Patent Application
20080069582
The present invention is further described in the detailed description which follows, with reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:
The embodiments of the present invention are explained in the following, in reference to the above-described drawings.
When a printing process (image forming process) is started at image forming apparatus 1, recording paper S of paper feeder 9 is sequentially transferred at a predetermined timing on guide member 12 provided along paper feeding path 11. When the toner image is transferred at a nip formed between photoconductive drum 2, which moves in the arrowed direction, and transfer roller 6. Then, fixing apparatus 8 performs a fixing process of the toner image and recording paper S is laid on ejecting tray 13 provided on an exterior portion of the apparatus. “Recording paper” used in the example is not limited to paper products in a strict meaning, but includes resin sheets and the like that can be used for image forming processes.
Fixing belt 23 can be provided with a polyimide film base (a heat-generating layer) containing, for examp silver particles. On the base,, an elastic layer having silicone rubber and the like, and a surface release layer having PTFE, PFA, or the like alone or mixed resin, provided in layer in order. Base (heat-generating layer) material may also be an extremely thin metal of copper, nickel, stainless, magnetic shunt alloy, and the like. Heat roller 21 has magnetic shunt alloy. Heat roller 21 may also have a heat-generating layer plated with copper, nickel, or the like, other than the heat-generation layer of magnetic shunt alloy. The magnetic shunt alloy may be, for instance, a Fe—Ni alloy, whose magnetic permeability declines near a Curie temperature and which turns into non-magnetic over the Curie temperature. When the Fe—Ni alloy is used as the magnetic shunt alloy, adjusting a Ni content allows setting of the Curie temperature to a predetermined value. The magnetic shunt alloy according to the present invention is provided such that the alloy has the Curie temperature higher than a fixing temperature (a temperature of a portion of fixing belt 23 corresponding to a paper feeding area of recording paper S in a fixing process). Therefore, in a fixing job to process recording paper having a predetermined width, for instance, when the temperature of an end portion of heat roller 21 (a portion corresponding to a non-paper feeding area of recording paper) increases near the Curie temperature due to electromagnetic-induction heating by induction heater 26, the portion loses magnetism and heating efficiency significantly declines, and thereby the temperature is kept from increasing further.
In the present embodiment, induction heater 26 heats fixing belt 23 and heat roller 21. It is possible, however, not to provide a heat-generating layer to either fixing belt 23 or heat roller 21, so as to heat only either of the components. For instance, a fixing belt may be configured with a polyimide film base having no heat-generating layer, and the elastic and release layers provided as described above, so as to be indirectly heated by heat roller 21.
In addition, a surface layer of fixing roller 22 may be provided with silicone sponge and the like, for example. Further, a surface layer of pressure roller 27 may be provided with silicone rubber and the like.
As shown in
A controller of fixing apparatus 8 mainly includes body controller (heat controller) 31 and fixing controller 32. Body controller 31 is provided with CPU 33, ROM 34, and RAM 35. CPU 33 controls entire processing operations of fixing apparatus 8. ROM 34 stores control programs that allow CPU 33 to perform control. RAM 35 provides a work area for CPU 33 control. CPU 33 is connected to operation input unit 36, so as to obtain input information related to various operation instructions and settings entered by an operator. Further, fixing controller 32 is provided with AC input unit 37 and IH power source 38, which controls power input from AC input unit 37 to magnetizing coil 24.
In a fixing job, CPU 33 executes heating control so as to maintain the fixing temperature at fixing nip N to a temperature suitable for fixing unfixed toner image D. More specifically, CPU 33 obtains temperature data detected by center thermistor 28A and executes heating control such that the temperature of center thermistor 28A is close to a target temperature (hereinafter referred to as a “preset temperature”), which is set based on a type of recording paper and the like. CPU 33 herein sets a preset power value according to the data detected by center thermistor 28A; IH power source 38, following a command from CPU 33, controls power supplied to magnetizing coil 24 of induction heater 26 to the preset power value.
For instance, when sheets of recording paper having a predetermined width (e.g., A4 size) are continuously fed in a fixing job, a temperature difference occurs on fixing belt 23 and heat roller 21 between portions corresponding to paper feeding and non-paper feeding areas of the recording paper (i.e., a portion corresponding to the non-paper feeding area has a higher temperature than a portion corresponding to the paper feeding area, where the recording paper dissipates the heat). When recording paper having a wider width (e.g., A3 size) is fed in a subsequent fixing job, the fixing temperature may differ between the portions corresponding to the paper feeding and non-paper feeding areas of the recording paper, thus causing an uneven gloss level.
To address the problem above, CPU 33 executes heating control for averaging the temperature difference generated between portions corresponding to paper feeding and non-paper feeding areas of recording paper on fixing belt 23 and heat roller 21 (hereinafter referred to as “average heating control”), during a period between fixing jobs (i.e., a period from an end of a preceding fixing job to a start of a subsequent fixing job), regardless of heating control for adjusting the fixing temperature in the above-described fixing job. The average heating control can be executed in a similar manner to heating control in a fixing job, by setting the preset temperature in heating control executed in the fixing job to a temperature suitable for averaging the temperature difference on fixing belt 23 and heat roller 21. Such average heating control reduces the temperature difference in the axis direction on each of fixing belt 23 and heat roller 21, and thereby allows an even gloss level to be maintained on a printed image on recording paper in a subsequent job. In the present embodiment, a temperature difference between side thermistor 28B and center thermistor 28A is used as an index to determine the level of evenness of the temperature difference in the axis direction on fixing belt 23 and heat roller 21.
The temperature transitions of the fixing belt are shown at post warm-up, Job 1 (preceding fixing job), and Job 2 (subsequent fixing job), which are sequentially executed. A4-size recording paper is processed in Job 1, and A3-size recording paper having a wider width is processed in Job 2. In Job 1, center thermistor 28A is positioned in the paper feeding area of the recording paper, while side thermistor 28B is positioned in the non-paper feeding area of the recording paper, as shown in
In each figure, when warm-up is completed, a preset temperature for Th1 is set at 170° C. and a fixing process is executed in Job 1. At this point, side thermistor 28B is positioned in the non-paper feeding area. Temperature difference Th2−Th1 of the thermistors is thus out of tolerance ΔTp (10° C. or 5° C.), while the fixing temperature within the recording paper width falls within tolerance ΔTp. Meanwhile, an area which was the non-paper feeding area in Job 1 is the paper feeding area in Job 2, and thus it is necessary to take a measure to set deviation of the fixing temperature (i.e., temperature difference Th2−Th1 of the thermistors herein) within tolerance ΔTp. To this end, fixing apparatus 8 executes average heating control during a period between fixing jobs (from an end of Job 1 to a start of Job 2). When the recording paper width processed in Job 2 is equal to or narrower than that processed in Job 1, average heating control can be omitted since the temperature in the area within the recording paper width of Job 1 is maintained within the tolerance. As described above, executing average heating control only when required during the period between fixing jobs allows efficient processing.
In
On heat roller 21 herein, the heating efficiency gradually decreases as the temperature increases toward the Curie temperature of the magnetic shunt alloy, which constitutes the heat-generating layer thereof. Thus, even when the power continues to be supplied to magnetizing coil 24 at the same level, calorific value thereof decreases as the temperature (a range of about 130° C. or more in this case) increases as shown in
Performing such average heating control sets the fixing temperature in Job 2 within a range of tolerance ΔTp. In this case, a stop time of the fixing process (i.e., a time from the end of Job 1 to the start of Job 2) is about 30 seconds.
The preset temperature for average heating control in
A level of calorific value decline shown in
Thus, it is preferable to set the preset temperature for average heating control near the preset temperature in Job 2, where a calorific value difference is generally large. In particular, setting the preset temperature for average heating control equal to the preset temperature in the subsequent fixing job (170° C. herein) allows easy execution of average heating control during the period between the fixing jobs, and smooth transition to the subsequent fixing job.
Next, in
Setting the preset temperature close to the Curie temperature and performing average heating control enable the fixing temperature in Job 2 to set within tolerance ΔTp. In this case, the fixing process stop time is about 15 seconds. The fixing process stop time can thus be further shortened compared to the case in
Next, in
Performing average heating control, where the preset temperature is set equal to or higher than the Curie temperature, can set the fixing temperature in Job 2 within a narrower range of tolerance ΔTp. Thus, it is suitable for a fixing process of material particularly prone to gloss unevenness, such as gloss paper, overhead projector film, and the like. In this case, the fixing process stop time is about 20 seconds. The fixing process stop time can thus be substantially shortened compared to the case shown in
When image forming apparatus 1 starts a printing process, CPU 33 first determines, based on input information from operation input unit 36, whether or not a recording paper width in a preceding fixing job (hereinafter referred to as a “preceding job”) is wider than a recording paper width in a fixing job to be executed subsequently (hereinafter referred to as a “subsequent job”) (ST 101). When the recording paper width in the subsequent job is wider than that in the preceding job, CPU 33 determines, based on detected temperatures Th1 and Th2 of thermistors 28A and 28B, whether or not temperature difference Th2−Th1 exceeds a predetermined reference value (e.g., 10° C.) (ST 102).
When temperature difference Th2−Th1 of the thermistors exceeds the reference value, CPU 33 starts executing average heating control during a period between fixing jobs (a period from the end of the preceding job to the start of the subsequent job herein) (ST 103). In the step, in order to equalize the temperature difference generated between portions corresponding to paper feeding and non-paper feeding areas of recording paper on fixing belt 23 and heat roller 21 in the preceding job, CPU 33 sets a preset temperature of center thermistor 28A, regardless of heating control for adjusting a fixing temperature in the preceding job. The preset temperature during the period between the jobs may be set at a temperature lower (e.g., 165° C.) than the preset temperature in the preceding job (e.g., 170° C.). In order to shorten a fixing process stop time, however, it is preferable to set at a temperature higher (e.g., 180° C.) than the preset temperature in the preceding job. In addition, for an overhead projector film and the like, which are prone to an uneven gloss level and have narrow tolerance ΔTp of deviation of the fixing temperature, the preset temperature during the period between the jobs can be set near a Curie temperature (e.g., 200° C.) or higher (e.g., 210° C.).
Subsequently, when CPU 33 determines that temperature difference Th2−Th1 of the thermistors has decreased below the predetermined reference value (ST 104: Yes), CPU 33 changes the preset temperature of center thermistor 28A to a preset temperature in the subsequent job (e.g., 170° C.), and starts heating control in a normal fixing job (ST 105). When the temperature of fixing belt 23 reaches near the preset temperature, a printing process for the subsequent job starts (ST 106). When the subsequent job ends (ST 107), CPU 33 determines whether or not a job exists which was received at operation input unit 36 and has not been processed (ST 108). When an unprocessed job exists, the procedure returns to ST 101 and executes the same operations as described above. In the process, the above-described subsequent job is treated as a preceding job for a new fixing job.
When CPU 33 determines in ST 101 that the recording paper width in the subsequent job is equal to or narrower than that in the preceding job, or when CPU 33 determines in ST 102 that temperature difference Th2−Th1 of the thermistors is equal to or less than the predetermined reference value, CPU 33 determines that average heating control is unnecessary during the period between the fixing jobs, and starts the printing process for the subsequent job without executing average heating control (ST 106). Further, when no preceding job exists in ST 101 immediately after image forming apparatus 1 starts up, or when a predetermined time or longer has elapsed since the preceding job was executed, CPU 33 similarly determines that average heating control is unnecessary. Eventually, when all fixing jobs are executed (ST 108: No), a series of procedure ends.
In ST 201, when a recording paper width in a subsequent job is wider than that in a preceding job, CPU 33 determines, based on input information from operation input unit 36, whether the number of fed paper in the preceding job exceeds a predetermined reference number of sheets (ST 202). The reference number of sheets is set such that when the subsequent job starts within a predetermined time (e.g., 30 seconds) with no execution of average heating control after the preceding job ends, a deviation of a fixing temperature in the subsequent job falls within tolerance ΔTp. When the number of fed paper in the preceding job exceeds the reference number of sheets, CPU 33 starts executing average heating control during a period between the fixing jobs.
In the step, a preset temperature during the period between the jobs may be set at a temperature between a fixing temperature of the preceding job and a Curie temperature of magnetic shunt alloy (e.g., 195° C.), considering tolerance ΔTp of deviation of the fixing temperature. In order to minimize deviation of the fixing temperature, however, it is preferable to set the temperature equal to or higher than the Curie temperature (e.g., 210° C.) of the magnetic shunt alloy. Thereby, temperature difference Th2−Th1 of the thermistors can be set substantially at 0. Then, when CPU 33 determines that temperature Th1 of center thermistor 28A increases higher than the preset temperature (ST 204: Yes), CPU 33 subsequently executes ST 205 to ST 208, similar to ST 105 to ST 108 in
The fixing apparatus and the image forming apparatus according to the present invention have a simple structure that can reduce the temperature difference generated on the heater between portions corresponding to paper feeding and non-paper feeding areas of a recording paper in a previously executed job. Even when processing a recoding paper having a wider width in a subsequent job, the structure equalizes the fixing temperature in the width direction of the recording paper so as to maintain an even gloss level on a printed image. Thereby, the structure is effective as a fixing apparatus that employs an electromagnetic-induction heating method and an image forming apparatus provided with such a fixing apparatus.
It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular structures, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.
The present invention is not limited to the above described embodiments, and various variations and modifications may be possible without departing from the scope of the present invention.
This application is based on the Japanese Patent Application No. 2006-250896 filed on Sep. 15, 2006, entire content of which is expressly incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-250896 | Sep 2006 | JP | national |
