JP2008134332A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which can highly accurately control the surface temperature of a fixing roller heated by a plurality of heaters. <P>SOLUTION: Openings 6511 and 6512 in a shield member 65 are switched by a detection area switching section 65, and an infrared light sensor 64 thereby detects the temperatures Ta and Tb of the detection areas A and B of different ranges on the surface of the fixing roller 62. A temperature distribution curve in the whole of the fixing roller 62 in its longitudinal direction at this time is estimated from the detected temperature Ta and the value of the difference ▵T between the detected temperatures Ta and Tb and energization control to a main heater and a sub-heater is performed while referring to a control table on which the controlled variables of the main heater and the sub-heater are preset in each temperature distribution curve. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device that fixes a toner image transferred onto a recording sheet to the recording sheet, and an image forming apparatus including the fixing device.

In general, in an electrophotographic image forming apparatus, a photosensitive drum is exposed and scanned, and an electrostatic latent image formed on the surface of the drum is developed by a developing device to form a toner image, which is formed on a recording sheet. Then, the toner image is fixed by being heated and pressed by a fixing roller.
As a heating means for the fixing roller, for example, a halogen lamp heater or a ceramic heater is incorporated in the hollow portion of the fixing roller. During fixing, the temperature of the fixing roller needs to be maintained in an appropriate temperature range necessary for fixing. However, when a large number of recording sheets are continuously fixed, the temperature of the central sheet passing portion is inevitably changed. Usually, the fixing roller heating means includes a heater that heats both ends of the fixing roller, and a heater that heats a central portion that is approximately the same width as the frequently used paper width. It has.

Conventionally, the temperature control of the fixing roller provided with such a plurality of heaters is performed by separately detecting the surface temperature of the central portion which is a sheet passing portion of the fixing roller and the end portion which is a non-sheet passing portion. The energization of the heater is controlled so that the fixing roller is maintained within a predetermined fixing temperature range throughout its longitudinal direction.
JP 2001-265156 A

However, the above-described control has a problem that the surface temperature of the fixing roller cannot be accurately controlled.
In other words, the amount of heat given to the fixing roller by the mutual heater is transferred to the heating area of the other heater due to heat conduction. In this method, since the temperature distribution in the longitudinal direction of the fixing roller is not taken into consideration, it is difficult to properly correct the temperature unevenness that occurs in the longitudinal direction of the fixing roller. However, there is a possibility that the boundary of the heating range of the heater slightly overlaps, and the heating by both heaters causes the temperature to become abnormally high, resulting in poor fixing.

  The present invention has been made in view of the above circumstances, and includes a fixing device capable of accurately controlling the surface temperature of a pressure contact member such as a fixing roller heated by a plurality of heating means, and the fixing device. An object is to provide an image forming apparatus.

  In order to achieve the above object, a fixing device according to the present invention is a fixing device that fixes a recording sheet on which a toner image has been transferred by pressing with a pressing member heated by a plurality of heating means. The means is arranged in a second direction orthogonal to the first direction in which the recording sheet is conveyed, and the surface temperature of two or more detection regions having different ranges in the second direction in the pressure contact member is determined. Temperature detecting means for detecting, and control means for controlling the plurality of heating means by predicting a surface temperature distribution of the pressure contact member in the second direction based on the detection result of the temperature detecting means. It is characterized by.

According to the above configuration, the temperature of the surface of the pressure contact member in the second direction in which the plurality of heating means are arranged is not controlled independently of the plurality of heating means for heating the pressure contact member of the fixing device as in the related art. Since each heating means is controlled while predicting the distribution, finer and more accurate temperature control becomes possible.
Here, the control unit includes a storage unit that stores a table indicating a control amount of each heating unit according to a surface temperature distribution predicted based on a detection result of the temperature detection unit, and refers to the table. You may make it control each said heating means.

Thereby, the control means can easily execute the temperature control based on the table created in advance by predicting the surface temperature distribution of the pressure contact member.
Further, the temperature detecting means may detect the surface temperature of two or more detection regions having different ranges in a portion where a temperature change occurs in the second direction as a result of fixing the recording sheet.

Thus, by detecting the surface temperature of at least two or more detection regions having different ranges, it is possible to predict the surface temperature distribution of the pressure contact member.
Here, the temperature detection means includes one infrared sensor and detection area changing means for changing the detection area by the infrared sensor to 2 or more, and the temperature of the changed two or more detection areas is respectively determined. You may make it detect.

In this way, since only one infrared sensor is required, the cost of the apparatus can be reduced.
Further, here, the detection area changing means includes a shielding member having two or more openings having different widths in the second direction between the sensor surface of the infrared sensor and the pressure contact member, and moves the shielding member. Then, the detection area of the infrared sensor may be changed by switching the opening.

Thereby, two or more different detection areas can be easily switched.
Here, the detection area changing means includes a detection area by the infrared sensor, which is a first detection area and an area wider in the second direction than the first detection area, And you may make it change into the 2nd detection area | region containing the said 1st detection area | region in the position except the center part in the said 2nd direction of the area | region.

In this way, even if there are two types of detection areas, the characteristics of the surface temperature distribution can be accurately grasped.
Further, the control unit may predict the surface temperature distribution based on a size of a recording sheet to be passed and a detection result of the temperature detection unit.
Thereby, the surface temperature distribution can be predicted finely according to the size of the recording sheet to be passed.

In addition, since the image forming apparatus according to the present invention includes the above-described fixing device, the fixing temperature can be controlled with high accuracy, and a good image without fixing failure can be formed.
Here, the control unit may accurately control the fixing temperature by predicting the surface temperature distribution based on the currently executed operation mode and the detection result of the temperature detection unit.
Thereby, the surface temperature distribution can be predicted in detail according to the operation mode to be executed, and the temperature control accuracy of the fixing device is further improved.

Hereinafter, embodiments of a fixing device and an image forming apparatus according to the present invention will be described by taking a monochrome electrophotographic copying machine (hereinafter simply referred to as “copying machine”) as an example.
(1) Outline of Configuration of Copying Machine FIG. 1 is a schematic diagram showing the overall configuration of the copying machine 1. The copying machine 1 includes an image reader unit 10 that reads a document image, and a printer unit 20 that prints and reproduces the read image on a recording sheet.

The image reader unit 10 is a well-known unit that scans a document image placed on a platen glass and converts it into an electrical signal to obtain image data.
Image data obtained by the image reader unit 10 is A / D converted by the control unit 100 to become a digital signal, and further subjected to necessary processing such as shading correction, density conversion, and edge enhancement, and then a laser diode drive signal. Is output as

The printer unit 20 forms an image on a recording sheet by an electrophotographic method, and includes an exposure scanning unit 30, an image processing unit 40, a paper feeding unit 50, and the like.
The exposure scanning unit 30 includes a laser diode 31, a polygon mirror 32, a scanning lens 33, and the like. The laser diode 31 emits laser light that has been optically modulated in response to the drive signal from the control unit 100. The emitted laser light is reflected and deflected by the mirror surface of the polygon mirror 32 that is driven to rotate at a constant speed, passes through the scanning lens 33, and exposes and scans the surface of the photosensitive drum 41 of the image processing unit 40. .

  The image processing unit 40 is configured by arranging a cleaner 42, an eraser lamp 43, a charging charger 44, a developing device 45, and the like around the photosensitive drum 41. The photosensitive drum 41 is uniformly charged by the charging charger 44 after the residual toner on the surface of the photosensitive member is removed by the cleaner 42 before being subjected to the exposure, and after being erased by irradiating the eraser lamp 43, When exposed in such a uniformly charged state, an electrostatic latent image is formed on the photoreceptor on the surface of the photoreceptor drum 41.

The electrostatic latent image is developed by the developing device 45 to form a toner image. This toner image is transferred onto a recording sheet fed from the paper feed unit 50 in synchronization with the image forming operation, thermally fixed by the fixing device 60, and then discharged onto the paper discharge tray 61. Thus, the image formation based on the document image data is completed.
FIG. 2 is a diagram showing an outline of the fixing device 60 and its control system.

As shown in the figure, the fixing device 60 includes a fixing roller 66 and a pressure roller 63 in which a main heater 621 and a sub-heater 622 are incorporated, and a heat retaining casing 61 for storing the roller pair. In practice, a cleaning member for cleaning the surface of the fixing roller 62 may be provided, but is omitted here.
An infrared sensor 64 and a detection area switching unit 65 for detecting the surface temperature of the fixing roller 66 are installed on the side surface of the housing 61. Under the control of the detection area switching control unit 67, the detection area switching unit 65 switches the area detected by the infrared sensor 64, and the conveyance direction of the recording sheet S on the surface of the fixing roller 66 by one infrared sensor 64 is detected. It enables temperature detection in different ranges in the orthogonal direction (hereinafter simply referred to as “longitudinal direction”).

The CPU 110 is the core of the entire control unit 100 (FIG. 1). The CPU 110 reads out programs and parameters necessary for controlling each part of the copying machine 1 from the ROM 112, and based on this, the operations of the image reader unit 10 and the printer unit 20 are performed. In FIG. 2, the image forming operation is executed smoothly, but is disclosed in a range necessary for explanation of temperature control of the fixing device 60 in FIG. 2.
The RAM 111 temporarily stores various control variables and provides a work area when executing the program.

The CPU 110 predicts the current surface temperature distribution in the longitudinal direction of the fixing roller 62 based on the detection output of the infrared sensor 64, and calculates the power supplied from the fixing heater power supply unit 66 to the main heater 621 and the sub heater 622. Thus, the surface temperature of the fixing roller 62 is maintained at an optimum temperature for fixing in the longitudinal direction. Details will be described later.
FIG. 3 is a schematic view showing detection positions by the fixing roller 62 and the infrared sensor 64. In the drawing, the fixing row 62 is shown in a state where the outer peripheral portion of the roller is watermarked so that the positional relationship between the main heater 621 and the sub heater 622 inside thereof can be seen.

  As shown in FIG. 3, the main heater 621 in the fixing roller 62 is arranged so as to heat the central portion in the longitudinal direction of the fixing roller 62. Although the heating range varies depending on the model and specifications, for example, it is set to heat a range slightly wider than the length in the vertical direction of A4 size, which is generally used frequently. The sub heater 622 heats both end portions outside the main heater 621.

In the present embodiment, detection area switching unit 65 and infrared sensor 64 are arranged to detect the position indicated by the arrow with respect to fixing roller 62 side.
FIGS. 4A and 4B are schematic cross-sectional views showing configurations of the infrared sensor 64 and the detection area switching unit 65.
As shown in FIG. 5A, the infrared sensor 64 has a thermopile chip 643 mounted on a base 644, and a cap-like case 641 is attached to the base 644 so as to cover it. An opening 645 for receiving infrared rays is provided at the top of the case 641, and a condensing silicon lens 642 is attached to the opening 645.

A detection area switching unit 65 for switching the detection range is disposed on the front surface (on the fixing roller 62 side) of the infrared sensor 64.
The detection area switching unit 65 moves the shielding plate 651 having two different types of slits 6511 and 6512 in the longitudinal direction of the fixing roller 62 (the left-right direction in the figure) by the driving mechanism 652, thereby fixing the fixing roller. The detection area on the surface of 62 is changed. In this embodiment, in the example of the fixing roller 62, the width of the detection area A is narrow, the width of the detection area B is set to a wide width including the detection area A, and the surface temperatures Ta and Tb of the respective areas are detected. To do.

  Since the temperature detection by the infrared sensor is obtained from the amount of infrared radiation per unit area of the detection area, the total detection area or the correction coefficient in each of the detection areas A and B is obtained in advance and stored in the ROM 112. The appropriate temperature detection is possible by performing an appropriate calculation such as dividing the output value of the infrared sensor 64 in each case by the sum of the areas of the detection regions at that time, or integrating the correction coefficients. . As a result, the temperatures Ta and Tb are detected as average temperatures of the detection areas A and B, respectively.

  In addition, it is desirable that the range of the detection area A is at a position excluding the central portion in the longitudinal direction of the range of the detection area B (in the present embodiment, the detection area A is positioned toward the right end of the detection area B). To be set). By doing so, the difference between the surface temperatures Ta and Tb becomes clearer, and the approximate tendency (simple increase or simple decrease) of the curve in the detection range B can be discriminated by the sign of the difference. . Details will be described later.

The drive mechanism 652 for moving the shielding plate 651 in the longitudinal direction as described above is not particularly limited, such as a known solenoid, cam mechanism, screw feed mechanism, etc., but from the viewpoint of cost and high drive speed. A solenoid would be desirable.
In the present embodiment, the shielding plate 651 is made of, for example, an opaque resin, but is not particularly limited as long as it is a material that does not transmit infrared rays.

As described above, the temperature distribution in the longitudinal direction of the fixing roller 62 can be estimated by detecting the temperatures of the two detection regions having different ranges.
FIG. 5 shows that the surface temperature of the central portion is initially adjusted by passing a predetermined number of sheets through the fixing roller 62 having a uniform temperature distribution in the longitudinal direction by high-speed processing (for example, 60 sheets per minute (CPM)). 6 is a diagram illustrating an example of a temperature distribution curve in the longitudinal direction of the surface of the fixing roller 62 when the temperature is decreased to 166 ° C. FIG.

In this figure, the horizontal axis indicates the distance from one end of the fixing roller 62 (the left end in FIG. 3 in this example), and the vertical axis indicates the surface temperature. Moreover, the arrow P shows the detection location of the detection area A in FIG.
Normally, in the standby state, the temperature distribution is almost uniform in the longitudinal direction at a predetermined temperature (182 ° C. in this example). However, when the sheet feeding starts, the amount of heat in the sheet passing portion is deprived by the recording sheet. Therefore, the main heater 621 heats.

  As the number of fixed sheets on the recording sheet increases, the temperature of the central sheet passing portion gradually decreases, but the temperature at the ends of the main heater 621 in the heating range where the sheet does not pass increases, while the sub heater is at this time. Since 622 is in an OFF state, the temperature gradually decreases toward the outside due to natural heat dissipation, and a concave portion is formed in the center as shown in FIG. 5, and both ends rise upward and become a temperature distribution curve that gradually decreases toward the outside. .

Here, the solid line curve indicates the temperature when the A4 size recording sheet is passed, the broken line curve indicates the temperature when the A5 size recording sheet passes, and the dotted line curve indicates the temperature when the A6 size recording sheet passes. Each distribution is shown (all in the vertical direction), and the width of the concave portion at the center of the temperature distribution curve is narrowed as the width of the recording sheet is narrowed.
FIG. 5 is an example for explaining the tendency of the temperature distribution curve. Even if the recording sheet has the same size, the heating capacity of the heater, the number of continuous fixing sheets, the CPM, the thickness of the recording sheet to be used, etc. However, the temperature distribution curve will be different.

  By accurately controlling the energization amounts of the main heater 621 and the sub heater 622 with reference to such a temperature distribution curve, temperature control with high accuracy becomes possible. If the temperature is continuously detected in the longitudinal direction of the fixing roller 62, an accurate temperature distribution curve as shown in FIG. 5 can be obtained, but a large number of temperature sensors are required and a great increase in cost can be avoided. Absent.

Therefore, in the present embodiment, the surface temperature distribution in the entire longitudinal direction of the fixing roller 62 from the detection temperature Ta of the detection area A and the detection temperature Tb of the detection area B by the single infrared sensor 64 shown in FIG. Like to guess.
That is, as can be seen from the temperature distribution curve in FIG. 5, except for the central paper passing portion, a curve where the temperature changes in the longitudinal direction is formed in other places, and a curve in a part of the range. The shape differs depending on the overall temperature distribution. Therefore, if the characteristics of the temperature distribution curve in the partial range are grasped, the entire temperature distribution curve can be estimated.

FIG. 6 is a diagram schematically showing an enlarged range of the detection region B in two different temperature distribution curves D1 and D2.
First, focusing on the value of the temperature Ta in the detection region A, the temperature distribution curve D1 is higher than the temperature distribution curve D2. Further, the detected temperature Tb in the detection region B indicates an average temperature in this range. Therefore, when the difference Ta−Tb = ΔT between Ta and Tb is calculated, the temperature distribution curve D1 having a larger decrease rate has a value of ΔT. It turns out that becomes large. Therefore, the characteristic of the temperature distribution curve in the detection region B can be grasped from the value of Ta and the value of ΔT, and thereby the entire temperature distribution curve can be predicted.

  Since the detection area A is set at the end portion of the detection area B as shown in FIG. 4, it can be said that the difference from Tb is clearer than the case where the detection area A is provided at the center part. , ΔT can be estimated whether the temperature distribution curve is decreasing toward the center in the detection region B (ΔT> 0) or increasing (ΔT <0). (For example, when the recording sheet is A4 size, the value of ΔT at the time of passing is always “positive”, but the left side of the position of the arrow P indicating the detection area A increases in the temperature distribution of A5 size. Therefore, the value of ΔT becomes “negative”.)

If a temperature distribution curve in the entire longitudinal direction of the fixing roller 62 can be estimated, a desirable energization control amount for the main heater 621 and the sub heater 622 can be determined accordingly based on empirical rules or accumulation of experimental data.
Therefore, in the present embodiment, a large number of temperature distribution curve data is obtained in advance for each recording sheet size by experiments or computer temperature simulation, and Ta and ΔT (= Ta−Tb) in each detection region B are obtained. ) And the control amounts of the main heater 621 and the sub heater 622 necessary for correcting the temperature distribution curve are stored in the ROM 112 as a control table.

  7, 8, 9, and 10 show examples of the above-described control table. FIG. 7 is a control table that is applied to temperature control during sheet passing when the recording sheet size is A4. 1 and 8 are a control table 2 applied to temperature control during sheet passing when the recording sheet size is A5, and FIGS. 9 and 10 are diagrams showing the control tables 3 and 4 in a standby state, respectively. is there.

  The control amount of the electric power supplied to the main heater 621 and the sub heater 622 is described for each value of the temperature Ta according to the large, medium, and small values of ΔT. In the present embodiment, as the control amount, duty control is employed in which the energization time to each heater is intermittently energized at a predetermined duty ratio within a minute cycle, and the duty ratio is described as the control amount. Has been. However, when another control method such as a phase control method is adopted, a control amount corresponding to the control method is set.

  It is to be noted that the duty ratio obtained here is assumed to be 50% and 50% when supplied to the main heater 621 and the sub heater 622 when ΔT is substantially 0 (during normal heating) (main heater). 621 and the sub-heater 622 are energized alternately for the same time within a minute period). In addition, only a part of the control amount is represented in each control table, and the others are omitted.

  First, in the control table 1 when the size of the recording sheet at the time of paper passing in FIG. 7 is A4, for example, when Ta is 194 ° C. and ΔT is “small”, the temperature distribution curve in the detection region B As a result, the central recess in the entire temperature distribution curve is considered to be relatively shallow, so the duty ratio of the main heater 621 and the sub heater 622 is set to 70% and 30%. If ΔT is “medium”, the central concave portion of the temperature distribution curve becomes deeper than when ΔT is “small”, and it is necessary to heat the central portion more strongly. Therefore, the main heater 621 and the sub heater of the main heater 621 The duty ratio of 622 is set to 80% and 20%.

If ΔT is “large”, the concave portion at the center of the temperature distribution curve becomes deeper, so the duty ratio of the main heater 621 and the sub heater 622 is set to 90% and 10%.
Moreover, when the temperature of Ta is 186 ° C. lower than 194 ° C., for example, it has been empirically found that the central recess is generally shallower than that at 194 ° C.
This is because, in the present embodiment, the temperature Ta detection region substantially corresponds to the end portion of the main heater 621, and therefore the temperature Ta becomes lower when the paper is passed. This is because it is not necessary to heat the main heater 621 to compensate for the temperature drop in the paper passing portion, that is, the amount of paper passing is not so large and the temperature drop in the central portion is considered to be small.

  Therefore, in this case, the duty ratio of the power supply to the main heater 621 and the sub heater 622 is (60%, 40%), (70%, 30%), ( 80% and 20%), the duty ratio of the main heater 621 is 10% lower than that at 194 ° C., and the sub heater 622 is increased by 10%.

FIG. 8 shows the control table 2 when a sheet is passed when the size of the recording sheet is A5. In this case, since the curve is an upward curve at the detection position P (FIG. 5), Ta <Tb as described above. Since the tendency of each control amount can be understood in substantially the same manner as in FIG. 7, a description thereof is omitted here.
9 and 10 show examples of the control tables 3 and 4 during standby.

  As shown in FIG. 5, when the sheet is passed, the temperature distribution curve of the fixing roller is such that only the sheet passing portion becomes extremely concave, and the non-sheet passing portion of the main heater 621 rises like a mountain and goes to the end side. Although the shape gradually decreases, since there is no sheet passing during standby, the temperature distribution curve may not be flat due to an imbalance of the heating amounts of the main heater 621 and the sub heater 622.

  As a temperature distribution curve in such a case, the above-described peaked portion is almost eliminated by heat conduction in the longitudinal direction, and (a) when a concave portion is simply formed in the center (the heating amount of the main heater 621) (B) less than the heating amount of the sub-heater 622, and (b) conversely, the center is swollen upward (when the heating amount of the main heater 621 is larger than the heating amount of the sub-heater 622).

  Therefore, if the detection result at the detection position P (see FIG. 5) is Ta> Tb (that is, ΔT> 0), this is the case of (a), and the heating amount by the main heater 621 as in the control table 3 of FIG. Is controlled to be larger than the heating amount of the sub-heater 622. It can be considered that the individual control amounts differ depending on the magnitudes of Ta and ΔT, as in the case of FIGS. 8 and 9 described above, but since the paper is not passed, the control amount of the main heater 621 is Compared with the case of FIG. 8 and FIG.

Further, in the case of Ta <Tb (ΔT <0), since it is the case of (b) above, the heating amount of the sub heater 622 according to the value of each Ta and the division of ΔT as in the control table 4 of FIG. The control to increase the heating amount by the main heater 621 is performed.
Note that the control tables in FIGS. 7 to 10 are merely examples. Each control amount actually depends on the heating capacity of the main heater 621 and sub heater 622 of the model to be used, the position of the detection position P, the width of each of the detection areas A and B, their relative positional relationship, the value of CPM, etc. Accordingly, those skilled in the art can appropriately set through experiments and simulations.

  In addition, for each table, ΔT is divided into large, medium, and small categories, for example, for each table, a range from the minimum ΔT that can be taken by each temperature distribution curve to the maximum ΔT is obtained in advance and divided into three. It may be determined depending on whether it belongs to the range. If the maximum / minimum ΔT that can be taken for each temperature Ta of each table is obtained more finely and this range is divided into three to determine the range, more accurate control is possible.

Furthermore, if the magnitude of ΔT is classified into four or more stages, the temperature distribution curve is estimated according to which range the detected ΔT corresponds to, and if the control amount is varied accordingly, finer temperature control is possible. It becomes possible.
(2) Temperature Control Operation Next, a specific temperature control operation will be described based on a flowchart.

The flowchart of FIG. 11 is mainly executed by the CPU 110 by reading the temperature control program from the ROM 112 and called as a subroutine of a main flowchart (not shown) for controlling the operation of the entire copying machine, and is performed at a constant short cycle. It is executed repeatedly.
First, in step S101, the light shielding member 651 of the detection area switching unit 65 is moved, and the slit 6511 is controlled to come to the position of FIG. 4A to detect the temperature Ta in the detection region A on the surface of the fixing roller 62. To do.

Subsequently, the temperature Tb in the detection region B on the surface of the fixing roller 62 is detected by moving the light shielding member 651 of the detection area switching unit 65 so that the slit 6512 comes to the position of FIG. 4B (step S102). , ΔT = Ta−Tb is calculated (step S103).
Then, it is determined whether or not ΔT = 0 (step S104). Here, ΔT may not be strictly equal to 0, and it may be determined whether or not −α <ΔT <+ α (α is about 1.0 ° C., for example).

If “YES” in the step S104, it is estimated that the temperature distribution curve is almost flat over the entire longitudinal direction of the fixing roller 62. Next, it is determined whether Ta is equal to or higher than a predetermined fixing temperature. judge. Here, as the “predetermined fixing temperature”, for example, a target temperature 182 ° C. (see FIG. 5) in a standby state is set.
If Ta does not reach the predetermined fixing temperature (step S105: NO), it is necessary to raise the fixing roller 62 as a whole, so that the electric power supplied to each of the main heater 621 and the sub heater 622 as normal temperature control. Are uniformly heated at 50% and 50% (step S106). If Ta has reached the predetermined fixing temperature (step S105: YES), the process returns to the main flowchart without energizing both heaters.

On the other hand, if it is determined in step S104 that ΔT = 0 is not satisfied (step S104: NO), the process moves to step S107, and temperature control based on the control table is executed.
FIG. 12 is a flowchart showing an example of a temperature control subroutine by this control table.
First, the current operation mode is determined (step S201). If the image is formed and the fixing operation is being executed (image forming mode), then the size of the recording sheet used is determined (step S202).

Note that control of image forming operation and paper feed cassette selection (recording sheet selection) is executed by the CPU, and in this control, for example, a flag indicating information on the operation mode and the recording sheet size being used. Is temporarily stored in the RAM 111 or the like and is referred to from time to time, so that the determinations in steps S201 and S202 can be easily performed.
Further, as described above, the temperature distribution curve in the image forming mode is ΔT> 0 in the case of A4 size, and ΔT <0 in the case of A5 size. In this case, the size of the recording sheet can also be determined based on the sign of ΔT.

If the size of the recording sheet being used is A4 size, the control table 1 shown in FIG. 7 is selected (step S204). If the size is A5 size, the control table 2 shown in FIG. 8 is selected. (Step S205).
If it is determined in step S201 that the current operation mode is the standby mode (the state in which the fixing roller 62 is maintained at a predetermined fixing temperature or more and is waiting for the next image forming operation). Next, it is determined whether or not ΔT> 0 is satisfied (step S203). If ΔT> 0, the control table 3 in FIG. 9 is selected (step S203: YES, step S206). If ΔT <0, the control table 4 in FIG. 10 is selected (step S203: NO). Step S207).

 It should be noted that immediately after a large number of images are continuously formed, the temperature distribution curve of the fixing roller 62 may remain as shown in FIG. 5 even in the standby state. In this case, ΔT Therefore, it is difficult to select from the control tables 3 and 4 unambiguously. As can be seen from the temperature distribution curve in FIG. 5, in the case of the A5 size, ΔT <0 because the detection position P rises to the left, but a concave portion is formed in the central portion. is there. Also in this case, if the control table 4 is selected in accordance with step S207 and the end portion is controlled to be heated more than the center portion, the temperature difference becomes larger.

  Therefore, for example, a predetermined time after image formation (this time may be a uniform value (for example, 10 minutes), or the length may be changed according to the magnitude of ΔT immediately after image formation. From the viewpoint of temperature control, it is determined that the image forming mode is still in progress or the surface temperature Tc at the center of the fixing roller 62 until the predetermined time is shortened as the value approaches 0. May be detected, and the control table to be selected may be determined by comparing Tc and Ta. In this case, even when ΔT <0 in the standby mode when the recording sheet is A5 size, if Tc is lower than Ta, the control table 4 is not selected and the control table 2 or 3 is adopted.

Furthermore, for the time being, based on step S207, the control table 4 is selected and the temperature control is executed, and when ΔT after the round of the routine is larger than the previous time, the control table 3 or 4 is switched. May be.
Based on the control table selected as described above, the control amount (duty ratio) of each heater is acquired from the values of Ta and ΔT, the temperature control is executed, and the process returns to the flowchart of FIG.

The main flowchart is cycled at a predetermined cycle, and the temperature control by the control table is repeated again. Each time, the magnitudes of Ta and ΔT also change and are controlled by different control amounts, so the temperature distribution curve gradually If flattening and ΔT = 0 in step S104, normal temperature control is executed based on the temperature of Ta.
As described above, according to this embodiment, the temperature in two different ranges of the fixing roller is detected to predict the temperature distribution over the entire longitudinal direction of the fixing roller, and the energization to the main heater and the sub heater is controlled based on this. Therefore, temperature control with higher accuracy is possible.

<Modification>
Although the embodiment of the present invention has been described above, the content of the present invention is not limited to the above-described embodiment, and for example, the following modifications can be considered.
(1) In the above embodiment, the detection area switching unit 65 changes the detection area of the infrared sensor 64 by sliding the shielding plate 651 having the openings 6511 and 6512 having different widths. It may be. For example, the temperature of different ranges of the fixing roller can be detected by switching the type of lens disposed on the front surface of the infrared sensor 64 from a convex lens to a concave lens, or by switching from the same convex lens to a lens having a different focal length. Is possible. In this case, in order for the detection area A to be offset from either end of the detection area B, for example, the positions of the optical axes of the two types of lenses after switching are different. It is suitably achieved by arranging them in a horizontal direction or using an asymmetric lens.

(2) In the above embodiment, the temperature distribution curve is predicted and the temperature control is executed by switching the two detection areas having different ranges by the detection area switching unit 65 and obtaining Ta and Tb. Two or more detection ranges may be switched to predict a temperature distribution curve from these temperatures.
In the above-described embodiment, the position P in FIG. 5 is set as the detection range. However, the present invention is not limited to this, and includes a location including a range in which a temperature change appears in the longitudinal direction of the fixing roller (maximum size recording sheet used). It is only necessary to be a portion excluding the central bottom portion of the temperature distribution curve. This is because the temperature distribution curve of the detection range differs somewhat depending on the shape of the temperature distribution curve in the entire longitudinal direction, and the entire temperature distribution curve can be predicted by detecting the temperature of different regions in the range. .

In addition, the detection ranges do not have to be in an inclusive relationship, and the entire temperature distribution curve can be predicted based on two or more different temperatures in which a temperature difference occurs.
(3) In the above embodiment, two different ranges of temperature are detected by switching the detection area of one infrared sensor by the detection area switching unit 65, but at different positions in the longitudinal direction. Two or more infrared sensors may be provided and controlled based on the respective detection values. However, since the infrared sensor is expensive, it is desirable to use this embodiment in terms of cost.

  (4) In the above embodiment, in order to determine the control table to be referred to, first, the operation mode is determined as to whether the image forming mode is the standby mode (step S201 in FIG. 12). However, if there are two detection areas, for example, the central part and the boundary between the main heater and the sub-heater, the temperature of these parts and the magnitude relationship between them, the central temperature in standby mode is more than the temperature of the end part. Since the predicted position can be obtained even when it becomes high, it is not always necessary to determine the operation mode in the present invention.

  On the other hand, for example, in a model that can switch the image forming speed (CPM) by changing the system speed (for example, in a tandem type color printer, to improve the reproducibility of an image when forming a color image). When the color image is formed, the system speed is lower than the system speed at the time of monochrome image formation), and the relationship between the main heater and the amount of heat taken away by the paper passing changes. The shape of the temperature distribution curve of the fixing roller tends to change according to the speed.

FIG. 13 shows an example of the temperature distribution curve on the surface of the fixing roller 62 when operating at a lower system speed than in the case of FIG. As shown in the figure, when the system speed is low, the number of recording sheets passing per unit time is reduced, so that the amount of heat taken away from the fixing roller during that time is reduced, and the depth of the central recess is smaller than that shown in FIG. It has a shallow shape.
Therefore, in such a case, the change of the system speed is added to the determination target of the “operation mode” (see step S201 in FIG. 12), and the control table is set based on a plurality of control tables set in advance according to the speed. Select the one corresponding to the system speed.

  (5) In the above embodiment, only the A4 size and the A5 size are determined in the determination of the size of the recording sheet in step S202 in FIG. 12, but this is only an example and is used in the model. Of course, other possible sheet sizes may also be determined, and a control table preset for the sheet size may be selected.

  On the other hand, in the case of a small image forming apparatus that uses only one type of recording sheet, it is not necessary to determine the size of the recording sheet. Even if there are two types of recording sheet sizes that can be used, the determination of the size of the recording sheet may not be a requirement even when the sizes are close (for example, A4 size and B5 size). In this case, the temperature distribution curves are not so different between the two sizes, and therefore, temperature control with higher accuracy than in the prior art is possible without changing the control table for each sheet size.

 (6) In the flowchart of FIG. 11, when ΔT = 0 is determined in step S104, the detected temperature Ta is compared with a predetermined fixing temperature (step S105), and the detected temperature Ta is the fixing temperature. Only when it becomes above, it is comprised so that it may return, without supplying with electricity to each heater. Therefore, until ΔT = 0, the temperature control by the control table in step S107 is repeatedly executed, and energization of each heater is continued.

  As described above, temperature control based on the control table is accurately and dynamically controlled based on the predicted temperature distribution curve, so it takes less time for the temperature distribution curve to converge flatly. Since it reaches step S105 and energization of each heater is stopped according to the determination result, it is considered that there is no possibility that the temperature of the fixing roller abnormally increases during the temperature control in step S107. The following measures may be taken.

 (A) In each control table, when the detected temperature Ta exceeds a relatively high temperature T1 in the fixing temperature range, the duty ratio of the main heater and the sub heater is made smaller while maintaining the relative ratio between the two. Set. For example, when T1 is set to 194 ° C., each duty ratio is halved in the control table of FIG. 7, and ΔT is set to “small”, “medium”, “large” (duty ratio of main heater, sub heater (Duty ratio) of (35%, 15%), (40%, 10%), (45%, 5%).

(B) As mentioned in the above embodiment, the determination content in step S104 in FIG. 11 is changed to determination whether or not −α <ΔT <α. In the negative case, the process proceeds to step S107. In this case, the value of α is adjusted (for example, set to 1.5 ° C.), and the temperature determination in step S105 is performed even if the temperature distribution curve is not completely flattened. If it does in this way, time for continuous heating will become short by circulation of Step S107, and it will not lead to abnormal temperature rise.
(C) Immediately before step S208 in FIG. 12, the detected temperature Ta and the maximum temperature T2 (for example, 210 ° C.) allowable for maintaining good fixing or the maximum temperature permitted by the safety standard of the image forming apparatus Steps for comparison with T3 (for example, 250 ° C.) are provided, and when it is determined that Ta> T2 or Ta> T3, energization of each heater is stopped and the process returns to the flowchart of FIG. skip). While circulating through the flowchart several times, the Ta temperature decreases due to natural heat dissipation and heat conduction in the longitudinal direction of the fixing roller, and the control returns to the control based on the control table.

It is considered that the above inconvenience does not occur when any one of (a), (b) and (c) above or two or more are used in an overlapping manner.
(7) In the above embodiment, an example in which the present invention is applied to a fixing device of a monochrome copying machine has been described. However, other color copying machines, simple printers, facsimile apparatuses, MFPs (Multiple Function Peripheral), etc. Any image forming apparatus having a fixing device can be applied.

  The present invention is particularly suitable for temperature control of a pressure contact member such as a fixing roller in a fixing device of an image forming apparatus.

1 is a schematic diagram showing a configuration of a copying machine 1 according to an embodiment of the present invention. 2 is a schematic diagram illustrating a configuration of a fixing device 60 and a control system of the copying machine 1. FIG. 4 is a schematic diagram showing detection positions by a fixing roller 62 and an infrared sensor 64. (A) (b) is a schematic sectional drawing which shows the structure of the said infrared sensor 64 and the detection area switching part 65. FIG. FIG. 6 is a diagram illustrating an example of a temperature distribution curve in a longitudinal direction of a fixing roller surface after a predetermined amount of recording sheets are continuously passed. It is a figure which expands the range of detection region B in two different temperature distribution curves D1 and D2, and shows typically. It is a figure which shows the example of the control table 1 applied to the temperature control at the time of paper passing in case the size of a recording sheet is A4. It is a figure which shows the example of the control table 2 applied to the temperature control at the time of paper passing in case the size of a recording sheet is A5. 3 is a diagram illustrating an example of a control table 3 applied when the copying machine 1 is in a standby state. FIG. 6 is a diagram illustrating an example of another control table 4 applied when the copying machine 1 is in a standby state. FIG. It is a flowchart which shows the operation | movement of the temperature control in a control part. It is a flowchart which shows the subroutine of the temperature control step by the control table in the flowchart of FIG. FIG. 6 is a diagram illustrating an example of a temperature distribution curve in the longitudinal direction of the surface of the fixing roller after a recording sheet is continuously passed at a lower system speed than in the case of FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copy machine 10 Scanner part 20 Printer part 60 Fixing device 20 Image forming part
DESCRIPTION OF SYMBOLS 30 Paper feed part 40 Secondary transfer part 60 Fixing part 62 Fixing roller 64 Infrared sensor 65 Detection area switching part 66 Heater power supply part 67 Detection area switching part 621 Main heater 622 Sub heater

Claims (9)

A fixing device that presses and fixes a recording sheet on which a toner image has been transferred by pressing members heated by a plurality of heating means,
The plurality of heating means are arranged in a second direction orthogonal to the first direction in which the recording sheet is conveyed,
Temperature detecting means for detecting surface temperatures of two or more detection regions having different ranges in the second direction in the pressure contact member;
And a control unit that controls the plurality of heating units by predicting a surface temperature distribution in the second direction of the press contact member based on a detection result of the temperature detection unit. The control means includes
According to the surface temperature distribution predicted based on the detection result of the temperature detection means, a storage unit that stores a table indicating the control amount of each heating means,
The fixing device according to claim 1, wherein each heating unit is controlled with reference to the table. The temperature detecting means includes
3. The fixing device according to claim 1, wherein the surface temperature of two or more detection areas having different ranges in a portion where a temperature change occurs in the second direction as a result of fixing the recording sheet is detected. The temperature detecting means includes
One infrared sensor,
Detection area changing means for changing the detection area by the infrared sensor to two or more;
With
The fixing device according to claim 1, wherein temperatures of the two or more changed detection areas are detected.   The detection area changing unit includes a shielding member having two or more openings having different widths in the second direction between the sensor surface of the infrared sensor and the pressure contact member, and switches the opening by moving the shielding member. The fixing device according to claim 4, wherein the detection area of the infrared sensor is changed by this.   The detection area changing means includes a detection area by the infrared sensor, which is a first detection area, an area wider in the second direction than the first detection area, and The fixing device according to claim 4, wherein the fixing device is changed to a second detection region including the first detection region at a position excluding a central portion in the second direction.   7. The fixing device according to claim 1, wherein the control unit predicts the surface temperature distribution based on a size of a recording sheet to be passed and a detection result of the temperature detection unit. .   An image forming apparatus comprising the fixing device according to claim 1.   The image forming apparatus according to claim 8, wherein the control unit predicts the surface temperature distribution based on an operation mode currently being executed and a detection result of the temperature detection unit.

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