JP2007058083A - Control method in image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of poor conveyance or image defects due to changes in conveyance speed accompanying changes in temperature of a pressure roller when performing recording material conveyance control using a loop sensor. <P>SOLUTION: An update value by which a counted value should be updated is changed in accordance with start time intervals of a fixing unit, and the counted value is updated in accordance with the update value each time the fixing unit is started, and the conveyance speed of the fixing unit is adjusted in accordance with the updated counted value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control method in an image forming apparatus that forms an image by an electrophotographic method and fixes the formed image on a recording material.

  First, the fixing unit in the color image forming apparatus will be described.

  In recent years, colorization has progressed in image forming apparatuses such as printers and copiers. As a fixing unit used in such a color image forming apparatus, a heat roller type fixing unit having an elastic layer on a fixing member is well known. This fixing unit has an elastic layer, thereby making it possible to obtain a uniform color gloss image.

  However, in a heat roller type fixing method having an elastic layer, the heat capacity of the heat roller itself increases, and the time required to raise the temperature of the fixing roller to a temperature suitable for toner image fixing (warm up time) ) Was long. Further, the cost of the fixing unit is also expensive.

  As a fixing unit that shortens the warm-up time without sacrificing a uniform color gloss image, a fixing unit in which a thin elastic layer is provided on a fixing belt in a belt fixing system often used in a monochrome image forming apparatus. It has come to be used in recent years (for example, refer to Patent Documents 1 and 2). FIG. 21 is a diagram illustrating an example of such a belt fixing unit 201.

  The fixing belt unit 202 is a saddle-shaped heater holder 207 having a substantially semicircular cross section, a fixing heater 204 fixedly disposed on the lower surface of the heater holder 207 along the length of the heater holder (perpendicular to the drawing), The assembly includes a fixing belt 203 having an endless belt-like (cylindrical) thin elastic layer that is loosely fitted to the heater holder 207.

  Reference numeral 205 denotes an elastic pressure roller, and both ends of the core metal are rotatably supported between the side plates of the fixing unit 201.

  The fixing belt unit 202 is arranged on the upper side of the elastic pressure roller 205 with the fixing heater 204 facing downward and in parallel with the pressure roller 205, and both end portions of the heater holder 207 are arranged with a predetermined biasing means (not shown). It is in a state of being pushed down by the pressing force. As a result, the lower surface of the fixing heater 204 is pressed against the upper surface of the elastic pressure roller 205 across the fixing belt 203 against the elasticity of the pressure roller 205 to form a fixing nip portion 206 having a predetermined width.

  The elastic pressure roller 205 is driven to rotate at a predetermined peripheral speed in the direction of the arrow by a drive mechanism (not shown). Due to the rotational drive of the elastic pressure roller 205, a rotational force acts on the fixing belt 203 by a frictional force between the elastic pressure roller 205 and the outer surface of the fixing belt 203 in the fixing nip portion 206, and the fixing belt 203 has an inner peripheral surface thereof. While being in close contact with the lower surface of the fixing heater 204 in the fixing nip portion 206, the outer circumference of the heater holder 207 is driven and rotated in a direction indicated by an arrow with a peripheral speed substantially corresponding to the peripheral speed of the elastic pressure roller 205.

  The fixing belt 203 has an elastic layer having a thickness of about 300 μm on an endless belt made of SUS having a thickness of about 30 μm, and a release layer having a thickness of about 30 μm is further coated thereon.

  The fixing heater 204 is formed by forming a resistance heating element on a ceramic substrate, and a temperature detecting means 209 is brought into contact with the back surface of the fixing heater 204, whereby the temperature of the fixing heater 204 is detected. In accordance with the detected temperature, the power supplied to the fixing heater 204 is controlled by a control unit (not shown) so that the temperature of the fixing heater 204 becomes a desired temperature, and the temperature is controlled.

  In a state where the elastic pressure roller 205 is driven to rotate, the fixing belt 203 is driven to rotate, and the fixing heater 204 rises to a predetermined temperature and is temperature-controlled, the recording material P carrying the unfixed toner image t is fixed to the fixing nip portion. It is introduced between the fixing belt 203 206 and the elastic pressure roller 205. The recording material P is nipped and conveyed through the fixing nip portion 206 together with the fixing belt 203 with the unfixed toner image carrying surface in close contact with the outer surface of the fixing belt 203. In the nipping and conveying process, the heat of the fixing heater 204 is applied to the recording material P via the fixing belt 203, and the unfixed toner image t is permanently applied to the recording material P by receiving the pressure of the fixing nip 206. It is fixed by heat and pressure as a fixed image. Thereafter, the recording material P passes through the fixing nip portion 206 and is discharged after being separated from the surface of the fixing belt 203 with a curvature.

  In the fixing unit 201 having such a configuration, the heat capacity of the fixing belt 203 is very small, and after the electric power is supplied to the fixing heater 204, the fixing nip portion 206 can be raised to a temperature capable of fixing the toner image in a short time. Is possible.

  In addition, since the configuration of the fixing unit is simple, there is an advantage that it can be provided at a low cost.

  For the reasons described above, a fixing unit in which a thin elastic layer is provided on a fixing belt is used in a low-cost color image forming apparatus.

  Next, the relationship between the recording material conveyance speed in the fixing unit and the recording material conveyance speed in the transfer unit will be described.

  In conventional image forming apparatuses, when the conveyance speed of the recording material in the transfer unit is compared with the conveyance speed of the recording material in the fixing unit, there is variation due to individual differences in the fixing unit and changes over time. The recording material conveyance speed (hereinafter referred to as “fixing speed”) in the fixing unit is set to the recording material conveyance speed (hereinafter referred to as “transfer speed”) in the transfer unit so as not to be pulled between the units. Slightly (about 1-2%).

  In other words, when the fixing speed is faster than the transfer speed, the recording material is forcibly pulled out of the transfer unit by the fixing unit, and image disturbance during transfer or a shift in copy magnification, especially color This is because, in the case of an image, color misregistration occurs, and it is necessary to never pull the images.

  In order to absorb the bending of the recording material caused by this speed difference, the conventional image forming apparatus prevents the recording material from being greatly bent in the conveyance path by keeping the distance from the transfer position to the fixing position long. Was.

  However, recently, in order to reduce the size of the image forming apparatus, it is necessary to shorten the distance from the transfer position to the fixing position as much as possible.

  If the distance between the transfer position and the fixing position is narrowed, the recording material will be greatly bent by a slight speed difference between the transfer unit and the fixing unit, which may cause recording material conveyance failure (such as jam) in the conveyance path. There is a problem that the image quality is increased, and an unfixed toner on the recording material adheres to a surrounding recording material guide and causes image rubbing.

  In order to solve the above problem, a loop detecting means for detecting the loop degree of the recording medium is provided between the transfer position and the fixing position, and the conveyance speed of the fixing unit is determined based on the detection result of the loop degree. A method for controlling the acceleration / deceleration so that the recording medium is not pulled between the transfer unit and the fixing unit, and at the same time, the recording medium loop generated by the speed difference between these units is within a certain range. Has been proposed (see, for example, Patent Document 3).

  In addition, in the case of an image forming apparatus using a heat roller, the heat of the recording material is taken away from the fixing roller by the fixing process of the toner image, so that the temperature of the fixing roller is lowered or the image forming operation is continuously executed. In such a case, when the outer diameter of the fixing roller changes due to an increase in the temperature of the fixing roller, there is a problem that a speed difference occurs between the transfer speed and the fixing speed.

At this time, the abnormality in the conveyance state is detected by the speed detection means, the paper conveyance position detection means, the temperature detection means of the fixing roller, the conveyance speed in the fixing unit is changed, and the recording medium of the recording medium by the conveyance mechanism of the image forming unit is changed. A method of controlling so that there is no speed difference with the conveyance speed, and further, when the fixing speed of the recording material is high and the detection ability of the temperature detecting means for detecting the surface temperature of the fixing roller is reduced, or the number of processed sheets As a process when there are many cases, a method of predicting in advance based on the number of processed sheets, the properties of the recording medium, the processing mode, etc. in addition to the temperature detection of the fixing roller by a temperature sensor has been proposed (for example, see Patent Document 4). .
Japanese Patent Laid-Open No. 10-10893 Japanese Patent Laid-Open No. 11-15303 JP 2000-89605 A JP 2000-344385 A

  However, in the system using the above-described fixing unit, when the loop amount control as shown in Patent Document 3 is performed in the system using the above-described fixing unit, the following problem occurs.

  When the fixing means is an on-demand type fixing unit such as surf fixing or electromagnetic induction type fixing, there is no heat source in the pressure roller as compared with the conventional heat roller type fixing unit, and the fixing unit in standby. Power consumption is almost zero or zero, and the heat storage state of the system in the morning is different from that in the continuous printing state. Therefore, the temperature change of the pressure roller is very large. Varies greatly depending on the printing status of the fixing unit. In order to keep the loop amount of the recording medium between the transfer portion and the fixing portion within a certain range against this variation, the fixing speed when the loop is smaller than a predetermined amount (when the outer diameter of the pressure roller is minimum) The loop speed is slower and the fixing speed when the loop is larger than the predetermined amount must be faster (to eliminate the loop even when the outer diameter of the pressure roller is maximum) and loop control May cause hunting. As a result, the recording material is too close to the fixing belt or too far away from the fixing belt, resulting in gloss unevenness corresponding to switching of the fixing speed and unevenness in OHT permeability, and in severe cases due to unstable conveyance. In some cases, paper wrinkles, pulling between the transfer unit and the fixing unit, image rubbing due to increased loops, and color misregistration of each color due to load fluctuations on the recording medium may occur.

  Similar to the method disclosed in Patent Document 4, a means for providing a temperature detecting means for the pressure roller 205 is conceivable. However, not only does the apparatus increase in size and cost, but the temperature detecting means 209 is provided with a pressure roller. 205, the pressure roller 205 is soiled with toner or paper dust, and the recording material P is soiled when the paper is passed, or the pressure roller 205 is damaged during standby. There is a problem that a mark corresponding to a scratch on the pressure roller 205 is formed on the image during duplex printing.

  Also, when non-contact type temperature detection means is used, the response of the temperature detection means is too slow compared to the speed change speed of the pressure roller in the on-demand fixing unit. There was a problem that the speed could not be determined.

  As for the method of predicting in advance based on the number of processed sheets, the nature of the recording medium, the processing mode, and the like, in the on-demand type fixing unit, as described above, the temperature change of the pressure roller is very large and Since the influence of the temperature change due to the heating of the pressure roller at that time is very large, there is a problem that the pressure roller temperature cannot be accurately predicted simply from the number of processed sheets and the moist mode.

  In particular, in a tandem color image forming apparatus that directly superimposes and transfers four colors of C, M, Y, and Bk onto a recording material, load fluctuation during transfer greatly affects the color misregistration of each color. Management of the recording material conveyance speed is very important.

  Furthermore, with recent miniaturization of image forming apparatuses, the distance between transfer and fixing often needs to be very narrow, and the margin for fluctuations in the recording material conveyance speed has become very small. It can also be easily estimated that this trend will increase further in the future.

  The present invention has been made in view of the above problems. In the case where the loop detecting means is used, the temperature of the pressure roller is accurately predicted, and the loop is smaller than a predetermined amount according to the temperature of the pressure roller. It is an object of the present invention to provide a control method for an image forming apparatus that performs stable loop control by determining a fixing speed and a fixing speed that is larger than a predetermined amount, and that does not cause image defects or color misregistration.

An image forming apparatus including a fixing unit for heating and fixing an unfixed toner image on a recording material,
Conveying means for conveying the unfixed toner image formed on the recording material to the fixing unit at a predetermined conveying speed;
A first rotating body of the fixing unit;
A temperature raising means for raising a temperature of a local part of the first rotating body by receiving power supply;
A second rotating body that sandwiches and conveys the first rotating body and the recording material;
Driving means for rotationally driving the second rotating body;
A first conveying speed of the fixing unit that is slower than a conveying speed of the conveying means;
A second conveying speed of the fixing unit that is faster than the conveying speed of the conveying means;
Loop detecting means for detecting the degree of loop of the recording material generated between the fixing unit and the conveying means by a speed difference between the conveying speed of the fixing unit and the conveying speed of the conveying means;
A speed control step of the fixing unit that controls switching between the first transport speed and the second transport speed of the fixing unit using the detection result of the loop detection means, and controls the generated loop;
An update process for updating the count value;
A drive control step of controlling the respective rotation speeds of the drive means for achieving the first transport speed and the second transport speed based on the count value updated by the update step;
It is characterized by having.

  According to the present invention, when recording material conveyance control using a loop sensor is performed, it is possible to prevent a conveyance defect or an image defect from occurring due to a conveyance speed change accompanying a pressure roller temperature change.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. It is not intended that the scope of the present invention be limited to the following embodiments.

[Description of Image Forming Apparatus]
FIG. 1 is a schematic configuration diagram illustrating a configuration of a recording unit of a color image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus according to the present embodiment will be described in the case of an electrophotographic tandem type full color printer.

  The image forming apparatus includes an image forming unit 1Y that forms a yellow image, an image forming unit 1C that forms a cyan image, an image forming unit 1M that forms a magenta image, and a black image. Four image forming units (image forming units) of the image forming unit 1Bk to be formed are provided, and these four image forming units are arranged in a line at a constant interval.

  Photosensitive drums 2a, 2b, 2c, and 2d are installed in the image forming units 1Y, 1C, 1M, and 1Bk, respectively. Around each photosensitive drum 2a, 2b, 2c, 2d, charging rollers 3a, 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d, a drum cleaning device 6a, 6b, 6c and 6d are installed, and exposure devices 7a, 7b, 7c and 7d are installed above the charging rollers 3a, 3b, 3c and 3d and the developing devices 4a, 4b, 4c and 4d, respectively. Yes. Each developing device 4a, 4b, 4c, and 4d contains yellow toner, cyan toner, magenta toner, and black toner, respectively.

  An endless belt-like recording material conveying belt 40 as a transfer medium is in contact with each transfer portion N of each of the photosensitive drums 2a, 2b, 2c, and 2d of the image forming portions 1Y, 1C, 1M, and 1Bk. The recording material transport belt 40 is stretched around a driving roller 41 and a support roller 42, and is rotated (moved) in the arrow direction (clockwise direction) by the rotational driving of the driving roller 41. An adsorption roller (not shown) for electrostatically adsorbing the recording material P as a transfer medium onto the recording material conveyance belt 40 is installed on the upstream side of the image forming unit 1M on the recording material conveyance belt 40.

  The transfer rollers 5a, 5b, 5c, and 5d for primary transfer are in contact with the photosensitive drums 2a, 2b, 2c, and 2d via the recording material conveyance belt 40 at the primary transfer nip portions N, respectively. A transfer power source (not shown) is connected to the transfer rollers 5a, 5b, 5c, and 5d.

  A belt cleaning device 45 is installed in the vicinity of the driving roller 41 outside the recording material conveyance belt 40.

  In addition, an environmental sensor 50 and a media sensor 51 are installed in the image forming apparatus.

  When an image forming operation start signal (print start signal) is issued, the photosensitive drums 2a, 2b, 2c, and 2d of the image forming units 1Y, 1C, 1M, and 1Bk that are rotationally driven at a predetermined process speed are respectively charged rollers. 3a, 3b, 3c and 3d are uniformly charged (negative polarity in the present embodiment). The exposure devices 7a, 7b, 7c, and 7d convert the color-separated image signals that are input into optical signals at a laser output unit (not shown), and laser light that is the converted optical signals. Are electrostatically scanned and exposed on the charged photosensitive drums 2a, 2b, 2c, and 2d, respectively, to form an electrostatic latent image.

  Then, yellow toner is charged on the surface of the photosensitive member by the developing device 4a in which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied on the photosensitive drum 2a on which the electrostatic latent image is formed. The electrostatic latent image is visualized by electrostatic attraction according to the electric potential to obtain a developed image.

  Then, the recording material P conveyed by the registration roller 46 in accordance with this timing is statically moved by an adsorption roller (not shown) to which an adsorption bias is applied to the surface of the recording material conveyance belt 40 that is moved by driving of the drive roller 41. A yellow toner image is recorded by the transfer roller 5a that is electroadsorbed and transported to the transfer unit N of the image forming unit 1M and applied with a transfer bias (opposite polarity (positive polarity) from the toner) from a transfer power source (not shown). Transferred onto the material P.

  The recording material P to which the yellow toner image has been transferred is attracted to the surface of the recording material conveyance belt 40 and moved to the image forming unit 1C side. Also in the transfer portion N of the image forming portion 1C, the cyan toner image formed on the photosensitive drum 2b in the same manner as described above is superimposed on the yellow toner image on the recording material P to transfer bias (toner and toner). Transfer is performed by the transfer roller 5b to which reverse polarity (positive polarity) is applied.

  In the same manner, magenta and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1M and 1Bk on the yellow and cyan toner images superimposed and transferred onto the recording material P in the same manner are transferred to the transfer units. A full color toner image is formed on the recording material P by sequentially superimposing them by the transfer rollers 5c and 5d to which the transfer bias (opposite polarity (positive polarity) to the toner) is applied at N.

  The recording material P on which the full-color toner image is thus formed is conveyed to the fixing unit 12. At this time, there is a loop sensor 30 between the recording material conveyance belt and the fixing nip, and the pressure roller 22 is driven at an appropriate speed by a driving source (not shown) according to the loop detection result of the loop sensor 30 to be stable. The recording material P is conveyed while forming a loop. The full-color toner image is heated and pressed at the fixing nip portion between the fixing belt 20 and the pressure roller 22, and the color image is melted and fixed on the surface of the recording material P. Thereafter, the image is discharged outside the apparatus and becomes an output image of the image forming apparatus. Thus, a series of image forming operations is completed.

  The image forming apparatus includes an environment sensor 50. The bias and fixing conditions for charging, developing, primary transfer, and secondary transfer are in accordance with the atmospheric environment (temperature, humidity) in the image forming apparatus. It can be changed. Thus, it is used for adjusting the density of the toner image formed on the recording material P and for achieving optimum transfer and fixing conditions. Further, the image forming apparatus includes a media sensor 51, and by determining the type of the recording material P, the transfer bias and the fixing condition can be changed according to the type of the recording material. And is used to achieve optimum transfer and fixing conditions for the recording material P.

  During the primary transfer described above, the primary transfer residual toner remaining on the photosensitive drums 2a, 2b, 2c, and 2d is removed and collected by the drum cleaning devices 6a, 6b, 6c, and 6d. Further, residual toner (color shift detection toner image and density detection toner image) remaining on the recording material conveyance belt 40 after the transfer is removed and collected by the belt cleaning device 45.

[Description of fixing unit]
FIG. 2 is a model diagram showing a schematic configuration (including a transfer unit portion) of the fixing unit 12 of the image forming apparatus according to the embodiment of the present invention. The fixing unit 12 according to the present embodiment is a heating device of a fixing belt heating method and a pressurizing rotating body driving method (tensionless type).

(1) Overall Configuration of Fixing Unit 12 Reference numeral 20 denotes a fixing belt as a first rotating body (first fixing member), which has a cylindrical shape (endless belt shape, sleeve shape) in which an elastic layer is provided on the belt-like member. ). The fixing belt 20 will be described in detail later. Reference numeral 22 denotes a pressure roller as a second rotating body (second fixing member). Reference numeral 17 denotes a heater holder having a substantially semicircular arc shape having a transverse cross section as a heating body holding member and having heat resistance and rigidity. Reference numeral 16 denotes a fixing heater as a heating body (heat source), which is disposed on the lower surface of the heater holder 17 along the length of the holder 17. The fixing belt 20 is loosely fitted on the heater holder 17. The fixing heater 16 is a ceramic heater which will be described in detail later in section 2) in this embodiment.

  The heater holder 17 is made of a liquid crystal polymer resin having high heat resistance, plays a role of holding the fixing heater 16 and guiding the fixing belt 20. In the present embodiment, DuPont Zenite 7755 (trade name) was used as the liquid crystal polymer. The maximum usable temperature of Zenite 7755 is about 270 ° C.

  The pressure roller 22 is formed by forming a silicone rubber layer having a thickness of about 3 mm on a stainless steel core by injection molding, and covering a PFA resin tube having a thickness of about 40 μm thereon, and has an outer diameter of 25 mm. . The pressure roller 22 is disposed such that both end portions of the core metal are rotatably supported by bearings between a side plate (not shown) and a front side plate of the apparatus frame 24. On the upper side of the pressure roller 22, a fixing belt unit including the fixing heater 16, the heater holder 17, the fixing belt 20, and the like is arranged in parallel with the pressure roller 22 with the heater 16 facing downward, and both ends of the heater holder 17 are not attached. The pressing mechanism shown in the figure urges the pressing roller 22 in the axial direction with a force of 98 N (10 kgf) on one side and a total pressure of 196 N (20 kgf). As a result, the downward surface of the fixing heater 16 is brought into pressure contact with the elastic layer of the pressure roller 22 via the fixing belt 20 with a predetermined pressing force against the elasticity of the elastic layer, and has a predetermined width necessary for heat fixing. A fixing nip portion 27 is formed. The pressurizing mechanism has a pressure releasing mechanism, and has a configuration in which the pressurization is released and the recording material P can be easily removed at the time of jam processing or the like.

  Reference numerals 18 and 19 denote two thermistors, main and sub, as first and second temperature detecting means. The main thermistor 18 serving as the first temperature detecting means is disposed in a non-contact manner on the fixing heater 16 that is a heating body, and in this embodiment, is elastically brought into contact with the inner surface of the fixing belt 20 above the heater holder 17. The temperature of the inner surface of the fixing belt 20 is detected. The sub-thermistor 19 serving as the second temperature detecting means is disposed closer to the fixing heater 16 that is a heat source than the main thermistor 18, and is in contact with the back surface of the fixing heater 16 in the present embodiment. Detect the backside temperature.

  In the main thermistor 18, a thermistor element is attached to the tip of a stainless steel arm 25 fixedly supported by the heater holder 17, and the movement of the inner surface of the fixing belt 20 becomes unstable due to the elastic swing of the arm 25. In this case, the thermistor element is always kept in contact with the inner surface of the fixing belt 20.

  FIG. 3 is a perspective model diagram illustrating the positional relationship between the fixing heater 16, the main thermistor 18, and the sub-thermistor 19 in the fixing unit 12 according to the present embodiment.

  The main thermistor 18 is disposed near the longitudinal center of the fixing belt 20, and the sub-thermistor 19 is disposed near the end of the fixing heater 16. The main thermistor 18 is disposed in contact with the inner surface of the fixing belt 20 and the back surface of the fixing heater 16. .

  The outputs of the main thermistor 18 and the sub-thermistor 19 are input to the control unit 21 via A / D converters 64 and 65 (FIG. 2), respectively. As a result, the control unit 21 determines the temperature control content of the fixing heater 16 based on the outputs of the main thermistor 18 and the sub-thermistor 19, and the heater drive circuit 28 (FIG. 2, FIG. 2) as the power supply unit (heating means). The energization to the fixing heater 16 is controlled by 4). The configuration of the control unit 21 will be described in detail with reference to FIG.

  Reference numerals 23 and 26 in FIG. 2 denote an entrance guide 23 and a fixing paper discharge roller 26 assembled to the apparatus frame 24, respectively. The entrance guide 23 transfers the recording material P so that the recording material P that has passed through the secondary transfer nip is accurately guided to the fixing nip portion 27 that is a pressure contact portion between the fixing belt 20 and the pressure roller 22 in the fixing heater 16 portion. To play a leading role. The entrance guide 23 of the present embodiment is made of polyphenylene sulfide (PPS) resin.

  The pressure roller 22 is rotationally driven by the drive unit 31 in the direction of the arrow at a predetermined peripheral speed. Due to the pressure contact frictional force at the fixing nip portion 27 between the outer surface of the pressure roller 22 and the fixing belt 20 due to the rotational driving of the pressure roller 22, a rotational force acts on the cylindrical fixing belt 20 so that the fixing belt 20 The inner surface of the heater holder 17 is in a state of being driven to rotate in the direction indicated by the arrow while sliding in close contact with the downward surface of the fixing heater 16. Grease is applied to the inner surface of the fixing belt 20 to ensure slidability between the heater holder 17 and the inner surface of the fixing belt 20.

  When the pressure roller 22 is rotationally driven, the cylindrical fixing belt 20 is driven and rotated, and when the fixing heater 16 is energized, the fixing heater 16 is heated to a predetermined temperature. The temperature is adjusted. In this state, when the recording material P carrying an unfixed toner image is guided and introduced along the entrance guide 23 between the fixing belt 20 and the pressure roller 22 of the fixing nip 27, the fixing nip 27 2, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the fixing belt 20 and is nipped and conveyed by the fixing nip portion 27 together with the fixing belt 20. In this nipping and conveying process, the heat of the fixing heater 16 is applied to the recording material P via the fixing belt 20, and the unfixed toner image t on the recording material P is heated and pressed on the recording material P to be melted and fixed. The The recording material P that has passed through the fixing nip 27 is separated from the fixing belt 20 by the curvature, and is discharged by the fixing discharge roller 26.

(2) Description of Main Thermistor 18 As shown in FIGS. 2 and 3, the main thermistor 18 is disposed near the longitudinal center of the fixing belt 20 and is disposed so as to contact the inner surface of the fixing belt 20. The main thermistor 18 is used as means for detecting the temperature of the fixing belt 20 that is closer to the temperature of the fixing nip portion 27. Therefore, in normal operation, temperature control is performed so that the detected temperature of the main thermistor 18 becomes the target temperature.

(3) Description of Sub-Thermistor 19 As shown in FIG. 3, the sub-thermistor 19 is disposed near the end of the fixing heater 16 and is disposed so as to contact the back surface of the fixing heater 16. The sub-thermistor 19 serves as a safety device that detects the temperature of the fixing heater 16 as a heating body and monitors the temperature of the fixing heater 16 so as not to exceed a predetermined temperature.

  Further, the sub-thermistor 19 monitors the temperature overshoot of the fixing heater 16 at the time of start-up and the temperature rise at the end of the fixing heater. When the temperature exceeds this temperature, it is used for judgment for performing control such as lowering the throughput so that the temperature rise at the end is not further deteriorated.

(4) Description of Fixing Heater 16 In the present embodiment, the fixing heater 16 as a heat source is a film-like film having a uniform thickness formed by screen printing on a conductive paste containing silver and palladium alloy on an aluminum nitride substrate. A ceramic heater is used, in which a resistance heating element is formed by coating and glass coating with pressure-resistant glass is applied.

  4A and 4B are structural model diagrams of an example of a ceramic heater used in the fixing heater 16 according to the present embodiment. FIG. 4A is a partially cutaway surface model diagram, FIG. 4B is a back model diagram, and FIG. ) Is an enlarged cross-sectional model view.

The fixing heater 16 is
(A) a horizontally long aluminum nitride substrate a having a direction perpendicular to the paper passing direction as a longitudinal direction;
(A) Conductivity including silver palladium (Ag / Pd) alloy that is heated on the surface side of the aluminum nitride substrate “a” along the length by screen printing in a linear or belt shape and generates heat when a current flows. A resistance heating element layer b having a paste thickness of about 10 μm and a width of about 1 to 5 mm;
(C) First and second electrode parts c and d and an extended electric circuit part, which are similarly formed by screen printing or the like of silver paste on the surface side of the aluminum nitride substrate a as a power supply pattern for the resistance heating element layer b. e, f,
(D) A thickness of about 10 μm capable of withstanding the rubbing with the fixing belt 20 formed on the resistance heating element layer b and the extension circuit portions e and f to ensure protection and insulation. A thin-walled glass coat,
(E) Sub-thermistor 19 provided on the back side of aluminum nitride substrate a
Etc.

  The fixing heater 16 is fixedly supported on the heater holder 17 with its surface side exposed downward. A power feeding connector 30 is attached to the first and second electrode portions c and d of the fixing heater 16. By supplying power from the heater drive circuit 28 to the first and second electrode portions c and d via the power supply connector 30, the resistance heating element layer b generates heat and the fixing heater 16 quickly rises in temperature. The heater drive circuit 28 is controlled by the control unit 21.

  During normal use, the rotation of the fixing belt 20 starts with the rotation of the pressure roller 22, and the temperature of the inner surface of the fixing belt 20 increases as the temperature of the fixing heater 16 increases. Energization of the fixing heater 16 is controlled by PID control, and the input power is controlled so that the inner surface temperature of the fixing belt 20, that is, the detected temperature of the main thermistor 18 becomes 190 ° C.

(5) Description of Fixing Heater Drive Circuit 28 FIG. 5 is a block diagram of the controller 21 and the fixing heater drive circuit 28 as temperature control means of the fixing unit 12 according to the present embodiment. The power supply electrodes c and d of the fixing heater 16 are connected to the fixing heater driving circuit 28 via a power supply connector (not shown).

  In this fixing heater driving circuit 28, 60 is an AC power source, 61 is a triac, 62 is a zero cross generating circuit, and 21 is a control unit. The triac 61 is controlled by the control unit 21. The triac 61 supplies and cuts off the heating resistor layer b of the fixing heater 16.

  The AC power supply 60 sends a zero cross signal to the control unit 21 via the zero cross detection circuit 62. The control unit 21 controls the triac 61 based on this zero cross signal. In this way, by energizing the heating resistor layer b of the fixing heater 16 from the fixing heater driving circuit 28, the temperature of the entire fixing heater 16 is rapidly increased. Outputs of the main thermistor 18 that detects the temperature of the fixing belt 20 and the sub-thermistor 19 that detects the temperature of the fixing heater 16 are taken into the control unit 21 via the A / D converters 64 and 65, respectively. Thus, the control unit 21 controls the heater energizing power by controlling the AC voltage applied to the fixing heater 16 by the triac 61 based on the temperature information of the fixing heater 16 from the main thermistor 18 by phase, wave number control, etc. Control is performed so that the temperature of 16 is maintained at a predetermined control target temperature (set temperature). That is, the temperatures of the main thermistor 18 and the sub-thermistor 19 are monitored by the control unit 21 as voltage values. Thus, the electric power supplied to the fixing heater 16 is controlled so that the temperature of the fixing belt 20 is maintained at a predetermined set temperature and the fixing heater 16 is driven within the predetermined temperature.

  The control unit 21 includes a CPU 210 such as a microprocessor, a ROM 211 that stores control programs and data for the CPU 210, a RAM 212 that is used as a work area when the CPU 210 executes control, temporarily stores various data, control information that will be described later, and the like. EEPROM213 etc. which memorize | store non-volatilely are provided. A timer 214 is used to measure a starting time interval of a fixing unit described later.

  Here, PID control is used as a typical temperature control method by the control unit 21. The power control method includes wave number control, phase control, and the like. Here, description will be given using phase control.

  Specifically, the control unit 21 detects the temperature of the main thermistor 18 every 2 μs, and the control unit 21 determines the power supply amount to the fixing heater 16 by PID control so that the temperature is controlled to a desired temperature. To do. For example, in order to specify power in increments of 5%, it is generally performed using energization angles in increments of 5% for one half wave of an AC waveform supplied from the AC power supply 60. This energization angle is obtained as a timing for turning on the triac 61, starting from when the zero-cross signal is detected by the zero-cross generation circuit 62.

(6) Description of Fixing Belt 20 In the present embodiment, the fixing belt 20 is a cylindrical (endless belt-shaped) member in which an elastic layer is provided on the belt-shaped member. Specifically, a stainless rubber layer (elastic layer) having a thickness of about 300 μm is formed by a ring coating method on an endless belt (belt base material) formed into a cylindrical shape having a thickness of 30 μm by SUS, and then a thickness of 30 μm. The PFA resin tube (outermost surface layer) is coated. When the heat capacity of the fixing belt 20 produced in such a configuration was measured, it was 12.2 × 10 ⁻² J / cm ² ° C. (heat capacity per 1 cm ^{2 of the} fixing belt).

(A) Fixing Belt Base Layer The base layer of the fixing belt 20 can be made of a resin such as polyimide, but a metal such as SUS or nickel has a thermal conductivity approximately 10 times larger and higher than polyimide. In this embodiment, SUS, which is a metal, is used for the base layer of the fixing belt 20 because on-demand characteristics can be obtained.

(A) Elastic layer of fixing belt A rubber layer having a relatively high thermal conductivity is used for the elastic layer of the fixing belt 20. This is to obtain higher on-demand characteristics. The material used in this embodiment has a specific heat of about 12.2 × 10 ⁻¹ J / g ° C.

(C) Release layer of fixing belt By providing a fluororesin layer on the surface of the fixing belt 20, the surface releasability is improved, and the toner once adheres to the surface of the fixing belt 20 and moves to the recording material P again. By doing so, the offset phenomenon that occurs can be prevented. Further, when the fluororesin layer on the surface of the fixing belt 20 is a PFA tube, a uniform fluororesin layer can be formed more easily.

(D) Heat capacity of the fixing belt Generally, when the heat capacity of the fixing belt 20 is increased, the temperature rise becomes dull and the on-demand property is impaired. For example, although it depends on the configuration of the fixing unit 12, the heat capacity of the fixing belt 20 needs to be about 4.2 J / cm ² ° C. or less when it is assumed that the temperature rises within one minute without standby temperature control. I know.

In the present embodiment, it is designed such that the fixing belt 16 starts up at 190 ° C. within 20 seconds by applying about 1000 W of power to the fixing heater 16 when starting up from a room temperature state. A material having a specific heat of about 12.2 × 10 ⁻¹ J / g ° C. is used for the silicone rubber layer. At this time, the thickness of the silicone rubber must be 500 μm or less, and the heat capacity of the fixing belt 20 is about It must be 18.9 × 10 ⁻² J / cm ² ° C. or lower. Conversely, if the temperature is set to 4.2 × 10 ⁻² J / cm ² ° C. or lower, the rubber layer of the fixing belt 20 becomes extremely thin and has an elastic layer in terms of image quality such as OHT permeability and gloss unevenness. Would be equivalent to no on-demand fixing unit.

In the present embodiment, the thickness of the silicone rubber necessary for obtaining a high-quality image such as OHT permeability and gloss setting is 200 μm or more. The heat capacity at this time was 8.8 × 10 ⁻² J / cm ² ° C.

In other words, the heat capacity of the fixing belt 20 in the configuration of the fixing unit similar to the present embodiment is generally targeted at 4.2 × 10 ⁻² J / cm ² ° C. or more and 4.2 J / cm ² ° C. or less. Among them, a fixing belt having a heat capacity of 8.8 × 10 ⁻² J / cm ² ° C or more and 18.9 × 10 ⁻² J / cm ² ° C or less that can achieve both on-demand and high image quality. I decided to use it.

(8) Description of Loop Sensor 30 FIG. 6 is a schematic configuration diagram of the loop sensor 30 according to the present embodiment.

  In FIG. 6, the loop detection sensor 30 includes a photo interrupter 30a and an actuator 30b, and the photo interrupter 30a is turned ON / OFF according to the displacement of the actuator 30b. When the transfer paper P is transported, the actuator 30b indicated by the dotted line in FIG. 6 is rotated on the recording material P due to the transport speed difference between the pressure roller 22 of the fixing device 12 and the photosensitive drums 1Y, 1C, 1M, 1Bk. A loop may occur. As described above, the fixing speed is slightly rotated (about 1 to 2%) with respect to the transfer speed so that the recording material P does not pull between the transfer unit and the fixing unit. This is because. In addition, since the conveyance speed varies depending on the state of the fixing device 12, the loop of the transfer paper P may not necessarily be a loop that rotates the actuator 30b.

  When a loop that causes the actuator 30b to rotate occurs, the photo interrupter 30a is shielded from light by the flag. The light shielding of the photo interrupter 30a is transmitted to the CPU 210 in the control unit 21 to perform interrupt processing (interrupt processing will be described later).

(9) Description of Drive Unit 31 FIG. 7 is a block diagram of the control unit 21 and the drive unit 31 as drive means of the fixing unit 12 according to the present embodiment.

  The drive unit 31 of the present embodiment includes a fixing motor 31a and a motor driver 31b, and uses a micro-step five-phase stepping motor as the fixing motor 31a. A driving signal for the fixing motor 31a is generated by the motor driver 31b, and a clock signal as a basis thereof is generated from the CPU 210 in the control unit 21. If the clock cycle is shortened, the fixing motor 31a is rotated at a high speed, and if the clock cycle is lengthened, the fixing motor 31a is rotated at a low speed.

  As described above, the CPU 210 performs control to switch the clock cycle in the interrupt processing from the loop detection sensor 30 and remove the generated loop.

[Loop control method]
(1) Description of Loop Control FIG. 8 is a diagram illustrating switching of the rotation speed of the fixing motor 31a. FIG. 8 is a graph in which the horizontal axis represents time and the vertical axis represents speed. The conveying speeds of the photosensitive drums 1Y, 1C, 1M, 1Bk and the recording material conveying belt 40 are the image forming process speed PS and are constant, and are not controlled by the present invention. The pressure roller 22 conveys the transfer paper at a predetermined constant speed CS1 that is slower than the image forming process speed PS. That is, the conveying speed of the pressure roller 22 is set to a constant speed CS1 that is several percent slower than the normal process speed PS.

  Since the conveyance speed of the pressure roller 22 varies depending on individual differences and changes with time, it is set to a speed that never exceeds the process speed PS even if the allowable amount is taken into account.

  When a certain amount of time has elapsed, the area surrounded by the speed straight line and the vertical and horizontal axes of the graph (the shaded area in FIG. 8) corresponds to the transfer distance of the transfer paper. If this exceeds a certain amount, the actuator 30b Shields the photo interrupter 30a and generates an interrupt to the CPU 210 in the control unit 21 (corresponding to the portion indicated by the arrow W in FIG. 8).

The CPU 210 performs an acceleration operation by setting the clock signal generation cycle to be shorter in the interrupt process. And if acceleration is carried out for a fixed time, the conveyance speed of the pressure roller 22 will be in the new constant speed state CS2. Thereafter, after the constant speed state CS2 is continued for a predetermined time, the decelerating operation is performed again, and the conveying speed of the pressure roller 22 is returned to the original constant speed CS1. The time for which the new constant speed state CS2 is continued is the area surrounded by the process speed PS and the acceleration / deceleration straight line (indicated by hatching in FIG. 8) (corresponding to the transport distance) is the loop of the transfer paper P shown in FIG. It is determined by the time corresponding to the difference between the distance between the solid line and the dotted line. This returns to the state without the first loop.
In addition, when the speed indicated by the new constant speed state CS2 is not in time, the loop can be removed at a higher speed as indicated by the faster constant speed state CS3.

(2) Description of Method for Predicting Pressure Roller Temperature Hereinafter, a method for predicting the temperature of the pressure roller 22 in the present embodiment will be described. The number of activations of the fixing unit 12 is referred to as the number of startups in the present embodiment, and the approximate time from the stop of the operation of the image forming apparatus to the next activation is referred to as an intermittent time in the present embodiment. In the present embodiment, FIG. 9 shows an example of values that are counted up at each start-up according to the intermittent time.

  FIG. 9 is a diagram for explaining the relationship between the intermittent time and the value counted up each time the fixing device 12 is started up.

  As shown in FIG. 9, a value to be counted up is set according to the intermittent time. Here, the reason why the count value varies depending on the intermittent time is that it corresponds to the temperature of the pressure roller 22 being cooled when the intermittent time is long. When the intermittent time is 300 seconds or more (* in FIG. 9), the count value is set to “0.2” regardless of the activation of the fixing unit 12 every 10 seconds after the intermittent time exceeds 300 seconds. I decided to draw them one by one. This numerical value is determined in the fixing unit in this embodiment. If necessary, as a counting method, a method in which a weight is given for each elapsed time and a calculation formula is used, or a method of selecting from a table may be used.

  In addition, as a correction amount based on the number of printed sheets, in the “plain paper mode”, “0.1” is counted up per printed sheet corresponding to the number of printed sheets. Also, the count-up value per print is made different depending on the print mode. In the “OHT mode”, the count-up value per print is “0.5”. This is because the process speed is slow and the interval between sheets is long, so that the temperature of the pressure roller 22 rises more.

  The count up result is stored in the EEPROM 213. Here, the EEPROM 213 is used so that the temperature of the pressure roller 22 can be accurately predicted even when the power is unexpectedly turned off and on immediately after printing in a state where the temperature of the pressure roller 22 is warm. It is to do. However, since the intermittent time is unknown after the power is turned off and on immediately after printing, it is counted again as 0 seconds when the power is turned on. The count at the time of printing is the value of the EEPROM 213 and the sub-thermistor 19 in FIG. The count value obtained from the detected temperature is compared.

  The tables shown in FIGS. 9 and 10 are preferably stored in the ROM of the control unit 21 or stored in the EEPROM 213 if appropriate updating is necessary.

  FIG. 11 is a flowchart for explaining the update process of the count value stored in the EEPROM 213, and a program for executing this process is stored in the ROM 211.

  This process is started when the printing process is activated. In step S1, the process waits for the fixing unit 12 to be activated. When activated, the process proceeds to step S2, and an elapsed time from the previous activation is obtained. This can be determined by the timer 214. In step S3, a value to be counted up (added value to be updated) is obtained according to the elapsed time and the set value in FIG. In step S4, the count value stored in the EEPROM 213 is read, and the value determined in step S3 is added to the count value and stored in the EEPROM 213 again.

  In step S5, if the fixing unit 12 is activated, the process proceeds to step S100 to check whether the print mode is the plain paper mode or the OHT mode. In the plain paper mode, the process proceeds to S101, where the count value stored in the EEPROM 213 is read out, incremented by 0.1 according to the continuous print number in the JOB, and stored in the EEPROM 213. And it progresses to step S5 again. In the OHT mode, the process proceeds to S102, where the count value stored in the EEPROM 213 is read out, incremented by 0.1 according to the number of continuous prints in the JOB, and stored in the EEPROM 213. And it progresses to step S5 again. While repeating in this way, it is temporarily stopped and waited for being started again.

  In step S5, once stopped and not activated, the process proceeds to step S6 to check whether 300 seconds or more have elapsed since the last fixing unit 12 was activated. If 300 seconds or more have not elapsed, the process returns to step S5, and if the fixing unit 12 is activated again or the fixing unit is stopped, the elapsed time is counted. When 300 seconds or more have elapsed in step S6, the process proceeds to step S7, and it is checked whether 10 seconds have elapsed. If 10 seconds have not elapsed, the process proceeds to step S8 to check whether the fixing unit 12 has been restarted. If restarted, the process returns to step S2, but if not, the process proceeds to step S7. In step S7, when 10 seconds have elapsed, the process proceeds to step S9, and the count value stored in the EEPROM 213 is decreased by -0.2. In this step S7, when the count value becomes negative, it remains “0”.

  In this way, the count value corresponding to the number of start-ups stored in the EEPROM 213 can be updated.

  FIG. 12 is a diagram illustrating the temperature of the pressure roller corresponding to the above-described count number in accordance with the type of recording material (recording sheet).

  In FIG. 12, the temperature value of the pressure roller in the “plain paper mode” and the “OHT mode” indicates a temperature value experimentally obtained corresponding to each count value, and the pressure roller predicted from the count value. It corresponds to the temperature value.

  In the present embodiment, the temperature of the pressure roller 22 is approximately 60 ° C. to 170 ° C. depending on the use state of the fixing device, and this temperature is predicted from the count value.

(3) Description of Method for Controlling Revolution Speed of Fixing Motor 31a FIG. 13 shows a target rotation speed of the fixing motor 31a with respect to the pressure roller temperature.
When the temperature of the pressure roller 22 changes, the outer diameter of the pressure roller 22 also changes. As described above, the temperature of the pressure roller 22 becomes approximately 60 ° C. to 170 ° C. depending on the use state of the fixing device, and at this time, the outer diameter of the pressure roller varies by about 4%.

Here, as shown in FIG. 13, in a state where the temperature of the pressure roller 22 is high (that is, a state where the outer diameter of the pressure roller 22 is large), the rotation speed of the fixing motor 31a is decreased, and conversely the pressure is applied. When the temperature of the roller 22 is low (that is, the outer diameter of the pressure roller 22 is low), the rotation speed of the fixing motor 31a is increased. By doing so, as shown in FIG. 14, regardless of the temperature of the pressure roller 22, the recording material conveyance speed (fixing speed) in fixing is made constant, and stable recording material conveyance control is performed.
The tables shown in the graphs in FIGS. 12 and 13 are preferably stored in the ROM of the control unit 21 or stored in the EEPROM 213 if appropriate updating is necessary.

  FIG. 15 is a flowchart for explaining the control of the fixing unit 12 according to the first embodiment. A program for executing this processing is stored in the ROM 211 and executed under the control of the CPU 210. This process is executed almost in parallel with the flowchart of FIG.

  This process is started when the fixing unit 12 is activated. First, in step S11, the count value stored in the EEPROM 213 is read. In step S12, it is determined whether the recording material type is plain paper or OHT. If it is plain paper, the process proceeds to step S13, and the count value and the pressure roller temperature corresponding to the plain paper mode obtained with reference to FIG. 12 are acquired. In step S12, if the type of the recording material is OHT, the process proceeds to step S14, and the count value and the pressure roller temperature corresponding to the OHT mode, which are obtained with reference to FIG. 12, are acquired. In step S15, the rotation speed CS1 of the fixing motor 31a when the photo interrupter of the loop sensor 30 is not shielded and the photo interrupter are shielded from the acquired pressure roller temperature, and the fixing motor 31a in the interrupt process is interrupted. Is determined. Then, the process proceeds to step S16. When the printing operation is completed, the control is terminated. When the printing operation is continued, the process returns to S11 and the same control is performed. The rotation speed control of the fixing motor 31a is executed by the motor driver 31b described above in accordance with an instruction from the control unit 21.

  In the first embodiment, different modes are set depending on the type of recording material. For example, when the recording material is plain paper having a basis weight of 60 to 105 [g / m], printing is performed as “plain paper mode”. When the recording material is OHT, printing is performed as “OHT mode”.

  As described above, by using the count value according to the number of start-ups of the fixing unit, the temperature of the pressure roller 22 can be accurately predicted regardless of the usage state of the fixing unit, and the temperature of the pressure roller 22 can be estimated. The fixing speed can be selected accordingly. As a result, it is possible to prevent the occurrence of image defects and JAM that occur when the fixing speed is inappropriate.

[Results of image output experiment using this embodiment]
Next, an image output result when this embodiment is used will be described.

(1) Experimental Method The process speed of the image forming apparatus is 100 mm / second in the “plain paper mode” and 30 mm / second in the “OHT mode”. As continuous printing, 400 sheets were continuously printed in the “plain paper mode” (a). Further, as intermittent printing, printing of 5 sheets was repeated 80 times for 10 seconds in the “plain paper mode” (b). Thereafter, 10 OHT sheets were printed after 30 seconds for both continuous printing (a) and intermittent printing (b). The reason why the continuous printing and the intermittent printing are performed is to evaluate the paper conveyance performance when the fixing unit is used in different states. An office planner (product name) was used as plain paper, and the number of JAM generated during printing and the number of image rubbing were examined. Further, color OHP paper TR-3 (trade name) was used as the OHT sheet, and the number of JAM and the number of occurrences of gloss unevenness were examined.

  The temperature of the pressure roller 22 is arranged in contact with an Anritsu E-type thermocouple 529E near the center of the surface of the pressure roller 22, and is A / D converted by a Keyence PC temperature recorder NR250 and taken into the PC. The temperature was measured by.

(2) Experimental results Next, experimental results will be described.

(A) OHT printing after continuous printing ○ Printing 400 sheets of plain paper JAM: Not generated.

        Image rubbing: Not generated.

○ 10 OHT printing JAM: Not generated.

        Gross unevenness: Not generated.

(B) OHT printing after intermittent printing ○ Printing 400 sheets of plain paper JAM: Not generated.

        Image rubbing: Not generated.

○ 10 OHT printing JAM: Not generated.

        Gross unevenness: Not generated.

  Thus, neither JAM, image rubbing, or gloss unevenness occurred in both continuous printing and intermittent printing.

[Comparative Examples 1 and 2]
Next, an image output result when the conventional example is used will be described.

(1) Experimental Method As a conventional example, the rotation speed CS1 of the fixing motor 31a when the photo interrupter of the loop sensor 30 is not shielded regardless of the use state of the fixing unit 12, that is, regardless of the temperature of the pressure roller 22. The rotation speed CS2 of the fixing motor 31a in the interrupt process in which the photo interrupter is shielded from light is determined.

  Specifically, as Comparative Example 1, as shown in FIG. 16, the relative rotational speed of CS1 was 98.0%, and the relative rotational speed of CS2 was 102%. As Comparative Example 2, as shown in FIG. 17, the relative rotational speed of CS1 was 96.1%, and the relative rotational speed of CS2 was 104.4%.

  Experiments equivalent to those described above were performed by the above two methods.

(2) Experimental results of Comparative Example 1 (a) OHT printing after continuous printing ○ 400 sheets of plain paper printed JAM: 3 times. (Occurs at the beginning of printing)
Image rubbing: Not generated.

○ 10 OHT printing JAM: Not generated.

        Gross unevenness: Not generated.

(B) OHT printing after intermittent printing ○ Printing 400 sheets of plain paper JAM: Generated 4 times. (Occurs twice at the beginning of printing and twice near the end of printing)
Image rubbing: Not generated.

○ 10 OHT printing JAM: Not generated.

        Gross unevenness: Not generated.

  In Comparative Example 1, image rubbing and gloss unevenness did not occur, but in continuous printing, JAM occurred three times in the initial stage. In intermittent printing, JAM occurred four times.

(3) Cause for Experimental Results of Comparative Example 1 When the temperature of the pressure roller 22 was measured, it was about 65 ° C. in the initial printing of plain paper, and after printing, about 140 ° C., intermittent in continuous printing. It was about 170 ° C. in printing.

  The relationship between the pressure roller temperature and the fixing speed in Comparative Example 1 is shown in FIG. It can be seen that while the transfer speed is conveyed at the process speed PS, both CS1 and CS2 are slower than the process speed at the beginning of printing. At this time, when the loop sensor detects a predetermined amount of loop, the fixing speed for canceling the loop is not reached, so that JAM occurs. It can be seen that near the end of printing, both CS1 and CS2 are faster than the process speed. At this time, JAM occurs because the paper is pulled by transfer and fixing.

(4) Experimental results of Comparative Example 2 (a) OHT printing after continuous printing ○ 400 sheets of plain paper printed JAM: Generated twice.

        Image rubbing: occurs 8 times.

○ 10 OHT printing JAM: Not generated.

        Gross unevenness: 5 times.

(B) OHT printing after intermittent printing ○ Printing 400 sheets of plain paper JAM: 3 times.

        Image rubbing: occurs 12 times.

○ 10 OHT printing JAM: Not generated.

        Gross unevenness: 6 times.

  In Comparative Example 2, JAM occurred twice during continuous printing. Image rubbing occurred 8 times on plain paper, and gloss unevenness occurred 5 times on OHT. In intermittent printing, JAM occurred three times. Image rubbing occurred 12 times on plain paper, and gloss unevenness occurred 6 times on OHT.

(5) Causes for Experimental Results of Comparative Example 2 FIG. 19 shows the relationship between the pressure roller temperature and the fixing speed in Comparative Example 2. Even when the pressure roller temperature is low or high, there is no case where CS1 becomes faster than the process speed PS as in Comparative Example 1, or CS2 becomes slower than the process speed PS, but the fixing speed CS1. The difference in CS2 was 8%, loop control was likely to cause hunting, and paper conveyance was unstable. As a result, JAM occurred, image rubbing and gloss unevenness occurred.

  As described above, according to the first embodiment, the temperature of the pressure roller 22 can be accurately predicted regardless of the use state of the fixing unit by using the count value according to the number of start-ups of the fixing unit. The fixing speed according to the temperature of the pressure roller 22 can be selected. As a result, it is possible to prevent the occurrence of image defects and JAM that occur when the fixing speed is inappropriate.

  In the second embodiment, the temperature of the pressure roller 22 is determined when the intermittent time is sufficiently long using the sub-thermistor 19 in contact with the fixing heater 16 using the fixing unit 12 described in the first embodiment. The temperature of the pressure roller 22 is further accurately detected by performing a count in consideration of the difference between the saturation point of the temperature rise of the temperature of the pressure roller 22 during continuous printing and intermittent printing. A method will be described.

  The configuration of the fixing unit in the second embodiment is the same as that in the first embodiment, and the description thereof is omitted. In the second embodiment, the counting method is different in that the temperature of the pressure roller 22 is detected when the intermittent time is sufficiently long.

  The method for counting up the number of times of startup is the same as in the first embodiment described above and is as shown in FIG.

  FIG. 10 is a diagram illustrating an example in which the count-up value is set when the intermittent time is sufficiently long in the image forming apparatus according to the second embodiment.

  Here, the temperature detected by the sub-thermistor 19 reflects the temperature of the pressure roller 22 because the heater 16 is not heated and is closest to the pressure roller 22 when the apparatus is powered off. Can be considered.

  As shown in FIG. 10, when the intermittent time is sufficiently long (for example, when it exceeds 300 seconds), the value to be counted up is changed at each start-up. Here, when the intermittent time is long, the detected temperature of the sub-thermistor 19 before startup is used. Thus, the temperature of the pressure roller 22 can be accurately detected by directly detecting the temperature of the pressure roller 22.

  Since the count value holding method by the EEPROM 213, the count method in consideration of the number of printed sheets, and the temperature adjustment temperature selection method are the same as those in the first embodiment, description thereof will be omitted.

  Here, for example, in FIG. 10, when the count value corresponding to the detected temperature of the sub-thermistor 19 is “4.0” or less, the power is turned off and on after the printing is completed, and a sufficient time has passed. Therefore, the count value obtained from the detected temperature of the sub-thermistor 19 shown in FIG. 10 is used as it is. When the count value corresponding to the detected temperature of the sub-thermistor 19 is “20.0” or more, the power is turned off / on after printing is finished, and it is determined that not much time has passed, and the value of the EEPROM 213 is counted. Used as In addition, when the count value corresponding to the detected temperature of the sub-thermistor 19 in FIG. 10 is “4.1” or more and “20.0” or less, it is determined to be intermediate between the above two cases, and the value of the EEPROM 213 is determined. Then, the intermediate value of the count value obtained from the detected temperature of the sub-thermistor 19 in FIG. 10 is obtained as the count value.

  By doing so, the temperature of the pressure roller 22 and the expected temperature (count value) are prevented from greatly deviating even when the power supply is unexpectedly turned off and on.

  Further, the temperature change of the pressure roller 22 during continuous printing and intermittent printing can be predicted with high accuracy by taking the following measures.

  In consideration of the saturation point of the temperature rise of the pressure roller 22, when the count value exceeds “50.0”, the temperature of the pressure roller 22 at that time is saturated. Since it is considered to be at temperature, the number of start-ups is not counted up. As for the number of printed sheets in the “plain paper mode”, when the count value exceeds “25.0”, the number of printed sheets is not counted up. Similarly, the number of printed sheets in the “OHT mode” is higher than that in the “plain paper mode” because the saturation temperature of the pressure roller 22 is higher than that in the “plain paper mode”, so when the count value exceeds “35.0”, The number of printed sheets is not counted up.

  As described above, the number of continuous prints and the count value may be appropriately determined according to the process speed, the temperature control temperature, and the sheet interval. By the above method, it is possible to make the appropriate pressure roller 22 temperature and count value correspond to the point that the saturation temperature of the pressure roller temperature differs between when continuous printing is performed and when intermittent printing is continued. .

  As described above, according to the second embodiment, the temperature of the pressure roller 22 can be accurately predicted regardless of the use state of the fixing unit by using the count value according to the number of times the fixing unit is started up. . As a result, the temperature adjustment temperature according to the temperature of the pressure roller 22 can be selected, and the occurrence of image defects and the occurrence of winding of the recording material when the fixing temperature adjustment temperature is inappropriate can be prevented. In this way, it is possible to obtain a high-quality image that exhibits good fixability and has no uneven print quality such as gloss value.

  In the third embodiment, the present invention can be applied to a fixing unit different from the fixing unit described in the first and second embodiments, and the same effect can be obtained. In the fixing unit used in the third embodiment, the temperature of the pressure roller 22 cannot be detected by the thermistor. By applying the present invention also to such a fixing unit, the temperature of the pressure roller can be accurately predicted regardless of the usage state of the fixing unit, and the temperature adjustment temperature according to the temperature of the pressure roller can be selected. Can do.

  As a fixing unit different from the fixing unit described in the first embodiment, a so-called induction heating type fixing unit will be used.

  FIG. 20 is a diagram showing a schematic configuration model diagram of an electromagnetic induction heating type fixing unit according to Embodiment 3 of the present invention.

  The magnetic field generating means includes magnetic cores 62a, 62b, 62c and an exciting coil 63. The magnetic cores 62a, 62b, and 62c are high magnetic permeability members, and are preferably made of a material used for a transformer core such as ferrite or permalloy, and more preferably ferrite having a low loss even at 100 kHz or higher.

  Reference numeral 67 denotes a high-frequency transmission circuit which is a power supply unit (power supply unit), which can generate a high frequency of 20 kHz to 500 kHz by a switching power supply. The exciting coil 63 generates an alternating magnetic flux by the alternating current (high-frequency current) supplied from the power supply unit 67. Reference numerals 61a and 61b are saddle-shaped belt guide members having a substantially semicircular arc cross section, which form a substantially cylindrical body with the opening sides facing each other, and a fixing belt (fixing sleeve) that is a cylindrical electromagnetic induction heating belt on the outside. The first rotating body 20 is externally fitted loosely. The belt guide member 61a holds magnetic cores 62a, 62b, 62c and an exciting coil 63 as magnetic field generating means inside. A sliding member 65 is disposed on the belt guide member 61 a on the inner surface of the fixing belt 20 on the side of the nip portion 27 facing the pressure roller 22. Reference numeral 64 denotes a laterally long pressurizing rigid stay disposed in contact with the inner surface flat portion of the belt guide member 61b. Reference numeral 66 denotes an insulating member for insulating the magnetic cores 62a, 62b, 62c and the exciting coil 63 from the pressurizing rigid stay 64.

  The pressing rigid stay 64 applies a pressing force by a pressing mechanism (not shown). As a result, the sliding member 65 on the lower surface of the belt guide member 61a and the pressure roller 22 are pressed against each other with the fixing belt 20 interposed therebetween to form a fixing nip portion 27 having a predetermined width.

  The pressure roller 22 is rotationally driven by the drive unit 31 in the counterclockwise direction indicated by the arrow. A rotational force acts on the fixing belt 20 by the frictional force between the pressure roller 22 and the outer surface of the fixing belt 20 by the rotation driving of the pressure roller 22, and the inner surface of the fixing belt 20 is a sliding member 65 in the fixing nip 27. The belt guide members 61a and 61b are rotated around the outer circumference of the belt guide members 61a and 61b in a clockwise direction indicated by an arrow with a peripheral speed substantially corresponding to the rotational peripheral speed of the pressure roller 22 while sliding in close contact with the lower surface of the belt. In this case, in order to reduce the mutual sliding frictional force between the lower surface of the sliding member 65 and the inner surface of the fixing belt 20 in the fixing nip portion 27, the lower surface of the sliding member 65 and the inner surface of the fixing belt 20 are fixed. A lubricant such as heat-resistant grease can be interposed between the two.

  The alternating magnetic flux guided to the magnetic cores 62a, 62b, 62c is an electromagnetic induction heating layer as a heating body of the fixing belt 20 between the magnetic cores 62a and 62b and between the magnetic cores 62a and 62c. An eddy current is generated (not shown). This eddy current generates Joule heat (eddy current loss) in the electromagnetic induction heat generating layer due to the specific resistance of the electromagnetic induction heat generating layer in the fixing belt 20 described later. Here, the heat generation region is defined as a region where the heat generation amount is Q / e or more, where Q is the maximum heat generation amount. This is an area where a heat generation amount necessary for fixing can be obtained.

  In the electromagnetic induction heating type fixing unit shown in the third embodiment, the fixing belt 20 used here is a heat generating layer (not shown) made of a metal belt or the like as a base layer of the electromagnetic induction heat generating fixing belt 20. ), An elastic layer (not shown) laminated on its outer surface, and a release layer (not shown) laminated on its outer surface. For adhesion between the heat generating layer and the elastic layer and adhesion between the elastic layer and the release layer, a primer layer (not shown) may be provided between the layers. In the fixing belt 20 having a substantially cylindrical shape, the heat generating layer is on the inner surface side, and the release layer is on the outer surface side. As described above, when an alternating magnetic flux acts on the heat generating layer, an eddy current is generated in the heat generating layer, and the heat generating layer generates heat. The heat heats the fixing nip portion 27 through the elastic layer and the release layer, and heats the recording material P as the material to be heated that is passed through the fixing nip portion 27 to heat and fix the toner image. .

  The temperature of the fixing belt 20 is controlled so that a predetermined temperature is maintained by controlling the current supply to the exciting coil 63 by the temperature control systems 21 and 67 including the main thermistor 18 and the sub-thermistor 19 as temperature detecting means. It is adjusted. That is, the main thermistor 18 is temperature detecting means for detecting the temperature of the fixing belt 20, and in the third embodiment, the main thermistor 18 is exposed to the heat generation area H on the inner surface of the fixing belt 20 on the outer surface of the belt guide member 61a. Are arranged. The main thermistor 18 contacts the inner surface of the fixing belt 20 and detects the temperature of the fixing belt 20. The temperature information of the fixing belt 20 measured by the main thermistor 18 is input to the control unit 21. The control unit 21 controls the current supply from the power supply unit 67 to the exciting coil 63 based on the input temperature information, and adjusts the temperature of the fixing belt 20, that is, the temperature of the fixing nip portion 27 to a predetermined temperature.

  Thus, the fixing belt 20 rotates, and the electromagnetic induction heat generation of the fixing belt 20 is performed as described above by the power supply from the power supply unit 67 to the excitation coil 63, and the fixing nip portion 27 rises to a predetermined temperature to control the temperature. In this state, the recording material P on which the unfixed toner image t conveyed from the image forming unit is formed has an image surface facing upward between the fixing belt 20 and the pressure roller 22 of the fixing nip 27, that is, fixing. The toner is introduced so as to face the belt surface, and in the fixing nip portion 27, the image surface is in close contact with the outer surface of the fixing belt 20, and the fixing nip portion 27 is nipped and conveyed together with the fixing belt 20. In the process in which the recording material P is nipped and conveyed together with the fixing belt 20 through the fixing nip portion 27, the fixing belt 20 is heated by electromagnetic induction heat generation, and the unfixed toner image t on the recording material P is heated and fixed. When the recording material P passes through the fixing nip portion 27, it is separated from the outer surface of the fixing belt 20 and discharged and conveyed. The heat-fixed toner image on the recording material is cooled to a permanent fixed image after passing through the fixing nip.

  Since the counting method in this case is the same as that in the first embodiment, the description thereof will be omitted. However, it is impossible to use the temperature detected by the thermistor in the configuration of the present embodiment. The method described below is used.

  In the present embodiment, as in the first embodiment, the intermittent time exceeds 300 seconds and the count value is subtracted by “0.2” every 10 seconds. This numerical value is determined in the fixing unit according to the third embodiment, and it is possible to obtain this count with a weight for each elapsed time and obtain it by a calculation formula or a method of selecting from a table. Good.

  The effect of using the third embodiment is the same as that of the first embodiment in principle, and the same effect can be obtained.

  As described above, according to the third embodiment, even when a fixing unit different from that of the first embodiment is used, particularly when the approximate temperature of the pressure roller 22 cannot be detected by the thermistor, the fixing unit is started up. By using the count value according to the number of times, the temperature of the pressure roller 22 can be accurately predicted regardless of the use state of the fixing unit, and the fixing speed according to the temperature of the pressure roller 22 can be selected. . As a result, it is possible to prevent the occurrence of image defects and JAM that occur when the fixing speed is inappropriate.

(Other examples)
In the first to third embodiments described above, the process speed is 100 mm / second in the “plain paper mode”, 30 mm / second in the “OHT mode”, and the temperature control temperature has been described as shown in FIG. However, depending on the type of recording material and the image quality of the image to be obtained, or depending on conditions such as obtaining better fixability, the present invention can be achieved even if the process speed, print speed, and temperature control temperature are set differently. It is possible to apply. At this time, it goes without saying that the table serving as the count condition varies depending on the process speed and the temperature control temperature.

  In the first, second, and fourth embodiments, the heating body does not necessarily have to be located in the fixing nip portion 27. For example, the heat source can be disposed upstream or downstream of the fixing nip portion 27 in the fixing belt moving direction.

  In the first to third embodiments, the single photo interrupter 30a used for the loop sensor 30 has been described. More stable loop control can be performed by arranging a plurality of photo interrupters and providing a fixing speed of three or more stages. Even in this case, the present invention can be applied.

  The fixing unit of the present embodiment carries not only a fixing unit that heat-fixes an unfixed image as a permanent image on a recording material, but also an image heating device that presupposes an unfixed image on a recording material, and an image. Also included is an image heating apparatus that reheats the recording material to improve image surface properties such as gloss.

  In the present invention, the image forming method of the image forming apparatus is not limited to the electrophotographic method, and may be an electrostatic recording method, a magnetic recording method, or the like, or may be a transfer method or a direct method.

  Note that the present invention can be applied to a system (for example, a copier, a facsimile machine, etc.) composed of a single device even if it is applied to a system composed of a plurality of devices (for example, a host computer, interface device, reader, printer). May be.

  Another object of the present invention is to supply a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and the computer (or CPU or CPU) of the system or apparatus. (MPU) can also be achieved by reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer is actually executed based on the instruction of the program code. This includes a case where part or all of the processing is performed and the functions of the above-described embodiments are realized by the processing.

  Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. The case where the CPU of the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing is also included. For example, it goes without saying that this processing is performed by a driver on a PC.

FIG. 2 is a schematic configuration diagram illustrating a configuration of a recording unit of a color image forming apparatus. 3 is a model diagram illustrating a schematic configuration (including a transfer unit portion) of the fixing unit 12 of the image forming apparatus. FIG. 3 is a perspective model diagram illustrating the positional relationship among a fixing heater 16, a main thermistor 18, and a sub-thermistor 19 in the fixing unit 12. FIG. Structural model diagram of an example of ceramic heater used in fixing heater 16 3 is a block diagram of a control unit 21 and a fixing heater driving circuit 28 as temperature control means of the fixing unit 12. FIG. 2 is a schematic configuration diagram of a loop sensor 30. FIG. 3 is a block diagram of a control unit 21 and a drive unit 31 as drive means for the fixing unit 12. FIG. It is a figure explaining switching of the rotation speed of a fixing motor. FIG. 6 is a diagram for explaining a relationship between an intermittent time and a value counted up each time the fixing device 12 is started up. It is a figure explaining the relationship between the thermistor detection temperature and the value counted up for every apparent start-up. It is a flowchart explaining the update process of the count value memorize | stored in EEPROM. It is a figure which shows the temperature of the pressure roller corresponding to a count number according to the kind of recording material (recording sheet). It is a figure which shows the target rotation speed of the fixing motor with respect to pressure roller temperature. It is a figure which shows the relationship between a pressure roller temperature and a fixing speed. 6 is a flowchart illustrating control of a fixing unit. It is a figure which shows the relationship between pressure roller temperature and fixing motor rotation speed. It is a figure which shows the relationship between pressure roller temperature and fixing motor rotation speed. FIG. 6 is a diagram illustrating a relationship between a pressure roller temperature and a fixing speed in Comparative Example 1. FIG. 6 is a diagram illustrating a relationship between a pressure roller temperature and a fixing speed in Comparative Example 2. FIG. 6 is a schematic configuration model diagram of an electromagnetic induction heating type fixing unit according to a third embodiment. FIG. 6 is a diagram illustrating an example of a conventional belt fixing unit 201.

Claims (10)

An image forming apparatus including a fixing unit for heating and fixing an unfixed toner image on a recording material,
Conveying means for conveying the unfixed toner image formed on the recording material to the fixing unit at a predetermined conveying speed;
A first rotating body of the fixing unit;
A temperature raising means for raising a temperature of a local part of the first rotating body by receiving power supply;
A second rotating body that sandwiches and conveys the first rotating body and the recording material;
Driving means for rotationally driving the second rotating body;
A first conveying speed of the fixing unit that is slower than a conveying speed of the conveying means;
A second conveying speed of the fixing unit that is faster than the conveying speed of the conveying means;
Loop detecting means for detecting the degree of loop of the recording material generated between the fixing unit and the conveying means by a speed difference between the conveying speed of the fixing unit and the conveying speed of the conveying means;
A speed control step of the fixing unit that controls switching between the first transport speed and the second transport speed of the fixing unit using the detection result of the loop detection means, and controls the generated loop;
An update process for updating the count value;
A drive control step of controlling the respective rotation speeds of the drive means for achieving the first transport speed and the second transport speed based on the count value updated by the update step;
And a control method in the image forming apparatus. A time interval measuring step of measuring a starting time interval of the fixing unit;
A determination step of determining an update value corresponding to the number of activations of the fixing unit according to the activation time interval measured by the time interval measurement step;
Further comprising
The control method according to claim 1, wherein the update step updates the count value based on the update value determined by the determination step. A sheet number measuring step of measuring the number of recording material transported sheets of the fixing unit;
3. The determination step according to claim 1, wherein the determining step determines an update value corresponding to the number of recording material transported sheets of the fixing unit in accordance with the number of recording material transported sheets measured in the number of sheet counting step. Control method.   4. The control method according to claim 1, wherein, in the determination step, the update value is determined to be a negative value when a predetermined time has elapsed after the heating operation of the fixing unit is stopped. 5. .   The control method according to any one of claims 1 to 4, wherein the count value corresponds to a temperature of the second rotating body. Further comprising a temperature detection element in the vicinity of the heating source,
2. The count value is updated based on a temperature value detected by the temperature detection element when an activation time interval of the fixing unit measured in the time interval measurement step is a predetermined value or more. 6. The control method according to any one of 5 above. The loop detection means includes an actuator that is displaced according to the degree of loop of the recording medium, a photo interrupter that generates a detection signal according to the displacement of the actuator,
The control method according to any one of claims 1 to 6, further comprising:   The control method according to claim 1, wherein the transport unit is a transfer unit that supports and transports the recording medium and transfers a toner image formed on an image carrier. . The transport speed control means is configured to switch the transport speed of the downstream unit stepwise in accordance with the loop degree of the recording medium detected by the loop detection means.
The control method according to any one of claims 1 to 8, wherein:   The temperature raising means includes a heater that is provided in the vicinity of the pressure contact portion and generates heat by energization, or a coil that generates an eddy current in the first rotating body by generating a magnetic field by energization. Item 10. The control method according to any one of Items 1 to 9.

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