Inkjet printing device

Abstract

To provide a technique that can precisely adjust a temperature, while reducing a time for starting-up ink in a low temperature state.SOLUTION: An inkjet printing device comprises an ink circulation path 41 for ink including a plurality of heads 80. A control part determines whether or not a first difference value determined by subtracting a detected result of a temperature of ink inside a supply-side manifold 61 from a first target temperature of ink in the manifold corresponds to a first phase that is above a first reference value or a third phase that is less than a second reference value smaller than the first reference value. When determining that the first difference value corresponds to the first phase, the control part controls driving of a second heater 77, on the basis of a value determined by multiplying a second difference value determined by subtracting the detected result of the temperature of ink inside the manifold from a second target temperature of ink in feedback piping 61, by a first coefficient. When determining that the first difference value corresponds to the third phase, the control part controls driving of the second heater 77, on the basis of a value determined by multiplying the second difference value by the first coefficient and a value determined by multiplying the first difference value by a third coefficient.SELECTED DRAWING: Figure 2

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. 2020-082392 Summary of the Invention [Problem to be solved by the invention]

[0004] The printing device (1) of Patent Document 1 has an ink circulation unit (3), an ink temperature adjustment unit (4), and a control unit (6) (paragraph 0016). The ink circulation unit (3) circulates the ink while supplying it to the inkjet head (2) (paragraph 0019). The ink flows from an upstream tank (21) through a pipe (27) to a distributor (25), where it is distributed to each of the multiple head modules (11) of the inkjet head (2) (paragraph 0026, Figure 2).

[0005] Furthermore, the ink temperature adjustment unit (4) adjusts the temperature of the ink flowing through the ink circulation unit (3) (paragraph 0029). The ink temperature detection unit (33) is disposed midway through the pipe (27) and detects the temperature of the ink flowing through the pipe (27) (paragraph 0032). When the ink temperature adjustment control unit (53) of the control unit (6) determines that the ink temperature needs to be adjusted based on the ink temperature detected by the ink temperature detection unit (33), it controls the ink circulation unit (3) and the ink temperature adjustment unit (4) to circulate the ink while adjusting the ink temperature to within the appropriate temperature range (paragraphs 0071 and 0073).

[0006] However, in Patent Document 1, the ink passes through a pipe (27) in which an ink temperature detection unit (33) is disposed, and is then distributed to the multiple head modules (11) of the inkjet head (2) via a distributor (25). Therefore, even if the ink temperature adjustment unit (4) is controlled based on the ink temperature detection result from the ink temperature detection unit (33) to adjust the ink temperature, there is a risk that the ink may fluctuate by the time it reaches each head module (11), and may not reach an appropriate temperature. On the other hand, if the temperature of the ink reaching each head module (11) is adjusted too precisely when starting up the printing device (1), there is a risk that the start-up process may take too long.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a technology that can shorten the time it takes for ink to warm up from a low temperature and that can precisely adjust the temperature of ink heading toward the head. [Means for solving the problem]

[0008] 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, comprising an ink circulation path, a heater, a return-side temperature sensor, a supply-side temperature sensor, and a control unit. The circulation path includes multiple heads that eject ink, a supply tank that stores ink to be supplied to the multiple heads, multiple individual supply-side pipes connected to each of the multiple heads, a supply-side manifold whose upstream end is connected to the supply tank and from which the multiple individual supply-side pipes branch, a recovery tank that stores ink recovered from the multiple heads, and a return pipe connecting the recovery tank and the supply tank. The heater is inserted in the return pipe and heats the ink flowing from the recovery tank to the supply tank. The return-side temperature sensor is inserted in the return pipe between the heater and the supply tank and detects the temperature of the ink in the return pipe. The supply-side temperature sensor is inserted in the supply-side manifold and detects the temperature of the ink in the supply-side manifold. The control unit is electrically connected to the heater, the return-side temperature sensor, and the supply-side temperature sensor. The control unit determines whether a first difference value, obtained by subtracting the temperature of ink in the supply-side manifold detected by the supply-side temperature sensor from a first target temperature of ink in the supply-side manifold, corresponds to a first phase in which the first difference value is equal to or greater than a first reference value, or a third phase in which the first difference value is less than a second reference value that is smaller than the first reference value. If the control unit determines that the temperature corresponds to the first phase, the control unit controls the operation of the heater based on a value obtained by multiplying the second difference value, obtained by subtracting the temperature of ink in the return pipe detected by the return-side temperature sensor, from a second target temperature of ink in the return pipe, by a first coefficient. If the control unit determines that the temperature corresponds to the third phase, the control unit controls the operation of the heater based on a value obtained by multiplying the second difference value by the first coefficient and a value obtained by multiplying the first difference value by a third coefficient.

[0009] A second invention of the present application is the inkjet printing device of the first invention, further including an internal temperature sensor that detects the temperature of the space outside the circulation path. The control unit determines whether the first difference value corresponds to a second phase in which the first difference value is less than the first reference value and greater than or equal to the second reference value. If the control unit determines that the second phase applies, it controls the heater based on a value obtained by multiplying the second difference value by the first coefficient and a heat radiation correction value obtained by multiplying the temperature of the space outside the circulation path detected by the internal temperature sensor by a second coefficient.

[0010] A third aspect of the present invention is the inkjet printing apparatus of the first aspect, wherein the control unit determines whether the first difference value corresponds to a second phase in which the first difference value is less than the first reference value and greater than or equal to the second reference value. If the control unit determines that the second phase applies, it controls driving of the heater based on a value obtained by multiplying the second difference value by the first coefficient and a heat radiation correction value obtained by multiplying a third difference value obtained by subtracting the detection result of the ink temperature in the supply-side manifold by the supply-side temperature sensor from the detection result of the ink temperature in the return pipe by the return-side temperature sensor, by a fourth coefficient.

[0011] A fourth invention of the present application is an inkjet printing device of the second or third invention, wherein when the control unit determines that the third phase applies, it controls the driving of the heater based on the value obtained by multiplying the second difference value by the first coefficient, the heat dissipation correction value, and the value obtained by multiplying the first difference value by the third coefficient.

[0012] A fifth aspect of the present invention is the inkjet printing apparatus of the first aspect, wherein the control unit determines whether the first difference value calculated every predetermined time by subtracting the detection result of the temperature of the ink in the supply-side manifold detected by the supply-side temperature sensor every predetermined time from the first target temperature of the ink in the supply-side manifold corresponds to the first phase, which is equal to or greater than the first reference value, or the third phase, which is less than the second reference value which is smaller than the first reference value. If the control unit determines that the first difference value corresponds to the third phase, the control unit controls driving of the heater based on a value obtained by multiplying the second difference value by the first coefficient and a value obtained by cumulatively adding, every predetermined time, values ​​obtained by multiplying the first difference value by the third coefficient.

[0013] A sixth aspect of the present invention is an inkjet printing apparatus according to any one of the first to fifth aspects, further comprising a plurality of supply-side temperature sensors, each of which is inserted in the supply-side manifold and detects the temperature of ink in the supply-side manifold, and the control unit determines the first difference value as the first target temperature of the ink in the supply-side manifold minus the average of the detection results of the ink temperature in the supply-side manifold by each of the plurality of supply-side temperature sensors.

[0014] A seventh aspect of the present invention is the inkjet printing apparatus according to any one of the second to fourth aspects, further comprising a flow rate measuring unit that measures the flow rate of ink flowing through the circulation path. The control unit is further electrically connected to the flow rate measuring unit. When the control unit determines that the second phase applies, the control unit controls the driving of the heater based on a value obtained by multiplying the second difference value by the first coefficient and the heat radiation correction value, which are corrected based on the measurement result of the ink flow rate measured by the flow rate measuring unit.

[0015] An eighth aspect of the present invention is the inkjet printing apparatus of any one of the first to seventh aspects, wherein the first coefficient is a positive value.

[0016] A ninth aspect of the present invention is the inkjet printing apparatus of the second aspect, wherein the first coefficient is a positive value and the second coefficient is a negative value.

[0017] A tenth aspect of the present invention is the inkjet printing apparatus of any one of the first to ninth aspects, wherein the first coefficient is a positive value and the third coefficient is a positive value.

[0018] An eleventh aspect of the present invention is the inkjet printing apparatus of the third aspect, wherein the first coefficient is a positive value and the fourth coefficient is a positive value. [Effects of the Invention]

[0019] According to the first to eleventh aspects of the present invention, in the first phase, the temperature of the ink in the supply-side manifold is low, and by driving the heater at high intensity, the warm-up time from a low temperature can be shortened. Meanwhile, in the third phase, the temperature of the ink in the supply-side manifold is close to the target temperature (first target temperature), and by referring to this, the heater can be driven more precisely to prevent the ink from overheating.

[0020] In particular, according to the second invention of the present application, in the second phase, by referring to the temperature of the external space of the circulation path within the inkjet printing device, heat dissipation from the ink can also be taken into account, allowing the heater to be driven more precisely than in the first phase.

[0021] In particular, according to the third invention of the present application, in the second phase, the heat dissipation of the ink from the position where the return side temperature sensor between the heater and the supply tank is located to the position where the supply side temperature sensor in the supply side manifold is located can also be taken into account, so the heater can be driven more precisely than in the first phase.

[0022] In particular, according to the fourth aspect of the present invention, in the third phase, the heater can be driven more precisely by referring to the heat radiation correction value in addition to the temperature of ink in the supply-side manifold.

[0023] In particular, according to the fifth aspect of the present invention, it is possible to prevent the heater driving value from becoming extremely large or small, and as a result, the heater can be driven more stably.

[0024] In particular, according to the sixth aspect of the present invention, even if there is a deviation in the temperature of the ink depending on the position in the supply side manifold, the heater can be driven stably in the first and third phases.

[0025] In particular, according to the seventh aspect of the present invention, by also referring to the ink flow rate in the second phase, the heater can be driven more precisely. [Brief explanation of the drawings]

[0026] [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 for determining whether a first difference value D1 corresponds to the first phase to the third phase. [Figure 5] FIG. 10 is a diagram conceptually showing the configuration of an ink supply unit and an ejection head according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] 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.

[0028] 1. First Embodiment <1-1. 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 internal temperature sensor 11.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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 that each eject ink. 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 individual supply side pipes 62, a plurality (five in this embodiment) of individual recovery side 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 flow rate measuring unit 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 fourth temperature sensor 87, a filter 88, and a degassing unit 89.

[0037] The supply tank 51 is a container for temporarily storing ink to be supplied to the five heads 80. 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.

[0038] The supply-side manifold 61 and the five individual supply-side pipes 62 are pipes that connect the supply tank 51 and the five heads 80 of one ejection 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 individual supply-side pipes 62 are each a thin pipe branching off from the supply-side manifold 61. That is, the upstream end of the supply-side manifold 61 is connected to the supply tank 51, and the five individual supply-side pipes 62 each branch off from the supply-side manifold 61. The upstream end of each of the five individual supply-side pipes 62 is connected to an 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. That is, the five individual supply-side pipes 62 are connected to each of the five heads 80.

[0039] Furthermore, in this embodiment, a supply-side on-off valve 73 is interposed in each individual supply-side pipe 62. For example, a solenoid valve that opens and closes under the control of the control unit 9 is used as the supply-side on-off valve 73. However, an on-off valve that is manually opened and closed may also be used as the supply-side on-off valve 73. When the supply-side on-off valve 73 is closed, communication between the internal passages of the individual supply-side 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 individual supply-side pipes 62 is permitted. However, the supply-side on-off valve 73 is not necessarily provided. Furthermore, a filter or the like may be interposed in the supply-side manifold 61 or the five individual supply-side pipes 62.

[0040] The five recovery side individual 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. The five recovery side individual pipes 63 are each a thin tube branching off from the recovery side manifold 64. The upstream end of each of the five recovery side individual 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. That is, the five recovery side individual pipes 63 are connected to each of the five heads 80. The recovery side manifold 64 is a thick tube whose downstream end is connected to communicate with an internal chamber 520 (described later) of the recovery tank 52. That is, the recovery side manifold 64 has its downstream end connected to the recovery tank 52, and the five recovery side individual pipes 63 branch off from it.

[0041] In this embodiment, a head outlet-side on-off valve 74 is inserted in each recovery-side individual pipe 63. The head outlet-side on-off valve 74 is, 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 be used as 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 individual 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 individual 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 individual pipes 63 or the recovery-side manifold 64.

[0042] The recovery tank 52 is a container for temporarily storing the ink collected from the five heads 80. An internal chamber 520 capable of temporarily storing 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.

[0043] 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.

[0044] 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 each of the five heads 80 of the ejection head 35, and further allows the ink remaining in each of the five heads 80 (ink that was not ejected from each of the five heads 80) to be collected in the recovery tank 52.

[0045] 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).

[0046] 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.

[0047] With the above configuration, an ink circulation path 41 is formed, which runs from the supply tank 51 through the supply manifold 61, the individual supply pipes 62, the internal tank 82 of the head 80, the individual recovery pipes 63, the recovery manifold 64, the recovery tank 52, and the return pipe 65, and then returns to the supply tank 51. That is, the ink circulation path 41 includes the supply tank 51, the supply manifold 61, five individual supply pipes 62, five heads 80, five individual recovery pipes 63, the recovery manifold 64, the recovery tank 52, and the return pipe 65. In addition, a circulation pump 71, a flow rate measurement unit 75, a first heater 76, a second heater 77, a second temperature sensor 85, a third temperature sensor 86, a fourth temperature sensor 87, a filter 88, and a degassing unit 89 are inserted in the return pipe 65.

[0048] 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 in the internal passage of the return pipe 65 from the recovery tank 52 to the supply tank 51 in accordance with an operation signal from the control unit 9. The circulation pump 71 in this embodiment is, for example, a pump such as a diaphragm pump that is less likely to generate foreign matter such as dust when driven.

[0049] The flow rate measurement unit 75 is interposed in the return pipe 65 between the circulation pump 71 and the supply tank 51. The flow rate measurement unit 75 measures the flow rate of ink flowing through the internal passage of the return pipe 65. In other words, the flow rate measurement unit 75 measures the flow rate of ink flowing through the circulation path 41. The flow rate measurement unit 75 is also electrically connected to the control unit 9. The flow rate measurement unit 75 outputs data related to the measurement result of the ink flow rate to the control unit 9.

[0050] The first heater 76 is a device that heats the ink being pumped 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 also controlled by switching between the ON state and the OFF state so that the temperature of the ink flowing out of the first heater 76 becomes a target temperature (hereinafter referred to as the "return upstream target temperature Tr1 (°C)") that is higher than room temperature.

[0051] The second heater 77 is a device that heats the ink being fed through the internal passage of the return pipe 65. 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 feeding 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 generates heat when the power is turned on, thereby heating the ink. The second heater 77 is controlled by switching between the ON state and the OFF state so that the temperature of the ink flowing out of the second heater 77 becomes a target temperature (hereinafter referred to as the "return downstream target temperature Tr2 (°C)") that is higher than the return upstream target temperature Tr1 (°C) (for example, n1°C higher than the return upstream target temperature Tr1 (°C)). Here, n1°C is a positive value of several degrees Celsius. That is, the ratio of the time that the second heater 77 is in the ON state per unit time (hereinafter referred to as the “duty value”) is greater than the duty value of the first heater 76.

[0052] Furthermore, the second heater 77 corresponds to the "heater" of the present invention. Furthermore, the return downstream target temperature Tr2 (°C) corresponds to the "second target temperature" of the present invention. 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. In other words, the "heater" of the present invention may be any heater that is inserted in the return pipe 65 and heats the ink flowing from the collection tank 52 to the supply tank 51.

[0053] As shown in FIG. 2, a first temperature sensor 84 is inserted into the supply-side manifold 61. The first temperature sensor 84 corresponds to the "supply-side temperature sensor" of the present invention. The first temperature sensor 84 detects the temperature of the ink being pumped through the internal passage of the supply-side manifold 61. In other words, the first temperature sensor 84 detects the temperature of the ink inside the supply-side manifold 61. 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.

[0054] A second temperature sensor 85 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 in the ink feed direction. The second temperature sensor 85 detects the temperature of the ink flowing into the first heater 76. The second temperature sensor 85 is electrically connected to the control unit 9. The second temperature sensor 85 outputs data related to the ink temperature detection result to the control unit 9. By referring to the data related to the detection result by the second temperature sensor 85, the control unit 9 can determine the temperature of the ink flowing into the first heater 76. This allows the control unit 9 to use the data as a guide to determine whether the first heater 76 and the second heater 77 are operating normally when controlling their drive, as described below. However, the second temperature sensor 85 is not necessarily provided.

[0055] A third temperature sensor 86 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 third temperature sensor 86 detects the temperature of the ink flowing out from the first heater 76. 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 third temperature sensor 86 does not necessarily have to be provided.

[0056] Furthermore, a fourth temperature sensor 87 is inserted into 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 fourth temperature sensor 87 corresponds to the "return side temperature sensor" of the present invention. The fourth temperature sensor 87 detects the temperature of the ink flowing out from the second heater 77. In other words, the fourth temperature sensor 87 detects the temperature of the ink in the return pipe 65. The fourth temperature sensor 87 is also electrically connected to the control unit 9. The fourth temperature sensor 87 outputs data related to the detection result of the ink temperature to the control unit 9.

[0057] The filter 88 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 88 filters the ink being fed through the internal passage of the return pipe 65 and removes foreign matter contained in the ink.

[0058] The degassing unit 89 is inserted in the return pipe 65 downstream of the filter 88 in the ink sending direction and upstream of the supply tank 51 in the ink sending direction. The degassing unit 89 in this embodiment is a so-called hollow fiber membrane degassing module. The degassing unit 89 removes air bubbles from the ink being sent through the internal passage of the return pipe 65.

[0059] The internal temperature sensor 11 is disposed inside the inkjet printing apparatus 1, for example, near the ejection head 35. For ease of explanation, the internal temperature sensor 11 is also shown in FIG. 2. The internal temperature sensor 11 detects the temperature of the space near the ejection head 35. That is, the internal temperature sensor 11 detects the temperature of the space outside the circulation path 41. The internal temperature sensor 11 is also electrically connected to the control unit 9. The internal temperature sensor 11 outputs data related to the detection result of the temperature of the space outside the circulation path 41 to the control unit 9. However, the location of the internal temperature sensor 11 is not limited to this. The location of the internal temperature sensor 11 is adjusted appropriately taking into consideration the flow of hot air from a dryer (not shown) separately provided inside the inkjet printing apparatus 1, etc. Furthermore, the internal temperature sensor 11 does not necessarily have to be provided.

[0060] 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 the ink, and controlling the ink temperature.

[0061] As shown in FIG. 3, the control unit 9 is electrically and communicatively connected to the conveying 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 opening / closing valves 73, the five head outlet side opening / closing valves 74, the flow rate measuring unit 75, the first heater 76, the second heater 77, the first temperature sensor 84, the second temperature sensor 85, the third temperature sensor 86, the fourth temperature sensor 87, the pressurizing mechanism 515, the decompression mechanism 524, and the internal temperature sensor 11.

[0062] That is, the control unit 9 can control 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 flow rate measurement unit 75, the first heater 76, the second heater 77, the first temperature sensor 84, the second temperature sensor 85, the third temperature sensor 86, the fourth temperature sensor 87, the pressurization mechanism 515, the decompression mechanism 524, and the internal temperature sensor 11. The control unit 9 controls the operation of each of these units in accordance with a computer program 9P.

[0063] <1-2. Continuous paper transport, printing, ink circulation, and ink temperature control> Next, the procedures for transporting the continuous paper 10, printing on the continuous paper 10, circulating the ink, and controlling the ink temperature, which are carried out in the inkjet printing device 1, will be described.

[0064] First, when transporting the continuous paper 10, printing on the continuous paper 10, and circulating ink, the control unit 9 operates the transport unit 2 to transport the continuous paper 10 in a transport direction along the longitudinal direction along a predetermined transport path. Also, while transporting the continuous paper 10, the control unit 9 controls the multiple nozzles 83 of each of the four ejection heads 35 to eject ink droplets onto the surface of the continuous paper 10. This records an image on the surface of the continuous paper 10.

[0065] 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 and the five head outlet-side on-off valves 74.

[0066] The control unit 9 then drives the circulation pump 71, the first heater 76, the second heater 77, the pressurizing mechanism 515, and the decompression mechanism 524 of each of the four ink supply units 4. That is, the control unit 9 drives the circulation pump 71 to circulate the ink in the ink circulation path 41, while driving the pressurizing mechanism 515 and the decompression mechanism 524 to supply the ink to the internal tank 82 of each ejection head 35.

[0067] Furthermore, the first temperature sensor 84, the second temperature sensor 85, the third temperature sensor 86, the fourth temperature sensor 87, and the internal temperature sensor 11 are powered on, and these sensors start measuring the temperature of the ink at their respective positions. Furthermore, the flow rate measuring unit 75 is powered on, and the flow rate measuring unit 75 starts measuring the flow rate of the ink flowing through the circulation path 41.

[0068] To transport and print on the continuous paper 10, it is necessary for the temperature of the ink ejected from each head 80 to be within a predetermined range. If the ink temperature is not within the predetermined range, the ink cannot be ejected properly from the nozzles 83, which may result in clogging of the nozzles 83. Furthermore, if the ink temperature remains excessively high for a certain period of time, the ink may deteriorate, resulting in a decrease in print quality. When the inkjet printing device 1 is first started up, the temperature of the ink present in the circulation path 41 and the ink refilled into the internal chamber 510 of the supply tank 51 is significantly low. Therefore, if the ink temperature has not yet reached a temperature suitable for ejection, it is possible to drive the second heater 77 at a high duty cycle, for example, while monitoring the temperature of the ink flowing out of the second heater 77 detected by the fourth temperature sensor 87.

[0069] However, even if the temperature of the ink flowing out from the second heater 77 is adjusted to be within a predetermined range, the temperature of the ink may drop again due to heat radiation as the ink travels through the long circulation path 41 and reaches each head 80, which may result in the head 80 not being able to maintain an appropriate temperature. Furthermore, if an attempt is made to set a higher target temperature for the ink flowing out from the second heater 77 and drive the second heater 77 at a higher duty value so that the temperature of the ink in the head 80 is within a predetermined range, precise control becomes difficult, and as a result, the temperature of the ink flowing out from the second heater 77 may become excessively high, which may lead to deterioration of the ink. Furthermore, if a temperature sensor is placed near the head 80 and an attempt is made to precisely control the drive of the second heater 77 based on the results of detection of the ink temperature by the temperature sensor from the beginning when the ink temperature has not yet reached a temperature suitable for ejection, it may take a long time to complete the adjustment of the ink temperature, which may reduce workability.

[0070] Therefore, in this embodiment, the drive of the second heater 77 is controlled in a plurality of phases based on the difference between the target temperature of the ink in the supply-side manifold 61 close to each head 80 (hereinafter referred to as the "supply-side target temperature Ts1 (°C)") and the detection result of the actual temperature of the ink in the supply-side manifold 61. More specifically, the control unit 9 determines whether a difference value (hereinafter referred to as the "first difference value D1") obtained by subtracting the detection result of the ink temperature in the supply-side manifold 61 by the first temperature sensor 84 from the supply-side target temperature Ts1 (°C) of the ink in the supply-side manifold 61 corresponds to any of the following first to third phases. FIG. 4 is a flowchart for determining whether the first difference value D1 corresponds to any of the first to third phases. The supply-side target temperature Ts1 (°C) corresponds to the "first target temperature" in this invention.

[0071] As shown in FIG. 4, the first phase refers to a case where the first differential value D1 is equal to or greater than a first reference value Rv1 (n0°C). Here, n0°C is, for example, a value that satisfies "n0°C > n1°C > 0°C." The second phase refers to a case where the first differential value D1 is less than the first reference value Rv1 and equal to or greater than a second reference value Rv2 (n2°C) that is smaller than the first reference value Rv1. Here, n2°C is, for example, a value that satisfies "n1°C > n2°C > 0°C." The third phase refers to a case where the first differential value D1 is less than the second reference value Rv2. If the controller 9 determines that the current state corresponds to the first, second, or third phase, it controls the driving of the second heater 77 as follows. However, the phases for controlling the driving of the second heater 77 are not limited to the above three types. The phases for controlling the driving of the second heater 77 may be two types, four types, or more.

[0072] <1-2-1. If you fall under Phase 1> When the first phase applies, it can be considered that there is a sufficient difference between the supply-side target temperature Ts1 (°C) of the ink in the supply-side manifold 61 and the actual temperature of the ink in the supply-side manifold 61. In other words, it can be considered that the actual temperature of the ink in the supply-side manifold 61 is sufficiently low. Therefore, the control unit 9 drives the second heater 77 while referring only to the result of the temperature of the ink flowing out from the second heater 77 detected by the fourth temperature sensor 87.

[0073] More specifically, the control unit 9 controls the second heater 77 so that the temperature of the ink detected by the fourth temperature sensor 87 becomes the above-mentioned preset downstream feedback temperature Tr2 (°C). Examples of a control method that can be used include PID control and PI control. That is, the control unit 9 generates a control value CV1 for controlling the second heater 77 and inputs it to the second heater 77. Here, the control value CV1 is, for example, a value indicating the power value applied to the heating element of the second heater 77. The control value CV1 is also a value obtained by multiplying a difference (hereinafter referred to as a "second difference value D2") obtained by subtracting the temperature of the ink detected by the fourth temperature sensor 87 from the downstream feedback temperature Tr2 (°C) by a first coefficient k1 (positive value). The first coefficient k1 is set, for example, by a preliminary experiment conducted in advance.

[0074] That is, when the control unit 9 determines that the first phase applies, it controls the driving of the second heater 77 based on a value obtained by multiplying a second difference value D2 obtained by subtracting the detection result of the ink temperature in the return pipe 65 by the fourth temperature sensor 87 (i.e., the return-side temperature sensor) from the return-downstream target temperature Tr2 (°C) (i.e., the second target temperature of the ink in the return pipe 65) by a first coefficient k1. As a result, in the first phase, the temperature of the ink in the supply-side manifold 61 is low, and by driving the second heater 77 at high intensity, the warm-up time from a low temperature can be shortened.

[0075] However, if the control unit 9 determines that the current state corresponds to the first phase, it may further control the driving of the first heater 76 based on a value obtained by multiplying a difference value obtained by subtracting the detection result of the ink temperature in the return pipe 65 by the third temperature sensor 86 from the return upstream target temperature Tr1 (°C) by a first coefficient k1 or another coefficient. Note that, although it is unlikely, if the actual temperature of the ink in the supply-side manifold 61 is higher than the supply-side target temperature Ts1 (°C) of the ink in the supply-side manifold 61 by at least a first reference value Rv1 (a positive value of about several degrees Celsius), the driving of the first heater 76 and the second heater 77 may be immediately stopped.

[0076] <1-2-2. If you fall under the second phase> Next, when the second phase applies, it can be considered that the actual temperature of the ink in the supply-side manifold 61 is somewhat close to the supply-side target temperature Ts1 (°C) of the ink in the supply-side manifold 61. In this case, it is possible that the actual temperature of the ink in the supply-side manifold 61 is not only lower than the supply-side target temperature Ts1 (°C), but also slightly higher than the supply-side target temperature Ts1 (°C) for some reason. When the second phase applies, the control unit 9 controls the driving of the second heater 77 by referring to the result of detection by the fourth temperature sensor 87 of the temperature of the ink flowing out from the second heater 77, while also taking into consideration heat dissipation from the ink passing through the circulation path 41 to reach each head 80.

[0077] More specifically, heat dissipation of ink is significantly affected by the temperature of the space near the circulation path 41. Therefore, the control unit 9 generates the heat dissipation correction value CV2, taking into account the temperature of the space near the ejection head 35, detected by the internal temperature sensor 11 disposed near the ejection head 35, for example. The heat dissipation correction value CV2 is calculated by multiplying the temperature of the space near the ejection head 35, detected by the internal temperature sensor 11, by a second coefficient k2 (a negative value). The second coefficient k2 is set, for example, by a preliminary experiment conducted in advance. The control unit 9 then inputs a value obtained by adding the heat dissipation correction value CV2 to the control value CV1 to the second heater 77, and performs PID control, PI control, or the like of the second heater 77. As a result, for example, if the temperature of the space near the ejection head 35 is considerably high, the amount of heat dissipated by the ink is thought to be small, so by multiplying the temperature by the second coefficient k2 (negative value) and adding the result to the above control value CV1, the drive strength of the second heater 77 can be made slightly gentler.

[0078] That is, when the control unit 9 determines that the second phase applies, it controls the drive of the second heater 77 based on a control value CV1 calculated by multiplying the second difference value D2 by a first coefficient k1 and a heat radiation correction value CV2 calculated by multiplying the temperature of the space outside the circulation path 41 detected by the internal temperature sensor 11 by a second coefficient k2. In this way, in the second phase, by referring to the temperature of the space outside the circulation path 41 within the inkjet printing device 1, heat radiation from the ink can also be taken into consideration, so the second heater 77 can be driven more precisely than in the first phase. However, the heat radiation correction value CV2 may also be derived by referring to a table created in advance from the temperature of the space near the ejection head 35 detected by the internal temperature sensor 11. In addition, the heat radiation correction value CV2 may be calculated by multiplying the difference value obtained by subtracting the temperature of the space near the ejection head 35 detected by the internal temperature sensor 11 from the detection result of the temperature of the ink flowing near the ejection head 35 in the circulation path 41 by a fifth coefficient k5 (a positive value).

[0079] Furthermore, if the control unit 9 determines that the current state corresponds to the second phase, the control unit 9 may further correct the control value CV1 using a heat radiation correction value CV3 calculated by a different method. For example, the control unit 9 may calculate the heat radiation correction value CV3 by multiplying a difference value (hereinafter referred to as a "third difference value D3") obtained by subtracting the ink temperature detected in the supply-side manifold 61 by the first temperature sensor 84 (i.e., the supply-side temperature sensor) from the ink temperature detected in the return pipe 65 by the fourth temperature sensor 87 (i.e., the return-side temperature sensor) by a fourth coefficient k4 (a positive value). The fourth coefficient k4 is set, for example, by a preliminary experiment. The control unit 9 then adds the heat radiation correction value CV3 to the control value CV1 and inputs the result to the second heater 77 to perform PID control, PI control, or the like of the second heater 77.

[0080] This allows the second heater 77 to be driven more precisely than in the first phase, since it takes into account the actual amount of heat dissipated by the ink from the position where the fourth temperature sensor 87 is located in the circulation path 41 to the position where the first temperature sensor 84 is located in the supply side manifold 61.

[0081] Furthermore, when the control unit 9 determines that the second phase applies, it may add the heat radiation correction value CV2 or CV3 to the control value CV1, further correct the result based on the measurement result of the flow rate of ink flowing through the circulation path 41 by the flow rate measurement unit 75, and input the result to the second heater 77 to perform PID control, PI control, or the like of the second heater 77. As a result, for example, if the measurement result of the flow rate of ink flowing through the circulation path 41 by the flow rate measurement unit 75 is a considerably large value, the value input to the second heater 77 can be increased, thereby driving the second heater 77 at high intensity. This makes it possible to increase the temperature of the ink in a shorter time.

[0082] That is, when the control unit 9 determines that the second phase applies, it may control the driving of the second heater 77 based on a control value CV1 calculated by multiplying the second difference value D2 by the first coefficient k1, and the heat radiation correction value CV2 or the heat radiation correction value CV3, which are corrected based on the measurement result of the ink flow rate by the flow rate measurement unit 75. In this way, in the second phase, the second heater 77 can be driven more precisely by also referring to the ink flow rate.

[0083] Furthermore, when the control unit 9 determines that the current phase corresponds to the second phase, it may further correct the control value CV1 using a heat radiation correction value calculated by a different method. Furthermore, when the control unit 9 determines that the current phase corresponds to the second phase, it may further control the driving of the first heater 76 based on the control value CV1 and the heat radiation correction value calculated by either method.

[0084] <1-2-3. If you fall into the third phase> Next, when the third phase applies, it can be considered that the actual temperature of the ink in the supply-side manifold 61 is sufficiently close to the supply-side target temperature Ts1 (°C) of the ink in the supply-side manifold 61. In this case, it is possible that the actual temperature of the ink in the supply-side manifold 61 is not only slightly lower than the supply-side target temperature Ts1 (°C), but also slightly higher than the supply-side target temperature Ts1 (°C) due to small fluctuations in the drive amount of the second heater 77, the ink flow, etc. When the third phase applies, the control unit 9 controls the drive of the second heater 77 while monitoring the temperature of the ink flowing out of the second heater 77 detected by the fourth temperature sensor 87, taking into account heat dissipation from the ink, and monitoring the actual temperature of the ink in the supply-side manifold 61 detected by the first temperature sensor 84.

[0085] More specifically, the control unit 9 calculates the final correction value CV4 by multiplying a first difference value D1, which is obtained by subtracting the detection result of the temperature of ink in the supply-side manifold 61 by the first temperature sensor 84, from the supply-side target temperature Ts1 (°C) of ink in the supply-side manifold 61, by a third coefficient k3 (a positive value). Here, the third coefficient k3 is set, for example, by a preliminary experiment conducted in advance. The control unit 9 then inputs a value obtained by adding the heat radiation correction value CV2 or CV3 and the final correction value CV4 to the control value CV1 to the second heater 77, and performs PID control, PI control, or the like of the second heater 77.

[0086] That is, when the control unit 9 determines that the third phase applies, it controls the driving of the second heater 77 based on the control value CV1 calculated by multiplying the second difference value D2 by the first coefficient k1, the heat radiation correction value CV2 or the heat radiation correction value CV3, and the final correction value CV4 calculated by multiplying the first difference value D1 by the third coefficient k3. In this way, in the third phase, the actual temperature of the ink in the supply-side manifold 61 is close to the supply-side target temperature Ts1 (°C) (first target temperature), so by driving the second heater 77 more precisely while referring to this, it is possible to prevent the ink from overheating.

[0087] However, in the third phase, the second heater 77 may be driven without considering the heat dissipation correction value CV2 or the heat dissipation correction value CV3. That is, when the control unit 9 determines that the third phase applies, it may control the driving of the second heater 77 based on the control value CV1 calculated by multiplying the second difference value D2 by the first coefficient k1 and the final correction value CV4 calculated by multiplying the first difference value D1 by the third coefficient k3. However, even in the third phase, the second heater 77 can be driven more precisely by considering the heat dissipation correction value CV2 or the heat dissipation correction value CV3 as described above.

[0088] As a modified example, instead of determining whether the current phase corresponds to the first phase, the second phase, or the third phase or calculating the final correction value CV4 based on the first difference value D1 at a certain point in time, the first difference value D1 and the final correction value CV4 may be calculated at predetermined time intervals. More specifically, the temperature of ink in the supply-side manifold 61 may be detected at predetermined time intervals using the first temperature sensor 84. The control unit 9 may then calculate the first difference value D1 at predetermined time intervals by subtracting the actual temperature of ink in the supply-side manifold 61 detected by the first temperature sensor 84 from the supply-side target temperature Ts1 (°C). The control unit 9 may then determine at predetermined time intervals whether the current phase corresponds to the first phase, the second phase, or the third phase based on the calculation result of the first difference value D1.

[0089] If it is determined that the current state corresponds to the third phase, the control unit 9 may further detect the temperature of the ink flowing out from the second heater 77 at predetermined time intervals using the fourth temperature sensor 87. The control unit 9 may then calculate a second difference value D2 at predetermined time intervals by subtracting the actual temperature of the ink in the return pipe 65 detected by the fourth temperature sensor 87 from the return downstream target temperature Tr2 (°C). Furthermore, the control unit 9 may input to the second heater 77 at predetermined time intervals a value obtained by adding together a control value CV1 calculated by multiplying the second difference value D2 by the first coefficient k1 and a final correction value CV4 calculated by multiplying the first difference value D1 by the third coefficient k3, and perform PID control, PI control, or the like of the second heater 77.

[0090] Here, the control unit 9 may cumulatively add the final correction value CV4 instead of adding the control value CV1 newly calculated at each predetermined time interval and the final correction value CV4 newly calculated at each predetermined time interval. That is, the control unit 9 may add the control value CV1 newly calculated at each predetermined time interval and all of the final correction values ​​CV4 calculated at each predetermined time interval up to that point, and input the resulting value to the second heater 77 to drive the second heater 77. This prevents the value input to the second heater 77 from becoming extremely large or small, even if the fourth temperature sensor 87 outputs an outlier for some reason. As a result, the second heater 77 can be driven more stably in the third phase, in which the actual temperature of the ink in the supply-side manifold 61 is sufficiently close to the supply-side target temperature Ts1 (°C). This allows the ink temperature to be adjusted more stably.

[0091] That is, in this modified example, the control unit 9 subtracts the detection result of the temperature of the ink in the supply-side manifold 61 detected by the first temperature sensor 84 (i.e., the supply-side temperature sensor) every predetermined time from the supply-side target temperature Ts1 (°C) of the ink in the supply-side manifold 61 (first target temperature), and determines whether the first difference value D1 calculated every predetermined time corresponds to the first phase, which is greater than or equal to the first reference value Rv1, or the third phase, which is less than the second reference value Rv2 that is smaller than the first reference value Rv1.If it determines that the first difference value D1 corresponds to the third phase, the control unit 9 may control the driving of the second heater 77 based on the value obtained by multiplying the second difference value D2 by the first coefficient k1 and the value obtained by cumulatively adding, every predetermined time, the value obtained by multiplying the first difference value D1 by the third coefficient k3.

[0092] 2. Second Embodiment Next, an inkjet printing apparatus 1 according to a second embodiment of the present invention will be described. Note that the inkjet printing apparatus 1 according to this embodiment differs from the inkjet printing apparatus 1 according to the first embodiment only in the detailed structure of the ink supply unit 4. Therefore, only this difference will be described below.

[0093] FIG. 5 is a conceptual diagram illustrating the configuration of one ink supply unit 4B and one ejection head 35 according to this embodiment. As shown in FIG. 5, a plurality of (two in this embodiment) first temperature sensors 841B, 842B are inserted into the supply-side manifold 61 of the ink supply unit 4B according to this embodiment. The first temperature sensors 841B, 842B each correspond to the "supply-side temperature sensor" of the present invention. The first temperature sensors 841B, 842B each detect the temperature of ink being pumped through the internal passage of the supply-side manifold 61. In other words, the first temperature sensors 841B, 842B each detect the temperature of ink inside the supply-side manifold 61. The first temperature sensors 841B, 842B are also electrically connected to the control unit 9. The first temperature sensors 841B, 842B each output data related to the detection results of the ink temperature to the control unit 9.

[0094] In this embodiment, the control unit 9 determines as the first difference value in the first and third phases the value obtained by subtracting the average of the detection results of the ink temperature in the supply-side manifold 61 by each of the first temperature sensors 841B and 842B from the supply-side target temperature Ts1 (°C) (first target temperature) of the ink in the supply-side manifold 61. This makes it possible to stably drive the second heater 77 in the first and third phases even if there is a deviation in the ink temperature depending on the position in the supply-side manifold 61.

[0095] It is desirable that the multiple first temperature sensors be arranged evenly in the supply-side manifold 61. For example, in the case of two first temperature sensors 841B, 842B, they are preferably arranged evenly near the upstream end and the downstream end of the supply-side manifold 61. This allows the second heater 77 to be driven more stably even if there is a deviation in the temperature of the ink depending on the position in the supply-side manifold 61.

[0096] <3. Modifications> Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments.

[0097] In the above embodiment, the first coefficient k1, the third coefficient k3, and the fourth coefficient k4 are all positive values, and the second coefficient k2 is a negative value. However, the positive and negative values ​​of the first coefficient k1 to the fourth coefficient k4 are not limited to this. Furthermore, the first coefficient k1 to the fourth coefficient k4 may be zero.

[0098] In the above embodiment, the upstream end of the supply-side manifold 61 is directly connected to the internal chamber 510 of the supply tank 51. However, the supply-side manifold 61 and the supply tank 51 do not necessarily have to be directly connected as long as ink can communicate between them. For example, a separate connecting pipe may be interposed between the supply-side manifold 61 and the supply tank 51.

[0099] In the above embodiment, the downstream end of the recovery manifold 64 is directly connected to the internal chamber 520 of the recovery tank 52. However, the recovery manifold 64 and the recovery tank 52 do not necessarily have to be directly connected as long as ink can communicate between them. For example, a separate connecting pipe may be interposed between the recovery manifold 64 and the recovery tank 52.

[0100] Furthermore, the elements appearing in the above-described embodiment and modified examples may be combined as appropriate within the scope of not causing any contradiction. [Explanation of symbols]

[0101] 1. Inkjet printing device 3 Printing Department 4,4B Ink supply unit 9 Control Unit 10 Continuous Paper 11. Internal temperature sensor 35 Discharge head 41 Circulation Route 51 Supply Tank 52 Recovery Tank 61 Supply side manifold 62 Supply side individual piping 63 Individual piping on recovery side 64 Recovery side manifold 65 Return piping 71 Circulation Pump 75 Flow measurement section 76 First heater 77 Second heater 80 head 83 nozzle 84 First temperature sensor (supply side temperature sensor) 85 Second temperature sensor 86 Third temperature sensor 87 4th temperature sensor (return side temperature sensor) 841B 1st temperature sensor (supply side temperature sensor) 842B 1st temperature sensor (supply side temperature sensor) D1 First difference value Rv1 First standard value Rv2 Second standard value

Claims

1. An inkjet printing device that prints by ejecting ink onto a print medium, an ink circulation path including: a plurality of heads that eject ink; a supply tank that stores ink to be supplied to the plurality of heads; a plurality of individual supply pipes connected to each of the plurality of heads; a supply manifold whose upstream end communicates with the supply tank and from which the plurality of individual supply pipes branch off; a recovery tank that stores ink recovered from the plurality of heads; and a return pipe that connects the recovery tank and the supply tank; a heater inserted in the return pipe for heating the ink flowing from the recovery tank to the supply tank; a return-side temperature sensor interposed between the heater and the supply tank in the return pipe and configured to detect the temperature of the ink in the return pipe; a supply-side temperature sensor that is inserted in the supply-side manifold and detects the temperature of the ink in the supply-side manifold; a control unit electrically connected to the heater, the feedback-side temperature sensor, and the supply-side temperature sensor; and The control unit determining whether a first difference value obtained by subtracting the temperature of the ink in the supply-side manifold detected by the supply-side temperature sensor from a first target temperature of the ink in the supply-side manifold corresponds to a first phase in which the first difference value is equal to or greater than a first reference value, or a third phase in which the first difference value is less than a second reference value that is smaller than the first reference value; If it is determined that the first phase applies, the driving of the heater is controlled based on a value obtained by multiplying a second difference value obtained by subtracting the detection result of the temperature of the ink in the return pipe by the return-side temperature sensor from a second target temperature of the ink in the return pipe by a first coefficient; When it is determined that the third phase applies, the inkjet printing device controls the driving of the heater based on the value obtained by multiplying the second difference value by the first coefficient and the value obtained by multiplying the first difference value by a third coefficient.

2. 10. The inkjet printing apparatus of claim 1, an internal temperature sensor that detects the temperature of the external space of the circulation path; and The control unit determining whether the first difference value corresponds to a second phase in which the first difference value is less than the first reference value and is equal to or greater than the second reference value; If it is determined that the second phase applies, the inkjet printing device controls the operation of the heater based on the value obtained by multiplying the second difference value by the first coefficient and a heat dissipation correction value obtained by multiplying the temperature detection result of the internal temperature sensor in the external space of the circulation path by the second coefficient.

3. 10. The inkjet printing apparatus of claim 1, The control unit determining whether the first difference value corresponds to a second phase in which the first difference value is less than the first reference value and is equal to or greater than the second reference value; If it is determined that the ink temperature falls within the second phase, the inkjet printing device controls the driving of the heater based on a value obtained by multiplying the second difference value by the first coefficient and a heat dissipation correction value obtained by multiplying a third difference value obtained by subtracting the detection result of the ink temperature in the supply side manifold by the supply side temperature sensor from the detection result of the ink temperature in the return piping by the return side temperature sensor by a fourth coefficient.

4. 4. The inkjet printing apparatus according to claim 2, wherein: The control unit When it is determined that the third phase applies, the inkjet printing device controls the driving of the heater based on the value obtained by multiplying the second difference value by the first coefficient, the heat dissipation correction value, and the value obtained by multiplying the first difference value by the third coefficient.

5. 10. The inkjet printing apparatus of claim 1, The control unit determining whether the first difference value calculated every predetermined time period corresponds to the first phase, which is equal to or greater than the first reference value, or the third phase, which is less than the second reference value that is smaller than the first reference value, by subtracting the detection result of the temperature of the ink in the supply-side manifold, which is detected every predetermined time period by the supply-side temperature sensor, from the first target temperature of the ink in the supply-side manifold; When it is determined that the third phase applies, the inkjet printing device controls the driving of the heater based on a value obtained by multiplying the second difference value by the first coefficient and a value obtained by cumulatively adding the value obtained by multiplying the first difference value by the third coefficient every predetermined time.

6. 4. The inkjet printing apparatus according to claim 1, a plurality of supply-side temperature sensors, each of which is inserted in the supply-side manifold and detects the temperature of ink in the supply-side manifold; and The control unit an inkjet printing apparatus, wherein the first difference value is a value obtained by subtracting an average value of detection results of the ink temperature in the supply side manifold by each of the plurality of supply side temperature sensors from the first target temperature of the ink in the supply side manifold.

7. 4. The inkjet printing apparatus according to claim 2, wherein: a flow rate measuring unit that measures the flow rate of ink flowing through the circulation path; and The control unit Furthermore, the flow rate measuring unit is electrically connected to the flow rate measuring unit, If it is determined that the second phase applies, the inkjet printing device controls the driving of the heater based on a value obtained by multiplying the second difference value by the first coefficient and the heat dissipation correction value, which is corrected based on the measurement result of the ink flow rate by the flow rate measurement unit.

8. 4. The inkjet printing apparatus according to claim 1, The inkjet printing apparatus, wherein the first coefficient is a positive value.

9. 3. The inkjet printing apparatus of claim 2, The first coefficient is a positive value and the second coefficient is a negative value.

10. 4. The inkjet printing apparatus according to claim 1, The inkjet printing apparatus, wherein the first coefficient is a positive value and the third coefficient is a positive value.

11. 4. The inkjet printing apparatus of claim 3, The inkjet printing apparatus, wherein the first coefficient is a positive value and the fourth coefficient is a positive value.

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