JP2025049875A - Inkjet Printing Device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique that can adjust a temperature of ink in a circulation path to a proper temperature even if the temperature of ink is out of a predetermined range.

SOLUTION: An inkjet printing device comprises: an outer tank 53 that stores ink, outside a circulation path; branched piping 66 through which a branching position 655 on the circulation path is connected to the outer tank 53; an outer pump 72 that pumps ink from the outer tank 53 to the circulation path; a switching valve 78; and a temperature sensor 761 that detects a temperature of ink in the circulation path. The switching valve 78 can switch between a state in which the outer tank 53 communicates with the branching position 655 through the outer pump 72 and the branched piping 66 and a state in which the outer tank communicates with the branching position 655 through bypass piping 67 without going through the outer pump 72. When a detected result by the temperature sensor 761 is out of a predetermined range, a control part feeds the ink in the circulation path to the outer tank 53 through the bypass piping 67. and then feeds the ink in the outer tank 53 to the circulation path through the branched piping 66.

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2025,JPO&INPIT

Description

The present invention relates to an inkjet printing device that prints by ejecting ink onto a print medium such as paper.

Conventionally, inkjet printing devices may be provided with an ink circulation path that supplies ink to an ejection head that ejects ink onto a print medium, and further collects 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, for example, in Patent Document 1.

Patent No. 3419220

In the inkjet recording device of Patent Document 1, the ink bag (41) in the cartridge (6) is pressurized to cause the ink in the ink bag (41) to flow into the inkjet recording head (8), while allowing some of the ink to pass through and flow into the subtank (10). The subtank (10) is also refilled with new ink (paragraphs 0022-0023, Figure 4). As a result, ink remaining near the nozzle opening (21) of the inkjet recording head (8) is discharged into the subtank (10) and mixed with the new refilled ink (paragraph 0024).

Then, the ink in the subtank (10) flows back through the inkjet recording head (8) into the ink cartridge (6) due to the head difference resulting from the height difference between the subtank (10) and the cartridge (6). This back-and-forth circulation between the subtank (10) and the ink cartridge (6) via the inkjet recording head (8) is repeated.

Here, in order to stably eject ink from the ejection head, it is desirable to set the ink temperature to, for example, about 35°C. However, if the device is not operated for a long period of time and ink remains in the circulation path, when the device is operated again, the ink temperature may have become excessively low. Furthermore, if ink whose temperature is excessively low is suddenly heated using a heater or the like, the ink temperature may conversely become excessively high. In this way, when the ink temperature is excessively high or low, it is difficult to adjust the ink to a temperature suitable for ejection, and there is a risk of reduced workability.

The present invention has been developed in consideration of these circumstances, and aims to provide a technology that can easily adjust the temperature of ink to a suitable temperature for ejection, even if the temperature of the ink in the circulation path becomes excessively high or low.

In order to solve the above problems, the first invention of the present application is an inkjet printing device that prints by ejecting ink onto a printing medium, and includes an ink circulation path, a circulation pump, an external tank, a branch pipe, an external pump, a switching valve, a control unit, and a temperature sensor. 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, a supply pipe that connects the supply tank and the ejection head, and a return pipe that connects the recovery tank and the supply tank. The circulation pump sends ink from the recovery tank to the supply tank via the return pipe. The external tank stores ink outside the circulation path. The branch pipe connects a branch position on the return pipe to the external tank. The external pump sends ink from the external tank to the circulation path via the branch pipe. The switching valve can switch between a state in which the external tank communicates with the branch position via the external pump and the branch pipe, and a state in which the external tank communicates with the branch position via a bypass pipe that connects the branch pipe and the external tank, without the external pump. The control unit can control the ejection head, the circulation pump, the external pump, and the switching valve. The temperature sensor detects the temperature of the ink in the circulation path. The control unit can selectively execute a refill mode in which ink in the external tank is sent to the circulation path via the branch pipe, and a backflow mode in which ink in the circulation path is sent to the external tank via the bypass pipe. When the control unit detects that the detection result by the temperature sensor is outside a predetermined range, it executes the backflow mode and then executes the refill mode.

The second invention of the present application is the inkjet printing device of the first invention, in which the switching valve is a three-way valve having an inlet, an outlet, and an inlet. The inlet is connected to the external pump. The outlet is connected to the external tank via the bypass piping. The outlet is connected to the circulation path. In the refill mode, the control unit drives the circulation pump and the external pump while closing the outlet of the switching valve to connect the inlet and the outlet, and in the reverse flow mode, drives the circulation pump while closing the inlet of the switching valve to connect the outlet and the outlet, and stops driving the external pump.

The third invention of the present application is the inkjet printing device of the first invention, further comprising a supply side on-off valve, a return side on-off valve, and a pressurizing mechanism. The supply side on-off valve is inserted in the supply piping. The return side on-off valve is inserted in the return piping between the circulation pump and the branch position. The pressurizing mechanism pressurizes the supply tank. The switching valve is a three-way valve having an inlet, an outlet, and an outflow/inflow port. The inlet is connected to the external pump. The outlet is connected to the external tank via the bypass piping. The outflow/inflow port is connected to the circulation path. The control unit is further capable of controlling the supply side on-off valve, the return side on-off valve, and the pressurizing mechanism. In the refill mode, the control unit drives the circulation pump and the external pump while closing the outlet of the switching valve to connect the inlet and the outflow/inflow port. In the reverse flow mode, the control unit closes the inlet of the switching valve to connect the outlet and the inlet, stops driving the circulation pump and the external pump, and drives the pressurizing mechanism while closing the supply side opening/closing valve and the return side opening/closing valve.

According to the first to third aspects of the present invention, the temperature of the ink can be quickly adjusted by backflowing a portion of the ink in the circulation path into the external tank based on the detection results of the ink temperature in the circulation path.

FIG. 1 is a diagram conceptually illustrating a configuration of an inkjet printing device. 2 is a diagram conceptually illustrating the configuration of an ink supply unit and an ejection head. 2 is a block diagram showing connections between a control unit and each unit of the inkjet printing apparatus. FIG. 4 is a flowchart showing the flow of transport and printing of continuous paper, supply of ink to the ejection head, and circulation of a portion of the ink. 5 is a flowchart showing a procedure for executing a reverse flow mode in the first embodiment. 10 is a flowchart showing a procedure for executing a reverse flow mode in the second embodiment.

The following describes an embodiment of the present invention with reference to the drawings. Note that the components described in this embodiment are merely examples, and are not intended to limit the scope of the present invention to these. In addition, in the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary for ease of understanding.

1. Configuration of the Inkjet Printing Apparatus
FIG. 1 is a conceptual diagram showing the configuration of an inkjet printing device 1 according to an embodiment of the present invention. The inkjet printing device 1 is an inkjet printer that conveys a long strip of continuous paper 10 and ejects droplets of water-based ink from a plurality of ejection heads 35 toward the continuous paper 10, thereby recording characters and images on the surface of the continuous paper 10. However, the long strip of continuous paper 10 is merely one example of a printing medium. The printing medium may be cut paper, or may be a plastic film, cardboard, metal foil, or a glass substrate. In other words, the inkjet printing device 1 may be any device that ejects ink onto a printing medium to perform printing. As shown in FIG. 1, the inkjet printing device 1 has a conveying unit 2, a printing unit 3, and a control unit 9.

The transport unit 2 is a mechanism that transports the continuous paper 10 in a transport direction along its length along a specified transport path. The continuous paper 10 is stretched over multiple transport rollers 12. The continuous paper 10 is transported along a transport path formed by 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 of 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.

The printing unit 3 has multiple (four in this embodiment) ejection heads 35 and multiple (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.

The four ejection heads 35 are arranged at intervals from each other 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) of the continuous paper 10. In this embodiment, the four ejection heads 35 eject ink of different colors (e.g., cyan, magenta, yellow, and black) to record single-color images on the surface (top) 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.

Figure 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 heads 80 (five in this embodiment). The five heads 80 have the same structure. For this reason, in Figure 2, only one of the five heads 80 is shown in detail, and the remaining four heads 80 are shown in a simplified manner. As shown in Figure 2, each of the five heads 80 has a housing 81, an internal tank 82, and multiple nozzles 83.

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 from each other in the transport direction and width direction of the continuous paper 10 at the bottom of the housing 81. Each of the multiple nozzles 83 communicates with the internal tank 82. Each of the multiple nozzles 83 also 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.

When ink is ejected, the ink flows down from the internal tank 82 into the ink chamber 832. Then, the ink in the ink chamber 832 is pressurized by controlling the piezoelectric element 831, 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.

Next, the ink supply unit 4 will be described. The ink supply unit 4 is a device for supplying ink to the ejection head 35 while circulating a portion of the ink. As described above, the inkjet printing device 1 of this embodiment has four ink supply units 4. Since the four ink supply units 4 have the same structure, only the structure of one ink supply unit 4 will be described below.

As shown in FIG. 2, each ink supply unit 4 includes a supply tank 51, a recovery tank 52, an external tank 53, 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 branch pipe 66, a bypass pipe 67, a circulation pump 71, an external pump 72, a plurality (five in this embodiment) of supply side opening/closing valves 73, a plurality (five in this embodiment) of head outlet side opening/closing valves 74, a return side opening/closing valve 75, a heater 76, a first switching valve 77, a second switching valve 78, a first filter 79, a second filter 84, and a degassing unit 85.

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 provided inside the supply tank 51. In addition, the supply tank 51 is equipped with a first upper liquid level sensor 511 and a first lower liquid level sensor 512.

The first upper liquid level sensor 511 and the first lower liquid level sensor 512 are each electrically connected to the control unit 9. When the first upper liquid level sensor 511 detects that the level of the ink stored in the internal chamber 510 of the supply tank 51 is the first upper reference value L11, it outputs a first upper signal to the control unit 9 via a communication circuit not shown. When the first lower liquid level sensor 512 detects that the level of the ink stored in the internal chamber 510 of the supply tank 51 is the first lower reference value L12, it outputs a first lower signal to the control unit 9 via a communication circuit not shown. Note that the first lower reference value L12 is a value lower than the first upper reference value L11.

The first upper liquid level sensor 511 corresponds to the "first liquid level sensor" in the present invention. The first upper reference value L11 detected by the first upper liquid level sensor 511 corresponds to the "first reference value" in the present invention. In other words, the inkjet printing device 1 has a first liquid level sensor (first upper liquid level sensor 511) that detects that the height of the liquid level of the ink stored in the supply tank 51 is the first reference value (first upper reference value L11).

The supply tank 51 may further be equipped with a "Full sensor" that detects when the ink stored in the internal chamber 510 is full, and an "Empty sensor" that detects when the ink stored in the internal chamber 510 is empty.

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 ejection head 35. The supply side manifold 61 is a thick pipe whose upstream end is connected to the internal chamber 510 of the supply tank 51. Each of the five supply side thin pipes 62 is a thin pipe that branches off from the supply side manifold 61. Each of the five supply side thin pipes 62 has an upstream end that is connected to the internal passage of the supply side manifold 61 and a downstream end that is connected to the internal tank 82 of one head 80. The supply side manifold 61 and the five supply side thin pipes 62 form the "supply pipes" of the present invention that connect the supply tank 51 and the ejection head 35.

In addition, in this embodiment, a supply side opening/closing valve 73 is inserted in each supply side thin pipe 62. That is, each supply side opening/closing valve 73 is inserted in the above-mentioned "supply pipe". For example, an electric valve that opens and closes under the control of the control unit 9 is used for the supply side opening/closing valve 73. However, an opening/closing valve that is manually opened and closed may be used for the supply side opening/closing valve 73. When the supply side opening/closing valve 73 is closed, the communication of the internal passage of the supply side thin pipe 62 is blocked. That is, when the supply side opening/closing 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 opening/closing valve 73 is open, the communication of the internal passage of the supply side thin pipe 62 is ensured. Note that a filter or the like may be further inserted in the supply side manifold 61 or the five supply side thin pipes 62.

The five recovery side thin pipes 63 and the recovery side manifold 64 are pipes that connect the five heads 80 of one ejection 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 the internal tank 82 of one head 80, and the downstream end is connected to the internal passage of the recovery side manifold 64. The recovery side manifold 64 is a thick pipe whose downstream end is connected to the internal chamber 520 of the recovery tank 52, which will be described later.

In addition, in this embodiment, a head outlet side opening/closing valve 74 is inserted in each recovery side thin pipe 63. For example, an electric valve that opens and closes under the control of the control unit 9 is used for the head outlet side opening/closing valve 74. However, a manually opened and closed opening valve may be used for the head outlet side opening/closing valve 74. When the head outlet side opening/closing valve 74 is closed, the communication of the internal passage of the recovery side thin pipe 63 is blocked. That is, when the head outlet side opening/closing 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 opening/closing valve 74 is open, the communication of the internal passage of the recovery side thin pipe 63 is ensured. However, the head outlet side opening/closing valve 74 does not necessarily have to be provided. Furthermore, a filter or the like may be inserted in the five recovery side thin pipes 63 or the recovery side manifold 64.

The recovery tank 52 is a container for temporarily storing the ink recovered from the ejection head 35. Inside the recovery tank 52, an internal chamber 520 capable of temporarily storing the ink is provided. In addition, the recovery tank 52 is equipped with a second liquid level sensor 521.

The second liquid level sensor 521 is electrically connected to the control unit 9. When the second liquid level sensor 521 detects that the liquid level of the ink stored in the internal chamber 520 of the recovery tank 52 is equal to the second reference value L2, it outputs a second signal to the control unit 9 via a communication circuit (not shown). In other words, the inkjet printing device 1 has the second liquid level sensor 521 that detects that the liquid level of the ink stored in the recovery tank 52 is equal to the second reference value L2.

The recovery tank 52 may further be equipped with another liquid level sensor that detects that the level of the ink stored in the internal chamber 520 of the recovery tank 52 is at another reference value. The recovery tank 52 may further be equipped with a "Full sensor" that detects when the ink stored in the internal chamber 520 is full, or an "Empty sensor" that detects when the ink stored in the internal chamber 520 is empty.

As shown in FIG. 2, a pressurizing mechanism 515 is connected to the supply tank 51. The pressurizing mechanism 515 pressurizes the supply tank 51 to adjust 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. In addition, a depressurizing mechanism 524 is connected to the recovery tank 52. The depressurizing mechanism 524 depressurizes the recovery tank 52 to adjust 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 depressurizing buffer tank, a pressure adjustment mechanism (regulator), etc.

The pressurizing mechanism 515 and the decompression mechanism 524 are configured so that their operations can be controlled 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 collected in the recovery tank 52.

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 to the internal chamber 520 of the recovery tank 52. Also, the downstream end of the internal passage of the return pipe 65 is connected to the internal chamber 510 of the supply tank 51.

The above configuration forms an ink circulation path that runs from the supply tank 51 through the supply pipe consisting of the supply side manifold 61 and five supply side thin pipes 62, the internal tank 82 of the ejection head 35, the recovery side thin pipes 63, the recovery side manifold 64, the recovery tank 52, and the return pipe 65, and then back to the supply tank 51. That is, the ink circulation path includes the ejection head 35, the supply tank 51, the recovery tank 52, the supply pipe, and the return pipe 65.

In addition, the return pipe 65 is provided with a circulation pump 71, a return side opening/closing valve 75, a heater 76, a first switching valve 77, a first filter 79, and a degassing unit 85. As will be described in detail later, a branch pipe 66 is connected to a branch position 655 between the return side opening/closing valve 75 and the heater 76 in the ink circulation path in the return pipe 65.

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 according to an operation signal from the control unit 9. For the circulation pump 71 of this embodiment, a pump that is unlikely to generate foreign matter such as dust when driven, such as a diaphragm pump, is used. For the circulation pump 71 of this embodiment, for example, one with a larger capacity than the external pump 72 is used.

The return side opening/closing valve 75 is inserted in the return pipe 65 downstream of the circulation pump 71 and upstream of the branch position 655. That is, the return side opening/closing valve 75 is inserted in the return pipe 65 between the circulation pump 71 and the branch position 655. For example, an electric valve that opens and closes under the control of the control unit 9 is used for the return side opening/closing valve 75. However, an opening/closing valve that is manually opened and closed may be used for the return side opening/closing valve 75. When the return side opening/closing valve 75 is closed, the communication of the internal passage of the return pipe 65 is blocked. That is, when the return side opening/closing 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 vicinity of the branch position 655 to the circulation pump 71 are prevented. On the other hand, when the return side opening/closing valve 75 is open, the communication of the internal passage of the return pipe 65 is ensured.

The heater 76 is a device that heats the ink being sent through the internal passage of the return pipe 65. The heater 76 is located in the return pipe 65 between the branch position 655 and the supply tank 51. A temperature sensor 761 is mounted near the end of the heater 76 on the downstream side in the ink sending direction. The temperature sensor 761 detects the temperature of the ink flowing out from the heater 76. The temperature sensor 761 is also electrically connected to the control unit 9. The temperature sensor 761 outputs data related to the detection result of the ink temperature to the control unit 9. However, the position at which the temperature sensor 761 is mounted is not limited to this. The temperature sensor 761 may be any sensor that detects the temperature of the ink in the circulation path and outputs the detection result to the control unit 9.

The first switching valve 77 is inserted in the return pipe 65 downstream of the heater 76 and upstream of the first filter 79. The first switching valve 77 is a three-way valve that switches the ink circulation path in the internal passage of the return pipe 65 to an ink waste path 774. The first switching valve 77 is, for example, an electric valve that performs a switching operation under the control of the control unit 9. However, the first switching valve 77 may be a switching valve that performs a switching operation manually. The first switching valve 77 has an inlet 771, a first outlet 772, and a second outlet 773.

The inlet 771 communicates with the heater 76 (upstream side of the circulation path). The first outlet 772 communicates with the first filter 79 (downstream side of the circulation path). The second outlet 773 communicates with the ink waste path 774. Normally, the second outlet 773 is blocked and the inlet 771 and the first outlet 772 are connected. This ensures communication of the internal passage of the return pipe 65. On the other hand, by blocking the first outlet 772 and connecting the inlet 771 and the second outlet 773, the ink flowing in from the inlet 771 can be directed to the waste path 774 and disposed of outside the inkjet printing device 1. However, the first switching valve 77 does not necessarily have to be provided.

The first filter 79 is inserted in the return pipe 65 downstream of the first switching valve 77 and upstream of the degassing unit 85. The first filter 79 filters the ink being pumped through the internal passage of the return pipe 65 and removes foreign matter contained in the ink.

The degassing unit 85 is inserted in the return pipe 65 downstream of the first filter 79 and upstream of the supply tank 51. In this embodiment, the degassing unit 85 is a so-called hollow fiber membrane degassing module. The degassing unit 85 removes air bubbles from the ink being pumped through the internal passage of the return pipe 65.

The external tank 53 is a container for storing ink outside the circulation path. The external tank 53 is provided outside the circulation path of the ink circulating between the supply tank 51 and the recovery tank 52. The external tank 53 stores ink to replenish the supply tank 51. An internal chamber 530 capable of storing ink is provided inside the external tank 53. A sufficient amount of ink is always stored in the internal chamber 530 of the external tank 53.

The branch pipe 66 is a pipe that connects the internal chamber 530 of the external tank 53 and the internal passage of the return pipe 65 so that they can communicate with each other. The branch pipe 66 connects a branch position 655 on the return pipe 65 to the external tank 53. As shown in FIG. 2, the internal passage of the branch pipe 66 is connected to the internal chamber 530 of the external tank 53 at the upstream end. In addition, the internal passage of the branch pipe 66 is connected to the internal passage of the return pipe 65 at the branch position 655 located at the downstream end. In addition, an external pump 72 and a second switching valve 78 are interposed in the branch pipe 66.

The external pump 72 is a device that performs a liquid transfer operation to transfer ink from the external tank 53 to the return pipe 65. The external pump 72 transfers ink from the external tank 53 to the circulation path via the branch pipe 66. For the external pump 72 in this embodiment, for example, a pump having the same type of structure as the circulation pump 71 (for example, a diaphragm pump) is used.

The second switching valve 78 is interposed between the external pump 72 and the branch position 655 in the branch pipe 66. The second switching valve 78 is a three-way valve that can switch between a state in which the external tank 53 communicates with the branch position 655 via the external pump 72 and the branch pipe 66, and a state in which the external tank 53 communicates with the branch position 655 via the bypass pipe 67 without the external pump 72. Here, the bypass pipe 67 is a pipe that connects the branch pipe 66 and the external tank 53. In addition, for example, an electric valve that performs a switching operation under the control of the control unit 9 is used for the second switching valve 78. However, a switching valve that performs a switching operation manually may be used for the second switching valve 78. The second switching valve 78 corresponds to the "switching valve" in this invention.

The second switching valve 78 has an inlet 781, an outlet 782, and an outlet 783. The inlet 781 is connected to the external pump 72 via the branch pipe 66. The outlet 782 is connected to the external tank 53 via the bypass pipe 67. The outlet 783 is connected to the above-mentioned circulation path via the branch pipe 66.

Normally, the outlet 782 is closed, and the inlet 781 and the outlet 783 are connected. This ensures that the entire internal passage of the branch pipe 66 is connected. On the other hand, when the "reverse flow mode" described below is executed, the inlet 781 is closed, and the outlet 783 and the outlet 782 are connected. This allows the second switching valve 78 to switch the flow of ink that is normally sent from the external tank 53 to the circulation path via the external pump 72 to flow back from the circulation path to the external tank 53 via the bypass pipe 67, without going through the external pump 72.

As described above, the bypass pipe 67 is a pipe that connects the outlet 782 of the second switching valve 78 to the internal chamber 530 of the external tank 53 so that they can communicate with each other. The second filter 84 is inserted in the bypass pipe 67.

The second filter 84 filters the ink being pumped through the internal passage of the bypass piping 67 and removes foreign matter contained in the ink. Here, the second filter 84, together with the external tank 53 and the external pump 72, is provided outside the ink circulation path and is easily removed from the ink circulation path. Therefore, an operator can remove the second filter 84 from the circulation path and easily remove foreign matter adhering to the second filter 84.

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 device 1. FIG. 3 is a block diagram showing the connection between the control unit 9 and each part of the inkjet printing device 1. As conceptually shown in FIG. 3, the control unit 9 has a processor 91 such as a CPU, a memory 92 such as a RAM, and a storage unit 93 such as a hard disk drive. The storage unit 93 stores a computer program 9P for executing a printing process while transporting the continuous paper 10, and for supplying ink to the ejection head 35 while circulating a portion of the ink.

As shown in FIG. 3, the control unit 9 is communicatively connected to the transport unit 2, the four ejection heads 35 of the printing unit 3, and the circulation pumps 71, external pumps 72, five supply side opening/closing valves 73, five head outlet side opening/closing valves 74, return side opening/closing valves 75, heaters 76, first switching valves 77, second switching valves 78, each liquid level sensor 511, 512, 521, pressurization mechanism 515, decompression mechanism 524, and temperature sensor 761 of each of the four ink supply units 4 of the printing unit 3. The control unit 9 controls the operation of each of these units according to a computer program 9P.

That is, the control unit 9 can control the transport unit 2, the four ejection heads 35 of the printing unit 3, and the circulation pump 71, external pump 72, five supply side opening/closing valves 73, five head outlet side opening/closing valves 74, return side opening/closing valve 75, heater 76, first switching valve 77, second switching valve 78, each liquid level sensor 511, 512, 521, pressure mechanism 515, pressure reduction mechanism 524, and temperature sensor 761 of each of the four ink supply units 4 of the printing unit 3. By controlling the operation of each of these units, the control unit 9 allows the transport and printing process of the continuous paper 10 to proceed, ink to be supplied to the internal tank 82 of each ejection head 35, and some of the ink to circulate.

2. Overview of Transport and Printing Process, and Ink Supply and Circulation Procedures
Next, an overview of the transport and printing process of the continuous paper 10 performed in the inkjet printing device 1, and the procedure for supplying ink to the internal tank 82 of each ejection head 35 and circulating some of the ink will be described. Figure 4 is a flowchart showing the flow of the transport and printing process of the continuous paper 10, and the supply of ink to the internal tank 82 of each ejection head 35 and circulating some of the ink.

When transporting and printing the continuous paper 10, as shown in FIG. 4, 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.

As described in detail below, when the continuous paper 10 is transported and printed, ink circulates through the circulation path and is ejected from the ejection head 35, and ink is replenished from the external tank 53 to the circulation path. When the continuous paper 10 is transported and printed, or before that, if the temperature of the ink in the circulation path becomes excessively high or low, a portion of the ink in the circulation path is caused to flow back into the external tank. That is, the control unit 9 of this embodiment can selectively execute a "circulation mode" in which ink is circulated through the circulation path, a "replenishment mode" in which ink in the external tank 53 is sent to the circulation path via the branch pipe 66, and a "backflow mode" in which ink in the circulation path is sent to the external tank 53 via the bypass pipe 67.

In preparation for transporting the continuous paper 10 and performing the printing process, ink is stored in the internal chamber 510 of the supply tank 51 until the height of the ink level becomes equal to or higher than the first upper reference value L11 (first reference value) (at least equal to or higher than the first lower reference value L12). As described above, a sufficient amount of ink is always stored in the internal chamber 530 of the external tank 53. When executing the "circulation mode", the control unit 9 opens the five supply side opening/closing valves 73, the five head outlet side opening/closing valves 74, and the return side opening/closing valve 75. The control unit 9 also closes the second outlet 773 of the first switching valve 77 to connect the inlet 771 and the first outlet 772. The control unit 9 also closes the outlet 783 of the second switching valve 78.

When executing the "circulation mode", the control unit 9 also drives the circulation pump 71, heater 76, pressurization mechanism 515, and decompression mechanism 524 of each of the four ink supply units 4. That is, the control unit 9 executes the "circulation mode" in which ink is circulated in the ink circulation path while being supplied to the internal tank 82 of each ejection head 35 by driving the circulation pump 71 (step S1). In addition, the control unit 9 turns on the power of each liquid level sensor 511, 512, 521, and temperature sensor 761, and these sensors each start measuring.

More specifically, by driving the pressurizing mechanism 515 and the decompression 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 that was not ejected from the ejection head 35) to be recovered in the recovery tank 52. In addition, by driving the circulation pump 71, a flow of ink is generated in the internal passage of the return pipe 65 from the recovery tank 52 to the supply tank 51.

In addition, by driving the heater 76, the ink being sent through the internal passage of the return pipe 65 can be heated before being sent to the supply tank 51. More specifically, the temperature sensor 761 detects the temperature of the ink flowing out of the heater 76 and outputs data related to the detection result to the control unit 9. The control unit 9 adjusts the amount of driving of the heater 76 based on the ink temperature detection result input from the temperature sensor 761. This allows the temperature of the ink passing through the heater 76 to be adjusted before being sent to the supply tank 51.

In addition, by passing the ink flowing through the internal passage of the return pipe 65 through the first filter 79, small impurities remaining in the ink can be removed and the ink can be sent to the supply tank 51. In addition, by passing the ink flowing through the internal passage of the return pipe 65 through the degassing unit 85, the ink can be degassed before being sent to the supply tank 51.

When the printing process is performed and ink droplets are ejected from each ejection head 35 onto the surface of the continuous paper 10, the amount of ink stored in the supply tank 51 decreases. Here, when the first lower liquid level sensor 512 detects that the level of the ink stored in the internal chamber 510 of the supply tank 51 is the first lower reference value L12, it outputs a first lower signal to the control unit 9. That is, when the first lower liquid level sensor 512 detects that the level of the ink stored in the supply tank 51 has dropped to below the first lower reference value L12, it outputs a first lower signal to the control unit 9. The control unit 9 recognizes whether the first lower signal has been output from the first lower liquid level sensor 512 (step S2). The control unit 9 continues to execute the "circulation mode" until the first lower liquid level sensor 512 outputs the first lower signal (step S2: No).

When the first lower signal is output from the first lower liquid level sensor 512 (step S2: YES), the control unit 9 closes the outlet 782 of the second switching valve 78 (switching valve) to connect the inlet 781 and the outlet 783, and drives the external pump 72. That is, the control unit 9 closes the outlet 782 of the second switching valve 78 to connect the inlet 781 and the outlet 783, and drives the circulation pump 71 and the external pump 72, thereby executing a "refill mode" in which ink is circulated in the above-mentioned ink circulation path while further refilling the ink circulation path with ink (step S3).

The control unit 9 starts the "refill mode" based on the first lower signal output from the first lower liquid level sensor 512. In this embodiment, the return side opening/closing valve 75 is opened even when the "refill mode" is executed. As a result, even in the "refill mode", a flow of ink occurs from the circulation pump 71 toward the supply tank 51, and the backflow of ink from the vicinity of the branch position 655 toward the circulation pump 71 is suppressed. However, when the "refill mode" is executed, the return side opening/closing valve 75 may be closed. As a result, the back pressure applied to the circulation pump 71 can be suppressed.

By driving the external pump 72, an ink flow is generated in the internal passage of the branch pipe 66 from the external tank 53 toward the branch position 655. The ink sent out by the external pump 72 reaches the branch position 655 and merges with the ink sent out by the circulation pump 71, then flows through the internal passage of the return pipe 65 toward the supply tank 51. The ink that merges at the branch position 655 can be sent to the supply tank 51 after the temperature of the ink is adjusted by passing it through the heater 76. Small impurities remaining in the ink can be removed by passing the ink through the first filter 79. The ink can be degassed by passing it through the degassing unit 85.

When the "refill mode" is executed, the amount of ink stored in the supply tank 51 increases. Here, when the first upper liquid level sensor 511 (first liquid level sensor) detects that the liquid level of the ink stored in the internal chamber 510 of the supply tank 51 is the first upper reference value L11 (first reference value), it outputs a first upper signal to the control unit 9. That is, when the first upper liquid level sensor 511 detects that the liquid level of the ink stored in the supply tank 51 has increased to the first upper reference value L11, it outputs a first upper signal to the control unit 9. The control unit 9 recognizes whether the first upper signal has been output from the first upper liquid level sensor 511. When the first upper signal is output from the first upper liquid level sensor 511, the control unit 9 ends the "refill mode" and executes the "circulation mode" again.

The control unit 9 then determines whether or not to end the transport of the continuous paper 10 and the printing process (step S4). If image data to be printed remains, the control unit 9 continues the transport of the continuous paper 10 and the printing process (step S4: No). In this case, the control unit 9 executes the processes of steps S1 to S3 again. In this way, by repeating the processes of steps S1 to S3, the control unit 9 can transport the continuous paper 10 and proceed with the printing process while maintaining the amount of ink stored in the internal chamber 510 of the supply tank 51 at a certain level or more.

When there is no more image data to be printed (step S4: Yes), the control unit 9 stops the operation of each unit, including the ink supply unit 4, and ends the transport and printing process of the continuous paper 10 and the supply of ink to the ejection head 35.

<3. Details of the reverse flow mode>
Next, the "reverse flow mode" executed by the control unit 9 will be described in detail. As described above, in order to stably eject ink from each ejection head 35, it is desirable to set the temperature of the ink to, for example, about 35°C. However, if the inkjet printing device 1 is not driven for a long period of time and ink remains in the circulation path, when the inkjet printing device 1 is driven again, the temperature of the ink in the circulation path may become excessively low. In addition, if the ink whose temperature is excessively low is heated all at once using the heater 76 or the like, the temperature of the ink in the circulation path may become excessively high. In this way, when the temperature of the ink is excessively high or low, it is difficult to adjust the temperature of the ink to a temperature suitable for ejection, and there is a risk of workability decreasing. The "reverse flow mode" is executed to solve this problem.

As described above, the "backflow mode" is a control method for sending ink in the circulation path to the external tank 53 via the bypass piping 67. The "backflow mode" is executed, for example, when the inkjet printing device 1 starts to operate, or immediately before the above-mentioned "refill mode" is executed. However, the timing for executing the "backflow mode" is not limited to this. Note that, before the "backflow mode" is executed, the power of each of the liquid level sensors 511, 512, 521 and the temperature sensor 761 is turned on, and these sensors are each performing measurements.

<3-1. First embodiment>
Fig. 5 is a flow chart showing the procedure for executing the "backflow mode" of the first embodiment. In the first embodiment, as shown in Fig. 5, the control unit 9 judges whether the ink temperature detected by the temperature sensor 761 is outside a predetermined range (e.g., 25°C or more and less than 40°C) based on data input from the temperature sensor 761 (step S101). If the ink temperature detected by the temperature sensor 761 is within the predetermined range (step S101: No), the control unit 9 does not execute the "backflow mode".

On the other hand, when the control unit 9 detects that the detection result by the temperature sensor 761 is outside the predetermined range (step S101: YES), the control unit 9 executes the "reverse flow mode" (step S102). Here, when the detection result by the temperature sensor 761 is higher than the predetermined range (e.g., 40°C or higher), the control unit 9 stops driving the heater 76 and executes the "reverse flow mode". On the other hand, when the detection result by the temperature sensor 761 is lower than the predetermined range (e.g., 25°C or lower), the control unit 9 executes the "reverse flow mode" while keeping the heater 76 driven. In addition, the two control methods described below can be executed as the "reverse flow mode" of the present invention.

When executing the first control method, the control unit 9 first opens the five supply side opening/closing valves 73, the five head outlet side opening/closing valves 74, and the return side opening/closing valve 75. The control unit 9 also closes the second outlet 773 of the first switching valve 77 to connect the inlet 771 and the first outlet 772. Meanwhile, the control unit 9 closes the inlet 781 of the second switching valve 78 (switching valve) to connect the outlet 782 and the outlet 783. The control unit 9 also drives the circulation pump 71, the heater 76, the pressurizing mechanism 515, and the decompression mechanism 524, and stops driving the external pump 72.

As a result, a portion of the ink flowing through the internal passage of the return pipe 65 from the recovery tank 52 toward the branch position 655 proceeds from the branch position 655 to the branch pipe 66, flows into the inlet/outlet 783 of the second switching valve 78, flows out from the outlet 782, and then flows back into the external tank 53 via the bypass pipe 67. As a result, even if the temperature of the ink in the circulation path becomes excessively high, the temperature can be quickly lowered by mixing it with the ink stored in the external tank 53. In other words, the temperature of the ink can be quickly adjusted by mixing a portion of the ink in the circulation path with the ink in the external tank 53.

On the other hand, by executing the "reverse flow mode", the total amount of ink present in the circulation path is temporarily reduced. Therefore, if the temperature of the ink in the circulation path is excessively low, the total amount of ink in the circulation path can be reduced and the reduced amount of ink can be heated using the heater 76 to quickly raise the temperature. In particular, when the total amount of ink present in the circulation path is large and the temperature of the ink is excessively low, executing the "reverse flow mode" is very effective.

As described above, in this embodiment, the ink temperature can be quickly adjusted by backflowing a portion of the ink in the circulation path into the external tank 53 based on the detection results of the ink temperature in the circulation path. The control unit 9 executes the "backflow mode" for a predetermined period of time, and then executes the above-mentioned "replenishment mode" (step S103). The period during which the "backflow mode" is executed may be determined in terms of time, or may be determined based on the detection results of the temperature sensor 761 that caused the "backflow mode" to start. The period during which the "backflow mode" is executed may also be determined by other methods.

When executing the second control method, the control unit 9 first closes each of the five supply side opening/closing valves 73 and the return side opening/closing valve 75. The control unit 9 also closes the second outlet 773 of the first switching valve 77 to connect the inlet 771 and the first outlet 772. Meanwhile, the control unit 9 closes the inlet 781 of the second switching valve 78 (switching valve) to connect the outlet 782 and the outlet 783. The control unit 9 also stops the operation of the circulation pump 71 and the external pump 72. Furthermore, the control unit 9 drives the pressurizing mechanism 515 connected to the supply tank 51 to strongly pressurize the inside of the supply tank 51. For example, when executing the "circulation mode" or "replenishment mode," the pressure mechanism 515 pressurizes the supply tank 51 to about 10 kPa in order to supply ink to the ejection head 35, whereas when executing the "reverse flow mode," the pressure in the supply tank 51 is pressurized to about 120 kPa.

As a result, ink flows back through the internal passage of the return pipe 65 from the supply tank 51 toward the branch position 655, proceeds from the branch position 655 to the branch pipe 66, flows into the inlet/outlet 783 of the second switching valve 78, flows out from the outlet 782, and then flows back through the bypass pipe 67 to the external tank 53. As a result, even if the temperature of the ink in the circulation path becomes excessively high, the temperature can be quickly lowered by mixing it with the ink stored in the external tank 53. In other words, the temperature of the ink can be quickly adjusted by mixing some of the ink in the circulation path with the ink in the external tank 53.

Similarly, by executing the "reverse flow mode", the total amount of ink present in the circulation path is temporarily reduced. Therefore, if the temperature of the ink in the circulation path is excessively low, the total amount of ink in the circulation path can be reduced and the reduced amount of ink can be heated using the heater 76 to quickly raise the temperature. In particular, if the total amount of ink present in the circulation path is large and the temperature of the ink is excessively low, executing the "reverse flow mode" is very effective.

As described above, even when the second control method is executed, the ink temperature can be quickly adjusted by causing a portion of the ink in the circulation path to flow back into the external tank 53 based on the detection results of the ink temperature in the circulation path. The control unit 9 similarly executes the "backflow mode" for a predetermined period of time, and then executes the above-mentioned "replenishment mode."

<3-2. Second embodiment>
Next, the "reverse flow mode" of the second embodiment will be described.

In the first embodiment described above, the control unit 9 executes the "reverse flow mode" when it detects that the detection result by the temperature sensor 761 is outside a predetermined range. However, as mentioned above, when the total amount of ink present in the circulation path is large, adjusting the temperature takes time in the first place, which tends to reduce workability. Therefore, in the second embodiment, the "reverse flow mode" is executed when it detects that the total amount of ink present in the circulation path is large. Figure 6 is a flowchart showing the procedure for executing the "reverse flow mode" in the second embodiment.

As shown in FIG. 6, in the second embodiment, the first upper signal output from the first upper liquid level sensor 511 (first liquid level sensor) and the second signal output from the second liquid level sensor 521 are referenced. Then, when the above-mentioned "refill mode" is being executed, if it is detected that the total amount of ink present in the circulation path has increased significantly, the "reverse flow mode" is executed. For example, if the "refill mode" is further executed after the first upper signal and the second signal have already been output and the total amount of ink present in the circulation path has further increased, it is detected that the total amount of ink present in the circulation path has increased significantly.

That is, the control unit 9 determines whether the level of the ink stored in the supply tank 51 exceeds the first upper reference value L11 (first reference value) based on the detection result by the first upper liquid level sensor 511 (first liquid level sensor), and determines whether the level of the ink stored in the recovery tank 52 exceeds the second reference value L2 based on the detection result by the second liquid level sensor 521 (step S201).

Then, when the control unit 9 detects that the liquid level of the ink stored in the supply tank 51 exceeds the first upper reference value L11 (first reference value) and detects that the liquid level of the ink stored in the recovery tank 52 exceeds the second reference value L2 (step S201: YES), it determines that the total amount of ink present in the circulation path is considerably large and executes the "backflow mode" (step S202).

In the "reverse flow mode," the same two control methods as described above can be executed. That is, in this embodiment, the temperature of the ink can be quickly adjusted by flowing part of the ink in the circulation path back into the external tank 53 based on the detection results of the ink level in the supply tank 51 and the recovery tank 52.

The control unit 9 executes the "backflow mode" for a predetermined period of time, and then executes the above-mentioned "replenishment mode" (step S203). In this embodiment, the control unit 9 can further refer to signals from the liquid level sensors 511, 512, and 521 as the end point of the period during which the "backflow mode" is executed. For example, the control unit 9 may end the "backflow mode" when the first lower signal is output from the first lower liquid level sensor 512, or may end the "backflow mode" based on a signal output from another liquid level sensor mounted on the supply tank 51 or the recovery tank 52.

This allows the height of the ink level in the supply tank 51 and the recovery tank 52 to be adjusted to the reference value that is the detection target of each liquid level sensor. As a result, it is possible to prevent the amount of ink present in the circulation path from becoming excessively large. It is also possible to more accurately grasp the amount of ink stored in the supply tank 51 and the recovery tank 52, and therefore the total amount of ink present in the circulation path. Furthermore, based on the results of grasping the total amount of ink present in the circulation path, the amount of ink in the circulation path can also be adjusted by additionally executing the above-mentioned "refill mode" or "backflow mode."

In other words, the configuration according to this embodiment reduces the total amount of ink present in the circulation path, making it easier to adjust the temperature, and also provides the effect of being able to more accurately grasp the total amount of ink present in each part of the circulation path, which could not be grasped from only the output from each liquid level sensor.

REFERENCE SIGNS LIST 1 Inkjet printing device 2 Transport section 3 Printing section 4 Ink supply section 9 Control section 10 Continuous paper 35 Discharge head 51 Supply tank 52 Recovery tank 53 External tank 61 Supply side manifold 62 Supply side thin pipe 65 Return pipe 66 Branch pipe 67 Bypass pipe 71 Circulation pump 72 External pump 73 Supply side opening/closing valve 75 Return side opening/closing valve 76 Heater 78 Second switching valve (switching valve)
511 First upper liquid level sensor (first liquid level sensor)
512 First lower liquid level sensor 515 Pressurizing mechanism 521 Second liquid level sensor 655 Branch position 761 Temperature sensor 781 Inlet (of switching valve) 782 Outlet (of switching valve) 783 Outlet/outlet (of switching valve) L11 First upper reference value (first reference value) (of first liquid level sensor)
L12: First lower reference value (of the first level sensor) L2: Second reference value (of the second level sensor)

Claims (3)

An inkjet printing device that prints by ejecting ink onto a print medium,
an ink circulation path including: an ejection head that ejects ink; a supply tank that stores ink to be supplied to the ejection head; a recovery tank that stores ink recovered from the ejection head; a supply pipe that connects the supply tank and the ejection head; and a return pipe that connects the recovery tank and the supply tank;
a circulation pump that sends the ink from the recovery tank to the supply tank through the return pipe;
an external tank that stores ink outside the circulation path;
a branch pipe connecting a branch position on the return pipe and the external tank;
an external pump that sends ink from the external tank to the circulation path through the branch pipe;
a switching valve capable of switching between a state in which the external tank is in communication with the branch position via the external pump and the branch pipe and a state in which the external tank is in communication with the branch position via a bypass pipe connecting the branch pipe and the external tank without going through the external pump;
a control unit capable of controlling the discharge head, the circulation pump, the external pump, and the switching valve;
a temperature sensor that detects a temperature of the ink in the circulation path;
having
The control unit is
a refill mode in which the ink in the external tank is sent to the circulation path via the branch pipe;
a backflow mode in which the ink in the circulation path is sent to the external tank via the bypass pipe;
can be selectively executed,
When the control unit detects that the detection result by the temperature sensor is outside a predetermined range, the control unit executes the reverse flow mode, and then executes the replenishment mode. 2. The inkjet printing apparatus of claim 1,
The switching valve is a three-way valve having an inlet, an outlet, and an inlet and outlet,
The inlet is in communication with the external pump,
the outlet communicates with the external tank via the bypass pipe;
The inlet/outlet port communicates with the circulation path,
The control unit is
In the refill mode, the outlet of the switching valve is closed to communicate the inlet and the outlet, while driving the circulation pump and the external pump;
In the reverse flow mode, the inkjet printing apparatus closes the inlet of the switching valve to communicate the outlet and the flow inlet, while driving the circulation pump and stopping the driving of the external pump. 2. The inkjet printing apparatus of claim 1,
A supply side opening/closing valve inserted in the supply pipe;
a return-side opening/closing valve interposed between the circulation pump and the branching position in the return pipe;
a pressurizing mechanism for pressurizing the inside of the supply tank;
and
The switching valve is a three-way valve having an inlet, an outlet, and an inlet and outlet,
The inlet is in communication with the external pump,
the outlet communicates with the external tank via the bypass pipe;
The inlet/outlet port communicates with the circulation path,
the control unit is capable of further controlling the supply side opening/closing valve, the return side opening/closing valve, and the pressurizing mechanism;
In the refill mode, the outlet of the switching valve is closed to communicate the inlet and the outlet, while driving the circulation pump and the external pump;
an inkjet printing device in which, in the reverse flow mode, the inlet of the switching valve is closed to connect the outlet and the outflow inlet, the operation of the circulation pump and the external pump is stopped, and the pressure mechanism is operated while the supply side opening/closing valve and the return side opening/closing valve are closed.

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