Reference is made to commonly-assigned, U.S. patent application Ser. No. 12/821,228, entitled “ALIGNMENT ASSEMBLY FOR USE WITH A PRINTHEAD” filed currently herewith and U.S. Patent Publication No. 2009/0295878 published Dec. 2, 2009, Hanchak et al.
The present invention relates to component alignment, and more particularly, to aligning various components of an inkjet printhead such as, for example, a continuous inkjet printhead.
The use of inkjet printers for printing information on recording medium is well established. Printers employed for this purpose include continuous inkjet systems which emit a continuous stream of drops from which specific drops are selected for printing in accordance with print data. Other printers include drop-on-demand inkjet systems that selectively form and emit printing drops only when specifically required by print data information. In some drop-on-demand inkjet systems, a printhead including a piezoelectric element is used to generate a pressure wave that expels drops in an on-demand fashion. In some drop-on-demand inkjet systems, drops are expelled from a printhead by the fast growth of a vapor bubble.
Continuous inkjet systems typically include a printhead that incorporates a liquid supply system and a nozzle plate having a plurality of nozzles fed by the liquid supply system. The liquid supply system provides a continuous flow of the liquid to the nozzles with a pressure sufficient to jet an individual stream of the liquid from each of the nozzles.
In order to create drops from a liquid stream, continuous inkjet systems include drop generators. A number of different mechanisms can be employed as drop generators. The drop generator influences the liquid stream emitted by a nozzle at a frequency that forces the liquid stream to be broken up into a series of drops at a point in the vicinity of the nozzle plate. Various drops are then separated from the series of drops. For example, some drops are selected for printing (i.e. printing drops) and are directed towards a recording medium while other drops that are not selected for printing (i.e. non-printing drops) are directed towards a disposal or recycling system.
Various methods known in the art are employed to separate printing drops from non-printing drops. One commonly employed practice includes electrostatically charging and electrostatically deflecting selective ones of the drops using a charge electrode positioned along the flight path of the drops. The function of the charge electrode is to selectively charge the drops as they break off from a liquid stream. One or more deflection plates positioned downstream from the charge electrode create an electric field which deflects a charged drop either towards a catcher assembly or towards a recording medium. Other systems that deflect drops using a gas flow are also known. For example, U.S. Pat. No. 4,068,241, issued to Yamada, on Jan. 10, 1978 describes a gas flow drop deflection system.
Conventional techniques for assembling various elements of a printhead include locating or aligning the elements using an assembly fixture, and then using an adhesive such as epoxy or mechanical fasteners to affix them together. Unfortunately, these assembly and alignment techniques have drawbacks. For example, using an adhesive can increase assembly time because it often takes several hours for the adhesive to cure. Using epoxy can be problematic because epoxy can be sensitive to heat and humidity. Using adhesives or epoxies can hinder the desire to have various printhead components be field replaceable components. Additionally, dedicated assembly fixtures employed for alignment purposes in the factory can also be a detriment when field repairs are necessary.
In some cases, locating elements are provided in various ones of the printhead elements to help provide the necessary alignment during assembly. These locating elements can provide self-aligning capabilities which are desirable in a field replaceable unit. Nonetheless, the locating elements must be formed in a manner that provides the high alignment accuracy required between the mated elements of the printhead such as, for example, the assembly of a jetting module and drop deflection device. Several conventional methods have been employed to form these high precision alignment elements. For example, elements such as precision ground balls or cylindrical pins have been used as locating elements. In many cases these elements must be located relative to one another with high multi-dimensional tolerance requirements. Typically, precision blind bores are machined in at least one of the mated printhead elements to receive the locating elements. A locating element and its corresponding precision blind bore are typically sized to allow for an interference fit between the two. An interference fit is generally provided by sizing two mating components so that one of the components slightly interferes with the space that the other component occupies. When the two components are mated, elastic deformations are generated in each of the components which generate frictional forces that secure the two components together.
Conventional techniques for positioning locating elements have drawbacks. For example,
As such, there is an ongoing need for improved techniques for positioning locating elements used to align components relative to one another. There is also an ongoing need for improved locating elements in a printhead suitable for providing high precision alignment between various components of the printhead.
According to an aspect of the present invention, a printhead includes a printhead module, a printhead frame, and an alignment assembly. The printhead module includes a plurality of nozzles adapted for emitting liquid from the printhead module. The alignment assembly aligns the printhead module and the printhead frame relative to each other and includes a base plate, a locator plate, a first set of locating elements, and a coupling member. The base plate includes a surface. The locator plate includes a plurality of through holes positioned relative to each other on a surface of the locator plate. The locator plate is affixed with the base plate such that a plurality of pockets are formed with each pocket having a wall corresponding to a wall of one of the through holes and a base corresponding to a surface of the surface of the base plate. Each of the locating elements of the first set are positioned with an interference fit in a respective one of the pockets. The walls of the pockets define positions of the locating elements of the first set relative to one another in a plane of the surface of the locator plate. The bases of the pockets define positions of the locating elements of the first set relative to one another in a direction normal to the surface of the base plate. The coupling member includes a second set of locating elements with each of the locating elements of the second set adapted for contact with one the locating elements of the first set.
In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. In the following description and drawings, identical reference numerals have been used, where possible, to designate identical elements.
The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of the ordinary skills in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention.
Referring to
Operation of the printhead 10 depends critically on the alignment of catcher 14 and drop deflection mechanism 12 relative to jetting module 18. In this example embodiment, printhead frame 12 includes a set 21 of locating elements 22. In this example embodiment, the catcher 14 and a portion of the drop deflection mechanism 12 are assembled together, and this catcher-drop deflector assembly is affixed to printhead frame 20. The jetting module 18 includes a set 29 of locating elements 30 (only one is shown in
Referring to
In this example embodiment, the plurality of locating elements 22 are arranged in various sets 21, each set 21 corresponding to one of the ports 40 and each set 21 includes three (3) of the locating elements 22 as shown in
Locating elements 22 are preferably kinematic alignment elements. Kinematic alignment elements allow a jetting module 18 to be precisely positioned in relation to printhead frame 20. One type of kinematic mount, known as a “2-2-2 mount” or a “three grove mount” is shown in
While the 2-2-2 mount is used in the example embodiment shown in
The use of kinematic mount elements can provide reproducible alignment of printhead elements, such as the alignment of jetting module 18 to printhead frame 20. Kinematic mount elements can be used to enable interchangeability of parts which can greatly enhance field replacement efforts. Also, the use of a kinematic mount to provide reproducible alignment between two elements such as jetting module 18 and printhead frame 20 can be used to establish required alignments with other printhead elements. For example, in the printhead production process, fixtures that engage the locating elements 30 of the jetting module 18 can be used to align a nozzle array 32 of a nozzle plate 34 (shown in
The consistency of alignment of the critical printhead elements, for example, nozzle array 32, drop deflection mechanism 12, and catcher 14, depend on the consistency of the locating elements 22, 30. The locating elements 22 are preferably fabricated from a material, for example, a ceramic or metallic material, that won't significantly deform under the influence of the contact forces that are generated during the engagement. In some example embodiments, metallic locating elements 22 are additionally hardened or toughened to improve characteristics such as yield strength and wear resistance. When locating elements 22 are hemispherical, the hemispherical locating elements 22A, 22B can be formed by securing a plurality of spherical members (i.e. precision bearing balls) in a fixture and grinding the members into the desired pseudo-hemispherical shapes as shown in
The locating elements 22 shown in
In this example embodiment, the printhead frame is formed as an assembly of a first member 24, a second member 26 and a third member 28. As each pocket in the printhead frame is of similar construction, the figure only shows reference numbers for a single pocket. Second member 26 includes a first through hole 27 and second through hole that are positioned relative to each other with a desired x-y spatial relationship for the first and second pockets. Third member 28 includes a set of through holes 49 that are spatially arranged on the member in the same arrangement as the through holes 27 in the second member 26. Second member 26 has been affixed with along with the third member 28 to the first member 24 such that a first pocket 48A and a second pocket 48B are formed in printhead frame 20. Each of the first pocket 48A and the second pocket 48B includes a surface defined by a wall 31 of a corresponding one of the first and second through holes 27. Each of the first pocket 48A and the second pocket 48B has a base corresponding to surface 25 of first member 24.
In this example embodiment, each of the locating elements 22A, 22B are positioned with an interference fit in a respective one of the pockets 48A and 48B. Each of the locating elements 22 includes a surface adapted for contact with a base of the corresponding pocket 48. Specifically, the flat surface 46 of each of the locating elements 22 is made to contact a base of a corresponding pocket 48.
Unlike conventional methods where a plurality of locating elements are positioned in relatively expensively machined holes having both precision hole-to-hole x-y tolerances as well as precision bore depth tolerances, the example embodiments of the present invention reduce the costs associated with the required alignment of the locating elements 22A and 22B.
Since an interference fit is employed in this example embodiment, the wall 31 of the first pocket 48A and the wall 31 of the second pocket 48B define a first component of position of the first locating element 22A relative to the second locating element 22B. In this example embodiment, the first component of position is the x-y position, that is, the position within the plane of the surface 25 of first member 24. The first component of position is a planar position relative to a surface of second member 26.
In this example embodiment, second member 26 is a relatively thin planar member as compared to first member 24. The “thin” form of second member 26 allows through holes 27A and 27B to be formed with reduced bore directional errors that can be associated with the machining of deeper bind holes. In some example embodiments, chemical machining techniques are employed to form a plurality of through holes 27 in a thin second member 26. Chemical machining is well suited for forming through holes in thin substrates, the formed holes having tight dimensional size tolerances as well as tight hole-to-hole positional tolerances.
In other example embodiments, a ganged machining process can be used to form the through holes 27 in a stack of thin second members 26. The ganged machining process can involve performing a rough cut with a laser or other process followed by a jig grinding process to achieve the precision required. Ganged machining techniques can be used to simultaneously form identical features in each of a plurality of second members 26. This provides more consistency between each of the second members 26 than would be achieved if each second member 26 was individually machined. This can be especially advantageous when the plurality of second members 26 is employed in the jetting modules 18 of a multi-color printer because the identical nature of each of the second members 26 can reduce color-to-color misalignments. It is to be understood that other thicknesses of the members can be employed. The choice of the thicknesses for the first, second, and third members should be consistent with the anticipated loading forces applied to the locating members and span of the printhead frame 20 for the application. In one example embodiment, the first member 24 has a thickness of 25 mm, the second member 26 a thickness of 1 mm, and the third member 28 a thickness of 2.5 mm.
Bases 25 of each of the first pocket 48A and the second pocket 48B define a second component of position of the first locating element 22A relative to the second locating element 22B. In this example embodiment, the second component of position is the normal or orthogonal position relative to surface 25 of first member 24. In other example embodiments, the second component of position is a normal or orthogonal position relative to a surface of second member 26.
Since each base is defined by the surface 25 of first member 24, this positioning is hence defined by a flatness tolerance of surface 25. Precision surface machining techniques (e.g. surface grinding or surface lapping techniques) can be employed to impart a desired flatness to surface 25. In this regard, the present inventors have determined that imparting a precision flat surface 25 on first member 24 produces a more accurate result and is more economical than forming a plurality of bores, each bore being machined with a precision depth tolerance. In some example embodiments, pluralities of surfaces of first member 24 are employed to define the bases of the pockets 48A and 48B. For example, the first member 24 may be initially cast or molded with a plurality of raised pads. Machining each of the pads to the desired flatness specification can be especially economical since less material needs to be removed. First member 24 can be manufactured from various materials including metals such as steel or stainless steel. It is noted that contact stresses are considerably reduced when the locating elements 22A and 22B are positioned within their corresponding pockets 48A and 48B since relatively large area contact is provided by the mated flat surfaces 46 and flat surface 25.
In other example embodiments, opposing surfaces of first member 24 are machined and a first second member 26 is attached to a first surface of the first member and a second second member 26 is attached to a second surface of the first member 24. Although the second surface of first member 24 is usually opposite that of the first surface of first member 24, other relative configurations of the second surface of first member 24 and the first surface of first member 24 are permitted. Locating elements can then be inserted onto pockets on the first and second sides of the first member for the precise alignment of printer components to both faces of the alignment component.
In the embodiment shown in
Reliefs 47 can be formed in various manners. In some example embodiments, reliefs 47 are formed with a machine tool such as a drill or chamfering tool. In other example embodiments, the relief is formed by machining a hole through the base plate. The through hole may optionally include a chamfer. As the machining of the relief by any of these methods may create a burr, typically, surface 25 is machined to the required flatness tolerances after the formation of reliefs 47.
Each of first locating element 22A and second locating element 22B can be positioned within their corresponding pockets 48A and 48B in a variety of ways. For example, the locating element can simply be pressed into a corresponding pocket for certain levels of an interference fit. In other example embodiments, the size of one or both of a locating element 22 and its corresponding pocket is changed by heating or cooling. The heating or cooling is conducted to temporarily alter the size of one or both of the locating element 22 and its corresponding pocket 48 to remove the interference between the two. Once these components are assembled together, the heated or cooled component(s) are restored to their ambient conditions to re-establish the interference fit which rigidly couples the locating element in the corresponding pocket. In some example embodiments, the present inventors have employed stainless steel pseudo-hemispherical locating elements 22 which were cooled in liquid nitrogen prior to being positioned into corresponding pockets 48. Interference fits of five (5) to twenty (20) microns have been used to position the locating elements within their corresponding pockets.
As shown in
In other example embodiments, mechanical fasteners are employed. For example, referring to
Although various example embodiments of the present invention have described the use of approximately hemispherically shaped locating elements 22, other example embodiments can employ locating elements 22 having other shapes. For example, cylindrically shaped locating elements 22 can be used in some applications.
Although the example embodiments of the present invention have been described in conjunction with the use of continuous inkjet systems, the present invention is not limited to continuous inkjet printing systems. For example, while the illustrated embodiments of the alignment component have formed the printhead frame for a multiple jetting module line head, the alignment component of the present invention can be employed as a printhead frame for a single jetting module printhead. Additionally, embodiments of the present invention can be employed to align various components in a drop-on-demand (DOD) printing systems. Without limitation, the present invention can be used to provide precision alignment of kinematic mount components employed in variety of different applications.
The invention has been described in detail with particular reference to certain example embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.
Number | Name | Date | Kind |
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3638474 | Hannaford | Feb 1972 | A |
4068241 | Yamada | Jan 1978 | A |
4080607 | Van Breemen et al. | Mar 1978 | A |
4636808 | Herron | Jan 1987 | A |
5782445 | Cleek | Jul 1998 | A |
6588888 | Jeanmaire et al. | Jul 2003 | B2 |
20090295878 | Hanchak et al. | Dec 2009 | A1 |
20100289854 | Hagiwara et al. | Nov 2010 | A1 |
Number | Date | Country | |
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20110316933 A1 | Dec 2011 | US |