Image transferring device and medium separating device for an image forming apparatus

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer medium movable in contact with said photoconductive element over a predetermined nip width to allow the toner image to be transferred from said photoconductive element to said transfer medium;
• transfer bias applying means for applying a predetermined transfer bias to said transfer medium;
• potential gradient generating means for providing the transfer bias applying means with a potential gradient;
• wherein said transfer medium comprises a sheet carried on and transported by a transfer belt which contacts said photoconductive element over a predetermined nip width;
• and wherein the potential gradient generating means includes means for providing the transfer bias applying means with an additional bias potential after the sheet has contacted said photoconductive element;
• the apparatus further including means for varying a time for applying the bias potential by said potential gradient generating means.

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer medium movable in contact with said photoconductive element over a predetermined nip width to allow the toner image to be transferred from said photoconductive element to said transfer medium;
• transfer bias applying means for applying a predetermined transfer bias to said transfer medium, said transfer bias applying means including an upstream bias applicator and a downstream bias applicator, said upstream and downstream applicators located respectively upstream and downstream from a nip location at which said photoconductive element contacts said transfer medium;
• potential gradient generating means for providing the transfer bias applying means with a potential gradient;
• and
• means for varying an amount of bias provided by said potential gradient generating means and applied by at least one of said upstream and downstream bias applicators in response to changes in position of said transfer medium;
• wherein said transfer medium comprises a sheet carried on and transported by a transfer belt which contacts said photoconductive element over a predetermined nip width at said nip location;
• and
• wherein said upstream bias applicator contacts said transfer belt at a position upstream of the nip location, and wherein said means for varying an amount of bias causes application of a bias lower than the transfer bias before the sheet contacts said photoconductive element and then application of a bias substantially equal to said transfer bias after said sheet has contacted said photoconductive element.

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer medium movable in contact with said photoconductive element over a predetermined nip width to allow the toner image to be transferred from said photoconductive element to said transfer medium;
• transfer bias applying means for applying a predetermined transfer bias to said transfer medium, said transfer bias applying means including an upstream bias applicator and a downstream bias applicator, said upstream and downstream applicators located respectively upstream and downstream from a nip location at which said photoconductive element contacts said transfer medium;
• potential gradient generating means for providing the transfer bias applying means with a potential gradient;
• and
• means for varying an amount of bias provided by said potential gradient generating means and applied by at least one of said upstream and downstream bias applicators in response to changes in position of said transfer medium;
• wherein said transfer medium comprises a sheet carried on and transported by a transfer belt which contacts said photoconductive element over a predetermined nip width at said nip location;
• and
• said downstream bias applicator and said nip location being separated by a distance shorter than a distance between said upstream bias applicator and said nip location;
• wherein said means for varying an amount of bias causes said upstream bias applicator to be applied with a bias after the sheet has been transported by said transfer belt over a distance exceeding the distance between said upstream bias applicator and said nip location;
• the apparatus further including means for varying a time for applying the bias potential to said upstream bias applicator.

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer belt in contact with said photoconductive element at a nip portion, said transfer belt transporting a sheet to allow the toner image to be transferred from said photoconductive element to said sheet;
• transfer potential bias applying means for applying a predetermined transfer bias to said transfer belt;
• potential gradient generating means for providing the transfer bias applying means with a first potential gradient having a magnitude greater than zero;
• and
• wherein said potential gradient generating means further includes means for providing the transfer potential bias applying means with an additional bias to thereby provide the transfer potential bias applying means with a second potential gradient after at least a portion of the sheet has entered the nip portion, and wherein a bias potential of at least a portion of said transfer belt has a larger magnitude when the second potential gradient is provided to said transfer bias applying means as compared with the first potential gradient.

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer belt in contact with said photoconductive element over a predetermined nip width at a nip location for transporting a sheet to allow the toner image to be transferred from said photoconductive element to said sheet;
• a downstream bias applicator contacting said transfer belt at a position downstream of said nip location for applying a predetermined bias to said transfer belt;
• and
• an upstream bias applicator having a dielectric layer on a surface thereof and contacting said transfer belt at a position upstream of said nip location, and wherein a common power source applies a voltage to each of said upstream and downstream bias applicators, and wherein said dielectric layer causes said upstream bias applicator to deposit a charge on said transfer belt less efficiently than said downstream bias applicator.

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer belt in contact with said photoconductive element over a predetermined nip width at a nip location for transporting a sheet to allow the toner image to be transferred from said photoconductive element to said sheet;
• a downstream bias applicator contacting said transfer belt at a position downstream of said nip location for applying a predetermined bias to said transfer belt;
• and
• an upstream bias applicator having an elastic dielectric layer on a surface thereof and contacting a rear of said transfer belt at a position upstream of said nip location, and wherein a common power source applies a voltage to each of said upstream and downstream bias applicators, and wherein said dielectric layer causes said upstream bias applicator to deposit a charge on said transfer belt less efficiently than said downstream bias applicator.

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer medium contacting said photoconductive element over a predetermined nip width in a transfer region and undergoing a step of transferring the toner image formed on said photoconductive element a plurality of times;
• a first electrode contacting said transfer medium at a position downstream of the transfer region;
• a second electrode contacting said transfer medium at a position upstream of the transfer region;
• and
• potential gradient generating means for providing a transfer bias with a potential gradient by applying a transfer bias to said first electrode, and applying, when a toner is absent on said transfer medium, a bias of the same polarity as the toner to said second electrode, and further applying, when the toner is present on said transfer medium, a bias of opposite polarity to the toner to said second electrode.

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer belt in contact with said photoconductive element over a predetermined nip width at a nip location for transporting a sheet to allow the toner image to be transferred from said photoconductive element to said sheet;
• a downstream bias applicator contacting said transfer belt at a position downstream of said nip location for applying a predetermined bias to said transfer belt;
• and
• an upstream bias applicator having a dielectric layer on a surface thereof and contacting said transfer belt at a position upstream of said downstream bias applicator, wherein a common power source applies a voltage to each of said upstream and downstream bias applicators, and wherein said dielectric layer causes said upstream bias applicator to deposit a charge on said transfer belt less efficiently than said downstream bias applicator.

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer belt which contacts said photoconductive element;
• first and second bias applicators which contact said transfer belt at separate locations;
• and
• means for applying voltages to each of said first and second bias applicators, said means for applying voltages applying a first voltage to said first bias applicator and a second voltage to said second bias applicator, wherein said second voltage has a same polarity as said first voltage but a smaller magnitude than said first voltage.

An image forming apparatus comprising:

• a photoconductive element for forming a toner image thereon;
• a transfer medium movable in contact with said photoconductive element over a predetermined nip width to allow the toner image to be transferred from said photoconductive element to said transfer medium;
• transfer bias applying means for applying a predetermined transfer bias to at least one of said transfer medium and a transfer belt carrying said transfer medium, said transfer bias applying means including an upstream bias applicator and a downstream bias applicator, said upstream and downstream applicators located respectively upstream and downstream from a nip location at which said photoconductive element contacts said transfer medium;
• and
• potential gradient generating means for providing the transfer bias applying means with a potential gradient;
• and
• the apparatus further comprising means for varying an amount of bias applied by said upstream bias applicator in response to changes in position of said transfer medium, such that a first voltage is applied to said upstream bias applicator before said transfer medium contacts said photoconductive element, and wherein a voltage applied to said upstream bias applicator is increased to a second voltage after said transfer medium contacts photoconductive element, and wherein a magnitude of said second voltage is greater than a magnitude of said first voltage, and further wherein a magnitude of said first voltage is greater than zero.