Fuser temperature control providing faster wake up from cold start by optimizing standby temperature of fuser roller Number:7,395,003 from the United States Patent and Trademark Office (PTO) owispatent An apparatus is disclosed which is for forming an image using a fuser unit, including: a fuser roller; a heater heating the fuser roller; a temperature sensor detecting a temperature of the fuser roller; and a controller controlling the heater to substantially achieve a desired temperature of the fuser roller, wherein the controller includes a desired-temperature setting device. The device is operated during a cold start of the fuser unit, so as to set the desired temperature to a second standby-temperature which is lower than a fusing temperature and higher than a normal standby-temperature, so as to maintain the desired temperature at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature to the normal standby-temperature upon termination of the heat-storing period.<H temperature, optimizing, Fuser, temperatu, 7395003.html, Patent, pto, 7395003

Title: Fuser temperature control providing faster wake up from cold start by optimizing standby temperature of fuser roller

Abstract: An apparatus is disclosed which is for forming an image using a fuser unit, including: a fuser roller; a heater heating the fuser roller; a temperature sensor detecting a temperature of the fuser roller; and a controller controlling the heater to substantially achieve a desired temperature of the fuser roller, wherein the controller includes a desired-temperature setting device. The device is operated during a cold start of the fuser unit, so as to set the desired temperature to a second standby-temperature which is lower than a fusing temperature and higher than a normal standby-temperature, so as to maintain the desired temperature at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature to the normal standby-temperature upon termination of the heat-storing period.

Patent Number: 7,395,003 Issued on 07/01/2008 to Dan

Inventors: Dan; Kenichi (Nagoya, JP)
Assignee: Brother Kogyo Kabushiki Kaisha (Nagoya, JP)

Appl. No.: 11/065,459

Filed: February 25, 2005

Foreign Application Priority Data


Mar 01, 2004 [JP]			2004-056491

Current U.S. Class: 399/70

Current International Class: G03G 15/20 (20060101)

Field of Search: 399/70,69

References Cited [Referenced By]

U.S. Patent Documents


5321479	June 1994	Yoshida et al.
6185388	February 2001	Yamamoto
6816686	November 2004	Hooper et al.
2001/0013943	August 2001	Hashimoto et al.

Foreign Patent Documents


A-05-127565	May., 1993	JP
B2-3119690	Dec., 2000	JP

Primary Examiner: Grainger; Quana M
Attorney, Agent or Firm: Oliff & Berridge, PLC

Claims

What is claimed is:

1. An apparatus for forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiver medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit comprising: a fuser roller; a heater heating the fuser roller; a temperature sensor detecting a temperature of the fuser roller; and a controller controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the temperature of the fuser roller detected by the temperature sensor, wherein the controller includes a desired-temperature setting device that selects one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one, the desired-temperature setting device is operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period, and the desired-temperature setting device comprises a first setting device setting the desired temperature in at least one of a first manner allowing the desired temperature to be initially set to the second standby-temperature during the cold start, and a second manner allowing the desired temperature to be set to any one of the plurality of optional temperatures excluding the second standby-temperature, prior to a setting of the desired temperature to the second standby-temperature.

2. An apparatus for forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiver medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit comprising: a fuser roller; a heater heating the fuser roller; a temperature sensor detecting a temperature of the fuser roller; and a controller controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the temperature of the fuser roller detected by the temperature sensor, wherein the controller includes a desired-temperature setting device that selects one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one, the desired-temperature setting device is operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period, the desired-temperature setting device comprises a limit setting device establishing an upper limit and a lower limit for each of the second standby-temperature and the normal standby-temperature, and wherein the controller is operated so as to deactivate the heater upon rise of the actual temperature of the fuser roller to the established upper limit, and so as to activate the heater upon drop of the actual temperature of the fuser roller to the established lower limit, and the limit setting device establishes the upper and the lower limit, such that a difference therebetween is smaller for the second standby-temperature during the heat-storing period than for the normal standby-temperature.

3. The apparatus according to claim 2, wherein the heat-storing period is shorter than a period during which the temperature of the fuser roller is maintained at the normal standby-temperature.

4. An apparatus for forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiver medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit comprising: a fuser roller; a heater heating the fuser roller; a temperature sensor detecting a temperature of the fuser roller; and a controller controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the temperature of the fuser roller detected by the temperature sensor, wherein the controller includes a desired-temperature setting device that selects one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one, the desired-temperature setting device is operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period, and the controller comprises a first period determining device determining a length of the heat-storing period based on at least one of a length of an elapsed time during which the temperature of the fuser roller rises from a temperature thereof at the cold start to a reference temperature, and a gradient of the temperature of the fuser roller, using the temperature of the fuser roller detected by the temperature sensor.

5. The apparatus according to claim 4, wherein the first period determining device determines the length of the heat-storing period such that the longer the length of the elapsed time, the longer the determined length of the heat-storing period.

6. The apparatus according to claim 4, wherein the reference temperature substantially coincides in level with the normal standby-temperature.

7. The apparatus according to claim 4, further comprising a first cold-start determining device determining an event of the cold start.

8. The apparatus according to claim 1, wherein the controller comprises a second period determining device determining a length of the heat-storing period based on the temperature of the fuser roller detected by the temperature sensor at the cold start.

9. The apparatus according to claim 8, wherein the second period determining device determines the length of the heat-storing period such that the lower the temperature of the fuser roller detected by the temperature sensor, the longer the determined length of the heat-storing period.

10. A method of forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiver medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit including a fuser roller and a heater heating the fuser roller, the method comprising the steps of: detecting the temperature of the fuser roller; and controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the detected temperature of the fuser roller, wherein the step of controlling includes a step of selecting one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one, the step of selecting is operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period, and the step of selecting comprises a step of selecting one of the second standby-temperature and the normal standby-temperature and setting the desired temperature to the selected one, based on a length of a period during which the temperature of the fuser roller was maintained at the second standby-temperature, upon termination of a fusing operation by the fuser unit during the heat-storing period.

11. The apparatus according to claim 1, wherein the desired-temperature setting device comprises a second setting device setting the desired temperature to the normal standby-temperature, upon termination of a fusing operation by the fuser unit during the heat-storing period.

12. The apparatus according to claim 11, further comprising a fusing-operation determining device determining whether or not a termination of the fusing operation occurs.

13. A method of forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiver medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit including a fuser roller and a heater heating the fuser roller, the method comprising the steps of: detecting the temperature of the fuser roller; and controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the detected temperature of the fuser roller, wherein the step of controlling includes a step of selecting one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one, the step of selecting is operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period, and the step of selecting comprises a step of selecting one of the second standby-temperature and the normal standby-temperature and setting the desired temperature to the selected one, wherein when a length of a period during which the temperature of the fuser roller has been maintained at the fusing temperature is longer than the predetermined value, then the normal standby-temperature is selected as the desired temperature of the fuser roller, and otherwise, the second standby-temperature is selected as the desired temperature of the fuser roller.

14. An apparatus for forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiver medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit comprising: a fuser roller; a heater heating the fuser roller; a temperature sensor detecting a temperature of the fuser roller; and a controller controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the temperature of the fuser roller detected by the temperature sensor, wherein the controller includes a desired-temperature setting device that selects one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one, and the desired-temperature setting device is operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period, the apparatus further comprising a measuring device measuring whether or not a length of a period during which the temperature of the fuser roller was maintained at the fusing temperature is longer than a predetermined value, based on an amount of the receiver medium processed during a continuous implementation of the fusing operation, wherein the desired-temperature setting device is operated based on a measurement provided by the measuring device, so as to select the normal standby-temperature as the desired temperature of the fuser roller when the length of a period during which the temperature of the fuser roller has been maintained at the fusing temperature is longer that the predetermined value, and so as to select the second standby-temperature as the desired temperature of the fuser roller when the length of the period is not longer than the predetermined value.

15. The apparatus according to claim 1, wherein the desired-temperature setting device comprises a fifth setting device selecting one of the second standby-temperature and the normal standby-temperature and setting the desired temperature to the selected one, based on a kind of the receiver medium for which a fusing operation was implemented by the fuser unit, upon termination of the fusing operation during the heat-storing period.

16. An apparatus for forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiver medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit comprising: a fuser roller; a heater heating the fuser roller; a temperature sensor detecting a temperature of the fuser roller; and a controller controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the temperature of the fuser roller detected by the temperature sensor, wherein the controller includes a desired-temperature setting device that selects one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one, the desired-temperature setting device is operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period, and the controller comprises an allowable-range setting device setting an allowable range for the second standby-temperature, such that a width of the allowable range is varied with time during the heat-storing period.

17. The apparatus according to claim 16, wherein the allowable-range setting device sets the allowable range such that the width of the allowable range becomes larger during a later part of the heat-storing period than during an early part of the same heat-storing period.

18. An apparatus for forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiver medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit comprising: a fuser roller; a heater heating the fuser roller; a temperature sensor detecting a temperature of the fuser roller; and a controller controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the temperature of the fuser roller detected by the temperature sensor, wherein the controller includes a desired-temperature setting device that selects one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one, the desired-temperature setting device is operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period, and the desired-temperature setting device is operated during a non-cold start of the fuser unit, so as to select one of the fusing temperature and the normal standby-temperature which excludes the second standby-temperature.

19. A method of forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiver medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit including a fuser roller and a heater heating the fuser roller, the method comprising the steps of: detecting the temperature of the fuser roller; and controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the detected temperature of the fuser roller, wherein the step of controlling includes a step of selecting one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one, the step of selecting is operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period, and the step of selecting comprises a step of setting the desired temperature in at least one of a first manner allowing the desired temperature to be initially set to the second standby-temperature during the cold start, and a second manner allowing the desired temperature to be set to any one of the plurality of optional temperatures excluding the second standby-temperature, prior to a setting of the desired temperature to the second standby-temperature.

Description

This application is based on Japanese Patent Application No. 2004-056491 filed Mar. 1, 2004, the content of which is incorporated hereinto by reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique employed in an image forming apparatus such as a laser printer, and more particularly to a technique of controlling the temperature of a fuser roller fusing an image to a receiver medium such as a print sheet.

2. Description of the Related Art

Typically, an image forming apparatus such as a laser printer is operated in combination with a fuser unit. The fuser unit is provided for heating a print sheet bearing an unfused toner thereon and then fusing the toner image to the print sheet.

The above fusing unit is typically configured to include: a fuser roller incorporating a heater therein; a pressure roller disposed in pressure contact with the fuser roller; a temperature sensor (e.g., a thermistor) detecting the surface temperature of the fuser roller; etc. In printing operation, the fuser unit controls the heater in an on-off manner based on a signal from the temperature sensor, to thereby perform a fusing operation such that the surface temperature of the fuser roller is maintained at a predetermined level.

In operation, such an image forming apparatus performs a warm-up operation once a printing operation becomes required soon after the occurrence of a cold start of the fuser unit. The term "cold start" may be defined to mean a start immediately from a power-on event of the image forming apparatus, a start immediately from the release of an operation mode of the image forming apparatus from a sleep mode, etc.

Conventionally, even when the temperature of the surface of the fuser roller reaches a desired fusing-temperature owing to the above warm-up operation, the remaining portion of the image forming apparatus (possibly including the remaining portion of the fuser roller and the remaining portion of the fuser unit) fails to become adequately warm. For the reason, once the printing operation begins, the heating process of the fuser roller runs short due to heat scattering and lost into the above remaining portion and the print sheet, possibly resulting in an inadequate fixing of the print sheet.

For avoiding the inadequate fixing, it is conventional to take an approach to inhibit a printing operation during a given length of period elapsed from the occurrence of the power-on event of the image forming apparatus, or an approach to temporally maintain the temperature of the fuser roller at a temperature higher than the desired fusing temperature, i.e., a desired operating temperature. The latter approach is disclosed in Japanese Patent No. 3,119,690.

BRIEF SUMMARY OF THE INVENTION

The inventor's research on the above two approaches has revealed that, the former approach suffers from a drawback that the user of the image forming apparatus is forced to wait for a prolonged time until a printing operation starts, and the latter approach suffers from a drawback that the fuser roller is possibly overheated due to application of too much heat to the print sheet, possibly resulting in re-attachment of a toner from the print sheet to the fuser roller.

It is therefore an object of the present invention to provide a technique of controlling the temperature of the fuser roller that allows reduction in length of time during which the user is required to wait until a printing operation starts during a cold start, and/or that allows avoidance of overheating of the print sheet.

According to the present invention, there is provided an apparatus for forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiving medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit comprising:

a fuser roller;

a heater heating the fuser roller;

a temperature sensor detecting a temperature of the fuser roller; and

a controller controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the temperature of the fuser roller detected by the temperature-sensor,

the controller including a desired-temperature setting device that selects one of a plurality of optional temperatures including; a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one,

the desired-temperature setting device being operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period.

As is evident from the above description, the above apparatus is configured, such that the heat-storing period for applying heat to the fuser roller for heat storage is provided. Further, the above apparatus is operated, such that the temperature of the fuser roller is maintained during the heat-storing period in the event of the cold start, at the second standby-temperature higher than the normal standby-temperature. As-a result, the whole fuser unit is warmed up quicker than when the temperature of the fuser roller is maintained at the normal standby-temperature.

The above apparatus is operated, such that the fuser unit is adequately warmed up with the temperature being at the second standby-temperature, with the result that deficiency in temperature of the fuser roller is not caused where the temperature of the fuser roller is raised up to the desired fusing temperature in response to issue of a print request from the user.

The above apparatus is configured, such that the second standby-temperature is set so as to be lower than the fusing temperature established for a fusing operation of the fuser unit, resulting in avoidance of re-attachment of a toner from the receiver medium to the fuser roller due to overheating of the receiver medium.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities show. In the drawings:

FIG. 1 is a sectional view illustrating a laser printer according to a first embodiment of the present invention;

FIG. 2 is an enlarged sectional view illustrating a fuser unit shown in FIG. 1;

FIG. 3 is a block diagram schematically illustrating the electrical construction of the laser printer shown in FIG. 1;

FIG. 4 is a flow chart schematically illustrating a routine for setting a timer for a second standby-mode, which is executed by a CPU shown in FIG. 3;

FIG. 5 is a flow chart schematically illustrating a standby-mode determination routine executed by the CPU shown in FIG. 3;

FIG. 6 is a flow chart schematically illustrating a temperature control-program executed by the CPU shown in FIG. 3;

FIG. 7 is a flow chart schematically illustrating a mode monitor routine executed by the CPU shown in FIG. 3;

FIG. 8 is a flow chart schematically illustrating a heater control program executed by the CPU shown in FIG. 3;

FIG. 9 is a state transition diagram for explaining a print control program executed by the CPU shown in FIG. 3 and shifting between operation modes of the laser printer shown in FIG. 1;

FIG. 10 is a graph showing an example of temporal changes in surface temperature of a fuser roller of the laser printer shown in FIG. 1;

FIG. 11A is a graph showing another example of temporal changes in surface temperature of the fuser roller of the laser printer shown in FIG. 1;

FIG. 11B is a graph showing still another example of temporal changes in surface temperature of the fuser roller of the laser printer shown in FIG. 1;

FIG. 12 is a flow chart schematically illustrating the print control program executed by the CPU shown in FIG. 3;

FIG. 13 is a graph showing an example of temporal changes in surface temperature of a fuser roller of a laser printer according to a second embodiment of the present invention;

FIG. 14 is a flow chart schematically illustrating a routine for setting a timer for a second standby-mode, executed by a computer of the laser printer according to the second embodiment; and

FIG. 15 is a flow chart schematically illustrating a routine for setting a timer for a second standby-mode, executed by a computer of a laser printer according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The object mentioned above may be achieved according to any one of the following modes of this invention.

These modes will be stated below such that these modes are sectioned and numbered, and such that these modes depend upon the other mode or modes, where appropriate. This is for a better understanding of some of a plurality of technological features and a plurality of combinations thereof disclosed in this description, and does not mean that the scope of these features and combinations is interpreted to be limited to the scope of the following modes of this invention.

That is to say, it should be interpreted that it is allowable to select the technological features which are stated in this description but which are not stated in the following modes, as the technological features of this invention.

Furthermore, stating each one of the selected modes of the invention in such a dependent form as to depend from the other mode or modes does not exclude a possibility of the technological features in a dependent-form mode to become independent of those in the corresponding depended mode or modes and to be removed therefrom. It should be interpreted that the technological features in a dependent-form mode is allowed to become independent according to the nature of the corresponding technological features, where appropriate.

(1) An apparatus for forming an image using a fuser unit that heats a receiver medium bearing an unfused toner image thereon, during a relative movement of the receiving medium to the fuser unit, to thereby fuse the unfused toner image onto the receiver medium, the fuser unit comprising:

a fuser roller;

a heater heating the fuser roller;

a temperature sensor detecting a temperature of the fuser roller; and

a controller controlling the heater for an actual temperature of the fuser roller to substantially achieve a desired temperature thereof, based on the temperature of the fuser roller detected by the temperature sensor,

the controller including a desired-temperature setting device that selects one of a plurality of optional temperatures including: a fusing temperature at which the unfused toner image is to be fused to the receiver medium; a normal standby-temperature which is a desired standby-temperature of the fuser roller in a normal standby period, lower than the fusing temperature; and a second standby-temperature which is a second desired standby-temperature of the fuser roller in a second standby period, lower than the fusing temperature and higher than the normal standby-temperature, and that sets the desired temperature of the fuser roller to the selected one,

the desired-temperature setting device being operated during a cold start of the fuser unit, so as to set the desired temperature of the fuser roller to the second standby-temperature, so as to maintain the desired temperature of the fuser roller at the second standby-temperature during a heat-storing period during which heat is stored in the fuser unit, and so as to set the desired temperature of the fuser unit to the normal standby-temperature upon termination of the heat-storing period.

As is readily understood from the above, the apparatus according to the above mode (1) is configured, such that the heat-storing period for applying heat to the fuser roller for heat storage is provided. Further, the apparatus is operated, such that the temperature of the fuser roller is maintained during the heat-storing period in the event of the cold start, at the second standby-temperature higher than the normal standby-temperature. As a result, the whole fuser unit is warmed up quicker than when the temperature of the fuser roller is maintained at the normal standby-temperature.

The apparatus according to the above mode (1) is operated, such that the fuser unit is adequately warmed up with the temperature being at the second standby-temperature, with the result that deficiency in temperature of the fuser roller is not caused where the temperature of the fuser roller is raised up to the desired fusing temperature in response to issue of a print request from the user.

The apparatus according to the above mode (1) allows a quick rise in temperature of the fuser roller from the second standby-temperature which is higher than the normal standby-temperature to the desired fusing temperature. This avoids the length of time during which the user has to wait until a printing operation starts from becoming longer than when the apparatus is operated such that a printing operation is inhibited for a given length of time after issue of a print request from the user.

The apparatus according to the above mode (1) is configured, such that the second standby-temperature is set so as to be lower than the fusing temperature established for a fusing operation of the fuser unit, resulting in avoidance of re-attachment of a toner from the receiver medium to the fuser roller due to overheating of the receiver medium.

The apparatus according to the above mode (1) may be operated such that the temperature of the fuser roller is raised as low as the second standby-temperature lower than the fusing temperature, where a printing operation does not start immediately after the initiation of a cold start of the fuser unit. This allows the power consumption of the fuser unit to become less than when the temperature of the fuser roller never fail to be temporally raised to a temperature higher than the fusing temperature.

(2) The apparatus according to mode (1), wherein the desired-temperature setting device comprises a first setting device setting the desired temperature in at least one of a first manner allowing the desired temperature to be initially set to the second standby-temperature during the cold start, and a second manner allowing the desired temperature to be set to any one of the plurality of optional temperatures excluding the second standby-temperature, prior to a setting of the desired temperature to the second standby-temperature.

(3) The apparatus according to mode (1) or (2), wherein the desired-temperature setting device comprises a limit setting device establishing an upper limit and a lower limit for each of the second standby-temperature and the normal standby-temperature, and wherein the controller is operated so as to deactivate the heater upon rise of the actual temperature of the fuser roller to the established upper limit, and so as to activate the heater upon drop of the actual temperature of the fuser roller to the established lower limit,

and wherein the limit setting device establishes the upper and the lower limit, such that a difference therebetween is smaller for the second standby-temperature during the heat-storing period than for the normal standby-temperature.

The apparatus according to the above mode (3) is configured, such that the operating state of the heater is controlled depending on the relationship in magnitude between the upper and lower limits of the respective desired standby-temperatures and the temperature of the fuser roller detected by the temperature sensor.

In the apparatus, the difference between the upper and lower limits corresponds to the width of a dead band or an allowable range over which the actual state of the heater is allowed not to respond to any variations in actual temperature of the fuser roller.

Too small width of the dead band would cause frequent shifts between an off and an on state of the heater, eventually leading to frequent flickers of room lights connected to the same power line.

In view of the above, the apparatus according to the above mode (3) is configured, such that the difference between the upper and lower limits, i.e., the width of the dead band for each of the normal and second standby-temperatures is set to be suitably large, to thereby eliminate flickers of the room lights.

On the other hand, too large width of the dead band would readily bring about variations in temperature of the fuser roller occurring immediately after the start of a fusing operation of the fuser unit, as it is especially true where the fusing operation starts with a previous heat-storage in the fuser unit being inadequate. This possibly results in an event of overheating due to excessive heat or otherwise an inadequate fixing due to deficiency of heat.

In view of the above, the apparatus according to the above mode (3) is configured, such that the difference between the upper and lower limits, i.e., the width of the dead band for the second standby-temperature is set to be smaller than that of the normal standby-temperature, to thereby eliminate variations in temperature occurring immediately after the start of the fusing operation even where the fusing operation starts with the heat storage in the fuser unit being inadequate, with the result of elimination of inadequate fixing.

In the apparatus according to the above mode (3), the possibility that the room lights frequently flicker due to changes in on-off state of the heater can be eliminated as a result of the setting of the length of the period during the temperature of the fuser roller is maintained at the second standby-temperature so as to be shorter than that of the period during which the temperature of the fuser roller is maintained at the normal standby-temperature.

(4) The apparatus according to mode (3), wherein the heat-storing period is shorter than a period during which the temperature of the fuser roller is maintained at the normal standby-temperature.

The apparatus according to the above mode (4) reduces how many times the on-off state of the heater is varied during the heat-storing period, resulting in an eliminated possibility that the aforementioned room lights frequently flicker due to changes in on-off state of the heater.

(5) The apparatus according to any one of modes (1) through (4), wherein the controller comprises a first period determining device determining a length of the heat-storing period based on at least one of a length of an elapsed time during which the temperature of the fuser roller rises from a temperature thereof at the cold start to a reference temperature, and a gradient of the temperature of the fuser roller, using the temperature of the fuser roller detected by the temperature sensor.

The apparatus according to the above mode (5) is configured, such that the desired length of the heat-storing period is determined based on at least one of the length of the elapsed time between the temperature of the fuser roller being at an actual temperature (e.g., an initial temperature) during the cold start and being at a reference temperature, and a gradient of the temperature of the fuser roller.

The apparatus according to the above mode (5) therefore allows the desired length of the heat-storing period to be determined so as not to be unnecessarily long, resulting in reduction in power consumption of the fuser unit, when practiced.

(6) The apparatus according to mode (5), wherein the first period determining device determines the length of the heat-storing period such that the longer the length of the elapsed time becomes, the longer the determined length of the heat-storing period becomes.

(7) The apparatus according to mode (5) or (6), wherein the reference temperature substantially coincides in level with the normal standby-temperature.

(8) The apparatus according to any one of modes (5) through (7), further comprising a first cold-start determining device determining an event of the cold start.

(9) The apparatus according to any one of modes (1) through (8), wherein the controller comprises a second period determining device determining a length of the heat-storing period based on the temperature of the fuser roller detected by the temperature sensor at the cold start.

The apparatus according to the above mode (9), because of the above construction, allows the desired length of the heat-storing period to be determined so as not to be unnecessarily long, resulting in reduction in power consumption of the fuser unit, when practiced.

(10) The apparatus according to mode (9), wherein the second period determining device determines the length of the heat-storing period such that the lower the temperature of the fuser roller detected by the temperature sensor becomes, the longer the determined length of the heat-storing period becomes.

(11) The apparatus according to mode (9) or (10), further comprising a second cold-start determining device determining whether or not an event of the cold start occurs.

(12) The apparatus according to-any one of modes (1) through (11), wherein the desired-temperature setting device comprises a second setting device setting the desired temperature to the normal standby-temperature, upon termination of a fusing operation by the fuser unit during the heat-storing period.

Where a fusing operation of the fuser unit is performed and then terminated in the course of the heat-storing period, it may be reasonable to consider that the fuser unit has been adequately warmed up because of the fusing operation even before the termination of the heat-storing period.

In view of the above findings, the apparatus according to the above mode (12) is configured, such that the desired temperature of the fuser roller is set to the normal standby-temperature, not to the second standby-temperature which is higher than the normal standby-temperature, upon termination of the fusing operation by the fuser during the heat-storing period. The apparatus therefore facilitates reduction in power consumption of the fuser unit, when practiced.

(13) The apparatus according to mode (12), further comprising a fusing-operation determining device determining whether or not a termination of the fusing operation occurs.

(14) The apparatus according to any one of modes (1) through (13), wherein the desired-temperature setting device comprises a third setting device selecting one of the second standby-temperature and the normal standby-temperature and setting the desired temperature to the selected one, based on a length of a period during which the temperature of the fuser roller was maintained at the second standby-temperature, upon termination of a fusing operation by the fuser unit during the heat-storing period.

Where a fusing operation of the fuser unit is performed and then terminated in the course of the heat-storing period, whether or not the fuser unit has been adequately warmed up because of the fusing operation may depend on the length of the duration time during which the temperature of the fuser roller was maintained at the second standby-temperature during the heat-storing period. The findings show that the known length of the duration time determines whether or not the fuser unit has been adequately warmed up.

In view of the above, the apparatus according to the above mode (14) is configured, such that the desired temperature is determined as one of the second standby-temperature and the normal standby-temperature, which is selected based on the length of a period during which the temperature of the fuser roller was maintained at the second standby-temperature, upon termination of the fusing operation during the heat-storing-period.

According to an arrangement of the above mode (14), the desired temperature of the fuser roller is set to the normal standby-temperature, not the second standby-temperature, where the length of the period during which the temperature of the fuser roller was maintained at the second standby-temperature is adequately long, while the desired temperature is set to the second standby-temperature, to thereby continue the heat storage of the fuser unit, where the above length is not adequately long.

The above arrangement allows reduction in power consumption of the fuser unit, while avoiding inadequate fixing due to deficiency in length of the heat storage of the fuser unit.

(15) The apparatus according to any one of modes (1) through (14), wherein the desired-temperature setting device comprises a fourth setting device selecting one of the second standby-temperature and the normal standby-temperature and setting the desired temperature to the selected one, based on a length of a period during the temperature of the fuser roller was maintained at the fusing temperature, upon termination of a fusing operation by the fuser unit during the heat-storing period.

Where a fusing operation of the fuser unit is performed and then terminated in the course of the heat-storing period, whether or not the fuser unit has been adequately warmed up because of the fusing operation may depend on the length of the duration time during which the temperature of the fuser roller was maintained at the fusing temperature. The findings show that the known length of the duration time determines whether or not the fuser unit has been adequately warmed up.

In view of the above, the apparatus according to the above mode (15) is configured, such that the desired temperature is determined as one of the second standby-temperature and the normal standby-temperature, which is selected based on the length of a period during which the temperature of the fuser roller was maintained at the fusing temperature, upon termination of the fusing operation during the heat-storing period.

(16) The apparatus according to mode (15), further comprising a measuring device measuring a length of a period during which the temperature of the fuser roller was maintained at the fusing temperature, based on an amount of the receiver medium processed during a continuous implementation of the fusing operation.

The amount of the receiver medium processed during a continuous implementation of the fusing operation reflects the length of a period during which the temperature of the fuser roller was maintained at the fusing temperature. In view of the findings, the apparatus according to the above mode (16) is constructed as described above.

The "receiver medium processed" means the "receiver medium fused." The "amount of the receiver medium" may be interpreted to mean, where the receiver medium is in the form of successive and separate print sheets, the page count of the print sheets that were fused during the newest cycle of implementation of the fusing operation.

(17) The apparatus according to any one of modes (1) through (16), wherein the desired-temperature setting device comprises a fifth setting device selecting one of the second standby-temperature and the normal standby-temperature and setting the desired temperature to the selected one, based on a kind of the receiver medium for which a fusing operation was implemented by the fuser unit; upon termination of the fusing operation during the heat-storing period.

Where a fusing operation of the fuser unit is performed and then terminated in the course of the heat-storing period, whether or not the fuser unit has been adequately warmed up because of the fusing operation may depend on the kind of the receiver medium fused during the fusing operation.

A typical example of the kind of the receiver medium may be the thermal properties thereof, and a typical example of the thermal properties, when the receiver medium is in the form of a print sheet, may be the thickness of the print sheet. The findings show that the known kind of the receiver medium determines whether or not the fuser unit has been adequately warmed up.

In view of the above, the apparatus according to the above mode (17) is configured, such that the desired temperature is determined as one of the second standby-temperature and the normal standby-temperature, which is selected based on the kind of the receiver medium for which a fusing operation was implemented by the fuser unit, upon termination of the fusing operation during the heat-storing period.

According to an arrangement of the above mode (17), the desired temperature of the fuser roller is set to the normal standby-temperature, where a thicker print sheet having a larger heat capacity was fused during the fusing operation, meaning that the heat storage in the fuser unit was adequately performed, while the desired temperature is set to the second standby-temperature, to thereby continue the heat storage of the fuser unit, where a normal print sheet having a normal thickness and heat capacity was fused during the fusing operation, meaning that the heat storage in the fuser unit was not adequately performed.

The above arrangement allows reduction in power consumption of the fuser unit, when practiced.

(18) The apparatus according to any one of modes (1) through (17), wherein the heater is in the form of a halogen heater disposed within the fuser roller.

The apparatus according to the above mode (18), because of the heater unit employing the halogen heater, is more advantageous in reduction of cost of manufacture than when the heater unit is constructed such that a resistive heating element is disposed in the vicinity of the surface of the fuser roller, for example.

(19) The apparatus according to any one of modes (1) through (18), wherein the controller comprises an allowable-range setting device setting an allowable range for the second standby-temperature, such that a width of the allowable range is varied with time during the heat-storing period.

In the apparatus according to the above mode (19), the allowable range corresponds to the aforementioned dead-band for the control of the heater. On the other hand, the smaller the width of the dead band, the higher the accuracy of the controlled temperature of the fuser roller at the beginning of the coming fusing operation. The larger the width of the dead band, the lower the frequency of the flickers of the room lights.

In view of the above findings, the apparatus according to the above mode (19) is operated, such that the width of the allowable range is varied with time during the heat-storing period.

(20) The apparatus according to mode (19), wherein the allowable-range setting device sets the allowable range such that the width of the allowable range becomes larger during a later part of the heat-storing period than during an early part of the same heat-storing period.

The apparatus according to the above mode (20) is operated, such that the actual state of the heater under control is more sensitive to the actual temperature of the fuser roller during the early part of the heat-storing period, than during the later part of the same heat-storing period.

Therefore, the actual temperature of the fuser roller tends to be controlled more accurately during the early part than during the later part, while the actual temperature of the fuser roller tends to be varied less frequently during the later part than during the early part.

(21) A fuser unit comprising:

a fuser roller;

a heater heating the fuser roller; and

a temperature sensor detecting a temperature of the fuser roller,

wherein the heater is controlled based on the temperature of the fuser roller detected by the temperature sensor during a cold start of the fuser unit, such that the temperature of the fuser roller substantially coincides with a second standby-temperature which is lower than an operating temperature of the fuser roller to be achieved during a fusing operation by the fuser unit and higher than a normal standby-temperature, during a heat-storing period during which heat is applied to and stored in the fuser unit, and such that the temperature of the fuser roller drops to the normal standby-temperature upon termination of the heat-storing period.

The fuser unit according to the above mode (21) allows for a faster wake up from a cold start of the fuser roller, and for a reduced re-attachment of a toner from a receiver medium to the fuser roller due to overheating of the receiver medium, according to basically the same principle as that employed in the fuser roller in the apparatus according to any one of the above mode (1) through (20).

Several presently preferred embodiments of the invention will be described in more detail by reference to the drawings in which like numerals are used to indicate like elements throughout.

FIG. 1 shows schematically in sectional view a laser printer 1 as an image forming apparatus in accordance with a first embodiment of the present invention.

The laser printer 1 has a body casing 2, and a first tray 3 and a second tray 4 which are disposed in the lower portion of the body casing 2. In the laser printer 1, an image forming unit 6 forms a toner image on a print sheet 5 which is an example of a receiver medium supplied from a selected one of the first tray 3 and the second tray 4. By a fuser unit 7, a fusing operation is then performed to fuse the toner image with heat, and the print sheet 5 is finally delivered to an exit tray 8 disposed at the top of the body casing 2.

The image forming unit 6 is constructed so as to include: a scanning unit 10; a process cartridge 13; a photoconductive drum 17; a charger 18; a transfer roller 19, etc.

The scanning unit 10, which is disposed at the top of the body casing 2, includes: a laser light emitter not shown; a polygon mirror 11; a plurality of reflective mirrors 12; a plurality of lenses not shown; etc. The scanning unit 10 illuminates the surface of the photoconductive drum 17 with laser light which is emitted from the laser light emitter, via the polygon mirror 11, the reflective mirrors 12, and the lenses, to the photoconductive drum 17, as shown by a dashed line in FIG. 1, to thereby scan the photoconductive drum 17 at a higher speed.

The process cartridge 13, which is removably mounted to the body casing 2, stores a toner made up of positively-charged non-magnetic component or material. At a toner delivery opening formed in the process cartridge 13, a developer roller 14 and a supply roller 15 are disposed in opposed relation with each other, and the developer roller 14 is arranged in opposed relation with the photoconductive drum 17. A development bias is applied to the developer roller 14 for development. The toner in the process cartridge 13 is supplied to the developer roller 14 because of the rotation of the supply roller 15, so that the toner is frictionally electrified positively between the developer roller 14 and the supply roller 15, whereby the toner becomes borne on the developer roller 14.

The photoconductive drum 17 is electrically grounded at a body thereof, so that the photoconductive drum 17 is constructed at the surface portion to form a positively charged photoconductive layer made of material such as polycarbonate.

A charger 18 is disposed over the photoconductive drum 17 to be spaced apart therefrom. The charger 18, which is of a Scorotron-type and for a positive charge, is configured to induce a corona discharge at a charging wire made of material such as tungsten, allowing the photoconductive drum 17 to be charged positively and uniformly on the surface of the photoconductive drum 17.

A transfe