Patent Publication Number: US-7589949-B2

Title: Fluid assisted emitter tip and method

Description:
FIELD OF THE INVENTION 
     The embodiments of the present invention relate generally to the field of electrostatic charge control and more particularly without limitation to corona discharge emitter tips. 
     BACKGROUND 
     Corona discharge ionizer devices are commonly used for controlling the presence of electrostatic charge in manufacturing environments involving sensitive components, such as in the semiconductor and data storage device industries. Corona discharge ionizers employ a number of emitter tips that, when energized with a sufficiently high voltage, create a corona discharge. The corona discharge is an ion cloud having a charge established by the polarity of the voltage. In many cases a non-hydrogen fluid stream is passed over the emitter tips in order to direct and advance the ion stream in order to statically charge or discharge a work piece. However, problems exist in the current state and use of corona discharge ionizers. 
     One problem is the tendency for precipitating ammonium nitrate on the emitter tip. In order for the tip to effectively create the corona discharge, the emitter tip must remain clean, sharp, and electrically conductive. Such a buildup reduces the tip&#39;s effectiveness in creating the corona discharge. Regularly scheduling maintenance activities to clean or replace the emitter tips can be a costly and unworkable production interruption. 
     Another problem is associated with bursts of submicron particles coming from the emitter tips that can be introduced into the manufacturing environment. In some cases the contamination comes from sputtering of the material from which the emitter tip is manufactured; in other cases the contamination is particles of the ammonium nitrate precipitation. 
     While various approaches have been proposed in the art to address the contamination that can be introduced into the manufacturing process by emitter tips, there nevertheless remains a continued need for improvements in the art. It is to such improvements that the claimed invention is directed. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention contemplate an emitter tip for a corona discharge device. The emitter tip comprises an elongated body with a tapered closed end. The body defines a central passage and the tapered end defines a medial tip passage in fluid communication with the central passage. 
     In some embodiments a method is provided for controlling electrostatic charge. The method comprises providing a voltage source; providing a pressurized fluid source; connecting the emitter tip to the voltage source and to the fluid source; passing the fluid through the emitter tip; and electrically energizing the emitter tip. 
     In other embodiments a corona discharge device is provided, comprising a voltage source connected to an emitter tip; and an arrangement for preparing a work piece for manufacturing by steps for controlling the electrostatic charge of the work piece. The steps for controlling is characterized by connecting a voltage source and a pressurized fluid source to the emitter tip, and by passing the pressurized fluid through the emitter tip while electrically energizing the emitter tip. 
     These and various other features and advantages which characterize the claimed invention will become apparent upon reading the following detailed description and upon reviewing the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of a corona discharge device constructed in accordance with embodiments of the present invention. 
         FIG. 2  is a side elevational view of an emitter tip of the corona discharge device of  FIG. 1  constructed in accordance with embodiments of the present invention. 
         FIG. 3  is a front elevational view of the emitter tip of  FIG. 2   
         FIG. 4  is a block diagram of a method for controlling electrostatic charge illustrating steps for practicing the embodiments of the present invention. 
         FIG. 5  is a side elevational view of the emitter tip of  FIG. 2  utilized in accordance with alternative embodiments of the corona discharge device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagrammatic illustration of a corona discharge device  100  constructed in accordance with embodiments of the present invention. The device  100  comprises an emitter tip  102  that is electrically connectable to a high voltage source  104  and to a pressurized fluid source  106 . The illustrative embodiments of  FIG. 1  identify the voltage source  104  as being an alternating current type voltage source. In equivalent alternative embodiments the voltage source  104  can be a pulsed direct current voltage source, and preferably can be a direct current steady state voltage source. The voltage source  104  electrically energizes the tip  102  which, by way of its construction, emits a corona discharge  108  of electrically charged ions. The pressurized fluid  106  aids in protecting the emitter tip  102  from adverse deterioration and/or ammonium nitrate precipitation by delivering a supply of pressurized fluid into the emitter tip  102 . The pressurized fluid  106  can also aid in propelling the ions toward a target object. 
       FIG. 2  is a side elevational view of the emitter tip  102 , which generally comprises an elongated body  110  with a tapered portion  112 . In the illustrative embodiments of  FIG. 1 , the body  110  defines a circular cross section with a diameter of about 0.100 inches. The tapered portion  112  is substantially contiguous with the body  110  at a proximal end  114  of the tapered portion  112 , and can terminate in a sharp or a radiused tip at a distal end  116  of the tapered portion  112 . In preferred embodiments the distal end  116  of the tapered portion  112  defines about a 0.003 inch radius. In the circular cross section embodiments of  FIG. 2  the converging surface defining the tapered portion  112  is conical. 
     The body  110  defines a longitudinal central passage  118 . The tapered end  112  defines one or more tip passages  120  passing through the tapered end  112  and in fluid communication with the central passage  118 . In the illustrative embodiments of  FIG. 2  the tip passage  120  has a bore diameter of about 0.01 inches. In this arrangement, pressurized fluid from the fluid source  106  ( FIG. 1 ) can be delivered into the central passage  118  and expelled through the one or more tip passages  120 . 
     The formation of ammonium nitrate is significantly reduced by passing an appropriate fluid through the tip passages  120  while electrically operating the emitter tip  102 . Ammonium nitrate is a compound formed of nitrogen, hydrogen, and oxygen. Thus, a source of hydrogen is necessary to precipitate ammonium nitrate. One source of hydrogen is atmospheric water vapor. By flowing a sufficiently dry gas through the tip passage  120  and thereby onto the distal end  116  of the tapered portion  112 , no ammonium nitrate can precipitate. Accordingly, the fluid source  106  can supply a pressurized and clean, non-hydrogen gas such as but not limited to dry air, oxygen, carbon dioxide, nitrogen, argon, or helium. It will be noted that passing the fluid from the fluid source  106  inside the emitter tip  102  rather than over it significantly reduces the volume of fluid that is necessary to prevent the unwanted precipitation. 
     In some embodiments (not shown), the pressurized fluid from the fluid source  106  ( FIG. 1 ) can be connected by an appropriate conduit and connector arrangement attached to an open end  122  of the central passage  118 . Alternatively, as shown in the embodiments of  FIG. 2 , the body  110  can define a transverse opening  124  in fluid communication with the central passage  118 . A connector (not shown), such as a barbed fitting, can be attached to the opening  124  for attaching a conduit from the fluid source  106  ( FIG. 1 ). It may be necessary, as illustrated in  FIG. 2 , to enlarge a portion  125  of the body  110  around the opening  124  in order to accommodate the fitting. 
     A connecting end  126  of the body  110 , opposite the tapered end  112 , is configured for electrically engaging a socket  128  which is, in turn, electrically connected to the high voltage source  104  ( FIG. 1 ) by leads  130 . In some embodiments illustrated in  FIG. 2  the voltage source  104  provides a voltage in the range of about 2,000 to 15,000 volts. 
     In some embodiments illustrated by  FIG. 2  the tip passage  120  is disposed substantially collinearly with the central passage  118 . In other words, the tip passage  120  is disposed substantially transverse to a plane defined by the proximal end  114  of the tapered portion  112 . Alternatively, in some embodiments (not shown), the tip passage  120  can be directed toward or away from the distal end  116  of the tapered portion  112 . In any event, preferably the tip passage  120  intersects a medial portion of the tapered portion  112  between the proximal end  114  of the tapered portion  112  and the distal end  116  of the tapered portion  112 , thereby preventing the tip passage  120  from interfering with the corona discharge formed at the sharp distal end  116  of the tapered portion  112 . 
       FIG. 3  best illustrates embodiments contemplate two or more tip passages  120  in the tapered end  112 . Preferably, the tip passages  120  are equidistantly arranged around the tapered end  112 . 
     In some embodiments the emitter tip  102  can be machined from pin stock to the desired body  110  size and tapered end  112  configuration. A drilling operation can be used to manufacture the central passage  118 , and an electrodischarge machining (EDM) operation can be used to manufacture the tip passage  120 . 
       FIG. 4  is a block diagram of a method  200  for CONTROLLING ELECTROSTATIC CHARGE illustrating steps for carrying out the embodiments of the present invention with the apparatus discussed above. The method begins at step  202  by providing the voltage source  104 , which includes providing the electrical connector  128  for electrically engaging the emitter tip  102 , and providing the interconnecting leads  130 . The method continues at step  204  by providing the fluid source  106 , which includes providing the fluid connector (not shown), such as for attachment in the opening  124 , and providing the interconnecting conduit (not shown). 
     In step  206  the emitter tip  102  is electrically connected to the voltage source  104 . In step  208  the emitter tip  102  is fluidly connected to the fluid source  106 . The method then provides pressurized fluid to the emitter tip  102  at step  210 , and finally electrically energizes the emitter tip at step  212 . 
       FIG. 5  is a side elevational view of the emitter tip  102  utilized in accordance with alternative embodiments of the corona discharge device of  FIG. 1 . Here, in addition to the fluid from the fluid source  106  ( FIG. 1 ) flowing inside the emitter tip  102 , an additional fluid flow  250  is provided in order to further advance the ionized particles toward a work piece (not shown). The fluid flow  250  can be directed around the emitter tip  102  by a dielectric partition  252  that defines one or more openings  254  for passing the fluid flow  250 . 
     Summarizing generally, an emitter tip (such as  102 ) is provided for a corona discharge device (such as  100 ). The emitter tip comprises an elongated body (such as  110 ) with a closed tapered end (such as  112 ). The body defines a central passage (such as  118 ) and the tapered end defines a tip passage (such as  120 ) in fluid communication with the central passage. 
     The body defines a characteristic size, and the tapered end is substantially contiguous with the body at a proximal end of the tapered portion (such as  114 ), and terminates in a sharp or radiused tip portion at a distal end of the tapered portion (such as  116 ). In some embodiments the body is circular and the converging surface defining the tapered portion is conical. 
     The tip passage is disposed substantially transverse to a plane defined by the tapered portion. The tip passage is disposed at a medial portion of the tapered portion between the proximal and distal ends. Preferably, the tapered portion comprises two or more tip passages which are equidistantly arranged around a longitudinal axis. 
     In some embodiments a method for controlling electrostatic charge is provided, comprising providing a voltage source; providing a pressurized fluid source; providing a corona discharge emitter tip; connecting the emitter tip to the voltage source and to the fluid source; passing the fluid through the emitter tip; and electrically energizing the emitter tip. 
     In some embodiments the providing a corona discharge emitter tip step comprises forming the emitter tip as comprising an elongated body with a tapered end, the body defining a central passage and the tapered end defining a tip passage in fluid communication with the central passage. 
     In some embodiments the providing a corona discharge emitter tip comprises forming the body with an outer surface defining a characteristic size, and foaming the tapered portion at a proximal end thereof as being substantially contiguous with the outer surface, and terminating the tapered portion at a distal end thereof as a sharp or radiused tip portion. The outer surface can be circular and the converging surface defining the tapered portion accordingly can be conical. 
     In some embodiments the providing a corona discharge emitter tip comprises disposing the tip passage substantially transverse to a plane defined by the proximal end of the tapered portion. The tip passage is preferably disposed at a medial portion of the tapered portion between the proximal and distal ends. The emitter tip can comprise disposing two or more tip passages in the tapered portion, wherein the tip passages are arranged equidistantly around a longitudinal axis. 
     In some embodiments a corona discharge ionizer device is provided, comprising a voltage source connected to a corona ionizer emitter tip; and steps for controlling contamination operably created on the emitter tip by the voltage source. The steps for controlling are characterized by connecting a voltage source and a pressurized fluid source to the emitter tip. The steps for controlling are further characterized by passing the pressurized fluid through the tip while electrically energizing the tip. 
     It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular configuration and arrangement of the emitter tip body and tapered end portions without departing from the spirit and scope of the present invention.