JP2016048327A - Fixation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device capable of executing control appropriate for the actual state of the fixation device even when the minute area heat resistance at a nip position opposite to a temperature detection element changes due to aging, and capable of realizing prevention of image defects such as offset and maximizing the throughput at the time of small-sized sheet passing.SOLUTION: A fixation device comprises: a heating element that generates heat by electrification; a fixation member that has low heat capacity and is rotatable; a rotation member that rotates in pressure contact with the fixation member; and a temperature detection element that detects a temperature of the heating element. The fixation device fixes an unfixed toner image on a recording material by heating and pressing the recording material while holding and conveying the recording material by a nip part. The fixation device comprises heat resistance detection means at the position of the temperature detection element, and changes the control parameter according to the result of the heat resistance detection means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine employing an electrophotographic system, and more particularly to a fixing device that heats and pressurizes an image on a recording material.

  Conventionally, as a heat fixing device, a heat roller type device or a belt heating type device has been widely used. In particular, a method that suppresses power consumption as much as possible without supplying power to the heat fixing device during standby, and more specifically, heating by a belt heating method in which a toner image on a recording material is fixed via a belt between a heater portion and a pressure roller. A fixing method has been proposed (see Patent Document 1 and Patent Document 2).

  However, in the conventional fixing device, there is a case where a fixed matter that inhibits heat transfer is generated due to a change with time in the nip portion between the heater portion and the belt. In this case, a resin member such as a flange or a belt regulating member, or a metal member such as a belt base layer that is scraped by sliding is mixed with sliding grease and fixed to the heater surface.

  As this sticking material accumulates, the heat transfer between the heater and the belt locally decreases at the place where the sticking matter occurs, and image defects such as uneven gloss are likely to occur. Is concerned.

  In order to solve the above problems, cleaning is strengthened during the assembly of the fixing device to suppress the entry of dust that causes scraping by sliding, and the conveyance of the belt regulating member that holds the heater A method of trapping sliding grease mixed with shaving powder by providing a groove shape on the downstream side in the direction has been proposed (see Patent Document 3).

JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP 2006-178315 A

  With the method proposed above, it is possible to suppress the occurrence of sticking of shaving powder to the heater surface to some extent, and it is possible to reduce uneven glossiness of the image. However, it is difficult to prevent fine shavings from adhering due to irregular foreign matters.

  On the other hand, in the configuration in which the temperature detection element (thermistor) is provided on the heater surface opposite to the nip, if shavings adhere to the position facing the thermistor, the thermal resistance between the heater and the belt increases, and the heater at the thermistor position The temperature increases locally, and a difference occurs between the thermistor detection temperature and the actual surrounding heater temperature.

  As a result, there are concerns about the influence on various temperature controls such as temperature control during printing and temperature control of non-sheet passing portions. For example, the heater temperature at the time of printing may become low, causing poor fixing and offset, and the productivity may be reduced more than necessary when a small-size sheet is passed.

  Therefore, a method is desired that can detect the thermal resistance state of the nip portion at the position where the thermistor for detecting the heater temperature is disposed (whether or not chipping powder adheres) and realize appropriate temperature control.

  The fixing device according to claim 1, a heating element that generates heat when energized, a fixing member that is rotatable with a low heat capacity, a rotating member that rotates in pressure contact with the fixing member, and a temperature that detects the temperature of the heating element. A fixing device for fixing an unfixed toner image on the recording material by heating and pressurizing while nipping and conveying the recording material by a nip portion, wherein the fixing device detects thermal resistance at the temperature detection element position. And a control parameter is changed according to the result of the thermal resistance detection means.

  The fixing device according to claim 2, wherein the thermal resistance detection means is performed based on a detection result of the temperature detection element.

  The fixing device according to claim 3, wherein the thermal resistance detection unit is periodically performed when the fixing device is started up.

  The fixing device according to claim 4, wherein the thermal resistance detection unit determines whether or not the thermal resistance detection unit can be implemented according to a temperature detection result of the heating element before the implementation. .

  The fixing device according to claim 5, wherein the thermal resistance detection unit determines whether or not the thermal resistance detection unit can be implemented according to a temperature detection result of the heating element before the implementation.

  According to the present invention, the thermal resistance at the nip position facing the temperature detection element can be detected from the detection result of the temperature transition of the temperature detection element arranged in the heater when the fixing device is started up. Also, the productivity control parameters such as print temperature control and small size paper can be changed according to the detection result.

  As a result, even if the micro-region thermal resistance at the nip position facing the temperature sensing element changes due to changes over time, it is possible to carry out control suitable for the actual fixing device state and prevent image defects such as offset. And maximizing throughput when small-size paper is passed.

FIG. 4 is a diagram illustrating an image forming apparatus using the fixing device of the present invention. FIG. 3 is a schematic cross-sectional view in the short-side direction of the fixing device according to the first exemplary embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of a fixing device according to the present invention. Schematic diagram of heater, temperature detecting element and recording material of the present invention Temperature rise curves of the temperature detection elements 23-a and 23-b during the start-up operation of the fixing device of the present invention Conceptual diagram of heat transfer at temperature sensing element 23 position Temperature rise curve of temperature detection element 23-b that performs thermal resistance detection in Example 1 of the present invention Throughput control at the time of small size paper passing using the temperature detecting element 23-b of the present invention Relationship between ΔTo−ΔTn detected by the thermal resistance detection means and threshold temperature offset Tp ′ in the first embodiment of the present invention. Relationship between the temperature of the temperature detecting element 23-b and the fixing belt temperature with respect to ΔTo−ΔTn in the first embodiment of the present invention. The flowchart which changes a control parameter by thermal resistance detection in Example 1 of the present invention. Temperature rise curve of temperature detection element 23-b that performs thermal resistance detection in Example 2 of the present invention Relationship between ΔT _N −ΔT _N−1 detected by the thermal resistance detecting unit and threshold temperature offset Tp ″ in Embodiment 2 of the present invention. The flowchart which changes a control parameter by thermal resistance detection in Example 2 of the present invention. The flowchart which changes a control parameter by thermal resistance detection in Example 3 of the present invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[Example 1]
In the present embodiment, a heating element that generates heat when energized, a fixing member that is rotatable with a low heat capacity, a rotating member that rotates in pressure contact with the fixing member, and a temperature detection element that detects the temperature of the heating element are provided. In the fixing device for fixing the unfixed toner image on the recording material by heating and pressurizing while nipping and conveying the recording material by the nip portion, the fixing device has a thermal resistance detection means at the temperature detection element position, A description will be given of a method in which the thermal resistance detection means determines from the result of the temperature detection element and changes the control parameter in accordance with the result.

Image Forming Apparatus FIG. 1 is a cross-sectional view of a color electrophotographic printer which is an example of an image forming apparatus of the present embodiment, and is a cross-sectional view along the sheet conveyance direction. In this embodiment, the color electrophotographic printer is simply referred to as “printer”.

  The sheet is a sheet on which a toner image is formed. Specific examples of the sheet include plain paper, a resin sheet that is a substitute for plain paper, cardboard, and overhead projector.

  The printer shown in FIG. 1 includes an image forming unit 10 for each color of Y (yellow), M (magenta), C (cyan), and Bk (black). The photosensitive drum 11 is charged in advance by a charger 12. Thereafter, a latent image is formed on the photosensitive drum 11 by the laser scanner 13. The latent image becomes a toner image by the developing device 14. The toner image on the photosensitive drum 11 is sequentially transferred by the primary transfer blade 17 to, for example, an intermediate transfer belt 31 that is an image carrier. After the transfer, the toner remaining on the photosensitive drum 11 is removed by the cleaner 15. As a result, the surface of the photosensitive drum 11 becomes clean and prepares for the next image formation.

  On the other hand, the sheets P are sent one by one from the paper feed cassette 20 or the multi paper feed tray 25 and sent to the registration roller pair 23. The registration roller pair 23 receives the sheet P once, and straightens it when the sheet is skewed. The registration roller pair 23 feeds the sheet between the intermediate transfer belt 31 and the secondary transfer roller 35 in synchronization with the toner image on the intermediate transfer belt 31. The color toner image on the intermediate transfer belt is transferred onto the sheet P by, for example, a secondary transfer roller 35 which is a transfer body. Thereafter, the toner image on the sheet is fixed to the sheet by the sheet being heated and pressed by the fixing device 40.

  When a toner image is formed only on one side of the sheet, the sheet is discharged to the discharge tray 64 disposed on the side surface of the image forming apparatus 1 by switching the switching flapper 61 or the sheet is discharged from the image forming apparatus 1 side by side. The paper is discharged to a paper discharge tray 65 disposed on the upper surface of the forming apparatus 1. When the switching flapper 61 is at the broken line position, the sheet P is discharged face up (the toner image is on the upper side) onto the paper discharge tray 64, and when the switching flapper 61 is at the solid line position, the sheet P is Then, the sheet is discharged to the sheet discharge tray 65 face down (the toner image is on the lower side).

  When forming a toner image on both sides of the sheet, the sheet P on which the toner image has been fixed by the fixing device 40 is guided upward by the flapper 61 located at the solid line, and when the trailing edge reaches the reversal point R, It is switched back by the conveyance path 73 and turned upside down. Thereafter, the sheet P is conveyed through the double-sided conveyance path 70, and a toner image is formed on the other side through the same process as the single-sided image formation, and is discharged onto the paper discharge tray 64 or the paper discharge tray 65. . The portion constituted by the flapper 61, the switchback conveyance path 73, and the like is an example of a reversing unit.

Fixing Device Next, the fixing unit 40 that is a characteristic part of the present invention will be described. FIG. 2 is a schematic cross-sectional view of the fixing device 40 in the short direction, and FIG. 3 is a schematic configuration diagram of the fixing device 40.

Reference numeral 20 denotes a cylindrical fixing belt (endless belt) provided with a heating element. A pressure roller 22 forms a fixing nip with the fixing belt.
Reference numeral 40 denotes left and right fixing flanges as regulating members that regulate the longitudinal movement and the circumferential shape of the fixing belt 20. Reference numeral 17 denotes a support stay disposed inside the fixing belt 20, which supports the backup member 16 that pressurizes and urges the fixing belt 20 toward the pressure roller 22.

  The fixing belt 20 is loosely covered on the outer side of the backup member 16, and the left and right fixing flanges 40 are fitted to the left and right outward extending arm portions 17 a of the support stay 17, respectively. FIG. 3 is a perspective view of the fixing flange 40 on one end side and the left and right outward extending arm portions 17 a of the support stay 17. Then, the pressure spring 42 is contracted between the pressure portions 40 b and the pressure arms 41 of the left and right fixing flanges 40. As a result, the fixing belt 20 is pressed against the upper surface of the pressure roller 22 through the left and right fixing flanges 40, the support stays 17, and the backup member 16 with a predetermined pressing force, and a fixing nip N having a predetermined width is formed. The In this embodiment, the applied pressure is 156.8 N on one end side, and the total applied pressure is 313.6 N (32 kgf).

  The support stay 17 is preferably made of a material that is difficult to bend even when a high pressure is applied. In this embodiment, SUS304 is used.

  Reference numeral 100 denotes a ceramic heater (hereinafter referred to as a heater) as a heating body. This heater 100 is basically composed of a thin and thin plate-like ceramic substrate whose longitudinal direction is perpendicular to the drawing, and an energization heating resistor layer provided on the surface of the substrate. It is a low heat capacity heater that raises the temperature with a good rise characteristic. In the present embodiment, a heating resistance layer is formed on a ceramic substrate having a thickness of 600 μm.

  Reference numeral 16 denotes a nip forming member on which the heater 100 is fixedly supported. The nip forming member 16 has a substantially semicircular arc shape in cross section and is a heat insulating member such as a heat resistant resin having a longitudinal direction in the drawing as a longitudinal direction. From the viewpoint of energy saving, it is desirable to use a material with low heat conduction to the support stay 17, and for example, heat resistant glass, polycarbonate, liquid crystal polymer or other heat resistant resin is used. In this example, Sumika Super E5204L manufactured by Sumitomo Chemical Co., Ltd. was used. The heater 100 is disposed in a groove formed along the length of the lower surface of the nip forming member 16 so that the heater surface is exposed downward and fixed with a heat resistant adhesive or the like.

  The pressure roller 22 has a multilayer structure in which a silicone rubber layer having a thickness of about 3 mm and a PFA resin tube having a thickness of about 50 μm are sequentially laminated on a stainless steel core. Both end portions of the metal core of the pressure roller 22 are rotatably supported by bearings between a not-shown back side and a front side plate of the apparatus frame 24.

  Reference numeral 23 denotes a thermistor as temperature detecting means. The heater thermistor 23 is in contact with the non-nip side of the ceramic heater and is arranged at the center of sheet passing reference in the longitudinal direction.

  The thermistor 23 is connected to a control circuit unit (CPU) as control means via an A / D converter (not shown). This control circuit section samples the output from the thermistor at a predetermined cycle, and reflects the obtained temperature information in the energization control to the heating element. That is, the control circuit unit determines the energization control content to the heating element based on the output of the thermistor 23 and controls the energization supplied from the power supply unit to the heating element. Note that the above control in the fixing device of the present embodiment is controlled so that the temperature detected by the thermistor 23 is constant at 220 ° C. in view of the temperature for fixing the toner image on the recording material.

  The fixing belt 20 is formed of an elastic layer made of a rubber material having a high thermal conductivity and superimposed on a metal layer having a high thermal conductivity and a high tensile strength, and a release layer made of a fluororesin is formed on the surface thereof. Is formed. The metal layer is a stainless material having a thickness of 50 μm, the elastic layer is a silicone rubber having a thermal conductivity of 1.0 W / m · K, and the release layer is a PFA tube having a thickness of 30 μm.

  The pressure roller 22 forms a flexible elastic layer of rubber material on the outside of a shaft member made of a cylindrical material such as iron or aluminum. The pressure roller 22 is formed with an outer diameter of 25 mm by covering the surface of the elastic layer with a release layer of a PFA tube.

  The shaft member is an aluminum tube having an outer diameter of φ10 mm and a wall thickness of 3 mm, the elastic layer is 3 mm thick, silicone rubber having an Asker hardness of 64 °, and the thickness of the PFA tube is 50 μm.

  The pressure roller 22 is rotationally driven in the direction of the arrow at a predetermined peripheral speed. The fixing belt 20 in pressure contact with the belt is driven by the pressure roller 22 and rotates at a predetermined speed.

  Grease is applied to the inner surface of the fixing belt 20 to reduce wear on the inner surface of the fixing belt 20 caused by friction between the backup member 16 and the inner surface of the fixing belt 20.

  When the pressure roller 22 is driven to rotate and the cylindrical fixing belt 20 is driven to rotate, the heat generation layer of the heater 100 is energized. When the temperature of the fixing belt 20 rises to the set temperature, the recording material P carrying the unfixed toner image in the fixing nip portion N is guided and introduced along the entrance guide 23.

  In the fixing nip portion N, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the fixing belt 20, and the recording material moves together with the fixing belt 20. In the nipping and conveying process at the fixing nip N, heat generated in the heat generation layer is applied to the recording material P, and the unfixed toner image t is melted and fixed on the recording material P. The recording material P that has passed through the fixing nip N is separated from the fixing belt 20 by the curvature, and is discharged by the fixing discharge roller 26.

● Temperature Sensing Element and Thermal Resistance Material Fig. 4 shows a schematic diagram of the heater, temperature sensing element and recording material. The temperature detection elements 23-a and 23-b are in contact with the back surface of the heater, 23-a is disposed at a position 148 mm from the sheet passing reference center, and 23-b is disposed at a position of 148 mm from the sheet passing reference center. 23-a is used for temperature control, and 23-b is used for throughput control of small size paper.

  Next, the relationship between the temperature detection element and the thermal resistance substance R will be described. FIG. 5 shows temperature rise curves of the temperature detecting elements 23-a and 23-b during the start-up operation of the fixing device.

  FIG. 5 (a) shows a temperature rise curve at the time of normal startup without the presence of a substance that becomes a thermal resistance at the position of the temperature detection element. The temperature detection elements 23-a and 23-b show almost the same transition.

  FIG. 5B is a temperature rise curve in the case where the substance R serving as thermal resistance exists in the portion where the heater and the belt facing the position of the temperature detecting element 23-b slide. The temperature detection element 23-a is equivalent to the temperature rise of FIG. 5A, but the temperature rise of the temperature detection element 23-b is large.

  FIG. 6 shows a conceptual diagram of heat transfer at the position of the temperature detecting element 23. h1 is the heat transfer between the normal heater and the belt, and h2 is the heat transfer between the heater and the belt when the thermal resistance material R is interposed. The heat transfer material R is held between the heat resistance substance R and the belt while being attached to the heater sliding layer, whereby the heat transfer h2 is reduced. When this thermal resistance material R exists at the position of the temperature detection element 23, the detection result of the temperature detection element 23 at the time of energization becomes high, and the temperature rise when the fixing device is started up becomes large. As a result, various temperature controls such as throughput control for small-size paper are affected.

  The thermal resistance material R is a material in which scraping powder of fixing device members such as a belt and a backup member, a lubricant applied to the heater sliding layer, and the like are mixed. Further, since the belt and the fixing flange slide at the end portion in the longitudinal direction of the belt, a lot of scraping powder is generated. As a result, the temperature sensing element 23-b disposed at the end in the longitudinal direction is more likely to generate the thermal resistance material R.

-Thermal resistance detection by temperature detection element Next, an example of the thermal resistance detection means in a present Example is demonstrated. In this embodiment, in order to accurately detect the local thermal resistance between the heater and the belt inner surface at the position where the temperature detection element is disposed, the temperature detection result of the temperature detection element when the fixing device is started up is used. .

  FIG. 7 shows a temperature rise curve of the temperature detecting element 23-b during the start-up operation of the fixing device. Here, 23-b_new is a temperature rise curve of the fixing device before use, and 23-b_old is a temperature rise curve after long-term use.

  Comparison of temperature rise from a certain time t1 to t2 during startup is performed. The temperature of the temperature detection element 23-b_new before use at time t1 is T1n, the temperature of the temperature detection element 23-b_old after long-term use is T1o, and the temperature of 23-b_new at time t2 is T2n, 23-b_old. Is set to T2o. At this time, by comparing ΔTo = (T2o−T1o) and ΔTn = (T2n−T1n), the amount of heat transfer in each use state is detected.

  By comparing the temperature rise rates of the temperature detecting elements, it is possible to detect the thermal resistance existing between the heater and the fixing belt.

● Control parameter change by thermal resistance detection Next, control parameter change by thermal resistance detection result will be described. FIG. 8 shows throughput control when a small-size sheet is passed as an example of control using the temperature detection element 23-b. The longitudinal paper width is the paper width in the main scanning direction, and the throughput change threshold temperature Tp is a throughput control parameter controlled by the temperature of the temperature detection element 23-b.

  The threshold temperature Tp for the temperature increase of the non-sheet passing portion at the time of small-size sheet passing is determined in advance from the viewpoint of the heat resistance of the fixing member, and the throughput is lowered when the temperature detecting element 23-b reaches the threshold temperature. When the throughput decreases, the time during which the paper does not pass through the fixing device increases, so the average amount of heat given to the non-sheet passing portion area decreases, and the temperature rise of the non-sheet passing portion is suppressed.

  Here, the width of the non-sheet passing portion changes in the longitudinal direction of the paper passing through the fixing device, and the state of the temperature rise curve and the peak position are different. Therefore, it is necessary to set a different threshold temperature Tp according to the paper width. The threshold value Tp shown in FIG. 8 is a value determined from a relationship obtained through experiments, and the temperature of the fixing belt is set not to exceed 230 ° C. from the viewpoint of heat resistance.

  However, the threshold temperature Tp differs depending on the fixing device to which the present invention is applied, such as the heat resistance of the fixing member, and is not uniquely determined.

  Here, if the thermal resistance material R exists between the heater and the fixing belt, the relationship between the heater temperature detected by the temperature detecting element 23-b and the fixing belt changes. Therefore, by changing the parameter of the threshold temperature Tp according to the detection result by the thermal resistance detection unit of the present embodiment, it is possible to control the throughput appropriately at the heat resistant temperature of the fixing belt, and the throughput decreases more than necessary. Can be prevented. FIG. 9 shows the relationship between ΔTo−ΔTn detected by the thermal resistance detection means and the threshold temperature offset Tp ′, and FIG. 10 shows the temperature and fixing of the temperature detection element 23-b relative to ΔTo−ΔTn detected by the thermal resistance detection means. The relationship of belt temperature is shown. Here, t1 and t2 are set to t1 = 6 s and t2 = 8 s with reference to the start of energization to the fixing device.

  However, the threshold temperature offset Tp ′ differs depending on the fixing device to which the present invention is applied, such as the configuration of the fixing device, and is not uniquely determined.

Printing Operation FIG. 11 is a flowchart for changing control parameters by detecting thermal resistance in the first embodiment. Thermal resistance detection is performed at the time of starting up the fixing device, and if the thermal resistance changes more than a certain value, the control parameter is changed to a predetermined value.

  Step 1: Obtain a temperature rise curve of the temperature detecting element 23-b when the fixing device is started up.

  Step 2: Calculate ΔTo−ΔTn from the detection result of the temperature detection element.

  Step 3: When ΔTo−ΔTn is 0 to 4 ° C., the normal printing operation is performed.

  Step 4: When ΔTo−ΔTn is not 0 to 4 ° C., the throughput change threshold temperature Tp is changed to Tp + Tp ′ according to the table shown in FIG.

Step 5: Print start As described above, the heating element that generates heat when energized, the fixing member that is rotatable with a low heat capacity, the rotating member that rotates while being pressed against the fixing member, and the temperature detection element that detects the temperature of the heating element. A fixing device for fixing an unfixed toner image on the recording material by heating and pressurizing the recording material while nipping and conveying the recording material by a nip portion, and the fixing device has a thermal resistance detection means at the temperature detection element position. In the above description, the thermal resistance detection unit is determined from the result of the temperature detection element, and the control parameter is changed according to the result.

  According to the above embodiment, the thermal resistance between the heater and the fixing belt is detected, and the control parameter can be changed according to the detection result.

As a result, it is possible to accurately know the change in the heat flow over time, and to perform appropriate control.

  As an example of the thermal resistance detection means of the present embodiment, the calculation of the rate of temperature increase over a fixed time is given as an example, but other thermal resistance detection means such as a comparison calculation is performed for the time required for a constant temperature increase. May be.

  Moreover, you may perform arbitrarily the timing which changes threshold temperature Tp.

  Furthermore, the numerical values used in this embodiment are optimized by experiment and are not uniquely determined by the configuration of the fixing device.

[Example 2]
In the present embodiment, a heating element that generates heat when energized, a fixing member that is rotatable with a low heat capacity, a rotating member that rotates in pressure contact with the fixing member, and a temperature detection element that detects the temperature of the heating element are provided. In the fixing device for fixing the unfixed toner image on the recording material by heating and pressurizing while nipping and conveying the recording material by the nip portion, the fixing device has a thermal resistance detection means at the temperature detection element position, A description will be given of a method in which the thermal resistance detection means periodically determines at the start-up of the fixing device, based on the result of the temperature detection element, and changes the control parameter in accordance with the result.

  The color electrophotographic printer in the second embodiment is the same as that in the first embodiment. The operation of the image forming unit is the same as that of the image forming unit described in the first embodiment, and a description thereof is omitted.

  The difference between the second embodiment and the first embodiment is that the thermal resistance detection means that is performed when the fixing device described in the first embodiment is started up is periodically performed.

  Each member constituting the fixing device deteriorates or changes shape with time. In the present invention, in order to detect the thermal resistance of the heater and the fixing belt accurately while minimizing the influence of other changes with time, it is desirable to periodically detect the thermal resistance.

  FIG. 12 shows a temperature rise curve of the temperature detection element 23-b during the startup operation of the fixing device. Here, 23-b (N) is a temperature rise curve of the current fixing device, and 23-b (N-1) is a temperature rise curve when the previous thermal resistance detection was performed.

Comparison of temperature rise from a certain time t1 to t2 during startup is performed. temperature sensing element prior to use in time t1 23-b of the temperature of the _{(N-1) T1 N-} 1, long-term temperature sensing element 23-b after use the temperature of the (N) and T1 _N, at time t2 23-b (N-1) is T2N _-1 , and 23-b (N) is T2o. At this time, by comparing ΔT _N = (T2 _N −T1 _N ) and ΔT _N−1 = (T2 _N−1 −T1 _N−1 ), the amount of heat transfer in each use state is detected.

FIG. 13 shows the relationship between ΔT _N −ΔT _N−1 detected by the thermal resistance detection means and the threshold temperature offset Tp ″. Here, t 1 and t 2 are based on the start of energization to the fixing device, and t 1 = 6 s and t 2 = 8 s. It is said.

  However, the threshold temperature offset Tp ″ differs depending on the fixing device to which the present invention is applied, such as the configuration of the fixing device, and is not uniquely determined.

  FIG. 14 shows a flowchart for changing the control parameter by detecting the thermal resistance in the second embodiment. In order to periodically perform the thermal resistance detection, the thermal resistance detection is performed when the number of sheets to be passed is a certain number or more since the previous thermal resistance detection.

  Step 1: If the number of sheets passed since the previous detection of thermal resistance is 1000 or more, go to Step 2. If it is less than 1000 sheets, the routine proceeds to a normal printing operation (Step 6).

  Step 2: Acquire a temperature rise curve of the temperature detecting element 23-b when the fixing device is started up.

Step 3: Calculate ΔT _N −ΔT _N−1 from the detection result of the temperature detection element.

Step 4: When ΔT _N −ΔT _{N−1 is} −4 to 4 ° C., the process proceeds to a normal printing operation (Step 6).

Step 5: If ΔT _N −ΔT _N−1 is not −4 to 4 ° C., the throughput change threshold temperature Tp is changed to Tp + Tp ″ according to the table shown in FIG.

Step 6: Start of printing As described above, the heating element that generates heat when energized, the fixing member that is rotatable with a low heat capacity, the rotating member that rotates while being pressed against the fixing member, and the temperature detection element that detects the temperature of the heating element. A fixing device for fixing an unfixed toner image on the recording material by heating and pressurizing the recording material while nipping and conveying the recording material by a nip portion, and the fixing device has a thermal resistance detection means at the temperature detection element position. In the above description, the thermal resistance detection unit judges from the result of the temperature detection element and changes the control parameter according to the result periodically when the fixing device is started up.

  As an example of the thermal resistance detection means of the present embodiment, the calculation of the rate of temperature increase over a fixed time is given as an example, but other thermal resistance detection means such as a comparison calculation is performed for the time required for a constant temperature increase. May be.

  Although the detection operation timing of this embodiment is performed at the start of a job for every 1000 printed sheets, it may be performed at an arbitrary number of printed sheets or time, and is not limited to the start of the printing operation, but may have a dedicated sequence. Good. Moreover, you may perform arbitrarily the timing which changes threshold temperature Tp.

  Furthermore, the numerical values used in this embodiment are optimized by experiment and are not uniquely determined by the configuration of the fixing device.

[Example 3]
In the present embodiment, a heating element that generates heat when energized, a fixing member that is rotatable with a low heat capacity, a rotating member that rotates in pressure contact with the fixing member, and a temperature detection element that detects the temperature of the heating element are provided. In the fixing device for fixing the unfixed toner image on the recording material by heating and pressurizing while nipping and conveying the recording material by the nip portion, the fixing device has a thermal resistance detection means at the temperature detection element position, The thermal resistance detection means is determined from the result of the temperature detection element, and the control parameter is changed periodically at the start-up of the fixing device according to the result, and the thermal resistance detection means is implemented. A method for determining whether or not it is possible according to the detected temperature of the heating element before implementation will be described.

  The color electrophotographic printer in the third embodiment is the same as those in the first and second embodiments. The operation of the image forming unit is the same as that of the image forming unit described in the first embodiment, and a description thereof is omitted.

  The third embodiment differs from the first and second embodiments in that the thermal resistance detection means performed at the time of starting up the fixing device described in the first and second embodiments is determined according to the heater temperature before the implementation. It is to be.

  FIG. 15 shows a flowchart for changing the control parameter by detecting the thermal resistance in the third embodiment. As a starting condition for the thermal resistance detection operation of the present embodiment, the temperature of the temperature detection element used for thermal resistance detection is set to the outside air temperature + 5 ° C. or lower. This is because if the temperature history from the previous print job remains, the heat transfer cannot be detected accurately based on the temperature rise rate.

  Step 1: If the number of sheets passed since the previous detection of thermal resistance is 1000 or more, go to Step 2. If it is less than 1000 sheets, the routine proceeds to a normal printing operation (Step 6).

  Step 2: Acquire the temperatures of the temperature detection elements 23-a and 23-b. If both of them are outside temperature + 5 ° C. or less by comparison with outside temperature, the process proceeds to Step 3. If either one is higher than the outside air temperature + 5 ° C., the thermal resistance detection is not performed and the routine proceeds to a normal printing operation (Step 6).

  Step 3: Obtain a temperature rise curve of the temperature detection element 23-b when the fixing device is started up.

Step 4: Calculate ΔT _N −ΔT _N−1 from the detection result of the temperature detection element.

Step 5: When ΔT _N −ΔT _{N−1 is} −4 to 4 ° C., the process proceeds to a normal printing operation (Step 6).

Step 6: When ΔT _N −ΔT _N−1 is not −4 to 4 ° C., the throughput change threshold temperature Tp is changed to Tp + Tp ″ according to the table shown in FIG.

Step 7: Print start As described above, the heating element that generates heat when energized, the fixing member that is rotatable with a low heat capacity, the rotating member that rotates while being pressed against the fixing member, and the temperature detection element that detects the temperature of the heating element. A fixing device for fixing an unfixed toner image on the recording material by heating and pressurizing the recording material while nipping and conveying the recording material by a nip portion, and the fixing device has a thermal resistance detection means at the temperature detection element position. The thermal resistance detection means judges from the result of the temperature detection element, and periodically changes the control parameter according to the result when the fixing device is started up. The method of determining whether or not it is possible to execute according to the detected temperature of the heating element before the implementation has been described.

  Whether or not the detection operation of the present embodiment can be performed is determined based on the outside air temperature + 5 ° C., but may be performed based on an arbitrary temperature relationship or the temperature of another member.

11 Photosensitive drum, 12 charger, 13 laser scanner, 14 developer,
16 backup member, 17 support stay, 18 fixing belt thermistor,
20 fixing belt, 22 pressure roller, 23 heater thermistor, 40 fixing flange,
100 Ceramic heater

Claims (4)

A heating element that generates heat when energized, a fixing member that is rotatable with a low heat capacity, a rotating member that rotates by pressing against the fixing member, and a temperature detection element that detects the temperature of the heating element are provided, and recording is performed by a nip portion. In a fixing device for fixing an unfixed toner image on the recording material by heating and pressing while nipping and conveying the material,
The fixing device includes a thermal resistance detection unit at the temperature detection element position, and changes a control parameter according to a result of the thermal resistance detection unit.   The fixing device according to claim 1, wherein the thermal resistance detection unit is performed based on a detection result of the temperature detection element.   The fixing device according to claim 2, wherein the thermal resistance detection unit is periodically performed when the fixing device is started up.   The fixing device according to claim 2, wherein the thermal resistance detection unit determines whether or not the thermal resistance detection unit can be implemented based on a temperature detection result of the heating element before the implementation.