JP2008225066A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a fixing device and an image forming apparatus, by which the circumferential speed of a fixing member is maintained as a fixed reference circumferential speed. <P>SOLUTION: A marking material 130 is provided to a fixing belt 102 and a photosensor 126 is arranged in a passage region of the marking material 130. A circumferential speed V of the fixing belt 102 is obtained, by dividing circumferential length of the fixing belt 102 by a period T1 of a pulse signal output from the photosensor 126. Here, when the circumferential speed V is different from a reference circumferential speed Vp, a drive motor 88 is driven based on speed difference between V-Vp. Thus, circumferential speed detection of the fixing belt 102 is performed and controlled so as to be predetermined circumferential speed. In addition, winding detection of a recording paper P to the fixing belt 102 is performed, by setting a standard value to pulse width of the pulse signal and comparing the standard value with the actually measured pulse width. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer or a copying machine that forms an image using an electrophotographic method, a toner image transferred onto a recording sheet is pressed with a fixing roll or a fixing belt having a heat source such as a halogen heater. A fixing device that melts and fixes toner by the action of heat and pressure through a nip formed by a roll is used.

  In such a fixing device, the fixing roll or the pressure roll is thermally expanded by heating, the outer diameter is changed, and the peripheral speed may be increased when the fixing roll or the pressure roll is rotated at a predetermined rotational speed.

  In some cases, the melted toner acts like an adhesive and the recording paper is wound around the fixing roll or the fixing belt.

  Here, a fixing device having means for preventing the recording paper from being wound around the fixing roll or the fixing belt or minimizing the winding has been proposed.

  As a fixing device having a winding prevention means, there is a fixing device that electrostatically attracts a recording sheet to the pressure belt side (see, for example, Patent Document 1).

  The fixing device of Patent Document 1 includes a fixing roll and a pressure belt. The charge roller imparts a charge having a polarity opposite to that of the toner to the surface of the pressure belt to polarize the charge in the recording paper. Recording paper is adsorbed.

  As a fixing device having means for minimizing winding, there is a fixing device that detects a winding state using a paper detection sensor (see, for example, Patent Document 2).

The fixing device of Patent Document 2 uses paper detection sensors at the entrance and the exit of the fixing device, respectively, and the recording paper is detected by the paper detection sensor at the exit within a predetermined time after the recording paper passes through the entrance paper detection sensor. If no is detected, it is determined that the belt is wound, and the fixing roll driving means is brake controlled.
Japanese Patent Laid-Open No. 2004-133377 Japanese Patent Laid-Open No. 2004-354983

  An object of the present invention is to provide a fixing device and an image forming apparatus in which the peripheral speed of the fixing member is maintained at a constant reference peripheral speed.

  According to a first aspect of the present invention, there is provided a fixing device in which both ends thereof are rotatably supported, a driving unit that rotationally drives the fixing member, a pressure member that pressurizes the surface of the fixing member, A detected portion provided on an outer peripheral surface of the fixing member; a light emitting portion that irradiates the light to a region where the detected portion is present; and a light receiving portion that receives the light reflected in the region where the detected portion is present; Detecting means for generating a pulse signal when the amount of light received by the light receiving unit varies, and measuring a pulse width and a period of the pulse signal, and based on the pulse width or the period, Control means for calculating the peripheral speed of the fixing member and driving the drive means so as to obtain a reference peripheral speed.

  According to the said structure, light is irradiated to the area | region with a to-be-detected part from the light emission part of a detection means. When the detected part exists on the optical path of the irradiated light, the light is reflected or transmitted by the detected part, and the amount of light received by the light receiving part varies. As a result, a pulse signal is generated with 1 (HI) when the amount of received light is large and 0 (LO) when the amount of received light is small.

  Subsequently, the control means measures the pulse width or period of the pulse signal. The width and period of the pulse signal have a constant width and a constant period while the fixing member rotates at a constant peripheral speed.

  Subsequently, the control means calculates the peripheral speed of the fixing member based on the pulse width or cycle. Here, when the peripheral speed of the fixing member fluctuates due to thermal expansion of the pressure member, a difference occurs between the peripheral speed obtained by calculation and the reference peripheral speed.

  Based on the difference in peripheral speed, the control means drives the drive means so that the peripheral speed of the fixing member is the same as the reference peripheral speed. In this way, the peripheral speed of the fixing member is maintained at a constant reference peripheral speed.

  In the fixing device according to claim 2 of the present invention, when the pulse width of the pulse signal is larger than a predetermined width, or when the cycle of the pulse signal is longer than the predetermined cycle, the control unit is configured to have the driving unit It is characterized by stopping.

  According to the above configuration, immediately after the recording medium passes between the fixing member and the pressure member, the electrostatic attractive force or the melted developer may act as an adhesive, and the recording medium may be wound around the fixing member. .

  When the recording medium is wound around the fixing member during fixing, a load is applied to the fixing member, the peripheral speed of the fixing member becomes slower than the reference peripheral speed, and the pulse width of the pulse signal becomes larger than a predetermined width. Further, the period of the pulse signal becomes longer than the predetermined period.

  Thus, by measuring and determining the pulse width or cycle, it is possible to detect the winding of the recording medium without a sensor for detecting the recording medium.

  In the fixing device according to claim 3 of the present invention, when the detected portion is disposed in a recording medium passage region of the fixing member, and the light receiving portion does not detect the light when the fixing member is rotated, The control means stops the driving means.

  According to the above configuration, while the recording medium passes between the fixing member and the pressure member, the detection unit detects the light reflected by the detected portion, and the control unit drives and controls the fixing member. Thus, the peripheral speed of the fixing member is kept constant.

  On the other hand, immediately after the recording medium passes between the fixing member and the pressure member, the electrostatic attraction force or the melted developer may act as an adhesive, and the recording medium may wrap around the fixing member.

  When the recording medium is wound around the fixing member, the detected portion is covered with the recording medium, so that light is not detected by the detecting means.

  Here, the control means detects that light is no longer detected by the detection means, and stops the drive means. Thereby, the amount of winding of the recording medium wound around the fixing member is reduced, and it becomes easy to remove the recording medium from the fixing member.

  An image forming apparatus according to a fourth aspect of the present invention is a fixing device according to any one of the first to third aspects, an exposure unit that emits exposure light, and a latent image formed by the exposure light. Is developed with a developer to form a developer image, a transfer unit that transfers the developer image made visible at the development unit onto a recording medium, and the developer image is transferred at the transfer unit. And a transport unit that transports the recorded recording medium to the fixing device.

  According to the above configuration, the peripheral speed of the fixing member in the fixing device is a constant reference peripheral speed, and the recording medium conveyance speed is constant, so that image disturbance is less likely to occur when the developer is fixed to the recording medium.

  According to the first aspect of the present invention, the peripheral speed of the fixing member is maintained at a constant reference peripheral speed as compared with the case where this configuration is not provided.

  According to the second aspect of the present invention, the winding of the recording medium can be detected without a sensor for detecting the recording medium.

  According to the third aspect of the present invention, the recording medium can be easily removed from the fixing member as compared with the case where this configuration is not provided.

  According to the fourth aspect of the present invention, image distortion is less likely to occur when the developer is fixed on the recording medium as compared with the case where the present configuration is not provided.

  A first embodiment of a fixing device and an image forming apparatus of the present invention will be described with reference to the drawings.

  FIG. 1 shows a printer 10 as an image forming apparatus.

  In the printer 10, optical scanning that emits a light beam corresponding to each toner of yellow (Y), magenta (M), cyan (C), and black (K) in a housing 12 constituting the main body of the printer 10. Devices 14Y, 14M, 14C and 14K are fixed. A control unit 70 that controls the operation of each unit of the printer 10 is provided at a position adjacent to the optical scanning device 14K.

  The optical scanning devices 14Y, 14M, 14C, and 14K scan the light beam emitted from the light source with a rotating polygon mirror (polygon mirror) (not shown) and reflect the light beam with a plurality of optical components such as a reflection mirror to each toner. Corresponding light beams 16Y, 16M, 16C, and 16K are emitted.

  The light beams 16Y, 16M, 16C, and 16K are guided to the corresponding photoreceptors 18Y, 18M, 18C, and 18K, respectively. Each of the photoconductors 18Y, 18M, 18C, and 18K is rotated in the direction of arrow A by driving means including a motor and a gear (not shown).

  Chargers 20Y, 20M, 20C, and 20K that charge the surfaces of the photoreceptors 18Y, 18M, 18C, and 18K are provided on the upstream side in the rotation direction of the photoreceptors 18Y, 18M, 18C, and 18K.

  Further, on the downstream side in the rotation direction of the photoconductors 18Y, 18M, 18C, and 18K, developing units 22Y, 22M that develop the Y, M, C, and K toners on the photoconductors 18Y, 18M, 18C, and 18K, respectively. 22C and 22K are provided.

  An intermediate transfer belt 28 on which the developed toner images are primarily transferred is disposed downstream of the developing units 22Y, 22M, 22C, and 22K in the rotation direction of the photoreceptors 18Y, 18M, 18C, and 18K.

  The intermediate transfer belt 28 is constituted by a film-like endless belt in which an appropriate amount of an antistatic agent such as carbon black is contained in a resin such as polyimide or polyamide. And the volume resistivity is formed so that it may become 106-1014 ohm-cm, The thickness is comprised by about 0.1 mm, for example.

  At the position where the photoconductors 18Y, 18M, 18C, 18K and the intermediate transfer belt 28 face each other, the respective color toner images formed on the photoconductors 18Y, 18M, 18C, 18K are placed inside the intermediate transfer belt 28. Primary transfer rolls 24Y, 24M, 24C, and 24K that transfer to the ink are disposed. The primary transfer rolls 24Y, 24M, 24C, and 24K constitute a primary transfer unit 25 that performs primary transfer from the photoreceptors 18Y, 18M, 18C, and 18K to the intermediate transfer belt 28.

  The primary transfer rolls 24Y, 24M, 24C, and 24K have a shaft (not shown) and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll made of a blend rubber of NBR, SBR, and EPDM blended with a conductive agent such as carbon black and having a volume resistivity of 107.5 to 108.5 Ωcm.

  The primary transfer rolls 24Y, 24M, 24C, and 24K are pressed against the photoreceptors 18Y, 18M, 18C, and 18K with the intermediate transfer belt 28 interposed therebetween. The primary transfer rolls 24Y, 24M, 24C, and 24K are applied with a voltage (primary transfer bias) having a polarity opposite to the charging polarity (negative polarity; the same applies hereinafter) of each toner by a voltage applying unit (not shown). It has become. As a result, the toner images on the photoconductors 18Y, 18M, 18C, and 18K are electrostatically attracted sequentially to the intermediate transfer belt 28, and a superimposed toner image is formed on the intermediate transfer belt 28. Yes.

  Further, cleaners 26Y, 26M, 26C, and 26K for removing residual toner on the photoconductors 18Y, 18M, 18C, and 18K are provided on the downstream side in the rotation direction of the photoconductors 18Y, 18M, 18C, and 18K.

  Inside the intermediate transfer belt 28, a driving roll 30 that is driven by a motor (not shown) having excellent constant speed to move the intermediate transfer belt 28, and the arrangement direction of the photoreceptors 18Y, 18M, 18C, and 18K A support roll 32 that extends in a substantially straight line and supports the intermediate transfer belt 28 is provided. Thereby, the intermediate transfer belt 28 is driven to circulate at a predetermined speed in the arrow B direction.

  A tension roll 34 is provided inside the intermediate transfer belt 28 to apply a constant tension to the intermediate transfer belt 28 and prevent the intermediate transfer belt 28 from meandering.

  A secondary transfer portion 42 that transfers the toner image on the fixing belt 28 onto the recording paper P is provided on the downstream side in the moving direction of the intermediate transfer belt 28.

  The secondary transfer unit 42 includes a secondary transfer roll 38 disposed on the toner image carrying surface side of the intermediate transfer belt 28 and a backup roll 36.

The secondary transfer roll 38 includes a shaft (not shown) and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is formed of a blend rubber of NBR, SBR, and EPDM containing a conductive agent such as carbon black, and has a volume resistivity of 1 × 10 ^7.5 Ωcm to 1 × 10 ^8.5 Ωcm. It is a cylindrical roll.

  The secondary transfer roll 38 is disposed in pressure contact with the backup roll 36 with the intermediate transfer belt 28 interposed therebetween. Here, the secondary transfer roll 38 is grounded and a secondary transfer bias is applied between the secondary transfer roll 38 and the backup roll 36, and the toner image is secondarily transferred onto the recording paper P conveyed to the secondary transfer unit 42. It is like that.

The backup roll 36 is composed of a EPDM and NBR blend rubber tube with carbon dispersed on the surface, and an EPDM rubber inside. The surface resistivity is 1 × 10 ⁷ Ω / □ or more and 10 ¹⁰ Ω / □ or less, and the hardness is set to 70 ° (Asker C), for example.

  The backup roll 36 is disposed on the back surface side of the intermediate transfer belt 28 to form a counter electrode of the secondary transfer roll 38, and the backup roll 36 is connected to the backup roll 36 through a metal power supply roll 40 disposed in contact with the backup roll 36. The next transfer bias is applied stably.

  An intermediate transfer belt cleaner 46 that removes residual toner and paper dust on the intermediate transfer belt 28 after the secondary transfer is provided downstream of the secondary transfer portion 42 in the moving direction of the intermediate transfer belt 28. It is provided so that it can contact and separate. A cleaning backup roll 44 is provided inside the intermediate transfer belt 28 in the intermediate transfer belt cleaner 46.

  On the other hand, on the upstream side of the primary transfer roll 24Y corresponding to yellow toner, a home position sensor 42 that generates a signal serving as a reference for adjusting the timing of image formation corresponding to each toner is provided.

  The home position sensor 42 detects a predetermined mark provided on the back side of the intermediate transfer belt 15 and generates a reference signal. Based on the reference signal, the control unit 70 operates each unit of the printer 10 to start image formation.

  An image density sensor 43 for adjusting image quality is provided on the downstream side of the primary transfer roll 24K corresponding to black toner.

  On the other hand, a paper tray 50 for storing the recording paper P is provided below the printer 10. A pickup roll 52 is provided at one end of the paper tray 50 to take out and transport the recording paper P at a predetermined timing.

  Above the pick-up roll 52, a plurality of transport rolls 54 that are driven to rotate by a driving means including a motor and gear (not shown) and transport the recording paper P delivered by the pick-up roll 52 to the secondary transfer unit 42 described above, 56 is provided.

  On the downstream side of the conveyance roll 56 in the conveyance direction of the recording paper P, a conveyance chute 58 for feeding the recording paper P to the secondary transfer unit 42 is provided.

  A conveying belt 60 that conveys the recording paper P, on which the secondary transfer of the toner image has been completed, to the fixing device 100 is provided in the sending direction of the recording paper P in the secondary transfer unit 42. The transport belt 60 is stretched by stretch rolls 57 and 59, and is provided so as to be movable by a driving means including a motor and a gear (not shown).

  A guide 62 for guiding the recording paper P to the fixing device 100 is provided on the inlet side of the fixing device 100. A paper stacking tray 64 fixed to the casing 12 of the printer 10 is provided on the exit side of the fixing device 100.

  Here, image formation of the printer 10 will be described.

  First, image data output from an image reading device (not shown) or a personal computer is subjected to predetermined image processing by an image processing device (not shown). The image processing apparatus performs predetermined image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, moving editing, and other various image editing on the input reflectance data. Is given. The image data subjected to the image processing is converted into color material gradation data of four colors Y, M, C, and K, and is output to the optical scanning devices 14Y, 14M, 14C, and 14K.

  The optical scanning devices 14Y, 14M, 14C, and 14K irradiate the photoconductors 18Y, 18M, 18C, and 18K with the light beams 16Y, 16M, 16C, and 16K according to the input color material gradation data.

  The surfaces of the photoreceptors 18Y, 18M, 18C, and 18K are charged in advance by the chargers 20Y, 20M, 20C, and 20K, and the surfaces are exposed by the light beams 16Y, 16M, 16C, and 16K, and an electrostatic latent image is formed. Is done. The formed electrostatic latent images are developed as toner images of respective colors Y, M, C, and K by developing units 22Y, 22M, 22C, and 22K.

  Subsequently, the toner images formed on the photoconductors 18Y, 18M, 18C, and 18K are transferred onto the intermediate transfer belt 28 in the primary transfer unit 25. In this transfer, the primary transfer rolls 24Y, 24M, 24C, and 24K apply a voltage (primary transfer bias) opposite to the toner charging polarity (minus polarity) to the intermediate transfer belt 28, and the toner image is transferred to the intermediate transfer belt 28. This is done by sequentially superimposing on the surface.

  Subsequently, the intermediate transfer belt 28 onto which the toner image has been transferred is conveyed to the secondary transfer unit 42.

  On the other hand, the pickup roll 52 rotates in accordance with the timing at which the toner image is conveyed to the secondary transfer unit 42, and a recording paper P having a predetermined size is sent from the paper tray 50.

  The recording paper P sent out by the pickup roll 52 is transported by the transport rolls 54 and 56, and reaches the secondary transfer unit 42 through the transport chute 58. Before reaching the secondary transfer portion 42, the recording paper P is temporarily stopped, and a registration roll (not shown) rotates in accordance with the movement timing of the intermediate transfer belt 28 on which the toner image is carried. The position of P and the position of the toner image are aligned.

  In the secondary transfer unit 42, the secondary transfer roll 38 is pressed against the backup roll 36 via the intermediate transfer belt 28. At this time, the recording paper P conveyed at the same timing is sandwiched between the intermediate transfer belt 28 and the secondary transfer roll 38.

  At this time, a voltage (secondary transfer bias) having the same polarity as the toner charging polarity (negative polarity) is applied from the power supply roll 40, and a transfer electric field is formed between the secondary transfer roll 38 and the backup roll 36. The The unfixed toner image carried on the intermediate transfer belt 28 is pressed by the secondary transfer roll 38 and the backup roll 36 and is electrostatically transferred onto the recording paper P at once.

  Subsequently, the recording paper P on which the toner image has been electrostatically transferred is conveyed as it is while being peeled off from the intermediate transfer belt 28 by the secondary transfer roll 38, and is conveyed to the conveyance belt 60.

  The conveyance belt 60 conveys the recording paper P to the fixing device 100 in accordance with the optimum conveyance speed in the fixing device 100. The unfixed toner image on the recording paper P conveyed to the fixing device 100 is fixed on the recording paper P by the fixing device 100.

  The recording paper P on which the fixed image is formed is discharged to the paper stacking tray 64 and stacked.

  On the other hand, after the transfer onto the recording paper P is completed, the residual toner remaining on the intermediate transfer belt 28 is conveyed to the intermediate transfer belt cleaner 46 as the intermediate transfer belt 28 rotates, and from the intermediate transfer belt 28. Removed.

  In this way, image formation by the printer 10 is performed.

  Next, the fixing device 100 will be described.

  As shown in FIG. 2, the fixing device 100 includes a fixing belt 102 having an endless peripheral surface inside a housing 106 made of heat-resistant resin and the like, and a fixing belt 102 that is in pressure contact with the outer peripheral surface of the fixing belt 102. The pressure roll 104 that is driven to rotate is arranged.

  Inside the fixing belt 102, a pressing member 108 that is pressed against the pressure roll 104 via the fixing belt 102, and a member support member 110 that supports the pressing member 108 and the like are provided.

  Outside the fixing belt 102, an electromagnetic induction heating unit 118 that generates a magnetic field and electromagnetically heats the fixing belt 102 in the longitudinal direction is provided.

  A ferrite member 112 that is formed following the shape of the peripheral surface of the fixing belt 102 and strengthens the magnetic field generated by the electromagnetic induction heating unit 118 is disposed inside the fixing belt 102 so as to have a predetermined gap. The ferrite member 112 increases the magnetic field and increases the heating efficiency of the fixing belt 102.

  On the other hand, a separation claw 128 for preventing the recording paper P from being wrapped around the fixing belt 102 is provided near the fixing belt 102 on the discharge side of the recording paper P.

  As shown in FIG. 3a, the fixing belt 102 includes a base layer 102a made of a sheet-like member having high heat resistance, a conductive layer 102b, an elastic layer 102c, and a surface release layer 102d serving as an outer peripheral surface in order from the inner peripheral side. And are laminated. In addition, a primer layer for adhesion may be provided between the layers.

  As the base layer 102a, a material having flexibility, excellent mechanical strength, and heat resistance, such as fluorine resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, PFA resin, PTFE resin, FEP resin, etc. Are preferably used. The thickness is 10 to 150 μm, preferably 30 to 100 μm. If the thickness is smaller than 10 μm, the strength as the fixing belt 61 cannot be obtained. If the thickness is larger than 150 μm, the flexibility is impaired, and the heat capacity increases and the temperature rise time becomes longer. is there. In the present embodiment, a sheet-like member made of polyimide resin having a thickness of 80 μm is used.

  The conductive layer 102b is a heat generation layer that generates heat by induction by a magnetic field induced by the electromagnetic induction heating unit 118, and is formed of a metal layer of iron, cobalt, nickel, copper, aluminum, chromium, or the like with a thickness of about 1 to 80 μm. Is used. The material and thickness of the conductive layer 102b are appropriately selected so as to realize a specific resistance value that can generate sufficient heat by eddy current due to electromagnetic induction. In the present embodiment, copper having a thickness of about 10 μm is used.

  The elastic layer 102c has a thickness of 10 to 500 [mu] m, preferably 50 to 300 [mu] m, and silicone rubber, fluorine rubber, fluorosilicone rubber or the like having excellent heat resistance and thermal conductivity is used. In the present embodiment, silicone rubber having a rubber hardness of 15 ° (JIS-A: JIS-KA type tester) and a thickness of 200 μm is used.

  By the way, when color image formation is performed, a solid image is often formed over a large area on the recording paper P, particularly when printing a photographic image or the like. Therefore, if the surface of the fixing belt 102 cannot follow the irregularities of the recording paper P or toner image, uneven heating occurs in the toner image, and uneven gloss occurs in the fixed image between the portion with a large amount of heat transfer and the portion with a small amount of heat transfer. To do. That is, the glossiness is high in the portion where the heat transfer amount is large, and the glossiness is low in the portion where the heat transfer amount is small.

  Such a phenomenon is likely to occur when the thickness of the elastic layer 102c is smaller than 10 μm. Therefore, the thickness of the elastic layer 102c is preferably set to 10 μm or more, more preferably 50 μm or more. On the other hand, when the elastic layer 102c is larger than 500 μm, the thermal resistance of the elastic layer 102c increases, and the quick start performance of the fixing device 100 decreases. Therefore, the thickness of the elastic layer 102c is preferably set to 500 μm or less, more preferably 300 μm or less.

  Further, if the rubber hardness of the elastic layer 102c is too high, glossiness unevenness is likely to occur in the fixed image because it cannot follow the unevenness of the recording paper P or toner image. Accordingly, the rubber hardness of the elastic layer 102c is 50 ° (JIS-A: JIS-KA type tester) or less, more preferably 35 ° or less.

Furthermore, regarding the thermal conductivity λ of the elastic layer 102c, λ is suitably 6 × 10 ⁻⁴ or more and 2 × 10 ⁻³ or less [cal / cm · sec · deg]. When the thermal conductivity λ is smaller than 6 × 10 ⁻⁴ [cal / cm · sec · deg], the thermal resistance is large, and the temperature rise in the surface layer (surface release layer 102d) of the fixing belt 102 is delayed.

On the other hand, when the thermal conductivity λ is larger than 2 × 10 ⁻³ [cal / cm · sec · deg], the hardness becomes excessively high or the compression set is deteriorated. Therefore, the thermal conductivity λ is 6 × 10 ⁻⁴ or more and 2 × 10 ⁻³ or less [cal / cm · sec · deg], more preferably 8 × 10 ⁻⁴ or more and 1.5 × 10 ⁻³ or less [cal / cm. • sec · deg] is preferable.

  Since the surface release layer 102d is a layer that is in direct contact with the unfixed toner image transferred onto the recording paper P, it is necessary to use a material having excellent release properties and heat resistance. Therefore, as a material constituting the surface release layer 102d, for example, tetrafluoroethylene perfluoroalkyl vinyl ether polymer (PFA), polytetrafluoroethylene (PTFE), fluororesin, silicone resin, fluorosilicone rubber, fluororubber, silicone Rubber or the like is preferably used.

  The thickness of the surface release layer 102d is preferably 5 μm or more and 50 μm or less. When the thickness of the surface release layer 102d is smaller than 5 μm, there is a problem that uneven coating occurs when the coating film is formed, an area having poor release properties is formed, or durability is insufficient. is there. In addition, when the thickness of the surface release layer 102d exceeds 50 μm, there is a problem that heat conduction is deteriorated, and in particular, the surface release layer 102d formed of a resin-based material has too high hardness, This is because the function of the elastic layer 102c is lowered. In this embodiment, PFA with a thickness of 30 μm is used.

  Here, in order to improve toner releasability in the surface release layer 102d, an oil application mechanism for applying oil (release agent) for preventing toner offset to the surface release layer 102d is brought into contact with the fixing belt 102. It is also possible to arrange them. This is particularly effective when a toner containing no low softening substance is used.

  Instead of the fixing belt 102, a fixing belt 202 as shown in FIG. 3b may be used. The fixing belt 202 is formed by dividing the heat resistant resin layers 202a and 202c into two layers, and a conductive layer 202b is formed therebetween. And the elastic layer 202d and the surface release layer 202e are laminated | stacked on the surface.

  In the fixing belt 202, even when the metal layer that is the conductive layer 202b is formed thin, deterioration due to repeated bending deformation can be suppressed. The heat resistant resin layers 202a and 202c are not limited to the heat resistant resin.

  On the other hand, as shown in FIG. 2, the pressure roll 104 is made of a metal cylindrical member 104a as a core material (core) and laminated on the surface of the cylindrical member 104a. Silicone rubber, foamed silicone rubber, fluorine rubber , A heat-resistant elastic layer 104b such as a fluororesin, and an outermost surface release layer 104c.

  The pressure roll 104 is disposed in parallel with the rotation axis of the fixing belt 102, and both ends thereof are urged and supported by the fixing belt 102 by spring members (not shown). The pressure roll 104 is urged by the pressing member 108 through the fixing belt 102 so as to have a total load 294N (30 kgf).

  Here, the fixing roll 102 is rotated in the arrow X direction by a driving unit such as a motor and a gear (not shown). The pressure roll 104 is driven to rotate in the direction indicated by the arrow Y by the rotation of the fixing roll 102.

  The pressing member 108 is made of an elastic material such as silicone rubber or fluororubber, a heat resistant resin such as polyimide resin, polyphenylene sulfide (PPS), polyethersulfone (PES), or liquid crystal polymer (LCP). Further, the pressing member 108 is arranged over a region slightly wider than the region (sheet passing region) through which the recording paper P passes in the width direction of the fixing belt 102, and the pressing member 108 has a substantially entire length in the longitudinal direction. It is comprised so that the pressure roll 104 may be pressed over.

  The contact surface between the pressing member 108 and the fixing belt 102 is formed as a concave curved surface following the outer surface shape of the pressure roll 104. Therefore, a sufficiently wide nip width can be formed with the pressure roll 104 via the fixing belt 102.

  Furthermore, between the pressing member 108 and the fixing belt 102, a polyimide film having excellent slidability and high wear resistance in order to improve the sliding property between the pressing member 108 and the fixing belt 102 in the fixing nip portion N. And a sliding sheet 108a made of a glass fiber sheet impregnated with fluorine resin or the like.

  A lubricant is applied to the inner peripheral surface of the fixing belt 102. As the lubricant, amino-modified silicone oil, dimethyl silicone oil, or the like is used. Accordingly, the frictional resistance between the fixing belt 102 and the pressing member 108 is reduced, and the fixing belt 102 can be smoothly rotated.

  The member support member 110 is a rod-shaped member having an axis in the width direction of the fixing belt 102. A pressing member 108 is attached to a portion of the member supporting member 110 that faces the pressing roll 104, and the pressing force acting on the pressing member 63 from the pressing roll 104 via the fixing belt 102 is applied by the member supporting member 110. I bear it.

  As the material constituting the member support member 110, a material having such a rigidity that the bending amount when receiving the pressing force from the pressure roll 104 is not more than a predetermined level, preferably not more than 1 mm is used.

  Further, the material of the member support member 110 needs to be hardly affected by the magnetic flux generated by the electromagnetic induction heating unit 118 described above. For this reason, as the member support member 110, for example, a heat-resistant resin such as PPS containing glass fiber, phenol, polyimide, or a liquid crystal polymer, heat-resistant glass, or a metal such as aluminum that has a small specific resistance and is not easily affected by induction heating is used. In the present embodiment, the member support member 110 is made of aluminum formed to have a rectangular cross-sectional shape having a long axis in the pressing force direction from the pressure roll 104.

  Further, a thermistor 116 for detecting the temperature of the fixing belt 102 is fixed to the side surface of the member supporting member 110 so as to be in pressure contact with the inner peripheral surface of the fixing belt 102 via a spring member 114.

  The thermistor 116 is disposed at the center in the longitudinal direction of the fixing belt 102. Further, another thermistor (not shown) is disposed at one end of the fixing belt 102. Further, the member support member 110 is also provided with a thermo switch (not shown) in contact with or close to the fixing belt 102.

  As the temperature detecting means, a thermistor for detecting the surface temperature of the pressure roll 104 may be provided instead of the thermistor 116 or the like, or in addition to the thermistor 70 or the like.

  Next, the electromagnetic induction heating unit 118 will be described.

  As shown in FIG. 2, the electromagnetic induction heating unit 118 includes a pedestal 120 having a curved surface following the outer peripheral surface shape of the fixing belt 102 along the width direction of the fixing belt 102, and an excitation coil 122 supported by the pedestal 120. And an exciting circuit 124 for supplying a high-frequency current to the exciting coil 122 constitutes a main part.

  The pedestal 120 is made of a material having insulating properties and heat resistance. For example, a phenol resin, a polyimide resin, a polyamide resin, a polyamideimide resin, a liquid crystal polymer resin, or the like can be used.

  As the exciting coil 122, for example, a long litz wire made by bundling a plurality of copper wires having a diameter of 0.1 to 0.5 mm insulated from each other by a heat-resistant insulating material (for example, polyimide resin, polyamideimide resin, etc.) is used. A closed loop shape such as a circular shape, an elliptical shape, or a rectangular shape is used that is wound a plurality of times (for example, 11 turns). And the excitation coil 122 is being fixed to the base 120, maintaining the shape by being hardened with the adhesive agent.

  Further, the distance between the exciting coil 122 and the ferrite member 112 and the conductive layer 102b of the fixing belt 102 is preferably set as close as possible in order to increase the magnetic flux absorption efficiency. Is set within 5 mm, for example, about 2.5 mm.

  In the electromagnetic induction heating unit 118, when a high-frequency current is supplied from the excitation circuit 124 to the excitation coil 122, magnetic flux repeatedly generates and disappears around the excitation coil 122. Here, the frequency of the high-frequency current is set to, for example, 10 kHz or more and 500 kHz or less, but is set to 20 kHz or more and 100 kHz or less in the present embodiment.

When the magnetic flux from the exciting coil 122 crosses the conductive layer 102b of the fixing belt 102, a magnetic field is generated in the conductive layer 102b to prevent the change of the magnetic field, thereby generating an eddy current in the conductive layer 102b. In the conductive layer 102b, Joule heat (W = I ² R) proportional to the skin resistance (R) of the conductive layer 102b is generated by the eddy current (I), and the fixing belt 102 is heated.

  The temperature of the fixing belt 102 controls the amount of power supplied to the exciting coil 122 or the supply time of the high-frequency current, etc., by the control unit 70 (see FIG. 1) of the image forming apparatus based on the measured value of the thermistor 116 described above. By doing so, it is maintained at a predetermined temperature.

  Next, driving of the fixing belt 102 will be described.

  The fixing device 100 (see FIG. 1) includes a drive motor 88 (see FIG. 5) that drives the fixing belt 102. The driving belt 88 drives the fixing belt 102, and the pressure roll 104 is driven to rotate as the fixing belt 102 rotates.

  In addition, the fixing device 100 includes a retract mechanism 90 (see FIG. 5) that fixes the attachment position on the fixing belt 102 side and contacts and separates the pressure roll 104 from the fixing belt 102.

  The retract mechanism 90 can be constituted by a combination of, for example, a motor and an eccentric cam. By this retract mechanism 90, the fixing belt 102 and the pressure roll 104 can be contacted and separated as required.

  On the other hand, as shown in FIG. 4, traveling guides 138 for supporting the fixing belt 102 and rotating the fixing belt 102 by the drive motor 88 are disposed at both ends in the axial direction of the member support member 110. . The fixing belt 102 is configured to rotate while maintaining a predetermined shape (for example, a substantially circular shape) by the inner peripheral surfaces of both ends being supported by the travel guide 138.

  The travel guide 138 is inserted into the end portion of the fixing belt 102 and supports the fixing belt 102. The travel guide 138 is integrally formed with the end cap 132, and is disposed outside the end cap 132 in the axial direction of the fixing belt 102. The drive gear 134 has a rotating shaft 136 that is configured integrally with the member support member 110 and that rotatably holds the end cap 132 and the drive gear 134. The drive gear 134 is engaged with a drive gear (not shown) provided on the drive motor 88.

  The fixing belt 102 rotates while being supported by the end cap 132. When the pressure roll 104 is in pressure contact with the fixing belt 102 by the retract mechanism 90 (see FIG. 5), the pressure roll 104 is driven to rotate as the fixing belt 102 rotates.

  Further, the fixing belt 102 is restricted from moving in the width direction of the fixing belt 102 (belt walk) by the drive gear 134, and is prevented from being shifted in the moving region of the fixing belt 102.

  Next, the control unit 70 of the printer 10 will be described.

  As shown in FIG. 5, the control unit 70 is measured by a central processing unit (CPU) 72 that performs various controls of the printer 10, a program storage unit (ROM) 74 that stores various control programs, and the thermistor 116 described above. A data storage unit (RAM) 76 that temporarily stores or deletes the measured temperature measurement data or other measurement data, and a timer 78 that operates at a predetermined clock.

  The central processing unit 72 is connected to an input / output interface 80 through which various signals are input / output. Via the input / output interface 80, a switch 82, a user interface (UI) 84, a thermistor 116, a drive motor 88, The retraction mechanism 90 and the excitation circuit 124 are connected. The switch 82 is a switch for turning on / off the power of the printer 10 (see FIG. 1), and the user interface 84 is configured by an input panel or the like for the user to directly instruct execution of image formation or the like. ing.

  Here, signals are input to the CPU 72 from the switch 82, the user interface 84, and the thermistor 116 via the input / output interface 80. On the other hand, a control signal from the CPU is output to the drive motor 88, the retract mechanism 90, and the excitation circuit 124 via the input / output interface 80.

  Next, generation of a pulse signal used for detecting the peripheral speed of the fixing belt 102 will be described.

  As shown in FIGS. 2 and 6, the photo sensor 126 is disposed opposite to the outer peripheral surface of the fixing belt 102 at a predetermined distance.

  As shown in FIG. 6 b, the photosensor 126 radiates the light emitting unit 123 that emits light and the reflected light (RL) reflected by the object to be detected into the housing 121 that constitutes the main body of the photosensor 126. A light receiving unit 125 that receives light and converts it into an electrical signal.

  A power supply line 127 and a signal line 129 are connected to the photosensor 126. Here, light is emitted from the emission unit 123 by being supplied with power from a power source (not shown) via the power line 127.

  The other end of the signal line 129 is connected to the CPU 72 (see FIG. 5) via the aforementioned input / output interface 80 (see FIG. 5), and is generated based on the amount of light received by the light receiving unit 125. The electrical signal (pulse signal) thus transmitted is sent to the CPU 72 through the signal line 129.

  As shown in FIG. 6a, in the longitudinal direction, the fixing belt 102 includes a paper passing area (L2) through which the recording paper P (traveling in the direction of the arrow C) passes and a non-paper passing area (L1, L3). Here, a rectangular mark member 130 made of aluminum foil is provided in the non-sheet passing region L3 of the fixing belt 102.

  As shown in FIG. 6b, the mark material 130 is embedded in advance between the elastic layer 102C and the surface release layer 102d in the process of manufacturing the fixing belt 102. The thickness of the mark material 130 is 6 μm.

  The surface release layer 102d of the fixing belt 102 is configured to be able to transmit the light emitted from the emission part 123 of the photosensor 126 described above, and the light incident on the surface release layer 102d is the mark material 130. The light is reflected by the surface and is received by the light receiving unit 125 as reflected light RL.

  Further, as shown in FIG. 6a, the mounting position of the photosensor 126 described above is a position facing the moving region (L4) in which the mark material 130 moves.

  Here, when the fixing belt 102 rotates in the arrow X direction, the mark material 130 also moves in the arrow X direction.

  When the mark material 130 comes to a position facing the photo sensor 126, light is reflected by the mark material 130, so that an HI signal is output from the photo sensor 126. On the other hand, when the mark material 130 is not located at the position facing the photosensor 126, the reflected light RL hardly enters the photosensor 126 because light is diffusely reflected on the surface of the fixing belt 102. Is output.

  Thereby, a pulse signal composed of the HI signal and the LO signal is generated.

  Next, the fixing operation of the fixing device 100 will be described.

  As shown in FIG. 2, power is supplied to the drive motor 88 (see FIG. 5) and the electromagnetic induction heating unit 118 almost simultaneously with the start of image formation of the toner image in the image forming process described above. Rotate. At this time, the pressure roll 104 is separated from the fixing belt 102 by the retract mechanism 90.

  Subsequently, as the fixing belt 102 passes through a heating region facing the electromagnetic induction heating unit 118, an eddy current is induced in the conductive layer 102b of the fixing belt 102, and the fixing belt 102 generates heat.

  Subsequently, the pressure roller 104 is pressed against the fixing belt 102 by the retract mechanism 90 at a predetermined timing. As a result, the pressure roll 104 rotates following the fixing belt 102.

  Subsequently, the temperature is detected by the thermistor 116 and feedback control is performed, whereby the fixing belt 102 is heated to a predetermined temperature. In this state, the recording paper P carrying the unfixed toner image is fed into the fixing nip portion N between the fixing belt 102 and the pressure roll 104.

  In the fixing nip portion N, the toner image is heated and pressurized and fixed on the recording paper P.

  Subsequently, the recording paper P is peeled from the fixing belt 102 due to a change in the curvature of the fixing belt 102 at the exit of the fixing nip N, and is conveyed to the paper stacking tray 64.

  Next, the operation of the first embodiment of the present invention will be described.

  First, the speed detection of the fixing belt 102 will be described.

  As shown in FIG. 8, when the recording paper P is not wrapped around the fixing belt 102 (see FIG. 2) (normal time), the pulse of the HI portion of the pulse signal output from the photosensor 126 (see FIG. 2). The width is W1. The period of the pulse signal is T1.

  Here, the peripheral speed V of the fixing belt 102 is obtained by dividing the outer peripheral length of the fixing belt 102 by the period T1 of the pulse signal. Alternatively, the length of the mark material 130 (see FIG. 6) in the moving direction may be divided by the time (t) of the pulse width W1.

  When the peripheral speed V of the fixing belt 102 is different from a predetermined peripheral speed Vp serving as a reference, the control unit 70 (see FIG. 5) controls the drive motor 88 (see FIG. 5) based on the V-Vp speed difference. Drive).

  In this manner, the speed of the fixing belt 102 is detected based on the pulse signal, and is controlled so as to have a predetermined speed.

  Next, detection of winding of the recording paper P around the fixing belt 102 will be described.

  A pulse signal when the recording paper P passes between the fixing belt 102 and the pressure roll 104 is measured in advance, and based on this, the pulse width when the recording paper P is not wound around the fixing belt 102 is measured. And determine the standard value of the cycle.

  At the time of fixing, in a state where the recording paper P starts to be wound around the image forming fixing belt 102 (at the time of winding), a continuous load acts on the fixing belt 102 and the peripheral speed V becomes slow. The pulse width W2 is enlarged. The period of the pulse signal also increases from T1 to T2.

  Here, the standard value (tp) of the pulse width is compared with the measured pulse width (t), and when t ≧ tp, it is determined that the recording paper P is wound. Although the period of the pulse signal can be compared, in the case of the period, since comparison cannot be performed until the fixing belt 102 makes one rotation, it is preferable to compare with the pulse width.

  In this manner, the winding of the recording paper P around the fixing belt 102 is detected based on the pulse width.

Next, a processing flow of the fixing device 100 will be described. FIG. 7 shows a processing flow for detecting the speed of the fixing belt 102 and detecting the winding of the recording paper P in the fixing device 100.

  As shown in FIGS. 1, 2, and 7, after the warm-up of the printer 10 is started, the fixing belt 102 starts to rotate and a timer (not shown) for measuring the peripheral speed V of the fixing belt 102. ) Is started (S101).

  Subsequently, a timer (not shown) for measuring the pulse width W1 (time t) of the pulse signal (see FIG. 8) output from the photosensor 126 is started (S102).

  Subsequently, when the peripheral speed V of the fixing belt 102 exceeds the predetermined starting speed V1 (S103), it is determined that the fixing belt 102 is rotating without any problem, and power is supplied to the excitation circuit 124 that is a heating source. (S104). If the peripheral speed V does not exceed the predetermined start speed V1, the rotation of the fixing belt 102 is stopped (S112).

  Subsequently, when the temperature of the fixing belt 102 detected by the thermistor 116 reaches a predetermined fixing set temperature T1 (S105), image formation of the printer 10 is started (S106). If the predetermined fixing set temperature T1 has not been reached, power is continuously supplied to the excitation circuit 124 and waits until the predetermined fixing set temperature T1 is reached.

  Subsequently, the timer timing for measuring the period T1 and the pulse width W1 (time t) of the pulse signal is started (S107).

  Subsequently, the peripheral speed V of the fixing belt 102 is measured based on the cycle T1, and speed control is performed based on the difference between the reference peripheral speed Vp (peripheral speed during fixing) and the peripheral speed V (S108). As a result, the peripheral speed of the fixing belt 102 becomes Vp.

  Subsequently, when the time t of the measured pulse width W1 is larger than the time tp of the predetermined pulse width (S109), it is determined that the recording paper P is wound around the fixing belt 102, and the power to the excitation coil 124 is determined. The driving of the supply and drive motor 88 is stopped, and the rotation of the fixing belt 102 is stopped (S112).

  When the measured time t of the pulse width W1 is smaller than the time tp of the predetermined pulse width, it is determined that the recording paper P is not wound and it is determined whether the image forming job is continued or not continued ( S110).

  If the job is continued, the process returns to S106 to continue image formation. If the job is not continued, the power supply to the exciting coil 124 is stopped (S111).

  In this way, the speed detection of the fixing belt 102 and the winding of the recording paper P are detected in the fixing device 100.

  In the present embodiment, light is applied to the mark material 130 to be reflected and the reflected light amount is detected. However, the mark material 130 may absorb or transmit light and detect the light amount reduction amount.

  Next, a second embodiment of the fixing device and the image forming apparatus of the present invention will be described with reference to the drawings.

  Note that components that are basically the same as those in the first embodiment described above are given the same reference numerals as those in the first embodiment, and descriptions thereof are omitted.

  As shown in FIGS. 9a to 9c, in the second embodiment, the photo sensor 126 is disposed in the center of the sheet passing area (L2) of the recording paper P in the fixing belt 102 and facing the nip exit side. Yes. Further, the mark material 130 is provided at the center of the sheet passing area (L2) of the recording paper P in the fixing belt 102.

  Next, the operation of the second embodiment of the present invention will be described.

  As shown in FIGS. 9 and 10, in a normal state, the pulse width of the pulse signal output from the photosensor 126 is W1, and the period is T1.

  When the time T3 elapses after the mark material 130 passes the detection area of the photosensor 126, the recording paper P enters the nip portion between the fixing belt 102 and the pressure roll 104 (FIG. 9b).

  When the recording paper P starts to be wound around the fixing belt 102 (FIG. 9c), the recording paper P covers the mark material 130, so that the emitted light from the photosensor 126 is not reflected. As a result, as shown by the broken line in FIG. 10, the pulse that should appear in the period T1 disappears.

  Here, since the disappearance of the pulse is detected by detecting the rising edge of the pulse every cycle T1, the winding of the recording paper P can be detected.

  In addition, this invention is not limited to said embodiment.

  The printer 10 may use a liquid developer as well as a dry electrophotographic system using a solid developer.

  The fixing device 100 uses the electromagnetic induction heating unit 118 to electromagnetically heat the fixing belt 102. For example, the fixing device 100 is provided inside the fixing belt 102 near the fixing nip N as a heating unit or a heat supply member. The fixing belt 102 may be rapidly heated by providing a ceramic heater and locally heating the fixing belt 102.

  Instead of the thermistor 116, a non-contact type temperature detection sensor may be used, and the temperature detection sensor may be disposed inside the fixing belt 102.

1 is an overall view of a printer according to a first embodiment of the present invention. 1 is a cross-sectional view of a fixing device according to a first embodiment of the present invention. 1 is a cross-sectional view of a fixing belt according to a first embodiment of the present invention. FIG. 3 is an end cross-sectional view of the fixing belt according to the first embodiment of the present invention. It is a schematic diagram of the control part which concerns on 1st Embodiment of this invention. (A) It is the schematic diagram which showed arrangement | positioning of the photosensor which concerns on 1st Embodiment of this invention. (B) It is the schematic diagram which showed the light detection state of the photosensor which concerns on 1st Embodiment of this invention. 3 is a flowchart illustrating a control method of the fixing device according to the first embodiment of the present invention. It is a schematic diagram of the pulse signal output from the photosensor which concerns on 1st Embodiment of this invention. It is the schematic diagram which showed arrangement | positioning of the photosensor which concerns on 2nd Embodiment of this invention. It is a schematic diagram of the pulse signal output from the photosensor which concerns on 2nd Embodiment of this invention.

Explanation of symbols

10 Printer (image forming device)
14Y optical scanning device (exposure unit)
22Y Developer (Developer)
42 Secondary transfer section (transfer section)
60 Conveyor belt (conveyor)
70 Control unit (control means)
78 Timer (Timer)
88 Drive motor (drive means)
100 Fixing device (fixing device)
102 Fixing belt (fixing member)
104 Pressure roll (Pressure member)
123 Emitting part (light emitting part)
125 Light receiving part (light receiving part)
126 Photosensor (detection means)
130 Mark material (detected part)
P Recording paper (recording medium)

Claims (4)

A fixing member having both ends rotatably supported;
Driving means for rotationally driving the fixing member;
A pressure member that pressurizes the surface of the fixing member;
A detected portion provided on an outer peripheral surface of the fixing member;
It has a light emitting part that irradiates the light to the area where the detected part is present, and a light receiving part that receives the light reflected by the area where the detected part is present, and the amount of light received by the light receiving part varies. Detecting means for generating a pulse signal when
A control means for measuring a pulse width and a period of the pulse signal, calculating a peripheral speed of the fixing member based on the pulse width or the period, and driving the driving means so as to become a reference peripheral speed;
A fixing device comprising:   The control means stops the driving means when the pulse width of the pulse signal becomes larger than a predetermined width or when the period of the pulse signal becomes longer than a predetermined period. The fixing device described.   The detection unit is disposed in a recording medium passage region of the fixing member, and the control unit stops the driving unit when the light receiving unit does not detect the light when the fixing member rotates. The fixing device according to claim 1, wherein: A fixing device according to any one of claims 1 to 3,
An exposure unit that emits exposure light; and
A developing unit that exposes the latent image formed by the exposure light with a developer to form a developer image; and
A transfer unit that transfers the developer image made visible in the developing unit onto a recording medium;
A transport unit that transports the recording medium onto which the developer image has been transferred in the transfer unit to the fixing device;
An image forming apparatus comprising:

Images