Abstract:
A capacitance-sensitive sensor array and associated touchpad sensor circuitry, the sensor array comprised of a flexible substrate having a plurality of printed conductor elements disposed thereon to form the sensor array, the printed conductor elements being coupled to touchpad sensor circuitry that includes data processing capabilities, wherein the sensor array is disposed along an outside surface of a container, wherein the sensor array is capable of conforming to a curved or irregular outside surface of the container, wherein the sensor array detects at least one characteristic of at least one fluid disposed within the container, and wherein the touchpad sensor circuitry processes data received from the sensor array to provide information regarding the at least one fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present invention incorporates by reference all of the subject matter of issued U.S. Pat. No. 6,680,731 B2. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to fluid level sensing devices. More specifically, the invention relates to the application of capacitive sensor-based touchpad technology in a fluid level sensor, wherein the touchpad is disposed on an exterior container wall, is able to conform to contours of the container wall, and provide precise fluid level sensing along its length. The invention also relates to the sensing of solids and gases using the same touchpad technology. 
         [0004]    2. Description of Related Art 
         [0005]    The need for accurate fluid level sensing is well known to those skilled in the art. Accurate determination of fluid levels has both industrial and environmental applications. Industrial applications include the measuring of petrochemicals at industrial and commercial sites. It is often the case that the containers for these materials are difficult to reach. Environmental applications include the monitoring of water levels in reservoirs, rivers, and even streams. Because of the diverse types of fluids (including gases and solids capable of flowing) that need to be monitored, the locations of containers, and the environments in which the fluids must be measured, the state of the art of the sensors used is quite varied. 
         [0006]    Along with the variety of sensors, another common factor is the cost. Many such sensors used at industrial sites can cost nearly $100,000 per device. 
         [0007]    The different types of technology used in the sensors include capacitance-sensitive devices that require multiple sensing devices, probes that utilize RF circuitry, complex arrays of sensors, moving probes, and sensors that can only be external to a container. There has been extensive development of fluid level sensors that can be used in various environments and with different fluids. Generally the sensors suffer from various drawbacks, not the least of which is that they can be complicated, expensive, unreliable, and applicable to only one type of fluid, or applicable in either a wet or a dry condition, but not both. There are also various other drawbacks specific to each type of technology being used. 
         [0008]    Accordingly, it would be an advantage over the state of the art of current fluid level sensors to provide a new fluid level sensing device that is versatile, inexpensive, can be provided in mass quantities, is reliable, will work with sloshing fluids, can be used in harsh environments, utilizes well-known technology that is being applied to a new purpose, and may be capable of providing more information about a fluid or fluids than just fluid level determination. 
         [0009]    In order to understand how a touchpad can be use as a fluid level and fluid characteristic determining device, it is useful to briefly review operation of a touchpad. 
         [0010]    The CIRQUE™ Corporation touchpad is a mutual capacitance-sensing device and an example is illustrated in  FIG. 1 . In this touchpad, a grid of row and column electrodes is used to define the touch-sensitive area of the touchpad. Typically, the touchpad is a rectangular grid of approximately 16 by 12 electrodes, or 8 by 6 electrodes when there are space constraints. Interlaced with these row and column electrodes is a single sense electrode. All position measurements are made through the sense electrode. 
         [0011]    In more detail,  FIG. 1  shows a capacitance sensitive touchpad  10  as taught by Cirque® Corporation includes a grid of row (12) and column (14) (or X and Y) electrodes in a touchpad electrode grid. All measurements of touchpad parameters are taken from a single sense electrode  16  also disposed on the touchpad electrode grid, and not from the X or Y electrodes  12 ,  14 . No fixed reference point is used for measurements. Touchpad sensor control circuitry  20  generates signals from P,N generators  22 ,  24  that are sent directly to the X and Y electrodes  12 ,  14  in various patterns. Accordingly, there is a one-to-one correspondence between the number of electrodes on the touchpad electrode grid, and the number of drive pins on the touchpad sensor control circuitry  20 . 
         [0012]    The touchpad  10  does not depend upon an absolute capacitive measurement to determine the location of a finger (or other capacitive object) on the touchpad surface. The touchpad  10  measures an imbalance in electrical charge to the sense line  16 . When no pointing object is on the touchpad  10 , the touchpad sensor control circuitry  20  is in a balanced state, and there is no signal on the sense line  16 . There may or may not be a capacitive charge on the electrodes  12 ,  14 . In the methodology of Cirque® Corporation, that is irrelevant. When a pointing device creates imbalance because of capacitive coupling, a change in capacitance occurs on the plurality of electrodes  12 ,  14  that comprise the touchpad electrode grid. What is measured is the change in capacitance, and not the absolute capacitance value on the electrodes  12 ,  14 . The touchpad  10  determines the change in capacitance by measuring the amount of charge that must be injected onto the sense line  16  to reestablish or regain balance on the sense line. 
         [0013]    The touchpad  10  must make two complete measurement cycles for the X electrodes  12  and for the Y electrodes  14  (four complete measurements) in order to determine the position of a pointing object such as a finger. The steps are as follows for both the X  12  and the Y  14  electrodes: 
         [0014]    First, a group of electrodes (say a select group of the X electrodes  12 ) are driven with a first signal from P, N generator  22  and a first measurement using mutual capacitance measurement device  26  is taken to determine the location of the largest signal. However, it is not possible from this one measurement to know whether the finger is on one side or the other of the closest electrode to the largest signal. 
         [0015]    Next, shifting by one electrode to one side of the closest electrode, the group of electrodes is again driven with a signal. In other words, the electrode immediately to the one side of the group is added, while the electrode on the opposite side of the original group is no longer driven. 
         [0016]    Third, the new group of electrodes is driven and a second measurement is taken. 
         [0017]    Finally, using an equation that compares the magnitude of the two signals measured, the location of the finger is determined. 
         [0018]    Accordingly, the touchpad  10  measures a change in capacitance in order to determine the location of a finger. All of this hardware and the methodology described above assume that the touchpad sensor control circuitry  20  is directly driving the electrodes  12 ,  14  of the touchpad  10 . Thus, for a typical 12×16 electrode grid touchpad, there are a total of 28 pins (12+16=28) available from the touchpad sensor control circuitry  20  that are used to drive the electrodes  12 ,  14  of the electrode grid. 
         [0019]    The sensitivity or resolution of the CIRQUE® Corporation touchpad is much higher than the 16 by 12 grid of row and column electrodes implies. The resolution is typically on the order of 960 counts per inch, or greater. The exact resolution is determined by the sensitivity of the components, the spacing between the electrodes on the same rows and columns, and other factors that are not material to the present invention. 
         [0020]    Although the CIRQUE® touchpad described above uses a grid of X and Y electrodes and a separate and single sense electrode, the sense electrode can also be the X or Y electrodes by using multiplexing. Either design will enable the present invention to function. 
       BRIEF SUMMARY OF THE INVENTION 
       [0021]    It is an object of the present invention to provide a fluid level sensing system that utilizes capacitance-sensitive touchpad technology. 
         [0022]    It is another object to provide the fluid level sensing system that is capable of determining the presence or the absence of a fluid in a container. 
         [0023]    It is another object to provide a fluid level sensing system that is capable of determining composition or characteristics of fluid materials stored in a container. 
         [0024]    It is another object to provide the fluid level sensing system that is capable of determining the level of the fluid in the container over the length of a capacitance-sensitive sensing device. 
         [0025]    It is another object to provide the fluid level sensing system that is easily able to conform to a surface of a container. 
         [0026]    It is another object to provide the fluid level sensing system that is able to operate through a non-metallic container. 
         [0027]    It is another object to provide the fluid level sensing system that utilizes mutual capacitance sensing technology. 
         [0028]    It is another object to detect different layers of fluids within a container. 
         [0029]    In a preferred embodiment, the present invention is a capacitance-sensitive sensor array and associated touchpad sensor circuitry, the sensor array comprised of a flexible substrate having a plurality of printed conductor elements disposed thereon to form the sensor array, the printed conductor elements being coupled to touchpad sensor circuitry that includes data processing capabilities, wherein the sensor array is disposed along an outside surface of a container, wherein the sensor array is capable of conforming to a curved or irregular outside surface of the container, wherein the sensor array detects at least one characteristic of at least one fluid disposed within the container, and wherein the touchpad sensor circuitry processes data received from the sensor array to provide information regarding the at least one fluid. 
         [0030]    These and other objects, features, advantages and alternative aspects of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description taken in combination with the accompanying drawings. 
     
     
       DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0031]      FIG. 1  is a block diagram of the components of a capacitance-sensitive touchpad as made by CIRQUE® Corporation. 
           [0032]      FIG. 2  is perspective view of a sensor array disposed on the outside of a container, and used to determine at least one characteristic of a fluid within. 
           [0033]      FIG. 3  is perspective view of a sensor array disposed inside a container, and used to determine at least one characteristic of a fluid within. 
           [0034]      FIG. 4  is a display showing an output that is illustrative of signal strength of various fluids being detected by a capacitance-sensitive sensor array of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    Reference will now be made to the drawings in which the various elements of the present invention will be given numerical designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention. It is to be understood that the following description is only exemplary of the principles of the present invention, and should not be viewed as narrowing the claims which follow. 
         [0036]    The presently preferred embodiment of the invention is essentially a capacitance-sensitive touchpad that is capable of performing proximity sensing of a fluid or fluids. Accordingly, a more accurate description is to state that the invention utilizes a capacitance-sensitive proximity sensing device that is disposed in a position relative to the container so that the device is capable of determining at least one characteristic of a fluid or fluids disposed within the container. 
         [0037]      FIG. 2  is provided to show a container  30  and a fluid  32  within the container. A sensor array  34  is disposed outside the container  30 , and flush against the container wall. In this configuration, the container  30  must either not interfere with the sensing technology of the invention, or provide an aperture or window into the container that will enable the sensor array  34  to operate. The touchpad sensor circuitry  36  is shown coupled to the sensor array  34  via ribbon cable or length of flexible substrate material  38 . 
         [0038]    It is noted that information from the touchpad sensor circuitry  36  can be transmitted to a computer or other receiving device via wired or wireless means, as known to those skilled in the art. 
         [0039]    Because the proximity sensing device operates on well-established principles of mutual capacitance-sensitive touchpad technology, as described in patents issued and pending of CIRQUE® Corporation, it is observed that the container  30  must be comprised of a non-metallic material in order to not interfere with the capacitance-sensitive proximity sensing device if the sensor array  34  is sensing through a wall of the container. In other words, any material that would interfere with the operation of a capacitance sensitive touchpad cannot be used for the container  30 , unless a non-interfering aperture is provided. However, a sensing aperture through which the sensor array  34  might operate can be comprised of a material that is different from the rest of the container  30 . 
         [0040]    The nature of the invention is such that the container  30  storing the at least one fluid  32  can have a curved surface for attachment of the sensor array  34 . This is because the capacitance-sensitive proximity sensing technology of the sensor array  34  is capable of being disposed on a flexible substrate such as MYLAR™. The use of MYLAR™ for the substrate material enables the sensor array  34  to conform to slight surface contours that might be found in the shape of the container  30 . For example, a generally cylindrical glass container such as a bottle provides an arcuate or curved surface that is suitable for the attachment of the sensor array  34 . Likewise, a cylindrical underground storage tank for petrochemicals such as gasoline will also provide a suitable surface. 
         [0041]    There are some useful observations that can be made regarding the container  30  through which the sensor array  34  can detect and/or examine a fluid  32  within. For example, the container  30  can have a variety of curved surfaces that can be used as a location for attachment of the sensor array  34 . When sensing directly through the walls of a container  30 , the materials used in the manufacture of the container are also many, and include glasses and plastics. This also means that while the sensor array  34  requires attachment to a non-metallic material in order to perform sensing of the at least one fluid  32  on the opposite side, the sensor array  34  could be disposed, for example, against a glass aperture that has been made part of a container wall, wherein the remainder of the container  30  can be constructed of metal or other materials that will otherwise interfere with the sensor array  34 . However, it is also important that the thickness of the material through which the capacitance-sensitive proximity sensing device must operate should not be made so thick as to interfere with fluid detection and/or examination. The closer the sensor array  34  of the capacitance-sensitive proximity sensing device is disposed to the at least one fluid  32 , the more accurate and perhaps the more detailed the information that can be obtained will be. 
         [0042]    The nature of the capacitance-sensitive proximity sensing device that includes the sensor array  34  described above utilizes mutual capacitance technology to detect and derive information about the at least one fluid  32  in the container  30 . Mutual capacitance sensor technology is described, for example, in U.S. Pat. No. 5,305,017 issued to CIRQUE® Corporation. However, the capacitance-sensitive proximity sensing device of the invention also utilizes hidden touch surface HTS™ technology as described in issued U.S. Pat. No. 6,680,731 B2. This technology enables proximity sensing. In other words, it is not necessary for the at least one fluid  32  to be in physical contact with the sensor array  34  of the capacitance-sensitive proximity sensing device. The at least one fluid  32  must only be sufficiently close so as to be within a range of detection and/or examination of the present invention. Thus, the sensor array  34  may be disposed on the outside of a container  30  as long as the container wall is of a thickness and material that enable proximity sensing. 
         [0043]    The electrodes of the sensor array  34  of the present invention are preferably comprised of a conductive ink that is “printed” onto MYLAR™ sheets and is described in the &#39;731 patent. This method of fabrication is very simple and inexpensive. However, more conventional fabrication techniques that are used to manufacture conventional touch-sensitive touchpads such as those found in computer input devices can also be used. 
         [0044]    So far, the specification has described a sensor array  34  of a capacitance-sensitive proximity sensing device that functions when disposed along the outside of a container  30 . Another aspect of the invention is to dispose the capacitance-sensitive proximity sensing device inside the container  30  itself. This process may be as simple as coupling the capacitance-sensitive proximity sensing device to an inside surface of the container  30 , and providing a means for signals to travel from the sensor array  34  to the touchpad control circuitry  36 . 
         [0045]    If the fluid within the container  30  will not harm the sensor array  34 , the sensor array may be disposed so as to enter the fluid  32 . This is illustrated in  FIG. 3 .  FIG. 3  shows the container  30 , the fluid  32  within the container, the sensor array  34  at least partially disposed within the fluid, and touchpad sensor circuitry  36  coupled to the sensor array. 
         [0046]    It is observed that given the fact that the invention utilizes electricity to function, it will most likely be necessary to cover and insulate all electrical circuitry and exposed elements and electrodes of the sensor array  34  the capacitance-sensitive proximity sensing device from the fluid  32  in the container  30 . It may also be necessary to protect the sensor array  34  from the corrosive and otherwise deleterious effects of the fluid  32  in the container  30 . Materials used to cover the all the elements of the capacitance-sensitive proximity sensing device are well known to those skilled in the art of insulating electronic components from fluids when working in wet and corrosive environments. 
         [0047]    Having described the invention in general terms, it is useful to examine some experimental results that demonstrate the capabilities of the invention. In this example, three fluids were poured into a container. No attempt was made to adjust the amount of each fluid disposed therein. The fluids were generally not miscible, and were comprised of tap water, automobile engine oil, and alcohol. The container was open to air. 
         [0048]    The three fluids and air have different densities. Accordingly, the fluids separated into vertically distinct layers in the container. The lowest fluid in the container was water, then oil, and finally alcohol. 
         [0049]    The fluids  32  have different dielectric and electrical properties, thereby causing each fluid to affect the conductive elements of the sensor array  34  in different and detectable ways. In this experiment, a normal touchpad from CIRQUE® Corporation that is used in computer input applications, and manufactured with a MYLAR™ substrate, was lowered directly into the fluid  32  in the container  30 . The sensor array  34  was held in a vertically parallel orientation with respect to the upright sidewalls of the container  30 . The sensor array  34  was coupled to touchpad sensor circuitry  36  also from CIRQUE® Corporation. The output of the electronic circuitry was then shown on a computer display as shown in  FIG. 4 . 
         [0050]    The computer display is simply one means by which signal strength information can be recognized as indicating a difference in detectable characteristics of different fluids that were in proximity to the capacitance-sensitive proximity sensing device. The output that was shown on the computer display indicates signal strength. Signal strength  40  thus can also be used to detect the presence or absence of a fluid, as well as the composition of detected fluids. 
         [0051]    The signal strength  40  is a function of the relative dielectric constants and other electrical properties of each fluid. The results indicated that water yielded the highest signal strength  42 , followed by alcohol  46  and then oil  44 . The surface air showed no substantial signal level as expected with the sensor array and touchpad sensor circuitry being used. It will most likely be necessary to test the sensing and examination capabilities of the present invention in order to understand fully what the present invention is capable of detecting. 
         [0052]    The output also indicates the level or depth  50  of each fluid, relative to the sensor array  34 . Thus, the invention indicates the boundary between each of the fluids as indicated by a zero-crossing  52  on the graph between the layers of each of the fluids. It is noted that depth in the x-axis is in arbitrary units, but in this case is approximately 0.5 mm. Likewise, the signal strength shown in the y-axis is also in arbitrary units. What was important is that the signal strengths of the various fluids can be compared in order to obtain the desired information. 
         [0053]    It is noted that previous experiments have shown that electrically conductive fluids (e.g. salt water) produce a maximum signal level that is not dependent on the dielectric constant of the conducting fluid for those conductive elements on the sensor array that are disposed in the conducting fluid. However, the sensing method of the present invention can still be applied to determine the fluid levels because measurements between conductive elements that are not in the conducting fluid will appear as previously described. 
         [0054]    It is envisioned that the invention can be applied to process management and control in a variety of industries, including oil pumping from wells, chemical processing and storage, and the storage of other materials which can be in solid, fluid or gaseous form. In other words, the present invention will also function with gases and solids, to varying degrees of success. 
         [0055]    It is also envisioned that the present invention can be used to: 1) detect changes in electrical properties of surrounding media due to chemical reactions or changes in temperature, 2) detect the existence and magnitude of waves or other disturbances in each of the layers of fluid, 3) detect the addition or removal of any fluid by any means, 4) detect the degree of mixing and/or separation of different fluids, 5) detect differences in properties of the fluid in multiple locations within the container by use of multiple sensing elements or sensing elements whose geometry is designed for such purposes, and 6) detect the effects in two or three dimensions, depending upon the sensor&#39;s geometry and accompanying data processing capabilities. 
         [0056]    Regarding separation of the sensor array from the fluid being detected and/or analyzed, separation of as much as 0.3 inches has been demonstrated. The present invention is probably capable of even greater separations. Successful detection may also depend upon the electrical properties such as the dielectric constant of the fluid being measured. Thus, the sensor array can be coated with a variety of non-conducting materials or be separated from the container by a variety of non-conducting materials. Furthermore, orientation and geometry of the sensor array with respect to the fluid being detected and/or analyzed can greatly influence functionality of the present invention. 
         [0057]    Other aspects of the present invention that should be mentioned are the ability to respond rapidly to changes over time, the ability to make continuous measurements as opposed to discrete, one-time measurements, and the fact that direct contact between the sensor and the fluid, solid, or gas is not required. 
         [0058]    It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention. The appended claims are intended to cover such modifications and arrangements.