JP4708878B2 - Image heating device - Google Patents

Description

  The present invention is an image heating suitable for use as a fixing device for heating and fixing an unfixed toner image formed and supported on a recording material, for example, in an image forming apparatus such as a copying machine or a printer that forms an image by electrophotography. It relates to the device.

  Recently, due to the trend of energy saving in OA equipment, as a fixing device, in order to achieve both energy saving and quick start performance, the fixing roller is a roller made of an induction heating element (conductive magnetic material) and magnetic flux generating means (induction heating coil) There has been proposed an induction heating type fixing device that heats the fixing roller by the generated magnetic flux and heats the fixing roller to a predetermined fixable temperature.

  In an induction heating type fixing device, conventionally, for example, iron or nickel is used as an induction heating element. A material (magnetic shunt alloy) with a controlled Curie temperature has also been proposed. There is a fixing roller material (induction heating element) in which a magnetic shunt alloy is used and a Curie point is provided at a temperature higher than the fixing temperature and lower than a hot offset (Patent Document 1).

In particular, when the magnetic shunt alloy is heated and exceeds the Curie point, the magnetism is lost. Therefore, the magnetic field in the magnetic shunt alloy is reduced, eddy current is reduced, and heat generation is suppressed. If a magnetic shunt alloy having a Curie temperature necessary for fixing is used as the material of the fixing roller, self-temperature control can be performed near the fixing temperature at which the roller temperature becomes the Curie point. Further, even for the non-sheet passing portion temperature rise caused by continuous small size sheet passing, there is an effect that the amount of heat generation is partially reduced when the Curie point is exceeded outside the sheet passing region.
Japanese Unexamined Patent Publication No. 2000-39797 (FIG. 1)

In this way, the magnetic shunt alloy has advantages, but as shown in FIG. 10, even when a constant current is passed through the induction heating coil at a temperature below the Curie point, the electric resistance starts to decrease and the amount of heat starts to decrease ( FIG. 8), there is a problem that when the temperature of the fixing roller is raised from room temperature, it is impossible to continuously input desired power. This is because when the temperature of the fixing roller as a heating element rises to near the Curie point, the resistance value of the fixing roller that contributes to heat generation decreases due to loss of magnetic properties, and the resistance value decreases before reaching the fixing temperature. This is because the heat generation efficiency starts to decrease and the heat generation efficiency decreases. The Curie point of iron and nickel used in the past was in a very high temperature range, so there was no problem. However, with a magnetic shunt alloy, the temperature rise slope becomes small (the state where the coil is attached to the fixing roller in FIG. 8). (The temperature at which the temperature characteristic of the resistance value of the coil reaches a maximum, which is also referred to as the power drop point hereinafter), and so on. If the Curie point is set near the fixing temperature, the warm-up time becomes longer and the quick start failure It becomes.

In addition, when a fixing roller with a Curie point set near the fixing temperature is used, it rotates at a constant rotational speed while contacting the fixing roller and the pressure roller during the warm-up period in which the fixing roller is heated to a predetermined fixing temperature. When the fixing roller and the pressure roller are heated while causing them to occur, there are the following problems. That is, after the temperature of the fixing roller exceeds the power lowering point, in addition to the reduction in the heat generation efficiency of the fixing roller as described above, heat is taken away to the pressure roller side (no heat is applied to the pressure roller side). mUST nOT) because, even more of the warm-up time becomes longer.

  Therefore, in the conventional configuration, the warm-up time is shortened by setting the temperature setting of the Curie point higher than the fixing temperature. However, when the Curie point is set to the fixing temperature, this cannot be dealt with. The upper limit is the hot offset temperature at which the toner on the recording material adheres again to the fixing roller. In practice, the Curie point must be as close to the hot offset temperature as possible. It was. In this case, the set temperature is inevitably high, and it is obvious that setting a temperature higher than necessary is not desirable from the viewpoint of energy saving or safety. Further, when the Curie point is set high, the temperature rises to the Curie point set higher in the non-sheet passing area than in the sheet passing area due to the temperature rise phenomenon of the non-sheet passing portion caused by continuous passing of the small size recording material. In this case, the fixing roller temperature difference in the longitudinal direction becomes large, and if a large size recording material is passed immediately after passing a small size recording material, an image defect may occur.

In the present invention, the Curie point is set near the image heating temperature as the material of the rotating heating element, thereby reducing the heating efficiency of the rotating heating element near the fixing temperature (measured with the excitation coil mounted on the rotating heating element). In the case of an induction heating type image heating apparatus in which the temperature characteristic of the resistance value of the exciting coil has a maximum point at a temperature lower than the image heatable temperature), the rotary heating element is set in advance to perform image heating processing. and an object thereof is to shorten the warm-up time of an image heating device for contacting rotating the rotary pressure member and the rotating heating body to the image heatable temperature during the warm-up period for heating as much as possible.

  The present invention is an image heating apparatus having the following configuration.

Magnetic flux generating means having an exciting coil, a rotatable heat generating element that generates heat by the magnetic flux from the magnetic flux generating means and heats an image on a recording material at an image heating temperature that is substantially equal to the Curie point, and the heat generating element It has a rotatable pressure member for pressurizing to form a nip, against the the warm-up period to warm to said image heating temperature the heating element in order to perform an image heating process and the heating element pressing In the image heating apparatus that rotates the pressure body in contact with the pressure body ,
The temperature at which the resistance value of the exciting coil with respect to the temperature when the exciting coil is attached to the apparatus is set to a temperature lower than the image heating temperature, and during the warm-up period, When the temperature exceeds the temperature indicating the maximum point, the image heating apparatus is switched to a rotation speed slower than the rotation speed until the temperature reaching the maximum point is reached .

  In an image heating apparatus using induction heating, when heating is started using a material (magnetic shunt alloy) in which the Curie point is set near the heating material heating temperature as the material of the rotating heating body, the exciting coil is turned into the rotating heating element. The heat generation efficiency of the rotating heating body decreases after the temperature at which the temperature characteristic of the resistance value of the exciting coil measured in the state where it is mounted is maximized, and the warm-up delay due to the decrease in the heating rate of the rotating heating body is reduced. It can be reduced or prevented.

(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this example is a transfer type electrophotographic process-use, laser scanning exposure type apparatus (copying machine, printer, facsimile, combined function machine thereof, etc.).

  Reference numeral 20 denotes an image forming apparatus main body (hereinafter referred to as an apparatus main body). Reference numeral 21 denotes a document reading device (image scanner), and 22 denotes an area designating device (digitizer), both of which are arranged on the upper surface side of the apparatus main body 20. The document reading device 21 scans the document surface placed on the document table of the device by a scanning illumination system, and reads the reflected light from the document surface by an optical sensor such as a CCD line sensor, whereby image information is time-series electric digital. Convert to pixel signal. The area designating device 22 sets a document reading area and outputs a signal. Reference numeral 23 denotes a control unit (CPU). The control unit 23 receives signals from the document reading device 21, the area designating device 22, the print controller 24, etc., and controls signal processing for sending commands to various process devices of the image forming mechanism and predetermined image forming sequence control.

  Reference numeral 25 denotes a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. The photosensitive drum 25 is rotationally driven at a predetermined speed in the clockwise direction of the arrow. The photosensitive drum 25 is subjected to a uniform charging process with a predetermined polarity and potential by the charging device 26 during the rotation process. Then, image exposure L by the image writing device 27 is performed on the uniformly charged surface. As a result, the potential of the exposed bright portion of the uniformly charged surface is attenuated, and an electrostatic latent image corresponding to the exposure pattern is formed on the photosensitive drum surface. In this example, the image writing device 27 is a laser scanner. The image writing device 27 outputs a laser beam L modulated according to the image data signal-processed by the control unit 23, and scans and exposes the uniformly charged surface of the rotating photosensitive drum 25. An electrostatic latent image corresponding to the image information is formed.

  Next, the electrostatic latent image is developed as a toner image by the developing device 28. The toner image is a recording material such as paper or OHP which is a material to be heated, which is fed from the sheet feeding mechanism side to the transfer portion T, which is the opposing portion of the photosensitive drum 25 and the transfer device 29, at a predetermined control timing Electrostatic transfer is sequentially performed on the surface of P (hereinafter referred to as a transfer material). In the case of this example, the paper feed mechanism section separates and feeds one transfer material P from the paper feed cassette 31 at a predetermined control timing. The transfer material P is transported to the transfer portion T at a predetermined timing by the transfer material transport path 32 including the registration rollers 33.

The transfer material P that has passed through the transfer portion T is separated from the surface of the photosensitive drum 25 and conveyed to the fixing device F. The fixing device F is treated thermally fixing the unfixed toner image on the transfer material P as a solid Chakugazo. The transfer material P that has undergone image fixing is discharged as an image formed product (copy, print) onto a discharge tray 34 outside the apparatus main body.

  The photosensitive drum 25 after separation of the transfer material is cleaned by the cleaning device 30 after removal of adhering contaminants such as transfer residual toner, and is repeatedly used for image formation.

(2) Fixing device F
The fixing device F includes a magnetic flux generating means having an exciting coil, an induction heating element (rotary heating element) that is electromagnetically heated and rotated by the action of the magnetic flux generated by the magnetic flux generating means, and a pressure member (rotary pressure element). ), The induction heating element is a magnetic shunt alloy having a Curie point in the vicinity of the fixing temperature. Temperature induction means for detecting temperature, the induction heating element and the pressurizing member are rotating, and the temperature of the induction heating element is determined by the temperature detection means to connect the induction heating element and the excitation coil. It is detected that the temperature characteristic of the impedance applied to both ends of the exciting coil in the state where the coil is incorporated has risen to a maximum temperature (hereinafter referred to as a power drop point), and the induction heating element The temperature detecting means detects that the temperature of the induction heating element has reached the fixing temperature, and makes the rotation of the induction heating element faster than the rotation control delayed at the power lowering point. It is the heating device characterized by performing control to do.

(2-1) Overall Schematic Configuration of Fixing Device F FIG. 2 is an enlarged cross-sectional model view of the main part of the fixing device F, and FIG. 3 is a front model diagram of the main part. The fixing device F is a heating roller type and is an electromagnetic induction heating type heating device.

  Reference numeral 1 denotes a fixing roller (heat roller) as a heating rotator. The fixing roller 1 is a cylindrical roller made of an induction heating element (conductive magnetic material). A release layer such as a fluororesin is formed on the outer peripheral surface.

  Reference numeral 2 denotes a pressure roller as a pressure rotator. The pressure roller 2 is an elastic roller that includes a shaft core 2a and an elastic body layer 2b such as a silicon rubber layer that is concentrically integrated with the shaft core.

  The fixing roller 1 and the pressure roller 2 are arranged in parallel in the vertical direction so as to be rotatably held via bearings 42 between the front side plate 41 and the rear side plate 41 of the fixing device frame. Is pressed against the lower surface of the fixing roller 1 by a predetermined pressing force against the elasticity of the elastic body layer 2b by a biasing means (not shown) to form a fixing nip portion N having a predetermined width in the roller rotation direction. Yes. A configuration in which the fixing roller 1 is brought into pressure contact with the pressure roller 2 can also be adopted.

  A drive gear G is fixed to one end of the fixing roller 1. When the rotational force is transmitted to the drive gear G from the drive source M through the transmission system, the fixing roller 1 is rotationally driven in the clockwise direction indicated by the arrow a in FIG. The pressure roller 2 is rotated counterclockwise as indicated by an arrow following the rotational driving of the fixing roller 1.

  Reference numeral 3 denotes a coil assembly as magnetic flux (magnetic field) generating means, which is inserted into the hollow portion of the fixing roller 1 and disposed.

  The coil assembly 3 is an assembly of a bobbin 4, a magnetic core 5, an exciting coil (induction heating coil) 6, a stay 7 made of an insulating material, and the like. The magnetic core 5 is inserted into a through hole formed in the bobbin 4. The exciting coil 6 is formed by winding a copper wire around the bobbin 4. The unit of the bobbin 4, the core 5, and the exciting coil 6 is fixedly supported on the stay 7. The coil assembly 3 is inserted into the hollow portion of the fixing roller 1, and both ends of the stay 7 are immovably supported by the fixing members 43 on the fixing device frame side. It is arranged in a predetermined position and posture in a contact state.

  The magnetic core 5 is preferably made of a material having a high magnetic permeability and a small self loss. For example, ferrite, permalloy, sendust and the like are suitable. The bobbin 4 also functions as an insulating part that insulates the magnetic core 5 from the exciting coil 6.

  The exciting coil 6 must generate an alternating magnetic flux sufficient for heating. For this purpose, it is necessary to have a low resistance component and a high inductance component. As the core wire of the exciting coil 6, a litz wire in which about 80 to 160 fine wires with a diameter of 0.1 to 0.3 are bundled is used. Insulated coated wires are used for the thin wires. In addition, an exciting coil is formed by winding a plurality of times in a horizontal long boat shape in accordance with the shape of the bobbin 4 so as to go around the magnetic core 5. The exciting coil 6 is wound in the longitudinal direction of the fixing roller 1. Reference numerals 6 a and 6 b denote two outward lead wires of the excitation coil 6, which are connected to a drive power source (excitation circuit) 35.

  Reference numeral 8 denotes a temperature sensor (temperature detection means) such as a thermistor for detecting the temperature of the fixing roller 1 and is disposed in contact with the fixing roller 1 or close to non-contact. Reference numeral 9 denotes a safety element such as a thermostat disposed in contact with the fixing roller 1 or close to non-contact. Reference numeral 10 denotes a separation claw that serves to prevent the transfer material P from the fixing nip N from being wound around the fixing roller 1 and to separate it from the fixing roller 1.

  The bobbin 4, stay 7, and separation claw 10 are made of heat-resistant and electrically insulating engineering plastic such as liquid crystal polymer, polyimide, polyphenylene sulfide, and the like.

Although the main power switch of the image forming apparatus main body is turned on, the fixing device F stops the rotational driving of the fixing roller 1 in the standby state in which the image forming apparatus main body is waiting for the input of the image forming start signal. In addition, energization to the exciting coil 6 is also stopped. When the image formation start signal is input, the control unit 23 executes a predetermined pre-rotation operation of the apparatus main body. For the fixing device F, at a predetermined control timing, the rotation of the fixing roller 1 is started and power supply from the drive power source 35 to the exciting coil 6 is started. The pressure roller 2 rotates following the rotational driving of the fixing roller 1. Then, the fixing roller 1 is heated by an electromagnetic induction action by a high-frequency magnetic field generated in the exciting coil 6, and the temperature is raised to a predetermined fixable temperature. The temperature of the fixing roller 1 is detected by the temperature sensor 20, and the detected temperature information is input to the control unit 23. The control unit 23 controls the driving power source 35 based on the input temperature information, and controls the temperature of the fixing roller 1 to a predetermined fixable temperature. Then, a transfer material P carrying an unfixed toner image t is introduced from the image forming mechanism side to the fixing nip portion N of the fixing roller 1 and the pressure roller 2 controlled in temperature, and the fixing nip portion N is nipped and conveyed. It will be done. In the process of the transfer material P is gradually being nipped and conveyed to fixing nip portion N, the unfixed toner image t is fixed as a solid Chakugazo the surface of the transfer material P and the heat of the fixing roller 1, by the pressure of the fixation nip N .

  The safety element 10 such as a thermostat urgently cuts off the power supply circuit from the drive power source 35 to the exciting coil 6 when the fixing device is thermally runaway.

(2-2) Control during process of raising temperature of fixing roller 1 The material of the induction heating element constituting the fixing roller 1 is made of Ni-Fe, Ni-Fe-Co, Ni-Fe-Cr, or the like. It is a magnetic shunt alloy and is set to have a Curie point near the fixing temperature. That is, the induction heating element constituting the fixing roller 1 generates heat due to the magnetic flux from the magnetic flux generating means, and the temperature dependency of the resistance of the exciting coil in a state where the exciting coil is mounted on the apparatus has a predetermined image heating temperature. It has a maximum point at a lower temperature.

  4, 5, and 7, the fixing roller temperature and the excitation coil supply during the warm-up period (during the heating process) in which the fixing roller 1 is heated to start image heating for heating the image to a predetermined image heatable temperature. A relationship between power and fixing roller rotation speed (rotation speed) and a schematic sequence of control operations will be described.

  FIG. 4 shows the temperature when the rotation speed of the fixing roller during the warm-up period is rotated at a constant speed as a conventional example, and when the rotation speed of the fixing roller is increased halfway and the rotation speed is decreased halfway as the present embodiment. Comparison of rising profiles.

At the time point T1 from the standby state in which the recording material is not heated, when the application of power to the exciting coil 6 is started while rotating the fixing roller 1, the temperature of the fixing roller 1 starts to rise. However, when a magnetic shunt alloy is used as the induction heating element constituting the fixing roller 1, when the Curie point is set near the fixing temperature, the magnetism of the fixing roller 1 starts to disappear near the power lowering point at time T2, so that the fixing is performed. The impedance of the roller 1 also changes accordingly, making it difficult to apply power. The power lowering point, depending on the formulation materials, at set approximately 50-60 ° C. under a temperature above the temperature range of relative Curie point (predetermined image heatable temperature (temperature lower than the fixing temperature) where The temperature range is such that the rate of temperature increase decreases.

In this embodiment, the Curie temperature (the temperature at which the magnetic permeability becomes 1) is set to be higher than the fixing temperature and lower than the heat resistance temperature of the apparatus. That is, the Curie temperature of the fixing roller 1 is equal to or higher than the image heatable temperature and lower than the heat resistance temperature of the apparatus. Therefore, due to this action, it takes a long time to reach the desired temperature at a constant rotational speed from the beginning of heating (time T1 → T4: rise time due to the broken temperature gradient).

  Further, since the temperature of the pressure roller 2 greatly affects the fixing process, a certain amount of heating (necessary minimum pressure roller temperature) is necessary.

Therefore, in this embodiment, the warm-up period, the fixing roller 1 and the pressure roller 2 by contact with rotating, allowed to warm to the pressure roller, further provided two steps the rotational speed of the fixing roller 1 ( Provide multiple rotation speeds).

That is, the control unit 23 controls the rotation at a predetermined first speed as shown by the solid line during the heating period from the start of heating to the power drop point (or the heating period when the temperature of the fixing roller 1 is relatively low). When it is detected from the signal detected by the temperature sensor 20 that the temperature of the fixing roller 1 has risen to the power drop point (time point T2), the rotation speed of the fixing roller 4 is lower than the first speed. Control is performed as follows. That is, the rotation speed of the fixing roller 1 during the warm-up period is controlled to rotate faster on the low temperature side and slower on the high temperature side.

Thus, if the temperature is lower than the power lowering point, the heat generation efficiency of the fixing roller is high and the maximum power can be continuously input. Therefore, the rotation speed until the power lowering point is reached is increased (T1 → T5) Or the rotational speed is increased compared to when the fixing roller is hot. As a result, heat conduction to the pressure roller increases and the pressure roller temperature rises faster. On the other hand, by increasing the rotation speed, the temperature rise of the fixing roller is slowed contrary to the pressure roller, and as a result, the time until the temperature of the fixing roller reaches the power lowering point becomes longer and the time for turning on the maximum power is increased. Can be long. The temperature is increased (the amount of heat supplied) to the pressure roller when the temperature of the fixing roller 1 is low and the heat generation efficiency is high. When the heat generation efficiency is low, the pressure roller side is a temperature necessary for fixing. Therefore, the rotation speed is decreased and the fixing roller is heated preferentially. That is, when the temperature of the fixing roller 1 reaches a predetermined temperature, the rotation speed of the fixing roller 1 is decreased. The predetermined temperature is equal to or lower than the temperature at which the temperature characteristic is maximized. By doing so, it is possible to supply more electric power than in the case of constant rotation and to improve the efficiency when viewed in total including the pressure roller and the fixing roller.

  Therefore, the temperature is increased to the power lowering point and the rotation is performed at a predetermined first speed before the power becomes difficult to enter, and the temperature of the pressure roller 2 as well as the fixing roller 1 is increased. Then, by rotating the fixing roller 1 at a slow speed (second rotational speed) from the time T2, conversely, the temperature rise of the fixing roller is accelerated, and only the minimum necessary amount of heat is applied to the pressure roller side. To do. After controlling the temperature gradient in this way, at the time T3 when the control unit 23 detects that the temperature of the fixing roller 1 can be fixed by the temperature sensor 20, the rotation of the fixing roller 1 is desired according to the fixing process. Change to a faster rotation.

  Then, when the fixing temperature is detected, the rotation is accelerated so that the sheet can be started without delay (T3).

  In this embodiment, the fixing roller (heating rotator) and the pressure roller (pressure rotator) are described as an example. However, for example, the configuration of the fixing roller or the fixing belt and the pressure belt is the same. In a configuration in which the heating side is in contact with the peripheral member, a temperature gradient correction effect due to power reduction can be obtained.

  In FIG. 4, as an example, the fixing roller rotation speed at the start of heating of the fixing roller 1 and the fixing roller rotation speed at the time of paper feeding are shown to be equivalent, but as shown in FIG. If the fixing roller rotation speed at the start of fixing roller heating is made slower than the fixing roller rotation speed at the time of paper, the heating start-up time of the fixing roller 1 becomes faster. On the contrary, as shown in (b), if the fixing roller rotation speed at the start of heating is made faster than the fixing roller rotation speed at the time of paper passing, the peripheral members will be sufficiently warmed, thereby preventing the temperature drop due to continuous paper passing. Is obtained. Here, the first rotation speed is preferably not more than twice the rotation speed of the heating roller when heating the maximum size (normal size) recording material from the viewpoint of noise and durability. The lower limit of the first rotation speed is that the heating roller is rotated at a constant speed so that the pressure roller temperature becomes the required minimum pressure roller temperature when the fixing roller reaches a predetermined image heating temperature. Rotation speed faster than the rotation speed in the case is necessary. The lower limit of the second rotational speed is preferably a rotational speed that is about 1/8 of the rotational speed of the heating roller when heating the maximum size recording material from the viewpoint of temperature unevenness. More preferably, the rotational speed is about 1/2 to 1/4 compared with the rotational speed at the time of feeding the maximum size recording material. Further, intermittent rotation control may be used. Further, the upper limit value of the second rotation speed may be slower than the first rotation speed.

(2-3) Power Reduction Mechanism and Measurement Method Here, the power reduction mechanism and measurement method of the fixing roller 1 will be described. In general, the resistance value of the fixing roller 1 that is an induction heating element is determined by the magnetic permeability μ and the resistivity ρ when the frequency is constant, as shown in Equation 1, and the resistivity generally increases gradually as the temperature rises. To do.

  FIG. 8 is a diagram showing a temperature dependence curve of the resistance value of the exciting coil (hereinafter also referred to as the apparent resistance value of the fixing roller 1 viewed from the coil) in a state where the exciting coil is mounted on the fixing roller 1 of the present embodiment. . In this embodiment, a magnetic shunt alloy whose Curie temperature is adjusted to a predetermined temperature is used as the material of the fixing roller 1, so that the Curie temperature is lower than the fixing temperature and the heat resistance temperature of the apparatus. Therefore, when the temperature of the heating roller reaches near the Curie temperature, the magnetic permeability rapidly decreases, and the resistance value of the fixing roller 1 viewed from the coil decreases in a temperature range lower than the heat resistance temperature of the apparatus as shown in FIG. Decreases. That is, the temperature at which the rate of temperature increase is a temperature at which the resistance value of the fixing roller 1 is maximized.

  Here, the point where the resistance value of the exciting coil takes a maximum value with the exciting coil attached to the fixing roller 1 is set as a power lowering point. Since the heat generation efficiency is good at a temperature lower than this temperature, the temperature of the pressure roller 2 is warmed. Therefore, the rotation speed of the fixing roller 1 is decreased in order to shorten the warm-up time above the power lowering point.

  Further, unlike the conventional heating roller whose resistance value increases with temperature, the heat generation efficiency (heat generation amount) is reduced as the temperature rises, so that the temperature rise of the non-sheet passing portion can be reduced. Further, as the magnetic permeability decreases, the amount of eddy current also decreases, so the amount of heat generation decreases rapidly.

  In addition, the Curie temperature is set in a temperature range above a predetermined fixing temperature and lower than the heat resistance temperature of the apparatus. By doing so, the amount of heat generated when the fixing roller 1 reaches the fixing temperature or more can be reduced, and the temperature rise of the non-sheet passing portion can be reduced.

(2-4) Apparent resistance value of fixing roller and method of measuring temperature dependency The apparent resistance value (skin resistance) Rs of fixing roller 1 is an exciting coil in a state where magnetic flux generating means 3 is mounted on the fixing roller. 6 corresponds to the difference between the resistance value of the exciting coil 6 when AC is passed and the resistance value measured when the exciting coil is not attached to the fixing roller.

  The apparent resistance value measurement method and the temperature dependence of the resistance value are measured as follows.

  Using an LCR meter (model number HP4194A) manufactured by Agilent, the resistance value of the fixing roller 1 when an alternating current with a frequency of 20 kHz was applied was measured. At this time, the fixing roller 1, the exciting coil 6 serving as magnetic flux generating means, and the magnetic core 5 are measured while mounted on a fixing device (heating device). At this time, the temperature characteristic curve of the resistance value of the fixing roller can be obtained by changing the temperature of the fixing roller and plotting the temperature and the resistance value of the fixing roller simultaneously.

  In order to change the temperature of the fixing roller, the temperature of the fixing roller 1 is changed by keeping the positional relationship in which the fixing roller 1 and the magnetic flux generating means 3 are mounted on the apparatus in a constant temperature chamber, and the fixing roller temperature is kept constant. After saturating to the room temperature, the resistance value is measured by the above measurement method. Strictly speaking, the value obtained by subtracting the resistance of the coil alone from the measured value is the apparent resistance value Rs of the fixing roller, but the resistance of the coil alone can be regarded as almost constant regardless of the temperature. Can be regarded as the maximum point of temperature dependence of Rs.

(2-5) Measurement of Curie temperature The Curie temperature is measured as follows. The measurement was performed using a BH analyzer (model number: SY-8232) manufactured by Iwatsu Measurement Co., Ltd. A predetermined primary coil and secondary coil of the apparatus are wound around the measurement sample, and measurement is performed at a frequency of 20 kHz. The measurement sample may be any shape as long as the coil is wound around it.

  After setting the coil to the sample, put the sample in a constant temperature room to saturate the temperature, and plot the permeability at that temperature. The temperature dependence curve of permeability can be obtained by changing the temperature of the temperature-controlled room. At this time, the temperature at which the magnetic permeability is 1 is defined as the Curie temperature. Here, the temperature at which the magnetic permeability is 1 is obtained as follows. The temperature of the temperature-controlled room is raised, and the permeability does not change at a certain temperature. This temperature is regarded as the temperature at which the magnetic permeability is 1 (Curie temperature).

  The fixing device of the present embodiment includes a magnetic flux generating means having an exciting coil, an induction heating element (rotary heating element) that can be rotated and electromagnetically induced by the action of the magnetic flux generated by the magnetic flux generating means, and a pressure member (rotating heating). In the image heating apparatus in which the toner is fixed to the recording material by heating and pressure contact with the pressure member, the induction heating element is a magnetic shunt alloy having a Curie point near the fixing temperature, and the induction heating element and the pressurizing element The member is rotating and has a time measuring means, which controls to slow down the rotation of the induction heating element after a certain period of time compared to when starting up, and is constant compared to the rotation control delayed at the point of power reduction. An image heating apparatus that performs control to speed up the rotation of the induction heating element after a lapse of time.

That is, in the first embodiment, the control during the temperature rising period of the fixing roller 1 is performed based on the fixing roller temperature information detected by the temperature sensor 20, but in the second embodiment, the temperature of the fixing roller 1 is raised. Control during the period is performed according to a predetermined timer time. That is, control is performed such that the rotation speed of the induction heating element is reduced when a predetermined time has elapsed during the warm-up period.

  The fixing device composed of the fixing roller 1 and the pressure roller 2 and the magnetic field generating means 3 by the exciting coil 6 and the magnetic core 5 is inserted because the mechanical position shift is very small in the assembled state. The power is usually the same. Therefore, the time from the power drop point (T1 → T2) and the time from the power drop point to the fixing temperature (T2 → T3) are almost constant and can be predicted, and control by time is possible.

  FIG. 9 is a schematic sequence of the control operation during the temperature rising period of the fixing roller 1 in this embodiment. A time signal is sent to the control unit 23 from a timer 36 (FIGS. 1 and 3). As shown in FIGS. 4 and 8, the control unit 23 controls the rotation of the fixing roller 1 to be slow after a predetermined time has elapsed from the heating start time T1 (T1 → T2). Further, after a predetermined time has elapsed (T2 → T3), the sheet feeding can be started (T3) by quickly controlling the rotation of the fixing roller. For the time, a signal is sent from the timer 36 to the controller 23 to control the rotation of the fixing roller 1. In particular, in this case, when the fixing roller 1 reaches the Curie point, the self-temperature control works, so that stable fixing can be performed without the temperature sensor 20 by combining with the time control.

  Here, the image heating apparatus according to the present invention is not limited to the image heating and fixing apparatus of the embodiment, but an assumption fixing apparatus that presupposes an unfixed image on a recording material, glossy by reheating a recording material carrying a fixed image, and the like. It is also effective when used as an image heating apparatus such as a surface modification apparatus for modifying the image surface property of the image.

  Further, in the present invention, when the main power source of the image forming apparatus main body is turned on during a period in which the rotary heating body is heated from a standby state where the heating target material is not heated to a predetermined heating target material heating temperature. 3 includes the warm-up period of the fixing device (heating device) during the pre-multi-rotation operation.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. Enlarged cross-sectional model view of the main part of the fixing device in Embodiment 1. Similarly, front view of the main part Figure showing the temperature gradient of the fixing roller, input power, and rotation speed Diagram showing schematic operation sequence when fixing roller is started up Diagram showing the number of rotations of the fixing roller Figure showing the temperature gradient of the fixing roller, input power, and rotation speed Figure showing the temperature dependence curve of the resistance value of the fixing roller FIG. 10 is a diagram illustrating a schematic operation sequence when the fixing roller is started up in the second embodiment. Diagram showing conventional configuration

Explanation of symbols

  F. Fixing device (image heating device), 1. Fixing roller (rotating heating body), 2. Pressure roller (rotating pressure body), 3. Coil assembly (magnetic flux generating means), 5. Magnetic core 6 ... Excitation coil 7 ... Stay 8 ... Temperature sensor 9 ... Thermostat 10 ... Separation claw P ... Recording material t ... Toner 20 ... Image forming device body 21 .. Document reading device, 22... Digitizer, 23 .. Control unit (CPU), 24 .. Print controller, 25 .. Photosensitive drum, 27 .. Image writing device, 28 .. Developing device, 29. Device, 35 ... Drive power supply, 36 ... Timer

Claims (2)

Magnetic flux generating means having an exciting coil, a rotatable heat generating element that generates heat by the magnetic flux from the magnetic flux generating means and heats an image on a recording material at an image heating temperature that is substantially equal to the Curie point, and the heat generating element It has a rotatable pressure member for pressurizing to form a nip, against the the warm-up period to warm to said image heating temperature the heating element in order to perform an image heating process and the heating element pressing In the image heating apparatus that rotates the pressure body in contact with the pressure body ,
The temperature at which the resistance value of the exciting coil with respect to the temperature when the exciting coil is attached to the apparatus is set to a temperature lower than the image heating temperature, and during the warm-up period, When the temperature exceeds the temperature indicating the maximum point, the image heating apparatus is switched to a rotation speed slower than the rotation speed until the temperature reaching the maximum point is reached . The image heating apparatus according to claim 1, wherein a rotation speed when the temperature indicating the maximum point is exceeded is lower than a rotation speed when the image on the recording material is heated.