INK RESIDUAL QUANTITY SENSOR OF INK JET PRINTER

Abstract: At the time of printing, the number of dots actually printed is stored in printed dot number storage means (28). At each operation of priming means (9), quantity of suctioned ink is cumulatively stored as a number of printed dots in printed dot number storage means (28) by means of storage control means (30). When it is desired to check residual quantity, ink residue detection means (31) computes it based on the ratio of a number of printable dots corresponding to the full volume capacity of ink cartridge (8) and the number of printed dots stored in printed dot number storage means (28). According to the present invention, an ink jet printer, which has a head having a head nozzle to eject ink for printing, ink cartridge (8) containing ink and priming means (9) to suction ink while applying pressure to the head nozzle, is provided with an ink residual quantity sensor characteristically having printable dot number storage means (27) to store a number of printable dots corresponding to the full volume capacity of said ink cartridge (8), printed dot number storage means (28) to store a number of dots actually printed by the head, storage control means (30) to cause quantity of the ink which has been suctioned to be cumulatively stored as a number of printed dots in printed dot number storage means (28) for each action of priming means (9), and ink residue detection means (31) which computes the residual quantity of ink based on said numbers of printable dots and printed dots.

Description: INK RESIDUAL Q UANTITY SENSOR OF INK JET PRINTER BACKfi OTIND OF THF. TNVF.NTION FIELD OF THE INVENTION The present invention relates to apparatus for sensing and displaying the amount of ink remaining in an ink cartridge of the type used in a conventional ink jet printer. DESCRIPTION OF THE PRIOR ART Conventional ink jet printers operate to print information on paper by selectively projecting drops of liquid ink supplied by an ink cartridge. Some of these printers are able to detect depletion of ink in order to prevent running out of ink during the process of printing. For example, detection of ink depletion has been heretofore done by means of a pair of electrodes so placed inside the ink cartridge that current between the electrodes is terminated when the ink level comes down below the electrodes. Another scheme is to place a magnetic float on the surface of the ink so that when the float comes down as the ink is depleted, it is detected by a magnetic sensor attached to the side of the ink tank, thereby making it possible to detect a shortage of ink. As described above, some conventional devices detect depletion of ink directly by the lowering of the ink level. Therefore, it is necessary to provide a cartridge with electrodes, a magnet float or other similar parts, which makes an ink cartridge cosdy. Further, with the above schemes, it is not possible to detect the residual quantity of ink, but only to detect a shortage of ink just before the ink contained in the ink cartridge runs out. U.S. Patent No. 4,714,937 to G.T Kaplinsky briefly mentions a concept of determining the level of ink in an ink supply by counting the number of nozzle firings. But this approach does not take into account the considerable volume of ink that may be sucked through the printhead during an ink-priming operation to remove ink clogs and the like from the printing nozzle(s). SUMMARY OF THE TNVENTTON Regarding the above problems, the present invention has as an objective the provision of an ink residual quantity sensor for an ink jet printer capable of accurate detection of the residual quantity of ink in an ink cartridge without increasing cost of the ink cartridge. According to the present invention, during the printing operation of an ink-jet printer, a number representing the number of dots actually printed by the printhead is stored in a first storage device. With each action of an ink priming means which serves to suction a predetermined quantity of ink through the printing nozzle(s), a storage control device serves to add to the stored number of dots actually printed a number representing the number of dots that could have been printed by the suctioned quantity of ink. The residual quantity of ink in the cartridge is determined by an ink residue detection means which compares (a) the sum of the number of dots actually printed and the number of dots which can be printed by the suctioned quantity of ink with (b) a number representing the number of dots which are printable by a full volume capacity of ink cartridge 8, such number of printable dots also being stored in a storage device. The result of this comparison is displayed by a gauge or the like on the printer housing, or by printing a display representing the residual quantity of ink on a sheet of paper. The invention and its advantages will be better understood from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings. BRTEF DESCRIPTION OF THE PRT R ART Figure 1 is a top plan view of an ink jet printer. Figure 2 is a block diagram showing an embodiment of an ink residual quantity sensor of an ink jet printer according to the present invention. Figure 3 is a flow chart illustrating various steps of a program for implementing the method of the invention. Figure 4 is an explanatory drawing showing an example of display of residual quantity of ink. DETATT ED DESCRIPTION OF PREFERRED EMBODIMENTS A preferred embodiment of the present invention is explained hereunder, referring to the drawings. Fig. 1 shows a top plan view of an ink jet printer. An opening 2 is formed in the upper surface of the printer housing 1, and a roller platen 3 and guide axis 4 are provided in parallel to each other within opening 2. Platen 3, which is rotatably supported, is rotated by the driving power of a stepping motor 5 through a plurality of gears 6. A carriage 7, which is moved laterally by the driving power of a stepping motor (not shown), is movably attached to guide axis 4. Replaceably attached to carriage 7 is an ink cartridge 8 which contains specified quantity of ink and is integrally provided with a printhead having a head nozzle to eject ink. An ink priming means 9 is attached to one end of platen 3. In the same manner as disclosed in published Japanese Patent Application No. 275709/1990, priming means 9 has a precision pumping mechanism which enables it to precisely control the quantity of ink it suctions with a single pumping action. Such mechanism comprises a pump, a stepping motor to drive this pump and a cap member having a tube connected to the suctioning end of the pump. When carriage 7 is positioned opposite or in front of the priming means 7, the cap covers the head nozzle in order to prevent drying up of ink on the nozzle, and a negative pressure is applied by the pump to the head nozzle in order to suction ink therefrom, thereby preventing the nozzle from clogging up. Further, this priming action is performed automatically when an ink cartridge is replaced, or after a predetermined amount of printing has been done (e.g.50 pages of printing), or whenever it is desired to do so., such as by depressing a switch 12. A printed circuit board 10 having a control circuit, which is described later, is positioned as shown in the printer housing. The printer housing is also provided, on the upper surface thereof, with power switch 11 and a plurality of operation switches 12 through 15. Optionally, a set of light-emitting diodes LED1 - LED4 can be mounted atop the printer housing to display, for example, the residual amount of ink in a cartridge and/or different selected printing fonts. Fig.2 is a block diagram of the control circuit on the aforementioned printed circuit board. Numeral 21 denotes a control unit for inputting printing data. It controls the printing operation by controlling a head driving unit 22 which drives the printhead, a carriage driving unit 23 which drives the stepping motor of carriage 7, and a paper feeder driving unit 24 which drives the stepping motor 5 of platen 3. Control unit 21 also performs ink priming by controlling a pump driving unit 25 which drives the stepping motor of the pump of priming means 9. Connected to control unit 21 is a memory unit 26 having a first storage means 27 for storing a number representing the total number of printable dots, which can be computed from the full volume capacity of ink cartridge 8, a second storage means 28 for storing a number representing the total number of dots actually printed by the printhead, as well as the number of drops that could have been printed by the ink suctioned through the print head during the priming operation©, and a counter 29 for counting a number of dots printed on a single line. Storage means 27 and 28 comprise nonvolatile memories. Control unit 21 comprises a suitably programmed microprocessor which enables it to function as (i) a storage control means 30 for causing, at each operation of priming means 9, the number of dots that could have been printed from a quantity of suctioned ink to be added to the number of actually printed dots stored in storage means 28; (ii) an ink residue detection means 31, which computes the residual quantity of ink based on respective numbers of printable and actually printed dots stored in storage means 27 and 28, respectively; and (iii) a display output means 32 for causing the computed residual quantity of ink to be displayed. The operation of the apparatus discussed above is explained hereunder, referring to Fig. 3. The explanation begins from the stage for replacing ink cartridge 8 with a new one (Step 4). The change mode begins when power switch 11 is turned on with switch 12 held down (Step 5). Since carriage 7 is always positioned opposite the priming means 9 except while printing, it is not generally possible to physically reach the ink cartridge 8 for the purpose of replacement. When the change mode has commenced, however, control unit 21 drives the stepping motor through carriage driving unit 33, thereby moving carriage 7 to the center of the printing range (Step 6) so that ink cartridge 8 can be replaced. Then, the operator releases the mechanical lock which holds the cartridge on the carriage, replaces ink cartridge 8 with a new cartridge and sets the mechanical lock again (Step 7). After changing the cartridge, when switch 12 is turned on (Step 8), control unit 21 clears the memory in printed dot number storage means 28 and causes carriage 7 to be moved to a position opposite priming means 9 (Step 9). When carriage 7 has moved to this position, the cap member covers the head nozzle, and priming is performed under this condition (Step 10). Control unit 21 drives the stepping motor of the pump through pump driving unit 25 and, using the action of the pump, applies negative pressure to the head nozzle to suction ink. Since the quantity of suctioned ink can be represented as a number of printed dots, such number can be stored in storage means 28 by control unit 21 functioning as storage control means 30 (Step 11). i the above description, the printer was set at the change mode at Step 5. In case ink cartridge 8 is not to be changed, however, by turning off power switch 11, carriage 7 can be moved to the priming position opposite priming means 9, thereby returning the printer to the stand-by mode (Steps 12 and 13). The power is cut off thereafter. Next, the function when printing is in progress is explained. When paper has been set at platen 3 and a command to start printing is given, any counted value by counter 29 is cleared and one line of image information is printed (Step 14). Printing is done with ink ejected onto the paper from the head nozzle, while carriage 7 is moving. At that time, the number of dots actually printed by the head is counted by counter 29. When a line of printing has been completed, the number of printed dots counted by counter 29 is cumulatively stored in printed dot number storage means 28 (Step 15). - Printing is performed with Steps 14 and 15 being repeated as above. When a number of printed pages has reached 50 in total (Step 16), carriage 7 is moved automatically to the front of priming means 9 (Step 17) to receive the priming action described above (Step 18). The quantity of ink suctioned by the above priming action is converted to a number of printed dots, and this number is stored in printed dot number storage means 28 by the storage control means 30 of control unit 21 (Step 19). If the current printing operation has not yet been completed, the printer is returned to Step 14, from which the process is resumed (Step 20). Next, the explanation is given as to the procedure of checking the residual quantity of ink prior to printing. The operator turns on power switch 11 while holding down switch 14 (Steps 1 and 2), thereby setting the printer at the test mode. Paper should be set on platen 3 beforehand. Control unit 21 determines, using its function as ink residue detection means 31, the residual quantity of ink by comparing the number of printable dots stored in printable dot number storage means 27 with the number of actually printed dots (which includes the dots that could have been printed by the suctioned ink), which was input in printed dot number storage means 28 in the manner described above. Then, using its function as display output means 32, control unit 21 causes the value of ink residual quantity to be displayed. According to a particularly preferred embodiment of the present invention, the residual quantity of ink is printed on paper. As it is shown in Fig. 4, it is indicated as a bar graph whose length represents residual quantity of ink in relation to the length representing the full volume capacity (Step 3). Therefore, residual quantity of ink can be easily confirmed by checking the display of the residual ink quantity. Thus, it is possible to accurately estimate the time when ink cartridge 8 should be changed. Jf it is found necessary to change ink cartridge 8, the operator should proceed to Step 5 to change the cartridge. In cases where replacement is not necessary, he may proceed to Step 14 to start printing. As described above, ink cartridge 8 is not provided with special parts for detecting residual quantity of ink, and, therefore, its cost can be kept low. Further, detection of residual ink quantity can be conducted through software in a microcomputer incorporated in an Inkjet printer. Priming action can be actuated by a manual command by operating switch 12 when power switch 11 is at the "on" position. The manner of displaying residual quantity of ink is not restricted to the aforementioned manner that calls for printing on paper, it may be indicated by . means of a liquid crystal display or a lamp. Alternatively, the output of the residual ink detector can be used to energize one or more of the LED's (LED1- LED4), the more LED's energized, the greater the quantity of ink remaining in the cartridge. According to the present invention, the number of dots actually printed is stored in a printed dot number storage means, and, whenever priming is performed, the quantity of suctioned ink is also cumulatively stored as a number of printed dots. By comparing the sum of these numbers with a number representing the total number of dots which are printable from a full ink cartridge, it is possible to accurately display the residual quantity of ink in the ink cartridge. Furthermore, this effect can be achieved by means of ink jet printer software without increasing cost of an ink cartridge.

Claims: We claim: 1. An ink residual quantity sensor of an ink jet printer provided with a head having a head nozzle to eject ink for printing, an ink cartridge containing ink and a priming means to suction ink while applying pressure to the head nozzle, said residual quantity sensor characteristically comprising: a printable dot number storage means to store a number of printable dots corresponding to the full volume capacity of said ink cartridge; a printed dot number storage means to store a number of dots actually printed by said head; a storage control means to cause quantity of the ink which has been suctioned to be cumulatively stored as a number of printed dots in said printed dot number storage means for each action of said priming means; and an ink residue detection means which computes the residual quantity of ink based on said numbers of printable dots and printed dots.

Inventors: HANAOKA ICHIRO, UOZUMI SATORU, YAMADA MORIHIKO, HANAOKA, ICHIRO, UOZUMI, SATORU, YAMADA, MORIHIKO
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1992
Main classification: B41J2
IPC codes: B41J2