Transfer bias applying method for an image forming apparatus and device for the same

In a bias applying device configured to form, at each of image transfer positions where a plurality of image carriers and an image transfer belt moving in contact with surfaces of said plurality of image carriers, an electric field for transferring a toner image formed on a respective image carrier to a transfer medium by applying a bias to said image transfer belt, said bias applying device comprising:

• a plurality of bias applying means each for applying the bias to said image transfer belt at a respective image transfer position;
• a plurality of high-potential power supply sections each being connected to one of said plurality of bias applying means for applying a bias, which consists of a DC component and a particular AC component superposed on said DC component, to respective bias applying means;
• a plurality of sensing sections each being connected one of said plurality of bias applying means for sensing the AC component of the bias of respective bias applying means;
• and
• a central processing unit configured to control said plurality of high-tension power supply sections and said plurality of sensing sections;
• a bias applying method for said bias applying device comprising the steps of:
• causing each of said high-tension power supply sections to apply a DC component on which alternating biases perpendicular to each other are superposed to particular bias applying means;
• selectively detecting said alternating biases to thereby measure an absolute value;
• calculating, based on said absolute value, a resistance between nodes;
• estimating a coupling impedance corresponding to the resistance and a leak current to appear when the DC component is applied alone;
• and
• adding the leak current to an original target DC current to thereby correct the bias.

A bias applying device configured to form, at each of image transfer positions where a plurality of image carriers and an image transfer belt moving in contact with surfaces of said plurality of image carriers, an electric field for transferring a toner image formed on a respective image carrier to a transfer medium by applying a bias to said image transfer belt, said bias applying device comprising:

• a plurality of bias applying means each for applying the bias to said image transfer belt at a respective image transfer position;
• a plurality of high-potential power supply sections each being connected to one of said plurality of bias applying means for applying a bias, which consists of a DC component and a particular AC component superposed on said DC component, to respective bias applying means;
• a plurality of sensing sections each being connected one of said plurality of bias applying means for sensing the AC component of the bias of respective bias applying means;
• a central processing unit configured to control said plurality of high-tension power supply sections and said plurality of sensing sections;
• and
• bias correcting means configured to detect an AC component of a second high-tension power supply section, which is detected in the vicinity of an output of a first high-tension power supply section, determine an AC resistance between said first high-tension power supply section and said second high-tension power supply section on the basis of an absolute value of said AC component detected, estimate a leak current of a DC component by referencing a table listing a correlation between AC resistances and DC resistances and prepared beforehand, and add said leak current to a set DC value assigned to said first high-tension power supply section to thereby correct the bias.

An image forming apparatus comprising:

• a plurality of image forming means each comprising an image carrier for forming a latent image thereon, latent image forming means forming said latent image on said image carrier, developing means for developing said latent image to thereby produce a corresponding toner image, and image transferring means for transferring said toner image to a transfer medium, and an image transfer belt movable in contact with surfaces of image carriers of said plurality of image forming means;
• said image transferring means comprising a bias applying means configured to form, at each of image transfer positions where a plurality of image carriers and an image transfer belt moving in contact with surfaces of said plurality of image carriers, an electric field for transferring a toner image formed on a respective image carrier to a transfer medium by applying a bias to said image transfer belt;
• said bias applying device comprising:
• a plurality of bias applying means each for applying the bias to said image transfer belt at a respective image transfer position;
• a plurality of high-potential power supply sections each being connected to one of said plurality of bias applying means for applying a bias, which consists of a DC component and a particular AC component superposed on said DC component, to respective bias applying means;
• a plurality of sensing sections each being connected one of said plurality of bias applying means for sensing the AC component of the bias of respective bias applying means;
• a central processing unit configured to control said plurality of high-tension power supply sections and said plurality of sensing sections;
• and
• bias correcting means configured to detect an AC component of a second high-tension power supply section, which is detected in the vicinity of an output of a first high-tension power supply section, determine an AC resistance between said first high-tension power supply section and said second high-tension power supply section on the basis of an absolute value of said AC component detected, estimate a leak current of a DC component by referencing a table listing a correlation between AC resistances and DC resistances and prepared beforehand, and add said leak current to a set DC value assigned to said first high-tension power supply section to thereby correct the bias.