Abstract:
A solid phase change ink melter assembly in a phase change ink image producing machine includes an array of a plurality of spaced apart fins, the array defining a top face for receiving the solid pieces of phase change ink, a bottom face for discharging melted ink, and opposite melter surfaces for melting the solid pieces in contact therewith. The assembly further including a number of heat transfer devices extending through and in heat transfer contact with the plurality of fins, the heat transfer devices including a heating element for heating the device. The bottom edge of the fins defines a plurality of apexes which serve as drip points for molten phase change ink.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a continuation of and claims priority to co-pending application Ser. No. 12/638,863, filed on Dec. 15, 2009, and assigned to the assignee of the present application. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to image producing machines, and more particularly to a solid phase change ink melter assembly and an image producing machine or printer including such an assembly 
     BACKGROUND 
     The present disclosure relates generally to image producing machines, and more particularly to a solid phase change ink melter assembly and an image producing machine or printer including such an assembly. 
     In general, phase change ink image producing machines or printers employ phase change inks that are in a solid phase at ambient temperature, but exist in the molten or melted liquid phase (and can be ejected as drops or jets) at an elevated operating temperature of the machine or printer. At such an elevated operating temperature, droplets or jets of the molten or liquid phase change ink are ejected from a printhead device of the printer onto a printing media. 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. 
     An example of such a phase change ink image producing machine or printer, and the process for producing images therewith onto image receiving sheets is disclosed in U.S. Pat. No. 6,905,201, issued on Jun. 14, 2005. The &#39;201 patent discloses an image producing machine, such as the high-speed phase change ink image producing machine or printer  10  shown in  FIG. 1  herewith. As illustrated, the machine  10  includes an imaging member  12 , shown in the form of a drum, having an imaging surface  14  that is movable in the direction  16 , and on which phase change ink images are formed. 
     The image producing machine  10  also includes a phase change ink delivery subsystem  20  that has at least one source  22  of one-color phase change ink in solid form. For a multicolor image producing machine, the ink delivery system  20  may include several sources, such as four sources  22 ,  24 ,  26 ,  28 , representing four different colors CYMK (cyan, yellow, magenta, black) of phase change inks. The ink delivery system also includes a melting and control apparatus  300  ( FIG. 2 ) for melting or phase changing the solid form of the phase ink into a liquid form, and then supplying the liquid form to a printhead system  30  including at least one printhead assembly  32 . Since the phase change ink image producing machine  10  is a high-speed, or high throughput, multicolor image producing machine, the printhead system includes four separate printhead assemblies  32 ,  34 ,  36  and  38  receiving molten ink from a corresponding source  22 ,  24 ,  26  and  28 . 
     As further shown, the machine  10  includes a substrate supply and handling system  40 . 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 control subsystem (ESS)  80 . Details of these systems and subsystems can be obtained from the &#39;201 patent. In operation, image data for an image to be produced is sent to the controller  80 , such as from a scanning system  70 , for processing and output to the printhead assemblies  32 ,  34 ,  36 ,  38 . Appropriate color solid forms of phase change ink are melted and delivered to the printhead assemblies to form the image on the surface  14 . 
     The &#39;201 patent discloses a number of melter assemblies  300 , as shown in  FIG. 2  that includes a housing  302  with walls  304  defining a melting chamber  306 . Each melter assembly  300  also includes a positive temperature coefficient (PTC) heating device  310  that is mounted within the melting chamber  306  for heating and melting solid pieces of phase change solid ink. Each housing  302  may include a screen device  314  that is mounted below the PTC heating device  310  for removing unwanted particles from the melted molten liquid ink coming from the heating device  310 . 
     The PTC heating device  310  disclosed in the &#39;201 patent includes a frame made of a conductive material such as aluminum, and a pair of folded fins  326 ,  328  that are also made of a conductive material such as aluminum. The folded fins  326 ,  328  act as a heating element for providing the heat and melting surface area that contact and melt the solid pieces phase change ink. A pair of electrodes connected the folded fins  322 ,  324  to an electrical supply. The folded fins define a series of channels between fin folds  332  that increase the heated surface area and therefore maximize the efficiency of the PTC heating device  310 . The molten liquid ink drops gravitationally from the folded fins and through the channels to the molten liquid ink storage and control assembly  400  located below the melter assembly  300 , as shown in  FIG. 2 . 
     As disclosed herein, the phase change ink printing process includes raising the temperature of a solid form of the phase change ink to melt the ink and form a molten liquid phase change ink. Conventionally, the solid form of the phase change is a “stick”, “block”, “bar” or “pellet” that is fed into a heated melting device, such as the device disclosed in the &#39;201 patent. Due to the requirement for the phase change of the ink, image producing machines or printers of this type are considered to be low throughput, typically producing at a rate of less than 30 prints per minute (PPM). The throughput rate (PPM) of a phase change ink image producing machine is directly dependent on how quickly the “stick”, “block”, “bar” or “pellet” form can be melted down into a liquid. 
     There a prevailing need for higher throughput for phase change ink image producing machines or printers particularly color images on plain paper substrates. 
     SUMMARY 
     A solid ink melter apparatus comprises an array of a plurality of spaced apart fins, with a number of heat transfer elements passing through the plurality of fins. Solid ink pellets are disposed on a top face of the array and melted by the fins when the fin array is heated by the heat transfer elements. In one embodiment, the fins are in the form of substantially flat plates with the top edges thereof defining the top face of the array. The opposite bottom edge of the fins are configured to define a number of drip points. In one embodiment, the drip points are in the form of a triangular apex so that solid ink that melts on the melting surfaces of the fins will follow the bottom edge of the fins to the number of drip points. 
     A solid phase change ink melter assembly in a phase change ink image producing machine comprises an array of a plurality of spaced apart fins, the array defining a top face for receiving the solid pieces of phase change ink, a bottom face for discharging melted ink, and opposite melter surfaces for melting the solid pieces in contact therewith. The assembly further comprises a number of heat transfer devices extending through and in heat transfer contact with the plurality of fins, the heat transfer devices including a heating element for heating the device. In one embodiment, the fins are in the form of substantially flat parallel plates spaced apart a distance approximately equal to a maximum dimension of the solid pieces of phase change ink. The bottom edge of the fins may define a plurality of apexes which serve as drip points for the molten phase change ink. 
     In another embodiment, a phase change ink image producing machine comprises: 
     (a) a control subsystem for controlling operation of all subsystems and components of the image producing machine; 
     (b) a movable imaging member having an imaging surface; 
     (c) a printhead system connected to the control subsystem for ejecting drops of melted molten liquid phase change ink onto the imaging surface to form an image; 
     (d) at least one ink supply for supplying solid pieces of phase change ink to be heated and melted; and 
     (e) a melter assembly associated with the at least one ink supply for heating and melting the solid pieces of phase change ink into melted molten liquid ink, the melter assembly including; 
     an array of a plurality of spaced apart fins, the array defining a top face for receiving the solid pieces of phase change ink, a bottom face for discharging melted ink, and opposite melter surfaces for melting the solid pieces in contact therewith; and 
     a number of heat transfer devices extending through and in heat transfer contact with the plurality of fins, the heat transfer devices including a heating element for heating the device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description presented below, reference is made to the drawings, in which: 
         FIG. 1  is a vertical schematic of a high-speed phase change ink image producing machine or printer that may incorporate the solid phase change ink melter assembly disclosed herein; 
         FIG. 2  is a perspective, partially exploded view of a solid phase change ink melter assembly of the prior art, as represented by U.S. Pat. No. 6,905,201; 
         FIG. 3  is a front perspective view of a solid ink melter apparatus according to one embodiment disclosed herein; 
         FIG. 4  is a rear view of the solid ink melter apparatus shown in  FIG. 3 ; 
         FIG. 5  is a side view of the solid ink melter apparatus shown in  FIG. 3  mounted within one embodiment of a solid ink melter assembly; 
         FIG. 6  is an enlarged top view of a portion of the solid ink melter apparatus shown in  FIG. 3 ; 
         FIG. 7  is a front view of a fin incorporated into the solid ink melter apparatus shown in  FIG. 3 ; 
         FIG. 8  is a bottom view of the fin shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment, a sold ink melter system  500  ( FIG. 5 ) includes a solid or phase-change ink melter apparatus  510 . As shown in  FIGS. 3-5 , the melter apparatus includes an array  511  of a plurality of spaced apart fins  512 . A number of heat transfer devices  513  pass through the array of fins  512 . The heat transfer devices are in heat transfer contact with the fins so that when the assemblies are heated the heat is conveyed to the fins. 
     The array  511  of fins  512  defines a top face  541  onto which a supply of solid ink pellets P rests, as shown in  FIG. 5 . The pellets may be introduced to and contained on the top face by a feed hopper  530  of the solid ink melter system  500 . In one embodiment, the fins  512  are spaced apart by a gap distance d ( FIG. 6 ) that is at least equal to an outer dimension of an individual pellet. For instance, in one specific embodiment, the pellets P may be generally spherical with a diameter of 0.9±0.3 mm. The gap distance d is at least equal to the maximum dimension or the largest pellet diameter of 1.2 mm so that all the pellets are able to pass between the heated fins. In one embodiment, the gap distance d is equal to or only slightly greater than the maximum dimension of the pellets P. The gap distance may be optimized in relation to the pellet size to achieve a predetermined melt flow rate. For instance, the gap distance may be calibrated to the pellet size to achieve a melt flow rate of 210 g/min. to maintain print speed at 28% coverage. 
     As shown in  FIGS. 7-8 , each fin  512  is in the form of a substantially flat and generally rectangular plate. The top edge  540  of the plate is substantially flat while the bottom edge  542  defines a number of drip points  544 . As shown in  FIG. 7 , these drip points are substantially triangular forming an apex. When the solid ink pellets are introduced into the fin array  511 , the pellets fall between the spaced-apart fins and contact the front and back melter surfaces  545  of the plates. When the ink melts on the surfaces, gravity forces the melted ink to flow toward the bottom edge  542 . Surface tension causes the dripping ink to follow the bottom edge to one of the apexes or drip points. When enough melted ink collects at the drip point, ink drops are formed which eventually drop into a melted ink reservoir  535  underneath the bottom face  543  of the melter apparatus  510 . The melted ink is then fed by a valve array  537  to the printheads in a conventional manner. 
     The fin plates define a number of openings to receive a corresponding number of heat transfer devices  513 . The devices  513  are operable to heat the fins in the fin array to thereby increase the temperature of the melter surfaces  545  sufficient to melt the solid ink pellets. As shown in  FIGS. 3-5 , four such heat transfer devices are provided. Each device  513  includes a tubular body  514  that extends through the fin array. Mounting plates  516  flank the fin array and include mounting flanges  517  for engaging and supporting the tubular body  514 . In one embodiment, the tubular body  514  defines a heater bore  520  and a sensor bore  522  extending parallel to and beneath the heater bore. The heater bore  520  is configured to receive a heating element  525  that may be in the form of a closed-loop controlled heating cartridge or thermistor. When the element is energized it generates heat that is conducted to the heater tube  520 . This heat is then transferred to the fins to heat the melter surfaces  545 . 
     The sensor bore  522  is configured to receive a temperature sensor  527 , such as a thermocouple. In one embodiment, the sensor bore  522  is integral or in direct communication with the heater bore  520  so that the sensor can provide an accurate measure of the temperature within the heater bore. The temperature sensor  527  is integrated into the closed-loop control for the heating element  525 , which may be a PID (proportional integral derivative) controller (not shown). The heating element  525  and sensor  527  are configured to maintain a temperature suitable for optimal melting of the solid ink pellets. In one embodiment, this heating element is controlled to a temperature of about 120° C. For certain inks, the melting temperature should not exceed a predetermined value, such as about 135° C., which might cause discoloration of the melted ink. The controller can be calibrated to maintain the desired temperature and to not exceed the maximum allowable temperature. 
     The heat transfer device  513  relies upon intimate contact between the heated tubular body  514  and the fins  512 . Thus, the fin plates define a plurality of openings corresponding to the configuration of the tubular body  514 . Thus, the plates define a first portion or heating tube opening  546  and a contiguous second portion or sensor tube opening  547 , as shown in  FIG. 7 . The openings are sized for a press fit between the tubular body and the fins. The openings  546  and  547  may be circular to correspond to a circular tubular shape of the tubular body  514 . 
     In order to maintain the optimum spacing between fins as the fins are assembled or stacked onto the plurality of heat transfer devices, the fins are provided with corresponding spacers  518  affixed to the fins  512 . The spacers  518  follow the perimeter of the heating tube opening, as shown in  FIG. 7 . In the illustrated embodiment, the spacers do not extend around the perimeter of the sensor tube opening  547  due to the proximity of the opening to the drip points  544 . 
     In one embodiment, the fins  512  and tubular bodies  513  are formed of aluminum for optimum heat transfer. The spacers  518  may also be formed of a heat transfer material, such as aluminum to avoid “cold spots” within the fin array  511 . The spacers  518  may be bonded to a surface  545  of the fin plate in a conventional manner capable of withstanding the operating temperatures of the solid ink melter apparatus  510 . The fins have a thickness t 1  of about 1 mm, while the spacers have a thickness t 2  of about 1.2 mm. The thickness of the spacers is dictated by the desired gap dimension d, as described above. 
     The fin array  512  of the apparatus  510  provides an extremely large melter surface area in a small package. In one embodiment, the fins are about 120 mm long and about 25 mm wide so that the entire fin array and solid ink melter apparatus  510  can fit within a 125×125 mm area. The fin watt density of the illustrated embodiment is about 3 watt/in 2 . Each heat transfer device  513  can develop about 52 watt/in 2 . In one embodiment, the fin array  511  includes 62 fins pressed onto four heat transfer devices  513 . This configuration is capable of generating 1800 total watts to achieve a melted ink flow rate of about 220 grams/minute. 
     It is contemplated that the size of the fin array can be adjusted in relation to space constraints, solid ink melting characteristics and desired flow rates. This, in some embodiments the fin array may require less or more than 62 fins. The fin configuration of the apparatus  510  simplifies construction of the apparatus and allows for simple modifications by pressing only the desired number of fins onto the tubular bodies  514 . Moreover, although the fins may incorporate four heat transfer devices  513 , not all of the assemblies need be incorporated or activated. 
     In the illustrated embodiment, the heating elements  525  are in direct contact with the tubular bodies  513  so that the bodies are heated by conduction. Thermal grease may be applied between the heating elements and the inside of the tubular bodies to enhance the conduction path. 
     It will be appreciated that various of the above-described features and functions, as well as other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 
     For example, the fin  512  of the fin array  511  described herein are constructed as generally rectangular flat plates; however, the configuration of the plates may vary according to space considerations within the particular printing machine. Thus, the fins may be curved or incorporate a zig-zag configuration, provided the plates in the array are generally parallel with proper spacing. Moreover, the plates within a given array may have different configurations to help ensure a uniform temperature across the surface  541 , or more particularly across the portion of the surface onto which the phase change pellets are dispensed. 
     Likewise, the heat transfer devices  513  may be modified provided they are capable of heating the fin array  511  to a proper melting temperature. Thus, while the heating elements  525  described herein rely upon conduction heat transfer, the heating elements may be configured for convection heat transfer within the interior of the heater bores  520 , although this approach may increase the energy requirements to produce the optimum melting temperature at the fins. In still another alternative, the heating elements may be replaced with a hot heat transfer fluid flowing through the heater bores. Other devices capable of increasing the temperature of the melter surfaces of the fin array may be contemplated.