JP2010260271A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a printing start time earlier at a low temperature while suppressing influence due to occurrence of mist in an inkjet image forming apparatus. <P>SOLUTION: This image forming apparatus includes an ink ejection means, a drive signal output means, a paper conveyance means, a resist means for conveying in a direction of the paper conveyance means, a conveyance control means for controlling a conveyance timing of the resist means, an ink temperature measurement means, and a printing ratio calculation means for calculating out a printing ratio of a page to be printed, and is controlled so that in the case where a temperature of ink is equal to or more than a first reference temperature, a drive signal of a first voltage value is output so as to make a paper interval of printing paper sheets to be a first interval, and in a case where a temperature measurement value of ink is a second reference temperature lower than the first reference temperature, when a printing ratio is larger than a reference value, a drive signal having a second voltage value larger than the first voltage value is output so as to make the paper interval to be a second interval smaller than the first interval. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ink jet image forming apparatus, and more particularly to an image forming apparatus capable of shortening a printing start time at a low temperature while suppressing an influence due to generation of mist.

  2. Description of the Related Art Inkjet printers that form images by ejecting ink from a print head onto printing paper are widely used. A print head of an ink jet printer ejects ink by applying a driving voltage to an ink ejection mechanism such as a piezoelectric element. Ink used in an ink jet printer generally has a characteristic that viscosity increases in a low temperature environment, and it becomes difficult to ensure an appropriate discharge amount with a normal driving voltage. For this reason, at a low temperature, the ink is heated by a heater so that printing is not performed until the ink reaches an appropriate temperature. For this reason, there is a problem that the printing start time is delayed in a low temperature environment. In particular, this problem becomes more prominent in an ink circulation type printer having an ink circulation path because the amount of ink to be heated is large.

  In addition to the delay in printing start time due to an increase in ink viscosity in a low-temperature environment, an inkjet printer prints mist, which is unnecessary fine ink droplets generated during ink ejection, as described in Patent Document 1. There is a problem that the print quality is deteriorated by adhering to the paper or the printer casing.

JP 2007-296754 A

  In order to advance the printing start time in a low temperature environment, it is conceivable to increase the drive voltage applied to the ink ejection mechanism to ensure an appropriate ink ejection amount. However, when the drive voltage is increased, the ink ejection speed increases and the amount of mist generated increases. As the amount of mist generated increases, the amount of mist adhering to the printer housing also increases, causing a problem that the mist scattered or accumulated in the printer housing contaminates the printing paper and lowers the print quality.

  SUMMARY An advantage of some aspects of the invention is that, in an inkjet image forming apparatus, the printing start time at a low temperature is shortened while suppressing the influence of mist generation.

  In order to solve the above problems, an image forming apparatus of the present invention includes a plurality of nozzles and an ink discharge mechanism corresponding to each nozzle, and discharges ink from each nozzle based on a drive signal that drives the ink discharge mechanism. Ink discharge means, drive signal output means for outputting the drive signal, paper transport means disposed on the opposite surface of the ink discharge means, for transporting printing paper, and transport control for controlling transport timing of the paper transport means And an ink temperature measuring means for measuring the ink temperature, and a printing rate calculating means for calculating the printing rate of the page to be printed, and the ink temperature measurement value of the ink temperature measuring means is equal to or higher than the first reference temperature. In addition, the drive signal output means outputs a drive signal having a first voltage value, and the conveyance control means conveys the paper so that the paper interval of the printing paper becomes the first interval. When the conveyance timing of the stage is controlled, and the ink temperature measurement value of the ink temperature measurement means is equal to or higher than a second reference temperature lower than the first reference temperature and lower than the first reference temperature, the drive signal output means is A drive signal having a second voltage value greater than the first voltage value is output, and the conveyance control means is configured such that when the printing rate is greater than a predetermined reference value, the sheet interval of the printing paper is greater than the first interval. The conveyance timing of the sheet conveying unit is controlled so as to be a narrow second interval, and when the printing rate is equal to or less than a predetermined reference value, the sheet conveying unit is configured such that the sheet interval of the printing sheet becomes the first interval. Is controlled.

  In the present invention, an appropriate ink discharge amount can be secured by outputting a drive signal having a voltage value larger than normal at a low temperature of the ink, so that the printing start time at a low temperature can be advanced. At this time, for pages with a printing rate larger than the reference value, the influence of the increase in the amount of mist generation is reduced by narrowing the interval of the printing paper.

  That is, by narrowing the sheet interval, it is possible to reduce the flow of the wind toward the outside of the print sheet generated on the ink ejection means side. As a result, it is possible to land the mist near the main droplet of the printing paper, and it is possible to prevent the mist from concentrating on the periphery of the printing paper and the accumulation of the mist in the image forming apparatus casing due to the mist scattering. . Therefore, even on a page having a high printing rate and a large ink discharge amount, the influence on the printed matter due to the mist adhesion is reduced. For this reason, in the present invention, it is possible to shorten the printing start time at a low temperature while suppressing the influence of mist generation.

  According to the present invention, the paper transport unit includes an endless transport band provided with a large number of ventilation holes, and a suction unit disposed inside the transport band, and the print paper is sucked through the ventilation holes. Thus, the present invention can be applied particularly effectively.

  In addition, since the ink storage means is included in the path, and the ink supply path further includes an ink circulation path for supplying ink to the ink discharge means and returning the ink that has not been discharged to the ink storage means, the amount of ink is large. The present invention can be effectively applied.

  At this time, an ink heating means for heating ink is provided in the ink circulation path, and the ink heating means heats the ink when the ink temperature measurement value of the ink temperature measurement means is lower than a first reference temperature, It is desirable to stop heating when the ink temperature measurement value is equal to or higher than the first reference temperature.

  Furthermore, the conveyance control unit can change the value of the second interval according to the calculated printing rate. Specifically, the value of the second interval is decreased as the printing rate is increased.

  According to the present invention, in an inkjet image forming apparatus, it is possible to shorten the printing start time at a low temperature while suppressing the influence of mist generation.

It is a figure which shows the outline | summary of the inkjet printer which concerns on this embodiment. It is a figure for demonstrating the structure of the ink path | route related mechanism of an inkjet printer, and a control part. It is a block diagram which shows the structure of an inkjet head. 6 is a flowchart illustrating a procedure of print processing according to the present exemplary embodiment. 6 is a flowchart for explaining printing processing in a low temperature printing mode. It is a figure which shows the example of the drive signal output to a piezo element group. It is a figure which shows the example of the paper space | interval in the low temperature printing mode of this embodiment. It is a figure which shows the influence of the flow of air and mist which generate | occur | produce with a suction fan. It is a figure explaining the effect of this embodiment which advances printing start time at the time of low temperature.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an outline of an inkjet printer 100 according to the present embodiment. In this figure, the printing paper conveyance path is shown in the center. As shown in the drawing, the ink jet printer 100 is a paper feed mechanism for supplying printing paper, and includes a side paper feed stand 320 exposed to the outside of the side of the housing and a plurality of paper feed trays (inside the housing). 330a, 330b, 330c, 330d). Further, a paper discharge port 340 is provided as a paper discharge mechanism for discharging printed printing paper.

  The inkjet printer 100 is an inkjet line color printer. The ink-jet line color printer includes a plurality of ink-jet heads that extend in a direction orthogonal to the paper transport direction and have a large number of nozzles as a printing mechanism. Then, black or color ink is ejected from each inkjet head to form an image in line units.

  The ink jet printer 100 includes a control unit 200 including a controller board on which a CPU, a memory, and the like are arranged, an operation panel 400 that displays a menu and receives an operation from a user, a power supply unit (not shown), and the like. Other functional parts are provided.

  The printing paper fed one by one from the paper feed mechanism of either the side paper feed tray 320 or the paper feed tray 330 is fed into a paper feed system conveyance path (black thick line in the figure) in the housing by a drive mechanism such as a roller. And is guided to the resist portion Rg. Here, the registration unit Rg is provided to perform alignment and skew correction of the leading edge of the printing paper, and includes a pair of registration rollers 350. The fed printing paper is temporarily stopped at the registration unit Rg and conveyed toward the printing mechanism at a predetermined timing.

  A plurality of inkjet heads 130 are provided further on the conveyance direction side of the resist portion Rg. In the present embodiment, it is assumed that four are arranged in the order of C (cyan), K (black), M (magenta), and Y (yellow) in the order from the resist portion Rg. The printing paper is image-formed in units of lines by the ink ejected from each inkjet head 130 while being conveyed at a speed determined by printing conditions by an annular conveyance belt 360 provided on the opposite surface of the inkjet head 130. A suction fan 370 is provided inside the transport belt 360. A large number of air holes are formed on the surface of the conveyance belt 360, and the printing paper is adsorbed to the conveyance belt 360 and conveyed by the suction force generated by the rotation of the suction fan 370.

  The printed printing paper is further conveyed in the housing by a driving mechanism such as a roller. In the case of single-sided printing in which printing is performed only on one side of the printing paper, the paper is directly guided to the paper discharge port 340 and discharged, and the print surface is lowered to a paper discharge tray 345 provided as a receiving tray for the paper discharge port 340. It will be loaded.

  In the case of double-sided printing in which printing is performed on both sides of the printing paper, the front side (the first printed side is “front side” and the next printed side is “back side”) is not guided to the paper discharge port 340 at the end of printing. In addition, it is transported in the housing. For this reason, the ink jet printer 100 includes a switching mechanism 380 for switching the conveyance path for backside printing. The printing paper that has not been led to the paper discharge port 340 by the switching mechanism 380 is drawn into the switchback path SR, and is switched back, so that the front and back are reversed with respect to the transport path. Then, it is guided again to the registration portion Rg by a driving mechanism such as a roller and temporarily stops. Thereafter, the sheet is conveyed in the direction of the printing mechanism at a predetermined timing, and the back side is printed by the same procedure as that for the front side. The printing paper on which the back side is printed and images are formed on both sides is guided to the paper discharge port 340 and discharged, and is stacked on the paper discharge tray 345.

  FIG. 2 is a diagram for explaining the configuration of the ink path-related mechanism and the control unit 200 of the inkjet printer 100. As described above, the ink jet printer 100 is a color printer that performs printing using inks of four colors of CMYK. Each ink is supplied from a removable ink bottle. An ink bottle 110C that supplies cyan ink, an ink bottle 110M that supplies magenta ink, an ink bottle 110Y that supplies yellow ink, and a black ink bottle. An ink bottle 110K that supplies ink is provided. In the following, the ink bottle 110 will be described as a representative. The same applies to other functional units provided for each ink color.

  Ink supplied from the ink bottle 110 passes through an ink path formed by a pipe made of resin, metal, or the like, and is temporarily stored in a downstream tank provided on the downstream side of the inkjet head 130. For this reason, the inkjet printer 100 includes a downstream tank 122C for storing cyan ink, a downstream tank 122M for storing magenta ink, a downstream tank 122Y for storing yellow ink, and a downstream tank 122K for storing black ink.

  The ink stored in the downstream tank 122 is sent to an upstream tank provided on the upstream side of the inkjet head 130 by a pump. Therefore, the inkjet printer 100 includes a pump 170C, a pump 170M, a pump 170Y, a pump 170K, an upstream tank 120C, an upstream tank 120M, an upstream tank 120Y, and an upstream tank 120K. The ink sent to the upstream tank 120 is sent to the inkjet head 130 provided with a number of nozzles for ejecting ink and used for image formation.

  As described above, the inkjet printer 100 includes the inkjet head 130C that ejects cyan ink, the inkjet head 130M that ejects magenta ink, the inkjet head 130Y that ejects yellow ink, and the inkjet head 130K that ejects black ink. Is provided. In the present embodiment, it is assumed that an ink jet head that ejects ink using a piezo element is used. However, another method, for example, an ink jet head that ejects ink by generating heat bubbles by applying heat to the ink using a heating element may be used.

  The inkjet head 130 is provided with a driver 132 (132C, 132M, 132Y, 132K) that outputs a drive signal for driving the piezo element based on the ink ejection data sent from the control unit 200. Note that the ink jet printer 100 employs a circulation system that circulates ink, and ink that has not been consumed during image formation by the ink jet head 130 is returned to the downstream tank 122. Ink feedback from the upstream tank 120 to the downstream tank 122 via the inkjet head 130 uses the water head difference between the upstream tank 120 and the downstream tank 122.

  The temperature range in which the printing quality is guaranteed is determined for the ink, and it is necessary to heat the ink when the environmental temperature is low and the ink temperature is below the guaranteed temperature range. For this reason, a heater 140 is provided in the ink path.

  On the other hand, the driver 132 and the piezo element generate heat when operated. The ink temperature rises due to these heat generation and Joule heat of ink vibration. In general, the viscosity of ink decreases with increasing temperature. To reduce the viscosity due to the ink temperature within the guaranteed temperature range, the print quality can be maintained by adjusting the voltage and cycle of the drive signal.However, if the ink temperature exceeds the guaranteed temperature range, adjustment of the voltage and cycle is not possible. It becomes impossible to cope with it, and there is a possibility that ejection failure may occur. Therefore, a cooler 160 for cooling the ink is provided in order to suppress the influence of an increase in the ink temperature at a high temperature. The ink that has passed through the heater 140 and the cooler 160 is sent to the upstream tank 120.

  Each inkjet head 130 includes a thermometer 134 (134C, 134M, 134Y, 134K) that directly or indirectly measures the ink temperature. Although not shown in the figure, a thermometer may also be provided in the upstream tank 120. By providing a thermometer also in the upstream tank 120, the temperature of the ink flowing from the upstream tank 120 into the inkjet head 130 can be estimated with high accuracy. For this reason, for example, when the ink temperature measured by the inkjet head 130 is less than or equal to the guaranteed temperature range, the temperature margin when determining that the ink temperature has increased to the guaranteed temperature as a result of ink heating can be reduced. Therefore, the time until the start of printing can be shortened.

  The control unit 200 is a functional unit that controls print job processing, ink temperature control, and other processing in the inkjet printer 100. In the present embodiment, the control unit 200 includes a print job control unit 210, an image processing unit 220, a conveyance control unit 240, an ink circulation control unit 250, and an ink temperature adjustment unit 260. These functional units are configured, for example, by the CPU executing a program recorded in the memory.

  The print job control unit 210 controls execution, suspension, restart, error handling, log recording, and the like of a print job received from a user. The print job can be, for example, a print process based on print data received from a PC (not shown), a copy process based on image data read by an image reading apparatus (not shown), or the like. In addition, the print job control unit 210 can accept from the user a selection as to whether or not to execute early printing start when the ink temperature is low, which will be described later.

  The image processing unit 220 performs image processing on the image data that is the target of the print job. The image processing performed by the image processing unit 220 can be, for example, print data expansion processing, image data color conversion processing, binarization processing, halftone processing, and the like. The image processing unit 220 includes an ink discharge control unit 221 and a print rate calculation unit 222.

  The ink ejection control unit 221 calculates an ink ejection amount for each dot based on the image data after image processing, and outputs the ink ejection amount to the driver 132 of the inkjet head 130. Here, the inkjet head 130 expresses the gradation by the number of ink drops, the highlight portion of the image is expressed by a small number of drops, and the shadow portion is expressed by a large number of drops.

  The printing rate calculation unit 222 calculates the printing rate for each page. The printing rate can be, for example, the area (or the number of dots) of the printing area with respect to the area (or the number of dots) of the printable area of the printing paper. Further, the printing rate may be calculated using the total number of ink drops or the like instead of the area of the printing area or the number of dots.

  The conveyance control unit 240 controls the operation of the sheet conveyance mechanism including the registration roller 350 and the conveyance belt 360 in order to convey the printing paper. In addition, when printing is performed when the ink temperature is low, the conveyance control unit 240 adjusts the sheet interval of the printing sheet by changing the conveyance timing of the registration roller 350 according to the size of the printing rate. Specifically, when printing is performed when the ink temperature is low, for paper with a high printing rate, the paper interval is made narrower than usual so as to suppress adverse effects due to the occurrence of mist.

  The ink circulation control unit 250 circulates ink in the ink circulation path by controlling the operation of the pump 170 and the like. The ink temperature adjustment unit 260 operates the heater 140 or the cooler 160 according to the measurement result of the thermometer 134 provided in the inkjet head 130 to control the ink temperature to be within the appropriate temperature range.

  FIG. 3 is a block diagram showing the configuration of the inkjet head 130. As shown in the drawing, the ink jet head 130 includes a thermometer 134 that measures the temperature of ink that is supplied through an ink path 135 that forms part of the ink circulation path and that flows through the ink path 135. .

  Control data indicating the number of ink drops for each pixel output from the ink ejection control unit 230 is input to the driver 132, and the driver 132 outputs a drive signal having a predetermined voltage value to the piezo element group 136 based on the control data. When the piezo element group 136 is deformed in accordance with the drive signal, ink is ejected from the nozzle group 137. Therefore, the piezo element group 136 and the nozzle group 137 function as ink ejection means. Here, the driver 132 functions as a drive signal output unit, and outputs a drive signal having a voltage larger than normal to the piezo element group 136 when the ink temperature is low.

  Next, the print execution process in this embodiment will be described. In the present embodiment, the lower limit value of the appropriate ink temperature is set as the first reference temperature. The first reference temperature can be set to 25 ° C., for example. For this reason, the ink temperature adjustment unit 260 operates the heater 140 to heat the ink when the ink temperature is lower than 25 ° C. At this time, the ink circulation control unit 250 circulates the ink.

  Here, if printing is not executed until the ink temperature reaches 25 ° C. or higher, the printing start time is delayed when the ink temperature is low. In particular, since the ink jet printer 100 of the present embodiment is an ink circulation type, the amount of ink to be heated is large, and extra ink heating time is required.

  Accordingly, the second reference temperature of the ink temperature is set, and if the user desires, printing is executed if the ink temperature is equal to or higher than the second reference temperature. Here, the second reference temperature is a temperature lower than the first reference temperature, and can be set to 20 ° C., for example. However, when the ink temperature is lower than the first reference temperature, the viscosity of the ink increases and an appropriate ink discharge amount cannot be secured. Therefore, an appropriate ink discharge amount is secured by increasing the voltage value of the drive signal output to the piezo element group 136 to be larger than usual.

  However, when the drive voltage is increased, the ink ejection speed increases and the amount of mist generated increases. When the amount of mist generated increases, the amount of mist adhering to the printing paper also increases, resulting in a problem that the print quality deteriorates. Therefore, in this embodiment, it is assumed that printing processing as shown in the flowcharts of FIGS. 4 and 5 is performed. Here, for the sake of simplicity, it is not handled when the ink temperature is high and exceeds the appropriate range.

  First, if the measured value of the ink temperature is equal to or higher than the first reference temperature, for example, 25 ° C. or higher (S101: Yes), normal printing processing is executed assuming that the ink temperature is within the appropriate temperature range (S110). If ink heating has been performed, ink heating is stopped (S109). Here, when the measured value of the temperature is different for each ink color, for example, it can be determined by an average value of each ink temperature, or can be determined based on the lowest ink temperature.

  In the normal printing process, the driver 132 outputs a drive signal having a normal voltage value that can secure an appropriate discharge amount within an appropriate temperature range to the piezo element group 136, and the conveyance control unit 240 prints at a normal sheet interval. The conveyance timing of the registration roller 350 is controlled so that the above is performed. The normal sheet interval is, for example, an interval that can ensure a sufficient time margin for various processes between printing sheets.

  On the other hand, if the measured value of the ink temperature is less than the first reference temperature, for example, less than 25 ° C. (S101: No), the ink temperature adjustment unit 260 operates the heater 140 to raise the ink temperature to an appropriate temperature, The ink is heated (S102).

  If the user has not instructed the early printing start at the time of low ink temperature (S103: No), it waits without printing until the measured value of the ink temperature becomes equal to or higher than the first reference temperature, and measures the ink temperature. When the value is equal to or higher than the first reference temperature (S101: Yes), ink heating is stopped (S109), and normal printing processing is executed (S110).

  Here, when the user determines that there is no problem in the sheet passing performance described later and desires to start early printing at a low ink temperature, for example, the user can set the early printing start with a printer driver that issues a print instruction. . Alternatively, the setting may be made via the operation panel 400 of the inkjet printer 100. Further, the administrator may be able to make a default setting as to whether or not to start early printing.

  If the early printing start is instructed when the ink temperature is low (S103: Yes), it is determined whether or not the measured value of the ink temperature is equal to or higher than the second reference temperature, for example, 20 ° C. or higher (S104). As a result, when the measured value of the ink temperature is lower than the second reference temperature (S104: No), the ink heating is continued, and the process waits until the measured value of the ink temperature becomes equal to or higher than the second reference temperature. This is because when the temperature is lower than the second reference temperature, the increase in the viscosity of the ink is large, and an appropriate ink discharge amount cannot be ensured even if the voltage of the drive signal is increased. In other words, a temperature at which an appropriate ink discharge amount cannot be secured even when the voltage of the drive signal is increased is set as the second reference temperature.

  When the measured value of the ink temperature is equal to or higher than the second reference temperature (S104: Yes), the printing process is executed (S105). At this time, in order to ensure an appropriate ink discharge amount, a drive signal having a voltage value larger than usual is output to the piezo element group 136 (S105).

  FIG. 6 is a diagram illustrating an example of a drive signal output to the piezo element group 136. FIG. 6A shows a drive signal output at normal time, and FIG. 6B shows a drive signal output at low temperature. Here, for one drop, the drive signal is applied to the piezo element as one set of a negative voltage pulse for expanding the ink chamber and a positive voltage pulse for contracting the ink chamber. Therefore, this pulse set is repeatedly applied to a plurality of dropped pixels. Further, in order to stabilize the ink ejection amount, a short pulse called a pre-pulse is inserted before the first pulse set.

  In this embodiment, when the measured value of the ink temperature is normal above the first reference temperature, as shown in FIG. 6A, the drive signal having the voltage value V1 is output to the piezo element, and the measured value of the ink temperature is the first value. When the temperature is lower than the second reference temperature and lower than the first reference temperature, as shown in FIG. 6B, a drive signal having a voltage value V2 larger than V1 is output to the piezo element.

  As a result, an appropriate ink discharge amount is ensured even at a low ink temperature, but the amount of mist generated increases as the drive voltage is increased. In this embodiment, in order to reduce the influence of the increase in the amount of mist generated, in the low temperature printing, printing in the low temperature printing mode is executed (S105).

  FIG. 5 is a flowchart for explaining printing processing in the low temperature printing mode. In the low temperature printing mode, the printing rate calculation unit 222 calculates the printing rate of the page to be printed (S201). As described above, the printing rate can be calculated using the area of the printing area, the number of dots, the number of drops, and the like.

  Then, it is determined whether or not the calculated printing rate is greater than a predetermined reference value (S202). The predetermined reference value can be determined as follows, for example. That is, in general, the greater the printing rate, the greater the amount of ink discharged and the greater the effect of mist generation. Therefore, when printing is performed with a high drive voltage at a low temperature, a printing rate in which the influence of mist generation exceeds an allowable amount is obtained in advance by experiments or the like, and the printing rate is determined as a reference value.

  As a result, when the printing rate is equal to or less than the predetermined reference value (S202: No), the drive voltage is increased and printing is performed at the same sheet interval as in the normal time. In this case, it is because the influence of mist generation is assumed to be an allowable range. That is, the drive voltage is increased in order to execute printing at a low temperature, and accordingly, the amount of mist generated increases. However, if the printing rate is small, the amount of ink discharged is small, so that the influence of mist generation is considered to be small. For this reason, printing is executed at the same sheet interval as usual. As a result, a sufficient time margin and various margins for various processes between the printing sheets can be secured.

  On the other hand, when the printing rate is larger than the predetermined reference value (S202: Yes), printing is executed while increasing the drive voltage and narrowing the interval between the front and back sheets more than usual. FIG. 7A is a diagram illustrating an example of the sheet interval in the low temperature printing mode of the present embodiment. As shown in the figure, the sheet interval between P1 and P2 whose printing ratios are both equal to or less than the reference value is the same W1 as in the normal state. On the other hand, when the printing rate P3 is larger than the reference value, printing is executed with the printing interval between the front and rear sheets P2 and P4 set to W2 narrower than W1. As described above, the calculation of the printing rate and the adjustment of the printing paper interval are performed for each page, and when the printing rate is large and the printing interval is narrowed, both the front and back paper intervals are narrowed.

  Note that when the sheet interval is narrowed, the suction force becomes weaker than usual, and the sheet passing performance is deteriorated. When the paper passing performance is deteriorated, there is a risk that a conveyance failure is likely to occur particularly with thick paper deformed in a curled shape. Therefore, it is preferable that the user should not start early printing at a low ink temperature when using paper that is easily affected by a decrease in paper passing performance and performing printing with a high printing rate. It is done. On the contrary, even if the paper is easily affected by the decrease in paper passing performance, early printing can be started at a low ink temperature when printing with a low printing rate is performed.

  Note that the narrowed printing interval W2 can be set to a predetermined value or variable depending on the printing rate. In this case, the printing interval W2 is decreased as the printing rate is increased.

  The registration roller 350 conveys the printing paper in the direction of the conveyance belt 360 at the timing of the paper interval as shown in FIG. FIG. 7B is a diagram showing a conventional sheet interval for reference. As shown in the figure, conventionally, the sheet interval is constant at W1 regardless of the printing rate.

  Here, the reason for narrowing the sheet interval when the printing rate is high will be described. By narrowing the sheet interval, as is apparent from FIG. 7A, the area of the conveyance belt 360 exposed between the printing sheets is reduced. As described above, a large number of air holes are formed on the surface of the conveyance belt 360, and the printing paper is adsorbed to the conveyance belt 360 by the suction force generated by the air flow generated by the suction fan 370. As shown in FIG. 8, this air flow is guided from the direction of the inkjet head 130 to the direction of the suction fan 370 in the region where there is no printing paper. For this reason, a wind flow toward the outside of the printing paper is generated around the printing paper.

  The mist generated in the ink jet head 130 is concentrated on the periphery of the printing paper along the wind flow, and as a result, the influence of the mist is conspicuous in the periphery of the printing paper. Further, when the printing paper is transported at a high speed, air flows along the transportation direction of the printing paper, so that the mist becomes more conspicuous at the end in the transportation direction of the printing paper.

  As shown in FIG. 8, the air flow generated by the suction fan 370 causes wind on the inkjet head 130 side through a large number of ventilation holes of the conveyance belt 360. FIG. 8 is a cross-sectional view showing a state where the printing paper P is adsorbed and conveyed by the conveyance belt 360 from the side surface side. For this reason, if the area of the air hole is reduced and the flow of air generated by the suction fan 370 is made difficult to pass through the transport belt 360, the flow of air generated on the ink jet head 130 side toward the outside of the printing paper is reduced. be able to. As a result, it is possible to land the mist near the main droplet of the printing paper, and it is possible to prevent the mist from concentrating on the periphery of the printing paper and the accumulation of the mist in the inkjet printer 100 casing due to the mist scattering. . Therefore, the influence on the printed matter due to mist adhesion is reduced. Therefore, in the present embodiment, the sheet interval is made narrower than normal when the printing rate is high during low temperature printing in which the piezo element is driven with a drive signal having a voltage higher than that in normal.

  Unlike the control of the air flow of the suction fan 370 that cannot be controlled in a short time, changing the paper interval can control the flow of air only by the conveyance timing of the registration roller 350. Optimal control can be performed.

  Returning to the description of the flowchart of FIG. 4, if the measured value of the ink temperature becomes equal to or higher than the first reference temperature during printing even in the low temperature printing mode (S106: Yes), the ink heating is stopped (S107), The printing is changed to a printing process at a driving signal having a normal voltage value and a normal paper interval, and printing is continued (S108).

  As a result of performing the above printing operation, in this embodiment, as shown in FIG. 9, when the measured value of the ink temperature is equal to or lower than the second reference temperature, the heater is operated to heat the ink, and the ink temperature is set to the second reference temperature. The printing operation can be started from time t1 when the temperature is reached. Conventionally, the influence of mist adhesion due to setting the drive signal to V2 larger than the normal V1 is large, and printing cannot be started until time t2 when the ink temperature becomes the first reference temperature.

  As described above, according to the present embodiment, it is possible to shorten the printing start time at a low temperature while reducing the influence of the mist on the printed matter in the ink jet printer.

DESCRIPTION OF SYMBOLS 100 ... Inkjet printer 110 ... Ink bottle 120 ... Upstream tank 122 ... Downstream tank 130 ... Inkjet head 132 ... Driver 134 ... Thermometer 135 ... Ink path 136 ... Piezo element group 137 ... Nozzle group 140 ... Heater 160 ... Cooler 170 ... Pump 200 ... Control unit 210 ... Print job control unit 220 ... Image processing unit 221 ... Ink ejection control unit 222 ... Print rate calculation unit 230 ... Ink ejection control unit 240 ... Conveyance control unit 250 ... Ink circulation control unit 260 ... Ink temperature adjustment unit 320 ... side paper feed tray 330 ... paper feed tray 340 ... discharge outlet 345 ... discharge tray 350 ... registration roller 360 ... conveying belt 370 ... suction fan 380 ... switching mechanism 400 ... operation panel

Claims (5)

An ink discharge unit that includes a plurality of nozzles and an ink discharge mechanism corresponding to each nozzle, and discharges ink from each nozzle based on a drive signal that drives the ink discharge mechanism;
Drive signal output means for outputting the drive signal;
A paper conveying means disposed on the opposite surface of the ink ejection means for conveying the printing paper;
A transport control means for controlling the transport timing of the paper transport means;
An ink temperature measuring means for measuring the ink temperature;
A printing rate calculation means for calculating the printing rate of the page to be printed,
When the ink temperature measurement value of the ink temperature measurement means is equal to or higher than the first reference temperature,
The drive signal output means outputs a drive signal having a first voltage value;
The transport control means controls the transport timing of the paper transport means so that the paper interval of the printing paper becomes the first interval;
When the ink temperature measurement value of the ink temperature measurement means is equal to or higher than a second reference temperature lower than the first reference temperature and lower than the first reference temperature,
The drive signal output means outputs a drive signal having a second voltage value larger than the first voltage value;
The transport control means includes
When the printing rate is greater than a predetermined reference value, the conveyance timing of the sheet conveying unit is controlled so that the sheet interval of the printing sheet is a second interval that is narrower than the first interval,
An image forming apparatus, wherein when the printing rate is equal to or less than a predetermined reference value, the conveyance timing of the sheet conveying unit is controlled so that the sheet interval of the printing sheet becomes the first interval. The image forming apparatus according to claim 1,
The paper transporting means includes an endless transport belt provided with a large number of air holes and suction means disposed inside the transport belt, and transports the printing paper by suction through the air holes. An image forming apparatus. The image forming apparatus according to claim 1,
An image forming apparatus comprising an ink circulation path that includes an ink storage means in the path, supplies ink to the ink discharge means, and returns ink that has not been discharged to the ink storage means. The image forming apparatus according to claim 3, wherein
An ink heating means for heating the ink in the ink circulation path;
The ink heating unit heats the ink when the ink temperature measurement value of the ink temperature measurement unit is lower than the first reference temperature, and stops heating when the ink temperature measurement value is equal to or higher than the first reference temperature. An image forming apparatus. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the conveyance control unit changes a value of the second interval according to the calculated printing rate.