Abstract:
A capacitive sensing system includes a conductive sensing element and a circuit configured to provide measurements related to a sensing current sent to the sensing element. The circuit is located remote from the sensing element. The system also includes a switch configured to selectively couple the sensing element to the circuit. The switch is located proximate to the sensing element. The system also includes an electrical conductor that electrically couples the switch and the circuit. The conductor carries sensing signals from the circuit to the sensing element when the switch is closed.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/136,178 filed on Aug. 15, 2008, the entirety of which is herein incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to the field of capacitive sensors and sensing methods. More specifically, the disclosure relates to capacitive sensors and sensing methods for occupants of a vehicle seat. 
       SUMMARY 
       [0003]    One disclosed embodiment relates to a capacitive sensing system for a vehicle. The system includes a capacitive sensing element and a circuit configured to provide measurements related to an occupant of the vehicle based on a signal received from the capacitive sensing element. The circuit is located remote from the capacitive sensing element. The system also includes a switch configured to selectively couple the capacitive sensing element to the circuit. The switch is located proximate to the capacitive sensing element. The system also includes a harness configured to carry an electrical conductor that electrically couples the switch and the circuit. The conductor carries sensing signals from the circuit to the capacitive sensing element when the switch is closed. 
         [0004]    Another disclosed embodiment relates to a capacitive sensing system including a conductive sensing element and a circuit configured to provide measurements related to a sensing current sent to the sensing element. The circuit is located remote from the sensing element. The system also includes a switch configured to selectively couple the sensing element to the circuit. The switch is located proximate to the sensing element. The system also includes an electrical conductor that electrically couples the switch and the circuit. The conductor carries sensing signals from the circuit to the sensing element when the switch is closed. 
         [0005]    Another disclosed embodiment relates to a method for measuring a change in capacitance at a vehicle sensor. The method includes the steps of closing a switch located proximate to the capacitive sensing element using a control signal from a circuit, transmitting a signal from the capacitive sensing element to the circuit over a conductor in a harness, generating an electric field at a capacitive sensing element, and providing a calculation or measurement based on the signal using the circuit. 
         [0006]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0007]    The disclosure will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings. 
           [0008]      FIG. 1  is a perspective view of a vehicle seat, according to an exemplary embodiment. 
           [0009]      FIG. 2  is a schematic diagram of a sensing system, according to an exemplary embodiment. 
           [0010]      FIG. 3  is a schematic diagram of a sensing system, according to a further exemplary embodiment. 
           [0011]      FIG. 4  is a schematic diagram of a sensing system, according to a yet further exemplary embodiment. 
           [0012]      FIG. 5  is a schematic diagram of a sensing system, according to a yet further exemplary embodiment. 
           [0013]      FIG. 6  is a schematic diagram of a shielded sensing system, according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION  
       [0014]    Before turning to the figures, which illustrate the exemplary embodiments in detail, it should be understood that the application is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting. 
         [0015]    Capacitive sensors may be configured for numerous applications in a vehicle. For example, a capacitive sensor may be used in an occupant classification system, an occupant presence sensor, a head position sensor, an anti-pinch sensor, non-touch controls, etc. Conventionally, these systems include signal conditioning electronics, a sensor, and a harness connecting the sensor to the signal conditioning electronics. However, unless properly shielded, the harness acts as a sensing device in addition to the sensor. As a result, in conventional systems, the harness connecting the sensor to the signal conditioning electronics is short. 
         [0016]    Further, the harness may act as a sensor and change orientation with an object that affects the measurement. As a result, the harness may create a measurement offset shift. One solution is to make the harness so short that the harness effectively is where the sensor should be. Another solution is to shield the harness with an electrical signal nearly identical to the sensor signal (also called a driven shield) or another consistent signal (e.g., the system&#39;s ground). A further solution is to mechanically shield the harness with a thick mechanical conduit such that there is only a small sensitivity to objects outside the conduit. Yet further, another solution is to configure the signal conditioning electronics to be small enough to be integrated very close to the sensor, for example with an application specific integrated circuit (ASIC). 
         [0017]    However, the aforementioned solutions have limitation or significant cost implications, especially when multiple sensors are used, when the sensor must be located far from the signal conditioning electronics, and/or when in-line connections must be used to complete the sensing harness. Therefore, it is desirable to provide a capacitive sensing system wherein the harness does not create a measurement offset shift. Further, it is desirable that the method does not have significant limitations or cost implications. 
         [0018]    Referring generally to the figures, a sensing system that reduces the effects of drift on sensing measurements is shown. The system may include a signal conditioning electronics, sensing harnesses, switches, capacitive sensing elements (e.g., capacitive sensing electrodes), capacitors, and/or in-line connectors. A circuit of the system may make measurements based on signals from the capacitive sensing elements. The switches may be used to couple the capacitive sensing elements and the circuit, and a harness may electrically couple the switch and the circuit and transmit sensing signals from the capacitive sensing element to the circuit. 
         [0019]    Referring to  FIG. 1 , a vehicle  10  is shown with an occupant  12  in a seat  14  of the vehicle  10 , according to an exemplary embodiment. The seat  14  may include an occupant sensing system  16 . As shown in  FIG. 1 , the occupant sensing system  16  may generally be located in the seat  14  below the area in which an occupant  12  of the vehicle  10  sits, or may be located in other areas of the seat  14  or vehicle  10 . 
         [0020]    The occupant sensing system  16  may generally include a sensor and sensing system for sensing occupancy of the seat  14 . For example, the sensor may determine the weight of the occupant in the seat  14  to determine occupancy characteristics. The occupant sensing system  16  may further include a seat heating system and/or other systems for the seat  14  of the vehicle  10 . 
         [0021]    According to an exemplary embodiment, the occupant sensing system  16  includes a capacitive sensor. The capacitive sensor may generally be capable of sensing properties such as a proximity, position, or weight of an object, or the like. The capacitive sensor may sense based on measuring a change in capacitance (e.g., changes in an electrical property between two conductive objects); the capacitive sensor generally consisting of a conductive object within the occupant sensing system  16  and an object such as an occupant  12 . Referring to the present disclosure, the capacitive sensor may be used as an occupancy sensor to detect the presence of an occupant  12  in the seat  14  the occupant sensing system  16  is associated with. As an occupant  12  sits on seat  14 , the capacitance change may be used to determine the presence of the occupant  12  by the occupant sensing system  16  or other occupant  12  properties (e.g., weight of the occupant  12 ). 
         [0022]    Referring to  FIG. 2 , a schematic diagram of a sensing system is shown, according to an exemplary embodiment. The sensing system  200  includes signal conditioning electronics  201 , a sensing harness  202 , a switch  204 , and capacitive sensing electrodes  206 . 
         [0023]    The signal conditioning electronics  201  may be any hardware or software configuration capable of executing instructions and operating on signals sent to the sensor. For example, in a vehicle, the signal conditioning electronics  201  may determine the environment above a seat cover. More specifically, the signal conditioning electronics  201  may determine the size, presence, position, etc. of an occupant based upon signals received from a sensor. 
         [0024]    The sensing harness  202  may be any conductive material configured to relay signals between the signal conditioning electronics  201 , switch  204 , and capacitive sensing electrode  206 . Further, the sensing harness  202  may vary in length depending upon the application. Additionally, the sensing harness  202  may be shielded electrically, mechanically, or with any other known shielding method. 
         [0025]    The switch  204  may be a remote switch used to connect or disconnect the signal conditioning electronics  201  from the capacitive sensing electrode  206 . The switch  204  may be any switch capable of connecting or disconnecting the signal conditioning electronics  201  from the capacitive sensing electrode  206 . For example, the switch  204  may be a relay contact, field-effect transistor (FET) switch, other electronic switch, etc. Further, the switch  204  preferably has a low impedance (at the sensing frequency) when closed, and a very high impedance (at the sensing frequency) when open. According to one exemplary embodiment, the switch  204  may be integrated with the capacitive sensing electrodes  206 . 
         [0026]    The capacitive sensing electrode  206  may be any capacitive element capable of detecting environmental changes. For example, the capacitive sensing electrode  206  may consist of a flexible plate capacitive sensor configured to detect changes in the environment above the seat cover of a vehicle seat. 
         [0027]    The sensing system  200  may be configured to open or close the switch  204  while the signal conditioning electronics  201  measures signals received via the sensing harness  202  and/or capacitive sensing electrode  206 . Therefore, the signal conditioning electronics  201  may take measurements with the sensing electrode  206  connected and without the sensing electrode  206  connected. The signal conditioning electronics  201  may calculate the difference between the signal with the sensing electrode  206  connected and without the sensing electrode  206  connected. Thus, the signal conditioning electronics  201  may obtain the effective sensor measurements by eliminating the contribution of the harness to the measurement, which may be constant if the measurements are performed in a short period of time. 
         [0028]    Referring to  FIG. 3 , a sensing system is shown according to a further exemplary embodiment. The sensing system  300  includes signal conditioning electronics  301 , a variable capacitor  302 , a sensing harness  304 , a switch  306  and a capacitive sensing electrode  308 . 
         [0029]    The sensing harness  304  may have a varying capacitance to ground  302 . However, the short term variation caused by the harness  304  and the capacitor  302  may be eliminated when the difference between when the switch  306  is open and when the switch  306  is closed is calculated. Thus, the signal conditioning electronics  301  may still make a repeatable measurement of the capacitive sensing electrode  308 . Further, changes in the variable capacitor  302  may be measured by the signal conditioning electronics  301  when the switch  306  is open. 
         [0030]    Referring to  FIG. 4 , a sensing system is shown according to a yet further exemplary embodiment. The sensing system  400  includes signal conditioning electronics  401 , a first sensing harness  402 , a second sensing harness  404 , and a third sensing harness  406 . The sensing system  400  additionally includes a first switch  408 , second switch  410 , and third switch  412 . The sensing system  400  further includes a first sensing electrode  414 , second sensing electrode  416 , and third sensing electrode  418 . 
         [0031]    According to an exemplary embodiment, each sensing electrode  414 ,  416 ,  418  of the sensing system  400  includes a switch  408 ,  410 ,  412 . Further, the location of the switch  408 ,  410 , or  412  is local to or located in proximity to the sensor  414 ,  416 , or  418 . Additionally, multiple sensors could be used, wherein each sensor includes a switch that is located in proximity to the sensor. Each harness  402 ,  404 , and  406  are configured to electrically couple the switches  408 ,  410 , and  412  to its corresponding sensor  414 ,  416 , and  418 . 
         [0032]    Referring to  FIG. 5 , a schematic diagram of a sensing system is shown, according to a yet further exemplary embodiment. The sensing system  500  includes signal conditioning electronics  501 , an in-line connector  502 , a sensing harness  503 , a switch  504 , and a capacitive sensing electrode  506 . 
         [0033]    According to an exemplary embodiment, the sensing harness  503  includes an in-line connector  502 . The in-line connector  502  may also be an integrated connector. The integrated connector may be located at the signal conditioning electronics  501  or at the switch  504  and may be configured for coupling to the sensing harness  503 . Further, the location of the switch  504  is located in proximity to the capacitive sensing electrode  506 . 
         [0034]    Referring to  FIG. 6 , a schematic diagram of a shielded sensing system is shown, according to an exemplary embodiment. The sensing system  600  includes signal conditioning electronics  601 , sensing harness  602 , shielding harness  604 , sensing switch  606 , and shielding switch  608 . The sensing system  600  additionally includes a capacitive sensing electrode  610  and a shield electrode  612 . 
         [0035]    According to an exemplary embodiment, some applications may use a shield electrode  612  near the capacitive sensing electrode  610  to prevent detection of objects on a side of the shield opposite of the electrode  612 . For example, the shield electrode  612  may be in another plane than sensing electrode  610 , in different orientation than sensing electrode  610 , around sensing electrode  610 , etc. The sensing system  600  may use the shield electrode  612  by opening or closing the sensing switch  606 , the shielding switch  608 , or both. According to various exemplary embodiments, the sensing system  600  may include additional shield electrodes with additional switches to couple the shield electrodes to the electronics  601  and additional harnesses configured to couple the switches and the electronics  601 . 
         [0036]    Further, the sensing switch  606  and the shielding switch  608  may be controlled such that they switch at appropriate times, thereby allowing the signal conditioning electronics  601  to take accurate measurements. To control the switching, the sensing system  600  could include control lines in parallel with the sensing harness  602  and the shielding harness  604 . Additionally, any other necessary signals, such as power lines to provide power to the switches  606  and  608  and ground lines to ground the switches  606  and  608 , may also be sent to the sensing switch  606  and shielding switch  608  along the sensing harness  602  and/or shielding harness  604 . The control lines, power lines, and/or ground lines may be parallel to the harnesses  602  and  604  and electrically couple the switches  606  and  608  to the electronics  601 . 
         [0037]    Additionally, it should be appreciated that other multi-measurement techniques that are used to eliminate other sources of system drift may be used with any of the embodiments shown in  FIGS. 2 through 6 . As a result, overall system measurement stability may be further improved. 
         [0038]    The present disclosure has been described with reference to exemplary embodiments, however workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the claimed subject matter. For example, although different example embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example embodiments or in other alternative embodiments. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements. 
         [0039]    It is also important to note that the construction and arrangement of the elements of the system as shown in the preferred and other exemplary embodiments is illustrative only. Although only a certain number of embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of the assemblies may be reversed or otherwise varied, the length or width of the structures and/or members or connectors or other elements of the system may be varied, the nature or number of adjustment or attachment positions provided between the elements may be varied. It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the present subject matter. It is also noted that the disclosed methods may be performed in any of a variety or sequence of steps and may include more or fewer steps than illustrated.