JP2013195502A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve energy saving while maintaining quality of a fixed image irrespective of print conditions and types of recording media.SOLUTION: A fixing device comprises: a fixing rotating member that is heated by a heat source and contacts an unfixed toner image on a recording medium; a pressure rotating member that comes into pressure contact with the fixing rotating member to form a fixing nip part; and a housing that accommodates the rotating members; and performs fixing processing by passing the recording medium through the fixing nip part and applying heat and pressure to the recording medium. An openable/closable shield plate is provided to at least one of an entrance and an exit of the housing in a recording medium conveyance path so that a temperature of the recording medium is controlled to become a predetermined temperature immediately after passing through the fixing nip part.

Description

  The present invention relates to a fixing device mounted on an image forming apparatus, such as a printer, a facsimile machine, a copying machine, or a multi-function machine having at least two of these functions, and in particular, fixing that achieves energy saving while maintaining a high fixing quality. It relates to the improvement of the device.

  In the image forming apparatus, various recording media such as those having a small basis weight or a large basis weight, or coated paper and non-coated paper are used. In addition, image forming apparatuses are used in various ways. In an image forming apparatus with a slow printing speed, a small number of sheets are printed and the power is often turned off. In an image forming apparatus with a high printing speed, many sheets are continuously printed. Often printed.

  Under such circumstances, there is a demand for energy saving (low power consumption) technology of a fixing device that consumes the most power energy in the electrophotographic process. In the flow, heat storage capable members such as a fixing roller and a pressure roller of the fixing device are being reduced in heat capacity, and the pressure roller itself is configured not to perform temperature control. Although such an apparatus configuration is energy saving, there is a problem that the fixing quality of the fixed toner image on the recording medium is easily affected by the temperature of the pressure roller that does not perform temperature control during printing. Even when the temperature of the pressure roller is low, the fixing roller temperature is controlled so that the fixing quality can be satisfied. May become excessively high, and when the recording medium is heated at the high temperature, there is a problem that an excessive amount of heat is applied to the recording medium.

  In order to save energy, for example, in Patent Document 1 and Patent Document 2, a shielding plate is provided at a paper passing opening (mainly at the fixing outlet) of the fixing device, and is shielded mainly during standby except during paper passing (at the time of image formation). A configuration is also proposed in which the heat of the heating member is not released to the outside of the apparatus by closing the plate.

  According to such a configuration, the heat of the member in the fixing device heated mainly during paper passing (image formation), mainly the fixing member of the fixing roller and the fixing belt, and the pressure member of the pressure roller and the pressure belt are fixed. It can be stored efficiently in the device. Accordingly, the time required for heating when starting a new image formation from the standby state can be shortened, and the power can be reduced accordingly.

  However, with the conventional fixing temperature control method, even when an open / close type shielding plate is used, the power during continuous image formation (paper passing) that requires a large amount of power after that cannot be reduced except for fixing start-up. .

  In view of the above problems, an object of the present invention is to realize energy saving while maintaining the quality of a fixed image regardless of printing conditions and the type of recording medium.

  According to the present invention, in order to achieve the above object, a fixing rotating member that is heated by a heating source and is in contact with an unfixed toner image on a recording medium, and a pressure that presses the fixing rotating member to form a fixing nip portion. A fixing device that has a rotating member and a housing that accommodates the rotating member, and performs fixing processing by heating and pressurizing the recording medium through the fixing nip portion, and includes an inlet and an outlet in the casing of the recording medium conveyance path A shield plate that can be opened and closed is provided on at least one side, and the temperature of the recording medium immediately after passing through the fixing nip is controlled to be a predetermined temperature.

  In the present invention, an openable / closable shielding plate is provided at at least one of the entrance and the exit of the casing of the recording medium conveyance path, and the temperature of the recording medium immediately after passing through the fixing nip is controlled to be a predetermined temperature. With this combination, it becomes possible to reduce the power supply other than fixing start-up.

1 is a cross-sectional view schematically illustrating an example of an electrophotographic image forming apparatus. 1 is a cross-sectional view schematically illustrating an example of a fixing device according to the present invention. 6 is a graph showing changes in detected temperature between a pressure roller and a fixing device casing. 6 is a graph showing a change in detected temperature and an integrated power amount at a fixing roller and a pressure roller in job 4. It is a graph which expands and shows a part of FIG. 6 is a graph in which a difference in electric energy with and without a shielding plate is plotted with the time axis aligned with the trailing edge of a final discharged sheet in job 4.

  FIG. 1 is a cross-sectional view schematically illustrating an example of an internal configuration of a general electrophotographic image forming apparatus. Since the configuration of the image forming apparatus is known except for the configuration of the fixing device and the temperature control method according to the present invention, which will be described later, the configuration and operation will be described first.

  An image reading device 200 is installed on the image forming apparatus main body 100, and a duplex unit 300 is attached to the side surface. In the image forming apparatus main body 100, an endless belt-like intermediate transfer belt 11 that is wound around a plurality of rollers and stretched almost horizontally is disposed, and is configured to run counterclockwise. Below the intermediate transfer belt 11, image forming devices 12c, 12m, 12y, and 12k for cyan, magenta, yellow, and black toners are arranged in a quadruple tandem manner along the traveling direction of the intermediate transfer belt 11. It has been. Each of the image forming devices 12c, 12m, 12y, and 12k is configured by installing a charging device, a developing device, a transfer device, a cleaning device, and the like around a drum-shaped image carrier that rotates clockwise in the drawing. Further, an exposure device 13 is provided below the image forming devices 12c, 12m, 12y, and 12k.

  Below the exposure device 13, there is provided a paper feed device 14 having a paper feed cassette 15 in which the recording media P are stacked and stored. The paper feed device 14 has a two-stage configuration in the illustrated example. Yes. In the upper right of each sheet feeding cassette 15, a sheet feeding roller 17 that feeds the recording medium P in each sheet feeding cassette 15 one by one and puts it into the recording medium conveyance path 16 is provided. The recording medium conveyance path 16 in the illustrated example is formed on the right side in the image forming apparatus main body 100 and vertically upward, and is formed in the cylinder formed between the image forming apparatus main body 100 and the image reading apparatus 200. It leads to the paper discharge unit 18. In the recording medium conveyance path 16, a conveyance roller 19, a secondary transfer device 21 facing the intermediate transfer belt 11, a fixing device 119, a paper discharge device 23 including a pair of paper discharge rollers, and the like are provided in the order of recording medium conveyance. ing. On the upstream side of the conveyance roller 19 in the conveyance direction of the recording medium, the recording medium P once formed and fixed on the surface is fed again from the duplex unit 300 to the recording medium conveyance path 16, or the duplex unit 300 A paper feed path 37 is provided to manually feed the recording medium P from the manual paper feeder 36 across the recording medium, and joins the recording medium conveyance path 16. Further, a re-feed conveyance path 24 to the duplex unit 300 is provided on the downstream side of the fixing device 119 in the recording medium conveyance direction.

  When taking a copy with this image forming apparatus, each image forming apparatus in which a document image is read by the image reading apparatus 200 and latent images corresponding to the color toner images of the read image are uniformly charged using a charging device. Writing is performed using the exposure apparatus 13 on the image carriers 12c, 12m, 12y, and 12k. Further, each color toner latent image on each image forming device 12c, 12m, 12y, 12k is provided with each color toner from the developing device to form a toner image, and the toner image is transferred to the primary transfer device 25c. , 25m, 25y, and 25k, the desired color image is formed on the intermediate transfer belt 11 by primary transfer sequentially onto the intermediate transfer belt 11.

  On the other hand, by selectively rotating one of the paper feed rollers 17 in the two-stage paper feed cassette, the recording medium P is fed out from the corresponding paper feed cassette 15 and put into the recording medium transport path 16 (or manually fed). A manual feed recording medium may be put into the paper feed path 37 from the paper device 36). The recording medium P conveyed to the conveying roller 19 through the recording medium conveying path 16 is subjected to the secondary transfer of the secondary transfer device 21 by the conveying roller 19 in timing with the toner image formed on the intermediate transfer belt 11. At this time, the color image on the intermediate transfer belt 11 is transferred to the recording medium P by the secondary transfer device 21. The recording medium P on which the image has been transferred is fixed by receiving heat and pressure by the fixing device 119, and then discharged onto the in-body discharge portion 18 by the discharge device 23 and stacked. Thus, the image forming operation is completed.

  When an image is also formed on the back surface of the recording medium P, the recording medium P once fixed on the surface of the recording medium P is switched using a switching claw (not shown) for switching the conveyance path. The sheet is placed in the refeed conveyance path 24 and introduced into the duplex unit 300. When passing through the duplex unit 300, the recording medium P is introduced into the paper feed path 37 with its front and back sides reversed, and is fed again to the recording medium transport path 16 through the paper feed path 37. . Thereafter, the color image for the back surface separately formed on the intermediate transfer belt 11 is secondarily transferred to the recording medium P in the same manner as that on the front surface, fixed again by the fixing device 119, and in the cylinder by the paper discharge device 23. The paper is discharged to the paper discharge unit 18.

Next, the configuration of the fixing device 119 will be described. Incidentally, the fixing device is not limited to the so-called heat roller type in this example, but may be of a so-called belt type.
As shown in FIG. 2, the fixing device 119 includes an induction heating unit 125 (magnetic flux generating means), a fixing roller 120 as a fixing rotation member facing the induction heating unit 125, and a pressure rotation member that is in pressure contact with the fixing roller 120. As a pressure roller 130, an inlet guide plate 141, a spur 142, a separation plate 143, a guide member 150, a shielding plate 155, and the like. Here, the fixing roller 120 is obtained by sequentially laminating a heat insulating elastic layer 122 made of foamed silicone rubber or the like and a sleeve layer 121 on a core metal 123 made of iron or stainless steel, and has an outer diameter of about 40 mm. Is formed. The sleeve layer 121 of the fixing roller 120 is a multilayer structure in which a base material layer, a first oxidation prevention layer, a heat generation layer, a second oxidation prevention layer, an elastic layer, and a release layer are sequentially laminated from the inner peripheral surface side. More specifically, the base material layer is formed of a stainless steel foil having a thickness of about 40 μm, and the first antioxidation layer and the second antioxidation layer are formed by strike plating with a nickel thickness of 1 μm or less. The heat generating layer is made of copper with a layer thickness of about 10 μm, the elastic layer is made of silicone rubber with a layer thickness of about 150 μm, and the release layer has a layer thickness of 30 μm. It is formed of about PFA (tetrafluoroethylene / barfluoroalkyl vinyl ether copolymer).

  In the fixing roller 120 configured as described above, the heat generating layer of the sleeve layer 121 is electromagnetically heated by the magnetic flux generated from the induction heating unit 125. The configuration of the fixing roller 120 is not limited to the one in this example, and for example, the sleeve layer 121 (fixing sleeve) can be separated without being bonded to the heat insulating elastic layer 122 (fixing auxiliary roller). . However, when the sleeve layer 121 is separated, it is preferable to install a member for preventing the sleeve layer 121 from moving in the width direction (thrust direction) during operation.

  A plurality of spurs 142 are arranged in parallel in the width direction of the recording medium at a position facing the fixing roller 120 and upstream of the fixing nip portion (upstream side in the recording medium conveyance direction). The spur 142 reliably guides the recording medium P fed into the fixing nip portion to the fixing nip portion. The peripheral surface of the spur 142 is formed in a saw-tooth shape so that even if an unfixed image on the recording medium P is brought into contact with the unfixed image, the image is not rubbed.

  A separation plate 143 is installed at a position facing the fixing roller 120 and downstream of the fixing nip portion (downstream of the recording medium conveyance direction). The separation plate 143 is for preventing a problem that the recording medium P after the fixing process sent from the fixing nip portion is wound around the fixing roller 120. That is, when the recording medium P after the fixing process is attracted to the fixing roller 120, the separation member 143 interferes with the leading end of the recording medium P, and the recording medium P is forcibly separated from the fixing roller 120.

  The fixing roller 120 is provided with a thermistor (contact temperature sensor, temperature probe) 157 for detecting the surface temperature. Instead of the thermistor, a thermopile (non-contact temperature sensor) may be arranged. And based on the detection result by such a temperature sensor, the heating amount by the induction heating part 125 is adjusted.

  A pressure roller 130 that forms a fixing nip portion by pressing against the fixing roller 120 is formed on a cylindrical member 132 made of aluminum, copper or the like, an elastic layer 131 made of silicone rubber, or a release layer made of PFA ( (Not shown). The elastic layer 131 of the pressure roller 130 is formed to have a thickness of 1 to 5 mm. Further, the release layer of the pressure roller 130 is formed to have a layer thickness of 20 to 50 μm. In this example, in order to increase the heating efficiency of the fixing roller 120, a heater 133 such as a halogen heater may be provided inside the pressure roller 130. By supplying power to the heater 133, the pressure roller 130 is heated by the radiant heat of the heater 313, and the surface of the fixing roller 120 is also heated via the pressure roller 130. A thermistor (contact temperature sensor, temperature probe) 156 for detecting the surface temperature of the pressure roller 130 is also provided. However, for the purpose of energy saving, the heater 313 on the pressure roller 130 side is turned off except when it is started up, and temperature control is not performed by the pressure roller.

  An inlet guide plate 141 is installed at a position facing the pressure roller 130 and upstream of the fixing nip portion. The entrance guide plate 141 guides the recording medium P fed into the fixing nip portion. A guide member 150 is located at a position facing the pressure roller 130 and downstream of the fixing nip portion (a side facing the back surface of the toner placement surface of the recording medium P sent from the fixing nip portion). is set up. The guide member 150 is for guiding the recording medium P after the fixing process sent from the fixing nip portion toward the conveyance path after the fixing process.

  The induction heating unit 125 includes a coil unit 126 (excitation coil), a core unit 127 (excitation coil core), a coil guide 128, and the like. The coil portion 126 extends in the width direction (perpendicular to the paper surface of FIG. 2) by winding a litz wire bundled with thin wires on a coil guide 128 disposed so as to cover a part of the outer peripheral surface of the fixing roller 120. It is a thing. The coil guide 128 is made of a resin material having high heat resistance, and holds the coil portion 126 on the side facing the fixing roller 120. The core portion 127 is made of a ferromagnetic material such as ferrite (relative magnetic permeability is about 2500), and is for forming an efficient magnetic flux toward the heat generating layer of the fixing roller 120, and includes an arch core, a center core, and a side core. Etc. The induction heating unit 125 is configured to be separable from the main part of the fixing device 119 (a unit excluding the induction heating unit in the fixing device shown in FIG. 2). The main part of the fixing device 119 is separated from the induction heating unit 125 and taken out from the image forming apparatus main body 1 with the cover (not shown) of the image forming apparatus main body 1 being opened. In other words, since the unit can be replaced while leaving the induction heating portion that is a heating member (by replacing the fixing roller, belt, etc., which is a life component), an expensive and durable heating member can be used repeatedly, which is efficient. .

  The configuration in which the induction heating unit 125 is separated from the main part of the fixing device 119 has been described above. However, the configuration is not limited to such a configuration, and the induction heating unit 125 may be configured integrally with the fixing device 119. If it is an integral structure, both positioning accuracy becomes high and can improve a heating efficiency. If the induction heating unit 125 becomes inexpensive or the life of the fixing roller or the like becomes long, the integrated configuration is an effective method. Further, the heating method is not limited to induction heating, and the same effect can be exhibited even if the heating method is replaced with a heating means having a good thermal response such as a planar heating element.

  The shielding plate 155 stands by at the position shown in FIG. 2 while the recording medium P is being conveyed, opens the recording medium conveyance path, and guides the recording medium P to the paper discharge path. On the other hand, for example, when the sheet is not continuously fed, until the next recording medium P is conveyed after the fixing process is completed, the recording medium P is moved to the right side in the drawing by an opening / closing mechanism (left / right slide mechanism) (not shown). Close the outlet. Such control (closing operation) may be performed when a so-called sleep mode is entered after a predetermined time has elapsed after the recording medium is discharged. In the fixing device of this example, since the recording medium is transported in a substantially vertical direction from the bottom to the top, the shielding plate is provided only at the top of the fixing device. It is reasonable to provide a shielding plate not only on the exit side of the recording medium conveyance path but also on the entrance side.

  In particular, when the induction heating unit 125 is configured to be separable from the main part of the fixing device 119, a sufficient clearance (gap) is required between the main part of the fixing device 119 and the induction heating unit 125 (vertical). In the case of conveyance, especially between the induction heating unit, the fixing roller 130, and the separation plate 143 A), in the conventionally known configuration, the heat accumulated from this gap escapes, but the shielding plate 155 also has this gap. At the same time, it can be covered (closed) to prevent heat dissipation to the outside.

  The shielding plate 155 and the opening / closing mechanism (not shown) are provided on the induction heating unit 125 side, that is, on the main body side separated from the fixing unit side. As a result, when replacing the fixing unit, only the units around the required durable parts can be replaced without replacing unnecessary parts, which is advantageous in terms of environment and cost.

  A temperature sensor 159 that detects the temperature inside the fixing device is provided in the vicinity of the pressure roller 130 inside the fixing device 119. If the temperature inside the machine becomes too high, the paper guide members such as the inlet guide plate 141 and the guide member 150 will dew and jam will occur, the paper will become weak and the leading edge will jam, or the paper curl after fixing Therefore, when the temperature detected by the temperature sensor 159 is equal to or higher than a certain value (for example, when the temperature is 55 ° C. or higher), the shielding plate 159 is opened to control the temperature in the apparatus to be lowered. As a result, the above problems can be suppressed.

  The fixing device 119 configured as described above operates as follows. The fixing roller 120 is driven to rotate counterclockwise in FIG. 2 by a drive motor (not shown), and the pressure roller 130 is rotated clockwise accordingly. The sleeve layer 121 (heat generation layer) of the fixing roller 120 is heated by the magnetic flux generated in the induction heating unit 125 at a position facing the induction heating unit 125. More specifically, the oscillation circuit causes a high frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) to flow from the coil unit 126 to the coil unit 126 from a power source unit (not shown) whose frequency is variable. The magnetic field lines are formed so as to alternately switch in both directions toward the sleeve layer 121. By forming an alternating magnetic field in this manner, an eddy current is generated in the heat generating layer of the sleeve layer 121, and the heat generating layer generates Joule heat due to its electrical resistance and is induction-heated. Thus, the sleeve layer 121 (fixing roller 120) is heated by induction heating of its own heat generation layer.

  Thereafter, the surface of the fixing roller 120 heated by the induction heating unit 125 reaches a contact portion (fixing nip portion) with the pressure roller 130 by roller rotation. Then, the toner image T (toner) on the conveyed recording medium P is heated and melted. More specifically, the recording medium P carrying the toner image T through the image forming process described above is fed between the fixing roller 120 and the pressure roller 130 while being guided by the entrance guide plate 141 (or the spur 142). (Arrow Y1). The toner image T is fixed on the recording medium P by the heat received from the fixing roller 120 and the pressure received from the pressure roller 130, and the recording medium P is sent out between the fixing roller 120 and the pressure roller 130 ( Arrow Y2). After that, the surface of the fixing roller 120 that has passed through the fixing nip portion again reaches a position facing the induction heating unit 25. Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

  Next, a temperature control method of the fixing device 119 will be described. As described above, the thermistor (contact temperature sensor) 157 is disposed around the fixing roller 120, and the temperature of the fixing roller 120 is detected by such a temperature sensor. Then, based on the information on the temperature deviation between the actually detected temperature of the fixing roller 120 and the target control temperature of the specified fixing roller 120, the temperature is detected via a fixing temperature controller (not shown) connected to the temperature sensor. Controlling the energization time (= DUTY) to the induction heating unit 125 per unit time, that is, controlling the electric power applied to the induction heating unit 125 to control the temperature of the fixing roller 120 through a PWM drive circuit (not shown). To do. In the above-described form, the power of the induction heating unit 125 is controlled so that the amount of heat applied to the recording medium P and the toner image is in a predetermined state.

  On the other hand, in the fixing device of this example, from the viewpoint of energy saving, the heater 313 on the pressure roller 130 side is turned off except when it is started up so that heat is not accumulated in the pressure roller on the non-image surface side. The temperature control of the pressure roller itself is not performed. In spite of this, the temperature of the recording medium immediately after passing through the fixing device is controlled to be a predetermined constant value or at least a constant temperature range. Thereby, the image quality after image fixing such as fixing strength and glossiness can be made constant. According to the experiments by the present inventors, it is preferable to control the temperature range of the post-fixing recording medium temperature within 5 ° C.

  In the fixing device having such a configuration, the simplest method for keeping the post-fixing recording medium temperature constant irrespective of the printing conditions and the recording medium to be used is as a recording medium temperature measuring device near the outlet of the fixing nip portion. A non-contact temperature sensor is installed, temperature is detected from the leading edge to the trailing edge of the recording medium immediately after fixing, for example, at a measurement cycle of 10 msec, and the average value is used as the recording medium temperature after fixing, and feedback control is performed based on this result. Is to do. However, such a temperature sensor has not been installed in the past, and a relatively expensive member is added, and in order for feedback control to follow the detected recording medium temperature after fixing well, a heating source is used. A member with higher performance in heating performance and heat transfer performance of the fixing roller, that is, a member having heating and heat dissipation performance capable of reaching the detection result temperature at a high speed is required, leading to an increase in cost of the image forming apparatus. . Therefore, the post-fixing recording medium temperature is not directly measured, but the post-fixing recording medium temperature is predicted based on the detection result by the thermistor (temperature sensor) 156 provided on the pressure roller side, and the fixing obtained by the calculation is performed. It is recommended to control the fixing roller temperature so that the post-recording medium temperature falls within a predetermined temperature range.

  In order to control the post-fixing recording medium temperature at a constant level, it is conceivable to control the nip time in addition to the pressure roller temperature control. However, the results obtained from the experiments by the present inventors have shown that the pressure roller temperature is most sensitive to the post-fixing recording medium temperature and has high controllability. It seems preferable to employ post-fixing recording medium temperature control based on the pressure roller temperature.

  Further, the pressure roller temperature bears a part of the amount of heat supplied to the recording medium by the fixing device and has a great influence on the temperature of the recording medium after fixing, so that the fixing roller according to the heat storage state of the pressure roller. To control the temperature. In other words, when the temperature of the pressure roller is low, the control temperature for the fixing member is set to a high temperature, and when the temperature of the pressure member increases, the control temperature for the fixing member is changed to a low value. The temperature of the post-recording medium is kept constant.

  In other words, when the pressure roller temperature is different, the relationship between the fixing roller temperature and the set temperature of the recording medium after fixing is obtained in advance. A target set value of the fixing roller temperature is determined according to the temperature, and the post-fixing recording medium temperature is kept within a certain temperature control range. Such a relationship can be obtained by repeating a laboratory experiment or an actual machine experiment in which the fixing roller set temperature and the pressure roller temperature are distributed.

  Incidentally, the degree of influence on the post-fixing recording medium temperature due to fluctuations in the pressure member temperature varies depending on recording medium information such as nip time, basis weight, thermal conductivity, specific heat, and moisture content. Therefore, in consideration of the recording medium information such as nip time, basis weight, thermal conductivity, specific heat, moisture content, etc., the relationship between the pressure member temperature difference and the fixing member temperature setting value can be adjusted more accurately. It is possible to make the recording medium temperature constant after fixing.

  For example, considering that the fixing member temperature setting value is corrected by the nip time (time defined as a value obtained by dividing the fixing nip width by the conveyance speed of the recording medium), when the fixing member and the pressure member are accumulated, Since the fixing nip width w (see FIG. 2) changes due to thermal expansion, it changes according to the heat storage state of the fixing device, so how the influence of the pressure member temperature changes depending on the nip time. Evaluate by experiment and simulation in actual machine and laboratory. In our experiments, it has been found that the longer the nip time, the greater the influence of the pressure member temperature on the recording medium temperature. Accordingly, the fixing roller set temperature is determined not only based on the detection result of the pressure roller temperature by the pressure roller thermistor (temperature sensor) 156 but also corrected by the recording medium information such as the nip time, and thus the recording medium temperature after fixing. Is more preferably corrected by the nip time. If the post-fixing recording medium temperature is corrected in this manner, temperature control closer to the target post-fixing recording medium temperature becomes possible.

  Regarding the basis weight of the recording medium, it has been found through experiments by the present inventors that the smaller the basis weight, the greater the influence of the temperature of the pressure member on the recording medium temperature. Regarding the thermal conductivity of the recording medium, it has been found through experiments by the present inventors that the influence of the temperature of the pressure member on the recording medium temperature increases as the thermal conductivity increases. Regarding the specific heat of the recording medium, it has been found through experiments by the present inventors that the effect of the temperature of the pressure member on the recording medium temperature is relatively small if the specific heat is small. Regarding the moisture content of the recording medium, it has been found through experiments by the present inventors that the effect of the temperature of the pressure member on the recording medium temperature is relatively small if the moisture content is small.

  Further, if the recording medium information such as nip time, basis weight, thermal conductivity, specific heat, and moisture content is combined, that is, at least two of these recording medium information is used to correct the post-fixing recording medium temperature, the accuracy is further improved. The post-fixing recording medium temperature can be calculated well, and as a result, the temperature control range of the post-fixing recording medium temperature can be further reduced.

  As described above, the recording medium temperature after fixing is controlled, and the power consumption when the shielding plate is opened and closed in the fixing device that suppresses heat radiation by the shielding plate, as well as the power consumption without the shielding plate and the temperature of each part. An example of measurement comparison is described below.

  In order to understand the power consumption of the fixing device, it is necessary to grasp the relationship between the temperatures of the fixing unit. Therefore, in addition to the temperature sensor for the pressure roller and the temperature sensor for the fixing roller already described in the fixing device, fixing A temperature probe (not shown) was also placed in contact with the upper cover of the apparatus. The shield plate 155 was opened and closed by sliding movement after shifting to the sleep mode after discharging the recording medium.

  Job 1 is the energy consumed when the image forming apparatus is left for 1 hour and then the job is started. The condition does not change depending on the presence or absence of a shielding plate. For this reason, energy consumption is the same value. Hereinafter, the difference in energy consumption between the two increases as the job repeats three times at regular intervals.

  Between jobs shown in FIG. 3 to be described later, the heat of the fixing roller and the pressure roller is released into the atmosphere in the apparatus and cooled down during a fixed time interval. In the case of a configuration with a shielding plate, heat does not escape to the outside of the machine, and the heat stays inside the fixing device, so that the fixing roller and the pressure roller are maintained at a high temperature (the heat stays inside the machine). The heat dissipation itself can be reduced.

  FIG. 3 shows the temperature change detected by the temperature probe 156 with respect to the pressure roller 130 and the temperature probe brought into contact with the fixing device upper cover. As the number of jobs increases, the difference in the amount of heat storage becomes remarkable. In job 4, the difference between the pressure roller and the upper cover is 3.3 ° C. and 6.2 ° C., respectively. The difference between the two is also clear by simulation, and in the case of the vertical conveyance type in particular, the effect is large when the shielding plate is provided on the upper side, and the result almost coincides with the temperature result measured in this example.

  FIG. 4 shows changes in the temperature and power consumption of the fixing roller pair in job 4 in which the difference in presence or absence of the shielding plate is most significant. If the time axis is aligned at the temperature rise start time, there will be no difference in the electric energy for a while after the start of job 4. When the temperature rises, the maximum power is applied to increase the temperature of the fixing roller pair (= start up). For this reason, even if there is a difference in the roller temperature at the start of the job as described above, the power amount transition is the same. The fixing temperature control in this example, in which the post-fixing recording medium temperature is controlled based on the pressure roller temperature, is effective in the middle of continuous paper feeding of the job, and a difference in electric energy starts to appear.

  Here, the temperature change of the pressure roller 130 will be described. The pressure roller 130 is deprived of heat by passing paper, and the temperature of the roller surface decreases each time a sheet of paper passes. In the graph of FIG. 4, a temperature drop (upper and lower peaks) corresponding to the number of sheets to be passed is recognized and coincides with the sheet passing timing, so that the sheet passing timing can be estimated by looking at the pressure roller temperature.

  Based on this fact, when a part is enlarged as shown in the graph of FIG. 5, the rise time of the fixing roller 120 is faster when the shielding plate 155 is closed. The last sheet is discharged about 0.5 seconds early. Therefore, the graph of FIG. 6 is a graph in which the time axis is aligned with the trailing edge of the final paper discharge, and the difference in power amount with or without the shielding plate 155 (without shielding plate−with shielding plate) is plotted. When the shielding plate is opened and closed, the rise of the fixing roller 120 is about 0.5 seconds earlier, which saves energy and provides an effect of about 0.13 Wh.

  Further, by using the fixing temperature control in this example, a further effect of about 0.5 Wh is obtained from the time when this control is effective until the final sheet of paper. That is, the heat of the fixing roller pair can maintain the temperature of the fixing roller 120 and the pressure roller 130 with a small amount of electric power. This can also be inferred from the fact that the temperature fluctuation of the fixing roller 120 is small.

  As described above, by combining the fixing temperature control based on the post-fixing recording medium temperature and the shielding plate, in addition to raising the temperature of the fixing roller pair, it is possible to reduce the power supplied during continuous paper feeding. It has been found that a new (specific) energy saving effect different from that of a heat source with low thermal response such as a lamp or a halogen lamp can be obtained.

119 Fixing device 120 Fixing roller 125 Induction heating unit 126 Coil unit (excitation coil)
127 Core (Excitation coil core)
130 Pressure roller 133 Heater 141 Entrance guide plate 142 Spur 143 Separation plate 150 Guide member 155 Shielding plate 156 Pressure roller thermistor 157 Fixing roller thermistor P Recording medium

JP 2003-241551 A JP 2007-086453 A

Claims (7)

  A fixing rotating member heated by a heating source and in contact with an unfixed toner image on the recording medium, a pressure rotating member that presses against the fixing rotating member to form a fixing nip portion, and a housing that accommodates these rotating members. And a fixing device that performs fixing processing by heating and pressurizing the recording medium through the fixing nip portion, and is provided with an openable / closable shielding plate at at least one of an inlet and an outlet in the casing of the recording medium conveyance path. A fixing device in which the temperature of the recording medium immediately after passing is controlled to be a predetermined temperature.   The temperature detection unit for the pressure rotating member is provided, and the temperature of the recording medium immediately after passing through the fixing nip is calculated based on the detection result of the temperature detection unit. Fixing device.   In calculating the temperature of the recording medium immediately after passing through the fixing nip, at least one of nip time, basis weight of the recording medium, thermal conductivity of the recording medium, specific heat of the recording medium, and content of the recording medium is used. The fixing device according to claim 2, wherein correction is performed.   The fixing device according to claim 1, wherein the heating source is of an induction heating type.   5. The recording medium conveyance path according to claim 1, wherein the recording medium conveyance path is formed in a substantially vertical direction from below to above, and the shielding plate is provided on the recording medium conveyance path outlet side of the housing. The fixing device according to Item.   Further temperature detecting means for detecting the temperature inside the casing is provided, and the shielding plate is opened when the temperature inside the casing detected by the further temperature detecting means is a specified temperature abnormality. The fixing device according to claim 1, wherein the fixing device is a feature.   An image forming apparatus comprising the fixing device according to claim 1.

Images