JP5043877B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device, a temperature control method for the fixing device, and an image forming apparatus.

  As a fixing device used in an image forming apparatus such as a copying machine or a printer, a sheet is inserted through a nip formed between a pair of rollers including a heating roller and a pressure roller, or similarly between a heating belt and a pressure roller. There is a fixing device for fixing a toner image by heating and pressing. As such a heating type fixing device, there is a conventional device for heating a metal conductive layer on the surface of a heating roller or a heating belt by an induction heating method. In the induction heating method, first, when a predetermined high-frequency current is supplied to the induction heating coil to generate a magnetic field, an eddy current is generated in the metal conductive layer by the magnetic field. When a current flows through the metal conductive layer in this way, the metal conductive layer has an electrical resistance, so Joule heat is generated by the current and the electric power (the product of the square of the current and the resistance). The heating roller or the heating belt is heated by Joule heat generated in the metal conductive layer.

  In such a fixing device, if the heat capacity of the heated body (heating roller, heating belt) is small, when the sheet comes into contact with the heated body, the sheet is deprived of heat and the surface temperature of the heated body is lowered. . For this reason, there is a case where a difference occurs in the surface temperature of the heated body after the paper contacts with respect to the surface temperature of the heated body before the paper contacts. As described above, when the surface temperature of the object to be heated is different, there is a possibility that a difference in the melting method of the toner occurs at different temperatures, and gloss unevenness may occur.

  Further, the surface of the heated body that does not come into contact with the paper (between the paper, hereinafter referred to as between the paper) is not deprived of heat compared to the temperature of the heated body in the portion that is in contact with the paper. Becomes higher. For this reason, the history of the portion where the surface temperature of the heated body is higher than the portion where the paper is in contact remains as a temperature difference in the heated body, and gloss unevenness may occur on the image.

  In order to solve the above problem, the sheet conveyed to the fixing device is detected and supplied to the induction heating coil so that the temporal power supply pattern based on the timing of the sheet detection becomes a preset pattern. Japanese Patent Application Laid-Open No. H10-228688 discloses a fixing device that controls the power to be generated.

  The fixing device disclosed in Patent Document 1 changes the power value applied to the induction heating coil over time based on a preset power pattern after detecting a sheet, and accurately detects a portion between sheets. It does not mean that the electric power given to the induction heating coil is controlled.

  The set value of the power pattern applied to the induction heating coil by the fixing device of Patent Document 1 is set based on the temperature detected by the temperature detecting means when the paper is not passed through the heated body. That is, the supplied power is determined based on the predicted value when the paper is not passed during paper passing.

  However, when the heat capacity of the heated body is small or when the image forming speed is high, the surface temperature of the heated body may exceed the control temperature during the sheet passing. Because it is difficult to deal with such cases, there is room for improvement.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fixing device and a temperature control method for the fixing device that can make the surface temperature of an object to be heated uniform.

In order to solve the above problem, a fixing device according to the present invention is a pressurizing unit that heats and pressurizes a sheet by passing the sheet between the heated body having a metal conductive layer and the heated body. An induction heating coil that is disposed in proximity to the heated body and generates an induction current in the metal conductive layer. And when the dimension of the paper in the transport direction is longer than the circumference of the heated body, the heated body contacts the heated body for the first time among the sheets based on the detection result of the paper detection unit. A third boundary that is a boundary between the part and the part that contacts the second time, a fourth boundary that switches from a part that contacts the heated body to a part that does not contact the heated body , and the paper on the heated body It switched to a site that is in contact from the site that is not in contact Detecting a fifth boundary that, after the third boundary storing third power value is supplied to the induction heating coil when facing the induction heating coil, electric power supplied to the induction heating coil The value is changed from the third power value to the fourth power value, and the fourth power value supplied to the induction heating coil when the fourth boundary faces the induction heating coil is stored. Thereafter, the power value supplied to the induction heating coil is changed from the fourth power value to the fifth power value, and the power supplied to the induction heating coil when the fifth boundary faces the induction heating coil. The value is changed from the fifth power value to the stored third power value, and the power value supplied to the induction heating coil when the third boundary faces the induction heating coil is changed to the third power. From the value, the stored fourth power Characterized by comprising a control unit for changing the value, the.

  ADVANTAGE OF THE INVENTION According to this invention, the fixing device which can make the surface temperature of a to-be-heated body uniform, the temperature control method of a fixing device, and an image forming apparatus can be provided.

1 is a schematic sectional view showing an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic cross-sectional view illustrating a fixing device according to a first embodiment of the present invention. The block diagram which shows the control system of the heating of the heating roller of the 1st Embodiment of this invention. The figure which showed the relationship between the temperature of the heating roller in a fixing apparatus, and fixing performance. 3 is a flowchart showing temperature control of the fixing device according to the first embodiment of the present invention. The figure showing the relationship between the value of a boundary and the electric power value supplied with respect to the site | part which a paper contacts. 1 is a schematic cross-sectional view illustrating a fixing device including a heating belt according to a first embodiment of the present invention. 9 is a flowchart showing temperature control of a fixing device according to a second embodiment of the present invention. The figure showing the relationship between the value of a boundary and the electric power value supplied with respect to the site | part which a paper contacts.

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)

  Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 7.

  FIG. 1 is a schematic cross-sectional view showing an image forming apparatus 1 on which a fixing device 101 according to this embodiment is mounted.

  The image forming apparatus 1 includes a cassette unit 3 that supplies a sheet P as a fixing medium to the image forming unit 2 at a lower portion, and a scanner unit 5 that reads a document supplied by an automatic document feeder 4 at an upper portion. A registration roller 7 is provided on the conveyance path 6 from the cassette unit 3 to the image forming unit 2. A position sensor 8 that detects the passage of the paper P is provided in front of the registration roller 7.

  The image forming unit 2 includes a charging device 10 that uniformly charges the photosensitive drum 9 sequentially around the photosensitive drum 9 in the rotation direction (clockwise), and the scanner unit 5 on the charged photosensitive drum 9. A laser exposure device 11, a developing device 12, a transfer charger 13, a peeling charger 14, a cleaner 15, and a static elimination LED 16 for forming a latent image based on image data from the image and image data inputted from the outside. With this configuration, the image forming unit 2 forms a toner image on the photosensitive drum 9 and transfers the toner image onto the paper P.

  A paper discharge conveyance path 18 for conveying the paper P on which the toner image is transferred in the direction of the paper discharge unit 17 is provided downstream of the image forming unit 2 in the conveyance direction of the paper P. A fixing device 101 that fixes the toner of the paper P peeled from the photosensitive drum 9 and a paper discharge roller 20 that discharges the paper P that has passed through the fixing device 101 to the paper discharge unit 17 are disposed on the paper discharge conveyance path 18. Provided.

  Next, the fixing device 101 will be described. FIG. 2 is a schematic sectional view showing the fixing device.

  The fixing device 101 includes a heating roller 102 that is a heated object, and a pressure roller 103 that is a pressure member that presses the heating roller 102 through a sheet P. The heating roller 102 is driven in a direction indicated by an arrow in FIG. 2 by a drive motor (not shown), and the pressure roller 103 is provided so as to be in contact with the heating roller 102 and rotated in the direction indicated by the arrow in FIG.

  The configuration of the heating roller 102 is configured from the inside in the order of a core metal 105a, foamed rubber (sponge) 105b, a metal conductive layer 105c, a solid rubber layer 105d, and a release layer 105e. In this embodiment, the foamed rubber 105b is 5 mm thick, the metal conductive layer 105c is 40 μm thick, the solid rubber layer 105d is 200 μm thick, and the release layer 105e is 30 μm thick. Further, nickel is used as the material of the metal conductive layer 105c.

In this embodiment, nickel is used as the material of the metal conductive layer 105c. However, stainless steel, aluminum, a composite material of stainless steel and aluminum, or the like may be used.
The pressure roller 103 is configured by covering the cored bar with silicon rubber, fluorine rubber, or the like. The pressure roller 103 is pressed against the heating roller 102 by a spring 104. When the paper P passes through a fixing point that is a pressure contact portion (nip) between the heating roller 102 and the pressure roller 103, the toner image on the paper P is fused and fixed.

  In addition, a temperature detection sensor 108 is arranged at the center in the longitudinal direction of the heating roller 102 at a position separated from the heating roller 102. The temperature detection sensor 108 detects the temperature of the surface of the heating roller 102.

  Next, the heating device will be described. The heating device includes an induction heating unit 110 disposed on the outer periphery of the heating roller 102, and the heating roller 102 is heated using the induction heating coil 110 a of the induction heating unit 110.

  The induction heating coil 110a is provided with a magnetic core 110b at the center thereof, so that a large induction magnetic field can be generated even with a small number of turns of the electric wire. Further, the shape of the induction heating coil 110a allows the magnetic flux to be focused on the metal conductive layer, so that the heating roller 102 is locally concentrated and heated.

  The induction heating coil 110a uses a copper wire material having a wire diameter of 0.5 mm, and is configured as a litz wire in which a plurality of wires insulated from each other are bundled. By using a litz wire, the skin effect can be reduced compared to a single conductor having the same conductor area, and an alternating current can be effectively passed. In this embodiment, 19 copper wires having a diameter of 0.5 mm are bundled. The coil covering material uses heat-resistant polyamideimide.

  Magnetic flux is generated by a high-frequency current applied to the induction heating coil 110a from an inverter circuit described later. This magnetic flux generates a magnetic flux and an eddy current so as to prevent a change in the magnetic field in the metal conductive layer 105 c of the heating roller 102. Joule heat is generated by the eddy current and the resistance of the metal conductive layer 105c, and the heating roller 102 is heated.

  Further, based on the difference between the temperature detected by the temperature detector 108 and the set temperature of the heating roller 102, the power output to the induction heating coil 110a is changed to maintain the heating roller 102 at the fixing temperature.

  Further, a paper detection sensor 111 that detects the conveyed paper P is provided upstream of the entrance of the fixing device 101. When the leading or trailing edge of the paper P passes through the paper detection sensor 111, a signal is sent from the paper detection sensor 111 to the control unit (CPU), and this signal is used to control the power of the induction heating coil 110a and the like thereafter. Used as a criterion.

  Next, a control system for heating the heating roller 102 will be described with reference to FIG.

  FIG. 3 is a block diagram showing a control system related to heating of the heating roller 102. That is, this control system is a part that functions as a high-frequency current supply unit that supplies a high-frequency current to the induction heating coil 110a. The control system includes an inverter circuit 201 that supplies a drive current to the induction heating coil 110a, a rectifier circuit 202 that supplies a DC power to the inverter circuit 201, a detection result of the paper P by the paper detection sensor 111, and a detection result of the temperature detection sensor 108. The CPU 203 controls the inverter circuit 201 according to the above.

  The rectifier circuit 202 converts the current from the commercial AC power supply 204 into a rectified and smoothed DC current and supplies it to the inverter circuit 201. A power detector (transformer) 205 is disposed between the rectifier circuit 202 and the commercial AC power supply 204, and the power value supplied to the induction heating coil 110a can be detected. This supplied power value is detected and fed back to the CPU 203.

  The inverter circuit 201 is configured such that a resonance capacitor 206 is connected in parallel to an induction heating coil 110a, and a switching element 207 is connected in series to the resonance circuit. The switching element 207 is an IGBT (insulated gate bipolar transistor) that can be used with a high breakdown voltage and a large current. The switching element 207 may be a MOS-FET or the like.

  A drive circuit 208 is connected to the control terminal of the switching element 207. In the drive circuit 208, a drive voltage is applied to the control terminal of the switching element 207, and the switching element 207 is turned ON / OFF. The control circuit 209 connected to the drive circuit 208 outputs timing for applying a drive voltage from the drive circuit 208 to the switching element 207. That is, the ON time of the switching element 207 is determined by the control circuit 209, and the supply power is changed by changing the ON time while feeding back the supply power to the inverter circuit 201.

  Increasing the ON time of the switching element 207 increases the power supplied to the inverter circuit 201. Further, when the ON / OFF time of the switching element 207 is changed, the time of one cycle of the current flowing through the induction heating coil 110a is changed, so that the drive frequency is changed. In the present embodiment, the frequency is changed in the range of 20 KHz to 100 KHz, and the supplied power is changed in the range of 200 W to 1000 W.

  Next, a control method for changing the power value supplied to the induction heating coil 110a during the image forming operation and keeping the temperature distribution in the circumferential direction of the heating roller 102 uniform will be described.

  As described above, when the heat capacity of the heating roller 102 is small, the sheet P passes between the heating roller 102 and the pressure roller 103 (that is, when the sheet P and the heating roller are in contact), and the sheet When P is not passing (that is, when the paper P and the heating roller are not in contact with each other: between the papers), the amount of heat taken from the heating roller 102 is different. That is, when the paper P is passing, the temperature of the heating roller 102 is lowered because the heat is taken away by the paper P, but when the paper P is not passing, the heat is not taken away so much. A difference appears in the temperature distribution within one round.

  FIG. 4 is a diagram showing the relationship between the temperature of the heating roller 102 and the fixing performance to the paper P, and is when the uniform power is supplied to the induction heating coil 110a.

  The upper part of the graph shows the fixing performance to the paper P. The square in the figure shows one paper, and black toner is transferred to the entire surface of the paper P and fixed. In the lower graph, time is plotted on the horizontal axis and the surface temperature of the heating roller 2 is plotted on the vertical axis, so that the temperature of the heating roller 102 changes with time. The squares in the graph indicate the time during which the paper P passes, and the numbers in parentheses indicate the rotation period of the heating roller 102.

  In the lower graph of FIG. 4, the heating roller rotates once while the first sheet Pb passes through the heating roller 102, and the temperature of the heating roller 102 rapidly decreases when entering the second turn. Due to the rapid temperature change of the heating roller, the black color fixed to the paper Pb in the middle of the paper Pb is thin as shown in the graph. Further, in the paper Pa, the temperature of the heating roller 102 increases with respect to the front and back of the paper Pa (G portion), and as a result, a black portion fixed at the central portion of the paper Pa appears. In other words, it can be said that the fixing performance to the paper P is lowered due to the rapid temperature change of the heating roller 102. As described above, since the fixing performance to the paper P changes due to the rapid temperature change of the heating roller 102, there is a possibility that uneven gloss fixation occurs in the image formed on the paper P.

  A method for controlling the temperature of the heating roller 102 for reducing the occurrence of such a rapid temperature change in the heating roller 102 will be described below.

  FIG. 5 is a flowchart of temperature control of the heating roller 102 in the present embodiment.

  FIG. 5 illustrates an example in which the temperature of the heating roller 102 in the portion between sheets described with reference to FIG. 4 is made constant and control is performed so as not to cause a rapid temperature change in the portion G of FIG.

  First, it is determined whether a copy or print job is designated by the user and an image formation start command is issued (S1). When an image formation start command is issued (S1: Yes), the image forming operation is started (S2). When the image forming operation is started, the CPU 203 sets power necessary for image formation and sends a signal to the control circuit 209 (S3). In this way, the heating roller 102 is raised to a predetermined temperature (fixing control temperature) by applying electric power necessary for image formation. In this embodiment, 1000 W is designated at the time of image formation, and a command is sent from the CPU to output 1000 W to the control circuit 209.

  On the control circuit 209 side at the start of image formation, control is performed so that the power becomes 1000 W while the ON time of the switching element 207 is gradually increased. On the control circuit 209 side, the reference set value of the ON time of the switching element 207 for setting the power to 1000 W is stored, but the induction heating coil 110a and the heating are heated depending on the temperature of the heating roller 102, the temperature of the induction heating coil 110a, and the like. Since the magnetic coupling of the roller 102 changes, the ON time of the switching element 207 is gradually changed while performing comparison with the power value detected by the power detector 205 so that the power becomes constant.

  That is, when the value of the reference set value for 1000 W stored in the CPU 203 is directly sent to the control circuit 209, the temperature of the heating roller 102, the induction heating coil 110a, the gap between the heating roller 102 and the induction heating coil 110a, There is a possibility that power of 1000 W or more may be output due to the influence of power fluctuation of the input voltage. Therefore, when the power is changed by the control circuit 209, feedback control is performed while the power detection unit 205 detects the power value after giving a power reference setting value smaller than the target power, and gradually becomes 1000 W. Control to approach to (soft start).

  When approaching 1000 W, feedback control of the power supplied to the induction heating coil 110a is performed based on the difference between the temperature detected by the temperature detector 108 and the set temperature of the heating roller 102, and the heating roller 102 is maintained at the fixing temperature ( S4).

  Next, based on a paper detection signal in which the paper detection sensor 111 detects the trailing edge of the paper P, it is determined whether the portion of the heating roller 102 that is in contact with the trailing edge of the paper faces the position of the induction heating coil 110a ( S5). This determination is based on the detection result of the trailing edge of the sheet P of the sheet detection sensor 111. The first boundary where the sheet contacts the heating roller 102 to the area where the sheet does not contact the heating roller 102 is the induction heating coil 110a. It is determined whether the position of is reached.

  Specifically, when the time t1 from when the paper detection sensor 111 detects the trailing edge of the paper until the portion where the trailing edge contacts the heating roller 102 reaches the induction heating coil 110a is calculated, t1 is calculated as paper detection. It is obtained from the relationship between the distance from the sensor 111 to the nip between the heating roller 102 and the pressure roller 103, the total distance from the nip to the position of the induction heating coil 110a, and the sheet conveyance speed. Accordingly, the time t1 is stored in advance, and it is determined that the first boundary has reached the position facing the induction heating coil 110a t1 time after the paper detection sensor 111 detects the trailing edge of the paper P. ing.

  If it is determined in S5 that the first boundary has reached the position of the induction heating coil 110a (S5: YES), the induction heating means 110 is heated only in the circumferential region of the heating roller 102 through which the inter-sheet portion passes. Control to weaken. That is, control is performed to reduce the power supply to the area of the heating roller 102 corresponding to the inter-sheet portion.

Specifically, the CPU 203 stores the power output setting value (the ON time of the switching element 207) output immediately before the power reduction control (S6). This output set value is a value set by detecting the temperature of the heating roller 102 and performing feedback control to change the power value based on the detected temperature from the reference set value of power stored in the CPU 203. The power value at this time is the first power value.

  After storing the output set value immediately before changing the power, the power is lowered (S7). This power value is the second power value. In this embodiment, the power is set to 300 W.

  When the power between the sheets is lowered, the power is instantaneously changed by directly giving the drive circuit 208 an output set value for setting the power to 300 W. This is because the time between sheets is very short, so it is necessary to change the electric power rapidly, and it is not in time for soft start.

  In this case, as described above, 300 W is not output accurately due to the temperature of the heating roller 102 and the induction heating coil 110a, the power fluctuation of the input voltage, etc., and an output error may occur, but the power is rapidly changed. This is more effective for changing the surface temperature of the heating roller 102. Therefore, even if 300 W is not output strictly, it does not matter much.

  For this reason, the output set value is directly given to the drive circuit 208.

  Further, the power transition time to 300 W can be a half wavelength time of commercial AC power supply 204 (10 ms at 50 Hz). This is because the power detection unit 205 detects power at a minimum of ½ of the cycle of the commercial AC power supply 204. Therefore, in order to change the power value while detecting the power, 1 / of the cycle of the commercial AC power supply 204 is used. This is because 2 is the minimum power transition time.

  After that, when the power is detected by the power detection unit 205 and maintained at 300 W, the ON time of the switching element 207 is adjusted to perform control to maintain 300 W. Only when the power is changed from 1000 W to 300 W for the first time, an ON time based on the reference set value is given, and then, based on the difference between the temperature detected by the temperature detection unit 108 and the set temperature of the heating roller 102 when the power approaches 300 W. The power value supplied to the induction heating coil 110a is feedback-controlled to maintain the heating roller 102 at the fixing temperature (S8).

  As described above, the region of the heating roller 102 through which the inter-sheet portion passes is heated at 300 W. By reducing the power value supplied to the induction heating coil 110a in this way, it is possible to prevent the surface temperature of the portion between the sheets of the heating roller 102 from rising from the portion where the paper P is in contact.

  Next, based on whether or not the paper detection sensor 111 detects the leading edge of the next paper P, it is determined whether or not there is the next paper P (S9). If the leading edge of the paper P is not detected (S9: NO), the supply of power to the induction heating coil 110a is stopped (S10) and the image formation is completed (S11).

  On the other hand, when the paper detection sensor 111 detects the leading edge of the next paper P (S9: YES), the CPU 203 starts from the part where the paper P does not contact the heating roller 102 based on the paper detection signal from the paper detection sensor 111. It is determined whether the second boundary where the sheet P contacts the heating roller 102 has reached the position of the induction heating coil 110a (S12).

  If it is determined that the second boundary has reached the position of the induction heating coil 110a (S12: YES), the control circuit 209 is instructed to change to a power value (second power value) necessary for image formation. In the present embodiment, control to return to the power value stored in S6 is performed (S13). That is, the ON time of the switching element 207 of the inverter circuit 201 gives the output set value a (ON time of the switching element 207) stored in S6.

  In normal power control, soft start is performed to gradually increase power, and feedback control is performed based on the detection result of the power detection unit 205. However, if the soft start is performed, the electric power cannot be rapidly returned. Therefore, it takes time to restore the surface temperature of the heating roller 102 to the original state. For this reason, the output value is given directly rather than the soft start. At this time, if the output value is a predetermined reference value, there is a possibility that the target power value may be exceeded due to the influence of the temperature of the heating roller 102 and the induction heating coil 110a, the fluctuation of the input voltage, and the like. May flow.

  Therefore, in the present embodiment, the output set value a stored in S6 is given before the CPU 203 reduces the power. This is because the time during which the power is reduced to 300 W is very short, and the temperature conditions of the heating roller 102 and the induction heating coil 101a, the input voltage fluctuation, and the like are considered to be almost the same as before the power is reduced. .

  After changing to the second power value required at the time of image formation, the process returns to S4, and the power output to the induction heating coil 110a based on the difference between the temperature detected by the temperature detector 108 and the set temperature of the heating roller 102 Feedback control is performed to maintain the heating roller 102 at the fixing temperature.

  Thereafter, as described above, it is determined whether the first boundary corresponding to the rear end portion of the sheet faces the induction heating coil 110a portion (S5).

  In this way, regardless of whether or not the heated object and the sheet are in contact with each other, the supply to the induction heating coil 110a is performed based on the difference between the temperature detected by the temperature detection unit 108 and the set temperature of the heating roller 102. Power feedback control is performed. By repeating the above control, it is possible to prevent the temperature of the heating roller 102 from rising between sheets, and the surface temperature of the heating roller 102 can be made uniform. Further, since the surface temperature of the heating roller 102 is always detected and feedback control is performed, the control temperature is not exceeded.

  In addition, the temperature distribution of the heating roller 102 can be instantaneously changed by changing the power rapidly. In addition, the power value immediately before the power change (output set value) is stored, and by returning to the power value, when the power is returned, the power greatly exceeds and the overcurrent flows. It became possible to prevent.

  When the above control is repeatedly performed, the value immediately before changing the power setting value between sheets to 300 W may be stored, and that value may be used as the power setting value between sheets in the next cycle.

  FIG. 6 shows the relationship between the boundary value and the supplied power value with respect to the part where the sheet contacts.

  In this embodiment, the trailing edge of the paper P conveyed to the fixing device 101 and the leading edge of the paper P are detected to grasp the space between the papers. First, the size of the paper P is detected, Only the leading edge of the paper P may be detected, and the space between the papers may be determined from the size of the paper P.

  Further, the decrease in the temperature of the heated object due to the passage of the paper P varies depending on the basis weight of the paper P and the number of sheets to be passed. Therefore, in consideration of the basis weight of the sheet P and the number of sheets to be passed, control for changing the value of the power supplied at the time of sheet interval may be performed. That is, as the basis weight of the paper P increases, the temperature drop of the heated object also increases. Therefore, the basis weight is detected, and the width of the power value changed between the sheets is changed according to the basis weight. In addition, as the number of sheets passed increases, the temperature difference between the sheet passing portion and the portion between the sheets tends to decrease. Accordingly, the amount of power to be changed between the sheet passing portion and the portion between the sheets can be changed accordingly. It is valid.

In the above-described embodiment, the description has been given of the fixing device in which the heating roller 102 and the pressure roller 103 are combined. However, the fixing device having the configuration shown in FIG.
The fixing device shown in FIG. 7 includes a heating belt 205 suspended between the fixing roller 202 and the tension roller 204.

  The pressure roller 203 is driven in the direction of the arrow in the figure by a drive motor (not shown). The fixing roller 202, the tension roller 204, and the heating belt 205 rotate by being driven. The pressure roller 203 is pressed against the fixing roller 202 by the pressure mechanism 210 and is maintained so as to have a constant nip width. The heating belt 205 is stretched with a constant tension between the fixing roller 202 and the tension roller 204.

The configuration of the fixing roller 202 is composed of a core metal 202a and foamed rubber 202b from the inside. In this embodiment, the thickness of the metal core is 2 mm, and the thickness of the foam rubber is 5 mm.
The heating belt 205 is configured from the inside in the order of a metal conductive layer 205a, a solid rubber layer 205b, and a release layer 205c. In this embodiment, nickel is used as the material of the metal conductive layer. In addition to this, the material of the metal conductive layer may be stainless steel, aluminum, a composite material of stainless steel and aluminum, or the like.

  The sheet P passes through the pressure contact portion (nip) between the fixing roller 202, the heating belt 205, and the pressure roller 203, so that the toner image on the sheet is fused and pressure-fixed.

  Even in the fixing device having such a configuration, it is possible to perform temperature control similar to that of the above-described embodiment to make the temperature of the heating belt uniform.

According to the above-described embodiment, it is possible to prevent a difference in surface temperature between a portion where the paper P is in contact with the object to be heated (the heating roller 102 and the heating belt 205) and a portion where the sheet P is not in contact, and uneven glossiness on the image. Further, the temperature of the heated body can be kept at the fixing control temperature by constantly detecting the surface temperature of the heated body by the temperature detection sensor 108 and performing feedback control of the electric power value applied to the induction heating coil 110a. It is also possible to prevent heat generation beyond the temperature.
(Second Embodiment)

  Since the structures of the image forming apparatus 1 and the fixing apparatus 101 and the configuration of the inverter circuit 201 are the same as those in the first embodiment, description thereof is omitted.

  According to this embodiment, when the paper P longer than the circumference of the heating roller 102 is passed, the power value supplied to the first circumference of the heating roller 102 and the trailing edge of the paper P from the second circumference of the heating roller 102 Thus, it is possible to perform power control for changing the power value supplied before and the power value supplied between sheets.

  FIG. 8 is a flowchart of power control in this embodiment. This flowchart will be described.

  First, it is determined whether a copy or print job is designated by the user and an image formation start command is issued (S101). When an image start command is issued (S101: Yes), it is determined whether or not the size of the paper P exceeds the circumference of the heating roller 102 (S102). If the size of the paper P does not exceed the peripheral length of the heating roller 102 (S102: NO), the operations after S2 in the flowchart of FIG. 5 in the first embodiment are performed.

  If the size of the paper P exceeds the circumference of the heating roller 102 (S102: YES), the process proceeds to S103, and the image forming operation is started (S103).

  When the image forming operation is started, the CPU 203 sets power necessary for image formation and sends a signal to the control circuit 209 (S104). In the present embodiment, the power required at the start of image formation is 800 W, and a command is sent from the CPU 203 to the control circuit 209 to output 800 W. When the power is output to 800 W, soft start is performed, and then feedback control is performed so that the temperature is kept constant from the detection result of the temperature detection sensor 108 as in the first embodiment. (S105).

  The time t2 from when the leading edge of the paper P is detected by the paper detection sensor 111 until the portion of the heating roller 102 where the leading edge of the paper P has contacted reaches the induction heating coil 110a, the portion of contact with the paper P is the heating roller 102. Similar to the first embodiment, the time t3 required to go around and the time t2 from when the trailing edge of the paper P is detected until the portion of the heating roller 102 that contacts the leading edge of the paper P reaches the induction heating coil 110a. It is obtained from the relationship between the distance from the sheet detection sensor 111 to the nip between the heating roller 102 and the pressure roller 103, the distance from the nip to the position of the induction heating coil 110a, and the sheet conveyance speed. Therefore, the times t2 and t3 are stored in advance, and the power may be controlled after t2 hours and t3 hours after the paper detection sensor 111 detects the leading edge or the trailing edge of the paper.

  That is, based on the output of the paper detection sensor 111, it is determined whether or not the part of the heating roller 102 with which the leading edge of the paper P is in contact with the position of the induction heating coil 110a (fifth boundary) (S106).

  When it is determined that the tip contact portion of the sheet P is opposed to the induction heating coil 110a (S106: YES), it is determined whether or not the current sheet is the first sheet (S107). If it is the first sheet (S107: YES), the power value of 800 W at the start of the image forming operation is maintained (S108).

  If it is determined in S107 that the sheet is not the first sheet (S107: NO), the CPU 203 stores the output setting value of the power currently supplied (S109). This output set value is a value set by detecting the temperature of the heating roller 102 in S105 and performing feedback control to change the power value based on the detected temperature from the reference set value of power stored in the CPU 203. is there.

  After storing the current power output set value in S109, the power value supplied at the end of the first round of the previous paper (the third power value stored in S113) is changed (S110). After changing to the third power value, feedback control is always performed so that the temperature is kept constant according to the detection result of the temperature detection sensor 108 (S111).

  Next, based on the paper detection signal, whether or not t4 time required for the contact portion with the paper P to make one round of the heating roller 102 has passed, that is, whether or not the second turn (third boundary) has been reached. Is determined (S112). When the second round is reached (S112: YES), first, the output set value (ON time of the switching element 207) of the output power is stored (S113). The power value at this time is the third power value.

  Then, it is determined whether or not the sheet P is the first sheet (S114), and if it is the first sheet, the power supplied to the induction heating coil 110a in the second circumference where the sheet P contacts the heating roller 102 by default. Is output (S115). The power value at this time is the fourth power value.

  In the present embodiment, the maximum output of 1000 W at the time of image formation is set at the second round portion where the paper P contacts the heating roller 102. If it is not the first sheet in S114 (S114: NO), it is changed to the power value supplied at the end of the second round of the previous sheet (the fourth power value stored in S122) (S116). After changing to the fourth power value, feedback control is always performed so that the temperature is kept constant according to the detection result of the temperature detection sensor 108 (S117).

  Thereafter, based on the detection of the trailing edge of the paper P by the paper detection sensor 111, it is determined whether or not the portion of the heating roller that has contacted the trailing edge of the paper is opposed to the induction heating coil (fourth boundary) ( S118). When the trailing edge of the paper P is opposed (S118: YES), it is determined whether or not there is a next paper (S119). When there is no next paper, the power supply to the heating coil 110a is stopped (S120). Image formation ends (S121).

  On the other hand, when there is a next sheet in S119 (S119: YES), the output setting value (ON time of the switching element 207) of the output power is first stored (S122). The power value at this time is the fourth power value. After storing the fourth power value, it is determined whether or not the sheet P is the first sheet (S123).

  If the sheet P is the first sheet (S123: YES), it is changed to the fifth power (300 W in this embodiment) that is the power value of the portion between the sheets (S124). When the sheet P is not the first sheet (S123: NO), it is changed to the power value stored at the fifth boundary of the current sheet (the fifth power value stored at S109) (S125).

  In S123 or S125, after the electric power supplied to the induction heating coil 110a is changed, the process returns to S105, and feedback control is always performed so that the temperature is kept constant according to the detection result of the temperature detection sensor 108.

  Thereafter, in S106, it is determined whether or not the leading end portion of the second sheet has reached the induction heating coil 110a. Thereafter, the same operation as described above is repeated, but since it is the second sheet in S107 (S107: NO), it is changed to “the power value stored in S113” in S110. In S114, since it is the second sheet (S114: NO), it is changed to “the power value stored in S122” in S116.

  FIG. 9 shows the relationship between the boundary value and the supplied power value for the part where the sheet contacts.

  In the above flowchart, the output set value before changing the power value is stored, and the control to return to the value later is performed to return to the stored power value as in the first embodiment. Therefore, when the power is returned, the power is greatly exceeded, and a problem that an overcurrent flows is prevented.

By repeating the control as described above, the electric power applied to the induction heating coil 110a can be changed between the first and second rounds where the paper P contacts the heating roller, in addition to the gap between the sheets.
By performing such control, the temperature distribution of the heating roller 102 can be made uniform even when the paper P is longer than the circumference of the heating roller 102 and the power required for image formation is the maximum output power.

  Similarly to the first embodiment, the temperature detection sensor 108 constantly detects the surface temperature of the heating roller 102 and performs feedback control of the power value applied to the induction heating coil 110a to fix the temperature of the heating roller 102. The control temperature can be maintained, and heat generation exceeding the control temperature can be prevented.

  Note that, similarly to the first embodiment, control may be performed to change the value of the power supplied during the interval between sheets in consideration of the basis weight of the sheet P and the number of sheets to be passed. In addition, the leading edge and the trailing edge of the paper are detected and the portion where each edge contacts the heating roller 102 is calculated. However, only the leading edge is detected, and the trailing edge contacts the heating roller 102 from the size of the sheet It is also possible to calculate the site.

  Further, in the above-described embodiment, the fixing device 101 in which the heating roller 102 and the pressure roller 103 are combined has been described. However, similarly to the first embodiment, the heating belt 205 illustrated in FIG. 7 is provided. A fixing device has the same effect.

1. Image forming apparatus 101. Fixing device 102. Heating roller 103. Pressure roller 108. Temperature detection sensor 110. Induction heating section 110a. Induction heating coil 111. Paper detection sensor 201. Inverter circuit 202. Rectifier circuit 203. CPU
204. Commercial AC power source 205. Electric power detection unit 206. Capacitor 207. Switching element 208. Drive circuit 209. Control circuit P Paper

Japanese Patent Laid-Open No. 10-333489

Claims (7)

An object to be heated having a metal conductive layer;
A pressure body that heats and pressurizes the paper by passing the paper between the heated body and the paper; and
A paper detection unit for detecting paper conveyed between the heated body and the pressure body;
An induction heating coil that is disposed adjacent to the object to be heated and generates an induction current in the metal conductive layer;
When the dimension in the conveyance direction of the paper is longer than the circumference of the heated body, based on the detection result of the paper detection unit, the portion that contacts the heated body for the first time in the one sheet of paper A third boundary that is a boundary with a portion that contacts the second time, a fourth boundary that switches from a portion that contacts the heated body to a portion that does not contact the heated body, and the paper that does not contact the heated body After detecting a fifth boundary that switches from a part to a part to be contacted and storing the third power value supplied to the induction heating coil when the third boundary faces the induction heating coil, The electric power value supplied to the induction heating coil is changed from the third electric power value to the fourth electric power value, and the fourth boundary is supplied to the induction heating coil when the fourth boundary faces the induction heating coil. After storing the power value of 4 The power value supplied to the induction heating coil is changed from the fourth power value to the fifth power value, and the power value supplied to the induction heating coil when the fifth boundary faces the induction heating coil The power value to be supplied to the induction heating coil when the third boundary is opposed to the induction heating coil is changed from the fifth power value to the stored third power value. A control unit for changing to the stored fourth power value ;
A fixing device. A high-frequency current supply unit for supplying a high-frequency current to the induction heating coil;
A power detection unit that detects the amount of power supplied from the AC power supply unit that supplies power to the high-frequency current supply unit;
The control unit performs feedback control by comparing the detection value of the power detection unit and the set power with respect to the power value supplied to the induction heating coil at the fourth boundary, and half the frequency of the AC power supply unit. the fixing device of claim 1, wherein changing the power value at a wavelength of time. Wherein the control unit, a fixing device according to the fourth power value to claim 1 or claim 2, characterized in that varied depending on the basis weight of the paper. Wherein the control unit, a fixing device according to any one of claims 1 to 3, characterized in that changing the fourth power value in accordance with the sheet passing number of the sheets. A heated body having a metal conductive layer; a pressure body that heats and pressurizes the paper by passing the paper between the heated body; and a proximity to the heated body, A fixing device having an induction heating coil for generating an induction current in a metal conductive layer,
Detecting the paper conveyed between the heated body and the pressure body,
When the dimension in the conveyance direction of the paper is longer than the circumference of the heated body, based on the detection result of the paper, the portion that contacts the heated body for the first time in the one sheet and the second time A third boundary that is a boundary with a contacted part, a fourth boundary that switches from a part that contacts the heated body to a part that does not contact the heated body, and a part that does not contact the heated body with the paper Detect the fifth boundary to switch to
After storing the third power value supplied to the induction heating coil when the third boundary faces the induction heating coil, change from the third power value to the fourth power value, After storing the fourth power value supplied to the induction heating coil when the fourth boundary faces the induction heating coil, the fourth power value is changed to the fifth power value, and When the fifth boundary faces the induction heating coil, the fifth power value is changed to the stored third power value, and when the third boundary faces the induction heating coil, the third power value is changed. fixing equipment, characterized in that the change to the fourth power value said storage from the power value. The surface temperature of the object to be heated is detected, and feedback control is performed on the power value according to a difference between a detection result of the surface temperature of the object to be heated and a set temperature of the object to be heated. 5 fusing equipment described. An image forming unit that forms a toner image on a photoconductor and transfers the toner image on the photoconductor to a sheet;
The fixing device according to claim 1, further comprising a fixing device that is provided on a downstream side of the image forming unit in a conveyance direction of the sheet and fixes the toner image on the sheet. Image forming apparatus.