Patent Publication Number: US-8526859-B2

Title: Conductivity sensor with cleaning apparatus

Description:
BACKGROUND 
     Control of liquid ink conductivity is important to color consistency within the field of liquid electrophotographic printing (LEP). Toward that goal, a conductivity sensor is needed that can detect variations in the ink&#39;s electrical charge during the process of forming an image on media. One approach to measuring LEP ink conductivity is to use two electrodes that are separated, or gapped, by several hundred microns. A voltage of dozens to hundreds of volts is applied and the resulting electrical current between the electrodes is measured and used to determine the electrical conductivity of the ink. 
     An undesirable aspect of using a high-voltage electric field is that ink “sludge” tends to form on the electrodes. This sludge acts to disrupt or skew subsequent conductivity measurements, with increasing error in the readings as the sludge accumulates. Thus, some means of cleaning is required in order to prevent ink sludge accumulation on electrode surfaces. Furthermore, a fresh supply of the liquid ink must be provided to the electrode surfaces in order to ensure meaningful ink conductivity readings. 
     Accordingly, the embodiments described hereinafter were developed in light of these and other drawbacks associated with LEP ink conductivity measurements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  depicts an illustrative conductivity measuring apparatus within an ink tank according to one embodiment; 
         FIG. 2  depicts a perspective view of an illustrative conductivity sensor according to one embodiment: 
         FIG. 3  depicts an exploded view of an illustrative conductivity sensor according to one embodiment. 
         FIG. 4  depicts a plan view of a portion of an illustrative conductivity sensor according to one embodiment. 
         FIG. 5  depicts an elevation sectional view of an illustrative conductivity sensor according to one embodiment. 
         FIG. 6  depicts a flowchart of a method in accordance with one embodiment. 
         FIG. 7  depicts a schematic diagram and respective signal diagrams according to concepts of the present teachings. 
     
    
    
     DETAILED DESCRIPTION 
     Introduction 
     A system and method are provided for determining ink conductivity in a liquid electrophotographic printing (LEP) context. A pair of electrodes is arranged to define a narrow gap there between. A non-conductive propeller rotates within the gap and causes liquid ink (i.e., imaging media) to flow over the respective, inward facing surfaces of the electrodes. The rotating propeller further prevents the accumulation of ink sludge within the gap and, in particular, on the inward facing surfaces of the electrodes. Pulses of electrical potential are selectively applied to the electrodes resulting in pulses of electrical current there between. The electrical current pulses are measured and used to determine the electrical conductivity value of the ink. 
     In one embodiment, an apparatus includes a first electrode and a second electrode, which are respectively disposed to define a gap there between. The apparatus also includes a propeller supported within the gap. The propeller is configured to cause a liquid ink to flow through the gap during rotation of the propeller. The propeller is further configured to prevent accumulation of ink sludge within the gap during rotation of the propeller. 
     In another embodiment, a method includes rotating a propeller so as to cause a liquid ink to flow through an electrode gap. According to the method, the rotating propeller also prevents accumulation of an ink sludge within the electrode gap. 
     In yet another embodiment, an apparatus includes a tank configured to contain a liquid ink. The apparatus also includes a pump supported within the tank, the pump being configured to cause a flow of the liquid ink. The pump is configured to be driven by the rotation of a pump shaft. The apparatus also includes a pair of electrodes supported within the tank and a propeller supported within the tank along the pump shaft. The propeller is configured to prevent ink sludge from accumulating on facing surfaces of the electrodes during rotation of the propeller. 
     System Overview 
       FIG. 1  is a partial cutaway elevation view depicting an ink tank  100  including aspects of the present teachings. Ink tank  100  includes a pump  102  (shown in part). The pump  102  is configured for circulating liquid ink (i.e., imaging media) through conduits (not shown) of an imaging device such as an LEP printer. The pump  102  is coupled to a motor or other source of rotational drive by way of a pump shaft  104 . Such motor (or other drive source) is located external to the housing  106  of the ink tank  100  and is not shown. 
     The ink tank  100  also includes a conductivity sensor (sensor)  108 . The sensor  108  includes a first electrode  110  and a second electrode  112  supported in a stacked, separated relationship. The electrodes  110  and  112  are closely spaced so as to define a gap there between. In one embodiment, the gap is defined by a spacing of about one millimeter (i.e., 1 mm). Other suitable gaps can also be used. The sensor  108  is supported by a platen or deck  124 , which in turn is secured to the housing  106  of the ink tank  100  by way of structural members  126 . 
     In turn, the electrodes  110  and  112  are defined by respective planar surfaces which face into the gap defined between the electrodes  110  and  112 . In one embodiment, the area of each respective planar surface is one thousand square millimeters (i.e., 1000 mm 2 ). Other electrodes having other respective planar areas can also be used. The electrodes  110  and  112  can be respectively formed from and/or surface plated with any suitable electrically conductive material such as, for non-limiting example, stainless steel, brass, gold, etc. 
     The sensor  108  further includes a propeller  114  supported within the gap between the electrodes  110  and  112 . The propeller  114  is coupled to the pump shaft  104  and is configured to rotate when the pump shaft  104  is rotationally driven. The propeller  114  is supported in non-contacting close adjacency to each of the electrodes  110  and  112 . The propeller  114  is formed of any suitable non-electrically conductive material. Non-limiting examples of propeller  114  materials include nylon, polyvinylchloride (PVC), plastic, etc. 
     The ink tank  100  also includes an electronics board  116 . The electronics board  116  is coupled to the electrodes  110  and  112  of the sensor  108 . The electronics board  116  includes electrical circuitry configured to measure the conductivity of liquid ink (i.e., media) in contact with the sensor  108 . 
     During normal operations, the ink tank  100  is filled with liquid imaging media (i.e., ink) such that the sensor  108  and the pump  102  are respectively submerged. The electronics board  116  provides pulses of electrical voltage to the electrodes  110  and  112 , resulting in pulses of electrical current flowing between the electrodes  110  and  112  through the liquid imaging media that is in contact therewith. In one embodiment, direct current (DC) pulses of four-hundred fifty volts are applied to the electrodes  110  and  112 . Other suitable voltages can also be used. The electronics board  116  senses (i.e., measures) the pulses of electrical current and the electrical conductivity of the liquid imaging media is determined by way of processor operation and/or other resources of the electronics board  116 . 
     During such normal operations, the propeller  114  is rotationally driven by way of the pump shaft  104  and serves to cause a flow of liquid imaging media through the gap between the electrodes  110  and  112 . The flow of such liquid imaging media (Le., ink) is generally into the center area of the gap by way of central apertures in the electrodes  110  and  112 , and then outward through the gap toward the circumferential edges of the electrodes  110  and  112 . 
     The propeller  114  further serves to keep ink sludge and other debris from accumulating within the gap and/or on the inward facing surfaces of the electrodes  110  and  112 . Such ink sludge and/or debris tend to have a distorting effect on the conductivity measurements made by way of the sensor  108 . In this way, greater accuracy and reliability in the conductivity measurements is had due to the liquid flow and cleaning actions of the propeller  114 . A boundary layer of liquid imaging media tends to keep the propeller  114  in close, non-contacting adjacency with the electrodes  110  and  112 , being approximately centered in the gap there between. It is important to note that the conductivity measurements can be made whether the propeller  114  is presently being rotated or not. The sensor  108  is shown to operate by way of mechanical drive provided to the propeller  114  by way of the pump shaft  104 . In another embodiment, a sensor in accordance with the present teachings can operate independent of any pump, wherein the propeller of such a sensor is rotationally driven by a motor or other means provided for that particular purpose. Other suitable configurations can also be used. 
     System Details 
       FIG. 2  is a perspective view depicting the conductivity sensor  108  as introduced above. The first electrode  110  and the second electrode  112  are respectively defined by central apertures with the pump shaft  104  extending there through. The electrodes  110  and  112  are supported in spaced adjacency to each other by way of a triad of spacers  118  and associated fasteners (Le., nut and bolt assemblies)  120 , thus defining three supports  122 . The supports  122  are mechanically secured to the deck  124 . The deck  124  is secured to the housing  106  of the ink tank  100  ( FIG. 1 ) by way of three structural r embers  126 . 
     The electrode  110  is electrically coupled to the electronics board  116  ( FIG. 1 ) by way of a connector  128  and a fastener  130 . The electrode  112  is similarly electrically coupled to the electronics board  116  by way of a fastener  132 . Connector, wiring and/or other electrical elements associated with coupling the electrode  112  to the electronics board  116  are not shown in  FIG. 2  in the interest of clarity. The propeller  114  is mechanically coupled to the pump shaft  104  by an adapter  134 . The adapter  134  is formed from any suitable non-electrically conductive material such as, for example, nylon, plastic, PVC, etc. Other materials can also be used. In any case, the propeller  114  is rotationally driven by the pump shaft  104  by way of adapter  134 . 
       FIG. 3  is an exploded view of the conductivity sensor  108  according to one embodiment. The first electrode  110  includes a threaded aperture  136  for receiving the fastener  130 . The first electrode  110  also includes a triad of hook-like extensions  138  for mechanically engaging the respective supports  122  when the first electrode  110  is supported adjacent to the second electrode  112 . 
     The propeller  114  includes (i.e., defines) a central aperture  140  including a pattern of four radial notches  142 . In turn, the radial notches  142  receivingly engage raised portions  144  of the adapter  134 . The propeller  114  is thus supported in non-slip engagement with the adapter  134  when the sensor  108  is fully assembled (e.g.,  FIG. 2 ). The propeller  114  includes (i.e., is defined by) a plurality of blades or outward extensions  146  respectively defined by opposite planar sides  148 . The propeller  114  of  FIG. 3  includes three blades  146 . However, it is to be understood that the propeller  114  is illustrative and non-limiting, and that any suitable number of blades (e.g., two, four, five, etc.) can be used. Furthermore, the blades  146  are depicted as having a generally curved, swept-back design. Other blade geometries (not shown) can also be used. The propeller  114  is shaped so as to prevent flow stagnation of the liquid imaging media, as well as to prevent ink sludge from accumulating on the propeller  114  edges. 
     The second electrode  112  is defined by a planar surface  150 . Similarly, the first electrode is defined by a planar surface  152 . The respective planar surfaces  150  and  152  face into the gap defined between electrodes  110  and  112  when the sensor  108  is fully assembled (e.g.,  FIG. 2 ). It is to be further appreciated that the pump shaft  104  extends through respective apertures defined in the first and second electrodes  110  and  112 , the propeller  114 , and the adapter  134 . 
       FIG. 4  is a plan view of a portion of the conductivity sensor  108 . The propeller  114  is depicted supported about the pump shaft  104  by way of the adapter  134 . Also depicted are the three respective supports  122 . Each of the spacers  118  is defined by a planar face portion  156 . The respective planar face portions  156  are disposed in contact with the second electrode  112  and serve to keep the second electrode  112  in an aligned, centered relationship with the first electrode  110  ( FIG. 2 ) about the pump shaft  104 . 
       FIG. 5  is an elevation sectional view of the conductivity sensor  108 . The first electrode  110  and the second electrode  112  are depicted in supported, spaced adjacency by way of the supports  122 . The pump shaft  104  extends through sensor  108  and couples to the pump  102  (shown in part). The propeller  114  is shown supported on the pump shaft  104  by way of the adapter  134 . It is to be understood that the propeller  114  is slightly separated from both of (is not contacting) the electrodes  110  and  112 . In turn, the sensor  108  assembly is secured to and supported by the deck  124 . 
     Exemplary Process 
       FIG. 6  is a flowchart depicting a method in accordance with one embodiment. The flowchart of  FIG. 6  depicts particular method aspects and order of execution. However, it is to be understood that other methods including and/or omitting certain details, and/or proceeding in other orders of execution, can also be used without departing from the scope of the present teachings. Therefore, the method of  FIG. 6  is illustrative and non-limiting in nature. 
     At  200 , a propeller  114  is rotated within a gap defined between electrodes  110  and  112 . At  202 , the rotating propeller  114  causes liquid ink (Le., imaging media) to flow through the electrode gap. Such flow of liquid ink is generally outward though the gap toward the circumferential edges of the electrodes  110  and  112 . At  204 , ink sludge and/or other debris is prevented from accumulating within the gap and/or on the inward facing surface of the electrodes by virtue of the rotating propeller action. At  206 , an electrical current is caused to flow between the electrodes and through the liquid ink in contact with the electrodes. Also, one or more characteristics of the electric current (e.g., peak magnitude, decay rate, etc.) is measured by corresponding electronic circuitry. Al  208 , the measured electrical current characteristics are used to determine the electrical conductivity of the liquid ink. The conductivity determination can then be used to control one or more aspects of a printing operation such as, for non-limiting example, adjustment of the liquid imaging media constituency, rate of printing, go/no-go printing decisions, etc. 
     Operating Concepts 
       FIG. 7  includes a schematic diagram of a circuit  300  and a voltage signal diagram  320  and a current signal diagram  340  corresponding to operational concepts of the present teachings. As such, the circuit  300  is a simplification of actual circuitry configured to perform methods of the present teachings. The circuit  300  is provided in the interest of clarity of understanding. 
     The circuit  300  includes a source of DC potential (i.e., voltage)  302  coupled to a switch  304 . The circuit  300  also includes a first electrode  306  and a second electrode  308 . The electrodes  306  and  308  are disposed in dose, spaced adjacency so as to define a narrow gap  310  there between. The gap  310  can also be referred to as an electrode gap. The electrodes  306  and  308  are submerged in liquid imaging media (Le., ink) during operation of the circuit  300 . The circuit  300  further includes current measurement means  312 . The current measurement means  312  is depicted in  FIG. 7  as an ammeter in the interest of simplicity, 
     During illustrative and non-limiting operations, the switch  304  is selectively opened and dosed so as to provide pulses of electrical voltage  322  to the electrodes  306  and  308 . Current flows in corresponding pulses  342  between the electrodes  306  and  308 , through the liquid imaging media (not shown) in contact with the electrodes  306  and  308 . These current pulses  342  also flow through the balance of the circuit  300  and are measured (i.e., indicated) by the current measurement means  312 . The peak value, period, rise, decay, and/or other characteristics of the current pulses  342  can be used to determine the electrical conductivity of the liquid imaging media. 
     The immediately foregoing operations would normally result in the development and accumulation of ink sludge within the gap  310 —namely, on the inward facing surfaces of the electrodes  306  and  308 . Ink sludge and/or other debris within the gap  310  generally have a distorting effect on the current pulses used to determine the electrical conductivity of the liquid imaging media. The present teachings resolve the ink sludge accumulation problem through the use of a rotating propeller (e.g., propeller  114  of  FIGS. 1-5 ) within the corresponding electrode gap. 
     In general, the foregoing description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent to those of skill in the art upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation and is limited only by the following claims.