Patent Application
20110148965
1. Field of the Invention
The present invention relates to an inkjet printing apparatus for performing printing on a printing medium by ejecting inks, and a recovery method.
2. Description of the Related Art
The inkjet printing apparatus ejects droplets of the inks from a plurality of nozzles (or ejection openings) of a print head using an electric heat conversion element or an electric mechanical conversion element, and prints an image on the printing medium such as paper.
In addition, the inkjet printing apparatus is equipped with a recovery device for recovering and maintaining ink ejection performance of the print head. This recovery device is normally equipped with a wiping device for removing inks, dust, etc. adhering to a nozzle surface by wiping them off. Moreover, the recovery device is equipped with a preliminary ejection unit for ejecting inks that do not participate in a printing processing (this is called preliminary ejection) from the nozzles to refresh the inks in the nozzles.
Incidentally, in the case of a print head that is provided with a plurality of nozzle rows each ejecting an ink of a different color, such as a print head for color printing, there is a problem that color mixture occurs immediately after the wiping and deteriorates an image quality. That is, execution of the wiping will push color-mixed inks adhering to the nozzle surface in a reverse flow direction into the interiors of the nozzles. Then, there may be a case where in a subsequent printing operation, the color of the printed image in an early stage of printing start will become different from a setup color and a quality of the printed image will be deteriorated.
Then, as a measure against this, the preliminary ejection of the predetermined number of shots is performed immediately after the wiping. When doing this, mixed color inks are discharged from the nozzles at the time of execution of the preliminary ejection, which makes it possible to suppress or prevent deterioration of the image quality at the early stage of printing start.
Incidentally, since the preliminary ejection is a processing of simply discarding the inks, it is desirable to lessen the number of preliminary ejections as less as possible. On the other hand, if the number of preliminary ejections is too small, the mixed color inks cannot be ejected fully, so that image quality deterioration will be caused. Therefore, it is desirable to lessen the number of preliminary ejections as less as possible in a range in which the mixed color inks can be fully discharged.
As a technique of reducing the number of preliminary ejections, there is one that is disclosed in Japanese Patent Laid-Open No. H08-058109 (1996), for example. This is a technique of performing the preliminary ejection from all the nozzles and the preliminary ejection from nozzles on ends of the nozzle row alternately. In view of an examination result that a degree of the color mixture is more remarkable in the end parts than in the central part of the nozzle row, the number of preliminary ejections is increased larger in the end parts than in the central part of the nozzle row. Conversely, the number of preliminary ejections is decreased smaller in the central part than in the end parts of the nozzle row.
However, a portion where the degree of the color mixture is large does not necessarily exist in the end parts of the nozzle row, and it is considered that it varies for each apparatus. Therefore, it is difficult to say that the method of always increasing the number of preliminary ejections as the Japanese Patent Laid-open No. H08-058109 (1996) is necessarily sufficient in terms of compatibility of an excellent image quality and decrease of the amount of waste inks.
For example, the recovery device controls so that a wiping blade may be operated at a constant speed in order to eliminate wiping unevenness in the wiping. However, because of friction by interference with a holder and the head etc., and because of occurrence of variation of a load in a mechanical mechanism (a cam, a spring, etc.) during a wiping operation, an actual speed of the blade varies in connection with these. As a result, the wiping unevenness by chatter called stick slip occurs, which produces a portion where the degree of the color mixture is large and a portion where it is small (including a portion where no color mixture exists).
At this time, since the same apparatus has the same load variation, a mark of chatter remains even when a plurality of times of wiping are performed, and an almost fixed portion has a large degree of the color mixture. However, a way in which the load varies in each apparatus is different due to variation of a part, etc. Therefore, a portion where the degree of the color mixture is large varies in a different apparatus. In this way, a portion where the degree of the color mixture is large varies for every apparatus.
The present invention is invented in view of this situation. Its object is to provide an inkjet printing apparatus and a recovery method that can achieve compatibility of an excellent image quality and decrease of the amount of waste inks by appropriately deciding the number of preliminary ejections of each nozzle according to the color mixture parts that vary for every apparatus.
An aspect of the present invention provides an ink jet printing apparatus including:
Another aspect of the present invention provides a recovery method of recovering an ink ejection state of a print head with a plurality of nozzle rows formed in a nozzle surface and through which ink in different colors is ejected, the method including:
According to the present invention, there are exerted excellent effects as follows: appropriately deciding the number of preliminary ejections of each nozzle according to the color mixture parts that vary for every apparatus; and capability of achieving excellent image quality and reduction of quantity of waste ink.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Hereafter, with reference to drawings, an embodiment of the present invention will be explained specifically.
The print head 3 is provided at a bottom part of the carriage 2, as in one piece. Moreover, a plurality of ink tanks (also called ink cartridges) 6 are mounted on the carriage 2 detachably. An ink in the ink cartridge 6 is supplied to the print head 3. The inkjet printing apparatus 1 is configured so that the printing medium, in a state of mounting on a platen, may be conveyed in a vertical scanning direction below the print head 3. The printing medium is conveyed by a conveyance motor and a conveying roller 7. The scanning direction A and the vertical scanning direction B are perpendicular to each other.
The print head 3 prints an image on the printing medium by ejecting the inks based on an image signal. The inkjet printing apparatus continues to print an image equivalent to one band on the printing medium by giving a drive signal based on the image signal to the print head 3 in synchronization with at least one of outward and return movements of the carriage 2. After the printing for even one band is finished, the printing medium is conveyed by a width equal to the even one band and halted. Once more, the carriage 2 is moved and the printing for the next even one band is performed. An image is formed on the printing medium by alternately repeating a printing operation and a conveyance operation like this. The printing medium that finished the printing is discharged from the apparatus body by the conveying roller 7.
The print head 3 is for color printing, and four ink cartridges 6 that house a plurality of kinds of inks, namely inks of respective colors of black (K), cyan (C), magenta (M), and yellow (Y) are mounted on the carriage 2. These four ink cartridges are independently detachable and exchangeable, respectively.
In the figure, a symbol Y1 designates the nozzle row 32 for ejecting yellow ink. Similarly, M1 and M2 designate nozzle rows of magenta, C1 and C2 designate nozzle rows of cyan, and K designates a nozzle row of black, respectively. In the each nozzle row 32, nozzles are arranged with a predetermined nozzle density (dpi). The nozzle rows 32 are mutually in parallel, and are prolonged in the vertical scanning direction B.
In the case of this embodiment, the nozzle rows of cyan and magenta are arranged symmetrically in a main scanning direction in the figure, as in a configuration of black, cyan, magenta, yellow, magenta, and cyan from the left. Performing the printing with such an arrangement makes it possible to give the inks in the same order in the scanning of the carriage reciprocating in both of an outward direction and a return direction. Therefore, a difference in coloring accompanying a difference of a giving order of the inks does not appear between the image printed by outward scanning and the image printed by return scanning, so that it becomes possible to output a color image at high speed.
Although not illustrated, each nozzle is made to communicate with a corresponding ink tank 6 through an ink channel, the ink is always filled therein near the nozzle by supply of the ink from the ink tank 6. The print head 3 is provided with electric heat transfer elements, namely heaters, for the respective nozzles. When a driving voltage or driving pulse is applied to this heater, air bubbles are generated in the ink by thermal energy that the heater generates. Then, a generated pressure of these air bubbles pushes the ink in the nozzle by a predetermined quantity, which performs ink ejection. Although, in this embodiment, the print head is specified to be one that ejects the ink by the bubble jet method, the print head may be one that ejects the ink by an other ejection method, such as the piezoelectric method. Moreover, the print head may be one that has different cases for respective ink colors or respective nozzle rows. Furthermore, the carriage 2 includes a scanner 9 configured to scan an image printed on a print medium.
Returning to
The capping device 11 includes a rectangular-frame-like cap main body that can be tightly contacted with the nozzle surface 33 outside all the nozzle rows 32 and an absorber accommodated in the cap main body . For example, the cap main body is formed of an elastic body such as rubber. The absorber is formed of a porous material such as a sponge. The capping device 11 also functions as an ink receiver during preliminary ejection. The preliminary ejection allows ink (particularly mixed color ink) and bubbles in each nozzle and ink passage to be discharged and removed.
The wiping device 12 includes a wiping blade formed of rubber and a base member configured to support the wiping blade. The wiping deice 12 is slid in the sub-scanning direction B by switching the driving source for the recovery device 10 to drive the motor M3 inside the recovery device. In the present example, the nozzle row 32 extends in the sub-scanning direction B. Thus, the wiping is performed in the direction of the nozzle row 32.
The recovery device 10 is configured to carry out a recovery process using an appropriate combination of the capping device 11, the wiping device 12, and the suction device, to maintain or recover the normal state of the ink ejection performance of the print head 3.
An operation panel 506 is equipped with keys, etc., which make possible inputting by an operator, etc. A recovery system control circuit 507 controls recovery operations, such as the preliminary ejection and the wiping in accordance with a recovery processing program stored in the RAM 502. A recovery system motor 508 drives the wiping device 12, the capping device 11, a suction pump 511, etc. at the time of the recovery processing. A head drive control circuit 515 controls heaters 513 of the respective nozzles of the print head 3 individually, and makes the print head 3 perform the ink ejection for normal printing and the preliminary ejection. Furthermore, a carriage drive control circuit 516 and a paper feeding control circuit 517 similarly control a movement of the carriage and paper feeding, respectively, in accordance with the program.
The print head 3 is providedwitha temperature keeping heater for keeping a ink temperature in the print head 3 at a predetermined temperature, and a thermistor 512 for detecting the ink temperature in the print head 3. A head temperature control circuit 514 controls the temperature keeping heater based on a detection signal from the thermistor 512.
Next, a processing for deciding the number of preliminary ejections (namely, the number of ink droplet ejections) in the preliminary ejection will be explained referring to
First, at Step S101, the wiping by the wiping device 12 is performed. At this time, there may be a case where chatter arises in connection with speed fluctuation at the time of the wiping, and the mixed color inks adhere to the nozzle surface 33 perpendicularly to the nozzle rows 33 thereof.
After execution of this wiping, at Step S102, the flow becomes in a standby state for a predetermined time Tx. Incidentally, in a normal operation, the printing apparatus is configured so that immediately after the printing operation, the print head 3 may move to right above the capping device 11, go into the standby state, and be ready to shift to the printing operation immediately after a print command comes in. Then, the printing apparatus is configured so that upon a lapse of a predetermined time Tw being in the standby state, it may perform the recovery operation, e.g., the wiping, perform the preliminary ejection, and execute the capping. The above-mentioned predetermined time Tx is set to a time slightly shorter than Tw, e.g., (Tw−1) seconds, in order to especially create a situation where color mixture occurs easily.
Next, printing of an evaluation patch is performed at Step S103. That is, the preliminary ejection is performed to the printing medium while making the print head 3 scan, and the evaluation patch is printed on the printing medium. Printing of this evaluation patch is performed for each color, specifically for each nozzle row except that of black.
The evaluation patch is printed with a sold one pass for each monochrome color, respectively. For example, a print head in which the nozzles are arranged with 256 nozzles per nozzle row at a spacing of 1200 dpi (=21 μm) is used. When an ink droplet (5 pl/shot) is ejected from one nozzle and this ink droplet is impacted on the printing medium, a dot of a diameter of about 20 μm is printed on the printing medium. When performing the printing with a carriage speed in the scanning direction A being set to 12.5 inch/sec (0.32 m/sec) and a drive frequency being set to 15 kHz, a dot arrangement in the scanning direction A becomes such that one dot is embedded in a grid of 1200 dpi. For this reason, the color mixture can be determined suitably, and it is possible to suitably bring a line of chatter in the nozzle surface and the number of preliminary ejections in the nozzle row of each color into correspondence with each other. Incidentally, although a routine of
Next, at Step S104, an image of the evaluation patch is scanned by the scanner 9.
Then, at Step S105, data of the image of the scanned evaluation patch is divided into a plurality of divided areas.
Next, at Step S106, a first divided area P_0_0 (x=0, y=0) is selected. Then, at Step S107, a color mixture determination processing of determining the existence/absence of the color mixture for the selected divided area is performed. Although details of this color mixture determination processing will be explained in full detail later, in the case of existence of the color mixture, a determination result of P_x_y=1 is obtained, and the in the case of the absence of the color mixture, a determination result of P_x_y=0 is obtained.
At the next Step S108, it is determined whether the determination result of Step S107 is P_x_y=1, namely, whether the color mixture exists. If the determination result is P_x_y=1, the number of preliminary ejections will be added to the divided area P_x_y at Step S109. On the other hand, if the determination result is P_x_y=0, namely no color mixture, Step S109 will be skipped.
Although the following will be understood in detail later, in this embodiment, a default or standard number of preliminary ejections per divided area is fixed to zero, and in the case of no color mixture, the number of preliminary ejections is fixed to zero. It is specified that in the case of the existence of the color mixture, a predetermined number of preliminary ejections, e.g., 16 shots, shall be added to the default number of preliminary ejections. However, these values can be decided arbitrarily: for example, it is all right that the default number of preliminary ejections is set to a predetermined value equal to or more than unity, the preliminary ejection(s) of one or more shots are performed even in the case of no color mixture. Moreover, it is also all right that in the case of the existence of the color mixture, an arbitrary number of preliminary ejections other than 16 may be added to the default number of preliminary ejections.
Next, at Step S110, it is judged whether evaluation on 16 nozzles to be objected (this is called one nozzle group) is finished in all the divided areas in the X-axis direction. If the evaluation is not finished, the flow will proceed to Step S111, where unity will be added to the value of X, and the flow will proceed to Step S107. In this way, the evaluation will be performed sequentially in each divided area in the X-axis direction for one nozzle group to be objected.
If it is judged that the evaluation is finished at Step S110, the flow will proceed to Step S112, where it will be judged whether the evaluation is finished in all the divided areas in the Y-axis direction. If the evaluation is not finished, the flow will proceed to Step S113, where unity will be added to the value of y, the value of x will be set to zero, and the flow will proceed to Step S107. In this way, the divided area to be subjected to the evaluation in the X-axis direction is set to the area of x=0 again, and the evaluation is performed sequentially in each of the divided areas in the X-axis direction for the next one nozzle group in the Y-axis direction.
If it is judged that the evaluation is finished at Step S112, a preliminary ejection count decision processing will be finished.
Next, the color mixture determination processing performed at Step S107 will be explained with reference to
Here, as shown in
As shown in
Next, at Step S202, Lab values of each dot area D_s_t are stored in (L_s_t, a_s_t, b_s_t), respectively.
At Step S203, in order to remove a part of the printing medium (paper), it is determined whether Dst satisfies conditions of L_s_t>90, |a_s_t|<10, and |b_s_t|<10, namely whether the lightness is high and the saturation is low. In the case of Yes, that part of the printing medium is regarded as a portion on which the printing is not done, it is excluded from the color mixture determination and the flow moves to Step S207.
If the part is not excluded at Step S203, it is assumed that it is printed, and the flow will proceed to the next Step S204. At Step S204, it is determined whether Dst satisfies the conditions of L_s_t<20, |a_s_t|<10, and |b_s_t|<10, namely whether the lightness is low and the saturation is low. In the case of Yes, it is assumed that the black ink is printed, and the flow moves to Step S206.
In the case of No, at Step S205, it is judged whether D_s_t satisfies conditions of 0≦L_s_t<100, and (|a_s_t|2+|b_s_t|2)(1/2)>50) (where “≦” means “=<”), namely where the saturation shows a high value. In the case of Yes, it is assumed that any one of color inks of cyan, magenta, and yellow is printed normally without the color mixture, and the flow moves to Step S206.
On the other hand, at Step S205, in the case of No, it is assumed that what is printed is the mixed color inks whose saturation is low and whose lightness falls somewhere in between high and low. Then, the flow proceeds to Step S211, where the whole of the divided area to which the dot area D_s_t belongs is given P_x_y=1, and a determination that the color mixture exists is performed. That is, if the color mixture is recognized even in one dot area in the one divided area P_x_y, the determination that the color mixture exists is made for the whole of the divided area. Then, the color mixture determination processing is ended.
At Step S206, it is judged in all the dot areas in an S-axis direction whether the determination is finished for one nozzle that is subject to the determination. If the determination is not finished, the flow will proceed to Step S207, where unity will be added to the value of S, and the flow will proceed to Step S202. In this way, for one nozzle to be subjected to the determination, the determination will be performed sequentially in each dot area in the S-axis direction.
If it is judged that the determination is finished at Step S206, the flow will proceed to Step S208, where it will be judged whether the determination is finished in all the dot areas in the t-axis direction. If the determination is not finished, the flow will proceed to Step S209, where unity will be added to the value of t and the value of S will be set to zero, and the flow will proceed to Step S202. In this way, the dot area in the S-axis direction will be set to an area of S=0 again, and the determination will be performed in each dot area in the S-axis direction sequentially for the next one nozzle in the t-axis direction.
If it is judged that the determination is finished at Step S208, the flow will proceed to Step S210, where the whole of the divided area P_x_y to which the dot area D_s_t to be subjected to the determination belongs will be set to P_x_y=0, and a determination of no color mixture will be made. That is, if the color mixture is not recognized in all the dot areas in the one divided area P_x_y, the determination of no color mixture will be made for the whole of the divided area. Then the color mixture determination processing is ended.
Incidentally, in order to perform the determination of the existence/absence of the color mixture, methods other than such a method is applicable. For example, a method of, when the color mixture is observed in dot areas of a predetermined ratio (for example, 30%, 50%, or 70%) or more in the one divided area, determining that the color mixture exists in the divided area is also possible. Furthermore, it is unnecessary to determine whether or not color mixture has occurred for each nozzle and for each dot as in the present embodiment. The size of the determination area may be appropriately set in accordance with conditions such as the resolution of the mounted scanner.
Now, in one example of the evaluation patch shown in
In the divided area P_6_2 shown in
Moreover, in the figure, the “number of preliminary ejection execution areas” means the number of areas where hatching is given in
Furthermore, in the figure, “the number of preliminary ejections” means the number of shots that all the nozzles belonging to one nozzle group preliminarily eject. For example, for the nozzle group 0, since the number of preliminary ejection execution areas is one, all the nozzles belonging to the nozzle group 0 perform the preliminary ejection of 1×16=16 shots uniformly. That is, the number of preliminary ejections of 16 shots as one unit is associated to the number of preliminary ejection execution areas of 1. On the other hand, for the nozzle group 6, since the number of preliminary ejection execution areas is eight, all the nozzles belonging to the nozzle group 6 perform the preliminary ejection of 8×16=128 shots uniformly.
For the nozzles of nozzle groups 6, 7 that formed a relatively large color mixture area in the evaluation patch, the number of preliminary ejections is made to increase to a larger number than the nozzles of the nozzle groups 1 to 5 and 8 to 15 that formed relatively small color mixture areas in the same patch. Incidentally, the “relatively small color mixture area” includes an area with no color mixture. Therefore, a large amount of preliminary ejection can be performed for nozzles having a large degree of the color mixture, and a small amount of preliminary ejection can be performed for nozzles having a small degree of the color mixture, so that effective ink consumption can be achieved. Furthermore, since the number of preliminary ejections for each nozzle is decided based on a result of actually printing the evaluation patch by the preliminary ejection, it is possible to appropriately decide the number of preliminary ejections for each nozzle according to the color mixture parts that vary for every apparatus. In this way, it becomes possible to achieve compatibility of an excellent image quality and decrease of the amount of waste inks.
In the present embodiment, description has been given of the method of determining the number of preliminary ejections for the color nozzle rows other than the black nozzle row (cyan, magenta, and yellow). However, even for the black nozzle row, a pattern may be formed so that the number of preliminary ejections can be determined based on the formation results. Processing similar to that described above and shown in
In the foregoing, although the embodiment of the present invention was described in detail, various embodiments of the present invention can be considered other than this.
For example, in the embodiment, the nozzle hole diameters of all the nozzles of all the nozzle rows were identical. On the other hand, it is all right that a plurality of kinds of nozzles each of which has a different nozzle hole diameter may be included in all the nozzles. This includes a case where nozzle hole diameters differ from one another within one nozzle row, and a case where the hole diameters are the same within one nozzle row but the hole diameters differ among the nozzle rows. In such a case, since the larger the nozzle hole diameter of the nozzle, the smaller a capillary force becomes, and consequently the mixed color inks invades more easily into the nozzles. Therefore, when increasing the number of preliminary ejections of a specific nozzle (in the embodiment, the nozzles of the nozzle groups 6, 7), the numbers of preliminary ejections may be increased to a larger number for a nozzle with a larger nozzle hole diameter. For example, consider a case where two kinds of nozzles, larger one and smaller one, in each nozzle group in the embodiment. It can be specified that for larger diameter nozzles among nozzles of the nozzle groups 6, 7, the number of shots is set to 144 (=8×18) shots larger than 128, and for smaller diameter nozzles, the number of shots is set to 128 (=8×16) shots.
Moreover, if the environmental temperature decreases, the viscosity of ink will increase and it will become difficult for the mixed color inks to invade into the nozzle. Therefore, when increasing the number of preliminary ejections of a specific nozzle, the number of preliminary ejections may be increased to a larger number for a higher environmental temperature. In this case, an environmental temperature detecting unit, such as a temperature sensor for detecting the environmental temperature, is provided, and the increased number of preliminary ejections is decided according to this detected temperature.
Moreover, since the nozzle surface dries with decreasing environmental humidity, it becomes difficult for the mixed color inks to invade into the nozzles Therefore, when increasing the number of preliminary ejections of a specific nozzle, the number of preliminary ejections may be increased to a larger number for a higher environmental humidity. In addition, in this case, an environmental humidity detecting unit, such as a humidity sensor for detecting an environmental humidity, is provided and an increased number of preliminary ejections is decided according to this detected humidity.
Furthermore, the above-described preliminary ejection number determination process need not necessarily be carried out after every wiping operation but may be executed after every predetermined number of wiping operations. Furthermore, in the above-described embodiment, the degree of occurrence of color mixture is sensed based on the results of formation of a pattern. However, the sensor may directly detect the status of color mixture on the ejection port surface (nozzle surface). Specifically, after the wiping is carried out, the sensor is used to determine whether or not ink droplets in a mixed color are attached to the ejection port surface. If the process determines that ink droplets in a mixed color are attached to the ejection port surface, then a predetermined time later, the sensor is used again to determine whether or not ink droplets in the mixed color are attached to the ejection port surface. If no ink droplets in the mixed color can be detected any longer, the process may determine that the mixed color ink has entered the nozzle. Then, in the subsequent preliminary ejection, the amount of preliminary ejection to the vicinity of the attached ink may be increased.
Moreover, although in the embodiment, the image of the evaluation patch was scanned by the scanner and the existence/absence of the color mixture was determined, it is all right that the user performs the determination by visual inspection. In this case, for example, the user inputs an area with the color mixture and an area without the color mixture using keys etc. of the operation panel 506 based on the image in the evaluation patch. Then, correspondingly to this input, the CPU 500 appropriately decides the number of preliminary ejections for each nozzle similarly to what was described above, and stores it in the RAM 502.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2009-287540, filed Dec. 18, 2009, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-287540 | Dec 2009 | JP | national |
