1. Field of the Invention
The present invention relates to an ink jet recording apparatus, and more particularly, to an ink storage unit for storing ink which is supplied to a recording head of the ink jet recording apparatus.
2. Related Background Art
An ink jet recording system performs recording in a manner that an ejection-energy-generating element provided at a portion communicating with orifice of a recording head, such as a heating element or a piezoelectric element, operates based on recording signals to eject ink droplets from the orifice, and to attach the ejected ink droplets to a recording medium. This system has such an advantage that high speed recording is possible and operation noises generated by-recording are fairly low, and is recently in the wide use in printers.
The configuration of an ink supplying system in the above recording system is as follows: Ink which is stored in an ink tank as an ink storage member, is supplied to a recording head via an ink supplying route member such as la tube. The ink supplied to the recording head is temporarily stored in an ink temporary storage portion such as a common liquid chamber, and then is supplied into ink paths in accordance with the ink ejection, the ink paths communicating with orifices correspondingly, an ejection energy generating element being provided in each ink path.
A pressure exerted on the ink in the ink supplying system comprising the ink storage member, the ink supplying route member, and the ink paths in the recording head and the like, is always maintained to be lower than the atmospheric pressure (a pressure lower than the atmospheric pressure is hereinafter referred to as a negative pressure). This can prevent ink from leaking out from the orifices of the recording head and an air communication port of the ink storage member, through each of which the ink paths and an inside of the ink storage member communicate with air respectively. An ink supply from the ink storage member to the ink paths, in which ink refilling into the ink paths is included, is mainly performed by the capillary force of the ink paths and the ink supplying tube.
In the above ink supplying system, the above described negative pressure in the ink supplying system is generally obtained by making the pressure of the inside of the ink storage member negative. Some configurations for making the pressure of the inside of the ink storage member negative, will be shown below.
FIG. 1 is a view showing a head cartridge where the recording head and the ink tank is integrally formed. As shown in FIG. 1, in an ink tank 1000 as the ink storage member, a portion where ink is stored communicates with air via an air communicating port (not shown). Moreover, for instance, as disclosed in the U.S. Pat. No. 4,771,295, a porous ink absorber 6000 typified by urethane sponge is housed in the ink storage portion. A force to hold ink, which is caused by a capillarity force of the ink absorber 6000 and is regarded as a virtual negative pressure, maintains the negative pressure in the inside of the ink supplying system composed of a series of members from the ink tank 1000 to the ink paths in a recording head unit IJU.
With respect to another configuration, as shown in FIG. 2, an ink storage portion 230 is made of flexible materials such as rubber, a plastic film, a laminated aluminum film, etc. in the shape of a bag. The inside of the bag and the whole ink supplying system are maintained at a negative pressure by sealing the inside of the ink storage portion 230 against air.
Besides the above configuration for generating the negative pressure, FIG. 3 shows still another configuration of the ink tank. In this configuration, a layer 130 of a liquid is formed on an upper surface of the ink 210 stored in the ink tank 110. The liquid has a specific gravity smaller than that of the ink and will not be mixed with the ink. In this configuration of the ink tank, since the inside of the ink tank communicates with air via an air communicating port 1120, the layer 130 of the liquid moves together with the ink liquid surface according to the ink consumption, and hence the layer can always separate the ink from air.
In the above described conventional ink storage member, as shown in FIG. 1, where the negative pressure is generated by the porous ink absorber which is provided in the ink tank and is typified by urethane sponge, an effective ink capacity (usable ink capacity) for the ink tank volume can not be obtained because of the existence of the ink absorber. In addition, when the amount of the ink in the ink tank decreases, the negative pressure increases to the contrary, and refilling of the ink into the ink paths accompanying the ink ejection can not be performed well. This may cause defective ejection such as non-ejection. In addition, since amount of remaining ink in the ink tank becomes large because of the negative pressure increasing, use efficiency of ink is difficult to raise.
Therefore, in the case where recording is performed by using the above conventional ink tank including the ink absorber so that a sufficient number of recorded sheets of paper can be obtained, there occurs a problem that the ink tank must be enlarged. Moreover, the urethane sponge of a porous absorber is relatively expensive, and its manufacturing process becomes complicated, and hence it is difficult to provide an ink tank of a low manufacturing cost and with high productivity.
In the configuration where the ink storage portion, as shown in FIG. 2, is made of flexible materials such as rubber formed in the shape of a bag, since the inside of the bag is always sealed and the bag is made of flexible materials, when the amount of the ink in the bag decreases in response to the ejection of ink and the like, the pressure in the bag decreases and causes deformation of the bag. As a result, and for the same reason as described above, all the ink in the bag can not be exhausted. Moreover, there also occurs a problem in that the ink tank must be enlarged in order to provide an amount of ink which is sufficient to record on the desired number of sheets of paper.
In the configuration of the ink storage member where the liquid layer is provided in the ink tank as shown in FIG. 3, a desired negative pressure can not be obtained by the ink tank itself. This may not prevent ink from leaking out from orifices of the recording head, and may have adverse effect on the ink ejection by the recording head in the recording apparatus, where the ink tank is mounted on a carriage and the ink in the ink tank vibrates markedly as a result of a movement of the carriage while a recording operation, so that the vibration is transmitted to the ink near the orifices. In addition, in the above configuration, the ink tank is only in the direction shown in FIG. 3. When the ink tank has another attitude or is moved violently, the movable wall, that is, the liquid layer may be destroyed and the ink may leak out via the air communicating port.
As for a configuration for solving the above problems in various kinds of the above ink storage member, for example, Japanese Patent Application Laying-Open No. 204355/1985 proposed by the assignee of the present invention discloses the ink storage member. This ink storage member has a movable wall therein. The movable Wall is disposed in the ink storage member in a manner that edges of the movable wall slidably contacts on internal wall of the ink storage member with one side face of the movable wall contacting ink stored in the ink storage member and with the other side face of the movable wall contacting air. This makes it possible to always maintain the constant negative pressure in the inside of the ink storage member by a friction force exerted on the sliding portion of the movable wall.
However, the ink storage member using the above movable wall has the following subject to be solved, which is associated with a setting of the friction force.
The ink storage member may have various attitudes according to the mount attitude of the recording apparatus on which the ink storage member is mounted. Incidentally, an ink jet recording apparatus of portable type may have various attitudes when transported, and may be subjected to a relatively great external force such as an impact. Consequently, the ink storage member mounted on such an ink jet recording apparatus, which uses the above movable wall, has a configuration that the movable wall must not move against various attitudes or the external force described above, and good ink supply must be always secured. In order to prevent the movable wall from moving easily in the case where a large amount of ink is stored in the ink storage member, it is considered that materials having relatively great friction coefficient may be employed for the movable wall, or that the maximum static friction force is designed to be great by making the contact area between the movable wall and the internal wall of the ink storage member large.
However, in this case, the movable wall may have a difficulty in moving according to the ink consumption by ink ejection or the like. As a result, the negative pressure in the ink storage portion increases excessively, so that the ink supply to the recording head may have a difficulty and then the ink ejection by the recording head may be disabled.
Besides the above described problem of setting the friction force of the movable wall, in the case where a large amount of ink is stored in the ink storage member, there may occur problems associated with the external force exerted on the ink storage member, a force of inertia produced when the ink storage member which moves together with a recording head, is accelerated or is decelerated during the recording operation and the variation of the pressure on ink in the ink storage member which is caused by a change in environmental temperatures or the like.
More specifically, when a large amount of ink is stored, the pressure on ink in the ink storage member fluctuates easily because of the above problems, so that ink may leak out from the orifices of the recording head when the pressure in the ink storage member is high, to the contrary, when the pressure is low, the ink may not be supplied to the recording head.