JP2019086746A - Image forming apparatus and charging device - Google Patents

Abstract

To provide an image forming apparatus and a charging device that can prevent easy occurrence of unevenness in density of an image to be formed.SOLUTION: An image forming apparatus 10 comprises: photoreceptor drums 202 that each hold a toner image on an outer peripheral surface 202a; and charging devices 300. The charging devices 300 each include a discharge wire 304, and a grid electrode 320 formed with a plurality of openings 326. The frequency during oscillation of the discharge wire 304 is determined such that the distance in which the outer peripheral surface 202a moves during one period of the oscillation of the discharge wire 304 does not interfere with the length of the plurality of openings 326 in a direction in which the outer peripheral surface 202 moves.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus and a charging device.

  Patent Document 1 discloses a charging device which is mounted on an electrophotographic apparatus and charges the surface of an electrostatic latent image carrier which is rotationally driven to a predetermined potential, and the surface of the electrostatic latent image carrier is at the predetermined potential. A charging portion characterized by comprising: a rough charging portion charging to a value close to the surface; and an adjusting charging portion uniformly charging the surface of the electrostatic latent image carrier charged by the rough charging portion to the predetermined potential. The device is described.

  In Patent Document 2, a discharge electrode is provided opposite to a photosensitive member whose circumferential surface moves circumferentially and to which a voltage obtained by superimposing alternating current on direct current or direct current is applied, and a conductive thin plate material having a large number of openings. A scorotron charger comprising a grid electrode between the discharge electrode and the photosensitive member and supported substantially parallel to the surface of the photosensitive member, wherein the shape of the opening is a hexagon formed by three pairs of parallel sides. The length of each pair of sides of the hexagon is equal, and at least one of the three pairs of sides is different in length from the other two pairs of sides; One of the pair of sides is provided in parallel with the moving direction (Y direction) of the photosensitive member, and a plurality of the openings are arranged to make the width of the strip portion formed between the adjacent openings substantially uniform. As described above, the opening is in a direction (X direction) perpendicular to the moving direction of the photosensitive member. The opening arrays formed in a direction having a certain angle, scorotron charger, characterized by having a plurality of opening rows in the moving direction of the photosensitive member is described.

Unexamined-Japanese-Patent No. 2007-121572 JP-A-8-36289

  In an image forming apparatus that forms an image using toner, unevenness of density may occur in the formed image.

  According to the present invention, the distance by which the outer peripheral surface of the image carrier moves during one cycle of the vibration of the first electrode is the length between the adjacent two of the plurality of openings formed in the second electrode and non-interference In order to provide an image forming apparatus and a charging device capable of preventing the occurrence of density unevenness in an image to be formed as compared with the case where the frequency at the time of vibration of the first electrode is not determined. To aim.

The present invention according to claim 1 is
An image carrier which moves an outer peripheral surface and holds a toner image transferred to a recording medium on the outer peripheral surface;
A charging device for charging the image carrier;
Have
The charging device is
A linear first electrode disposed at a position facing the outer peripheral surface;
A second electrode disposed between the outer circumferential surface and the first electrode and having a plurality of openings formed therein;
Have
The first electrode has a distance by which the outer peripheral surface moves during one cycle of vibration of the first electrode, and a length in a moving direction of the outer peripheral surface between two adjacent ones of the plurality of openings. It is an image forming apparatus in which the frequency at the time of vibration is determined so as to be non-interference.

  According to a second aspect of the present invention, in the first electrode, a distance in which the outer peripheral surface moves during one cycle of vibration is a moving direction of the outer peripheral surface between two adjacent ones of the plurality of openings. 2. The image forming apparatus according to claim 1, wherein the frequency at the time of vibration is determined so as to be a non-integer multiple of the length at.

  According to a third aspect of the present invention, in the first electrode, the distance of movement of the outer peripheral surface during one cycle of vibration of the first electrode is within a range of 1 mm to 15 mm. The image forming apparatus according to claim 1 or 2, wherein the frequency at the time of vibration is determined so as to be non-interference with the length in the moving direction of the outer peripheral surface between two adjacent ones.

The present invention according to claim 4 is
An image carrier which moves an outer peripheral surface and holds a toner image transferred to a recording medium on the outer peripheral surface;
A charging device for charging the image carrier;
Have
The charging device is
A linear first electrode disposed at a position facing the outer peripheral surface;
A second electrode disposed between the outer circumferential surface and the first electrode and having a plurality of openings formed therein;
Have
The first electrode has a maximum value of the spatial frequency power spectrum obtained by two-dimensional Fourier transform of the image of the second electrode in which the distance the outer circumferential surface moves during one cycle of the vibration of the first electrode The first electrode vibration frequency at the time of vibration is determined so as not to interfere with the component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency components at the time of.

  According to the fifth aspect of the present invention, in the first electrode, a distance traveled by the outer peripheral surface during one cycle of vibration of the first electrode is a two-dimensional Fourier transform of an image of the second electrode. The component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency component at the maximum value of the spatial frequency power spectrum obtained, and the interference time in the range of 1 mm or more and 15 mm or less The image forming apparatus according to claim 4, wherein the first electrode vibration frequency is determined.

  According to a sixth aspect of the present invention, in the first electrode, a distance traveled by the outer peripheral surface during one cycle of vibration of the first electrode is a two-dimensional Fourier transform of an image of the second electrode. The component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency component of a value larger than 30% of the difference between the maximum value and the minimum value of the spatial frequency power spectrum obtained 6. The image forming apparatus according to claim 4, wherein a frequency at the time of vibration is determined.

  The present invention according to claim 7 is the image forming apparatus according to any one of claims 1 to 6, wherein toner having an average particle diameter of 6 μm or less is used for image formation.

  The present invention according to claim 8 is the image forming apparatus according to any one of claims 1 to 7, wherein the moving speed of the outer peripheral surface at the time of image formation is 300 mm / s or more at the time of image formation.

  In the present invention according to claim 9, the frequency at the time of vibration is determined by changing at least one of the diameter, density and length of the first electrode in the first electrode. 8 is an image forming apparatus according to any one of the above.

The present invention according to claim 10 is
A linear first electrode disposed at a position opposed to the outer peripheral surface of the image carrier which moves the outer peripheral surface and holds the toner image transferred to the recording medium on the outer peripheral surface;
A second electrode disposed between the outer circumferential surface and the first electrode and having a plurality of openings formed therein;
Have
The first electrode has a distance by which the outer peripheral surface moves during one cycle of vibration of the first electrode, and a length in a moving direction of the outer peripheral surface between two adjacent ones of the plurality of openings. It is a charging device in which the frequency at the time of vibration is determined so as to be non-interference.

The present invention according to claim 11 is
A linear first electrode disposed at a position opposed to the outer peripheral surface of the image carrier which moves the outer peripheral surface and holds the toner image transferred to the recording medium on the outer peripheral surface;
A second electrode disposed between the outer circumferential surface and the first electrode and having a plurality of openings formed therein;
Have
The first electrode has a maximum value of the spatial frequency power spectrum obtained by two-dimensional Fourier transform of the image of the second electrode in which the distance the outer circumferential surface moves during one cycle of the vibration of the first electrode The first electrode vibration frequency at the time of vibration is determined so as not to interfere with the component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency components at the time of.

  According to the first aspect of the present invention, the distance by which the outer peripheral surface of the image carrier moves during one cycle of the vibration of the first electrode is two adjacent ones of the plurality of openings formed in the second electrode. As compared with the case where the frequency at the time of vibration of the first electrode is not determined so as to be non-interfering with the length in the moving direction of the outer peripheral surface of the image carrier between Can be provided.

  According to the second aspect of the present invention, the distance by which the outer peripheral surface of the image carrier moves during one cycle of the vibration of the first electrode is the outer periphery of the image carrier between two adjacent ones of the plurality of openings. As compared with the case where the frequency at the time of vibration is determined so as to be an integral multiple of the length in the direction in which the surface moves, unevenness in density can be less likely to occur in the formed image.

  According to the third aspect of the present invention, the distance of movement of the outer peripheral surface during one cycle of the vibration of the first electrode is at least one of the range smaller than 1 mm and the range larger than 15 mm. The frequency at the time of vibration of the first electrode is determined so as to be non-interfering with the length in the moving direction of the outer peripheral surface of the image carrier between two adjacent ones of the plurality of openings formed in the second electrode. Compared to the case, the frequency constraint of the vibration of the first electrode can be reduced.

  According to the fourth aspect of the present invention, the spatial frequency at which the distance the outer circumferential surface of the image carrier moves during one cycle of the vibration of the first electrode is obtained by two-dimensional Fourier transformation of the image of the second electrode. An image formed as compared with the case where the first electrode vibration frequency is determined so as to interfere with the component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency component at the maximum value of the power spectrum The present invention can provide an image forming apparatus capable of making it difficult to cause density spots.

  According to the fifth aspect of the present invention, the distance moved by the outer circumferential surface during one cycle of the vibration of the first electrode is at least one of the range smaller than 1 mm and the range larger than 15 mm. The component distance of the movement direction of the outer peripheral surface of the plurality of apertures calculated from the frequency component at the maximum value of the spatial frequency power spectrum obtained by the two-dimensional Fourier transform of the image of the second electrode The restriction on the frequency of the vibration of the first electrode can be reduced as compared with the case where the frequency at the time of the vibration of the electrode is defined.

  According to the sixth aspect of the present invention, the spatial frequency at which the distance the outer circumferential surface of the image carrier moves during one cycle of the vibration of the first electrode is obtained by two-dimensional Fourier transformation of the image of the second electrode. At the time of vibration of the first electrode so as to interfere with the component distance in the moving direction of the outer peripheral surface of the plurality of apertures calculated from the frequency component of a value larger than 30% of the difference between the maximum value and the minimum value of the power spectrum Thus, it is possible to provide an image forming apparatus capable of making it less likely to cause density spots in an image to be formed as compared with the case where the frequency of.

  According to the seventh aspect of the present invention, the quality of the formed image is improved as compared to the case where toner having an average particle diameter of more than 6 μm is used while making it difficult to cause unevenness of density in the formed image. be able to.

  According to the eighth aspect of the present invention, the image is formed compared to the case where the speed of the outer peripheral surface of the image carrier is smaller than 300 mm / S while making it difficult to cause density spots in the formed image. You can increase the speed.

  According to the ninth aspect of the present invention, the frequency at the time of vibration of the first electrode can be easily defined as compared with the case where none of the diameter, density and length of the first electrode is changed. .

  According to the tenth aspect of the present invention, the distance by which the outer peripheral surface of the image carrier moves during one cycle of the vibration of the first electrode is two adjacent ones of the plurality of openings formed in the second electrode. As compared with the case where the frequency at the time of vibration of the first electrode is not determined so as to be non-interfering with the length in the moving direction of the outer peripheral surface of the image carrier between Can be provided.

  According to the eleventh aspect of the present invention, the spatial frequency at which the distance the outer circumferential surface of the image carrier moves during one cycle of the vibration of the first electrode is obtained by two-dimensional Fourier transformation of the image of the second electrode. An image formed as compared with the case where the first electrode vibration frequency is determined so as to interfere with the component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency component at the maximum value of the power spectrum The present invention can provide a charging device capable of preventing the occurrence of concentration spots.

FIG. 1 is a diagram showing a configuration of an image forming apparatus used in an embodiment of the present invention. FIG. 2 is a diagram showing a configuration of an image forming unit included in the image forming apparatus shown in FIG. It is a graph explaining the relationship between the time which electrically charges the photosensitive drum which the image forming apparatus shown in FIG. 1 has, and the electric potential of the outer peripheral surface of a photosensitive drum. It is a figure which shows the 1st example of the grid electrode which the charging device shown in FIG. 2 has. FIG. 5 (A) is a diagram showing the state of the charging device while charging the photosensitive drum, and FIG. 5 (B) is shown in FIG. 5 (A). FIG. 5C is a view showing the state of the charging device after a predetermined time has elapsed from the state, and FIG. 5C is a view showing the state of the charging device after the predetermined time has elapsed from the state shown in FIG. is there. It is a figure which shows the result of the experiment which experimented whether it changed the vibration pitch of the discharge wire, and it produced whether the diagonal line | wire arose in the image. It is a figure which shows the 2nd example of the grid electrode which the charging device shown in FIG. 2 has. FIG. 8 (A) is a diagram showing an intensity distribution of a two-dimensional power spectrum obtained by two-dimensional Fourier transform of an image of the second example of the grid electrode, and FIG. 8 (B) is a diagram showing the obtained two-dimensional It is a figure which shows the range which extracts local maximum from a power spectrum. It is a graph which shows the integrated value which integrated the absolute value of a two-dimensional power spectrum for every component distance of the movement direction of the peripheral face of the image carrier of a plurality of openings of a grid electrode. It is a graph which converts the horizontal axis of Drawing 9 into the frequency of the 1st electrode, and shows the integrated value which accumulated the absolute value of a two-dimensional power spectrum for every frequency of the 1st electrode. Figure 11 shows details of the data plotted in Figure 10;

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an image forming apparatus 10 used in the embodiment of the present invention. The image forming apparatus 10 has an image forming apparatus main body 12, and an image forming unit 100, a transfer device 500, a fixing device 600, and a sheet feeding device 700 are disposed in the image forming apparatus main body 12. Further, in the image forming apparatus main body 12, a conveyance path 750 for conveying a recording medium such as a sheet is formed.

  The image forming unit 100 adopts an electrophotographic method, and forms an image on a recording medium. The image forming unit 100 includes, for example, a plurality of, for example, a plurality of image forming units 200. The four image forming units 200 form toner images of different colors such as yellow, magenta, cyan, black, etc., for example.

  The image forming unit 200 has a photosensitive drum 202. The photosensitive drum 202 is an example of an image carrier, and moves so as to rotate the outer peripheral surface 202a (see FIG. 2), and holds the toner image transferred to the recording medium on the outer peripheral surface 202a.

  The image forming unit 200 further includes a charging device 300 that charges the photosensitive drum 202. Further, in the image forming unit 200, the toner image formed on the outer peripheral surface 202a of the photosensitive drum 202 is primarily transferred onto an intermediate transfer belt 510 described later. The details of the charging device 300 and the image forming unit 200 will be described later.

  The transfer device 500 has an intermediate transfer belt 510. The toner images are primarily transferred from the photosensitive drums 202 to the intermediate transfer belt 510, and the primarily transferred toner images are secondarily transferred to the recording medium.

  The intermediate transfer belt 510 is supported so as to be rotatable by a plurality of support members, and a drive roll 512 which is one of the plurality of support members transmits the drive to the intermediate transfer belt 510.

  The transfer device 500 transfers a toner image from each photosensitive drum 202 to the intermediate transfer belt 510, and further includes primary transfer rolls 514 equal in number to the photosensitive drum 202, and the toner image from the intermediate transfer belt 510 onto a recording medium And a secondary transfer roll 516 for transferring the

  The fixing device 600 fixes the toner image transferred to the recording medium to the recording medium using, for example, heat and pressure.

  The sheet feeding device 700 has a storage portion 702 for storing the recording medium in a stacked state, and a delivery roll 704 for feeding the recording medium stored in the storage portion 702 toward the conveyance path 750.

  The conveyance path 750 conveys the recording medium from the paper feeding device 700 to the secondary transfer position N, further conveys the recording medium to the fixing device 600, and is further discharged out of the image forming apparatus main body 12 Transport the recording medium.

  In the image forming apparatus 10 configured as described above, the toner images formed on the outer peripheral surface 202 a of the photosensitive drum 202 are primarily transferred to the intermediate transfer belt 510, and are primarily transferred to the intermediate transfer belt 510. The image is secondarily transferred to the recording medium, and the toner image secondarily transferred to the recording medium is fixed to the recording medium by the fixing device 600. Arrows in FIG. 1 indicate the rotational directions of the respective photosensitive drums 202 and the intermediate transfer belt 510 when forming an image.

  The configuration of the image forming unit 200 and the configuration in the vicinity of the image forming unit 200 are shown in FIG. As described above, the image forming unit 200 includes the photosensitive drum 202 and the charging device 300, and further, forms a latent image on the surface of the charged photosensitive drum 202 (see FIG. 1). And the developing device 208 for developing the latent image formed on the photosensitive drum 202 into a toner image, and after the toner image is transferred to the intermediate transfer belt 510 by the primary transfer roll 514, the photosensitive drum 202 And a cleaning device 212 for cleaning the toner remaining on the outer peripheral surface 202a of the toner.

  In the developing device 208, it is desirable to use toner having an average particle diameter of 6 μm or less for developing a latent image. That is, in the image forming apparatus 10, it is desirable to use toner having an average particle diameter of 6 μm or less for image formation. Further, in the developing device 208, it is more preferable to use toner having an average particle diameter of 5 μm or less for development. That is, in the image forming apparatus 10, it is more preferable to use toner having an average particle diameter of 5 μm or less for image formation.

  Here, as the toner having a smaller average particle diameter is used, it is possible to improve the quality of the formed image. On the other hand, as the toner having a smaller average particle diameter is used, the possibility that density unevenness may occur in the image finally formed when the charging unevenness is on the photosensitive drum 202 is increased. The details of density unevenness generated in the image will be described later.

  The transfer device 500 is a corona discharge type charging device, and includes a discharge wire 302, a discharge wire 304 disposed downstream of the discharge wire 302 in the moving direction of the outer peripheral surface 202a of the photosensitive drum 202, and a power supply 310. And a controller 312.

  The discharge wire 304 is an example of the first electrode. The discharge wire 302 and the discharge wire 304 are disposed at positions facing the outer peripheral surface 202a of the photosensitive drum 202, respectively, and each has a linear shape. Further, current is supplied from the power supply 310 to the discharge wire 302 and the discharge wire 304. The controller 312 also controls the power supply 310.

  The charging device 300 further includes a grid electrode 320 and a power source 330. The grid electrode 320 is an example of a second electrode, and is disposed between the outer peripheral surface 202a of the photosensitive drum 202 and the discharge wire 302 and the discharge wire 304, and has a plurality of openings 326 (for example, FIG. 4). See)). Further, the power supply 330 applies a voltage to the grid electrode 320.

  In the image forming unit 200 configured as described above, the moving speed of the outer peripheral surface 202a of the photosensitive drum 202 at the time of image formation is preferably 300 mm / sec or more, and more preferably 350 mm / sec or more. desirable. Here, as the speed of the outer peripheral surface 202a of the photosensitive drum 202 is higher, the time required for image formation can be shortened. On the other hand, as the moving speed of the outer peripheral surface 202a becomes higher, the time when a specific part of the outer peripheral surface 202a passes through the vicinity of the charging device 300 becomes shorter, and the outer peripheral surface 202a becomes less likely to be saturated and charged.

  FIG. 3 is a graph for explaining the relationship between the time for charging the photosensitive drum 202 and the potential of the outer peripheral surface 202 a of the photosensitive drum 202 when the charging voltage is constant. In FIG. 3, a potential V1 is a potential in a state where the photosensitive drum 202 is saturated and charged. As shown in FIG. 3, the photosensitive drum 202 has a potential of approximately V1 when the charging time is t1 or more, and is in a substantially saturated charging state.

  In the image forming apparatus 10, when the moving speed of the outer peripheral surface 202a is low and charging time longer than time t1 can be secured as in time t2, for example, the surface of the photosensitive drum 202 can be substantially saturated charged. Charged spots are less likely to occur on the outer peripheral surface 202 a of the body drum 202. On the other hand, when the moving speed of the outer peripheral surface 202a is high, for example, when the charging time longer than the time t1 can not be secured as in the time t3, the outer peripheral surface 202a of the photosensitive drum 202 can not be saturated charged. Charged spots easily occur on the outer peripheral surface 202 a of the body drum 202.

  As described above, in the image forming apparatus 10, as the moving speed of the outer peripheral surface of the photosensitive drum 202 is higher, density unevenness of the image caused by charging unevenness of the outer peripheral surface 202a is more likely to occur. More specifically, in the image forming apparatus 10, when the moving speed of the outer peripheral surface 202a is 300 mm / sec or more, charging of the outer peripheral surface 202a is higher than when the moving speed of the outer peripheral surface 202a is less than 300 mm / sec. When the movement speed of the outer peripheral surface 202a is 350 mm / sec or more, the charging unevenness of the outer peripheral surface 202a is more likely than when the movement speed of the outer peripheral surface 202a is less than 50 mm / sec. And image density spots are likely to occur. The details of density unevenness generated in the image will be described later.

  FIG. 4 is a view showing a first example of the grid electrode 320 from the arrow AA direction in FIG. As shown in FIG. 4, in the grid electrode 320, the plurality of openings 326 described above are formed in a plate member 322 which can use a conductive thin plate. Each of the plurality of openings 326 has the same width, is strip-shaped, is parallel to each other, and is arranged to be inclined with respect to the moving direction of the outer peripheral surface 202 a of the photosensitive drum 202 indicated by the arrow a. Further, two adjacent ones of the plurality of openings 326 are separated by a dividing portion 324 which forms a part of the plate-like member 322. As shown in FIG. 4, the partition portions 324 have the same width.

  In the following description, the moving direction of the outer peripheral surface 202a of the photosensitive drum 202 indicated by the arrow a may be referred to as the arrow a direction. Further, in the following description, the longitudinal direction of the grid electrode 320 which is a direction intersecting the arrow a direction and which is a direction indicated by the arrow b may be referred to as an arrow b direction.

  Further, in this first example, the length between two adjacent ones of the plurality of openings 326 in the direction of arrow a, that is, the two adjacent lengths L of the plurality of partition parts 324 in the direction of arrow a, is 2 It is .0 mm.

  In charging device 300 configured as described above, an opening formed in grid electrode 320 is an ion or electron (hereinafter referred to as “ion or the like”) generated by corona discharge of discharge wire 302 and discharge wire 304. It passes through 326 and reaches the outer peripheral surface 202 a of the photosensitive drum 202 to charge the outer peripheral surface 202 a of the photosensitive drum 202.

  FIG. 5 illustrates the operation of the charging device 300. FIG. 5 (A) is a diagram showing the state of the charging device 300 while the photosensitive drum 202 is being charged, and FIG. 5 (B) is a diagram. FIG. 5C is a diagram showing the state of the charging device 300 after a predetermined time has elapsed from the state of 4 (A), and FIG. 5C shows the state of the charging device 300 after the predetermined time has elapsed from the state shown in FIG. FIG. In FIG. 5, for convenience of illustration, the distances between the discharge wire 302 and the discharge wire 304 and the grid electrode 320, and the distance between the grid electrode 320 and the photosensitive drum 202 are drawn longer than they actually are. It is done.

  As shown in FIG. 5, the discharge wire 302 and the discharge wire 304 vibrate when current is supplied from the power supply 310. For example, the discharge wire 302 and the discharge wire 304 rotate in the clockwise direction from the position closest to the outer peripheral surface 202a shown by a solid line in FIG. 5A, and the outer periphery shown by a solid line in FIG. It moves to a position farthest from the surface 202a and rotates clockwise, and then repeats a movement to move to a position closest to the outer peripheral surface 202a shown in FIG. 5C. .

  Here, the amount of ions or the like generated by the discharge wire 302 and the discharge wire 304 reaches the outer peripheral surface 202 a as the discharge wire 302 and the discharge wire 304 are closer to the outer peripheral surface 202 a. Further, the amount of ions generated by the discharge wire 302 and the discharge wire 304 reaches the outer peripheral surface 202 a as the discharge wire 302 and the discharge wire 304 are farther from the outer peripheral surface 202 a. That is, when the discharge wire 302 and the discharge wire 304 are at the positions shown by solid lines in FIGS. 5A and 5C, the amount of ions etc. reaching the outer peripheral surface 202a is the largest, and the discharge wire When the wire 302 and the discharge wire 304 are in the position shown by the solid line in FIG. 5B, the amount of ions etc. reaching the outer peripheral surface 202a is minimized.

  In addition, although ions generated by the discharge wire 302 and the discharge wire 304 pass through the opening 326 of the grid electrode 320, they reach the outer peripheral surface 202a of the photosensitive drum 202, but collide with the partition portion 324 of the grid electrode 320 , And it does not reach the outer peripheral surface 202 a because it is interrupted by the partition portion 324. For this reason, in the outer peripheral surface 202a, the amount of ions and the like reaching the portion closer to the partition portion 324 decreases, and the amount of the ions and the like reaching the portion farther from the partition portion 324 increases.

  Then, the discharge wire 302 and the discharge wire 304 cause the vibration of each of the outer peripheral surface 202 a resulting in the difference in the amount of ions etc. arriving at each position, and the difference in the distance from the partition 324 for each position of the outer peripheral surface 202 a. When the difference in the amount of ions and the like reaches each other overlaps, for example, in whole or in part, the difference in the amount of the ions reaching each position of the outer peripheral surface 202a becomes large, and unevenness occurs in the charging of the outer peripheral surface 202a. There may be density spots in the image formed when spots occur on the charge. Here, as an example of density unevenness that occurs in an image, for example, oblique streaks that occur in the direction inclined with respect to the direction of arrow a can be mentioned on the surface of the recording medium.

  For this reason, in the image forming apparatus 10, the frequency when the discharge wire 304 vibrates is one cycle of the vibration of the discharge wire 304 so that the difference in the amount of ions and the like reaching each position of the outer peripheral surface 202a does not increase. The distance by which the outer peripheral surface 202a of the photosensitive drum 202 moves is determined so as not to interfere with the length L in the moving direction (the direction of the arrow a) of two adjacent outer peripheral surfaces 202a of the plurality of openings 326 ing.

  More specifically, in the image forming apparatus 10, the frequency at which the discharge wire 304 vibrates is defined by a plurality of distances by which the outer peripheral surface 202a of the photosensitive drum 202 moves during one cycle of the vibration of the discharge wire 304. The two adjacent outer peripheral surfaces 202a of the opening 326 are set to be a non-integer multiple of the length L in the moving direction.

In the following description, the distance by which the outer peripheral surface 202a of the photosensitive drum 202 moves during one cycle of the vibration of the discharge wire 304 may be referred to as the vibration pitch of the discharge wire 304. Also, the vibration pitch of the discharge wire 304 is
Movement speed of outer peripheral surface 202a [mm / sec] ÷ Vibration frequency of discharge wire 304 [1 / sec]
It can be calculated by Further, the vibration pitch of the discharge wire 304 can be changed by changing the vibration frequency of the discharge wire 304.

  FIG. 6 shows the result of an experiment on whether or not oblique streaks, which are an example of density unevenness of an image to be formed, are generated by changing the vibration pitch of the discharge wire 304 in the image forming apparatus 10 described above. It is done. In the image forming apparatus 10, the length L between two adjacent ones of the plurality of openings 326 in the moving direction (direction of arrow a) of the outer peripheral surface 202a of the photosensitive drum 202 is 2.0 mm as described above. It is.

  As shown in FIG. 6, the vibration pitch of the discharge wire 304 is 1.6 mm, 1.8 mm, 2.2 mm or 2.4 mm, and the vibration pitch of the discharge wire 304 is 2.0 mm in length L. In the case of non-integer multiples of, no diagonal streaks occurred in the image. On the other hand, when the vibration pitch of the discharge wire 304 is 2.0 mm or 4.0 mm and is an integral multiple of the length L which is 2.0 mm, oblique streaks are generated in the image.

  Here, the vibration pitch of the discharge wire 304 preferably does not interfere with the length L in the range of 1.0 mm or more and 15.0 mm or less, and is preferably a non-integer multiple of the length L. On the other hand, when the vibration pitch of the discharge wire 304 is in a range smaller than 1.0 mm or larger than 15.0 mm, the diagonal stripes that may be generated have a size that is difficult to visually recognize, so the length necessarily It does not need to be non-interfering with L and does not necessarily have to be a non-integer multiple of the length L.

As described above, the vibration pitch of the discharge wire 304 can be changed by changing the vibration frequency f of the discharge wire 304. And, the vibration frequency f of the discharge wire 304 is
L: Length T of discharge wire 304: Tension of discharge wire 304: Diameter: of discharge wire 304: density of discharge wire 304, calculated as follows.

  Therefore, the vibration frequency f and the vibration pitch of the discharge wire 304 can be changed by changing at least one of the diameter d, the density 、, the length L and the tension T of the discharge wire 304, and can do.

  FIG. 7 is a view showing a second example of the grid electrode 320 from the arrow AA direction in FIG. In the first example of the grid electrode 320 described above, the plate-like member 322 is formed with a plurality of band-like openings 326. On the other hand, in the second example of the grid electrode 320, a plurality of hexagonal openings 326 are formed in the plate member 322. Although the shape is different from the first example of the grid electrode 320 described above, the second example of the grid electrode 320 similarly to the grid electrode 320 described above divides the two partitions 326 adjacent to each other. Have.

  Further, as in the case of using the first example of the grid electrode 320 described above, even in the case of using the second example of the grid electrode 320, the outer peripheral surface is caused by the difference in the distance from the partition portion 324. A difference occurs in the amount of ions and the like reached for each position of 202a. Further, as in the case of using the first example of the grid electrode 320 described above, even in the case of using the second example of the grid electrode 320, the vibration of the discharge wire 302 and the discharge wire 304 is the cause. A difference occurs in the amount of ions and the like that reach each position of the outer peripheral surface 202a.

  Then, as in the case of using the first example of the grid electrode 320 described above, even in the case of using the second example of the grid electrode 320, it is caused due to the vibration of the discharge wire 302 and the discharge wire 304. For example, all or the difference between the amount of ions etc. arriving at each position of the outer peripheral surface 202 a resulting from the difference in the distance from the partitioning part 324 due to the difference in the amount of ions etc. arriving at each position of the outer peripheral surface 202 a When partially overlapping, the difference in the amount of ions, etc. arriving at each position on the outer peripheral surface 202a increases, causing charging spots on the outer peripheral surface 202a, and density spots on the image formed due to the charging spots. May occur.

  Therefore, in the image forming apparatus 10, when using the second example of the grid electrode 320, during one cycle of the vibration of the discharge wire 304, the difference in the amount of ions reaching the outer peripheral surface 202a does not increase. The distance by which the outer peripheral surface of the photosensitive drum 202 moves (the vibration pitch of the discharge wire 304) is calculated from the frequency component at the maximum value of the spatial frequency power spectrum obtained by two-dimensional Fourier transformation of the image of the grid electrode 320. The frequency at the time of vibration of the discharge wire 304 is defined so as not to interfere with the component distance in the movement direction of the outer peripheral surface 202 a of the plurality of openings 326. The details will be described below.

  In the following description, the length between two adjacent ones of the plurality of openings 326 may be referred to as an opening pitch. In the following description, a length component in the moving direction (direction of arrow a) of the outer peripheral surface 202a of the opening pitch calculated from the two-dimensional power spectrum may be referred to as an arrow a direction component of the opening pitch. Here, the arrow a direction component of the opening pitch is an example of the distance component of the moving direction of the outer peripheral surface 202 a of the plurality of openings 326.

  FIG. 8A shows the intensity distribution of the two-dimensional power spectrum obtained by the two-dimensional Fourier transform of the image of the second example of the grid electrode 320. More specifically, in FIG. 8A, the image of the second example of the grid electrode 320 is binarized, and the two-dimensional Fourier transform is performed on the binarized image to generate the intensity distribution of the two-dimensional power spectrum. The result of calculating is shown. In FIG. 8, the horizontal axis indicates the above-mentioned arrow a direction, that is, the frequency in the moving direction of the photosensitive drum 202, and the vertical axis is the direction intersecting the above-described arrow b direction, that is, the arrow a direction. The frequency in the longitudinal direction of 320 is shown. In addition, FFT (Fast Fourier Transform) is adopted as the two-dimensional Fourier transform.

  FIG. 8B shows a range in which the two-dimensional power spectrum is extracted from the calculated intensity distribution of the two-dimensional power spectrum (spatial frequency two-dimensional power spectrum). The inner circle C1 shown in FIG. 8B corresponds to the maximum value of the extracted wavelength, and is a circle of radius r1 centered on the two-dimensional power spectrum origin, and the maximum value of the extracted wavelength is 15 mm. Further, the outer circumference circle C2 shown in FIG. 8B corresponds to the minimum value of the extracted wavelength, is a circle of radius r2 centered on the origin of the two-dimensional power spectrum, and the minimum value of the extracted wavelength is 1 mm. is there. As described above, when the image forming apparatus 10 uses the second example of the grid electrode 320, the range from which the two-dimensional power spectrum is extracted from the calculated two-dimensional power spectrum intensity distribution is 1 mm or more and 15 mm or less It is determined to be

  FIG. 9 is a graph showing an integrated value obtained by integrating the absolute value of the two-dimensional power spectrum for each component of the opening pitch in the arrow a direction. Here, when the vibration pitch of the discharge wire 304 interferes with the component of the opening pitch in the direction of the arrow a, charging spots easily occur on the photosensitive drum 202, and density spots of the image easily occur. Further, interference between the vibration pitch of the discharge wire 304 and the component of the opening pitch in the arrow a direction is more likely to occur at the opening pitch where the integrated value of the two-dimensional power spectrum is larger.

  Therefore, when using the second example of the grid electrode 320 in the image forming apparatus 10, using the integration data of the two-dimensional power spectrum shown in FIG. 9, the vibration pitch of the discharge wire 304 and the two-dimensional power spectrum The vibration pitch of the discharge wire 304 is defined and the frequency of the discharge wire 304 is defined so that the integrated value hardly interferes with the component of the large opening pitch in the arrow a direction.

  The line M in FIG. 9 indicates the maximum value of the integrated value of the two-dimensional power spectrum, and the line m in FIG. 9 indicates the minimum value of the integrated value of the two-dimensional power spectrum. Furthermore, line l1 in FIG. 9 is the minimum value indicated by line m, assuming that the value obtained by subtracting the minimum value of the integration values indicated by line m from the maximum value of the integrated values indicated by line M is 100%. It shows the value added 30%. Line 12 in FIG. 9 is the minimum value shown by line m when the value obtained by subtracting the minimum value of the integration values shown by line m from the maximum value of the integrated value shown by line M is 100%. It shows the value added 40%. Further, line l3 in FIG. 9 is the minimum value indicated by line m, assuming that the value obtained by subtracting the minimum value of the integration values indicated by line m from the maximum value of the integrated values indicated by line M is 100%. It shows the value added 50%.

  FIG. 10 is a graph showing an integrated value obtained by integrating the absolute value of the two-dimensional power spectrum for each value obtained by converting the component in the direction of the arrow a of the opening pitch shown as the horizontal axis in FIG. .

Here, the following relational expression is used to convert the component of the opening pitch in the direction of the arrow a into the frequency of the discharge wire 304.
f: Frequency v of the discharge wire 304: Speed P of the outer peripheral surface 202a: When the opening pitch
f = v / P

  Also in FIG. 10, the line M indicates the maximum value of the integrated value of the two-dimensional power spectrum, and the line m indicates the minimum value of the integrated value of the two-dimensional power spectrum. Also in FIG. 10, line l1 is the minimum shown by line m when the value obtained by subtracting the minimum value of the integrated values shown by line m from the maximum value of the integrated values shown by line M is 100%. The value obtained by adding 30% to the value is shown, and the line 12 is a value obtained by subtracting the minimum value of the integrated values shown by the line m from the maximum value of the integrated values shown by the line M as 100%. A value obtained by adding 40% to the minimum value indicated by the line m is shown, and the line 13 is a value obtained by subtracting the minimum value of the integration values indicated by the line m from the maximum value of the integration values indicated by the line M In the case of%, the value obtained by adding 30% to the minimum value indicated by the line m is shown.

  Further, in FIG. 10, if the frequency of the discharge wire 304 is changed and the photosensitive drum 202 is charged at each of the frequencies of the discharge wire 304, if an image is formed, oblique stripes may be generated in the image formed? The result of experimenting whether or not it is shown is shown. That is, in FIG. 10, the frequency of the discharge wire 304 which did not generate oblique streaks in the formed image is plotted with .smallcircle., And the frequency where slight oblique streaks of the formed image are plotted with .DELTA. The frequency at which a large diagonal line is generated in the formed image is plotted by ×.

  Referring to FIG. 10, it can be understood that the frequency of the discharge wire 304 may be defined so that the integrated value of the two-dimensional spectrum is equal to or less than the line l1 in order to prevent the generation of oblique streaks in the formed image. That is, in order to prevent the generation of oblique streaks in the formed image, the frequency of the discharge wire 304 may be set so that the integrated value of the two-dimensional power spectrum is smaller than the value indicated by the line l1. The distance traveled by the outer peripheral surface 202a during one cycle of the vibration of the wire 304 is larger than 30% of the difference between the maximum value and the minimum value of the spatial frequency power spectrum obtained by the two-dimensional Fourier transform of the image of the grid electrode 320 It can be understood that the frequency of the discharge wire 304 may be determined so as not to interfere with the component distance in the moving direction of the outer peripheral surface 202a of the plurality of openings 326 calculated from the frequency component of the value.

  FIG. 11 shows the details of the data plotted in FIG. In the example shown in FIG. 11, changing the tension T of the discharge wire 304 having the same length L, diameter d and density ρ of one and the same discharge wire 304 changes the frequency at the time of vibration of the discharge wire 304. I am doing it. Further, the frequency at the time of vibration of the discharge wire 304 is calculated using the above-mentioned equation.

10: Image forming apparatus 202: Photosensitive drum 202a: Outer peripheral surface 300: Charging device 302, 304: Discharge wire 320: Grid electrode 322: Plate member 324 ..・ Partition part 326 ... opening

Claims (11)

An image carrier which moves an outer peripheral surface and holds a toner image transferred to a recording medium on the outer peripheral surface;
A charging device for charging the image carrier;
Have
The charging device is
A linear first electrode disposed at a position facing the outer peripheral surface;
A second electrode disposed between the outer circumferential surface and the first electrode and having a plurality of openings formed therein;
Have
The first electrode has a distance by which the outer peripheral surface moves during one cycle of vibration of the first electrode, and a length in a moving direction of the outer peripheral surface between two adjacent ones of the plurality of openings. An image forming apparatus in which the frequency at the time of vibration is determined so as to be non-interference.   In the first electrode, a distance traveled by the outer peripheral surface during one cycle of vibration is a non-integer multiple of a length in a moving direction of the outer peripheral surface between two adjacent ones of the plurality of openings. The image forming apparatus according to claim 1, wherein the frequency at the time of vibration is determined.   The first electrode has an outer periphery between two adjacent ones of the plurality of openings in a range of 1 mm or more and 15 mm or less in which the outer peripheral surface moves during one cycle of the vibration of the first electrode. 3. The image forming apparatus according to claim 1, wherein the frequency at the time of vibration is determined so as to be non-interference with the length in the moving direction of the surface. An image carrier which moves an outer peripheral surface and holds a toner image transferred to a recording medium on the outer peripheral surface;
A charging device for charging the image carrier;
Have
The charging device is
A linear first electrode disposed at a position facing the outer peripheral surface;
A second electrode disposed between the outer circumferential surface and the first electrode and having a plurality of openings formed therein;
Have
The first electrode has a maximum value of the spatial frequency power spectrum obtained by two-dimensional Fourier transform of the image of the second electrode in which the distance the outer circumferential surface moves during one cycle of the vibration of the first electrode An image forming apparatus in which the first electrode vibration frequency at the time of vibration is determined so as not to interfere with the component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency components at.   The first electrode has a maximum value of the spatial frequency power spectrum obtained by two-dimensional Fourier transform of the image of the second electrode in which the distance the outer circumferential surface moves during one cycle of the vibration of the first electrode The first electrode vibration frequency at the time of vibration is determined such that the component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency components of The image forming apparatus according to claim 4.   The first electrode has a maximum value of the spatial frequency power spectrum obtained by two-dimensional Fourier transform of the image of the second electrode, in which the distance the outer circumferential surface moves during one cycle of the vibration of the first electrode The frequency at the time of vibration is determined so as to be non-interference with the component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency component of a value larger than 30% of the difference between The image forming apparatus according to claim 4 or 5,   The image forming apparatus according to any one of claims 1 to 6, wherein toner having an average particle diameter of 6 μm or less is used for image formation.   The image forming apparatus according to any one of claims 1 to 7, wherein a moving speed of the outer peripheral surface at the time of forming an image is 300 mm / s or more.   The image forming apparatus according to any one of claims 1 to 8, wherein a frequency at the time of vibration is determined by changing at least one of a diameter, a density, and a length of the first electrode. A linear first electrode disposed at a position opposed to the outer peripheral surface of the image carrier which moves the outer peripheral surface and holds the toner image transferred to the recording medium on the outer peripheral surface;
A second electrode disposed between the outer circumferential surface and the first electrode and having a plurality of openings formed therein;
Have
The first electrode has a distance by which the outer peripheral surface moves during one cycle of vibration of the first electrode, and a length in a moving direction of the outer peripheral surface between two adjacent ones of the plurality of openings. A charging device whose frequency at the time of vibration is determined so as not to interfere. A linear first electrode disposed at a position opposed to the outer peripheral surface of the image carrier which moves the outer peripheral surface and holds the toner image transferred to the recording medium on the outer peripheral surface;
A second electrode disposed between the outer circumferential surface and the first electrode and having a plurality of openings formed therein;
Have
The first electrode has a maximum value of the spatial frequency power spectrum obtained by two-dimensional Fourier transform of the image of the second electrode in which the distance the outer circumferential surface moves during one cycle of the vibration of the first electrode The first electrode vibration frequency at the time of vibration is determined so as to be non-interfering with the component distance of the movement direction of the outer peripheral surface of the plurality of openings calculated from the frequency components at.