JP2016170384A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device capable of determining a smoothing degree of a surface of an image carrier, without providing new detection means.SOLUTION: An image formation device comprises: an image carrier; a drive device; a cleaning member; a torque detection part; and a control part. A toner image is formed on a surface of the image carrier. The drive device drives and rotates the image carrier. The cleaning member is disposed to contact the surface of the image carrier, and performs cleaning of the surface of the image carrier. The torque detection part detects a torque of the drive device when rotating and driving the image carrier. The control part calculates a torque increase factor until the torque of the drive device reaches a maximum value, since start of printing, based on the torque detected by the torque detection part, and then determines a smoothing degree of the surface of the image carrier, based on the calculated torque increase factor.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus that forms an image on recording paper, and more particularly to a method for determining the surface state of an image carrier on which a toner image is formed.

  In image forming apparatuses such as printers, copiers, facsimiles, or multifunction devices having these functions, a photosensitive drum as an example of an electrophotographic photosensitive member, and a charging member such as a charging roller that charges the surface of the photosensitive drum And a cleaning blade that is disposed in contact with the surface of the photosensitive drum and removes toner and external additives remaining on the surface of the photosensitive drum.

  Such a charging member is disposed in contact with or close to the image carrier, and a discharge product generated by discharge from the charging member adheres to the surface of the image carrier. As a result, the frictional resistance between the surface of the image carrier and the cleaning blade increases, chattering, chipping, and stick slip of the cleaning blade are likely to occur, and the cleaning ability of the cleaning blade decreases. As a result, the amount of toner and external additives slipping through increases, the charging member is contaminated, and the toner and external additives left uncleaned adhere to the surface of the image carrier, resulting in deterioration in image quality and poor image formation. May occur.

  In particular, when an image carrier having an amorphous silicon layer formed on the surface is used as the photosensitive layer, the contact area between the image carrier surface and the cleaning blade is initially reduced due to the unevenness of crystal grains generated when the amorphous silicon layer is formed. Although it is small, the frictional resistance is small, but the unevenness on the surface of the image carrier is worn and smoothed during use, and the frictional resistance between the surface of the image carrier and the cleaning blade increases, resulting in the above problems. It becomes easy.

  Therefore, in order to reduce the load on the cleaning blade, the generation of discharge products is suppressed by a method such as supplying toner as a lubricant as in Patent Document 1 or reducing the charging bias as in Patent Document 2. Such measures are taken.

JP 2007-25270 A JP 2007-108421 A

  However, the suppression of the increase in frictional resistance is greatly affected by the surface roughness of the image carrier, so it must be controlled accordingly, but it is predicted that there is no means to detect the surface roughness of the image carrier. Control must be done by Providing a new means for detecting the surface roughness of the image bearing member causes an increase in cost.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of determining the degree of smoothness of the surface of an image carrier without providing new detection means.

  In order to achieve the above object, a first configuration of the present invention is an image forming apparatus including an image carrier, a driving device, a cleaning member, a torque detection unit, and a control unit. A toner image is formed on the surface of the image carrier. The driving device rotationally drives the image carrier. The cleaning member is disposed so as to contact the surface of the image carrier, and cleans the surface of the image carrier. The torque detector detects the torque of the driving device when the image carrier is rotationally driven. The control unit determines the surface state of the image carrier based on the torque detected by the torque detection unit. The control unit calculates a torque increase coefficient from the start of printing until the torque of the driving device reaches the maximum value based on the torque detected by the torque detection unit, and the image carrier based on the calculated torque increase coefficient The degree of smoothing of the surface is determined.

  When the surface of the image carrier is worn and smoothed, the contact area between the image carrier and the cleaning blade increases, so that the frictional resistance between the image carrier and the cleaning blade increases, and the image carrier rotates. The torque increase coefficient of the driving device to be driven increases. That is, the torque increase coefficient of the driving device increases as the surface of the image carrier is worn and smoothed. According to the first configuration of the present invention, the degree of smoothing of the image carrier surface is determined based on the torque increase coefficient from the start of printing until the torque of the driving device reaches the maximum value. Thereby, it is possible to easily and accurately determine whether or not the surface of the image carrier is smoothed without newly providing a sensor or the like for detecting the surface state of the image carrier.

1 is a schematic cross-sectional view showing a schematic configuration of a tandem color printer as an image forming apparatus 11 according to an embodiment of the present disclosure. 1 is a diagram illustrating a schematic configuration of a main part including an image formation processing unit 15 of an image forming apparatus 11 according to the present embodiment. The figure which shows the uneven | corrugated shape when skewness Rsk is larger than 0 The figure which shows the uneven | corrugated shape when skewness Rsk is smaller than 0 The flowchart which shows the processing content of the image quality fall suppression control in the image forming apparatus 11 of this embodiment. The graph which shows the torque fluctuation of the drive motor 36 from the printing start to 300 second at the time of using the new photosensitive drums a and b in an Example. 6 is an enlarged graph of torque fluctuation from the start of printing to 50 seconds. A graph showing the arithmetic average roughness Ra of the surface of a new photosensitive drum a Graph showing the arithmetic mean roughness Ra of the surface of the photosensitive drum a1 after durable printing Graph showing the arithmetic mean roughness Ra of the surface of a new photosensitive drum b Graph showing the arithmetic mean roughness Ra of the surface of the photosensitive drum b1 after durable printing A graph showing torque fluctuation of the drive motor 36 from the start of printing to 600 seconds when the photosensitive drums a1, b1, b2, and b3 are used after durable printing. 12 is a graph showing an enlarged torque fluctuation from the start of printing to 100 seconds in FIG. A graph showing torque fluctuations of the drive motor 36 from the start of printing to 300 seconds when the photosensitive drums a and b and the photosensitive drums a1, b1, b2, and b3 are used.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus 11 according to an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of a main part including the image forming processing unit 15 of the image forming apparatus 11 shown in FIG.

1. Configuration of image forming apparatus 11 (overall configuration)
As shown in FIG. 1, the image forming apparatus 11 according to the present embodiment is a tandem color printer. The image forming apparatus 11 includes, inside a printer main body 12, a paper feed cassette 13 that stores recording paper (not shown), a paper feeding unit 14 that feeds recording paper one by one from the paper feeding cassette 13, and paper feeding An image forming processing unit 15 that performs an image forming process on the recording paper supplied from the cassette 13 or the manual feed tray (not shown), and a recording paper transport path for transporting the recording paper supplied from the paper feed cassette 13 or the manual feed tray 16, a secondary transfer unit 17 that transfers the toner image formed in the image forming processing unit 15 to the recording paper conveyed along the recording paper conveyance path 16, and the toner image transferred in the secondary transfer unit 17 And a fixing unit 18 that fixes the recording paper.

(Configuration of the image forming processing unit 15)
For example, the image forming processing unit 15 employs a tandem system that performs image forming processing using toner (developer) of four colors of yellow (Y), magenta (M), cyan (C), and black (K). ing. In the following explanation, only in the case of color designation, the symbol of each arithmetic numeral is attached with a color of (Y, M, C, K) in parentheses, and in the common case, only the arithmetic numeral is included. A description will be given with reference numerals.

  The image forming processing unit 15 corresponds to each color (Y, M, C, K) and print data (images) transmitted from a plurality of toner containers 19 containing replenishing toner and an externally connected device such as a personal computer. A plurality of photosensitive drums 20 for forming toner images of respective colors based on the data), a plurality of developing devices 21 for supplying toner to each of the photosensitive drums 20, and a toner image formed on each of the photosensitive drums 20. The endless intermediate transfer belt 22 to which the toner image is primarily transferred, the residual toner attached to the surface of the intermediate transfer belt 22 and disposed upstream of the photosensitive drum 20 on the most upstream side in the rotational movement direction of the intermediate transfer belt 22 A belt cleaning device 24 that removes the light, and an exposure unit 25 that emits beam light to each photosensitive drum 20.

(Configuration of Photosensitive Drum 20)
The photosensitive drum 20 is formed by forming a photosensitive layer on the surface of a support (base). Here, the photosensitive drum 20 includes a cylindrical cylindrical tube made of metal and a photosensitive layer formed on the surface of the tube. Note that the raw tube corresponds to an example of the “support” of the present invention. Examples of the metal forming the base tube include aluminum, iron, titanium, and magnesium. As the photosensitive layer, an organic photosensitive layer using an organic photoconductor or an inorganic photosensitive layer using an inorganic photoconductor can be used. However, because of its high durability, an amorphous silicon photosensitive film formed by vapor deposition of silane gas or the like is used. A layer is preferred. Each photosensitive drum 20 carries a toner image of each color on the surface thereof based on the beam light emitted from the exposure unit 25 and transfers the toner image to the intermediate transfer belt 22, as shown in FIG. As described above, the developing device 21 is disposed below the intermediate transfer belt 22. The surface state of the photosensitive drum 20 in the initial use will be described later.

  As shown in FIGS. 1 and 2, a charging roller (charging member) 26, an exposure unit 25, a developing device 21, a cleaning device 28, and a static eliminating device 29 are disposed around the photosensitive drum 20, A primary transfer roller 27 is disposed opposite to the photosensitive drum 20 with the transfer belt 22 interposed therebetween.

  The toner image transferred onto the intermediate transfer belt 22 at each primary transfer portion configured by the cooperation of the photosensitive drum 20 and the primary transfer roller 27 passes through the recording paper transport path 16 from the paper feed cassette 13 or the manual feed tray. The recording paper that has been conveyed through is transferred by the secondary transfer unit 17.

(Configuration of developing device 21)
Each developing device 21 basically has the same configuration and is arranged below the intermediate transfer belt 22 along the rotational movement direction. The developing device 21 develops the electrostatic latent image formed on the surface of the photosensitive drum 20 into a toner image by attaching a toner containing a toner external additive (abrasive particles) made of metal particles such as titanium oxide. A conventionally known developing device 21 can be used.

(Configuration of the intermediate transfer belt 22)
The intermediate transfer belt 22 is an endless belt that is horizontally stretched between a driving roller and a driven roller in the printer main body 12, and accompanies an image forming operation as the driving roller is rotated by a belt driving motor (not shown). It is circulated and driven.

(Configuration of toner density detection sensor 23)
The toner density detection sensor 23 measures the reflection density of the toner image on the intermediate transfer belt 22 and outputs the detected value to the control circuit 30 (see FIG. 2). The toner density detection sensors 23 can be provided at a plurality of locations along the rotational movement direction of the intermediate transfer belt 22 and the width direction orthogonal to the rotational movement direction. At this time, if the toner density detection sensor 23 detects the toner density only on one side in the width direction of the intermediate transfer belt 22, for example, a phenomenon in which a density difference occurs on both ends in the width direction of the intermediate transfer belt 22 (single burn phenomenon). It is preferable to dispose near the both ends in the width direction because it is not possible to cope with the occurrence of this.

(Configuration of charging roller 26)
The charging roller 26 is made of, for example, conductive rubber and is disposed so as to contact the photosensitive drum 20. As shown in FIG. 2, when the photosensitive drum 20 rotates in the clockwise direction, the charging roller 26 that contacts the surface of the photosensitive drum 20 is driven to rotate counterclockwise. At this time, the surface of the photosensitive drum 20 is uniformly charged by applying a predetermined voltage to the charging roller 26. Further, as the charging roller 26 rotates, a charging cleaning roller (not shown) that contacts the charging roller 26 is driven to rotate in the clockwise direction to remove foreign matters attached to the surface of the charging roller 26.

(Configuration of the cleaning device 28)
The cleaning device 28 has a cleaning housing 40 having a depth in the recording paper width direction (a direction orthogonal to the recording paper conveyance direction), and is disposed near the lower inside of the cleaning housing 40 and rotates clockwise in FIG. A collection spiral 41 that conveys the collected toner to one side in the paper width direction and sends it to a waste toner container (not shown), a cleaning blade 42 attached to the outside lower side of the cleaning housing 40, and an inside upper side of the cleaning housing 40 A rubbing roller (cleaning roller) 43 disposed in contact with the surface of the photosensitive drum 20, and a scraper 44 disposed above the rubbing roller 43 and in contact with the surface of the rubbing roller 43.

  The cleaning blade 42 is made of urethane rubber or the like. The cleaning blade 42 is disposed so that the tip abuts against the surface of the photosensitive drum 20 from below the rotational axis of the photosensitive drum 20. At this time, the tip of the cleaning blade 42 is in contact with the rotation direction of the photosensitive drum 20 (see the arrow in FIG. 2) in the counter direction.

  The rubbing roller 43 collects waste toner from the surface of the photoconductive drum 20 and polishes the surface of the photoconductive drum 20 with the waste toner adhering to the surface of the rubbing roller 43. For this reason, the rubbing roller 43 is formed in a cylindrical shape that extends in the recording paper width direction using foamed rubber (for example, carbon-containing conductive foamed EPDM) in order to maintain high retention of waste toner. It is arranged upstream of the front end in the rotational direction of the photosensitive drum 20. Further, the rotation direction of the rubbing roller 43 is opposite to the rotation direction of the photosensitive drum 20. The scraper 44 is made of a thin sheet metal that ensures durability, and in order to make the amount of toner adhering to the surface of the rubbing roller 43 uniform, a counter direction is provided downstream of the rubbing roller 43 in the rotation direction. The tip is in contact.

(Configuration of static elimination device 29)
The static eliminator 29 is disposed on the downstream side of the cleaning device 28 along the rotation direction of the photosensitive drum 20. An LED (light emitting diode) is used for the static elimination device 29, and a reflector is provided as necessary. The static eliminator 29 irradiates the photosensitive drum 20 with static elimination light (erase light), thereby removing the charged charges on the surface thereof and preparing for the charging process in the next image forming operation.

(Configuration of control circuit 30)
The control circuit 30 executes an image forming process (print job) based on various control programs related to the entire image forming process stored in the ROM 31, and at the time of the image forming process, a DC voltage and an AC voltage are applied to the charging roller 26. The applied voltage of the high-voltage power supply 34 for applying the superimposed bias is controlled.

  Further, the control circuit 30 controls a drive motor (drive device) 36 that rotates the photosensitive drum 20 via a motor drive driver 35, and detects the detected value from the torque detection unit 37 that detects the torque of the drive motor 36. Based on this, image quality deterioration suppression control is performed. Further, the count value from the counter 39 that counts the cumulative number of image forming processes is input to the control circuit 30.

  In the present embodiment, the torque detector 37 detects the output current value of the drive motor 36. That is, in this embodiment, the output current value of the drive motor 36 is used as an index representing torque. Note that a means for detecting the torque of the drive motor 36 is usually provided in the image forming apparatus 11 in order to prevent the drive motor 36 from being damaged due to an excessive load.

  The ROM 31 also stores a control program related to image formation processing correction according to the present invention, and a microcomputer is configured with the control circuit 30 that executes the image formation processing control program. Note that image data and the like when executing the image forming process are temporarily stored in the RAM 32 or the HDD 33. Further, the control circuit 30 stores the detection result from the toner density detection sensor 23 in the RAM 32 or the HDD 33.

  In addition to the above control, the control circuit 30 supplies toner to each developing device 21, developing conditions such as a bias voltage applied to the developing device 21, and the laser power of the laser light P (see FIG. 1) emitted from the exposure unit 25. Calibration of exposure conditions, etc. is executed.

2. Image Forming Procedure Next, an image forming procedure of the image forming apparatus 11 will be described. When image data is input from an external connection device such as a personal computer, the surface of the photosensitive drum 20 is first uniformly charged by the charging roller 26, and then the laser beam P is applied to the surface of the photosensitive drum 20 by the exposure unit 25. And an electrostatic latent image corresponding to the image data is formed on each photosensitive drum 20. The developing device 21 is filled with a predetermined amount of a two-component developer (hereinafter, also simply referred to as a developer) containing toner of each color of yellow, magenta, cyan, and black. In addition, when the ratio of the toner in the two-component developer filled in each developing device 21 is less than a predetermined value due to the formation of a toner image described later, the toner is supplied from the toner container 19 to each developing device 21. . The toner in the developer is supplied onto the photosensitive drum 20 by the developing device 21 and electrostatically adheres, whereby a toner image corresponding to the electrostatic latent image formed by exposure from the exposure unit 25 is formed. It is formed.

  On the other hand, the recording paper is fed from the paper feed cassette 13 (or the manual feed tray) in accordance with the toner image formation timing in the image forming processing unit 15, and conveyed to the registration roller pair 30 a through the recording paper conveyance path 16. .

  The primary transfer roller 27 applies an electric field between the primary transfer roller 27 and the photosensitive drum 20 at a predetermined transfer voltage, and yellow, magenta, cyan, and black toner images on the photosensitive drum 20 are transferred to the intermediate transfer belt. 22 is primarily transferred onto 22. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full color image. Thereafter, the toner remaining on the surface of the photosensitive drum 20 after the primary transfer is removed by the cleaning device 28 in preparation for the subsequent formation of a new electrostatic latent image. Further, the residual charge on the surface of the photosensitive drum 20 is removed by the static eliminator 29.

  When the intermediate transfer belt 22 starts to rotate counterclockwise in FIG. 1, the recording paper is conveyed from the registration roller pair 30a to the secondary transfer portion 17 provided adjacent to the intermediate transfer belt 22 at a predetermined timing. The full color image on the intermediate transfer belt 22 is secondarily transferred onto the recording paper. The recording paper on which the toner image is secondarily transferred is conveyed to the fixing unit 18. Residual toner or the like adhering to the surface of the intermediate transfer belt 22 is removed by the belt cleaning device 24.

  The recording paper conveyed to the fixing unit 18 is heated and pressurized to fix the toner image on the surface of the recording paper, thereby forming a predetermined full color image. The recording paper on which the full-color image is formed is guided to the end portion of the recording paper transport path 16 and is discharged onto the discharge tray 12a that also serves as the upper surface of the printer body 12 by the discharge roller pair 30b.

3. Determination of Surface State of Photoreceptor Drum 20 Using Torque Increasing Factor Hereinafter, the characteristic part of the image forming apparatus 11 of the present invention will be described. In the image forming apparatus 11 of the present invention, the torque increase coefficient from the start of printing is calculated based on the torque information of the drive motor 36 detected by the torque detector 37, and the calculated torque increase coefficient exceeds the threshold value. In this case, it is determined that the surface of the photosensitive drum 20 has been smoothed. In this embodiment, the torque increase value (mNm / second) in a predetermined time (seconds) from the start of printing until the torque reaches the maximum value is represented by a torque increase coefficient (mNm / second), and the torque increase coefficient (mNm / second). When the value exceeds the threshold, it is determined that the surface of the photosensitive drum 20 has been smoothed. That is, the degree of smoothing of the surface of the photosensitive drum 20 is determined based on the torque increase coefficient (mNm / sec).

  The threshold value of the torque increase coefficient is preferably in the range of 0.0 to 0.4 mNm / sec, particularly preferably in the range of 0.0 to 0.25 mNm / sec. When the surface of the photosensitive layer of the photosensitive drum 20 is smoothed and the torque increase coefficient exceeds a threshold value, the friction coefficient between the cleaning blade 42 and the photosensitive drum 20 increases and the edge portion of the cleaning blade 42 is worn. As a result, there is a tendency that the cleaning ability of the cleaning blade 42 is deteriorated or the toner external additive slips out and the image quality is deteriorated and the image formation is poor. The threshold value is set in advance in consideration of materials such as the photosensitive drum 20, the cleaning blade 42, and the rubbing roller 43, and is stored in the HDD (storage unit) 33.

  The photosensitive drum 20 used in the image forming apparatus 11 of the present embodiment has an arithmetic average roughness Ra of the surface of the photosensitive layer in the initial use within a range of 20 [nm] to 100 [nm], and a ten-point average roughness. Rz is in the range of 0.2 [μm] or more and 1.0 [μm] or less, the average interval Sm of unevenness is 20 [μm] or less, and the arithmetic average roughness with respect to the average interval Sm [μm] of unevenness The surface roughness is preferably such that the ratio of Ra [nm] (Ra [nm] / Sm [μm]) is 3 or more and the skewness Rsk is 0.3 or more. In this specification, the initial use of the photosensitive drum 20 refers to a new state before durable printing. Further, the surface state described above may be at least in the initial use of the photosensitive drum 20 (the state at the start of use, in other words, the state after factory shipment). The arithmetic average roughness Ra, the ten-point average roughness Rz, and the average interval Sm are measured by a surface roughness measuring method defined in 1994 edition of JIS B0601 using a stylus type two-dimensional roughness measuring instrument.

(1) Arithmetic mean roughness Ra
When the arithmetic average roughness Ra is smaller than 20 [nm], the cleaning blade 42 is worn by long-term use, and the amount of slipping through of the external additive that leads to image defects increases. When the arithmetic average roughness Ra is larger than 100 [nm], the amount of slipping out of the external additive is large from the beginning, and the contamination of the charging roller 26 starts from a relatively early stage of durable printing, which makes it difficult to use for a long time. Become. Accordingly, the arithmetic average roughness Ra of the surface of the photosensitive layer in the initial use is preferably in the range of 20 [nm] to 100 [nm].

(2) Ten-point average roughness Rz
When the arithmetic average roughness Ra of the photosensitive layer surface in the initial use of the photosensitive drum 20 is in the range of 20 [nm] to 100 [nm], the ten-point average of the photosensitive layer surface in the initial use of the photosensitive drum 20 is used. The roughness Rz is preferably in the range of 0.2 [μm] to 1.0 [μm].

  Even if the arithmetic average roughness Ra is within the above range, if there are large irregularities, the cleaning blade 42 is not able to follow the surface of the photosensitive drum 20 although it deforms to some extent, and the photosensitive drum 20 and the cleaning blade 42 This is a rule for preventing the gap between the two. Note that when the interval between the photosensitive drum 20 and the cleaning blade 42 is increased, slipping of external additives or the like occurs.

  In other words, if a large convex portion exists on the surface of the photosensitive drum 20 and the tip of this convex portion comes into contact with the cleaning blade 42, the concave portion located between the large convex portions contacts the cleaning blade 42. This is because it does not make sense to define the magnitude of the arithmetic average roughness Ra. That is, it is preferable that the surface of the photoconductor drum 20 has no irregularities and has minute irregularities, and this condition is defined by the ten-point average roughness Rz and the arithmetic average roughness Ra. . Note that the ten-point average roughness Rz defines that there are no sudden irregularities.

(3) The average interval Sm of the irregularities
Even if the arithmetic average roughness Ra and the ten-point average roughness Rz are within the above ranges, the cleaning blade 42 contacts (supports) the large convex portion when the large convex portion exists apart. . Here, the average interval Sm of the unevenness is used for determining whether or not the large convex portion is separated.

  The cleaning blade 42 is elastically deformable, and is deformed so as to come into contact with the photosensitive drum 20 between large protrusions (portions). In particular, when the interval between the convex portions is wide, the contact area between the cleaning blade 42 and the photosensitive drum 20 increases. When the contact area increases, the driving torque of the photosensitive drum 20 increases due to friction with the cleaning blade 42 and the wear of the cleaning blade 42 increases, eventually causing stick slip of the cleaning blade 42 and slipping of the external additive. Or the edge of the cleaning blade 42 is lost. Needless to say, if the edge of the cleaning blade 42 is lost, a good image cannot be obtained.

  Further, when the average interval Sm is increased, the convex portion (mountain) is increased (the crest of the peak is wide), and when the top portion of the convex portion is worn due to long-term use, a wide flat portion is formed at the top portion and contact with the cleaning blade 42 is achieved. The area increases. Accordingly, the arithmetic average roughness Ra of the surface of the photosensitive layer in the initial use of the photosensitive drum 20 is in the range of 20 [nm] to 100 [nm], and the ten-point average roughness Rz is 0.2 [μm] to 1 When it is in the range of 0.0 [μm] or less, the average interval Sm of the unevenness is preferably 20 [μm] or less.

  By forming irregularities on the surface of the photosensitive layer irregularly in the axial direction and the circumferential direction so that the surface roughness satisfies the above range, friction between the photosensitive drum 20 and the cleaning blade 42 is reduced. As a result, it is possible to reduce the driving torque of the photosensitive drum 20 and the wear of the edge of the cleaning blade 42. In particular, when Ra [nm] / Sm [μm] ≧ 3 is satisfied, the uneven shape having a height (depth) of three times or more with respect to the average interval Sm is obtained, so that the photosensitive drum 20 and the cleaning blade 42 are obtained. The contact area is reduced, and friction is effectively reduced. The unevenness of the surface of the photosensitive layer that satisfies the above range is obtained by, for example, subjecting the outer peripheral surface of a metal tube (aluminum base tube, etc.) such as aluminum as a support to a surface roughening treatment by blasting or the like. It can be adjusted by forming an amorphous silicon layer (photosensitive layer).

(4) Skewness Rsk
Further, by satisfying the skewness Rsk ≧ 0.3, the contact area between the photosensitive drum 20 and the cleaning blade 42 is reduced, and friction is effectively reduced. The surface roughness is such that the skewness Rsk is 0.3 or more. The arithmetic average roughness Ra, the ten-point average roughness Rz, and the average interval Sm are measured in the same manner as in the first and second embodiments.

Here, the skewness Rsk is one of the parameters representing the strength of the surface roughness, and represents the symmetry (degree of distortion of the irregularities) between the peak and valley when the average line is the center, and the following formula ( In the reference length made dimensionless by the cube of the root mean square height Rq as in 1), it is represented by the root mean square of Z (x).
... (1)

  When Rsk is greater than 0, the unevenness is a shape that is biased downward with respect to the average line L as shown in FIG. On the other hand, when Rsk is smaller than 0, as shown in FIG. 4, the unevenness has a shape biased upward with respect to the average line. In other words, it is considered that when the skewness Rsk of the photosensitive layer is larger than 0, the contact area is reduced because the contact with the cleaning blade 42 is more pointed.

(5) DUH hardness It is preferable that the DUH hardness of the photosensitive layer in the initial use of the photosensitive drum 20 is in the range of 500 [kgf / mm ² ] to 1200 [kgf / mm ² ]. This is because if the DUH hardness is smaller than 500 [kgf / mm ² ], the photosensitive layer of the photosensitive drum 20 is easily worn by contact with the cleaning blade 42 and the rubbing roller 43 and cannot be used for a long time. From this viewpoint, a higher DUH hardness is preferable. For this reason, the upper limit of the DUH hardness is defined by the hardness of the photosensitive layer having the highest hardness that can be used at present. The DUH hardness refers to an indentation hardness (Martens hardness) measured by a dynamic ultra-micro hardness meter (DUH series, manufactured by Shimadzu Corporation).

(6) Form of Unevenness It is preferable that unevenness on the drum surface is present irregularly in the axial direction and circumferential direction of the photosensitive drum 20. Irregular means that the irregularity does not have a certain regularity when the irregularity is seen in any one direction within a certain plane.

(7) Area The arithmetic average roughness Ra, the ten-point average roughness Rz, and the average interval Sm are preferably in the above ranges over the entire image forming area on the surface of the photosensitive drum 20.

(8) Toner External Additive Titanium oxide or silica as conductive abrasive fine particles is externally added to the toner as an external additive. If the arithmetic average roughness Ra of the photosensitive layer surface is large, the cleaning blade 42 is used. The external additive slips through the uneven gap that cannot follow. For this reason, it is preferable that the toner external additive used in the photosensitive drum 20 of the present embodiment has an average primary particle diameter of 10 nm or more.

4). Image Quality Reduction Suppression Control FIG. 5 is a flowchart showing the processing content of image quality reduction suppression control performed by the control circuit 30 in the image forming apparatus 11 according to the present embodiment. Note that there is a main routine (not shown) for controlling the entire image forming apparatus 11, and the flow shown in FIG. 5 is a subroutine of the main routine. The subroutine for image quality deterioration suppression control shown in FIG. 5 starts when the image forming apparatus 11 is turned on.

  First, the control circuit 30 monitors whether or not a print job has been accepted (step S1). A print job is received by an input from a user via the operation panel of the image forming apparatus 11 or an input from a PC connected via a communication line such as a LAN or the Internet. If a print job has not been received (No in step S1), the control circuit 30 continues monitoring.

  When a print job is received (Yes in step S1), the control circuit 30 calculates a torque increase coefficient based on the drive torque of the drive motor 36 detected by the torque detector 37 (step S2). Here, the torque increase coefficient is obtained by using torque T1 immediately after the start of printing (first time t1) and torque T2 after a predetermined time from the start of printing until the torque reaches the maximum value (second time t2). , Calculated from the equation (T2-T1) / (t2-t1).

  Next, the control circuit 30 determines whether or not the torque increase coefficient exceeds a threshold value (step S3). Note that the threshold value of the torque increase coefficient may be stored in the HDD 33 in advance before the image forming apparatus 11 is shipped from the factory, or may be stored in the HDD 33 when the user first uses the image forming apparatus 11. . Further, the threshold value of the torque increase coefficient may be stored in the HDD 33 each time the photosensitive drum 20 is replaced. If the torque increase coefficient does not exceed the threshold value (No in step S3), the control circuit 30 returns to step S1 and monitors whether a print job has been accepted.

  If the torque increase coefficient exceeds the threshold (Yes in step S3), the control circuit 30 determines that the surface of the photosensitive drum 20 has been smoothed (step S4), and performs a frictional resistance suppression process (step S5). As the frictional resistance suppressing process, when the cleaning device 28 cleans the surface of the photosensitive drum 20, a method of increasing the amount of toner and external additive supplied to the surface of the photosensitive drum 20 as a lubricant, There is a method of reducing the charging bias applied to the roller 26.

  The frictional resistance suppression process is a cleaning process in which toner on the developing roller 35 in the developing device 21 is forcibly discharged toward the photosensitive drum 20 when non-image formation is performed, for example, when a predetermined number of prints are performed. This is a process for supplying the cleaning blade 42 of the apparatus 28 and suppressing the frictional resistance between the cleaning blade 42 and the surface of the photosensitive drum 20.

  By increasing the supply amount of the toner and the external additive when the cleaning device 28 cleans the surface of the photosensitive drum 20, the frictional resistance between the cleaning blade 42 and the photosensitive drum 20 can be reduced. Further, by reducing the charging bias applied to the charging roller 26, the generation of discharge products and the adhesion of the generated dischargeable organisms to the photosensitive layer are suppressed, so that the friction between the cleaning blade 42 and the photosensitive drum 20 occurs. The increase in resistance is suppressed.

  As a result, chattering of the cleaning blade 42, chipping (wear) of the edge portion, and stick slip can be suppressed. Further, the toner and the external additive can be easily removed at the time of cleaning by the cleaning blade 42, and the effect that the amount of the external additive that slips between the surface of the photosensitive drum 20 and the cleaning blade 42 can be expected.

  Thereafter, returning to step S1, the control circuit 30 monitors whether or not a print job has been accepted, and thereafter repeats the same procedure (steps S1 to S5). In the flow of FIG. 5, Steps S <b> 1 to S <b> 4 can be regarded as a photosensitive drum (image carrier) surface smoothing determination process.

  As described above, according to the image forming apparatus 11 of the present embodiment, whether the surface of the photosensitive drum (image carrier) 20 (photosensitive layer surface) has been smoothed is determined by the torque of the drive motor 36 from the start of printing. Judgment is based on the torque increase coefficient until the maximum value is reached. When the torque increase coefficient exceeds the threshold value, it is determined that the surface of the photosensitive drum 20 has been smoothed. Thereby, it can be determined whether the surface of the photosensitive drum 20 has been smoothed without providing a new device, which can contribute to cost reduction. If it is determined that the surface of the photosensitive drum 20 has been smoothed, a frictional resistance suppression process is performed to suppress the frictional resistance between the cleaning blade 42 and the surface of the photosensitive drum 20, Occurrence of defects and stick-slip can be suppressed. As a result, it is possible to suppress slipping of the external additive and suppress deterioration in image quality.

<Modification>
As described above, the embodiment of the image forming apparatus 11 of the present invention has been described as an example. However, the present invention is not limited to the above embodiment, and for example, the following modification may be used. Moreover, what combined embodiment, a modification, and modifications may be sufficient. In addition, examples that are not described in the embodiment and design changes that do not depart from the gist of the present invention are also included in the present invention.

(Modification 1) The method of detecting the torque of the drive motor 36 is not limited to the detection of the output current value of the drive motor 36, and the torque of the rotating shaft of the drive motor 36 may be directly detected by a torque sensor.
(Modification 2) The threshold value of the torque increase coefficient is not limited to the configuration set in advance and stored in the HDD 33. For example, the value of the torque detected at the start of use, and the smoothness of the surface of the photosensitive drum 20 It is also possible to employ a configuration that is calculated after the start of use from the value of a factor that affects the performance and stored in the HDD 33.
(Modification 3) The storage unit storing the threshold value of the torque increase coefficient is not limited to the HDD 33. When the threshold value of the torque increase coefficient is set in advance before shipment, it may be stored in the ROM 31. In this case, the ROM 31 serves as a storage unit.
(Modification 4) The frictional resistance suppressing process is not limited to the process of increasing the supply amount of the toner and the external additive and the process of decreasing the charging bias voltage. For example, the urging force with which the cleaning blade 42 is pressed against the surface of the photosensitive drum may be weakened, or a lubricant other than the toner and the external additive may be supplied. In the latter case, it is necessary to select a lubricant that does not negatively affect the image forming process. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

(Torque fluctuation at the beginning of printing)
First, a photosensitive drum a in which an amorphous silicon layer (thickness: 21 μm) is formed on a mirror-finished aluminum tube (diameter: 30 mm), and an amorphous silicon layer on a roughened aluminum tube (diameter: 30 mm). A photosensitive drum b on which (thickness: 21 μm) was formed was prepared. As will be described later, the arithmetic average roughness Ra of the photosensitive layer surface in the initial use (new) of the photosensitive drum a is 8 nm (see FIG. 8), and the arithmetic average of the photosensitive layer surface in the initial usage of the photosensitive drum b. The roughness Ra was 24 nm (see FIG. 10).

  Next, new photoconductor drums a and b were mounted on the image forming apparatus 11 as shown in FIG. 1, and torque fluctuations from the start of printing to 300 seconds were measured. FIG. 6 is a graph showing torque fluctuations of the drive motor 36 from the start of printing to 300 seconds when new photoreceptor drums a and b are used, and FIG. 7 is a graph from the start of printing in FIG. 6 to 50 seconds. It is the graph which expanded torque fluctuation of. 6 and 7, A shows the torque fluctuation of the new photoconductor drum a, and B shows the torque fluctuation of the new photoconductor drum b. Here, the start of printing is to start driving each part of the image forming apparatus 11 for printing.

  As shown in FIGS. 6 and 7, when new photoconductor drums a and b are used, the torque of the drive motor 36 hardly increases until 300 seconds from the start of printing in both A and B. Recognize. Therefore, in either case of using a photosensitive drum a in which an amorphous silicon layer is formed on a mirror-finished aluminum base tube or a photosensitive drum b in which an amorphous silicon layer is formed on a roughened aluminum base tube. In the initial stage of printing, it can be said that the torque increase coefficient (slope) from the start of printing is very small.

(Photosensitive drum surface roughness Ra)
FIG. 8 is a graph showing the arithmetic average roughness Ra of the surface of the photosensitive layer of the above-described new photosensitive drum a. FIG. 9 is a cumulative image forming number (durable printing number) 600 k of the new photosensitive drum a. It is a graph which shows the arithmetic mean roughness Ra of the photosensitive layer surface of the photosensitive drum a1 after (600,000) sheets printing. In addition, arithmetic surface roughness Ra shows the arithmetic average roughness as described in JISB0601 as mentioned above. Specifically, a reference length is extracted from the roughness curve in the direction of the average line, and the absolute value of the deviation from the average line of the extracted part to the measurement curve is summed and averaged to the micrometer (μm) The one represented by

  The arithmetic average roughness Ra of the photosensitive layer surface of the new photosensitive drum a is 8 nm (see FIG. 8), but the arithmetic average roughness of the photosensitive layer surface of the photosensitive drum a1 after durable printing (after printing 600 k sheets). Ra was 3 nm (see FIG. 9), and it was found that the surface of the photosensitive layer of the photosensitive drum a1 after durable printing was in a very smooth state.

  FIG. 10 is a graph showing the arithmetic average roughness Ra of the surface of the photosensitive layer of the new photosensitive drum b described above. FIG. 11 shows the cumulative number of processed images (number of durable prints) of the new photosensitive drum b. ) A graph showing the arithmetic average roughness Ra of the photosensitive layer surface of the photosensitive drum b1 after printing 620k sheets. The arithmetic average roughness Ra of the surface of the photosensitive layer of the new photosensitive drum b is 24 nm (see FIG. 10), but the surface roughness Ra of the photosensitive drum b1 after durable printing (after printing 620k sheets) is 14 nm. (See FIG. 11).

  Furthermore, an amorphous silicon layer was formed on a newly roughed aluminum tube, and a photosensitive drum having an arithmetic average roughness Ra of 50 nm on the surface of the photosensitive layer in the initial use was prepared, and durability evaluation was performed. . As a result, the arithmetic average roughness Ra of the surface of the photosensitive layer is 30 nm on the photosensitive drum (photosensitive drum b3) after printing 200k cumulative images, and the photosensitive drum (photosensitive drum b2) after printing 520k copies is photosensitive. The arithmetic average roughness Ra of the layer surface was 24 nm, and the arithmetic average roughness Ra changed as the number of durable printed sheets increased.

(Torque fluctuation after durable printing)
FIG. 12 is a graph showing torque fluctuations of the drive motor 36 from the start of printing to 600 seconds when the photosensitive drums a1, b1, b2, and b3 after endurance printing are used, and FIG. It is the graph which expanded the torque fluctuation | variation from printing start to 100 second. FIG. 14 shows torque fluctuations of the drive motor 36 from the start of printing to 300 seconds when new photosensitive drums a and b and photosensitive drums a1, b1, b2 and b3 after durable printing are used. It is a graph. 12 to 14, A shows torque fluctuation when using a new photosensitive drum a, B shows torque fluctuation when using a new photosensitive drum b, and A1 is after endurance (600 k). Shows the torque fluctuation when the photosensitive drum a1 is used, B1 shows the torque fluctuation when the photosensitive drum b1 after endurance (620k) is used, and B2 shows the photosensitive drum b2 after endurance (520k). The torque fluctuation when used is shown, and B3 shows the torque fluctuation when the photosensitive drum b3 after durability (200k) is used.

  As shown by A1 in the graphs of FIGS. 12 to 14, when the photosensitive drum a1 after durable printing (600 k) is used, the torque increase coefficient (slope) from the start of printing is large, and about 5 seconds from the start of printing. There is a tendency to reach the inflection point and saturate (to reach the maximum value). On the other hand, as shown in B1, B2, and B3, when the photosensitive drums b1, b2, and b3 after the endurance printing are used, the torque increase coefficient (inclination) from the start of printing is moderate and several tens of seconds ( The torque increases linearly over 30 seconds), and after 30 to 60 seconds, an inflection point is reached and saturation is observed.

  In FIG. 12 to FIG. 14, the torque increase coefficient (slope) from the start of printing until the torque reaches the maximum value is A1 = 0.526 mNm / sec, B1 = 0.146 mNm / sec, B2 = 0.200 mNm. / Sec, B3 = 0.227 mNm / sec. From the above results, it can be seen that the surface state of the photosensitive drum 20 can be detected by calculating the torque increase coefficient of the drive motor 36 from the start of printing.

  The present invention is applicable to an image forming apparatus including an image carrier on which a toner image is formed on the surface. By using the present invention, an image forming apparatus capable of detecting that the surface of the image carrier has been smoothed without providing a new detection means by using the torque increase coefficient of the drive device that drives the image carrier is provided. can do.

11 Image forming apparatus 20 Photosensitive drum (image carrier)
21 Developing device 26 Charging roller (charging member)
30 Control circuit (control unit)
31 ROM (storage unit)
33 HDD (storage unit)
34 High-voltage power supply 36 Drive motor (drive device)
42 Cleaning blade (cleaning member)
43 Rub roller (cleaning member)

Claims (9)

An image carrier on which a toner image is formed on the surface;
A driving device for rotationally driving the image carrier;
A cleaning member arranged to contact the surface of the image carrier and cleaning the surface of the image carrier;
A torque detector for detecting torque of the driving device when the image carrier is rotationally driven;
A controller that determines the surface state of the image carrier based on the torque detected by the torque detector;
An image forming apparatus having
The control unit calculates a torque increase coefficient from the start of printing until the torque of the driving device reaches a maximum value based on the torque detected by the torque detection unit, and based on the calculated torque increase coefficient And determining the degree of smoothness of the surface of the image carrier.   The image forming apparatus according to claim 1, wherein the torque detection unit detects an output current value of the driving device required for rotationally driving the image carrier as an index representing torque of the driving device.   The control unit performs a frictional resistance suppressing process for reducing a frictional resistance between the surface of the image carrier and the cleaning member when it is determined that the degree of smoothing of the surface of the image carrier is not less than a predetermined level. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A developing device that develops an electrostatic latent image formed on the surface of the image carrier by attaching toner containing abrasive particles into a toner image;
The image forming apparatus according to claim 3, wherein the control unit performs the frictional resistance suppression process by supplying toner from the developing device to the image carrier during non-image formation.   The image forming apparatus according to claim 4, wherein the controller increases the amount of toner supplied from the developing device to the image carrier as the degree of smoothing of the surface of the image carrier increases. A charging member for charging the image carrier;
A high-voltage power supply that applies a charging bias in which a DC bias and an AC bias are superimposed on the charging member;
The image forming apparatus according to claim 3, wherein the controller performs the frictional resistance suppression process by reducing the AC bias applied to the charging member from the high-voltage power supply during image formation.   The image forming apparatus according to claim 6, wherein the charging member is disposed in contact with or close to a surface of the image carrier.   The image forming apparatus according to claim 1, wherein an arithmetic average roughness Ra of the surface of the image carrier in the initial use of the image carrier is in a range of 20 to 100 nm.   9. The image forming apparatus according to claim 1, wherein an amorphous silicon photosensitive layer is formed on a surface of the image carrier.