JP2005300840A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which increases accuracy in detecting the temperature of a recording material after heating and fixing. <P>SOLUTION: A temperature sensing part of temperature sensing means is arranged to come into contact with the surface opposite to the image surface of a recording material during one-sided printing without providing such an opposed member that comes into contact with the image surface of the recording material at least in a position corresponding to the position of the temperature sensing part that is in contact with the recording material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using a recording technique such as an electrophotographic recording technique or an electrostatic recording technique, and more particularly, to form an image having a temperature detecting means for detecting the temperature of a recording material after heat fixing. Relates to the device.

  2. Description of the Related Art Image forming apparatuses such as copying machines and printers that use recording technology such as electrophotographic recording technology and electrostatic recording technology are equipped with a fixing device that heats and fixes a toner image formed on a recording material. Various measures have been taken to ensure good fixability of the image.

  As one of them, there has been proposed one that detects the temperature of a recording material after heat-fixing and feeds it back to a control target temperature of the fixing device (for example, see Patent Documents 1 to 9).

  For example, FIG. 9 shows an example of a heat fixing apparatus that detects the temperature of the recording material after heat fixing using a non-contact sensor. In this heat fixing apparatus, a non-contact sensor 20 such as an infrared sensor is installed downstream of the fixing nip, and measures the temperature of the recording material in a non-contact manner.

FIG. 10 shows an example of a heat fixing apparatus that detects the temperature of the recording material after heat fixing using a contact sensor. In this heating and fixing apparatus, a temperature sensor 18 such as a thermistor is installed downstream of the fixing nip, and an opposing member 19 such as a rubber roller is installed at a position facing it, and the recording material is sandwiched between the temperature sensor and the opposing member. Is measuring the temperature.
JP-A-1-150185 Japanese Utility Model Publication No. 1-160473. JP-A-6-308854 Japanese Patent Laid-Open No. 7-230231 JP-A-10-161468 JP 2000-66461 A JP 2001-13816 A JP 2002-23555 A JP 2002-216961 A

  However, in the case of such a configuration that detects the temperature of the recording material and applies feedback, temperature detection accuracy becomes a problem.

  When the recording material is heat-fixed, water contained in the recording material is also heated at the same time, so that water vapor is generated from the surface of the recording material. In the case of temperature detection using a non-contact sensor, the surface of the non-contact sensor is clouded by the water vapor, so that it is difficult to accurately detect the temperature of the recording material.

  Also, in the case of detecting the temperature by contacting a temperature sensor and a counter member such as a roller and sandwiching the recording material between the temperature sensor and the counter member, the heat of the recording material is deprived by the counter member, and the recording material is also accurate. It is difficult to detect the temperature.

  The present invention for solving the above-described problems includes an image forming unit that forms an image on a recording material, a fixing unit that includes a fixing nip portion that sandwiches and conveys the recording material, and that heat-fixes the image on the recording material, and fixing. An image forming apparatus including a temperature detection unit that detects a temperature of the recording material downstream of the nip portion in the recording material moving direction, wherein the temperature detection unit of the temperature detection unit is on the image surface side during single-sided printing of the recording material Is arranged so as to be in contact with the surface opposite to the recording material, and in a state where the temperature detection unit is in contact with the recording material, at least an area corresponding to the temperature detection unit on the image surface side of the recording material is in contact with the recording material There is no opposing member to be used.

  According to the present invention, the temperature detection accuracy of the recording material after heat fixing is improved.

(First embodiment)
FIG. 8 is a schematic sectional view of an electrophotographic printer which is an example of an image forming apparatus to which the present invention is applied.

  This printer includes a sheet feeding device including a sheet feeding tray 1, a sheet stacking table 2, and a sheet feeding roller 3. The recording material P stacked on the sheet stacking table 2 in the sheet feeding tray 1 is picked up one by one from the uppermost recording material by the sheet feeding roller 3 and sent to the registration unit by the conveying roller 4 and the conveying roller 5. . The recording material is fed to the image forming unit (image forming unit) after the conveying direction is aligned by a resist unit including the registration roller 6 and the registration roller 7.

  Among the image forming units, the photosensitive drum 8, a charger (not shown in the drawing) disposed around the photosensitive drum 8, and development for developing a latent image formed on the photosensitive drum with toner. A cleaner (also omitted) and a cleaner (also omitted) for removing residual toner on the photosensitive drum are unitized as a toner cartridge 9 and are configured to be detachable from the printer main body. . A laser scanner unit 10 for writing an image according to image information on the photosensitive drum 8 includes a laser light source (not shown in the drawing), a laser beam deflection mirror (polygon mirror) 11, a deflection mirror rotating motor (not shown in the drawing). Etc.) are housed.

  When the image information is input, the printer scans the photosensitive drum 8 charged to a predetermined potential by the charger with the laser light L based on the image information, and forms an electrostatic latent image on the photosensitive drum 8. Thereafter, the latent image is developed with toner as a developer by a developing unit, and the developed toner image is transferred from the photosensitive drum 8 to the recording material by the transfer roller 12.

  After the transfer of the toner image, the recording material is conveyed to a fixing unit having a heat generating unit 13 and a backup unit 14, and the toner image on the recording material is heated and fixed. Thereafter, the recording material is discharged to a discharge tray 17 through a discharge unit including an intermediate discharge roller 15 and a discharge roller 16.

  FIG. 1 is a cross-sectional view of the vicinity of the temperature fixing means for detecting the temperature of the heat fixing device and the recording material after heat fixing.

  The printer of this embodiment is equipped with a film heating type heating fixing device (on-demand fixing device) that heats paper through a flexible sleeve (hereinafter referred to as a fixing film) in the form of a film or belt. Yes. However, the present invention is not limited to an image forming apparatus equipped with such an on-demand fixing device. A heat roller heating fixing device that heats the paper while nipping and conveying the sheet by a heating roller that is temperature controlled so as to maintain a predetermined temperature, and a pressure roller that has an elastic layer and is in pressure contact with the heating roller, etc. The present invention can be applied to an image forming apparatus equipped with various heat fixing devices.

  After the toner image formed in the image forming unit as described above is transferred to the recording material, the recording material is sent to the heat fixing unit. The heat fixing unit mainly includes a heat generating unit 13 and a backup unit 14, and the front end of the recording material is a pressure nip (fixing nip) N formed by the heat generating unit and the backup unit via a fixing inlet guide 21. Led to.

  The heat generating unit mainly includes a fixing film 22, a heater (heating body) 23 that is in contact with the inner surface of the fixing film, a film guide member 25 that holds the heater 23 and has a function of guiding the fixing film, and a backup of the film guide member. It has a metal stay that presses against the unit side. The backup unit mainly has a pressure roller 24. Then, the end of the metal stay is biased toward the pressure roller by a force of a coil spring or the like, so that pressure is applied to the fixing nip portion N.

  A fixing film 22 has a release layer formed on the surface. This fixing film is externally fitted with a margin in the circumference with respect to the film guide member 25 having a semicircular cross section.

  The fixing film 22 preferably has a small heat capacity in order to improve quick start performance. For example, the total thickness is preferably 100 μm or less, preferably 20 μm or more and 60 μm or less, and the base layer is preferably made of a heat-resistant resin film such as polyimide or PEEK. In addition, the base layer is preferably made of a metal film such as Ni electroformed or stainless steel. In the case of a metal film, since the thermal conductivity is good, the thickness can be 150 μm or less and sufficient quick start performance can be exhibited.

The heating element 23 is, for example, a ceramic heater, and a heating resistor (resistor pattern) is formed on a ceramic substrate as a heat generation source that generates heat when power is supplied, and the resistor is energized by energizing the resistor pattern. The pattern generates heat and the heater rises in temperature. This heating element was formed by printing a paste-like resistor made of silver / palladium on an alumina (Al ₂ O ₃ ) or aluminum nitride (AlN) substrate to form a resistor pattern having a desired resistance value. Is. Further, a glass layer is formed on the resistor pattern, and this glass layer serves as a sliding layer that slides on the inner surface of the fixing film while protecting the resistor pattern. A thermistor, which is a temperature detection element, is bonded and fixed to the surface of the substrate opposite to the resistor pattern forming surface. The temperature information monitored by this thermistor is input to a control circuit unit (not shown). The control circuit unit controls the energization amount from the AC power source to the heating element (resistor pattern) by controlling the AC driver so that the detected temperature of the thermistor maintains the set temperature.

  A pressure roller 24 has an elastic layer of silicone rubber on a core metal such as iron or aluminum, and further has a PFA tube layer as a release layer thereon. This pressure roller is driven by a drive motor (not shown).

  The fixing film 22 receives a driving force from the pressure roller 24 and rotates in the clockwise direction in FIG. 1 following the rotation of the pressure roller. A recording material carrying an unfixed toner image is nipped and conveyed through a fixing film 22 at a fixing nip N formed by a heating body 23 and a pressure roller 24. While passing through the fixing nip N, the toner image is heated and fixed on the recording material.

  In this way, thermal energy is applied to the recording material from the heating body through the fixing film in the process of passing the fixing nip portion of the recording material, and the unfixed toner image on the recording material is heated and melted and fixed. The recording material P that has passed through the fixing nip portion N and separated from the fixing film is sent to a paper discharge portion by a paper discharge roller pair (conveying means) 113.

  Although the image forming apparatus of the present embodiment has only a single-sided printing function and no double-sided printing function, the temperature detection unit of the present invention detects temperature in both the image forming apparatus having the double-sided printing function and the image forming apparatus having only the single-sided function. The part is arranged so as to contact the surface (non-printing surface) opposite to the image surface side during single-sided printing of the recording material, and the temperature detection unit is fixed downstream from the fixing nip portion in the recording material conveyance direction. The recording material comes into contact with the conveyance means closest to the nip portion. Note that this transport means is driven by a drive source.

  Here, there are two advantages of detecting the temperature on the non-printing surface side of the recording material. First, during normal single-sided printing, the recording material comes into contact with a heat transfer plate (hereinafter referred to as a heat collecting plate) on the side opposite to the surface on which the toner is fixed. Is difficult to adhere. That is, there is an advantage that the temperature detection accuracy is not lowered due to the toner adhering to the heat collecting plate. Secondly, since thermal energy is applied to the recording material from the printing surface side of the recording material, the temperature is detected on the non-printing surface, so that the non-printing surface from the recording material printing surface side according to the type of recording material is not used. It is possible to predict the type of recording material from the detected temperature by utilizing the difference in heat conduction characteristics toward the printing surface. For example, since the temperature on the non-printing surface side of the thin recording material is higher than the temperature on the non-printing surface side of the thick recording material, the detection temperature of the temperature detection unit disposed downstream of the fixing nip portion is When the temperature is higher than the reference temperature, it is determined that the recording material is thin, and when the detected temperature is lower than the reference temperature, it can be determined that the recording material is thick. In such a recording material temperature detection method, as in the present embodiment, only one surface of the recording material (printing surface side in this example) has a heat generating portion, and the other surface of the recording material (non-printing in this example). This is particularly effective in the construction of a fixing device having no heat generating part on the surface side.

(Configuration of temperature detection means)
In FIG. 1, a fixing paper discharge guide (recording material guide member) 103 that forms a recording material transport path between a fixing nip portion N and a paper discharge roller (conveying means closest to the fixing nip portion N) nip 102. Is provided. One roller of the paper discharge roller pair is driven by a motor (not shown). The fixing paper discharge guide 103 is made of a material having high heat resistance such as PBT or PET. The conveyance surface 103 a of the fixing paper discharge guide 103 is disposed below an imaginary straight line L connecting the downstream end portion 101 of the fixing nip portion N in the recording material moving direction and the paper discharge roller nip portion 102. In addition, the recording material conveyance speed in the paper discharge roller pair is set to be faster than the recording material conveyance speed in the fixing nip portion. That is, in a state where the recording material is conveyed by both the fixing nip portion N and the paper discharge roller nip portion 102, the recording material is set to exhibit a behavior approaching a straight line L connecting both nips in this section. .

  A part of the direction perpendicular to the recording material conveyance direction (the width direction of the recording material) on the conveyance surface of the fixing paper discharge guide 103 can be a thin plate having a thickness of about 0.1 mm such as aluminum or stainless steel having a small heat capacity. The heat collecting plate 104 is fixedly installed. At least a part of the heat collecting plate 104 protrudes above the imaginary straight line L, and the protruding portion (temperature detection unit) is in direct contact with the recording material when passing through the recording material. That is, the temperature detection unit is on the side opposite to the side where the recording material guide member is disposed, with a virtual straight line connecting the fixing nip N and the nip 102 of the conveying unit as a boundary. In this way, by reducing the heat capacity of the heat collecting plate 104 and positively contacting the heat collecting plate 104, the temperature of the heat collecting plate 104 can be made substantially the same as the temperature of the recording material in a short time. .

  On the back surface of the heat collecting plate 104, a highly responsive temperature detection sensor 105 such as a thermistor is fixed by a method such as adhesion. Further, as shown in FIG. 1, recording is performed above the heat collecting plate 104, that is, in an area corresponding to at least the temperature detecting portion on the image surface side of the recording material in a state where the temperature detecting portion of the heat collecting plate 104 is in contact with the recording material. There is no member (opposing member) that contacts the material. When the recording material after image fixing is conveyed from the heat fixing device 106, the non-printing surface of the recording material comes into contact with the heat collecting plate 104, and the recording material is deprived of heat by the heat collecting plate 104. Thereby, heat is conducted to the temperature detection sensor 105 installed on the back surface of the heat collecting plate 104 to detect the temperature of the recording material. At this time, since the temperature detection sensor 105 is attached directly below the position (temperature detection unit) where the recording material and the heat collecting plate 104 are in contact, the influence of the temperature gradient in the heat collecting plate 104 can be minimized, The temperature detection state is substantially the same as when the temperature detection sensor directly contacts the recording material to detect the temperature, thereby improving the temperature detection accuracy. Further, since there is no member (opposing member) that contacts the recording material in the region corresponding to at least the temperature detecting portion on the image surface side of the recording material in a state where the temperature detecting portion of the heat collecting plate 104 is in contact with the recording material, recording is performed. The heat stored in the material is difficult to escape to other than the heat collecting plate 104, and the temperature detection accuracy is high. A configuration in which there is no member (opposing member) in contact with the recording material in an area corresponding to at least the temperature detection unit on the image surface side of the recording material in a state where the temperature detection unit of the heat collecting plate is in contact with the recording material will be described later. This configuration is common to all the embodiments. Furthermore, by using a metal member for the sliding portion (heat collecting plate) with the recording material, wear of the sliding portion can be prevented and durability can be improved.

  The temperature detection sensor 105 is an element typified by a thermistor that changes a resistance value according to temperature. The temperature detection sensor 105 is enclosed in glass with a dumet wire 114 baked on an electrode of the thermistor chip. The dumet line 114 is connected to a control circuit unit (not shown) and transmits information detected by the thermistor. The image forming apparatus sets, for example, the control temperature (set temperature) of the heater to an optimum temperature according to the type of the recording material in accordance with the detected temperature information.

  Here, in order to reduce the heat capacity of the heat collecting plate 104, the heat collecting plate 104 should be made as small as possible in the recording material conveyance direction and in the direction perpendicular to the recording material conveyance direction and in the direction substantially parallel to the width of the recording material. Is desirable. In addition, by providing the metal heat collecting plate 104 with a small heat capacity in the plastic fixing and discharging guide 103 having a low thermal conductivity as in this embodiment, the heat capacity can be reduced and the heat insulation can be improved at the same time. The responsiveness of the temperature detection sensor 105 can be improved.

(Second Embodiment)
A second embodiment will be described with reference to FIG. The portion near the heat collecting plate 104 of the fixing paper discharge guide 103 is formed as far as possible from the recording material being conveyed, so that temperature detection with higher accuracy is possible. FIG. 2 is a perspective view when the vicinity of the heat collecting plate 104 of the fixing and discharging guide 103 is separated from the sheet passing surface by a step. By forming the step 107, it is possible to prevent the heat of components other than the heat collecting plate 104 from affecting the temperature of the heat collecting plate 104 or the recording material in the vicinity of the heat collecting plate 104.

  It is possible to further improve the temperature detection responsiveness by bringing the recording material into contact with the heat collecting plate 104 in such a limited region. In the case of the present embodiment as well, as in the first embodiment, there is no facing member in the facing portion of the heat collecting plate. From this point of view, such as a roller that feeds the recording material together with the temperature detection sensor as in the conventional example The temperature detection accuracy is superior to the case where an opposing member is present.

  Note that, as a configuration that can be applied not only to the present embodiment but also to the first embodiment and the embodiments that will be described later, when performing double-sided printing with an image forming apparatus having a double-sided printing function, heat is collected when the second page is passed. Since the plate 104 comes into contact with the toner image on the first surface of the recording material, there is a concern that the toner adheres to the surface of the heat collecting plate 104. As a countermeasure, the surface of the heat collecting plate 104 may be coated with Teflon (registered trademark) or a surface treatment such as UV coating within a range that does not affect the heat conduction of the heat collecting plate 104. Further, the surface of the heat collecting plate 104 may be coated with PI (polyimide) or the like.

(Third embodiment)
A third embodiment will be described with reference to FIG. FIG. 3 is a perspective view when a notch is provided in the vicinity of the heat collecting plate 104 of the fixing and discharging guide 103. By providing the cutout hole 108 in this way, it becomes possible to prevent the heat of components other than the heat collecting plate 104 from affecting the temperature of the heat collecting plate 104 or the recording material in the vicinity of the heat collecting plate 104. .

(Fourth embodiment)
Next, a fourth embodiment will be described with reference to FIGS.

  Since the recording material conveyance speed in the discharge roller pair 113 is set faster than the recording material conveyance speed in the fixing nip portion, depending on the speed setting and the type of the recording material, It is conceivable that the rubbing resistance against the recording material increases and damages the recording material. 4 and 5 show an example of a configuration in which the heat collecting plate 104 attached to the fixing paper discharge guide 103 is retracted when receiving a force from the recording material. FIG. 4 shows the state of the home position, and FIG. 5 shows the state of the temperature detection position. In FIG. 4, the heat collecting plate 104 is formed integrally with a slide member (moving member) 109, and can move up and down with respect to the slide guide portion 103 b of the fixing paper discharge guide 103. The slide member 109 is always urged upward by a spring 110, and the heat collecting plate 104 is held in the state shown in FIG. 4 by a stopper (not shown). When the recording material 111 presses the heat collecting plate 104 downward as shown in FIG. 5, the heat collecting plate 104 can be retracted downward against the spring force of the spring 110. Thereby, it is possible to reduce the rubbing resistance of the heat collecting plate 104 to the recording material 111. Also in the present embodiment, at least before the leading edge of the recording material passes through the fixing nip portion, the temperature detecting portion of the temperature detecting means has a virtual straight line connecting the fixing nip portion of the fixing means and the nip portion of the conveying means. The recording material guide member is on the opposite side to the side on which the recording material guide member is disposed. This improves the temperature detection accuracy.

(Fifth embodiment)
Next, a fifth embodiment will be described with reference to FIGS.

  6 and 7 show an example of another configuration in which the heat collecting plate 104 attached to the fixing paper discharge guide 103 is retracted when receiving a force from the recording material. FIG. 6 shows the state of the home position, and FIG. 7 shows the state of the temperature detection position. In FIG. 6, the heat collecting plate 104 is fixed to the heat collecting plate mounting portion 103 c of the fixing paper discharge guide 103 at one end by the mounting member 112. When the recording material 111 presses the heat collecting plate 104 downward as shown in FIG. 7, the heat collecting plate 104 rotates in the direction of arrow M by its own spring property and can be retracted. Therefore, in this embodiment, the heat collecting plate itself corresponds to the moving member. Even in such a configuration, it is possible to reduce the rubbing resistance of the heat collecting plate 104 against the recording material 111.

(Sixth embodiment)
Next, a sixth embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

  Between the fixing nip portion N and the paper discharge roller (conveying means) nip portion, a fixing paper discharge guide 28 that forms a recording material conveyance path is provided. The fixing paper discharge guide is made of a material having high heat resistance such as PBT or PET. The conveyance surface of the fixing paper discharge guide is set below a virtual straight line A (see FIG. 13) connecting the fixing nip portion and the paper discharge roller nip portion, and the recording material conveyance speed in the paper discharge roller is the fixing nip portion N. Is set faster than the recording material conveyance speed in the recording medium, and when the recording material is sandwiched between the nip portion and fixing nip portion of the paper discharge roller, the conveyance surface of the recording material and the fixing paper discharge guide is not touched directly. It is like that.

  The fixing paper discharge guide 28 is provided with a moving member 29 having one end fixed to the apparatus main body. The moving member bends due to the urging force of the recording material when the recording material contacts (FIG. 12), and returns to the home position when the recording material does not contact (FIG. 11). This moving member is made of a thin plate having a thickness of about 0.1 mm, such as aluminum or stainless steel having a spring property and a small heat capacity.

  The heat collecting portion 31 of the moving member 29 is disposed so as to be above a virtual straight line A connecting the fixing nip and the paper discharge roller nip when the moving member 29 is located at the home position. Sometimes it comes in direct contact with the recording material. In other words, at least before the leading edge of the recording material passes through the fixing nip portion, the temperature detecting portion of the temperature detecting means is arranged with the recording material guide member as a boundary from the virtual straight line connecting the fixing nip portion of the fixing means and the nip portion of the conveying means. It is on the opposite side to the side that was made. In this way, by reducing the heat capacity of the recording material contact portion of the moving member and positively bringing it into contact with the recording material, the temperature of the heat collecting portion can be made substantially the same as the temperature of the recording material in a short time. become.

  When performing double-sided printing, the moving member comes into contact with the toner image on the first surface of the recording material when the second surface is passed, so there is a concern that toner adheres to the surface of the heat collecting portion. As a countermeasure, a surface treatment such as Teflon (registered trademark) or surface treatment such as UV coating may be applied to the surface of the heat collecting part as long as the heat conduction of the heat collecting part is not affected. Further, the surface of the heat collecting part may be coated with PI (polyimide) or the like.

  A highly sensitive temperature detection sensor 32 such as a thermistor is attached to the back surface of the heat collecting portion 31 at the tip of the moving member by a method such as adhesion (FIG. 14). When the recording material after image fixing is conveyed from the heat fixing device, the moving member falls due to the contact of the recording material, the heat collecting part comes into contact with the non-printing surface of the recording material, and the recording material is deprived of heat. The temperature of the recording material is detected by conducting heat to a temperature detection sensor installed in the printer. At this time, the temperature detection sensor is attached directly below the position where the recording material and the heat collecting part are in contact with each other, and by minimizing the influence of the temperature gradient in the heat collecting part, the temperature detection accuracy of the recording material is improved. It is increasing. Further, by using a metal member for the sliding portion with the recording material, wear of the sliding portion can be prevented and the durability of the moving member can be improved.

  The thermistor is an element that changes its resistance value according to temperature, and is enclosed in glass with a dumet wire 33 baked on the electrode of the thermistor chip. This dumet line is connected to the control circuit section and conveys temperature information detected by the thermistor.

  Further, the vicinity of the moving member will be described with reference to FIG. The pair of paper discharge rollers (conveying means) includes a paper discharge rubber roller 26 driven by a drive motor and a paper discharge roller 27 that rotates by receiving a drive from the paper discharge rubber roller 26. The fixing discharge guide 28 has a large clearance 36 with respect to the position where the moving member 29 rotates, and the recording material and the sheet passing surface of the fixing discharge guide are in contact with each other in the vicinity of the portion where the recording material and the moving member are in contact with each other. It is configured not to. As a result, the heat in the vicinity of the heat collecting portion can be prevented from being released to the fixing paper discharge guide, and the temperature detection accuracy of the recording material is improved. Further, when the moving member is pushed down by the recording material (temperature detection position) as shown in FIGS. 12 and 14, the position of the temperature detecting portion of the moving member is the same as the paper discharge rubber roller 26 in the sheet passing direction of the recording material. The position is set to be substantially the same as the position of the nip portion of the paper roller 27. With this configuration, when the moving member 29 is in the temperature detection position, the recording material urging position of the moving member 29 and the nip position by the paper discharge rubber roller 26 and the paper discharge roller 27 are substantially the same in the recording material conveyance direction. The bending of the recording material due to the urging force of the member 29 can be suppressed. Further, since the bending of the recording material can be suppressed, the recording material can be prevented from floating from the temperature detection unit, which is effective in improving the temperature detection accuracy.

(Seventh embodiment)
FIG. 16 is a cross-sectional view of the vicinity of the recording material temperature detecting portion of the seventh embodiment of the image forming apparatus of the present invention, FIG. 17 is a perspective view when the moving member is viewed from the upstream side in the recording material moving direction, and FIG. FIG. 6 is a perspective view when the member is viewed from the downstream side in the recording material moving direction. Here, only the characteristic part is shown, and since other configurations and operations are the same as those of the sixth embodiment, description thereof will be omitted.

  The moving member 29 of the present embodiment is formed by integrating a plastic base material and a heat collecting plate 31 made of a thin plate having a thickness of about 0.1 mm (such as aluminum or stainless steel having a small heat capacity) by a technique such as outsert molding. It is configured. An electrode 34 of the thermistor described later is also integrally formed, and this electrode 34 has a function of urging the moving member from the temperature detection position toward the home position.

  As in the fourth to sixth embodiments, when the moving member 29 is at the home position, the heat collecting plate 31 is disposed above the virtual straight line connecting the fixing nip portion and the discharge roller nip portion. The leading end of the recording material that has passed through the fixing nip first contacts the plastic portion of the moving member. Further, when the recording material is sent to the downstream side, the moving member is pushed by the recording material and rotates, and the heat collecting plate 31 contacts the non-printing surface side of the recording material. Thus, by reducing the heat capacity of the heat collecting plate and positively contacting the recording material, the temperature of the heat collecting plate can be made substantially the same as the temperature of the recording material in a short time. Here, in order to reduce the heat capacity of the heat collecting plate, it is desirable that the heat collecting plate be as small as possible in the recording material conveyance direction and in the direction perpendicular to the recording material conveyance direction and in the direction substantially parallel to the width of the recording material. . Similarly to the sixth embodiment, when the moving member 29 is pushed down by the recording material (temperature detection position), the position of the temperature detecting portion of the moving member 29 is in the direction of passing the recording material with the paper discharge rubber roller. It is set to be substantially the same position as the position of the nip portion of the paper roller. With this configuration, when the moving member 29 is at the temperature detection position, the recording material urging position of the moving member 29 and the nip position by the paper discharge rubber roller and the paper discharge roller are substantially the same in the recording material conveyance direction. The bending of the recording material due to the urging force can be suppressed. Further, since the bending of the recording material can be suppressed, the recording material can be prevented from floating from the temperature detection unit, which is effective in improving the temperature detection accuracy.

  A highly sensitive temperature detection sensor 32 such as a thermistor is attached to the back surface of the heat collecting plate 31 at the tip of the moving member by a method such as adhesion. When the recording material P after image fixing is conveyed from the heat fixing device, the moving member is pushed and rotated by the recording material, the heat collecting plate 31 comes into contact with the non-printing surface of the recording material P, and the recording material P is heated. The heat is conducted to the temperature detection sensor 32 installed on the back surface to detect the temperature of the recording material. The temperature detection sensor is attached directly below the position where the recording material and the heat collecting plate are in contact with each other when the moving member rotates (when it is in the temperature detection position). By minimizing, the accuracy of temperature detection of the recording material is increased. Further, by using a metal member for the sliding portion with the recording material, wear of the sliding portion can be prevented and the durability of the moving member can be improved.

  The thermistor is an element whose resistance value changes with temperature, and is enclosed in glass with a dumet wire 33 baked on the electrode of the thermistor chip. In addition, the moving member 29 includes two electrodes 34 made of a metal such as stainless steel and is integrally formed with the plastic portion by a technique such as outsert molding (FIGS. 17 and 18). The aforementioned dumet wire 33 is welded to these two electrodes 34. Further, these electrodes 34 are connected to the control circuit unit and transmit temperature information detected by the thermistor.

  The electrode 34 is made of a sheet metal such as thin stainless steel having a thickness of about 0.1 mm. The electrode 34 serves to transmit temperature information of the thermistor to the control circuit unit, and at the same time, attaches the moving member from the temperature detection position to the home position. It also has a function to support. The end portion of the electrode 34 on the thermistor side is integrally formed with the plastic portion of the moving member, welded to the dumet wire 33 of the thermistor, and the other end portion is connected to a terminal fixed to the fixing sheet discharge guide. ing. When the moving member 29 rotates from the home position toward the temperature detection position, the electrode 34 is twisted about the terminal connection portion fixed as the moving member 29 rotates, and the moving member 29 is returned to the home position by this twisting. Directional force is generated. Further, the electrode 34 is configured in a crank shape as shown in FIGS. 17 and 18 so as to give an appropriate turning force to the moving member 29 and to prevent the electrode itself from being permanently deformed or broken by receiving repeated stress. The

  The moving member front end will be described in more detail. As described above, the heat collecting plate 31 made of a material having a small heat capacity is integrally formed with the plastic member 29 having a low thermal conductivity at the distal end portion of the moving member. Here, the back surface of the heat collecting plate is a cavity 35 except for the joint portion with the plastic member. That is, the rear surface of the heat collecting plate 31 is exposed when the moving member 29 is viewed from the downstream side in the recording material moving direction. As a result, the heat capacity in the vicinity of the heat collecting portion can be reduced, so that the heat collected in the temperature detecting sensor 32 can be prevented from being released, and the responsiveness of the temperature detecting sensor can be improved.

(Eighth embodiment)
Further, an eighth embodiment will be described with reference to FIG. In the present embodiment, the dumet wire of the thermistor is directly connected to the lead wire 37. This lead wire is connected to the control circuit section along the vicinity of the rotating shaft of the moving member, and transmits temperature information detected by the thermistor. The rotating force is applied to the moving member by a normal torsion coil spring 38.

  As described above, when the rotational force of the moving member is energized by the torsion coil spring 38 and the lead wire for transmitting the output of the thermistor is turned around the rotating shaft of the moving member, the moving member is rotated less frequently. Makes it possible to realize a sufficiently functioning temperature detection sensor with an inexpensive and simple configuration.

FIG. 3 is a cross-sectional view of the vicinity of a recording material temperature detection unit according to the first embodiment of the present invention. The perspective view of the recording material temperature detection part vicinity of the 2nd Embodiment of this invention. The perspective view of the recording material temperature detection part vicinity of the 3rd Embodiment of this invention. FIG. 10 is a cross-sectional view of the vicinity of a recording material temperature detection unit according to a fourth embodiment of the present invention, in which a recording material does not pass. FIG. 10 is a cross-sectional view of the vicinity of a recording material temperature detection unit according to a fourth embodiment of the present invention, in a state where the recording material passes. FIG. 10 is a cross-sectional view of the vicinity of a recording material temperature detection unit according to a fifth embodiment of the present invention, in which a recording material does not pass. FIG. 10 is a cross-sectional view of the vicinity of a recording material temperature detection unit according to a fifth embodiment of the present invention, in a state where the recording material is passing. 1 is a cross-sectional view of an electrophotographic printer showing an example of an image forming apparatus of the present invention. FIG. 6 is a cross-sectional view of an example in which the temperature of the recording material is detected using a temperature sensor that is not in contact with the recording material. FIG. 3 is a cross-sectional view of an example in which a recording material is sandwiched between a temperature sensor and a counter roller to detect the temperature of the recording material. It is sectional drawing of the recording material temperature detection part vicinity of the 6th Embodiment of this invention, and sectional drawing of the state which has not passed the recording material. It is sectional drawing of the recording material temperature detection part vicinity of the 6th Embodiment of this invention, and sectional drawing of the state through which the recording material has passed. Sectional drawing which showed the positional relationship of the virtual line which connects the fixing nip part of the 6th Embodiment of this invention, and the nip part of a conveyance roller, and a recording material conveyance guide. Sectional drawing which shows the recording material temperature detection state of the 6th Embodiment of this invention. The perspective view of the recording material temperature detection part vicinity of the 6th Embodiment of this invention. Sectional drawing which shows the recording material temperature detection state of the 7th Embodiment of this invention. The perspective view when the temperature detection means of the 7th Embodiment of this invention is seen from the recording material conveyance direction upstream. The perspective view when the temperature detection means of the 7th Embodiment of this invention is seen from the recording material conveyance direction downstream. The perspective view when the temperature detection means of the 8th Embodiment of this invention is seen from the recording material conveyance direction downstream.

Explanation of symbols

21 Fixing entrance guide 22 Fixing film 23 Heating element (heater)
24 Pressure Roller 25 Film Guide 103 Fixing and Discharging Guide 104 Heat Collection Plate 105 Temperature Sensor 106 Fixing Device 113 Discharge Roller Pair 114 Dumet Line

Claims (15)

An image forming unit that forms an image on a recording material, a fixing unit that has a fixing nip portion that sandwiches and conveys the recording material, and that heats and fixes an image on the recording material, and recording on the downstream side of the fixing nip portion in the recording material movement direction In an image forming apparatus having a temperature detecting means for detecting the temperature of the material,
The temperature detector of the temperature detector is disposed so as to be in contact with the surface opposite to the image surface at the time of single-sided printing of the recording material, and the recording material is in a state where the temperature detector is in contact with the recording material. An image forming apparatus characterized in that there is no opposing member in contact with the recording material in at least a region corresponding to the temperature detection unit on the image surface side.   The apparatus further includes a conveying unit that is driven by a driving source and conveys the recording material downstream of the fixing nip portion in the recording material moving direction, and the temperature detection unit is downstream of the fixing nip portion in the recording material moving direction. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is in contact with the recording material up to the conveying unit closest to the fixing nip portion.   The apparatus further includes a recording material guide member between the fixing unit and the conveying unit, and the recording material conveying speed of the conveying unit is set higher than the recording material conveying speed of the fixing unit. The image forming apparatus according to claim 2, wherein the recording material is set so as not to contact the recording material guide member in a state where the recording material is sandwiched between the fixing unit and the conveying unit.   The apparatus further includes a recording material guide member between the fixing unit and the conveying unit, and at least before the leading end of the recording material passes through the fixing nip, the temperature detecting unit of the temperature detecting unit is the fixing unit. 3. The image forming apparatus according to claim 2, wherein the image forming apparatus is located on a side opposite to a side where the recording material guide member is disposed, with a virtual straight line connecting the fixing nip portion of the recording medium and the nip portion of the conveying unit as a boundary.   The temperature detecting means includes a moving member that can move to a temperature detecting position when detecting the temperature of the home position and the recording material, and the temperature detecting unit is provided on the moving member. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 5, wherein the moving member moves from a home position to a temperature detection position by contact of the recording material, and returns to the home position when the recording material leaves.   The image forming apparatus according to claim 6, wherein the moving member is movable in a direction substantially perpendicular to the surface of the recording material.   The image forming apparatus according to claim 6, wherein the moving member is tilted in a recording material moving direction by contact of the recording material.   The image forming apparatus according to claim 6, wherein an electrode of the temperature detection unit is attached to the moving member, and the electrode has a function of returning the moving member to a home position.   The apparatus further includes an urging member that urges the moving member toward a home position, and an electrical wiring extending from the temperature detection unit is provided in the vicinity of the rotating shaft of the moving member. The image forming apparatus according to claim 8.   The apparatus further includes a conveying unit that is driven by a driving source and conveys the recording material downstream of the fixing nip portion in the recording material moving direction, and when the moving member moves to a temperature detection position, the temperature detection unit 6. The image forming apparatus according to claim 5, wherein the position is substantially the same position as the nip portion of the conveying unit in the recording material moving direction.   The temperature detection unit is provided with a heat transfer plate, and the temperature detection element is in contact with a surface opposite to the recording material contact surface of the heat transfer plate. Image forming apparatus.   The image forming apparatus according to claim 12, wherein the heat transfer plate is a metal.   The image forming apparatus according to claim 12, wherein the heat transfer plate is attached to a resin base material.   2. The fixing unit according to claim 1, wherein the fixing unit forms the fixing nip portion by a heat generating unit and a backup unit, and the heat generating unit is disposed on an image surface side during single-sided printing of a recording material. Image forming apparatus.

Images