FIXING APPARATUS AND IMAGE FORMING APPARATUS INCLUDING THE SAME

Abstract

A fixing apparatus includes: a fixing roller which has a halogen lamp and an elastic layer therein, the elastic layer being located close to an outer surface of the fixing member; a pressure roller which is pressed against the fixing roller so that a fixing nip area is provided between the pressure roller and the fixing roller, the fixing nip area causing a toner image formed on a recording paper P to be fixed thereon; and an external heating device which has a halogen lamp and is disposed on the outer surface of the fixing member so that a second nip area is provided between the external heating device and the fixing member. In the fixing apparatus, a temperature difference between a surface temperature of the external heating device and a surface temperature of the fixing roller is controlled in accordance with a length of the second nip area in a direction of transport of the recording paper, so that the surface temperature of the fixing roller is maintained to fall within a temperature range in which offset does not occur, the offset being a phenomenon in which part of a toner formed on the recording paper P sticks onto the surface of the fixing roller. This prevents the offset phenomenon that occurs when paper passing operation is performed immediately after the completion of warm-up.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating the structure of a fixing apparatus according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating internal structure of an image forming apparatus including the fixing apparatus illustrated in FIG. 1.

FIG. 3 is a graph showing changes in surface temperatures of an endless belt, a fixing roller, and a pressure roller in the fixing apparatus illustrated in FIG. 1 during a warm-up time.

FIG. 4 is a flow chart illustrating a flow of control performed by a control device of the fixing apparatus illustrated in FIG. 1 during a warm-up.

FIG. 5 is graph showing the progression of surface temperatures of the endless belt of the external heating device and the fixing roller during a time between immediately before and after the completion of the warm-up.

FIG. 6 is an explanatory view illustrating a relationship between (a) a difference in surface temperature between the external heating device and the fixing roller, (b) a nip length of a nip area provided between the external heating device and the fixing roller, and (c) undershoot and overshoot of the surface temperature of the fixing roller after the completion of a warm-up in the fixing apparatus illustrated in FIG. 1.

FIG. 7 is a graph showing a relationship between a nip length La of the nip area provided between the external heating device and the fixing roller and a temperature difference Ta between the surface temperature of the fixing roller and the surface temperature of the external heating device, in a case where undershoot occurred immediately after the completion of the warm-up of the fixing roller is in the range within 5° C. from the warm-up completion temperature of the fixing roller.

FIG. 8 is a graph showing a relationship between a nip length La of the nip area provided between the external heating device and the fixing roller and a temperature difference Ta between the surface temperature of the fixing roller and the surface temperature of the external heating device, in a case where overshoot occurred immediately after the completion of the warm-up of the fixing roller is in the range within 5° C. from the warm-up completion temperature of the fixing roller.

FIG. 9 is an explanatory view illustrating a common non-offset range between fixing of a monochrome image and fixing of a color image in a fixing apparatus included in a 4-cycle image forming apparatus.

FIG. 10 is an explanatory view illustrating a common non-offset range between fixing of a monochrome image and fixing of a color image in a fixing apparatus included in a four drum tandem engine image forming apparatus.

Claims

1. A fixing apparatus comprising: a fixing member which has a heat source and an elastic layer therein, the elastic layer being located close to an outer surface of the fixing member in relation to the heat source;a pressure member which is pressed against the fixing member so that a first nip area is provided between the pressure member and the fixing member, the first nip area causing a toner image formed on a recording paper to be fixed on the recording paper; andan external heating device which has a heat source and is disposed on the outer surface of the fixing member so that a second nip area is provided between the external heating device and the fixing member, whereina temperature difference between a surface temperature of the external heating device and a surface temperature of the fixing member is controlled in accordance with a length of the second nip area in a direction of transport of the recording paper, so that the surface temperature of the fixing member is maintained to fall within a temperature range in which offset does not occur, the offset being a phenomenon in which part of a toner formed on the recording paper sticks onto a surface of the fixing member due to overheating or insufficient heating of the recording paper.

2. The fixing apparatus according to claim 1, wherein the external heating device comprises: a plurality of rollers, at least one of which has a heat source; and a belt which is set over the plurality of rollers and pressed against the fixing member so that the second nip area is provided between the belt and the fixing member.

3. The fixing apparatus according to claim 2, wherein the fixing member is a fixing roller and has the heat source which heats when power is supplied to the heat source, the pressure member is a pressure roller and is rotated in opposite direction to rotation of the fixing roller, and the belt of the external heating device is supported by the plurality of rollers of the external heating device so as to be along a curved outer surface of the fixing roller.

4. The fixing apparatus according to claim 1, further comprising: control means which controls power supply to the heat source of the fixing member and the heat source of the external heating device, the control means giving a first priority to power supply to the heat source of the external heating device until the external heating device reaches a setting temperature for warm-up.

5. An image forming apparatus comprising: a fixing apparatus comprising:a fixing member which has a heat source and an elastic layer therein, the elastic layer being located close to an outer surface of the fixing member in relation to the heat source;a pressure member which is pressed against the fixing member so that a first nip area is provided between the pressure member and the fixing member, the first nip area causing a toner image formed on a recording paper to be fixed on the recording paper; andan external heating device which has a heat source and is disposed on the outer surface of the fixing member so that a second nip area is provided between the external heating device and the fixing member, whereina temperature difference between a surface temperature of the external heating device and a surface temperature of the fixing member is controlled in accordance with a length of the second nip area in a direction of transport of the recording paper, so that the surface temperature of the fixing member is maintained to fall within a temperature range in which offset does not occur, the offset being a phenomenon in which part of a toner formed on the recording paper sticks onto a surface of the fixing member due to overheating or insufficient heating of the recording paper.

6. A fixing apparatus comprising: a fixing member which has a heat source and an elastic layer therein, the elastic layer being located close to an outer surface of the fixing member in relation to the heat source;a pressure member which is pressed against the fixing member so that a first nip area is provided between the pressure member and the fixing member, the first nip area causing a toner image formed on a recording paper to be fixed on the recording paper; andan external heating device which has a heat source and is disposed on the outer surface of the fixing member so that a second nip area, which is a contact area where the external heating device is in contact with the fixing member, is provided between the external heating device and the fixing member, whereinit is Ta≦99.842×La−0.4599 where Ta is a difference between a surface temperature of the fixing member and a surface temperature of the external heating device and La is a length of the second nip area in a direction of transport of the recording paper.

7. The fixing apparatus according to claim 6, wherein the external heating device comprises: a plurality of rollers, at least one of which has a heat source; and a belt which is set over the plurality of rollers and pressed against the fixing member so that the second nip area is provided between the belt and the fixing member.

8. The fixing apparatus according to claim 7, wherein the fixing member is a fixing roller and has the heat source which heats when power is supplied to the heat source, the pressure member is a pressure roller and is rotated in opposite direction to rotation of the fixing roller, and the belt of the external heating device is supported by the plurality of rollers of the external heating device so as to be along a curved outer surface of the fixing roller.

9. The fixing apparatus according to claim 6, further comprising: control means which controls power supply to the heat source of the fixing member and the heat source of the external heating device, the control means giving a first priority to power supply to the heat source of the external heating device until the external heating device reaches a setting temperature for warm-up.

10. An image forming apparatus comprising: a fixing apparatus comprising:a fixing member which has a heat source and an elastic layer therein, the elastic layer being located close to an outer surface of the fixing member in relation to the heat source;a pressure member which is pressed against the fixing member so that a first nip area is provided between the pressure member and the fixing member, the first nip area causing a toner image formed on a recording paper to be fixed on the recording paper; andan external heating device which has a heat source and is disposed on the outer surface of the fixing member so that a second nip area, which is a contact area where the external heating device is in contact with the fixing member, is provided between the external heating device and the fixing member, whereinit is Ta≦99.842×La−0.4599 where Ta is a difference between a surface temperature of the fixing member and a surface temperature of the external heating device and La is a length of the second nip area in a direction of transport of the recording paper.

11. A fixing apparatus comprising: a fixing member which has a heat source and an elastic layer therein, the elastic layer being located close to an outer surface of the fixing member in relation to the heat source;a pressure member which is pressed against the fixing member so that a first nip area is provided between the pressure member and the fixing member, the first nip area causing a toner image formed on a recording paper to be fixed on the recording paper; andan external heating device which has a heat source and is disposed on the outer surface of the fixing member so that a second nip area, which is a contact area where the external heating device is in contact with the fixing member, is provided between the external heating device and the fixing member, whereinit is 113.87×La−0.9899≦Ta where Ta is a difference between a surface temperature of the fixing member and a surface temperature of the external heating device and La is a length of the second nip area in a direction of transport of the recording paper.

12. The fixing apparatus according to claim 11, wherein the external heating device comprises: a plurality of rollers, at least one of which has a heat source; and a belt which is set over the plurality of rollers and pressed against the fixing member so that the second nip area is provided between the belt and the fixing member.

13. The fixing apparatus according to claim 12, wherein the fixing member is a fixing roller and has the heat source which heats when power is supplied to the heat source, the pressure member is a pressure roller and is rotated in opposite direction to rotation of the fixing roller, and the belt of the external heating device is supported by the plurality of rollers of the external heating device so as to be along a curved outer surface of the fixing roller.

14. The fixing apparatus according to claim 11, further comprising: control means which controls power supply to the heat source of the fixing member and the heat source of the external heating device, the control means giving a first priority to power supply to the heat source of the external heating device until the external heating device reaches a setting temperature for warm-up.

15. An image forming apparatus comprising: a fixing apparatus comprising:a fixing member which has a heat source and an elastic layer therein, the elastic layer being located close to an outer surface of the fixing member in relation to the heat source;a pressure member which is pressed against the fixing member so that a first nip area is provided between the pressure member and the fixing member, the first nip area causing a toner image formed on a recording paper to be fixed on the recording paper; andan external heating device which has a heat source and is disposed on the outer surface of the fixing member so that a second nip area, which is a contact area where the external heating device is in contact with the fixing member, is provided between the external heating device and the fixing member, whereinit is 113.87×La−0.9899≦Ta where Ta is a difference between a surface temperature of the fixing member and a surface temperature of the external heating device and La is a length of the second nip area in a direction of transport of the recording paper.

16. A fixing apparatus comprising: a fixing member which has a heat source and an elastic layer therein, the elastic layer being located close to an outer surface of the fixing member in relation to the heat source;a pressure member which is pressed against the fixing member so that a first nip area is provided between the pressure member and the fixing member, the first nip area causing a toner image formed on a recording paper to be fixed on the recording paper; andan external heating device which has a heat source and is disposed on the outer surface of the fixing member so that a second nip area, which is a contact area where the external heating device is in contact with the fixing member, is provided between the external heating device and the fixing member, whereinit is 113.87×La−0.9899≦Ta≦99.842×La−0.4599 where Ta is a difference between a surface temperature of the fixing member and a surface temperature of the external heating device and La is a length of the second nip area in a direction of transport of the recording paper.

17. The fixing apparatus according to claim 16, wherein the external heating device comprises: a plurality of rollers, at least one of which has a heat source; and a belt which is set over the plurality of rollers and pressed against the fixing member so that the second nip area is provided between the belt and the fixing member.

18. The fixing apparatus according to claim 17, wherein the fixing member is a fixing roller and has the heat source which heats when power is supplied to the heat source, the pressure member is a pressure roller and is rotated in opposite direction to rotation of the fixing roller, and the belt of the external heating device is supported by the plurality of rollers of the external heating device so as to be along a curved outer surface of the fixing roller.

19. The fixing apparatus according to claim 16, further comprising: control means which controls power supply to the heat source of the fixing member and the heat source of the external heating device, the control means giving a first priority to power supply to the heat source of the external heating device until the external heating device reaches a setting temperature for warm-up.

20. An image forming apparatus comprising: a fixing apparatus comprising:a fixing member which has a heat source and an elastic layer therein, the elastic layer being located close to an outer surface of the fixing member in relation to the heat source;a pressure member which is pressed against the fixing member so that a first nip area is provided between the pressure member and the fixing member, the first nip area causing a toner image formed on a recording paper to be fixed on the recording paper; andan external heating device which has a heat source and is disposed on the outer surface of the fixing member so that a second nip area, which is a contact area where the external heating device is in contact with the fixing member, is provided between the external heating device and the fixing member, whereinit is 113.87×La−0.9899≦Ta≦99.842×La−0.4599 where Ta is a difference between a surface temperature of the fixing member and a surface temperature of the external heating device and La is a length of the second nip area in a direction of transport of the recording paper.