JP2007199343A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of accurately detecting the basis weight of a recording medium without causing a cost increase and preventing the erroneous input of the recording medium by a user. <P>SOLUTION: The fixing device includes: an image density detection means for detecting the image density of an unfixed toner image to be fixed on the recording medium; a speed detection means for detecting at least the conveyance speed of the recording medium obtained immediately after the recording medium rushes in a fixing nip part; and a sort detection means for detecting the sort including the basis weight of the recording medium on the basis of the image density detected by the image density detection means and the conveyance speed of the recording medium detected by the speed detection means. <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 a different type of recording medium such as cardboard or coated paper. The present invention relates to a fixing device capable of discriminating types such as basis weight.

JP 2004-277057 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.

  In addition, when a user performs a print operation or the like, it is necessary to accurately input the type of recording medium to be used according to the type of recording medium such as cardboard or coated paper by a user interface or the like. If there is an input error, the toner image cannot be fixed on a desired recording medium under appropriate conditions.

  Therefore, in order to prevent a user from making a mistake in inputting a recording medium, as disclosed in Japanese Patent Application Laid-Open No. 2004-277057 and the like, a means for detecting the paper type is provided in the paper feeding unit. Has already been proposed.

  An image forming apparatus according to Japanese Patent Application Laid-Open No. 2004-277057 includes a sheet storage unit that stacks and holds sheets, a separation sheet feeding unit that separates and feeds the sheets one by one from the sheet storage unit, and the separation sheet feeding unit. Image forming means for forming an image on the paper fed by the means, paper type detecting means for detecting a paper type including at least the paper thickness of the paper fed by the separation paper feeding means, and paper feeding Paper type detection that feeds a predetermined amount of the leading edge of one sheet from the paper storage unit by the separation paper feeding unit and detects the paper type of the paper by the paper type detection unit at a timing prior to the command. Sheet feeding timing control means.

  However, the conventional technique has the following problems. That is, in the case of the image forming apparatus according to Japanese Patent Application Laid-Open No. 2004-277057, it is necessary to provide a paper type detection unit that detects a paper type including at least the paper thickness of the paper fed by the separation paper feeding unit. As a result, the number of parts increases, resulting in an increase in cost, and the paper type detection means detects the paper type of the paper in a non-contact manner using an optical measurement method, or detects the transmittance of the paper. The paper type is detected using a transmission type optical sensor, the paper type of the paper is detected by converting a mechanical displacement amount into an electrical signal, and the capacitance sensor for measuring the capacitance of the paper is used. However, in the case of these paper type detection means, even if the physical thickness of the paper can be detected, the weight per unit area is the basis weight. If the quantity cannot be detected accurately Cormorants had a problem.

  Accordingly, 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 accurately detect the basis weight of the recording medium without increasing the cost. Another object of the present invention is to provide a fixing device that can prevent an input error of a recording medium by a user.

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,
Image density detecting means for detecting an image density of an unfixed toner image fixed on the recording medium, speed detecting means for detecting a conveyance speed of the recording medium immediately after entering the fixing nip, and the image density detection And a type detecting means for detecting a type including the basis weight of the recording medium based on the image density detected by the means and the conveyance speed of the recording medium detected by the speed detecting means. This is a fixing device.

  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, the invention described in claim 3 uses a sensor for detecting the passage of two recording media arranged at a predetermined distance downstream of the fixing device as the speed detecting means. The fixing device according to claim 1, wherein the fixing device is a fixing device.

  The invention described in claim 4 is characterized in that the type detecting means detects the type of the recording medium using the first recording medium conveyed as a dummy. The fixing device according to any one of the above.

  Further, in the invention described in claim 5, the toner image is not transferred to the dummy recording medium conveyed to the first sheet, and the toner image is transferred again to the dummy recording medium. The fixing device according to claim 4, wherein the fixing device is conveyed to a position.

  The invention described in claim 6 further comprises temperature change detecting means for detecting a temperature change of the fixing member immediately after the recording medium enters the fixing nip portion, and the type detecting means is based on the temperature change detecting means. The fixing device according to claim 1, wherein the type of the recording medium is detected including a detection result.

  Furthermore, the invention described in claim 7 is provided with an environmental temperature detection means for detecting the temperature of the environment, and controls the surface temperature of the fixing member having the heating source based on the detection result of the environmental temperature detection means. 7. The fixing device according to claim 1, wherein the type of the recording medium is detected including the surface temperature of the fixing member controlled based on the environmental temperature.

  According to the present invention, it is possible to provide a fixing device that can accurately detect the basis weight or the like of a recording medium without incurring an increase in cost, and can prevent an input error of the recording medium by a user. .

  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 The outlet roll 61 disposed at the outlet portion of the fixing device 36 detects the surface temperature of the heating roll 52 and controls energization to the heating source 51 so that the surface temperature of the heating roll 52 becomes a predetermined temperature. Temperature sensors as temperature detecting means for controlling to be shown are respectively 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. An image density detecting unit for detecting an image density of an unfixed toner image fixed on the recording medium; and at least a recording medium immediately after entering the fixing nip portion. A type including a basis weight of the recording medium based on a speed detecting means for detecting a conveying speed, an image density detected by the image density detecting means, and a conveying speed of the recording medium detected by the speed detecting means. And a type detecting means for detecting.

  Further, in this embodiment, it is provided with a temperature change detecting means for detecting a temperature change of the fixing member immediately after the recording medium enters the fixing nip portion, and the type detecting means has a detection result by the temperature change detecting means. In addition, the type of the recording medium is detected.

  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 the recording immediately after entering the fixing nip N of the fixing device 36 by the fourth 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.

  Reference numeral 61 denotes a temperature sensor as temperature detecting means for detecting the surface temperature of the heating roll 52 as described above.

  Further, reference numeral 108 denotes an image for detecting the image density of an unfixed toner image fixed on the recording paper 34 based on image data of a document read by the scanner 2 and subjected to predetermined image processing by the image processing device 12. The density detection means is shown. The image density detecting unit 108 performs ROS 14C, 14M, 14Y, and 14K to perform image exposure based on image data of a document that has been subjected to predetermined image processing by the image processing device 12, and the ROS 14C, 14M, 14Y, The image density of the unfixed toner image is detected by counting the number of pixels of the image applied by 14K.

  The image density detection unit 108 may be provided separately from the image processing apparatus 12, but the image density detection unit 108 is usually provided inside the image processing apparatus 12.

  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 image density detected by the image density detecting means 108 by the control means 107 that also functions as a type detecting means and a fixing device speed varying means for the next recording medium, and the nip passage. Based on the conveyance speed of the recording medium detected by the recording paper speed detection means 103, the type including the basis weight of the recording medium is detected, and the pre-passage paper speed detection means 100 and the nip passage paper speed detection means 103 are detected. Based on the speed of the recording paper 34 immediately before and after entering the fixing nip N detected by the above, the conveyance speed of the recording paper 34 passing through the fixing nip N is changed to match the target speed. ing.

  That is, in FIG. 4, reference numeral 107 denotes a control means 107 that also functions as a recording medium type detection means and a fixing device speed variable means. This fixing device speed variable means 107 is, for example, an operation of a full-color printer. In accordance with a program stored in a ROM or the like, a type including a basis weight of the recording medium is detected, and the sheet conveyance speed at the fixing nip portion N of the fixing device 34 is determined. Configured to control.

  Specifically, the control unit 107 controls the recording medium conveyance speed in the fixing device to be a predetermined fixing speed according to the type of the recording medium. The recording medium is plain paper, cardboard, The fixing conditions such as the optimum fixing speed and fixing temperature vary depending on the type of recording medium such as coated paper.

  For example, as shown in FIG. 6, the conveyance speed of the recording medium in the fixing device with respect to the process speed is the basis weight (thickness per unit area) of the recording medium or the unfixed toner fixed on the recording medium. Various changes are made according to the image density of the image.

  Therefore, the control means 107 determines whether the recording medium type is plain paper or coated paper, and whether the image density of the unfixed toner image fixed on the recording medium is white paper (no full image) or a solid image ( The conveyance speed of the recording medium in the fixing device is appropriately controlled according to the entire image).

  At this time, the control unit 107 determines the basis weight of the recording medium based on the image density detected by the image density detecting unit 108 and the conveyance speed of the recording medium detected by the paper speed detecting unit 103 when passing through the nip. Is automatically detected, and the conveyance speed of the recording medium in the fixing device is variably controlled as appropriate.

  More specifically, the control means 107 changes the conveyance speed of the recording paper 34 passing through the fixing nip portion N based on the detection result of the type including the basis weight of the recording medium so as to match the target speed. The sheet conveying speed of the fixing device 36 is variably controlled.

  In FIG. 4, reference numeral 109 denotes a user interface. The user interface 109 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.

  In the above configuration, the full-color printer according to the first embodiment can accurately detect the basis weight of the recording medium without causing an increase in cost as follows, and the user can input the recording medium. It is possible to prevent mistakes.

  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 a desired number of sheets, as shown in FIG. 7, the user interface 109 designates the number of prints, a tray for feeding recording paper, and the like, and the start button is pressed to start the job. (Step 101).

  Then, the control means 107 detects the image mode, the image density, and the paper size based on the instruction from the user interface 109 and the image data of the original read by the scanner 2 (step 102), and then the recording. Based on the paper length in the process direction of the paper 34 and the image density in the process direction, a threshold value corresponding to each paper type is calculated in order to determine the type of the recording paper 34 (step 103).

  Next, the control means 107 determines whether the dummy running of the recording paper 34 is permitted or prohibited by an instruction from the user interface 109 (step 104), and the dummy running of the recording paper 34 is permitted. In the case where the toner is to be recorded on the first recording paper 34, the toner image is run without being formed, and is not discharged onto the discharge tray 37 as it is. Transport to the transfer position (step 105).

  At that time, the control means 107 calculates the transport speed when the recording paper 34 passes the fixing nip portion by the paper speed detection means 103 at the time of passing through the nip (step 105), and based on the transport speed of the recording paper 34. As shown in FIG. 6, the basis weight such as whether the recording paper 34 is plain paper or coated paper is detected (step 106).

  In FIG. 6, for the sake of convenience, only the data for plain paper and coated paper is shown, but in addition to the data for plain paper and coated paper, the data for plain paper and coated paper can be added by adding data such as thick paper. It is possible to discriminate cardboard and the like.

  On the other hand, when the control means 107 determines that the dummy running of the recording paper 34 is prohibited, the first recording paper 34 enters the fixing nip portion of the fixing device 36 as shown in FIG. A predetermined time (t) is measured and the conveyance speed of the recording paper 34 is calculated, and the recording paper 34 is based on the conveyance speed of the recording paper 34 as shown in FIG. The basis weight such as whether the paper 34 is plain paper or coated paper is detected (step 106).

  If the basis weight of the detected recording paper 34 is different from the basis weight of the recording paper 34 in the paper feed tray instructed from the user interface 109, the control means 107 gives a warning to that effect to the user. It may be configured to display on the interface 109 and stop the printing operation.

  Further, as shown in FIG. 8, the control means 107 detects a decrease in the surface temperature of the heating roll 52 when the first recording sheet 34 enters the fixing nip portion of the fixing device 36 by the temperature sensor 61. Then, whether the basis weight of the recording paper 34 is large or small is determined depending on whether or not the decrease in the surface temperature of the heating roll 52 is equal to or less than a threshold value.

  Further, as shown in FIG. 6, the control means 107 detects that the recording paper 34 has passed through the fixing nip portion by the paper speed detecting means 103 at the time of nip with respect to the conveyance speed of the recording paper 34 in a preset fixing device. It is determined how much the conveyance speed has changed, and even if dummy running of the recording paper 34 is prohibited, the image density of the toner image fixed on the recording paper 34 is determined. The image density of the toner image can be determined based on the change in the conveyance speed when the recording paper 34 passes through the fixing nip portion.

  Therefore, the control means 107 can determine the basis weight of the same coated paper as shown in FIG. 6 based on the determination result regarding the image density of the toner image on the recording paper 34. It has become. In FIG. 6, since the image density is detected in advance by the image density detecting means 108, it is possible to discriminate between the case where the basis weight of the paper is high and the case where it is low.

  The control means 107 previously determines whether the image density in the process direction is 0%, 50% or 100%, and whether the recording paper 34 is plain paper or coated paper, and whether the same plain paper or coated paper is the basis weight. FIG. 9 and FIG. 10 show data on how the recording sheet conveyance speed at the fixing nip portion of the fixing device 36 changes with respect to a preset process speed depending on whether the toner is low or high. As described above, the table is set in advance.

  Here, plain paper refers to paper having a basis weight (gsm) of 104 gsm or less, and coated paper refers to paper having a basis weight (gsm) of 105 gsm to 280 gsm.

  In FIGS. 9 and 10, 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.

  Further, when the image density is high, 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 an image having an image density of 0%. Due to the thickness (basis weight) of the recording medium 34 and the like, the tendency of the conveyance speed of the recording paper 34 to be faster is slightly smaller. In order to correct this, the color image is more fixed than the monochrome image. A negative value is set small as the target value of the sheet conveyance speed.

  As described above, in the above-described embodiment, the basis weight of the recording medium can be accurately detected without causing an increase in cost, and it is possible to prevent a user from making an input mistake in the recording medium.

  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. It is also possible to do.

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 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. 7 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. 8 is a timing chart showing changes in the heating roll surface temperature in the fixing device according to Embodiment 1 of the present invention. FIG. 9 is a graph showing the relationship between the difference in sheet conveyance speed in the fixing device with respect to the image density and machine speed. FIG. 10 is a chart showing the control state of the fixing device according to Embodiment 1 of the present invention.

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 nip), 104: third paper sensor, 108: image density detection means, N: fixing nip portion.

Claims (7)

A recording medium carrying an 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,
Image density detecting means for detecting an image density of an unfixed toner image fixed on the recording medium, speed detecting means for detecting a conveyance speed of the recording medium immediately after entering the fixing nip, and the image density detection And a type detecting means for detecting a type including the basis weight of the recording medium based on the image density detected by the means and the conveyance speed of the recording medium detected by the speed detecting means. Fixing device to do. 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 fixing device according to claim 1, wherein a sensor that detects the passage of two recording media arranged at a predetermined distance on the downstream side of the fixing device is used as the speed detection unit. 4. The fixing device according to claim 1, wherein the type detection unit detects the type of the recording medium using the recording medium conveyed to the first sheet as a dummy. 5. The dummy recording medium transported to the first sheet is transported to the toner image transfer position again without transferring the toner image. 5. The fixing device according to 4. A temperature change detecting means for detecting a temperature change of the fixing member immediately after the recording medium enters the fixing nip portion, and the type detecting means detects the type of the recording medium including the detection result by the temperature change detecting means. The fixing device according to claim 1, wherein the fixing device is a fixing device. A fixing member comprising environmental temperature detecting means for detecting the temperature of the environment, controlling the surface temperature of the fixing member having the heating source based on the detection result of the environmental temperature detecting means, and controlled based on the environmental temperature The fixing device according to claim 1, wherein the type of the recording medium is detected including the surface temperature of the recording medium.

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