JP5040957B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which removes a foreign matter adhering to a photoreceptor while minimizing the shortening of the life of the photoreceptor caused by the removal of the foreign matter. <P>SOLUTION: The image forming apparatus having a plurality of photoreceptors is provided with a photoreceptor cleaner in each of the plurality of photoreceptors, and with a press-contact part which sets each of the plurality of photoreceptors to one of a press-contact state and a release state, where a recovery mode for cleaning a surface of the photoreceptor by the photoreceptor cleaner while rotating at least one of the photoreceptors when an image is not formed is performed. In the recovery mode, when a part of the plurality of photoreceptors is set to an object of the recovery mode, at least one of the photoreceptor that is the object of the recovery mode and the photoreceptor that is not the object of the recovery mode is set to the release state by the press-contact part. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus for forming an image by forming a toner image on a photoreceptor and transferring the toner image onto a medium. More specifically, the present invention relates to an image forming apparatus that performs a recovery mode in which a photoconductor is rotated at a time other than image formation as a countermeasure against so-called image flow that is a kind of image noise.

  In an image forming apparatus using a photoreceptor, a charging process for charging the photosensitive layer to a constant potential is performed prior to exposure for writing an electrostatic latent image on the photosensitive layer. In the case of a device that performs this charging process by a non-contact discharge method such as a scorotron method, discharge products such as nitrogen oxides are generated. This discharge product tends to promote the attachment of hygroscopic foreign matter to the surface of the photoreceptor. For this reason, the surface resistance of the photoconductor in a state where foreign matter has accumulated decreases in a high humidity environment. As a result, the potential contrast between the image portion and the background portion in the electrostatic latent image is lowered, and the image is disturbed. This is image flow. For this reason, the adhering foreign matter is scraped and removed by a member such as a blade.

  By the way, the photosensitive layer wears down with use and the film thickness decreases. When the film thickness of the photosensitive layer is less than the minimum required amount, the life of the photoreceptor is exhausted. In particular, in the case where an organic photosensitive material is used for the photosensitive layer, the degree of wear of the photosensitive layer is large. For this reason, various measures have been proposed, such as providing a wear-resistant coat layer on the surface of the photosensitive layer, or using a material that is as hard to wear as possible as the material of the photosensitive layer.

  However, there is another problem in making the photosensitive layer difficult to wear in this way. If the photosensitive layer is hard to be polished, it is difficult to scrape foreign matter with the aforementioned blade. For this reason, in the technique of Patent Document 1, the photosensitive member is rotated by a predetermined number of rotations at a time other than the time of image formation (recovery mode). Since only the rotation of the photoconductor during image formation is insufficient to scrape foreign matter, this can be compensated by rotating the photoconductor even during non-image formation. Thereby, the surface resistance of the photoreceptor can be recovered to a high state. For this recovery mode, it is only necessary to rotate the photoconductor, and peripheral devices such as a charger may remain in a resting state.

JP 2003-29474 A

  Incidentally, some image forming apparatuses form color images. Some color image forming apparatuses are called a tandem type having a plurality of photoconductors for each color. A tandem type color image forming apparatus usually includes image forming units for four colors of Y (yellow), M (magenta), C (cyan), and K (black).

  However, these four image forming units do not always operate. For example, when forming a black and white image, it is sufficient to operate only the K color image forming unit. Rather, if all the four color image forming units are operated in this case, the life of the photoconductor and the like is wasted in the Y, M, and C color image forming units that do not need to be operated. In addition, it takes extra time for image formation. For this reason, only the image forming unit of a necessary color is operated according to the color included in the image to be formed.

  Therefore, the cumulative usage amount of each image forming unit is different for each color. For this reason, the degree to which the above-described recovery mode is required is also different for each color. This is because the accumulation state of foreign matter on the surface of the photosensitive layer depends on the cumulative usage amount. Therefore, the number of rotations at which the photoconductor should be rotated in the recovery mode is also different for each image forming unit. For this reason, if the recovery mode is performed all at once in accordance with the worst-case imaging unit, depending on the imaging unit, rotation in the recovery mode is excessively performed. As a result, the image forming unit has a problem that the life of the photoconductor is wasted and the original life cannot be achieved.

  The present invention has been made to solve the above-described problems of the prior art. That is, an object of the present invention is to provide an image forming apparatus in which the foreign matter adhering to the photoconductor is removed and the lifetime of the photoconductor is thereby minimized.

The image forming apparatus of the present invention, which has been made for the purpose of solving this problem, has a plurality of photoconductors, forms toner images on the photoconductors, and transfers the toner images onto the transfer body. An apparatus for forming an image by superimposing the plurality of photoconductors, the photoconductor cleaner provided on each of the plurality of photoconductors and contacting the position after transfer of the photoconductor, and the plurality of photoconductors, respectively, with respect to the transfer body. Image forming for forming an image by rotating at least one of the pressure contact portion in the pressure contact state in which the pressure contact is made and the release state in which the pressure contact is released, and at least one of the photosensitive members by the pressure contact portion. a control unit, and a recovery mode control unit for recovery mode for cleaning the surface of the photosensitive member by at least one is rotated during non-image formation photoconductor cleaner of the photosensitive member, the recovery mode controller, When performing recovery mode while Utsushitai is stopped, at least the target is a photosensitive member of the recovery mode, it is an unlocked state by the pressure contact portion.

In this image forming apparatus, the recovery mode is performed during non-image formation. In the recovery mode, the photosensitive member is rotated and the surface of the photosensitive member is cleaned by the photosensitive member cleaner. Here, in the present invention, a pressure contact portion is provided. As a result, the recovery mode can be performed in a state in which the pressure contact between the photosensitive member and the transfer member is released. In particular, when the recovery mode is executed while the transfer member is stopped, at least the photosensitive member that is the target of the recovery mode is set to the released state. Thus, when the recovery mode is executed for only some of the photoconductors, the other photoconductors do not need to rotate. Therefore, excessive rotation of the photoreceptor is prevented.

Here, the recovery mode control unit sets the rotation time required to rotate the photoconductor in the recovery mode for each of the plurality of photoconductors, the environmental conditions, the standing time from the previous image formation, and the durable use of the photoconductor. conditions determined based on at least one of the group comprising, as an object to be rotated is determined to require a photoreceptor, and executes a recovery mode for a time determined as the rotation time required. This avoids performing the recovery mode for an excessively long time.

The image formation control unit performs color image formation using two or more of the plurality of photoconductors, and the recovery mode control unit receives the color image formation when there is a request for color image formation. The required rotation time is determined for each photoconductor used for forming, and based on the determined required rotation time, execution of the recovery mode of each photoconductor is started so that the end times thereof are aligned, and of the execution time period of the recovery mode, for those respective photosensitive hours to carry out the recovery mode for all bodies, by rotating the transfer member with all of the photosensitive member thereof to the pressure contact state, the end of the recovery mode At the same time, it is desirable to start color image formation by the image formation control unit. It is also desirable that the recovery mode control unit determines zero for a photoconductor whose cumulative usage is less than or equal to a predetermined minimum amount when determining the necessary rotation time of each photoconductor in the recovery mode.

  Alternatively, the image formation control unit performs non-full-color image formation using a part of the plurality of photoconductors, and the recovery mode control unit receives the request for non-full-color image formation. A required rotation time is determined for a photoconductor used for non-full-color image formation, and based on the determined required rotation time, a recovery mode of the photoconductor is executed with the photoconductor in a pressure contact state, and the recovery mode is determined. The non-full-color image formation by the image formation control unit is started at the end of the process, and the necessary rotation time is determined for the resting photoconductor other than the non-full-color image photoconductor. In parallel with the recovery mode or the subsequent non-full-color image formation, the recovery mode of the resting photoreceptor is rested on the basis of the determined required rotation time. It is desirable to carry out the photoreceptor as the released state by the pressure contact portion.

  In this case, it is desirable that the recovery mode control unit starts the execution of the recovery mode of the pause photoconductor after a request for a new image formation using the pause photoconductor. In this way, the recovery mode performed for the resting photoreceptor is not wasted.

  Further, in this case, when there is a new request, the recovery mode control unit, the remaining required time until the scheduled end time of the non-full-color image formation previously requested, and the photoconductor used for image formation according to the new request. Compared with the longest required rotation time of a resting photoconductor that is not currently used for non-full-color image formation, and the former is greater than the latter, The execution of the rest photoconductor recovery mode is started so that the time when the full color image formation is scheduled to end and the end of the rest photoconductor recovery mode are aligned, and the previously requested non-full color image formation and rest photoconductor recovery are started. At the end of the mode, the image formation control unit starts image formation according to a new request, and when the latter is longer than the former, the recovery mode for the longest rotation time of the photosensitive member is immediately executed. The recovery mode of the rest of the rest photoreceptors other than the one associated with the longest rotation time is started so that the end of the rest mode of each rest photoreceptor is completed, and the recovery mode of each rest photoreceptor is started. It is desirable to start image formation related to a new request by the image formation control unit at the end.

  The image forming apparatus of the present invention also has a humidity sensor that outputs the humidity in the apparatus, and the recovery mode control unit sets the recovery mode only when the humidity output by the humidity sensor is equal to or higher than a predetermined value. It is desirable to execute. This is because adhesion of foreign matter to the photoconductor is not a problem in a low humidity situation.

  According to the present invention, there is provided an image forming apparatus in which the foreign matter adhering to the photoconductor is removed and the lifetime of the photoconductor is thereby minimized.

1 is an overall configuration diagram of an image forming apparatus according to an embodiment. 2 is a block diagram illustrating a configuration of a control system of the image forming apparatus according to the embodiment. FIG. 6 is a timing chart illustrating an example (Example 1) of recovery mode execution timing in the image forming apparatus according to the embodiment. 10 is a timing chart illustrating an example (Example 2) of execution timing of a recovery mode in the image forming apparatus according to the embodiment. 10 is a timing chart illustrating an example (Example 3) of execution timing of a recovery mode in the image forming apparatus according to the embodiment. 10 is a timing chart illustrating an example (Example 4) of execution timing of a recovery mode in the image forming apparatus according to the embodiment. 10 is a timing chart illustrating an example of execution timing of a recovery mode in the image forming apparatus according to the embodiment (modified example of Example 4).

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to the image forming apparatus having the basic configuration shown in FIG. The image forming apparatus 10 of FIG. 1 has a transfer belt 12, and four color image forming portions 20 Y (yellow), 20 M (magenta), 20 C (cyan), and 20 K (black) are arranged along the transfer belt 12. This is a tandem type image forming apparatus. The transfer belt 12 is a semiconductive material in which carbon is dispersed in a resin material such as polycarbonate, polytetrafluoroethylene, or polyimide, and is stretched around rollers 14 and 15. A secondary transfer roller 17 is provided facing the roller 14, and a belt cleaner 18 is provided facing the roller 15.

  The image forming unit 20Y includes a charging device 27, an exposure device 28, a developing device 23 (which may be a two-component system or a one-component system), a primary transfer roller 24, a photoconductor cleaner 25, and a charge removal device 26 with the photoconductor 21 as the center. It is arranged and configured. The photoconductor 21 in this embodiment uses an aluminum tube as a base material and uses an organic photosensitive material for the photosensitive layer (thickness of about 25 μm). Further, an overcoat layer having a thickness of about 2 to 3 μm is laminated on the photosensitive layer to extend the life. Among the peripheral devices of the photosensitive member 21, the charging device 27 is of a scorotron type and includes a stabilizing plate and a mesh electrode in addition to the discharge electrode. It is desirable to have an internal exhaust mechanism. The developing device 23 includes a developing roller 19.

  The primary transfer roller 24 is provided with a pressure contact / separation switching mechanism 29. As a result, the transfer belt 12 can take two states, that is, a pressure contact state in which the transfer belt 12 is pressed against the photosensitive member 21 and a release state in which the pressure contact is released via the primary transfer roller 24. Yes. Switching between the two states is possible for each photosensitive member 21. FIG. 1 shows a state in which all are in a pressure contact state. In the released state, it is desirable that the transfer belt 12 and the photosensitive member 21 are completely separated from each other, but the pressure contact force may be weakened as compared with the pressure contact state.

  In many cases, the static eliminator 26 is disposed at a position downstream of the photoconductor cleaner 25 and upstream of the charging device 27. However, as is the case with this embodiment, it may be disposed at a position upstream of the photoconductor cleaner 25. . This is because if the transfer efficiency of primary transfer is high, that is, if there is little transfer residual toner, the effect of the transfer residual toner on the charge removal is small. In addition, this arrangement is rather advantageous in terms of space efficiency and cleaning efficiency.

  The other image forming units 20M, 20C, and 20K have the same configuration as the image forming unit 20Y. Thus, the four color toner images formed by the image forming units 20Y, 20M, 20C, and 20K are superimposed on the paper P via the transfer belt 12. An environment sensor 30 is disposed inside the image forming apparatus 10.

  Subsequently, a control system of the image forming apparatus 10 will be described. The control system of the image forming apparatus 10 is configured as shown in the block diagram of FIG. The image forming apparatus 10 includes a control unit 31. The control unit 31 rotates the photosensitive member 21, applies a bias to the charging device 27, emits light from the exposure device 28 based on image data, and applies a bias to the developing device 23 (for example, Vb: −400 V, Vpp: 1.5 kV, DCAC superimposing bias of about 3 kHz) and rotation of a rotating object (developing roller 19 and the like) inside thereof, bias application to the primary transfer roller 24, light emission of the static elimination device 26 (this is not related to the image data), pressure contact / separation switching mechanism Each control of the state 29, rotation of the transfer belt 12, and application of a bias to the secondary transfer roller 17 are performed. The control unit 31 also controls each part (paper feeding, fixing, etc.) not appearing in FIG. Therefore, the control unit 31 has necessary functions such as a memory function, a calculation function, and a timekeeping function.

  For this purpose, job commands and environmental data are input to the control unit 31. The job command is a print execution command signal input to the image forming apparatus 10 from an external device such as a personal computer. The environmental data is environmental value data acquired by the environmental sensor 30.

  In the image forming apparatus 10 configured as described above, image formation (image forming mode) is performed as follows under the control of the control unit 31. First, the surface of the photoconductor 21 is charged to a uniform potential (for example, about −600 V) by the charging device 27. Thereafter, the electrostatic latent image is written on the surface of the photosensitive member 21 by the exposure device 28, the toner is applied to the electrostatic latent image by the developing device 23, and the toner image is transferred to the transfer belt 12 by the primary transfer roller 24. Transfer, removal of transfer residual toner by the photoconductor cleaner 25, and charge removal of the residual charge by the charge removal device 26 are performed. The toner image transferred to the transfer belt 12 is transferred onto the paper P by the secondary transfer roller 17 after the four colors are superimposed on the transfer belt. Thereafter, the toner image fixing process is performed on the paper P which has received the transfer of the toner image.

  When the image is formed, the transfer belt 12 is naturally brought into a pressure contact state by the pressure contact / separation switching mechanism 29. When forming a full-color image, the transfer belt 12 is brought into a pressure contact state at the positions of all the primary transfer rollers 24. When only a part of the image forming units 20Y, 20M, 20C, and 20K is used as in the case of a monochrome image, only the position of the primary transfer roller 24 of the image forming unit to be used is brought into a pressure contact state. Therefore, it is desirable that the position of the primary transfer roller 24 of the image forming unit that is not used be in a released state. This prevents wasteful consumption of the photoreceptor 21 of the image forming unit that is not used.

  Next, the recovery mode in this embodiment will be described. In the image forming apparatus 10 of the present embodiment, a recovery mode in which the photosensitive member is rotated at a time other than the time of image formation is performed as a measure against image flow. As described in the section of the prior art, foreign substances accumulate on the photosensitive member 21 due to discharge products generated by the discharge in the charging device 27, so that they are removed. The recovery mode is also performed under the control of the control unit 31.

  That is, in the recovery mode, only the photosensitive member 21 is rotated, and other devices such as the charging device 27 remain stopped. The transfer belt 12 is also stopped. In the recovery mode, the surface of the photoconductor 21 is polished by the photoconductor cleaner 25 by rotating the photoconductor 21. As a result, the foreign matter adhering to the surface of the photoconductor 21 is stripped off, and the surface of the photoconductor 21 is cleaned. In this way, it is restored to a state where an image with good image quality can be formed.

  The recovery mode may be performed simultaneously for all four photoconductors 21. In addition, a specific one of the four photoconductors 21 may be performed. Details thereof will be described later. When the recovery mode is executed, the transfer belt 12 is released by the press contact / separation switching mechanism 29 in principle. However, the recovery mode may be executed with the transfer belt 12 in a pressure contact state. Details of this point will be described later.

  Here, it has been described above that the devices other than the photoconductor 21 remain stopped. However, the developing roller 19 of the developing device 23 may be stopped or rotated. By rotating the developing roller 19 together with the photosensitive member 21 in the recovery mode, a small amount of external additive material or toner (amount of fog in the background portion during image formation) is supplied to the photosensitive member 21 from the developing device 23. Become. Since this acts as an abrasive in the photoconductor cleaner 25, the photoconductor 21 can be cleaned more satisfactorily. In the case of an image forming apparatus in which the photoreceptor cleaner 25 can be retracted, the photoreceptor cleaner 25 must not be in the retracted state in the recovery mode.

  Next, the execution time of the recovery mode will be described. As described above, the recovery mode is performed to remove foreign matter accumulated on the photosensitive member 21. Its purpose is to prevent image drift. The degree of occurrence of image flow depends on factors such as the cumulative usage of the photosensitive member 21 (the number of images formed so far), the humidity, and the time for which the image formation is left after the previous image formation. That is, as the photoconductor 21 approaches the end of life from the new product, the image flow is likely to occur. Also, image flow is more likely to occur when the humidity is higher than when the humidity is low. Also, the longer the standing time, the easier the image flow occurs. When the image flow is likely to occur, it is necessary to rotate the photoconductor 21 many times in the recovery mode.

  Therefore, a table that gives the execution time of the recovery mode according to the status of these factors is prepared in advance in the internal memory of the control unit 31. Table 1 is a part of it. The unit is seconds. The vertical axis in Table 1 represents the ratio of the accumulated usage of the photoconductor 21 to the total lifetime. In Table 1, the higher the humidity, the longer the execution time is given. Also, a longer execution time is given as the photoconductor approaches the end of its life.

  However, in Table 1, when the relative humidity is less than 55%, it is uniformly zero regardless of the cumulative usage amount of the photoconductor 21. That is, the recovery mode is not performed when the relative humidity is less than 55%. That is, the minimum humidity for executing the recovery mode is predetermined. Even when the cumulative usage of the photoconductor 21 is 50% or less, it is uniformly zero regardless of the humidity. That is, even when the life of the photoconductor 21 is more than half, the recovery mode is not performed for the photoconductor 21. That is, the minimum accumulated usage amount for executing the recovery mode is also determined in advance.

  Table 1 is a table applied when the neglected time from the end of the previous image formation is within a range of 4 to 20 hours. There are a plurality of tables similar to Table 1 depending on the leaving time. In each of these tables, two points are common: the higher the humidity, the longer the execution time, and the closer the end of life, the longer the execution time. Comparing columns in which the humidity and accumulated usage are the same between the tables, the table corresponding to the longer standing time has a longer execution time than the table corresponding to the shorter aging time. In the table when the standing time is less than 4 hours, the table is uniformly zero regardless of the humidity and the accumulated usage amount. That is, the recovery mode is not performed for the photoconductor 21 until 4 hours have elapsed since the end of the previous image formation. That is, the minimum leaving time for executing the recovery mode is also determined in advance.

  Here, the execution time is determined by three factors, that is, the cumulative usage amount of the photoreceptor 21, the humidity, and the leaving time from the end of the previous image formation. However, the execution time is not necessarily limited to these three factors. Absent. Although the control accuracy is lowered, the execution time may be determined using only two or one of the above three factors. Conversely, other factors may be taken into account.

  In addition, two factors other than humidity among the above three may be different depending on colors in one image forming apparatus 10. This is because only some of the four image forming units 20Y, 20M, 20C, and 20K may be used. This is also because the photoconductors 21 of the four image forming units may be individually replaced. Therefore, the recovery mode execution times required by the four photoconductors 21 do not always match.

  For this reason, for example, when the recovery mode is performed on all four photoconductors 21, if the recovery mode is executed in line with the longest of the four execution times, depending on the photoconductor 21, excessive wear may occur. Will end up. Therefore, even when the recovery mode is executed for all four photoconductors 21, the execution time should be determined for each photoconductor 21. Even in such a case, the recovery mode can be executed for all four photoconductors 21 simultaneously for the shortest execution time portion of the four execution times. For the remaining execution time, the recovery mode is executed for only a part of the photoconductors 21. At that time, it is possible to perform image formation using only the photoconductor 21 that is not executing the recovery mode in parallel with the recovery mode. That is, the recovery mode can be executed for each photoconductor 21 at the time of non-image formation for each photoconductor 21.

  The execution timing of the recovery mode may be any time during non-image formation, but is preferably before the start of image formation. If there is a gap between the end of the recovery mode and the start of image formation, the state of the photoreceptor 21 may deteriorate again during that time. This is because the recovery mode must be executed again before starting image formation.

  A specific example of recovery mode execution timing will be described below. First, as a first exemplary embodiment, a case where the image forming apparatus 10 receives a full-color image formation command will be described. In the formation of a full-color image, all four photosensitive members 21 are used. FIG. 3 is a timing chart of the recovery mode performed in this case. In the example shown in FIG. 3, it is assumed that the switching between the pressure contact state and the release state of the transfer belt 12 by the pressure contact / separation switching mechanism 29 is performed uniformly at the positions of the primary transfer rollers 24 of all colors. . The release state is the initial state. In FIG. 3, it is assumed that a full-color image formation command is received at time T1. Then, first, the required amount of the recovery mode in each photoconductor 21 is determined (see Table 1 and the description before and after that).

  Here, the three necessary parameters are the accumulated usage amount of the photosensitive member 21, the standing time from the end of the previous image formation, and the humidity. Of these, the two other than humidity may differ for each photoconductor 21. Therefore, the required amount of the recovery mode in each photoconductor 21 may be different for each photoconductor 21. FIG. 3 shows an example in which the required amounts for the three color photoreceptors 21 of Y, M, and C are the same, and the necessary amount for the K photoreceptor 21 is about half that amount. ing.

  For this reason, first, the rotation of the photosensitive member 21 of three colors of Y color, M color, and C color is started, and the recovery mode for these three colors is started. Time T2 is the time at which the rotation of the photosensitive members 21 of these three colors starts up. The rotation of the transfer belt 12 has not yet started. Then, the rotation of the K-color photoconductor 21 is started so that the K-color recovery mode can be started at a time T3 later than the time T2. After time T3, the recovery mode is simultaneously executed for all four color photoconductors 21. Then, the recovery mode is terminated at time T4, and the mode is shifted to the image forming mode. Therefore, at this time, the pressure separation / separation switching mechanism 29 is switched to the pressure contact state. Also, the rotation of the transfer belt 12 starts. Thereafter, a full-color image is formed by each clean photoconductor 21 immediately after the recovery mode is executed.

  In FIG. 3, the time from time T2 to time T4 is the necessary amount of the recovery mode for the three-color photoconductor 21 of Y color, M color, and C color. That is, when a full-color image formation command is received at time T1, the time required to start up rotation of the photosensitive member 21 (time T1 to time T2) and the necessary amount of the three-color recovery mode (time T2 to time T4) Thus, the start time T4 of the image forming mode is determined. Then, retroactively, time T3 is determined. Naturally, the retroactive amount is a necessary amount of the recovery mode for the K-color photoconductor 21. In other words, the K color recovery mode is started with a delay corresponding to the difference in the required amount as compared with the multicolor recovery mode. As a result, the end of the recovery mode is aligned for the K color, the Y color, the M color, and the C color.

  In the example of FIG. 3, the recovery mode for the K photoconductor 21 is not executed before the time T3. Therefore, the K-color photoconductor 21 is not polished during this period. For this reason, excessive wear of the photosensitive member 21 with a small necessary amount is suppressed as compared with the case where the recovery mode is executed for all four color photosensitive members 21 regardless of the necessary amount for each color. As a result, the wear of each photoconductor 21 is minimized.

Next, as a second embodiment, an example of the timing chart of FIG. 4 will be described. The example of FIG. 4 is common to the example of FIG. 3 in the following points.
The switching between the pressure contact state and the release state of the transfer belt 12 by the pressure contact / separation switching mechanism 29 is performed uniformly at all the color positions.
-A full color image formation command was received at time T1.
The required amount of the recovery mode for each color determined is the same for the three colors, Y, M, and C, and about half that for the K color.

  4 differs from the example of FIG. 3 in the state of the pressure contact / separation switching mechanism 29 in the period (time T3 to time T4) in which the photoconductors 21 of all four colors are targeted for the recovery mode. That is, the pressure contact / separation switching mechanism 29 in this period remains in the released state in the example of FIG. 3, but is in the pressure contact state in the example of FIG. Therefore, in the example of FIG. 4, the transfer belt 12 is rotated during the period (time T3 to time T4). That is, the rotation of the transfer belt 12 is started at time T3.

  On the other hand, the period from time T2 to time T3 is a period in which the K-color photoconductor 21 is not the target of the recovery mode. In other words, this period is a period in which only a part of the photoconductors 21 is the target of the recovery mode. During this period, the pressure contact / separation switching mechanism 29 is in a released state. For this reason, the K-color photoreceptor 21 is prevented from over-rotating. If the pressure contact / separation switching mechanism 29 can be switched independently for each photoconductor 21, it is not always necessary to release all the photoconductors 21 during this period. It suffices that at least one of the photoreceptor 21 that is the object of the recovery mode and the photoreceptor 21 that is not the object of the recovery mode is in the released state.

  Even in this case, the wear of each photoconductor 21 can be minimized. This is because, during this period, all the four color photoconductors 21 and the transfer belt 12 are rotated, so that the wear of the photoconductor 21 due to friction with the transfer belt 12 does not cause a problem. By doing as shown in FIG. 4, when the recovery mode ends at time T4, image formation can be started quickly.

  Subsequently, as a third embodiment, an example of a timing chart of FIG. 5 will be described. The example shown in FIG. 5 is an example in the case of receiving a command for forming a monochrome image of K color. In the formation of a K monochrome image, only the K color of the four photoreceptors 21 is used. In the example of FIG. 5, the switching between the pressure contact state and the release state of the transfer belt 12 by the pressure contact / separation switching mechanism 29 is performed uniformly for the positions of the three colors of Y color, M color, and C color. Shall. This initial state is a released state. On the other hand, the position of the K color is assumed to be switched independently of the three colors. This initial state is a pressure contact state, which is not shown in FIG. 5, but remains in the pressure contact state during the period shown in FIG.

  In such an example, when a monochrome image formation command is received, the recovery mode can be executed only for the K color. However, the present invention is not limited to this, and the recovery mode can also be executed for the three colors of the pause colors Y, M, and C. In this case, the recovery modes for the Y, M, and C colors can be performed in parallel with the K color recovery mode and monochrome image formation.

  In the example of FIG. 5, when a monochrome image formation command is received at time T5, the necessary amount of each color recovery mode is determined as follows. That is, for K color, the required amount is determined by the table in Table 1 as in the case of the first and second embodiments. Further, the necessary amount of the recovery mode is determined for the three colors of Y, M, and C. The required quantities for these three colors determined here must be common. Therefore, the longest required amount for these three colors obtained from the table in Table 1 is determined as the required amount for these three colors.

  Then, the rotation of the K-color photosensitive member 21 is started, and the recovery mode for the K color is started. Time T6 is the time when the rotation of the K-color photosensitive member 21 has started. The rotation of the transfer belt 12 also starts at this time. Then, the rotation of the three-color photoconductors 21 (resting photoconductors) is started so that the three-color recovery mode of Y color, M color, and C color can be started at time T7 later than time T6. After time T7, the recovery mode is simultaneously executed for all four color photoconductors 21. That is, the recovery mode of the photoconductor 21 used for monochrome image formation and the recovery mode of the other photoconductors 21 are performed in parallel. When the K color recovery mode ends at time T8, the K color image forming unit 20K continues to shift to the image forming mode and forms a monochrome image.

  In the example of FIG. 5, the recovery mode for the three colors Y, M, and C is not yet completed at time T8. For this reason, after time T8, the formation of a monochrome image of K color and the recovery mode of three colors of Y color, M color, and C color are performed in parallel. Here, the three color recovery modes of Y color, M color, and C color do not affect the formation of a monochrome image of K color. This is because the transfer belt 12 is in the released state at the position of the primary transfer roller 24 for these three colors.

  Then, the monochrome image formation is completed at time T9, and the three color recovery modes of Y, M, and C are completed at time T10. The prior relationship between time T9 and time T10 depends on the required amount of the three-color recovery mode of Y color, M color, and C color and the content of monochrome image formation. Naturally, in the example of FIG. 5, the press-contact / separation switching mechanism 29 remains in the released state for the three colors of Y, M, and C.

  By doing so, the three-color photoconductor 21 of Y color, M color, and C color is in a clean state. Therefore, when a color image formation command is received thereafter, image formation can be started quickly. In particular, if it is less than 4 hours from time T9, the formation of a full-color image can be started immediately (see the end of [0037]). In the third embodiment, when the monochrome image of K color is formed, the recovery mode for the remaining three colors that are not used for image formation is executed, so that the overall efficiency of the apparatus is excellent. For the K color, only the necessary recovery mode is performed before the image formation, so that the K-color photoconductor 21 is not excessively worn.

  In FIG. 5, time T8 may precede time T7. This happens when the required amount of K color recovery mode is small. The third embodiment is not limited to the case of forming a monochrome image, but can be applied to the case of non-full-color image formation using some of the four photoconductors 21. For example, this is a case of image formation of two colors of K color and M color.

  In FIG. 5, a period from time T6 to time T7 is a period in which only some of the four photoconductors 21 are targeted for the recovery mode. Further, the period from time T8 to time T10 is also a period in which only some of the four photoconductors 21 are targeted for the recovery mode. In any of these periods, at least one of the photoreceptor 21 that is the object of the recovery mode and the photoreceptor 21 that is not the object of the recovery mode is in the released state. That is, during the period from time T6 to time T7, the photoconductor 21 that is not the target of the recovery mode is in the released state. This prevents over-rotation of the photoconductor 21 that is not the target of the recovery mode. On the other hand, during the period from time T8 to time T10, the photoconductor 21 that is the object of the recovery mode is in the released state. As a result, an image can be formed on the photoreceptor 21 that is not the target of the recovery mode.

  In the third embodiment, the press contact / separation switching mechanism 29 may be configured so that the K primary transfer roller 24 is always in the press contact state. In fact, full-color image forming apparatuses often have two types of image forming modes, a full-color mode and a K monochrome mode. For this reason, even if the primary transfer roller 24 of K color is always pressed, there is no disadvantage, and it is advantageous in terms of simplifying the device configuration.

  Subsequently, as a fourth embodiment, an example of a timing chart in FIG. 6 will be described. This example is a modification based on the third embodiment shown in FIG. The difference between the fourth embodiment and the third embodiment is that the execution of the recovery mode for the three colors of Y, M, and C is started after a color image formation instruction is issued.

  In the example of FIG. 6, when a monochrome image formation command is received at time T5, the necessary amount of the recovery mode is determined only for the K color. This determination itself is made in the same manner as in the first to third embodiments. At time T6, the K color recovery mode is started. Up to this point, there is no significant difference from the case of the third embodiment except that the required amount of the recovery mode for the three colors of Y, M, and C has not yet been determined. However, in the third embodiment, the recovery mode for the three colors Y, M, and C is started at time T7, but in the fourth embodiment, it is not yet started. In the example of FIG. 6, the three-color recovery mode is not started and time T8 is reached, and the K-color recovery mode is terminated and the mode is shifted to an image forming mode for forming a monochrome image.

  In the example of FIG. 6, a full color image formation instruction is received at time T11 during the formation of a monochrome image. At this point, the necessary amount of recovery mode for the three colors Y, M, and C is determined. This determination itself is made in the same manner as in the third embodiment. Then, the rotation of these three-color photoconductors 21 (resting photoconductors) is started, and the three-color recovery mode is started from time T12. Thereafter, the K color image forming mode and the other three color recovery modes are performed in parallel. At this time, the primary transfer roller 24 for the three colors of Y, M, and C is still in the released state.

  In the example of FIG. 6, the monochrome image formation of K color is completed at time T13. At this point, the other three color recovery modes are not yet finished. Therefore, the K-color photoconductor 21 continues to rotate as it is. This is because a full-color image will be formed soon. When the other three-color recovery mode ends at time T14, the mode shifts to an image forming mode for forming a full-color image. At this time, the primary transfer roller 24 of the three colors of Y, M, and C is brought into a pressure contact state. The transition to the press-contact state for the Y color, M color, and C color may be advanced ahead of time T13.

  The advantage of doing this over the third embodiment is that the recovery modes performed for the other three colors are not wasted even when the execution frequency of monochrome image formation is high. That is, when the execution frequency of monochrome image formation is high, in the example of FIG. 5, there may be a considerable gap between time T10 (the end of the three-color recovery mode) and the actual color image formation command. . In that case, it is possible that the recovery mode is required again when the color image formation command is actually received. In this case, the three-color recovery mode performed in FIG. 5 is eventually wasted. In Embodiment 4 shown in FIG. 6, there is no such waste.

  In FIG. 6, both the period from time T6 to time T8 and the period from time T12 to time T14 are periods in which only some of the four photoconductors 21 are targeted for the recovery mode. As described in the third embodiment, in any of these periods, at least one of the photoconductor 21 that is the target of the recovery mode and the photoconductor 21 that is not the target of the recovery mode are in the released state.

  In the example of FIG. 6, time T13 (monochrome image formation end) precedes time T14 (recovery mode for other three colors). However, the order of these two times is not fixed. It depends on the magnitude relationship between the remaining time for monochrome image formation at time T11 (when a full-color image formation instruction is received) and the required amount of the three-color recovery mode determined at that time. In the example of FIG. 6, the latter, that is, the required amount of the three-color recovery mode is longer. The processing time required for monochrome image formation (time from time T8 to time T13) is determined by the content of the image formation request at time T5.

  Conversely, if the former, that is, the remaining time for monochrome image formation is longer, if the three-color recovery mode is started at time T12 as shown in FIG. 6, time T14 from time T13 (monochrome image formation end). (End of other three color recovery modes) will precede. In this case, the three-color photoconductors 21 wait for the end of monochrome image formation while rotating after the end of the recovery mode. This is because a full color image is formed thereafter.

  Therefore, in such a case, the start of the three-color recovery mode may be delayed to a time later than time T12. That is, the start time is determined retroactively from the time T13 (monochrome image formation end) to the time corresponding to the required amount of the three-color recovery mode. By doing so, as shown in FIG. 7, time T13 (monochrome image formation end) coincides with time T14 (recovery mode end for the other three colors). This eliminates the need to rotate the three-color photoconductors 21 wastefully.

  In the fourth embodiment, the image formation required at time T5 is not limited to monochrome image formation, and may be image formation using some of the four photoconductors 21. For example, image formation of two colors of K color and M color is performed. Further, the image formation required at time T11 is not limited to a full-color image. Any image formation may be used as long as at least one photosensitive member 21 that is not used for image formation requested at time T5, that is, one or more resting photosensitive members.

  Even in the case of the fourth embodiment, as in the case of the third embodiment, the pressure contact / separation switching mechanism 29 may be configured so that the primary transfer roller 24 of K color is always in a pressure contact state.

  As described in detail above, according to the image forming apparatus 10 of the present embodiment, the recovery mode is executed when the recovery mode is executed. As a result, the discharge products accumulated on the photosensitive member 21 are removed, and the clean photosensitive member 21 can obtain a high-quality image without image flow. Here, the required amount of the recovery mode is determined for each color targeted for the recovery mode. Then, the recovery mode is performed based on the determined necessary amount. Thereby, excessive wear of the photoconductor 21 is prevented while appropriately removing the discharge products accumulated on the photoconductor 21.

  Further, a pressure contact / separation switching mechanism 29 for operating the primary transfer roller 24 of each color is provided so that the pressing of the transfer belt 12 to the photoconductor 21 can be released for each location of the photoconductor 21 of each color. As a result, a recovery mode for a certain color and an imaging mode for another color can be performed in parallel. Therefore, productivity reduction is minimized while performing recovery mode.

  Even when a monochrome image formation command is received, the recovery mode is performed not only on the photosensitive member 21 of the color of the monochrome image but also on the photosensitive member 21 of other colors (Example 3). As a result, idle periods of other colors during the monochrome image color recovery mode or imaging mode are effectively used as the execution time of the recovery mode. Furthermore, the execution of the recovery mode for another color is started after receiving an image formation command using that color (Embodiment 4). This prevents the executed recovery mode from being wasted.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the transfer belt 12 may be a paper carrying belt.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Transfer belt 21 Photoconductor 25 Photoconductor cleaner 29 Pressure contact / separation switching mechanism 24 Primary transfer roller 30 Environmental sensor 31 Control part

Claims (7)

In an image forming apparatus that includes a plurality of photoconductors, forms a toner image on each of the plurality of photoconductors, and transfers and superimposes the toner images on a transfer body to form an image. A photoconductor cleaner provided on each of the photoconductors and contacting the post-transfer position of the photoconductor;
Each of the plurality of photoconductors is in a pressure-contact state where the pressure-contact is pressed against the transfer body;
An image forming control unit for performing image formation by rotating at least one of the photosensitive members in a pressed state by the pressing unit;
A recovery mode control unit that performs a recovery mode in which at least one of the photoconductors is rotated during non-image formation and the surface of the photoconductor is cleaned by the photoconductor cleaner;
The recovery mode control unit
The rotation time required to rotate the photoconductor in the recovery mode includes a plurality of photoconductors each including an environmental condition, a standing time from the previous image formation, and a durable use condition of the photoconductor. Based on at least one of them,
The recovery mode is executed over the time determined as the required rotation time for the photoconductor determined to be rotated,
An image forming apparatus, wherein , when the recovery mode is executed while the transfer member is stopped, at least the photosensitive member that is the target of the recovery mode is released by the press contact portion. The image forming apparatus according to claim 1 ,
The image formation control unit performs color image formation using two or more of the plurality of photosensitive members;
When the recovery mode control unit requests color image formation,
Determine the required rotation time for each photoconductor used for color image formation, and start execution of the recovery mode for each photoconductor based on the determined required rotation time so that the end times thereof are aligned. As well as
Of the execution time period of the recovery mode, for those respective photosensitive hours to carry out the recovery mode for all bodies, by rotating the transfer member with all of the photosensitive member thereof to the pressure contact state,
An image forming apparatus that starts color image formation by the image forming control unit upon completion of a recovery mode. 3. The image forming apparatus according to claim 1, wherein the recovery mode control unit determines a necessary rotation time of each photoconductor in the recovery mode.
An image forming apparatus, wherein a photoconductor whose cumulative usage is equal to or less than a predetermined minimum is determined to be zero. In the image forming apparatus according to any one of claims 1 to 3,
The image formation control unit performs non-full-color image formation using a part of the plurality of photosensitive members;
When the recovery mode control unit requests non-full-color image formation,
A rotation time required for the photoconductor used for the non-full-color image formation is determined, and based on the determined required rotation time, the recovery mode of the photoconductor is executed with the photoconductor in a pressed state, and the recovery is performed. With the end of the mode, the image formation control unit starts the non-full color image formation,
Determine the necessary rotation time for the resting photoreceptor other than the non-full color image photoreceptor, and determine it in parallel with the recovery mode of the non-full color image photoreceptor or the subsequent non-full color image formation. An image forming apparatus characterized in that, based on the required rotation time, the resting photoconductor recovery mode is performed with the resting photoconductor released by the press contact portion. The image forming apparatus according to claim 4, wherein the recovery mode control unit includes:
An image forming apparatus, wherein execution of the resting photoreceptor recovery mode is started after a request for image formation using the resting photoreceptor (hereinafter referred to as “new request”) is made. 6. The image forming apparatus according to claim 5, wherein the recovery mode control unit has the new request,
The remaining required time until the scheduled end time of the non-full color image formation requested previously, and a rest that is not used for the non-full color image formation currently being executed, which is a photoconductor used for the image formation related to the new request. Compare the required rotation time of the photoconductor with the longest,
If the former is greater than or equal to the latter,
The execution of the recovery mode of the paused photoconductor is started so that the scheduled end of the non-full-color image formation requested earlier and the end of the recovery mode of the paused photoconductor are aligned.
With the completion of the previously requested non-full-color image formation and the rest photoconductor recovery mode, the image formation control unit starts image formation related to the new request,
If the latter is longer than the former,
Immediately start execution of the recovery mode of the resting photosensitive member related to the longest rotation time,
Start the recovery mode of the rest of the rest photoreceptors other than those associated with the longest rotation time so that the end of the rest mode of the rest photoreceptors is complete,
An image forming apparatus comprising: starting the image formation according to the new request by the image formation control unit upon completion of the recovery mode of each paused photoconductor. In the image forming apparatus according to any one of claims 1 to 6,
It has a humidity sensor that outputs the humidity inside the device,
The image forming apparatus, wherein the recovery mode control unit executes the recovery mode only when the humidity output from the humidity sensor is equal to or higher than a predetermined value.

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