Patent Publication Number: US-6336756-B1

Title: Ink jet printer that carries out printing with strut moving along arc

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to ink jet printers, and particularly to a small ink jet printer that has a narrow lateral width for the runway portion and the overrun portion of the ink carriage. 
     2. Description of the Background Art 
     Referring to FIG. 1, a conventional ink jet printer  261  includes a scan guide  264  formed of a linear metal rod, and an ink carriage  263  that moves linearly along scan guide  264  to eject ink onto a recording sheet  62  for printing. At both sides of the printing region by ink carriage  263  are provided a region called the runway portion provided to bring ink carriage  263  from a stop state to a certain speed and a region called the overrun portion provided to stop ink carriage  263  moving at a constant speed. More specifically, ink carriage  263  runs over the runway portion to prepare for printing from position A to position B in the drawing along scan guide  264 . Then, printing is carried out at a constant rate in the printing region. When ink carriage  263  moves passed the printing region to arrive at the overrun portion, ink carriage  263  decelerates and then stops. The change in speed of ink carriage  263  during this travel is as shown in FIG.  1 . 
     Referring to FIG. 2, an ink jet printer  271  disclosed in U.S. Pat. No. 5,831,655 includes a heat roller  274  to transport and apply heat to recording sheet  62  for drying the ink jetted out on recording sheet  62 , a recording head  275  located opposite to heat roller  274  to spray out ink on recording sheet  62  for printing, and an exhaust fan  276  for discharging the heat accumulated in ink jet printer  271  outside. Recording sheet  62  is heated by heat roller  274  while ink is sprayed on recording sheet  62  by recording head  275  for printing. Recording sheet  62  continues to be heated by a similar method even after printing. Accordingly, the ink jetted out on recording sheet  62  is dried. 
     According to ink jet printer  261 , a runway portion and an overrun portion are required in addition to the printing region. A region besides the region required for printing must be provided in ink jet printer  261 . This accounts for preventing reduction of the size of ink jet printer  261 . Ink jet printer  271  has a similar problem since printing is effected in a similar manner. 
     In ink jet printer  271 , the entire heat roller  274  discharges heat. Heat is provided to elements other than recording sheet  62 . Heat roller  274  dries one horizontal line at a time on recording sheet  62 . Therefore, the size of heat roller  274  per se is great and the heat generated from heat roller  274  is increased. Thus, ink jet printer  271  is increased in size and power consumption. There is also the problem of modification in the quality of the ink caused by recording head  275  being heated since the distance between heat roller  274  and recording head  275  is small. Although cooling is effected by exhaust fan  276  to reduce the heat effect, space and power are required to install and drive, respectively, exhaust fan  276 . This also leads to increase in the size and power consumption of ink jet printer  271 . 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of the present invention is to provide a small-size ink jet printer. 
     Another object of the present invention is to provide a compact ink jet printer that has many and high density of ink heads arranged in the ink carriage. 
     A further object of the present invention is to provide a compact ink jet printer without deviation between dots in printing. 
     Still another object of the present invention is to provide a compact ink jet printer without deviation between dots in printing and capable of printing without arc-like distortion. 
     A still further object of the present invention is to provide a compact ink jet printer without deviation between dots in printing and capable of printing without arc-like distortion, and that can dry printed out ink with lower power. 
     Yet a further object of the present invention is to provide an ink jet printer that can dry printed out ink without quality modification or coagulation of ink in the ink carriage. 
     Yet another object of the present invention is to provide an ink jet printer that can dry printed out ink without quality modification of ink sprayed out onto a recording sheet and without deformation of the recording sheet. 
     Yet a still further object of the present invention is to provide an ink jet printer that can dry printed out ink without quality modification or coagulation of ink in the ink carriage caused by heated air flow generated from a heat generator and that does not deform the spray out of ink droplets jetted out from the ink carriage caused by air blow. 
     An additional object of the present invention is to provide an ink jet printer that can dry printed out ink without erroneous spray out of ink from the ink carriage and without disturbance in the printed out image or text due to vibration of a heat generator. 
     Yet an additional object of the present invention is to provide a compact ink jet printer that can carry out printing at high speed. 
     According to an aspect of the present invention, an ink jet printer includes a shaft provided rotatably about a predetermined axis, a strut fixed to the shaft so as to move along an arc about the axis with rotation of the shaft, an ink carriage having a plurality of ink heads provided at a predetermined position from the shaft of the strut, and a control device controlling forwarding of a recording sheet, rotational motion of the shaft, and ink jetting from the plurality of ink heads. 
     The scanning operation of the ink carriage is effected by a reciprocating arc motion about the shaft. Therefore, even if the runway portion and the overrun portion of the same running distance as the conventional case are provided along the circular segment, the lateral widths of the runway portion and the overrun portion can be made smaller than those of the conventional ink jet printer. Thus, the travel width in the lateral direction of the ink carriage can be reduced to allow a smaller ink jet printer. 
     Preferably, the control device controls forwarding of a recording sheet, the rotational motion of the shaft, and ink jetting from a plurality of ink heads by defining the reciprocating motion width of printing for the ink carriage on the basis of the relationship between the width of the reciprocating motion of the ink head out of the plurality of ink heads located farthest away from the shaft and the width of the recording sheet. 
     The width of the reciprocating motion of printing for the ink carriage is defined on the basis of the relationship between the width of the reciprocating motion of the ink head located farthest away from the shaft and the width of the recording sheet. Therefore, by setting the width of the reciprocating motion of printing for the ink head located farthest from the shaft equal to the width of the recording sheet, printing can be carried out by the ink carriage at the minimum width of the reciprocating motion. Accordingly, the travel width of the ink carriage in the lateral direction can be reduced to allow a more compact ink jet printer. 
     Further preferably, a maintenance mechanism of the ink carriage is provided outside the printing motion range of the ink carriage, located opposite to the ink carriage. 
     The maintenance mechanism is provided on the extension of the reciprocating arc motion of the ink carriage. Therefore, the travel width of the ink carriage in the lateral direction can be suppressed to approximately the diameter of the circle at most, i.e., two times the length from the shaft to the leading edge of the ink carriage. Therefore, the ink jet printer can be reduced in size. 
     Further preferably, the ink carriage includes a plurality of ink heads fixed at the other end of the strut in a radial arrangement. 
     Since the ink heads are arranged radially, the ink heads can be arranged in an honeycomb manner. The number and density of the ink heads arranged at the ink carriage can be increased. 
     Further preferably, the control device defines the ink spray out timing from the plurality of ink heads corresponding to the distance between the shaft and each of the plurality of ink heads to control forwarding of a recording sheet, rotational motion of the shaft, and ink jetting from the plurality of ink heads. 
     Since the ink head moves along an arc, the scanning speed differs depending upon the distance from the strut. The ink spray out timing from the ink head is defined according to the distance from the strut. Therefore, the problem of deviation between dots during printing caused by difference in the scanning speed between ink heads can be eliminated. 
     According to another aspect of the present invention, an ink jet printer includes two shafts provided rotatably about two predetermined axes arranged at a predetermined distance, two struts fixed to the two shafts, respectively, to move along an arc about two axes with the rotation of the two shafts, an ink carriage having a plurality of ink heads provided at a predetermined position from the shaft of the two struts, and a control device controlling forwarding of a recording sheet, rotational motion of the two shafts, and ink jetting from the plurality of ink heads. 
     The two shafts, the ink carriage, and the two struts form a link mechanism. Accordingly, the ink carriage can move back and forth along arc. Therefore, even if the runway portion and the overrun portion of the same running distance as the conventional case are provided along the circular segment, the lateral widths of the runway portion and the overrun portion can be made smaller than those of the conventional ink jet printer. Thus, the ink jet printer can be reduced in size. Furthermore, the scanning speed of all the ink heads is identical since the ink carriage moves while maintaining the same posture. Therefore, the problem of deviation between dots during printing caused by difference in the scanning speed between ink heads is eliminated. 
     Preferably, the control device converts image data according to the curvature of the trajectory of the ink carriage moving back and forth along an arc to control forwarding of a recording sheet, rotational motion of the two shafts, and ink jetting from the plurality of ink heads according to the converted image data. 
     Therefore, there is the advantage that printing without arc-like distortion is allowed even if the ink carriage moves along an arc. 
     Further preferably, the control device sequentially prepares data of a predetermined number of lines corresponding to division of image data of one page. The control device converts the prepared data of a predetermined number of the lines according to the curvature of the trajectory of the ink carriage moving back and forth along an arc to control forwarding of a recording sheet, rotational motion of the two shafts and ink jetting from the plurality of ink heads according to the converted data. 
     Therefore, printing without arc-like distortion is allowed even in the case where image data can be obtained only for every one or plurality of lines such as image data obtained by facsimile and the like. 
     Further preferably, the ink jet printer includes a heat generator provided at the two struts. 
     The heat generator carries out a reciprocating arc motion in synchronization with the reciprocating arc motion of the ink carriage. By the heat output from the heat generator, the ink sprayed out on a recording sheet conveyed from the direction of the ink carriage towards the shaft can be dried in parallel to the printing operation. Since the heat generator per se carries out the motion, the entire recording sheet can be dried even if the heat generator is reduced in size. Therefore, power consumption and the amount of heat induced by the heat generator are reduced. An exhaust fan to discharge the heat outside is no longer required. Thus, a smaller ink jet printer can be provided. 
     Further preferably, the ink jet printer includes a heat generator provided at the leading end of the ink carriage. 
     The heat generator carries out a reciprocating arc motion in synchronization with the reciprocating arc motion of the ink carriage. Therefore, by the heat discharged from the heat generator, the ink sprayed out on a recording sheet conveyed from the direction of the shaft towards the ink carriage can be dried in parallel to the printing operation. Therefore, the heat generator can be reduced in size, which in turn allows the ink jet printer to be reduced in size. Since the heat generator per se carries out the motion, the entire recording sheet can be dried even if the heat generator is smaller in size. Thus, the power consumed by the heat generator and the amount of heat output from the heat generator can be reduced. 
     According to another aspect of the present invention, an ink jet printer includes a shaft provided rotatably about a predetermined axis, a strut fixed to the shaft to move along an arc about the axis with the rotation of the shaft, two parallel guide rails, an ink carriage including a plurality of ink heads and that can run along the two guide rails, and that has an opening with the longitudinal direction corresponding to the direction orthogonal to the running direction, and having the end of the strut fitted to allow movement in the opening, and a control device controlling forwarding of a recording sheet, arc motion of the strut, and ink jetting from the plurality of ink heads. 
     The ink carriage moves along the two guide rails to carry out printing while moving linearly. The scanning operation of the ink carriage is carried out by the strut moving back and forth along an arc. The reciprocating arc motion of the strut is divided into a vertical linear motion in which the strut moves along the opening of the ink carriage and a horizontal linear motion in which the ink carriage runs along the guide rail. Therefore, even if the runway portion and the overrun portion of the same running distance as the conventional case are provided along the circular segment, the lateral widths of the runway portion and the overrun portion can be made smaller than those of the conventional ink jet printer. Thus, the travel width of the ink carriage in the horizontal direction can be set smaller to allow reduction in the size of the ink jet printer. 
     Preferably, the control device controls forwarding of a recording sheet, arc motion of the strut, and ink jetting from the plurality of ink heads according to image data. 
     The ink carriage is controlled according to the image data. Therefore, by providing control so that the ink carriage is moved only along the region where printing is carried out and suppressing travel of the ink carriage where printing is not carried out, extra motion of the ink carriage is eliminated to allow high speed printing. 
     Further preferably, the control device controls forwarding of a recording sheet, the arc motion of the strut, and ink jetting from the plurality of ink heads according to the size of the recording sheet. 
     Therefore, the operation range of the ink carriage for printing can be limited to that within the recording sheet to eliminate extra motion of the ink carriage. Therefore, printing can be carried out at a high speed. 
     Further preferably, the portion of the two guide rails coupled with the ink carriage is formed of a ball bearing. The portion of the strut coupled with the ink carriage is formed of a ball bearing. 
     The junction of the two guide rails and the ink carriage and also the junction of the strut and the ink carriage are respectively formed of ball bearings. Accordingly, abrasion of these junctions is prevented to allow smooth travel of the ink carriage. 
     According to still another aspect of the present invention, an ink jet printer includes a shaft provided rotatably about a predetermined axis, a strut fixed to the shaft so as to move along an arc about the axis with the rotation of the shaft, an ink carriage having a plurality of ink nozzles spaying out ink in a direction parallel to the plane including the strut, and provided at a predetermined position from the shaft of the strut, and a sheet holding unit holding a sheet at the curvature defined by the relationship with the motion curvature of the ink carriage at a position opposite to the ink carriage. 
     Printing is carried out by the ink carriage moving along an arc. Therefore, the length of printing required in the horizontal direction can be reduced to allow reduction in the size of the ink jet printer. Also, complicated readout of image data is not required. Therefore, high-speed printout is allowed. 
     Preferably, the axial direction of the axis is in parallel with the direction of transportation of a sheet. 
     By this parallel arrangement, the direction of the motion of the ink carriage can be made orthogonal to the direction of transportation of a sheet. It is therefore not necessary to read out image data according to a complicated procedure to generate print data. Therefore, the printout speed can be improved. 
     Further preferably, the ink carriage has an ink eject plane where a plurality of ink nozzles are formed. The curvature of the ink eject plane is not more than the curvature of the sheet held by the sheet holding unit. 
     By such a curvature, the contact between the ink carriage and the sheet can be reduced. This provides the advantage that sheet jamming is relatively suppressed. 
     Further preferably, each of the plurality of ink nozzles ejects ink in the direction of the line connecting the center of the shaft and each ink nozzle. 
     This provides the advantage that the output direction of ink ejection and the direction of the centrifugal force is in coincidence. Therefore, control of the direction of ink ejection becomes easier. Additionally, the centrifugal force can be utilized in ink ejection to improve the ink ejection speed. 
     Further preferably, the ink carriage ejects ink by moving back and forth on the same line of a sheet. 
     By spraying out ink according to a reciprocation motion on the same line, a resolution two times that of ejecting ink at either the forward drive or the backward drive can be obtained. 
     The ink ejection timing of each of the plurality of ink nozzles is defined according to the distance from the center of the shaft to the ink nozzle, the distance between the ink carriage and the sheet, the position of the ink nozzle, and the speed of ink. 
     The ink hit position can be calculated according to various parameters. Accordingly, the ink ejection timing can be defined correctly. 
     Further preferably, the plurality of ink nozzles are arranged on a crossing line between the plane orthogonal to the direction of motion of the ink carriage and the ink eject plane. 
     By providing the ink nozzles in one row in a direction perpendicular to the direction of motion of the ink carriage, the printing resolution is defined depending on only the travel angle of the ink head. 
     Further preferably, a sheet size sensor that senses the size of a sheet is further provided. The swing angle of the strut is defined according to the output of the sheet size sensor. Therefore, unnecessary overrunning of the ink carriage can be prevented to allow efficient printout. 
     Further preferably, the sheet holding unit includes a transportation guide having a cross section of an arc with a concave plane opposite to the ink carriage, and a plurality of transportation rollers arranged to sandwich a sheet with a plane of the transportation guide opposite to the ink carriage. 
     The sheet is transported by a plurality of transportation rollers arranged circularly along the inner side of the transportation guide. Therefore, the sheet can be transported properly without meander. 
     Further preferably, the plurality of transportation rollers are jointly driven in the direction of motion of the ink carriage. This provides the advantage that the sheet can be transported uniformly. Therefore, sheet meander and delay in transportation to a certain position can be prevented. 
     Further preferably, each of the plurality of transportation rollers has a fusiform shape with a curvature smaller than the curvature of the sheet. 
     This provides the advantage that buckling of the sheet caused by contact with the end of a transportation roller can be prevented. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram to describe a runway portion, a printing region, and an overrun portion of a conventional ink jet printer. 
     FIG. 2 is a side view of the interior of a conventional ink jet printer. 
     FIG. 3 is a top view of the interior of an ink jet printer according to a first embodiment of the present invention. 
     FIG. 4 is a side view of the interior of the ink jet printer of the first embodiment. 
     FIG. 5 is a diagram to describe the printing region of an ink head  67 . 
     FIG. 6 is a diagram to describe the arrangement of ink heads  67 . 
     FIG. 7 is a top view of the interior of an ink jet printer according to a second embodiment of the present invention. 
     FIG. 8 is a side view of the interior of the ink jet printer of the second embodiment. 
     FIG. 9 is a diagram to describe the runway portion and the overrun portion of ink carriage  63 . 
     FIGS. 10A and 10B are diagrams to describe conversion of image data. 
     FIGS. 11A and 11B are diagrams to describe the method of producing print image data. 
     FIG. 12 is a flow chart of a printing operation of an ink jet printer. 
     FIG. 13 is a diagram to describe print image data. 
     FIG. 14 is a flow chart of a printing operation while carrying out a reception operation of an ink jet printer. 
     FIG. 15 is a top view of the interior of an ink jet printer according to a third embodiment of the present invention. 
     FIG. 16 is a side view of the interior of an ink jet printer according to the third embodiment. 
     FIGS. 17A and 17B are diagrams to describe image data conversion. 
     FIGS. 18A and 18B are diagrams to describe a method of producing print image data. 
     FIG. 19 is a diagram to describe print image data. 
     FIG. 20 is a top view of the interior of an ink jet printer according to a fourth embodiment of the present invention. 
     FIG. 21 is a side view of the interior of the ink jet printer of the fourth embodiment. 
     FIG. 22 is a diagram to describe the size of a heat generator. 
     FIG. 23 is a diagram to describe the direction of heated air generated from the heat generator. 
     FIG. 24 is a diagram to describe an ink undried portion at completion of printing. 
     FIG. 25 is a diagram to describe the mounting position of a heat generator. 
     FIG. 26 is a sectional view taken along line A—A of the heat generator of FIG.  25 . 
     FIG. 27 is a diagram to describe the size of a heat generator. 
     FIG. 28 is a diagram to describe the direction of heated air generated from a heat generator. 
     FIG. 29 is a top view of the interior of an ink jet printer according to a fifth embodiment of the present invention. 
     FIG. 30 is a side view of the interior of the ink jet printer of the fifth embodiment. 
     FIG. 31 is a diagram to describe an ink undried portion when printing is completed. 
     FIG. 32 is a diagram to describe the mounting position of a heat generator. 
     FIG. 33 is a top view of the interior of an ink jet printer according to a sixth embodiment of the present invention. 
     FIG. 34 is a side view of the interior of the ink jet printer of the sixth embodiment. 
     FIG. 35 is a sectional view of a strut and an ink carriage. 
     FIG. 36 shows the strut viewed from the direction of X1 of FIG.  35 . 
     FIG. 37 shows the strut viewed from the direction of X2 of FIG.  36 . 
     FIG. 38 shows the ink carriage viewed from the direction of X3 of FIG.  35 . 
     FIG. 39 shows ink carriage  154  viewed from the direction of X4 of FIG.  38 . 
     FIGS. 40-42 are flow charts of a printing operation of an ink jet printer. 
     FIG. 43 is a diagram to describe a manual feed sheet positioning member. 
     FIG. 44 is a diagram to describe the readout sequence of pixel values of image data by the ink jet printer of the first to fifth embodiments. 
     FIG. 45 is a side sectional view of an ink jet printer according to a seventh embodiment of the present invention. 
     FIG. 46 is a sectional view of the ink jet printer of FIG. 45 taken along line A—A. 
     FIGS. 47A-47C are diagrams to describe the relationship between the shape of the ink carriage and the shape of the transportation guide. 
     FIG. 48 is a diagram corresponding to the case where ink is ejected from an ink nozzle towards the major axis of the strut. 
     FIG. 49 is a diagram showing the relationship between the force acting on ink and the ink ejection direction. 
     FIG. 50 is a diagram corresponding to the case where ink is ejected in a direction of a line connecting the center of the shaft and an ink nozzle. 
     FIG. 51 is a diagram showing the relationship of the ink ejected position between the forward drive and the backward drive. 
     FIG. 52 is a diagram to describe the method of calculating an ink hit position. 
     FIGS. 53A and 53B are diagrams to show the relationship between sheet size and swing angle of the strut. 
     FIG. 54 is a flow chart of the printing process by an ink jet printer. 
     FIG. 55 shows ink nozzles arranged in one row in a direction orthogonal to the main scanning direction. 
     FIG. 56 is a cross sectional view of an ink jet printer according to an eighth embodiment of the present invention. 
     FIG. 57 is a sectional view of the ink jet printer of FIG. 56 taken along line A—A. 
     FIGS. 58A and 58B are diagrams to describe the arranged position of transportation rollers. 
     FIG. 59 is a diagram to describe the shape of a transportation roller. 
     FIG. 60 is a diagram showing the connection of transportation rollers by the same axis. 
     FIG. 61 is a diagram to describe arrangement of transportation rollers connected by the same axis. 
     FIGS. 62A-62C are diagrams to describe the contact position relationship between transportation rollers and a recording sheet delivered by the transportation rollers. 
     FIG. 63 is a diagram to describe the relationship between sheet size and transportation roller position. 
     FIG. 64 is a diagram representing air flow formed above and below a recording sheet. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An ink jet printer which is an embodiment of the present invention will be described hereinafter with reference to the drawings. 
     First Embodiment 
     Referring to FIGS. 3 and 4, an ink jet printer according to a first embodiment of the present invention includes a shaft  66 , an ink carriage  63  having a plurality of ink heads  67 , a strut  65  having one end rotatably connected to shaft  66  and the other end fixed to ink carriage  63 , a sheet tray  68  to store recording sheets  62 , a pickup roller  69  to take out a recording sheet  62  from sheet tray  68  one at a time, a transportation roller  70  to sequentially convey recording sheet  63  taken out by pickup roller  69 , and a control device (not shown) to control forwarding of recording sheet  62 , the motion of ink carriage  63 , and ink jetting from ink head  67 . 
     Ink carriage  63  includes an ink bottle and the like to store ink in addition to ink head  67 . 
     The printing region by ink head  67  will be described with reference to FIG.  5 . The reciprocating arc motion, i.e., back and forth swing, of strut  65  about shaft  66 , causes ink carriage  63  mounted at the leading end of strut  65  to move back and forth along an arc. By this reciprocating arc motion, an image is sequentially printed on recording sheet  62 . The motion range of ink carriage  63  in a printing operation is defined so that ink head  67 A located farthest from shaft  66  covers recording sheet  63 . The runway portion and overrun portion of ink carriage  63  are provided outside the printing motion range of ink carriage  63 . When ink head  67 A is located corresponding to the runway portion or the overrun portion, ink heads  67 B- 67 D located closer to shaft  66  than ink head  67 A do not spray out ink. For example, the region where ink head  67 D does not spray out ink on a recording sheet  62  is depicted as the hatched region  72  in FIG. 5. A maintenance mechanism  73  to clean ink head  67  and the like are provided on the overrun portion in the ink jet printer. 
     According to the ink jet printer of the present embodiment, the scanning trajectory of ink carriage  63  represents an arc, i.e., a circular segment. Therefore, the scanning speed differs for each ink head  67 . If the ink ejection cycle from all ink heads  67  is identical, deviation between printed dots will occur due to difference in the scanning speed. Therefore, the control device provides control to alter the ink ejection cycle for each of ink heads  67 A- 67 D. More specifically, the ink ejection cycle is delayed as towards ink head  67 A from ink head  67 D to solve the problem of deviation between printed out dots. 
     Referring to FIG. 6, ink heads  67  are arranged radially from shaft  66 . This arrangement allows ink heads  67  to be arranged in a honeycomb manner. Accordingly, the number and density of ink heads  67  arranged in ink carriage  63  can be increased. 
     In the above-described ink jet printer, ink carriage  63  carries out an arc motion. Therefore, even if the runway portion and the overrun portion of the same running distance as the conventional case are provided along the circular segment, the lateral widths of the runway portion and the overrun portion can be made smaller than those of the conventional ink jet printer. Therefore, the ink jet printer can be reduced in size. 
     Maintenance mechanism  73  is provided on a line of extension of the scanning trajectory of ink carriage  63  that carries out an arc motion. However, the motion width of ink carriage  63  in the horizontal direction can be defined by the radius of the arc motion, i.e., the length from shaft  66  to the leading end of ink carriage  63 . Therefore, the motion width of ink carriage  63  in the horizontal direction can be suppressed to approximately two time the length from shaft  66  to the leading end of ink carriage  63  even if maintenance mechanism  73  is provided. Therefore, a compact ink jet printer can be provided. 
     Second Embodiment 
     Referring to FIGS. 7 and 8, an ink jet printer according to a second embodiment of the present invention includes two shafts  66  arranged at a predetermined distance, an ink carriage  63  having a plurality of ink heads  67 , two struts  65  having one ends rotatably attached to respective shafts  66  and the other ends rotatably connected to ink carriage  63  with a predetermined distance therebetween, a sheet tray  68  for storing recording sheets  62 , a pickup roller  69  to take out a recording sheet  62  from recording tray  68  one at a time, a transportation roller  70  to sequentially transport recording sheet  62  taken out from pickup roller  69 , a control device (not shown) to control forwarding of recording sheet  62 , the motion of ink carriage  63  and ink jetting from ink head  67 , and a reception device (not shown) to receive image data. 
     Ink carriage  63  includes an ink bottle and the like to store ink in addition to ink head  67 . 
     The two shafts  66 , the two struts  65  and ink head  67  form a link mechanism. By respective reciprocating arc motions of the two struts  65  about the two shafts  66 , ink carriage  63  can carry out a reciprocating arc motion while maintaining the same posture as shown in FIG.  7 . Also, a runway portion and overrun portion of ink carriage  63  are provided outside the range of the printing motion of ink carriage  63 , as shown in FIG.  9 . 
     Referring to FIG. 10A, when image data  80  received by the reception device is used intact to printout onto recording sheet  62  by the ink jet printer of the present embodiment, an image with arc-like distortion as indicated by printing result  82  will be formed since the scanning trajectory of ink carriage  63  represents an arc. Therefore, referring to FIG. 10B the control device corrects image data  80  to produce print image data  84  from which printing is carried out on recording sheet  62 . Accordingly, a printed result  86  eliminated of distortion is formed on recording sheet  62 . 
     The method of producing print image data  84  will be described with reference to FIGS. 11A and 11B. Image data  80  received by the reception device corresponds to image data of a rectangle with (X0, Y0)−(Xm, Yn) as a diagonal. The coordinates on print image data  84  corresponding to coordinates (Xp, Yp) in image data  80  can be represented as (Xp, Yp+R(Xp)). In other words, the Y coordinates is altered by a value R(Xp) defined by a coordinate value Xp whereas the X coordinate does not change. The line passing through (X0, Y0), (X(m/2), Y0) and (Xm, Y0) on image data  80  is converted into a concave arc curved line passing through (X0, Yp+R(X0)), (X(m/2), Yp+(R (X(m/2)))) and (Xm, Yp+R(Xm)) on print image data  84 . The curvature of this concave arc curved line is identical to the curvature of the convex arc curved line corresponding to the scanning trajectory of ink carriage  63 . 
     By carrying out printing based on print image data  84  obtained as described above, an image absent of arc-like distortion can be formed on recording sheet  62  transported in the direction from shaft  66  towards ink carriage  63 . 
     The printing operation of the ink jet printer will be described with reference to FIG.  12 . The control device clears the memory for reception (not shown) provided in the ink jet printer to receive image data  80  and the memory for printing (not shown) in which print image data  84  is stored (S 1 ). 
     The reception device receives and stores image data  80  of one page in the reception memory (S 2 ). When the received image data  80  does not correspond to bit map data, a process for conversion into bit map data is applied. 
     The control device converts image data  80  of one page into print image data  84  according to the above-described method, and then stores print image data  84  in the print memory (S 3 ). 
     The control device sets the value of a counter (not shown) to 1 (S 4 ). The control device reads out print image data D(t) required for one scan of ink carriage  63  from the print memory, and printing is carried out according to print image data D(t) (S 5 ). This print image data D(t) will be described afterwards. 
     The control device determines whether printing of one page has been completed or not (S 6 ). When printing of one page has ended (YES at S 6 ), the printing process ends. When the printing of one page has not yet ended (NO at S 6 ), the counter is incremented by one (S 7 ), and the process of S 4  onward is repeated. 
     Print image data D(t) will be described with reference to FIG.  13 . Assuming that the number of pixels required in one scanning operation of ink carriage  63  is h in the Y direction (the transportation direction of recording sheet  62 ), print image data D(t) required at the t-th scanning operation of ink carriage  63  corresponds to data of a rectangular region with (x0, y(h×(t−1)))−(xm, y(h×t−1)) in print image data  84  as the diagonal. 
     When the reception device is connected to a scanner, a facsimile, or the like, image data is received for every one line or every several lines. In this case, the printing speed can be improved since a printing operation can be carried out while receiving image data. Since it is no longer necessary to wait for the reception and storage of image data of one complete page, the running cost of the ink jet printer can be reduced. 
     The operation of carrying out printing while receiving data will be described with reference to FIG.  14 . The control device clears the print memory (S 11 ), and then clears the reception memory (S 12 ). The control device determines whether reception of image data  80  of one page has ended or not (S 13 ). When reception of image data  80  of one page is not yet ended (NO at S 13 ), the reception device receives and stores image data  80  of one line into the reception memory (S 14 ). When the received image data  80  is not bit map data, a process for conversion into bit map data is applied. 
     The control device converts image data  80  of one line according to the above-described method, and then additionally stores the converted data into the print memory (S 15 ). 
     The control device determines whether print image data  84  required for one scanning operation of ink carriage  63  has been accumulated in the print memory (S 16 ). When print image data  84  required for one scanning operation has not yet been stored (NO at S 16 ), control returns to S 12  to repeat the process of S 12  onward until print image data  84  required for one scanning operation has been accumulated. 
     When print image data  84  required for one scanning operation has been accumulated (YES at S 16 ), the control device reads out print image data D( 1 ) from the print memory to carry out printing according to print image data D( 1 ) (S 17 ). 
     For the next printout, the control device sequentially stores print image data D(t) as print image data D(t−1) until there is no more print image data D(t) (t≧2) stored in the print memory (S 18 ). In other words, the data to be printed next is stored as print image data D( 1 ). Then, the process of S 12  is repeated. 
     When reception of image data  80  of one page has ended (YES at S 19 ), the control device determines whether there is print image data D( 1 ) remaining(S 19 ). When there is no more print image data D( 1 ) (NO at S 19 ), the control device ends the process. When there is more print image data D( 1 ) (YES at S 19 ), the control device reads out print image data D( 1 ) from the print memory to carry out printing (S 20 ). Then, the process ends. 
     In the above-described ink jet printer, ink carriage  63 , two struts  65  and shafts  66  form a link mechanism. Therefore, ink carriage  63  can carry out a reciprocating arc motion under the same posture. Therefore, even if the runway portion and the overrun portion of the same running distance as the conventional case are provided along the circular segment, the lateral widths of the runway portion and the overrun portion can be made smaller than those of the conventional ink jet printer. Therefore, the size of the ink jet printer can be reduced. Furthermore, the scanning speed of all ink heads  67  is identical since ink carriage  63  moves while maintaining the same posture. Therefore, the problem of deviation between dots during printing caused by difference in the scanning speed between ink heads  67  is eliminated. 
     The printing process is carried out after the image data is converted according to an arc on the basis of the curvature of the trajectory of the reciprocating arc motion of ink carriage  63 . Therefore, printing with no arc-like distortion is allowed even when ink carriage  63  moves along an arc. 
     When image data can be obtained only for every one line or every several lines such as image data obtained via facsimile and the like, image data is received and subjected to the conversion process for every one line or a plurality of lines, followed by a print process. Accordingly, the capacity of the reception memory can be reduced. 
     Third Embodiment 
     Referring to FIGS. 15 and 16, an ink jet printer according to a third embodiment of the present invention includes two shafts  66  arranged at a predetermined distance, an ink carriage  63  having a plurality of ink heads  67 , two struts  65  having one ends respectively coupled rotatably to two shafts  66  and the other ends rotatably coupled to ink carriage  63  with a predetermined distance, a sheet tray  68  to store recording sheets  62 , a pickup roller  69  to take out a recording sheet  62  one at a time from sheet tray  68 , a transportation roller  70  to sequentially convey recording sheet  62  output from pickup roller  69 , a control device (not shown) to control forwarding of recording sheet  62 , the motion of ink carriage  63 , and ink jetting from ink head  67 , and a reception device (not shown) to receive image data. 
     Ink carriage  63  includes an ink bottle and the like to store the ink in addition to ink head  67 . 
     The ink jet printer of the present embodiment differs in the travel direction of printing sheet  62  from that of the ink jet printer of the second embodiment. More specifically, recording sheet  62  is shifted in the direction from shaft  66  to ink carriage  63  in the ink jet printer of the second embodiment whereas recording sheet  62  is shifted in the direction from ink carriage  63  to shaft  66  in the ink jet printer of the third embodiment. 
     Referring to FIG. 17A, an image with arc-like distortion will be formed as shown by print result  82  if printing is carried out by the ink jet printer of the present embodiment using intact image data  80  received at the reception device since the scanning trajectory of ink carriage  63  corresponds to an arc. Therefore, the control device corrects image data  80  to generate print image data  84  from which printing is carried out on recording sheet  62 . As a result, a print result  86  absent of distortion is formed on recording sheet  62 , as shown in FIG.  17 B. 
     The method of producing print image data  84  will be described with reference to FIGS. 18A and 18B. Image data  80  received at the reception device corresponds to image data of a rectangle with (X0, Y0)−(Xm, Yn) as the diagonal. The coordinates on print image data  84  corresponding to coordinates (Xp, Yp) in image data  80  can be represented as (Xp, Yp−R(Xp)). In other words, the Y coordinates is altered by a value R(Xp) defined by the coordinate value Xp whereas there is no change in the X coordinates. The line passing through (X0, Y0), (X(m/2), Y0) and (Xm, Y0) on image data  80  is converted into a convex curved line passing through (X0, Yp−R(X0)), (X(m/2), Yp−(R (X(m/2)))) and (Xm, Yp−R(Xm)) on print image data  84 . The curvature of this convex curved line is identical to the curvature of the convex curved line corresponding to the scanning trajectory of ink carriage  63 . 
     By carrying out printing using print image data  84  obtained as described above, an image with no arc-like distortion can be formed similar to the received image data on recording sheet  62  conveyed in the direction from shaft  66  to ink carriage  63 . 
     The printout operation by the ink jet printer of the present embodiment is similar to that of the second embodiment described with reference to FIGS. 12-14, provided that the method of generating print image data  84  is carried out as described above. Therefore, details of the printout operation will not be repeated. Print image data D(t) required in one scanning operation of ink carriage  63  for the process of S 5  in FIG. 12 is shown in FIG.  19 . More specifically, assuming that the number of pixels in the Y direction (the direction of transportation of recording sheet  62 ) required in one scanning operation of ink carriage  63  is h, print image data D(t) required in the t-th scanning operation of ink carriage  63  corresponds to data in a rectangular region with (x0, y(h×(t−1)))−(xm, y(h×(t−1))) of print image data  84  as the diagonal. 
     In the above-described ink jet printer, an arc motion is carried out with ink carriage  63  at the same posture. Therefore, even if the runway portion and the overrun portion of the same running distance as the conventional case are provided along the circular segment, the lateral widths of the runway portion and the overrun portion can be made smaller than those of the conventional ink jet printer. Thus, the ink jet printer can be reduced in size. Also, the running speed of all ink heads  67  is identical since ink carriage  63  is moved while maintaining the same posture. Therefore, the problem of deviation between dots during printing caused by difference in the scanning speed between ink heads  67  is eliminated. 
     The printout process is carried out after the image data is converted according to an arc on the basis of the curvature of the trajectory of the reciprocating arc motion of ink carriage  63 . Therefore, printing with no arc-like distortion is allowed even if ink carriage  63  moves along an arc. 
     In the case where image data can be obtained only for every one line or every several lines such as image data obtained through facsimile and the like, the image data is received and subjected to conversion for every one line or every several lines, followed by a printing process. Accordingly, the capacity of the reception memory can be reduced. 
     Fourth Embodiment 
     Referring to FIGS. 20 and 21, an ink jet printer according to a fourth embodiment of the present invention corresponds in structure to the ink jet printer of the third embodiment described with reference to FIGS. 15 and 16, further including a heat generator  110  provided at the two struts  65 . Heat generator  110  generates hot air or infrared rays from a heat generation vent  112  to dry ink on recording sheet  62 . 
     The method of producing print image data and the printout operation of the ink jet printer of the fourth embodiment are similar to those of the third embodiment. Therefore, description thereof will not be repeated. 
     Referring to FIG. 22, print ink on recording sheet  62  output from ink carriage  63  is dried by the heat generated from heat generation vent  112  of heat generator  110  when located beneath heat generator  110  according to transportation of recording sheet  62 . Referring to FIG. 23, the heated air is directed downwards as shown by arrow  120 . Heat generator  110  dries ink on recording sheet  62  by moving back and forth along an arc similar to the motion of ink carriage  63 . It is to be noted that the radius of the reciprocating arc motion of heat generator  110  is smaller than the radius of the reciprocating arc motion of ink carriage  63 . The lateral width of heat generator  110  is defined so that heated air can be delivered up to the left and right corners of the print region of recording sheet  62  when ink carriage  63  is located at respective leftmost and rightmost ends of the print region. 
     Referring to FIG. 24, recording sheet  62  moves in the direction from ink carriage  63  to heat generator  110 . Therefore, an undried region  130  located between ink carriage  63  and heat generator  110  is present at the stage when printing by ink carriage  63  ends. The control device effects the reciprocating arc motion of heat generator  110  for a predetermined period of time even after printing by ink carriage  63  ends to dry this region  130 . 
     In drying ink printed on recording sheet  62 , the heat of the hot air or infrared rays from heat generator  110  is to be applied only to the area where there is ink. Therefore, the control device controls the operation of heat generator  110  so that heat is applied only to the portion where ink is present and not to the portion where there is no ink. The control device determines the presence of ink according to the print image data stored in the print memory. When the area printed out by ink carriage  63  arrives at the position beneath heat generator  110 , the control device actuates heat generator  110  to provide heat to that area. When the area that has no print out by ink carriage  63  is located at the position below heat generator  110 , the control device disables heat generator  110  to inhibit heat towards that area. It is to be noted that heat is not generated instantly. The control device controls the operation of heat generator  110  taking into consideration the time required for heat to be generated for drying ink subsequent to actuation of heat generator  110 . 
     The position of mounting heat generator  110  will be described with reference to FIG.  25 . Heat generator  110  is provided at a position relatively close to ink carriage  63 . The heat generated by heat generator  110  per se and the hot air or infrared rays generated from heat generator  110  may adversely affect the ink in the ink tank or ink head  67 . Therefore, the distance between heat generator  110  or heat generation vent  112  and the ink tank or ink head  67  is defined to correspond to a temperature of a level at which the ink in the ink tank or ink head  67  is not modified in quality or not coagulated. 
     There is a possibility that the heat generated by heat generator  110  per se or the extra heat or infrared rays generated from heat generator  110  causes deformation of recording sheet  62  and modification in the quality of the ink on the recording sheet  62 . Therefore, the distance between heat generator  110  or heat generation vent  112  and recording sheet  62  is defined so as to obviate deformation of recording sheet  62  and modification in the quality of the ink on recording sheet  62 . 
     There is also the case where the ink in the ink tank or ink head  67  is modified in quality or coagulated depending upon the direction of the hot air or infrared rays generated from heat generator  110 . This may distort the spray out trajectory of ink ejected from ink head  67  to result in disturbance in the image or text printed out. Therefore, the heat generation direction from heat generator  110  is set to a direction away from ink carriage  63 , i.e., set to the travel direction of recording sheet  62 . 
     A movable unit such as a fan is provided in heat generator  110  to generate hot air from heat generation vent  112 . Heat generator  110  vibrates during operation. Therefore, this vibration is conveyed to ink carriage  63  and ink head  67  through strut  65  to which heat generator  110  is mounted. This may cause erroneous spray out of ink or disturbance in the text or image printed out. Therefore, a vibration absorption member  140  to absorb the vibration of heat generator  110  is attached between heat generator  110  and the two struts  65 . 
     In the previous FIG. 22, the lateral width of heat generator  110  is defined so that the range of movement of heat generator  110  covers the print area. However, a heat generator  110  of a small lateral width as shown in FIG. 27 can be used to dry the entire recording sheet  62  instead of heat generator  110  of a large lateral width. Referring to FIG. 27, the width of the lateral movement of ink carriage  63  is set equal to the width of the printing plane of recording sheet  62 . However, the width of the lateral movement of heat generator  110  becomes smaller than the width of the lateral movement of ink carriage  63 . Therefore, the direction of hot air generated from heat generator  110  is set radially as shown by arrow  120  in FIG.  28 . Therefore, hot air can be applied at a width greater than the width of the lateral movement of heat generator  110  to allow the entire recording sheet  62  to be dried. 
     The above-described ink jet printer provides the advantages set forth in the following in addition to the advantages of the ink jet printer of the third embodiment. Heat generator  110  provided between shaft  66  and ink carriage  63  carries out a reciprocating arc motion in synchronization with the reciprocating arc motion of ink carriage  63 . Therefore, by virtue of the heat discharged from heat generator  110 , the ink sprayed out on recording sheet  62  can be dried parallel to the printout operation. Since heat generator  110  per se moves, the entire recording sheet  62  can be dried even if heat generator  110  is reduced in size. Accordingly, power consumption and the amount of heat discharged from heat generator  110  can be reduced. Therefore, the exhaust fan to discharge heat outwards is dispensable to allow reduction in the size of the ink jet printer. 
     Also, heat generator  110  is increased in size and the direction of the heated air generated from heat generator  110  is set radially in order to provide hot air all over the print region of recording sheet  62 . Also, heat generator  110  is operated for a predetermined period of time after printout ends. Accordingly, the ink on the entire printout plane can be dried before recording sheet  62  is output. Therefore, this can prevent the printout plane being smudged by the overlay of output recording sheets  62 . 
     Furthermore the power consumed by heat generator  110  can be reduced than that of the case where the entire recording sheet  62  is dried by drying only the area where ink is output. Also, the amount of heat generated from heat generator  110  can be reduced. Therefore, heat generator  110  per se can be made smaller and the space for exhausting the heat from the ink jet printer can be reduced. Therefore, the entire size of the ink jet printer can be reduced. 
     By mounting heat generator  110  at an appropriate position, the problem of the ink in the ink tank or ink head  67  being modified in quality or coagulated is eliminated. Also, recording sheet  62  is not deformed and the quality of the ink printed on recording sheet  62  is not modified. 
     By setting the direction of the hot air or infrared rays generated from heat generator  110  farther away from ink carriage  63 , the ink in the ink tank or ink head  67  will not be modified in quality or coagulated. Disturbance in the printed out image or text caused by distortion of the spray out trajectory of ink from ink head  67  is no longer seen. 
     By providing vibration absorption member  140  between heat generator  110  and strut  65 , vibration of ink carriage  63  can be prevented to eliminate the problem of erroneous spray out of ink and disturbance in the printed text and image. 
     Fifth Embodiment 
     Referring to FIGS. 29 and 30, an ink jet printer according to a fifth embodiment of the present invention corresponds to the structure of the ink jet printer of the second embodiment described with reference to FIGS. 7 and 8, further including a heat generator  110  at the leading end of ink carriage  63 . Heat generator  110  generates hot air or infrared rays from heat generation vent  112  to dry the ink on recording sheet  62 . 
     The print image data generation method and printout operation of the ink jet printer are similar to those of the second embodiment. Therefore, description thereof will not be repeated. 
     The lateral width of heat generator  110  is defined so that hot air or infrared rays can be emitted in the printing range when ink carriage  63  carries out printing in the printing range of recording sheet  62 . 
     Referring to FIG. 31, recording sheet  62  is transferred in the direction from ink carriage  63  to heat generator  110 . When printing by ink carriage  63  ends, an undried region  132  located between ink carriage  63  and heat generator  110  remains. Therefore, the control device causes heat generator  110  to continue the reciprocating arc motion for a predetermined period of time even after printing by ink carriage  63  ends in order to dry region  132 . 
     The control device of the fifth embodiment controls heat generator  110  to apply heat or infrared rays only to the area with ink on recording sheet  62 , similar to the control device of the fourth embodiment. 
     The position of mounting heat generator  110  will be described with reference to FIG.  32 . Similar to the mounted position of heat generator  110  described with reference to FIG. 25, the distance between heat generator  110  and ink carriage  63  is defined to avoid modification of the quality or coagulation of the ink in the ink tank or ink head  67 . Also, the distance between heat generator  110  and recording sheet  62  is defined to prevent deformation of recording sheet  62  and to prevent modification of the quality of the ink on recording sheet  62 . Furthermore, the heat generation direction from heat generator  110  is set to become farther away from ink carriage  63 , i.e., set in the direction of the transfer of recording sheet  62 , to prevent ink quality modification or ink coagulation in the ink tank or ink head  67  and to prevent distortion of the spray out trajectory of the ink output from ink head  67 . 
     In order to prevent erroneous spray out of ink from ink head  67  or disturbance of the printed out text or image due to vibration of the movable unit in heat generator  110  such as a fan, a vibration absorption member  140  is connected between ink carriage  63  and heat generator  110 . 
     The above-described ink jet printer can provide advantages similar to those of the ink jet printer of the fourth embodiment. 
     Sixth Embodiment 
     Referring to FIGS. 33 and 34, an ink jet printer according to a sixth embodiment of the present invention includes a shaft  66 , two parallel guide rails  150  and  152 , an ink carriage  154  that can run along two guide rails  150  and  152  having a plurality of ink heads  67  and an opening  156  with the direction orthogonal to the running direction as the longitudinal direction, a strut  158  having one end coupled rotatably to shaft  66  and the other end fitted with opening  156  in a movable manner, a sheet tray  68  to store recording sheets  62 , a pickup roller  69  to take out a recording sheet  62  from sheet tray  68  one by one, a transportation roller  70  to sequentially transfer a recording sheet  62  taken out by pickup roller  69 , a control device (not shown) to control forwarding of recording sheet  62 , the motion of ink carriage  63 , and ink jetting from ink head  67 , and a reception device (not shown) to receive image data. 
     The portion of the two guide rails  150  and  152  coupled with ink carriage  154  is formed of a ball bearing. The portion of strut  158  coupled with ink carriage  154  is formed of a ball bearing. FIG. 35 is a sectional view of strut  158  and ink carriage  154  of FIG. 33 taken along line Y-Y′. FIG. 36 is a diagram of strut  158  viewed from the direction of X1 of FIG.  35 . FIG. 37 is a diagram of strut  158  viewed from the direction of X2 of FIG.  36 . FIG. 38 is a diagram of ink carriage  154  viewed from the direction of X3 of FIG.  35 . FIG. 39 is a diagram of ink carriage  154  viewed from the direction of X4 of FIG.  38 . 
     Strut  158  and opening  156  of ink carriage  154  are fitted together by a fit member  162 . Ink carriage  154  includes an ink bottle to store ink in addition to ink head  67 . 
     The ink jet printer of the first to fifth embodiments carry out printing while moving along an arc in order to narrow the lateral widths of the runway portion and the overrun portion. However, printing cannot be carried out using the intact image data due to the arc motion. A particular image process such as that described in the second embodiment is required. The ink jet printer of the present embodiment is directed to carry out printing using the intact image data while reducing the lateral widths of the runway portion and the overrun portion by converting the arc motion into linear motion. 
     Ink carriage  154  moves along guide rails  150  and  152 . The arc motion of strut  158  is divided into the vertical motion of fitting member  162  and the lateral motion of ink carriage  154 . 
     The printing operation of the ink jet printer of the present embodiment will be described with reference to FIG.  40 . The control device receives a print request by a computer and the like connected to the ink jet printer (S 31 ). Following reception of the print request, the reception device receives image information from the computer and the like (S 32 ). The control device determines the image size on the basis of the received data (S 33 ). The control device determines the amplitude of strut  158  according to the image size (S 34 ). The control device conveys recording sheet  62  from sheet tray  68  (S 35 ). The control device selects data for every one line from the image information to prepare data to be printed out by ink head  67  (S 36 ). The reception device determines whether recording sheet  62  has arrived at the printout portion or not (S 37 ). When recording sheet  62  has not arrived at the printout portion (NO at S 37 ), the process of S 35  onward is repeated. 
     When recording sheet  62  has arrived at the printing portion (YES at S 37 ), the control device drives strut  158  to carry out a reciprocating arc motion. Printing of one page is effected on recording sheet  62  according to the prepared data (S 38 ). The control device determines whether there is data left to be printed out (S 39 ). When there is data to be printed out (YES at S 39 ), the process of S 36  onward is repeated. When there is no data to be printed out (NO at S 39 ), the control device determines whether to print out the next page (S 40 ). When the next page is to be printed out (YES at S 40 ), the process of S 32  onward is repeated. When there is no next page to be printed out (NO at S 40 ), the control device ends the process. 
     Another embodiment of the printing operation by the ink jet printer will be described with reference to FIG.  41 . The process of S 31 -S 32  and the process of S 35  are similar to those of FIG.  40 . Therefore, description thereof will not be repeated. Following the process of S 35 , the control device detects the sheet width of recording sheet  62  that is currently transported by a sensor not shown (S 41 ). The control device determines the amplitude of strut  158  corresponding to the detected sheet width (S 42 ). Then, the process of S 36 -S 40  is carried out. Since the process of S 36 -S 40  is similar to that of FIG. 40, details thereof will not be repeated. 
     A still further embodiment of the printing operation of the ink jet printer will be described with reference to FIG.  42 . The process of S 31 -S 32  is similar to that of FIG.  40 . Therefore, description thereof will not be repeated. Following the process of S 32 , the control device determines whether a sheet is fed out from sheet tray  68 (S 51 ). When a sheet is fed out from sheet tray  68  (YES at S 51 ), the control device determines the size of recording sheet  62  according to the information from a positioning member (not shown) to measure the size of recording sheet  62  stored in sheet tray  68 . When a sheet is not fed out from sheet tray  68  (NO at S 51 ), the control device determines whether a sheet is fed manually (S 52 ). When a sheet is fed manually (YES at S 52 ), the size of recording sheet  62  is determined according to the information of the fixed position from a manual feed sheet positioning member  174  provided in sheet tray  172  as shown in FIG. 43 to hold recording sheet  62  (S 54 ). When a sheet is not fed from sheet tray  68  or from sheet tray  172  (NO at S 52 ), the control device repeats the process of S 51 . 
     Upon determination of the size of recording sheet  62  by the process of S 53  or S 54 , the control device conveys recording sheet  62  from sheet tray  68  or sheet tray  172  (S 55 ). The control device determines the amplitude of strut  158  according to the sheet size (S 56 ). Then, the process of S 36 -S 40  is carried out. The process of S 36 -S 40  is similar to that of FIG. 38, and details thereof will not be repeated. 
     As mentioned before, ink carriage  154  moves along two guide rails  150  and  152  to carry out printing while moving linearly. The scanning operation of ink carriage  154  is effected by the reciprocating arc motion of strut  158 . The reciprocating arc motion of strut  158  is divided into the vertical linear motion of strut  158  moving in opening  156  of ink carriage  154  and the lateral linear motion of ink carriage  154  running along guide rails  150  and  152 . Therefore, even if the runway portion and the overrun portion of the same running distance as the conventional case are provided along the circular segment, the lateral widths of the runway portion and the overrun portion can be made smaller than those of the conventional ink jet printer. Thus, the width of the lateral movement of ink carriage  154  can be reduced to allow reduction in the size of the ink jet printer. 
     The portion of the two guide rails  150  and  152  coupled with ink carriage  154  is formed of a ball bearing. The portion of strut  158  coupled with ink carriage  154  is formed of a ball bearing. Therefore, the movement of ink carriage  154  is carried out smoothly. 
     Since the control device determines the amplitude of strut  158  according to the image size, high speed print out is allowed without any extra reciprocating motion of ink carriage  154 . 
     Furthermore, the movement of ink carriage  154  is controlled according to the size of recording sheet  62 . Therefore, the range of movement of ink carriage  154  in the printing operation can be limited to that within recording sheet  62 . Therefore, extra motion of ink carriage  154  is eliminated. Thus, printing can be carried out at high speed. 
     Seventh Embodiment 
     The ink jet printer of the first to fifth embodiments must read out the pixel value according to the scanning direction of ink carriage  63  as shown in FIG.  44 . For example, the pixel value must be read out in a particular sequence such as pixels  3 - 9 ,  2 - 8 ,  1 - 7 ,  1 - 6 ,  1 - 5 ,  1 - 4 ,  1 - 3 ,  2 - 2 ,  3 - 1 . Therefore, complicated readout must be carried out in producing print data. For the purpose of printing out at high speed, print data must be generated in advance and stored in a region differing from the memory region of the image data. 
     The ink jet printer of the seventh embodiment is directed to a compact ink jet printer that does not have to read out the pixel values in a particular sequence. 
     Referring to FIGS. 45 and 46, an ink jet printer according to the seventh embodiment includes a sheet cassette  206  storing recording sheets  62 , a printer unit  182  to print out on recording sheet  62 , and a control device (not shown) to control the motion of ink carriage  186  and the ink ejected from ink carriage  86 . 
     Sheet cassette  206  includes a side guide  198  to hold recording sheet  62  in an arc manner, a rack  204  and a pinion  202 , and sheet size sensors  200 A,  200 B and  200 C to detect whether the size of recording sheet  62  is B4, A4, or B5. 
     Printer unit  182  includes a transportation guide  195  partially intruding into sheet cassette  206 , and formed of a portion of a cylinder to hold recording sheet  62  in an arc manner, a sheet bail  196  for pressing recording sheet  62  placed on transportation guide  195 , a pickup roller  192  to take out recording sheet  62  held by sheet bail  196  one by one, a transportation roller  190  and a guide roller  188  sandwiching recording sheet  62  with transportation guide  195  to guide recording sheet  62  to a position facing ink carriage  186  while maintaining the same curvature with transportation guide  195 , a shaft  212  provided rotatably about a predetermined axis, a strut  184  fixed to shaft  212  to move along an arc about the axis with the rotation of shaft  212 , and an ink carriage  186  provided at a predetermined position from shaft  212  of strut  184 . 
     Ink carriage  186  carries out an arc motion about shaft  212  to eject ink onto recording sheet  62  bent in an arc manner. 
     The relationship between the shape of ink carriage  186  and the shape of transportation guide  195  will be described with reference to FIGS. 47A-47C. As mentioned above, the cross section of transportation guide  195  corresponds to an arc segment. Therefore, the shape of the ink eject plane of ink carriage  186  corresponds to an arc having a curvature smaller than the curvature of transportation guide  195  as shown in FIG. 47A, or a curvature identical to that of transportation guide  195  as shown in FIG.  47 B. If the configuration of the ink eject plane of ink carriage  186  is set to a curve that has a curvature greater than the curvature of transportation guide  195 , the end of ink carriage  186  will easily come into contact with recording sheet  62  to cause sheet jam. A structure with the less possibility of sheet jamming is provided by setting the curvature of the ink eject plane smaller than the curvature of transportation guide  195 . 
     The direction of ink ejection from the plurality of ink nozzles  214  of ink carriage  186  will be described. Consider the case where ink is ejected from each ink nozzle  214  in a direction  222  parallel to the major side of strut  184  as shown in FIG.  48 . Referring to FIG. 49, the centrifugal force ( 2 ) and inertia force ( 3 ) are applied in addition to the ink ejecting force ( 1 ) when ink is output from ink nozzle  214 . Therefore, ink  224  is sprayed out in the direction of the resultant force ( 4 ) of ejection force ( 1 ), centrifugal force ( 2 ), and inertia force ( 3 ). The direction of centrifugal force ( 2 ) and inertia force ( 3 ) differs depending upon the position of ink nozzle  214 . However, ink ejection force ( 1 ) always acts in a constant direction irrespective of the position of ink nozzle  214 . Therefore, control of the ink hit position of ink  224  is difficult since the level of resultant force ( 4 ) differs from each of ink nozzles  214 . Therefore, the direction of ink ejection force ( 1 ) is defined in the direction of the line connecting the center of shaft  212  and ink nozzle  214 , as shown in FIG.  50 . Accordingly, the direction of ink ejection force ( 1 ) matches the direction of centrifugal force ( 2 ), so that the magnitude of resultant force ( 4 ) is always constant. This facilitates the control of the hit position of ink  224 . In addition to ejection force ( 1 ) of ink  224 , centrifugal force ( 2 ) can be used for ink  224  ejection. Thus, the ejection speed of ink  224  can be improved. 
     Ink carriage  186  sprays out ink while moving back and forth along an arc. By moving ink carriage  186  in a reciprocating manner on the same line on recording sheet  62  and ejecting ink according to the same image data, the resolution can be doubled than the case where ink is ejected in either the forward drive or the backward drive of ink carriage  186 . 
     The ink ejection direction is affected by the inertia force ( 3 ) of ink carriage  186 . Therefore, the ink hit position will differ between the forward drive and the backward drive even with respect to ink ejected at the same position. Therefore, ink is ejected by shifting the angle by just θ between the ink ejection position of the forward drive and the ink ejection position of the backward drive to obtain the same ink hit position  232 , as shown in FIG.  51 . 
     The method of calculating the hit position of ink  224  will be described with reference to FIG.  52 . It is assumed that the curvature of the ink ejection plane of ink carriage  186  is equal to the curvature of recording sheet  62 . The distance from ink nozzle  214  to recording sheet  62  is a constant value L 1  irrespective of the position of ink nozzle  214 . When the angle of the line connecting shaft  212  and ink nozzle  214  with respect to strut  184  is a, it is considered that a takes a sufficient small value. Therefore, the distance from shaft  212  to ink nozzle  214  can be considered to correspond to a constant value L 2 . When it is assumed that ink  224  is hit on recording sheet  62  by means of only ink ejection force ( 1 ) and centrifugal force ( 2 ) neglecting inertia force ( 3 ), the distance L 3  from the crossing of the line of extension of the axis of strut  184  and recording sheet  62  to the hit position of ink  224  is represented by: 
     
       
           L   3 =( L   1 + L   2 )×sin α 
       
     
     The ink spray out time T is represented as: 
     
       
           T=L   1 / V   1   
       
     
     neglecting the friction of air and gravity. Here, V 1  is the speed of ink  224  applied by ink ejection force ( 1 ) and centrifugal force ( 2 ). 
     Assuming that the speed of ink  224  by inertia force ( 3 ) is V 2 , the distance L 4  of ink  224  proceeding within time T affected by inertia force ( 3 ) is represented as: 
     
       
           L   4 = V   2 × T   
       
     
     Therefore, the distance L from the crossing position of the line of extension of shaft  212  and recording sheet  62  to the hit position of ink  224  can be represented as: 
     
       
           L=L   3 + L   4 =( L   1 + L   2 )×sin α+ L   1 × V   2 / V   1   
       
     
     in approximation. Therefore, the ink ejection timing can be calculated taking into consideration distance L. 
     Referring to FIGS. 45 and 46 again, sheet size sensors  200 A- 200 C detect the presence of light reflected from the light emitted from itself. The control device determines that the size of recording sheet  62  set at sheet cassette  206  is B4 when all the sheet size sensors  200 A- 200 C receive reflected light. When sheet size sensor  200 A does not receive reflected light and sheet size sensors  200 B and  200 C receive reflected light, determination is made that the size of recording sheet  62  is A4. When only sheet size sensor  200 C receives reflected light, determination is made that the size of recording sheet  62  is B5. The control device determines the swing angle of strut  184  according to the size of recording sheet  62 . Referring to FIG. 53A, the swing angle of strut  184  is set small when recording sheet  62  is of a small size such as B 5 . Referring to FIG. 53B, the swing angle of strut  184  is set to a large value when the size of recording sheet  62  is of a large size such as B4. By adjusting the swinging width of strut  184  depending upon the size of recording sheet  62 , extra overrun of ink carriage  186  can be prevented to allow print out to be carried out efficiently. 
     The operation of the ink jet printer will be described with the reference to FIG.  54 . When a print request is transmitted to the control device (S 92 ), the control device receives image data of one page from a computer connected to the ink jet printer (S 94 ). The control device determines the size of recording sheet  62  by the received image data (S 96 ). The amplitude of strut  184  is defined according to the size of recording sheet  62  (S 98 ). The orientation of image data is modified according to recording sheet  62  (S 100 ). A recording sheet  62  is conveyed from sheet cassette  206  (S 102 ). If recording sheet  62  arrives at the printer unit (YES at S 104 ), image data is transmitted to ink carriage  186  for every one line (S 106 ). Ink is ejected for printing according to the image data while ink carriage  186  moves along an arc (S 108 ). The process of S 106 -S 108  is repeated until there is no more image data of the next line (S 110 ). When printing of one page ends (NO at S 110 ), recording sheet  62  is discharged (S 112 ). Then, determination is made whether there is image data to be printed out (S 114 ). If there is image data to be printed out (YES at S 114 ), the process of S 94  onward is repeated. If there is no image data to be printed out (NO at S 114 ), the process ends. 
     As shown in FIG. 55, ink nozzles  214  can be arranged in one row in a direction orthogonal to the main scanning direction. In this case, the printing resolution is defined exclusively by the movement angle of the ink head. The main scanning direction is the direction of motion of ink carriage  186 . 
     According to the ink jet printer of the present invention, printing is carried out by ink carriage  186  moving along an arc. Therefore, the length in the lateral direction required for printing can be reduced to allow a compact ink jet printer to be provided. Complicated readout of data as in the ink jet printer of the first to fifth embodiments in which the ink carriage moves along an arc is not required. High speed printing is allowed. 
     Eighth Embodiment 
     Referring to FIGS. 56 and 57, an ink jet printer according to an eighth embodiment of the present invention includes a sheet cassette  251  storing recording sheets  62 , a transportation guide  195  formed of a portion of a cylinder for holding recording sheet  62  output from sheet cassette  251  in an arc manner, a sheet bail  196  for recording sheet  62  placed on transportation guide  195 , a pickup roller  192  taking out recording sheet  62  one by one held by sheet bail  196 , a transportation roller  252  and a guide roller  188  sandwiching recording sheet  62  with transportation guide  195  to guide recording sheet  62  to a position facing ink carriage  186  while maintaining a curvature identical to that of transportation guide  195 , a shaft  212  provided rotatably about a predetermined axis, a strut  184  fixed to shaft  212  to move along an arc about the axis together with the rotation of shaft  212 , and an ink carriage  186  provided at a predetermined position from shaft  212  of strut  184 . 
     Ink carriage  186  moves along an arc about shaft  212  to spray out ink on a recording sheet  62  that is bent in an arc manner. 
     Referring to FIGS. 58A and 58B, transportation rollers  252  are arranged on a straight line parallel to the transportation direction of recording sheet  62  to be sequentially in contact with recording sheet  62  from the center portion to the periphery in accordance with transportation of recording sheet  62 . Transportation rollers  252  in the proximity of the scanning trajectory of ink carriage  186  are arranged on a straight line parallel to the main scanning direction. Transportation rollers  252  are arranged to release the contact with recording sheet  62  from the periphery to the center portion after printing is carried out. Transportation rollers  252  located at the discharge sheet side than the scanning trajectory of ink carriage  186  out of the plurality of transportation rollers  252  are arranged in a star wheel manner. 
     Referring to FIG. 59, transportation roller  252  has a fusiform shape of a curvature smaller than the curvature of recording sheet  62 . Referring to FIGS. 60 and 61, a plurality of transportation rollers  252  of each line are connected by the same axis in the direction of width of recording sheet  62 . Transportation rollers  252  are driven symmetrically left and right on recording sheet  62 . By transportation roller  252  of a fusiform shape having a curvature smaller than the curvature of recording sheet  62 , the buckling of recording sheet  62  caused by contact with the end of transportation roller  252  can be prevented. 
     Transportation of recording sheet  62  will be described with reference to FIGS. 62A-62C. As shown in FIG. 62A, the center portion of recording sheet  62  in the width direction is fastened between transportation roller  252  and transportation guide  195 . Accordingly, the center of recording sheet  62  is positioned, and the relationship in position with ink carriage  186  is fixed. Upon transportation of recording sheet  62 , recording sheet  62  passes through transportation rollers  252  located symmetrically and transportation guide  195 , as shown in FIG.  62 B. Here, recording sheet  62  is bent in a configuration of a curvature identical to that of transportation guide  195 . Then, recording sheet  62  passes through symmetrically located transportation rollers  252  and transportation guide  195 , as shown in FIG.  62 C. Thus, recording sheet  62  is conveyed without meander along the inner side of transportation guide  195 . 
     The position of arranging transportation rollers  252  is determined by the smallest size and largest size of recording sheet  62  that can be printed by the ink jet printer. More specifically, when ½ the smallest width is A and ½ the largest width is B in the main scanning direction of recording sheet  62  as shown in FIG. 63, transportation roller  112 A is arranged at a position of distance A from transportation roller  112 C located at the center, and transportation roller  112 B is located at distance B. Accordingly, a recording sheet  62  of all sizes can be transported by a minimum number of transportation rollers  112 . 
     Referring to FIG. 64, an air flow is formed at the upper plane or bottom plane, or at both planes of recording sheet  62 , whereby recording sheet  62  is secured to transportation guide  195 . By using air flow for the securement of recording sheet  62 , the drying operation of ink  224  can be facilitated to increase the number of printouts per unit time. 
     The current position of ink carriage  186  can be detected directly or indirectly by using a motor that can control the rotation angle such as a stepping motor for the motor (not shown) that drives strut  184 . 
     According to the ink jet printer of the present embodiment, recording sheet  62  is conveyed by a plurality of transportation rollers  252  arranged in an arc manner along the inner side of transportation guide  195 . Therefore, recording sheet  62  can be conveyed properly without meander. 
     Transportation rollers  252  are arranged so that recording sheet  62  comes into contact with a transportation roller  252  sequentially from the center portion towards the periphery when transferred by transportation guide  195 . Accordingly, recording sheet  62  can be gradually bent as being transported to prevent buckling caused by bending of recording sheet  62 . 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.