Patent Publication Number: US-7216968-B2

Title: Media electrostatic hold down and conductive heating assembly

Description:
BACKGROUND 
   Inkjet printers have become popular for printing on media, especially when precise printing of color images is needed. For instance, such printers have become popular for printing color image files generated using digital cameras, for printing color copies of business presentations, and so on. An inkjet printer is more generically a fluid-ejection device that ejects fluid, such as ink, onto media, such as paper. 
   To maintain positioning of the media while fluid is being ejected onto the media, some fluid-ejection devices utilize various hold down elements to keep the media properly in place. Furthermore, to expedite drying of the fluid that has been ejected onto the media, some fluid-ejection devices utilize various heating elements. However, including both a hold down element and a heating element in the same fluid-ejection device can cause the two elements to interfere with one another, such that one or both of the elements may not function correctly or optimally. 
   SUMMARY OF THE INVENTION 
   A media hold down and heating assembly of one embodiment of the invention includes a dielectric against which media is positioned, a conductive heating element, and an electrostatic hold down element. The conductive heating element is to conductively heat the media through the dielectric. The electrostatic hold down element is to electrostatically hold down the media against the dielectric. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings referenced herein form a part of the specification. Features shown in the drawing are meant as illustrative of only some embodiments of the invention, and not of all embodiments of the invention, unless otherwise explicitly indicated, and implications to the contrary are otherwise not to be made. 
       FIG. 1  is a diagram of a side view of a media hold down and heating assembly, according to an embodiment of the invention. 
       FIG. 2  is a diagram of a cross-sectional top view of a media hold down and heating assembly, according to an embodiment of the invention. 
       FIGS. 3A and 3B  are diagrams of side views depicting how electrodes of a media hold down and heating assembly can be situated within a dielectric of the assembly, according to varying embodiments of the invention. 
       FIGS. 4A and 4B  are diagrams depicting how a dielectric of a media hold down and heating assembly can be implemented as or within a drum and a belt, respectively, according to varying embodiments of the invention. 
       FIG. 5  is a block diagram of a fluid-ejection device, according to an embodiment of the invention. 
       FIG. 6  is a flowchart of a method of use, according to an embodiment of the invention. 
       FIG. 7  is a flowchart of a method of manufacture, according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE DRAWINGS 
   In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
   Media Electrostatic Hold Down and Conductive Heating Assembly 
     FIG. 1  shows a side view of a media hold down and heating assembly  100 , according to an embodiment of the invention. The assembly  100  is specifically depicted in  FIG. 1  in which a fluid-ejection mechanism  112 , such as an inkjet printhead, ejects fluid  114 , such as ink, onto media  108 . The media  108  in this case may be paper, transparencies, cardboard, or another type of media that is amenable to receiving fluid ejection. However, in other embodiments of the invention, the assembly  100  can be utilized in conjunction with other types of media in which the fluid-ejection mechanism  112  is not present. For instance, the assembly  100  may be utilized in conjunction with media that is a semiconductor wafer, for utilization in semiconductor processing. 
   The media hold down and heating assembly  100  includes a dielectric  102 , an electrostatic hold down element  104  and a conductive heating element  106 . The dielectric  102  may be a polymer or plastic strip or sheet, or another type of dielectric. Preferably but not necessarily, the dielectric  102  is solid, without any perforations or holes. The electrostatic hold down element  104  and the conductive heating element  106  may share some components, as indicated by the overlapping region  116  between the elements  104  and  106 . Furthermore, some of the components of the element  104  and/or  106  may be at least partially embedded or situated within the dielectric  102 , which is not specifically depicted in  FIG. 1 . 
   The electrostatic hold down element  104  generates an electric field that attracts, or holds down, the media  108  against the dielectric  102 , as indicated by the arrows  118 . As such, it is preferably a capacitive hold down element. The element  104  performs this electrostatic hold down functionality so that the media  108  is properly positioned against the dielectric  102  for the fluid-ejection mechanism  112  to eject the fluid  114  on the media  108 . The conductive heating element  106  generates heat, as indicated by the squiggly lines  120 , that conducts through the dielectric  102  and to the media  108  and the fluid  114  that has been ejected onto the media  108 . The element  106  performs this conductive heating functionality to dry or expedite drying of the fluid  114  that has been ejected onto the media  108 . 
     FIG. 2  shows a top view of the media hold down and heating assembly  100  in detail, according to an embodiment of the invention. The electrostatic hold down element  104  of  FIG. 1  is inclusive of a high-voltage source  202  and a number of electrodes  206 A,  206 B, . . . ,  206 N, which are collectively referred to as the electrodes  206 . The electrodes  206  may also be referred to as resistive elements without loss of generality. The conductive heating element  106  of  FIG. 1  is inclusive of a pair of electric heater power supplies  204 A and  204 B, which are collectively referred to as the electric heater power supplies  204 , as well as the electrodes  206 . The elements  104  and  106  thus share the electrodes  206  between themselves. The dielectric  102  is indicated as a dotted line, to indicate the cross-sectional nature of  FIG. 2 , such that the electrodes  206  are situated under at least the top surface of the dielectric  102 , on which the media  108  is positioned in  FIG. 1 . 
   The high-voltage source  202  has a positive terminal  208  and a negative terminal  210 . The electric heater power supply  204 A has a positive terminal  212 A and a negative terminal  214 A, whereas the electric heater power supply  204 B has a positive terminal  212 B and a negative terminal  214 B. Each of the electrodes  206  is preferably substantially shaped as an elongated U having two ends. For instance, the electrode  206 A has a first end  216 A and a second end  218 A, the electrode  206 B has a first end  216 B and a second end  218 B, and the electrode  206 N has a first end  216 N and a second end  218 N. Although there are six of the electrodes  206  in  FIG. 2 , this is provided as an illustrative example, and other embodiments may have more or less of the electrodes  206 . The electrodes  206  are situated or positioned parallel to one another on their long sides. 
   The electrodes  206  may be logically numerated from the first electrode  206 A to the last electrode  206 N, such that the electrodes  206  include both odd-numbered and even-numbered electrodes. The positive terminal  212 A of the first electric heater power supply  204 A is connected to the positive terminal  208  of the high-voltage source  202  and to the second ends  218  of odd-numbered of the electrodes  206 , whereas the negative terminal  214 A of the first electric heater power supply  204 A is connected to the first ends  216  of the odd-numbered of the electrodes  206 . The positive terminal  212 B of the second electric heater power supply  204 B is connected to the negative terminal  210  of the high-voltage source  202  and to the first ends  216  of even-numbered of the electrodes  206 , whereas the negative terminal  214 B of the second electric heater power supply  204 B is connected to the second ends  218  of the even-numbered of the electrodes  206 . The import of this spatial positioning of the electrodes  206 , the electric heater power supplies  204 , and the high-voltage source  202  of this embodiment of the invention is described in the next section of the detailed description. 
   The high-voltage source  202  creates an electric field between adjacent electrodes  206 . This is the electric field that electrostatically attracts the media  108  against the dielectric  102  in  FIG. 1 . The electric heater power supplies  204  cause the electrodes  206  to generate heat. This is the heat that conducts through the dielectric  102  to the media  108  and the fluid  114  ejected thereon in  FIG. 1 . Also depicted in  FIG. 2  is a voltage  220  between a point  222  of the electrode  206 A and a point  224  of the electrode  206 B, as is specifically described in the next section of the detailed description. 
     FIGS. 3A and 3B  show side views of different manners by which the electrodes  206  may be situated or positioned relative to the dielectric  102 , according to varying embodiments of the invention. In  FIG. 3A , the electrodes  206  are situated or positioned under the dielectric  102 . The electrodes  206  may or may not make actual contact with the dielectric  102 . In  FIG. 3B , the electrodes  206  are partially situated, positioned, or disposed within the dielectric  102 . The electrodes  206  may also be completely disposed within the dielectric  102 . 
     FIGS. 4A and 4B  show how the dielectric  102  may be implemented, according to varying embodiments of the invention. In the side view of  FIG. 4A  the dielectric  102  is part of or includes a drum  402  that rotates counter-clockwise, as indicated by the arrow  404 . The media  108  moves around the drum  402  as is depicted in  FIG. 4A , ultimately moving in the direction indicated by the arrow  406 . In the side view of  FIG. 4B , the dielectric  102  is part of or includes a belt  452  that moves clockwise, as indicated by the arrow  460 , around the pulleys  458  and  460 . The belt  460  moves the media  108  from left to right, as indicated by the arrow  456  (consistent with the arrow  110  of  FIG. 1 ), under the fluid-ejection mechanism  112 , which may be stationary, or move in and out of the plane of  FIG. 4B . By comparison to  FIGS. 4A and 4B , the previously described  FIG. 1  can be considered in one embodiment to depict the dielectric  102  as part of or included in a platen. 
   Non-Interference Between Hold Down Element and Heating Element 
   In at least some embodiments of the invention, the electrostatic hold down element  104  and the conductive heating element  106  of the media hold down and heating assembly  100  of  FIG. 1  do not affect one another. For instance, the electric field generated by the electrostatic hold down element  104  is not affected by the conductive heating element  106 , such that the elements  104  and  106  do not interfere with one another in the functionalities that they perform. More specifically, the electrodes  206 , the electric heater power supplies  204 , and the high-voltage source  202  of  FIG. 2  are spatially positioned such that the electric field created by the high-voltage source  202  within the electrodes  206  is unaffected by the electric heater power supplies  204 . 
   Such non-interference between the high-voltage source  202  and the electric heater power supplies  204  of  FIG. 2  is demonstrated in one specific embodiment by the voltage between each adjacent pair of electrodes  206 , such as the voltage  220  of  FIG. 2  between the points  222  and  224 , being equal to the voltage of the high-voltage source  202 . Because the voltage between each adjacent pair of electrodes  206  is equal to the voltage of the high-voltage source  202 , the electric heater power supplies  204  do not affect the high-voltage source  202  and thus do not affect the electric field created by the high-voltage source  202  within the electrodes  206 . This is now particularly described in relation to the voltage  220  being equal to the voltage of the high-voltage source  202 . 
   The hold down force is caused by an electric field between adjacent electrodes  206 , such as the electrodes  206 A and  206 B. The electric field is generated by the voltage difference between the electrodes  206 A and  206 B, also referred to as the voltage  220 . Where the resistance of the electrodes  206  is equal, the resistance from the second end  218 A to the point  222  of the electrode  206 A, referred to as R be , is identical to the resistance from the first end  216 B to the point  224  of the electrode  206 B, referred to as R cf . Likewise, the resistance from the first end  216 A to the point  222  of the electrode  206 A, referred to as R ae , is identical to the resistance from the second end  218 B to the point  224  of the electrode  206 B, referred to as R df . 
   The voltage between the points  222  and  224  is then given by:
 
 V   ef   =V   eb   +HV+V   cf ,  (1)
 
where V ef  is the voltage  220 , V eb  is the voltage from the point  222  to the second end  218  of the first electrode  206 A, HV is the voltage of the high-voltage source  202 , and the voltage V cf  is the voltage from the point  224  to the first end  216 B of the second electrode  206 B. Since
 
                     V   eb     =     -         V   ht1     ⁢     R   be           R   be     +     R   ae             ,           (   2   )               
where V ht1  is the voltage of the first electric heater power supply  204 A, and since
 
                     V   cf     =         V   ht2     ⁢     R   cf           R   cf     +     R   df           ,           (   3   )               
where V ht2  is the voltage of the second electric heater power supply  204 B, then
 
                   V   ef     =       -         V   ht1     ⁢     R   be           R   be     +     R   ae           +   HV   +           V   ht2     ⁢     R   cf           R   cf     +     R   df         .               (   4   )               
Further, since R cf  equals R be  and R df  equals R ae , then
 
                     V   ef     =       -         V   ht1     ⁢     R   be           R   be     +     R   ae           +   HV   +         V   ht2     ⁢     R   be           R   be     +     R   ae             ,           (   5   )               
or,
 
                   V   ef     =           (       V   ht2     -     V   ht1       )     ⁢     R   be           R   be     +     R   ae         +     HV   .               (   6   )               
Thus, if V ht1  equals V ht2 , then
 V ef =HV.  (7) 
   Therefore, if the voltage of the first electric heater power supply  204 A is equal to the voltage of the second electric heater power supply  204 B, then the voltage  220 , which is representative of the voltage between each adjacent pair of the electrodes  206 , is equal to the voltage of the high-voltage source  202 . This means that the electric heater power supplies  204  do not affect or interfere with the electric field created by the high-voltage source  202  within the electrodes  206 . The voltages of the electric heater power supplies  204  are equal to one another in one embodiment where the electric heater power supplies  204  are themselves identical. 
   It is noted that the differences in the magnitudes of the voltages of the electric heater power supplies  204 , and the differences in the resistances of the heating elements, can result in the heater power supplies  204  affecting the electric field holding down the media. There is substantially no interference between the heater power supplies  204  and the high-voltage source  202  on the electric field holding down the media where the resistances of the power supplies  204  are substantially equal. 
   Fluid-Ejection Device and Methods 
     FIG. 5  shows a block diagram of a fluid-ejection device  500 , according to an embodiment of the invention. The fluid-ejection device  500  includes the fluid-ejection mechanism  112  and the hold down and heating assembly  100  that have been described. The fluid-ejection device  500  also optionally includes a duplexing mechanism  502  and/or a media-advance mechanism  504 . The fluid-ejection device  500  may include other components in addition to or in lieu of those depicted in  FIG. 5 , as can be appreciated by those of ordinary skill within the art. 
   The fluid-ejection mechanism  112  ejects fluid onto the media  108  of  FIG. 1 . Where the fluid is ink, the fluid-ejection mechanism  112  is an inkjet-printing mechanism, such as an inkjet printhead, and the fluid-ejection device  500  is an inkjet-printing device, such as an inkjet printer or another device that includes inkjet-printing functionality. The hold down and heating assembly  100  is an electrostatic hold down and conductive heating assembly, and may be implemented in one embodiment as has been described in the preceding sections of the detailed description. Thus, the assembly  100  electrostatically holds down the media  108  for the fluid-ejection mechanism  112  to eject fluid onto the media  108 , and conductively heats the media  108  to substantially dry the fluid ejected onto the media  108 . 
   The duplexing mechanism  502  is a mechanism that allows the fluid-ejection mechanism  112  to eject fluid onto both sides of the media  108  of  FIG. 1  without manual reinsertion of the media  108  into the fluid-ejection device  500  by a user, after one side of the media  108  has had fluid ejected onto it. For instance, the fluid-ejection mechanism  112  may eject fluid over the media swaths of one side of the media  108 . The duplexing mechanism  502  then effectively flips over the media  108 , so that the fluid-ejection mechanism  112  may eject fluid over the media swaths of the other side of the media  108 , as can be appreciated by those of ordinary skill within the art. 
   The media-advance mechanism  504  is a mechanism that advances the media  108  of  FIG. 1  past and between the fluid-ejection mechanism  112  and the media hold down and heating assembly  100  in one embodiment of the invention. For instance, the media-advance mechanism  504  may advance the media so that a current swath of the media  108  lies between the mechanism  112  and  100 . The fluid-ejection mechanism  112  ejects fluid onto this media swath while the media hold down and heating assembly  100  electrostatically holds down the media  108 . The media hold down and heating assembly  100  then conductively heats the media  108  to substantially dry the fluid ejected onto the media swath. The media-advance mechanism  504  advances the media  108  to a next media swath on which fluid is to be ejected, and this process continues until the media  108  has had fluid ejected thereon as intended. 
     FIG. 6  shows a method of use  600 , according to an embodiment of the invention. The method  600  may be performed by the fluid-ejection device  500  of  FIG. 5 , and/or the media hold down and heating assembly  100  of  FIG. 1 . A current swath of the media  108  is electrostatically held down against the dielectric  102  of  FIG. 1  ( 602 ). While the current swath of the media  108  of  FIG. 1  is held down, the fluid  114  of  FIG. 1  is ejected onto the current swath ( 604 ), and the current swath of the media  108  is conductively heated through the dielectric  102  to at least substantially dry the fluid  114  ejected ( 606 ). If there are any more swaths on the media  108  ( 608 ), then the current swath is advanced to the next swath of the media  108  ( 610 ), and the method  600  repeats at  602 . Otherwise, the method  600  is finished ( 612 ). 
     FIG. 7  shows a method of manufacture  700 , according to an embodiment of the invention. The method  700  may be performed to at least partially manufacture the media hold down and heating assembly  100  of  FIG. 1 , and/or the fluid-ejection device of  FIG. 5 . The dielectric  102  of  FIG. 1  is provided, against which the media  108  of  FIG. 1  is positionable ( 702 ). The conductive heating element  106  of  FIG. 1  is also provided, which is capable of conductively heating the media  108  through the dielectric  102  ( 704 ). Finally, the electrostatic hold down element  104  of  FIG. 1  is provided, which is capable of electrostatically holding down the media  108  against the dielectric  102  ( 706 ). 
   CONCLUSION 
   It is noted that, although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any adaptations or variations of embodiments of the present invention. Therefore, it is manifestly intended that this invention be limited only by the claims and equivalents thereof.