Abstract:
A latching valve assembly which controls the flow of air and purge vapor between a fuel module and a carbon canister, where a change in an electrical property of the latching valve assembly is used to detect whether the latching valve is in the open position or the closed position. The latching valve assembly of the present invention eliminates the need for a physical switch solution, mechanical or non contact solutions, eliminates complexity of valve hardware requirements, and only adds minor electric components and software to identify the latch position. This system eliminates valve complexity and mechanical connections required for electrical conductivity.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/003,304 filed May 27, 2014, and U.S. Provisional Application No. 62/126,007 filed Feb. 27, 2015. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to a latching valve assembly which has a latching mechanism that is able to hold a valve in an open position and a closed position, where the latching valve assembly is controlled by a circuit, and a change is detected in an electrical property of the circuit to identify the position of the latching mechanism, and therefore identify the position of the valve. 
       BACKGROUND OF THE INVENTION 
       [0003]    There are many different types of valve assemblies, which are actuated by different methods. One type of valve assembly is used to control the flow of air and purge vapor between a fuel module of a fuel tank, and a carbon canister. Some types of valve assemblies include solenoids which control the position of some type of valve member, and are used to change the valve member between open and closed positions. It is often necessary to have some type of sensor device to detect the position of the valve member when the valve member is in the open position or the closed position. One example of an existing design approach is to use a mechanical sensing system through a reed switch, MR position sensor, mechanical switch or other position sensing either through contact or non contact methods. However, these types of solutions add more components, and increase cost. 
         [0004]    Other types of approaches include using a pressure sensor in the fuel tank which determines position by monitoring pressure changes in the fuel tank as the valve assembly is changed between an open position and a closed position. However, this approach is not effective in applications which implement bleed flows in the valve assembly. 
         [0005]    Accordingly, there exists a need for an approach to detect the position of a valve assembly which does not add unnecessary components, but is still effective in detecting the position of the valve assembly. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is a latching valve assembly which controls the flow of air and purge vapor between a fuel module and a carbon canister, where a change in an electrical property of the latching valve assembly is used to detect whether the latching valve is in the open position or the closed position. The latching valve assembly of the present invention eliminates the need for a physical switch solution, mechanical or non contact solutions, eliminates complexity of valve hardware requirements, and only adds minor electric components and software to identify the latch position. This system eliminates valve complexity and mechanical connections required for electrical conductivity. 
         [0007]    In one embodiment, the present invention includes a valve portion controlled by a solenoid portion, where the valve portion latches in two positions, an open position and a closed position, and is held in either the open position or the closed position by a latching mechanism. The latching valve assembly uses two different portions of a coil to change the position of a valve assembly and detect the position of the valve assembly. 
         [0008]    In each position, the armature is at rest at different locations within the solenoid. This results in a change in coil inductance that is electronically measured in one of the portions of the coil to identify the position of the valve portion when solenoid portion is inactive. With this embodiment, the position of the valve portion may be detected with one additional connector pin (using a ground common with the valve coil). This embodiment includes a separate coil wind that is used to enhance signal to noise ratio and part to part variation of inductance measurement. 
         [0009]    In another embodiment, the present invention is a latching valve assembly which includes a solenoid portion having a magnet path, and a valve portion having an open position and a closed position, where the valve portion controlled by the solenoid portion. The valve assembly also includes a latching mechanism for maintaining the position of the valve position in the open position or the closed position when the solenoid portion is deactivated. A voltage pulse is emitted to the solenoid portion and used to detect whether the valve position is in the open position or the closed position. The voltage pulse is emitted over a time interval such that the latching mechanism and valve portion remain stationary, and is not long enough to actuate the latching mechanism or valve portion. 
         [0010]    The solenoid portion includes an armature connected to the valve portion, and a coil substantially surrounding the armature, where the coil is also part of the solenoid portion. The armature is in a first position relative to the coil when the valve portion is in the closed position, and a second position relative to the coil when the valve portion is in the open position, such that different current measurements are produced when the armature is in the first position or the second position. The different current measurements correspond to whether the valve portion is in the open position or the closed position. 
         [0011]    In an alternate embodiment, a magnet is disposed on the armature. The magnet is disposed in the magnet path when the valve portion is in the open position, and the magnet is out of the magnet path when the valve portion is in the closed position. The position of the valve assembly is detected by emitting more than one voltage pulse into the solenoid portion, and measuring the current generated by each voltage pulse. A different level of current is measured when the magnet is in the magnet path compared to when the magnet is out of the magnet path. 
         [0012]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a perspective view of a latching valve assembly, according to embodiments of the present invention; 
           [0015]      FIG. 2  is a sectional side view of a first embodiment of a latching valve assembly in an open position, according to embodiments of the present invention; 
           [0016]      FIG. 3  is a sectional side view of a first embodiment of a latching valve assembly in a closed position, according to embodiments of the present invention; 
           [0017]      FIG. 4  is a sectional side view of a second embodiment of a latching valve assembly in an open position, according to embodiments of the present invention; 
           [0018]      FIG. 5  is a sectional side view of a second embodiment of a latching valve assembly changing between an open position and a closed position, according to embodiments of the present invention; 
           [0019]      FIG. 6  is a sectional side view of a second embodiment of a latching valve assembly in a closed position, according to embodiments of the present invention; 
           [0020]      FIG. 7  is a sectional side view of a third embodiment of a latching valve assembly in an open position, according to embodiments of the present invention; 
           [0021]      FIG. 8  is a sectional side view of a third embodiment of a latching valve assembly changing between an open position and a closed position, according to embodiments of the present invention; 
           [0022]      FIG. 9  is a sectional side view of a third embodiment of a latching valve assembly in a closed position, according to embodiments of the present invention; 
           [0023]      FIG. 10  is a chart depicting the application of voltage to a coil to change the latching valve assembly between the open position and the closed position, and applying a voltage pulse before and after the latching valve assembly changes positions to obtain current measurements to detect the position of the latching valve assembly, according to embodiments of the present invention; 
           [0024]      FIG. 11  is a chart depicting the application of voltage to a coil to change the latching valve assembly between the closed position and the open position, and applying a voltage pulse before and after the latching valve assembly changes positions to obtain current measurements to detect the position of the latching valve assembly, according to embodiments of the present invention; and 
           [0025]      FIG. 12  is a chart depicting various current measurements taken during the operation of a third embodiment of a latching valve assembly, according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0027]    A latching valve assembly according to the present invention is shown in the Figures generally at  10 . The valve assembly  10  includes a solenoid portion, shown generally at  12 , and a valve portion, shown generally at  14 . The solenoid portion  12  operates to change the valve portion  14  between an open position, shown in  FIG. 2 , and a closed position, shown in  FIG. 3 . 
         [0028]    The solenoid portion  12  includes an armature  16  connected to the valve portion  14 . Surrounding the armature  16  is a bobbin  18 , and surrounding the bobbin  18  is a coil  20  having a first portion  20   a  and a second portion  20   b.  Both portions  20   a,   20   b  of the coil  20  are in electrical communication with a connector, shown generally at  22 . The connector  22  includes a plurality of terminals. More specifically, the connector  22  includes a first terminal, a second terminal, and a third terminal. The first terminal is in electrical communication with the both portions  20   a,   20   b  of the coil  20 , the second terminal is in electrical communication with only the second portion  20   b  of the coil  20 , and the third terminal is in electrical communication with only the first portion  20   a  of the coil  20 . 
         [0029]    The first portion  20   a  of the coil  20  is has a resistance of around 20 Ohms, and the second portion  20   b  of the coil  20  has a resistance of about less than 5 Ohms, but it is within the scope of the invention that other levels of resistance may be used. 
         [0030]    When the valve portion  14  is in the closed position and the armature  16  is in a first position, as shown in  FIG. 3 , and a current is applied to the first portion  20   a  of the coil  20  using the first and third terminals, the armature  16  moves to a second position shown in  FIG. 2  such that the valve portion  14  is in the open position. The valve portion  14  is held in the open position by a latching mechanism, shown generally at  24 , which has multiple positions. The latching mechanism  24  may be one similar to the latching mechanism described in U.S. application Ser. No. 14/487,448, the entire disclosure of which is incorporated herein by reference. One of the positions of the latching mechanism  24  functions to hold the valve portion  14  in the open position as shown in  FIG. 2 , such that the coil  20  may be de-energized when the coil  20  is not being used to change the valve portion  14  between the open position and closed position. 
         [0031]    The solenoid portion  12  is located in an overmold assembly  26 , where the overmold assembly  26  includes an overmold assembly cavity, shown generally at  28 , that is in fluid communication with a first port  30 , where the first port  30  is connected to and in fluid communication with a carbon canister. Connected to the overmold assembly  26  is a reservoir  32  having a reservoir cavity, shown generally at  34 . The valve portion  14  is partially disposed in the overmold assembly  26  and is adjacent the overmold assembly cavity  28 . A portion of the valve portion  14  is also partially disposed in the reservoir cavity  34 . Formed as part of the armature  16  is an extension rod  36 , which is part of the latching mechanism  24 . Connected to the extension rod  36  is a valve member, shown generally at  38 , which is selectively in contact with a valve seat  40 , where the valve seat  40  is formed as part of the reservoir  32 . Also formed as part of the reservoir  32  is a second port  42 , which is in fluid communication with the reservoir cavity  34 . The second port  42  is connected to and in fluid communication with a fuel module of a fuel tank. The valve member  38  includes a rigid core member  44  connected to the rod  36 , and a flexible stopper portion  46  connected to the core member  44 , and selectively in contact with the valve seat  40 . 
         [0032]    There is also a stator insert  48  which is part of the solenoid portion  12 , and surrounded by the bobbin  18 . There is a gap  50  between the stator insert  48  and the armature  16 , where the gap  50  fluctuates in size, depending on whether or not the valve member  38  is in contact with the valve seat  40 , and the armature  16  is in the first position or second position. 
         [0033]    To change the valve member  38  between open and closed positions, and the valve portion  14  is in the closed position, as shown in  FIG. 3 , a current is applied to the first portion  20   a  of the coil  20 , causing the armature  16  to move towards the stator insert  48  and the valve member  38  to move away from the valve seat  40 , decreasing the size of the gap  50 . The configuration of the latching mechanism  24  changes as the armature  16  moves relative to the latching mechanism  14 , regardless of whether the valve member  38  is in the open position of the closed position. Once the valve member  38  has moved far enough away from the valve seat  40 , the configuration of the latching mechanism  24  changes to maintain the valve member  38  in the open position, even when current is no longer applied to the coil  20 . The coil  20  is then de-energized, allowing the armature  16  and valve member  38  move a small amount away from the stator insert  48 , and be held in the open position because of the configuration of the latching mechanism  24 . Once the valve member  38  is in the open position and the armature  16  is in the second position, there is established fluid communication between the first port  30  and the second port  42  through the cavities  28 , 34 . 
         [0034]    When it is desired to move the valve member  38  back to the closed position and the armature  16  back to the first position, a current is again applied to the first portion  20   a  of the coil  20 , to move the armature  16 , rod  36 , and valve member  38  towards the stator insert  48 , reconfiguring the latching mechanism  24  such that when the current is no longer applied to the coil  20 , the armature  16 , rod  36 , and valve member  38  move towards and contact the valve seat  40 , placing the valve member  38  back in the closed position, as shown in  FIG. 3 . 
         [0035]    When the armature  16  is moved to change the valve portion  14  between the open position and closed position, there is a change in inductance in the second portion  20   b  of the coil  20 , depending upon the position of the armature  16  relative to the coil  20 . A smaller gap  50  produces higher levels of inductance, and a larger gap  50  produces lower levels of inductance. There is one level of inductance measured when the armature  16  is in the position shown in  FIG. 2 , and another level of inductance measured when the armature  16  is in the position shown in  FIG. 3 . This change in inductance in the second portion  20   b  of the coil  20  is measured through the first and second terminals. The change in inductance is measured by emitting a 12 Volt pulse through the second portion  20   b  of the coil  20 . In one embodiment, the voltage pulse typically lasts between 5-15 milliseconds, and is therefore not long enough, or strong enough, to move the armature  16 , but is significant enough to cause a change in inductance in the coil  20   b  that is measureable. It should be noted that it is within the scope of the invention that the voltage pulse used to detect the position of the valve portion  14  may last for longer or shorter time intervals, as long as the armature  16  and valve member  38  remain stationary. Because the change in inductance in the second portion  20   b  of the coil  20  is measured, and the level of inductance change depends on the location of the armature  16  and corresponds to the location of the valve member  38  and the armature  16 , the location of the valve member  38  and the armature  16  is therefore detected and used to identify the position of the latching mechanism  24 . 
         [0036]    A second embodiment of the present invention is shown in  FIGS. 4-6 , with like numbers referring to like elements. In this embodiment, there is a magnet  52  mounted to the armature  16 , which moves into a magnet path  54  when the valve portion  14  is in the open position and the armature  16  is in the second position, shown in  FIG. 4 , and moves out of the magnet path  54  when the valve portion  14  is in the closed position and the armature  16  is in the first position, shown in  FIG. 6 . As with the previous embodiment, the latching mechanism  24  is able to maintain the position of the valve member  38  and the armature  16  in either the first position or the second position. The connector  22  of the latching valve assembly  10  in this embodiment only has two terminals, instead of three, as with the previous embodiment. Additionally, there is only one portion of the coil  20   a,  instead of the coil  20  having a first portion  20   a  and a second portion  20   b.    
         [0037]    The operation of the latching valve assembly  10  is substantially the same as described in the previous embodiment, with one of the differences being the magnet  52  being attached to the armature  16 , and used for increasing the S/N ratio of the inductance measurement. In this embodiment, the inductance of the coil  20  is measured when the valve member  38  is in either the open position or the closed position, and is stationary (i.e., not transitioning between the open position and closed position as shown in  FIG. 5 ). In this embodiment, a 12 Volt pulse is emitted through the coil  20 , and a measurement of the inductance of the coil  20  is then taken. The inductance of the coil  20  changes, depending upon whether the magnet  52  is located in the magnet path  54 , or the magnet  52  is not in the magnet path  54 . The presence of the magnet  52  in the magnet path  54  increases the signal-to-noise (S/N) ratio of the inductance measurement, whereas if the magnet  52  were not used, the S/N ratio would be insufficient, and the inductance would be difficult to measure. The magnet  52  essentially amplifies the inductance measurement when the valve member  38  is in the open position. 
         [0038]    The voltage pulse lasts between 1-15 milliseconds, and is not long enough or strong enough to move the armature  16 , but is significant enough such that a change in inductance in the coil  20  is measureable. It should be noted that it is within the scope of the invention that the voltage pulse used to detect the position of the armature  16  and valve member  38  may last for longer or shorter time intervals, as long as the armature  16  and valve member  38  remain stationary. If the valve member  38  is in the open position, the armature  16  is in the second position, and the magnet  52  is in the magnet path  54 , the inductance of the coil  20  is at a certain level. If the valve member  38  is in the closed position, the armature  16  is in the first position, and the magnet  52  is not in the magnet path  54 , the inductance of the coil  20  is at a different level. The different levels of inductance correspond to the position of the valve member  38  and armature  16 . This change in inductance of the coil  20  is therefore used to determine whether the armature  16  and valve member  38  are in the open position or the closed position. 
         [0039]    Another embodiment of the present invention is shown in  FIGS. 7-12 , and has substantially the same structural configuration as the latching valve assembly  10  shown in  FIGS. 4-6 , with the exception that the embodiment in  FIGS. 7-12  does not have a magnet  52 . The solenoid portion  12 , the valve portion  14 , and the latching mechanism  24  work in substantially the same manner. However, the position of the armature  16 , and therefore the valve member  38  is detected by measuring current. The position of the valve portion  14  is able to be detected when the valve portion  14  is in either the open position, as shown in  FIG. 7 , or the closed position, as shown in  FIG. 9 . To detect the position of the valve member  38  and the armature  16 , a voltage pulse is sent across a sense resistor, and into the coil  20  of the solenoid portion  12 . The voltage pulse is not large enough or long enough to move the armature  16 , but creates a voltage across the sense resistor that is measured, which then corresponds to the current flowing through the sense resistor. It is within the scope of the invention that the voltage pulse used to detect the position of the valve portion  14  may last for any desired time interval, as long as the armature  16  and valve member  38  remain stationary. This value of the current varies depending on the location of the armature  16 , and valve member  38 , and therefore the position of the valve portion  14 . Although in this embodiment, a sense resistor is used to detect the position of the valve member  38  and armature  16 , it is within the scope of the invention that other electrical components in circuits having different configurations may be used. 
         [0040]    Referring to  FIG. 10 , a chart, shown generally at  70 , depicts the application of a voltage pulse to change the armature  16  and valve member  38  between the open position and the closed position, as well as the application of voltage pulses to detect the position of the armature  16  and the valve member  38 . There are two parameters plotted on the chart  70 , the first line  72  represents voltage, the second line  74  represents current. This chart  70  shows the voltage  72  at approximately zero up until approximately 1.25 milliseconds, at which point at a first voltage pulse  76  of about 15 Volts for 1.0 milliseconds is applied to the coil  20 , and a measurement of current is taken. As shown in  FIG. 10 , the peak current taken during the 1.0 millisecond pulse was about 0.189 Amps. At about 1.38 milliseconds, a second voltage pulse  78  is applied to the coil  20 . This second voltage pulse  78  lasts about 150 milliseconds, but the current measurement is again taken at 1.0 millisecond of the second voltage pulse  78 , and as shown in  FIG. 10 , the peak current measurement at 1.0 millisecond of the second voltage pulse  78  is about 0.179 Amps. The second voltage pulse  78  lasts a longer period of time, and functions to change the position of the valve potion  14  and the latching mechanism  24 . A third voltage pulse  80  is applied to the coil  20  at about 1.65 milliseconds. Similarly to the first voltage pulse  76 , the third voltage pulse  80  is about 1.0 milliseconds, and a third current measurement is taken at the peak current value during the third voltage pulse  80 . As shown in  FIG. 10 , the peak current measured during the third voltage pulse  80  is about 0.274 Amps. The position of the armature  16  and valve member  38  is then determined by comparing the peak current measurements taken during the first voltage pulse  76  and the third voltage pulse  80 . As shown in  FIG. 10 , the peak current measurement (0.189 Amps) taken during the first voltage pulse  76  is less than the peak current measurement (0.274 Amps) taken during the third voltage pulse  80 . The higher of the two current measurements indicates that the armature  16  and valve member  38  are in the closed position, and the lower of the two current measurements indicates that the armature  16  and valve member  38  are in the closed position. Therefore, when looking at  FIG. 10 , armature  16  and the valve member  38  are initially in the open position, and then once the second voltage pulse  78  is applied to the coil  20 , the armature  16  and the valve member  38  are in the closed position. 
         [0041]    Referring not to  FIG. 11 , another chart, shown generally at  82 , depicts the application of a voltage pulse to change the armature  16  and valve member  38  between the closed position and the open position, as well as the application of voltage pulses to detect the position of the armature  16  and the valve member  38 . Both voltage  72  and current  74  are again depicted on the chart  82 . On this chart  82 , there are again three voltage pulses applied to the coil  20 , a fourth voltage pulse  84 , a fifth voltage pulse  86 , and a sixth voltage pulse  88 . The fifth voltage pulse  86  is used to change the position of the armature  16  and valve member  38 , and the current measurement is taken at about 1.0 milliseconds of the fifth voltage pulse  86 . The fourth voltage pulse  84  and sixth voltage pulse  88  are both about 1.0 millisecond, and are used to detect the position of the armature  16  and valve member  38 . Again the current measurements for the voltage pulses  84 , 88  are the peak current measurements. In  FIG. 11 , it is shown that the peak current measurement taken during the fourth voltage pulse  84  is about 0.279 Amps, and the peak current measurement taken during the sixth voltage pulse  88  is about 0.183 Amps. The higher of the two current measurements indicates that the armature  16  and valve member  38  are in the closed position, and the lower of the two current measurements indicates that the armature  16  and valve member  38  are in the closed position. Therefore, when looking at  FIG. 11 , armature  16  and the valve member  38  are initially in the closed position, and then once the fifth voltage pulse  86  is applied to the coil  20 , the armature  16  and the valve member  38  are in the open position. 
         [0042]    Additionally, the voltage pulse being applied for different lengths of time produces different current measurements, which also depends on whether the valve member  38  is in the open position or closed position. Referring to  FIG. 12 , there are several examples of current measurements taken at different time intervals, which are plotted on the chart  58  shown in  FIG. 12 . The first of the current measurements are taken from a voltage pulse lasting 1.0 millisecond. The first measurements taken from the 1.0 millisecond pulse are shown at  60   a  and  60   b,  where the first curve  60   a  represents a current measurement taken that corresponds to the armature  16  and valve member  38  being in the closed position, and the second curve  60   b  represents a current measurement taken that corresponds to the armature  16  and valve member  38  being in the open position, and the magnet  52  is disposed in the magnet path  54 . It is shown in the chart  58  that the second curve  60   b  has a greater peak than the first curve  60   a,  and the difference between the peaks in the two curves  60   a,   60   b  provides an indication of the position of the valve member  38  and armature  16 . 
         [0043]    The third curve  62   a  and fourth curve  62   b  represent current measurements taken when a voltage pulse is applied for about 2.0 milliseconds. The fifth curve  64   a  and sixth curve  64   b  represent current measurements taken when a voltage pulse is applied for about 3.0 milliseconds. The seventh curve  66   a  and eighth curve  66   b  represent current measurements taken when a voltage pulse is applied for about 4.0 milliseconds. The ninth curve  68   a  and tenth curve  68   b  represent current measurements taken when a voltage pulse is applied for about 5.0 milliseconds. The peak of each curve  60   a,   60   b,   62   a,   62   b,   64   a,   64   b,   66   a,   66   b,   68   a,   68   b,  represents the peak value, or RMS value, of the current at a set time, which in this embodiment is between 1.0 and 5.0 milliseconds, but it is within the scope of the invention that other time periods may be used. More specifically, the voltage pulse may be applied to the coil  20  for any length of time, as long as there is no movement of the valve member  28  and armature  16 . 
         [0044]    It is also shown in the chart that the longer the voltage pulse, the greater amount of current is measured when the valve member  38  is in either of the open or closed positions. The current measurements taken at 1.0 millisecond are generally less than the current measurements taken at 2.0 milliseconds, the current measurements taken at 2.0 milliseconds are generally less than the current measurements taken at 3.0 milliseconds, the current measurements taken at 3.0 milliseconds are generally less than the current measurements taken at 4.0 milliseconds, and the current measurements taken at 4.0 milliseconds are generally less than the current measurements taken at 5.0 milliseconds. 
         [0045]    However, the longer the voltage pulse, the greater the difference in the peak of each current measurement. For example, the difference between the peak of the first curve  60   a  and the peak of the second curve  60   b  is about 70 milliamps. When looking at the remaining curves on the chart  58 , it is shown that the difference between the peak of the third curve  62   a  and the peak of the fourth curve  62   b  is about 90 milliamps, the difference between the peak of the fifth curve  64   a  and the peak of the sixth curve  64   b  is 150 milliamps, the difference between the peak of the seventh curve  66   a  and the peak of the eighth curve  66   b  is 180 milliamps, and the difference between the peak of the ninth curve  68   a  and the peak of the tenth curve  68   b  is 290 milliamps. 
         [0046]    One of the advantages of the present invention is that there is no need to change the construction of the valve assembly  10 . The current measurement, and therefore the position of the valve member  38  and armature  16 , is therefore detected by measuring the current in the coil  20  after applying the voltage pulse to the coil  20  for a specified time period. The specified time period of the voltage pulse may be any desired time period, as long as the valve member  28  and armature  16  remain stationary during the application of the voltage pulse. In yet another embodiment of the present invention, the magnet  52  may be attached to the armature  16 , and used for increasing the S/N ratio, and therefore improve the signal of the current measurement. 
         [0047]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.