JP4829700B2 - Fixing apparatus, image forming apparatus using the same, and abnormality determination method - Google Patents

Description

  The present invention relates to a fixing device that melts and fixes an unfixed image such as a toner image on a recording medium, an image forming apparatus using the same, and an abnormality determination method, and more particularly, a fixing device that uses a heating rotator such as a heating roller or a heating belt. The present invention relates to an abnormality determination method.

  2. Description of the Related Art Image forming apparatuses such as printers, facsimiles, and copiers using an electrophotographic system or an electrostatic recording system use a fixing device that melts and fixes a toner image electrostatically supported on a recording medium onto the recording medium.

  In this fixing device, temperature detection means such as a thermistor is usually provided, and the fixing temperature is controlled by adjusting the heat supplied to the heating rotator according to the detected temperature. However, if the temperature of the heating rotator cannot be detected correctly due to an abnormality in the thermistor, the heating rotator may be overheated.

  Thus, for example, Patent Document 1 discloses a technique for preparing a plurality of thermistors for detecting the temperature of the heating rotator and detecting that an abnormality has occurred in the temperature detection of the thermistor based on the difference in the detected temperatures.

In the fixing device described in Patent Document 1, one thermistor is arranged in each of the portions of the heating rotator that contact the recording paper and the portions that do not contact the recording paper. In the fixing device described in Patent Document 1, first, when the warm-up operation for raising the temperature of the heating rotator to the temperature at which the toner image can be fused and fixed on the recording medium (fixable temperature) is completed, Stores the detected temperature difference of the thermistor. When the fixing process is performed, the comparison between the detected temperature difference ΔT of the two thermistors and the stored detected temperature difference is repeated intermittently. As a result of the comparison, when the difference in the detected temperature difference is larger than the prescribed threshold value, it is determined that the thermistor cannot correctly detect the temperature of the heating rotator, and heating is stopped.
Japanese Patent Application Laid-Open No. 2003-066760

  However, in the fixing device described in Patent Document 1, when the heating rotator is rapidly heated, there is a possibility that excessive heating of the heating rotator cannot be effectively prevented.

  In recent years, for the purpose of reducing power consumption and shortening the warm-up time, a fixing device that employs a heating belt with a small heat capacity for the heating rotator, and fixing by an electromagnetic induction heating method that heats the heating rotator with Joule heat generated by electromagnetic induction action. The device has been put into practical use. In such a fixing device, the temperature of the heating rotator rises more rapidly than the conventional fixing device constituted by a metal heating roller and a halogen lamp.

  Under such circumstances, in the fixing device described in Patent Document 1, when the temperature of the heating rotator rapidly rises during the warm-up operation, the temperature of the fixing device damages each part before starting the comparison process. There is a risk of rising to the level. In addition, when the end of the warm-up operation is determined based on the detected temperature of the thermistor, if an abnormality occurs in the thermistor, the comparison process is not performed indefinitely, and the heating rotator may overheat. is there.

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device, an image forming apparatus, and an abnormality determination method that can more reliably prevent overheating of a heating rotator.

The fixing device of the present invention detects a heating rotator that rotates in contact with an image recording medium on which an unfixed image is formed, a heating unit that heats the heating rotator, and an electric power supplied to the heating unit. and input power detection means for the plurality of temperature detection means for detecting the temperature of the heating rotating body, a plurality of detection results one of the following the heating rotator target temperature in the warm-up operation of by the plurality of temperature detection means When it is determined by the temperature determination means that determines whether or not a predetermined temperature has been reached, and one of the detection results by the plurality of temperature detection means has reached a predetermined temperature by the temperature determination means, a temperature difference calculating means for calculating the temperature difference between the detection result and another detection result reached to the predetermined temperature, the temperature difference calculated by said temperature difference calculation means, by the input power detecting means There is an abnormality when the temperature difference comparing means for comparing with a predetermined threshold value changed according to the output electric power and the temperature difference calculated by the temperature difference comparing means is equal to or greater than the predetermined threshold value And an abnormality determination unit that determines that

  The image forming apparatus of the present invention employs a configuration having an image forming means for forming an unfixed image on an image recording medium and the fixing device having the above configuration.

The abnormality determination method of the present invention includes a heating rotator that rotates in contact with an image recording medium on which an unfixed image is formed, a heating unit that heats the heating rotator, and an electric power supplied to the heating unit. An abnormality determination method in a fixing device having input power detection means for detecting and a plurality of temperature detection means for detecting the temperature of the heating rotator, wherein one of a plurality of detection results by the plurality of temperature detection means is One of a temperature determination step for determining whether or not a predetermined temperature that is equal to or lower than a target temperature of the heating rotator in the warm-up operation, and one of a plurality of detection results by the plurality of temperature detection means in the temperature determination step is If it is judged to have reached the predetermined temperature, the temperature difference calculating step of calculating a temperature difference between the detection result and another detection result reached to the predetermined temperature, the temperature difference calculating step Thus, a temperature difference comparison step that compares the calculated temperature difference with a predetermined threshold that is changed according to the power detected by the input power detection means, and the temperature difference calculated by the temperature difference comparison step is And an abnormality determining step for determining that there is an abnormality when the predetermined threshold value is exceeded .

  According to the present invention, it is possible to quickly determine whether there is an abnormality when the temperature of the heating rotator reaches a predetermined temperature without relying on a specific temperature detection means. It becomes possible to detect. Thereby, the excessive temperature rise of a heating rotary body can be prevented more reliably.

A fixing device according to a first aspect of the present invention includes a heating rotator that rotates in contact with an image recording medium on which an unfixed image is formed, a heating unit that heats the heating rotator, and a heating unit that includes: An input power detection means for detecting the input power, a plurality of temperature detection means for detecting the temperature of the heating rotator, and one of a plurality of detection results by the plurality of temperature detection means is the heating rotation in the warm-up operation. One of a plurality of detection results by the plurality of temperature detecting means has reached a predetermined temperature by the temperature determining means for determining whether or not a predetermined temperature that is equal to or lower than a target temperature of the body has been reached. when it is determined that the temperature difference calculating means for calculating the temperature difference between the detection result and another detection result reached to the predetermined temperature, the temperature difference calculated by said temperature difference calculation means, said input power A temperature difference comparison means for comparing with a predetermined threshold value that is changed according to the power detected by the output means, and a temperature difference calculated by the temperature difference comparison means is greater than or equal to the predetermined threshold value, And an abnormality determining means for determining that there is an abnormality.

  According to this configuration, even if an abnormality has occurred in any of the plurality of temperature detection means, it can be determined whether there is an abnormality when the detection result of the normal temperature detection means reaches a predetermined temperature. . Therefore, when an abnormality occurs in any of the temperature detection means, even if the temperature of the heating rotator suddenly increases, the abnormality is detected before the heating rotator reaches a high temperature state that damages each part. It is possible to detect and take measures such as stopping heating of the heating rotator for safety. That is, it is possible to prevent overheating of the heating rotator.

Furthermore , the electric power input to the heating means can be specified. Further, the threshold value serving as a criterion for abnormality determination can be changed according to the electric power supplied to the heating means, that is, according to the degree of the temperature rise of the heating rotator, thereby improving the accuracy of abnormality determination. it can.

  The image forming apparatus of the present invention employs a configuration including an image forming unit that forms an unfixed image on an image recording medium, and a fixing device having the above-described configuration.

  According to this configuration, the effect obtained by each of the fixing devices described above can be exhibited by the image forming apparatus that forms an unfixed image on the image recording medium.

The abnormality determination method of the present invention includes a heating rotator that rotates in contact with an image recording medium on which an unfixed image is formed, a heating unit that heats the heating rotator, and an electric power supplied to the heating unit. An abnormality determination method in a fixing device having input power detection means for detecting and a plurality of temperature detection means for detecting the temperature of the heating rotator, wherein one of a plurality of detection results by the plurality of temperature detection means is One of a temperature determination step for determining whether or not a predetermined temperature that is equal to or lower than a target temperature of the heating rotator in the warm-up operation, and one of a plurality of detection results by the plurality of temperature detection means in the temperature determination step is If it is judged to have reached the predetermined temperature, the temperature difference calculating step of calculating a temperature difference between the detection result and another detection result reached to the predetermined temperature, the temperature difference calculating step Thus, a temperature difference comparison step that compares the calculated temperature difference with a predetermined threshold that is changed according to the power detected by the input power detection means, and the temperature difference calculated by the temperature difference comparison step is An abnormality determining step for determining that there is an abnormality when the threshold is equal to or greater than the predetermined threshold value .

According to this method, even if an abnormality has occurred in any of the plurality of temperature detecting means, it is possible to determine whether or not there is an abnormality when the detection result of the normal temperature detecting means reaches a predetermined temperature. . Therefore, when an abnormality occurs in any of the temperature detection means, even if the temperature of the heating rotator suddenly increases, the abnormality is detected before the heating rotator reaches a high temperature state that damages each part. It is possible to detect and take measures such as stopping heating of the heating rotator for safety. That is, it is possible to prevent overheating of the heating rotator.
Furthermore, the electric power input to the heating means can be specified. Further, the threshold value serving as a criterion for abnormality determination can be changed according to the electric power supplied to the heating means, that is, according to the degree of the temperature rise of the heating rotator, thereby improving the accuracy of abnormality determination. it can.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the component and equivalent part which have the same structure or function, and the description is abbreviate | omitted.

  FIG. 1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus using a fixing device according to an embodiment of the present invention.

  In FIG. 1, the image forming apparatus 100 includes a document reading unit 110, a paper feeding unit 120, an image forming unit 130, a fixing unit 200 (fixing device), and a paper discharge unit 140. The image forming unit 130 includes a charging roller 131, an electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 132, a laser scanning unit 133, a developing unit 134, a developing roller 135, and a transfer roller 136.

  The document reading unit 110 reads a document using an image sensor (not shown) and outputs a time-series electric digital pixel signal of image information.

  The paper feeding unit 120 feeds recording paper (image forming medium) to the image forming unit 130 one by one at a predetermined timing synchronized with the operation of the image forming unit 130.

  The image forming unit 130 applies toner to recording paper fed from the paper feeding unit 120 based on image information output from the document reading unit 110 and image information sent from an external host device such as a computer (not shown). Form an image.

  Specifically, in the image forming unit 130, the photosensitive drum 132 is rotationally driven by a driving device (not shown), and the charging roller 131 rotates while contacting the photosensitive drum 132 so that the surface of the photosensitive drum 132 is negative. Charge uniformly to a predetermined potential. The laser scanning unit 133 outputs a laser beam modulated in accordance with a time-series electric digital signal of image information input from the document reading unit 110 or the host device, and scans and exposes the surface of the photosensitive drum 132. An electrostatic latent image corresponding to image information is formed on the surface (image forming surface) of the photosensitive drum 132 by decreasing the absolute potential value of the portion exposed by the laser beam.

  In the image forming unit 130, the developing unit 134 stores toner, and the developing roller 135 supplies the toner stored in the developing unit 134 to the surface of the photosensitive drum 132. However, a predetermined developing bias voltage is applied to the developing roller 135 so that the developing roller 135 has a potential between the potential of the exposed portion of the surface of the photosensitive drum 132 and the potential of the unexposed portion. . As a result, toner adheres only to the exposed portion of the photosensitive drum 132, the electrostatic latent image formed by the laser beam is developed, and an unfixed toner image is formed on the photosensitive drum 132.

  In the image forming unit 130, the recording paper fed from the paper feeding unit 120 is sent to the nip portion between the photosensitive drum 132 and the transfer roller 136. The transfer roller 136 is applied with a predetermined transfer bias voltage, and transfers an unfixed toner image on the surface of the photosensitive drum 132 onto a recording sheet at the nip portion. The recording paper that has passed through the nip is fed to the fixing unit 200.

  The fixing unit 200 melts and fixes the unfixed toner image on the recording paper on the recording paper by heat, and feeds the recording paper on which the fixing process has been completed to the paper discharge unit 140. The configuration of the fixing unit 200 will be described in detail later with reference to another drawing.

  The paper discharge unit 140 discharges the recording paper fed from the fixing unit 200 and stacks the discharged recording paper in a state where it can be easily taken out from the outside.

  FIG. 2 is a cross-sectional view showing a basic configuration of the fixing unit 200 used in the image forming apparatus shown in FIG.

  In FIG. 2, the fixing unit 200 includes a heating roller 211, a fixing roller 212, a heating belt 213 (heating rotating body), a pressure roller 221, a coil (heating means) 231, a coil holder 232, a housing 233, a thermistor (temperature detection means). ) 241, leaf spring 242, and sensor stay 243.

  The heating belt 213 is endless and is wound around the heating roller 211 and the fixing roller 212. The pressure roller 221 is a portion of the peripheral surface of the fixing roller 212 around which the heating belt 213 is wound, and is in pressure contact with the fixing roller 212 with the heating belt 213 interposed therebetween. As a result, a fixing nip portion 290 is formed between the fixing roller 212 and the pressure roller 221 to sandwich the recording paper 301 and fix the unfixed toner image 302 on the recording paper 301 to the recording paper 301. Yes.

  Further, the pressure roller 221 is rotated in the direction of the arrow 311 by a driving device (not shown). The fixing roller 212 and the heating belt 213 are driven to rotate in the direction of the arrow 312 by the rotation of the pressure roller 221. As a result, the recording paper 301 that has entered the fixing nip 290 moves in the direction of the arrow 313 at the same speed as the movement speed of the peripheral surface of the heating belt 213 while being pressed by the pressure roller 221.

  The coil 231 is disposed so as to face a portion around the heating belt 211 around which the heating belt 213 is wound. The coil holder 232 holds the coil 231 on the heating roller 211 side so as to cover the periphery of the heating roller 211 over a circular cross-sectional area centering on the heating roller 211. The housing 233 covers the side of the coil 231 that does not face the heating roller 211, that is, the side of the coil 231 that is opposite to the coil holder 232.

  The widths of the heating roller 211, the fixing roller 212, the heating belt 213, and the pressure roller 221 in the rotation axis direction (perpendicular to the paper surface) are the passage areas of the recording paper 301 in the fixing nip 290 (hereinafter “sheet passing area”) Is wider than the corresponding width. The coil 231 is arranged over a width corresponding to the paper passing area.

  The thermistor 241 is disposed in the space inside the heating belt 213 in contact with the inner surface of the heating belt 213, that is, the surface that does not contact the toner image forming surface of the recording paper 301. More specifically, the thermistor 241 is disposed at a position from when the heating belt 213 passes through a portion facing the coil 231 until it contacts the fixing roller 212. The sensor stay 243 uses the elastic force of the leaf spring 242 to keep the thermistor 241 in contact with the heating belt 213 with an appropriate contact pressure.

  A plurality of thermistors 241 are provided, and are arranged side by side in the rotation axis direction of the heating belt 213.

  FIG. 3 is a schematic diagram illustrating the axial direction of the fixing unit 200. As shown in FIG. 3, three thermistors 241 a, 241 b, and 241 c are arranged in the fixing unit 200 side by side in the axial direction of the fixing unit 200. The thermistors 241a and 241b are for controlling the temperature of the heating belt 213 during the fixing process. The thermistor 241c is used to detect an emergency stop of the image forming apparatus 100 when the heating belt 213 becomes abnormally hot.

  Returning to FIG. 2, the description will be continued. The heating roller 211 and the heating belt 213 have a heat generating layer made of a conductive magnetic member over the entire circumference in the rotation direction and at least the width corresponding to the paper passing area. The coil 231 generates an alternating magnetic field corresponding to the supplied power, and generates eddy currents in the heat generating layer of the heating roller 211 and the heat generating layer of the heating belt 213. That is, the coil 231 causes the heating roller 211 and the heating belt 213 to generate heat by electromagnetic induction. In order to increase the temperature of the heating belt more rapidly, it is desirable to reduce the heat capacity of the heating belt.

  On the other hand, the coil holder 232 is formed of a heat-resistant resin having low conductivity. As a result, the coil holder 232 can be prevented from generating heat due to the electromagnetic induction effect of the coil 231. The housing 233 is formed of a magnetic shielding material that can block an alternating magnetic field generated by the coil 231 such as an aluminum alloy. Thereby, the passage of the magnetic flux to the side of the coil 231 that does not face the heating roller 211 and the heating belt 213 can be blocked, and the alternating magnetic field can be prevented from affecting other devices.

  Heat generation due to the electromagnetic induction action of the coil 231 occurs at a portion of the heating roller 211 and the heating belt 213 facing the coil 231. On the other hand, since the heating roller 211 and the heating belt 213 rotate, the heating roller 211 and the heating belt 213 are uniformly heated over the entire circumference in the rotation direction. As a result, stable heat can be supplied to the recording paper 301 that has entered the fixing nip 290.

  In the fixing device 200 configured as described above, the recording paper 301 enters the fixing nip 290 in the direction of the arrow 313 so that the surface on which the unfixed toner image 302 is transferred contacts the heating belt 213. The unfixed toner image 302 on the recording paper 301 can be melt-fixed on the recording paper 301. As described with reference to FIG. 3, the fixing unit 200 can measure the temperatures of two or more portions of the heating belt 213.

  The temperature of the heating belt 213 has an appropriate value according to the operation state of the image forming apparatus 100. In addition, the temperature of the heating belt 213 changes according to the power supplied to the coil 231. Therefore, the fixing unit 200 uses the temperature detection results of the heating belt 213 by the plurality of thermistors 241 to adjust the power supplied to the coil 231 or to the coil 231 when the temperature of the heating belt 213 becomes abnormally high. Control such as stopping the power supply.

  Hereinafter, the control of the fixing unit 200 will be described.

  FIG. 4 is a schematic configuration diagram illustrating a schematic configuration of a main part related to the control of the fixing unit 200.

  In FIG. 4, the fixing unit 200 further includes a control unit 250 (abnormality determination unit), a power supply unit 260, and an operation display unit 270.

  The control unit 250 includes a control board, and includes a CPU (Central Processing Unit) 251, a ROM (Read Only Memory) 252 that stores a control program executed by the CPU 251, and a RAM (Random Access Memory) as a working memory of the CPU 251. ) 253.

  The power supply unit 260 includes a power supply board, and includes an AC input unit 261 that inputs AC power by connecting to an AC (Alternating Current) power source (not shown), and an IH power source 262 that functions as a power source for the coil 231. The CPU 251 of the control unit 250 is connected to the thermistor 241, the power supply unit 260, and the operation display unit 270. The IH power supply 262 of the power supply unit 260 is connected to the control unit 250 and the coil 231.

  The controller 250 executes a predetermined control program stored in the ROM 252 by the CPU 251 to realize a temperature control process described later. In this temperature control process, the control unit 250 outputs a control signal for controlling the temperature of the heating belt 213 by adjusting the power applied to the coil 231 to the IH power source 262. The ROM 252 stores a threshold value table that defines threshold values for determining whether the fixing unit 200 is abnormal.

  The IH power source 262 applies appropriate power to the coil 231 in accordance with a control signal input from the control unit 250 to drive the coil 231. Further, the IH power source 262 includes an input power detection unit (not shown) that detects the power input to the coil 231. The IH power source 262 feeds back the input power detected by the input power detection unit to the CPU 251.

  In the fixing unit 200 configured as described above, the strength of the alternating electric field of the coil 231 is controlled in accordance with the temperature of a plurality of locations of the heating belt 213 detected by the thermistor 241 and the power supplied to the coil 231, and the heating belt The heat generation of 213 can be controlled. That is, in the fixing unit 200, the temperature of the heating belt 213 can be feedback controlled.

  The control unit 250 executes a temperature control process as a warm-up operation when the image forming apparatus 100 is turned on or returned from the hibernation state. Here, the warm-up operation means that the temperature of the heating belt 213 is raised to a target temperature such as a temperature at which the unfixed toner image 302 can be fused and fixed on the recording paper 301 (hereinafter referred to as “fixable temperature”). Refers to movement. When executing the temperature control process, the control unit 250 determines whether or not the heating belt 213 has reached the fixable temperature based on the temperature detected by the thermistor 241.

  However, as described above, the thermistor 241 may not be able to correctly detect the temperature of the heating belt 213. For example, this may be the case when the leaf spring 242 is loosened or dust adheres to the inner surface of the thermistor or the heating belt 213 and the contact state between the thermistor 241 and the heating belt 213 deteriorates.

  In this case, although the temperature of the heating belt 213 actually exceeds the fixable temperature, this cannot be detected, and there is a possibility that the temperature of the heating belt 213 is further increased. . Therefore, as shown in FIG. 3, a plurality of thermistors 241 are prepared, and the controller 250 compares the respective temperature information. If the temperature difference is large, it is assumed that an abnormality has occurred in any of the thermistors 241 and the coil 231 is connected. Stop power supply. However, as described above, the abnormality detection may be delayed depending on the timing at which the temperature information is compared.

  Here, the relationship between the elapsed time from the start of warm-up and the detected temperature will be described.

FIG. 5 shows an example of the relationship between the elapsed time from the start of warm-up and the detected temperatures T ₁ and T ₂ of the thermistors 241a and 241b when an abnormality occurs in any of the thermistors 241a and 241b in a certain fixing device. FIG. The horizontal axis indicates the elapsed time from the start of warm-up, and the vertical axis indicates the detected temperature.

When an abnormality occurs in either the thermistor 241a or 241b, the detected temperature T cannot follow the actual temperature change of the heating belt 213. For example, when such dust contact portion between the heating belt 213 of the thermistor 241b is adhered, although the detected temperature T ₂ are gradually increased, as shown in FIG. 5, the detected temperature T ₁ of the thermistor 241a The increase is moderate compared to. Then, the temperature difference ΔT between the detected temperature T ₂ and the detected temperature T ₁ increases as the temperature of the heating belt 213 increases with time.

Accordingly, the detected temperature T ₁ is, for example, when it reaches the fixable temperature T _S, the temperature difference ΔT is, by both whether in the range of the temperature difference caused when the normal, either thermistors 241a, 241b It is possible to determine whether or not an abnormality has occurred.

  However, for example, when an abnormality has occurred in the thermistor 241a instead of the thermistor 241b, the abnormality determination itself is not performed, and the heating belt 213 may be overheated.

  Therefore, the control unit 250 compares the temperature information when any of the temperature information input from the thermistors 241a and 241b reaches the fixable temperature in the temperature control process described above.

  FIG. 6 is a flowchart showing the flow of temperature control processing of the control unit 250.

  In step S1100, the start of the warm-up operation is monitored. The warm-up operation is started, for example, by starting power supply to the coil 231 with respect to the power supply unit 260. When power is supplied to the coil 231, magnetic flux is generated, and the heat generating layer of the heating roller 211 and the heat generating layer of the heating belt 213 generate heat. On the other hand, during the warm-up operation, the pressure roller 221 rotates and rotates the heating belt 213 at a predetermined constant speed. Thereby, the temperature of the heating belt 213 rises substantially uniformly over the entire circumference in the rotation direction.

In step S1200, temperature detection is performed at a plurality of locations on the heating belt 213. In other words, to obtain a detection temperatures _{T 1} inputted from the thermistor 241a, the detection temperature _{T 2} which is inputted from the thermistor 241b.

Next, in step S1300, it is monitored whether any of the detected temperatures T ₁ and T ₂ has reached the fixable temperature T _S. If either has reached the fixing temperature _{T S} (S1300: YES), the process proceeds to step S1400.

In step S1400, calculates the temperature difference ΔT between the detected temperature _{T 2} detected temperatures _{T 1} and the thermistor 241b of the thermistor 241a.

Incidentally, the detected temperature _{T 1} of the thermistor 241a because approximately equal to the fixable temperature _{T S,} may be calculated the temperature difference ΔT based on the detected temperature _{T 2} of the fixing temperature _{T S} and the thermistor 241b.

  Next, in step S1500, the value of input power to the coil 231 is acquired from the power supply unit 260.

In step S1600, a temperature difference threshold value ΔT _thr is determined based on the acquired input power value and the threshold value table.

FIG. 7 is an explanatory diagram showing an example of the contents of the threshold value table. In the threshold value table 350, a temperature difference threshold value ΔT _thr of the thermistor 241 is set in association with the input power value. The input power of the coil 231 changes according to the usage state of the image forming apparatus 100 such as whether an optional device such as a sorter is operating. Here, the threshold value ΔT _thr of the temperature difference is 20 ° C. (degrees) for an input power value of 700 W (watts) or more and less than 900 W (700 to 900 W), and for an input power value of 900 W or more and less than 1100 W (900 to 1100 W). 30 ° C. is set for each of 25 ° C. and input power value of 1100 W or more and less than 1300 W (1100 to 1300 W). That is, the larger the input power value, the larger the temperature difference threshold value ΔT _thr is set. The reason for this will be described later.

Returning to FIG. 6, the description will be continued. In step S1700, it is determined whether or not the temperature difference ΔT calculated in step S1400 exceeds the temperature difference threshold value ΔT _thr determined in step S1600. When the temperature difference ΔT is equal to or _smaller than the temperature difference threshold value ΔT _thr (S1700: NO), the process proceeds to step S1800. If the temperature difference ΔT exceeds the temperature difference threshold value ΔT _thr (S1700: YES), the process proceeds to step S1900.

  In step S1800, the fixing unit 200 is shifted to a standby state (normal operation mode) in which the fixing process can be performed, the warm-up operation is completed, and the series of processes ends.

On the other hand, if the temperature difference ΔT exceeds the temperature difference threshold value ΔT _thr , either the thermistor 241a or 241b may be abnormal. However, there is a possibility that erroneous detection has occurred in any of the thermistors 241 due to some temporary abnormality. Therefore, in step S1900, in order to increase the accuracy of abnormality detection, the thermistor abnormality detection is retried at the first temperature rise after the start of warm-up, and the temperature difference ΔT is the temperature difference threshold value even at the second temperature rise. When ΔT _thr is exceeded, it is determined not to retry. When retrying (S1900: YES), the process proceeds to step S2000. When not retrying (S1900: NO), the process proceeds to step S2100.

In step S2000, in order to perform a retry, the temperature of the fixing unit 200 is once lowered and then raised again (cool down). Specifically, first, instructs the suspension of power supply to the coil 231, the detection temperature T ₁ of the both detected temperature T ₂ of the thermistor 241b are fixable temperature T a temperature well below _S the thermistor 241a Then, the power supply to the coil 231 is resumed. Then, the process returns to step S1200, and the monitoring of the detected temperatures T ₁ and T ₂ is started again.

In step S2100, since the temperature difference ΔT exceeds the temperature difference threshold value ΔT _thr twice, it is determined that an abnormality has occurred in either the thermistor 241a or 241b, and the power supply unit 260 is connected to the coil 231. Instruct to stop power supply. At this time, the operation of the apparatus may be restricted by stopping power supply to each part of the image forming apparatus 100 except for the operation display unit 270 and the control unit 250. Further, the operation display unit 270 is used to warn that an abnormality has occurred in the fixing unit 200. Specifically, display processing such as displaying a predetermined error message or turning on a warning lamp is performed on the operation display unit 270, and an operator operating the device stops the device due to an abnormal temperature rise. Notification to that effect. Then, a series of processing ends.

In step S1300, it is determined whether or not any of the detected temperatures T ₁ and T ₂ has reached a predetermined temperature other than the fixable temperature T _{S. If} any of the detected temperatures T ₁ and T ₂ has reached, the process proceeds to step S1400. Good. However, performs abnormality determination of the thermistor 241 during the warm-up operation, to prevent more reliably excessive temperature rise of the fixing unit 200, it is desirable that the predetermined temperature is below fixable temperature T _S. Further, on the premise that no retry is performed, when the temperature difference ΔT exceeds the temperature difference threshold ΔT _thr in step S1700, the process may unconditionally proceed to step S2100. In step S2100, a signal indicating an abnormal stop may be transmitted to a monitoring terminal or the like connected via a predetermined communication medium. In step S2100, only a warning that the fixing unit 200 may be overheated may be issued, and then the process may proceed to step S1800. Further, it is determined whether or not the temperature difference ΔT is greater than a predetermined threshold value, and whether or not the temperature difference ΔT is equal to or greater than the threshold value. You may make it determine.

Such temperature control process, even one of the thermistors 241a, 241b is abnormal, after the start of the warm-up operation, when the heating belt 213 reaches the fixable temperature T _S, to detect this it can. Then, it is possible to take necessary measures to prevent overheating of the heating belt 213, such as stopping the power supply to the coil 231 and issuing a warning of occurrence of abnormality.

The relationship between the elapsed time from the start of warm-up and the detected temperatures T ₁ and T ₂ of the thermistors 241a and 241b is the reason why the threshold value ΔT _{thr of the} temperature difference is set to be larger as the power input to the coil 231 is larger. A description will be given with reference to a graph showing.

  FIG. 8 is a graph showing an example of the relationship between the time when the power of 1200 W is applied to the coil 231 and the detected temperature when the thermistor is normal. The horizontal axis indicates the elapsed time from the start of the warm-up operation, and the vertical axis indicates the detected temperature.

When both the thermistors 241a and 241b are normal, the detected temperatures T ₁ and T ₂ rise with almost no temperature difference, as shown in FIG. When the detected temperature T ₁ reaches the fixable temperature T _S when the specified time t ₀ has elapsed from the start of the warm-up operation, the temperature difference ΔT between the detected temperatures T ₁ and T ₂ is at most 5 ° C. . On the other hand, the temperature difference threshold ΔT _thr corresponding to the input power value of 1200 W is 30 ° C. as shown in FIG. Therefore, since the temperature difference ΔT is smaller than the temperature difference threshold value ΔT _thr , the control unit 250 determines that the thermistors 241a and 241b are normal, and the detected temperature T ₁ has reached the fixing possible temperature T _S. At this point, the warm-up operation ends. Since there is almost no temperature difference between the detected temperatures T ₁ and T ₂ , the warm-up operation ends before and after the timing when the specified time t ₀ has elapsed. As a result, the fixing unit 200 enters a standby state in which the fixing process can be performed.

FIG. 9 is a graph showing an example of the relationship between the time when the power of 1200 W is applied to the coil 231 and the detected temperature when the thermistor is abnormal, and corresponds to FIG. Here, a case which is lower than the temperature of the abnormality occurs, such as a contact failure to the heating belt 213 to the thermistor 241a, the detected temperature T ₁ is the actual heating belt 213.

If the thermistor 241a is abnormal, the detected temperature _{T 1} of the thermistor 241a is lower than the detected temperature _{T 2} of the thermistor 241b. Here, the temperature difference ΔT at which the detected temperature T ₂ has reached the fixing temperature T _S is assumed to be 35 ° C. as shown in FIG. On the other hand, the temperature difference threshold ΔT _thr corresponding to the input power value of 1200 W is 30 ° C. as shown in FIG. Therefore, since the temperature difference ΔT exceeds the temperature difference threshold value ΔT _thr , the control unit 250 determines that the fixing unit 200 is abnormal and stops the power supply to the coil 231. Perform necessary processing to prevent overheating. As a result, the detected temperature T ₁ of the thermistor 241a although not reached the fixing temperature T _S, it is possible to prevent excessive temperature rise of the heating belt 213.

Usually, the higher the input power to the coil 231, the higher the heating rate of the heating belt 213, so that the temperature of the heating belt 213 at the detection temperature T of the thermistor 241 cannot be immediately followed, and the detected temperature of the thermistor 241 varies. Becomes larger. Therefore, in the threshold value table 350 shown in FIG. 7, the threshold value ΔT _{thr of the} temperature difference is set to be larger as the input power value is larger. Therefore, even if the temperature difference ΔT is the same, if the input power is different, the abnormality determination results are different.

  FIG. 10 is a graph showing an example of the relationship between the time when the power of 800 W is applied to the coil 231 and the detected temperature when the thermistor is abnormal, and corresponds to FIG.

Here, as shown in FIG. 10, the detected temperature T _1, T ₂ of the temperature difference ΔT at the time when the detected temperature T ₂ has reached the fixing temperature T _S is assumed to be 25 ° C.. On the other hand, the temperature difference threshold ΔT _thr corresponding to the input power value 800 W is 20 ° C. as shown in FIG. Accordingly, the control unit 250 determines that the fixing unit 200 is abnormal because the temperature difference ΔT exceeds the temperature difference threshold value ΔT _thr .

However, even if the temperature difference ΔT is the same 25 ° C., in the case where 1200 W of power is supplied to the coil 231 as shown in FIG. 9, the corresponding temperature difference threshold ΔT _thr is 35 ° C. Since the difference ΔT is smaller than the temperature difference threshold value ΔT _thr , the abnormality is not determined. Thus, by referring to the threshold value table 350, it is possible to make an abnormality determination according to the input power to the coil 231 and to increase the accuracy of the determination.

  As described above, according to the present embodiment, a plurality of thermistors that detect the temperature of the heating belt 213 are prepared in the fixing unit 200, and whether or not the temperature difference between the detected temperatures is greater than a predetermined threshold value. If it is larger, it is determined that an abnormality has occurred in the thermistor. Thereby, the abnormality of the thermistor can be detected, and it becomes possible to prevent a situation in which this cannot be detected even though the heating belt is overheated. In addition, since this determination is performed when any of the thermistors reaches a predetermined temperature, before the temperature rise is detected by the thermistor provided for detecting the temperature rise, the temperature at which fixing can be reached is reached. An abnormality of the thermistor provided for determination can be detected. Furthermore, since it is rare that an abnormality occurs in all of the thermistors at the same time, it is possible not only to detect the abnormality of the thermistor reliably, but also to prompt the repair or replacement of the thermistor where the abnormality occurred. This can be provided when an abnormality occurs in another thermistor. Therefore, excessive temperature rise can be prevented more reliably.

  In addition, since the fixing unit 200 performs the determination during the warm-up operation, the thermistor abnormality can be determined at an early stage. In addition, since the heating belt 213 is endless, it is possible to measure an intermittent change in temperature rise with high accuracy.

  Further, since the temperature of the heating belt 213 is increased using electromagnetic induction, temperature control when the heating belt 213 generates heat can be easily performed by power control. Further, such a fixing unit 200 has a heating speed faster than that of a conventional fixing unit constituted by a metal heating roller and a halogen lamp. However, as described above, since the abnormality is promptly determined, the heating belt 213 is used. Can be reliably prevented from overheating. Furthermore, since the electric power input to generate heat by the heating belt 213 is detected and the threshold value of the allowable temperature difference is set in association with the input electric power value, more appropriate according to the input electric power. Abnormality determination can be realized.

  In this embodiment, two thermistors arranged side by side in the axial direction of the heating belt are used. However, as long as two or more thermistors are arranged to detect temperature at two or more locations. The number and arrangement are not limited to this. For example, an emergency thermistor such as the thermistor 241c in FIG. 3 or a detection result by a thermistor provided for other purposes may be used for detecting the abnormality of the thermistor.

  Moreover, although the case where the heating belt is used as the heating rotator has been described in the present embodiment, the present invention is not limited to this. For example, in a fixing device that directly melts and fixes an unfixed toner image with a heating roller, the heating roller corresponds to a heating rotator. In this case, temperature detection may be performed at a plurality of locations on the heating roller.

  The fixing device according to the present invention and the image forming apparatus using the fixing device are useful as a fixing device and an image forming apparatus that can more reliably prevent an excessive temperature rise of the heating rotator.

1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus using a fixing device according to an embodiment of the present invention. Sectional drawing which shows the fundamental structure of the fixing | fixed part in this Embodiment. Schematic diagram showing the axial direction of the fixing unit in the present embodiment Schematic configuration diagram showing a schematic configuration of a main part related to control of the fixing unit in the present embodiment. The graph which shows an example of the relationship between the elapsed time from the start of warm-up, and detection temperature when abnormality occurs in the temperature detection of the thermistor arranged in the part which contacts the recording paper of the heating rotator The flowchart which shows the flow of the temperature control process of the control part in this Embodiment. Explanatory drawing which shows an example of the content of the threshold value table in this Embodiment The graph figure which shows an example of the relationship between time and detection temperature when the power of 1200 W is supplied to the coil when the thermistor is normal The graph which shows an example of the relationship between time and detection temperature when the power of 1200 W is supplied to the coil when the thermistor is abnormal The graph which shows an example of the relationship between time and detection temperature when the power of 800 W is supplied to a coil when the thermistor is abnormal

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 110 Document reading part 120 Paper feeding part 130 Image forming part 200 Fixing part 140 Paper discharge part 131 Charging roller 132 Photosensitive drum 133 Laser scanning unit 134 Developing unit 135 Developing roller 136 Transfer roller 211 Heating roller 212 Fixing roller 213 Heating belt 221 Pressure roller 231 Coil 232 Coil holder 233 Housing 241 Thermistor 242 Leaf spring 243 Sensor stay 250 Control unit 260 Power supply unit 270 Operation display unit 251 CPU
252 ROM
253 RAM
261 AC input unit 262 IH power supply

Claims (3)

A heating rotator that rotates in contact with an image recording medium on which an unfixed image is formed;
Heating means for heating the heating rotator;
Input power detection means for detecting power input to the heating means;
A plurality of temperature detecting means for detecting the temperature of the heating rotating body;
Temperature determination means for determining whether one of a plurality of detection results by the plurality of temperature detection means has reached a predetermined temperature that is equal to or lower than a target temperature of the heating rotor in a warm-up operation ;
When it is determined by the temperature determination means that one of the plurality of detection results by the plurality of temperature detection means has reached a predetermined temperature, the temperature difference between the detection result that has reached the predetermined temperature and the other detection results Temperature difference calculating means for calculating
A temperature difference comparison means for comparing the temperature difference calculated by the temperature difference calculation means with a predetermined threshold value that is changed according to the power detected by the input power detection means;
An abnormality determination unit that determines that there is an abnormality when the temperature difference calculated by the temperature difference comparison unit is equal to or greater than the predetermined threshold ;
A fixing device. Image forming means for forming an unfixed image on an image recording medium;
A fixing device according to claim 1 ;
An image forming apparatus comprising: A heating rotator that rotates in contact with an image recording medium on which an unfixed image is formed, a heating unit that heats the heating rotator, and an input power detection unit that detects electric power input to the heating unit; A plurality of temperature detection means for detecting the temperature of the heating rotator, and an abnormality determination method in a fixing device,
A temperature determination step of determining whether one of a plurality of detection results by the plurality of temperature detection means has reached a predetermined temperature that is equal to or lower than a target temperature of the heating rotor in a warm-up operation ;
When the one of the plurality of detection results at a temperature determining step by the plurality of temperature detection means but is judged to have reached the predetermined temperature, the temperature difference between the detection result and another detection result reached to the predetermined temperature A temperature difference calculating step to calculate;
A temperature difference comparison step of comparing the temperature difference calculated by the temperature difference calculation step with a predetermined threshold value that is changed according to the power detected by the input power detection means;
An abnormality determination step of determining that there is an abnormality when the temperature difference calculated by the temperature difference comparison step is equal to or greater than the predetermined threshold ;
An abnormality determination method having:

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