Abstract:
A method for preventing a vehicular door or window panel from pinching an obstruction extending through an aperture of the vehicle by measuring a capacitance of a field extending through the aperture using a capacitive sensor as a motor drives the panel between the open and closed positions, correlating the measured capacitance to panel position to create closing data, comparing the closing data to a reference map to create a compare value, and detecting an object in a path of the panel as it moves toward the closed position when the compare value exceeds a threshold value. The threshold value is dependent on the relative wetness of the sensor, which is determined by comparing the capacitance of the sensor at predetermined panel positions against a calibration wetness profile.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the art of vehicular non-contact anti-pinch systems for preventing a closure panel such as a window or sliding door from pinching an object such as a person&#39;s hand as the closure panel moves into its closed position. 
     BACKGROUND OF THE INVENTION 
     Proximity sensors are widely used in the automotive industry to automate the control of power accessories. For instance, proximity sensors are often used in power window controllers to detect the presence of obstructions in the window frame when a window panel is being directed to the closed position. Such sensors can also be used to detect the presence of obstructions in other types of automotive closures such as sunroofs, side doors, sliding doors, lift gates, and deck lids. 
     A variety of capacitor-based proximity sensors are known in the art. For example, U.S. Pat. No. 6,377,009 discloses a system for preventing the pinching or trapping of a foreign object by a closing panel (such as a window) through the use of a sensing electrode or plate. This electrode is a metal strip or wire which is embedded in a plastic or rubber molding strip placed behind a piece of fascia or other trim part. The metal strip or wire and the chassis of the vehicle collectively form the two plates of a sensing capacitor. A foreign object placed between these two electrodes changes the dielectric constant and thus varies the amount of charge stored by the sensing capacitor over a given period of time. The charge stored by the sensor capacitor is transferred to a reference capacitor in order to detect the presence of a foreign object. Similar capacitive sensing applications are known from DE 4036465A, DE 4416803A, DE 3513051A1, DE 4004353A. 
     There are two major problems that have to be overcome for capacitive anti-pinch systems to work well in practice. 
     The first problem relates to the large background capacitance presented by the relatively enormous area of the sheet metal and plastic surrounding the closure aperture. For instance, in a power sliding door application, there is a large gap in between the sliding door and the vehicle frame. The presence of a small element such as a child&#39;s finger may not make an appreciable difference to the overall capacitance, and thus may be rejected as noise. Alternatively, if a relatively high sensitivity is employed to detect such a small change, too many false positives may occur (it being understood that no system is perfect and that there many some acceptable degree of false positives). 
     The second problem relates to the variable capacitance presented by changing humidity or water levels. The existence of high humidity or water will increase the dielectric constant of the system and thus will either mask the presence of a small object such as a child&#39;s finger or cause too many false positives. 
     In order to deal with such issues, it is known to utilize capacitive shielding and a differential capacitance sensing system which reduces the effect of parasitic capacitance arising from the sheet metal. It is also known to map the background capacitance as the closure panels opens and use that map as a reference as the closure panel closes to detect a differential. And it is known to vary the sensitivity of the system as the closure panel nears its final closing position. See, for instance, Applicant&#39;s PCT Publication Nos. WO 2002/101929, WO 2002/012699, WO 2003/038220, and WO 2005/059285. 
     However, the presence of water can still cause too many false positives, particularly when the sensor itself is wet. And since a human being&#39;s dielectric constant is similar to the dielectric constant of water, there could be a situation when the presence of water on the sensor causes too many false positives. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, a method is provided for preventing a closure panel from pinching an obstruction extending through an aperture of a motor vehicle having a motor to drive the closure panel between an open position and a closed position. The method includes: measuring a capacitance of a field extending through the aperture using a capacitive sensor as the motor drives the closure panel between the open and closed positions; identifying a position of the motor using a position sensor as the motor drives the closure panel between the open and closed positions; correlating the measured capacitance to the position identified to create closing data; comparing the closing data to a reference map to create a compare value; and detecting an object in a path of the closure panel as the closure panel moves toward the closed position when the compare value exceeds a threshold value dependent on the relative wetness of the sensor. 
     The threshold value is preferably adjusted for each closure of the panel by comparing the capacitance of the sensor at predetermined closure panel positions against a calibration wetness profile to determine the relative wetness of the capacitive sensor and determine a threshold adjustment value based on the relative wetness of the capacitive sensor. 
     The reference map is preferably generated each time the closure panel moves from the closed position to the open position by: measuring a capacitance of the field extending through the aperture using the capacitive sensor as the motor drives the closure panel, identifying a position of the motor using the position sensor as the motor drives the closure panel, and correlating the measured capacitance to the position identified. 
     Preferably, the method also includes measuring a time period that the compare value exceeds the threshold value to distinguish the detection of the object from noise. 
     The capacitance may be measured indirectly by cyclically charging the capacitance sensor and transferring charge therefrom to a reference capacitor, and either measuring the voltage of the reference capacitor after a predetermined number of charging cycles or measuring the number of cycles required to charge the reference capacitor to a predetermined voltage. 
     The capacitive sensor preferably includes a non-conductive casing, a first at least partially conductive body embedded in the casing, a second at least partially conductive body embedded in the casing, an air gap between the first and second at least partially conductive bodies, a first conductive strip electrode embedded in the first dielectric body, and a second conductive strip electrode embedded in the second dielectric body, wherein the casing, the at least partially conductive bodies and the strip electrodes are sufficiently flexible to allow the first and second at least partially conductive bodies to contact one another upon the application of a predetermined pinch force. 
     Utilizing such a capacitive sensor, the method preferably includes further detecting an object in the path of the closure panel as it moves toward the closed position when the electrical resistance between the first and second electrodes falls below a predetermined resistance. 
     The method may also include further detecting an object in the path of the closure panel as it moves toward the closed position by monitoring the position sensor to for lack of change therein or by monitoring the current drawn by the motor. 
     Once an object is detected, the closure panel is prevented from continuing to move toward the closed position and is preferably reversed. 
     A controller and control circuitry is enabled to carry out the foregoing functions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other aspects of the invention will be better understood from the following detailed description of preferred embodiments of the invention in conjunction with the drawings thereof, wherein: 
         FIG. 1  is a diagram of an automotive door having an obstruction sensor mounted thereto; 
         FIG. 2  is a cross-sectional view of a portion of an elongate obstruction sensor taken along line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a system block diagram of an anti-pinch system; 
         FIG. 4  is a schematic graph illustrating a method of detecting an object based on capacitive sensing; 
         FIG. 5  is a graph of the capacitance of a sensor over varying wetness conditions; and 
         FIG. 6  is a graph of an adjustment factor based on the degree of sensor wetness. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This application incorporates the following publications by reference in their entirety:
         PCT Publication No. WO 2002/101929   PCT Publication No. WO 2002/012699   PCT Publication No. WO 2003/038220   PCT Publication No. WO 2005/059285       

       FIG. 1  illustrates a typical automotive door  12  that is comprised of sheet metal and includes an aperture  14 , structured as a window frame  40 , which may be closed by a window pane or glass panel  16 . The glass panel  16  is raised or lowered by a window regulator (not shown) which includes an electric motor as the motive driving source, as well known in the art per se. The motor is controlled in part by a non-contact obstruction sensor or anti-pinch assembly  10 , the particulars of which are described in greater detail below. The anti-pinch assembly  10  includes an elongate sensor  18  that prevents the glass panel  16  from pinching or crushing a foreign object such a finger (not shown) that may be extending through the aperture  14  when the panel nears its closed position. It will be appreciated by those skilled in the art that the anti-pinch assembly  10  can be applied to any motorized or automated closure panel structure that moves between an open position and a closed position. For example, a non-exhaustive list of closure panels includes window panes, sliding doors, lift gates, sunroofs and the like. For applications such as window panes or sun roofs, the elongate sensor  18  may be mounted on the frame of the vehicle, and for applications such as powered sliding doors the elongate sensor  18  may be mounted on the closure panel itself, .e.g., at the leading edge of the sliding door. For ease of description, the remainder of this disclosure will focus on the windowpane and window frame combination, it being understood that the apparatus and methods described herein can be applied to other types of vehicular closure systems. 
     Referring additionally to  FIG. 2 , the elongate sensor  18  includes a non-conductive casing  20  mounted near or on the upper part of window frame  40  as seen in  FIG. 1 . Two conductive strip electrodes  24   a  and  24   b  such as wires are preferably disposed in the casing  20 . Electrode  24   a  is embedded in a first partially conductive body  26   a  and electrode  24   b  is embedded in a second partially conductive body  26   b . These partially conductive bodies  26   a ,  26   b  may be formed from a carbonized or electrically conductive rubber, and the surfaces  28   a ,  28   b  of these bodies preferably have a greater concentration of carbon or conductive material and thus able to carry a greater current than the inner part of the body. An air gap  22  separates the two partially conductive bodies  26   a ,  26   b , and an adhesive tape  30  provides a means for fastening the casing  20  to the window frame  40 . 
     The casing  20  is preferably formed as an extruded, oblong, elastomeric trim piece with co-extruded upper and lower partially conductive bodies  26   a ,  26   b , and the electrodes  24   a  and  24   b  are molded directly into the bodies  26   a ,  26   b . The trim piece can be part of the window water sealing system, i.e., form part of a seal, or can form part of the decorative fascia of the vehicle. 
     The air gap  22  electrically insulates the two electrodes  24   a ,  24   b  so electrical charge can be stored therebetween in the manner of a conventional capacitor. However, unlike a conventional capacitor, the elongate sensor  18  is flexible enough to enable the surfaces  28   a ,  28   b  of the first and second partially conductive bodies  26   a ,  26   b  to touch one another when pinched (i.e., as a result of a pinch condition), but not so flexible as to cause contact with one another as the closure panel ordinarily closes. The flexibility of the elongate sensor  18  can be controlled by its cross sectional configuration, including controlling the thickness of the casing walls and the thickness of the partially conductive bodies  26   a ,  26   b.    
     Referring additionally to  FIG. 3 , the anti-pinch assembly  10  includes a controller  50  connected to the two electrodes  24   a ,  24   b  that measures the resistance R between the electrodes. The resistance R will be very high when the partially conductive bodies  26   a ,  26   b  are separated from each other by the air gap  22 , and will substantially reduce in magnitude if a portion of the partially conductive bodies  26   a ,  26   b  contact one another. Thus, the elongate sensor  18  and anti-pinch assembly  10  is capable of functioning as a fail-safe contact pinch strip. 
     In addition to functioning as a contact pinch strip, the elongate sensor  18  also functions as a non-contact capacitive sensor, and is utilized by the controller  50  to measure a capacitance of a field extending through the aperture  14 . In the illustrated embodiment, electrode  24   b  functions as a shielding electrode since it is closer to the sheet metal whereby the electric field sensed by electrode  24   a  will be more readily influenced by the closer electrode  24   b  than the vehicle sheet metal. For best signal quality it is most preferable if the door is electrically isolated from the remainder of the vehicle. A powered sliding door, for instance, may be isolated through the use of non-conductive rollers. 
     The capacitance of the elongate sensor  18  is measured as follows: The electrodes  24   a  and  24   b  are preferably charged by controller  50  to the same potential using a pre-determined pulse train. For each cycle the controller  50  transfers charge accumulated between the electrodes  24   a  and  24   b  to a larger reference capacitor  52 , and records an electrical characteristic indicative of the capacitance of the system. The electrical characteristic may be the resultant voltage of the reference capacitor  52  where a fixed number of cycles is utilized to charge the electrodes  24   a  and  24   b , or a cycle count (or time) where a variable number of pulses are utilized to charge the reference capacitor  52  to a predetermined voltage. The average capacitance of the sensor  18  over the cycles may also be directly computed. See, for example, the foregoing publications incorporated by reference herein, which describe various circuitry for carrying out such functions. It will be noted that where an obstruction exists, the dielectric constant between the electrodes  24   a  and  24   b  will change, typically increasing the capacitance of the elongate sensor  18  and thus affecting the recorded electrical characteristic. 
     In preferred embodiments, whenever the glass panel  16  is opened the controller  50  creates an opening capacitive reference map  60  by plotting the recorded electrical characteristic against the position (provided by a position sensor such as Hall effect sensor  54 ) of the glass panel  16 . In  FIG. 4 , the opening reference map  60  is shown as a graph correlating cycle count against glass panel position. The controller  50  also measures a second capacitance map  62  (the “closing data”) as the glass panel  16  closes that is compared against the opening reference map  60 . Whenever the comparison exceeds a threshold value X for a period of time t, such as at dip  64 , an obstacle is detected. (Cycle count decreases if the capacitance of the sensor  18  increases.) 
     In order to deal with the possible presence of water on the sensor  18 , the controller  50  adjusts the threshold value based on the relative wetness of the sensor  18 , as shown in plot  80  of  FIG. 6 . In this profile, “0” represents a dry seal  18 , and “3” a drenched seal  18 . For a dry seal, no change is made to an initial threshold value X 0 , but for wet seals the threshold value X varies in accordance with the degree of wetness. 
     The controller  50  determines the degree of wetness based on a calibration wetness profile  70  such as shown in  FIG. 5  which is stored in non-volatile memory. The calibration profile  70  is based on empirical data obtained through known conditions of the elongate seal  18 . For instance, plot  72  is based on a dry seal; plots  74 ,  75  are based on a seal that is wetted along ⅓ rd  and ⅔ rd  of its length respectively; and plot  76  is obtained from a completely wet seal all along its length. As will be seen, while the shape of each plot is quite similar, the cycle count differs because the capacitance of the seal  18  differs in each case. More granular data can be obtained, if desired, by further varying the wetting conditions. 
     Thus, in effecting the obstacle determination, the controller  50  compares the opening reference map  60  against the calibration wetness profile  70  to find the plot  72 ,  74 ,  75  or  76  that best matches the opening reference map  60  in order to identify the degree of wetness. In order to prevent the situation of the seal  18  becoming wet only after the glass panel is open (which is a more likely scenario with a powered sliding door system), the capacitance of the elongate seal  18  may more preferably be measured at a certain point such as at full opening (or over a certain range of positions) and compared against the capacitance value of these plots  72 ,  74 ,  75  or  76  at the same position(s) to determine the degree of wetness. Upon closing the glass panel  16 , the controller  50  signals an obstacle when the difference between the closing data  62  and the opening map  60  (at common positions) exceeds a threshold value X=X 0 +D (as a function degree wetness) for a period of time t. When an obstacle is signaled, the controller  50  preferably reverses motor  56  to move the glass panel  16  open. 
     In a third mode of operation, the controller  50  also monitors the position sensor  54  and/or the current drawn by the motor  56 . In the event of an obstacle, the position sensor will not increment and the current drawn by the motor will spike, thus indicating a pinch condition. 
     Preferably, the controller  50  utilizes all three modes of obstacle detection—sensor impedance, capacitive sensing and position/current monitoring to detect a pinch condition. The controller  50  may also eliminate the capacitive sensing mode from consideration after two or three serial obstacle detections and rely only on the other two modes in case the capacitive sensing mode has triggered a false positive. 
     While the above describes a particular embodiment(s) of the invention, it will be appreciated that modifications and variations may be made to the detailed embodiment(s) described herein without departing from the spirit of the invention.