JP2008164659A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of exhibiting appropriate cleaning performance for the surface of an image carrier even if a processing speed is slowed down due to use of special paper. <P>SOLUTION: A printer 1 operates a photoreceptor drum 21 and cleaning roller 32 in a first mode in which they are rotated at predetermined peripheral speeds or in a second mode in which they are rotated at peripheral speeds lower than those in the first speed mode. The photoreceptor drum 21 and cleaning roller 32 are rotated having a peripheral speed difference greater than that in the first speed mode. Thus, even if the peripheral speed between the photoreceptor drum 21 and cleaning roller 32 is slowed down due to a processing speed decrease because of using special paper such as cardboard or an OHP sheet, a required peripheral speed difference between the photoreceptor drum 21 and cleaning roller 32 can be maintained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus represented by a copying machine or a printer.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, a photosensitive drum is widely used as an image carrier. A general image forming operation using the photosensitive drum is as follows. The surface of the photosensitive drum is uniformly charged with a predetermined potential by a charging device, and by irradiating the LED light or the like of the exposure device there, the potential is partially attenuated to form an electrostatic latent image of an original image. Is done. The electrostatic latent image is developed with a developing device, whereby a toner image is formed on the surface of the photosensitive drum. This toner image is transferred to the sheet when the sheet is inserted into a transfer region formed by bringing the photosensitive drum and the transfer member into contact with each other or close to each other.

  In such an image forming apparatus, after a toner image is transferred to a sheet, a small amount of toner may remain on the surface of the photosensitive drum without being transferred to the sheet. The residual toner adhering to the surface of the photosensitive drum becomes an obstacle to the next new image formation, so that it needs to be cleaned. As a cleaning method used for such a purpose, a method of moving and collecting residual toner on the rotating member by pressing a cleaning roller, a rotating brush, or the like that is a rotating member on the surface of the photosensitive drum, or a surface of the photosensitive drum A method of scraping residual toner by bringing a cleaning blade into contact therewith, or a cleaning method combining these methods is widely known.

  When amorphous silicon is used as the photosensitive member of the photosensitive drum, it is known that discharge products easily adhere to the surface of the photosensitive member due to the discharge of the charging device. When this discharge product absorbs moisture, the electrical resistance on the surface of the photoreceptor is lowered, and a problem of image flow that disturbs the electrostatic latent image may occur. For this reason, a small amount of abrasive is mixed in the toner, and the cleaning roller and the cleaning blade are used in combination to remove the residual toner adhering to the surface of the photosensitive member, and a small amount of toner is carried on the surface of the cleaning roller. There is known a method of cleaning by discharging the discharge product adhering to the surface of the photoreceptor.

  An example of such an image forming apparatus can be seen in Patent Document 1. In the image forming apparatus described in Patent Document 1, a suitable cleaning performance is obtained by setting a predetermined peripheral speed difference between the photosensitive drum and the cleaning roller (rubbing roller).

  On the other hand, in the image forming apparatus, in addition to the commonly used copy paper, a wide variety of paper such as a thick paper such as a postcard and an OHP sheet may be used. If all of these sheets are conveyed at the same speed, the image quality may be degraded. This is because cardboard and OHP sheets have a large heat capacity, so that a sufficient amount of heat must be applied to obtain a high-quality image. Therefore, a control method has been proposed in which the peripheral speed of the heat roller and pressure roller in the fixing device is decreased depending on the type of paper, and the toner is sufficiently melted and fixed.

Examples of the image forming apparatus that changes the process speed in accordance with the paper type as described above can be seen in Patent Document 2 and Patent Document 3. These image forming apparatuses can change the process speed of the entire apparatus, including the paper conveyance speed, so that the paper can be conveyed in the optimum speed mode regardless of the paper type, and image formation and printing can be performed. It has become.
Japanese Patent Laying-Open No. 2005-338205 (page 8, FIG. 6) Japanese Patent No. 3189846 (page 3-4, FIG. 1) JP 2004-354831 A (page 6-7, FIG. 2-3)

  The image forming apparatuses described in Patent Document 2 and Patent Document 3 change the process speed of the entire apparatus according to the paper type, thereby giving a sufficient amount of heat to the paper and realizing high-quality image formation. It is said. If the process speed of the entire apparatus is reduced in order to give a sufficient amount of heat to the paper, the peripheral speed of the photosensitive drum in the image forming unit will also be reduced. Here, the cleaning roller for cleaning the surface of the photosensitive drum is connected to the same drive mechanism as that of the photosensitive drum. That is, when the peripheral speed of the photosensitive drum is decreased, the peripheral speed of the cleaning roller is also decreased at the same rate. In order to exert a suitable cleaning performance by the cleaning roller, the peripheral speed difference between the photosensitive drum and the cleaning roller is affected. However, when the process speed is reduced as described above, the peripheral speed difference is also reduced. There is a risk that sufficient polishing power due to the above cannot be obtained.

  Further, when the peripheral speed of the photosensitive drum decreases, the charging time and the time from development to development become longer. Thereby, more discharge products are discharged from the charging device. Therefore, the image flow due to the discharge product is likely to occur, and the possibility of image defects is increased.

  The present invention has been made in view of the above points, and is a case where the process speed is lowered by using special paper such as cardboard or OHP sheet, and the peripheral speed of the image carrier and the cleaning roller is lowered. In addition, the present invention provides an image forming apparatus capable of ensuring a sufficient polishing force against the deposits such as toner remaining on the surface of the image carrier by the cleaning roller and exhibiting a suitable cleaning performance for the surface of the image carrier. For the purpose.

  In order to solve the above-described problems, the present invention includes an image carrier and a cleaning roller that removes deposits on the surface of the image carrier while rotating in contact with the image carrier, and the image carrier and the cleaning member. In the image forming apparatus that operates using a first speed mode in which the roller is rotated at a predetermined peripheral speed and a second speed mode in which the roller is rotated at a peripheral speed slower than the first speed mode. In this speed mode, the image carrier and the cleaning roller rotate at a peripheral speed difference equal to or greater than the peripheral speed difference between the image carrier and the cleaning roller in the first speed mode.

  In the image forming apparatus having the above configuration, the peripheral speed difference between the image carrier and the cleaning roller in the second speed mode is different from the peripheral speed difference between the image carrier and the cleaning roller in the first speed mode. Of 1.05 times or more.

  In the image forming apparatus having the above configuration, the peripheral speed difference between the image carrier and the cleaning roller is 30 to 40 mm / s.

  In the image forming apparatus having the above configuration, the image carrier includes an amorphous silicon photoconductor.

  According to the configuration of the present invention, an image carrier and a cleaning roller that removes deposits on the surface of the image carrier while rotating in contact with the image carrier are provided. In an image forming apparatus that operates using a first speed mode that rotates at a peripheral speed and a second speed mode that rotates at a peripheral speed slower than the first speed mode, the image carrier in the second speed mode And the cleaning roller are rotated at a peripheral speed difference equal to or greater than the peripheral speed difference between the image carrier and the cleaning roller in the first speed mode, so that by using special paper such as thick paper or an OHP sheet, etc. Even if the process speed decreases and the peripheral speed of the image carrier and the cleaning roller decreases, the difference in peripheral speed between the desired image carrier and the cleaning roller is maintained. It can be. As a result, it is possible to fix the sheet by applying a sufficient amount of heat, and to secure a sufficient polishing force against the deposits such as toner remaining on the surface of the image carrier by the cleaning roller. Therefore, it is possible to provide an image forming apparatus capable of exhibiting suitable cleaning performance for the surface of the image carrier.

  Further, the peripheral speed difference between the image carrier and the cleaning roller in the second speed mode is 1.05 times or more than the peripheral speed difference between the image carrier and the cleaning roller in the first speed mode. Therefore, the polishing force by the cleaning roller can be increased so that effective cleaning can be performed in the second speed mode, which is slower than the first speed mode. Furthermore, it is possible to cope with the use of the image forming apparatus in an environment where image flow is likely to occur such as high temperature and high humidity. Therefore, it is possible to improve the cleaning performance for the surface of the image carrier.

  If the peripheral speed difference between the image carrier and the cleaning roller is relatively small, sufficient polishing force cannot be obtained by the cleaning roller, but if the peripheral speed difference is too large, the cleaning roller rotates. Can impose a load on the rotation of the elephant carrier. As a result, the image carrier does not rotate smoothly and the rotation may become unstable, and there is a high possibility that a band-like or stripe-like image defect called jitter noise will occur due to the rotational misalignment. . To solve this problem, as in the present invention, by setting the peripheral speed difference between the image carrier and the cleaning roller to 30 to 40 mm / s, it is possible to secure a sufficient polishing force on the surface of the image carrier by the cleaning roller. Further, it is possible to prevent the occurrence of image defects due to the rotation unevenness of the image carrier. Therefore, the cleaning performance for the surface of the image carrier can be further improved.

  Photoconductors made of amorphous silicon are used in many image forming apparatuses because of high hardness, excellent wear resistance, and a very long life. However, on the other hand, there is also a problem that image flow is likely to occur due to discharge products adhering to the surface of the photoreceptor. For such a problem, by combining the image forming apparatus of the present invention with a photoconductor composed of amorphous silicon, it is possible to prevent the adhesion of discharge products to the surface of the photoconductor, so that the image flow is reduced. Therefore, it is possible to form a high-quality image without causing occurrence of an image and to obtain an image forming apparatus having a longer life.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  First, an image output operation of an image forming apparatus equipped with a paper conveyance device according to an embodiment of the present invention will be described while explaining the outline of the structure with reference to FIG. FIG. 1 is a left side view of a schematic vertical section showing a schematic structure of a color printer which is an example of an image forming apparatus. This color printer is a type using an intermediate transfer belt. In FIG. 1, the right side is the front side of the printer, and the left side is the back side.

  As shown in FIG. 1, a paper feed cassette 3 is disposed below the inside of the main body 2 of the printer 1. The paper P is stacked and accommodated inside the paper feed cassette 3. The sheets P are separated and sent one by one toward the upper right of the sheet feeding cassette 3 in FIG. The paper feed cassette 3 can be pulled out horizontally from the front side of the main body 2, that is, from the right side in FIG.

  A paper feed path 4, a paper feed transport roller 5, a registration roller 6, an image forming unit 20, and a secondary transfer unit 50 are disposed downstream of the paper feed cassette 3 in the paper transport direction. The paper P sent out from the paper feed cassette 3 enters the paper feed paper transport path 4, is transported by the paper feed transport roller 5, and reaches the registration roller 6. The registration roller 6 corrects the oblique feeding of the paper P, measures the timing with the color toner image or black toner image formed by the image forming unit 20, and sends the paper P to the secondary transfer unit 50.

  The image forming unit 20 includes a photosensitive drum 21 which is a rotating image carrier at the center thereof. The photosensitive drum 21 rotates counterclockwise in FIG. Around the photosensitive drum 21, a charging device 22, a developing device 23, and a drum cleaning device 30 are sequentially arranged along the rotation direction.

  On the other hand, an optical unit 7 is provided above the image forming unit 20, and a laser beam L is emitted from the optical unit 7 toward the photosensitive drum 21. The two-dot chain line in the figure indicates the laser beam L. Image data signals such as characters, graphics, and patterns from an external computer (not shown) are transmitted to the printer 1, and the laser light L is controlled by the optical unit 7 based on the image data. As a result, an electrostatic latent image of the original image is formed on the surface of the photosensitive drum 21 in the image forming unit 20. For this electrostatic latent image, an electrostatic latent image corresponding to each color is formed in order for each color image forming process.

The developing device 23 of the image forming unit 20 is mainly composed of a rotary rack 23a that is a rotating body that rotates clockwise in FIG. 1, and a total of four developing devices are arranged at equal intervals in the circumferential direction on the rotary rack 23a. Has been placed. The four developing devices are a black developing device 23B, a cyan developing device 23C, a magenta developing device 23M, and a yellow developing device 23Y. The rotary rack 23a is rotated by driving means (not shown), and the four developing devices are sequentially moved to positions facing the photosensitive drum 21 to supply toner of each color to the surface of the photosensitive drum 21 to thereby generate electrostatic latent images. The image is developed to form a toner image. Each color toner contains titanium oxide (TiO ₂ ) as an external additive, that is, an abrasive.

  Of the respective colors of black, cyan, magenta, and yellow, first, a black toner image, which is the first color, is formed on the surface of the photosensitive drum 21, so that the black developing unit 23 </ b> B faces the photosensitive drum 21. The rack 23a rotates. The black developing device 23B develops the electrostatic latent image on the surface of the photosensitive drum 21 to form a black toner image.

  An intermediate transfer belt 40 using an intermediate transfer member in the form of an endless belt is disposed immediately below the photosensitive drum 21. The intermediate transfer belt 40 is pressed against the photosensitive drum 21 from below to form a primary transfer nip portion. The intermediate transfer belt 40 is supported by being wound around a plurality of rollers, and rotates clockwise in FIG. The toner image formed on the surface of the photosensitive drum 21 is primarily transferred to the surface of the intermediate transfer belt 40 at a primary transfer nip portion formed by press-contacting the photosensitive drum 21 and the intermediate transfer belt 40.

  After the primary transfer, the black toner remaining on the surface of the photosensitive drum 21 is removed by the drum cleaning device 30. The intermediate transfer belt 40 rotates once so as to coincide with a predetermined primary transfer position with respect to the photosensitive drum 21 in order to perform primary transfer of the next color. When the toner image to be formed is a black toner image, the primary transfer process ends here. When the toner image to be formed is a color toner image, the image forming process of development, transfer, and cleaning similar to the first color is continuously repeated for each color from the second color to the fourth color, and the surface of the intermediate transfer belt 40 A color toner image is formed by superimposing four color toner images of black, cyan, magenta, and yellow.

  A secondary transfer unit 50 is disposed at a position where the intermediate transfer belt 40 is suspended on the sheet conveyance path. The secondary transfer unit 50 includes a secondary transfer roller 51, and the sheet P is inserted into a secondary transfer nip portion formed by press-contacting the intermediate transfer belt 40 and the secondary transfer roller 51. The secondary transfer roller 51 is movable in the vertical direction in FIG. 1, and is brought into pressure contact with or separated from the intermediate transfer belt 40 as necessary. When a four-color color toner image or a black toner image is formed on the surface of the intermediate transfer belt 40, the paper P sent in synchronization by the registration roller 6 is transferred to the secondary transfer portion 50. By being inserted into the next transfer nip portion, the toner image is transferred by being brought into pressure contact with the intermediate transfer belt 40. The secondary transfer roller 51 is separated from the intermediate transfer belt 40 while the toner images of the respective colors are sequentially primary transferred to the intermediate transfer belt 40.

  A belt cleaning device 60 is provided downstream of the secondary transfer unit 50 in the sheet conveyance direction. The cleaning roller 61 of the belt cleaning device 60 is also pressed against or separated from the intermediate transfer belt 40 as necessary. After the secondary transfer, the toner remaining on the surface of the intermediate transfer belt 40 is removed by the cleaning roller 61 that is in pressure contact with the intermediate transfer belt 40. Note that the cleaning roller 61 is separated from the intermediate transfer belt 40 while the toner images of the respective colors are sequentially primary-transferred to the intermediate transfer belt 40.

  A fixing unit 8, a discharge paper transport path 9, and a paper discharge unit 10 are disposed downstream of the image forming unit 20 and the secondary transfer unit 50 in the paper transport direction. The paper P carrying an unfixed color toner image or black toner image is sent to the fixing unit 8 and the toner image is fixed by a heat roller and a pressure roller.

  The paper P discharged from the fixing unit 8 is sent upward through the discharge paper transport path 9 and is discharged to the paper discharge unit 10 provided on the upper surface of the main body 2. The paper discharge unit 10 is provided on the upper surface of the main body 2 at a position where the printed paper P can be taken out from the outside.

  A sheet conveyance path 11 for double-sided printing is disposed below the fixing unit 8 and the secondary transfer unit 50 and between the sheet feeding cassette 3. The double-sided printing paper conveyance path 11 branches from the middle of the discharge paper conveyance path 9, passes under the fixing unit 8 and under the secondary transfer unit 50, and conveys the paper for paper feeding immediately upstream of the registration roller 6. It merges with Road 4.

  When performing double-sided printing, the paper P discharged from the fixing unit 8 is switched to the reverse direction and switched back immediately before being discharged to the paper discharge unit 10 through the discharge paper transfer path 9. The Then, the paper P is sent to the double-sided printing paper transport path 11, merged with the paper feed paper transport path 4 immediately upstream of the registration rollers 6, and sent again to the secondary transfer unit 50.

  Next, a detailed configuration around the image forming unit 20 of the printer 1 will be described with reference to FIG. 2 in addition to FIG. FIG. 2 is a partial enlarged vertical sectional view showing the periphery of the image forming unit of the printer.

  As shown in FIGS. 1 and 2, the image forming unit 20 includes a photosensitive drum 21 that is an image carrier at the center thereof. An intermediate transfer belt 40 using an intermediate transfer member in the form of an endless belt is disposed immediately below the photosensitive drum 21. With respect to the primary transfer nip portion where the photosensitive drum 21 and the intermediate transfer belt 40 are in pressure contact with each other, the charging device 22 and the developing device 23 described above are disposed upstream of the drum rotation direction, and the drum device is disposed downstream. A cleaning device 30 is provided.

  The photoconductive drum 21 extends in the paper width direction perpendicular to the paper conveyance direction in the printer 1, that is, the paper surface depth direction in FIGS. 1 and 2, and is arranged with its axial direction horizontal. The photosensitive drum 21 is an inorganic photosensitive drum in which an amorphous silicon photosensitive layer, which is an inorganic photoconductive material, is provided on the outside of a conductive roller-shaped substrate made of aluminum or the like by vacuum deposition or the like, and has a diameter of 30 mm. It is. The photosensitive drum 21 is rotated by a driving device (not shown) so that the peripheral speed thereof is substantially the same as the paper conveyance speed (152 mm / s).

  The charging device 22 includes a charging roller 22 a in contact with the photosensitive drum 21 inside the housing. The charging roller 22 a is pressed against the photosensitive drum 21 with a predetermined pressure, and rotates according to the rotation of the photosensitive drum 21. The surface of the photosensitive drum 21 is uniformly charged with a predetermined polarity and potential by the charging roller 22a. The charging potential at this time is plus 350V. A cleaning member (not shown) is provided in the housing of the charging device 22 at a position separating the charging roller 22a from the photosensitive drum 21, and the surface of the charging roller 22a is cleaned by this cleaning member.

  As shown in FIGS. 1 and 2, the intermediate transfer belt 40 is wound around a primary transfer roller 41, a tension roller 42, a driving roller 43, and a guide roller 44. The intermediate transfer belt 40 is composed of a single-layer resin belt formed only of a synthetic resin such as polyimide, or an elastic belt in which a rubber layer is laminated on the surface of such a synthetic resin. The primary transfer roller 41 is provided in the primary transfer nip portion so as to contact the photosensitive drum 21 from below via the intermediate transfer belt 40. A primary transfer bias is applied to the primary transfer roller 41 as necessary.

  As shown in FIG. 2, the cleaning device 30 for the photosensitive drum 21 includes a cleaning roller 32, a cleaning blade 33, and a discharge screw 34 as a discharge member inside the housing 31.

  The cleaning roller 32 is provided on the upstream side in the drum rotation direction of the cleaning blade 33 and pressed against the photosensitive drum 21 with a predetermined force by urging means (not shown) provided at both ends of the shaft portion. . The cleaning roller 32 is configured by providing an ethylene propylene rubber (EPDM) having a hardness of Asker C45 around a core metal having a diameter of 8 mm, the roller portion has a diameter of 12 mm, and is substantially the same axis as the photosensitive drum 21. It has a directional length. For the cleaning roller 32, EPDM having a hardness in the range of Asker C30-60 can be used.

  The cleaning roller 32 is rotated by a driving mechanism (not shown) composed of a motor or the like. In order to efficiently polish the surface of the photosensitive drum 21, it is necessary to rotate the cleaning roller 32 at a predetermined peripheral speed. As a result, the cleaning roller 32 is rotated in such a direction that the surface at the contact point with the photosensitive drum 21 moves in the same direction as the surface of the photosensitive drum 21, and the circumferential speed of the cleaning roller 32 is one of that of the photosensitive drum 21. .2x is set. The cleaning roller 32 collects deposits such as residual toner from the surface of the photoconductive drum 21 and cleans the surface of the photoconductive drum 21 with the toner containing the abrasive adhered to the surface of the cleaning roller 32. Fulfill.

  The cleaning blade 33 is disposed downstream of the cleaning roller 32 in the rotation direction of the photosensitive drum 21. The cleaning blade 33 is provided by being pressed with a predetermined force against the photosensitive drum 21 by an urging means (not shown). The cleaning blade 33 is a rectangular parallelepiped member such as a plate extending in the drum axial direction, which is made of polyurethane rubber having Asker C70 hardness, and has substantially the same axial length as the photosensitive drum 21. is doing. The cleaning blade 33 plays a role of cleaning so as to scrape off deposits such as toner remaining on the surface of the photosensitive drum 21.

  As shown in FIG. 2, the discharge screw 34 is provided in the housing 31 at a position further away from the photosensitive drum 21 with the cleaning roller 32 interposed therebetween. The discharge screw 34 extends from the inside of the housing 31 to a waste toner collection container (not shown) provided outside the image forming unit 20. The discharge screw 34 is removed from the surface of the photosensitive drum 21 and serves to discharge waste toner and the like in the housing 31 used for cleaning (polishing) to the outside of the housing 31, that is, to a waste toner collection container.

  Next, details of the process speed in the printer 1 will be described.

  The printer 1 operates in the first speed mode during normal printing using copy paper or the like. In this first speed mode, the peripheral speed of the photosensitive drum 21 is 152 mm / s, the peripheral speed of the cleaning roller 32 is 1.2 times that of 182.4 mm / s, and the difference between these peripheral speeds is 30.4 mm / s. It is. In this case, image flow and color shift (jitter noise) did not occur even in a high temperature and high humidity environment such as a temperature of 32.5 ° C. and a humidity of 80%.

  Regarding the occurrence of image flow and color misregistration (jitter noise), the generation of color images having a toner occupancy ratio of 2% on the paper surface was continuously printed on 1000 sheets, and the occurrence was evaluated. In order to make the image flow relatively easy to occur, the image is printed for 8 hours in a high temperature and high humidity environment with a temperature of 32.5 ° C. and a humidity of 85%, and the state of the image is visually observed. Evaluated. Regarding color misregistration (jitter noise), halftone images of each color were printed, and the presence or absence of shading unevenness caused by the rotation pitch of the cleaning roller 32 was visually evaluated.

  The printer 1 operates in the second speed mode during special printing using a sheet having a large heat capacity such as a thick sheet or an OHP sheet. In this second speed mode, the peripheral speed of the photosensitive drum 21 is 76 mm / s, which is half of that in the first speed mode, the peripheral speed of the cleaning roller 32 is 106.4 mm / s, and the peripheral speed difference is 30.4 mm. / S. Also in this case, as in the first speed mode, image flow and color shift (jitter noise) did not occur in a high temperature and high humidity environment.

  On the other hand, in the second speed mode, if the peripheral speed of the cleaning roller 32 is also 91.2 mm / s, which is half of that in the first speed mode, the peripheral speed difference from the peripheral speed of the photosensitive drum 21 is 76 mm / s. Decreases to a half of 15.2 mm / s. In this case, image flow and color shift (jitter noise) occurred in a high temperature and high humidity environment.

  As a result, the printer 1 according to the embodiment of the present invention causes the photosensitive drum 21 and the cleaning roller 32 in the second speed mode to move, and the peripheral speed between the photosensitive drum 21 and the cleaning roller 32 in the first speed mode. It is supposed to rotate at a peripheral speed difference greater than the difference.

  Next, when the cleaning device 30 for the photosensitive drum 21 is used to clean the surface of the photosensitive drum 21, the difference in the peripheral speed between the photosensitive drum 21 and the cleaning roller 32 is caused by the image flow and color. The influence on the occurrence of deviation (jitter noise) will be described with reference to FIGS. FIG. 3 is a table showing the influence of the difference in the peripheral speed difference between the photosensitive drum and the cleaning roller in the first and second speed modes on the occurrence of image flow. FIG. 4 is a chart showing the photosensitive drum and the cleaning roller. It is a table | surface which shows the influence which the difference in the peripheral speed difference with a roller has on generation | occurrence | production of image flow and color shift (jitter noise).

  3 is the ratio of the peripheral speed difference between the photosensitive drum 21 and the cleaning roller 32 in the second speed mode to the peripheral speed difference in the first speed mode. Show.

  The evaluation method for the occurrence of image flow and color shift (jitter noise) is the same as described above. Regarding the image flow, the state of the image is visually evaluated in three ranks, “○” indicates that the image flow is hardly confirmed, “△” indicates that the image flow is slightly confirmed, and “Image flow”. Is marked “x”. Regarding color misregistration (jitter noise), the presence / absence of shading unevenness is visually evaluated in two ranks, and “○” indicates that shading unevenness is hardly confirmed, and “×” indicates that shading unevenness is remarkable. .

  Regarding the difference in the peripheral speed difference between the photosensitive drum 21 and the cleaning roller 32 in the first and second speed modes, according to FIG. 3, the peripheral speed difference ratio is 1.00 times and 1.03. In the case of doubling, it can be seen that image flow occurs in a high-temperature and high-humidity environment with a temperature of 35.0 ° C. and a humidity of 85%. Further, if the peripheral speed difference in the second speed mode is further increased and the ratio to the peripheral speed difference in the first speed mode is set to 1.05 times or more, image flow can be prevented and good results are obtained. Met.

  Regarding the difference in the peripheral speed difference between the photosensitive drum 21 and the cleaning roller 32, according to FIG. You can see that it is made. It can also be seen that color drift (jitter noise) is likely to occur when the peripheral velocity difference is 25 mm / s and the image flow is 45 mm / s.

  In summary, the ratio of the peripheral speed difference between the photosensitive drum 21 and the cleaning roller 32 in the second speed mode to the peripheral speed difference in the first speed mode is greater than 1.05 times. The configuration of the printer 1 in which the peripheral speed difference between the body drum 21 and the cleaning roller 32 is 30 to 40 mm / s resulted in the most favorable evaluation.

  In this manner, the photosensitive drum 21 that is an image carrier and the cleaning roller 32 that removes deposits on the surface of the photosensitive drum 21 while rotating in contact with the photosensitive drum 21 are provided. In the printer 1 that operates using the first speed mode in which the roller 32 is rotated at a predetermined peripheral speed and the second speed mode in which the roller 32 is rotated at a peripheral speed slower than the first speed mode, The photosensitive drum 21 and the cleaning roller 32 in the speed mode rotate at a peripheral speed difference that is equal to or greater than the peripheral speed difference between the photosensitive drum 21 and the cleaning roller 32 in the first speed mode. When the process speed decreases due to the use of paper or the like, and the peripheral speed of the photosensitive drum 21 or the cleaning roller 32 decreases. Even it can be held on the peripheral speed difference between the desired photoreceptor drum 21 and the cleaning roller 32. Accordingly, it is possible to fix the sheet by applying a sufficient amount of heat, and it is possible to secure a sufficient polishing force for the toner and other deposits remaining on the surface of the photosensitive drum 21 by the cleaning roller 32. Therefore, it is possible to provide the printer 1 that can exhibit a suitable cleaning performance for the surface of the photosensitive drum 21.

  Further, the peripheral speed difference between the photosensitive drum 21 and the cleaning roller 32 in the second speed mode is 1.05 times or more than the peripheral speed difference between the photosensitive drum 21 and the cleaning roller 32 in the first speed mode. Therefore, the polishing force by the cleaning roller 32 can be increased so that effective cleaning can be performed in the second speed mode, which is slower than the first speed mode. Furthermore, it is possible to cope with the use of the printer 1 in an environment where image flow is likely to occur such as high temperature and high humidity. Therefore, the cleaning performance for the surface of the photosensitive drum 21 can be improved.

  If the peripheral speed difference between the photosensitive drum 21 and the cleaning roller 32 is relatively small, sufficient polishing force by the cleaning roller 32 cannot be obtained. However, if the peripheral speed difference is too large, cleaning is performed. The rotation of the roller 32 may place a load on the rotation of the photosensitive drum 21. As a result, the photosensitive drum 21 does not rotate smoothly, and the rotation may become unstable, and a band-like or stripe-like image defect called jitter noise may occur due to the rotational misalignment. high. To solve this problem, the circumferential speed difference between the photosensitive drum 21 and the cleaning roller 32 is set to 30 to 40 mm / s as in the above embodiment, so that the surface of the photosensitive drum 21 by the cleaning roller 32 is sufficient. A sufficient polishing force can be secured, and it is possible to prevent image defects caused by uneven rotation of the photosensitive drum 21. Therefore, the cleaning performance for the surface of the photosensitive drum 21 can be further improved.

  Photoconductors made of amorphous silicon are used in many image forming apparatuses because of high hardness, excellent wear resistance, and a very long life. However, on the other hand, there is also a problem that image flow is likely to occur due to discharge products adhering to the surface of the photoreceptor. In order to solve such a problem, it is possible to prevent adhesion of discharge products to the surface of the photosensitive member by combining the printer 1 which is the image forming apparatus of the present invention with a photosensitive member made of amorphous silicon. Therefore, it is possible to form a high-quality image with no image flow and to obtain the printer 1 having a longer life.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  For example, in the above-described embodiment, the printer 1 is a color that includes the rotary rack 23a in which four developing devices are arranged at equal intervals in the circumferential direction in the developing device 23, and the endless intermediate transfer belt 40 as an intermediate transfer member. Although it is an image forming apparatus for printing, it may be an image forming apparatus for tandem color printing or an image forming apparatus for monochrome printing using only black toner without using an intermediate transfer member.

  Further, in each color toner, titanium oxide is mixed as an abrasive (external additive), but strontium titanate, cerium oxide, and alumina oxide may be mixed as an abrasive instead.

  The present invention can be used in general image forming apparatuses.

It is a model vertical cross-section left side view of a printer according to an embodiment of the present invention. FIG. 2 is a partially enlarged vertical cross-sectional view illustrating the periphery of an image forming unit of the printer of FIG. 1. 6 is a table showing the influence of the difference in the peripheral speed difference between the photosensitive drum and the cleaning roller in the first and second speed modes on the occurrence of image flow. 6 is a table showing the effect of difference in peripheral speed between the photosensitive drum and the cleaning roller on image flow and color misregistration.

Explanation of symbols

1 Printer (image forming device)
20 Image forming unit 21 Photosensitive drum (image carrier)
22 Charging device 22a Charging roller 23 Developing device 30 Cleaning device (for photosensitive drum)
32 Cleaning roller 33 Cleaning blade

Claims (4)

An image carrier, and a cleaning roller that rotates in contact with the image carrier and removes deposits on the surface of the image carrier, and rotates the image carrier and the cleaning roller at a predetermined peripheral speed. In an image forming apparatus that operates using a first speed mode and a second speed mode that rotates at a lower peripheral speed than the first speed mode,
The image carrier and the cleaning roller in the second speed mode rotate with a peripheral speed difference equal to or greater than a peripheral speed difference between the image carrier and the cleaning roller in the first speed mode. Forming equipment.   The peripheral speed difference between the image carrier and the cleaning roller in the second speed mode is 1.05 times or more of the peripheral speed difference between the image carrier and the cleaning roller in the first speed mode. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 1, wherein a difference in peripheral speed between the image carrier and the cleaning roller is 30 to 40 mm / s.   The image forming apparatus according to claim 1, wherein the image carrier includes an amorphous silicon photoconductor.

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