JP2010210784A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device performing successful fixing on leading edge part of a sheet to which a toner image is to be fixed. <P>SOLUTION: The fixing device includes a heating roller 132 the outer circumferential surface of which the sheet 90 to be conveyed is brought into pressurized contact with by a pressurization member 131. The fixing device further includes: a heat source 4 provided inside the heating roller 132; heat ray focusing parts 5, 6, 7 which are provided inside the heating roller 132 so as to be rotatable in the peripheral direction with respect to the heating roller 132, and focus a heat ray generated by the heat source 4 on a certain heat ray focusing direction regarding the peripheral direction of the heating roller 132. In accordance with rushing of the leading edge part 90f of the sheet 90 into a nip area N, with which the sheet 90 is brought into pressurized contact, of the circumferential surface of the heating roller 132, the heat ray focusing direction by the heat ray focusing parts 5, 6, 7 is moved from an entrance part Nu to the center part Nc of the nip area N. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device, and more particularly to a fixing device including a heating roller in which a conveyed sheet is pressed against an outer peripheral surface by a pressing member.

  The present invention also relates to an image forming apparatus provided with such a fixing device.

  Conventionally, as a fixing device of this type, a nip for fixing is formed by a heating roller and a pressure member pressed against the heating roller, and a heat source and heat generated by the heat source are provided inside the heating roller. There is known one provided with a movable reflecting plate that reflects in a desired direction (see, for example, Japanese Patent Application Laid-Open No. 2006-337540). While the fixing device does not function, the reflection plate reflects heat to the nip position, and while the fixing device functions, the reflection plate is driven to reflect heat toward the nip entrance.

  As a result, while the fixing device is functioning, the heat transmitted to the inlet of the nip is transferred from the inside to the surface while the heating roller rotates, and reaches the maximum temperature at the nip. Further, while the fixing device is not functioning, the reflecting plate reflects heat to the nip position, so that it is possible to prevent the temperature of the nip and the pressure member from being lowered even if the heating roller does not rotate. As a result, even when the operation of the fixing device is changed from standby to operation, the operation can be performed directly. This document describes the above.

JP 2006-337540 A

  In recent fixing devices, in order to shorten the warm-up time, the thickness of the heating roller is set to be thin so that the heat capacity is reduced. For this reason, when the leading edge of the paper enters the nip, especially when the paper is thick paper, the heat of the heating roller is rapidly taken away by the paper, the temperature of the nip decreases, and the leading edge of the paper There is a tendency for fixing properties to be insufficient.

  In particular, in the above-described conventional example, the nip entrance is heated while the fixing device is functioning, and the center of the nip is not heated. Therefore, when the leading edge of the paper reaches the center of the nip, the temperature at the center of the nip decreases. As a result, there is a problem that the fixing property of the leading edge of the paper becomes insufficient.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device capable of performing good fixing with respect to the leading end portion of a sheet (such as paper) on which a toner image is to be fixed.

  Another object of the present invention is to provide an image forming apparatus provided with such a fixing device.

In order to solve the above problems, the fixing device of the present invention is:
A heating roller in which the conveyed sheet is pressed against the outer peripheral surface by a pressing member;
A heat source provided inside the heating roller;
A heat ray converging unit provided inside the heating roller so as to be rotatable in the circumferential direction with respect to the heating roller, and for converging the heat ray generated by the heat source in a certain heat ray converging direction with respect to the circumferential direction of the heating roller;
As the leading edge of the sheet enters the nip region where the sheet is pressed against the outer peripheral surface of the heating roller, the heat ray converging direction of the heat ray converging unit is changed from the inlet to the center of the nip region. A drive control unit that performs the first control to move is provided.

  Here, the “heat rays” may include not only infrared rays but also rays having a shorter wavelength than infrared rays.

  The “sheet” includes not only paper but also a resin sheet such as an OHP (overhead projector) film.

  The “pressing member” includes a roller or a belt around which the roller is wound.

  In the fixing device of the present invention, the drive control unit is configured to cause the heat ray converging unit to converge the heat ray as the leading end of the sheet enters the nip region where the sheet is pressed against the outer peripheral surface of the heating roller (heat ray). The first control is performed to move the focusing direction) from the entrance to the center of the nip region. Therefore, while the leading edge of the sheet moves from the inlet portion to the center of the nip region, the portion of the nip region corresponding to the leading edge of the sheet is continuously heated by the heat rays. Therefore, it is possible to prevent the temperature of the nip region from being lowered as the leading edge of the sheet enters the nip region. As a result, according to this fixing device, it is possible to perform excellent fixing with respect to the leading end portion of the sheet.

  In the fixing device according to an embodiment, when the first control is performed, the drive control unit moves the heat ray focusing direction by the heat ray focusing unit at the same speed as the sheet conveyance speed with respect to the nip region. It is characterized by making it.

  In the fixing device according to this embodiment, when the drive control unit performs the first control, the heat ray focusing direction by the heat ray focusing unit is set to the same speed as the sheet conveyance speed with respect to the nip region. Move. Therefore, while the leading edge of the sheet moves from the entrance to the center of the nip region, the portion corresponding to the leading edge of the sheet in the nip region continues to be accurately heated by the heat rays. Therefore, according to this fixing device, it is possible to perform better fixing with respect to the leading end portion of the sheet.

In the fixing device of one embodiment,
A sensor for detecting the sheet is provided at a position upstream of the nip region with respect to the conveyance direction of the sheet,
Before the sheet is detected by the sensor, the drive control unit directs the heat ray converging direction by the heat ray converging unit toward the center of the nip region, and when the sheet is detected by the sensor. Immediately, preliminary control is performed to move the heat ray focusing direction by the heat ray focusing portion to the entrance portion of the nip region. The first control is started.

  In the fixing device of this embodiment, before the sheet is detected by the sensor, the heat ray converging direction by the heat ray converging portion is directed to the center portion of the nip region. As a result, the central portion of the nip region is continuously heated by the heat rays. Therefore, before the sheet is detected by the sensor, not only the heating roller but also the pressing member is in the nip region through the central portion where the heating roller and the pressing member are in close contact with each other. Heated by hot wire. Therefore, it is possible to more effectively prevent the temperature of the nip region from being lowered as the leading edge of the sheet enters the nip region. As a result, according to this fixing device, it is possible to perform better fixing with respect to the leading end portion of the sheet.

In the fixing device of one embodiment,
A sensor for detecting the sheet at a position upstream of the nip region with respect to the conveyance direction of the sheet;
When the drive control unit determines that the trailing edge of the sheet has passed through the center of the nip region based on the output of the sensor, the drive control unit determines the heat beam focusing direction by the heat beam focusing unit at the center of the nip region. It is characterized by performing the second control to move from the section toward the entrance section.

  In the fixing device according to the one embodiment, the drive control unit determines that the trailing edge of the sheet has passed through the center of the nip region based on the output of the sensor, and the heat ray focusing unit performs the above operation. Second control is performed to move the heat ray focusing direction from the center of the nip region toward the inlet. Therefore, when it is determined that the leading edge of the next sheet following the sheet has reached the entrance of the nip region, the first control can be started immediately. Therefore, according to this fixing device, good fixing can be performed also for the leading end portion of the next sheet.

  In the fixing device according to an embodiment, the drive control unit performs the second control, and when the next sheet following the sheet is not detected by the sensor even after a predetermined period has elapsed, the heat ray focusing is performed. The third control is performed to return the heat ray focusing direction by the portion from the entrance portion to the center portion of the nip region.

  If the next sheet following the sheet is not detected by the sensor even after a predetermined period has elapsed after the second control has been performed, a standby for waiting for the next print job after a certain print job is completed It is thought that it was in a state. Therefore, in the fixing device according to the embodiment, the drive control unit performs the second control, and when the next sheet following the sheet is not detected by the sensor even after a predetermined period has elapsed, Third control for returning the heat ray focusing direction by the heat ray focusing portion from the entrance portion to the center portion of the nip region is performed. Thereby, while in the standby state, the central portion of the nip region is continuously heated by the heat rays. Therefore, not only the heating roller but also the pressing member is heated by the heat ray through a central portion where the heating roller and the pressing member are in close contact with each other in the nip region. Therefore, at the start of the next print job, it is possible to effectively prevent the temperature of the nip region from decreasing as the leading edge of the sheet enters the nip region. As a result, according to this fixing device, it is possible to perform satisfactory fixing with respect to the leading edge of the sheet at the start of the next print job. Further, the next print job can be started immediately, and productivity can be improved.

  The image forming apparatus according to the present invention includes an image forming unit that attaches toner to the sheet and the fixing device according to the invention.

  In the image forming apparatus of the present invention, toner is adhered to the sheet by the image forming unit, and the toner is fixed on the sheet as an image by the fixing device of the present invention. Therefore, a good image can be formed with respect to the leading edge of the sheet.

1 is a diagram illustrating a cross-sectional structure of a color tandem type image forming apparatus including a fixing device according to an embodiment of the present invention. It is a figure which shows the block configuration of the control system which the said image forming apparatus has. FIG. 2 is a diagram illustrating a schematic configuration of the fixing device. FIG. 6 is a diagram illustrating a distribution of heat amount given to each part of a sheet by a fixing operation in the fixing device. It is a figure which shows the structure of the drive mechanism 8 for rotating integrally the heat source of the said fixing device, a holding member, a condensing lens, and a reflecting plate. It is a figure which shows the AA 'line arrow cross section in FIG. It is a figure which shows arrangement | positioning of the member in several processes of the fixing operation | movement in the said fixing device. FIG. 4 is a diagram illustrating a flow of a fixing operation in the fixing device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a cross-sectional structure of a color tandem type image forming apparatus 100 including a fixing device 130 according to an embodiment of the present invention. The image forming apparatus 100 includes an intermediate transfer belt 108 as an annular image carrier that moves in the circumferential direction and is wound around two rollers 102 and 106 at a substantially central position in a main body casing 101. Of the two rollers 102 and 104, one roller 102 is arranged on the left side in the figure, and the other roller 106 is arranged on the right side in the figure. The intermediate transfer belt 108 is supported by these rollers 102 and 106 and is driven to rotate in the arrow X direction.

  Above the intermediate transfer belt 108, toner containers 128Y, 128M, 128C, and 128K containing toners of yellow (Y), magenta (M), cyan (C), and black (K) are sequentially arranged from the left side in the drawing. They are arranged side by side. The toner is supplied from the toner containers 128Y, 128M, 128C, and 128K to the developing units 193 of the corresponding image forming units 110Y, 110M, 110C, and 110K described later.

  Below the intermediate transfer belt 108, in order from the left side in the figure, an image forming unit 110Y as an image forming unit corresponding to each color toner of yellow (Y), magenta (M), cyan (C), and black (K), 110M, 110C, and 110K are arranged side by side.

  The image forming units 110Y, 110M, 110C, and 110K are configured in exactly the same manner except for the difference in the toner colors that they handle. Specifically, for example, the yellow image forming unit 110Y includes a photosensitive drum 190, a charging device 191, an exposure device 192, a developing device 193 that performs development using toner, and a cleaner device 195. It is configured. A primary transfer roller 194 is provided at a position facing the photosensitive drum 190 with the intermediate transfer belt 108 interposed therebetween. At the time of image formation, the surface of the photosensitive drum 190 is first uniformly charged by the charging device 191. Subsequently, the surface of the photosensitive drum 190 is output by the exposure device 192 in accordance with an image signal input from an external device (not shown), for example. Are exposed to form a latent image there. Next, the latent image on the surface of the photosensitive drum 190 is developed by the developing device 193 to become a toner image. This toner image is transferred to the intermediate transfer belt 108 by applying a voltage between the photosensitive drum 190 and the primary transfer roller 194. The transfer residual toner on the surface of the photosensitive drum 190 is cleaned by a cleaner device 195.

  As the intermediate transfer belt 108 moves in the arrow X direction, four color toner images are superimposed on the intermediate transfer belt 108 by the image forming units 110Y, 110M, 110C, and 110K.

  On the left side of the intermediate transfer belt 108, a cleaning device 125 that removes residual toner from the surface of the intermediate transfer belt 108 and a toner collection box 126 that collects toner removed by the cleaning device 125 are provided. A secondary transfer roller 112 is provided on the right side of the intermediate transfer belt 108 with a conveyance path 124 for paper interposed therebetween. Conveying rollers 120 and 119 are provided in positions corresponding to the upstream and downstream sides of the secondary transfer roller 112 in the conveying path 124, respectively. An optical sensor (toner density sensor) for detecting a toner pattern on the intermediate transfer belt 108 is provided integrally with the conveying roller 120.

  A fixing device 130 for fixing the toner to the paper is provided at the upper right portion in the main body casing 101. The fixing device 130 includes a sheet passing sensor 116 as a sheet sensor for detecting a sheet as a sheet conveyed into the fixing device 130, a heating roller 131 extending perpendicularly to the paper surface of FIG. Similarly, a pressure roller 132 as a pressure member that extends perpendicularly to one paper surface and is in pressure contact with the heat roller 131 is provided. In this example, a heating source (not shown) is built in the heating roller 131. The pressure roller 132 is urged toward the heating roller 131 by a spring (not shown). Thereby, the heating roller 131 and the pressure roller 132 form a nip region N for fixing. When the sheet 90 on which the toner image is transferred passes through the nip region N, the toner image is fixed on the sheet 90. The sheet passing sensor 116 is provided on the upstream side of the nip region N with respect to the conveyance direction of the sheet 90. The fixing device 130 operates based on the timing when the paper passing sensor 116 detects the paper 90.

  Also, at the lower part of the main casing 101, there are two stages of paper feed cassettes 116A and 116B that accommodate sheets 90 as sheets on which images are to be formed (for simplicity, the paper feed cassette 116A has Only the sheet 90 is accommodated).

  At the time of image formation, the sheet 90 is fed one sheet at a time from, for example, the sheet feeding cassette 116A to the conveying path 124 by the sheet feeding roller 118, and to the toner transfer position between the intermediate transfer belt 108 and the secondary transfer roller 112 by the conveying roller 120. It is sent. On the other hand, as described above, four color toner images are formed on the intermediate transfer belt 108 by the image forming units 110Y, 110M, 110C, and 110K. The four-color toner images on the intermediate transfer belt 108 are transferred by the secondary transfer roller 112 to the sheet 90 sent to the toner transfer position described above. The sheet 90 on which the toner image is transferred is conveyed through a nip region N formed by the heating roller 131 and the pressure roller 132 of the fixing unit 130, and is heated and pressed. As a result, the toner image is fixed on the sheet 90. Then, the sheet 90 on which the toner image is fixed is discharged by a discharge roller 121 to a discharge tray portion 122 provided on the upper surface of the main body casing 101.

  The image forming apparatus 100 has a control system having a block configuration as shown in FIG. The control system of the image forming apparatus 200 includes an operation display unit 202 that performs operation settings of various functions, an image reading unit 205 and an image processing unit 206 that read an image into electronic data, and an image that is converted into electronic data. ROM (Read Only Memory) 203, RAM (Random Access Memory), a data storage unit 208 for storing various data, and electronic data to be printed on paper An image forming unit 207 that forms an image, an I / F unit 209 that transmits and receives data to and from the outside of the image forming apparatus through a network 210 such as an in-house LAN (local area network), and a fixing device 130 that will be described in detail later. Drive control unit 138 for controlling the control unit 2 and a central processing unit (CPU) that centrally controls each of these units It has one and.

  As shown in FIG. 3, the fixing device 130 includes a cylindrical heating roller 131 and a cylindrical pressure roller 132 that extend perpendicular to the paper surface of FIG. 3. The heating roller 131 is urged toward the heating roller 131 by an elastic body (not shown) such as a spring (not shown). As a result, the heating roller 131 and the pressure roller 132 are pressed against each other to form the nip region N for fixing.

  In this example, the heating roller 131 includes a cylindrical core metal having thermal conductivity, an elastic layer made of silicone rubber or the like covering the outside of the core metal, and a separation made of a fluororesin or the like covering the outside. It consists of a mold layer. Similarly, the pressure roller 132 is composed of a cylindrical core bar having thermal conductivity, an elastic layer covering the outside of the core bar, and a release layer covering the outside.

  The heating roller 131 and the pressure roller 132 are supported by a frame 25 (see FIG. 5) to be described later so as to be rotatable around their respective centers. One of the heating roller 131 and the pressure roller 132, in this example, the heating roller 131 is rotated clockwise (in the direction of the arrow b) in FIG. 3 around the center by a drive motor (not shown), and the other pressure roller 132 is 3 is driven to rotate counterclockwise (in the direction of arrow a) in FIG. Note that the pressure roller 132 may be driven by a driving source, and the heating roller 131 may be driven to rotate.

  Inside the heating roller 131, a rod-shaped heat source (in this example, made of a halogen lamp) 4 is provided substantially coaxially with the heating roller 131. The heat source 4 radiates heat rays radially in the radial direction. A holding member 5 made of a transparent resin that transmits heat rays is fitted and attached so as to surround the heat source 4. The condensing lens 6 is attached to the outer peripheral surface of the holding member 5 on the side closer to the nip region N than the heat source 4, while the semicylindrical reflector 7 is provided on the outer peripheral surface of the holding member 5 farther than the heat source 4. Is attached. The reflection plate 7 reflects the heat rays received from the heat source 4 toward the condenser lens 6. The condenser lens 6 receives the heat rays received from the heat source 4 and the reflecting plate 7 in a certain heat ray focusing direction L with respect to the circumferential direction of the heating roller 131, specifically, the width of the nip region N (in the inner peripheral surface of the heating roller 131 ( In FIG. 3, it means a dimension in the direction along the conveyance direction of the sheet 90.

  The heat source 4, the holding member 5, the condenser lens 6, and the reflection plate 7 are integrally rotatable around the center of the heat source 4, that is, in the circumferential direction with respect to the heating roller 132 by a driving mechanism 8 described later. It has become. These heat source 4, holding member 5, condenser lens 6, reflector 7, and driving mechanism 8 described later constitute a heat ray converging unit.

  During the fixing operation, the sheet 90 with the toner 91 attached on one side is conveyed in the direction indicated by the arrow c through the nip region N and is heated and pressurized in the nip region N. As a result, the toner image is fixed on the sheet 90 (details of the fixing operation will be described in detail later).

  5 and 6 show the configuration of the drive mechanism 8 for rotating the heat source 4, the holding member 5, the condenser lens 6 and the reflection plate 7 together. 5 shows a view from a direction perpendicular to the axial direction of the heat source 4, and FIG. 6 shows a cross section taken along line AA 'in FIG.

  The drive mechanism 8 includes a stepping motor 13 fixed to the frame 23, a small gear 15 fixedly attached to the output shaft 22 of the stepping motor 13, and rotation of the small gear 15 by the heat source 4 and the holding member 5. And a rotating member 14 that transmits to one end.

  The frame 23 is supported directly or indirectly by the main body casing 101 together with the frame 25 that supports the heating roller 132 (and the pressure roller 131).

  The stepping motor 13 is controlled by the drive control unit 138 shown in FIG.

  As can be clearly understood from FIG. 5, the rotating member 14 includes a boss 16 formed in a columnar shape and a plate-like flange 17 formed integrally with an end of the boss 16 on the heat source 4 side. . As can be clearly seen from FIG. 6, the flange 17 extends radially outward from the end of the boss 16 and projects mainly toward the small gear 15 side and the opposite side. A side surface 19 on the small gear 15 side of the flange 17 is formed in a generally arc shape, and a plurality of teeth 18 that mesh with the teeth of the small gear 15 are formed therein.

  The boss 16 of the rotating member 14 is provided with a bottomed mounting hole 20 that passes through the flange 17 and stops inside the boss. The end of the rod-like heat source 4 is inserted into and engaged with the mounting hole 20, whereby the heat source 4 is fixed substantially coaxially with the boss 16 of the rotating member 14. Further, the flange 17 includes a protrusion 21 around the opening of the mounting hole 20. One end of the holding member 5 is fixed to the protrusion 21. Thereby, the holding member 5 is integrally fixed to the rotating member 14 together with the reflector 7 and the condenser lens 6 shown in FIG.

  Further, the boss 16 of the rotating member 14 is rotatably supported by the frame 23.

  In such a configuration, when the drive control unit 138 controls the stepping motor 13 of the drive mechanism 8 to rotate the small gear 15 clockwise or counterclockwise in FIG. 6, the rotation is rotated from the small gear 15. It is transmitted to the moving member 14. Then, the heat source 4, the holding member 5, the condenser lens 6, and the reflection plate 7 can be integrally rotated around the center of the heat source 4 via the rotating member 14. That is, under the control of the drive control unit 138, the heat ray focusing direction L by the heat ray focusing unit (the heat source 4, the holding member 5, the condenser lens 6, the reflection plate 7 and the drive mechanism 8) is rotated around the center of the heat source 4. And can be moved along the inner peripheral surface of the heating roller 132.

  The heating roller 132 is rotatably supported by the frame 25 independently of the rotating member 14. Therefore, the heating roller 132 and the rotating member 14 can rotate independently of each other.

  FIG. 8 shows a flow of the fixing operation by the drive control unit 138 of the fixing device 130, and FIG. 7 shows the arrangement of members in several steps in the fixing operation. Next, based on FIG. 8, a specific fixing operation will be described with reference to FIG. A horizontal broken line i in FIG. 7 is a reference line indicating the central portion Nc of the nip region N. In FIG. 8, “paper passing sensor ON” indicates that the paper passing sensor 116 detects the paper 90, and “paper passing sensor OFF” indicates that the paper passing sensor 116 does not detect the paper 90. In the following description of the operation, “the leading end portion 90f of the sheet 90” is considered for the sake of convenience, excluding an image missing area that is a margin at the forefront of the sheet 90.

  i) First, a printing operation is performed in the image forming apparatus 100, and a toner image (unfixed) is transferred onto the sheet 90 (S1 in FIG. 8). The fixing device 130 waits in the state shown in FIG. 3 until the sheet 90 on which the unfixed toner image is transferred is detected by the sheet passing sensor 116. That is, the pressure roller 131 and the heating roller 132 are rotated in the directions of arrows a and b so as to convey the paper sheet 90 in the direction of arrow c. At the same time, the drive control unit 138 sets the heat ray focusing direction L toward the center Nc of the nip region N before the sheet 90 is detected by the sheet passing sensor 116.

  As a result, the central portion Nc of the nip region N is continuously heated by the heat rays. Therefore, before the sheet 90 is detected by the sheet passing sensor 116, not only the heating roller 132 but also the pressure roller 131 passes through the central portion Nc in the nip region N where the heating roller 132 and the pressure roller 131 are in close contact. And heated by hot wire. Accordingly, it is possible to effectively prevent the temperature of the nip region N from being lowered as the leading end portion 90f of the sheet 90 enters the nip region N.

  ii) Next, when the sheet 90 is detected by the sheet passing sensor 116 (S2 in FIG. 8), as shown in FIG. 7A, the drive control unit 138 immediately sets the heat ray focusing direction L in the nip region N. Preliminary control to move to the inlet portion Nu of the head is performed (S3 in FIG. 8).

  As a result, the entrance portion Nu of the nip region N is heated by the heat rays until the leading end 90f of the sheet 90 reaches the entrance portion Nu of the nip region N. Accordingly, preparation is made when the leading end portion 90f of the sheet 90 enters the inlet portion Nu of the nip region N.

  iii) Next, when a predetermined time T1 has elapsed since the sheet 90 was detected by the sheet passing sensor 116, the drive control unit 138 reached the leading end 90f of the sheet 90 at the entrance portion Nu of the nip region N. (S4 in FIG. 8). From that time point, as shown in FIG. 7B, the drive control unit 138 moves the heat ray focusing direction L in the nip region N at the same speed as the conveyance speed of the sheet 90 with respect to the nip region N. First control is performed to move from Nu to the central portion Nc (S5 in FIG. 8).

  As a result, while the leading end portion 90f of the sheet 90 moves from the inlet portion Nu to the central portion Nc of the nip region N, the portion corresponding to the leading end portion 90f of the sheet 90 in the nip region N is continuously accurately heated by the heat rays. Accordingly, it is possible to prevent the temperature of the nip region N from being lowered as the leading end portion 90f of the sheet 90 enters the nip region N. As a result, according to the fixing device 130, good fixing can be performed with respect to the leading end portion 90f of the sheet 90.

  The time T1 is calculated from the sheet conveyance distance from the sheet passing sensor 116 to the entrance portion Nu of the nip region N and the sheet conveyance speed unique to the image forming apparatus. For example, when the paper transport distance is 30 mm and the paper transport speed is 165 mm / s, the time T1 is 30/165 × 1000 = about 182 ms.

  iv) Next, when a predetermined time T2 has elapsed after the sheet 90 is detected by the sheet passing sensor 116, the drive control unit 138 causes the trailing end 90r of the sheet 90 to pass through the central portion Nc of the nip region N. (S6 in FIG. 8). Immediately at that time, as shown in FIG. 7C, the drive control unit 138 performs the second control for moving the heat ray focusing direction L from the central portion Nc of the nip region N toward the inlet portion Nu. (S7 in FIG. 8).

  Accordingly, when it is determined that the leading end 90f ′ of the next sheet 90 ′ following the sheet 90 has reached the inlet portion Nu of the nip region N, the first control (S5 in FIG. 8) is performed. You can start immediately. Therefore, according to the fixing device 130, good fixing can be performed also for the leading end portion 90f 'of the next sheet 90'.

  The time T2 is calculated from the paper size to be transported and the paper transport speed. For example, the paper size is A4Y (refers to a case where A4 size paper defined in Japanese Industrial Standard (JIS) is transported in the horizontal direction, that is, in a direction in which the longitudinal direction of the paper is perpendicular to the transport direction). Shall. In this case, when the paper length in the transport direction is 210 mm and the paper transport speed is 165 mm / s, the time T2 is 210/165 = about 1.27 s.

  v) Next, the drive control unit 138 performs the second control (S7 in FIG. 8), and the next sheet following the sheet 90 'is passed through the sheet passing sensor 116 even after the predetermined period T3 has elapsed. If it is not detected (S8 in FIG. 8), it is determined that a certain print job is finished and a standby state for waiting for the next print job is entered. Then, when it is determined that the standby state has been reached, the drive control unit 138 performs third control for returning the heat ray focusing direction L from the inlet portion Nu of the nip region N to the central portion Nc (S9 in FIG. 8).

  Thereby, while in the standby state, the central portion Nc of the nip region N is continuously heated by the heat rays. Therefore, not only the heating roller 132 but also the pressure roller 131 is heated by the heat ray through the central portion Nc in the nip region N where the heating roller 132 and the pressure roller 131 are in close contact. Therefore, it is possible to effectively prevent the temperature of the nip area N from being lowered as the leading edge of the sheet enters the nip area N at the start of the next print job. As a result, according to the fixing device 130, it is possible to perform satisfactory fixing with respect to the leading end portion of the sheet at the start of the next print job. Further, the next print job can be started immediately, and productivity can be improved.

  In step S8 in FIG. 8, when the next sheet following the sheet 90 'is detected by the sheet passing sensor 116, the process returns to step S4 and the above-described fixing operation is repeated.

  The time T3 is calculated from the sheet interval (interval between sheets conveyed sequentially) and the sheet conveyance speed. For example, when the sheet interval is 30 mm and the sheet conveyance speed is 165 mm / s, the time T3 is about 182 ms.

  Further, in the fixing device 130, the movement speed in the heat ray focusing direction L is changed by the stepping motor 13 according to the conveyance speed of the paper 90, so that the movement of the leading end portion 90 f of the paper 90 is always followed. it can. Thereby, it is possible to perform better fixing with respect to the leading end portion 90f of the sheet 90.

  Here, the conveyance speed of the sheet 90 is set and controlled according to the specifications of the image forming apparatus 100 by the control unit 201 shown in FIG. Normally, the conveyance speed of the sheet 90 is set according to the type of sheet (sheet thickness). The operation display unit 202 selects the type of paper used by the user, and the conveyance speed is determined according to the selected paper type. The drive control unit 138 sets and controls the moving speed in the heat ray focusing direction L according to the transport speed.

FIG. 4 shows the distribution of heat per unit area given to each part of the sheet 90 by the fixing operation in the fixing device 130. As can be seen from FIG. 4, when the fixing operation as described above, the distal end portion 90f of the sheet 90 so to follow the heat ray focusing direction L, most large amount of heat Q ₁ is given. Heat As the toward the central portion of the sheet 90 is reduced, in most portions other than the tip portion 90f of the sheet 90, the inherent heat Q ₀ is given. As a result, even when the sheet 90 is a sheet having a large heat capacity such as a thick sheet, it is possible to perform better fixing with respect to the leading end portion 90f of the sheet 90.

In the above description, for the sake of convenience, the “tip portion 90f of the sheet 90” has been described without considering that there is an image missing area that is a margin at the forefront of the sheet. However, an actual image forming apparatus such as a printer or a copying machine has an image missing area (indicated by reference numeral 90n in FIG. 4). In this case, the “leading end portion 90f of the sheet 90” in the above-described fixing operation is not regarded as the true leading edge of the sheet, but as being equivalent to a portion that is retracted from the true leading edge by the image missing area 90n. In other words, the control timing of each step is set by assuming that the portion retracted from the true leading edge by the amount of the image missing region 90n is the “leading portion 90f of the sheet 90”. If you do so, as can be seen from FIG. 4, the image missing region 90n are given the inherent heat Q _0. Since it is not necessary to give a particularly large amount of heat to the image missing region 90n where no image is formed, such a handling is considered preferable.

  In the above-described embodiment, the heat ray converging unit (specifically, the condensing lens 6) receives the heat rays received from the heat source 4 and the reflection plate 7 on the inner peripheral surface of the heating roller 131 and the width of the nip region N (see FIG. 3 is a dimension in the direction along the conveyance direction of the sheet 90.) However, the present invention is not limited to this, and the inner surface of the heating roller 131 may be converged to a width approximately equal to the width of the nip region N. In addition, the width | variety of a heat ray is prescribed | regulated by the full width at half maximum of the intensity distribution of a heat ray, for example.

  Further, the “heat rays” generated by the heat source 4 may include not only infrared rays but also rays having a shorter wavelength than infrared rays.

  In the above-described embodiment, an image is formed on the paper 90 as a sheet. However, the image may be formed not only on paper but also on a resin such as an OHP (overhead projector) film.

  In the above-described embodiment, the pressure member is the pressure roller 131, but the present invention is not limited to this. The pressing member may be a belt around which a roller is wound.

4 Heat source 5 Holding member 6 Condensing lens 7 Reflector 131 Pressure roller 132 Heating roller N Nip area

Claims (6)

A heating roller in which the conveyed sheet is pressed against the outer peripheral surface by a pressing member;
A heat source provided inside the heating roller;
A heat ray converging unit provided inside the heating roller so as to be rotatable in the circumferential direction with respect to the heating roller, and for converging the heat ray generated by the heat source in a certain heat ray converging direction with respect to the circumferential direction of the heating roller;
As the leading edge of the sheet enters the nip region where the sheet is pressed against the outer peripheral surface of the heating roller, the heat ray converging direction of the heat ray converging unit is changed from the inlet to the center of the nip region. A fixing device comprising a drive control unit that performs first control to be moved. The fixing device according to claim 1,
The drive control unit, when performing the first control, moves the heat ray converging direction by the heat ray converging unit at the same speed as the sheet conveyance speed with respect to the nip region. . The fixing device according to claim 1 or 2,
A sensor for detecting the sheet is provided at a position upstream of the nip region with respect to the conveyance direction of the sheet,
Before the sheet is detected by the sensor, the drive control unit directs the heat ray converging direction by the heat ray converging unit toward the center of the nip region, and when the sheet is detected by the sensor. Immediately, preliminary control is performed to move the heat ray focusing direction by the heat ray focusing portion to the entrance portion of the nip region, and then, when it is determined that the leading edge of the sheet has reached the entrance portion of the nip region, A fixing device which starts the first control. The fixing device according to claim 1 or 2,
A sensor for detecting the sheet is provided at a position upstream of the nip region with respect to the conveyance direction of the sheet,
When the drive control unit determines that the trailing edge of the sheet has passed through the center of the nip region based on the output of the sensor, the drive control unit determines the heat beam focusing direction by the heat beam focusing unit at the center of the nip region. A fixing device that performs second control to move from the first portion toward the inlet portion. The fixing device according to claim 4.
After the second control, the drive control unit determines the heat ray focusing direction by the heat ray focusing unit when the next sheet following the sheet is not detected by the sensor even after a predetermined period of time elapses. A fixing device that performs third control to return from the entrance portion of the nip area to the center portion. An image forming unit for attaching toner to the sheet;
An image forming apparatus comprising the fixing device according to claim 1.

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