JP5283445B2 - Secondary transfer belt cleaning method for image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary transfer belt cleaning method finely complying with measures for balancing between performance and power saving in an image forming apparatus. <P>SOLUTION: In the image forming apparatus, an electrostatic latent image is formed on an electrostatic latent image carrier 3 when printing is started while the electrostatic latent is developed by a toner in a development means 2 and transferred to an intermediate transfer belt 61 to be then transferred to a recording medium by a secondary transfer belt 81 and fixed by a fixing means 7 having a heating roller 71, and consequently, an image is formed on the recording medium and printing is completed. In the image forming apparatus, a plurality of stain toner cleaning methods based on a different electric field control to stain toner sticking to the secondary transfer belt 81 are used, and a plurality of stain toner cleaning methods are used selectively according to the length of a cleaning allowance period to the secondary transfer belt 81. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an intermediate transfer belt and a method for cleaning the secondary transfer belt in an image forming apparatus including the secondary transfer belt.

  In an image forming apparatus using an intermediate transfer belt system, a system is adopted in which image information on an intermediate transfer belt is collectively transferred onto a recording sheet using a secondary transfer mechanism including a secondary transfer belt. That is, an electrostatic latent image is formed on the electrostatic latent image carrier, the electrostatic latent image is developed with toner in a developing unit, transferred to an intermediate transfer belt, and then transferred to a recording sheet by a secondary transfer belt. The image is formed on the recording paper by fixing by a fixing means having a heating roller.

  In such a transfer system using the secondary transfer mechanism, a transfer electric field is applied from the back surface of the secondary transfer belt to transfer the toner image formed on the intermediate transfer belt onto a recording sheet. It is very difficult to control so that the transfer electric field applied from the back surface of the belt is applied only to the recording paper to be transferred.

  For this reason, since the transfer electric field applied from the back surface of the secondary transfer belt is also applied to portions other than the recording paper, so-called “fogging toner” smudge toner adhering to the intermediate transfer belt is removed. It is transferred onto the secondary transfer belt.

  If the printing process is further continued in a state where the dirty toner transferred on the secondary transfer belt is left unattended, the dirty toner adheres to the back surface of the recording paper, resulting in a reduction in the printing quality of the recording paper. In order to prevent this, various methods for removing dirt on the secondary transfer belt have been proposed. Conventionally, as a method for removing dirt on the secondary transfer belt, a method for mechanically cleaning the secondary transfer belt and a method for electrically cleaning the secondary transfer belt are used.

  The above-mentioned method of mechanically cleaning the secondary transfer belt is performed by pressing a cleaning blade, a roller, a brush, or the like with a predetermined pressure against the secondary transfer belt, and the contact pressure causes dirt on the secondary transfer belt. The toner is collected.

  In this mechanical cleaning method, since the secondary transfer belt used is a thin film (approximately 100 to 250 μm thick), the secondary cleaning belt can be damaged, wrinkled, meandered, etc. May occur.

  Therefore, a method of electrically cleaning the secondary transfer belt has attracted attention (see, for example, Patent Documents 1 and 2). In the method described in Patent Document 1, the stain toner adhering to the secondary transfer belt adheres to the secondary transfer belt a DC electric field having the same polarity as the charged polarity charged in the developing unit. In this method, the secondary transfer belt is cleaned by applying to the toner and retransferring the dirty toner onto the intermediate transfer belt.

On the other hand, the method described in Patent Document 2 is similar to the method described in Patent Document 1, in which the secondary toner is re-transferred onto the intermediate transfer belt by transferring the dirty toner adhering to the secondary transfer belt to This is a method for cleaning the transfer belt, and is intended to further enhance the cleaning effect of the secondary transfer belt by using an electric field obtained by superimposing an AC electric field on a DC electric field having the same polarity as the toner charging polarity. is there.
Japanese Patent Laid-Open No. 10-198196 JP 2001-175099 A

  By the way, in recent years, energy saving measures have been demanded from the viewpoint of preventing global warming, and while improving the performance of electrical products as well, on the other hand, power saving is required. In this regard, the image forming apparatus is no exception, and measures are required to save power while improving performance.

  Therefore, in order to cope with the above-described demands on the image forming apparatus, the following measures are newly adopted as measures for improving the performance and saving power. For example, in the image forming apparatus, as a preparation mode period in which the image forming apparatus does not perform the printing process, a standby mode period (a period in which the image forming apparatus can shift to the printing process state almost immediately), a power saving mode period, an energy saving mode period, or a shut down An off mode period is provided.

  In an image forming apparatus that forms an electrostatic latent image on an electrostatic latent image carrier, develops it with toner, and transfers and fixes it on a recording sheet, the power consumption of the fixing means for fixing with a heating roller is large. Therefore, this measure is adopted from the viewpoint of balancing the performance of the image forming apparatus and power saving.

  That is, in the image forming apparatus in which the above countermeasure is adopted, the surface temperature of the heating roller of the fixing unit is the highest when the preparation mode period is the standby mode period, and this preparation mode period is the power saving mode period, It is controlled to become lower as the energy saving mode period and the shut-off mode period are shifted. The preparation mode period shifts according to the above described order unless a printing process request (printing request) is made to the image forming apparatus during each mode period.

  Further, from the viewpoint of balancing the performance of the image forming apparatus and power saving, different fixing temperatures are used depending on the size and thickness of the recording paper as the recording medium as a countermeasure in the fixing means.

  In the image forming apparatus provided with the measures as described above, in order to change from the state in the preparation mode period to the printing process state, it is necessary to shift the temperature of the heating roller of the fixing unit in the preparation mode period to a temperature suitable for the printing process. Yes, the time required for this transition varies depending on which mode period the preparation mode period is, or the size and thickness of the recording paper. Further, the time required to shift to the preparation mode period from the time when the printing process is completed is the same as described above.

  For this reason, the secondary transfer belt in the image forming apparatus is required to be finely performed in response to the above-described countermeasures. However, it is difficult to say that the above-described conventional method for cleaning the secondary transfer belt is sufficiently fine-tuned from the viewpoint described above.

  Accordingly, the present invention has been made to cope with such a situation, and in the image forming apparatus, a measure for balancing the performance and power saving of the image forming apparatus is taken. Accordingly, it is an object of the present invention to provide a secondary transfer belt cleaning method for an image forming apparatus in which fine measures corresponding to these measures are taken.

  The secondary transfer belt cleaning method of the image forming apparatus of the present invention forms an electrostatic latent image on an electrostatic latent image carrier when printing is started, and develops the electrostatic latent image with toner in a developing unit to provide an intermediate. In the image forming apparatus in which the image is transferred to the recording medium by the secondary transfer belt after being transferred to the transfer belt and fixed by a fixing unit having a heating roller, thereby forming an image on the recording medium and finishing the printing. A transfer belt cleaning method.

  In the secondary transfer belt cleaning method of the image forming apparatus described above, a plurality of dirty toner cleaning methods using different electric field controls for the dirty toner adhering to the secondary transfer belt are used, and the plurality of dirty toner cleaning methods are used. The secondary transfer belt is characterized in that it is properly used according to the cleaning allowable period.

  Therefore, in an image forming apparatus of a type in which an electrostatic latent image is formed on an electrostatic latent image carrier, developed with toner, and transferred and fixed on a recording sheet using an intermediate transfer belt and a secondary transfer belt. By properly using a plurality of dirty toner cleaning methods in accordance with the cleaning allowable period of the secondary transfer belt, it is possible to take a fine measure in balancing the performance of the image forming apparatus and power saving.

  In the secondary transfer belt cleaning method of the image forming apparatus described above, as one of the dirty toner cleaning methods, the dirty toner attached to the secondary transfer belt is charged by the developing unit with respect to the dirty toner. It is preferable to employ the first cleaning method that performs electric field control in which a DC electric field having the same polarity as the charging polarity is applied.

  According to the first cleaning method, a part of the dirty toner is transferred to the intermediate transfer belt by applying a DC electric field having the same polarity as that of the dirty toner to the dirty toner attached on the secondary transfer belt. . That is, in this case, among the dirty toners that are laminated and adhered in a plurality of layers on the secondary transfer belt, the dirty toners that are attached in the middle and upper layers are cleaned, but the dirty toner that is attached in the lowermost layer. The toner remains on the secondary transfer belt and is difficult to clean.

  However, the dirt toner adhering to the lowermost layer remaining on the secondary transfer belt has a large adsorbing force with respect to the secondary transfer belt, so that it is difficult to be separated from the secondary transfer belt, and it is easy to put on the recording paper. Is not transcribed. Accordingly, there is little adhesion of the dirty toner to the back surface of the recording paper in the subsequent next printing process, and the back dirt of the recording paper in the subsequent next printing process can be reduced.

  In the first cleaning method, it is preferable that the application time of the DC electric field is longer than the time required for the secondary transfer belt to make one revolution. This is because there is a possibility that dirt toner adheres to the entire circumference of the secondary transfer belt. Therefore, in order to remove all the dirt toner, the secondary transfer belt is at least completely rotated once. This is because it is necessary to execute the first cleaning method.

  In the secondary transfer belt cleaning method of the image forming apparatus described above, as one of the dirty toner cleaning methods, the dirty toner adhering to the secondary transfer belt is charged by the developing means with respect to the dirty toner. After applying an AC electric field in which an electric field having the same polarity as the charged polarity and an electric field having the opposite polarity are alternately applied, electric field control is performed in which a DC electric field having the same polarity as that of the dirty toner is applied. It is preferable to employ the second cleaning method.

  According to the second cleaning method, an AC electric field in which an electric field having the same polarity as that of the dirty toner and an electric field having the opposite polarity are applied alternately first causes the following state. First, by applying an electric field having the same polarity, the dirty toner adhering to the middle and upper layers on the secondary transfer belt is transferred to the intermediate transfer belt. Then, by applying an electric field having the opposite polarity, the dirty toner adhering to the lowermost layer on the secondary transfer belt vibrates and the adsorbing force on the secondary transfer belt becomes weak. Further, when a DC electric field having the same polarity is applied, the dirty toner adhering to the lowermost layer whose adhesion to the secondary transfer belt is weakened is transferred to the intermediate transfer belt.

  Therefore, almost all the dirt toner adhering to the secondary transfer belt can be transferred to the intermediate transfer belt. Accordingly, since the dirty toner adhering to the secondary transfer belt can be completely removed, the secondary transfer belt can be completely cleaned.

  In the second cleaning method, the application time of the same polarity electric field in the AC electric field and the application time of the opposite polarity electric field are both the same as the time required for the secondary transfer belt to make one revolution. The DC electric field application time in the second cleaning method is preferably equal to or longer than the time required for the secondary transfer belt to make one revolution.

  This is because there is a possibility that the dirty toner adheres to the secondary transfer belt over the entire circumference as described above. Therefore, in order to remove all the dirty toner, while the secondary transfer belt makes a complete turn, in the second cleaning method, the application of the same polarity electric field in the AC electric field and the electric field of the opposite polarity are performed. Must be applied. Similarly, it is necessary to apply the DC electric field as long as the secondary transfer belt makes at least one full turn.

  In the second cleaning method, it is preferable that the AC electric field has an electric field having the same polarity as the charging polarity of the dirty toner and an electric field having the opposite polarity alternately generated the same number of times. By doing so, the electric field having the same polarity and the electric field having the opposite polarity can be balanced, so that the effect of the second cleaning method can be enhanced.

  In the secondary transfer belt cleaning method for the image forming apparatus, the following measures are taken in the image forming apparatus. That is, first, the surface temperature of the heating roller of the fixing unit during the preparation mode period of the fixing unit is the preparation mode temperature.

  At the time when a print request is made to the image forming apparatus, the surface temperature of the heating roller of the fixing unit starts to shift from the preparation mode temperature to the proper fixing start temperature, and an appropriate temperature transition period, which is a period required for the transition, is set. When the time has elapsed, printing of the image forming apparatus is started.

  At the end of printing of the image forming apparatus, the surface temperature of the heating roller of the fixing unit starts to shift to the standby mode temperature in the standby mode period of the fixing unit, and a standby mode temperature transition period, which is a period required for the transition, When the time has elapsed, the standby mode period of the fixing unit is started.

  In the image forming apparatus in which such a countermeasure is taken, the cleaning allowable period corresponds to an appropriate temperature transition period, a standby mode temperature transition period, or both.

  In the above case, it is preferable that the length of the appropriate temperature transition period and the standby mode temperature transition period is equal to or longer than the time required for the secondary transfer belt to make one revolution. This is because, as described above, since there is a possibility that dirty toner is attached to the entire circumference of the secondary transfer belt, at least the first cleaning method described above is required to remove all the dirty toner. Must be executable.

  For this purpose, the length of the appropriate temperature transition period and the standby mode temperature transition period is as long as it is necessary to execute the first cleaning method while the secondary transfer belt makes one complete revolution. This is because at least the time required for the secondary transfer belt to complete one revolution is required.

  Further, in the above-described secondary transfer belt cleaning method of the image forming apparatus, if the length of the proper temperature transition period is less than the time required for the secondary transfer belt to make three revolutions, during the proper temperature transition period, It is preferable to execute the first cleaning method.

  This is because, as can be seen from the above description, it is preferable to use the second cleaning method for the first cleaning method and the second cleaning method. However, when the second cleaning method is performed, as described above, the secondary transfer belt makes one turn both in the application time of the electric field of the same polarity in the AC electric field and in the application time of the electric field of the opposite polarity. And the DC electric field application time must be equal to or longer than the time required for the secondary transfer belt to make one revolution. On the other hand, when the first cleaning method is performed, as described above, the application time of the DC electric field may be longer than the time required for the secondary transfer belt to make one revolution.

  That is, when the second cleaning method is executed, at least the time required for the secondary transfer belt to make three revolutions is required, whereas when the first cleaning method is executed, the secondary transfer belt is It may be longer than the time required for one round.

  Therefore, the second cleaning method cannot be executed when the length of the appropriate temperature transition period is less than the time required for the secondary transfer belt to make three turns, but the first cleaning method can be executed. is there.

  Then, as can be seen from the above description, when the length of the proper temperature transition period is longer than the time required for the secondary transfer belt to make three revolutions, the second cleaning method is performed during the proper temperature transition period. It is preferable to execute.

  If the length of the standby mode temperature transition period is less than the time required for the secondary transfer belt to make three revolutions for the same reason as described above, the standby mode temperature transition period During this, it is preferable to execute the first cleaning method. If the length of the standby mode temperature transition period is less than the time required for the secondary transfer belt to make three revolutions, it is preferable to execute the second cleaning method during the standby mode temperature transition period. It is.

  In the secondary transfer belt cleaning method of the image forming apparatus, it is preferable that the image forming apparatus is provided with a surface temperature measuring unit that measures the surface temperature of the heating roller of the fixing unit.

  In this way, the length of the appropriate temperature transition period can be obtained by calculation based on the surface temperature of the heating roller measured by the surface temperature measuring means at the time when the print request is made and the fixing start appropriate temperature. it can.

  In this case, when the length of the obtained appropriate temperature transition period is less than the time required for the secondary transfer belt to make one revolution, the secondary transfer belt makes one revolution for the reason already described. Time required.

  As with the length of the appropriate temperature transition period, the surface temperature measuring means for measuring the surface temperature of the heating roller of the fixing means is provided in the image forming apparatus with respect to the length of the standby mode temperature transition period. It is preferable to do this.

  In this way, the length of the standby mode temperature transition period is obtained by calculation based on the surface temperature of the heating roller measured by the surface temperature measuring means at the time when the print request is made and the fixing start appropriate temperature. Can do.

  In this case, when the length of the obtained standby mode temperature transition period is less than the time required for the secondary transfer belt to make one revolution, the secondary transfer belt makes one revolution for the same reason as described above. It takes time to complete.

  Further, in the above-described secondary transfer belt cleaning method of the image forming apparatus, when a recording sheet is used as a recording medium, an appropriate fixing start temperature that differs depending on the size and thickness of the recording sheet is used. Also good. By doing so, fine control in the image forming apparatus can be performed, and fine response can be made to cleaning of the secondary transfer belt.

  In the above-described secondary transfer belt cleaning method of the image forming apparatus, the preparation mode period of the fixing unit includes at least the standby mode period, and the standby mode period first appears as the preparation mode period. It is common to do.

  The standby mode period is a period during which it is possible to shift to a state where the printing process can be performed almost immediately when a print request is made to the image forming apparatus. Therefore, the image forming apparatus is generally provided with this standby mode period.

  Regarding the preparation mode period of the fixing unit, as the preparation mode period, in addition to the standby mode period, the preparation mode temperature which is the surface temperature of the heating roller of the fixing unit in the preparation mode period is the standby mode temperature in the standby mode period. The image forming apparatus includes a power saving mode period that is a lower power saving mode temperature, an energy saving mode period that is an energy saving mode temperature lower than the power saving mode temperature, and a shut-off mode period in which heating of the heating roller is stopped. You may make it provide.

  In this case, unless a print request is made to the image forming apparatus during each mode period, the preparation mode period shifts in accordance with the above described order, and with this shift, the power consumption of the heating roller decreases, Power saving can be achieved.

  According to the secondary transfer belt cleaning method of the image forming apparatus of the present invention, a plurality of dirty toner cleaning methods using different electric field controls for the dirty toner adhering to the secondary transfer belt are used, and the plurality of dirty toners are used. The cleaning method can be properly used according to the cleaning allowable period of the secondary transfer belt.

  Therefore, in an image forming apparatus of a type in which an electrostatic latent image is formed on an electrostatic latent image carrier, developed with toner, and transferred and fixed on a recording sheet using an intermediate transfer belt and a secondary transfer belt. By properly using a plurality of dirty toner cleaning methods in accordance with the cleaning allowable period of the secondary transfer belt, it is possible to take a fine measure in balancing the performance of the image forming apparatus and power saving.

  Next, a method for cleaning the secondary transfer belt 81 of the image forming apparatus according to the embodiment of the present invention will be described in detail with reference to the drawings.

<Description of Image Forming Apparatus>
First, an image forming apparatus using the secondary transfer belt cleaning method for an image forming apparatus according to an embodiment of the present invention will be described. FIG. 1 is a configuration diagram showing the configuration of the image forming apparatus. FIG. 2 is an enlarged configuration diagram enlarging main portions of an intermediate transfer belt unit, a secondary transfer unit, and a fixing unit, which will be described later, among the elements constituting the image forming apparatus.

  The image forming apparatus forms multicolor and single color images on a predetermined recording sheet in accordance with image data transmitted from the outside. 1 and 2, the image forming apparatus mainly includes an exposure unit 1, a developing device 2, a photosensitive drum 3, a charger 5, a cleaner unit 4, an intermediate transfer belt unit 6, a secondary transfer unit 8, and a fixing unit. 7, a paper transport path S, a paper feed tray 91, a manual feed tray 92, and a paper discharge tray 93.

  Note that reference numeral 100 in FIG. 1 denotes a reading unit that reads a document or the like of an image on which image formation is performed by the image forming apparatus. The reading unit 100 is not directly related to the description in the present embodiment. The description of the unit 100 is omitted.

  Image data handled in the image forming apparatus is color image data having each color of black (K), cyan (C), magenta (M), and yellow (Y). Therefore, four each of the developing device 2, the photosensitive drum 3, the charger 5, and the cleaner unit 4 are provided in order to form these four types of latent images. These constitute four image stations set to black, cyan, magenta and yellow, respectively.

  The photosensitive drum 3 is disposed (mounted) on the upper part of the image forming apparatus. The charger 5 is a charging means for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. In this image forming apparatus, as shown in FIGS. A vessel is used. However, as the charger, a roller-type or brush-type charger or a charger-type charger may be used.

  As shown in FIG. 1, the exposure unit 1 is configured by a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror. In addition to this, for example, an EL or LED writing head in which light emitting elements are arranged in an array may be used as the exposure unit.

  The exposure unit 1 exposes the charged photosensitive drum 3 based on image data input to the image forming apparatus, whereby an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 3. Has the function of forming.

  The developing device 2 has a function of developing the electrostatic latent image formed on each photosensitive drum 3 with each color (K, C, M, Y) toner. As the toner used for the development, in the present image forming apparatus, a toner having a characteristic that the charging polarity of the toner in the developing device 2 is negative (−) is used.

  The electrostatic latent image visualized by the developing device 2 on the photosensitive drum 3 is transferred to the intermediate transfer belt 61 of the intermediate transfer belt unit 6. The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after image transfer.

  An intermediate transfer belt unit 6 is disposed above the photosensitive drum 3. The intermediate transfer belt unit 6 mainly includes an intermediate transfer belt 61, an intermediate transfer belt drive roller 63, an intermediate transfer belt tension mechanism, an intermediate transfer belt driven roller 62, an intermediate transfer roller 64, and an intermediate transfer belt cleaning unit 65. Has been.

  Among these, the intermediate transfer belt driving roller 63, the intermediate transfer belt tension roller, the intermediate transfer roller 64, the intermediate transfer belt driven roller 62, and the like are used to stretch and drive the intermediate transfer belt 61.

  The intermediate transfer roller 64 is rotatably supported by an intermediate transfer roller mounting portion of an intermediate transfer belt tension mechanism (not shown) in the intermediate transfer belt unit 6. The intermediate transfer roller 64 is a roller formed based on a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm.

  The intermediate transfer roller 64 has a function as a transfer electrode that applies an electric field for transferring the toner image on the photosensitive drum 3 onto the intermediate transfer belt 61. Therefore, the surface of the intermediate transfer roller 64 is covered with a conductive elastic material (for example, EPDM, urethane foam, etc.).

  With this conductive elastic material, the intermediate transfer roller 64 can uniformly apply a high voltage to the intermediate transfer belt 61. In this image forming apparatus, the intermediate transfer roller 64 in the shape of a roller is used as a transfer electrode, but a brush or the like can also be used.

  The intermediate transfer belt 61 is an endless belt formed using a film having a thickness of about 100 μm to 150 μm. The intermediate transfer belt 61 sequentially transfers the color toner images formed on the photosensitive drum 3 onto the intermediate transfer belt 7 in a superimposed manner, whereby a color toner image ( A multi-color toner image). Therefore, the intermediate transfer belt 61 is provided so as to come into contact with each photosensitive drum 3.

  Transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 61 is performed by an intermediate transfer roller 64 that is in contact with the back side of the intermediate transfer belt 61. That is, a high voltage transfer electric field is applied to the intermediate transfer roller 64 in order to transfer the toner image. This transfer electric field is an electric field having a positive polarity (+) opposite to the negative polarity (−) which is the charging polarity of the toner described above.

  The secondary transfer unit 8 is mainly composed of a secondary transfer belt 81 and a secondary transfer roller 82. In the secondary transfer unit 8, a secondary transfer belt 81 that constitutes the secondary transfer unit 8 and an intermediate transfer belt 61 that constitutes the intermediate transfer belt unit 6 include a secondary transfer roller 82 of the secondary transfer unit 8. , And the intermediate transfer belt driven roller 62 of the intermediate transfer belt unit 6 is arranged so as to come into contact with it. A nip is formed at a position where the intermediate transfer belt 61 and the secondary transfer belt 81 are in contact with each other, and a recording sheet is conveyed to the nip via a sheet conveyance path S described later.

  In order to obtain the above nip constantly, either the secondary transfer roller 82 of the secondary transfer unit 8 or the intermediate transfer belt driven roller 62 is made of a hard material such as metal, and the other is made of the other. It is formed using a soft material such as elastic rubber or foamable resin.

  The secondary transfer unit 8 has a function of transferring a toner image formed on the intermediate transfer belt 61 of the intermediate transfer belt unit 6 onto a recording sheet. Therefore, a voltage is applied to the secondary transfer roller 82 of the secondary transfer unit 8 to form an electric field necessary for transferring the toner onto the recording paper. The electric field formed by this voltage is a positive (+) electric field having a polarity opposite to the negative (−) charging polarity of the toner.

  In the above-described intermediate transfer belt unit 6, the toner attached to the intermediate transfer belt 61 due to contact with the photosensitive drum 3 is not transferred onto the recording paper by the secondary transfer roller 82 and remains on the intermediate transfer belt 61. The toner that has been removed becomes a cause of toner color mixture during the subsequent printing process, and is therefore removed and collected by the intermediate transfer belt cleaning unit 65. The intermediate transfer belt cleaning unit 65 is used for this purpose.

  The intermediate transfer belt cleaning unit 65 includes, as a cleaning member, for example, a cleaning blade that contacts the intermediate transfer belt 7, and a portion of the intermediate transfer belt 61 that contacts the cleaning blade is an intermediate transfer belt driving roller 63. Is supported by

  The fixing unit 7 mainly includes a heating roller 71 and a pressure roller 72. The heating roller 71 and the pressure roller 72 are configured to rotate with the recording paper interposed therebetween.

  The fixing unit 7 has a function of fixing the toner image transferred to the recording paper. For this reason, the heating roller 71 of the fixing unit 7 is controlled to have a predetermined fixing temperature based on a signal from a temperature detector (not shown). The multicolor toner image transferred to the recording paper is melted, mixed, and pressed, and thermally fixed to the recording paper.

  The paper feed tray 91 is a tray for storing sheet-like recording paper used for image formation, and is provided on the lower side of the image forming apparatus. Further, as described above, a paper discharge tray 93 for placing printed recording paper face down is provided at the top of the image forming apparatus.

  In the image forming apparatus, the recording paper stored in the paper feed tray 91 is transported toward the paper discharge tray 93 via the secondary transfer unit 8 and the fixing unit 7. A substantially vertical sheet conveyance path S is provided.

  Further, a pickup roller, a registration roller 13, a secondary transfer unit 8, a fixing unit 7, a transport roller for transporting recording paper, and the like are arranged in the vicinity of the paper transport path S from the paper feed tray 91 to the paper discharge tray 93. Has been.

  The transport rollers are small rollers for promoting and assisting the transport of the recording paper, and a plurality of the transport rollers are provided along the paper transport path S. The pickup roller is a roller that is provided at the end of the paper feed tray 91 and supplies recording paper from the paper feed tray 91 to the paper transport path S one by one.

  The registration roller 13 temporarily holds the recording paper conveyed through the paper conveyance path S. The recording paper is transported to the secondary transfer unit 8 at the timing when the leading edge of the toner image on the intermediate transfer belt 61 is aligned with the leading edge of the recording paper.

  Further, the recording paper after the toner image is fixed is conveyed to the reverse discharge path of the paper transfer path S by the transfer roller, and is reversed, that is, the toner image is directed downward on the discharge tray 93. It is supposed to be discharged.

  Next, in the image forming apparatus described above, a process from when the recording paper is discharged from the paper feed cassette 91 to being stored in the paper discharge tray 93 will be described. As described above, the image forming apparatus is provided with the paper feed cassette 91 for storing the recording paper, and it is not necessary to open and close the paper feed cassette 91 when printing a small number of sheets. A manual feed tray 92 is provided. Each of the sheet feeding cassette 91 and the manual feed tray 92 is provided with a pickup roller so as to guide the recording sheets one by one to the conveyance path.

  First, in the case of recording paper conveyed from a paper feeding cassette, the recording paper conveyed from the paper feeding cassette is conveyed to the registration roller 13 by a conveying roller in the paper conveying path S, and the leading edge of the recording paper and the intermediate transfer belt At the timing when the leading edge of the image information on 61 is aligned, the toner image is transferred to the secondary transfer unit 8 and transferred onto the recording paper. Thereafter, the recording paper passes through the fixing unit 7 so that the unfixed toner on the recording paper is melted and fixed by heat, and is discharged from the paper discharge roller onto the paper discharge tray 93 via the transport roller (for single-sided printing). If).

  Next, in the case of the recording paper loaded on the manual paper feed tray 92, the recording paper loaded on the manual paper feed tray 92 is discharged by the pickup roller and reaches the registration roller 13 through a plurality of transport rollers. Thereafter, the paper is discharged to the paper discharge tray 93 through the same process as the recording paper fed from the paper feed cassette 91 (in the case of single-sided printing).

  In each of the above, when double-sided printing is performed, similarly to single-sided printing, the trailing edge of the recording paper is chucked by the paper discharge roller with respect to the recording paper that has passed through the fixing unit. Is reversely rotated to be guided to the transport roller, and then printed on the back surface through the registration roller 13 and discharged to the paper discharge tray 93.

<Description of Secondary Transfer Belt Cleaning Method of Image Forming Apparatus>
Next, a secondary transfer belt cleaning method of the image forming apparatus in the embodiment of the present invention used in the above-described image forming apparatus will be described. In the secondary transfer belt cleaning method of this image forming apparatus, “the surface temperature of the heating roller 71 in the fixing unit 7” and “the influence of the applied electric field on the toner adhering to the secondary transfer belt 81” are important. These points will be described first.

<Description of surface temperature of heating roller in fixing unit>
First, the “surface temperature of the heating roller 71 in the fixing unit 7” will be described. FIG. 3 is a configuration diagram showing the main part of the fixing unit 7. As shown in FIG. 3, the fixing unit 7 is mainly composed of a heating roller 71 and a pressure roller 72, and receives heat from the heating roller 71 as the recording paper passes through the pressure contact portions of both rollers. The unfixed toner on the recording paper is melted / fixed.

  A heating heater 71a for heating the heating roller 71 is disposed inside the heating roller 71, and according to the detected temperature of a surface temperature detection unit 73 (corresponding to the surface temperature measuring means described above) disposed on the outer periphery of the heating roller 71. Then, ON-OFF control of the heater 71a is performed.

  Further, on the surface of the heating roller 71, a recording sheet separating claw 74 and a fixing unit cleaning unit 75 for removing residual toner on the surface of the heating roller 71 are arranged. Among these, the recording paper separating claw 74 is for avoiding the occurrence of the conveyance JAM due to the recording paper being wound around the surface of the heating roller 71. The fixing unit cleaning unit 75 is for cleaning the surface of the heating roller 71.

  The fixing unit 7 configured as described above has a plurality of set temperatures as shown in FIG. In FIG. 4, when energization of the fixing unit 7 is started, the warm-up mode is started based on the temperature detected by the surface temperature detector 73. This warm-up mode is a mode in which the surface temperature of the heating roller 71 is raised to a fixing set temperature (corresponding to the above-mentioned fixing start appropriate temperature).

  In the initial state of the warm-up mode, the fixing unit 7 does not rotate the heating roller 71 and the like. That is, since the fixing unit 7 is at a low temperature when it is stopped, the solidified residual toner adhering to the fixing unit cleaning unit 75, the recording paper separation claw 74, and the like rotates the heating roller 71 / pressure roller 72. This is to prevent the surface from being damaged.

  When the surface temperature of the heating roller 71 reaches the softening temperature of the toner (there is a slight difference in the type of toner used, approximately 100 to 130 ° C.), the rotation driving of the heating roller 71 and the like in the fixing unit 7 is started and the heating is started. While the roller 71 / pressure roller 72 rotates, the surface temperature of the heating roller 71 is made uniform, and the temperature of the pressure roller 72 starts to be increased by transferring heat from the pressure contact portion.

  By passing through the warm-up mode, the surface of the heating roller 71 reaches the fixing set temperature (approximately 170 to 200 ° C.), and the fixing unit 7 is ready for printing. The fixing unit 7 in a printable state enters a standby mode (a mode in the above-described standby mode period) when no print request is made to the image forming apparatus at this point. The surface temperature of the heating roller 71 in the standby mode corresponds to the standby mode temperature described above.

  This standby mode is a mode in which the image forming apparatus shifts from the warm-up mode described above, and first shifts when the fixing unit 7 ends the printing process and shifts to a state in which the printing process is not performed. It is a mode to do.

  In this standby mode, as described above, since the surface temperature of the heating roller 71 is the fixing set temperature, when a print request is made to the image forming apparatus, the state is shifted to a state where the printing process can be performed almost immediately. Can do. Therefore, by adopting this standby mode as a mode to be shifted to after the printing process of the fixing unit 7 is completed, it is possible to ensure a state that can immediately respond to a subsequent print request. .

  If the standby mode continues for a predetermined time without making a print request to the image forming apparatus during the standby mode, the power consumption of the fixing unit 7 is reduced and the heating roller 71 / pressure roller 72 is thermally deteriorated. In order to prevent the temperature of the fixing unit 7 from increasing and to reduce the temperature inside the fixing unit 7, the surface temperature of the heating roller 71 of the fixing unit 7 is shifted to a new mode.

  Even in this new mode, if the mode continues for a predetermined time without making a print request to the image forming apparatus during the mode, a new surface temperature of the heating roller 71 of the fixing unit 7 is further lowered. Enter mode.

  In this way, the mode is shifted to a different mode as the period during which no print request is made to the image forming apparatus becomes longer. These modes are the power saving mode, the energy saving mode, and the shut-off mode in addition to the standby mode described above, and are shifted in the order of description.

  During the period of each mode, the time measurement unit provided in the control unit of the fixing unit 7 measures the duration time of each mode, and when this duration time is a predetermined length, It moves to the next mode in order.

  Among the modes other than the standby mode, the power saving mode (the mode in the power saving mode period described above) is a mode in which the surface temperature of the heating roller 71 is the fixing power saving temperature (corresponding to the power saving mode temperature described above). This fixing power saving temperature is lower than the fixing set temperature in the standby mode. This fixing power saving temperature is determined during the initialization process of the fixing unit 7 (photosensitive drum) when a print request is made to the image forming apparatus in a state where the surface temperature of the heating roller 71 is controlled by the fixing power saving temperature. 3 is a temperature at which the potential adjustment can be restored. This fixing power saving temperature is usually a fixing lower limit temperature (not shown in FIG. 4, but about 150 to 160 ° C.).

  The fixing energy saving mode (the mode in the energy saving mode period described above) is a mode in which the surface temperature of the heating roller 71 is the fixing energy saving temperature (corresponding to the energy saving mode temperature described above). This fixing energy saving temperature is lower than the fixing power saving temperature. This fixing energy saving temperature is a temperature that cannot be returned to the reference fixing setting temperature during the initialization process time of the fixing unit 7 when printing is requested, but is set for the purpose of power saving of the fixing unit 7. Is. The fixing energy saving temperature is often set to the surface temperature of the heating roller 71 at the start of driving of the fixing unit 7 in the warm-up mode (the temperature at which the toner is softened, which is approximately 100 to 130 ° C.).

  The shut-off mode (the mode in the above-described shut-off mode period) is a mode in which the surface temperature of the heating roller 71 is the shut-off temperature. In this image forming apparatus, when the fixing unit 7 is left for a long time, it is useless from the viewpoint of energy saving to continuously heat the heating roller 71 / pressure roller 72.

  Therefore, power is supplied only to the display unit of the operation unit of the image forming apparatus and the control unit that communicates with the network to which the image forming apparatus is connected, and power supply to other parts of the image forming apparatus is stopped. The mode in this state is the shut-off mode, and the surface temperature of the heating roller 71 in this shut-off mode is the shut-off temperature. This shut-off temperature is a temperature in a state where the energization to the fixing unit 7 is stopped, and is the same temperature as the power-off state of the fixing unit 7.

  The standby mode, the power saving mode, the energy saving mode, and the shut-off mode are modes during a period in which the fixing unit 7 is not performing printing processing. This period corresponds to the above-described preparation mode period, and this preparation mode. Specifically, the mode period is any of the above-described standby mode period, power saving mode period, energy saving mode period, or shut-off mode period.

  Further, the surface temperature of the heating roller 71 in the preparation mode period is the preparation mode temperature described above. Specifically, the fixing setting temperature (corresponding to the standby mode temperature described above), the fixing power saving temperature (described above). The power saving mode temperature), the fixing energy saving temperature (corresponding to the above energy saving mode temperature), or the shut-off temperature.

  In this image forming apparatus, even when the main power supply of the fixing unit 7 is in the ON state, the surface temperature of the heating roller 71 is different depending on the mode as described above. Specifically, the surface temperature of the heating roller 71 is any one of a fixing set temperature, a fixing power saving temperature, a fixing energy saving temperature, or a shut-off temperature.

  When the surface temperature of the heating roller 71 is in such a state and a printing request is made to the image forming apparatus, the surface temperature of the heating roller 71 of the fixing unit 7 is determined by the surface temperature detecting unit. The fixing unit 7 is controlled so as to return to the fixing set temperature from the detected temperature.

  In the present image forming apparatus, a plurality of types of fixing set temperatures that are restored when the above printing request is made are prepared instead of one type. Therefore, when the surface temperature of the heating roller 71 of the fixing unit 7 returns to the above-mentioned fixing setting temperature, a fixing setting temperature that matches various conditions at that time is selected from the plurality of fixing setting temperatures. The

  For example, in the printing process of the image forming apparatus, the type and size (size) of the recording paper used for printing are selected. Different fixing set temperatures are used depending on the type or size of the recording paper. It is done. Specifically, as the fixing set temperature corresponding to the type of recording paper, three types of reference fixing set temperature, high temperature fixing set temperature, and low temperature fixing set temperature are used.

  Thus, the reason why different fixing set temperatures are used depending on the type of recording paper is that, for example, the amount of heat taken from the surface of the heating roller 71 by the type of recording paper (specifically, thick paper / plain paper / thin paper). This is because they are different. Therefore, by setting the fixing set temperature to a temperature corresponding to the recording paper used for printing, the instability of the fixing performance caused by the change in the surface temperature of the heating roller 71 is eliminated, and a constant fixing performance is always obtained. So that you can get. This also applies to the recording paper size.

  More specifically, when using plain paper, the reference fixing set temperature is set. When using thick paper, the high temperature fixing set temperature (reference fixing set temperature +10 to 20 ° C.) is used. When using thin paper, the low temperature fixing is set. A set temperature (reference fixing set temperature −10 to 20 ° C.) is used as the set fixing temperature. This point is dealt with in the same way for the size of the recording paper.

  As described above, the fixing set temperature is used as the standby mode temperature in the standby mode. Specifically, the reference fixing set temperature among the above three types of fixing set temperatures is used. This is because, by using this reference fixing set temperature as the fixing set temperature, it is possible to quickly cope with any of the above recording paper types used for printing in the subsequent next printing process. .

  FIG. 5 is a graph showing a specific example of the surface temperature of the heating roller 71 in the fixing unit 7 of the image forming apparatus. In FIG. 5, the mode in which the fixing unit 7 is not performing the printing process is the shut-off mode, and the recording paper used for printing in the printing process of the fixing unit 7 is five thick sheets.

  In FIG. 5, when a print request is made to the image forming apparatus in the energy saving mode state (energy saving mode period), the heating roller 71 is heated and the surface temperature of the heating roller 71 of the fixing unit 7 is changed to the energy saving mode. From the temperature to the high fixing temperature. A period in which the surface temperature of the heating roller 71 of the fixing unit 7 is changed from the energy saving mode temperature to the high temperature fixing set temperature is referred to as a set temperature transition period (corresponding to the above-described appropriate temperature transition period).

  When the surface temperature of the heating roller 71 of the fixing unit 7 reaches the high-temperature fixing set temperature, printing is started, and the surface temperature of the heating roller 71 temporarily decreases for each printing, but the heating roller 71 is heated. As it continues, the return rises.

  When printing is completed, as described above, in order to shift to the standby mode, generally, the surface temperature of the heating roller 71 rises and reaches the reference fixing set temperature that is the standby mode temperature. A period from when the surface temperature of the heating roller 71 reaches the reference fixing set temperature, which is the standby temperature, from the temperature immediately after the end of printing is referred to as a standby temperature return period (corresponding to the standby mode temperature transition period described above).

  The length of the set temperature transition period differs depending on which mode the preparation mode is in and the type of recording paper used for printing. Further, the length of the standby temperature return period varies depending on the number of print processed sheets, the ambient temperature of the fixing unit 7 and the like.

  In FIG. 5, the surface temperature of the heating roller 71 during the standby temperature recovery period is rising, but the recording roller used for printing is thick and immediately after a large amount of printing is performed, the heating roller 71. In some cases, the surface temperature of the heating roller 71 during the standby temperature recovery period may decrease.

  As can be seen from the above description, in the present image forming apparatus, during the printing process, a set temperature transition period exists before the printing process, and a standby temperature return period exists after the printing process. That is, the printing process is not performed in the set temperature transition period and the standby temperature return period. Therefore, in order to effectively use this period, the image forming apparatus performs secondary transfer belt cleaning described later in the set temperature transition period and the standby temperature return period.

<Description of Effect of Applied Electric Field on Toner Adhering on Secondary Transfer Belt>
Next, “the influence of the applied electric field on the toner adhering to the secondary transfer belt” will be described. FIG. 6 is an explanatory diagram showing the state of the dirt toner adhering to the secondary transfer belt 81 in the secondary transfer unit 8 of the image forming apparatus. In this image forming apparatus, as described above, toner having a characteristic that the charging polarity of the toner in the developing device 2 is negative (−) is used as the toner.

  In this image forming apparatus, a transfer electric field is applied from the back surface of the secondary transfer belt 81 to transfer the toner image formed on the intermediate transfer belt 61 onto the recording paper. It is very difficult to control the transfer electric field to be applied only to the recording paper to be transferred.

  For this reason, the transfer electric field applied from the back surface of the secondary transfer belt 81 is also applied to portions other than the recording paper, so that the so-called “fogging toner” that adheres to the intermediate transfer belt 61 is contaminated. The toner is transferred onto the secondary transfer belt 81.

  Specifically, after the charged toner adheres to the non-image area on the intermediate transfer belt 61 as a dirty toner that is “fogging toner”, it is applied from the back surface of the secondary transfer belt 81 by the secondary transfer roller 82. Is attached to the secondary transfer belt 81 by an electric field (a polarity (+) opposite to the charging polarity (−) of the toner).

  FIG. 6 shows an adhesion state of the dirt toner adhered to the secondary transfer belt 81 at the stage immediately before the secondary transfer is performed, at the time of the secondary transfer performed last time. Since this dirty toner is an unfixed toner, it is adsorbed to the secondary transfer belt 81 in a state in which the negative (positive) negative polarity, which is the polarity of the developing device 2, is maintained.

  Unlike the toner that visualizes the electrostatic latent image, the dirty toner adsorbed on the secondary transfer belt 81 is not transferred onto the recording paper and is used as the dirty toner on the secondary transfer belt 81. It remains on the next transfer belt 81 and causes “backside contamination” of the recording paper conveyed during the subsequent next printing process.

  Therefore, when the recording paper is not conveyed to the secondary transfer unit 8, the “stain toner” on the secondary transfer belt 81 is efficiently transferred back to the intermediate transfer belt to clean the secondary transfer belt 81. is necessary. Therefore, what is performed is cleaning of the secondary transfer belt by the secondary transfer belt cleaning method of the image forming apparatus in the present embodiment.

<Specific Explanation of Secondary Transfer Belt Cleaning Method of Image Forming Apparatus>
Next, the secondary transfer belt cleaning method of the image forming apparatus in the present embodiment will be specifically described. As the secondary transfer belt cleaning method of the image forming apparatus in the present embodiment, two types of cleaning methods are prepared: a first cleaning method and a second cleaning method.

  First, the first cleaning method will be described. FIG. 7 is an explanatory diagram relating to the first cleaning method, and FIG. 9 is a time chart of electric field application in the first cleaning method.

  In this first cleaning method, the dirt toner adhering to the secondary transfer belt 81 has the same polarity as the negative polarity (−) which is the charge polarity of the dirt toner charged in the developing device 2. Electric field control for applying a negative (−) DC electric field is performed (FIG. 8).

  Then, a DC electric field having the same polarity as that of the dirty toner is applied to the dirty toner adhered on the secondary transfer belt, whereby a part of the dirty toner is transferred to the intermediate transfer belt (FIG. 7A). . That is, in this case, among the dirty toners that are laminated and adhered in a plurality of layers on the secondary transfer belt, the dirty toners that are attached in the middle and upper layers are cleaned, but the dirty toner that is attached in the lowermost layer. The toner remains on the secondary transfer belt (FIG. 7B).

  However, the dirt toner adhering to the lowermost layer remaining on the secondary transfer belt has a large adsorbing force with respect to the secondary transfer belt, so that it is difficult to be separated from the secondary transfer belt, and it is easy to put on the recording paper. Is not transcribed. Accordingly, there is little adhesion of the dirty toner to the back surface of the recording paper in the subsequent next printing process, and the back dirt of the recording paper in the subsequent next printing process can be reduced.

  In this first cleaning method, the DC electric field application time is set to be longer than the time required for the secondary transfer belt 81 to make one revolution. This is because there is a possibility that dirt toner adheres to the entire circumference of the secondary transfer belt 81. Therefore, in order to remove all the dirt toner, the secondary transfer belt 81 makes at least one round. This is because it is necessary to execute the first cleaning method.

  Next, the second cleaning method will be described. FIG. 8 is an explanatory diagram relating to the second cleaning method, and FIG. 10 is a time chart of electric field application in the second cleaning method. In the second cleaning method, an electric field having the same polarity as the negative polarity (−), which is the charging polarity of the dirty toner charged in the developing device 2, is applied to the dirty toner attached on the secondary transfer belt 81. After applying an AC electric field in which the negative polarity (−) and the positive polarity (+), which is an electric field of opposite polarity, are alternately applied (FIGS. 8A and 8B), further contamination A negative (−) DC electric field having the same polarity as the negative polarity (−), which is the charging polarity of the toner, is applied (FIG. 8C), and electric field control is performed (FIG. 10). As a result, almost all of the dirt toner adhering to the secondary transfer belt can be transferred to the intermediate transfer belt (FIG. 8D).

  In the second cleaning method, an AC electric field in which an electric field having the same polarity as that of the dirty toner and an electric field having the opposite polarity are applied first, the following state is generated. First, by applying an electric field having the same polarity, the dirty toner adhering to the middle and upper layers on the secondary transfer belt is transferred to the intermediate transfer belt (FIG. 8A). Then, by applying an electric field having the opposite polarity, the dirty toner adhering to the lowermost layer on the secondary transfer belt vibrates and the adsorbing force on the secondary transfer belt is weakened (FIG. 8B). Further, by applying a DC electric field having the same polarity, the dirty toner adhering to the lowermost layer whose adhesion to the secondary transfer belt is weakened is transferred to the intermediate transfer belt (FIG. 8C). .

  Therefore, almost all the dirt toner adhering to the secondary transfer belt can be transferred to the intermediate transfer belt (FIG. 8D). Accordingly, since the dirty toner adhering to the secondary transfer belt can be completely removed, the secondary transfer belt can be completely cleaned.

  In this second cleaning method, the application time of the electric field of the same polarity in the AC electric field and the application time of the electric field of the opposite polarity are both made the same as the time required for the secondary transfer belt to make one revolution, The DC electric field is applied for at least the time required for the secondary transfer belt to make one turn (see FIG. 10).

  This is because there is a possibility that the dirty toner adheres to the secondary transfer belt over the entire circumference as described above. Therefore, in order to remove all the dirty toner, while the secondary transfer belt makes a complete turn, in the second cleaning method, the application of the same polarity electric field in the AC electric field and the electric field of the opposite polarity are performed. Must be applied. Similarly, it is necessary to apply the DC electric field as long as the secondary transfer belt makes at least one full turn.

  In the second cleaning method, the AC electric field is such that an electric field having the same polarity as the charging polarity of the dirty toner and an electric field having the opposite polarity are alternately generated the same number of times (see FIG. 10). By doing so, the electric field having the same polarity and the electric field having the opposite polarity can be balanced, so that the cleaning effect by the second cleaning method can be enhanced.

  Next, a specific method of the secondary transfer belt cleaning method in the image forming apparatus described above will be described. As described above, in the first cleaning method and the second cleaning method, the use of the second cleaning method is superior to the first cleaning method because the cleaning effect is better. desirable.

  However, when the second cleaning method is performed, as described above, the secondary transfer belt makes one turn both in the application time of the electric field of the same polarity in the AC electric field and in the application time of the electric field of the opposite polarity. And the DC electric field application time must be equal to or longer than the time required for the secondary transfer belt to make one revolution. That is, when the second cleaning method is executed, at least the time required for the secondary transfer belt to make three revolutions is required to clean the secondary transfer belt.

  On the other hand, when the first cleaning method is performed, as described above, the application time of the DC electric field may be longer than the time required for the secondary transfer belt to make one revolution. That is, when the first cleaning method is executed, the cleaning can be performed if the time required for the secondary transfer belt to make one round is required for cleaning the secondary transfer belt. Therefore, the length of the period during which the secondary transfer belt cleaning can be performed becomes a problem.

  Further, in the image forming apparatus, as described above, during the printing process, the printing process is not performed during the set temperature transition period existing before and after the printing process and during the standby temperature recovery period. Since the recording paper is not conveyed onto the secondary transfer belt, the secondary transfer belt cleaning is performed using these periods. Therefore, the time length of these set temperature transition periods or standby temperature return periods becomes a problem.

  Therefore, in the present image forming apparatus, the length of the set temperature transition period at the time when the print request is made to the image forming apparatus is used by using the surface temperature detection unit 73 provided in the heating roller 71 of the fixing unit 7. And calculated by calculation. That is, the length of the set temperature transition period is obtained by calculation based on the surface temperature of the heating roller measured by the surface temperature detecting unit 73 at the time when the print request is made and the fixing set temperature.

  Similarly, the length of the standby temperature return period at the end of printing is obtained by calculation using the surface temperature detection unit 73 provided in the heating roller 71 of the fixing unit 7. That is, the length of the standby temperature recovery period is obtained by calculation based on the surface temperature of the heating roller 71 measured by the surface temperature detection unit 73 at the end of printing and the standby mode temperature, that is, the reference fixing set temperature. .

  The calculation of the length of the set temperature transition period and the length of the standby temperature recovery period is configured by the present image forming apparatus or a microprocessor provided in the secondary transfer unit 8 or the fixing unit 7. A process performed by a control unit (not shown).

  Among the above, during the set temperature transition period, the surface temperature of the heating roller 71 measured by the surface temperature detection unit 73 at the time when the heating roller 71 of the fixing unit 7 makes a print request to the image forming apparatus, This is the time for shifting to the fixing set temperature. Therefore, during this set temperature transition period, an arithmetic expression is created based on various data relating to heating of the fixing unit 7 obtained so far in the image forming apparatus, and the surface temperature is added to the created arithmetic expression. It can be obtained by substituting the surface temperature of the heating roller 71 and the fixing set temperature measured by the detection unit 73 or other necessary numerical values.

  The standby temperature recovery period is a time period during which the heating roller 71 of the fixing unit 7 shifts from the surface temperature of the heating roller 71 measured by the surface temperature detection unit 73 immediately after the end of printing to the reference fixing set temperature. Therefore, it can be obtained by calculation in the same manner as in the set temperature transition period.

  When the length of the set temperature transition period and the length of the standby temperature return period obtained by the above-described method are less than the time required for one revolution of the secondary transfer belt, the secondary temperature can be increased for the reason already described. It is the time required for the transfer belt to make one revolution.

  Next, a specific method of the secondary transfer belt cleaning method performed by the above-described method using the obtained length of the set temperature transition period and the standby temperature return period will be described. This method is as follows.

  First, a specific method of the secondary transfer belt cleaning method performed during the set temperature transition period will be described. FIG. 11A is a graph showing the surface temperature of the heating roller 71 in the secondary transfer belt cleaning method performed during the set temperature transition period, and FIG. 11B is a table showing the method of cleaning the secondary transfer belt. It is. T in FIG. 11A represents a set temperature transition period.

  First, when the length of the set temperature transition period is less than the time required for the secondary transfer belt to make three revolutions, the first cleaning method is performed during the set temperature transition period (FIG. 11B). # 1). This is because, as can be seen from the above description, it is preferable to use the second cleaning method for the first cleaning method and the second cleaning method. However, when the second cleaning method is performed, as described above, the secondary transfer belt makes one turn both in the application time of the electric field of the same polarity in the AC electric field and in the application time of the electric field of the opposite polarity. And the DC electric field application time must be equal to or longer than the time required for the secondary transfer belt to make one revolution. On the other hand, when the first cleaning method is performed, as described above, the application time of the DC electric field may be longer than the time required for the secondary transfer belt to make one revolution.

  That is, when the second cleaning method is executed, at least the time required for the secondary transfer belt to make three revolutions is required, whereas when the first cleaning method is executed, the secondary transfer belt is It may be longer than the time required for one round.

  For this reason, the second cleaning method cannot be executed if the length of the set temperature transition period is less than the time required for the secondary transfer belt to make three revolutions, but the first cleaning method can be executed. is there.

  As can be seen from the above description, when the length of the set temperature transition period is longer than the time required for the secondary transfer belt to make three revolutions, the second cleaning method is performed during the set temperature transition period. (# 2 in FIG. 11B).

  If the length of the standby temperature return period is less than the time required for the secondary transfer belt to make three revolutions for the same reason as in the set temperature transition period, during the standby temperature return period, The first cleaning method is performed. If the length of the standby temperature return period is less than the time required for the secondary transfer belt to make three revolutions, the second cleaning method is performed during the standby temperature return period.

  Next, a specific procedure of the secondary transfer belt cleaning method in the image forming apparatus described above will be described. 12 to 16 are flowcharts showing specific procedures of the secondary transfer belt cleaning method in the image forming apparatus.

  12 to 16, first, when a print request is made to the image forming apparatus that is on standby (STEP 1), the surface temperature of the heating roller 71 is detected by the surface temperature detecting unit 73 provided on the outer peripheral portion of the heating roller 71. Is detected (STEP 2).

  Furthermore, the recording paper size used for printing and the thickness of the recording paper are confirmed among the printing request contents made in the printing request (STEP 3 and STEP 4). Next, based on the recording sheet size / recording sheet thickness confirmed in STEP 3 and STEP 4, the surface temperature setting when the recording sheet passes through the heating roller 71 of the fixing unit 7 is the reference fixing setting temperature (STEP 5), the high temperature It is confirmed whether the fixing set temperature (STEP 12) or the low-temperature fixing set temperature (STEP 17).

  If it is determined in this confirmation step that the surface temperature setting of the heating roller 71 is the “reference fixing setting temperature” (Yes in STEP 5), the surface temperature of the heating roller 71 is the temperature detected in STEP 2 ( A time (T1 sec.) For raising to the reference fixing set temperature is calculated from (A ° C.) (STEP 6).

  Next, the number of rotations of the secondary transfer belt 81 is calculated for the time (T1 sec.) Calculated in STEP 6 (STEP 7). When the calculation result is “3 or more rotations”, the image forming apparatus is driven. The initialization process of the image forming apparatus is started using the source (STEP 8), and the second cleaning method for the secondary transfer belt 81 is executed (STEP 9).

  On the other hand, when the calculation result in STEP 7 is not “three or more rounds”, the initialization process of the image forming apparatus is started using the drive source of the image forming apparatus (STEP 10), and the first of the secondary transfer belt 81 is started. A cleaning method is executed (STEP 11).

  Next, in the same manner as the processing at the reference fixing set temperature from STEP 5 to STEP 11, the processing at the high temperature fixing set temperature from STEP 12 to STEP 16 and from STEP 9 to STEP 11, and from STEP 17 to STEP 21, and from STEP 9 to STEP 11 are performed. The process for the case of the low temperature fixing set temperature is performed.

  After completion of each of the above processes, the completion of the process is confirmed (STEP 22), and after confirming that the surface temperature of the heating roller 71 has reached an appropriate set temperature (STEP 23), the image forming apparatus performs the printing process. Is started (STEP 24).

  In this way, when the printing process is continued and all the printing processes of the printing request content are completed (STEP 25), the surface temperature (B ° C.) of the heating roller 71 immediately after the printing is finished is set to the outer circumference of the heating roller 71. It is detected by the surface temperature detector 73 provided in the section (STEP 26). Next, based on the surface temperature (B ° C.) of the heating roller 71 detected in STEP 26, a return time (T4 sec.) Until returning to the reference fixing set temperature is calculated (STEP 27).

  Next, the number of rotations of the secondary transfer belt 81 is calculated for the time calculated in STEP 27 (T4 sec.) (STEP 28). When the calculation result is “3 or more rotations”, the driving of the image forming apparatus is performed. The post-processing step of the image forming apparatus is started using the source (STEP 29), and the second cleaning method for the secondary transfer belt 81 is executed (STEP 30).

  On the other hand, when the calculation result in STEP 28 is not “three or more rounds”, the post-processing step of the image forming apparatus is started using the drive source of the image forming apparatus (STEP 34), and the second transfer belt 81 is scanned. One cleaning method is executed (STEP 35).

  After completion of each of the above processes, the completion of the processes is confirmed (STEP 31 and STEP 36), and it is confirmed that the surface temperature of the heating roller 71 has reached the reference fixing set temperature (STEP 32), and the process proceeds to the standby mode. Then (STEP 33), it stands by in a state where it can accept the subsequent next printing process.

1 is a configuration diagram illustrating a configuration of an image forming apparatus. FIG. 2 is an enlarged configuration diagram in which main parts constituting the image forming apparatus are enlarged. FIG. 2 is a configuration diagram illustrating a main part of a fixing unit of the image forming apparatus. FIG. 4 is an explanatory diagram showing each mode of a fixing unit of the image forming apparatus. 6 is a graph showing a specific example of the surface temperature of the heating roller in the fixing unit of the image forming apparatus. FIG. 4 is an explanatory diagram illustrating a state of dirty toner adhering to a secondary transfer belt in a secondary transfer unit of the image forming apparatus. FIG. 10 is an explanatory diagram relating to a first cleaning method of the image forming apparatus. FIG. 10 is an explanatory diagram relating to a second cleaning method of the image forming apparatus. 6 is a time chart of electric field application in the first cleaning method of the image forming apparatus. 6 is a time chart of electric field application in a second cleaning method of the image forming apparatus. In the secondary transfer belt cleaning method performed during the set temperature transition period of the image forming apparatus, (a) is a graph showing the surface temperature of the heating roller, and (b) is a table showing the secondary transfer belt cleaning method. is there. 3 is a flowchart (part 1) illustrating a specific procedure of a secondary transfer belt cleaning method in the image forming apparatus. 5 is a flowchart (part 2) illustrating a specific procedure of a secondary transfer belt cleaning method in the image forming apparatus. 6 is a flowchart (part 3) illustrating a specific procedure of a secondary transfer belt cleaning method in the image forming apparatus. 6 is a flowchart (part 4) illustrating a specific procedure of a secondary transfer belt cleaning method in the image forming apparatus. 7 is a flowchart (part 5) illustrating a specific procedure of a secondary transfer belt cleaning method in the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exposure unit 2 Developer 3 Photoconductor drum 4 Cleaner unit 5 Charger 6 Intermediate transfer belt unit 7 Fixing unit 8 Secondary transfer unit 13 Registration roller 61 Intermediate transfer belt 62 Intermediate transfer belt driven roller 63 Intermediate transfer belt drive roller 64 Intermediate Transfer roller 65 Intermediate transfer belt cleaning unit 71 Heating roller 71a Heating heater 72 Pressure roller 73 Surface temperature detection unit 74 Recording paper separation claw 75 Fixing unit cleaning unit 76 Rotating direction 77 Paper conveying direction 81 Secondary transfer belt 82 Secondary transfer roller 91 Paper feed tray 92 Manual feed tray 93 Paper discharge tray 100 Reading unit S Paper transport path S

Claims (11)

When printing starts, an electrostatic latent image is formed on the electrostatic latent image carrier, and the electrostatic latent image is developed with toner in the developing unit and transferred to an intermediate transfer belt, and then transferred to a recording medium by a secondary transfer belt. And a cleaning method for the secondary transfer belt in an image forming apparatus that forms an image on the recording medium and completes printing by fixing by a fixing means having a heating roller,
The first cleaning method and the second cleaning method are used as a plurality of dirty toner cleaning methods by different electric field control for the dirty toner adhering to the secondary transfer belt, and the plurality of dirty toner cleaning methods are used as the secondary toner cleaning method. Regarding the method to use properly according to the length of the cleaning allowable period for the transfer belt ,
The first cleaning method is an electric field control in which a DC electric field having the same polarity as the charged polarity of the dirty toner charged in the developing unit is applied to the dirty toner adhering to the secondary transfer belt. Is a way to do
In the second cleaning method, the electric field having the same polarity as the charged polarity of the dirty toner charged in the developing unit and the opposite polarity is applied to the dirty toner adhering to the secondary transfer belt. And an electric field control in which a DC electric field having the same polarity as the charging polarity of the dirty toner is further applied after an AC electric field generated alternately with the electric field is applied.
In the image forming apparatus,
The surface temperature of the heating roller of the fixing unit during the preparation mode period of the fixing unit is a preparation mode temperature,
When a printing request is made to the image forming apparatus, the surface temperature of the heating roller of the fixing unit starts to shift from the preparation mode temperature to the fixing start appropriate temperature, and an appropriate temperature transition period is a period required for the transition When the time elapses, the printing of the image forming apparatus is started,
At the end of printing of the image forming apparatus, the surface temperature of the heating roller of the fixing unit starts to shift to the standby mode temperature in the standby mode period of the fixing unit, and the standby mode temperature shift that is a period required for the transition When the period has elapsed, the standby mode period of the fixing unit is started,
The cleaning allowable period is the appropriate temperature transition period, or the appropriate temperature transition period and the standby mode temperature transition period,
When the length of the proper temperature transition period is less than the time required for the secondary transfer belt to make three revolutions, the first cleaning method is executed during the proper temperature transition period,
The second cleaning method is executed during the proper temperature transition period when the length of the proper temperature transition period is equal to or longer than the time required for the secondary transfer belt to make three revolutions. A secondary transfer belt cleaning method of a forming apparatus. When printing starts, an electrostatic latent image is formed on the electrostatic latent image carrier, and the electrostatic latent image is developed with toner in the developing unit and transferred to an intermediate transfer belt, and then transferred to a recording medium by a secondary transfer belt. And a cleaning method for the secondary transfer belt in an image forming apparatus that forms an image on the recording medium and completes printing by fixing by a fixing means having a heating roller,
The first cleaning method and the second cleaning method are used as a plurality of dirty toner cleaning methods by different electric field control for the dirty toner adhering to the secondary transfer belt, and the plurality of dirty toner cleaning methods are used as the secondary toner cleaning method. Regarding the method to use properly according to the length of the cleaning allowable period for the transfer belt,
The first cleaning method is an electric field control in which a DC electric field having the same polarity as the charged polarity of the dirty toner charged in the developing unit is applied to the dirty toner adhering to the secondary transfer belt. Is a way to do
In the second cleaning method, the electric field having the same polarity as the charged polarity of the dirty toner charged in the developing unit and the opposite polarity is applied to the dirty toner adhering to the secondary transfer belt. And an electric field control in which a DC electric field having the same polarity as the charging polarity of the dirty toner is further applied after an AC electric field generated alternately with the electric field is applied.
In the image forming apparatus,
The surface temperature of the heating roller of the fixing unit during the preparation mode period of the fixing unit is a preparation mode temperature,
When a printing request is made to the image forming apparatus, the surface temperature of the heating roller of the fixing unit starts to shift from the preparation mode temperature to the fixing start appropriate temperature, and an appropriate temperature transition period is a period required for the transition When the time elapses, the printing of the image forming apparatus is started,
At the end of printing of the image forming apparatus, the surface temperature of the heating roller of the fixing unit starts to shift to the standby mode temperature in the standby mode period of the fixing unit, and the standby mode temperature shift that is a period required for the transition When the period has elapsed, the standby mode period of the fixing unit is started,
The cleaning allowable period is the standby mode temperature transition period, or the appropriate temperature transition period and the standby mode temperature transition period,
When the length of the standby mode temperature transition period is less than the time required for the secondary transfer belt to make three revolutions, the first cleaning method is executed during the standby mode temperature transition period,
When the length of the standby mode temperature transition period is equal to or longer than the time required for the secondary transfer belt to make three revolutions, the second cleaning method is executed during the standby mode temperature transition period.
A secondary transfer belt cleaning method for an image forming apparatus. The secondary transfer belt cleaning method for an image forming apparatus according to claim 1 or 2,
The secondary transfer belt cleaning method for an image forming apparatus, wherein the application time of the DC electric field in the first cleaning method is equal to or longer than the time required for the secondary transfer belt to make one revolution. The secondary transfer belt cleaning method for an image forming apparatus according to any one of claims 1 to 3 ,
The application time of the same polarity electric field and the application time of the opposite polarity electric field in the AC electric field in the second cleaning method are both the same as the time required for the secondary transfer belt to make one revolution. As well as
The secondary transfer belt cleaning method for an image forming apparatus, wherein the application time of the DC electric field in the second cleaning method is equal to or longer than the time required for the secondary transfer belt to make one revolution. The secondary transfer belt cleaning method for an image forming apparatus according to any one of claims 1 to 4 ,
In the second cleaning method, the AC field of the second cleaning method is the secondary transfer of the image forming apparatus in which the electric field having the same polarity as the charging polarity of the dirty toner and the electric field having the opposite polarity alternately occur the same number of times. Belt cleaning method. The secondary transfer belt cleaning method for an image forming apparatus according to claim 1,
The secondary transfer belt cleaning method for an image forming apparatus, wherein the appropriate temperature transition period and the standby mode temperature transition period are longer than a time required for the secondary transfer belt to make one revolution. The secondary transfer belt cleaning method for an image forming apparatus according to any one of claims 1 to 6 ,
The image forming apparatus includes a surface temperature measuring unit that measures a surface temperature of the heating roller of the fixing unit.
The length of the appropriate temperature transition period is obtained by calculation based on the surface temperature of the heating roller measured by the surface temperature measuring means at the time when the printing request is made and the fixing fixing appropriate temperature,
When the obtained length of the appropriate temperature transition period is less than the time required for the secondary transfer belt to make one revolution, the image forming apparatus sets the time required for the secondary transfer belt to make one revolution. Secondary transfer belt cleaning method. The secondary transfer belt cleaning method for an image forming apparatus according to any one of claims 1 to 6 ,
The image forming apparatus includes a surface temperature measuring unit that measures a surface temperature of the heating roller of the fixing unit.
The length of the standby mode temperature transition period is obtained by calculation based on the surface temperature of the heating roller measured by the surface temperature measuring means at the end of printing and the standby mode temperature,
When the obtained length of the appropriate temperature transition period is less than the time required for the secondary transfer belt to make one revolution, the image forming apparatus sets the time required for the secondary transfer belt to make one revolution. Secondary transfer belt cleaning method. The secondary transfer belt cleaning method for an image forming apparatus according to any one of claims 1 to 8 ,
A secondary transfer belt cleaning method for an image forming apparatus in which, when a recording sheet is used as the recording medium, the fixing start appropriate temperature at a different temperature is used depending on the size and thickness of the recording sheet. The secondary transfer belt cleaning method for an image forming apparatus according to any one of claims 1 to 9 ,
The preparation mode period of the fixing unit includes at least the standby mode period, and the standby mode period is a secondary transfer belt cleaning method for an image forming apparatus that first appears as the preparation mode period. The secondary transfer belt cleaning method for an image forming apparatus according to claim 10 ,
As the preparation mode period of the fixing unit, in addition to the standby mode period, the preparation mode temperature, which is the surface temperature of the heating roller of the fixing unit in the preparation mode period, is lower than the standby mode temperature. A power saving mode period, an energy saving mode period that is an energy saving mode temperature lower than the power saving mode temperature, and a shut-off mode period in which heating of the heating roller is stopped,
The secondary transfer belt cleaning method for an image forming apparatus in which the preparation mode period shifts in the order described above unless a print request is made to the image forming apparatus during each mode period.

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