JP6155431B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus such as a printer or a copying machine that heats and fixes a toner image transferred onto a transfer sheet.

  In general, in an electrophotographic image forming apparatus, a toner image transferred onto a transfer sheet is conveyed to a nip portion between a fixing roller and a pressure roller, and is fixed by applying heat to the nip portion. Patent Document 1 describes a fixing device that heats a fixing belt by laminating a resistance heating element layer on a fixing belt and causing the resistance heating element layer to generate Joule heat. As the fixing belt, it is preferable to use an endless belt made of an extruded resin material that can be mass-produced at low cost. However, such a fixing belt has a variation in thickness in the circumferential direction in manufacturing, and the resistance heating element layer also varies in resistance value per unit area, so that a fixed amount of electric power is supplied. However, there is a problem that the temperature varies depending on the circumferential position of the fixing belt.

  Patent Document 2 describes that the temperature of the outer peripheral surface of the fixing belt is detected and the electric power is corrected using the average temperature of one round. However, the correction is based on the average temperature, and it is difficult to reduce the temperature unevenness at the fixing nip portion.

JP 2003-271209 A JP 2009-109997 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of accurately reducing temperature unevenness of a fixing nip portion even in a fixing belt whose temperature tends to vary in the circumferential direction.

An image forming apparatus according to an aspect of the present invention is
In an image forming apparatus that heats and fixes a toner image transferred onto a transfer paper,
An endless fixing belt disposed in contact with the toner image and heated by a resistance heating element;
A support member disposed inside the fixing belt and retaining the fixing belt in a substantially circular shape;
A pressure member that forms a fixing nip portion in contact with the outer peripheral surface of the fixing belt;
Temperature detecting means for detecting the temperature of the outer peripheral surface of the fixing belt;
Position detecting means for detecting a circumferential position of the fixing belt;
Power supply means for supplying power to the resistance heating element;
Storage means for storing the temperature and position detected by the temperature detection means and the position detection means;
Control means for controlling at least the power supply means, the temperature detection means, the position detection means, and the storage means;
With
The control means has the following operation modes;
During a non-fixing operation, a constant power is supplied to the resistance heating element to heat the fixing belt, and a temperature related to a circumferential position is detected by the temperature detecting means and the position detecting means to store the memory. Characteristic storage mode to be stored in the means,
A fixing execution mode for correcting the power supplied to the resistance heating element from the position and temperature stored in the storage means during the fixing operation, and controlling the power supply means so that the temperature of the fixing nip portion becomes a target temperature;
It is characterized by.

  In the image forming apparatus, the characteristic storage mode is executed during the non-fixing operation, and the temperature related to the circumferential position of the fixing belt is detected and stored in the storage unit. During the fixing operation, while performing normal fixing temperature control, the power supplied to the resistance heating element is corrected based on the stored position and temperature, and the fixing belt is adjusted so that the temperature of the fixing nip portion becomes the target temperature. Feedback to temperature adjustment control.

  According to the present invention, even in a fixing belt whose temperature tends to vary in the circumferential direction, temperature unevenness in the fixing nip portion can be accurately reduced.

1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment. 1A and 1B are schematic cross-sectional views and FIG. FIG. 3 is a cross-sectional view of a main part of a fixing belt. FIG. 3 is a block diagram illustrating a control unit of the fixing device. It is a chart figure which shows the table used for fixing control. It is explanatory drawing which shows the positional relationship of the temperature detection sensor with respect to a fixing belt, and a phase detection sensor. 6 is a graph showing a temperature change of a fixing belt during warming up. It is a graph which shows the state which correct | amended the detected temperature shown in FIG. It is a graph for demonstrating calculation of a correction coefficient. 6 is a graph showing a temperature change of the fixing belt in a temperature rising state. 6 is a graph showing a temperature change of the fixing belt in a temperature-decreasing state. It is a perspective view for demonstrating a phase detection means. It is a flowchart figure which shows the control procedure in characteristic storage mode. FIG. 10 is a flowchart illustrating a main part of a control procedure in a fixing execution mode.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same member and part in each figure, and the overlapping description is abbreviate | omitted.

  First, a schematic configuration of an image forming apparatus 1 according to an embodiment will be described with reference to FIG. The image forming apparatus 1 is configured to form a color image by a tandem method. The photoconductor 10Y for forming a yellow image, the photoconductor 10M for forming a magenta image, and a cyan image are formed. A photoconductor 10C and a photoconductor 10K for forming a black image are juxtaposed, and toner images of the respective colors formed on these photoconductors 10Y, 10M, 10C, and 10K are transferred / combined onto the intermediate transfer belt 15 (1 And the secondary transfer of the composite toner image onto the transfer paper by the electric field applied from the transfer roller 16. Around each of the photoconductors 10Y, 10M, 10C, and 10K, charging chargers 11Y, 11M, 11C, and 11K, image exposure devices 12Y, 12M, 12C, and 12K, developing units 13Y, 13M, 13C, and 13K are arranged. The image is formed by electrophotography. Such an image forming process is well known, and a description thereof will be omitted.

  The transfer sheets are stacked and accommodated in the sheet feeding unit 21 and are fed one by one by the sheet feeding roller 22. The fed transfer paper is conveyed to the secondary transfer section via the registration roller pair 31, and the toner image is secondarily transferred. Thereafter, the transfer paper is heated and fixed with toner by the fixing device 40 and is discharged from the discharge roller pair 33 to the upper surface of the device 1.

  Here, the fixing device 40 will be described. As shown in FIG. 2, the fixing device 40 includes an endless fixing belt 41, a pressure roller 51 that contacts the outer peripheral surface of the fixing belt 41 with a predetermined pressure to form a fixing nip portion N, and a fixing belt 41. And a support roller 46 that holds the lens in a substantially circular shape from the inside. In other words, the fixing belt 41 has flexibility and softness that are held in a substantially circular shape while being sandwiched between the support roller 46 and the pressure roller 51. The pressure roller 51 is rotationally driven in the direction of arrow A, and the fixing belt 41 is maintained in a substantially circular state by this rotational driving force and is driven to rotate in the direction of arrow B. The transfer sheet is conveyed to the fixing nip N in the direction of arrow C with the toner transfer surface facing the fixing belt 41.

  As shown in FIG. 3, the fixing belt 41 is laminated in a four-layer structure including an insulating layer 61, a resistance heating element layer 62, an elastic layer 63, and a release layer 64 from the inside. The elastic layer 63 is made of an endlessly extruded resin material, and a heat-resistant resin material such as silicone rubber or fluororubber is used. Both end portions of the resistance heating element layer 62 are exposed from the elastic layer 63, and electrodes 65 are provided over the entire circumference of the exposed portion. A sliding power supply member 67 connected to a pulse control type power source 66 is in pressure contact with the electrode 65. The resistance heating element layer 62 generates heat by the electric power supplied from the sliding power supply member 67 through the electrode 65, and the elastic layer 63 is heated.

  Further, a temperature detection sensor SE1 is disposed in the vicinity of the outer peripheral surface of the fixing belt 41, and a phase detection sensor is disposed in the vicinity of the inner peripheral surface. The thermistor or thermopile is used for the temperature detection sensor SE1. The phase detection sensor SE2 is for detecting the position in the circumferential direction with reference to a predetermined home position of the fixing belt 41, and will be described in detail below with reference to FIG.

  The elastic layer 63 of the fixing belt 41 is made of the resin material extruded in an endless manner as described above, and has a variation in thickness in the circumferential direction as a problem peculiar to the extruded product. Therefore, as described in the background art, when the fixing belt 41 is heated with a certain amount of energy, the temperature differs at the circumferential position. The present embodiment aims to accurately control the temperature of the fixing nip N even with the fixing belt 41 having such temperature characteristics.

  As shown in FIG. 4, the control unit 70 of the fixing device 40 is configured around a CPU 71, a memory 72 as a storage unit, a temperature detection circuit 73 including a temperature detection sensor SE1, and a phase detection circuit including a phase detection sensor SE2. 74 is provided. A power source 66 is connected to the CPU 71 via an on / off switching circuit 75. Further, the CPU 71 also controls the rotation drive unit 76 of the pressure roller 51.

  The CPU 71 controls the fixing device 40 in the characteristic storage mode and the fixing execution mode. The characteristic storage mode is related to the position in the circumferential direction by the temperature detection sensor SE1 and the phase detection sensor SE2 by supplying a constant power to the resistance heating element layer 62 during the non-fixing operation to cause the fixing belt 41 to generate heat. The temperature is detected and stored in the memory 72. In the fixing execution mode, while fixing temperature control in a normal image forming apparatus is executed, the power supplied to the resistance heating element layer 62 is corrected from the position and temperature stored in the memory 72 during the fixing operation, and the fixing nip is corrected. The power supply 66 is controlled so that the temperature of the part N becomes the target temperature.

  In this embodiment, in the characteristic storage mode, the temperature related to the circumferential position (phase) of the fixing belt 41 is detected, and the correction coefficient K (x) is calculated (see FIG. 5). That is, the temperature is detected in units of 1 mm with respect to the circumferential position of the fixing belt 41 while supplying a constant power to the resistance heating element layer 62, and the table A is created. Next, the ratio of the temperature T (x + α) of the fixing nip N to the detected temperature T (x) at a certain position, that is, T (x) / T (x + α) is a correction coefficient K (x). And Table B is created. This table B is stored in the memory 72.

  By the way, the positional relationship between the circumferential position of the fixing belt 41 and the temperature detection sensor SE1 and the phase detection sensor SE2 is as shown in FIG. When the fixing nip N is set to the home position, the phase detection sensor SE2 detects the phase at the home position, and the temperature detection sensor SE1 detects the temperature of the outer peripheral surface of the fixing belt 41 at an angle position α (approximately 90 °) from the home position. Is detected. That is, the portion detected by the temperature detection sensor SE1 reaches the fixing nip portion N with a phase shifted by α. Here, when the phase detection sensor SE2 detects the phase x of the fixing belt 41, the temperature of the fixing belt 41 output at the detection position by the temperature detection sensor SE1 is T (x), and the temperature at the fixing nip portion N is set. Let T (x + α).

  The characteristic storage mode is executed in various operation modes of the image forming apparatus 1. Here, a case where the characteristic storage mode is executed during warm-up will be described. First, the fixing belt 41 is rotated N times while the fixing belt 41 and the pressure roller 51 are in pressure contact with each other with a predetermined pressure. At this time, the power supplied to the resistance heating element layer 62 is constant, and the temperature is detected for each phase of the fixing belt 41 (if the belt diameter is 30 mm, the circumference is about 94 mm, for example, every 1 mm). And stored in the memory 72. In FIG. 7, the temperature detection value is indicated by a solid line, and the temperature rise characteristic is indicated by a dotted line. That is, it is preferable that the temperature of the fixing belt 41 rises according to the temperature rise characteristic over the entire circumference, but the temperature rises for each turn in a state where the temperature variation shown by the solid line occurs based on the variation in the thickness in the circumferential direction. . The temperature rise at a certain slope of the temperature rise characteristic occurs when a certain amount of energy is input to the resistance heating element layer 62.

  The rise in temperature per unit time is subtracted from the data at the time of measurement in the temperature rise state (see FIG. 7) and stored in the memory 72. That is, it correct | amends to the value which made the inclination of temperature rise 0 (refer FIG. 8). This temperature characteristic corresponds to temperature unevenness caused by uneven thickness of the fixing belt 41 or the like. In order to prepare for a case where a temperature or phase measurement error occurs during N rotations, the measurement data for N rotations may be averaged in order to reduce the influence of the error.

  Next, a mode of calculating the correction value K (x) from the data shown in FIG. 8 when actual fixing is executed will be described with reference to FIG. The temperature T (x + α) of the fixing nip N can be predicted by obtaining K (x) × T (x). K (x) is the output T (x) of the temperature detection sensor SE1 when detecting the phase (x) on the fixing belt 41 from the data obtained in FIG. 8, and the phase (x) similarly obtained in FIG. The ratio with the output T (θ + α) of the temperature detection sensor SE1 at the position of the phase difference α (that is, the fixing nip portion N) is calculated. That is, K (x) = T (x) / T (x + α).

  In the fixing execution mode, as described above, the normal fixing temperature control is executed, and the supply to the resistance heating element layer 62 is performed using the correction value K (x) from the position (phase) and temperature stored in the memory 72. The power is determined, and the power supply 66 is controlled so that the temperature of the fixing nip portion N becomes the target temperature (180 °). The normal fixing temperature control is control in which the temperature of the fixing belt 41 is detected by the sensor SE1 and the supplied power is determined so that the temperature of the fixing belt 42 maintains the target temperature.

  The characteristic storage mode may be executed at any timing as long as the main power is supplied to the image forming apparatus 1. The characteristic storage mode is preferably executed when the fixing belt 41 is replaced due to its life. This is because the variation in the thickness of the fixing belt 41 in the circumferential direction differs for each belt. If the characteristic storage mode is executed during warm-up as described above, time is saved. The characteristic storage mode may be executed immediately before executing the image forming operation in one job. In this case, as shown in FIG. 10, the temperature data of the fixing belt 41 is acquired in a temperature-increasing state with a constant inclination (see dotted line). In this case as well, the temperature detected by the temperature detection sensor SE1 is subtracted from the temperature rise per unit time and stored in the memory 72.

  On the other hand, the characteristic storage mode may be executed while the fixing belt 41 is in the cooled state (for example, after the end of the image forming operation). In this case, as shown in FIG. 11, temperature data is acquired with the fixing belt 41 in a temperature-decreasing state (see the dotted line) with a constant inclination. In this case, the descending temperature per unit time is subtracted from the temperature detected by the temperature detection sensor SE1 and stored in the memory 72. When the characteristic storage mode is executed in the temperature-decreasing state, power is not supplied to the resistance heating element layer 62. This saves energy. Further, if the characteristic storage mode is executed at the cool-down immediately after the end of the image forming operation, time can be saved.

  As shown in FIG. 12, the phase (circumferential position) of the fixing belt 41 is detected by forming a plurality of slits 81 at the end of the fixing belt 41, and using these slits 81 as a phase detection sensor SE2 (photo sensor). It is done by detecting with. The home position can be detected, for example, by forming one slit 81 deep and detecting the position with another photosensor. Instead of the slit 81, a linear pattern or the like may be used. The phase of the fixing belt 41 can also be detected by other methods. The phase detection is preferably performed at or near the fixing nip N. This is because it is possible to prevent the occurrence of a phase detection error due to deformation such as bending that occurs in the fixing belt 41 during rotation.

  The procedure for executing the characteristic storage mode will be described below with reference to the flowchart of FIG. If it is time to execute the characteristic storage mode (YES in step S1), the memory 72 is initialized (step S2), and the data stored so far is erased. Note that step S2 may be omitted if the stored contents of the memory 72 are sequentially updated. Subsequently, the power supplied to the resistance heating element layer 62 is set to be constant (step S3).

  Next, the temperature and phase of the fixing belt 41 are detected while supplying a constant power to the resistance heating element layer 62 (step S4). The period for detecting the temperature and phase is preferably shorter than the time for which the fixing belt 41 makes one revolution. For example, it is detected in units of 1 mm in the circumferential length. Subsequently, a correction value K (x) [= T (x) / T (x + α)] is calculated (step S5). The calculated correction value K (x) is stored in the memory 72 in association with the phase (step S6). Until the storage of data for one rotation of the fixing belt 41 is completed (NO in step S7), steps S4 to S6 are repeated. The time required to complete the data storage for one belt cycle is until the fixing belt 41 reaches the target temperature. The target temperature here may be an actual fixing temperature, or may be a temperature specific to the characteristic storage mode. When it is confirmed that the data storage for one round is completed (YES in step S7), this control is terminated.

  The main part of the control in the fixing execution mode is as shown in FIG. During the fixing operation, the phase and temperature of the fixing belt 41 are detected (step S11), and the electric power Wo supplied to the resistance heating element layer 62 is set based on the target temperature and the detected temperature (normal fixing temperature control). Step S12), and the correction value K (x) is retrieved from the memory 72 based on the phase and temperature data (Step S13), and is output to the resistance heating element layer 62 so as to reach the target temperature for fixing. The power is corrected (step S14). The temperature to be controlled is K (x) × T (x) as described above. That is, if the power supplied to the resistance heating element layer 62 is Wo in order to obtain the target temperature (180 °), the power Wx supplied to the resistance heating element layer 62 is set to K (x) × Wo in step S13. .

  The correction value K (x) may be calculated not when the characteristic storage mode is executed but when the fixing execution mode is executed.

(Other examples)
The image forming apparatus according to the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the gist thereof.

  In particular, the image forming apparatus may be a monochrome image forming apparatus in addition to a color image forming apparatus, or may be a multifunction machine having a communication function or a facsimile function. Further, the detailed configuration of the fixing device is arbitrary.

  As described above, the present invention is useful for an image forming apparatus, and is particularly excellent in that the temperature of the fixing nip portion can be accurately detected in advance and the temperature of the fixing nip portion can be accurately controlled.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 40 ... Fixing apparatus 41 ... Fixing belt 46 ... Support roller 51 ... Pressure roller 62 ... Resistance heating layer 66 ... Power supply 71 ... CPU
72 ... Memory 81 ... Slit SE1 ... Temperature detection sensor SE2 ... Phase detection sensor

Claims (9)

In an image forming apparatus that heats and fixes a toner image transferred onto a transfer paper,
An endless fixing belt disposed in contact with the toner image and heated by a resistance heating element;
A support member disposed inside the fixing belt and retaining the fixing belt in a substantially circular shape;
A pressure member that forms a fixing nip portion in contact with the outer peripheral surface of the fixing belt;
Temperature detecting means for detecting the temperature of the outer peripheral surface of the fixing belt;
Position detecting means for detecting a circumferential position of the fixing belt;
Power supply means for supplying power to the resistance heating element;
Storage means for storing the temperature and position detected by the temperature detection means and the position detection means;
Control means for controlling at least the power supply means, the temperature detection means, the position detection means, and the storage means;
With
The control means has the following operation modes;
During a non-fixing operation, a constant power is supplied to the resistance heating element to heat the fixing belt, and a temperature related to a circumferential position is detected by the temperature detecting means and the position detecting means to store the memory. Characteristic storage mode to be stored in the means,
A fixing execution mode for correcting the power supplied to the resistance heating element from the position and temperature stored in the storage means during the fixing operation, and controlling the power supply means so that the temperature of the fixing nip portion becomes a target temperature;
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the position detecting unit detects a circumferential position of the fixing belt at or near the fixing nip portion.   The image forming apparatus according to claim 1, wherein the position detecting unit detects a pattern in the circumferential direction of the fixing belt by detecting a pattern formed on the fixing belt. The control means stores the correction coefficient K (x) = T (x) / T (x + α) in the storage means when the detected temperature at a certain position is T (x), and the correction power W (x) = Calculating K (x) × Wo,
2. The image forming apparatus according to claim 1, wherein x is a phase angle from the home position of the fixing belt and α is a circumferential phase difference between the temperature detecting unit and the fixing nip portion. Wo is a predetermined power.   The image forming apparatus according to claim 1, wherein the control unit executes the characteristic storage mode when the fixing belt is replaced.   The image forming apparatus according to claim 1, wherein the control unit executes the characteristic storage mode when warming up.   The image forming apparatus according to claim 1, wherein the fixing belt is made of an extruded resin material.   The image forming apparatus according to claim 1, wherein the control unit executes the characteristic storage mode while the fixing belt is heated.   The said control means subtracts the rising temperature per unit time from the temperature detected by the said temperature detection means, and memorize | stores it in the said storage means, when performing the said characteristic storage mode in a temperature rising state. Item 9. The image forming apparatus according to Item 8.

Images