Flow control system for ink cartridges

Abstract: An ink cartridge system is provided which includes a reservoir (47) maintained at a negative pressure in communication with a printing system (45). As the printing system (45) is activated, ink is expelled from the cartridge which draws ink from the reservoir (47) by capillary action. To prevent the reverse flow of air and ink into the reservoir (47), a control unit (40) is provided. The control unit (40) includes an ink conduit (48) communicating with a standpipe (46). A medial section (62) is provided between the ink conduit (48) and standpipe (46). The medial section (62) includes an opening (63) adapted to receive a ball (80) within the ink conduit (48). The ball (80) is freely movable within the ink conduit (48), but is larger than the opening (63). As a result, the outward flow of ink from the reservoir (47) is allowed, while the backflow of ink and air into the reservoir (47) is prevented by movement of the ball (80) into the opening (63) of the medial section (62).

Description: Background of the Invention The present invention generally relates to ink cartridge printing systems, and more particularly to an ink cartridge having a control unit designed to prevent the reverse flow of ink and air into the cartridge reservoir. The development of sophisticated ink jet printing systems has created a corresponding need for improved ink delivery cartridges. To satisfy this need, ink cartridges have been manufactured which include an ink reservoir in fluid communication with an orifice plate and resistor assembly. Activation of the resistor assembly generates heat which thermally excites the ink and expels it from the cartridge. This delivery procedure is known in the art, and described in the Hewlett-Packard Journal , May 1985, Vol. 36, No. 5. In addition, an exemplary cartridge using thermal ink excitation is illustrated in U.S. Patent No. 4,500,895. In the system described above, ink within the reservoir is normally maintained at a negative pressure. Ink is drawn out of the reservoir by capillary action which occurs when the ink is excited and expelled from the orifice plate. However, this type of system often experiences problems associated with the reverse flow of air and ink into the reservoir. This is caused by the negative pressure within the reservoir which draws air into the cartridge and pulls ink away from the orifice plate. When ink is displaced from the orifice plate, the printing process is interrupted, causing what is commonly known as a "deprime." In addition, the introduction of air into the cartridge and reservoir causes the ink therein to bubble or foam, thereby reducing the operating efficiency of the cartridge. Furthermore, any air in the reservoir will expand when ambient temperatures are increased. This expansion can force ink out of the reservoir and cartridge when not in use, causing uncontrolled leakage. US-A-4527175 describes an ink supply system for nonimpact printers. The system is designed to minimise ink pressure variations at the print head due to sudden stopping, starting or reversal of the print head. To this end, ink is supplied to the print head through a pair of identical, flexible conduits which are connected from first and second spaced apart outlets of an ink container. The container is not airtight with the outside, so that it can act as a pressure absorber. The effect of pressure absorption is still further enhanced by the employment of a pair of novel check valves disposed in each of the conduits, respectively. Each check valve comprises an open-ended tubular arrangement having smaller inner diameter portions at the opposite ends thereof and a larger inner diameter portion between them. Inside the tube is movably provided a spherical member such as a steel ball. The ball has a diameter larger than the smaller inner diameters of the tube but smaller than the larger diameter, so that it is freely movable between the opposite ends of the tube under the pressure of ink. The ball allows ink to flow during normal operation of the check valve, but blocks the flow of ink in response to sudden variations in the pressure of ink across the tube. EP-A-0238829 describes an ink jet print head having a preloaded check valve to prevent leakage of ink from an ink reservoir maintained at positive pressure. The check valve has an opening pressure greater than the gravitational hydrostatic pressure of ink in the reservoir. A variety of methods have been attempted to eliminate problems associated with the reverse flow of ink and air into ink cartridges. For example, a system exists in which a small screen is positioned in the cartridge between the ink reservoir and orifice plate. The surface tension of the ink and small mesh size of the screen minimize the reverse flow of air and ink into the reservoir. However, this technique is not entirely effective, and frequently causes the generation of air bubbles in the cartridge when the vacuum from the reservoir pulls air through the screen. As a result, the operating efficiency of the cartridge is reduced. A need therefore exists for an ink cartridge system having means for effectively controlling the reverse flow of air and ink into the system. The present invention satisfies this need in a manner not heretofore known in the art, as described below. It is an object of the present invention to provide an ink cartridge system of improved efficiency and design. It is another object of the invention to provide an ink cartridge system which delivers ink in a smooth, rapid and uniform manner. It is another object of the invention to provide an ink cartridge system which requires minimal cleaning and maintenance. It is a still further object of the invention to provide an ink cartridge system which uses a minimal number of operating components. It is a still further object of the invention to provide an ink cartridge system which minimizes problems associated with the introduction of air into the cartridge. It is an even further object of the invention to provide an ink cartridge system which minimizes problems associated with ink deprimes, thereby facilitating a smooth and uninterrupted flow of ink. The present invention provides a flow control unit for use in an ink cartridge having a reservoir maintained at a negative pressure in combination with printing means for withdrawing ink from said reservoir comprising: a first conduit in fluid communication with said reservoir; a second conduit positioned between and in fluid communication with said first conduit and said printing means, said second conduit comprising a primary ink channel and a secondary ink channel in fluid communication with each other; a medial section positioned between said first conduit and said second conduit, said medial section defining an opening between said first conduit and said primary ink channel of said second conduit; and a spherical ink flow control member positioned within said primary ink channel of said second conduit, said control member having a diameter greater than that of said opening, said primary ink channel of said second conduit being sufficiently large to allow the free movement of said control member therein, said secondary ink channel having a height which is less than said diameter of said control member and a width which is greater than said diameter of said control member, said secondary ink channel allowing ink to flow therethrough while preventing passage of said control member therethrough, said control member allowing ink to flow outwardly from said reservoir through said first conduit, medial section and second conduit to said printing means, while preventing the reverse flow of air and ink into said cartridge and reservoir by blocking said opening. For convenience, the first conduit is also referred to as the ink delivery stand pipe and the free-floating spherical member is also referred to as the ball. In operation, ink moves out of the reservoir, through the standpipe, and into the ink conduit for delivery from the cartridge. However, the reverse movement of air and ink into the reservoir is prevented by blockage of the opening in the medial section with the ball. Specifically, the ball is carried by the ink into the opening of the medial section, preventing the flow of ink and air therethrough. As a result, ink deprimes and the generation of air bubbles within the cartridge are controlled. Moreover, the ball is especially sensitive to directional changes in ink flow, since it is unencumbered and entirely free-floating. These and other objects, features and advantages of the invention will be more fully described in the following brief description of the drawings and detailed description of a preferred embodiment presented below. Brief Description of the Drawings Fig. 1 is a perspective view of an exemplary ink cartridge designed to incorporate the flow control unit of the present invention. Fig. 2 is an exploded perspective view of the cartridge of Fig. 1. Fig. 3 is a cross-sectional view of a flow control unit manufactured in accordance with the invention. Fig. 4 is a view taken along lines 4-4 of Fig.3. Fig. 5 is a view taken along lines 5-5 of Fig.3. Detailed Description of a Preferred Embodiment The present invention involves an improved ink cartridge system which is characterized by a high degree of efficiency and minimal maintenance requirements. An ink cartridge 10 usable in connection with the invention is illustrated in Fig. 1. This type of cartridge is manufactured by the Hewlett-Packard Company of Palo Alto, California. With reference to Fig. 2, the cartridge 10 includes a housing 12, backing plate 14, and bladder-like ink reservoir 16. Also included is a substrate 20 with an ink feed hole 22 and thin film resistor pattern 23 thereon. Secured to the substrate 20 as shown in Fig. 2 is an orifice plate 26 having drop expulsion holes 28 which communicate with the ink feed hole 22. Additional operating characteristics of this apparatus are presented in U. S. Patent 4,500,895 which is incorporated by reference. However, the invention as described herein is not limited to any specific type of ink cartridge or printing system. Instead, it may be used with any ink delivery/printing system having an ink reservoir maintained at a negative pressure. With reference to Figs. 3-5, a flow control unit 40 produced in accordance with the invention is illustrated. Control unit 40 includes an outer cover 42 and an ink feed orifice 44. The ink feed orifice 44 communicates with an ink printing/delivery system 45. The system 45 may take a variety of forms, including the resistor unit described above and discussed in U. S. Patent 4,500,895. If the control unit 40 is used in the cartridge 10 of Figs. 1 and 2, the substrate 20 could function as the outer cover 42. Likewise, the ink feed orifice 44 could operate as the ink feed hole 22 described above. The interior of the control unit 40 includes a first conduit 46 (commonly known is a standpipe) which is attached to an ink reservoir 47 maintained at a negative pressure. If the control unit 40 is used in the cartridge 10 of Figs. 1 and 2, the reservoir 47 may consist of the bladder-like structure 16 shown in Fig. 2. The control unit 40 also includes a second conduit 48 preferably consisting of a primary ink channel 49 which is circular in cross section as illustrated in Fig. 5, and having a diameter D₁ (Fig. 3). The primary ink channel 49 communicates with a secondary ink channel 56 shown in Fig. 3. In a preferred embodiment, the primary ink channel 49 is positioned at a angle "X" of about 90 degrees relative to the secondary ink channel 56 (Fig. 3.) With continued reference to Fig. 3, the secondary ink channel 56 has a height H₁. In a preferred embodiment, the secondary ink channel 56 has a maximum width W₁ at position 57 (Figs. 4-5.) The secondary ink channel 56 progressively decreases in width from position 57 toward ink feed orifice 44 due to the use of inwardly sloping side walls 58 illustrated in Figs. 4-5. Positioned between the primary ink channel 49 and the standpipe 46 is a frustoconical medial section 62 illustrated in Fig. 3. The medial section 62 has an opening 63 with a diameter progressively decreasing in the direction of reservoir 47. The opening 63 is surrounded by an annular, inwardly sloping interior wall 64. The opening 63 progressively decreases in diameter due to the inwardly sloping configuration of the wall 64. Positioned within the primary ink channel 49 is a spherical flow control member in the form of a ball 80. The ball 80 is preferably constructed of a material impervious to corrosion or reaction with ink. The ball 80 may be manufactured of a variety of materials including polypropylene plastic. It has a diameter D₂ which is less than the diameter D₁ of the primary ink channel 49. As a result, the ball 80 may freely move within the primary ink channel 49 (Fig. 3). Free, unencumbered movement of the ball 80 within the primary ink channel 49 is important. Accordingly, the primary ink channel 49 should be sufficiently large to allow the free movement of ball 80 therein whether the channel 49 is circular in cross section or not. With respect to the secondary ink channel 56, the diameter D₂ of the ball 80 is less than the width W₁ (Fig.4), but greater than the height H₁ (Fig. 3) of the secondary ink channel 56. This design prevents the ball 80 from passing out of the primary ink channel 49 into the secondary ink channel 56, as shown in dashed lines in Fig 3. However, ink is allowed to pass between channel 49 and channel 56 because the diameter D₂ of the ball 80 is less than the width W₁ of the secondary ink channel 56, as previously described and illustrated in Fig. 4. In addition, the ball 80 is larger than the opening 63 as shown in Fig. 3. This design prevents the ball 80 from passing through the medial section 62 into the standpipe 46, as described in greater detail below. In operation, ink is expelled from the cartridge using the printing/delivery system 45 which may take a variety of forms, as described above. As a result, ink flows by capillary action out of the reservoir 47 through the standpipe 46, medial section 62, primary ink channel 49, and secondary ink channel 56 prior to ejection. The ball 80 remains free-floating within the primary ink channel 49 due to the dimensional differences between the ball 80 and the primary ink channel 49 as previously described. As ink is delivered, the ball 80 assumes the position shown in dashed lines in Fig. 3. However, if the negative pressure within the reservoir 47 causes air to enter the cartridge, ink will be displaced from the printing/delivery system. As a result, ink and air will begin moving in a reverse direction toward the reservoir 47. When this occurs, the ball 80 is moved by the ink toward and into the medial section 62. Since the ball 80 is larger than the opening 63 in the medial section 62, it will engage the wall 64 surrounding the opening 63 as shown in solid lines in Fig. 3. As a result, ink and air are prevented from flowing rearwardly into the standpipe 46 and reservoir 47, thereby minimizing the introduction of air into the reservoir and controlling deprimes. Use of the control unit 40 as described herein represents an important advance in the art of ink delivery. It offers superior results compared with the screen systems previously discussed. Moreover, the use of a free-floating, unencumbered ball 80 enables the ball 80 to be extremely responsive to minute directional changes in ink flow. As a result, the control unit 40 operates instantaneously, and offers minimal resistance to the outward flow of ink in comparison with other flow control systems. Having herein described a preferred embodiment of the invention, it is anticipated that suitable modifications may be made thereto by individuals skilled in the art. Accordingly, the invention shall only be construed in connection with the following claims:

Claims: A flow control unit (40) for use in an ink cartridge having a reservoir (47) maintained at a negative pressure in combination with printing means (45) for withdrawing ink from said reservoir (47) comprising: a first conduit (46) in fluid communication with said reservoir (47); a second conduit (48) positioned between and in fluid communication with said first conduit (46) and said printing means (45), said second conduit (48) comprising a primary ink channel (49) and a secondary ink channel (56) in fluid communication with each other; a medial section (62) positioned between said first conduit (46) and said second conduit (48), said medial section (62) defining an opening (63) between said first conduit (46) and said primary ink channel (49) of said second conduit (48); and a spherical ink flow control member (80) positioned within said primary ink channel (49) of said second conduit (48), said control member (80) having a diameter greater than that of said opening (63), said primary ink channel (49) of said second conduit (48) being sufficiently large to allow the free movement of said control member (80) therein, said secondary ink channel (56) having a height (H1) which is less than said diameter of said control member (80) and a width (W1) which is greater than said diameter of said control member (80), said secondary ink channel (56) allowing ink to flow therethrough while preventing passage of said control member (80) therethrough, said control member (80) allowing ink to flow outwardly from said reservoir (47) through said first conduit (46), medial section (62) and second conduit (48) to said printing means (45), while preventing the reverse flow of air and ink into said cartridge and reservoir (47) by blocking said opening (63). A flow control unit (40) according to claim 1 wherein said opening (63) has a progressively decreasing diameter. A flow control unit (40) according to claim 1 or 2 wherein said primary ink channel (49) is positioned at a 90° angle relative to said secondary ink channel (56). A flow control unit (40) according to any preceding claim, wherein said spherical ink flow control member (80) is comprised of plastic. A flow control unit (40) according to any preceding claim wherein said medial section (62) comprises an annular, inwardly angled interior wall (54) defining said opening (63), said spherical ink flow control member (80) being adapted to engage said wall (64) to block said opening (63) in order to prevent said reverse flow of said air and ink into said cartridge and reservoir (47).

Inventors: DUNN JOHN B R, LEWEY KAREN M, MCDANIEL LOWELL R, SHELLEY PATRICK W, DUNN, JOHN B.R., LEWEY, KAREN M., MCDANIEL, LOWELL R., SHELLEY, PATRICK W.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1990
Main classification: B41J2
IPC codes: B41J2