JP2016032896A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which can suppress image quality degradation of a sheet and contamination in the apparatus by controlling suction force in accordance with the state of the sheet conveyed on a conveyor belt.SOLUTION: An inkjet printer which forms an image on a sheet P by discharging ink in accordance with image data of each page to the sheet P conveyed on a conveyance path comprises: conveyance means which conveys the sheet P by making the sheet P suctioned to the upper surface of a conveyor belt 133 sliding along the conveyance path; a printing condition detection part which detects the printing condition of an image; and a suction control part which calculates the ratio of the sheet P to the suction area of the conveyor belt surface on the basis of the printing condition detected by the printing condition detection part and controls the conveyance means to control the suction force in accordance with the calculation result.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an ink jet image forming apparatus that forms an image on a print medium by ejecting ink corresponding to image data onto a print medium conveyed on a conveyance path.

  2. Description of the Related Art Inkjet image forming apparatuses print on a print medium by ejecting ink droplets with an inkjet head, and are generally well known. Such an ink jet printing apparatus includes a transport belt for transporting a print medium below the ink jet head, and transports the print medium at a predetermined transport speed while sucking the print medium onto the transport belt by a suction fan installed in the transport belt. However, there is a full-line type that prints with ink ejected from an inkjet head.

  As described above, when the print medium is sucked on the transport belt by the suction of the suction fan and transported, an air flow (suction air) that wraps around the print medium by suction is generated. At this time, fine droplets (satellite) that are not used for image formation generated by ink ejection are swept away by this suction wind, and the image quality of the printing paper is reduced due to landing of the swept satellite at a location that is shifted from the ejection position. Deterioration and contamination inside the machine due to satellites being swept away by the air current and landing as mist on members around the recording area have been problems.

  For example, Patent Document 1 discloses a method for reducing image quality deterioration and in-flight contamination due to satellites as described above. The technique disclosed in Patent Document 1 is provided with a satellite suction fan, controls the rotation state of the satellite suction fan based on the ink discharge amount, and suppresses satellite adhesion. However, the technique disclosed in Patent Document 1 has a problem that a satellite suction fan must be provided separately from the suction means for sucking and transporting the print medium, and the mechanism becomes complicated.

  As a method for reducing image deterioration due to satellites without using special suction means, there is one disclosed in Patent Document 2. In the technique disclosed in Patent Document 2, the conveyance timing is controlled by the ink temperature in suction conveyance, and the amount of air between the sheets is adjusted to suppress satellite adhesion to the printed matter at low temperatures.

JP 2007-136847 A JP 2010-105208 A

  However, the problem of deterioration of image quality and in-machine contamination due to satellites is caused by the conveyance state of the print medium. In other words, when the suction force of suction conveyance is constant, when the number of printed sheets is one or the paper size is small, the influence of the suction air around the medium is greater than when the print medium is continuously conveyed. There is a problem that image quality is likely to deteriorate due to satellite.

  More specifically, when the ratio of the print medium to the upper surface of the conveyance belt is low, the ratio of the open vent holes is relatively high, and the open area is also increased, and therefore the suction fan generates. When the air flow becomes easier to pass through the transport belt and the print medium is sucked with the same suction force as when the print medium is continuously transported on the transport belt, the wind flow toward the outside of the print medium generated on the inkjet head side Will increase. As a result, the satellites land at positions different from the main droplets of the print medium, and the satellites concentrate on the periphery of the print medium, or the satellites scatter into the inkjet printer casing and contaminate the inside of the apparatus.

  Although the technology disclosed in Patent Document 2 copes with deterioration of image quality due to satellites caused by temperature factors, it does not take into account the conveyance state of the print medium. When the size was small, image quality deterioration and in-flight contamination due to satellites could not be prevented.

  The present invention has been made in view of the above problems, and by controlling the suction force in accordance with the number of print media transported on the transport belt, it is possible to suppress degradation in image quality and in-machine contamination of the print media. An object of the present invention is to provide an image forming apparatus capable of performing the above.

  In order to achieve the above object, a first feature of the image forming apparatus according to the present invention is that the print medium is ejected to the print medium conveyed on the conveyance path based on the image data of each page. An image forming apparatus for forming an image on the image forming apparatus, wherein a conveying unit that adsorbs and conveys the printing medium onto an upper surface of a conveying belt along the conveying path; a printing condition detecting unit that detects a printing condition of the image; Based on the printing conditions by the printing condition detection unit, the ratio of the print medium to the suction area on the surface of the transport belt is calculated, and the transport unit is controlled to obtain a suction force according to the calculation result. And a suction control unit.

  A second feature of the ink jet printing apparatus according to the present invention is that the suction control unit determines the suction force of the conveying unit for the first page and the last page in the image data from the suction force for the other pages therebetween. It is to reduce.

  A third feature of the ink jet printing apparatus according to the present invention is that, when the printing condition includes a double-sided printing mode in which image formation is performed on both sides of the printing medium, the transport unit finishes surface printing. In the cyclic conveyance in which the print medium is reversed on the front and back for printing on the back side and then conveyed again on the conveyance belt, an interrupt operation is performed to interrupt the print medium to a page to be interrupted between the conveyed print media, The suction control unit is configured to determine a suction force when the page to be interrupted passes through the conveyance belt in a state where the interrupt operation is not performed, and a page to be interrupted performs the interrupt operation. In this state, the suction force is lower than that when passing through the conveyor belt.

  A fourth feature of the ink jet printing apparatus according to the present invention is that the printing conditions are the size of the print medium, the gap value between the ink discharge means for discharging the ink and the print medium, and the ink discharge means. One or more of the ink temperature of the ink or the transport speed of the transport means is included.

According to a first feature of the inkjet printing apparatus according to the present invention,
The suction control unit calculates the ratio of the print medium to the suction area on the surface of the transport belt based on the printing conditions, and controls the transport unit so as to obtain a suction force according to the calculation result. The suction force of the transport means can be reduced when the ratio of the print medium to the suction area on the surface of the transport belt is low, such as when the number of printed sheets is one or the paper size is small. As a result, the flow of air to the outside of the print medium generated on the ink jet head side can be reduced, so that the satellites are prevented from landing away from the main droplet, and the image quality of the print medium is deteriorated and internal contamination is prevented. Can be suppressed.

According to a second feature of the inkjet printing apparatus according to the present invention,
It is possible to suppress deterioration in image quality of the print medium and internal contamination that occur during continuous printing. That is, when continuous printing is performed, since the first page in the image data does not carry any other print medium prior to the print medium, the ratio of the print medium to the suction area on the conveyance belt surface Is small, and the influence of the suction air around the print medium is large. Similarly, in the last page of the image data, since no other print medium is transported thereafter, the ratio of the print medium to the suction area on the surface of the transport belt is small, and suction around the print medium is performed. The effect of wind increases.

  Accordingly, since the suction control unit reduces the suction force of the conveying means for the first page and the last page in the image data, the influence of the suction wind on the print medium of the first page and the last page in the image data. As a result, the satellite can be prevented from landing away from the main droplet, and the deterioration of the image quality of the printing medium and the contamination in the machine can be suppressed.

According to a third feature of the inkjet printing apparatus according to the present invention,
It is possible to suppress image quality deterioration of the printing medium and internal contamination that occur during duplex printing. That is, in the double-sided printing mode, the printing medium that has been printed on the front side is circulated and returned to the conveying belt by reversing the front and back for backside printing, and the printing medium is interrupted between pages that are conveyed. Therefore, the conveying means of the image forming apparatus has a wide space between the print media. At this time, since the image forming apparatus performs a plurality of surface printings after the surface printing is started and before the printing medium is reversed and returns to the transport path, the surface printing print medium has a wide space between papers. It is conveyed in the state. On the other hand, after the front surface printing is completed, only the printing medium related to the back surface printing is printed, but in this case, the printing medium for the back surface printing and the printing medium related to the front surface printing are scheduled to be alternately conveyed. Therefore, the printing medium for backside printing is transported with a wide space between the sheets.

  As described above, in the double-sided printing mode, the printing medium for the front surface printing or the printing medium for the back surface printing is transported in the first predetermined section and the last predetermined section of the printing process without other print media being continuous before and after. Therefore, the ratio of the print medium to the suction area on the surface of the conveyor belt is small, and the influence of the suction air around the print medium is large.

  Therefore, the suction control unit interrupts the suction force when passing through the conveyor belt when the page to be interrupted is not interrupted when the duplex printing mode is included in the printing conditions. This lowers the suction force when the page to be operated passes through the conveyor belt in the interrupted state, so the area around the print medium relative to the print medium in the section where the print medium is conveyed without being continuous is reduced. The influence of the suction air can be suppressed, and as a result, the satellite can be prevented from landing away from the main droplet, and the deterioration of the image quality of the print medium and the contamination inside the apparatus can be suppressed.

  According to the fourth feature of the ink jet printing apparatus according to the present invention, it is possible to suppress deterioration in the image quality of the print medium and contamination inside the apparatus due to a quantity other than the number of print media transported on the transport belt. That is, when the size of the print medium is small, the influence of the suction air around the medium becomes large, so that the print medium is easily affected by the air current, and the image quality is deteriorated by the satellite and the machine is easily contaminated by the mist. If the gap between the ink ejection means and the print medium is large, the distance from ejection to landing will be longer, making it more susceptible to airflow, causing satellite image quality degradation and in-machine contamination due to mist. Cheap. Furthermore, since the viscosity of the ink is high when the ink temperature is low, the drive signal output means applies a higher voltage than the case where the ink temperature is high in order to eject a predetermined amount of ink. The high voltage increases the ink ejection speed and increases the generation of satellites, which tends to cause image quality degradation due to satellites and in-machine contamination due to mist. Further, when the conveyance speed is increased, the same thing occurs because the airflow in the image forming space becomes stronger.

  Therefore, the suction control unit determines the suction force of the transport unit according to one or more of the gap value between the ink discharge unit and the print medium, the ink temperature of the ink discharged by the drive signal output unit, or the transport speed of the transport unit. Therefore, the deterioration in the image quality of the print medium due to satellites and the in-machine contamination due to mist can be further suppressed.

1 is a configuration diagram illustrating a configuration of an inkjet printing apparatus according to a first embodiment of the present invention. (A) is a block diagram which shows the structure of the printing part which is 1st Embodiment of this invention from a side surface, The same figure (b) is a top view of an inkjet unit. BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows typically the suction mechanism of the printing part which is 1st Embodiment of this invention, (a) shows a side cross section, (b) is a top view which shows the belt hole formed in the conveyance belt. It is. It is the figure which showed the function structure of the inkjet printing apparatus which is 1st Embodiment of this invention. It is explanatory drawing which shows from the upper surface the ratio for which the printing paper accounts with respect to the suction area on the conveyance belt which is 1st Embodiment of this invention, (a) shows the state in which several printing paper is conveyed continuously, FIG. 5B shows a state where one print sheet is being conveyed. It is explanatory drawing which shows from the upper surface the printing paper on the conveyance belt at the time of the single-sided printing which is 1st Embodiment of this invention, (a) shows the state in which the printing paper of the 1st page was located on the conveyance belt, (B) shows a state in which the printing paper of the last page is positioned on the conveyance belt. (A)-(c) is explanatory drawing which shows the printing schedule at the time of the double-sided printing which is 1st Embodiment of this invention. It is explanatory drawing which shows the printing paper on the conveyance belt at the time of the double-sided printing which is 1st Embodiment of this invention from an upper surface, (a) shows the conveyance state of the printing paper before back surface interruption, (b) The conveyance state of the printing paper after completion | finish of surface printing is shown. FIG. 3 is a top view illustrating a ratio of a printing paper having a large size on the conveyance belt according to the first embodiment of the present invention. 4 is a timing chart of suction force control in the suction controller according to the first embodiment of the present invention, where (a) shows control during single-sided printing, and (b) shows control during double-sided printing. It is a flowchart which shows the operation | movement of the suction control which is 1st Embodiment of this invention. It is a flowchart which shows the operation | movement of the suction control which is 2nd Embodiment of this invention. It is a flowchart which shows the detail of the suction force setting based on the printing conditions which are 2nd Embodiment of this invention. It is a timing chart of suction force control in the suction control part which is a modification of the present invention, (a) shows control at the time of single-sided printing, and (b) shows control at the time of double-sided printing. It is a timing chart of attraction | suction force control in the attraction | suction control part which is a modification of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First embodiment]
(Overall configuration of inkjet printing apparatus)
The configuration of the inkjet printing apparatus 1 according to an embodiment of the present invention will be described in detail. FIG. 1 is a configuration diagram illustrating a configuration of an inkjet printing apparatus 1 according to an embodiment of the present invention.

  As shown in FIG. 1, an inkjet printing apparatus 1 is an image forming apparatus that forms an image on a sheet by ejecting ink corresponding to image data onto a sheet P that is a printing medium conveyed on a conveyance path. Thus, a side paper feeding unit 10, an internal paper feeding unit 20, a printing unit 30, a paper discharge unit 40, and a reversing unit 50 are provided.

  The side paper feeding unit 10 includes a paper feeding table 11 on which the paper P is stacked, a pickup paper feeding unit 12 that conveys only the uppermost paper P from the paper feeding table 11 onto the paper feeding conveyance path FR, and the pickup. And a registration unit 14 that corrects the skew of the sheet P conveyed by the sheet feeding unit 12 and conveys the sheet P onto the circulation conveyance path CR at a predetermined conveyance timing. A registration sensor 141 is provided in front of the registration unit 14 in the conveyance direction, and detects the leading edge or the trailing edge of the sheet P to be conveyed.

  The internal paper feed unit 20 includes a paper feed tray 21a on which the paper P is stacked, a pickup paper feed unit 22a that transports only the uppermost paper P from the paper feed tray 21a onto the paper feed transport path FR, and a paper P Are stacked, a pickup sheet feeding unit 22b that conveys only the uppermost sheet P from the sheet feeding table 21b onto the sheet feeding conveyance path FR, and a sheet feeding table 21c on which the sheets P are stacked. The pickup sheet feeding unit 22c that conveys only the uppermost sheet P from the sheet feeding table 21c onto the sheet feeding conveyance path FR, the sheet feeding table 21d on which the sheets P are stacked, and the uppermost position from the sheet feeding table 21d. Pickup paper feed section 22d for transporting only paper P on the paper feed transport path FR.

  As described above, the paper P is transported to the registration unit 14 from the side paper feeding unit 10 and the internal paper feeding unit 20, and the paper P is also transported from the reversing unit 50 described later. Therefore, in front of the registration unit 14 in the transport direction, there is a joining point where the transport path of the fed paper P and the transport path where the paper on which one side is printed is circulated and transported are merged. To do. Based on this merging point, the path on the paper feed mechanism side is referred to as a paper feed transport path FR, and the other transport path is referred to as a circulation transport path CR. A printing unit 30 is provided further on the side of the registration unit 14 in the conveyance direction.

  The printing unit 30 includes an ink jet unit 31 that is an ink discharge unit in which a plurality of print heads are incorporated, and an annular conveyance belt 133 that is provided on the opposite surface of the ink jet unit 31 and slides along the circulation conveyance path CR. The paper P fed by the registration unit 14 is installed in the annular transport belt 133 corresponding to the back surface of the paper transport path BP, and transported by adsorbing the paper P on the top surface of the transport belt 133. The ink is sucked onto the conveying belt 133 by the suction fan 131 and printed on the paper P by the ink ejected from the inkjet unit 31 while being conveyed at a predetermined conveying speed.

  The paper P printed by the printing unit 30 is conveyed on the circulation conveyance path CR in the housing by a conveyance roller or the like disposed on the circulation conveyance path CR. On the circulation conveyance path CR, a switching mechanism 43 that switches between guiding the paper P conveyed on the circulation conveyance path CR to the paper discharge unit 40 or recirculating on the circulation conveyance path CR is provided. .

  The switching mechanism 43, which is one of the transporting means, switches the paper P in order to guide the paper P to either one of the paper discharge unit 40 and the reversing unit 50 described later. The paper discharge unit 40 includes a tray-shaped paper discharge table 41 protruding from the casing of the inkjet printing apparatus 1 and a pair of paper discharge rollers 42 that guide the paper P to the paper discharge table 41. Then, the paper P guided to the paper discharge unit 40 by the switching mechanism 43 is transported to the paper discharge table 41 by the paper discharge roller 42 and stacked on the paper discharge table 41 with the printing surface down.

  The reversing unit 50, which is one of the conveying means, conveys the paper P from the reversing table 51 to the reversing table 51 from the reversing conveyance path CR, or from the reversing table 51 onto the recirculating conveying path CR. And a reversing roller 52 for conveying.

  The sheet P guided to the reversing unit 50 by the switching mechanism 43 is transported from the circulation transport path CR to the reversing table 51 by the reversing roller 52, and is transported from the reversing table 51 to the circulation transport path CR after a predetermined time. The front and back are reversed with respect to the circulation conveyance path CR. The sheet P with the front and back reversed is conveyed toward the printing unit 30 on the circulation conveyance path CR by a plurality of rollers such as a conveyance roller 53 provided on the circulation conveyance path CR. In this way, during duplex printing, the reversing unit 50 causes the switching mechanism 43 to cause the reversing unit 50 to reverse the front and back of the paper P for front side printing and then return the paper P to the circulation conveyance path CR and carry the paper. An interrupt operation for interrupting the sheet P to the page to be interrupted between P is performed.

  Moreover, it has the control part 80 which controls the whole inkjet printing apparatus 1. FIG. The control unit 80 is configured by a processor such as a CPU or DSP (Digital Signal Processor), memory, hardware such as other electronic circuits, software such as a program having the function, or a combination thereof. An arithmetic module. The control unit 80 virtually constructs various functional modules by appropriately reading and executing a program, and by using each constructed functional module, processing related to image data, operation control of each unit, and various processing for user operations. I do. Specifically, the control unit 80 controls the side paper feeding unit 10, the internal paper feeding unit 20, the printing unit 30, the paper discharge unit 40, and the reversing unit 50 to perform printing based on the print job. Execute the process.

  2A is a configuration diagram showing the configuration of the printing unit 30 according to an embodiment of the present invention from the side, and FIG. 2B is a plan view of the inkjet unit 31 according to the embodiment of the present invention. It is. 3A and 3B are explanatory views schematically showing the suction mechanism of the printing unit, in which FIG. 3A is a side cross-sectional view, and FIG. 3B is a plan view showing belt holes formed in the transport belt.

  In the printing unit 30, the paper P is transported by the transport belt 133 at a speed determined by the printing conditions. Above the printing unit 30, the ink jet unit 31 is disposed to face the transport belt 133, and the transport belt 133 provided on the facing surface of the ink head 33 from the nozzles of each ink head 33 provided in the ink jet unit 31. Ink of each color is ejected on the upper sheet P in line units, and a plurality of images are formed so as to overlap each other.

  Specifically, as shown in FIG. 2A, the printing unit 30 includes a conveyance belt 133 that is an endless conveyance belt, a driving roller 132 that is a driving mechanism of the conveyance belt 133, a driven roller 134, and the like. A head holder 32 is provided above the printing unit 30 to hold the ink head 33.

  The head holder 32 is a box having a head holder surface 32a on the bottom surface, and holds and fixes the ink head 33, and stores other functional parts for discharging ink from the ink head 33 as a unit. The head holder surface 32a, which is the bottom surface of the head holder 32, is disposed so as to be parallel to the transport path. A plurality of mounting openings having the same shape as the horizontal cross-sections of the plurality of ink heads 33 constituting the ink jet unit 31 are arranged on the head holder surface 32a. The plurality of ink heads 33 are inserted through the mounting openings, respectively. The discharge port protrudes from the head holder surface 32a.

  As shown in FIG. 2B, the ink heads 33 are arranged in a plurality of rows in a direction (main scanning direction) orthogonal to the transport direction (sub-scanning direction), and are included in each row within the plurality of rows. The ink heads 33 are arranged in a staggered manner.

  In the present embodiment, the ink head 33 is configured to eject ink of four colors K (black), C (cyan), M (magenta), and Y (yellow). A plurality of nozzles that eject ink are arranged in the main scanning direction. By ejecting an appropriate amount (drop amount) of a predetermined ink liquid for each pixel from the plurality of nozzles, a gradation-processed image is formed. Specifically, the ink ejected from the nozzles is ejected in units of drops to each pixel in accordance with a drive signal sent from the control unit 80. The density of each color is changed according to the number of ink droplets to be ejected (the number of drops), and the droplet amount is adjusted as a drop size. Note that the arrangement of the ink heads 33 is not limited to the illustrated arrangement, and can be variously changed.

  In addition, the printing unit 30 includes a print gap adjusting mechanism that switches a distance (print gap) from the ejection surface of the ink head 33 to the transport belt 133 in order to prevent the paper P from colliding with the ink head 33. Although not shown, the print gap adjusting mechanism moves the transport belt 133 up and down relative to the ink head 33 to change the distance between the ejection surface of the ink head 33 and the transport belt 133.

  In the printing unit 30, a paper sensor 142 that detects the presence or absence of the paper P conveyed to the printing unit 30 is provided upstream of the conveyance belt 133 (between the registration sensor 141 and the conveyance belt 133). The sheet sensor 142 can detect the leading end portion of the sheet P and also detect the trailing end portion of the sheet P by detecting that the sheet P passes over the sheet sensor 142. A detection signal (pulse width) detected by the paper sensor 142 is input to the control unit 80.

  On the other hand, the transport belt 133 is an endless belt member that transports the paper, and is moved around by the driving roller 132 and slides in a range facing the ink head 33 as shown in FIG. Transport P. Specifically, the transport belt 133 is wound around a pair of driving rollers 132 and driven rollers 134 arranged orthogonal to the transport direction in which the paper P is transported, and transported by the driving force of the drive rollers 132. Circulated in the direction.

  Further, as shown in FIGS. 3A and 3B, the transport belt 133 has a number of belt holes 133 a that attract the paper P, and a plastic template (not shown) is disposed below the transport belt 133. Has been. The plastic template is a plate-like member that supports the transport belt 133 so as to be slidable at a position facing the ink head 33 and has a large number of suction holes penetrating in places where the belt holes 133a pass. A suction fan 131, which is one of conveying means, is provided below the plastic template.

  The suction fan 131 is a suction unit that generates a negative pressure for sucking the paper P on the upper surface of the platen belt through the belt hole 133a and the suction hole. The sheet P is sucked onto the transport belt 133 by the negative pressure generated by the suction fan 131.

  In the printing unit 30 configured in this manner, the paper P is imaged line by line with the ink ejected from each of the plurality of ink heads 33 while being transported on the transport belt 133 at a speed according to the printing conditions. .

(Functional configuration of inkjet printing apparatus 1)
Next, the functional configuration of the inkjet printing apparatus 1 according to an embodiment of the present invention will be described. FIG. 4 is a diagram illustrating a functional configuration of the inkjet printing apparatus 1 according to an embodiment of the present invention.

  As shown in FIG. 4, the inkjet printing apparatus 1 includes a side paper feed unit 10, an internal paper feed unit 20, a printing unit 30, a paper discharge unit 40, a reversing unit 50, an operation panel unit 70, and a control. Part 80. Among these configurations, the side paper feed unit 10, the internal paper feed unit 20, the paper discharge unit 40, and the reversing unit 50 have been described above, and thus description thereof will be omitted.

  The control unit 80 is transmitted by the CPU 81, the ROM 82 storing the operation program of the CPU 81 and various tables, the image data read by the image reading unit (not shown), the computer device (not shown), and the like. It has a RAM 83 for storing print data including image data and various printing conditions from the operation panel unit 70 or a computer device (not shown).

  As shown in FIG. 4, the CPU 81 executes the operation program stored in the ROM 82, whereby the entire apparatus, that is, the side paper feeding unit 10, the internal paper feeding unit 20, the printing unit 30, and the paper ejection unit. 40, the reversing unit 50, the operation panel unit 70, and the like are controlled. The CPU 81 also includes a printing condition detection unit 81a, a conveyance control unit 81b, a suction control unit 81c, and an ink ejection control unit 81d. The print condition detection unit 81a is a module that detects an image print condition from the print condition set by the personal computer or the print job set by the operation panel unit 70. The printing conditions include the number of pages to be printed, the number of copies, a printing mode (a single-sided printing mode in which an image is formed on one side of the paper P, and a double-sided printing mode in which an image is formed on both sides of the paper P). It is.

  The conveyance control unit 81b controls driving of the conveyance units of the side paper feeding unit 10, the internal paper feeding unit 20, the paper discharge unit 40, and the reversing unit 50 according to the printing conditions included in the print job. At the same time, it is a module that controls driving of the conveyor belt 133 of the printing unit 30. Under the control of the conveyance control unit 81b, the paper P is conveyed at a predetermined speed and a predetermined interval.

  The ink ejection control unit 81d is a module that controls the inkjet unit 31 of the printing unit 30 based on the image data included in the print job and the printing conditions (such as paper type), and based on the image data after image processing. The ink discharge amount for each dot is calculated and output to the driver of the inkjet unit 31. Here, the inkjet unit 31 expresses the gradation by the number of ink drops, and expresses the highlight portion of the image with a small number of drops and the shadow portion with a large number of drops. The driver outputs a drive signal having a predetermined voltage value to the piezoelectric element group based on the acquired control data. Ink is ejected from the nozzles of each ink head 33 as the piezo element group deforms in response to the drive signal.

  The suction control unit 81c is a module that controls the suction force of the suction fan 131. In this embodiment, the sheet P occupies the suction area on the surface of the transport belt 133 based on the printing conditions by the printing condition detection unit 81a. The ratio is calculated, and the suction force of the suction fan 131 is controlled so as to obtain the suction force according to the calculation result. Hereinafter, the control of the suction control unit 81c will be described in detail.

  FIG. 5 is an explanatory view showing the sheet P transported on the transport belt according to the embodiment of the present invention from the top, and (a) shows a state where a plurality of sheets P are transported on the transport belt. , (B) shows a state in which one sheet of paper P is being transported on the transport belt.

  In FIG. 5A, two sheets of paper P are arranged on the transport belt 133. As described above, when two (a plurality of) sheets P are continuously conveyed on the conveyance belt 133, the ratio of the sheet P to the suction area of the conveyance belt 133 is high. When the ratio is high, the area of the vent hole is small, so that the air flow generated by the suction fan 131 is difficult to pass through the transport belt 133, and the wind flow toward the outside of the paper P generated on the ink jet unit 31 side is difficult. Less. As a result, the satellite is prevented from landing away from the main droplet, the satellite is concentrated on the peripheral portion of the paper P, and the accumulation of mist in the casing of the inkjet printing apparatus 1 due to the mist scattering hardly occurs.

  On the other hand, as shown in FIG. 5B, when one sheet P is arranged on the conveyance belt 133, the ratio of the sheet P to the suction area of the conveyance belt 133 is low. When the ratio of the sheet P is low, the area of the vent hole is increased. Therefore, when a plurality of sheets are sucked with the same suction force as when the sheet is conveyed on the conveying belt 133, the air generated by the suction fan 131 is generated. Becomes easier to pass through the conveying belt 133, and the flow of wind toward the outside of the paper P generated on the ink jet unit 31 side increases. As a result, the satellites land at positions different from the main droplets of the paper P, the satellites concentrate on the periphery of the paper P, and mist accumulates in the case of the inkjet printing apparatus 1 due to the scattering of the satellites.

  Therefore, in the present embodiment, as shown in FIG. 5B, in the suction control unit 81c, the ratio of the sheet P to the suction area of the conveyance belt 133 is a predetermined ratio as in the case of printing one sheet P. When the value is less than the value, the suction force of the suction fan 131 is made lower than normal.

  Furthermore, the suction control unit 81c also changes the suction force of the suction fan 131 according to the transport state when printing a plurality of sheets P. Here, the printing mode is divided into a single-sided printing mode and a double-sided printing mode.

  First, suction force control in the single-sided printing mode will be described. FIG. 6 is an explanatory view showing the paper P on the transport belt from the top surface in the case of continuous single-sided printing according to an embodiment of the present invention, and FIG. 6A shows the paper P of the first page on the transport belt. (B) shows a state in which the paper P of the last page is conveyed on the conveyance belt.

  In the case where the paper P is continuously printed on one side, as shown in FIG. 6A, when the first page enters the transport belt 133, the downstream side in the transport direction is closer to the first page of the paper P. Since the sheet P does not exist, the ratio of the sheet P to the suction area of the transport belt 133 is low. Therefore, the suction control unit 81c reduces the suction force of the suction fan 131 from the normal time while the first page of paper P is being transported on the transport belt 133 from the start of the printing process. Note that when the paper P of the second page enters the transport belt 133, the ratio of the paper P to the suction area of the transport belt 133 increases, so that the suction control unit 81c has the rear end of the first page on the transport belt 133. At the timing of entering, the control is performed so that the suction force of the suction fan 131 is returned to the normal suction force.

  On the other hand, as shown in FIG. 6B, even when the last page is located on the conveyance belt 133, the sheet P does not exist upstream from the sheet P of the last page. The ratio of the sheet P to the suction area of the belt 133 is reduced. Therefore, the suction control unit 81c reduces the suction force of the suction fan 131 as compared to the normal time while the paper P of the last page is being transported on the transport belt 133. Note that when the trailing edge of the last page enters the transport belt 133, the sheet P is not transported thereafter, and the ratio of the sheet P to the suction area of the transport belt 133 becomes low. When the rear end of the page enters the conveying belt 133, the suction force of the suction fan 131 is reduced as compared with the normal time. In this manner, the suction control unit 81c reduces the suction force of the suction fan 131 for the first page and the last page in the image data, compared to the suction force for the other pages in the meantime.

  Next, suction force control in the duplex printing mode will be described.

  FIGS. 7A to 7C are explanatory views showing a printing schedule at the time of double-sided printing, and FIG. 8 is an explanatory view showing the sheet P on the conveyance belt at the time of double-sided printing according to the present embodiment from the upper surface. Yes, (a) shows the transport state of the paper P before the back side interruption, and (b) shows the transport state of the paper P after the front side printing is finished. FIG. 8 shows the transport state of the paper P when printing is performed according to the print schedule shown in FIG.

  First, the conveyance schedule at the time of duplex printing controlled by the conveyance control unit 81b will be described. FIG. 7A shows a double-sided printing schedule when the paper size is A3 and the circulation number N of the printing apparatus is 2. Specifically, after printing the surface of the first sheet, the surface of the second sheet is printed with an interval of one sheet, and then the back side of the first sheet that has been circulated and conveyed is printed. Then, the front surface of the third sheet is printed immediately, and then the back surface of the second sheet that has been circulated and conveyed is printed. By performing such control, after the surface printing of the second sheet, printing is continuously performed as in the case of single-sided printing. Thereafter, after the last sheet on the front surface (seventh sheet in FIG. 7A) is printed, the back surface of the sixth sheet, which is one before the last sheet, is printed, and then the interval for one sheet is printed. And print the back of the last sheet.

  FIG. 7B shows a double-sided printing schedule when the paper size is A4 landscape and the circulation number N of the printing apparatus is 4. Specifically, after printing the surface of the first sheet, the surface of the second sheet is printed with an interval of one sheet, and after that, the surface of the third sheet, And the fourth surface is printed. After the front surface of the fourth sheet is printed, the back surface of the first sheet that has been circulated and conveyed is printed. Then, the front surface of the fifth sheet is printed immediately, and then the back surface of the second sheet that has been circulated and conveyed is printed. By performing such control, after the surface printing of the fourth sheet, printing is continuously performed as in the case of single-sided printing. Then, after the surface of the last sheet (the seventh sheet in FIG. 7B) is printed, the back surface of the fourth sheet is printed, and the back surface of the fifth sheet is printed with an interval of one sheet. To do. Thereafter, printing is performed up to the back side of the last sheet with an interval of one sheet.

  FIG. 7C shows a double-sided printing schedule when the paper size is A4 portrait and the circulation number N of the printing apparatus is 3. Specifically, after printing the surface of the first sheet, the second surface is printed with an interval of one sheet, and then the third surface is spaced with an interval of one sheet. Print. After the front surface of the third sheet is printed, the back surface of the first sheet that has been circulated and conveyed is printed. Then, the front surface of the fourth sheet is printed immediately, and then the back surface of the second sheet that has been circulated and conveyed is printed. By performing such control, after the surface printing of the third sheet, printing is continuously performed as in the case of single-sided printing. Then, after the surface of the last sheet (the seventh sheet in FIG. 7C) is printed, the back surface of the fifth sheet is printed, and the back surface of the sixth sheet is printed with an interval of one sheet. To do. Thereafter, printing is performed up to the back side of the last sheet with an interval of one sheet.

  As described above, in the duplex printing mode, the paper on which the front surface printing is finished is circulated and transported back to the transport belt by reversing the front and back for back surface printing, and between the papers related to the reversed and transported printing (back surface printing). Since the paper for the new front surface printing is interrupted in the page of FIG. 8, the paper for the front surface printing and the paper for the back surface printing are alternately and continuously printed in the intermediate section S2, but in FIG. As shown in the figure, immediately after the start of printing, the paper for the back side printing is not interrupted between the papers for the front side printing, and there is an interval (blank) for one sheet. In the section S1 before the sheet is interrupted between the sheets for front side printing, the ratio of the sheet P to the suction area of the transport belt 133 is low.

  In addition, even after the printing of the paper for front side printing is finished, the paper P for front side printing and the paper P for back side printing are scheduled to be conveyed alternately. In the printing section S3 of the paper related to the back side printing after the paper related to the front side printing is finished, the paper P related to the front side printing is transported on the transport belt and printed, while securing the interval for the paper P related to the front side printing to be interrupted. As shown in FIG. 8B, the ratio of the sheet P to the suction area of the transport belt 133 is low.

  Therefore, the suction control unit 81c determines the suction force when the page to be interrupted passes through the transport belt 133 in a state where the interrupting operation is not performed when the double-sided printing mode is included in the printing condition. The suction force when the page to be interrupted passes through the conveyor belt 133 in the interrupted state is reduced.

  That is, the suction control unit 81c sucks the suction fan 131 more than usual during the period from the start of printing to before the sheet related to the first backside printing is interrupted between the sheets related to the front side printing (printing section S1). Reduce power. At this time, the suction control unit 81c performs control so that the suction force of the suction fan 131 is returned to normal when the rear end of the paper for front side printing before the paper for back side printing enters the conveyor belt 133. To do. As a result, normal suction is performed after the paper for backside printing has interrupted the paper for frontside printing and the interval for interrupting the paper for backside printing has passed through the transport belt 133 between the paper for front side printing. It will return to power.

  In addition, the suction control unit 81c increases the suction force of the suction fan 131 during normal printing (printing section S3) after the last page of the front surface printing is printed and during the time when only the paper related to the back surface printing is printed. Reduce. At this time, the suction control unit 81c normally sets the suction force of the suction fan 131 at the time when the rear end of the paper related to the backside printing that is transported after the last page of the front surface printing has entered the transport belt 133. Decrease than time. As a result, the suction force is reduced after the front surface printing is finished and before the interval for interrupting the paper for front side printing between the papers for back side printing reaches the conveying belt 133.

Further, in the suction control unit 81c, the suction force of the suction fan 131 is changed according to the paper size of the paper P. FIG. 9 is a top view showing the proportion of the large size paper P on the transport belt according to the embodiment of the present invention. Specifically, as shown in FIG. 9, the paper Pa having a predetermined paper size is shown. For the paper Pb having a larger paper size, the ratio of the paper Pb to the suction area of the transport belt 133 is higher. Since the paper Pb having a large paper size needs to be appropriately adsorbed on the transport belt 133 by the negative pressure generated by the suction fan 131, the suction controller 81c does not handle the paper Pb having a large paper size. The suction force that is reduced as described above (hereinafter, this suction force is referred to as “suction force 1”) is set to be larger (hereinafter, this suction force is referred to as “suction force F2”). The value of the suction force 2 is higher than the low suction force 1 and lower than the normal suction force (hereinafter, this suction force is referred to as “suction force F3”).

  Note that the suction control in the suction control unit 81c is controlled according to a detection signal from the sheet sensor 142 located upstream of the transport belt 133.

  FIG. 10 is a timing chart of suction force control in the suction control unit 81c according to an embodiment of the present invention, where (a) shows control during single-sided printing, and (b) shows control during double-sided printing. Show. The horizontal axis of this timing chart represents time (t), and the vertical axis represents the duty ratio (rotation amount) of the suction fan 131. This figure also shows changes in the detection output of the paper sensor 142.

  When performing single-sided printing continuously, as shown in FIG. 10A, when printing is started (at time t0), the suction control unit 81c sets the suction force F1 lower than the normal suction force F3. Then, the suction fan 131 is driven. Thereafter, when the paper sensor 142 detects the rear end of the first page at time t1, the suction force F1 is changed to the normal suction force F3 at that timing. Thereafter, suction is performed with a normal suction force F3 until the paper of the last page is detected. When the paper sensor 142 detects the trailing edge of the last page at time t2, the normal suction force F3 is reduced to the suction force F1 at that timing. Whether or not the paper P is the last page is determined based on the number of printed sheets included in the printing conditions and the number of counts counted by the paper sensor 142.

  At this time, if the size of the paper P included in the printing condition is larger than the predetermined size, the suction control unit 81c performs printing from the time t0 to the time t1 and from the time t2 as shown in FIG. Until the processing is completed, the suction force F2 is set to be larger than the suction force F1 and smaller than the suction force F3 as indicated by a broken line in the figure.

  On the other hand, in the case of duplex printing, as shown in FIG. 10B, when printing is started (at time t0), the suction control unit 81c sets the suction force F1 lower than the normal suction force F3, The suction fan 131 is driven. After that, when the paper sensor 142 detects the rear end of the paper related to the front side printing conveyed before the paper related to the back side printing of the first page (at time t4), the suction force F1 is changed to the normal suction force F3 at that timing. To change.

  Thereafter, while the paper for front side printing and the paper for back side printing are alternately and continuously printed, suction is performed with a normal suction force F3. Thereafter, when the paper sensor 142 detects the trailing edge of the paper related to the back side printing that is conveyed after the last page of the front surface is printed (at time t5), the normal suction force F3 is changed to the suction force F1 at that timing. Whether or not the paper P is the last page is determined based on the number of printed sheets included in the printing conditions and the number of counts counted by the paper sensor 142.

  At this time, if the size of the paper P included in the printing condition is larger than the predetermined size, the suction control unit 81c performs printing from the time t0 to the time t4 and from the time t5 as shown in FIG. 10B. Until the processing is completed, the suction force F2 is set to be larger than the suction force F1 and smaller than the suction force F3 as indicated by a broken line in the figure.

(Suction control processing)
Next, the suction control process will be described.

  FIG. 11 is a flowchart showing the operation of suction control. In the printing condition detection unit 81a of the CPU 81, image data read by an image reading unit (not shown) or image data transmitted from a computer device (not shown) or the like, and further, an operation panel unit 70 or a computer. It is determined whether a print job including various printing conditions from an apparatus (not shown) has been acquired (step S101).

  In step S101, when a print job is acquired (“YES”), the printing conditions are input to the conveyance control unit 81b, the suction control unit 81c, and the ink discharge control unit 81d, respectively.

  The conveyance control unit 81b controls driving of the conveyance units of the side paper feeding unit 10, the internal paper feeding unit 20, the paper discharge unit 40, and the reversing unit 50 according to the printing conditions included in the print job. At the same time, the driving of the conveying belt 133 of the printing unit 30 is controlled. The ink ejection control unit 81d controls the inkjet unit 31 of the printing unit 30 based on the image data included in the print job and the printing conditions (such as the paper type), and for each dot based on the image data after image processing. The ink discharge amount is calculated and output to the inkjet unit 31.

  The suction control unit 81c refers to the printing conditions included in the print job and sets suction control of the suction fan 131 when the paper P is transported on the transport belt 133. First, the suction control unit 81c determines whether or not double-sided printing settings are included (step S102). If the setting for duplex printing is not included (step S102 “NO”), the suction timing during single-sided printing is set (step S104), and the process proceeds to step S105. On the other hand, when the setting for duplex printing is included (“YES” in step S102), the suction timing for duplex printing is set (step S103), and the process proceeds to step S105.

  In step S105, the suction control unit 81c determines whether the paper size is larger than the predetermined size paper P (step S105). When the paper size is large (S105 “YES”), the setting for reducing the suction force of the suction fan 131 is set to “suction force 2”. On the other hand, if the paper size is equal to or smaller than the predetermined size (step S105 “NO”), the setting for reducing the suction force of the suction fan 131 is set to “suction force 1”. Thereafter, the printing process is started, and the driving of the suction fan 131 is controlled based on the detection signal of the paper sensor 142 according to each setting.

  As described above, according to one embodiment of the present invention, the ratio of the sheet P to the suction area on the surface of the conveyor belt 133 is calculated based on the printing conditions, and the suction fan 131 stage is calculated according to the result. Since the suction force is controlled, for example, when the number of printed sheets is one or the paper size is small, the suction force of the suction fan 131 is low when the ratio of the paper P to the suction area on the surface of the transport belt 133 is low. Can be reduced. As a result, the air flow toward the outside of the paper P generated on the ink jet unit 31 side can be reduced, so that the satellites can be prevented from landing away from the main droplets, and the image quality of the paper P can be reduced, and in-flight contamination. Can be suppressed.

  In the present embodiment, when performing single-sided printing continuously, the suction control unit 81c lowers the suction force of the suction fan 131 for the first page and the last page in the image data, compared to the suction force for other pages in the meantime. Therefore, it is possible to suppress the influence of the suction air on the first page and the last page of the image data P, and even when printing one side continuously, the satellites land away from the main droplet. It is possible to suppress the deterioration of the image quality of the paper P and the contamination inside the apparatus. Since the pages other than the first page and the last page are sucked with the normal suction force F3, the paper P is transported in a state of being properly sucked by the transport belt 133. Occurrence can be prevented.

  In this embodiment, the suction control unit 81c interrupts the suction force when the page that is the target of the interrupt operation passes through the transport belt 133 in a state where the interrupt operation is not performed. Since it is lower than the suction force when passing the transport belt 133 in the operated state, the paper P with respect to the paper P in the sections S1 and S3 in which the paper P is transported without being continuous during double-sided printing. The influence of the surrounding suction air can be suppressed, and as a result, the satellite can be prevented from landing away from the main droplet, and the image quality of the paper P can be prevented from being deteriorated and the contamination inside the apparatus can be suppressed.

  Further, in the present embodiment, when the paper P is a large paper Pb having a predetermined paper size, the value of the suction force to be reduced is set to a suction force F2 that is slightly larger than the suction force F1 for the paper P of the predetermined size. Therefore, the paper Pb having a large paper size can be transported while being appropriately attracted to the transport belt 133, and transport jam can be prevented.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The gist of the second embodiment of the present invention is to change the suction force of the suction fan 131 including other printing conditions in addition to the printing conditions described above. In the present embodiment, the same components as those in the first embodiment described above are denoted by the same reference numerals, and the functions and the like are the same unless otherwise specified, and the description thereof is omitted.

  In the present embodiment, the suction control unit 81c in the CPU 81 varies the rate of reducing the suction force of the suction fan 131 based on the parameters set in the transport control unit 81b and the ink discharge control unit 81d shown in FIG. . Here, the parameter for varying the suction force refers to the value of the print gap set by the ink ejection control unit 81d, the ink temperature of the ejected ink, or the conveyance speed of the conveyance belt 133 set by the conveyance control unit 81b. Either.

(1) Suction force control with respect to the conveyance speed First, the conveyance control unit 81b varies the conveyance speed of the conveyance belt 133 based on the type of the paper P included in the printing conditions. Here, the paper type includes plain paper, matte paper, glossy paper, inkjet paper, postcard paper, and the like. Since the number of drops ejected from the ink head 33 is different when the paper type is different, the conveyance control unit 81b performs control so that the conveyance speed is appropriate for the number of drops. For example, since the number of drops is small for plain paper, the conveyance speed is high. For example, for mat paper or postcard paper, the number of drops is high, so the printing speed is low.

  Here, when the conveyance speed is set to be high for printing plain paper or the like, an air flow is likely to be generated in the printing unit 30, and image deterioration due to satellites is likely to occur. Therefore, in the suction control unit 81c, when the parameter of the transport speed set by the transport control unit 81b is faster than the predetermined speed, the suction force set by the suction force 1 and the suction force 2 described above is further reduced. Control. On the other hand, with matte paper or postcard paper, the number of drops increases, so the printing speed is slowed down. Therefore, airflow is less likely to occur and image deterioration due to satellites is less likely to occur. Therefore, the suction control unit 81c performs control so as to increase the suction force set by the suction force 1 and the suction force 2 described above when the parameter of the transport speed set by the transport control unit 81b is slower than the predetermined speed. To do.

(2) Suction force control with respect to print gap The ink discharge control unit 81d has a function of adjusting the print gap adjustment mechanism. Specifically, the print gap adjustment is to change the distance between the ejection surface of the ink head 33 and the transport belt 133, and is changed according to the type of paper. For example, the print gap value is large for thick paper such as postcard paper, and the print gap value is small for thin paper such as plain paper.

  At this time, if the value of the print gap is increased, the distance from ejection to landing is increased, so that it is easily affected by the air flow, and the image is likely to be deteriorated by the satellite. Therefore, the suction controller 81c performs control so as to further lower the set values of the suction force 1 and the suction force 2 described above when the value of the print gap set by the ink discharge controller 81d is larger than a predetermined value. . On the other hand, for paper with no thickness such as plain paper, since the distance from ejection to landing is shortened, the influence of the air current is small and image deterioration due to satellite is unlikely to occur. Therefore, in the suction control unit 81c, when the print gap value parameter set by the ink discharge control unit 81d is smaller than a predetermined value, the suction force set by the suction force 1 and the suction force 2 described above is further increased. To control.

(3) Suction force control with respect to ink temperature The ink ejection control unit 81d has a function of adjusting the temperature of ink ejected from the ink head 33. Here, when the temperature of the ink accumulated in the ink head 33 is low, the viscosity of the ink is high. Therefore, the ink ejection control unit 81d ejects ink by applying a high voltage to the piezo element group. . When such a high voltage is applied, satellites increase, and image degradation due to satellites is likely to occur. Therefore, the suction control unit 81c acquires the measurement result of the ink temperature in the ink head 33, and if the ink temperature is lower than the predetermined value, the set values of the suction force 1 and the suction force 2 described above are further set. Control to lower.

  On the other hand, when the ink temperature is higher than the predetermined value, the ink ejection control unit 81d applies a low voltage, and thus the generation of satellites can be suppressed. Therefore, image deterioration due to satellites is unlikely to occur. Therefore, the suction control unit 81c acquires the measurement result of the ink temperature in the ink head 33, and if the ink temperature is higher than a predetermined value, the set values of the suction force 1 and the suction force 2 described above are further set. Control to lower.

  A suction force setting operation that is set based on such other printing conditions will be described. FIG. 12 is a flowchart showing the operation of suction control according to the second embodiment of the present invention, and FIG. 13 is a flowchart showing details of suction force setting based on printing conditions according to the second embodiment of the present invention. .

  As shown in FIG. 12, in the present embodiment, after a print job is acquired (“NO” in step S201), processing for changing the set value of the suction force based on other printing conditions is performed (step S202). In the setting value variable process in step S202, as shown in FIG. 13, first, the print condition detection unit 81a acquires paper type information from the header of the print job (step S301). Thereafter, the paper type information is input to the ink ejection control unit 81d and also input to the transport control unit 81b.

  The ink ejection control unit 81d calculates a print gap value based on the paper type information (step S302). Further, the transport control unit 81b determines the transport speed of the transport belt 133 based on the paper type information (step S303). Further, the ink ejection control unit 81d measures the ink temperature in the ink head 33 (step S304). The parameters of the print gap value, the sales promotion speed of the transport belt 133, and the ink temperature are input to the suction control unit 81c. The suction control unit 81c varies preset values of the suction force 1 and the suction force 2 based on any of the parameters (step S305).

  Thereafter, the process returns to step 203 shown in FIG. 12, and after determining whether or not the data to be printed is double-sided printing (step S203) and whether or not the paper size is a paper P larger than a predetermined size (step S206). The suction force of the suction fan 131 is set to either suction force 1 or suction force 2 in accordance with each determination result (steps S207 and S208). Here, if the suction force is varied in step S202, the value of the varied suction force is set. In addition, since the process from step S203 to step S208 is the same process as step S102 to step S107 mentioned above, the description is abbreviate | omitted.

  As described above, according to the second embodiment of the present invention, in addition to the state of the paper P transported on the transport belt 133, the gap value between the ink head 33 and the paper P, the ink ejected by the ink head 33, The rate at which the suction force of the suction fan 131 is reduced is made variable in accordance with any of the parameters relating to the ink temperature or the conveyance speed of the conveyance belt 133, so that the deterioration of the image quality of the paper P due to satellites and the contamination inside the machine are further suppressed. can do.

[Modification]
The description of each embodiment described above is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made according to the design or the like as long as the technical idea according to the present invention is not deviated. FIGS. 14A and 14B are timing charts of suction force control in the suction control unit according to the modification. FIG. 14A shows the control during single-sided printing, and FIG. 14B shows the control during double-sided printing.

  In the first and second embodiments described above, the suction force is changed by detecting the trailing edge of the paper P. For example, the suction force is changed by detecting the front edge of the paper P. Also good. At this time, the suction control unit 81c acquires a detection signal indicating that the front end of the paper P has been detected from the paper sensor 142, and changes the suction force in accordance with the detection signal.

  For example, when performing single-sided printing continuously, as shown in FIG. 14A, when printing is started (at time t0), the suction control unit 81c sets the suction force F1 to be lower than the normal suction force F3. The suction fan 131 is driven by setting. Thereafter, in this modification, when the paper sensor 142 detects the front edge of the second page (at time t6), the suction force F1 is changed to the normal suction force F3 at that timing. Thereafter, suction is performed with a normal suction force F3 until the paper of the last page is detected. When the paper sensor 142 detects the front edge of the last page (time t7), the normal suction force F3 is changed to the suction force F1 at that timing.

  Whether or not the paper P is the last page is determined based on the number of printed sheets included in the printing conditions and the number of counts counted by the paper sensor 142. At this time, also in the present modification, when the size of the paper P included in the printing conditions is larger than the predetermined size, the suction control unit 81c performs the period from the time t0 to the time t6 as shown in FIG. From time t7 to the end of the printing process, the suction force F2 is set to be larger than the suction force F1 and smaller than the suction force F3, as indicated by a broken line in the figure.

  In the case of double-sided printing as well, the front end of the paper P is similarly detected and the suction force is made variable. Even in this case, the suction control unit 81c uses the suction force when the page that is the target of the interrupt operation passes through the transport belt 133 in a state where the interrupt operation is not performed as the target of the interrupt operation. This is lower than the suction force when passing through the transport belt 133 in a state where the page to be interrupted is interrupted. That is, before the paper for back side printing is interrupted to the paper for front side printing and after the interval for interrupting the paper for back side printing passes between the papers for front side printing, the normal suction force F3 is restored. To control. Further, the suction control unit 81c performs control so that the suction force is reduced to the suction force F1 after the front surface printing is finished and before the interval for interrupting the paper for front side printing between the papers for back side printing comes. To do.

  Specifically, as shown in FIG. 14B, when printing is started (at time t0), the suction control unit 81c sets the suction force F1 to be lower than the normal suction force F3, and the suction fan. 131 is driven. Thereafter, when the paper sensor 142 detects the front edge of the paper related to the back side printing of the first page (at time t8), the suction force F1 is changed to the normal suction force F3 at that timing. As a result, the normal suction force F3 is applied before the paper for backside printing is interrupted to the paper for frontside printing and after the interval for interrupting the paper for backside printing passes between the papers for front side printing. Will return.

  Thereafter, while the paper for front side printing and the paper for back side printing are alternately and continuously printed, suction is performed with a normal suction force F3. Thereafter, when the paper sensor 142 detects the front edge of the paper related to the back side printing that is conveyed after the last page of the front surface is printed (at time t9), the normal suction force F3 is changed to the suction force F1 at that timing. As a result, the suction force is reduced to the suction force F1 after the front surface printing is finished and before the interval for interrupting the paper for front side printing between the papers for back side printing comes. Whether it is the first page on the back side or the last page on the front side is determined based on the number of printed sheets included in the printing conditions and the count number counted by the paper sensor 142.

  Further, also here, when the size of the paper P included in the printing condition is larger than the predetermined size, the suction control unit 81c, as shown in FIG. 14B, between the time t0 and the time t8 and the time t9 From the time until the end of the printing process, as shown by the broken line in the figure, the suction force F2 is set to be larger than the suction force F1 and smaller than the suction force F3.

  As described above, according to the present modification, the suction force is changed at the timing when the front end of the predetermined paper P is detected, so the timing at which the low suction force F1 or F2 is returned to the normal suction force F3 is the first implementation. It can be delayed from the form. As a result, the suction force F1 is low until the second page of continuous paper (simply the second page for single-sided printing, and the paper for backside printing of the first page for double-sided printing) immediately before entering the transport belt 133. It is possible to prevent image quality deterioration due to satellites more appropriately.

  In this modification, the suction force is changed at the timing when the front edge of the predetermined paper P is detected. Therefore, the timing at which the normal suction force F3 is changed to the lower suction force F1 or F2 is changed from that in the first embodiment. You can expedite. As a result, the suction force can be changed to the predetermined suction force F1 or F2 before the gap between sheets is formed on the transport belt 133, and deterioration of image quality due to satellites can be prevented more appropriately.

  Further, in each of the above-described embodiments, switching between the low suction force F1 (F2) and the normal suction force F3 is instantaneously switched. However, the change in the suction force may be controlled stepwise. This change in suction force switching will be described by taking the case of single-sided printing as an example. FIG. 15 is a timing chart of suction force control in the suction control unit according to this modification.

  When returning from the low suction force F1 or F2 to the normal suction force F3, as shown in FIG. 15, first, the low suction force F1 (or suction force F2) is set, and the paper sensor 142 is set to the leading edge of the first page. The suction force is gradually increased at the timing (time t10) at which is detected, and the normal suction force F3 is set at the timing (time t11) when the front edge of the second page passes the paper sensor 142. Here, the timing at which the normal suction force F3 is set is the timing at which the front edge of the second page passes the paper sensor 142 (at time t11). For example, the rear edge of the first page passes through the paper sensor 142. Control may be performed so that the normal suction force F3 is obtained at the timing.

  On the other hand, when the normal suction force F3 is decreased to the low suction force F1 or F2, the suction force gradually increases from the normal suction force F3 at the timing when the paper sensor 142 detects the leading edge of the last page (at time t12). Is set so that the suction force F1 (or suction force F2) is low at the timing when the trailing edge of the last page passes the paper sensor 142 (at time t13). Here, the timing for decelerating from the normal suction force F3 is the timing for detecting that the front edge of the last page has passed the paper sensor 142 (time t12), but, for example, the sheet is conveyed before the last page. The timing of detecting that the trailing edge of the paper P has passed the paper sensor 142 may be used.

  In this way, when control for accelerating or decelerating the suction force in stages is performed, the timing for starting acceleration or deceleration starts based on a detection signal from the paper sensor 142. On the other hand, the timing for reaching a predetermined suction force is calculated based on the paper size and the transport speed of the transport belt 133 by calculating the time until the front end or the rear end of the next paper P reaches the transport belt 133. It is designed to control based on the time.

  According to this modified example, since the suction force is changed step by step, adverse effects caused by instantaneously switching the suction force (for example, sudden air flow generation or timing for reaching a predetermined suction force). Misalignment etc.) can be prevented.

  Note that the front end or the rear end of the paper P as described above can be combined. For example, when returning to the normal suction force F3, the rear end of the paper P is detected and the low suction force F1 is detected. Alternatively, in the case of F2, the front end of the paper P may be detected. Furthermore, it is also possible to use a combination of whether the change in suction force is switched instantaneously or stepwise.

DESCRIPTION OF SYMBOLS 1 ... Inkjet printing apparatus 10 ... Side paper feed part 11 ... Paper feed stand 12, 22a, 22b, 22c, 22d ... Pickup paper feed part 14 ... Registration part 20 ... Internal paper feed part 21a, 21b, 21c, 21d ... Paper feed Table 30 ... Printing section 31 ... Inkjet unit 32 ... Head holder 32a ... Head holder surface 33 ... Ink head 36 ... Sub-scanning flow path 40 ... Paper discharge section 41 ... Paper discharge table 42 ... Paper discharge roller 43 ... Mechanism 50 ... Reversing section DESCRIPTION OF SYMBOLS 51 ... Reverse table 52 ... Reverse roller 53 ... Conveyance roller 70 ... Operation panel part 80 ... Control part 81 ... CPU
81a ... Printing condition detection unit 81b ... Conveyance control unit 81c ... Suction control unit 81d ... Ink ejection control unit 82 ... ROM
83 ... RAM
DESCRIPTION OF SYMBOLS 111 ... Main scanning flow path 131 ... Suction fan 132 ... Drive roller 133 ... Conveyance belt 133a ... Belt hole 134 ... Driven roller 141 ... Registration sensor 142 ... Paper sensor

Claims (4)

An image forming apparatus that forms an image on the print medium by ejecting ink based on image data of each page with respect to the print medium conveyed on the conveyance path,
Conveying means for adsorbing and conveying the print medium on an upper surface of a conveying belt along the conveying path;
A printing condition detection unit for detecting the printing condition of the image;
Based on the printing conditions by the printing condition detection unit, the ratio of the print medium to the suction area on the surface of the transport belt is calculated, and the transport unit is controlled to obtain a suction force according to the calculation result. A suction control unit;
An image forming apparatus comprising: 2. The image according to claim 1, wherein the suction control unit lowers the suction force of the conveyance unit for the first page and the last page in the image data from the suction force for the other pages in the meantime. Forming equipment. When the printing condition includes a double-sided printing mode for forming an image on both sides of the printing medium,
The transport means prints on a page to be interrupted between transported print media in a circular transport in which the front and back surfaces of the print medium for which front surface printing has been completed is reversed and then transported onto the transport belt again. Perform an interrupt operation to interrupt the medium,
The suction control unit is configured to determine a suction force when the page to be interrupted passes through the conveyance belt in a state where the interrupt operation is not performed, and the page to be interrupted is the interrupt operation. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus further reduces the suction force when passing through the conveying belt in a state where the toner image is passed. The printing conditions include the size of the print medium, the gap value between the ink discharge means for discharging the ink and the print medium, the ink temperature of the ink discharged from the ink discharge means, or the transport speed of the transport means The image forming apparatus according to claim 1, comprising one or more.

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