Patent Publication Number: US-7899375-B2

Title: Developing apparatus, image forming apparatus, image forming system and image forming method

Description:
The disclosures of Japanese Patent Application No. 2007-096603 which is filed Apr. 2, 2007, Japanese Patent Application No. 2007-134101 which is filed on May 21, 2007, and Japanese Patent Application No. 2007-195001, Japanese Patent Application No. 2007-195002, and Japanese Patent Application No. 2007-195003 which are filed on Jul. 26, 2007, including specifications, drawings and claims are incorporated herein by reference in its entireties. 
     BACKGROUND 
     The present invention relates to a developing apparatus, an image forming apparatus, an image forming system, and an image forming method. 
     An image forming apparatus such as a laser beam printer is known well. Such an image forming apparatus includes an image carrier holding a latent image and a developing apparatus developing the latent image held by the image carrier by the use of a developer. When an image signal, etc. is transmitted from an external apparatus such as a computer, the image forming apparatus forms a developer image and then transfers the developer image onto a medium, thereby finally forming an image on the medium. 
     The developing apparatus includes a developer carrier rotating with a developer held thereon and the developer carrier develops the latent image held by the image carrier by the use of the developer. Concave portions regularly arranged might be formed on the surface of the developer carrier so as to hold a sufficient amount of developer. The developing apparatus might be provided with a contact member being made of a rubber elastic body and coming in contact with the surface of the developer carrier. An example of the contact member is a layer thickness regulating member regulating the layer thickness of the developer held by the developer carrier. 
     Patent Document 1: Japanese Patent Publication No. 2006-259384A 
     It is known that the contact member made of a rubber elastic body exhibits a rubber-like characteristic or a glass-like characteristic depending on the temperature of the contact member. At the temperature at which the contact member usually operates, the contact member exhibits the rubber-like characteristic. Accordingly, even when the contact member is disposed in the developing apparatus, it is required that the contact member should be used with the rubber-like characteristic. 
     It is also known that the contact member may vibrate and the contact member exhibits the rubber-like characteristic or the glass-like characteristic depending on the magnitude of the vibration frequency. That is, it is assumed that a value obtained by dividing the loss elastic modulus of the contact member by the storage elastic modulus is a loss tangent (tan δ). Then, when the frequency of the contact member is greater than the frequency at which the loss tangent (tan δ) is the greatest (hereinafter, also referred to as “greatest loss tangent frequency”), the contact member exhibits the glass-like characteristic. On the other hand, when the frequency of the contact member is smaller than the greatest loss tangent frequency, the contact member exhibits the rubber-like characteristic. 
     As described above, the contact member is in contact with the surface (which includes the concave portions) of the developer carrier and the developer carrier frictionally slides on the contact member at the time of rotation thereof, thereby causing the contact member to vibrate. When the number of vibrations of the contact member vibrating with the rotation of the developer carrier is greater than the greatest loss tangent frequency, the contact member exhibits the glass-like characteristic and thus the above-mentioned requirement cannot be satisfied. 
     It is known that the contact member may vibrate with the rotation of the developer carrier and the contact member exhibits the rubber-like characteristic or the glass-like characteristic depending on the number of vibrations. Accordingly, in order to satisfy the above-mentioned requirement, it is preferable that the frequency of the contact member at the time of the rotation of the developer carrier is controlled so as for the contact member to exhibit the rubber-like characteristic. 
     On the other hand, when the contact member is used with the rubber-like characteristic, abnormal noises may be generated with the vibration of the contact member. Here, the contact member made of the rubber elastic body exhibits dynamic viscoelasticity (an elastic behavior and a viscous behavior). When the elastic behavior of the two behaviors is superior, the amplitude of the vibration of the contact member increases and thus the abnormal noises are easily generated. 
     It is known that the contact member may vibrate with the rotation of the developer carrier and the contact member exhibits the rubber-like characteristic or the glass-like characteristic depending on the magnitude of the number of vibrations. Accordingly, in order to satisfy the above-mentioned requirements it is preferable that the frequency of the contact member is controlled so as for the contact member to exhibit the rubber-like characteristic. 
     On the other hand, when the contact member is used with the rubber-like characteristic, the temperature of the contact member may rise with the vibration of the contact member. Here, the contact member made of the rubber elastic body exhibits dynamic viscoelasticity (an elastic behavior and a viscous behavior). When the viscous behavior of the two behaviors is superior, the molecular chains constituting the contact member easily vibrates and thus heat may be easily generated. As a result, the temperature of the contact member easily rises. 
     As described above, the contact member is in contact with the surface of the developer carrier and the surface of the developer carrier is provided with concave portions regularly arranged. Accordingly, when the developer carrier rotates, the developer carrier slides on the contact member and thus the contact vibrates. 
     When the number of vibrations of the contact member (the value obtained by dividing the movement speed of the surface with the rotation of the developer carrier by the pitch of the concave portions in the peripheral direction of the developer carrier corresponds to the number of vibrations) is too great, it is known that the contact member made of the rubber elastic body exhibits the glass-like characteristic, not the rubber-like characteristic. Accordingly, at the time of development, it is necessary to allow the developer carrier to rotate at a rotation speed at which the frequency is too great (that is, the contact member does not exhibit the glass-like characteristic). 
     However, when the development is made in a state where the contact member exhibits the rubber-like characteristic, a filming is generated in the contact member due to tackiness of the contact member based on the rubber-like characteristic. When the filming becomes remarkable, the quality of an image developed and finally formed on the medium is deteriorated. 
     SUMMARY 
     An object of the invention is to provide a developing apparatus, an image forming apparatus, and an image forming system in which the contact member is properly used with the rubber-like characteristic at the time of rotation of the developer carrier. 
     Another object of the invention is to properly use the contact member with the rubber-like characteristic at the time of rotation of the developer carrier and to suppress abnormal noises from being generated with the vibration of the contact member. 
     Another object of the invention is to properly use the contact member with the rubber-like characteristic at the time of rotation of the developer carrier and to suppress the temperature from rising. 
     Another object of the invention is to properly prevent the image quality from being deteriorated. 
     In order to accomplish the above-mentioned objects, according to a first aspect of the invention, there is provided a developing apparatus including: a developer carrier having concave portions regularly arranged on the surface thereof and being rotatable with a developer thereon; and a contact member being made of an elastic rubber material, being in contact with the surface of the developer carrier, and vibrating with the rotation of the developer carrier, wherein a value obtained by dividing a movement speed of the surface at the time of rotation of the developer carrier by a pitch of the concave portions in a peripheral direction of the developer carrier is smaller than the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest. 
     In the developing apparatus, it is preferable that the contact member is a layer thickness regulating member coming in contact with the surface to regulate the layer thickness of the developer held in the developer carrier. In this case, the layer thickness regulating member is used with a glass-like characteristic, thereby preventing the layer thickness of the developer from being improperly regulated. 
     In the developing apparatus, it is preferable that the contact member is in contact with the surface so that the longitudinal direction thereof is parallel to the axial direction of the developer carrier and an end in the width direction faces the upstream in the rotation direction of the developer carrier and that a contact portion of the contact member is apart from the end in the width direction. 
     In the developing apparatus, it is preferable that the concave portions are two types of spiral grooves having different tilt angles about the peripheral direction, the two types of spiral grooves intersect each other to form a lattice shape, the developer carrier has square-like top faces surrounded with the two types of spiral grooves, and one of two diagonals of each square-like top face is parallel to the peripheral direction. In this case, the regular concave portions can be easily formed on the surface of the developer carrier. 
     In the developing apparatus, it is preferable that the developing apparatus can be mounted on and demounted from an image forming apparatus body of an image forming apparatus, an operating temperature range is set in the image forming apparatus, the number of vibrations of the contact member when the loss tangent is the greatest varies depending on the magnitude of a temperature, and the value obtained by dividing the movement speed of the surface at the time of rotation of the developer carrier by the pitch of the concave portions in the peripheral direction of the developer carrier is smaller than the number of vibrations of the contact member when the loss tangent is the greatest at all the temperatures in the operating temperature range. In this case, the contact member is necessarily used with a rubber-like characteristic when the image forming apparatus forms an image. 
     In the developing apparatus, it is preferable that the contact member is made of thermoplastic elastomer. 
     In the developing apparatus, it is preferable that the value obtained by dividing the movement speed of the surface at the time of rotation of the developer carrier by the pitch of the concave portions in the peripheral direction of the developer carrier is smaller than the number of vibrations of the contact member when the loss tangent is the greatest and is smaller than the number of vibrations at which the loss tangent at the number of vibrations is a half of the greatest value. In this case, the contact member is more properly used with the rubber-like characteristic. 
     Similarly, according to the first aspect of the invention, there is provided an image forming apparatus including: (a) an image carrier holding a latent image; and (b) a developing apparatus developing the latent image held by the image carrier with a developer, (c) wherein the developing apparatus includes: a developer carrier having concave portions regularly arranged on the surface thereof and being rotatable with the developer thereon; and a contact member being made of an elastic rubber material, being in contact with the surface of the developer carrier, and vibrating with the rotation of the developer carrier, wherein a value obtained by dividing a movement speed of the surface at the time of rotation of the developer carrier by a pitch of the concave portions in a peripheral direction of the developer carrier is smaller than the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest. According to the image forming apparatus, the contact member can be used with the rubber-like characteristic at the time of rotation of the developer carrier. 
     Similarly, according to the first aspect of the invention, there is provided an image forming system including: (A) a computer; and (B) an image forming apparatus connectable to the computer, (C) wherein the image forming apparatus includes: (a) an image carrier holding a latent image; and (b) a developing apparatus developing the latent image held by the image carrier with a developer, (c) wherein the developing apparatus includes: a developer carrier having concave portions regularly arranged on the surface thereof and being rotatable with the developer thereon; and a contact member being made of an elastic rubber material, being in contact with the surface of the developer carrier, and vibrating with the rotation of the developer carrier, wherein a value obtained by dividing a movement speed of the surface at the time of rotation of the developer carrier by a pitch of the concave portions in a peripheral direction of the developer carrier is smaller than the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest. According to the image forming system, the contact member can be used with the rubber-like characteristic at the time of rotation of the developer carrier. 
     In order to accomplish the above-mentioned object, according to a second aspect of the invention, there is provided a developing apparatus including: a developer carrier having concave portions regularly arranged on the surface thereof and being rotatable with a developer thereon; and a contact member being made of an elastic rubber material, being in contact with the surface of the developer carrier, and vibrating with the rotation of the developer carrier, wherein a value obtained by dividing a movement speed of the surface at the time of rotation of the developer carrier by a pitch of the concave portions in a peripheral direction of the developer carrier has the same magnitude of the number of vibrations at which the storage elastic modulus is smaller than the loss elastic modulus among the numbers of vibrations smaller than the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest. According to the developing apparatus, it is possible to properly use the contact member with the rubber-like characteristic at the time of rotation of the developer carrier and to suppress the generation of an abnormal noise resulting from the vibration of the contact member. 
     In the developing apparatus, it is preferable that the contact member is a layer thickness regulating member coming in contact with the surface to regulate the layer thickness of the developer held in the developer carrier. In this case, the layer thickness regulating member can be used with the rubber-like characteristic, thereby properly regulating the layer thickness of the developer. 
     In the developing apparatus, it is preferable that the concave portions are two types of spiral grooves having different tilt angles about the peripheral direction, the two types of spiral grooves intersect each other to form a lattice shape, the developer carrier has square-like top faces surrounded with the two types of spiral grooves, and one of two diagonals of each square-like top face is parallel to the peripheral direction. In this case, the regular concave portions can be easily formed on the surface. 
     Similarly, according to the second aspect of the invention, there is provided an image forming apparatus including: (a) an image carrier holding a latent image; and (b) a developing apparatus developing the latent image held by the image carrier with a developer, (c) wherein the developing apparatus includes: a developer carrier having concave portions regularly arranged on the surface thereof and being rotatable with a developer thereon; and a contact member being made of an elastic rubber material, being in contact with the surface of the developer carrier, and vibrating with the rotation of the developer carrier, wherein a value obtained by dividing a movement speed of the surface at the time of rotation of the developer carrier by a pitch of the concave portions in a peripheral direction of the developer carrier has the same magnitude of the number of vibrations at which the storage elastic modulus is smaller than the loss elastic modulus among the numbers of vibrations smaller than the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest. According to the image forming apparatus, it is possible to properly use the contact member with the rubber-like characteristic at the time of rotation of the developer carrier and to suppress the generation of an abnormal noise resulting from the vibration of the contact member. 
     Similarly, according to the second aspect of the invention, there is provided an image forming system including: (A) a computer; and (B) an image forming apparatus connectable to the computer, (C) wherein the image forming apparatus includes: (a) an image carrier holding a latent image; and (b) a developing apparatus developing the latent image held by the image carrier with a developer, (c) wherein the developing apparatus includes: a developer carrier having concave portions regularly arranged on the surface thereof and being rotatable with a developer thereon; and a contact member being made of an elastic rubber material, being in contact with the surface of the developer carrier, and vibrating with the rotation of the developer carrier, wherein a value obtained by dividing a movement speed of the surface at the time of rotation of the developer carrier by a pitch of the concave portions in a peripheral direction of the developer carrier has the same magnitude of the number of vibrations at which the storage elastic modulus is smaller than the loss elastic modulus among the numbers of vibrations smaller than the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest. According to the image forming system, it is possible to properly use the contact member with the rubber-like characteristic at the time of rotation of the developer carrier and to suppress the generation of an abnormal noise resulting from the vibration of the contact member. 
     In order to accomplish the above-mentioned object, according to a third aspect of the invention, there is provided a developing apparatus including: a developer carrier having concave portions regularly arranged on the surface thereof and being rotatable with a developer thereon; and a contact member being made of an elastic rubber material, being in contact with the surface of the developer carrier, and vibrating with the rotation of the developer carrier, wherein a value obtained by dividing a movement speed of the surface at the time of rotation of the developer carrier by a pitch of the concave portions in a peripheral direction of the developer carrier has the same magnitude of the number of vibrations at which the loss elastic modulus is smaller than the storage elastic modulus among the numbers of vibrations smaller than the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest. According to the developing apparatus, it is possible to properly use the contact member with the rubber-like characteristic at the time of rotation of the developer carrier and to suppress the increase in temperature of the contact member. 
     In the developing apparatus, it is preferable that the contact member is a layer thickness regulating member coming in contact with the surface to regulate the layer thickness of the developer held in the developer carrier. In this case, the layer thickness regulating member can be properly used with the rubber-like characteristic, thereby properly regulating the layer thickness of the developer. 
     In the developing apparatus, it is preferable that the layer thickness regulating member is in contact with the surface so that the longitudinal direction thereof is parallel to the axial direction of the developer carrier and an end in the width direction faces the upstream in the rotation direction of the developer carrier, and a contact portion of the layer thickness regulating member is apart from the end in the width direction. In this case, the generation of the filming between the contact portion and an end is suppressed. 
     In the developing apparatus, it is preferable that the concave portions are two types of spiral grooves having different tilt angles about the peripheral direction, the two types of spiral grooves intersect each other to form a lattice shape, the developer carrier has square-like top faces surrounded with the two types of spiral grooves, and one of two diagonals of each square-like top face is parallel to the peripheral direction. In this case, the regular concave portions can be easily formed on the surface. 
     Similarly, according to the third aspect of the invention, there is provided an image forming apparatus including: (a) an image carrier holding a latent image; and (b) a developing apparatus developing the latent image held by the image carrier with a developer, (c) wherein the developing apparatus includes: a developer carrier having concave portions regularly arranged on the surface thereof and being rotatable with a developer thereon; and a contact member being made of an elastic rubber material, being in contact with the surface of the developer carrier, and vibrating with the rotation of the developer carrier, wherein a value obtained by dividing a movement speed of the surface at the time of rotation of the developer carrier by a pitch of the concave portions in a peripheral direction of the developer carrier has the same magnitude of the number of vibrations at which the loss elastic modulus is smaller than the storage elastic modulus among the numbers of vibrations smaller than the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest. According to the image forming apparatus, it is possible to properly use the contact member with the rubber-like characteristic at the time of rotation of the developer carrier and to suppress the increase in temperature of the contact member. 
     Similarly, according to the third aspect of the invention, there is also provided an image forming system including: (A) a computer; and (B) an image forming apparatus connectable to the computer, (C) wherein the image forming apparatus includes: (a) an image carrier holding a latent image; and (b) a developing apparatus developing the latent image held by the image carrier with a developer, (c) wherein the developing apparatus includes: a developer carrier having concave portions regularly arranged on the surface thereof and being rotatable with a developer thereon; and a contact member being made of an elastic rubber material, being in contact with the surface of the developer carrier, and vibrating with the rotation of the developer carrier, wherein a value obtained by dividing a movement speed of the surface at the time of rotation of the developer carrier by a pitch of the concave portions in a peripheral direction of the developer carrier has the same magnitude of the number of vibrations at which the loss elastic modulus is smaller than the storage elastic modulus among the numbers of vibrations smaller than the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest. According to the image forming system, it is possible to properly use the contact member with the rubber-like characteristic at the time of rotation of the developer carrier and to suppress the increase in temperature of the contact member. 
     In order to accomplish the above-mentioned object, according to a fourth aspect of the invention, there is provided an image forming apparatus including: (A) an image carrier holding a latent image; (B) a developer carrier having concave portions regularly arranged on a surface thereof, being rotatable with a developer held thereon, and developing the latent image with the developer held thereon; (C) a contact member made of an elastic rubber material being in contact with the surface of the developer carrier and vibrating with the rotation of the developer carrier; and (CD) a controller starting the rotation of the developer carrier, then raising a rotation speed of the developer carrier to a first rotation speed at which a movement speed of the surface at the time of rotation of the developer carrier is greater than a product of a pitch of the concave portions in a peripheral direction of the developer carrier and the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest, lowering the rotation speed of the developer carrier to a second rotation speed at which the movement speed is smaller than the product after the rotation speed of the developer carrier becomes the first rotation speed, and allowing the developer carrier rotating at the second rotation speed to develop the latent image. According to the image forming apparatus, it is possible to properly prevent the deterioration in image quality. 
     The image forming apparatus may further include a developing bias application section applying a developing bias for developing the latent image to the developer carrier, and the controller may lower the rotation speed of the developer carrier from the first rotation speed to the second rotation speed via a third rotation speed at which the movement speed is equal to the product after the rotation speed of the developer carrier becomes the first rotation speed and starts the application of the developing bias from the developing bias application section after the rotation speed of the developer carrier becomes the third rotation speed. 
     In this case, the filming can be properly collected. 
     The controller may start the application of the developing bias from the developing bias application section after a time point in a time period, when a portion, on the surface of the developer carrier, in contact with the contact member when the rotation speed of the developer carrier becomes the third rotation speed moves to a position opposed to the image carrier with an additional rotation of the developer carrier, after the rotation speed of the developer carrier becomes the third rotation speed. 
     In this case, the filming can be more properly collected. 
     In order to accomplish the above-mentioned object, according to a fifth aspect of the invention, there is provided an image forming apparatus including: (A) an image carrier holding a latent image; (B) a developer carrier having concave portions regularly arranged on a surface thereof being rotatable with a developer held thereon, and developing the latent image with the developer held thereon; (C) a contact member made of an elastic rubber material being in contact with the surface of the developer carrier and vibrating with the rotation of the developer carrier; and (D) a controller allowing the developer carrier which rotates at a fifth rotation speed at which a movement speed of the surface at the time of rotation of the developer carrier is smaller than a product of a pitch of the concave portions in a peripheral direction of the developer carrier and the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest, to develop the latent image, raising the rotation speed of the developer carrier to a fourth rotation speed at which the movement speed is greater than the product after the developing of the latent image is ended, and stopping the rotation of the developer carrier after the rotation speed of the developer carrier becomes the fourth rotation speed. 
     According to the image forming apparatus, it is possible to properly prevent the deterioration in image quality. 
     The image forming apparatus may further include a developing bias application section applying a developing bias for developing the latent image to the developer carrier, and the controller may raise the rotation speed of the developer carrier from the fifth rotation speed to the fourth rotation speed via a third rotation speed at which the movement speed is equal to the product after ending the developing of the latent image, and may stop the application of the developing bias from the developing bias application section before a time point in a time period, when a portion, on the surface of the developer carrier, in contact with the contact member when the rotation speed of the developer carrier becomes the third rotation speed moves to a position opposed to the image carrier with an additional rotation of the developer carrier, after the rotation speed of the developer carrier becomes the third rotation speed. 
     In this case, the filming can be properly collected. 
     The controller may stop the application of the developing bias from the developing bias application section before the rotation speed of the developer carrier becomes the third rotation speed. 
     In this case, the filming can be more properly collected. 
     The image forming apparatus may further include a rake-out member coming in contact with the surface of the developer carrier to rake out the developer from the developer carrier. Here, the controller may stop the rotation after a time point in a time period, when a portion, on the surface of the developer carrier, in contact with the contact member when the rotation speed of the developer carrier becomes the third rotation speed moves to a position opposed to the image carrier with an additional rotation of the developer carrier, after the rotation speed of the developer carrier becomes the third rotation speed, at the time of stopping the rotation of the developer carrier after the rotation speed of the developer carrier becomes the fourth rotation speed. 
     In this case, the filming can be properly raked out by the rake-out member before the developer carrier is stopped. 
     Similarly, according to the fourth aspect of the invention, there is provided an image forming system including: a computer; and an image forming apparatus being connectable to the computer, wherein the image forming apparatus includes: an image carrier holding a latent image; a developer carrier having concave portions regularly arranged on a surface thereof, being rotatable with a developer held thereon, and developing the latent image with the developer held thereon; a contact member made of an elastic rubber material being in contact with the surface of the developer carrier and vibrating with the rotation of the developer carrier; and a controller starting the rotation of the developer carrier, then raising a rotation speed of the developer carrier to a first rotation speed at which a movement speed of the surface at the time of rotation of the developer carrier is greater than a product of a pitch of the concave portions in a peripheral direction of the developer carrier and the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest, lowering the rotation speed of the developer carrier to a second rotation speed at which the movement speed is smaller than the product after the rotation speed of the developer carrier becomes the first rotation speed, and allowing the developer carrier rotating at the second rotation speed to develop the latent image. 
     According to the image forming system, it is possible to properly prevent the deterioration in image quality. 
     Similarly, according to the fifth aspect of the invention, there is provided an image forming system including: a computer; and an image forming apparatus being connectable to the computer, wherein the image forming apparatus includes: an image carrier holding a latent image; a developer carrier having concave portions regularly arranged on a surface thereof, being rotatable with a developer held thereon, and developing the latent image with the developer held thereon; a contact member made of an elastic rubber material being in contact with the surface of the developer carrier and vibrating with the rotation of the developer carrier; and a controller allowing the developer carrier which rotates at a fifth rotation speed at which a movement speed of the surface at the time of rotation of the developer carrier is smaller than a product of a pitch of the concave portions in a peripheral direction of the developer carrier and the number of vibrations of the contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus is the greatest, to develop the latent image, raising the rotation speed of the developer carrier to a fourth rotation speed at which the movement speed is greater than the product after the developing of the latent image is ended, and stopping the rotation of the developer carrier after the rotation speed of the developer carrier becomes the fourth rotation speed. 
     According to the image forming system, it is possible to properly prevent the deterioration in image quality. 
     Similarly, according to the fourth aspect of the invention, there is provided an image forming method including: a step of raising a rotation speed of a developer carrier to a first rotation speed at which a movement speed of a surface of the developer carrier at the time of rotation of the developer carrier is greater than a product of a pitch of concave portions in a peripheral direction of the developer carrier and the number of vibrations of a contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus thereof is the greatest after starting the rotation of the developer carrier, the developer carrier having the concave portions regularly arranged on the surface, being rotatable with a developer held thereon, and developing the latent image with the developer held thereon, the contact member being made of an elastic rubber material being in contact with the surface of the developer carrier and vibrating with the rotation of the developer carrier; a step of lowering the rotation speed of the developer carrier to a second rotation speed at which the movement speed is smaller than the product after the rotation speed of the developer carrier becomes the first rotation speed; and a step of allowing the developer carrier rotating at the second rotation speed to develop the latent image. 
     According to the image forming system, it is possible to properly prevent the deterioration in image quality. 
     Similarly, according to the second aspect of the invention, there is provided an image forming method including: a step of allowing a developer carrier to develop a latent image, the developer carrier rotating at a fifth rotation speed at which a movement speed of a surface of the developer carrier at the time of rotation of the developer carrier is smaller than a product of a pitch of concave portions in a peripheral direction of the developer carrier and the number of vibrations of a contact member when a loss tangent obtained by dividing a loss elastic modulus of the contact member by a storage elastic modulus thereof is the greatest, the developer carrier having the concave portions regularly arranged on the surface, being rotatable with a developer held thereon, and developing the latent image with the developer held thereon, the contact member being made of an elastic rubber material being in contact with the surface of the developer carrier and vibrating with the rotation of the developer carrier; a step of raising the rotation speed of the developer carrier to a fourth rotation speed at which the movement speed is greater than the product after the rotation speed of the developer carrier becomes the first rotation speed after ending the developing of the latent image; and a step of stopping the rotation of the developer carrier after the rotation speed of the developer carrier becomes the fourth rotation speed. 
     According to the image forming system, it is possible to properly prevent the deterioration in image quality. 
     Other features of the invention will be apparently understood from the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
         FIG. 1  is a diagram illustrating main elements of a printer  10 ; 
         FIG. 2  is a block diagram illustrating a control unit of the printer  10  shown in  FIG. 1 ; 
         FIG. 3  is a conceptual diagram of a developing apparatus; 
         FIG. 4  is a sectional view illustrating main elements of the developing apparatus; 
         FIG. 5  is a perspective view schematically illustrating a developing roller  510 ; 
         FIG. 6  is a front view schematically illustrating the developing roller  510 ; 
         FIG. 7  is a diagram schematically illustrating a sectional shape of grooves  512 ; 
         FIG. 8  is an enlarged schematic view of  FIG. 6 ; 
         FIG. 9  is a graph illustrating a storage elastic modulus and the like relative to a temperature of a rubber portion  562 ; 
         FIG. 10  is a graph illustrating the storage elastic modulus relative to a frequency of the rubber portion  562 ; 
         FIG. 11  is a graph illustrating a loss tangent (tan δ) relative to the number of vibrations of the rubber portion  562 ; 
         FIG. 12  is a graph illustrating loss tangents (tan δ) of materials; 
         FIG. 13  is a diagram illustrating the loss tangent (tan δ) of the rubber portion  562  in Example 1; 
         FIG. 14  is a diagram illustrating the loss tangent (tan δ) of the rubber portion  562  in Example 2; 
         FIG. 15  is a diagram illustrating the loss tangent (tan δ) of the rubber portion  562  in Example 3; 
         FIGS. 16A to 16E  are schematic diagrams illustrating a change of the developing roller  510  in a process of manufacturing the developing roller  510 ; 
         FIG. 17  is an explanatory diagram illustrating a rolling process on the developing roller  510 ; 
         FIGS. 18A to 18C  are diagrams illustrating variations of a surface shape of the developing roller  510 ; 
         FIG. 19  is an explanatory diagram illustrating an appearance of an image forming system; 
         FIG. 20  is a block diagram illustrating a configuration of the image forming system shown in  FIG. 19 ; 
         FIG. 21  is a graph illustrating the storage elastic modulus and the like relative to the (number of vibrations) frequency of the rubber portion  562 ; 
         FIG. 22  is a table illustrating measurement results; 
         FIG. 23A  is a diagram illustrating the rubber portion  562  and the periphery thereof and  FIG. 23B  is a diagram illustrating the rubber portion  562  in which the filming is generated; 
         FIG. 24  is a table illustrating test results; 
         FIG. 25  is a graph illustrating the storage elastic modulus G′ and the like relative to the (number of vibrations) frequency of the rubber portion  562  according to Examples 7 to 9; 
         FIG. 26  is a table illustrating test results; 
         FIG. 27  is a diagram schematically illustrating a change of a rotation speed of the developing roller  510  when a driving control of the developing roller  510  is performed; and 
         FIG. 28  is a diagram schematically illustrating a change of a rotation speed of the developing roller  510  when a stopping control of the developing roller  510  is performed. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a developing apparatus, an image forming apparatus, an image forming system, and an image forming method according to embodiments of the invention will be described with reference to the accompanying drawings. 
     Entire Configuration of Image Forming Apparatus 
     A laser beam printer  10  (hereinafter, also referred to as a printer) as an image forming apparatus will be roughly described with reference to  FIGS. 1 and 2 .  FIG. 1  is a diagram illustrating main elements of the printer  10 .  FIG. 2  is a block diagram illustrating a control unit of the printer  10  shown in  FIG. 1 . In  FIG. 1 , the vertical direction is indicated by an arrow. For example, a sheet feed tray  92  is disposed in a lower portion of the printer  10  and a fixing unit  90  is disposed in an upper portion of the printer  10 . 
     Configuration of Printer  10   
     As shown in  FIG. 1 , the printer  10  according to this embodiment includes a charging unit  30 , an exposure unit  40 , a YMCK developing unit  50 , a primary transfer unit  60 , an intermediate transfer member  70 , and a cleaning unit  75  in the rotation direction of a photosensitive member  20  as an example of an image carrier holding a latent image, and further includes a secondary transfer unit  80 , a fixing unit  90 , a display unit  95  serving as notification means for a user and including a liquid crystal panel, and a control unit  100  controlling the units to operate as a printer. 
     The photosensitive member  20  includes a cylindrical conductive base and a photosensitive layer formed on the periphery thereof, rotates about the center axis thereof. In this embodiment, the photosensitive member rotates clockwise as indicated by an arrow in  FIG. 1 . 
     The charging unit  30  serves to charge the photosensitive member  20 . The Exposure unit  40  serves to form a latent image on the charged photosensitive member  20  by applying a laser beam thereto. The exposure unit  40  includes a semiconductor laser, a polygon mirror, and an F-θ lens and applies a modulated laser beam to the charge photosensitive member  20  on the basis of an image signal input from a host computer not shown such as a personal computer and a word processor. 
     The YMCK developing unit  50  serves to develop the latent image formed on the photosensitive member  20  by the use of a toner as an example of a developer contained in the developing apparatus, that is, a black (K) toner contained in a black developing apparatus  51 , a magenta (M) toner contained in a magenta developing apparatus  52 , a cyan (C) toner contained in a cyan developing apparatus  53 , and a yellow (Y) toner contained in a yellow developing apparatus  54 . 
     The YMCK developing unit  50  allows the positions of the four developing apparatus  51 ,  52 ,  53 , and  54  to move by rotating with the four developing apparatus  51 ,  52 ,  53 , and  54  mounted thereon. That is, the YMCK developing unit  50  holds the four developing apparatus  51 ,  52 ,  53 , and  54  in four holding sections  55   a ,  55   b ,  55   c , and  55   d . The four developing apparatus  51 ,  52 ,  53 , and  54  can rotate about the center axis  50   a  with the relative positions maintained. Every when the formation of an image corresponding to 1 page ends, the developing apparatus are selectively opposed to the photosensitive member  20  to sequentially develop the latent image formed on the photosensitive member  20  with the toner received in the four developing apparatus  51 ,  52 ,  53 , and  54 . The four developing apparatus  51 ,  52 ,  53 , and  54  each can be attached to and detached from a printer body  10   a  (specifically, the holding sections of the YMCK developing unit  50 ) as an example of an image forming apparatus body. Details of the developing apparatus are described later. 
     The primary transfer unit  60  serves to transfer a monochromatic toner images formed on the photosensitive member  20  to the intermediate transfer member  70 . When four color toners are sequentially transferred in an overlapping manner, a full color toner image is formed on the intermediate transfer member  70 . The intermediate transfer member  70  is an endless belt in which a tin deposited layer is formed on the surface of a PET film and semi-conductive paint is formed and stacked on the surface thereof, and rotates substantially at the same peripheral speed as the photosensitive member  20 . The secondary transfer unit  80  serves to transfer the monochromatic toner image or the full color toner image formed on the intermediate transfer member  70  to a medium such as paper, film, and cloth. The fixing unit  90  serves to fix the monochromatic toner image or the full color toner image transferred to the medium to form a permanent image. 
     The cleaning unit  75  is disposed between the primary transfer unit  60  and the charging unit  30 , includes a rubber cleaning blade  76  in contact with the surface of the photosensitive member  20 , and serves to rake out and remove the toner remaining on the photosensitive member  20  by the use of the cleaning blade  76  after the toner image is transferred to the intermediate transfer member  70  by the primary transfer unit  60 . 
     As shown in  FIG. 2 , the control unit  100  includes a main controller  101  and a unit controller  102 . The main controller  101  includes an image memory  113  that is electrically connected to the host computer through an interface  112  and that stores the image signal input from the host computer. The unit controller  102  is electrically connected to the units and controls the units to form an image on the basis of signals input from the main controller  101  while detecting the states of the units, by receiving signals from sensors thereof. 
     &lt;Operation of Printer  10 &gt; 
     An operation of the printer  10  having the above-mentioned configuration is described now. 
     First, when an image signal and a control signal from the host computer not shown are input to the main controller  101  of the printer  10  through the interface (I/F)  112 , the photosensitive member  20  and the intermediate transfer member  70  rotate under the control of the unit controller  102  based on an instruction from the main controller  101 . 
     The photosensitive member  20  is sequentially charged at a charging position by the charging unit  30  while rotating. The charged region of the photosensitive member  20  reaches an exposure position with the rotation of the photosensitive member  20  and a latent image based on image information of a first color, for example, yellow Y, is formed in the region by the exposure unit  40 . In the YMCK developing unit  50 , the yellow developing apparatus  54  containing the yellow (Y) toner is located at a developing position facing the photosensitive member  20 . The latent image formed on the photosensitive member  20  reaches the developing position with the rotation of the photosensitive member  20  and is developed with the yellow toner by the yellow developing apparatus  54 . Accordingly, a yellow toner image is formed on the photosensitive member  20 . The yellow toner image formed on the photosensitive member  20  reaches a primary transfer position with the rotation of the photosensitive member  20  and is transferred to the intermediate transfer member  70  by the primary transfer unit  60 . At this time, a primary transfer voltage having a polarity opposite to the charged polarity of the toner T (negative polarity in this embodiment) is applied to the primary transfer unit  60 . In the meantime, the photosensitive member  20  is in contact with the intermediate transfer member  70  and the secondary transfer unit  80  is separated from the intermediate transfer member  70 . 
     By repeatedly performing the above-mentioned process on the developing apparatus of the second color, the third color, and the fourth color, four color toner images corresponding to the image signals are transferred to the intermediate transfer member  70  in an overlapping manner. Accordingly, a full color toner image is formed on the intermediate transfer member  70 . 
     The full color toner image formed on the intermediate transfer member  70  reaches a secondary transfer position with the rotation of the intermediate transfer member  70  and is transferred to a medium by the secondary transfer unit  80 . The medium is transported from the sheet feed tray  92  to the secondary transfer unit  80  through a feed roller  94  and a register roller  96 . At the time of performing the transfer operation, the secondary transfer unit  80  is pressed against the intermediate transfer member  70  and is supplied with a secondary transfer voltage. 
     The full color toner image transferred to the medium is heated and pressurized by the fixing unit  90  and is fixed to the medium. On the other hand, after the photosensitive member  20  passes through the primary transfer position, the toner T attached to the surface thereof is raked out by the cleaning blade  76  supported by the cleaning unit  75  and the charging operation for forming a next latent image is prepared. The raked-out toner T is collected in a remaining toner recovering section of the cleaning unit  75 . 
     Control Unit 
     A configuration of the control unit  100  is described now with reference to  FIG. 2 . The main controller  101  of the control unit  100  includes an image memory  113  that is electrically connected to the host computer through the interface  112  and that stores the image signals input from the host computer. The unit controller  102  is electrically connected to the units (the charging unit  30 , the exposure unit  40 , the YMCK developing unit  50 , the primary transfer unit  60 , the cleaning unit  75 , the secondary transfer unit  80 , the fixing unit  90 , and the display unit  95 ) of the apparatus body and controls the units on the basis of the signals input from the main controller  101  while detecting the states of the units, by receiving the signals from sensors of the units. 
     Developing Apparatus 
     A configuration and an operation of the developing apparatus are described now with reference to  FIGS. 3 to 8 .  FIG. 3  is a conceptual diagram of the developing apparatus.  FIG. 4  is a sectional view illustrating main elements of the developing apparatus.  FIG. 5  is a schematic perspective view of a developing roller  510 .  FIG. 6  is a schematic front view of the developing roller  510 .  FIG. 7  is a schematic diagram illustrating a sectional shape of grooves  512 .  FIG. 8  is a schematic enlarged diagram of  FIG. 6 , where the grooves  512  and top faces  515  are shown. The sectional view shown in  FIG. 4  illustrates a section obtained by cutting the developing apparatus in a plane perpendicular to the longitudinal direction shown in  FIG. 3 . In  FIG. 4 , similarly to  FIG. 1 , the vertical direction is indicated by an arrow and the center axis  510   b  of the developing roller  510  is located below the center axis of the photosensitive member  20 . In  FIG. 4 , the yellow developing apparatus  54  is located at the developing position opposed to the photosensitive member  20 . In  FIGS. 5 to 8 , the scales of the grooves  512  are different from real ones for the purpose of easy understanding of the drawing. 
     The YMCK developing unit  50  includes the black developing apparatus  51  containing the black (K) toner, the magenta developing apparatus  52  containing the magenta (M) toner, the cyan developing apparatus  53  containing the cyan (C) toner, and the yellow developing apparatus  54  containing the yellow (Y) toner. Configurations of the developing apparatus are equal to each other and thus the yellow developing apparatus  54  is representatively described now. 
     &lt;Configuration of Developing Apparatus&gt; 
     The yellow developing apparatus  54  includes a developing roller  510  as an example of the developer carrier, an upper seal  520 , a toner container  530 , a housing  540 , a toner supply roller  550  as an example of the removing member, and a regulating blade  560  as an example of the contact member. 
     The developing roller  510  transports the toner T to the opposed position (developing position) opposed to the photosensitive member  20  by rotating with the toner T held therein. The latent image held by the photosensitive member  20  is developed with the toner T (the toner T held by the developing roller  510 ). The developing roller  510  is made of aluminum ally or steel alloy. 
     As shown in  FIGS. 5 and 6 , the developing roller  510  includes grooves  512  as an example of the concave portions on the surface of a central portion  510   a  so as to properly hold the toner T. In this embodiment, two kinds of spiral grooves  512  different from each other in the winding direction, that is, first grooves  512   a  and second grooves  512   b , are disposed as the grooves  512 . As shown in  FIG. 6 , the tilt angles of the first grooves  512   a  and the second grooves  512   b  about the peripheral direction of the developing roller  510  are different from each other and the magnitude of an acute angle formed by the longitudinal direction of the first grooves  512   a  and the axial direction of the developing roller  510  and the magnitude of an acute angle formed by the longitudinal direction of the second grooves  512   b  and the axial direction are both about 45 degrees. As shown in  FIG. 7 , the width of the first grooves  512   a  in the X direction and the width of the second grooves  512   b  in the Y direction are about 42 μm, the depth of the grooves  512  is about 7 μm, and the groove angle (an angle indicated by reference sign a in  FIG. 7 ) is about 90 degrees. 
     Each groove  512  includes a bottom surface  514  and a side surface  513  and the slope angle of the side surface  513  is about 45 degree (see  FIG. 7 ). 
     As shown in  FIGS. 5 ,  6 , and  8 , two types of spiral grooves  512  having the above-mentioned configuration are regularly arranged on the surface of the central portion  510   a  of the developing roller  510  and intersect each other to form a lattice shape. Plural top faces  515  having a diamond shape (square shape) surrounded with the grooves  512  are formed in a mesh shape in the central portion  510   a.    
     As described above, in this embodiment, since the magnitude of the acute angle formed by the longitudinal direction of the first grooves  512   a  and the axial direction of the developing roller  510  and the magnitude of the acute angle formed by the longitudinal direction of the second grooves  512   b  and the axial direction are both about 45 degrees, the top face  515  has a square plane shape and one (the other) of two diagonals of the top face  515  is parallel to the peripheral direction (axial direction) of the developing roller  510 . The length of one side of the square top face  515  is about 38 μm as shown in  FIG. 7 . The pitch (width LT in  FIG. 8 ) of the grooves  512  in the peripheral direction is about 113 μm. 
     The developing roller  510  is rotatable about the center axis and as shown in  FIG. 4 , rotates in the opposite direction an the counterclockwise direction in  FIG. 4 ) of the rotation direction (clockwise direction in  FIG. 4 ) of the photosensitive member  20 . In this embodiment, the movement speed V (that is, the linear speed of the developing roller  510  on the surface of the developing roller  510 ) of the surface of the developing roller  510  when the developing roller  510  rotates at the time of developing the latent image is about 320 mm/s. The movement speed V (that is, the linear speed of the photosensitive member  20  on the surface of the photosensitive member  20 ) of the surface of the photosensitive member  20  when the photosensitive member  20  rotates at the time of developing the latent image is about 200 mm/s. The peripheral speed ratio of the developing roller  510  to the photosensitive member  20  is about 1.6. 
     In the state where the yellow developing apparatus  54  is opposed to the photosensitive member  20 , a gap is disposed between the developing roller  510  and the photosensitive member  20 . That is, the yellow developing apparatus  54  develops the latent image formed on the photosensitive member  20  in a non-contact manner. In the printer  10  according to this embodiment, a jumping developing method is employed and an alternating electric field is formed between the developing roller  510  and the photosensitive member  20  at the time of developing the latent image formed on the photosensitive member  20 . The printer  10  includes a developing bias applying portion  121  ( FIG. 2 ) for applying a developing bias (a developing voltage in which a DC voltage overlaps with an AC voltage in this embodiment) to the developing roller  510  to develop the latent image. By applying the developing bias to the developing roller  510 , the alternating electric field is formed in the gap. The toner T on the developing roller  510  moves to the photosensitive member  20  by means of the alternating electric field and thus the latent image on the photosensitive member  20  is developed. 
     The housing  540  is formed by welding plural resin housing portions incorporated in a body, that is, an upper housing portion  542  and a lower housing portion  544 , and a toner container  530  containing the toner T is formed therein. The toner container  530  is divided into two toner containing portions, that is, a first toner containing portion  530   a  and a second toner containing portion  530   b , by a partition wall  545  protruding inward (in the vertical direction in  FIG. 4 ) from an inner wall to partition the toner T. As shown in  FIG. 4 , the housing  540  (that is, the first toner containing portion  530   a ) has an opening  572  in a lower side thereof and the developing roller  510  is disposed to face the opening  572 . 
     A toner supply roller  550  is disposed in the&#39;first toner containing portion  530   a , and serves to supply the toner T contained in the first toner containing portion  530   a  to the developing roller  510  and to rake out the toner T remaining in the developing roller  510  from the developing roller  510  after the developing. The toner supply roller  550  is made of polyurethane foam or the like and is in contact with the developing roller in an elastically deformed state (in contact with the surface of the developing roller  510 ). The toner supply roller  550  is disposed below the first toner containing portion  530   a  and the toner T contained in the first toner containing portion  530   a  is supplied to the developing roller  510  on the lower side of the first toner containing portion  530   a  by the toner supply roller  550 . The toner supply roller  550  is rotatable about the center axis thereof and the center axis is disposed below the rotation center axis  510   b  of the developing roller  510 . The toner supply roller  550  rotates in the opposite direction (clockwise direction in  FIG. 4 ) of the rotation direction (counterclockwise direction in  FIG. 4 ) of the developing roller  510 . 
     The upper seal  520  comes in contact with the developing roller  510  in the axial direction thereof so as to allow the movement of the toner T remaining on the developing roller  510  after passing through the developing position into the housing  540  and to regulate the movement of the toner T in the housing  540  from the housing  540 . 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 supporting metal plate  522 . An upper seal urging member  524  made of an elastic body such as MOLTOPREN (Registered Trademark) is disposed in a compressed state on the other side of the developing roller  510  about the upper seal  520 . The upper seal urging member  524  pressed the upper seal  520  on the developing roller  510  by urging the upper seal  520  to the developing roller  510  with the urging force thereof. The contact position where the upper seal  520  comes in contact with the developing roller  510  is higher than the center axis  510   b  of the developing roller  510 . 
     The regulating blade  560  comes in contact with the surface of the developing roller  510  from one end in the axial direction of the developing roller  510  to the other end to regulate the layer thickness of the toner T held on the developing roller  510  and to give charges to the toner T held on the developing roller  510 . The regulating blade  560  includes a rubber portion  562  as an example of the contact member and a rubber supporting portion  564  as shown in  FIG. 4 . 
     The rubber portion  562  is a layer thickness regulating member coming in contact with the surface of the developing member  510  to regulate the layer thickness of the toner T held on the developing roller  510 . The rubber portion  562  is disposed so that the longitudinal direction thereof is parallel to the axial direction ( FIG. 6 ) of the developing roller  510  and one end in the width direction thereof (an end  560   a  of the regulating blade  560 ) faces the upstream side in the rotation direction of the developing roller  510  (see  FIG. 4 ). That is, the rubber portion  562  comes in counter contact with the developing roller. The end (the end  560   a  of the regulating blade  560 ) of the rubber portion  562  is not in contact with the developing roller  510 , and the contact portion  562   a  of the rubber portion  562  coming in contact with the surface of the developing roller  510  is apart from the end  560   a  in the width direction. That is, the rubber portion  562  is not in contact with the developing roller  510  at the edge, but is in contact with the developing roller at the center. By allowing the plane of the rubber portion  562  to come in contact with the developing roller  510 , the layer thickness is regulated. The contact position where the rubber portion  562  comes in contact with the developing roller  510  is below the center axis  510   b  of the developing roller  510  and below the center axis of the toner supply roller  550 . The rubber portion  562  performs a function of preventing the toner T from leaking from the toner container  530  by coming in contact with the developing roller  510  in the axis direction. 
     The rubber portion  562  is made of an elastic rubber material. Here, the elastic rubber material is defined as an elastic material having rubber elasticity. The elastic rubber material is classified in a rubber and a thermoplastic elastomer, where the rubber is an elastic material (that is, an elastic material exhibiting a thermosetting characteristic) hardened from a fluidized state by heating and the thermoplastic elastomer is an elastic material (that is, an elastic material exhibiting a thermoplastic characteristic) fluidized from a solidified state by heating. An example used for the rubber portion  562  is urethane rubber. The rubber portion  562  in this embodiment is made of the thermoplastic elastomer in view of easy processing due to the thermoplastic characteristic. 
     The rubber supporting portion  564  includes a thin plate  564   a  and a thin plate supporting portion  564   b  and supports the rubber portion  562  by the use of an end  564   d  (that is, an end close to the thin plate  564   a ) in the width direction thereof. The thin plate  564   a  is made of phosphor bronze or stainless and has elasticity. The thin plate  564   a  supports the rubber portion  562  and pressed the rubber portion  562  to the developing roller  510  with the urging force thereof. The thin plate supporting portion  564   b  is a metal plate disposed at the other end  564   e  in the width direction of the rubber supporting portion  564 . The thin plate supporting portion  564   b  is attached to the housing  540  while supporting an end of the thin plate  564   a  opposite to the side supporting the rubber portion  562 . A blade back member  570  made of MOLTOPREN (Registered Trademark) is disposed on the opposite side of the developing roller  510  about the thin plate supporting portion  564   b.    
     &lt;Operation of Developing Apparatus&gt; 
     In the yellow developing apparatus  54  having the above-mentioned configuration, the toner supply roller  550  supplies the toner T contained 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  with the rotation of the developing roller  510 , the layer thickness is regulated and the toner is provided with negative charges (negatively charged) at the time of passing through the contact position. The toner T on the developing roller  510  having been regulated in layer thickness and supplied with the negative charges is trans ported to the opposed position (developing position) opposed to the photosensitive member  20  with the addition rotation of the developing roller  510  and is provided to the development of the latent image formed on the photosensitive member  20  at the opposed position. The toner T on the developing roller  510  passing through the developing position with the rotation of the developing roller  510  passes through the upper seal  520  and is collected in the developing apparatus without being raked out by the upper seal  520 . The toner T remaining on the developing roller  510  can be raked out by the toner supply roller  550 . 
     Relation Between Physical Properties of Rubber Portion  562  and Temperature 
     The storage elastic modulus and the loss elastic modulus are known as indicating dynamic viscoelasticity of a material of the rubber portion  562  made of an elastic rubber material. The storage elastic modulus indicates an elastic behavior of a material and the loss elastic modulus indicates a viscous behavior of the material. The magnitudes of the storage elastic modulus and the loss elastic modulus vary depending on the temperature of the material. The material exhibits the rubber-like characteristic (physical property) or the glass-like characteristic depending on the variation in magnitude of the storage elastic modulus (loss elastic modulus). Specifically, when the storage elastic modulus or the loss elastic modulus is great, the material exhibits the glass-like characteristic. When the storage elastic modulus or the loss elastic modulus is small, the material exhibits the rubber-like characteristic. 
     Details thereof are described with reference to  FIG. 9 .  FIG. 9  is a graph illustrating a relation of the storage elastic modulus relative to the temperature of the rubber portion  562 .  FIG. 9  shows the storage elastic modulus (G′ in  FIG. 9 ) and the loss elastic modulus (G″ in  FIG. 9 ) of the rubber portion  562  according to this embodiment. As shown in the graph, the magnitudes of the storage elastic modulus and the loss elastic modulus exhibit a great value when the temperature of the rubber portion  562  is low, and exhibit a small value when the temperature of the rubber portion  562  is high. As described above, when the storage elastic modulus (loss elastic modulus) is great, the glass-like characteristic is exhibited. Accordingly, when the temperature of the rubber portion  562  is low C (or example, −40° C.), the rubber portion  562  exhibits the glass-like characteristic. On the other hand, when the storage elastic modulus (loss elastic modulus) is small, the rubber-like characteristic is exhibited. Accordingly, when the temperature of the rubber portion  562  is high (for example, 40° C.), the rubber portion  562  exhibits the rubber-like characteristic. 
     The loss tangent (tan δ in  FIG. 9 ) obtained by dividing the loss elastic modulus G″ by the storage elastic modulus G′ is shown in  FIG. 9 . The characteristic of the rubber portion  562  is changed at the peak temperature T (in the vicinity of −35° C. in  FIG. 9 ) as the boundary at which the loss tangent is the greatest. That is, the rubber portion  562  exhibits the glass-like characteristic at a temperature lower than the peak temperature T. The rubber portion  562  exhibits the rubber-like characteristic at a temperature higher than the peak temperature T. The peak temperature T is also called a glass transition temperature. 
     The graph shown in  FIG. 9  can be obtained by the following measurement. ARES made by TA instruments is used as a measurer for the measurement and a torsion type jig is used as a jig for the measurement. A temperature dependence measuring mode is selected as a measuring mode and the temperature range for the measurement is −50° C. to 60° C. ( FIG. 9 ). The temperature rising rate from −50° C. to 60° C. is 5° C./min. The storage elastic modulus G′, the loss elastic modulus G″, and the loss tangent (tan δ) of the rubber portion  562  are obtained by the measurement under the measuring condition. 
     In the printer  10  according to this embodiment, the operating temperature range is set and specifically, the operating temperature range is 10° C. to 35° C. The temperatures of the rubber portion  562  of the developing apparatus  51 ,  52 ,  53 , and  54  mounted on the printer body  10   a  are slightly (by about 10° C.) higher than the operating temperature range. Accordingly, the rubber portion  562  is used at a temperature higher than the peak temperature T (about −35° C.), the rubber-like characteristic is exhibited in relation to the temperature. 
     As can be seen from the fact that the rubber portion  562  exhibits rubber-like characteristic in relation to the temperature, it is required that the rubber portion  562  is used with the rubber-like characteristic when the rubber portion  562  is usually used. 
     Relation between Physical Characteristic of Rubber Portion  562  and Number of Vibrations (Frequency) 
     As described above, since the rubber portion  562  is in contact with the surface of the developing roller  510 , the developing roller  510  frictionally slides on the rubber portion  562  at the time of rotation thereof. Accordingly, the rubber portion  562  vibrates with the rotation of the developing roller  510 . Particularly, since the grooves  512  are formed on the surface of the developing roller  510 , the rubber portion  562  easily vibrates with the rotation of the developing roller  510 . It is known that the characteristic of the rubber portion  562  is changed depending on the magnitude of the number of vibrations of the rubber portion  562 . That is, it is known that the rubber portion  562  exhibits the rubber-like characteristic or the glass-like characteristic depending on the magnitude of the number of vibrations. This point is described now. 
       FIG. 10  is a graph illustrating the storage elastic modulus relative to the number of vibrations (frequency) of the rubber portion  562 . Hereinafter, for the purpose of convenience, the number of vibrations is used instead of the number of vibrations. The scales of the horizontal axis in the graph shown in  FIG. 10  are marked by logarithm (the same is true in  FIGS. 11 and 12 ). The storage elastic modulus (G′ in  FIG. 10 ) and the loss elastic modulus (G″ in  FIG. 10 ) of the rubber portion  562  are shown in  FIG. 10 , similarly to  FIG. 9 . As shown in the graph, the magnitudes of the storage elastic modulus and the loss elastic modulus are small when the frequency of the rubber portion  562  is small and are great when the frequency of the rubber portion  562  is great. Accordingly, the rubber portion  562  exhibits the rubber-like characteristic at a small frequency of the rubber portion  562  and the rubber portion  562  exhibits the glass-like characteristic at a great frequency of the rubber portion  562 . 
     The loss tangent (tan δ in  FIG. 10 ) obtained by dividing the loss elastic modulus G″ by the storage elastic modulus G′ is shown in  FIG. 10 , similarly to  FIG. 9 . The characteristic of the rubber portion  562  is changed at the peak frequency f (about 100000 Hz in  FIG. 10 ) as the boundary at which the loss tangent is the greatest. That is, the rubber portion  562  exhibits the glass-like characteristic at a frequency f higher than the peak frequency f. The rubber portion  562  exhibits the rubber-like characteristic at a frequency lower than the peak frequency. 
     Accordingly, in order to satisfy the above-mentioned requirement, that is, the requirement for using the rubber portion  562  vibrating with the rotation of the developing roller  510  with the rubber-like characteristic, it is necessary to allow the number of vibrations (frequency) of the rubber portion  562  to be lower than the peaks frequency f. 
     The graph shown in  FIG. 10  can be obtained by the same measurement as the graph shown in  FIG. 9 . That is, the ARES is used as the measurer and the frequency dependence measuring mode is selected as the measuring mode. The range of frequency applied to the rubber portion  562  as the measurement target is 10-4 to 1014 ( FIG. 10 ) and the application strain of the frequency is 0.1% (constant). The temperature of the rubber portion  562  at the time of measurement is kept at 20° C. The graphs shown in  FIGS. 11 and 12  can be obtained by the same measurement. 
     &lt;Effectiveness of Developing Apparatus  51 ,  52 ,  53 , and  54  According to this Embodiment&gt; 
     In the developing apparatus  51 ,  52 ,  53 , and  54  according to this embodiment, the value obtained by dividing the movement speed of the surface of the developing roller  510  at the time of rotation of the developing roller  510  by the pitch of the grooves  512  in the peripheral direction of the developing roller  510  is smaller than the number of vibrations of the rubber portion  562  when the loss tangent of the rubber portion  562  obtained by dividing the loss elastic modulus by the storage elastic modulus is the greatest (V/L 1 &lt;f). Accordingly, the rubber portion  562  vibrating with the rotation of the developing roller  510  can be properly used with the rubber-like characteristic. 
     The details are described in detail with reference to  FIG. 8 , etc. As described above, two types of spiral grooves  512  having different tilt angles about the peripheral direction are formed on the surface of the developing roller  510  according to this embodiment and the two types of spiral grooves  512  intersect each other to form a lattice shape. The developing roller  510  has square-shaped top faces  515  surrounded with the two types of spiral grooves  512  and one of two diagonals of each square-shaped top face is parallel to the peripheral direction ( FIG. 8 ). In the developing roller  510 , the pitch (width L 1  in  FIG. 8 ) of the grooves  512  in the peripheral direction is about 113 μm. 
     As described above, the movement speed V of the surface of the developing roller  510  at the time of rotation of the developing roller  510  is 320 mm/s. Accordingly, the value V/L 1  obtained by dividing the movement speed of the surface of the developing roller  510  at the time of rotation of the developing roller  510  by the pitch of the grooves  512  in the peripheral direction of the developing roller  510  is about 2831 Hz. As shown in  FIG. 10 , since the peak frequency f of the rubber portion  562  when the loss tangent (tan δ) of the rubber portion  562  obtained by dividing the loss elastic modulus by the storage elastic modulus is the greatest is about 100000 Hz in the example shown in  FIG. 10 , the relation of V/L 1 &lt;f is satisfied in this embodiment. 
     When the relation of V/L 1 &lt;f is satisfied, why the rubber portion  562  can be used with the rubber-like characteristic at the time of rotation of the developing roller  510  is described now. As described above, the rubber portion  562  is in contact with the surface of the developing roller  510  and the grooves  512  regularly arranged are formed on the surface. Accordingly, the grooves  512  frictionally slide on the rubber portion  562 , whereby the rubber portion  562  vibrates at a constant number of vibrations. The magnitude of the number of vibrations of the rubber portion  562  is determined depending on the pitch L 1  of the grooves  512  in the peripheral direction and the movement speed V of the surface of the developing roller  510 . That is, the number of vibrations of the rubber portion  562  at the time of rotation of the developing roller  510  is V/L 1 . Accordingly, when V/L 1  is smaller than the peak frequency f of the rubber portion  562  (V/L 1 &lt;f, the rubber portion  562  is used with the rubber-like characteristic. 
     Accordingly, in the developing apparatus  51 ,  52 ,  53 , and  54  according to this embodiment, since the relation of V/L 1 &lt;f is satisfied, the number of vibrations of the rubber portion  562  vibrating with the rotation of the developing roller  510  is smaller than the peak frequency f (about 100000 Hz) of the rubber portion  562 . Accordingly, the rubber portion  562  is used with the rubber-like characteristic at the time of rotation of the developing roller  510 . As a result, the rubber portion  562  can properly perform the function of regulating the layer thickness of the toner held on the developing roller  510 . 
     &lt;Relation Between Peak Frequency f and Temperature of Rubber Portion  562 &gt; 
     As described above, the operating temperature range (that is, 10° C. to 35° C.) and the temperature of the rubber portion  562  varies depending on the operating temperature of the printer  10 . The peak frequency f of the rubber portion  562  when the loss tangent (tan δ) of the rubber portion  562  is the greatest varies depending on the magnitude of the temperature of the rubber portion  562 . This point is described now with reference to  FIG. 11 . 
       FIG. 11  is a graph illustrating the loss tangent (tan δ) relative to the number of vibrations (frequency) of the rubber portion  562 . While the loss tangent (tan δ) of the rubber portion  562  when the temperature of the rubber portion  562  is 20° C. is shown in  FIG. 10 , the loss tangent (tan δ) of the rubber portion  562  when the temperature of the rubber portion  562  is 10° C., 20° C., and 30° C. is shown in  FIG. 11 . As can be seen from the graph shown in  FIG. 11 , the loss tangent (tan δ) increases with the increase in temperature of the rubber portion  562 . Accordingly, the peak frequency f of the rubber portion  562  when the loss tangent (tan δ) of the rubber portion  562  is the greatest increases with the increase (rising) in temperature of rubber portion  562 . Since the value V/L 1  is about 2831 Hz, it is smaller than the peak frequencies at 10° C., 20° C., and 30° C. 
     Accordingly, in this embodiment, since the above-mentioned relation V/L 1 &lt;f is satisfied at all the temperatures in the operating temperature range (10° C. to 35° C.) of the printer  10 , the rubber portion  562  is necessarily used with the rubber-like characteristic at the time of rotation of the developing roller  510  with the image forming operation of the printer  10 . 
     &lt;Relation Between Peak Frequency f and Material of Rubber Portion  562 &gt; 
     The rubber portion  562  is made of T8175 (Example 1) made by DIC. However, a material other than T8125 may be used as the rubber portion  562  and for example, T7350 (Example 2) made by TOYO TIRE &amp; RUBBER Co., LTD. or SS2 (Example 3) made by Bando GUM may be used. Three materials have the following characteristics. That is, T8175 of Example 1 is a thermoplastic elastomer and the hardness (shore A) thereof is 78. T7350 of Example 2 is a urethane rubber and the hardness thereof (JIS A) is 75. SS2 of Example 3 is a urethane rubber and the hardness thereof (JIS A) is 78. 
       FIG. 12  is a graph illustrating the loss tangents (tan δ) of the above-mentioned three materials. As can be seen from the graph shown in  FIG. 12 , the peak frequency f of T8175 of Example 1 is about 100000 Hz, the peak frequency f of T7350 of Example 2 is about 5000 Hz, and the peak frequency f of SS2 of Example 3 is about 4000 Hz. Accordingly, when the three materials are used as the rubber portion  562 , the relation of V/L 1 &lt;f is satisfied. Accordingly, the rubber portions  562  made of the three materials are used with the rubber-like characteristic at the time of rotation of the developing roller  510 . In the above-mentioned embodiment, T8175 of Example 1 of which the peak frequency f is the greatest among the three materials is used as the rubber portion  562 . 
     The loss tangent (tan δ) of 201759 made by Hokushin Industries Inc. and usable for the cleaning blade  76  is shown as Comparative Example 1 in  FIG. 12 . The peak frequency f of the material is about 300 Hz. When the material is used as the rubber portion  562 , the relation of V/L 1 &lt;f is not satisfied and the rubber portion  652  may be used with the glass-like characteristic at the time of rotation of the developing roller  510 . 
     The graph of the loss tangent of T8175 of Example 1 shown in  FIG. 12  is equivalent to the graph of the loss tangent shown in  FIG. 10  and the temperature of T8175 at the time of measuring T8175 is 20° C. The temperatures of T7350 of Example 2, SS2 of Example 3, and 201759 of Comparative Example 1 at the time of measuring them are 20° C. 
     &lt;Pitch L 1  of Grooves  512  in Peripheral Direction and Movement Speed V of Developing Roller  510 &gt; 
     Although it has been described in the above-mentioned embodiment, the pitch L 1  of the grooves  512  in the peripheral direction is about 113 μm and the movement speed of the surface of the developing roller  510  is 320 mm/s, the invention is not, limited to the embodiment. The pitch L 1  and the movement speed V may have any value as long as they can satisfy the relation of V/L 1 &lt;f. Here, it is preferable that the magnitude of the pitch L 1  is in the range of about 85 μm to about 142 μm and the movement speed V is in the range of 1000 mm/s to 480 mm/s. 
     Countermeasure for Maintaining Relation of V/L 1 &lt;f During Operation of Developing Apparatus 
     As described above, the movement speed V of the developing roller  510  is 320 mm/s, the pitch L 1  of the grooves  512  is about 113 μm and the value V/L 1  (about 2831 Hz) obtained by dividing the movement speed V by the pitch L 1  is smaller than the peak frequency f of the rubber portion  562 . 
     The magnitude of the value V/L 1  may vary during operation of the developing apparatus. For example, when an external disturbance acts on the developing apparatus  51 ,  52 ,  53 , and  54  and the movement speed V of the developing roller  510  in rotation is greater than 320 mm/s, the value V/L 1  also increases in other words, the number of vibrations (frequency) of the rubber portion  562  vibrating with the rotation of the developing roller  510  increases). When the peak frequency f of the rubber portion  562  is close to 2831 Hz (which is the frequency when the movement speed V/L 1  is 320 mm/s), the magnitude of the value V/L 1  may be greater than the peak frequency f at the time of variation (that is, the relation of V/L 1 &lt;f may not be maintained during operation of the developing apparatus but the relation of V/L 1 &gt;f may be satisfied). When the value V/L 1  is greater than the peak frequency f, as described above, there is a problem in that the rubber portion  562  exhibits the glass-like characteristic. 
     In order to solve the above-mentioned problem, as a countermeasure for maintaining the relation of V/L 1 &lt;f even when the movement speed V and the like vary in the course of operation of the developing apparatus, the value V/L 1  obtained by dividing the movement speed V of the developing roller  510  by the pitch L 1  of the grooves  512  is smaller than the peak frequency f when the loss tangent (tan δ) is the greatest and smaller than the frequency (hereinafter, also referred to as frequency f 2 ) when the loss tangent at the frequency is the half of the greatest value (V/L 1 &lt;f 2 ). 
     The details are described with reference to  FIG. 13 .  FIG. 13  is a diagram illustrating the loss tangent (tan δ) and the like of the rubber portion  562  (T8175) of Example 1, where the frequency f 2  and the like are added to the graph shown in  FIG. 10 . As shown in  FIG. 13 , the greatest value of the loss tangent (tan δ) is about 0.58 and the frequency (peak frequency f) at this time is about 100000 Hz. Accordingly, the half of the greatest value is 0.29 and the frequency f 2  at this time is about 1000 Hz. When the frequency f 2  is about 1000 Hz, for example, the movement speed V is determined as 100 mm/s and the pitch L 1  is determined 125 μm so as to satisfy the relation of V/L 1 &lt;f 2 . In this case, the value V/L 1  is 800 Hz and the relation of V/L 1 &lt;f 2  is established. 
     In this way, when the relation of V/L 1 &lt;2 is established and the magnitude of the value V/L 1  varies with the variation in magnitude of the movement speed V, the value V/L 1  is hardly greater than the peak frequency f. This is because the frequency f 2  (about 1000 Hz) is 1/100 of the peak frequency f (about 100000 Hz). As a result, the relation of V/L 1 &lt;f is maintained during operation of the developing apparatus (during rotation of the developing roller  510 ) and the rubber portion  562  can be properly used with the rubber-like characteristic at the time of rotation of the developing roller  510 . 
     Although it has been described that the value V/L 1  is smaller than the frequency f 2 , the loss tangent may be smaller than the frequency which is a mean value (about 0.28) of the greatest value (about 0.58) and the least value (about 0.02 in  FIG. 13 ) thereof. However, in this embodiment, since the least value is close to 0, the mean value (about 0.28) is almost equivalent to the half (0.29) of the greatest value. Accordingly, the frequency at the mean value and the frequency f 2  are almost equivalent to each other (the same is true in the rubber portions  562  of Examples 2 and 3). 
     The relation of V/L 1 &lt;f 2  in the rubber portion  562  (T7350) according to Example 2 and the rubber portion  562  (SS2) according to Example 3 will be described now with reference to  FIGS. 14 and 15 .  FIG. 14  is a diagram illustrating the loss tangent (tan δ) and the like of the rubber portion  562  of Example 2 and  FIG. 15  is a diagram illustrating the loss tangent (tan δ) of the rubber portion  562  and the like of Example 3. 
     In the rubber portion  562  of T7350 of Example 2, as shown in  FIG. 14 , the greatest value of the loss tangent (tan δ) is about 0.76 and the peak frequency f is about 5000 Hz. Accordingly, the half of the greatest value is 0.38 and the frequency f 2  is about 100 Hz. Therefore, by determining the movement speed V and the pitch L 1  so as to allow the value V/L 1  to be smaller than 100 Hz in the rubber portion  562  of T7350, the rubber portion  562  is continuously used with the rubber-like characteristic during the operation of the developing apparatus. 
     In the rubber portion  562  of SS2 of Example 3, as shown in  FIG. 15 , the greatest value of the loss tangent (tan δ) is about 0.60 and the peak frequency f is about 4000 Hz. Accordingly, the half of the greatest value is 0.30 and the frequency  12  is about 60 Hz. Therefore, by determining the movement speed V and the pitch L 1  so as to allow the value V/L 1  to be smaller than 60 Hz in the rubber portion  562  of SS2, the rubber portion  562  is continuously used with the rubber-like characteristic during the operation of the developing apparatus. 
     As shown in  FIGS. 13 to 15 , at a frequency smaller than the frequency f 2 , the variation in storage elastic modulus G′ of the rubber portion  562  is smaller than that at a frequency between the frequency f 2  and the peak frequency f. Here, the storage elastic modulus G′ indicates the elastic behavior of the material and it is known that the degree of vibration of the rubber portion  562  varies depending on the magnitude of the storage elastic modulus G. When the variation in storage elastic modulus G′ of the rubber portion  562  is small, the degree of vibration of the rubber portion  562  is stabilized and thus the contact of the rubber portion  562  with the developing roller  510  is stabilized. As a result, the rubber portion  562  can property perform the function (function of giving charges to the toner) of regulating the layer thickness of the toner held on the developing roller  510 . 
     The loss tangent (tan δ in  FIG. 21 ) obtained by dividing the loss elastic modulus G″ by the storage elastic modulus G′ is shown in  FIG. 21 , similarly to  FIG. 9 . The characteristic of the rubber portion  562  is changed at the peak frequency f (about 20000 Hz in  FIG. 21 ) as the boundary at which the loss tangent is the greatest. That is, the rubber portion  562  exhibits the glass-like characteristic at a frequency lower than 20000 Hz. The rubber portion  562  exhibits the rubber-like characteristic at a frequency higher than 20000 Hz. 
     Accordingly, in order to satisfy the above-mentioned requirement, that is, the requirement for using the rubber portion  562  vibrating with the rotation of the developing roller  510  with the rubber-like characteristic, it is necessary to make the number of vibrations (frequency) of the rubber portion  562  lower than the peak frequency f. 
     The graph shown in  FIG. 21  can be obtained by the same measurement as the graph shown in  FIG. 9 . That is, the ARES is used as the measurer and the frequency dependence measuring mode is selected as the measuring mode. The range of frequency applied to the rubber portion  562  as the measurement target is 10-4 to 1014 ( FIG. 21 ) and the application strain of the frequency is 0.1% (constant). The temperature of the rubber portion  562  at the time of measurement is maintained at 20° C. 
     &lt;Countermeasure for Allowing Vibrating Rubber Portion  562  to be Used with Rubber-Like Characteristic&gt; 
     A specific counter measure for allowing the rubber portion  562  vibrating with the rotation of the developing roller  510  to be used with the rubber-like characteristic is described now. As the countermeasure, in this embodiment, the value obtained by dividing the movement speed of the surface of the developing roller  510  at the time of rotation of the developing roller  510  by the pitch of the grooves  512  in the peripheral direction of the developing roller  510  is smaller than the number of vibrations of the rubber portion  562  when the loss tangent obtained by dividing the loss elastic modulus of the rubber portion  562  by the storage elastic modulus is the greatest. 
     The point is described in more detail with reference to  FIG. 8 , etc. As described above, two types of spiral grooves  512  having different tilt angles about the peripheral direction are formed on the surface of the developing roller  510  according to this embodiment and the two types of spiral grooves  512  intersect each other to form a lattice shape. The developing roller  510  has square-shaped top faces  515  surrounded with the two types of spiral grooves  512  and one of two diagonals of each square-shaped top face is parallel to the peripheral direction ( FIG. 8 ). In the developing roller  510 , the pitch (width L 1  in  FIG. 8 ) of the grooves  512  in the peripheral direction is about 113 μm. 
     As described above, the movement speed V of the surface of the developing roller  510  at the time of rotation of the developing roller  510  is 320 mm/s. Accordingly, the value V/L 1  obtained by dividing the movement speed V of the surface of the developing roller  510  at the time of rotation of the developing roller  510  by the pitch L 1  is about 2831 Hz. As shown in  FIG. 21 , since the peak frequency f of the rubber portion  562  when the loss tangent (tan δ) of the rubber portion  562  is the greatest is about 20000 Hz in the example shown in  FIG. 21 , the relation of V/L 1 &lt;f is satisfied in this embodiment. 
     When the relation of V/L 1 &lt;f is satisfied, why the rubber portion  562  can be used with the rubber-like characteristic at the time of rotation of the developing roller  510  is described now. As described above, the rubber portion  562  is in contact with the surface of the developing roller  510  and the grooves  512  regularly arranged are formed on the surface. Accordingly, the grooves  512  frictionally slide on the rubber portion  562 , whereby the rubber portion  562  vibrates at a constant number of vibrations. The magnitude of the number of vibrations of the rubber portion  562  is determined depending on the pitch L 1  of the grooves  512  in the peripheral direction and the movement speed V of the surface of the developing roller  510 . That is, the number of vibrations of the rubber portion  562  at the time of rotation of the developing roller  510  is V/L 1 . Accordingly, when V/L 1  is smaller than the peak frequency f of the rubber portion  562  (V/L 1 &lt;), the rubber portion  562  is used with the rubber-like characteristic. 
     Accordingly, in the developing apparatus  51 ,  52 ,  53 , and  54  according to this embodiment, since the relation of V/L 1 &lt;f is satisfied, the number of vibrations (frequency) of the rubber portion  562  vibrating with the rotation of the developing roller  510  is smaller than the peak frequency f (about 20000 Hz) of the rubber portion  562 . Accordingly, the rubber portion  562  is used with the rubber-like characteristic at the time of rotation of the developing roller  510 . As a result, the rubber portion  562  can properly perform the function of regulating the layer thickness of the toner held on the developing roller  510 . 
     Abnormal Noises Accompanied with Vibration of Rubber Portion  562   
     By satisfying the relation of V/L 1 &lt;f, the rubber portion  562  is used with the rubber-like characteristic. However, when the rubber portion  562  is used with the rubber-like characteristic, the rubber portion  562  vibrates with the rotation of the developing roller  510 , thereby causing the abnormal noises. The abnormal noises are specifically wind roar (sound resulting from the vibration of air) due to the rubber portion  562  vibrating with the rotation of the developing roller  510 . 
     The abnormal noises have a predetermined relation with the dynamic viscoelasticity (the elastic behavior and the viscous behavior) of the rubber portion  562 . That is, when the elastic behavior of two behaviors is superior an other words, when the storage elastic modulus G′ is superior), the amplitude of the vibration of the rubber portion  562  increases, thereby easily causing the abnormal noises (wind roar). When the abnormal noises are generated, a user may misunderstand that a problem is caused with the printer  10 . 
     &lt;Countermeasure for Suppressing Generation of Abnormal Noise&gt;&gt; 
     A countermeasure for suppressing the generation of the abnormal noises is described now. As this countermeasure, the value V/L (this value V/L 1  is the number of vibrations of the rubber portion  562  at the time of rotation of the developing roller  510 ) obtained by dividing the movement speed V of the developing roller  510  by the pitch L 1  of the grooves  512  has the same magnitude as the frequency (number of vibrations) where the storage elastic modulus G′ is smaller than the loss elastic modulus G″. 
     The details are described now with reference  FIG. 21 . The value V/L 1  is smaller than the peak frequency f (20000 Hz). As shown in  FIG. 21 , a frequency domain smaller than the peak frequency f includes a frequency domain in which the storage elastic modulus G′ is greater than the loss elastic modulus G″ and a frequency domain in which the storage elastic modulus G′ is smaller than the loss elastic modulus G′. Specifically, the frequency f 1  at which the graph of the storage elastic modulus G′ and the graph of the loss elastic modulus G′ intersect each other is about 760 Hz, the storage elastic modulus G′ is smaller than the loss elastic modulus G″ in the domain 760 Hz to 20000 Hz, and the storage elastic modulus G′ is greater than the loss elastic modulus G″ in the domain of 760 Hz or less. Since the value V/L 1  (the number of vibrations of the rubber portion  562 ) is about 2831 Hz, the storage elastic modulus G′ is smaller than the loss elastic modulus G 7  at the time of vibration of the rubber portion  562 . 
     In this way, when the storage elastic modulus G′ is smaller than the loss elastic modulus G′, the viscous behavior is superior to (more dominant than) the elastic behavior. Since the amplitude of the vibration of the rubber portion  562  is suppressed from increasing by suppressing the elastic behavior of the rubber portion  562 , it is possible to suppress the generation of the abnormal noises (wind roar). 
     Specific advantages of this countermeasure are described with reference to the measurement result shown in  FIG. 22 .  FIG. 22  is a table illustrating the measurement results, where the relation between the value V/L 1  and the magnitude of the abnormal noise is shown. The measurement is performed by the following method. NA-28 (noise meter) made by RION CO., LTD. is used as the measurer. This measurer is set at a position apart by about 10 mm from the printer  10  (specifically, an exterior portion of the printer  10  dose to the developing unit  50 ) and the magnitude (volume) of the abnormal noise during the rotation of the developing roller  510  is measured. The volume is expressed by dB (decibel) and a large value of the volume means a large abnormal noise (feels “noisy”). In this measurement, the volume of the abnormal noise is measured in three cases (Example 4, Example 5, and Comparative Example 2) where the magnitudes of the movement speed V 1  of the developing roller  510  and the pitch L 1  of the grooves  512  are changed. 
     As in this embodiment, when the movement speed V is 320 mm/s and the pitch L 1  is 113 μm, that is, when the value V/L 1  (the number of vibrations of the rubber portion  562 ) is 2831 Hz (Example 4), the storage elastic modulus G′ is smaller than the loss elastic modulus G″ (see  FIG. 21 ) and the volume of the abnormal noise is 27 dB. In Example 5, when the movement speed V is 100 mm/s and the pitch L 1  is 85 μm (when the value V/L 1  is 1176 Hz), the storage elastic modulus G′ is smaller than the loss elastic modulus G″ and the volume of the abnormal noise is 31 dB. On the other hand, in Comparative Example 2, when the movement speed V is 50 mm/s and the pitch L 1  is 141 μm (when the value V/L 1  is 442 Hz), the storage elastic modulus G′ is greater than the loss elastic modulus G″ and the volume of the abnormal noise is 69 dB. 
     As can be seen from the measurement result, when the storage elastic modulus G′ is smaller than the loss elastic modulus G″ at the time of vibration of the rubber portion  562  (Examples 4 and 5), the volume of the abnormal noise is the half or less of the volume of the abnormal noise when the storage elastic modulus G′ is greater than the loss elastic modulus G″ at the time of vibration of the rubber portion  562  (Comparative Example 2). Accordingly, when the number of vibrations of the rubber portion  562  is the number of vibrations at which the storage elastic modulus G′ is smaller than the loss elastic modulus G″, the generation of the abnormal noise in the rubber portion  562  is suppressed. 
     As described above, in the printer  10  according to this embodiment, since the value V/L 1  has the same magnitude as the number of vibrations at which the storage elastic modulus G′ is smaller than the loss elastic modulus G″ among the frequencies smaller than the number of vibrations (peak frequency f) of the rubber portion  562  when the loss tangent (tan δ) of the rubber portion  562  is the greatest, it is possible to properly use the rubber portion  562  with the rubber-like characteristic at the time of rotation of the developing roller  510  and to suppress the generation of the abnormal noise accompanied with the vibration of the rubber portion  562 . 
     Filming Generated with Increase in Temperature of Rubber Portion  562   
     By satisfying the relation of V/L 1 &lt;f, the rubber portion  562  can be used with the rubber-like characteristic. However; when the rubber portion  562  is used with the rubber-like characteristic, the temperature of the rubber portion  562  may increase due to the frictional sliding of the developing roller  510  on the rubber portion  562  during the rotation. Particularly, when the developing roller  510  continuously performs the developing operation (the image forming operation), the developing roller  510  frictionally slides on the rubber portion  562  for a long time and thus the temperature of the rubber portion  562  can easily increase. 
     There is a predetermined relation between the increase in temperature of the rubber portion  562  and the dynamic viscoelasticity (the elastic behavior and the viscous behavior) of the rubber portion  562 . That is, when the elastic behavior of two behaviors is superior an other words, when the loss elastic modulus G″ is superior), the molecular chains of the rubber portion  562  can easily vibrate. Accordingly, heat can be easily generated and thus the temperature of the rubber portion  562  can easily increase. 
     In general, the rubber usually has tackiness (viscosity). Accordingly, when the rubber portion  562  is used with the rubber-like characteristic, the toner may be secured to the surface of the rubber portion  562 . When the temperature of the rubber portion  562  increases (that is, when the loss elastic modulus G″ is superior), the securing of the toner is promoted and the filming (lump of secured toner) may be generated on the surface of the rubber portion  562 . When the filming is generated, the charting of the toner by the rubber portion  562  is not proper, thereby causing the deterioration in image quality. 
     &lt;Generation of Filming Accompanied with Increase in Temperature of Rubber Portion  562 &gt; 
     The generation of the filming is described with reference to  FIGS. 23A and 23B .  FIG. 23A  is a diagram illustrating the rubber portion  562  and the peripheral portions thereof  FIG. 23B  is a diagram illustrating the rubber portion  562  in which the filming is generated on the surface thereof. 
     As described above, the rubber portion  562  according to this embodiment is in contact with the surface of the developing roller  510  so that the longitudinal direction thereof is parallel to the axial direction of the developing roller  510  and one end in the width direction thereof (that is, an end  560   a  of the regulating blade  560 ) faces the upstream side in the rotation direction of the developing roller  510 . The contact portion  562   a  of the rubber portion  562  coming in contact with the surface of the developing roller  510  is apart from the end (end  560   a ) in the width direction. In this configuration, since the toner flows into the portion D (a portion between the rubber portion  562  and the developing roller  510 ) shown in  FIG. 23A  with the rotation of the developing roller  510 , the toner can be easily secured to the surface (a portion between the contact portion  562   a  and the end) of the rubber portion  562 . 
     When the temperature of the rubber portion  562  increases with the rotation of the developing roller  510 , the securing of the toner is promoted. As a result, as shown in  FIG. 23B , the filming (which is hatched in  FIG. 23B ) may be generated from the contact portion  562   a  (the contact portion  562   a  is indicated by a dotted line in  FIG. 23B ) to the end (the end  560   a ). 
     Countermeasure for Suppressing Increase in Temperature of Rubber  562   
     A countermeasure for suppressing an increase in temperature of the rubber portion  562  is described now. As this countermeasure, the value V/L 1  (this value V/L 1  is the number of vibrations of the rubber portion  562  at the time of rotation of the developing roller  510 ) obtained by dividing the movement speed V of the developing roller  510  by the pitch L 1  of the grooves  512  has the same magnitude as the frequency (number of vibrations) where the loss elastic modulus G″ is smaller than the storage elastic modulus G′. 
     The details are described now with reference  FIG. 21 . The value V/L 1  is smaller than the peak frequency f (2000 Hz). As shown in  FIG. 21 , a frequency domain smaller than the peak frequency f includes a frequency domain (hereinafter, also referred to as frequency domain A 1 ) in which the storage elastic modulus G′ is greater than the loss elastic modulus G″ and a frequency domain (hereinafter, also referred to as frequency domain A 2 ) in which the storage elastic modulus G′ is smaller than the loss elastic modulus G″. Specifically, the frequency f 1  at which the graph of the storage elastic modulus G′ and the graph of the loss elastic modulus G″ intersect each other is about 760 Hz, the storage elastic modulus G′ is smaller than the loss elastic modulus G′ in the domain (frequency domain M 2 ) of 760 Hz to 20000 Hz, and the storage elastic modulus G′ is greater than the loss elastic modulus G″ in the domain (frequency domain A 1 ) of 760 Hz or less. Since the value V/L 1  (the number of vibrations of the rubber portion  562 ) is about 442 Hz, the loss elastic modulus G″ is smaller than the storage elastic modulus G′ at the time of vibration of the rubber portion  562 . 
     In this way, when the loss elastic modulus G″ is smaller than the storage elastic modulus G′, the elastic behavior is superior to (more dominant than) the viscous behavior. Since the vibration of the molecular chains of the rubber portion  562  is suppressed by suppressing the viscous behavior of the rubber portion  562 , it is possible to suppress the generation of heat and to suppress the increase in temperature of the rubber portion  562 . Accordingly, it is possible to suppress the generation of the filming in the rubber portion  562 . 
     Specific advantages of this countermeasure are described with reference to the measurement result shown in  FIG. 24 .  FIG. 24  is a table illustrating the measurement results, where the relation between the magnitude of the value V/L 1  and the temperature and generation of the filming in the rubber portion  562  is shown. The temperature of the rubber portion  562  shown in  FIG. 24  is measured by the following method. That is, a thermoelectric couple is attached to the rubber portion  562  and the temperature of the rubber portion  562  is measured by the use of NR-1000 (temperature recorder) made by KEYENCE CORPORATION. The generation of the filming is determined by the following method. That is, after continuously performing a printing operation on 3000 sheets, it is determined with a naked eye whether the filming is generated on the surface of the rubber portion  562 . In this measurement, the temperature of the rubber portion  562  and the generation of the filming are measured in three cases where the movement speed V of the developing roller  510  and the pitch L 1  of the grooves  512  are changed (Example 6, Comparative Example 3, and Comparative Example 4). 
     As in this embodiment, when the movement speed V is 50 mm/s and the pitch L 1  is 141 μm, that is, when the value V/L 1  (the number of vibrations of the rubber portion  562 ) is 442 Hz (Example 6), the loss elastic modulus G″ is smaller than the storage elastic modulus G′ (see  FIG. 21 ). The temperature of the rubber portion  562  is 43.2° C. and the filming is not generated on the surface of the rubber portion  562 . 
     On the other hand, in Comparative Example 3, when the movement speed V is 160 mm/s and the pitch L 1  is 141 μm (when the value V/L 1  is 1135 Hz), the loss elastic modulus G″ is greater than the storage elastic modulus G′, the temperature of the rubber portion  562  is 50.3° C., and the filming is generated on the surface of the rubber portion  562 . In Comparative Example 4, when the movement speed V is 320 mm/s and the pitch L 1  is 113 μm (when the value V/L 1  is 2831 Hz), the loss elastic modulus G″ is greater than the storage elastic modulus G′, the temperature of the rubber portion  562  is 54.7° C., and the filming is generated on the surface of the rubber portion  562 . 
     In this way, when the loss elastic modulus G′ is smaller than the storage elastic modulus G′ at the time of vibration of the rubber portion  562  (Example 6), the temperature of the rubber portion  562  is lower than that when the loss elastic modulus G″ is greater than the storage elastic modulus G′ at the time of vibration of the rubber portion  562  (Comparative Examples 3 and 4), and the filming is not generated on the surface of the rubber portion  562 . Accordingly, the effectiveness of this countermeasure is validated by the measurement. 
     As described above, in the printer  10  according to this embodiment, since the value V/L 1  has the same magnitude as the number of vibrations at which the loss elastic modulus G″ is smaller than the storage elastic modulus G′ among the numbers of vibrations smaller than the number of vibrations (peak frequency of the rubber portion  562  when the loss tangent (tan δ) of the rubber portion  562  is the greatest, it is possible to properly use the rubber portion  562  with the rubber-like characteristic at the time of rotation of the developing roller  510  and to suppress the increase in temperature of the rubber portion  562  (as a result, it is possible to suppress the generation of the filming). 
     Rubber Portion  562  According to Examples 7 to 9 
     The rubber portion  562  according to Examples 7 to 9 different in material from the rubber portion  562  according to the above-mentioned embodiment (Example 6) is described now. The configurations of the developing roller  510  and the like are the same as Example 6. 
       FIG. 25  is a graph illustrating the storage elastic modulus G′ relative to the number of vibrations (frequency) of the rubber portion  562  according to Example 7. The storage elastic modulus G′, the loss elastic modulus G″, and the loss tangent (tan δ) of the rubber portion  562  are shown in  FIG. 25 , similarly to  FIG. 21 . The scales of the horizontal axis are marked by logarithm. 
     The peak frequency f when the loss tangent (tan δ) of the rubber portion  562  according to Example 7 is the greatest is about 6700 Hz as shown in  FIG. 25 . As described above, since the movement speed V of the developing roller  510  is 50 mm/s and the pitch L 1  of the grooves  512  is 141 μm, the value V/L 1  (the number of vibrations of the rubber portion  562 ) is about 442 Hz. In this case, the relation of V/L 1 &lt;f is established and the rubber portion  562  is used with the rubber-like characteristic at the time of rotation of the developing roller  510 . 
     As shown in  FIG. 25 , the frequency domain smaller than the peak frequency f includes a frequency domain where the storage elastic modulus G′ is greater than the loss elastic modulus G″, but does not include the frequency domain where the storage elastic modulus G′ is smaller than the loss elastic modulus G″, unlike  FIG. 21 . Since the value V/L 1  (the number of vibrations of the rubber portion  562 ) is about 442 Hz, the loss elastic modulus G′ is smaller than the loss elastic modulus G″ at the time of vibration of the rubber portion  562 . Accordingly, in the rubber portion  562  according to Example 7, the elastic behavior is superior to the viscous behavior and the temperature of the rubber portion  562  is suppressed from increasing, thereby suppressing the generation of the filming. 
     Here, the advantage of suppressing the increase in temperature of the rubber portion  562  according to Example 7 (of accordingly suppressing the generation of the filming) is specifically described with reference to the measurement results shown in  FIG. 26 .  FIG. 26  is a table illustrating the measurement result, where the relation between the magnitude of the value V/L 1  and the temperature and generation of the filming in the rubber portion  562  is shown. The temperature measuring method and the method of determining the generation of the filming shown in  FIG. 26  are as describe a above. 
     When the movement speed V is 50 mm/s and the pitch L 1  is 141 μm, that is, when the value V/L 1  is 442 Hz (Example 7), the loss elastic modulus G″ is smaller than the storage elastic modulus G′. The temperature of the rubber portion  562  is 42.4° C. and the filming is not generated on the surface of the rubber portion  562 . 
     Similarly, when the movement speed V is, 160 mm/s and the pitch L 1  is 141 μm in Example 8 (when the value V/L 1  is 1135 Hz) or when the movement speed V is 320 mm/s and the pitch L 1  is 113 μm in Example 9 (when the value V/L 1  is 2830 Hz), the loss elastic modulus G″ is smaller than the storage elastic modulus G′. The temperature of the rubber portion  562  in two cases is almost equal to the temperature of Example 7 and the filming is not generated on the surface of the rubber portion  562 . 
     As described above, in Examples 7 to 9, since the value V/L 1  has the same magnitude as the frequency at which the loss elastic modulus G′ is smaller than the storage elastic modulus G′ among the frequencies smaller than the number of vibrations (peak frequency C) of the rubber portion  562  when the loss tangent (tan δ) of the rubber portion  562  is the greatest, it is possible to properly use the rubber portion  562  with the rubber-like characteristic at the time of rotation of the developing roller  510  and to suppress the increase in temperature of the rubber portion  562  (as a result, it is possible to suppress the generation of the filming). 
     Driving Control and Stopping Control Developing Roller  510   
     As described above, the developing roller  510  transports the toner to the developing position by rotating and develops the latent image held on the photosensitive member  20  with the toner (the toner held on the developing roller  510 ). The developing roller  510  rotates at a constant rotation speed (hereinafter, referred to as a developing rotation speed) at the time of performing the developing operation (rotates at the rotation speed at which the movement speed of the surface of the developing roller  510  is 320 mm/s). 
     Accordingly, the control unit  100  needs to control the rotation of the developing roller  510  stopped at the time of starting the developing operation to raise the rotation speed of the developing roller  510  up to the developing rotation speed. The control unit  100  needs to control the rotation of the developing roller  510  rotating at the developing rotation speed to lower the rotation speed of the developing roller  510  at the time of ending the developing operation up to 0 (that is, it is necessary to stop the rotation of the developing roller  510 ). 
     Here, until the developing roller  510  rotates at the developing rotation speed from the stopped state, how the control unit  100  should control the rotation of the developing roller  510  (which is hereinafter referred to as a driving control of the developing roller  510  for the purpose of convenience) is described now. In addition, until the developing roller  510  is stopped from the state where it rotates at the developing rotation speed, how the control unit  100  should control the rotation of the developing roller  510  (which is hereinafter referred to as a stopping roller of the developing roller  510  for the purpose of convenience) is described now. 
     Basic Concept of Control 
     As described in the Problems that the Invention is to Solve, the contact member (the rubber portion  562  as the layer thickness regulating member in this embodiment) is in contact with the surface of the developing roller  510  and the grooves  512  regularly arranged are formed on the surface of the developing roller  510 . Accordingly, when the developing roller  510  rotates, the rubber portion  562  vibrates with the sliding movement of the developing roller  510  on the rubber portion  562 . 
     It is known that when the number of vibrations of the rubber portion  562  (the value obtained by dividing the movement speed of the surface at the time of rotation of the developing roller  510  by the pitch of the grooves  512  in the peripheral direction of the developing roller  510  correspond to the number of vibrations) is too great, the rubber portion  562  made of a elastic rubber material exhibits the glass-like characteristic, not the rubber-like characteristic. Accordingly, at the time of development, it is necessary to allow the developing roller  510  to rotate at a rotation speed at which the number of vibrations is not too great (at which the rubber portion  562  does not exhibit the glass-like characteristic), so as to allow the rubber portion  562  made of a elastic rubber material to properly perform its function. 
     This point is described in more details. The storage elastic modulus and the loss elastic modulus indicate dynamic viscoelasticity of a material of the rubber portion  562  made of an elastic rubber material. The storage elastic modulus indicates an elastic behavior of the material and the loss elastic modulus indicates a viscous behavior of the material. Both values vary with the variation in the number of vibrations of the material when the material vibrates. Since both values vary with the variation in the number of vibrations, the loss tangent (tan δ) obtained by dividing the loss elastic modulus G″ by the storage elastic modulus G′ varies with the variation in the number of vibrations. It is known that the characteristic of the material is changed at the number of vibrations (hereinafter, also referred to as boundary number of vibrations f)) as the boundary at which the loss tangent (tan δ) is the greatest. That is, the material exhibits the rubber-like characteristic when the number of vibrations of the material at the time of vibration of the material is lower than the boundary number of vibrations f. The material exhibits the glass-like characteristic when the number of vibrations is higher than the boundary number of vibrations f. 
       FIG. 25  is a graph illustrating a relation between the number of vibrations (hereinafter, also referred to as frequency for the purpose of convenience) of the material (that is, the rubber portion  562 ) according to this embodiment and the storage elastic modulus, loss elastic modulus, and loss tangent thereof. As shown in  FIG. 25 , in the rubber portion  562  according to this embodiment, the storage elastic modulus G′, the loss elastic modulus G″, and the loss tangent (tan δ) vary with the variation in frequency of the rubber portion  562 . The boundary number of vibrations f of the rubber portion  562  is about 6700 Hz. Accordingly, when the number of vibrations of the rubber portion  562  at the time of vibration of the rubber portion  562  is smaller than about 6700 Hz, the rubber portion  562  exhibits the rubber-like characteristic. When the frequency is greater than about 6700 Hz, the rubber portion  562  exhibits the glass-like characteristic. 
     The graph shown in  FIG. 25  is obtained by the following measurement. ARES made by TA instruments is used as a measurer for the measurement and a torsion type jig is used as a jig for the measurement. A temperature dependence measuring mode is selected as a measuring mode and the application strain of the frequency is 0.1% (constant). The temperature of the rubber portion  562  for the measurement is kept at 20° C. 
     In this way, when the number of vibrations of the rubber portion  562  is greater than the boundary number of vibrations f, the rubber portion  562  made of a rubber elastic material exhibits the glass-like characteristic, not the rubber-like characteristic. Accordingly, at the time of performing the developing operation, it is possible to control the frequency to allow the rubber portion  562  made of the elastic rubber material to perform its function, so that the number of vibrations is not greater than the boundary number of vibrations f (the frequency is smaller than the boundary number of vibrations f). 
     The control of the number of vibrations is accomplished by controlling the rotation speed of the developing roller  510 . That is, as described above, since the number of vibrations of the rubber portion  562  is the value obtained by dividing the movement speed of the surface at the time of rotation of the developing roller  510  by the pitch of the grooves  512  in the peripheral direction of the developing roller  510 , the frequency is proportional to the movement speed. Since the movement speed is proportional to the rotation speed of the developing roller  510 , the number of vibrations is proportional to the rotation speed of the developing roller  510 . That is, when the rotation speed of the developing roller  510  is enhanced, the number of vibrations increases. When the rotation speed is reduced, the number of vibrations decreases. 
     Accordingly, when the rotation speed (the developing rotation speed) of the developing roller  510  at the time of developing is made to be the rotation speed at which the number of vibrations (that is, the value obtained by dividing the movement speed by the pitch) is smaller than the boundary number of vibrations, that is, the rotation speed at which the movement speed is smaller than the product of the pitch and the boundary number of vibrations, it is possible to keep the rubber portion  562  made of the elastic rubber material in the rubber-like characteristic at the time of developing, thereby allowing the rubber portion  562  to properly perform its function. 
     In this embodiment, as described above, the movement speed, the pitch, and the boundary number of vibrations at the time of developing are about 320 mm/s, about 113 μm and about 6700 Hz, respectively and the product is 757.1 mm/s. Accordingly, the movement speed of the surface of the developing roller  510  when the developing roller  510  rotates at the developing rotation speed at the time of developing is smaller than the product. That is, in order to allow the rubber portion  562  to properly perform its function, the control unit  100  according to this embodiment controls the rotation of the developing roller  510  so that the developing rotation speed of the developing roller  510  is made to be the rotation speed at which the movement speed is smaller than the product of the pitch and the boundary number of vibrations. 
     However, as described in the BACKGROUND, etc., when the developing operation is performed in a state where the rubber portion  562  exhibits the rubber-like characteristic, the filming is generated in the rubber portion  562  due to the tackiness of the rubber portion  562  based on the rubber-like characteristic. 
       FIG. 23A  is a schematic diagram illustrating a state where the filming is generated in the rubber portion  562 . As described above, the rubber portion  562  according to this embodiment is in contact with the surface of the developing roller  510  so that the longitudinal direction thereof is parallel to the axial direction of the developing roller  510  and one end in the width direction thereof (that is, an end  560   a  of the regulating blade  560 ) faces the upstream side in the rotation direction of the developing roller  510 . The contact portion  562   a  of the rubber portion  562  coming in contact with the surface of the developing roller  510  is apart from the end (end  560   a ) in the width direction. In this configuration, since the toner flows into the portion D (a portion between the rubber portion  562  and the developing roller  510 ) shown in  FIG. 23A  with the rotation of the developing roller  510 , the filming is generated in the portion of the rubber portion  562  hatched in  FIG. 23A . 
     When the filming is remarkable, the quality of an image developed and finally formed on the medium is deteriorated. 
     Accordingly, the control unit  100  according to this embodiment makes a control of shaking and removing the filming from the rubber portion  562  temporarily in the course of the driving control and the stopping control. 
     Here, the control of shaking and removing the filming from the rubber portion  562  is described now. As described above, the rubber portion  562  exhibits the rubber-like characteristic or the glass-like characteristic depending on the number of vibrations of the rubber portion  562 . When the vibrating rubber portion  562  exhibits the glass-like characteristic, the tackiness of the rubber portion  562  based on the rubber-like characteristic is weakened to make it easy to remove the filming from the rubber portion  562 . When the rubber portion  562  exhibits the glass-like characteristic, the rubber portion  562  is harder than when the rubber portion exhibits the rubber-like characteristic. Accordingly, the vibration generated in the contact portion  562   a  when the developing roller  510  slides on the rubber portion  562  at the contact portion  562   a  is easily transmitted to the portion in which the filming exists and which is hatched in  FIG. 23A  (on the contrary, when the rubber portion  562  exhibits the rubber-like characteristic, the vibration generated in the contact portion  562   a  is absorbed by the rubber portion  562  in the course of transmitting the vibration to the filming portion and thus is hardly transmitted to the portion) for this reason, when the vibrating rubber portion  562  exhibits the glass-like characteristic, the vibration is effectively transmitted to the filming portion which can be easily removed, whereby the filming is properly shaken and removed from the rubber portion  562 . 
     On the other hand, as described above, when the rotation speed of the developing roller  510  is made to be the rotation speed at which the number of vibrations (that is, the value obtained by dividing the movement speed by the pitch) is smaller than the boundary number of vibrations, that is, the rotation speed at which the movement speed is smaller than the product of the pitch and the boundary number of vibrations, the vibrating rubber portion  562  exhibits the rubber-like characteristic. On the contrary, when the rotation speed of the developing roller  510  is made to be the rotation speed at which the number of vibrations (that is, the value obtained by dividing the movement speed by the pitch) is greater than the boundary number of vibrations, that is, the rotation speed at which the movement speed is greater than the product of the pitch and the boundary number of vibrations, the vibrating rubber portion  562  exhibits the glass-like characteristic. Accordingly, by controlling the rotation of the developing roller  510  so that the rotation speed of the developing speed  510  is made to be the rotation speed at which the movement speed is greater than the product of the pitch and the boundary number of vibrations, it is possible to properly shake and remove the filming from the rubber portion  562 . 
     Accordingly, in this embodiment, in order to shake and remove the filming from the rubber portion  562 , the control unit  100  controls the rotation of the developing roller  510  so that the rotation speed of the developing roller  510  is temporarily made to be the rotation speed at which the movement speed is greater than the product of the pitch and the boundary number of vibrations during the driving control and the stopping control. 
     More specifically, in the driving control, the control unit  100  starts the rotation of the developing roller  510  and then raises the rotation speed of the developing roller  510  up to the rotation speed (hereinafter, also referred to as first rotation speed V 1 ) at which the movement speed is greater than the product of the pitch and the boundary number of vibrations so as to shake and remove the filming from the rubber portion  562 . Thereafter (that is, after the rotation speed of the developing roller  510  becomes the first rotation speed V 1 ), the control unit  100  lowers the rotation speed of the developing roller  510  up to the rotation speed (hereinafter, also referred to as second rotation speed V 2 ) at which the movement speed is smaller than the product of the pitch and the boundary number of vibrations so as to allow the developing roller rotating at the second rotation speed V 2  to develop the latent image. That is, the control unit  100  shakes and removes the filming from the rubber portion  562  by raising the rotation speed of the developing roller  510  up to the first rotation speed V 1  before performing the developing operation, when it is not necessary to allow the rubbing portion  562  made of the elastic rubber material to perform its function. Thereafter, in the state where the filming is properly removed, the developing roller  510  develops the latent image. 
     The control unit  100  allows the developing roller  510  rotating at the rotation speed (hereinafter, also referred to as fifth rotation speed V 5 ; the fifth rotation speed V 5  is equal to the second rotation speed V 2  in this embodiment) at which the movement speed is smaller than the product of the pitch and the boundary number of vibrations to develop the latent image, finishes the developing of the latent image by the developing roller, raising the rotation speed of the developing roller  510  up to the rotation speed (hereinafter, also referred to as fourth rotation speed V 4 ; the fourth rotation speed V 4  is equal to the first rotation speed V 1  in this embodiment) at which the movement speed is greater than the product of the pitch and the boundary number of vibrations in the stopping control, and thereafter (that is, after the rotation speed of the developing roller  510  becomes the fourth rotation speed V 4 ) stops the rotation of the developing roller  510 . That is, the control unit  100  raises the rotation speed of the developing roller  510  up to the fourth rotation speed V 4  so as to shake and remove the filming generated at the time of developing from the rubber portion  562  after performing the developing operation, when it is not necessary to allow the rubber portion  562  made of the elastic rubber material to perform its function. 
     Although it has been described that the second rotation speed V 2  and the fifth rotation speed V 5  are the rotation speeds at which the movement speed of the surface of the developing roller  510  is about 320 mm/s, the first rotation speed V 1  and the fourth rotation speed V 4  in this embodiment are the rotation speeds (2.5 times the second rotation speed V 2  and the fifth rotation speed V 5 ) at which the movement speed of the surface of the developing roller  510  is about 800 mm/s. As described above, since the product of the pitch and the boundary number of vibrations is 757.1 mm/s. Accordingly, by setting the first rotation speed V 1  and the fourth rotation speed V 4  to the above-mentioned rotation speed, it is possible to shake and remove the filming from the rubber portion  562 . However, the value of the rotation speed is not limited to the above-mentioned numerical values, but may be properly determined depending on the values of the pitch or the boundary number of vibrations. 
     &lt;Specific Example of Driving Control of Developing Roller  510 &gt; 
     A specific example of the driving control of the developing roller  510  is described now with reference to  FIG. 27 .  FIG. 27  is a schematic diagram illustrating the change of the rotation speed of the developing roller  510  when the driving control of the developing roller  510  is performed, where the horizontal axis represents time and the vertical axis represents the rotation speed of the developing roller  510 . In this section, developing start timing for starting developing the latent image and application start timing for starting applying the developing bias for developing the latent image are mentioned. 
     When the time in the horizontal axis is 0 in  FIG. 27 , the developing roller  510  is stopped. In order to shake and remove the filming from the rubber portion  562 , the control unit  100  gives to the developing roller  510  an instruction for allowing the developing roller  510  to rotate at the first rotation speed V 1  at time ta 1  so as to start the rotation of the developing roller  510  and raises the rotation speed of the developing roller  510  to the first rotation speed V 1 . The rotations speed of the developing roller  510  slowly increases from 0, passes through the rotation speed (hereinafter, also referred to as third rotation speed V 3 ) at which the movement speed is equal to the product of the pitch and the boundary number of vibrations at time ta 2 , and becomes the first rotation speed V 1  at time ta 3 . 
     In order to allow the rubber portion  562  to properly perform its function at the time of developing, at ta 4 , the control unit  100  instructs the developing roller  510  to allow the developing roller  510  to rotate at the second rotation speed V 2  (that is, the developing rotation speed) and lowers the rotation speed of the developing roller  510  to the second rotation speed. The rotation speed of the developing roller  510  slowly decreases from the first rotation speed V 1 , passes through the third rotation speed V 3  at time ta 5 , and becomes the second rotation speed V 2  at time ta 6 . In this embodiment, ta 4  is set so that the time from time ta 3  to time ta 4 , that is, the time when the developing roller  510  is rotating at the first rotation speed V 1  is greater than the time (about 70 msec in this embodiment) when the developing roller  510  rotates once. 
     After the rotation speed of the developing roller  510  becomes the third rotation speed V 3  at time ta 5 , more specifically, after a time point (which is represented by time ta 7  in  FIG. 27 ) in a time, when a portion, on the surface of the developing roller  510 , in contact with the rubber portion  562  when the rotation speed of the developing roller  510  becomes the third rotation speed V 3  moves to the position opposed to the photosensitive member  20  with the additional rotation of the developing roller  510 , after the rotation speed of the developing roller  510  becomes the third rotation speed V 3 , the control unit  100  allows the developing bias application section  121  to start the application of the developing bias at time ta 8 . 
     The reason for defining the application start timing of the developing bias as described above is described. As described above, in order to shake and remove the filming from the rubber portion  562 , the control unit  100  allows the developing roller  510  to rotate at the first rotation speed V 1  from time ta 3  to time ta 4 . Specifically, since the time period when the rubber portion  562  exhibits the glass-like characteristic is from time ta 2  to time ta 5 , the filming is shaken and removed from the rubber portion  562  in the meantime. When the filming is shaken and removed from the rubber portion  562 , the filming falls in the gravity direction and is collected by the toner container  530 , but some of the filming moves to the developing roller  510  and is attached to the surface of the developing roller  510 . The filming attached to the surface moves from the contact position in contact with the rubber portion  562  with the rotation of the developing roller  510 , finally reaches the contact position in contact with the toner supply roller  550 , is raked out at the contact position by the toner supply roller  550 , and is properly collected into the toner container  530 . However, when the filming attached to the surface of the developing roller  510  moves from the contact position with the rotation of the developing roller  510  to the position opposed to the photosensitive member  20  and the developing bias is applied thereto, the filming may move to the photosensitive member  20 . When the filming moves to the photosensitive member  20 , the proper collection of the filming into the toner container  530  is hindered. 
     Accordingly, in order to avoid such a problem, the control unit  100  according to this embodiment allows the developing bias application section  121  to start the application of the developing bias at time ta 8  after the time point (time ta 7 ) in a time (that is, a time until the filming finally attached to the surface moves to the position opposed to the photosensitive member  20  with the rotation of the developing roller  510 ), when a portion, on the surface of the developing roller  510 , in contact with the rubber portion  562  when the rotation speed of the developing roller  510  becomes the third rotation speed V 3  (time ta 5 ) moves to the position opposed to the photosensitive member  20  with the additional rotation of the developing roller  510 , after the rotation speed of the developing roller  510  becomes the third rotation speed V 3  at time ta 5  (that is, after the filming is finally attached to the surface of the developing roller  510 ). 
     In a time when the developing bias is sufficiently stabilized after the application of the developing bias is started at time ta 8 , the control unit  100  allows the developing roller  510  rotating at the second rotation speed V 2  to develop the latent image at time ta 9 . That is, at time ta 9 , the latent image on the photosensitive member  20  is opposed to the developing roller  510  and the developing of the latent image is started. 
     &lt;Specific Example of Stopping Control of Developing Roller  510 &gt; 
     A specific example of the stopping control of the developing roller  510  is described now with reference to  FIG. 28 .  FIG. 28  is a schematic diagram illustrating the change of the rotation speed of the developing roller  510  when the stopping control of the developing roller  510  is performed, where the horizontal axis represents time and the vertical axis represents the rotation speed of the developing roller  510 . In this section, developing end timing for ending developing the latent image and application end timing for ending applying the developing bias for developing the latent image are mentioned. 
     When the time in the horizontal axis is 0 in  FIG. 28 , the developing roller  510  is rotating at the fifth rotation speed V 5  and the developing of the latent image is performed. That is, the control unit  100  allows the developing roller  510 , which rotates at the fifth rotation speed V 5  at which the rubber portion  562  can properly perform its function at the time of developing, to develop the latent image. 
     The control unit  100  ends the developing of the latent image at time tb 1 , gives the developing roller  510  an instruction for allowing the developing roller  510  to rotate at the fourth rotation speed V 4  at time tb 2  so as to shake and remove the filming from the rubber portion  562 , and raises the rotation speed of the developing roller  510  to the fourth rotation speed V 4 . The rotation speed of the developing roller  510  slowly increases from the fifth rotation speed V 5 , passes through the third rotation speed V 3  at which the movement speed is equal to the product of the pitch and the boundary number of vibrations at time tb 4 , and becomes the fourth rotation speed V 4  at time tb 5 . 
     The application end timing for ending the application of the developing bias is described. In this embodiment, in consideration of the possibility that the application end timing is earlier than the developing end timing due to an error of the timing control, the application end timing is not equal to the developing end timing, but the application end timing is made to be later than the developing end timing. That is, the control unit  100  ends the application of the developing bias from the developing bias application section  121  after ending the developing of the latent image at time tb 1 . The control unit  100  ends the application of the developing bias at time tb 3  before the rotation speed of the developing roller  510  becomes the third rotation speed V 3  at time tb 4 . More specifically, before the time point (which is represented by time tb 6  in  FIG. 28 ) in a time, when a portion, on the surface of the developing roller  510 , in contact with the rubber portion  562  when the rotation speed of the developing roller  510  becomes the third rotation speed V 3  moves to the position opposed to the photosensitive member  20  with the additional rotation of the developing roller  510 , after the rotation speed of the developing roller  510  becomes the third rotation speed V 3 . 
     That is, in order to avoid the above-mentioned problem, that is, a problem in that the filming moves to the photosensitive member  20  when the filming attached to the surface of the developing roller  510  moves from the contact position with the rotation of the developing roller  510  and reaches the position opposed to the photosensitive member  20  and the developing bias is applied thereto, the control unit  100  ends the application of the developing bias at time tb 3  before the time point (time tb 6 ) in a time (that is, a time when the filming first attached to the surface moves from the contact position with the rotation of the developing roller  510  and reaches the position opposed to the photosensitive member  20 ), when a portion, on the surface of the developing roller  510 , in contact with the rubber portion  562  when the rotation speed of the developing roller  510  becomes the third rotation speed V 3  (time tb 4 ) moves to the position opposed to the photosensitive member  20  with the additional rotation of the developing roller  510 , after the rotation speed of the developing roller  510  becomes the third rotation speed V 3  at time tb 4  (that is, after the filming is first attached to the surface of the developing roller  510 ). 
     After the rotation speed of the developing roller  510  becomes the fourth rotation speed V 4  at time tb 5 , the control unit  100  lowers the rotation speed of the developing roller  510  to start stopping the rotation of the developing roller  510  at time tb 7 . Here, the control unit  100  according to this embodiment stops the rotation at time tb 12  after the time point (which is represented by time tb 10  in  FIG. 28 ) in a time period, when the portion, on the surface of the developing roller  510  in contact with the rubber portion  562  when the rotation speed of the developing roller  510  becomes the third rotation speed V 3  moves to the contact position in contact with the toner supply roller  550  with the additional rotation of the developing roller  510 , after the rotation speed of the developing roller  510  becomes the third rotation speed V 3  at time tb 8 , at the time of stopping the rotation of the developing roller  510 . 
     The reason for defining the stop timing of the developing roller  510  as described above is described now. As described above, in order to shake and remove the filming from the rubber portion  562 , the control unit  100  allows the developing roller  510  to rotate at the fourth rotation speed V 4  from time tb 5  to time tb 7 . Specifically, since the time period when the rubber portion  562  exhibits the glass-like characteristic is from time tb 4  to time tb 8 , the filming is shaken and removed from the rubber portion  562  in the meantime. As described above, when the filming is shaken and removed from the rubber portion  562 , some of the filming moves to the developing roller  510  and is attached to the surface of the developing roller  510 . The filming attached to the surface moves from the contact position in contact with the rubber portion  562  with the rotation of the developing roller  510 , finally reaches the contact position in contact with the toner supply roller  550 , is raked out at the contact position by the toner supply roller  550 , and is properly collected into the toner container  530 . It is preferable that the filming shaken and removed and attached to the surface from time tb 4  to time tb 8  is preferably raked out at the contact position by the toner supply roller  550  before the developing roller  510  is stopped at time tb 12 . 
     Accordingly, in consideration of the above-mentioned point, the control unit  100  according to this embodiment stops the rotation at time tb 12  after the time point (time tb 10 ) in a time period (that is, a time period when the filming finally attached to the surface moves from the contact position with the rotation of the developing roller  510  and reaches the contact position), when the portion, on the surface of the developing roller  510 , in contact with the rubber portion  562  when the rotation speed of the developing roller  510  becomes the third rotation speed V 3  (time tb 8 ) moves to the contact position in contact with the toner supply roller  550  with the additional rotation of the developing roller  510 , after the rotation speed of the developing roller  510  becomes the third rotation speed V 3  at time tb 8  (that is, after the filming is finally attached to the surface of the developing roller  510 ), at the time of stopping the rotation of the developing roller  510 . 
     After starting stopping the rotation of the developing roller  510  at time tb 7 , the control unit  100  stops the developing roller  510  for a sufficient time period so as to embody the above-mentioned point. More specifically, the control unit  100  gives the developing roller  510  an instruction for allowing the developing roller  510  to rotate at the fifth rotation speed V 5  (that is, the developing rotation speed) at time tb 7 , and lowers the rotation speed of the developing roller  510  to the second rotation speed V 2 . The rotation speed of the developing roller  510  slowly decreases from the fourth rotation speed V 4 , passes through the third rotation speed V 3  at time tb 8 , and reaches the fifth rotation speed V 5  at time tb 9 . After allowing the developing roller  510  at the fifth rotation speed V 5  for a moment, the control unit gives the developing roller  510  an instruction for stopping the developing roller  510  at time tb 11 , and lowers the rotation speed of the developing roller  510  to 0. The rotation speed of the developing roller  510  slowly decreases from the fifth rotation speed V 5  and becomes 0 at time tb 12  (the developing roller  510  is stopped). In this embodiment, time tb 7  is set so that the time period from time tb 5  to time tb 7 , that is, the time period when the developing roller  510  rotates at the fourth rotation speed V 4  is greater than the time period (about 70 msec in this embodiment) when the developing roller  510  rotates once. 
     Effectiveness of Printer  10  According to Embodiment 
     As described above, in the printer  10  according to this embodiment, the control unit  100  starts the rotation of the developing roller  510 , then raises the rotation speed of the developing roller  510  up to the first rotation speed V 1  at which the movement speed is greater than the product of the pitch and the boundary number of vibrations, lowers the rotation speed of the developing roller  510  up to the second rotation speed V 2  at which the movement speed is smaller than the product of the pitch and the boundary number of vibrations after the rotation speed of the developing roller  510  becomes the first rotation speed V 1 , and allows the developing roller  510  rotating at the second rotation speed V 2  to develop the latent image. Accordingly, the filming is properly shaken and removed from the rubber portion  562  before the filming is remarkable. As a result, the deterioration in image quality of an image developed and finally formed on the medium can be properly prevented. 
     In the printer  10  according to this embodiment, the control unit  100  lowers the rotation speed of the developing roller  510  from the first rotation speed V 1  to the second rotation speed V 2  via the third rotation speed V 3  at which the movement speed is equal to the product after the rotation speed of the developing roller  5  to becomes the first rotation speed V 1 , and starts the application of the developing bias by the developing bias application section  121  after the rotation speed of the developing roller  510  becomes the third rotation speed V 3 . More specifically, the control unit starts the application of the developing bias after the time point in a time period, when the portion, on the surface of the developing roller  510 , in contact with the rubber portion  562  when the rotation speed of the developing roller  510  becomes the third rotation speed V 3  moves to the position opposed to the photosensitive member  20  with the additional rotation of the developing roller  510 , after the rotation speed of the developing roller  510  becomes the third rotation speed V 3 . Accordingly, the filming hardly moves to the photosensitive member  20  and is properly collected by the toner container  530 . By starting the application of the developing bias from the developing bias application section  121  after the rotation speed of the developing roller  510  becomes the third rotation speed V 3 , the above-mentioned advantage (that is, the advantage of allowing the toner container  530  to properly collect the filming) is obtained even when the application of the developing bias is started before the above-mentioned time point. For the purpose of obtaining the complete advantage, it is preferable that the application of the developing bias is started after the above-mentioned time point. 
     In the printer  10  according to this embodiment, the control unit  100  allows the developing roller  510 , which rotates at the fifth rotation speed V 5  at which the movement speed is smaller than the product of the pitch and the boundary number of vibrations, to develop the latent image, raises the rotation speed of the developing roller  510  to the fourth rotation speed V 4  at which the movement speed is greater than the product after ending the developing of the latent image, and stops the rotation of the developing roller  510  after the rotation speed of the developing roller  510  becomes the fourth rotation speed V 4 . Accordingly, the filming is properly shaken and removed from the rubber portion  562  before the filming is remarkable. Accordingly, the deterioration in image quality of the image developed and finally formed on the medium is properly prevented. 
     In the printer  10  according to this embodiment, the control unit  100  raises the rotation speed of the developing roller  510  from the fifth rotation speed V 5  to the fourth rotation speed V 4  via the third rotation speed V 3  at which the movement speed is equal to the product after ending the developing of the latent image, and stops the application of the developing bias from the developing bias application section  121  before the rotation speed of the developing roller  510  becomes the third rotation speed V 3 . More specifically, the control unit stops the application of the developing bias before the time point in the time period, when the portion, on the surface of the developing roller  510 , in contact with the rubber portion  562  when the rotation speed of the developing roller  510  becomes the third rotation speed V 3  moves to the position opposed to the photosensitive member  20  with the additional rotation of the developing roller  510 , after the rotation speed of the developing roller  510  becomes the third rotation speed V 3 . Accordingly, the filming hardly moves to the photosensitive member  20  and is properly collected in the toner container  530 . By stopping the application of the developing bias before the above-mentioned time point, the above-mentioned advantage (that is, the advantage of allowing the toner container  530  to properly collect the filming) is obtained. For the purpose of obtaining the complete advantage with a margin, it is preferable that the application of the developing bias is stopped before the rotation speed of the developing roller  510  becomes the third rotation speed V 3 . 
     In the printer  10  according to this embodiment, at the time of stopping the rotation of the developing roller  510  after the rotation speed of the developing roller  510  becomes the fourth rotation speed V 4 , the control unit  100  stops the rotation after the time point in the time period, when the portion, on the surface of the developing roller  510 , in contact with the rubber portion  562  when the rotation speed of the developing roller  510  becomes the third rotation speed V 3  moves to the position in contact with the toner supply roller  550  with the additional rotation of the developing roller  510 , after the rotation speed of the developing roller  510  becomes the third rotation speed V 3 . Accordingly, the filming is properly removed by the toner supply roller  550  before the rotation of the developing roller  510  is stopped. 
     Method of Manufacturing Developing Roller  510   
     A method of manufacturing the developing roller  510  is described now with reference to  FIGS. 16A to 16E  and  FIG. 17 .  FIGS. 16A to 16E  are schematic diagrams the change of the developing roller  510  in a process of manufacturing the developing roller  510 .  FIG. 17  is an explanatory diagram illustrating a rolling process of the developing roller  510 . 
     First as shown in  FIG. 16A , a pipe member  600  is prepared as a base member of the developing roller  510 . The thickness of the pipe member  600  is 0.5 to 3 mm. Next, as shown in  FIG. 16B , a flange pressing-insertion portion  602  is formed at both ends in the longitudinal direction of the pipe member  600 . The flange pressing-insertion portion  602  is formed by a cutting process. Next, as shown in  FIG. 16C , a flange  604  is inserted into the flange pressing-insertion portion  602 . In order to reliably fix the flange  604  to the pipe member  60   p , the flange  604  may be bonded or welded to the pipe member  600  after the flange  604  is inserted. Next, as shown in  FIG. 16D , a centerless grinding process is performed on the surface of the pipe member  600  into which the flange  604  is inserted. The centerless grinding process is performed on the entire surface and the 10-point average roughness Rz of the surface having been subjected to the centerless grinding process is 1.0 μm or less. Next, as shown in  FIG. 16E , a rolling process is performed on the pipe member  600  into which the flange  604  is inserted. In this embodiment, a so-called throughfeed rolling process using two round dices  650  and  652  is performed. 
     That is, as shown in  FIG. 17 , in a state where two round dices  650  and  652  disposed to interpose the pipe member  600  as a workpiece therebetween are pressed against the pipe member  600  with a predetermined pressure (of which the direction is indicated by reference sign P in  FIG. 17 ), two round dices  650  and  652  are made to rotate in the same direction (see  FIG. 17 ). In the throughfeed rolling process, with the rotation of the round dices  650  and  652 , the pipe member  600  moves in the direction indicated by reference sign H in  FIG. 17  while rotating in the opposite direction of the rotation direction of the round dices  650  and  652 . Convex portions  650   a  and  652   a  for forming grooves  680  are formed on the surface of the round dices  650  and  652 . The convex portions  650   a  and  652   a  deform the pipe member  600  to form the grooves  680  (corresponding to the grooves  512  in  FIG. 5 ) in the pipe member  600 . 
     After the rolling process is finished, the surface of the center portion  510   a  is plated. In this embodiment, electroless Ni—P plating is used, but the invention is not limited to it. For example, hard chrome plating or electrical plating may be used. 
     Other Embodiments 
     Although the image forming apparatus, etc. according to the invention have been described with reference to the above-mentioned embodiments, the embodiments are intended to easily understand the invention, but not to define the invention. The invention may be modified in various forms without departing from the gist thereof and the invention includes equivalents thereof. 
     Although an intermediate transfer type full color laser beam printer has been described as the image forming apparatus in the embodiments, the invention may be applied to various image forming apparatuses such as a full color laser beam printer other than the intermediate transfer type, a monochrome laser beam printer, a copier, and a facsimile. 
     As the photosensitive member, a so-called photosensitive belt in which a photosensitive layer is formed on the surface of a belt-like conductive base member may be employed as well as a so-called photosensitive roller in which a photosensitive layer is formed on the peripheral surface of a cylindrical conductive base member. 
     In the above-mentioned embodiments, as shown in  FIG. 4 , the rubber portion  562  being in contact with the surface of the developing roller  510  so as to regulate the layer thickness of the toner held on the developing roller  510  has been employed as the contact member, but the invention is not limited to the rubber portion. For example, the upper seal  520  or the toner supply roller  550  may be used as the contact member as long as it is made of an elastic rubber material. 
     However, when the rubber portion  562  is used as the contact member, it is possible to prevent the layer thickness of the toner from being improperly regulated due to the use of the rubber portion  562  with the glass-like characteristic by satisfying the relation of V/L 1 &lt;f. As a result, the above-mentioned embodiments are more preferable, in that the developing can be more properly performed by the developing roller  510 . 
     In the above-mentioned embodiment, the rubber portion  562  is in contact with the surface so that the longitudinal direction thereof is parallel to the axial direction of the developing roller  510  and one end in the width direction thereof (that is, the end  560   a  of the regulating blade  560 ) faces the upstream side in the rotation direction of the developing roller  510 . The contact portion  562   a  of the rubber portion  562  coming in contact with the surface of the developing roller  510  is apart from the end in the width direction (that is, the rubber portion  562  is in contact with the developing roller  510  at the center portion). However, the invention is not limited to the embodiment. For example, the contact portion  562   a , that is, the rubber portion  562 , may be in contact with the developing roller  510  at the edge. 
     In the above-mentioned embodiments, the rubber portion  562  has been made of thermoplastic elastomer as a kind of elastic rubber material, but the invention is not limited to the thermoplastic elastomer. For example, the rubber portion  562  may be made of rubber (more specifically, urethane rubber). 
     In the above-mentioned embodiments, as shown in  FIG. 4 , the rubber portion  562  (layer thickness regulating member) being in contact with the surface of the developing roller  510  so as to regulate the layer thickness of the toner held on the developing roller  510  has been employed as the contact member, but the invention is not limited to the rubber portion. For example, the upper seal  520  or the toner supply roller  550  may be used as the contact member as long as it is made of an elastic rubber material. 
     However, when the rubber portion  562  is used as the contact member, the above-mentioned embodiments are more preferable in that the rubber portion  562  can be used with the rubber-like characteristic to properly regulate the layer thickness of the toner by satisfying the relation of V/L 1 &lt;f. 
     In the above-mentioned embodiment, as shown in  FIG. 4 , the rubber portion is in contact with the surface of the developing roller  510  so that the longitudinal direction thereof is parallel to the axial direction of the developing roller  510  and one end in the width direction thereof (that is, an end  560   a  of the regulating blade  560 ) faces the upstream side in the rotation direction of the developing roller  510 . The contact portion  562   a  of the rubber portion  562  coming in contact with the surface of the developing roller  510  is apart from the end in the width direction (that is, the rubber portion  562  is in contact with the developing roller  510  at the center portion). However, the invention is not limited to the embodiment. For example, the contact portion of the rubber portion  562  is the end (that is, the rubber portion  562  is in contact with the developing roller  510  at the edge thereof). 
     However, as described below, the above-mentioned embodiments are more preferable in that the generation of the filming can be suppressed between the contact portion  562   a  of the rubber portion  562  and the end (end  560   a ). That is, when the rubber portion  562  is in contact with the developing roller  510  at the center portion, the filming may be generated between the contact portion  562   a  and the end due to the increase in temperature of the rubber portion  562 . Therefore, by setting the value V/L 1  to the same magnitude as the number of vibrations at which the loss elastic modulus G″ is smaller than the storage elastic modulus G′, the increase in temperature of the rubber portion  562  can be suppressed. As a result, the filming is suppressed from being generated between the contact portion  562   a  and the end. 
     In the above-mentioned embodiments, as shown in  FIG. 6 , two types of spiral grooves  512  of which the tilt angles about the peripheral direction of the developing roller  510  are different from each other have been employed as the concave portions and two types of spiral grooves  512  intersect each other to form a lattice shape, but the invention is not limited to the grooves. For example, the concave portions may not have a groove shape. When the concave portions have a groove shape, the grooves may not have a spiral shape. One type of grooves may be employed as the concave portions. 
     In the above-mentioned embodiments, as shown in  FIG. 6 , the developing roller  510  has the square-like top faces  515  surrounded with two types of spiral grooves  512  and one of two diagonals of each square-like top face  515  is parallel to the peripheral direction of the developing roller  510 , but the invention is not limited to such a developing roller. For example, as shown in  FIG. 18B , the top face may have a diamond shape instead of the square shape. The top face may have a circular shape as shown in  FIG. 18C , instead of the diamond shape. As shown in  FIG. 18A , both of two diagonals of the square-like top face may not be parallel to the peripheral direction.  FIGS. 18A to 18C  are diagrams illustrating variations of the surface shape of the developing roller  510 . 
     In the above-mentioned embodiments, the grooves  512  have the bottom surface  514  and the side surface  513  and the slope angle of the side surface  513  is about 45 degree (see  FIG. 7 ), but the invention is not limited to it. For example, the slope angle of the side surfaces  513  may be about 90 degree. 
     In the above-mentioned embodiments, the developing apparatuses  51 ,  52 ,  53 , and  54  can be mounted on and demounted from the printer body  10   a  of the printer  10  (see  FIG. 1 ), the operating temperature range is set in the printer  10 , and the number of vibrations of the rubber portion  562  when the loss tangent (tan δ) is the greatest varies depending on the magnitude of the temperature (see  FIG. 11 ). The value V/L 1  obtained by dividing the movement speed V of the surface at the time of the rotation of the developing roller  510  by the pitch L 1  of the grooves  512  in the peripheral direction of the developing roller  510  is set to be smaller than the peak frequency f of the rubber portion  562  when the loss tangent (tan δ) is the greatest at all the temperatures in the operating temperature range (specifically, 10° C. to 35° C., but the invention is not limited to the setting. For example, the relation of V/L 1 &lt;f may not be satisfied at some temperatures in the operating temperature range. 
     However, when the relation of V/L 1 &lt;f is satisfied at all the temperatures in the operating temperature range, the above-mentioned embodiments are more preferable in that the rubber portion  562  can be used with the rubber-like characteristic when the printer  10  forms an image. 
     In the above-mentioned embodiments, the rubber portion  562  is made of thermoplastic elastomer, but the invention is not limited to the material. For example, the rubber portion  562  may be made of urethane rubber. 
     In the above-mentioned embodiments, the value V/L 1  obtained by dividing the movement speed V of the surface at the time of the rotation of the developing roller  510  by the pitch L 1  of the grooves  512  in the peripheral direction of the developing roller  510  is set to be smaller than the peak frequency (number of vibrations) f of the rubber portion  562  when the loss tangent (tan δ) is the greatest, and to be smaller than the number of vibrations f 2  (see  FIGS. 13 to 15 ) at which the loss tangent (tan δ) is a half of the greatest value at the frequency, but the invention is not to the setting. For example, the value V/L 1  may be set to have a magnitude between the peak frequency f 1  and the frequency B 2 . 
     However, when the value V/L 1  is smaller than the frequency f 2  and the movement speed V of the developing roller  510  varies to change the number of vibrations (frequency) of the rubber portion  562 , the number of vibrations (frequency) is hardly greater than the peak frequency f (in other words, the rubber portion  562  hardly exhibits the glass-like characteristic. Accordingly, the above-mentioned embodiments are more preferable in that the rubber portion  562  can be properly used with the rubber-like characteristic at the time of the rotation of the developing roller  510 . 
     In the printer  10 , the operating temperature range (for example, the range of temperature in which no problem is guaranteed to occur at the time of using the printer  10 ) is set. However, even when the printer  10  is used at any temperature in the operating temperature range, it is preferable that the rotation speed of the developing roller  510  is raised up to the first rotation speed V 1  or the fourth rotation speed V 4  at which the movement speed is greater than the product of the pitch and the boundary number of vibrations. 
     It is known that the value of the number of vibrations minutely varies with the variation in temperature of the rubber portion  562 . Accordingly, the value of the boundary number of vibrations slightly varies depending on what temperature in the operating temperature range the printer  10  is used at. Therefore, when the rotation speed of the developing roller  510  is set to a predetermined rotation speed, the predetermined rotation speed may become a rotation speed at which the movement speed is greater than the product of the pitch and the boundary number of vibrations at some temperatures in the operating temperature range, and the predetermined rotation speed may become a rotation speed at which the movement speed is smaller than the product of the pitch and the boundary number of vibrations at other temperatures in the operating temperature range. 
     Even when the rotation speed of the developing roller  510  is raised to the first rotation speed V 1  or the fourth rotation speed V 4  at which the movement speed is greater than the product of the pitch and the boundary number of vibrations at some temperatures in the operating temperature range, the above-mentioned advantage (that is, the advantage of properly preventing the deterioration in image quality) is sufficiently obtained, but it is preferable that the rotation speed of the developing roller  510  is raised to the first rotation speed V 1  or the fourth rotation speed V 4  at which the movement speed is greater than the product of the pitch and the boundary number of vibrations in the entire operating temperature range. 
     Configuration of Image Forming System 
     An image forming system according to an embodiment of the invention is described now with reference to the drawings. 
       FIG. 19  is a diagram illustrating an appearance of an 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 . The computer  702  is received in a mini tower type chassis in this embodiment, but is not limited to such a type. The display device  704  usually employs a cathode ray tube (CRT), or a plasma display, or a liquid crystal display, but is not limited to the devices. The printer  706  employs the above-mentioned printer. The input device  708  employs a keyboard  708 A and a mouse  708 B in this embodiment, but is not limited to such devices. The reading device  710  employs a flexible disk drive  710 A and a CD-ROM drive  710 B in this embodiment, but is not limited to such device. For example, other devices may be employed, such as an MO (Magneto Optical) disk drive or a DVD (Digital Versatile Disk). 
       FIG. 20  is a block diagram illustrating a configuration of the image forming system shown in  FIG. 19 . An internal memory  802  such as RAM and an external memory such as a hard disk drive unit  804  are additionally disposed in the chassis in which the computer  702  is received. 
     It has been described above that the image forming system is constructed by connecting the printer  706  to the computer  702 , the display device  704 , the input device  708 , and the reading device  710 , but the invention is not limited to such a construction. For example, the image forming system may includes the computer  702  and the printer  706  and the image forming system may not include any one 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 . For example, the printer  706  may be constructed to have an image processing unit processing an image, a display unit performing various display operations, and a recording medium mounting unit to and from which a recording medium in which image data photographed with a digital camera are recorded is attached and detached. 
     The image forming system embodied in the above-mentioned way is more excellent than a conventional system as a whole.