JP2007175907A - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent skewing of a printing medium and to accurately control an ejection timing of an ink droplet by markedly accurately detecting the conveying condition of the printing medium. <P>SOLUTION: A plurality of conveyance belts 1 are arranged in a direction intersecting a conveyance direction of a printing medium 2. In the case where printing is performed by attracting the printing medium 2 to the outer circumference face of the charged conveyance belt 1, a follower roller 4 to which the central conveyance belt 1 is wound and a follower shaft 7, are united with each other and follower rollers 4 to which the other conveyance belts 1 are wound, are movably engaged with the follower shaft 7 so that the conveyance force of the central conveyance belt 1 for conveying the printing medium 2 is greater than that of each of the other conveyance belts 1, thereby preventing the printing medium from skewing. By attaching a rotary disk 9 to the follower shaft 7 and reading the rotary encoder by means of a sensor 8, it is possible to markedly accurately detect the conveying condition of the printing medium according to the moving condition of the central conveyance belt 1 which is not deviated from the printing medium 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, for example, minute characters of liquid inks of a plurality of colors are ejected from a plurality of nozzles to form fine particles (ink dots) on a print medium, thereby drawing a predetermined character or image. The present invention relates to an ink jet printer.

Such inkjet printers are generally inexpensive and can easily obtain high-quality color prints, and therefore have become widespread not only in offices but also in general users with the spread of personal computers and digital cameras.
In such an ink jet printer, a moving body called a carriage or the like, which is integrally provided with an ink cartridge and a print head (also called an ink jet head), generally reciprocates on a print medium in a direction intersecting the transport direction. While ejecting (injecting) liquid ink droplets from the nozzles of the print head to form minute ink dots on the print medium, a predetermined character or image is drawn on the print medium to produce a desired printed matter. It is designed to create. The carriage is equipped with four color (yellow, magenta, cyan) ink cartridges including black (black) and a print head for each color, so that not only monochrome printing but also full-color printing combining each color is easy. (Furthermore, 6 colors, 7 colors, or 8 colors in which light cyan, light magenta, etc. are added to these colors are also put into practical use).

  Further, in this type of ink jet printer in which printing is executed while reciprocating the ink jet head on the carriage in the direction intersecting with the conveyance direction of the print medium, the ink jet head is set to 10 in order to cleanly print the entire page. It is necessary to reciprocate several times to several tens of times. In contrast, in an inkjet printer of a type in which a long inkjet head (not necessarily integrated) having the same dimensions as the width of the print medium is disposed and the carriage is not used, the inkjet head is moved in the width direction of the print medium. This is not necessary, and so-called one-pass printing is possible, so that high-speed printing similar to a laser printer is possible. The former inkjet printer is generally referred to as a “multi-pass (serial) inkjet printer”, and the latter inkjet printer is generally referred to as a “line head inkjet printer”.

Among these line head type ink jet printers, the one described in Patent Document 1 below includes a plurality of conveying belts that place and convey a print medium, and the plurality of conveying belts are driven by the same driving source. Thus, the variation in the conveyance speed between the plurality of conveyance belts is eliminated, and the skew feeding of the print medium is prevented.
JP-A-8-132700 (page 3, FIG. 6)

  However, in the conventional line head type inkjet printer, in order to prevent the skew of the print medium by eliminating the variation in the conveyance speed between the plurality of conveyance belts, the thicknesses of the plurality of conveyance belts are all the same, and these It is not sufficient to drive the conveyor belt with a common drive source. In other words, in order to eliminate variations in the conveyance speed between the conveyor belts, in addition to these, the circumference of the conveyor belt, the outer diameter and concentricity of each roller around which the conveyor belt is wound, the concentricity, the roller rotation shaft Bending accuracy must be the same between the conveyor belts. That is, in the line head type ink jet printer of Patent Document 1, the dimensional accuracy of various parts must be extremely high, and the skew of the print medium can be prevented by eliminating the variation in the conveyance speed among the plurality of conveyance belts. There is an unresolved issue that is difficult in practice.

  In order to avoid such a problem, for example, the print medium conveyance capability of any one of the plurality of conveyance belts is made larger than the print medium conveyance capability of the other conveyance belts, and the print medium conveyance capability is maximized. It is conceivable that the printing medium is mainly conveyed by the conveying belt, and the other conveying belt is conveyed while supporting the printing medium. According to this configuration, the conveyance belt other than the conveyance belt having the maximum print medium conveyance capability and the print medium slide with each other, or the roller around which the conveyance belt is wound and the rotation shaft slide with each other, thereby skewing the print medium. It becomes possible to prevent. However, in this case, there is an unsolved problem of how to detect the conveyance state of the print medium that determines the ink droplet ejection timing, that is, the movement state of the conveyance belt.

  The present invention has been made paying attention to the above-described problems, and the printing medium conveying ability of any one of the conveying belts is made larger than the printing medium conveying ability of the other conveying belts. In order to prevent this, an object of the present invention is to provide an ink jet printer that can accurately detect the conveyance state of a print medium from the movement state of the conveyance belt and control the ink droplet ejection timing.

  [Invention 1] In order to solve the above-described problem, an inkjet printer of Invention 1 includes a plurality of conveyor belts that rotate and move in the conveyance direction of the print medium, arranged side by side in a direction intersecting the conveyance direction of the print medium. In an inkjet printer that prints by placing a print medium on an outer peripheral surface of a conveyance belt and conveying the print medium by ejecting ink droplets from nozzles of an inkjet head on the print medium, any one of the plurality of conveyance belts Conveying belt moving state detecting means for detecting the moving state of the conveying belt having the maximum printing medium conveying ability, wherein the conveying medium moving capacity of the conveying belt is larger than the printing medium conveying ability of the other conveying belt, and the conveying belt moving state is provided. The ink droplet ejection timing is controlled based on the movement state of the conveyor belt detected by the detecting means.

  The print medium transport capability referred to in the present invention indicates the capability of transporting the print medium in the transport direction, and is evaluated, for example, by how the print medium can be transported without shifting. That is, it is evaluated that the print medium conveyance capability is larger as the movement of the print medium and the conveyance belt, or the roller and the conveyance belt around which the conveyance belt is wound, or the print medium and the roller are synchronized. According to the ink jet printer according to the first aspect of the present invention, the plurality of conveyor belts that rotate and move in the conveyance direction of the print medium are arranged side by side in the direction intersecting the conveyance direction of the print medium, and the print medium is disposed on the outer circumferential surface of these conveyance belts. In the ink jet printer that prints by ejecting ink droplets from the nozzles of the ink jet head onto the print medium, the print medium transport ability of any one of the plurality of transport belts is different. And a configuration for detecting the movement state of the conveyance belt having the maximum printing medium conveyance capability and controlling the ink droplet ejection timing based on the detected movement state of the conveyance belt. Therefore, the skew of the print medium can be prevented and the conveyance state of the print medium can be detected most accurately. It is possible to accurately control the ink ejection timing based on the transport state of the detected printing medium.

[Invention 2] The ink jet printer according to Invention 2 is the ink jet printer according to Invention 1, wherein the conveying belt moving state detecting means is a rotary that rotates synchronously with a roller around which a conveying belt having the maximum printing medium conveying ability is wound. It is characterized by comprising an encoder.
In the ink jet printer according to the second aspect of the present invention, since the rotary encoder that rotates synchronously with the roller around which the conveyance belt having the maximum print medium conveyance capability is wound is configured to detect the movement state of the conveyance belt, the size of the rotary encoder Can be increased to increase the conveying belt moving state detection capability, and the rotary encoder can be separated from the ink jet head to prevent the contamination due to mist and the like.

 [Invention 3] The ink jet printer according to Invention 3 is the ink jet printer according to Invention 1 or 2, wherein the roller around which any one of the conveying belts is wound and a rotating shaft are integrated, and the other conveying belt is wound. By making the roller to be rotated and the rotating shaft freely, the print medium conveyance capability of any one of the conveyance belts is made larger than the print medium conveyance capability of the other conveyance belts.

  According to the ink jet printer according to the third aspect of the present invention, the roller around which one of the conveyor belts is wound and the rotation shaft are integrated, and the roller around which the other conveyor belt is wound and the rotation shaft can be freely set. Thus, since the print medium conveyance capability of any one of the conveyance belts is set to be larger than the print medium conveyance capability of the other conveyance belt, the print medium conveyance capability of any one conveyance belt and the print medium of the other conveyance belt It can be easily differentiated from the carrying capacity.

Next, a first embodiment of the inkjet printer of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an ink jet printer according to the present embodiment. Reference numeral 1 in the drawing denotes an endless conveyance belt for conveying the print medium 2. The printing medium 2 is a medium / high resistance sheet-like member such as printing paper or an OHP sheet. Further, the conveyor belt 1 is made of an insulator, and five conveyor belts 1 that rotate in the conveyance direction of the print medium 2 are arranged side by side in a direction intersecting the conveyance direction of the print medium 2. These conveyor belts 1 are wound around a driving roller 3 disposed at the left end of the figure and a driven roller 4 disposed at the right end of the figure. All of the five drive rollers 3 are fixed to the drive shaft 5, and a drive roller motor 6 is connected to the drive shaft 5. The driven roller 4 is attached to a driven shaft 7. Therefore, when the drive roller 3 is driven to rotate in the direction of the arrow by the drive roller motor 6 while the print medium 2 is attracted to the conveyance belt 1 charged by the charging means described later, the print medium 2 is moved to the right in the figure. From left to right, that is, in the direction of the arrow.

  Examples of the charging means for the conveying belt 1 include a configuration in which a charging roller connected to a DC power source is brought into contact with the outer peripheral surface of the conveying belt 1. When a charge is charged from the charging roller to the outer peripheral surface of the conveyance belt 1 made of an insulator, dielectric polarization occurs in the print medium 2 due to the charge, and the charge of the print medium 2 due to the dielectric polarization and the charge on the outer peripheral surface of the conveyance belt 1. The printing medium 2 is attracted to the outer peripheral surface of the conveyor belt 1 by the electrostatic force generated by Examples of the charging means for the outer peripheral surface of the conveyor belt 1 include corona discharge for dropping electric charges. These charging means are so-called DC charging methods in which the outer peripheral surface of the conveyor belt 1 is charged to the positive electrode or the negative electrode, but there is also a so-called AC charging method in which the outer peripheral surface of the conveyor belt 1 is charged alternately to the positive electrode and the negative electrode. A printing member which is an insulator on the outer peripheral surface of the AC-charged conveyance belt 1 is electrostatically adsorbed.

A gate roller 13 is disposed upstream of the driven roller 4 in the conveyance direction of the print medium 2. The gate roller 13 adjusts the timing at which the print medium 2 fed from the paper feed unit is fed onto the conveyor belt 1 and also bends the print medium 2 in the conveyance direction and corrects so-called skew. Reference numeral 14 in the figure denotes a paper discharge roller for discharging the print medium 2 to the paper discharge unit.
Reference numeral 11 in FIG. 1 denotes an inkjet head. The ink-jet head 11 is arranged so as to be shifted in the transport direction of the printing medium 2 for each of the four colors of yellow (Y), magenta (M), cyan (C), and black (K). Ink is supplied to each inkjet head 11 from an ink tank of each color (not shown) via an ink supply tube. Each inkjet head 11 is formed with a plurality of nozzles in a direction intersecting with the conveyance direction of the print medium 2, and by ejecting a necessary amount of ink droplets from these nozzles to a necessary location at the same time, the print medium 2. A minute ink dot is formed and output on the top. By performing this for each color, it is possible to perform so-called one-pass printing by passing the print medium 2 adsorbed on the conveyor belt 1 once. That is, the area where the inkjet head 11 is disposed corresponds to the print area.

  As a method for discharging and outputting ink from each nozzle of the ink jet head, there are an electrostatic method, a piezo method, a film boiling ink jet method, and the like. In the electrostatic system, when a drive signal is given to the electrostatic gap, which is an actuator, the diaphragm in the cavity is displaced, causing a pressure change in the cavity, and ink drops are ejected from the nozzle by the pressure change. It is. In the piezo method, when a drive signal is given to a piezo element that is an actuator, the diaphragm in the cavity is displaced to cause a pressure change in the cavity, and ink droplets are ejected from the nozzle by the pressure change. . In the film boiling ink jet method, there is a minute heater in the cavity, the ink is instantaneously heated to 300 ° C. or more, the ink becomes a film boiling state, bubbles are generated, and ink droplets are ejected from the nozzle by the pressure change. That's it. Any ink output method can be applied to the present invention.

  A control device for controlling itself is provided in the ink jet printer. For example, as shown in FIG. 2, the control device prints on a print medium by controlling a printing device, a paper feeding device, and the like based on print data input from a host computer 60 such as a personal computer or a digital camera. The processing is performed. An input interface unit 61 that receives print data input from the host computer 60 and an output signal of the rotary encoder sensor 8 described later, and print processing based on the print data input from the input interface unit 61 and print medium position information. For example, a control unit 62 constituted by a microcomputer, a gate roller motor driver 63 for driving and controlling the gate roller motor 51 for driving the gate roller 13, and a driving roller motor driver for driving and controlling the driving roller motor 6. 64, an inkjet head driver 65 that drives and controls the inkjet head 11, and a discharge roller motor driver 66 that drives and controls a discharge roller motor 52 for driving the discharge roller 14.

  The control unit 62 temporarily stores a CPU (Central Processing Unit) 62a that executes various processes such as a print process, and print data input through the input interface 61 or various data when the print data print process is executed. A ROM (Read-Only ROM) comprising a RAM (Random Access Memory) 62c that temporarily stores an application program such as print processing or the like, and a non-volatile semiconductor memory that stores a control program executed by the CPU 62a Memory) 62d. When the control unit 62 obtains print data (image data) from the host computer 60 via the interface unit 61, the CPU 62a performs a predetermined process on the print data and ejects ink droplets from any nozzle. Alternatively, print data indicating how many ink droplets are to be ejected is output, and control signals are output to the drivers 63 to 66 based on the print data and input data from various sensors. A drive signal obtained by converting the control signal is output from each of the drivers 63 to 66, whereby the actuator corresponding to the plurality of nozzles of the inkjet head 11, the gate roller motor 51, the drive roller motor 6, and the paper discharge roller motor 52 are operated. Thus, the feeding and transport of the printing medium 2, the printing process on the printing medium 2, and the discharging of the printing medium 2 are executed. Each component in the control unit 62 is electrically connected through a bus (not shown).

  By the way, in the case of the line head type ink jet printer as in the present embodiment, if the moving speed between the respective conveyor belts is not the same, the print medium 2 is distorted (deformed) during the conveyance, and the flatness of the print medium 2 is increased. As a result, the distance between the ink ejection surface (nozzle surface) of the inkjet head 11 and the print medium 2 becomes difficult to maintain constant. In addition, since the moving speed of the print medium is not uniform, the landing position accuracy of the ink droplets is lowered, color misregistration, color unevenness, and streaks are likely to occur, thereby causing serious image defects. Further, even if no serious image defect occurs, the moving speed difference between the plurality of conveying belts leads to the skew of the printing medium 2 as shown in FIG. 3, for example.

  Therefore, in the present embodiment, as shown in FIG. 4, of the five driven rollers 4, only the central driven roller (hereinafter also referred to as the central driven roller) 4 in the direction intersecting the print medium 2 conveyance direction is used. The other driven roller 4 is integrally formed with the driven shaft 7, and is rotatably fitted to the driven shaft 7, and is moved by the E-type retaining ring 10 in the axial direction, that is, in the direction intersecting the print medium 2 conveyance direction. regulate. Therefore, the driven rollers 4 other than the central driven roller 4 in the direction intersecting the print medium 2 conveyance direction freely rotate with respect to the driven shaft 7.

  Further, the conveyor belt 1 (hereinafter also referred to as the central conveyor belt) 1 wound around the central driven roller 4 is configured such that the resistance value of the surface layer is larger than that of the other conveyor belts 1 and the same voltage. Even if charged at the center, the central conveying belt 1 adsorbs the printing medium 2 more strongly than the other conveying belts 1. That is, the central conveyance belt 1 has a larger printing medium 2 conveyance capability than the other conveyance belts 1. Therefore, even if each of the conveyor belts 1 is driven by the driving roller 3 with the print medium 2 adsorbed to the outer peripheral surface of each of the conveyor belts 1 as described above, the conveyor belts 1 other than the central conveyor belt 1 are not driven rollers. 4 is shifted from the central conveying belt 1 via 4, and the skew of the printing medium 2 can be suppressed and prevented by this deviation. Note that the conveyance belt 1 that increases the conveyance capacity of the print medium 2 is not necessarily limited to the conveyance belt 1 at the center, but considering the conveyance balance of the print medium 2, the conveyance belt in the center or near the center in the direction intersecting the print medium conveyance direction. Is preferred. In addition, the method for making the print medium conveyance capability of any one of the conveyance belts larger than the print medium conveyance capability of the other conveyance belts is not limited to this. For example, the width of the conveyance belt, the charging condition, etc. It can also be changed. Further, the method for transporting the print medium is not limited to the electrostatic adsorption method, and the print medium may be mechanically pressed against the transport belt and sandwiched.

  In this embodiment, as shown in FIG. 4, a rotary disk 9 is attached to the left end of the driven shaft 7 integrated with the central driven roller 4 and the rotary encoder provided on the rotary disk 9 is attached. Reading is performed by the rotary encoder sensor 8. The central driven roller 4 is wound around the central conveyance belt 1 having the maximum print medium 2 conveyance capability. Therefore, the rotary encoder provided on the rotary disk 9 is the central conveyance belt having the maximum print medium 2 conveyance capability. 1 movement state is detected. Unlike the other transport belts 1, the central transport belt 1 having the maximum transport capability of the print medium 2 is not displaced from the print medium 2. Therefore, the central transport belt 1 having the maximum transport capability of the print medium 2 is moved. If the state is detected, the conveyance state of the print medium 2 is detected most accurately.

  Further, by attaching the rotary encoder to the driven shaft 7 integrated with the central driven roller 4, the rotary disk 9 can be separated from the printing region, and as a result, the size of the rotary disk 9 can be increased. it can. As is well known, even if the resolution of the rotary encoder sensor 8 is equivalent, if the rotary disk 9 can be enlarged, the resolution of the rotary encoder itself can be increased. The conveyance state detection accuracy of the medium 2 can be increased. Further, by separating the rotary disk 9 from the printing area, that is, from the inkjet head 11, it is possible to suppress and prevent contamination due to mist or the like.

  Therefore, according to the ink jet printer of the present embodiment, the plurality of conveyor belts 1 that rotate and move in the conveyance direction of the print medium 2 are arranged side by side in a direction that intersects the conveyance direction 1 of the print medium 2, and these conveyance belts 1 are arranged. The print medium 2 is placed (adsorbed) on the outer peripheral surface of the print medium 2 and conveyed, and when printing is performed by ejecting ink droplets from the nozzles of the inkjet head 11 to the print medium 2, one of the plurality of conveyance belts 1 is used. Detecting the movement state of the central conveying belt 1 having the largest printing medium 2 conveying capability while making the printing medium 2 conveying capability of one conveying belt 1 larger than the printing medium 2 conveying capability of the other conveying belt 1 Since the ink droplet discharge timing is controlled based on the movement state of the central transport belt 1 that has been made, skew of the print medium 2 can be prevented and the print medium 2 Can be most accurately detect a transmission state, it is possible to accurately control the ink ejection timing based on the transport state of the detected printing medium 2.

  Further, the moving state of the conveyance belt 1 is detected by a rotary disk 9 and a rotary encoder sensor 8 (rotary encoder) that rotate synchronously with the driven roller 4 around which the central conveyance belt 1 having the maximum conveyance capacity of the print medium 2 is wound. As a result, the size of the rotary encoder can be increased to improve the moving state detection ability of the conveyor belt 1, and the rotary encoder can be separated from the inkjet head 11 to prevent contamination due to mist or the like.

  Further, the driven roller 4 and the driven shaft 7 around which the central conveying belt 1 is wound are integrated, and the driven roller 4 and the driven shaft 7 around which the other conveying belt 1 is wound can be freely configured. Since the printing medium 2 conveyance capability of the central conveyance belt 1 is made larger than the printing medium 2 conveyance capability of the other conveyance belt 1, the printing medium 2 conveyance capability of the central conveyance belt 1 and the printing medium of the other conveyance belt 1 3 conveyance ability can be easily differentiated.

  Next, a second embodiment of the ink jet printer of the present invention will be described with reference to FIGS. In the present embodiment, for example, by changing the charging condition, the printing medium conveyance capability of the central conveyance belt 1 in the direction intersecting the printing medium 2 conveyance direction is made larger than the printing medium conveyance capability of the other conveyance belts 1. Then, a relay roller 15 having a smaller diameter is integrally formed adjacent to the axial direction of the central driven roller 4 around which the central conveying belt 1 is wound, and the central driven roller is the same as the other driven rollers 4. The roller 4 and the relay take-out roller 15 are rotatably fitted on the driven shaft 7 and the E-type retaining ring 10 restricts the movement in the axial direction, that is, the direction intersecting the print medium 2 conveyance direction.

  A relay belt 17 is wound around a relay roller 15 and a pair of encoder pulleys 16. A rotary disk 9 is fixed to the encoder pulley 16, and the rotary encoder sensor 8 reads the rotary encoder of the rotary disk 9. The relay belt 17 is constituted by a toothed belt, and there is no deviation between the rotation state of the center driven roller 4, that is, the movement state of the center conveyance belt 1 and the rotation state of the rotary disk 9. Accordingly, if the rotary encoder detects the movement state of the conveyance belt 1 having the largest print medium 2 conveyance capability, the conveyance state of the print medium 2 can be detected most accurately as in the first embodiment. Ink droplet ejection timing can be accurately controlled based on the detected conveyance state of the print medium 2. Of course, the printing medium 2 can be prevented from skewing by making the printing medium 2 conveying ability of the central conveying belt 1 larger than the printing medium 2 conveying ability of the other conveying belts 1.

  Similarly to the first embodiment, the rotary belt 9 and the rotary encoder sensor 8 (rotary encoder) that rotate synchronously with the driven roller 4 around which the central conveyance belt 1 having the maximum conveyance capacity of the print medium 2 is wound, and the conveyance belt. Therefore, the size of the rotary encoder can be increased to increase the moving belt 1's ability to detect the moving state, and the rotary encoder can be separated from the inkjet head 11 to prevent contamination caused by mist or the like. Suppression can be prevented.

  In the above embodiment, only an example in which the ink jet printer of the present invention is applied to a so-called line head type ink jet printer has been described in detail. However, the ink jet printer of the present invention includes all types of ink jet including a multi-pass printer. Applicable to printers.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows 1st Embodiment of the line head type inkjet printer to which the inkjet printer of this invention is applied, (a) is a top view, (b) is a front view. It is a block block diagram of the control apparatus of the inkjet printer of FIG. It is explanatory drawing of the light-shielding state of a printing medium. It is a longitudinal cross-sectional view of the driven roller of the inkjet printer of FIG. It is a schematic block diagram which shows 2nd Embodiment of the line head type inkjet printer to which the inkjet printer of this invention is applied, (a) is a top view, (b) is a front view. It is a longitudinal cross-sectional view of the driven roller of the inkjet printer of FIG.

Explanation of symbols

  1 is a conveying belt, 2 is a printing medium, 3 is a driving roller, 4 is a driven roller, 5 is a driving shaft, 6 is a driving roller motor, 7 is a driven shaft, 8 is a rotary encoder sensor, 9 is a rotary disk, and 11 is an inkjet. Head, 15 relay roller, 16 encoder roller, 17 relay belt

Claims (3)

  A plurality of conveyor belts that rotate and move in the conveyance direction of the print medium are arranged side by side in a direction intersecting the conveyance direction of the print medium, and the print medium is placed on the outer peripheral surface of these conveyance belts and conveyed. In an ink jet printer that performs printing by ejecting ink droplets from nozzles of an ink jet head, the print medium transport capability of any one of the plurality of transport belts is greater than the print medium transport capability of the other transport belts. And a conveyance belt movement state detection unit that detects a movement state of the conveyance belt having the maximum print medium conveyance capability, and the ink droplet ejection timing is determined based on the movement state of the conveyance belt detected by the conveyance belt movement state detection unit. An ink jet printer characterized by controlling.   2. The ink jet printer according to claim 1, wherein the transport belt moving state detecting means is constituted by a rotary encoder that rotates synchronously with a roller around which a transport belt having the maximum print medium transport capability is wound.   The roller around which any one of the conveyor belts is wound and the rotating shaft are integrated, and the roller around which the other conveyor belt is wound and the rotating shaft are made freely, so that any one of the conveyor belts 3. The ink jet printer according to claim 1, wherein the print medium transport capability is made larger than the print medium transport capability of other transport belts.

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