Inkjet printing apparatus

Abstract

To provide a technique capable of suppressing deterioration of ink remaining in a heater by continuing circulation for a while even when a command to stop ink circulation is input, and minimizing the circulation continuation time.SOLUTION: An inkjet printing apparatus includes an ink circulation path in which a circulation pump for circulating ink and a heater for heating the circulating ink are inserted. A control unit executes processes of: a) when a signal relating to a command to stop driving of the circulation pump is input, stopping driving of the heater, and determining a circulation continuation time for continuing ink circulation in the circulation path by continuously driving the circulation pump, on the basis of a duty value of the heater in a predetermined period before the time when the signal is input and a flow rate of ink in the circulation path in the predetermined period; and b) after the circulation continuation time elapses, stopping the driving of the circulation pump.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an inkjet printing apparatus that performs printing by ejecting ink onto a print medium such as paper. [Background technology]

[0002] Conventionally, inkjet printing devices have sometimes been provided with an ink circulation path that supplies ink to an ejection head that ejects ink onto a print medium, and then recovers ink that is not ejected from the ejection head and supplies it again to the ejection head. An inkjet printing device provided with such an ink circulation path is described in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-053103 Summary of the Invention [Problem to be solved by the invention]

[0004] The inkjet recording device (1) of Patent Document 1 employs a circulation-type ink supply system, and an ink supply unit (15) is provided in the middle of a flow path connecting a recording head (8) that ejects ink and an ink tank unit (14) that stores ink to be supplied to the recording head (8). The ink supply unit (15) adjusts the pressure of the ink supplied to the recording head (8) and the flow rate of the ink recovered from the recording head (8) within appropriate ranges (paragraph 0016). The inkjet recording device (1) is also provided with a sub-heater (not shown) that adjusts the temperature by heating the ink in the recording head (8) (paragraph 0088).

[0005] Furthermore, in the inkjet recording device (1) of Patent Document 1, ink circulation begins when a recording operation is performed and stops when the recording operation ends. As the ink circulates, ink that has begun to thicken near the nozzles (1006) of the recording head (8) is dispersed within the flow path. This prevents thickened ink from accumulating near the nozzles (1006). As a result, it is possible to prevent thickened ink from solidifying near the nozzles (1006) and preventing ink from being ejected normally (paragraphs 0048, 0049, and 0063).

[0006] Here, if the printing operation is completed in a short time, the ink circulation also ends in a short time corresponding to the printing time. In this case, the thickened ink near the ejection orifice (1006) cannot be sufficiently resolved (paragraph 0050). Therefore, in the inkjet printing apparatus (1) of Patent Document 1, if the printing operation is completed in a short time, in addition to the time for circulating the ink corresponding to the printing operation, a process for continuing the circulation for a predetermined time is performed. More specifically, it determines whether the elapsed time (Tc) from the circulation start time (Ts) is less than a specified value (Tmin). If it is less than the specified value (Tmin), the circulation continues for a predetermined time (Tadd) even after the printing operation is completed. Note that the specified value (Tmin) and the value of the time for continuing the circulation (Tadd) can be set appropriately. This allows the thickened ink near the ejection orifice (1006) to diffuse into the flow path, thereby eliminating the thickened ink near the ejection orifice (1006) (paragraphs 0060 and 0061).

[0007] However, in the above-mentioned Patent Document 1, the time for which the circulation should continue to eliminate ink viscosity increase is likely to be greatly influenced by the driving status of the sub-heater that heats the ink and the flow rate of the ink circulating in the flow path. Therefore, if the time for continuing the circulation is set without taking these factors into consideration, it may be longer than necessary or may be insufficient. Furthermore, there are many times when the circulation of ink must be stopped other than after the end of a printing operation.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide a technology that can determine the time for which ink circulation should continue when a command to stop ink circulation is input, taking into account the heater driving status up to the time the command was input and the flow rate at which ink is circulating. [Means for solving the problem]

[0009] To solve the above problems, a first invention of the present application is an inkjet printing device that prints by ejecting ink onto a print medium, and includes an ink circulation path, a circulation pump, a heater, an input unit, and a control unit. The circulation path includes an ejection head that ejects ink, a supply tank that stores ink supplied to the ejection head, a recovery tank that stores ink recovered from the ejection head, and a return pipe that connects the recovery tank to the supply tank. The circulation pump is inserted into the return pipe and sends ink from the recovery tank to the supply tank via the return pipe. The heater is inserted into the return pipe and heats the ink flowing from the recovery tank to the supply tank. The input unit is capable of receiving a command to stop driving the circulation pump. The control unit is electrically connected to each of the circulation pump, the heater, and the input unit. The control unit is capable of sequentially executing the following steps: a) when a signal related to the command is input from the input unit, stopping the driving of the heater, and determining a circulation duration for continuing to drive the circulation pump from the time the signal is input to continue circulating ink in the circulation path based on the duty value of the heater at a predetermined time before the signal is input and the flow rate of ink in the circulation path at the predetermined time; and b) stopping the driving of the circulation pump after the circulation duration has elapsed from the time the signal is input.

[0010] A second aspect of the present invention is the inkjet printing apparatus of the first aspect, wherein the circulation duration is inversely proportional to the flow rate of ink in the circulation path during the predetermined time.

[0011] A third aspect of the present invention is the inkjet printing apparatus of the first or second aspect, wherein the circulation duration is proportional to the duty value of the heater during the predetermined time. [Effects of the Invention]

[0012] According to the first to third aspects of the present invention, when a command to stop the circulation of ink is input, the heater is stopped and the ink continues to circulate, thereby lowering the heater temperature. This makes it possible to prevent deterioration of ink remaining in the heater. Furthermore, because the time for which the ink continues to circulate is determined based on the heater duty value and the flow rate of the circulating ink, this time can be kept to a minimum.

[0013] In particular, according to the second aspect of the present invention, the greater the ink flow rate, the more efficiently the heater temperature can be lowered when the ink is circulated, thereby shortening the duration of circulation. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram conceptually illustrating the configuration of an inkjet printing device. [Figure 2] FIG. 2 is a diagram conceptually illustrating the configuration of an ink supply unit and an ejection head. [Figure 3] FIG. 2 is a block diagram showing connections between a control unit and each unit of the inkjet printing device. [Figure 4] 10 is a flowchart showing the procedure for transporting continuous paper, printing on continuous paper, circulating ink, and stopping the circulation of ink. [Figure 5] FIG. 10 is a diagram showing the relationship between the temperature of ink passing through a heater and the duty value of the heater corresponding to that temperature. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the components described in these embodiments are merely examples and are not intended to limit the scope of the present invention. Furthermore, in the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary to facilitate understanding.

[0016] <1. Configuration of inkjet printing device> FIG. 1 is a conceptual diagram illustrating the configuration of an inkjet printing apparatus 1 according to one embodiment of the present invention. This inkjet printing apparatus 1 is an inkjet printer that conveys a long strip of continuous paper 10 while ejecting droplets of aqueous ink from multiple ejection heads 35 toward the continuous paper 10, thereby recording characters and images on the surface of the continuous paper 10. Note, however, that the long strip of continuous paper 10 is merely one example of a print medium. The print medium may be cut paper, plastic film, cardboard, metal foil, or a glass substrate. In other words, the inkjet printing apparatus 1 may be any apparatus that ejects ink onto a print medium to perform printing. As shown in FIG. 1, the inkjet printing apparatus 1 includes a conveying unit 2, a printing unit 3, a control unit 9, and an input unit 11.

[0017] The transport unit 2 is a mechanism that transports the continuous paper 10 in a transport direction along its longitudinal direction along a predetermined transport path. The continuous paper 10 is passed over multiple transport rollers 12. The continuous paper 10 is transported along a transport path formed by the multiple transport rollers 12. Each transport roller 12 rotates around an axis extending perpendicular to the transport direction, thereby guiding the continuous paper 10 downstream along the transport path. In addition, tension is applied to the continuous paper 10 in the transport direction. This prevents the continuous paper 10 from sagging or wrinkling during transport.

[0018] The printing unit 3 has a plurality of (four in this embodiment) ejection heads 35 and a plurality of (four in this embodiment) ink supply units 4. The four ejection heads 35 have the same structure. The four ink supply units 4 also have the same structure.

[0019] The four ejection heads 35 are arranged at intervals from one another in the transport direction. Each of the four ejection heads 35 ejects ink droplets from a nozzle 83 (see FIG. 2, described later) toward the surface (top surface) of the continuous paper 10. In this embodiment, the four ejection heads 35 eject ink of different colors (for example, cyan, magenta, yellow, and black) to record a single-color image on the surface (top surface) of the continuous paper 10. Then, a multi-color image is formed on the top surface of the continuous paper 10 by superimposing the four single-color images.

[0020] FIG. 2 is a conceptual diagram showing the configuration of one ink supply unit 4 and one ejection head 35. In this embodiment, each ejection head 35 has multiple (five in this embodiment) heads 80. The five heads 80 have the same structure. For this reason, FIG. 2 shows only one of the five heads 80 in detail, and the remaining four heads 80 are shown in a simplified manner. As shown in FIG. 2, each of the five heads 80 has a housing 81, an internal tank 82, and multiple nozzles 83.

[0021] The housing 81 forms the outer frame of the head 80. The internal tank 82 is disposed inside the housing 81 and is capable of temporarily storing ink. The multiple nozzles 83 are arranged at equal intervals in the transport direction and width direction of the continuous paper 10 in the lower part of the housing 81. Each of the multiple nozzles 83 communicates with the internal tank 82. Each of the multiple nozzles 83 has multiple piezoelectric elements 831 as pressure generating elements, an ink chamber 832, and an ejection port 830. The ink chamber 832 communicates with the internal tank 82.

[0022] When ink is ejected, the ink flows down from the internal tank 82 to the ink chamber 832. Then, by controlling the piezoelectric element 831, the ink in the ink chamber 832 is pressurized, causing the ink to be ejected as droplets from the ejection port 830. However, the nozzle 83 may be of a so-called thermal type, in which the ink in the ink chamber 832 is heated to generate bubbles, thereby pressurizing the ink.

[0023] Next, the ink supply unit 4 will be described. The ink supply unit 4 is a device that supplies ink to the ejection head 35 while circulating a portion of the ink. As described above, the inkjet printing apparatus 1 of this embodiment has four ink supply units 4. Since the four ink supply units 4 have the same structure, the following will describe the structure of only one ink supply unit 4.

[0024] As shown in FIG. 2, each ink supply unit 4 includes a supply tank 51, a recovery tank 52, a supply side manifold 61, a plurality (five in this embodiment) of supply side thin pipes 62, a plurality (five in this embodiment) of recovery side thin pipes 63, a recovery side manifold 64, a return pipe 65, a circulation pump 71, a plurality (five in this embodiment) of supply side on-off valves 73, a plurality (five in this embodiment) of head outlet side on-off valves 74, a return side on-off valve 75, a first heater 76, a second heater 77, a first temperature sensor 84, a second temperature sensor 85, a third temperature sensor 86, a filter 87, and a degassing unit 88.

[0025] The supply tank 51 is a container for temporarily storing ink to be supplied to the ejection head 35. An internal chamber 510 capable of temporarily storing ink is disposed inside the supply tank 51. The supply tank 51 may be equipped with a liquid level sensor for detecting the height of the liquid surface of the ink stored in the internal chamber 510 of the supply tank 51.

[0026] The supply-side manifold 61 and the five supply-side thin pipes 62 are pipes that connect the supply tank 51 and the five heads 80 of one discharge head 35. The supply-side manifold 61 is a thick pipe whose upstream end is connected to communicate with the internal chamber 510 of the supply tank 51. The five supply-side thin pipes 62 are thin pipes that branch off from the supply-side manifold 61. The upstream end of each of the five supply-side thin pipes 62 is connected to communicate with the internal passage of the supply-side manifold 61, and the downstream end is connected to communicate with the internal tank 82 of one head 80.

[0027] In this embodiment, a supply-side on-off valve 73 is inserted in each of the supply-side thin pipes 62. The supply-side on-off valve 73 may be, for example, a solenoid valve that opens and closes under the control of the control unit 9. However, the supply-side on-off valve 73 may also be a manually opened and closed on-off valve. When the supply-side on-off valve 73 is closed, communication between the internal passages of the supply-side thin pipes 62 is blocked. That is, when the supply-side on-off valve 73 is closed, the flow of ink from the supply tank 51 to the head 80 is blocked. On the other hand, when the supply-side on-off valve 73 is open, communication between the internal passages of the supply-side thin pipes 62 is permitted. However, the supply-side on-off valve 73 is not necessarily provided. A filter or the like may be inserted in the supply-side manifold 61 or the five supply-side thin pipes 62.

[0028] The five recovery side thin pipes 63 and the recovery side manifold 64 are pipes that connect the five heads 80 of one discharge head 35 to the recovery tank 52. Each of the five recovery side thin pipes 63 is a thin tube that branches off from the recovery side manifold 64. The upstream end of each of the five recovery side thin pipes 63 is connected to communicate with the internal tank 82 of one head 80, and the downstream end is connected to communicate with an internal passage of the recovery side manifold 64. The recovery side manifold 64 is a thick pipe that is connected to communicate with an internal chamber 520 (described later) of the recovery tank 52 at its downstream end.

[0029] In this embodiment, a head outlet-side on-off valve 74 is inserted in each recovery-side thin pipe 63. The head outlet-side on-off valve 74 may be, for example, a solenoid valve that opens and closes under the control of the control unit 9. However, a manually opened and closed on-off valve may also be used for the head outlet-side on-off valve 74. When the head outlet-side on-off valve 74 is closed, communication between the internal passages of the recovery-side thin pipes 63 is blocked. That is, when the head outlet-side on-off valve 74 is closed, the flow of ink from the head 80 to the recovery tank 52 is blocked. On the other hand, when the head outlet-side on-off valve 74 is open, communication between the internal passages of the recovery-side thin pipes 63 is permitted. However, the head outlet-side on-off valve 74 is not necessarily provided. Furthermore, a filter or the like may be inserted in each of the five recovery-side thin pipes 63 or the recovery-side manifold 64.

[0030] The recovery tank 52 is a container for temporarily storing the ink recovered from the ejection head 35. An internal chamber 520 capable of temporarily storing the ink is disposed inside the recovery tank 52. The recovery tank 52 may be equipped with a liquid level sensor for detecting the height of the ink surface stored in the internal chamber 520 of the recovery tank 52.

[0031] 2, a pressurizing mechanism 515 is connected to the supply tank 51. The pressurizing mechanism 515 pressurizes the inside of the supply tank 51 and adjusts the air pressure in the internal chamber 510 of the supply tank 51 to a positive pressure (pressure higher than atmospheric pressure). The pressurizing mechanism 515 is composed of, for example, a compressor, a pressurized buffer tank, a pressure adjustment mechanism (regulator), etc. Furthermore, a depressurizing mechanism 524 is connected to the recovery tank 52. The depressurizing mechanism 524 depressurizes the inside of the recovery tank 52 and adjusts the air pressure in the internal chamber 520 of the recovery tank 52 to a negative pressure (pressure lower than atmospheric pressure). The depressurizing mechanism 524 is composed of, for example, a vacuum pump, a depressurized buffer tank, a pressure adjustment mechanism (regulator), etc.

[0032] The operations of the pressurizing mechanism 515 and the decompression mechanism 524 are configured to be controllable by the control unit 9. When the pressurizing mechanism 515 and the decompression mechanism 524 are driven, a pressure difference is created between the internal chamber 510 of the supply tank 51 and the internal chamber 520 of the recovery tank 52. This allows the ink stored in the supply tank 51 to be supplied to the ejection head 35, and further allows the ink remaining in the ejection head 35 (ink that was not ejected from the ejection head 35) to be recovered in the recovery tank 52.

[0033] However, as long as the pressurizing mechanism 515 and the depressurizing mechanism 524 can adjust the air pressure in the internal chamber 510 of the supply tank 51 to be higher than the air pressure in the internal chamber 520 of the recovery tank 52, it is not necessary for the air pressure in the internal chamber 510 of the supply tank 51 to be a positive pressure and the air pressure in the internal chamber 520 of the recovery tank 52 to be a negative pressure. For example, the pressurizing mechanism 515 may adjust the air pressure in the internal chamber 510 of the supply tank 51 to be the same as atmospheric pressure, and the depressurizing mechanism 524 may adjust the air pressure in the internal chamber 520 of the recovery tank 52 to be a negative pressure (a pressure lower than atmospheric pressure).

[0034] The return pipe 65 is a pipe that connects the internal chamber 520 of the recovery tank 52 and the internal chamber 510 of the supply tank 51 so that they can communicate with each other. That is, the return pipe 65 connects the recovery tank 52 and the supply tank 51. As shown in FIG. 2 , the upstream end of the internal passage of the return pipe 65 is connected in communication with the internal chamber 520 of the recovery tank 52. In addition, the downstream end of the internal passage of the return pipe 65 is connected in communication with the internal chamber 510 of the supply tank 51.

[0035] With the above configuration, an ink circulation path 41 is formed, which runs from the supply tank 51 via the supply manifold 61, the supply thin pipe 62, the internal tank 82 of the ejection head 35, the recovery thin pipe 63, the recovery manifold 64, the recovery tank 52, and the return pipe 65, and returns to the supply tank 51. That is, the ink circulation path 41 includes the supply tank 51, the ejection head 35, the recovery tank 52, and the return pipe 65. In addition, a circulation pump 71, a return-side opening / closing valve 75, a first heater 76, a second heater 77, a first temperature sensor 84, a second temperature sensor 85, a third temperature sensor 86, a filter 87, and a degassing unit 88 are inserted in the return pipe 65.

[0036] The circulation pump 71 is a device that performs a liquid transfer operation to transfer ink from the recovery tank 52 to the supply tank 51 via the return pipe 65. The circulation pump 71 generates a flow of ink from the recovery tank 52 to the supply tank 51 in the internal passage of the return pipe 65 in accordance with an operation signal from the control unit 9. The circulation pump 71 in this embodiment is, for example, a diaphragm pump, which is less likely to generate foreign matter such as dust when driven. The circulation pump 71 applies pressure to the ink inside the circulation pump 71 by the reciprocating movement of an internal piston, and ejects the ink from an outlet that communicates with the internal passage of the return pipe 65. The circulation pump 71 is also electrically connected to the control unit 9. The circulation pump 71 outputs data to the control unit 9 regarding a value calculated by multiplying the load factor by the ratio of the time the pump is in an ON state per unit time (e.g., 1 second) (hereinafter, this value will be referred to as a "pump duty value" to distinguish it from the duty values ​​of the first and second heaters 76 and 77, which will be described later).

[0037] The return-side on-off valve 75 is inserted in the return pipe 65 downstream of the circulation pump 71 in the ink feed direction and upstream of the first heater 76 and the second heater 77 in the ink feed direction. The return-side on-off valve 75 is, for example, a solenoid valve that opens and closes under the control of the control unit 9. However, the return-side on-off valve 75 may also be a manually opened and closed on-off valve. When the return-side on-off valve 75 is closed, communication between the internal passages of the return pipe 65 is blocked. That is, when the return-side on-off valve 75 is closed, the flow of ink from the recovery tank 52 to the supply tank 51 and the backflow of ink from the supply tank 51 to the recovery tank 52 are prevented. On the other hand, when the return-side on-off valve 75 is open, communication between the internal passages of the return pipe 65 is permitted. That is, the return-side on-off valve 75 permits or blocks the flow of ink from the recovery tank 52 to the supply tank 51.

[0038] The first heater 76 is a device that heats the ink being transported through the internal passage of the return pipe 65. The first heater 76 heats the ink flowing from the recovery tank 52 to the supply tank 51. The first heater 76 is located in the return pipe 65 between the circulation pump 71 and the supply tank 51. The first heater 76 has a heating element such as a carbon heater, and is connected to a power source via an ON / OFF circuit (not shown). The first heater 76 can heat the ink by generating heat when the power is turned on. The first heater 76 is controlled by switching between the ON state and the OFF state, for example, so that the temperature of the ink passing through the first heater 76 becomes 30°C.

[0039] The second heater 77 is a device that heats the ink being sent through the internal passage of the return pipe 65. The second heater 77 heats the ink flowing from the recovery tank 52 to the supply tank 51. The second heater 77 is located in the return pipe 65 between the first heater 76 and the supply tank 51. That is, the second heater 77 is located downstream of the first heater 76 in the ink sending direction. The second heater 77 has a heating element such as a carbon heater and is connected to a power source via an ON / OFF circuit (not shown). The second heater 77 can heat the ink by generating heat when the power is turned on. The second heater 77 is controlled by switching between the ON state and the OFF state, for example, so that the temperature of the ink passing through the second heater 77 becomes 35°C.

[0040] The first heater 76 and the second heater 77 are each electrically connected to the control unit 9. The first heater 76 and the second heater 77 output data relating to the proportion of time that each heater is in an ON state per unit time (for example, one second) (hereinafter referred to as a "duty value") to the control unit 9. However, in the present invention, the number of heaters inserted in the return pipe 65 between the circulation pump 71 and the supply tank 51 may be one, or may be three or more. The heater may be any heater that is inserted in the return pipe 65 between the circulation pump 71 and the supply tank 51 and heats the ink flowing from the recovery tank 52 to the supply tank 51.

[0041] A first temperature sensor 84 is inserted in the return pipe 65 downstream of the return-side on-off valve 75 in the ink feed direction and upstream of the first heater 76 in the ink feed direction. The first temperature sensor 84 detects the temperature of the ink flowing into the first heater 76. The first temperature sensor 84 is also electrically connected to the control unit 9. The first temperature sensor 84 outputs data related to the detection result of the ink temperature to the control unit 9.

[0042] A second temperature sensor 85 is inserted in the return pipe 65 downstream of the first heater 76 in the ink feed direction and upstream of the second heater 77 in the ink feed direction. The second temperature sensor 85 detects the temperature of the ink flowing out from the first heater 76. The second temperature sensor 85 is also electrically connected to the control unit 9. The second temperature sensor 85 outputs data related to the detection result of the ink temperature to the control unit 9.

[0043] A third temperature sensor 86 is inserted in the return pipe 65 downstream of the second heater 77 in the ink feed direction and upstream of the supply tank 51 in the ink feed direction. The third temperature sensor 86 detects the temperature of the ink flowing out from the second heater 77. The third temperature sensor 86 is also electrically connected to the control unit 9. The third temperature sensor 86 outputs data related to the detection result of the ink temperature to the control unit 9. However, the first temperature sensor 84, the second temperature sensor 85, and the third temperature sensor 86 described above do not necessarily have to be provided.

[0044] The filter 87 is inserted in the return pipe 65 downstream in the ink feeding direction from the second heater 77 and upstream in the ink feeding direction from the supply tank 51. The filter 87 filters the ink being fed through the internal passage of the return pipe 65 and removes foreign matter contained in the ink.

[0045] The degassing unit 88 is inserted in the return pipe 65 downstream of the filter 87 in the ink sending direction and upstream of the supply tank 51 in the ink sending direction. The degassing unit 88 in this embodiment is a so-called hollow fiber membrane degassing module. The degassing unit 88 removes air bubbles from the ink being sent through the internal passage of the return pipe 65.

[0046] Next, the control unit 9 will be described. The control unit 9 is an information processing device for controlling each part of the inkjet printing apparatus 1. FIG. 3 is a block diagram showing the connection between the control unit 9 and each part of the inkjet printing apparatus 1. As conceptually shown in FIG. 3, the control unit 9 has a processor 91 such as a CPU, a memory 92 such as RAM, and a storage unit 93 such as a hard disk drive. The storage unit 93 stores a computer program 9P for transporting the continuous paper 10, printing on the continuous paper 10, circulating ink, and stopping the circulation of ink based on commands described below.

[0047] 3, the control unit 9 is electrically and communicatively connected to the transport unit 2, the four ejection heads 35 of the printing unit 3, the circulation pumps 71 of each of the four ink supply units 4 of the printing unit 3, the five supply-side on-off valves 73, the five head outlet-side on-off valves 74, the return-side on-off valves 75, the first heater 76, the second heater 77, the temperature sensors 84, 85, 86, the pressurizing mechanism 515, and the decompression mechanism 524. The control unit 9 controls the operation of each of these units in accordance with a computer program 9P.

[0048] As shown in FIG. 3 , the control unit 9 is electrically and communicatively connected to the input unit 11. The input unit 11 is a device capable of receiving a command to stop the operation of the circulation pump 71. The input unit 11 includes an input interface such as a touch panel. An operator inputs a command to stop the operation of the circulation pump 71 to the input unit 11 via the input interface. When the command is input, the input unit 11 outputs a signal related to the command to the control unit 9. However, the input unit 11 may be configured integrally with the control unit 9 and other components. The control unit 9 controls the operation of the above-mentioned components to transport the continuous paper 10, print on the continuous paper 10, and circulate ink in the circulation path 41, and further stops the circulation of ink at a delayed time based on the signal, as described below.

[0049] <2. Procedures for feeding continuous paper, printing, and circulating and stopping ink> Next, we will explain the procedures for transporting the continuous paper 10, printing the continuous paper 10, circulating ink, and stopping the circulation of ink, which are performed in the inkjet printing device 1. Figure 4 is a flowchart showing the procedures for transporting the continuous paper 10, printing the continuous paper 10, circulating ink, and stopping the circulation of ink.

[0050] First, when transporting the continuous paper 10, printing the continuous paper 10, and circulating the ink, the control unit 9 operates the transport unit 2 to transport the continuous paper 10 longitudinally along a predetermined transport path, while controlling the multiple nozzles 83 of each of the four ejection heads 35 to eject droplets of ink onto the surface of the continuous paper 10, thereby recording an image on the surface of the continuous paper 10 (step S1).

[0051] Here, a sufficient amount of ink is stored in the internal chamber 510 of the supply tank 51 as preparation for transporting the continuous paper 10, printing the continuous paper 10, and circulating the ink. The control unit 9 also opens the five supply-side on-off valves 73, the five head outlet-side on-off valves 74, and the return-side on-off valve 75.

[0052] The control unit 9 then drives the circulation pump 71, first heater 76, second heater 77, pressurizing mechanism 515, and decompression mechanism 524 of each of the four ink supply units 4. The control unit 9 also turns on the power of the first temperature sensor 84, second temperature sensor 85, and third temperature sensor 86, causing these sensors to start measuring. That is, the control unit 9 drives the circulation pump 71 to circulate ink in the ink circulation path 41, while driving the pressurizing mechanism 515 and decompression mechanism 524 to supply ink to the internal tank 82 of each ejection head 35.

[0053] More specifically, by driving the pressurizing mechanism 515 and the decompressing mechanism 524, a pressure difference is created between the internal chamber 510 of the supply tank 51 and the internal chamber 520 of the recovery tank 52. This allows the ink stored in the supply tank 51 to be supplied to the ejection head 35, and further allows the ink remaining in the ejection head 35 (ink not ejected from the ejection head 35) to be recovered in the recovery tank 52. Furthermore, by driving the circulation pump 71, a flow of ink is generated in the internal passage of the return pipe 65, flowing from the recovery tank 52 to the supply tank 51.

[0054] The volumes of the portions of the ink circulation path 41 through which the ink passes, including the supply tank 51, the recovery tank 52, the supply-side manifold 61, the supply-side thin pipes 62, the recovery-side thin pipes 63, the recovery-side manifold 64, and the return pipe 65, are preset values. Therefore, the flow rate of ink circulating through the circulation path 41 can be calculated based on the amount of ink delivered per unit time by the circulation pump 71 that delivers the ink (this "delivery amount" can be calculated from the above-mentioned "pump duty value") and the air pressures in the internal chamber 510 of the supply tank 51 and the internal chamber 520 of the recovery tank 52, which are adjusted by the pressurizing mechanism 515 and the decompressing mechanism 524.

[0055] Furthermore, the inkjet printing apparatus 1 is configured so that an operator can select either a "high-speed circulation mode" or a "low-speed circulation mode" regarding the flow rate of ink circulating in the circulation path 41. When the "high-speed circulation mode" is selected, the circulation pump 71 is controlled, for example, so that the pump duty value is "100(%)." The pressurizing mechanism 515 is controlled, for example, so that the air pressure in the internal chamber 510 of the supply tank 51 is "+10 kPa." The decompression mechanism 524 is controlled, for example, so that the air pressure in the internal chamber 520 of the recovery tank 52 is "-10 kPa." As a result, the flow rate of ink in the circulation path 41 in this embodiment is, for example, 800 (ml / min).

[0056] Furthermore, when the "low-speed circulation mode" is selected, the circulation pump 71 is controlled, for example, so that the pump duty value is "50(%)." The pressurizing mechanism 515 is controlled, for example, so that the air pressure in the internal chamber 510 of the supply tank 51 is "+3 kPa." The decompression mechanism 524 is controlled, for example, so that the air pressure in the internal chamber 520 of the recovery tank 52 is "-3 kPa." As a result, the flow rate of ink in the circulation path 41 in this embodiment is, for example, 300 (ml / min).

[0057] However, in addition to the "high-speed circulation mode" and "low-speed circulation mode," one or more modes may be provided with pump duty values ​​and air pressure values ​​in the internal chambers 510 and 520 that are different from those described above with respect to the flow rate of ink circulating in the circulation path 41. Also, a flow meter may be separately provided to measure the flow rate of ink in the circulation path 41.

[0058] Furthermore, by driving the first and second heaters 76, 77, the ink being sent through the internal passage of the return pipe 65 can be heated and then sent to the supply tank 51. More specifically, the control unit 9 first controls the temperature of the ink passing through the first heater 76 to be, for example, 30°C by switching the first heater 76 between an ON state and an OFF state. Here, as described above, the second temperature sensor 85 detects the temperature of the ink flowing out from the first heater 76 and outputs data related to the detection result to the control unit 9. The control unit 9 adjusts the drive amount of the first heater 76 based on the ink temperature detection result input from the second temperature sensor 85.

[0059] FIG. 5 is a diagram showing an example of the temperature of ink passing through the first and second heaters 76, 77 and the ratio of the time the heaters 76, 77 are in the ON state per unit time (e.g., 1 second) when the heaters are driven (i.e., the heater "duty value"). As shown in FIG. 5, when the temperature of the ink passing through the first heater 76 is less than 27.5°C, the control unit 9 drives the first heater 76 at a duty value of 100%. Then, when the temperature of the ink passing through the first heater 76 reaches 27.5°C or higher, the control unit 9 gradually reduces the duty value. When the temperature of the ink passing through the first heater 76 reaches 27.5°C or higher, the control unit 9 drives the first heater 76 at a duty value of 50% or less. When the temperature reaches 30°C or higher, the control unit 9 drives the first heater 76 at a duty value of 0%. In other words, when the temperature reaches 30°C or higher, the control unit 9 stops driving the first heater 76. By controlling in this manner, the temperature of the ink passing through the first heater 76 can be adjusted to 30°C.

[0060] Furthermore, the control unit 9 controls the temperature of the ink passing through the second heater 77 to be, for example, 35°C by switching the second heater 77 between an ON state and an OFF state. As described above, the third temperature sensor 86 detects the temperature of the ink flowing out from the second heater 77 and outputs data related to the detection result to the control unit 9. The control unit 9 adjusts the drive amount of the second heater 77 based on the ink temperature detection result input from the third temperature sensor 86.

[0061] As shown in FIG. 5, when the temperature of the ink passing through the second heater 77 is below 28.5°C, the control unit 9 drives the second heater 77 at a duty value of 100%. Then, when the temperature of the ink passing through the second heater 77 reaches 28.5°C or higher, the control unit 9 gradually reduces the duty value. When the temperature reaches 30°C or higher, the control unit 9 drives the second heater 77 at a duty value of 50% or less. When the temperature reaches 31.5°C or higher, the control unit 9 drives the second heater 77 at a duty value of 0%. In other words, when the temperature reaches 31.5°C or higher, the control unit 9 stops driving the second heater 77. By controlling in this manner, the temperature of the ink passing through the second heater 77 can be adjusted to 35°C. Furthermore, by adjusting the temperature of the ink passing through the second heater 77 to 35°C, the ink can be ejected from the ejection head 35 in a satisfactory manner.

[0062] As described above, the first temperature sensor 84 detects the temperature of the ink flowing into the first heater 76 and outputs data related to the detection results to the control unit 9. By referencing the data related to the detection results by the first temperature sensor 84, the control unit 9 can determine what the temperature of the ink flowing into the first heater 76 was in the first place. This can be used as a guide to determine whether the first heater 76 and the second heater 77 are operating normally. Furthermore, the drive amounts (duty values) applied by the control unit 9 to the first heater 76 and the second heater 77 are stored in the memory 92 as historical data so that they can be referenced at any time.

[0063] Furthermore, by passing the ink flowing through the internal passage of the return pipe 65 through a filter 87, small impurities remaining in the ink can be removed, and the ink can be sent to the supply tank 51. Furthermore, by passing the ink flowing through the internal passage of the return pipe 65 through a degassing unit 88, the ink can be degassed before being sent to the supply tank 51.

[0064] Here, the operation of the circulation pump 71 may be stopped when switching between the "high-speed circulation mode" and the "low-speed circulation mode" or when wiping off dirt from the ejection head 35. In this case, the circulation of ink in the circulation path 41 is stopped, causing ink to accumulate inside the first and second heaters 76, 77. In addition, the power supply to the first and second heaters 76, 77 is also cut off.

[0065] As described above, the first and second heaters 76, 77 each have a heating element formed from a carbon heater or the like. The heating element continues to be maintained at a high temperature even after the power supply to the first and second heaters 76, 77 is cut off. Therefore, if the ink circulation is stopped for a certain period of time, the ink remaining inside the first and second heaters 76, 77 may be excessively heated and may be altered or deteriorated. If the altered or deteriorated ink is subsequently used, the ink may not be ejected properly from the ejection head 35, or the desired color gamut may not be obtained. For this reason, in this embodiment, the following process is performed before the circulation pump 71 is stopped.

[0066] Specifically, the operator first inputs a command to stop the operation of the circulation pump 71 via the input interface of the input unit 11. Then, when the command is input, the input unit 11 outputs a signal related to the command to the control unit 9. Then, the control unit 9 detects whether or not the signal related to the command has been input from the input unit 11 (step S2). The control unit 9 continues to transport the continuous paper 10, print on the continuous paper 10, and circulate the ink until it detects that the signal related to the command has been input from the input unit 11 (step S2: No).

[0067] On the other hand, when the control unit 9 detects that a signal related to the command has been input from the input unit 11 (step S2: Yes), it refers to the duty value of the first heater 76 and the duty value of the second heater 77 for a predetermined time (for example, one second) before it detects that the signal related to the command has been input from the input unit 11. Note that, since the duty values ​​may change as described above, the control unit 9 may set a period of about several minutes as the predetermined time, and refer to a value calculated as an average value per unit time by dividing the integral value of each of the duty values ​​of the first and second heaters 76, 77 over that period by that period.

[0068] The control unit 9 determines that the duty values ​​of the first and second heaters 76, 77 for the above-mentioned predetermined time are large, meaning that the heating elements inside the first and second heaters 76, 77 are already generating a lot of heat and reaching high temperatures. In such a case, the control unit 9 determines that if the circulation of ink in the circulation path 41 is immediately stopped, the ink remaining inside the first and second heaters 76, 77 will be excessively heated, and there is a high possibility that it will be altered or deteriorated.

[0069] Furthermore, the control unit 9 refers to whether the "high-speed circulation mode" or the "low-speed circulation mode" was selected for the flow rate of ink circulating in the circulation path 41 during the predetermined time. Based on the result of this reference, the control unit 9 determines the flow rate Qi (ml / min) of ink circulating in the circulation path 41 during that predetermined time. For example, if the "high-speed circulation mode" was selected during that predetermined time, the ink flow rate is 800 (ml / min), and if the "low-speed circulation mode" was selected during that predetermined time, the ink flow rate is 300 (ml / min). However, the flow rate of ink circulating in the circulation path 41 may also be determined based on the measurement results of a separately provided flow meter.

[0070] Next, the control unit 9 calculates the circulation duration ΔT (s) by substituting the determined ink flow rate Qi (ml / min) and the larger of the duty values ​​Dl (%) of the first heater 76 and the second heater 77 at the predetermined time into the following equation (1). Then, even after detecting that the signal has been input, the control unit 9 continues to drive the circulation pump 71 for the circulation duration ΔT (s) to circulate the ink within the circulation path 41 (step S3). In equation (1), "Ks" is a coefficient that is determined in advance based on the length of the ink circulation path 41, the inner diameter of the return pipe 65, etc.

[0071] ΔT(s)=Ks×Dl(%)÷Qi(ml / min)...Equation (1)

[0072] Then, after the circulation duration time ΔT(s) has elapsed, the control unit 9 stops driving the circulation pump 71 and stops the circulation of ink in the circulation path 41 (step S4). That is, the control unit 9 of this embodiment can sequentially execute the following steps: a) when a signal instructing the circulation pump 71 to stop driving is input from the input unit 11, stopping the driving of the first and second heaters 76, 77 and determining the circulation duration time ΔT(s) for continuing to drive the circulation pump 71 from the time the signal is input to continue circulating ink in the circulation path 41 based on the duty values ​​of the first and second heaters 76, 77 at a predetermined time before the signal is input and the flow rate of ink in the circulation path 41 at the predetermined time; and b) after the circulation duration time ΔT(s) has elapsed from the time the signal is input, stopping the driving of the circulation pump 71.

[0073] In this manner, in this embodiment, when a command to stop the circulation of ink is input, the driving of the first and second heaters 76, 77 is stopped and the circulation of ink continues for a determined period, thereby lowering the temperatures of the first and second heaters 76, 77. This makes it possible to prevent deterioration of the ink remaining in the first and second heaters 76, 77. As a result, it is possible to reduce the amount of ink that is discarded due to deterioration or the amount of continuous paper 10 that is discarded due to printing defects. Furthermore, in this embodiment, the circulation duration ΔT(s) for continuing the circulation of ink is determined based on the duty values ​​of the first and second heaters 76, 77 and the ink flow rate, so the circulation duration ΔT(s) can be kept to a necessary minimum.

[0074] Furthermore, as shown in formula (1), the circulation duration ΔT(s) is proportional to the larger of the duty values ​​Dl (%) of the first heater 76 and the second heater 77 during the predetermined time. In other words, the circulation duration ΔT(s) is proportional to the duty values ​​of the first and second heaters 76, 77 during the predetermined time. This is because a large duty value of the first and second heaters 76, 77 during the predetermined time means that the heating elements inside the first and second heaters 76, 77 have already generated a lot of heat and reached high temperatures, and therefore it is necessary to continue circulating the ink for that long.

[0075] The control unit 9 also substitutes the larger of the duty values ​​Dl (%) of the first heater 76 and the second heater 77 for the predetermined time into equation (1). This makes it possible to sufficiently lower the temperature of either the heating element inside the first heater 76 or the heating element inside the second heater 77, even if that heating element generates an extremely large amount of heat and becomes very hot. As a result, deterioration of ink remaining near that heating element can be sufficiently suppressed.

[0076] Furthermore, as shown in formula (1), the circulation duration ΔT (s) is inversely proportional to the ink flow rate Qi (ml / min) in the circulation path 41 during the above-mentioned predetermined time. This is because the greater the ink flow rate Qi (ml / min), the more ink can be brought closer to the heating elements inside the first and second heaters 76, 77 when the ink is circulated, and the faster the temperatures of the heating elements of the first and second heaters 76, 77 can be lowered. As a result, the temperatures of the first and second heaters 76, 77 can be lowered efficiently, shortening the circulation duration ΔT (s) and improving workability.

[0077] Thereafter, when the power supply to the inkjet printing device 1 is resumed and the continuous paper 10 is transported, the continuous paper 10 is printed, and the ink is circulated, the control unit 9 again drives the circulation pump 71. The control unit 9 also resumes driving the first and second heaters 76, 77, while transporting the continuous paper 10, printing the continuous paper 10, and circulating the ink.

[0078] 4, the control unit 9 then determines whether or not to end the transport and printing of the continuous paper 10 (step S5). If image data to be printed remains, the control unit 9 continues transport and printing of the continuous paper 10 (step S5: No). When there is no more image data to print (step S5: Yes), the control unit 9 stops the operation of each unit and ends the transport of the continuous paper 10, printing on the continuous paper 10, and circulation of ink.

[0079] <3. Modifications> Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments.

[0080] Furthermore, the elements appearing in the above embodiments may be combined as appropriate within the scope of not causing any contradiction. [Explanation of symbols]

[0081] 1. Inkjet printing device 2. Conveyor section 3 Printing Department 4 Ink supply unit 9 Control Unit 10 Continuous Paper 11 Input section 35 Discharge head 51 Supply Tank 52 Recovery Tank 65 Return piping 71 Circulation Pump 76 First heater 77 Second heater 515 Pressure Mechanism 524 Pressure reducing mechanism

Claims

1. An inkjet printing device that prints by ejecting ink onto a print medium, an ink circulation path including a discharge head that discharges ink, a supply tank that stores ink to be supplied to the discharge head, a recovery tank that stores ink recovered from the discharge head, and a return pipe that connects the recovery tank and the supply tank; a circulation pump inserted in the return pipe for sending ink from the recovery tank to the supply tank via the return pipe; a heater inserted in the return pipe for heating the ink flowing from the recovery tank to the supply tank; an input unit capable of receiving a command to stop driving the circulation pump; a control unit electrically connected to the circulation pump, the heater, and the input unit; and The control unit a) when a signal related to the command is input from the input unit, stopping the driving of the heater, and determining a circulation duration for which the circulation pump is continuously driven from the time when the signal is input to continue circulating ink in the circulation path, based on the duty value of the heater at a predetermined time before the time when the signal is input and the flow rate of ink in the circulation path at the predetermined time; b) stopping the operation of the circulation pump after the circulation duration has elapsed since the signal was input; An inkjet printing device capable of sequentially executing the above steps.

2. 10. The inkjet printing apparatus of claim 1, An inkjet printing apparatus, wherein the circulation duration is inversely proportional to the flow rate of ink in the circulation path during the predetermined time.

3. 3. The inkjet printing apparatus according to claim 1, An inkjet printing apparatus, wherein the circulation duration is proportional to the duty value of the heater during the predetermined time.

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