Abstract:
The present invention provides an ink supply mechanism for use in an electrostatic ink jet recording apparatus having a stable recording quality by maintaining a predetermined amount and a predetermined pressure of ink in the discharge section. The ink supply mechanism includes: a printing head 11 having an ink discharge section; an ink tank 10; an ink flow-in pipe path 30 provided between the printing head and the ink tank, and having a flow-in pump for supplying ink from the ink tank to the printing head; and an ink flow-out pipe path 31 having a flow-out pump for recovering the ink from the printing head to the ink tank.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink supply mechanism in an electrostatic ink jet recording apparatus and in particular, to an ink supply mechanism for use in a serial type electrostatic ink jet recording apparatus. 
     2. Description of the Related Art 
     For example, Japanese Patent Publication (unexamined) A7-76105 discloses an ink chamber pressure regulating means for use in an ink jet recording apparatus using a liquid ink as a recording material. 
     This ink chamber pressure regulating means includes a pressure regulating valve having a slit in an elastic member. When the pressure difference between the inside and the outside of the ink tank increases, the elastic member is greatly deformed to open the slit so that the interior of the ink tank communicates with the atmospheric air so that the pressure in the ink tank increases up to the atmospheric pressure, thus regulating the pressure in the ink tank. 
     Moreover, Japanese Patent Publication (unexamined) A61-112648 discloses a printing head including a pressure regulating path pipe having a first end communicating with the ink changer and a second end closed. A pressure change in the ink chamber is absorbed by a volume change of a closed air layer. 
     However, the aforementioned devices have various problems as follows. 
     The first problem is efficiency of absorbing the pressure fluctuation. 
     The pressure regulating device should rapidly absorb a shock type pressure change when one has occurred, so as to maintain a predetermined inner pressure of the ink chamber. The shock type pressure is caused by high-speed ink movement in the ink chamber in the main scan direction (first reason) or by a pressure fluctuation generated from an ink circulation member such as a pump (second reason). In the aforementioned configuration having a closed air chamber, it is difficult to sufficiently absorb the pressure fluctuation caused by the second reason. 
     This is because the ink chamber communicates with the ink circulator and a pressure wave is transferred in the fluid. 
     That is, in order to effectively absorb these pressure fluctuations, it is preferable that the ink in the ink chamber be disconnected as a fluid from the ink in the ink circulator. 
     The second problem is that these pressure regulating means are intended for the ink almost in a still state. Most of the conventional ink jet printers do not need an ink circulation, and for the ink discharged from a nozzle, a new ink is added by the capillary effect or mechanical force. These methods can perform pressure adjustment. However, in an ink jet printer of serial type in which the ink continuously circulates, it is difficult to maintain a predetermined pressure, and ink circulation may be disturbed. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an ink supply mechanism in an electrostatic ink jet recording apparatus, which mechanism enables to maintain a constant discharge ink amount under a constant pressure, thus improving the recording quality. 
     The ink supply mechanism according to the present invention includes: a printing head having an ink discharge section; an ink tank; an ink flow-in pipe path 30 provided between the printing head and the ink tank, and having a flow-in pump for supplying ink from the ink tank to the printing head; and an ink flow-out pipe path 31 having a flow-out pump for recovering the ink from the printing head to the ink tank. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows an ink supply mechanism according to an embodiment of the present invention. 
     FIG. 2 is an enlarged cross sectional view of a printing head according to the embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 schematically shows an ink circulation system of the electrostatic ink jet recording apparatus according to the present invention. 
     As shown in FIG. 1, an ink tank 10 is connected to a printing head block 11 (hereinafter, referred to as the head block) via at least three pipe paths. 
     One of the three paths is an ink flow-in pipe 30 through which an ink 41 flows from the ink tank 10 to the head block 11 and which is provided with a flow-in quantitative pump 34. 
     Another path is an ink flow-out pipe through which the ink 41 is flows out from the head block 11 to the ink tank 10 and which is provided with a flow-out quantitative pump 35. 
     Moreover, in the present embodiment, there is provided an ink return pipe 32 connecting the head block 11 to the ink tank 10 so that an excessive portion of the ink 41 can drop into the ink tank 11 by the gravitational force. 
     FIG. 2 is a cross sectional view of the head block 11. 
     The ink flow-in pipe 30 is connected to an ink flow-in path 37 formed in the head block 11. The ink flow-in path is branched to paths: one of them (hereinafter, referred to as a first branch) leads to the ink chamber 12 and the other (hereinafter, referred to as a second branch) leads to a flow-in regulating section 26. 
     This flow-in pressure regulating section 26 is provided below an ink discharge section 13 (hereinafter, referred to as the discharge section). The flow-in pressure regulating section includes an atmospheric opening 20 at its top and a space having an ink return path 39 at its bottom. The ink flow-in path 21 branched from the ink flow-in pipe 30 protrudes upward into the space of the flow-in pressure regulating section 26 and the upper end is open. 
     The ink 41 in the ink chamber 12 goes to the ink flow-out pipe via an ink flow-out path 38 in the head block 11. 
     Moreover, the ink flow-out path 38 includes a flow-out pressure regulating section 27 having an air chamber 25 formed in the head block 11. This air chamber 25 has a partition 23 to divide the air chamber 25 into a space for the ink 41 and a space having an elastic film F. These spaces communicate with each other through a small hole 24 formed in the partition 23. 
     The elastic film F has a surface parallel to the paper feed direction 40 which is vertical to the movements of the head block 11. 
     Description will now be directed to the operation of the present embodiment with reference to FIG. 1 and FIG. 2. 
     The ink 41 flowing from the ink flow-in pipe 30 into the head block 11 is branched into the two branches within the head block 11. Through the first branch, the ink 41 flows into the ink chamber 12 via the ink flow-in path 37. Through the second branch, the ink 41 flows into the flow-in pressure regulating section 26. The ink which has flown into the ink chamber 12 flows through the ink discharge section 13 forming a free surface exposed to the atmospheric air, and goes into the flow-out pressure regulating section 27 and then into the ink flow-out pipe 31 and returns into the ink tank 10. 
     The ink flow-out and flow-in are both forced by the quantitative pumps, so that a predetermined amount of the ink 41 flows constantly at the tip end of the printing head. Actually, however, the consumption of the ink 41 for printing operation, cleaning operation, and leak is not constant and the pump performance may not be constant. Accordingly, a necessary flow-in amount and a necessary flow-out amount are not always constant, and it is difficult to maintain a constant amount of the ink 41 in the ink chamber 12. What can be done is to define the flow-in ink amount sufficiently greater than the flow-out ink amount and to make the pipe path resistance into the flow-in pressure regulating section 26 sufficiently smaller than the pipe path resistance into the ink chamber 12. 
     Moreover, the head of the ink flowing into the flow-in pressure regulating section 26 is adjusted to be lower than the discharge section by 5 to 10 mm. 
     Thus, the ink 41 which has flown into the head block 11 is branched into the flow-in pressure regulating section 26 and begins to circulate through the ink return pipe 32. 
     Here, in the second branch, i.e., the flow-in path 37, the ink 41 comes up to the vicinity of the ink chamber 12 by the liquid pressure and stops at the height 44 where the ink flows into the flow-in pressure regulating section 26. 
     Next, when the flow into the flow-in pressure regulating section 26 is closed by an electromagnetic valve or the like, the ink flows into the ink chamber 12 and ink circulation starts within the ink flow-out pipe 31. Immediately after this, the flow into the flow-in pressure regulating section 26 is opened. Thus, the ink 41 returns into the ink flow-out returns to the ink tank 10 through the ink flow-out pipe 31 and the ink return pipe 32. The ink inner pressure at the tip end of the discharge section 13 is maintained under a negative pressure corresponding to the difference between the head 44 where the ink flows into the flow-in pressure regulating section 26 and the ink head 46 at the discharge section. 
     The amount of the ink 41 coming from the ink chamber 12 is fixed by the performance of the flow-out pump 34 and an excessive portion of the ink 41 is recovered by the ink return pipe 32. Thus, it is possible to create a stationary state, i.e., to maintain a constant amount of the ink at the tip end of the discharge section while the ink is circulating under a constant pressure. 
     In this stationary state, a vibration may be caused by situations as follows. 
     (1) pressure fluctuation during a spacing operation caused by an external shock such as operation of the ink flow-in pipe 30 or the ink-flow-out pipe 31 
     (2) Pressure fluctuation during a spacing operation caused by an inertia of the ink flow-in pipe 30 or the ink-flow-out pipe 31 itself. 
     (3) Pressure fluctuation during a spacing operation caused by the inertia of the ink 41 itself in the head block 11. 
     (4) Mechanical vibration during operation of the flow-in pump 34 or the flow-out pump 35. 
     Among these reasons, the (1) is considered to have the greatest affect. In the present embodiment, the ink flow-in pipe 30 and the ink flow-out pipe 31 are directly connected to the flow-in pump 35 and the flow-out pump 35, respectively. Accordingly, the ink flow is maintained constant at the end connected to the pumps and no flow fluctuation is caused by pressure fluctuation by spacing. 
     The (2), (3), and (4) are considered to have comparatively small vibrations, which are all absorbed in the flow-in pressure regulating section 26 when passing through the air chamber open to the atmosphere. Moreover, in the flow-out pressure regulating section 27, pressure fluctuations are absorbed in the pressure drop and air volume change by deformation of the elastic film F in the closed air chamber 25. 
     According to the embodiment of the present invention, the ink flow-in pipe and the ink flow-out pipe are directly connected to the flow-in pump and the flow-out pump so that the ink flow is made constant at the ends where the pumps are attached, thus preventing the pressure fluctuation during a spacing operation. 
     Moreover, the pressure fluctuation during a movement in the main scan direction is effectively attenuated in the pressure regulating section. This stabilizes the ink meniscus at the discharge section. 
     Thus, it is possible to improve the recording quality in a serial printer. 
     Furthermore, the pressure adjustment can be realized only by the pipe layout in the small head block in combination with the air chamber and the elastic film. This enables to effectively attenuate the pressure fluctuation by using a small mechanism. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristic thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 
     The entire disclosure of Japanese Patent Application No. 10-247755 (Filed on Aug. 19 th , 1998) including specification, claims, drawings and summary are incorporated herein by reference in its entirety.