JP2007206615A - Image heating device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent fixing defects caused by increasing the thickness of a thin fixing film made of resin as a countermeasure against breakage of the fixing film in an image heating device employing a film heating method. <P>SOLUTION: In the case that a temperature detection element of a heating member detects a prescribed or more reduction in temperature during performance of heat fixing, a target fixing control temperature of a recording medium being subjected to heat fixing is changed to set a higher target fixing control temperature, whereby a heating value from the heating member is increased to prevent fixing defects. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image heating apparatus that is used in an image forming apparatus such as a copying machine, a printer, and a facsimile machine and heats an image on a recording material. The present invention also relates to an image forming apparatus including the image heating apparatus.

  Examples of the image heating device include an image heating and fixing device that fixes an unfixed image on a recording material, and a gloss increasing device that increases the glossiness of an image by heating the image fixed on the recording material.

  Conventionally, in an image forming apparatus using an electrophotographic method or an electrostatic recording method, as a fixing device for heating and fixing an unfixed image formed and supported on a recording material as a permanently fixed image on a recording material surface, a heat roller method or a film A heating type image heating apparatus is widely used.

  A film heating type image heating apparatus basically includes a heating member that is controlled to a predetermined temperature by temperature control means, a flexible member that moves while being in contact with the heating member, and the flexible member. And a backup member that forms a nip portion. Then, the recording material carrying the image is nipped and conveyed at the nip portion, whereby the heat of the heating member is applied to the recording material via the flexible member. A so-called ceramic heater is generally used as the heating member. As the flexible member, a thin heat-resistant resin film is generally used in the form of a cylindrical body or an endless belt body. As the backup member, a heat-resistant elastic roller is generally used. Therefore, hereinafter, the heating member is referred to as a heater. The flexible member is referred to as a film. The backup member is referred to as a pressure roller.

  This film heating type image heating apparatus can be configured as an on-demand type apparatus using a low heat capacity member as a heater and a film. That is, it is only necessary that the heater is energized and heated to a predetermined fixing temperature only when image formation is performed by the image forming apparatus. Therefore, in comparison with the heat roller type apparatus, the waiting time from the power-on of the image forming apparatus to the image forming executable state is short (quick start), and the power consumption during standby is significantly small (power saving). There are advantages.

  In order to realize a quick start that shifts to a state in which fixing can be performed in an extremely short time, members constituting a film heating type image heating apparatus are configured with members having a low heat capacity as much as possible. Therefore, each member of the image heating apparatus is heated up as continuous fixing is performed. For this reason, if the fixing temperature control temperature is kept constant, excessive fixing occurs and high temperature offset occurs. Therefore, when performing continuous heat-fixing, it is common to control the temperature of the fixing temperature to be lowered step by step according to the number of sheets that have been continuously passed.

  Further, the fixing temperature adjustment temperature is suitable according to the detection temperature of the temperature detection element of the heating member when starting the heat fixing, and the image heating device is in an overheated state if the detection temperature at the start is high. Judgment is made and the fixing temperature control temperature is set low. Generally, energization control is performed such that if the detected temperature at the start is low, the image heating device is determined to be in a cold state, and the fixing temperature adjustment temperature is set high (Patent Document 1).

  As described above, when the film heating type image heating apparatus described above is widely used, a problem that a thin heat-resistant resin film (fixing film) as a flexible member is damaged has become apparent. There are several causes of film breakage and will be described below.

(1) What is caused by the jam processing When the film is damaged by improper jam processing (2) Film perforation The recording material, dust, and pebbles that are still stipple are formed in the film. This is likely to occur when an image is formed on a recording material to which a minute hard foreign matter such as is adhered and this recording material is nipped and conveyed at the fixing nip portion. That is, when the parts near the fixing nip and the above foreign matter come into contact with each other, a small hole is generated in the thin film.

  When a hole having a thickness of about 1.0 mm is present in the film, white spots are present in the film cycle, resulting in an image defect.

(3) Film tear due to film perforation When the above-mentioned “film perforation” occurs, the tip of the rib 21b provided on the sticker 21 shown in FIGS. The hole may be further enlarged by rotating and sliding and rubbing or catching on the film 22. And if it continues using in this state, the film 22 will tear from this hole part, and it may eventually lead to a film tear.

  Therefore, in order to achieve the quick start and low power consumption that are the advantages of the film heating type image heating device, the strength of the film formed from the thin resin sleeve is strengthened, thereby taking measures against film breakage. The following measures are being considered as means.

a: Add a material that serves as a reinforcing agent / reinforcing agent to the resin material of the film base layer. b: Change the material used for the film base layer. c: Increase the film thickness of the film base layer. Means for changing the materials used are becoming particularly used. Specifically, a technique has been established in which a thin metal sleeve having excellent thermal conductivity as compared with a resin material is used as a film base layer. However, there is a technical problem with the molding of metal thin sleeves, and the cost of industrial products is higher than that of resin-based films. At present, thin-film sleeve films made of resin-based materials Is widely spread.

  Regarding the means for adding a reinforcing agent / reinforcing substance to the resin material of the film base layer a, although the strength of the film is increased, there is a disadvantage that the thermal conductivity is lowered, At present, no technology has been established to achieve both thermal conductivity.

  Therefore, as a countermeasure against film breakage, means for increasing the film thickness of the film base layer c is adopted.

  More specifically, a film in which the thickness of the base layer of a film made of a resin-based material that has been widely used in the past is increased from about 45 to 55 μm to 60 μm or more is used. As a result, measures can be taken to increase the strength of the film alone, prevent damage to the film, and not impair the advantages of quick start and low power consumption.

  In other words, the film thickness of the base layer of the film is preferably 60 μm or more as a measure for increasing the strength against film breakage. Here, the strength of the film alone when the thickness of the film base layer is increased from 50 μm to 60 μm will be described. Regarding strength, the following regarding film breakage was confirmed.

  The force (tearing strength) required to cut a film into 50 mm squares and tear one side thereof is about 1.4 times, from about 50 gf (in the case of 50 μm) to 70 gf (in the case of 60 μm).

  The force (buckling strength) required for crushing the end face of the film is about 1.38 times from 3.2 kgf (in the case of 50 μm) to 4.4 kgf (in the case of 60 μm).

  The force (piercing strength) required to press the R0.3 mm sphere on the film to form a hole is about 1.2 times from about 890 gf (in the case of 50 μm) to about 1075 gf (in the case of 60 μm).

In this way, by increasing the film thickness of the film base layer, a film whose strength is increased solely by the film is employed to prevent damage to the film.
JP 7-248700 A

  However, the above-described conventional system has a drawback as described below because the thermal resistance increases in order to increase the thickness of the base layer of the film, which is a flexible member, to obtain strength.

  Since the film using the thin sleeve is configured so that the heat capacity becomes as small as possible, the film heats up instantaneously, but also has a characteristic that the temperature is instantaneously lowered due to the small heat capacity stored.

  Since the film that has reached the fixing nip portion heats and fixes the unfixed toner image on the recording material, heat energy is transmitted from the film to the recording material, and the temperature of the film surface decreases. In order to maintain thermal equilibrium in the film, heat energy is transferred in the film. That is, the heat energy on the heater surface side that is a heating member moves to the recording material surface side. Thermal energy is supplied from the heater to the film on the heater surface side where the temperature has decreased due to the movement of thermal energy within the film. In this way, a series of thermal energy transfers that cause thermal energy transfer to be in thermal equilibrium with the heater, the heater surface side film, the recording material side film, and the recording material are Is done instantly to pass through.

  However, since the thickness of the film base layer is increased as a measure against damage to the film, the distance traveled by heat in the thickness direction within the film is increased. For this reason, a phenomenon occurs in which a decrease in thermal energy generated on one side (contact surface side with the recording material) becomes difficult to be transmitted to the other side (contact surface side with the heater), resulting in an increase in thermal resistance. It was. As a result, the following malfunctions occurred.

  When the film that has reached the fixing nip portion comes into contact with the recording material, its surface temperature decreases. However, since the temperature drop is not instantaneously transmitted to the contact surface side with the heater, which is the opposite surface, the temperature drop is small and the amount of heat energy transferred from the heater is small. In this state, the film that has passed through the fixing nip becomes a non-fixing nip area where the heater does not contact the inner surface of the film, and the film surface temperature is further lowered by heat radiation to the air. It reaches the department.

  At that time, the film surface temperature is lower, not at a temperature at which proper image heating and fixing can be performed, and as a result, the fixing property is impaired. At this time, the temperature on the inner surface side of the film in contact with the heater is also lowered, and heat is supplied from the heater so as to maintain thermal equilibrium at the interface with the heater. However, since the thickness of the film base layer is increased as a measure against film breakage, it takes time for the thermal energy supplied from the heater to reach the recording material surface side. Therefore, this series of heat flows is not performed instantaneously when the film is in the fixing nip portion, and the film passes through the fixing nip portion.

  As described above, the surface temperature of the film that has passed through the fixing nip portion is further lowered due to heat radiation into the air. Then, it reaches the fixing nip portion three times. At that time, the surface temperature of the film is further lowered, and it becomes impossible to perform appropriate image heating and fixing, and the fixing property is further deteriorated. In other words, the first round of the film has no problem with the fixing property, and the second round is deteriorated, and the third round is further deteriorated, and the fixing property is gradually deteriorated toward the rear end of the recording material. It becomes.

  At this point, the temperature on the heater surface side decreases due to the heat flow on the inner surface of the film, and the heat flow from the heater increases to maintain thermal equilibrium at the interface with the heater. Along with this, the temperature of the heater is lowered, and the temperature detection means detects the temperature drop, so that the heater is controlled to generate more heat.

  Although there are several methods for energization control, PID control is generally used in order to accurately control the film temperature formed of a thin sleeve having a small heat capacity. In this control, the energization rate per unit time is controlled so as to reduce the temperature difference between the detected temperature of the temperature detection means currently detected and the fixing temperature control temperature to be originally controlled. In the state where the heater temperature is lowered, energization control is performed so as to eliminate the temperature difference by increasing the energization ratio to the heater.

The phenomenon described above is disadvantageous for cardboard having a large basis weight (for example, a recording material having a weight of 120 g / m ² or more) as a recording material having a large heat capacity that takes away more heat energy from the film. A recording material having a smooth surface with a large contact area is disadvantageous.

  Conventionally, in a film having a film base layer thickness of 50 μm, which has been widely used, the temperature drop that occurs on the recording material surface side in the fixing nip is instantly transmitted to the inner surface of the film, and from the heat flow at the interface with the heater As the temperature of the film increases, the temperature of the heater decreases. Then, a temperature detection means detects the temperature drop, and a series of heat energy amounts are flown instantaneously for energization control so as to maintain the fixing temperature adjustment temperature. For this reason, there was no occurrence of the fixing failure phenomenon on the smooth cardboard as described above.

  As a countermeasure against such a problem that the fixing property is impaired, it can be dealt with by setting a target temperature control temperature higher, but there are the following problems.

  A safety element having a higher operating temperature must be used in the heater, which increases costs. The element becomes large and the size of the image heating apparatus is increased. There is no safety element that operates at the desired temperature. Therefore, it is not preferable to set the target fixing temperature adjustment temperature higher.

  In addition, it is possible to set a plurality of target control temperatures from the leading end to the trailing end of the recording material and set them sequentially higher, but this is unnecessary for recording materials that do not cause poor fixing, and conversely, such as high temperature offset. There is a possibility of incurring it, which is not preferable.

  Therefore, the present invention causes the above-described problem of image heating failure that occurs when the film is thickened as a countermeasure against damage to the flexible member (film) in the film heating type image heating apparatus. It aims to prevent without letting.

  In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes a heating member that is controlled to a predetermined temperature by temperature control means, and a flexible member that moves while contacting the heating member. And a backup member that forms a nip portion with the heating member via the flexible member, and a recording material that carries an image between the flexible member of the nip portion and the backup member. In the image heating apparatus for nipping and conveying and heating, the temperature adjusting means has a control mode in which the control temperature is changed to be high during the execution of the image heating operation for a single recording material.

  That is, at the timing when the recording material is nipped and conveyed through the nip portion, the energization ratio to the heating member is increased, the control temperature is set high, and the heating temperature is increased. As a result, even when a flexible member having a thick film is used as a countermeasure against damage to the flexible member, it is possible to prevent a heating failure that deteriorates the image heating property toward the trailing edge of the recording material, which occurs on smooth cardboard. it can.

(1) Example of Image Forming Apparatus FIG. 2 is a schematic configuration diagram of an example of an image forming apparatus. This image forming apparatus is a laser beam printer using an electrophotographic system.

  Reference numeral 1 denotes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum), which is rotationally driven in a clockwise direction indicated by an arrow. The peripheral surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2. The uniformly charged surface is subjected to scanning exposure with laser light L corresponding to image information by the laser scanner 3. As a result, an electrostatic latent image corresponding to the image information is formed on the peripheral surface of the photosensitive drum 1. The electrostatic latent image is developed as a toner image by the developing device 4. In the transfer nip portion T, which is a contact portion between the photosensitive drum 1 and the transfer roller 5, the toner image is sequentially applied to the recording material S fed to the transfer nip portion T from the paper feeding portion at a predetermined timing. Is transcribed.

  The recording material S is stacked and stored in the paper feed cassette 7, and is separated and fed by the paper feed roller 8 being driven at a predetermined paper feed timing, and passes through the sheet path 9 to the transfer nip T. be introduced. In the middle of the sheet path 9, a reference sensor lever 10a for detecting the passage of the recording material S and a photo interrupter 10 are provided, and the passage of the recording material S is detected. After detecting the passage of the recording material S, laser light scanning exposure on the photosensitive drum 1 is started by the laser scanner 3 after a predetermined time has elapsed. Thus, when the leading end of the toner image formed on the photosensitive drum 1 reaches the transfer nip T, the leading end of the recording material S also reaches the transfer nip T and is introduced into the transfer nip T. .

  The recording material S exiting the transfer nip T is separated from the surface of the photosensitive drum 1, passes through the sheet path 11, is introduced into the fixing device 12 that is an image heating device, and is nipped and conveyed by the fixing nip N. As a result, the unfixed toner image on the recording material S is heated and pressurized on the surface of the recording material and fixed as a permanently fixed image. Then, the recording material S exits the fixing device 12, passes through the sheet path 13, and is discharged to the discharge tray 14. Further, the surface of the photosensitive drum 1 after the separation of the recording material is cleaned by removing residual deposits such as transfer residual toner by the cleaning device 6 and repeatedly used for image formation.

  When the double-sided printing mode for forming images on both the front and back sides of the recording material is selected, the recording material S printed on the first side that has passed through the fixing device 12 and has entered the sheet path 13 is conveyed in a switchback manner. The sheet path 15 is introduced. As a result, the recording material S is reversed and introduced from the sheet path 15 to the sheet path 9 and fed again to the transfer nip T, and the toner image is transferred and formed on the second surface side of the recording material S. The Thereafter, the recording material S passes through the sheet path 11, the fixing device 12, and the sheet path 13 and is discharged to the discharge tray 14 as a recording material that has been printed on both sides.

  Reference numeral 16 denotes an electrical component, which has a power supply unit of the apparatus and a control board for controlling the apparatus. In this printer, the photosensitive drum 1, the charging roller 2, the developing device 4, and the cleaning device 6 are configured as a process cartridge 17 that can be attached to and detached from the printer main body (image forming apparatus main body).

(2) Fixing device 12
(2-1) Overall Schematic Configuration of Fixing Device FIG. 3 is a schematic cross-sectional view of the fixing device 12. The fixing device 12 is a so-called tensionless type image heating device using a film heating method or a backup member driving method.

  In the following description, the longitudinal direction of the fixing device or the members constituting the fixing device is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The width direction (short direction) is the recording material conveyance direction. The width is a dimension in the recording material conveyance direction. The upstream side and the downstream side are the upstream side or the downstream side in the recording material conveyance direction.

  Reference numeral 21 denotes a stick holder (hereinafter abbreviated as a holder) as a holding member (support). Reference numeral 22 denotes a cylindrical heat-resistant film (thin rotating body, fixing film: hereinafter abbreviated as film) as a flexible member. Reference numeral 23 denotes a horizontally long thin plate-like ceramic heater (hereinafter abbreviated as a heater) as a heating member (heating body). Reference numeral 24 denotes a pressure stay as a pressure member. Reference numeral 25 denotes an elastic pressure roller as a backup member.

  FIG. 4 is an external perspective model view of the holder 21 as viewed from above. FIG. 5 is an exploded perspective model view of the holder 21, the film 22, and the heater 23.

  The holder 21 is a heat-resistant member having a substantially semicircular shape in cross section, and is formed of, for example, heat-resistant plastic. The holder 21 holds the heater 23 and also serves as a conveyance guide for the film 22. That is, a heater fitting groove 21a is provided on the lower surface of the holder 21 along the longitudinal direction, and the heater 23 is fitted into the groove 21a and fixedly supported. Reference numeral 21 b denotes a plurality of film inner surface guide ribs arranged at predetermined intervals along the length of the holder 21. The cylindrical film 22 is loosely fitted on the holder 21 holding the heater 23.

  The pressure roller 25 includes a metal core 25a and a heat-resistant elastic body layer 25b having good releasability such as silicon rubber formed by covering the metal core. The pressure roller 25 is disposed such that both longitudinal end portions of the cored bar 25a are rotatably supported by a pair of device side plates (not shown) via bearings.

  The assembly (fixing member) 20 of the holder 21, the heater 23, and the film 22 is disposed in parallel with the pressure roller 25 on the apparatus side plate pair. Then, the film 24 is penetrated, and the stay 24 disposed on the holder 21 is pressed in the direction of the pressure roller 25 by a pressure spring (not shown). Thus, the heater portion of the holder 21 is pressed against the pressure roller 25 with the film 22 interposed therebetween. In this case, due to the high rigidity of the heater 23, the elastic body layer 25b of the pressure roller 25 bends flatly at the pressure contact portion along the flat bottom surface of the heater 23 with a predetermined pressure of the stay 24 by the pressure spring. A fixing nip N having a predetermined width is formed between the assembly 20 and the pressure roller 25.

  The film 22 has a three-layer structure including a film base layer 22a, a primer layer 22b, and a release layer 22c, as shown in a layer structure model diagram of FIG. The film base layer 22a side is the heater 23 side (film inner surface side), and the release layer 22c side is the pressure roller 25 side (film outer surface side).

  The film base layer 22a has heat resistance and high elasticity formed of polyimide, polyamideimide, PEEK, or the like, which is higher in insulation than the glass protective layer 23c described later, on the surface of the heater 23. The film base layer 22a is formed as a flexible resin sleeve having a thickness of 60 μm or more. The film 22 maintains mechanical strength such as tear strength of the entire film 22 by the film base layer 22a. Therefore, in order to maintain the mechanical strength of the film 22, the thickness of the film base layer 22a is preferably 60 μm or more.

  The primer layer 22b is formed of a thin layer having a thickness of about 3 to 6 μm, and as an anti-static property of the film 22, the conductivity is imparted by dispersing carbon, metal oxide, or the like so as to form an electrically conductive path. In general, a primer layer is used.

  The release layer 22c is a toner offset prevention layer in which toner adheres to the film 22, and is formed by coating a fluororesin such as PFA, PTFE, or FEP to a thickness of about 8 to 15 μm. This release layer 22c also reduces the electrification of the surface layer of the film 22, and imparts conductivity by dispersing carbon, metal oxide, etc. in the release layer to prevent phenomena such as electrostatic offset widely known in electrophotography. It is common to do.

  The pressure roller 25 is rotated by the drive system M in a counterclockwise direction indicated by an arrow in FIG. As the pressure roller 25 rotates, a rotational force acts on the film 22 by the frictional force between the pressure roller 25 and the outer surface of the film 22 at the fixing nip portion N. The inner surface of the film 22 is in close contact with the surface of the heater 23 and the lower surface of the holder 21 in the fixing nip N and slides around the holder 21 in the clockwise direction indicated by the arrow in the clockwise direction of the pressure roller 25. Rotate following. The holder 21 also serves as a guide member for the film 22 that is driven to rotate. In order to smoothly rotate the film 22, heat resistant grease is interposed on the inner surface of the film 22, the surface of the heater 23, and the outer peripheral surface of the holder 21.

  Then, the pressure roller 25 and the film 22 are rotated, and a recording in which an unfixed toner image is carried on the fixing nip portion N in a state where the heater 23 is energized and heated to a predetermined temperature as described later. The material S is introduced. As a result, the recording material S is brought into close contact with the surface of the film 22 at the fixing nip portion N, and is nipped and conveyed together with the film 22. In the fixing nip portion N, the recording material S and the toner image are heated by the heater 23 via the film 22, and the toner image on the recording material S is heated and fixed. The recording material portion that has passed through the fixing nip N is conveyed while being separated from the film surface by the curvature. Then, it is relayed by the fixing paper discharge roller pair 27a and 27b (FIG. 3) and discharged and conveyed from the fixing device 12. A sensor lever 26a and a photo interrupter 26 as a paper discharge sensor for detecting the passage of the recording material S are provided upstream of the fixing paper discharge roller pair 27a and 27b, and the passage of the recording material S is detected. The detection signal is input to the control board of the electrical unit 16. Reference numeral 28 denotes a static elimination brush (static elimination means) brought into contact with the film 22.

(2-2) Configuration of Heater 23 and Energization System FIG. 7 is an explanatory diagram of a configuration of an example of the heater 23. More specifically, it has the following structural members a to i.

a: Elongated and thin plate heater substrate of ceramics with electrical insulation, good thermal conductivity, low heat capacity, such as alumina, etc., whose longitudinal direction is the direction intersecting (orthogonal) with the recording material conveyance direction in the fixing nip N 23a
b: An electric resistance member such as silver palladium (Ag / Pd) .Ta ₂ N, for example, is applied to the surface side of the heater substrate 23a by screen printing or the like to a thickness of about 10 μm and a width of 1 to 5 mm, for example. -Two parallel energized heating resistor layers 23b formed by firing
c: First and second energization electrodes 23d, which are formed on the heater substrate surface on one end side of the two parallel energization heating resistance layers 23b by being electrically connected to the energization heating resistance layer 23b, respectively. 23e
d: a conductive portion 23f formed on the heater substrate surface by electrically connecting the other end portion of the parallel two-line energization heating resistor layer 23b in series;
e: First and second temperature information output electrodes 23g and 23h formed on the heater substrate surface on the conductive portion 23f side.
f: A glass protective layer (surface protective layer) 23c having a thickness of about 50 μm, which is provided on the surface side of the heater substrate 23a so as to cover the energization heating resistor layer 23b and the conductive portion 23f.
g: Temperature detection element (temperature detection means) 31 such as a thermistor provided in contact with the longitudinal center of the substrate on the back surface (back surface) side of the heater substrate 23a.
h: First and second conductive paths 23i and 23j which are electrically connected to the temperature detecting element 31 and formed on the back surface of the heater substrate 23a.
i: Conductivity in which the end portions of the first and second conductive paths 23i and 23j are electrically connected to the first and second temperature information output electrodes 23g and 23h on the heater substrate surface side, respectively. Through hole 23k ・ 23l
The heater 23 is fitted and held in the groove 21a of the holder 21 so that the surface side is exposed to the outside with the film sliding surface.

  Reference numeral 32 denotes a thermo protector such as a temperature fuse or a thermo switch as a safety element, which is disposed in contact with the back surface of the heater.

  Reference numeral 33 denotes a power feeding connector, which is fitted to the first and second current-carrying electrodes 23d and 23e of the heater 23 held by the holder 21, and electrical contacts on the power-feeding connector 33 side are respectively connected to the current-carrying electrodes. Get in contact.

  Reference numeral 34 denotes a temperature control connector, which is fitted to the first and second temperature information output electrodes 23g and 23h of the heater 23 held by the holder 21, and is connected to each of the temperature information output electrodes. The electrical contact on the 34th side is brought into contact.

  An electrical component 16 includes a control board (CPU) 16a for controlling the device, a triac 16b, and a power supply unit 16c for the device.

  The heater 23 is supplied with power from the power supply unit (AC power supply) 16c to the energizing heat generating resistor layer 23b through the power supply connector 33 and the first and second energizing electrodes 23d and 23e. The temperature rises rapidly and steeply by generating heat over time.

  The temperature rise of the heater 23 is detected by the temperature detection element 31. Electrical information of the detected temperature includes first and second conductive paths 23i and 23j, conductive through holes 23k and 23l, first and second temperature information output electrode patterns 23g and 23h, and a temperature control connector 34. To the control board 16a.

  The control board 16a controls the triac 16b based on the input detected temperature information and controls the electric power supplied from the power supply unit 16c to the energization heating resistor layer 23b of the heater 23 by phase, wave number control, etc. The temperature is controlled to a predetermined temperature.

  The thermo protector 32 disposed on the back surface of the heater 23 is electrically inserted in series in an energization circuit for the energization heating resistor layer 23b of the heater 23. The thermo protector 32 operates when the energization from the power supply unit 16c to the energization heat generating resistor layer 23b of the heater 23 becomes uncontrolled due to some failure cause such as the control board 16a or the triac 16b. That is, when the energization falls into the uncontrolled state and the energization to the energization heat generating resistor layer 23b is continued and the heater 23 is in an overheated state exceeding an allowable value (during thermal runaway), the thermo protector 32 operates to cut off the electric circuit. Thus, energization to the energization heat generating resistance layer 23b is forcibly shut down.

  In the apparatus of the present embodiment, the recording material S passes through the center reference conveyance, A is the maximum paper passing area width of the recording material S, and B is the minimum paper passing area width. The temperature detecting element 31 and the thermo protector 32 are arranged in a portion corresponding to the minimum paper passing area width B of the heater 23.

  Even when the recording material S having the minimum width that can be transported by the image forming apparatus main body is transported, the temperature detection element 31 does not cause problems such as poor fixing and high temperature offset of the toner image on the recording material S. In order to heat and fix at an appropriate fixing temperature, it is provided within the minimum sheet passing area width B.

  On the other hand, the thermo protector 32 also does not cause problems such as malfunction due to overheating due to the temperature rise of the non-sheet passing portion of the heater that occurs when the recording material S having the minimum width is conveyed, and shutdown of energization. Are provided within the minimum sheet passing area width B.

  In general, the thermo protector 32 is set so as to operate (shut down the energization) at a temperature equal to or higher than the highest fixing temperature control temperature used by the fixing device. It is also common to provide a high temperature abnormality detection temperature that suppresses energization between the highest fixing temperature adjustment temperature and the operating temperature of the thermo protector 32. The high temperature abnormality detection is set so that the thermo protector 32 does not operate by detecting the temperature by the temperature detection element 31 and performing energization control so as to reduce the energization to the energization heating resistor layer 23b of the heater 23. .

(2-3) Fixing Temperature Control The fixing temperature control performed by the fixing device 12 of this embodiment is that the output of the temperature detection element (thermistor) 31 that is the temperature information of the heater 23 is analog as described above. / After being digitally converted, it is taken into the electrical equipment section 16. Based on the input information, the electrical component 16 controls the energization power by applying phase, wave number control, and the like to the AC voltage that is energized to the energization heating resistor layer 23b of the heater 23.

  By repeating the sampling cycle for detecting the temperature of the heater 23 in an extremely short time every 10 to 100 msec, more accurate fixing temperature control is realized.

  Here, the meaning of the word “wave number” will be briefly explained. For example, the wave number control when the voltage input to the image forming apparatus is a frequency of 110 V and a frequency of 60 Hz has a minimum unit in which one wave is from 0 V to 0 V of a sine wave, as shown in FIG. For example, the 15/15 wave input is a case where all 15 waves are energized. For example, the case where 2 of 15 waves are input is referred to as 2/15 wave (2 wave) input.

  FIG. 8 is a detailed view showing the state of 1-wave input to 15-wave input. Referring to the one-wave input in the figure, only one of the 15 waves is shaded. The heater 23 is heated by outputting / energizing only the shaded portion. Similarly, when the three-wave portion is viewed, only three of the 15 waves are hatched as in the case of one wave. Energization heat generation control is performed in which the heater 23 is energized to generate heat only in the wave number portion painted on the oblique lines.

  In this way, the energization control is based on wave number control, and the well-known PID control is performed as means for controlling the temperature difference between the detected temperature of the thermistor 31 and the target control temperature more accurately and with smaller accuracy.

  PID control is a well-known control method and will not be described in detail, but P control is proportional control that increases or decreases the control term in proportion to the difference between the detected temperature of the thermistor 31 and the target control temperature. . In an image heating apparatus using wave number control, energization control is performed so that the wave number corresponds to the temperature difference. The I control is an integral control in which the difference between the detected temperature of the thermistor 31 and the target control temperature is added and the control term is increased or decreased when the added value reaches a certain value. In an image heating apparatus using wave number control, the integral term is used to add or subtract the wave number corresponding to the integral value. The D control is a differential term for corresponding to a rapid change between the detected temperature of the thermistor 31 and the target control temperature. In an image heating apparatus using wave number control, control is performed by adjusting the wave number according to a temperature difference.

  More specific description will be given below. Since the fixing device used in this embodiment has a target control temperature of 210 ° C., description will be made at 210 ° C.

  Until the difference between the detected temperature of the thermistor 31 and the target control temperature is equal to or lower than a predetermined temperature, for example, 20 ° C. (detected temperature is 190 ° C.), the energization of the energization heating resistor layer 23b is full energization (full-wave energization). As a result, the heater 23 is heated in a short time.

  When the difference between the detected temperature and the target control temperature is raised to 20 ° C., energization control is started so as not to cause an overshoot that exceeds the target control temperature.

  First, the energization wave number is expressed with the fundamental wave number as 10 waves. The P control shown in 1 is started.

1) For example, when the difference between the target control temperature and the detected temperature of the thermistor is 10 ° C. or higher,
Energized wave number = [wave number to be adjusted by P control] + [fundamental wave number] = 5 + 10 = 15 (wave)
Full-wave energization.

2) If the difference between the target control temperature and the thermistor detection temperature falls below 9.9 ° C,
Energized wave number = [wave number to be adjusted by P control] + [fundamental wave number] = 4 + 10 = 14 (wave)
The 14-wave energization and the energization control reduced by one wave are sequentially performed, and the energization control by the P control is performed so that the difference between the target control temperature and the detected temperature of the thermistor converges within 5 ° C.

  3) When the difference from the target control temperature reaches 5 ° C. or less (detected temperature is 205 ° C.), I control is started. For I control, the difference between the target control temperature and the thermistor detection temperature is added. 2 determines the wave number to be adjusted by I control.

For example, when the difference between the target control temperature and the detected temperature of the thermistor 14 is 3.5 ° C. and the cumulative difference is 10 ° C. or more,
Energized wave number = [wave number to be adjusted by P control] + [wave number to be adjusted by I control] + [fundamental wave number]
= 1 + 1 + 10 = 12 (wave)
12-wave energization.

  As described above, when the detected temperature of the thermistor 31 converges to the target control temperature by the PI control described above in the range of −1 to 2 ° C., the control board 16a gives permission to execute the image forming operation and performs the image forming operation. start. As a result, the recording material S to which the unfixed toner image t is transferred is conveyed to the fixing nip portion N of the fixing device 12.

  The control board 16a predicts the timing at which the recording material S reaches the fixing nip portion N based on the recording material passage detection signal from the reference sensor lever 10a and the photo interrupter 10 that detects the passage of the recording material S, and performs D control. Start. The D control is energization control performed mainly to cope with a rapid temperature change accompanying a sudden change in the power supply voltage or the like. Table D for D control. The energization control is performed according to 3.

For example, when the difference between the target temperature and the detected temperature of the thermistor 31 is in the range of −5.9 to 5.9 ° C., the PI control described above is performed. When the power supply voltage value is boosted for some reason, the amount of heat generation increases because the voltage applied to the energization heat generating resistor layer 23b increases even at the same energization wave number. Thereby, when the difference between the target control temperature and the detected temperature of the thermistor 31 is −6.0 ° C. or more (the detected temperature of the thermistor 31 exceeds the target control temperature),
Energized wave number = [wave number to be adjusted by P control] + [wave number to be adjusted by I control] + [D wave control
Adjusting wave number] + [fundamental wave number]
= -4 + 0 + (-2) + 10 = 4 (wave)
Reduce the number of energized waves to 4 wave energies. Thereby, the energization control is performed so as to control the energization ratio applied to the energization heat generating resistance layer 23b and suppress abnormal temperature rise.

  Regarding the D control, when the recording material S passes through the fixing nip N, the D control is not performed, and the temperature control is performed only by the PI control. This is because the D control is a control term that corresponds to the case where the detected value and the target value are abruptly changed. Therefore, when the recording material S is not present in the fixing nip portion N, the image heating of the unfixed toner image is performed. This is because fixing is not performed and is unnecessary.

  As described above, by performing PID control regardless of the presence of the recording material S in the fixing nip N, the difference between the temperature detected by the thermistor 31 and the target control temperature is always made smaller and more accurate. It is configured to control energization.

(2-4) Control Change of Control Temperature FIG. 9 shows the detected temperature of the thermistor 31 when a thick card having a smooth surface is passed as the recording material S that takes more heat energy from the film 22, and the energization wave The result of measuring the number is shown in FIG.

In this measurement, the recording material S having a basis weight of 163 g / m ² was passed in an environment of 15 ° C./10% as a low temperature and low humidity environment. Moreover, the film 22 used for the confirmation is one in which the thickness of the base layer 22a is set to 70 μm as a measure against film breakage.

  As shown in FIG. 9, in the conventional energization control (the target temperature 210 ° C. is constant in the recording material S), the temperature detected by the thermistor 31 during the execution of fixing is reduced, and the target temperature control temperature is set. The energization control to be held is not performed. This can also be seen from the fact that energization control for adding the energized wave numbers is not performed, as is apparent from the energized wave numbers shown in FIG.

  Next, when the detected temperature of the thermistor 31 falls below the target temperature adjustment temperature by a predetermined temperature, a description will be given of setting the target control temperature higher.

  In this embodiment, specifically, when the detected temperature of the thermistor 31 is lowered by 3 ° C. (detects 207 ° C.) from the target temperature adjustment temperature, the target temperature adjustment temperature is changed to 3 degrees higher (213 ° C.). To do. As shown in FIG. 9, in this embodiment, when the temperature detected by the thermistor 31 during the fixing is detected to be 207 ° C., the target temperature is changed to 213 ° C. Therefore, in each item of the PID control described above, The following energization control is performed.

Energized wave number = [wave number to be adjusted by P control] + [wave number to be adjusted by I control] + [D wave control
Adjusting wave number] + [fundamental wave number]
= 3 + 0 + 0 + 10 = 13 (wave)
The energization control is performed so as to increase the wave number to the 13-wave energization.

In the conventional example,
Energized wave number = [wave number increased / decreased by P control] + [wave number increased / decreased by I control] + [D wave control
Adjusting wave number] + [fundamental wave number]
= 1 + 0 + 0 + 10 = 11 (wave)
11-wave energization.

  In this embodiment, the energization control of these two waves is performed to increase the amount of heat generated from the heater 23 and increase the amount of heat applied to the film 22, thereby preventing fixing failure.

  As shown in FIG. 9, the energization control of this embodiment (when the target temperature falls below a predetermined temperature, the target temperature adjustment temperature is set to a higher setting), so that the recording material S is fixed. When the recording material S is applied to the second half, the target temperature control temperature is set high. It can be seen that the detected temperature of the thermistor 31 is rising in the second half of the recording material S. This can also be seen from the fact that the energized wave number is added and the energized wave number increases toward the latter half of the recording material S as is apparent from the energized wave number shown in FIG.

  With respect to the effect, when the thickness of the film base layer 22a is increased to 70 μm as a countermeasure against film breakage, the current control of the conventional example (the target temperature is constant in the recording material S) causes the film 22 to be in the second round, Fixability deteriorated as the 3rd lap was reached. By using energization control of this embodiment (when the target temperature falls below a predetermined temperature, the target temperature adjustment temperature is set to a higher setting), the energization wave number is increased by two compared to the conventional example. Thus, the heat generated from the heater 23 increases during the fixing operation, and the temperature of the film surface does not decrease. For this reason, even if smooth thick paper is used as the recording material S, no fixing failure occurs.

  In the present embodiment, when energization control is started, the target temperature adjustment temperature is set high (+ 3 ° C.), so that the difference from the high temperature detection abnormal temperature and the thermoprotector operating temperature becomes small. For this reason, the energization control of this embodiment is applied only during the fixing of the recording material S, and when the recording material S passes through the fixing nip N, the target temperature adjustment temperature is returned (210 ° C. in this embodiment). It was supposed to be.

  As described above, when the temperature detection element of the heater detects a temperature drop of a predetermined value or more during execution of heat fixing, the target fixing control temperature is changed to a high setting for the recording material being heat fixed. This increases the amount of heat generated from the heater and prevents fixing failure. That is, in a film heating type image heating apparatus, as a countermeasure against damage to a fixing film formed from a thin resin, fixing failure that occurs when the fixing film is thickened is prevented.

  FIG. 1 shows a flowchart regarding the energization control described above.

  With the widespread use of personal computers throughout the world, laser printers have become widespread throughout the world, and the recording material S to be printed has been widely used. In order to cope with this, an image forming apparatus having a plurality of printing modes for each type of the recording material S has become common. For example, a “thick paper mode” is used as a printing mode for fixing thick paper, a “rough paper mode” is used as a printing mode for fixing a recording material S having a large surface unevenness (not smooth), and a “thin paper mode” for fixing a thin recording material S is used. is there. In addition, there are various printing modes such as an “OHP mode” that executes image formation and fixing suitable for overhead parenthood.

  The energization control proposed in the present invention (when the target temperature falls below a predetermined temperature, the target temperature adjustment temperature is set to a higher value) is changed to a print mode in which the fixability is liable to be impaired, for example, “thick paper mode”, “ It is suitable to use in combination with “rough paper mode”.

  In addition, the usage environment is expanding as it is used all over the world. In the past, laser beam printers have started to be used in so-called office environments, but they have also been used in workplaces such as warehouses and outdoors. Are also becoming more common. If the outside temperature can be known by installing a temperature detection element for detecting the outside temperature in the image forming device, the target temperature adjustment temperature is changed according to the usage environment. If the temperature is low, the target temperature adjustment temperature is set high. In addition, there is an increasing number of image forming measures that perform temperature control such as setting a low value when the temperature is high. Even in such an image forming apparatus, when a “low temperature environment” that is a use environment in which the fixing property is easily impaired is detected, it is also suitable to use the embodiment of the present invention in combination.

  That is, the control temperature change control mode can be executed only in a specific image heating mode that can be selected by the user.

(2-5) Modified Configuration, etc. 1) The temperature control configuration of the heater 23 is not limited to the above. For example, the surface temperature of the pressure roller 25 or the temperature of the film 22 can be detected by a temperature detection means to control the amount of current supplied to the heater 23.

  2) In the present invention, the heating member is not limited to the so-called ceramic heater of the embodiment, and for example, other heating bodies such as a PTC (Positive Temperature Coefficient) heater and an electromagnetic induction heating member can be used. In addition, the heater substrate 23a may be a ceramic substrate in which a metal plate surface is insulated. A back heating type heater can also be used.

  3) The flexible member 22 is not limited to a cylindrical shape or an endless one. It is also possible to adopt an apparatus configuration in which a long end film with roll winding travels from the feeding side to the winding side via a fixing nip portion.

  4) Further, the backup member 25 is not limited to a roller body, and may be a rotating belt body. The flexible member 22 may be moved by a drive member other than the backup member 25, and the backup member 25 may be driven.

  5) The image heating apparatus of the present invention is not only an image heating and fixing apparatus of the embodiment, but also an image heating apparatus that heats a recording material carrying an image to improve surface properties such as gloss, and an unfixed image on the recording material. It can also be used as an image heating device that presupposes an image.

Flow chart of energization control Schematic configuration diagram of an image forming apparatus Cross-sectional model of fixing device External perspective model view of holder viewed from above Exploded perspective view of holder, film and heater Film layer structure model diagram Heater configuration explanatory diagram Illustration of wave number for wave number control Diagram showing effect of implementation system (Part 1) Diagram showing effect of implementation system (Part 2)

Explanation of symbols

  12. .. Fixing device (image heating device), 21 .. Stick holder (holding member), 22 .. Film (flexible member), 23 .. Heater (heating member), 24. · Elastic pressure roller (backup member), N · · Fixing nip, S · · Recording material, 16 · · Electrical component, 16a · · Control board, 16b · Triac, 16c · · Power supply, 31 · · Temperature detection Element, 32 ・ ・ Safety element

Claims (6)

A heating member that is controlled to a predetermined temperature by temperature control means, a flexible member that moves while contacting the heating member, and a backup member that forms a nip portion with the heating member via the flexible member; An image heating apparatus that sandwiches and conveys a recording material carrying an image between the flexible member of the nip portion and the backup member, and heats the recording material.
The image heating apparatus according to claim 1, wherein the temperature adjusting unit has a control mode in which the control temperature is changed to a high level during the execution of the image heating operation for a single recording material.   The image heating apparatus according to claim 1, wherein the flexible member has a resin layer having a thickness of 60 μm or more as a base layer.   3. The image heating apparatus according to claim 1, wherein the changed control temperature is changed to the control temperature before the change at the same time as the end of the image heating operation of the single recording material.   4. The image heating apparatus according to claim 1, wherein the control temperature change control mode can be executed only in a specific image heating mode selectable by a user. 5.   The heating member has a resistance member that generates heat when energized, and the temperature adjusting means is based on a temperature detection result of a temperature detecting means for detecting the temperature of the heating member so that the temperature of the heating member follows the control temperature. The image heating apparatus according to claim 1, wherein energization of the resistance member is controlled. In an image forming apparatus having an image forming unit that forms an unfixed image on a recording material, and a fixing unit that heat-fixes an unfixed image on the recording material as a permanent image.
An image forming apparatus comprising the image heating apparatus according to claim 1 as the fixing unit.