JP4952734B2 - Image forming apparatus - Google Patents

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

  However, the conventional techniques described above have the following problems. In recent years, many image forming apparatuses have a sleep mode function for power saving. The sleep mode is of course during non-image formation, but the recovery mode cannot be executed. For this reason, the recovery mode is executed only after returning from the sleep mode in response to an image formation instruction. Accordingly, the execution time of the recovery mode remains as it is, and the waiting time until the start of image formation is reached. This is particularly noticeable when image formation is performed at a low rotation speed in an image forming apparatus having a plurality of levels of rotation speed of the photoreceptor during image formation. This is because the rotation speed in the recovery mode is also slow, and it takes a lot of time to rotate at the required number of rotations. Furthermore, since the polishing effect per rotation number tends to be low when the rotation speed is low, it is necessary to increase the necessary rotation number itself.

  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 that minimizes the waiting time for removing foreign substances adhering to the photoreceptor.

  The image forming apparatus of the present invention, which has been made for the purpose of solving this problem, is a device that has a photoreceptor and forms an image by forming a toner image on the photoreceptor and transferring the toner image onto a medium. An image formation control unit that rotates the photoconductor to perform image formation, and a recovery mode control unit that performs a recovery mode in which the photoconductor is rotated during non-image formation and the surface of the photoconductor is cleaned by the photoconductor cleaner. The recovery mode control unit rotates the photosensitive member at a recovery mode speed that is a rotational speed equal to or higher than the fastest rotational speed among the rotational speeds of the photosensitive member during image formation.

  In this image forming apparatus, a recovery mode in which the photosensitive member is rotated at a time other than the time of image formation is performed to recover the surface of the photosensitive member to a clean state. This recovery mode is performed while most of the various devices other than the photoconductor are stopped. Here, the rotation speed of the photoconductor in the recovery mode is set to be equal to or higher than the highest speed among the rotation speeds of the photoconductor during image formation. That is, the rotational speed of the photosensitive member in the recovery mode is the same as or faster than the fastest rotational speed among the rotational speeds of the photosensitive member during image formation. This prevents the processing time required for the recovery mode from becoming excessively long.

The image forming apparatus of the present invention further includes a recovery mode based on at least one of a group including an environmental condition, a standing time from the previous image formation, and a durable use condition of the photoconductor when an image formation is requested. that having a recovery mode determination unit for determining a rotation speed to be performed. For this reason, when the rotational speed determined by the recovery mode determination section is equal to or greater than a predetermined threshold value, the recovery mode control section performs the photosensitive member over the determined rotational speed prior to image formation relating to the image formation request. was subjected to recovery mode for rotating, when the rotation speed that is determined is less than the threshold value, without performing the restoration mode, Ru to initiate image formation according to the image forming request. Thus, the recovery mode is performed prior to image formation over an appropriate number of revolutions depending on the situation.

  The image forming apparatus of the present invention can have a speed selection unit that selects the rotation speed of the photoconductor during image formation from a plurality of predetermined levels according to the contents of image formation. In this case, the image formation control unit rotates the photosensitive member at the rotation speed selected by the speed selection unit during image formation, and the recovery mode control unit is selected by the speed selection unit when executing the recovery mode. Regardless of the rotation speed, the photosensitive member is rotated at the recovery mode speed. As a result, even when image formation is performed at a low rotation speed, the photoreceptor is rotated at a high rotation speed in the recovery mode. This prevents the processing time required for the recovery mode from becoming excessively long regardless of the contents of image formation.

  In the image forming apparatus of the present invention, it is desirable that the recovery mode speed is faster than the fastest rotational speed among the rotational speeds of the photoconductor during image formation. This is more effective in reducing the processing time required for recovery mode.

  According to the present invention, there is provided an image forming apparatus that removes foreign matter adhering to a photoconductor while minimizing the waiting time.

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 graph showing the relationship between the peripheral speed of a photosensitive member and a necessary rotation speed in a recovery mode. FIG. 6 is a timing diagram showing changes in the rotational speed of a photoconductor after receiving a job command.

  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 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 photosensitive member 21 uses an organic photosensitive material for the photosensitive layer. Among the peripheral devices of the photosensitive member 21, the charging device 27 is of a scorotron type. 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 primary transfer roller 24 can take two states, a pressure contact state in which the primary transfer roller 24 is pressed against the transfer belt 12 and the photosensitive member 21 and a release state in which the pressure contact is released. The pressure contact state is shown in FIG. 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 is performed as follows under the control of the control unit 10. 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.

  Here, in the image forming apparatus 10, the rotational speed of the photosensitive member 21 has a plurality of levels according to the operation mode. This is shown in Table 1. Of the four levels of rotation speeds shown in Table 1, the “highest speed” is not used during image formation, but is used only during execution of a recovery mode to be described later. This “highest speed” is the highest rotational speed at which the photosensitive member 21 and its drive system alone can be continuously rotated over a certain period of time.

  The three levels of “low speed”, “standard”, and “high speed” are rotational speeds used at the time of image formation, and are selectively used according to the contents of image formation. The rotational speeds at these levels are determined within a range in which not only the photosensitive member 21 but also all parts that operate during image formation can be stably followed. For example, since it is restricted by the control frequency of the exposure device 28, the rotation speed when the exposure device 28 is provided with a polygon mirror, restrictions on the power consumption of the image forming apparatus 10 as a whole, image formation is performed at “highest speed”. It is impossible to do. In other words, the “highest speed” used only in the recovery mode is a higher rotational speed than the fastest “high speed” among the rotational speeds used during image formation. The controller 31 stores these rotational speeds and their uses. When a job command is input to the image forming apparatus 10, the control unit 31 selects a rotation speed according to the content of the command and drives each unit.

  Next, the recovery mode in this embodiment will be described. Also 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 in order to prevent 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.

  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. When the recovery mode is executed, the primary transfer roller 24 is released by the pressure contact / separation switching mechanism 29.

  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.

  In the image forming apparatus 10 of this embodiment, as the rotation speed of the photoconductor 21 in the recovery mode, the “highest speed”, that is, the maximum rotation speed at which the photoconductor 21 can rotate is used as described above. This is because it is not necessary to follow other parts. Therefore, the recovery mode execution time can be reduced. This is because if the rotation speed is high, the time required for rotation at the required number of rotations is short.

  Also, the fact that the rotational speed is fast means that the peripheral speed of the photoconductor 21 is also high, and the polishing force at the photoconductor cleaner 25 is correspondingly large. For this reason, the required number of revolutions itself can be reduced. This will be described with reference to the graph of FIG. This graph shows the result of a test for cleaning the photosensitive member 21 in which image flow has occurred by performing the recovery mode. In this test, a new photoconductor 21 was used to continuously print 50,000 sheets, and then the photoconductor 21 was left in an environment of a temperature of 30 ° C. and a relative humidity of 85% for 12 hours as a starting state. This starting state is a state in which an intense image flow occurs if an image is formed as it is.

  In the test, three modes of rotation speeds of 95 mm / second, 190 mm / second, and 285 mm / second were used as the peripheral speed of the photosensitive member 21, and the recovery mode was performed until no image flow occurred. The rotational speed in the recovery mode at that time is the vertical axis in FIG. As is apparent from FIG. 3, the image flow disappears at a lower rotational speed as the rotational speed is faster. This tendency appears more prominently when compared with the required time instead of comparing with the rotation speed. In this mode, the recovery mode is performed at the "highest speed", which significantly reduces the time required for the recovery mode compared to the case where the recovery mode is performed at a rotational speed other than the "highest speed". .

  Here, the necessary number of rotations in the recovery mode depends on the accumulated usage amount of the photoconductor 21, the humidity, and the standing time from the end of the previous image formation. For this reason, the control unit 31 of the image forming apparatus 10 according to the present embodiment includes a table as shown in Table 2 or Table 3. Table 2 is a table that gives the necessary number of revolutions in the recovery mode by two factors, the life expectancy of the photoreceptor and the humidity.

  As is clear from Table 2, the shorter the life expectancy and the higher the humidity, the greater the required number of revolutions. In Table 2, “life expectancy” is described, but the cumulative number of prints on the photosensitive member 21 may be used. In any case, this value is always monitored by the control unit 31 and the latest value is stored. Table 3 is a table that gives a coefficient to be multiplied to the result of Table 2 depending on the standing time. As can be seen from Table 3, the coefficient increases as the standing time increases. In other words, the longer the standing time, the higher the number of rotations is necessary. In Table 3, although shown as a coefficient to be multiplied, a table of the number of rotations to be added to or subtracted from the result in Table 2 may be used. Instead of having the table in Table 3, a plurality of types of tables in Table 2 may be provided according to the leaving time. Another parameter may be added.

  In this embodiment, the recovery mode is performed before the start of image formation. In other words, when receiving a job command for image formation, the control unit 31 determines the necessary number of rotations and executes the recovery mode. The image forming mode is subsequently executed after the recovery mode. Needless to say, the required number of revolutions is determined by the tables shown in Tables 2 and 3 above. If the determined rotational speed is zero, the image forming mode is immediately started without performing the recovery mode. In other words, the determination of the necessary number of rotations is determination of whether or not to execute the recovery mode, and determination of the number of rotations of the photoconductor 21 when executing the recovery mode.

  FIG. 4 is a timing chart showing the operation state of the photoconductor 21 when an image forming job command is actually received. FIG. 4 shows a case where the recovery mode is performed. When a job command is received at time t1, first, the necessary rotational speed is determined as described above. The parameters required at this time include the life expectancy of the photosensitive member 21, humidity, and the standing time from the end of the previous image formation. The life expectancy is stored in the control unit 31 as described above. Humidity is an acquired value of the environmental sensor 30. It may be the humidity value at the time of job reception, or the average of the humidity value at the time of job reception and the humidity value at the end of the previous job. As long as the humidity value is monitored even when left unattended, an appropriate representative value based on the history during that period may be used. The leaving time depends on the time counting function of the control unit 31. When the image forming apparatus 10 has a sleep mode function, the return from the sleep mode is usually performed at time t1.

  If the determined rotational speed is not zero, the recovery mode is executed as shown in FIG. Therefore, the rotation speed of the photosensitive member 21 is increased to “highest speed” regardless of the contents of the job command. Naturally, during this recovery mode, the pressure contact / separation switching mechanism 29 is released. The photosensitive member 21 is rotated at the “highest speed” over the determined rotation speed. As a result, the photoreceptor 21 is cleaned. As described above, even if the content of the job command requires image formation at “low speed”, the recovery mode preceding that is performed at “highest speed”. Therefore, the processing time required for the recovery mode is not excessively long.

  When the recovery mode ends at time t2, the image forming mode is immediately shifted to without stopping. For this reason, the rotational speed of the photosensitive member 21 is set to one of three levels of “low speed”, “standard”, and “high speed” according to the contents of the job command. FIG. 4 shows the case of “standard”. In addition, the charging device 27, the transfer belt 12, and the like are also in an operating state. The pressure contact / separation switching mechanism 29 is also brought into a pressure contact state. Thereby, image formation based on the command content is executed.

  By executing the recovery mode prior to the image forming mode in this way, there are the following advantages. In general, when image formation is started from a stopped state, there are pre-processing such as starting up motors of each unit and contacting the transfer belt 12 to the photosensitive member 12. In this embodiment, these pre-processing can be performed during execution of the recovery mode so that image formation can be started immediately at time t2. In this way, it is efficient without having to stop and restart. For this reason, compared with the case where the recovery mode is not performed, the processing time required for the recovery mode is not directly added to the waiting time until the first copy.

  In the description so far, the recovery mode has been described focusing on only one image forming unit 20. However, as shown in FIG. 1, the image forming apparatus 10 includes a four-color image forming unit 20. Therefore, the image forming apparatus 10 determines the necessity of the recovery mode and the number of rotations for each color. That is, the recovery mode is determined independently for each color. If the rotation speed of the recovery mode differs depending on the color, the recovery mode of each color may be started so that the time points (t2 in FIG. 4) of transition from the recovery mode to the image forming mode are aligned. In addition, the determination of the recovery mode can be made common to the four colors. In this case, the recovery mode is executed for all four colors. Alternatively, only one of the four colors (usually black) may be independently performed in the recovery mode, and the remaining three colors may be combined to perform the recovery mode.

  As described above in detail, in the present embodiment, the rotational speed of the photoconductor 21 in the recovery mode is set to “highest speed” regardless of the rotational speed in the subsequent image forming mode. As a result, an image forming apparatus is realized in which the photosensitive member 21 in a state in which foreign matters resulting from discharge are adhered is cleaned before image formation to ensure image quality and an increase in waiting time is minimized. Yes. Further, the number of rotations for rotating the photosensitive member 21 in the recovery mode is determined according to environmental conditions and other factors. Thereby, the recovery mode is appropriately implemented according to the situation.

  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 rotation speed of the photosensitive member 21 in the recovery mode may be the fastest rotation speed used in image formation (“high speed” in Table 1). Such a setting is effective when the photosensitive member 21 and its drive system are not provided with an allowance for rotation at a rotational speed exceeding the rotational speed used during image formation. This is because such a device cannot be rotated at the “highest speed” in the first place. Nevertheless, it is faster than “Standard” or “Low” in Table 1, and the recovery mode can be completed in a shorter time compared to executing the recovery mode at these speeds.

  Further, the number of rotational speed levels of the photosensitive member 21 shown in Table 1 is not limited to “4”. The present invention can be established if there are at least two levels. There may be a total of two levels, one rotational speed for image formation and a faster rotational speed for recovery mode. There are two rotational speeds for image formation, and the faster one is also used for recovery mode. It may be used. Further, as parameters used for determining whether to execute the recovery mode, all three parameters of the environmental condition, the life expectancy of the photosensitive member 21 and the standing time are not necessarily used. If any one or more are used, the present invention is established.

  In determining whether to execute the recovery mode, it is determined not to execute the recovery mode not only when the determined rotation speed is zero but also when the predetermined threshold value (for example, “5”) is not reached. It is good. That is, if this threshold value is “1”, as described above, the recovery mode is not performed only when the determined rotational speed is zero, but is not limited thereto. If the threshold value is not “1”, the number of rotations that have been postponed at that time may be stored and added to the newly determined number of rotations when the next recovery mode execution is determined. Further, the present invention is not limited to the tandem type shown in FIG. 1 but can be applied to a 4-cycle type or monochrome image forming apparatus. The present invention is also applicable regardless of the type of toner.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 21 Photoconductor 25 Photoconductor cleaner 31 Control part

Claims (3)

In an image forming apparatus having a photoconductor and forming an image by forming a toner image on the photoconductor and transferring the toner image onto a medium,
A photoreceptor cleaner in contact with the post-transfer position of the photoreceptor;
An image forming control unit for rotating the photoconductor to form an image;
A recovery mode control unit for performing a recovery mode in which the photoconductor is rotated during non-image formation and the surface of the photoconductor is cleaned by the photoconductor cleaner ;
When there is an image formation request, the rotational speed at which the recovery mode is to be executed is determined based on at least one of the group including the environmental conditions, the time for which the image formation has been performed since the previous image formation, and the durable use conditions of the photoconductor. A recovery mode determination unit ,
The recovery mode control unit
If the number of rotations determined by the recovery mode determination unit is equal to or greater than a predetermined threshold, prior to image formation according to the image formation request, the rotation speed of the photoconductor during image formation is determined over the determined number of rotations . Performing a recovery mode in which the photoconductor is rotated at a recovery mode speed that is equal to or higher than the highest rotational speed among the rotational speeds ;
An image forming apparatus, wherein when the determined number of rotations is less than the threshold, image formation according to the image formation request is started without performing a recovery mode . The image forming apparatus according to claim 1,
A speed selection unit for selecting the rotation speed of the photoconductor during image formation from a plurality of predetermined levels according to the contents of image formation;
The image formation control unit rotates the photoconductor at a rotation speed selected by the speed selection unit during image formation,
The recovery mode control unit rotates the photoconductor at the recovery mode speed regardless of the rotation speed selected by the speed selection unit when the recovery mode is executed. The image forming apparatus according to claim 1 or claim 2,
2. The image forming apparatus according to claim 1, wherein the recovery mode speed is a rotational speed faster than a fastest rotational speed among the rotational speeds of the photoconductor during image formation.

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