Abstract:
An ink jet printhead composed of: a reservoir storing a quantity of printing ink, an ink manifold defining an ink supply volume in communication with the reservoir for holding a supply of ink received from the reservoir and a plurality of individually controlled ink jet delivery channels, each of the channels having an ink drop ejection transducer and an orifice to eject successive ink drops on demand in response to pressure pulses produced by the transducer, and each of the channels being in communication with the ink supply volume for receiving ink from the ink supply volume. The manifold is constructed to give the ink supply volume a large acoustic compliance to minimize propagation of pressure disturbances in the ink supply volume and acoustic signal crosstalk between the channels.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to inkjet printheads in which ink in the liquid state is delivered to a plurality of nozzles and ink drops are ejected on demand from each nozzle in response to actuation of an associated ejection transducer. 
     Ink jet printers are widely used for printing documents in both the office and the home, as well as for industrial printing applications on a variety of surfaces. Such printers include an ink jet printhead having a plurality of ink ejection chambers, or channels, each containing one or more ink jet ejection orifices, or nozzles. The ejection of ink from each nozzle is controlled by a pattern of pressure pulses. 
     Each nozzle constitutes the outlet end of an ink delivery channel. The inlet ends of all of the channels communicate with an ink supply volume formed within an ink manifold. As ink is withdrawn from the manifold, it is replaced by fresh ink from a reservoir that is in communication with the manifold. The printhead is designed so that the ink supply volume is always filled with ink. 
     The pressure pulses for ejecting ink from each nozzle are produced by an associated ink jet ejection transducer. The transducer, in turn, is responsive to electrical drive pulses produced by a print engine. 
     When a pressure pulse is generated within a channel, one part of the resulting pressure disturbance acts to eject an ink drop from the associated nozzle while another part of the resulting pressure disturbance is propagated in a backward direction through the channel and into the ink supply volume within the manifold. Pressure disturbances which enter the ink supply volume are transmitted acoustically throughout the ink supply volume. 
     As a result, a time varying manifold pressure, known as crosstalk, will influence the pressure in all of the other channels. This will affect the flow dynamics within all of the channels. In particular, crosstalk can cause variations to occur in the velocity, shape and/or size of the ink drops ejected from the nozzles of the other channels and such variations will have an adverse effect on the quality of the resulting printed material. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to minimize the transmission of pressure disturbances, or crosstalk, between the channels of a printhead of the type described above. 
     The invention is embodied in an ink jet printhead comprising: a reservoir storing a quantity of printing ink; at least one ink manifold defining an ink supply volume in communication with the reservoir for holding a supply of ink received from the reservoir; and a plurality of individually controlled ink jet delivery channels, each of the channels having an ink drop ejection transducer and an orifice to eject successive ink drops on demand in response to pressure pulses produced by the transducer, and each of the channels being in communication with the ink supply volume for receiving ink from the ink supply volume, wherein the manifold is constructed to give the ink supply volume a large acoustic compliance to minimize propagation of pressure disturbances in the ink supply volume and acoustic signal crosstalk between the channels. 
     The invention is applicable to any existing type of printhead, including those of the bubble jet type. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a cross-sectional view of a printhead according to a preferred embodiment of the present invention. 
     FIG. 2 is a perspective view of the embodiment shown in FIG.  1 . 
     FIG. 3 is a detail plan view of a component of a second embodiment of the invention. 
     FIG. 4 is a cross-sectional view along line IV—IV of FIG.  3 . 
     FIG. 5 is a simplified pictorial view of a third embodiment of the invention. 
     FIG. 6 is a perspective view showing the basic components of a printhead to which the invention may be applied. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a cross-sectional view of an inkjet printhead which utilizes hot-melt inks with properties (surface tension, viscosity, density etc.) in a certain range. However, the invention can be applied to printheads using any ink having properties in the design range and being chemically compatible. The basic components of the printhead include, as will be described in greater detail below, a reservoir  12  holding a supply of ink, a manifold which receives ink from the reservoir and which remains filled with ink until the reservoir supply has been exhausted and a plurality of individually controlled ink jet delivery channels, each ending in a nozzle from which successive ink drops can be ejected. 
     Referring more specifically to FIG. 1, reservoir  12  is coupled to the interior of a manifold via an ink supply conduit  14 . 
     The manifold provides an ink supply space, or volume,  16  delimited, or enclosed, by a chamber plate  18 , wall members  20 ,  22 ,  24  and  26  and a thin plate  30 . Plate  30  is supported by further wall member  34 . 
     A filter  38  extends across space  16 , and conduit  14  is in communication with the portion of space  16  that is located between filter  38  and plate  30 . 
     The printhead further includes a plurality of delivery channels each of which has an inlet end communicating with space  16 . The plurality of channels are arranged in a stack perpendicular to the plane of FIG. 1, the elements of one of these channels being visible in FIG.  1 . Each channel includes an inlet path  40  and an outlet chamber  42 . Outlet chamber  42  is bounded by an orifice plate  44  in which is formed a plurality of nozzles, or ink ejection orifice,  46 . Each chamber  42  communicates with a single nozzle  46 . 
     Each delivery channel further includes a diaphragm  50  located at the side of chamber  42  that is remote from nozzle  46 . Diaphragm  50  is coupled to a respective transducer  54  that may be a piezoelectric transducer composed of a stack of piezoelectric plates. Transducer  54  is enclosed by silicone members  56 . Each transducer  54  is sandwiched between an associated diaphragm  50  and a ceramic plate  58  that is common to all channels. Electrodes (not shown) are connected in a conventional manner to each transducer  54  via passages (not shown) provided in plate  58 . 
     The printhead is completed by a member  62  that serves to support a portion of members  34  and  56  and diaphragm  50 , along with two side plates  66  and  68  that form parts of the housing for the printhead. 
     It will be noted that in the illustrated embodiment, the ink manifold has an inlet in communication with reservoir  12  and outlets in communication with inlet paths  40  of the delivery channels, and the ink manifold outlets are spaced from the ink manifold inlet in the direction of ink flow through the manifold. Wall  30  extends generally perpendicular to the direction of ink flow through space  16 . However, wall  30  can have other orientations relative to the direction of ink flow through the manifold, provided that it forms one boundary wall of space  16 . In addition, wall  30 , which constitutes one of the surfaces bounding space  16 , preferably has an area at least as large as the area of any other one of the surfaces bounding space  16 . 
     When a drop of ink is to be ejected from any one orifice  46 , an electrical actuation pulse is applied to transducer  54 , causing the transducer to expand momentarily and deflect diaphragm  50 . The deflection of diaphragm  50  creates a pressure pulse in chamber  42  and this pulse acts to eject a drop of ink from orifice  46 . 
     A portion of the energy of the pressure pulse produced by deflection of diaphragm  50  is propagated as a pressure disturbance via inlet path  40  into space  16 , where it will influence the pressure in the other ink jet delivery channels. 
     According to the present invention, the propagation of pressure disturbances between ink jet deliver channels is prevented, or at least substantially minimized, by giving the manifold, or more specifically space  16 , a high fluidic compliance. In the illustrated embodiment, this is achieved by forming plate  30  to be sufficiently flexible to minimize the pressure disturbances that are propagated into space  16 . 
     According to one preferred embodiment of the invention, this is achieved by forming plate  30  as a stainless steel sheet having a thickness on the order of 12 μm, although smaller thicknesses can be envisioned. The degree of compliance increase afforded by the present invention is influenced by the mechanical characteristics of both plate  30  and filter  38 . 
     As a general rule, the compliance increase afforded by the present invention will be inversely proportional to the thickness of plate  30 . A thickness less than 12 μm may prove advantageous if such a thickness proves to be feasible in practice. 
     Filter  38  may be made of stainless steel, nickel, etc., an electroformed nickel material presently being preferred. Because of the necessary position of filter  38  in space  16 , the compliance of filter  38  will influence the compliance the manifold. The compliance of filter  38  will depend on the size and number of the ink passages therein, which are determined by the required ink flow and filtering parameters, and the thickness and material of filter  38 . The compliance of filter  38  will be essentially inversely proportional to its thickness. The thickness can have any value compatible with the required ink flow and filtering parameters and mechanical strength. It is presently believed that the thickness can be between 10 and 25 μm, although other thickness values can be used. 
     For a filter  38  having given dimensions and given ink passage size and spacing, an electroformed nickel filter will have a higher compliance than a stainless steel filter. 
     Depending on the combination of materials and dimensions chosen for plate  30  and filter  38 , it is believed that the compliance of the manifold can be increased by a factor of the order of 140 or more. 
     It may be noted that, apart from plate  30 , the printhead shown in FIG. 1 can be constructed according to techniques and principles already known in the art. 
     FIG. 2 is a partly cut-away perspective view of the embodiment shown in FIG.  1 . Elements already shown in FIG. 1 are identified with the same reference numerals. FIG. 2 illustrates several additional elements which were omitted from FIG. 1 to facilitate an understanding of the basic structure of an ink manifold and ink jet delivery channels according to the invention. 
     Additional elements that are illustrated in FIG. 2 include a heater  70  which maintains ink at a desired temperature for printing, a bonding plate  72 , a further support plate  74  and a restricter plate  76 . In addition, FIG. 2 shows a silicone rubber sheet  80  positioned between a transducer  54  and diaphragm  50 . Also shown in FIG. 2 are electrodes  82  associated with several transducers  54 . All of these elements are, however, conventional in the art. 
     According to a second embodiment of the invention, plate  30  can be replaced by a plate  90 , as shown in FIGS. 3 and 4. This plate is provided with an array of capillary orifices  92 . In the illustrated embodiment, orifices  92  taper from a relatively large diameter at the side  94  of plate  90  which faces ink volume  16  to a small diameter at the side  96  of plate  90  that faces wall  34 . However, orifices  92  need not be tapered. As illustrated in FIGS. 1 and 2, an air space exists between wall  34  and plate  30 , or plate  90  of FIGS. 3 and 4, and this air space may be vented to the environment. 
     Each passage  92  is delimited by a surface formed by rotating a generatrix constituted by a quarter circle around the longitudinal axis of the passage. Each passage  92 , and particularly the small diameter end thereof, has a sufficiently small diameter that ink present in space  16  will not flow out of passages  92 . Ink contained within each passage  92  will form a meniscus  98 . 
     When a pressure disturbance occurs in space  16 , it will be attenuated by a variation in the quantity of ink in each passage  92 , associated with a change in the position and/or curvature of each meniscus  98 . Under normal operating conditions, this variation will not result in the flow of ink into the air space between plate  90  and wall member  34 . 
     The spacing between passages  92  is determined by the compliance that it is desired to provide for space  16 . The closer the spacing between passages, the greater will be the resulting compliance. The maximum number of passages  92  is limited essentially only by the surface area of plate  90 . 
     The maximum size of passages  92  is determined by the requirement for the surface tension of meniscus  98  and to prevent meniscus  98  from being pulled back into space  16  in the presence of the normal operating pressure, which may be of the order of 2-3 cm below atmospheric The maximum hole size also depends on the surface tension of the ink. Assuming a surface tension of 30 dyne/cm, these considerations would lead to a maximum radius of about 150 microns at the outlet end of each passage  92 . 
     Since a large number of passages having this size would provide a more than adequate increase in compliance, a practical form of construction of this embodiment could satisfactorily employ smaller diameter passages. The exit diameter of each passage  92  could typically be in the range of 75 to 100 microns. 
     These passages may be formed in a thin plate by a variety of processes, including etching, drilling, laser drilling, electroforming, piercing, or electro-discharge machining. Passages having the form illustrated in FIGS. 3 and 4 result naturally from using a thin film electroform process. 
     In normal practice, during priming or purging of a printhead, it is necessary to apply a relatively high positive pressure to the ink in the manifold. In view of this, it may be desirable to provide an additional device which would cover passages  92  while pressure is being applied, in order to prevent ink from leaking out through passages  92 . 
     In further accordance with the invention, plate  90  can be made relatively thin to have a flexibility comparable to that of plate  30  of FIGS. 1 and 2. In this case, a high level of compliance can be provided by a combination of the flexing of plate  90  and the effect produced in capillary passages  92 . 
     Yet another embodiment of the invention is shown in FIG. 5 which is a simplified, diagrammatic plan view of the interior of a manifold. According to this embodiment, a thin walled air sac  102  may be installed in space  16 . Sac  102  is filled with air and may be made of a material which can be made very thin and is chemically compatible with the ink employed in ink jet printers. For some inks, latex rubber may be compatible. Pressure disturbances within space  16  will be attenuated, or dissipated, by compression or expansion of the air within sac  102 . The nominal pressure of the air in sac  102  may be equal to or slightly greater than the nominal pressure of ink in space  16 . Sac  102  can be made of other materials and can, for example, be a thin-walled metal box made of stainless steel. In the latter form of construction, the nominal pressure within the box can be slightly lower than the nominal pressure of ink in space  16 . 
     It should be appreciated that the embodiment shown in FIG. 5 can be combined with the embodiments of FIGS. 1 and 2 or FIGS. 3 and 4 to provide space  16  with a very high level of compliance with respect to pressure disturbances. 
     FIG. 6 is a respective view showing, in simplified form, the basic physical form of one exemplary printhead which may be equipped with manifolds according to the present invention. This is a color printhead in which reservoir  12  is provided with a plurality of receptacles  110  each for storing a supply of ink of a respectively different color. The printhead includes a plurality of vertical rows of nozzles (not shown), each row being associated with a row of transducers  114 . Each transducer corresponds to transducer  54  shown in FIGS. 1 and 2. Adjacent each row of transducers  114  is a respective manifold that contains an ink space  16 . Each manifold may be constructed to have the form shown in FIGS. 1 and 2 and/or FIGS. 3 and 4 and may optionally be provided with a sac  102  as shown in FIG.  5 . As is conventional in this art, reservoir  12  would lower than the manifolds to maintain a negative pressure at all orifices. Although FIG. 6 shows three receptacles  110  and six rows of nozzles, there can also be provided, in accordance with standard practice in the art, four receptacles and, correspondingly, eight rows of nozzles. As will be apparent to those skilled in the art, the number of rows of nozzles can vary from those mentioned above. 
     For some printing applications the printhead may be used with reservoirs other than the built-in ones shown e.g. if another orientation of the printhead is required. 
     While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. 
     The presently disclosed 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 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.