Printing device and printing method

Abstract

A printing device according to the present invention supplies ink to a print head from a supply tank through a supply flow path, recovers the ink recovered from the print head to a recovery tank through a recovery flow path, and circulates the ink from the recovery tank to the supply tank while adjusting the temperature of the ink by using a heater inserted into a circulation flow path connecting the recovery tank and the supply tank. A printing operation is executed while executing a first circulation mode in which the print head is included in the circulation flow path. When it is determined that an interruption condition set in advance as a condition for interrupting the printing operation is satisfied, the printing operation is interrupted and execution of a second circulation mode in which the print head is not included in the circulation flow path is started.

Description

Printing apparatus and printing method

[0001] The present invention relates to a printing apparatus and a printing method that perform printing by ejecting ink from a print head. In particular, the present invention relates to a technique for adjusting ink to a temperature suitable for printing while circulating the ink.

[0002] In a printing apparatus that performs printing by ejecting ink from a print head, an ink circulation system in which ink is supplied to the print head while being circulated is sometimes adopted for purposes such as suppressing drying of nozzles that eject ink. Such ink circulation is also advantageous in that it maintains ink at a temperature suitable for printing. That is, by inserting a heater on the ink circulation path and heating the ink with the heater while circulating the ink, it is possible to keep the temperature of the ink on the path uniform. On the other hand, there may be cases where ink cannot be circulated normally due to an abnormality of the apparatus or the like. In such a case, ink will stagnate on the path.

[0003] As a technique that takes measures against this problem into consideration, there is, for example, one described in Patent Document 1. In this technique, in a printing apparatus having a plurality of independently replaceable head modules, when one head module is replaced, ink circulation is configured to be continued even during standby. As a result, for head modules other than the one to be replaced, it is possible to maintain a state where the printing operation can be resumed immediately after the end of the standby period.

[0004] Japanese Unexamined Patent Application Publication No. 2014-046515

[0005] In this conventional technology, ink circulation passing through head modules other than the one to be replaced is performed with the cap for closing the ejection openings of the nozzles removed when the head module is not in use. At this time, it is desirable that the ink surface at the ejection opening of the nozzle maintains a state where an appropriate meniscus is formed by its surface tension. This is because otherwise, problems such as circulating ink dripping from the ejection opening may occur. However, the above conventional technology does not take into consideration the state of the ink liquid surface at the nozzle ejection opening of each head module.

[0006] Stopping ink circulation can avoid the ink dripping problem described above, but in this case, the ink temperature will drop during standby. Therefore, it will take longer to return to printing operation from standby. Also, if you try to increase the ink flow rate in the circulation path to raise the ink temperature in a short time, it may accelerate ink degradation (such as aggregation).

[0007] Therefore, it is desirable to achieve a standby state that, even if it becomes necessary to temporarily interrupt the printing process, prevents ink from dripping from the nozzles and allows for a quick return to printing.

[0008] This invention has been made in view of the above problems, and aims to realize a suitable ink circulation when it becomes necessary to temporarily interrupt the printing operation in a printing apparatus and printing method that ejects ink from a print head while circulating and heating the ink.

[0009] One aspect of the printing apparatus according to the present invention includes a print head for ejecting ink, a supply tank for storing the ink supplied to the print head, a supply unit that forms a supply channel for transporting the ink from the supply tank to the print head, a recovery tank for storing the ink recovered from the print head, a recovery unit that forms a recovery channel for transporting the ink from the print head to the recovery tank, a recirculation unit that forms a recirculation channel for recirculating the ink from the recovery tank to the supply tank, a heater interposed in the recirculation channel for heating the ink, and a front The device includes a bypass forming unit that forms a bypass channel for transporting the ink from the supply tank to the recovery tank, and a control unit that selectively executes a first circulation mode in which the ink is circulated from the supply tank to the supply tank via the supply channel, the print head, the recovery channel, the recovery tank, and the recirculation channel, while the temperature of the ink is adjusted by the heater, and a second circulation mode in which the ink is circulated from the supply tank to the supply tank via the bypass channel, the recovery tank, and the recirculation channel, while the temperature of the ink is adjusted by the heater.

[0010] Furthermore, one aspect of the printing method according to the present invention is a printing method in which ink is supplied from a supply tank to a print head that ejects ink via a supply channel, the ink recovered from the print head is recovered in a recovery tank via a recovery channel, and the ink is recirculated from the recovery tank to the supply tank while adjusting the temperature of the ink with a heater inserted in a recirculation channel connecting the recovery tank and the supply tank. In this printing method, a first circulation mode is selectively performed in which the ink is circulated from the supply tank to the supply tank via the supply channel, the print head, the recovery channel, the recovery tank and the recirculation channel while adjusting the temperature of the ink with the heater, and a second circulation mode is selectively performed in which a bypass channel is formed from the supply tank to the recovery tank without going through the print head, and the ink is circulated from the supply tank to the supply tank via the bypass channel, the recovery tank and the recirculation channel while adjusting the temperature of the ink with the heater.

[0011] In these inventions, a printing operation is performed in which ink is ejected from the print head while the first circulation mode is being executed. When it is determined that a preset interruption condition has been met, the printing operation is interrupted and the execution of the second circulation mode is started.

[0012] In this configured invention, when a reason arises that requires interrupting the printing operation, the printing operation is interrupted, and the system switches from the first circulation mode to the second circulation mode to continue ink circulation. In the first circulation mode, ink circulation is achieved through the print head, and the ink temperature is regulated by a heater installed along this path. In the second circulation mode, ink circulation is achieved through a bypass channel that does not pass through the print head, and in this case as well, the ink temperature is regulated by a heater.

[0013] Reasons for interrupting a printing operation include, for example, any malfunction in the device during the printing operation, or maintenance work performed by the user. Therefore, the interruption conditions referred to in this invention can include, for example, the detection of an operational error by sensors provided in various parts of the device, or operations performed by the user to interrupt the printing operation. The head replacement work in the above-mentioned prior art may also fall under this category.

[0014] In this second circulation mode, which is executed when the printing operation needs to be interrupted, the print head is not included in the circulation path, so the problem of ink dripping from the print head does not occur. In addition, the ink temperature can be maintained at an appropriate level through ink circulation, so a drop in ink temperature during standby is prevented. Therefore, printing can be resumed quickly once the issue that caused the interruption is resolved.

[0015] As described above, according to the present invention, even if an event occurs that requires interrupting the printing operation, the ink can be circulated and the temperature adjusted without going through the print head. This prevents ink from dripping from the print head in the standby state, and allows the printing operation to be quickly resumed once the event is resolved.

[0016] The aforementioned and other purposes and novel features of this invention will become more fully apparent upon reading the following detailed description with reference to the accompanying drawings. However, the drawings are for illustrative purposes only and do not limit the scope of this invention.

[0017] This is a diagram showing the configuration of an inkjet printing apparatus according to the first embodiment. This is a diagram conceptually showing the configuration of the ink supply unit and the head unit. This is a perspective view showing a part of the head unit and the ink supply unit. This is a block diagram showing the electrical configuration of this inkjet printing apparatus. This is a diagram schematically showing the piping system involved in ink circulation. This is a diagram showing the flow of ink in the first circulation mode. This is a diagram showing the flow of ink in the second circulation mode. This is a diagram showing the flow of ink in the second circulation mode. This is a flowchart showing an example of the printing process in this printing apparatus. This is a diagram showing the flow of ink in the circulation mode of the second embodiment. This is a diagram showing the flow of ink in the circulation mode of the second embodiment. This is a diagram showing the flow of ink in the circulation mode of the third embodiment. This is a diagram showing the flow of ink in the circulation mode of the third embodiment. This is a diagram showing the flow of ink in the circulation mode of the third embodiment.

[0018] Hereinafter, several embodiments of the present invention will be described with reference to the attached drawings. Note that the components described in these embodiments are merely illustrative and are not intended to limit the scope of the present invention to them alone. In the drawings, for ease of understanding, the dimensions and number of parts may be exaggerated or simplified as needed.

[0019] <First Embodiment> Figure 1 is a diagram showing the configuration of an inkjet printing apparatus according to the first embodiment. The inkjet printing apparatus 1 is an inkjet type printer that records characters and images on the surface of a continuous sheet of paper 10 by transporting the continuous sheet 10 and ejecting droplets of water-based ink from a plurality of head units 35 toward the continuous sheet 10. The continuous sheet 10 is an example of a printing medium. The printing medium may be single sheets of paper, plastic film, corrugated cardboard, metal foil, or a glass substrate. The ink ejected by the head unit 35 in the inkjet printing apparatus 1 is, for example, water-based ink. However, the ink ejected by the head unit 35 may be oil-based ink or UV ink, etc.

[0020] As shown in Figure 1, the inkjet printing apparatus 1 comprises an unwinding roller 11, a winding roller 12, a transport unit 2, a printing unit 3, a drying unit 5, and a control unit 9.

[0021] The unwinding roller 11 holds the continuous paper 10 wound into a roll. The unwinding roller 11 rotates to unwind the continuous paper 10 and supply it to the transport unit 2. The take-up roller 12 winds the continuous paper 10 into a roll. In the inkjet printing apparatus 1, the continuous paper 10 is transported roll-to-roll by the unwinding roller 11 and the take-up roller 12.

[0022] The conveying unit 2 conveys the continuous paper 10 supplied from the unwinding roller 11 to the take-up roller 12. The conveying unit 2 has a drive roller 21, a nip roller 23, and a plurality of conveying rollers 25. The drive roller 21 is connected to a motor (not shown) and rotates actively by the power of the motor. The nip roller 23 grips the continuous paper 10 together with the drive roller 21. The nip roller 23 presses against the drive roller 21 via the continuous paper 10, thereby generating a gripping force for the drive roller 21 to convey the continuous paper 10. The plurality of conveying rollers 25 rotate passively. At least some of the plurality of conveying rollers 25 may be configured to rotate actively.

[0023] The printing unit 3 has four head units 35 and four ink supply units 4. The four head units 35 have similar structures to each other, and the four ink supply units 4 have similar structures to each other.

[0024] The four head units 35 are arranged spaced apart from each other in the transport direction. Each of the four head units 35 ejects droplets of ink from a nozzle 83 (Figure 2) toward the surface of the continuous paper 10. The four head units 35 each record a monochrome image on the surface of the continuous paper 10 by ejecting ink of different colors (e.g., cyan, magenta, yellow, and black). A multicolor image is formed on the upper surface of the continuous paper 10 by superimposing the four monochrome images.

[0025] The printed continuous paper 10 is then sent to the drying section 5. In the drying section 5, the ink ejected onto the continuous paper 10 is heated and dried. Heating for drying may be done by radiant heat from a heater, or by blowing hot air. These may be used in combination. After drying, the continuous paper 10 is wound into a roll by the winding roller 12.

[0026] Figure 2 is a conceptual diagram showing the configuration of the ink supply unit and the head unit. In this embodiment, each head unit 35 has a plurality of ejection heads 80. In this example, each head unit 35 has five ejection heads 80. The plurality of ejection heads 80 have the same structure as each other. In Figure 2, only one ejection head 80 is shown in detail, while the remaining four ejection heads 80 are shown in a simplified manner. As shown in Figure 2, the ejection head 80 has a housing 81, an internal tank 82, and a plurality of nozzles 83.

[0027] The housing 81 forms the outer frame of the discharge head 80. The internal tank 82 is located inside the housing 81 and is capable of temporarily storing ink. 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 lower part of the housing 81. Each of the multiple nozzles 83 communicates with the internal tank 82. Each nozzle 83 also has a piezoelectric element 831, an ink chamber 832, and a discharge port 830. The piezoelectric element 831 is a pressure generating element. The ink chamber 832 communicates with the internal tank 82.

[0028] The ink in the internal tank 82 flows down into the ink chamber 832. Then, the ink in the ink chamber 832 is pressurized by the piezoelectric element 831, causing ink droplets to be ejected from the ejection port 830. The ink ejection method may also be a so-called thermal method, which uses a heater as the pressure generating element.

[0029] The ink supply unit 4 is a device that circulates ink by supplying ink to the head unit 35 and recovering any ink that is not discharged from the head unit 35. The structure of the four ink supply units 4 is the same as that of the others.

[0030] As shown in Figure 2, the ink supply unit 4 includes a supply tank 51, a recovery tank 52, a replenishment tank 53, a supply-side manifold 61, a plurality (five in this embodiment) of supply-side branch pipes 62, a plurality (five in this embodiment) of recovery-side branch pipes 63, a recovery-side manifold 64, a connecting pipe 65, a replenishment pipe 66, a circulation pump 71, a replenishment pump 72, a backflow prevention on / off valve 73, a heater 74, a first filter 75, a second filter 76, and a degassing unit 77. In Figure 2, the supply-side manifold 61 and the recovery-side manifold 64 are shown with thick lines to distinguish them from other pipes.

[0031] The supply tank 51 is a container for temporarily storing ink supplied to the head unit 35. The supply tank 51 has an internal chamber, which is capable of temporarily storing ink.

[0032] Figure 3 is a perspective view showing a part of the head unit and ink supply section. The supply-side manifold 61 and five supply-side branch pipes 62 connect the supply tank 51 to the five discharge heads 80 of one head unit 35. Note that in Figure 3, only one of the five discharge heads 80 of the head unit 35 is shown, only one of the five supply-side branch pipes 62 connected to the supply-side manifold 61 is shown, and only one of the five recovery-side branch pipes 63 connected to the recovery-side manifold 64 is shown.

[0033] As shown in Figures 2 and 3, the upstream end of the supply-side manifold 61 is connected to the internal chamber of the supply tank 51. Five supply-side branch pipes 62 branch off from the supply-side manifold 61. The supply-side manifold 61 is a thicker pipe than the supply-side branch pipes 62. The upstream end of each supply-side branch pipe 62 is connected to the internal passage of the supply-side manifold 61. The downstream end of each supply-side branch pipe 62 is connected to the internal tank 82 of the discharge head 80. As will be described later, a solenoid valve 621 is interposed in the supply-side branch pipe 62. Furthermore, a filter may be provided in the supply-side branch pipe 62.

[0034] The five recovery-side branch pipes 63 and the recovery-side manifold 64 connect the five discharge heads 80 of a single head unit 35 to the recovery tank 52. As shown in Figures 2 and 3, the five recovery-side branch pipes 63 are thin pipes branching off from the recovery-side manifold 64. The upstream end of each recovery-side branch pipe 63 is connected to the internal tank 82 of the discharge head 80. The downstream end of each recovery-side branch pipe 63 is connected to the internal passage of the recovery-side manifold 64. The downstream end of the recovery-side manifold 64 is connected to the internal chamber of the recovery tank 52. The recovery-side manifold 64 is a thicker pipe than the recovery-side branch pipes 63. As will be described later, solenoid valves 631 are interposed in the recovery-side branch pipes 63. Furthermore, filters may be provided in the recovery-side branch pipes 63.

[0035] The recovery tank 52 temporarily stores the ink recovered from the head unit 35. The recovery tank 52 has an internal chamber for storing the ink.

[0036] As shown in Figure 3, the supply-side manifold 61 extends horizontally directly from the lower side of the supply tank 51, that is, without piping, and their internal spaces are in communication with each other. On the other hand, the recovery-side manifold 64 extends horizontally directly from the lower side of the recovery tank 52, and their internal spaces are in communication with each other.

[0037] The extension direction D1 from the supply tank 51 to the supply-side manifold 61 and the extension direction D2 from the recovery tank 52 to the recovery-side manifold 64 are parallel to each other and in opposite directions. In addition, the supply-side manifold 61 and the recovery-side manifold 64 are located close together in the horizontal direction perpendicular to the extension directions D1 and D2, that is, in the direction perpendicular to the plane of the paper. In the vertical direction, the supply-side manifold 61 and the recovery-side manifold 64 can be at the same height. That is, the supply-side manifold 61 and the recovery-side manifold 64 are located at a certain distance from each other in the horizontal direction.

[0038] As shown in Figure 2, the ink supply unit 4 has a pressure difference forming unit 55. The pressure difference forming unit 55 is connected to the supply tank 51 and the recovery tank 52. The pressure difference forming unit 55 forms a pressure difference between the internal chambers of the supply tank 51 and the recovery tank 52 by adjusting the pressure (internal pressure) of the internal chambers of the supply tank 51 and the recovery tank 52. As for a more specific structure of the pressure difference forming unit 55, for example, it is possible to apply the one described in Japanese Patent Application Publication No. 2023-154128, previously disclosed by the applicant of this application.

[0039] In detail, the pressure difference forming unit 55 has a pressurizing unit 551 and a depressurizing unit 553. The pressurizing unit 551 and the depressurizing unit 553 are controlled by the control unit 9. The pressurizing unit 551 makes the internal pressure of the supply tank 51 a positive pressure greater than atmospheric pressure by supplying gas to the internal chamber of the supply tank 51, etc. The depressurizing unit 553 makes the internal pressure of the recovery tank 52 a negative pressure less than atmospheric pressure by sucking gas from the internal chamber of the recovery tank 52, etc.

[0040] The differential pressure formed by the pressure difference forming unit 55 causes the ink stored in the supply tank 51 to be sent to the internal tank 82 of each discharge head 80 via the supply-side manifold 61 and each supply-side branch pipe 62. In addition, the differential pressure formed by the pressure difference forming unit 55 causes the ink that was not discharged from each discharge head 80 to be sent to the recovery tank 52 via each recovery-side branch pipe 63 and recovery-side manifold 64.

[0041] The supply tank 51 is equipped with a liquid level sensor 511 for detecting the amount of ink stored in the tank. On the other hand, the recovery tank 52 is equipped with a liquid level sensor 521 for detecting the amount of ink stored in the tank. The control unit 9 grasps the amount of ink stored in the supply tank 51 and the recovery tank 52 based on the output signals from these liquid level sensors 511 and 521, and controls each part of the ink supply unit 4 to maintain them within an appropriate range.

[0042] The connection pipe 65 connects the internal chamber of the supply tank 51 and the internal chamber of the recovery tank 52 in a communicable manner. As shown in Figure 2, the upstream end of the connection pipe 65 is communicatively connected to the internal chamber of the recovery tank 52. Further, the downstream end of the connection pipe 65 is communicatively connected to the internal chamber of the supply tank 51. A circulation pump 71, a backflow prevention on-off valve 73, a heater 74, a second filter 76, and a degassing unit 77 are attached to the connection pipe 65. Note that a replenishment pipe 66 is connected to a connection portion 655 between the backflow prevention on-off valve 73 and the heater 74 in the connection pipe 65.

[0043] The circulation pump 71 performs a liquid feeding operation of sending ink from the recovery tank 52 to the supply tank 51. The circulation pump 71 generates a flow of ink from the recovery tank 52 toward the supply tank 51 in the internal passage of the connection pipe 65. The circulation pump 71 is preferably a diaphragm pump that hardly generates foreign matters such as dust during driving. The flow rate of the circulation pump 71 is changed in a plurality of levels of magnitude by a control signal output from the control unit 9. The flow rate of the circulation pump 71 is changed in at least three stages: zero (second circulation flow rate), a basic circulation flow rate larger than zero, and a high circulation flow rate (first circulation flow rate) larger than the basic circulation flow rate.

[0044] The backflow prevention on-off valve 73 is located on the downstream side of the circulation pump 71 and on the upstream side of the connection portion 655 in the connection pipe 65. When the backflow prevention on-off valve 73 is closed, the connection pipe 65 is shut off. That is, in a state where the backflow prevention on-off valve 73 is closed, backflow of ink from the connection portion 655 toward the circulation pump 71 is prevented. When the backflow prevention on-off valve 73 is opened, the connection pipe 65 is brought into communication.

[0045] The heater 74 heats ink passing through the connection pipe 65. The heater 74 is located between the connection portion 655 of the connection pipe 65 and the supply tank 51. The heater 74 has a temperature sensor 741. The temperature sensor 741 measures the temperature of ink flowing into the heater 74. Note that the temperature sensor 741 may measure the temperature of ink that has passed through the heater 74. The heater 74 is electrically connected to the control unit 9. The heater 74 outputs data indicating the temperature measured by the temperature sensor 741 to the control unit 9. The control unit 9 controls the heater 74 based on the temperature measured by the temperature sensor 741.

[0046] The second filter 76 is located between the connection portion 655 of the connection pipe 65 and the supply tank 51. The second filter 76 filters ink flowing in the connection pipe 65 and removes foreign substances contained in the ink. A filtration diameter of the second filter 76 (a mesh size of the second filter 76) is, for example, 4 to 6 μm.

[0047] The degassing unit 77 is located between the connection portion 655 of the connection pipe 65 and the supply tank 51. The degassing unit 77 of the present embodiment is, for example, a hollow fiber membrane degassing module. The degassing unit 77 removes air bubbles from ink flowing in the connection pipe 65.

[0048] The connection pipe 65 and each member interposed therein, that is, the circulation pump 71, the backflow prevention on-off valve 73, the heater 74, the second filter 76, the degassing unit 77, and the like constitute a reflux flow path that refluxes ink from the recovery tank 52 to the supply tank 51. As shown in FIG. 2, a flat-plate ink receiving tray 79 is disposed below the reflux flow path to catch ink leaking from these members. This prevents ink from scattering into the apparatus even if ink leaks out.

[0049] A liquid leakage sensor 791 is provided on the ink receiving tray 79. When the amount of ink accumulated in the ink receiving tray 79 exceeds a predetermined amount, the liquid leakage sensor 791 sends a signal indicating this fact to the control unit 9. This allows the control unit 9 to recognize that ink leakage has occurred.

[0050] The replenishment tank 53 stores the ink that is to be replenished to the supply tank 51. The replenishment tank 53 has an internal chamber capable of storing ink. The replenishment tank 53 is located outside the ink circulation path that circulates between the supply tank 51 and the recovery tank 52.

[0051] The replenishment piping 66 connects the internal chamber of the replenishment tank 53 to the connecting piping 65 so that they can communicate with each other. As shown in Figure 2, the replenishment piping 66 is connected to the internal chamber of the replenishment tank 53 at its upstream end. The replenishment piping 66 is also connected to the connecting piping 65 at a connection point 655 at its downstream end. The connection point 655 is located between the circulation pump 71 and the supply tank 51 in the connecting piping 65. The connection point 655 is located between the backflow prevention valve 73 and the supply tank 51 in the connecting piping 65. The replenishment piping 66 is also connected to the replenishment pump 72 and the first filter 75.

[0052] The replenishment pump 72 performs a liquid delivery operation to send ink from the replenishment tank 53 to the connecting pipe 65. The replenishment pump 72 is, for example, a diaphragm pump. The flow rate of the replenishment pump 72 is changed in multiple stages by a control signal output by the control unit 9. Hereinafter, the flow rate of the replenishment pump 72 will be referred to as the "replenishment flow rate". The replenishment flow rate is changed in at least three stages: a basic replenishment flow rate of zero, a high replenishment flow rate (first replenishment flow rate) that is greater than the basic replenishment flow rate, and a low replenishment flow rate (second replenishment flow rate) that is greater than the basic replenishment flow rate but less than the high replenishment flow rate.

[0053] The first filter 75 is located in the replenishment piping 66 between the replenishment pump 72 and the connection point 655. The first filter 75 filters the ink flowing through the replenishment piping 66 and removes foreign matter contained in the ink. The filtration diameter of the first filter 75 (the size of the mesh of the first filter 75) is, for example, about 10 to 30 μm. That is, the filtration diameter of the first filter 75 is greater than or equal to the filtration diameter of the second filter 76. However, the filtration diameter of the first filter 75 may be less than the filtration diameter of the second filter 76.

[0054] A first bypass pipe 67 is provided to connect the supply tank 51 and the recovery manifold 64. A solenoid valve 671 is inserted into the first bypass pipe 67. On the other hand, a second bypass pipe 68 is provided to connect the supply manifold 61 and the recovery tank 52. A solenoid valve 681 is inserted into the second bypass pipe 68. The functions of these will be described later. Multiple (five in this embodiment) discharge heads 80 are associated with the supply manifold 61 and the recovery manifold 64. That is, the supply manifold 61 supplies ink to these five discharge heads 80, and the recovery manifold 64 recovers ink from these five discharge heads 80. Neither the first bypass pipe 67 nor the second bypass pipe 68 has any discharge heads 80 associated with the supply manifold 61 or the recovery manifold 64 inserted into it.

[0055] The control unit 9 is an information processing device for controlling each part of the inkjet printing apparatus 1. As shown in Figure 1, the control unit 9 includes 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 program 931 for executing the process of transporting the continuous paper 10 while performing the printing process, and the process of supplying ink to the head unit 35. The storage unit 93 also stores print data 933 indicating the image to be printed on the continuous paper 10.

[0056] Figure 4 is a block diagram showing the electrical configuration of this inkjet printing apparatus. As shown in Figure 4, the control unit 9 is communicatively connected to the transport unit 2, each head unit 35, valves (such as the backflow prevention on / off valve 73), pumps (such as the circulation pump 71 and replenishment pump 72), heater 74, sensors including the temperature sensor 741, and the pressure difference forming unit 55 of each ink supply unit 4. The control unit 9 controls the operation of each of these units according to the program 931. As a result, the transport and printing of the continuous paper 10 proceeds, and ink is supplied to the internal tanks 82 of each ejection head 80.

[0057] In the inkjet printing apparatus 1 configured as described above, ink supplied from the ink supply unit 4 to the ejection head 80 is ejected from the nozzle 83, and printing is performed on the continuous paper 10, which is the printing medium. As will be explained next, the viscosity of the ink is temperature-dependent, and it is necessary to heat the ink in order to maintain an ink viscosity suitable for printing.

[0058] The ink used in the inkjet printing apparatus 1 has the general property that its viscosity decreases as the temperature rises. In an inkjet printing apparatus that ejects ink droplets using the fluidity of the ink, it is required that the viscosity of the ink supplied to the ejection head 80 falls within a range suitable for printing. In the following description, the term "optimal printing temperature range" used in relation to ink temperature refers to the range of ink temperatures in which the ink can be maintained at a viscosity suitable for printing.

[0059] In the ink supply unit 4, the ink temperature is maintained within the appropriate printing temperature range by heating the low-temperature ink with the heater 74 while circulating it. However, the supply-side branch pipe 62 and the recovery-side branch pipe 63, which are directly connected to the ejection head 80, are particularly narrow pipes and may be made of, for example, resin tubing. For this reason, they are not suitable for pressurizing high-viscosity ink, and ink aggregation may occur in the tubing, or the tubing may be damaged or detached. Also, because the ink flow rate is small, it takes a long time to circulate the ink.

[0060] Thus, the circulation of ink through the ejection head 80 is undesirable because it may damage the device and requires a long time for the ink to heat up. Therefore, in this embodiment, as has been done in the prior art, an ink circulation channel is formed that bypasses the ejection head 80.

[0061] Figure 5 is a schematic diagram showing the piping system involved in ink circulation. More specifically, Figure 5 is a schematic diagram that extracts and illustrates the components of the ink flow path shown in Figures 2 and 3 that are involved in ink circulation. In Figure 5, the supply tank 51, supply-side manifold 61, recovery tank 52, and recovery-side manifold 64 correspond to cross-sectional views of their horizontal cross-sections viewed from above. Here, in order to show the piping around the discharge head 80, the supply-side manifold 61 and the recovery-side manifold 64 are shown separated vertically. However, as mentioned above, in the actual device, these are arranged adjacent to each other horizontally.

[0062] As shown in Figure 5, the internal spaces of the supply tank 51 and the supply-side manifold 61 are directly connected without the need for piping, and the internal space of the supply-side manifold 61 extends to the right in the figure. In other words, the internal space of the supply-side manifold 61 is connected to the supply tank 51 at its left end. Similarly, the internal spaces of the recovery tank 52 and the recovery-side manifold 64 are directly connected without the need for piping, and the internal space of the recovery-side manifold 64 extends to the left in the figure. In other words, the internal space of the recovery-side manifold 64 is connected to the recovery tank 52 at its right end.

[0063] Furthermore, the supply tank 51 and the left end of the recovery-side manifold 64, that is, the end opposite to the recovery tank 52, are connected by a first bypass pipe 67 into which a solenoid valve 671 is inserted. In addition, the right end of the supply-side manifold 61, that is, the end opposite to the supply tank 51, and the recovery tank 52 are connected by a second bypass pipe 68 into which a solenoid valve 681 is inserted.

[0064] Both the first bypass pipe 67 and the second bypass pipe 68 have the function of bypassing the ejection head 80 from the ink flow path that normally passes through the ejection head 80. In other words, by using the first bypass pipe 67 and the second bypass pipe 68, a circulation flow path that does not pass through the ejection head 80 (hereinafter referred to as the "bypass flow path") can be formed.

[0065] Since the first bypass pipe 67 and the second bypass pipe 68 are provided to form a bypass flow path, their flow path cross-sectional area can be determined arbitrarily. It is desirable to increase the flow path cross-sectional area in order to ensure a sufficient ink flow rate in the bypass flow path. This makes it possible to raise the ink temperature to the appropriate printing temperature range in a short time.

[0066] Furthermore, in the actual device, the supply-side manifold 61 and the recovery-side manifold 64 are located in close proximity, making it possible to make the lengths of the first bypass pipe 67 and the second bypass pipe 68 extremely short. This shortens the flow path length of the bypass pipes, further reducing the time required to heat the ink to the appropriate printing temperature range.

[0067] In this embodiment, the ink supply unit 4 can selectively execute two operating modes for achieving ink circulation: a "first circulation mode" in which ink is circulated through all ejection heads 80, and a "second circulation mode" in which ink is circulated without passing through all ejection heads 80. Specific examples of these circulation modes will be described in detail below.

[0068] Figure 6 shows the ink flow in the first circulation mode. In Figure 6 and the following Figures 7A and 7B, a black-filled solenoid valve indicates a closed state. Other white-outlined solenoid valves indicate an open state. Solid arrows represent the ink flow.

[0069] As shown in Figure 6, in the first circulation mode, the solenoid valve 671 on the first bypass pipe 67 and the solenoid valve 681 on the second bypass pipe 68 are closed, while the solenoid valve 621 on the supply-side branch pipe 62 and the solenoid valve 631 on the recovery-side branch pipe 63, which are connected to each of the discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64, are all opened.

[0070] The pressure difference forming unit 55 creates a pressure difference between the supply tank 51 and the recovery tank 52, causing the ink in the supply tank 51 to be pumped to all the discharge heads 80 via the supply-side manifold 61 and the supply-side branch pipe 62. As a result, the ink flows from the supply-side manifold 61 through each discharge head 80 to the recovery-side manifold 64. The circulation pump 71 operates, causing the ink to recirculate from the recovery tank 52 back to the supply tank 51. A heater 74 installed in this recirculation path adjusts the temperature of the ink flowing into the supply tank 51 to the appropriate temperature range for printing.

[0071] Thus, in the first circulation mode, ink, whose temperature has been adjusted to the optimal printing temperature range, circulates through the circulation path via all the ejection heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64. Therefore, the control unit 9 can control the ejection heads 80 to eject ink with a viscosity suitable for printing. This makes it possible to obtain high-quality printing results.

[0072] Figures 7A and 7B show the flow of ink in the second circulation mode. As shown in Figure 7A, in one example of the second circulation mode, the solenoid valve 671 on the first bypass pipe 67 and the solenoid valve 681 on the second bypass pipe 68 are opened. On the other hand, the solenoid valve 621 on the supply-side branch pipe 62 and the solenoid valve 631 on the recovery-side branch pipe 63, which are connected to each of the discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64, are all closed.

[0073] Considering the supply tank 51 as the starting point, the ink in the supply tank 51 flows through two bypass channels, as shown by the solid arrows: one from the first bypass pipe 67 via the recovery-side manifold 64 to the recovery tank 52, and the other from the supply-side manifold 61 via the second bypass pipe 68 to the recovery tank 52, both of which flow into the recovery tank 52. The ink flowing out of the recovery tank 52 is sent to the heater 74 by the connecting pipe 65 and the circulation pump 71 inserted in the middle of it.

[0074] If the heater 74 is turned on at this time, the ink is heated and returned to the supply tank 51 via the connecting pipe 65. By heating and circulating the ink in this way, the ink temperature can be raised. There is no need to circulate low-temperature ink to the ejection head 80, and a circulation path with a large flow rate and short flow path length can be formed. Therefore, it is possible to raise the ink temperature from a relatively low initial ink temperature to the appropriate printing temperature range in a short time.

[0075] Furthermore, solenoid valves (solenoid valve 621) inserted in the upstream branch pipe (supply side branch pipe 62) and solenoid valves (solenoid valve 631) inserted in the downstream branch pipe (recovery side branch pipe 63) of all discharge heads 80 associated with the supply side manifold 61 and the recovery side manifold 64 are closed. As a result, all discharge heads 80 associated with the supply side manifold 61 and the recovery side manifold 64 are isolated from the ink flow in the first bypass pipe 67 and the ink flow in the second bypass pipe 68. Therefore, the nozzle pressure of all discharge heads 80 can be kept constant regardless of the amount of ink flow in the first bypass pipe 67 and the second bypass pipe 68. As a result, ink leakage from all discharge heads 80 nozzles can be suppressed throughout the period during which an example of the second circulation mode shown in Figure 7A is performed.

[0076] On the other hand, another example of the second circulation mode shown in Figure 7B differs from the example shown in Figure 7A in that the solenoid valve 671 on the first bypass piping 67 is closed. Therefore, ink circulation does not occur through the first bypass piping 67. Ink circulates only through the path from the supply tank 51 to the recovery tank 52 via the supply-side manifold 61 and the second bypass piping 68.

[0077] In the second circulation mode shown in Figure 7B, the solenoid valves (solenoid valve 621) inserted in the upstream branch pipe (supply side branch pipe 62) and the solenoid valve (solenoid valve 631) inserted in the downstream branch pipe (recovery side branch pipe 63) of all discharge heads 80 associated with the supply side manifold 61 and the recovery side manifold 64 are closed. As a result, all discharge heads 80 associated with the supply side manifold 61 and the recovery side manifold 64 are isolated from the ink flow in the first bypass pipe 67 and the ink flow in the second bypass pipe 68. Therefore, the nozzle pressure of all discharge heads 80 can be kept constant regardless of the amount of ink flow in the first bypass pipe 67 and the second bypass pipe 68. As a result, ink leakage from the nozzles of all discharge heads 80 can be suppressed throughout the period during which an example of the second circulation mode shown in Figure 7B is performed.

[0078] Thus, in this embodiment, two modes are provided as a second circulation mode that does not go through the discharge head 80: one in which two bypass flow paths are used in parallel (Figure 7A), and another in which only the bypass flow path including the second bypass pipe 68 is used (Figure 7B). The differences in how to use these modes will be explained later.

[0079] Figure 8 is a flowchart showing an example of the printing process in this inkjet printer 1. This process is achieved when the processor 91 of the control unit 9 executes a program 931 that has been stored in the storage unit 93 in advance, causing each part of the device to perform a predetermined operation. When the control unit 9 receives a print command to perform the printing process, either from the user (operator) or from an external control device, it starts preparing each part of the device to be ready for printing (step S101).

[0080] For example, in the drying section 5, heater heating is started to generate the amount of heat necessary for drying the ink. Also, in each head unit 35, a cap (not shown) that closes the nozzle 83 of the ejection head 80 when not in use is separated from the ejection head 80.

[0081] At this time, the ink supply unit 4 executes the "second circulation mode" as an operating mode for circulating the ink while adjusting its temperature. This adjusts the ink temperature to the appropriate temperature range for printing. At this time, as shown in Figure 7A, the ink is circulated using two bypass channels in parallel. By increasing the cross-sectional area of ​​the bypass channels, the flow rate of the circulating ink can be increased, and the ink can be heated up in a short time.

[0082] When the ink temperature reaches an appropriate value, for example, the optimal printing temperature range (YES in step S102), the ink circulation mode is switched to the first circulation mode (step S103). This ensures that ink at a temperature suitable for printing circulates through the ejection head 80. In this state, the control unit 9 turns the ink ejection from each ejection head 80 on or off based on the print data, thereby executing the printing operation on the continuous paper 10 (step S104).

[0083] During the printing operation, the control unit 9 monitors the operating status of the device based on detection signals from sensors in various parts of the device. If the operating status indicated by these signals is normal (NO in step S105), the printing operation continues until printing based on the given print command is completed (YES in step S106). On the other hand, if the operating status matches an interruption condition that is pre-set to interrupt the execution of the printing operation (YES in step S105), the printing operation is interrupted (step S111). Typically, the interruption condition can be the detection of an operational error that causes some kind of abnormality in the device during the execution of the printing operation.

[0084] Next, it is determined whether or not ink circulation can continue (step S112). This determination can be made based on the operating status of the device at that time, in particular the state of each part involved in ink circulation, such as the internal pressure and liquid level of the supply tank 51 and the recovery tank 52, the ink temperature, etc.

[0085] For example, if the leak sensor 791 detects an ink leak and causes an operational error, recovery is not expected immediately, and therefore the circulation should be stopped. Similarly, if the ink pressure detected in the flow path deviates from the appropriate value, or if the circulation pump 71 malfunctions, these are also conditions that warrant stopping the circulation. Therefore, if the interruption is caused by any of these factors, it is determined that continuation of circulation is impossible (NO in step S112), and the ink circulation is stopped (step S113). In other words, the pumps involved in ink circulation are stopped, and the valves are closed.

[0086] According to the inventor's experiments using an ink circulation system equivalent to that of an actual machine, for example, if the ink circulation is stopped for 10 minutes, the ink temperature drops by about 2°C. It then takes 2 to 3 minutes to return to the original temperature. In other words, if an event causing the circulation to stop occurs and it takes 10 minutes to be resolved, then an additional 2 to 3 minutes of preparation time will be required before the printing operation can be resumed.

[0087] It is desirable that users be notified when the circulation stops. This allows users to understand the operational error and take timely measures to resolve it. As a result, the period during which the circulation is down can be minimized.

[0088] On the other hand, interruption conditions occurring at locations other than the ink circulation system, such as operational errors in the transport unit 2 or the drying unit 5, are not considered to affect ink circulation. Therefore, it can be determined that ink circulation can continue (YES in step S112).

[0089] Furthermore, even in the case of interruption conditions caused by operational errors in the ink circulation system, the inkjet printer 1 may be able to autonomously recover from such conditions. For example, this can occur when the operational error is caused by the amount of ink stored in the supply tank 51 and the recovery tank 52, as detected by the liquid level sensors 511 and 521, not being within the appropriate range. In this case, it is possible to adjust the amount of ink stored and then continue the ink circulation.

[0090] For example, in the case of an operational error caused by the amount of ink stored in the supply tank 51 exceeding the upper limit of the appropriate range, the differential pressure between the supply tank 51 and the recovery tank 52, provided by the pressure difference forming unit 55, can be increased. By increasing the amount of ink delivered from the supply tank 51 in this way, the operational error can be resolved. Conversely, in the case of an operational error caused by the amount of ink stored in the supply tank 51 falling below the lower limit of the appropriate range, the amount of ink delivered by the circulation pump 71 can be increased, or ink can be replenished from the replenishment tank 53. In this way, by increasing the amount of ink flowing into the supply tank 51, the operational error can be resolved.

[0091] For example, an operational error caused by the amount of ink stored in the recovery tank 52 exceeding the upper limit of the appropriate range can be resolved by increasing the amount of ink delivered by the circulation pump 71 and lowering the liquid level in the recovery tank 52. Similarly, an operational error caused by the amount of ink stored in the recovery tank 52 falling below the lower limit of the appropriate range can be resolved by increasing the amount of ink delivered from the supply tank 51 by adjusting the differential pressure.

[0092] As described above, if the interruption conditions are not related to the ink circulation system or are due to an operational error that the device can resolve autonomously, it is determined that ink circulation can continue (YES in step S112). Then, ink circulation is performed in a second circulation mode using the bypass channel (step S121). At the same time, the ink levels in the supply tank 51 and the recovery tank 52 are adjusted as necessary (step S122). The method for adjusting the liquid level by increasing or decreasing the amount of ink stored is as described above.

[0093] Furthermore, although these do not constitute operational errors, the printing operation must be interrupted accordingly if, for example, the user inputs an operation to stop the printing operation during the printing process, or if, for example, the cover of the device housing is opened. For example, the cover may be opened for the purpose of performing maintenance work on the head unit 35 by the user. This includes work such as replacing the ejection head 80 or cleaning the nozzle surface of the ejection head 80. Even in such cases, it is possible to set these as interruption conditions that allow ink circulation.

[0094] In these cases, when the second circulation mode is applied, using the two bypass channels shown in Figure 7A in parallel, the amount of ink circulated and sent to the heater 74 is increased, thereby efficiently raising the ink temperature and making the ink temperature uniform throughout the entire circulation channel. On the other hand, when the mode using only one bypass channel shown in Figure 7B is applied, the ink in the supply-side manifold 61, which is upstream of the ejection head 80 in the ink flow direction, can be given priority in temperature adjustment. Because the amount of circulating ink is small, it can be heated quickly with low power consumption. By prioritizing temperature adjustment for the ink in the supply-side manifold 61, which will be supplied to the ejection head 80 in the initial stage of resuming printing, it is possible to quickly resume printing operations.

[0095] After the printing operation is interrupted and the system switches to the second cycle mode, it remains in this state until the event causing the interruption is resolved (step S123). Once such an event is resolved (YES in step S123), the process returns to step S102. If the ink temperature is appropriate (YES in step S102), the printing operation resumes. Because the ink temperature is maintained by the execution of the second cycle mode in the standby state (step S121), it is expected that the printing operation will resume quickly. In other words, the waiting time from the removal of the cause of the interruption to the resumption of printing can be shortened.

[0096] If the event that triggers the interruption condition is not resolved (NO in step S123), and the duration of the second circulation mode reaches a predetermined time (YES in step S124), the target temperature for controlling the ink by the heater 74 is changed (step S125). In ink circulation using the bypass channel, some of the ink around the ejection head 80 is not included in the circulation channel. As time passes, the temperature of this ink decreases, and a temperature difference is created between it and the ink in circulation.

[0097] In step S103, when ink circulation via the ejection head 80 is restarted, in the initial stage, the ink whose temperature has been regulated by circulation and the ink whose temperature has dropped due to lack of circulation will be mixed. In this case as well, in order to ensure the appropriate ink temperature and enable the printing operation to be performed quickly, the target temperature of the circulating ink is changed to a higher value than before. By raising the temperature of the circulating ink in advance in this way, a large temperature drop is avoided even if ink with a lower temperature is mixed in.

[0098] When the normal target ink temperature is denoted by the symbol Ta, the modified target temperature Ta' can be determined, for example, based on the following equation: Ta' = Ta + ΔT … (Equation 1) where ΔT = (Q1・Ta + Q2・Tb) / (Q1 + Q2) + (Ta - Tb)α Here, the value Q1 is the total amount of ink circulating in the second circulation mode. The values ​​Q2 and Tb represent the total amount of ink not circulating in the second circulation mode and the assumed ink temperature after temperature reduction for such ink, respectively. The value α is a correction coefficient that takes into account the amount of heat dissipated in the ink circulation system and depends on the temperature difference between the ink temperature and the ambient temperature. This value α can be determined experimentally in advance.

[0099] If the duration of the second circulation mode becomes prolonged, the control target temperature is changed based on (Equation 1) above. This allows setting a control target temperature Ta' that takes into account the amount of non-circulating ink and its temperature drop, in addition to the amount and temperature of circulating ink. The second circulation mode is then executed based on this changed control target temperature. This ensures that even if the second circulation mode is run for a long time, the ink temperature is properly maintained when the first circulation mode is restarted. As a result, the waiting time until printing can be resumed can be reduced.

[0100] At this time, the temperature of the circulating ink will be adjusted to a temperature higher than the original target temperature Ta, but calculations suggest that the increase in the target temperature will be at most a few degrees Celsius. If the ink is already heated, raising its temperature by this amount will result in negligible ink degradation.

[0101] Furthermore, the temperature Tb of the non-circulating ink decreases over time. Therefore, it is desirable to change the target temperature not just once, but repeatedly over time. It is also possible that it may take even longer to resolve the cause of the error. For this reason, in order to suppress power consumption during this time, for example, if the execution duration of the second circulation mode reaches a predetermined upper limit, the ink circulation (and heater heating in the drying section 5) may be temporarily stopped. In that case, it is preferable to restart the printing process from step S101 after the cause of the error has been eliminated.

[0102] As described above, in this embodiment, if an event occurs that necessitates interrupting the printing operation, the system switches from the first circulation mode to the second circulation mode. This allows the ink circulation to continue as long as possible and maintain the ink temperature. As a result, when such an event is resolved and printing becomes possible again, printing can be resumed with only a short waiting time. Furthermore, since there is no need to rapidly raise the ink temperature to shorten the waiting time, ink degradation such as aggregation can be suppressed. This reduces clogging of the filter in the ink flow path, extends its lifespan, and improves print quality.

[0103] This effect can be obtained regardless of the structure of the bypass flow path, but it is particularly effective in the structure of the ink supply unit 4 of this embodiment. In this ink supply unit 4, the supply tank 51 and the supply-side manifold 61 are directly connected without piping. Similarly, the recovery tank 52 and the recovery-side manifold 64 are also directly connected without piping. Ink is supplied to the discharge head 80 via a supply-side branch pipe 62 that branches off from the middle of the supply-side manifold 61. Ink is recovered from the discharge head 80 via a recovery-side branch pipe 63 that is connected to the middle of the recovery-side manifold 64.

[0104] On the other hand, the bypass flow path is provided with a first bypass pipe 67 connected from the supply tank 51 to the vicinity of the upstream end of the recovery-side manifold 64 in the ink flow direction, and a second bypass pipe 68 running in parallel from the vicinity of the downstream end of the supply-side manifold 61 in the ink flow direction to the recovery tank 52. This allows for the circulation of ink at a high flow rate and enables the configuration of a bypass flow path with a short flow length.

[0105] In addition, as shown by the solid arrows in Figures 6 and 7A and 7B, the flow pattern of ink in the supply-side manifold 61 and the recovery-side manifold 64 is the same (always to the right in these figures) between the first circulation mode, in which ink is circulated via the ejection head 80, and the second circulation mode, in which ink is circulated via a bypass channel without going through the ejection head 80.

[0106] When the ink circulates differently depending on whether it passes through the ejection head 80 or through the bypass channel, turbulence such as vortices occurs in the ink flow when switching between these two states. Such turbulence causes ink to accumulate in the piping and not participate in circulation, which slows down the temperature rise of the ink throughout the entire piping system.

[0107] For example, if only the speed of circulation is considered, it would be advantageous to create a bypass channel that directly bypasses from the supply tank to the recovery tank. However, in this case, the ink in the manifold will be separated from the circulation channel, causing ink stagnation in this section. Alternatively, a bypass channel connecting the supply-side manifold to the recovery-side manifold could be considered for the purpose of bypassing only the ejection head 80. In this case, ink stagnation will not occur within the manifold. However, since the two manifolds will be connected in series, the overall length of the circulation channel will increase. As a result, the time required to raise the ink temperature to the appropriate printing temperature range will increase.

[0108] In contrast, the bypass flow path in this embodiment consists of two systems: one that bypasses the supply-side manifold 61 and discharge head 80 from the supply tank 51 to the recovery tank 52, and another that bypasses the discharge head 80 and recovery-side manifold 64 from the supply tank 51 to the recovery tank 52, and these two systems are in parallel. Furthermore, given the positional relationship between the supply tank 51, supply-side manifold 61, recovery-side manifold 64, and recovery tank 52 shown in Figure 3, the first bypass pipe 67 and the second bypass pipe 68 can be made extremely short.

[0109] For example, if the supply-side manifold 61 and the recovery-side manifold 64 are located at the same position in the vertical direction, the first bypass pipe 67 and the second bypass pipe 68 can also be constructed using simple horizontal piping.

[0110] Furthermore, in the manifold spaces inside the supply-side manifold 61 and the recovery-side manifold 64, ink flows in from one end and out from the other, so ink does not accumulate in the manifold spaces.

[0111] As will be detailed in the second embodiment, even when a bypass channel is provided to connect the supply-side manifold 61 (particularly its downstream end) and the recovery-side manifold 64 (particularly its upstream end), the advantage of not changing the ink flow pattern within the manifold can be obtained. The configuration of this embodiment is more advantageous in that it allows for a shorter bypass channel length and a larger cross-sectional area.

[0112] Furthermore, if the printing operation is interrupted for a predetermined period of time or longer, the target temperature for controlling the ink is changed to a higher value and the second circulation mode is continued. This minimizes the decrease in ink temperature even if ink that has cooled down without participating in the circulation is mixed in. As a result, printing operations can be performed quickly after a long period of time has elapsed.

[0113] <Second Embodiment> Figures 9A to 9C illustrate the flow of ink in the first and second circulation modes of the second embodiment. In describing the second embodiment, components having the same or corresponding structure and operation as those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and detailed descriptions are omitted. The main differences between the piping system of the first embodiment and the piping system of the second embodiment are as follows. In other words, in the piping system of the first embodiment, the bypass piping that bypasses all discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 consists of a first bypass pipe 67 connecting the recovery-side manifold 64 and the supply tank 51, and a second bypass pipe 68 connecting the supply-side manifold 61 and the recovery tank 52.

[0114] In contrast, in the piping system of the second embodiment, as shown in Figure 9A, the bypass piping that bypasses all discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 is comprised of a third bypass pipe 600 connecting the supply-side manifold 61 and the recovery-side manifold 64. More specifically, the third bypass pipe 600 connects the downstream end 61a of the supply-side manifold 61 and the upstream end 64a of the recovery-side manifold 64 in the ink flow direction. A solenoid valve 601 is interposed in the third bypass pipe 600.

[0115] Figure 9B illustrates the first circulation mode in the second embodiment. The first circulation mode is an ink circulation mode mainly performed during printing. In the first circulation mode, all solenoid valves 621 and 631 corresponding to each of the discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 are opened. Also, solenoid valve 601 is closed and the heater 74 is turned on. In this state, a pressure difference is formed between the supply tank 51 and the recovery tank 52. As a result, the ink in the supply tank 51 passes through the supply-side manifold 61, through all the supply-side branch pipes 62, discharge heads 80 and recovery-side branch pipes 63 associated with the supply-side manifold 61 and the recovery-side manifold 64, and is recovered into the recovery-side manifold 64. The ink recovered in the recovery-side manifold 64 is returned to the supply tank 51 by the operation of the circulation pump 71, passing through the connection pipe 65 from the recovery tank 52, and after its temperature is adjusted by the heater 74.

[0116] Figure 9C illustrates the second circulation mode in the second embodiment. The second circulation mode is an ink circulation mode mainly performed when printing is interrupted. In the second circulation mode, all solenoid valves 621 and 631 corresponding to each of the ejection heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 are closed. Also, solenoid valve 601 is opened and the heater 74 is turned on. The magnitude of the pressure difference between the supply tank 51 and the recovery tank 52 is adjusted as appropriate. In this state, the circulation pump 71 is driven. As a result, the ink in the supply tank 51 passes through the supply-side manifold 61, bypasses all the ejection heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64, and is recovered to the recovery-side manifold 64 through the third bypass pipe 600. The ink recovered in the recovery-side manifold 64 is returned to the supply tank 51 by the operation of the circulation pump 71, passing through the connection pipe 65 from the recovery tank 52, and after its temperature is adjusted by the heater 74.

[0117] <Third Embodiment> Figures 10A to 10C illustrate the flow of ink in the first and second circulation modes of the third embodiment. In describing the third embodiment, components having the same or corresponding structure and operation as those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and detailed descriptions are omitted. The main differences between the piping system of the first embodiment and the piping system of the third embodiment are as follows. In other words, in the piping system of the first embodiment, the bypass piping that bypasses all discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 consists of a first bypass pipe 67 connecting the recovery-side manifold 64 and the supply tank 51, and a second bypass pipe 68 connecting the supply-side manifold 61 and the recovery tank 52.

[0118] In contrast, in the piping system of the third embodiment, as shown in Figure 10A, a bypass pipe that bypasses all discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 is made up of a fourth bypass pipe 700 that connects the supply tank 51 and the recovery tank 52. More specifically, the fourth bypass pipe 700 connects the vicinity of the bottom surface of the supply tank 51 and the vicinity of the bottom surface of the recovery tank 52. A solenoid valve 701 is interposed in the fourth bypass pipe 700.

[0119] Figure 10B illustrates the first circulation mode in the third embodiment. The first circulation mode is an ink circulation mode mainly performed during printing. In the first circulation mode, all solenoid valves 621 and 631 corresponding to each of the discharge heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 are opened. Also, the solenoid valve 701 is closed and the heater 74 is turned on. In this state, a pressure difference is formed between the supply tank 51 and the recovery tank 52. As a result, the ink in the supply tank 51 passes through the supply-side manifold 61, through all the supply-side branch pipes 62, discharge heads 80 and recovery-side branch pipes 63 associated with the supply-side manifold 61 and the recovery-side manifold 64, and is recovered into the recovery-side manifold 64. The ink recovered in the recovery-side manifold 64 is returned to the supply tank 51 by the operation of the circulation pump 71, passing through the connection pipe 65 from the recovery tank 52, and after its temperature is adjusted by the heater 74.

[0120] Figure 10C illustrates the second circulation mode in the third embodiment. The second circulation mode is an ink circulation mode mainly performed when printing operations are interrupted. In the second circulation mode, all solenoid valves 621 and 631 corresponding to each of the ejection heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64 are closed. Also, the solenoid valve 701 is opened and the heater 74 is turned on. The magnitude of the pressure difference between the supply tank 51 and the recovery tank 52 is adjusted as appropriate. In this state, the circulation pump 71 is driven. As a result, the ink in the supply tank 51 bypasses the supply-side manifold 61, bypasses all the ejection heads 80 associated with the supply-side manifold 61 and the recovery-side manifold 64, and is recovered to the recovery tank 52 through the fourth bypass pipe 700. The ink recovered in the recovery tank 52 is returned to the supply tank 51 by the operation of the circulation pump 71, through the connecting pipe 65, and after its temperature is adjusted by the heater 74.

[0121] <Other> As described above, the inkjet printing apparatus 1 described above corresponds to one embodiment of the "printing apparatus" of the present invention. In this embodiment, the ejection head 80, supply tank 51, recovery tank 52, circulation pump 71, heater 74, and control unit 9 function as the "printing head," "supply tank," "recovery tank," "pump," "heater," and "control unit" of the present invention, respectively.

[0122] Furthermore, the supply-side manifold 61 corresponds to the "supply-side manifold section" of the present invention, and together with the supply-side branch pipe 62 and the solenoid valve 621, it functions as a "supply section" that forms the "supply flow path" of the present invention. Similarly, the recovery-side manifold 64 corresponds to the "recovery-side manifold section" of the present invention, and together with the recovery-side branch pipe 63 and the solenoid valve 631, it functions as a "recovery section" that forms the "recovery flow path" of the present invention.

[0123] Furthermore, the connecting pipe 65 corresponds to the "recirculation channel" of the present invention, and together with the solenoid valve 73, it functions as the "recirculation section" of the present invention. The first bypass channel formed by the first bypass pipe 67 and the solenoid valve 671, and the second bypass channel formed by the second bypass pipe 68 and the solenoid valve 681, each correspond to the "bypass channel" of the present invention. These components together function as the "bypass forming section" of the present invention.

[0124] Furthermore, in the above embodiment, various sensors provided in each part of the device to detect their operational status, including the temperature sensor 741, liquid level sensors 511 and 521, and liquid leak sensor 791, can function as "error detection units" of the present invention together with the control unit 9 that performs error determination when their detection results constitute an interruption condition that stops the printing operation.

[0125] It should be noted that the present invention is not limited to the first to third embodiments described above, and various modifications other than those described above can be made without departing from the spirit of the invention. For example, in the above embodiment, the temperature sensor 741 is integrated with the heater 74, but they may be configured as separate units and each inserted into the reflux channel. Also, multiple sets of heaters and temperature sensors may be connected in series.

[0126] Furthermore, in the above embodiment, for example, a mode in which ink circulation is performed using only the bypass channel without passing through the ejection head 80, and a mode in which ink circulation is performed via the ejection head 80 without using the bypass channel are selectively executed. Alternatively, or in addition to this, a circulation mode may be provided in which the ink is divided between the channel passing through the ejection head 80 and the bypass channel.

[0127] Furthermore, although each of the solenoid valves in the above embodiment functions as an on / off valve that switches the flow of ink on and off, at least some of them may be equipped with a flow rate control function.

[0128] Furthermore, in the above-described embodiment, the pressure difference forming unit 55 includes a pressurizing unit 551 that sets the internal pressure of the supply tank 51 to a positive pressure greater than atmospheric pressure, and a depressurizing unit 553 that sets the internal pressure of the recovery tank 52 to a negative pressure less than atmospheric pressure. However, the pressure difference forming unit 55 may also include a first depressurizing unit that sets the internal pressure of the supply tank 51 to a first negative pressure less than atmospheric pressure, and a second depressurizing unit that sets the internal pressure of the recovery tank 52 to a second negative pressure less than the first negative pressure.

[0129] Furthermore, while several examples of interruption conditions for stopping the printing operation were given in the description of the embodiments above, the interruption conditions are not limited to these. Also, it is not necessarily required that all of the interruption conditions listed above be used; some of them, or other interruption conditions, can be used in appropriate combinations for controlling the device.

[0130] As described above with examples of specific embodiments, in the printing apparatus according to the present invention, the control unit may be configured to resume execution of the first circulation mode when the interruption condition is resolved. By resuming ink circulation through the print head in this way, a state in which printing operation can be performed can be achieved. At this time, since ink circulation in the second circulation mode has already been performed, the ink is maintained in a heated state, and printing operation can be resumed quickly.

[0131] Alternatively, for example, a supply-side manifold section whose internal space communicates with the internal space of the supply tank may be connected to the supply tank, the supply flow path may connect the supply-side manifold section and the print head, and in the second circulation mode, the ink may be circulated via a bypass flow path connecting the supply-side manifold section and the recovery tank.

[0132] With this configuration, the ink flows through the supply-side manifold in both the first and second circulation modes. Therefore, the amount of ink excluded from circulation in the second circulation mode can be reduced. This reduces the impact of the temperature drop of the uncirculated ink on the overall ink temperature. Furthermore, when printing is resumed, the temperature-controlled ink in the supply-side manifold is sent to the print head, thus shortening the waiting time until printing resumes.

[0133] In this case, a recovery-side manifold section is further connected to the recovery tank, the internal space of which is in communication with the internal space of the recovery tank, the recovery flow path connects the print head and the recovery-side manifold section, and the bypass forming section has a first bypass pipe that forms a bypass flow path connecting the supply tank and the recovery-side manifold section, and a second bypass pipe that forms a bypass flow path connecting the supply-side manifold section and the recovery tank, and in the second circulation mode, ink may be circulated through the bypass flow path through the first bypass pipe and the bypass flow path through the second bypass pipe, respectively.

[0134] With this configuration, ink can be circulated not only through the bypass channel via the supply-side manifold section described above, but also through a bypass channel connecting the supply tank and the recovery-side manifold section. This effectively increases the cross-sectional area of ​​the circulation channel. As a result, the amount of ink circulated can be increased, making it possible to regulate the ink temperature more efficiently through circulation.

[0135] In this case, for example, the supply-side manifold section supplies ink to multiple print heads, and the recovery-side manifold section recovers ink from multiple print heads. In the first circulation mode, ink is circulated from the supply tank to the supply tank via the supply-side manifold section, multiple print heads, recovery-side manifold section, recovery tank, and recirculation channel, while the ink temperature is adjusted by a heater. In the second circulation mode, with all of the multiple print heads bypassed, the ink may be circulated via a bypass channel through the first bypass piping and a bypass channel through the second bypass piping.

[0136] With this configuration, in the first circulation mode, ink can be circulated to all print heads to perform ink circulation while simultaneously adjusting the ink temperature. Therefore, ink adjusted to a temperature suitable for printing can be quickly ejected from the print heads as needed. On the other hand, in the second circulation mode, ink can be circulated even when no ink is supplied to the print heads, thereby suppressing ink aggregation and other issues. In this case, by including the supply-side manifold and the recovery-side manifold in the ink circulation flow path, the difference in the ink flow path between the first and second circulation modes can be reduced. Therefore, switching from the second circulation mode to the first circulation mode can be performed smoothly.

[0137] Alternatively, for example, the system may be configured to adjust the amount of ink stored in the supply tank and the recovery tank before restarting the first circulation mode. With such a configuration, the first circulation mode is restarted with the ink levels in the supply tank and the recovery tank maintained at an appropriate level. As a result, the quality of the subsequent printing operations can be maintained well.

[0138] For example, if the execution duration of the second circulation mode exceeds a predetermined value, a setting may be changed so that the target value for temperature adjustment by the heater is increased. In the second circulation mode, the temperature of ink that is not involved in ink circulation decreases over time. By setting a high target value for ink temperature, it becomes possible to maintain an appropriate ink temperature even if such cooled ink mixes with the circulating ink.

[0139] Furthermore, for example, if the printing device is equipped with an error detection unit that detects operational errors, the detection of an operational error by the error detection unit can be used as a condition for interruption. When the operation of the printing device deviates from the normal state and an operational error occurs, it is considered that the printing operation should be interrupted from the viewpoint of safety and print quality. In such cases, it is preferable not to stop the ink circulation but to continue circulation in the second circulation mode to maintain the ink temperature. By doing so, it becomes possible to quickly resume the printing operation when the operational error is resolved.

[0140] More specifically, a pressure adjustment unit is provided to adjust the pressure in the internal spaces of the supply tank and the recovery tank, and a pump for delivering ink may be inserted into the recirculation channel. In this case, for example, if the amount of ink in the supply tank exceeds a predetermined upper limit, an operational error can be determined. At this time, the second circulation mode can be executed, and the pressure adjustment unit can be used to raise the pressure in the supply tank to higher than that in the recovery tank, and the ink can be pumped using the differential pressure between them. In this way, the amount of ink in the supply tank can be reduced to below the upper limit.

[0141] For example, a pump for delivering ink may be inserted into the recirculation channel, and if the amount of ink in the recovery tank exceeds a predetermined upper limit, it may be determined to be an operational error, and the second circulation mode may be executed, and the pump may be activated to reduce the amount of ink in the recovery tank to below the upper limit. In this way, by making the amount of ink flowing out of the recovery tank greater than the amount of ink flowing into the recovery tank, the amount of ink in the recovery tank can be reduced to below the upper limit.

[0142] For example, in a printing apparatus that includes a transport unit for transporting printing media during printing and a drying unit for drying the ink-covered printing media, the second circulation mode may be initiated when an operational error is detected in the transport unit or the drying unit. Operational errors occurring in these areas are not expected to affect ink circulation. Therefore, by running the second circulation mode to maintain the ink temperature appropriately, printing can be resumed quickly after the error is resolved.

[0143] Furthermore, user operations related to maintenance work on the printing device may also be considered interruption conditions. This includes cases where the user wants to stop a printing operation that is currently in progress for any reason, or when the cover of the device housing is opened for maintenance work. In such cases, instead of continuing the printing operation, ink circulation using the second circulation mode is performed to maintain the ink temperature, allowing printing to start immediately after the work is completed.

[0144] Furthermore, for example, if ink leakage from the ink flow path is detected, the printing operation may be stopped, and neither the first circulation mode nor the second circulation mode may be executed. Possible malfunctions of the device may include cases where it is undesirable to continue ink circulation. For example, this would apply if there is ink leakage in the ink flow path. Executing ink circulation in such a case would induce further ink leakage. In situations where ink circulation should not be performed, or where it cannot be confirmed that it is acceptable to perform ink circulation, neither the first circulation mode nor the second circulation mode should be executed, and ink circulation should be stopped. This prevents further problems from occurring.

[0145] Although the invention has been described above in accordance with specific embodiments, this description is not intended to be interpreted restrictively. As with other embodiments of the invention, various modifications of the disclosed embodiments will be apparent to those familiar with the art by referring to the description of the invention. Therefore, the appended claims are intended to include such modifications or embodiments without departing from the true scope of the invention.

[0146] This invention can be applied to all printing apparatuses that use ink for printing, and is particularly suitable for printing apparatuses that circulate ink in order to preheat the ink.

[0147] 1 Inkjet printing apparatus 9 Control unit 51 Supply tank 52 Recovery tank 61 Supply side manifold (supply side manifold section, supply channel) 62 Supply side branch piping (supply channel, supply section) 63 Recovery side branch piping (recovery channel, recovery section) 64 Recovery side manifold (recovery side manifold section, recovery channel) 65 Connecting piping (recirculation channel, recirculation section) 67 First bypass piping (bypass channel, bypass forming section) 68 Second bypass piping (bypass channel, bypass forming section) 71 Circulation pump (pump) 73 Solenoid valve (recirculation section) 74 Heater 80 Discharge head (printing head) 511, 521 Liquid level sensor (error detection section) 621 Solenoid valve (supply section) 631 Solenoid valve (recovery section) 791 Leak sensor (error detection section)

Claims

1. A print head that ejects ink; a supply tank that stores the ink supplied to the print head; a supply unit that forms a supply channel for transporting the ink from the supply tank to the print head; a recovery tank that stores the ink recovered from the print head; a recovery unit that forms a recovery channel for transporting the ink from the print head to the recovery tank; a recirculation unit that forms a recirculation channel for recirculating the ink from the recovery tank to the supply tank; a heater interposed in the recirculation channel for heating the ink; and a bypass forming unit that forms a bypass channel for transporting the ink from the supply tank to the recovery tank without passing through the print head. A printing apparatus comprising a control unit that selectively executes a first circulation mode in which ink is circulated from the supply tank to the supply tank via the supply channel, the print head, the recovery channel, the recovery tank, and the recirculation channel, while the temperature of the ink is adjusted by the heater, and a second circulation mode in which ink is circulated from the supply tank to the supply tank via the bypass channel, the recovery tank, and the recirculation channel, while the temperature of the ink is adjusted by the heater, wherein the control unit executes a printing operation in which ink is ejected from the print head while executing the first circulation mode, and when it determines that a preset interruption condition has been met for interrupting the printing operation, it interrupts the printing operation and starts executing the second circulation mode.

2. The printing apparatus according to claim 1, wherein the control unit resumes execution of the first cycle mode when the interruption condition is resolved.

3. The printing apparatus according to claim 1, wherein a supply-side manifold section is connected to the supply tank, the internal space of which is in communication with the internal space of the supply tank, the supply flow path connects the supply-side manifold section and the print head, and in the second circulation mode, the ink is circulated through the bypass flow path connecting the supply-side manifold section and the recovery tank.

4. The printing apparatus according to claim 3, wherein a recovery-side manifold section is connected to the recovery tank, the internal space of which is in communication with the internal space of the recovery tank, the recovery flow path connects the print head and the recovery-side manifold section, the bypass forming section has a first bypass pipe that forms the bypass flow path connecting the supply tank and the recovery-side manifold section, and a second bypass pipe that forms the bypass flow path connecting the supply-side manifold section and the recovery tank, and in the second circulation mode, the ink is circulated through the bypass flow path through the first bypass pipe and the bypass flow path through the second bypass pipe, respectively.

5. The printing apparatus according to claim 4, wherein the supply-side manifold section supplies the ink to a plurality of print heads, the recovery-side manifold section recovers the ink from the plurality of print heads, in the first circulation mode, the ink is circulated from the supply tank to the supply tank via the supply-side manifold section, the plurality of print heads, the recovery-side manifold section, the recovery tank and the recirculation channel, while the temperature of the ink is adjusted by the heater, and in the second circulation mode, with all of the plurality of print heads bypassed, the ink is circulated via the bypass channel through the first bypass piping and the bypass channel through the second bypass piping, respectively.

6. The printing apparatus according to claim 2, wherein the control unit adjusts the amount of ink stored in the supply tank and the recovery tank, respectively, prior to restarting the first circulation mode.

7. The printing apparatus according to claim 2, wherein the control unit raises the target value for temperature adjustment by the heater when the execution duration of the second circulation mode exceeds a predetermined value.

8. The printing apparatus according to any one of claims 1 to 7, further comprising an error detection unit for detecting an operational error in the operating status of the printing apparatus, wherein the interruption condition is that the error detection unit has detected the operational error.

9. The printing apparatus according to claim 8, further comprising a pressure adjustment unit for adjusting the pressure in the internal space of the supply tank and the recovery tank, wherein a pump for delivering the ink is interposed in the recirculation channel, and the control unit determines that the operation error has occurred when the amount of ink in the supply tank exceeds a predetermined upper limit, executes the second circulation mode, and uses the pressure adjustment unit to raise the pressure in the supply tank higher than that in the recovery tank to reduce the amount of ink in the supply tank to below the upper limit.

10. The printing apparatus according to claim 8, wherein a pump for delivering the ink is interposed in the recirculation channel, and the control unit determines that an operation error has occurred when the amount of ink in the recovery tank exceeds a predetermined upper limit, executes the second circulation mode, and operates the pump to reduce the amount of ink in the recovery tank to below the upper limit.

11. The printing apparatus according to claim 8, comprising a transport unit for transporting a printing medium in the printing operation, and a drying unit for drying the printing medium to which the ink has adhered, wherein the control unit starts executing the second cycle mode when an operation error is detected in the transport unit or the drying unit.

12. The printing apparatus according to any one of claims 1 to 7, wherein the interruption condition is a user operation corresponding to maintenance work on the printing apparatus.

13. The printing apparatus according to any one of claims 1 to 7, wherein the control unit stops the printing operation when it detects leakage of the ink from the ink flow path and does not perform either the first circulation mode or the second circulation mode.

14. A printing method comprising supplying ink from a supply tank to a print head that ejects ink via a supply channel, recovering the ink recovered from the print head in a recovery channel, and recirculating the ink from the recovery tank to the supply tank while adjusting the temperature of the ink with a heater inserted in a recirculation channel connecting the recovery tank and the supply tank, wherein a first circulation mode is performed in which the ink is circulated from the supply tank to the supply tank via the supply channel, the print head, the recovery channel, the recovery tank and the recirculation channel, while adjusting the temperature of the ink with the heater, and a second circulation mode is performed in which a bypass channel is formed from the supply tank to the recovery tank without going through the print head, and the ink is circulated from the supply tank to the supply tank via the bypass channel, the recovery tank and the recirculation channel, while adjusting the temperature of the ink with the heater, A printing method comprising: executing the first circulation mode while performing a printing operation in which ink is ejected from the print head; and, when it is determined that a preset interruption condition has been met for interrupting the printing operation, interrupting the printing operation and starting the execution of the second circulation mode.

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