Ink tank and ink jet recording apparatus using the aforesaid ink tank

Abstract: An ink tank for storing ink comprises an ink storage unit (B), an induction outlet (17a) provided in the ink storage unit (B) for delivering to the outside the ink stored in the ink storage unit (B), and a partition member (17e) for partitioning the region where the induction outlet (17a) is provided from the other region, having at least a part higher than the height at which the induction outlet (17a) is provided and at least a part lower than the liquid level of ink stored in the ink storage unit; thus preventing any inconveniences resulting from the mixture of air and ink by vibration in order to obtain a stable printing condition for an ink jet recording apparatus to be operated at a high speed.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an ink tank and an ink jet recording apparatus using the aforesaid ink tank. Related Background Art An ink jet recording apparatus has an advantage that high-speed recordings can be performed quietly with a low running cost. In recent years, therefore, the ink jet recording apparatus has been in use in many ways as the recording apparatus for a coping machine, facsimile apparatus, and the like, the printer for a word processor, electronic typewriter, and the like, or the image output terminal for a computer and the like. In an ink jet recording apparatus such as this, there are the so-called serial printer type therein the recording is performed while the recording head is being scanned in the predetermined direction with respect to the recording medium, and the line printer type using the full multitype recording head in which the discharging ports are aligned to cover the entire region corresponding to the full width of the recording medium. Particularly, the former is such that its recording head itself performs the operation (the reciprocal or shuttling motion along the platen roller), and a structure such as given below is often employed. In the ink jet recording apparatus, liquified ink is supplied form an ink supply source to the recording head main body. At this juncture, in the recording head used for the serial printer type recording apparatus, an ink tank, which is detachably connected to the recording head, is provided as an intermediate reservoir member or sub-tank in the ink supply system for the recording head in such a manner that this sub-tank is allowed to scan together with the recording head. This sub-tank is not filled with ink completely in its inside but is used with a predetermined amount of air reserved therein. Then, with the existence of this air portion, the shock generated by the motion of the ink head at the time of recording or at the time of the head coming to a stop is softened to prevent the ink leakage from the discharging port due to such shock or the ingression of air into the discharging port effectively. Here, the mode of the sub-tank will be described. Fig. 9 is a plan view showing an example of the sub-tank arranged in a conventional reading head, and Fig. 10 is a cross-sectional side view thereof. In Fig. 9 and Fig. 10, a reference numeral 117 designates the entire body of the sub-tank; 117a, the outlet of a ink supply tube for supplying ink to the recording head; 117b, the connecting portion of the tube (sub-tank tube) communicated with a suction means for sucking air or ink in the sub-tank 117 therethrough; and 117c, an induction port for the ink supply. Also, the dashed line represents the actual liquid level (horizontal plane) to be formed when the sub-tank is installed in the carriage in the main body of the apparatus. Now, the height, measured from the bottom face of the tank, of the outlet 117a of the ink supply tube for supplying ink contained in the sub-tank 117 to the head is lower than the connecting portion 117b to the sub-tank tube. Then, by actuating the suction means to induce ink into the sub-tank 117 from the induction port 117c, it is possible to perform a stable ink supply because the liquid level is usually positioned sufficiently higher than the outlet 117a of the supply tube to the head. Also, the structure is arranged so that a reservoir of air is always maintained above the connecting portion 117b to the sub-tank tube. Usually, at the time of recording (printing) with the sub-tank 117 being installed in the carriage of the main body of the apparatus, the ink contained in the sub-tank 117 maintains the liquid level represented by the dashed line in Fig. 10. Then, a substantially equal amount of ink to that of the ink consumed by the head is refilled from the ink supply source through the ink inlet 117c because the sub-tank 117 is of closed system. Now, in the serial printer, while the printing is performed by causing the recording head to travel, the ink supply system (the supply tube connecting the ink supply source and the sub-tank, for example) swings at that time, and if no sub-tank is provided, ink in the recording head is compressed or decompressed due to ink in the swinging supply tube. However, if the sub-tank 117 with the air reservoir therein is provided, it is possible to prevent the fluctuation of the pressure exerted on the ink in the recording head by the damper effect thereof; thus making the stable printing possible. Nevertheless, for the recent ink jet recording apparatus, a higher speed printing is required. Accordingly, the motion of the recording head has increasingly been quicker and more intense as a matter of course. Therefore, the motion of the supply tube and the like accompanying the recording head in scanning is more intense, leading to the necessity of a sufficient air reservoir. In the above-mentioned ink jet recording apparatus by the conventional art, however, there is a problem given below. In other words, for obtaining a sufficient air reservoir, the liquid level in the sub-tank 117 is arranged at a position considerably low in the inner space of the sub-tank 117 while the motion of the recording head is quick and considerably violent. Consequently, when the entire body of the sub-tank 117, which integrally travels to scan, swings violently, ink and air in the sub-tank 117 are allowed to mix themselves considerably. As a result, there is a possibility that air is carried into the recording head through the supply tube to the head when bubbles generated by such mixture approach the outlet 117a for carrying ink in the sub-tank 117 to the head. Here, there is known a structure disclosed in document JP-U-54-48652, i.e., a structure whereby the inside of the ink tank installed in the head carriage is divided into a plurality of tank chambers by partition plates. However, there is still a possibility that bubbles are carried into the recording head once bubbles are generated by the vibration. Further, document JP-A-59-165660 discloses an ink tank comprising the features of the pre-characterizing clause of claim 1. This known ink tank is secured in an ink jet recording apparatus and comprises an ink storage unit having an ink supply chamber and an ink collecting chamber and a partition member for dividing the chambers. The ink supply chamber is communicated with the ink collecting chamber at the bottom of the ink tank, and an ink flow path is formed at the lower portion of the ink tank. The ink flow path stands at the same height as an outlet for delivering the ink stored in the storage unit through a supply tube to the outside of the ink tank. In this arrangement, if the ink tank is mounted on the carriage, air bubbles included in the collected ink may reach through the ink flow path to the ink outlet due to the vibration of the ink tank, thus supplying the air bubbles to the recording head. There is also considered a structure as shown in Figs. 7 and 8 thereby to prevent the mixture of air and ink by vibration with the provision of an inner wall 117d in the sub-tank 117. There is still a possibility that air is not sufficiently prevented from reaching the outlet 117a to the head. SUMMARY OF THE INVENTION It is an object of the invention to provide an ink tank capable of maximizing the blocking of air bubbles mixed in the ink to be supplied to the recording head, and an ink jet recording apparatus using the improved ink tank. This object is achieved by the ink tank according to claim 1 and by the ink jet recording apparatus according to claim 5. According to the invention, an enclosure is provided around the supply tube, this enclosure defining an ink flow path to the outlet along which the ink is forced to flow in a downward direction so that the direction of the buoyancy of the air bubbles is opposite to the direction of the flow of the ink along said flow path, and thereby the air bubbles are prevented from reaching the outlet. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 and Fig. 2 are a perspective view and a schematic side view respectively showing an ink jet recording apparatus according to an embodiment of the present invention; Fig. 3 and Fig. 4 are a plan view and a side cross-sectional view respectively showing an ink tank according to a first embodiment of the present invention; Fig. 5 and Fig. 6 are a plan view and a side cross sectional view respectively showing an ink tank according to a second embodiment of the present invention; Fig. 7 and Fig. 8 are a plan view and a side cross-sectional view showing another ink tank; and Fig. 9 and Fig. 10 are a plan view and a side cross-sectional view showing a conventional ink tank. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, in reference to the accompanying drawings, the embodiments suited for the present invention will be described. Fig. 1 is a perspective view showing an ink jet recording apparatus according to an embodiment of the present invention. Fig. 2 is a schematic side view thereof. Here, a reference numeral 1 designates a recording head having an ink discharging port 1a, utilizing thermal energy generated by an electrothermal converter which generates heat in response to image information to discharge ink; 2, a carriage with the recording head 1 installed therein, which shuttles along a guide shaft 3; 4, a timing belt connected to the carriage 2 to allow it to travel; and 5, a shift motor for driving the timing belt 4 by predetermined timing. A reference numeral 6 designates a platen for holding a recording medium such as recording sheet 7 at a position facing the ink discharging face of the recording head 1 with a predetermined space to the ink discharging face; 8, a feed roller for feeding the recording sheet 7; and 9, a sheet feeding motor for driving the feed roller 8 through a sheet feeding gear 10. The feed roller 8, the sheet feeding motor 9 and the sheet feeding gear 10 form a conveying means for conveying the recording medium. Also, a reference numeral 11 designates a printed circuit board which is connected to the recording head 1 through a flexible cable 12 electrically, and provided with a circuitry to drive the recording head 1 and control the recording apparatus; and 13, a main tank which is the supply source of ink supplied to the recording head 1. In the present embodiment, the recording ink is supplied from a supply source formed by a main tank 13 to the recording head 1 through a flexible supply tube 14 which follows the carriage traveling. In the recording apparatus structured such as this, when the carriage 2 is traveled along the recording sheet 7 by the shift motor 5, ink is discharged from the discharging port 1a of the recording head 1 in response to its timing to perform the recording on the recording sheet 7. Also, when the recording for one-line portion is completed, the sheet feed roller 8 is driven by the sheet feeding motor 9 to perform the sheet feeding corresponding to the one-line portion. Also, in the present embodiment, the recording is performed likewise when the carriage 2 is traveled in the opposite direction, i.e., the so-called reciprocal motion recording type. A reference numeral 15 designates a recovery means arranged outside the recording area for the recording head 1 for recovering the function of the ink discharging, which has a cap 15a to cover the ink discharging port; and 16, is a blade arranged in series with the recovery means 15 for cleaning the ink discharging face of the recording head 1. These recovery means 15 and blade 16 are provided to keep the ink discharging in an excellent condition. In this respect, a reference numeral 13c designates a supply needle and 13d, an ink exhausting needle. Further, in reference with Fig. 2, the function of a sub-tank formed by an ink tank 17 will be described. The ink tank 17 is installed on the carriage 2 and provided between the recording head 1 and the ink supply tube 14 for supplying ink from the main tank 13 to the recording head 1. Then, by a pump 18 in the recovery means 15, air or ink in the ink tank 17 can be sucked through a sub-tank tube 19. In this respect, the connective communication between the ink tank 17 and head 1 can be released by removing a tube 19a. Furthermore, the ink which is sucked from the ink tank 17 is reserved in the exhaust ink reservoir 13b in an ink cassette 13a through a pump 18. Also, the ink cassette 13a has an ink tank 13 and the exhaust ink reservoir 13b and is attachable to and detachable from the main body of the apparatus. Further, it is possible to induce any waste ink in the discharging port 1a of the recording head 1 also to the exhaust ink reservoir 13b by actuating the pump 18 with the cap 15a having capped the discharging port 1a of the recording head 1. Also, the height from the tank bottom face of an outlet 17a1 provided in the ink tank 17 (ink induction outlet connectively communicated with the record head 1 side) of an ink supply tube 17a for supplying ink to the recording head 1 is defined lower than a connecting portion 17b between the ink tank 17 and the sub-tank tube 19. Here, at the outset of installing the ink tank 17 in the carriage 2, the recovery means 15 (pump 18) is actuated with the discharging port 1a being capped to induce ink in the main tank 13 to the ink tank 17 through an induction port 17c. Thus, it is usually possible to position the liquid level sufficiently higher than the outlet 17a1 for supplying ink to the recording head 1; hence performing a stable ink supply to the recording head 1. Also, the ink tank 17 is structured so that the air reservoir is maintained at all times above its connecting portion 17b to the sub-tank tube 19. Usually, here, the ink tank 17 keeps the liquid level as shown in Fig. 2. Then, since the ink tank 17 is of closed system, the ink consumed in the recording head 1 is supplied sequentially from the ink tank 13 to the recording head 1 through the supply tube 14. As described earlier, the printing on the recording sheet 7 is performed as the carriage 2 travels, but with the air reservoir in the ink tank 17, the compression or decompression to the ink in the recording head 1 is prevented thereby to make a stable printing possible. In this respect, the X region circled by the dashed line in Fig. 2 represents the carriage portion while the Y region, the main body of the ink jet recording apparatus. Now, Fig. 3 and Fig. 4 a plan view and side cross-sectional view respectively showing the ink tank 17 according to a first embodiment of the present invention. The ink tank 17 in the present embodiment is installed on the carriage 2 with an inclination in practice. Therefore, the liquid level is usually in a state as designated by the dashed line. As in the structure shown in Fig. 7 and Fig. 8, there is provided an inner wall 17d in a four-column type ink storage unit B in such a manner that the inner wall is fixed on the bottom face 17f thereof in its diagonal direction to prevent ink in the ink tank 17 from vibrating greatly. Further, in the present embodiment, there is provided a partition member forming an enclosure 17e having two sides 17e1 and 17e2 rectangular to each other fixed on the bottom face 17f to encircle the supply tube 17a for supplying ink to the recording head side. In this respect, the enclosure 17e encircles the supply tube 17a with its two sides 17e1 and 17e2 in cooperation with the side wall of the tank 17. Also, the height from the tank bottom face 17f of the enclosure 17e is defined sufficiently higher than the supply tube outlet 17a1 for supplying ink to the head 1, and lower than the height of the usual liquid level. With this arrangement, the aforesaid enclosure 17e serves to prevent the air ingression into the supply tube 17a for supplying ink to the head 1 and to perform the ink supply smoothly. Also, in order to enhance the aforesaid effect, the space A between the supply tube 17a and the enclosure 17e is approximately 1 mm for the narrow place and approximately 2 mm or less for the wide place. Further, the aforesaid effect is more enhanced by making the height of the enclosure 17e higher than that of the ink induction port 17c. As the above describes, according to the present embodiment, not only the vibration of ink in the ink tank 17 is restricted as much as possible by the inner wall 17d to reduce the mixture of air into ink, but the air mixed with ink is not allowed to approach the outlet 17a1 by the afroesaid enclosure 17e to prevent it even if air is mixed into ink. Therefore, it is possible to reduce significantly the probability of air ingression into the recording head 1. In this respect, a reference numeral 17a2 designates the inlet to the recording head side. Here, an example of the size of each part constituting the present embodiment is given below. (i) Ink storage unit B Length (a) approx. 11 mm Width (b) approx. 11 mm Height (c) approx. 23 mm (ii) Inner wall 17d Length (d) approx. 9 mm Height (e) approx. 15 mm (iii) Enclosure 17e (17e1 and 17e2) Length 17e1 (f) approx. 6 mm 17e2 (g) approx. 6 mm Height (h) approx. 8 mm (iv) Space (i) between the outlet 17a1 and bottom face 17f approx. 1 mm (v) Tube diameter (j) of supply tube 17a approx. 2 mm (vi) Height of the connecting portion 17b from the bottom face 17f (k) approx. 7 mm (vii) Height of the ink induction port 17c from the bottom face 17f (1) approx. 4 mm Subsequently, Fig. 5 and Fig. 6 illustrate an ink tank according to a second embodiment of the present invention. In the present embodiment, unlike the example shown in Fig. 3 and Fig. 4, a part 17g which is lower than the liquid level is provided for the enclosure 17e while the height of the other part is defined higher than the usual liquid level; thus making it possible to control air and ink more effectively so as not to mix them by vibration and at the same time, to perform the ink supply smoothly. In this respect, it may be possible to provide a hole in the lower part of the enclosure to induce ink into the inside thereof in place of the part having a lower height in the enclosure 17e as in the second embodiment. With the structure set forth above, while the ink supply is smoothly maintained, the ingression of air into the supply tube to the recording head side can be effectively prevented despite the violent shaking of the sub-tank. In this respect, the present invention is not limited to the above-mentioned embodiment, and various modifications thereof will be possible. For example, while in the above-mentioned embodiment the recording head 1 and the ink tank 17 are separate bodies, it may be possible to configure these separate bodies into one integrated body. Also, in the above-mentioned embodiment, the main tank which is the ink supply source is fixed to the apparatus while the main tank 13 and the ink tank 17 are connected by the flexible supply tube 14. However, it may be possible to install the main tank on the same carriage or on a second carriage which is interlocked with the carraige, on which the recording head or the ink tank is installed, to travel following such carriage. Also, for the main tank which is integrally formed with the recording head or sub-tank, if there is a problem such as described earlier in the ink supply system, the present invention can be applied effectively. Furthermore, if only the aforesaid enclosure 17e has at least a part which is higher than the height at which the aforesaid outlet 17a1 is provided, it is possible obtain the intended effect. According to the aforesaid embodiment, in the ink tank forming the intermediate reservoir member (sub-tank) installed on the carriage with the recording head, there is provided the above-mentioned enclosure comprising walls encircling the four sides in the vicinity of the supply tube for supplying ink to the recording head, being higher than the outlet of the supply tube and having at least a part which is lower than the usual liquid level thereby preventing air ingression into the supply tube. Hence, it is possible to prevent air from being supplied to the recording head and materialize a stable printing condition despite the high speed at which the printing is performed. Thus, it is possible to prevent any incoveniences resulting from the mixture of air and ink by vibration as well as to implement an ink jet recording apparatus thereby obtaining a stable printing condition at a high-speed printing without any significant increase in its manufacturing cost and installation space. In this respect, the present invention is effective for the ink jet recording systems. Particularly, this invention produces an excellent effect on the recording head and recording apparatus of the ink jet system wherein the recording is performed by forming flying droplets utilizing thermal energy. This is because of the fact that with a system such as this a higher density and finer precision of the recording is implemented. For the typical structure and principle thereof, it is desirable to adopt for its implementation the fundamental principle disclosed, for example, in the documents US-A-4723129 and US-A-4740796. This system is applicable to either so-called on demand type and continuance type. Particularly, in the case of the on demand type, at least one driving signal, which gives a recording liquid a rapid temperature rise exceeding the nuclear boiling, is applied in response to the recording information to the electrothermal converter arranged with respect to a sheet or liquid path holding a recording liquid (ink) thereby causing the electrothermal converter to generate thermal energy. Hence, film boiling is generated on the thermoactive plane of the recording head, resulting in the formation of bubble in the recording liquid (ink) one to one in response to this driving signal efficiently. The recording liquid (ink) is discharged into the atmosphere through the discharging port by the active force generated in the course of the growth and contraction of this bubble to form at least one droplet. It is more desirable to produce this driving signal in the form of pulses. Then, the growth and contraction of the bubble is appropriately performed instantaneously to implement the discharging of recording liquid (ink) having particularly excellent responsivility. For this pulse type driving signal, the one such as disclosed in documents US-A-4463359 and US-A-4345262 is suitable. In this respect, if the condition disclosed in document US-A-4313124 concerning the invention as regards the temperature rise on the above-mentioned thermoactive plane, it is possible to perform more excellent recordings. As the structure of the recording head, this may include a combination of the discharging port, liquid path, electrothermal converter (linear liquid path or rectangular liquid path) such as disclosed in each of the above-mentioned documents as well as the structure having the thermoactive portion arranged in the bending region using the configuration disclosed in documents US-A-4558333 and US-A-4459600. In addition, in the serial type recording apparatus as exemplified above, the present invention is effective in the case of using a recording head fixed to the main body of the apparatus, or a freely replaceable chip type recording head for which the electrical connection to the main body of the apparatus and ink supply become possible when it is installed therein, or a cartridge type recording head having the ink tank integrally provided for the recording head itself. Also, as to the kind of recording head installed or the numbers thereof, it may be possible to install a plurality of recording heads with respect to the different kinds of ink having different recording colors and densities besides the one having only one recording head for a monochrome ink. In other words, the present invention is extremely effective not only to the recording mode having one main color such as black but also to the apparatus provided for at least one of the compound colors formed by various colors or full colors produced by mixing colors irrespective of whether the recording head is constructed integrally as one body or by a combination of plural heads. Furthermore, as to the mode of the ink jet recording apparatus according to the present invention, there may be many taking various modes including the image output terminals for information processing apparatuses such as computers, those used for copying machines in combination with readers, and for facsimile apparatuses having transmitter and receiver, and the like. As the above describes, the present invention makes it possible to provide an ink tank thereby maintaining stable recordings and a ink jet recording apparatus using the aforesaid ink tank.

Claims: An ink tank comprising an ink storage unit (B) for storing ink, said storage unit (B) having a bottom face (17f); an ink induction port (17c) for supplying ink to the ink storage unit (B); an ink supply tube (17a) positioned in said storage unit (B), said supply tube extending downwardly in said storage unit and terminating in an outlet (17a1) for delivering the ink stored in said storage unit through said supply tube (17a) to the outside of said ink tank; and a partition member (17e) positioned in said storage unit (B), characterized in that a connecting portion (17b) is provided through which air or ink can be sucked for maintaining the liquid level of the stored ink constant, and in that said partition member (17e) forms an enclosure around said supply tube (17a) and comprises a wall which is fixed to said bottom face (17f) and is positioned proximate to said supply tube (17a), wherein the height of said wall from said bottom face (17f) is larger than the distance of said outlet (17a1) from said bottom face (17f), and wherein the sole ink flow path to said outlet (17a1) is from above said partition member (17e) and between said wall and said supply tube (17a). The ink tank according to claim 1, wherein an inner second wall (17d) is provided in said storage unit (B) and is fixed to said bottom face (17f) on a diagonal line of said storage unit (B), said second wall (17d) having a larger height from said bottom face (17f) than said partition member (17e). The ink tank according to claim 1, wherein said wall of said partition member (17e) comprises a plate member having two sides (17e1, 17e2) rectangular to each other. The ink tank according to claim 1, wherein a recording head is provided integrally with said ink tank (17). An ink jet recording apparatus for performing recording onto a recording medium (7), comprising an ink jet recording head (1); conveying means (8 to 10) for conveying said recording medium; and a carriage (2) capable of shuttling in a direction intersecting the conveying direction of the recording medium, characterized in that an ink tank (17) according to one of claims 1 to 4 is installed on said carriage (2). The ink jet recording apparatus according to claim 5, comprising a recording ink supply source (13) for supplying ink to said ink tank (17), wherein at the same time at which said ink is received by said ink tank (17) it is delivered to said ink jet recording head (1) from said ink tank (17) through said outlet (17a1). The ink jet recording apparatus according to claim 5 or 6, comprising means for installing said ink jet recording head (1) on said carriage (2) and recording control means for driving said ink jet recording head (1) to discharge ink in the course of said shuttling movement of said carriage (2) for the performance of recording on the recording medium (7). The ink jet recording apparatus according to one of claims 5 to 7, wherein said ink jet recording head (1) comprises an electro-thermal converter for generating thermal energy to cause ink to generate film boiling as means to generate the energy to be utilized for ink discharging.

Inventors: HIRAMATSU SOICHI, MATSUI SHINYA, YAMAGUCHI HIDEKI, HIRAMATSU, SOICHI, MATSUI, SHINYA, YAMAGUCHI, HIDEKI, HIRAMATSU, SOICHI, C/O CANON KABUSHIKI KAISHA, MATSUI, SHINYA, C/O CANON KABUSHIKI KAISHA, YAMAGUCHI, HIDEKI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: B41J2
IPC codes: B41J2