Printing apparatus

Abstract

To appropriately adjust the pressure within a storage part of ink in a printing device that performs ink jet type printing.SOLUTION: A printing device 100 includes an ink jet head 102, an ink circulation path 110, a pressure adjustment unit 112, and a control unit 120. The ink circulation path 110 includes an upstream storage part and a downstream storage part. Before the printing device is brought into a stopped state, the control unit 120 determines a stop duration being the time in which the stopped state is continued on the basis of the change in the position of a liquid surface of ink in the upstream storage part and the downstream storage part. The control unit 120 transitions the printing device 100 into the stopped state in a state where the pressure in the upstream storage part and the pressure in the downstream storage part are equalized, returns the printing device 100 from the stopped state according to the elapse of the stop duration, and then transitions the printing device 100 into the stopped state again.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a printing apparatus and a method for controlling a printing apparatus. [Background technology]

[0002] In recent years, printing devices that perform printing using an inkjet method have come into widespread use. In addition, a configuration that uses a subtank that stores ink near an inkjet head is known as a configuration of a printing device that performs printing using an inkjet method (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-226625 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a printing device that performs printing using an inkjet system, when ink is stored in an ink storage unit such as a subtank, the pressure in the ink storage unit may be adjusted to adjust the pressure of the ink supplied to the inkjet head. In such cases, it is desirable to adjust the pressure in the ink storage unit more appropriately, for example. Therefore, an object of the present invention is to provide a printing device and a control method for a printing device that can solve the above problems. [Means for solving the problem]

[0005] The inventor of the present application has conducted intensive research into a method for more appropriately adjusting the pressure in an ink storage unit, such as a subtank, in a printing device that prints using an inkjet method, in a configuration in which ink is stored using an ink storage unit such as a subtank. More specifically, the inventor of the present application has conducted intensive research into a method for more appropriately adjusting the pressure in an ink storage unit when the printing device transitions to a stopped state in which power consumption is reduced by stopping some of the functions of the printing device, in a configuration in which ink is circulated through an inkjet head and ink storage units are used that store ink on the upstream and downstream sides of the inkjet head. In this case, for example, it is conceivable to adjust the pressure in the ink storage units on the upstream and downstream sides of the inkjet head to equal pressures (e.g., equal pressures of a predetermined negative pressure) when transitioning to the stopped state so that ink is not circulated in the stopped state. In addition, after transitioning to the stopped state, it is conceivable to periodically return the printing device from the stopped state and readjust (reset) the pressure in the ink storage unit. With this configuration, the printing device can be appropriately stopped during periods when the printing device is not being used, such as at night or on holidays.

[0006] However, in such a printing device, a pressure difference may occur between the upstream ink storage unit and the downstream ink storage unit during the stop state due to, for example, a slight air leak (air leak) in the ink storage unit or the air flow path. As a result, for example, a difference in the position of the ink liquid surface between the upstream and downstream ink storage units may occur, and overflow may occur in which ink leaks from one of the ink storage units. In this case, problems such as backflow of ink and dripping of ink from the inkjet head may occur. In response to this, the inventor of the present application has considered determining the stop duration, which is the time for which the stop state is to continue, before the printing device is stopped. In addition, in this case, the inventor has considered detecting a change in the position of the ink liquid surface in the upstream and downstream ink storage units under a predetermined condition, and determining the stop duration based on the detection result. With this configuration, for example, the stop duration can be appropriately determined according to the state of air leak, which differs for each individual printing device. In this case, for example, after the printing device transitions to a stopped state, the printing device may be temporarily resumed when the stop duration has elapsed, and the pressure in the ink storage section may be readjusted. With this configuration, the pressure in the ink storage section may be appropriately readjusted before a problem such as an overflow occurs.

[0007] Furthermore, the inventors of the present application have conducted further intensive research and have found the characteristics necessary to obtain such effects, which led to the present invention. In order to solve the above-mentioned problems, the present invention provides a printing device that performs printing by an inkjet system, the printing device including an inkjet head that ejects ink by an inkjet system, an ink circulation flow path that is an ink flow path that circulates ink along a path that passes through the inkjet head and has a plurality of ink storage sections that store ink, a pressure adjustment section that adjusts the pressure applied to the ink storage sections in the ink circulation flow path, and a control section that controls at least the operation of the pressure adjustment section, the ink circulation flow path including an upstream storage section that is the ink storage section that stores ink at a position that is upstream of the inkjet head when circulating ink in the ink circulation flow path, a downstream storage section that is the ink storage section that stores ink at a position that is downstream of the inkjet head when circulating, a head passing flow path that is a flow path that flows ink from the upstream storage section to the downstream storage section via the inkjet head, a head non-passing flow path that is a flow path that flows ink from the downstream storage section to the upstream storage section without passing through the inkjet head, and a control section that controls the operation of the head. and an ink pump which is a pump for causing ink to flow into a head non-passage flow path, the pressure adjustment unit having an upstream pressure generating unit which generates a pressure to be transmitted to the upstream storage unit, a downstream pressure generating unit which generates a pressure to be transmitted to the downstream storage unit, an upstream valve which opens and closes an air flow path between the upstream pressure generating unit and the upstream storage unit, and a downstream valve which opens and closes an air flow path between the downstream pressure generating unit and the downstream storage unit, and during the circulation, the control unit controls the pressure adjustment unit to control the upstream pressure generating unit to generate the downstream pressure by opening the upstream valve and the downstream valve while generating a pressure higher than that of the force generating unit, the pressure in the upstream storage unit is made higher than the pressure in the downstream storage unit, causing ink to flow through the head passing flow path, and the printing device is capable of transitioning to a stopped state in which power consumption is reduced by stopping some of its functions, and before the printing device transitions to the stopped state, the control unit determines a stop duration, which is the time for which the stopped state is to continue, based on a change in the position of the ink liquid surface in the upstream storage unit and the downstream storage unit,At the time of transition to the stopped state, the control unit causes the pressure adjustment unit to close the upstream valve and the downstream valve while making the pressure in the upstream reservoir equal to the pressure in the downstream reservoir, and after the printing device has entered the stopped state, the control unit returns the printing device from the stopped state in accordance with the lapse of the stop duration, causes the pressure adjustment unit to open at least one of the upstream valve and the downstream valve, and then causes the upstream valve and the downstream valve to close again, thereby transitioning the printing device to the stopped state.

[0008] In this configuration, for example, the stop duration can be determined based on the change in the position of the ink level in the upstream storage section and the downstream storage section, so that the stop duration can be more appropriately determined according to the state of the printing device. This also makes it possible to more appropriately prevent, for example, the occurrence of ink overflow in the upstream storage section or the downstream storage section while the printing device is in a stopped state. Therefore, with this configuration, for example, the pressure in the upstream storage section or the downstream storage section, which is the ink storage section, can be appropriately adjusted. In this configuration, the printing device may further include, for example, a carriage that holds the inkjet head. In this case, the carriage holds, for example, the upstream storage section and the downstream storage section together with the inkjet head. With this configuration, for example, the upstream storage section and the downstream storage section can be appropriately disposed near the inkjet head.

[0009] In this configuration, at the timing of returning from the stopped state according to the lapse of the stop duration, the control unit, for example, generates a predetermined pressure in at least one of the upstream pressure generating unit and the upstream pressure generating unit, and opens at least one of the upstream valve and the downstream valve in the pressure adjusting unit, thereby readjusting (resetting) the pressure in at least one of the upstream storage unit and the downstream storage unit. After that, the control unit again transitions the printing device to the stopped state, for example, as described above. The operation of such a printing device can be considered as an intermittent operation operation in which the stopped state and the return are repeated, for example, by periodically returning from the stopped state and adjusting the pressure. In addition, during printing, the printing device circulates ink in, for example, the ink circulation flow path. In this case, the control unit, for example, as described above, makes the pressure in the upstream storage unit higher than the pressure in the downstream storage unit, and flows the ink in the head passing flow path. In this case, it is considered that the pressure in the upstream storage unit and the downstream storage unit is set to a negative pressure, which is a pressure lower than the atmospheric pressure, for example. In this case, regarding such pressure control, for example, in the negative pressure control, it can be considered that the pressure in the upstream storage section is set to a negative pressure closer to atmospheric pressure than the pressure in the downstream storage section. Also, when transitioning to the stopped state, the control section, for example, as described above, equalizes the pressure in the upstream storage section and the pressure in the downstream storage section. In this case, it can be considered that the printing device starts intermittent operation by, for example, equalizing the pressure in the upstream storage section and the pressure in the downstream storage section. In this case, it can be considered that by determining the stop duration as described above, for example, it is possible to more appropriately prevent the occurrence of problems that are unlikely to occur in a state in which ink is circulated with a difference between the pressure in the upstream storage section and the pressure in the downstream storage section, and that are likely to occur in a state in which the pressure in the upstream storage section and the pressure in the downstream storage section are equalized in advance and maintained.

[0010] In addition, in this configuration, the printing device may further include a liquid level sensor that detects the position of the ink level in the upstream storage section and the downstream storage section. In this case, the control unit detects a change in the position of the ink level based on, for example, the output of the liquid level sensor. With this configuration, for example, the position of the ink level in the upstream storage section and the downstream storage section can be appropriately detected. In addition, when such a liquid level sensor is used, the control unit may detect, for example, the position of the ink level in the upstream storage section and the downstream storage section at the timing when the printing device returns from the stopped state according to the lapse of the stop duration. In addition, in this case, it is also possible to circulate the ink based on the result of this detection, for example, as necessary. With this configuration, for example, even if the ink level rises excessively in either the upstream storage section or the downstream storage section during the continued stopped state, the position of the ink level can be optimized by circulating the ink. More specifically, when the ink level in either the upstream storage unit or the downstream storage unit is higher than a preset reference level when the printing device returns from a stopped state, the control unit adjusts the ink level in the upstream storage unit and the downstream storage unit, for example, by opening the upstream valve and the downstream valve to the pressure adjustment unit and circulating the ink in the ink circulation flow path. In this case, the control unit then closes the upstream valve and the downstream valve to transition the printing device to a stopped state. When the ink level in either the upstream storage unit or the downstream storage unit is below the reference level when the printing device returns from a stopped state, the control unit then closes the upstream valve and the downstream valve to transition the printing device to a stopped state. With this configuration, for example, ink can be circulated as necessary when the printing device returns from a stopped state.This also makes it possible to more appropriately prevent ink overflow in the upstream storage section or the downstream storage section, for example, even if the ink level rises significantly in either the upstream storage section or the downstream storage section while the stopped state continues.

[0011] In addition, in this configuration, the operation of determining the stop duration can be considered to be, for example, an operation performed before the printing device is shifted to a stopped state (an operation performed in advance). When determining the stop duration, the control unit, for example, causes the pressure adjustment unit to close the upstream valve and the downstream valve while making the pressure in the upstream storage unit different from the pressure in the downstream storage unit. Then, the control unit determines the stop duration based on, for example, a change in the position of the ink level in the upstream storage unit and the downstream storage unit that occurs thereafter. In this configuration, by intentionally creating a pressure difference in the upstream storage unit and the downstream storage unit, for example, when a difference in the position of the ink level occurs thereafter due to the influence of an air leak or the like, the change in the position of the ink level can be caused in a shorter time. In addition, this, for example, shortens the required measurement time and allows the stop duration to be determined in a shorter time. In determining the stop duration in this way, making the pressure in the upstream storage unit different from the pressure in the downstream storage unit can also be considered to correspond to, for example, accelerating the required measurement. In this case, it is preferable that the control unit detects the change in the ink level by, for example, increasing the pressure in the upstream storage unit and the downstream storage unit. More specifically, in this case, the control unit determines the stop duration based on the change in the ink level in the upstream storage unit and the downstream storage unit that occurs when the upstream valve and the downstream valve are closed with the pressure in the upstream storage unit higher than the pressure in the downstream storage unit, and the change in the ink level in the upstream storage unit and the downstream storage unit that occurs when the upstream valve and the downstream valve are closed with the pressure in the upstream storage unit lower than the pressure in the downstream storage unit. With this configuration, the stop duration can be determined more appropriately, for example, when determining the stop duration based on the change in the ink level detected by applying a pressure difference. Depending on the configuration of the printing device and the conditions required when determining the duration of the stop, the duration of the stop may be determined based on, for example, a change in the position of the ink level detected when the pressure in the upstream storage section and the pressure in the downstream storage section are made equal. Even in such a configuration, the duration of the stop can be appropriately determined, for example.

[0012] Also, in this configuration, the printing device transitions to a stopped state in response to, for example, a user's instruction. In this case, the printing device receives the user's instruction, for example, through the user's operation on the operation unit of the printing device or a computer that controls the printing device. Also, when the printing device receives an instruction from the user to transition the printing device to a stopped state, the control unit executes a process for determining the duration of the stop as a process to be performed before the printing device transitions to the stopped state in response to the user's instruction. With this configuration, for example, the duration of the stop can be appropriately determined before the printing device transitions to the stopped state. Also, in this configuration, the printing device may include, for example, a plurality of inkjet heads and a plurality of ink circulation channels corresponding to the plurality of inkjet heads. In this case, in the pressure adjustment unit, the upstream pressure generation unit generates, for example, a pressure to be transmitted to an upstream storage unit in the plurality of ink circulation channels. Also, the downstream pressure generation unit generates, for example, a pressure to be transmitted to a downstream storage unit in the plurality of ink circulation channels. With this configuration, for example, pressure adjustment can be appropriately performed using a configuration commonly arranged for a plurality of inkjet heads and a plurality of ink circulation channels.

[0013] In addition, in the printing device, for example, in a state other than the stopped state, it is also conceivable to equalize the pressure in the upstream storage section and the pressure in the downstream storage section. For example, when performing maintenance on the inkjet head using a liquid such as a cleaning liquid during a printing operation, it is conceivable to equalize the pressure in the upstream storage section and the pressure in the downstream storage section to stop the circulation of ink in order to prevent the liquid from being drawn from the nozzles of the inkjet head. In such a case, it is preferable to appropriately adjust the pressure in the upstream storage section and the downstream storage section. More specifically, in this case, the printing device further includes a maintenance section that performs maintenance on the inkjet head by bringing a liquid into contact with the nozzle surface, which is the surface on which the nozzles are formed in the inkjet head. Then, during maintenance in which the maintenance section performs maintenance, the control section equalizes the pressure in the upstream storage section and the downstream storage section, for example, by generating a pressure lower than atmospheric pressure and the same pressure in the upstream pressure generating section and opening the upstream valve and the downstream valve. Furthermore, if the liquid level difference, which is the difference between the ink level in the upstream storage section and the ink level in the downstream storage section, becomes greater than a predetermined difference while maintenance is being performed, the control section, for example, closes one of the upstream valve and the downstream valve, which is the valve corresponding to the upstream storage section or the downstream storage section whose liquid level is higher, thereby suppressing the increase in the liquid level difference. With this configuration, for example, even if a difference occurs in the ink level positions in the upstream storage section and the downstream storage section during maintenance due to some cause, the increase in the liquid level difference can be appropriately suppressed. This also makes it possible to more appropriately adjust the pressure in the upstream storage section and the downstream storage section during maintenance, for example.

[0014] In addition, as a configuration of the present invention, for example, a configuration focusing on the above-mentioned features related to maintenance can be considered. In this case, the present invention can be, for example, a printing device that performs printing by an inkjet method, comprising an inkjet head that ejects ink by an inkjet method, an ink circulation flow path that is an ink flow path for circulating ink along a path passing through the inkjet head and has a plurality of ink storage sections for storing ink, a pressure adjustment section that adjusts the pressure applied to the ink storage sections in the ink circulation flow path, a control section that controls the operation of at least the pressure adjustment section, and a maintenance section that performs maintenance on the inkjet head, the ink circulation flow path comprising an upstream storage section that is the ink storage section that stores ink at a position that is upstream of the inkjet head when circulating ink in the ink circulation flow path, a downstream storage section that is the ink storage section that stores ink at a position that is downstream of the inkjet head when circulating, a head passing flow path that is a flow path for flowing ink from the upstream storage section to the downstream storage section via the inkjet head, and a head passing flow path that is the ink passing flow path that does not pass through the inkjet head. a head non-passing flow path which is a flow path for flowing ink from a downstream side storage portion to the upstream side storage portion, and an ink pump which is a pump for flowing ink into the head non-passing flow path, and the pressure adjustment portion has an upstream side pressure generating portion which generates a pressure to be transmitted to the upstream side storage portion, a downstream side pressure generating portion which generates a pressure to be transmitted to the downstream side storage portion, an upstream side valve which opens and closes an air flow path between the upstream side pressure generating portion and the upstream side storage portion, and a downstream side valve which opens and closes an air flow path between the downstream side pressure generating portion and the downstream side storage portion, During circulation, the control unit causes the pressure adjustment unit to open the upstream valve and the downstream valve while causing the upstream pressure generating unit to generate a pressure higher than that of the downstream pressure generating unit, thereby making the pressure in the upstream storage unit higher than the pressure in the downstream storage unit and causing ink to flow through the head passing flow path, the inkjet head has nozzles that eject ink, and the maintenance unit brings liquid into contact with a nozzle surface, which is a surface of the inkjet head on which the nozzles are formed,During the maintenance of the inkjet head, the control unit causes the upstream pressure generating unit and the downstream pressure generating unit to generate pressures lower than atmospheric pressure and equal to each other, and opens the upstream valve and the downstream valve, thereby equalizing the pressure in the upstream storage unit and the pressure in the downstream storage unit, and when a liquid level difference between the ink level in the upstream storage unit and the ink level in the downstream storage unit becomes greater than a predetermined difference while the maintenance is being performed, closes either the upstream valve or the downstream valve, which corresponds to the upstream storage unit or the downstream storage unit where the liquid level is higher, thereby suppressing the increase in the liquid level difference. In addition, as a configuration of the present invention, for example, a configuration of a control method for a printing device having the same characteristics as above can be considered. In this case, for example, the same effect as above can be obtained. Effect of the Invention

[0015] According to the present invention, for example, in a printing device that performs printing by an inkjet method, the pressure inside the ink storage unit can be more appropriately adjusted. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram showing an example of the configuration of a printing device 100 according to an embodiment of the present invention. [Diagram 2] 2 is a diagram showing an example of a detailed configuration of an ink circulation channel 110 and a pressure adjustment unit 112. FIG. [Diagram 3] 3A is a diagram illustrating further features of the ink circulation flow path 110 and the pressure adjustment unit 112. Fig. 3A shows an example of the relationship between a plurality of circulation units 204, a pressure distribution unit 206, and a common pressure supply unit 208. Fig. 3B shows an example of the configuration of a liquid level sensor 504 and items detected by the liquid level sensor 504. [Figure 4] 4 is a flowchart showing an example of the operation of the printing device 100. [Diagram 5] 10 is a flowchart showing an example of the operation of the printing device 100 when maintenance is performed by the maintenance unit 114. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an example of the configuration of a printing device 100 according to an embodiment of the present invention. In this example, the printing device 100 is an inkjet printer that performs printing on a medium 50 to be printed by an inkjet method, and includes a plurality of inkjet heads 102, a carriage 104, a platen 106, an ink supply unit 108, an ink circulation channel 110, a pressure adjustment unit 112, a maintenance unit 114, a scan drive unit 116, an operation unit 118, and a control unit 120. Except for the points described below, the printing device 100 and each unit of the printing device 100 may have the same or similar features as a known printing device and each unit thereof.

[0018] The inkjet heads 102 are ejection heads (print heads) that eject ink by an inkjet method, and have a nozzle row in which a plurality of nozzles are arranged in a predetermined nozzle row direction, and eject ink from the nozzles in the nozzle row when printing is performed. In this example, the nozzle row direction is a direction parallel to a predetermined sub-scanning direction that is set in advance in the printing device 100. The inkjet heads 102 eject ink of different colors, for example. In this case, it is considered that the inkjet heads 102 eject ink of each color of process colors, for example. The process colors can be considered as, for example, basic colors of color expression. More specifically, it is considered that ink of each color of process colors is used, for example, cyan (C color), magenta (M color), yellow (Y color), and black (K color). Any of the inkjet heads 102 may eject ink of a special color that is a color other than each color of the process colors. The carriage 104 is a holding member that holds the inkjet heads 102, and holds the inkjet heads 102 at a position facing the medium 50. In this example, the carriage 104 further holds a part of the configuration of the ink circulation channel 110. The platen 106 is a platform-like member that holds the medium 50 at a position facing the inkjet heads 102. The ink supply unit 108 is configured to supply ink to the inkjet heads 102, and supplies ink of each color to the inkjet heads 102. In this example, the ink supply unit 108 supplies ink to the inkjet heads 102 through the ink circulation channel 110. The ink supply unit 108 also has an ink tank for each color of ink, for example. In this case, the ink supply unit 108 stores ink supplied from an ink bottle replaceably installed in the ink supply unit 108 in the ink tank, and supplies ink from the ink tank to the inkjet heads 102 through the ink circulation channel 110.

[0019] The ink circulation flow path 110 is an ink flow path that supplies the ink supplied from the ink supply unit 108 to the inkjet head 102. In this example, the ink circulation flow path 110 is an ink flow path that circulates the ink along a path that passes through the inkjet head 102, and includes a path control unit 202 and a circulation unit 204. The path control unit 202 is configured to control the supply of ink supplied from the ink supply unit 108 to the ink circulation flow path 110 as necessary while circulating the ink in the ink circulation flow path 110. In addition, the circulation unit 204 is configured to include a portion of the ink circulation flow path 110 that passes through the inkjet head 102. In this example, the ink circulation flow path 110 has an ink storage unit that stores ink, and causes the ink to flow through a flow path that supplies the ink to the inkjet head 102 via the ink storage unit. In addition, in this example, the circulation unit 204 is held by the carriage 104 together with the multiple inkjet heads 102. In this case, each part of the circulation unit 204 can be considered to be disposed on the carriage 104, for example. With this configuration, for example, the circulation unit 204 can be appropriately disposed near the inkjet head 102. The configurations of the path control unit 202 and the circulation unit 204 will be described in more detail later. The pressure adjustment unit 112 is configured to adjust the pressure applied to the ink in the ink circulation flow path 110. The pressure adjustment unit 112 can be considered to be, for example, an air pressure system (Air Pressure Control) that adjusts the pressure in the printing device 100. In this example, the pressure adjustment unit 112 adjusts the pressure applied to the ink storage unit in the circulation unit 204 of the ink circulation flow path 110. The configuration of the pressure adjustment unit 112 will also be described in more detail later.

[0020] The maintenance unit 114 is configured to perform maintenance on the inkjet head 102, and performs maintenance on the inkjet head 102 in the middle of a printing operation or the like, according to the control of the control unit 120. In this example, the maintenance unit 114 performs maintenance on the inkjet head 102 by bringing a liquid such as a cleaning liquid into contact with a nozzle surface, which is a surface of the inkjet head 102 on which nozzles are formed. In addition, in this maintenance, the maintenance unit 114 cleans the periphery of the nozzles of the inkjet head 102, for example, with the cleaning liquid or the like. The scan drive unit 116 is a drive unit that causes the inkjet head 102 to perform a scanning operation in which the inkjet head 102 moves relatively to the medium 50. In this example, the scan drive unit 116 causes the multiple inkjet heads 102 to perform a main scanning operation and a sub-scanning operation as the scanning operation. The main scanning operation can be considered to be, for example, an operation of ejecting ink while moving relatively to the medium 50 in a main scanning direction perpendicular to the sub-scanning direction. During the execution of the main scanning operation, the scan driver 116, for example, in response to the control of the controller 120, causes the multiple inkjet heads 102 to eject ink onto positions selected according to the image to be printed from among ink ejection positions set according to the printing resolution. The sub-scanning operation can be considered, for example, as an operation of moving in the sub-scanning direction relative to the medium 50. The sub-scanning operation can also be considered, for example, as corresponding to a feeding operation of feeding the medium 50 relative to the inkjet heads 102. In this example, the scan driver 116 causes the multiple inkjet heads 102 to perform sub-scanning operations between main scanning operations, thereby changing the area on the medium 50 onto which ink is ejected in the next main scanning operation.

[0021] The operation unit 118 is configured to accept user operations on the printing device 100. In this example, the operation unit 118 accepts, for example, operations to set printing conditions and operations to switch the power of the printing device 100 on and off from the user. The operation unit 118 accepting user operations can be considered to correspond to, for example, accepting user instructions. In addition, the operation unit 118 may accept user operations via, for example, a computer that controls the printing device 100. The control unit 120 is, for example, a part including the CPU of the printing device 100, and controls the operation of each part of the printing device 100. In this case, the control unit 120 controls the operation of each part of the printing device 100 according to, for example, a program such as firmware of the printing device 100. According to this example, for example, the printing device 100 can appropriately perform printing on the medium 50. In addition, the printing device 100 may further have the same or similar configuration as a known printing device in addition to the configuration described above. For example, the printing device 100 may further include a fixing means for fixing the ink on the medium 50. In this case, it is considered to use a means according to the ink used in the printing device 100 as the fixing means. For example, it is considered to use ultraviolet curable ink that is cured by irradiation with ultraviolet rays in the printing device 100. In this case, the printing device 100 includes, for example, an ultraviolet light source as the fixing means. It is also considered to use, for example, an evaporation drying type ink that is fixed on the medium 50 by evaporating the solvent in the printing device 100. In this case, it is considered to use, for example, a heating means such as a heater as the fixing means.

[0022] Next, the configurations of the path control unit 202 and the circulation unit 204 in the ink circulation flow path 110 and the pressure adjustment unit 112 will be described in more detail. FIG. 2 shows an example of the detailed configuration of the ink circulation flow path 110 and the pressure adjustment unit 112. For convenience of illustration, FIG. 2 shows only the ink circulation flow path 110 and the pressure adjustment unit 112 that correspond to one inkjet head 102. More specifically, in this example, the ink circulation flow path 110 has the path control unit 202 and the circulation unit 204 of the illustrated configuration for each inkjet head 102. Furthermore, the pressure adjustment unit 112 has two-way valves 320a, b in the portion shown as the pressure distribution unit 206 in the figure for each inkjet head 102. In this case, the configuration of the portion shown as the common pressure supply unit 208 in the pressure adjustment unit 112 can be considered as a common configuration for the multiple inkjet heads 102, for example. In a modified example of the configuration of the pressure adjusting unit 112, the pressure adjusting unit 112 may have the same or similar configuration as the common pressure supply unit 208 for each inkjet head 102.

[0023] In the ink circulation flow path 110 of this example, the path control unit 202 has a three-way valve 302, a pump 304, a filter 306, and a connection unit 308. The three-way valve 302, the pump 304, and the filter 306 are components that become part of the flow path through which ink circulates in the ink circulation flow path 110, and are arranged in series along the ink flow path, for example, as shown in the figure. Among these components, the three-way valve 302 is a valve that merges ink supplied from the ink supply unit 108 into the flow path through which ink circulates in the ink circulation flow path 110, and is opened and closed under the control of the control unit 120 (see FIG. 1 ) to replenish the ink supplied from the ink supply unit 108 to the ink circulation flow path 110. The pump 304 is a pump that flows ink into the ink circulation flow path 110, and is arranged, for example, downstream of the three-way valve 302 in the direction in which the ink flows. As the pump 304, for example, a tube pump or the like can be suitably used. In this example, the pump 304 is an example of an ink pump that flows ink to a non-head passing flow path in the ink circulation flow path 110. The non-head passing flow path can be considered as, for example, a flow path of ink in the ink circulation flow path 110 that does not pass through the inkjet head 102. The filter 306 is a filter that removes foreign matter and the like in the ink downstream of the pump 304 in the ink flow direction. The filter 306 can also be considered to be disposed, for example, between the pump 304 and the circulation unit 204. The connection unit 308 is configured to be a connection part that connects the path control unit 202 and the circulation unit 204, and connects a part of the flow path in which the ink circulates in the ink circulation flow path 110 that is within the path control unit 202 to a part of the circulation unit 204.

[0024] In the ink circulation flow path 110, the circulation unit 204 includes a sub-tank 312, flow paths 314, 316, and a plurality of filters 318a, b. The sub-tank 312 is configured to store ink on the upstream side and downstream side of the inkjet head 102 in the ink circulation flow path 110. In the present embodiment, the sub-tank 312 includes a plurality of ink storage sections 402a, b, a plurality of inlets 412, a plurality of outlets 414, and a plurality of vents 416. The plurality of ink storage sections 402a, b are portions that store ink in the sub-tank 312. In the present embodiment, the ink storage section 402a is an example of an upstream storage section, and stores ink at a position that is upstream of the inkjet head 102 when the ink is circulated in the ink circulation flow path 110. The ink storage section 402b is an example of a downstream storage section, and stores ink at a position that is downstream of the inkjet head 102 when the ink is circulated. The multiple inlets 412 are openings for introducing ink into the multiple ink storage units 402a and 402b. In this example, the inlet 412 in the ink storage unit 402a is connected to the ink flow path 316 connected to the path control unit 202, thereby introducing ink flowing from the path control unit 202 through the flow path 316 into the ink storage unit 402a. The outlet 414 in the ink storage unit 402a is connected to the ink flow path 314 connected to the inkjet head 102, thereby allowing ink to flow toward the inkjet head 102. The inlet 412 in the ink storage unit 402b is connected to the ink flow path 314 connected to the inkjet head 102, thereby allowing ink that has passed through the inkjet head 102 to be introduced into the ink storage unit 402b. The outlet 414 in the ink storage unit 402b is connected to the ink flow path 316 connected to the path control unit 202, thereby allowing ink to flow toward the path control unit 202. Moreover, the vent 416 in the ink storage portions 402a, 402b is an opening for passing air between the ink storage portion 402a and the pressure adjustment portion 112. In this example, the vent 416 in the ink storage portion 402a is connected to the pressure adjustment portion 112 via a filter 318a. Moreover, the vent 416 in the ink storage portion 402b is connected to the pressure adjustment portion 112 via a filter 318b.

[0025] In this embodiment, the subtank 312 is provided with a heater 502 and a liquid level sensor 504. The heater 502 is a heating unit that heats the ink stored in the ink storage units 402a and 402b of the subtank 312. The heater 502 heats the ink in response to the control of the control unit 120, for example, during printing. The liquid level sensor 504 is a detection unit that detects the position of the ink level in the ink storage units 402a and 402b. In this case, the control unit 120 detects a change in the position of the ink level based on, for example, the output of the liquid level sensor 504. With this configuration, for example, the position of the ink level in the ink storage units 402a and 402b can be appropriately detected. In this embodiment, the heater 502 and the liquid level sensor 504 can also be considered to be included in the circulation unit 204. Depending on how the configuration of the printing device 100 (see FIG. 1) is divided, the printing device 100 may be provided with the heater 502 and the liquid level sensor 504 as components separate from the ink circulation flow path 110 and the circulation unit 204. As described above, in the subtank 312 of this example, the ink storage units 402a and 402b are connected to the ink flow paths 314 and 316. In this example, the ink flow path 314 is an example of a head passing flow path, and causes ink to flow from the ink storage unit 402a to the ink storage unit 402b via the inkjet head 102. The flow path 314 may also be considered, for example, as a flow path connecting the ink storage units 402a and 402b to the inkjet head 102. The flow path 316 is an example of a head non-passing flow path, and causes ink to flow from the ink storage unit 402b to the ink storage unit 402a without passing through the inkjet head 102 by connecting to the path control unit 202. In addition, the multiple filters 318a, b are filters for preventing backflow, and by being disposed between the pressure adjustment unit 112 and the subtank 312, they prevent, for example, ink from flowing from the ink storage sections 402a, b in the subtank 312 into the pressure adjustment unit 112.

[0026] In this embodiment, the pressure adjustment unit 112 has a pressure distribution unit 206 and a common pressure supply unit 208. The pressure distribution unit 206 has a plurality of two-way valves 320a, b. Although not shown in FIG. 2, as described above, in this embodiment, the pressure distribution unit 206 has a plurality of two-way valves 320a, b for each inkjet head 102. The two-way valve 320a is an example of an upstream valve, connects the ink storage unit 402a in the subtank 312 to the common pressure supply unit 208, and opens and closes under the control of the control unit 120. The two-way valve 320b is an example of a downstream valve, connects the ink storage unit 402b in the subtank 312 to the common pressure supply unit 208, and opens and closes under the control of the control unit 120. More specifically, in this example, the two-way valves 320a, b are connected to the ink storage units 402a, b via the filters 318a, b, to transmit the pressure generated in the common pressure supply unit 208 to the ink storage units 402a, b. The transmission of the pressure generated in the common pressure supply unit 208 to the ink storage units 402a, b can be considered, for example, as adjusting the pressure in the ink storage units 402a, b to the pressure generated in the common pressure supply unit 208. In this example, the carriage 104 (see FIG. 1) holds the three-way valves 302a, b together with the inkjet head 102, etc. In this case, the pressure distribution unit 206 can also be considered, for example, as a part of the pressure adjustment unit 112 that is disposed on the carriage 104, etc.

[0027] In this example, the common pressure supply unit 208 has a plurality of pressure generating units 322a, b and a connection unit 324. The pressure generating unit 322a is an example of an upstream pressure generating unit, and is connected to the ink storage unit 402a via the connection unit 324, the two-way valve 320a, and the filter 318a, thereby transmitting the generated pressure to the ink storage unit 402a when the three-way valve 302a is open. In this case, the pressure generating unit 322a can be considered to generate pressure to be transmitted to the ink storage unit 402a, for example. The two-way valve 320a can be considered to open and close the air flow path between the pressure generating unit 322a and the ink storage unit 402a, for example. The pressure generating unit 322b is an example of a downstream pressure generating unit, and is connected to the ink storage unit 402b via the connection unit 324, the two-way valve 320b, and the filter 318b, and transmits the generated pressure to the ink storage unit 402b when the three-way valve 302b is open. In this case, the pressure generating unit 322b can be considered to generate pressure to be transmitted to the ink storage unit 402b, for example. Also, the two-way valve 320b can be considered to open and close the air flow path between the pressure generating unit 322b and the ink storage unit 402b, for example. Also, the connection unit 324 is configured to be a connection portion that connects the common pressure supply unit 208 and the pressure distribution unit 206. In this example, the connection unit 324 connects the pressure generating unit 322a and the two-way valve 320a, and connects the pressure generating unit 322b and the two-way valve 320b. With this configuration, for example, the pressure generated in the pressure generating units 322a and 322b can be appropriately transmitted to the ink storing units 402a and 402b.

[0028] In this example, the pressure generating units 322a, b have, for example, a pump (pressure pump) for adjusting pressure, an air chamber, and a pressure sensor (negative pressure sensor), and generate a predetermined negative pressure lower than atmospheric pressure according to the control of the control unit 120, and transmit the negative pressure to the ink storage units 402a, b. More specifically, for example, with regard to the control over the pressure adjusting unit 112, when circulating ink in the ink circulation flow path 110 during printing or the like, the control unit 120 opens the two-way valves 320a, b while causing the pressure generating unit 322a to generate a higher pressure (negative pressure closer to atmospheric pressure) than the pressure generating unit 322b, thereby making the pressure in the ink storage unit 402a higher than the pressure in the ink storage unit 402b. In this case, due to the pressure difference between the ink storage section 402a and the ink storage section 402b, the ink flows from the ink storage section 402a to the ink storage section 402b through the inkjet head 102 in the flow path 314. In addition, in this case, the control section 120, for example, drives the pump 304 to cause the ink to flow from the ink storage section 402b to the ink storage section 402a in the flow path 316. With this configuration, for example, when printing is performed, the ink can be appropriately circulated in the ink circulation flow path 110. In addition, in this case, for example, as described above, the pressure generating sections 322a and 322b generate negative pressure, so that the pressure in the ink storage sections 402a and 322b is set to negative pressure. With this configuration, for example, it is possible to appropriately prevent the ink from leaking from the nozzles of the inkjet head 102, while appropriately supplying the ink to the inkjet head 102.

[0029] In this example, the control unit 120 stops the circulation of ink in the ink circulation flow path 110 at a predetermined timing, for example. Then, at the timing when ink is not circulated in the ink circulation flow path 110, the control unit 120 controls the pressure generating units 322a, b and the two-way valves 320a, b, etc., so that the pressures in the ink storage units 402a, b are equal (equal pressure). More specifically, in this example, the printing device 100 can transition to a sleep state in which power consumption is reduced, and transitions to the sleep state in response to, for example, a user's instruction. Then, when transitioning to the sleep state, the control unit 120 controls the pressure generating units 322a, b and the two-way valves 320a, b, etc., so that the pressures in the ink storage units 402a, b are equal. In this example, the sleep state is an example of a stop state in which power consumption is reduced by stopping some functions. The sleep state can also be considered, for example, as a standby state in which the printing device 100 is placed on standby in a power-saving state. The operation of the printing device 100 when transitioning to the sleep state will be described in more detail later. According to this embodiment, for example, the pressure adjustment unit 112 can appropriately supply pressure to the ink circulation channel 110. This can also, for example, allow ink to be circulated appropriately through the ink circulation channel 110. In addition, at least one of the pressure generating units 322a and 322b may generate a positive pressure greater than atmospheric pressure in accordance with the control of the control unit 120 during a predetermined operation of the printing device 100. For example, when ink is discharged from the ink circulation channel 110 during cleaning of the printing device 100, it is possible to generate a positive pressure in the pressure generating unit 322a to discharge ink outside the ink circulation channel 110.

[0030] As described above, in this example, the printing device 100 includes a plurality of inkjet heads 102. The ink circulation flow path 110 includes a path control unit 202 and a circulation unit 204 for each inkjet head 102. The pressure adjustment unit 112 includes two-way valves 320a, 320b in the pressure distribution unit 206 for each inkjet head 102. The pressure adjustment unit 112 also includes a common pressure supply unit 208 shared by the plurality of inkjet heads 102. In this case, the pressure distribution unit 206 and the common pressure supply unit 208 in the pressure adjustment unit 112 are connected to the plurality of circulation units 204 in the ink circulation flow path 110, for example, as shown in FIG. 3(a).

[0031] 3 is a diagram for explaining further features of the ink circulation flow path 110 and the pressure adjustment unit 112. FIG. 3(a) shows an example of the relationship between the multiple circulation units 204, the pressure distribution unit 206, and the common pressure supply unit 208. As can be understood from the illustrated configuration, in this example, the pair of two-way valves 320a, b and the circulation unit 204 correspond one-to-one. In this case, as can be understood from the configuration of the circulation unit 204 described above, the ink storage unit 402a (see FIG. 2) in the circulation unit 204 corresponds one-to-one to the two-way valve 320a, and the ink storage unit 402b (see FIG. 2) corresponds one-to-one to the two-way valve 320b. In this case, for example, if the printing device 100 (see FIG. 1) has N inkjet heads 102 (see FIG. 1) (N is an integer equal to or greater than 2), the ink circulation flow path 110 (see FIG. 1) has N circulation parts 204, and the pressure distribution part 206 has N two-way valves 320a and N three-way valves 302b. In this example, the common pressure supply part 208 generates pressure commonly for the multiple circulation parts 204. In this case, the common pressure supply part 208 supplies pressure to the multiple circulation parts 204 via the multiple two-way valves 320a, b. More specifically, as described above with reference to FIG. 2, in the common pressure supply part 208, the pressure generating part 322a (see FIG. 2) generates pressure to be transmitted to the ink storage part 402a in the circulation part 204. In addition, the pressure generating part 322b (see FIG. 2) generates pressure to be transmitted to the ink storage part 402b in the circulation part 204. In this case, the relationship between the pressure generating units 322a, b and the circulation unit 204 can be considered to be, for example, a 1:N correspondence. With this configuration, for example, the pressure can be appropriately adjusted by the pressure generating units 322a, b provided in common for the multiple inkjet heads 102 and the multiple ink circulation channels 110. In this case, the control unit 120 (see FIG. 1) of the printing device 100 controls, for example, the opening and closing of the two-way valves 320a, b corresponding to the circulation unit 204, thereby controlling whether or not to supply the pressure generated by the common pressure supply unit 208 to the ink storage units 402a, b in the circulation unit 204 for each circulation unit 204.With this configuration, for example, a common pressure for the multiple circulation parts 204 can be generated in the common pressure supply part 208 while the pressure for each circulation part 204 can be appropriately controlled individually.

[0032] As explained above, in this example, the liquid level sensor 504 is attached to the subtank 312 (see FIG. 2). In this case, it is possible to use a sensor having a configuration shown in FIG. 3(b) as the liquid level sensor 504. FIG. 3(b) shows an example of the configuration of the liquid level sensor 504 and an example of an item detected by the liquid level sensor 504. In FIG. 3(b), for the sake of illustration and convenience, the multiple ink storage sections 402a, 402b in the subtank 312 are not distinguished and are shown as the ink storage sections 402, and the configuration of the liquid level sensor 504 is illustrated in relation to the case where the position of the ink level in the ink storage section 402 is detected by the liquid level sensor 504.

[0033] In this example, the liquid level sensor 504 has a float 512 and a detection unit 514. The float 512 is a member that floats on the ink in the ink storage unit 402. The detection unit 514 detects the position of the float 512 in the height direction of the ink level. With this configuration, for example, the position of the ink level in the ink storage unit 402 can be appropriately detected. In this case, the control unit 120 determines which of a plurality of preset stages the ink level is in based on the output of the liquid level sensor 504 (output of the detection unit 514). More specifically, in this case, it is possible to use a plurality of stages including stages that are distinguished as Low, Middle, High, Near Full, and Full in the figure as the plurality of stages. Of these stages, Low can be considered to indicate, for example, a state in which the ink level in the ink storage unit 402 is low. Middle can be considered to indicate, for example, a state in which the ink level in the ink storage unit 402 is in a middle level that is higher than the Low state. High can be considered to indicate, for example, a state in which the ink level in the ink storage section 402 is higher than the Middle state. Near Full can be considered to indicate, for example, a state in which the ink level in the ink storage section 402 is higher than the High state and is approaching the upper limit. Full can be considered to indicate, for example, a state in which the ink level in the ink storage section 402 is higher than the Near Full state and is even closer to the upper limit. Full can also be considered, for example, a dangerous state in which the possibility of ink overflow is high. In this example, the control section 120 detects the ink level positions for the multiple ink storage sections 402a and 402b in the subtank 312 based on the output of the level sensor 504. In addition, the control section 120 thereby further detects, for example, a difference in the ink level positions between the multiple ink storage sections 402a and 402b as necessary. According to this example, for example, the ink level positions in the multiple ink storage sections 402a and 402b in the subtank 312 can be appropriately detected.

[0034] In this example, the control unit 120 controls the operation of the printing device 100 based on the position of the ink level in the ink storage units 402a and 402b, which is detected based on the output of the level sensor 504. Hereinafter, an example of the operation of the printing device 100 will be described with respect to the control performed by the control unit 120 based on the position of the ink level in the ink storage units 402a and 402b. As described above, in this example, the control unit 120 controls the pressure generating units 322a and 322b and the two-way valves 320a and 320b, etc., so that the pressures in the ink storage units 402a and 402b are equalized when the sleep state is entered. In this case, the control unit 120 adjusts the pressures generated by the pressure generating units 322a and 322b with the two-way valves 320a and 320b open to equalize the pressures in the ink storage units 402a and 402b. After equalizing the pressures in the ink storage units 402a and 402b, the control unit 120 closes the two-way valves 320a and 320b to maintain equal pressures in the ink storage units 402a and 402b in the sleep state. In this case, the pressures in the ink storage units 402a and 402b may change during the sleep state due to, for example, air leakage. Therefore, in this example, after the printing device 100 transitions to the sleep state, the control unit 120 periodically wakes the printing device 100 from the sleep state and adjusts (readjusts, resets) the pressures in the ink storage units 402a and 402b as necessary. Such an operation of the printing device 100 may be considered, for example, as an intermittent operation in which the sleep state and the wake-up are repeated.

[0035] However, in this case, if the frequency of returning from the sleep state is increased, the effect of reducing power consumption in the sleep state is reduced. Conversely, if the frequency of returning from the sleep state is reduced, the pressure in the ink storage sections 402a and 402b may change significantly during the sleep state. In this case, for example, a pressure difference may occur between the ink storage sections 402a and 402b, and ink may flow from one of the ink storage sections 402a and 402b to the other through the flow path 314 (see FIG. 2) or the like. As a result, for example, the ink level may rise excessively in either of the ink storage sections 402a and 402b, causing an overflow. In addition, a change in the pressure in the ink storage sections 402a and 402b may cause, for example, a backflow of ink or dripping of ink leaking from the inkjet head 102. In this regard, it seems that such problems can be prevented by appropriately setting the time for which the sleep state is to continue, for example, when designing or manufacturing the printing device 100. However, in an actual printing device 100, air leaks and the like may occur in various locations in the printing device 100 due to various causes that arise after the manufacturing or shipping of the printing device 100. Therefore, it may not be possible to set an appropriate time for the time to continue the sleep state simply by setting it at the time of designing the printing device 100.

[0036] In contrast, in this example, the control unit 120 performs a predetermined operation at the time of transition to the sleep state, thereby determining the sleep duration, which is the time for which the sleep state continues. In this case, the sleep duration is an example of a stop time. In addition, in this example, the printing device 100 transitions to the sleep state in response to a user's instruction. In this case, the printing device 100 receives a user's instruction, for example, by the user's operation on the operation unit 118. More specifically, in this case, the printing device 100 receives a user's instruction based on, for example, the user's operation on the power button on the operation unit 118, and transitions to the sleep state. The printing device 100 may receive a user's instruction, for example, via a computer that controls the printing device 100. In addition, when the printing device 100 receives an instruction from a user to transition the printing device 100 to the sleep state, the control unit 120 in the printing device 100 executes a process of determining the sleep duration, for example, as a process to be performed before transitioning to the sleep state. With this configuration, for example, the sleep duration can be appropriately determined before the printing device 100 transitions to the sleep state. In this case, the printing device 100 transitions to a sleep state and performs the subsequent operations, for example, as shown in FIG.

[0037] FIG. 4 is a flowchart showing an example of the operation of the printing device 100, and shows an example of the operation of the printing device 100 at the time of transition to a sleep state and after transition, with respect to an example of control performed by the control unit 120 based on the position of the ink level in the ink storage units 402a and 402b. The operation shown in FIG. 4 can be considered as an example of the operation of the control method of the printing device 100, for example. The operation shown in FIG. 4 is an example of the operation after the printing device 100 receives an instruction from a user to transition the printing device 100 to a sleep state. In this case, before the printing device 100 goes into a sleep state, the control unit 120 determines the sleep duration (S102). In addition, in step S102 of this example, the control unit 120 detects a change in the position of the ink level in the ink storage units 402a and 402b based on the output of the level sensor 504. Then, the control unit 120 determines the sleep duration based on the detection result. In this case, the control unit 120 determines the sleep duration so that, for example, no problematic change in the liquid level occurs in either of the ink storage units 402a, b while the sleep state continues. A problematic change in the liquid level while the sleep state continues is, for example, a change in the liquid level that increases the risk of overflow or the like. In this case, the control unit 120 detects, for example, a change in the ink level position in the ink storage units 402a, b from a Middle state, and measures the liquid level change time, which is the time it takes for the ink level position to reach a Near Full state. Then, the control unit 120 determines the sleep duration based on this liquid level change time.

[0038] Also, as described above, in step S102, the control unit 120 determines the sleep duration so that problems such as overflow do not occur in the ink storage units 402a and 402b while the sleep state continues. In this case, one method is to, for example, make the pressure in the ink storage units 402a and 402b the same as the pressure in the sleep state and measure the time it takes for the ink level position in either of the ink storage units 402a and 402b to reach a state from a middle state to a near full state. However, in this case, the time required for the ink level position to change in the ink storage units 402a and 402b becomes longer, so that, for example, it takes a long time to determine the sleep duration. Therefore, in this example, the control unit 120 determines the sleep duration based on the change in the ink level position that occurs in the ink storage units 402a and 402b when the pressure in the ink storage units 402a and 402b are different. More specifically, in step S102, the control unit 120 causes the pressure adjustment unit 112 to close the two-way valves 320a and 320b while making the pressure in the ink storage unit 402a different from the pressure in the ink storage unit 402b. Then, the control unit 120 determines the sleep duration based on the change in the ink level in the ink storage units 402a and 402b that occurs thereafter. In this configuration, by intentionally creating a pressure difference in the ink storage units 402a and 402b, for example, when a difference in the ink level occurs thereafter due to the influence of an air leak or the like, the change in the ink level can be caused in a shorter time. This also makes it possible to shorten the required measurement time, for example, and to determine the sleep duration in a shorter time. In this case, making the pressure in the ink storage unit 402a different from the pressure in the ink storage unit 402b can be considered to correspond to, for example, accelerating the required measurement.

[0039] In this example, the control unit 120 detects the change in the ink level by changing the side of the ink storage unit 402a, b on which the pressure is increased. More specifically, in this case, the control unit 120 determines the sleep duration based on the change in the ink level in the ink storage unit 402a, b that occurs when the two-way valves 320a, b are closed with the pressure in the ink storage unit 402a higher than the pressure in the ink storage unit 402b, and the change in the ink level in the ink storage unit 402a, b that occurs when the two-way valves 320a, b are closed with the pressure in the ink storage unit 402a lower than the pressure in the ink storage unit 402b. With this configuration, the sleep duration can be determined more appropriately, for example, when determining the sleep duration based on the change in the ink level detected by applying a pressure difference. Furthermore, depending on the configuration of the printing device 100 and the conditions required when determining the sleep duration, for example, the sleep duration may be determined based on the change in the position of the ink liquid surface detected by making the pressure in the ink storage section 402a and the pressure in the ink storage section 402b equal, without necessarily making a difference between the pressures in the ink storage sections 402a and 402b. Even with such a configuration, the sleep duration can be appropriately determined.

[0040] Here, as described above, in this example, the printing device 100 includes a plurality of ink circulation channels 110. Therefore, in step S102 in this example, the control unit 120 measures the liquid level change time for each ink circulation channel 110. In addition, the control unit 120 determines the sleep duration based on the liquid level change time measured in the ink circulation channel 110 in which the ink level change occurs in the shortest time among the plurality of ink circulation channels 110. With this configuration, for example, the sleep duration can be appropriately determined so that problems such as overflow do not occur in the ink storage sections 402a and 402b in any of the ink circulation channels 110. In addition, the method of determining such a sleep duration can be, for example, a method of determining the time to return from the sleep state next time (next sleep start time) based on the time when the ink level reaches the near full state from the middle state earliest in either of the ink storage sections 402a and 402b among the plurality of ink circulation channels 110. Moreover, such a method can be considered to adjust the interval (sleep interval) until the printer 100 returns from the sleep state by acquiring the time until the difference in the ink level occurs between the ink reservoirs 402a and 402b while the sleep state continues. Adjusting the sleep interval can be considered to cause the printer 100 to return from the sleep state (next sleep start) earlier than the next overflow is expected to occur. In step S102, the control unit 120 may further adjust the target pressure value, which is the pressure value in the ink reservoirs 402a and 402b set by the pressure adjustment unit 112, as necessary, based on the measurement result of the liquid level change time. More specifically, for example, when a similar problem occurs not only in a specific ink circulation flow path 110 (specific path) but in all ink circulation flow paths 110 (all paths) with respect to the measurement result of the liquid level change time, it may be considered that the target pressure value for the ink reservoirs 402a and 402b is not an appropriate value, rather than a problem such as air leakage in a specific path.Therefore, in such a case, the control unit 120 may correct the target pressure value so as to adjust the target pressure value to a value that alleviates the problem in all paths, based on, for example, the measurement results of the liquid level change time for the multiple ink circulation paths 110. With this configuration, for example, the printing device 100 can be more appropriately transitioned to the sleep state.

[0041] Furthermore, following the operation of step S102, the control unit 120 causes the pressure adjustment unit 112 to close the two-way valves 320a and 320b while equalizing the pressure in the ink storage unit 402a and the pressure in the ink storage unit 402b (S104), and causes the printing device 100 to transition to a sleep state (S106). Furthermore, in step S104 of this example, the control unit 120 adjusts the pressure in the ink storage units 402a and 402b to a negative pressure by causing the pressure generation units 322a and 322b in the pressure adjustment unit 112 to generate equal negative pressures. In this case, the operations of steps S104 and S106 can be considered, for example, as operations for adjusting the ink storage units 402a and 402b to equal negative pressures when transitioning to a sleep state. Furthermore, after transitioning to a sleep state, the control unit 120 checks the elapse of the sleep duration (S110) while maintaining the printing device 100 in the sleep state (S108). In addition, the control unit 120 thereby causes the printing device 100 to continue the sleep state until the sleep duration time continues after transition to the sleep state (S110, No). In addition, in this example, while the sleep state continues, the control unit 120 stops the circulation of ink in the ink circulation flow path 110, for example, by stopping the pump 304 in the path control unit 202 of the ink circulation flow path 110. In this case, the three-way valves 302a and 302b are closed, and the ink storage units 402a and 402b are at equal pressure, so that the position of the ink level in the ink storage units 402a and 402b does not change by design. For example, in the sleep state in which ink is not circulated in the ink circulation flow path 110, the negative pressure generated in the ink storage units 402a and 402b at the time of transition to the sleep state can be considered as a state in which the ink level in the ink storage units 402a and 402b is maintained until recovery from the sleep state.

[0042] Also, in step S110, if the control unit 120 determines that the sleep duration has elapsed (S110, Yes), the control unit 120 causes the printing device 100 to return from the sleep state (S112). In this case, the operation of the control unit 120 in steps S110 and S112 can be considered as, for example, an operation of returning the printing device 100 from the sleep state in response to the elapse of the sleep duration after the printing device 100 has entered the sleep state. Returning the printing device 100 from the sleep state can be considered as, for example, operating some of the functions of the printing device 100 that were stopped in the sleep state. More specifically, in the sleep state, the control unit 120, for example, stops the supply of electricity to the actuators of each part of the printing device 100. For example, in the sleep state of this example, the control unit 120 stops the pump 304, etc. In this case, the circuit in the pump 304 becomes, for example, in an open state. Also, in this example, the two-way valves 320a and b use valves that become open when energized. In the sleep state, the control unit 120 stops the power supply to the three-way valves 302a and 302b. In this case, when the sleep state is entered, the power supply is stopped, and the two-way valves 320a and 320b are closed, so that the negative pressure previously applied in the ink storage units 402a and 402b is maintained. In the return from the sleep state in step S112, the control unit 120 returns the printing device 100 from the sleep state by, for example, operating at least a function required for updating the negative pressure in the next step S114. In this case, the control unit 120, for example, generates a predetermined negative pressure in the pressure adjustment unit 112, and makes the two-way valves 320a and 320b openable and closable as necessary. In addition, the control unit 120, for example, makes the pump 304 drivable as necessary.

[0043] Following the operation of step S112, the control unit 120 causes the pressure adjustment unit 112 and the like to update the negative pressure in the ink storage units 402a, b (S114). In step S114, the control unit 120 updates the negative pressure in the ink storage units 402a, b, for example, by opening the two-way valves 320a, b and applying the negative pressure generated by the pressure generation units 322a, b in the pressure adjustment unit 112 to the ink storage units 402a, b. In this case, the control unit 120 updates the negative pressure in the ink storage units 402a, b, for example, by causing the pressure generation units 322a, b to generate the same pressure as that during adjustment to the equal negative pressure in step S104. With this configuration, for example, even if the pressure in the ink storage units 402a, b changes due to an air leak or the like while the sleep state continues, the pressure in the ink storage units 402a, b can be appropriately reset. The operation of the control unit 120 in step S114 can be considered to be, for example, the operation of the control unit 120 at the timing when the printing device 100 returns from the sleep state as the sleep duration elapses. Depending on the specific configuration of the printing device 100, it is also possible to update the negative pressure only for the ink storage units 402a, b that require pressure adjustment. Therefore, the control operation performed by the control unit 120 in step S114 can be considered to be, for example, an operation of readjusting (resetting) the pressure of at least one of the ink storage units 402a, b by generating a predetermined pressure in at least one of the pressure generating units 322a, b in the pressure adjusting unit 112 and causing the pressure adjusting unit 112 to open at least one of the two-way valves 320a, b.

[0044] After updating the negative pressure in the ink storage units 402a and 402b in step S114, the control unit 120 returns to step S106, transitions the printing device 100 to a sleep state again, and repeats the subsequent operations. This also causes the control unit 120 to perform intermittent operation in which the printing device 100 repeatedly transitions between a sleep state and a return state. In this case, the operation of the control unit 120 in steps S114 and S106 can be considered as, for example, an operation of causing the pressure adjustment unit 112 to open at least one of the two-way valves 320a and 320b, and then to close the two-way valves 320a and 320b again, transitioning the printing device 100 to a sleep state. In this configuration, for example, by periodically waking up the printing device 100 from a sleep state and updating the negative pressure in the ink storage units 402a and 402b, the printing device 100 can be brought into a sleep state while preventing problems such as overflow in the ink storage units 402a and 402b. This also allows the power consumption of the printing device 100 to be appropriately reduced, for example, at a timing when the printing device 100 is not printing. As described above, in this example, the control unit 120 determines the sleep duration based on the change in the ink level position in the ink storage units 402a and b before (in advance of) the printing device 100 transitions to the sleep state. Therefore, according to this example, for example, the sleep duration can be appropriately determined according to the state of the printing device 100. This also allows, for example, the ink overflow in the ink storage units 402a and b to be more appropriately prevented while the printing device 100 is in the sleep state. In this case, it can also be considered that this example allows the pressure in the ink storage units 402a and b to be more appropriately adjusted. As described above, in this example, the printing device 100 starts intermittent operation by equalizing the pressure in the ink storage units 402a and b. In this case, by determining the sleep duration as described above, it can be considered that it is possible to more appropriately prevent the occurrence of problems that are unlikely to occur in a state in which ink is circulated by creating a pressure difference between the ink storage sections 402a, b (differential pressure, circulation state), and that are likely to occur in a state in which the pressures in the ink storage sections 402a, b are previously equalized and maintained.The state in which the pressure in the ink storage sections 402a, b is equalized in advance and maintained can be considered to be, for example, a state in which the pressure is adjusted to be equal before transitioning to a sleep state, and no pressure (negative pressure) is supplied from the pressure generating units 322a, b to the ink storage sections 402a, b while the sleep state continues.

[0045] Here, as described above, in this example, the control unit 120 determines the sleep duration in step S102, which is the timing before the start of intermittent operation. In this case, it can be considered that the control unit 120 determines the sleep duration for the sleep state repeated in the subsequent intermittent operation before the transition to the first sleep state. In addition, it is also considered that the preferable sleep duration changes depending on the elapsed time from the start of the intermittent operation. More specifically, as described above, in this example, the heater 502 is attached to the subtank 312 having the ink storage units 402a and 402b. The heater 502 heats the ink stored in the ink storage units 402a and 402b, for example, when printing is performed. In addition, in the sleep state, the control unit 120 stops heating the ink by the heater 502. Therefore, for example, immediately after the start of intermittent operation (for example, within about one hour), the ink in the ink storage units 402a and 402b gradually cools, causing a change in pressure (increase in negative pressure) in response to the contraction of air in the ink storage units 402a and 402b. In addition, in this case, after the ink has cooled sufficiently, the pressure change due to such factors does not occur. Therefore, for example, it is preferable to update the negative pressure at a shorter period immediately after the start of intermittent operation. In this case, in step S102, the control unit 120 may determine the sleep duration in the first predetermined period (for example, within about one hour) and the sleep duration thereafter. In this case, it is considered that the sleep duration in the first predetermined period is set to a shorter time (for example, about half the time) than the sleep duration thereafter. With this configuration, for example, when the ink is heated by the heater 502 during printing, the printing device 100 can be made to perform intermittent operation more appropriately.

[0046] In addition, in step S114, the control unit 120 may cause the printing device 100 to perform an operation other than updating the negative pressure. In this case, the control unit 120 may adjust the position of the ink level in the ink storage units 402a and 402b, for example, by circulating ink in the ink circulation channel 110 as necessary. More specifically, in this case, in step S114, the control unit 120 detects the position of the ink level in the ink storage units 402a and 402b, for example, based on the output of the liquid level sensor 504. Then, if the position of the ink level in the ink storage units 402a and 402b is out of a predetermined allowable range, the control unit 120 circulates ink in the ink circulation channel 110 to optimize the position of the ink level in the ink storage units 402a and 402b. In this case, the control unit 120 circulates ink in the ink circulation channel 110, for example, by operating each unit of the ink circulation channel 110 and the pressure adjustment unit 112 in the same manner as when printing is performed. With this configuration, for example, even if the ink level rises in either of the ink storage units 402a and 402b while the sleep state continues, the ink level can be adjusted in a short time. More specifically, the control unit 120 determines that the ink level is higher than a preset reference level when the ink level is equal to or higher than the Near Full level. In this case, the ink level being equal to or higher than the Near Full level can be considered to be, for example, a state in which the ink level is higher than a preset reference level. When the printing device 100 returns from the sleep state, if the ink level in either of the ink storage units 402a and 402b is equal to or higher than the Near Full level, the control unit 120 adjusts the ink level in the ink storage units 402a and 402b by, for example, generating a predetermined pressure in the pressure generating units 322a and 322b in the pressure adjusting unit 112, opening the two-way valves 320a and 320b, and circulating the ink in the ink circulation channel 110. By configuring in this manner, the position of the liquid level can be appropriately adjusted in a short time even in cases where it is difficult to adjust the position of the liquid level simply by updating the negative pressure in the ink storage sections 402a, b, or where adjustment takes time.In this case, the control unit 120 updates the negative pressure by, for example, circulating the ink in the ink circulation flow path 110 and then equalizing the pressure in the ink storage units 402a and 402b to the negative pressure. Then, the process returns to step S106, and the control unit 120 closes the two-way valves 320a and 320b to transition the printing device 100 to a sleep state. When the ink level in either of the ink storage units 402a and 402b is not equal to or higher than the Near Full level (is equal to or lower than the reference level) at the time when the printing device 100 returns from the sleep state, the control unit 120 updates the negative pressure in the ink storage units 402a and 402b without circulating the ink in the ink circulation flow path 110. Then, the process returns to step S106, and the control unit 120 closes the two-way valves 320a and 320b to transition the printing device 100 to a sleep state. With this configuration, for example, when the printing device 100 returns from the sleep state, ink can be circulated in the ink circulation flow path 110 as necessary. This also makes it possible to more appropriately prevent ink overflow from the ink storage units 402a, b, for example, even if the ink level rises significantly in either of the ink storage units 402a, b while the sleep state continues.

[0047] In addition, in the printing device 100, the pressures in the ink storage units 402a and 402b may be equalized even at a timing other than when the sleep state continues. For example, as described above, in this example, the printing device 100 performs maintenance on the inkjet head 102 in the maintenance unit 114 using a liquid such as a cleaning liquid during a printing operation. In addition, in this maintenance, for example, the periphery of the nozzles of the inkjet head 102 is cleaned with the cleaning liquid. In this case, if maintenance is performed on the inkjet head 102 while ink is circulating in the ink circulation flow path 110, the cleaning liquid may be drawn from the nozzles, and the cleaning liquid may circulate through the ink circulation flow path 110 together with the ink, which may affect the ink in the ink circulation flow path 110. For example, when ultraviolet-curable ink is used as the ink, poor curing of the ink may occur during printing immediately after maintenance. In contrast, for example, if the ink storage sections 402a, b are made equal in pressure, ink does not circulate, and even if the pressure in the ink storage sections 402a, b is made negative, liquid such as cleaning liquid is not easily sucked from the nozzles. Therefore, in this example, the control section 120 makes the pressure in the ink storage sections 402a, b equal and stops the circulation of ink even when performing maintenance in the maintenance section 114. With this configuration, for example, it is possible to appropriately prevent cleaning liquid and the like from being sucked from the nozzles of the inkjet head 102 during maintenance.

[0048] However, even in this case, by making the pressures in the ink storage sections 402a and 402b equal, problems that do not occur when, for example, ink is circulated through the ink circulation channel 110 may occur. More specifically, even in this case, an unintended difference in pressure between the ink storage sections 402a and 402b may occur due to the influence of air leakage or the like, causing the ink level in either of the ink storage sections 402a and 402b to rise. In this case, the rise in the ink level may cause an overflow in either of the ink storage sections 402a and 402b. In response to this, in this example, the control section 120 generates a predetermined negative pressure in the pressure generating sections 322a and 322b in the pressure adjusting section 112, and causes the maintenance section 114 to perform maintenance on the inkjet head 102 with the two-way valves 320a and 320b open. Furthermore, while maintenance is being performed by the maintenance unit 114, the control unit 120 detects the ink level in the ink storage units 402a, b, and when the level in either one of the ink storage units 402a, b becomes higher than a predetermined level, the control unit 120 closes the two-way valve 320a, b that corresponds to the side of the ink storage units 402a, b where the level has risen, thereby suppressing an increase in the level difference, which is the difference in the ink levels in the ink storage units 402a, b. More specifically, in this case, the control unit 120 controls the operation of each unit of the printing device 100, for example, as shown in FIG.

[0049] FIG. 5 is a flowchart showing an example of the operation of the printing device 100 when performing maintenance in the maintenance unit 114, and shows an example of the operation of the printing device 100 with respect to the control performed by the control unit 120 based on the position of the ink liquid surface in the ink storage units 402a and 402b when performing maintenance. The operation shown in FIG. 5 can also be considered, for example, as an example of the operation of the control method of the printing device 100. In addition, the operation shown in FIG. 5 can be considered, for example, as an operation in a state in which the printing device 100 is not in a sleep state and ink can be circulated to the ink circulation flow path 110 immediately as needed (a state in which the circulation system can be continuously operated). The state in which ink can be circulated to the ink circulation flow path 110 immediately as needed can be considered, for example, as a state in which the printing device 100 is starting up or is on standby.

[0050] In this example, when the maintenance unit 114 is to perform maintenance on the inkjet head 102, the control unit 120 moves the inkjet head 102 to be maintained to the position of the maintenance unit 114 and causes the maintenance unit 114 to perform maintenance on the inkjet head 102. In this case, the control unit 120 adjusts the pressures in the ink storage units 402a, b to equal negative pressures (S122). Also, in this case, as described above, the control unit 120 causes the pressure generating units 322a, b in the pressure adjusting unit 112 to generate a predetermined negative pressure and opens the two-way valves 320a, b. More specifically, in this case, the control unit 120 causes the pressure generating units 322a, b to generate pressures that are lower than and equal to atmospheric pressure and opens the two-way valves 320a, b to adjust the pressures in the ink storage units 402a, b to equal negative pressures. In step S122 of this example, the control unit 120 equalizes the pressure in the ink storage units 402a and 402b and stops the pump 304 in the path control unit 202 of the ink circulation flow path 110, thereby stopping the circulation of ink in the ink circulation flow path 110. Then, in this state, the control unit 120 causes the maintenance unit 114 to start maintenance of the inkjet head 102.

[0051] While the maintenance unit 114 is performing maintenance on the inkjet head 102, the control unit 120 monitors the liquid level difference in the ink storage units 402a, b based on the output of the liquid level sensor 504 (S124), and if the liquid level difference is within an appropriate range (S124, Yes), while maintaining the state of the two-way valves 320a, b, checks whether the maintenance in the maintenance unit 114 is completed (S126). If the maintenance is not completed (S126, No), the control unit 120 returns to S124 and repeats the subsequent operations. As a result, the control unit 120 continues to monitor the liquid level difference in the ink storage units 402a, b until the maintenance is completed. Also, if it is determined in step S126 that the maintenance in the maintenance unit 114 is completed (S126, Yes), the control unit 120 ends the adjustment of the pressure in the ink storage units 402a, b to an equal negative pressure (S128), and ends the operation shown in FIG. 5. In this case, the control unit 120, for example, makes the pressure in the ink storage unit 402a higher than the pressure in the ink storage unit 402b, and circulates the ink through the ink circulation channel 110 again. Also, in step S124, when it is determined that the liquid level difference is greater than a predetermined difference (S124, No), the control unit 120 changes the state of the valve by closing the valve on the side where the liquid level is rising, among the two-way valves 320a, b (S130). This operation can be considered as, for example, an operation of closing one of the two-way valves 320a, b, which corresponds to the ink storage unit 402a, b, whose liquid level position is higher, when the liquid level difference is greater than a predetermined difference. Also, by changing the state of the valve in this way, the control unit 120 suppresses the increase in the liquid level difference in the ink storage units 402a, b.

[0052] Here, as in this example, when equal negative pressure is generated in the pressure generating units 322a, b and the two-way valves 320a, b are opened, it seems that there will be no difference in the liquid level in the ink storage units 402a, b. However, in the actual printing device 100, even though the ink storage units 402a, b are kept under equal pressure conditions, a liquid level difference may occur in the ink storage units 402a, b due to the influence of air leakage, the influence of pressure sensor errors, etc. In addition, in this case, it is considered that the liquid level difference will increase over time. In contrast, in this example, the three-way valves 302a, b are sealed on the side corresponding to the side where the liquid level rises, and the side corresponding to the side where the liquid level falls continues to provide negative pressure to the ink storage unit 402. With this configuration, for example, it is possible to appropriately prevent the pressure difference (differential pressure) in the ink storage units 402a, b from increasing, and appropriately suppress the increase in the liquid level difference. More specifically, in this case, by changing the state of the three-way valves 302a, b as described above, it is possible to prevent an increase in the pressure difference due to a decrease in the negative pressure in the ink storage sections 402a, b caused by air leakage or the like, and to maintain or eliminate the liquid level difference. Therefore, according to this example, even if a difference occurs in the ink level positions in the ink storage sections 402a, b due to some cause such as air leakage, it is possible to appropriately suppress an increase in the liquid level difference. This also makes it possible to more appropriately adjust the pressure in the ink storage sections 402a, b during maintenance, for example.

[0053] In addition, after changing the state of the two-way valves 320a, b in step S130 of this example, the control unit 120 returns to step S124 and repeats the subsequent operations. In this case, the control unit 120 maintains the state of the two-way valves 320a, b after changing it in step S130 until the liquid level difference returns to an appropriate range, for example. Therefore, after changing the state of the two-way valves 320a, b in step S130, if it is determined in step S124 that the liquid level difference is again greater than the predetermined difference (S124, No), in step S130, the control unit 120 maintains the changed state of the two-way valves 320a, b. Therefore, the operation of the control unit 120 in step S130 can be considered as, for example, an operation of changing the state of the two-way valves 320a, b as necessary. Furthermore, when the liquid level difference in the ink storage portions 402a, b is eliminated by changing the state of the three-way valves 302a, b as described above, for example, in step S124, the control portion 120 confirms that the liquid level difference is within an appropriate range. In this case, in response to this confirmation, the control portion 120 reopens, for example, one of the two-way valves 320a, b that was closed. In this case, the operation of closing one of the three-way valves 302a, b in step S130 can also be considered, for example, as an operation of temporarily closing a valve as necessary.

[0054] Regarding the control of the pressure on the ink storage portions 402a and 402b during maintenance, it seems that in order to prevent the cleaning liquid and the like from being sucked from the nozzles, it is sufficient to simply stop applying negative pressure to the ink storage portions 402a and 402b during maintenance. In this case, for example, it is possible to apply negative pressure to the ink storage portions 402a and 402b before maintenance and stop the supply of negative pressure during maintenance to maintain the negative pressure generated before maintenance. However, in this case, if there is an air leak, for example, near the ink storage portions 402a and 402b, the negative pressure may become insufficient due to leaving the ink storage portions 402a and 402b unattended during maintenance, making it impossible to maintain the meniscus in the inkjet head 102. As a result, it is possible that problems such as dripping may occur in the inkjet head 102. In contrast, according to this example, the pressure on the ink storage portions 402a and 402b can be more appropriately controlled during maintenance.

[0055] Next, supplementary explanations regarding each of the configurations described above will be given. As described above, in this example, the printing device 100 creates a negative pressure in the ink storage units 402a and 402b during printing and the like, and circulates ink through the ink circulation flow path 110 with a pressure difference. More specifically, in this case, the control unit 120 of the printing device 100 controls the pressure so that the upstream side, which is the input side of ink to the inkjet head 102, and the downstream side, which is the output side of ink, are both under negative pressure. When circulating ink through the ink circulation flow path 110, the control unit 120 makes the negative pressure on the downstream side stronger than the negative pressure on the upstream side, thereby creating a pressure difference and causing ink to flow from the upstream side to the downstream side in the ink flow path 314 that passes through the inkjet head 102. Also, in this case, the pump 304 for causing ink to flow through the flow path 316 that does not pass through the inkjet head 102 is used to send ink from the downstream side to the upstream side. With this configuration, for example, ink can be appropriately circulated through the ink circulation flow path 110. In this case, the printing device 100 can be considered as, for example, a system (ink circulation system) that circulates ink for the ink-circulating inkjet head 102 using a negative pressure control method.

[0056] As described above, in this example, the control unit 120 equalizes the pressures in the ink storage units 402a and 402b and stops the circulation of ink to the ink circulation channel 110 when transitioning to the sleep state or when performing maintenance on the inkjet head 102. When transitioning to the sleep state, the control unit 120 equalizes the pressures in the ink storage units 402a and 402b and closes the two-way valves 320a and 320b. In contrast, when performing maintenance, the control unit 120 equalizes the pressures in the ink storage units 402a and 402b with the two-way valves 320a and 320b open. Therefore, the operation of the control unit 120 when equalizing the pressures in the ink storage units 402a and 402b can be considered to be, for example, an operation of equalizing the pressures in the ink storage units 402a and 402b and closing the two-way valves 320a and 320b as necessary. Furthermore, during intermittent operation, the control unit 120 periodically updates the negative pressure in the ink storage units 402a, b by opening the two-way valves 320a, b when returning from a sleep state. In contrast, during maintenance, while there is no rise in the ink level in the ink storage units 402a, b, the control unit 120 keeps the three-way valves 302a, b open, thereby constantly supplying negative pressure to the ink storage units 402a, b. Therefore, when considering both intermittent operation and maintenance, the method of supplying negative pressure to the ink storage units 402a, b in this example can be, for example, a method of periodically or constantly supplying negative pressure.

[0057] As described above, when the pressures in the ink storage sections 402a and 402b are equalized during the sleep state, if air leaks or the like occur in the ink storage sections 402a and 402b or in the air flow paths connected to the ink storage sections 402a and 402b, the negative pressure in at least one of the ink storage sections 402a and 402b may weaken, resulting in a pressure difference in the ink storage sections 402a and 402b. If a pressure difference occurs in the ink storage sections 402a and 402b, the ink level may rise in one of the ink storage sections 402a and 402b, causing an overflow. If the pressure in the ink storage sections 402a and 402b changes, for example, the ink may backflow or ink may drip from the inkjet head 102. In contrast, according to this embodiment, such problems can be appropriately prevented by periodically updating the negative pressure through the intermittent operation described above. More specifically, if there is no problem such as leakage in the mechanism for maintaining the pressure (air pressure) and the liquid surface position in the ink storage sections 402a, b during the sleep state, the pressure in the ink storage sections 402a, b can be adjusted to a predetermined negative pressure before the sleep state is entered, and the pressure of the ink supplied to the inkjet head 102 (pressure on the nozzle surface) can be appropriately maintained at a negative pressure until the device returns from the sleep state. Usually, at least a small leak exists in one of the locations. Therefore, it is preferable to periodically update the negative pressure in the ink storage sections 402a, b by intermittent operation. In this case, it is preferable to set a standard sleep duration time taking into consideration the normal effects caused by a small leak.

[0058] However, for example, if there is a larger air leak or the like than normal at any point, performing intermittent operation using the standard sleep duration may cause various problems due to the negative pressure in the ink storage units 402a and 402b weakening during the sleep state or the pressure difference between the ink storage units 402a and 402b increasing. In contrast, in this example, the control unit 120 determines the sleep duration before transitioning to the sleep state as described above. With this configuration, for example, even if there is a large air leak or the like, the sleep duration can be appropriately determined taking into account its influence. Also, for example, even if there is a large air leak or the like, the negative pressure in the ink storage units 402a and 402b can be appropriately updated before a problem due to its influence occurs. Therefore, according to this example, for example, the printing device 100 can be made to perform intermittent operation more appropriately. Also, as described above, when updating the negative pressure, ink may be circulated through the ink circulation channel 110 as necessary. In this configuration, even if a large air leak occurs, the ink level difference that occurs in the ink storage units 402a and 402b during the sleep state can be appropriately eliminated unless it is fatal. This also allows the printing device 100 to perform intermittent operation for a longer period of time more appropriately. The sleep duration can be set to, for example, about 1 to 30 minutes. In this case, as described above, the sleep duration for a predetermined period (for example, within about 1 hour) immediately after the start of intermittent operation can be made different from the sleep duration thereafter, taking into consideration that the ink in the ink storage units 402a and 402b gradually cools after the start of intermittent operation. More specifically, the standard sleep duration can be set to about 10 minutes immediately after the start of intermittent operation. The standard sleep duration thereafter can be set to, for example, about 20 minutes. In this case, in step S102 of FIG. 4, the control unit 120 determines the sleep duration by adjusting these standard sleep durations based on the measured liquid level change time. With this configuration, for example, the sleep duration can be appropriately determined.

[0059] In the above, the cause of the change in the ink level position in the ink storage sections 402a, b when the ink storage sections 402a, b are kept at equal pressure has been mainly explained as being due to air leakage. However, in the printing device 100, such a change in the ink level position may be caused by a failure (failure mode) other than air leakage. For example, when there is variation in the characteristics (variation in characteristic values) of the liquid level sensor 504 that detects the ink level position in the ink storage sections 402a, b, or when there is an error (control error) in the pressure control such as an error (air control feedback error) in the feedback control performed in the air pressure control (air control), a difference may occur in the actual pressure in the ink storage sections 402a, b, causing a change in the ink level position, even if the ink storage sections 402a, b are kept at equal pressure as the control performed by the control section 120. Then, according to this example, even if the position of the ink level changes due to a cause other than such an air leak, for example, it is possible to appropriately prevent the occurrence of ink overflow in the ink storage sections 402a, b. Furthermore, when taking this point into consideration, in this example, making the ink storage sections 402a, b have equal pressures can also be considered to mean, for example, making the ink storage sections 402a, b have equal pressures under the control of the control section 120. Making the ink storage sections 402a, b have equal pressures under the control of the control section 120 can also be considered to mean, for example, executing design control in the control section 120 for making the ink storage sections 402a, b have equal pressures.

[0060] Regarding the overflow of ink in the ink storage sections 402a and 402b, the actual leakage of ink from either of the ink storage sections 402a and 402b can be considered as, for example, a form of ink backflow. As can be understood from the matters described above, according to this embodiment, not only the actual leakage of ink from either of the ink storage sections 402a and 402b but also the increased risk of ink leakage can be prevented. In this case, the control section 120 can be considered to prevent the ink storage sections 402a and 402b from being in a state where a certain amount or more of ink is present, for example, as an operation to prevent overflow. More specifically, in this case, the control section 120 prevents the ink level in the ink storage sections 402a and 402b from being in a full state, for example, by the operation described above. With this configuration, for example, the occurrence of ink overflow in the ink storage sections 402a and 402b can be more appropriately prevented. In addition, when the ink level in either of the ink storage sections 402a and 402b is in a full state, there is a possibility that overflow has already occurred. Therefore, in the control of the control unit 120, for example, regardless of whether ink is actually leaking from either of the ink storage units 402a, b, it may be determined that an overflow has occurred when the ink level in either of the ink storage units 402a, b is in the Full state. In this case, the overflow can also be considered to correspond to a state in which a certain amount or more of ink is present in the ink storage units 402a, b.

[0061] As described above, in this example, the printing device 100 receives a user instruction based on, for example, the user's operation of the power button on the operation unit 118, and transitions to a sleep state. The control unit 120 also executes a process for determining a sleep duration, for example, as a process to be performed before transitioning to a sleep state. In contrast, in a modified example of the operation of the printing device 100, the control unit 120 may receive, for example, an instruction from the user to start a process for determining a sleep duration, separate from an instruction to transition to a sleep state. In this case, the printing device 100 presents, for example, an operation menu including an item related to the process for determining a sleep duration to the user, and executes a process for determining a sleep duration in response to a user's operation to select this process from the operation menu. Even in this configuration, for example, the sleep duration can be appropriately determined before transitioning to a sleep state.

[0062] As described above, in this example, the control unit 120 controls the pressure of each of the circulation units 204 individually while generating a common pressure in the common pressure supply unit 208 for the plurality of circulation units 204. In this case, the configuration for connecting the plurality of circulation units 204 and the ink circulation flow paths 110 can be considered as, for example, a configuration in which the plurality of ink circulation flow paths 110 each having the ink storage units 402a, b is bundled by the pressure distribution unit 206 having the two-way valves 320a, b for each ink circulation flow path 110, and the pressure is adjusted by the common (single) common pressure supply unit 208. Adjusting the pressure by the common common pressure supply unit 208 can be considered as, for example, making the pressure pump, pressure sensor, etc. constituting at least a part of the pressure generating units 322a, b of the common pressure supply unit 208 common (the same) among the plurality of ink circulation flow paths 110. Also, the operation described above using Figures 4, 5, etc. can be considered as, for example, a particularly suitable operation in such a configuration. In a modified configuration of the printing device 100, the pressure adjustment unit 112 may have a pressure supply unit for each ink circulation channel 110 (for each inkjet head 102) that has the same or similar configuration as the common pressure supply unit 208. Even in such a configuration, for example, the pressure supplied to the ink circulation channel 110 can be appropriately adjusted.

[0063] Furthermore, the inventor of the present application actually conducted an experiment to confirm the effect of preventing overflow, etc., of the operation described above with reference to Figure 5. In this experiment, the capacity of the ink storage sections 402a and 402b was set to 40cc, the amount of ink was set to 16 to 20cc, which is the middle state, and the differential pressure within the ink storage sections 402a and 402b was varied. The time until overflow occurred was confirmed when the increase in the liquid level difference was suppressed by changing the state of the two-way valves 320a, b in the operation of step S130 in FIG. 5 and when it was not suppressed. More specifically, when the increase in the liquid level difference was not suppressed, when the differential pressure was set to 0.2 kPa, overflow occurred in either of the ink storage sections 402a, b in about 7 to 11 minutes. When the differential pressure was set to 0.3 kPa, overflow occurred in either of the ink storage sections 402a, b in just under 5 minutes. When the differential pressure was set to 0.5 kPa, overflow occurred in either of the ink storage sections 402a, b in 3 minutes. When the differential pressure was set to 0.7 kPa, overflow occurred in either of the ink storage sections 402a, b in 1.5 minutes. In contrast, when the increase in the liquid level difference was suppressed, no overflow occurred during the 30 minutes or more during which measurements were performed, regardless of the differential pressure setting. Therefore, this experimental result also shows that overflow can be appropriately prevented by the operation explained using FIG. [Industrial Applicability]

[0064] The present invention can be suitably used in, for example, a printing device. [Explanation of symbols]

[0065] 100 printing device, 102 inkjet head, 104 carriage, 106 platen, 108 ink supply unit, 110 ink circulation flow path, 112 pressure adjustment unit, 114 maintenance unit, 116 scan drive unit, 118 operation unit, 120 control unit, 202 path control unit, 204 circulation unit, 206 pressure distribution unit, 208 common pressure supply unit, 302 three-way valve, 304 pump, 306 filter, 308 connection part, 312 subtank, 314 flow path, 316 flow path, 318 filter, 320 two-way valve, 322 pressure generating part, 324 connection part, 402 ink storage part, 412 inlet, 414 outlet, 416 vent, 50 medium, 502 heater, 504 liquid level sensor, 512 float, 514 detection part

Claims

1. An inkjet head for ejecting ink, This inkjet head has ink storage units that store ink on the upstream and downstream sides, respectively. An ink circulation channel comprising a channel for circulating ink from the upstream side to the downstream side via the inkjet head and a channel for circulating ink from the downstream side to the upstream side without passing through the inkjet head, This ink circulation channel generates a pressure generating unit that transmits pressure to the ink storage unit, This includes a valve that opens and closes the air passage between the pressure generating section and the ink storage section. During ink circulation, the valve is opened with the pressure on the upstream side set higher than the pressure on the downstream side, and the pressure in the upstream storage section is made higher than the pressure in the downstream storage section to circulate the ink. When transitioning to sleep mode, the pressure in the upstream reservoir and the pressure in the downstream reservoir are made equal for a certain period of time, and then the valve is closed. A printing apparatus characterized by entering a sleep state, waking up from the sleep state to open the valve, and then returning to the sleep state with the valve closed.

2. The printing apparatus according to claim 1, characterized in that the certain time during the transition to sleep is determined based on the position of the ink level in the ink reservoir.

3. The printing apparatus according to claim 1, further comprising a liquid level sensor for detecting changes in the liquid level of the ink in the ink storage section, wherein the constant time during transition to sleep is determined based on the output of the liquid level sensor.

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