Abstract:
A position sensor assembly comprising ( 15 ) a housing ( 16 ) having a least one inner cavity, a stator ( 22 ) disposed within the housing, a moving element ( 23 ) disposed within the housing and configured and arranged to move relative to the stator ( 22 ), the stator comprising primary windings ( 24 ) and secondary windings ( 25, 26 ), the secondary windings configured and arranged to provide an output signal ( 27 ) as a function of movement of the moving element ( 23 ) relative to the stator ( 22 ), electronics ( 28 ) disposed in the housing and communicating with the primary windings ( 24 ) and the secondary windings ( 25, 26 ), the electronics comprising an integrated circuit ( 29 ) configured and arranged to provide excitation of the primary windings ( 24 ) and to demodulate the output signal ( 27 ) of the secondary windings ( 25, 26 ), and an input element ( 35 ) extending through the housing ( 16 ) and connected to the moving element ( 23 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Patent Application No. 62/068,516 filed on Oct. 24, 2014, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to the field of position sensors, and more particularly to a fully integrated position sensor assembly. 
       BACKGROUND ART 
       [0003]    Position sensors are used in many applications, including aircraft, military, transportation, energy, automation and industrial. Such sensors may include encoders, hall position sensors, potentiometers, resolvers and rotary variable differential transformers (RVDTs). RVDTs and resolvers are used in critical applications where more reliable solutions are required. For example, in the aircraft market, the use of fly-by-wire and fly-by-light architectures means that more position sensors are required on each airframe. RVDTs are well known in the market. An electromechanical transducer is used to provide a variable alternating current output voltage that is generally linearly proportional to the angular displacement of an input shaft. 
       DISCLOSURE OF THE INVENTION 
       [0004]    With parenthetic reference to the corresponding parts, portions, or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, provided is a position sensor assembly ( 15 ) comprising a housing ( 16 ) having a least one inner cavity ( 20 ,  21 ), a stator ( 22 ) disposed within the housing, a moving element ( 23 ) disposed within the housing and configured and arranged to move relative to the stator, the stator comprising primary windings ( 24 ) and secondary windings ( 25 ,  26 ), the secondary windings configured and arranged to provide an output signal ( 27 ) as a function of movement of the moving element relative to the stator, signal conditioning electronics ( 28 ) disposed in the housing and communicating with the primary windings and the secondary windings, the signal conditioning electronics comprising an integrated circuit ( 29 ) configured and arranged to provide excitation of the primary windings and to demodulate the output signal of the secondary windings, and an input element ( 35 ) extending through the housing and connected to the moving element. 
         [0005]    The housing may comprise a sensor housing subassembly ( 18 ) having a first inner cavity ( 20 ) and an electronics housing subassembly ( 19 ) having a second inner cavity ( 21 ), and the stator and the moving element may be disposed within the first inner cavity of the sensor housing subassembly, and the signal conditioning electronics may be disposed within the second inner cavity of the electronics housing subassembly. The electronics housing subassembly may be removably connected to the sensor housing subassembly. The sensor housing subassembly may comprise a bearing end portion ( 36 ), a sensor body portion ( 38 ) and an intermediate portion ( 39 ), and the electronics housing subassembly may comprise an electronics body portion ( 40 ) and a second end portion ( 41 ). The sensor housing subassembly may comprise a signal output port. The moving element may be configured and arranged to move linearly along a central axis relative to the stator or to rotate about a central axis relative to the stator. The moving element may comprise a magnet. The stator and moving element may be selected from a group consisting of a rotary variable differential transformer and a resolver. The signal conditioning electronics may comprise a converter configured and arranged to convert the output signal to a digital signal. The signal conditioning electronics may comprise a signal filter configured and arranged to filter out a carrier frequency. The signal conditioning electronics may comprise a DC signal buffer. The assembly may comprise a temperature sensor ( 55 ) configured and arranged to provide a temperature signal ( 101 ) to the integrated circuit and the integrated circuit is configured and arranged to provide mover position output ( 104 ) compensated ( 84 ) as a function of the temperature signal. The assembly may comprise a mover positional calibration data ( 127 ) and the integrated circuit is configured and arranged to provide a mover position output ( 94 ) compensated ( 83 ) as a function of the calibration data. The assembly may comprise a temperature sensor ( 55 ) configured and arranged to provide a temperature signal ( 101 ) to the integrated circuit and a mover positional calibration data ( 117 ,  127 ), and the integrated circuit is configured and arranged to provide a mover position output ( 85 ) compensated as a function of the calibration data and the temperature signal. 
         [0006]    In another aspect, a method of calibrating a position sensor assembly ( 15 ) is provided comprising the steps of providing a position sensor assembly having a housing with at least one inner cavity, a stator disposed within the housing, a moving element disposed within the housing and configured and arranged to move relative to the stator, an input element extending through the housing and connected to the moving element, the stator comprising primary windings and secondary windings, the secondary windings configured and arranged to provide an output signal as a function of movement of the moving element relative to the stator. The calibration method further comprises providing signal conditioning electronics in the housing having a memory and an integrated circuit communicating with the primary windings and the secondary windings and configured and arranged to provide excitation of the primary winding and to condition the output signal of the secondary windings, providing a temperature sensor in said housing, mounting the position sensor assembly on an external actuator ( 111 ,  121 ), wherein the external actuator is configured and arranged to drive the moving element of the position sensor assembly through a range of reference positions, operating the external actuator through the range of reference positions, calculating a position error ( 115 ) as a function of the output signal of the secondary windings ( 113 ) and the reference position ( 112 ), sensing a measured temperature ( 124 ) with the temperature sensor of the position sensor assembly, calculating a temperature error ( 125 ) as a function of the output signal of the secondary windings ( 123 ), the measured temperature ( 124 ), and a temperature reference ( 122 ), and storing the position error ( 116 ) and the temperature error ( 126 ) in the memory ( 59 ). The method may further comprise the step of providing a mover position output ( 85 ) compensated as a function of the position error ( 117 ) and the temperature error ( 127 ). 
         [0007]    In another aspect, a method of compensating a position sensor assembly is provided comprising the steps of providing a position sensor assembly having a housing with at least one inner cavity, a stator disposed within said housing, a moving element disposed within the housing and configured and arranged to move relative to the stator, an input element extending through the housing and connected to the moving element, the stator comprising primary windings and secondary windings, the secondary windings configured and arranged to provide an output signal as a function of movement of the moving element relative to the stator; providing signal conditioning electronics in the housing having a memory and an integrated circuit communicating with the primary windings and said secondary windings and configured and arranged to provide excitation of the primary winding and to condition the output signal of the secondary windings, providing a positional calibration dataset ( 117 ), providing a temperature calibration dataset ( 127 ), providing a temperature sensor in the housing; connecting the moving element to an external actuator; operating the external actuator; taking temperature measurements with the temperature sensor, and providing a mover position output ( 85 ) compensated as a function of the output signal of the secondary windings ( 81 ), the temperature measurements ( 101 ), the positional calibration dataset and the temperature calibration dataset. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a first embodiment of an improved position sensor assembly. 
           [0009]      FIG. 2  is a cross-sectional view of the position sensor assembly shown in  FIG. 1 . 
           [0010]      FIG. 3  is an exploded view of the position sensor assembly shown in  FIG. 1 . 
           [0011]      FIG. 4  is a schematic view of the integrated signal conditioning electronics of the position sensor assembly shown in  FIG. 1 . 
           [0012]      FIG. 5  is a perspective view of a second embodiment of an improved position sensor assembly. 
           [0013]      FIG. 6  is a cross-sectional view of the position sensor assembly shown in  FIG. 5 . 
           [0014]      FIG. 7  is an exploded view of the position sensor assembly shown in  FIG. 5 . 
           [0015]      FIG. 8  is a block diagram of an embodiment signal conditioning of the position sensor assembly shown in  FIG. 1 . 
           [0016]      FIG. 9  is a block diagram of an embodiment of the linearity compensation shown in  FIG. 8 . 
           [0017]      FIG. 10  is a block diagram the temperature compensation shown in  FIG. 8 . 
           [0018]      FIG. 11  is a block diagram of the initial linearity calibration for the linearity compensation shown in  FIG. 9 . 
           [0019]      FIG. 12  is a block diagram of the initial temperature calibration for the temperature compensation shown in  FIG. 10 . 
           [0020]      FIG. 13  is a plot of measured and compensated angle (ordinate) vs. actual angle (abscissa) showing linearity compensation. 
           [0021]      FIG. 14  is a plot of measured and compensated angle (ordinate) vs. sensor temperature (abscissa) showing temperature compensation. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., crosshatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
         [0023]    Referring now to the drawings, and more particularly to  FIGS. 1-4 , a position sensor assembly is provided, a first embodiment of which is generally indicated at  15 . As shown, assembly  15  generally includes RVDT  17 , integrated conversion and signal conditioning electronics  28  and housing  16 . 
         [0024]    RVDT  17  is an electromechanical transducer that provides a variable alternating current output voltage that is linearly proportional to the angular displacement of input shaft  35 . When energized by electronics  28  with a fixed AC source  32 , output signal  27  is linear within a specific range over the angular displacement. RVDT  17  generally comprises iron core rotor  23  rotationally supported within cavity  20  of subassembly housing  18 . Stator  22  includes primary longitudinally extending linked excitation coils  24  and a pair of secondary longitudinally extending linked output coils  25  and  26 . A fixed alternating current excitation  32  is applied to primary stator coils  24 , which are electromagnetically coupled to secondary coils  25  and  26 . This coupling is proportional to the angular displacement of rotor  23  and input shaft  35  about axis x-x. Output pairs  25  and  26  are structured so that one coil set  25  is in phase with excitation coils  24 , and the second set  26  is  180  degrees out of phase with excitation coils  24 . When rotor  23  is in a position that directs the available flux equally in both the in phase and out of phase coils, the output voltage is cancelled and results in a zero value signal. This is referred to as the electrical zero position or E.Z. When rotor shaft  23  is displaced from E.Z., the resulting output signal  27  has a magnitude in phase relationship proportional to the direction of rotation. Because RVDT  17  performs essentially like a transformer, excitation voltage changes will cause direction proportional changes to the output (transformation ratio). In this embodiment, a MOOG-MCG-MURPHY AS-827 RVDT may be used. 
         [0025]    As shown in  FIGS. 3 and 4 , integrated electronics  28  generally includes circuit board  30  and mezzanine or expansion board  31 . Circuit board  30  includes microcontroller integrated circuit  29 , having configurable blocks  33  and  34  that excite  32  primary windings  24  and filter signal  27  from secondary windings  25  and  26 , and interface  44 . Integrated circuit  29  controls the frequency and amplitude of excitation signal  32 , demodulates signal  27  from the secondary windings, filters to eliminate the carrier frequency, samples and converts  82  the received analog signal  27  into digital format, and calibrates  110 ,  120 , compensates  83 ,  84 , amplifies, scales and buffers the signal for output  85 . Mezzanine board  31  is provided to allow for custom interfaces, such as a digital interface for a standard digital bus. As shown, circuit board  30  includes additional chip set  58 , which in this embodiment includes temperature sensor  55 , voltage reference chip  56  and oscillator  57 , with outputs to integrated circuit  29 . 
         [0026]    As shown in  FIGS. 1-3 , electronics  28  are fully integrated with RVDT  17  in housing  16  such that RVDT  17  and signal conditioning electronics  28  are fully contained and enclosed within the interior cavities of unitary housing  16 . In this embodiment, housing  16  generally comprises sensor housing subassembly  18  having cavity  20 , and electronics housing subassembly  19  having cavity  21 . Sensor housing subassembly  18  is formed by annular bearing end portion  36 , hollow cylindrical body portion  38  and circular intermediate end plate  39 . The left end of cylindrical portion  38  includes inwardly extending double seat  48 , defined by rightwardly-facing annular surface  49 , inwardly-facing cylindrical surface  50 , and rightwardly-facing annular surface  51 . The left ends of coils  24 ,  25  and  26  abut against and are axially restrained by surface  49  and the left annular face of bearing  42  abuts against and is axially restrained by surface  51 . 
         [0027]    Annular bearings  42  and  43 , positioned axially along axis x-x on the left and right outer sides, respectively, of cavity  20 , support rotor  23  within cavity  20  of housing subassembly  18  so as to allow rotor  23  to rotate about axis x-x relative to housing  16 . Coil assembly  22  is positioned axially interior to bearings  42  and  43 , respectively, within cavity  20 . Coil  24  is positioned circumferentially between coils  25  and  26 . Thus, bearing  42 , coil assembly  22  and bearing  43  are stacked axially within housing subassembly  18 , with end plate  39  separating cavity  20  from cavity  21  of electronics housing subassembly  19 . 
         [0028]    Electronic housing subassembly  19  generally comprises hollow cylindrical body  40  having circular end plate  41  and forming inner cylindrical cavity  21 . Integrated electronics  28  are stacked axially along axis x-x within cavity  21  of subassembly housing  19 . In particular, circuit board  30  is positioned axially to the right of intermediate housing plate  39  and mezzanine board  31  is positioned axially to the right of board  30 . As shown, each of coils  24 - 26 , bearing  43 , intermediate housing plate  39 , board  30  and mezzanine board  31  has an outer diameter slightly less than the inner diameter of cylindrical housing portions  38  and  40  so as to allow for the axial stacking transversely along axis x-x described above. 
         [0029]    Mechanical threaded stand-off spacers, severally indicated at  45 , provide proper axial spacing of transversely extending boards  30  and  31  in cavity  21  between intermediate housing plate  39  and housing end plate  41 . Electronics subassembly  19  is connected to sensor subassembly  18  by spacers  45 , attached to each other by threaded connections, and machine screws  46  extending through end portion  41  and attached to respective spacers  45  by threaded connections. Thus, housing  16  contains both RVDT  17  and electronics  28  in a fully integrated package. 
         [0030]    Microcontroller integrated circuit  29  is configured to provide initial calibration for inherent non-linearity in the stator  22 , rotor  23  and their mechanical assembly, as well as for thermal non-linearity, of each assembly  15  and to provide operational compensation  80  for such linearity and temperature variations. Thus, compensation routine  80  is directed to producing a linear output signal  85  and is described with reference to  FIGS. 8-14 . At step  81  of  FIG. 8 , signal  27  is received  81  as an output from RVDT  17  in the form of an AC signal (sine wave) of varying amplitude and phase with respect to excitation signal  32 . Output signal  27  is then converted from analog to digital at step  82 . With respect to the conversion of step  82 , the voltage reference from voltage chip  56  is used to provide an accurate and stable voltage reference in the conversion and the signal from oscillator  57  is applied to provide more accurate timing during sampling. Sampling can be synchronous with demodulation occurring in the analog domain, or sampling can be asynchronous with demodulation occurring in the digital or software domain. The ability of integrated circuit  29  to handle both synchronous and asynchronous sampling provides flexibility regarding execution of the signal acquisition and processing techniques described herein, and further allows for the implementation of all described position sensor assembly  15  embodiments. After demodulation at step  82 , the signal is compensated for linearity at step  83  and temperature at step  84 . 
         [0031]    A method of linear compensation  83  is further shown and described with reference to  FIG. 9 . Initially, the system acquires a measured position  91  from the raw position value output from the demodulation and analog to digital conversion at step  82 . From here, the system may perform either of error correction or error lookup at step  92 . Error correction, or polynomial correction, maps the error as a function of a measured position of rotor  23 . Constants are generated, which provide a polynomial fit to the measured error. The generated polynomial can be used to compensate for any error that is present in the measured position. The generated polynomial will take the form: 
         [0000]      Error= a   n   X   n   +a   n−1   X   n−1   + . . .  +a   2   X   2   +a   1   X+a   0    
         [0000]    wherein X represents measured position, and wherein the constants a n  . . . a 0  are calculated at linear calibration  110 , which is discussed below in greater detail with reference to  FIG. 11 . 
         [0032]    Polynomial correction requires less memory than error lookup, but may not be able to compensate all situations. Conversely, utilizing error lookup at step  92  may require more memory than error correction, but error lookup can compensate all situations. Like polynomial error correction, error lookup also maps the error as a function of measured rotor position. However, the measured error is stored directly into a table and is directly looked up at run time. According to one embodiment of the disclosure, a table may be generated which holds all possible position values and all position errors at those values. According to another embodiment, a table may be generated which holds only a portion of the possible position values and position errors, and then linear interpolation or similar techniques may be used to fill in any gaps in the acquired data. In the case of utilizing error lookup at step  92 , the necessary equation will take the form of: 
         [0000]      Error=errorValues[X] 
         [0000]    wherein X represents the measured position. After performing either error correction or error lookup at step  92 , linear compensation method  83  then performs error subtraction at step  93 , wherein a linearized (compensated) position  94  is calculated as being equal to the measured position  91  minus the error (taken from step  92 ). In one embodiment, the linear compensation steps of  FIG. 9  may be performed at a production factory, resulting in a position sensor assembly that will be able to be continuously corrected for linear compensation during operation using the factory corrected values. The linearized (compensated) position  94  is a position that has been fully compensated for linear errors in the assembly  15 . However, errors due to temperature may still be present. 
         [0033]    Accordingly, position sensor method  80  of  FIG. 8  proceeds to temperature compensation method  84 , which is herein described in detail with reference to  FIG. 10 . Initially, linearized position  94  is calculated with respect to the procedure illustrated in  FIG. 9  and disclosed hereinabove. At step  101 , temperature of the position sensor assembly is measured. Preferably, the temperature is measured by discrete temperature sensor  55  on main processor board  30  of position sensor assembly  15 . In an additional embodiment of the disclosure, temperature is alternatively measured by means of a thermistor embedded within stator  22 , or by any other thermal transducer or sensor disposed at any other location within housing  16 . 
         [0034]    After receiving linearized position  94  and a measured temperature (from step  101 ), temperature compensation method  84  proceeds to step  102 , wherein either polynomial error correction or error lookup is performed. The procedure of step  102  is substantially the same as the error correction/lookup step  92  described with reference to  FIG. 9  hereinabove, however constants a n  . . . a 0  (if using error correction) and/or position errors (if using error lookup) used in the corresponding error calculations will have been determined during temperature calibration  120  (as opposed to during linear calibration), discussed below in more detail with reference to  FIG. 12 . 
         [0035]    Temperature compensation method  84  next proceeds to step  103 , wherein a temperature compensated position  104  is calculated by subtracting the error calculated in step  102  from linearized position  94 . In one embodiment, the temperature compensation steps of  FIG. 10  may be performed at a production factory, resulting in a position sensor assembly that will be able to be continuously corrected for temperature compensation during operation using the factory corrected values. The resulting compensated position  104  is a position that has now been fully compensated for both linearity errors in the sensor in addition to errors resulting from fluctuations in the sensor temperature. 
         [0036]    Referring back to  FIG. 8 , compensated position  104  is now stored within memory  59  of microcontroller integrated circuit  29  as compensated output  85 . In a preferred embodiment, integrated circuit  29  comprises an internal digital register  59  to store the compensated output  85 , which may then be presented to a user via mezzanine board  31  as an analog or digital signal via RS-232, RS-48, CAN, USB, SPI, I2C, or any other means of signal delivery as known in the art. 
         [0037]    Turning to  FIG. 11 , a process of linearity calibration  110  is disclosed. Position sensor assembly  15  is driven by an external actuator  111  through its entire position range while the temperature is held constant at a preferred 25 degrees Celsius, though any other suitable temperature may be used. An external reference position  112  for rotor  23  is provided to the system, preferably taken from a previously calibrated high resolution reference. Next, the system determines a sensor measured position  113  and compares this position to the known good reference position  112  in order to calculate a detected error  115 . The detected error  115  is then preferably processed and/or stored in memory  59  in step  116 , wherein depending on the type of compensation method being used (error correction or error lookup), polynomial constant(s) will be either generated for immediate output or stored in memory  59  in a lookup table for future use at step  117 . 
         [0038]    Temperature calibration process  120  is now disclosed with reference to  FIG. 12 . Position sensor assembly  15  is driven by an external actuator  121 , wherein the sensor may be driven through its entire position range. Alternatively, the sensor may be held in a stable position. Position sensor assembly  15  is then subjected to external temperatures over its entire temperature range, while the system measures and records the sensor position  123  and temperature  124 . The measured position  123  and measured temperature  124  of the sensor are then compared to a known good reference position at a preferred 25 degrees Celsius  122 , in order to calculate a detected error  125 . Similarly to the linearity calibration method  110 , the detected error  115  of temperature calibration method  120  is then preferably processed and/or stored in memory  59  in step  126 , wherein depending on the type of compensation method being used (error correction or error lookup), polynomial constant(s) will be either generated for immediate output or stored in memory  59  in a lookup table for future use at step  127 . 
         [0039]      FIG. 13  is a plot of measured and compensated angle (ordinate) vs. actual angle (abscissa) showing linearity compensation at a preferred constant temperature of 25 degrees Celsius. Solid line  131  illustrates an embodiment of measured positions of the sensor, while the dotted line  132  illustrates the preferred positions compensated for linearity.  FIG. 14  is a plot of measured and compensated angle (ordinate) vs. sensor temperature angle (abscissa) showing temperature compensation at a preferred constant rotor angle of 30 degrees. Solid line  141  illustrates an embodiment of measured positions of the sensor, while the dotted line  142  illustrates the preferred positions compensated for temperature. 
         [0040]    The integration of the electronics and the use of a digital interface provides for improved noise immunity, reduces system weight and cost and provides ease of integration. The use of a digital bus interface also allows for a chaining of multiple devices. The output of assembly  15  can provide both position and rate information. Assembly  15  thereby simplifies the integration of an AC RVDT position transducer device by integrating the necessary conversion and conditioning electronics  28  in the body or housing  16  of the device. Integrated electronics  28  provide the excitation to the primary windings, demodulation of the secondary windings, conversion of the demodulated AC signal to a DC signal, provide amplification of the DC signal, provides for hardware/software signal filtering, and compensates for nonlinearity in the signal from the RVDT. The output signal of assembly  15  can be DC voltage or current or any standard digital bus signal. For fly-by-light applications, assembly  15  can also integrate a fiber optic front end. 
         [0041]    While a RVDT sensor is shown and described in this embodiment, it is contemplated that other high reliability rotary or linear transducer types can be employed, including but not limited to resolvers, synchros and linear variable differential transformers (LVDTs). In an LVDT embodiment, coils  25  and  26  may be oriented annularly about axis x-x and coil  24  may be positioned axially between coils  25  and  26  such that bearing  42 , coil  25 , coil  24 , coil  26  and bearing  43  are stacked axially within housing subassembly  18 , with end plate  39  separating cavity  20  from cavity  21  of electronics housing subassembly  19 . 
         [0042]    A second embodiment  115  is shown in  FIGS. 5-7 . This embodiment is generally the same as assembly  15  but differs in that housing  116  is not formed from two connected subassemblies and does not include intermediate housing portion  39 , as in assembly  15 . Rather, housing  116  is formed from a longer cylindrical body portion  118  and a circular end plate  141  fixed to the annular right end of cylinder  118  and has a unitary inner cavity  120 . 
         [0043]    While the presently preferred form of the improved position sensor assembly has been shown and described, and several modification thereof discussed, persons skilled in this art will readily appreciate the various additional changes and modifications may be made without departing from the scope of the invention, as defined and differentiated by the following claims.