Abstract:
A controller for a vehicular power accessory includes an elongate sensor electrode ( 102 ), a capacitive shield ( 104 ) extending significantly beyond the sensor electrode ( 102 ). A dielectric ( 106 ) is disposed between the capacitive shield ( 104 ) and the sensor electrode ( 102 ) to isolate the sensor electrode ( 102 ) from the capacitive shield ( 104 ). A sensor processor ( 114 ) is in electrical communication with the sensor electrode ( 102 ) for processing sense data received from the sensor electrode ( 102 ). A power actuator ( 202 ) is in electrical communication with the sensor processor ( 114 ) for effecting movement of the power accessory in accordance with the processed sense data. The sensor electrode ( 102 ) can be applied to various vehicle locations with the purpose of detecting obstacles and activating an alarm or display.

Description:
This application claims the benefit of provisional application No. 60/296,483, filed Jun. 8, 2001. 

   FIELD OF THE INVENTION 
   The present invention relates to a non-contact proximity sensor. In particular, the present invention relates to a capacitive sensor for use in controlling movement of a power accessory in an automobile. 
   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 the window pane is being directed to the closed position. 
   One proximity sensor commonly used as a power window controller comprises a voltage sensor coupled between the window actuator and the actuator power source. When an obstruction is encountered in the window frame as the window is closing, the obstruction increases the electrical load imposed on the window actuator, thereby causing the load voltage at the window actuator to drop. The voltage sensor is configured to sense any drop in load voltage and to command the window actuator to stop or to reverse the direction of movement of the window pane when such a voltage drop is detected. 
   Another proximity sensor commonly used as a power window controller comprises a speed sensor coupled to the window actuator. When an obstruction is encountered in the window frame as the window is closing, the obstruction increases the mechanical load imposed on the window actuator, thereby causing the speed of the actuator to drop. The speed sensor is configured to sense any change in actuator speed and to command the window actuator to stop or to reverse the direction of movement of the window pane when such a change in actuator speed is detected. 
   Another proximity sensor employed comprises a pressure sensitive strip disposed around the upper edge of the window frame. When an obstruction is detected between the window pane and the window frame, the pressure sensitive strip signals the window actuator to stop further movement of the window pane. 
   Although voltage sensors, speed sensors and pressure sensors are commonly used in power window controllers, they cannot react with sufficient speed to prevent an obstruction, such as a hand, from being pinched between the window pane and the window frame. Consequently, attempts have been made to improve upon the conventional proximity sensor mechanism. 
   For instance, Peter (U.S. Pat. No. 5,801,340) teaches a solution which uses a capacitive sensor mounted on the weather seal at the top of the window frame. The capacitive sensor comprises a first insulating layer disposed over the window sheet metal, a conductive guard layer disposed over the first insulating layer, a second insulating layer disposed over the guard layer, and a touch plate disposed over the second insulating layer. The guard layer is driven by an alternating voltage signal which is identical in amplitude and phase to the voltage imposed on the touch plate. With this arrangement, capacitance between the touch plate and the window sheet metal is cancelled out, thereby increasing the sensitivity of the sensor to capacitive changes arising from obstructions in the window frame. 
   Although Peter allows the window actuator to respond more rapidly to obstructions in the window frame, Peter requires that the guard layer be the same size as the touch plate for optimum cancellation of touch plate capacitance. In fact, Peter points out that if the guard plate extends beyond the touch plate, the sensitivity of the sensor to obstructions will be reduced. Consequently, Peter discloses that the guard layer extends only   10/1000th of an inch beyond the touch plate. The disclosed manufacturing tolerances can greatly increase the manufacturing cost of the capacitive sensor. Consequently, there remains a need for a proximity sensor which will not allow an obstruction to become pinched between the window pane and the window frame when the window pane is being directed to the closed position.    
   SUMMARY OF THE INVENTION 
   The disadvantages of the prior art may be overcome by providing a capacitive sensor that can be used as a non-contact pinch sensor and a non-contact obstacle sensor. 
   According to one aspect of the present invention, there is provided a capacitive proximity sensor which includes an elongate sensor electrode, a conductive metal sheet extending significantly beyond the sensor electrode, a dielectric disposed between the metal sheet and the sensor electrode, a substrate layer, and a dielectric layer interposed between the substrate layer and the conductive metal sheet and bonded to the substrate and the metal sheet. 
   According to another aspect of the present invention, there is provided a vehicular power accessory controller which includes an elongate sensor electrode, a capacitive shield extending significantly beyond the sensor electrode, a dielectric disposed between the capacitive shield and the sensor electrode and bonded to the sensor electrode from the capacitive shield, a sensor processor in electrical communication with the sensor electrode for processing sense data received from the sensor electrode, and a power accessory actuator in electrical communication with the sensor processor for effecting movement of the power accessory in accordance with the processed sense data: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a top plan view of the capacitive proximity sensor, according to the present invention, depicting the sensor electrode, the capacitive shield, the dielectric and the sensor processor; 
       FIG. 2  is a longitudinal cross-sectional view of the proximity sensor shown in  FIG. 1 ; 
       FIG. 3  is a schematic representation of the power accessory controller, according to the present invention, depicting the proximity sensor shown in  FIG. 1 , and the power accessory actuator coupled to the sensor processor; 
       FIG. 4  is a schematic representation of one variation of the power accessory controller shown in  FIG. 3 ; and 
       FIG. 5  is a flow chart depicting a proximity detection process using the proximity sensor. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Turning now to  FIGS. 1 and 2 , a capacitive proximity sensor, denoted generally as  100 , is shown comprising a sensor electrode  102 , a capacitive shield  104  and a dielectric  106 . The sensor electrode  102  is used to detect the strength of the electric field in proximity to the sensor electrode  102 , and comprises a straight elongate electrically-conductive wire. Preferably, the sensor electrode  102  has a substantially circular or flat transverse cross-section. The suggested shapes for the sensor electrode  102  increase the surface area of the sensor electrode  102 , thereby enhancing the sensitivity of the proximity sensor  100 . However, other conductor shapes and orientations may be utilized in accordance with the application of the proximity sensor  100 . 
   The capacitive shield  104  is configured to provide partial capacitive shielding for the sensor electrode  102 . The capacitive shield  104  comprises an electrically-conductive metal sheet  108 , an adhesive layer  110 , and a dielectric layer  112  interposed between the adhesive layer  110  and the metal sheet  108 . Preferably, the metal sheet  108  comprises a substantially planar metal sheet and is disposed substantially parallel to the longitudinal axis of the sensor electrode  102 . Further, as shown, for proper shielding of the sensor electrode  102 , the area occupied by the metal sheet  108  is substantially greater than that of the sensor electrode  102 . 
   The dielectric  106  is disposed between the capacitive shield  104  and the sensor electrode  102  and electrically isolates the sensor electrode  102  from the capacitive shield  104 . Preferably, the dielectric  106  encloses the sensor electrode  102 , thereby protecting the sensor electrode  102  from external impact. Further, preferably, the dielectric layer  112  of the capacitive shield  104  is integrally formed with the dielectric  106 , such that the dielectric  106  and the dielectric layer  112  together form a unitary dielectric body which encloses the sensor electrode  102  and the metal sheet  108 . 
   In addition to the sensor electrode  102 , the capacitive shield  104  and the dielectric  106 , preferably the proximity sensor  100  also includes a sensor processor  114  disposed within the dielectric layer  112  of the capacitive shield  104 . However, the sensor processor  114  may also be disposed externally to the proximity sensor  100 , if desired. Preferably, the sensor processor  114  comprises an Application Specific Integrated Circuit (ASIC), and is in electrical communication with the sensor electrode  102  for processing sense data received from the sensor electrode  102 . 
   The sensor process  114  includes an I/O port connected to the proximity sensor  100 , a voltage pulse train generator, a first electronic switch connected between the pulse train generator and the I/O port for applying voltage pulses to the proximity sensor  100 , an internal storage capacitor, a second electronic switch connected between the storage capacitor and the I/O port for transferring electronic charge from the proximity sensor  100  to the storage capacitor, and a third electronic switch connected between the storage capacitor and ground for bleeding off any parasitic voltage resulting from the charge transfer. 
   In order to obtain the sense data from the sensor electrode  102 , the sensor processor  114  is configured to apply voltage pulse trains from the pulse train generator to the sensor electrode  102  (by closing the first electronic switch), and to transfer the resulting charge from the proximity sensor  100  to the storage capacitor (by closing the second electronic switch) at the end of each pulse train. The sensor processor  114  is also configured to bleed off parasitic voltage effects resulting from the charge transfer (by momentarily closing the third electronic switch), at the end of each charge transfer. 
   The sensor processor  114  is able to detect objects in proximity to the proximity sensor  100 , while also compensating for capacitive changes arising from environmental conditions (eg. humidity, temperature, dirt over the sensor electrode  102 ). To do so, the sensor processor  114  is configured to measure the cycle count of the storage capacitor after a predetermined number of charge transfer cycles, and to calculate an average quiescent cycle count value from the measured cycle count values. The sensor processor  114  is also configured to compare the rate of change of measured cycle counts against the rate of change in average quiescent cycle count value. If the measured cycle count exceeds the rate of change in average quiescent cycle count value, the sensor processor  114  assumes that the change in cycle count resulted from the presence of an object in proximity to the proximity sensor  100 , rather than a change in environmental conditions. 
     FIG. 3  depicts the proximity sensor  100  implemented as a component of a power accessory controller. The proximity sensor  100  is secured to an automobile metal body part (eg. disposed within the rubber sealing strip of a window frame or a power sliding door), with the sensor processor  114  being connected to the automobile&#39;s power actuator  202  (which controls the movement of the window pane in the window frame or the movement of the sliding door). In addition, the figure depicts the intrinsic capacitance Ci associated with the automobile, and the capacitance Co associated with an obstruction, such as a human hand. 
     FIG. 4  is a schematic representation of a proximity sensor  200  which is a variation of the proximity sensor  100 . The proximity sensor  200  is substantially similar to the proximity sensor  100 , and is implemented as a component of a power accessory controller. However, in contrast to  FIG. 3 , the sensor processor  114  of the proximity sensor  200  is in electrical communication with the sensor electrode  102  and the metal sheet  108  and is configured to transmit electrical pulses to the sensor electrode  102  and the metal sheet  108 , and to process the resulting sense data received from the sensor electrode  102 . This variation is advantageous since the electric field produced by the metal sheet  108  (due to the electrical pulses transmitted from the sensor processor  114 ) reduces the impact the steel body of the automobile body part can have on the shape of the electric field detected by the sensor electrode  102 . 
   The operation of the proximity sensor  100 ,  200  will now be described with reference to FIG.  5 . At step  300 , the sensor processor  114  resets a loop counter, removes all charge stored in the internal storage capacitor. The sensor processor  114  then transmits a train of electrical pulses to the sensor electrode  102  (or both the sensor electrode  102  and the metal sheet  108 ), at step  302 , causing an electrical charge to be transferred to the sensor electrode  102 . The sensor processor  114  transfers the charge stored on the sensor electrode  102  to the internal storage capacitor, at step  304 . After the charge on the sensor electrode  102  is stored in the storage capacitor, at step  306  the sensor processor  114  bleeds off any parasitic voltage effects resulting from the charge transfer step (ie. step  304 ). 
   At step  308 , the sensor processor  114  increments the loop counter, and then determines whether the loop counter has reached a predetermined maximum loop value. If the maximum loop value has not been reached, the sensor processor  114  repeats steps  302  to  306  again. However, if the maximum loop value has been reached, the sensor processor  114  measures the cycle count of the charge stored in the storage capacitor, at step  310 . The pulse width of each electrical pulse and the number of electrical pulses transferred to the sensor electrode  102  (at step  302 ), and the maximum loop value are all selected in accordance with the length and type of the sensor electrode  102  such that the capacitive value of the sensor electrode  102  can be determined from the cycle count of the storage capacitor when the maximum loop value has been reached. 
   At step  312 , the sensor processor  114  integrates all the sensor cycle count values (measured at step  310 ) to determine a reference quiescent sensor cycle count. Since the reference cycle count is determined dynamically, the reference cycle count varies in accordance with capacitive drift due to, for example, dirt over the sensor electrode  102 . At step  314 , the sensor processor  114  compares the instantaneous rate of change of the sensor cycle count with the average rate of change of the reference cycle count. If the instantaneous rate of change of the sensor cycle count exceeds the average rate of change of the reference cycle count (eg. due to the presence of a human hand in the window frame), the sensor processor  114  transmits an output control signal to the power actuator  202 , at step  316 , thereby alerting the power actuator  202  of the obstruction. Otherwise, the sensor processor  114  repeats steps  300  to  312 . 
   If the sensor processor  114  detects an obstruction, the sensor processor  114  operatively effects the power actuator  202  to terminate movement of the accessory. Alternatively, the sensor processor  114  can effect the power actuator  202  to terminate and reverse movement of the accessory. 
   As will be apparent, the magnitude of the measured cycle count will vary in accordance with the area occupied by the sensor electrode  102 , the magnitude of the gap between the sensor electrode  102  and the automobile body part, and the presence or absence of the obstruction capacitance Co. However, since the metal sheet  108  of the capacitive shield  104  is electrically isolated from the sensor electrode  102 , and the metal sheet  108  is substantially larger in terms of area than the sensor electrode  102 , the measured cycle count is not affected appreciably by the intrinsic capacitance Ci associated with the automobile. 
   If the power actuator  202  is directing the window pane of the automobile window frame (or the sliding door) to a closed position, upon receipt of the control signal the power actuator  202  immediately stops movement of the window pane (or sliding door). However, since the cycle count measured by the sensor processor  114  does not depend appreciably on the intrinsic capacitance Ci associated with the automobile, the presence of a cycle count differential due to the obstruction capacitance Co will be more readily identified than if the measured cycle count was affected by the intrinsic capacitance Ci. Consequently, the requisite output control signal to the power actuator  202  will be produced more rapidly and more reliably than with proximity sensor configurations which lack the capacitive shield  104 . 
   The present invention is defined by the claims appended hereto, with the foregoing description being illustrative of the preferred embodiment of the invention. Those of ordinary skill may envisage certain additions, deletions and or modifications to the described embodiment, which although not explicitly suggested herein, do not depart from the scope of the invention, as defined by the appended claims.