage 1) is actually output and supplied. At this time, when the primary transfer voltage is supplied from the primary transfer power supply unit 16 (for example, when the primary transfer voltage supply start timing t9 is reached), the primary transfer rolls in the image forming apparatuses 2Y, 2M, and 2C that are not used in the second mode. The supply of the primary transfer voltage (voltage 1) from the primary transfer power supply unit 16 is also started to 25Y, 25M, and 25C. It should be noted that the rotation of the photosensitive drum 21 and the voltage supply to the charging device 22 in the image forming device 2K used in the second mode before switching are not interrupted as shown in FIG. To continue.

  Thus, the control operation in the case of switching from the black and white mode of the second mode to the full color mode of the first mode is completed. The image forming operation in the full color mode which is the first mode after the switching is performed as described above.

  In this image forming apparatus 1, when the first mode and the second mode are switched during the continuous image forming operation, the above-described control operation (particularly, before the separation operation or the contact operation is started). Until the process is completed, control is performed such that the switching voltage that is changed to a value smaller than the primary transfer voltage at the time of image formation is supplied from the primary transfer power supply unit 16 and supplied, so the following effects can be obtained.

  That is, when switching between the first mode and the second mode during the continuous image forming operation, the photosensitive drums 21 and the intermediate transfer belts of the image forming apparatuses 2Y, 2M, and 2C that are not used in the second mode image forming operation. 31 and the primary transfer rolls 25Y, 25M, and 25C are less likely to be discharged when they are separated or contacted by the separation operation or the contact operation, and as a result, occurrence of streak-like image quality defects due to such discharge is suppressed. The The streak-like image quality failure mainly means that the poorly charged portions scattered in a streak-like manner along the axial direction of the image holding surface of the photosensitive drum 21 remain locally as electrostatic history, and the poorly charged portion. Is a phenomenon in which streaky density unevenness occurs in the toner image, and the density unevenness appears periodically in the rotation direction of the photosensitive drum 21 and is included in the final image.

  In addition, since the switching voltage supplied from the primary transfer power supply unit 16 is not turned off (0 V) at the time of the switching, the switching voltage supplied from the primary transfer power supply unit 16 before switching is supplied after switching. It is possible to shorten the time required for stabilization by changing to the primary transfer voltage to be output, and as a result, the above-mentioned streak-like image quality failure is caused by the image formation in the mode after the switching. This can be suppressed without increasing the waiting time until the operation is started.

  FIG. 7 shows the results of a test relating to the relationship between the switching voltage and the presence or absence of occurrence of streak-like image quality defects, performed using the image forming apparatus 1.

  In this test, the contact operation between the photosensitive drums 21 of the image forming apparatuses 2Y, 2M, and 2C not used in the second mode, the intermediate transfer belt 31, and the primary transfer rolls 25Y, 25M, and 25C is performed under the following conditions. The voltage at the time of switching supplied from the primary transfer power supply unit 16 is variously changed from before until the operation is completed, and the test image with the entire halftone in the image forming operation in the mode (second mode) after the switching is performed on plain paper Whether or not a streak-like image quality defect occurred in the obtained image and the state of the occurrence were examined.

  As the primary transfer roll 25 (Y, M, C, K) in the four image forming apparatuses 2 (Y, M, C, K), the image forming apparatus 1 has a predetermined roll diameter (for example, made of a metal material such as stainless steel). A conductive inelastic roll having a diameter of 8 mm) was applied. Further, these primary transfer rolls 25 (Y, M, C, K) have a predetermined distance from the portion where the intermediate transfer belt 31 of the photosensitive drum 21 (outer diameter is about 30 mm) contacts to the downstream side in the rotation direction of the drum 21. It arrange | positioned so that it may oppose in the position which shifted | deviated (for example, 5 mm). The intermediate transfer belt 31 has a thickness of 80 μm, a surface resistivity of 10.5 × log Ω / □, and a volume resistivity of 10.0 × log Ω · cm formed by mixing a resistance adjuster with polyimide resin. A semiconductive belt was applied, and the belt was rotated so that the surface moving speed was 120 mm / sec. From the primary transfer power supply unit 16, a high voltage of 2.0 kV was supplied as a primary transfer voltage before the separation operation (before switching). Other conditions were the same.

  From the results shown in FIG. 7, it is possible to suppress the occurrence of streak-like image quality to some extent when the switching voltage is +1.0 kV, and to cause streak-like image quality failure when the switching voltage is +0.8 kV or less. It can be seen that the occurrence of can be prevented. When the switching voltage is +1.4 kV or 1.2 kV, the switching voltage is a value that is smaller than the primary transfer voltage (here, 2.0 kV). It can be seen that a noticeable image quality failure occurs. From this test result, when the switching voltage becomes at least +1.0 kV or more, it is assumed that at least the photosensitive drum 21 and the intermediate transfer belt 31 have exceeded the discharge start voltage and discharge has occurred. Is done.

  Further, according to the research of the present inventor, when the switching voltage is set to an extremely small value of “0V” and “a value close to 0V”, as shown in FIG. ) The required time m1 required to change the output voltage from an extremely small value such as 0V to the value of the primary transfer voltage (2.0 kV) and stabilize it (from the change start time t0). Accumulated time required until time ta: FIG. 8A) is, for example, the required time m2 required to change the output voltage from 0.8 kV to the value of the primary transfer voltage (2.0 kV) and make it settled (change start time) It has been confirmed that the accumulated time required from t0 to the time point tb when the state is stabilized is longer than that in FIG. 8b) (m1> m2). When the required time m increases, the waiting time until the image forming operation in the mode after switching is started is increased. For this reason, it is preferable to set the voltage at the time of switching not to 0 V, and to a value that can relatively shorten the required time m.

  The voltage at the time of switching is the discharge start voltage between each photosensitive drum 21 of the image forming devices 2Y, 2M, 2C not used in the second mode and the intermediate transfer belt 31, or each photosensitive drum 21 and each photosensitive drum 21. It is possible to set a voltage value as high as possible within a range not exceeding the discharge start voltage between the primary transfer rolls 25Y, 25M, and 25C facing the above, for example, preventing the occurrence of streak-like image quality defects and the standby time. It is preferable from the viewpoint of achieving both increase avoidance.

[Other embodiments]
In the first embodiment, the primary transfer roll 25 and the intermediate transfer belt 31 are in contact with each other when being separated from the photosensitive drum 21 in the image forming apparatuses 2Y, 2 and 2C that are not used in the image forming operation in the second mode. In this case, the primary transfer roll 25 and the intermediate transfer belt 31 may be separated from each other in a state of being separated from each other.

  In the first embodiment, as the switching voltage, as shown in FIG. 6, the voltage A supplied when the switching is performed by performing the separation operation and the voltage B supplied when the switching is performed by the contact operation. Are set to the same voltage (voltage A = voltage B), but different values may be set as necessary. In addition, as the primary transfer voltage, the voltage 1 supplied during the image forming operation in the first mode and the voltage 2 supplied during the image forming in the second mode are set to different values (for example, voltage 1> voltage 2). Although it is assumed, the same value may be set as necessary. For example, regarding the primary transfer voltage, the voltage 1 can be set to +2.0 kV and the voltage 2 can be set to +1.8 kV. In this case, for example, 0.8 kV can be used as the switching voltage. Furthermore, as the primary transfer power supply unit 16, a constant voltage control type power supply device is illustrated, but a constant current control type power supply device may be applied.

  As an image forming apparatus, the image forming apparatus 2 may include a plurality of image forming apparatuses other than four. The primary transfer roll 25 may be a semiconductive elastic roll. Further, the second mode monochromatic mode may be a mode for forming a monochromatic image composed of a color other than black. The photosensitive drum 21 may be a belt-shaped photosensitive member.

  In addition, the image forming apparatus 1 is an example of an annular belt that conveys the recording paper 9 so as to sequentially pass the primary transfer positions in the plurality of image forming apparatuses 2 instead of the intermediate transfer apparatus 3 (intermediate transfer belt 31). The present invention can be similarly applied even to an image forming apparatus (in this case, there is no secondary transfer process) having a sheet conveying belt (apparatus).

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 2 ... Image forming apparatus 2Y, 2M, 2C, 2K ... Multiple image forming apparatus 6 ... Central control part (a part of control means)
9: Recording paper (an example of recording material)
16: Primary transfer power supply section (an example of power supply means)
21 ... Photosensitive drum (an example of an image carrier)
22: Charging device (an example of an imaging device)
23. Exposure apparatus (an example of image forming equipment)
24. Developing device (an example of image forming device)
25. Primary transfer device (an example of a transfer member)
31 ... Intermediate transfer belt (an example of an annular belt)
62 ... Power control unit (part of control means)

Claims (2)

A plurality of image forming apparatuses including at least an image holding body and an image forming device that forms a toner image on the image holding body;
An annular belt rotating in sequence through the image carrier of each of the imaging devices;
A recording target in which the outer peripheral surface of the annular belt is brought into contact with the image carrier of each image forming device and the toner image on each image carrier is conveyed by the outer peripheral surface of the annular belt or the annular belt. A plurality of transfer members each transferred to the material;
Power supply means for supplying a common transfer voltage to each of the transfer members and capable of changing an output voltage;
A first mode in which an image is formed using all of the plurality of image forming devices; and an annular shape from an image holding body of an image forming device that uses a part of the plurality of image forming devices and does not use the image forming device. When switching between the second mode in which the image is formed while the belt and the transfer member are separated from each other during the continuous image forming operation, the image carrier of the unused image forming device, the annular belt, and the transfer Control means for controlling the power supply means to supply a switching voltage changed to a value smaller than the transfer voltage at the time of image formation from the start of the separation operation or contact operation with the member to the completion of the operation. An image forming apparatus comprising:   The voltage at the time of switching is a value smaller than a discharge start voltage between the image carrier of the unused image forming device and the annular belt or between the image carrier and the transfer member facing the image carrier. The image forming apparatus according to claim 1, wherein the voltage is a negative voltage.

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