Insertable baffle for an ink supply reservoir

Abstract: A baffle assembly (10) for insertion into an ink supply reservoir (12) includes a first baffle plate (14) having a first end and a second end, wherein a first end plate (18a) is coupled to the first end of the first baffle plate and a second end plate (18b) is coupled to the second end of the first baffle plate. The first baffle plate, the first end plate, and the second end plate form an integral structure. When the baffle assembly is inserted into the ink supply reservoir, a distance, "b", between the first baffle plate and an adjacent side-wall of the ink supply reservoir satisfies the inequality relationship b<(g/a)Dm/2k, wherein "g" is the local acceleration of gravity; "a" is the acceleration experienced by the ink supply reservoir during a change in a travel direction, "Dm" is the change in an ejected ink drop mass due to a change in an ink reservoir pressure in the ink supply reservoir, and "k" is a slope of the ink drop mass versus the ink reservoir pressure. The baffle assembly loosely divides a volume of the ink supply reservoir into a plurality of smaller compartments. An ink flow between the plurality of compartments may be provided by a gap between the first baffle plate and the floor of the ink supply reservoir.

Description: The present invention relates to a baffled ink supply reservoir, and more particularly, to a baffle assembly for insertion into an ink supply reservoir. Baffle elements have long been used to limit the amount of movement of the liquid in a reservoir. Baffles have been incorporated into ink jet print head cartridges to reduce the mass of the liquid ink allowed to slosh unimpeded by the containing walls of the ink supply reservoir. The use of baffles in ink reservoirs has been disclosed, for example, in U.S. Patent Nos. 5,408,257; 4,631,558; 4,484,202; and 4,463,362. Prior baffles incorporated into ink supply reservoirs are integral with, or permanently attached to, at least one of the walls forming the ink supply reservoir. U.S. Patent No. 5,408,257 discloses an ink tank, or reservoir, having an inner wall portion or member attached to the bottom face of a sub-tank, and arranged in a diagonal direction to prevent ink in the sub-tank from vibrating greatly. U.S. Patent No. 4,631,558 discloses an ink liquid reservoir mounted on a reciprocating cartridge in an ink jet system printer having a plurality of standing plates that are disposed in the ink liquid reservoir in a manner such that the top free edges of the standing plates are separated from the sealing wall of the ink liquid reservoir. The standing plates are secured to the bottom wall of the ink liquid reservoir. U.S. Patent No. 4,484,202 discloses an ink reservoir containing a plurality of vertically arranged baffles, or plate elements. The plate elements create a series of narrow compartments. An opening is provided in each baffle plate to enable flow of ink fluid among the separate compartments formed by the baffles. The baffles constrain excessive movement of the ink into narrow spaces as the print head is moved in a lateral direction by an appropriate carriage during the printing operation. U.S. Patent No. 4,463,362 discloses an ink reservoir which includes a plurality of baffles to provide individual ink tanks for print heads and to prevent or substantially minimize the sloshing motion of the ink as the reservoir is accelerated and decelerated during the printing operation. The baffles are in the form of plates extending from the front wall to the rear wall of the reservoir and are formed as an integral part of the reservoir at the floor thereof. A plurality of apertures are provided in the baffle plates near the bottom thereof and located near the rear wall of the reservoir for equalizing the levels of ink in the respective baffle-formed chambers or tanks. Regardless of whether the baffles are formed integral with the ink supply reservoir body, or are later attached to one or more of the walls of the ink reservoir body, the baffles form rigid structures which generate shock waves within the ink as the ink is sloshed from side-to-side in the ink supply reservoir. Furthermore, ink supply reservoirs having rigidly mounted baffles are complex to manufacture, in that either the baffles must be formed as a part of the reservoir body during the molding process, or the baffles are separately molded from the reservoir body and attached to one or more walls of the ink supply reservoir after the ink supply reservoir is molded, thereby requiring additional steps in its manufacture. According to the present invention there is provided a printer cartridge comprising a reservoir body forming a container for storing a supply of ink, and a baffle assembly positioned in said reservoir body, characterised in that said baffle assembly is not affixed to or integral with said reservoir body. The baffle assembly may comprise a first baffle plate having a first end and a second end, a first end plate coupled to the first end of the first baffle plate and a second end plate coupled to the second end of the first baffle plate. In preferred embodiments of the invention, the first baffle plate, the first end plate, and the second end plate form an integral structure. Preferably a distance, "b", between the first baffle plate and an adjacent side-wall of the reservoir body satisfies the relationship b<(g/a)Dm/2k, wherein "g" is the local acceleration of gravity, "a" is the acceleration experienced by the cartridge during a change in travel direction in use, "Dm" is the change in an ejected ink drop mass due to a change in an ink reservoir pressure in the cartridge, and "k" is a slope of the graph of ink drop mass versus the ink reservoir pressure. The baffle assembly may loosely divide a volume of the reservoir body into a plurality of smaller compartments. Ink flow between the plurality of compartments may be provided by establishing a gap between the first baffle plate and the floor of the ink supply reservoir. The baffle assembly, or the baffle plate, may be formed from a material different from a material from which the reservoir body is formed. In such a case, for example, the baffle plate may be formed from a compliant material, such as for example, plastics, rubber or metal. In some embodiments of the invention, the baffle assembly is sized to allow the assembly to move in the reservoir body in a direction parallel to a direction of motion of the printer carriage in use. In other preferred embodiments, the baffle assembly further includes a second baffle plate arranged substantially parallel to the first baffle plate, wherein the second baffle plate has a first end and a second end, and wherein the first end plate is coupled to the first end of the second baffle plate and the second end plate is coupled to the second end of the second baffle plate. In such an assembly, it is preferred that a distance, "b", between the first baffle plate and the second baffle plate satisfies the algebraic relationship set forth above. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- FIG. 1 shows a perspective view of a baffle insert according to the invention; and FIG. 2 is a graph showing the relationship between ejected ink drop mass and reservoir pressure. FIG. 1 shows a baffle insert 10 suitable for insertion in the direction indicated by arrow 11 into an ink supply reservoir body 12, such as can be found in an ink jet printhead cartridge. Baffle insert 10 includes at least one baffle plate 14, and as shown in FIG. 1, can include a plurality of baffle plates 14, which are individually identified as baffle plates 14a, 14b, and 14c. Reservoir body 12 includes a floor wall 16 and sidewalls 17a, 17b, 17c and 17d. Baffle plates 14 are arranged to be substantially perpendicular to the floor 16 of reservoir body 12 . Furthermore, when a plurality of plates 14 are used, the plates 14 are oriented such that the plane of each plate is substantially parallel to the adjacent plate. Each baffle plate is oriented to be substantially parallel to reservoir side-walls 17a and 17c. The orientation and spacing of plates 14 are maintained by end plates 18a and 18b. End plates 18a and 18b may be formed integral with baffle insert 10 during a molding process, or may be attached to the baffle plates 14 by welding or with adhesives. Baffle insert 10 may be sized to form a snug fit in reservoir body 12. Alternatively, baffle insert 10 may be sized to form a loose fit in reservoir body 12, thereby further enhancing the mechanical energy absorption capability of the baffle by allowing slight movement of the baffle insert in reservoir body 12 as the container liquid ink sloshes from side-to-side. Such movement of the baffle insert is preferably primarily in the direction of print head carriage motion as indicated by double headed arrow 20. The baffle plates 14 of baffle insert 10 loosely divide the reservoir volume into smaller compartments. Ink flow between the compartments can be insured with strategically placed slots or holes in the baffle walls or by maintaining a loose fit, or gap, between the lower edge of each of the baffle elements 14a-14c and floor 16. Baffle assembly 10 is preferably designed using the criteria set forth below. A critical dimension in the design of an effective baffle is the distance between adjacent baffle plates 14a and 14b, the distance between adjacent baffle plates 14b and 14c, the distance between the outer baffle plate 14a and adjacent reservoir body wall 17a, and the distance between outer baffle plate 14c and adjacent reservoir body wall 17c, in the direction parallel to print carriage motion indicated by double headed arrow 20. This is because the maximum acceleration sustained by the print cartridge during operation usually occurs when the carriage reverses direction between print swaths. This acceleration can be precisely determined by employing an accelerometer, or is given approximately by the formula: a = 2v/t, wherein: a = acceleration experienced by the print cartridge when the carriage changes direction; v = printer carriage velocity; and t = time required for the printer carriage to change directions between printed swaths. The condition on the baffle spacing is given by the simple inequality: dab < Dp, wherein: d = ink mass density; a = acceleration experienced by the print cartridge when the carriage changes direction; b = baffle spacing in the direction parallel to the carriage motion; and Dp = maximum acceptable amplitude of pressure impulse, where the upper case D denotes a change in pressure from the relatively constant hydrostatic ink pressure in the print cartridge reservoir. The amplitude Dp of the pressure impulse is conveniently expressed as an equivalent change in hydrostatic pressure: Dp = dgDh, wherein: Dp = maximum acceptable amplitude of pressure impulse; d = ink mass density; g = local acceleration of gravity (approximately 980 cm/sec2) ; and Dh = hydrostatic pressure equivalent to the maximum acceptable pressure impulse amplitude. The inequality for the baffle spacing b can therefore be rewritten as: b < (g/a)Dh, wherein: b = baffle spacing in the direction parallel to the carriage motion; g = local acceleration of gravity (approximately 980 cm/sec2) ; a = acceleration experienced by the print cartridge when the carriage changes direction; and Dh = hydrostatic pressure equivalent to the maximum acceptable pressure impulse amplitude. The effect of an impulsive pressure change on print quality can be assessed experimentally. The principle effect on print quality of change in reservoir pressure is reflected in a change in the mass of an expelling ink droplet. Since a pressure impulse is by nature a wave phenomenon, it can manifest itself as particularly visible variation in print density. The relationship between ejected ink drop mass and reservoir pressure can be described by a straight line with slope k, as shown in Fig. 2. k = Dm/Dh, wherein: k = regression slope of the graph of drop mass versus reservoir pressure; Dm = change in ejected drop mass due to a change in reservoir pressure (drop mass) ; and Dh = hydrostatic pressure equivalent to the maximum acceptable pressure impulse amplitude (backpressure). The magnitude of the effect varies with the particular print element and its operating conditions. However, a representative value for the constant slope k is: k is approximately 2 nanograms change in ink mass per centimeter change in hydrostatic reservoir pressure. If it is judged that a variation in drop mass of magnitude Dm is barely acceptable, then the distance b between baffles (in the direction perpendicular with carriage motion) can be chosen so that the reservoir experiences changes in hydrostatic pressure no larger than a value Dh, to satisfy the inequality: 2 Dh < Dm/k. The factor of two is necessary because the wave nature of the pressure impulse causes the hydrostatic pressure to vary by an amount Dh both above and below the equilibrium reservoir pressure. The distance b between baffles required to attenuate variations in drop mass below the threshold value Dm therefore must satisfy the inequality: b < (g/a)Dm/2k, wherein: b = baffle spacing in the direction parallel to the carriage motion; g = local acceleration of gravity (approximately 980 cm/sec2) ; a = acceleration experienced by the print cartridge when the carriage changes direction; Dm= change in ejected drop mass due to a change in reservoir pressure; and k = regression slope of the graph of drop mass versus reservoir pressure. The design criteria set forth above may be used to design a baffle insert which fits snugly in the ink reservoir, or, as in some embodiments, is sized to form a loose fit in the ink reservoir. Design Example Suppose that an ink jet printer with 300 dots per inch print resolution operates the print element at 6000 dots per second. The resultant carriage speed would be: v = 20 inch/second = 50.8 centimeters/second, wherein v = printer carriage velocity. A reasonable time for the carriage direction reversal is 50 milliseconds; therefore, a = 2v/t = 2(50.8 cm/s)/(0.050s) = 2032 cm/s a/g = (2032 cm/s2)/(980 cm /s2) = 2.07. Further suppose that a barely tolerable change in drop mass is 15 nanograms and that the slope k is 2 nanograms per centimeter hydrostatic pressure. Then (g/a)Dm/2k = (2.07)(15ng)/(2(2ng/cm)) = 1.8 cm. Therefore, the baffle spacing must conform to the following inequality to insure that intolerable variations in drop mass do not occur, i.e. b < 1.8 centimeters, wherein b = baffle spacing in the direction parallel to the carriage motion. The values for the variables used in the equations above are dependent upon factors associated with the printer mechanism, printer cartridge and/or ink being used. For example, acceleration (a) is dependent upon the physical characteristics of the printer mechanism, and in particular, the printhead carrying; backpressure (Dh) and the slope (k) will be dependent upon the physical characteristics of the printer cartridge; and the variation in drop mass (Dm) will be dependent upon, for example, the type of print medium, the size of the ink jet nozzles, and the spacing between the print medium and the ink jet nozzles. Typical parameters ranges for these variables are: a = 700 to 7000 centimeters per second 2; a/g = 0.5 to 10; Dm = 2 to 40 nanagrams; Dh = 0.5 to 10 centimeters water column; and k = 0.2 to 6 nanagrams per centimeter water column. Additional advantages of the invention may be obtained by manufacturing the insertable baffle 10 from a material different from that of the ink supply reservoir body 12. For example, a lower cost material may be chosen, since restrictions on the dimensional and structural integrity of the baffle are not as stringent as for the ink supply body 12. Furthermore, a more compliant material may be chosen, thereby enhancing the effectiveness of the baffle as a slosh attenuator. By selecting a material for baffle insert 10 which is a compliant material, i.e. having somewhat fexible or pliable characteristics, the effectiveness of baffle insert 10 as a slosh attenuator is enhanced by absorbing some of the mechanical energy of the sloshing liquid. Accordingly, shock impulses generated when the ink comes in contact with the baffle are reduced since the baffle plates 14 are allowed to flex upon contact. Accordingly, in preferred embodiments of the invention, baffle insert 10 is manufactured from a compliant material, such as for example plastics, rubber or metal. The thickness of the baffle plates is chosen, based upon the material selected, so that the baffle plates have the desired compliancy.

Claims: A printer cartridge comprising a reservoir body (12) forming a container for storing a supply of ink, and a baffle assembly (10) positioned in said reservoir body, characterised in that said baffle assembly is not affixed to or integral with said reservoir body. A cartridge as claimed in claim 1, wherein said baffle assembly (10) comprises a first baffle plate (14a) having a first end and a second end, a first end plate (18a) coupled to the first end of said first baffle plate, and a second end plate (18b) coupled to the second end of said first baffle plate. A cartridge as claimed in claim 2, further comprising a second baffle plate (14b) arranged substantially parallel to said first baffle plate (14a), said second baffle plate having a first end and a second end, wherein said first end plate (18a) is coupled to the first end of said second baffle plate and said second end plate (18b) is coupled to the second end of said second baffle plate. A cartridge as claimed in claim 2 or 3, wherein the or each said baffle plate (14), said first end plate (18a), and said second end plate (18b) form an integral structure. A cartridge as claimed in any of claims 2 to 4, wherein said baffle assembly (10) loosely divides a volume of said reservoir body (12) into a plurality of smaller compartments, and wherein ink flow between said plurality of compartments is provided by a gap between the or each said baffle plate (14) and a floor wall (16) of said reservoir body. A cartridge as claimed in any of claims 2 to 5, wherein the or each said baffle plate is formed from a material different from a material from which said reservoir body (12) is formed. A cartridge as claimed in any of claims 2 to 6, wherein said baffle assembly (10) is sized to allow said assembly to move in said reservoir body (12) in a direction parallel to a direction of motion of the printer carriage in use. A cartridge as claimed in any of claims 2 to 7, wherein the or each said baffle plate (14) is formed from a compliant material. A cartridge as claimed in any of claims 2 to 7, wherein said baffle assembly (10) is formed from a compliant material. A cartridge as claimed in claim 8 or 9, wherein said compliant material is plastics, rubber or metal. A cartridge as claimed in any of claims 2 to 10, wherein a distance, b, between said first baffle plate (14a) and an adjacent side-wall (17a) of said reservoir body (12) satisfies the inequality relationship b<(g/a)Dm/2k, wherein g is the local acceleration of gravity, a is the acceleration experienced by the cartridge during a change in travel direction in use, Dm is the change in an ejected ink drop mass due to a change in an ink reservoir pressure in said cartridge, and k is a slope of a graph of said ink drop mass versus said ink reservoir pressure. A cartridge as claimed in any of claims 2 to 10, wherein a distance, b, between said first baffle plate (14a) and an adjacent side-wall (17a) of said reservoir body (12) satisfies the inequality relationship b<(g/a)Dh, wherein g is the local acceleration of gravity (approximately 980 cm/sec2), a is the acceleration experienced by the cartridge when the carriage changes direction in use, and Dh is the hydrostatic pressure equivalent to the maximum acceptable pressure impulse amplitude.

Inventors: POWERS JAMES HAROLD, POWERS, JAMES HAROLD
Applicants: LEXMARK INT INC, LEXMARK INTERNATIONAL, INC.
Application year: 1996
Main classification: B41J2
IPC codes: B43L25, G01D15, B41J2