This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-050072, filed on Feb. 28, 2007, the entire contents of which are incorporated herein by reference.
The present invention relates to a liquid ejection device, such as an inkjet printer.
As an inkjet printer to which a cartridge type main tank storing ink is removably mounted, there is an inkjet printer including a sensor configured to detect a remaining amount of ink in the main tank. As an example of the detection of the remaining ink amount, the remaining ink amount sensor optically detects a position of a float provided in the main tank which descends with the lowering of the ink level. Accordingly, the remaining ink amount can be detected with high accuracy. However, the float reaches the bottom of the main tank even in a state where the ink remains in the main tank. Therefore, a state where the remaining ink amount becomes zero cannot be detected, and the ink cannot be used up.
Meanwhile, as another method for detecting the remaining ink amount in the main tank, there is a method of cumulatively calculating an ink amount ejected from an inkjet head with software. This method enables the state of zero remaining ink amount to be detected. However, since minute errors may be contained in the ejected liquid amount used in the calculation for each ejection, such errors accumulate by the time the ink in the main tank is used up. Therefore, the remaining ink amount cannot be detected with high accuracy.
In JP-A-2005-246781, the former method for optically detecting the remaining ink amount using the float and the latter method for detecting the remaining ink amount with software are combined to enable the ink to be fully used up and detect the remaining ink amount precisely. Specifically, a seesaw-like float blocks light to a light receiving unit of an optical sensor when ink is filled, and with the lowering of the liquid level according to ink consumption, the float swings and allows the light to enter the light receiving unit of the optical sensor. Accordingly, it is firstly detected that the ink has decreased up to a threshold level (remaining amount detection). Then, the number of ink droplets ejected from the inkjet head is cumulatively calculated with software, which starts at the time of the remaining amount detection. Accordingly, it is secondarily calculated and detected that the remaining ink amount becomes zero (remaining amount calculation). That is, since the calculation of the remaining ink amount with software starts after the amount of ink in the main tank becomes low, error does not accumulate so much and the remaining ink amount can be detected accurately.
In a case where the ink in the main tank is used up and then the main tank is exchanged with a new one, air may enter an ink supplying path leading up to the inkjet head. In a tube supplying type inkjet printer disclosed in JP-A-2005-66906, a sub tank open to an atmosphere is disposed between the main tank and an ink supplying tube to prevent the entry of air into the ink supplying path even if the ink in the cartridge type main tank is used up. Accordingly, even if the ink in the main tank is used up, air does not enter the ink supplying tube since the ink remains in the sub tank. Moreover, even if air enters a connection portion between the main tank and the sub tank during exchange of the main tank, the air is separated by buoyancy from the ink in the sub tank and is thereby prevented from entering the ink supplying tube.
However, in a case where the remaining ink amount detection method of JP-A-2005-246781 is assumed to be applied to the arrangement disclosed in JP-A-2005-66906, when the main tank is exchanged with a new tank in a state where there is small remaining ink amount in the sub tank, ink flows into the sub tank all at once due to the hydraulic head pressure, thereby causing the ink level in the main tank to drop significantly immediately after exchange. That is, simply exchanging the main tank results in that the ink level may fall below the threshold level at which the remaining amount detection by the optical sensor is performed. Incidentally, the remaining amount calculation by software is started immediately from that point, and an initial level of the remaining amount calculation is programmed to be the threshold level. Therefore, when the actual ink level is lower than the threshold level from the beginning, the remaining ink amount is calculated to be greater than the actual amount.
An object of an aspect of the present invention is to perform precise detection of a remaining liquid amount in the main tank while enabling the liquid in the main tank to be used up as much as possible, in a liquid ejection device with a sub tank into which a liquid flows from a main tank due to a hydraulic head pressure.
According to an aspect of the invention, there is provided a liquid ejection device comprising: a main tank mounting unit to which a main tank capable of storing liquid is removably mountable; a sub tank comprising: an inlet configured to be brought into fluid communication with the main tank in a state where the main tank is mounted to the main tank mounting unit; and an outlet; an ejection head having a nozzle configured to eject the liquid supplied from the sub tank via the outlet; a remaining amount detecting unit configured to detect whether an amount of the liquid in the main tank is equal to or smaller than a predetermined liquid amount, where a liquid level of the liquid in the main tank at the predetermined liquid amount is positioned at a threshold level; and a remaining amount calculating unit configured to determine a liquid amount ejected from the ejection head during a term starting from a detection of the threshold level by the remaining amount detecting unit, thereby calculating a remaining liquid amount in the main tank; wherein the sub tank is configured to satisfy the following formula: SH−SL≦MH−MN, where, SH is a liquid amount in the sub tank in a balanced state at which the liquid has flowed into the sub tank by a hydraulic head pressure on mounting the main tank with the liquid fully filled; SL is a liquid amount in the sub tank in a state where the liquid level is positioned at the outlet of the sub tank; MH is a liquid amount in the main tank when the liquid is fully filled in the main tank; and MN is a liquid amount in the main tank in a state where the liquid level is positioned at the threshold level.
An embodiment according to the present invention shall now be described with reference to the drawings.
An image recording unit 16 is disposed at the printing region 15. A platen 17 having larger size than a sheet is disposed below the image recording unit 16. A conveying roller 18 and a pinch roller 19 are disposed at an upstream side of the image recording unit 16 with respect to the conveying path 13 and configured to nip a recording sheet 12 fed from the sheet feeding tray 6 and convey the sheet onto the platen 17. A sheet discharging roller 20 and a pinch roller 21 are disposed at a downstream side of the image recording unit 16 and configured to nip the recording sheet 12 on which printing has been performed and convey the sheet to the sheet discharging tray 7 (see
The image recording unit 16 includes: an inkjet head 22 (ejection head) of piezoelectric driven type which ejects ink (liquid) toward the platen 17 from a plurality of nozzles; a buffer tank 23 capable of storing the ink to be supplied to the inkjet head 22; a head control board 24 configured to perform drive control of the inkjet head 22; and a carriage 25 on which these elements are mounted. The buffer tank 23 is connected to a sub tank 27, as described later, via an ink supplying tube 26. The main tank mounting unit 28, to which a main tank 29 is removably mountable, is disposed at a position adjacent to the sub tank 27. The opening/closing cover 8 is attached to the main tank mounting unit 28. The main tank mounting unit 28 is provided with a remaining amount detecting sensor 30 (remaining amount detecting unit) that optically detects a remaining ink amount in the main tank 29 in a state where the main tank 29 is mounted.
The remaining amount detecting sensor 30 is connected to a controller 31 (remaining amount calculating unit). The controller 31 is configured to perform the task of detecting the remaining ink amount in the main tank 29, and in addition, the controller 31 is configured to execute operation control of ink ejection from the inkjet head 22, feeding and discharging the recording sheet 12, and various other tasks of the inkjet printer 3. The controller 31 includes a CPU (central processing unit), a ROM configured to store program executed by the CPU and data used in the program, a RAM configured to temporarily store data during execution of a program, a rewritable EEPROM or other memory, an input/output interface, etc. In regard to the remaining ink amount detection function, the controller 31 includes: a processing unit 32 configured to perform process and control; a print data receiving unit 33 configured to receive print data from the personal computer 11; a remaining amount counting unit 34 configured to perform cumulative calculation (remaining amount calculation) of the remaining ink amount in the main tank 29 based on the ink ejection amount at the inkjet head 22; and a remaining amount transmitting unit 35 configured to transmit the remaining ink amount in the main tank 29 to the personal computer 11.
An inflow port 48a is formed at a lower portion of the cover portion 48, and the valve housing chamber 45 is brought into fluid communication with the ink storage chamber 43 via the valve port 47 and the inflow port 48a. The valve port 47 is provided with a check valve 49, and the check valve 49 opens the valve port 47 when the ink storage chamber 43 becomes positive in pressure with respect to the valve housing chamber 45 and closes the valve port 47 when the ink storage chamber 43 becomes negative in pressure with respect to the valve housing chamber 45. An annular sealing member 50 is disposed at the opening 44, and an ink outflow port 50a is formed at a center portion of the sealing member 50. The diameter of the ink outflow port 50a is reduced by elastic force in a non-loaded state.
An opening 60 and a tubular valve chamber 61 continuous with the opening 60 are disposed at an upper portion of the surface (at the right side in
A recess 42 continuous with the ink storage chamber 43 is formed at a portion of the main tank 29 on the side the sub tank 27. Each of the both side walls of the recess 42 has a light transmitting portion 51 formed of a transmissive material for detecting the remaining amount of the ink stored in the ink storage chamber 43. The main tank 29 includes a supporting portion 52 configured to swingably support a sensor arm 53. The sensor arm 53 includes: a connecting portion 54 having a connecting shaft 54a axially supported by the supporting portion 52; a float portion 55 extending to one side (the left side in
The float portion 55 is formed to be hollow so that an average specific gravity thereof is less than a specific gravity of the ink. The arm portion 56 includes a first arm 56a, a second arm 56b, and a blocking portion 56c. The first arm 56a extends upward substantially perpendicularly with respect to the float portion 55. The second arm portion 56b extends from a front end of the first arm 56a in a direction away from the float portion 55. The blocking portion 56c positioned in the recess 42 is formed at a front end of the second arm portion 56b.
The arm portion 56 is less in weight than the float portion 55. Therefore, in a state where there is no ink in the ink storage chamber 43, the sensor arm 53 rotates about the connecting shaft 54a in a direction in which the float portion 55 descends. In this process, the blocking portion 56c of the sensor arm 53 moves so as to retreat diagonally upward from the recess 42. On the other hand, when the ink storage chamber 43 is adequately filled with ink, the float portion 55 is immersed in the ink, the weight balance of the float portion 55 and the arm portion 56 is reversed due to buoyancy, and the sensor arm 53 rotates about the connecting shaft 54a in a direction in which the float portion 55 rises. In this process, the blocking portion 56c of the sensor arm 53 moves diagonally downward so as to enter the recess 42.
That is, in a state where the blocking portion 56c of the sensor arm 53 enters the recess 42 and is sandwiched by the light transmitting portions 51 at both side walls, the light emitted from the light emitting portion 30a is blocked by the blocking portion 56c and is not detected by the light receiving portion 30b. In this state, the controller 31 (see
As shown in
A tubular needle portion 73 protrudes toward the main tank 29 side from an outer wall of the sub tank 27, and the needle portion 73 has an inlet 73a that opens toward the lower region 70a. In a state where the needle portion 73 is inserted in the ink outflow port 50a of the sealing member 50 of the main tank 29, the lower region 70a of the ink storage space 70 of the sub tank 27 is brought into fluid communication with the ink storage chamber 43 of the main tank 29. At a position opposite the inlet 73a, a flow path wall 74 extends downward from the upper wall portion 71. Furthermore, on an outer wall of the sub tank 27, a protrusion 75 is protruded in a direction away from the inside of the main tank 29. The protrusion 75 has a space defined therein which forms a portion of the lower region 70a and a tubular tube attachment portion 76 that protrudes from an upper wall of the protrusion 75 and allows fluid communication with this space.
The tube attachment portion 76 has an outlet 76a that opens toward the lower region 70a, and the outlet 76a is disposed at a position lower than the inlet 73a. In a state where the ink supplying tube 26 is connected to the tube mounting portion 76, the lower region 70a of the ink storage space 70 of the sub tank 27 is brought into fluid communication with the buffer tank 23 (see
A relationship of the threshold level of the main tank 29 detected by the remaining amount detecting sensor 30 and a volume of the sub tank 27 will be described. As shown in
Also, the threshold level detected by the remaining amount detecting sensor 30 has a tolerance (upper limit value and lower limit value) due to manufacturing variation. In consideration thereof, the positions of the inlet 73a and the outlet 76a of the sub tank 27 are set. Specifically, the positions are set to satisfy the following equation: SM−SL≧MN1−MN2. In this equation, SM is an ink amount in the sub tank 27 in a state where the ink level is positioned at the lower edge of the inlet 73a of the sub tank 27; MN1 is an ink amount in the main tank 29 when the upper limit value of the remaining amount detecting sensor 30 is detected; and MN2 is an ink amount in the main tank 29 when the lower limit value of the remaining amount detecting sensor 30 is detected. Here, the upper limit value and the lower limit value in this description indicates an upper limit value and a lower limit value of a detection variation of the remaining amount detecting sensor 30, which is obtained by performing a sampling study of a considerable number of inkjet printers 3.
Operation of the inkjet printer 3 will be described with reference to
Also in the state of
According to the configuration described above, in the balanced state at which, upon mounting of the new main tank 29 with fully filled ink to the main tank mounting unit 28, the ink in the main tank 29 has flowed into the sub tank 27 due to the hydraulic head pressures and the ink levels in the main tank 29 and the sub tank 27 have reached substantially the same height, the ink levels are not below the threshold level that is the detection threshold of the remaining amount detecting sensor 30. As the ink in the main tank 29 decreases gradually due to the ink being consumed via the inkjet head 22, the level of the ink in the main tank 29 firstly reaches the threshold level. The remaining amount calculation with software by the remaining amount counting unit 34 of the controller 31 then starts at the point at which the ink level in the main tank 29 matches the threshold level. Therefore, the initial value of the remaining ink amount of the remaining amount calculation matches the actual remaining ink amount. The remaining amount detection and the remaining amount calculation can be used to precisely detect the remaining ink amount in the main tank 29 even while improving the performance of using the ink in the main tank 29.
Furthermore, if an error occurs in the detection by the remaining amount detecting sensor 30 so that the remaining amount detecting sensor 30 detects the threshold level although the actual level is positioned at a level slightly lower than the threshold level, the remaining amount counting unit 34 of the controller 31 may judge that ink still remains even when the ink in the main tank 29 runs out. However, since the outlet 76a of the sub tank 27 is disposed at the position lower than the inlet 73a, the ink remaining in the sub tank 27 is supplied to the inkjet head 22, thereby preventing the air from being supplied to the inkjet head 22 side.
Also, since the level difference between the inlet 73a and the outlet 76a of the sub tank 27 is set large in consideration of the tolerance due to manufacturing variations of the remaining amount detecting sensor 30, an adequate amount of ink to be supplied to the inkjet head 22 side can be made to remain in the sub tank 27 even when the ink in the main tank 29 runs out.
Furthermore, since the horizontal cross-sectional area of the upper region 70b of the sub tank 27 is considerably smaller than the horizontal cross-sectional area of the lower region 70a, when the ink in the main tank 29 flows into the sub tank 27 due to the hydraulic head pressure, the ink levels in the main tank 29 and the sub tank 27 become equal in height with a low inflow amount. Therefore, an adequate ink volume to be supplied to the inkjet head 22 side is secured in the lower region 70a. Also, the ink in the main tank 29 can be favorably prevented, during exchange of the main tank 29, from falling below the threshold level that is the detection threshold of the remaining amount detecting sensor 30. Although in the above-described embodiment, the present invention is applied to an inkjet printer, the present invention may be applied to a liquid ejection device that ejects liquid other than ink.
The remaining amount detecting sensor 30 optically detects a remaining ink amount. Accordingly, the liquid level in the main tank can be detected easily in a non-contacting manner. Although the remaining amount detecting sensor 30 is configured to optically detect the sensor arm 53 provided in the main tank 29 in the above embodiment, the remaining amount detecting sensor 30 is not limited to this example. For example, the remaining amount detecting sensor 30 may optically detect the liquid level directly or may detect indirectly using a float provided in the main tank 29. In addition, the remaining amount detecting sensor may perform other than the optical detection.
As described above, the liquid ejection device according to the present embodiment exhibits the excellent advantage that the remaining amount detecting unit and the remaining amount calculating unit can be used to precisely detect the remaining liquid amount in the main tank even while improving the performance of using the main tank liquid to depletion, and is beneficially applied to an inkjet printer, etc., with which the significance of this effect can be exhibited.
Number | Date | Country | Kind |
---|---|---|---|
2007-050072 | Feb 2007 | JP | national |