JP2011152765A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent friction between an ink head and paper in an image forming apparatus. <P>SOLUTION: The image forming apparatus for executing multipath printing includes: a resist roller and a resist pressure roller for feeding paper intermittently to a printing area; a platen for keeping the paper flat in the printing area; a chamber and a suction fan disposed under the platen for sucking the paper on the platen; an ink head for forming an image by ejecting ink on the paper on the platen; and a carriage for carrying the ink head 6 which moves in a direction orthogonal to a conveying direction of the paper. The image forming apparatus further includes: a paper sensor for detecting the paper; a head-moving motor which moves a position of the ink head 6 to the upstream and the downstream in the paper-conveying direction; and a head moving control means which drives and controls the head moving means based on a position detected by a means for detecting a paper position, wherein a position of the ink head 6 is moved to the upstream side or the downstream side in the paper-conveying direction according to print condition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and in particular, a conveying unit that intermittently feeds paper fed from a paper feeding device to a print area, a platen for keeping the paper flat in the print area, and a lower part of the platen. A suction mechanism that sucks the paper on the platen, an ink head that forms an image by ejecting ink onto the paper on the platen, and a carriage that is mounted with the ink head and moves in a direction perpendicular to the paper transport direction. And an image forming apparatus that executes multi-pass printing.

  2. Description of the Related Art Conventionally, an image forming apparatus such as an ink jet printer employs multi-pass printing in which divided recording data is sequentially recorded by relative scanning of an ink head a plurality of times with respect to the same recording area. 12 and 13 are schematic views showing a state of conventional multi-pass printing. In the present specification, printing with the ink head scanning in the main scanning direction is called a pass, and printing with one scan is called n-pass printing and scanning n times and n times at the same place. When printing is performed to complete an image, it is called n-pass printing. The print width printed in one pass is called a band. In the figure used for explaining the operation of multi-pass printing, the circled number on the paper indicates how many times the image is overlaid at that time. For example, when 2 is shown in the circle, it is overlaid twice. Indicates the printing range.

  In the example shown in FIG. 12, when printing on the paper 22 by the ink head 21, the number of multi-passes is set to 4, and the print range of the ink head 21 is set to bands 21-1 to 21- 4, printing is started from the band 21-1 at the upstream end of the ink head 21, printing is performed on the band (one pass), paper feeding of a width of one band is executed, and the next Printing (two passes) is performed and this is repeated sequentially. As a result, the image is printed by overlapping a plurality of times in each band, and the same area of the paper is printed a plurality of times by different nozzles, thereby reducing streaks and unevenness due to variations in the nozzles.

  Further, in the example shown in FIG. 13, in order to widen the area on which the paper is placed on the platen and improve the suction state of the paper, the position of the leading end of the printing area of the paper 22 at the start of printing is previously set downstream of the ink head. Placed at the side position, the paper feed amount at the time of initial printing is made smaller than the width of one band (4 mm in this example) (1 mm in this example), and printing is performed. After the sheet is conveyed to the downstream end of the width, the sheet 22 is fed with the sheet feed amount set to a normal width (4 mm) for one band. In this method, the leading end position of the sheet at the start of printing is determined by the initial sheet feeding amount and the number of multi-passes. Therefore, if the minimum feeding amount is reduced, the leading end position of the sheet can be conveyed downstream. For this reason, among the suction ports arranged on the platen, the number of suction holes that are opened without the paper being arranged is reduced, and the suction force of the paper is increased. However, in reality, the lower limit of the minimum feed amount is determined by restrictions such as control, parts accuracy, paper feed accuracy, and transport time, and the area where the paper covers the platen at the start of printing cannot be increased beyond that amount. End up.

  Japanese Patent Application Laid-Open No. 2004-133830 discloses a paper conveying direction, a paper suction means for sucking paper to a platen, a storage means for storing image data, and a paper conveyance direction based on the stored image data. Different from print data for each nozzle area, ink head for printing on paper while scanning in a direction substantially perpendicular to the nozzle, nozzle mask means for performing nozzle mask for each nozzle area divided by the number of passes Data mask means for performing data masking with a mask pattern selected from the mask patterns, and performing an initial multi-pass printing process that does not involve paper conveyance for each pass for at least one band at the leading edge of the paper at the start of printing. After that, by performing control to perform normal multi-pass printing processing with paper conveyance, the paper leading edge position reaches the downstream edge of the printing width. Image forming apparatus for carrying out the initial multi-pass printing is disclosed without conveying the sheet is conveyed.

  In Patent Document 2, ruled lines can be recorded seamlessly, and ink can be ejected from the nozzles of the recording head and recorded on the recording medium so that the apparatus can be recorded at high speed without increasing the size of the apparatus. In the ink jet recording apparatus, the graphic recording control means for performing recording control for graphic drawing commands such as ruled lines, and the bitmap recording control means for performing recording control by bitmap development for drawing commands other than the graphic drawing commands The recording command for each of the recording control means is independently controlled, and the recording head that ejects ink according to the drawing command is opposed to the ink ejection surface of the recording head by the recording medium holding means. A recording medium that moves relative to a recording medium held at a position in two intersecting directions is described.

  However, the one described in Patent Document 1 does not change the nozzle to be used even when multipass printing is performed, and cannot exhibit the advantages of multipass printing that eliminates streaks and unevenness due to nozzle variation. Since the ink is ejected from the same nozzle to the same location of the stopped paper, there is a problem that when printing an image with a high printing rate, the paper swells and floats easily due to cockling. Moreover, since the thing of patent document 2 does not perform multipass printing, there exists a problem that the stripe and nonuniformity resulting from the dispersion | variation in a nozzle cannot be eliminated.

  As an ink jet printer, there is an ink jet printer that uses a suction mechanism to attract and transfer the paper to the platen surface with high accuracy in order to keep the paper flatness of the printing unit with high precision. The width of the platen surface to be adjusted is matched with the print width of the ink head. For this reason, it is necessary to fix the leading edge of the paper further upstream than the downstream edge of the print width of the ink head during multi-pass printing, and the suction force acting on the paper is smaller than that during normal printing, and the leading edge floats on the paper In some cases, the ink head or carriage and the paper are not sufficiently in contact with each other.

  Also, in a conventional image forming apparatus that performs multi-pass printing, the leading edge of the paper at the start of printing is determined by the initial feed amount and the number of multi-passes, so if the initial feed amount is reduced, the leading edge of the paper at the start of printing The position can be set downstream, the number of suction holes opened is reduced, and the suction force applied to the sheet is increased. Actually, the minimum value of the initial feed amount is determined due to constraints such as control, parts accuracy, paper feed accuracy, and transport time, but the paper leading edge position at the start of printing with the determined initial feed amount and the set number of multi-passes As a result, it becomes impossible to increase the area where the paper covers the platen any more, and even if the paper is fully covered on the platen due to the restriction of the minimum feed amount, the paper floats up. There's a problem.

  Furthermore, this problem becomes significant in an ink jet printer in which the color head is set to be smaller than the black head and is offset from the upstream side of the black head, and color printing is performed with the printer having such a configuration. In some cases, the leading edge of the paper is conveyed to the downstream end of the color head, so no paper is placed on the platen in the print area of only the black head, so the suction holes are opened and the suction force applied to the paper is increased. When the color multi-pass printing is performed, the suction force necessary for preventing the sheet from being lifted cannot be applied even if the above method is performed.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of preventing the ink head and paper from rubbing without losing the effect of multi-pass printing.

  According to the first aspect of the present invention, there is provided a conveying means for intermittently feeding a sheet fed from a sheet feeding device to a print area, a platen for keeping the sheet in the print area, and a platen disposed below the platen on the platen. A suction mechanism that sucks paper, an ink head that forms an image by ejecting ink onto the paper on the platen, and a carriage that mounts the ink head and moves in a direction perpendicular to the paper transport direction. In an image forming apparatus that performs pass printing, a sheet information detecting unit that detects position information of the sheet, a head moving unit that can move the position of the ink head to the upstream side and the downstream side in the sheet transport direction, and the sheet And a head movement control means for drivingly controlling the head movement means based on paper information including information from the detection means and set printing conditions. That is an image forming apparatus.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the head movement control means moves the ink head downstream before detecting the leading edge of the paper at the start of printing, The head moving means is controlled to start printing after detecting the leading edge.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the head movement control unit is configured such that the leading end position of the sheet at the start of image printing calculated from the input image is greater than a predetermined position. In the case of the upstream side, the head moving means is controlled so as to start the printing by moving the ink head to the downstream side.

  According to a fourth aspect of the present invention, in the image type apparatus according to any one of the first to third aspects, the head movement control means is configured to perform the printing of the ink head N times during multi-pass printing. When the width is L, the ink head is moved to the downstream side to start printing, and at the start of printing, the ink head is moved to the downstream side by (L-L / N). The head is moved upstream (L / N) and this process is repeated (N-1) times. After the ink head returns to the home position, the paper is conveyed (L / N) and printing is performed. The head moving means is controlled as described above.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the ink head includes a black head that performs black printing and a color head that performs color printing other than black. The print width dimension of the black head is larger than the print width dimension of the color head, and when performing color printing using the color head, the head movement control means moves only the color head downstream. Then, the head moving means is controlled to start printing.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the head movement control unit moves the ink head when the width dimension of the sheet is equal to or smaller than a predetermined width. The head moving means is controlled to move to the downstream side and start printing.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the head movement control means inputs whether to start printing by moving the ink head downstream. Judgment is made on the basis of the paper type data thus obtained.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the head movement control unit moves the ink head to the upstream side when printing the trailing edge of the paper. The head moving means is controlled to move.

  According to the image forming apparatus of the present invention, the paper position detecting means for detecting the paper position, the head moving means for moving the ink head position in the paper transport direction, and the paper position detected by the paper position detecting means. And the head movement control means for driving and controlling the head movement means based on this, the position of the leading edge of the paper at the start of printing is arranged downstream or downstream of normal multi-pass printing and printing is performed. Thus, the ink head and the paper can be prevented from being rubbed while exhibiting the effect of multi-pass printing.

1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. FIG. 5 is a schematic diagram illustrating the movement of the ink head and the paper conveyance state. FIG. 5 is a schematic diagram illustrating the movement of the ink head and the paper conveyance state. 2 is a block diagram illustrating a control system of the image forming apparatus. FIG. FIG. 6 is a block diagram illustrating an operation of the image forming apparatus according to the embodiment. FIG. 6 is a block diagram illustrating an operation of the image forming apparatus according to the embodiment. FIG. 10 is an explanatory diagram illustrating a multipass printing operation of the image forming apparatus. It is a schematic diagram which shows schematic structure of the image forming apparatus which concerns on a 2nd Example. 6 is a flowchart illustrating an operation of the image forming apparatus according to the second embodiment. 6 is a flowchart illustrating an operation of the image forming apparatus according to the second embodiment. FIG. 6 is a schematic diagram illustrating the movement of an ink head and the conveyance state of a sheet in an image forming apparatus according to a second embodiment. FIG. 10 is a schematic diagram illustrating the movement of an ink head and the conveyance state of a sheet in an image forming apparatus according to a third embodiment. FIG. 10 is a schematic diagram of an image forming apparatus illustrating a movement of an ink head and a conveyance state of a sheet in an image forming apparatus according to a fourth embodiment. It is a schematic diagram showing a state of multipass printing of a conventional image forming apparatus. It is a schematic diagram showing a state of multipass printing of a conventional image forming apparatus.

  An image forming apparatus according to the present invention includes a conveying unit that intermittently feeds a sheet fed from a sheet feeding device to a printing area, a platen for keeping the sheet in the printing area, and the platen disposed below the platen. A suction mechanism that sucks the upper sheet; an ink head that forms an image by ejecting ink onto the sheet on the platen; and a carriage that is mounted with the ink head and moves in a direction perpendicular to the sheet conveyance direction. In an image forming apparatus that performs multi-pass printing, a sheet information detecting unit that detects position information of the sheet, a head moving unit that can move the position of the head to the upstream side and the downstream side in the sheet conveyance direction, A head movement control means for driving and controlling the head movement means on the basis of the paper information including information from the paper detection means and the set printing conditions. . According to the image forming apparatus of this example, the ink head is moved by the head moving unit under the control of the head moving control unit, and the position of the leading edge of the paper at the start of printing is set downstream of the normal multi-pass printing. In addition to preventing the paper and ink head from rubbing, the ink head can then be moved upstream to prevent carriage yawing, and the effect of multi-pass printing can be achieved by changing the nozzles used. Demonstrate.

  The head movement control means of the image forming apparatus according to the present invention may move the ink head downstream before detecting the leading edge of the paper at the start of printing, and start printing after detecting the leading edge of the paper. The head moving means can be controlled. According to this example, since the ink head is moved to the downstream side when the leading edge of the paper is detected, the ink head is not separated from the paper when the leading edge of the paper is detected, and the ink head is not rubbed against the paper.

  Further, the head movement control unit of the image forming apparatus according to the present invention moves the ink head to the downstream side when the leading end position of the paper at the start of image printing calculated from the input image is upstream from the predetermined position. The head moving means can be controlled to start printing by moving the head to the position. According to this example, when the sheet is sufficiently on the platen, a sufficient suction force can be applied, so that the movement of the ink head can be minimized when performing normal printing.

  Further, the head movement control means of the image forming apparatus according to the present invention moves the ink head to the downstream side when the width of the ink head is set to L when printing is performed N times in multi-pass printing. When printing starts, the ink head is moved downstream by (L-L / N), and the ink head is moved upstream by L / N each time one-pass printing is performed. The processing is repeated (N-1) times, and after the ink head returns to the home position, the head moving means is controlled so as to carry out printing by conveying the paper (L / N). According to this example, the paper leading edge can be detected with high accuracy without contact between the carriage and the paper by feeding the paper while sucking with a suction force that matches the paper size. The mask area can be reduced.

  In the image forming apparatus according to the present invention, the ink head includes a black head that performs black printing and a color head that performs color printing other than black, and a printing width dimension of the black head is a printing width dimension of the color head. When carrying out color printing using the color head, the head movement control means controls the head movement means to start printing by moving only the color head downstream. I can do it. According to this example, even when the color head is offset to the upstream side, by moving the paper head to the downstream side as much as possible by moving it to the downstream side, the adsorption force to the platen is sufficiently The sheet can be prevented from floating.

  Further, the head movement control unit of the image forming apparatus according to the present invention is configured to move the ink head downstream to start printing when the width of the sheet is equal to or less than a predetermined width. It can be controlled. According to this example, when the paper is small, the suction force of the paper is low and floating is likely to occur.Therefore, when printing is started in a state where the paper is sufficiently placed in the transport direction of the platen, the ink head is not rubbed. Less likely.

  Further, the head movement control means of the image forming apparatus according to the present invention can determine whether to start printing by moving the ink head downstream based on the input paper type data. According to this example, when printing on thick paper that is stiff and easy to float, printing can be started with the paper sufficiently loaded in the transport direction of the platen, and the ink head and the paper are rubbed. Can be prevented.

  Further, the head movement control unit of the image forming apparatus according to the present invention may control the head movement unit to move the ink head to the upstream side when printing the trailing edge of the paper. According to this example, since normal printing is performed in a state where the paper is sufficiently placed on the platen, if the registration roller and the ink head are separated from each other, the suction force applied to the paper becomes larger. Floating is unlikely to occur. However, in order to minimize the trailing edge margin, it is desirable that the registration roller and the ink head be close to each other. Therefore, when printing at the trailing edge, the ink head is brought close to the upstream registration roller to perform printing. And the trailing edge margin can be minimized.

  The image forming apparatus according to the embodiment will be described below. 1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment, FIG. 2 is a schematic diagram illustrating movement of an ink head and a conveyance state of a sheet, and FIG. 3 illustrates movement of the ink head and a conveyance state of the sheet. It is a schematic diagram shown.

  The image forming apparatus 10 according to the embodiment is an ink jet printer, and a registration roller 1 that is a conveyance unit that conveys a sheet conveyed from a sheet feeding device (not illustrated) in a sub-scanning direction, and a sheet that comes into contact with the registration roller 1. A resist pressure roller 2 that is a transport means for transporting the liquid, a suction fan 5 that is a suction mechanism, a chamber 3 that is held at a negative pressure by the suction fan 5, and a plurality of suction ports that communicate with the chamber 3 are opened. A platen 4 that sucks paper, an ink head 6 that is disposed above the platen 4 so as to face the platen 4, ejects ink onto the paper, a carriage 7 that holds the ink head 6, and the carriage 7 A guide rod 8 for guiding reciprocation in the paper width direction, that is, the main scanning direction, and a main scanning stay 9 for supporting the guide rod 8 are provided. . The carriage 7 is equipped with an optical sensor (not shown) for detecting the leading end of the sheet and the width of the sheet. The suction fan 5 is PWM-controlled to cope with various paper sizes and types, and the suction force for bringing the paper into close contact with the platen 4 is changed by changing the duty value of the PWM signal.

  In such an image forming apparatus 10, when a sheet is conveyed from a sheet feeding device (not shown) to the registration roller 1, the sheet is conveyed between the registration roller 1 and the registration pressure roller 2 and is placed on the platen 4. Be transported. The sheet transported onto the platen 4 is sucked by the chamber 3 and is brought into close contact with the platen 4 to maintain flatness, and ink is ejected from the ink head 6 transported in the main scanning direction, while the guide rod 8 is guided by the carriage 7. The sheet is reciprocated in the width direction of the sheet along the direction of the sheet, and the ink is ejected toward the sheet on the platen 4 so that the image is formed on the sheet and conveyed by the registration roller 1 in the sub-scanning direction to perform printing.

  In this image forming apparatus 10, as shown in FIG. 3, a carriage 7 on which an ink head 6 is mounted, a guide rod 8 that holds the carriage 7, and a main scanning stay 9 are driven by a head moving motor 12 that is a head moving means. It can be freely moved to the downstream side and the upstream side in the paper transport direction. The head movement motor 12 is monitored by an encoder 14 (see FIG. 5 and not shown in FIG. 3) for the amount of movement, and is controlled with high accuracy by the head movement control means 13 (see FIG. 5). In this embodiment, the state where the ink head 6 is arranged on the most upstream side is the head position used for normal printing, and this position is referred to as a home position.

  Next, control of the image forming apparatus 10 will be described. FIG. 4 is a block diagram showing a control system of the image forming apparatus. The head movement motor 12 is driven and controlled by a head movement control means 13, and the head movement control means 13 is connected to the encoder 14 and a paper sensor 11 for detecting the position of the paper. The head movement control means 13 performs predetermined control by executing predetermined software on a computer having a CPU, ROM, RAM, and the like.

  Next, the operation of the image forming apparatus 10 according to the embodiment will be described. 5A and 5B are flowcharts illustrating the operation of the image forming apparatus according to the embodiment. When the user gives an instruction to start printing (step SA1), the head moving motor 12 is driven to move the ink head 6, the carriage 7, the guide rod 8, and the main scanning stay 9 to the downstream side (step SA2). The carriage 7 is moved onto the platen 4. Next, the suction fan 5 is actuated to start a suction operation under the conditions according to the paper size and type (step SA3), and the paper is further transported and the leading edge of the paper is detected by the paper sensor 11 on the carriage (step SA4). Then, the paper is conveyed to the printing start position (step SA5). Then, the printing method is determined based on the paper type and printing quality input by the user (step SA6).

  If the determined printing method is not normal one-pass printing (step SA7), the head moving motor 12 is driven to return the ink head 6 to the home position (step SA8), and one-pass printing is executed. (Step SA9).

  In the case of multipass printing, it is determined whether or not the amount of the leading edge margin determined from the print image input by the user exceeds a predetermined amount (step SA10), and a leading edge margin equal to or larger than the predetermined amount is ensured. If it is, the paper is transported to the print start position, the ink head 6 is returned to the home position (step SA11), and multi-pass printing is performed (step SA12). The predetermined amount at this time is that when the ink head 6 is disposed at the home position, the normal multi-pass printing is performed at a position where the multi-pass printing starts at the downstream end of the ink head 6 as shown in FIG. Therefore, the leading edge margin amount at which the leading edge of the sheet does not sufficiently float at that position.

  When the print width of the ink head 6 is 16 mm and the number of multi-passes is 4 (example shown in FIG. 12), if the width of the platen 4 in the transport direction is approximately 16 mm corresponding to the print width, the print start position is the head The position is 4 mm from the upstream end. In order to prevent floating at that time, it is necessary to feed the platen 4 almost to the downstream end, so that the predetermined margin at the front end is 12 mm. Since this numerical value is unique to the machine, the width in the transport direction of the platen 4 may actually be larger than the printing width of the ink head 6, and it is necessary to set a value that does not cause the sheet to float.

  If the leading edge margin is smaller than the predetermined amount (No in Step SA10), multi-pass printing is performed while moving the ink head 6 (Step SA13). Thereafter, multi-pass printing is performed while moving the ink head 6 upstream (step SA13). When the ink head 6 returns to the home position (step SA15), normal multi-pass printing is executed.

  On the other hand, if the margin is sufficient (step SA10: yes), the ink head 6 is returned to the home position (step SA16), and normal multi-pass printing is performed while the paper is being conveyed (step SA17).

  In this example, when multi-pass printing is performed N times, when the width of the ink head is L, the ink head is moved to the downstream side to start printing, and at the start of printing, the ink head Is moved downstream by (L / L / N), and the ink head is moved upstream by (L / N) each time one-pass printing is performed, and this process is repeated (N-1) times. After returning to the home position, the paper is conveyed (L / N) at a time for printing.

  A specific example in which the print width of the ink head 6 is 16 mm and the number of multi-passes is four will be described. FIG. 6 is an explanatory diagram showing a multi-pass printing operation of the image forming apparatus. In the following drawings, the shaded portion indicates the range of nozzles to be used, and the circled numbers on the paper indicate how many times images are superimposed at that time. The sheet is moved so that the print start position of the image is at the downstream end of the print width when the ink head 6 is at the home position. Further, the head moving motor 12 is driven to move the ink head 6 so that the downstream end of the print width of the ink head 6 is 4 mm upstream of the image start position, and a nozzle 4 mm downstream of the print width is used. Start printing. When the first pass printing is completed, the ink head 6 is moved 4 mm upstream, the second pass printing is performed using the 8 mm nozzle on the print width downstream side, and the print width is similarly increased by moving 4 mm upstream. The third pass is printed using a 12 mm nozzle on the downstream side. When the ink head 6 is further moved to the upstream side by 4 mm, the ink head 6 returns to the home position, and the fourth pass printing is performed using the nozzles in the entire printing width.

  Since it is multi-pass printing in which an image is completed by 4-pass printing, an image in a range of 4 mm from the image start position is completed. After this, the paper is conveyed by 4 mm as in normal multi-pass printing, printing is performed, and an image having a width of 4 mm is completed for each pass. By carrying out such a method, it is possible to avoid the conveyance of the sheet under the ink head 6 when the sheet is not sufficiently placed on the platen 4, which is caused by the floating of the sheet due to insufficient suction force. It is possible to prevent the ink head 6 and the paper from being rubbed. In addition, the nozzles used in all areas to be printed, which is a feature of multi-pass printing, are overlaid and printed, and a high-quality image with reduced streaks and unevenness can be obtained.

  Next, an image forming apparatus according to a second embodiment will be described. Similar to the image forming apparatus of the first embodiment, the image forming apparatus 30 according to the present embodiment is a registration roller 1, a resist pressure roller 2, a chamber 3, a platen 4, a suction fan 5, an ink head 6, and a carriage 7. , A guide rod 8 and a main scanning stay 9 are provided. Further, in this example, the lengths of the registration roller 1 and the platen 4 are set so that the corresponding paper can correspond to a maximum of 914 mm.

  FIG. 7 is a schematic diagram illustrating a schematic configuration of the image forming apparatus according to the second embodiment. In the image forming apparatus 30, the ink head 6 is disposed in the carriage 7. In this example, the ink head 6 includes a black head 6-1 and a cyan head 6-2, which is a color head, a magenta head 6-3, and a yellow head 6-4. The black head 6-1 is a color head. The cyan head 6-2, magenta head 6-3, and yellow head 6-4 are configured so that they can move integrally along the paper transport direction upstream in the transport direction. Yes. The carriage 7 is provided with a head moving motor 12 which is a head moving means for moving the cyan head 6-2, magenta head 6-3, and yellow head 6-4 as a unit. 2. The magenta head 6-3 and the yellow head 6-4 can be moved by the head moving motor 12 from the upstream end position to the downstream end position of the black head 6-1. Similarly to the image forming apparatus 10 according to the first embodiment, the head movement motor 12 is precisely driven and controlled by the head movement control unit 13 based on the output of the encoder 14 and the paper sensor 11 that detect the position of the head. (See FIG. 4). In the carriage 7, a paper sensor 11 used for detecting the leading edge and width of the paper is disposed so as not to overlap the ink head 6 in the width direction.

  Next, the operation of the image forming apparatus 30 according to the second embodiment will be described. 8A and 8B are flowcharts illustrating the operation of the image forming apparatus according to the second embodiment. When there is a printing instruction (step SB1), the carriage 7 is moved to the paper leading edge detection position, the paper is conveyed, and when the paper sensor 11 detects the paper, the conveyance of the paper is stopped (step SB2). Next, the suction fan 5 is actuated to start a suction operation under conditions that match the paper size and type (step SB3), and the paper is further transported and the leading edge of the paper is detected by the paper sensor 11 on the carriage (step SB4). Then, the paper is conveyed to the print start position (step SB5). Then, the printing method is determined based on the paper type and printing quality input by the user (step SB6).

  When monochrome printing or one-pass printing is selected according to the type of paper and the printing mode (step SB7), the paper is conveyed to the printing start position and printing is performed by moving the carriage 7 in the main scanning direction (step SB7). SB8).

  If color multi-pass printing is selected in step SB9, it is determined whether to move the color head downstream from the paper type input by the user and the paper width detected in the initial operation (step SB9). SB9). Here, for example, for paper that is difficult to lift, such as plain paper, if the paper width is 420 mm or more, printing is started without moving the ink head, and paper that is easily stiff and floats such as inkjet coated paper. In the case of 610 mm or more, printing is started without moving the ink head (step SB16).

  Next, the margin from the image input by the user to the position where printing starts from the leading edge of the paper is calculated. When the above conditions are not met and a paper type and size other than the paper type that starts printing without moving the ink head are selected, the ink head is determined according to whether the margin is equal to or greater than a predetermined amount as in the first embodiment. It is determined whether to move (step SB10). For example, when printing on 420 mm wide inkjet coated paper is selected, if the margin obtained from the input image is less than a predetermined amount, the paper is printed after the ink head is moved downstream. It moves to the start position and executes the printing process (step SB11 to step SB15).

  The above printing process will be described. FIG. 9 is a schematic diagram illustrating the movement of the ink head and the sheet conveyance state in the image forming apparatus according to the second embodiment. In this example, the width of the black head 6-1 is 25 mm, the width of the cyan head 6-2, the magenta head 6-3, and the yellow head 6-4 is 16 mm, and four-pass printing is performed in which printing is performed four times. In this example, the minimum movement amount of the ink head is set to 1 mm from the control and component accuracy, the paper is conveyed so that the image start position is 3 mm from the downstream end of the black head 6-1, and the head moving motor 12 is driven. Is moved 9 mm downstream so that its downstream end is aligned with the downstream end of the black head, and then the carriage 7 is scanned in the main scanning direction to start printing.

  When printing of the first pass is completed, the color heads 6-2 to 6-4 are moved 1 mm downstream to start printing of the second pass. Similarly, in the third pass and the fourth pass, the color heads 6-2 to 4 are moved 1 mm downstream to perform printing. At this time, the image of the 4 mm portion from the image start position on the paper has been completed, and the paper does not cover the entire platen 4, so the paper is transported 4 mm downstream and the fifth pass printing is performed. Since the color heads 6-2 to 4-4 have not returned to the home position, the head is moved 4 mm upstream to print the sixth pass.

  Further, the color heads 6-2 to 6-4 are moved 2 mm downstream, and the paper is conveyed 2 mm downstream to further align the printing position, and the seventh pass printing is performed. Thereafter, only the paper is conveyed 4 mm downstream for printing, and printing is performed without moving the color heads 6-2 to 4 to complete the image. By performing printing in this way, it is possible to increase the suction force applied to the sheet through the platen 4 by starting printing with the leading end of the sheet being conveyed as far downstream as possible under conditions where floating tends to occur. Thus, rubbing with the head 6 due to paper floating, jamming, and abnormal images can be prevented.

  Next, an image forming apparatus according to a third embodiment will be described. FIG. 10 is a schematic diagram illustrating the movement of the ink head and the sheet conveyance state of the image forming apparatus according to the third embodiment. The image forming apparatus according to the third embodiment has the same configuration as the image forming apparatus according to the second embodiment. Then, as shown in FIG. 10, the black head 6-1 has a width of 25 mm, a width of 16 mm, and performs four-pass printing in which printing is performed four times. The minimum movement amount of the ink head is 1 mm, the minimum sheet feed amount is 1 mm, the image start position is 3 mm from the downstream end of the black head 6-1, and the downstream ends of the color heads 6-2 to 4 are black. The conditions are aligned at the downstream end of the head 6-1. In this example, after printing the first pass, the paper is transported by 1 mm of the minimum feed amount, and the second pass is printed. Similarly, in the third pass and the fourth pass, printing is performed by conveying the paper by 1 mm. Further, in order to return the color heads 6-2 to 4 to the home position while continuing printing, the fifth pass printing is performed after moving 4 mm to the upstream side. Similarly, the sixth pass printing is also performed for the color head 6-2. Printing is performed after moving 4 to 4 mm further upstream. Since the home position is 1 mm at this time, the color heads 6-2 to 4 are moved 1 mm upstream, and the paper is further conveyed 3 mm downstream to align the image position and print the seventh pass. In the printing after the eighth pass, the color heads 6-2 to 4 are not moved, and the paper is conveyed by 4 mm downstream and printed.

  Next, an image forming apparatus according to a fourth embodiment will be described. FIG. 11 is a schematic diagram of the image forming apparatus showing the movement of the ink head and the sheet conveyance state of the image forming apparatus according to the fourth embodiment. Similar to the image forming apparatus 10 according to the first embodiment, the image forming apparatus 40 includes a registration roller 1 and a registration pressure roller 2, and conveys a sheet onto the platen 4. A chamber 3 and a suction fan 5 are disposed under the platen 4, and a carriage 7 is disposed on the platen 4 so as to be movable along the main scanning stay 9 and the guide rod 8. An ink head 6 for ejecting ink onto a sheet fixed on the platen 4 is mounted in the carriage 7. In this example, the main scanning stay 9 can be moved in the paper transport direction by a motor (not shown).

  When the paper conveyed from the registration roller 1 is printed on the platen, the ink head 6 starts printing at a downstream position. At this time, since the area on which the paper is placed on the platen 4 is large, the ink head is disposed on the downstream side, so that the ink head and the paper can be prevented from being rubbed due to the paper floating. In the image forming apparatus 40 according to this example, when the rear end of the sheet is printed, the main scanning stay 9, the ink head 6 and the like are moved to the positions indicated by the two-dot chain line in FIG. This is to prevent the sheet from being transported if the trailing edge is removed from the nip formed by the registration roller 1 and the registration pressure roller 2. To solve this problem, it is necessary to add a transport roller and a spur to the downstream side of the platen. However, this may cause a cost increase, which may cause an abnormal image with a spur mark on the printed image. Will also increase. Therefore, in this embodiment, the distance between the registration roller 1 and the nip between the registration pressure rollers is shortened by moving the ink head 6 to the upstream side, and the trailing edge margin at which no image is formed at the trailing edge of the sheet is minimized. can do.

1 Registration roller (conveying means)
2 Registration pressure roller (conveying means)
3 Chamber (suction mechanism)
4 Platen 5 Suction fan (suction mechanism)
6 Ink head 7 Carriage 8 Guide rod 9 Main scanning stay 10 Image forming apparatus 11 Paper sensor (paper detection means)
12 Head moving motor (head moving means)
13 Head Movement Control Unit 14 Encoder 30 Image Forming Apparatus 40 Image Forming Apparatus

Japanese Patent No. 3987759 JP 2001-121689 A

Claims (8)

Conveying means for intermittently feeding the paper fed from the paper feeding device to the print area, a platen for keeping the paper in the print area, and a suction mechanism arranged below the platen for sucking the paper on the platen And an ink head that forms an image by ejecting ink onto a sheet of paper on the platen, and a carriage that carries the ink head and moves in a direction perpendicular to the paper conveyance direction, and performs multi-pass printing. In the device
Paper information detection means for detecting position information of the paper;
A head moving means capable of moving the position of the ink head to the upstream side and the downstream side in the paper transport direction;
Head movement control means for driving and controlling the ink head movement means based on paper information including information from the paper detection means and set printing conditions;
An image forming apparatus comprising:   The head movement control means controls the head movement means to start the printing after detecting the leading edge of the paper by moving the ink head downstream before detecting the leading edge of the paper at the start of printing. The image forming apparatus according to claim 1.   The head movement control means moves the ink head to the downstream side to start printing when the leading edge position of the paper at the start of image printing calculated from the input image is upstream of the predetermined position. The image forming apparatus according to claim 1, wherein the head moving unit is controlled.   The head movement control means moves the ink head to the downstream side by (L−L / N) at the start of printing when the width of the ink head is L when performing multi-pass printing N times. Each time one-pass printing is performed, the ink head is moved upstream by (L / N), and this process is repeated (N-1) times. After the ink head returns to the home position, the paper (L The image forming apparatus according to any one of claims 1 to 3, wherein the head moving unit is controlled so as to carry out printing by carrying / N) at a time.   The ink head includes a black head that performs black printing and a color head that performs color printing other than black, and a printing width dimension of the black head is larger than a printing width dimension of the color head, and the color head is used. 2. When performing color printing, the head movement control means controls the head movement means to start printing by moving only the color head downstream. 5. The image forming apparatus according to any one of 4 above.   The head movement control unit controls the head movement unit to start printing by moving the ink head downstream when the width dimension of the sheet is equal to or less than a predetermined width. The image forming apparatus according to claim 5.   7. The head movement control unit determines whether to start printing by moving the ink head downstream based on input paper type data. The image forming apparatus described in 1. 8. The head movement control unit controls the head movement unit to move the ink head to the upstream side when printing the trailing edge of the sheet. The image forming apparatus described in 1.