Fixing device and image forming apparatus incorporating same

1. An image forming apparatus comprising:

a rotatable fixing member to contact an unfixed image;

a pressing member disposed opposite the fixing member to form a fixing nip between the pressing member and the fixing member;

a plurality of heat generators arrayed in a longitudinal direction perpendicular to a direction in which a recording medium is conveyed to heat respective heating areas of the fixing member;

a plurality of temperature detectors disposed to detect a surface temperature of the fixing member and temperatures of the plurality of heat generators;

a power source to supply electric power to the plurality of heat generators to heat the respective heating areas; and

a heat controller to control the power source according to data provided by the temperature detectors, such that, when the unfixed image on the recording medium conveyed to the fixing nip contains an imaged area and a blank area, a temperature T 2 corresponding to the blank area is lower than a temperature T 1 corresponding to the imaged area,

wherein the plurality of heat generators include a first heat generator to heat a heating area of the fixing member corresponding to the imaged area and a plurality of second heat generators to heat heating areas of the fixing member corresponding to the blank area,

wherein the heat controller controls the power source such that one of the plurality of second heat generators located adjacent to the first heat generator is set to a temperature of T 1 −ΔT, where ΔT is a temperature lower than a difference between the temperature T 1 and the temperature T 2 , when the unfixed image on the recording medium conveyed to the fixing nip contains the imaged area and the blank area, and

wherein the heat controller changes ΔT between when a first side of the recording medium is printed upon duplex printing and upon single-sided printing.

2. The image forming apparatus according to claim 1 , wherein the heat controller changes ΔT between when the first side of the recording medium is printed upon the duplex printing and when a second side of the recording medium is printed upon the duplex printing.

3. The image forming apparatus according to claim 1 , wherein the heat controller sets ΔT to zero when the first side of the recording medium is printed upon the duplex printing.

4. The image forming apparatus according to claim 1 , wherein the heat controller controls the power source such that heating areas of the fixing member heated by adjacent heat generators of the plurality of second heat generators acquire a temperature difference of ΔT therebetween in a phased manner starting from the one of the plurality of second heat generators located adjacent to the first heat generator, and

wherein the heat controller determines whether a control temperature is not lower than the temperature T 2 , and controls the power source such that, if a relation of T 1 −n·ΔT>T 2 is satisfied, a heating area of the fixing member heated by an n-th heat generator of the plurality of second heat generators acquires a temperature of T 1 −n·ΔT, where “n” represents an order of the plurality of second heat generators starting from 1 with the one of the plurality of second heat generators located adjacent to the first heat generator, and if a relation of T 1 −n·ΔT<T 2 is satisfied, the heating area of the fixing member heated by the n-th heat generator acquires the temperature T 2 .

5. The image forming apparatus according to claim 1 , wherein the heat controller changes ΔT according to a thickness of the recording medium.

6. The image forming apparatus according to claim 1 , wherein the heat controller changes ΔT according to a type of the recording medium.

7. A fixing device comprising:

a rotatable fixing member to contact an unfixed image;

a pressing member disposed opposite the fixing member to form a fixing nip between the pressing member and the fixing member; and

a plurality of heat generators arrayed in a longitudinal direction perpendicular to a direction in which a recording medium is conveyed to heat respective heating areas of the fixing member such that, when the unfixed image on the recording medium conveyed to the fixing nip contains an imaged area and a blank area, a temperature T 2 corresponding to the blank area is lower than a temperature T 1 corresponding to the imaged area,

wherein the plurality of heat generators include a first heat generator to heat a heating area of the fixing member corresponding to the imaged area and a plurality of second heat generators to heat heating areas of the fixing member corresponding to the blank area,

wherein one of the plurality of second heat generators located adjacent to the first heat generator is set to a temperature of T 1 −ΔT, where ΔT is a temperature lower than a difference between the temperature T 1 and the temperature T 2 , when the unfixed image on the recording medium conveyed to the fixing nip contains the imaged area and the blank area, and

wherein ΔT is different between when a first side of the recording medium is printed upon duplex printing and upon single-sided printing.

8. The fixing device according to claim 7 , wherein ΔT is different between when the first side of the recording medium is printed upon the duplex printing and when a second side of the recording medium is printed upon the duplex printing.

9. The fixing device according to claim 7 , wherein ΔT is zero when the first side of the recording medium is printed upon the duplex printing.

10. The fixing device according to claim 7 , wherein ΔT depends on a thickness of the recording medium.

11. The fixing device according to claim 7 , wherein ΔT depends on a type of the recording medium.