Inkjet printer and method for controlling inkjet printer

Abstract

Provided is an inkjet printer capable of continuing a printing operation even during replacement work of a main tank, the inkjet printer including: an inkjet head for discharging ink; a sub-tank for accommodating the ink to be supplied to the inkjet head; and a main tank for accommodating the ink to be supplied to the sub-tank.　An inkjet printer 1 is provided with: an inkjet head 5; a sub-tank 11; a main tank 17; a buffer tank 18 which is disposed in a piping path between the sub-tank 11 and the main tank 17, and in which ink is accommodated; a pump 19 which is disposed in a piping path between the sub-tank 11 and the buffer tank 18; and a check valve 20 which is disposed in parallel with the buffer tank 18 in a piping path between the main tank 17 and the pump 19, and which allows a flow of ink only in a direction from the main tank 17 to the pump 19.

Description

Inkjet printer and method for controlling an inkjet printer

[0001] The present invention relates to an inkjet printer for printing on a medium, and also to a method for controlling such an inkjet printer.

[0002] Inkjet printers that print on media such as paper are known (see, for example, Japanese Patent Application Laid-Open No. 2003-121998). The inkjet printer described in Japanese Patent Application Laid-Open No. 2003-121998 includes an inkjet head that ejects ink, a carriage on which the inkjet head is mounted, a sub-tank that contains ink to be supplied to the inkjet head, a main tank that contains ink to be supplied to the sub-tank, and an ink pump that sends ink from the main tank to the sub-tank. The sub-tank is mounted on the carriage. The main tank is detachably attached to the body frame of the inkjet printer.

[0003] Inkjet printers that print on media such as paper are also known (see, for example, Japanese Patent Application Laid-Open No. 2003-121594). The inkjet printer described in Japanese Patent Application Laid-Open No. 2003-121594 includes an inkjet head that ejects ink, a main tank that contains the ink, and an ink supply system that supplies ink from the main tank to the inkjet head. The main tank is, for example, an ink container that can be removed and replaced from the inkjet printer.

[0004] In the inkjet printer described in Patent Document 2, the ink supply system includes a sub-tank located midway along the ink supply path from the main tank to the inkjet head, a supply flow path through which ink flows from the main tank to the sub-tank, a circulation path through which ink flows from the sub-tank to the main tank, a pump for causing ink to flow in the supply path, and a pump for causing ink to flow in the circulation path. The supply flow path and the circulation path are, for example, tubes through which ink flows. In the inkjet printer described in Patent Document 2, it is possible to circulate ink between the main tank and the sub-tank, thereby making it possible to suppress settling of ink particles in the main tank and the sub-tank.

[0005] Also, conventionally, inkjet recording devices equipped with a recording head (inkjet head) are known (see, for example, Patent Document 3). In the inkjet recording device described in Patent Document 3, an ink supply system that supplies ink to the recording head includes a main tank, a buffer tank, a supply sub-tank connected to the supply port of the recording head, and a recovery sub-tank connected to the discharge port of the recording head. The supply sub-tank is connected to the main tank via the buffer tank.

[0006] In addition, in the inkjet recording apparatus described in Patent Document 3, a pump is installed in the flow path between the buffer tank and the supply sub-tank to supply ink to the supply sub-tank. Also, a pump is installed in the flow path between the main tank and the buffer tank to supply ink to the buffer tank. An on-off valve is disposed in the flow path between the pump and the main tank. In the inkjet recording apparatus described in Patent Document 3, the on-off valve is completely closed to shut off the flow path when the main tank is replaced.

[0007] JP 2020-116813 A JP 2023-7061 A JP 2010-83021 A

[0008] In the inkjet printer described in Patent Document 1, when the ink in the main tank runs out, the main tank is replaced. In this inkjet printer, ink cannot be supplied from the main tank to the sub-tank during the main tank replacement process, so the inkjet printer cannot continue printing. In other words, in the inkjet printer described in Patent Document 1, printing operations of the inkjet printer must be interrupted during the main tank replacement process.

[0009] Therefore, an object of the present invention is to provide an inkjet printer that is equipped with an inkjet head that ejects ink, a sub-tank that stores ink to be supplied to the inkjet head, and a main tank that stores ink to be supplied to the sub-tank, and that is capable of continuing printing operations even while the main tank is being replaced.

[0010] Furthermore, in the inkjet printer described in Patent Document 2, if the main tank is a replaceable ink container, for example, if a connection failure occurs in which the supply flow path is not properly connected to the replaced main tank, the amount of ink flowing from the main tank to the sub-tank will decrease, and an ink supply failure may occur in which an appropriate amount of ink is not supplied from the main tank to the sub-tank. In the inkjet printer described in Patent Document 2, if this ink supply failure occurs, there is a risk of interference with printing on media.

[0011] Furthermore, in the inkjet printer described in Patent Document 2, if this ink supply failure occurs, when ink is circulated between the main tank and the sub-tank, an appropriate amount of ink flows into the main tank while the amount of ink flowing out of the main tank decreases, which can cause ink to overflow from the main tank. Therefore, it is preferable that the inkjet printer described in Patent Document 2 be designed to make it easy for the operator of the inkjet printer to recognize that an ink supply failure has occurred, in which ink is not being properly supplied from the main tank to the sub-tank.

[0012] Therefore, an object of the present invention is to provide an inkjet printer that includes a main tank that stores ink and a supply-side tank that is located closer to the inkjet head than the main tank in a piping path between the main tank and the inkjet head and stores ink supplied from the main tank, and that can easily make an operator aware of an ink supply problem that prevents ink from being properly supplied from the main tank to the supply-side tank.Another object of the present invention is to provide an inkjet printer control method that can easily make an operator aware of an ink supply problem that prevents ink from being properly supplied from the main tank to the supply-side tank, and that can easily make an operator aware of an ink supply problem that prevents ink from being properly supplied from the main tank to the supply-side tank.

[0013] The inventors have also developed an inkjet printer that includes a sub-tank that stores ink to be supplied to an inkjet head, a buffer tank that stores ink to be supplied to the sub-tank, a main tank that stores ink to be supplied to the buffer tank, and a pump located in a piping path between the buffer tank and the sub-tank. In the inkjet printer under development, the inventors have decided to provide a piping path for returning ink from the buffer tank to the main tank in order to circulate ink between the main tank and the buffer tank and prevent ink particles from settling in the buffer tank.

[0014] Specifically, the inventors of the present invention have provided a first piping path connecting the pump and the sub-tank, a second piping path connecting the first piping path and the main tank, a first on-off valve disposed in the piping path between the sub-tank and a junction of the first piping path and the second piping path, and a second on-off valve disposed in the second piping path. In this inkjet printer, when the pump is driven with the second on-off valve open and the first on-off valve closed, ink flows from the buffer tank to the main tank, circulating ink between the main tank and the buffer tank. Furthermore, when the pump is driven with the first on-off valve open and the second on-off valve closed, ink flows from the buffer tank to the sub-tank, supplying ink to the sub-tank.

[0015] The inventors have also decided to connect the second piping path and the main tank in an inkjet printer under development with a joint having a piping-side joint attached to the end of the second piping path and a tank-side joint attached to the main tank and to which the piping-side joint is connected. Furthermore, the inventors have decided to employ a piping-side joint that is sealed when separated from the tank-side joint, in order to prevent ink from leaking from the piping-side joint when the piping-side joint and the tank-side joint are separated.

[0016] In the inkjet printer under development, if a poor connection occurs between the piping-side joint and the tank-side joint, the pump may be unable to send ink when attempting to circulate ink between the main tank and the buffer tank, placing excessive strain on the pump and causing the pump to malfunction. Furthermore, if a poor connection occurs in the joint, the pressure inside the second piping path may become excessively high when attempting to circulate ink between the main tank and the buffer tank, potentially causing ink to leak from the second piping path. Therefore, in the inkjet printer under development, it is preferable that ink not circulate between the main tank and the buffer tank when a poor connection occurs in the joint.

[0017] Therefore, the object of the present invention is to provide an inkjet printer that is equipped with a sub-tank, a buffer tank, a main tank, a pump arranged in a piping path between the buffer tank and the sub-tank, a first piping path connecting the pump and the sub-tank, and a second piping path connecting the first piping path and the main tank, and that is capable of preventing ink from circulating between the main tank and the buffer tank when there is a poor connection between a piping-side joint attached to the end of the second piping path and a tank-side joint attached to the main tank and to which the piping-side joint is connected.

[0018] Another object of the present invention is to provide a control method for an inkjet printer that includes a sub-tank, a buffer tank, a main tank, a pump arranged in a piping path between the buffer tank and the sub-tank, a first piping path connecting the pump and the sub-tank, and a second piping path connecting the first piping path and the main tank, which is capable of preventing ink from circulating between the main tank and the buffer tank when there is a poor connection between a piping-side joint attached to the end of the second piping path and a tank-side joint attached to the main tank and to which the piping-side joint is connected.

[0019] In order to solve the above problems, the inkjet printer of the present invention is characterized by comprising an inkjet head that ejects ink, a sub-tank that stores ink to be supplied to the inkjet head, a main tank that stores ink to be supplied to the sub-tank, a buffer tank that is arranged in a piping path between the sub-tank and the main tank and stores ink, a pump that is arranged in the piping path between the sub-tank and the buffer tank, and a check valve that is arranged in parallel to the buffer tank in the piping path between the main tank and the pump and allows ink to flow only in a direction from the main tank toward the pump.

[0020] The inkjet printer of the present invention is equipped with a buffer tank disposed in the piping path between the sub-tank and the main tank. Therefore, with this invention, ink can be supplied from the buffer tank to the sub-tank even during the replacement of the main tank. Therefore, with this invention, the inkjet printer can continue to print even during the replacement of the main tank.

[0021] In the present invention, if, for example, the consumption of ink ejected from the inkjet head increases to perform high-density printing, increasing the amount of ink flowing from the buffer tank to the sub-tank per unit time, or if a low-temperature environment causes the viscosity of the ink to increase and the amount of ink flowing from the main tank to the buffer tank per unit time decreases, the supply of ink from the main tank to the buffer tank during printing may not be able to keep up, and the amount of ink remaining in the buffer tank may become low during printing.On the other hand, in the present invention, because a pump is disposed in the piping path between the sub-tank and the buffer tank to supply ink from the buffer tank to the sub-tank, if the amount of ink remaining in the buffer tank becomes low during printing and ink is no longer supplied from the buffer tank to the sub-tank, it may become difficult for the inkjet printer to print properly.

[0022] However, the inkjet printer of the present invention is equipped with a check valve that is arranged parallel to the buffer tank in the piping path between the main tank and the pump and allows ink to flow only in the direction from the main tank toward the pump. Therefore, with this invention, even if the amount of ink remaining in the buffer tank becomes low during printing and ink can no longer be supplied from the buffer tank to the sub-tank, ink can still be supplied from the main tank to the sub-tank via the check valve. Therefore, with this invention, even if the amount of ink remaining in the buffer tank becomes low during printing and ink can no longer be supplied from the buffer tank to the sub-tank, the inkjet printer can continue to print properly.

[0023] In addition, in the present invention, the inkjet printer preferably includes an on-off valve disposed in the piping between the main tank and the buffer tank. With this configuration, the main tank can be replaced with the on-off valve closed. This makes it easy to replace the main tank.

[0024] Furthermore, in the present invention, it is preferable that ink be supplied from the main tank to the buffer tank by a hydraulic head difference. This configuration simplifies the configuration of the inkjet printer compared to when a pump is installed in the piping between the main tank and the buffer tank. On the other hand, compared to when ink is supplied from the main tank to the buffer tank by a pump, when ink is supplied from the main tank to the buffer tank by a hydraulic head difference, it becomes more difficult to supply ink to the buffer tank, increasing the likelihood that the amount of ink remaining in the buffer tank will become low during printing. However, in the present invention, the inkjet printer can continue to print properly even if the amount of ink remaining in the buffer tank becomes low during printing.

[0025] In the present invention, the buffer tank is, for example, a bag-shaped ink pack. In this case, when the amount of ink remaining in the buffer tank becomes small, the buffer tank, which is an ink pack, collapses.

[0026] In the present invention, the inkjet printer preferably includes a second on-off valve disposed in a piping path between the subtank and the pump, and a third on-off valve disposed in a piping path having one end connected to the piping path between the second on-off valve and the pump and the other end connected to the main tank. With this configuration, closing the second on-off valve and opening the third on-off valve makes it possible to form an ink circulation path passing through the main tank and the buffer tank. Therefore, driving the pump with the second on-off valve closed and the third on-off valve open makes it possible to circulate ink in the circulation path, thereby making it possible to suppress settling of ink particles in the main tank and the buffer tank.

[0027] In the present invention, the inkjet printer preferably includes an on-off valve disposed in the piping path between the main tank and the buffer tank. This configuration allows the main tank to be replaced with the on-off valve closed. Therefore, the main tank can be easily replaced. Furthermore, this configuration allows the ink in the buffer tank to be drained into the main tank by driving the pump with the on-off valve and the second on-off valve closed and the third on-off valve open. Therefore, for example, when the buffer tank needs to be replaced, the ink in the buffer tank can be drained.

[0028] In the present invention, it is preferable that the inkjet printer is provided with a detection mechanism for detecting the volume of ink contained in the main tank, and that the volume of ink contained in the buffer tank is indirectly detected by the detection mechanism. With this configuration, it is possible to detect the volume of ink contained in the buffer tank even if a mechanism for detecting the volume of ink contained in the buffer tank is not installed, thereby simplifying the configuration of the inkjet printer.

[0029] In order to solve the above-mentioned problems, an inkjet printer of the present invention is an inkjet printer equipped with an inkjet head that ejects ink, the inkjet printer comprising: a main tank that stores ink; a supply-side tank that is arranged closer to the inkjet head than the main tank in a piping path between the main tank and the inkjet head and stores ink supplied from the main tank; a pump for circulating ink between the main tank and the supply-side tank; a first piping path that is a supply piping path through which ink flows from the main tank to the supply-side tank; a second piping path that is a circulation piping path through which the pump is arranged and through which ink flows from the supply-side tank to the main tank; a detection mechanism for detecting the amount of ink stored in the main tank; and a control unit for controlling the inkjet printer, wherein the control unit drives the pump to circulate ink between the main tank and the supply-side tank and detects the amount of ink stored in the detection mechanism. The ink change amount in the main tank over a first fixed time period is calculated based on the detection results at a predetermined first fixed time interval, and if the calculated increase amount is equal to or greater than a predetermined first reference amount multiple times in succession, a predetermined error process is executed; and while circulating ink, the ink change amount in the main tank over a second fixed time period is calculated based on the detection results of the detection mechanism, and an ink change difference, which is the difference between the ink change amount in the main tank over the second fixed time period calculated previously and the ink change amount in the main tank over the second fixed time period calculated this time, is calculated at the second fixed time interval, and the amount of ink in the main tank when the absolute value of the calculated ink change difference is equal to or less than a predetermined second reference amount that is smaller than the first reference amount multiple times in succession, is stored as an initial ink amount; and error process is also executed if the ink increase amount in the main tank from the stored initial ink amount becomes a predetermined third reference amount that is greater than the first reference amount.

[0030] In order to solve the above-mentioned problems, a control method for an inkjet printer of the present invention is a control method for an inkjet printer comprising an inkjet head that ejects ink, a main tank that stores ink, a supply-side tank that is arranged closer to the inkjet head than the main tank in a piping path between the main tank and the inkjet head and stores ink supplied from the main tank, a pump for circulating ink between the main tank and the supply-side tank, a first piping path that is a supply piping path through which ink flows from the main tank to the supply-side tank, a second piping path that is a circulation piping path through which the pump is arranged and through which ink flows from the supply-side tank to the main tank, and a detection mechanism for detecting the amount of ink stored in the main tank, wherein the control method drives the pump to circulate ink between the main tank and the supply-side tank and determines a predetermined amount of ink based on a detection result of the detection mechanism. the amount of ink in the main tank during the first fixed time interval is calculated at a first fixed time interval, and if the calculated amount of ink in the main tank exceeds a predetermined first reference amount several times in succession, a predetermined error process is executed; and while circulating ink, the amount of ink change in the main tank during the second fixed time interval is calculated at a second fixed time interval based on the detection result of the detection mechanism, and an ink change difference, which is the difference between the amount of ink change in the main tank during the second fixed time interval calculated last time and the amount of ink change in the main tank during the second fixed time calculated this time, is calculated at the second fixed time interval, and the amount of ink in the main tank when the absolute value of the calculated ink change difference becomes equal to or less than a predetermined second reference amount that is smaller than the first reference amount several times in succession, is stored as an initial ink amount; and thereafter, error process is executed when the amount of ink increase in the main tank from the stored initial ink amount becomes a predetermined third reference amount that is larger than the first reference amount.

[0031] In this invention, during ink circulation in which ink is circulated between the main tank and the supply-side tank, the increase in the amount of ink in the main tank over a first fixed time period is calculated at first fixed time intervals based on the detection results of the detection mechanism, and if the calculated increase exceeds a first reference amount multiple times in succession, a predetermined error process is executed. Also, during ink circulation, the change in the amount of ink in the main tank over a second fixed time period is calculated at second fixed time intervals based on the detection results of the detection mechanism, and an ink change difference, which is the difference between the amount of ink change in the main tank over the second fixed time period calculated previously and the amount of ink change in the main tank over the second fixed time period calculated this time, is calculated at the second fixed time intervals. The amount of ink in the main tank when the absolute value of the calculated ink change difference becomes equal to or less than a second reference amount that is less than the first reference amount multiple times in succession is stored as the initial ink amount. Also, if the increase in the amount of ink in the main tank from the stored initial ink amount becomes a third reference amount that is greater than the first reference amount, an error process is executed.

[0032] That is, in the present invention, if the increase in the amount of ink in the main tank over a first fixed period of time exceeds the first reference amount multiple times in succession, or if the increase in the amount of ink from the initial ink amount, which is the amount of ink in the main tank stored at a predetermined timing, reaches the third reference amount, error processing is executed. This makes it possible for the operator to easily recognize that an ink supply problem has occurred, in which ink is not being supplied appropriately from the main tank to the supply-side tank.

[0033] Furthermore, in the present invention, if the increase in the amount of ink in the main tank over a first fixed period of time exceeds the first reference amount multiple times in succession, or if the increase in the amount of ink from the initial ink amount stored at a predetermined timing reaches a third reference amount that is greater than the first reference amount, error processing is executed, thereby making it possible to execute error processing while suppressing the effects of error in the detection mechanism and noise on the detection mechanism. Therefore, in the present invention, it is possible to accurately notify the operator that there is a problem with the ink supply from the main tank to the supply-side tank.

[0034] Furthermore, in the present invention, error processing is executed when the increase in the amount of ink in the main tank over a first fixed period of time exceeds the first reference amount multiple times in succession. Therefore, when the ink supplied from the main tank to the supply-receiving tank decreases significantly and the amount of ink in the main tank increases significantly in a relatively short period of time, the operator can quickly recognize that there is a problem with the supply of ink from the main tank to the supply-receiving tank.

[0035] Furthermore, in the present invention, error processing is executed when the increase in the amount of ink from the initial amount of ink stored at a predetermined timing reaches a third reference amount. Therefore, even if there is a problem with the supply of ink from the main tank to the supply-receiving tank, the degree of decrease in the ink supplied from the main tank to the supply-receiving tank is small and the amount of ink in the main tank does not increase significantly in a short period of time, the operator can be made aware of the problem.

[0036] Furthermore, the present invention calculates the amount of change in the ink in the main tank over a second fixed time interval, and also calculates an ink change difference, which is the difference between the previously calculated amount of change in the ink in the main tank over the second fixed time interval and the currently calculated amount of change in the ink in the main tank over the second fixed time interval, at the second fixed time interval. The amount of ink in the main tank when the absolute value of the calculated ink change difference is equal to or less than the second reference amount multiple times in succession is stored as the initial ink amount. This makes it possible to store the amount of ink in the main tank when no disturbances or other disturbances are occurring in the main tank (i.e., when the main tank is in a stable state) as the initial ink amount. In other words, the present invention makes it possible to accurately set the initial ink amount. Therefore, the present invention makes it possible to accurately notify the operator of poor ink supply from the main tank to the supply-side tank based on the accurately set initial ink amount.

[0037] In the present invention, for example, the main tank can be removed from the inkjet printer and replaced. In this case, there is a risk that a connection failure or the like will occur, in which the replaced main tank is not properly connected to the first piping path, which will result in a high possibility of a failure in the supply of ink from the main tank to the supply-side tank. However, with the present invention, it is possible to easily make the operator aware of a failure in the supply of ink from the main tank to the supply-side tank.

[0038] In the present invention, the inkjet printer includes, for example, a sub-tank that stores ink to be supplied to the inkjet head, a buffer tank as a supply-side tank that stores ink to be supplied to the sub-tank from the main tank, a first on-off valve, and a second on-off valve. A connection point is provided in the middle of a piping path connecting the buffer tank and the sub-tank, and the other end of the piping path is connected to the main tank. A second piping path is formed by a third piping path that is the piping path between the buffer tank and the connection point, and a fourth piping path that is the piping path between the connection point and the main tank. A pump is disposed in the third piping path, the first on-off valve is disposed in the piping path between the connection point and the sub-tank, and the second on-off valve is disposed in the fourth piping path. When the pump is driven with the second on-off valve open and the first on-off valve closed, ink flows from the buffer tank toward the main tank. When the pump is driven with the first on-off valve open and the second on-off valve closed, ink flows from the buffer tank toward the sub-tank.

[0039] In this case, a common pump can supply ink to the sub-tank and circulate ink between the main tank and the supply-side tank. This simplifies the configuration of the inkjet printer. Furthermore, in this case, a buffer tank is placed in the piping path between the main tank and the sub-tank, so ink can be supplied from the buffer tank to the sub-tank even during the replacement of the main tank. This allows the inkjet printer to continue printing even during the replacement of the main tank.

[0040] In the present invention, the ink jet printer includes an ink filter disposed in the third piping path, for example, and ink is supplied from the main tank to the buffer tank by the head difference.

[0041] In this case, because an ink filter is disposed in the third piping path, depending on the condition of the ink filter (specifically, the degree of clogging of the ink filter), the amount of ink circulating between the main tank and the buffer tank during ink circulation may decrease, and even though there is a problem with the ink supply from the main tank to the supply-side tank, the amount of ink in the main tank may not increase significantly in a short period of time. However, with the present invention, even if there is no significant increase in the amount of ink in the main tank in a short period of time, it is possible to make the operator aware of the problem with the ink supply from the main tank to the supply-side tank.

[0042] Furthermore, in this case, because ink is supplied from the main tank to the buffer tank due to a hydraulic head difference, if air is introduced into the first piping path when connecting one end of the first piping path to the main tank, the introduced air may remain in the first piping path, causing a supply failure of ink from the main tank to the buffer tank. However, even if this supply failure occurs, the amount of ink supplied from the main tank to the buffer tank is only reduced to a small extent, so the amount of ink in the main tank does not increase significantly in a short period of time. However, with this invention, even if the amount of ink in the main tank does not increase significantly in a short period of time, it is possible to make the operator aware of a supply failure of ink from the main tank to the buffer tank.

[0043] In order to solve the above-mentioned problems, an inkjet printer of the present invention is an inkjet printer equipped with an inkjet head that ejects ink, the inkjet printer comprising: a sub-tank that stores ink to be supplied to the inkjet head; a buffer tank that stores ink to be supplied to the sub-tank; a main tank that stores ink to be supplied to the buffer tank; a pump arranged in a piping path between the buffer tank and the sub-tank; a first piping path that is a piping path connecting the pump and the sub-tank; a second piping path that is a piping path connecting the first piping path and the main tank; a joint having a piping-side joint attached to an end of the second piping path and a tank-side joint attached to the main tank and to which the piping-side joint is connected; a first on-off valve arranged in the piping path between the sub-tank and a junction of the first piping path and the second piping path; a second on-off valve arranged in the second piping path; a detection mechanism for detecting the amount of ink stored in the sub-tank; and a control unit for controlling the inkjet printer. When the pump is driven with the second on-off valve open and the first on-off valve closed, ink flows from the buffer tank toward the main tank; when the pump is driven with the first on-off valve open and the second on-off valve closed, ink flows from the buffer tank toward the sub-tank; when the piping-side joint and the tank-side joint are normally connected, when the pump is driven with the first on-off valve and the second on-off valve open, the amount of ink flowing from the buffer tank to the main tank becomes greater than the amount of ink flowing from the buffer tank to the sub-tank; when the piping-side joint and the tank-side joint are disconnected, the piping-side joint is sealed to prevent ink from leaking; and when the amount of ink in the sub-tank is set to a predetermined first reference amount, the control unit opens the first on-off valve and the second on-off valve and drives the pump at a constant speed for a predetermined first time, and performs a confirmation operation to determine whether the amount of ink in the sub-tank exceeds a predetermined second reference amount based on the detection result of the detection mechanism.

[0044] Furthermore, in order to solve the above-mentioned problems, a control method for an inkjet printer of the present invention includes an inkjet head that ejects ink, a sub-tank that contains ink to be supplied to the inkjet head, a buffer tank that contains ink to be supplied to the sub-tank, a main tank that contains ink to be supplied to the buffer tank, a pump arranged in a piping path between the buffer tank and the sub-tank, a first piping path that is a piping path connecting the pump and the sub-tank, a second piping path that is a piping path connecting the first piping path and the main tank, a joint having a piping-side joint part attached to an end of the second piping path and a tank-side joint part attached to the main tank and to which the piping-side joint part is connected, a first on-off valve arranged in the piping path between the sub-tank and a junction of the first piping path and the second piping path, a second on-off valve arranged in the second piping path, and a detection mechanism for detecting the amount of ink contained in the sub-tank, wherein when the second on-off valve is open and the first on-off valve is closed, When the pump is driven with the first on-off valve open and the second on-off valve closed, ink flows from the buffer tank to the sub-tank. When the pump is driven with the first on-off valve open and the second on-off valve closed, ink flows from the buffer tank to the sub-tank. When the piping-side joint and the tank-side joint are normally connected, when the pump is driven with the first on-off valve and the second on-off valve open, the amount of ink flowing from the buffer tank to the main tank becomes greater than the amount of ink flowing from the buffer tank to the sub-tank. When the piping-side joint and the tank-side joint are disconnected, the piping-side joint is sealed to prevent ink from leaking. This inkjet printer control method is characterized in that, with the amount of ink in the sub-tank set to a predetermined first reference amount, the first on-off valve and the second on-off valve are opened and the pump is driven at a constant speed for a predetermined first time, and a confirmation operation is performed to determine whether the amount of ink in the sub-tank exceeds a predetermined second reference amount based on the detection result of the detection mechanism.

[0045] In this invention, with the amount of ink in the sub-tank set to a predetermined first reference amount, the first and second on-off valves are opened and the pump is driven at a constant speed for a predetermined first time period, and a confirmation operation is performed to determine whether the amount of ink in the sub-tank exceeds a predetermined second reference amount based on the detection result of the detection mechanism. Also, in this invention, when the piping-side joint and the tank-side joint are properly connected and the pump is driven with the first and second on-off valves open, the amount of ink flowing from the buffer tank to the main tank is greater than the amount of ink flowing from the buffer tank to the sub-tank, and when the piping-side joint and the tank-side joint are disconnected, the piping-side joint is sealed to prevent ink from leaking.

[0046] Therefore, in this invention, when the piping-side joint and the tank-side joint are properly connected, the confirmation operation prevents the amount of ink in the subtank from exceeding the second reference amount, and when the piping-side joint and the tank-side joint are not properly connected, the confirmation operation allows the amount of ink in the subtank to exceed the second reference amount. Therefore, in this invention, when the amount of ink in the subtank exceeds the second reference amount, a predetermined process is executed to prevent ink from circulating between the main tank and the buffer tank, making it possible to prevent ink from circulating between the main tank and the buffer tank when a poor connection of the joint has occurred. Furthermore, in this invention, when the amount of ink in the subtank exceeds the second reference amount, a predetermined process is executed to notify the operator that a poor connection of the joint has occurred, making it possible to easily make the operator aware of the poor connection of the joint.

[0047] In the present invention, for example, the main tank can be removed from the inkjet printer and replaced. In this case, there is a high possibility that a poor connection will occur at the joint after replacing the main tank. However, with the present invention, even if a poor connection occurs at the joint, it is possible to prevent ink from circulating between the main tank and the buffer tank.

[0048] In the present invention, it is preferable that the pump driving speed when the confirmation operation is performed is slower than the pump driving speed when printing with an inkjet printer, the pump is driven with the first on-off valve open and the second on-off valve closed, and ink flows from the buffer tank to the sub-tank.

[0049] If the pump drive speed when printing with an inkjet printer and the pump is driven with the first on-off valve open and the second on-off valve closed to cause ink to flow from the buffer tank to the subtank is defined as the "normal drive speed," then according to the inventor's investigations, if the pump drive speed when the checking operation is performed is equal to or higher than the normal drive speed, ink is more likely to flow from the buffer tank to the subtank when the pump is driven with the first on-off valve and the second on-off valve open, even if the piping-side joint and the tank-side joint are properly connected. Therefore, in this case, even if the piping-side joint and the tank-side joint are properly connected, there is a risk that the amount of ink in the subtank will exceed the second reference amount during the checking operation.

[0050] In contrast, according to the inventor's investigations, if the pump driving speed when the checking operation is performed is slower than the normal driving speed, and the piping-side joint and the tank-side joint are properly connected, when the pump is driven with the first and second on-off valves open, ink will not easily flow from the buffer tank to the sub-tank. Therefore, if the pump driving speed when the checking operation is performed is slower than the normal driving speed, and the piping-side joint and the tank-side joint are properly connected, it is possible to prevent the amount of ink in the sub-tank from exceeding the second reference amount during the checking operation.

[0051] In the present invention, for example, an inkjet printer includes a maintenance unit that performs a cleaning operation of the inkjet head to prevent clogging of the nozzles of the inkjet head, and the control unit executes a checking operation during the cleaning operation.

[0052] In the present invention, the cleaning operation preferably includes a purging operation in which the pressure in the subtank is made positive and ink is ejected from the inkjet head. After the purging operation, the amount of ink in the subtank reaches a first reference amount, and the control unit preferably executes the verification operation when predetermined conditions are met after the purging operation. This configuration eliminates the need to eject ink from the inkjet head until the amount of ink in the subtank reaches the first reference amount just to execute the verification operation. Therefore, even when the verification operation is executed, it is possible to reduce unnecessary ink consumption.

[0053] In the present invention, it is preferable that, after the purging operation, the control unit drives the pump with the first on-off valve open and the second on-off valve closed to supply ink to the subtank until the amount of ink in the subtank reaches a second reference amount, measures the second time, which is the time it takes for the amount of ink in the subtank to reach the second reference amount, and, if the confirmation operation is not performed after the purging operation, stores the most recent measured second time and calculates the first time based on the second time. With this configuration, even if the condition of the ink supply path from the buffer tank to the subtank changes over time, the control unit can accurately determine, in the confirmation operation, whether the amount of ink in the subtank exceeds the second reference amount.

[0054] In the present invention, the pump drive speed when the checking operation is performed is preferably slower than the pump drive speed when ink is supplied to the subtank after the purging operation without the checking operation. If the pump drive speed when ink is supplied to the subtank after the purging operation without the checking operation is defined as the "normal drive speed," the inventors' investigations have shown that if the pump drive speed when the checking operation is performed is equal to or higher than the normal drive speed, ink is more likely to flow from the buffer tank to the subtank when the pump is driven with the first and second on-off valves open, even if the piping-side joint and the tank-side joint are properly connected. Therefore, in this case, even if the piping-side joint and the tank-side joint are properly connected, the amount of ink in the subtank may exceed the second reference amount during the checking operation.

[0055] In contrast, according to the inventor's investigations, if the pump driving speed when the checking operation is performed is slower than the normal driving speed, and the piping-side joint and the tank-side joint are properly connected, when the pump is driven with the first and second on-off valves open, ink will not easily flow from the buffer tank to the sub-tank. Therefore, if the pump driving speed when the checking operation is performed is slower than the normal driving speed, and the piping-side joint and the tank-side joint are properly connected, it is possible to prevent the amount of ink in the sub-tank from exceeding the second reference amount during the checking operation.

[0056] In the present invention, the cleaning operations include a soft cleaning operation and a hard cleaning operation which requires a longer time and ejects more ink than the soft cleaning operation, the soft cleaning operation includes a first purging operation in which the pressure inside the subtank is made positive to eject ink from the inkjet head, and the hard cleaning operation includes a second purging operation in which the pressure inside the subtank is made positive to eject ink from the inkjet head, the amount of ink ejected from the inkjet head in the second purging operation is greater than the amount of ink ejected from the inkjet head in the first purging operation, the time required for the second purging operation is longer than the time required for the first purging operation, and after the first purging operation, the amount of ink in the subtank becomes a first reference amount, and when the hard cleaning operation is to be performed, the control unit preferably performs the first purging operation before performing the second purging operation when predetermined conditions are met, and performs a confirmation operation after the first purging operation when predetermined conditions are met, and then performs the second purging operation. With this configuration, it is possible to reduce the time required for the confirmation operation compared to when the confirmation operation is executed when predetermined conditions are met after the second purging operation.

[0057] As described above, in an inkjet printer equipped with an inkjet head that ejects ink, a sub-tank that contains ink to be supplied to the inkjet head, and a main tank that contains ink to be supplied to the sub-tank, the present invention makes it possible to continue printing operations of the inkjet printer even while the main tank is being replaced.

[0058] Furthermore, as described above, in an inkjet printer equipped with a main tank that stores ink, and a supply-receiving tank that is located closer to the inkjet head than the main tank in the piping path between the main tank and the inkjet head and stores ink supplied from the main tank, the present invention makes it possible for the operator to easily recognize that an ink supply problem has occurred, in which ink is not being supplied appropriately from the main tank to the supply-receiving tank.

[0059] Furthermore, as described above, in an inkjet printer having a sub-tank, a buffer tank, a main tank, a pump arranged in a piping path between the buffer tank and the sub-tank, a first piping path connecting the pump and the sub-tank, and a second piping path connecting the first piping path and the main tank, the present invention makes it possible to prevent ink from circulating between the main tank and the buffer tank when there is a poor connection between the piping side joint attached to the end of the second piping path and the tank side joint attached to the main tank and to which the piping side joint is connected.

[0060] 1 is a schematic diagram illustrating the configuration of an inkjet printer according to an embodiment of the present invention. FIG. 1 is a schematic diagram illustrating the configuration of the printer main body shown in FIG. 1. FIG. 1 is a diagram illustrating an ink supply path when the amount of ink remaining in the buffer tank shown in FIG. 1 is low. FIG. 2 is a diagram illustrating an ink circulation path passing through the main tank and buffer tank shown in FIG. 1. FIG. 2 is a diagram illustrating an ink path when ink contained in the buffer tank shown in FIG. 1 is returned to the main tank. FIG. 1 is a schematic diagram illustrating the configuration of an inkjet printer according to an embodiment of the present invention. FIG. 6 is a schematic diagram illustrating the configuration of the inkjet printer shown in FIG. 6. FIG. 7 is a block diagram illustrating the configuration of the inkjet printer shown in FIG. 7. FIG. 7 is a flowchart illustrating the procedure for detecting an ink supply failure in which ink is not adequately supplied from the main tank to the supply-side tank shown in FIG. 7. FIG. 7 is a flowchart illustrating the procedure for detecting an ink supply failure in which ink is not adequately supplied from the main tank to the supply-side tank shown in FIG. 7. FIG. 8 is a graph illustrating the procedure for detecting an ink supply failure in which ink is not adequately supplied from the main tank to the supply-side tank shown in FIG. 7. FIG. 12 is a schematic diagram illustrating the configuration of the inkjet printer shown in FIG. 12. Fig. 13 is a block diagram for explaining the configuration of the inkjet printer shown in Fig. 12. Fig. 14 is a flowchart for explaining an example of the procedure for the soft cleaning operation and normal cleaning operation of the inkjet head shown in Fig. 12. Fig. 15 is a flowchart for explaining an example of the procedure for the hard cleaning operation of the inkjet head shown in Fig. 12.

[0061] First Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0062] (Configuration of Inkjet Printer) Fig. 1 is a schematic diagram illustrating the configuration of an inkjet printer 1 according to an embodiment of the present invention. Fig. 2 is a schematic diagram illustrating the configuration of the printer main body 3 shown in Fig. 1. Fig. 3 is a diagram illustrating the ink supply path when the amount of ink remaining in the buffer tank 18 shown in Fig. 1 becomes small. Fig. 4 is a diagram illustrating the ink circulation path passing through the main tank 17 and buffer tank 18 shown in Fig. 1. Fig. 5 is a diagram illustrating the ink path when the ink contained in the buffer tank 18 shown in Fig. 1 is returned to the main tank 17.

[0063] The inkjet printer 1 (hereinafter referred to as "printer 1") of this embodiment is, for example, a commercial inkjet printer that prints on a medium 2 such as paper. The printer 1 includes a printer main body 3 and an external supply unit 4 that supplies ink to the printer main body 3. The printer main body 3 includes an inkjet head 5 (hereinafter referred to as "head 5") that ejects ink, a carriage 6 on which the head 5 is mounted, a carriage drive mechanism 7 that moves the carriage 6 in the main scanning direction, a guide rail 8 that guides the carriage 6 in the main scanning direction, and a platen 9 on which the medium 2 is placed during printing. When printing on the medium 2 with the printer 1, the head 5 ejects ink while the carriage 6 moves back and forth in the main scanning direction.

[0064] The printer body 3 also includes a subtank 11 that contains ink to be supplied to the head 5, a pressure adjustment mechanism (not shown) for adjusting the pressure inside the subtank 11, an on-off valve 12, a degassing module 13 for removing gas from the ink, and a filter 14. The subtank 11 is equipped with a liquid level detection mechanism for detecting the liquid level of the ink contained in the subtank 11. The liquid level detection mechanism includes, for example, a float placed inside the subtank 11 and a sensor for detecting the float. The on-off valve 12 is, for example, an electromagnetic valve. The on-off valve 12 is located in the piping path between the subtank 11 and the pressure adjustment mechanism. The degassing module 13 and filter 14 are located in the piping path between the subtank 11 and the head 5.

[0065] The printer main body 3 also includes an on-off valve 15 disposed in the piping between the subtank 11 and a pump 19 (described below) of the external supply unit 4. The on-off valve 15 is a solenoid valve. In this embodiment, the on-off valve 15 is a second on-off valve. The subtank 11, on-off valves 12 and 15, degassing module 13, and filter 14 are mounted on the carriage 6. The on-off valves 12 and 15 may be manual valves that are manually opened and closed.

[0066] The external supply unit 4 is formed separately from the printer body 3 and is attached to the printer body 3. The external supply unit 4 includes a main tank 17 that stores ink to be supplied to the subtank 11, a buffer tank 18 that is arranged in the piping path between the subtank 11 and the main tank 17 and stores ink, a pump (liquid supply pump) 19 that is arranged in the piping path between the subtank 11 and the buffer tank 18, and a check valve 20 that is arranged in parallel with the buffer tank 18 in the piping path between the main tank 17 and the pump 19.

[0067] The external supply unit 4 also includes an on-off valve 21 arranged in the piping path between the main tank 17 and the buffer tank 18, an on-off valve 22 arranged in the piping path having one end connected to the piping path between the on-off valve 15 and the pump 19 and the other end connected to the main tank 17, a detection mechanism 23 for detecting the volume of ink contained in the main tank 17, and a filter 24 arranged before the pump 19 in the direction of ink supply to the subtank 11. The on-off valve 22 in this embodiment is a third on-off valve.

[0068] The external supply unit 4 and the carriage 6 are connected by ink supply piping. This ink supply piping is formed from a flexible resin tube. Most of this ink supply piping is housed in a Cableveyor®. One end of the Cableveyor® is fixed to the external supply unit 4. The other end of the Cableveyor® is fixed to the carriage 6. Note that while FIG. 1 shows one main tank 17, the external supply unit 4 is equipped with multiple main tanks 17. The external supply unit 4 is also equipped with multiple buffer tanks 18, pumps 19, check valves 20, etc., corresponding to the number of main tanks 17. The printer main body 3 is equipped with multiple sub-tanks 11, etc., corresponding to the number of main tanks 17.

[0069] The main tank 17 is, for example, a hard ink bottle made of resin. The capacity of the main tank 17 is, for example, 10 liters. The buffer tank 18 is an ink pack formed in a bag shape. The buffer tank 18 has a bag-shaped tank body made of flexible film, and an ink inlet and outlet attached to the tank body. The buffer tank 18 is, for example, an aluminum pack having an aluminum tank body. The capacity of the buffer tank 18 is, for example, 2 liters.

[0070] The ink stored in the buffer tank 18 is supplied from the main tank 17. In this embodiment, ink is supplied from the main tank 17 to the buffer tank 18 by the head difference. That is, ink is supplied from the main tank 17 to the buffer tank 18 by utilizing the difference in the ink level between the main tank 17 and the buffer tank 18.

[0071] The check valve 20 includes a valve body and a spring member that biases the valve body toward the main tank 17, and allows ink to flow only in the direction from the main tank 17 toward the pump 19. When the pressure in the piping path on the pump 19 side of the check valve 20 becomes lower than the pressure in the piping path on the main tank 17 side of the check valve 20 by a certain value or more, ink flows from the main tank 17 toward the pump 19 through the check valve 20. The on-off valves 21 and 22 are, for example, solenoid valves. The on-off valve 21 is disposed in the piping path between the buffer tank 18 and the check valve 20 and the main tank 17. The on-off valves 21 and 22 may be manual valves.

[0072] The detection mechanism 23 is a load cell for detecting the weight of ink contained in the main tank 17. The detection mechanism 23 is electrically connected to the control unit 25 of the printer 1. The control unit 25 detects the volume of ink contained in the main tank 17 based on the detection result of the detection mechanism 23. In this embodiment, as the volume of ink in the buffer tank 18 decreases, ink is supplied from the main tank 17 to the buffer tank 18, causing the volume of ink in the main tank 17 to decrease. The control unit 25 indirectly detects the volume of ink contained in the buffer tank 18 based on the detection result of the detection mechanism 23. That is, in this embodiment, the volume of ink contained in the buffer tank 18 is indirectly detected by the detection mechanism 23.

[0073] In the printer 1, printing on the medium 2 is performed with the on-off valves 15 and 21 open and the on-off valve 22 closed. During printing on the medium 2, ink is normally supplied from the buffer tank 18 to the subtank 11 by the pump 19 (see the arrow in FIG. 1 ). That is, during printing on the medium 2, the pump 19 normally sends ink from the buffer tank 18 to the subtank 11. Therefore, even when the ink in the main tank 17 runs out during printing on the medium 2 and the main tank 17 is being replaced, ink is still supplied from the buffer tank 18 to the subtank 11. Note that the main tank 17 is replaced after the on-off valve 21 is closed, and the on-off valve 21 is opened once the replacement of the main tank 17 is complete.

[0074] Here, for example, if the consumption of ink ejected from the head 5 increases in order to perform high-density printing on the medium 2, increasing the amount of ink flowing out from the buffer tank 18 to the subtank 11 per unit time, or if a low-temperature environment causes the viscosity of the ink to increase and the amount of ink flowing into the buffer tank 18 from the main tank 17 per unit time to decrease, the supply of ink from the main tank 17 to the buffer tank 18 may not be able to keep up while printing on the medium 2, and the amount of ink remaining in the buffer tank 18 may become low while printing on the medium 2. When the amount of ink remaining in the buffer tank 18 becomes low, ink will no longer be supplied from the buffer tank 18 to the subtank 11.

[0075] Specifically, when the amount of ink remaining in the buffer tank 18 becomes small, the buffer tank 18, which is an ink pack, collapses and ink is no longer supplied from the buffer tank 18 to the subtank 11. Because the pump 19 is driven while printing on the medium 2, if the amount of ink remaining in the buffer tank 18 becomes small while printing on the medium 2 and ink is no longer supplied from the buffer tank 18 to the subtank 11, the pressure in the piping path on the pump 19 side of the check valve 20 becomes negative.

[0076] In this embodiment, when the pressure in the piping path on the pump 19 side of the check valve 20 becomes negative and the pressure in the piping path on the pump 19 side of the check valve 20 becomes lower by a certain value or more than the pressure in the piping path on the main tank 17 side of the check valve 20, ink flows through the check valve 20. In other words, when the amount of ink remaining in the buffer tank 18 becomes low during printing of the medium 2 and ink is no longer supplied from the buffer tank 18 to the subtank 11, a bypass path (bypass flow path) for ink passing through the check valve 20 is formed, and ink is supplied from the main tank 17 to the subtank 11 by the pump 19 via the check valve 20 (see the arrow in FIG. 3 ).

[0077] Furthermore, in order to prevent ink particles from settling in the main tank 17 and the buffer tank 18, the printer 1 circulates ink between the main tank 17 and the buffer tank 18 when the carriage 6 is stopped for a predetermined period of time without printing on the medium 2. Specifically, the on-off valve 15 is closed and on-off valves 21 and 22 are opened to form an ink circulation path that passes through the main tank 17 and the buffer tank 18, and the pump 19 is then driven to circulate the ink through this circulation path (see the arrow in FIG. 4). Furthermore, in the printer 1, for example, when the buffer tank 18 needs to be replaced and the ink in the buffer tank 18 needs to be drained, the on-off valves 15 and 21 are closed and on-off valve 22 is opened, and the pump 19 is then driven to return the ink in the buffer tank 18 to the main tank 17 (see the arrow in FIG. 5).

[0078] (Major Effects of This Embodiment) As described above, in this embodiment, the printer 1 is provided with the buffer tank 18 located in the piping path between the subtank 11 and the main tank 17, and while printing on the medium 2, ink is normally supplied from the buffer tank 18 to the subtank 11 by the pump 19. Therefore, in this embodiment, as described above, even when the ink in the main tank 17 runs out while printing on the medium 2 and the main tank 17 is being replaced, ink is still supplied from the buffer tank 18 to the subtank 11. Therefore, in this embodiment, it is possible to continue printing operations of the printer 1 even while the main tank 17 is being replaced.

[0079] In this embodiment, the printer 1 is provided with a check valve 20 that is arranged in parallel with the buffer tank 18 in the piping path between the main tank 17 and the pump 19. Therefore, in this embodiment, as described above, even if the amount of ink remaining in the buffer tank 18 becomes low and ink is no longer supplied from the buffer tank 18 to the subtank 11 while printing on the medium 2, ink flows through the check valve 20, and the pump 19 supplies ink from the main tank 17 to the subtank 11 via the check valve 20. Therefore, in this embodiment, even if the amount of ink remaining in the buffer tank 18 becomes low and ink is no longer supplied from the buffer tank 18 to the subtank 11 while printing on the medium 2, the printer 1 can continue to perform appropriate printing operations.

[0080] In this embodiment, ink is supplied from the main tank 17 to the buffer tank 18 by the hydraulic head difference. Therefore, in this embodiment, the configuration of the external supply unit 4 can be simplified compared to when a pump is installed in the piping path between the main tank 17 and the buffer tank 18.

[0081] Compared to when ink is supplied from the main tank 17 to the buffer tank 18 by a pump, when ink is supplied from the main tank 17 to the buffer tank 18 by a head difference, it becomes more difficult for ink to be supplied from the main tank 17 to the buffer tank 18, increasing the likelihood that only a small amount of ink will remain in the buffer tank 18 while printing on the medium 2. In particular, if the difference between the ink level in the main tank 17 and the ink level in the buffer tank 18 is reduced (i.e., the head difference is reduced) in order to reduce the size of the external supply unit 4, it becomes more difficult for ink to be supplied from the main tank 17 to the buffer tank 18, increasing the likelihood that only a small amount of ink will remain in the buffer tank 18 while printing on the medium 2. However, in this embodiment, it is possible for the printer 1 to continue proper printing operations even if only a small amount of ink remains in the buffer tank 18 while printing on the medium 2.

[0082] In this embodiment, the printer 1 includes an on-off valve 15 disposed in a piping path between the subtank 11 and the pump 19, and an on-off valve 22 disposed in a piping path having one end connected to the piping path between the on-off valve 15 and the pump 19 and the other end connected to the main tank 17. Therefore, in this embodiment, as described above, by closing the on-off valve 15 and opening the on-off valves 21 and 22, an ink circulation path passing through the main tank 17 and the buffer tank 18 can be formed. Furthermore, in this embodiment, by driving the pump 19 in this state, ink can be circulated through the formed circulation path. Therefore, in this embodiment, it is possible to suppress settling of ink particles in the main tank 17 and the buffer tank 18.

[0083] In this embodiment, the printer 1 is provided with an on-off valve 21 disposed in the piping path between the main tank 17 and the buffer tank 18, and the on-off valve 21 is closed when replacing the main tank 17. Therefore, in this embodiment, the main tank 17 can be easily replaced. Also, in this embodiment, the on-off valves 15 and 21 are closed and the on-off valve 22 is opened, and then the pump 19 is driven to return the ink in the buffer tank 18 to the main tank 17. Therefore, in this embodiment, for example, when the buffer tank 18 needs to be replaced, it is possible to drain the ink from the buffer tank 18.

[0084] In this embodiment, the volume of ink contained in the buffer tank 18 is indirectly detected by the detection mechanism 23. Therefore, in this embodiment, it is possible to detect the volume of ink contained in the buffer tank 18 even if a mechanism for detecting the volume of ink contained in the buffer tank 18 is not installed. Therefore, in this embodiment, it is possible to simplify the configuration of the printer 1.

[0085] (Other Embodiments) The above-described embodiment is one example of a preferred embodiment of the present invention, but the present invention is not limited to this and various modifications can be made within the scope that does not change the gist of the present invention.

[0086] In the above-described embodiment, the buffer tank 18 does not have to be an ink pack. For example, the buffer tank 18 may be a hard ink bottle made of resin. Even in this case, when the remaining amount of ink in the buffer tank 18 becomes small and ink is no longer supplied from the buffer tank 18 to the subtank 11, ink will flow through the check valve 20. Also, in the above-described embodiment, the printer 1 may be provided with a pump arranged in the piping path between the main tank 17 and the buffer tank 18. In this case, ink is supplied from the main tank 17 to the buffer tank 18 by this pump.

[0087] In the above-described embodiment, the detection mechanism 23 may be a detection mechanism other than a load cell. Furthermore, in the above-described embodiment, the printer 1 may be provided with a detection mechanism for detecting the volume of ink contained in the buffer tank 18. Furthermore, in the above-described embodiment, the printer main body 3 may be provided with the main tank 17, the buffer tank 18, the pump 19, the check valve 20, the on-off valves 21 and 22, the detection mechanism 23, and the filter 24. In this case, the printer 1 does not include the external supply unit 4. Furthermore, in the above-described embodiment, the printer 1 is a device for printing on the medium 2, but the printer 1 may be used for purposes other than printing on the medium 2. For example, the printer 1 may be a 3D printer for creating three-dimensional objects. Furthermore, the printer 1 may be an inkjet printer for general consumers.

[0088] Second Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0089] (Configuration of Inkjet Printer) Fig. 6 is a schematic diagram for explaining the configuration of an inkjet printer 101 according to an embodiment of the present invention. Fig. 7 is a schematic diagram for explaining the configuration of the inkjet printer 101 shown in Fig. 6. Fig. 8 is a block diagram for explaining the configuration of the inkjet printer 101 shown in Fig. 6.

[0090] The inkjet printer 101 (hereinafter referred to as "printer 101") of this embodiment is, for example, a commercial inkjet printer that prints on a medium 102 such as paper. The printer 101 includes an inkjet head 103 (hereinafter referred to as "head 103") that ejects ink, a carriage 104 on which the head 103 is mounted, a carriage drive mechanism 105 that moves the carriage 104 in the main scanning direction, a guide rail 106 that guides the carriage 104 in the main scanning direction, and a platen 107 on which the medium 102 is placed during printing. When printing on the medium 102 with the printer 101, the head 103 ejects ink while the carriage 104 moves back and forth in the main scanning direction.

[0091] The printer 101 also includes a subtank 111 that contains ink to be supplied to the head 103, a buffer tank 112 that contains ink to be supplied to the subtank 111, and a main tank 113 that contains ink to be supplied to the buffer tank 112. In this embodiment, one buffer tank 112 is connected to one main tank 113. Two subtanks 111 are connected to one buffer tank 112, and ink is supplied from one buffer tank 112 to two subtanks 111. Although FIG. 7 shows only one main tank 113, the printer 101 actually includes multiple main tanks 113. The printer 101 includes multiple buffer tanks 112 and subtanks 111 corresponding to the number of main tanks 113.

[0092] The printer 101 also includes a pump (liquid supply pump) 114 and an ink filter 115 (hereinafter referred to as "filter 115") arranged in a piping path between the buffer tank 112 and the subtank 111, a detection mechanism 116 for detecting the amount of ink contained in the main tank 113, and a control unit 117 for controlling the printer 101. The printer 101 also includes a piping path 119 connecting the main tank 113 and the buffer tank 112, a piping path 120 connecting the buffer tank 112 and the pump 114, a piping path 121 connecting the pump 114 and the two subtanks 111, a piping path 122 connecting the piping path 121 and the main tank 113, an on-off valve 123 arranged in the piping path 119, an on-off valve 124 arranged in the piping path 121, and an on-off valve 125 arranged in the piping path 122.

[0093] The printer 101 also includes an ink filter 127 (hereinafter referred to as "filter 127") located in the piping path between the subtank 111 and the head 103, a degassing module 128 for removing gas from the ink, and a pressure adjustment mechanism (not shown) for adjusting the pressure inside the subtank 111. The degassing module 128 is located in the piping path between the subtank 111 and the filter 127. The pressure adjustment mechanism includes a negative pressure pump for creating a negative pressure inside the subtank 111, and a positive pressure pump for creating a positive pressure inside the subtank 111.

[0094] A connection point (junction point) 130 is provided in the middle of the piping path 121, to which one end of a piping path 122, the other end of which is connected to the main tank 113, is connected. That is, the connection point 130 is provided in the middle of the piping path connecting the buffer tank 112 and the sub-tank 111. In this embodiment, the piping path 131 between the buffer tank 112 and the connection point 130 and the piping path 122 between the connection point 130 and the main tank 113 form a circulating piping path 132 through which ink flows from the buffer tank 112 to the main tank 113.

[0095] In this embodiment, piping path 132 is the second piping path, piping path 131 is the third piping path, and piping path 122 is the fourth piping path. Furthermore, piping path 119 in this embodiment is the first piping path, which is a supply piping path through which ink flows from main tank 113 to buffer tank 112. Pump 114 and filter 115 are disposed in piping path 132, which is the second piping path. Specifically, pump 114 and filter 115 are disposed in piping path 131, which is the third piping path. Furthermore, filter 115 is disposed in piping path 120.

[0096] Two sub-tanks 111 connected to one buffer tank 112 are connected in parallel to the pump 114 via a piping path 121. The piping path 121 branches off closer to the sub-tank 111 than the connection point 130. The on-off valves 124 are arranged in the piping path between the branching point of the piping path 121 and the sub-tank 111, and two on-off valves 124 are arranged in the piping path 121. That is, the on-off valves 124 are arranged in the piping path between the connection point 130 and the sub-tank 111. The on-off valve 124 in this embodiment is a first on-off valve. Also, the on-off valve 125 in this embodiment is a second on-off valve arranged in the piping path 122, which is the fourth piping path.

[0097] The subtank 111 is mounted on the carriage 104. The main tank 113 is, for example, a hard ink bottle made of resin. The main tank 113 contains ink that is supplied to the head 103 via the buffer tank 112 and the subtank 111 and ejected from the head 103. The capacity of the main tank 113 is, for example, 10 liters. The main tank 113 is removable from the printer 101 and replaceable, and is replaced when the ink inside the main tank 113 runs out. One end of the piping path 119 is connected to the main tank 113 via a joint 133. One end of the piping path 122 (i.e., one end of the piping path 132) is connected to the main tank 113 via a joint 134. The joints 133 and 134 allow the main tank 113 to be disconnected from the piping paths 119 and 122.

[0098] The buffer tank 112 is an ink pack formed in a bag shape. The buffer tank 112 includes a bag-shaped tank body made of flexible film and an ink inlet and an ink outlet attached to the tank body. The buffer tank 112 is, for example, an aluminum pack having an aluminum tank body. The capacity of the buffer tank 112 is, for example, 2 liters. Ink is supplied from the main tank 113 to the buffer tank 112 by a head difference. That is, ink is supplied from the main tank 113 to the buffer tank 112 by utilizing the difference between the ink liquid level in the main tank 113 and the ink liquid level in the buffer tank 112. In this embodiment, the buffer tank 112 is a supply-side tank that stores ink supplied from the main tank 113, and is located closer to the head 103 than the main tank 113 in the piping path between the main tank 113 and the head 103.

[0099] The on-off valves 123 to 125 are electromagnetic valves. The on-off valves 123 to 125 are electrically connected to the control unit 117. In this embodiment, when the pump 114 is driven with the on-off valve 124 open and the on-off valve 125 closed, ink flows from the buffer tank 112 toward the subtank 111. When the pump 114 is driven with the on-off valve 125 open and the on-off valve 124 closed, ink flows from the buffer tank 112 toward the main tank 113, and the ink in the buffer tank 112 returns to the main tank 113. When the pump 114 is driven with the on-off valves 123 and 125 open and the on-off valve 124 closed, ink circulates between the main tank 113 and the buffer tank 112.

[0100] In this way, the pump 114 serves to supply ink from the buffer tank 112 to the subtank 111 and to circulate ink between the main tank 113 and the buffer tank 112. The pump 114 is electrically connected to the control unit 117. The detection mechanism 116 is a load cell for detecting the weight of ink contained in the main tank 113. The detection mechanism 116 is equipped with a sensor 135. The sensor 135 is a strain gauge, and is electrically connected to the control unit 117. The control unit 117 calculates the amount of ink contained in the main tank 113 based on the detection result of the detection mechanism 116 (specifically, the detection result of the sensor 135).

[0101] (Inkjet printer control method) Figures 9 and 10 are flow charts for explaining the procedure for detecting the occurrence of an ink supply failure in which ink is not adequately supplied from the main tank 113 to the buffer tank 112 shown in Figure 7. Figure 6 is a graph for explaining the procedure for detecting the occurrence of an ink supply failure in which ink is not adequately supplied from the main tank 113 to the buffer tank 112 shown in Figure 7.

[0102] When printing on the medium 102, the control unit 117 opens the on-off valves 123 and 124 and drives the pump 114 with the on-off valve 125 closed, based on the detection results of a detection mechanism (not shown) that detects the amount of ink contained in the subtank 111, to supply ink from the buffer tank 112 to the subtank 111. During printing on the medium 102, ink is supplied from the buffer tank 112 to the subtank 111. Therefore, even when the ink in the main tank 113 runs out during printing on the medium 102 and the main tank 113 is being replaced, ink is supplied from the buffer tank 112 to the subtank 111. Note that the replacement of the main tank 113 during printing on the medium 102 is performed after the on-off valve 123 is closed, and the on-off valve 123 is opened once the replacement of the main tank 113 is complete.

[0103] Furthermore, in the printer 101, in order to suppress settling of ink particles in the main tank 113 and the buffer tank 112, when the carriage 104 is stopped for a predetermined period of time or longer without printing on the medium 102, the control unit 117 circulates ink between the main tank 113 and the buffer tank 112. Specifically, the control unit 117 closes the on-off valve 124 and opens the on-off valves 123 and 125 to form an ink circulation path that passes through the main tank 113 and the buffer tank 112, and then drives the pump 114 to circulate the ink through this circulation path.

[0104] As described above, in this embodiment, the main tank 113 is replaceable, and is replaced when the ink inside the main tank 113 runs out. Therefore, if a connection failure occurs in which the piping path 119 is not properly connected to the replaced main tank 113 (i.e., the main tank 113 and the piping path 119 are not properly connected by the joint 133), the amount of ink flowing from the main tank 113 to the buffer tank 112 will decrease, and there is a risk of an ink supply failure occurring in which an appropriate amount of ink is not supplied from the main tank 113 to the buffer tank 112.

[0105] Therefore, in this embodiment, when ink is circulated between the main tank 113 and the buffer tank 112 by driving the pump 114 with the on-off valve 124 closed and the on-off valves 123 and 125 open, the control unit 117 detects whether or not there is a problem with the ink supply from the main tank 113 to the buffer tank 112, as shown in the flowchart of Figure 9, and executes a predetermined error processing if there is a problem with the ink supply from the main tank 113 to the buffer tank 112.

[0106] That is, when ink circulation begins, the control unit 117 first calculates the amount of ink in the main tank 113 based on the detection result of the detection mechanism 116 (step S1). Then, when a certain time T1 has elapsed since the control unit 117 calculated the amount of ink in the main tank 113 in step S1, the control unit 117 again calculates the amount of ink in the main tank 113 based on the detection result of the detection mechanism 116 (steps S2 and S3). In this embodiment, the certain time T1 is one minute. Also in this embodiment, in steps S1 and S3, the control unit 117 calculates the volume of ink in the main tank 113 from the weight of the main tank 113 measured by the detection mechanism 116.

[0107] The control unit 117 then calculates the amount of ink increase by subtracting the amount of ink calculated in step S1 from the amount of ink calculated in step S3 (step S4). That is, in step S4, the control unit 117 calculates the amount of ink increase in the main tank 113 over the fixed time T1. Also in step S4, the control unit 117 calculates the amount of ink increase. The control unit 117 then determines whether the amount of ink increase calculated in step S4 is equal to or greater than a predetermined reference amount M1 (step S5). In this embodiment, the volume of ink sent from the buffer tank 112 to the main tank 113 by the pump 114 is 90 cc (ml) per minute, and the reference amount M1 is 50 cc, which is approximately half the volume of ink sent from the buffer tank 112 to the main tank 113 per minute.

[0108] If the increased amount of ink is equal to or greater than the reference amount M1 in step S5, the control unit 117 increments a count value indicating the number of times the increased amount of ink is equal to or greater than the reference amount M1 (step S6). That is, in step S6, the control unit 117 increments the count value by one. In the first step S6 after ink circulation has started, the count value is "1." On the other hand, if the increased amount of ink is less than the reference amount M1 in step S5, the control unit 117 resets the count value (step S9) and returns to step S2. In step S9, the control unit 117 resets the count value to "0." Returning to step S2, the control unit 117 calculates the amount of ink in the main tank 113 again after a certain time T1 has elapsed since the previous calculation of the amount of ink in the main tank 113 in step S3 (steps S2 and S3).

[0109] Furthermore, after incrementing the count value in step S6, the control unit 117 determines whether the count value is a predetermined reference value V1 (step S7). The reference value V1 is an integer equal to or greater than 2. In this embodiment, the reference value V1 is "3." If the count value is not equal to the reference value V1 in step S7, the process returns to step S2, and the control unit 117 calculates the amount of ink in the main tank 113 again after a certain time T1 has elapsed since the control unit 117 calculated the amount of ink in the main tank 113 in the previous step S3 (steps S2 and S3).

[0110] On the other hand, if the count value is equal to the reference value V1 in step S7 (i.e., if the increase in the amount of ink calculated in step S4 is equal to or greater than the reference amount M1 three times in a row), the control unit 117 determines that there is a problem with the supply of ink from the main tank 113 to the buffer tank 112, and executes a predetermined error process (step S8). In step S8, the control unit 117 displays a predetermined error message on a predetermined display unit 145 such as a display.

[0111] In step S4 after steps S7 and S9, the control unit 117 calculates an increased amount of ink by subtracting the amount of ink calculated in the previous step S3 from the amount of ink calculated in the current step S3. The control of the printer 101 shown in the control flow of Figure 9 is stopped when ink circulation ends (for example, when ink circulation ends to supply ink from the buffer tank 112 to the subtank 111), and is then resumed when ink circulation resumes.

[0112] For example, if the amount of ink in the main tank 113 before ink circulation begins is 6 liters (i.e., 6000 cc), and the increase in ink calculated from the first step S4 to the third step S4 after ink circulation begins is continuously 50 cc, the amount of ink in the main tank 113 will increase over time as shown by the line L1 in Figure 11. In this case, error processing will be executed three minutes after ink circulation begins.

[0113] In this way, during ink circulation between the main tank 113 and the buffer tank 112, the control unit 117 calculates the amount of ink increase in the main tank 113 over the fixed time T1 at fixed time intervals based on the detection results of the detection mechanism 116, and executes error processing if the calculated amount of ink increase exceeds the reference amount M1 multiple times in succession (specifically, three times). In this embodiment, the fixed time T1 is a first fixed time, and the reference amount M1 is a first reference amount.

[0114] In addition to the above, in this embodiment, the control unit 117 detects whether or not there is a problem with the supply of ink from the main tank 113 to the buffer tank 112, as shown in the flowchart of Figure 10, and performs a predetermined error processing when there is a problem with the supply of ink from the main tank 113 to the buffer tank 112.

[0115] When ink circulation begins, the control unit 117 first calculates the amount of ink in the main tank 113 based on the detection result of the detection mechanism 116 (step S11). The control unit 117 then waits until a certain period of time T2 has elapsed, and then calculates the amount of ink in the main tank 113 again based on the detection result of the detection mechanism 116 (steps S12 and S13). In this embodiment, the certain period of time T2 is one minute. In this embodiment, in steps S11 and S13, the control unit 117 calculates the volume of ink in the main tank 113 from the weight of the main tank 113 measured by the detection mechanism 116. In this embodiment, the certain period of time T1 and the certain period of time T2 are equal, so steps S1 to S3 shown in FIG. 9 become steps S11 to S13 shown in FIG. 10.

[0116] Thereafter, the control unit 117 calculates and stores the amount of ink change, which is the difference between the amount of ink calculated in step S11 and the amount of ink calculated in step S13 (step S14). That is, in step S14, the control unit 117 calculates and stores the amount of ink change in the main tank 113 after a certain time T2. Also in step S14, the control unit 117 calculates and stores the ink volume change. Thereafter, when the certain time T2 has elapsed since the control unit 117 calculated the amount of ink in the main tank 113 in step S13, the control unit 117 again calculates the amount of ink in the main tank 113 based on the detection result of the detection mechanism 116 (steps S15 and S16).

[0117] Thereafter, the control unit 117 calculates the ink change amount, which is the difference between the ink amount calculated in step S13 and the ink amount calculated in step S16 (step S17). The control unit 117 also calculates the ink change amount difference, which is the difference between the ink change amount calculated and stored in step S14 and the ink change amount calculated in step S17 (step S18). That is, in step S18, the control unit 117 calculates the ink change amount difference, which is the difference (difference) between the ink change amount in the main tank 113 over the fixed time T2 calculated previously and the ink change amount in the main tank 113 calculated this time over the fixed time T2.

[0118] Thereafter, the control unit 117 determines whether the absolute value of the ink change amount difference calculated in step S18 is equal to or less than a predetermined reference amount M2 (step S19). The reference amount M2 is an amount smaller than the reference amount M1, which is 10 (cc) in this embodiment. If the absolute value of the ink change amount difference is equal to or less than the reference amount M2 in step S19, the control unit 117 increments a count value indicating the number of times the absolute value of the ink change amount difference has been equal to or less than the reference amount M2 (step S20). That is, in step S20, the control unit 117 increments the count value by one. In the first step S20 after ink circulation has started, the count value is "1."

[0119] On the other hand, if the absolute value of the change in the amount of ink exceeds the reference amount M2 in step S20, the control unit 117 resets the count value (step S22), stores the amount of change in ink calculated in step S17 (step S23), and then returns to step S15. In step S22, the control unit 117 resets the count value to "0." When returning to step S15, the control unit 117 waits a certain time T2 since the previous calculation of the amount of ink in the main tank 113 in step S16, and then calculates the amount of ink in the main tank 113 again (steps S15 and S16).

[0120] Furthermore, after incrementing the count value in step S20, the control unit 117 determines whether the count value is equal to a predetermined reference value V2 (step S24). The reference value V2 is an integer equal to or greater than 2, and in this embodiment, is "3." If the count value is not equal to the reference value V2 in step S24, the control unit 117 proceeds to step S23, stores the ink change amount calculated in step S17, and then returns to step S15. Then, when a certain time T2 has elapsed since the previous calculation of the ink amount in the main tank 113 in step S16, the control unit 117 again calculates the ink amount in the main tank 113 (steps S15 and S16). On the other hand, if the count value is equal to the reference value V2 in step S24 (i.e., if the absolute value of the ink change difference calculated in step S18 is equal to or less than the reference amount M2 three times in a row), the control unit 117 stores the ink amount in the main tank 113 at that time as the initial ink amount (step S25).

[0121] The control unit 117 then waits until a certain time T2 has elapsed, and again calculates the amount of ink in the main tank 113 based on the detection results of the detection mechanism 116 (steps S26 and S27). The control unit 117 then calculates the increased amount of ink by subtracting the initial amount of ink stored in step S25 from the amount of ink calculated in step S27 (step S28). That is, in step S28, the control unit 117 calculates the increased amount of ink in the main tank 113 from the initial amount of ink. The control unit 117 then determines whether the increased amount of ink calculated in step S28 is equal to or greater than a predetermined reference amount M3 (step S29). The reference amount M3 is an amount greater than the reference amount M1, and in this embodiment, it is 150 (cc).

[0122] If, in step S29, the increased amount of ink is less than the reference amount M3, the process returns to step S26, and the control unit 117 calculates the amount of ink in the main tank 113 again after a certain time T2 has elapsed since the previous calculation of the amount of ink in the main tank 113 in step S27 (steps S26 and S27). On the other hand, if, in step S29, the increased amount of ink is equal to or greater than the reference amount M3, the control unit 117 determines that a failure in the supply of ink from the main tank 113 to the buffer tank 112 has occurred, and executes error processing (step S30). In step S30, the control unit 117 displays a predetermined error message on the display unit 145, for example, as in step S8.

[0123] In step S17 after step S23, the control unit 117 calculates the ink change amount, which is the difference between the ink amount calculated in the previous step S16 and the ink amount calculated in the current step S16. In step S18 after step S23, the control unit 117 calculates the ink change amount difference, which is the difference between the ink change amount stored in step S23 and the ink change amount calculated in step S17. That is, in step S18 after step S23, the control unit 117 calculates the ink change amount difference, which is the difference between the ink change amount in the main tank 113 over the fixed time T2 calculated previously and the ink change amount in the main tank 113 over the fixed time T2 calculated currently. The control of the printer 101 shown in the control flow of FIG. 10 is stopped when ink circulation ends (for example, when ink circulation ends to supply ink from the buffer tank 112 to the subtank 111) and is resumed when ink circulation resumes.

[0124] For example, if the amount of ink in the main tank 113 before ink circulation began was 6,000 cc, and the absolute value of the difference in ink change amount calculated from the first to third steps S18 after ink circulation began remains a constant amount of 10 cc or less (specifically, 0), and the amount of ink in the main tank 113 is increasing, the amount of ink in the main tank 113 will increase over time as shown by line L2 in FIG. 11. In this case, the amount of ink in the main tank 113 four minutes after ink circulation began is stored as the initial amount of ink. Furthermore, in this case, if the amount of ink in the main tank 113 continues to increase at a constant rate as shown by line L2 in FIG. 11, then 19 minutes after ink circulation began, the amount of ink in the main tank 113 will increase from the initial amount to 150 cc (i.e., the reference amount M3), and error processing will be executed.

[0125] In this way, during ink circulation, the control unit 117 calculates the amount of ink change in the main tank 113 at regular intervals of time T2 based on the detection results of the detection mechanism 116, and also calculates the ink change difference, which is the difference between the previously calculated ink change amount and the currently calculated ink change amount, at regular intervals of time T2. Furthermore, the control unit 117 stores the amount of ink in the main tank 113 when the absolute value of the calculated ink change difference is equal to or less than a reference amount M2, which is less than the reference amount M1, multiple times in a row (specifically, three times), as the initial ink amount. Thereafter, if the amount of ink in the main tank 113 that has increased from the stored initial ink amount reaches a reference amount M3, which is greater than the reference amount M1, the control unit 117 executes error processing. In this embodiment, the regular time T2 is a second regular time, the reference amount M2 is a second reference amount, and the reference amount M3 is a third reference amount.

[0126] If the amount of ink in the buffer tank 112 is low before ink circulation starts, the amount of ink flowing out of the main tank 113 to the buffer tank 112 may become greater than the amount of ink flowing into the main tank 113 from the buffer tank 112 after ink circulation starts, resulting in a decrease in the amount of ink in the main tank 113. Even if the amount of ink in the main tank 113 decreases after ink circulation starts, if the absolute value of the difference in ink change amount calculated in step S18 is equal to or less than the reference amount M2, the process proceeds to step S20.

[0127] (Major Effects of the Present Embodiment) As described above, in the present embodiment, the control unit 117 executes error processing when, during ink circulation between the main tank 113 and the buffer tank 112, the increase in the amount of ink in the main tank 113 over a certain time period T1 exceeds a reference amount M1 multiple times in succession, and when the increase in the amount of ink from the initial amount of ink, which is the amount of ink in the main tank 113 stored at a predetermined timing, reaches a reference amount M3. Therefore, in the present embodiment, it is possible to easily make the operator aware of the occurrence of an ink supply failure in which ink is not being supplied appropriately from the main tank 113 to the buffer tank 112.

[0128] Furthermore, in this embodiment, error processing is executed when the increase in the amount of ink in the main tank 113 over a certain period of time T1 exceeds the reference amount M1 multiple times in succession, and when the increase in the amount of ink from the initial amount of ink stored at a predetermined timing reaches a reference amount M3 that is greater than the reference amount M1, so that error processing can be executed while suppressing the effects of errors in the detection mechanism 116 and noise on the detection mechanism 116. Therefore, in this embodiment, it is possible to accurately notify the operator that a supply problem has occurred in the ink supply from the main tank 113 to the buffer tank 112.

[0129] Furthermore, in this embodiment, error processing is performed when the increase in the amount of ink in the main tank 113 over a certain period of time T1 exceeds the reference amount M1 several times in succession. Therefore, when the decrease in the ink supplied from the main tank 113 to the buffer tank 112 is large and the amount of ink in the main tank 113 increases significantly in a relatively short period of time, the operator can quickly recognize that there is a problem with the supply of ink from the main tank 113 to the buffer tank 112.

[0130] That is, for example, even if the replaced main tank 113 has a poor connection to the piping path 119, causing the amount of ink in the main tank 113 to increase significantly in a short period of time, it is possible to quickly make the operator aware of a problem in the supply of ink from the main tank 113 to the buffer tank 112. Specifically, for example, as shown in Fig. 11, by executing error processing three minutes after the start of ink circulation, it is possible to make the operator aware of a problem in the supply of ink from the main tank 113 to the buffer tank 112 three minutes after the start of ink circulation.

[0131] Furthermore, in this embodiment, error processing is executed when the amount of ink increased from the initial amount of ink stored at a predetermined timing reaches the reference amount M3, so even if a supply of ink from the main tank 113 to the buffer tank 112 is poor but the decrease in the ink supplied from the main tank 113 to the buffer tank 112 is small and the amount of ink in the main tank 113 does not increase significantly in a short period of time, it is possible to make the operator aware of a supply of ink from the main tank 113 to the buffer tank 112. Specifically, for example, as shown by the line L2 in Figure 11, it is possible to make the operator aware of a supply of ink from the main tank 113 to the buffer tank 112 even if the amount of ink in the main tank 113 does not increase significantly in a short period of time.

[0132] Furthermore, in this embodiment, ink is supplied from the main tank 113 to the buffer tank 112 due to a hydraulic head difference. Therefore, if air gets into the piping 119 when replacing the main tank 113 (specifically, when connecting the main tank 113 to the piping 119), the air may remain in the piping 119, causing a supply failure of ink from the main tank 113 to the buffer tank 112. However, even if this supply failure occurs, the amount of ink supplied from the main tank 113 to the buffer tank 112 does not decrease significantly in a short period of time, so the amount of ink in the main tank 113 does not increase significantly in a short period of time. However, in this embodiment, even if the amount of ink in the main tank 113 does not increase significantly in a short period of time, it is possible to make the operator aware of a supply failure of ink from the main tank 113 to the buffer tank 112.

[0133] Furthermore, in this embodiment, depending on the condition of the filter 115 (specifically, the degree of clogging of the filter 115), the amount of ink circulating between the main tank 113 and the buffer tank 112 during ink circulation may decrease, and even if there is a problem with the supply of ink from the main tank 113 to the buffer tank 112, the amount of ink in the main tank 113 may not increase significantly in a short period of time. However, in this embodiment, even if there is no significant increase in the amount of ink in the main tank 113 in a short period of time, it is possible to make the operator aware of the fact that there is a problem with the supply of ink from the main tank 113 to the buffer tank 112.

[0134] Furthermore, in this embodiment, the change in the amount of ink in the main tank 113 over the given time T2 is calculated at regular intervals, and the ink change difference, which is the difference between the previously calculated change in the amount of ink in the main tank 113 over the given time T2 and the currently calculated change in the amount of ink in the main tank 113 over the given time T2, is calculated at regular intervals, and the amount of ink in the main tank 113 when the absolute value of the calculated ink change difference is equal to or less than the reference amount M2 multiple times in succession is stored as the initial ink amount. This makes it possible to store the amount of ink in the main tank 113 when no disturbances or other disturbances are occurring in the main tank 113 (i.e., when the main tank 113 is in a stable state) as the initial ink amount. In other words, this embodiment makes it possible to accurately set the initial ink amount. Therefore, in this embodiment, it is possible to accurately notify the operator of a malfunction in the ink supply from the main tank 113 to the buffer tank 112 based on the accurately set initial ink amount.

[0135] In this embodiment, a common pump 114 supplies ink from the buffer tank 112 to the subtank 111 and circulates ink between the main tank 113 and the buffer tank 112. Therefore, in this embodiment, the configuration of the printer 101 can be simplified compared to when a pump for supplying ink from the buffer tank 112 to the subtank 111 and a pump for circulating ink between the main tank 113 and the buffer tank 112 are provided separately.

[0136] In this embodiment, a buffer tank 112 is disposed in the piping path between the main tank 113 and the subtank 111. Therefore, in this embodiment, ink can be supplied from the buffer tank 112 to the subtank 111 even during replacement of the main tank 113. Therefore, in this embodiment, printing operations of the printer 101 can be continued even during replacement of the main tank 113.

[0137] (Other Embodiments) The above-described embodiment is one example of a preferred embodiment of the present invention, but the present invention is not limited to this and various modifications can be made within the scope that does not change the gist of the present invention.

[0138] In the embodiment described above, the fixed time T1 and the fixed time T2 are equal, but they do not have to be equal. Also, in the embodiment described above, the fixed time in step S26 does not have to be the fixed time T2. For example, the fixed time in step S26 may be longer than the fixed time T2. Furthermore, in the embodiment described above, the reference value V1 may be an integer greater than or equal to 2 or 4, and the reference value V2 may also be an integer greater than or equal to 2 or 4. Also, in the embodiment described above, a pump for supplying ink from the buffer tank 112 to the subtank 111 and a pump for circulating ink between the main tank 113 and the buffer tank 112 may be provided separately.

[0139] In the above-described embodiment, at least one of the on-off valves 123 to 125 may be a manual valve that is manually opened and closed. Furthermore, in the above-described embodiment, the detection mechanism 116 may be a detection mechanism other than a load cell. Furthermore, in the above-described embodiment, the buffer tank 112 does not have to be an ink pack. For example, the buffer tank 112 may be a hard ink bottle made of resin. Furthermore, in the above-described embodiment, the filter 115 may be disposed on the discharge side of the pump 114.

[0140] In the above-described embodiment, the printer 101 does not have to be equipped with the buffer tank 112. In this case, the subtank 111 becomes a supply-side tank that stores ink supplied from the main tank 113, and is disposed closer to the head 103 than the main tank 113 in the piping path between the main tank 113 and the head 103. In this case, ink may be supplied from the main tank 113 to the subtank 111 by a pump, or ink may be supplied from the main tank 113 to the subtank 111 by a head difference. In this case, ink is circulated between the main tank 113 and the subtank 111, and the printer 101 is equipped with a pump that sends ink from the subtank 111 to the main tank 113. In other words, the printer 101 is equipped with a pump for circulating ink between the main tank 113 and the subtank 111.

[0141] In the embodiment described above, the printer 101 may include a pump disposed in the piping path 119. In this case, ink is supplied from the main tank 113 to the buffer tank 112 by this pump. In this case, the printer 101 may not include the on-off valve 123. In the embodiment described above, the printer 101 is a device for printing on the medium 102, but the printer 101 may be used for purposes other than printing on the medium 102. For example, the printer 101 may be a 3D printer for forming three-dimensional objects. The printer 101 may also be an inkjet printer for general consumers.

[0142] Third Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0143] (Configuration of Inkjet Printer) Fig. 12 is a schematic diagram for explaining the configuration of an inkjet printer 201 according to an embodiment of the present invention. Fig. 13 is a schematic diagram for explaining the configuration of the inkjet printer 201 shown in Fig. 12. Fig. 14 is a block diagram for explaining the configuration of the inkjet printer 201 shown in Fig. 12.

[0144] The inkjet printer 201 (hereinafter referred to as "printer 201") of this embodiment is, for example, a commercial inkjet printer that prints on a medium 202 such as paper. The printer 201 includes an inkjet head 203 (hereinafter referred to as "head 203") that ejects ink, a carriage 204 on which the head 203 is mounted, a carriage drive mechanism 205 that moves the carriage 204 in the main scanning direction, a guide rail 206 that guides the carriage 204 in the main scanning direction, and a platen 207 on which the medium 202 is placed during printing.

[0145] The platen 207 is disposed below the head 203. The head 203 ejects ink downward. A plurality of nozzles (specifically, a large number of nozzles) that eject ink are formed on the underside of the head 203. The underside of the head 203 serves as an ink ejection surface. The head 203 is equipped with a piezoelectric element that ejects ink from each of the plurality of nozzles. When the printer 201 prints on the medium 202, the head 203 ejects ink while the carriage 204 moves back and forth in the main scanning direction.

[0146] The printer 201 also includes a subtank 211 that stores ink to be supplied to the head 203, a buffer tank 212 that stores ink to be supplied to the subtank 211, and a main tank 213 that stores ink to be supplied to the buffer tank 212. In this embodiment, one buffer tank 212 is connected to one main tank 213. Two subtanks 211 are connected to one buffer tank 212, and ink is supplied from one buffer tank 212 to two subtanks 211. Although only one main tank 213 is shown in FIG. 13 , the printer 201 actually includes a plurality of main tanks 213. The printer 201 includes a plurality of buffer tanks 212 and subtanks 211 corresponding to the number of main tanks 213.

[0147] Furthermore, the printer 201 is equipped with a pump (liquid supply pump) 214 and a filter (ink filter) 215 disposed in a piping path between the buffer tank 212 and the sub-tank 211, and a control unit 217 for controlling the printer 201. The printer 201 is also equipped with a piping path 22219 connecting the main tank 213 and the buffer tank 212, a piping path 2220 connecting the buffer tank 212 and the pump 214, a piping path 2221 connecting the pump 214 and the two sub-tanks 211, and a piping path 222 connecting the piping path 2221 and the main tank 213. In this embodiment, the piping path 2221 is a first piping path, and the piping path 222 is a second piping path.

[0148] The printer 201 also includes an on-off valve 223 arranged in the piping path 22219, an on-off valve 224 arranged in the piping path 2221, an on-off valve 225 arranged in the piping path 222, a pressure adjustment mechanism 226 for adjusting the pressure inside the subtank 211, an on-off valve 227 arranged in the piping path between the pressure adjustment mechanism 226 and the subtank 211, and a detection mechanism 228 for detecting the amount of ink contained in the subtank 211. The pressure adjustment mechanism 226 includes a negative pressure pump for creating a negative pressure inside the subtank 211, and a positive pressure pump for creating a positive pressure inside the subtank 211. The on-off valve 227 is an electromagnetic valve.

[0149] A connection point (junction point) 230 is provided in the middle of the piping path 2221, to which one end of the piping path 222, the other end of which is connected to the main tank 213, is connected. That is, the connection point 230 is provided in the middle of the piping path connecting the buffer tank 212 and the sub-tank 211. In this embodiment, the piping path 231 between the buffer tank 212 and the connection point 230 and the piping path 222 between the connection point 230 and the main tank 213 form a piping path for circulation, through which ink flows from the buffer tank 212 to the main tank 213.

[0150] The two sub-tanks 211 connected to one buffer tank 212 are connected in parallel to the pump 214 via a piping path 2221. The piping path 2221 branches off closer to the sub-tank 211 than the connection point 230. The on-off valve 224 is disposed in the piping path between the branching point of the piping path 2221 and the sub-tank 211, and two on-off valves 224 are disposed in the piping path 2221. That is, the on-off valve 224 is disposed in the piping path between the connection point 230 of the piping path 2221 and the piping path 222 and the sub-tank 211. The filter 215 is disposed in the piping path 2220. The on-off valve 224 in this embodiment is a first on-off valve. The on-off valve 225 in this embodiment is a second on-off valve disposed in the piping path 222, which is the second piping path.

[0151] The subtank 211 is mounted on the carriage 204. The main tank 213 is, for example, a hard ink bottle made of resin. The main tank 213 is attached to the body frame of the printer 201. The main tank 213 is removable from the printer 201 and replaceable (i.e., removable from the body frame of the printer 201 and replaceable), and when the ink inside the main tank 213 runs out, the main tank 213 is replaced. One end of the piping path 22219 is connected to the main tank 213 via a joint 233. One end of the piping path 222 is connected to the main tank 213 via a joint 234. That is, the printer 201 is equipped with joints 233 and 234. The joints 233 and 234 allow the main tank 213 to be disconnected from the piping paths 22219 and 222.

[0152] The joint 234 includes a pipe-side joint 235 attached to the end of the pipe path 222 and a tank-side joint 236 attached to the main tank 213. The joint 234 is composed of the pipe-side joint 235 and the tank-side joint 236. The pipe-side joint 235 is connected to the tank-side joint 236. When the pipe-side joint 235 and the tank-side joint 236 are separated from each other, the pipe-side joint 235 and the tank-side joint 236 are sealed to prevent ink from leaking from the pipe-side joint 235 and the tank-side joint 236. Similar to the joint 234, the joint 233 is composed of a pipe-side joint attached to the end of the pipe path 22219 and a tank-side joint attached to the main tank 213.

[0153] The buffer tank 212 is an ink pack formed in a bag shape. The buffer tank 212 includes a bag-shaped tank body made of flexible film and an ink inlet and an ink outlet attached to the tank body. The buffer tank 212 is, for example, an aluminum pack having an aluminum tank body. The buffer tank 212 is disposed in the piping path between the sub-tank 211 and the main tank 213. Ink is supplied from the main tank 213 to the buffer tank 212 by a head difference. That is, the ink level in the main tank 213 is higher than the ink level in the buffer tank 212, and ink is supplied from the main tank 213 to the buffer tank 212 by utilizing the difference (head difference) between the ink levels in the main tank 213 and the buffer tank 212.

[0154] The pump 214 is equipped with a motor as a drive source. The pump 214 is electrically connected to the control unit 217. Specifically, the motor of the pump 214 is electrically connected to the control unit 217. The on-off valves 223 to 225 are solenoid valves. The on-off valves 223 to 225 are electrically connected to the control unit 217.

[0155] In this embodiment, when the pump 214 is driven with the on-off valve 224 open and the on-off valve 225 closed, ink flows from the buffer tank 212 toward the sub-tank 211. When the pump 214 is driven with the on-off valve 225 open and the on-off valve 224 closed, ink flows from the buffer tank 212 toward the main tank 213, and the ink in the buffer tank 212 returns to the main tank 213. When the pump 214 is driven with the on-off valves 223 and 225 open and the on-off valve 224 closed, ink circulates between the main tank 213 and the buffer tank 212. In this way, the pump 214 fulfills the function of supplying ink from the buffer tank 212 to the sub-tank 211 and the function of circulating ink between the main tank 213 and the buffer tank 212.

[0156] The detection mechanism 228 is a liquid level detection mechanism for detecting the height of the ink level in the subtank 211. The detection mechanism 228 includes a float 239 that floats on the ink in the subtank 211, a permanent magnet (not shown) built into the float 239, and three sensors 240-242 that are arranged outside the subtank 211 and detect the permanent magnet. The sensors 240-242 are magnetic sensors such as Hall ICs. The sensor 240 is fixed to the outer surface of the subtank 211 at the upper end. The sensor 241 is fixed to the outer surface of the subtank 211 below the sensor 240. The sensor 242 is fixed to the outer surface of the subtank 211 at the lower end.

[0157] The sensor 240 is a sensor for detecting whether the ink level in the subtank 211 is higher than a predetermined upper limit. The sensor 241 is a sensor for detecting whether the ink level in the subtank 211 is within an appropriate range. The sensor 242 is a sensor for detecting whether the ink level in the subtank 211 is lower than a predetermined lower limit. The sensors 240 to 242 are electrically connected to the control unit 217. The control unit 217 detects the ink level in the subtank 211 based on the detection results of the detection mechanism 228 (specifically, the detection results of the sensors 240 to 242), thereby detecting the amount (volume) of ink contained in the subtank 211. Note that only one detection mechanism 228 is shown in FIG. 14 .

[0158] The printer 201 also includes a maintenance unit 243 for preventing clogging of the multiple nozzles of the head 203. The maintenance unit 243 is disposed in a position in the main scanning direction outside the printing area where printing on the medium 202 is performed. The maintenance unit 243 includes a wiper member for wiping the ink ejection surface (lower surface) of the head 203, and an ink receiving container for receiving ink ejected from the head 203. The maintenance unit 243 performs a cleaning operation on the head 203 to prevent clogging of the multiple nozzles of the head 203.

[0159] The cleaning operation of the head 203 includes a purging operation in which the pressure inside the subtank 211 is made positive to forcibly eject ink from the head 203. The cleaning operation also includes a wiping operation in which a wiper member wipes the ink ejection surface of the head 203, and a flushing operation in which the piezoelectric element of the head 203 is driven to forcibly eject ink from the head 203. The cleaning operation is automatically executed by the control unit 217.

[0160] There are three types of cleaning operations for the head 203: a soft cleaning operation; a normal cleaning operation, which ejects a larger amount of ink from the head 203 and takes a longer time than the soft cleaning operation; and a hard cleaning operation, which ejects a larger amount of ink from the head 203 and takes a longer time than the normal cleaning operation. The soft cleaning operation is performed, for example, to refresh the nozzles of the head 203 before printing on the medium 202. The normal cleaning operation is performed, for example, when multiple nozzle clogs have occurred, meaning that ink is not ejected from the nozzles even though the piezoelectric elements of the head 203 are driven. The hard cleaning operation is performed, for example, when a nozzle clog has occurred that cannot be resolved by the normal cleaning operation.

[0161] (Inkjet Printer Control Method) When printing on the medium 202, the control unit 217 opens the on-off valves 223 and 224 based on the detection result of the detection mechanism 228, and drives the pump 214 with the on-off valve 225 closed to supply ink from the buffer tank 212 to the subtank 211. When printing on the medium 202, a negative pressure is created inside the subtank 211. Because ink is supplied from the buffer tank 212 to the subtank 211 while printing on the medium 202, ink is supplied from the buffer tank 212 to the subtank 211 even when the main tank 213 runs out of ink and is being replaced while printing on the medium 202. Note that the replacement of the main tank 213 while printing on the medium 202 is performed after the on-off valve 223 is closed, and the on-off valve 223 is opened once the replacement of the main tank 213 is complete.

[0162] Furthermore, in the printer 201, in order to suppress settling of ink particles in the buffer tank 212, when printing is not performed on the medium 202 and the carriage 204 is stopped for a predetermined period of time or longer, the ink is circulated between the main tank 213 and the buffer tank 212. Specifically, the control unit 217 closes the on-off valve 224 and opens the on-off valves 223 and 225 to form an ink circulation path that passes through the main tank 213 and the buffer tank 212, and then drives the pump 214 to circulate the ink through this circulation path. As described above, in this embodiment, when the piping-side joint 235 and the tank-side joint 236 are separated from each other, the piping-side joint 235 is sealed to prevent ink from leaking out of the piping-side joint 235.

[0163] Therefore, for example, if a poor connection occurs in the joint 234 where the piping-side joint 235 and the tank-side joint 236 are not properly connected after the main tank 213 has run out of ink and been replaced (i.e., a poor connection where the piping path 222 is not properly connected to the replaced main tank 213), when attempting to circulate ink between the main tank 213 and the buffer tank 212, the pump 214 will not be able to send ink, causing an excessive load to act on the pump 214 and possibly causing a breakdown of the pump 214. Furthermore, if a poor connection occurs in the joint 234, when attempting to circulate ink between the main tank 213 and the buffer tank 212, the pressure inside the piping path 222 may become excessively high, causing ink to leak from the piping path 222.

[0164] Therefore, in this embodiment, the control unit 217 executes a predetermined operation to check whether the piping-side joint 235 and the tank-side joint 236 are properly connected, for example, after replacing the main tank 213 or starting up the printer 201. Specifically, the control unit 217 opens the on-off valves 224, 225 and drives the pump 214 at a constant speed for a predetermined first period of time while the amount of ink in the subtank 211 is set to a predetermined first reference amount, and executes a checking operation CO to determine whether the amount of ink in the subtank 211 exceeds a predetermined second reference amount based on the detection result of the detection mechanism 228.

[0165] In this embodiment, when the piping-side joint 235 and the tank-side joint 236 are properly connected, if the pump 214 is driven with the on-off valves 224 and 225 open, the amount of ink flowing from the buffer tank 212 to the main tank 213 will be greater than the amount of ink flowing from the buffer tank 212 to the subtank 211. Specifically, the ink liquid levels in the subtank 211 and the main tank 213 are higher than the ink liquid level in the buffer tank 212, and the head difference between the subtank 211 and the buffer tank 212 is greater than the head difference between the main tank 213 and the buffer tank 212. Therefore, when the piping-side joint 235 and the tank-side joint 236 are properly connected, if the pump 214 is driven with the on-off valves 224 and 225 open, the amount of ink flowing from the buffer tank 212 to the main tank 213 will be greater than the amount of ink flowing from the buffer tank 212 to the subtank 211.

[0166] Therefore, in this embodiment, if the piping-side joint 235 and the tank-side joint 236 are properly connected, the amount of ink flowing from the buffer tank 212 to the main tank 213 will be greater than the amount of ink flowing from the buffer tank 212 to the subtank 211 in the confirmation operation, and the amount of ink in the subtank 211 will not exceed the second reference amount. On the other hand, if the piping-side joint 235 and the tank-side joint 236 are not properly connected, ink will not flow from the buffer tank 212 to the main tank 213, and the amount of ink flowing from the buffer tank 212 to the subtank 211 will be greater in the confirmation operation, and the amount of ink in the subtank 211 will exceed the second reference amount. Therefore, in this embodiment, by performing the confirmation operation, it is possible to confirm whether the piping-side joint 235 and the tank-side joint 236 are properly connected.

[0167] In this embodiment, the control unit 217 performs the checking operation during the cleaning operation. Specifically, the control unit 217 does not perform the checking operation during the cleaning operation performed while printing the medium 202, but performs the checking operation during the cleaning operation performed before printing the medium 202 starts or after printing is completed. Also, in this embodiment, the procedures for the soft cleaning operation and normal cleaning operation are different from the procedures for the hard cleaning operation. Below, the procedures for the soft cleaning operation and normal cleaning operation, and the procedures for the hard cleaning operation are described in this order, and the procedures for the checking operation are described.

[0168] (Soft Cleaning Operation and Normal Cleaning Operation) FIG. 15 is a flowchart for explaining an example of the procedure for the soft cleaning operation and normal cleaning operation of the head 203 shown in FIG.

[0169] When a soft cleaning operation or a normal cleaning operation of the head 203 is started before printing of the medium 202 begins or after printing is completed, the control unit 217 first opens the on-off valve 224 and drives the pump 214 with the on-off valve 225 closed, to supply ink from the buffer tank 212 to the subtank 211 until the amount of ink in the subtank 211 reaches a second reference amount (step S0).

[0170] Thereafter, the control unit 217 performs a purging operation (step S1). In step S1, the control unit 217 ejects ink from the head 203 until the amount of ink in the subtank 211 reaches a first reference amount. In other words, after the purging operation, the amount of ink in the subtank 211 reaches the first reference amount. Also, in step S1, when the ejection of ink is finished, the control unit 217 opens the subtank 211 to the atmosphere, sets the pressure inside the subtank 211 to atmospheric pressure, and then sets the pressure inside the subtank 211 to a slight negative pressure.

[0171] The control unit 217 then determines whether or not a confirmation operation needs to be performed (step S2). In this embodiment, the control unit 217 determines that a confirmation operation needs to be performed if the state of the joint 234 stored in the control unit 217 is an "unconfirmed state." Also, in this embodiment, the state of the joint 234 stored in the control unit 217 is an "unconfirmed state" when the cleaning operation is performed for the first time after the main tank 213 is replaced, when the cleaning operation is performed for the first time after the printer 201 is started, or when the "unconfirmed state" is stored in the control unit 217 in step S17 (described later). On the other hand, if the state of the joint 234 stored in the control unit 217 is not an "unconfirmed state," the control unit 217 determines that a confirmation operation does not need to be performed. The printer 201 is equipped with a detection mechanism for detecting that the main tank 213 has been replaced, and this detection mechanism detects that the main tank 213 has been replaced.

[0172] If it is determined in step S2 that it is not necessary to perform the checking operation, the control unit 217 drives the pump 214 at a constant speed with the on-off valve 224 open and the on-off valve 225 closed, to supply ink from the buffer tank 212 to the subtank 211 until the amount of ink in the subtank 211 reaches a second reference amount that is greater than the first reference amount (step S3). That is, after the purging operation, the control unit 217 drives the pump 214 with the on-off valve 224 open and the on-off valve 225 closed, to supply ink to the subtank 211 until the amount of ink in the subtank 211 reaches the second reference amount. In step S3, the control unit 217 measures the second time, which is the time it takes for the amount of ink in the subtank 211 to reach the second reference amount.

[0173] The driving speed of the pump 214 in step S3 (specifically, the rotational speed (rotational speed) of the motor of the pump 214) is equal to the driving speed of the pump 214 when ink flows from the buffer tank 212 to the subtank 211 with the on-off valve 224 open and the on-off valve 225 closed when the printer 201 prints on the medium 202. For example, the rotational speed of the motor of the pump 214 in step S3 is 216 (rpm). Hereinafter, the driving speed of the pump 214 in step S3 (i.e., the driving speed of the pump 214 when ink is supplied to the subtank 211 after the purging operation without performing the confirmation operation) is referred to as the "normal driving speed."

[0174] Thereafter, the control unit 217 determines whether or not a confirmation operation was performed before executing step S3 (step S4). Specifically, the control unit 217 determines in step S4 whether or not at least steps S12 and S13, described below, were performed before executing step S3. If in step S4 a confirmation operation was not performed before executing step S3, the control unit 217 stores the time measured in step S3 as the second time (step S5). When proceeding from step S2 to step S3, a confirmation operation was not performed before executing step S3, so in step S5 the control unit 217 stores the time measured in step S3 as the second time.

[0175] Thereafter, the control unit 217 executes the wiping operation and the flushing operation in this order (steps S6 and S7). When the flushing operation is completed in step S7, the soft cleaning operation or normal cleaning operation of the head 203 is completed.

[0176] On the other hand, if it is determined in step S2 that a confirmation operation needs to be performed, control unit 217 determines whether a second time period has been stored in control unit 217 (step S9). If the second time period has not been stored in control unit 217 in step S9, control unit 217 proceeds to step S3. When control unit 217 proceeds from step S9 to step S3, no confirmation operation has been performed before step S3 is performed, and therefore control unit 217 stores the time period measured in step S3 as the second time period in step S5.

[0177] On the other hand, if the second time is stored in the control unit 217 in step S9, the control unit 217 calculates the first time to execute the confirmation operation (step S10). In step S10, the control unit 217 calculates the first time based on the second time stored in the control unit 217.

[0178] In this embodiment, the drive speed of the pump 214 when the checking operation is performed (specifically, the drive speed of the pump 214 in step S12 described below) is slower than the normal drive speed of the pump 214. For example, the rotation speed of the motor of the pump 214 when the checking operation is performed is about half the rotation speed of the motor of the pump 214 when it is driven at the normal drive speed. In step S10, the control unit 217 calculates the first time by multiplying the second time stored in the control unit 217 by the ratio of the drive speed of the pump 214 when the checking operation is performed to the normal drive speed and by a margin. The first time is longer than the second time. For example, the first time is about four times the second time.

[0179] Thereafter, the control unit 217 determines whether the first time calculated in step S10 exceeds a predetermined reference time (step S11). If the first time exceeds the reference time, the execution time of the confirmation operation will be excessively long, and the cleaning time of the head 203 will be excessively long. Therefore, if the first time exceeds the reference time in step S11, the process proceeds to step S3. When the process proceeds from step S11 to step S3, the confirmation operation has not been executed before step S3 is executed, and therefore the control unit 217 stores the time measured in step S3 as the second time in step S5.

[0180] On the other hand, if the first time is less than the reference time in step S11, the control unit 217 opens the on-off valves 224 and 225 and drives the pump 214 at a constant speed to supply ink to the main tank 213 and the subtank 211 (step S12). In step S12, the control unit 217 drives the pump 214 for only the first time. As described above, the drive speed of the pump 214 in step S12 is slower than the normal drive speed of the pump 214.

[0181] Thereafter, the control unit 217 determines whether the amount of ink in the subtank 211 exceeds the second reference amount based on the detection result of the detection mechanism 228 (step S13). If the amount of ink in the subtank 211 exceeds the second reference amount in step S13, the control unit 217 determines that the piping-side joint 235 and the tank-side joint 236 are not properly connected, and stores "abnormal state" as the state of the joint 234 in the control unit 217 (step S14). Then, the process proceeds to step S6.

[0182] On the other hand, if the amount of ink in the subtank 211 is less than the second reference amount in step S13, the control unit 217 determines whether the pump 214 was brought to an emergency stop in step S12 (step S15). For example, if replacement of the main tank 213 is started during execution of step S12, if the printer 201 is brought to an emergency stop, or if an abnormality such as an abnormality in the pressure adjustment mechanism 226 is detected, the pump 214 is brought to an emergency stop in step S12 before operating for the first period. On the other hand, if no such abnormality occurs, the pump 214 continues to operate for the first period in step S12 without being brought to an emergency stop.

[0183] If the pump 214 has not been stopped in an emergency in step S15, the control unit 217 determines that the pipe-side joint 235 and the tank-side joint 236 are normally connected, and stores the "normal state" as the state of the joint 234 in the control unit 217 (step S16). Then, the process proceeds to step S3. When the process proceeds from step S16 to step S3, the confirmation operation has been performed before step S3 is executed, and therefore the process proceeds from step S4 to step S6.

[0184] On the other hand, if the pump 214 has made an emergency stop in step S15, the control unit 217 cannot determine whether the pipe-side joint 235 and the tank-side joint 236 are normally connected, and therefore stores the "unconfirmed state" as the state of the joint 234 in the control unit 217 (step S17). Then, the process proceeds to step S3. When the process proceeds from step S17 to step S3, the confirmation operation has been performed before step S3 is executed, and therefore the process proceeds from step S4 to step S6.

[0185] As described above, in this embodiment, the control unit 217 performs a checking operation when predetermined conditions are met after the purging operation in step S1 (specifically, when the conditions are met in steps S2, S9, and S11). Also, in this embodiment, when a "normal state" is stored in the control unit 217 in step S16, ink circulates between the main tank 213 and the buffer tank 212, as described above. Also, when an "abnormal state" is stored in the control unit 217 in step S14, the control unit 217 performs predetermined processing. Specifically, the control unit 217 performs predetermined processing to prevent ink from circulating between the main tank 213 and the buffer tank 212. Also, when an "abnormal state" is stored in the control unit 217 in step S14, the control unit 217 displays a predetermined error message on the display unit 45, such as a display panel of the printer 201 connected to the control unit 217.

[0186] (Hard Cleaning Operation) Fig. 16 is a flowchart for explaining an example of the procedure for the hard cleaning operation of the head 203 shown in Fig. 12. Note that in Fig. 16, steps that are the same as those shown in Fig. 15 are given the same reference numerals.

[0187] In the following description, the purging operation in the soft cleaning operation will be referred to as the "first purging operation," and the purging operation in the hard cleaning operation will be referred to as the "second purging operation." In other words, the soft cleaning operation includes a first purging operation in which the pressure inside the subtank 211 is made positive to cause ink to be ejected from the head 203, and the hard cleaning operation includes a second purging operation in which the pressure inside the subtank 211 is made positive to cause ink to be ejected from the head 203. The amount of ink ejected from the head 203 in the second purging operation is greater than the amount of ink ejected from the head 203 in the first purging operation, and the time required for the second purging operation is longer than the time required for the first purging operation.

[0188] When a hard cleaning operation of the head 203 is initiated before printing on the medium 202 begins or after printing is completed, the control unit 217 first opens the on-off valve 224 and drives the pump 214 with the on-off valve 225 closed to supply ink from the buffer tank 212 to the subtank 211 until the amount of ink in the subtank 211 reaches a second reference amount (step S21). In step S21, the control unit 217 sets the pressure in the subtank 211 to a slight negative pressure. Thereafter, the control unit 217 determines whether or not a confirmation operation needs to be performed (step S22). As in step S2, in step S22, the control unit 217 determines whether or not a confirmation operation needs to be performed based on whether or not the state of the joint 234 stored in the control unit 217 is in an "unconfirmed state."

[0189] If step S22 determines that a confirmation operation is not necessary, the control unit 217 performs a second purging operation (step S23). Also, in step S23, after ink ejection is complete, the control unit 217 opens the subtank 211 to the atmosphere, sets the pressure inside the subtank 211 to atmospheric pressure, and then sets the pressure inside the subtank 211 to a slight negative pressure. The control unit 217 then drives the pump 214 with the on-off valve 224 open and the on-off valve 225 closed to supply ink from the buffer tank 212 to the subtank 211 until the amount of ink in the subtank 211 reaches a second reference amount (step S24). The control unit 217 then performs a wiping operation and a flushing operation in this order (steps S25 and S26). When the flushing operation is completed in step S26, the hard cleaning operation of the head 203 is completed.

[0190] On the other hand, if it is determined in step S22 that a confirmation operation needs to be performed, the control unit 217 performs a first purging operation (step S27). In step S27, the control unit 217 ejects ink from the head 203 until the amount of ink in the subtank 211 reaches a first reference amount. Also in step S27, after ink ejection is complete, the control unit 217 opens the subtank 211 to the atmosphere, sets the pressure inside the subtank 211 to atmospheric pressure, and then sets the pressure inside the subtank 211 to a slight negative pressure. Thereafter, the control unit 217 determines whether a second time has been stored in the control unit 217, as described above (step S9). If the second time has not been stored in the control unit 217 in step S9, the process proceeds to step S3.

[0191] Thereafter, the control unit 217 determines whether or not a confirmation operation was performed before executing step S3 (step S4), and if a confirmation operation was not performed before executing step S3, stores the time measured in step S3 as the second time (step S5). When the process proceeds from step S9 to step S3, since a confirmation operation was not performed before executing step S3, the control unit 217 stores the time measured in step S3 as the second time in step S5. Then, the process proceeds to step S23.

[0192] On the other hand, if the second time is stored in the control unit 217 in step S9, the control unit 217 calculates the first time (step S10). Thereafter, the control unit 217 determines whether the first time calculated in step S10 exceeds the reference time (step S11). If the first time exceeds the reference time in step S11, the process proceeds to step S3. When the process proceeds from step S11 to step S3, the confirmation operation has not been performed before step S3 is executed, and therefore the control unit 217 stores the time measured in step S3 as the second time in step S5.

[0193] On the other hand, if the first time is less than the reference time in step S11, the control unit 217 opens the on-off valves 224 and 225 and drives the pump 214 at a constant speed to supply ink to the main tank 213 and the subtank 211 (step S12). Thereafter, the control unit 217 determines whether the amount of ink in the subtank 211 exceeds a second reference amount based on the detection result of the detection mechanism 228 (step S13). If the amount of ink in the subtank 211 exceeds the second reference amount in step S13, the control unit 217 stores "abnormal state" as the state of the joint 234 in the control unit 217 (step S14). Then, the process proceeds to step S23.

[0194] On the other hand, if the amount of ink in the subtank 211 is less than the second reference amount in step S13, the control unit 217 determines whether the pump 214 was stopped in an emergency in step S12 (step S15). If the pump 214 was not stopped in an emergency in step S15, the control unit 217 stores the "normal state" as the state of the joint 234 in the control unit 217 (step S16), and then proceeds to step S3. When proceeding from step S16 to step S3, the confirmation operation has been performed before step S3 is executed, so the process proceeds from step S4 to step S23.

[0195] Furthermore, if the pump 214 makes an emergency stop in step S15, the control unit 217 stores the "unconfirmed state" as the state of the joint 234 in the control unit 217 (step S17), and then proceeds to step S3. When proceeding from step S17 to step S3, the confirmation operation has been performed before step S3 is executed, so the process proceeds from step S4 to step S23. Thus, in this embodiment, when a hard cleaning operation of the head 203 is executed, the control unit 217 executes the first purging operation in step S27 when predetermined conditions are met, before executing the second purging operation in step S23, and also executes the confirmation operation after the first purging operation when predetermined conditions are met, and then executes the second purging operation.

[0196] (Main effect of this embodiment) As described above, in this embodiment, the control unit 217 opens the on-off valves 224, 225 and drives the pump 214 at a constant speed for a first period of time while the amount of ink in the subtank 211 is set to a first reference amount, and performs a confirmation operation to determine whether the amount of ink in the subtank 211 exceeds a second reference amount based on the detection result of the detection mechanism 228.

[0197] Furthermore, in this embodiment, if the piping-side joint 235 and the tank-side joint 236 are properly connected, the amount of ink flowing from the buffer tank 212 to the main tank 213 will be greater than the amount of ink flowing from the buffer tank 212 to the subtank 211 in the confirmation operation, and the amount of ink in the subtank 211 will not exceed the second reference amount. On the other hand, if the piping-side joint 235 and the tank-side joint 236 are not properly connected, ink will not flow from the buffer tank 212 to the main tank 213, and so the amount of ink flowing from the buffer tank 212 to the subtank 211 will be greater in the confirmation operation, and the amount of ink in the subtank 211 will exceed the second reference amount.

[0198] Furthermore, in this embodiment, when the amount of ink in the subtank 211 exceeds the second reference amount during the checking operation, the control unit 217 stores the state of the joint 234 as "abnormal state" in the control unit 217, and executes a predetermined process to prevent ink from circulating between the main tank 213 and the buffer tank 212. Therefore, in this embodiment, when a connection failure of the joint 234 occurs, it is possible to prevent ink from circulating between the main tank 213 and the buffer tank 212.

[0199] Furthermore, in this embodiment, when the amount of ink in the subtank 211 exceeds the second reference amount during the confirmation operation, the control unit 217 executes a predetermined error process, such as displaying a predetermined error message on the display unit 45, so that the operator can easily recognize that a poor connection has occurred in the fitting 234.

[0200] In particular, in this embodiment, the main tank 213 can be removed from the printer 201 and replaced, which increases the possibility of a connection failure in the joint 234 occurring after replacing the main tank 213. However, in this embodiment, even if a connection failure occurs in the joint 234, it is possible to prevent ink from circulating between the main tank 213 and the buffer tank 212. Furthermore, even if a connection failure occurs in the joint 234, it is possible to make the operator easily aware that a connection failure has occurred in the joint 234.

[0201] In this embodiment, the drive speed of the pump 214 when the checking operation is performed is slower than the normal drive speed of the pump 214. According to studies by the inventors of the present application, if the drive speed of the pump 214 when the checking operation is performed is equal to or higher than the normal drive speed, even if the piping-side joint 235 and the tank-side joint 236 are properly connected, ink is likely to flow from the buffer tank 212 to the subtank 211 when the pump 214 is driven with the on-off valves 224 and 225 open. Therefore, in this case, even if the piping-side joint 235 and the tank-side joint 236 are properly connected, there is a risk that the amount of ink in the subtank 211 will exceed the second reference amount during the checking operation.

[0202] In contrast, according to studies by the inventors of the present application, if the drive speed of the pump 214 when the checking operation is performed is slower than the normal drive speed, then as long as the piping-side joint 235 and the tank-side joint 236 are properly connected, driving the pump 214 with the on-off valves 224, 225 open makes it difficult for ink to flow from the buffer tank 212 to the subtank 211. In this embodiment, because the drive speed of the pump 214 when the checking operation is performed is slower than the normal drive speed, it is possible to prevent the amount of ink in the subtank 211 from exceeding the second reference amount during the checking operation if the piping-side joint 235 and the tank-side joint 236 are properly connected.

[0203] In this embodiment, after the purging operation is performed during the soft cleaning operation or normal cleaning operation of the head 203, or after the first purging operation is performed during the hard cleaning operation of the head 203, the amount of ink in the subtank 211 becomes the first reference amount, and the control unit 217 performs the confirmation operation when predetermined conditions are met after the purging operation. Therefore, in this embodiment, there is no need to eject ink from the head 203 until the amount of ink in the subtank 211 becomes the first reference amount just to perform the confirmation operation. Therefore, in this embodiment, unnecessary consumption of ink is suppressed even when the confirmation operation is performed.

[0204] In this embodiment, after a purging operation in a soft cleaning operation or a normal cleaning operation of the head 203 has been performed, or after a first purging operation in a hard cleaning operation of the head 203 has been performed, the control unit 217 drives the pump 214 with the on-off valve 224 open and the on-off valve 225 closed to supply ink to the subtank 211 until the amount of ink in the subtank 211 reaches a second reference amount, and measures the second time, which is the time it takes for the amount of ink in the subtank 211 to reach the second reference amount. Also, in this embodiment, if the control unit 217 does not perform a confirmation operation after the purging operation, it stores the most recent measured second time and calculates the first time based on the second time.

[0205] Therefore, in this embodiment, even if the condition of the ink supply path from the buffer tank 212 to the subtank 211 changes over time, it is possible to accurately determine in the checking operation whether or not the amount of ink in the subtank 211 exceeds the second reference amount. For example, even if the filter 215 becomes clogged and it becomes difficult for ink to flow from the buffer tank 212 to the subtank 211 over time, it is possible to accurately determine in the checking operation whether or not the amount of ink in the subtank 211 exceeds the second reference amount.

[0206] In this embodiment, when the hard cleaning operation is performed, the control unit 217 performs the first purging operation before performing the second purging operation when predetermined conditions are met, and performs the verification operation when predetermined conditions are met after the first purging operation, and then performs the second purging operation. Therefore, in this embodiment, it is possible to reduce the time required for the verification operation compared to when the verification operation is performed when predetermined conditions are met after the second purging operation.

[0207] (Other Embodiments) The above-described embodiment is one example of a preferred embodiment of the present invention, but the present invention is not limited to this and various modifications can be made within the scope that does not change the gist of the present invention.

[0208] In the above-described embodiment, the hard cleaning operation of the head 203 may be the same as the soft cleaning operation and normal cleaning operation of the head 203. That is, the hard cleaning operation of the head 203 may be performed according to the procedure shown in the flowchart of FIG. 15. Also, in the above-described embodiment, the driving speed of the pump 214 when the confirmation operation is performed may be equal to or higher than the normal driving speed. Furthermore, in the above-described embodiment, the second time may be a fixed value that is not updated.

[0209] In the above-described embodiment, the checking operation may be performed during a cleaning operation that is performed during printing of the medium 202. Also, in the above-described embodiment, the checking operation does not have to be performed during a cleaning operation. For example, the checking operation may be performed immediately after the main tank 213 is replaced or immediately after the printer 201 is started. Furthermore, in the above-described embodiment, the detection mechanism 228 may be a detection mechanism other than a liquid level detection mechanism. Also, in the above-described embodiment, at least one of the on-off valves 223 to 225 may be a manual valve that is manually opened and closed. Also, in the above-described embodiment, the buffer tank 212 does not have to be an ink pack.

[0210] In the above-described embodiment, the printer 201 may include a pump disposed in the piping path 22219. In this case, the pump supplies ink from the main tank 213 to the buffer tank 212. In the above-described embodiment, the printer 201 is a device for printing on the medium 202, but the printer 201 may be used for purposes other than printing on the medium 202. For example, the printer 201 may be a 3D printer for forming three-dimensional objects. The printer 201 may also be an inkjet printer for general consumers.

[0211] REFERENCE SIGNS LIST 1 Printer (inkjet printer) 5 Head (inkjet head) 11 Sub-tank 15 On-off valve (second on-off valve) 17 Main tank 18 Buffer tank 19 Pump 20 Check valve 21 On-off valve 22 On-off valve (third on-off valve) 23 Detection mechanism 101 Printer (inkjet printer) 103 Head (inkjet head) 111 Sub-tank 112 Buffer tank (supplied side tank) 113 Main tank 114 Pump 115 Filter (ink filter) 116 Detection mechanism 117 Control unit 119 Pipe path (first pipe path) 122 Pipe path (fourth pipe path) 124 On-off valve (first on-off valve) 125 On-off valve (second on-off valve) 130 Connection point 131 Pipe path (third pipe path) 132 Pipe path (second pipe path) M1 Reference amount (first reference amount) M2 Reference amount (second reference amount) M3 Reference amount (third reference amount) T1 Fixed time (first fixed time) T2 Fixed time (second fixed time) 201 Printer (inkjet printer) 203 Head (inkjet head) 211 Sub-tank 212 Buffer tank 213 Main tank 214 Pump 217 Control unit 221 Pipe path (first pipe path) 222 Pipe path (second pipe path) 224 On-off valve (first on-off valve) 225 On-off valve (second on-off valve) 228 Detection mechanism 230 Connection point 234 Joint 235 Pipe side joint 236 Tank side joint 243 Maintenance unit

Claims

1. An inkjet printer comprising: an inkjet head for ejecting ink; a sub-tank for storing ink to be supplied to the inkjet head; a main tank for storing ink to be supplied to the sub-tank; a buffer tank arranged in a piping path between the sub-tank and the main tank and for storing ink; a pump arranged in the piping path between the sub-tank and the buffer tank; and a check valve arranged in parallel with the buffer tank in the piping path between the main tank and the pump, for allowing ink to flow only in the direction from the main tank toward the pump.

2. The ink jet printer according to claim 1, further comprising an opening / closing valve disposed in a piping path between said main tank and said buffer tank.

3. The ink jet printer according to claim 1 or 2, wherein ink is supplied from said main tank to said buffer tank by a water head difference.

4. The ink jet printer according to claim 1 or 2, wherein said buffer tank is an ink pack formed in a bag shape.

5. An inkjet printer as described in claim 1, further comprising: a second on-off valve arranged in a piping path between the sub-tank and the pump; and a third on-off valve arranged in a piping path having one end connected to the piping path between the second on-off valve and the pump and the other end connected to the main tank.

6. The ink jet printer according to claim 5, further comprising an on-off valve disposed in a piping path between said main tank and said buffer tank.

7. An ink jet printer as claimed in claim 1 or 2, further comprising a detection mechanism for detecting the volume of ink contained in said main tank, said detection mechanism indirectly detecting the volume of ink contained in said buffer tank.

8. An inkjet printer equipped with an inkjet head that ejects ink, comprising: a main tank that contains ink; a supplied tank that is located closer to the inkjet head than the main tank in a piping path between the main tank and the inkjet head and contains ink supplied from the main tank; a pump for circulating ink between the main tank and the supplied tank; a first piping path that is a supply piping path through which ink flows from the main tank to the supplied tank; a second piping path in which the pump is located and is a circulation piping path through which ink flows from the supplied tank to the main tank; a detection mechanism for detecting the amount of ink contained in the main tank; and a control unit for controlling the inkjet printer, wherein the control unit calculates an increase in the amount of ink in the main tank during the first fixed time period based on a detection result of the detection mechanism during ink circulation in which the pump is driven to circulate ink between the main tank and the supplied tank, and executes a specified error process when the calculated increase becomes equal to or exceeds a specified first reference amount several times in succession; an inkjet printer comprising: a detecting mechanism for detecting a change in ink amount in the main tank during the ink circulation, the detecting mechanism detecting a change in ink amount in the main tank during the second fixed time interval; a detecting mechanism for detecting a change in ink amount in the main tank during the second fixed time interval; a detecting mechanism for detecting a change in ink amount in the main tank during the second fixed time interval; a detecting mechanism for detecting a change in ink amount in the main tank during the second fixed time interval; a detecting mechanism for detecting a change in ink amount in the main tank during the second fixed time interval; 9. The ink-jet printer according to claim 8, wherein said main tank is removable from said ink-jet printer and replaceable.

10. A liquid ejection head comprising: a sub-tank for storing ink to be supplied to the inkjet head; a buffer tank as the supply-side tank for storing ink to be supplied to the sub-tank from the main tank; a first on-off valve; and a second on-off valve; a piping path connecting the buffer tank and the sub-tank has a connection point to which one end of the piping path connected to the main tank is connected; a second piping path is formed by a third piping path which is a piping path between the buffer tank and the connection point, and a fourth piping path which is a piping path between the connection point and the main tank; the pump is disposed in the third piping path; the first on-off valve is disposed in the piping path between the connection point and the sub-tank; and the second on-off valve is disposed in the fourth piping path; when the pump is driven with the second on-off valve open and the first on-off valve closed, ink flows from the buffer tank toward the main tank; 10. The ink jet printer according to claim 9, wherein when the pump is driven with the first on-off valve open and the second on-off valve closed, ink flows from the buffer tank to the sub-tank.

11. The inkjet printer according to claim 10, further comprising an ink filter disposed in the third piping path, wherein ink is supplied from the main tank to the buffer tank by a water head difference.

12. A control method for an inkjet printer comprising an inkjet head for ejecting ink, a main tank for storing ink, a supply-side tank arranged on the inkjet head side of the main tank in a piping path between the main tank and the inkjet head and for storing ink supplied from the main tank, a pump for circulating ink between the main tank and the supply-side tank, a first piping path which is a supply piping path through which ink flows from the main tank to the supply-side tank, a second piping path in which the pump is arranged and which is a circulation piping path through which ink flows from the supply-side tank to the main tank, and a detection mechanism for detecting the amount of ink stored in the main tank, wherein, during ink circulation in which the pump is driven to circulate ink between the main tank and the supply-side tank, an increase in the amount of ink in the main tank during the first fixed time period is calculated at a first fixed time interval based on a detection result of the detection mechanism, and when the calculated increase becomes equal to or exceeds a first reference amount several times in succession, a specified error process is executed, a control method for an inkjet printer, comprising: calculating an amount of change in the ink in the main tank during the second fixed time interval based on a detection result of the detection mechanism during the ink circulation, and calculating, at the second fixed time interval, an ink change difference which is the difference between the amount of change in the ink in the main tank during the second fixed time calculated previously and the amount of change in the ink in the main tank during the second fixed time calculated currently; storing the amount of ink in the main tank when the absolute value of the calculated ink change difference becomes equal to or less than a predetermined second reference amount which is less than the first reference amount a plurality of times in succession as an initial ink amount; and executing the error processing even if the amount of increase in the ink in the main tank from the stored initial ink amount becomes a predetermined third reference amount which is greater than the first reference amount.

13. An inkjet printer equipped with an inkjet head that ejects ink, comprising: a subtank for storing ink to be supplied to the inkjet head, a buffer tank for storing ink to be supplied to the subtank, a main tank for storing ink to be supplied to the buffer tank, a pump arranged in a piping path between the buffer tank and the subtank, a first piping path which is a piping path connecting the pump and the subtank, a second piping path which is a piping path connecting the first piping path and the main tank, a coupling having a piping side coupling part attached to an end of the second piping path and a tank side coupling part attached to the main tank and to which the piping side coupling part is connected, a first opening / closing valve arranged in the piping path between the subtank and a connection point of the first piping path and the second piping path, a second opening / closing valve arranged in the second piping path, a detection mechanism for detecting the amount of ink stored in the subtank, and a control unit for controlling the inkjet printer, when the pump is driven with the second on-off valve open and the first on-off valve closed, ink flows from the buffer tank toward the main tank; when the pump is driven with the first on-off valve open and the second on-off valve closed, ink flows from the buffer tank toward the sub-tank; when the piping-side joint and the tank-side joint are normally connected, when the pump is driven with the first on-off valve and the second on-off valve open, the amount of ink flowing from the buffer tank to the main tank becomes greater than the amount of ink flowing from the buffer tank to the sub-tank; when the piping-side joint and the tank-side joint are separated, the piping-side joint is sealed to prevent ink from leaking out; an inkjet printer characterized in that, while the amount of ink in the subtank is set to a predetermined first reference amount, the control unit opens the first on-off valve and the second on-off valve and drives the pump at a constant speed for a predetermined first period of time, and performs a confirmation operation to determine whether the amount of ink in the subtank exceeds a predetermined second reference amount based on the detection result of the detection mechanism.

14. The ink-jet printer according to claim 13, wherein said main tank is removable from said ink-jet printer and replaceable.

15. An inkjet printer as described in claim 13 or 14, characterized in that the driving speed of the pump when the confirmation operation is performed is slower than the driving speed of the pump when the inkjet printer is printing and the pump is driven with the first on-off valve open and the second on-off valve closed to cause ink to flow from the buffer tank to the sub-tank.

16. An inkjet printer as described in claim 13 or 14, further comprising a maintenance unit that performs a cleaning operation of the inkjet head to prevent clogging of multiple nozzles of the inkjet head, and the control unit executes the confirmation operation during the cleaning operation.

17. An inkjet printer as described in claim 16, characterized in that the cleaning operation includes a purging operation in which the pressure inside the subtank is made positive to cause ink to be ejected from the inkjet head, and after the purging operation, the amount of ink in the subtank becomes the first reference amount, and the control unit executes the confirmation operation when predetermined conditions are met after the purging operation.

18. The inkjet printer according to claim 17, characterized in that after the purging operation, the control unit drives the pump with the first on-off valve open and the second on-off valve closed to supply ink to the subtank until the amount of ink in the subtank reaches the second reference amount, measures a second time which is the time it takes for the amount of ink in the subtank to reach the second reference amount, and if the confirmation operation is not performed after the purging operation, stores the most recent measured second time and calculates the first time based on the second time.

19. An inkjet printer as claimed in claim 18, characterized in that the driving speed of the pump when the confirmation operation is performed is slower than the driving speed of the pump when ink is supplied to the subtank after the purging operation without performing the confirmation operation.

20. An inkjet printer as described in claim 16, wherein the cleaning operations include a soft cleaning operation and a hard cleaning operation which increases the amount of ink ejected from the inkjet head and takes a longer time than the soft cleaning operation, the soft cleaning operation includes a first purging operation in which the pressure inside the subtank is made positive to eject ink from the inkjet head, and the hard cleaning operation includes a second purging operation in which the pressure inside the subtank is made positive to eject ink from the inkjet head, the amount of ink ejected from the inkjet head in the second purging operation is greater than the amount of ink ejected from the inkjet head in the first purging operation, the time required for the second purging operation is longer than the time required for the first purging operation, and after the first purging operation, the amount of ink in the subtank becomes the first reference amount, and the control unit, when the hard cleaning operation is performed, performs the first purging operation before performing the second purging operation when specified conditions are met, and performs the confirmation operation when specified conditions are met after the first purging operation, and then performs the second purging operation.

21. An inkjet head for ejecting ink, a subtank for storing ink to be supplied to the inkjet head, a buffer tank for storing ink to be supplied to the subtank, a main tank for storing ink to be supplied to the buffer tank, a pump arranged in a piping path between the buffer tank and the subtank, a first piping path which is a piping path connecting the pump and the subtank, a second piping path which is a piping path connecting the first piping path and the main tank, a coupling having a piping side coupling part attached to an end of the second piping path and a tank side coupling part attached to the main tank and to which the piping side coupling part is connected, a first on-off valve arranged in a piping path between the subtank and a connection point of the first piping path and the second piping path, a second on-off valve arranged in the second piping path, and a detection mechanism for detecting an amount of ink stored in the subtank, wherein when the pump is driven with the second on-off valve open and the first on-off valve closed, ink flows from the buffer tank toward the main tank, When the pump is driven with the first on-off valve open and the second on-off valve closed, ink flows from the buffer tank to the sub-tank, and when the piping-side joint and the tank-side joint are normally connected, when the pump is driven with the first on-off valve and the second on-off valve open, the amount of ink flowing from the buffer tank to the main tank becomes greater than the amount of ink flowing from the buffer tank to the sub-tank, and when the piping-side joint and the tank-side joint are disconnected, the piping-side joint is sealed to prevent ink from leaking. A control method for an inkjet printer, comprising the steps of: opening the first on-off valve and the second on-off valve and driving the pump at a constant speed for a predetermined first period of time with the amount of ink in the sub-tank set to a predetermined first reference amount; and executing a confirmation operation to determine whether the amount of ink in the sub-tank exceeds a predetermined second reference amount based on the detection result of the detection mechanism.

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