Abstract:
A non-contact position sensor comprises a first reactive element for accepting radio frequency (RF) energy from an oscillator and radiating said RF energy to generate an excitation flux. A second reactive element intercepts the excitation flux and an RF voltage is induced therein. An RF voltage detector, operatively coupled to the second reactive element, detects the RF voltage induced in the second reactive element to generate an output voltage. A third reactive element is capable of intercepting the excitation flux to generate a back electromagnetic force (EMF) in the second reactive element such that, upon the third reactive element being displaced relative to at least one of the first and second reactive elements, the RF voltage detector generates a position-dependent output signal indicative of the displacement of the third reactive element.

Description:
BACKGROUND  
       [0001]     The present invention relates generally to sensing devices and, more particularly, to inductively coupled, non-contacting position sensors.  
         [0002]     A variety of automotive and industrial control systems require non-contacting linear or angular position sensors capable of operating down to zero speed. For many system applications, a certain amount of physical ruggedness is required, thus precluding the use of optical or capacitive sensors. The most frequently utilized sensor satisfying the foregoing requirements is a magnetic sensor comprising an analog Hall or anisotropic magnetoresistor (MR) device. Hall devices utilize a current-carrying element, such as a semiconductor, that responds to an applied magnetic field by generating a voltage potential perpendicular to both the direction of current flow and the applied field. A magnetoresistor (MR) device is a two-terminal device that changes its resistance in accordance with changes in the applied magnetic field. These magnetic sensors operate in conjunction with a position responsive magnetic flux generating mechanism. The flux generation mechanism provides a magnetic flux which varies as a function of absolute position.  
         [0003]     Hall and MR devices are disadvantageous in that they require a costly magnetic circuit capable of driving a bulky bias magnet. Moreover, the Hall or MR device must be equipped with integrated signal processing capabilities, further increasing the cost and complexity of the overall system. Accordingly, there still remains a need for providing a simple, inexpensive non-contact position sensor that is sufficiently rugged for use in a variety of automotive and industrial applications.  
       SUMMARY  
       [0004]     The aforementioned drawbacks and deficiencies of the prior art are addressed by providing a non-contact position sensor comprising a first reactive element for accepting radio frequency (RF) energy from an oscillator and radiating said RF energy to generate an excitation flux. A second reactive element intercepts the excitation flux and an RF voltage is induced therein. An RF voltage detector, operatively coupled to the second reactive element, detects the RF voltage induced in the second reactive element to generate an output voltage. A third reactive element is capable of intercepting the excitation flux to generate a back electromagnetic force (EMF) in the second reactive element such that, upon the third reactive element being displaced relative to at least one of the first and second reactive elements, the RF voltage detector generates a position-dependent output signal indicative of the displacement of the third reactive element.  
         [0005]     Pursuant to another embodiment, a non-contacting differential position sensor comprises a first reactive element for accepting radio frequency (RF) energy from an oscillator and radiating said RF energy to generate an excitation flux. A second reactive element and a third reactive element are also utilized. Upon the second reactive element intercepting the excitation flux, a first RF voltage is induced therein. Upon the third reactive element intercepting the excitation flux, a second RF voltage is induced therein. An RF voltage detector, operatively coupled to the second and third reactive elements, detects at least one of the first and second RF voltages and, in response thereto, generates an output voltage. A fourth reactive element is capable of intercepting the excitation flux to generate a back electromagnetic force (back EMF) in at least one of the second reactive element or the third reactive element, such that, upon the fourth reactive element being displaced relative to at least one of the first, second, or third reactive elements, the RF voltage detector generates a position-dependent output signal indicative of the displacement of the fourth reactive element.  
         [0006]     Pursuant to yet another embodiment, a non-contacting position sensor array comprises a first reactive element for accepting radio frequency (RF) energy from an oscillator and radiating said RF energy to generate an excitation flux. A reactive element array comprises a plurality of receiving elements wherein, upon at least one of the receiving elements intercepting the excitation flux, an RF voltage is induced in the reactive element array. An RF voltage detection mechanism, operatively coupled to the reactive element array, detects the RF voltage induced in the reactive element array to generate an output voltage. A second reactive element is capable of intercepting the excitation flux to generate a back electromagnetic force (back EMF) in the reactive element array such that, upon the second reactive element being displaced relative to at least one of the first reactive element and the reactive element array, the RF voltage detector generates a position-dependent output signal indicative of the displacement of the second reactive element. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:  
         [0008]      FIG. 1  is a diagrammatic representation of a position sensor constructed in accordance with a first set of embodiments of the present invention;  
         [0009]      FIG. 2  is graph depicting the relationship between relative amplitude and relative displacement for the position sensor of  FIG. 1 ;  
         [0010]      FIG. 3  is a diagrammatic representation of a differential position sensor constructed in accordance with a second set of embodiments of the present invention;  
         [0011]      FIG. 4  is a diagrammatic representation of a differential position sensor constructed in accordance with a third set of embodiments of the present invention;  
         [0012]      FIG. 5  is a graph depicting the relationship between relative output voltage and relative displacement for the differential position sensor of  FIG. 3 ; and  
         [0013]      FIG. 6  is a diagrammatic representation of a sensor array constructed in accordance with a third set of embodiments of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  is a diagrammatic representation of a position sensor  100  constructed in accordance with a first set of embodiments of the present invention. A receiver coil  101  is operatively coupled to an RF voltage detector  107 , and an excitation coil  105  is operatively coupled to an oscillator  109 . Oscillator  109  is capable of generating electromagnetic energy at one or more radio frequencies which, illustratively, may be in the range of approximately 0.4 to 30 MHz. When excitation coil  105  is fed with electromagnetic energy produced by oscillator  109 , the excitation coil generates a magnetic excitation flux in a flux region surrounding the coil. According to one embodiment of the invention, oscillator  109  operates at a frequency in the range of 0.5 to 1.0 MHz. An unmodulated sinusoidal or square-wave oscillator could, but need not, be employed to implement oscillator  109 . For some system applications, the power output of oscillator  109  may be selected so as not to exceed applicable Federal Communications Commission (FCC) limitations governing RF emissions, and also to avoid interference with other users of the RF spectrum, especially in situations where the frequency of oscillator  109  falls within the AM broadcast band.  
         [0015]     The magnetic excitation flux generated by excitation coil  105  induces radio frequency (RF) currents to flow in receiver coil  101 . The induced current in receiver coil  101  creates a voltage potential across receiver coil  101 . RF voltage detector  107  detects the voltage potential across receiver coil  101 , and uses this detected voltage potential to produce a detected waveform. Exemplary embodiments of RF voltage detector  107  include a peak detector, a rectifier, one or more semiconductor diodes, an envelope detector, or the like. Optionally, RF voltage detector  107  may include one or more amplifier or buffer stages, so as to provide sufficient voltage or current to interface with other electronic equipment, such as a microprocessor or a computing device. Pursuant to another optional feature, RF voltage detector  107  may include output filtering circuitry, such as a low-pass filter, to smooth a waveform envelope corresponding to the detected RF voltage as a function of time. Pursuant to yet another optional feature, RF voltage detector  107  may include input filtering circuitry, such as a bandpass filter tuned approximately to the frequency of oscillator  109 , to enhance detection of RF energy emitted by oscillator  109  while reducing detection of ambient sources of RF interference.  
         [0016]     Receiver coil  101 , target coil  103 , and excitation coil  105  each represent reactive elements capable of generating a magnetic excitation flux in response to RF energy being applied thereto. Pursuant to the principle of reciprocity, an alternating RF voltage will be induced in these reactive elements in the presence of an applied electromagnetic field. From a practical standpoint, receiver coil  101 , target coil  103 , and excitation coil  105  may each be implemented using reactive elements such as coils, conductive traces, wires, or inductors. Illustratively, receiver coil  101 , target coil  103 , and excitation coil  105  may each be fabricated using stationary planar air-core coils formed on one or more printed circuit boards. For example, receiver coil  101  may be implemented by forming one or more conductive traces on a printed circuit board, whereby the conductive traces together form a coil that includes at least one turn or loop having a first end  131  and a second end  132 . Excitation coil  105  may be implemented in a manner substantially similar to that of receiver coil  101 , so as to include at least one turn or loop having a first end  141  and a second end  142 . Target coil  103  may be formed using one or more traces on a printed circuit board but, unlike receiver coil  101 , the conductive traces together form a continuous coil of at least one turn or loop, such that the first and second ends of the coil are effectively joined together.  
         [0017]     Receiver coil  101 , target coil  103 , and excitation coil  105  could, but need not, be fabricated such that two or more of these coils are of equal size and have substantially identical dimensions. For example, the aspect ratio of one or more of these coils can be selected to obtain a desired resolution or detection range for target coil  103 . Instead of using a single excitation coil  105 —receiver coil  101  pair, several excitation coil  105 -receiver coil  101  pairs could be employed for increased target resolution accuracy, and/or to cover a broader target detection volume. The size of excitation coil  105  could be increased relative to that of receiver coil  101 , so as to provide an excitation flux for more than one receiver coil  101 , and/or so as to provide a relatively constant level of excitation flux across an expected range of target coil  103  movement. Pursuant to another variation, the size of receiver coil  101  could be increased relative to that of excitation coil  105 , so as to provide reception of excitation flux from more than one excitation coil  105 .  
         [0018]     Receiver coil  101  includes a mechanism by which RF energy may be extracted from the coil, such that the coil may be utilized to sense an applied magnetic excitation flux. Excitation coil  105  includes a mechanism by which RF energy may be fed to the coil, such that the coil may be utilized to generate an excitation flux. In the exemplary embodiment of  FIG. 1 , an RF feedline  121  is connected to the first end  131  and second end  132  of receiver coil  101 . Similarly, an RF feedline  123  is connected to the first end  141  and second end  142  of excitation coil  105 . However, the foregoing RF feedline arrangement is described for illustrative purposes only, as any of a variety of techniques could be used to feed RF into excitation coil  105 , and to extract RF from receiver coil. For example, at least one of receiver coil  101  and excitation coil  105  could be fabricated in a manner similar to that of target coil  103 , using conductive traces which together form a continuous coil of at least one turn or loop, such that the first and second ends of the coil are effectively joined together. The resulting continuous loop could then be shunt-fed using feedline  121  or  123 . As a further alternative, RF energy may be capacitively coupled from receiver coil  101  to RF power detector  107 , and from oscillator  109  to excitation coil  105 . Finally, any of various combinations of the foregoing RF feed mechanisms may be employed.  
         [0019]     Position sensor  100  is capable of sensing the relative position of target coil  103  along X-axis  151  with reference to stationary receiver coil  101  and stationary excitation coil  105 . Illustratively, receiver coil  101  and excitation coil  105  remain at a stationary position while the position of target coil  103  is changed. Position sensor  100  can sense the position of target coil  103  even if the velocity of the target coil is zero with respect to stationary receiver coil  101  and stationary excitation coil  105 . Together, excitation coil  105 , target coil  103  and receiver coil  101  function as a high frequency (0.5-30 MHz) variable transformer. The shorted turn(s) of target coil  103  create a back electromagnetic force (EMF) which counters the excitation flux generated by excitation coil  105  within an area where target coil  103  overlaps excitation coil  105  and receiver coil  101 . This countering of excitation flux results in a proportional decrease in the amplitude of RF energy intercepted by receiver coil  101 . As used herein, the term “back EMF” refers to any electromagnetic force that opposes a change of current in an inductive element, such as receiver coil  101 .  
         [0020]     The dependence of the voltage (V 0 ) detected by RF voltage detector  107  as a function of target coil  103  displacement along X-axis  151  is graphically depicted in  FIG. 2 . The RF voltage generated by oscillator  109  ( FIG. 1 ) is denoted mathematically as V ex =V 0  sin ωt, with the corresponding RF current being denoted as I ex =I 0  sin ωt. As used herein, V 0  is the amplitude of oscillator  109 , I 0  is the current delivered by oscillator  109 , ω is the angular frequency in radians of oscillator  109 , and t refers to time. When applied to excitation coil  105 , V ex  generates an excitation flux that induces a current (and a voltage) in receiver coil  101 . The voltage induced in receiver coil  101  for detection by RF voltage detector  107  is given by V out=f(x, I   ex )sin(ωt+φ).  
         [0021]     Referring now to  FIG. 2 , assume that receiver coil  101  and excitation coil  105  are at a substantially fixed position, with movable target coil  103  free to move along X-axis  151 . As relative displacement of target coil  103  from receiver coil  101  and excitation coil  105  approaches a minimum along X-axis  151 , the voltage detected by RF voltage detector  107  ( FIG. 1 ) is at a minimum. As displacement of target coil  103  from receiver coil  101  and excitation coil  105  increases along X-axis  151  ( FIG. 2 ), the voltage detected by the RF voltage detector also increases. However, once a substantial relative displacement is achieved, in this example represented by a relative displacement of at least plus or minus two, no further increase in detected RF voltage is observed.  
         [0022]      FIG. 3  is a diagrammatic representation of a differential position sensor constructed in accordance with a second set of embodiments of the present invention. The configuration of  FIG. 3  is similar to that of  FIG. 2 , except that  FIG. 3  employs an additional receiver coil in the form of a second receiver coil  302 . Illustratively, first and second receiver coils  301  and  302  are positioned substantially at either side of excitation coil  305 . It is possible, but not required, to position first receiver coil  301 , second receiver coil  302 , and excitation coil  305  in the same plane (i.e., reference plane  310 ). However, if these coils  301 ,  302 , and  305  are all positioned in reference plane  310 , this permits coils  301 ,  302  and  305  to be fabricated using a single printed circuit board.  
         [0023]     In operation, target coil  303  is moved along a path, such as linear path  311  or nonlinear path  312 . Linear path  311  and nonlinear path  312  are shown only for purposes of illustration, it being understood that target coil  303  could be moved along any path, so long as target coil  303  receives a magnetic excitation flux from excitation coil  305  at least throughout a portion of this path. For example, the path could, but need not, be substantially parallel to first reference plane  310 .  
         [0024]      FIG. 4  is a diagrammatic representation of a differential position sensor constructed in accordance with a third set of embodiments of the present invention. The configuration of  FIG. 4  is similar to that of  FIG. 3 , except that first receiver coil  301  and second receiver coil are situated substantially along reference plane  310 , whereas excitation coil  305  is situated in another plane denoted as excitation coil plane  314 . Reference plane  310  and excitation coil plane  314  could, but need not, be parallel planes.  
         [0025]     In operation, target coil  303  is moved along a path, such as path  315 , which may be a linear path or a nonlinear path. Path  315  is shown only for purposes of illustration, it being understood that target coil  303  could be moved along any path, so long as the path includes at least one point wherein target coil  303  receives a magnetic excitation flux from excitation coil  305  and this flux is substantially simultaneously received by at least one of first receiver coil  301  and second receiver coil  302 . In the present example, a portion of path  315  passes between excitation coil  305  and at least one of first receiver coil  301  and second receiver coil  302 .  
         [0026]      FIG. 5  is a graph depicting the relationship between relative output voltage and relative displacement for the differential position sensor of  FIG. 3  when target coil  303  is moved along linear path  311  substantially parallel to first reference plane  310 . When target coil  303  is moved to a position along linear path  311  closest to excitation coil  305 , denoted by a relative displacement value of zero, the relative output voltage generated by RF voltage detector  107  ( FIG. 1 ) is zero. As target coil  303  is moved to the left along linear path  311  ( FIG. 5 ) from a relative displacement value of zero, the relative voltage generated by RF voltage detector  107  decreases. However, once the relative displacement of target coil  303  moves beyond −1.50 to −2.00, further displacements to the left (i.e., in a negative direction) do not result in substantial changes in relative output voltage.  
         [0027]     As target coil  303  is moved to the right along linear path  311  from a relative displacement value of zero, the relative voltage generated by RF voltage detector  107  ( FIG. 1 ) increases. However, once the relative displacement of target coil  303  moves beyond +1.50 to +2.00, further displacements to the right (i.e., in a positive direction) do not result in substantial changes in output voltage. It is to be understood that the values presented in  FIG. 5  are for purposes of illustration only, as the actual voltage values obtained will depend upon the implementational details of specific system applications.  
         [0028]      FIG. 6  is a diagrammatic representation of a sensor array constructed in accordance with a third set of embodiments of the present invention. Similar to the configuration of  FIG. 1 , oscillator  109  of  FIG. 6  feeds RF energy into excitation coil  105 , so as to generate a magnetic excitation flux. However, excitation coil  105  of  FIG. 6  is dimensioned so as provide a magnetic excitation flux for receipt at a plurality of receiver coils including first receiver coil  501 , second receiver coil  511 , and third receiver coil  521 . First receiver coil  501  is operatively coupled to a first RF voltage detector  507 , second receiver coil  511  is operatively coupled to a second RF voltage detector  517 , and third receiver coil  521  is operatively coupled to a third RF voltage detector  527 .  
         [0029]     First RF voltage detector  507  is capable of detecting a magnetic flux intercepted by first receiver coil  501 . The magnetic flux is detected in the form of a voltage denoted as V 1 . Similarly, second RF voltage detector  517  is capable of detecting a magnetic flux intercepted by second receiver coil  511 , wherein the magnetic flux is detected in the form of a voltage denoted as V 2 . Finally, third RF voltage detector  527  is capable of detecting a magnetic flux intercepted by third receiver coil  521 , wherein the magnetic flux is detected in the form of a voltage denoted as V 3 .  
         [0030]     Illustratively, RF voltage detectors  507 ,  517  and  527  may each be implemented using a peak detector, a rectifier, one or more semiconductor diodes, an envelope detector, or the like. However, a single device such as a single peak detector, rectifier, or diode could optionally be employed to implement a plurality of RF voltage detectors  507 ,  517 ,  527 , wherein a switching mechanism would be employed to sequentially direct voltage detected from first, second, and third receiver coils  501 ,  511 ,  521  to the single device. Optionally, RF voltage detectors  507 ,  517 , and  527  may include one or more amplifier or buffer stages, so as to provide sufficient voltage or current to interface with other electronic equipment, such as a microprocessor or a computing device. Pursuant to another optional feature, RF voltage detectors  507 ,  517 , and  527  may include output filtering circuitry, such as low-pass filters, to smooth a waveform envelope corresponding to the detected RF voltage as a function of time. Pursuant to yet another optional feature, RF voltage detectors  507 ,  517 ,  527  may include input filtering circuitry, such as a bandpass filter tuned approximately to the frequency of oscillator  109 , to enhance detection of excitation flux generated by oscillator  109  while reducing detection of ambient sources of interference.  
         [0031]     Detected voltages V 1 , V 2 , and V 3  are fed to respective data input ports of a processing mechanism  540 . Processing mechanism  540  may be implemented, for example, using a microprocessor, microcontroller, logic gates, discrete circuitry, computing device, or the like. Illustratively, processing mechanism  540  is programmed to apply a mathematical algorithm to detected voltages V 1 , V 2 , and V 3 , so as to generate an output voltage  530 .  
         [0032]     Illustratively, first, second, and third receiver coils  501 ,  511 , and  521  are arranged to form an array. Such an array could be linear (as shown in  FIG. 6 ), curvilinear, angular, or two-dimensional, so as to meet the requirements of specific system applications. Optionally, processing mechanism  540  may be programmed to implement pattern-based or value-based target sensing.  
         [0033]      FIG. 6  displays a graph of output voltage  530  versus position of target coil  103  along X-axis  151 . A first waveform  531  corresponds to detected voltage V 1  detected by first RF voltage detector  507  as a function of the position of target coil  103 . Similarly, a second waveform  532  corresponds to detected voltage V 2  detected by second RF voltage detector  517  as a function of the position of target coil  103 . Finally, a third waveform  533  corresponds to detected voltage V 3  as a function of the position of target coil  103 .  
         [0034]     As will be also appreciated, the above described method embodiments may take the form of computer or controller implemented processes and apparatuses for practicing those processes. The disclosure can also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer or controller, the computer becomes an apparatus for practicing the invention. The disclosure may also be embodied in the form of computer program code or signal, for example, whether stored in a storage medium, loaded into and/or executed by a computer or controller, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.  
         [0035]     While the invention has been described with reference to a preferred embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.