Heat roll fixing unit with uniform heat distribution

Claim 2

A fixing device comprising a heat roller and a back-up roller, having a predetermined axial length and defining a central portion and side portions each extending from said central portion along the axial length, said fixing device fusing an unfixed toner image carried on a recording sheet during a fixing operation, said sheet having a width less than the predetermined axial length of said back-up roller and contacting said central portion of said back-up roller, wherein said heat roller comprises heater means having an output at axial end portions of said heater means higher than at a central portion of said heater means, for heating a portion of said heat roller corresponding to a passing area of said recording sheet to a higher temperature than of the remaining portions of said heat roller when said rollers are separated, said remaining portions correspond to said side portions of said back-up roller, said heater means of said heat roller comprising means for ensuring that a temperature distribution of said back-up roller becomes substantially uniform along the axial length of said back-up roller while said recording sheet is passing between said heat roller and said back-up roller, and means for moving one of said heat roller and said back-up roller between positions contacting each other and spaced from each other, said heat roller and said back-up roller being in said contacting position during said fixing operation.

Claim 3

The fixing device according to claim 1, wherein said recording sheet is arranged to pass through the axial center portion of the fixing device and the temperature of the axial center portion of said heater means is set to be higher than both axial end portions thereof.

Claim 4

The fixing device according to claim 1, wherein said heating means comprises a halogen lamp extending along the axial direction of said heat roller, said lamp comprising a heat generating element that is arranged to be dense at the axial end portions of said heat roller and sparse at the axial central portion of said heat roller.

Claim 5

The fixing device according to claim 1, wherein said heating means comprises a plurality of heating elements arranged in parallel along the axial direction of said heat roller, said heating elements being arranged to partially heat predetermined axial areas of said heat roller, respectively.

Claim 6

The fixing device according to claim 1, wherein said heating means comprises at least a pair of heating elements arranged in parallel along the axial direction of said heat roller, one of said heating elements being arranged to heat the axial center portion of said heat roller and the other of said heating elements being arranged to heat the axial end portions of said heat roller.

Claim 7

A heat roller employed in an electrophotographic imaging apparatus in connection with a back-up roller for fusing an unfixed toner image carried on a recording sheet during a fixing operation, said recording sheet having a width less than the width of the back-up roller, said heat roller comprising heater means, having an output at axial end portions of said heater means higher than at a central portion of said heater means, for heating a portion of said heat roller corresponding to a passing area of said recording sheet to a higher temperature than that of the remaining portions of said heat roller when said back-up roller is separated from said heat roller, said heater means of said heat roller comprising means for ensuring that a temperature distribution of said back-up roller is substantially uniform along an axial direction of said heat roller, while said recording sheet is passing between said heat roller and said back-up roller, said back-up roller and said fixing roller being in a contacting position during said fixing operation, and being mounted for movement to a separated position.

Claim 8

A heat roller employed in an electrophotographic imaging apparatus in connection with a back-up roller for fusing an unfixed toner image carried on a recording sheet during a fixing operation, said recording sheet having a width less than the width of the back-up roller, said heat roller comprising heater means, having an output at axial end portions of said heater means higher than at a central portion of said heater means, for heating a portion of said heat roller corresponding to a passing area of said recording sheet to a higher temperature than that of the remaining portions of said heat roller when said back-up roller is separated from said heat roller, said heater means of said heat roller comprising means for ensuring that a temperature distribution of said back-up roller is substantially uniform along an axial direction of said heat roller, while said recording sheet is passing between said heat roller and said back-up roller, said back-up roller and said fixing roller being in a contacting position during said fixing operation, and being mounted for movement to a separated position.

Claim 9

A fixing device comprising a heat roller and a back-up roller, said back-up roller having a predetermined axial length defining a central portion and side portions each extending from said central portion, said fixing device fusing an unfixed toner image carried on a recording sheet during a fixing operation, said recording sheet having a width less than the predetermined axial length of said back-up roller and contacting said central portion of said back-up roller, said heat roller comprising heater means installed therein for heating said heat roller, said fixing device being able to load various types of recording sheets having different widths, wherein said heater means comprises a plurality of heating elements arranged in parallel along the axial direction of said heat roller and having an output at axial end portions of said heater means higher than at a central portion of said heater means, said heating elements being arranged to partially heat predetermined axial areas of said heat roller, respectively, so that, when said rollers are in a non-contacting position, the temperature of a portion of said heat roller corresponding to a passing area of the recording sheet is higher than that of the remaining portions of said heat roller by selectively actuating said plurality of heating elements depending upon the width of the recording sheet being loaded, said heating means within said heat roller comprising means for ensuring that a temperature distribution of said back-up roller becomes substantially uniform along its axial direction while the recording sheet is passing between said heat roller and said back-up roller, regardless of the width of the recording sheet to be loaded, said back-up roller and heat roller being in a contacting position during said fixing operation, at least one of said roller mounted for movement to a non-contacting position.

Claim 10

A fixing device comprising a heat roller and a back-up roller, said back-up roller having a predetermined axial length defining a central portion and side portions each extending from said central portion, said fixing device fusing an unfixed toner image carried on a recording sheet during a fixing operation, said recording sheet having a width less than the predetermined axial length of said back-up roller and contacting said central portion of said back-up roller, said heat roller comprising heater means installed therein for heating said heat roller, said fixing device being able to load various types of recording sheets having different widths, wherein said heater means comprises a plurality of heating elements arranged in parallel along the axial direction of said heat roller and having an output at axial end portions of said heater means higher than at a central portion of said heater means, said heating elements being arranged to partially heat predetermined axial areas of said heat roller, respectively, so that, when said rollers are in a non-contacting position, the temperature of a portion of said heat roller corresponding to a passing area of the recording sheet is higher than that of the remaining portions of said heat roller by selectively actuating said plurality of heating elements depending upon the width of the recording sheet being loaded, said heating means within said heat roller comprising means for ensuring that a temperature distribution of said back-up roller becomes substantially uniform along its axial direction while the recording sheet is passing between said heat roller and said back-up roller, regardless of the width of the recording sheet to be loaded, said back-up roller and heat roller being in a contacting position during said fixing operation, at least one of said roller mounted for movement to a non-contacting position.

Claim 11

The fixing device according to claim 7, further comprising: detecting means for detecting the width of the recording sheet loaded; and selecting means for selecting the heating elements to be operational depending upon the result of the detection by said detecting means.

Claim 12

The fixing device according to claim 8, wherein said detecting means comprises a pair of guide members arranged in parallel in the feed direction of said recording sheet, the interval between said guide members being able to change in accordance with the width of the recording sheet loaded.

Claim 13

The fixing device according to claim 7, wherein said heater means comprises a halogen lamp extending in the axial direction of said heat roller, and said heating elements comprise heat generating elements installed therein.

Claim 14

A fixing device comprising a heat roller and a back-up roller, said back-up roller having a predetermined axial length and defining a central portion and side portions each extending from said central portion along the axial length, said fixing device fusing an unfixed toner image carried on a recording sheet during a fixing operation, said sheet having a width less than the predetermined axial length of said back-up roller and contacting said central portion of said back-up roller, said heat roller comprising heater means installed therein for heating said heat roller, said heater means having an output at axial end portions of said heater means higher than at a central portion of said heater means, said fixing device being able to load at least two types of recording sheets having different widths, said heater means comprises at least a pair of heating elements arranged in parallel along the axial direction of said heat roller, one of said heating elements being arranged to partially heat a principle portion of said heat roller corresponding to a passing area of a predetermined one of said types recording sheets, the other of said heating elements being arranged to heat the remaining portions of said heat roller, said heater means comprising means for heating a portion of said heat roller corresponding to a width of a sheet to a higher temperature than of remaining portions of said heat roller when said heat roller is in a non-contacting position with respect to said back-up roller; and wherein said other one of said heating elements is actuated only when a recording sheet loaded is other than said predetermined type of said recording sheets, said heater means within said heat roller comprising means for ensuring that a temperature distribution of said back-up roller is substantially uniform along the axial direction of said heat roller when said recording sheets pass between said heat roller and said back-up roller, regardless of the type of said recording sheets, said heat roller and back-up roller contacting each other during said fixing operation and being mounted for movement to a non-contacting position.

Claim 15

A fixing device comprising a heat roller and a back-up roller, said back-up roller having a predetermined axial length and defining a central portion and side portions each extending from said central portion along the axial length, said fixing device fusing an unfixed toner image carried on a recording sheet during a fixing operation, said sheet having a width less than the predetermined axial length of said back-up roller and contacting said central portion of said back-up roller, said heat roller comprising heater means installed therein for heating said heat roller, said heater means having an output at axial end portions of said heater means higher than at a central portion of said heater means, said fixing device being able to load at least two types of recording sheets having different widths, said heater means comprises at least a pair of heating elements arranged in parallel along the axial direction of said heat roller, one of said heating elements being arranged to partially heat a principle portion of said heat roller corresponding to a passing area of a predetermined one of said types recording sheets, the other of said heating elements being arranged to heat the remaining portions of said heat roller, said heater means comprising means for heating a portion of said heat roller corresponding to a width of a sheet to a higher temperature than of remaining portions of said heat roller when said heat roller is in a non-contacting position with respect to said back-up roller; and wherein said other one of said heating elements is actuated only when a recording sheet loaded is other than said predetermined type of said recording sheets, said heater means within said heat roller comprising means for ensuring that a temperature distribution of said back-up roller is substantially uniform along the axial direction of said heat roller when said recording sheets pass between said heat roller and said back-up roller, regardless of the type of said recording sheets, said heat roller and back-up roller contacting each other during said fixing operation and being mounted for movement to a non-contacting position.

Claim 16

The fixing device according to claim 1, said heating means being positioned exclusively in said heat roller.

Claim 17

The heat roller according to claim 6, said heater means being positioned exclusively within said heat roller.

Claim 18

The fixing device according to claim 7, said heater means being positioned exclusively within said heat roller.

Claim 19

The fixing device according to claim 11, said heater means being positioned exclusively within said heat roller.