Abstract:
A sensor assembly for sensing angular position of one object relative to another object. A capacitor is formed between a transmitter capacitor plate having a pair of transmitter electrodes and a receiver capacitor plate having preferably eight receiver electrodes forming four receiver electrode pairs. A dielectric rotor rotates between the plates, the rotor having first and second segments each subtending 67.5 which are mutually separated by a vacancy subtending 45 degrees, and further having a third segment subtending 45 degrees disposed between the first and second segments diametrically opposite the vacancy. An electrical circuit measures net charge induced on each of the receiver electrode pairs, wherein the charges indicate the angular position of said rotor relative to said transmitter and receiver capacitor plates.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part application of Ser. No. 10/228,817, filed on Aug. 27, 2002 now U.S. Pat. No. 6,774,642. 
    
    
     TECHNICAL FIELD 
     This present invention relates to position sensors and particularly to angular or rotary position sensors. 
     BACKGROUND OF THE INVENTION 
     Position measurements, including both linear and angular measurements, are widely implemented in industrial automation control. In particular, the automotive industry is using more and more linear/angular position sensors for closing various control loops. For example, sensors are used in steer-by-wire systems to determine the angular position of the steering column; sensors are used to determine the angular position of the throttle in engine control modules; sensors are used to determine the brake pedal position and/or the brake master cylinder position in brake-by-wire systems; and sensors are used in vehicle smart suspension systems. 
     Known technologies that can be used to determine angular position include contact measurement, such as a resistance stripe, or non-contact measurement effects, based on inductance, capacitance, optical, or magnetic field. Sensors based upon a capacitive effect have been found to be particularly desirable in many automotive applications. Whereas some known capacitive position sensors are generally effective to provide an accurate indication of angular position in a non-contact environment, they tend to be rather complex and rather expensive and therefore not always amenable to the high volume and low cost requirements of automotive applications. 
     SUMMARY OF THE INVENTION 
     This present invention is directed to the provision of an improved angular position sensor. More particularly, this present invention is directed to the provision of an improved capacitive angular position sensor especially suitable for various automotive applications. 
     The sensor of the present invention is intended for use in sensing the angular position of a rotatable body such as, for example, a steering column of a motor vehicle. 
     According to the present invention, the sensor includes a stationary transmitter capacitor plate defining a transmitter surface area, the transmitter surface area including at least one transmitter electrode and a stationary receiver capacitor plate defining a receiver surface area generally corresponding in size to the transmitter surface area, the receiver surface area including at least a first receiver electrode and a second receiver electrode, the electrodes of the respective capacitor plates facing each other. Positioned in an air gap between the capacitor plates is a rotor formed of a dielectric material adapted to be fixedly secured to the rotatable body so as to rotate with the rotatable body. The rotor defines a rotor area at least as large as a transmitter electrode surface area and a receiver electrode surface area and is sized so that, in response to angular movement of the rotatable body, the rotor varies a capacitance between each transmitter electrode and an opposed receiver electrode. The sensor includes means for measuring the charge induced on the receiver electrodes whereby the charges indicate the angular position of the rotatable body. 
     The sensor can include an alternating current source for supplying an excitation signal to at least the first transmitter electrode. Preferably, the sensor includes means for comparing at least a first charge induced on a first receiver electrode to a second charge induced on a second receiver electrode to determine the angular position. 
     In a preferred embodiment of the present invention, the transmitter capacitor plate is generally circular with an aperture adapted to receive a shaft of the rotatable body and includes a first transmitter electrode and a second transmitter electrode, the first and second transmitter electrodes being equally-sized and located about an outside edge of the transmitter capacitor plate. This embodiment can include means for supplying a first alternating current (AC) excitation signal to the first transmitter electrode and for supplying a second AC excitation signal to the second transmitter electrode wherein the first and second AC excitation signals are the same amplitude but with 180 degrees out of phase from each other. These AC excitation signals are preferred to be square waveform signals. 
     In another embodiment of the present invention, the receiver capacitor plate is generally circular with an aperture adapted to receive a shaft of the rotatable body and includes at least four equal-sized receiver electrodes located about an outside edge of the receiver capacitor plate, each of two diametrically opposed electrodes forming a receiver electrode pair. Preferably, then, the rotor has at least one circular wedge whose outside edge is a circular arc larger in size to a portion of the outside edge of the receiver capacitor plate, the size of the circular wedge equivalent to at least a size of one receiver electrode wherein the radius of the circular wedge is larger than that of the receiver electrode. Thus, the high dielectric constant of the rotor as compared to the air gap will result in changing capacitance between the transmitter electrodes and at least one of the receiver electrode pairs. 
     Yet another embodiment of the present invention is seen where each of the capacitor plates is circular with aligned central apertures through which a shaft of the rotatable body can rotate, and the rotor has at least one circular wedge configuration and is adapted to be fixedly secured to the shaft at a center of the circle of which the circular arc of the outside edge of the circular wedge is a portion of the circumference of the rotor. 
     In a first aspect of the present invention used to measure 360 degrees of rotation of the rotatable body, the transmitter capacitor plate is generally circular with an aperture adapted to receive a shaft of the rotatable body and includes a first transmitter electrode and a second transmitter electrode, the two electrodes being equally-sized and generally semi-circular. Similarly, the receiver capacitor plate is generally circular with an aperture adapted to receive the shaft and includes four equally-sized receiver electrodes located about an outside edge of the receiver capacitor plate, each of two diametrically opposed electrodes being connected to form a first receiver electrode pair and a second receiver electrode pair. The rotor has a semi-circular shape and is adapted to be fixedly secured to the shaft at the geometric center of the circle defined by the circumference of the semi-circular rotor. The rotor with a larger radius is sized so that, in response to rotation of the shaft, the rotor varies the capacitance between the first transmitter electrode and a first pair of adjacent receiver electrodes and the capacitance between the second transmitter electrode and a second pair of adjacent receiver electrodes. Finally, a charge to voltage measuring means of the sensor, for example a current to voltage converter, converts a first charge induced on the first receiver electrode pair and converts a second charge induced on the second receiver electrode pair whereby the first and second converted voltages indicate the angular position of the rotatable body. 
     In a second aspect of the present invention used to measure 360 degrees of rotation of the rotatable body, the transmitter capacitor plate is, preferably, identical to the transmitter capacitor plate of the first aspect of the present invention. The transmitter capacitor plate is generally circular with an aperture adapted to receive a shaft of the rotatable body and includes a first transmitter electrode and a second transmitter electrode, the two electrodes being equally-sized and generally semi-circular. Similarly, the receiver capacitor plate is generally circular with an aperture adapted to receive the shaft and includes eight equally-sized receiver electrodes located about an outside edge of the receiver capacitor plate, each of two diametrically opposed electrodes being connected to form a first receiver electrode pair, a second receiver electrode pair, a third receiver electrode pair, and a fourth receiver electrode pair. The rotor, derived from the semi-circular shaped rotor of the first aspect of the present invention, has three generally circular wedge sections or segments, wherein a generally circular wedge subtending an angle of 45 degrees, 22.5 degrees on either side of the center of the semi-circular rotor, is removed from the semi-circular rotor and is rotated 180 degrees about the chord of the semi-circular rotor, thereby being positioned equidistant from the resulting two 67.5 degree generally circular wedges, and is adapted to be fixedly secured to the shaft at the geometric center of the circle defined by the circumference of the semi-circular rotor. The rotor is designed such that when at least one edge of a receiver electrode is aligned with at least one edge of a rotor segment at least one edge of a rotor segment will be located at the center of at least one receiver electrode. The rotor with a larger radius is sized so that, in response to rotation of the shaft, the rotor varies the capacitance between the first transmitter electrode and a first set of four adjacent receiver electrodes and the capacitance between the second transmitter electrode and a second set of four adjacent receiver electrodes wherein two diametrically opposed receiver electrodes, one of the first set and the other of the second set, form a first receiver electrode pair, a second receiver electrode pair, a third receiver electrode pair, and a fourth receiver electrode pair. Finally, a current to voltage converter means of the sensor converts a first, second, third, and fourth charge induced on the first, second, third, and fourth receiver electrode pairs whereby the first, second, third, and fourth converted voltages indicate the angular position of the rotatable body. 
     The first and second aspects of the present invention can include means for supplying a first AC excitation signal to the first transmitter electrode and for supplying a second AC excitation signal to the second transmitter electrode wherein the first and second AC excitation signals are 180 degrees out of phase from each other. This supply means can include a square wave generator with a frequency in a preferred range of 20 to 100 kHz (it could be up to MHz range, but the range from 1 kHz to 100 kHz is preferred) supplying the first AC excitation signal and an analog inverter receiving the first AC excitation signal and producing the second AC excitation signal. 
     The voltage measuring means can include a current to voltage converter for receiving a current difference between one receiver electrode of a receiver electrode pair and the other receiver electrode of the receiver electrode pair and producing an AC voltage representing a charge induced on the receiver electrode pair. Then, the sensor can include means for converting the AC voltage to a direct current (DC) voltage. 
     The means for converting the AC voltage can include an integrating, or level hold, capacitor for receiving the AC voltage and converting the AC voltage to a DC voltage. In the first and second aspects of the present invention including this feature, the sensor can also include means for connecting the integrating capacitor to receive the AC voltage only during either a positive half cycle or a negative half cycle of the first AC excitation signal. 
     In order to minimize temperature effects by having separate voltage measuring channels, only one voltage measuring means is preferred to measure the voltages of each receiver electrode pair in the first and second aspects of the present invention. Thus, the sensor preferably includes a receiver pair select switch for selectively enabling a current flow from each individual receiver electrode pair, depending upon the position of the switch. In order to sample all receiver pairs, the sensor may include means for controlling the receiver pair select switch. 
     In the first and second aspects of the present invention including the integrating capacitor, the sensor can also compare at least a first DC voltage at the integrating capacitor resulting from a current difference between one receiver electrode of at least a first receiver electrode pair and the other receiver electrode of the first receiver electrode pair to known voltages corresponding to angular positions of the rotatable shaft. The actual angular position is the result of the comparisons between receiver electrode pairs. This can be done using a look up table in an integral microcontroller or in the engine microcontroller. 
     Preferably, in the first and second aspects of the present invention the receiver capacitor plate includes a guard trace on the receiver surface area, the guard trace adjacent an outside edge of the receiver capacitor plate and located so as to prevent the interaction of adjacent electric fields. Of course, the transmitter capacitor plate can include such a guard trace, which is particularly desirable when the plate includes two transmitter electrodes. 
     Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the present invention is read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of a sensor according to the first aspect of the present invention. 
         FIG. 2  is a view of an electrode face of a receiver capacitor plate of the sensor according to the first aspect of the present invention. 
         FIG. 3  is a view of a shielded face of the receiver capacitor plate according to the first aspect of the present invention. 
         FIG. 4  is a view of an electrode face of a transmitter capacitor plate of the sensor according to the first and second aspects of the present invention. 
         FIG. 5  is a view of a shielded face of the transmitter capacitor plate according to the first and second aspects of the present invention. 
         FIG. 6  is a view of a dielectric rotor of the sensor according to the first aspect of the present invention. 
         FIG. 7  is a side elevational view of the sensor according to the first aspect of the present invention. 
         FIGS. 8A-8D  are progressive views showing the successive rotational positions of the rotor according to the first aspect of the present invention. 
         FIG. 9  is a graph of the sensor outputs related to the rotational positions of the rotor according to the first aspect of the present invention. 
         FIG. 10  is a circuit diagram of control circuitry for the sensor according to the first aspect of the present invention. 
         FIG. 11  is a view of a dielectric rotor of the sensor according to the second aspect of the present invention. 
         FIG. 12  is a pictorial representation of an electrode face of a receiver capacitor plate of the sensor according to the second aspect of the present invention. 
         FIG. 13  is a circuit diagram of control circuitry for the sensor according to the second aspect of the present invention. 
         FIGS. 14A-14P  are progressive views showing the successive rotational positions of the rotor according to the second aspect of the present invention. 
         FIG. 15  is a graph of a first receiver electrode pair output related to the rotational positions of the rotor according to the second aspect of the present invention. 
         FIG. 16  is a graph of sensor outputs related to the rotational positions of the rotor according to the second aspect of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The sensor assembly of the present invention is intended for use in measuring the angular position of any rotatable body, but is especially suitable for use in automotive applications where it is desired to determine the angular position of a rotating shaft, such as, for example, the vehicle steering column shaft. 
     The sensor of the first aspect of the present invention is illustrated for use with a shaft, such as the shaft  10  seen in  FIG. 1  (in the example above, the steering column shaft) and, broadly considered, includes a transmitter plate  12 , a receiver plate  14 , a rotor  16  and sensor electronics  21 ,  22 . 
     As shown in detail in  FIGS. 4 and 5 , the transmitter plate  12 , utilized in the first and second aspects of the present invention, has a generally circular configuration and includes a central hole  12   a  sized to freely pass shaft  10 . One face of the plate  12  is electrically shielded by a shield  18  and the other face of the plate  12  is divided into two equally-sized, semicircular transmitter plates, or electrodes, E and F. A ground guard trace  11 , which operates to prevent the interaction of adjacent electric fields, mostly encircles the peripheral edge  12   b  of the plate  12  and forms the boundary between transmitter electrodes E and F. Specifically, as shown in  FIG. 4 , the ground guard trace  11  encircles the peripheral edge  12   b , except for the area around the terminals  26 ,  28 , discussed herein. The trace  11  also extends in a line from the far side of the peripheral edge  12   b  to a point between the terminals  26 ,  28  and encircling the central hole  12   a.    
     The receiver plate  14 , shown in detail in  FIGS. 2 and 3 , utilized in the first aspect of the present invention, has a generally circular configuration corresponding to the size and shape of the transmitter plate  12  and has a central aperture  14   a  sized to pass shaft  10 . One face of the receiver plate  14  is shielded by a shield  20 . The other face of the receiver plate  14  is divided into four equally-sized, roughly pie-shaped receiver plates, or electrodes A, B, C, and D, defining two receiver electrode pairs AC and BD, wherein the electrodes in each pair are located on the plate  14  diametrically opposed to each other. A ground guard trace  13  mostly encircles the peripheral edge  14   b  of the plate  14 , which, like the ground guard trace  11 , operates to prevent the interaction of adjacent electric fields. Specifically, as shown in  FIG. 2 , the ground guard trace  13  encircles the peripheral edge  14   b , except for the area around the terminals  38 ,  42 , discussed herein. The trace  13  extends in a line from the far side of the peripheral edge  14   b , separating receiver electrodes A and B from receiver electrodes C and D and encircling the central hole  14   a . The guard trace  13  then extends in two lines from the portion encircling the central hole  14   a  to points between each of the pairs of terminals  38 ,  42 , separating receiver electrodes A and D from receiver electrodes B and C. 
     In construction, the electrodes of the transmitter plate  12  and the electrodes of the receiver plate  14  face each other. The rotor  16 , shown in  FIG. 6 , has a semicircular configuration and is fixedly secured to shaft  10  at the geometric center of the circle defined by the circumference  16   a  of the semicircular rotor  16 . The rotor  16  may be formed of any suitable high dielectric constant material and preferably a material having a dielectric constant of 10 or more. The radius of the rotor  16  is preferred to be greater than the both the radius of the receiver electrodes A, B, C and D and the radius of the transmitter electrodes E and F. The rotor  16  is positioned for rotation between the capacitor plates  12  and  14  as discussed below. 
     The circuit block diagram of  FIGS. 1 and 10  depicts a circuit  21  for energizing the transmitter electrodes E and F of the transmitter plate  12  and a circuit  22  for decoding the output of the sensor, providing DC analog output voltages indicative of the angular position of the rotatable body. As shown in  FIG. 7 , the circuitry means  21  and  22  may be provided, for example, on a printed circuit board  44 . Similarly, capacitor plates  12  and  14  can be formed as printed circuit boards. Together with the rotor  16 , the board  44  and capacitor plates  12  and  14  may be positioned within a suitable housing  46  seen in dashed lines, whereby to provide a compact package for the assembly. Plates  12  and  14  define an air gap  19  in which the rotor  16  rotates. The rotor  16  is of a thickness that fills the air gap  19  to change the capacitance between the plates due to its high dielectric constant with respect to air. However, the rotor  16  is not in tight contact with the plates  12  and  14 . Specifically, small air gaps  15  and  17  are defined between the capacitor plates  12  and  14  and the rotor  16 , respectively, on each side of the rotor  16 . The width of the air gap  15  on one side of the rotor  16  is substantially equal to the width of the air gap  17  on the other side of the rotor  16 . Although it is clear from the description that the rotor  16  does not completely fill the air gap  19  due to the presence of air gaps  15  and  17 , the air gaps  15  and  17  are small enough that the rotor  16  can be referred to as filling the air gap  19  between the plates  12  and  14 . Because the plates  12  and  14  are stationary, it is clearly seen that no electrical connection needs to be made to any rotating part. 
     The rotor  16  has a radius generally larger to the radius of the plates  12  and  14  so that, by virtue of its semicircular configuration, it is spaced to fill the air gap  19  between one complete transmitter electrode and a pair of complete receiver electrodes, or portions of the two transmitter electrodes and one complete receiver electrode and portions of two adjacent receiver electrodes, or half of the two transmitter electrodes and two complete receiver electrodes, at any given time. Specifically, and with reference to  FIGS. 8A-8D , as the rotor  16  turns in response to rotation of the shaft  10 , the rotor  16 , in successive angular positions, is spaced in, and fills, the air gap between: 
     (1) transmitter electrode E and its opposed pair of adjacent receiver electrodes A and B, which position is arbitrarily considered to be the 0 or 360 degrees start point of rotation and is shown in  FIG. 8A ; 
     (2) portions of transmitter electrodes E and F and receiver electrode B and portions of receiver electrodes A and C; 
     (3) portions of transmitter electrodes E and F and receiver electrodes B and C, which is 90 degrees of rotation of the rotor and is shown in  FIG. 8B ; 
     (4) portions of transmitter electrodes E and F and receiver electrode C and portions of receiver electrodes B and D; 
     (5) transmitter electrode F and its opposed pair of adjacent receiver electrodes C and D, which represents 180 degrees of rotation of the rotor as shown in  FIG. 8C ; 
     (6) portions of transmitter electrodes F and E and receiver electrode D and portions of receiver electrodes C and A; 
     (7) portions of transmitter electrodes F and E and receiver electrodes D and A, which is shown in FIG.  8 D and which represents 270 degrees of rotation of the rotor; 
     (8) portions of transmitter electrodes F and E and receiver electrode A and portions of receiver electrodes D and B; and 
     (9) finally back to its starting point, between transmitter electrode E and its opposed pair of adjacent receiver electrodes A and B, shown in FIG.  8 A. 
     This capacitance position sensor thus varies the dielectric constant between the electrodes of the plates  12 ,  14  in order to change the capacitance between them by rotation of the rotor  16 . The capacitance between the electrodes is directly related to their area, times the dielectric constant, divided by the spacing between the electrodes. Air has a dielectric constant of 1.0006, and the rotor  16 , as mentioned, preferably has a dielectric constant greater than 10. Thus, as the rotor  16  rotates, the capacitance between the electrodes increases until the high dielectric constant rotor  16  fills the space between the electrodes. 
       FIG. 10  shows the circuit block diagram of the circuitry means  21  and  22  with the electrodes A-F of the plates  12  and  14  schematically represented. The control circuitry for the sensor includes means  21  for applying an alternating current to the transmitter plate  12  and means  22  for measuring the voltage induced on the receiver plate  14 , wherein voltages measured serve as a measure of the angular position of the shaft  10 . The circuit means  21  and  22  are best described with reference to the operation of the sensor. 
     The means  21  for applying alternating current to the transmitter electrodes E, F of the transmitter plate  12  includes a square wave generator  23  and an analog inverter  24 . Preferably, the square wave generator  23  generates an output voltage of, for example, −5 volts direct current (DC) to +5 volts DC at a frequency between, but not limited to, 1 kHz and 100 kHz. The signal to transmitter electrode E is transmitted from the generator  23  via a lead  25  and the terminal  26 . The signal to the transmitter electrode F is transmitted from the generator  23  via a lead  27  and the terminal  28 . Prior to the signal being received at the terminal  28 , it passes through an inverter  24 . Thus, the voltage signals supplied to the two electrodes E and F are 180 degrees out of phase with each other. For example, when the square wave from the generator  23  makes the transition from −5 volts to +5 volts DC, a +5 volt level will be supplied to transmitter electrode E through lead  25  and the analog inverter  24  will invert the +5 volts to −5 volts, which is supplied to the transmitter electrode F through lead  27  (wherein, lead  27  better indicates the line between the analog inverter  24  and the terminal  28 ). 
     In operation, the rotor  16  is first in the 0 degree position, which has been previously arbitrarily assigned the position shown in  FIG. 8A  wherein the rotor  16  fills the space between transmitter electrode E and its pair of adjacent receiver electrodes A and B. Thus, the capacitance between transmitter electrode E and receiver electrodes A and B is greater than the capacitance between transmitter electrode F and its pair of adjacent receiver electrodes C and D. The receiver pair select switch  29  will be in the first input position  29   a . The first input position  29   a  is connected to receiver electrode pair AC via leads  36  and terminals  38 . With the transmitter electrode E at a positive potential, the receiver electrodes A and B are negative with respect to transmitter electrode E. Similarly, with the transmitter electrode F at a −5 volt potential, receiver electrodes C and D are positive with respect to transmitter electrode F. At this point in the operation of the sensor, the capacitor formed by electrodes A and E has more charge than the capacitor formed by electrodes C and F due to the high dielectric constant of the rotor  16  as compared to air. With electrode pair AC connected through the lead  36 , a net positive charge flows through the analog switch  29  to the inverting input of an operational amplifier (op amp)  31  configured as a current to voltage converter  31   a  with negative feedback containing an impedance  32 . The non-inverting input of the op amp  31  is grounded. 
     The output of the op amp  31  is a negative voltage whose voltage level is determined by the resistance of the feedback impedance  32 . When the square wave output of generator  23  makes its transition from +5 volts DC to −5 volts DC, the capacitor formed by electrodes A and E and the capacitor formed by electrodes C and F reverse charge, which means that a net negative charge flows into the inverting input of the op amp  31  from the lead  36  connecting electrode pair AC. The negative input to the op amp  31  results in a positive voltage output from the op amp. Thus, the output of the current to voltage converter  31   a  is a square wave that matches the frequency of the drive square wave from the generator  23 , and whose amplitude is dependent on the charge difference between the connected pair of electrodes, here electrode pair AC. 
     If the rotor  16  is rotated 45 degrees clockwise from  FIG. 8A , then half of the receiver electrode A and half of the receiver electrode C is affected by the influence of the rotor  16 . The capacitor formed by electrodes A and E and the capacitor formed by electrodes C and F have the same capacitance, or charge, but the charge is of opposite polarity so the net charge is zero. A zero input signal into the current to voltage converter  31   a , of course, results in a zero output voltage. Thus, on the negative half cycles of the output of generator  23 , as the rotor  16  turns through 45 degrees, the amplitude of the square wave output of the op amp  31  goes from its maximum voltage to zero. As the rotor  16  reaches 90 degrees, which is shown in  FIG. 8B , the amplitude of the op amp  31  output decreases to a minimum voltage. Between 90 and 180 degrees, the voltage output stays at the minimum. Between 180 and 225 degrees, the output of the op amp  31  rises from the minimum voltage to zero, and between 225 and 270 degrees, the output of the op amp rises from zero to the maximum output voltage. Finally, between 270 and 360, or 0, degrees, the voltage output generated at the output of the op amp  31  stays constant at the maximum voltage. 
     The synchronous switch  34 , which receives as its input the alternating current (AC) analog output voltage of the op amp  31 , closes the switch to a level hold capacitor  35  when the square wave drive is, for example, negative through the lead  33 . Through the synchronous switch  34 , a DC analog output is produced from the AC analog output of the current to voltage converter  31   a . Specifically, starting the measurement again at zero degrees, the square wave output of the generator  23  has just made its transition to −5 volts DC. The net negative charge from receiver electrode pair AC flows through the lead  36  and the analog switch  29  into the inverting input of the op amp  31 , and the positive output voltage of the current to voltage converter  31   a  flows through the closed synchronous switch  34  to the level hold capacitor  35 . Thus, a DC analog output representing the capacitance of the electrode pair AC results. When the generator  23  square wave switches to +5 volts DC, the synchronous switch  34  opens. The level hold capacitor  35  holds the charge until the next negative transition. If the rotor  16  turns 45 degrees clockwise from its position in  FIG. 8A , the capacitor formed by electrodes A and E and the capacitor formed by electrodes C and F are equal but have opposite charge which results in a net input of zero volts into the current to voltage converter  31   a  and an output of zero volts. The level hold capacitor  35  thus has zero volts across it after a couple of cycles at the frequency of the generator  23 . 
     As the rotor  16  rotates to its 90 degree position, shown in  FIG. 8B , the capacitor formed by electrodes C and F has a greater capacitance than the capacitor formed by the electrodes A and E due to the presence of the high dielectric rotor  16  between electrodes C and F. This means that on the negative portion of the square wave of the generator  23 , there is greater positive charge at the junction of the electrode pair AC that flows into the inverting input of the op amp  31 , and thus a correspondingly greater negative voltage output. The level hold capacitor  35  charges to the negative output voltage. Note that the level hold capacitor  35  is only connected by the synchronous switch  34  during the negative part of the generator  23  cycle. This means that what happens during the other half of the cycle does not affect the output voltage on the level hold capacitor  35 . This DC analog output developed for the receiver pair AC as the rotor  16  rotates from zero to 90 degrees is shown in  FIG. 9  as the solid curve labeled  50 . In the same manner, the remainder of the output curve for the receiver pair AC shown in  FIG. 9  is developed. When the analog switch  29  is connected so that the signal from the receiver pair BD is supplied to the current to voltage converter  31   a  through the terminals  42  and leads  40 , that is, the analog switch  29  is connected to its input  29   b , the output curve for the receiver pair BD is developed. This curve is shown in  FIG. 9  as the dashed line  48 . It is to be noted that the level hold capacitor  35  may also be only connected by the synchronous switch  34  during the positive portion of the generator  23  cycle instead of the negative portion to obtain correspondingly similar output curves. 
       FIG. 11  is a view of a dielectric rotor  16 ′ of the sensor according to the second aspect of the present invention. The rotor  16 ′ is comprised of three generally circular wedge segments  51 ,  52 ,  54  fixedly secured to a shaft  10 ′ at the geometric center of the circle defined by the circumference  16 ′ a . The rotor  16 ′ may be formed of any suitable high dielectric constant material and preferably a material having a dielectric constant of 10 or more. The radius of the rotor  16 ′ is preferred to be greater than the radius of the receiver electrodes A′-H′ of FIG.  12  and the radius of the transmitter electrodes E and F. The construction, properties, and positioning of the rotor  16 ′ are analogous to that of the rotor  16  ( FIG. 6 ) previously described according to the first aspect of the present invention. 
       FIG. 12  is a pictorial representation of an electrode face of a receiver capacitor plate  14 ′ of the sensor according to the second aspect of the present invention. The construction, properties, and positioning of the receiver  14 ′ are analogous to that of the receiver  14  ( FIGS. 2 and 3 ) previously described according to the first aspect of the present invention with the exception that the receiver  14 ′ is divided into eight equally sized, roughly pie-shaped electrodes A′-H′, instead of four electrodes A-D. The electrodes A′-H′ define four receiver electrode pairs A′E′, B′F′, C′G′, and D′H′ wherein the electrodes in each pair are located on the plate  14 ′ diametrically opposed to each other. 
       FIG. 13  shows the circuit block diagram of the circuitry means  21 ′ and  22 ′ with the receiver electrodes A′-H′ of receiver plate  14 ′ and transmitter electrodes E and F of transmitter plate  12  schematically represented according to the second aspect of the present invention. Single pole four throw switch  29 ′ selects receiver pairs A′E′, B′F′, C′G′, and D′H′ through inputs  29 ′ a ,  29 ′ b ,  29 ′ c , and  29 ′ d , respectively, in a manner analogous to switch  29  of FIG.  10 . The electrical operation of circuitry means  21 ′ and  22 ′ of  FIG. 13  is analogous to the electrical operation of circuitry means  21  and  22  of FIG.  10  and will be later described by example. 
       FIGS. 14A-14P  are progressive views of successive counterclockwise rotational positions of the rotor  16 ′ from an arbitrary zero degree position of  FIG. 14A  according to the second aspect of the present invention wherein transmitter electrode E is opposed by receiver electrodes A′-D′ and transmitter electrode F is opposed by receiver electrodes E′-H′. The rotor  16 ′ is within the space between transmitter electrode E and F and receiver electrodes A′-H′ analogously as described in  FIGS. 8A-8D . In operation, receiver electrodes A′-H′ are ordered in pairs wherein A′E′ constitute a first pair of receiver electrodes, B′F′ constitute a second pair of receiver electrodes, C′G′ constitute a third pair of receiver electrodes, and D′H′ constitute a fourth pair of receiver electrodes. The operation will be exemplified by referring to the position of the rotor  16 ′ as it rotates counterclockwise from the arbitrary zero position of FIG.  14 A through  FIG. 14P  with respect to receiver electrode pair A′E′ in an analogous manner as described in  FIGS. 8A-8D . 
     Initially, switch  29 ′ is in, for example, position  29 ′ a  thereby selecting receiver electrode pair A′E′ and switch  34  closes, for example, on the negative half of the square wave output of generator  23 , for example −5 volts DC, via lead  33  resulting in transmitter electrode E having a negative potential and transmitter electrode F having a positive potential, whereby receiver electrode A′ is at a positive potential and receiver electrode E′ is at a negative potential and the rotor  16 ′ is positioned at the arbitrary zero position of FIG.  14 A. At this point in the operation of the sensor, segment  51  of the rotor  16 ′ occupies the entire space between electrodes E and A′ while air occupies the entire space between electrodes F and E′ by which the capacitor formed by electrodes E and A′ has the most charge and the capacitor formed by electrodes F and E′ has the least charge due to the high dielectric constant of the segment  51  of the rotor  16 ′ as compared to air. Analogously, as previously described for the configuration of  FIGS. 8A-8D , net maximum negative charge from receiver electrode pair A′E′ flows through analog switch  29 ′ a  into the inverting input of the op amp  31 , and maximum positive output voltage of the current to voltage converter  31   a  passes through the closed synchronous switch  34  to the level hold capacitor  35  as output  60 . Thus, a maximum positive DC analog output  60  representing the capacitance of the electrode pair A′E′ results. When the generator  23  square wave switches to the positive half of the square wave output of generator  23 , for example +5 volts DC, via lead  33 , the synchronous switch  34  opens. The level hold capacitor  35  holds the output  60  at a maximum positive until the next negative transition of the generator  23  square wave, whereby the output  60  remains at a maximum positive. As the rotor  16 ′ turns 22.5 degrees counterclockwise from its position in  FIG. 14A  to its position in  FIG. 14B , segment  51  of the rotor  16 ′ still occupies the entire space between electrodes E and A′ while air still occupies the entire space between electrodes F and E′ thereby maintaining the output  60  maximum positive as described above and exemplified by the plot in  FIG. 15  between 0 and 22.5 degrees. 
     As the rotor  16 ′ turns 22.5 degrees counterclockwise from its position in  FIG. 14B  to its position in  FIG. 14C , segment  51  of the rotor  16 ′ rotates out of the space between electrodes E and A′ while segment  54  rotates into the space between electrodes F and E′ thereby decreasing the charge on the capacitor formed by electrodes E and A′ and increasing the charge on the capacitor formed by electrodes F and E′ until in  FIG. 14C  segment  51  of the rotor  16 ′ occupies half the space between electrodes E and A′ while segment  54  occupies half the space between electrodes F and E′ at which time the charge on the capacitor formed by electrodes E and A′ and the charge on the capacitor formed by electrodes F and E′ are equal and opposite by which the net charge is zero. Therefore, on the negative half cycles at the frequency of generator  23 , the net negative charge from receiver electrode pair A′E′ through analog switch  29 ′ a  into the inverting input of the op amp  31  decreases, and the positive output voltage of the current to voltage converter  31   a  passing through the closed synchronous switch  34  to the level hold capacitor  35  as output  60  also decreases such that the output is zero in  FIG. 14C  when the net charge is zero, exemplified by the plot in  FIG. 15  between 22.5 and 45 degrees. 
     As the rotor  16 ′ turns 22.5 degrees counterclockwise from its position in  FIG. 14C  to its position in  FIG. 14D , segment  51  of the rotor  16 ′ continues to rotate out of the space between electrodes E and A′ while segment  54  continues to rotate into the space between electrodes F and E′ thereby decreasing the charge on the capacitor formed by electrodes E and A′ and increasing the charge on the capacitor formed by electrodes F and E′ until in  FIG. 14D  air occupies the entire space between electrodes E and A′ while segment  54  occupies the entire space between electrodes F and E′. Therefore, analogously as previously described for the configuration of  FIGS. 8A-8D , on the negative half cycles at the frequency of generator  23 , net positive charge from receiver electrode pair A′E′ through analog switch  29 ′ a  into the inverting input of the op amp  31  increases, and negative output voltage of the current to voltage converter  31   a  passing through the closed synchronous switch  34  to the level hold capacitor  35  as output  60  also increases such that the output is at a minimum (maximum negative) in  FIG. 14D , exemplified by the plot in  FIG. 15  between 45 and 67.5 degrees. When the generator  23  square wave switches to the positive half of the square wave output of generator  23 , for example +5 volts DC, via lead  33 , the synchronous switch  34  opens. The level hold capacitor  35  holds the output  60  at a minimum until the next negative transition of the generator  23  square wave whereby the output  60  remains minimum. 
     As the rotor  16 ′ turns 22.5 degrees counterclockwise from its position in  FIG. 14D  to its position in  FIG. 14E , segment  52  of the rotor  16 ′ rotates into the space between electrodes E and A′ while segment  54  rotates out of the space between electrodes F and E′ thereby increasing the charge on the capacitor formed by electrodes E and A′ and decreasing the charge on the capacitor formed by electrodes F and E′ until in  FIG. 14E  segment  52  of the rotor  16 ′ occupies half the space between electrodes E and A′ while segment  54  occupies half the space between electrodes F and E′ at which time the charge on the capacitor formed by electrodes E and A′ and the charge on the capacitor formed by electrodes F and E′ are equal and opposite by which the net charge is zero. Therefore, on the negative half cycles at the frequency of generator  23 , the net positive charge from receiver electrode pair A′E′ through analog switch  29 ′ a  into the inverting input of the op amp  31  decreases, and the negative output voltage of the current to voltage converter  31   a  passing through the closed synchronous switch  34  to the level hold capacitor  35  as output  60  also decreases (becomes more positive) such that the output is zero in  FIG. 14E  when the net charge is zero, exemplified by the plot in  FIG. 15  between 67.5 and 90 degrees. 
     As the rotor  16 ′ turns 22.5 degrees counterclockwise from its position in  FIG. 14E  to its position in  FIG. 14F , segment  52  of the rotor  16 ′ continues to rotate into the space between electrodes E and A′ while segment  54  continues to rotate out of the space between electrodes F and E′ thereby increasing the charge on the capacitor formed by electrodes E and A′ and decreasing the charge on the capacitor formed by electrodes F and E′ until in  FIG. 14F  segment  52  occupies the entire space between electrodes E and A′ while air occupies the entire space between electrodes F and E′. Therefore, analogously as previously described for the configuration of  FIGS. 8A-8D , on the negative half cycles at the frequency of generator  23 , net negative charge from receiver electrode pair A′E′ through analog switch  29 ′ a  into the inverting input of the op amp  31  increases, and positive output voltage of the current to voltage converter  31   a  passing through the closed synchronous switch  34  to the level hold capacitor  35  as output  60  also increases such that the output is at a maximum positive in  FIG. 14F , exemplified by the plot in  FIG. 15  between 90 and 112.5 degrees. When the generator  23  square wave switches to the positive half of the square wave output of generator  23 , for example +5 volts DC, via lead  33 , the synchronous switch  34  opens. The level hold capacitor  35  holds the output  60  at a maximum until the next negative transition of the generator  23  square wave whereby the output  60  remains maximum. As the rotor  16 ′ turns 22.5 degrees counterclockwise from its position in  FIG. 14F  to its position in  FIG. 14G , segment  52  of the rotor  16 ′ still occupies the entire space between electrodes E and A′ while air still occupies the entire space between electrodes F and E′ thereby maintaining the output  60  maximum positive as described above and exemplified by the plot in  FIG. 15  between 112.5 and 135 degrees. 
     As the rotor  16 ′ turns 45 degrees counterclockwise from its position in  FIG. 14G  to its position in  FIG. 14I , segment  52  of the rotor  16 ′ rotates out of the space between electrodes E and A′ while segment  51  rotates into the space between electrodes F and E′ in an analogous manner to segment  51  and  54 , respectively, of  FIGS. 14B-14D  thereby resulting in a decrease of output  60  from a maximum in  FIG. 14G  to a minimum in  FIG. 14I  analogously as previously described for  FIGS. 14B-14D  and exemplified by the plot in  FIG. 15  between 135 and 180 degrees. As the rotor  16 ′ turns 22.5 degrees counterclockwise from its position in  FIG. 14I  to its position in  FIG. 14J , air still occupies the entire space between electrodes E and A′ while segment  51  of rotor  16 ′ still occupies the entire space between electrodes F and E′ thereby maintaining the output  60  minimum as described above and exemplified by the plot in  FIG. 15  between 180 and 202.5 degrees. 
     As the rotor  16 ′ turns 45 degrees counterclockwise from its position in  FIG. 14J  to its position in  FIG. 14L , segment  54  of the rotor  16 ′ rotates into the space between electrodes E and A′ while segment  51  rotates out of the space between electrodes F and E′ in an analogous manner to segment  52  and  54 , respectively, of  FIGS. 14D-14F  thereby resulting in an increase of output  60  from a minimum in  FIG. 14J  to a maximum in  FIG. 14L  analogously as previously described for  FIGS. 14D-14F  and exemplified by the plot in  FIG. 15  between 202.5 and 247.5 degrees. 
     As the rotor  16 ′ turns counterclockwise from 247.5 to 360 degrees from its position in FIG.  14 L through its positions in  FIGS. 14M-14P  and back to its position in  FIG. 14A , the output  60  exemplified by the plot in  FIG. 15  between 247 and 360 degrees is obtained analogously to the rotor turning counterclockwise from its position in FIG.  15 G through its positions in  FIGS. 14H-14L  as previously described and exemplified by the plot in  FIG. 15  between 135 and 247.5 degrees.  FIG. 15 , therefore, represents the output  60  for one revolution of the rotor  16 ′ with respect to the receiver electrode pair A′E′. 
     When switch  29 ′ is connected to its inputs  29 ′ b ,  29 ′ c , and  29 ′ d  the output curves  62 ,  64 , and  66  for receiver electrode pairs B′F′, C′G′, and D′H′, respectively, are developed. These curves are shown in FIG.  16 . It is to be noted that the level hold capacitor  35  may also be only connected by the synchronous switch  34  during the positive portion of the generator  23  cycle instead of the negative portion to obtain correspondingly similar output curves. 
     In normal operation of the first and second aspects of the present invention, a microcontroller  30  operates the receiver pair select analog switch  29  and  29 ′ and the DC analog outputs  48 ,  50 ,  60 ,  62 ,  64 , and  66 , preferably, connect to an analog-to-digital (A/D) input of the microcontroller  30 . The microcontroller  30  is a standard microcontroller used for automotive applications and can be included as part of the sensor or it can be the engine microcontroller sending and receiving data discussed herein through, for example, the electrical connector  45  of the sensor which is shown in  FIG. 7  according to the first aspect of the present invention. The microcontroller  30  selects a receiver pair through analog switch  29  and  29 ′, waits a few time periods of the generator  23 , and then measures the DC analog output voltage. The microcontroller  30  then switches to the next receiver pair through analog switch  29  and  29 ′ to repeat the process of measuring the DC analog output voltage. 
     With the measured pair of output voltages from the receiver electrode pairs, a simple lookup table developed according to the procedure outlined above, and located in memory of the microcontroller  30  or the engine microcontroller, can determine the absolute angular position. The microcontroller  30  or the engine microcontroller can then output a digital signal or an analog level or an output in any required format. If the microcontroller  30  is utilized, this signal would, probably, be sent to the engine microcontroller. 
     The sensor of the present invention will be seen to provide many important advantages. Specifically, all of the materials utilized in the sensor are relatively low cost materials so that the overall cost of the sensor is relatively low. Further, the sensor may be provided in a relatively small package which is desirable in automotive applications. Also, since the present invention uses at least two pairs of receiver electrodes, at any time at least one pair of the electrode output signals gives a pure temperature effect. This information can be used to compensate the temperature impact on the results of the measurements. Of course, only one transmitter electrode can be used, but the sensor can then only measure the angular position over a 180 degree rotation of the rotatable body  10 , which is acceptable for many applications. 
     While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the present invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.