1. Field of the Invention
The present invention relates to a liquid discharging device which produces a bubble by exerting a heat energy to a liquid and discharges the liquid utilizing the bubble, and more specifically a liquid discharging device which comprises a movable member displaced by utilizing production of a bubble.
A term of xe2x80x9crecordingxe2x80x9d used in this specification means impairment of not only a significant image such as a character or a figure but also of an insignificant image such as a pattern to a recording medium.
2. Related Background Art
This is conventionally known an ink-jet recording method, or the so-called bubble-jet recording method, which produces a bubble by exerting an energy such as heat to liquid ink contained in a flow path of a recording apparatus such as a printer and discharges the ink through a discharging port utilizing a force generated by an abrupt volumetric change caused by the production of the bubble, thereby allowing the ink to adhere to a recording medium so as to form an image. A recording apparatus which uses the bubble-jet recording method generally comprises a discharging port to discharge ink, a flow path communicated with the discharging port and an electrothermal converting element as energy generating means as disclosed by U.S. Pat. No. 4,723,129.
Such a recording method permits not only recording a high quality image at a fast speed and with low noise but also arranging discharging ports to discharge ink at a high density in a head adopted to carry out the method, thereby having a lot of merits such as a capability to record a high resolution image and even a color image easily with a compact apparatus. Accordingly, the bubble-jet recording method has recently been utilized for many kinds of office appliances such as printers, copying machines and facsimiles, and further for industrial systems such as printing machines.
Demands which are mentioned below have recently been stronger as a bubble jet method has been utilized for products in many fields.
There have been proposed driving conditions to provide a liquid discharging method which permits stable production of a bubble for favorable discharge of ink at a fast speed, thereby obtaining a high quality image as well as improvement in a shape of a flow path for a liquid discharging head which refills a discharged liquid into a flow path at a fast speed in terms of high speed recording.
Speaking apart from such a head, Japanese Patent Application Laid-Open No. 6-31918 pays attention to a back wave (a pressure applied in a direction reverse to a direction toward discharging ports) which is produced when a bubble is produced and discloses an invention of a structure to prevent the back wave due to which a liquid discharging energy is lost. In the structure according to this invention, a triangular plate like member is opposed to a heater which produces a bubble. This invention suppresses the back wave with the triangular plate like member temporarily and slightly. However, the patent makes no reference to correlation between growth of the bubble and the triangular member nor has a conception of this correlation, whereby the invention mentioned above poses problems which are below.
The invention disclosed by the patent cannot stabilize a forms of a liquid drops due to a fact that the heater is located at a bottom of a cavity and cannot the communicated linearly with a discharging port and allows the bubble to grow within an entire range from a side to an opposite side of the triangular plate like member due to a fact that the bubble is allowed to grow from surroundings of a vertex portion of a triangle, thereby providing a result that the bubble is grown as usual in a liquid as if the plate like member were not used. Accordingly, existence of the plate like member has not relation to a grown bubble. Inversely, the plate like member is surrounded as a whole by the bubble, and allows a refilling liquid to the heater located in the cavity to produce a turbulent flow at a contraction stage of the bubble and constitutes a cause for accumulation of minute bubbles in the cavity, thereby disturbing a principle itself to discharge the liquid on the basis of growth of the bubble.
On the other hand, EP Publication Laid-Open No. 436047A1 proposes an invention which alternately opens and closes a first valve which shields a section in the vicinity of discharging ports from a bubble producing section, and a second valve which shields the bubble producing section and an ink supplying section (FIGS. 4 through 9 in EP No. 436047A1). However, this invention partitions these three sections into two, thereby allowing ink which follows a liquid drop to remarkably tail at a discharging stage, thereby producing satellite dots in a number prettily larger than that of satellite dots produced by the ordinary discharging method which grows, contracts and breaks a bubble (assumed to be incapable of utilizing an effect of retreat of a meniscus caused by breaking the bubbles). Furthermore, the invention allows discharged liquid drops to be remarkably variable and provides an extremely low discharge response frequency which is not a practically usable level since it is incapable of supplying the liquid to a region in the vicinity of a discharging port until a next bubble is produced through it allows the liquid to be supplied into the bubble producing section as the bubble is broken at a refilling stage.
The applicant has proposed a large number of inventions using movable members (a plate like member which has a free end on a side of discharging ports from a fulcrum or the like) which can effectively contribute to discharge of liquid drops quite differently from the prior art described above. Out of the inventions, Japanese Patent Application Laid-Open No. 9-48127 discloses an invention which restricts an upper limit of displacement of the movable member described above to prevent a behavior of the movable member from being slightly disturbed. Furthermore, Japanese Patent Application Laid-Open No. 9-323420 discloses an invention which enhances a refilling capability by shifting a common upstream liquid chamber toward a free end, or downstream, relative to the movable member utilizing a merit of the movable member described above. These inventions are based on a conceptional premise that growth of bubbles is open at a breath toward a side of discharging ports from a condition where the bubble is enwrapped by the movable member temporally and pay no attention to individual factors of the bubbles as a whole which relate to formation of liquid drops or correlation among these factors.
At a next step, the applicant disclosed an invention which partially opens a bubble producing region from the movable member described above as an invention which pays attention to a growth of bubbles due to propagation of a pressure wave as a factor related to liquid discharge (acoustic wave) in Japanese Patent Application Laid-Open No. 10-24588. However, even this invention pays attention only to the growth of the bubbles at a liquid discharging stage, but not to the individual factors of the bubbles as a whole which relate to the formation of the liquid drops themselves nor correlation among the factors.
Though it is conventionally known that discharge of a liquid is largely influenced by a front portion (edge chutter type) of bubbles produced by film boiling, no one has ever paid attention to this portion which may effectively contribute to formation of liquid drops to be discharged and the inventor et al. eagerly made researches to accomplish an invention which solves these technical problems.
Paying attention to the displacement of the movable member described above and produced bubbles, the inventor et al. obtained useful knowledge which is described below.
Paying attention to xe2x80x9ca form of an inter-flow path wallxe2x80x9d which is effective also for restriction of growing bubbles as a new structure to restrict the movable member, the inventor et al. conceived to restrict an upper limit of displacement of the movable member for growth of the bubbles using an inter-flow path wall. Obtained knowledge was that a stopper of the movable member which is disposed on the inter-flow path wall makes it possible to broaden a range permissible for minute working together with an image forming area in the presence of bubbles while allowing a required liquid flow.
Speaking concretely, a larger clearance between the movable member and the inter-flow path wall which is located sideways is more desirable to absorb manufacturing variations of the movable member which displaces in the flow path.
Inversely, the larger clearance allows the bubbles to penetrate between the movable member and the interflow path wall which is located sideways as the bubbles grow, whereby the bubbles may grow up to a top surface of the movable member. Accordingly, it is considered that the clearance must be narrow in the end. However, these problems which are conflicting with each other can be solved by imparting a stopper function for the movable member to the inter-flow path wall which is located sideways. Speaking concretely, manufacturing variations of the flow path and the movable member can be absorbed even when the clearance is large (for example, 5 xcexcm to 8 xcexcm). The clearance between the movable member and a side stopper 12b is gradually narrowed as the movable member displaces along with growth of the bubbles, the stopper starts to restrict passage of the bubbles when the clearance is on the order of 3 xcexcm and passage of the bubbles can be completely checked in the vicinity of a contact portion between the side stopper 12b and a portion of the movable member.
The present invention has been achieved from a viewpoint and the new knowledge which have been described above.
Furthermore, growth of the bubbles was accelerated in a space between the movable member and a bubble producing surface in a direction reverse to that toward discharging ports by ensuring the restriction of the upper limit of the growth of bubbles from a bubble producing surface when the side stopper 12b is disposed. This growth of the bubbles may be neglected since it is not a factor which lowers a discharge efficiency, but the inventor et al. made examinations whether or not the growth of the bubbles could be rationally utilized for the displacement of the movable member. As a result, the inventor et al. obtained knowledge that the growth of the bubbles could rationally be utilized by integrating the movable member with a pressure wave receiver which is disposed at a location close to (for example, 20 xcexcm or shorter) but apart from the bubble producing surface.
Furthermore, checks of the movable member which extends from the fulcrum to the free end clarified that it actually has a movable fulcrum between the free end and the fulcrum. It was judged that the variations were conventionally caused due to design which was made on the basis of a shifting volume of the movable member calculated from a displacement angle "THgr" for a distance 1 between the free end and the fulcrum.
Examinations which were made while paying attention to these facts clarified that the variations can be corrected by specifying a spatial volume substantially required for moving the movable member.
Furthermore, the present invention also provides a method to manufacture a liquid discharging head which embodies the knowledge described above.
A primary object of the present invention is to provide a liquid discharging head for discharging a liquid through a discharging port with an energy generated by producing a bubble comprising an heat generating element which generates a heat energy for producing the bubble in the liquid, a discharging port which discharges the liquid, a liquid flow path which is communicated with the discharging port and has a bubble producing region producing the bubble in the liquid, a movable plate which is disposed in the bubble producing region and displaced as the bubble grows, and a restricting member which restricts displacement of the movable plate within a desired range, wherein the liquid flow path is composed of a substrate which is equipped with the heat generating element and substantially planar, an opposed plate which is opposed to the substrate, and two side walls located between the substrate and the opposed plate,
wherein the movable plate has a free end which has a width larger than that of the heat generating element,
wherein the free end of the movable plate is opposed to a middle of the bubble producing region formed by the heat generating element, the movable plate is opposed to the substrate and a side end of the movable plate is displaced while it is opposed to the side walls, and
wherein the restricting member has a tip restricting portion which is to be brought into substantial contact with the free end of the displaced movable plate, and a side restricting portion which is located beside the bubble producing region and on a side opposite to the substrate with regard to the movable plate, and to be brought into substantial contact at least partially with both sides of the side end of the displaced movable plate so as to keep open the middle of the liquid flow path, whereby the bubble produced from the bubble producing region is restricted by the contact between the movable plate and the side restricting portion.
Another object of the present invention is to provide a liquid discharging head for discharging a liquid through a discharging port with an energy generated by producing a bubble comprising a liquid flow path which comprises an heat generating element which generates a heat energy for producing the air bubble in the liquid, a discharging port which discharges the liquid, a liquid flow path which is communicated with the discharging port and has a bubble producing region producing the air bubble in the liquid, a movable plate which is disposed in the air bubble producing region and displaced as the air bubble grows, and a restricting member which restricts displacement of the movable plate within a desired range, and
wherein the movable plate has a convexity which is close to the air bubble producing region and protrudes from the movable plate toward the substrate, the restricting member is disposed in opposition to the air bubble producing region of the liquid flow path which has the air bubble producing region forms a space which is substantially closed except the discharging port when the displaced movable plate is brought into substantial contact with the restricting member.
Still another object of the present invention is to provide a method to discharge a liquid through a discharging port of a liquid discharging head with an energy generated by producing a bubble comprising an heat generating element which generates a heat energy for producing the air bubble in the liquid, the discharging port which discharges the liquid, a liquid flow path which is communicated with the discharging port and has a bubble producing region producing the air bubble in the liquid, a movable plate which is disposed in the air bubble producing region and displaced as the air bubble grows, and a restricting member which restricts displacement of the movable plate within a desired range, wherein the liquid flow path is composed of a substrate which is equipped with the heat generating element and substantially planar, an opposed plate which is opposed to the substrate, and two side walls located between the substrate and the opposed plate,
wherein the movable plate has a free end which has a width larger than that of the heat generating element,
wherein the free end of the movable plate is opposed to a middle of the air bubble producing region formed by the heat generating element, the movable plate is opposed to the substrate and a side end of the movable plate is displaced while it is opposed to the side walls,
wherein the restricting member has a tip restricting portion which is to be brought into substantial contact with the free end of the displaced movable plate, and a side restricting portion which is located beside the air bubble producing region and on a side opposite to the substrate with regard to the movable plate, and to be brought into substantial contact at least partially with both sides of the side end of the displaced movable plate so as to keep open the middle of the liquid flow path, and
wherein the method comprises a step to bring the movable plate into contact with the restricting member before maximum growth of the air bubble and bring the side restricting portion into contact with the movable plate to restrict the air bubble produced from the air bubble producing region, whereby the liquid flow path having the air bubble producing region forms a space which is substantially closed except the discharging port.
A further object of the present invention is to provide a method to discharge a liquid through a discharging port of a liquid discharging head with an energy generated by producing a bubble comprising an heat generating element which generates a heat energy for producing the air bubble in the liquid, a discharging port which discharges the liquid, a liquid flow path which is communicated with the discharging port and has a bubble producing region producing the air bubble, a movable plate which is disposed in the air bubble producing region and displaced as the air bubble grows, and a restricting member which restricts displacement of the movable plate within a desired range, wherein the liquid flow path is composed of a substrate which is equipped with the heat generating element and substantially planar, an opposed plate which is opposed to the substrate, and two side walls which are located between the substrate and the opposed plate,
wherein the movable plate has a free end which has a width larger than that of the heat generating element,
wherein the free end of the movable plate is opposed to a middle of the air bubble producing region formed by the exohermic body, the movable plate is opposed to the substrate and a side end of the movable plate is displaced while it is opposed to the side walls,
wherein the restricting member has a tip restricting portion which is to be brought into substantial contact with the free end of the displaced movable plate, and a side restricting portion which is located beside the air bubble producing region and on a side opposite to the substrate with regard to the movable plate, and to be brought into substantial contact at least partially with both sides of the side end of the displaced movable plate so as to keep open the middle of the liquid flow path, and
wherein the method comprises a step to make a distance between the movable plate and the side restricting portion shorter than a gap between the movable plate and the side walls as the movable plate comes nearer the side restricting portion after allowing the liquid to flow around the movable plate which is displaced as the air bubble grows, thereby restricting advance of the air bubble toward the movable plate.