JP2007199342A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of surely preventing deviation or rubbing on an image which is transferred and fixed on a recording medium even when the kind of the recording medium and the kind of the image are varied while restraining a cost increase associated with the increase of the number of components by optimizing the conveyance state of the recording medium between a transfer part and a fixing means. <P>SOLUTION: The fixing device includes a speed detection means for detecting at least the conveying speed of the recording medium obtained immediately after the recording medium rushes in a fixing nip part, and a speed changing means for changing the conveying speed of the recording medium which passes through the fixing nip part. It is constituted to change the conveyance speed of the recording medium which passes through the fixing nip part by the speed changing means on the basis of the speed of the recording medium obtained immediately after the recording medium rushes in the fixing nip part detected by the speed detection means, and adjusts it to target speed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device used in an image forming apparatus such as a copying machine or a printer that employs an electrophotographic method, and in particular, when fixing a toner image on different types of recording media such as cardboard and coated paper. The present invention relates to a fixing device capable of preventing image misalignment, rubbing, and the like caused by pulling a recording medium during transfer due to fluctuations in the conveyance speed of the recording medium in a fixing nip portion.

JP 2001-282072 A JP 2001-106380 A JP 2000-338805 A

  In recent years, there has been a strong demand for energy saving, high speed, cost reduction, and the like in image forming apparatuses such as copying machines and printers that employ this type of electrophotographic method. Along with the various demands required for these image forming apparatuses, there are a wide variety of demands for a fixing apparatus for fixing a full-color or monochrome unfixed toner image on a recording medium such as recording paper. .

  As a demand for the fixing device, in particular, in the color market, there is an increasing demand for a print to satisfactorily fix a full-color image on different types of paper such as thick paper and coated paper in addition to plain paper.

  These different types of recording media such as thick paper and coated paper differ in surface properties and basis weight (thickness) of the paper from plain paper. Therefore, in the case of thick paper, when the thick paper is nipped and conveyed by a fixing member such as a pair of fixing rolls, the deformation amount of the elastic layer of the fixing roll becomes larger than that of plain paper and passes through the fixing nip portion. The paper transport speed tends to be faster than a predetermined speed. In the case of coated paper, the surface is flat compared to plain paper, the coefficient of friction is small, and slipping easily occurs, and the conveyance speed of the paper passing through the fixing nip is increased by the thickness of the coated paper. However, the increased speed tends to be smaller than that of uncoated cardboard. As a result, the speed when the recording medium such as thick paper or coated paper passes through the fixing nip portion of the fixing device varies with respect to a predetermined fixing speed.

  Therefore, in the fixing device, the fixing speed is individually determined in advance according to the type of recording medium such as cardboard or coated paper, and the predetermined fixing speed is input for each type of recording medium. Although it is necessary to input the base information of all the recording medium types to the image forming apparatus in advance, there is a problem that it is very complicated.

  Also, when fixing toner images on both sides of the recording medium, the fixing conditions differ depending on whether the first side or the second side. Furthermore, the conveyance speed of the recording medium at the fixing nip portion of the fixing device also changes depending on whether the image to be fixed on the recording medium is a solid image or a character image.

  Therefore, in the conventional fixing device, the recording medium in the fixing nip portion of the fixing device depends on all the conditions such as the type of the recording medium, the first or second side of the both surfaces, or the type of image. It is difficult to respond by setting the conveyance speed, and there is a possibility that the recording medium being transferred is pulled due to the speed fluctuation of the recording medium in the fixing nip, and the image is misaligned or rubbed. Had the problem of being.

  Therefore, as a technique that can solve such a problem, for example, techniques disclosed in Japanese Patent Laid-Open Nos. 2001-282072, 2001-106380, 2000-338805, etc. have already been proposed. Yes.

An image forming apparatus according to the above Japanese Patent Application Laid-Open No. 2001-282072 includes an image carrier, and an image forming unit that forms an image on the image carrier according to image information;
Conveying means for conveying the transfer material through a transfer position for transferring the image formed on the image carrier to the transfer material;
Fixing means for fixing the image transferred to the transfer material while conveying the transfer material at a speed slower than the conveyance speed of the conveyance means;
Detecting means for detecting a loop of a transfer material between the conveying means and the fixing means;
Control means for switching and controlling the conveyance speed of the fixing means based on the detection information of the detection means,
After the detecting means detects a loop of the transfer material, the conveying speed of the fixing means is switched to a speed higher than the conveying speed of the conveying means for a certain time.

Further, the sheet conveying apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 2001-106380 has a loop that detects the loop amount of the sheet material by receiving light emitted from the light emitting element and reflected by the sheet material by the light receiving element. A quantity detection means;
Conveying means for conveying the sheet material;
Driving means for driving the conveying means;
Control means for controlling the drive means based on detection information of the loop amount detection means,
The driving unit is controlled so that a loop amount obtained by the loop amount detecting unit is substantially equal to a preset loop amount.

Further, the double-sided image forming apparatus according to Japanese Patent Application Laid-Open No. 2000-338805 is capable of transferring and transferring an image carrier, means for forming a toner image on the image carrier, and a toner image on the image carrier. An intermediate transfer member that is a means for conveying the material, a transfer material supply unit that supplies the transfer material in synchronization with the toner images on the image carrier and the intermediate transfer member, Transfer material charging means for electroadsorption, first transfer means for transferring the toner image on the image carrier onto the surface of the intermediate transfer body or transfer material, and transferring the toner image on the intermediate transfer body to the back surface of the transfer material In a double-sided image forming apparatus having a second transfer means and a fixing means for fixing a toner image on a transfer material,
The fixing unit is a fixing unit that simultaneously fixes and conveys toner images on both the front and back surfaces of the transfer material by pressure heating of a pair of heat rollers, and is configured such that the transfer speed of the transfer material is changed after entering the fixing unit. It is a thing.

  However, the conventional technique has the following problems. That is, in the case of the technique disclosed in the above Japanese Patent Laid-Open No. 2001-282072 and Japanese Patent Laid-Open No. 2001-282072, the detecting means for detecting the loop of the transfer material between the conveying means and the fixing means, A loop amount detection unit that detects the loop amount is provided. The detection unit and the loop amount detection unit detect the loop amount of the transfer material, and control the speed of the fixing unit so that the loop amount of the transfer material is constant. However, since it is necessary to provide detection means and loop amount detection means, there is a problem in that the number of parts is increased by that amount, resulting in an increase in cost.

  Further, in the case of the double-sided image forming apparatus according to Japanese Patent Application Laid-Open No. 2000-338805, the fixing unit is a fixing unit that simultaneously fixes and conveys the toner images on both the front and back sides of the transfer material by pressure heating of a pair of heat rollers. The transfer material is configured such that the transfer speed is changed after entering the fixing unit to form a certain amount of loop of the transfer material, but the transfer material and the type of image are different. Then, since the speed at which the transfer material passes through the fixing unit fluctuates with respect to a predetermined speed, the loop amount of the transfer material fluctuates unreasonably, and image misalignment, rubbing, and the like are surely prevented. It had the problem that it was not possible.

  Therefore, the present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to optimize the conveyance state of the recording medium between the transfer unit and the fixing unit. Even if the recording medium or the type of image fluctuates, while suppressing the increase in cost associated with an increase in the number of parts, it is ensured that the image transferred or fixed on the recording medium will be displaced or rubbed. It is an object of the present invention to provide a fixing device that can be prevented.

In other words, the invention described in claim 1 allows a recording medium carrying an unfixed toner image to pass through a fixing nip portion formed between a pair of fixing members, at least one of which has a heating source, and is heated. In a fixing device for fixing an unfixed toner image on a recording medium by pressing,
A speed detecting means for detecting a conveyance speed of the recording medium immediately after entering the fixing nip, and a speed changing means for changing the conveyance speed of the recording medium passing through the fixing nip,
Based on the speed of the recording medium immediately after entering the fixing nip detected by the speed detecting means, the speed changing means changes the conveyance speed of the recording medium passing through the fixing nip to match the target speed. The fixing device characterized by the above.

  The invention described in claim 2 is characterized in that a sensor for detecting the passage of two recording media arranged at a predetermined distance before and after the fixing device is used as the speed detecting means. The fixing device according to claim 1.

  Furthermore, in the invention described in claim 3, the speed changed by the speed changing means is the first one and the second and subsequent sheets among a plurality of recording media that continuously pass through the fixing nip portion. The fixing device according to claim 1, wherein the values are different from each other.

  According to a fourth aspect of the present invention, there is provided the fixing device according to any one of the first to third aspects, wherein an initial recording medium conveyance speed of the fixing device is lower than a target speed. is there.

  Furthermore, the invention described in claim 5 is characterized in that the initial recording medium conveyance speed of the fixing device is preset according to the type of the recording medium. The fixing device according to claim 1.

  According to a sixth aspect of the present invention, the speed changing unit includes the fixing nip when the conveyance speed of the recording medium detected by the second speed detecting unit is deviated from the target speed by a predetermined value or more. 6. The fixing device according to claim 1, wherein a conveyance speed of the recording medium passing through the section is changed.

  Further, in the invention described in claim 7, when the type of the unfixed toner image fixed on the recording medium is changed, the speed changing unit again conveys the recording medium passing through the fixing nip portion. The fixing device according to claim 1, wherein the speed is changed.

  Further, the invention described in claim 8 is characterized in that the speed changing means changes the conveyance speed of the recording medium passing through the fixing nip portion again when the type of the recording medium is changed. A fixing device according to any one of claims 1 to 6.

  Furthermore, the invention described in claim 9 is characterized in that, when the size of the recording medium is changed, the speed changing means changes the conveyance speed of the recording medium passing through the fixing nip portion again. A fixing device according to any one of claims 1 to 6.

  Further, in the invention described in claim 10, when the paper feed tray for supplying the recording medium is changed, the speed changing unit again changes the conveyance speed of the recording medium passing through the fixing nip portion. The fixing device according to claim 1, wherein the fixing device is a fixing device.

  Further, in the invention described in claim 11, when the unfixed toner image is fixed on both sides of the recording medium, the speed changing unit performs recording passing through the fixing nip portion depending on whether the first side or the second side is used. The fixing device according to claim 1, wherein the medium conveyance speed is changed.

  According to the present invention, by optimizing the conveyance state of the recording medium between the transfer unit and the fixing unit, the recording medium, the type of the image, and the like are changed while suppressing an increase in cost due to an increase in the number of parts. Even in such a case, it is possible to provide a fixing device capable of reliably preventing the occurrence of deviation or rubbing in an image transferred or fixed on the recording medium.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
FIG. 2 shows a tandem-type full-color printer as an image forming apparatus to which the fixing device according to Embodiment 1 of the present invention is applied. Note that this tandem full-color printer includes an image reading device and functions as a full-color copying machine. Of course, the full-color printer does not have to include an image reading device.

  In FIG. 2, reference numeral 1 denotes a main body of a tandem full-color printer, and a scanner 2 as an image reading device (IIT: Image Input Terminal) that reads an image of a document (not shown) is provided above the full-color printer main body 1. Is arranged. The scanner 2 illuminates a document transported onto a platen glass 5 by an automatic document feeder (ADF: Auto Document Feeder) 3 with a light source 6, and reflects a reflected light image from the document into a full rate mirror 7 and a half rate mirror 8. , 9 and an image forming lens 10 are scanned and exposed on an image reading element 11 made of a CCD or the like through a reduction optical system, and an image of a document is scanned by the image reading element 11 to a predetermined dot density (for example, 1200 dpi or 2400 dpi). ).

  The document image read by the scanner 2 is sent to the image processing device 12 (Image Processing System) as image data of three colors, for example, red (R), green (G), and blue (B) (8 bits each). In this image processing apparatus 12, predetermined image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color / moving editing, and the like is performed on the image data of the document.

  The image data subjected to the predetermined image processing by the image processing device 12 as described above is an image of four colors of cyan (C), magenta (M), yellow (Y), and black (K) (each 8 bits). As described below, cyan (C), magenta (M), yellow (Y), and black (K) image forming units 13C, 13M, 13Y, and 13K ROSs 14C, 14M, 14Y, These ROSs 14C, 14M, 14Y, and 14K are subjected to image exposure using a laser beam LB in accordance with the image data of each color.

  Incidentally, four image forming units 13C, 13M, 13Y, and 13K of cyan (C), magenta (M), yellow (Y), and black (K) are horizontally provided in the tandem full-color printer main body 1. They are arranged in series at regular intervals in the direction.

  These four image forming units 13C, 13M, 13Y, and 13K are basically configured in the same manner, and are roughly divided into a photosensitive drum 15 that rotates at a predetermined speed in the direction of the arrow, and the photosensitive drum. A primary charging scorotron or charging roll (charging roll in the illustrated example) 16 that uniformly charges the surface of the drum 15 and an image corresponding to each color are exposed on the surface of the photosensitive drum 15 to form an electrostatic latent image. , A developing device 17 that develops the electrostatic latent image formed on the photosensitive drum 15 with a corresponding color toner, and a cleaning device 18. In this embodiment, the diameter of the photosensitive drum 15 used in the black (K) image forming unit 13K is equal to the photosensitive drums 14M, 14Y, and 14K of the other color image forming units 13M, 13Y, and 13K. Is set to be larger.

  As shown in FIG. 2, the ROS 14 modulates the semiconductor laser 19 according to the image data, and emits a laser beam LB from the semiconductor laser 19 according to the image data. The laser beam LB emitted from the semiconductor laser 19 is deflected and scanned by the rotary polygon mirror 22 via the reflecting mirrors 20 and 21, and the focal length is adjusted according to the scanning angle by an unshown f-θ lens. Then, scanning exposure is performed on a photosensitive drum 15 as an image carrier through a plurality of reflecting mirrors 23 and 24.

  From the image processing device 12, each color of cyan (C), magenta (M), yellow (Y), and black (K) image forming units 13 C, 13 M, 13 Y, and 13 K ROS 14 C, 14 M, 14 Y, and 14 K Are sequentially output, and laser beams LB emitted according to the image data from these ROSs 14C, 14M, 14Y, and 14K are scanned and exposed on the surfaces of the respective photosensitive drums 15C, 15M, 15Y, and 15K. An electrostatic latent image is formed. The electrostatic latent images formed on the photosensitive drums 15C, 15M, 15Y, and 15K are converted into cyan (C), magenta (M), yellow (Y), and yellow (Y) by developing devices 17C, 17M, 17Y, and 17K, respectively. The toner image is developed as a black (K) color toner image.

  Cyan (C), magenta (M), yellow (Y), and black (K) sequentially formed on the photosensitive drums 15C, 15M, 15Y, and 15K of the image forming units 13C, 13M, 13Y, and 13K. As shown in FIG. 2, the toner images of the respective colors are respectively transferred to primary transfer rolls 26C, 26M, and 26Y on an intermediate transfer belt 25 as an intermediate transfer body disposed below the image forming units 13C, 13M, 13Y, and 13K. , And 26K, the images are transferred in a superimposed state. The intermediate transfer belt 25 is wound around a drive roll 27, a tension roll 28, a steering roll 29, an idle roll 30, a backup roll 31, and an idle roll 32 with a constant tension. The drive roll 27 is rotationally driven by a dedicated drive motor with excellent constant speed, and is circulated at a predetermined speed equal to the photosensitive drums 15C, 15M, 15Y, and 15K along the direction of the arrow. Yes. As the intermediate transfer belt 25, for example, a flexible synthetic resin film such as polyimide is formed in an endless belt shape.

  The cyan (C), magenta (M), yellow (Y), and black (K) toner images transferred in multiple onto the intermediate transfer belt 25 are pressed against the backup roll 31 via the intermediate transfer belt 25. The recording sheet 34 that has been secondarily transferred onto a recording sheet 34 as a recording medium by a pressing force and electrostatic force by the secondary transfer roll 33, and the toner image of each color is transferred, is fixed to the fixing device 36 by the transport belt 35. It is conveyed to. The recording paper 34 onto which the toner images of the respective colors have been transferred is subjected to a fixing process by heat and pressure by a fixing device 36, and in the case of single-sided printing, on a discharge tray 37 provided outside the printer main body 1 as it is. To be discharged.

  As shown in FIG. 2, the recording paper 34 has a predetermined size or material from any one of a plurality of paper trays 38, 39, 40, 41, and a pair of paper feed rollers 42 and a pair of paper transport rollers. The paper is once transported to the registration roll 47 via a paper transport path 46 composed of 43, 44, and 45 and then stopped. The recording paper 34 supplied from any one of the paper trays 38, 39, 40, and 41 is sent to the secondary transfer position of the intermediate transfer belt 25 by a resist roll 47 that is rotationally driven at a predetermined timing.

  Further, when images are formed on both sides of the recording paper 34 by the full-color printer, the recording paper 34 on which the image is fixed on one side by the fixing device 36 is not discharged out of the apparatus as it is, but by a switching gate (not shown). Then, the conveyance path of the recording paper 34 is switched downward, and the recording paper 34 is once conveyed to the reversal paper conveyance path 48. Then, the recording paper 34 conveyed to the reversing paper conveyance path 48 is reversed, with the conveyance direction reversed, through the double-sided paper conveyance path 49 and the normal paper conveyance path 46. In this state, the sheet is conveyed again to the secondary transfer position of the intermediate transfer belt 25 and an image is formed on the back surface thereof. Then, the image is fixed by heat and pressure by the fixing device 36 and provided outside the printer body 1. It is discharged onto the discharge tray 37.

  FIG. 3 is a sectional view showing a fixing device according to the embodiment of the present invention.

  As shown in FIG. 3, the fixing device 36 according to this embodiment includes a heating roll 52 having three heating sources 51 inside as a fixing member, and a fixing nip portion N formed in pressure contact with the heating roll 52. And a fixing belt 53 as an endless belt member. The fixing belt 53 is pressed against the surface of the heating roll 52 with a predetermined pressing force by a pressing member 54 disposed therein. The pressing member 54 is urged so as to be in pressure contact with the surface of the heating roll 52 by the elastic repulsive force of the coil spring 55. Further, the surface of the pressing member 54 is covered with a sheet-like low friction member in order to reduce sliding resistance with the fixing belt 53, and a liquid lubricant is supplied to the inner surface of the fixing belt 53. A felt member 56 as a member is disposed. The felt member 56 is made of, for example, Nomex (trade name), and the felt member 56 is impregnated with about 2.0 g of oil as a liquid lubricant made of amino Si oil having a viscosity of 300 cs.

  The heating roll 52 is driven to rotate at a predetermined rotation speed by a drive motor 57 via a gear (not shown).

  In the fixing device 36, the heating side is constituted by the heating roll 52 and the pressure side is constituted by the fixing belt 53. However, the present invention is not limited to this, and both the heating side and the pressure side may be constituted by rolls. The heating side may be constituted by a belt, and the pressure side may be constituted by a roll. Further, both the heating side and the pressure side may be constituted by a belt.

  In FIG. 1, 58 is an inlet chute for guiding the recording sheet to the fixing nip N of the fixing device 36, 59 is an outlet chute disposed at the outlet of the fixing nip N of the fixing device 36, and 60 is Each of the exit rolls disposed at the exit of the fixing device 36 is shown.

  The heating roll 52 includes a thin cylindrical cored bar made of iron or stainless steel, an elastic layer made of silicon rubber or the like coated on the surface of the cored bar, and a surface of the elastic layer. And a release layer having a thickness of about 30 μm, which is made of PFA or the like that is coated. Further, three 650 W halogen lamps 51 are disposed inside the heating roll 52 as a heating source.

  The fixing belt 53 is formed in an endless belt shape having an outer diameter of 30 mm and a wall thickness of 75 μm by a synthetic resin such as polyimide, and a release layer made of PFA or the like is provided on the surface as needed. It is done.

  Furthermore, the pressing member 54 is mainly composed of an elastic member and a support member made of a metal such as stainless steel that supports the elastic member.

  By the way, in this embodiment, a recording medium carrying an unfixed toner image passes through a fixing nip portion formed between a pair of fixing members, at least one of which has a heating source, and is determined by heating and pressing. In a fixing device for fixing a received toner image on a recording medium, a first speed detecting means for detecting a conveyance speed of the recording medium immediately before entering the fixing nip portion, and a recording medium immediately after entering the fixing nip portion A second speed detecting means for detecting the transport speed of the recording medium, and a speed changing means for changing the transport speed of the recording medium passing through the fixing nip, and detected by the first and second speed detecting means. Based on the speed of the recording medium immediately before and immediately after entering the fixing nip, the speed changing means changes the conveyance speed of the recording medium passing through the fixing nip to change the target speed. It is those configured to fit in.

  In this embodiment, as the first and second speed detecting means, sensors for detecting the passage of two recording media arranged at a predetermined distance before and after the fixing device are used. It is comprised as follows.

  FIG. 4 is a block diagram showing a control circuit of the fixing device according to the embodiment of the present invention. Note that the control circuit of the fixing device does not need to be provided independently, and may be configured as a control circuit of a full-color printer.

  In FIG. 4, reference numeral 100 denotes a pre-passage paper speed detection means as a first transport speed detection means. The pre-passage paper speed detection means 100 is located upstream of the fixing device 36 as shown in FIG. 1, immediately before the first sheet sensor 101 disposed near the outlet of the secondary transfer portion of the intermediate transfer belt 25 and the recording sheet 34 conveyed by the conveyance belt 35 enter the fixing nip N of the fixing device 36. And the second paper sensor 102 disposed at the position.

  Reference numeral 103 denotes a nip passage paper speed detection means as a second conveyance speed detection means. The nip passage paper speed detection means 103 is a fixing nip of the fixing device 36 as shown in FIG. The second sheet sensor 102 is disposed at a position immediately before entering the portion, and the third sheet sensor 104 is disposed at a position immediately after passing through the fixing nip portion N of the fixing device 36. As shown in FIG. 1, the sheet speed detecting means 103 at the time of passing through the nip includes a third sheet sensor 104 disposed at a position immediately after passing through the fixing nip portion N of the fixing device 36, and a sheet discharge roll. You may comprise with the 4th paper sensor 105 arrange | positioned by this side.

  The first to fourth paper sensors 101, 102, 104, and 105 are paper sensors for detecting a jam of the recording paper 34 previously set in the full color printer main body 1, and are newly installed in the present invention. Not a thing.

  As shown in FIG. 5, the second sheet sensor 102 detects the leading edge of the recording sheet 34 just before entering the fixing nip portion N of the fixing device 36, and the second sheet sensor 102 detects the leading edge of the recording sheet 34. The time when the paper sensor 102 detects the leading edge of the recording paper 34 is t0, and the third paper sensor 104 detects the leading edge of the recording paper 34 immediately after passing through the fixing nip N of the fixing device 36. The time when the third paper sensor 104 detects the leading edge of the recording paper 34 is t1, and the difference between the time t0 and the time t1 is obtained as Δt = t1−t0, and the second paper sensor 102 is compared with the time difference Δt. By dividing the distance L from the third paper sensor 104, the conveyance speed of the recording paper 34 immediately after entering the fixing nip N of the fixing device 36 is detected. It has become.

  At this time, since the second paper sensor 102 is disposed on the front side of the fixing nip portion N of the fixing device 36, the second paper sensor 102 detects the leading edge of the recording paper 34 and then the recording paper. Since the recording paper 34 is not transported by the fixing device 36 until the leading end of the recording paper 34 enters the fixing nip portion N, the transport speed of the recording paper 34 obtained as described above is precisely the fixing device 36. This is not the conveyance speed of the recording paper 34 immediately after entering the fixing nip portion N.

  Therefore, in order to obtain the conveyance speed of the recording paper 34 immediately after entering the fixing nip N of the fixing device 36, the third paper sensor 104 and the fourth paper sensor 105 are used, or the third paper sensor is used. A fifth sheet sensor is disposed in the vicinity of the downstream side of the sheet 104 by a predetermined distance L2, and recording immediately after entering the fixing nip portion N of the fixing device 36 by the third sheet sensor 104 and the fifth sheet sensor. You may comprise so that the conveyance speed of the paper 34 may be detected.

  The pre-passage paper speed detection means 100 similarly detects the conveyance speed of the recording paper 34 just before entering the fixing nip portion of the fixing device 36.

  When the sheet speed detecting means 103 at the time of passing through the nip detects the conveying speed of the recording sheet 34 immediately after entering the fixing nip portion N of the fixing device 36, depending on the size of the recording sheet 34, A3 size, B4 size, etc. In the case of the recording paper 34 having a long length along the process direction, as shown in FIG. 1, the rear end of the recording paper 34 is still in a state where the toner image is being transferred at the secondary transfer portion. Yes. For this reason, in the fixing device 36, when the conveyance speed of the recording paper 34 passing through the fixing nip N of the fixing device 36 varies with respect to the target speed and varies depending on the type of the recording paper 34 and the image, the secondary transfer portion. In this case, the recording paper 34 during the transfer of the toner image is pulled, and the toner image transferred onto the recording paper 34 may be displaced or rubbed.

  Therefore, in this embodiment, the recording immediately before and immediately after entering the fixing nip portion N detected by the pre-passage paper speed detection means 100 and the paper speed detection means 103 when passing through the nip by the next fixing device speed variable means 107. Based on the speed of the paper 34, the conveyance speed of the recording paper 34 passing through the fixing nip N is changed to match the target speed.

  That is, in FIG. 4, reference numeral 107 denotes a fixing device speed variable means. The fixing device speed variable means 107 is constituted by, for example, a CPU or MCU as a control means for controlling the operation of the full-color printer, such as a ROM. The sheet conveyance speed at the fixing nip portion N of the fixing device 34 is controlled according to the program stored in FIG.

  Specifically, the fixing device speed varying means 107 is the speed of the recording paper 34 immediately before and immediately after entering the fixing nip N detected by the pre-passage paper speed detection means 100 and the paper speed detection means 103 when passing through the nip. Based on the above, the sheet conveyance speed of the fixing device 36 is variably controlled so that the conveyance speed of the recording sheet 34 passing through the fixing nip N is changed to match the target speed.

  In FIG. 4, reference numeral 108 denotes a user interface. The user interface 108 is a full-color printer, such as the size and type of the recording paper 34 to be printed or copied, the number of prints or copies, and black and white or color. This is for specifying and inputting the type of image.

  Note that the full-color printer can automatically determine the size and type of the recording paper 34 simply by specifying the paper feed tray through the user interface 108, or the original image type (monochrome or color) (not shown) by the scanner 2. Etc.) is automatically determined.

  In the above configuration, in the full-color printer according to the first embodiment, the cost associated with the increase in the number of parts is achieved by optimizing the conveyance state of the recording medium between the transfer unit and the fixing unit as follows. Even if the recording medium or the type of image fluctuates, it is possible to reliably prevent the image transferred or fixed on the recording medium from being misaligned or rubbed. Yes.

  That is, in the above-described full-color printer, full-color and black-and-white images have different types such as plain paper, thick paper, or coated paper, and recording paper 34 having different sizes such as A3 size, A4 size, B4 size, and B5 size. In addition, when printing or copying the desired number of copies, as shown in FIG. 4, the user interface 108 specifies the number of prints, the type of paper to be printed, the type of image, etc., and the start button is pressed. The job starts (step 101).

  Then, the fixing device speed varying means 107 detects the image mode and the image density based on the instruction from the user interface 108 and the image data of the original read by the scanner 2 (step 102), and then the recording sheet. A provisional passage time t0 that is expected to pass through the second paper sensor 102 is input (step 103).

  Next, the fixing device speed varying means 107 determines whether or not the process direction length of the recording paper 34 is equal to or greater than a specified value (step 104), and the process direction length of the recording paper 34 is equal to or greater than the specified value. If there is not, the fixing process is executed by setting a predetermined target speed without changing the paper conveyance speed of the fixing device 36 (step 105).

  On the other hand, when the length of the recording paper 34 in the process direction is equal to or greater than a specified value, the fixing device speed varying unit 107 passes the second paper sensor 102 at the leading edge of the recording paper 34 as shown in FIG. It is determined whether or not the difference between the measured time t0 and the time t1 when the leading edge of the recording paper 34 passes the third paper sensor 104 is equal to or greater than a specified value (step 106). If the time difference between the time t1 and the time t0 is not equal to or greater than the specified value, the fixing device speed varying unit 107 sets the paper transport speed of the fixing device 36 to a predetermined target speed without changing the fixing processing. Is executed (step 105).

  On the other hand, if the fixing device speed variable means 107 determines that the time difference between the time t1 and the time t0 is equal to or greater than a specified value, the fixing device 36 adjusts the sheet conveyance speed to the target speed. The operation for controlling the drive motor 57 of the fixing device 36 is started (step 107).

  The fixing device speed varying means 107 previously determines the sheet conveyance speed of the fixing device 36 according to whether the image type is black and white or color, and the type of the recording paper 34 is plain paper, thick paper 1 or thick paper 2. As shown in FIG. 9, various target values are set.

  Here, the plain paper is a paper having a basis weight (gsm) of 104 gsm or less, the thick paper 1 is a paper having a basis weight (gsm) of 105 gsm to 176 gsm, and the thick paper 2 is a basis weight (gsm) of 177 gsm. Refers to 280 gsm of paper.

  In FIG. 9, minus indicates that the target value of the sheet conveyance speed of the fixing device 36 is set in a direction that is slower than the process speed. When the negative value is larger, when the recording paper 34 passes through the fixing nip portion N, the conveyance speed of the recording paper 34 is increased due to the thickness (basis weight) of the recording paper 34 and the like. Therefore, in order to correct this, a negative value is set larger as the target value of the sheet conveyance speed of the fixing device 36 for the recording sheet 34 having a larger basis weight such as the thick paper 1 and the thick paper 2.

  In the case of a color image, the image area of the unfixed toner image is large and the adhesion between the unfixed toner image and the fixing member is higher than that of the black-and-white image. ) And the like, the tendency to increase the conveyance speed of the recording paper 34 is slightly smaller, and in order to correct this, the target value of the paper conveyance speed of the fixing device 36 is higher for the color image than for the monochrome image. As a negative value is set small.

  As described above, the fixing device speed varying means 107 determines in advance the fixing device 36 according to whether the type of image is black and white or color, and the type of recording paper 34 is plain paper, thick paper 1 or thick paper 2. Various target values of the sheet conveyance speed are set. When the recording sheet 34 on which the unfixed toner image is actually transferred is passed, as shown in FIGS. 10 and 11, the fixing nip portion N of the fixing device 36 is set. The conveyance speed of the recording paper 34 that actually passes through is different from the target speed, and in some cases, the recording paper being transferred may be pulled, causing image misalignment or rubbing.

  Therefore, in this embodiment, as shown in FIG. 5, the conveyance speed at the front end of the recording paper 34 that actually passes through the fixing nip portion N of the fixing device 36 is detected by the paper speed detecting means 103 when passing through the nip. When the conveyance speed of the recording paper 34 detected by the paper speed detecting means 103 when passing through the nip is different from the target speed of the recording paper 34 of the fixing device 36 as shown in FIG. 7 or FIG. The conveyance speed of the recording paper 34 in the fixing nip N of the fixing device 36 is changed so that the conveyance speed of the paper 34 matches the target speed.

  As shown in FIG. 7, the fixing device speed varying unit 107 determines that the time difference between the time t1 and the time t0 is less than a specified value, that is, the recording paper 34 in the fixing nip portion N of the fixing device 36. When it is determined that the transport speed is slower than the target speed, the drive motor 57 of the fixing device 36 is controlled so that the transport speed of the recording paper 34 in the fixing nip N of the fixing device 36 is within the target speed range ( (OK region) is controlled.

  At this time, the fixing device speed varying means 107 determines whether the recording sheet 34 whose transport speed is detected is the first sheet or the second and subsequent sheets among a plurality of prints, and the recording whose transport speed is detected. When the paper 34 is the first of a plurality of prints, as shown in FIG. 7, it is within the target speed range (OK region) and still has the higher target speed V3. To control.

  The reason for this is that the first recording paper 34 of the plurality of prints has a higher transport speed of the recording paper 34 because the transport speed of the recording paper 34 in the fixing nip N of the fixing device 36 is slower than the target speed. This is for setting the target speed V3 at a high speed. In addition, when the recording sheet 34 for which the conveyance speed is detected is the second and subsequent sheets of the plurality of prints, since the control for increasing the speed has already been performed, the conveyance speed of the recording sheet 34 is set to the target speed. This is because a target speed V2 that is slower than V3 is sufficient.

  On the other hand, as shown in FIG. 8, the fixing device speed varying means 107 determines that the time difference between the time t1 and the time t0 is equal to or greater than a specified value, that is, the recording paper in the fixing nip N of the fixing device 36. When it is determined that the conveyance speed of the recording medium 34 is higher than the target speed, the drive motor 57 of the fixing device 36 is controlled so that the conveyance speed of the recording paper 34 in the fixing nip portion N of the fixing device 36 is within the target speed range. Control is performed so as to enter the inside (OK region).

  At this time, similarly, the fixing device speed varying means 107 determines whether the recording paper 34 whose transport speed is detected is the first sheet of the plurality of prints, the second sheet or later, and the transport speed is detected. When the recording sheet 34 is the first of a plurality of prints, as shown in FIG. 8, it is within the target speed range (OK region) and the lower target speed V3. Control to be.

  As described above, in the above-described embodiment, by optimizing the conveyance state of the recording paper 34 to and from the fixing device 36, the recording paper 34 and the type of image are suppressed while suppressing an increase in cost due to an increase in the number of parts. Even when the image is fluctuated, it is possible to reliably prevent the image transferred or fixed on the recording paper 34 from being displaced or rubbed.

  In the above embodiment, the case where the image is fixed on one side of the recording medium has been described. However, the present invention can be similarly applied to the case where the image is fixed on both sides of the recording medium.

In this case, when fixing the unfixed toner image on both sides of the recording medium, the speed changing unit is configured to change the conveyance speed of the recording medium passing through the fixing nip portion depending on whether the first side or the second side is used. Is done.

FIG. 1 is a block diagram showing a main part of a tandem-type full-color printer as an image forming apparatus to which a fixing device according to Embodiment 1 of the present invention is applied. FIG. 2 is an overall configuration diagram showing a tandem full-color printer as an image forming apparatus to which the fixing device according to the first embodiment of the present invention is applied. FIG. 3 is a cross-sectional configuration diagram showing the fixing device according to Embodiment 1 of the present invention. FIG. 4 is a block diagram showing a control circuit of a tandem-type full-color printer as an image forming apparatus to which the fixing device according to Embodiment 1 of the present invention is applied. FIG. 5 is a schematic diagram showing a method for detecting the conveyance speed of the recording paper in the fixing device according to Embodiment 1 of the present invention. FIG. 6 is a flowchart showing the operation of a tandem full-color printer as an image forming apparatus to which the fixing device according to Embodiment 1 of the present invention is applied. FIG. 7 is a timing chart showing the operation of the fixing device according to Embodiment 1 of the present invention. FIG. 8 is a timing chart showing the operation of the fixing device according to Embodiment 1 of the present invention. FIG. 9 is a chart showing the control state of the fixing device according to Embodiment 1 of the present invention. FIG. 10 is a graph showing the relationship between the basis weight of the sheet and the difference in sheet conveyance speed in the fixing device with respect to the machine speed. FIG. 11 is a graph showing the relationship between the paper basis weight and the difference in paper conveyance speed in the fixing device with respect to the machine speed.

Explanation of symbols

  34: recording paper, 36: fixing device, 100: first transport speed detection means (pre-passage paper speed detection means), 101: first paper sensor 101, 102: second paper sensor, 103: second transport speed Detection means (paper speed detection means when passing through the nip), 104: third paper sensor, N: fixing nip portion.

Claims (11)

The recording medium carrying the unfixed toner image is passed through a fixing nip formed between a pair of fixing members, at least one of which has a heating source, and is heated and pressed to place the unfixed toner image on the recording medium. In the fixing device for fixing,
A speed detecting means for detecting a conveyance speed of the recording medium immediately after entering the fixing nip, and a speed changing means for changing the conveyance speed of the recording medium passing through the fixing nip,
Based on the speed of the recording medium immediately after entering the fixing nip detected by the speed detecting means, the speed changing means changes the conveyance speed of the recording medium passing through the fixing nip to match the target speed. A fixing device characterized by the above. The fixing device according to claim 1, wherein a sensor that detects the passage of two recording media disposed at a predetermined distance before and after the fixing device is used as the speed detection unit. The speed changed by the speed changing unit is characterized in that the value is different between the first and second sheets among the plurality of recording media passing through the fixing nip portion continuously. The fixing device according to claim 1. The fixing device according to claim 1, wherein an initial recording medium conveyance speed of the fixing device is slower than a target speed. The fixing device according to claim 1, wherein an initial recording medium conveyance speed of the fixing device is preset according to a type of the recording medium. The speed changing unit changes the conveyance speed of the recording medium passing through the fixing nip when the conveyance speed of the recording medium detected by the second speed detection unit is deviated from the target speed by a certain value or more. The fixing device according to claim 1, wherein 2. The speed changing unit, when the type of an unfixed toner image fixed on a recording medium is changed, changes the conveying speed of the recording medium passing through the fixing nip portion again. The fixing device according to any one of Items 6 to 6. 7. The speed changing unit according to claim 1, wherein when the type of the recording medium is changed, the speed changing unit again changes the conveyance speed of the recording medium that passes through the fixing nip portion. Fixing device. 7. The speed changing unit according to claim 1, wherein when the size of the recording medium is changed, the speed changing unit again changes the conveying speed of the recording medium that passes through the fixing nip portion. Fixing device. The speed changing means changes the transport speed of the recording medium passing through the fixing nip portion again when the paper feed tray for supplying the recording medium is changed. A fixing device according to claim 1. When the unfixed toner image is fixed on both sides of the recording medium, the speed changing unit changes the conveyance speed of the recording medium passing through the fixing nip portion depending on whether the first side or the second side is used. The fixing device according to claim 1.

Images