JP2015043020A - Image heating device - Google Patents

Abstract

Provided is an image heating apparatus capable of suppressing the occurrence of image defects caused by uneven temperature in the circumferential direction of a heating rotator and shortening the start-up time by shortening the standby time for eliminating the temperature ripple. . In an image heating apparatus, a heating rotator, a pressurizing member that contacts the heating rotator and forms a nip portion for heating while nipping and conveying the recording material, and image heating the recording material Image heating preparation for starting the rotation of the heating rotator at a second rotation speed slower than the first rotation speed and increasing the rotation speed to the first rotation speed before the recording material enters the nip portion. Control means for displacing the heating rotator at least once during the period. [Selection] Figure 1

Description

  The present invention relates to an image heating apparatus and is suitable for an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer. As an image heating device, a fixing device that heats and fixes an unfixed toner image formed on a recording material as a fixed image, or a glossiness increasing device that increases the glossiness of an image by heating the image fixed on the recording material Etc.

  A fixing device as an image heating device mounted on an image forming apparatus forms a fixing nip portion with a fixing sleeve as a heating rotator and a pressure roller as a pressure member in pressure contact therewith. It is well known that a recording material carrying an unfixed toner image at a fixing nip is heated while nipping and transporting the recording material to fix the toner image on the recording material.

  Here, with the recent increase in the speed and on-demand of image forming apparatuses, the image forming apparatus has a first printout time (the time from the input of a print signal to the completion of the first image output). There is a demand for shortening of FPOT. For this reason, in a fixing device as an image heating device mounted on an image forming apparatus, the time required to raise the temperature of the fixing sleeve to a temperature at which the recording material can be fixed without causing image defects (hereinafter referred to as startup) Time) is required.

  As a fixing device that makes it possible to shorten the start-up time, there has been proposed a fixing device that directly heats the conductive layer of the thin fixing sleeve and generates heat (Patent Documents 1 and 2). Patent Documents 1 and 2 disclose a fixing device configured to generate an alternating magnetic field in the axial direction (longitudinal direction) of a heating rotator and generate heat by Joule heat generated by a current generated in the circumferential direction of the fixing sleeve.

  Patent Document 3 discloses a fixing device configured to generate heat by directly energizing a fixing sleeve having a resistance heating layer formed by dispersing carbon nanomaterials and filamentary metal particles in a polyimide resin. ing. These fixing devices are characterized by a short start-up time because the fixing sleeve itself with a thin wall and a low heat capacity generates heat.

  Further, as a method for further shortening the start-up time of the fixing device, in Patent Document 1, the rotation speed of the fixing sleeve is rotated at a speed slower than the rotation speed during normal operation for a predetermined time from the start of power supply to the induction coil. Thus, a configuration for increasing the temperature rise of the fixing sleeve is disclosed.

  As another method, Patent Document 4 discloses that when the fixing device is started up, the fixing sleeve and the pressure roller are separated from each other and only the fixing sleeve is heated, thereby suppressing the heat transfer to the heating roller. A configuration for increasing the temperature rise is disclosed.

JP 2002-334774 A JP 2011-248098 A JP 2007-272223 A JP 2007-57827 A

  After receiving the print signal, the image forming apparatus starts an image forming operation and starts up the fixing device. At this time, the fixing device needs to raise the temperature of the fixing sleeve to a temperature at which the recording material can be fixed before the recording material carrying the unfixed image enters the fixing device.

  However, in the conventional fixing device, although the rise time can be shortened, a large temperature unevenness may occur in the circumferential direction of the fixing sleeve. That is, when the rotation speed of the fixing sleeve and the pressure roller that have been rotated at a low speed is suddenly switched to the process speed, the temperature rise state of the fixing sleeve largely fluctuates before and after the speed switching.

  The fixing sleeve is heated between passing through the fixing nip portion and entering the fixing nip portion again, and the temperature rises. When the rotation speed is switched suddenly, the time for the fixing sleeve to rise in temperature is relatively long before the speed switching, whereas the time for the fixing sleeve to rise in temperature after the speed switching is relatively short. Become. For this reason, particularly when the rotation speed is switched in a shorter time than one rotation of the fixing sleeve, a region where the temperature rise amount is large and a region where the temperature rise is small are formed in the circumferential direction of the fixing sleeve. As a result, large temperature unevenness occurs in the circumferential direction of the fixing sleeve.

  In particular, priority is given only to shortening of the fixing device start-up time, and when the rotation speed of the fixing sleeve is switched from low speed to process speed immediately before the recording material enters the fixing device, the circumferential direction of the fixing sleeve The fixing operation of the recording material is performed in a state where the temperature unevenness is large. When the fixing operation of the recording material is performed in a state where the temperature unevenness in the circumferential direction of the fixing sleeve is large, image defects such as fixing defects and gloss unevenness may occur.

  As another conventional method, in order to accelerate the temperature rise of the fixing sleeve, the fixing sleeve and the pressure roller are separated from each other when the fixing device is started up. In this case, at least until the recording material enters the fixing nip, the fixing sleeve and the pressure roller must be in a pressure state when fixing the recording material. However, when the fixing sleeve and the pressure roller that have been separated from each other are rapidly switched to the contact state, the amount of heat that moves from the fixing sleeve to the pressure roller increases rapidly before and after that, and immediately after the transition to the contact state. Will cause the temperature of the fixing sleeve to drop significantly.

  As a result, large temperature unevenness occurs in the circumferential direction of the fixing sleeve. In particular, when the recording material is switched from the separated state to the pressure state immediately before entering the fixing device, the fixing operation of the recording material is performed in a state where the fixing sleeve generates a large temperature unevenness in the circumferential direction. Become.

  As described above, when the fixing operation of the recording material is performed in a state where the temperature unevenness in the circumferential direction of the fixing sleeve is large, an image defect such as a fixing defect or a gloss unevenness may occur.

  An object of the present invention is to provide an image heating apparatus that can suppress the occurrence of image defects caused by uneven temperature in the circumferential direction of a heating rotator and can shorten the start-up time by shortening the standby time for eliminating temperature ripples Is to provide.

   In order to achieve the above object, an image heating apparatus according to the present invention includes a heating rotator, a pressurizing member that contacts the heating rotator and forms a nip portion that heats the recording material while nipping and conveying the recording material. The rotation of the heating rotator is started at a second rotation speed that is lower than the first rotation speed when the recording material is image-heated, and the first rotation until the recording material enters the nip portion. Control means for displacing the heating rotator at least once during the period of the image heating preparation period for increasing the speed.

  Another image heating apparatus according to the present invention includes a heating rotator, a pressurizing member that contacts the heating rotator and forms a nip portion that heats the recording material while nipping and conveying the recording material, and the recording material. The rotation of the heating rotator is started with a second pressure smaller than the first pressure when the image is heated, and the pressure is increased to the first pressure until the recording material enters the nip portion. Control means for displacing the heating rotator at least once during the image heating preparation period.

  According to the present invention, it is possible to suppress the occurrence of image defects due to the temperature unevenness in the circumferential direction of the heating rotator, and to shorten the start-up time by reducing the standby time for eliminating the temperature ripple.

(A) is a schematic block diagram of an image forming apparatus using a fixing device as an image heating device according to the first embodiment of the present invention, and (b) is a diagram for explaining the rotational speed and moving distance of the fixing sleeve. . FIG. 3 is a cross-sectional side view of a main part of the fixing device according to the first embodiment. FIG. 3 is a front model view of a main part of the fixing device according to the first embodiment. FIG. 3 is a perspective view of a main part of the fixing device according to the first embodiment. It is sectional drawing of a fixing sleeve and a pressure roller. 6 is a graph showing a change in rotational speed of the fixing sleeve according to the first embodiment. 6 is a graph showing a temperature rise of the fixing sleeve according to the first embodiment. FIG. 6 is a cross-sectional view of a fixing device according to a second embodiment. FIG. 6 is a diagram illustrating a pressure adjustment unit of a fixing device according to a second embodiment. 6 is a graph showing the transition of the contact pressure between the fixing sleeve and the pressure roller according to the second embodiment. 6 is a graph showing a temperature rise of a fixing sleeve according to a second embodiment. 10 is a graph showing a temperature rise of a fixing sleeve according to a third embodiment. 6 is a graph showing a temperature rise of a fixing sleeve in a modified example. It is a front model figure which shows the fixing device in a modification. It is a cross-sectional side model figure which shows the fixing device in a modification.

<< First Embodiment >>
Hereinafter, preferred embodiments for carrying out the present invention will be described in detail with reference to the drawings.

(Image forming device)
FIG. 1A is a schematic configuration diagram of an image forming apparatus 100 equipped with a fixing device as an image heating apparatus according to the present embodiment. The image forming apparatus 100 is an electrophotographic laser beam printer. Reference numeral 101 denotes a photosensitive drum as an image carrier, which is driven to rotate in a clockwise direction indicated by an arrow at a predetermined process speed (circumferential speed). The photosensitive drum 101 is uniformly charged to a predetermined polarity and potential by the charging roller 102 during its rotation.

  Reference numeral 103 denotes a laser beam scanner as an image exposure unit, which outputs a laser beam S that is on / off modulated in response to a digital pixel signal input from an external device such as a computer (not shown) to output the photosensitive drum 101. The charged surface is subjected to scanning exposure. By this scanning exposure, the charge of the exposed bright portion on the surface of the photosensitive drum 101 is removed, and an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 101.

  A developing device 104 supplies developer (toner) to the surface of the photosensitive drum 101 from the developing roller 104a, and the electrostatic latent image on the surface of the photosensitive drum 101 is sequentially developed as a toner image which is a transferable image. Is done. Reference numeral 105 denotes a paper feed cassette on which the recording material P is loaded and stored. The paper feed roller 106 is driven based on the paper feed start signal, and the recording material P in the paper feed cassette 105 is separated and fed one by one. Then, the toner is introduced at a predetermined timing into a transfer portion 108T that is a contact nip portion with the transfer roller 108 that is rotated by contact with the photosensitive drum 101 via the registration roller pair 107.

  That is, the conveyance of the recording material P is controlled by the registration roller 107 so that the leading edge of the toner image on the photosensitive drum 101 and the leading edge of the recording material P reach the transfer portion 108T at the same time. Thereafter, the recording material P is nipped and conveyed at the transfer portion 108T, and during that time, a transfer voltage (transfer bias) controlled to a predetermined level is applied to the transfer roller 108 from a transfer bias application power source (not shown). A transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 108, and the toner image on the surface side of the photosensitive drum 101 is electrostatically transferred onto the surface of the recording material P at the transfer portion 108T.

  The recording material P after the transfer is separated from the surface of the photosensitive drum 101, passes through the conveyance guide 109, and is introduced into a fixing device 113 as a heating device. The fixing device A receives a thermal fixing process for the toner image. On the other hand, the surface of the photosensitive drum 101 after the transfer of the toner image onto the recording material P is cleaned by the cleaning device 110 after removal of transfer residual toner, paper dust, and the like, and is repeatedly used for image formation. The recording material P that has passed through the fixing device 113 is discharged from the discharge port 111 onto the discharge tray 112.

(Image heating device)
In the present embodiment, the fixing device 113 is an electromagnetic induction heating type device. 2 is a cross-sectional side view of the main part of the fixing device 113 of this example, FIG. 3 is a front model view of the main part, and FIG. 4 is a perspective view of the main part.

1) Configuration and Principle of Electromagnetic Induction Heating FIG. 4 is a perspective view showing an exciting coil 3 and a magnetic core 2 for induction heating the heat generating layer 1a of the fixing sleeve, and the fixing sleeve. The magnetic core 2 as a magnetic core material is disposed by penetrating (inserting) the hollow portion of the fixing sleeve by a fixing means (not shown). The exciting coil 3 is formed in a hollow portion of the fixing sleeve 1 by being spirally wound around the magnetic core 2 (winding is performed).

Since the exciting coil 3 is wound inside the fixing sleeve 1 in a direction crossing the axis X of the fixing sleeve 1, a high-frequency current (alternating current) is passed through the exciting coil 3 via the high-frequency converter 305 and the power supply contact portions 3a and 3b. When an electric current is applied, an alternating magnetic flux whose polarity reverses periodically acts. This alternating magnetic flux is generated in a direction parallel to the axis X.
The magnetic core 2 functions as a member that guides a magnetic force line generated by the alternating magnetic field generated by the exciting coil 3 into the fixing sleeve 1 and forms a path (magnetic path) of the magnetic force line.

  Then, by an alternating magnetic flux parallel to the axis X induced in the fixing sleeve 1, an induction current (circulating current) in the circumferential direction is generated in the heat generation layer 1a of the fixing sleeve, and the heat generation layer 1a generates heat. This heat is transmitted to the elastic layer 1b and the release layer 1c, the entire fixing sleeve 1 is heated, and the recording material P passed through the fixing nip portion (hereinafter referred to as nip portion) N is heated to form the toner image T. Fixing is done.

  Here, if the circular resistance of the heat generating layer 1a is within a predetermined range, a heat generation amount necessary for fixing can be obtained. If the circulation resistance of the heat generation layer 1a is too high, no circulation current flows through the heat generation layer 1a and heat cannot be generated. On the other hand, if the circulation resistance of the heat generation layer 1a is too low, the circulation current flows but the resistance is small, so the amount of heat generation is small and necessary for fixing. Cannot generate a large amount of heat.

2) Heating rotator The fixing sleeve 1 which is a cylindrical endless belt as a heating rotator is made of a metallic member such as SUS, nickel, Ni alloy or the like having a diameter of 10 to 50 mm as shown in FIG. The heat generating layer 1a is provided. And the elastic layer 1b which consists of silicone rubber etc. which were laminated | stacked on the outer surface of the heat generating layer 1a, and the mold release layer 1c which consists of a fluororesin etc. which were laminated | stacked on the outer surface are provided. As shown in FIG. 4, the magnetic core 2 is inserted into the fixing sleeve 1 in the rotational axis direction.

3) Pressure body and pressure mechanism The pressure roller 8 as the pressure body shown in FIG. 2 is rotationally driven in the counterclockwise direction indicated by the arrow by the rotational drive control means M, and the frictional force with the outer surface of the fixing sleeve 1 Thus, a rotational force is applied to the fixing sleeve 1, and the fixing sleeve 1 is rotated by the rotation of the pressure roller 8.

  The pressure roller 8 includes a cored bar 8a, a heat-resistant elastic material layer 8b such as silicone rubber, fluororubber, and fluororesin that is concentrically formed and coated around the cored bar, and a surface release layer 8c. Is provided. The elastic layer 8b is preferably made of a material having good heat resistance such as silicone rubber, fluorine rubber, fluorosilicone rubber or the like. Note that both ends of the cored bar 8a shown in FIG. 3 are disposed between the chassis side metal plates (not shown) of the apparatus so as to be freely rotatable via conductive bearings.

  Further, as shown in FIG. 3, pressure springs 17a and 17b as pressure mechanisms are respectively provided between the both ends of the pressure stay 5 and the spring receiving members 18a and 18b on the apparatus chassis side, so A pressing force is applied to the pressure stay 5. In the fixing device 113 of the present embodiment, a total pressure of about 100 N to about 250 N is applied. As a result, the lower surface of the sleeve guide member 6 (FIG. 2) made of heat-resistant resin PPS or the like and the upper surface of the pressure roller 8 are pressed against each other with the fixing sleeve 1 in between, and a fixing nip portion N (see FIG. 2) is formed.

4) Flange members The flange members 12a and 12b shown in FIG. 3 are fitted on the left and right ends of the sleeve guide 6 and are rotatably mounted while the left and right positions are fixed by the restriction members 13a and 13b. When the fixing sleeve 1 rotates, it receives the end of the fixing sleeve 1 and regulates the movement of the fixing sleeve 1 along the longitudinal direction of the sleeve guide 6.

  The material of the flange members 12a and 12b is preferably phenol resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, or fluororesin (PFA, PTFE, FEP, etc.). Alternatively, materials having good heat resistance such as LCP (Liquid Crystal Polymer) resin and mixed resins thereof are preferable.

5) Temperature detection As shown in FIGS. 3 and 4, the temperature detection of the fixing device 113 is performed at the center and both ends of the longitudinal direction on the side where the recording material P is conveyed to the fixing device 113. This is performed by a temperature measuring element 9 of a non-contact type thermistor disposed in The fixing temperature control unit 303 shown in FIG. 4 controls the voltage control unit 305 based on the temperature detected by the temperature measuring element 9 at the center in the longitudinal direction of the fixing sleeve 1. As a result, the fixing sleeve 1 is induction-heated, and the surface temperature is maintained and adjusted to a predetermined target temperature.

6) Control Unit In FIG. 1A, the control unit 600 heats the recording material as the rotation speed of the fixing sleeve 1 during the image heating preparation period until the recording material enters the nip portion N. The rotation of the fixing sleeve 1 is started at a second rotation speed slower than the first rotation speed. Then, the control unit 600 increases the speed to the first rotational speed and displaces the fixing sleeve 1 by at least one rotation during the image heating preparation period until the recording material enters the nip portion N. This will be described in detail below.

(Rotation speed during fixing device start-up control and temperature increase of fixing sleeve)
In the fixing device 113 (FIG. 1A) as in the present embodiment, the temperature of the fixing sleeve 1 is increased by the rotation speed of the fixing sleeve 1 when performing start-up control that is control during the image heating preparation period. Is known to be different. Specifically, the lower the rotation speed of the fixing sleeve 1, the faster the temperature of the fixing sleeve 1 increases.

  The mechanism will be described. FIG. 5 is a sectional view of the fixing sleeve 1 and the pressure roller 8 when the recording material is not conveyed. In the fixing device configured as in the present embodiment, the temperature of the fixing sleeve 1 is the lowest immediately after the nip portion N, that is, the downstream side of the nip portion N in the rotational direction, and the highest temperature upstream of the nip portion N. This is because, in the nip portion N, the fixing sleeve 1 and the pressure roller 8 are in pressure contact with each other, so that the heat of the fixing sleeve 1 is taken away by the pressure roller 8. With the rotation, after passing through the nip portion N, the fixing sleeve 1 is not deprived of heat by the pressure roller until entering the nip portion N again, so that the temperature is likely to rise.

  The temperature at the point A immediately after passing through the nip N at a certain point rises to A ′ immediately before entering the nip N with rotation. The slower the rotation speed of the fixing sleeve 1 is, the longer it takes to move from the point A to the point A ′. Therefore, the amount of temperature rise increases as the rotation speed is slower. As a result, as the entire circumferential direction of the fixing sleeve, the temperature is likely to rise as the rotational speed is lower.

  In the present embodiment, in view of the above properties, in the start-up control of the fixing device 113, the fixing sleeve 1 is slower (second rotation) than the speed (first rotation speed) corresponding to the process speed of the image forming apparatus. Rotation starts at speed. As a result, the temperature of the fixing sleeve 1 can be raised faster than when the start-up control is performed at the same speed as the process speed of the image forming apparatus from the start of rotation.

  However, before the recording material is introduced into the nip portion N, the rotational speed of the fixing sleeve 1 and the pressure roller 8 needs to be set to the process speed of the image forming apparatus. Therefore, when the fixing device 113 is started up, the rotational speed of the fixing sleeve 1 is increased nonlinearly as shown by a graph (thick solid line) in FIG.

  The reason for this will be described below. If it is only to raise the temperature of the fixing sleeve 1 quickly, it is preferable to slow down the rotation speed of the fixing sleeve 1 until just before the recording material is introduced into the nip portion N. However, in that case, immediately before the recording material is introduced into the nip portion N, the rotational speed of the fixing sleeve 1 is rapidly increased. When the rotation speed of the fixing sleeve 1 is rapidly increased, the temperature rise state of the fixing sleeve 1 before and after the speed change greatly fluctuates. As described above, the temperature is likely to rise because the heating is performed for a long time from the time when the nip portion N is exited until the speed is changed until the speed is changed at a low speed.

  After the speed change, the heating time from passing through the nip portion N to entering the nip portion N is abruptly shortened, so that the temperature rise amount of the fixing sleeve 1 is greatly reduced as compared to before the speed change. As a result, the temperature of the fixing sleeve 1 upstream of the nip portion N varies greatly, and a large ripple occurs in the detected temperature of the temperature measuring element 9. During speed switching as is generally done, the speed is largely switched in a short time such as 0.1 seconds to 0.3 seconds. In this case, the rotation speed is largely switched in a shorter time than one rotation of the fixing sleeve 1, and a large temperature ripple is generated within one rotation of the fixing sleeve 1.

  As described above, when the recording material is introduced into the nip portion N in the state where the temperature of the fixing sleeve 1 greatly fluctuates within one circumference at the upstream side of the nip portion N, image defects such as defective fixing and gloss unevenness occur. There is a case.

  In order not to cause the image defect as described above, it is necessary to wait for the temperature ripple of the fixing sleeve 1 to decrease before fixing the recording material. That is, even if the temperature of the fixing sleeve 1 is increased quickly, a waiting time until the temperature ripple is eliminated occurs, so that the time until the recording material can actually be introduced into the nip portion N increases. The effect of shortening the substantial startup time of the fixing device is reduced.

  Therefore, in order to increase the temperature of the fixing sleeve 1 with the shortest start-up time, the fixing sleeve 1 is increased so that a large temperature ripple does not occur within one rotation of the fixing sleeve 1. It is good to carry out over a time longer than the time for one rotation.

  The time ts for the fixing sleeve 1 to make one turn will be supplementarily described with reference to FIG. The circumferential length of the fixing sleeve is L, and the rotation speed of the fixing sleeve at time t is V (t). In this embodiment, since the rotation speed of the fixing sleeve is increased, the speed V is not constant but V (t) that is a function of time. Further, it is assumed that the speed of the fixing sleeve 1 is increased from the low speed Vl (second rotational speed) to the process speed Vp (first rotational speed) between time ta and time tb. In this case, the distance that the fixing sleeve 1 rotates during the time tb-ta when the speed of the fixing sleeve 1 is increased is the area of the hatched portion in FIG. 1B, that is, V (t) from the time ta to the time tb. The value X integrated between

  When X = L, tb-ta = ts. In order to increase the rotation speed over a longer time than the rotation of the fixing sleeve 1 as in this embodiment, the following is performed. That is, if V (t) is set so that the distance X> the circumferential length L of the fixing sleeve 1 (tb-ta> ts) during the period of increasing the rotational speed of the fixing sleeve 1> the distance X of the fixing sleeve 1. good.

  From the above, in this embodiment, at the start-up control of the fixing device 113, the rotation starts at a speed slower than the process speed when the fixing sleeve 1 starts to rotate, and the rotational speed until the recording material is introduced into the nip portion N. Is controlled to increase to the process speed. By controlling the rotation speed of the fixing sleeve 1 in this way, the fixing sleeve 1 can be rotated at a low speed at the initial stage of the start-up control of the fixing device, and the temperature rise can be accelerated.

  Further, the rotation speed of the fixing sleeve 1 is increased continuously over at least a time longer than the time required for the fixing sleeve 1 to make one rotation. By thus increasing the rotation speed of the fixing sleeve 1 over a longer time than the rotation of the fixing sleeve 1, it is possible to suppress the generation of temperature ripple and the generation of useless waiting time. As a result, it is possible to shorten the startup time of the fixing device.

  As a specific example, control is performed to increase the rotational speed according to a quadratic function as shown in the graph (thick solid line) in the embodiment of FIG. 6 (the acceleration of the fixing sleeve 1 is gradually increased during the image heating preparation period). The fixing sleeve 1 is rotated at least once during that period. More specifically, in the image forming apparatus of this embodiment, the process speed is 300 mm / sec and the diameter of the fixing sleeve 1 is 30 mm. Also, after receiving the print command and starting the image forming operation, the recording material is introduced into the nip portion in 4 seconds.

Therefore, the start-up control of the fixing device 113 that is started simultaneously with the start of the operation of the image forming apparatus is performed as follows. That is, the rotation drive control means M starts to rotate the pressure roller 8, and after the rotation of the fixing sleeve 1, the time t of the fixing sleeve 1 is adjusted so that the process speed is 300 mm / sec in 4 seconds. Is a quadratic function of t.
V (t) = (300/4 ² ) × t ² = 18.75 × t ²
Control according to.

  At this time, the distance X that the fixing sleeve 1 rotates in 4 seconds is a value obtained by integrating V (t) between t = 0 and t = 4, and X = 400 mm. That is, the fixing sleeve 1 is displaced by a plurality of rotations (specifically, about 4.2 rounds) during the rotation speed increase period, and a large temperature unevenness is generated within one round of the fixing sleeve 1. No.

  As an example, Table 1 shows the results when the start-up control of the fixing device 113 at room temperature is performed under four conditions with different rotation speeds of the fixing sleeve 1 and the recording material is fixed. Further, the transition of the rotation speed of the fixing sleeve 1 under each condition in this comparative experiment is shown in FIG. 6, and the temperature rise curve of the fixing sleeve 1 when the fixing device is started up at the rotation speed of the fixing sleeve 1 shown in FIG. Is shown in FIG.

  This comparative experiment was performed under the conditions that the process speed of the image forming apparatus was 300 mm / sec, the temperature control target temperature was 170 ° C., the maximum input power was 1000 W, and the diameter of the fixing sleeve 1 was 30 mm. The recording material passed is plain paper having a basis weight of 90 g / m2. This is a case where a solid image having a density of 100% is printed on this recording material. Further, the experiment was performed in a state where the recording material was introduced into the nip portion N in 4 seconds from the start of the printing operation, that is, the start-up operation of the fixing device A.

  In the embodiment shown in Table 1, as shown by a thick solid line in FIG. 6, the control is performed to increase the rotation speed of the fixing sleeve 1 nonlinearly so that the process speed reaches 300 mm / sec, which is the process speed in 4 seconds from the start of rotation. It is a result when performing. At this time, as described above, the fixing sleeve 1 rotates a plurality of times (specifically, about 4.2 turns) during the rotation speed increasing period. Further, Comparative Example 1 is a result when the rotation speed of the fixing sleeve is controlled to be a constant process speed of 300 mm / sec from the start of rotation, as indicated by a thin solid line in FIG.

  In Comparative Example 2, as indicated by a broken line in FIG. 6, the rotation speed of the fixing sleeve 1 is started at 60 mm / sec, which is 1/5 of the process speed. Then, a result when the recording material is switched to the process speed of 300 mm / sec 0.2 seconds before the recording material is introduced into the nip portion N, that is, 3.8 seconds after the start of starting is shown. The rotation speed was changed over in 0.2 seconds. Since the speed increased from 60 mm / sec to 300 mm / sec in 0.2 seconds, the fixing sleeve 1 rotates 36 mm during that period. This is a distance of about 0.4 turns of the fixing sleeve 1.

  In Comparative Example 3, as indicated by a dotted line in FIG. 6, the rotation speed of the fixing sleeve 1 is started at 60 mm / sec, which is 1/5 of the process speed. Then, the result when the recording material is switched to the process speed of 300 mm / sec 1 second before the recording material enters the nip portion N, that is, after 3 seconds from the start of starting, is shown. The rotation speed was changed over in 0.2 seconds. As in the comparative example 2, the fixing sleeve 1 makes about 0.4 turn during the period in which the rotation speed is increased (the displacement of one rotation is not satisfied).

  As shown in Table 1, in the case of the example, a good image with neither fixing failure nor gloss unevenness was obtained. The temperature rise curve of the fixing sleeve 1 in this case is shown by a thick solid line in FIG. As can be seen from FIG. 7, the temperature of the fixing sleeve 1 rises smoothly, and reaches the target temperature of 170 ° C. at the point of 4 seconds from the start of starting up when the recording material is introduced into the nip portion N. Further, since the rotation speed is increased in a longer period than the rotation of the fixing sleeve 1 once, no temperature ripple occurs thereafter. Therefore, a good image was obtained. It can be said that the fixing device startup time is 4 seconds.

  On the other hand, in Comparative Example 1, fixing failure occurred in the recording material after fixing. This result will be described. In Comparative Example 1, the fixing sleeve 1 was rotated at a process speed of 300 mm / sec from the start of the start-up of the fixing device 113. The temperature rise curve of the fixing sleeve 1 in this case is shown by a thin solid line in FIG. As can be seen from FIG. 7, the temperature rise of the fixing sleeve 1 was slow, and when the recording material was introduced into the nip portion N, the temperature upstream of the nip portion N did not reach the temperature adjustment target temperature of 170 ° C. .

  Since the fixing operation was performed in a state where the temperature of the fixing sleeve 1 was lower than the temperature control target temperature, a fixing failure occurred. In order to prevent a fixing failure from occurring in the configuration of Comparative Example 1, it was necessary to extend the time for the recording material to be introduced into the nip portion N from 4 seconds to 6 seconds after the start-up of the fixing device. That is, it can be said that the fixing device startup time is 6 seconds.

  In Comparative Example 2, fixing failure occurred in the recording material after fixing. This result will be described. In Comparative Example 2, the fixing sleeve 1 was rotated at a low speed for 3.8 seconds from the start of the start-up of the fixing device 113. The temperature rise curve of the fixing sleeve 1 in this case is indicated by a broken line in FIG. Since the fixing sleeve 1 was rotated at a low speed, the temperature upstream of the nip portion N of the fixing sleeve 1 reached 170 ° C., which is the temperature adjustment target temperature, at 3.8 seconds.

  However, since the rotational speed is increased in a short period of 0.4 rotation of the fixing sleeve 1, the temperature upstream of the nip portion N of the fixing sleeve 1 varies greatly. Immediately after this, since the recording material was introduced into the nip portion N, the temperature ripple of the fixing sleeve 1 was large, and a fixing defect occurred in a portion corresponding to the low temperature portion of the fixing sleeve 1 on the recording material. In the configuration of Comparative Example 2, in order not to cause a fixing failure due to the temperature ripple of the fixing sleeve 1, it is necessary to wait until the ripple is eliminated.

  Actually, it was necessary to extend the time for the recording material to be introduced into the nip portion N from 4 seconds to 5 seconds from the start of the start-up of the fixing device. That is, it can be said that the fixing device startup time is 5 seconds.

  In Comparative Example 3, gloss unevenness occurred in the recording material after fixing. This result will be described. In Comparative Example 3, the fixing sleeve 1 was rotated at a low speed for 3 seconds after the start-up of the fixing device 113, and then increased to the process speed. The temperature rise curve of the fixing sleeve 1 in this case is indicated by a dotted line in FIG. Immediately after the speed switching, as described above, the temperature upstream of the nip N of the fixing sleeve 1 fluctuates greatly.

  After that, since the temperature ripple gradually decreases because of rotation at a constant process speed, the temperature ripple still remains when the recording material is introduced into the nip portion N. Although the temperature at the upstream of the fixing nip N of the fixing sleeve 1 has reached 170 ° C., which is the temperature adjustment target temperature, the rotational speed is increased in a short period of 0.4 rotations of the fixing sleeve 1. Therefore, a ripple of about 10 ° C. remained around 170 ° C.

  Since the fixing operation was performed in this state, no fixing failure occurred, but gloss unevenness occurred. Here, the gloss unevenness means that the gloss difference (gloss difference) of the fixed image is large between the leading edge and the trailing edge of the recording material.

  In order to prevent the occurrence of gloss unevenness in the configuration of Comparative Example 3, it was necessary to extend the time for the recording material to be introduced into the nip portion N from 4 seconds to 4.5 seconds from the start of the fixing device. That is, it can be said that the startup time of the fixing device is 4.5 seconds.

  As described above, during the start-up control of the fixing device 113, the rotation starts at a speed slower than the process speed when the fixing sleeve 1 starts to rotate. Then, the rotational speed is increased to the process speed before the recording material is introduced into the nip portion N, and control is performed so as to obtain the rotational speed for fixing the recording material. By controlling the rotation speed of the fixing sleeve 1 in this way, the temperature rise of the fixing sleeve 1 can be accelerated.

  Further, the rotation speed of the fixing sleeve 1 is gradually increased to the process speed over a time longer than at least one rotation of the fixing sleeve 1 until the recording material is introduced into the fixing device 113. To implement. By doing so, it is possible to suppress the temperature ripple of the fixing sleeve 1 that occurs at the time of speed switching. As a result, the stand-by time for eliminating the temperature ripple is shortened, so that the start-up time of the fixing device can be shortened.

<< Second Embodiment >>
Since an image forming apparatus equipped with a fixing device as an image heating apparatus according to the present embodiment is the same as that of the first embodiment, description thereof is omitted.

(Image heating device)
A fixing device 200 as an image heating device according to the present embodiment will be described with reference to FIG. Note that members and portions that are the same as those of the fixing device in the first embodiment are denoted by the same reference numerals. The fixing device 200 in the present embodiment has only a pressure control means 300 (FIG. 8) as a control means for controlling the pressure at the nip portion N when the fixing sleeve 1 and the pressure roller 8 are in contact. Is different from the first embodiment.

  FIG. 9A and FIG. 9B are cross-sectional views of the fixing device 200 for explaining the pressure control means 300. In addition, what is a and b with the same number by the code | symbol in a figure is a component which exists also in the other side in a figure in the left-right symmetric position. The pressure control means 300 includes a cored bar member 205 that is rotatably supported by the chassis portion of the fixing device, a cam 201 fixed to the cored bar member 205, a pressure sheet metal 202, and the like.

  The cam 201 is fixed in an eccentric state with respect to the cored bar member 205, and the cam 201 is also rotated eccentrically when the cored bar member is rotated by a cored bar member rotating means (not shown). When the cam 201 rotates eccentrically, the pressure sheet metal 202 moves in the vertical direction in the figure around the rotation fulcrum 204. As a result, the pressure applied to the contact point 203 (pressure point) between the pressure sheet metal 202 and the pressure stay 5 changes, and the contact pressure between the pressure roller 8 and the fixing sleeve 1 can be adjusted.

  FIG. 9A shows a state in which the maximum pressing force is applied to the pressing point, and the contact pressing force 250N (fixing pressure at the time of fixing) when the pressing roller 8 and the fixing sleeve 1 fix the recording material. The pressure adjusting means is set so as to come into contact with each other. FIG. 9B shows a state in which the minimum pressure is applied to the pressure point. In this embodiment, the minimum contact pressure that allows the fixing sleeve 1 to be driven to rotate as the pressure roller 8 rotates. The pressurizing force adjusting means is set to 50 N (denoted as weak pressurizing force).

(Pressure control during fixing device start-up control)
In the fixing device 200 as in the present embodiment, it is known that the temperature rise of the fixing sleeve 1 varies depending on the contact state between the fixing sleeve 1 and the pressure roller 8 when performing start-up control. Specifically, the temperature rise of the fixing sleeve 1 is faster as the contact pressure is smaller.

  This is because the smaller the contact pressure between the fixing sleeve 1 and the pressure roller 8, the smaller the elastic deformation of the pressure roller 8 at the nip portion N, and the width in the circumferential direction of the nip portion N (hereinafter referred to as nip width). This is because. When the width of the nip portion N is small, the amount of heat that moves from the fixing sleeve 1 to the pressure roller 8 becomes small, and the temperature of the fixing sleeve 1 tends to rise.

  In the present embodiment, in view of the above properties, when the fixing device 200 is started up, the contact pressure between the fixing sleeve 1 and the pressure roller 8 is the contact pressure when fixing the recording material. It starts from the state of contact with a pressing force smaller than the pressing force. As a result, the temperature of the fixing sleeve 1 can be raised earlier than when the fixing sleeve 1 and the pressure roller 8 are brought into contact with each other in the pressing state at the time of fixing from the start of the fixing device.

  However, before the recording material is introduced into the nip portion N, the contact pressure between the fixing sleeve 1 and the pressure roller 8 needs to be set at the fixing pressure. Therefore, in this embodiment, when the fixing device 200 is started up, the contact pressure between the fixing sleeve 1 and the pressure roller 8 is set to a weak pressure at the start of the start until the recording material is introduced into the nip portion N. The pressure is controlled so that the pressure is fixed during fixing.

  Specifically, the start-up of the fixing device 200 is started with the cam 201 shown in FIG. 9 in the state shown in FIG. 9B (a weak pressure with a small nip width). Then, the cam 201 is gradually rotated so that the cam 201 is controlled to be in the state shown in FIG. 9A (fixing pressure when the nip width is large) at the timing when the recording material is introduced into the nip portion N. . In the image forming apparatus of the present embodiment, after receiving the print command, the recording material is introduced into the nip portion N in 4 seconds after starting the image forming operation. For this reason, the contact pressure between the fixing sleeve 1 and the pressure roller 8 in the fixing device 200 is controlled from the weak pressure to the pressure at the time of fixing over 4 seconds from the start of the start-up of the fixing device 200.

  Here, the reason why the contact pressure between the fixing sleeve 1 and the pressure roller 8 is controlled to gradually increase will be described. For the purpose of quickly raising the temperature of the fixing sleeve 1, it is preferable to weaken the contact pressure between the fixing sleeve 1 and the pressure roller 8 just before the recording material is introduced into the nip portion N. However, in this case, immediately before the recording material is introduced into the nip portion N, the pressure increases from a weak pressure to a pressure at the time of fixing. When the pressing force of the fixing sleeve 1 and the pressure roller 8 is suddenly changed to the pressing force at the time of fixing, the temperature rise state of the fixing sleeve 1 before and after the pressing force change greatly fluctuates.

  In this regard, as described above, the width of the nip portion N is small and the temperature of the fixing sleeve 1 is likely to rise before the pressure change, which was in a weakly pressurized state. After the pressure change, the width of the nip portion N becomes large, so that the heat is easily taken away by the pressure roller 8, and the temperature increase amount of the fixing sleeve 1 is significantly reduced as compared with that before the pressure change. As a result, the temperature of the fixing sleeve 1 upstream of the nip portion N varies greatly, and a large ripple occurs in the detected temperature of the temperature measuring element 9.

  When switching the pressing force as is generally performed, the pressing force is switched in a short time of 0.1 seconds to 0.3 seconds, and as a result, the width of the nip portion N is switched greatly. In this case, the width of the nip portion N suddenly increases in a shorter time than one rotation of the fixing sleeve 1, and a large temperature ripple is generated within one circumference of the fixing sleeve 1.

  As described above, when the recording material is introduced into the fixing device 200 in a state in which the temperature of the fixing sleeve 1 greatly fluctuates upstream of the nip portion N, image defects such as fixing defects and gloss unevenness may occur. .

  Here, in order not to cause the image defect as described above, it is necessary to wait for the temperature ripple of the fixing sleeve 1 to decrease before fixing the recording material. That is, even if the temperature of the fixing sleeve 1 is increased quickly, a waiting time until the temperature ripple is eliminated occurs, so that the time until the recording material can actually be introduced into the nip portion N increases. The effect of shortening the substantial startup time of the fixing device is reduced. Therefore, it is better to increase the contact pressure between the fixing sleeve 1 and the pressure roller 8 over a longer time than at least one rotation of the fixing sleeve 1.

  As described above, in this embodiment, when the start-up control of the fixing device 200 is started, the contact pressure between the fixing sleeve 1 and the pressure roller 8 is set to a weak press-up time when the start-up control is started, and the recording material is introduced into the nip N. It is controlled so as to increase to the pressing force at the time of fixing. By controlling the contact pressure between the fixing sleeve 1 and the pressure roller 8 in this way, the temperature rise of the fixing sleeve 1 can be accelerated.

  Further, the increase in the pressing force is performed over a time longer than at least the time required for the fixing sleeve 1 to make one round. Specifically, in the image forming apparatus of this embodiment, the process speed is 300 mm / sec, and after receiving a print command and starting an image forming operation, the recording material is introduced into the nip portion N in 4 seconds. . Therefore, in the start-up control of the fixing device 200 that is started simultaneously with the start of the operation of the image forming apparatus, the following is performed. In other words, the contact pressure between the fixing sleeve 1 and the pressure roller 8 is sufficiently longer than 0.314 seconds, which is one turn of the fixing sleeve 1, so that the pressure during fixing is 4 seconds after the start-up control is started. To control.

  By controlling the applied pressure in this way, it is possible to suppress the occurrence of temperature ripples in the fixing sleeve 1 and suppress the generation of useless waiting time. As a result, it is possible to optimally shorten the startup time of the fixing device.

  Further, in the fixing device 200 of the present embodiment, as soon as the fixing operation of the recording material is completed, the contact pressure between the fixing sleeve 1 and the pressure roller 8 is switched from the pressing force during fixing to the weak pressing force. Prepare for start-up control for fixing operations. At this time, the switching from the pressing force during fixing to the weak pressing force may be performed in a short time as is generally performed.

As an example, Table 2 shows the results when the start-up control of the fixing device 200 is performed under the conditions in which the pressing forces of the fixing sleeve 1 and the pressure roller 8 are different and the recording material is fixed. In this comparative experiment, the process speed of the image forming apparatus is 300 mm / sec, the rotation speed of the fixing sleeve and the pressure roller is the same 300 mm / sec, the temperature control target temperature is 170 ° C., the maximum input power is 1000 W, the fixing sleeve 1 The diameter was 30 mm. The recording material passed is plain paper with a basis weight of 90 g / m ² . This is a case where a solid image having a density of 100% is printed on this recording material.

  Further, the experiment was performed in a state where the recording material was introduced into the nip portion N in 4 seconds from the start of the printing operation, that is, the start-up operation of the fixing device 200.

  In the examples in Table 2, the pressing force of the fixing sleeve 1 and the pressure roller 8 is set to 50 N, which is a weak pressing force at the start of the start-up control of the fixing device 200, and then, the pressing force at fixing is 250 N in 4 seconds. This is the result when control is performed so that Comparative Example 1 is a case where control is performed at a fixing pressure of 250 N from the start of startup of the fixing device 200. In comparative example 2, the fixing device 200 is set to a weak pressure of 50 N at the start of start-up, and is fixed 0.2 seconds before the recording material is introduced into the nip portion N, that is, 3.8 seconds after the start of start-up. It is a result at the time of switching to 250N which is an applied pressure. Switching of the applied pressure was performed in 0.2 seconds.

  In Comparative Example 3, the fixing device 200 is set to a weak pressure of 50 N at the start of start-up, and 1 sec before the recording material is introduced into the nip portion N, that is, after the start of start-up, the pressurizing pressure is set to 3 N This is the result when switching to a certain 250N. Switching of the applied pressure was performed in 0.2 seconds.

  As shown in Table 2, in the case of the example, a good image in which neither fixing failure nor gloss unevenness occurred was obtained. The temperature rise curve of the fixing sleeve 1 in this case is shown by a thick solid line in FIG. As can be seen from FIG. 11, the temperature of the fixing sleeve 1 rises smoothly and reaches the target temperature of 170 ° C. before the recording material is introduced into the fixing device 113. There is no temperature ripple after that. Therefore, a good image was obtained. It can be said that the start-up time of the fixing device is 4 seconds.

  On the other hand, in Comparative Example 1, fixing failure occurred in the recording material after fixing. This result will be described. In Comparative Example 1, the pressing force of the fixing sleeve 1 and the pressure roller 8 was set to 25 kgf, which is the pressing force at the time of fixing, from the start of the start-up of the fixing device 200. Therefore, as shown by a thin solid line in FIG. 11, the temperature rise of the fixing sleeve 1 is slow, and when the recording material is introduced into the nip portion N, the temperature upstream of the nip N reaches a temperature adjustment target temperature of 170 ° C. It was not reached.

  Since the fixing operation was performed in a state where the temperature of the fixing sleeve 1 was lower than the temperature control target temperature, a fixing failure occurred. In order to prevent a fixing failure from occurring in the configuration of Comparative Example 1, it was necessary to extend the time for the recording material to be introduced into the nip portion N from 4 seconds to 6 seconds after the start-up of the fixing device. That is, it can be said that the fixing device startup time is 6 seconds.

  In Comparative Example 2, fixing failure occurred in the recording material after fixing. This result will be described. In Comparative Example 2, the fixing sleeve 1 and the pressure roller 8 were pressed with a slight pressure for 3.8 seconds from the start of the start-up of the fixing device 200. The temperature rise curve of the fixing sleeve 1 in this case is indicated by a broken line in FIG. As can be seen from FIG. 11, at the time point of 3.8 seconds, the temperature upstream of the nip portion N of the fixing sleeve 1 has reached 170 ° C., which is the temperature adjustment target temperature. However, the temperature at the upstream of the nip portion N of the fixing sleeve 1 greatly fluctuates due to a rapid increase in the applied pressure thereafter.

  Immediately after this, since the recording material was introduced into the nip portion N, the temperature ripple of the fixing sleeve 1 was large, and a fixing defect occurred in a portion corresponding to the low temperature portion of the fixing sleeve 1 on the recording material. In the configuration of Comparative Example 2, in order not to cause a fixing failure due to the temperature ripple of the fixing sleeve 1, it is necessary to wait until the ripple is eliminated. Actually, it was necessary to extend the time for the recording material to be introduced into the nip portion N from 4 seconds to 5 seconds from the start of the start-up of the fixing device. That is, it can be said that the fixing device startup time is 5 seconds.

  In Comparative Example 3, gloss unevenness occurred in the recording material after fixing. Here, the gloss unevenness means that the gloss difference (gloss difference) of the fixed image is large between the leading edge and the trailing edge of the recording material as described above.

  In Comparative Example 3, the fixing sleeve 1 and the pressure roller 8 were pressurized with a weak pressure for 3 seconds from the start of the start-up of the fixing device 200, and then switched to the pressure at the time of fixing. The temperature rise curve of the fixing sleeve 1 in this case is shown by a dotted line in FIG. As can be seen from FIG. 11, immediately after the pressure is switched, the temperature upstream of the nip N of the fixing sleeve 1 fluctuates greatly as described above. Thereafter, the pressure ripple is constant at the time of fixing, and thus the temperature ripple is gradually reduced. However, when the recording material is introduced into the fixing device 200, the temperature ripple still remains. .

  The temperature upstream of the nip portion N of the fixing sleeve 1 has reached a temperature adjustment target temperature of 170 ° C., but a ripple of about 10 ° C. remains around 170 ° C. Since the fixing operation was performed in this state, no fixing failure occurred, but gloss unevenness occurred. In order to prevent the occurrence of gloss unevenness in the configuration of Comparative Example 3, it was necessary to extend the time for the recording material to be introduced into the nip portion N from 4 seconds to 4.5 seconds from the start of the fixing device. That is, it can be said that the startup time of the fixing device is 4.5 seconds.

  As described above, at the start-up control of the fixing device 200, the start-up is started with the contact pressure between the fixing sleeve 1 and the pressure roller 8 being a weak pressure smaller than the pressure applied when fixing the recording material. To do. Then, the pressurizing force is controlled so that the pressurizing force is reached before the recording material is introduced into the fixing device 200. By controlling the pressure applied between the fixing sleeve 1 and the pressure roller 8 in this way, the temperature rise of the fixing sleeve 1 can be accelerated.

  Further, the pressure increase of the pressure applied by the fixing sleeve 1 and the pressure roller 8 to the pressure applied at the time of fixing is at least longer than the time during which the fixing sleeve 1 rotates once before the recording material is introduced into the fixing device 200. Over time, gradually implement. By doing so, it is possible to suppress the temperature ripple at the upstream portion of the nip portion N of the fixing sleeve that is generated when the pressure is switched. As a result, the stand-by time for eliminating the temperature ripple is shortened, so that the start-up time of the fixing device can be shortened.

<< Third Embodiment >>
An example of the image forming apparatus according to this embodiment is the same as that of the first embodiment, and thus the description thereof is omitted. The fixing device in this embodiment is the same as that in the second embodiment, and a description thereof will be omitted.

  In the present embodiment, at the start-up control of the fixing device, when the rotation of the fixing sleeve 1 is started, the rotation is started at a second rotational speed that is lower than the first rotational speed corresponding to the process speed. Then, before the recording material is introduced into the nip portion N, the rotational speed is increased to a first rotational speed corresponding to the process speed, and control is performed so that the rotational speed becomes when fixing the recording material.

  Furthermore, the start-up is started with the pressure applied by the fixing sleeve 1 and the pressure roller 8 as a weak pressure (second pressure) smaller than the first pressure when fixing the recording material. The pressurizing force is controlled so that the pressurizing force during fixing before being introduced into the portion N. The detailed control contents and effects of both the rotational speed control and the pressurizing force control are the same as those described in the first embodiment and the second embodiment, respectively. Note that the pressure control means 300 (FIG. 8) as the control means in the second embodiment can also be used in the control means 600 in the first embodiment.

Hereinafter, the fixing device is started up under the conditions that the process speed of the image forming apparatus is 300 mm / sec, the temperature control target temperature of the fixing sleeve 1 is 170 ° C., the maximum input power is 1000 W, and the diameter of the fixing sleeve 1 is 30 mm. The result of fixing is shown. The recording material passed is plain paper with a basis weight of 90 g / m ² . This is a case where a solid image having a density of 100% is printed on this recording material. The rotation speed of the fixing sleeve 1 is controlled as shown by the thick solid line in FIG. 6 as in the first embodiment, and the contact pressure between the fixing sleeve 1 and the pressure roller 8 is the second embodiment. In the same manner as shown in FIG.

  As a result, even when the recording material was introduced into the nip portion 3.5 seconds after the start-up of the fixing device, a good image could be obtained. The temperature rise curve of the fixing sleeve 1 in this case is shown in FIG. As can be seen from FIG. 12, in the case of this embodiment, the temperature of the fixing sleeve 1 reaches 170 ° C. in 3.5 seconds from the start of the start-up of the fixing device, and no temperature ripple occurs.

  In the present embodiment, the control of the rotation speed of the fixing sleeve 1 and the control of the contact pressure between the fixing sleeve 1 and the pressure roller 8 are performed together, so that only one of them is performed. Compared to 4 seconds in the case of the configuration, the startup time can be further reduced by 0.5 seconds.

  As described above, at the start-up control of the fixing device, when the rotation of the fixing sleeve 1 starts, the rotation starts at a speed slower than the process speed, and the rotation speed is increased to the process speed until the recording material is introduced into the fixing nip N. The speed increases over a longer time than the time for 1 to make one rotation. In addition, the pressing force of the fixing sleeve 1 and the pressure roller 8 is started as a weak pressing force smaller than the pressing force when fixing the recording material, and the pressing force at the time of fixing until the recording material is introduced into the nip portion N. Thus, the pressurizing force is increased over a longer time than the fixing sleeve 1 rotates once.

  By doing so, it is possible to suppress the temperature ripple of the fixing sleeve 1 that occurs at the time of speed switching. As a result, the stand-by time for eliminating the temperature ripple is shortened, so that the start-up time of the fixing device can be shortened.

(Modification 1)
In the first and third embodiments, the rotational speed of the fixing sleeve 1 is increased according to a quadratic function. However, the present invention is not limited to this. In order to speed up the temperature rise of the fixing sleeve 1 as much as possible, the period of rotation at a low speed is set as long as possible, and then the speed is increased from the speed at the start of rotation to the process speed without a rapid speed increase. In addition, any configuration may be used as long as the fixing sleeve rotates at least once.

  For example, as shown by a thin solid line in FIG. 13, the rotational speed may be increased by a higher order function than the embodiment shown by a thick solid line so that the low speed period becomes longer. Further, the speed may be increased stepwise as indicated by a broken line. The speed change when increasing the speed may be linear or non-linear. However, in order to speed up the temperature rise of the fixing sleeve 1, it is desirable to increase the speed in a non-linear manner and increase the time for rotating at the lowest possible speed.

(Modification 2)
In the above-described embodiment, the fixing device has a configuration in which a circulation current is generated in the heat generation layer of the fixing sleeve 1 by an electromagnetic induction method and the fixing sleeve generates heat. It is not limited.

  For example, the fixing device may be configured such that the entire circumference of the fixing sleeve generates heat by directly supplying power to the fixing sleeve having the resistance heating layer. An example is shown in FIG. Note that members similar to those of the fixing device 113 of the first embodiment are denoted by the same reference numerals. The fixing device of FIG. 14 is configured such that the fixing sleeve 1 generates heat by directly supplying power to the conductive layer of the fixing sleeve 1 through the flange members 200a and 200b made of a conductive member.

(Modification 3)
Further, even if the fixing sleeve itself does not generate heat by the exciting coil and the magnetic core, a halogen lamp separated from the inner surface of the fixing sleeve, a heater that contacts the inner surface of the fixing sleeve, or the like may be used. For example, the fixing device in FIG. 15 uses a halogen lamp 500. In this configuration, the fixing sleeve 1 is heated by the radiant heat from the halogen lamp 500.

(Modification 4)
In the above-described embodiment, the nip portion N is formed by the fixing sleeve 1 as the heating rotator and the pressure roller 8 as the driving roller. However, the present invention is not limited to this, and the fixing roller 1 is replaced with a pressure roller. A pressure pad may be used. In this case, the heating rotator can be configured as an endless belt suspended on a plurality of pulleys including a drive pulley.

1 ··· Fixing sleeve (heated rotating body), 8 · · Pressure roller (pressing body), 300 · · Pressure control means (control means), 600 · · Control means, N · · Nip

Claims (9)

A heating rotor,
A pressurizing member that contacts the heating rotator and forms a nip portion that heats the recording material while nipping and conveying the recording material;
The rotation of the heating rotator is started at a second rotation speed that is lower than the first rotation speed when the recording material is image-heated, and the first rotation until the recording material enters the nip portion. Control means for displacing the heating rotator at least once during the period of the image heating preparation period to be increased to a speed;
An image heating apparatus comprising: A heating rotor,
A pressurizing member that contacts the heating rotator and forms a nip portion that heats the recording material while nipping and conveying the recording material;
The rotation of the heating rotator is started with a second pressing force smaller than the first pressing force when the recording material is image-heated, and the first pressing force is applied until the recording material enters the nip portion. Control means for displacing the heating rotator at least once during the period of the image heating preparation period for increasing pressure.
An image heating apparatus comprising:   3. The method according to claim 1, further comprising a period of gradually increasing the acceleration of the heating rotator during the image heating preparation period, wherein the heating rotator is rotated at least once during the period. Image heating device.   The image heating apparatus according to claim 1, wherein the heating rotator is displaced by a plurality of rotations during the image heating preparation period. A magnetic core inserted through the heating rotator, and an excitation coil formed by winding the magnetic core in a direction intersecting the rotation axis of the heating rotator,
5. The heating rotating body is heated by the induced current by causing an induction current to flow in the circulation direction of the heating rotating body by passing an alternating current through the exciting coil. 2. An image heating apparatus according to item 1.   The image heating apparatus according to claim 1, wherein the pressure body is a pressure roller as a driving roller.   The image heating apparatus according to claim 1, wherein the heating rotator is an endless belt.   The image heating apparatus according to claim 1, wherein the pressure body is a fixed pressure pad. The image heating apparatus according to claim 8, wherein the heating rotator is an endless belt suspended on a plurality of pulleys including a driving pulley.