JP5249711B2 - Inkjet image forming apparatus - Google Patents

Description

  The present invention relates to an inkjet image forming apparatus, and more particularly to an image forming apparatus capable of shortening a printing start time at a low temperature while reducing the influence on printed matter due to mist adhesion.

  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 deteriorates due to adhesion to the paper.
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. 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.

  Accordingly, an object of the present invention is to shorten the printing start time at a low temperature while reducing the influence on the printed matter due to the mist adhesion in the inkjet image forming apparatus.

  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. Positioning of the print paper, 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 the print paper in an endless transport belt, A registration unit configured to convey in the direction of the sheet conveyance unit; a conveyance control unit configured to control a conveyance timing of the registration unit; and an ink temperature measurement unit configured to measure an ink temperature. The ink temperature measurement value of the ink temperature measurement unit is When the temperature is equal to or higher than the first reference temperature, the drive signal output means outputs a drive signal having a first voltage value, and the transport control means transports to the paper transport means The transfer timing of the registration means is controlled so that the paper interval of the printing paper to be printed becomes the first interval, and the ink temperature measurement value of the ink temperature measurement means is equal to or higher than the second reference temperature lower than the first reference temperature, When the temperature is lower than the first reference temperature, the drive signal output unit outputs a drive signal having a second voltage value larger than the first voltage value, and the transport control unit prints the transported by the paper transport unit. The conveyance timing of the registration unit is controlled so that the sheet interval of the sheet becomes a second interval that is narrower than the first interval.

  According to 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, 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, the mist spreads over a wide range, and the mist can be prevented from concentrating on the periphery of the printing paper. Therefore, the influence on the printed matter due to mist adhesion is reduced.

  The present invention further includes a suction unit disposed inside a transport band of the paper transport unit, and the paper transport unit sucks and transports the printing paper through a plurality of air holes provided in the transport band. It can be applied particularly effectively in cases.

  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 the 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 the first reference temperature. It is desirable to stop the heating when the ink temperature measurement value is equal to or higher than the first reference temperature.

An image forming apparatus according to the present invention includes a plurality of nozzles and an ink discharge mechanism corresponding to each nozzle, an ink discharge unit that discharges ink from each nozzle based on a drive signal that drives the ink discharge mechanism, and the drive A driving signal output means for outputting a signal, a paper conveying means arranged on the opposite surface of the ink ejection means, for conveying the printing paper in an endless conveying belt, positioning the printing paper, and conveying in the direction of the paper conveying means An ink temperature measuring means for measuring the ink temperature of the ink temperature measuring means, a resist control means for controlling the paper conveying speed of the resist conveying means and a paper conveying speed of the paper conveying means, and an ink temperature measuring means for measuring the ink temperature. If the value is equal to or higher than the first reference temperature, the driving signal outputting means outputs a driving signal of the first voltage value, the drive signal of the first driving frequency And force, the transfer control means may sheet interval of the printing paper is conveyed to the sheet conveying means controls the conveyance timing of the register means such that the first distance, the sheet conveying speed of said sheet conveying means When the first speed is set and the ink temperature measurement value of the ink temperature measurement means is equal to or higher than the second reference temperature lower than the first reference temperature and lower than the first reference temperature, the drive signal output means outputs the first speed A drive signal having a second voltage value greater than the voltage value is output, and a drive signal having a second drive frequency lower than the first drive frequency is output. The transport control unit is transported to the paper transport unit. with sheet interval of the printing paper controls the conveyance timing of the register means so as to narrow the second interval than the first distance, slower than the first speed the sheet conveying speed of said sheet conveying means And 2 speed.

  By setting the paper transport speed to a second speed that is slower than the first speed, it is possible to reduce the influence of the wind generated by the paper transport, and to prevent mist from concentrating on the edge of the print paper in the paper transport direction. Can do. Therefore, the influence on the printed matter due to mist adhesion is reduced. Further, the amount of mist generated can be reduced by outputting a drive signal having a second drive frequency lower than the first drive frequency.

  At this time, in order to ensure the time required for the preparation of image data, the transport control unit is configured to obtain a time interval between sheets when the ink temperature measurement value of the ink temperature measurement unit is equal to or higher than the first reference temperature. The second speed is set so that the time interval between sheets when the ink temperature measurement value of the ink temperature measurement means is not less than the second reference temperature and less than the first reference temperature is not shortened.

  In any case, when receiving an instruction from the user not to perform printing below the first reference temperature, the ink temperature measurement value of the ink temperature measurement means is lower than the first reference temperature. The drive signal output means and the transport control means do not perform the above operation and do not perform ink discharge by the ink discharge means even when the temperature is equal to or higher than two reference temperatures and lower than the first reference temperature. Can do.

  According to the present invention, it is possible to shorten the printing start time at a low temperature while reducing the influence on the printed matter due to the mist adhesion in the inkjet image forming apparatus.

  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. An inkjet line color printer has a plurality of inkjet heads that extend in a direction perpendicular to the paper transport direction and has a large number of nozzles as a printing mechanism, and discharges black or color ink from each inkjet head. Image formation is performed in line units.

  In addition, the inkjet 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, and other functional units ( (Not shown).

  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. The paper discharge table 345 has a tray shape protruding from the casing, and has a certain thickness. The discharge tray 345 is inclined, and the printing paper that is discharged from the discharge outlet 340 and slides down along the inclination by the wall formed at a lower position of the inclination is naturally arranged and overlapped. ing.

  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 a paper discharge table 345 provided as a receiving base for the paper discharge port 340. .

  In the ink jet printer 100, switchback at the time of double-sided printing is performed using a space provided in the paper discharge tray 345. The space provided in the paper discharge tray 345 is configured to be covered so that printing paper cannot be taken out from the outside during switchback. As a result, it is possible to prevent the user from accidentally pulling out the printing paper during the switchback operation. Further, the paper discharge table 345 is originally provided in the ink jet printer 100. By performing switchback using the space in the paper discharge table 345, a separate switchback is provided in the ink jet printer 100. There is no need to provide space. Therefore, an increase in the size of the housing can be prevented. Further, since the paper discharge port and the switchback path are not shared, the switchback process and the paper discharge of other sheets can be performed in parallel.

  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 shown in the figure, the ink jet printer 100 is a color printer that performs printing using four colors of CMYK inks. 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 description, the ink bottle 110 will be used as a representative when the ink color is not particular. The same applies to other functional units.

  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. Therefore, 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. 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 due to the Joule heat of the heat generation and the ink vibration. 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.

  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, an ink ejection control unit 230, a conveyance control unit 240, an ink circulation control unit 250, and an ink temperature adjustment unit 260.

  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. 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 ink ejection control unit 230 calculates the 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 conveyance control unit 240 controls the operation of the registration roller 350 and the sheet conveyance unit 390 including the conveyance belt 360 in order to convey the printing paper. Specifically, the sheet interval of the printing sheet is changed by changing the conveyance timing of the registration roller 350 based on the ink temperature. Further, the conveyance speed of the printing paper by the conveyance belt 360 is changed based on the ink temperature.

  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. Further, the frequency of the drive signal is changed according to the paper conveyance speed of the conveyance belt 360. Specifically, the lower the paper transport speed, the lower the frequency of the drive signal in order to match the ink ejection timing.

  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 a print execution process as shown in the flowchart of FIG. 4 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. A method for determining a normal sheet interval will be described later.

  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 desires to start early printing at a low temperature of the ink, for example, the user can set the early printing start with a printer driver that issues a print instruction. Alternatively, settings may be made via the operation panel 400 of the inkjet printer 100. Further, a default setting may be made as to whether or not the administrator starts early printing.

  If the early printing start is instructed when the ink temperature is low (S103: Yes), it is determined whether the measured value of the ink temperature is equal to or higher than the second reference temperature, for example, 20 ° C. (S104). As a result, when the measured value of the ink temperature is lower than the second reference temperature (S104: No), 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 secured 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. 5 is a diagram illustrating an example of a drive signal output to the piezo element group 136. FIG. 5A shows a drive signal output at normal time, and FIG. 5B 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 the present embodiment, when the measured value of the ink temperature is normally equal to or higher than the first reference temperature, as shown in FIG. 5A, 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. 5B, 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, the sheet interval is made narrower than usual in printing at a low temperature (S105). In other words, the conveyance control unit 240 controls the conveyance timing of the registration rollers 350 so that the sheet interval is narrower than usual in printing at a low temperature.

  FIG. 6 is a diagram illustrating an example of the sheet interval during printing. FIG. 6A shows the sheet interval in normal printing, and FIG. 6B shows the sheet interval in low temperature printing. Here, printing is performed in the order of the printing papers P1, P2, and P3. In the state shown in the drawing, the registration roller 350 temporarily stops the printing paper P3, and the conveyance belt 360 is set at an appropriate paper interval. The printing paper P3 is conveyed in the direction.

  In this embodiment, when the measured value of the ink temperature is a normal value equal to or higher than the first reference temperature, as shown in FIG. 6A, the registration roller 350 timing control is performed so that the sheet interval is W1, and the ink temperature is measured. When the value is lower than the second reference temperature and lower than the first reference temperature, as shown in FIG. 6B, the registration roller 350 timing control is performed so that the sheet interval is W2 narrower than W1.

  Here, the reason for narrowing the sheet interval will be described. By narrowing the sheet interval, the area of the conveyor belt 360 exposed between the printing sheets is reduced as shown in FIG. 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. 7, 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. 7, 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. For this reason, if the area of the air holes 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, the mist spreads over a wide range, and the mist can be prevented from concentrating on the periphery of the printing paper. 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 during low temperature printing in which the piezo element is driven with a drive signal having a voltage higher than that in normal.

  If the measured value of the ink temperature becomes equal to or higher than the first reference temperature during printing with a drive signal having a voltage higher than normal and a paper interval narrower than normal (S106: Yes), ink heating is stopped (S107). ), The printing process is changed to the printing process at the driving signal of the normal voltage value and the normal sheet interval (S108).

  As a result of performing the above printing operation, in this embodiment, as shown in FIG. 8, 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. For this reason, in this 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.

  Next, how to determine the normal paper interval W1 will be described. As described above, FIG. 6A shows the sheet interval W1 at the normal time when the ink temperature is equal to or higher than the first reference temperature. In general, the printing speed (number of printed sheets per unit time) is first affected by the ink discharge capability of the inkjet head 130. If the ink discharge capability is high, the time required to form an image for one line is shortened, and the paper conveyance speed can be increased. Since a higher printing speed is desirable, a paper conveyance speed that makes the best use of the ink discharge capability can be determined according to the ink discharge capability of the inkjet head 130.

  If the paper conveyance speed is increased, the time interval of the printing paper is shortened even if the paper interval (distance) is the same. However, during the time interval of the printing paper, it is necessary to secure time for preparation of ejection data to be printed next. In order to secure this time, the sheet interval W1 with respect to the sheet conveyance speed V1 that maximizes the ink discharge capability of the inkjet head 130 is determined in the normal state.

  As shown in FIG. 6 (b) at the same paper conveyance speed V1, if the paper interval is set to W2 narrower than W1 at low temperatures, the time interval of the print paper is also shortened. Time cannot be secured. Therefore, in the present embodiment, as shown in the modified example of the flowchart in FIG. 9, in printing at a low temperature where the ink temperature is equal to or higher than the second reference temperature and lower than the first reference temperature, printing is performed corresponding to the narrowing of the sheet interval. By setting the paper transport speed to V2, which is slower than the normal transport speed V1, the necessary time interval of the print paper is secured (FIG. 9: S105a). That is, the conveyance speed V2 is set so that the paper time interval at the low temperature does not become shorter than the paper time interval at the normal time.

  In addition, the frequency of the drive signal output from the driver 132 to the piezo element group 136 is made lower than usual in order to adjust the ink ejection timing as the transport speed is slower than the normal transport speed when the ink temperature is low. You may make it (FIG. 9: S105a).

  FIG. 10 is a diagram illustrating an example of a drive signal focusing on the drive frequency. FIG. 10A shows a drive signal with a drive frequency H1 output at normal time, and FIG. 5B shows a drive signal with a drive frequency H2 output at low temperature. Here, the drive frequency H2 is a frequency lower than the drive frequency H1.

  Furthermore, in this embodiment, the amount of wind generated by the conveyance of the printing paper can be reduced by slowing the conveyance speed of the printing paper when the ink temperature is low. By reducing the amount of wind generated in the printing paper conveyance direction, it is possible to prevent the generated mist from concentrating on the edge of the printing paper conveyance direction. The influence can be further reduced.

  Further, since the amount of mist generated generally increases as the drive frequency increases, in this embodiment, the amount of mist generated itself can be reduced by lowering the drive frequency when the ink temperature is low.

  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.

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 print execution processing according to the present embodiment. It is a figure which shows the example of the drive signal which changed the voltage value. It is a figure explaining change of a paper interval. It is a figure explaining the flow of the wind by a suction fan. It is a figure which shows the relationship between ink temperature and printing start time. It is a modification of a flowchart. It is a figure which shows the example of the drive signal which paid its attention to the drive frequency.

Explanation of symbols

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, DESCRIPTION OF SYMBOLS 140 ... Heater, 160 ... Cooler, 170 ... Pump, 200 ... Control part, 210 ... Print job control part, 220 ... Image processing part, 230 ... Ink discharge control part, 240 ... Conveyance control part, 250 ... Ink circulation control part , 260 ... Ink temperature adjustment unit, 320 ... Side paper feed tray, 330 ... Paper feed tray, 340 ... Paper discharge port, 345 ... Paper discharge tray, 350 ... Registration roller, 360 ... Conveyor belt, 370 ... Suction fan, 380 ... Switching mechanism, 390... Paper transport unit, 400.

Claims (3)

An ink discharge means including a plurality of nozzles and an ink discharge mechanism corresponding to each nozzle, and discharging ink from each nozzle based on a drive signal for driving the ink discharge mechanism;
Drive signal output means for outputting the drive signal;
A paper transporting means that is disposed on the opposite surface of the ink ejection means and transports the printing paper in an endless transport belt;
Registration means for positioning the printing paper and transporting it in the direction of the paper transporting means;
A transport control means for controlling the transport timing of the registration means and the paper transport speed of the paper transport means;
An ink temperature measuring means for measuring the ink temperature,
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 and outputs a drive signal having a first drive frequency,
The conveyance control unit controls the conveyance timing of the registration unit such that the sheet interval of the printing sheet conveyed to the sheet conveyance unit becomes the first interval, and sets the sheet conveyance speed of the sheet conveyance unit to the first speed. age,
When the ink temperature measurement value of the ink temperature measuring means is not less than the second reference temperature lower than the first reference temperature and less 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, and outputs a drive signal having a second drive frequency lower than the first drive frequency;
The conveyance control unit controls the conveyance timing of the registration unit so that the sheet interval of the printing sheet conveyed to the sheet conveyance unit becomes a second interval that is narrower than the first interval . An image forming apparatus, wherein a sheet conveyance speed is a second speed that is slower than the first speed. The image forming apparatus according to claim 1 ,
The transport control means is configured such that the ink temperature measurement value of the ink temperature measurement means is greater than the second reference temperature than the time interval between sheets when the ink temperature measurement value of the ink temperature measurement means is greater than or equal to the first reference temperature. As described above, the second speed is set so that the time interval between sheets when the temperature is lower than the first reference temperature is not shortened. The image forming apparatus according to claim 1,
When receiving an instruction from the user not to perform printing below the first reference temperature, the ink temperature measurement value of the ink temperature measurement means is equal to or higher than the second reference temperature lower than the first reference temperature; The image forming apparatus, wherein even if the temperature is lower than the first reference temperature, the drive signal output unit and the transport control unit do not perform the operation and do not perform ink ejection by the ink ejection unit.