JP4835778B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, an image forming method, and an image forming system.

  Image forming apparatuses such as laser beam printers are already well known. Such an image forming apparatus includes, for example, an image carrier for carrying a latent image and a developer for conveying the developer to a position facing the image carrier by rotating in a state of carrying the developer. An agent carrier, and a charging member that faces the image carrier and charges the image carrier. When an image signal or the like is transmitted from an external device such as a host computer, the charging member The latent image carried on the charged image carrier is developed with the developer conveyed to the opposite position by the developer carrier to form a developer image, and the developer image is transferred to a medium. Finally, an image is formed on the medium.

JP-A-5-142950 JP 2004-219640 A

  In the image forming apparatus described above, when developing the latent image with a developer, a first voltage for directing the developer from the developer carrier to the image carrier and the development from the image carrier. There is one that applies an alternating voltage having a second voltage for directing the developer to the developer carrying member, to the developer carrying member. In addition, a sufficient amount of developer is carried on the surface of the developer carrying body (in other words, the surface area of the surface carrying the developer is a sufficiently large value). In some cases, the concave portions arranged regularly are provided.

In such an image forming apparatus, a discharge phenomenon may occur between the image carrier and the developer carrier when developing the latent image. When the discharge phenomenon occurs, a developer image is not appropriately formed on the image carrier, and thus a defective image is finally formed on the medium.
In addition, as described above, an alternating voltage having a first voltage and a second voltage is applied to the developer carrying member, and it is known that density unevenness occurs in the image due to the alternating voltage. It has been. Similarly, a superposed voltage obtained by superimposing a DC voltage and an AC voltage is applied to the charging member that charges the image carrier, and it is known that unevenness in image density occurs due to this superposed voltage. ing. When these two types of density unevenness occur, if the two types of density unevenness are overlapped, the density unevenness becomes conspicuous. As a result, the density unevenness of the image becomes conspicuous.

  The present invention has been made in view of such problems, and an object of the present invention is to appropriately suppress the occurrence of a discharge phenomenon and to suppress the occurrence of image density unevenness.

In order to solve the above problems, the main present invention is:
An image carrier for carrying a latent image;
A developer carrying member for transporting the developer to a facing position facing the image carrier by rotating in a state of having a concave portion regularly arranged on the surface and carrying the developer;
For developing the latent image by the developer conveyed to the facing position, a first voltage for directing the developer from the developer carrier to the image carrier and the developer from the image carrier An alternating voltage having a second voltage for directing the developer to the carrier, and an alternating voltage application unit for applying to the developer carrier,
A charging member facing the image carrier and charging the image carrier;
A superimposed voltage in which a DC voltage and an AC voltage are superimposed, and a superimposed voltage application unit that applies to the charging member;
An image forming apparatus having
The period of the alternating voltage is
Greater than a value obtained by dividing the minimum width of the recess along the circumferential direction of the developer carrier by the moving speed of the surface of the developer carrier when the developer carrier rotates, and
The image forming apparatus is different from a value obtained by multiplying the magnitude of the period of the superimposed voltage by a natural number and a value obtained by dividing the period by a natural number.

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

FIG. 2 is a diagram illustrating main components constituting the printer. FIG. 2 is a block diagram illustrating a control unit of the printer 10 in FIG. 1. FIG. 3A is a schematic diagram showing the photoreceptor 20 and the charging unit 30. FIG. 3B is a schematic diagram illustrating a charging bias applied to the charging roller 31. It is a conceptual diagram of a developing device. It is sectional drawing which showed the main components of the image development apparatus. 3 is a schematic perspective view of a developing roller 510. FIG. 2 is a schematic front view of a developing roller 510. FIG. FIG. 5 is a schematic diagram showing a cross-sectional shape of a groove portion 512. FIG. 8 is an enlarged schematic diagram of FIG. 7. 5 is a perspective view of a restriction blade 560. FIG. FIG. 5 is a perspective view of a holder 526. FIG. 5 is a perspective view showing a state where an upper seal 520, a regulating blade 560, and a developing roller 510 are assembled to a holder 526. FIG. 6 is a perspective view showing a state in which a holder 526 is attached to a housing 540. FIG. 6 is a schematic diagram illustrating a developing bias applied to a developing roller 510. It is explanatory drawing for demonstrating the predominance of the printer 10 which concerns on this Embodiment. FIG. 16A is a schematic diagram showing density unevenness due to the developing bias. FIG. 16B is a schematic diagram illustrating density unevenness caused by the charging bias. FIG. 16C is a schematic diagram illustrating a state in which the degree of density unevenness is increased. 4 is a flowchart for explaining the operation of the printer 10 according to the present control. 6 is a table showing the relationship between the type of medium and the moving speed V of the developing roller 510 and the like. FIG. 19A to FIG. 19C are schematic diagrams showing the transition of the developing roller 510 in the manufacturing process of the developing roller 510. FIG. 6 is an explanatory diagram for explaining a rolling process of the developing roller 510. 4 is a flowchart for explaining a method of assembling the yellow developing device 54. 22A to 22C are diagrams showing variations on the surface shape of the developing roller 510. FIG. 23A and 23B are diagrams showing variations on the developing bias. 1 is an explanatory diagram showing an external configuration of an image forming system. FIG. 25 is a block diagram illustrating a configuration of the image forming system illustrated in FIG. 24.

  At least the following will be made clear by the description of the present specification and the accompanying drawings.

An image carrier for carrying a latent image;
A developer carrying member for transporting the developer to a facing position facing the image carrier by rotating in a state of having a concave portion regularly arranged on the surface and carrying the developer;
For developing the latent image by the developer conveyed to the facing position, a first voltage for directing the developer from the developer carrier to the image carrier and the developer from the image carrier An alternating voltage having a second voltage for directing the developer to the carrier, and an alternating voltage application unit for applying to the developer carrier,
A charging member facing the image carrier and charging the image carrier;
A superimposed voltage in which a DC voltage and an AC voltage are superimposed, and a superimposed voltage application unit that applies to the charging member;
An image forming apparatus having
The period of the alternating voltage is
Greater than a value obtained by dividing the minimum width of the recess along the circumferential direction of the developer carrier by the moving speed of the surface of the developer carrier when the developer carrier rotates, and
2. An image forming apparatus according to claim 1, wherein a value obtained by multiplying a magnitude of the cycle of the superimposed voltage by a natural number and a value obtained by dividing the magnitude of the cycle by a natural number are different from each other.
According to such an image forming apparatus, there is a situation in which the discharge phenomenon can occur remarkably because the period of the alternating voltage is larger than the value obtained by dividing the minimum width of the recess by the moving speed. Since it does not occur continuously in a short time, the occurrence of the discharge phenomenon is appropriately suppressed. Further, the alternating voltage cycle period is different from both the value obtained by multiplying the period of the superimposed voltage by a natural number and the value obtained by dividing the period by a natural number. Therefore, it is possible to prevent the occurrence of the density unevenness of the image from being conspicuous.

  In the image forming apparatus, it is preferable that the charging member is a rotatable charging roller, and the charging roller faces the image carrier through a gap. In such a case, the effect of suppressing the noticeable density unevenness of the image is more effectively exhibited.

  Further, in the image forming apparatus, the image carrier is rotatable, and the alternating voltage application unit alternately applies the first voltage and the second voltage for a predetermined period, The developer positioned at the charging position charged by the charging member when the superimposed voltage application unit starts applying the superimposed voltage is conveyed to the facing position as the image carrier rotates. It is preferable that the alternating voltage application unit starts to apply the first voltage or the second voltage to the developer carrying member when positioned at a development position where development is performed. In such a case, the effect of suppressing the noticeable density unevenness of the image is more effectively exhibited.

  Further, in this image forming apparatus, the concave portion is two types of spiral groove portions having different inclination angles with respect to the circumferential direction, and the two types of spiral groove portions intersect with each other to form a lattice shape. The developer carrying member has a square top surface surrounded by the two types of spiral grooves, and one of the two diagonal lines of the square top surface is the circumferential direction. It is desirable that

And (a) a developer carrying member for transporting the developer to a facing position facing the image carrier by rotating in a state where the concave portions are regularly arranged on the surface and carrying the developer. ,
Changing the moving speed of the surface of the developer carrying member when rotating,
(B) a first voltage for directing the developer from the developer carrier to the image carrier and a second voltage for directing the developer from the image carrier to the developer carrier. The period of the alternating voltage is
The minimum width of the concave portion along the circumferential direction of the developer carrier is larger than the value divided by the moving speed after change.
Changing the magnitude of the period of the alternating voltage;
(C) Both the value obtained by multiplying the magnitude of the period of the superimposed voltage obtained by superimposing the DC voltage and the AC voltage by a natural number and the value obtained by dividing the period by a natural number are the alternating voltage. Changing the magnitude of the cycle of the superimposed voltage to be different from the magnitude of the cycle after the change,
(D) applying the superposed voltage whose period has been changed to a charging member facing the image carrier to charge the image carrier;
(E) A step of applying the alternating voltage whose cycle size has been changed to the developer carrier and developing the latent image carried on the image carrier by the developer conveyed to the facing position. When,
An image forming method comprising (f).
According to such an image forming method, even if the moving speed of the developer carrying member is changed, it is possible to appropriately suppress the occurrence of a discharge phenomenon and to suppress the occurrence of image density unevenness.

  Further, in such an image forming method, the types of media on which an image can be formed are plain paper and cardboard, and when the image is formed on the plain paper, the moving speed of the surface of the developer carrier is set. When the image is formed on the thick paper, it is desirable to reduce the moving speed of the surface of the developer carrier. In such a case, even if the type of the medium is changed, it is possible to appropriately suppress the occurrence of the discharge phenomenon and to suppress the uneven density of the image from being noticeable.

(A) a computer; and
(B) An image forming apparatus connectable to the computer,
(A) an image carrier for carrying a latent image;
(B) a developer carrying member for transporting the developer to a facing position facing the image carrier by rotating in a state where the concave portions arranged regularly are carried on the surface and carrying the developer; ,
(C) For developing the latent image by the developer conveyed to the facing position, the first voltage for directing the developer from the developer carrier to the image carrier and the image carrier An alternating voltage having a second voltage for directing the developer to the developer carrying member, and an alternating voltage applying unit for applying to the developer carrying member,
(D) a charging member facing the image carrier and charging the image carrier;
(E) a superimposed voltage application unit that applies a superimposed voltage obtained by superimposing a DC voltage and an AC voltage to the charging member;
(F) The period of the alternating voltage is:
Greater than a value obtained by dividing the minimum width of the recess along the circumferential direction of the developer carrier by the moving speed of the surface of the developer carrier when the developer carrier rotates, and
An image forming apparatus that is different from both a value obtained by multiplying the magnitude of the cycle of the superimposed voltage by a natural number and a value obtained by dividing the magnitude of the cycle by a natural number;
An image forming system comprising (C).
According to such an image forming system, it is possible to appropriately suppress the occurrence of the discharge phenomenon and to prevent the uneven density of the image from being noticeable.

=== Example of Overall Configuration of Image Forming Apparatus ===
Next, an outline of a laser beam printer (hereinafter also referred to as a printer) 10 as an example of the “image forming apparatus” will be described with reference to FIG. FIG. 1 is a diagram illustrating main components constituting the printer 10. In FIG. 1, the vertical direction is indicated by arrows. For example, the paper feed tray 92 is disposed at the lower part of the printer 10, and the fixing unit 90 is disposed at the upper part of the printer 10.

  As shown in FIG. 1, the printer 10 according to the present embodiment includes a charging unit 30 and an exposure unit 40 along the rotation direction of the photoconductor 20 as an example of an “image carrier” for carrying a latent image. , YMCK development unit 50, primary transfer unit 60, intermediate transfer body 70, cleaning unit 75, secondary transfer unit 80, fixing unit 90, and a display unit 95 comprising a liquid crystal panel as a means for notifying the user, A control unit 100 that controls these units and controls the operation as a printer is provided.

  The photoreceptor 20 has a cylindrical conductive substrate and a photosensitive layer formed on the outer peripheral surface thereof, and is rotatable around a central axis. In the present embodiment, the photoreceptor 20 is indicated by an arrow in FIG. Rotate clockwise.

  The charging unit 30 is a device for charging the photoconductor 20. Details of the charging unit 30 will be described later. The exposure unit 40 is a device that forms a latent image on the photoreceptor 20 charged by irradiating a laser. The exposure unit 40 includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and charges the modulated laser based on an image signal input from a host computer (not shown) such as a personal computer or a word processor. The irradiated photoconductor 20 is irradiated.

  The YMCK developing unit 50 converts the latent image formed on the photoconductor 20 into toner as an example of a developer contained in the developing device, that is, black (K) toner contained in the black developing device 51, magenta development. An apparatus for developing using magenta (M) toner stored in the device 52, cyan (C) toner stored in the cyan developing device 53, and yellow (Y) toner stored in the yellow developing device 54. is there.

  The YMCK developing unit 50 can move the positions of the four developing devices 51, 52, 53, 54 by rotating with the four developing devices 51, 52, 53, 54 mounted. Yes. That is, the YMCK developing unit 50 holds the four developing devices 51, 52, 53, 54 by four holding portions 55a, 55b, 55c, 55d, and the four developing devices 51, 52, 53, 54 is rotatable around the central axis 50a while maintaining the relative position thereof. Each time image formation for one page is completed, it is selectively opposed to the photoconductor 20, and is formed on the photoconductor 20 with the toner accommodated in each developing device 51, 52, 53, 54. The latent images are developed sequentially. Each of the four developing devices 51, 52, 53, 54 described above is detachable from the holding portion of the YMCK developing unit 50. Details of each developing device will be described later.

The primary transfer unit 60 is a device for transferring a single color toner image formed on the photoconductor 20 to the intermediate transfer body 70. When four color toners are sequentially transferred in a superimposed manner, the full color toner is transferred to the intermediate transfer body 70. An image is formed. This intermediate transfer body 70 is an endless belt in which a tin vapor deposition layer is provided on the surface of a PET film and a semiconductive paint is formed on the surface layer and laminated. The intermediate transfer body 70 is driven to rotate at substantially the same peripheral speed as the photoconductor 20.
The secondary transfer unit 80 is a device for transferring a single color toner image or a full color toner image formed on the intermediate transfer body 70 to a medium such as paper, film, or cloth. The fixing unit 90 is a device for fusing a single-color toner image or a full-color toner image transferred onto a medium to form a permanent image.

  The cleaning unit 75 is provided between the primary transfer unit 60 and the charging unit 30 and has a rubber cleaning blade 76 that is in contact with the surface of the photoconductor 20. The cleaning unit 75 is disposed on the intermediate transfer body 70 by the primary transfer unit 60. After the toner image is transferred, the toner remaining on the photoreceptor 20 is scraped off and removed by the cleaning blade 76.

  As shown in FIG. 2, the control unit 100 includes a main controller 101 and a unit controller 102. An image signal and a control signal are input to the main controller 101, and in response to a command based on the image signal and the control signal. A unit controller 102 controls each of the units and forms an image.

Next, the operation of the printer 10 configured as described above will be described.
First, when an image signal and a control signal from a host computer (not shown) are input to the main controller 101 of the printer 10 via the interface (I / F) 112, the unit controller 102 based on a command from the main controller 101. The photosensitive member 20 and the intermediate transfer member 70 are rotated by the control. The photoconductor 20 is sequentially charged by the charging unit 30 at the charging position while rotating.

  The charged area of the photoconductor 20 reaches an exposure position as the photoconductor 20 rotates, and a latent image corresponding to image information of the first color, for example, yellow Y, is formed in the area by the exposure unit 40. . In the YMCK developing unit 50, a yellow developing device 54 that contains yellow (Y) toner is located at a developing position facing the photoconductor 20. The latent image formed on the photoconductor 20 reaches the development position as the photoconductor 20 rotates, and is developed with yellow toner by the yellow developing device 54. As a result, a yellow toner image is formed on the photoreceptor 20. The yellow toner image formed on the photoconductor 20 reaches the primary transfer position as the photoconductor 20 rotates, and is transferred to the intermediate transfer body 70 by the primary transfer unit 60. At this time, a primary transfer voltage having a polarity opposite to the charging polarity of the toner T (negative polarity in the present embodiment) is applied to the primary transfer unit 60. During this time, the photosensitive member 20 and the intermediate transfer member 70 are in contact with each other, and the secondary transfer unit 80 is separated from the intermediate transfer member 70.

  The above processing is sequentially executed for each developing device for the second color, the third color, and the fourth color, so that four color toner images corresponding to the respective image signals are transferred to the intermediate transfer member 70. It is transcribed and superimposed. As a result, a full color toner image is formed on the intermediate transfer member 70.

The full color toner image formed on the intermediate transfer body 70 reaches the secondary transfer position as the intermediate transfer body 70 rotates, and is transferred to the medium by the secondary transfer unit 80. The medium is conveyed from the paper feed tray 92 to the secondary transfer unit 80 via the paper feed roller 94 and the registration roller 96. When performing the transfer operation, the secondary transfer unit 80 is pressed against the intermediate transfer body 70 and a secondary transfer voltage is applied.
The full color toner image transferred to the medium is heated and pressed by the fixing unit 90 and fused to the medium.

  On the other hand, after the primary transfer position has passed, the photosensitive member 20 is scraped off by the cleaning blade 76 supported by the cleaning unit 75 and the toner T adhering to the surface thereof is charged to form the next latent image. Prepare for. The toner T thus scraped off is collected by a residual toner collecting unit provided in the cleaning unit 75.

=== Overview of Control Unit ===
Next, the configuration of the control unit 100 will be described with reference to FIG. The main controller 101 of the control unit 100 is electrically connected to a host computer via an interface 112 and includes an image memory 113 for storing an image signal input from the host computer. The unit controller 102 is electrically connected to each unit (charging unit 30, exposure unit 40, YMCK developing unit 50, primary transfer unit 60, cleaning unit 75, secondary transfer unit 80, fixing unit 90, display unit 95) of the apparatus main body. Each unit is controlled based on a signal input from the main controller 101 while detecting a state of each unit by receiving a signal from a sensor included in the unit.

  The YMCK developing unit drive control circuit 128 connected to the YMCK developing unit 50 is provided with an alternating voltage applying unit 132 (also simply referred to as a voltage applying unit). The alternating voltage application unit 132 applies an alternating voltage (hereinafter also referred to as a developing bias) to the developing roller 510 for developing the latent image with toner, and an alternating electric field is generated between the developing roller 510 and the photoconductor 20. (The details will be described later). The charging unit drive control circuit 129 connected to the charging unit 30 includes a superimposed voltage application unit 133. The superimposed voltage application unit 133 applies a superimposed voltage (hereinafter also referred to as a charging bias) to the charging roller 31 in order to charge the photosensitive member 20, thereby forming an alternating electric field between the charging roller 31 and the photosensitive member 20. To play a role.

=== Regarding the Charging Unit 30 ===
Next, the charging unit 30 that charges the photoreceptor 20 will be described with reference to FIGS. 3A and 3B. FIG. 3A is a schematic diagram showing the photoreceptor 20 and the charging unit 30. FIG. 3B is a schematic diagram illustrating the superimposed voltage applied to the charging roller 31.

  The charging unit 30 is opposed to the photoconductor 20 through a gap and is a rotatable charging roller 31 as an example of a “charging member” for charging the photoconductor 20, and the charging roller 31 in contact with the charging roller 31. And a cleaning roller 35 (not shown in FIG. 1) for cleaning the surface of 31. The charging roller 31 has a configuration in which a conductive paint is applied to the surface of a metal shaft. The charging roller 31 has a tape 32 attached to both end portions in the axial direction so as to contact the photoreceptor 20. Since the outer diameter of the tape 32 is larger than the outer diameter of the central portion of the charging roller 31, a gap G is formed between the central portion and the photoconductor 20. For this reason, the charging roller 31 charges the photoconductor 20 in a non-contact state.

  The charging unit 30 includes a bearing 33 that rotatably supports the charging roller 31, and a spring 34 that biases the charging roller 31 toward the photoconductor 20 via the bearing 33. The charging roller 31 is biased toward the photoconductor 20 by the biasing force of the spring 34, so that the tape 32 comes into contact with the photoconductor 20.

  Here, charging of the photoconductor 20 will be described with reference to FIG. 3B. When charging of the photoconductor 20 is executed, a superimposed voltage (charging bias) in which a DC voltage and an AC voltage are superimposed is applied to the charging roller 31 by the superimposed voltage application unit 133. Specifically, a voltage (an AC voltage component) having an amplitude between −540 V and −620 V centering on −580 V (AC voltage component) is applied to the charging roller 31. The period of the charging bias period (this period is T2) is 1.0 ms (milliseconds).

=== About Development Device ===
Next, the developing device will be described with reference to FIGS. FIG. 4 is a conceptual diagram of the developing device. FIG. 5 is a cross-sectional view showing the main components of the developing device. FIG. 6 is a schematic perspective view of the developing roller 510. FIG. 7 is a schematic front view of the developing roller 510. FIG. 8 is a schematic diagram showing a cross-sectional shape of the groove 512. FIG. 9 is an enlarged schematic view of FIG. 7 and shows the groove portion 512 and the top surface 515. FIG. 10 is a perspective view of the regulating blade 560. FIG. 11 is a perspective view of the holder 526. FIG. 12 is a perspective view showing a state in which the upper seal 520, the regulating blade 560, and the developing roller 510 are assembled to the holder 526. FIG. 13 is a perspective view showing a state in which the holder 526 is attached to the housing 540. FIG. 14 is a schematic diagram showing a developing bias applied to the developing roller 510. Note that the cross-sectional view shown in FIG. 5 represents a cross section of the developing device taken along a plane perpendicular to the longitudinal direction shown in FIG. In FIG. 5, the vertical direction is indicated by arrows as in FIG. 1. For example, the central axis of the developing roller 510 is below the central axis of the photoconductor 20. Further, in FIG. 5, the yellow developing device 54 is shown in a state where the yellow developing device 54 is located at the developing position facing the photoconductor 20. Further, in FIGS. 6 to 9, the scales of the groove portions 512 and the like are different from the actual ones for easy understanding of the drawings.

  The YMCK developing unit 50 includes a black developing device 51 containing black (K) toner, a magenta developing device 52 containing magenta (M) toner, a cyan developing device 53 containing cyan (C) toner, and a yellow ( Y) Although a yellow developing device 54 containing toner is provided, the configuration of each developing device is the same, so the yellow developing device 54 will be described below.

The yellow developing device 54 includes a developing roller 510, an upper seal 520, a toner container 530, a housing 540, a toner supply roller 550, a regulation blade 560, a holder 526, and the like as examples of a “developer carrier”.
The developing roller 510 conveys the toner T to a facing position (developing position) facing the photoconductor 20 by rotating in a state where the toner T is carried. The developing roller 510 is a member made of an aluminum alloy, an iron alloy, or the like.

As shown in FIGS. 6 and 7, the developing roller 510 has a groove portion 512 as an example of a “concave portion” on the surface of the central portion 510a in order to appropriately carry the toner T. In the present embodiment, as the groove portion 512, two types of spiral groove portions 512 having different winding directions, that is, a first groove portion 512a and a second groove portion 512b are provided. As shown in FIG. 7, the inclination angles of the first groove portion 512a and the second groove portion 512b with respect to the circumferential direction of the developing roller 510 are different from each other, and the longitudinal direction of the first groove portion 512a and the axial direction of the developing roller 510 are different. And the magnitude of the acute angle formed by the longitudinal direction of the second groove portion 512b and the axial direction are both about 45 degrees. As shown in FIG. 8, the width of the first groove 512a in the X direction and the width of the second groove 512b in the Y direction are about 50 μm, the depth of the groove 512 is about 7 μm, and the groove angle (in FIG. Is an angle of about 90 degrees.
Furthermore, the groove part 512 is provided with the bottom face 513 and the side surface 514, and the inclination | tilt angle of the side surface 514 is about 45 degree | times in this Embodiment (refer FIG. 8).

  The two types of spiral grooves 512 configured as described above are regularly arranged on the surface of the central portion 510a of the developing roller 510 and intersect each other as shown in FIGS. And has a lattice shape. Therefore, a large number of diamond-shaped top surfaces 515 surrounded by the grooves 512 on the four sides are formed on the mesh at the central portion 510a.

  As described above, in the present embodiment, the size of the acute angle formed by the longitudinal direction of the first groove portion 512a and the axial direction, and the size of the acute angle formed by the longitudinal direction of the second groove portion 512b and the axial direction, Since both are approximately 45 degrees, the top surface 515 has a square planar shape, and one (the other) of the two diagonal lines of the top surface 515 is the circumferential direction of the developing roller 510. (Axial direction). The length of one side of the square top surface 515 is about 30 μm as shown in FIG.

  Further, the developing roller 510 is provided with a shaft portion 510b. The shaft portion 510b is supported by a developing roller support portion 526b of a holder 526, which will be described later, via a bearing 576 (FIG. 12). 510 is rotatably supported. As shown in FIG. 5, the developing roller 510 rotates in a direction (counterclockwise in FIG. 5) opposite to the rotation direction of the photoconductor 20 (clockwise in FIG. 5). In the present embodiment, the moving speed V of the surface of the developing roller 510 when the developing roller 510 rotates (that is, the linear velocity of the developing roller 510 on the surface of the developing roller 510) is 300 mm / s. . Further, the moving speed of the surface of the photoconductor 20 when the photoconductor 20 rotates (that is, the linear velocity of the photoconductor 20 on the surface of the photoconductor 20) is 210 mm / s. The peripheral speed ratio with respect to the photoconductor 20 is about 1.4.

  Further, a gap exists between the developing roller 510 and the photoconductor 20 in a state where the yellow developing device 54 faces the photoconductor 20. That is, the yellow developing device 54 develops the latent image formed on the photoconductor 20 in a non-contact state. In the printer 10 according to the present embodiment, a jumping development method is used, and an alternating electric field is generated between the developing roller 510 and the photoconductor 20 when the latent image formed on the photoconductor 20 is developed. Formed (to be described in detail later).

The housing 540 is manufactured by welding a plurality of integrally formed resin housing parts, that is, the upper housing part 542 and the lower housing part 544, and in order to accommodate the toner T therein. The toner container 530 is formed. The toner containing body 530 has two toner containing portions, that is, a first toner containing portion 530a and a second toner, by a partition wall 545 for separating the toner T projected inwardly (in the vertical direction in FIG. 5) from the inner wall. It is divided into the accommodating portion 530b. The upper portions of the first toner storage portion 530a and the second toner storage portion 530b communicate with each other, and the movement of the toner T is restricted by the partition wall 545 in the state shown in FIG. However, when the YMCK developing unit 50 rotates, the toner accommodated in the first toner accommodating portion 530a and the second toner accommodating portion 530b is once collected on the upper communicating side of the developing position. When returning to the state shown in FIG. 5, the toners are mixed and returned to the first toner storage portion 530a and the second toner storage portion 530b. That is, when the YMCK developing unit 50 rotates, the toner T in the developing device is appropriately agitated.
For this reason, in this embodiment, the toner container 530 is not provided with a stirring member, but a stirring member for stirring the toner T stored in the toner container 530 may be provided. Further, as shown in FIG. 5, the housing 540 (that is, the first toner storage portion 530 a) has an opening 572 in the lower portion, and the developing roller 510 is provided so as to face the opening 572.

  The toner supply roller 550 is provided in the first toner storage portion 530a described above, supplies the toner T stored in the first toner storage portion 530a to the development roller 510, and remains on the development roller 510 after development. The toner T is peeled off from the developing roller 510. The toner supply roller 550 is made of polyurethane foam or the like, and is in contact with the developing roller 510 in an elastically deformed state. The toner supply roller 550 is disposed below the first toner storage portion 530a, and the toner T stored in the first toner storage portion 530a is transferred by the toner supply roller 550 below the first toner storage portion 530a. Supplied to the developing roller 510. The toner supply roller 550 is rotatable about a central axis, and the central axis is below the rotation central axis of the developing roller 510. Further, the toner supply roller 550 rotates in a direction (clockwise in FIG. 5) opposite to the rotation direction of the developing roller 510 (counterclockwise in FIG. 5).

The upper seal 520 is in contact with the developing roller 510 along the axial direction thereof, allows the toner T remaining on the developing roller 510 after passing through the developing position to move into the housing 540, and the housing 540. The movement of the toner T inside the housing 540 is restricted. The upper seal 520 is a seal made of a polyethylene film or the like. The upper seal 520 is supported by an upper seal support portion 526a of a holder 526, which will be described later, and is provided so that its longitudinal direction is along the axial direction of the developing roller 510 (FIG. 12). The contact position where the upper seal 520 contacts the developing roller 510 is above the central axis of the developing roller 510.
Further, a malt is provided between the surface of the upper seal 520 opposite to the contact surface 520b that contacts the developing roller 510 (this surface is also referred to as the opposite surface 520c) and the upper seal support portion 526a. An upper seal urging member 524 made of an elastic body such as a plane is provided in a compressed state. The upper seal urging member 524 presses the upper seal 520 against the developing roller 510 by urging the upper seal 520 toward the developing roller 510 with the urging force.

The regulating blade 560 abuts against the developing roller 510 at the abutting portion 562a from one end to the other end in the axial direction of the developing roller 510 to regulate the layer thickness of the toner T carried on the developing roller 510, In addition, a charge is applied to the toner T carried on the developing roller 510. As shown in FIGS. 5 and 10, the regulating blade 560 includes a rubber part 562 and a rubber support part 564.
The rubber part 562 is made of silicon rubber, urethane rubber, or the like, and is in contact with the developing roller 510.

The rubber support portion 564 includes a thin plate 564a and a thin plate support portion 564b, and supports the rubber portion 562 at one end portion 564d in the short direction (that is, the end portion on the thin plate 564a side). The thin plate 564a is made of phosphor bronze, stainless steel or the like and has a spring property. The thin plate 564a supports the rubber part 562 and presses the rubber part 562 against the developing roller 510 by the biasing force. The thin plate support portion 564b is a metal sheet metal disposed on the other end 564e in the short side direction of the rubber support portion 564, and the thin plate support portion 564b is a side of the thin plate 564a that supports the rubber portion 562. It is attached to the said thin plate 564a in the state which supported the edge on the opposite side.
The regulating blade 560 is attached to the regulating blade support portion 526c in a state where both longitudinal end portions 564c of the thin plate supporting portion 564b are supported by the regulating blade support portion 526c of the holder 526 described later.

  The end of the regulating blade 560 opposite to the thin plate support portion 564b side, that is, the tip 560a is not in contact with the developing roller 510, and is a portion separated from the tip 560a by a predetermined distance (that is, the contact portion 562a). ) Is in contact with the developing roller 510 with a width. In other words, the regulating blade 560 is not in contact with the developing roller 510 at the edge but is in contact with the antinode, and the flat surface of the regulating blade 560 comes into contact with the developing roller 510 to regulate the layer thickness. To do. Further, the regulating blade 560 is disposed so that its tip 560a faces the upstream side in the rotation direction of the developing roller 510, and is in contact with a so-called counter. The contact position where the regulating blade 560 contacts the developing roller 510 is below the central axis of the developing roller 510 and below the central axis of the toner supply roller 550. Further, the regulation blade 560 exhibits a function of preventing leakage of the toner T from the toner container 530 by contacting the developing roller 510 along the axial direction thereof.

  As shown in FIG. 12, an end seal 574 is provided on the outer side in the longitudinal direction of the rubber portion 562 of the regulating blade 560. The end seal 574 is formed of a non-woven fabric, contacts the axial end of the developing roller 510 along the peripheral surface of the developing roller 510, and toner from between the peripheral surface and the housing 540. Demonstrates the function of preventing T leakage.

  The holder 526 is a metal member for assembling various members such as the developing roller 510, and as shown in FIG. 11, the upper seal support portion along the longitudinal direction (that is, the axial direction of the developing roller 510). 526a, a developing roller support portion 526b provided outside the upper seal support portion 526a in the longitudinal direction (the axial direction), intersecting the longitudinal direction (the axial direction), and intersecting the developing roller support portion, A regulating blade support portion 526c facing the longitudinal end of the upper seal support portion 526a.

Then, as shown in FIG. 12, the upper seal 520 is supported by the upper seal support portion 526a at its short-side end portion 520a (FIG. 5), and the developing roller 510 is at its end. , And is supported by a developing roller support portion 526b.
Further, the regulating blade 560 is supported by the regulating blade support portion 526c at both longitudinal end portions 564c thereof. The restriction blade 560 is fixed to the holder 526 by being screwed to the restriction blade support portion 526c.

  Thus, the holder 526 in which the upper seal 520, the developing roller 510, and the regulating blade 560 are assembled prevents leakage of the toner T from between the holder 526 and the housing 540, as shown in FIG. It is attached to the housing 540 described above via a housing seal 546 (FIG. 5).

  In the yellow developing device 54 configured as described above, the toner supply roller 550 supplies the toner T stored in the toner container 530 to the developing roller 510. The toner T supplied to the developing roller 510 reaches the contact position of the regulating blade 560 as the developing roller 510 rotates, and when the toner T passes through the contact position, the layer thickness is regulated and a negative charge is applied. Is imparted (negatively charged). The toner T on the developing roller 510 to which the layer thickness is regulated and to which a negative charge is applied is conveyed to a facing position (developing position) facing the photoconductor 20 by further rotation of the developing roller 510, and is moved to the facing position. Then, the latent image formed on the photoconductor 20 is developed.

  Here, the development of the latent image will be described with reference to FIG. As described above, in the printer 10 according to the present embodiment, the jumping development method is used. When the jumping development is executed, a rectangular alternating voltage is applied to the developing roller 510 by the alternating voltage applying unit 132. As shown in FIG. 14, the alternating voltage includes a first voltage V1 and a second voltage V2.

The first voltage V1 is a voltage for directing toner from the developing roller 510 to the photoconductor 20, and its value is -900V. In the present embodiment, as shown in FIG. 14, during development, the potential of the photoconductor 20 is −500 V in the non-image portion (portion corresponding to the white image), and the image portion (portion corresponding to the black image). ) And −50 V, and the toner is negatively charged. Therefore, when the first voltage V1 is applied to the developing roller 510, the developing roller 510 and the photosensitive member 20 are An electric field for directing the toner from the developing roller 510 to the photoconductor 20 is formed, and the toner on the developing roller 510 moves toward the photoconductor 20.
On the other hand, the second voltage V2 is a voltage for directing the toner from the photoconductor 20 to the developing roller 510, and its value is 500V. When the second voltage V <b> 2 is applied to the developing roller 510, an electric field is formed between the developing roller 510 and the photoconductor 20 to direct toner from the photoconductor 20 to the developing roller 510. The toner moves (retracts) to the developing roller 510.

  As shown in FIG. 14, since the first voltage V1 and the second voltage V2 are alternately applied by the alternating voltage application unit 132, the toner is transferred from the developing roller 510 to the photosensitive member when developing the latent image. The movement to 20 and the movement (return) from the photosensitive member 20 to the developing roller 510 are alternately repeated.

  In the present embodiment, the time during which the alternating voltage application unit 132 continues to apply the first voltage V1 and the time during which the second voltage V2 continues are both 0.15 ms (milliseconds). Seconds) (ie, the duty ratio is 50%). Therefore, the period of the alternating voltage (the period is defined as period T1) is 0.3 ms (milliseconds) (see FIG. 14). The average voltage applied to the developing roller 510 by the alternating voltage application unit 132 is larger than the non-image portion potential (−500 V) and smaller than the image portion potential (−50 V), and the value is −. 200 V (= (− 900 + 500) / 2).

  The toner T on the developing roller 510 that has passed the developing position by the rotation of the developing roller 510 passes through the upper seal 520 and is collected in the developing device without being scraped off by the upper seal 520. Further, the toner T still remaining on the developing roller 510 can be peeled off by the toner supply roller 550.

=== Discharge phenomenon ===
As described above, in the printer 10 according to the present embodiment, the first voltage V1 for directing the toner from the developing roller 510 to the photoconductor 20 and the developing roller from the photoconductor 20 when the latent image is developed with toner. An alternating voltage application unit 132 that applies an alternating voltage (development bias) including a second voltage V2 for directing the toner to 510 is applied to the developing roller 510. On the surface of the developing roller 510, Grooves 512 are provided as an example of regularly arranged recesses. As described in the section “Problems to be Solved by the Invention”, in such a printer 10, when the latent image is developed, an image formation defect is caused between the photosensitive member 20 and the developing roller 510. The discharge phenomenon that causes the above may occur.

  In this section, first, the circumstances under which the discharge phenomenon can occur will be described. The printer 10 according to the present embodiment is less likely to cause the discharge phenomenon than the conventional printer. Subsequently, this point (that is, the printer 10 according to the present embodiment is effective). (Gender) will be explained in detail.

<<< Situation where discharge phenomenon may occur >>>
It is known that the discharge phenomenon is likely to occur in the following cases.

1) When the voltage of the alternating voltage is switched When the voltage of the alternating voltage (development bias) is switched, a discharge phenomenon is likely to occur. There are two types of switching of the development bias: switching from a negative voltage to a positive voltage and switching from a positive voltage to a negative voltage. However, the discharge phenomenon is likely to occur in the former case. Is the case. In the printer 10 according to the present embodiment, a discharge phenomenon is likely to occur when the development bias is switched from the first voltage V1 (−900 V) to the second voltage V2 (+500 V).

2) When a boundary portion between the groove portion 512 and the top surface 515 (a recessed portion and a non-recessed portion) is located at a facing position facing the photoconductor 20, the developing roller 510 is provided with a regularly disposed groove portion 512. Therefore, when the developing roller 510 rotates during the development of the latent image, the groove 512 reaches the facing position facing the photoconductor 20 or the top surface 515 reaches the facing position (both are repeated). And when the boundary part (For example, the part shown with the symbol A and B in FIG. 9) of the groove part 512 and the top surface 515 reaches the said opposing position, it becomes easy to generate | occur | produce a discharge phenomenon.
When developing the latent image, the situations 1) and 2) may occur simultaneously. For example, when the boundary between the groove 512 and the top surface 515 reaches the facing position, the developing bias is switched from the first voltage V1 (−900 V) to the second voltage V2 (+500 V). . In such a case, it can be said that the discharge phenomenon can occur remarkably.

<<< Effectiveness of Printer 10 According to the Present Embodiment >>>
In the printer 10 according to the present embodiment, the developing roller 510 rotates such that the development bias period (period T1) described above is the minimum width Lmin of the groove 512 along the circumferential direction of the developing roller 510. This value is larger than the value divided by the moving speed V of the surface of the developing roller 510 (T1> Lmin / V). In the printer 10 according to this embodiment in which the width of the groove 512 and the magnitude of the developing bias cycle satisfy such a relationship, the occurrence of a discharge phenomenon is appropriately suppressed.

  Hereinafter, this matter will be described in more detail with reference to FIGS. As described above, the surface of the developing roller 510 according to the present embodiment is provided with two types of spiral grooves 512 having different inclination angles with respect to the circumferential direction, and the two types of spiral grooves 512 are mutually connected. It intersects to form a lattice shape. The developing roller 510 has a square top surface 515 surrounded by the two types of spiral grooves 512, and one of the two square top surfaces is along the circumferential direction (see FIG. 9). In such a developing roller 510 (shown in FIG. 9), the width of the groove 512 along the circumferential direction of the developing roller 510 is defined in a number of ways, such as a width L1 and a width L2, but the minimum width is The width Lmin shown in FIG. 9 (the distance between AB in FIG. 9). Note that the value of the width Lmin is approximately 70.71 μm.

  Further, as described above, the moving speed V of the surface of the developing roller 510 when the developing roller 510 rotates is 300 mm / s. Accordingly, a value Lmin / V obtained by dividing the minimum width Lmin by the moving speed V of the surface of the developing roller 510 when the developing roller 510 rotates is about 0.236 ms (milliseconds). As shown in FIG. 14, the development bias cycle size (cycle T1) is 0.3 ms. In this embodiment, the relationship of T1> Lmin / V is satisfied.

  Next, how the occurrence of the discharge phenomenon is appropriately suppressed when such a relationship of T1> Lmin / V is satisfied will be described with reference to FIG.

  When the boundary portion between the groove portion 512 and the top surface 515 (for example, portions indicated by symbols A and B in FIG. 9) reaches the facing position, the developing bias is changed from the first voltage V1 (−900 V) to the first bias voltage. In the case of switching to two voltages V2 (+500 V) (in other words, the situation of 1) and 2) described above occurs simultaneously) However, in reality, the discharge phenomenon does not always occur in such a situation, and the occurrence of the discharge phenomenon may be avoided in this situation. However, even if the occurrence of the discharge phenomenon is avoided in this situation during the development of the latent image, if the same situation occurs immediately (without much time interval), the discharge phenomenon is likely to occur at this time. Will occur.

  Attention is now directed to FIG. FIG. 15 is an explanatory diagram for explaining the effectiveness of the printer 10 according to the present embodiment, and shows two diagrams (upper and lower diagrams) and a time axis in order from the top. .

  Here, the lower part of FIG. 15 shows which part of the developing roller 510 is located at a position facing the photoconductor 20 at a certain time t when the development of the latent image is being performed. ing. For example, when developing a latent image, when the portion indicated by symbol A in FIG. 9 is located at the opposite position at time t1, after about 0.236 ms (= Lmin / V) from time t1, The developing roller 510 rotates and the portion indicated by symbol B in FIG. 9 is located at the facing position. Since Lmin is the minimum width, the figure below shows that the situation 1) occurs again after 0.236 ms in the shortest after the situation 1) described above has occurred.

  On the other hand, since the development bias period (0.3 ms) is larger than Lmin / V (0.236 ms), for example, when developing a latent image, the situation 1) and development described above at time t1. Even if the situation in which the bias is switched from the first voltage V1 (−900 V) to the second voltage V2 (+500 V) (that is, the situation 2 described above) occurs at the same time (see the upper and lower diagrams in FIG. 15). Next, when the situation 1) occurs in the shortest time (after 0.236 ms), the situation 2) does not necessarily occur. As described above, in the printer 10 according to the present embodiment, the situation in which the discharge phenomenon can occur remarkably (that is, the situation in which the above 1) and 2) occur simultaneously does not occur continuously in a short time. As a result, the occurrence of the discharge phenomenon is appropriately suppressed.

=== About Density Unevenness Caused by Development Bias and Charging Bias ===
As described in the section “Problems to be Solved by the Invention”, an alternating voltage (developing bias) having a first voltage V1 and a second voltage V2 is applied to the developing roller 510. This is known to cause density unevenness in the image. This density unevenness is likely to occur for each period of the developing bias (period T1). Similarly, a superposed voltage (charging bias) obtained by superimposing a DC voltage and an AC voltage is applied to the charging roller 31. Due to the AC voltage component of the charging bias, image density unevenness occurs. It is known. This density unevenness is likely to occur for each charging bias period (period T2). When these two types of density unevenness occur, if the two types of density unevenness are overlapped, the density unevenness becomes conspicuous. As a result, the density unevenness in the image becomes conspicuous.

  This phenomenon will be specifically described with reference to comparative examples shown in FIGS. 16A to 16C. FIG. 16A is a schematic diagram showing density unevenness due to the developing bias. FIG. 16B is a schematic diagram illustrating density unevenness caused by the charging bias. FIG. 16C is a schematic diagram illustrating a state in which the degree of density unevenness is increased.

  As shown in FIG. 16A, density unevenness caused by the developing bias occurs at every predetermined interval L1. The predetermined interval L1 is a value obtained by multiplying the moving speed of the photosensitive member 20 by the period T1 of the developing bias. Similarly, the density unevenness due to the charging bias occurs at every predetermined interval L2, as shown in FIG. 16B. The predetermined interval L2 is a value obtained by multiplying the moving speed of the photoconductor 20 by the charging bias period T2. These two types of density unevenness occur independently.

  In addition, when an image is formed, the first occurrence position of density unevenness caused by the developing bias and the first occurrence position of density unevenness caused by the charging bias may overlap (region surrounded by a dotted line in FIG. 16C). X1) When the occurrence positions of two types of density unevenness overlap, the density unevenness becomes significant. In this case, for example, when the period T1 of the developing bias is the same as a value obtained by dividing the period T2 of the charging bias by a natural number, the occurrence position of density unevenness due to the charging bias, which occurs thereafter, Since the occurrence position of density unevenness due to the developing bias tends to continuously overlap (region X2 surrounded by a dotted line in FIG. 16C), the density unevenness becomes more noticeable at each predetermined interval L2. It will stand out.

On the other hand, in the printer 10 according to the present embodiment, as shown in FIGS. 3B and 14, the developing bias cycle T1 (0.2 ms) described above is equal to the charging bias cycle T2 (0.9 ms). It differs from both a value obtained by multiplying a natural number and a value obtained by dividing the period T2 by a natural number. That is, T1 and T2 are related to T1 ≠ nT2 (where n is a natural number multiple or a fraction of a natural number). Even in such a case, the occurrence position of density unevenness due to the developing bias and the occurrence position of density unevenness due to the charging bias may overlap, but even if the occurrence positions of the two types of density unevenness overlap, Unlike the comparative example, it is possible to prevent the subsequent occurrence of density unevenness due to the developing bias and the position where density unevenness due to the charging bias from occurring successively from each other. For this reason, it can suppress that the density nonuniformity in an image is conspicuous.
As described above, in the printer 10 according to the present embodiment in which the period T1 of the developing bias and the period T2 of the charging bias satisfy such a relationship, it is possible to suppress the noticeable density unevenness of the image. .

=== Regarding Change Control of Development Bias and Charging Bias Period ===
As described above, the printer 10 can form an image on a medium. Examples of the medium include special paper such as thick paper and an OHP sheet, and plain paper. Then, the printer 10 determines the process speed of the printer (for example, the moving speed of the surface of the photoconductor 20 or the surface of the developing roller 510 according to the type of medium so that an image is appropriately formed according to the type of medium. The moving speed V is changed. Specifically, the printer 10 increases the process speed when forming an image on plain paper, and decreases the process speed when forming an image on special paper.

  In the printer 10 according to the present embodiment, the process speed of the printer is changed according to the type of the medium in order to appropriately suppress the occurrence of the discharge phenomenon and to prevent the density unevenness of the image from being noticeable. As a result (as a result, the moving speed V of the surface of the developing roller 510 is also changed), control for changing the magnitude of the developing bias period and the magnitude of the charging bias period is executed. Specifically, the control unit 100 (1) changes the minimum width Lmin of the groove 512 along the circumferential direction of the developing roller 510 with the magnitude of the period of the developing bias (hereinafter referred to as the period T1) after the change. The development bias period T1 is changed so as to be larger than the value divided by the moving speed V, and (2) a value obtained by multiplying the magnitude of the charging bias period (hereinafter referred to as period T2) by a natural number, In addition, the charging bias period T2 is changed so that the value obtained by dividing the period T2 by a natural number is different from the period T1 after the change of the developing bias.

  Hereinafter, an operation example of the printer 10 according to the present control will be described with reference to FIG. FIG. 17 is a flowchart for explaining the operation of the printer 10 according to this control.

  Various operations when the operation of the printer 10 is executed are mainly realized by the control unit 100. In particular, in the present embodiment, it is realized by the CPU processing a program stored in the ROM. And this program is comprised from the code | cord | chord for performing the various operation | movement demonstrated below.

This control is executed when an image signal and a control signal are input to the printer 10 from a computer which is an external device. This control signal includes information on the type of medium selected by the user or the like (specifically, any one of “plain paper”, “thick paper”, and “OHP sheet”).
First, the control unit 100 determines whether or not the type of the medium included in the control signal matches a predetermined medium type (here, “plain paper” is a predetermined medium type). Is determined (step S102).
In this embodiment, it is assumed that the type of medium included in the control signal is “thick paper”. In such a case, since the medium type (“thick paper”) included in the control signal does not match the predetermined medium type (“plain paper”) (step S102: No), the control unit 100 Then, the process speed (moving speed V of the developing roller 510) is changed (step S104).

FIG. 18 is a table showing the relationship between the type of medium and the moving speed V of the developing roller 510, and is stored in the ROM of the control unit 100. As can be seen from this table, the moving speed V of the developing roller 510 when forming an image on “plain paper” is 300 mm / s, and the developing roller 510 when forming an image on “thick paper” has a moving speed V. The moving speed V is 225 mm / s, and the moving speed V of the developing roller 510 when forming an image on the “OHP sheet” is 150 mm / s.
In this embodiment, since an image is formed on “thick paper”, the control unit 100 changes the moving speed V of the developing roller 510 from 300 mm / s to 225 mm / s.
When the moving speed V of the developing roller 510 is changed, the control unit 100 changes the developing bias period T1 and the charging bias period T2 (steps S106 and S108).

  The table shown in FIG. 18 shows the relationship between the medium type, the developing bias period T1 and the charging bias period T2. For example, when the moving speed V of the developing roller 510 is 225 mm / s, the developing bias cycle T1 is 0.3 ms, and the charging bias cycle T2 is 1.0 ms. As can be seen from the table, the developing bias period T1 and the charging bias period T2 increase as the moving speed V of the developing roller 510 decreases.

  In this embodiment, the moving speed V of the developing roller 510 is changed from 300 mm / s to 225 mm / s. Therefore, the control unit 100 changes the developing bias cycle T1 from 0.3 ms to 0.4 ms and changes the charging bias cycle T2 from 1.0 ms to 1.ms in accordance with the change in the moving speed V of the developing roller 510. Change to 1 ms.

  As described above, when the moving speed V of the developing roller 510 is 300 mm / s, the developing bias cycle T1 (0.3 ms) and the charging bias cycle T2 (1.0 ms) are two. This is a relationship that satisfies the equation (that is, T1> Lmin / V and T1 ≠ nT2). The development bias cycle T1 and the charging bias are set so that these two expressions hold true when the moving speed V of the developing roller 510 is 225 mm / s and when the moving speed is 150 mm / s. The period T2 is set. For this reason, even if the moving speed V of the developing roller 510 is changed according to the type of medium (for example, changed from 300 mm / s to 225 mm / s), the developing bias cycle T1 (0.4 ms) Since the charging bias period T2 (1.1 ms) is changed so that the above-described two equations (ie, T1> Lmin / V and T1 ≠ nT2) are satisfied, the occurrence of the discharge phenomenon is appropriately suppressed. In addition, it is possible to suppress the noticeable density unevenness of the image.

Returning to the flowchart shown in FIG. 17, the description of the operation of the printer 10 according to this control will be continued.
The control unit 100 applies a charging bias to the charging roller 31 to charge the photoconductor 20 (step S110). In this embodiment, the superimposed voltage application unit 133 applies the charging bias whose period T2 is changed to 1.1 ms in step S108 to the rotating charging roller 31, whereby the photoconductor 20 is charged. .

  Next, the control unit 100 applies a developing bias to the developing roller 510 to develop the latent image on the photoconductor 20 (step S112). In this embodiment, the alternating voltage application unit 132 applies the developing bias whose period T1 is changed to 0.4 ms in step S106 to the rotating developing roller 510, thereby developing the latent image.

In the above description, the control unit 100 changes the moving speed V of the developing roller 510, but the medium type included in the control signal matches the predetermined medium type ("plain paper"). (Step S102: Yes), the control unit 100 does not change the moving speed V of the developing roller 510. In such a case, the control unit 100 does not change the cycle T1 of the developing bias and the cycle T2 of the charging bias. That is, the moving speed V of the developing roller 510 is 300 mm / s, the developing bias cycle T1 is 0.3 ms, and the charging bias cycle T2 is 1.0 ms. Then, the superimposed voltage application unit 133 applies a charging bias with a cycle T2 of 1.0 ms to charge the charging roller 31 (step S110), and the alternating voltage application unit 132 has a cycle T1 of 0.3 ms. The latent image is developed by applying a certain developing bias (step S112).
Even in such a case, since the above-described two expressions (that is, T1> Lmin / V and T1 ≠ nT2) are satisfied, the occurrence of the discharge phenomenon is appropriately suppressed and the density unevenness of the image is suppressed from being noticeable. It becomes possible to do.

=== Method for Manufacturing Developing Device ===
Here, a method for manufacturing the developing device will be described with reference to FIGS. 19A to 21. FIG. 19A to FIG. 19E are schematic diagrams showing the transition of the developing roller 510 in the manufacturing process of the developing roller 510. FIG. 20 is an explanatory diagram for explaining the rolling process of the developing roller 510. FIG. 21 is a flowchart for explaining a method of assembling the yellow developing device 54. When the developing device is manufactured, after the housing 540, the holder 526, the developing roller 510, the toner supply roller 550, the regulating blade 560, etc. are manufactured, the developing device is assembled using these members. To be implemented. In this section, the manufacturing method of the developing roller 510 among the manufacturing methods of these members will be described first, and then the developing device assembly method will be described. In the following description, among the black developing device 51, the magenta developing device 52, the cyan developing device 53, and the yellow developing device 54, the yellow developing device 54 will be described as an example.

<<< About Manufacturing Method of Developing Roller 510 >>>
Here, a method for manufacturing the developing roller 510 will be described with reference to FIGS. 19A to 20.

  First, as shown in FIG. 19A, a pipe material 600 as a base material of the developing roller 510 is prepared. The wall thickness of the pipe material 600 is 0.5 to 3 mm. Next, as shown in FIG. 19B, flange press-fit portions 602 are formed at both ends in the longitudinal direction of the pipe material 600. The flange press-fit portion 602 is made by cutting. Next, as shown in FIG. 19C, the flange 604 is press-fitted into the flange press-fit portion 602. In order to ensure the fixing of the flange 604 to the pipe material 600, the flange 604 may be bonded or welded to the pipe material 600 after the flange 604 is press-fitted. Next, as shown in FIG. 19D, centerless polishing is performed on the surface of the pipe member 600 into which the flange 604 is press-fitted. The centerless polishing is performed over the entire surface, and the 10-point average roughness Rz of the surface after the centerless polishing is 1.0 μm or less. Next, as shown in FIG. 19E, the pipe material 600 into which the flange 604 is press-fitted is subjected to a rolling process. In the present embodiment, so-called through-feed rolling (also called step rolling or through rolling) using two round dies 650 and 652 is performed.

  That is, as shown in FIG. 20, two round dies 650 and 652 arranged so as to sandwich the pipe material 600 as a work are placed on the pipe material 600 with a predetermined pressure (the direction of the pressure in FIG. The two round dies 650 and 652 are rotated in the same direction (see FIG. 20) in a state where they are pressed with a symbol P). In the through feed rolling, as the round dies 650 and 652 rotate, the pipe material 600 rotates in the direction opposite to the rotation direction of the round dies 650 and 652 (see FIG. 20). Move in the direction shown. Protrusions 650 a and 652 a for forming grooves 680 are provided on the surfaces of the round dies 650 and 652, and the grooves 680 are formed in the pipe material 600 by deforming the pipe material 600 by the protrusions 650 a and 652 a. Is formed.

  Then, after the rolling process is finished, the surface of the central portion 510a is plated. In the present embodiment, electroless Ni—P plating is used as the plating, but is not limited to this, and for example, hard chrome plating or electroplating may be used.

<<< Assembly Method of Yellow Developing Device 54 >>>
Next, a method for assembling the yellow developing device 54 will be described with reference to FIG.
First, the housing 540, the holder 526, the developing roller 510, the regulating blade 560 and the like described above are prepared (step S2). Next, the regulating blade 560 is fixed to the holder 526 by screwing the regulating blade 560 to the regulating blade support 526c of the holder 526 (step S4). Note that the end seal 574 described above is attached to the regulating blade 560 in advance before the step S4.

  Next, the developing roller 510 is attached to the holder 526 to which the regulating blade 560 is fixed (step S6). At this time, the developing roller 510 is attached to the holder 526 so that the regulating blade 560 comes into contact with the other end of the developing roller 510 in the axial direction. Note that the above-described upper seal 520 is attached to the holder 526 in advance before the step S6.

  Then, the assembly of the yellow developing device 54 is completed by attaching the holder 526 to which the developing roller 510, the regulating blade 560, and the like are attached to the housing 540 via the housing seal 546 (step S8). The toner supply roller 550 described above is previously attached to the housing 540 before step S8.

=== Other Embodiments ===
The image forming apparatus and the like according to the present invention have been described above based on the above embodiment. However, the above embodiment of the present invention is for facilitating understanding of the present invention and limits the present invention. is not. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes the equivalents thereof.

  In the above embodiment, an intermediate transfer type full color laser beam printer has been described as an example of the image forming apparatus. However, the present invention is not limited to the intermediate transfer type, such as a full color laser beam printer, a monochrome laser beam printer, a copying machine, and a facsimile. The present invention can be applied to various image forming apparatuses.

  Also, the photosensitive member is not limited to a so-called photosensitive roller, which is configured by providing a photosensitive layer on the outer peripheral surface of a cylindrical conductive substrate, and is configured by providing a photosensitive layer on the surface of a belt-shaped conductive substrate. A so-called photosensitive belt may be used.

In the above embodiment, as shown in FIG. 3A, the charging member is a rotatable charging roller 31, and the charging roller 31 faces the photoconductor 20 with a gap (that is, the charging roller). 31 is that the photosensitive member 20 is charged in a non-contact state with the photosensitive member 20), but is not limited thereto. For example, the charging roller 31 may charge the photoconductor 20 in contact with the photoconductor 20.
However, in the case of so-called non-contact charging in which the charging roller 31 is not in contact with the photoreceptor 20, it is known that density unevenness is likely to occur due to charging. Therefore, the effect of the printer 10 according to the above embodiment in which the period T1 of the developing bias and the period T2 of the charging bias satisfy the relationship of T1 ≠ nT2, that is, the effect of suppressing the conspicuous density unevenness of the image can be suppressed. The above embodiment is more desirable in that it is more effective.

In the above embodiment, as shown in FIG. 19, the types of media on which an image can be formed are plain paper and cardboard. When an image is formed on the plain paper, the surface of the developing roller 510 is When the moving speed V is increased (300 mm / s) and an image is formed on the thick paper, the moving speed V on the surface of the developing roller 510 is decreased (150 mm / s). Is not to be done. For example, the moving speed V of the developing roller 510 may be changed according to the environment in which the printer 10 is installed.
When the moving speed V of the developing roller 510 is changed according to the type of medium, the degree of change tends to increase in order to form an image according to the medium. Therefore, by changing the developing bias cycle T1 and the charging bias cycle T2 in accordance with the moving speed V of the developing roller 510, the above-described two equations (that is, T1> Lmin / V and T1 ≠ nT2) can be established reliably. As a result, even if the type of the medium is changed, the above embodiment is more preferable in that the occurrence of the discharge phenomenon can be appropriately suppressed and the density unevenness of the image can be suppressed.

In the above embodiment, the concave portions are two types of spiral groove portions 512 having different inclination angles with respect to the circumferential direction of the developing roller 510, and the two types of spiral groove portions 512 intersect with each other to form a lattice. The shape is assumed to be, but is not limited to this.
For example, the recess may not be a groove. Moreover, when a recessed part is a groove part, a groove part does not need to be helical. Further, only one type of groove may be provided as the recess.

Further, in the above embodiment, the developing roller 510 has a rhombus top surface 515 surrounded by the two types of spiral grooves 512, and among the two diagonal lines that the rhombus top surface 515 has However, the present invention is not limited to this.
For example, as shown in FIG. 22A, both of the two diagonal lines on the top surface of the rhombus may not be along the circumferential direction.

In the above embodiment, the developing roller 510 has the square top surface 515 surrounded by the two types of spiral grooves 512, but the invention is not limited to this.
For example, as shown in FIG. 22B, the top surface may be a diamond that is not square. Further, the top surface is not a rhombus, and may be a circle as shown in FIG. 22C, for example. 22A to 22C are diagrams showing variations on the surface shape of the developing roller 510 (in each figure, the above-described minimum width Lmin is shown as reference information).

Moreover, in the said embodiment, although the groove part 512 was provided with the bottom face 513 and the side surface 514, and the inclination angle of the side surface 514 was about 45 degree | times (refer FIG. 8), it is limited to this. For example, the inclination angle of the side surface 514 may be about 90 degrees.
In the above embodiment, the alternating voltage application unit 132 applies only the first voltage V1 and the second voltage V2 to the developing roller 510, and the alternating voltage application unit 132 includes the first voltage V1 and the second voltage V2. The voltage V2 and the voltage V2 are alternately applied, but the present invention is not limited to this. For example, the alternating voltage application unit 132 may apply an alternating voltage as shown in FIG. 23A.
In the above embodiment, the duty ratio of the alternating voltage is 50%. However, the present invention is not limited to this, and an alternating voltage as shown in FIG. 23B may be used.
FIG. 23A and FIG. 23B are diagrams showing variations of the alternating voltage (and each figure shows the above-described period size T1 as reference information).

=== Configuration of Image Forming System etc. ===
Next, an embodiment of an “image forming system” which is an example of an embodiment according to the present invention will be described with reference to the drawings.

  FIG. 24 is an explanatory diagram showing an external configuration of the image forming system. The image forming system 700 includes a computer 702, a display device 704, a printer 706, an input device 708, and a reading device 710. In this embodiment, the computer 702 is housed in a mini-tower type housing, but is not limited thereto. The display device 704 is generally a CRT (Cathode Ray Tube), a plasma display, a liquid crystal display device, or the like, but is not limited thereto. As the printer 706, the printer described above is used. In this embodiment, the input device 708 uses a keyboard 708A and a mouse 708B, but is not limited thereto. In this embodiment, the reading device 710 uses a flexible disk drive device 710A and a CD-ROM drive device 710B. However, the reading device 710 is not limited to this. Disk) etc. may be used.

  FIG. 25 is a block diagram showing a configuration of the image forming system shown in FIG. An internal memory 802 such as a RAM and an external memory such as a hard disk drive unit 804 are further provided in a housing in which the computer 702 is housed.

  In the above description, the example in which the printer 706 is connected to the computer 702, the display device 704, the input device 708, and the reading device 710 to configure the image forming system has been described. However, the present invention is not limited to this. Absent. For example, the image forming system may include a computer 702 and a printer 706, and the image forming system may not include any of the display device 704, the input device 708, and the reading device 710.

  For example, the printer 706 may have a part of the functions or mechanisms of the computer 702, the display device 704, the input device 708, and the reading device 710. As an example, the printer 706 includes an image processing unit that performs image processing, a display unit that performs various displays, a recording medium attachment / detachment unit for attaching / detaching a recording medium that records image data captured by a digital camera or the like. It is good also as a structure to have.

  The image forming system realized in this way is a system superior to the conventional system as a whole system.

  DESCRIPTION OF SYMBOLS 10 Printer, 20 Photoconductor, 30 Charging unit, 31 Charging roller, 32 Tape, 33 Bearing, 34 Spring, 35 Cleaning roller, 40 Exposure unit, 50 YMCK developing unit, 50a Central axis, 51 Black developing device, 52 Magenta developing device , 53 Cyan developing device, 54 Yellow developing device, 55a, 55b, 55c, 55d Holding unit, 60 Primary transfer unit, 70 Intermediate transfer member, 75 Cleaning unit, 76 Cleaning blade, 80 Secondary transfer unit, 90 Fixing unit, 92 Paper feed tray, 94 Paper feed roller, 95 Display unit, 96 Registration roller, 100 Control unit, 101 Main controller, 102 Unit controller, 112 Interface, 113 Image memory, 128 YMC K developing unit drive control circuit, 129 charging unit drive control circuit, 132 alternating voltage application unit, 133 superposed voltage application unit, 510 developing roller, 510a center portion, 510b shaft portion, 512 groove portion, 512a first groove portion, 512b second groove portion 513 Bottom surface, 514 Side surface, 515 Top surface, 520 Top seal, 520a Short end, 520b Contact surface, 520c Opposite surface, 524 Top seal biasing member, 526 Holder, 526a Top seal support, 526b Developer roller Support portion, 526c Regulating blade support portion, 530 Toner container, 530a First toner storage portion, 530b Second toner storage portion, 540 Housing, 542 Upper housing portion, 544 Lower housing portion, 545 Partition wall, 546 Housing seal, 550 Toner supply roller 56 Regulating blade, 560a tip, 562 Rubber part, 562a Contact part, 564 Rubber support part, 564a Thin plate, 564b Thin plate support part, 564c Longitudinal ends, 564d Short end, 564e Short end, 572 Opening, 574 End seal, 576 Bearing, 600 Pipe material, 602 Flange press-fitting part, 604 Flange, 650 Round die, 650a Convex part, 652 Round die, 652a Convex part, 680 Groove, 700 Image forming system, 702 Computer, 704 Display device, 706 printer, 708 input device, 708A keyboard, 708B mouse, 710 reader, 710A flexible disk drive device, 710B CD-ROM drive device, 802 internal memory, 804 hard disk drive unit Door, T toner.

Claims (2)

An image carrier for carrying a latent image;
A charging member for charging the image carrier;
A developer carrying member for transporting the developer to a facing position facing the image carrier by rotating regularly in a state where the developer has the developer on the surface,
For developing the latent image by the developer conveyed to the facing position, a first voltage for directing the developer from the developer carrier to the image carrier and the developer from the image carrier An alternating voltage having a second voltage for directing the developer to the carrier, and an alternating voltage application unit for applying to the developer carrier,
A superimposed voltage application unit that applies a superimposed voltage in which a DC voltage and an AC voltage are superimposed on the charging member;
A control unit for controlling the alternating voltage and the superimposed voltage;
An image forming apparatus having
The period of the alternating voltage is
Of all the convex portions existing in the axial direction of the developing carrier, the first convex portion and the first convex portion that are closest to each other in the direction perpendicular to the axial direction are present. Divide the minimum width of the top surfaces of the second convex portion perpendicular to the circumferential direction of the developer carrier by the moving speed of the surface of the developer carrier when the developer carrier rotates. It was much larger than the value,
Control by the control unit so as to be different from both a value obtained by multiplying the magnitude of the cycle of the superimposed voltage by a natural number and a value obtained by dividing the magnitude of the cycle by a natural number;
An image forming apparatus. The image forming apparatus according to claim 1,
The convex portion has a rectangular top surface;
An image forming apparatus, wherein one of two diagonal lines on the top surface of the quadrangle is along the circumferential direction.

Images