Method of and apparatus for stabilizing electrophotographic images

Claim 1

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image on an image bearing member by an electrostatic image formation process including charging and image exposure steps applied to the surface of the member; detecting the light region and the dark region surface potentials of the electrostatic latent image formed on the member; determining the difference between said light region surface potential and dark region surface potential to obtain an electrostatic contrast value and modifying the charging condition in accordance with the value of said contrast to adjust said electrostatic contrast to a predetermined value; and modifying the background portion potential to a predetermined potential, which would not create fog when said electrostatic image is developed into a visible image, without substantially varying the modified electrostatic contrast.

Claim 2

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image on an image bearing member by an electrostatic image formation process including charging and image exposure steps applied to the surface of the member; detecting the light region and the dark region surface potentials of the electrostatic latent image formed on the member; determining the difference between said light region surface potential and dark region surface potential to obtain an electrostatic contrast value and modifying the charging condition in accordance with the value of said contrast to adjust said electrostatic contrast to a predetermined value; and modifying the background portion potential to a predetermined potential, which would not create fog when said electrostatic image is developed into a visible image, without substantially varying the modified electrostatic contrast.

Claim 9

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image on an image bearing member by an electrostatic image formation process including charging and image exposure steps applied to the surface of the member; detecting the light region and the dark region surface potentials of the electrostatic latent image formed on the member; determining the difference between said light region surface potential and dark region surface potential to obtain an electrostatic contrast value and modifying the charging condition in accordance with the value of said contrast to adjust said electrostatic contrast to a predetermined value; and modifying the background portion potential to a predetermined potential, which would not create fog when said electrostatic image is developed into a visible image, without substantially varying the modified electrostatic contrast; wherein said electrostatic image bearing member is a movable drum shaped photosensitive medium, and wherein the step of detecting the surface potential of said image bearing member is preformed by measuring the surface potential and comprises rotating a rotatable electrode in opposed relationship with the surface potential of said photosensitive medium, said electrode having a center of rotation parallel to the support shaft of said photosensitive medium and having a shape in which the electrostatic capacity with respect to the photosensitive medium differs in accordance with the angle of rotation, varying the electrostatic capacity with respect to the potential surface within the range of C 2 -C 3 (C 2 >C 3 ) in accordance with the shape variation of said electrode, wherein C 2 and C 3 are the electrostatic capacities at the nearest point and the most remote point, respectively, of the electrode with respect to the photosensitive medium, said electrode being disposed so that the ground capacity C 4 of said electrode excepting said photosensitive medium satisfies C 4 <<C 2 , rendering the charge Q induced in said electrode substantially equal to the product of constants C 1 , C 2 and C 3 and the surface potential V 1 of the photosensitive medium, to thereby measure the surface potential V 1 of said photosensitive medium, wherein C 1 is the electrostatic capacity of the potential surface of said photosensitive medium.

Claim 10

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image on an image bearing member by an electrostatic image formation process including charging and image exposure steps applied to the surface of the member; detecting the light region and the dark region surface potentials of the electrostatic latent image formed on the member; determining the difference between said light region surface potential and dark region surface potential to obtain an electrostatic contrast value and modifying the charging condition in accordance with the value of said contrast to adjust said electrostatic contrast to a predetermined value; and modifying the background portion potential to a predetermined potential, which would not create fog when said electrostatic image is developed into a visible image, without substantially varying the modified electrostatic contrast; wherein said electrostatic image bearing member is a movable drum shaped photosensitive medium, and wherein the step of detecting the surface potential of said image bearing member is preformed by measuring the surface potential and comprises rotating a rotatable electrode in opposed relationship with the surface potential of said photosensitive medium, said electrode having a center of rotation parallel to the support shaft of said photosensitive medium and having a shape in which the electrostatic capacity with respect to the photosensitive medium differs in accordance with the angle of rotation, varying the electrostatic capacity with respect to the potential surface within the range of C 2 -C 3 (C 2 >C 3 ) in accordance with the shape variation of said electrode, wherein C 2 and C 3 are the electrostatic capacities at the nearest point and the most remote point, respectively, of the electrode with respect to the photosensitive medium, said electrode being disposed so that the ground capacity C 4 of said electrode excepting said photosensitive medium satisfies C 4 <<C 2 , rendering the charge Q induced in said electrode substantially equal to the product of constants C 1 , C 2 and C 3 and the surface potential V 1 of the photosensitive medium, to thereby measure the surface potential V 1 of said photosensitive medium, wherein C 1 is the electrostatic capacity of the potential surface of said photosensitive medium.

Claim 13

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image on an image bearing member by an electrostatic image formation process including charging and image exposure steps applied to the surface of the member; detecting the light region and the dark region surface potentials of the electrostatic latent image formed on the member; determining the difference between said light region surface potential and dark region surface potential to obtain an electrostatic contrast value and modifying the charging condition in accordance with the value of said contrast to adjust said electrostatic contrast to a predetermined value; and modifying the background portion potential to a predetermined potential, which would not create fog when said electrostatic image is developed into a visible image, without substantially varying the modified electrostatic contrast; wherein said electrostatic image bearing member is a movable drum shaped photosensitive medium, and wherein the step of detecting the surface potential of said image bearing member is performed by measuring the surface potential and comprises providing a rotatable electrode having a rotary shaft parallel to the shaft of the movable photosensitive medium and having a shape in which the electrostatic capacities C 2 and C 3 at the nearest point and the most remote point, respectively, of the electrode with respect to the surface of the photosensitive member differ (C 2 >C 3 ) in accordance with the angle of rotation, said electrode being disposed in a spaced apart relationship with various elements disposed around said electrode so that the ground capacity C 4 of the electrode excepting the photosensitive medium is negligible with respect to C 2 , whereby C 4 does not substantially affect the charge induced on said electrode.

Claim 14

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image on an image bearing member by an electrostatic image formation process including charging and image exposure steps applied to the surface of the member; detecting the light region and the dark region surface potentials of the electrostatic latent image formed on the member; determining the difference between said light region surface potential and dark region surface potential to obtain an electrostatic contrast value and modifying the charging condition in accordance with the value of said contrast to adjust said electrostatic contrast to a predetermined value; and modifying the background portion potential to a predetermined potential, which would not create fog when said electrostatic image is developed into a visible image, without substantially varying the modified electrostatic contrast; wherein said electrostatic image bearing member is a movable drum shaped photosensitive medium, and wherein the step of detecting the surface potential of said image bearing member is performed by measuring the surface potential and comprises providing a rotatable electrode having a rotary shaft parallel to the shaft of the movable photosensitive medium and having a shape in which the electrostatic capacities C 2 and C 3 at the nearest point and the most remote point, respectively, of the electrode with respect to the surface of the photosensitive member differ (C 2 >C 3 ) in accordance with the angle of rotation, said electrode being disposed in a spaced apart relationship with various elements disposed around said electrode so that the ground capacity C 4 of the electrode excepting the photosensitive medium is negligible with respect to C 2 , whereby C 4 does not substantially affect the charge induced on said electrode.

Claim 15

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image corresponding to the light and dark regions of an original by an electrostatic image formation process including charging and image exposure steps; measuring the light region and the dark region potentials of said electrostatic latent image formed on the member; determining the difference between said light region potential and said dark region potential to obtain an electrostatic contrast value and modifying the charging condition in accordance with the value of said contrast to adjust said electrostatic contrast to a predetermined value; adjusting the light or the dark region of the electrostatic image under said modified condition; measuring the light or the dark region potential of said adjusted image; and controlling a bias voltage during development of said adjusted image in accordance with said last-measured light or said dark region potential.

Claim 16

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image corresponding to the light and dark regions of an original by an electrostatic image formation process including charging and image exposure steps; measuring the light region and the dark region potentials of said electrostatic latent image formed on the member; determining the difference between said light region potential and said dark region potential to obtain an electrostatic contrast value and modifying the charging condition in accordance with the value of said contrast to adjust said electrostatic contrast to a predetermined value; adjusting the light or the dark region of the electrostatic image under said modified condition; measuring the light or the dark region potential of said adjusted image; and controlling a bias voltage during development of said adjusted image in accordance with said last-measured light or said dark region potential.

Claim 20

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image by an electrostatic image formation process including primary charging and secondary charging or discharging and image exposure steps; measuring the light region and the dark region potential of said electrostatic latent image; determining the difference between said two potentials to thereby obtain an electrostatic contrast value and modifying the primary charging condition in accordance with the value of the contrast to thereby adjust said electrostatic contrast to a predetermined value; forming an electrostatic image under the said modified condition; measuring the potential of the light or the dark region of said reformed electrostatic image; and controlling the secondary charging or discharging condition in accordance with the last-measured value to thereby adjust the light or the dark region potential to a predetermined value.

Claim 21

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image by an electrostatic image formation process including primary charging and secondary charging or discharging and image exposure steps; measuring the light region and the dark region potential of said electrostatic latent image; determining the difference between said two potentials to thereby obtain an electrostatic contrast value and modifying the primary charging condition in accordance with the value of the contrast to thereby adjust said electrostatic contrast to a predetermined value; forming an electrostatic image under the said modified condition; measuring the potential of the light or the dark region of said reformed electrostatic image; and controlling the secondary charging or discharging condition in accordance with the last-measured value to thereby adjust the light or the dark region potential to a predetermined value.

Claim 22

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image on a photosensitive medium by an electrostatic image formation process including primary charging and secondary charging or discharging and exposure steps; measuring the light region and the dark region potential of said electrostatic latent image formed on the member; determining the difference between said two potentials to thereby obtain an electrostatic contrast value and modifying the primary charging condition in accordance with the value of the contrast to thereby adjust said electrostatic contrast to a predetermined value; reforming an electrostatic image under said modified condition; measuring the potential of a light and dark region of said reformed electrostatic image; controlling the secondary charging or discharging condition in accordance with the last-measured value to thereby adjust the light or the dark region potential to a predetermined value; and adjusting the amount of exposure so as to impart a proper quantity of light in accordance with the photosensitive medium used.

Claim 23

A method of stabilizing a contrast value of electrophotographic images comprising the steps of: forming an electrostatic latent image on a photosensitive medium by an electrostatic image formation process including primary charging and secondary charging or discharging and exposure steps; measuring the light region and the dark region potential of said electrostatic latent image formed on the member; determining the difference between said two potentials to thereby obtain an electrostatic contrast value and modifying the primary charging condition in accordance with the value of the contrast to thereby adjust said electrostatic contrast to a predetermined value; reforming an electrostatic image under said modified condition; measuring the potential of a light and dark region of said reformed electrostatic image; controlling the secondary charging or discharging condition in accordance with the last-measured value to thereby adjust the light or the dark region potential to a predetermined value; and adjusting the amount of exposure so as to impart a proper quantity of light in accordance with the photosensitive medium used.

Claim 24

An apparatus for stabilizing a contrast value of electrophotographic images comprising: means for uniformly charging a movable photosensitive medium; means for imparting image light to the charged surface of said photosensitive medium to thereby provide an electrostatic latent image thereon; means for detecting the light region and the dark region surface potentials of the electrostatic image formed on said photosensitive medium; means for determining the difference bewteen said detected surface potentials to obtain an electrostatic contrast value and for modifying the charging condition in accordance with the value of said contrast to adjust the electrostatic contrast to a predetermined value; means for modifying the background portion potential, without substantially varying the modified electrostatic contrast, to a potential which would not create fog from a developer when the electrostatic image is developed; and means for developing the electrostatic image having a predetermined electrostatic contrast by the use of developer.

Claim 25

An apparatus for stabilizing a contrast value of electrophotographic images comprising: means for uniformly charging a movable photosensitive medium; means for imparting image light to the charged surface of said photosensitive medium to thereby provide an electrostatic latent image thereon; means for detecting the light region and the dark region surface potentials of the electrostatic image formed on said photosensitive medium; means for determining the difference bewteen said detected surface potentials to obtain an electrostatic contrast value and for modifying the charging condition in accordance with the value of said contrast to adjust the electrostatic contrast to a predetermined value; means for modifying the background portion potential, without substantially varying the modified electrostatic contrast, to a potential which would not create fog from a developer when the electrostatic image is developed; and means for developing the electrostatic image having a predetermined electrostatic contrast by the use of developer.

Claim 26

An apparatus for stabilizing a contrast value of electrophotographic images comprising: means for uniformly charging a movable photosensitive medium; means for imparting image light to the charged surface of said photosensitive medium to thereby provide an electrostatic latent image thereon; means for detecting the light region and the dark region surface potentials of the electrostatic image formed on said photosensitive medium; means for determining the difference between said detected surface potentials to obtain an electrostatic contrast value and for modifying the charging condition in accordance with the value of said contrast to adjust the electrostatic contrast to a predetermined value; means for modifying the background portion potential, without substantially varying the modified electrostatic contrast, to a potential which would not create fog from a developer when the electrostatic image is developed; and means for developing the electrostatic image having a predetermined electrostatic contrast by the use of developer; wherein said photosensitive medium is drum shaped and supported on a shaft, and said means for detecting the surface potentials includes a rotatable electrode in opposed relationship with the surface of said photosensitive medium, said electrode having an axis of rotation parallel to the support shaft of said photosensitive medium and having a shape in which the electrostatic capacities C 2 and C 3 at the nearest point and the most remote point, respectively, of the electrode with respect to the surface of the photosensitive medium, differ in accordance with the angle of rotation, and means for spacing said electrode apart from various elements disposed around said electrode so as to enable the ground capacity C 4 of said electrode excepting the photosensitive medium to be negligible as compared with C 2 , and for maintaining a constant separation between the electrode and the surface of said photosensitive medium.

Claim 27

An apparatus for stabilizing a contrast value of electrophotographic images comprising: means for uniformly charging a movable photosensitive medium; means for imparting image light to the charged surface of said photosensitive medium to thereby provide an electrostatic latent image thereon; means for detecting the light region and the dark region surface potentials of the electrostatic image formed on said photosensitive medium; means for determining the difference between said detected surface potentials to obtain an electrostatic contrast value and for modifying the charging condition in accordance with the value of said contrast to adjust the electrostatic contrast to a predetermined value; means for modifying the background portion potential, without substantially varying the modified electrostatic contrast, to a potential which would not create fog from a developer when the electrostatic image is developed; and means for developing the electrostatic image having a predetermined electrostatic contrast by the use of developer; wherein said photosensitive medium is drum shaped and supported on a shaft, and said means for detecting the surface potentials includes a rotatable electrode in opposed relationship with the surface of said photosensitive medium, said electrode having an axis of rotation parallel to the support shaft of said photosensitive medium and having a shape in which the electrostatic capacities C 2 and C 3 at the nearest point and the most remote point, respectively, of the electrode with respect to the surface of the photosensitive medium, differ in accordance with the angle of rotation, and means for spacing said electrode apart from various elements disposed around said electrode so as to enable the ground capacity C 4 of said electrode excepting the photosensitive medium to be negligible as compared with C 2 , and for maintaining a constant separation between the electrode and the surface of said photosensitive medium.

Claim 28

A method for stabilizing a contrast value of images comprising the steps of: forming an electrostatic latent image on an image bearing member by an electrostatic image formation process including charging and image exposure steps applied to the surface of the member; detecting a difference between the light region surface potential and the dark region surface potential of the electrostatic latent image on the member to obtain an electrostatic contrast value; modifying the charging conditions in accordance with the detected value of said contrast to adjust said electrostatic contrast to a predetermined value; and modifying the background portion potential to a predetermined potential to prevent background development without substantially varying the modified electrostatic contrast.

Claim 29

A method for stabilizing a contrast value of images comprising the steps of: forming an electrostatic latent image on an image bearing member by an electrostatic image formation process including charging and image exposure steps applied to the surface of the member; detecting a difference between the light region surface potential and the dark region surface potential of the electrostatic latent image on the member to obtain an electrostatic contrast value; modifying the charging conditions in accordance with the detected value of said contrast to adjust said electrostatic contrast to a predetermined value; and modifying the background portion potential to a predetermined potential to prevent background development without substantially varying the modified electrostatic contrast.