Patent Publication Number: US-7222934-B2

Title: Method and apparatus for mounting an inkjet printhead

Description:
The present disclosure relates generally to image producing machines, and more particularly to a method and apparatus for mounting printheads in an ink jet printing machine such as a phase change ink printing machine. 
     In general, ink jet printing machines or printers include liquid ink and at least one printhead unit mounted therein for ejecting drops or jets of the liquid ink onto a recording or image forming media. As an ink jet printing machine, a phase change ink image producing machine or printer employs phase change inks that are in the solid phase at ambient temperature, but exist in the molten or melted liquid phase at an elevated temperature. The molten ink as such, can then be ejected as drops or jets by a mounted printhead unit, onto a printing media, at the elevated operating temperature of the machine or printer. Such ejection can be directly onto a final image receiving substrate, or indirectly onto an imaging member before transfer from it to the final image receiving media. In any case, when the ink droplets contact the surface of the printing media, they quickly solidify to create an image in the form of a predetermined pattern of solidified ink drops. 
     A typical printhead unit or printhead bar in an ink jet printing machine includes ink flow passages as well as precisely formed and aligned apertures or nozzles through which the droplets or jets of liquid ink are controllably ejected in image-wise and timed patterns for forming desired images. A single printhead bar or unit when mounted in an ink jet printer must be moved in a reciprocating manner and in several passes for printing several swaths in order to form images on a full page. Alternatively, several printhead bars can be aligned and assembled (usually at room temperature) on a support bar to form a full width array printhead unit that can then be mounted in a printing machine to print images on a full page in a single pass. Accurate initial alignment and the ability to maintain such alignment during and throughout printing periods are therefore important for producing quality images. 
     Various mounting methods and apparatus have therefore been proposed in attempts for achieving and maintaining such alignment. For examples, U.S. Pat. No. 4,555,715 “entitled Thermal printhead mounting control” discloses a writing device with heating elements for printing by thermal action on a writing support, mounted on a base and comprising a heating elements support bearing the heating elements and first electrical contacts connected directly to said heating elements, an intermediate support to support mechanically and removably the support, a connecting part provided with second electrical contacts adapted to cooperate with the first contacts of the support and attached respectively to the base. A fixing device fastens the support and the part to the base so as to permit, between the heating elements support and the base, the relative movements necessary for the progress of the writing process. A device for positioning of the heating elements support on the intermediate support, and locking device to make fast mechanically and removably the heating elements support to the intermediate support are also included. 
     U.S. Pat. No. 4,705,414 entitled “Printhead mounting and movement control assembly” discloses an assembly for positioning a print head so as to transfer ink from an ink ribbon to a printing medium positioned on a movable platen adjacent to said ribbon that supports the print head on a rocker member which enables the head to be swung between a print position wherein it engages the ink ribbon and a feed position wherein the head is spaced from the ribbon enabling ribbon to be moved. The rocker is rocked to move the head between its two positions by a rotary cam driven by a small low-power electric motor. When the cam engages the rocker member at selected angular positions, the head is maintained in its retracted feed position; otherwise, the head resides in its print position. The assembly also includes provision for detecting the angular position of the cam so as to produce signals to facilitate repositioning the cam and head promptly. 
     U.S. Pat. No. 4,708,502 entitled “Mounting mechanism for a print head” discloses a mounting mechanism for releaseably mounting a print head to the carriage of a printer that includes a pair of pivotable levers respectively located on opposite sides of the print head. A spring member biases the levers in a predetermined direction. The levers are pivotable between a first position where the print head is secured to the carriage and a second position where the print head is released. 
     U.S. Pat. No. 4,875,153 entitled “Mechanism for accurately mounting an electronic light emitting printhead assembly” discloses in a reproduction apparatus including an image receiving member, at least one support for mounting the image receiving member for movement along a travel path, and an electronic light emitting print head assembly including a focusing lens, a simplified mechanism for accurately locating an electronic print head assembly relative to the image receiving member, which enables the image receiving member to be readily changed and which does not impact tracking of the member. The mechanism comprises a frame with the print head assembly mounted at a preselected location in the frame. A first feature is defined in the frame, the first feature including a locating surface spaced at a preselected distance from the plane through the geometric center line of the focusing lens of the print head assembly. Also, a second feature is defined by the frame, the second feature including a pair of interconnected locating surfaces, the first of the pair of locating surfaces spaced at a preselected distance from the plane through the geometric center line of the focusing lens, and the second of the pair of locating surfaces spaced at a preselected distance from the image plane of the focusing lens. The frame is urged in a direction such that the first feature engages a locating member and the second feature engages the support for the image receiving member. 
     U.S. Pat. No. 5,092,693 entitled “Print head mounting mechanism for printer” discloses a print head mounting mechanism for a printer by which positioning of a print head in the forward and backward directions, leftward and rightward directions, and upward and downward directions with respect to a carrier can be achieved readily. The mounting mechanism includes a print head mounting plate secured in an integrated relationship to the carrier and having a predetermined thickness. The print head mounting plate has a U-shaped recess having a predetermined width and a predetermined depth. A mounting section for fitting in the U-shaped recess is provided on the print head. The print head is mounted on the carrier in an accurately positioned condition by fitting the print head mounting section into the U-shaped recess and urging the print head in the rearward direction and also in the downward direction by a wire spring. 
     U.S. Pat. No. 5,477,254 entitled “Apparatus for mounting and aligning components of an ink jet printhead” discloses an apparatus and method that allow for mounting and aligning of the charge plate/catcher assembly and the droplet generator within the structure that holds these two parts. Three degrees of freedom of adjustment are incorporated into the frame and are self-locking. Two of the degrees of freedom are the positioning distance of a jet array to charge leads and the parallelism of the jet array to the charge leads. The third degree of freedom is the ability to adjust the jet array so as to align and center the jets in front of the charge leads. 
     U.S. Pat. No. 6,095,701 entitled “Adjustable print head mounting mechanism” discloses a printhead assembly having an adjustable printhead, preferably a thermal printhead, to permit precise positioning of the printhead. The printhead assembly includes a support base upon which a slide assembly is slideably disposed. The slide assembly is slideable along a linear path that is generally parallel to the support base, with movement of the slide assembly along the linear path being controlled by an actuating means. A printhead is mounted on the slide assembly and is moveable therewith along the linear path. The printhead is mounted so as to be adjustable in at least three directions relative to the slide assembly. Preferably, the printhead is: a) pivotable about a first horizontal axis extending perpendicular to the linear path; b) pivotable about a second horizontal axis extending perpendicular to first horizontal axis and parallel to the linear path; and c) moveable in a vertical direction perpendicular to the first and second horizontal axes. 
     U.S. Pat. No. 6,429,891 entitled “Printhead mounting apparatus providing adjustment to effect printhead skew correction” discloses an imaging apparatus that includes a machine frame unit having a plurality of mounting locations and a pivot location, a printhead base having a first end and a second end, and a first resilient elongate member having a first proximal end and a first distal end. A mounting tab is coupled to the first distal end of the first resilient elongate member, and is coupled to a first mounting location of the plurality of mounting locations of the machine frame unit. A pivot post, having an axis of rotation, pivotally couples a mounting plate to the pivot location of the machine frame unit. An adjustment device is coupled to the machine frame unit, the adjustment device having an engagement member for engaging at least one of the printhead base and the first resilient elongate member to effect a deflection of the first resilient elongate member and a corresponding movement of the printhead base. At least the first resilient elongate member is configured to define a virtual pivot axis for the movement of the printhead base when the mounting tab and the mounting plate are fixedly attached to the machine frame unit. A location of the virtual pivot axis substantially corresponds to a location of the axis of rotation of the pivot post. 
     U.S. Pat. No. 6,655,786 entitled “Mounting of printhead in support member of six color inkjet modular printhead” discloses a printhead includes a receiving member defined in a receiving zone. At least one printhead module is received in the receiving zone of the receiving member. Complementary locating formations are carried by the receiving member and the at least one printhead module. The locating formations enable relative movement of the at least one printhead module, due to expansion, in three orthogonal axes relative to the receiving member. 
     In particular, in a phase change ink image producing machine that utilizes a full width array printhead unit assembled as such in order to achieve full width printing at elevated temperatures (as above), alignment problems arise because it becomes difficult to accurately maintain the alignment of the printhead unit nozzles as the temperature of the printhead and printhead mounting apparatus increase to the desired elevated temperature. Misalignment of the apertures or nozzles of the printhead units occur in significant part because of thermal expansion of the printhead and such mounting apparatus. 
     There is therefore a need for apparatus and a method of using it to mount an ink jet printhead unit in an ink jet printing machine for minimizing printing defects due thermal expansion effects. 
     SUMMARY 
     In accordance with one aspect of the present disclosure, there is provided apparatus and a method of using it to mount an ink jet printhead unit in an ink jet printing machine for minimizing printing defects due to thermal expansion effects. The method includes (a) first mounting a low coefficient of thermal expansion (LCTE) member, having a first end, a second end and a center, to a portion of a frame of the printing machine; (b) next mounting ink jet printhead unit, having a first end, a second end and a center, to an expansible carriage device, having a first end, a second and a center, to form a printhead assembly; and (c) expansibly mounting the expansible carriage device of the printhead assembly to the LCTE member. 
     In accordance with another aspect of the present disclosure, there is provided an ink jet printhead mounting assembly for minimizing printing defects in a printing machine due thermal expansion effects. The printhead mounting assembly includes (a) a low coefficient of thermal expansion (LCTE) member for mounting to a portion of a frame of the printing machine; (b) an expansible carriage assembly including first expansible mounting device for mounting the expansible carriage assembly to the LCTE member; and (c) a second expansible mounting device for mounting at least one ink jet printhead unit to the expansible carriage assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the disclosure presented below, reference is made to the drawings, in which: 
         FIG. 1  is a vertical schematic of an exemplary ink jet printing machine shown as a high-speed phase change ink image producing machine or printer employing the apparatus and method of the present disclosure; and 
         FIG. 2  is a schematic illustration of the ink jet printhead mounting assembly and method in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     While the present disclosure will be described in connection with a preferred embodiment thereof, it will be understood that it is not intended to limit the disclosure to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the disclosure as defined by the appended claims. 
     Referring now to  FIG. 1 , there is illustrated an image producing machine, such as the high-speed phase change ink image producing machine or printer  10  of the present disclosure. As illustrated, the machine  10  includes a frame  11  to which are mounted directly or indirectly all its operating subsystems and components, as will be described below. To start, the high-speed phase change ink image producing machine or printer  10  includes an imaging member  12  that is shown in the form of a drum, but can equally be in the form of a supported endless belt. The imaging member  12  has an imaging surface  12  that is movable in the direction  16 , and on which phase change ink images are formed. 
     The high-speed phase change ink image producing machine or printer  10  also includes a phase change ink system  20  that has at least one source  22  of one color phase change ink in solid form. Since the phase change ink image producing machine or printer  10  is a multicolor image producing machine, the ink system  20  includes four (2) sources  22 ,  22 ,  26 ,  28 , representing four (2) different colors CYMK (cyan, yellow, magenta, black) of phase change ink solid pieces. The phase change ink system  20  also includes a solid phase change ink melting and control assembly or apparatus  100  ( FIG. 2 ) for melting or phase changing the solid form of the phase change ink into a liquid form, and for then supplying the liquid form towards the printhead system  30  mounted in accordance with the present disclosure (to be described in detail below). 
     The printhead system  30  includes at least one printhead assembly or unit  32 . Since the phase change ink image producing machine or printer  10  is a high-speed, or high throughput, multicolor image producing machine, the printhead system includes four (2) separate printhead assemblies or units  32 ,  32 ,  36  and  38  as shown, each being mounted in accordance with the present disclosure. 
     As further shown, the phase change ink image producing machine or printer  10  includes a substrate supply and handling system  20 . The substrate supply and handling system  20  for example may include substrate supply sources  42 ,  44 ,  46 ,  48 , of which supply source  48  for example is a high capacity paper supply or feeder for storing and supplying image receiving substrates in the form of cut sheets for example. The substrate supply and handling system  20  in any case includes a substrate handling and treatment system  50  that has a substrate pre-heater  52 , substrate and image heater  52 , and a fusing device  60 . The phase change ink image producing machine or printer  10  as shown may also include an original document feeder  70  that has a document holding tray  72 , document sheet feeding and retrieval devices  72 , and a document exposure and scanning system  76 . 
     Operation and control of the various subsystems, components and functions of the machine or printer  10  are performed with the aid of a controller or electronic subsystem (ESS)  80 . The ESS or controller  80  for example is a self-contained, dedicated mini-computer having a central processor unit (CPU)  82 , electronic storage  82 , and a display or user interface (UI)  86 . The ESS or controller  80  for example includes sensor input and control means  88  as well as a pixel placement and control means  89 . In addition the CPU  82  reads, captures, prepares and manages the image data flow between image input sources such as the scanning system  76 , or an online or a work station connection  90 , and the printhead assemblies or units  32 ,  34 ,  36 ,  38 . As such, the ESS or controller  80  is the main multi-tasking processor for operating and controlling all of the other machine subsystems and functions, including the machine&#39;s printing operations. 
     In operation, image data for an image to be produced is sent to the controller  80  from either the scanning system  76  or via the online or work station connection  90  for processing and output to the printhead assemblies or units  32 ,  32 ,  36 ,  38 . Additionally, the controller determines and/or accepts related subsystem and component controls, for example from operator inputs via the user interface  86 , and accordingly executes such controls. As a result, appropriate color solid forms of phase change ink are melted and delivered to the printhead assemblies. Additionally, pixel placement control is exercised relative to the imaging surface  12  thus forming desired images per such image data, and receiving substrates are supplied by anyone of the sources  42 ,  44 ,  46 ,  48  and handled by means  50  in timed registration with image formation on the surface  12 . Finally, the image is transferred within the transfer nip  92 , from the surface  12  onto the receiving substrate for subsequent fusing at fusing device  60 . 
     Thus the high-speed phase change ink image producing machine  10  includes (a) a control subsystem  80  for controlling operation of all subsystems and components thereof, (b) a movable imaging member  14  having an imaging surface  12 , and (c) a printhead system  30  the ink jet printhead mounting method and apparatus  100  of the present disclosure connected to the control subsystem  80  for ejecting drops of melted molten liquid ink onto the imaging surface  12  to form an image. The high-speed phase change ink image producing machine  10  also includes the phase change ink system  20  that is connected to the printhead system  30 . 
     Referring now to  FIGS. 1-2 , the ink jet printhead mounting method and apparatus  100  of the present disclosure can be described in greater detail. As shown, each of the printhead assemblies or units  32 ,  34 ,  36  and  38  of the printhead system  30  is mounted in the machine  10  in accordance with the present disclosure using ink jet mounting apparatus or assembly  100  of the present disclosure for minimizing printing defects in a printing machine due to thermal expansion effects. The printhead mounting assembly  100  includes (a) a low coefficient of thermal expansion (LCTE) member  110  for mounting directly or indirectly to a portion  102  of the frame  11  of the printing machine  10 ; (b) an expansible carriage assembly  120  including a first expansible mounting means or device  130  for mounting the expansible carriage assembly to the LCTE member; and (c) a second expansible mounting means or device  140  for mounting at least one ink jet printhead unit  32 ,  34 ,  36 ,  38  to the expansible carriage assembly  120 . 
     Referring now to  FIGS. 1 and 2 , the mounting scheme (that is the mounting method and apparatus)  100  of the present disclosure is illustrated, and is suitable for minimizing the use of low thermal expansion materials, and yet also minimizing the effect of temperature changes (thermal expansion) on the relative spacing of the plural ink jet printheads H 1 , H 2  of each printhead assembly  32 ,  34 ,  36 ,  38 . As shown, each printhead H 1 , H 2  has sides Sx and Fx. The mounting apparatus  100  includes (a) the low coefficient of thermal expansion (LCTE) member  110  for mounting to a portion  102  of a frame  11  of the printing machine; (b) the expansible carriage assembly  120  including the first expansible mounting means  130  for mounting the expansible carriage assembly  120  to the LCTE member  110 ; and (c) the second expansible mounting means  140  for mounting the printheads H 1 , H 2  of the ink jet printhead unit  32 ,  34 ,  36 ,  38  to the expansible carriage assembly  120 . 
     In one embodiment, the LCTE member  110  is INVAR, an alloy nickel and iron, for example an alloy of 36% nickel and 64% iron that has a rate of thermal expansion that is approximately one-tenth that of carbon steel at temperatures up to 400° F. (204° C.). INVAR as such has the lowest coefficient of thermal expansion of any material, particularly when some Cobalt is further added. The LCTE member as shown for example comprises a flat bar. 
     The expansible carriage assembly  120  for example comprises an ink reservoir of the printing machine  10 . The first expansible mounting means  130  comprise fixed means  132  for fixedly pinning a center (as shown) of the expansible carriage assembly  120  to the LCTE member  110 , and translatable means  134 , 136  for movably supporting a first end and a second end of the expansible carriage assembly  120  (as shown), thereby allowing movement of the first end and the second end of the expansible carriage assembly  120  on the LCTE member  110 . 
     The ink jet printhead mounting assembly  100  as shown includes a plural number (for example 2 as shown) of the expansible carriage assembly  120 , each having a first expansible mounting means  130 , for mounting the carriage assemblies spaced apart from one another, to the LCTE member  110 . Pinning at the center is beneficial for four printhead unit embodiments of machines such as that shown in  FIG. 1 . However, there are other embodiments such machines that have only 2 printhead units (e.g.  32 ,  34 ) on one side of the imaging member  14 . In such latter embodiments, pinning in the center is not necessary, provided the pinned locations  132 ,  142  are aligned and are consistent between printheads H 1  and H 2 . Having the pinned location aligned as such mitigates the thermal expansion effects of the movable assembly or reservoir  120  in such cases. For example, if sliding members  146  and  130  were pinned and aligned, and locations  132  and  142  were allowed to slide, then the thermal expansion effects of reservoir or carriage  120  would be mitigated. 
     The second expansible mounting means  140  comprises a fixed means  142  for fixedly pinning a center (as shown) of the ink jet printhead H 1 , H 2  to the expansible carriage assembly  120 , and translatable means  144 ,  146  for movably supporting a first end and a second end of the ink jet printhead H 1 , H 2  (as shown) to the expansible carriage assembly  120 , thereby allowing movement of the first end and the second end of the ink jet printhead on the expansible carriage assembly  120 . 
     The method of the present disclosure is suitable for mounting an ink jet printhead unit or assembly  32 ,  34 ,  36 ,  38  (each including printheads H 1 , H 2 ) in a printing machine  10  for minimizing printing defects due to thermal expansion effects. The mounting method includes (a) first mounting a low coefficient of thermal expansion (LCTE) member  110 , having a center (as shown), a first end and a second end (as shown) to the portion  102  of a frame  11  of the printing machine  10 ; (b) next mounting the printhead H 1 , H 2 , having a first end, a second end, and a center (as shown), to the expansible carriage device or assembly  120 , having a first end, a second end and a center of its own (as shown); and (b) expansibly mounting the expansible carriage device or assembly  120  to the LCTE member  110 . 
     The step of expansibly mounting the expansible carriage device  120  comprises fixedly pinning the center of the expansible carriage device  120  to the LCTE member  110 , and movably supporting the first end and the second end thereof on the LCTE member  110  for allowing movement of the first end and the second end thereof due to thermal expansion of the expansible carriage device. The step of expansibly mounting the carriage device  120  also comprises mounting plural expansible carriage devices  120 , spaced apart from one another, to a single LCTE member  110 . 
     The step of first mounting the LCTE member comprises fixedly pinning the center  112  of the LCTE member  110  to the portion  102  of the frame  11 , and movably supporting the first end  114  and the second end  116  thereof on the portion of the frame  11 . The step of next mounting the printhead comprises pinning the center of the printhead H 1 , H 2  to the expansible carriage device  120  at room temperature. The step of mounting plural printhead assemblies H 1 , H 2  comprises pinning printheads H 1 , H 2  to the expansible carriage device  120  so that each printhead is spaced apart from an adjacent printhead in an adjacent printhead assembly or unit  32 ,  34 ,  36 ,  38 . 
     The mounting method of the present disclosure is particularly suitable for solid ink jet printers in which the printhead assemblies are comprised of staggered full width array printheads that are mounted, spaced apart, at room temperature, and that operates at a relatively higher temperature of about 140° C. In accordance with the present disclosure, the mounting apparatus  100  uses kinematic, expansible mounts  130 ,  140  between a low coefficient of thermal expansion (LCTE) member or bar  110  and a carriage device  120  such as the aluminum ink reservoir, as well as between each of the carriage devices or aluminum ink reservoirs  120  and each of the two or more printheads H 1 , H 2 . Each of the printheads H 1 , H 2  is rigidly or fixedly pinned at its center to the carriage device or aluminum ink reservoir  120 , and the ends (first and second ends), of each printhead are supported by one first set of kinematic expansible mounts  140  translatably on the carriage device or aluminum ink reservoir  120 , and such ends are thus free to expand and move when the temperature of each printhead changes. 
     The center of the carriage device or aluminum ink reservoir  120  is in turn rigidly or fixedly pinned and mounted to the low LCTE member or bar  110 , and its ends (first and second ends) of each carriage device are supported by another set of kinematic expansible mounts  130  translatably on the LCTE member  110 , and are thus free to expand and to move under the influence of a temperature change or thermal expansion of the reservoir  120 . Thus, the fixed center of each of the two printheads H 1 , H 2  in a printhead assembly  32 ,  34 ,  36 ,  38  will have minimal relative movement as determined by the length of the low LCTE member  110  and by the temperature difference. The mounting scheme thus minimizes the thermal expansion between the printheads as well as the use of the more costly LCTE members or material. 
     In other words, the method and apparatus of the present disclosure operate to minimize the sensitivity of the initially aligned printhead aperture or nozzle locations to temperature changes or thermal expansion changes. Thermal expansion is minimized thus by kinematically or expansibly mounting components  130 ,  140  of the ink jet printhead assembly such that the length available for thermal expansion is cut in half or eliminated. The method and apparatus in addition also minimize the use of low coefficient of thermal expansion LCTE materials. This is important because materials with low coefficient of thermal expansion are usually quite expensive when compared to other typical engineering materials such as steel and aluminum. 
     As can be seen, there has been provided apparatus and a method of using it to mount an ink jet printhead unit in an ink jet printing machine for minimizing printing defects due thermal expansion effects. The method includes (a) first mounting a low coefficient of thermal expansion (LCTE) member, having a first end, a second end and a center, to a portion of a frame of the printing machine; (b) next mounting ink jet printhead unit, having a first end, a second end and a center, to an expansible carriage device, having a first end, a second and a center, to form a printhead assembly; and (c) expansibly mounting the expansible carriage device of the printhead assembly to the LCTE member. 
     While the embodiment of the present disclosure disclosed herein is preferred, it will be appreciated from this teaching that various alternative, modifications, variations or improvements therein may be made by those skilled in the art, which are intended to be encompassed by the following claims: