JP2008058825A - Conveying apparatus, image forming apparatus, and control program thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conveying apparatus that can reduce cost and control results of variation, even if the conveyance speed of paper is varied, with a simple configuration. <P>SOLUTION: The conveying apparatus includes: a first conveyance means for conveying the paper where an image is formed; a second conveyance means, which is arranged downstream in the conveyance direction of the paper of the first conveyance means, for conveying the paper; a measurement means for measuring the duration time required from a measurement start time before the paper arrives at the second conveyance means until the leading edge of the paper passes a predetermined position of the downstream of the second conveyance means; and a control means for controlling the conveyance speed of the second conveyance means on the basis of the duration time measured by the measurement means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a conveyance device, an image forming apparatus, and a control program therefor.

U.S. Pat. No. 4,928,141 JP 2005-181507 A JP 2005-331507 A JP 2002-278191 A

  Conventionally, among image forming apparatuses such as printers and copiers adopting an electrophotographic system, for example, image forming apparatuses capable of forming color images include yellow (Y), magenta (M), cyan (C), Yellow (Y), magenta (M), cyan (C), multiple transferred toner images of multiple colors such as black (K) are transferred onto the intermediate transfer belt and then transferred onto the intermediate transfer belt. There is a configuration in which a color image is formed by transferring toner images of a plurality of colors such as black (K) all at once onto a sheet and fixing them by a fixing device.

  As an image forming apparatus capable of forming the color image, for example, toner images of a plurality of colors such as yellow (Y), magenta (M), cyan (C), black (K), etc. There is a configuration in which a color image is formed by multiple transfer onto a sheet conveyed in an adsorbed state, and then separating the sheet from a sheet conveyance belt and fixing it by a fixing device.

  In such an image forming apparatus, when a toner image of a plurality of colors is fixed on a sheet conveyed by an intermediate transfer belt, a sheet conveying belt, or the like, the conveyance speed of the sheet in the fixing apparatus varies. When the sheet conveyance speed of the fixing device is faster than a predetermined value, the sheet whose rear end is transferring the toner image is pulled by the fixing device, or conversely, the sheet conveyance speed of the fixing device is slower than the predetermined value. In this case, the sheet whose rear end is transferring the toner image is pushed back by the fixing device, causing image misregistration including color misregistration along the moving direction of the intermediate transfer belt and the sheet conveying belt.

  Therefore, in order to suppress the occurrence of such color misregistration, various methods disclosed in U.S. Pat. No. 4,928,141, JP-A-2005-181507, JP-A-2005-331507, JP-A-2002-278191, etc. This technology has already been proposed.

  The technique disclosed in the above-mentioned U.S. Pat. No. 4,928,141 is based on detecting a slack amount of paper formed upstream of the fixing device with a sensor and feeding back the slack amount detected by the sensor to the driving speed of the fixing device. The image forming apparatus is configured to avoid an image trouble called “smudge” that occurs when the fixing device pulls the paper.

In addition, the image forming apparatus according to the above-mentioned JP-A-2005-181507
An image forming means for forming an image;
A transfer means for transferring an image formed by the image forming means onto a recording medium;
Fixing means for fixing the image transferred onto the recording medium by the transfer means;
First driving means for driving the transfer means;
A second driving means for driving the fixing means;
When the recording medium is in contact with both the transfer unit and the fixing unit, a difference in driving speed between the first driving unit and the second driving unit causes a gap between the transfer unit and the fixing unit. Speed control means for increasing or decreasing the driving speed of the second driving means with reference to the speed reference value of the second driving means so that the amount of slack that is the amount of deflection of the recording medium that occurs is constant;
A slack detecting means for detecting the slack amount;
Speed reference value changing means for changing the speed reference value based on the detection result of the looseness detecting means;
It is comprised so that it may be equipped with.

  Further, the image forming apparatus according to Japanese Patent Application Laid-Open No. 2005-331777 is driven to rotate a recording medium carrying a toner image conveyed from a transfer process for transferring the toner image onto the recording medium at a constant process speed. An image forming apparatus including a fixing device that is carried into a nip portion formed by rolling a movable endless belt on a rotating member, and that is fixed by pressurization and heating. When performing the fixing process by performing an experiment for each type of the recording medium by the instruction input means configured to allow an operation to specify the type of the recording medium to be fixed and the fixing device. Each of the information for each thickness type of the recording medium and the fixing device are determined by determining the respective conveying speeds so as to cancel the characteristic that the conveying speed varies depending on the thickness of the recording medium. A memory for storing a table representing a correspondence relationship with a feed speed value, a motor capable of rotating the rotation member of the fixing device and capable of controlling the rotation speed, and the input by the instruction input means The fixing device corresponding to the transferred information according to the thickness type of the recording medium obtained by receiving the information according to the thickness type of the recording medium and collating with the table stored in the memory. And a control device that controls the number of revolutions of the motor based on a feed speed value.

  Further, an image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 2002-278191 includes an image carrier for forming a toner image, a transport device for sending a transfer material to the transfer device, a transport material and a transfer device. A transfer device that transfers the formed toner image onto a transfer material, and the transfer material transport speed in the transport device and the transfer material transport speed in the transfer device are factors of fluctuation in the transfer material transport speed. Based on the estimation, the transfer speed of the transfer material in the transfer device is controlled.

  By the way, the problem to be solved by the present invention is to provide a transport device that can reduce the cost and can suppress the fluctuation result even when the paper transport speed fluctuates with a simple configuration. There is to do.

That is, the invention described in claim 1 includes a first transport unit that transports a sheet on which an image is formed;
A second transport unit disposed downstream of the first transport unit in the transport direction of the paper and transports the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the second transport means from a measurement start time before the paper reaches the second transport means; And a control unit that controls the transport speed of the second transport unit based on the required time measured by the measuring unit.

  According to a second aspect of the present invention, the second transport unit is a fixing unit that performs a fixing process on the paper while transporting the paper separated from the first transport unit. It is a conveying apparatus of Claim 1.

Furthermore, the invention described in claim 3 includes a conveying unit that conveys a sheet on which an image is formed,
A fixing unit disposed downstream of the conveying unit in the conveyance direction of the paper and performing a fixing process while conveying the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the fixing means from a measurement start time before the paper reaches the fixing means;
An image forming apparatus comprising: a control unit that controls a sheet conveyance speed of the fixing unit based on a required time measured by the measuring unit.

According to a fourth aspect of the present invention, there is provided a conveying means for conveying a sheet on which a plurality of color images are formed,
A fixing unit disposed downstream of the conveying unit in the conveyance direction of the paper and performing a fixing process while conveying the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the fixing means from a measurement start time before the paper reaches the fixing means;
An image forming apparatus comprising: a control unit that controls a sheet conveyance speed of the fixing unit based on a required time measured by the measuring unit.

  Furthermore, the invention described in claim 5 is characterized in that the conveying means is an endless belt that conveys the paper while being circulated by being stretched between a plurality of rolls. The image forming apparatus described.

The invention described in claim 6 is an endless belt in which a plurality of color images are formed while being circulated while being stretched between a plurality of rolls,
Fixing means for carrying out a fixing process on the paper while conveying the paper after the image formed on the endless belt is transferred to the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the fixing means from a measurement start time before the paper reaches the fixing means;
An image forming apparatus comprising: a control unit that controls a sheet conveyance speed of the fixing unit based on a required time measured by the measuring unit.

  Furthermore, the invention described in claim 7 is such that the control unit controls the sheet to be conveyed in a state where a predetermined amount of slack is formed between the conveying unit and the fixing unit. The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus.

  Further, in the invention described in claim 8, the control unit is configured such that when the time difference between the required time measured by the measuring unit and the reference time reaches a predetermined value or more, the fixing device The image forming apparatus according to claim 3, wherein the sheet conveying speed is controlled.

  Further, in the invention described in claim 9, when the time difference between the required time measured by the measuring means and the reference time is a positive value, the control means increases the paper conveyance speed of the fixing device. The image forming apparatus according to claim 8, wherein the image forming apparatus is controlled to do so.

  According to a tenth aspect of the present invention, when the time difference between the required time measured by the measuring means and the reference time is a negative value, the control means increases the paper conveyance speed of the fixing device. The image forming apparatus according to claim 8, wherein the image forming apparatus is controlled to do so.

  Furthermore, the invention described in claim 11 is characterized in that the measurement start time before the paper reaches the fixing unit is determined by a write start signal of the final color image. The image forming apparatus according to any one of the above.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to the eleventh aspect, the write start signal for the final color image is a black image write start signal.

  Further, in the invention described in claim 13, the measurement start time before the sheet reaches the fixing unit is output from the detection unit provided in the conveyance path before the sheet reaches the fixing unit. 11. The image forming apparatus according to claim 6, wherein the image forming apparatus is determined by a detection signal.

  According to a fourteenth aspect of the present invention, the detecting means is disposed downstream of the final color image forming position of the endless belt in the paper transport direction and upstream of the fixing means. The image forming apparatus according to claim 13, wherein the image forming apparatus is an image forming apparatus.

  Furthermore, the invention described in claim 15 is characterized in that an image detecting means for detecting an image for detecting image deviation formed on the endless belt corresponding to the paper is used as the detecting means. The image forming apparatus according to claim 13 or 14.

According to a sixteenth aspect of the present invention, there is provided at least a first conveying unit that conveys a sheet on which an image is formed;
A second transport unit disposed downstream of the first transport unit in the transport direction of the paper and transports the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the second conveying means from a measurement start time before the paper reaches the second conveying means; Used for the image forming apparatus provided,
A control program for an image forming apparatus in which a program for controlling a sheet conveyance speed of the second conveyance unit is stored in association with the required time measured by the measurement unit.

  According to the first aspect of the present invention, even when the conveyance speed of the paper fluctuates, the result of the fluctuation is suppressed by controlling the conveyance speed of the second conveyance means, and the occurrence of image defects is prevented. it can.

  According to the second aspect of the present invention, even when the paper conveyance speed fluctuates, by controlling the conveyance speed of the fixing unit, the fluctuation result can be suppressed and the occurrence of image defects can be prevented. .

  Further, according to the third aspect of the present invention, it is possible to suppress the occurrence of image defects even when the sheet conveyance speed in the fixing unit fluctuates. Compared with the case where it does not, a high quality image can be obtained.

  According to the fourth aspect of the present invention, it is possible to suppress the occurrence of image defects even when the sheet conveyance speed in the fixing unit fluctuates. Compared with the case where it does not, a high-quality color image can be obtained.

  Furthermore, according to the fifth aspect of the present invention, it is possible to stably convey a sheet and form an image, and to suppress the occurrence of an image defect. Compared with the case where it does not, a high quality image can be obtained.

  Further, according to the invention described in claim 6, it is possible to suppress the occurrence of image defects in the image transferred to the paper, and the image quality is higher than that in the case where the present configuration is not provided. An image can be obtained.

  Furthermore, according to the invention described in claim 7, moderate slack can be formed, and the occurrence of image defects can be suppressed.

  According to the eighth aspect of the present invention, the sheet conveyance speed of the fixing unit can be appropriately controlled, and an image defect occurs even when the sheet conveyance speed in the fixing unit fluctuates. Can be suppressed.

  Further, according to the ninth aspect of the present invention, the sheet conveyance speed of the fixing unit can be appropriately controlled, and an image defect occurs even when the sheet conveyance speed in the fixing unit fluctuates. Can be suppressed.

  According to the tenth aspect of the present invention, the sheet conveyance speed of the fixing unit can be appropriately controlled, and an image defect occurs even when the sheet conveyance speed in the fixing unit fluctuates. Can be suppressed.

  Furthermore, according to the invention described in claim 11, the time required for the measurement means to measure can be set short, the structure of the measurement means can be simplified, and the output timing of image writing varies. Therefore, the required time can be accurately measured.

  Further, according to the twelfth aspect of the present invention, the same control can be adopted for the color image and the monochrome image, and the control operation becomes easy.

  Furthermore, according to the thirteenth aspect of the present invention, it is possible to suppress the occurrence of image defects as compared with the case where the present configuration is not provided.

  According to the invention described in claim 14, the time required for the measurement means to measure can be set short, and the configuration of the measurement means can be simplified.

  Furthermore, according to the invention described in claim 15, the existing detection means can be used, the configuration is simplified, and the cost can be reduced.

  According to the invention described in claim 16, the control program can be updated.

  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 employing the paper direct transfer system according to Embodiment 1 of the present invention. This full-color printer is configured to execute a printing operation based on image data sent from a personal computer, a scanner, or the like.

  In FIG. 2, reference numeral 1 denotes a main body of a tandem type full-color printer. Inside the full-color printer main body 1, an image forming unit 2 is arranged along the vertical direction at a substantially central portion thereof. . Further, inside the full color printer main body 1, a sheet on which toner images of a plurality of colors formed by the image forming unit 2 are transferred is adsorbed to one side (right side in the illustrated example) of the image forming unit 2. In addition to the sheet conveying belt unit 3 to be conveyed, the control unit 4 having a control circuit or the like is provided on the other side (left side in the illustrated example) of the image forming unit 2. On the lower side, power supply circuit units 5 each including a high-voltage power supply circuit and the like are disposed. A paper feeding device 6 for feeding paper 37 or the like as a transfer material is disposed at the bottom of the full color printer main body 1.

  The image forming unit 2 includes four image forming units 7Y, 7M, 7C, and 7K that form toner images of yellow (Y), magenta (M), cyan (C), and black (K) in order from the bottom. These four image forming units 7Y, 7M, 7C, and 7K are arranged in series at regular intervals along the vertical direction.

  These four image forming units 7Y, 7M, 7C, and 7K are configured in the same manner except for the color of the image to be formed. As shown in FIG. 3, a predetermined rotational speed is provided along the arrow direction. The photosensitive drum 8 rotating at the same time, the charging roll 9 for primary charging that uniformly charges the surface of the photosensitive drum 8, and an image corresponding to each color is exposed on the surface of the photosensitive drum 8 to electrostatically A ROS (Raster Output Scanner) 10 that forms a latent image, a developing device 11 that develops the electrostatic latent image formed on the photosensitive drum 8 with toner of a corresponding color, and a transfer that remains on the photosensitive drum 8 A cleaning device 12 that cleans the remaining toner and a toner replenishing device 13 that replenishes the developing device 11 with toner are configured.

  As shown in FIG. 2, the ROS 10 is configured in common to the four image forming units 7Y, 7M, 7C, and 7K of yellow (Y), magenta (M), cyan (C), and black (K). , Yellow (Y), magenta (M), cyan (C), and black (K), the four semiconductor lasers 14 that emit laser beams LB based on the image data of the respective colors, and the four semiconductor lasers 14, respectively. The collimator lens 15 that collimates the four laser beams LB that have been generated, the reflection mirror 16 that reflects the laser beam LB emitted from the semiconductor laser 14, and the laser beam LB reflected by the reflection mirror 16 is deflected. The rotating polygon mirror 17 that scans and the laser beam LB reflected by the rotating polygon mirror 17 is used as the photosensitive drum 8 of each of the image forming units 7Y, 7M, 7C, and 7K. To a plurality of reflecting mirrors 18, 19 for scanning exposure, and is configured with a transparent glass 20 that transmits the laser beam LB. The reflection mirrors 18 and 19 have a function of changing the focal length (f) according to the deflection angle (θ) of the laser beam LB. Of course, the ROS 10 may be provided individually for each of the image forming units 7Y, 7M, 7C, and 7K.

  Further, as shown in FIG. 3, the developing device 11 stirs the two-component or one-component developer 22 accommodated in the developer accommodating portion 21 and supplies the developer roll 24 via the developer supply member 23. The developer 22 supplied to the developing roll 24 is conveyed to a developing region facing the photosensitive drum 8 while the layer thickness is regulated by the layer thickness regulating member 25, and the surface of the photosensitive drum 8 is conveyed. The electrostatic latent image formed is developed with toner of a predetermined color.

  Further, as shown in FIG. 3, the cleaning device 12 removes the transfer residual toner remaining on the surface of the photosensitive drum 8 by the cleaning blade 26, and conveys the removed transfer residual toner in an elliptical manner. The member 27 is transported and accommodated inside the cleaning device 12. In FIG. 3, the cleaning blade 26 is in a state before being brought into contact with the surface of the photosensitive drum 8 and elastically deforming.

  The toner replenishing device 13 contains a developer 28 composed of only toner or toner and a carrier, and the developer 28 contained in the toner replenishing device 13 is given a predetermined timing by an agitator 29. The developing device 11 is replenished while stirring.

  As shown in FIG. 2, a control unit 4 is disposed inside the full-color printer main body 1, and the control unit 4 includes, for example, an image processing apparatus that performs predetermined image processing on image data. 30 is provided. From the image processing device 30, image data of each color of yellow (Y), magenta (M), cyan (C), and black (K) is sequentially output to the ROS 10 and emitted from the ROS 10 according to the image data. The four laser beams LB are scanned and exposed on the respective photosensitive drums 8Y, 8M, 8C, and 8K to form electrostatic latent images. The electrostatic latent images formed on the photosensitive drums 8Y, 8M, 8C, and 8K are respectively yellow (Y), magenta (M), cyan (C), and cyan by developing devices 11Y, 11M, 11C, and 11K. The toner image is developed as a black (K) color toner image.

  Further, as shown in FIG. 2, the sheet conveying belt unit 3 is provided with a sheet conveying belt 31 that circulates and moves without a break as an endless belt, and the sheet conveying belt 31 is connected to each image forming unit 8Y. , 8M, 8C, and 8K formed in yellow (Y), magenta (M), cyan (C), and black (K), the sheet 37 on which the toner image is transferred is conveyed in an electrostatically adsorbed state. Is configured to do. Further, the paper transport belt unit 3 is integrally formed with a transport roll 49 provided in a reversing paper transport path 50 described later, and when the paper 37 is jammed, FIG. As indicated by a broken line, by opening the side cover 32 of the printer main body 1, the printer main body 1 can be moved to a retracted position rotated clockwise.

  As shown in FIG. 5, the paper transport belt 31 is stretched with a predetermined tension between a drive roll 33 and a driven roll 34 as a stretch roll disposed along the vertical direction. For example, it is configured to circulate and move in the clockwise direction at a predetermined speed by a drive roll 33 that is rotationally driven by a drive motor 35 via a gear or the like (not shown). The drive motor 35 that drives the paper transport belt 31 may be one that is provided for the paper transport belt 31 or may be one that drives with other image forming members such as the photosensitive drum 8. Of course. For example, the distance between the driving roll 33 and the driven roll 34 is set to be substantially equal to the length of the A3 size sheet 37, but the distance between the driving roll 33 and the driven roll 34 is not limited to this. Of course, it may be set arbitrarily. As the paper transport belt 31, for example, a flexible synthetic resin film such as polyimide is formed in an endless belt shape.

  Further, as shown in FIG. 2, a suction roll 36 for electrostatically attracting the paper 37 to the surface of the paper transport belt 31 abuts on the surface of the driven roll 34 via the paper transport belt 31. It is arranged like this. The suction roll 36 is configured, for example, by covering the surface of a metal cored bar with conductive rubber in the same manner as the charging rolls 9 of the image forming units 7Y, 7M, 7C, and 7K. A predetermined bias voltage for adsorption is applied. The suction roll 36 is configured to electrostatically charge the sheet 37 sent from the sheet feeding device 6 and suck the sheet 37 on the surface of the sheet transport belt 31. Note that the suction roll 36 is not necessarily used.

  For each color of yellow (Y), magenta (M), cyan (C), and black (K) formed on the photosensitive drums 8Y, 8M, 8C, and 8K of the image forming units 7Y, 7M, 7C, and 7K. As shown in FIG. 2, the toner images are transferred in multiple on the sheet 37 conveyed while being attracted to the surface of the sheet conveying belt 31 while being superimposed on each other by the transfer rolls 38Y, 38M, 38C, and 38K. Is done. The transfer rolls 38Y, 38M, 38C, and 38K are integrally attached to the sheet conveying belt unit 3 side as shown in FIGS.

  As shown in FIG. 2, the sheet 37 is fed from a sheet feeding device 6 disposed at the bottom of the printer body 1. The paper feeding device 6 includes a paper tray 39 containing paper 37 having a desired size and material, and a transfer paper 37 having a desired size and material is fed from the paper tray 39 by a feed roll 40. At the same time, the sheets are fed one by one by the supply roll 41 and the separating roll 42 and conveyed to a suction position on the sheet conveyance belt 31 at a predetermined timing via a registration roll 43 as a sheet feeding means. It has come to be.

  The sheet 37 is a sheet-like member, for example, various sizes such as A4 size, A3 size, B5 size and B4 size, and thick paper such as plain paper and coated paper, an OHP sheet, etc. Various materials are used. Further, even if the paper 37 is made of the same material such as plain paper, the characteristics such as the rigidity of the paper, the surface condition, and the occurrence of warping change depending on the storage environment such as a high temperature and high humidity environment or a low temperature and low humidity environment. In some cases, the paper 37 has different transportability depending on the material, rigidity, surface condition, characteristics such as warpage, and the amount of toner transferred.

  Then, the sheet 37 on which the toner images of each color of yellow (Y), magenta (M), cyan (C), and black (K) are transferred in a multiple manner has rigidity as shown in FIG. After being separated from the sheet conveying belt 31 by so-called stiffness or auxiliary separating means, the sheet is conveyed to the fixing device 44 through the guide member 53, and the toner images of the respective colors are generated by heat and pressure by the fixing device 44. It is fixed on the paper 37. The paper transport belt 31 and the fixing device 44 are disposed close to each other, and the paper 37 separated from the paper transport belt 31 is transported to the fixing device 44 by the transport force of the paper transport belt 31. Thereafter, the sheet 37 on which the toner image of each color is fixed is placed on the discharge tray 47 provided on the upper part of the full-color printer main body 1 by the discharge roll 46 through the outlet roll 45 of the fixing device 44. The print operation is completed.

  The full-color printer is capable of printing an image of a desired color such as monochrome as well as a full-color image, and yellow (Y) and magenta (M) depending on the color of the image to be printed. , Cyan (C), black (K), or some of the image forming units 7Y, 7M, 7C, and 7K form toner images.

  Further, when images are formed on both sides of the sheet 37 by the full-color printer, the sheet 37 on which the image is fixed on one side by the fixing device 44 is not discharged onto the discharge tray 47 by the discharge roll 46 as it is. With the rear end of the sheet 37 held by the discharge roll 46, the discharge roll 46 is temporarily stopped and reversed, and the switching gate 48 switches the conveyance path of the sheet 37 upward to the one side of the printer main body 1. The paper is transported to a reversing paper transport path 50 having a transport roll 49 provided along the transport path. Then, the sheet 37 conveyed to the reversing sheet conveying path 50 is conveyed again to the suction position of the sheet conveying belt 31 by the registration roll 43 with the front and back sides reversed, and the toner image is transferred to the back surface. After that, fixing processing is performed by heat and pressure by the fixing device 44, and the paper is discharged onto a discharge tray 47 provided on the upper portion of the printer body 1 by a discharge roll 46.

  In FIG. 2, reference numeral 51 denotes a paper feed roll for feeding paper of a desired size and material from a manual tray (not shown) provided on the side surface of the printer body 1, and 52 denotes a paper feed roll 51. Each of the conveyance rolls for conveying the paper sheet to the registration roll 43 is shown.

  By the way, in this embodiment, an endless belt that conveys a sheet on which images of a plurality of colors are formed while being circulated and moved while being stretched between a plurality of rolls, and a conveyance direction of the sheet of the endless belt A fixing unit that is arranged downstream and performs a fixing process while conveying the paper, and from a measurement start time before the paper reaches the fixing unit until the leading edge of the paper passes a predetermined position downstream of the fixing unit. Measuring means for measuring the required time required for the control, and control means for controlling the sheet conveyance speed of the fixing means based on the required time measured by the measuring means.

  That is, in the first embodiment, as shown in FIG. 2, the image forming units 7Y, 7M, 7C, and 7K for yellow (Y), magenta (M), cyan (C), and black (K) are formed. The toner images of the respective colors are transferred onto the paper 37 that is attracted to the surface of the paper transport belt 31 and transported, and the paper 37 on which the toner images of the respective colors are transferred has the rigidity (cohesion) of the paper 37 itself. Or after being separated from the paper conveying belt 31 by an auxiliary separating means, and then conveyed to the fixing device 44 and subjected to a fixing process.

  As shown in FIG. 6, the fixing device 44 conveys the heating roller 60 and the fixing belt by holding and transporting the sheet 37 to which the unfixed toner image is transferred by the heating roller 60 and the fixing belt 61 that are pressed against each other. The unfixed toner image is melted and pressurized and fixed on the paper 37 by the heat and pressure generated by 61. The heating roll 60 is rotationally driven at a predetermined speed via a drive gear (not shown) by a drive motor 74 such as a stepping motor. At that time, the fixing device 44 conveys the sheet 37 while holding the sheet 37 with a high pressure by the heating roll 60 and the fixing belt 61, so that the conveyance speed Vf of the sheet 37 by the fixing device 44 is set to the sheet conveying belt. When the speed is higher than the paper transport speed Vt 31, the fixing device 44 pulls the transfer paper 37, so that the toner image being transferred is rubbed on the transfer paper 37 in the downstream image forming unit 7 </ b> K or the like. An image quality defect occurs. Therefore, as shown in FIG. 7, the sheet conveying speed Vf of the fixing device 44 is set to be equal to or slower than the sheet conveying speed Vt of the sheet conveying belt 31, that is, satisfy the relationship Vf ≦ Vt. ing. In this embodiment, for example, the conveyance speed Vf of the sheet 37 by the fixing device 44 is set to be, for example, about 0.5 to several percent slower than the sheet conveyance speed Vt of the sheet conveyance belt 31.

  Then, the sheet 37 conveyed from the sheet conveying belt 31 to the fixing device 44 is loosened by, for example, a predetermined amount D between the sheet conveying belt 31 and the fixing device 44 as shown in FIG. In this state, the printer enters the fixing device 44. Here, the predetermined amount D means that there is no influence on the image and the control by the control means described later does not work.

  FIG. 8 is a sectional view showing a fixing device used in the full-color printer according to this embodiment.

  As shown in FIG. 8, the fixing device 44 includes a heating roll 60 having a heating source 62 therein, an endless belt-like fixing belt 61, and the fixing belt 61 so that the fixing belt 61 is rotatable. A belt guide member 63 that supports both ends, a pressure contact member 64 that is disposed inside the fixing belt 61 and presses the fixing belt 61 against the surface of the heating roll 60, and supplies oil to the inner surface of the fixing belt 61. A felt member 65 as an oil supply member is provided. In FIG. 8, 45 indicates an exit roll of the fixing device 44, and 66 indicates a discharge detection sensor.

  As shown in FIG. 8, the discharge detection sensor 66 is disposed adjacent to the downstream side of the outlet roll 45 in the paper conveyance direction, and as shown in FIG. 9, the paper 37 conveyed by the outlet roll 45. And an optical sensor 81 for detecting the rotation state of the actuator 80. The actuator 80 is configured to rotate around a fulcrum 82. With the actuator 80 being rotated to a predetermined position by the leading end of the sheet 37, the optical sensor 81 is turned on, and the sheet The tip of 37 is detected.

  As shown in FIG. 6, the heating roll 60 has a thin cylindrical cored bar 67 made of iron, stainless steel or the like, and an elastic having a thickness of about 0.65 mm made of silicon rubber coated on the surface of the cored bar. The layer 68 includes a release layer 69 having a thickness of about 30 μm and made of PFA or the like coated on the surface of the elastic layer 68. A 600 W halogen lamp 62 is disposed inside the heating roll 60 as a heating source.

  The fixing belt 61 is formed of a synthetic resin such as polyimide into an endless belt shape having an inner diameter of 30 mm and a wall thickness of 75 μm, and a release layer made of PFA or the like is provided on the surface as needed. .

  Further, as shown in FIG. 10, the belt guide member 63 is configured to be integrally assembled with the pressure contact member 64.

  As shown in FIGS. 10 and 11, the pressure contact member 64 includes a belt housing 67 made of synthetic resin, and a metal belt frame 68 having a substantially U-shaped cross section that is fitted to the belt housing 67. The nip head member 69 for pressing the fixing belt 61 against the heating roll 60 and the pad member 70 attached to the nip head member 69 are mainly configured.

  Further, as shown in FIGS. 10 and 11, the belt guide member 63 is fitted into fitting portions 68a protruding in parallel with each other at both ends of the belt frame 68, and both ends of the belt housing 67. It comes to be attached to the part.

  Further, the felt member 65 as the oil supply member is made of, for example, Nomex (trade name), and the felt member 65 is impregnated with about 2.0 g of oil made of amino Si oil having a viscosity of 300 cs. . As shown in FIGS. 8 and 12, the felt member 65 is attached to the back side of the belt frame 68 in a state of being fixed by means such as adhesion.

  Further, as shown in FIG. 12, both ends of the pressure contact member 64 are respectively attached to arm members 71 at both ends via a belt guide member 63, and these arm members 71 are biased at both ends. A coil spring 72 as a means is configured so that the pressure contact member 64 is pressed against the heating roll 60 with a predetermined pressure (for example, 24 kgf). 11 and 12, reference numeral 73 denotes a synthetic resin film-like sheet member interposed between the fixing belt 61 and the press contact member 64. The friction between the two is reduced, but not necessarily provided.

  Of course, the fixing device 44 is not limited to the above-described one, and a fixing roller and a pressure roll that are in pressure contact with each other, or a device that includes a belt-like member on the heating side may be used. .

  As described above, the fixing device 44 configured as described above conveys the sheet 37 on which the unfixed toner image has been transferred by the heating roll 60 and the fixing belt 61 that are pressed against each other, as shown in FIG. As a result, the unfixed toner image is melted and pressed by the heat and pressure of the heating roll 60 and the fixing belt 61 and fixed onto the transfer paper 37. At that time, the fixing device 44 conveys the sheet 37 while holding the sheet 37 with a high pressure by the heating roll 60 and the fixing belt 61, so that the conveyance speed Vf of the sheet 37 by the fixing device 44 is set to the sheet conveying belt. When the paper transport speed Vt is faster than 31, the fixing device 44 pulls the paper 37, so that the toner image being transferred is rubbed on the transfer paper 37 in the downstream image forming unit 7K or the like. Defects occur. Therefore, as shown in FIG. 7, the sheet conveying speed Vf of the fixing device 44 is set to be equal to or slower than the sheet conveying speed Vt of the sheet conveying belt 31, that is, satisfy the relationship Vf ≦ Vt. ing.

  The sheet 37 conveyed from the sheet conveying belt 31 to the fixing device 44 forms a slack that is bent by a predetermined amount D between the sheet conveying belt 31 and the fixing device 44 as shown in FIG. In this state, the printer enters the fixing device 44.

  The fixing device 44 conveys the sheet 37 on which the unfixed toner image has been transferred by the heating roll 60 and the fixing belt 61 that are in pressure contact with each other. The sheet conveying speed depends on the type of the sheet 37. Even when the configuration is such that Vf is set appropriately, the sheet conveyance speed Vf by the fixing device 44 varies depending on the type and state of the sheet 37, the amount of toner image transferred onto the sheet 37, and the like.

  For example, when the paper 37 is a thick paper, as shown in FIG. 13, the deformation amount of the elastic layer 68 of the heating roll 60 is increased, and the moving speed of the surface of the heating roll 60 is increased by the deformation amount of the elastic layer 68. However, it is known that the speed becomes faster than the set sheet conveyance speed Vf.

  As described above, when the sheet conveyance speed Vf by the fixing device 44 varies depending on the type and state of the sheet 37 or the amount of the toner image transferred onto the sheet 37, the gap between the sheet conveyance belt 31 and the fixing device 44. When the slack amount of the formed paper 37 changes, and as a result, the transport speed Vf of the paper 37 by the fixing device 44 becomes faster than the paper transport speed Vt of the paper transport belt 31, the fixing device 44 pulls the paper 37. As a result, an image quality defect called “smudge” in which the toner image being transferred is rubbed onto the paper 37 in the image forming unit 7K or the like on the downstream side may occur.

  Further, if the conveyance speed Vf of the sheet 37 by the fixing device 44 becomes too slower than the sheet conveyance speed Vt of the sheet conveyance belt 31, the sheet 37 formed between the sheet conveyance belt 31 and the fixing device 44 is loosened. The transfer sheet 37 is pushed back to the most downstream image forming unit 7K side by the rigidity (so-called stiffness) of the sheet 37, and the toner image transferred onto the transfer sheet 37 is transferred to the sheet conveying belt 31 by an excessive amount. There is a possibility that an image quality defect that deforms in a compressed state along the moving direction may occur.

  Therefore, in this embodiment, from the predetermined timing start timing before the leading edge of the transfer paper 37 enters the fixing device 44, the leading edge of the transfer paper 37 actually passes through a predetermined position downstream of the fixing device 44. And a speed control means for controlling the transfer material conveyance speed of the fixing means based on the required time measured by the measuring means.

  FIG. 1 is a block diagram showing a control circuit of a tandem full-color printer according to this embodiment.

  In FIG. 1, reference numeral 100 denotes a control device disposed in the control unit 4 shown in FIG. 2, and this control device 100 is an MPU (Machine Processing Unit) as control means for controlling the printing operation of a full-color printer. ) 101, the timer circuit 102 as a measuring unit that measures time by counting the clock 101 a output from the MPU 101 at a constant cycle, and the driving motor 74 that drives the fixing device 44. And a clock signal generation circuit 103 for generating a clock signal 103a for rotationally driving. The MPU 101 functions as a speed control means, and controls the frequency of the clock signal 103a generated by the clock signal generation circuit 103 based on the required time T measured by the timer circuit 102, thereby providing a stepping motor or the like. The rotational speed of the drive motor 74 is controlled by increasing or decreasing by a predetermined rate.

  As shown in FIG. 1, the timer circuit 102 is supplied with an image writing signal 110 for determining the timing at which the timer circuit 102 starts measurement, and at the timing at which the timer circuit 102 ends measurement. A detection signal 111 from the discharge detection sensor 66 to be determined is input. The timer circuit 102 measures the time from when the image writing signal 110 is input to when the detection signal 111 is input from the discharge detection sensor 66.

  As the image writing signal 110, an image writing signal by the ROS 10 in any of the image forming units 7Y, 7M, 7C, and 7K of yellow (Y), magenta (M), cyan (C), and black (K) is used. However, as the image writing signal 110, for example, a black image writing start signal 110K input to the ROS 10 of the black (K) image forming unit 7K disposed on the most downstream side is used.

  In the full-color printer configured as described above, as shown in FIG. 2, it is formed by yellow (Y), magenta (M), cyan (C), and black (K) image forming portions 7Y, 7M, 7C, and 7K. The toner images of the respective colors thus transferred are multiplexedly transferred onto the paper 37 being conveyed while being attracted to the surface of the paper conveying belt 31, and the paper 37 onto which the toner images of the respective colors are transferred is transferred from the paper conveying belt 31. After being separated, it is conveyed to the fixing device 44 and subjected to fixing processing.

  At this time, the transfer speed Vf of the transfer paper 37 by the fixing device 44 is set to be, for example, about 0.5 to several percent slower than the paper transport speed Vt of the paper transport belt 31 as described above. As shown in FIG. 6, a slack of the paper 37 is formed between the paper transport belt 31 and the fixing device 44.

  However, in the full color printer, as shown in FIG. 13, when the paper 37 is a thick paper such as a coated paper, the conveyance speed of the paper 37 is faster than the set speed Vf, or the paper is like a full-color solid image. If the amount of the toner image transferred onto the sheet 37 is large, a minute slip that does not affect the image with the heating roll 60 occurs, and the conveyance speed Vf of the sheet 37 by the fixing device 44 is set in advance. It may fluctuate, such as becoming slower than the set speed.

  Therefore, in the full-color printer according to this embodiment, as shown in FIG. 14, when the type of paper 37 is designated by the user interface, the printer driver, or the like at the start of the printing operation, the MPU 101 The fixing speed is determined according to the type of the paper 37 (step 101). However, if there is no designation, it is set to plain paper. For example, if the designated paper 37 is plain paper, the MPU 101 sets the fixing speed of the fixing device 44 to the normal fixing speed Vf. If the designated paper 37 is thick paper, the MPU 101 sets the fixing speed to the normal speed. The fixing speed Vf / 2 is set to half. Note that the conveyance speed of the sheet conveyance belt 31 is similarly set according to the fixing speed of the fixing device 44.

  Then, the MPU 101 starts an image forming operation and starts conveying the sheet 37 from the sheet feeding device 6 (step 102). As shown in FIG. 1, when the MPU 101 outputs an image write signal 110 from the MPU 101 along with the image forming apparatus, the timer circuit 102 starts counting the clock signal (step 103). Thereafter, the sheet 37 is subjected to a fixing process by the fixing device 44, and when the leading end of the sheet 37 is detected by the sheet discharge sensor 66 as shown in FIG. 9 and the discharge detection signal 111 is output, the timer circuit 102 As shown in FIG. 15, after the count of the clock signal is stopped and the image writing start signal 110 is output, the leading edge of the sheet 37 passes through the fixing device 44 and the detection signal is output from the discharge detection sensor 66. Is measured (step 103).

  As shown in FIG. 14, the MPU 101 determines whether or not the absolute value of the difference between the required time T and the reference passage time T0 at which the amount of slack is optimal is equal to or greater than a predetermined value ΔT (step 104). If the absolute value of the difference between the time T and the reference passage time T0 is not equal to or greater than the predetermined value ΔT, the fixing process by the fixing device 44 is continued as it is, and the speed control operation of the fixing device 44 is terminated. . Here, the predetermined value T varies depending on the type of the sheet 37 and the like, and is stored in the nonvolatile memory 104 of the MPU 101 by the number of sheets that can be selected in advance. Furthermore, the fixing speed corresponding to the predetermined value T and the type of paper can be updated as needed via a network (not shown). For example, when an OHP supply device for supplying an OHP sheet is added below the main body 1. This can be dealt with by newly storing a predetermined value or fixing speed according to the OHP sheet.

  Further, as shown in FIG. 14, when the MPU 101 determines that the absolute value of the difference between the required time T and the reference passing time T0 at which the amount of slack is optimum is equal to or greater than a predetermined value ΔT, The operation of switching the fixing speed of the fixing device 44 is executed by controlling the frequency of the clock signal 103a applied to the drive motor 74 via the generating circuit 103 (step 105).

  Therefore, when the MPU 101 determines that the absolute value of the difference between the required time T and the reference reference passage time T0 is equal to or greater than the predetermined value ΔT, the MPU 101 determines the difference between the required time T and the reference reference time T0 ( When T−T0) is positive, the conveyance speed Vf of the fixing device 44 is switched to a speed higher than the set speed, and when the difference between the required time T and the reference passage time T0 is negative. The conveyance speed Vf of the fixing device 44 is switched to a speed slower than the set speed. How much the conveyance speed is switched differs depending on the type of the paper 37 and the like. For example, in the case of plain paper, it is switched about ± 0.5%.

  As described above, in the above embodiment, when the paper 37 is a thick paper such as a coated paper, or when the amount of toner images transferred onto the paper 37 is large such as a full-color solid image, or in a high-temperature and high-humidity environment. In the state where the transfer sheet 37 has absorbed moisture, the MPU does not move the sheet 37 even if the conveyance speed Vf of the sheet 37 by the fixing device 44 fluctuates with respect to a preset speed. The sheet conveyance speed of the fixing device 44 is switched according to the time required for the leading edge to pass through the fixing device.

  Therefore, in the fixing device 44, the conveyance speed of the paper 37 can be controlled with the leading edge of the paper 37 passing through the fixing device 44.

  Further, there is almost no variation in the output timing of the image writing signal 110 output from the MPU 101.

Embodiment 2
FIG. 16 shows a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals. In the second embodiment, the sheet is used as a fixing unit. The measurement start time before the arrival is determined by the detection signal output from the detection means provided in the conveyance path before the paper reaches the fixing means.

  In the second embodiment, the detection unit is arranged downstream of the transfer position of the final color image of the endless belt and upstream of the fixing unit.

  That is, in the second embodiment, as shown in FIG. 16, in the vicinity of the surface of the sheet conveying belt 31, the downstream side of the final color black (K) image forming unit 7 K and the upstream side of the fixing device 44. On the side, a paper detection sensor 90 is arranged as a detection means for detecting the paper 37 conveyed by the paper conveyance belt 31. As the paper detection sensor 90, for example, a sensor that detects the paper 37 that is optically transported by the paper transport belt 31 is used.

  In the second embodiment, as shown in FIG. 17, the feeding of the sheet 37 is started, and the yellow (Y), magenta (M), cyan (C), and black (K) image forming units 7Y, The toner images of the respective colors formed by 7M, 7C, and 7K are transferred onto the paper 37 that is conveyed while being attracted to the surface of the paper conveying belt 31, and the paper 37 on which the toner images of the respective colors are transferred. When the paper passes the paper detection sensor 90, the front end of the paper 37 is detected by the paper detection sensor 90, and after the paper detection signal is output by the timer circuit 102, the front end of the paper 37 passes through the fixing device 44 and is discharged. The required time T ′ until the detection signal is output from the detection sensor 66 is measured.

  In the second embodiment, the conveyance path of the sheet 37 from the sheet detection sensor 90 to the discharge detection sensor 66 is from the final color image writing start timing of the first embodiment to the detection signal output by the discharge detection sensor 66. Since it is shorter than the time, the measurement time of the timer circuit 102 is shortened. In the second embodiment, the sheet 37 actually conveyed is directly detected, and the measurement start time is determined by the detection signal.

  The sheet detection sensor 90 is not limited to the sheet detection sensor 90 disposed downstream of the final color black (K) image forming unit 7K and upstream of the fixing device 44. Of course, it is also possible to use the one arranged in the above.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

Embodiment 3
FIG. 18 shows a third embodiment of the present invention. The same parts as those in the first embodiment will be described with the same reference numerals. An image detection means for detecting an image shift detection image formed on the endless belt corresponding to the paper is used.

  That is, in the third embodiment, as shown in FIG. 19, for example, an image for detecting image misalignment is formed in a portion other than a region where the sheet 37 in the width direction orthogonal to the conveying direction of the sheet conveying belt 31 is held. 16 is formed as a toner image of each color of yellow (Y), magenta (M), cyan (C), and black (K). As shown in FIG. 18, a pattern detection sensor 96 that detects a color misregistration detection pattern 95 is arranged at the position of the detection sensor 90.

  A pattern 95 for detecting color misregistration of one color (for example, black) is formed on the surface of the paper transport belt 31 at a position corresponding to the front end of the paper 37 (not necessarily the same position) during image formation. The required time T is measured by forming and detecting the color misalignment detection pattern 95 by the pattern detection sensor 96.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

Embodiment 4
FIG. 20 shows Embodiment 4 of the present invention. The same reference numerals are given to the same parts as those in Embodiment 1, and in Embodiment 6, a plurality of endless belts are used. An intermediate transfer belt is used in which toner images of a plurality of colors to be transferred onto a sheet are transferred while being circulated and moved between the rolls.

  That is, in the fourth embodiment, as shown in FIG. 20, four image forming units 7Y of yellow (Y), magenta (M), cyan (C), and black (K) are provided inside the full-color printer main body 1. , 7M, 7C, and 7K are arranged in an obliquely inclined state, and an intermediate transfer belt 200 is stretched over the four image forming units 7Y, 7M, 7C, and 7K.

  The yellow (Y), magenta (M), cyan (C), and black (K) image forming portions 7Y, 7M, 7C, and 7K are formed in the same manner except for the color of the toner image to be formed. A photosensitive drum 8 that is rotationally driven at a predetermined speed along an arrow direction, a charging roll 9 that uniformly charges the surface of the photosensitive drum 8, and an LED exposure device 10 that performs image exposure according to image data; The developing device 11 and the cleaning device 12 are included.

  The intermediate transfer belt 200 is stretched between the drive roll 201, the backup roll 202, and the driven roll 203 with a predetermined tension. The intermediate transfer belt 200 is circulated and moved by the drive roll 201 at a predetermined speed. It is configured.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images formed by the image forming units 7Y, 7M, 7C, and 7K are intermediately transferred by the primary transfer roll 204. After multiple transfer onto the transfer belt 200, secondary transfer is performed collectively on the paper 37 by the secondary transfer roll 205. Further, by sharing one photoconductor, a plurality of image forming units 7Y, 7M, 7C, and 7K are integrally configured, and the intermediate transfer belt 200 is rotated a plurality of times to perform multiple transfer, and then collectively onto the sheet 37. Then, it may be configured to perform secondary transfer.

  Incidentally, in the fourth embodiment, as shown in FIG. 20, the full-color printer main body 1 is configured in a small size, and the sheet 37 fed from the sheet feeding tray 39 is transferred to the intermediate transfer belt 200 at the secondary transfer position. After the toner images of each color of yellow (Y), magenta (M), cyan (C), and black (K) are collectively transferred from the intermediate transfer belt 200, the intermediate transfer belt 200 It is conveyed to a fixing device 44 disposed downstream of the secondary transfer position.

  At that time, since the full-color printer main body 1 is configured to be small, the leading edge of the sheet 37 on which the toner image is secondarily transferred at the secondary transfer position of the intermediate transfer belt 200 has reached the fixing device 44. Even so, the rear end of the sheet 37 is in a state where the toner image is transferred from the intermediate transfer belt 200.

  Therefore, in the fourth embodiment, as shown in FIG. 20, a paper detection sensor 210 for jam detection is disposed on the downstream side of the registration roll 43, and the front end of the paper 37 is moved by the paper detection sensor 210. Detected. The sheet detection sensor 210 functions as a means for determining a measurement start time before the transfer sheet 37 reaches the fixing device 44. Alternatively, the measurement start time may be determined based on the image writing signal.

  In the fourth embodiment, as shown in FIG. 20, when the paper 37 is fed, it is detected by the paper detection sensor 210 disposed on the downstream side of the registration roll 43, and the timer circuit 102 starts measuring time. Then, the time T required until the leading edge of the sheet 37 passes through the fixing device 44 and the detection signal is output from the discharge detection sensor 66 is measured.

  Since the driving of the registration roll 43 is synchronized with the toner image transferred onto the intermediate transfer belt 200, the leading edge of the sheet 37 is detected by the sheet detection sensor 210 disposed on the downstream side of the registration roll 43. Thus, a time synchronized with the conveyance state until the sheet 37 passes through the fixing device 44 is measured.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

  Furthermore, the present invention is not limited to the above-described embodiment, and can be variously implemented without changing the gist of the present invention. For example, the present invention can be implemented in an ink jet printer, a printing machine, a FAX, and the like. is there.

FIG. 1 is a block diagram showing a control circuit of a tandem type full color printer as an image forming apparatus employing a paper direct transfer system according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a tandem type full color printer as an image forming apparatus employing the paper direct transfer system according to the first embodiment of the present invention. FIG. 3 is a block diagram showing the image forming unit. FIG. 4 is a configuration diagram of a cover open / close state showing a tandem type full color printer as an image forming apparatus employing the paper direct transfer system according to the first embodiment of the present invention. FIG. 5 is a configuration diagram showing a stretched state of the sheet conveying belt. FIG. 6 is a cross-sectional configuration diagram illustrating the fixing device. FIG. 7 is a configuration diagram illustrating a transfer state of the transfer sheet in the sheet transfer belt and the fixing device. FIG. 8 is a cross-sectional configuration diagram illustrating the fixing device. FIG. 9 is a configuration diagram illustrating the paper discharge detection sensor. FIG. 10 is a perspective configuration diagram illustrating the pressure contact member of the fixing device. FIG. 11 is an exploded perspective view showing a pressure contact member of the fixing device. FIG. 12 is a schematic sectional view showing the fixing device. FIG. 13 is an enlarged schematic diagram showing the pressure contact portion of the fixing device. FIG. 14 is a flowchart showing the control operation of the tandem type full color printer as the image forming apparatus employing the paper direct transfer system according to the first embodiment of the present invention. FIG. 15 is a timing chart showing the control operation of the tandem type full color printer as the image forming apparatus employing the paper direct transfer system according to the first embodiment of the present invention. FIG. 16 is a block diagram showing a tandem type full-color printer as an image forming apparatus employing a paper direct transfer system according to Embodiment 2 of the present invention. FIG. 17 is a timing chart showing the control operation of a tandem type full-color printer as an image forming apparatus employing the paper direct transfer system according to Embodiment 2 of the present invention. FIG. 18 is a block diagram showing a tandem type full color printer as an image forming apparatus adopting a paper direct transfer system according to Embodiment 3 of the present invention. It is. FIG. 19 is a block diagram showing a main part of a tandem type full-color printer as an image forming apparatus employing a paper direct transfer system according to Embodiment 3 of the present invention. FIG. 20 is a block diagram showing a tandem type full color printer as an image forming apparatus employing an intermediate transfer system according to Embodiment 4 of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1: Printer main body, 31: Paper conveyance belt (endless belt), 37: Transfer paper, 44: Fixing device, 101: MPU (Speed control circuit), 102: Timer circuit (measuring means)

Claims (16)

First conveying means for conveying a sheet on which an image is formed;
A second transport unit disposed downstream of the first transport unit in the transport direction of the paper and transports the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the second transport means from a measurement start time before the paper reaches the second transport means; And a control unit that controls a transport speed of the second transport unit based on the required time measured by the measurement unit.
The transport apparatus according to claim 1, wherein the second transport unit is a fixing unit that performs a fixing process on the paper while transporting the paper separated from the first transport unit. .
Conveying means for conveying a sheet on which an image is formed;
A fixing unit disposed downstream of the conveying unit in the conveyance direction of the paper and performing a fixing process while conveying the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the fixing means from a measurement start time before the paper reaches the fixing means;
An image forming apparatus comprising: a control unit that controls a sheet conveyance speed of the fixing unit based on a required time measured by the measuring unit.
Transport means for transporting paper on which images of a plurality of colors are formed;
A fixing unit disposed downstream of the conveying unit in the conveyance direction of the paper and performing a fixing process while conveying the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the fixing means from a measurement start time before the paper reaches the fixing means;
An image forming apparatus comprising: a control unit that controls a sheet conveyance speed of the fixing unit based on a required time measured by the measuring unit.
5. The image forming apparatus according to claim 3, wherein the conveying unit is an endless belt that conveys the paper while being circulated and stretched between a plurality of rolls.
An endless belt on which a plurality of color images are formed while being stretched and circulated between a plurality of rolls;
Fixing means for carrying out a fixing process on the paper while conveying the paper after the image formed on the endless belt is transferred to the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the fixing means from a measurement start time before the paper reaches the fixing means;
An image forming apparatus comprising: a control unit that controls a sheet conveyance speed of the fixing unit based on a required time measured by the measuring unit.
7. The control unit according to claim 3, wherein the control unit controls the sheet to be conveyed in a state where a predetermined amount of slack is formed between the conveying unit and the fixing unit. The image forming apparatus described.

The control unit controls the sheet conveyance speed of the fixing device when a time difference between the required time measured by the measurement unit and a reference time reaches a preset value or more. The image forming apparatus according to claim 3.
The control unit controls the sheet conveying speed of the fixing device to be increased when a time difference between the required time measured by the measuring unit and a reference time is a positive value. The image forming apparatus according to 8.
The control unit controls the sheet conveying speed of the fixing device to be increased when the time difference between the required time measured by the measuring unit and a reference time is a negative value. The image forming apparatus according to 8.
11. The image forming apparatus according to claim 6, wherein a measurement start time before the sheet reaches the fixing unit is determined by a write start signal for an image of a final color.
12. The image forming apparatus according to claim 11, wherein the final color image write start signal is a black image write start signal.
The measurement start time before the sheet reaches the fixing unit is determined by a detection signal output from a detection unit provided in a conveyance path before the sheet reaches the fixing unit. The image forming apparatus according to claim 6.
14. The detection unit according to claim 13, wherein the detection unit is disposed downstream of the final color image forming position of the endless belt in the sheet conveyance direction and upstream of the fixing unit. Image forming apparatus.
15. The image forming apparatus according to claim 13, wherein an image detection unit that detects an image shift detection image formed on the endless belt corresponding to the sheet is used as the detection unit. .
At least first conveying means for conveying a sheet on which an image is formed;
A second transport unit disposed downstream of the first transport unit in the transport direction of the paper and transports the paper;
Measuring means for measuring a time required for the leading edge of the paper to pass a predetermined position downstream of the second conveying means from a measurement start time before the paper reaches the second conveying means; Used for the image forming apparatus provided,
A control program for an image forming apparatus in which a program for controlling a sheet transport speed of the second transport unit is stored in association with the required time measured by the measurement unit.

Images