Abstract:
An apparatus senses an object proximate to a laminar fluid flow by using the fluid as part of the sensing system. For more distant objects, an electrical system detects the capacitance between the proximate object and the flowing fluid via an impedance measurement. For objects touching the flow, an optical system detects the loss of total internal reflection. Together, the two systems allow the proximity to be determined over a wide range. A fluid flow is produced through a nozzle. An electrode is placed in the fluid. A complex impedance is measured between the electrode and an object due to capacitive coupling between the object and the fluid flow. The complex impedance is inversely proportional to a distance between the object and the fluid flow and proportional to an area of proximity of the object.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to sensing objects, and more particularly to sensing objects proximate to fluid flows.  
       BACKGROUND OF THE INVENTION  
       [0002]     Laminar fluid flow occurs when velocity and pressure characteristics of a fluid are substantially constant over time. A useful consequence of this property is that electro-optical characteristics of the fluid are also relatively constant. Laminar flow is easy to recognize in practice by its smooth flowing appearance.  
         [0003]     In many applications, it is desired to determine the proximity and/or contact of an object to a fluid flow. Examples include various coating processes. Many types of sensors can be used to determine the relative positions of the fluid and the object, and thus their relative spacing.  
         [0004]     There are many known methods for determining proximity and/or contact to a static fluid. For example, the Dwyer Model 1430, Microtector Electronic Point Gage, manufactured by Dwyer Instruments, Inc., Michigan City, Ind., U.S.A., determines fluid contact with a test probe by measuring the electrical resistance between the probe and the fluid.  
         [0005]     U.S. Pat. No. 5,730,165, “Time domain capacitive field detector,” issued to Philipp on Mar. 24, 1998, describes a system and method of sensing the proximity of a hand to a faucet, and continued presence of a hand in the flowing water via a capacitance measurement. However, that system does not measure the relative proximity of an object to the flowing fluid, in a general sense. The system yields a binary response—either the hand is in the fluid flow or not. That system cannot determine a degree of proximity to the fluid flow, or a degree of insertion into the fluid flow.  
         [0006]     It is also known in the art that laminar fluid flows can transmit light via internal reflection. A common physics demonstration is to shine a laser beam through water in a container with a drain hole on an opposite side. The light follows the curving fluid flow until the fluid flow breaks apart. This effect is used in fountains to create aesthetically pleasing displays.  
         [0007]     It is desired to accurately measure a relative position of a laminar fluid flow with respect to an object.  
       SUMMARY OF THE INVENTION  
       [0008]     Laminar flow allows a fluid to have substantially constant electro-optical characteristics over time. The embodiments of the present invention use the fluid flow as a sensing element in a sensor system. The laminar fluid flow is produced by an appropriately shaped nozzle. A light source is suitably arranged, e.g., in the nozzle, so as to allow light to travel through the fluid flow via total internal reflection. Essentially, the fluid serves as a light pipe. This requires the fluid to be substantially transparent to the wavelength of the light used.  
         [0009]     When an object approaches the flow, the object changes the optical characteristics of the fluid ‘light pipe’. This change can be detected with optical sensors in three distinct ways.  
         [0010]     First, a sensor can be placed on the other side of the detection area to measure the intensity of the light traveling through the fluid. Second, a sensor can be placed near the light source and arranged to detect a change in reflectance. Third, a sensor can be placed so as to detect light escaping from the fluid in a detection area. Examples of appropriate light sensors include photodiodes, photoresistors, and cameras.  
         [0011]     This optical technique only detects objects touching the fluid flow, or objects in extreme close proximity to the fluid flow.  
         [0012]     In order to extend the sensing range, the fluid flow is used as an electrode in a capacitive proximity sensing apparatus. This requires the fluid, e.g., water, to be somewhat electrically conductive.  
         [0013]     Laminar flow ensures a consistent physical shape of the fluid, and also maintains electrical continuity. Thus, an electrical contact placed in the flowing stream provides an electrical connection to the entire stream. Any sufficiently conductive object that is placed near the stream will effectively form a capacitor with the fluid serving as one electrode, and the object as the other. The magnitude of this capacitive coupling will be roughly proportional to the area of the proximate surfaces and inversely proportional to the distance between them.  
         [0014]     In one embodiment of the invention, the object is electrically connected to ground via a sufficiently small impedance and thus the capacitance of the fluid to ground increases as the distance between the fluid and the object decreases. In many circumstances, the proximity of the object to grounded surfaces provides adequate capacitive coupling and hence, low impedance, without additional connections. The result is that one can measure the impedance between the fluid contact and ground, and this will change depending upon the placement of the object with respect to the flowing fluid.  
         [0015]     The impedance between a contact in the fluid stream and the object will include a resistive component due to the resistivity of the fluid. This component will vary depending upon how far down the stream the proximate object is positioned. By looking at both the resistive and reactive components of the impedance, both the distance between the object and the fluid flow, and the positioning of the object along the fluid flow can be determined.  
         [0016]     Because the flowing fluid is resistive, the impedance measurement includes a resistive component that is indicative of the position along the flowing stream of the proximate object with respect to the point of electrical contact.  
         [0017]     The electrical and optical sensing modes are independent and can be used singularly, or in combination at any time. Because the two techniques work best at different distances, using both concurrently enables a greater working range.  
         [0018]     Furthermore, it is possible to detect where the object is along the fluid flow, that is, the distance from the nozzle to the object measured along the fluid flow. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a side view of an apparatus for measuring a distance between an object and a fluid flow according to an embodiment of the invention;  
         [0020]      FIG. 2  is a side view of a fountain according to an embodiment of the invention;  
         [0021]      FIG. 3  is a side view of a water harp according to an embodiment of the invention; and  
         [0022]      FIG. 4  is a side view of a bidet according to an embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]      FIG. 1  shows an apparatus  100  for measuring a proximity of an object  108  to a fluid flow  102  according to one embodiment of the invention. That is, the apparatus measures the width of an air gap  111  between the object  108  and the fluid flow  102 . A nozzle  101  produces the flow of the fluid  102  having a laminar flow. The fluid is obtained from a suitable fluid source  107 . It should be noted, that the flow does not need to be perfectly laminar. Any flow that is sufficiently uniform over time to maintain substantially constant electrical and optical characteristics suffices.  
         [0024]     Two mechanisms, one electrical and the other optical, are used to accommodate measuring a large range of distances. A light source  104  is suitably arranged to allow light to travel through the fluid flow  102 , due to internal reflection. Hence, the fluid flow serves as an optical waveguide. The light source  104  is held in place by flow straightening fins  103  so that the light source does not impede laminar flow from the nozzle  101 .  
         [0025]     An optical sensor  105  measures, via controller  113 , an intensity of light that passes through the fluid flow  102 . As the object  108  approaches and then touches the fluid flow  102 , the internal reflection is compromised and light escapes in the region of contact. This decreases the intensity of the light at the optical sensor  105 . The location of the optical source  104  and the optical sensor can be reversed without changing the functionality of the apparatus.  
         [0026]     The optical sensor can be placed near the point of contact between the fluid and the object to detect the escaped light, or adjacent to the light source  104  to detect light reflected by the object and traveling back ‘upstream’. Alternatively, multiple optical sensors can be placed at various positions relative to the fluid flow, such as near the nozzle, near the point of contact, and near the end of the fluid flow.  
         [0027]     Unfortunately, the optical system is only useful for detecting extremely close proximity of the object, that is, within the near field of the waveguide, or actual contact. To increase the range, an electrical system is utilized. An electrode  106  provides an electrical connection to the fluid source  107 . The electrode is connected to a controller  113 , an electronic circuit capable of measuring capacitance or, more generally, complex impedance from the electrode to the object, via some electrical path. In  FIG. 1 , the connection between the controller  113  and the object  108  is shown schematically as capacitors  114  and  109  which both connect to each other via ground connections  115  and  110 , respectively. In other embodiments, the connection can take other forms so long as the impedance between the controller and the object is sufficiently small. In this embodiment, capacitors  109  and  114  represent a point that is electrically connected to the object. Typically, this other point is the circuit ground  110 . In  FIG. 1 , the capacitance  109  of the object  108  to ground  110  comprises the electrical connection to ground and is shown schematically. This represents the inherent capacitance due to proximity to ground rather than an additional component of the system.  
         [0028]     Due to the nature of laminar flow, the fluid in the source  107  is continuously connected to the fluid flow  102  exiting the nozzle  101 . It is presumed that the fluid, e.g., water, is at least moderately conductive, and thus provides an electrical connection between the electrode  106  and the fluid flow  102 , having a relatively constant impedance over time. It should be noted that the electrode, e.g., a small diameter copper wire, can also be placed directly in the fluid flow  102 , for example, at the nozzle  101 . Any conductor in contact with the fluid could suffice.  
         [0029]     The object  108 , e.g., a hand, is also at least moderately conductive. The object is either directly or capacitively coupled to the controller  113  via some electrical path to ground. In  FIG. 1 , this is shown schematically as capacitors  114  and  109 , which are connected via ground connections  115 , and  110 .  
         [0030]     The air gap  111  between the object  108  and the fluid flow  102  forms a capacitor  112 . The capacitor can be measured by the controller  113  via a change in the reactive component of the complex impedance between the electrode  106  and its connection to ground  115 . The resistive component of the impedance is typically dominated by the resistance of the fluid between the electrode and the area in proximity to the object. This can be used to determine the approximate location of the proximal object  108  along the stream  102 .  
         [0031]     In many instances, it is desirable to isolate different fluid regions so that the different fluid regions can have independent sensing. For the optical technique, this can be accomplished by having sufficiently sharp turns in the fluid flow, breaking the light path. For the electrical technique, isolation can be achieved by having sufficiently long and narrow connections to yield a high impedance. Thus, the proximity of the object  108  to the fluid flow  102  can be measured at a distance. In addition, the resistive component of the complex impedance can be used to determine the approximate location along the stream of the additional capacitance  109  associated with the proximal object  108 .  
         [0032]     The measurements can also indicate approximately at which point along the fluid flow the object is positioned, i.e., the distance, along the flow fluid, from the object to the nozzle. It should be noted that the distance is not necessarily a straight line distance, but rather a distance that follows the flow.  
         [0033]     While the two measurement techniques can be used together to cover a broad range of distances, either technique can be used by itself when only a limited range is required.  
         [0000]     Applications  
         [0034]     There are numerous applications for the embodiments of the invention in process control, where the distance between a fluid flow and an object must be sensed and maintained precisely.  
         [0035]     It is also possible to use the invention to measure the distance between two fluids. In this case, the object  108  is also a fluid.  
         [0036]     A particularly novel application of the invention concerns interactive water displays. Water is both sufficiently transparent and sufficiently conductive to allow for both optical and electrical measurements as described above. This allows laminar flowing water displays to react to proximity and/or touch by a person.  
         [0037]     Typically, a person standing directly or indirectly on the ‘ground’ has a capacitance to ground of about 100 pF. Thus, no additional electrical connection between the person and ground is required to enable capacitive sensing.  
         [0038]     In one embodiment, the fluid flow is shaped into a ‘water bell,’ a common term in fountain design, via an appropriately shaped deflector. The pump speed is varied depending upon a measured capacitance, which indicates hand proximity. The system attempts to keep the water at a constant minimum distance from the person&#39;s hand. This creates the illusion that a person can sculpt the water bell by bringing a hand near the flowing water.  
         [0039]     This embodiment can be understood with the aid of  FIG. 2 . Fountain  200  uses water  203  which is pumped upward via pump  206 . When the water hits deflector  204 , it is shaped into a water bell  208 . The fountain uses this laminar flowing water  208  as an electrode to measure capacitance to ground. The capacitance of the person to ground is shown schematically on  FIG. 2  as capacitor  202 . A grounded controller  205  is connected to the fluid  208  via an immersed electrode  207 . When a person approaches the fluid flow in the fountain  208 , for example, by reaching out and attempting to touch the water with a hand  201 , the capacitance increases, and the controller  205  detects this change and decreases pump speed of pump  206 . The overall effect is that the water flow in the fountain  200  withdraws from an attempted touch. Similarly, if the hand is withdrawn, the capacitance will decrease, and the controller  205  then increases the pump speed allowing the water bell to increase in size. Thus, the water bell grows and shrinks in accordance with hand gestures. Other interactive programs can easily be added to the controller  205 . For example, the fountain  200  can be programmed to withdraw only up to a point. When that point is reached, the pump speed is rapidly increased, purposely wetting the user&#39;s hand  201 .  
         [0040]     A second example of an interactive display is a ‘water harp’  300  where the strings are made of laminar flowing water as shown in  FIG. 3 . Water  301  in a reservoir  302  flows out of a plurality of nozzles  307 , forming laminar streams  308 . Each nozzle  307  incorporates a light emitting device  303  which allows light to be transmitted down the stream  308  via total internal reflection. Light detectors  305  are positioned a in receiving reservoir  306  so as to detect the light. A controller  309  is connected to the light emitters  303  and detectors  305 . When a finger  304  contacts the stream, the total internal reflection is partially broken, and light escapes. This causes the light reaching detector  305  to decrease. Controller  309  notes this change and triggers a musical sound. The escaping light provides a pleasing visual effect. A pump, not shown in the figure, maintains the water levels in the reservoirs. Playing the harp is a unique experience due to the tactile feedback of touching a water stream, and the visual appearance of the escaping light as each note is played and heard.  
         [0041]      FIG. 4  shows another novel application of the invention in the area of personal hygiene. A bidet  400  produces a water stream  406 , which provides a cleansing function. A person  407  sits on a seat  408  that is grounded, shown schematically via ground  409 , and that provides a low impedance path between the seated person and ground. A water supply  404  is forced through nozzle  405  to produce the water stream  406 . Electrode  403  provides an electrical contact to the stream. Light emitter  401  sends light through the stream, and light detector  402  measures the light which is reflected back through the stream. With this arrangement, the controller  410  can electrically determine the proximity of a person to the stream via an impedance measurement, allowing the flow to be suitably adjusted. The connection between the controller  410  and the person  407  should be of sufficiently low impedance, and is represented schematically on the figure as capacitor  411  and ground connections  412  and  409 . The reflectance of light off the area being cleansed can give an indication of the current state of cleanliness, and this can be used to adjust timing and flow rate.  
         [0042]     Although the invention has been described by way of examples of preferred embodiments, it is to be understood that various other adaptations and modifications can be made within the spirit and scope of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention.