Abstract:
An ultrasonic system for measuring the volume of liquid in a container having a lid in which an ultrasonic signal is emitted and received by a sensor subsystem located on the underside of the lid of the ultrasonic system. The ultrasonic system can measure the exact amount of liquid or the level of the liquid held in the container by processing the roundtrip time the ultrasonic signals took to travel from the sensor subsystem to the surface of the liquid where the ultrasonic signals are reflected back to the ultrasonic sensor subsystem. A solid state, three-phase SCR/diode bridge converts a three-phase alternating current (AC) to a direct current (DC) power source for heating the liquid in a boiler subsystem prior to its transport to the container. A second, triac controlled heater is powered by a single phase of the three phase power source, and is used to warm and maintain the liquid held within the container at a constant temperature.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority of U.S. Provisional Application No. 60/245,324, filed Nov. 1, 2000, under Title 35, United States Code, Section 119(e). 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to measuring systems for measuring the level of liquid held in a container. More specifically, the present invention relates to a measuring system that emits and receives ultrasonic signals and processes the ultrasonic signals to determine the level of liquid held in an underlying container and plays a major role in controlling operation of the system.  
         DESCRIPTION OF THE PRIOR ART  
         [0003]    Devices for brewing coffee, especially while on board an aircraft, are well known in the industry. FIG. 1 is a block diagram portraying an airline coffee brewer typical in the prior art.  
           [0004]    The prior art system includes a control board  10  that is normally constructed of discreet integrated circuits, input power from a 3-phase, 115 volt, 400 Hz aircraft power system  12 , mechanical relay contacts  14 ,  16  and  18  that are actuated by coil  20  when coil  20  is energized with a signal  22  from control board  10 . Mechanical relay contacts  14 ,  16  and  18  electrically isolate the low voltage control board  10  from the high voltage AC power lines supplying heating elements  24 ,  26  and  28 . Heating elements  24 ,  26  and  28  are individually connected to the three phases of power system  12 . A plurality of pot water level probes  30  are employed, in this example, as two free swinging metallic probes. Probes  30  come into contact with the water in the brewer when the carafe is full, as indicated at Level  4  and numeral  72  (FIG. 3). Probes  30  will momentarily swing out of the way when the carafe is inserted or removed from the brewer pocket. When probes  30  are in contact with the electrically conductive coffee in the carafe, a signal  32  occurs which will serve to close a coldwater input valve  34  that supplies cold water to boiler  39  which then heats it in preparation for brewing.  
           [0005]    An additional probe, or sensor,  36  is located in boiler  39 . Sensor  36 , in conjunction with a processing circuit  37 , that is external to boiler  39 , will provide a control board input  38  when the boiler is filled with water. Sensor  36  and processing circuit  37  also serve to close relay contacts  14 ,  16  and  18  which provide power to heating elements  24 ,  26  and  28 , which can be safely energized after the boiler is filled with water.  
           [0006]    A temperature sensor  40  is also located in boiler  39 . The external processing circuit  41  of temperature sensor  40  provides an input signal  42  to control board  10  when power to heating elements  24 ,  26  and  28  is needed in order to maintain a target temperature for the water.  
           [0007]    One problem with the aforementioned prior art example is that the method for detecting a full carafe is subject to failure if sediment, carried by the water, forms on the sliding electrical surfaces of the probes  30 . Another problem found in the prior art is that measuring intermediate levels of water in the container is either highly difficult, or not even possible. This will limit processor ability to determine other important performance characteristics of the brewer system. U.S. Pat. No. 5,880,364 (Dam) discloses a non-contact ultrasonic system for determining the volume of liquid in a container in which an ultrasonic sensor is disposed opposite the open top of the container. A circuit provides pulses of ultrasonic energy for transmission through the air to the air-liquid interface of liquid in the container and for measuring the round trip transit time from the sensor to the interface and back to the sensor. The system can determine the level of liquid in a plurality of containers using a plurality of sensors that are operated in sequence or simultaneously, or with a single sensor in which the plurality of sensors are moved relative to the single sensor for the volume of each of the sensors to be sequentially measured.  
           [0008]    Regarding the &#39;364 patent, the components are not compactly located in the lid assembly of a container. The system of the present invention seeks to improve upon this system by presenting the ultrasonic transducers and their signal processing function in a lid assembly, thus making the system more compact, cost efficient, and resistant to splashing in turbulent conditions when used in aircraft or moving vehicles.  
           [0009]    Thus, there is an unsatisfied need to realize a less complex, more cost efficient coffee brewing system having a significant increase in system reliability.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention is directed to a system for measuring liquid levels in a container by means of an ultrasonic signal. The present invention is further directed to a system having all of the ultrasonic components located in the lid of the system. This design creates a more compact, cost efficient, lightweight and reliable system.  
           [0011]    According to the present invention, a narrow ultrasonic beam is emitted from an ultrasonic signal transmitting transducer and directed to an underlying liquid column. The ultrasonic beam is reflected upward at the liquid/air interface to be detected by an ultrasonic signal receiving transducer that interfaces with a signal processor on the system. By knowing the speed of sound in air, the system is able to determine the exact distance traveled by the ultrasonic signal. In turn, by knowing the dimensions of the container, the exact amount of liquid within the container can be determined, or the liquid level in the container regardless of its dimensions. The present invention is described herein in the context of being used on board an aircraft, however, the present invention can be adapted to be employed in any other environment such as in household use, or on board any other type or mode of transportation, such as a train or cruise liner.  
           [0012]    In one embodiment of the present invention, the mechanical relay contacts in each of the three AC lines of the prior art are replaced with an electrically isolated, optically coupled triac for controlling heater power. In this embodiment, the present invention allows for a single heating element to be direct current driven from the rectified three phase, 400 Hz alternating current power that is typical of aircraft systems. This design improves reliability and cost effectiveness of the system over the prior art.  
           [0013]    It is an object of the invention to provide a brewing system that eliminates a typical mode of power failure associated with the prior art.  
           [0014]    It is another object of the present invention to provide a brewing system that is more cost efficient, more space efficient, more lightweight and more reliable than the prior art.  
           [0015]    It is yet another object of the present invention to provide a brewing system having all of the components compactly located in the lid assembly for measuring liquid level in a container.  
           [0016]    Still yet another object of the present invention is to provide a brewing system having a single design for delivering power to the heating elements of both AC and DC aircraft power systems with very little design change. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a block diagram for the circuitry of a typical airline brewer found in the prior art.  
         [0018]    [0018]FIG. 2 is a block diagram for the circuitry of the brewing system of the present invention.  
         [0019]    [0019]FIG. 3 is a side view of the components used for measuring liquid level in the brewing system of the present invention.  
         [0020]    [0020]FIG. 4 is a top view of the lid in the brewing system shown in FIG. 3.  
         [0021]    [0021]FIG. 5 is a bottom view of the lid in the brewing system shown in FIG. 3.  
         [0022]    [0022]FIG. 6 is a graph showing the three-phase SCR/diode bridge input/output waveforms of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    The present invention is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, and for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident, however, to one skilled in the art that the present invention may be practiced without these specific details.  
         [0024]    Referring now to FIG. 2, a block diagram of the system of the present invention is shown and referred to generally as numeral  50 . It has been found that the numerous operational checks, control system functions and visual signals for a modern aircraft brewer are best served with a far more compact design than that found in the prior art. It is also noted that although system  50  of the present invention is explained in terms of being used on board an aircraft, it is within the scope of the present invention for system  50  to be applied to a brewer used in any other environment, such as household use, on board a passenger train, a commercial train or on board a nautical vessel.  
         [0025]    System  50  includes a control board  51 , a control board processor  52 , and a user-input accessible keyboard  53 . Control board processor  52  is implemented with a software controlled Field Programmable Gate Array (FPGA) or a microprocessor, or any other programmable device that will be accessible to changes that occur for different models, locations, installation techniques or modifications to the operation of system  50 . For the case where such operational changes or variations are unlikely, and where the number of systems  50  produced will justify the production cost, the lower manufactured price for an Application Specific Integrated Circuit (ASIC) is a viable option. System  50  further includes a boiler  57  (FIG. 2A) for heating the water to a target temperature at about just below the water boiling temperature prior to having it pass through a compartment containing the coffee granules. After the coffee is brewed, it will then go to a depression  104  (FIG. 3) in lid  73  before passing through access hole  106  and into a carafe  65  (FIG. 3).  
         [0026]    Control board processor  52  provides system  50  with the ability to monitor a variety of variables involved with operation of system  50 . Processor  52  processes information and controls the reset of system  50  via system reset controller  94 , system power loss via a power loss monitor  92 , the turning on and off of system  50  via an on/off controller, which can be a button  54 , the coffee brewing cycle via a brew cycle button  56 , hot water via a hot water tap valve controller  58 , cold water via a cold water tap valve controller  60 , carafe levels  66 ,  68 ,  70 , and  72 , and determines low water temperature in boiler  57  via a water temperature sensor  80  and its processor  82 , whose input on the controller board  52  is located at  61 . High water temperature in boiler  57  is detected with the same temperature sensor and processor and is input to the controller board at location  62 . User inputs to control board  51  of system  50  are provided by keyboard  53  located on the front panel of system  50 . Keyboard  53  includes a system on/off controller, which can be a button  54 , a coffee-brew cycle button  56  which begins the brew cycle when all of the required conditions have been received by processor  52 , hot water tap valve controller  58  which provides un-brewed hot water to an outlet tap, and cold water tap valve button  60  which does the same for unheated water. The brew cycle of system  50  will automatically pause when processor  52  determines that the water temperature in boiler  57  either reaches or falls below a predetermined low temperature threshold as measured by boiler water temperature sensor  80  and its temperature sensor processor  82 . Alternatively, the brew cycle will cease power to heater  84  when the water temperature in boiler  57  either reaches or exceeds an upper predetermined temperature as measured by boiler water temperature sensor  80 .  
         [0027]    The brew cycle of system  50  will also end when carafe  65  (FIG. 3) is full, shown at level  72  (FIG. 3), also referred to as Level  4 . The brew cycle will pause and/or issue a malfunction alert if the time needed to fill carafe  65  reaches or exceeds a programmable time limit.  
         [0028]    System  50  further includes an ultrasonic water level sensor subsystem  64 , shown in both FIGS. 2 and 3. Subsystem  64  serves to first transmit, and then receive sound signals after they bounce off of the horizontal surface. The sound signals are processed by calculating the round-trip time of the sound pulse. The longest roundtrip time will occur when carafe  65  is either empty, or out of the brewer pocket, wherein, the pocket signal represents a first water level  66  that is needed to enable the brew cycle. Subsystem  64  also performs the same function upon water levels  68 ,  70  and  72  (FIG. 3) in carafe  65  during the brewing cycle. As pointed out above, the ultrasonic technique of sensor subsystem  64  relies on the round trip time for a transmitted sound pulse to reach a target and then bounce back to the ultrasonic receiver. The actual process of employing ultrasonic sound signals to determine the amount of liquid in a container is known in the art and an example of a technical description for this technique is given in U.S. Pat. No. 5,880,364. However, in U.S. Pat. No. 5,880,364, the components are not compactly located in the lid of the assembly of a container as described in this application.  
         [0029]    An ultrasonic pulse transmitter shown as  101  on FIG. 4 and  5  is located on sensor subsystem  64 , and when properly driven, transmits a very short ultrasonic pulse. The effective length chosen for the ultrasonic pulse is substantially shorter than the shortest roundtrip time anticipated, and the choice is also influenced by the resonant frequency of the device. For example, a pulse of 1.0 Milliseconds is long enough for a 40 KHz device. For devices having higher resonant frequencies and the associated shorter wavelengths, correspondingly shorter pulses are acceptable. Devices are effectively assembled with frequencies in the range of 25 KHz to 2 MHz. Generally speaking, as resonant frequencies of the ultrasonic transducers get higher, the devices get smaller, resolution increases and settling times following a drive pulse are shorter, thus allowing for bounce measurements at closer distances. By the same token, higher frequency devices are more difficult to assemble, causing them to be more expensive as well.  
         [0030]    Transmitter  101  is adapted to transmit a narrow ultrasonic beam through the air to then be reflected at the surface of the underlying column of liquid in carafe  65 . Transmitter  101  has a generally cylindrical body of any suitable material compatible with the environment under which the measuring process is being performed. Subsystem  64  provides an electrical lead (not shown) to transmitter  101  and also has all of the necessary output wires to supply operating signals to control board  51 . Transmitter  101  and processor  64  are of any dimensions suitable for fitting in the space provided by lid  73  for the application at hand. Lid  73  may preferably be made of any suitable material, such as a soft rubber, malleable rubber, plastic, or any other material suitable for deadening structure vibration in lid  73  and the resulting interference, thereby reducing the likelihood of cross-talk between transducers if multiple transducers are employed. The leading edge of an ultrasonic pulse transmission begins the time measurement by processor subsystem  64 . The time measurement is completed upon detection of the return signal by receiving sensor  102  in subsystem  64 . Knowing that the speed of sound in air is approximately 332 m/s at zero degrees centigrade, along with its correction for ambient temperature, will allow for a calculation by sensor subsystem  64  of the distance traveled by the ultrasonic signals. The ability of sensor subsystem  64  to detect the distance traveled by the ultrasonic signals allows sensor subsystem  64  to determine the presence of carafe  65  in brewer pocket  67  as well as the water level in carafe  65  at any moment during the brewing cycle. Furthermore, determining the water level in carafe  65  allows a user to know the amount of servings that remain in carafe  65  at any given time.  
         [0031]    It is noted that the selection of ultrasonic transducers for applications where steam is typically present in the measurement area should be carefully performed. This is especially true for a subsystem  64  where condensed steam will deposit water droplets on the surfaces of lid  73  that house the transducers. For example, a subsystem having two-transducers could have droplets that cause a short circuit of the sound waves from transmitter to receiver if the design of lid  73 , and its transducer elements, is not properly considered.  
         [0032]    In another embodiment of the present invention, it is shown that the best solution for a steamy environment resides in system  50  having the same transducer to both emit and receive the ultrasonic signal in subsystem  64 . However, even in this embodiment, transducer vibration after the transmission pulse is terminated will only settle quickly enough when using the small physical size and low mass associated with high frequency, more expensive devices.  
         [0033]    Having explained the various functions and their purpose in system  50 , a more concise explanation for a typical brew cycle sequence follows. Assuming that electrical power is available to system  50 , and that system on/off button  54  has been actuated, boiler water sensor  74 , along with water sensor signal processing circuit (or boiler processor)  76  will detect the presence of water in boiler  57 . Upon detection of a sufficient amount of water in boiler  57 , processor  76  provides a first enabling signal  78  as required to begin a new brew cycle. A second boiler sensor  80 , also located in boiler  57 , will detect the temperature of water in the boiler at any given time. If boiler water temperature is below an upper limit threshold, temperature processor  82  will provide a second, or heater enabling signal to control board  52 . The presence of a carafe in the brewer pocket is detected by water level subsystem  64  to provide a third enabling signal  66  to controller  52 . Finally, if brew button  56  is depressed, and all other enabling signals are present, SCR/Diode 3 phase rectifying bridge  96  is activated to send electrical power to a single heating element  84 , thus beginning the heating cycle for the water in boiler  57 . The water is heated to a point just below its boiling point, taking into account the expected cabin pressures.  
         [0034]    System  50  also includes a warmer pad  86 , located in base  67  of the brewer pocket (FIG. 3). Warming pad  86  is a low power device compared to boiler heater  84 , and because of this, is typically connected to a single phase of the three-phase aircraft power system without the risk of an electrical unbalance in the system. Consequently, warming pad  86  is conveniently controlled by a semiconductor triac which is able to conduct both the positive and negative regions of the AC wave when triggered to the ON state. Upon the detection of a sufficient amount of water in carafe  65  as indicated by level  66  in FIG. 3, warming pad  86  will turn on and provide heat to the coffee collected in carafe  65 . Warmer pad  86  is employed to maintain a constant temperature once the brewing cycle has started, thus maintaining the brewed coffee in carafe  65  at the same constant temperature both during and after the brew cycle is completed.  
         [0035]    System  50  further includes a brew counter/maintenance indicator  88 . Maintenance indicator  88  includes a memory feature so that the user may create a predetermined maintenance schedule for system  50 . Maintenance indicator  88  serves to notify the user once the predetermined maintenance time, or number of brew cycles has arrived. The brewing status is displayed throughout the life of the brewer. Maintenance indicator  88  includes a service light  90 . Maintenance indicator  88  will also monitor and display via service light  90  any time-out errors that occur. Therein, service light  90  will also indicate the need for a maintenance correction on system  50 .  
         [0036]    If input AC power is lost for any reason during the course of a brew cycle, a power loss controller  92  will cause control board  51  to save the status of the current brew cycle for a pre-selected period of time. One example of such power disruption occurs when an aircraft is being started. Once power returns within the pre-selected time, brewer status is restored. However, if power does not return within the preselected time, the brew cycle status is lost and a restart must be initiated by the user.  
         [0037]    As stated earlier, boiler  57  in the present invention contains a single DC heating element  84 . This technique is designed to save cost, space, and weight for system  50 , an especially useful factor in aircraft applications. The method for controlling heating power via single heating element  84  includes an on/off controllable switch, solid state, three phase SCR/diode bridge  96 . Bridge  96  converts the three-phase, 400 Hz AC aircraft power to DC power in order to control water temperature in boiler  57 . Bridge  96  replaces mechanical relay  19  (FIG. 1) of the prior art brewer, thus eliminating a typical mode of failure with the limited life for contacts  14 ,  16 ,  18  which often “pit” or “weld” shut when used with the high load currents required for the boiler heaters in this application.  
         [0038]    The “on” state of bridge  96  is controlled with an appropriate signal to the low current gate of the SCR (Silicon Controlled Rectifier) that can be switched “on” or “off” with a plurality of long-life, optically-coupled solid state switches  98 , or alternatively, a three-contact low current mechanical relay having a resistor and diode in series with each of the contacts. For purposes of the present invention, three solidstate switches  98  are represented, one going to each of the SCR gates, although any number may be employed. Either the mechanical or optical gate switches  98  provide the required isolation between signals of control board  51  and the AC power. The SCR&#39;s of bridge  96  turn off upon removal of the “On” signal from  98 , and the voltage summation of the three phases reverse biases of the cathode to anode junction of the SCR&#39;s.  
         [0039]    Turning now to FIG. 3, a side view of carafe  65  is shown having a lid  73  and the various regions for ultrasonic measurement of distances  66 ,  68 ,  70  and  72 . FIGS. 4 and 5 show the top and bottom views of lid  73  respectively. However, not shown in these figures is the mounting structure that will cause lid  73  to cover or uncover carafe  65  as it is inserted or removed from the brewer pocket floor  67 .  
         [0040]    Lid  73  serves as a housing for transmitter  101  and receiver transducer  102 , both of which are mounted directly to sensor subsystem  64 . As mentioned before, lid  73  can effectively include a plurality of transducer/receiver combinations. Lid  73  may be of any size and have any dimensions, depending on the size of the opening in the container, so that a highly compact design is realized while still housing transmitter  101  and receiver  102 . For example, at the range of 40 KHz, the transducers in lid  73  may be of ½ inch in diameter and at 250 KHz, the transducers can be about ⅜ inch in diameter or less. While lid  73  is a housing for the transducers and their processor, it also contains a brewed coffee catching region  104 , where the brewed coffee will flow through a hole  106  in region  104 , and then into carafe  65 . Sensor subsystem  64  controls transmission of the sound pulse. Upon emission of a sound pulse, subsystem  64  begins a time measurement of the round-trip travel. Upon receipt of the return signal, sensor subsystem  64  records a value for actual distance traveled by the ultrasonic signal and instantly emits a signal to control board  51  to indicate which of the target ranges was recorded, i.e. whether empty level  66 , second level  68 , third level  70  or carafe full level  72  was recorded. Again, once the distance and time associated with an empty carafe  65  is detected at first level  66 , boiler  57  is full of water, and the water temperature is below the predetermined low temperature threshold, the heating portion of the brew cycle may commence when the user depresses brew button  56 .  
         [0041]    During the course of the brew cycle, a second ultrasonic distance occurs when a predetermined amount of water has entered carafe  65  and water has reached second level  68 . Once second level  68  is reached, warmer pad  86  is initiated so that an acceptable temperature for the brewed coffee is maintained. The distance/level measurement is repeated until third level  70  is reached. Upon reaching third level  70 , the time associated with this signal is fed back to control board  51  as an indicator that water is entering carafe  65  at the proper rate. A final measurement occurs when carafe  65  is full at high level  72 . Upon reaching high level  72 , cold input valve  100  is closed and the brew cycle is terminated.  
         [0042]    Turning now to FIG. 6, a graph showing the three-phase SCR/diode bridge input/output waveforms is presented having the Phase angles for each of the phases on the x-axis and the voltages measured in volts on the y-axis. FIG. 6 shows how the three-phase AC input appears after having been rectified to DC power through the three-phase SCR/diode bridge  96 . The DC output shown in FIG. 6 has the ability to deliver or remove power to heating element  84  when bridge  96  is switched to its “on” state, but has the added capability of independently controlling the on/off state to any one of the three phases to provide even greater flexibility in the power delivery stage of the brewer. If system  50  turn-off time is not fast enough, bridge  96  will enter into a “run-away” condition by re-conducting when the next cycle of AC is imposed on bridge  96 , therefore, careful attention must be given to component selection in order to assure effective and safe operation with the more rapid transitions that exist in a 400 Hz (or greater) power system.  
         [0043]    What has been described above are preferred aspects of the present invention. It is of course not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, combinations, modifications, and variations that fall within the spirit and scope of the appended claims.