Ink jet printer

Abstract

To provide an ink jet printer which can reduce deterioration of printing image quality.SOLUTION: An ink jet head 11 has a nozzle for discharging ink. A pressure tank 21 and a negative pressure tank 23 are connected to the ink jet head 11. A circulation path 41 is a path for circulating ink between the pressure tank 21, the ink jet head 11, and the negative pressure tank 23. A control section 7 controls a pressure adjustment section 5 to adjust pressure of the pressure tank 21 and the negative pressure tank 23 so that nozzle pressure of the ink jet head 11 is maintained within a prescribed pressure range on the basis of a temperature of ink in an upstream side path 42 for connecting the pressure tank 21 and the ink jet head 11 and a temperature of ink in a downstream side path 43 for connecting the ink jet head 11 and the negative pressure tank 23.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to inkjet printing devices. [Background technology]

[0002] 2. Description of the Related Art An ink-circulation type ink-jet printing device is known in which ink is ejected from an ink-jet head to print while circulating ink between a tank arranged upstream of the ink-jet head and a tank arranged downstream of the ink-jet head.

[0003] In such an inkjet printing device, the temperature of the ink may change while flowing through the circulation path due to the influence of the environmental temperature and heat generated by the inkjet head, which may cause the temperature of the ink flowing through the path upstream of the inkjet head in the ink circulation direction (upstream path) and the temperature of the ink flowing through the path downstream of the inkjet head (downstream path) to change.

[0004] Here, the viscosity of the ink changes according to the change in the temperature of the ink, and the flow path resistance of the path through which the ink flows changes according to the change in the viscosity of the ink. Therefore, the flow path resistance ratio, which is the ratio of the flow path resistance of the upstream path to the flow path resistance of the downstream path, may change due to the change in the temperature of the ink in each of the upstream path and the downstream path. When this flow path resistance ratio changes, the nozzle pressure of the inkjet head may change and go out of the stable ejection range.

[0005] In response to this, Patent Document 1 discloses a technique for achieving a flow path resistance ratio for maintaining the nozzle pressure at a predetermined pressure by adjusting the temperature of ink in the upstream path and the downstream path. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-56477 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the technology of Patent Document 1, since it takes a certain amount of time to adjust the temperature of the ink in the upstream and downstream paths, it is difficult to quickly change the flow path resistance ratio between the upstream and downstream paths. This can cause the nozzle pressure of the inkjet head to fall outside the stable ejection range, making the ejection of the ink unstable. This can result in a deterioration in print quality.

[0008] The present invention has been made in view of the above, and has an object to provide an inkjet printing apparatus capable of reducing degradation in print image quality. [Means for solving the problem]

[0009] In order to achieve the above object, an inkjet printing apparatus of the present invention comprises an inkjet head having nozzles for ejecting ink, a pressurized tank and a negative pressure tank connected to the inkjet head, a circulation path for circulating ink between the pressurized tank, the inkjet head, and the negative pressure tank, a pressure adjustment unit for adjusting the pressure of the pressurized tank and the negative pressure tank, and a control unit for controlling the pressure adjustment unit, wherein the control unit controls the pressure adjustment unit to adjust the pressure of the pressurized tank and the negative pressure tank so as to maintain the nozzle pressure of the inkjet head within a predetermined pressure range, based on the temperature of ink in a path of the circulation path connecting the pressurized tank and the inkjet head, and the temperature of ink in a path connecting the inkjet head and the negative pressure tank. Effect of the Invention

[0010] According to the inkjet printing apparatus of the present invention, deterioration in print image quality can be reduced. [Brief description of the drawings]

[0011] [Figure 1]1 is a schematic configuration diagram of an inkjet printing apparatus according to an embodiment; [Diagram 2] 2 is a schematic configuration diagram of a head block of the inkjet printing apparatus shown in FIG. [Diagram 3] FIG. [Figure 4] FIG. 2 is a diagram showing a fluid circuit model of the inkjet printing device shown in FIG. [Diagram 5] 2 is a diagram showing an example of a change in temperature of ink in a path along which the ink flows from a pressure tank to a negative pressure tank of the inkjet printing device shown in FIG. 1. [Figure 6] 1. FIG. 4 is a diagram showing another example of the transition of the temperature of the ink in the path through which the ink flows from the pressure tank to the negative pressure tank of the inkjet printing device shown in FIG. [Figure 7] 1. FIG. 9 is a diagram showing yet another example of the transition of the temperature of the ink in the path through which the ink flows from the pressure tank to the negative pressure tank of the inkjet printing apparatus shown in FIG. [Figure 8] 1. FIG. 9 is a diagram showing yet another example of the transition of the temperature of the ink in the path through which the ink flows from the pressure tank to the negative pressure tank of the inkjet printing apparatus shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same or equivalent parts and components are denoted by the same or equivalent reference numerals throughout the drawings.

[0013] The following embodiments are examples of devices for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the material, shape, structure, arrangement, etc. of each component to those described below. The technical idea of ​​the present invention can be modified in various ways within the scope of the claims.

[0014] Fig. 1 is a schematic diagram of an inkjet printing device according to an embodiment of the present invention. Fig. 2 is a schematic diagram of a head block of the inkjet printing device shown in Fig. 1. In the following description, the direction perpendicular to the plane of Fig. 1 is defined as the front-rear direction, and the front direction of the plane of the paper is defined as the forward direction. Furthermore, the top, bottom, left, right, and top-bottom directions on the plane of Fig. 1 are defined as the up-down, left-right directions. The up-down direction is the vertical direction, and the left-right and front-to-back directions are mutually perpendicular, and are all perpendicular to the up-down direction and parallel to the horizontal direction.

[0015] As shown in FIG. 1, an inkjet printing apparatus 1 according to this embodiment includes a head module unit 2, an ink circulation unit 3, an ink supply unit 4, a pressure adjustment unit 5, an environmental temperature sensor 6, and a control unit .

[0016] The head module unit 2 performs printing by ejecting ink onto a print medium such as paper. The head module unit 2 includes an inkjet head 11, ink buses 12 and 13, a plurality of inlet pipes 14, a plurality of outlet pipes 15, and a plurality of downstream ink temperature sensors 16.

[0017] The inkjet head 11 ejects ink supplied by the ink circulation unit 3. The inkjet head 11 has a plurality of head blocks 17. In this embodiment, the inkjet head 11 has six head blocks 17.

[0018] In the inkjet head 11, the head blocks 17 are arranged in a staggered manner along the left-right direction. That is, in the inkjet head 11, the six head blocks 17 arranged along the left-right direction are arranged with their positions shifted alternately in the front-rear direction. The six head blocks 17 are arranged at the same height position.

[0019] As shown in Fig. 2, the head block 17 has a plurality of nozzles 18 that eject ink. Fig. 2 is a view of the head block 17 as seen from below.

[0020] The nozzles 18 are arranged in the left-right direction. The nozzles 18 open to a nozzle surface 17a, which is the lower surface of the head block 17, and eject ink downward.

[0021] The ink bus 12 supplies ink sent from a pressurized tank 21 (described later) via an ink supply pipe 22 (described later) to each head block 17 via each inlet pipe 14 .

[0022] The ink bus 13 recovers the ink not consumed in each head block 17 via each outflow pipe 15, and causes it to flow to an ink recovery pipe 24, which will be described later.

[0023] The inflow pipes 14 connect the head blocks 17 and the ink bus 12. One inflow pipe 14 is provided corresponding to each head block 17.

[0024] The outflow pipes 15 connect the head blocks 17 and the ink bus 13. One outflow pipe 15 is provided corresponding to each head block 17.

[0025] The downstream ink temperature sensors 16 detect the temperature of ink in the outflow pipes 15. The downstream ink temperature sensors 16 are provided corresponding to each outflow pipe 15. Each downstream ink temperature sensor 16 detects the ink temperature T f In order to obtain the ink temperature T f is the average value of the ink temperatures detected by each downstream ink temperature sensor 16.

[0026] The ink circulation unit 3 circulates the ink and supplies it to the head module unit 2. The ink circulation unit 3 includes a pressurized tank 21, an ink supply pipe 22, a negative pressure tank 23, an ink recovery pipe 24, an ink pump 25, an ink delivery pipe 26, an ink temperature adjustment unit 27, and an upstream ink temperature sensor 28.

[0027] The pressurized tank 21 stores the ink to be supplied to the inkjet head 11. A positive pressure is applied to the pressurized tank 21 by the pressure adjustment unit 5 to send the ink to the inkjet head 11. The pressurized tank 21 is connected to each head block 17 of the inkjet head 11 via an ink supply pipe 22, an ink bus 12, and each inlet pipe 14. An air layer is formed above the ink surface inside the pressurized tank 21. The pressurized tank 21 is disposed at a lower position (below) than the inkjet head 11.

[0028] The pressurized tank 21 is provided with a pressurized tank liquid level sensor 31. The pressurized tank liquid level sensor 31 is for detecting whether or not the liquid level of the ink in the pressurized tank 21 has reached a reference height. The pressurized tank liquid level sensor 31 outputs a signal indicating "on" when the liquid level of the ink in the pressurized tank 21 is equal to or higher than the reference height, and outputs a signal indicating "off" when the liquid level is less than the reference height.

[0029] The ink supply pipe 22 connects the pressurized tank 21 and the ink bus 12. A part of the ink supply pipe 22 is composed of a heat sink 56 and a heater pipe 58, which will be described later.

[0030] The negative pressure tank 23 receives and stores ink that has not been consumed by the inkjet head 11. A negative pressure is applied to the negative pressure tank 23 by the pressure adjustment unit 5 to collect ink from the inkjet head 11. The negative pressure tank 23 is connected to each head block 17 of the inkjet head 11 via each outflow pipe 15, the ink bus 13, and an ink collection pipe 24. The negative pressure tank 23 also stores ink that is replenished from an ink cartridge 61 of the ink supply unit 4, which will be described later. An air layer is formed above the liquid surface of the ink inside the negative pressure tank 23. The negative pressure tank 23 is disposed at the same height as the pressurized tank 21.

[0031] The negative pressure tank 23 is provided with a negative pressure tank level sensor 32. The negative pressure tank level sensor 32 is for detecting whether or not the ink level in the negative pressure tank 23 has reached a reference height. The negative pressure tank level sensor 32 outputs a signal indicating "on" when the ink level in the negative pressure tank 23 is equal to or higher than the reference height, and outputs a signal indicating "off" when the ink level is below the reference height.

[0032] The ink recovery pipe 24 connects the ink bus 13 and the negative pressure tank 23 .

[0033] The ink pump 25 sends ink from the negative pressure tank 23 to the pressurized tank 21. The ink pump 25 is provided midway along an ink sending tube 26.

[0034] The ink supply pipe 26 forms a flow path for ink to be sent from the negative pressure tank 23 to the pressurized tank 21 by the ink pump 25 .

[0035] Here, a circulation path 41 is formed by the ink supply tube 22, the ink recovery tube 24, the ink delivery tube 26, the ink baths 12 and 13, the inlet tubes 14, and the outlet tubes 15. The circulation path 41 is a path for circulating the ink among the pressurized tank 21, the inkjet head 11, and the negative pressure tank 23.

[0036] The ink supply pipe 22, the ink bus 12, and the inlet pipes 14 form an upstream path 42. The upstream path 42 is a path in the circulation path 41 that connects the pressurized tank 21 and the inkjet head 11.

[0037] The outflow pipes 15, the ink bath 13, and the ink recovery pipe 24 form a downstream path 43. The downstream path 43 is a path in the circulation path 41 that connects the inkjet head 11 and the negative pressure tank 23.

[0038] The ink temperature adjustment unit 27 adjusts the temperature of the ink in the circulation path 41 in order to maintain the ink temperature within an appropriate temperature range for printing. The ink temperature adjustment unit 27 is provided midway through the ink supply pipe 22. The ink temperature adjustment unit 27 includes a cooling unit 51 and a heating unit 52.

[0039] The cooling unit 51 includes a heat sink 56 and a cooling fan 57. The heat sink 56 cools the ink flowing therein by dissipating heat. The cooling fan 57 sends cooling air to the heat sink 56.

[0040] The heating unit 52 includes a heater pipe 58, a heater 59, and a heater temperature sensor 60. The heater pipe 58 transfers heat from the heater 59 to the ink flowing inside the heater pipe 58 to heat the ink. The heater 59 heats the heater pipe 58. The heater temperature sensor 60 detects the temperature of the heater pipe 58 heated by the heater 59.

[0041] The upstream ink temperature sensor 28 detects the ink temperature T k The upstream ink temperature sensor 28 is disposed in the vicinity of the downstream side of the ink temperature adjustment unit 27 in the ink circulation direction of the circulation path 41.

[0042] The ink supply unit 4 supplies ink to the ink circulation unit 3. The ink supply unit 4 includes an ink cartridge 61, an ink supply valve 62, and an ink supply tube 63.

[0043] The ink cartridge 61 contains ink to be used for printing by the inkjet head 11. The ink in the ink cartridge 61 is supplied to the negative pressure tank 23 of the ink circulation unit 3 via an ink supply pipe 63.

[0044] The ink supply valve 62 opens and closes the ink flow path in the ink supply pipe 63. When ink is supplied to the negative pressure tank 23, the ink supply valve 62 is opened.

[0045] The ink supply pipe 63 connects the ink cartridge 61 and the negative pressure tank 23 .

[0046] The pressure adjustment unit 5 adjusts the pressure of the pressurized tank 21 and the negative pressure tank 23 of the ink circulation unit 3. The pressure adjustment unit 5 includes a pressurized tank atmosphere release valve 71, a pressurized tank atmosphere release pipe 72, a pressurized tank pressure adjustment valve 73, a pressurized tank pressure adjustment pipe 74, a pressurized pressure sensor 75, a negative pressure tank atmosphere release valve 76, a negative pressure tank atmosphere release pipe 77, a negative pressure tank pressure adjustment valve 78, a negative pressure tank pressure adjustment pipe 79, a negative pressure sensor 80, an air pump 81, and an air pump pipe 82.

[0047] The pressurized tank atmosphere release valve 71 opens and closes the air flow path in the pressurized tank atmosphere release pipe 72 to switch the pressurized tank 21 between a sealed state (a state cut off from the atmosphere) and an atmosphere open state (a state open to the atmosphere).

[0048] The pressurized tank atmosphere release pipe 72 forms an air flow path for releasing the pressurized tank 21 to the atmosphere. One end of the pressurized tank atmosphere release pipe 72 is connected to the air space of the pressurized tank 21, and the other end is connected to the atmosphere.

[0049] The pressurized tank pressure regulating valve 73 opens and closes the air flow path in the pressurized tank pressure regulating pipe 74 in order to regulate the pressure in the pressurized tank 21 .

[0050] The pressurized tank pressure adjustment pipe 74 forms an air flow path for adjusting the pressure inside the pressurized tank 21. The pressurized tank pressure adjustment pipe 74 is made of a pipe with a higher flow resistance than the pressurized tank atmosphere release pipe 72. Specifically, the pressurized tank pressure adjustment pipe 74 is made of a pipe that is thinner than the pressurized tank atmosphere release pipe 72. One end of the pressurized tank pressure adjustment pipe 74 is connected to the air space in the pressurized tank 21, and the other end is connected to the atmosphere.

[0051] The pressurized pressure sensor 75 detects the pressure inside the pressurized tank 21 .

[0052] The negative pressure tank air release valve 76 opens and closes the air flow path in the negative pressure tank air release pipe 77 in order to switch the negative pressure tank 23 between a sealed state and an air open state.

[0053] The negative pressure tank air release pipe 77 forms an air flow path for opening the negative pressure tank 23 to the atmosphere. One end of the negative pressure tank air release pipe 77 is connected to the air space of the negative pressure tank 23, and the other end is connected to the atmosphere.

[0054] The negative pressure tank pressure regulating valve 78 opens and closes the air flow path in the negative pressure tank pressure regulating pipe 79 in order to regulate the pressure in the negative pressure tank 23 .

[0055] The negative pressure tank pressure adjustment pipe 79 forms an air flow path for adjusting the pressure inside the negative pressure tank 23. The negative pressure tank pressure adjustment pipe 79 is made of a pipe with a higher flow resistance than the negative pressure tank atmosphere release pipe 77. Specifically, the negative pressure tank pressure adjustment pipe 79 is made of a pipe that is thinner than the negative pressure tank atmosphere release pipe 77 and has a diameter similar to that of the pressurized tank pressure adjustment pipe 74. One end of the negative pressure tank pressure adjustment pipe 79 is connected to the air space of the negative pressure tank 23, and the other end is connected to the atmosphere.

[0056] The negative pressure sensor 80 detects the pressure inside the negative pressure tank 23 .

[0057] The air pump 81 generates pressure for circulating ink in the pressurized tank 21 and the negative pressure tank 23 by sending air from the negative pressure tank 23 to the pressurized tank 21. The air pump 81 is also used to adjust the pressure in the pressurized tank 21 and the negative pressure tank 23 during ink circulation.

[0058] The air pump piping 82 forms a flow path for air sent from the negative pressure tank 23 to the pressurized tank 21 by the air pump 81. One end of the air pump piping 82 is connected to the air space of the negative pressure tank 23, and the other end is connected to the air space of the pressurized tank 21.

[0059] Here, the ink circulation section 3 excluding a part of the ink supply tube 22 on the ink bus 12 side and a part of the ink recovery tube 24 on the ink bus 13 side, the ink refill section 4 and the pressure adjustment section 5 constitute a main module section 86 .

[0060] Additionally, the portions of the ink supply tube 22 of the upstream path 42 and the ink recovery tube 24 of the downstream path 43 between the main body module portion 86 and the head module portion 2 are defined as an ink path exposed portion 87. The ink path exposed portion 87 is a portion where the temperature of the ink flowing inside the ink supply tube 22 and the ink recovery tube 24 is easily affected by the environmental temperature (room temperature), which is the temperature of the environment in which the inkjet printing device 1 is installed.

[0061] The environmental temperature sensor 6 detects the environmental temperature T a Detect.

[0062] The control unit 7 controls the operation of each unit of the inkjet printing apparatus 1. The control unit 7 includes a CPU, a RAM, a ROM, a hard disk, and the like.

[0063] The control unit 7 stores a pressure table 91 shown in FIG. 3. The pressure table 91 is a table of the ink temperature T k , the ink temperature T f , environmental temperature T a , the pressure P of the pressure tank 21 k , and the pressure P of the negative pressure tank 23 f This is a table that associates the above.

[0064] As described above, the ink temperature T k is the temperature of the ink detected by the upstream ink temperature sensor 28. Also, the ink temperature T f is the average value of the ink temperatures detected by each downstream ink temperature sensor 16.

[0065] Pressure P in Pressure Table 91 k ,P f The value of is the ink temperature T k,T f , and the environmental temperature T a While maintaining the ink circulation flow rate Q in the circulation path 41 within a predetermined flow rate range according to the combination of n This is a value for maintaining the pressure P in the stable discharge range (corresponding to the predetermined pressure range). k ,P f The value of was calculated in advance. Here, the nozzle pressure P n The stable ejection range of the nozzle 18 is the nozzle pressure P n The predetermined flow rate range is a range of an appropriate ink circulation flow rate during ink circulation (printing).

[0066] During the printing operation, the control unit 7 controls the ink temperature T k ,T f and the environmental temperature T a Based on this, the pressure table 91 is referenced, and the nozzle pressure P is increased while the circulation flow rate Q is maintained within a predetermined flow rate range. n The pressure P of the pressurized tank 21 and the negative pressure tank 23 is set to be within a stable discharge range. k ,P f The pressure adjusting unit 5 is controlled to adjust the pressure.

[0067] Next, the pressure P in the pressure table 91 k ,P f The details of the value are explained below.

[0068] Nozzle pressure P of the inkjet head 11 n is expressed by the following equation (1).

[0069] P n =(ΛP k +P f ) / (Λ+1)+P H …(1) Here, P H is the head pressure of the inkjet head 11. Also, Λ is the flow path resistance ratio between the upstream path 42 and the downstream path 43. From the formula (1), the nozzle pressure P nIt can be seen that changes depending on the flow path resistance ratio Λ. In this embodiment, the height position of the inkjet head 11 (height difference between the inkjet head 11 and the pressure tank 21 and the negative pressure tank 23) is fixed, and the head pressure P H is a fixed value.

[0070] The flow resistance of the upstream path 42 is R k , the flow resistance of the downstream path 43 is R f Then, the flow path resistance ratio Λ is expressed by the following equation (2).

[0071] Λ=R f / R k …(2) In addition, the flow resistance of the upstream path 42 is R k , the flow resistance of the downstream path 43 is R f are expressed by the following equations (3) and (4), respectively.

[0072] R k =R ik +R k0 +R k1 …(3) R f =R if +R f0 +R f1 …(4) Here, as shown in Figure 4, R ik is the flow path resistance of the portion of the upstream path 42 that is included in the ink path exposed portion 87. k0 is the flow path resistance of the upstream path 42 in the main module section 86. k1 is the flow path resistance of the upstream path 42 in the head module unit 2. if is the flow path resistance of the downstream path 43 included in the ink path exposed portion 87. f0 is the flow resistance of the downstream path 43 in the main module section 86. f1 is the flow path resistance of the portion of the downstream path 43 inside the head module unit 2.

[0073] The circulating flow rate Q of the ink in the circulation path 41 is expressed by the following formula (5).

[0074] Q=(P k -P f ) / (R k +R f ) …(5) Generally, the flow path resistance R of an ink flow path is expressed by the following formula (6).

[0075] R=128Lμ / πD 4 …(6) Here, L is the flow path length, D is the flow path diameter, and μ is the ink viscosity. The ink viscosity μ is expressed by the following formula (7).

[0076] μ = α exp(β / T) …(7) Here, α and β are constants depending on the physical properties of the ink, and T is the temperature of the ink.

[0077] From equations (6) and (7), when the temperature T of the ink flowing through the flow path changes, the flow path resistance R changes. In other words, the higher the ink temperature T, the lower the ink viscosity μ and the smaller the flow path resistance R. Therefore, the flow path resistance R of the above-mentioned upstream path 42 k and the flow resistance R of the downstream path 43 f varies depending on the average temperature of the ink flowing through each path.

[0078] 5 to 8 show examples of changes in the temperature of the ink along the path through which the ink flows from the pressurized tank 21 to the negative pressure tank 23. In the examples of Fig. 5 to Fig. 8, the temperature of the ink is higher than the environmental temperature.

[0079] FIG. 5 shows the change in ink temperature when the ink is heated by the heater 52 in a case where the exposed ink path portion 87 is configured to be relatively long.

[0080] 5, the ink flowing through the upstream path 42 is heated by the heating unit 52, and then is affected by the environmental temperature for a relatively long period of time in the ink path exposed portion 87, and is cooled before reaching the inkjet head 11. Similarly, in the downstream path 43, the ink is cooled by the environmental temperature in the ink path exposed portion 87. For this reason, a relatively large difference occurs between the average temperature of the ink flowing through the upstream path 42 and the average temperature of the ink flowing through the downstream path 43.

[0081] FIG. 6 shows the change in ink temperature when the ink path exposed portion 87 is configured to be relatively long and the ink is cooled by the cooling portion 51. In FIG.

[0082] 6, the ink flowing through the upstream path 42 is cooled by the cooling unit 51, and then is exposed to the environmental temperature for a relatively long period of time in the exposed ink path portion 87, thereby being further cooled before reaching the inkjet head 11. The cooled ink is warmed in the inkjet head 11 by heat generated when the inkjet head 11 is driven. The ink warmed in the inkjet head 11 is cooled by the environmental temperature in the exposed ink path portion 87 in the downstream path 43. In the example of FIG. 6, the difference between the average temperature of the ink flowing through the upstream path 42 and the average temperature of the ink flowing through the downstream path 43 is smaller than in the example of FIG. 5.

[0083] FIG. 7 shows the change in ink temperature when the ink is heated by the heater 52 in a case where the ink path exposed portion 87 is configured to be relatively short.

[0084] 7, as in the example of Fig. 5, the ink flowing through the upstream path 42 and the ink flowing through the downstream path 43 are cooled in the ink path exposed portion 87. However, in the example of Fig. 7, since the ink path exposed portion 87 is relatively short, the degree of decrease in the ink temperature is relatively small. Therefore, the difference between the average temperature of the ink flowing through the upstream path 42 and the average temperature of the ink flowing through the downstream path 43 is relatively small.

[0085] FIG. 8 shows the change in ink temperature when the ink path exposed portion 87 is configured to be relatively short and the ink is cooled by the cooling portion 51.

[0086] In the example of Fig. 8, similarly to the example of Fig. 6, the ink heated in the inkjet head 11 is cooled by the influence of the environmental temperature at the exposed ink path portion 87 of the downstream path 43. However, in the example of Fig. 8, the exposed ink path portion 87 is relatively short, so the degree of drop in the ink temperature is relatively small. In the example of Fig. 8, the difference between the average temperature of the ink flowing in the upstream path 42 and the average temperature of the ink flowing in the downstream path 43 is large compared to the example of Fig. 7. This temperature difference is likely to become larger as the amount of heat generated by the inkjet head 11 (print rate) increases.

[0087] In this way, even if the ink path exposed portion 87 is relatively long, as in the examples of Figures 5 and 6, or relatively short, as in the examples of Figures 7 and 8, the difference between the average temperature of the ink flowing through the upstream path 42 and the average temperature of the ink flowing through the downstream path 43 may change.

[0088] As described above, the flow resistance R of the upstream path 42 k and the flow resistance R of the downstream path 43 f changes according to the average temperature of the ink flowing through each path. Therefore, the flow path resistance ratio Λ changes according to the change in the difference between the average temperature of the ink flowing through the upstream path 42 and the average temperature of the ink flowing through the downstream path 43.

[0089] In contrast, the average temperature of the ink flowing through the upstream path 42 is the ink temperature T k and the environmental temperature T a The average temperature of the ink flowing through the downstream path 43 can be predicted from the ink temperature T f and the environmental temperature T a Therefore, the flow resistance R k ,R f and the flow path resistance ratio Λ is the ink temperature Tk ,T f and can be calculated from the environmental temperature Ta.

[0090] In addition, from the formula (1), the pressure P of the pressurized tank 21 and the negative pressure tank 23 changes according to the change in the flow path resistance ratio Λ. k ,P f By adjusting the nozzle pressure P n It is possible to maintain the ink within a stable ejection range.

[0091] Furthermore, from equation (5), the flow resistance R k ,R f In response to the change in k ,P f By adjusting the flow rate Q, it is possible to maintain the circulation flow rate Q within a predetermined flow rate range.

[0092] Therefore, the ink temperature T k ,T f , and the environmental temperature T a Based on this, the circulation flow rate Q is maintained within a predetermined flow rate range, while the nozzle pressure P n Pressure P that can maintain within the stable discharge range k ,P f can be sought.

[0093] Therefore, in this embodiment, the ink temperature T k ,T f , and the environmental temperature T a For each combination, the nozzle pressure P n Adjustment pressure P that can maintain the discharge within the stable range k ,P f The values ​​are calculated in advance and stored in the pressure table 91.

[0094] Next, the operation of the inkjet printing apparatus 1 will be described.

[0095] When a print job is input, the control unit 7 causes the pressure adjustment unit 5 to generate the respective set pressures for circulating ink in the pressurized tank 21 and the negative pressure tank 23. The set pressure of the pressurized tank 21 is a positive pressure, and the set pressure of the negative pressure tank 23 is a negative pressure.

[0096] Specifically, first, the control unit 7 closes the pressurized tank atmosphere release valve 71 and the negative pressure tank atmosphere release valve 76. Here, during standby when the inkjet printing device 1 is not in operation, the pressurized tank atmosphere release valve 71 and the negative pressure tank atmosphere release valve 76 are open, and the pressurized tank pressure adjustment valve 73 and the negative pressure tank pressure adjustment valve 78 are closed.

[0097] Next, the control unit 7 starts driving the air pump 81. As a result, positive pressure and negative pressure start to be generated in the pressurized tank 21 and the negative pressure tank 23, respectively.

[0098] This starts the ink circulation in the ink circulation unit 3, and the ink flows from the pressurized tank 21 through the inkjet head 11 to the negative pressure tank 23.

[0099] Thereafter, the control unit 7 controls the opening and closing of the pressurized tank pressure regulating valve 73 and the negative pressure tank pressure regulating valve 78 based on the detection values ​​of the pressurized pressure sensor 75 and the negative pressure sensor 80. When the set pressures are generated in the pressurized tank 21 and the negative pressure tank 23, respectively, the control unit 7 stops the air pump 81.

[0100] Next, the control unit 7 starts executing the print job. Specifically, the control unit 7 causes the inkjet head 11 to eject ink to print an image on the print medium based on the print job.

[0101] During execution of a print job, ink is supplied from the pressurized tank 21 to the inkjet head 11, and ink not consumed by the inkjet head 11 is collected in the negative pressure tank 23. When the pressurized tank liquid level sensor 31 is off and the negative pressure tank liquid level sensor 32 is on, the control unit 7 drives the ink pump 25. This sends ink from the negative pressure tank 23 to the pressurized tank 21. When the pressurized tank 21 is turned on, the control unit 7 stops the ink pump 25. In this manner, printing is performed while the ink is circulated.

[0102] Furthermore, when both the pressurized tank liquid level sensor 31 and the negative pressure tank liquid level sensor 32 are turned off, the control unit 7 opens the ink supply valve 62. This causes ink to be supplied from the ink cartridge 61 to the negative pressure tank 23. When the negative pressure tank liquid level sensor 32 is turned on, the control unit 7 closes the ink supply valve 62.

[0103] Furthermore, during a printing operation, the control unit 7 controls the ink temperature adjustment unit 27 to adjust the temperature of the ink supplied to the inkjet head 11 so that the temperature of the ink is maintained within an appropriate temperature range.

[0104] During the printing operation, the control unit 7 detects the ink temperature T k , and the environmental temperature T detected by the environmental temperature sensor 6 a The control unit 7 also monitors the detection values ​​of the downstream ink temperature sensors 16, and calculates the ink temperature T f is calculated.

[0105] Then, the control unit 7 determines the ink temperature T k ,T f and the environmental temperature T a Based on this, the pressure table 91 is referred to and the pressure P of the pressurized tank 21 and the negative pressure tank 23 is calculated. k ,P f The pressure adjusting unit 5 is controlled to adjust the pressure.

[0106] Specifically, the control unit 7 controls the ink temperature T k ,T f , and the environmental temperature T a Pressure P according to the combination of k ,P f The control unit 7 obtains the pressure P of the pressurized tank 21 and the negative pressure tank 23 from the pressure table 91. k ,P f The air pump 81, the pressurized tank pressure regulating valve 73, and the negative pressure tank pressure regulating valve 78 are controlled so that the pressure Vp becomes the value obtained from the pressure table 91.

[0107] By controlling the pressure adjustment unit 5 in this manner, the circulating flow rate Q of the ink in the circulation path 41 is maintained within a predetermined flow rate range, and the nozzle pressure P n is maintained within the stable discharge range.

[0108] When printing based on the print job is completed, the control unit 7 controls the pressure adjustment unit 5 to end the ink circulation in the ink circulation unit 3. Specifically, the control unit 7 stops the air pump 81 and closes the pressurized tank pressure adjustment valve 73 and the negative pressure tank pressure adjustment valve 78. Next, the control unit 7 opens the pressurized tank atmosphere release valve 71 and the negative pressure tank atmosphere release valve 76. This completes the series of operations.

[0109] As described above, in the inkjet printing apparatus 1, the control unit 7 controls the ink temperature T k , the ink temperature T f , and the environmental temperature T a Based on this, the circulation flow rate Q is maintained within a predetermined flow rate range, while the nozzle pressure P n The pressure P of the pressurized tank 21 and the negative pressure tank 23 is set to be within a stable discharge range. k ,P f The pressure adjusting unit 5 is controlled to adjust the pressure.

[0110] As a result, even if the flow path resistance ratio Λ changes due to a change in the temperature (average temperature) of the ink flowing through each of the upstream path 42 and the downstream path 43, the pressure P k ,P f By adjusting the nozzle pressure P n As a result, the nozzle pressure P n Since the ink is prevented from falling out of the stable ejection range and the circulation flow rate Q is prevented from becoming insufficient, deterioration in print image quality can be reduced.

[0111] In the above embodiment, the nozzle pressure P n The pressure P of the pressurized tank 21 and the negative pressure tank 23 is set to be within a stable discharge range. k ,P f However, the condition for maintaining the circulation flow rate Q within a predetermined range may be omitted. Even in this case, the nozzle pressure P n Since it is possible to reduce deviation from the stable ejection range, deterioration of print image quality can be reduced.

[0112] Here, if the condition for maintaining the circulation flow rate Q within the predetermined flow rate range is omitted, the circulation flow rate Q will be smaller than the lower limit of the predetermined flow rate range, and the time it takes for the ink to pass through the ink path exposed portion 87 may become longer. In this case, the effect of the environmental temperature on the ink temperature will be greater than expected, and the previously obtained adjustment pressure P k ,P f In response to this, the value of the nozzle pressure P can be adjusted by maintaining the circulation flow rate Q within a specified flow rate range. n It is possible to further prevent the ink from straying from the stable ejection range.

[0113] In the above embodiment, the ink temperature T k ,T f , and the environmental temperature T detected by the environmental temperature sensor 6 a Based on this, the pressure P of the pressurized tank 21 and the negative pressure tank 23 k ,P fHowever, this pressure P k ,P f From the conditions used for adjusting the environmental temperature T a may be omitted.

[0114] In this case, for example, the ink temperature T k ,T f Pressure P according to k ,P f The value of is stored in a table, and the ink temperature T k ,T f Based on this, the circulation flow rate Q is maintained within a predetermined flow rate range, while the nozzle pressure P n The pressure P of the pressurized tank 21 and the negative pressure tank 23 is set to be within a stable discharge range. k ,P f In this case, the condition for maintaining the circulation flow rate Q within a predetermined flow rate range may be omitted. n Since it is possible to reduce deviation from the stable ejection range, deterioration of print image quality can be reduced.

[0115] In the above embodiment, the pressure table 91 is used to calculate the pressure P k ,P f However, the control unit 7 adjusts the ink temperature T k ,T f and the environmental temperature T a Based on this, the circulation flow rate Q is maintained within a predetermined flow rate range, while the nozzle pressure P n Pressure P that can maintain within the stable discharge range k ,P f The value of is calculated, and the pressure P k ,P f In this case, the condition for maintaining the circulation flow rate Q within a predetermined flow rate range may be omitted. k ,P f From the conditions used for adjusting the temperature T a may be omitted.

[0116] In the above embodiment, the height position of the inkjet head 11 is fixed, and the head pressure P H However, the height position of the inkjet head 11 may be configured to be changeable.

[0117] In this case, the head pressure P H When changes occur, from equation (1), the nozzle pressure P n Therefore, in this case, the control unit 7 changes the ink temperature T k ,T f and the environmental temperature T a In addition, the nozzle pressure P is adjusted based on the height position of the inkjet head 11 while maintaining the circulation flow rate Q within a predetermined flow rate range. n The pressure P of the pressurized tank 21 and the negative pressure tank 23 is set to be within a stable discharge range. k ,P f The pressure adjusting unit 5 may be controlled to adjust the pressure.

[0118] In this case, for example, a table such as the pressure table 91 in FIG. 3 is prepared for each height position of the inkjet head 11, and the pressure P k ,P f Instead of using a table, the pressure P can be calculated. k ,P f In this case, the pressure P k ,P f From the conditions used for adjusting the temperature T a may be omitted.

[0119] As described above, the pressure P k ,P f By adjusting this, it is possible to accommodate a configuration in which the height position of the inkjet head 11 can be changed, thereby increasing the degree of freedom in arranging the inkjet head 11.

[0120] In the above embodiment, the ink temperature T k ,T f , and the environmental temperature T a Based on this, the circulation flow rate Q is maintained within a predetermined flow rate range, while the nozzle pressure P n The pressure P of the pressurized tank 21 and the negative pressure tank 23 is set to be within a stable discharge range. k ,P f However, the pressure P of the pressurized tank 21 and the negative pressure tank 23 k ,P f Instead of adjusting the flow resistance R k and the flow resistance R of the downstream path 43 f may be adjusted.

[0121] Here, from equations (1) and (2), the flow resistance R k ,R f By adjusting the flow resistance ratio Λ, the nozzle pressure P n Also, from equation (5), the flow resistance R k ,R f By adjusting the amount of circulation, the circulation flow rate Q can be adjusted.

[0122] For example, by providing a mechanism for adjusting the flow path resistance in each of the ink supply pipe 22 of the upstream path 42 and the ink recovery pipe 24 of the downstream path 43, the flow path resistance R k ,R f As a mechanism for adjusting the flow path resistance, for example, an adjustment valve for adjusting the cross-sectional area of ​​the flow path can be used.

[0123] The present invention is not limited to the above-described embodiment, and the components can be modified and embodied in the implementation stage without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining the multiple components disclosed in the above-described embodiment. For example, some components may be deleted from all the components shown in the embodiment.

[0124] [Note] This application discloses the following inventions.

[0125] (Appendix 1) an inkjet head having nozzles for ejecting ink; a pressure tank and a negative pressure tank connected to the inkjet head; a circulation path for circulating ink among the pressurized tank, the inkjet head, and the negative pressure tank; a pressure adjusting unit that adjusts the pressure of the pressurized tank and the negative pressure tank; A control unit that controls the pressure adjustment unit, an inkjet printing device characterized in that the control unit controls the pressure adjustment unit to adjust the pressure of the pressurized tank and the negative pressure tank so as to maintain the nozzle pressure of the inkjet head within a predetermined pressure range, based on the temperature of the ink in the path connecting the pressurized tank and the inkjet head of the circulation path, and the temperature of the ink in the path connecting the inkjet head and the negative pressure tank.

[0126] (Appendix 2) The inkjet printing apparatus of claim 1, wherein the control unit controls the pressure adjustment unit to adjust the pressure of the pressurized tank and the negative pressure tank so as to maintain the nozzle pressure of the inkjet head within the specified pressure range, further based on an environmental temperature.

[0127] (Appendix 3) The inkjet head is capable of changing its height position, 3. The inkjet printing apparatus according to claim 1, wherein the control unit controls the pressure adjustment unit to adjust the pressure of the pressurized tank and the negative pressure tank in accordance with a height position of the inkjet head so as to maintain the nozzle pressure of the inkjet head within the predetermined pressure range.

[0128] (Appendix 4) The inkjet printing device described in any one of Appendices 1 to 3, characterized in that the control unit controls the pressure adjustment unit to adjust the pressure of the pressurized tank and the negative pressure tank so as to maintain the circulation flow rate of ink in the circulation path within a predetermined flow rate range. [Explanation of symbols]

[0129] 1 Inkjet printing device 2 Head module 3 Ink Circulation Section 4 Ink supply unit 5 Pressure adjustment section 6. Environmental Temperature Sensor 7 Control section 11 Inkjet head 12,13 Inkbus 14 Inflow pipe 15 Outflow pipe 16 Downstream ink temperature sensor 17 Head Block 17a Nozzle surface 18 Nozzles 21 Pressurized Tank 22 Ink supply pipe 23 Negative Pressure Tank 24 Ink recovery pipe 25 Ink Pump 26 Ink delivery tube 27 Ink temperature adjustment unit 28 Upstream ink temperature sensor 41 Circulation Route 42 Upstream route 43 Downstream Route 51 Cooling section 52 Heating section 71 Pressure tank atmospheric release valve 72 Pressure tank atmospheric release pipe 73 Pressurized tank pressure regulator 74 Pressure tank pressure adjustment pipe 75 Pressurized pressure sensor 76 Negative pressure tank atmospheric release valve 77 Negative pressure tank atmospheric release pipe 78 Negative pressure tank pressure regulator 79 Negative pressure tank pressure adjustment pipe 80 Negative pressure sensor 81 Air Pump 82 Air pump piping 86 Main module section 87 Exposed ink path 91 Pressure Table

Claims

1. an inkjet head having nozzles for ejecting ink; a pressure tank and a negative pressure tank connected to the inkjet head; a circulation path for circulating ink among the pressurized tank, the inkjet head, and the negative pressure tank; a pressure adjusting unit that adjusts the pressure of the pressurized tank and the negative pressure tank; A control unit that controls the pressure adjustment unit, an inkjet printing device characterized in that the control unit controls the pressure adjustment unit to adjust the pressure of the pressurized tank and the negative pressure tank so as to maintain the nozzle pressure of the inkjet head within a predetermined pressure range, based on the temperature of the ink in the path connecting the pressurized tank and the inkjet head of the circulation path, and the temperature of the ink in the path connecting the inkjet head and the negative pressure tank.

2. 2. The inkjet printing apparatus according to claim 1, wherein the control unit controls the pressure adjustment unit to adjust the pressure of the pressurized tank and the negative pressure tank so as to maintain the nozzle pressure of the inkjet head within the predetermined pressure range, further based on an environmental temperature.

3. The inkjet head is capable of changing its height position, 3. The inkjet printing apparatus according to claim 1, wherein the control unit controls the pressure adjustment unit to adjust the pressure of the pressurized tank and the negative pressure tank so as to maintain the nozzle pressure of the inkjet head within the predetermined pressure range in accordance with a height position of the inkjet head.

4. 3. The inkjet printing apparatus according to claim 1, wherein the control unit controls the pressure adjustment unit to adjust the pressure of the pressurized tank and the negative pressure tank so as to maintain a circulation flow rate of the ink in the circulation path within a predetermined flow rate range.

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