Existing desktop-type ink jet printers mostly use a print head having a cartridge house. A cartridge has a limited capacity and is removably inserted into the cartridge house to supply ink to the print head. Due to the limited capacity, only a limited number of standard pages can be printed out using a single cartridge. Therefore, it is necessary to replace the cartridge frequently, which is inconvenient to the printer users.
Accordingly, people use a device as shown in FIG. 1, which includes: an ink storage tank 3, the capacity of which is much larger than the cartridge, disposed adjacent to a printer 1, wherein the ink storage tank 3 is connected to a print head 4 via a flexible pipe 2. In this configuration, the ink capacity of one ink storage tank 3 is equivalent to several cartridges and ink liquid may be conveniently added to the ink storage tank 3 at any moment. Therefore, users may print a large number of pages without having to replace the cartridge.
The technical solution described above has provided a relatively primal device for continuously supplying ink. A problem associated with this device is the highest liquid level of the ink storage tank 3 must be equal to or slightly lower than the height at which the nozzle of the print head 4 lies. If the highest liquid level of the ink storage tank 3 is higher than the nozzle of the print head 4, the pressure at the print head will increase and may cause ink to leak out from the print head. The leaking of ink from the print head will contaminate the printer and the print medium. Furthermore, if the lowest liquid level of the ink storage tank 3 is lower than the largest suction lift of the print head, the suction force applied by the print head will not be great enough to draw ink from the ink storage tank to the print head, ultimately causing the printing operation to stop. Therefore, this device for continuously supplying ink must simultaneously meet the following requirements as shown in FIG. 1 (choosing the plane in which the print head 4 lies as a reference, upward from this reference plane is positive and downward from which is negative):
H2≦0; and
|H1|≦S;
wherein H1 is the distance from the lowest part of the ink storage tank 3 to the plane in which the nozzle of the print head 4 lies, H2 is the distance from the highest liquid level in the ink storage tank 3 to the plane in which the nozzle of the print head 4 lies, and S is the largest suction lift of the print head 4. Thus, to satisfy the requirements described above, the height of the ink storage tank 3 will be limited and under a certain floor area, the ink capacity will be limited.
At present, there is a developed technical solution to solve the problem described above. As shown in FIG. 2, which is a functional diagram of a device for continuously supply ink to a wide-format ink jet printer, an ink storage tank 3 may be disposed lowly enough to be out of the largest suction lift of the print head 4. In addition, a pump 5, a relay container 6, the location of which lies in the largest lift, and a sensor are added in this device. After ink liquid in the relay container 6 has been consumed to reach a certain liquid level, the pump 5 will be activated to supply ink from the ink storage tank 3 to the relay container 6. After the relay container 6 has been filled to reach a full liquid level, the pump 5 will be shut off and the passage between the ink storage tank 3 and the relay container 6 will be cut off. This way, supplying ink under constant pressure may be carried out recurrently. This so-called supplying ink under constant pressure means the suction force applied by the print head during operation does not change between zero and the largest suction lift, but changes within the height range of the relay container 6. It has been proven by practice that a print head operating within a relatively small change of suction force will exhibit optimal print quality. However, this ink supply device is relatively complex and expensive because it uses electromechanical devices such as a pump and a sensor. In addition, the print head may be damaged if gas enters into the pipe via the ink outlet port as ink is filled into the ink storage tank.