JP2010151983A - Fixing device, image forming apparatus, and pressure control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device that reduces a change in a load on a recording medium and suppresses image disturbance. <P>SOLUTION: The fixing device includes: a pressure roller; a fixing roller that forms a fixing nip part which is an area where it is brought into pressure-contact with the pressure roller; a pressure varying mechanism that changes the pressure of the fixing nip; a running detecting section that detects the running state of a recording medium; a pressure control section that calculates, on the basis of the running state, first timing when the leading end of a recording medium rushes into the fixing nip, and controls driving of the pressure varying mechanism; and a timing detecting section that detects timing of actuating the pressure varying mechanism. On the basis of the detection result of the first timing obtained by the timing detecting section, the pressure control section performs control such that until the leading end of the recording medium rushes in the fixing nip part, the pressure of the fixing nip part is made a first pressure which enables conveyance of the recording medium, and after the leading end of the recording medium rushes in the fixing nip part, the pressure varying mechanism is driven to raise the pressure of the fixing nip part to a second pressure which is necessary for fixing an unfixed toner image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device, an image forming apparatus, and a pressure control method.

  In an image forming apparatus that forms an image on a recording medium using an electrophotographic image forming system such as a laser printer, a copying machine, or a facsimile, the toner image transferred on the recording medium is fixed to form a permanent image. is required. The toner image fixing method can be broadly classified as follows: a method in which the toner is melted by heat and further penetrated into the recording medium by pressure; a method in which a large pressure is applied to the toner and the recording medium to crush the toner and adhere to the recording medium; There is a method in which the toner is dissolved with a solvent and penetrated into the recording medium.

  At present, in electrophotographic apparatuses, a fixing method using heat and pressure is most frequently used. The reason for this is that the structure is relatively simple, and good and stable fixing properties can be obtained in a wide range from low speed to high speed.

  For example, a heat roll type fixing device includes a heating (fixing) roller including a heat source and a pressure roller that presses and contacts the heating roller. The heating roller is made of, for example, a cylinder using a metal such as aluminum or iron, and an elastic layer made of, for example, silicon rubber and a release layer made of, for example, PFA are formed on the outermost peripheral surface. A radiant heat source such as a halogen lamp is provided inside the metal cylinder. In such a fixing device, the entire heating roller is heated from the inside of the heating roller by a radiant heat source, and the recording medium on which the toner image is transferred passes through a fixing nip formed between the pressure roller and the toner is melted and fixed. Let

JP 2008-116819 A

  However, when the recording medium enters the fixing nip portion where the heating roller and the pressure roller are in press contact with each other, there is a problem that a shock wave propagates to the recording medium and disturbs the transfer image on the recording medium. For example, as shown in FIG. 11, the recording medium is transferred by a transfer unit 10 including a suspension roller 12 that suspends a transfer belt (not shown) and a transfer roller 14 that sandwiches the transfer belt together with the suspension roller 12. The upper toner image is transferred. Thereafter, the recording medium is transported to the fixing unit 20 provided by pressing the heating roller 22 and the pressure roller 24. At this time, if the load at the fixing nip portion is too large, the recording medium hardly enters the fixing nip portion, and the recording medium receives an impact from the fixing unit 20 and the transferred image on the recording medium is disturbed.

  Further, if the load at the fixing nip portion when the recording medium enters the fixing nip portion is too large, the recording medium is difficult to enter the fixing nip portion, but the recording medium is conveyed to the fixing unit 20 side at a predetermined speed. continuing. For this reason, as shown in FIG. 12, in the recording medium (for example, paper P), when the leading end portion of the recording medium is positioned at the fixing nip portion, the portion sandwiched by the transfer unit 10 is displaced. . Furthermore, even when the gear teeth are displaced in accordance with the rotational load fluctuation for entering the fixing nip portion of the recording medium, a slight deviation occurs in the image plane.

  When the area z of the paper P in FIG. 12 is enlarged, when the transfer image on the recording medium is not disturbed or the recording medium is not displaced due to the impact, the toner regularly adheres as shown in the area z1. Yes. However, when the transfer image is disturbed or the recording medium is displaced, as shown in the region z2, the toner adheres to the position where the toner should be, that is, from the position of the white circle in FIG. 12 to the position of the gray circle. When the image is fixed on the recording medium by the fixing unit 20 in such a state, a difference in density occurs in the image, and a streak-shaped image is formed. In particular, such a problem becomes conspicuous when the leading end portion of the recording medium enters the fixing nip portion while a part of the recording medium is sandwiched between the transfer units 10.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to reduce load fluctuations on a recording medium by a fixing device and to suppress image disturbance. It is an object of the present invention to provide a new and improved fixing device, image forming apparatus, and pressure control method.

  In order to solve the above-described problem, according to an aspect of the present invention, a pressure roller that presses a recording medium, and a fixing nip portion that is provided so as to face the pressure roller and is a region that presses and contacts the pressure roller. A fixing roller for fixing an unfixed toner image on the recording medium conveyed to the sheet, a pressure variable mechanism for changing the pressure in the fixing nip as a load generated between the pressure roller and the fixing roller, and the running of the recording medium A travel detection unit that detects a state; a pressure control unit that calculates a first timing at which the leading end of the recording medium enters the fixing nip portion based on the detected travel state; There is provided a fixing device including a timing detection unit that detects timing of operating the variable mechanism. Based on the detection result of the first timing by the timing detection unit, the pressure control unit uses the first pressure at which the pressure of the fixing nip can be conveyed until the leading end of the recording medium enters the fixing nip. After the leading end of the recording medium enters the fixing nip portion, the pressure variable mechanism is driven to increase the pressure in the fixing nip portion to a second pressure necessary for fixing the unfixed toner image.

  According to the present invention, until the leading end of the recording medium enters the fixing nip, the pressure of the fixing nip is set to the first pressure capable of conveying the recording medium, and when the leading end of the recording medium enters the fixing nip. The pressure variable mechanism is driven to increase the pressure in the fixing nip portion to a second pressure necessary for fixing the unfixed toner image. As described above, the pressure (first pressure) when the recording medium enters the fixing nip portion is made lower than the pressure (second pressure) necessary for the fixing process of the unfixed toner image. It is possible to reduce the impact that occurs when the toner enters the fixing nip portion. As a result, it is possible to reduce the occurrence of the disturbance of the transfer image and the shift of the recording medium.

  Here, the pressure control unit may calculate the first timing based on the conveyance speed of the recording medium and the distance from the travel detection unit to the entrance of the fixing nip unit. Accordingly, it is possible to acquire an appropriate timing for operating the pressure variable mechanism in order to increase the pressure of the fixing nip portion from the first pressure to the second pressure.

  The pressure control unit can further calculate a second timing at which the unfixed toner image on the recording medium passes through the fixing nip. The pressure control unit lowers the pressure of the fixing nip portion from the second pressure to the first pressure based on the detection result of the second timing by the timing detection unit. As described above, by reducing the pressure of the fixing nip portion from the second pressure to the first pressure after the unfixed toner image on the recording medium passes through the fixing nip portion, the load on the constituent members of the fixing device and the recording are reduced. Damage to the medium can be reduced.

  At this time, the pressure control unit can calculate the second timing based on the conveyance speed of the recording medium and the image formation position on the recording medium. As a result, it is possible to obtain an appropriate timing for operating the variable pressure mechanism to lower the pressure of the fixing nip portion from the second pressure to the first pressure.

  The variable pressure mechanism moves the pressure roller or the fixing roller in a linear direction connecting the rotation center of the pressure roller and the rotation center of the fixing roller to change the pressure of the fixing nip portion. be able to.

  Furthermore, the travel detection unit can be provided on the conveyance path from when the toner image is transferred to the recording medium until the recording medium enters the fixing nip portion, for example. Thereby, the timing which operates a pressure variable mechanism can be calculated more correctly.

  In order to solve the above problems, according to another aspect of the present invention, a recording medium transport unit that accommodates a recording medium and transports the recording medium onto a recording medium transport path, and an electrostatic latent image on the peripheral surface An electrostatic latent image carrier, a developing unit that develops the electrostatic latent image on the electrostatic latent image carrier to generate a toner image, a transfer unit that transfers the toner image to a recording medium, and a recording medium An image forming apparatus is provided that includes a fixing unit that fixes the upper unfixed toner image. The fixing unit is provided with a pressure roller that presses the recording medium, and an unfixed toner image on the recording medium that is provided to face the pressure roller and is conveyed to a fixing nip portion that is in a pressing contact with the pressure roller. A fixing roller for fixing, a pressure variable mechanism for changing the pressure in the fixing nip, which is a load generated between the pressure roller and the fixing roller, a travel detection unit for detecting the travel state of the recording medium, and the detected travel Calculating a first timing at which the leading end of the recording medium enters the fixing nip portion based on the state, a pressure control unit for driving and controlling the pressure variable mechanism, and a timing detecting unit for detecting timing for operating the pressure variable mechanism; . Based on the detection result of the first timing by the timing detection unit, the pressure control unit uses the first pressure at which the pressure of the fixing nip can be conveyed until the leading end of the recording medium enters the fixing nip. After the leading end of the recording medium enters the fixing nip portion, the pressure variable mechanism is driven to increase the pressure in the fixing nip portion to a second pressure necessary for fixing the unfixed toner image.

  Furthermore, in order to solve the above-described problem, according to another aspect of the present invention, a pressure roller that presses a recording medium, and a region that is provided to face the pressure roller and press-contact with the pressure roller. Until the leading end of the recording medium enters the fixing nip, the pressure in the fixing nip, which is a load generated between the pressure roller and the fixing roller, is set as the first pressure that can convey the recording medium And a step of detecting the traveling state of the recording medium by the traveling detection unit, and a step of calculating a first timing at which the leading end of the recording medium enters the fixing nip portion based on the detected traveling state by the pressure control unit. The leading edge of the recording medium is fixed on the basis of the step of detecting the timing for operating the variable pressure mechanism by the timing detector and the detection result of the first timing by the timing detector. Driving a pressure variable mechanism that changes the pressure in the fixing nip portion after entering the portion to increase the pressure in the fixing nip portion to a second pressure necessary for fixing the unfixed toner image. A pressure control method is provided.

  As described above, according to the present invention, it is possible to provide a fixing device, an image forming apparatus, and a pressure control method capable of reducing load fluctuations on a recording medium by a fixing device and suppressing image disturbance. .

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  First, a schematic configuration of an image forming apparatus 100 including a fixing unit 150 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram showing a schematic configuration of the image forming apparatus 100 according to the present embodiment.

<Schematic configuration of image forming apparatus>
The fixing unit 150 according to the present embodiment can be provided in, for example, a tandem image forming apparatus as shown in FIG. As shown in FIG. 1, the image forming apparatus 100 includes a recording medium conveyance unit 110, a transfer unit including a transfer belt 120 as a primary transfer member, a photosensitive drum 130 that carries an electrostatic latent image, and a photosensitive drum 130. The image forming apparatus includes a developing unit 140 that develops the electrostatic latent image formed thereon, and a fixing unit 150.

  The recording medium conveyance unit 110 accommodates a recording medium on which an image is finally formed and conveys the recording medium onto the recording medium conveyance path. The recording medium is, for example, paper P and is stacked and accommodated in a cassette. The recording medium transport unit 110 causes the paper P to reach the secondary transfer area at the timing when the toner image transferred to the paper P is formed and reaches the secondary transfer area.

  The transfer unit conveys a toner image formed by a developing unit 140, which will be described later, to a secondary transfer area for secondary transfer to a recording medium. The transfer unit includes a transfer belt 120, suspension rollers 120a, 120b, 120c, and 120d that suspend the transfer belt 120, a primary transfer roller 122 that sandwiches the transfer belt 120 together with the photosensitive drum 130, and the transfer belt 120 together with the suspension roller 120d. The secondary transfer roller 124 sandwiches the toner.

  The transfer belt 120 is an endless belt that is circulated by the suspension rollers 120a, 120b, 120c, and 120d. The primary transfer roller 122 is provided so as to press the photosensitive drum 130 from the inner peripheral side of the transfer belt 120. On the other hand, the secondary transfer roller 124 is provided so as to press the suspension roller 120 d from the outer peripheral side of the transfer belt 120. Although not shown in FIG. 1, the transfer unit may further include a belt cleaning device that removes toner attached to the transfer belt 120.

  The photosensitive drum 130 is an electrostatic latent image carrier on which an image is formed on a peripheral surface, and is made of, for example, OPC (Organic PhotoConductor). The image forming apparatus 100 according to the present embodiment is an apparatus capable of forming a color image. For example, four photosensitive drums 130 are arranged in the rotation direction of the transfer belt 120 corresponding to each color of magenta, yellow, cyan, and black. Is provided. As shown in FIG. 1, a charging roller 132, an exposure unit 134, a developing unit 140, and a cleaning unit 138 are provided on the circumference of each photosensitive drum 130.

  The charging roller 132 uniformly charges the surface of the photosensitive drum 130 to a predetermined potential. The exposure unit 134 performs exposure according to an image forming the surface of the photosensitive drum 130 charged by the charging roller 132. As a result, the potential of the portion of the surface of the photosensitive drum 130 exposed by the exposure unit 134 changes, and an electrostatic latent image is formed. The developing unit 140 develops the electrostatic latent image formed on the photosensitive drum 130 with the toner supplied from the toner tank 136 (136M, 136Y, 136C, 136B), and generates a toner image.

  The cleaning unit 138 collects toner remaining on the photosensitive drum 130 after the toner image formed on the photosensitive drum 130 is primarily transferred to the transfer belt 120. For example, the cleaning unit 138 can be configured to provide a cleaning blade and scrape the remaining toner on the photosensitive drum 130 by bringing the cleaning blade into contact with the peripheral surface of the photosensitive drum 130. A neutralizing lamp (not shown) for resetting the potential of the photosensitive drum 130 is provided between the cleaning unit 138 and the charging roller 132 in the rotation direction of the photosensitive drum 130 on the circumference of the photosensitive drum 130. It can also be arranged.

  The developing unit 140 includes a developing roller 141 and stirring and conveying units 142 and 143. The developing roller 141 is a developer carrier that supplies toner to the electrostatic latent image formed on the peripheral surface of the photosensitive drum 130. The agitating / conveying units 142 and 143 agitate the magnetic carrier and the non-magnetic or weak magnetic toner constituting the developer to charge the carrier and the toner. The first agitating / conveying unit 142 is arranged to face the developing roller 110 in a substantially vertical direction, and supplies the developer that has been mixed and agitated to the developing roller 141. The second agitating and conveying unit 143 has a role of mixing and agitating the developer to sufficiently charge the developer, and conveys the charged developer to the first agitating and conveying unit 142. The second agitating and conveying unit 143 is provided with a toner concentration sensor (not shown) for detecting the toner concentration. When the toner concentration in the conveying path decreases, development from the toner tank 136 into the conveying path is performed. Agent is supplied.

  The fixing unit 150 adheres and fixes the toner image secondarily transferred from the transfer belt 120 to the recording medium. The fixing unit 150 includes, for example, a heating roller 152 and a pressure roller 154. The heating roller 152 is a cylindrical member that can rotate around a rotation shaft that functions as a fixing roller, and a heat source such as a halogen lamp is provided therein. The pressure roller 154 is a cylindrical member that can rotate around the rotation axis, and is provided so as to press the heating roller 152. On the outer peripheral surface of the heating roller 152 and the pressure roller 154, for example, a heat-resistant elastic layer such as silicon rubber is provided. By passing the recording medium through a fixing nip, which is a contact area between the heating roller 152 and the pressure roller 154, the toner image is melted and fixed on the recording medium.

  Note that a travel sensor 170 that detects the travel state of the recording medium is provided between the fixing unit 150 and the secondary transfer region in which the transfer is performed from the transfer belt 120 to the recording medium. The travel sensor 170 detects whether or not the recording medium has passed the position where the travel sensor 170 is provided. Further, the fixing unit 150 according to the present embodiment includes a variable pressure mechanism (reference numeral 160 in FIG. 2) that adjusts the pressing force between the heating roller 152 and the pressure roller 154. Details of the configuration of the pressure variable mechanism will be described later.

  Further, the image forming apparatus 100 is provided with discharge rollers 104 and 106 for discharging the recording medium on which the toner image is fixed by the fixing unit 150 to the outside of the apparatus.

  In such an image forming apparatus 100, first, when the image forming apparatus 100 is operated, an image signal of a recorded image is transmitted to a control unit (not shown). Next, the control unit uniformly charges the surface of the photosensitive drum 130 to a predetermined potential by the charging roller 132 based on the received image signal, and then applies laser light to the surface of the photosensitive drum 130 by the exposure unit 134. Irradiate to form an electrostatic latent image.

  On the other hand, in the developing unit 140, the toner and the carrier are mixed and stirred to be sufficiently charged, and then the developer is carried on the developing roller (reference numeral 141 in FIG. 1). Then, when the developer is conveyed to a region facing the photosensitive drum 130 by the rotation of the developing roller 141, toner is formed on the peripheral surface of the photosensitive drum 130 among the developer carried on the developing roller 141. Move to the electrostatic latent image and develop the electrostatic latent image. The toner image formed in this manner is primarily transferred from the photosensitive drum 130 to the transfer belt 120 in a region where the photosensitive drum 130 and the transfer belt 120 face each other. On the transfer belt 120, the toner images formed on the four photosensitive drums 130 are sequentially stacked to form one stacked toner image. The laminated toner image is secondarily transferred to the recording medium conveyed from the recording medium conveyance unit 110 in the area where the suspension roller 120d and the secondary transfer roller 124 are in contact with each other.

  The recording medium on which the laminated toner image is secondarily transferred is conveyed to the fixing unit 150. By passing the recording medium between the heating roller 152 and the pressure roller 154 while applying heat and pressure, the laminated toner image is fused and fixed on the recording medium. Thereafter, the recording medium is discharged to the outside of the image forming apparatus 1 by the discharge rollers 104 and 106. On the other hand, when the transfer belt 120 includes a belt cleaning device, the toner remaining on the transfer belt 120 is removed by the belt cleaning device after the laminated toner image is secondarily transferred to the recording medium.

  The tandem image forming apparatus 100 shown in FIG. 1 is an example of an image forming apparatus using the fixing unit 150 according to the present embodiment, and the fixing unit 150 according to the present embodiment can use various types of image forming apparatuses. It can be applied to a forming apparatus.

  The schematic configuration of the image forming apparatus 100 including the fixing unit 150 according to the present embodiment has been described above. In the image forming apparatus 100 according to the present embodiment, by adjusting the load applied between the heating roller 152 and the pressure roller 154 of the fixing unit 150, the transfer image on the recording medium is disturbed by the impact on the recording medium. Reduce the occurrence of displacement of the recording medium. Therefore, the fixing unit 150 is provided with a variable pressure mechanism that adjusts the load applied between the heating roller 152 and the pressure roller 154.

  Hereinafter, based on FIGS. 2-5, the structure and effect | action of a pressure variable mechanism are demonstrated. FIG. 2 is a partial side view showing the configuration of the pressure variable mechanism 160 according to the present embodiment. FIG. 3 is a perspective view showing the first connecting portion 162 of the pressure variable mechanism 160 according to the present embodiment. 4 and 5 are explanatory diagrams for explaining the operation of the pressure variable mechanism 160 according to the present embodiment.

<Configuration of variable pressure mechanism>
First, based on FIG. 2 and FIG. 3, the structure of the pressure variable mechanism 160 concerning this embodiment is demonstrated. As described above, the pressure variable mechanism 160 according to the present embodiment is a mechanism that adjusts the load between the heating roller 152 and the pressure roller 154, and includes a gear portion 161, a first connecting portion 162, The second connecting portion 163, the spring portion 164, and the support member 165 are configured.

  The gear portion 161 is a disk-like member that can rotate around the central axis, and gear teeth 161a are formed on the outer periphery at a predetermined pitch. In FIG. 2, the gear teeth 161a are shown in a simplified manner. The gear portion 161 is provided so that the gear teeth 161 a mesh with the gear teeth 162 b of the first connecting portion 162. The gear part 161 is rotated clockwise or counterclockwise around the central axis by a driving part (not shown) such as a motor.

  The first connecting portion 162 is a transmission member that transmits the rotational motion of the gear portion 161 to the pressure roller 154. As shown in FIG. 3, the first connecting portion 162 is a substantially fan-shaped member. The first connecting portion 162 includes a first through-hole 162 a through which the rotation shaft 103 fixed to the housing 102 is inserted, a gear tooth 162 b that meshes with the gear tooth 161 a of the gear portion 161, and a protrusion of the support member 165. A second through hole 162c through which the portion 165a is inserted, and an arc portion 162d in which the support shaft 154a of the pressure roller 154 is located. As the gear portion 161 rotates, the first connecting portion 162 rotates around the rotation shaft 103 inserted through the first through hole 162a. Although not shown, the first connecting portion 162 is connected to the support shaft 154a of the pressure roller 154. As a result, the support shaft 154b of the pressure roller 154 moves with the movement of the first connecting portion 162, and the pressure applied to the heating roller 152 can be increased or decreased.

  The second connecting portion 163 is a member that connects the pressure variable mechanism 160 to the housing 102. The second connecting portion 163 connects the variable pressure mechanism 160 to the image forming apparatus 100 by connecting the gear portion 161 and the housing 102.

  The spring portion 164 is an elastic member that adjusts the load between the heating roller 152 and the pressure roller 154 constituting the fixing unit 150. The spring portion 164 is, for example, a compression coil spring, and a substantially columnar support member 165 is inserted into an inner space formed by winding. The support member 165 is provided with a protruding portion 165a inserted into the second through hole 162c on the outer peripheral surface on one end side so as to be connected to the first connecting portion 162, and a spring portion 164 on the other end side. A locking portion 165b for locking is provided. As the first connecting portion 162 moves, the support member 165 moves along the shape of the second through-hole 162c having a long hole shape, and the spring portion 164 expands and contracts.

  In such a pressure variable mechanism 160, when the gear unit 161 is rotated in the first direction (clockwise in FIG. 2) by the driving unit, the first coupling unit 162 is rotated and the pressure roller 154 is moved to the heating roller. 152 is pressed. At this time, the spring portion 154 is compressed and adjusted so that the pressure roller 154 does not suddenly press the heating roller 152. On the other hand, when the drive unit rotates the gear unit 161 in a second direction (counterclockwise in FIG. 2) that is opposite to the first direction, the first connecting unit 162 rotates and the pressure roller 154 is rotated. Is separated from the heating roller 152.

<Operation of variable pressure mechanism>
The operation of the variable pressure mechanism 160 will be described with reference to FIGS. 4 and 5 which show the variable pressure mechanism 160 according to the present embodiment as a model. First, FIG. 4 shows a state in which the applied pressure between the heating roller 152 and the pressure roller 154 is low. At this time, it is assumed that the elastic force acting on the pressure roller 154 from the spring portion 164 is substantially zero.

  Next, when increasing the pressing force between the heating roller 152 and the pressure roller 154, the gear portion 161 is rotated in the first direction (counterclockwise in FIG. 4), and the first connecting portion 162 is rotated. Rotate around 103. In the example of FIG. 4, the first connecting portion 162 rotates clockwise. Then, the pressure roller 154 connected to the first connecting portion 162 and the support shaft 154a moves linearly so as to press the heating roller 152, and as shown in FIG. The load in between increases. At this time, the spring portion 164 is compressed with the rotational movement of the first connecting portion 162, and causes a restoring force to return to the original state to act on the first connecting portion 162 and the pressure roller 154. Due to the restoring force of the spring portion 164, the load between the heating roller 152 and the pressure roller 154 can be prevented from increasing suddenly, and the pressure can be controlled more easily.

  On the other hand, when the gear portion 161 is rotated in the second direction (clockwise in FIG. 5), the first connecting portion 162 moves counterclockwise around the rotation shaft 103. Along with this, the pressure roller 154 connected to the first connecting portion 162 also moves downward in FIG. Thereby, the pressure roller 154 is separated from the heating roller 152, and the load between the heating roller 152 and the pressure roller 154 can be reduced. At this time, the compression of the spring portion 164 is weakened, and the restoring force acting on the first connecting portion 162 and the pressure roller 154 is also reduced.

  The configuration and operation of the pressure variable mechanism 160 according to the present embodiment have been described above. The configuration of the pressure variable mechanism 160 is not limited to this example. For example, as shown in FIG. 6, a worm 260 that meshes with the gear teeth 161 a of the gear portion 161 instead of the substantially fan-shaped first connecting portion 162. May be used. In this case, when the gear portion 161 rotates in the first direction (counterclockwise in FIG. 6), the worm 260 moves to the upper side in FIG. 6 while rotating. Then, the connecting portion 261 that connects the worm 260 and the pressure roller 154 also moves, and accordingly, the support shaft 154 a of the pressure roller 154 also moves linearly so as to press the heating roller 152. In this way, the load between the heating roller 152 and the pressure roller 154 can be increased.

  On the other hand, when the gear portion 161 is rotated in the second direction (clockwise in FIG. 6), the worm 260 is also moved downward in FIG. 6 while rotating. Then, the connecting portion 261 that connects the worm 260 and the pressure roller 154 also moves, and the support shaft 154 a of the pressure roller 154 is also separated from the heating roller 152. Thereby, the load between the heating roller 152 and the pressure roller 154 can be reduced.

  Further, the pressure variable mechanism 160 according to the present embodiment can be applied not only to the two-roll type fixing unit 150 as shown in FIG. 4, but also to a belt type fixing unit as shown in FIG. As shown in FIG. 7, the belt-type fixing unit includes a heating roller 252 having a heating source (not shown), a fixing roller 254, an endless belt 256 suspended by the heating roller 252 and the fixing roller 254, The pressure roller 154 is in contact with the fixing roller 254 with the endless belt 256 interposed therebetween. Also in such a fixing unit, by providing the pressure roller 154 in connection with the pressure variable mechanism 160, the pressure variable mechanism 160 is operated as described with reference to FIGS. The load between 254 and the pressure roller 154 can be adjusted.

[Control of variable pressure mechanism]
Next, a method for controlling the pressure variable mechanism 160 described above will be described with reference to FIGS. The fixing unit 150 according to the present embodiment includes a control unit 300 that controls the operation of the pressure variable mechanism 160. Therefore, the configuration of the control unit 300 and the pressure control method using the control unit 300 will be described below. FIG. 8 is a block diagram illustrating a configuration of the control unit 300 that controls the pressure variable mechanism 160 according to the present embodiment. FIG. 9 is a flowchart showing a control method of the pressure variable mechanism 160 according to the present embodiment. FIG. 10 is a graph showing the load fluctuation at the fixing nip portion of the fixing unit 150 that changes according to the control method of the pressure variable mechanism 160 according to the present embodiment.

<Configuration of control unit>
First, based on FIG. 8, the structure of the control part 300 which controls the pressure variable mechanism 160 is demonstrated. As shown in FIG. 8, the control unit 300 according to the present embodiment includes an image input unit 310, an image processing unit 320, a pressure control unit 330, a travel detection unit 340, a timing detection unit 350, and a drive control unit. 360.

  The image input unit 310 is an input unit to which image data is input. An image to be formed on a recording medium by the image forming apparatus 100 is input, for example, read from a scanner unit (not shown) or read from a storage unit of a personal computer. The image input unit 310 receives the image data acquired in this way and outputs it to the image processing unit 320.

  The image processing unit 320 is a functional unit that performs image processing on image data. The image processing unit 320 can analyze the image data and acquire the contents of the image data (for example, the color of the image and the required quality) and the formation position of the image data on the recording medium. The image processing unit 320 outputs these pieces of information to the pressure control unit 330.

  The pressure control unit 330 is a control unit that controls the timing at which the load between the heating roller 152 and the pressure roller 154 is changed by the pressure variable mechanism 160. Based on the content of the image data input from the image processing unit 320, the position where the image data is formed on the recording medium, and the detection information of the travel detection unit 340 and the timing detection unit 350, the pressure control unit 330 and the heating roller 152 are added. The timing for changing the load with the pressure roller 154 is controlled. Such a control method will be described later. The pressure control unit 330 outputs a drive instruction to drive the variable pressure mechanism 160 to the drive control unit 360 based on the timing at which the load between the heating roller 152 and the pressure roller 154 is changed.

  The travel detection unit 340 detects the travel state of the recording medium. The travel detection unit 340 is provided between the transfer area where the toner image is transferred to the recording medium by the transfer unit and the fixing area where the unfixed toner image on the recording medium is fixed by the fixing unit 150. The travel detection unit 340 corresponds to the travel sensor 170 in FIG. When the travel detection unit 340 detects that the recording medium has passed the position where the travel detection unit 340 is provided, the travel detection unit 340 outputs the result to the pressure control unit 330.

  The timing detection unit 350 detects the timing at which the load between the heating roller 152 and the pressure roller 154 is changed by operating the pressure variable mechanism 160. For the timing detection unit 350, for example, a CPU timer provided in the image forming apparatus 100 can be used. When the timing detection unit 350 detects the timing at which the pressure variable mechanism 160 is activated, the timing detection unit 350 outputs the result to the pressure control unit 330.

  The drive control unit 360 is a control unit that controls the drive of the pressure variable mechanism 160. The drive control unit 360 actually drives the variable pressure mechanism 160 based on the timing for operating the variable pressure mechanism 160 input from the pressure control unit 330 and the target load between the heating roller 152 and the pressure roller 154. The control amount for calculating is calculated. Then, the drive control unit 360 operates the pressure variable mechanism 160 based on the calculated control amount.

<Control method of variable pressure mechanism>
Next, based on FIG. 9 and FIG. 10, the control method of the pressure variable mechanism 160 by the control part 300 mentioned above is demonstrated. In the following description, the recording medium is assumed to be paper P. First, before the sheet P enters the fixing nip of the fixing unit 150, the pressure in the fixing nip portion (i.e., the load between the heating roller 152 and pressure roller 154) to the pressure P ₁ is first It has been set (step S110). The first pressure P ₁ is a minimum pressure necessary for transporting the paper P. By setting the pressure until the paper P enters the fixing nip portion in this way, it is possible to reduce the impact generated when the paper P enters the fixing nip portion.

  Next, it is determined whether or not the travel of the paper P is detected by the travel detection unit 340 (step S120). When the traveling detection unit 340 detects the leading edge of the paper P, it outputs the result to the pressure control unit 330. When the detection of the paper P is notified from the travel detection unit 340, the pressure control unit 330 calculates the arrival timing at which the leading edge of the paper P reaches the fixing nip (step S130). The arrival timing is determined from the conveyance speed of the recording medium defined in the image forming apparatus 100 according to the content of the image data, and the distance from the travel detection unit 340 to the entrance of the fixing nip unit. That is, the arrival time t1 from when the leading edge of the sheet P passes through the travel detection unit 340 to the entrance of the fixing nip is obtained from the conveyance speed of the recording medium and the above distance. After calculating the arrival time t1, the pressure control unit 330 causes the timing detection unit 350 to start counting time.

  Thereafter, it is determined whether or not the leading edge of the paper P has reached the fixing nip (step S140). The determination in step S140 can be made based on whether the time count by the timing detection unit 350 has reached the arrival time t1. If the time counted by the timing detection unit 350 has not reached the arrival time t1, the determination is repeated until the arrival time t1 is reached. When the time counted by the timing detection unit 350 reaches the arrival time t1, the timing detection unit 350 outputs the result to the pressure control unit 330.

Then, the sheet P from the timing detection unit 350 is notified that reaches the fixing nip portion, the pressure control unit 330 raises the pressure of the fixing nip portion to a second pressure P ₂ (step S150). When the paper P enters the fixing nip portion, in order to fix the unfixed toner image attached to the paper P, it is necessary to set the pressure in the fixing nip portion to a pressure necessary for the fixing process (second pressure P ₂ ). is there. The pressure necessary for the fixing process is larger than the pressure P ₁ necessary for conveying the paper P. Therefore, the pressure control unit 330, the sheet P reaches the fixing nip portion, as shown in FIG. 10, raises the pressure of the fixing nip portion from a first pressure P ₁ to a second pressure P _2. That is, the pressure roller 154 is moved in the direction in which the heating roller 152 is pressed by the pressure variable mechanism 160 to increase the pressure in the fixing nip portion. At this time, the speed of change of the pressure at the fixing nip portion is determined according to the performance of the driving portion, and the pressure at the fixing nip portion is changed from the first pressure P ₁ to the second pressure P immediately after the recording medium enters the fixing nip portion. Can be raised to ₂ .

Incidentally, when the second pressure P ₂ becomes excessively large, load and to members such as the heating roller 152 and pressure roller 154 constituting the fixing unit 150, the damage is increased with respect to the paper P. The size of the second pressure P _2, taking into account these points, performs a fixing process of an unfixed toner image reliably, even components and the influence of the paper P of the fixing unit 150 by considering determined It is desirable to do.

When the pressure in the fixing nip portion is increased to a second pressure P _2, then pressure controller 330, or the image portion of the sheet P (unfixed toner image is adhered portion) passes through the fixing nip portion It is determined whether or not (step S160). The determination in step S160 is, for example, calculated from the image data formation position on the paper P input from the image processing unit 320 and the conveyance speed of the paper P. This can be done based on the passage time t2 until the passage.

The pressure control unit 330, the pressure in the fixing nip portion is increased to a second pressure P _2, the forming position of the image data in the sheet P which is input from the image processing unit 320 and time passing from the conveying speed of the sheet P t2 is calculated. Then, after calculating the passage time t2, the pressure control unit 330 causes the timing detection unit 350 to start counting time. If the time count by the timing detection unit 350 has not reached the passage time t2, the determination is repeated until the passage time t2 is reached. When the time counted by the timing detector 350 reaches the passage time t2, the timing detector 350 outputs the result to the pressure controller 330.

When an image portion from the timing detection unit 350 is notified that has passed through the fixing nip portion, the pressure control unit 330 lowers the pressure in the fixing nip portion to a first pressure P ₁ (step S170). That is, the pressure roller 154 is moved in the direction away from the heating roller 152 by the pressure variable mechanism 160 to reduce the pressure in the fixing nip portion. When the image portion of the sheet P passes through the fixing nip portion, it is not necessary to add a second pressure P ₂ necessary for fixing process on the sheet P, the sheet P need be transported in the transport direction. Further, by reducing the pressure applied to the paper P, the life of members such as the heating roller 152 and the pressure roller 154 constituting the fixing unit 150 can be extended. Further, it is possible to reduce damage accompanying deformation of the paper P caused by applying a large load to the paper P.

  As described above, the processes from steps S110 to S170 are repeated, and the pressure variable mechanism 160 is operated according to the traveling state of the paper P to adjust the pressure in the fixing nip portion.

The control method of the pressure variable mechanism 160 by the control unit 300 according to the present embodiment has been described above. According to the control method according to the present embodiment, until the recording medium enters between the heating roller 152 and the pressure roller 154 of the fixing unit 150, the pressure at the fixing nip portion is set to the pressure (first step) at which the recording medium can be conveyed. set to 1 pressure P _1), the recording medium when enters the fixing nip portion, thereby increasing the pressure in the fixing nip portion to a pressure (second pressure P ₂₎ required for the fixing process.

  As a result, the recording medium can easily enter the fixing nip portion, and impact generated by entering the fixing nip portion can be reduced. In addition, it is possible to reduce a deviation that occurs in a portion of the recording medium that is sandwiched by the transfer unit when the leading end portion of the recording medium is positioned at the fixing nip portion, and to reduce an impact that the recording medium receives from the fixing unit. You can also. Therefore, the disturbance of the transfer image on the recording medium can be reduced, and the deterioration of the image quality can be prevented.

Further, after the recording medium has entered the fixing nip portion and after the image portion of the recording medium has passed through the fixing nip portion, the pressure of the fixing nip portion is set to a pressure necessary for conveying the recording medium (first pressure P _1). ). Thereby, the lifetime of the members constituting the fixing unit 150 can be extended, and damage to the paper P can also be reduced.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

For example, in the above embodiment, the timing at which the pressure of the fixing nip portion is lowered after the recording medium has entered the fixing nip portion is set when the image portion of the recording medium passes the fixing nip portion. It is not limited. For example, the end of the recording medium may be changed pressure of the fixing nip portion after passing through the fixing nip portion from the second pressure P ₂ to the first pressure P _1. In this case, when the travel detection unit 340 notifies the end of the recording medium, the pressure control unit 330 calculates the time for the end of the recording medium to pass through the fixing nip. The time can be calculated from the conveyance speed of the recording medium and the distance from the travel detection unit 340 to the exit of the fixing nip unit. When the pressure control unit 330 counts the time required for the timing detection unit 350 and receives a notification from the timing detection unit 350 that the time has been reached, the pressure control unit 330 operates the pressure variable mechanism 160 to change the pressure in the fixing nip unit. Reduce to a pressure P ₁ of ₁ . In this way, the pressure at the fixing nip can be changed.

  In the above embodiment, the position of the heating roller 152 is fixed, and only the pressure roller 154 is moved by the pressure variable mechanism 160 to change the pressure of the fixing nip portion. However, the present invention is not limited to such an example. For example, the pressure of the fixing nip portion may be changed by fixing the position of the pressure roller 154 and moving only the heating roller 152 by the pressure variable mechanism 160.

1 is an explanatory diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a partial side view which shows the structure of the pressure variable mechanism concerning the embodiment. It is a perspective view which shows the 1st connection part of the pressure variable mechanism concerning the embodiment. It is explanatory drawing explaining operation | movement of the pressure variable mechanism concerning the embodiment, Comprising: The state when the load between a heating roller and a pressure roller is low is shown. It is explanatory drawing explaining operation | movement of the pressure variable mechanism concerning the embodiment, Comprising: The state when the load between a heating roller and a pressure roller is raised is shown. It is explanatory drawing which shows the other structural example of the pressure variable mechanism concerning the embodiment. FIG. 9 is an explanatory diagram illustrating a configuration of another fixing unit to which the pressure variable mechanism according to the embodiment can be applied. It is a block diagram which shows the structure of the control part which controls the pressure variable mechanism concerning the embodiment. It is a flowchart which shows the control method of the pressure variable mechanism concerning the embodiment. 6 is a graph showing a load variation in a fixing nip portion of a fixing unit that is changed by a control method of a pressure variable mechanism according to the embodiment. FIG. 6 is an explanatory diagram illustrating a positional relationship between a transfer unit and a fixing unit. FIG. 6 is an explanatory diagram illustrating a toner adhesion state on a recording medium when a transfer image on the recording medium is disturbed or a recording medium is displaced due to an impact.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 110 Recording medium conveyance unit 130 Photosensitive drum 140 Developing unit 150 Fixing unit 152 Heating roller 154 Pressure roller 160 Pressure variable mechanism 161 Gear part 162 First connection part 163 Second connection part 164 Spring part 165 Support Member 170 Travel sensor 300 Control unit 310 Image input unit 320 Image processing unit 330 Pressure control unit 340 Travel detection unit 350 Timing detection unit 360 Drive control unit

Claims (8)

A pressure roller for pressing the recording medium;
A fixing roller that is provided facing the pressure roller and fixes an unfixed toner image on a recording medium conveyed to a fixing nip portion that is a region that is in pressure contact with the pressure roller;
A variable pressure mechanism for changing the pressure of the fixing nip portion, which is a load generated between the pressure roller and the fixing roller;
A travel detection unit for detecting the travel state of the recording medium;
A pressure control unit that calculates a first timing at which the leading end of the recording medium enters the fixing nip portion based on the detected running state, and drives and controls the pressure variable mechanism;
A timing detection unit for detecting timing for operating the pressure variable mechanism;
With
The pressure control unit can convey the recording medium with the pressure of the fixing nip portion until the leading end of the recording medium enters the fixing nip portion based on the detection result of the first timing by the timing detecting portion. After the leading end of the recording medium has entered the fixing nip, the pressure variable mechanism is driven so that the pressure in the fixing nip reaches the second pressure necessary for fixing the unfixed toner image. The fixing device to raise.   The fixing device according to claim 1, wherein the pressure control unit calculates the first timing based on a conveyance speed of the recording medium and a distance from the travel detection unit to an entrance of the fixing nip unit. The pressure controller is
Further calculating a second timing at which the unfixed toner image on the recording medium passes through the fixing nip,
3. The fixing device according to claim 1, wherein the pressure of the fixing nip portion is decreased from the second pressure to the first pressure based on a detection result of the second timing by the timing detection unit.   The fixing device according to claim 3, wherein the pressure control unit calculates the second timing based on a conveyance speed of the recording medium and an image formation position on the recording medium.   The pressure variable mechanism moves either the pressure roller or the fixing roller in a linear direction connecting the rotation center of the pressure roller and the rotation center of the fixing roller, so that the fixing nip portion The fixing device according to claim 1, wherein the pressure is changed.   The fixing device according to claim 1, wherein the travel detection unit is provided on a conveyance path from when the toner image is transferred to the recording medium to when the recording medium enters the fixing nip portion. A recording medium conveying unit for accommodating the recording medium and conveying the recording medium onto the recording medium conveying path;
An electrostatic latent image carrier that carries an electrostatic latent image on a peripheral surface;
A developing unit for developing the electrostatic latent image on the electrostatic latent image carrier to generate a toner image;
A transfer unit for transferring the toner image to a recording medium;
A fixing unit for fixing an unfixed toner image on a recording medium;
With
The fixing unit includes:
A pressure roller for pressing the recording medium;
A fixing roller that is provided facing the pressure roller and fixes an unfixed toner image on a recording medium conveyed to a fixing nip portion that is a region that is in pressure contact with the pressure roller;
A variable pressure mechanism for changing the pressure of the fixing nip portion, which is a load generated between the pressure roller and the fixing roller;
A travel detection unit for detecting the travel state of the recording medium;
A pressure control unit that calculates a first timing at which the leading end of the recording medium enters the fixing nip portion based on the detected running state, and drives and controls the pressure variable mechanism;
A timing detection unit for detecting timing for operating the pressure variable mechanism;
With
The pressure control unit can convey the recording medium with the pressure of the fixing nip portion until the leading end of the recording medium enters the fixing nip portion based on the detection result of the first timing by the timing detecting portion. After the leading end of the recording medium has entered the fixing nip, the pressure variable mechanism is driven so that the pressure in the fixing nip reaches the second pressure necessary for fixing the unfixed toner image. An image forming apparatus to be raised. A pressure roller that presses the recording medium and the pressure roller until the leading end of the recording medium enters a fixing nip portion that is provided in opposition to the pressure roller and is in contact with the pressure roller. A pressure at the fixing nip portion, which is a load generated between a roller and the fixing roller, is set as a first pressure capable of conveying a recording medium;
Detecting the running state of the recording medium by the running detection unit;
Calculating a first timing at which the leading edge of the recording medium enters the fixing nip portion based on the detected running state by the pressure controller;
Detecting a timing for operating the pressure variable mechanism by a timing detector;
Based on the detection result of the first timing by the timing detection unit, after the leading end portion of the recording medium has entered the fixing nip portion, a pressure variable mechanism that changes the pressure of the fixing nip portion is driven to perform the fixing. Increasing the nip pressure to a second pressure required to fix the unfixed toner image;
Including a pressure control method.

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